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AEGIS ENVIRONMENTAL, INC. STANDARD OPERATING PROCEDURE RE: MEASURING LIQUID LEVELS USING WATER-LEVEL OR INTERFACE PROBE SOP-12 Field equipment used for liquid-level gauging typically includes the measuring probe (water-level or interface) , light filter(s) , and product bailer(s) . The field kit also includes cleaning supplies (buckets, TSP, spray bottles, and deionized water) to be used in cleaning the equipment between wells. Prior to measurement, the probe tip is lowered into the well until it touches bottom. Using the previously established top-of-casting (TOC) point, the probe cord (or halyard) is marked and an measuring tape (graduated in hundredths of a foot) is used to determine the distance between the probe end and the marking on the cord. This measurement is then recorded on the liquid-level data sheet as the depth to water (DTW) . When using the interface probe to measure liquid levels, the probe is first electrically grounded to either the metal stove pipe or another metal object nearby. When no ground is available, reproducible measurements can be obtained by clipping the ground lead to the handle of the interface probe case. After grounding �-' the probe, the top of the well casing is fitted with a light filter to insure that sunlight does not interfere with the operation of the probe ' s optical mechanisms. The probe tip is then lowered into the well and submerged in the groundwater. An oscillating (beeping) tone indicates that the probe is in water. The probe is slowly raised until either the oscillating tone ceases or becomes a steady tone. In either case, this is the depth-to-water indicator and the DTW measurement is made accordingly. The steady tone indicates floating hydrocarbons. In this case, the probe is slowly raised until the steady tone ceases. This is the depth-to- product (DTP) indicator and the DTP measurement is made accordingly. The process of lowering and raising the probe must be repeated several times to ensure accurate measurements. The DTW and DTP measurements are recorded on the liquid level data sheet. When floating product is indicated by the probe's response, a product bailer is lowered partially through the product-water interface to conf irm the product on the water surface, and as further indication of product thickness , particularly in cases where the product layer is quite thin. This measurement is recorded on the data sheet as product thickness (PT) . In order to avoid cross contamination of wells during the liquid- level measurement process, wells are measured in the order of "clean" to "dirty" (where such information is available) . In addition, all measurement equipment is cleaned with TSP solution and thoroughly rinsed with deionized water before use, between