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CV=(n)(CD/2)2 (HW)(7.48) where: CV = casing volume(gallons) CD = casing diameter(feet) HW = height of water column within well (feet) 7.48 = conversion from cubic feet to gallons. • Each well with sufficient recharge was purged of a minimum of three casing volumes and allowed to recover to 80 percent of the original well volume prior to sampling. Slow- recharge wells were purged of a minimum of one well volume and also allowed to recover sufficiently(for a period of no more than two hours)prior to sampling. • For domestic wells the water was left to run for approximately 30 minutes prior to sample collection. • To assess the presence of fresh water coming into the well, a Horiba U-10 Water Quality Meter®(or equivalent)was used to measure electrical conductivity(EC),pH, turbidity, and temperature. The water quality meter was calibrated daily with a manufacturer supplied auto- calibration solution. After approximately every two to five gallons of purging, field parameters were recorded on a Well Data Sheet. Sampling was performed when the total estimated purge volume was reached and the EC,pH, turbidity, and temperature stabilized to within 10%between consecutive readings. Groundwater Sampling_Using Low-Flow Purging Methods • Groundwater monitoring wells at the Austin Unit that are equipped with dedicated sampling equipment were purged and sampled using low-flow purging methods. • With the weighted water-level meter in the well,the submersible pump was operated at a discharge rate that would minimize the decline in water level. • Discharged water was routed through a sampling chamber equipped with probes for measuring EC,pH, turbidity, and temperature with the water quality meter. When three consecutive readings of these field parameters had stabilized to within 10%of each other, with no discernible upward or downward trend, the water quality was determined to be stable and samples were collected. 2 DAForwardSAplan.doc Geologic Associates