3.4.2.4 Groundwater

removal of existing vegetation covering approximately 114 acres, exposing soils to increased erosion. Increased sediment loading in this area could discharge to the swale feature identified as Dry Lake Creek on the USGS topographic map. These effects will be minimized through the implementation of BMPs and Black Canyon’s compliance with relevant permits.

Construction of the proposed Project will require the use of a variety of motorized heavy equipment including, but not limited to, 4x4 pickups, fuel trucks, cranes, dozers, concrete trucks, backhoes, conductor pullers, shield tensioners, and drill rigs. Much of this equipment will require job-site replenishment of petroleum products and other hazardous materials, including oils, grease, coolants, lubricants, and other fluids. The accidental spill of these products, or similar construction-related materials, could lead to the discharge of contaminants onto the soil or into existing surface waters located within the Footprint of Potential Disturbance. Conveyance of contaminants could take place directly at the time of the spill or could be retained in place (such as soil contaminants) until a runoff event delivered them to a watercourse later or could infiltrate into the soil and/or groundwater below. A chemical spill affecting a water body, stream channel, wetland area, or groundwater is a potentially significant impact; however, any potential impact is anticipated to be minimized through the implementation of a Hazardous Substances Spill Prevention and Cleanup Plan. In addition, in order to minimize potential construction impacts on the aquatic environment within the Footprint of Potential Disturbance, Black Canyon proposes to develop and implement an Erosion and Sediment Control Plan that incorporates BMPs designed to minimize the potential for erosion and sedimentation to stream and wetland areas.

The Project is not expected to impact water quality within or adjacent to the Project, including to ephemeral, intermittent, or perennial streams. Any potential impacts to surface waters due to ground disturbance during construction will be managed through the Project’s Erosion and Sediment Control Plan.

3.4.2.4 Groundwater

The upper reservoir will be constructed with a liner system to prevent leakage into groundwater. Black Canyon proposes to design this liner system to prevent upper reservoir water losses or groundwater impacts, and to prevent groundwater from entering the upper reservoir. The tunnel system between the reservoirs (depending on depth, location, pipe runs, and the design of other subsurface facilities) could impact groundwater flow by causing it to move around those impediments.

Due to the semi-arid classification for the Project vicinity and the short duration of construction assumed prior to placement of an impermeable liner in the upper reservoir during construction, the potential for a discernible effect during construction on the shallow aquifers that may exist in the area of the upper reservoir is minimal. Black Canyon proposes to design the liner system to prevent leakage from the upper reservoir. Therefore, no significant effects to groundwater quality are expected from construction of the upper reservoir.