SITE INFORMATION AND CORRESPONDENCE FILE 1

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i 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. Plot and Cross Section drawings shall show the location of former and present tank systems. Report your results in the SWI Report requested below. 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. Additionally, if you have any MTBE,other fuel additivesiblending agents, or any other contaminant 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 Benzene/MTBE/Additive contaminant mass flux across plume transects or fences located perpendicular to the plume(s). We request the use of expedited site assessment tools and/or appropriately screened monitoring wells to provide data for these estimates. In deciding the location of transects and developing mass flux estimates, please consider the variable dissolution of MTBE and other contaminants from the source. We request that you install permanent monitoring wells and/or monitoring well clusters (screened at appropriate discrete depths with appropriate length of screen)to monitor the plume. Include your proposal for the installation of these wells in the work plan requested below. Please report your results in the SWI Report requested below. We request that you monitor the groundwater contaminant plumes on a quarterly basis. Additional wells will be required to define the down gradient extent of the plume if the plume continues to migrate or the first set of wells fail to define the plume(s). In the event continued plume migration is identified,or impact to water supply wells is predicted please include recommendations for the installation of additional wells or remediation alternatives in the Quarterly Reports requested below. Please submit technical reports to the San Joaquin County Public Health Services Environmental Health Division(PHS/EHD),Attention: Ron Rowe, according to the following schedule: • November 25,1997, 5:00 pm-Work Plan Addendum for completion of SWI • 45 days from work plan submittal-Soil and Water Investigation(SWI)Report • 210 days from work plan submittal-Corrective Action Plan We request that all required work be performed in a prompt and timely manner under the direct supervision (witnessed) of PHS/EHD staff. We have proposed a schedule for the submittal of the SWI Report and the CAP. Revisions to the proposed schedule shall be requested in writing with appropriate justification for anticipated delays. PHS/EHD recommends that all site assessment and remediation related activities in which the responsible party(s) engages in and anticipates reimbursement from the Underground Storage Tank Cleanup Fund(USTCF)be reviewed and pre-approved prior to commencing work. 3