MIRA LOMA, CA
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The Stringfellow site is a hazardous waste facility and plume of contaminated groundwater in Jurupa Valley, California. Improper disposal practices contaminated soil, surface water and groundwater with volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), pesticides and metals, among other contaminants. Cleanup, operation and maintenance activities, and monitoring are ongoing.
What Has Been Done to Clean Up the Site?
The site is being addressed through federal, state and potentially responsible party (PRP) actions.
From the 1970s to 1990s, EPA, the Santa Ana Regional Water Quality Control Board, the California Department of Toxic Substances Control (DTSC) and PRPs carried out or funded cleanup work at the site. Currently, the DTSC is implementing all cleanup work at the site. DTSC became the primary response party at the site in 2002. DTSC operates and maintains three groundwater treatment systems, has made numerous improvements to the three systems since they were constructed, has completed several technology evaluations, conducts periodic groundwater and surface water monitoring, and prepares a variety of site-related technical reports. EPA is responsible for overseeing all remediation work at the site.
EPA has conducted several five-year reviews of the site’s remedy. These reviews ensure that the remedies put in place protect public health and the environment, and function as intended by site decision documents. The most recent review concluded that response actions at the site are in accordance with the remedy selected by EPA and that the remedy continues to be protective of human health and the environment in the short term. Continued protectiveness of the remedy requires optimization of existing monitoring and extraction well systems, evaluation of the need for additional monitoring or extraction wells, and verification of off-site perchlorate sources.
What Is the Current Site Status?
EPA divided the site into four areas to help manage and prioritize cleanup activities.
Zone 1: The long-term remedy included off-site disposal of liquid wastes, groundwater extraction, surface water control, erosion control and fencing the site.
Zone 2: The long-term remedy included groundwater migration control and construction of an on-site groundwater treatment plant.
Zone 3: The long-term remedy included groundwater migration control and surface water control.
Zone 4: The long-term remedy included groundwater dewatering and groundwater restoration.
Cleanup activities in Zone 1 have included draining, filling and capping the disposal pits; construction of an upgradient groundwater and surface water interception system; construction of a subsurface clay barrier dam; and a groundwater control and dewatering system. The pre-treatment plant began operation in 1985, removing metals, pesticides and other organic contaminants from Zone 1 and Zone 2 groundwater before discharging treated water to an industrial sewer line. The state is constructing a new treatment plant to replace the pre-treatment plant and expects it to begin operation in 2015.
A second groundwater treatment system began operation in 1990. This system treats groundwater from Zone 3 and Zone 4. A third groundwater treatment system began operation in 1998 to treat groundwater from Zone 4. Studies are ongoing to determine whether water quality conditions require additional cleanup. EPA is conducting studies to determine whether other perchlorate sources exist on or off the site.