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February 14, 1992 _-- <br /> ARCO Service Station No. 2130, Stockton. California <br /> of the monitoring wells were referenced to within 0.01 foot of the Bench Mark. The <br /> horizontal distances were measured to the nearest 0.1 foot. The elevations were taken to <br /> either the notch or the arrow on the well casing. Elevations of the ground-water surface <br /> with respect to mean sea level for the January 1992 monitoring event are presented in Table ' <br /> 6. The local ground-water flow direction was toward the east on January 7, 1992 as shown <br /> or the Potentiometric Map (Plate 3). The evaluated groundwater gradient was 0.0018. <br /> Vapor-Extraction Test <br /> A vapor-extraction test (VET) was conducted on December 30, 1991, to evaluate whether i <br /> vapor extraction is feasible at the site. Based on data obtained during the VET and the i <br /> distances between the wells, RESNA estimates that wellhead flowrates of 30 cubic feet per <br /> minute will result in an effective radius of influences of approximately 25 feet. RESNA <br /> concludes that vapor extraction is a feasible method of remediating soil at this site. The <br /> radius of influences and flow rates estimated above can be further refined and the number <br /> and location of additional vapor-extraction wells will be selected during an additional <br /> subsurface environmental investigation. A copy of the vapor-extraction test report is <br /> included in Appendix D of this document. <br /> SCOPE OF WORK <br /> During the tank removal, we will: <br /> o Observe removai of four underground storage tanks and associated product <br /> lines. <br /> o Observe excavation of soil in and around the gasoline-tank cavity and product <br /> lines. <br /> o Collect and analyze appropriate samples of native soil within 2 feet below the <br /> -- base of the former tanks to-evaluate if hydrocarbons remain in the sotl. <br /> 3W3-4w <br />