SITE INFORMATION AND CORRESPONDENCE

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to be 3. Y Question: utili ed to define investigative and vvertical d lextent of contamination. Response: To define the lateral extent of groundwater contamination to the east we propose that two additional wells be installed. Figure 1 shows the proposed locations . This work will be performed in accordance with our April 20, 1989 Preliminary Report . A revised PAR will be submitted after the laboratory results are received. 4. Question: The gasoline contamination detected in groundwater samples ( 2, 000 parts per billion) should be addressed, in addition to the diesel and other residual contaminants found in the soil and groundwater samples. Response: A review of the laboratory chromatogram for MW3 and MW4 indicates that the contamination is diesel fuel. The gasoline analysis picked up diesel where it overlaps into the gasoline range. An explanation from the laboratory is attached for your records. 5. Question: Refer to the Tri-Regional Board Staff Recommendations, table 2 ( page 17 ) for the minimum verification methods to be used for gasoline and diesel products . The detection limits most applicable to this investigation are those in the LUFT Manual. Response: During future investigations the lower detection limits will be used. 6. Question: Groundwater samples obtained from on-site monitoring wells were analyzed for total and fecal coliform bacteria. Total coliform concentrations in excess of 1600 per 100 milliliters were reported in two of the monitoring wells. This poses a serious health threat. The source of the coliform analyses is to be performed. Response: Total coliform concentrations of 1600 MPN/100 ml do not necessarily indicate a "serious health threat" , however, requests for further sampling and investigation of the coliform found in the groundwater should be directed to the Municipal Utilities District and not included as a part of a underground tank program investigation.