Stringfellow

Investigation and Cleanup Activities

This site is being addressed in five phases: an initial action phase, and four long-term remedial action phases including the installation of a pre-treatment plant, contaminant source control, the cleanup of the lower canyon, and the hydraulic control and cleanup of the contamination affecting the community water supply wells.

Initial Actions

Initial Actions: From 1980 to 1984, three groundwater extraction wells, a subsurface barrier structure, and an on-site surface water drainage system with gunite channels were built. All liquid wastes at the surface of the site were removed to a Federally approved hazardous waste disposal facility. With the exception of 1,000 cubic yards of DDT-contaminated soil, which were taken to a Federally approved disposal facility, contaminated soils from the Site were used to backfill on-site waste ponds. The waste ponds were filled, graded, covered with clean soil, and seeded. In 1984, the State completed initial cleanup measures including fencing, soil cap maintenance, implementing erosion control measures, and disposing of leachate extracted from above and below the on-site clay barrier dam. In 1989, residences that had been receiving bottled water from the State were connected to the Jurupa Community Services District water supply system .

Cleanup Ongoing

Pre-Treatment Plant: In 1984, the EPA selected a remedy for interim treatment of contaminated groundwater. The remedy featured installing a pre-treatment system consisting of lime precipitation for removing heavy metals and granular activated carbon treatment for removing VOCs. The treated groundwater is discharged into the sanitary sewer system. Interceptor wells were installed to extract contaminated groundwater downgradient of the Site. The State completed installation of the pre-treatment plant in 1985. As of March 1996, nearly 128 million gallons of groundwater had been extracted and treated.

Cleanup Ongoing

Source Control: In 1984, the State completed its evaluation of alternatives for groundwater contaminant source reduction and determined that the existing pump and treat system would be sufficient to cleanup groundwater TCE contamination at the Site. The treatment system will operate until established cleanup levels have been met.

Extraction and treatment of contaminated groundwater started in 1985 and is ongoing. Bench-scale testing of groundwater treatment technologies was performed in 2004. Following the evaluation of the results (ongoing), a new pretreatment plant (Pyrite Canyon Treatment Facility) will be designed and build. Procurement of land for the new plant is ongoing, the new plant was designed and will be built in 2013. The final site wide remedy will be selected in 2015.

Cleanup Complete

Lower Canyon: In 1987, the EPA selected a remedy to: 1) capture and treat groundwater in the lower canyon area of the Site with a groundwater barrier system; 2) install a peripheral channel to divert clean surface water run-off from up-gradient areas; 3) extend the existing gunite channels southward to discharge the diverted water into Pyrite Creek; and 4) reconstruct the Pyrite Creek Channel. The State designed the groundwater barrier system and completed the construction of the channels in 1990.

Remedy Design

Community Wells and Source Control: In 1988, the State and the EPA completed an investigation for the type and extent of groundwater contamination in the Pyrite Canyon and in Jurupa Valley area. In 1990, the EPA selected downgradient in Lower Canyon. In 1992, the potentially responsible parties installed groundwater extraction wells to hydraulically control the plume of contaminated groundwater. An additional extraction well was added in 1997 to increase the area of capture in downgradient areas. This collective groundwater extraction and treatment system, called the Community Wellhead Treatment System (CWTS), is located on private property at 5020 Pedley Road in Jurupa Valley and treats groundwater from two Zone 4 wells using granular activated carbon (GAC). The treated water (approximately 25 gallons per minute) is reused for local irrigation, i.e., tree farm/nursery irrigation.

In 1997, the State carried out additional investigation of the source area and began a well drilling program for additional extraction wells to enhance the capability of the de-watering facilities at the site.

Investigation of the extent of perchlorate contamination in downgradient areas (Zone 4) started in 2004 and is on-going. The Zone 4 Remedial Investigation was completed in February 14, 2010, and the Feasibility Study is scheduled to be completed in 2014.

In 1983, the Department of Justice, on behalf of the EPA, joined with the State to file a suit against 32 potentially responsible parties. As a result of a 1988 Administrative Order on Consent, an amendment to that Order in 1992, and a 1992 Consent Decree, the potentially responsible parties developed the engineering designs and agreed to construct cleanup remedies for certain aspects of the cleanup. As of January 1996, the majority of this work had been completed. However, additional work may still be required. The State assumed responsibility for the cleanup of the Stringfellow Superfund Site in 2001. The State is currently conducting a Zone 4 Supplemental Feasibility Study to evaluate remedial alternatives for the cleanup of perchlorate contamination. EPA is also conducting a Zone 5 Remedial Investigation / Feasibility Study to evaluate potential sources west of Pyrite Creek. These studies will form the basis for decisions about long term remedies for the site.