Skip directly to search Skip directly to A to Z list Skip directly to site content

PUBLIC HEALTH ASSESSMENT

PADUCAH GASEOUS DIFFUSION PLANT (U.S. DOE)
PADUCAH, MCCRACKEN COUNTY, KENTUCKY


ENVIRONMENTAL CONTAMINATION, EXPOSURE PATHWAYS AND POTENTIALLY EXPOSED POPULATIONS

Introduction

This section discusses the various chemicals and radioactive materials (contaminants) evaluated forthis 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 andbiota.

ATSDR scientists evaluate chemicals and radioactive materials that exist in off-site media (groundwater, surface water, air, soil/sediment, and food/biota) where humans can be exposed. Not all contaminants from the site are at levels that pose a health hazard.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 a chemicalor radioactive substance in water, air, soil, orbiota (plants and animals) should be considereda "contaminant of concern." The criteria weuse include (1) environmental levels exceeding media-specific comparison values, (2) notedcommunity health concerns, and (3) the quality and extent of the sampling data we can use toevaluate potential exposure and human health hazard. For inorganic compounds (metals) andradionuclides, background values may also be considered, since some of these substances occurnaturally. For chemicals, the highest environmental concentration detected off site is compared withmedia-specific comparison values to determine if further evaluation is warranted. Generally, if acontaminant's concentration exceeds one or more media-specific comparison values, then thecontaminant is evaluated further in this section and in the public health implications section. (Refer toAppendix C for a description of comparison values.)

A release of a chemical or radioactive material into the environment does not always result in humanexposure. For an exposure to occur, a completed exposure pathway must exist. A completedexposure pathway exists when all of the following five elements are present: (1) a source ofcontamination, (2) an environmental medium through which the contaminant is transported, (3) apoint of human exposure, (4) a route of human exposure, and (5) an exposed population. A potentialexposure pathway exists when one or more of the elements is missing, but available informationindicates that human exposure is possible. Also, an exposure pathway is considered potential whenmodeled data are used to predict human exposure. An incomplete exposure pathway exists whenone or more of the elements is missing and available information indicates that human exposure isunlikely to occur [24]. Figure 3 illustrates the necessary components of an exposure pathway.

Pathways to exposure from contamination
Figure 3. Pathways to exposure from contamination

In addition, for each exposure pathway, ATSDR scientists identify whether releases of contaminantsand exposures are likely to have occurred in the past, currently, or potentially in the future. Allreleases from the uranium process facilities have dramatically decreased since the first 10 years ofplant 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 uraniumcylinders in outdoor cylinder yards. (Of these cylinders, 28,351 were generated by DOE and about12,000 were generated by the U.S. Enrichment Corporation, or USEC.) Since USEC is still operatingthis plant, these numbers may vary with time.

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-site contamination"describes environmental media (soil, sediment, surface water, groundwater, air, or biota) that arecontaminated as a result of chemical or radioactive contaminants leaving the site and are no longerbeing controlled by DOE or USEC. In this report, on-site sources of contamination are beingconsidered only as sources of off-site contamination or for their impact on the community. (Theimpact of potential exposures to contaminants by workers is being studied by other organizations.)

Groundwater

Background and Site Hydrogeology

In August 1988, contamination by trichloroethylene, an organic solvent, and technetium 99, a beta-emitting radionuclide, were detected in four residential wells north of the PGDP boundary.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 [37]. 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 [38].

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. Since verylittle measured data exist to support the evaluation of public health effects for past exposures (prior to1988), evaluation of past exposures is based on predicted or estimated contaminant concentrationsand exposure durations. There is also potential for future exposures if contaminated groundwatermigrates into areas not covered by DOE's Water Policy, if future property owners drill new wellsinto the contaminated groundwater plumes, or if DOE does not renew their water policy andlandowners go back to using private wells in the area.

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 Bayou Creekimmediately south of the Ohio River [38]. 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 for theirdrinking water. In the census block group that includes PGDP, 24% of the houses relied on privatelydrilled wells [29].

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 the upperMcNairy formation may make up the lowermost portion of the RGA in areas north of the PGDPfacilities. Also, erosion of clay in the vicinity of PGDP allows interaction of the RGA with theMcNairy and presents the potential for RGA contaminants to move into the McNairy formation [39].Flow within the McNairy formation is north to northeast from the PGDP site. The McNairyformation is used as a drinking and industrial water source north of the Ohio River. According toanalysis of hydraulic gradients in the McNairy formation, flow should discharge into the Ohio River[39]. The Kentucky Department for Environmental Protection analyzed samples taken north of theOhio River, and did not detect contaminants characteristic of PGDP.

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

Contaminants entered the groundwater system as a result of several processes: (1) disposal practices, (2) accidental releases and spills, and (3) indirect leaching from buried waste material.Contaminants entered the groundwater as aresult of several processes: (1) disposalpractices (e.g., oil landfarming), (2) accidentalreleases or spills (e.g., cylinder leaks andruptures, cylinder drop test area, C-400 wastesystem leak), and (3) indirect leaching fromburied waste materials (e.g., C-749 uraniumburial ground, C-404 low-level radioactive waste burial ground). Table 1 gives a description andbrief history of these sources. Several site-wide investigations have been conducted, and additionalcharacterization and remediation of the contaminant source areas are currently ongoing.

Releases of contaminants into the groundwater varied widely over time and happened throughout theoperating history of the plant. Leaching from disposal areas occurred over time, because burieddrums and containers decompose slowly. There are now three groundwater contaminant plumes: thenorthwest 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 ofcontaminant 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 covers and(2) establishing extraction and treatment systems to remove contaminants from groundwater. Thenorthwest plume treatment system was established in 1995, the northeast plume treatment system in1997.

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 thePGDP 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 TVA plantbefore the PGDP plume reached the plant. Because these contaminants are the same as those detectedat 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 [40,41,7]
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-400 sump/203;C-400 south end storm sewerFacility maintenance area; leak in waste processing lines and sump--repaired1986TCE 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 1958 to 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 contaminated burialyard/4Landspreading of contaminated waste oil; site operated 1973-1979 Petroleum 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/SWMU Source Description/History Contaminants
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 line TCE (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: [42,43]
2 Source: [43]
3 Source: [43,44]
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 supporting documents orcommunications with site personnel were not used in the screening process. Electronic data were supplemented with published documents.

Contaminants of Concern

Groundwater contaminants evaluated further are those substances found in off-site groundwater wells at levels that exceed media-specific comparison values and where exposure to the off-site community is possible.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 presentor potentially present in residential wells. Thirty of the forty-seven contaminants have been found inoff-site groundwater wells where exposure to the community is possible. Table 2 providesinformation about these contaminants, the number of samples analyzed, the number of samples withpositive detections, and maximum concentrations detected in off-site wells. Note that inclusion of asubstance 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 groundwatercontaminants in areas of potential exposure with their respective comparison values. Contaminantconcentrations below these comparison values are not expected to cause adverse health effectsfollowing exposure. For contaminant concentrations above comparison values, ATSDR evaluated potential or documented exposures and public health implications.

Table 2.

Off-site groundwater contaminants [45,46,47,48,49]
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
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 g/L Background Range in g/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: [46,47,48]
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 of off-site detections above the comparison value. For each contaminant, the table indicates which wells hadmaximum concentrations exceeding comparison values and presents the range of maximumconcentrations in these wells. Residential wells are denoted with an "R" or "RW" well number. Fewcontaminants were detected in residential wells; however, only a few chemicals were tested for inresidential well samples. Therefore, for screening purposes, we assumed that contaminants found inoff-site monitoring wells could have been present in residential wells. Table 4 lists 17 groundwatercontaminants (out of 47) that are not considered contaminants of concern and explains why weexcluded these contaminants from further evaluation.

When a contaminant's maximum concentration exceeded a comparison value, that contaminant wasconsidered 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 ofcontaminant presence), and (2) quality and quantity of environmental sampling data (e.g., suspectedlaboratory contaminants or inappropriate detection levels). For an example, bis(2-ethylhexyl)phthalate was frequently detected above its comparison value in off-site groundwatersamples; however, it is not a constituent of the PGDP processes or waste products but is a commonconstituent of plastic gloves and sampling equipment used in field sampling. It was detected withsimilar frequency in on-site, off-site, and background samples. For these reasons, positive detectionswere interpreted as an artifact of the sampling and laboratory processes. Bis(2-ethylhexyl)phthalatewas 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 contaminantseither were found at levels of potential health concern or, because of inadequate analysis, could bepresent at levels of health concern. Fifteen off-site contaminants, for which adequate analyses havebeen 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 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 for thesecontaminants were measured in the groundwater plumes between the PGDP facility and the TVAplant. Beryllium, nickel, and sulfate are not contaminants of concern in groundwater due to their lowoverall frequency of detection, their maximum concentrations, and the limited potential for exposure.Cadmium, thallium, pentachlorophenol, and vinyl chloride were selected as contaminants ofconcern for this exposure pathway, because analytical detection limits were greater than theirrespective comparison values. Zinc was measured above its comparison value only once off site, butthe sample was taken from a residential well; therefore, zinc was selected as a contaminant ofconcern for this exposure pathway.

Arsenic, chromium, lead, nitrate, vanadium, and TCE were selected as contaminants of concern,because their maximum concentrationsin 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, theconcentrations 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 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 the MCL was notrepeated in subsequent analyses, uranium metal (i.e., uranium as a chemical) is not a contaminantof concern in groundwater. (Note: EPA's National Primary Drinking Water Regulations final rule,published December 7, 2000, has the MCL for uranium as 30 µg/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 thereis no accepted comparison value for Rn-222 in drinking water, ATSDR converted the groundwaterconcentration into a potential airborne dose using EPA's recommended procedures for determiningpotential radon gas concentrations in residential air. According to these calculations, the highestpotential air concentrations in a home are less than EPA's recommended action level of 4 picocuriesper liter (pCi/L) [50]. Also, using information from a recent article in Radiation Research [51] andthe maximum concentration of Rn-222 found in well water, and assuming that a person ingests 2liters of contaminated water per day, we calculated a whole body committed effective dose:(2) 50millirems (or 0.5 millisieverts). This is less than a typical background dose from naturally occurringradon. 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, exceedEPA's proposed drinking water standards. Tc-99, U-238, and U-234 were selected as contaminantsof concern.

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

Arsenic, cadmium, chromium, lead, nitrate, thallium, vanadium, zinc, pentachlorophenol, trichloroethylene, vinyl chloride, technetium 99, uranium 234, and uranium 238 were selected as contaminants of concern for the groundwater exposure pathway. These substances are discussed further in the pathway analysis and in the public health implications section of this report.

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 CV Wells With Detections Above CVs Maximum Concentration Range in g/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)2 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 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)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)
(CV Source)3
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

(3094 )

Many wells4 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;5 annual dose approx. 50 mrem (0.5 mSv)6
Technetium 99

3,790 (140)

2

MW-261 5,125 to 5,804
(190 to 215)
Yes, above CV
Uranium 234

15; 30 total U7
(0.56; 1.11)

2

MW-141, MW-148 17 and 24
(0.6 to 0.9)
Yes, above CV
Uranium 235

15; 30 total U7
(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 U7
(0.56; 1.11)

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 EPA's "action level" for lead in drinking water, 40 CFR Parts 141 and 142.
3 For radioactive contaminants, the CV source is the current and/or proposed EPA Safe Drinking Water Standards [52].
4 Data collected from 1990, 1991, 1992, and 1993 PGDP Environmental Reports [46,47,48,49]. (Number of detects above 300 pCi/L, EPA's proposed standard)
5 Source: [50]
6 Source: [51]
7 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 [http://www.epa.gov/safewater/mcl.html] ; 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 [45]
Contaminant Maximum Concentration (in g/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: 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, we estimatedhuman exposure doses for contaminants in these exposure pathways. In the public healthimplications section, we discuss potential health hazards from exposure to contaminants of concern at the estimated doses.

Current Exposure

Currently, residents near the PGDP site are not being exposed to groundwater contamination originating from this site.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 [53]. Although contaminated groundwater fromthe northwest plume may be discharging into the Ohio River or the portion of Little Bayou Creekdirectly adjacent to the Ohio River, the concentrations at those locations do not exceed comparisonvalues [38]. Therefore, there are no exposure pathways identified for current exposure togroundwater contaminants from the site.

Prior testing of private wells in the PGDP area revealed contamination by lead. Of the 12 residentialwells tested for lead, three were above the EPA action level of 15 g/L [46,47,48,49,54,55,56]. Oneof 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 haveresulted from materials used in plumbing. The wells are no longer used as a source of drinkingwater, but if the lead originated in plumbing that is still being used, the source and exposurepathway for lead exposure may still exist. Persons who are concerned about the possibility of leadcontamination in their drinking water may wish to have their water tested. A list at the end of thecommunity health concerns section of this report provides names and phone numbers for persons tocontact at the local health department. Additional information is available from EPA's SafeDrinking Water Hotline at 1-800-426-4791. As a general precaution, EPA recommends runningtaps for 30 seconds to 2 minutes before using the tap water. Possible adverse health effects fromexposure to lead in drinking water are discussed in the public health implications section of thisreport.

Past Exposure

Off-site residential wells in the northeast plume area were plugged or converted to monitoring wellsbefore contaminant concentrations exceeded comparison values. Therefore, no completed exposurepathways are identified for past exposure to contaminants in the northeast plume.

Past exposures to groundwater contaminants in the northwest plume occurred or potentially occurred. No exposures to contaminants in the northeast or southwest plumes were identified. Health effects from exposures or potential exposures are discussed in the public health implications sectionFor 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, wellsamples collected after 1988 indicate that other contaminants may have been present in thenorthwest plume along with TCE and Tc-99.Arsenic, lead, nitrate, and zinc were detected insamples from residential wells after 1988,although they may not be related to thenortheast and northwest plumes. Therefore,TCE, Tc-99, arsenic, lead, nitrate, and zincare contaminants of concern for pastexposure via completed exposure pathwaysfor groundwater. Completed exposurepathways 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 these contaminantswere not performed for most residential well samples. Because residential wells may havecontained cadmium, chromium, fluoride, pentachlorophenol, thallium, vanadium, or vinylchloride, 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. Thesamples were collected in the deep RGA. Maximum concentrations exceeded EPA's drinking waterstandard. Although these results were not repeated and these contaminants were not detected inresidential wells, U-234 and U-238 were detected in on-site groundwater and are consideredcontaminants 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 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 within theDOE property boundary. There are no residential drinking water wells within the past or currentarea of the southwest plume. Therefore, there are no exposure pathways identified for past orcurrent 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 4 and 5 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 withTCE above the comparison value (5 g/L) before 1988. Evaluation of contaminant transport ratesindicate that TCE concentrations were estimated to be greater than 100 g/L for 5 to 15 years priorto 1988. Concentrations less than 100 g/L may have been present in these wells for a longerperiod; however, that period's duration cannot be estimated with certainty. Therefore, we assumedan exposure duration of 5 to 15 years for all contaminants in the wells associated with the northwestplume. In evaluating contaminant transport, we assumed a concentration of 100 g/L--but this isnot a health-based concentration. Appendix D details the evaluation of contaminant migration andpresents supporting information.

Past exposure doses for contaminants of concern in completed and potential exposure pathways areestimated 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 wasthe primary route of exposure for this exposure pathway, although inhalation and skin contact forsome contaminants were secondary exposure routes. Studies have shown that volatile organiccompounds 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 [57,58]. Absorption of thesecontaminants through the skin can contribute a dose up to 30% of the ingested dose [59]. As aconservative estimate, ATSDR scientists assumed that ingestion doses for volatile organiccompounds, TCE, and vinyl chloride would increase 70% from inhalation and 30% from dermalabsorption.

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 70kilograms 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 thecontaminants in groundwater were used to calculate exposure doses. Exposure doses for TCE andTc-99 were based on maximum concentrations measured in 1988 at the most contaminated drinkingwater well (960 g/L for TCE and 400 pCi/L for Tc-99). For U-234 and U-238, the exposure doseswere 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 andpotential 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 has recentlybeen detected in several wells northeast of the site property. Although other contaminants (such asTc-99 and arsenic) have been detected in the northeast plume, they have not migrated off site atconcentrations exceeding health comparison values. The northeast plume is migrating to thenortheast and is close to the eastern boundary of the Water Policy-affected area (Metropolis LakeRoad), as Figure 6 shows. Although a groundwater extraction and treatment system was establishedfor this plume in August 1997, contaminants at the leading edge may migrate beyond MetropolisLake Road in the future. If the plume continues to migrate, it may contaminate additional privatewater wells before it discharges into the Ohio River.(3) DOE is continuing to monitor the movement ofthe northeast plume. DOE has indicated that they will expand the boundaries of the Water Policyarea if ongoing monitoring indicates that additional wells may become contaminated [37]. If theplume migrates outside the water policy boundary and contaminated wells are capped usingapproved 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 wellswithin the area of groundwater contamination. Therefore, there is a potential for future exposure ifnew wells are drilled into the northeast or northwest contaminant plumes.

The southwest plume was recently characterized. There is no current completed exposure pathwayfor this plume. Its future migration direction is unknown. The plume may turn north and join withthe 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 in Illinoispresents 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 OhioRiver 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 samplehad TCE at a concentration of 9 g/L). According to available data, the well from which this samplewas 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 pathway iffuture 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 toremediate the groundwater aquifer. Several options and combinations of options have been presentedto the public, along with estimated costs and timeframes [43]. No matter what options are chosen, the remediation will probably take a very long time.

TCE Concentrations in Residential Wells
Figure 4. TCE Concentrations in Residential Wells

Tc-99 Concentration in Residential Wells
Figure 5. Tc-99 Concentration in Residential Wells

TCE and Tc-99 groundwater contamination, 1997
Figure 6. TCE and Tc-99 groundwater contamination, 1997


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 g/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 (CED3 from annual intake)

Children 1.2 mrem (0.012 mSv)
Adults 0.69 mrem (0.007 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:4

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)

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

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 [60].
2 TCE and Tc-99 exposure doses based on maximum measured concentrations in residential wells for 1988.
3 CED = Committed Effective Dose (See Glossary, Appendix K).
4 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 1 Arsenic

Cadmium

Chromium

Thallium

Vanadium

Pentachlorophenol

Vinyl chloride

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:

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 (CED2 from annual intake):

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

Uranium 238 (CED2 from annual intake):

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

Lead3 Residential wells N and NW of site Ingestion   Potential current and future See text
For NE 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 River Ingestion (also, for TCE, inhalation and skin absorption during showering) Households and visitors to about eight residences Potential future Future 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 River Ingestion (also, for TCE, inhalation and skin absorption during showering) Anyone using public water supply Potential future Future potential doses were not estimated
For NE and NW plumes:
leaching of contaminants from multiple sources listed 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 purposes Potential 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 CED = Committed Effective Dose (See Glossary, Appendix K)
3 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); N = north; NE = northeast; NW = northwest;Tc-99 = technetium 99; TCE = trichloroethylene



1. Uranium is always a chemical; in this document, "uranium as a chemical" means uranium considered for its chemical effects on people, rather than its radioactive effects.
2. Appendix K defines this and other important terms.
3. A measurement in well MW-191 (4/1/91; sample ID #CH210170-00000) indicates TCE at 130 g/L. Use of this value in interpreting the distribution of the northeast plume indicates a more easterly direction for plume migration and suggests that the plume may affect residential wells east of the water policy boundary before reaching the Ohio River. However, both concurrent and subsequent sampling of this well indicates that the measured value is an analytical error and should not be used to re-interpret the direction or distribution of the plume.


Next Section     Table of Contents

  
 
USA.gov: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #