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i <br /> approximated for each source area, lateral contaminant definition may commence. All wells installed and <br /> surveyed shall be referenced to an appropriate and designated bench mark. Discuss your proposal for <br /> performing this work in the workplan addendum requested below. Report the results of your investigation <br /> to this agency within 30 days of completion of the approved scope of work. i <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 /> I <br /> You shall also evaluate the probability of the contaminants 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 acrial 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 /> 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 f <br /> penetrometry together with other methods to understand the hydrogeology at your site. Discrete soil . k <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. The site specific <br /> geotechnical data can be employed to compliment and assess contaminant'migration potential; receptor l <br /> risk, mass balances, remediation feasibility and ultimately site closure requests. We also request that you <br /> evaluate local groundwater flow conditions and establish a site-specific localized flownet that is dependent <br /> on hydrology and geologic conditions and is reflected on hyrdrogeologic cross sections and fence <br /> diagrams. Additionally, you are required to prepare a rose diagram for groundwater gradient at this site, I' <br /> plot it on the groundwater contour maps. All future plot and cross section drawings shall show the location f <br /> of former tank systems. Report your results in the SWI Report requested below. <br /> Additionally, if you have any fuel additivesfblending agents, or any other; contaminant data previously f <br /> collected at your site that has not been submitted to PHSIEHD, you are requested to notify this agency, <br /> submit this data immediately and update cumulative data tables accordingly. <br /> We request that you employ approaches to estimating contaminant mass flux across plume transects or <br /> fences located perpendicular to the plume(s). We request the use of expedited site assessment tools and/or u <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 contaminants from <br /> the source. We request that you install permanent monitoring wells and/or monitoring well clusters <br /> (screened at appropriate discrete depths with appropriate length of screen) to monitor the plume. Include <br /> your proposal for the installation of these wells in the work plan addendum requested below. Please report <br /> your 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 h <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. <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 /> • November 15, 1997,5:00 pm-Complete and Submit Comprehensive Cross Sections to PHSIEHD <br /> 2 <br />