PUBLIC HEALTH ASSESSMENT
PADUCAH GASEOUS DIFFUSION PLANT (U.S. DOE)
PADUCAH, MCCRACKEN COUNTY, KENTUCKY
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 possible. 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 [24]. Figure 3 illustrates the necessary components of an exposure pathway.
Figure 3. 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 were generated by DOE and about 12,000 were generated by the U.S. Enrichment Corporation, or USEC.) Since USEC is still operating this plant, these numbers may vary with time.
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 [37]. 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
[38].
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, if future property owners drill new wells into the contaminated groundwater plumes, or if DOE does not renew their water policy and landowners go back to using private wells in the area.
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 Bayou Creek immediately south of the Ohio River [38]. 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 [29].
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 [39]. 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 [39]. 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 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 [40,41,7]
| 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: [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 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 [45,46,47,48,49]
| 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: [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, 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, bis(2-ethylhexyl)phthalate was frequently detected above its comparison value in off-site groundwater samples; however, it is not a constituent of the PGDP processes or waste products but is a common constituent of 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 concentrationsin 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 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 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) [50]. Also, using information from a recent article in Radiation Research [51] 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)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 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 |
(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 |
2 |
MW-141, MW-148 | 17 and 24 (0.6 to 0.9) |
Yes, above CV |
| Uranium 235 |
15; 30 total U7 |
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 |
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
 ] ; 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 [45]
| 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 [53]. Although contaminated groundwater from
the northwest plume may be discharging into the Ohio River or the portion of Little Bayou Creek
directly adjacent to the Ohio River, the concentrations at those locations do not exceed comparison
values [38]. 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 [46,47,48,49,54,55,56]. 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 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 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 [57,58]. Absorption of these contaminants through the skin can contribute a dose up to 30% of the ingested dose [59]. 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 6 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 [37]. 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 [43]. No matter what options are chosen, the remediation will probably take a very long time.
Figure 4. TCE Concentrations in Residential Wells
Figure 5. Tc-99 Concentration in Residential Wells
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 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 (CED3 from 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: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) | |
| 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: 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 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: Chromium: Thallium: Vanadium: Pentachlorophenol: Vinyl chloride: Uranium 234 (CED2 from annual intake): Uranium 238 (CED2 from annual intake): |
| 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. |
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| 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 | ||||||
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