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' Analytical results for soil sampling indicated that hydrocarbon residue was present in soil beneath the former underground tank site Groundwater sampling results indicated the presence ' of hydrocarbons and lead in groundwater in two of the three wells, with the highest concentra- tion present in well MW-2, located directly over the former underground storage tank area, and lower concentrations in well MW-3, located north of the former tank area No hydrocarbon ' concentrations were detected in well MW-1, located west of the former tank site A review of the soil and groundwater analytical results by the EHD concluded that the initial ' investigation had adequately defined the extent of fuel residues in soil and that soil remediation was required Several potential remediation techniques were evaluated and it was decided that the most feasible option was to excavate and dispose of the hydrocarbon impacted soil 1 Excavation and disposal was conducted under WESTON's supervision and consisted of excavating a pit roughly 58 feet wide and 44 feet long down to approximately 30 feet. This ' excavation resulted in the removal of approximately 2,000 cubic yards of soil Following excavation, the pit was backfilled with clean soil ' While the source material had been removed through excavation, analytical results of groundwater sampling indicated that hydrocarbons were present in groundwater in the vicinity of monitoring wells MW-2 and MW-3 In order to define the extent of this impact to ' groundwater, the EHD determined that a second phase of groundwater investigation was needed at the site 1.2 Phase II Scope of Work ' The Phase II Scope of Work was proposed in a Work Plan prepared by WESTON entitled "Work Plan for Phase II Groundwater Investigation Human Services Building Site" dated September 26, 19$9 This Work Plan was reviewed and approved by the San Joaquin County ' EHD prior to starting work Well installation permits and encroachment permits, necessary for installing the wells on city sidewalks and in landscaped areas were also acquired prior to field work All field work was conducted under the direction of a registered California geologist IImplementation of Phase II field work took place in May through August of 1991 The Phase II Scope of Work consisted of the following elements. ' 0 Review of available hydrogeological information for the site ' 0 Installation and development of five new groundwater monitoring wells identified as MW-4, MW-5, MW-6, MW-7 and MW-8 ' 0 Collection and analysis of groundwater samples from each of the new wells • Testing of aquifer characteristics Evaluation of the groundwater flow direction and gradient magnitude beneath the site and vicinity ' Rff&WcwP 4 o"Im