Module Foundation Installation. Several module mounting types will be considered to best address the slope of land and soil stability at the project site. For example, large land areas with a slope toward the south are excellent for single-axis tracking systems (see Expanded SEPA Checklist Supplement Attachment J, Figure 4b). Land areas that are sloped to the east, southeast, west, or southwest will not as easily accommodate single-axis tracking systems, and are better suited to a fixed-tilt mounting structure (see Expanded SEPA Checklist Supplement Attachment J, Figure 4c). The foundations securing the solar modules will be designed to withstand high winds and snow loads. The site may have multiple foundation types to match the ground conditions and type of mounting structures used. The mounting-system support structures could consist of embedded posts, poles, or structural steel angle. The embedment could be completed via a vibratory drill or similar installation method to depths of approximately 8 feet. Pending final design, the solar module foundations will require site work and potential boring. The posts will not be anchored unless a patch of bedrock is encountered during installation. The embedment could be completed via a vibratory drill or similar installation method to depths of approximately 8 feet. After the posts are installed, they are held in place by friction from the surrounding soil, without the use of concrete. Driven piles develop their strength by utilizing a definable skin friction between the pile and the soil. As the pile is forced into the ground, the displaced material compresses and that, in turn, creates the friction at the pile/soil interface. Piles are typically driven to a depth that prevents seasonal and temporary changes from affecting their strength. A geotechnical engineer will determine the parameters to be used in the structural design. Expanded SEPA Checklist Supplement Attachment J, Figure 4d illustrates the footing installation methods for both the fixed tilt and single axis panels. No concrete will be used when installing the foundations for the modules. For one type of single-axis support approach, 1,936 posts are needed for every megawatt of energy. If the entire 75 MWdc were to be installed with this mounting system, then approximately 145,200 posts would need to be set. If a fixed-tilt approach is used, up to 8,000 steel angles would be needed. The impervious surface associated with these structures is presented in more detail in Expanded SEPA...
