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6230 Pacific, Stockton Canepa's Car Wash, Page 2 (MCL) for MTBE of 13 ppb or below; this may be resolved by going to the EPA 8260 analysis. If your laboratory cannot produce these detection limits, EHD requests you look for a laboratory with that capability. Results of non-detect at detection limits above 13 ppb will not be accepted by EHD. 4) EHD agrees with your request to reduce the schedule of groundwater sampling of MWS, MW6, and MWy from a quarterly to an annual basis, but continue conducting groundwater elevation measurement on a quarterly schedule. 5) EHD does not agree with the proposal to completely eliminate MW-8. MW-8 is required for zero concentration delineation of the groundwater plume in the southeast direction. EHD will approve destruction of MW-8 to accommodate construction development at the site on the condition that MW-8 must be replaced with a monitoring well in the southeast area. 6) The down gradient (east) extent of the methyl tert butyl ether (MTBE) contamination in groundwater has not been defined. Analytical results of the groundwater samples from the furthest-most sampling point toward the east, MW-3, show increasing MTBE concentrations in groundwater, indicating active migration of the MTBE plume. Submit to EHD a work plan that includes installation of at least one monitoring well beyond MW-3 toward the east to define the lateral extent of the contamination. 7) Include in the above-requested work plan a proposal to implement interim remediation to enhance the soil vapor extraction (SVE) system currently in operation at the site. The SVE has had minimal effectiveness removing dissolved MTBE, which has been consistently reported in the groundwater samples collected from the source area at concentrations above 10,000 ppb. According to State Water Resources Control Board final draft guidelines for investigation and cleanup of MTBE and other oxygenates, dated March 30, 2000, aggressive interim remediation in the source area is necessary to prevent potential impact to downgradient receptors and to reduce the spreading out of a diluted plume. In addition to the domestic and municipals wells identified in the 2000- foot well survey report dated August 16, 2001 , prepared by CET, multiple City of Stockton public wells exist northeast and east of the site: three wells are located just north of Lincoln, and another one to the east, south of Benjamin Holt and west of El Dorado. Interim remedial action should be implemented as soon as possible to control migration of the plume toward these receptors. Please feel free to contact Jeffrey Wong at (209) 468-0335 if you have any questions. Donna Heran, REHS, Director ] E viro mental Health Department-� c ' � 0 ° Jr.Jeffrey ong , Sr. RENS Nuel C. Henderson, , RG LOP/Site Mitigation Unit IV LOP/Site Mitigation, Unit IV c: RWQCB, Central Valley Region —James L. L. Barton, RG C Condor Earth Technologies — Don Kresse/Jeff Willett