SITE INFORMATION AND CORRESPONDENCE FILE 1

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t Both the 2nd and 3rd quarter 1997 monitoring event reports prepared by Enviros, Inc. comment on the relative loss of efficiency and effectiveness of the SVE system. PHS/EHD disagrees with comments found in the Quarterly Monitoring Report- Second Quarter 1997 prepared by Enviros, Inc. The effectiveness of the SVE system has been poor since ground water rose above 30' bgs as evidenced by precipitous removal rate declines beginning immediately after start-up(See Plate 3 dated September 26, 1997 in the Quarterly Monitoring Report - Third Quarter 1997 prepared by Enviros, Inc). The SVE system removal rate decreased from 16.95 lbs of Total Purgeable Petroleum Hydrocarbons (TPPH) per hour to 1.74 lbs of TPPH per hour in less than 5 months after start up operating less than 24 hours per day during this period. PHS/EHD has provided verbal recommendations to the consultant (Mat Donahue, Enviros) on September 29, 1997 to renew the Air District Permit rather than allow the system permit to expire citing economic advantages to renewal compared to the costs of reapplying. This recommendation was provided recognizing that site assessment and remediation is incomplete and the possibility of evaluating air sparging technology is likely. This letter presents a directive for an immediate full three dimensional definition and investigation of soil and groundwater contamination by fuel hydrocarbon constituents resulting from an unauthorized release documented at this site. In evaluating the lateral extent of contaminant distribution at this site it is imperative that the vertical aspect be defined at source areas first. Following vertical definition additional borehole placement can begin to define the lateral extent of contaminant distribution. Fuel Additives/Blending agents have been identified in ground water at this site (MTBE). Other fuel additives may also be present in the subsurface environment at this site. You are required to analyze all water and selected soil samples for Tertiary Butanol, MTBE, DIPE, ETBE, and TAME employing EPA 8260(see CVRWQCB attachment 91)for all samples until further written notice from this office. Selected soil samples shall include at a minimum the historic low and high groundwater elevation equivalent and the current capillary fringe.Traditional TPH as gasoline and BTEX analyses are also required. Conventional monitoring well networks existing at this Underground Fuel Tank (UST) leak site are insufficient to properly locate and define the extent of contaminant distribution in the saturated zone or existence of MTBE / Fuel Additive plumes as evidenced by the vertical and horizontal variations of contamination observed at this site. For example, MTBE plumes can be non-elliptical, long, narrow and erratic(meandering). Additional boreholes shall be distributed at this site and off site preferentially to the east. Boreholes completed as monitoring wells must be placed with appropriate discrete screen intervals (each borehole may require more than one well completion).At least one and preferably two boreholes shall be continuous cores and shall be located near known source areas (ie, former tank cavity). These boreholes shall be employed to further define any plume which may have originated from the former or current use practices at this site. The workplan shall consider historic low and high groundwater elevations in the definition of the vertical aspect of contaminant distribution at this site. All wells installed and surveyed shall be referenced to an appropriate and designated bench mark. Well screen intervals shall not exceed 20' in total length. Discuss your proposal for performing this work in the workplan requested below. Report the results of your investigation to this agency within 30 days of completion of the approved scope of work. Please note, you are requested to immediately pursue any off-site access agreements that you may need to complete your investigation activities. You shall also evaluate the probability of the contaminants plume encountering preferential conduits that could spread the contamination particularly in the vertical direction. The conduit study is to include a detailed survey of all wells in the vicinity. Please contact the Department of Water Resources (DWR) for procedures to request well information. Please include prints of historic aerial photos used as part of your study, and use data tables and maps to report the data collected as part of your survey. Report your results in the Soil and Water Investigation(SWI)Report requested below. 2