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Workplan for Subsurface Investigation L �9LGQn Stockton Police Facility Working To Restore Nature Project No.OW0148.02 Page 2 a groundwater monitoring well (MW1). The soil boring/monitoring well was located as close as possible to the area of suspected soil contamination near the product line. Laboratory analyses of soil samples collected at five foot intervals from 10.0 to 40.0 feet in the well boring did not detect the presence of gasoline constituents above the method detection limit. The depth to first groundwater beneath the site was recorded at approximately 38 feet below grade. Historical analyses of groundwater samples collected from NMI indicate that groundwater beneath the site has not been impacted by petroleum hydrocarbons. Excavation On July 23, 1992, under the direction of RESNA, excavation activities were initiated. The excavation was performed by Falcon Energy Associates (Falcon Energy, license#584524) using a backhoe tractor. Visible hydrocarbon impaction of soil was evident to a depth of approximately 6 to 6.5 feet below grade. PID measurements detected vapors intermittently to approximately 8 feet below grade. Analytical results of confirmation soil samples collected from the excavation floor and sidewalls (Table 1) indicated hydrocarbon impacted soils remained in place along the northern wall of the excavation, apparently extending some distance beneath the existing structure. All excavated materials were transported to the City of Stockton Municipal Service Center where they were placed on asphalt and covered by 6 mil plastic sheeting. Approximately 300 cubic yards of native and backfilled soil were excavated from the subject site and stockpiled at the City Service Center. Subsequent to excavation and soil sample collection, the open excavation was backfilled with clean engineered sand under the requirements set forth by the City of Stockton Public Works Department. The limits of the excavation are shown on Figure 2. Proposed Scope of Work RESNA proposes to further define the extent of residual soil contamination underneath the building and Bay entrance. Three soil borings are proposed, one within the estimated extent of soil contamination and two outside the estimated extent of soil contamination as shown on Figure 2. Two soil borings will be located within the existing concrete walkway and one boring will be located within the concrete floor of the Bay entrance. RESNA will provide an experienced subcontractor to sawcut the concrete. The borings will then be hand augered to a total depth of WP-1093.DRF