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101 S Wilson Way, Stockton <br /> Page 2 <br /> The faxed analytical results for MW6 and MW7 of the sampling event that took place at this site on <br /> December 12, 2001, show MtBE as high as 21,000 µg11 in MW6A and BTEX and TPH-g in all the <br /> ground water samples collected <br /> The consultant for the ARCO at 130 S Wilson Way, Stockton, completed a well survey and reported <br /> the results in August 2001 There are three inactive and one active well operated by California Water <br /> IService down gradient and within 2000 feet of their site and your site <br /> According to Step 3 within the State Water Resources Control Board Guidelines for Investigation and <br /> I Cleanup of MtBE and other Oxygenates (Guidelines) final draft dated 30 March 2000, sites with <br /> persistent concentrations of MtBE over 10,000 ppb should perform interim remediation to reduce the <br /> concentrations and mass before the plume can spread <br /> MtBE nas been detected in groundwater samples from VW31B and MW6A at concentrations above <br /> 10,000 ppb, so interim remediation should be proposed for this site <br /> The Quarterly Reports recommend performance of a ground water aquifer pumping test to predict <br /> general aquifer characteristics at the site in order to design an interim ground water pump and treat <br /> remediation system The pump test data along with the other site geologic data should also be used <br /> to estimate the approximate travel time for the contaminant plume to reach nearby receptors If the <br /> contaminant travel time to the nearest receptor is estimated to be less than 5 years, then a remedial <br /> action plan should be implemented in less than a year <br /> An eight hour vapor extraction test was performed on VW1 B (screened interval 28 to 43 feet) in <br /> January 1996 when first groundwater was about 55 feet below surface grade A Corrective Action <br /> Plan—March 1996 was submitted to EHD in April 1996, which recommended vapor extraction and air <br /> sparging In a letter dated October 22, 1996, EHD requested a specific design and cost estimate for a <br /> modified remediation system be submitted for review An August 13, 1997, Quarterly Report states <br /> that a Remedial Action Work Plan dated July 3, 1997, was submitted to EHD for this site_ EHD files do <br /> not contain that work plan <br /> Remedial options of vapor extraction, air sparging, groundwater extraction, and ozone injection should <br /> all be evaluated for this site A work plan to install any wells necessary to evaluate these alternatives <br /> along with a plans for performing tests for these alternatives should be submitted to EHD by March 4, <br /> 2002 In addition, the lateral and vertical extent of the soil and groundwater contamination must <br /> continue to be investigated The work plan submitted should include installation of additional <br /> ,Monitoring wells that will define the extent of the contamination at and emanating from this site <br /> I Please be advised that groundwater samples from monitoring wells MW3, MW4 and MW14 at 102 S <br /> Wilson Way, Stockton, which is across the street and down gradient from this site have increasing <br /> concentrations of MTBE that may be emanating from this site Please work with the responsible <br /> I parties and consultants for the sites at 102 S Wilson Way and 130 S Wilson Way, Stockton, to <br /> determine current and previous groundwater flow direction and provide delineation of the contaminant <br /> plumes for each site <br /> If you have any questions or comments call Rebecca E Setliff at (209) 468-3440 <br /> Donna Heran, REHS, Director <br /> vironmental Health Department <br /> ebecca EteW&S Margaret Lagono, Supervising REHS <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> I c:. Marty Hartzell, CVRWQCB <br /> V/imothy J Cuellar, Advanced GeoEnvironmental, Inc <br />