The tunnel alignment would be constructed more than 120 feet below the ground surface, including foundations of trestle bridges. Prior to the completion of design, geotechnical field investigations would identify the soil types and locations as well as the groundwater pressures along the entire alignment, including areas of concern such as levees and bridge foundations. Based upon the results of the geotechnical information, the TBM operator would control the rate of boring to minimize changes in the soil structure above and below the TBM.