Laserfiche WebLink
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 discrete screen intervals(each borehole may require more than one well <br /> completion).At least one and preferably two boreholes shall be continuous cores. These boreholes shall be <br /> employed to further define any plume which may have originated from the former or current use practices <br /> at this site. PHS/EHD recognizes that the former waste oil tanks may not be the only source of chlorinated <br /> solvent observed in groundwater. The workplan shall consider historic low and high groundwater <br /> elevations in the definition of the vertical aspect of contaminant distribution at this site. All wells installed <br /> and surveyed shall be referenced to an appropriate and designated bench mark. Well screen intervals shall <br /> not exceed 20' in total length. <br /> Discuss your proposal for performing this work in the workplan requested below. Report the results of <br /> your investigation to this agency within 30 days of completion of the approved scope of work. <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 contaminants plume encountering preferential conduits <br /> that could spread the contamination particularly in the vertical direction. The conduit study is to <br /> include a detailed survey of all wells in the vicinity. Please contact the Department of Water Resources <br /> (DWR) for procedures to request well information. Please include prints of historic aerial photos used as <br /> part of your study, and use data tables and maps to report the data collected as part of your survey. Report <br /> your results in the SWI Report requested below. <br /> You are requested to properly characterize the hydrogeology and groundwater flow conditions in the <br /> vicinity of your site. During SWI activities, we request that you gather detailed lithologic information <br /> using borings, continuous core sampling, dual tube expedited site assessment methods, or cone <br /> penetrometry together with other methods to understand the hydrogeology at your site. Discrete soil <br /> samples collected from each significantly different lithological unit shall be analyzed by a qualified <br /> laboratory for permeability, porosity, bulk density, moisture, and organic carbon content. We also request <br /> that you evaluate local groundwater flow conditions and establish a site-specific localized flownet that is <br /> dependent on geologic conditions and is reflected on geologic cross sections and fence diagrams. <br /> Additionally, you are required to prepare a rose diagram for groundwater gradient at this site, plot it on <br /> the groundwater contour maps. Plot and cross section drawings shall show the location of former and <br /> present tank systems. Report your results in the SWI Report requested below. <br /> Based upon elevated and variable MTBE concentrations we request that you immediately characterize the <br /> potential ongoing sources of dissolved phase MTBE Blending Agents contamination at your site. Please <br /> report the results of your characterization in the SWI Report and evaluate cost effective clean up methods <br /> during the SWI phase. <br /> Please determine(1)the approximate time frame of the MTBE/Additives/Solvents release first occurring at <br /> your site; (2) the use history of MTBE/Additives/Solvents at your site; and (3) the history of all <br /> unauthorized releases and spills at your site. <br /> Additionally, if you have any MTBE, other fuel additives/blending agents, or any other contaminant data <br /> previously collected at your site that has not been submitted to PHS/EHD, you are requested to submit this <br /> data immediately and update cumulative data tables accordingly. <br /> We request that you employ approaches to estimating MTBE/Additive/Solvent contaminant mass flux <br /> across plume transects or fences located perpendicular to the MTBE/Additive plume. We request the use <br /> 2 <br />