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In this section, ATSDR evaluates exposure pathways to determine whether people having access to or living near Sharpe could have been, are, or will be exposed to site-related contaminants. In evaluating exposure pathways, ATSDR considers whether people might come into contact with contaminated media. ATSDR also considers possible routes of exposure, including ingestion, dermal contact, or inhalation of vapors. If exposure was or is possible, ATSDR then considers whether contamination is present at levels that might affect public health. Figure 4 explains the exposure evaluation process in more detail.

ATSDR uses comparison values in selecting contaminants for further evaluation within an exposure pathway. Because comparison values do not represent thresholds of toxicity, exposure to chemical concentrations above comparison values does not necessarily produce health effects. In fact, ATSDR comparison values are designed to be many times lower than levels at which no effects were observed in experimental animals or epidemiologic studies. Comparison values used in this document include state of California (CA) and EPA's maximum contaminant levels (MCLs); ATSDR's environmental media evaluation guides (EMEGs), reference dose media guides (RMEGs), and cancer risk evaluation guides (CREG); and EPA's lifetime health advisory (LTHA) for drinking water. MCLs are enforceable drinking water regulations developed to protect public health, but they also consider economic and technological factors. CREGs, EMEGs, and RMEGs are strictly health-based comparison values developed by ATSDR that are not enforceable. A description of the comparison values and a glossary of environmental and health terms used in this public health assessment are provided in Appendix A and Appendix B, respectively.

ATSDR has identified several potential exposure pathways that necessitate evaluation, including the following:

  • Consumption of contaminated groundwater
  • Dermal contact with surface soils
  • Inhalation of soil gases
  • Consumption of locally grown foods

This section evaluates these potential exposure pathways in more detail, considering any data gathered and remedial activities conducted since ATSDR's 1991 site visit to determine whether they represent, under site-related conditions, a threat to human health. Table 2 lists the potential exposure pathways discussed in this section of the document.

Consumption of Contaminated Groundwater

The groundwater beneath the site is contaminated with VOCs at levels exceeding the comparison values in the former site operations (see Table 3). Through the RI process, Sharpe identified six VOC groundwater plumes in the three shallowest aquifer zones beneath the site. The plumes include plume 1 in the South Balloon Area, plumes 2, 3, 4/5, and 6 in the Central Area, and plume 7/8 in the North Balloon Area (see Figure 5). (Eight plumes were originally identified on site. Plumes 4 and 5 and plumes 7 and 8 were initially identified as separate plumes, but more recent sampling indicates that they are single plumes and are designated as plume 4/5 and plume 7/8.) TCE was the most predominant VOC detected at concentrations greater than the EPA and CA MCL (5 parts per billion [ppb]) in the plumes with the exception of a portion of plume 7/8 where PCE predominated and exceeded the EPA and CA MCLs of 5 ppb. Several of the plumes (i.e., plumes 3, 4/5, 6, and 7/8) have migrated off site. A more detailed description of the plumes is provided in Appendix C.

Sharpe also monitored groundwater for a range of pesticides and metals and found that elevated levels of arsenic, selenium, nitrate, and bromacil were present in the groundwater beneath the site (see Table 3) and in off-site areas (see Table 4). For these chemicals, the highest concentrations were encountered in the A zone beneath the site. Other pesticides and metals, including lead, were not present in the groundwater at levels known to cause health hazards.

Arsenic was detected in all four zones beneath the site and in the three shallowest zones off site at levels above the EPA and CA MCL of 50 ppb. The highest concentration of arsenic (1,193 ppb) was detected in the upper water bearing zone or the A zone of the North Balloon Area. Arsenic is not very mobile in groundwater and does not migrate as plumes. Migration, if any, tends to be more horizontal than vertical to the deeper aquifer layers. Sharpe has not used arsenic in current or former operations; consequently, other potential sources were investigated, such as arsenic-containing pesticides, phosphate-containing fertilizers, and naturally occurring mineral deposits common to the San Joaquin Valley (ESE, 1991b; ATSDR, 1993a; DOD, 1997b).

Selenium was detected only in the A zone of both on-site (25 ppb) and off-site (20.9 ppb) areas at maximum levels marginally above the ATSDR comparison value of 20 ppb. There is no evidence that Sharpe used selenium and it has not been detected in on-site or nearby off-site surface soil. Several studies of other sites near Sharpe, however, have shown that levels of selenium occur naturally in the San Joaquin Valley and that problems with selenium contamination are usually associated with agricultural runoff (ESE, 1991a).

Nitrate is present in the three shallowest zones, but only in the A (37,200 ppb) and B (19,600 ppb) zones beneath the site and in the A zone (17,700 ppb) off site at levels above the MCL (10,000 ppb). The source of nitrate is not known with certainty. It may be related to local agricultural and cattle operations being conducted off post in the vicinity of Sharpe.

Bromacil, a herbicide, was used and stored on site in the past to control unwanted vegetation. Bromacil was detected in the A zone beneath the site at 776 ppb and beyond the site boundary in several areas up to 9.32 ppb, but at levels below ATSDR's comparison value of 90 ppb (ESE, 1993).

Recent monitoring data indicate that chromium is present in the A zone beneath the South Balloon Area at a maximum concentration of 188 ppb and above the CA MCL of 50 ppb (Radian, 1997a). Chromium was not detected in the deeper aquifer zones that supply the potable wells; therefore, chromium is not expected to pose a public health hazard. Sharpe is evaluating remediation measures to address the chromium contamination in the groundwater (DOD, 1997b, Radian 1997a).

Sharpe installed three groundwater extraction and treatment systems to restore the groundwater to reuse conditions and reduce further off-site migration of VOC-contaminated groundwater. Because arsenic, selenium, and nitrate have not been used in past or current mission activities and bromacil was infrequently detected, the Army has not considered these constituents in their groundwater treatment system design. Concentrations of these chemicals discharged off site with the groundwater treatment system effluent are regulated by the National Pollution Discharge Elimination System. The compliance limits were developed with CRWQCB oversight. Currently, the system is meeting all ROD Substantive Waste Discharge requirements.

The Sharpe continues to review treatment system performance data and monitor groundwater in the area of the site. Contaminant levels have decreased since the implementation of the groundwater treatment system. If it becomes apparent, however, that the system will not reach levels protective of public health, Sharpe will reevaluate groundwater treatment alternatives.

ATSDR evaluated available environmental monitoring data for the wells located on site and in the vicinity of Sharpe as well as local water use patterns to determine whether people using these wells have been or could be exposed to site-related contamination at levels that pose public health hazards.

On-Site Wells

Current and Future Exposures

The Sharpe facility water supply serves on-site workers and on-site residents. Although six wells exist on site, the Sharpe water supply is currently fed by three active wells: 3, 5, and 6. (Wells 3, 5, and 6 were activated in 1943, 1988, and 1989, respectively.) Since the mid-1980s, the three other wells have been taken out of service or closed. These wells include well 1, which is used only for emergency, nondrinking water purposes; well 2, which was closed in 1988 due to its proximity to plume 7/8; and well 4, which was permanently closed in 1988 for silting problems. Under its Restoration Program Monitor Plan, Sharpe started monitoring on-site wells for VOCs during the mid-1980s. Currently, they monitor wells 1, 3, 5, and 6 for VOCs on a quarterly basis. The monitoring results indicate that well water continues to meet CA drinking water quality standards (see Table 5) (Radian, 1996).

Sharpe also monitors its on-site wells for metals and pesticides. Arsenic was the most consistently detected constituent in the Sharpe wells. The highest arsenic level of 49 ppb was detected during a 1991 sampling effort in well 5. This value exceeds ATSDR's CREG of 0.02 ppb but is lower than the CA and EPA MCL of 50 ppb. Results from the 1996 monitoring effort indicate that arsenic levels (15 ppb to 41 ppb) still exceed ATSDR's CREG. Because the CREG is a screening tool, exposure to arsenic concentrations above the CREG are not necessarily associated with health effects. ATSDR evaluated the health significance of exposure to on-site residents and to on-site workers and personnel by deriving an exposure dose associated with the consumption of 2 liters of water per day containing the maximum arsenic concentration (49 ppb). The methods used and assumptions applied in this evaluation are presented in Appendix D.

On the basis of an assessment of the exposure dose estimates, ATSDR concludes that consumption of arsenic in on-site well water is not expected to result in health problems for either on-site residents or on-site workers and personnel. ATSDR also concludes that there is no health hazard associated with inhalation or dermal contact with on-site potable water. The arsenic doses associated with exposure either via inhalation or dermal contact are expected to be much lower than those incurred via consumption of well water. Although considerable absorption occurs following ingestion, absorption following dermal contact or inhalation exposure is substantially less, and not likely to result in exposures that cause adverse health effects.

Past Exposure

Before its closure in 1988, well 2 also served the on-site water supply used by workers and on-site residents. Sampling conducted after its closure, however, detected benzene and TCE at levels marginally above the ATSDR comparison values but at levels below the EPA MCLs (see Table 5). (Benzene concentrations exceeded the CA MCL of 1 ppb, but TCE fell below the CA MCL of 5 ppb.) It is doubtful, however, that any similarly low-level contamination posed a public health hazard to past on-site well users while well 2 was operational. Water from each operational on-site potable well was delivered to an aboveground storage tank, where it was combined and diluted with other well water, stored in a water tower, and distributed to the installation users. Therefore, no one well served as a sole source for the facility's water supply (ESE, 1991b).

Arsenic concentrations similar to those levels detected during the RI were probably present in the on-site drinking wells in the past (before mid-1980s). As indicated above, these levels are not expected to pose adverse health effects to on-site residents, workers, or personnel.

Past, current, or future use of on-site drinking water by on-site residents and on-site workers or personnel is not likely to result in adverse heath effects.

Off-Site Wells

Municipal Water Supply: Past, Current, and Future Exposures

The community of Lathrop is served by the municipal water supply, which is fed by five wells that draw water from the deep, uncontaminated aquifer. The municipal wells are not located in the direction of groundwater flow from the site; therefore, they are unlikely to be affected by contamination migrating from the site. Regular monitoring of the water supply by the Lathrop Public Works Department (LPWD) has not detected VOCs or arsenic at levels above California drinking water standards (LPWD, 1996). In 1992, TCE was detected at 0.34 ppb in one well located just 50 feet south of the southeastern perimeter of the site; TCE has not since been detected in the well and the well is currently out of service because of a silting problem. The city plans to replace the well in the near future (Gebhardt, 1996). The LPWD will continue to monitor the municipal water supply to ensure the water meets drinking water quality standards.

Area residents who receive their drinking water from the municipal water supply are not currently, nor have they been in the past, exposed to site-related contaminants. The city of Lathrop will continue to regularly monitor their water supply to ensure that the water continues to meet CA drinking water standards.

Private Wells: Current and Future Exposures

Approximately 30 to 40 private wells serve several small businesses and private residences located north, northwest, and west of the site. Sharpe detected PCE in a private well at a concentration of 1.0 ppb during a 1987 sampling event. Since then, Sharpe has continued monitoring private wells for VOCs on a quarterly basis. TCE and PCE have been detected in three private wells, PW19, PW20, and PW21 (see Figure 5) located approximately 1,200 feet northwest of the site. No other wells have been affected.

Table 6 summarizes the quarterly monitoring data for the affected wells. As the table indicates, PCE has been detected in two wells (PW19 and PW21) at levels above ATSDR's CREG of 0.7 ppb but, with the exception of a 1994 detection of 6.3 ppb in PW19, below the EPA and CA MCLs of 5 ppb. More recent monitoring (quarter 2, 1997) detected PCE at levels of 1.5 ppb and 2.0 ppb in PW19 and PW21, respectively (DOD, 1997a). These levels exceed ATSDR's CREG screening value but fall below the EPA and CA MCLs of 5 ppb.

TCE has also been detected in private wells, but much less frequently than PCE. TCE was detected in wells PW19 and PW20 at levels below ATSDR's CREG, with the exception of a 1995 detection of 3.1 ppb (PW19). During 1997 sampling, TCE was not present in well PW19. Although TCE was present in PW20, the well is currently unavailable for drinking water use as it is located on vacant property (U.S. ACE, 1996).

Sharpe will continue to monitor VOCs in private wells down gradient of the plume on a quarterly basis and will take action (e.g., provide alternative water sources) if the contaminant levels consistently exceed the MCLs (DOD, 1997b). Sharpe shares private well monitoring data with well owners and, upon request, serves as a point of contact to direct concerned private well owners to appropriate agencies for health information on chemicals found in the well water (DOD, 1997a).

Another contaminant, 1,2-dichloroethane (1,2-DCA), has consistently been detected in one private well (PW22) located on industrial-use property along the northern perimeter of the site. The levels detected range between 1.0 ppb and 20 ppb and above the EPA MCL of 5 ppb and the CA MCL of 0.5 ppb. The well water has not been used for drinking since at least 1981 when the current industry owners acquired the property and started providing employees bottled water for drinking (DOD, 1998). Furthermore, monitoring results suggest that the 1,2-DCA in this private well may not be related to Sharpe because the well is not situated in the direction of groundwater flow from the site (DOD, 1997a). Sharpe conducted additional groundwater monitoring with a strategically placed network of monitoring wells located north of Sharpe, and, on the basis of the results, Sharpe determined that the 1,2-DCA contamination did not originate at the site (DOD, 1997a).

In 1987, Sharpe began monitoring private wells for arsenic. Sharpe discontinued this routine monitoring in 1994 because the arsenic concentrations measured in the private wells were consistently below the MCL. To ensure that private wells are not affected by arsenic, Sharpe will monitor private wells for arsenic if arsenic is present in a nearby monitoring well at a concentration that approaches (greater than 40 ppb) or exceeds the MCL (greater than 50 ppb) (DOD, 1997b).

ATSDR evaluated the health significance of the private well owners' exposure to contaminants in their drinking water by deriving an exposure dose. In estimating exposure, ATSDR makes assumptions about exposure extent and duration because uncertainty when contamination was first present in the wells and at what concentrations (e.g., sampling data are available for the private well only after to 1987). Therefore, ATSDR conservatively assumed that people could have been exposed to these contaminants at the maximum PCE and TCE levels of 6.3 ppb and 3.1 ppb, respectively over a 30-year period. As a prudent public health measure, ATSDR also evaluated exposure to 1,2-DCA in the private well water, even though the well has not been used for drinking and the contamination may be unrelated to Sharpe. The methods used and additional assumptions applied are presented in Appendix D. On the basis of an assessment of the exposure dose estimates, ATSDR concludes that consumption of water from private wells is not expected to result in adverse health problems. ATSDR also concludes that inhalation or dermal contact with on-site potable water are not likely to increase the risk of developing adverse health effects1.

Future exposure potential is likely to be minimal. Sharpe will continue to monitor off-site private wells closely to ensure that VOC levels remain below the CA MCLs (Radian, 1996). Sharpe also will continue to monitor plume 7/8 in the North Balloon Area, the suspected PCE and TCE source area. Recent monitoring results indicate that the 7/8 plume does not appear to be advancing any further in the direction of these off-site private wells. Furthermore, no new private wells are likely to be installed in the area because state legislation allows regulatory agencies to place restrictions on activities within 2,000 feet of a hazardous waste site boundary.

Private Wells: Past Exposures

PCE has been detected in private wells since 1987. Low PCE concentrations (slightly above the CREG) similar to those detected in 1987 (1.0 ppb) may have been present in the off-site private wells before 1987. As indicated above, these levels are not expected to pose adverse health effects to private well users, even over 30 years of use.

VOCs have been detected at levels above ATSDR's CREG in private wells located north-northwest of the site. ATSDR determined that use of water from these private wells is not associated with a public health hazard. Sharpe will continue to monitor off-site private wells in the vicinity of the site to ensure that private well water use does not pose a public health hazard.

Agricultural Wells

Fourteen former agricultural wells are located between West Perimeter Road and Harlan Road. These wells were used for irrigation and have never been used for drinking water sources. CRWQCB ordered their closure in 1991, suspecting that these downgradient wells influenced the migration of the site's contaminated groundwater plumes (ESE, 1991b; DOD, 1996).

Dermal Contact With Surface Soils

On-Site Surface Soil: Industrial Areas (North Balloon, Central, and South Balloon Areas)

Past operations and disposal activities have released chemicals to the surrounding on-site soil. To characterize contamination in the on-site soil, Sharpe collected samples between 1987 and 1990 from the North Balloon Area, the Central Area, and the South Balloon Area, and analyzed them for VOCs, semivolatile organic compounds, metals, and pesticides. Table 7 presents the results of Sharpe on-site surface soil sampling. ATSDR typically evaluates surface soil data because it represents the most likely point of human contact. The sampling results indicate that surface soils in localized areas of the North Balloon Area, the Central Area, and the South Balloon Area are contaminated with elevated levels of lead, chromium, and pesticides. The areas where the soil contamination has been detected are fenced or restricted to public access and no unauthorized access has been reported (DOD, 1996). Workers in these areas are expected to have limited contact with surface soil and to wear protective clothing.

North Balloon Area

Between 1987 and 1990, Sharpe collected 59 samples from 29 soil borings installed in the North Balloon Area. Of the contaminants detected, lead, chromium, and pesticides were detected in the highest concentrations. Some of the highest lead levels were found within the railroad tracks along the western part of the area, where sandblasting waste associated with lead-based paint was dumped. (A soil comparison value does not currently exist for lead.) This area is approximately 600 feet from the on-site residential housing area (ESE, 1994b). Chromium was detected less frequently than lead, but at levels exceeding its comparison value.

Sharpe completed additional soil sampling in the North Balloon Area in 1996. Lead (8,600 parts per million [ppm]) and chromium (1,400 ppm) concentrations exceeded the clean-up standards of 1,000 ppm and 300 ppm, respectively, in two locations where the contamination appears to be restricted to the top 6 inches of soil. The clean-up standards are based on a state of California evaluation which determined that exposure to levels below the clean-up goals is unlikely to pose adverse health problems for the industrial worker (ESE, 1996). For the two locations, Sharpe proposes (1) excavating the lead- and chromium-contaminated soil to clean-up standards; (2) disposing of contaminated soil in an off-site landfill; (3) collecting verification samples; and (4) backfilling areas to natural grade (Radian, 1997a).

The pesticides 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (DDT), 1,1-dichloro-2,2-bis(4-chlorophenyl)-ethylene (DDE), 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethane (DDD), and chlordane were frequently detected in the surface soils of the pesticide management area adjacent to both North Avenue and the administrative area. In the past, Sharpe employees mixed and stored pesticides in this mostly unpaved area. A shallow, unlined ditch drains the area to a depression located about 330 feet east from the pesticide management area. The highest levels of DDT (181 ppm), DDE (31.5 ppm), and DDD (8.14 ppm) were detected in the mixing area and near the head of the drainage ditch. These levels exceed ATSDR comparison values. Chlordane concentrations generally ranged from 0.045 ppm to 55 ppm and were above the CREG of 0.5 ppm; however, one very high level (470 ppm) was detected at the head of the ditch. Pesticide levels appear to decrease rapidly with increasing distance from the mixing area, dropping to levels lower than 1 ppm near the site fence (ESE, 1994b). Pesticide-contaminated soil was removed in March 1995, when soil containing chlordane concentrations greater than 1 ppm and DDT, DDE, and DDD concentrations greater than 3 ppm was excavated and disposed of in an off-site landfill (ESE, 1996).

Central Area

Metals were not widely distributed in the more than 80 soil samples collected from the Central Area. Elevated levels of lead (maximum concentration of 3,720 ppm) were only infrequently detected in the former maintenance areas. VOCs, primarily TCE, were predominant in samples collected from the Firefighting Training Area, the runway, and maintenance buildings. The highest concentrations (greater than 1,200 ppm) were found in the soil at depths from 10 to 15 feet below ground surface (ESE, 1994a, 1994b). Locations of TCE concentrations that exceeded the ATSDR comparison value of 60 ppm coincided with the TCE groundwater plume 6.

Sharpe collected additional soil gas samples from the Central Area during a 1996 sampling event. The soil gas results suggest that VOCs in soils are leaching to the underlying groundwater in an area near plume 6. Sharpe plans to implement an in-situ volatilization (ISV) system, which will minimize the impact of VOC-contaminated soil to groundwater. Sharpe also will monitor an area near plume 4 to further characterize the effects of VOC-contaminated soil on groundwater quality (Radian, 1997a).

South Balloon Area

A 1983 geophysical survey identified several irregularly shaped trenches and pits in the southeastern corner of the South Balloon Area. The trenches and pits primarily contained debris, including glass, ash, and burned material. Lead was detected in a majority of samples collected. With the exception of the very high levels (3,990 ppm, 17,500 ppm, and 27,500 ppm) detected in two trenches, most lead concentrations were below the clean-up goal of 1,000 ppm proposed in the FS (ESE, 1994b). During a 1996 sampling event, Sharpe detected lead and chromium at levels less than the cleanup standards of 1,000 and 300 ppm, respectively. Recent groundwater data, however, suggest that chromium-contaminated soil may be contributing to elevated chromium concentrations in the underlying groundwater. Sharpe is currently evaluating measures to address this situation (DOD, 1997b; Radian, 1997b).

Soil gas data also collected during the 1996 sampling event indicates that VOC-contaminated soil is threatening the underlying groundwater in portions of the South Balloon Area associated with plume 1 (Radian, 1997a). Sharpe plans to install ISV systems in those areas to minimize the amount of VOCs migrating from contaminated soil to the underlying groundwater.

On-Site Surface Soil: Residential Area

Because of its proximity to the North Balloon Area where elevated levels of lead were detected, Sharpe analyzed soil samples from the on-site residential area for lead in March 1993. Lead levels detected in the residential area surface soil ranged from 11.3 ppm to 33.9 ppm (ESE, 1994c).

Young children are especially sensitive to the toxic effects of lead. Incidental ingestion of lead-contaminated soil that might occur during normal play and hand-to-mouth activities can contribute to elevated blood lead levels. Blood lead levels of 10 micrograms per deciliter (µg/dL) and above have been associated with health effects in young children. Although the relationship between levels of lead in soil and blood lead levels in children vary widely, blood lead levels have been reported to rise 3 to 7 µg/dL for every 1,000 mg lead/kg soil (CDC, 1991). The soil lead concentrations in the residential area are much lower than levels contributing to elevated blood lead levels in young children. For this reason, ATSDR determined that residential area soils do not pose a health hazard.

The general public, on-site residents, and workers/ personnel are unlikely to have access to areas of on-site contamination or directly come in contact with contaminated on-site soil. On-site workers in these areas wear protective clothing to reduce the risk of exposure. Any exposure they may incur is likely to be minimal and not threatening to human health. Only low levels below those associated with public health hazards were detected in the soil of the residential area.

Off-Site Surface Soil

Sharpe collected off-site surface soil samples along the east, west, and southern boundaries of the site and analyzed the samples for metals, pesticides, and nitrates. The results of the sampling are presented in Table 8. Of the contaminants, only arsenic was widely distributed in the off-site soils at a maximum concentrations of 22.6 ppm, in excess of the ATSDR's CREG (0.5 ppm). Most values, however, were within the levels typical of western soils (10 ppm) (ATSDR, 1993a). The source of the arsenic has not been determined and may be related to agricultural practices or naturally occurring sources. Given that the relatively low levels of arsenic in soil are neither appreciably absorbed through skin nor likely to be consumed in large quantities via incidental ingestion, ATSDR does not expect off-site soil to pose a health hazard.

No adverse health effects are expected to occur from contact with off-site surface soil where only low level contamination has been detected.

Inhalation of Soil Gas

Exposure to soil gas is a concern when high levels of VOCs migrate via soil gas into basements through cracks in foundation walls of buildings. Soil gas accumulates in the small spaces between soil particles when chemicals volatilize from contaminated soil or groundwater. Generally, VOCs in the upper layers of soils gradually diffuse to the surface through soil gas. Under certain circumstances, however, such as when a low-permeability layer in the unsaturated subsurface zone inhibits the upward diffusion of gas, horizontal spreading of soil gas may occur (EPA, 1992). When this happens, contaminants may migrate with soil gas into a building's basement through foundation walls.

Sharpe sampled soil gas as a technique to characterize the presence of VOCs in groundwater. This approach is considered a good predictive tool for identifying general patterns of VOC contamination. Although most residential structures in the area of the site do not have basements, ATSDR reviewed the soil gas data collected near the residential area to determine whether soil gas could potentially contribute to the indoor air environment.

Of the VOCs measured in soil gas, TCE was the most frequently detected in the residential area, but at levels (0 ppb to 100 ppb) much lower than those measured in contaminated areas of the site (maximum concentration of 79,900 ppb in the South Balloon Area). The amount of TCE that may enter a residential building varies as a function of several properties, including soil characteristics. EPA predicts that indoor air contaminant concentrations, however, typically do not exceed 5% of the surrounding soil gas concentrations (EPA, 1992). Applying this percent to TCE concentrations measured in soil gas within the residential area, ATSDR estimated that indoor air TCE concentrations are not expected to exceed 5 ppb, a value 20 times lower than ATSDR's comparison value for airborne TCE of 100 ppb. ATSDR concludes that even if soil gas migrates into indoor environments, TCE and other VOCs are not likely to accumulate to levels that may pose health hazards.

No adverse health effects are likely to occur from exposure to soil gas. VOC levels in soil gas are not expected to appreciably accumulate in on-site buildings.

Consumption of Locally Grown Foods

Alfalfa, fruits, and vegetables are grown in cropland and cattle are housed in stockyards located to the east of the Western Pacific Railroad and Airport Way and to the west of the site (ESE, 1994a). Locally grown or raised foods may accumulate site-related contaminants through uptake from soil or via contaminated irrigation sources. ATSDR evaluated whether people may be indirectly exposed to site contaminants if they consume locally grown or raised foods.


Typically, contaminant uptake by crops is evaluated by assessing contaminant concentrations in soil where the crops are grown. Arsenic was the only contaminant detected at levels (0.86 ppm to 22.6 ppm) greater than ATSDR's soil comparison value (0.5 ppm). ATSDR used uptake rates, or uptake factors, to approximate how much arsenic in soil may accumulate in the edible portion of the area-grown crops (EPA, 1989). Table 9 lists the uptake factors and the estimated accumulated arsenic concentrations in common crops. As the table indicates, the concentrations of arsenic in selected common crops range from 0.0045 ppm to 0.9 ppm. Many common foods contain small amounts of arsenic, and typical dietary levels of arsenic range from 0.02 ppm in grains and 0.14 ppm in meats, fish, and poultry to 4 to 5 ppm in fish (ATSDR, 1993b). Because the estimated concentrations of arsenic in locally grown crops is within ranges typically found in consumer foods, ATSDR does not expect consumers of area-grown produce to be exposed to arsenic at levels above background dietary levels.

Until a few years ago, the SSJIDC provided irrigation water to the area. The SSJIDC is fed by the on-site industrial waste/storm water sewer system and effluent from the North and South Balloon groundwater treatment system. Although SSJIDC water has not been sampled for site-related contaminants, industrial waste/storm water entering the SSJIDC complies with appropriate permit application requirements that limit site-related contaminant concentrations in effluent.


Available soil and estimated crop uptake information does not indicate that grazing areas in the vicinity of the site contain significant levels of site-related chemicals; however, no information is available to determine whether cattle housed near Sharpe may have accumulated contaminants while grazing. In the absence of this information, ATSDR reviewed deer bioaccumulation studies conducted at other federal facilities in the United States. (ATSDR assumes that deer and cattle exhibit similar grazing habits and uptake chemicals at comparable rates.) Compounds either used or detected on site at the facilities are similar to those found in Sharpe soil, including arsenic. The findings of these studies indicate that deer grazing near hazardous waste sites show only very limited uptake of compounds, and ATSDR determined that these low levels are not likely to pose a health threat to people who consume venison (ATSDR, 1996b; US ACHPPM, 1994; US AEHA, 1994). Assuming that cattle have grazing habits and chemical uptake rates similar to those of deer, ATSDR concludes that cattle grazing near the Sharpe site should not accumulate contaminants at levels that pose a health threat to consumers.

No adverse health effects are expected to result from eating locally grown or raised foods. Crops and cattle in the vicinity of the site most likely have not accumulated, nor are they likely to accumulate, site-related contaminants to levels of health concerns.


No community health concerns have been brought to ATSDR's attention by community members through the public health assessment process. Community involvement in the Sharpe site dates to 1990, when the Army first established a technical review community to inform and interface with the public and other involved agencies on the environmental studies being conducted. The Army also has released documents for public review and comment and held public meetings.

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