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Soil samples collected for volatile organic compounds will be ' p g p periodically screened, as determined by the site geologist, in the field by head space analysis. Samples are placed in a clean glass container and covered with aluminum foil and covered with a screw lid. A ' photoionization detector (PID) is used to analyze the headspace of the samples. The PID will be calibrated using calibration gas. The results of this screening will be used for selection of representative samples for laboratory analysis, and as data for determining the boring depth. ' • All soil samples will be described in the field. Field observations noting sediment type, color, grain size, sorting, hardness, texture, clay content, moisture content, visible evidence ' of contamination, odor, and any other information important to the investigation. These soil sampling procedures are designed to: • ensure that representative soil samples are collected p p d and accurately described in the field. ' • ensure that all boring logs, sample descriptions, and field observations are consistent and accurate. ' • minimize the risk of cross-contamination between samples. `N 3.3 Well Water Sampling Procedures Prior to sampling of monitoring or other wells, the water level will be measured and the wells will be purged of three to five casing volumes or until well is dry. Bailers or submersible pumps used for purging will be thoroughly cleaned before and between samples, or disposable bailers ' may used. The amount of casing volume of water in the well can be calculated with the formula: r2 X (hl -h2) X 7.48 gallons/ft3 = gallons/casing volume, where: ' r=inner radius of casing (ft) hl = depth of well (ft) from top point measurement (normally from I ' reference mark in casing) h2 = depth to water(ft) from to of point of measurement (POM). t f' i a American Geological Services, Inc. 4