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PUBLIC HEALTH ASSESSMENT

PADUCAH GASEOUS DIFFUSION (USDOE)
PADUCAH, MCCRACKEN COUNTY, KENTUCKY


EXECUTIVE SUMMARY

The U.S. Department of Energy (DOE)'s Paducah Gaseous Diffusion Plant (PGDP) was added tothe U.S. Environmental Protection Agency's Superfund National Priorities List (NPL) on May31, 1994, because elevated concentrations of trichloroethylene (TCE) and technetium 99 (Tc-99)were found in off-site groundwater (residential wells). The Superfund law (CERCLA) requiresthat the Agency for Toxic Substances and Disease Registry (ATSDR) conduct a public healthassessment for all sites listed on the NPL. This public health assessment evaluates contaminantdistributions, community health concerns, and available health outcome information to determinethe potential for community exposures to hazardous substances and adverse public health effectsresulting from those exposures.

The plant, which is about 10 miles (16 kilometers) west of Paducah, Kentucky, began operationin 1952. PGDP produces enriched uranium with a higher than natural concentration of uranium235, using a gaseous form of uranium (uranium hexafluoride). TCE was used as a solvent toclean metal parts. Tc-99, a radioactive substance, was introduced at the site when uranium usedin a reactor was reprocessed. This public health assessment presents an evaluation of these andother chemical and radioactive contaminants in human exposure pathways. ATSDR alsoconsidered other hazards--such as accidents involving the depleted uranium cylinders stored atand transported to and from this site--in evaluating the public health effects of past, current, andfuture PGDP operations on the surrounding community.

According to the information reviewed by ATSDR, under normal operating conditions, thePaducah Gaseous Diffusion Plant currently poses no apparent public health hazard for thesurrounding community from exposure to groundwater, surface water, soil and sediment, biota,or air. "No apparent public health hazard" means that people may be exposed to contaminatedmedia near the site, but that exposure to the contamination is not expected to cause any adversehealth effects. We define "current" as ranging from 1990 to the present. This conclusion assumesthe effectiveness of access restrictions to Little Bayou Creek, the outfalls, and the North-SouthDiversion Ditch; the fish advisories issued for Little Bayou Creek and some of the ponds in theWestern Kentucky Wildlife Management Area; and existing regulation of discharges to air andsurface water.

Historical groundwater exposure to TCE and lead was a public health hazard for childrenroutinely drinking water from four residential wells. This means that long-term exposureoccurred at concentrations that may have caused adverse health effects in children. A futuregroundwater exposure pathway could exist if new wells are drilled into the northwest ornortheast plumes. No current exposure pathways to contaminated groundwater exist, but thecurrent restrictions between DOE and the property owners do not restrict the drilling of newwells by future owners of this land. Although it is unlikely, potential future exposures couldoccur if new wells are drilled into these plumes.

Groundwater exposures to vinyl chloride (a degradation product of TCE) and acute air exposuresto uranium and hydrogen fluoride are an indeterminate public health hazard for past and potentialfuture exposures. This means that the information available is incomplete.

Information on vinyl chloride exposures is incomplete because the detection limits in mostanalyses of samples from tested residential wells were well above the levels of concern. Also, notall residential wells in or near the plume were tested for vinyl chloride. Future groundwatermonitoring for vinyl chloride and other TCE degradation products should be low enough todetermine whether concentrations exceed health-based guidelines. However, there appears to beno current exposure to vinyl chloride since these wells are not being used.

Past short-term, or acute air exposures to uranium and hydrogen fluoride are indeterminate,because total release quantities and completed exposure pathways are uncertain. The worstreported accidental release happened at 4:00 am on November 17, 1960. Potentially hazardousuranium and hydrogen fluoride concentrations, estimated using air dispersion models, reachedoff-site areas, but because the accident occurred at 4:00 a.m., it is not known if any residentswere exposed. If people were exposed at the concentrations estimated by the model, adversehealth effects may have resulted. Currently, we have no reports of health effects related to thisaccident; however, if data become available suggesting that health effects did occur, we will re-evaluate the need for followup activities.

Past long-term, or chronic uranium and hydrogen fluoride exposures were below levels of publichealth concern.

In the future, the rupture of one or more depleted uranium cylinders, which could occur from atransportation accident involving a fire, would create an urgent public health hazard for anyonenear the accident. Weather conditions and duration of exposure would affect the distance fromthe accident at which there would be a hazard; however, we predict that (1) the maximallyexposed individual would be 100 feet (30 meters) or less from the accident and (2) an urgentpublic health hazard could exist out to 230 feet (70 meters) from the accident. Less-severe healtheffects could be experienced by individuals within several thousand meters of the accident. Thistype of accident is very unlikely.

For other accident scenarios such as a plane crash, severe weather, or natural disasters involvingthe on-site depleted uranium cylinders, a temporary public health hazard could exist off site fromhydrogen fluoride exposure. It is very unlikely that such an accident would happen.

ATSDR representatives reviewed available health outcome data, such as cancer registries and vital statistics. We evaluated the data using age-adjusted rates, concentrating mostly on nine general types of cancer. The health outcome data reviewed do not apply specifically to small groups of people who have been, or could be, exposed to PGDP contaminants. The data are recorded for larger areas (area development districts or counties) which include many people with no exposures to contaminants from the site (approximately 63,000 in McCracken County, 8,000 in Ballard County, and 15,000 in Massac County). The population of concern for the exposure pathways in the PDGP area (approximately 15 to 90 persons) is small. The associations between exposure from this site and any adverse health effects would be obscured or distorted by the presence of the much larger unexposed population.

ATSDR has collected people's concerns from the communities around PGDP for this publichealth assessment. Many people expressed concerns related to the incidence of cancer and otherillnesses in the area and the possibility of exposure to contaminants through various media.Community concerns and our responses are presented in the main part of this document.

Based on the data and information obtained and evaluated for this public health assessment,ATSDR recommends the following:

  1. Ship depleted uranium to and from PGDP in new transport cylinders or overpacks approved by the U.S. Department of Transportation.

  2. Develop and implement emergency plans for the transport (by rail or truck) of uraniumhexafluoride (and hydrogen fluoride) cylinders. (The U.S. Enrichment Corporation isrequired to provide site-wide emergency response services to DOE pursuant to their leaseagreement and has an emergency management plan and procedures for this purpose;however, the procedures are for on-site accidents and emergencies and do not cover off-site transportation accidents.)

  3. Prevent installation of new wells in the contaminated groundwater plume areas through institutional controls.

  4. Prevent the future use of contaminated wells by disconnecting water pipes to homes or businesses and plugging or dismantling the wells.

  5. Encourage residents who are concerned about lead in their drinking water to have their water tested. (Lead did not appear to be related to the groundwater plumes.)

  6. Continue groundwater monitoring, including monitoring in areas possibly affected by theplumes and areas near Little Bayou Creek, Big Bayou Creek, and the North-SouthDiversion Ditch.

  7. Ensure that detection limits of degradation products of TCE, such as vinyl chloride, in thegroundwater analyses are low enough to determine whether concentrations exceed health-based guidelines.

  8. Continue monitoring the McNairy Aquifer wells to detect possible migration ofcontaminants from the Regional Gravel Aquifer--if monitoring wells do not create a conduit for vertical migration.

  9. Continue to restrict access to Little Bayou Creek, the outfalls, and the North-SouthDiversion Ditch. Determine if existing signage adequately restricts public access to the southwest inactive landfill and the adjoining area.

  10. Continue monitoring biota to ensure that it is safe to consume.

  11. Develop a spatially and statistically consistent soil sampling program to assess accumulation of airborne contaminants in residential areas.

Several of these recommendations may already be addressed by actions taken by DOE, the U.S.Enrichment Corporation, or other agencies. These actions are discussed in the Public HealthAction Plan in the main part of this document.

ATSDR staff will continue to monitor environmental issues and remedial activities at PGDP, aswell as proposals related to storage and transport of the depleted uranium cylinders. Theinterpretation, conclusions, and recommendations provided in this public health assessment arebased on the data and information referenced. Additional data could alter those conclusions andrecommendations. The conclusions and recommendations are site specific and should not be considered applicable to any other situation.


BACKGROUND

Site Description and History

The Paducah Gaseous Diffusion Plant (PGDP) is a U.S. Department of Energy (DOE) owned,contractor-operated uranium enrichment facility. It is about 10 miles (16 kilometers) west of thecity of Paducah and 3.5 miles (5.6 kilometers) south of the Ohio River in McCracken County,Kentucky (Figure 1) [1,2]. The site was added to the U.S. Environmental Protection Agency's(EPA's) Superfund National Priorities List (NPL) on May 31, 1994, because elevatedconcentrations of trichloroethylene and technetium 99 were found in off-site groundwater.

The primary plant process, gaseous diffusion, is aphysical process to enrich uranium hexafluoride(UF6)--that is, to increase the percentage of uranium235 (U-235) above natural concentrations in the UF6.In the process, solid UF6 containing about 0.7% U-235 is heated to form a compressed gas. The gas isfed through diffusion stages--compressors and converters. PGDP has 1,812 diffusion stageshoused in five buildings, which cover about 74 acres (30 hectares) [3]. The "product" (UF6enriched up to 2.75% U-235 [4]) and "tails" (UF6 depleted between 0.2% and 0.4% U-235) areremoved and put in cylinders [5]. The product is shipped to another uranium enrichment facilityin Piketon, Ohio for further enrichment; however, the Piketon enrichment operation is scheduledto shut down in the summer of 2001. PGDP is being upgraded to enrich uranium up to 5% U-235by the spring of 2001 [6]. Most of the tails have been stored in cylinders in storage yards on site.

The enrichment process requires large amounts of electric power, lubrication, and air cooling.Electricity for the diffusion processes comes from the steam plant in Joppa, Illinois, and from theTennessee Valley Authority (TVA) Shawnee Steam Plant, north of the site on the Ohio River.The compressed gases are cooled by heat exchange fluid, which in turn is cooled by recirculatingwater processed through four sets of cooling towers.

The PGDP facilities include process buildings, four major electrical switchyards, a three-boilersteam plant, a water treatment facility, a chemical cleaning and decontamination building, thenorthwest groundwater treatment facility, the northeast groundwater treatment system,maintenance and laboratory facilities, two active landfills, and several inactive facilities inside afenced security area (Figure 2) [1,7]. The steam plant provides process and comfort heating forother buildings on site. In 1974 and 1975, two boilers were converted to burn low-sulfur coal andoil instead of natural gas. The third boiler burns natural gas or oil but cannot be converted to burncoal [8,9]. The site also includes a raw-water treatment plant, a residential landfill, an inertlandfill, a former sanitary landfill, two industrial treatment lagoons, and several concrete rubblepiles outside the fenced area.

Plant Location and Vicinity
Figure 1. Plant Location and Vicinity (jpg)
Plant Location and Vicinity
Figure 1. Plant Location and Vicinity (pdf)
Plant Map
Figure 2. Plant Map (jpg)
Plant Map
Figure 2. Plant Map (pdf)

PGDP was built on a portion of 16,126 acres (6,450 hectares) of farmland acquired by the U.S.Department of Defense (DOD) during World War II. DOD acquired this land for a munitionsfacility, the Kentucky Ordnance Works (KOW), which was operated by Atlas Powder Companyuntil it was closed in 1946 [1]. The KOW included a trinitrotoluene (TNT) manufacturing area;an acid production area; coal, sulfur, toluene, and ordnance storage areas; a sewage treatmentplant; a water treatment plant; and burning grounds. PGDP now uses the water treatment plant. In1950, 7,556 acres (3,022 hectares) of the land east of the former KOW were acquired by theAtomic Energy Commission as a site for a uranium enrichment facility--that is, PGDP. Theplant began operating in 1952, but construction was not completed until 1954. The facilityreservation covered a total of 3,424 acres (1,397 hectares), with about 750 acres (300 hectares)within the security fence. The rest of the land was transferred to TVA for the Shawnee SteamPlant and to the Commonwealth of Kentucky for wildlife conservation and recreational purposes[2].

In the early years, the facilities included the gaseous diffusion plant, the uranium hexafluoride manufacturing plant, the uranium metals plant, and over a hundred support buildings [10,11]. The uranium hexafluoride manufacturing plant converted natural uranium trioxide to UF6. It also converted uranium reprocessed from plutonium production reactor tails. The reprocessing of uranium brought to the site other radioactive materials not associated with naturally occurring uranium, e.g., technetium 99 (Tc-99), americium 241 (Am-241), neptunium 237 (Np-237), and plutonium 239 (Pu-239). Tc-99 was first reported in airborne releases in 1953 [12]. Tc-99, Np-237, and Pu-239 were first reported in liquid releases in 1953. The uranium hexafluoride manufacturing plant was deactivated in 1964, but reactivated in 1968 and used until 1977. At the uranium metals plant, depleted UF6 was reacted with hydrogen to recover hydrogen fluoride and to convert the volatile UF6 to more easily stored uranium tetrafluoride (UF4). Some of the UF4 was reduced with magnesium to uranium metal. The uranium metals plant stopped operating in 1975 [13].

In 1974, the responsibility for PGDP wasgiven to the newly formed U.S. EnergyResearch and Development Administration,which became DOE in 1977. DOE's primarycontractor for all operations was MartinMarietta Energy Systems, Inc., which laterbecame Lockheed Martin Energy Systems (LMES) and Lockheed Martin Utility Services(LMUS). Beginning July 1, 1993, LMUS operated and maintained PGDP under contract to theUnited States Enrichment Corporation (USEC), the government-owned corporation formed bythe National Energy Policy Act of 1992 to take over the nation's uranium enrichment business[2]. DOE remains as site owner of the original property. Environmental compliance and wastegenerated from the operating plant since July 1, 1993, are the responsibility of the USEC. TheU.S. Nuclear Regulatory Commission assumed oversight of these activities on March 3, 1997[14]. DOE and LMES retained the responsibility for environmental remediation and wastehandling from activities performed prior to July 1, 1993 [2]. As of April 1, 1998, the new DOEcontractor for these responsibilities is Bechtel-Jacobs Company [15].

Site Visits and Collection of Community Concerns

ATSDR representatives visited the PGDP site in May 1994, as part of a program to evaluateDOE NPL sites and to develop a workplan to address those sites. Some community healthconcerns were identified during this site visit and during ATSDR's participation in six DOEpublic meetings in June 1994, May 1995, July 1995, November 1996, January 1998, and July1999 [16].

Community concerns also were identified through written correspondence, telephoneconversations, informal meetings, and public availability sessions. In 1995 ATSDR solicitedconcerns from community members by direct mail inquiry: a package containing a query letter,an information brochure about ATSDR, and a self-addressed business reply envelope was mailedto about 1,700 community members. A total of 60 people responded to this mailing. In May 1996ATSDR held five public availability sessions in Paducah and Heath, Kentucky, to solicitadditional concerns. The public availability sessions were informal and allowed citizens todiscuss their health concerns related to the site, one-on-one, with an ATSDR team member [17].Staff from ATSDR and Boston University gathered concerns by attending several Site SpecificAdvisory Board (SSAB) meetings and DOE technical presentations. All in all, ATSDR receivedabout 500 community concerns. These concerns are discussed in Appendix B and in thecommunity health concerns section later in this report. Most of the concerns relate to theincidence of cancer, the incidence of other illnesses, and the possibility of exposure throughvarious media.

ATSDR staff members visited the site in January 1996 to discuss the ATSDR public healthassessment (PHA) process and ATSDR's data needs with DOE and LMES officials [18].

In March 1996, project representatives visited the area to discuss the PHA process with citizens,gauge the community's interest in public availability sessions, and meet with the newly formedSite Specific Advisory Board (SSAB) and local health officials [19]. They toured the WesternKentucky Wildlife Management Area (WKWMA) with a community member and staff fromKentucky's Department of Fish and Wildlife Resources and Kentucky's Department forEnvironmental Protection.

ATSDR representatives visited the area in December 1996, to gather relevant demographic andland-use data and to investigate possible exposure pathways in the community near the facility[20]. In June 1997, the ATSDR team conducted another site visit to address the SSAB and tomeet with various officials and residents in the area [21]. In February 1998, staff attended theSSAB meeting and the first public meeting for the Draft Programmatic Environmental ImpactStatement for Alternative Strategies for the Long-Term Management and Use of DepletedUranium Hexafluoride [22]. In July 2000, ATSDR staff attended DOE's public meeting on theGroundwater Operable Unit Feasibility Study and the SSAB meeting.

On September 11, 2000, an ATSDR representative addressed Active Citizens for Truth (ACT), alocal community group, to discuss ATSDR and ATSDR's role at the PGDP site.

Demographics

Demographic information characterizes the people in the communities potentially affected by thesite, how long these people have lived there, and the current population trends [23]. Delineatingthe number of children and elderly people is particularly important, because these people tend tobe more sensitive to environmental exposures than the general population [24]. Also, informationon occupation, education level, poverty status, and household income can give clues to factorssuch as access to health care and subsistence fishing, hunting, or farming. Demographicinformation is essential when analyzing health outcome data and behavior patterns in acommunity.

PGDP is in northwestern McCracken County, Kentucky, near the border of Ballard County.North of the site (on the north side of the Ohio River) lies Massac County, Illinois. In the past,this area of Kentucky and southern Illinois was predominantly rural, with little populationgrowth; now, however, McCracken County's population is growing [25]. The addition of newhousing subdivisions west of the city of Paducah accounts for the bulk of the growth [26]. Also,there is an initiative to bring new industries into the area, which will undoubtedly affect themake-up of the population near the site. McCracken County, at 60,000 residents, has the largestpopulation of the three counties near the site [27].

According to the 1990 U.S. Census, the largest cities in a 10-mile (16-kilometer) radius of thesite are Paducah, Kentucky (27,256 persons); Metropolis, Illinois (6,734 persons); and Joppa,Illinois (492 persons) [25]. There are several small communities closer to the site: Heath,Grahamville, Rossington, Woodville, and Kevil. The two closest are Grahamville at 1.24 miles(2 kilometers) and Heath at 1.86 miles (3 kilometers) east of the plant [4].

The three counties encompassing the site have more people over 65 years of age than under 10years of age [25]. This is unusual compared to the 1990 national averages, but not unusual forrural areas.

In the census tracts surrounding the site, approximately 70% of people 25 and older have highschool diplomas, and approximately 15% are below the poverty level [28]. Over 75% of theresidents live in owner-occupied housing units, which suggests a stable, non-transient population.Also, 25% of the housing units get their water from drilled wells or sources other than public orprivate suppliers. DOE has offered to provide municipal water to some residents of westernMcCracken County (in an area described in DOE's Water Policy), who previously used privatewells (see the groundwater section of this report). For more detailed demographic information forthis site, refer to Appendix A.

Land Use and Natural Resources

Land-use patterns and natural resource use in the area of the site can demonstrate if or howpeople could be exposed to environmental contaminants. Using well water, farming or gardening,and hunting or fishing are some of the activities that can result in exposure to site contaminants.Knowing the locations of schools, hospitals, and nursing homes is also important, since thepopulations of these institutions tend to be elderly, sick, or very young, and consequently may beat higher risk for adverse health effects. Reviewing zoning patterns helps us understand futureuse of land around the site and helps us evaluate the potential hazard to the community.

PGDP is in a rural/suburban area of McCracken County. The residential area near the plant is in astate of transition. Farmlands are increasingly being subdivided for additional residentialdevelopment. The area west of Paducah, along US Route 60 (Figure 1), is the site of newsubdivisions. A new US Route 60 is being built to accommodate the projected heavier traffic inthe corridor between Paducah (Interstate 24) and the emerging suburbs. According to aDecember 1997 communication with the McCracken County Planning Office, US Route 60 willnot be moved near the plant entrance, but will be widened. The closest residences to the site areapproximately 3,280 feet (1,000 meters) north and 3,609 feet (1,100 meters) east of the PGDPfence line [29]. The closest schools are Heath Elementary, Middle, and High Schools. These are1.86 miles (3 kilometers) southeast of the plant. According to information obtained from HeathElementary school, there was another school--Forestdale Elementary--1.16 miles (1.86kilometers) southwest of the plant; that school was closed in 1981 when Heath Elementaryopened (Figure 3).

According to a June 1997 communication with the West McCracken County Water District, newhomes being built in the area are served by municipal water through their local water districts,which receive water from the Ohio River. Other residents use drilled wells, except for thoseresidents living in the Water Policy area that DOE has connected to a municipal water supply.Neither the Kentucky Department for Environmental Protections (KDEP)'s Division of Waternor the Purchase District Health Department routinely test existing wells; however, the healthdepartment will do limited testing on a well if asked. Newly drilled wells are tested for bacteria,iron, copper, and nitrates. Hand-dug (shallow) wells are illegal in Kentucky and are not underregulation by the Division of Water. Heath Elementary, Middle, and High Schools are suppliedwith municipal water from the Western McCracken County Water District. The high school was put on municipal water in 1968.

Property boundaries and other features
Figure 3. Property Boundaries and Other Features (jpg)
Property Boundaries and other features
Figure 3. Property Boundaries and Other Features (pdf)

There are approximately 400 active farms in McCracken County, Kentucky, with 45 to 50operating in the area near PGDP [30]. Soybeans, wheat, corn, and tobacco are the dominant cropsbeing cultivated. Although the number of individual tobacco farms has declined, the acreage usedfor this crop has been steady: farms have been consolidated under fewer owners. In general, thedominant crops grown in the area are shipped to national and international markets. There arepeople who grow their own vegetables in the area for personal use; however, this practice (aswell as cultivating specialty crops for commercial sale) is on the decline. There areapproximately 350 head of dairy cattle and 4,000 head of beef cattle in McCracken County.

Hand-dug wells are not used for irrigation of farmland. The farms rely on rainfall to water theircrops and to supply large ponds used for recreation and watering livestock. The water for theseponds is not supplied by wells. The area receives an average of 47 inches (1.19 meters) ofprecipitation per year; the heaviest precipitation usually comes in March, April, and May[8,9,31].

Industrial activity now accounts for less than 5% of the land use [5]. With increasing residentialuse and the widening of US Route 60, however, this percentage may increase in the near future.The TVA Shawnee Steam Plant and PGDP are the main employers in the area. There is also aprivately owned steam plant in Joppa, Illinois, across the Ohio River. (The steam plants, bothcoal-fired, were built in the early 1950s to supply electricity to PGDP). The Allied Signal Plant,which makes uranium fluoride products for PGDP, is across the Ohio River west of Metropolis,Illinois. Calvert City, a major industrial area, is approximately 13 miles (21 kilometers) east ofthe city of Paducah. It has the largest concentration of industry in western Kentucky; however, itis not believed to have an impact on public health in the PGDP area [32].

The WKWMA includes a 2,781-acre (1,125-hectare) buffer zone that surrounds PGDP [5]. Thisarea is open to the public and is a popular location for local sports, fishing, and hunting. TheWKWMA is accessible from Dyke Road, Ogden Landing Road, McCaw Road, and WoodvilleRoad (Figure 3). Within the WKWMA are signs denoting DOE property and a fence separatingthe federal facility from public areas. Two families live on or within the WKWMA. One personwho lives there maintains the area for the Kentucky Department of Fish and Wildlife Resources.The WKWMA supports an abundance and diversity of wild animals. Deer, fowl, turtles, fish, andsmall mammals such as raccoons are some of the animals caught in the area. Most communitymembers believe that these animals are consumed by the hunters and fishers themselves [17].Sports enthusiasts tend to come from a wide area within the region, whereas subsistence userstend to live near the city of Paducah. We found no evidence of camping.

The WKWMA includes the former KOW, where abandoned bunkers and other debris associatedwith past activities still exist. The former KOW's remedial investigation and cleanup are beingmanaged by the U.S. Army Corp of Engineers (USACE) [16]. Some of the old bunkers havebeen used for hunting clubs, dog pens, and horse barns. Six ponds (or gravel pits), which are usedfor fishing, are part of the USACE's investigation and cleanup. Mercury advisories are posted atFire Hydrant Pond, Horseshoe Pond, New Pond, Box Factory, and Gravel Pit #1 for largemouthbass [33]. No advisories have been issued for channel catfish or bluegills, which also are present.

One of the largest organized annual events to take place in the WKWMA is Earth Day, whichtakes place in the spring. On Earth Day, large groups of preteens gather to learn about nature andthe environment [1]. Many area schools participate in this event, which is sponsored by DOE,Bechtel Jacobs Company, and the Kentucky Department of Fish and Wildlife Resources.

PGDP is on relatively flat land--ranging from 367 to 380 feet (112 to 116 meters) above sealevel--on a drainage divide between Big Bayou and Little Bayou Creeks [13]. Both creeks flownorth to the Ohio River, and receive surface water discharges from the plant. When the TVAShawnee Power Plant was built in 1951 and 1952, Little Bayou Creek was diverted to the west,where it now joins with Big Bayou Creek before entering the Ohio River (Figure 1) [34,35]. BigBayou Creek flows past a residential area to the west of the plant and overflows into people'sfields during times of flooding. Channel catfish and bluegill appear in Big Bayou only when it isfilled with backwater from the Ohio River, and fishing occurs occasionally. Little Bayou Creek isan intermittent stream on the eastside of the plant. Little flow occurs in Little Bayou Creekexcept for effluent from the plant [8,9]. Fishing does not normally occur in this creek. Warningsigns for polychlorinated biphenyl (PCB) contamination in fish are posted at access areas alongthis creek, and these areas are partially fenced off. Fences and "No Trespassing" signs are presentat all plant outfalls; however, in the past, access to Little Bayou Creek was generally unrestricted.

Residents of the surrounding communities also use the Ohio River and Metropolis Lake forrecreational purposes. These surface water bodies are located approximately 3 miles (4.8kilometers) north and northeast of PGDP, respectively. Metropolis Lake connects to the OhioRiver and is part of a nature reserve. There is a warning issued against eating bass, carp, channelcatfish, paddlefish and paddlefish eggs caught in the Ohio River due to chlordane and PCBcontamination. Recently, a fish advisory was issued for Metropolis Lake due to mercury and PCBcontamination.

At PGDP, the wind predominantly comes from the south-southwest, at an average speed of 14.4feet per second (4.4 meters per second) [8,9,31]. The monthly average temperatures vary from34oF (1oC) during January to about 77oF (26oC) in July. The average annual temperature is 59oF(14oC).


ENVIRONMENTAL CONTAMINATION, EXPOSURE PATHWAYS, AND POTENTIALLY EXPOSED POPULATIONS

Introduction

This section discusses the various chemicals and radioactive materials (contaminants) evaluatedfor this site, how people may come into contact with them, and what populations are potentiallyexposed. These discussions are presented for groundwater, air, surface water, soil and sediment,and food and biota.

A release of a chemical or radioactivematerial from a site does not always meanthat this substance will be a contaminant ofhealth concern to an off-site population.ATSDR scientists first determine if achemical or radioactive substance in water,air, soil, or biota (plants and animals) shouldbe considered a "contaminant of concern."The criteria we use include (1) environmental levels exceeding media-specific comparisonvalues, (2) noted community health concerns, and (3) the quality and extent of the sampling datawe can use to evaluate potential exposure and human health hazard. For inorganic compounds(metals) and radionuclides, background values may also be considered, since some of thesesubstances occur naturally. For chemicals, the highest environmental concentration detected offsite is compared with media-specific comparison values to determine if further evaluation iswarranted. Generally, if a contaminant's concentration exceeds one or more media-specificcomparison values, then the contaminant is evaluated further in this section and in the publichealth implications section. (Refer to Appendix C for a description of comparison values.)

A release of a chemical or radioactive material into the environment does not always result inhuman exposure. For an exposure to occur, a completed exposure pathway must exist. Acompleted exposure pathway exists when all of the following five elements are present: (1) asource of contamination, (2) an environmental medium through which the contaminant istransported, (3) a point of human exposure, (4) a route of human exposure, and (5) an exposedpopulation. A potential exposure pathway exists when one or more of the elements is missing,but available information indicates that human exposure is likely. Also, an exposure pathway isconsidered potential when modeled data are used to predict human exposure. An incomplete exposure pathway exists when one or more of the elements is missing and available informationindicates that human exposure is unlikely to occur [23]. Figure 4 illustrates the necessary components of an exposure pathway.

Pathways to exposure from contamination
Figure 4. Pathways To Exposure From Contamination

In addition, for each exposure pathway, ATSDR scientists identify whether releases ofcontaminants and exposures are likely to have occurred in the past, currently, or potentially in thefuture. All releases from the uranium process facilities have dramatically decreased since the first10 years of plant operation; however, releases from other sources such as landfills and spill areashave increased.

This section also discusses potential hazards created by the storage of about 40,351 depleteduranium cylinders in outdoor cylinder yards. (Of these cylinders, 28,351 came from DOE andabout 12,000 came from the U.S. Enrichment Corporation, or USEC.)

In this report, "on-site contamination and releases" describes contamination and releases ofmaterial within the fenced security area of the site or in areas for which public access is restricted(i.e., groundwater wells outside the security fence but on DOE property). "Off-sitecontamination" describes environmental media (soil, sediment, surface water, groundwater, air,or biota) that are contaminated as a result of chemical or radioactive contaminants leaving thesite and are no longer being controlled by DOE or USEC. In this report, on-site sources ofcontamination are being considered only as sources of off-site contamination or for their impacton the community. (The impact of potential exposures to contaminants by workers is beingstudied by other organizations.)

Groundwater

Background and Site Hydrogeology

In August 1988, contamination by trichloroethylene (TCE), an organic solvent, and technetium 99 (Tc-99), a beta-emitting radionuclide, was detected in four residential drinking water wells located just north of the PGDP facility boundary [36]. Concentrations of TCE ranged from 1.5 to 960 g/L. Tc-99 concentrations ranged from 25 to 400 pCi/L. During that same year, residents were supplied with an alternate water source, and DOE initiated an extensive groundwater monitoring and analysis program [37].

Although no residents are currently exposed to off-site groundwater contaminants, four familiesliving north of the facility were exposed to contamination prior to the August 1988 action. Sincevery little measured data exist to support the evaluation of public health effects for pastexposures (prior to 1988), evaluation of past exposures is based on predicted or estimatedcontaminant concentrations and exposure durations. There is also potential for future exposuresif contaminated groundwater migrates into areas not covered by DOE's Water Policy supplyprogram or if future property owners drill new wells into the contaminated groundwater plumes.

The primary aquifer underlying the PGDP site is the Regional Gravel Aquifer (RGA). Flow isgenerally toward the north, with presumed discharge into the Ohio River or Big Bayou Creekimmediately south of the Ohio River [37]. The aquifer is 10 to 40 feet (3 to 12 meters) thick andcomposed of very permeable sands and gravels. The RGA is the source of drinking water forresidents with drilled wells in the PGDP area. In 1990, approximately 8% of the homes inMcCracken County and 9% of the homes in Ballard County relied on privately drilled wells fortheir drinking water. In the census block group that includes PGDP, 24% of the houses relied onprivately drilled wells [28].

The McNairy formation underlies the RGA. Water-bearing zones within the McNairy formationoccur within sand layers interspersed in a relatively thick sequence of clays. Sandy units of theupper McNairy formation may make up the lowermost portion of the RGA in areas north of thePGDP facilities. Also, erosion of clay in the vicinity of PGDP allows interaction of the RGAwith the McNairy and presents the potential for RGA contaminants to move into the McNairyformation [38]. Flow within the McNairy formation is north to northeast from the PGDP site.The McNairy formation is used as a drinking and industrial water source north of the Ohio River.According to analysis of hydraulic gradients in the McNairy formation, flow should dischargeinto the Ohio River [38]. The Kentucky Department for Environmental Protection analyzedsamples taken north of the Ohio River, and did not detect contaminants characteristic of PGDP.

Groundwater is also present in the alluvial, loess, and Upper Continental deposits, which areabove the RGA. The water table in these shallow units is typically 10 to 15 feet (3 to 4 meters)below land surface in the northwestern part of the site, and up to 46 feet (14 meters) below landsurface in other areas [7]. Water flow in the shallow units is predominantly downward into theRGA, but lateral flow occurs in more permeable units and toward the surface water reaches.Surface water from Big Bayou Creek and Little Bayou Creek contributes to groundwater in theRGA for areas south of the site, with a transition to discharge from the RGA to surface watersnorth of the site [7].

Contaminants entered the groundwater as aresult of several processes: (1) disposalpractices (e.g., oil landfarming), (2)accidental releases or spills (e.g., cylinderleaks and ruptures, cylinder drop test area,C-400 waste system leak), and (3) indirectleaching from buried waste materials (e.g.,C-749 uranium burial ground, C-404 low-level radioactive waste burial ground). Table 1 gives adescription and brief history of these sources. Several site-wide investigations have beenconducted, and additional characterization and remediation of the contaminant source areas arecurrently ongoing.

Releases of contaminants into the groundwater varied widely over time and happened throughoutthe operating history of the plant. Leaching from disposal areas occurred over time, becauseburied drums and containers decompose slowly. There are now three groundwater contaminantplumes: the northwest plume, the northeast plume, and the southwest plume. Each plume hasseveral sources; therefore, it is not possible to establish a specific time of origin for the plumesbased on times of contaminant releases.

Several source control or interim remedial actions have been established to reduce contaminantmigration from the site. These actions include (1) capping source areas with impermeable coversand (2) establishing extraction and treatment systems to remove contaminants from groundwater.The northwest plume treatment system was established in 1995, the northeast plume treatmentsystem in 1997.

The distribution of several contaminants suggests that the Tennessee Valley Authority (TVA)Shawnee Steam Plant may be a source of some groundwater contaminants. Contaminants fromthe PGDP site have migrated in the northwest plume to the TVA plant. However, groundwaterconcentrations of arsenic, cadmium, chromium, lead, and uranium 238 at the TVA site are higherthan concentrations in the northwest plume, and these contaminants were detected at the TVAplant before the PGDP plume reached the plant. Because these contaminants are the same asthose detected at PGDP and are present in the same environmental media, they will be evaluatedthrough the same exposure pathways.


Table 1.

Groundwater contaminant sources at the Paducah Gaseous Diffusion Plant [39,40,7]
Northwest Plume1 Contaminant Source/SWMU Source Description/History Contaminants
C-400 area; TCE leak site/11, C-400 to C-404underground transfer line/26, C-403 neutralizationtank/40, C-400 Tc-99 storage tank/47, C-400sump/203; C-400 south end storm sewerFacility maintenance area; leak in waste processing lines andsump--repaired 1986TCE DNAPL (up to 890,000 g/L in UCRS),Tc-99, 1,2-DCE, PCE, total PAHs, chromium
C-746-A septic system/196Sinks, showers, toilets, and floor drains; system was used from 1958to 1980; contaminants probably released into drainsHeavy metals, radionuclides, possible TCE
C-745-B Cylinder drop test area/91TCE-based slush bath used to chill UF6 cylinders for shock tests; testsconducted in 1979TCE DNAPL (up to 160,000 g/L in UCRS),1,2-DCE, 1,1,1-TCA, PCE, chloroform
C-749 Uranium burial ground/2Burial ground in the northwest corner inside the security fence TCE
C-404 Low-level waste burial ground/3 Low-level radioactive and hazardous waste burial ground TCE
C-747-A Burial ground/7 and 30Burial ground in the northwest corner inside the security fenceTCE
Southwest Plume2 Contaminant Source/SWMU Source Description/History Contaminants
C-747-C oil landfarm/1; C-747-C contaminatedburial yard/4Landspreading of contaminated waste oil; site operated 1973-1979Petroleum products, TCE,
1,1,1-TCA, uranium, PCBs
C-720 Building and storm sewerMaintenance facilityTCE, Tc-99
C-740 TCE spill site/136TCE spill siteTCE
Northeast Plume3 Contaminant Source/SWMUSource Description/HistoryContaminants
C-745 Kellog building Site/99Building used for pipe fabrication during plant construction(1951-1956); extensive use of TCE; building demolished in 1956TCE, 1,1-DCE, low concentrations of Tc-99
C-400 area/40 (C-403 neutralization tank)Possible leak from tank or transfer lineTCE (up to 11,000 g/L in RGA),
Tc-99 (up to 1,735 pCi/L in RGA)
McGraw underground storage tank, southside cylinder yard, and construction facility; SWMUs 183, 193, and 194,respectivelySite characterization studies ongoing
1 Source: [41,42]
2 Source: [42]
3 Source: [42,43]
Key: 1,1-DCE = 1,1-dichloroethene; 1,1,1-TCA = 1,1,1-trichloroethane; 1,2-DCE = 1,2-dichloroethene; DNAPL = dense nonaqueous-phase liquid;
PAHs = polyaromatic hydrocarbons; PCBs = polychlorinated biphenyls; PCE = tetrachloroethylene; SWMU = solid waste management unit; Tc-99 = technetium 99; TCE = trichloroethylene; UCRS = Upper Continental Recharge System

Results of groundwater monitoring, provided to ATSDR in several databases from DOE and theCommonwealth of Kentucky, were screened to determine contamination concentrations anddistributions. These databases were transferred electronically and checked for completeness andconsistency. Incomplete or missing records that could not be corrected with supportingdocuments or communications with site personnel were not used in the screening process.Electronic data were supplemented with published documents.

Contaminants of Concern

Because numerous chemical analyses were performed for groundwater, ATSDR scientists used a series of screening techniques to focus their evaluation on contaminants that may be a human health hazard. The first phase of screening involved identifying contaminants detected above media-specific comparison values in on-site or off-site well samples. Forty-seven contaminants have been detected in groundwater wells at concentrations above these comparison values. (Refer to Appendix C for a description of comparisonvalues).

The second phase of screening was to determine whether the groundwater contaminants arepresent or potentially present in residential wells. Thirty of the forty-seven contaminants havebeen found in off-site groundwater wells where exposure to the community is possible. Table 2provides information about these contaminants, the number of samples analyzed, the number ofsamples with positive detections, and maximum concentrations detected in off-site wells. Notethat inclusion of a substance in Table 2 does not mean that anyone was exposed to thatsubstance.

The third phase of screening involved comparing maximum concentrations of off-sitegroundwater contaminants in areas of potential exposure with their respective comparison values.Contaminant concentrations below these comparison values are not expected to cause adversehealth effects following exposure. For contaminant concentrations above comparison values,ATSDR evaluated potential or documented exposures and public health implications.


Table 2.

ff-site groundwater contaminants [44,45,46,47,48]
Metals and Elements Number of Off-Site Samples Number of Off-Site Detects Off-Site Maximum Concentration in g/L Background Range
in g/L
Arsenic77990ND-10
Beryllium4174010
Cadmium35110NT
Chromium8244270ND-70
Fluoride2020550NT
Lead674029010
Nickel11042210ND-140
Nitrate353421,800NT
Sulfate (dissolved and total)7069743,0001,200
Sulfide (dissolved and total)63175,160ND
Thallium9 0(detection limit = 10)NT
Vanadium373021010-170
Zinc122775,09010-330
Organic CompoundsNumber of Off-Site SamplesNumber of Off-Site DetectsOff-Site Maximum Concentration in g/LBackground Range
in g/L
Bis(2-ethylhexyl)phthalate10613300(lab contaminant)
Bromodichloromethane435216ND
Carbon tetrachloride43838ND
Chloroform438656ND
1,2-Dichloroethane436157ND
1,1-Dichloroethene438213ND
1,2-Dichloroethene1733418ND
Methylene chloride142127ND
Pentachlorophenol91 18 (residential detection limit = 50)ND
Tetrachloroethylene4381

1

ND
Trichloroethylene5,6981,091

167,000

ND
Vinyl chloride4382

110

ND
Radioactive Contaminants Number of Off-Site Samples Number of Off-Site Detects Off-Site Maximum Concentration in pCi/L (Bq/L) Background Range in pCi/L (Bq/L)
Radon 222 386238421,855 (68.7)NA3
Technetium 99~5,000898

5,804 (215)

<25 (<0.93)
Uranium 23413980

24 (0.9)

<2 (<0.07)
Uranium 2351193

3 (0.1)

<1 (<0.04)
Uranium 238140120

97 (3.6)

<2 (<0.07)
1 1,2-Dichloroethene includes data recorded as 1,2-dichloroethylene, 1,2-dichloroethene-cis, and 1,2-dichloroethene-trans.
2 Source: [45,46,47]
3 Background levels of radon 222 in groundwater vary; they are naturally high in some areas of the country.
Key: < = less than; Bq/L = becquerels per liter, g/L = micrograms per liter; NA = not applicable; ND = not detected; NT = not tested; pCi/L = picocuries per liter

Table 3 lists 30 off-site groundwater contaminants, their comparison values, and the number ofoff-site detections above the comparison value. For each contaminant, the table indicates whichwells had maximum concentrations exceeding comparison values and presents the range ofmaximum concentrations in these wells. Residential wells are denoted with an "R" or "RW" wellnumber. Few contaminants were detected in residential wells; however, only a few chemicalswere tested for in residential well samples. Therefore, for screening purposes, we assumed thatcontaminants found in off-site monitoring wells could have been present in residential wells.Table 4 lists 17 groundwater contaminants (out of 47) that are not considered contaminants ofconcern and explains why we excluded these contaminants from further evaluation.

When a contaminant's maximum concentration exceeded a comparison value, that contaminantwas considered a possible contaminant of concern. Other criteria used to select contaminantswere (1) the frequency and location of detections (e.g., single detections are not reliableindicators of contaminant presence), and (2) quality and quantity of environmental sampling data(e.g., suspected laboratory contaminants or inappropriate detection levels). For an example of thelatter, bis(2-ethylhexyl)phthalate was frequently detected above its comparison value in off-sitegroundwater samples. This contaminant is not a constituent of the PGDP process operations orwaste products, but it is a common constituent of the plastic gloves and sampling equipment usedin field sampling. It was detected with similar frequency in on-site, off-site, and backgroundsamples. For these reasons, positive detections were interpreted as an artifact of the sampling andlaboratory processes. Bis(2-ethylhexyl)phthalate was not selected as a contaminant of concern forthis exposure pathway.

Of the 30 off-site groundwater contaminants detected in areas of potential exposure, 15contaminants either were found at levels of potential health concern or, because of inadequateanalysis, could be present at levels of health concern. Fifteen off-site contaminants, for whichadequate analyses have been conducted, are not considered contaminants of concern based oncontaminant concentrations, distribution, and frequency of detection. The rationale for selectionor exclusion is listed in Tables 3 and 4.

Beryllium, cadmium, nickel, sulfate, and zinc each had only one off-site measurement above theircomparison values (as shown in Table 3). Beryllium, cadmium, nickel, and sulfate were onlydetected in wells near the TVA plant and the Ohio River, and no elevated concentrations forthese contaminants were measured in the groundwater plumes between the PGDP facility and theTVA plant. Beryllium, nickel, and sulfate are not contaminants of concern in groundwater due totheir low overall frequency of detection, their maximum concentrations, and the limited potentialfor exposure. Cadmium, thallium, pentachlorophenol, and vinyl chloride were selected ascontaminants of concern for this exposure pathway, because analytical detection limits weregreater than their respective comparison values. Zinc was measured above its comparison valueonly once off site, but the sample was taken from a residential well; therefore, zinc was selectedas a contaminant of concern for this exposure pathway.

Arsenic, chromium, lead, nitrate, vanadium, and TCE were selected as contaminants of concern,because their maximum concentrations in off-site well samples were above their respectivecomparison values (as shown in Table 3). Maximum concentrations of chromium and vanadiumwere not above comparison values in the residential wells tested for these contaminants;however, the concentrations were above comparison values in monitoring wells near untestedresidential wells.

Uranium (as a chemical)(1) was detected in six off-site wells. The uranium concentration exceededEPA's 1991 proposed maximum contaminant level (MCL)--20 micrograms per liter (g/L)--inonly one well (MW-135; 24 g/L). Six subsequent analyses of MW-135 all indicated non-detects. Because uranium is rarely detected in off-site wells and the single detection above theMCL was not repeated in subsequent analyses, uranium metal (i.e., uranium as a chemical) is nota contaminant of concern in groundwater. (Note: EPA's National Primary Drinking WaterRegulations final rule, published December 7, 2000, has the MCL for uranium as 30 g/L.)

Several of the chemical and radioactive contaminants listed in Table 3 are naturally occurring metals or elements. Some of these (e.g., nickel and vanadium) have background concentrations that exceed comparison values. Four of the five radioactive contaminants in Table 3 are naturally occurring, although process operations at PGDP may have caused groundwater concentrations to be elevated above background levels. However, vanadium and two of the naturally occurring radioactive contaminants (uranium 234 and uranium 238, also called U-234 and U-238) were selected as contaminants of concern for this exposure pathway regardless of their source.

Radon 222 (Rn-222) was detected in most of the wells around PGDP. Radon (a radioactive gas)occurs naturally in groundwater; and its presence may not be related to site activities. Becausethere is no accepted comparison value for Rn-222 in drinking water, ATSDR converted thegroundwater concentration into a potential airborne dose using EPA's recommended proceduresfor determining potential radon gas concentrations in residential air. According to thesecalculations, the highest potential air concentrations in a home are less than EPA's recommendedaction level of 4 picocuries per liter (pCi/L) [49]. Also, using information from a recent article in Radiation Research [50] and the maximum concentration of Rn-222 found in well water, andassuming that a person ingests 2 liters of contaminated water per day, we calculated a wholebody committed effective dose:(2) 50 millirems (or 0.5 millisieverts). This is less than a typicalbackground dose from naturally occurring radon. Therefore, Rn-222 was not selected as acontaminant of concern for this exposure pathway.

Maximum concentrations of three other radioactive contaminants, Tc-99, U-238, and U-234,exceed EPA's proposed drinking water standards. Tc-99, U-238, and U-234 were selected ascontaminants of concern.

Contaminants of concern in the groundwater exposure pathways are discussed further in thenext section. Contaminants that were detected on site and/or off site but were not considered inthe initial screening (17 of the original 47 chemicals, compounds, and elements in Table 2) arelisted in Table 4 with the reasons why they were not considered. The contaminants listed inTable 4 will not be evaluated further.


Table 3.

Groundwater contaminants detected off site, comparison values, and locations
Metals and Inorganic Compounds CV1 (CV Source)
in g/L
Number of Off-Site Detects Above CVWells With Detections Above CVsMaximum Concentration Range in g/LSelected as Contaminant of Concern? Why?
Arsenic3 (Chr.EMEGc)9MWD-009, -025; MW-121, -143,
-150, -192; RW-004, -294; TVA-04
7 to 90Yes, above CV
Beryllium20 (Chr.EMEGc)1MWD-01440No, one off-site detection > CV and no exposure
Cadmium2 (Chr.EMEGc)1MWD-01410Yes, all DLs > CV
Chromium30 (Chr.RMEGc for hexavalent)
100 (MCL for trivalent)
28MWD-009, -019, -024, -025, -027;
MW-121, -123, -125, -127, -133, -134, -138, -141, -142, -149, -153, -192, -194,
-195, -199, -200, -201, -202, -234, -235;
TVA-27
40 to 270Yes, above CV
Fluoride600 (Chr.EMEGc)0 550No, less than CV
Lead15 (Action Level)16MWD-014, -019, -024, -025;
MW-121, -123, -200, -202;
RW-004, -113, -297;
TVA-04, -27
20 to 290Yes, above CV; also, non-detects have DLs > CV
Nickel200 (Chr.RMEGc)1MWD-014210 No, one off-site detection > CV and no exposure
Nitrate (dissolved and total)20,000 (Chr.RMEGc)2 RW-156; RW-29421,800 to 29,200 Yes, above CV
Sulfate (dissolved and total)500,000 (MCL)1TVA-25743,000 (dissolved)No, one off-site detection > CV and no exposure
Sulfide (dissolved and total)500,000 (MCL)0 5,160No, less than CV
Thallium2 (MCL)All DLs > CVNALowest residential well DL = 10Yes, all DLs > CV
Vanadium30 (Int.EMEGc)24MWD-009, -014, -019, -024, -025, -027;
MW-121, -123, -125, -142, -149, -153, -194, -195,-199,-200,-202;
TVA-04, -27
30 to 210Yes, above CV
Zinc3,000 (Chr.EMEGc)1RW-1135,090Yes, single detect in residential well
Organic Compounds CV1 (CV Source)
in g/L
Number of Off-Site Detects Above CV Wells With Detections Above CVs Maximum Concentration Range in g/L Selected as Contaminant of Concern? Why?
Bis(2-ethylhexyl)phthalate6 (MCL)11MWD-003, -005, -019; MW-121, -125, -133, -143, -191; RW-021; RW-294 To 300No, artifact of collecting and sampling
Bromodichloromethane100 (MCL)0 16No, less than CV
Carbon tetrachloride70 (Int.EMEGc)0 8No, less than CV
Chloroform100 (Chr.EMEGc)0 56No, less than CV
1,2-Dichloroethane2,000 (Int.EMEGc)0 57No, less than CV
1,1-Dichloroethene90 (Chr.RMEGc)0 13No, less than CV
1,2-Dichloroethene (includes cis- and trans-)2,000 (Int.EMEGc)0 18No, less than CV
Methylene chloride2000 (Chr.EMEGc)0 27No, less than CV
Pentachlorophenol10 (Int.EMEGc)DLs > CV NALowest residential well DL = 50Yes, DLs for residential wells above CV
Tetrachloroethylene100 (Chr.RMEGc)0 1No, less than CV
Trichloroethylene

5 (MCL)

722

Many wellsUp to 167,000Yes, above CV
Vinyl chloride

0.2 (Chr.EMEGc)

2

MW-9754 to 110Yes, above CV and DL for wells in plume above CV
Radioactive Contaminants CV in pCi/L (Bq/L)
(CV Source)2
Number of Off-Site Detects Above CV Wells With Detections Above CVs Maximum Concentration Range in pCi/L (Bq/L) Selected as Contaminant of Concern? Why?
Radon 222

None available

(3093 )

Many wells3328 to 1,855
(12.1 to 68.7)
No, 1,855 pCi/L is equal to or less than 4 pCi/L in home air using EPA's recommended procedures to determine max. in residential air;4 annual dose approx. 50 mrem (0.5 mSv)5
Technetium 99

3,790 (140)

2

MW-2615,125 to 5,804
(190 to 215)
Yes, above CV
Uranium 234

15; 30 total U6
(0.56; 1.11)

2

MW-141, MW-14817 and 24
(0.6 to 0.9)
Yes, above CV
Uranium 235

15; 30 total U6
(0.56; 1.11)

0

 3 (0.1)No, less than CV--but estimated dose will be added to dose from other uranium isotopes and Tc-99
Uranium 238

15; 30 total U6
(0.56; 1.11)

3

MWD-009; MW-141; TVA-1417 to 97
(0.6 to 3.6)
Yes, above CV
1 Refer to Appendix C for a discussion of comparison values (CVs).
2 For radioactive contaminants, the CV source is the current and/or proposed EPA Safe Drinking Water Standards [51].
3 Data collected from 1990, 1991, 1992, and 1993 PGDP Environmental Reports [45,46,47,48]. (Number of detects above 300 pCi/L, EPA's proposed standard)
4 Source: [49]
5 Source: [50]
6 EPA's 1991 proposed Drinking Water Standard, 40 CFR Parts 141 and 142.
Key: Bq/L = becquerels per liter; DLs = detection limits; Chr.EMEGc = Chronic Environmental Media Evaluation Guide for children;
Chr.RMEGc = Chronic Reference Dose Media Evaluation Guide for children; CV = comparison value; Int.EMEGc = Intermediate Environmental Media Evaluation Guide for children;
MCL = EPA's Maximum Contaminant Level; g/L = micrograms per liter; mSv = millisieverts; mrem = millirems; pCi/L = picocuries per liter


Table 4.

Groundwater contaminants (on and off site) excluded from further analysis [44]
ContaminantMaximum Concentration (in g/L)Number of DetectionsComments
Arsenic, dissolved2016Considered contaminant as total arsenic
(non-reproducible results as dissolved)
Benzene124No off-site detections (only on site)
Boron1,54034No off-site detections (only on site)
Cadmium, dissolved207Considered contaminant as total cadmium
(non-reproducible results as dissolved)
Chloromethane1804No off-site detections (only on site)
2-Chlorophenol731Single on-site detection; no off-sitedetections
Chromium, dissolved11035Considered contaminant as total chromium
(non-reproducible results as dissolved)
2,4-Dinitrotoluene281Single on-site detection; no off-sitedetections
Lead, dissolved8022Considered contaminant as total lead
(non-reproducible results as dissolved)
n-Nitroso-di-n-propylamine351Single on-site detection; no off-sitedetections
Nickel, dissolved660104Considered contaminant as total nickel
(non-reproducible results as dissolved)
Nitrate, nitrite68,600 (on site)414Considered contaminant as nitrate
PCB (Aroclor 1254)11Single on-site detection; no off-sitedetections
1,1,1-Trichloroethane167No off-site detections (only on site)
Uranium (as achemical)9029Not tested off site as chemical
(Analyzed as U-234, U-235, and U-238)
Vanadium, dissolved7015Considered contaminant as total vanadium
(non-reproducible results as dissolved)
Zinc, dissolved37,40015Considered contaminant as total zinc
(non-reproducible results as dissolved)
Key: g/L = micrograms per liter; PCB = polychlorinated biphenyl;
U-234, U-235, and U-238 = uranium 234, uranium 235, and uranium 238

Groundwater Exposure Pathways

ATSDR scientists identified completed and potential human exposure pathways for past, current,and potential future exposure to contaminants of concern in groundwater. In addition, weestimated human exposure doses for contaminants in these exposure pathways. In the publichealth implications section, we discuss potential health hazards from exposure to contaminants ofconcern at the estimated doses.

Current Exposure

Currently, off-site residents are not beingexposed to groundwater contaminationoriginating from the PGDP site. Formerresidential wells within the northwest andnortheast plumes either are used to monitorcontaminant distributions or have been plugged using procedures approved by EPA and theKentucky Department for Environmental Protection [52]. Although contaminated groundwaterfrom the northwest plume may be discharging into the Ohio River or the portion of Big BayouCreek directly adjacent to the Ohio River, the concentrations at those locations do not exceedcomparison values [37]. Therefore, there are no exposure pathways identified for currentexposure to groundwater contaminants from the site.

Prior testing of private wells in the PGDP area revealed contamination by lead. Of the 12residential wells tested for lead, three were above the EPA action level of 15 g/L[53,54,45,46,47,48]. One of these wells was at a horse barn and was not a private residence'sprimary drinking water source. Lead found in these wells may not originate from the PGDP site;lead contamination may have resulted from materials used in plumbing. The wells are no longerused as a source of drinking water, but if the lead originated in plumbing that is still being used,the source and exposure pathway for lead exposure may still exist. Persons who are concernedabout the possibility of lead contamination in their drinking water may wish to have their watertested. A list at the end of the community health concerns section of this report provides namesand phone numbers for persons to contact at the local health department. Additional informationis available from EPA's Safe Drinking Water Hotline at 1-800-426-4791. As a generalprecaution, EPA recommends running taps for 30 seconds to 2 minutes before using the tapwater. Possible adverse health effects from exposure to lead in drinking water are discussed inthe public health implications section of this report.

Past Exposure

Off-site residential wells in the northeast plume area were plugged or converted to monitoringwells before contaminant concentrations exceeded comparison values. Therefore, no completedexposure pathways are identified for past exposure to contaminants in the northeast plume.

For the northwest plume, TCE and Tc-99 were first detected in four private residential wells inAugust 1988. At that time, these were the only contaminants measured in these wells; however,well samples collected after 1988 indicatethat other contaminants may have beenpresent in the northwest plume along withTCE and Tc-99. Arsenic, lead, nitrate, andzinc were detected in samples fromresidential wells after 1988, although theymay not be related to the northeast andnorthwest plumes. Therefore, TCE, Tc-99,arsenic, lead, nitrate, and zinc arecontaminants of concern for past exposurevia completed exposure pathways forgroundwater. Completed exposure pathways are described in Table 5.

Thallium, pentachlorophenol, and vinyl chloride were not detected in off-site residential wells;however, the lowest level of analytical detection exceeded the comparison value. Four otherchemicals or metals (cadmium, chromium, fluoride, and vanadium) were detected in monitoringwells at maximum concentrations that exceeded comparison values. Analyses for thesecontaminants were not performed for most residential well samples. Because residential wellsmay have contained cadmium, chromium, fluoride, pentachlorophenol, thallium, vanadium, orvinyl chloride, they are contaminants of concern for past exposure via potential exposurepathways. Potential exposure pathways are described in Table 6.

Two radioactive contaminants, U-234 and U-238, were detected in off-site monitoring wells. Thesamples were collected in the deep RGA. Maximum concentrations exceeded EPA's drinkingwater standard. Although these results were not repeated and these contaminants were notdetected in residential wells, U-234 and U-238 were detected in on-site groundwater and areconsidered contaminants of concern for past exposure via potential exposure pathways forgroundwater. (Refer to Table 6.)

After the initial discovery and mapping of the northeast and northwest plumes, an additionalgroundwater contaminant plume, called the southwest plume, was identified from new sourcecharacterization and monitoring wells. The current mapped distribution of the southwest plume islargely inside the fenced security area on the west side of the plant property and entirely withinthe DOE property boundary. There are no residential drinking water wells within the past orcurrent area of the southwest plume. Therefore, there are no exposure pathways identified forpast or current exposure to contaminants in the southwest plume.

Past Exposure Evaluation

Because sampling and analysis data are not available for times before 1988; therefore, ATSDRscientists used measurements of TCE migration rates for 1988 through 1995 to estimate theduration of past exposure to groundwater contaminants.

Figures 5 and 6 show the concentrations of TCE and Tc-99 in four residential wells by year,beginning in 1988, when monitoring began. These wells were likely to have been contaminatedwith TCE above the comparison value (5 g/L) before 1988. Evaluation of contaminant transportrates indicate that TCE concentrations were estimated to be greater than 100 g/L for 5 to 15years prior to 1988. Concentrations less than 100 g/L may have been present in these wells for alonger period; however, that period's duration cannot be estimated with certainty. Therefore, weassumed an exposure duration of 5 to 15 years for all contaminants in the wells associated withthe northwest plume. In evaluating contaminant transport, we assumed a concentration of 100g/L--but this is not a health-based concentration. Appendix D details the evaluation of contaminant migration and presents supporting information.

Past exposure doses for contaminants of concern in completed and potential exposure pathwaysare estimated using assumptions about who may have been exposed, how they may have beenexposed, how long their exposures lasted, and how often they were exposed. We assumed thatingestion was the primary route of exposure for this exposure pathway, although inhalation andskin contact for some contaminants were secondary exposure routes. Studies have shown thatvolatile organic compounds released from water to air during showering or bathing can produce,through inhalation, a dose that is 50% to 90% as large as the dose through ingestion [55,56].Absorption of these contaminants through the skin can contribute a dose up to 30% of theingested dose [57]. As a conservative estimate, ATSDR scientists assumed that ingestion dosesfor volatile organic compounds, TCE, and vinyl chloride would increase 70% from inhalationand 30% from dermal absorption.

ATSDR scientists estimated doses to adults and children. Exposures are estimated for a 1- to 6-year-old child who weighs 13 kilograms and ingests 1 liter of water daily and for an adult whoweighs 70 kilograms and drinks 2 liters of water daily at the maximum detected concentration.

Except for TCE, Tc-99, U-234, and U-238, the maximum off-site concentrations of the contaminants in groundwater were used to calculate exposure doses. Exposure doses for TCE and Tc-99 were based on maximum concentrations measured in 1988 at the most contaminated drinking water well (960 g/L for TCE and 400 pCi/L for Tc-99). For U-234 and U-238, the exposure doses were based on maximum concentrations measured in MW-141 (24 pCi/L for both U-234 and U-238). Tables 5 and 6 show maximum estimated exposure doses for contaminants in completed and potential exposure pathways.

Potential Future Exposure

Potential future exposure pathways exist for contaminants in the northeast and northwestplumes, and possibly the McNairy Aquifer and the southwest plume.

For the northeast plume, the primary contaminant of concern is TCE. Also, chromium hasrecently been detected in several wells northeast of the site property. Although othercontaminants (such as Tc-99 and arsenic) have been detected in the northeast plume, they havenot migrated off site at concentrations exceeding health comparison values. The northeast plumeis migrating to the northeast and is close to the eastern boundary of the Water Policy-affectedarea (Metropolis Lake Road), as Figure 7 shows. Although a groundwater extraction andtreatment system was established for this plume in August 1997, contaminants at the leadingedge may migrate beyond Metropolis Lake Road in the future. If the plume continues to migrate,it may contaminate additional private water wells before it discharges into the Ohio River.(3) DOEis continuing to monitor the movement of the northeast plume. DOE has indicated that they willexpand the boundaries of the Water Policy area if ongoing monitoring indicates that additionalwells may become contaminated [36]. If the plume migrates outside the water policy boundaryand contaminated wells are capped using approved procedures, no exposure will occur.

Residents who have been provided with municipal water have agreed not to drill additionalwells; however, new residents or new landowners in the area are not restricted from drilling newwells within the area of groundwater contamination. Therefore, there is a potential for futureexposure if new wells are drilled into the northeast or northwest contaminant plumes.

The southwest plume was recently characterized. There is no current completed exposurepathway for this plume. Its future migration direction is unknown. The plume may turn north andjoin with the northwest plume.

The McNairy Aquifer also represents a potential source for future human exposure. Lowconcentrations of groundwater contaminants have been detected in the McNairy Aquifer.Subsequent northward transport to the Ohio River or under the river to water supply wells inIllinois presents a limited potential for exposure. In order for this exposure pathway to becompleted, contaminants must migrate from the RGA into the McNairy Aquifer and then flowunder the Ohio River to public supply wells. TCE and Tc-99 have been detected in McNairywells (TCE in MW-114, MW-121, and MW-128; Tc-99 in all wells, including the backgroundwell MW-140). Contaminant concentrations are low: one TCE sample was above the comparisonvalue (the sample had TCE at a concentration of 9 g/L). According to available data, the wellfrom which this sample was taken (MW-114) has not been re-sampled.

Continued monitoring of contaminants in the northeast, northwest, and southwest plumes isnecessary until these flow systems are well defined and the effects of the extraction and treatmentsystems or other remedial techniques are known. ATSDR will re-evaluate this exposure pathwayif future monitoring results indicate a potential for human exposure to groundwatercontaminants.

DOE contractors are currently performing pilot studies for various technologies that might beable to remediate the groundwater aquifer. Several options and combinations of options havebeen presented to the public, along with estimated costs and timeframes [42]. No matter whatoptions are chosen, the remediation will probably take a very long time.

TCE Concentrations in Residential Wells
Figure 5. TCE Concentrations in Residential Wells

Tc-99 Concentration in Residential Wells
Figure 6. Tc-99 Concentration in Residential Wells

Paducah Gaseous Diffusion Plant
Figure 7. TCE and Tc-99 Groundwater Contamination, 1997 (jpg)

Figure 7. TCE and Tc-99 groundwater contamination, 1997 (pdf)


Table 5.

Summary of contaminants of concern and exposure doses in completed exposure pathways for off-site groundwater
Major SourcesContaminantsExposure PointExposure RouteExposed PersonsPeriod of Time and DurationMaximum Estimated Exposure Doses 1
Leaching ofcontaminantsfrom disposalpractices,accidentalreleases orspills, andburied wastematerials tothe RegionalGravelAquiferTCE2
(960 g/L)
Residentialwells drilledinto northwest plume in RGAIngestion(TCEincludesinhalationand skinabsorption)Children and adultsusing RW-002, RW-017, and RW-113(RW-004 at horsebarn)Past only
5 to 15 years chronic exposure ending in 1988
TCE:2

Children 0.148 mg/kg/d
Adults 0.055 mg/kg/d
Tc-992
(400 pCi/L)
Tc-99:2 (for annual intake)

Children 1.2 mrem (0.012 mSv)
Adults 0.69 mrem (0.007 mSv)

ArsenicTworesidentialwellsIngestionChildren and adultsusing RW-294 (RW-004 at horse barn)Past only
Wells no longer in use; exposure duration unknown
Arsenic:3

Children 0.001 mg/kg/d
Adults 0.0003 mg/kg/d
LeadResidentialwellsnorthwest ofsiteIngestionChildren and adultsusing RW-113 andRW-297 (RW-004 athorse barn)Past
Wells no longer in use; exposure duration unknown; see Table 6
Lead:

Children 0.009 mg/kg/d
Adults 0.003 mg/kg/d

(RW-004)

Children 0.022 mg/kg/d
Adults 0.008 mg/kg/d

NitrateThreeresidentialwellsIngestionChildren using RW-002, RW-030, andRW-294Past only
Wells no longer in use; exposure duration unknown
Nitrate:

Children 1.69 mg/kg/d
Adults 0.63 mg/kg/d
ZincOneresidentialwell IngestionChildren and adultsusing RW-113Past
Well no longer in use; exposure duration unknown
Zinc:

Children 0.392 mg/kg/d
Adults 0.145 mg/kg/d
1 In calculating exposure doses, ATSDR assumed 13 kg body weight and 1 liter water per day for children and 70 kg body weight and 2 liters water per day for adults. ATSDR used dose conversions from ICRP 72 [58].
2 TCE and Tc-99 exposure doses based on maximum measured concentrations in residential wells for 1988.
3 Doses based on detections in residential wells.
Key: g/L = micrograms per liter; mg/kg/d = milligrams contaminant per kilogram body weight per day (exposure unit used for chemicals);
mrem = millirems (unit used for radiation exposure); mSv = millisieverts (1 mSv = 100 mrem); pCi/L = picocuries per liter; Tc-99 = technetium 99; TCE = trichloroethylene


Table 6.

Summary of contaminants of concern and exposure doses in potential exposure pathways for off-site groundwater
Major Sources Contaminants Point of Exposure Route of Exposure Exposed Population Period of Time and Duration Maximum Estimated Exposure Doses1
Leaching of contaminants from multiple on-site sources described in Table 1Arsenic

Cadmium

Chromium

Thallium

Vanadium

Pentachloro-
phenol

Vinyl
chloride

Uranium 234

Uranium 238

Residential wells northwest, north, and northeast of siteIngestionChildren and adults living in houses in these areas with drilled wellsPotential past and futureArsenic:

Children 0.007 mg/kg/d
Adults 0.003 mg/kg/d

Cadmium:

Children 0.001 mg/kg/d
Adults 0.0003 mg/kg/d

Chromium:

Children 0.021 mg/kg/d
Adults 0.008 mg/kg/d

Thallium:

Children 0.001 mg/kg/d
Adults 0.0003 mg/kg/d

Vanadium:

Children 0.016 mg/kg/d
Adults 0.006 mg/kg/d

Pentachlorophenol:

Children 0.0039 mg/kg/d
Adults 0.0014 mg/kg/d

Vinyl chloride:

Children 0.017 mg/kg/d
Adults 0.0063 mg/kg/d

Uranium 234 (for annual intake):

Children 2.9 mrem (0.029 mSv)
Adults 3.2 mrem (0.032 mSv)

Uranium 238 (for annual intake):

Children 2.6 mrem (0.026 mSv)
Adults 2.9 mrem (0.029 mSv)

Lead2Residential wells north and northwest of siteIngestion Potential current and futureSee text
For northeast Plume:
Building C-745,
underground storage tanks,
southside cylinder yard, construction facility, historical staging area
TCE and
potentially
Tc-99
Eight residential wells drilled east of Metropolis Lake Road, north of McCaw Road, south of Ohio RiverIngestion (also, for TCE, inhalation and skin absorption during showering)Households and visitors to about eight residencesPotential futureFuture potential doses were not estimated.
For McNairy Aquifer:
leaching of contaminants from Regional Gravel Aquifer
TCE
Tc-99
Public water supply wells north of Ohio RiverIngestion (also, for TCE, inhalation and skin absorption during showering)Anyone using public water supplyPotential futureFuture potential doses were not estimated
For northeast and northwest plumes:
leaching of contaminants from multiple on-site sources described in Table 1
TCE
Tc-99
New wells drilled into existing northeast and northwest plumes Ingestion (also, for TCE, inhalation and skin absorption during showering)Persons using new wells for residential purposesPotential future Future potential doses were not estimated.
1 For calculating exposure doses, ATSDR assumed 13 kg body weight and 1 liter water per day for children, and 70 kg body weight and 2 liter water per day for children. Maximum estimated exposure doses are based on maximum concentrations reported for off-site monitoring wells.
2 Lead may not be related to PGDP or the northwest plume: it may be related to pluming materials.
Key: mg/kg/d = milligrams contaminant per kilogram body weight per day (exposure unit used for chemicals); mrem = millirems (unit used for radiation exposure);
mSv = millisieverts (1 mSv = 100 mrem); Tc-99 = technetium 99; TCE = trichloroethylene

Air

Background

PGDP operations and waste disposal activities have resulted in airborne releases of radioactiveand chemical compounds. ATSDR scientists reviewed PGDP processes that produce aircontaminant releases, selected contaminants of concern, identified potentially exposedpopulations, and evaluated exposure to those populations. Determination of contaminants ofconcern is based largely on information about process operations and accidents that produce aircontamination, release information, data reported from the perimeter fence and off-site airmonitors, and air dispersion modeling. Descriptions of air dispersion models used to evaluate airreleases from the PGDP facility are included as Appendices E through H.

Contaminant releases to the atmosphere at PGDP occur or have occurred as a result of primary operations/processes and accidental releases. These processes include (1) uranium hexafluoride (UF6) enrichment and handling, (2) uranium fluoride manufacturing, (3) metal finishing and grease removal, (4) releases from the water cooling towers, and (5) generation of electricity by the coal-fired steam plant. Other process releases are caused by secondary operations, such as groundwater treatment and cylinder maintenance (cleaning and painting cylinders). Each operation is a source of specific air contaminants; one can determine which contaminants an operation produces by estimating material usage or loss. (Refer to Figure 2 for locations of facilities on site.) Table 7 lists contaminants released to the air from processes at the PGDP site, maximum annual releases with the year of release, and major operations or release points. Contaminant sources or release points that no longer exist are noted in the table.

During the uranium enrichment process, UF6 is released to the atmosphere mainly through ventsin the process buildings and through a 61-meter stack at Building C-310 [60]. These releasesoccur primarily during the transfer of the gaseous UF6 from the cascade equipment into thestorage cylinders. UF6 is the primary contaminant released in this process. Once released into theair, UF6 reacts rapidly with atmospheric water to form hydrogen fluoride (HF) gas, uranylfluorides, and uranium oxides [61]. The year in which the most uranium was released was 1956[12]. Better filtration and operational procedures reduced the total air release of uranium in 1977to less than one-tenth the release in 1956. (Refer to Table 8A.) Also, major modifications weremade to the C-310 stack in 1983 to reduce uranium emissions further [62].

Large quantities of uranium and fluoride were released from 1952 until 1977, when UF6 wasproduced from uranium oxides at the feed plant (Building C-410) and when UF6 was convertedto uranium tetrafluoride (UF4) at the metals plant (Building C-340). Most airborne uraniumduring these years originated at the Feed Plant, where UF6 was produced from uranium oxide[63].


Table 7.

Airborne releases (from PGDP processes) and major release sources [40,7]
Air Contaminants Maximum Reported Annual Release (Year)Major Release Sources
Hexavalentchromium1,700 kg (1990)Cooling towers
Fluorine
Fluoride
Hydrogen fluoride
(See Appendix F)Plant operations (includes building vents, seal exhaust/wetexhaust, product/tail withdrawals, and laboratory hoods); C-310stack emissions; U metals plant (past); C-400 UF4 pulverizer(past); C-410 HF storage and production areas (past)
Sulfur dioxide
Nitrogen oxides
399,579 kg (1993)
314,400 kg (1985)
PGDP's coal-burning steam plant
Trichloroethylene62,826 kg (1986)C-400 and C-720 degreasing operations, and spills (past);northeast and northwest water treatment facilities
Technetium 996.3 Ci (233.1 GBq)
(1958)
Plant operations (includes building vents, seal exhaust/wetexhaust, product/tail withdrawals, and laboratory hoods); C-310stack emissions; U metals plant (past); C-400 spray booths, rotaryvacuum dissolver, laundry, cylinder drying station
Uranium 234
Uranium 235
Uranium 238
1.62 Ci (59.9 GBq)
0.08 Ci (2.96 GBq)
3.50 Ci (130 GBq)
(1956)
Plant Operations (includes building vents, seal exhaust/wetexhaust, product/tail withdrawals, and laboratory hoods); C-310stack emissions; U metals plant (past); C-400 spray booths, rotaryvacuum dissolver, laundry, cylinder drying station; C-400 UF4 pulverizer (past)
Key: Ci = curies; GBq = gigabecquerels; kg = kilograms; HF = hydrogen fluoride; U = uranium; UF4 = uranium tetrafluoride

In addition to ongoing operational contaminant releases, accidental releases of UF6 and HF haveoccurred throughout the operating history of the plant. The largest reported accidental releaseoccurred in 1960, when a cylinder ruptured inside Building C-333 as a result of overfilling andreleased 17,800 pounds (8,074 kilograms) of UF6. Another major accident occurred in December1962 during a fire in Building C-337; in that accident, 5,062 pounds (2,296 kilograms) of UF6were released. There have been several other accidents, but these have involved much smallerquantities [64]. Refer to Appendices E and F for further details.

Also, four deliberate releases of UF6 were made as part of experiments to model the behavior ofatmospheric releases of UF6 [59]. There were two releases in 1955 and two releases in 1974; the1955 releases involved 4.4 kilograms and 0.68 kilograms (10 pounds and 1.5 pounds) of UF6,and both 1974 releases involved about 0.16 kilograms (0.4 pounds).

Fluoride releases were not reported for most of the years of operation. From 1955 until 1993, theAtomic Energy Commission, DOE, and their contractors used off-site air monitors to detectairborne fluorides, uranium, and beta-emitters in the surrounding environment [65]. Acontinuous stack sampler for HF was installed in the C-310 stack; however, the reviewed reportsdo not indicate when it was installed or how much fluoride was released before 1985. Starting in1985, total annual releases of HF were reported in the annual reports. Fluoride releases from theC-310 stack and sulfur dioxide releases from the C-600 steam plant were sampled continuouslyuntil 1993. Other emissions from plant operations were intermittently sampled. The majority ofthe releases were determined by material balancing or engineering calculations using emissiondesign factors from EPA's Compilation of Air Pollutant Emission Factors (cited in 40 CFR 61,Subpart H, Appendix D) and coal content information provided by the coal supplier [46].

Most of the uranium used at PGDP was extracted from uranium ore and shipped to PGDP asuranium oxide. However, from 1953 to 1975, some reprocessed uranium, which contained tracesof other radioactive materials, was fed into the cascade system [4]. The other radioactivematerials included technetium 99 (Tc-99), thorium 230 (Th-230), neptunium 237 (Np-237), andplutonium 239 (Pu-239). Significant quantities of Tc-99 were released to the air as early as 1953,with the largest annual release occurring in 1958 [12]. Several reports and studies, from as earlyas 1957, describe operational problems caused by these other radioactive materials, especiallyneptunium and plutonium [66,67,68,69,70]. Airborne releases of Th-230, Np-237, and Pu-239were not reported in the annual environmental reports until the 1990s. These materials werereleased in much less quantity than Tc-99. (Refer to Table 8B.) These constituents in thereprocessed uranium were in very low concentrations when the material was received and mostlyconcentrated in the flame tower ash during the manufacturing of UF6.

PGDP also has operated two vapor degreasers in Building C-400 and one in Building C-720 formetal cleaning and degreasing. Two systems used trichloroethylene (TCE) and one used 1,1,1-trichloroethane (1,1,1-TCA) as organic solvents and degreasers. Both chemicals vaporize orevaporate readily, so PGDP assumed that 90% of the TCE and 1,1,1-TCA was released to theatmosphere [47]. Use of TCE and 1,1,1-TCA was discontinued in 1993; therefore, ATSDRscientists evaluated only past airborne exposures from these sources. Operation of the Northwestand Northeast Groundwater Treatment Systems (beginning in 1995 and 1997, respectively) hasalso resulted in small releases of TCE to the atmosphere.

PGDP uses four recirculating water cooling systems to dissipate heat generated by the diffusionprocess. Moisture in the air flow (drifts) from PGDP's cooling towers contains elements found inthese recirculating water systems. These elements come from chemicals used as corrosioninhibitors, algicides, etc.; the corrosion inhibitor used at PGDP until 1993 was a chromate-zinc-phosphate compound. Of the contaminants released from the cooling towers, the two with thegreatest potential environmental impact are hexavalent chromium and zinc. These wereinvestigated by Oak Ridge National Laboratory in 1978 [71]. At that time, the hexavalentchromium was detected on vegetation and in the soil at a distance of about 0.9 miles (1,500meters) from the cooling towers (extending outside the PGDP boundary). We do not have therelease quantities for hexavalent chromium before 1988, so we cannot compare releases in 1978with quantities seen in the off-site environment in 1978. Available data indicate that the highestannual quantity was released in 1992. In 1993, use of the chromium-zinc-phosphate anti-corrosion compound was discontinued [47].

PGDP operates a coal-burning steam plant to provide steam and generate supplementalelectricity. In 1974 and 1975, two of the three boilers at the steam plant were converted to burnlow-sulfur coal and oil instead of natural gas. Electrostatic precipitators with 97% efficiency forthe capture of particulates were installed [47]. One boiler continues to use natural gas and oil.PGDP reports releases of sulfur dioxide, nitrogen oxides, particulates, carbon monoxide, non-methane volatile organic compounds, and methane. Sulfur dioxide was continuously monitoredat the steam plant stacks from 1979 until 1993 [72]. The reported results were based on thequantity released per unit of heat (BTU) produced or total released for the year. Other emissionswere calculated from fuel usage and emission factors [46]. Annual releases have been reported inDOE's annual reports for 1985 through 1993. No off-site air monitoring for sulfur dioxide andnitrogen oxides has been performed near the PGDP site.

Release quantities in Tables 8A and 8B were estimated by DOE, their predecessors, or theircontractors, mainly through material balance records or by engineering calculations. Values listedwith "est." in Table 8A are estimated by ATSDR using available information. Table 8A includesannual estimated release quantities for uranium and Tc-99. Table 8B includes annual estimatedreleases of other radioactive materials and chemicals from 1985 through 1996.


Table 8A.

Annual estimated release quantities of uranium and technetium 99 from process operations at PGDP for 1952 through 1993 and 1996 [12,65,4]
YearU (in kg)U (in Ci)U-234 (in Ci)U-235 (in Ci)U-238 (in Ci)Tc-99 (in Ci)
1952

30

0.02

est. 0.0056est. 0.0003est. 0.010------
1953

500

0.25

est. 0.078est. 0.0038est. 0.1671
1954

4,800

2.4

est. 0.75est. 0.04est. 1.601
1955

8,400

4.2

est. 1.31est. 0.06est. 2.812.6
1956

10,500

5.2

est. 1.62est. 0.08est. 3.502.6
1957

3,900

2.4

est. 1.10est. 0.05est. 1.204.8
1958

3,500

2.2

est. 0.98est. 0.05est. 1.176.3
1959

3,300

2.1

est. 0.93est. 0.04est. 1.105.1
1960

3,000

2.0

est. 0.94est. 0.05est. 1.004.1
1961

3,600

2.4

est. 1.12est. 0.05est. 1.204.3
1962

2,400

1.3

est. 0.45est. 0.02est. 0.804.1
1963

2,400

1.3

est. 0.45est. 0.02est. 0.804.4
1964

900

0.6

est. 0.28est. 0.01est. 0.305.3
1965

20

0.02

est. 0.01est. 0.00est. 0.014.4
1966

30

0.02

est. 0.0056est. 0.0003est. 0.010.1
1967

20

0.02

est. 0.01est. 0.00est. 0.010.1
1968

600

0.3

est. 0.11est. 0.006est. 0.200.1
1969

1,800

1.0

est. 0.34est. 0.02est. 0.600.1
1970

900

0.5

est. 0.17est. 0.01est. 0.303.2
1971

1,200

0.7

est. 0.30est. 0.01est. 0.403.0
1972

1,200

0.7

est. 0.30est. 0.01est. 0.400.1
1973

1,400

0.8

est. 0.35est. 0.02est. 0.473.4
1974

1,100

0.6

est. 0.17est. 0.01est. 0.376.0
1975

1,100

0.7

0.34340.01590.36620.8
1976

1,500

1.0

0.46830.02010.49960.1
1977

610

0.4

0.19040.00910.2030.1
1978

96

0.06

0.02940.00140.0320.06
1979

48

0.03

0.00900.00050.0160.06
1980

22

0.02

0.00960.00050.00730.053
1981

140

0.06

0.01750.00060.04680.006
1982

300

0.14

0.03750.00130.10040.01
1983

11

0.0045

0.00060.00020.00370.003
1984

3.2

0.0019

8.99E-044.12E-050.00110.0349
1985

4.4

3.7E-03

1.99E-039.10E-051.4E-030.0155
1986

0.79

3.6E-04

9.34E-054.25E-062.63E-040.0088
1987

<1.0

2.9E-04

7.30E-053.28E-062.11E-040.0009
1988

0.14

0.6E-04

1.88E-058.60E-074.43E-050.0038
1989

0.2

2.9E-04

2.12E-048.0E-066.70E-050.0036
1990

0.03

3.37E-05

2.22E-051.03E-061.05E-053.86E-04
1991

0.005

6.63E-06

4.65E-062.30E-071.75E-063.07E-03
1992

1.42

2.12E-03

1.59E-036.20E-054.67E-042.06E-04
19931

3.06

3.19E-03

2.37E-039.30E-057.25E-043.31E-03
1996

-----

4.37E-03

4.37E-031.19E-041.36E-034.89E-02
1 Uranium and uranium isotope values reported for 1993 were not consistent in the annual environmental report; maximum values were used.
Key: Ci = curies; kg = kilograms; est. = estimated; U = uranium; U-234, U-235, and U-238 = uranium 234, uranium 235, and uranium 238; Tc-99 = technetium 99


Table 8B.

Annual estimated release quantities of major airborne contaminants other than uranium and technetium 99 for 1985 through 1993 and 1996 [65,4]
YearNp-237
(in Ci)
Pu-239
(in Ci)
Th-230
(in Ci)
Fluoride
(in kg)
Hexavalent Chromium
(in kg)
TCE
(in kg)
SO2
(in kg)
NOx
(in kg)
1985******5,268**38,652212,400314,400
1986******6,464**62,856176,575262,800
1987******7,100**34,400178,700252,900
1988******6,84487047,900188,103256,800
1989******6,8011,50041,000292,309282,380
1990******5,7501,70028,000276,380278,613
1991******5,7221,52017,205317,922256,234
19923.8E-072.4E-062.7E-076,5472,01510,221388,648258,696
19932.1E-084.8E-065.9E-063,77886016,000399,579269,265
19962.7E-062.3E-062.1E-06****1,271(DOEonly)****
** Quantities were not reported in the documents reviewed.
Key: Np-237 = neptunium 237; Pu-239 = plutonium 239; Th-230 = thorium 230; TCE=trichloroethylene; SO2 = sulfur dioxide; NOx = nitrogen oxides; Ci = curies; kg = kilograms

Since 1993, when the U.S. Enrichment Corporation (USEC) became responsible for the processfacilities, DOE has not reported process release information or off-site air monitoring data. DOEretains responsibility for four sources of air emissions. The sources are the NorthwestGroundwater Treatment Facility, the C-337 Cooling Tower (as part of the NortheastGroundwater Treatment System), the cylinder refurbishment operations, and two separatefluorescent lamp crushers [73]. The groundwater treatment systems released approximately 2tons of TCE in 1997. Only the cylinder refurbishment operations require a permit from theKentucky Division of Air Quality (KDAQ); these operations are the largest current source ofnon-radioactive air emissions [73]. Sandblasting of UF6 cylinders produced an estimated 4.5 tonsof particulates or dust in 1996 [1] and approximately 5 tons in 1997 [73]. Cylinder paintingoperations released up to 3.4 tons of volatile organic compounds in 1996 [1] and 3.5 tons in 1997[73]. These sources are classified as minor sources of hazardous air pollutants under the CleanAir Act, because they have limited potential for public health effects. DOE is also responsible forfour empty TCE tanks. DOE has no plans to use these tanks at this time [73].

In 1988 and 1989, KDAQ cited PGDP for excessive dust emissions from the C-726 sandblastingfacility [53,54]. The facility was shut down in May 1989. PGDP planned to install a dustcollection filter system and return the facility to use, but the facility never re-opened.

Contaminants of Concern

Each release of a contaminant to the air represents a potential human exposure. ATSDRscientists used information about contaminant releases to identify and select possiblecontaminants of concern for air exposure pathways. Contaminant concentrations in off-site areasare used to determine contaminants of concern. Additional criteria used to select contaminants ofconcern were (1) maximum concentrations exceeding media-specific comparison values, (2)toxicity and radioactivity, and (3) community concerns. Modeling was used to estimate off-siteair concentrations for those contaminants that did not have adequate off-site air monitoring. Wecompared modeling results to ambient air monitoring measurements, when possible, in order toevaluate the accuracy of model predictions.

In estimating the airborne release concentrations and the potential exposure doses for radioactivematerials other than uranium and Tc-99, we assumed that process operations released thesematerials into the air in the same proportion to uranium as in the materials shipped to Paducahfrom other DOE facilities. Actually, most of these radioactive materials are removed in the ashresidue when UF4 is converted to UF6. About 25% of the neptunium and trace amounts of theplutonium are converted to hexafluoride compounds and processed with the UF6. Under theoriginal, conservative assumption, the contribution to the dose estimates from radioactivematerials other than uranium and Tc-99 would be at least an order of magnitude smaller than thecontribution from uranium isotopes, and would not add significantly to the dose estimates [68].

Zinc was released from the cooling tower with chromium. Zinc concentrations in foliage werestudied at Oak Ridge Gaseous Diffusion Plant (ORGDP), where zinc and chromiumconcentrations were a little higher than at PGDP [74]. Beyond 660 feet (200 meters) from thebase of the ORGDP cooling towers, zinc could not be differentiated from background levels. AtPGDP, 660 feet from the base of the cooling towers would still be on site. Also, a study ofmature tree cross sections showed that the zinc emissions were uniform over the past 20 years ofcooling tower operations. This indicates that off-site air concentrations have not changedsignificantly. Based on the estimated quantities of zinc emissions and the probability that zincwould not be seen off site at PGDP, zinc was not selected as a contaminant of concern.

Lastly, 1,1,1-TCA was not selected as a contaminant of concern, because the small quantityreleased to the atmosphere would not produce adverse health effects off site.

ATSDR scientists used computer modeling to predict chronic and acute off-site concentrations ofseveral contaminants known to be released from the PGDP site. These include uranium isotopes,Tc-99, uranium (as a chemical), HF, TCE, sulfur dioxide, nitrogen oxides, and hexavalentchromium. For chemical contaminants, maximum off-site concentrations were compared tomedia-specific comparison values to determine whether the contaminants should be selected ascontaminants of concern for the air exposure pathways. For radioactive contaminants, ATSDRscientists estimated total committed effective doses.

Uranium Isotopes and Technetium 99

Historically, the PGDP site has released uranium isotopes (primarily U-234, U-235, and U-238)and Tc-99 into the air. ATSDR scientists evaluated off-site exposures (committed effectivedoses) to airborne radioactive materials using the Clean Air Act Assessment Package-1988(CAP88-PC) [75,76]. This computer model was developed by EPA for assessing regulatorycompliance with EPA's National Emission Standards for Hazardous Air Pollutants (NESHAP).The model has a number of adjustable parameters, which are discussed in Appendix E. Annualcommitted effective doses were based on air emissions of U-234, U-235, U-238, and Tc-99, andwere calculated for chronic exposures using data from the highest-release years (1956, 1957,1958, and 1959) and from 1996 (a recent year for which we have complete information). Theseestimated chronic doses (shown in Table 9) were calculated for the maximally exposedindividual (the closest resident downwind, about 0.9 miles--1,500 meters--north of the source;CAP88 assumes the source is in the center of the site [29]). The total estimated annual committedeffective doses for 1960 through 1963 were also calculated; these were between 100 and 150millirems per year (1.0 to 1.5 millisieverts per year). The estimated committed effective dosefrom other constituents in reprocessed uranium could add up to 10% to these total doses.

The total estimated annual committed effective doses, shown in Table 9, were not compared todoses calculated from ambient air monitoring data: the air monitoring stations were located at thesecurity fence perimeter, whereas the doses in Table 9 are estimated for the closest downwindresidence--again, approximately 1,500 meters north of the fence. Both calculations result inpotential exposures greater than 10 millirems per year, the current NESHAP emission standardfor radionuclides (40 CFR 61). Therefore, these radionuclides were selected, as a group, ascontaminants of concern for the air exposure pathway.

For acute (short-term) exposure, the highest estimated off-site exposure occurred when a cylinderruptured in Building C-333 at 4:00 a.m. on November 17, 1960. According to our modeling ofthis accident (refer to Appendix E), an estimated uranium inhaled dose of 1.5 rems (0.015sieverts) could have been received by the maximally exposed resident southeast of the site.Therefore, the uranium isotopes were selected as contaminants of concern for the air exposurepathway.


Table 9.

Off-site estimated annual committed effective doses from uranium 234, uranium 235, uranium 238, and technetium 99 air releases from PGDP to the maximally exposed individual (approximately 1,500 meters north of the source)1
YearReleases in curies (gigabecquerels)Total estimated annual committed effective dose2 from releases in millirems (millisieverts) [58]
U-234U-235U-238Tc-99
19561.62 (59.9)0.08 (2.96)3.50 (129.5)2.6 (96.2)340 (3.40)
19571.10 (40.7)0.05 (1.85)1.20 (44.4)4.8 (177.6)156 (1.56)
19581.09 (40.3)0.05 (1.85)1.16 (42.9)6.3 (233.1)147 (1.47)
19590.93 (34.4)0.04 (1.48)1.10 (40.7)5.1 (188.7)132 (1.32)
19962.9E-03
(0.107)
1.2E-04
(0.044)
1.4E-03
(0.052)
3.6E-02
(1.332)
0.43
(0.0043)
1 Predominant wind direction from south-southwest.
2 Estimated using the Clean Air Act Assessment Package-1988 (CAP-88-PC) [76].
Key: U-234 = uranium 234; U-235 = uranium 235; U-238 = uranium 238; Tc-99 = technetium 99

Uranium as a Chemical

Accidental uranium releases were also evaluated for uranium as a chemical--that is, based on its chemical toxicity as a heavy metal, not its radioactivity. Only one reported accident (same as above) could have caused significant off-site uranium exposures: an accident at Building C-333 at 4:00 a.m. on November 17, 1960. According to estimated exposures from modeling this accident (see Appendix E), the highest potential dose of inhaled uranium was 5 to 20 milligrams (mg) for residents living southeast of the site, 0.9 to 2.5 miles (1,500 to 4,000 meters) from Building C-333. The U.S. Nuclear Regulatory Commission's action level for intake of soluble uranium is 10 mg. (At this action level, residents may be instructed to evacuate or to stay indoors with windows closed.) Uranium as a chemical contaminant was selected as a contaminant of concern for the air exposure pathway.

Hydrogen Fluoride

HF (including fluoride and fluorine) was released at the PGDP site. This contaminant is also anoted community concern. Although fluoride emission data from the plant are limited, there is astrong correlation between uranium and fluoride releases, and there is historical information onuranium releases. Current fluoride releases are much smaller than past releases, because processand filtration equipment have changed and chemical manufacturing at the PGDP facilities hasbeen discontinued.

Fluoride releases from the plant were not reported in annual reports until 1986. Results from off-site air monitoring were reported in the annual environmental reports from 1958 until 1993.However, results for each monitoring location and sampling period were not reported. For thefirst 3 years, the median value for all off-site air concentrations was reported. From 1961 until1993, the mean values for each year were reported [65].

Because there is a strong correlation between uranium releases and ambient air concentrations ofHF, ATSDR scientists assumed that the largest chronic HF release coincided with the highestannual uranium release in 1956. To evaluate off-site HF exposures for 1956, one must estimateor model HF emissions from periods of consistent data reporting when the processes on site weresimilar (e.g., 1962 through 1970). The method we used is discussed in Appendix F.

For chronic HF exposures, the maximally exposed individual is assumed to be at the perimeternorth air monitoring station. This station is closer to the fluoride processing facility than others[65], and is downwind of the processing facility with respect to prevailing south-southwest winds[1]. Kentucky's ambient air standard for average annual exposure is 500 parts per billion (ppb)[77], and ATSDR's provisional guidance for long-term exposure (365 days or more) is 10micrograms per cubic meter (g/m3), or 12 ppb [78].

Modeling results indicate that long-term estimated HF concentrations at the north perimeterstation did not exceed the Kentucky ambient air standard but exceeded ATSDR's provisionalguidance in 1955, 1956, and 1961. However, estimated HF concentrations did not exceedATSDR's provisional guidance 1 mile north of the perimeter. The estimated annual averageairborne HF concentration at the nearest houses to the site was 22 ppb for 1956, which was aboveATSDR's provisional guidance but approximately 25 times lower than Kentucky's standard.This was the only year for which the estimated concentration from long-term releases exceededthe provisional guidance at this location.

Of the documented accidental HF releases, the largest release occurred on November 17, 1960,when a cylinder ruptured in Building C-333. During this accident, 8,074 kilograms (17,800pounds) of UF6 were released at approximately 4:00 a.m. As discussed in Appendix F, modelingof this accident estimates short-term hazardous HF concentrations more than a kilometer to thesoutheast of Building C-333, which would include property immediately off site. Therefore,hydrogen fluoride was selected as a contaminant of concern for the air exposure pathway.

Trichloroethylene

Past operations at PGDP involved large quantities of TCE as an organic solvent and degreaser. Historical air releases of TCE were several orders of magnitude larger than current releases from the groundwater treatment facilities. Although significant amounts of TCE were released to the groundwater in the past, most operational releases of TCE volatilized into the atmosphere [47]. To determine if airborne releases presented a potential inhalation exposure to nearby residents,ATSDR scientists estimated the air dispersion of TCE using the Industrial Source Complex (ISC3) model [79], the maximum annual quantities of TCE released from the site, and very conservative assumptions about dispersion, plume rise, and atmospheric degradation. The model and assumptions are discussed in Appendix G.

The maximum estimated airborne TCE concentration at 1,000 meters (3,280 feet) north ofBuilding C-400 is 112 g/m3 for a 1-hour averaging period (i.e., an acute exposure) and 3 g/m3for an annual averaging period. Estimated concentrations were several times lower than themedia-specific comparison values for TCE in air (10,920 g/m3 for acute exposure and 546g/m3 for intermediate-duration exposure) [23]. Therefore, TCE was not selected as acontaminant of concern for air exposure pathways.

Sulfur Dioxide and Nitrogen Oxides

Sulfur dioxide and nitrogen oxides are both released to air from the PGDP site. Off-sitemonitoring for these contaminants has not been performed near the site; therefore, ATSDRscientists used the ISC3 model to estimate off-site concentrations of sulfur dioxide and nitrogenoxides from the on-site coal-burning steam plant. Modeling results indicated that off-siteestimated concentrations of sulfur dioxide and nitrogen oxides for chronic exposure are not likelyto exceed comparison values. Therefore, sulfur dioxide and nitrogen oxides were not selected ascontaminants of concern for air exposure pathways.

Chromium

Although airborne releases of hexavalent chromium from the cooling towers at PGDP were notreported until 1988, the plant used hexavalent chromium since the early days of operations. From1988 until 1993, releases of hexavalent chromium from the cooling towers were estimated fromconcentrations in the cooling water and known annual quantities of chromium compound addedto the water. As early as 1958, hexavalent chromium was considered a potential environmentalcontaminant [81]; however, only surface water samples were analyzed for chromium.

Union Carbide studied chromium contamination in the late 1970s: they evaluated chromiumreleases from the cooling towers to assess the potential for chromium transport and accumulationin the terrestrial environment [71,74]. Although the Union Carbide studies did not specificallyaddress airborne hexavalent chromium concentrations, they do provide information aboutdeposition of hexavalent chromium on vegetation and soil from the airborne releases. The studiesalso indicate that chromium deposited from the drift cloud was present as hexavalent chromium;therefore, it is reasonable to assume that airborne chromium was also present in the hexavalentform. Hexavalent chromium was detected on vegetation and in soil at a distance of 1,500 meters(about 0.9 miles) from the towers in 1978. Beyond 1,500 meters, soil and vegetationconcentrations could not be differentiated from background chromium concentrations [74].

According to release data from 1988 and later, the maximum annual release of airbornehexavalent chromium occurred in 1992. Therefore, ATSDR scientists used 1992 release data andthe ISC3 air dispersion model [79] to estimate maximum air concentrations on site, immediatelyoff site, and at the closest downwind off-site residence for 1-hour, 8-hour, 24-hour, and annualexposures. Appendix H describes the model and the estimated exposure concentrations.Maximum off-site air concentrations were estimated to be at least 100 times lower thanATSDR's comparison values for hexavalent chromium in air. Therefore, chromium was notselected as a contaminant of concern for air exposure pathways.

Airborne Exposure Pathways

ATSDR scientists identified completed and potential exposure pathways for past, current, andpotential future exposure to air contaminants. Contaminants of concern in these exposurepathways will be evaluated further in the public health implications section of this report.

Current Exposure

Off-site airborne radioactive material concentrations are currently being monitored by theKentucky Department of Health's Radiation Control Program. Since monitoring began in 1996,no concentrations of radioactive materials have been detected above emission standards [80].ATSDR's estimated committed effective dose for radioactive releases in 1996 is 0.43 milliremsper year (0.0043 millisieverts per year)--more than 20 times smaller than the NESHAPrequirement of 10 millirems per year (0.10 millisieverts per year) whole body dose.

The current maximum estimated or modeled off-site concentrations of HF, TCE, sulfur dioxide,nitrogen oxides, and hexavalent chromium are low and do not exceed their respective health-based comparison values.

Therefore, ATSDR scientists did not identify any contaminants of concern for current airexposure pathways.

Past Exposure

In the past, TCE, sulfur dioxide, nitrogen oxides, and hexavalent chromium were released from PGDP; however, the maximum estimated off-site concentrations did not exceed health-based comparison values. As discussed previously, radionuclides (U-234, U-235, U-238, and Tc-99), uranium (as a chemical), and HF were identified as contaminants of concern for past exposure via completed and potential air exposure pathways. These contaminants will be discussed further in the public health implications section.

Potential Future Exposure

As long as on-site processes remain similar to the current operations and no major accidentoccurs, future off-site releases of airborne contaminants should continue at current levels, whichdo not exceed health-based comparison values. Therefore, we did not identify any airbornecontaminants of concern for potential future chronic exposure. Future releases of airbornecontaminants from the processing facility will be the responsibility of USEC under the currentprivatization plans.

DOE is considering alternatives for the management of the aging depleted uranium cylinders atPGDP. Should any chemical processing or additional handling of the cylinders or storage ofwaste from remedial projects be done at this site, the potential for airborne releases will be partof the environmental impact considerations during the planning for the new operations. If on-siteactivities and operations change, then the potential for off-site exposure should be re-evaluated.


Table 10.

Summary of completed and potential exposure pathways for airborne contaminants
Major SourcesRadioactive ContaminantsPoint of ExposureRoute of ExposureExposed PopulationPeriod of TimeMaximum Estimated Annual Committed Effective Dose
Process operations,
Bldg. C-310 stack,
Bldg. C-410 feed plant,
Bldg. C-340 metals plant
U-234, U-235, U-238

Tc-99

Downwind off-siteambient air (mainlynorth of the site)InhalationResidents living within ~500meters (~0.3 miles) north of fencePast only
1954 to 1963
1955 to 1965; 1970, 1971, 1973 and 1974
Maximum in 1956:
340 mrem
(3.4 mSv)
Major acute releases:

1960 cylinder rupture

1962 fire

U-234, U-235, U-238

U-234, U-235, U-238

Downwind off-site ambient air
(Both accidents toward the southeast)
InhalationResidents outdoors within 1.5 to 3kilometers (~0.9 to 1.8 miles) ofaccident, which happened atBuilding C-333

Residents outdoors more than 0.2kilometers (0.12 miles) from theaccident

11/17/60
4:00 a.m.

12/13/62
4:00 p.m.

0.5 to 1.5 rem
(5 to 15 mSv)

< 1 mrem
(< 0.01mSv)

Major SourcesChemical ContaminantsPoint of ExposureRoute of ExposureExposed PopulationPeriod of TimeMaximum Estimated Exposure Dose (Chemicals)
Process operationsHydrogen fluorideDownwind off-siteambient air (north ofsite)InhalationResident living within ~500meters (~0.3 miles) north of fence1956 only22 ppb average hydrogenfluoride concentration
Major acute releases:

1960 cylinder rupture

Uranium

Hydrogen fluoride

Downwind off-siteambient air (towardthe southeast)InhalationResidents outdoors within 1.5 to 4kilometers (~0.9 to 1.8 miles) ofaccident, which happened atBuilding C-333 11/17/60
4:00 a.m.
5 to 20 mg uranium

1 to 5 ppm hydrogen fluoride

Key: mg = milligrams; mrem = millirems; mSv = millisieverts; ppm = parts per million; ppb = parts per billion;
U-234= uranium 234; U-235 = uranium 235; U-238 = uranium 238; Tc-99 = technetium 99

Surface Water

Background

Surface waters around the PGDP site have elevated concentrations of chemical and radioactivecontaminants as a result of process operations and past waste disposal activities at the facility.Surface waters may also receive contaminants as a result of groundwater discharge to Big BayouCreek and the Ohio River [82] and deposition of airborne particles [71]. Surface watermonitoring data reflect total contaminant load. Surface water drainage from PGDP is either eastor northeast to Little Bayou Creek or theNorth/South Diversion Ditch, or west ornorthwest to Big Bayou Creek. TheNorth/South Diversion Ditch has flow onlyduring periods of heavy rain and releasesfrom the plant. The ditch flows to thenorth/northeast and discharges into LittleBayou Creek. Big Bayou and Little Bayoucreeks converge about 3 miles (5 kilometers)north of the facility and discharge directly into the Ohio River about a quarter mile (half akilometer) further downstream.

Surface water discharges from the PGDP site to Big Bayou and Little Bayou Creeks are regulatedunder Kentucky Pollutant Discharge Elimination System (KPDES) permits. Surface water runofffrom the plant into the North/South Diversion Ditch and from the landfills and the plant intoLittle Bayou and Big Bayou Creeks are also monitored under KPDES permits. These permitsspecify allowable contaminant concentrations in discharges and require DOE or the U.S.Enrichment Corporation to monitor effluents and take corrective action if discharges exceedpermitted limits.

ATSDR scientists reviewed data for 258 different off-site surface water monitoring stations thatPGDP sampled between 1987 and 2000. All stations included in this evaluation are outside thesecurity fence. Samples were analyzed for 511 different chemicals and radiological parameters[44]. PGDP sampled a few monitoring stations as early as 1958 [81]. However, these sampleswere analyzed for only a few contaminants, including fluoride, nitrate, hexavalent chromium,uranium, and gross beta activity. Maximum concentrations of fluoride, nitrate, hexavalentchromium, uranium, and gross beta activity in historical samples collected close to the siteboundary in Big Bayou and Little Bayou Creeks were higher than in samples analyzed from 1987to 2000 [65]. However, historical data are not directly comparable to more recent measurements,because there have been changes in sampling and analytical techniques over time. Becauseprocess operations and waste disposal practices have also changed over time, currentcontaminant releases to surface waters are generally one to two orders of magnitude lower thanhistorical releases.

Concentrations for most surface water contaminants are not evenly distributed; maximum valuesmay be two orders of magnitude higher than the next highest sample. The maximumconcentrations for all surface water contaminants were obtained at one of two locations. Formetals, the highest concentrations are at several surface water stations in Big Bayou Creekadjacent to the southwest landfill. Stations at the PGDP outfalls into Little Bayou Creek have thehighest concentrations of fluoride, nitrate, polychlorinated biphenyls (PCBs), trichloroethylene(TCE), and radioactive materials.

According to samples collected upstream and downstream of the point where Big Bayou andLittle Bayou Creeks discharge into the Ohio River, the river has several chemical contaminantsthat may be related to PGDP, including chloride, fluoride, and sulfate. Maximum concentrationsdownstream, however, are barely above the concentrations upstream, and are much lower thanlevels found in Big Bayou and Little Bayou Creeks [1]. Also, a different source may beresponsible for these elevated concentrations of chloride, fluoride, and sulfate.

Contaminants of Concern

ATSDR scientists used a series of screening techniques to select contaminants of concern forsurface water exposure pathways. The first phase of this screening involved determining ifmaximum off-site concentrations exceeded health-based comparison values for chemicals and ifmaximum radiation doses exceed 4 millirems per year (EPA's Drinking Water Standard forradioactive contaminants). Contaminants of concern for other exposure pathways were alsoevaluated if detections were above comparison values. Seventeen chemicals (14 metals, TCE,nitrate, and total PCBs) were detected in areas ofpotential exposure at levels requiring additionalexposure analysis. Eleven radionuclides areevaluated for potential exposure doses todetermine if they should be consideredcontaminants of concern.

The second phase of contaminant screening isbased on the calculation of potential exposure doses for each surface water contaminant.Concentrations of most surface water contaminants were log-normally distributed, meaning that afew samples had high concentrations while most of the samples had much lower concentrations.Consequently, the estimated exposure doses were calculated using the 67th percentile of theconcentration distribution. The exposure analyses, along with the detection ranges, the 67thpercentile concentrations, and the calculated exposure doses, for these contaminants are presented in Tables 11 and 12 in the following section.

Thallium is one of the seventeen chemical surface water contaminants and is the only one thathas estimated exposure doses that exceed health guidelines. Therefore, thallium is a contaminantof concern for the surface water pathway and will be discussed further in the following pathwayanalysis section and in the public health implications section of this report.

Di(ethylhexyl)phthalate is not considered a contaminant of concern. Although this chemical wasdetected in surface water samples, it is not directly used or stored at PGDP. It is a commonadditive to plastic sample bottles, rubber gloves, and other plastic products. It was detected threetimes at different stations with widely varying concentrations. Therefore, ATSDR scientistspresumed that di(ethylhexyl)phthalate was introduced during the sampling process and is not asite-related contaminant of concern for surface water.

For current concentrations of radioactive materials in the surface water we used the 67thpercentile for reasons described previously; however, we did not have as much data for pastconcentrations so we used the annual average concentration at the sampling location that hadmaximum results. Also, there are important differences between current and past analyses ofradioactive substances in surface water. Measured concentrations changed over time, but so didthe methods of analysis used and the list of radioactive materials being measured. Historicalanalyses for radioactive materials included total uranium, gross alpha, and gross beta activity. Inthese analyses, the highest average annual total uranium concentration was 474 picocuries perliter (pCi/L), measured in samples collected from Big Bayou Creek in 1960. The highest averageannual gross beta activity was 21,700 pCi/L (Little Bayou Creek, 1960) [83]. Most of this betaactivity was attributed to technetium 99 (Tc-99). Therefore, ATSDR scientists used themaximum annual average concentrations for uranium and Tc-99 (gross beta) to estimate pastexposure doses (annual committed effective doses) for children and adults. These doses arepresented in Table 12 in the following section.

By the 1980s, maximum uranium concentrations had decreased to levels that were less than 1%to 5% of levels reported in 1960. Other radioactive contaminants (strontium 90, neptunium 237,plutonium 239, and thorium 230) were quantified in the 1987-1996 analyses. ATSDR includedthese other radioactive contaminants in the estimated current exposure doses (annual committedeffective doses) for children and adults. These doses are also presented in Table 12 in thefollowing section.

Surface Water Exposure Pathways

The greatest potential for human exposure tocontaminated off-site surface water has beenin Little Bayou Creek, Big Bayou Creek, andthe Ohio River downstream of Big BayouCreek. Persons may fish, wade, and play inthe creeks. In addition, there are notedcommunity health concerns about potentialhuman exposures. Because contaminants arepresent in the creeks and humans may accessthese areas, ATSDR scientists identified potential exposure pathways for past, current, and futureexposure to contaminants in surface water. Contaminants of concern in these exposure pathwayswill be evaluated further in the public health implications section of this report.

As stated above, the highest concentrations of all surface water contaminants occur at one of twolocations: either within the WKWMA property directly adjacent to the southwest landfill or inDOE buffer property at surface and storm water outfalls into Little Bayou Creek. (This includesthe North-South Diversion Ditch.) Although exposure is possible in these areas, ongoing monthlyingestion of surface water is unlikely. Also, the 67th percentile concentrations of off-sitecontaminant levels is much more realistic for calculating potential surface water exposuresaround PGDP.

Exposure doses are estimated assuming incidental contact and ingestion, because surface water inthis area is not used to supply drinking water. For chemical contaminants above the health-basedcomparison values, we assumed ingestion of 0.5 liters of water per exposure and one exposureper month for 12 months per year. We estimated exposure doses for a child (1 to 6 years old) andan adult, assuming incidental ingestion of surface water contaminated at the 67th percentile ofoff-site concentrations. For volatile organic compounds, dermal (skin) contact may contribute adose up to 30% as large as the ingestion dose [56]. TCE was the only volatile organic compounddetected in surface water off site. Therefore, we assumed that dermal contact contributed anadditional 30% to the estimated ingestion dose for TCE. The estimated exposure doses forcurrent exposure to most chemical contaminants and past exposure to hexavalent chromium,fluoride, and nitrate are shown in Table 11 (using pre-1987 annual average values). Theestimated current and past exposures to radioactive contaminants are shown in Table 12. It wasnot possible to estimate past exposure doses to most chemicals and radioactive materials,because historical measurements are lacking.

Health guidelines provide a basis for evaluating exposure doses estimated from contaminant concentrations in soil, air, water, and food. Exposure doses depend on the characteristics of the people who might be exposed and the length of their exposure. The health guidelines are described in Appendix C. Most of the health guidelines were derived for chronic exposure--that is, exposure lasting more than 364 consecutive days. By contrast, human exposure to off-site contaminated surface water is likely to have occurred infrequently throughout the year and possibly not at all during winter months. According to local residents, there is very little swimming, wading, or other human activity in Big Bayou and Little Bayou Creeks. All of Little Bayou Creek is in DOE or Tennessee Valley Authority property, except for a small area that borders private property to the east of the plant. According to the Kentucky Radiation Control Program, Little Bayou Creek has been restricted and posted at access points since July 19, 1993.


Table 11.

Estimated exposure doses for chemical contaminants in off-site surface water at PGDP and health guidelines
Chemical
Contaminant
Contaminant Range (and 67th percentile) in g/LEstimated Exposure Dose for Children (mg/kg/day)1Estimated Exposure Dose for Adults
(mg/kg/day)1
Oral Health Guideline in mg/kg/day and Source1Estimated Exposure Dose Greater Than Health Guideline?
Antimony

10-50 (42)

0.0000840.0000130.0004 (Chronic RfD)No
Arsenic6-90 (38)0.0000760.0000110.0003 (Chronic MRL)No
Beryllium0-150 (75)0.000150.0000230.002 (Chronic RfD)No
Cadmium0-90 (32)0.0000640.000010.0002 (Chronic MRL)No
Chromium4-820 (210)0.000420.0000631.5 (Oral RfD)No
Chromium,hexavalent20-7,8802
(1,626)
0.00330.000490.003 (ATSDR InterimOral Intake)No
Fluoride(Fluorine)100-35,0002
(1,047)
0.00210.000310.05 (Chronic MRL) No
Lead2-12,200 (1,945)0.00390.000580.0203No
Manganese8-187,000
(22,447)
0.0450.00670.07 (ATSDR InterimGuidance Value)No
Nickel5-1,350 (320)0.000640.0000960.02 (Chronic RfD)No
Nitrate150-900,0002
(2,492)
0.0050.000751.6 (Chronic RfD)No
Total PCBs1-42 (4.5)0.000010.0000020.00002 (Chronic MRLfor Aroclor 1254)4No
Sulfate3,800-1,680,000
(108,184)
0.220.03214.295No
Thallium16-5,260 (417)0.000830.000130.00008 (Chronic RfD)Yes
Trichloroethylene1-51 (5)0.000010.0000020.2 (Acute MRL)No
Uranium1-3,000 (74)0.000150.0000220.002 (Int./Chronic MRL)No
Vanadium2-1,430 (156)0.000310.0000470.003 (Int. MRL)No
1 For an explanation of health guidelines and of how we calculated exposure doses, refer to Appendix C.
2 These concentrations are maximum annual averages from historical annual environmental reports [65]. The other concentrations are from the 1987-2000 electronic data and reports [44].
3 Based on lowest-observed-adverse-effect level (acute) from ATSDR, 1997 [84].
4 This MRL is based on Aroclor 1254, not total polychlorinated biphenyls. This provides a conservative evaluation.
5 Based on EPA's MCLG and equivalent exposure for a 70-kg adult ingesting 2 liters per day.
Key: mg/kg/day = milligrams of contaminant per kilogram of body weight per day; g/L = micrograms per liter


Table 12.

Past and current maximum estimated exposure doses (annual committed effective doses) for radioactive contaminants in surface water [58]
Radioactive ContaminantPast Maximum Concentration
in pCi/L (and in Bq/L)
Current Concentration Range and 67th Percentile in pCi/L (and Bq/L)Maximum Annual Estimated Committed Effective Dose for Child in mrem (and mSv)Maximum Annual Estimated Committed Effective Dose for Adult in mrem (and mSv)
PastCurrentPastCurrent
Americium 241

------

0.05-17.1 (0-0.63)
13.7 (0.507)
------0.08
(8.2E-04)
------0.06
(6.1E-04)
Neptunium 237------0.04-13.6 (0-0.50)
0.8 (0.030)
------0.00
(2.5E-05)
------0.00
(2.0E-05)
Plutonium 238------0.5-3.2 (0.02-0.12)
2.7 (0.100)
------0.02
(1.9E-04)
------0.01
(1.4E-04)
Plutonium 239------0.01-2.7 (0-0.10)
0.3 (0.011)
------0.00
(2.2E-05)
------0.00
(1.6E-05)
Strontium 90------6.1-131.3 (0.23-4.86)
64 (2.37)
------0.07
(6.7E-04)
------0.04
(4.0E-04)
Technetium 9921,700 (803.7)21-4,000 (0.04-148.1)
61 (2.259)
1.11
(1.11E-02)
0.00
(3.1E-05)
0.309
(3.1E-03)
0.00
(8.7E-06)
Thorium 230------0.002-6.0 (0-0.22)
1.4 (0.052)
------0.01
(9.7E-05)
------0.01
(6.6E-05)
Uranium, total1

474 (17.56)2

0.06- 9.5 (0-0.35)
3.4 (0.126)
0.88
(8.8E-03)
 0.50
(5.0E-03)
 
Uranium 234------0.01-119 (0-4.41)
7.5 (0.278)
------0.01
(1.5E-04)
------0.01
(8.2E-05)
Uranium 235 ------0.01-2.34 (0-0.09)
0.6 (0.022)
------0.01
(8.5E-05)
------0.00
(4.7E-05)
Uranium 238------0.33-194 (0.01-7.19)
16.4 (0.607)
------0.01
(8.0E-05)
------ 
Total committedeffective dose------------1.99 (0.02)30.21 (0.00)0.81 (0.01)30.13 (0.00)
1 Total uranium = uranium-234, uranium-235, and uranium-238 (only used for past exposure calculations).
2 These concentrations are maximum annual averages from historical annual environmental reports [65]. The other concentrations are from the 1987-2000 electronic data and reports [44].
3 Past total committed effective doses do not include potential exposure to several radionuclides, because there are not enough historical data.
Key: pCi/L = picocuries per liter; Bq/L = becquerels per liter; mSv = millisieverts; mrem = millirems

Current and Past Exposure

Several chemical and radioactive contaminants have been detected in surface water samplestaken from Big Bayou Creek, Little Bayou Creek, and the portion of the Ohio River downstreamof Big Bayou Creek. Only one chemical contaminant, thallium, was selected as a contaminant ofconcern for surface water. The highest concentrations of thallium are reported for Big BayouCreek and its tributaries near the inactive southwest landfill. Concentrations of thallium are alsoelevated in Little Bayou Creek east of the plant. ATSDR scientists cannot determine withcertainty how long the streams may have been contaminated with thallium, because samples werenot analyzed for thallium until 1987. Because thallium may have been present in off-site surfacewater prior to 1987, thallium is a contaminant of concern for past and current exposure viapotential exposure pathways for off-site surface water (as shown in Table 13) and will bediscussed in the public health implications section of this report.

Radioactive contaminants were present at low levels in samples taken from Little Bayou and BigBayou creeks. Because the annual total committed effective doses are less than 4 millirems (0.04millisieverts) for current exposures, radioactive contaminants are not contaminants of concernfor current exposure to surface water. Lack of data for historical concentrations of radioactivematerials other than Tc-99 and the uranium isotopes makes it difficult to determine pastexposures to all radionuclides in surface waters. It is possible that, during a past release fromthe site, a person exposed to the surface waters could have received a dose in excess of 4millirems. Therefore, radioactive materials are considered contaminants of concern for pastexposures via potential exposure pathways for off-site surface water and will be discussed in thepublic health implications section of this report.

Potential Future Exposure

With partial restrictions on access to Little Bayou Creek, permitting discharges to off-site surfacewater, and remedial activities to remove sources of contamination, future exposures to surfacewater contaminants should either not occur or be much lower than current exposures. Therefore,ATSDR scientists did not identify any potential future exposure pathways for surface water.However, if new processes are initiated at the site or new sources of contamination are identified,future exposures should be addressed at that time.


Table 13.

Summary of potential exposure pathways for off-site surface water contaminants
Major SourcesContaminantsPoint of ExposureRoute of ExposureExposed PopulationPeriod of TimeMaximum Estimated Exposure Doses
Processoperationsdischarge,surface waterrunoff,leachingfrom pastwastedisposalactivities,groundwaterdischarge,airbornedepositionThallium







Total uranium
Technetium 99
Americium 241
Strontium 90
Neptunium 237
Plutonium 238
Plutonium 239
Thorium 230

Duringwading orimmersionin LittleBayou orBig BayouCreeksIncidentalingestionanddermalcontactChildren playing in the creeks once per month, and adults fishing and wading in the creeks once per monthPast and current





Past
(before 1987)

Thallium (mg/kg/d)

Children: 0.00083
Adult: 0.00013


Radiation exposure
:
uncertain (however, estimated committed effective doses were > 4 mrem but < 200 mrem for annual intake in both scenarios)

Key: mg/kg/d = milligrams of contaminant per kilogram of body weight per day;
mrem = millirems

Soil and Sediment

Background

Process operations and waste disposalactivities at PGDP have contaminated soiland sediment. Off-site surface soil hasbecome contaminated mainly as a result ofreleases from disposed waste material anddeposition of airborne releases. Surface soilconcentrations are highest in the predominantdownwind directions from the site and in soils near the creek and ditches as a result of leachingfrom landfills and occasional flooding of the creeks and ditches. Sediment in nearby streams hasbecome contaminated as a result of surface water discharges and surface runoff from the site.Deposition of airborne materials also introduces contaminants to streams and ponds, where theyare adsorbed to sediments.

Soil and sediment data evaluated were obtained via electronic transfer from the PGDPenvironmental database [44], the Kentucky Department for Environmental Protection (HazardousWaste Branch) and the Kentucky Department for Public Health (Radiological Health and ToxicAgents Branch). The cumulative data set consists of 292,062 chemical and radiologicalmeasurements for 457 analytes from 1,737 locations. Data were available for five differentsample types and depth profiles:

  • Sediment.

  • Soil at unspecified depth.

  • Subsurface soil more than 12 inches (30 centimeters) deep.

  • Surface soil less than or at 12 inches deep but more than 3 inches deep (that is, from 8 centimeters to 30 centimeters).

  • Top soil less than or at 3 inches (8 centimeters) deep.

Because chronic human exposure to subsurface material is very unlikely, ATSDR evaluated onlysurface and top soil samples (including unspecified depth samples), as well as sediment samples.Sample station names did not designate whether any off-site samples were collected onresidential properties. If the stations appeared to be located near residential properties, theresidential properties were assumed to have similar soil concentrations. Samples in the electronicdata set were collected and analyzed for 1987 through 2000. Additional soil and sediment data,available from annual environmental monitoring reports, were used to corroborate contaminantdistributions. A limited soil sampling program began in 1971; however, few samples werecollected and were analyzed only for uranium.

Off-site sample locations were not uniformly spaced. They were too far apart to determinewhether contaminant distributions followed a regular pattern based on transport and fate (e.g.,airborne dispersal) processes. For example, maximum concentrations of technetium 99 andneptunium 237 were found to the north of the fenced area and near the edge of the buffer zone;maximum concentrations of metals, uranium isotopes, thorium 230, and cesium 137 were foundwest and southwest of the site; and maximum concentrations of most of the radioactivecontaminants in sediment were found in drainage ditches and in Little Bayou Creek. Also, mostsoil sampling stations have not had multiple sampling over time. Consequently, it is not possibleto evaluate historical trends of soil contamination at PGDP. This evaluation will assume that ifPGDP contaminants have been detected at a soil sampling location, that location has beencontaminated since the beginning of PGDP operations. As with surface water, concentrations ofmost soil and sediment contaminants are not evenly distributed.

Contaminants of Concern

ATSDR scientists used a screening technique to select contaminants of concern for soil andsediment exposure pathways. This screeninginvolved determining if maximum concentrationsof these contaminants in areas of potential humanexposure exceeded health-based comparisonvalues for chemicals and if maximum radiationdoses exceeded 25 millirems per year (mrem/year)for radionuclides. Thirteen chemical contaminantsand twelve radionuclides were consistentlydetected in areas of potential exposure at concentrations requiring additional exposure analyses.

Most of the contaminants remaining after the first phase of screening are naturally occurringmetals with concentrations that may have been elevated above background levels by processoperations or waste disposal activities. In addition, polychlorinated biphenyls (PCBs or Aroclors)have been detected above comparison levels. The PCBs have been analyzed as both individualspecies (Aroclor 1016, Aroclor 1242, Aroclor 1254, etc.) and as total PCBs. Only total PCBs willbe evaluated further.

Several detected contaminants are not considered further. Metallic mercury, 1,2-dichloroethene(cis and trans), and ammonia each had only one sample above comparison values. These singlehigh values were not repeated in other analyses, which indicates that the high values are samplingor analytical anomalies, or that the spatial extent of the contaminants is so limited that significantexposure is not possible. Silver was also detected at several on-site sediment or soil samples forwhich no chronic (long-term) community exposure is possible. Off-site detections of silver werebelow levels of health concern. Also, trichloroethylene, a contaminant of concern for thegroundwater exposure pathway, was detected in five samples. However, those detections were aton-site stations and below levels of health concern. Chromium is also not evaluated further,because concentrations are below health-based comparison values for trivalent chromium.Although the valence of the chromium soil samples is not specified, other studies have shownthat virtually all of the soil chromium is in the trivalent form, not the more toxic hexavalent form[71,74].

Most of the contaminants evaluated further have higher concentrations on site than off site. Thismeans that site activities may be responsible for contaminant distributions. Arsenic, lead, andnickel have higher off-site concentrations, which suggests that PGDP activities may not beresponsible for the distributions of these contaminants. It is also possible that several of the soiland sediment contaminants are at background levels--that is, that they do not represent site-related contamination. Prior use of the PGDP site by the Kentucky Ordnance Works could alsocontribute metals contamination. Because arsenic, lead, and nickel exceed health-basedcomparison values, the following exposure analyses will identify their potential exposurepathways and estimated exposure doses.

Soil and Sediment Exposure Pathways

Contaminated soils and sediments are presentboth inside and outside of the PGDP securityfence. The most significant soilcontamination is within the fence but haslittle potential for public exposure. However,soil contaminants with concentrations abovehealth comparison values are present withinthe unsecured buffer area maintained as partof the Western Kentucky WildlifeManagement Area (WKWMA) and on privateland outside the buffer area. The most contaminated sediments are similarly located within theaccess-restricted drainage ditches and Little Bayou, but contaminated sediments are also presentwithin the open access areas of Big Bayou, nearby ponds, and private lands.

The distribution of land uses surrounding PGDP presents two scenarios by which the public maybe exposed to soil and sediment contaminants. Scenario 1 covers WKWMA workers and visitors,who may be exposed to soil and sediment contaminants in the buffer zone and adjacentWKWMA property. Scenario 2 covers people living adjacent to PGDP. As with surface water,concentrations of most soil and sediment contaminants are log-normally distributed, meaningthat a few samples had high concentrations while most of the samples had much lowerconcentrations [85]. Consequently, the estimated exposure doses were calculated using the 67thpercentile of the concentration distribution. The following sections present the exposureattributes, contaminant concentrations, and estimated exposure doses that are specific to each ofthose scenarios. The following scenarios assume that soils and sediments became contaminatedshortly after the beginning of PGDP operations and that the exposure pathways are complete inthe past, present, and future. The detection ranges, the 67th percentile concentrations and thecalculated exposure doses are presented in Tables 14.A, 14.B, 15.A, and 15.B.

Scenario 1--WKWMA Workers and Visitors

WKWMA workers involved with maintenance of the buffer zone property have a high potentialfor contact with contaminated soil. This scenario also includes visitors to WKWMA, althoughthey would be exposed less often than WKWMA workers and receive a commensurately lowerexposure dose.

For this scenario, ATSDR scientists assumed that workers could be exposed to top soil, surfacesoil, or soil at unspecified depth and would spend approximately 8 hours a day for 1.5 days aweek (i.e., 30% of their work week) in contaminated buffer zone areas. We also assumed that thesame WKWMA workers were exposed to contaminated sediment for 0.75 days each week (15%of the work week). We assumed that these soil and sediment exposures went on for 50 weeks peryear for 10 years, which is an approximate maximum period of employment at the WKWMA.Soil contaminant concentrations for these exposures were derived from buffer zone soil samples.Sediment contaminant concentrations were derived from all sediment samples taken outside thesecurity fence.

Exposure was assumed to occur via direct (dermal) contact and ingestion for chemicalcontaminants and via ingestion and external exposure for radioactive contaminants. Foringestion, we assumed an ingestion rate of 200 milligrams (mg) of soil per day (four times thedaily average adult rate [23]) and 100 mg of sediment per day (two times the average adult rate).We assumed that workers were men and women. Table 14A shows the estimated exposure dosesfor chemical contaminants (along with additional assumptions we made in calculating them).Table 14B shows estimated exposure doses (annual committed effective doses) for radioactivecontaminants in this scenario. Table 14B does not show estimated external exposure toradioactive contaminants. (The estimated external exposure from surface and/or top soil wouldadd approximately 8 mrem/year for this scenario [86].)

For this scenario, no chemical exposure doses exceed the health guidelines, and the estimatedtotal annual committed effective dose for radioactive materials does not exceed 25 mrem (0.25millisieverts, or mSv). Although this exposure pathway is presumed complete for past, current,and potential future exposures, the estimated exposure doses are not expected to produceadverse health effects.


Table 14A.

Estimated exposure doses to WKWMA workers and visitors for chemical contaminants in buffer zone soil and sediment (Scenario 1)
ChemicalSoil Range and 67th Percentile
(mg/kg)
Sediment range and 67th Percentile
(mg/kg)
Combined Soil-Sediment Exposure Dose1 (mg/kg/day) Health Guideline (mg/kg/day) (source)1Does Est. Exposure Dose Exceed Health Guideline?
Antimony1-18
2.7
0.5-1,320
11.3
0.0000090.0004 (chronic RfD)No
Arsenic1-38
8.3
0.7-30
7.6
0.000020.0003 (chronic MRL)No
Barium7-360
102
11.6-1,160
134
0.00020.07 (chronic RfD)No
Beryllium1-17
4.4
0.2-8.2
1.0
0.0000060.002 (chronic RfD)No
Cadmium1-4
1.5
0.1-21
1.3
0.0000020.0002 (chronic MRL) No
Fluoride200-310
301.6
170-210
182
0.00050.05 (chronic MRL)No
Lead0.1-705
46
6-635
51.1
0.000090.022No
Manganese34-4,020
612
33-2,830
587
0.0010.07 (ATSDR InterimGuideline)No
Nickel2-461
26.8
2.5-540
29
0.000050.02 (chronic RfD) No
Uranium0.04-1,850
43.1
0.3-13,070
85
0.000040.002 (chronic MRL)No
Vanadium4-460
50.4
6.5-460
47.2
0.0000070.003 (intermediateMRL)No
Polychlorinatedbiphenyls (PCBs)0.07-2.4
0.8
0.01-58.7
1.4
0.0000020.00002 (chronic MRLfor Aroclor 1254)No
1 For an explanation of health guidelines, and of how we calculated exposure doses, refer to Appendix C.
2 Based on the acute lowest-observed-adverse-effect level from ATSDR, 1997 [84].
Key: mg/kg = milligrams per kilogram; mg/kg/day = milligrams of contaminant per kilogram of body weight per day; RfD = EPA's reference dose; MRL = ATSDR's minimal risk level




Next Section     Table of Contents

  

Fluoride releases were not reported for most of the years of operation. From 1955 until 1993, theAtomic Energy Commission, DOE, and their contractors used off-site air monitors to detectairborne fluorides, uranium, and beta-emitters in the surrounding environment [65]. Acontinuous stack sampler for HF was installed in the C-310 stack; however, the reviewed reportsdo not indicate when it was installed or how much fluoride was released before 1985. Starting in1985, total annual releases of HF were reported in the annual reports. Fluoride releases from theC-310 stack and sulfur dioxide releases from the C-600 steam plant were sampled continuouslyuntil 1993. Other emissions from plant operations were intermittently sampled. The majority ofthe releases were determined by material balancing or engineering calculations using emissiondesign factors from EPA's Compilation of Air Pollutant Emission Factors (cited in 40 CFR 61,Subpart H, Appendix D) and coal content information provided by the coal supplier [46].

Most of the uranium used at PGDP was extracted from uranium ore and shipped to PGDP asuranium oxide. However, from 1953 to 1975, some reprocessed uranium, which contained tracesof other radioactive materials, was fed into the cascade system [4]. The other radioactivematerials included technetium 99 (Tc-99), thorium 230 (Th-230), neptunium 237 (Np-237), andplutonium 239 (Pu-239). Significant quantities of Tc-99 were released to the air as early as 1953,with the largest annual release occurring in 1958 [12]. Several reports and studies, from as earlyas 1957, describe operational problems caused by these other radioactive materials, especiallyneptunium and plutonium [66,67,68,69,70]. Airborne releases of Th-230, Np-237, and Pu-239were not reported in the annual environmental reports until the 1990s. These materials werereleased in much less quantity than Tc-99. (Refer to Table 8B.) These constituents in thereprocessed uranium were in very low concentrations when the material was received and mostlyconcentrated in the flame tower ash during the manufacturing of UF6.

PGDP also has operated two vapor degreasers in Building C-400 and one in Building C-720 formetal cleaning and degreasing. Two systems used trichloroethylene (TCE) and one used 1,1,1-trichloroethane (1,1,1-TCA) as organic solvents and degreasers. Both chemicals vaporize orevaporate readily, so PGDP assumed that 90% of the TCE and 1,1,1-TCA was released to theatmosphere [47]. Use of TCE and 1,1,1-TCA was discontinued in 1993; therefore, ATSDRscientists evaluated only past airborne exposures from these sources. Operation of the Northwestand Northeast Groundwater Treatment Systems (beginning in 1995 and 1997, respectively) hasalso resulted in small releases of TCE to the atmosphere.

PGDP uses four recirculating water cooling systems to dissipate heat generated by the diffusionprocess. Moisture in the air flow (drifts) from PGDP's cooling towers contains elements found inthese recirculating water systems. These elements come from chemicals used as corrosioninhibitors, algicides, etc.; the corrosion inhibitor used at PGDP until 1993 was a chromate-zinc-phosphate compound. Of the contaminants released from the cooling towers, the two with thegreatest potential environmental impact are hexavalent chromium and zinc. These wereinvestigated by Oak Ridge National Laboratory in 1978 [71]. At that time, the hexavalentchromium was detected on vegetation and in the soil at a distance of about 0.9 miles (1,500meters) from the cooling towers (extending outside the PGDP boundary). We do not have therelease quantities for hexavalent chromium before 1988, so we cannot compare releases in 1978with quantities seen in the off-site environment in 1978. Available data indicate that the highestannual quantity was released in 1992. In 1993, use of the chromium-zinc-phosphate anti-corrosion compound was discontinued [47].

PGDP operates a coal-burning steam plant to provide steam and generate supplementalelectricity. In 1974 and 1975, two of the three boilers at the steam plant were converted to burnlow-sulfur coal and oil instead of natural gas. Electrostatic precipitators with 97% efficiency forthe capture of particulates were installed [47]. One boiler continues to use natural gas and oil.PGDP reports releases of sulfur dioxide, nitrogen oxides, particulates, carbon monoxide, non-methane volatile organic compounds, and methane. Sulfur dioxide was continuously monitoredat the steam plant stacks from 1979 until 1993 [72]. The reported results were based on thequantity released per unit of heat (BTU) produced or total released for the year. Other emissionswere calculated from fuel usage and emission factors [46]. Annual releases have been reported inDOE's annual reports for 1985 through 1993. No off-site air monitoring for sulfur dioxide andnitrogen oxides has been performed near the PGDP site.

Release quantities in Tables 8A and 8B were estimated by DOE, their predecessors, or theircontractors, mainly through material balance records or by engineering calculations. Values listedwith "est." in Table 8A are estimated by ATSDR using available information. Table 8A includesannual estimated release quantities for uranium and Tc-99. Table 8B includes annual estimatedreleases of other radioactive materials and chemicals from 1985 through 1996.


Table 8A. Annual estimated release quantities of uranium and technetium 99 from process operations at PGDP for 1952 through 1993 and 1996 [12,65,4]

Year

U (in kg)

U (in Ci)

U-234 (in Ci)U-235 (in Ci)U-238 (in Ci)Tc-99 (in Ci)
1952

30

0.02

est. 0.0056
est. 0.0003
est. 0.010
------
1953

500

0.25

est. 0.078
est. 0.0038
est. 0.167
1
1954

4,800

2.4

est. 0.75
est. 0.04
est. 1.60
1
1955

8,400

4.2

est. 1.31
est. 0.06
est. 2.81
2.6
1956

10,500

5.2

est. 1.62
est. 0.08
est. 3.50
2.6
1957

3,900

2.4

est. 1.10
est. 0.05
est. 1.20
4.8
1958

3,500

2.2

est. 0.98
est. 0.05
est. 1.17
6.3
1959

3,300

2.1

est. 0.93
est. 0.04
est. 1.10
5.1
1960

3,000

2.0

est. 0.94
est. 0.05
est. 1.00
4.1
1961

3,600

2.4

est. 1.12
est. 0.05
est. 1.20
4.3
1962

2,400

1.3

est. 0.45
est. 0.02
est. 0.80
4.1
1963

2,400

1.3

est. 0.45
est. 0.02
est. 0.80
4.4
1964

900

0.6

est. 0.28
est. 0.01
est. 0.30
5.3
1965

20

0.02

est. 0.01
est. 0.00
est. 0.01
4.4
1966

30

0.02

est. 0.0056
est. 0.0003
est. 0.01
0.1
1967

20

0.02

est. 0.01
est. 0.00
est. 0.01
0.1
1968

600

0.3

est. 0.11
est. 0.006
est. 0.20
0.1
1969

1,800

1.0

est. 0.34
est. 0.02
est. 0.60
0.1
1970

900

0.5

est. 0.17
est. 0.01
est. 0.30
3.2
1971

1,200

0.7

est. 0.30
est. 0.01
est. 0.40
3.0
1972

1,200

0.7

est. 0.30
est. 0.01
est. 0.40
0.1
1973

1,400

0.8

est. 0.35
est. 0.02
est. 0.47
3.4
1974

1,100

0.6

est. 0.17
est. 0.01
est. 0.37
6.0
1975

1,100

0.7

0.3434
0.0159
0.3662
0.8
1976

1,500

1.0

0.4683
0.0201
0.4996
0.1
1977

610

0.4

0.1904
0.0091
0.203
0.1
1978

96

0.06

0.0294
0.0014
0.032
0.06
1979

48

0.03

0.0090
0.0005
0.016
0.06
1980

22

0.02

0.0096
0.0005
0.0073
0.053
1981

140

0.06

0.0175
0.0006
0.0468
0.006
1982

300

0.14

0.0375
0.0013
0.1004
0.01
1983

11

0.0045

0.0006
0.0002
0.0037
0.003
1984

3.2

0.0019

8.99E-04
4.12E-05
0.0011
0.0349
1985

4.4

3.7E-03

1.99E-03
9.10E-05
1.4E-03
0.0155
1986

0.79

3.6E-04

9.34E-05
4.25E-06
2.63E-04
0.0088
1987

<1.0

2.9E-04

7.30E-05
3.28E-06
2.11E-04
0.0009
1988

0.14

0.6E-04

1.88E-05
8.60E-07
4.43E-05
0.0038
1989

0.2

2.9E-04

2.12E-04
8.0E-06
6.70E-05
0.0036
1990

0.03

3.37E-05

2.22E-05
1.03E-06
1.05E-05
3.86E-04
1991

0.005

6.63E-06

4.65E-06
2.30E-07
1.75E-06
3.07E-03
1992

1.42

2.12E-03

1.59E-03
6.20E-05
4.67E-04
2.06E-04
19931

3.06

3.19E-03

2.37E-03
9.30E-05
7.25E-04
3.31E-03
1996

-----

4.37E-03

4.37E-03
1.19E-04
1.36E-03
4.89E-02
1 Uranium and uranium isotope values reported for 1993 were not consistent in the annual environmental report; maximum values were used.
Key: Ci = curies; kg = kilograms; est. = estimated; U = uranium; U-234, U-235, and U-238 = uranium 234, uranium 235, and uranium 238; Tc-99 = technetium 99


Table 8B. Annual estimated release quantities of major airborne contaminants other than uranium and technetium 99 for 1985 through 1993 and 1996 [65,4]

YearNp-237
(in Ci)
Pu-239
(in Ci)
Th-230
(in Ci)
Fluoride
(in kg)
Hexavalent Chromium
(in kg)
TCE
(in kg)
SO2
(in kg)
NOx
(in kg)
1985******5,268**38,652212,400314,400
1986******6,464**62,856176,575262,800
1987******7,100**34,400178,700252,900
1988******6,84487047,900188,103256,800
1989******6,8011,50041,000292,309282,380
1990******5,7501,70028,000276,380278,613
1991******5,7221,52017,205317,922256,234
19923.8E-072.4E-062.7E-076,5472,01510,221388,648258,696
19932.1E-084.8E-065.9E-063,77886016,000399,579269,265
19962.7E-062.3E-062.1E-06****1,271(DOEonly)****
** Quantities were not reported in the documents reviewed.
Key: Np-237 = neptunium 237; Pu-239 = plutonium 239; Th-230 = thorium 230; TCE=trichloroethylene; SO2 = sulfur dioxide; NOx = nitrogen oxides; Ci = curies; kg = kilograms

Since 1993, when the U.S. Enrichment Corporation (USEC) became responsible for the processfacilities, DOE has not reported process release information or off-site air monitoring data. DOEretains responsibility for four sources of air emissions. The sources are the NorthwestGroundwater Treatment Facility, the C-337 Cooling Tower (as part of the NortheastGroundwater Treatment System), the cylinder refurbishment operations, and two separatefluorescent lamp crushers [73]. The groundwater treatment systems released approximately 2tons of TCE in 1997. Only the cylinder refurbishment operations require a permit from theKentucky Division of Air Quality (KDAQ); these operations are the largest current source ofnon-radioactive air emissions [73]. Sandblasting of UF6 cylinders produced an estimated 4.5 tonsof particulates or dust in 1996 [1] and approximately 5 tons in 1997 [73]. Cylinder paintingoperations released up to 3.4 tons of volatile organic compounds in 1996 [1] and 3.5 tons in 1997[73]. These sources are classified as minor sources of hazardous air pollutants under the CleanAir Act, because they have limited potential for public health effects. DOE is also responsible forfour empty TCE tanks. DOE has no plans to use these tanks at this time [73].

In 1988 and 1989, KDAQ cited PGDP for excessive dust emissions from the C-726 sandblastingfacility [53,54]. The facility was shut down in May 1989. PGDP planned to install a dustcollection filter system and return the facility to use, but the facility never re-opened.

Contaminants of Concern

Each release of a contaminant to the air represents a potential human exposure. ATSDRscientists used information about contaminant releases to identify and select possiblecontaminants of concern for air exposure pathways. Contaminant concentrations in off-site areasare used to determine contaminants of concern. Additional criteria used to select contaminants ofconcern were (1) maximum concentrations exceeding media-specific comparison values, (2)toxicity and radioactivity, and (3) community concerns. Modeling was used to estimate off-siteair concentrations for those contaminants that did not have adequate off-site air monitoring. Wecompared modeling results to ambient air monitoring measurements, when possible, in order toevaluate the accuracy of model predictions.

In estimating the airborne release concentrations and the potential exposure doses for radioactivematerials other than uranium and Tc-99, we assumed that process operations released thesematerials into the air in the same proportion to uranium as in the materials shipped to Paducahfrom other DOE facilities. Actually, most of these radioactive materials are removed in the ashresidue when UF4 is converted to UF6. About 25% of the neptunium and trace amounts of theplutonium are converted to hexafluoride compounds and processed with the UF6. Under theoriginal, conservative assumption, the contribution to the dose estimates from radioactivematerials other than uranium and Tc-99 would be at least an order of magnitude smaller than thecontribution from uranium isotopes, and would not add significantly to the dose estimates [68].

Zinc was released from the cooling tower with chromium. Zinc concentrations in foliage werestudied at Oak Ridge Gaseous Diffusion Plant (ORGDP), where zinc and chromiumconcentrations were a little higher than at PGDP [74]. Beyond 660 feet (200 meters) from thebase of the ORGDP cooling towers, zinc could not be differentiated from background levels. AtPGDP, 660 feet from the base of the cooling towers would still be on site. Also, a study ofmature tree cross sections showed that the zinc emissions were uniform over the past 20 years ofcooling tower operations. This indicates that off-site air concentrations have not changedsignificantly. Based on the estimated quantities of zinc emissions and the probability that zincwould not be seen off site at PGDP, zinc was not selected as a contaminant of concern.

Lastly, 1,1,1-TCA was not selected as a contaminant of concern, because the small quantityreleased to the atmosphere would not produce adverse health effects off site.

ATSDR scientists used computer modeling to predict chronic and acute off-site concentrations ofseveral contaminants known to be released from the PGDP site. These include uranium isotopes,Tc-99, uranium (as a chemical), HF, TCE, sulfur dioxide, nitrogen oxides, and hexavalentchromium. For chemical contaminants, maximum off-site concentrations were compared tomedia-specific comparison values to determine whether the contaminants should be selected ascontaminants of concern for the air exposure pathways. For radioactive contaminants, ATSDRscientists estimated total committed effective doses.

Uranium Isotopes and Technetium 99

Historically, the PGDP site has released uranium isotopes (primarily U-234, U-235, and U-238)and Tc-99 into the air. ATSDR scientists evaluated off-site exposures (committed effectivedoses) to airborne radioactive materials using the Clean Air Act Assessment Package-1988(CAP88-PC) [75,76]. This computer model was developed by EPA for assessing regulatorycompliance with EPA's National Emission Standards for Hazardous Air Pollutants (NESHAP).The model has a number of adjustable parameters, which are discussed in Appendix E. Annualcommitted effective doses were based on air emissions of U-234, U-235, U-238, and Tc-99, andwere calculated for chronic exposures using data from the highest-release years (1956, 1957,1958, and 1959) and from 1996 (a recent year for which we have complete information). Theseestimated chronic doses (shown in Table 9) were calculated for the maximally exposedindividual (the closest resident downwind, about 0.9 miles--1,500 meters--north of the source;CAP88 assumes the source is in the center of the site [29]). The total estimated annual committedeffective doses for 1960 through 1963 were also calculated; these were between 100 and 150millirems per year (1.0 to 1.5 millisieverts per year). The estimated committed effective dosefrom other constituents in reprocessed uranium could add up to 10% to these total doses.

The total estimated annual committed effective doses, shown in Table 9, were not compared todoses calculated from ambient air monitoring data: the air monitoring stations were located at thesecurity fence perimeter, whereas the doses in Table 9 are estimated for the closest downwindresidence--again, approximately 1,500 meters north of the fence. Both calculations result inpotential exposures greater than 10 millirems per year, the current NESHAP emission standardfor radionuclides (40 CFR 61). Therefore, these radionuclides were selected, as a group, ascontaminants of concern for the air exposure pathway.

For acute (short-term) exposure, the highest estimated off-site exposure occurred when a cylinderruptured in Building C-333 at 4:00 a.m. on November 17, 1960. According to our modeling ofthis accident (refer to Appendix E), an estimated uranium inhaled dose of 1.5 rems (0.015sieverts) could have been received by the maximally exposed resident southeast of the site.Therefore, the uranium isotopes were selected as contaminants of concern for the air exposurepathway.


Table 9. Off-site estimated annual committed effective doses from uranium 234, uranium 235, uranium 238, and technetium 99 air releases from PGDP to the maximally exposed individual (approximately 1,500 meters north of the source)1

YearReleases in curies (gigabecquerels)Total estimated annual committed effective dose2 from releases in millirems (millisieverts) [58]
U-234U-235U-238Tc-99
19561.62 (59.9)0.08 (2.96)3.50 (129.5)2.6 (96.2)340 (3.40)
19571.10 (40.7)0.05 (1.85)1.20 (44.4)4.8 (177.6)156 (1.56)
19581.09 (40.3)0.05 (1.85)1.16 (42.9)6.3 (233.1)147 (1.47)
19590.93 (34.4)0.04 (1.48)1.10 (40.7)5.1 (188.7)132 (1.32)
19962.9E-03
(0.107)
1.2E-04
(0.044)
1.4E-03
(0.052)
3.6E-02
(1.332)
0.43
(0.0043)
1 Predominant wind direction from south-southwest.
2 Estimated using the Clean Air Act Assessment Package-1988 (CAP-88-PC) [76].
Key: U-234 = uranium 234; U-235 = uranium 235; U-238 = uranium 238; Tc-99 = technetium 99

Uranium as a Chemical

Accidental uranium releases were also evaluated for uranium as a chemical--that is, based on its chemical toxicity as a heavy metal, not its radioactivity. Only one reported accident (same as above) could have caused significant off-site uranium exposures: an accident at Building C-333 at 4:00 a.m. on November 17, 1960. According to estimated exposures from modeling this accident (see Appendix E), the highest potential dose of inhaled uranium was 5 to 20 milligrams (mg) for residents living southeast of the site, 0.9 to 2.5 miles (1,500 to 4,000 meters) from Building C-333. The U.S. Nuclear Regulatory Commission's action level for intake of soluble uranium is 10 mg. (At this action level, residents may be instructed to evacuate or to stay indoors with windows closed.) Uranium as a chemical contaminant was selected as a contaminant of concern for the air exposure pathway.

Hydrogen Fluoride

HF (including fluoride and fluorine) was released at the PGDP site. This contaminant is also anoted community concern. Although fluoride emission data from the plant are limited, there is astrong correlation between uranium and fluoride releases, and there is historical information onuranium releases. Current fluoride releases are much smaller than past releases, because processand filtration equipment have changed and chemical manufacturing at the PGDP facilities hasbeen discontinued.

Fluoride releases from the plant were not reported in annual reports until 1986. Results from off-site air monitoring were reported in the annual environmental reports from 1958 until 1993.However, results for each monitoring location and sampling period were not reported. For thefirst 3 years, the median value for all off-site air concentrations was reported. From 1961 until1993, the mean values for each year were reported [65].

Because there is a strong correlation between uranium releases and ambient air concentrations ofHF, ATSDR scientists assumed that the largest chronic HF release coincided with the highestannual uranium release in 1956. To evaluate off-site HF exposures for 1956, one must estimateor model HF emissions from periods of consistent data reporting when the processes on site weresimilar (e.g., 1962 through 1970). The method we used is discussed in Appendix F.

For chronic HF exposures, the maximally exposed individual is assumed to be at the perimeternorth air monitoring station. This station is closer to the fluoride processing facility than others[65], and is downwind of the processing facility with respect to prevailing south-southwest winds[1]. Kentucky's ambient air standard for average annual exposure is 500 parts per billion (ppb)[77], and ATSDR's provisional guidance for long-term exposure (365 days or more) is 10micrograms per cubic meter (µg/m3), or 12 ppb [78].

Modeling results indicate that long-term estimated HF concentrations at the north perimeterstation did not exceed the Kentucky ambient air standard but exceeded ATSDR's provisionalguidance in 1955, 1956, and 1961. However, estimated HF concentrations did not exceedATSDR's provisional guidance 1 mile north of the perimeter. The estimated annual averageairborne HF concentration at the nearest houses to the site was 22 ppb for 1956, which was aboveATSDR's provisional guidance but approximately 25 times lower than Kentucky's standard.This was the only year for which the estimated concentration from long-term releases exceededthe provisional guidance at this location.

Of the documented accidental HF releases, the largest release occurred on November 17, 1960,when a cylinder ruptured in Building C-333. During this accident, 8,074 kilograms (17,800pounds) of UF6 were released at approximately 4:00 a.m. As discussed in Appendix F, modelingof this accident estimates short-term hazardous HF concentrations more than a kilometer to thesoutheast of Building C-333, which would include property immediately off site. Therefore,hydrogen fluoride was selected as a contaminant of concern for the air exposure pathway.

Trichloroethylene

Past operations at PGDP involved large quantities of TCE as an organic solvent and degreaser. Historical air releases of TCE were several orders of magnitude larger than current releases from the groundwater treatment facilities. Although significant amounts of TCE were released to the groundwater in the past, most operational releases of TCE volatilized into the atmosphere [47]. To determine if airborne releases presented a potential inhalation exposure to nearby residents,ATSDR scientists estimated the air dispersion of TCE using the Industrial Source Complex (ISC3) model [79], the maximum annual quantities of TCE released from the site, and very conservative assumptions about dispersion, plume rise, and atmospheric degradation. The model and assumptions are discussed in Appendix G.

The maximum estimated airborne TCE concentration at 1,000 meters (3,280 feet) north ofBuilding C-400 is 112 µg/m3 for a 1-hour averaging period (i.e., an acute exposure) and 3 µg/m3for an annual averaging period. Estimated concentrations were several times lower than themedia-specific comparison values for TCE in air (10,920 µg/m3 for acute exposure and 546µg/m3 for intermediate-duration exposure) [23]. Therefore, TCE was not selected as acontaminant of concern for air exposure pathways.

Sulfur Dioxide and Nitrogen Oxides

Sulfur dioxide and nitrogen oxides are both released to air from the PGDP site. Off-sitemonitoring for these contaminants has not been performed near the site; therefore, ATSDRscientists used the ISC3 model to estimate off-site concentrations of sulfur dioxide and nitrogenoxides from the on-site coal-burning steam plant. Modeling results indicated that off-siteestimated concentrations of sulfur dioxide and nitrogen oxides for chronic exposure are not likelyto exceed comparison values. Therefore, sulfur dioxide and nitrogen oxides were not selected ascontaminants of concern for air exposure pathways.

Chromium

Although airborne releases of hexavalent chromium from the cooling towers at PGDP were notreported until 1988, the plant used hexavalent chromium since the early days of operations. From1988 until 1993, releases of hexavalent chromium from the cooling towers were estimated fromconcentrations in the cooling water and known annual quantities of chromium compound addedto the water. As early as 1958, hexavalent chromium was considered a potential environmentalcontaminant [81]; however, only surface water samples were analyzed for chromium.

Union Carbide studied chromium contamination in the late 1970s: they evaluated chromiumreleases from the cooling towers to assess the potential for chromium transport and accumulationin the terrestrial environment [71,74]. Although the Union Carbide studies did not specificallyaddress airborne hexavalent chromium concentrations, they do provide information aboutdeposition of hexavalent chromium on vegetation and soil from the airborne releases. The studiesalso indicate that chromium deposited from the drift cloud was present as hexavalent chromium;therefore, it is reasonable to assume that airborne chromium was also present in the hexavalentform. Hexavalent chromium was detected on vegetation and in soil at a distance of 1,500 meters(about 0.9 miles) from the towers in 1978. Beyond 1,500 meters, soil and vegetationconcentrations could not be differentiated from background chromium concentrations [74].

According to release data from 1988 and later, the maximum annual release of airbornehexavalent chromium occurred in 1992. Therefore, ATSDR scientists used 1992 release data andthe ISC3 air dispersion model [79] to estimate maximum air concentrations on site, immediatelyoff site, and at the closest downwind off-site residence for 1-hour, 8-hour, 24-hour, and annualexposures. Appendix H describes the model and the estimated exposure concentrations.Maximum off-site air concentrations were estimated to be at least 100 times lower thanATSDR's comparison values for hexavalent chromium in air. Therefore, chromium was notselected as a contaminant of concern for air exposure pathways.

Airborne Exposure Pathways

ATSDR scientists identified completed and potential exposure pathways for past, current, andpotential future exposure to air contaminants. Contaminants of concern in these exposurepathways will be evaluated further in the public health implications section of this report.

Current Exposure

Off-site airborne radioactive material concentrations are currently being monitored by theKentucky Department of Health's Radiation Control Program. Since monitoring began in 1996,no concentrations of radioactive materials have been detected above emission standards [80].ATSDR's estimated committed effective dose for radioactive releases in 1996 is 0.43 milliremsper year (0.0043 millisieverts per year)--more than 20 times smaller than the NESHAPrequirement of 10 millirems per year (0.10 millisieverts per year) whole body dose.

The current maximum estimated or modeled off-site concentrations of HF, TCE, sulfur dioxide,nitrogen oxides, and hexavalent chromium are low and do not exceed their respective health-based comparison values.

Therefore, ATSDR scientists did not identify any contaminants of concern for current airexposure pathways.

Past Exposure

In the past, TCE, sulfur dioxide, nitrogen oxides, and hexavalent chromium were released from PGDP; however, the maximum estimated off-site concentrations did not exceed health-based comparison values. As discussed previously, radionuclides (U-234, U-235, U-238, and Tc-99), uranium (as a chemical), and HF were identified as contaminants of concern for past exposure via completed and potential air exposure pathways. These contaminants will be discussed further in the public health implications section.

Potential Future Exposure

As long as on-site processes remain similar to the current operations and no major accidentoccurs, future off-site releases of airborne contaminants should continue at current levels, whichdo not exceed health-based comparison values. Therefore, we did not identify any airbornecontaminants of concern for potential future chronic exposure. Future releases of airbornecontaminants from the processing facility will be the responsibility of USEC under the currentprivatization plans.

DOE is considering alternatives for the management of the aging depleted uranium cylinders atPGDP. Should any chemical processing or additional handling of the cylinders or storage ofwaste from remedial projects be done at this site, the potential for airborne releases will be partof the environmental impact considerations during the planning for the new operations. If on-siteactivities and operations change, then the potential for off-site exposure should be re-evaluated.


Table 10. Summary of completed and potential exposure pathways for airborne contaminants

Major SourcesRadioactive ContaminantsPoint of ExposureRoute of ExposureExposed PopulationPeriod of TimeMaximum Estimated Annual Committed Effective Dose
Process operations,
Bldg. C-310 stack,
Bldg. C-410 feed plant,
Bldg. C-340 metals plant
U-234, U-235, U-238

Tc-99

Downwind off-siteambient air (mainlynorth of the site)InhalationResidents living within ~500meters (~0.3 miles) north of fencePast only
1954 to 1963
1955 to 1965; 1970, 1971, 1973 and 1974
Maximum in 1956:
340 mrem
(3.4 mSv)
Major acute releases:

1960 cylinder rupture

1962 fire

U-234, U-235, U-238

U-234, U-235, U-238

Downwind off-site ambient air
(Both accidents toward the southeast)
InhalationResidents outdoors within 1.5 to 3kilometers (~0.9 to 1.8 miles) ofaccident, which happened atBuilding C-333

Residents outdoors more than 0.2kilometers (0.12 miles) from theaccident

11/17/60
4:00 a.m.

12/13/62
4:00 p.m.

0.5 to 1.5 rem
(5 to 15 mSv)

< 1 mrem
(< 0.01mSv)

Major SourcesChemical ContaminantsPoint of ExposureRoute of ExposureExposed PopulationPeriod of TimeMaximum Estimated Exposure Dose (Chemicals)
Process operationsHydrogen fluorideDownwind off-siteambient air (north ofsite)InhalationResident living within ~500meters (~0.3 miles) north of fence1956 only22 ppb average hydrogenfluoride concentration
Major acute releases:

1960 cylinder rupture

Uranium

Hydrogen fluoride

Downwind off-siteambient air (towardthe southeast)InhalationResidents outdoors within 1.5 to 4kilometers (~0.9 to 1.8 miles) ofaccident, which happened atBuilding C-333 11/17/60
4:00 a.m.
5 to 20 mg uranium

1 to 5 ppm hydrogen fluoride

Key: mg = milligrams; mrem = millirems; mSv = millisieverts; ppm = parts per million; ppb = parts per billion;
U-234= uranium 234; U-235 = uranium 235; U-238 = uranium 238; Tc-99 = technetium 99

Surface Water

Background

Surface waters around the PGDP site have elevated concentrations of chemical and radioactivecontaminants as a result of process operations and past waste disposal activities at the facility.Surface waters may also receive contaminants as a result of groundwater discharge to Big BayouCreek and the Ohio River [82] and deposition of airborne particles [71]. Surface watermonitoring data reflect total contaminant load. Surface water drainage from PGDP is either eastor northeast to Little Bayou Creek or theNorth/South Diversion Ditch, or west ornorthwest to Big Bayou Creek. TheNorth/South Diversion Ditch has flow onlyduring periods of heavy rain and releasesfrom the plant. The ditch flows to thenorth/northeast and discharges into LittleBayou Creek. Big Bayou and Little Bayoucreeks converge about 3 miles (5 kilometers)north of the facility and discharge directly into the Ohio River about a quarter mile (half akilometer) further downstream.

Surface water discharges from the PGDP site to Big Bayou and Little Bayou Creeks are regulatedunder Kentucky Pollutant Discharge Elimination System (KPDES) permits. Surface water runofffrom the plant into the North/South Diversion Ditch and from the landfills and the plant intoLittle Bayou and Big Bayou Creeks are also monitored under KPDES permits. These permitsspecify allowable contaminant concentrations in discharges and require DOE or the U.S.Enrichment Corporation to monitor effluents and take corrective action if discharges exceedpermitted limits.

ATSDR scientists reviewed data for 258 different off-site surface water monitoring stations thatPGDP sampled between 1987 and 2000. All stations included in this evaluation are outside thesecurity fence. Samples were analyzed for 511 different chemicals and radiological parameters[44]. PGDP sampled a few monitoring stations as early as 1958 [81]. However, these sampleswere analyzed for only a few contaminants, including fluoride, nitrate, hexavalent chromium,uranium, and gross beta activity. Maximum concentrations of fluoride, nitrate, hexavalentchromium, uranium, and gross beta activity in historical samples collected close to the siteboundary in Big Bayou and Little Bayou Creeks were higher than in samples analyzed from 1987to 2000 [65]. However, historical data are not directly comparable to more recent measurements,because there have been changes in sampling and analytical techniques over time. Becauseprocess operations and waste disposal practices have also changed over time, currentcontaminant releases to surface waters are generally one to two orders of magnitude lower thanhistorical releases.

Concentrations for most surface water contaminants are not evenly distributed; maximum valuesmay be two orders of magnitude higher than the next highest sample. The maximumconcentrations for all surface water contaminants were obtained at one of two locations. Formetals, the highest concentrations are at several surface water stations in Big Bayou Creekadjacent to the southwest landfill. Stations at the PGDP outfalls into Little Bayou Creek have thehighest concentrations of fluoride, nitrate, polychlorinated biphenyls (PCBs), trichloroethylene(TCE), and radioactive materials.

According to samples collected upstream and downstream of the point where Big Bayou andLittle Bayou Creeks discharge into the Ohio River, the river has several chemical contaminantsthat may be related to PGDP, including chloride, fluoride, and sulfate. Maximum concentrationsdownstream, however, are barely above the concentrations upstream, and are much lower thanlevels found in Big Bayou and Little Bayou Creeks [1]. Also, a different source may beresponsible for these elevated concentrations of chloride, fluoride, and sulfate.

Contaminants of Concern

ATSDR scientists used a series of screening techniques to select contaminants of concern forsurface water exposure pathways. The first phase of this screening involved determining ifmaximum off-site concentrations exceeded health-based comparison values for chemicals and ifmaximum radiation doses exceed 4 millirems per year (EPA's Drinking Water Standard forradioactive contaminants). Contaminants of concern for other exposure pathways were alsoevaluated if detections were above comparison values. Seventeen chemicals (14 metals, TCE,nitrate, and total PCBs) were detected in areas ofpotential exposure at levels requiring additionalexposure analysis. Eleven radionuclides areevaluated for potential exposure doses todetermine if they should be consideredcontaminants of concern.

The second phase of contaminant screening isbased on the calculation of potential exposure doses for each surface water contaminant.Concentrations of most surface water contaminants were log-normally distributed, meaning that afew samples had high concentrations while most of the samples had much lower concentrations.Consequently, the estimated exposure doses were calculated using the 67th percentile of theconcentration distribution. The exposure analyses, along with the detection ranges, the 67thpercentile concentrations, and the calculated exposure doses, for these contaminants are presented in Tables 11 and 12 in the following section.

Thallium is one of the seventeen chemical surface water contaminants and is the only one thathas estimated exposure doses that exceed health guidelines. Therefore, thallium is a contaminantof concern for the surface water pathway and will be discussed further in the following pathwayanalysis section and in the public health implications section of this report.

Di(ethylhexyl)phthalate is not considered a contaminant of concern. Although this chemical wasdetected in surface water samples, it is not directly used or stored at PGDP. It is a commonadditive to plastic sample bottles, rubber gloves, and other plastic products. It was detected threetimes at different stations with widely varying concentrations. Therefore, ATSDR scientistspresumed that di(ethylhexyl)phthalate was introduced during the sampling process and is not asite-related contaminant of concern for surface water.

For current concentrations of radioactive materials in the surface water we used the 67thpercentile for reasons described previously; however, we did not have as much data for pastconcentrations so we used the annual average concentration at the sampling location that hadmaximum results. Also, there are important differences between current and past analyses ofradioactive substances in surface water. Measured concentrations changed over time, but so didthe methods of analysis used and the list of radioactive materials being measured. Historicalanalyses for radioactive materials included total uranium, gross alpha, and gross beta activity. Inthese analyses, the highest average annual total uranium concentration was 474 picocuries perliter (pCi/L), measured in samples collected from Big Bayou Creek in 1960. The highest averageannual gross beta activity was 21,700 pCi/L (Little Bayou Creek, 1960) [83]. Most of this betaactivity was attributed to technetium 99 (Tc-99). Therefore, ATSDR scientists used themaximum annual average concentrations for uranium and Tc-99 (gross beta) to estimate pastexposure doses (annual committed effective doses) for children and adults. These doses arepresented in Table 12 in the following section.

By the 1980s, maximum uranium concentrations had decreased to levels that were less than 1%to 5% of levels reported in 1960. Other radioactive contaminants (strontium 90, neptunium 237,plutonium 239, and thorium 230) were quantified in the 1987-1996 analyses. ATSDR includedthese other radioactive contaminants in the estimated current exposure doses (annual committedeffective doses) for children and adults. These doses are also presented in Table 12 in thefollowing section.

Surface Water Exposure Pathways

The greatest potential for human exposure tocontaminated off-site surface water has beenin Little Bayou Creek, Big Bayou Creek, andthe Ohio River downstream of Big BayouCreek. Persons may fish, wade, and play inthe creeks. In addition, there are notedcommunity health concerns about potentialhuman exposures. Because contaminants arepresent in the creeks and humans may accessthese areas, ATSDR scientists identified potential exposure pathways for past, current, and futureexposure to contaminants in surface water. Contaminants of concern in these exposure pathwayswill be evaluated further in the public health implications section of this report.

As stated above, the highest concentrations of all surface water contaminants occur at one of twolocations: either within the WKWMA property directly adjacent to the southwest landfill or inDOE buffer property at surface and storm water outfalls into Little Bayou Creek. (This includesthe North-South Diversion Ditch.) Although exposure is possible in these areas, ongoing monthlyingestion of surface water is unlikely. Also, the 67th percentile concentrations of off-sitecontaminant levels is much more realistic for calculating potential surface water exposuresaround PGDP.

Exposure doses are estimated assuming incidental contact and ingestion, because surface water inthis area is not used to supply drinking water. For chemical contaminants above the health-basedcomparison values, we assumed ingestion of 0.5 liters of water per exposure and one exposureper month for 12 months per year. We estimated exposure doses for a child (1 to 6 years old) andan adult, assuming incidental ingestion of surface water contaminated at the 67th percentile ofoff-site concentrations. For volatile organic compounds, dermal (skin) contact may contribute adose up to 30% as large as the ingestion dose [56]. TCE was the only volatile organic compounddetected in surface water off site. Therefore, we assumed that dermal contact contributed anadditional 30% to the estimated ingestion dose for TCE. The estimated exposure doses forcurrent exposure to most chemical contaminants and past exposure to hexavalent chromium,fluoride, and nitrate are shown in Table 11 (using pre-1987 annual average values). Theestimated current and past exposures to radioactive contaminants are shown in Table 12. It wasnot possible to estimate past exposure doses to most chemicals and radioactive materials,because historical measurements are lacking.

Health guidelines provide a basis for evaluating exposure doses estimated from contaminant concentrations in soil, air, water, and food. Exposure doses depend on the characteristics of the people who might be exposed and the length of their exposure. The health guidelines are described in Appendix C. Most of the health guidelines were derived for chronic exposure--that is, exposure lasting more than 364 consecutive days. By contrast, human exposure to off-site contaminated surface water is likely to have occurred infrequently throughout the year and possibly not at all during winter months. According to local residents, there is very little swimming, wading, or other human activity in Big Bayou and Little Bayou Creeks. All of Little Bayou Creek is in DOE or Tennessee Valley Authority property, except for a small area that borders private property to the east of the plant. According to the Kentucky Radiation Control Program, Little Bayou Creek has been restricted and posted at access points since July 19, 1993.


Table 11. Estimated exposure doses for chemical contaminants in off-site surface water at PGDP and health guidelines

Chemical
Contaminant
Contaminant Range (and 67th percentile) in µg/LEstimated Exposure Dose for Children (mg/kg/day)1Estimated Exposure Dose for Adults
(mg/kg/day)1
Oral Health Guideline in mg/kg/day and Source1Estimated Exposure Dose Greater Than Health Guideline?
Antimony

10-50 (42)

0.0000840.0000130.0004 (Chronic RfD)No
Arsenic6-90 (38)0.0000760.0000110.0003 (Chronic MRL)No
Beryllium0-150 (75)0.000150.0000230.002 (Chronic RfD)No
Cadmium0-90 (32)0.0000640.000010.0002 (Chronic MRL)No
Chromium4-820 (210)0.000420.0000631.5 (Oral RfD)No
Chromium,hexavalent20-7,8802
(1,626)
0.00330.000490.003 (ATSDR InterimOral Intake)No
Fluoride(Fluorine)100-35,0002
(1,047)
0.00210.000310.05 (Chronic MRL) No
Lead2-12,200 (1,945)0.00390.000580.0203No
Manganese8-187,000
(22,447)
0.0450.00670.07 (ATSDR InterimGuidance Value)No
Nickel5-1,350 (320)0.000640.0000960.02 (Chronic RfD)No
Nitrate150-900,0002
(2,492)
0.0050.000751.6 (Chronic RfD)No
Total PCBs1-42 (4.5)0.000010.0000020.00002 (Chronic MRLfor Aroclor 1254)4No
Sulfate3,800-1,680,000
(108,184)
0.220.03214.295No
Thallium16-5,260 (417)0.000830.000130.00008 (Chronic RfD)Yes
Trichloroethylene1-51 (5)0.000010.0000020.2 (Acute MRL)No
Uranium1-3,000 (74)0.000150.0000220.002 (Int./Chronic MRL)No
Vanadium2-1,430 (156)0.000310.0000470.003 (Int. MRL)No
1 For an explanation of health guidelines and of how we calculated exposure doses, refer to Appendix C.
2 These concentrations are maximum annual averages from historical annual environmental reports [65]. The other concentrations are from the 1987-2000 electronic data and reports [44].
3 Based on lowest-observed-adverse-effect level (acute) from ATSDR, 1997 [84].
4 This MRL is based on Aroclor 1254, not total polychlorinated biphenyls. This provides a conservative evaluation.
5 Based on EPA's MCLG and equivalent exposure for a 70-kg adult ingesting 2 liters per day.
Key: mg/kg/day = milligrams of contaminant per kilogram of body weight per day; µg/L = micrograms per liter


Table 12. Past and current maximum estimated exposure doses (annual committed effective doses) for radioactive contaminants in surface water [58]

Radioactive ContaminantPast Maximum Concentration
in pCi/L (and in Bq/L)
Current Concentration Range and 67th Percentile in pCi/L (and Bq/L)Maximum Annual Estimated Committed Effective Dose for Child in mrem (and mSv)Maximum Annual Estimated Committed Effective Dose for Adult in mrem (and mSv)
PastCurrentPastCurrent
Americium 241

------

0.05-17.1 (0-0.63)
13.7 (0.507)
------0.08
(8.2E-04)
------0.06
(6.1E-04)
Neptunium 237------0.04-13.6 (0-0.50)
0.8 (0.030)
------0.00
(2.5E-05)
------0.00
(2.0E-05)
Plutonium 238------0.5-3.2 (0.02-0.12)
2.7 (0.100)
------0.02
(1.9E-04)
------0.01
(1.4E-04)
Plutonium 239------0.01-2.7 (0-0.10)
0.3 (0.011)
------0.00
(2.2E-05)
------0.00
(1.6E-05)
Strontium 90------6.1-131.3 (0.23-4.86)
64 (2.37)
------0.07
(6.7E-04)
------0.04
(4.0E-04)
Technetium 9921,700 (803.7)21-4,000 (0.04-148.1)
61 (2.259)
1.11
(1.11E-02)
0.00
(3.1E-05)
0.309
(3.1E-03)
0.00
(8.7E-06)
Thorium 230

------

0.002-6.0 (0-0.22)
1.4 (0.052)
------0.01
(9.7E-05)
------0.01
(6.6E-05)
Uranium, total1

474 (17.56)2

0.06- 9.5 (0-0.35)
3.4 (0.126)
0.88
(8.8E-03)
0.50
(5.0E-03)
Uranium 234

------

0.01-119 (0-4.41)
7.5 (0.278)
------0.01
(1.5E-04)
------0.01
(8.2E-05)
Uranium 235

------

0.01-2.34 (0-0.09)
0.6 (0.022)
------0.01
(8.5E-05)
------0.00
(4.7E-05)
Uranium 238------0.33-194 (0.01-7.19)
16.4 (0.607)
------0.01
(8.0E-05)
------
Total committedeffective dose------------1.99 (0.02)30.21 (0.00)0.81 (0.01)30.13 (0.00)
1 Total uranium = uranium-234, uranium-235, and uranium-238 (only used for past exposure calculations).
2 These concentrations are maximum annual averages from historical annual environmental reports [65]. The other concentrations are from the 1987-2000 electronic data and reports [44].
3 Past total committed effective doses do not include potential exposure to several radionuclides, because there are not enough historical data.
Key: pCi/L = picocuries per liter; Bq/L = becquerels per liter; mSv = millisieverts; mrem = millirems

Current and Past Exposure

Several chemical and radioactive contaminants have been detected in surface water samplestaken from Big Bayou Creek, Little Bayou Creek, and the portion of the Ohio River downstreamof Big Bayou Creek. Only one chemical contaminant, thallium, was selected as a contaminant ofconcern for surface water. The highest concentrations of thallium are reported for Big BayouCreek and its tributaries near the inactive southwest landfill. Concentrations of thallium are alsoelevated in Little Bayou Creek east of the plant. ATSDR scientists cannot determine withcertainty how long the streams may have been contaminated with thallium, because samples werenot analyzed for thallium until 1987. Because thallium may have been present in off-site surfacewater prior to 1987, thallium is a contaminant of concern for past and current exposure viapotential exposure pathways for off-site surface water (as shown in Table 13) and will bediscussed in the public health implications section of this report.

Radioactive contaminants were present at low levels in samples taken from Little Bayou and BigBayou creeks. Because the annual total committed effective doses are less than 4 millirems (0.04millisieverts) for current exposures, radioactive contaminants are not contaminants of concernfor current exposure to surface water. Lack of data for historical concentrations of radioactivematerials other than Tc-99 and the uranium isotopes makes it difficult to determine pastexposures to all radionuclides in surface waters. It is possible that, during a past release fromthe site, a person exposed to the surface waters could have received a dose in excess of 4millirems. Therefore, radioactive materials are considered contaminants of concern for pastexposures via potential exposure pathways for off-site surface water and will be discussed in thepublic health implications section of this report.

Potential Future Exposure

With partial restrictions on access to Little Bayou Creek, permitting discharges to off-site surfacewater, and remedial activities to remove sources of contamination, future exposures to surfacewater contaminants should either not occur or be much lower than current exposures. Therefore,ATSDR scientists did not identify any potential future exposure pathways for surface water.However, if new processes are initiated at the site or new sources of contamination are identified,future exposures should be addressed at that time.


Table 13. Summary of potential exposure pathways for off-site surface water contaminants

Major SourcesContaminantsPoint of ExposureRoute of ExposureExposed PopulationPeriod of TimeMaximum Estimated Exposure Doses
Processoperationsdischarge,surface waterrunoff,leachingfrom pastwastedisposalactivities,groundwaterdischarge,airbornedepositionThallium







Total uranium
Technetium 99
Americium 241
Strontium 90
Neptunium 237
Plutonium 238
Plutonium 239
Thorium 230

Duringwading orimmersionin LittleBayou orBig BayouCreeksIncidentalingestionanddermalcontactChildren playing in the creeks once per month, and adults fishing and wading in the creeks once per monthPast and current





Past
(before 1987)

Thallium (mg/kg/d)

Children: 0.00083
Adult: 0.00013


Radiation exposure
:
uncertain (however, estimated committed effective doses were > 4 mrem but < 200 mrem for annual intake in both scenarios)

Key: mg/kg/d = milligrams of contaminant per kilogram of body weight per day;
mrem = millirems

Soil and Sediment

Background

Process operations and waste disposalactivities at PGDP have contaminated soiland sediment. Off-site surface soil hasbecome contaminated mainly as a result ofreleases from disposed waste material anddeposition of airborne releases. Surface soilconcentrations are highest in the predominantdownwind directions from the site and in soils near the creek and ditches as a result of leachingfrom landfills and occasional flooding of the creeks and ditches. Sediment in nearby streams hasbecome contaminated as a result of surface water discharges and surface runoff from the site.Deposition of airborne materials also introduces contaminants to streams and ponds, where theyare adsorbed to sediments.

Soil and sediment data evaluated were obtained via electronic transfer from the PGDPenvironmental database [44], the Kentucky Department for Environmental Protection (HazardousWaste Branch) and the Kentucky Department for Public Health (Radiological Health and ToxicAgents Branch). The cumulative data set consists of 292,062 chemical and radiologicalmeasurements for 457 analytes from 1,737 locations. Data were available for five differentsample types and depth profiles:

  • Sediment.

  • Soil at unspecified depth.

  • Subsurface soil more than 12 inches (30 centimeters) deep.

  • Surface soil less than or at 12 inches deep but more than 3 inches deep (that is, from 8 centimeters to 30 centimeters).

  • Top soil less than or at 3 inches (8 centimeters) deep.

Because chronic human exposure to subsurface material is very unlikely, ATSDR evaluated onlysurface and top soil samples (including unspecified depth samples), as well as sediment samples.Sample station names did not designate whether any off-site samples were collected onresidential properties. If the stations appeared to be located near residential properties, theresidential properties were assumed to have similar soil concentrations. Samples in the electronicdata set were collected and analyzed for 1987 through 2000. Additional soil and sediment data,available from annual environmental monitoring reports, were used to corroborate contaminantdistributions. A limited soil sampling program began in 1971; however, few samples werecollected and were analyzed only for uranium.

Off-site sample locations were not uniformly spaced. They were too far apart to determinewhether contaminant distributions followed a regular pattern based on transport and fate (e.g.,airborne dispersal) processes. For example, maximum concentrations of technetium 99 andneptunium 237 were found to the north of the fenced area and near the edge of the buffer zone;maximum concentrations of metals, uranium isotopes, thorium 230, and cesium 137 were foundwest and southwest of the site; and maximum concentrations of most of the radioactivecontaminants in sediment were found in drainage ditches and in Little Bayou Creek. Also, mostsoil sampling stations have not had multiple sampling over time. Consequently, it is not possibleto evaluate historical trends of soil contamination at PGDP. This evaluation will assume that ifPGDP contaminants have been detected at a soil sampling location, that location has beencontaminated since the beginning of PGDP operations. As with surface water, concentrations ofmost soil and sediment contaminants are not evenly distributed.

Contaminants of Concern

ATSDR scientists used a screening technique to select contaminants of concern for soil andsediment exposure pathways. This screeninginvolved determining if maximum concentrationsof these contaminants in areas of potential humanexposure exceeded health-based comparisonvalues for chemicals and if maximum radiationdoses exceeded 25 millirems per year (mrem/year)for radionuclides. Thirteen chemical contaminantsand twelve radionuclides were consistentlydetected in areas of potential exposure at concentrations requiring additional exposure analyses.

Most of the contaminants remaining after the first phase of screening are naturally occurringmetals with concentrations that may have been elevated above background levels by processoperations or waste disposal activities. In addition, polychlorinated biphenyls (PCBs or Aroclors)have been detected above comparison levels. The PCBs have been analyzed as both individualspecies (Aroclor 1016, Aroclor 1242, Aroclor 1254, etc.) and as total PCBs. Only total PCBs willbe evaluated further.

Several detected contaminants are not considered further. Metallic mercury, 1,2-dichloroethene(cis and trans), and ammonia each had only one sample above comparison values. These singlehigh values were not repeated in other analyses, which indicates that the high values are samplingor analytical anomalies, or that the spatial extent of the contaminants is so limited that significantexposure is not possible. Silver was also detected at several on-site sediment or soil samples forwhich no chronic (long-term) community exposure is possible. Off-site detections of silver werebelow levels of health concern. Also, trichloroethylene, a contaminant of concern for thegroundwater exposure pathway, was detected in five samples. However, those detections were aton-site stations and below levels of health concern. Chromium is also not evaluated further,because concentrations are below health-based comparison values for trivalent chromium.Although the valence of the chromium soil samples is not specified, other studies have shownthat virtually all of the soil chromium is in the trivalent form, not the more toxic hexavalent form[71,74].

Most of the contaminants evaluated further have higher concentrations on site than off site. Thismeans that site activities may be responsible for contaminant distributions. Arsenic, lead, andnickel have higher off-site concentrations, which suggests that PGDP activities may not beresponsible for the distributions of these contaminants. It is also possible that several of the soiland sediment contaminants are at background levels--that is, that they do not represent site-related contamination. Prior use of the PGDP site by the Kentucky Ordnance Works could alsocontribute metals contamination. Because arsenic, lead, and nickel exceed health-basedcomparison values, the following exposure analyses will identify their potential exposurepathways and estimated exposure doses.

Soil and Sediment Exposure Pathways

Contaminated soils and sediments are presentboth inside and outside of the PGDP securityfence. The most significant soilcontamination is within the fence but haslittle potential for public exposure. However,soil contaminants with concentrations abovehealth comparison values are present withinthe unsecured buffer area maintained as partof the Western Kentucky WildlifeManagement Area (WKWMA) and on privateland outside the buffer area. The most contaminated sediments are similarly located within theaccess-restricted drainage ditches and Little Bayou, but contaminated sediments are also presentwithin the open access areas of Big Bayou, nearby ponds, and private lands.

The distribution of land uses surrounding PGDP presents two scenarios by which the public maybe exposed to soil and sediment contaminants. Scenario 1 covers WKWMA workers and visitors,who may be exposed to soil and sediment contaminants in the buffer zone and adjacentWKWMA property. Scenario 2 covers people living adjacent to PGDP. As with surface water,concentrations of most soil and sediment contaminants are log-normally distributed, meaningthat a few samples had high concentrations while most of the samples had much lowerconcentrations [85]. Consequently, the estimated exposure doses were calculated using the 67thpercentile of the concentration distribution. The following sections present the exposureattributes, contaminant concentrations, and estimated exposure doses that are specific to each ofthose scenarios. The following scenarios assume that soils and sediments became contaminatedshortly after the beginning of PGDP operations and that the exposure pathways are complete inthe past, present, and future. The detection ranges, the 67th percentile concentrations and thecalculated exposure doses are presented in Tables 14.A, 14.B, 15.A, and 15.B.

Scenario 1--WKWMA Workers and Visitors

WKWMA workers involved with maintenance of the buffer zone property have a high potentialfor contact with contaminated soil. This scenario also includes visitors to WKWMA, althoughthey would be exposed less often than WKWMA workers and receive a commensurately lowerexposure dose.

For this scenario, ATSDR scientists assumed that workers could be exposed to top soil, surfacesoil, or soil at unspecified depth and would spend approximately 8 hours a day for 1.5 days aweek (i.e., 30% of their work week) in contaminated buffer zone areas. We also assumed that thesame WKWMA workers were exposed to contaminated sediment for 0.75 days each week (15%of the work week). We assumed that these soil and sediment exposures went on for 50 weeks peryear for 10 years, which is an approximate maximum period of employment at the WKWMA.Soil contaminant concentrations for these exposures were derived from buffer zone soil samples.Sediment contaminant concentrations were derived from all sediment samples taken outside thesecurity fence.

Exposure was assumed to occur via direct (dermal) contact and ingestion for chemicalcontaminants and via ingestion and external exposure for radioactive contaminants. Foringestion, we assumed an ingestion rate of 200 milligrams (mg) of soil per day (four times thedaily average adult rate [23]) and 100 mg of sediment per day (two times the average adult rate).We assumed that workers were men and women. Table 14A shows the estimated exposure dosesfor chemical contaminants (along with additional assumptions we made in calculating them).Table 14B shows estimated exposure doses (annual committed effective doses) for radioactivecontaminants in this scenario. Table 14B does not show estimated external exposure toradioactive contaminants. (The estimated external exposure from surface and/or top soil wouldadd approximately 8 mrem/year for this scenario [86].)

For this scenario, no chemical exposure doses exceed the health guidelines, and the estimatedtotal annual committed effective dose for radioactive materials does not exceed 25 mrem (0.25millisieverts, or mSv). Although this exposure pathway is presumed complete for past, current,and potential future exposures, the estimated exposure doses are not expected to produceadverse health effects.


Table 14A. Estimated exposure doses to WKWMA workers and visitors for chemical contaminants in buffer zone soil and sediment (Scenario 1)

ChemicalSoil Range and 67th Percentile
(mg/kg)
Sediment range and 67th Percentile
(mg/kg)
Combined Soil-Sediment Exposure Dose1 (mg/kg/day) Health Guideline (mg/kg/day) (source)1Does Est. Exposure Dose Exceed Health Guideline?
Antimony1-18
2.7
0.5-1,320
11.3
0.0000090.0004 (chronic RfD)No
Arsenic1-38
8.3
0.7-30
7.6
0.000020.0003 (chronic MRL)No
Barium7-360
102
11.6-1,160
134
0.00020.07 (chronic RfD)No
Beryllium1-17
4.4
0.2-8.2
1.0
0.0000060.002 (chronic RfD)No
Cadmium1-4
1.5
0.1-21
1.3
0.0000020.0002 (chronic MRL) No
Fluoride200-310
301.6
170-210
182
0.00050.05 (chronic MRL)No
Lead0.1-705
46
6-635
51.1
0.000090.022No
Manganese34-4,020
612
33-2,830
587
0.0010.07 (ATSDR InterimGuideline)No
Nickel2-461
26.8
2.5-540
29
0.000050.02 (chronic RfD) No
Uranium0.04-1,850
43.1
0.3-13,070
85
0.000040.002 (chronic MRL)No
Vanadium4-460
50.4
6.5-460
47.2
0.0000070.003 (intermediateMRL)No
Polychlorinatedbiphenyls (PCBs)0.07-2.4
0.8
0.01-58.7
1.4
0.0000020.00002 (chronic MRLfor Aroclor 1254)No
1 For an explanation of health guidelines, and of how we calculated exposure doses, refer to Appendix C.
2 Based on the acute lowest-observed-adverse-effect level from ATSDR, 1997 [84].
Key: mg/kg = milligrams per kilogram; mg/kg/day = milligrams of contaminant per kilogram of body weight per day; RfD = EPA's reference dose; MRL = ATSDR's minimal risk level




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