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Work Plan for SVE/AS Feasibility iesfina S E C O R - ARCO Service Station 548 Stockton, California Page 4 of 9 suggest that significant downgradient migration of impacted groundwater has not occurred . Groundwater analytical data is presented in Tables 2 and 3. Currently, groundwater is being monitored and sampled quarterly from all existing monitoring , SVE, and AS wells. As requested in the letter from the SJEHD dated March 2, 2006, all wells at the site were resurveyed by a California Licensed Land Surveyor on May 4, 2006 . Revised groundwater flow information indicates groundwater flow across the site has ranged from east to northeast, with hydraulic gradients ranging from 0. 02 feet/foot (ft/ft) to 0. 008 fUft and an average depth to water for the site is approximately 30 ' feet bgs . Historical groundwater gradient information is included in Table 4. The site conceptual model (URS, 2004) estimated remaining hydrocarbon mass at the site as 12. 6 pounds of TPHg , 0. 2 pounds of benzene, and 0 .4 pounds of MtBE. PROPOSED SCOPE OF WORK The proposed scope of work included in this work plan consists of completion of an SVE and AS feasibility test. The locations of the AS and VW wells are shown on Figure 2. The wells are located near and downgradient of the LISTS in areas of the maximum concentrations. The objective of the feasibility test is to measure the radius of influence of the SVE and AS system and to determine the system operating parameters . Task 1 - Preliminary Field Activities l Prior to conducting the SVE and AS testing , a Site-specific Health and Safety Plan (HASP) will be prepared for use by personnel during implementation of this work plan. . At a minimum , the HASP will define the proposed activities , describe physical and chemical hazards that may be associated with the work, provide a map to the nearest emergency medical facility, and include MSDS sheets for any hazardous chemicals that will be used or produced during the work. A copy of the HASP will be available onsite at all times during field work. Subcontractors performing field activities will be provided a copy of the HASP prior to initiating work. Prior to conducting remedial feasibility testing , any necessary permits will be obtained for performance of the SVE pilot test from the San Joaquin Valley Air Pollution Control District (APCD) . Task 2 — SVE Feasibility Testing To evaluate the effectiveness and feasibility of extracting and removing hydrocarbon contamination from the vadose zone at the Site , a one-day SVE test is proposed . SVE pilot testing will be conducted using the existing SVE system. The SVE test will be conducted using vapor wells VW-1 , VW-2, VW-3, VW-4, and VW-5D. A vacuum will be induced and soil vapor will be extracted from each of the vapor wells. During testing , field measurements including influent hydrocarbon concentrations (using a PID or FID) and soil vapor extraction flow rates will be collected at regular intervals from surrounding wells and recorded on test data collection sheets. Depending upon field conditions, the applied