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5 FIELD PROCEDURE The following section describes procedures used by Ultramar field personnel in the performance of ground-water sampling. Ground Water and Free Product -Depth Determination A water/petroleum product interface probe is used to determine free product and water depth in each well to the nearest 0.01-foot. The thickness of free product is determined by subtracting the depth to product from the depth to water. if a free product layer is not detected by the interface probe, the tip of the probe is subjectively analyzed for a product sheen. Visual Analysis of Ground Water Prior to purging and sampling ground water monitoring wells, a water sample is collected from each well for subjective analysis. The visual analysis involves gently lowering a clean, disposable, polyethylene bailer to approximately one-half the bailer length past the water table interface. The bailer is then retrieved, and the sample contained within the bailer is examined for floating product or the appearance of a petroleum product sheen. Monitorinq Well Purging. and Sampling Monitoring wells are purged by bailing' a minimum of four casing volumes of water from the well using a clean disposable bailer or electrical submersible purge pump. Purge volumes are calculated prior to purging. . During purging the temperature, pH, and electric conductivity are monitored. The well is sufficiently purged when: the four casing volumes have been removed; the temperature, pH, and conductivity have stabilized to within 10% of the initial readings; and the ground water being removed is relatively free of suspended solids. After purging, ground water levels are allowed to stabilize to within 80% of the initial water level reading. A water sample is then collected from each well with a clean, disposable polyethylene bailer. If the well is bailed dry prior to removing the minimum volume of water, the ground water is allowed to recharge. If the well has recharged to within 80% of the initial reading within two hours, the well will continue to be purged until the minimum volume of water has been removed. If the well has not recharged to at least 80% of the initial reading within two hours, the well is considered to contain formational water and a ground water sample is collected. Ground water removed from the well is stored in 55-gallon drums at the site and labelled pending disposal . In wells where free product is detected, the wells will be bailed to remove the free product. An estimate of the volume of product and water will be recorded. If the free product thickness is reduced to the point where a measurable thickness is no longer present in the well , a ground-water sample will be collected. If free product persist throughout bailing, a final free product thickness measurement will be taken and a ground-water sample will not be collected.