SITE INFORMATION AND CORRESPONDENCE_FILE 1

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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. We request that you perform a conduit study that details the potential migration pathways and potential conduits (sewers, storm drains, etc.)that may be present in the vicinity of the site. Provide a map showing the location and depth of all utility lines and trenches including sewers and storm drains within and near the plume area. The conduit study is to include a detailed survey of all wells. 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. You shall also evaluate the probability of the MTBE plume encountering preferential conduits that could spread the contamination particularly in the vertical direction. 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. Collection of soil samples 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 requestthat 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. Report your results in the SWI Report requested below. Additionally,you are required to prepare a rose diagram for groundwater gradient at this site, plot it on the groundwater contour maps, and update this diagram in all future reports submitted for your site. Based upon elevated and variable MTBE concentrations we request that you immediately characterize the 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 determine if your UST system is currently leaking. Please determine (1) the approximate time frame of the MTBE/Additives release first occurring at your site;(2)the use history of MTBE/Additives 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 or estimate or quantify the level of MTBE present during previous sampling events in many cases. Report your findings in the SWI Report requested below. Additionally, if you have any MTBE, other fuel additives, or any other data previously collected at your site that has not been submitted to PHS/EHD, you are requested to submit this data immediately and update cumulative data tables accordingly. We request that you employ approaches to estimating MTBE/Additive contaminant mass flux across plume transects or fences located perpendicular to the MTBE/Additive plume. We request the use of expedited site assessment tools and/or appropriately screened monitoring wells to provide data for these estimates. In