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Treatability Study Report and Feasibility Evaluation for In Situ Petroleum Hydrocarbon Remediation Field Maintenance Shop #24, 8020 South Airport Way Stockton, California 2.2.1. Soil Vapor Extraction Well Well SVE-1 was installed in the target area using 10'/4 -inch -diameter augers to a depth of approximately 29 feet bgs, and constructed of 4 -inch schedule 40 polyvinyl chloride (PVC) casing. The well was screened across the vadose zone from approximately 18.5 to 28.5 feet bgs using 0.020 -slot schedule 40 PVC screen. Construction details for SVE-1 are presented in Table 1. Based on field observations during the installation of groundwater monitoring well FMS-MW5, it was determined that the petroleum hydrocarbon -impacted screened interval is characterized by the most coarse-grained, sandy material, which provides the most suitable conditions for SVE implementation. The wellbore for SVE-1 was backfilled with a filter pack of #2/12 silica sand. The filter pack was sealed with 5 feet of hydrated bentonite chips or pellets. A bentonite/cement grout was placed above the bentonite seal from approximately 2 to 11.5 feet bgs. The well was fitted with a lockable, water tight well cap, and completed with a 12 -inch -diameter flush mount, traffic -rated well vault set in concrete with positive drainage to facilitate conveyance of surface water runoff away from the well vault. These construction details are indicated in the soil borings and well completion logs presented in Appendix B. It is noted that the location of SVE-1 is not consistent with the location identified in the Work Plan (i.e., within the approximate outline of the former diesel UST). OTIE attempted to complete the well at six locations in the immediate vicinity of the former diesel UST, but encountered what appeared to be a concrete slab, presumably related to the former diesel UST footings, at approximately 12 feet bgs at each of those locations. It was ultimately necessary to move the location to the west, within the approximate outline of the former gasoline UST, as shown in Figure 3, in order to complete the well. 2.2.2. Dual -Nested Air Sparge Well The dual -nested AS wells (AS -1A/1 B) were installed approximately 15 feet northeast of SVE-1, using 10'/4 -inch -diameter augers (Figure 3). Each of the wells was constructed using 2 -inch schedule 80 PVC blank casing and 0.020 slot schedule 80 PVC screen, with a 2 -foot blank casing sump at the base of each. Well AS -1A was screened within the upper portion of the saturated zone, at a depth of approximately 37-39 feet bgs. Well AS -1 B was screened at a depth interval of approximately 64-66 feet bgs. Details for these wells are presented in Table 1, and on the boring log and well completion diagrams presented in Appendix B. The purpose of installing the nested wells was to conserve costs associated with drilling an additional borehole. OTIE actually considered constructing a triple -nested set of wells (in combination with SVE-1), but was advised by SJCEHD that because of the department's requirement for over-drilling when abandoning wells, it would be more practical to construct the three wells in two borings. The wellbores for the nested AS wells were backfilled with a filter pack of #2/12 silica sand. The filter pack will be sealed with 5 feet of hydrated bentonite chips or pellets. A bentonite/cement grout was placed above each seal to the bottom of the next filter pack (2 to 31 feet bgs in each well). The nested wells were fitted with a lockable, water tight well cap, and completed with a 12 -inch -diameter flush mount, traffic -rated well vault set in concrete with positive drainage to facilitate conveyance of surface water runoff away from the well vault. 2.2.3. Dual Phase Extraction / Monitoring Wells Wells FMS-DPE1 and FMS-DPE2) were installed for purposes of evaluating HVDPE as a remedial technology (Figure 3). FMS-DPE1 was installed in the central area of the contaminant plume, based on historical investigation data for the site, and FMS-DPE2 was installed OTIE 10