Site Name: SAN GABRIEL VALLEY (AREA 1)
EPA ID: CAD980677355 EPA Region: 09 Metro Statistical Area: 4480
PECK RD & REAL, EL MONTE, CA 91733
Operable Unit: 04
ROD ID: EPA/ROD/R09-93/102 ROD Date: 09/22/93
Contaminant: VOCs
Keys: Carcinogenic Compounds; Contingent Remedy; Direct Contact; Floodplain; Ground Water; Ground Water Monitoring; MCLs; PCE; ROD Amendment; Safe Drinking Water Act; Solvents; State Standards/ Regulations; TCE; VOCs
Abstract:
SITE HISTORY/DESCRIPTION:
The San Gabriel Valley Area 1 (Operable Unit 4) site is one of four Superfund sites located approximately 10 to 20 miles east of Los Angeles, Los Angeles County, California. Land use in the area is mixed industrial, commercial, residential, and undeveloped. The site includes four broad areas of ground water contamination underlying significant portions of the cities of Azusa, Baldwin Park, La Puente, Industry, West Covina, El Monte, South El Monte, Monrovia, Arcadia, Rosemead, Alhambra, and other municipalities. In 1983, VOC contamination in ground water was detected by Aerojet Electrosystems in Azusa. Samples taken from a nearby well, owned by the Valley County Water District, identified elevated levels of TCE to 1,800 ug/l. Subsequent State investigations revealed over 50 wells throughout the San Gabriel Basin that were contaminated with TCE, PCE, and/or carbon tetrachloride, and computer modeling predicted that contaminant levels would exceed SDWA MCLs within several years. A 1988 ROD addressed the potential threat to human health posed by contaminated ground water beneath the Suburban Water System's (SWS) Bortolo Well Field, as OU4. The well field consists of four public supply wells located along the east side of the San Gabriel River in the Whittier Narrows area, south of the city of South El Monte. An estimated 51,200 people and approximately 17,000 commercial and residential water connections use these four wells as a water supply. The 1988 ROD also provided for extraction and treatment of ground water onsite using an air stripping system to a level of 1 ug/l, with discharge of the treated water into the SWS's existing water distribution system and installing a granular activated carbon offgas treatment system to control VOC emissions. However, recent investigations have shown that, due to factors such as natural attenuation, dilution and flow patterns, contaminant levels have not risen as expected in the ground water beneath the well field. This ROD amends the 1988 selected remedy for ground water. The primary contaminants of concern affecting the ground water are VOCs, including PCE and TCE.
SELECTED REMEDIAL ACTION:
The amended remedial action for this site includes continuing ground water monitoring for the next five years to evaluate contaminant levels; delaying the construction of the ground water treatment system until such time that monitoring data demonstrates steadily increasing levels of contamination above MCLs for at least 4 months; not treating ground water if contaminant levels remain the same or diminish, or treating ground water, if necessary, using the specified treatment system documented in the 1988 ROD, if appropriate. The estimated present worth cost for this amended remedial action is $24,000,000. This cost change is due to the fact that the original design accounted for less stringent air emissions controls than are now required, and also that the current estimate was based on more detail.
PERFORMANCE STANDARDS OR GOALS:
Subsequent to issuance of the 1988 ROD, EPA and the State developed a new drinking water standard for PCE; therefore, the chemical-specific ground water cleanup goal for PCE is 5 ug/l. Additionally, newly developed State air quality standards for emissions control of the treatment system are considered applicable and will be adhered to during operation of the remedy.
INSTITUTIONAL CONTROLS: Not provided.
Record of Decision Amendment
Suburban Water Systems/Bartolo Well Field Operable Unit
San Gabriel Valley Superfund Site Areas 1-4
Declaration
Statement of Basis and Purpose
This decision document presents the Amendment to the Record of Decision (ROD) for the Suburban Water Systems (SWS)/Bartolo Well Field Operable Unit, in the San Gabriel Valley Superfund Sites Areas 1-4. This decision was made in accordance with the Comprehensive Environmental Response, Compensation, And Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), and the National Contingency Plan (NCP). This decision is based on the Administrative Record file for this Operable Unit (OU). The State of California concurs with this decision.
Description of the Amendment
The remedy selected in the September 29, 1988, ROD for the SWS' Bartolo Well Field OU consisted of the installation of a groundwater treatment system at the SWS' Bartolo Well Field to treat water contaminated with perchloroethene (PCE) to 1 part per billion (ppb). At the time of the 1988 ROD, there was no state or federal standard for PCE. Subsequent to the original ROD, EPA and the State of California have established a new drinking water standard of 5 ppb for PCE. This Amendment sets the treatment level for all contamination at the federal or state drinking water standard, whichever is lower. This Amendment also considers Southern California Air Quality Management District Regulation 13 and Rule 1401 as ARARs for the emissions control system of the treatment plant. Because contaminant levels have not increased in the SWS' Bartolo Well Field (contrary to computer modeling predictions), this Amendment also delays the building of the treatment system until certain conditions are met as described below. EPA will instead evaluate, for at least a 5 year period, water quality sampling results from the SWS' Bartolo Wells in conjunction with sampling results obtained from the Whittier Narrows monitoring network.
If groundwater conditions change to where monitoring data from the three "low" capacity wells or monitoring data from the "high" capacity well and one "low" capacity well, in the SWS' Bartolo Well Field, demonstrate a trend of steadily increasing contamination levels above MCLs for at least a four (4) month period, EPA will begin evaluating optimal locations for a treatment system and begin reevaluating the existing treatment system design or begin evaluating a new treatment system, under the observed groundwater conditions. If the trend above MCLs in the wells mentioned above continues for an additional two (2) month period, EPA will either begin construction of the current treatment system design, if appropriate, or complete design of a new treatment system and implement the design. In the interim, while the treatment system is being designed or constructed, EPA will evaluate the use of, and if feasible, implement mobile or temporary treatment systems.
Declaration
Current groundwater conditions at the SWS' Bartolo Well Field pose no public health threat, therefore, no remedial action is necessary at this time. However, future groundwater conditions cannot be accurately predicted and may change over time. EPA will therefore monitor and evaluate groundwater data from the SWS' Bartolo Well Field over a five-year period, to ensure continued protection of public health. The five-year period to be used for the review will start when field work (monitoring well installation) for the Whittier Narrows ROD commences.
9-22-93
John C. Wise, Acting Regional Administrator Date
Remedy: