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August 5, 1997 <br /> 38737 001 Harding Lawson Associates <br /> Ms Mary Meays <br /> San Joaquin County Public Health Services <br /> Page 2 <br /> Locally the gradient is relatively flat and is subject to variable flow directions, most likely due to local <br /> pumping from nearby irrigation wells (WaterWork, 1991) <br /> SITE HISTORY AND PREVIOUS WORK <br /> Previous Site Investigations <br /> Site investigations were performed under the regulatory oversight of the PHS/EHD and the Regional Water <br /> Quality Control Board (RWQCB) The Site investigation and regulatory history is briefly outlined below <br /> ♦ Removal of five underground storage tanks by TVG in 1987 <br /> ♦ Installation of suc monitoring wells in three phases <br /> • Monitoring wells MW-1, MW-2, and MW-3 (Exceltech, 1987) <br /> • Monitoring well MW-4 (Exceltech, 1988) <br /> + Monitoring wells MW-5 and MW-6 (WaterWork, 1989) <br /> ♦ Quarterly monitoring activities from third quarter of 1989 through second quarter of 1994 (various <br /> reports by WaterWork and RESNA, 1989 to 1994) <br /> ♦ Groundwater pump and treat system second quarter of 1991 through second quarter of 1994 (various <br /> reports by WaterWork and RESNA, 1991 to 1994) <br /> ♦ Soil and groundwater investigation, in two phases, 1994 and 1995 (RAH Environmental 1995a &b) <br /> • Soil borings SB-1 to SB-7 soil and groundwater sampling <br /> • Hand augered borings HA1 to HA3 within the forklift shop soil and groundwater sampling <br /> o Additional soil and groundwater investigation 1996 (Draft SECOR report) <br /> • Soil borings SB-8 to SB-10 soil and groundwater sampling <br /> The locations of the monitoring wells and soil borings, the approximate location and dimensions of the <br /> former USTs and the excavation, the forklift shop and other relevant features are shown on Plate 3 <br /> Following the installation of six monitoring wells, quarterly monitoring activities began in the third <br /> quarter 1989 Continuous operation of a groundwater pump and treat system began in second quarter <br /> 1991 and continued through second quarter 1994 In June 1994,based on previous work and quarterly <br /> monitoring results, PHS/EHD requested additional investigation of the site to assess the potential presence <br /> for remaining impacted soils Two phases of investigation were performed by RAH in 1994 and 1995 <br /> Recent Site Investigation <br /> The PHS/EHD reviewed the two RAH reports(RAH, 1995a and 1995b) and requested that TVG submit a <br /> Corrective Action Plan by July 24, 1995 On June 19, 1995,TVG forwarded a remedial approach proposed <br /> by SECOR International to PHS/EHD for review and comment After PHS/EHD reviewed the plan, a <br /> meeting of representatives for PHS/EHD, TVG, and SECOR took place on September 5, 1995 In this <br /> meeting the PHS/EHD made the following comments and suggestions <br /> ♦ The plan does not adequately address soil contamination Reevaluate soil issues <br /> • The proposed removal of soils between the forklift shop and the historical tank excavation <br /> does not address contamination to 20 feet <br /> + Other contamination may still exist from the original tank removal <br /> Estimate the volume of contaminants in the soil and groundwater <br /> Estimate remediation removal rate and time to complete cleanup <br /> lip, ♦ Develop a Remedial Action Plan and justify the option selected <br /> ♦ Consider the potential impact of the groundwater contamination found on the neighboring property <br /> 1 �+ <br />