SAN GABRIEL VALLEY (AREA 1) El Monte, South El Monte, Whittier Narrows

Description and History

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 sites include four large areas of groundwater contamination that 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 parallels the San Gabriel River to the east. 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

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.

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 is to identify areas of the site for focused study and provide support to ongoing cleanup efforts. This study is expected to continue through late 1997.

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. Since 1996 contaminant levels had increased significantly. EPA evaluated new alternatives to control the migration of the contaminated groundwater, and in 1999 issued a Record of Decision Amendment 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 now meet 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.

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.

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 one of the Potentially Responsible Parties. A cleanup plan is to be proposed in mid 1999. An Interim Record of Decision (ROD) was signed in September 2000. A ROD amendment is being prepared to incorporate treatment of emergent chemicals in the area.

Source Identification and Control: The California Regional Water Quality Control Board, Los Angeles Region, working under a Cooperative Agreement with the EPA, is identifying the sources of contamination. To date, nearly 400 individual facilities have been confirmed as having soil contamination.

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 has entered into an agreement with the City of Whittier to operate and maintain the treatment facility and to supply treated water to local businesses and residents. EPA conducted the first Five-Year Review for the remedy in September 2006 and is currently implementing recommendations from the report.

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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.

Description	File
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

Administrative Records
		El Monte Operable Unit
		El Monte OU, Remedial, Update 5
		South El Monte Operable Unit
		South El Monte OU, Remedial, Update 2 & 3
		Whittier Narrows Operable Unit
Fact Sheets
	10/01/98	EPA Proposes Plan to Address Groundwater Contamination at El Monte Operable Unit of the San Gabriel Valley Superfund Site
	10/01/98	EPA Proposes Plan to Address Groundwater Contamination in the Whittier Narrows Operable Unit (155 Kbytes)
	02/01/00	Groundwater Well Installation and Sampling Program / Programa de Instalación y Monitoreo de Agua Subterránea
	05/01/02	U.S. EPA Completes Whittier Narrows Groundwater Treatment System
	11/01/05	The U.S. Environmental Protection Agency (EPA) Announces Changes To The Cleanup Plan For The San Gabriel Valley Superfund Site (Area 1) South El Monte Operable Unit
Images
		Whittier Narrows treatment plant
Legal Documents
	04/21/04	Consent Decree
Records of Decision
	05/11/84	Richwood Operable Unit, Record of Decision
	09/01/87	Richwood Operable Unit, Record of Decision Amendment, Decision Summary
	06/22/88	Bartolo Well Field, Operable Unit Feasibility Study for the Record of Decision
	09/27/88	Suburban Operable Unit (Bartolo Well Field), Record of Decision
	03/31/93	Whittier Narrows Operable Unit, Record of Decision
	09/22/93	Suburban Operable Unit (Bartolo Well Field), Record of Decision Amendment
	06/01/99	El Monte Operable Unit, Interim Record of Decision, text, tables and figures
	11/01/99	Whittier Narrows Operable Unit, Interim Record of Decision Amendment
	11/01/99	Whittier Narrows Operable Unit, Interim Record of Decision Amendment, Figures
	11/01/99	Whittier Narrows Operable Unit, Interim Record of Decision Amendment, Tables
	09/01/00	South El Monte Operable Unit, Interim Record of Decision
	09/01/00	South El Monte Operable Unit, Interim Record of Decision, Figures (all PDF files)
	09/01/00	South El Monte Operable Unit, Interim Record of Decision, Tables
	08/22/02	El Monte Operable Unit, Explanation of Significant Differences to the 1999 Record of Decision
	11/10/05	South El Monte Operable Unit, Explanation of Significant Differences To The 2000 Interim Record of Decision
Technical Documents
	09/28/06	Whittier Narrows Five Year Review Report

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Community Involvement

Public Meetings:

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Public Information Repositories

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Additional Links

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Contacts

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