PUBLIC HEALTH ASSESSMENT
PADUCAH GASEOUS DIFFUSION (USDOE)
PADUCAH, MCCRACKEN COUNTY, KENTUCKY
The U.S. Department of Energy (DOE)'s Paducah Gaseous Diffusion Plant (PGDP) was added to the U.S. Environmental Protection Agency's Superfund National Priorities List (NPL) on May 31, 1994, because elevated concentrations of trichloroethylene (TCE) and technetium 99 (Tc-99) were found in off-site groundwater (residential wells). The Superfund law (CERCLA) requires that the Agency for Toxic Substances and Disease Registry (ATSDR) conduct a public health assessment for all sites listed on the NPL. This public health assessment evaluates contaminant distributions, community health concerns, and available health outcome information to determine the potential for community exposures to hazardous substances and adverse public health effects resulting from those exposures.
The plant, which is about 10 miles (16 kilometers) west of Paducah, Kentucky, began operation in 1952. PGDP produces enriched uranium with a higher than natural concentration of uranium 235, using a gaseous form of uranium (uranium hexafluoride). TCE was used as a solvent to clean metal parts. Tc-99, a radioactive substance, was introduced at the site when uranium used in a reactor was reprocessed. This public health assessment presents an evaluation of these and other chemical and radioactive contaminants in human exposure pathways. ATSDR also considered other hazards--such as accidents involving the depleted uranium cylinders stored at and transported to and from this site--in evaluating the public health effects of past, current, and future PGDP operations on the surrounding community.
According to the information reviewed by ATSDR, under normal operating conditions, the Paducah Gaseous Diffusion Plant currently poses no apparent public health hazard for the surrounding 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 contaminated media near the site, but that exposure to the contamination is not expected to cause any adverse health effects. We define "current" as ranging from 1990 to the present. This conclusion assumes the effectiveness of access restrictions to Little Bayou Creek, the outfalls, and the North-South Diversion Ditch; the fish advisories issued for Little Bayou Creek and some of the ponds in the Western Kentucky Wildlife Management Area; and existing regulation of discharges to air and surface water.
Historical groundwater exposure to TCE and lead was a public health hazard for children routinely drinking water from four residential wells. This means that long-term exposure occurred at concentrations that may have caused adverse health effects in children. A future groundwater exposure pathway could exist if new wells are drilled into the northwest or northeast plumes. No current exposure pathways to contaminated groundwater exist, but the current restrictions between DOE and the property owners do not restrict the drilling of new wells by future owners of this land. Although it is unlikely, potential future exposures could occur if new wells are drilled into these plumes.
Groundwater exposures to vinyl chloride (a degradation product of TCE) and acute air exposures to uranium and hydrogen fluoride are an indeterminate public health hazard for past and potential future exposures. This means that the information available is incomplete.
Information on vinyl chloride exposures is incomplete because the detection limits in most analyses of samples from tested residential wells were well above the levels of concern. Also, not all residential wells in or near the plume were tested for vinyl chloride. Future groundwater monitoring for vinyl chloride and other TCE degradation products should be low enough to determine whether concentrations exceed health-based guidelines. However, there appears to be no 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 worst reported accidental release happened at 4:00 am on November 17, 1960. Potentially hazardous uranium and hydrogen fluoride concentrations, estimated using air dispersion models, reached off-site areas, but because the accident occurred at 4:00 a.m., it is not known if any residents were exposed. If people were exposed at the concentrations estimated by the model, adverse health effects may have resulted. Currently, we have no reports of health effects related to this accident; 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 public health concern.
In the future, the rupture of one or more depleted uranium cylinders, which could occur from a transportation accident involving a fire, would create an urgent public health hazard for anyone near the accident. Weather conditions and duration of exposure would affect the distance from the accident at which there would be a hazard; however, we predict that (1) the maximally exposed individual would be 100 feet (30 meters) or less from the accident and (2) an urgent public health hazard could exist out to 230 feet (70 meters) from the accident. Less-severe health effects could be experienced by individuals within several thousand meters of the accident. This type of accident is very unlikely.
For other accident scenarios such as a plane crash, severe weather, or natural disasters involving the on-site depleted uranium cylinders, a temporary public health hazard could exist off site from hydrogen 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 public health assessment. Many people expressed concerns related to the incidence of cancer and other illnesses 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:
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 Health Action Plan in the main part of this document.
ATSDR staff will continue to monitor environmental issues and remedial activities at PGDP, as well as proposals related to storage and transport of the depleted uranium cylinders. The interpretation, conclusions, and recommendations provided in this public health assessment are based on the data and information referenced. Additional data could alter those conclusions and recommendations. The conclusions and recommendations are site specific and should not be considered applicable to any other situation.
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 the city 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 elevated concentrations of trichloroethylene and technetium 99 were found in off-site groundwater.
The primary plant process, gaseous diffusion, is a
physical process to enrich uranium hexafluoride
(UF6)--that is, to increase the percentage of uranium
235 (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 is
fed through diffusion stages--compressors and converters. PGDP has 1,812 diffusion stages
housed in five buildings, which cover about 74 acres (30 hectares) [3]. The "product" (UF6
enriched up to 2.75% U-235 [4]) and "tails" (UF6 depleted between 0.2% and 0.4% U-235) are
removed and put in cylinders [5]. The product is shipped to another uranium enrichment facility
in Piketon, Ohio for further enrichment; however, the Piketon enrichment operation is scheduled
to shut down in the summer of 2001. PGDP is being upgraded to enrich uranium up to 5% U-235
by 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 the Tennessee 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 recirculating water processed through four sets of cooling towers.
The PGDP facilities include process buildings, four major electrical switchyards, a three-boiler steam plant, a water treatment facility, a chemical cleaning and decontamination building, the northwest groundwater treatment facility, the northeast groundwater treatment system, maintenance and laboratory facilities, two active landfills, and several inactive facilities inside a fenced security area (Figure 2) [1,7]. The steam plant provides process and comfort heating for other buildings on site. In 1974 and 1975, two boilers were converted to burn low-sulfur coal and oil instead of natural gas. The third boiler burns natural gas or oil but cannot be converted to burn coal [8,9]. The site also includes a raw-water treatment plant, a residential landfill, an inert landfill, a former sanitary landfill, two industrial treatment lagoons, and several concrete rubble piles outside the fenced area.
 Figure 1. Plant Location and Vicinity (jpg) |
 Figure 1. Plant Location and Vicinity (pdf) |
 Figure 2. Plant Map (jpg) |
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 munitions facility, the Kentucky Ordnance Works (KOW), which was operated by Atlas Powder Company until 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 treatment plant; a water treatment plant; and burning grounds. PGDP now uses the water treatment plant. In 1950, 7,556 acres (3,022 hectares) of the land east of the former KOW were acquired by the Atomic Energy Commission as a site for a uranium enrichment facility--that is, PGDP. The plant began operating in 1952, but construction was not completed until 1954. The facility reservation 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 Steam Plant 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 was
given to the newly formed U.S. Energy
Research and Development Administration,
which became DOE in 1977. DOE's primary
contractor for all operations was Martin
Marietta Energy Systems, Inc., which later
became Lockheed Martin Energy Systems (LMES) and Lockheed Martin Utility Services
(LMUS). Beginning July 1, 1993, LMUS operated and maintained PGDP under contract to the
United States Enrichment Corporation (USEC), the government-owned corporation formed by
the 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 waste
generated from the operating plant since July 1, 1993, are the responsibility of the USEC. The
U.S. Nuclear Regulatory Commission assumed oversight of these activities on March 3, 1997
[14]. DOE and LMES retained the responsibility for environmental remediation and waste
handling from activities performed prior to July 1, 1993 [2]. As of April 1, 1998, the new DOE
contractor 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 evaluate DOE NPL sites and to develop a workplan to address those sites. Some community health concerns were identified during this site visit and during ATSDR's participation in six DOE public meetings in June 1994, May 1995, July 1995, November 1996, January 1998, and July 1999 [16].
Community concerns also were identified through written correspondence, telephone conversations, informal meetings, and public availability sessions. In 1995 ATSDR solicited concerns 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 mailed to about 1,700 community members. A total of 60 people responded to this mailing. In May 1996 ATSDR held five public availability sessions in Paducah and Heath, Kentucky, to solicit additional concerns. The public availability sessions were informal and allowed citizens to discuss 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 Specific Advisory Board (SSAB) meetings and DOE technical presentations. All in all, ATSDR received about 500 community concerns. These concerns are discussed in Appendix B and in the community health concerns section later in this report. Most of the concerns relate to the incidence of cancer, the incidence of other illnesses, and the possibility of exposure through various media.
ATSDR staff members visited the site in January 1996 to discuss the ATSDR public health assessment (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 formed Site Specific Advisory Board (SSAB) and local health officials [19]. They toured the Western Kentucky Wildlife Management Area (WKWMA) with a community member and staff from Kentucky's Department of Fish and Wildlife Resources and Kentucky's Department for Environmental Protection.
ATSDR representatives visited the area in December 1996, to gather relevant demographic and land-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 to meet with various officials and residents in the area [21]. In February 1998, staff attended the SSAB meeting and the first public meeting for the Draft Programmatic Environmental Impact Statement for Alternative Strategies for the Long-Term Management and Use of Depleted Uranium Hexafluoride [22]. In July 2000, ATSDR staff attended DOE's public meeting on the Groundwater Operable Unit Feasibility Study and the SSAB meeting.
On September 11, 2000, an ATSDR representative addressed Active Citizens for Truth (ACT), a local community group, to discuss ATSDR and ATSDR's role at the PGDP site.
Demographic information characterizes the people in the communities potentially affected by the site, how long these people have lived there, and the current population trends [23]. Delineating the number of children and elderly people is particularly important, because these people tend to be more sensitive to environmental exposures than the general population [24]. Also, information on occupation, education level, poverty status, and household income can give clues to factors such as access to health care and subsistence fishing, hunting, or farming. Demographic information is essential when analyzing health outcome data and behavior patterns in a community.
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 population growth; now, however, McCracken County's population is growing [25]. The addition of new housing 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 the make-up of the population near the site. McCracken County, at 60,000 residents, has the largest population 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 the site 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 10 years of age [25]. This is unusual compared to the 1990 national averages, but not unusual for rural areas.
In the census tracts surrounding the site, approximately 70% of people 25 and older have high school diplomas, and approximately 15% are below the poverty level [28]. Over 75% of the residents 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 or private suppliers. DOE has offered to provide municipal water to some residents of western McCracken County (in an area described in DOE's Water Policy), who previously used private wells (see the groundwater section of this report). For more detailed demographic information for this 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 how people 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 the populations of these institutions tend to be elderly, sick, or very young, and consequently may be at higher risk for adverse health effects. Reviewing zoning patterns helps us understand future use 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 a state of transition. Farmlands are increasingly being subdivided for additional residential development. The area west of Paducah, along US Route 60 (Figure 1), is the site of new subdivisions. A new US Route 60 is being built to accommodate the projected heavier traffic in the corridor between Paducah (Interstate 24) and the emerging suburbs. According to a December 1997 communication with the McCracken County Planning Office, US Route 60 will not be moved near the plant entrance, but will be widened. The closest residences to the site are approximately 3,280 feet (1,000 meters) north and 3,609 feet (1,100 meters) east of the PGDP fence line [29]. The closest schools are Heath Elementary, Middle, and High Schools. These are 1.86 miles (3 kilometers) southeast of the plant. According to information obtained from Heath Elementary school, there was another school--Forestdale Elementary--1.16 miles (1.86 kilometers) southwest of the plant; that school was closed in 1981 when Heath Elementary opened (Figure 3).
According to a June 1997 communication with the West McCracken County Water District, new homes 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 those residents 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 Water nor the Purchase District Health Department routinely test existing wells; however, the health department 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 under regulation by the Division of Water. Heath Elementary, Middle, and High Schools are supplied with municipal water from the Western McCracken County Water District. The high school was put on municipal water in 1968.
 Figure 3. Property Boundaries and Other Features (jpg) |
Figure 3. Property Boundaries and Other Features (pdf) |
There are approximately 400 active farms in McCracken County, Kentucky, with 45 to 50 operating in the area near PGDP [30]. Soybeans, wheat, corn, and tobacco are the dominant crops being cultivated. Although the number of individual tobacco farms has declined, the acreage used for this crop has been steady: farms have been consolidated under fewer owners. In general, the dominant crops grown in the area are shipped to national and international markets. There are people who grow their own vegetables in the area for personal use; however, this practice (as well as cultivating specialty crops for commercial sale) is on the decline. There are approximately 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 their crops and to supply large ponds used for recreation and watering livestock. The water for these ponds is not supplied by wells. The area receives an average of 47 inches (1.19 meters) of precipitation 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 residential use 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 a privately owned steam plant in Joppa, Illinois, across the Ohio River. (The steam plants, both coal-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 of the city of Paducah. It has the largest concentration of industry in western Kentucky; however, it is 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]. This area is open to the public and is a popular location for local sports, fishing, and hunting. The WKWMA is accessible from Dyke Road, Ogden Landing Road, McCaw Road, and Woodville Road (Figure 3). Within the WKWMA are signs denoting DOE property and a fence separating the federal facility from public areas. Two families live on or within the WKWMA. One person who 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, and small mammals such as raccoons are some of the animals caught in the area. Most community members 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 users tend 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 associated with past activities still exist. The former KOW's remedial investigation and cleanup are being managed by the U.S. Army Corp of Engineers (USACE) [16]. Some of the old bunkers have been used for hunting clubs, dog pens, and horse barns. Six ponds (or gravel pits), which are used for fishing, are part of the USACE's investigation and cleanup. Mercury advisories are posted at Fire Hydrant Pond, Horseshoe Pond, New Pond, Box Factory, and Gravel Pit #1 for largemouth bass [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, which takes place in the spring. On Earth Day, large groups of preteens gather to learn about nature and the 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 sea level--on a drainage divide between Big Bayou and Little Bayou Creeks [13]. Both creeks flow north to the Ohio River, and receive surface water discharges from the plant. When the TVA Shawnee 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]. Big Bayou Creek flows past a residential area to the west of the plant and overflows into people's fields during times of flooding. Channel catfish and bluegill appear in Big Bayou only when it is filled with backwater from the Ohio River, and fishing occurs occasionally. Little Bayou Creek is an intermittent stream on the eastside of the plant. Little flow occurs in Little Bayou Creek except for effluent from the plant [8,9]. Fishing does not normally occur in this creek. Warning signs for polychlorinated biphenyl (PCB) contamination in fish are posted at access areas along this creek, and these areas are partially fenced off. Fences and "No Trespassing" signs are present at 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 for recreational purposes. These surface water bodies are located approximately 3 miles (4.8 kilometers) north and northeast of PGDP, respectively. Metropolis Lake connects to the Ohio River and is part of a nature reserve. There is a warning issued against eating bass, carp, channel catfish, paddlefish and paddlefish eggs caught in the Ohio River due to chlordane and PCB contamination. Recently, a fish advisory was issued for Metropolis Lake due to mercury and PCB contamination.
At PGDP, the wind predominantly comes from the south-southwest, at an average speed of 14.4 feet per second (4.4 meters per second) [8,9,31]. The monthly average temperatures vary from 34oF (1oC) during January to about 77oF (26oC) in July. The average annual temperature is 59oF (14oC).
ENVIRONMENTAL CONTAMINATION, EXPOSURE PATHWAYS, AND POTENTIALLY EXPOSED POPULATIONS
This section discusses the various chemicals and radioactive materials (contaminants) evaluated for this site, how people may come into contact with them, and what populations are potentially exposed. These discussions are presented for groundwater, air, surface water, soil and sediment, and food and biota.
A release of a chemical or radioactive
material from a site does not always mean
that this substance will be a contaminant of
health concern to an off-site population.
ATSDR scientists first determine if a
chemical or radioactive substance in water,
air, soil, or biota (plants and animals) should
be considered a "contaminant of concern."
The criteria we use include (1) environmental levels exceeding media-specific comparison
values, (2) noted community health concerns, and (3) the quality and extent of the sampling data
we 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 these
substances occur naturally. For chemicals, the highest environmental concentration detected off
site is compared with media-specific comparison values to determine if further evaluation is
warranted. Generally, if a contaminant's concentration exceeds one or more media-specific
comparison values, then the contaminant is evaluated further in this section and in the public
health 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 in human exposure. For an exposure to occur, a completed exposure pathway must exist. A completed exposure pathway exists when all of the following five elements are present: (1) a source of contamination, (2) an environmental medium through which the contaminant is transported, (3) a point of human exposure, (4) a route of human exposure, and (5) an exposed population. 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 is considered 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 information indicates that human exposure is unlikely to occur [23]. Figure 4 illustrates the necessary components of an exposure pathway.
Figure 4. Pathways To Exposure From Contamination
In addition, for each exposure pathway, ATSDR scientists identify whether releases of contaminants and exposures are likely to have occurred in the past, currently, or potentially in the future. All releases from the uranium process facilities have dramatically decreased since the first 10 years of plant operation; however, releases from other sources such as landfills and spill areas have increased.
This section also discusses potential hazards created by the storage of about 40,351 depleted uranium cylinders in outdoor cylinder yards. (Of these cylinders, 28,351 came from DOE and about 12,000 came from the U.S. Enrichment Corporation, or USEC.)
In this report, "on-site contamination and releases" describes contamination and releases of material 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-site contamination" describes environmental media (soil, sediment, surface water, groundwater, air, or biota) that are contaminated as a result of chemical or radioactive contaminants leaving the site and are no longer being controlled by DOE or USEC. In this report, on-site sources of contamination are being considered only as sources of off-site contamination or for their impact on the community. (The impact of potential exposures to contaminants by workers is being studied by other organizations.)
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 µg/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 families living north of the facility were exposed to contamination prior to the August 1988 action. Since very little measured data exist to support the evaluation of public health effects for past exposures (prior to 1988), evaluation of past exposures is based on predicted or estimated contaminant concentrations and exposure durations. There is also potential for future exposures if contaminated groundwater migrates into areas not covered by DOE's Water Policy supply program 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 is generally toward the north, with presumed discharge into the Ohio River or Big Bayou Creek immediately south of the Ohio River [37]. The aquifer is 10 to 40 feet (3 to 12 meters) thick and composed of very permeable sands and gravels. The RGA is the source of drinking water for residents with drilled wells in the PGDP area. In 1990, approximately 8% of the homes in McCracken County and 9% of the homes in Ballard County relied on privately drilled wells for their drinking water. In the census block group that includes PGDP, 24% of the houses relied on privately drilled wells [28].
The McNairy formation underlies the RGA. Water-bearing zones within the McNairy formation occur within sand layers interspersed in a relatively thick sequence of clays. Sandy units of the upper McNairy formation may make up the lowermost portion of the RGA in areas north of the PGDP facilities. Also, erosion of clay in the vicinity of PGDP allows interaction of the RGA with the McNairy and presents the potential for RGA contaminants to move into the McNairy formation [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 discharge into the Ohio River [38]. The Kentucky Department for Environmental Protection analyzed samples 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 are above 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 land surface in other areas [7]. Water flow in the shallow units is predominantly downward into the RGA, 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 the RGA for areas south of the site, with a transition to discharge from the RGA to surface waters north of the site [7].
Contaminants entered the groundwater as a
result of several processes: (1) disposal
practices (e.g., oil landfarming), (2)
accidental releases or spills (e.g., cylinder
leaks and ruptures, cylinder drop test area,
C-400 waste system leak), and (3) indirect
leaching from buried waste materials (e.g.,
C-749 uranium burial ground, C-404 low-level radioactive waste burial ground). Table 1 gives a
description and brief history of these sources. Several site-wide investigations have been
conducted, and additional characterization and remediation of the contaminant source areas are
currently ongoing.
Releases of contaminants into the groundwater varied widely over time and happened throughout the operating history of the plant. Leaching from disposal areas occurred over time, because buried drums and containers decompose slowly. There are now three groundwater contaminant plumes: the northwest plume, the northeast plume, and the southwest plume. Each plume has several sources; therefore, it is not possible to establish a specific time of origin for the plumes based on times of contaminant releases.
Several source control or interim remedial actions have been established to reduce contaminant migration from the site. These actions include (1) capping source areas with impermeable covers and (2) establishing extraction and treatment systems to remove contaminants from groundwater. The northwest plume treatment system was established in 1995, the northeast plume treatment system 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 from the PGDP site have migrated in the northwest plume to the TVA plant. However, groundwater concentrations of arsenic, cadmium, chromium, lead, and uranium 238 at the TVA site are higher than concentrations in the northwest plume, and these contaminants were detected at the TVA plant before the PGDP plume reached the plant. Because these contaminants are the same as those detected at PGDP and are present in the same environmental media, they will be evaluated through 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-404 underground transfer line/26, C-403 neutralization tank/40, C-400 Tc-99 storage tank/47, C-400 sump/203; C-400 south end storm sewer | Facility maintenance area; leak in waste processing lines and sump--repaired 1986 | TCE DNAPL (up to 890,000 µg/L in UCRS), Tc-99, 1,2-DCE, PCE, total PAHs, chromium |
| C-746-A septic system/196 | Sinks, showers, toilets, and floor drains; system was used from 1958 to 1980; contaminants probably released into drains | Heavy metals, radionuclides, possible TCE |
| C-745-B Cylinder drop test area/91 | TCE-based slush bath used to chill UF6 cylinders for shock tests; tests conducted in 1979 | TCE DNAPL (up to 160,000 µg/L in UCRS), 1,2-DCE, 1,1,1-TCA, PCE, chloroform |
| C-749 Uranium burial ground/2 | Burial 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 30 | Burial ground in the northwest corner inside the security fence | TCE |
| Southwest Plume2 Contaminant Source/SWMU | Source Description/History | Contaminants |
| C-747-C oil landfarm/1; C-747-C contaminated burial yard/4 | Landspreading of contaminated waste oil; site operated 1973-1979 | Petroleum products, TCE, 1,1,1-TCA, uranium, PCBs |
| C-720 Building and storm sewer | Maintenance facility | TCE, Tc-99 |
| C-740 TCE spill site/136 | TCE spill site | TCE |
| Northeast Plume3 Contaminant Source/SWMU | Source Description/History | Contaminants |
| C-745 Kellog building Site/99 | Building used for pipe fabrication during plant construction (1951-1956); extensive use of TCE; building demolished in 1956 | TCE, 1,1-DCE, low concentrations of Tc-99 |
| C-400 area/40 (C-403 neutralization tank) | Possible leak from tank or transfer line | TCE (up to 11,000 µg/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, respectively | Site 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 the Commonwealth of Kentucky, were screened to determine contamination concentrations and distributions. These databases were transferred electronically and checked for completeness and consistency. Incomplete or missing records that could not be corrected with supporting documents or communications with site personnel were not used in the screening process. Electronic data were supplemented with published documents.
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 comparison
values).
The second phase of screening was to determine whether the groundwater contaminants are present or potentially present in residential wells. Thirty of the forty-seven contaminants have been found in off-site groundwater wells where exposure to the community is possible. Table 2 provides information about these contaminants, the number of samples analyzed, the number of samples with positive detections, and maximum concentrations detected in off-site wells. Note that inclusion of a substance in Table 2 does not mean that anyone was exposed to that substance.
The third phase of screening involved comparing maximum concentrations of off-site groundwater contaminants in areas of potential exposure with their respective comparison values. Contaminant concentrations below these comparison values are not expected to cause adverse health effects following exposure. For contaminant concentrations above comparison values, ATSDR evaluated potential or documented exposures and public health implications.
Table 2. Off-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 µg/L | Background Range in µg/L |
| Arsenic | 77 | 9 | 90 | ND-10 |
| Beryllium | 41 | 7 | 40 | 10 |
| Cadmium | 35 | 1 | 10 | NT |
| Chromium | 82 | 44 | 270 | ND-70 |
| Fluoride | 20 | 20 | 550 | NT |
| Lead | 67 | 40 | 290 | 10 |
| Nickel | 110 | 42 | 210 | ND-140 |
| Nitrate | 35 | 34 | 21,800 | NT |
| Sulfate (dissolved and total) | 70 | 69 | 743,000 | 1,200 |
| Sulfide (dissolved and total) | 63 | 17 | 5,160 | ND |
| Thallium | 9 | 0 | (detection limit = 10) | NT |
| Vanadium | 37 | 30 | 210 | 10-170 |
| Zinc | 122 | 77 | 5,090 | 10-330 |
| Organic Compounds | Number of Off-Site Samples | Number of Off-Site Detects | Off-Site Maximum Concentration in µg/L | Background Range in µg/L |
| Bis(2-ethylhexyl)phthalate | 106 | 13 | 300 | (lab contaminant) |
| Bromodichloromethane | 435 | 2 | 16 | ND |
| Carbon tetrachloride | 438 | 3 | 8 | ND |
| Chloroform | 438 | 6 | 56 | ND |
| 1,2-Dichloroethane | 436 | 1 | 57 | ND |
| 1,1-Dichloroethene | 438 | 2 | 13 | ND |
| 1,2-Dichloroethene1 | 733 | 4 | 18 | ND |
| Methylene chloride | 142 | 1 | 27 | ND |
| Pentachlorophenol | 91 | 1 | 8 (residential detection limit = 50) | ND |
| Tetrachloroethylene | 438 | 1 |
1 |
ND |
| Trichloroethylene | 5,698 | 1,091 |
167,000 |
ND |
| Vinyl chloride | 438 | 2 |
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 | 3862 | 3842 | 1,855 (68.7) | NA3 |
| Technetium 99 | ~5,000 | 898 |
5,804 (215) |
<25 (<0.93) |
| Uranium 234 | 139 | 80 |
24 (0.9) |
<2 (<0.07) |
| Uranium 235 | 119 | 3 |
3 (0.1) |
<1 (<0.04) |
| Uranium 238 | 140 | 120 |
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, µg/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 of off-site detections above the comparison value. For each contaminant, the table indicates which wells had maximum concentrations exceeding comparison values and presents the range of maximum concentrations in these wells. Residential wells are denoted with an "R" or "RW" well number. Few contaminants were detected in residential wells; however, only a few chemicals were tested for in residential well samples. Therefore, for screening purposes, we assumed that contaminants 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 of concern and explains why we excluded these contaminants from further evaluation.
When a contaminant's maximum concentration exceeded a comparison value, that contaminant was considered a possible contaminant of concern. Other criteria used to select contaminants were (1) the frequency and location of detections (e.g., single detections are not reliable indicators 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 the latter, bis(2-ethylhexyl)phthalate was frequently detected above its comparison value in off-site groundwater samples. This contaminant is not a constituent of the PGDP process operations or waste products, but it is a common constituent of the plastic gloves and sampling equipment used in field sampling. It was detected with similar frequency in on-site, off-site, and background samples. For these reasons, positive detections were interpreted as an artifact of the sampling and laboratory processes. Bis(2-ethylhexyl)phthalate was not selected as a contaminant of concern for this exposure pathway.
Of the 30 off-site groundwater contaminants detected in areas of potential exposure, 15 contaminants either were found at levels of potential health concern or, because of inadequate analysis, could be present at levels of health concern. Fifteen off-site contaminants, for which adequate analyses have been conducted, are not considered contaminants of concern based on contaminant concentrations, distribution, and frequency of detection. The rationale for selection or exclusion is listed in Tables 3 and 4.
Beryllium, cadmium, nickel, sulfate, and zinc each had only one off-site measurement above their comparison values (as shown in Table 3). Beryllium, cadmium, nickel, and sulfate were only detected in wells near the TVA plant and the Ohio River, and no elevated concentrations for these contaminants were measured in the groundwater plumes between the PGDP facility and the TVA plant. Beryllium, nickel, and sulfate are not contaminants of concern in groundwater due to their low overall frequency of detection, their maximum concentrations, and the limited potential for exposure. Cadmium, thallium, pentachlorophenol, and vinyl chloride were selected as contaminants of concern for this exposure pathway, because analytical detection limits were greater than their respective comparison values. Zinc was measured above its comparison value only once off site, but the sample was taken from a residential well; therefore, zinc was selected as 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 respective comparison values (as shown in Table 3). Maximum concentrations of chromium and vanadium were not above comparison values in the residential wells tested for these contaminants; however, the concentrations were above comparison values in monitoring wells near untested residential wells.
Uranium (as a chemical)(1) was detected in six off-site wells. The uranium concentration exceeded EPA's 1991 proposed maximum contaminant level (MCL)--20 micrograms per liter (µg/L)--in only one well (MW-135; 24 µg/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 the MCL was not repeated in subsequent analyses, uranium metal (i.e., uranium as a chemical) is not a contaminant of concern in groundwater. (Note: EPA's National Primary Drinking Water Regulations 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. Because there is no accepted comparison value for Rn-222 in drinking water, ATSDR converted the groundwater concentration into a potential airborne dose using EPA's recommended procedures for determining potential radon gas concentrations in residential air. According to these calculations, the highest potential air concentrations in a home are less than EPA's recommended action 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, and assuming that a person ingests 2 liters of contaminated water per day, we calculated a whole body committed effective dose:(2) 50 millirems (or 0.5 millisieverts). This is less than a typical background dose from naturally occurring radon. Therefore, Rn-222 was not selected as a contaminant 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 as contaminants of concern.
Contaminants of concern in the groundwater exposure pathways are discussed further in the next section. Contaminants that were detected on site and/or off site but were not considered in the initial screening (17 of the original 47 chemicals, compounds, and elements in Table 2) are listed in Table 4 with the reasons why they were not considered. The contaminants listed in Table 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 µg/L |
Number of Off-Site Detects Above CV | Wells With Detections Above CVs | Maximum Concentration Range in µg/L | Selected as Contaminant of Concern? Why? |
| Arsenic | 3 (Chr.EMEGc) | 9 | MWD-009, -025; MW-121, -143, -150, -192; RW-004, -294; TVA-04 |
7 to 90 | Yes, above CV |
| Beryllium | 20 (Chr.EMEGc) | 1 | MWD-014 | 40 | No, one off-site detection > CV and no exposure |
| Cadmium | 2 (Chr.EMEGc) | 1 | MWD-014 | 10 | Yes, all DLs > CV |
| Chromium | 30 (Chr.RMEGc for hexavalent) 100 (MCL for trivalent) |
28 | MWD-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 270 | Yes, above CV |
| Fluoride | 600 (Chr.EMEGc) | 0 | 550 | No, less than CV | |
| Lead | 15 (Action Level) | 16 | MWD-014, -019, -024, -025; MW-121, -123, -200, -202; RW-004, -113, -297; TVA-04, -27 |
20 to 290 | Yes, above CV; also, non-detects have DLs > CV |
| Nickel | 200 (Chr.RMEGc) | 1 | MWD-014 | 210 | No, one off-site detection > CV and no exposure |
| Nitrate (dissolved and total) | 20,000 (Chr.RMEGc) | 2 | RW-156; RW-294 | 21,800 to 29,200 | Yes, above CV |
| Sulfate (dissolved and total) | 500,000 (MCL) | 1 | TVA-25 | 743,000 (dissolved) | No, one off-site detection > CV and no exposure |
| Sulfide (dissolved and total) | 500,000 (MCL) | 0 | 5,160 | No, less than CV | |
| Thallium | 2 (MCL) | All DLs > CV | NA | Lowest residential well DL = 10 | Yes, all DLs > CV |
| Vanadium | 30 (Int.EMEGc) | 24 | MWD-009, -014, -019, -024, -025, -027; MW-121, -123, -125, -142, -149, -153, -194, -195,-199,-200,-202; TVA-04, -27 |
30 to 210 | Yes, above CV |
| Zinc | 3,000 (Chr.EMEGc) | 1 | RW-113 | 5,090 | Yes, single detect in residential well |
| Organic Compounds | CV1 (CV Source) in µg/L |
Number of Off-Site Detects Above CV | Wells With Detections Above CVs | Maximum Concentration Range in µg/L | Selected as Contaminant of Concern? Why? |
| Bis(2-ethylhexyl)phthalate | 6 (MCL) | 11 | MWD-003, -005, -019; MW-121, -125, -133, -143, -191; RW-021; RW-294 | To 300 | No, artifact of collecting and sampling |
| Bromodichloromethane | 100 (MCL) | 0 | 16 | No, less than CV | |
| Carbon tetrachloride | 70 (Int.EMEGc) | 0 | 8 | No, less than CV | |
| Chloroform | 100 (Chr.EMEGc) | 0 | 56 | No, less than CV | |
| 1,2-Dichloroethane | 2,000 (Int.EMEGc) | 0 | 57 | No, less than CV | |
| 1,1-Dichloroethene | 90 (Chr.RMEGc) | 0 | 13 | No, less than CV | |
| 1,2-Dichloroethene (includes cis- and trans-) | 2,000 (Int.EMEGc) | 0 | 18 | No, less than CV | |
| Methylene chloride | 2000 (Chr.EMEGc) | 0 | 27 | No, less than CV | |
| Pentachlorophenol | 10 (Int.EMEGc) | DLs > CV | NA | Lowest residential well DL = 50 | Yes, DLs for residential wells above CV |
| Tetrachloroethylene | 100 (Chr.RMEGc) | 0 | 1 | No, less than CV | |
| Trichloroethylene |
5 (MCL) |
722 |
Many wells | Up to 167,000 | Yes, above CV |
| Vinyl chloride |
0.2 (Chr.EMEGc) |
2 |
MW-97 | 54 to 110 | Yes, above CV and DL for wells in plume above CV |
| Radioactive Contaminants |
CV in pCi/L (Bq/L) |
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 wells3 | 328 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-261 | 5,125 to 5,804 (190 to 215) |
Yes, above CV |
| Uranium 234 |
15; 30 total U6 |
2 |
MW-141, MW-148 | 17 and 24 (0.6 to 0.9) |
Yes, above CV |
| Uranium 235 |
15; 30 total U6 |
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 |
3 |
MWD-009; MW-141; TVA-14 | 17 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; µg/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]
| Contaminant | Maximum Concentration (in µg/L) | Number of Detections | Comments |
| Arsenic, dissolved | 20 | 16 | Considered contaminant as total arsenic (non-reproducible results as dissolved) |
| Benzene | 12 | 4 | No off-site detections (only on site) |
| Boron | 1,540 | 34 | No off-site detections (only on site) |
| Cadmium, dissolved | 20 | 7 | Considered contaminant as total cadmium (non-reproducible results as dissolved) |
| Chloromethane | 180 | 4 | No off-site detections (only on site) |
| 2-Chlorophenol | 73 | 1 | Single on-site detection; no off-site detections |
| Chromium, dissolved | 110 | 35 | Considered contaminant as total chromium (non-reproducible results as dissolved) |
| 2,4-Dinitrotoluene | 28 | 1 | Single on-site detection; no off-site detections |
| Lead, dissolved | 80 | 22 | Considered contaminant as total lead (non-reproducible results as dissolved) |
| n-Nitroso-di-n-propylamine | 35 | 1 | Single on-site detection; no off-site detections |
| Nickel, dissolved | 660 | 104 | Considered contaminant as total nickel (non-reproducible results as dissolved) |
| Nitrate, nitrite | 68,600 (on site) | 414 | Considered contaminant as nitrate |
| PCB (Aroclor 1254) | 1 | 1 | Single on-site detection; no off-site detections |
| 1,1,1-Trichloroethane | 16 | 7 | No off-site detections (only on site) |
| Uranium (as a chemical) | 90 | 29 | Not tested off site as chemical (Analyzed as U-234, U-235, and U-238) |
| Vanadium, dissolved | 70 | 15 | Considered contaminant as total vanadium (non-reproducible results as dissolved) |
| Zinc, dissolved | 37,400 | 15 | Considered contaminant as total zinc (non-reproducible results as dissolved) |
| Key: µg/L = micrograms per
liter; PCB = polychlorinated biphenyl; U-234, U-235, and U-238 = uranium 234, uranium 235, and uranium 238 |
|||
ATSDR scientists identified completed and potential human exposure pathways for past, current, and potential future exposure to contaminants of concern in groundwater. In addition, we estimated human exposure doses for contaminants in these exposure pathways. In the public health implications section, we discuss potential health hazards from exposure to contaminants of concern at the estimated doses.
Currently, off-site residents are not being
exposed to groundwater contamination
originating from the PGDP site. Former
residential wells within the northwest and
northeast plumes either are used to monitor
contaminant distributions or have been plugged using procedures approved by EPA and the
Kentucky Department for Environmental Protection [52]. Although contaminated groundwater
from the northwest plume may be discharging into the Ohio River or the portion of Big Bayou
Creek directly adjacent to the Ohio River, the concentrations at those locations do not exceed
comparison values [37]. Therefore, there are no exposure pathways identified for current
exposure to groundwater contaminants from the site.
Prior testing of private wells in the PGDP area revealed contamination by lead. Of the 12 residential wells tested for lead, three were above the EPA action level of 15 µg/L [53,54,45,46,47,48]. One of these wells was at a horse barn and was not a private residence's primary 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 longer used 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 concerned about the possibility of lead contamination in their drinking water may wish to have their water tested. A list at the end of the community health concerns section of this report provides names and phone numbers for persons to contact at the local health department. Additional information is available from EPA's Safe Drinking Water Hotline at 1-800-426-4791. As a general precaution, EPA recommends running taps for 30 seconds to 2 minutes before using the tap water. Possible adverse health effects from exposure to lead in drinking water are discussed in the public health implications section of this report.
Off-site residential wells in the northeast plume area were plugged or converted to monitoring wells before contaminant concentrations exceeded comparison values. Therefore, no completed exposure 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 in
August 1988. At that time, these were the only contaminants measured in these wells; however,
well samples collected after 1988 indicate
that other contaminants may have been
present in the northwest plume along with
TCE and Tc-99. Arsenic, lead, nitrate, and
zinc were detected in samples from
residential wells after 1988, although they
may not be related to the northeast and
northwest plumes. Therefore, TCE, Tc-99,
arsenic, lead, nitrate, and zinc are
contaminants of concern for past exposure
via completed exposure pathways for
groundwater. 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 other chemicals or metals (cadmium, chromium, fluoride, and vanadium) were detected in monitoring wells at maximum concentrations that exceeded comparison values. Analyses for these contaminants were not performed for most residential well samples. Because residential wells may have contained cadmium, chromium, fluoride, pentachlorophenol, thallium, vanadium, or vinyl chloride, they are contaminants of concern for past exposure via potential exposure pathways. Potential exposure pathways are described in Table 6.
Two radioactive contaminants, U-234 and U-238, were detected in off-site monitoring wells. The samples were collected in the deep RGA. Maximum concentrations exceeded EPA's drinking water standard. Although these results were not repeated and these contaminants were not detected in residential wells, U-234 and U-238 were detected in on-site groundwater and are considered contaminants of concern for past exposure via potential exposure pathways for groundwater. (Refer to Table 6.)
After the initial discovery and mapping of the northeast and northwest plumes, an additional groundwater contaminant plume, called the southwest plume, was identified from new source characterization and monitoring wells. The current mapped distribution of the southwest plume is largely inside the fenced security area on the west side of the plant property and entirely within the DOE property boundary. There are no residential drinking water wells within the past or current area of the southwest plume. Therefore, there are no exposure pathways identified for past or current exposure to contaminants in the southwest plume.
Because sampling and analysis data are not available for times before 1988; therefore, ATSDR scientists used measurements of TCE migration rates for 1988 through 1995 to estimate the duration 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 contaminated with TCE above the comparison value (5 µg/L) before 1988. Evaluation of contaminant transport rates indicate that TCE concentrations were estimated to be greater than 100 µg/L for 5 to 15 years prior to 1988. Concentrations less than 100 µg/L may have been present in these wells for a longer period; however, that period's duration cannot be estimated with certainty. Therefore, we assumed an exposure duration of 5 to 15 years for all contaminants in the wells associated with the northwest plume. In evaluating contaminant transport, we assumed a concentration of 100 µg/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 pathways are estimated using assumptions about who may have been exposed, how they may have been exposed, how long their exposures lasted, and how often they were exposed. We assumed that ingestion was the primary route of exposure for this exposure pathway, although inhalation and skin contact for some contaminants were secondary exposure routes. Studies have shown that volatile 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 the ingested dose [57]. As a conservative estimate, ATSDR scientists assumed that ingestion doses for volatile organic compounds, TCE, and vinyl chloride would increase 70% from inhalation and 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 who weighs 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 µg/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 pathways exist for contaminants in the northeast and northwest plumes, and possibly the McNairy Aquifer and the southwest plume.
For the northeast plume, the primary contaminant of concern is TCE. Also, chromium has recently been detected in several wells northeast of the site property. Although other contaminants (such as Tc-99 and arsenic) have been detected in the northeast plume, they have not migrated off site at concentrations exceeding health comparison values. The northeast plume is migrating to the northeast and is close to the eastern boundary of the Water Policy-affected area (Metropolis Lake Road), as Figure 7 shows. Although a groundwater extraction and treatment system was established for this plume in August 1997, contaminants at the leading edge 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) DOE is continuing to monitor the movement of the northeast plume. DOE has indicated that they will expand the boundaries of the Water Policy area if ongoing monitoring indicates that additional wells may become contaminated [36]. If the plume migrates outside the water policy boundary and contaminated wells are capped using approved procedures, no exposure will occur.
Residents who have been provided with municipal water have agreed not to drill additional wells; however, new residents or new landowners in the area are not restricted from drilling new wells within the area of groundwater contamination. Therefore, there is a potential for future exposure if new wells are drilled into the northeast or northwest contaminant plumes.
The southwest plume was recently characterized. There is no current completed exposure pathway for this plume. Its future migration direction is unknown. The plume may turn north and join with the northwest plume.
The McNairy Aquifer also represents a potential source for future human exposure. Low concentrations 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 in Illinois presents a limited potential for exposure. In order for this exposure pathway to be completed, contaminants must migrate from the RGA into the McNairy Aquifer and then flow under the Ohio River to public supply wells. TCE and Tc-99 have been detected in McNairy wells (TCE in MW-114, MW-121, and MW-128; Tc-99 in all wells, including the background well MW-140). Contaminant concentrations are low: one TCE sample was above the comparison value (the sample had TCE at a concentration of 9 µg/L). According to available data, the well from which this sample was taken (MW-114) has not been re-sampled.
Continued monitoring of contaminants in the northeast, northwest, and southwest plumes is necessary until these flow systems are well defined and the effects of the extraction and treatment systems or other remedial techniques are known. ATSDR will re-evaluate this exposure pathway if future monitoring results indicate a potential for human exposure to groundwater contaminants.
DOE contractors are currently performing pilot studies for various technologies that might be able to remediate the groundwater aquifer. Several options and combinations of options have been presented to the public, along with estimated costs and timeframes [42]. No matter what options are chosen, the remediation will probably take a very long time.
Figure 5. TCE Concentrations in Residential Wells
Figure 6. Tc-99 Concentration in Residential Wells
 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 Sources | Contaminants | Exposure Point | Exposure Route | Exposed Persons | Period of Time and Duration | Maximum Estimated Exposure Doses 1 |
| Leaching of contaminants from disposal practices, accidental releases or spills, and buried waste materials to the Regional Gravel Aquifer | TCE2 (960 µg/L) |
Residential wells drilled into northwest plume in RGA | Ingestion (TCE includes inhalation and skin absorption) | Children and adults using RW-002, RW-017, and RW-113 (RW-004 at horse barn) | 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) | |||||
| Arsenic | Two residential wells | Ingestion | Children and adults using 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 |
|
| Lead | Residential wells northwest of site | Ingestion | Children and adults using RW-113 and RW-297 (RW-004 at horse 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) | |
| Nitrate | Three residential wells | Ingestion | Children using RW-002, RW-030, and RW-294 | Past only Wells no longer in use; exposure duration unknown |
Nitrate: Children 1.69 mg/kg/d Adults 0.63 mg/kg/d |
|
| Zinc | One residential well | Ingestion | Children and adults using RW-113 | Past 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: µg/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 1 | Arsenic
Cadmium Chromium Thallium Vanadium Pentachloro- Vinyl Uranium 234 Uranium 238 |
Residential wells northwest, north, and northeast of site | Ingestion | Children and adults living in houses in these areas with drilled wells | Potential past and future | Arsenic: Children 0.007 mg/kg/d Adults 0.003 mg/kg/d Cadmium: Chromium: Children 0.021 mg/kg/d Thallium: Vanadium: Pentachlorophenol: Children 0.0039 mg/kg/d Vinyl chloride: Children 0.017 mg/kg/d Uranium 234 (for annual intake): Children 2.9 mrem (0.029 mSv) Uranium 238 (for annual intake): Children 2.6 mrem (0.026 mSv) |
| Lead2 | Residential wells north and northwest of site | Ingestion | < |
