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09:12:97 16:49 GR.,GS[-5ACTC � 12094640138 [719 <br /> G51 FWd Mcthuds and rto"4u, <br /> Field Screening of�pil Sarntinles <br /> A PID is used to perform head-space analysis in the field for the presence of organic <br /> vapors from the soil sample. This test procedure involves removing some soil from one <br /> of the sample tubes not retained for chemical analysis and immediately covering the end <br /> of the tube with a plastic cap. The PTD probe is inserted into the headspace inside the tube <br /> through a hole in the plastic cap. Head-space screening results are recorded on the boring <br /> log. Head-space gcreelting procedures are performed and results recorded as <br /> reconnaissance data. GSI does not consider field screening techniques to be verification <br /> of the presence or absence of hydrocarbons. <br /> CouAmetion of Mon toric Welts <br /> Monitoring wells are constructed in the exploratory soil borings with Schedule 40 polyvinyl <br /> chloride (PVC) cashig, All joints are thread joined; no glues, cements, or solvents are <br /> used in well construction. The screened interval is constructed of machine-slotted PVC <br /> well screen which generally extends from the total well depth to a point above the <br /> groundwater. An appropriately-sized sorted sand is placed in the annular space adjacent <br /> to the entire screened interval. A bentonite transition seal is placed in the annular space <br /> above the sand, and the remaining annular space is sealed with neat cement or cement <br /> grout. <br /> Wellheads are protected with water-resistant traffic-rated vault boxes placed flush with the <br /> ground surface. The top of the well casing is sealed with a locking waterproof cap. A <br /> lock is plat d on the well cap to prevent vandalism and unintentional introduction of <br /> materials into the well. <br /> Measurement of Water Levels <br /> The top of the newly-installed well casing is surveyed by a California-licensed Land <br /> Surveyor to mean sea level (MSL). Depth-to-groundwater in the well is measured from <br /> the top of the well casing with an electronic water-level indicator. Depth-to-groundwater <br /> is measured to the nearest 0.01-foot, and referenced to MSL. <br /> Well Develenment and SamRllag <br /> The purpose of well development is to improve hydraulic communication between the well <br /> and the surrounding aquifer. Prior to development, each well is monitored for the presence <br /> of floating product and the depth-to-water is recorded. Wells are then developed by <br /> A-2 <br />