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Mr. Russell F. Chapin, Sr. <br /> November 15, 1995 <br /> Page 4 <br /> corner of the site and another which would be located near the northwest corner of the site (see <br /> Site Plan). We will make use of the wells near the southwest and southeast corners of the <br /> northerly parking area as vapor extraction wells and use the existing air sparging well as the only <br /> sparging point initially. It is our opinion that the design as previously presented would lead to <br /> additional migration of contaminants by forcing contaminants offsite to the east when air <br /> sparging is initiated at the proposed locations. <br /> Vapor Well Construction <br /> All vapor extraction wells will be constructed using flush jointed, 4-in inner diameter, <br /> Schedule 40 polyvinyl chloride (PVC) casing set to depths of 25 to 30 ft. No chemical cements, <br /> glues, or solvents will be used in well construction. The base of each well will be fitted with a <br /> threaded PVC plug. The screened portion of each well will consist of factory-perforated casing <br /> with 0.060-in-wide slots. The well screen will be set through the augers and will extend from the <br /> total depth of the boring to approximately 5 ft below the ground surface. The annular space of <br /> the well will be packed with sorted sand to a point approximately 0.5 ft above the top of the <br /> perforated casing. A 2-ft thick plug consisting of bentonite pellets or chips will be placed above <br /> the sand in the wells to prevent cement from entering the sand pack. The remaining annulus will <br /> be backfilled with a mixture of neat cement and powdered bentonite (<5%)to grade. <br /> Soil samples will be collected at maximum 5-ft intervals and at lithologic contacts in the <br /> borings using a California-modified split-spoon sampler fitted with clean brass sleeves. Soil <br /> samples from each sample interval will be sealed and placed in iced storage for possible <br /> laboratory analysis. A photoionizing organic vapor meter(OVM) will be used during sampling <br /> to detect potential hydrocarbon concentrations in the soil samples. Two soil samples from each <br /> boring will be analyzed for TPHg using EPA Method 8015 (modified) and for BTEX using EPA <br /> Method 8020. <br /> DESIGN AND INSTALL SYSTEM <br /> The remedial system selected for installation will be designed, permitted, and installed. <br /> This phase will include appropriate negotiations with agencies regulating soil and groundwater <br /> assessment and cleanup projects, air emissions, sewer disposal of treated water, and others. The <br /> system recommended is capable of extracting and treating both soil vapor and groundwater, and <br /> will include subgrade trenches for extraction and sparging lines. <br /> 4058-P3 <br /> LUSH GEOSCIENCES <br />