The San Gabriel Valley’s groundwater Basin has the dubious distinction of being one of the most contaminated in the nation. The Basin’s groundwater is contaminated from the ground disposal—dating back to World War II— of volatile organic compounds used primarily as solvents in industrial and commercial activities.

The seriousness of the groundwater contamination problem became evident when high concentrations of volatile organic compounds (“VOCs”) were discovered in Azusa in 1979 near a major industrial complex. Over the next four years, further investigation revealed widespread VOC contamination significantly impacting the Basin. This discovery led USEPA to place four portions of the Basin on the National Priorities List (“NPL”) under authority of CERCLA, also known as the Superfund program. These areas are referred to as Operable Units (“OUs”) under CERCLA. Currently, there are six active OUs: Baldwin Park, El Monte, South El Monte, Puente Valley, Area 3 and Whittier Narrows.