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July 14, 2000 Page 2 extractable petroleum hydrocarbons (TEPH), benzene and methyl tertiary-butyl ether(MtBE) have been reported at elevated concentrations in Wells MW-11, MW-16 and MW-l7 located in the northeast section of the facility. During the most recent groundwater monitoring event (April 17, 2000)the maximum concentrations of TPPH,TEPH and benzene from the three wells were reported from Well MW-16 at 14,000 micrograms per liter(µg/t), 8,350 µg/1 and 2,650 µg/I respectively. The maximum concentration of MtBE from the three wells was reported from Well MW-1 I at 344 µg/1. Subsurface Investigation TOXICHEM proposes to advance two soil borings east of wells MW-11 and MW-17 adjacent to the eastern perimeter fence of the facility (Figure 1). The soil borings will be converted to groundwater monitoring wells to provide groundwater quality information. The borings for existing monitoring wells MW-1 I and MW-17 encountered sandy clay or silty sand from ground surface to between 8 and 10 feet bgs which was underlain by clayey silt or silty clay to the total depth explored of 28 feet bgs. The following tasks will be performed in association with the soil boring and groundwater monitoring well installation. • Obtain permits from the San Joaquin County Public Health Services Department. • Provide notification for underground utility service clearance prior to field work activities. Review facility underground plans and utilize a private utility locator as necessary. • Prepare a site specific Health and Safety Plan for the proposed scope of work. • Drill the proposed soil borings after hand clearing the locations to a depth of approximately 5-feet bgs. • Collect soil samples for logging, and possible chemical analysis at a minimum of five-foot depth intervals. • Perform field analysis for organic vapor concentrations on selected soil samples using a photo-ionization detector (PID). • Submit a minimum of two soil samples per boring to a state certified laboratory for chemical analysis. The submitted soil sample will be analyzed for TPPH,TEPH, benzene, toluene, ethyl benzene, xylenes (BTEX compounds)and MtBE. • Install 4-inch diameter groundwater monitoring wells within the selected borings. • Develop and survey the groundwater monitoring wells and incorporate them into the quarterly groundwater monitoring program. Field procedures for the soil boring advancement and monitoring well installation and sampling are presented as Attachment A. C9T0XICHEM\Projects\Eq\I4\I A\workplan.doc