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the field (e.g., tightening fittings) and the test was repeated. If the <10% criteria cannot be achieved, that location and depth was eliminated from the validation program. Additional QAIQC for Soil Gas Sampling An additional QA/QC step was employed during sampling activities associated with the use of the Summa canisters to avoid the collection of invalid data. This step included checking the vacuum pressure of each canister to verify an initial vacuum of at least minus 28 inches of mercury. If a canister had a vacuum less than minus 28 inches of mercury, the canister was not used as this is indicative of a leak that may have developed during shipment or handling of the canisters. 3.2.4 Well Installation and Groundwater Sampling Procedures The scope of work for soil sampling and well installation was conducted by, or under the supervision of, a California Professional Geologist. All installation and subsequent sampling procedures followed DTSC guidance manuals, specifically, "Monitoring Well Design and Construction for Hydrogeologic Characterization," (DTSC, 1995) and "Representative Sampling of Groundwater for Hazardous Substances" (DTSC, 2006). Prior to beginning any fieldwork, appropriate well construction permits (Appendix G) were obtained and Underground Services Alert was notified. The SJCDEH requires: 1) a permit for the installation of any groundwater monitoring wells; and 2) that the wells be installed by a driller who has the C57 Well Driller's License. 3.2.4.1 Well Installation and Development Procedures The technical work scope for this Report included the drilling, sampling, installation of one groundwater monitoring well (TW-5) and development of five groundwater monitoring wells (TW-1 through TW-5) for inclusion into the monitoring well network at the Site (Figure 9). These wells were used to determine the potential impacts in groundwater from previous Site operations and/or the potential impacts from off-site sources. In addition, monitoring wells TW-1 and TW-2 were video logged to determine if sediment in these wells was due to the well being damaged or if it was due to ongoing natural infiltration of fines into the wells. The following provides information regarding the installation and development of the monitoring wells at the Site: • Borehole A3-2 Stratigraphy — The stratigraphy of one borehole (A3-2) was drilled and logged for the purpose of. (1) assessing for possible perched groundwater; (2) identifying the top of groundwater table; and (3) converting Boring A3-2 into Monitoring Well TW- 5. The borehole was advanced to a depth of 26 feet bgs. The augers were advanced at intervals of 5 feet and continuous core subsurface soil samples were collected using an 18-inch California modified split spoon sampler lined with brass sleeves. Boring logs are provided in Appendix E. • Borehole A3-2 Sample Collection - Soil samples were collected from Boring A3-2 at one, three, five, and 10 feet bgs. Thereafter, samples were collected for analysis at 5 foot intervals. As outlined in the April 2008 Workplan (Parsons, 2008), soil samples were analyzed for PAHs using EPA Method 8310; TPH as gasoline, diesel and motor oil using PARSONS 24 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010