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December 8, 1993 Working to Restore Nature ARCO Station No 760, Lodi, California The annular space in the well is packed with sand compatible with well slot size to approximately 1 to 2 feet above the slotted interval A 3-foot thick bentonite plug is added above the sand pack to prevent the cement from entering the well pack The remaining annulus is backfilled to grade with a bentonite cement slurry Wells are protected with a traffic-rated, cast-aluminum utility box equipped with a PVC skirt The box has a watertight seal to protect against surface-water infiltration and must be opened with a special wrench. The design of this box discourages vandalism and reduces the possibility of accidental disturbance of the well Well Development We wait a minimum of 24 hours after well installation before developing the groundwater monitoring wells to allow the grout to seal Before developing the monitoring wells, a water sample is collected for subjective analysis from near the water surface in the well with a Teflon bailer cleaned with a laboratory-grade detergent and deionized water The wells are developed with a surge block and pump Well development continues until the discharge water is clear of silt and sand Clay-size sediments derived from the screened portion of the formation cannot be entirely eliminated by well development After the wells stabilize for a minimum of 24 hours, the wells are purged of stagnant water and a sample is collected for laboratory analysis See the section on groundwater sampling Subjective Analysis of Q iroundwater Samples Groundwater samples are collected for subjective analysis from dust below the air-fluid interface in a monitoring well by lowering approximately half the length of a clean Teflon bailer through the interface The bailer is retrieved and the water sample examined for floating product, sheen, or other subjective evidence of hydrocarbons Measurement of the Depth to Groundwater in Monitoring Wells The depth of the groundwater surface in a monitoring well is measured from the top of the well casing to the nearest 0 01 foot with a Solinst or similar electric water-level indicator _ The well will be vented to the atmosphere before obtaining depth-to-water measurements Venting is conducted to allow the groundwater to equilibrate to barometric pressure These measurements will be combined to evaluate the elevation of the groundwater surface in each well and the slope of the groundwater surface across the site. 0913ccar 38048-10