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Geoelectric Leak Detection Final Report September 18, 2008 Forward Landfill WU-08 Page 3 Dipole Method for Geomembrane covered with soil material Method / Procedure The method used to perform the geoelectric leak detection survey on the soil covered geomembrane was the dipole method. Testing was performed in accordance with ASTM D7007-03. For this electrical leak location method, a voltage potential is introduced between the insulative geomembrane and the earth beneath it. In the case of holes in the geomembrane, current exits through the hole in the membrane, causing an anomaly in the voltage potential field at that location. Measurements of voltage potential are taken in a grid pattern throughout the survey area in order to locate these perturbations. The survey was performed by three dipole operators. As the operators proceeded, they observed the amplitude of change in voltage and watched for spikes or dips in the potential field. Whenever a significant change was encountered, the area was flagged and rechecked immediately until the anomaly could be validated or dismissed. A signal of greater than three times the background noise is validated when it can be reproduced at least five times over the same location. Am The calibration hole consisted of an artificial leak fabricated and placed in accordance in with ASTM D7007-03. The calibration test showed that a one quarter inch diameter hole could be located. ASTM procedures require that the target hole size produce a signal to noise ratio of at least 3. As shown in the following graph, a signal to noise ratio of approximately 800 was created by the quarter inch hole. Figure 3 — Calibration Graph 143E Spring Hill Drive • Grass Valley, California 95945 • (530) 272-2448 • Fax: (530) 272-8533 USA 0 CENTRAL & SOUTH AMERICA 0 PHILIPPINES