RIVERBANK ARMY AMMUNITION PLANT

Description and History

The 173-acre Riverbank Army Ammunition Plant site has been used to manufacture materials, including cartridge cases, grenades, and projectiles, since 1951. The site comprises the 145-acre main facility and four unlined industrial waste treatment ponds in the flood plain of the Stanislaus River, located approximately 1 1/2 miles north of the main facility. In 1942, the Aluminum Company of America built the site plant as an aluminum reduction facility to supply the military. The plant closed in 1944 and reopened in 1951, with Norris Industries, Inc. as the operating contractor. As a result of industrial activities, the site has generated corrosive wastes, solvents, and wastewater containing heavy metals. Chromium and cyanide have been released onto the property and have subsequently leached into the groundwater, and over the years the contaminant plumes have migrated beyond the installation boundary. In addition, a variety of waste and debris were burned or disposed of on the ground surface and in trenches in a landfill area at the facility. Studies also have determined that sediments in the waste treatment ponds contain elevated levels of zinc. Overflows from the ponds have dumped into the Stanislaus River, and the river has occasionally overflowed into the ponds during periods of flooding. Approximately 13,700 people obtain drinking water from public and private wells within 3 miles of the site, and at least 3,500 acres of nut and fruit orchards are irrigated partially by groundwater. The Stanislaus River is used for irrigation and recreational activities.

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Contaminants and Risks

Groundwater is contaminated with chromium and cyanide. Soils in the landfill are contaminated with chromium and arsenic. Sediments in the industrial waste treatment ponds contain zinc and petroleum. Potential human health threats include drinking contaminated groundwater and showering or bathing with the water, and accidentally coming into contact with or ingesting contaminated soils from the landfill or sediments from the ponds. Potential ecological threats include exposure of local land-dwelling and migratory species to contaminated soils from the landfill and to sediments from the ponds.

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Who is Involved

This site is being addressed through Federal actions.

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Investigation and Cleanup Activities

This site is being addressed in two stages: immediate actions and a long-term remedial phase focusing on cleanup of the entire site.

Immediate Actions: When chromium was found in off-site domestic water wells in 1989, the Army supplied affected residents with bottled water. The Army subsequently closed the contaminated wells and replaced them with new deeper, clean wells. The Army completed an interim groundwater treatment system that became fully operational in October 1991. This system treats chromium and cyanide contaminants from extracted groundwater. In 1991, the Army began work to extend the existing City of Riverbank's public water supply system to all residents who have been, or could potentially be, affected by the contaminated groundwater. By December 1992, the residents were connected to the Riverbank water system. In 1993, the Army removed petroleum and zinc-contaminated sediments from its industrial waste treatment ponds and disposed of the sediments off-site. Groundwater around the ponds is monitored quarterly as a requirement in the National Pollution Discharge Elimination System (NPDES) permit for the ponds.

Entire Site: A remedy was selected in the spring of 1994 that includes a comprehensive groundwater extraction and treatment system for the contaminated groundwater; stabilization, capping, and monitoring of the landfill; and no further cleanup action for the ponds, which were cleaned up through the immediate actions described above. The Army completed its design of the landfill cap in late 1994. Design and construction of the groundwater extraction and treatment system were completed in November 1996.

Groundwater Extraction and Treatment. The groundwater extraction system and treatment plant is in operations and maintenance (O&M) mode. The groundwater treatment plant and extraction wells are monitored daily. Groundwater treatment influent is sampled monthly. Groundwater from certain monitoring wells are sampled quarterly.

Evaporation Ponds. A removal action of the contaminated soil was completed in December 1993.

A Record of Decision (ROD) signed in March 1994 documented no further action for the evaporation ponds.

Landfill. Construction of the landfill cap was completed in November 1995. Routine landfill O&M such as mowing and weed control, occasional revegetation, minor erosion and drainage repair is continues.

The Riverbank Army Ammunition Plant is participating in the Installation Restoration Program, a specially funded program established by the Department of Defense (DOD) in 1978 to identify, investigate, and clean up petroleum and hazardous contaminants at DOD facilities. In April 1990, the Army, the EPA, and the State of California signed a Federal Facility Agreement, which established a procedural framework and schedule for the Army to carry out the necessary site cleanup actions.

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Cleanup Results to Date

Supplying residences with clean water, replacing contaminated wells, treating and monitoring the groundwater, and disposing of contaminated sediments have reduced the potential for exposure while final cleanup activities are being planned at the Riverbank Army Ammunition Plant site.

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Potentially Responsible Parties

Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.

Online information about the PRPs for the site is not yet available.

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Documents and Reports

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Community Involvement

Public Meetings:

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Public Information Repositories

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Additional Links

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Contacts

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