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<br />Soil Investigations for Data Collection in the Delta <br />Initial Study/Proposed Mitigated Negative Declaration 17 <br />in other electrodes are taken. This procedure is repeated over a period of a few hours <br />and is repeated along the survey line which is planned to be up to 2,300 feet long. <br /> <br />*Source: Plattner Geophysics Group 2019 <br />Figure 9. Electrical Resistivity Tomography (ERT) <br />Seismic Refraction/Reflection (Seismic) <br />For the seismic surveys, seismic sensors (approximately 0.5 inches in diameter and 5 <br />inches long) are driven into the ground 3 to 5 inches deep at a spacing of approximately <br />6.5 feet. The EnviroVibe Minibuggy is a vehicle that is positioned every 10 to 20 feet <br />and a pad is lowered onto the ground to inject a seismic signal into the ground using <br />swept frequency vibratory motion (Figure 10). The frequency sweeps are performed <br />while sensor readings are taken. The sweeps take less than 30 seconds to complete. <br />The source is then moved along the line and another sweep is performed. This process <br />is repeated along the entire length of the survey line which is up to 2,300 feet long. The <br />EnviroVibe Minibuggy is a small rubber-tire truck-mounted source (approximately 8 feet <br />wide, 20 feet long, and 8 feet high) that creates minimal ground disturbance, much like <br />typical rubber-tired farming equipment. Vibrations induced are relatively small, while