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�NOW/ 14WI, Geologica(rech csInc. Page 3 Dual Phase Extraction Pilot Test Work Plan Valentine(Castle Motors) v Project No.764.2 September 8,2003 The site geology is presented in two cross section diagrams Figures 3A and 4A (see Figure 2 for section locations). The site exhibits a primarily clayey geology with clayey sands, silts and gravel layers occurring less frequently. Figures 313 & 4B are cross section diagrams 6w with soil contaminant concentrations indicated next to the borings and the groundwater TPH-G concentrations from.the June 2003 quarterly monitoring event are also depicted next to the screened intervals of the wells. In these diagrams, a soil plume is shown in the vicinity of the former dispenser island (near borings SB-101, MW-101 and MW-201). The 6d groundwater plume is depicted as extending across the site as evidenced in the site wells. The vertical extent is depicted from the historical water table depths to a depth of approximately 110 feet bgs. This is regarded as the bottom of the groundwater plume because a soil sample from MW-201 at this depth was non-detect for all analytes. Contamination has been detected in well MW-201 that is screened from 148 — 150.5 feet bgs. GTI believes that this contamination may be an artifact from drilling of the well by mud rotary in October 2001 and not representative of actual groundwater conditions. r 2.1 Dual Phase Extraction System We propose utilizing the services of Cal Clean I.nc. of Tustin, California, a dual phase extraction services contractor. (See Appendix B for Cal Clean Inc. information) The general process for dual phase extraction is as follows: ■ Extract vapors and groundwater from an extraction well using a 450 cfrn vacuum pump capable of greater than 20 inches of mercury vacuum. The vapors and water are drawn out of the well through a stinger set at the desired depth for extraction. ■ Separate vapors and the influent water in a vacuum tank. ■ The contaminated vapor is then pumped to and oxidized in a thermal oxidizer. ■ The captured contaminated groundwater is transferred to a storage tank via a high vacuum pump. Cal Clean has a separate water treatment unit that will be utilized to treat the extracted water prior to discharge to City of Stockton municipal sewer. ■ Collect data for actual vacuum flow and contaminant concentrations. `w ■ Delineate the area of influence from the applied vacuum through use of observation wells. ■ Continue the test for a maximum of five days. (The test will not exceed 5 days to alleviate the requirement for a permit from the San Joaquin Valley Unified Air Pollution Control District). 2.2 Groundwater Extraction Well Installation The site exhibits a primarily clayey geology and this is problematic when considering soil vapor or groundwater extraction. But as evident in Figure 4A, there are some sand and gravels layers present in the strata beneath the site near borings MW-101 & SB-B. A single extraction well EW-1, will be installed near the near SB-B location to use for the extraction test. See Figure 5 for the proposed well location. The well will be constructed of four-inch two PVC casing to facilitate greater pumping capacity than the existing two inch monitoring wells at the site. The existing monitoring wells will be used as observation points for the vapor extraction and groundwater extraction tests. `1 i� 4r