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Pacific Southwest, Region 9: Superfund

Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations

San Gabriel Valley (area 1) El Monte, South El Monte, Whittier Narrows

EPA #: CAD980677355

State: California(CA)

County: Los Angeles

City: El Monte

Congressional District: 28,31

Other Names:

Bulletin Board

On 10/13/17, this website will no longer be updated. Site information will be migrated to the new web page at: http://www.epa.gov/superfund/sangabrielelmonte .
EPA appreciates your patience through this transition. If you have questions, please contact EPA staff listed below.


Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 09/08/83

Final Date: 05/08/84

Deleted Date:

The San Gabriel Valley (Area 1) site is an area of contaminated groundwater over 4 miles long and 1½ miles wide located in the San Gabriel Valley. In 1984, the EPA identified four large areas of groundwater contamination in the San Gabriel Valley; each area is a separate Superfund site. The Superfund sites underlie significant portions of the Cities of Alhambra, Arcadia, Azusa, Baldwin Park, Industry, El Monte, La Puente, Monrovia, Rosemead, South El Monte, West Covina, and other areas of the 170 square-mile San Gabriel Valley. Over 30 square miles of groundwater under the Valley may be contaminated. Contamination of the groundwater by volatile organic compounds (VOCs) was first detected in 1979 when Aerojet Electrosystems in Azusa sampled nearby wells in the Valley County Water District. Subsequently, the California Department of Health Services (CDHS) initiated a well sampling program to assess the extent of contamination. By 1984, 59 wells were found to be contaminated with high levels of VOCs. Hundreds of individual facilities could be contributing to the contamination in the basin through improper handling and disposal practices. The area of contamination is to the east of and along the San Gabriel River. The basin's groundwater provides approximately 90 percent of the domestic water supply for over 1,000,000 people who live in the Valley. Over 400 water supply wells are used in the basin to extract groundwater for industrial, business, agricultural, and domestic uses. Forty-five different water suppliers operate in the basin and provide drinking water to more than 1,000,000 people. In 1992, EPA completed construction of a water treatment plant for the Richwood Mutual Water Company to assist them in providing water that meets drinking water standards.

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Contaminants and Risks

Contaminated Media
  • Groundwater
  • Soil and Sludges

Groundwater and soil are contaminated with various VOCs, predominantly trichloroethylene (TCE) and tetrachloroethylene (PCE). People who inhale vapors from groundwater that contain VOCs could be exposed to hazardous substances. Currently, all drinking water provided meets Federal and State drinking water standards.

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Who is Involved

This site is being addressed through Federal and State actions.

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Investigation and Cleanup Activities

This site is being addressed in five long-term remedial phases focusing on cleanup of area-wide contamination, the Whittier Narrows area, the Suburban Water System's Bartolo Well Fields, the Richwood Mutual Water Company area, the El Monte Area, the South El Monte Area, and identification and cleanup of the source of contamination.

Site Studies

Area-wide Contamination: In 1984, the EPA began a study into the nature and extent of contamination throughout the four San Gabriel Valley sites. The intent of the investigation was to identify areas of the site for focused study and provide support to ongoing cleanup efforts. The investigation and cleanup were split into multiple areas. A Five Year Review for the entire Area 1 Site was completed in 2013.

Source Identification and Control: The California Regional Water Quality Control Board, Los Angeles Region, and the California Department of Toxic Substances Control are investigating and remediating some sources of contamination.

Remedy Selected

Whittier Narrows Area: In 1987, the EPA began a study of the nature and extent of contamination in the Whittier-Narrows area of the San Gabriel Valley. The investigation led to a decision in 1993 that no immediate action was needed but that monitoring would continue. Starting in 1996, contaminant levels had increased significantly, so EPA evaluated new alternatives to control the migration of the contaminated groundwater. In 1999, EPA issued an amended Record of Decision calling for extraction and treatment of groundwater from extraction wells just north of the Whittier Narrows Dam.

Suburban Water Systems: Bartolo Well Field: Design of the potential cleanup activities was completed in 1991. However, groundwater contamination levels at the Bartolo Well Field and throughout the area adjacent to and upgradient from the wells dropped and met federal drinking water standards. Therefore, the remedy was amended in the fall of 1993 to include monitoring only, with a contingency plan to treat groundwater should contaminant levels again exceed federal drinking water standards. The contingency has not yet been necessary.

El Monte : In March 1995, an agreement was reached between U.S. EPA and 15 Potentially Responsible Parties (PRPs). In the agreement, the PRPs have committed to complete the regional investigation of the area which was completed in early 1998. A cleanup plan was proposed in late 1998. An Interim Record of Decision was signed in June 1999. An Explanation of Significant Differences was signed in 2002 which incorporated treatment for emergent chemicals in the area.

South El Monte : Regional investigation of the area was completed in late 1998 under an agreement between U.S. EPA and a group of Potentially Responsible Parties. An Interim Record of Decision (ROD) was signed in September 2000. An ESD was issued in 2005 to address the treatment of emerging chemicals. The remedy was declared Operational and Functional in 2013. EPA is currently conducting a supplemental RI to evaluate additional cleanup options.

Cleanup Ongoing

Richwood Mutual Water Company: In 1992, the EPA installed a water treatment system to provide clean water to the Richwood Mutual Water Company. In 1993, responsibility for operating the plant was transferred from the EPA to the California State Department of Toxic Substances. San Gabriel Valley Water Company now serves these customers and the treatment system has been dismantled.

Whittier Narrows OU: The 1999 ROD Amendment selected groundwater extraction and treatment as the remedy. EPA started construction of the Whittier Narrows Groundwater Extraction and Treatment Facility in June 2001 and completed construction in March 2002. The facility consists of seven groundwater extraction wells, conveyance pipelines, and 20 pairs of granular activated carbon (GAC) filter vessels for removal of VOCs. EPA conducted the first Five-Year Review for the remedy in September 2006, a subsequent Five-Year Review in 2011, and a third one in 2016. The Operation and Maintenance of the remedy was transferred to DTSC in May 2013. DTSC is currently pursuing a long term operation and maintenance agreement with water rights holders to accept the treated water.

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Cleanup Results to Date

Completed actions to ensure that residents are being provided with a safe drinking water supply have addressed immediate site contamination concerns. The EPA performed preliminary investigations and determined that residents near the San Gabriel Valley (Area 1) site are protected while studies are taking place and final cleanup actions are being planned.

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Potentially Responsible Parties

Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.

August 1995 Remedial Investigation/Feasibility Study notice letter recipients, South El Monte operable unit
February 2001 Pre-Remedial Design/Remedial Action notice letter recipients, South El Monte operable unit
July 2001 Remedial Design/Remedial Action special notice letter recipients, El Monte operable unit
March 2002 Remedial Design/Remedial Action special notice letter recipients, South El Monte operable unit

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Documents and Reports

Show details for Administrative RecordsAdministrative Records
Show details for Fact SheetsFact Sheets
Show details for ImagesImages
Show details for Legal DocumentsLegal Documents
Show details for Records of DecisionRecords of Decision
Show details for Technical DocumentsTechnical Documents

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Community Involvement

Public Meetings:

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Public Information Repositories

The public information repositories for the site are at the following locations:

Rosemead Library
8800 Valley Boulevard
Rosemead, CA 91770
(626) 573-5220

West Covina Library
1601 West Covina Parkway
West Covina, CA 91790
(626) 962-3541

South El Monte Library
1430 North Central Avenue
South El Monte, CA 91733
(626) 443-4158

The most complete collection of documents is the official EPA site file, maintained at the following location:

Superfund Records Center

Mail Stop SFD-7C

95 Hawthorne Street, Room 403

San Francisco, CA 94105

(415) 820-4700

Enter main lobby of 75 Hawthorne street, go to 4th floor of South Wing Annex.

Additional Links

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EPA Site Manager
Rebecca Connell
Mariam Fawaz
Kathleen Aisling
US EPA Region 9
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
Viola Cooper
US EPA Region 9
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
State Contact
Christine Bucklin
Department of Toxic
Substances Control

Carlos Ortez


5796 Corporate Avenue
Cypress, CA 90630-4732

Regional Water Quality
Control Board
PRP Contact
Community Contact
Other Contacts
After Hours (Emergency Response)
(800) 424-8802

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