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Admkk <br />k" KLEINFELDER <br />geologist called their Reno office to discuss their field operation. <br />Hydro -Search's Reno office decided to eliminate construction of MW -4 and <br />abandon the three existing wells. <br />%Abandonment of the three monitoring wells was begun on April 28, 1988, and <br />completed on April 29, 1988. Hydro -Search's geologist supervised the <br />abandonment of MW -1, MW -2 and, MW -3, but was not at the site when boring <br />MB-1 was backfilled. Kleinfelder's geologist observed the abandonment <br />procedures on April 28 and April 29,-1988. <br />Hunt Drilling performed the abandonment and grout work. The first step <br />was to remove as much of the PVC casing as possible. The entire PVC <br />casing was removed from MW -3, while only the top 5 to 10 feet were removed <br />N from MW -1 and MW -2. The sand pack, bentonite, and remaining PVC was <br />removed as the well was drilled out to the diameter and depth of the <br />original boring. A cement slurry was pumped down the open borehole, using <br />a 1 -inch -diameter tremie pipe, until the cement reached the ground <br />surface. <br />4.4 GAS MONITORING BORINGS <br />Ten 3 -foot -deep gas monitoring borings were drilled at locations around <br />and within the landfill boundaries (see Figure 2), and monitored for <br />soil -gas using an HNU Model P101 PID and a combustible gas indicator. A <br />PID measures the concentration of volatile gases in parts per million <br />(ppmv) in a volumetric ratio in relation to a known standard. Calibration <br />with a known calibration gas is generally performed to check whether the <br />PID is functioning within acceptable limits of the device. The PID was <br />zeroed prior to each reading, but was not calibrated in the field. A <br />combustible gas indicator measures a gas's concentration as a percentage <br />of its explosive limit. Neither device used identifies the specific type <br />of hydrocarbon(s) present nor provides a quantitative measurement of the <br />concentration. <br />Soil -gas monitoring borings MB -1 and MB -2 were drilled on April 27, 1988, <br />and MB -3 through MB -10 were drilled on April 28, 1988. <br />0 104-88-683 7 <br />