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CV= (n)(CD/2)2 (HW)(7.48) <br /> where: <br /> CV = casing volume(gallons) <br /> CD = casing diameter(feet) <br /> HW = height of water column within well (feet) <br /> 7.48 = conversion from cubic feet to gallons. <br /> • Each well with sufficient recharge was purged of a minimum of three casing volumes and <br /> allowed to recover to 80 percent of the original well volume prior to sampling. Slow- <br /> recharge wells were purged of a minimum of one well volume and also allowed to recover <br /> 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), electrical <br /> conductivity(EC), pH, turbidity, and temperature were monitored after approximately every <br /> two to five gallons of purging and were recorded on a Well Data Sheet. Sampling was <br /> performed when the total estimated purge volume was reached and the EC,pH,turbidity, and <br /> temperature stabilized to within 10%between consecutive readings. <br /> • Where a bailer was used for sample collection, a bottom-emptying device was inserted into <br /> the bailer, and the sample was transferred from the bailer to the container at a rate so as to <br /> minimize aeration. <br /> Groundwater Sqmpling Using Low-Flow Purging Methods <br /> • Groundwater monitoring wells that are equipped with dedicated sampling equipment were <br /> purged and sampled using low-flow purging methods. <br /> • With the weighted water-level meter in the well, the submersible pump was operated at a <br /> 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 of <br /> these field parameters had stabilized to within 10% of each other, with no discernible upward <br /> or downward trend, the water quality was determined to be stable and samples were <br /> collected. <br /> Groundwater Sampling Collection and Preparation <br /> • Samples, including field, trip, and equipment blanks,were collected in approved sample <br /> containers (Table 1), and each container was filled completely and immediately capped, <br /> labeled, and placed in a cooler with ice. Samples for VOC analysis were filled by pouring the <br /> sample down the side of the container to minimize aeration and capped with no airspace. <br /> 2 <br /> DAFC_SApian2SA09.doc <br /> Geologic Associates <br />