3.4.3 Cumulative Environmental Effects Related to Water Resources

Review of the Groundwater Atlas of Wyoming (Stafford et al. 2017), revealed no active wells in the vicinity of the upper reservoir; however, several groundwater wells are located in the vicinity of Seminoe Reservoir, some associated with the North Red Hills Campground and others on BLM and Wyoming State Park lands within the Project vicinity. Static water levels reported in these other wells ranged from 15 to 158 feet (Stafford et al. 2017).

Extensive tunneling will be required to construct the underground powerhouse, power tunnel between the upper reservoir and the powerhouse, tailrace tunnel between the powerhouse and a new intake in Seminoe Reservoir, powerhouse access tunnel, and the high-voltage transmission tunnel. Excavation activities associated with that tunneling could encounter or destabilize artesian groundwater systems. In addition, the placement of a possible underdrain system for leak detection and water evacuation in the upper reservoir, could destabilize localized artesian groundwater.

As noted in Table 3.2-1, the geographic scope for water resources is the HUC-8 watersheds in the Project vicinity since watersheds are natural, well-defined boundaries for surface water flow, and commonly contribute to the recharge of groundwater resources. The HUC-8 watersheds that comprise the geographic scope are the Pathfinder-Seminoe Reservoirs watershed (HUC 10180003) and the Medicine Bow watershed (HUC 10180004). The geographic scope encompasses surface waters, groundwater, and wetlands. As detailed in Table 3.2-2, there are six projects that occur within the geographic scope for water resources: 1) WPCI Project, 2) Two Rivers Wind Energy Project, 3) Lucky Star 1 Wind Project, 4) Gateway West Transmission Line Project, 5) Gateway South Transmission Line Project, and 6) Rock Creek Wind Energy Center.

Issues Identified for Analysis

Reasonably foreseeable future actions with the potential to affect water resources include actions that impact soils and subsequently water such as removing surface vegetation, disturbing soils, and creating the potential for soil erosion and subsequent sedimentation impacts to surrounding waterbodies. Cumulative effects on water resources can include impacts on groundwater, surface waters, and wetlands.

• Black Canyon currently anticipates relying on surface water from existing water rights within the North Platte River Basin as its water source for the Project.

Therefore, cumulative effects on groundwater resources from the Project were not assessed further. • Surface water quality is an important feature of watershed health that, when maintained, provides long-term, beneficial effects on the environment. • Modification of wetlands and riparian areas can result in cumulative effects on the functional capacity of these vegetation communities to maintain water quality.

Results

Reasonably foreseeable projects within the watersheds primarily include transmission line projects and wind energy projects. Due to the inherent nature of overhead transmission systems and wind turbines, they are anticipated to produce relatively little effect on erosion and sedimentation and, therefore, water quality in the watersheds. However, construction of access roads is expected to increase the potential for erosion and sedimentation associated with the Project and those listed in Table 3.2-2. Some access roads might involve stream crossings and could include culverts, bridges, or low-water crossings. Open streams may also be channeled through culverts over the course of construction. Construction of these roads and stream crossings could cause or contribute to erosion.

Each of the projects either have or would be required to obtain water use and discharge permits, implement erosion and sediment controls, and adhere to various spill plans as mandated by federal and state agencies. Impacts to water quality as the result of accidental releases of hazardous materials into water resources would depend on the proximity to or potential to be transported to a waterway or vulnerable aquifer. The current BLM RMPs include specific stipulations for site-specific projects to prevent cumulative long-term impacts to water resources. For these reasons, impacts from the Project, in combination with other actions, would likely be minor and highly localized and would not result in a significant cumulative effect on water resources in the watershed.

Ground-disturbing activities associated with past and present activities in the geographic scope, which could currently be affecting water resources, include transmission line facilities, pipelines, residential developments, and wind-energy facilities. Past and present development has contributed to some level of ground disturbance which, over time, is expected to be compliant with federal and state requirements. Where past and present developments are not meeting federal and state requirements, water resources could be cumulatively affected by increased sediment loading in the intermittent and perennial systems located near the Project.

Ground disturbance from the construction of the Project, and other projects within the geographic scope, has the potential for localized short-term cumulative effects on water resources. Short-term impacts could include degradation of the quality of waters from sedimentation as a result of destabilization of fragile soils and modification of upland, riparian, and wetland vegetation. These impacts, such as increased turbidity, would individually result in temporary impacts because they would return to baseline levels over a period of days or weeks following construction. Long-term impacts could include reduced riparian cover and sedimentation that remains in the river system. However, implementation of design features of the Project and selective mitigation measures, including reclamation of disturbed areas, would minimize cumulative effects on water resources. Cumulative effects on surface waters, if any, would dissipate the farther from they occur from the Project. Because the Project only overlaps with other projects in the vicinity of Aeolus substation, an already-constructed and disturbed area, the potential for newly-initiated cumulative effects related to ground disturbance is considered minor.