SITE INFORMATION AND CORRESPONDENCE_1987-1992

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MEMORANDUM* CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: Antonia Vorster FROM: Michael Higgins Senior Engineer Project Engineer DATE: 26 June 1991 SIGNATURE: SUBJECT: PHASE II SITE ASSESSMENT REPORT, LINCOLN VILLAGE CENTER, STOCKTON, SAN JOAQUIN COUNTY I have reviewed the 24 April 1991 "Phase II Site Assessment Report" on the ground water and soil pollutant characterization at the Lincoln Village Center. Kennedy/Jt�ks Consultants (kJC) are preparing a Phase III workplan for additional site characterization. The workplan will include a proposed time schedule through which Lincoln Village Properties (LVP) will clean up the polluted ground water. LVP has agreed the time schedule will be incorporated into a Cleanup and Abatement Order. SUMMARY The Phase II site assessment has not defined the extent of the polluted ground water plume in either the vertical or the horizontal directions. Lincoln Village Properties (LVP) needs to complete additional monitoring wells, appropriately located and screened, to determine the pollution's extent. The report does not adequately demonstrate the water-bearing zones independence nor does it fully substantiate the derivation of the aquifer transmissivities and storativities. Pumping tests of the extraction wells must be adequately justified. BACKGROUND In 1984, sampling and analysis detected tetrachloroethane (PCE) , trichloroethene (TCE) and trans-1,2 dichloroethene (DCE) in concentrations exceeding Title 22 MCLS in San Joaquin County Public Works municipal supply well LVMD1. Likely sources of the volatile halocarbons (VOCs) are three dry cleaning operations. Based on the first phase of the investigation, wherein KJC installed four ground water monitoring wells (MWs) , leaking sewer lines appear to be the pollutants' source. A soil vapor survey identified several areas beneath which significant soil or ground water VOCs pollution were suspected. In Phase II of the site assessment, the approved scope of work included: the completion of 8 shallow MWs and three intermediately deep MWs to try to define the VOCs' extent, the installation of eight soil borings, a videotape survey of the water supply wells, and slug and pumping tests to estimate aquifer parameters. KJC also surveyed 44 drinking water supply wells and an irrigation well within a one-mile radius of the site to determine the well depth and the depth of the screened interval . The Phase II investigation determined the VOCs have migrated off-site in both the westerly and north-easterly directions. The report recommends to further assess the VOCs' extent in the shallow and intermediate water-bearing zones, confirm that the deepest zone contains no VOCs, further investigate soil source areas and install an early warning MW. In a 23 May 1991 letter, we approved the early warning well .