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CV — CD/2 2 HW 7.48 <br />where: <br />CV = <br />casing volume (gallons) <br />CD = <br />casing diameter (feet) <br />HW = <br />height of water column within well (feet) <br />7.48 = <br />conversion from cubic feet to gallons. <br />• Each well with sufficient recharge was purged of a minimum of three casing volumes <br />and allowed to recover to 80 percent of the original well volume prior to sampling. <br />Slow -recharge wells were purged of a minimum of one well volume and also allowed <br />to recover sufficiently (for a period of no more than two hours) prior to sampling. <br />To assess the presence of fresh water coming into the well, dissolved oxygen (DO), <br />electrical conductivity (EC), pH, turbidity, and temperature were monitored after <br />approximately every two to five gallons of purging and were recorded on a Well Data <br />Sheet. Sampling was performed when the total estimated purge volume was reached <br />and the EC, pH, turbidity, and temperature stabilized to within 10% between <br />consecutive readings. <br />• Where a bailer was used for sample collection, a bottom -emptying device was <br />inserted into the bailer, and the sample was transferred from the bailer to the <br />container at a rate so as to minimize aeration. <br />Groundwater Sampling Using Low -Flow Purging Methods <br />• Groundwater monitoring wells that are equipped with dedicated sampling equipment <br />were purged and sampled using low -flow purging methods. <br />• With the weighted water -level meter in the well, the submersible pump was operated <br />at a discharge rate that would minimize the decline in water level. <br />• Discharged water was routed through a sampling chamber equipped with probes for <br />measuring DO, EC, pH, turbidity, and temperature. When three consecutive readings <br />of these field parameters had stabilized to within 10% of each other, the water quality <br />was determined to be stable and samples were collected. <br />Groundwater Sampling Collection and Preparation <br />• Samples, including field, trip, and equipment blanks, were collected in approved <br />sample containers (Table 1), and each container was filled completely and <br />immediately capped, labeled, and placed in a cooler with ice. Samples for VOC <br />analysis were filled by pouring the sample down the side of the container to minimize <br />aeration and capped with no airspace. <br />• <br />2 Geo -Logic Associates <br />