The historical presence of agricultural and industrial pollutants in the Main San Gabriel Valley Basin has made groundwater quality a long-standing integral focus of the San Gabriel Valley Water Association.
Groundwater contamination discovered in the late 1970s led the U.S. Environmental Protection Agency (EPA) to place the Basin on the National Priorities List (NPL), leading to the 1986 declaration of five Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also known as Superfund, contamination sites: Baldwin Park, El Monte, Whittier Narrows, South El Monte and Puente Valley.
In 1993, the state Legislature created the San Gabriel Valley Water Quality Authority (WQA) and provided additional state funding to tackle the longstanding groundwater contamination issues in the Valley. The Watermaster maintains groundwater quality and the WQA manages the funding.
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