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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 approximately 25 feet downgradient of the former USTs. FMS-DPE2 may be incorporated into future groundwater monitoring program efforts, as appropriate. Each well was installed in a separate 8 -inch -diameter borehole, and was constructed with 4 -inch schedule 40 PVC blank casing and 0.020 slot schedule 40 PVC screen. Historical monitoring data from FMS-MW5 indicated that groundwater in this area is approximately 31 to 34 feet bgs, which was confirmed during well drilling activities. As a result, FMS-DPE1 was screened from approximately 20 to 60 feet bgs and FMS-DPE2 was screened from approximately 24 to 59 feet bgs, across the area demonstrated to be impacted with petroleum hydrocarbons. The top of the screened interval in well FMS-DPE1 was positioned 5 feet below the base of any backfill associated with the former USTs. The filter pack, consisting of #2/12 silica sand, extended to a minimum of 2 feet above the top of the screen and was sealed with 5 feet of hydrated bentonite chips or pellets. A bentonite/cement grout was placed above the seal to approximately 2 feet bgs. Each 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. Details for the wells are presented in Table 1, and on the boring log and well completion diagrams presented in Appendix B. 2.3. SOIL EVALUATION/SAMPLING DURING WELL INSTALLATION During well drilling activities, the soils encountered were visually evaluated for evidence of impacts, and select soil samples were collected for off-site laboratory analysis. Each borehole was continuously cored to total depth, and samples were periodically screened for petroleum hydrocarbons using a photoionization detector (PID). The site geologist logged soils using the Unified Soil Classification Scheme (USCS) for purposes of establishing appropriate intervals for well screening, as described above, and for preparing boring logs for incorporation into the report documenting the treatability study. Below approximately 15 feet bgs, soil samples were collected at approximately 5 -foot intervals to the occurrence of first groundwater for organic and inorganic analyses, as follows: TPH-g and TPH-d using U.S. EPA Method 8015 -Modified; VOCs including Naphthalene, BTEX, and Fuel Oxygenates using U.S. EPA Method 8260B; and Total Lead using U.S. EPA Method 6010B. Sample analyses were performed by BC Laboratories, a California -certified analytical laboratory, under full COC documentation. Analytical results for soil samples are summarized in Table 2. Laboratory analytical reports and COC documentation for soil samples are presented in Appendix C (CD-ROM only). Only analytes detected in one or more samples are indicated in Table 2. Continuously cored samples were also collected below the groundwater table within the approximate proposed screened zone for each proposed well. These samples were not analyzed for contaminants, but were collected for logging purposes and to allow for field adjustments of screen depth based on the soils encountered. No samples were collected for laboratory analysis from SVE-1, due to the close proximity to FMS-DPE1 and the nested AS wells (Figure 3). Soil samples for lead analysis were collected in sterile 8 -ounce glass containers. Pre -packed 25 -gram En -Core° samplers were used to collect volatile samples. Soil samples were labeled with a unique sample designation identifying the location and depth, in that order (e.g., FMS-DPE-1-15'). Sample designations, collection times, and analysis OTIE 11