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Mr. Greg Vaughn Project No. OC42-001.20 <br /> April 11, 1995 <br /> Page 4 <br /> effects of flowing sand conditions during drilling and well installation. The casing hammer <br /> method utilizes a heavy wall metal casing, driven as the drill bit advances, to seal off the <br /> boring from the surrounding formation. Continuous samples are collected from cuttings <br /> and drilling fluids are not used. An EMCON geologist will prepare detailed boring logs <br /> based on samples and drilling return materials. Samples will be logged according to the <br /> Unified Soils Classification System. All work will be supervised by a Registered California <br /> Geologist and will conform to regulatory standards. <br /> Drilling equipment will be decontaminated by steam cleaning after each boring to reduce <br /> potential cross-contamination. <br /> Monitoring wells will be constructed using 4-inch-diameter, schedule 40 polyvinyl chloride <br /> casing. Five- to ten-foot screen intervals will be set across sand units identified in CPT <br /> profiles and exploratory borings. Gravel pack intervals will extend 2 to 5 feet above the <br /> screened interval, and a minimum 2-foot-thick bentonite seal will be placed above the <br /> sand. The remaining annular space will be grouted to ground surface with cement grout <br /> containing 5 percent bentonite tremied from the base of the boring. <br /> Monitoring wells will be developed by surging, bailing, pumping, or a combination of <br /> these methods. Monitoring well development procedures will be consistent with those <br /> discussed in the Phase H Assessment Report (EMCON, September, 1995). Well <br /> development water will be contained in a portable tank pending evaluation of disposal <br /> options. <br /> GROUNDWATER SAMPLING AND LABORATORY ANALYSIS <br /> Groundwater samples will be collected approximately 48 hours after completion of well <br /> development following the procedures discussed in the Phase H Assessment Report. <br /> Groundwater samples collected during HydroPunch investigation and from monitoring <br /> wells will be labeled, recorded on chain-of-custody documents, and submitted to a state <br /> certified analytical laboratory. Samples will be analyzed for the following parameters: <br /> • Total petroleum hydrocarbons as gasoline (TPHG) using U.S. Environmental <br /> Protection (EPA) Agency Method 8015 Modified <br /> • Benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Method <br /> 8020 <br /> • Total petroleum hydrocarbons as diesel (TPHD) using EPA Method 8015 <br /> Modified <br /> SAC\N�PJW42DC420012.OES-94W b:3 <br />