DOE/EIS-0332; McNary-John Day Transmission Line Project Draft ...

Environmental Consequences—Proposed Action
Construction
BPA McNary-John Day Transmission Project
Draft EIS
February 2002
Affected Environment,
Environmental Impacts, and Mitigation
Of the 43 acres of wetlands located within the project corridor, no wetland areas would
be filled to construct the proposed project. Vegetation would be cut within wetlands for
McNary Substation Alternative B where the line would cross the wildlife refuge.
Construction of access roads or towers located adjacent to some wetlands may require
removal of wetland buffer vegetation. The quality of vegetation of the wetland buffers in
these areas is marginal; the areas are mostly used for grazing and are dominated by
invasive weeds such as cheatgrass. However, the reduction of some of the vegetated
buffers adjacent to these wetlands would reduce overland flow and slightly increase the
likelihood of silts and sediments entering wetland surface waters, thus decreasing water
quality. These anticipated impacts are minor.
Oils and pollutants from machinery could also enter surface water, potentially effecting
fish or wildlife species. The construction of roads and tower pads could also alter
overland flow patterns, thereby either increasing or decreasing wetland hydroperiod (the
duration of soil saturation or inundation within a wetland).
The potential for impacts on groundwater is minor due to the use of construction
techniques that avoid trenching and drilling. Potential groundwater impacts that could
occur during construction include the potential for localized groundwater contamination
from refueling and equipment maintenance. Erosion in areas of soil disturbance and
vegetation removal could result in increased groundwater turbidity, and interception of
groundwater seeps in road cutbanks could alter the hydrology or water quality of adjacent
wetlands and streams.
Operation and Maintenance
Impacts during operation and maintenance of the proposed line could result from the use
of access roads for tower maintenance, and from vegetation clearing. These activities
could potentially introduce sediment into local wetlands through surface runoff,
potentially affecting water quality. These operational impacts on groundwater are
considered minimal.
Environmental Consequences—Short-Line Routing Alternatives
The potential impacts of the short-line routing alternatives are presented in Table S-2.
S-15