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<br />Soil Investigations for Data Collection in the Delta <br />Initial Study/Proposed Mitigated Negative Declaration 16 <br /> <br />*Source: Rogers et al. 2005 <br />Figure 8. Cesium Vaper Total Field Magnetometer (CVTFM) <br />Electrical Resistivity Tomography (ERT) <br />For the ERT method, a linear array of removable small steel spike electrodes <br />(approximately 0.5 inches in diameter by 8 inches long) will be driven 6 to 8 inches into <br />the ground approximately every 10 feet over several hundred feet. Low amperage <br />current is injected into the ground between varying pairs of electrodes and readings are <br />taken (Figure 9). At each test setup, which consists of an 84-electrod array, low <br />amperage currents are sent over two electrodes for up to a few seconds while readings