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Total Petroleum Hydrocarbons, Benzene, Solvents and other known or suspected contaminants in <br /> groundwater. <br /> Additional boreholes shall be distributed at this site. Boreholes completed as monitoring wells must be <br /> placed at the site with appropriate screen intervals. At least two borehoies shall be continuous cores. <br /> These boreholes shall be employed to further define any plume that may have originated from the former <br /> use practices at this site. The workplan shall consider historic low and high groundwater elevations in the <br /> definition of the vertical aspect of contaminant distribution at this site. All wells installed and surveyed <br /> shall be referenced to an appropriate and designated benchmark. Well screen intervals shall not exceed 20' <br /> in total length. <br /> Selected soil samples shall include at a minimum the historic low and high groundwater elevation <br /> equivalent and the current capillary fringe. Traditional TPH as gasoline, BTEX and fuel blending <br /> agent/additives analyses are required. Given the confirmed presence of 1,2-DCA the responsible party(s) <br /> shall analyze selected soil and groundwater samples by EPA Method 8270 and 8260 (both as full scan <br /> reports)on a quarterly basis until further written notice from this office. <br /> Please note you are requested to immediately pursue any off-site access agreements that you may <br /> need to complete your investigation activities. <br /> You shall also evaluate the probability of the contaminant plume encountering preferential conduits that <br /> could spread the contamination particularly in the vertical direction. The conduit study is to include a <br /> detailed survey of all wells in the vicinity. Please contact the Department of Water [resources (DWR) for <br /> procedures to request well information. Please include prints of historic aerial photos used as part of your <br /> study, and use data tables and maps to report the data collected as part of your survey. Report your results <br /> in the Soil and Water Investigation(SWI) Report requested below. <br /> We request that you employ approaches to estimating contaminant mass Flux across plume transects or <br /> fences located perpendicular to the plume. We request the use of expedited site assessment tools and/or <br /> appropriately screened monitoring wells to provide data for these estimates. In deciding the location of <br /> transects and developing mass flux estimates, please consider the variable dissolution of fuel hydrocarbon <br /> contaminants from the source. We request that you install permanent monitoring wells and/or monitoring <br /> well clusters (screened at appropriate depths and appropriate screen length to monitor the plume. Include <br /> ,your proposal for the installation of these wells in the work plan requested below. Please report your <br /> results in the SWI Report requested below. <br /> We request that you monitor the groundwater contaminant plumes on a quarterly basis. Additional wells <br /> will be required to define the down gradient extent of the plume if the plume continues to migrate or the <br /> next set of wells fail to define the plume(s). In the event continued plume migration is identified,or impact <br /> to water supply wells is predicted please include recommendations for the installation of additional wells or <br /> remediation alternatives in the Quarterly (reports requested below. Discuss your proposal for performing <br /> this work in rhe workplan requested below. <br /> Please submit technical reports to the San Joaquin County Public Health Services Environmental Health <br /> Division(PHS/EHD),Attention: Ron Rowe, according to the following schedule: <br /> • August 25, 1999, 5:00 PM-Work Plan for completion of Soil and Water Investigation(SWI) <br /> • 45 days from work plan submittal-Soil and Water Investigation Report <br /> • 210 days from work plan submittal-Corrective Action Plan <br />