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19 ATTACHMENT 2 WATER TABLE AND HYDROCARBON MONITOR WELL MEASUREMENTS The measurements are made with a transparent plastic bailer -type sampler suspended on a fiberglass measuring tape. A ball check valve in the bottom of the bailer allows a sample showing the product thickness to be withdrawn from the well. Figure A illustrates the measurement process. The measuring tape is attached to the lower end of the bailer and passes up through the center of the body of the bailer. This arrangement :flows direct readings from the tape, where it passes through the top of the product layer and at the product/water interface. The bailer is lowered into the well so that roughly 80 percent of the bailer body is below the top of the liquid surface. The length of measuring tape in the well indicates the depth of the sampler and is recorded as the "Tape Ref.," as is shown in Table A. The bailer is then pulled back to the surface, where the length of measuring tape extending below the product surface is read and recorded as "Tape Read.," under the heading "Product Readings" in Table A. Similarly, the length of tape below the product/ water interface is recorded as the "Tape Read." under the heading "Water Readings" in Table A. If the product layer is thicker than the length of the bailer, then a second deeper measurement is made until the pro- duct/water interface is found. Under these circumstances, a deeper tape .reference is shown for the water measurements than the product measure- ments. The depth to water and depth to product are calculated from the table readings and shown in the fourth and seventh columns in Table A. The datum elevation is the reference elevation for the top of the casing on the well where the tape reference was noted. The last four columns show the calculated values for product thickness, Water Elevation, Piezo- metric Elevation, and the Product Elevation. The product thickness is the difference between the depth to water and the depth to product. The water elevation is the datum elevation less the depth to water. If product is present, the piezometric surface will be different than either the water or product elevation. The piezometric surface is determined for gasoline plumes by multiplying the product thickness by 0.8 and adding the result to the water elevation. The density of gaso- line is approximately 0.8, and this calculation corrects for the differ- ence in density and provides a value that would be the water table surface if no gasoline were present. The product elevation is deter- mined by subtracting the depth to product from the datum elevation. 0