COMPLIANCE INFO_1997-1999 - Laserfiche WebLink

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from the former waste oil tanks. PHS/EHD recognizes that the former waste oil tanks may not be the only source of chlorinated solvent observed in groundwater. The workplan addendum 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. Please omit all references in Appendix A which refer to the California State Regional Water Quality Control Board San Francisco Bay Region from the REE workplan and include references to appropriate regulatory authorities regarding well design,installation,and sampling. Discuss your proposal for performing this work in the workplan addendum 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 if necessary. 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 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. Report your results in the SWI Report requested below. Based upon elevated and variable MTBE concentrations we request that you immediately characterize the potential ongoing sources of dissolved phase MTBE contamination at your site. Please report the results of your characterization in the SWI Report and evaluate cost effective clean up methods during the SWI phase. We also request that you perform a tank system tightness test and visually inspect all underground storage tank (UST) sumps and other appurtenances to help determine if your UST system is currently leaking. 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. Using chromatograms from previously analyzed samples,the laboratory should be able to determine the presence or absence, and estimate/quantify the level of MTBE present during previous sampling events in many cases. PHS/EHD has reviewed the report letter from WEST Laboratories dated July 2, 1997. No written quantification estimates are provided in the WEST report. As indicated in correspondence from PHS/EHD previously it is unlikely that fuel blending agent (MTBE) concentrations from previous sampling events are as high across the site as observed most recently. Please report amended findings in the work plan amendment and SWI Report requested below. 3