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CeologkdTechnics Inc. Page 5 City of Escalon Project No. 750.3 February 26,2001 not meeting the minimum cleanup goal established by PHS/EHD. Therefore, RNA as a remedial alternative is rejected as infeasible based on the historical groundwater data. 2.1.3. Soil Vapor Extraction Soil vapor extraction (SVE) has proven to be an effective in situ remedial method for soils of a permeable nature and can also be used to mitigate volatile hydrocarbons in groundwater by drawing air through permeable geologic units above the capillary fringe. Vapor extraction is the process of removing volatile organic compounds in the subsurface by drawing air through the subsurface sediments, which allow a transfer of chemical mass from the liquid state to the vapor state. As vapor, the chemicals are removed from the subsurface in the extraction air stream and destroyed aboveground via thermal oxidation. It has been shown by Beckett and Huntley (Ground Water Vol. 32, No. 2, March-April 1994, Published by the National Ground Water Association), that not only horizontal flow of air in the subsurface, but also vertical flow is an important component of soil vapor extraction remedial process. This is especially true for mitigation of low permeable units such as silts and clays. This site is primarily sand, which is coarse-grained sediment. In our March 31, 1999 work plan, GTI proposed the installation of two soil vapor extraction wells. PHS/EHD approved the work plan in their April 20, 1999 letter and a total of four SVE wells were subsequently installed on April 29–30, 1999. r 2.2 Soil Vapor Extraction Pilot Test Results In order to determine if the site is conducive to vapor extraction as a remedial alternative, Geological Technics Inc. drilled and installed four vapor extraction wells VEW-1 through VEW-4. The four (4) soil borings were drilled (2 to a depth of 55 feet and 2 to a depth of 27 feet) and converted into vapor extraction wells. The borings VEW-1 and VEW-2 were drilled at the eastern edge of the site, under the former sidewalk along the old Escalon/Bellota Road. The borings for VEW-3 and VEW-4 were drilled in the northern part of the excavation, adjacent to the northern dispenser island (see Figure 8). The vapor extraction wells were constructed using 4-inch diameter PVC casing with flush ,r threads. The table below shows the construction details. Well o. Dia./TD Screen Slot Filter Pack Trans. Grout Seal Seal _EW=I - '0-.U40" ea grave 3S_-55 –S6_-39'_VEW-2 - ea graveF-3 - 0= - 4- 3-54'— . eagrave - - - - . - 40_ Paeggraev_FT On June 12, 2000, the soil vapor pilot test was conducted utilizing a large capacity blower that was temporarily attached to one of the vapor extraction wells and activated. Vacuum pressure was monitored at the other vapor extraction wells and the three surrounding groundwater monitoring wells that had screened intervals exposed above the water table (MW-1, MW-2 and MW-3). The wells had 4.5 to 5.5 feet of screen above the water table. V