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102 S. Wilson Way <br /> Page 2 <br /> The vapor extraction system should not be removed from this site. The vapor <br /> extraction system appears to have removed contamination above groundwater in <br /> the areas of confirmation borings CB1 , CB2 and CB4. When boring TB5 (area of <br /> former dispensers) was drilled soil samples showed contamination existed from 5 <br /> to 25 feet below surface grade. Soil samples from confirmation boring CB3 <br /> showed that soil contamination still exists above groundwater in this area. Vapor <br /> extraction well VW5 is screened from 14 to 42 feet. The feasibility of vapor <br /> extraction in the area of CB3 and T65 should be investigated. In addition, the <br /> feasibility of using air sparging and/or groundwater extraction with vapor <br /> extraction to remediate the soil and groundwater contamination should be <br /> investigated. Contaminant levels in the groundwater from monitoring wells MW5, <br /> MW13 and the vapor wells are high and require active remediation. <br /> In a letter dated April 10, 2000, PHS/EHD recommended you destroy MW13 and <br /> replace it with multi-level cluster wells. This is still our recommendation. <br /> PHS/EHD does not agree with the destruction of any other wells. <br /> Quarterly monitoring and reporting for this site must continue until the <br /> investigation and cleanup are complete. Groundwater samples collected should <br /> continue to be analyzed for the same contaminants by the same methods <br /> previously used. In order to reduce monitoring costs for this site PHS/EHD would <br /> approve the following sampling routine: <br /> 1) MW3, MW4, MW5, MW8, MW14'to be sampled every quarter. <br /> 2) MW1, MW2, MW7, MW9, MW12, VW1, VW3 to be sampled semi-annually. <br /> 3) MW6, MW10, MW11, VW2, VW4, VW5, VW6 to be sampled semi-annually <br /> during the quarters that the wells in #2 are not sampled. <br /> A work plan for the installation of monitoring well clusters or multi level wells, <br /> destruction of MW13 and investigation of remedial alternatives should be <br /> submitted to PHS/EHD by September 17, 2001. <br /> If you have any questions contact me at (209) 468-3449. <br /> Donna Heran, RENS, Director <br /> Environmental Health Division <br /> � <br /> Margaret Lagorio, Supervising REHS <br /> Unit IV <br /> C: Ground Zero Analysis, Inc. — Greg Stahl <br /> CVRWQCB — Marty Hartzell <br />