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Page 2 Determination of Sheen After depth to water and free product measurements are performed, a test for the presence of sheen is conducted. A transparent bailer is lowered into the well in a manner such that only part of the bailer is submerged. The bailer is withdrawn from the well and the surface of the water in the bailer is observed for the presence of sheen as determined by the presence of iridescence or emul- sification. Presence of sheen is not investigated if it is determined that free product is present in the well. Total Well Depth Measurement Once the test for sheen presence has been conducted, the total depth of the well is measured. Total well depth is determined by measuring from the reference elevation described in the section for Depth to Water level Measurement, above, to the depth at which tension in the tape measure to which the electric probe is attached or the steel tape to which the yardstick is attached becomes slack. Total well depth measurements are made to the nearest 0. 05 feet. Well Purging In order to obtain a representative sample of the water in the aquifer being sampled, stagnant water in the well casing must be removed to permit well recharge with non-stagnant aquifer water. The removal of stagnant water will be accomplished by the removal of the water to the surface where it will be either disposed of or stored for future disposal. The purging rate used at a particular monitoring well will depend on the expected or known hydraulic yield of the well. In moderate to high yield formation wells the purging device will be placed near the top of the screened interval of the well to ensure that non-stagnant formation water will move upward in the screened interval. When purging low yield formation wells, water will be removed from the bottom of the screened interval. when purging low-yield wells (wells which yield less than 3 casing volumes) , the wells will be purged to dryness once. As soon as the well has recovered to a volume sufficient for sampling, samples will be collected. At no time will a well be purged to dryness if the rate of recharge is such that formation water will cascade down the sides of the casing. During purging operations, the yield parameters of pH, temperature, electrical conductivity (EC) and turbidity will be monitored in the purged water.