SITE INFORMATION AND CORRESPONDENCE

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101 S.Wilson Way, Stockton Page 2 The faxed analytical results for MW6 and MW7 of the sampling event that took place at this site on December 12, 2001, show MtBE as high as 21,000 pg/I in MW6A and BTEX and TPH-g in all the ground water samples collected. The consultant for the ARCO at 130 S Wilson Way, Stockton, completed a well survey and reported the results in August 2001. There are three inactive and one active well operated by California Water Service down gradient and within 2000 feet of their site and your site. According to Step 3 within the State Water Resources Control Board Guidelines for Investigation and Cleanup of MtBE and other Oxygenates (Guidelines)final draft dated 30 March 2000,sites with persistent concentrations of MtBE over 10,000 ppb should perform interim remediation to reduce the concentrations and mass before the plume can spread. MtBE has been detected in groundwater samples from VW36 and MW6A at concentrations above 10,000 ppb, so interim remediation should be proposed for this site. The Quarterly Reports recommend performance of a ground water aquifer pumping test to predict general aquifer characteristics at the site in order to design an interim ground water pump and treat remediation system. The pump test data along with the other site geologic data should also be used to estimate the approximate travel time for the contaminant plume to reach nearby receptors. If the contaminant travel time to the nearest receptor is estimated to be less than 5 years,then a remedial action plan should be implemented in less than a year. An eight hour vapor extraction test was performed on VW 1 B (screened interval 28 to 43 feet) in January 1996 when first groundwater was about 55 feet below surface grade. A Corrective Action Plan—March 1996 was submitted to EHD in April 1996,which recommended vapor extraction and air sparging. In a letter dated October 22, 1996, EHD requested a specific design and cost estimate for a modified remediation system be submitted for review. An August 13, 1997, Quarterly Report states that a Remedial Action Work Plan dated July 3, 1997,was submitted to EHD for this site. EHD files do not contain that work plan. Remedial options of vapor extraction, air sparging, groundwater extraction, and ozone injection should all be evaluated for this site. A work plan to install any wells necessary to evaluate these alternatives along with a plan for performing tests for these alternatives should be submitted to EHD by March 4, 2002. In addition, the lateral and vertical extent of the soil and groundwater contamination must continue to be investigated. The work plan submitted should include installation of additional monitoring wells that will define the extent of the contamination at and emanating from this site. Please be advised that groundwater samples from monitoring wells MW3, MW4 and MW 14 at 102 S. Wilson Way, Stockton, which is across the street and down gradient from this site have increasing concentrations of MTBE that may be emanating from this site. Please work with the responsible parties and consultants for the sites at 102 S.Wilson Way and 130 S.Wilson Way, Stockton,to determine current and previous groundwater flow direction and provide delineation of the contaminant plumes for each site. If you have any questions or comments call Rebecca E. Setliff at(209) 468-3440. Donna Heran, REHS, Director vironmental Health Department J� �--f11.ea U ebecca E. etli HS Margaret Lagorio, Supervising REHS LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV cc: Marty Hartzell, CVRWOCB Timothy J. Cuellar, Advanced GeoEnviron mental, Inc.