SITE INFORMATION AND CORRESPONDENCE

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w 2905 West Benjamin Holt Drive September 1997 Page 2 vapor extraction may be difficult. PHS/EHD has been informed that the depth to water is regularly checked during the remediation system's maintenance checks. An update on the operation of the soil vapor extraction system should have been included in the Addendum. The draft Addendum and the Corrective Action Plan stated that the operation of the SVE system will continue until the system is no longer effective on a mass-removal basis and that effectiveness will be evaluated on the basis of SVE influent concentrations attaining asymptotic levels. Since there has not been radius of influence estimates submitted and there are always questions regarding design efficiencies, physical evidence through confirmation soil sampling will be required at the conclusion of the soil remediation effort to evaluate effectiveness and to estimate the extent of any remaining soil contamination. The air sparging wells which have been installed were screened between 27 and 30 feet bgs. PHS/EHD understands that the air sparging system (biosparging system) is currently in operation. The operation specifications were not included in the Addendum, although air sparging is reported as responsible for the increase in concentrations observed in MW5. A description of the operation of the air sparging system should have been included in the Addendum. The final Addendum must include an evaluation of the interim remediation system which was installed,a radius of influence, and the expected time and cost to remediate the soil and groundwater. Cleanup Goals The draft Addendum stated that it is PHS/EHD's requirement to clean up to below the Maximum Contaminant Levels(MCLS)established for drinking water. PHS/EHD clearly stated in correspondence dated November 30, 1995 that cleanup goals should be in accordance with the Central Valley Regional Water Quality Control Board's Basin Plan. Soil cleanup goals were not included in the draft Addendum. Soil cleanup goals which must be included in the final Addendum, should be based on the threat which remaining soil contamination may pose to groundwater quality. A Final Addendum incorporating PHS/EHD's comments shall be submitted by October 10, 1997. The third quarter's monitoring report must be submitted immediately. If you have any questions or comments, please contact Mary Meays at(209)468-0337. Donna Heran, REHS,Director Environmental Health Division Mary Meays, Senior REHS Margaret agorio, RENS Site Mitigation Unit Supervisor cc: Elizabeth Thayer, CVRWQCB cc: SWRCB, Cleanup Fund Unit cc: David Irey, San Joaquin District Attorney's Office, Environmental Prosecution Unit cc: Kent O'Brien, Geraghty and Miller