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Soil Investigations for Data Collection in the Delta Initial Study/Proposed Mitigated Negative Declaration 14 2.1.4 On-Land Geophysical Survey Equipment Vehicles at each Impact Area during the surveys will include a rubber-tired truck to induce source vibrations (referred to as the EnviroVibe Minibuggy); a tractor-trailer lowboy truck for the EnviroVibe Minibuggy; and support passenger vehicles (assume up to 14 vehicles). The EnviroVibe Minibuggy is powered by a 113-horsepower diesel engine and will be on site for seismic reflection surveys at some geophysical survey sites. While this complete list of vehicles may be used, not all of them are necessary for every site. For example, many of the Impact Areas will likely not require a tractor-trailer lowboy truck or EnviroVibe Minibuggy. 2.1.5 On-Land Geophysical Surveys Methods Geophysical surveys consist of noninvasive (i.e. does not require a soil boring) techniques that can be used to provide information on subsurface conditions and anomalies, such as buried casings or abandoned wells. Geophysical surveys will be conducted on up to five Impact Areas within a location on Bouldin Island (see Figure 2b). The five Impact Areas are comprised of three arrays approximately 2,300 feet long and 100 feet wide and two area grids (each approximately 1,000 feet by 1,000 feet; although surveys will only be conducted within a portion of the full grid measuring 500 feet by 500 feet). The geophysical surveys will be used as a test program to determine if these noninvasive surveys are appropriate for future use in other regions of the Delta, thereby reducing the potential need for soil borings or CPTs in certain areas. One or more of the following geophysical survey techniques will be used at an Impact Area: Time Domain Electromagnetic (TDEM), Cesium Vaper Total Field Magnetometer (CVTFM), Electrical Resistivity Tomography (ERT), and Seismic Refraction/Reflection (Seismic). Each of these methods is described in detail below. The duration to perform all of the geophysical surveys using any of the four aforementioned methods will be up to 21 days for the five Impact Areas. 2.1.5.1 Time Domain Electromagnetic (TDEM) For the TDEM method, 10-gauge wire loop transmitters will be laid on the ground in a 100-foot by 100-foot grid transmitter wire to induce a low current in the ground, readings will be taken, and then the loop will be moved along a survey line up to 2,300-feet-long (Figure 7).