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Workplan for Additional Assessment and Feasibility Testing 4 7-Eleven Inc.Store No.21756,853 East Yosemite Avenue,Manteca,CA October 17 2001 Schedule/Report Drilling will commence within 6 months of receipt of written approval of this workplan, pending permit approval. Report preparation will be completed within 6-8 weeks of well installation WORKPLAN FOR PROPOSED INITIAL FEASIBILITY TESTING Soil Vapor Extraction Testing Soil vapor extraction (SVE) can be used to remove the soil source of the dissolved hydrocarbon plume and supply additional oxygen to the subsurface to enhance intrinsic biodegradation,with the anticipated goal of reduction of dissolved gasoline constituents. Compared with other gasoline constituents, MTBE is both more hydrophilic and adsorbs much less. These properties result in decreased extraction potential in moist soils, but increased vapor mobility in dry soils. Given the site's current active status, and the relative low cost of vapor extraction as a remediation technique,it is considered prudent to test the site for venting capability. The extraction test will be performed by applying a vacuum to well MW-1 using a mobile 150-cubic feet per minute (cfm)thermal oxidizer. During the test, extracted air will be channeled to the unit after passing through a moisture knockout device and an air filter. Soil vapors will then be treated by passing them through the unit prior to discharge to the atmosphere. Observation wells (all wells not undergoing extraction)will be fitted with caps and Magnehelic gauges to monitor vacuum pressure changes during the test. Extracted vapor concentrations will be measured using a photo-or flame-ionization detector. Samples of extracted vapors will also be collected into Tedlar bags or SUMMA canisters, for laboratory analysis and permitting purposes. The test begins by sealing the observation wells, calibrating the Magnehelic gauges, and then starting the thermal unit,which is connected to the well undergoing extraction. After completion of the warm-up cycle, the unit is set to extract at different vacuum rates from the test well. Each test phase consists of applying a vacuum to the test well until equilibrium conditions (as evidenced by steady-state flow) are attained. Observation well pressure readings, extracted flowrates, and extracted vapor concentrations are obtained during each test phase. Test duration is typically 8 hours. The well proposed to be used during the test is selected based on proximity to the known area of highest dissolved MTBE/hydrocarbon concentrations and access to the capillary fringe/upper saturated zone zone. Application of vapor extraction treatment to this portion of the site has the most chance to beneficially affect dissolved MTBE/hydrocarbon concentrations by removing the mass closest to the water table. 21756SAW.DOC