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`- N11TTELco poration <br /> Field Protocol 2 June 1991 <br /> DETERMINATION OF SHEEN <br /> l <br /> After depth to water and free-product thickness measurements are <br /> �- performed, a test for the presence of sheen is conducted. A transparent bailer is <br /> lowered into the well in a manner such that only part of the bailer is submerged. The <br /> bailer is withdrawn from the well and the surface of the water in the bailer is <br /> examined for the presence of sheen as determined by the presence of iridescence or <br /> emulsification. Presence of sheen is not investigated if it is determined that free <br /> product is present in the well. Use of a cleaned dark colored bucket is helpful for <br /> sheen-determination purposes. <br /> TOTAL WELL DEPTH MEASUREMENT <br /> Once the test for sheen presence has been conducted, the total depth <br /> of the well is measured. Total well depth is determined by measuring from the <br /> reference elevation described in the section for Water Level Measurement, above, to <br /> l the depth at which tension in the tape measure (to which the electric probe is <br /> attached or the steel tape is attached) becomes slack. The tape measurement is <br /> rcorrected for probe length. Total well depth measurements are made to the nearest <br /> 0.05 feet. <br /> WELL PURGING <br /> In order to obtain a representative sample of the water in the aquifer <br /> being sampled, stagnant water in the well casing must be removed to permit well <br /> recharge with non-stagnant aquifer water. The removal of stagnant water is <br /> accomplished by the removal of the water to the surface where it will be either <br /> I disposed of or stored for future disposal. <br /> The purging rate used at a particular monitoring well will depend on the <br /> expected or known hydraulic yield of the well. <br /> In moderate to high yield formation wells the purging device will be <br /> Tplaced near the top of the screened interval of the well to ensure that non-stagnant <br /> formation water will move upward in the screened interval. When purging low-yield <br /> formation wells, water will be removed from the bottom of the screened interval. <br /> When purging low-yield wells (wells which yield less than 3 casing <br /> volumes), the wells will be purged to dryness once. As soon as the well has <br /> 1 recovered to a volume sufficient for sampling, samples will be collected. At no time <br /> will a well be purged to dryness if the rate of recharge is such that formation water <br /> will cascade down the sides of the casing. <br />