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Riverbank Army Ammunition Plant (RBAAP) is in Stanislaus County near Riverbank, California, approximately 100 miles east of San Francisco, California. RBAAP comprises about 175 acres, consisting of 145 acres within the Main Plant Area, and 30 acres of evaporation-percolation (E-P) ponds located about 1½ miles north of the Main Plant Area. RBAAP was listed on the National Priorities List (NPL) in 1990, primarily as a result of groundwater contamination.

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 nine scenarios which had a potential for human exposure. These scenarios are grouped in our evaluation into two sets of general settings: 1) Exposures from Groundwater Contamination in the Study Area West of the Main Facility, and 2) Exposures from contamination at the E-P Ponds area (1½ miles north of the main facility). We evaluated exposure situations from past, current, and future scenarios.

We concluded that all current potential exposure situations pose No Apparent Public Health Hazard.

1) Exposures From Groundwater Contamination in the Study Area west of RBAAP: Off-site groundwater in the area immediately west of the facility has been documented to be contaminated with chromium and cyanide. Residences located in the area of the offsite plume have been provided with alternative water supplies since 1993.

One possible exposure situation, Past Crop Consumption, was evaluated as being an Indeterminate Past Public Health Hazard. This was the possibility of past exposure to cyanide via consumption of produce (fruits, nuts, vegetables) watered with contaminated groundwater in the Study Area.

The amount of uptake of cyanide, and the amount of accumulation that occurs in plants varies greatly from species to species. Also, we do not know the actual amount of home gardening in the affected area of the Study Area during the past. Past exposure via this pathway would not be likely to cause long-term effects, or latent effects (effects that might not be apparent for a number of years).1 There are no reports of past adverse acute health effects occurring in the area. Even though there is no evidence that harmful exposure occurred in the past, because of the lack of actual information2, past exposure via consumption of homegrown produce watered with contaminated groundwater is considered an Indeterminate (due to lack of data) Public Health Hazard. A detailed discussion of this evaluation is provided in the " Past Crop Consumption" subsection of "Evaluation of Possible Groundwater Exposure Pathways West of the Main Facility".

All other situations related to groundwater contamination in the Study Area west of RBAAP were evaluated to pose No Apparent Public Health Hazards. Those included: Current Crop and Livestock Consumption, Past Livestock Consumption, and Past Drinking Water Consumption.

The current levels of cyanide and chromium contamination detected in groundwater in the Study Area are not sufficient to present a public health hazard via consumption of livestock or crops currently watered with groundwater. Past consumption of livestock would not have resulted in a public health hazard, in that accumulation of the contaminants, in livestock, is unlikely.

Although, in the past contact with contaminated groundwater likely occurred from a limited number of domestic wells, the relatively low concentrations of contaminants were not likely to have resulted in a public health hazard. The low levels of contamination present now, combined with the provision of alternate water supplies further reduces the likelihood that harmful exposure is occurring. For these reasons, these situations pose No Apparent Public Health Hazard.

2) Exposures From Contamination at the E-P Ponds Area: The other location where contamination has moved outside the main facility boundaries is the E-P ponds area, located about 1½ miles north of the main facility. The contamination has migrated into groundwater under the E-P ponds and possibly into sediment in the Stanislaus River adjacent the ponds. Contamination levels are low and likelihood of exposure is limited and posesNo Apparent Public Health Hazard.


Riverbank Army Ammunition Plant (RBAAP) is in Stanislaus County, near Riverbank, California, approximately 100 miles east of San Francisco, California. (Note: Appendix A provides a listing of all abbreviations and acronyms used in this public health assessment.) Figure 1 shows the location of RBAAP in relation to the city of Riverbank and surrounding area. RBAAP comprises about 175 acres, consisting of 145 acres within the Main Plant Area, and 30 acres of evaporation-percolation (E-P) ponds located about 1½ miles north of the Main Plant Area. The predominant land use in the vicinity is agricultural, with scattered single-family residential development (1).

Riverbank's population is approximately 8,500. The population within a 1-mile radius of the facility is about 3,400. The population in the immediate vicinity of RBAAP is predominantly concentrated within the residential area located adjacent to the western boundary of RBAAP.

The facility is bordered on the east by pasture land, and on the north, west and south by sparsely populated residential areas. The densest housing is located west of the plant. This residential area of about 230 acres, consists of 72 "ranchettes" with small-scale agricultural activities producing livestock and crops intended primarily for the personal use of the owners. The first eight of these residences were built in 1950 (2). This area is referred to as the "Study Area" in this report and in remedial reports generated for RBAAP.

The primary focus of this report is on the groundwater contamination and the potential for public health impacts on the community.

Site History

RBAAP was originally constructed by the Aluminum Company of America (ALCOA), under the authority of the Defense Plant Corporation. The plant started production on May 18, 1943, producing about 40,000 tons of aluminum per year. The plant was closed by order of the War Production Board on August 7, 1944. After it was closed as a production facility, the plant was used for storage of a variety of government surplus materials, including corn and grain. Following a series of intergovernmental transfers, the property was assigned to the Army on June 1, 1951, and was converted to the manufacture of steel cartridge cases. Cyanide was used in large quantities in the plating processes that were a part of the casing production. Cyanide wastes were initially disposed in a landfill in the northeastern portion of the Main Plant Area (1). Other wastes generated by the plating process were primarily metals, such as chromium, cobalt, copper, lead, mercury, nickel, silver, and zinc.

Figure 1
Figure 1: Site Location Map

A series of evaporation-percolation (E-P) ponds have been used 1952 to the present for disposal of industrial wastewater generated by RBAAP. Since 1992, the discharge has been regulated by National Pollutant Discharge Elimination System (NPDES) regulations administered by the U.S. Environmental Protection Agency (EPA) and the state.

On September 17, 1952, production commenced under Norris Thermador Corporation, continuing until the end of the Korean conflict (1954), when the plant was placed on standby status. The Army used the landfill from 1952 to 1954 to dispose of a wide variety of materials including solid waste and sludge. During the 1952-1954 production period, zinc-plated shells were produced for the U.S. Navy. Zinc was electroplated from a cyanide solution. Cyanide waste was diverted to a specially-constructed portion of the Industrial Wastewater Treatment Plant (IWTP), using chlorine to treat the cyanide. These wastes were then pumped into the E-P ponds. It is estimated that a total of 3.95x109 gallons of wastewater have passed through the IWTP (3). There were no records maintained for amounts of plating wastes disposed at the landfill. Starting in 1966, solid waste, including plating waste was disposed offsite (3).

The facility was reactivated in 1966 to produce 105 millimeter (mm) artillery casings and 60 and 81 mm mortar casings and operated until 1975 (1). From 1975 to 1994, operations were limited to small scale and short-term production runs. In 1994, the facility was deactivated and placed in preservation status. Other than environmental restoration activities, the only activities occurring at present are those necessary for long-term storage or surplusing of the manufacturing equipment.

Remedial Activities

EPA regulates hazardous waste at RBAAP under both the Resource Conservation and Recovery Act (1976) (RCRA) and Comprehensive Environmental Response, Compensation and Recovery Act (1980) (CERCLA), known as Superfund. Generally speaking, RCRA covers waste generated at existing, functional industrial facilities, whereas CERCLA covers waste facilities that are no longer active. Environmental studies were first conducted at RBAAP in 1980. RBAAP was listed on the National Priorities List (NPL) in 1990, primarily as a result of groundwater contamination. Between 1987 and 1994, RBAAP characterized the nature and extent of contamination. The chemicals used, generated or disposed have contaminated groundwater, soils and sediment. Information on this contamination characterization appears in numerous environmental documents generated by the facility. Chromium and cyanide are the primary off-site groundwater contaminants, while various metals, primarily zinc, have contaminated soils and sediments in the area of the E-P ponds.

Remedial Actions (RA) recommended in the March 1994 Record of Decision are nearing completion (5). The inactive landfill has been capped with clean soil and has a drainage system to direct surface water runoff into the plant waste water treatment system. Additionally, metals-contaminated soils and sediment have been removed from the E-P ponds north of the main facility. The on-site groundwater treatment system has been active since the spring of 1995. The off-site groundwater extraction system began operation in the fall of 1996. These remedial activities are intended to reduce or eliminate the groundwater contamination. Groundwater monitoring wells, located on- and off-site, are sampled quarterly to check for reduction in concentrations of chromium and cyanide. Confirmatory sampling and analysis will serve to verify the success of the groundwater treatment systems.

ATSDR Involvement

After entering into a memorandum of understanding with the Department of Defense (DOD) in 1991, Agency for Toxic Substances and Disease Registry (ATSDR) sent representatives to the 96 DOD installations then on the NPL and ranked them according to their potential public health hazards. ATSDR personnel visited RBAAP in December, 1991. On this initial visit, ATSDR staff reviewed the available site-specific information and visually inspected the contaminated sites and areas where hazardous substances have been released into the environment. ATSDR staff also met with the mayor of the city of Riverbank and with representatives of the city water department. The focus of the visit was to determine if people could come into contact with site contaminants at levels that pose a health hazard, and if necessary, to recommend actions to stop or prevent such exposures. RBAAP's priority for public health assessment ranked relatively low among DOD installations. In June 1996, ATSDR staff visited the site again to obtain updated environmental information collected during remedial activities that began in 1991. ATSDR staff met with representatives of the Army, U.S. Environmental Protection Agency (EPA) and state environmental regulators. ATSDR evaluated the current environmental situations, the potential for ongoing exposure of the community to contaminated groundwater, and collected information about the nature and extent of community health concerns.

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