RBAAP consists of facilities at two locations, the main facility, and the E-P ponds located about 1½ miles north of the main facility, adjacent to the Stanislaus River. Within the main facility, the primary sites of contamination are the landfill, the IWTP, the storage tank area and the sanitary sewage and effluent sludge beds (see Figure 2). The E-P ponds have been used since their construction in 1952 to contain waste water from RBAAP. As such, the E-P ponds are the location of contaminated surface water and sediment and a source for contaminated groundwater.
ATSDR's public health assessments are exposure, or contact driven. A public health hazard will only occur as a result of a hazardous chemical release when there is exposure sufficient to present a health problem. Chemical contaminants disposed or released into the environment at RBAAP have the potential to cause adverse health effects. However, a release does not always result in exposure. People are only exposed to a chemical if they actually come in contact with the chemical. Exposure may occur by breathing, eating, or drinking a substance containing the contaminant or by skin (dermal) contact with a substance containing the contaminant.
Whether a health effect occurs (as well as the type and severity of the health effects) in an individual from contact with a contaminant depend on the exposure concentration (how much), the frequency and/or duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or skin contact), and the multiplicity of exposure (combination of contaminants). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, life style, and health status of the exposed individual influence how the individual absorbs, distributes, metabolizes, and excretes the contaminant. Together these factors and characteristics determine the health effects that may occur as a result of exposure to a contaminant.
This section examines the pathways of exposure to contamination at RBAAP, using environmental information collected by RBAAP environmental personnel under the oversight of the U.S. EPA and state environmental regulatory agencies. ATSDR examined each of the exposure situations to determine whether people in the community are exposed to (or in contact with) the contamination. If people were exposed to contamination, we evaluated whether there was enough contamination to pose a health hazard to people in the community.
Exposure Evaluation Outline and Summary
We evaluated the exposure potential from the identified areas of potential contamination or sites. From the data and information gathered during and after our site visits, we identified scenarios with potential for human exposure. These scenarios are grouped in our evaluation into two sets: 1) Exposures from Groundwater Contamination in the Study Area west of the Main Facility, and 2) Exposures past, current, and future exposure scenarios. These scenarios are outlined in Table 1 and are detailed in Tables 2 and 3.
We concluded that seven of the nine exposure situations, including all current potential exposure situations, pose no apparent public health hazard. In each of these cases, exposure to the contaminants is occurring or may have occurred in the past, but the concentrations are below levels which are likely to cause health effects.
No public health hazard is posed by the possible current use of groundwater in the residential area as a drinking water source.
The final exposure scenario, Past Crop Consumption, was determined to be an indeterminate public health hazard. Our evaluation of acute (short-term) exposure to cyanide in home garden produce watered with contaminated groundwater is driven by (1) the limited information in scientific literature on differential uptake , and accumulation by plants; (2) limited information on whether long-term effects occur as a result of exposure to low levels cyanide via ingestion of contaminated produce; (3) limited information available about specific watering techniques that may have been used in any of the home gardens in the Study Area; and (4) the actual nature of home gardening in the Study Area, as well as the types and quantities of home garden produce consumed.
Table 1: Possible Exposure Situations
|TABLE 1. Possible Exposure Situations|
|I. Exposures from Groundwater Contamination in the Study Area West of the Facility|
|A. Indeterminate Past Public Health Hazard||1. Past Crop Consumption|
|B. No Apparent Public Health Hazards||1. Current Crop Consumption
2. Current Livestock Consumption
3. Past Livestock Consumption
4. Past Drinking Water Consumption/ Showering
|C. No Public Health Hazard||1. Current Drinking Water Consumption/Showering|
|II. Exposures from Contamination at the E-P Ponds Area (1½ miles north of the main facility)|
|A. No Apparent Public Health Hazards||1. Current Dermal Contact with Surface Water/Sediment in the
2. Current Fish Consumption - Stanislaus River
3. Past Sediment Contact with Contaminants in E-P Ponds
|PATHWAY NAME||CONTAMINANTS||EXPOSURE PATHWAYS ELEMENTS||TIME||CONCLUSION CATEGORY||COMMENTS|
|SOURCE||ENVIRONMENTAL MEDIA||POINT OF EXPOSURE||ROUTE OF EXPOSURE||EXPOSED POPULATION|
|Crops||Cyanide||Contaminated well water from groundwater contamination originating from the landfill and Industrial Wastewater Treatment Plant||Crops||Crops watered with contaminated water in the Study Area via private wells||Long-term, frequent consumption of vegetables, fruit, nuts grown in home gardens||People who may have eaten crops watered with contaminated water (estimated 15 -20 households in "Study Area" - 60 +/- individuals)||Past
(From about 1963)
|Indeterminate Public Health Hazard||Past exposure
depend on watering
methods, types and
amounts of produce
grown and eaten.
Most likely effect
would have been
Current exposure is possible, but to levels below concern. Pump and treat will further significantly reduce contaminant levels.
|Livestock||Cyanide and Chromium||See above||Livestock||Consuming livestock watered with contaminated well water||Long-term, frequent consumption of livestock||People who ate livestock given contaminated well water (estimated 15 -20 households in "Study Area" - 60 +/- individuals)||Current||No Apparent||Bioaccumulation unlikely|
|Past (from about 1963)||No Apparent|
|Drinking Water||Cyanide and Chromium||See above||Groundwater||Domestic wells
(drinking water [DW])
|Long-term, frequent consumption of DW.
possibly Inhalation, or dermal exposure
|People using private wells (estimate 15 -20 households in "Study Area" - 60+/- individuals)||Past (from about 1963 to 19 86)||No Apparent||Levels not likely to cause health effects.
Current exposure unlikely due to use of public drinking water supplies
|PATHWAY NAME||CONTAMINANTS||EXPOSURE PATHWAYS ELEMENTS||TIME||CONCLUSION CATEGORY||COMMENTS|
|SOURCE||ENVIRONMENTAL MEDIA||POINT OF EXPOSURE||ROUTE OF EXPOSURE||EXPOSED POPULATION|
|Surface Water/Sediment in Stanislaus River||Primarily metals||Landfill, IWTP, E/P Ponds||Surface water and sediment||Stanislaus River near E-P Ponds||Dermal exposure, incidental ingestion||Recreational users of Stanislaus River in the immediate vicinity of E-P Ponds||Current||No Apparent||Does not appear that significant amount of contaminants are reaching the river.|
|Fish in Stanislaus River||Primarily metals||Landfill, IWTP, E/P Ponds||Fish||Fish||Ingestion||People eating fish from the Stanislaus River in the immediate vicinity of E-P Ponds||Current||No Apparent||Does not appear that significant amount of contaminants are reaching the river.|
|Sediment in E-P Ponds||Primarily metals||Landfill, IWTP,||Sediment||E/P Ponds||Dermal exposure and incidental ingestion||People who may have gone into the E-P Ponds||Past
( 1952 - 1992)
|No Apparent||Past - health hazard
unlikely from the
that would be the
most likely to
Remediation activities have been reducing contamination in E-P Ponds that are available to leach into river. Measured levels are below those that could present possible public health hazard.
I. Evaluation of Possible Groundwater Exposure Pathways West of the Main Facility
The primary groundwater contaminants at RBAAP are cyanide and chromium. Both chemicals have been detected in off-site wells in the Study Area immediately west of RBAAP. The residents of the Study Area have been provided with alternate water supplies since 1993.
ATSDR investigated cyanide levels in home garden produce because cyanide can be concentrated (bioaccumulated3) above ambient water concentrations. Therefore, even though the groundwater might have a safe drinking water concentration, irrigation of garden produce with groundwater could result in concentrated levels of cyanide. The possibility of exposure to cyanide through homegrown produce is considered an indeterminate public health hazard for the following reasons: (1) there is limited information about the past extent of gardening and consumption of produce watered by the contaminated wells; (2) there are no analytical data on cyanide levels in crops grown in the Study Area; (3) to this time, no evidence has been found to indicate past adverse exposure; and, (4) there is limited scientific information about uptake and bioaccumulation of cyanide in produce.
Without knowing the gardening and cultural preferences of the resident population, it would be impossible to predict the potential risk of ingesting home grown produce. We include the evaluation of the scenario to indicate that a potential risk is possible and residents engaging in home gardening should be aware of potential hazards and seek more specific information.
The current levels of chromium contamination detected in groundwater in the Study Area are not sufficient to represent a present or future public health hazard via consumption of livestock or crops currently watered with groundwater. Cyanide has not been detected in recent sampling, so that it would not represent a present or future public health hazard.
Past exposure to contaminated groundwater also occurred in this area through ingestion, dermal contact, and inhalation from water in private wells. This exposure situation presents no apparent public health hazard because the contaminant levels were low and not expected to cause adverse health effects. Moreover, public water supplies, provided as a precaution, essentially eliminate the possibility of a future public health hazard.
Hydrogeology of the Main Facility: Following is a brief summary of the hydrogeology of the RBAAP area, presented to provide a basic description of the potential transport of contaminants in groundwater in the area. The primary source of natural groundwater recharge in the RBAAP area occurs directly from precipitation and from runoff infiltration in the foothills and high terraces located to the east of the facility. Direct precipitation recharge is somewhat limited by rapid evaporation, and in some cases by shallow impermeable hardpan in the local soils. A significant additional source of recharge is from local irrigation (4).
The general groundwater flow direction from RBAAP is to the west, from the facility under the adjacent residential area comprising 72 "ranchettes," the area referred to as the Study Area (see Figure 3A)(4). The local shallow subsurface geology consists of a complex sequence of discontinuous, interlayered permeable sand and impermeable clay layers. There are five generally accepted local hydrostratigraphic shallow aquifer zones, designated A, A', B, C, and D. These aquifer zones range to a depth of about 155 feet below ground surface. The uppermost zones, A-C are considered to be hydraulically interconnected to a varying extent across the area of the facility. Contaminants found in one of these upper aquifer zones could be considered to have the potential to migrate into the others. (In addition to allowing for the potential for migration of contaminants, the interconnectivity of these zones would also allow for potential dilution of the contaminants.) However, zone D is considered to be hydraulically separated from the overlying zones by an impermeable clay aquiclude (4). Contamination is much less likely to migrate across the aquiclude from the upper zones into the deeper D zone. It is reasonable to assume contaminants are more likely to migrate between the upper aquifers than from the A - C aquifer zones into the D aquifer zone.
Sources of Groundwater Contamination: The principal sources for groundwater contaminants at RBAAP are the inactive landfill in the northeastern portion of the facility, a complex of "redwood" storage tanks formerly located in the area of the IWTP in the east-central portion of the facility, and the E-P ponds north of the main facility (1). Figure 2 presents the locations of the landfill and the IWTP, where the storage tank complex was located. The landfill was used from 1942 until 1966, when on-site disposal was discontinued. The IWTP and E-P ponds were built in 1952. The primary contaminants disposed were cyanide and metals. Chromium and cyanide are the only contaminants detected at high enough levels to warrant further health evaluation.
First Detection of Groundwater Contamination - Study Area: The first on-site environmental sampling at RBAAP was conducted in 1980. Soil and groundwater contamination, consisting primarily of metals (chromium, lead, zinc, manganese) and cyanide was detected in the sampling (6). Twelve off-site groundwater samples were collected in September 1985. These samples, collected from private wells west of RBAAP, revealed chromium (maximum concentration of 117 micrograms per liter [ug/l]) and cyanide contamination (maximum concentration of 95 ug/l) (2,8). Appendix C lists the cyanide and chromium analytical results for sampling conducted between 1985 and 1995. The maximum contaminant level (MCL) set by EPA for public drinking water systems is 50 ug/l for chromium and 200 ug/l for cyanide. Figure 3A shows the Study Area where these residences are located.
Assumptions Used For The Evaluation Of Past Groundwater Exposure Pathways - Study Area: Because off-site environmental sampling was not conducted until 1985, it is not possible to accurately determine the length of time that RBAAP neighbors might have been exposed to groundwater contamination. However, based on several assumptions, a very conservative estimate can be made for the earliest possible date for off-site exposure.
Time: The first homes were built in the Study Area in 1950. This is the baseline date for possible exposure of neighbors to contaminated groundwater. The landfill and the IWTP are about 1,300 feet and 1,100 feet from the Study Area, respectively. A 1987 study conducted for the Army estimated groundwater flow in the A, B and C aquifer zones to be about 100 feet per year (ft/yr) (2). Based on a groundwater flow rate of 100 ft/yr (2), it can be conservatively assumed that contaminated groundwater reached off-site from the landfill (beginning operation in 1952) in or around 1965. Potentially contaminated groundwater from the storage tanks would have reached offsite in about 1963 Based on this assumption, it is possible that a limited number of the residences in the Study Area (those closest to the western boundary) were exposed to some amount of these contaminants in drinking water from about 1963 until 1993, when bottled water was first provided.
Concentration and Extent of Contamination: Because no information exists on the extent of groundwater contamination prior to the 1980s, it is not possible to precisely define the area that would have been affected by cyanide or chromium contamination. Domestic well monitoring has been conducted quarterly since 1985. Low levels of cyanide (less than 10 ug/l) have been found in numerous domestic wells across the Study Area4. The extent of the higher concentrations of cyanide (more than 10 ug/l) was fairly consistent from 1986 to 1994, within the Study Area (12). For evaluation purposes this health assessment uses the extent of contamination from 1985 to 1995 to approximate the past maximum geographic extent of groundwater contamination. Appendix C lists the domestic wells and the cyanide detections from 1985 to 1995. Figures 3B and 3C depict the extent of cyanide, at concentrations of 10 ug/l and greater, and 50 ug/l and greater, from 1985 to 19955. Based on the estimated flow rate of groundwater in the area, it is not likely that the contamination reached further than the Study Area in the approximately 24 years that groundwater may have been contaminated by RBAAP sources. For this reason, maximum concentrations detected in the private wells during the environmental sampling activities are used to estimate the historical exposure levels of contaminants in these wells.
On- and off-site groundwater monitoring for chromium and cyanide has occurred quarterly since 1985. Contamination has been detected in monitoring wells set in the A', B and C aquifers. There is a noticeable difference in chromium and cyanide levels detected in monitoring wells relative to levels detected in the domestic wells. Monitoring wells are constructed to collect water from a specific zone or aquifer. Monitoring wells are useful in the collecting of groundwater information since detailed construction records are made for each well. Domestic wells, however, may be constructed in such a way as to collect water from a number of zones or aquifers. Well construction records providing information on which specific zones are used for water supplies do not exist for the domestic wells in the Study Area (13). As a result, it is not possible to draw definitive conclusions about the causes of these contaminant level differences except that overall concentrations appear to decrease with depth. It is also likely that the domestic wells collect water from more than one of the aquifer zones, resulting in decreasing the level of contamination by blending (or dilution) of water from several aquifer zones.
Summary: In order to estimate the potential contaminant exposure to residents in the Study Area, we used the following assumptions: the maximum exposure time period, 1963 to 1993; the maximum concentrations of the contaminants detected in the domestic wells; and in the most toxic forms of these contaminants.
Based on the assumptions that the maximum amount of time during which exposure to contaminants in the groundwater off-site near RBAAP was from about 1963 to 1993, the years of operation, and the estimated groundwater flow rate (100 ft/yr), we estimated that the maximum extent of the chromium and cyanide contaminant plumes would be within the boundaries of this Study Area. Sampling conducted from 1985 to the present confirms that the significant amounts of contamination are not likely to have reached beyond the down-gradient boundaries of the Study Area (5).
Current data support the projection that off-site chromium and cyanide groundwater contamination is actually limited to the portion of the Study Area as shown in Figure 3.
1. Past Crop Consumption
Total chromium levels in most fresh produce are extremely low, higher concentrations of chromium have been reported in plants growing in high chromium-containing soils, compared with plants grown in normal soils (21). Appendix B contains an evaluation was made of the potential for harmful health effects of this consumption based on the maximum levels detected in RBAAP groundwater samples to date. This evaluation indicates that no adverse health effect are expected. Additionally, there is no indication of biomagnification of chromium along the terrestrial food chain (soil-plant-animal) (21).
A limited number of studies exist on accumulation of cyanide in plants. Not all types of fruit and vegetables bioaccumulate cyanide. Nonetheless, in some types of produce, cyanide can accumulate at levels higher than found in the water used for irrigation (22), so that exposure might be possible through the consumption of certain homegrown produce watered from wells in the Study Area.
The primary cyanide source in food is cyanogenic glycosides. Over 2650 plant species can produce hydrogen cyanide, but cyanogenic glycoside content varies widely and is affected by heat processing. The potential toxicity of cyanogenic plants depends on their ability to release hydrogen cyanide at concentrations of concern for human health. While cyanide concentrations in fresh foods are extremely variable, cyanide has been generated from vegetables such as cabbage, broccoli, turnips, and cauliflower, and unpitted fruits such as peaches, plums, apricots, and cherries. Cyanide levels in cassava root have been reported to be as high as 1515 ppm, which is considerably above the level identified in the conservative scenario described above. The actual exposure scenario is unknown. Because of this uncertainty, ATSDR examined the scenario to evaluate whether cyanide in homegrown produce could be of concern.
It is not possible to make a general statement regarding the potential for harmful levels of cyanide to accumulate in these home garden crops. There is little information in scientific literature on the potential for long-term effects of exposure to low levels of cyanide in plants (22).
The most likely adverse effect would be the result of an acute (short-term) exposure to fruit or vegetables with sufficient cyanide accumulated to cause an immediate reaction. Systemic poisoning with (hydrogen) cyanide include; shortness of breath, acidosis, nausea, vomiting, headaches, or a general feeling of weakness. If an adverse effect is not detected immediately after consumption, no public health hazard is expected to result from the exposure to produce watered with contaminated groundwater. The acute exposure effect would not be the type that occur at any great length of time (e.g., days or years) after the exposure, but would be evident within hours of consuming the affected produce (22).
No Study Area home garden samples have been collected and analyzed for cyanide bioaccumulation. Without information on the specific bioaccumulation or information on types and quantities of produce consumed it is not possible to predict or estimate whether accumulation would have occurred at levels that might be of concern. It is also not possible to extrapolate accumulation levels in plants from concentrations of cyanide found in wells without specific information about watering techniques (e.g. water sprinklers would tend to dissipate much of the cyanide before it would be available to the plants); types of produce grown; and amounts consumed.
Since information is lacking on bioaccumulation in produce, on past home gardening practices, on consumption habits for residents in the area of the contaminant plume, and on past health effects that might have resulted from consumption of homegrown produce, the public health hazard is considered indeterminate for this pathway.
To date, residents in the affected area outside RBAAP have not expressed health concerns to regulators or the Army during the provision of alternate water supplies or during RBAAP public involvement activities (15). As a result, there are no reported or documented adverse health effects that might have resulted from consumption of contaminated groundwater. The small numbers of people in the affected area (about 72 families) precludes the use of formal epidemiological statistical analyses to estimate possible effects. Appendix B describes the evaluation of the potential for harmful health effects of cyanide in home grown produce and the conditions under which the potential for harmful health effects might occur. Residents of the Study Area with concerns about the possibility of cyanide contamination of home gardens can contact the ATSDR information "hotline" (1-800-447-1544) for further information. (Please refer to Riverbank Army Ammunition Plant when asking for assistance.)
1. Current Crop Consumption
In 1993, at the time that public water supplies were provided, the Army notified the residents of the Study Area by letter about the potential for cyanide or chromium contamination (7). As a result, current use of groundwater in the Study Area should be limited to non-domestic purposes, however, the water is available for use in watering livestock and crop irrigation. We evaluate here the current use of groundwater for irrigation and potential bioaccumulation in plants.
Environmental sampling conducted for the RI/FS has been analyzed for a complete list of hazardous substances required by EPA. In addition to chromium and cyanide, other hazardous substances intermittently detected in well water samples, on- and off-site include several volatile organic compounds (VOCs) reported in a 1990 document (11). The VOCs detected are 1,1 dichloroethene (up to 3.9 ug/l); toluene (up to 4.1 ug/l);, methylene chloride (up to 7.0 ug/l); chloroform (up to 6.7 ug/l); trichloroethene (up to 2.6 ug/l); carbon tetrachloride (3.7 ug/l); 1,1,1 trichloroethane (2.0 ug/l); and chloroethane (1.0 ug/l). VOCs are not likely to accumulate in plants because the VOCs would volatilize during watering. Furthermore, these concentrations do not exceed ATSDR comparison values for drinking water contamination, so that no harmful health effects are expected.
As mentioned, the most frequently and regularly detected contaminants are chromium and cyanide. These are also the contaminants found in concentrations high enough to require a more detailed evaluation.
We looked at 1996 analytical information for this report to determine the likely scenario for current exposure situations. In sample analyses performed in the fourth quarter of 1996, none of the private well samples contained chromium or cyanide above California's or EPA's Safe Drinking Water Standards, or MCLs of 50 ug/l for chromium and 200 ug/l for cyanide. A maximum level of 24.3 ug/l chromium was found in one private well, D-62. Cyanide was not detected in any of the private wells above the detection level of 16 ug/l (14).
If the current maximum concentration in groundwater were applied to home gardens, the pathway of interest would be ingestion of fruits and vegetables. Total chromium levels in most fresh foods are extremely low. Higher concentrations of chromium have been reported in plants growing in high chromium-containing soils, compared with plants grown in normal soils (21). Appendix B contains an evaluation of the potential for harmful health effects of this consumption based on the maximum levels detected to date. The evaluation indicates that no adverse health effects are expected. Additionally, there is no indication of biomagnification of chromium along the terrestrial food chain (soil-plant-animal) (21). Therefore, consumption of crops which have been watered using chromium-contaminated groundwater is not expected to result in a public health hazard.
Since cyanide is not currently found in groundwater in private wells, uptake of cyanide via consumption of homegrown agricultural products watered from these wells is not a public health hazard.
2. Current Livestock Consumption
Chromium is not likely to accumulate in animals (21). Therefore, consumption of livestock that have been watered using chromium-contaminated groundwater is not expected to result in a public health hazard.
Cyanide is not currently found in groundwater in private wells, more importantly, cyanide does not accumulate in animals and biomagnification does not occur through the food chain, therefore uptake of cyanide via consumption of livestock watered from these wells is not a public health hazard.
3. Past Livestock Consumption
We also investigated the past use of groundwater for irrigation and the potential biomagnification in livestock. Chromium is not likely to accumulate in animals, and is therefore not likely to result in a public health hazard as a result of consumption of livestock watered from domestic wells in the Study Area (22).
Cyanide does not accumulate in animals and is not likely to have resulted in a public health hazard from consumption of livestock watered with contaminated water from domestic wells in the Study Area in the past (22).
4. Past Drinking Water Consumption/Showering
Chromium: Possible past exposures may have included oral ingestion of drinking water, and inhalation and dermal (skin) contact while showering. Based on a maximum level of chromium of 117 ug/l detected in domestic wells (of those residence not receiving bottled water), for an exposure period of 1963 to 1993, past contact via ingestion of groundwater from domestic wells is not likely to be a public health hazard. Appendix B presents the evaluation.
Past exposure pathways of inhalation and dermal absorption are more difficult to evaluate. However, because chromium is not readily absorbed through the skin, the low levels detected in groundwater are not likely to present a health hazard. Therefore, we do not expect past and current dermal contact to present a public health hazard.
Because it is rare for soluble chromium compounds to volatilize from water to the air, it is highly unlikely that adverse health effects would result via the inhalation pathway (21). A small amount of inhalation of chromium may occur via inhalation of mist or particulate matter, but these inhalation pathways would not be expected to cause adverse health effects. Therefore, they do not represent public health hazards.
Cyanide: Currently, there is not adequate scientific research information available to show that adverse health effects can occur as a result of long-term (chronic) exposure to low levels of cyanide. The most likely effects are acute, occurring as a result of short-term exposure. Using the maximum cyanide level detected in any of the domestic wells (169 ug/l)(8), and using a maximum exposure time period of 1963 to 1993, we determined that past exposure to contamination via ingestion of groundwater from domestic wells is not likely to be a public health hazard. Appendix B contains the evaluation.
Because hydrogen cyanide is volatile, we also examined an estimate of the past exposure of individuals to cyanide via inhalation during showering. This scenario includes the following assumptions: (1) the maximum concentration of cyanide detected in domestic wells (113 ug/l) was assumed to be the exposure concentration; (2) all cyanide was assumed to be in the form of hydrogen cyanide and available for inhalation for 15 minutes, once per day for 24 years; and (3) absorption was assumed to be 100%. Based on these assumptions, we concluded that no adverse health effects are expected. We did not investigate dermal exposure to cyanide because it is less toxic than exposure via inhalation at low levels, and considering all of the cyanide available for inhalation did not result in levels of concern for health effects.
1. Current Drinking Water Consumption
An evaluation of the potential public health hazard is being made to determine whether a public health hazard could result from consumption of groundwater In 1993, the residents of the Study Area were connected to the municipal water supply, thus, ATSDR assumes that no one is using the groundwater as a source of drinking water. However, if the groundwater is being used for drinking, it would not present a public health hazard because the level of chromium detected is below the MCL (50 ug/l). Also, in the recent groundwater sampling investigations, cyanide has not been detected in any of the off-site private wells.
Groundwater is not currently used as a drinking water source at RBAAP. According to information provided by the facility, bottled water has been provided as drinking water for workers by RBAAP since 1986 (7). The former source of drinking water was a facility well located in a deep aquifer (about 600' in depth) that has not been affected by RBAAP contamination. As worker populations declined during the late 1980s, there was concern that bacteriological contamination might occur in water lines in the lesser-used areas of the facility. Bottled water has been provided as a precaution against this bacteriological contamination. ATSDR staff observed during the 1996 site visit that remaining water taps are labeled to prevent people from unknowingly drinking the potentially contaminated water.
Future Actions: The remedial actions recommended in the Army's March 1994 Record of Decision are nearing completion (5). The following actions were recommended, and are being implemented to reduce or eliminate groundwater contamination:
- The inactive landfill has been capped.
- On-site groundwater extraction and treatment have been in effect since 1991.
- The off-site extraction system began operation in the fall of 1996.
Although it is unlikely that people are drinking groundwater in the Study Area, the successful completion of these actions will serve as effective elimination of the potential for any adverse public health effect from RBAAP groundwater contamination in the Study Area.
II. Exposures From Contamination at the E-P Ponds Area.
We determined that another situation poses no apparent public health hazard because, although contamination exists, it is not likely that anybody is being exposed, and the contaminant levels are low. This exposure situation involves residual metals in the groundwater, surface water and sediment contamination in the area of the E-P ponds. Also a part of this exposure situation is the potential for contamination, via recharge of groundwater into the Stanislaus River, of water, sediment or fish in that river. Moreover, current disposal practice, as required by state and federal regulatory oversight, will not result in additional hazardous chemicals being released into this area.
Contamination in the E-P Ponds: Since 1952, a series of evaporation-percolation (E-P) ponds have been used to collect waste water. The waste water contained zinc and other metals, as well as cyanide, used in the electroplating of shell casings. Waste water in the E-P ponds was allowed to evaporate, or percolate into the subsurface, causing contaminants to settle out into sediment or be transported into the subsurface and groundwater. Between 1952 and 1992 untreated waste water containing cyanide and metals was diverted to the E-P ponds. Cyanide was neutralized there, but the metals were deposited in the sediment. After 1965, waste water was diverted to a specially-constructed portion of the Industrial Wastewater Treatment Plant (IWTP), which used chlorine to treat the cyanide. These wastes were then pumped into the E-P ponds. An estimated total of 3.95x109 gallons of wastewater passed through the IWTP (3).
Since 1992, waste water has been treated before release to the E-P ponds according to standards set and monitored by the state of California (17,18). Those current regulatory limits are protective of public health. In the event that limits are exceeded, treatment is required to reduce levels to within the limits set. Because the permits monitor for and regulate contaminants (including cyanide and chromium) in the effluent discharged by RBAAP, it is unlikely that the treated water is a current source of appreciable contamination to the E-P ponds and adjacent area.
As a result of past disposal practices, the E-P ponds contained metals at levels that EPA determined required remediation. Analysis of surface sediment samples collected from these ponds in 1990 detected varying levels of metals contamination. Zinc was detected at levels up to 12,000 mg/kg. In addition to zinc, the following metals were detected in sediments in 1990: antimony (0.2 mg/kg), arsenic (18.3 mg/kg), cobalt (up to 20.7 mg/kg), chromium III (up to 370 mg/kg), chromium VI (up to 1.5 mg/kg), copper (up to 70 mg/kg), fluoride (up to 5,300 mg/kg), lead (up to 93 mg/kg), mercury (up to 1.7 mg/kg), nickel (up to 207 mg/kg), silver (up to 2.7 mg/kg), and vanadium (up to 73 mg/kg).
In 1993, the Army removed from the E-P ponds zinc-contaminated sediments that exceeded the state action level of 5,000 mg/kg. A total of 1,118.5 cubic yards of soil was removed to an off-site disposal area. It should be noted that short-term and infrequent contact with sediments containing these levels is not considered an imminent hazard . Contact with sediment contaminated with zinc at this level would only be a potential public health hazard if exposure was frequent and long-term. Such long-term and frequent exposure is unlikely at the E-P ponds.
The metals detected in groundwater in the area of the E-P ponds include arsenic (up to 9 ug/l), chromium (20 ug/l), copper (up to 30 ug/l), manganese (200 ug/l), nitrate (up to 14,000 ug/l), selenium (4 ug/l) and sulfate (up to 150,000 ug/l). None were detected at levels that exceeded comparison values (16). Moreover, there are no groundwater wells located down gradient between the E-P ponds and the Stanislaus River. It is therefore, not likely that people have been exposed groundwater contamination from this source. Also, removal of "hotspots" of metal contamination at the E-P ponds further reduces the potential for groundwater contamination in this area. For these reasons, groundwater contamination in the vicinity of the E-P ponds does not represent a public health hazard.
1. Current Exposure Via Possible Groundwater Discharge to the Stanislaus River
The Stanislaus River is a surface water body potentially at risk from hazardous materials at RBAAP. The path of concern for the Stanislaus River would be via discharge of groundwater from under the E-P ponds into the river.
The low levels of contaminants detected in groundwater under the E-P ponds of the Stanislaus River via groundwater do not represent a public health hazard. Furthermore, the levels of contaminants would be lowered upon mixing with river water in the event that discharge from contaminated into the Stanislaus River did occur.
Sediment samples from the Stanislaus River were collected to determine whether contaminants were reaching the river at levels of concern. The following contaminants were found in the sediment samples; aluminum (up to 7780 mg/kg), barium (up to 90.1 mg/kg), chromium (up to 59.3 mg/kg), copper (up to 25 mg/kg), lead (up to 5.0 mg/kg), magnesium (up to 3900 mg/kg), manganese (up to 329 mg/kg), nickel (up to 28.9 mg/kg), silver (2.5 mg/kg), vanadium (up to 33.3 mg/kg) and zinc (up to 53.9 mg/kg). These levels of contaminants are not likely to result in public health effects, particularly with the limited potential for exposure. These contaminants were found in upstream sampling at similar levels, so that it is not likely that the E-P ponds are contributing significant amounts of contaminants to the river sediments.
2. Past Sediment Contact With Contaminants in the E-P Ponds
Until 1995, access by the public to the E-P ponds was not restricted. People might have been exposed to contaminants in water or sediment in the E-P ponds primarily by dermal contact or accidental ingestion. However, the ponds are located in a remote area, so that it is unlikely that regular and frequent exposure would occur. It is unlikely that members of the public would swim in or otherwise be in dermal contact with the water and sediment in these ponds on a regular or frequent, long-term basis. It is also very unlikely that water or sediment was ingested except incidentally or infrequently. The levels of contaminants found do not present a public health hazard from the type of infrequent, short-term and irregular contact that would occur as a result of trespassing onto the grounds of the E-P ponds.
Based on these assumptions, our conclusion is that sediment contamination in the E-P ponds
(both past and present) presents no apparent public health hazard.