The El Monte Operable Unit (EMOU) addresses a 1 ½-square-mile area of contamination underlying parts of the cities of El Monte and Rosemead, and a small portion of Temple City. The primary contaminants are volatile organic compounds (VOCs).

The U.S. Environmental Protection Agency (EPA) adopted a cleanup plan for the El Monte area in 1999, and updated the plan in 2002. Four water treatment systems have been constructed as part of the cleanup.

This operable unit is generally characterized by contamination in the shallow zone that is mostly contained in the upper 100 feet of the aquifer. Limited amounts of VOC contamination have migrated into the deeper drinking water supplies and the recent discovery of perchlorate in monitoring and production wells threatens to further complicate cleanup efforts.

Responsibility for implementing the remedy has been divided into two groups of Potentially Responsible Parties. Each side has its own remedies to construct. The WQA funded early actions and continues to work with the EPA, water suppliers and Potentially Responsible Parties to facilitate the cleanup.

WQA is a co-lead agency with the City of El Monte for the EMOU East Side Interim Remedial Action Eastside Shallow Zone and Southern Deep Zone Remedy.

Additional information:

Appendix A in WQA’s Groundwater Quality Management and Remediation Plan (406 Plan)