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9 • hydrocarbon content. The analytical data was then used to characterize the lateral and vertical extent of diesel/oil. ' Soil sample results taken from these borings confirmed both TPH-d and Oil & Grease above 1000 mg/kg in one 8" boring, and three (3) 1.5" geoprobe locations. Each of the ' locations where petroleum hydrocarbon levels exceeded 1000 mg/kg was down slope of SWMU #21. The TPH-d concentration found in S-26 at a depth of 35' was 23,000 mg/kg. At S-26 at a depth of 40' the TPH-d concentration was 1,100 mg/kg. At the BH- ' 4 location at 40', TPH-d concentration was 3500 mg/kg and 1100 mg/kg at 45'. At 50', 55' and 60' depths, both the TPH-d and oil & grease results from BH-4 were well below the clean up objective of 1,000 mg/kg. Although the soil in BH-4 was wet at 60' bgs, ' (See BH-4 boring log page 2.) a productive groundwater zone was not encountered. ' Based on the analytical results, vertical migration of the hydrocarbons appears to be limited to the upper 45' — 50'. Very little, if any, hydrocarbons appear to have migrated to groundwater. ' 3.0 SCOPE OF WORK ' The following subsection of this workplan responds to the DTSC letter of January 7, 2003, and presents tasks to further assess the vertical and lateral extent of hydrocarbon impacted soil and to assess the possible impact to groundwater, if any, at the site. 3.1 Safety Plan Preparation and Implementation ' The Site Specific Safety Plan (SP) employed will be the same as that used during site ' evaluation in 2002. The equipment used for the sampling and drilling operation will be the same (less the direct push probe) as used previously. Modifications to the plan may be implemented upon the Direction of the Site Safety Officer or Project Manager if there ' are any changes in the site or work conditions. ' 3.2 Permitting Prior to the performance of soil sampling activities that require the installation of borings, CE will secure permits from the San Joaquin County Public Health Service Environmental Health Division. Installation of soil borings and groundwater monitoring wells (MW), if required, will be in accord with applicable local and State of California ' requirements. 3.3 Areal Assessment of TPHd and O&G Soil Impact ' CE proposes to collect soil samples at three locations positioned in a direction down the depositional slope from S-26 and S-27, and at the storm drain outfall east of SWMU ' #21, using a rotary drill rig equipped with hollow stem augers. Boring S-30 is proposed CE Project No.99R-4041 Additional Investigation Work Plan 3