SITE INFORMATION AND CORRESPONDENCE_1

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Del Monte/Disco Page 2 This factor as well as dilution must be considered when evaluating contaminant levels . PHS/EHD has received recommendations from the Regional Water Quality Control Board, State Water Resources Control Board, and Department of Health Services, Drinking Water Branch to request groundwater samples undergo analysis for methyl tert- butyl ether (MTBE) . MTBE was introduced into gasoline in the late 1970' s as an oxygenator. Groundwater samples are to be analyzed using EPA Method 8020 (602) with a one time only confirmation analysis using EPA Method 8260 (624) . Subsequent to this confirmation, MTBE can be identified and quantified during routine BTEX analysis . Please include MTBE in the quarterly groundwater sampling analysis . If MTBE is not detected after two rounds of groundwater sampling its, analysis may be discontinued. In order to reduce groundwater sampling costs for this site, PHS/EHD recommends that the perimeter wells MW-DIS-3 , MW-DIS-BS, MW-DIS-BD, MW-DIS-9, and MW-DIS-10, be sampled every 6 months instead of every three months . The resultant schedule would be as follows : the sampling of MW-DIS-1, MW-DIS-2, MW-DIS-3 , and MW- DIS-10 one quarter and the sampling of MW-DIS-1, MW-DIS-2, MW- DIS-8S, MW-DIS-BD, and MW-DIS-9 the next quarter. This rotation would continue until other changes are proposed. The following items were requested in the PHS/EHD letter dated October 2 , 1995 and have not been submitted; the amount of soil generated from November 1994 through February 1995, with an explanation as to how the drill cuttings were shown to be clean or contaminated; the amount of water generated during the pump tests; the disposition of the purge water from quarterly monitoring; the as built specifications for the vapor extraction system. These items should be submitted as an addendum to this report by April 1, 1996 . The PID reading for February 16, 1995 was 10, 000 ppmv not 6, 000 ppmv as shown on Table 3 , so the pounds of TPH(g) removed should be recalculated accordingly. Please include this information in the above requested addendum along with the mathematical formula used to calculate the pounds of hydrocarbon removed. Wells SVE-3 and SVE-4 were installed in December 1995 . These wells are screened from 55 feet below grade (fbg) to 75 fbg instead of 50 fbg to 70 fbg, as agreed to in your letter dated November 29, 1995 . Depth to groundwater measured on February 13 , 1996, was approximately 62 fbg, which leaves only 7 feet of screened interval in the vadose zone. PHS/EHD has been informed by Del Tech that these wells have been connected to the vapor extraction system. PHS/EHD recommends that further tests be conducted using these wells to determine the radius of influence of vapor extraction and air sparge wells .