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e4 <br /> September 13, 1991 <br /> Unocal Station No. 6981, Stockton, California <br /> that vapor extraction is recommended. Applied GeoSystems will perform the test in <br /> accordance with San Joaquin County Air Quality District guidelines. <br /> i A portable vapor-extraction system will be transported to the site and operated as required <br /> to obtain vapor samples and vacuum pressure and flow rate information. Vapor-extraction <br /> vacuum, flow rate, and vacuum at the observation wells will be monitored. By inducing a <br /> particular vacuum and flow rate at each v-+por-extraction well, an approximate effective <br /> radius of iriliuence of can be established. <br /> Vapor samples will be collected into sample bags at the inlet and outlet of the VET system. <br /> and submitted to a State-certified laboratory for analysis of Tf T-ig and BTEX. Chain-of- <br /> Custody protocol will bu followed throughout field and laboratory procedures. <br /> The VET will provided preliminary data of tite effective radius of influence. We can also <br /> calculate t,.e TPHg concentration a vapor-extraction system can remove in twelve months. <br /> Gradient Evaluation <br /> The cle.vation of the top of each well casing in the new wells will be measured relative to <br /> mean sea level by a licensed land surveyor. The local groundwater gradient will be <br /> evaluated using existing arid new wells. Water-depth measurements will be made to the <br /> nearest 0.01 foot in each well with an electric water-level indicator. The well will be vented <br /> to the atmosphere for a minimum of 1 hour before obtaining depth-to-water measurements. <br /> Venting is conducted to allow t''f-ground water to equilibrate to barometric pressure. This <br /> data will be combined to evaluate the elevation of the ground-water surface in each well and <br /> the slope of the ground-water surface across the site. <br /> �rt <br /> M032-4W 16 <br />