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PUBLIC &ALTH SERV?CES O.p4�IN' .0 <br /> ..o <br /> SAN JOAQUIN COUNTY :Z <br /> ENVIRONMENTAL HEALTH DIVISION P. <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Offic� �^ <br /> 304 E. Weber Ave., Third Floor • P. O. Box 388 • Stockton, CA 95201-0388 acfSoaa•P <br /> 209/468-3420 AtJ U L 1 i iy56 <br /> BOB BOUST <br /> UNOCAL <br /> 2000 CROW CANYON PL STE 400 <br /> SAN RAMON CA 94583 <br /> RE: 437 East Miner Ave SITE CODE: 1181 <br /> Stockton CA 95202 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> completed review of the "Quarterly Data Report" dated May 30, 1996 which was prepared by <br /> MPDS and the "Soil Remediation Feasibility Study Work Plan" dated April 30, 1996 which was <br /> prepared by GeoStrategies. PHS/EHD has the following comments for your consideration. <br /> The results of the groundwater sampling event of May 7, 1996 continued to evidence significant <br /> contamination on site and off site, both in downgradient and crossgradient directions. Also, <br /> Sequoia Analytical indicated that the sample collected from monitoring well, U3, contained methyl <br /> tertiary butyl ether (MTBE) at/or in excess of 40 ppb. As you know regulatory standards for MTBE <br /> have not yet been established, but that the action level is 35 ppb. Laboratories are generally able to <br /> quantify MTBE to concentrations less than 40 ppb. All wells should undergo MTBE analysis with <br /> EPA Method 8020 using detection limits as close to 0.5 ppb as possible, with numerical results <br /> reported. <br /> The work plan proposed to use the existing vapor extraction well, UV1 (screened 15 - 40 feet <br /> below grade) to evaluate the feasibility of vapor extraction to remediate the estimated volume of <br /> contamination, 8,900 cubic yards, with 56,819 pounds of TPH-gas and 236 pounds of benzene. <br /> The proposed feasibility test will be scheduled over a six month period with the other existing <br /> groundwater monitoring wells to be used to estimate a radius of influence. Current depth to <br /> groundwater is approximately 37 feet below grade and the nearest groundwater monitoring wells, <br /> U1 - U3, are screened from 30 to 55 feet below grade. Once the feasibility test is initiated, it may <br /> be necessary to install additional vapor extraction wells for the express purpose of evaluating the <br /> potential effectiveness of vapor extraction and to obtain system design information. Also, since <br /> UV1 contains sufficient groundwater for sampling, during the feasibility test groundwater samples <br /> should be collected for analysis. <br /> Please proceed with permitting with the San Joaquin Valley Air Pollution Control District to start up <br /> the vapor extraction test. Also, please contact the City of Stockton to obtain building permits. <br /> If you have any questions, please contact me at (209) 468-0337. <br /> Donna Heran, REHS, Director <br /> Environmental Health Division <br /> Mary Meay�r REHS M rg e agorio, REHS <br /> 10 <br /> Site Mitigation Unit Lead Senior <br /> MM/437MINER <br /> cc: Elizabeth Thayer, CVRWQCB <br /> cc: Stephen Carter, GeoStrategies 3164 Gold Camp Ste. 240, Sacramento CA 95670 <br /> cc: Sutter Office Center, 2001 Union Street Ste.300, San Francisco CA 94123 <br /> A Division of San Joaquin County Health Care Services <br />