SITE INFORMATION AND CORRESPONDENCE

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and TAME employing EPA Method 8260 (see CVRWQCB and PHS/EHD attachments) for all samples until further written notice from this office. Conventional monitoring well networks existing at this Underground Fuel Tank (UST) leak site may be insufficient to properly locate and define the extent or existence of MTBE / Fuel Additive/ Chlorinated Solvent plumes as evidenced by the vertical and horizontal variations of contamination observed at this site and adjacent sites. Therefore, PHS/EHD directs you to perform a detailed, expedited site assessment using depth discrete and continuous core sampling to define and quantify the full three-dimensional extent of fuel additives, Total Petroleum Hydrocarbons, Benzene, Solvents and other known or suspected contaminants in groundwater. Additional boreholes shall be distributed at this site. Boreholes completed as monitoring wells must be placed at the site with appropriate discrete screen intervals. At least one and preferably two boreholes shall be continuous cores. These boreholes shall be employed to further define any plume which may have originated from the former or current use practices at this site. PHS/EHD recognizes that the former waste oil tanks may not be the only source of chlorinated solvent observed in groundwater. 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. 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 diesel as well as BTEX and fuel blending agentladditives analyses are required. Given the confirmed presence of 1,2-DCA and 1,2- DCP constituents the responsible party(s) shall analyze selected soil and groundwater samples by EPA Method 8270 and 8260(both as full scan reports)on a quarterly basis until further written notice from this office. 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. You are requested to properly characterize the hydrogeology and groundwater flow conditions in the vicinity of your site. During SWI activities, we request that you gather detailed lithologic information using borings, continuous core sampling, dual tube expedited site assessment methods, or cone penetrometry together with other methods to understand the hydrogeology at your site. Discrete soil samples collected from each significantly different lithological unit shall be analyzed by a qualified laboratory for permeability, porosity, bulk density, moisture, and organic carbon content. We also request that you evaluate local groundwater flow conditions and establish a site-specific localized flownet that is dependent on geologic conditions and is reflected on geologic cross sections and fence diagrams. Additionally, you are required to prepare a rose diagram for groundwater gradient at this site, plot it on the groundwater contour maps. Plot and cross section drawings shall show the location of former and present tank systems. Report your results in the SWI Report requested below. Please determine(1)the approximate time frame of the MTBE/Additives/Solvents release first occurring at your site; (2) the use history of MTBE/Additives/Solvents at your site; and (3) the history of all unauthorized releases and spills at your site. 2