SITE INFORMATION AND CORRESPONDENCE

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Shell Station (former) page 3 1267 Country Club Blvd, Stockton Work plan addendum comment Please be advised that any contaminants found in grab ground water samples are to be further investigated by installing a monitoring well screen at that depth. Multiple impacted depths require screened intervals placed at each zone for further sampling. There is adequate subsurface lithological data available in the waste oil UST area to support monitoring well discrete screen installations now. Instead of placing CPT-8, EHD will require two monitoring wells to be placed at this time. A discrete screen is required at 40-45 feet bgs and another at 69-74 feet bgs, clustered in the area of where CPT-8 was to be placed. If repeatable ground water sampling reveals any of the above noted analytes are detected, additional lateral and deeper screened monitoring wells may be needed. The Addendum noted that a report was to be submitted after laboratory results are received. EHD hereby directs Shell to submit the report of findings in the format of a Site Conceptual Model (SCM). Multiple cross-sections shall be included that clearly show lithological interpretations for the site based on the site boring logs. Superimposed over the bore log information in the cross-sections shall be soil and ground water data for contaminants detected to date. Several cross-sections may be needed to fully interpret the site conditions. Iso- concentrations maps for each sand zone shall be included that show zero lines as supported by data. TPH (as gas, diesel, oil and grease, and motor oil) MtBE, 1 ,2-DCA, BTEX, and all of the waste oil UST constituents shall be mapped on as many iso-con maps as needed to model the site and provide an understanding of the dispersion and zero-lines of the contaminant mass. Areas where data is not available to support delineation conclusions shall be discussed in the recommendation and conclusion section of the SCM. A professional geological interpretation of the nature and extent of the contamination shall be included in the SCM. The Addendum is not approved as submitted. A revision is required. Shell is hereby directed to submit a work plan by August 15, 2005 to install at least two monitoring wells in the area just northeast of the former waste oil UST. A screened interval is to be constructed at each of the two sand intervals (-40-47 feet bgs and 69-75 feet bgs). No soil sample collection or soil analysis was proposed in the Addendum. Shell is to collect and analyze an adequate number of soil samples so that conclusions of delineation and mass (balance, transport, etc) required in the SCM can be supported.