I-10 Twin Peaks Traffic Interchange, Environmental Assessment

Affected Environment and Environmental Impacts October 2005
channel. Temporary impacts would include the removal of riparian vegetation
within the area of construction of the bridge structure and embankments. Potential
wetlands and riparian vegetation would be restored following construction
according to the revegetation plan. Permanent impacts would result from the
shading of riparian vegetation from the overhead bridges. Shading of vegetation
reduces the amount of direct sunlight available to vegetation resulting in plants of
smaller size and the establishment of more shade tolerant plants. Approximately
0.07 acres of potential wetland would be permanently lost due to shading.
The low flow channel of the Santa Cruz River would be widened to compensate
for the roadway and bridge embankment fill placed with the high flow Santa Cruz
River channel (see Floodplain Section, page 4-14). This action would temporarily
impact approximately 1.5 acres of riparian habitat in the low flow channel of the
Santa Cruz River. Because of the widening of the low flow channel that would
occur with the preferred alternative, the area available for the establishment of
riparian habitat would be larger and the size and quality of riparian habitat to be
used by wildlife would be improved. As a result of the revegetation plan, the value
of the vegetation in the disturbed area of the floodplain would be improved by
construction of the preferred alternative.
Mitigation
The preferred alternative would implement measures to minimize impacts caused
by the proposed improvements and to restore vegetation, riparian habitat, and
potential wetlands impacted by the preferred alternative. Vegetation removal
would be the minimum required for the construction of the proposed
improvements. Prior to the removal of vegetation during construction, the Town of
Marana would develop a revegetation plan that would comply with the ANPL, and
NPPOs of the Town of Marana and Pima County. The revegetation plan would
include Corps’ recommendations from the TRDN Feasibility Study. The main
constituents of the revegetation plan were discussed earlier (see Threatened and
Endangered Species Section, page 4-26). During design, a wetland delineation
would be completed. In the event that jurisdictional wetlands are impacted by the
preferred alternative, coordination with the Corps would occur and appropriate
permits would be obtained.
Conclusion
The preferred alternative would have temporary and permanent impacts to
vegetation, riparian habitat, and potential wetlands within the project area. These
impacts would be minimized by limiting the amount of vegetation removed to the
minimum required for the construction of the proposed improvements and through
the development and implementation of the revegetation plan. The proposed
improvements would provide a larger area for riparian vegetation through a
widening of the low flow channel of the Santa Cruz River and the revegetation
plan would restore or improve the value of riparian habitat in disturbed areas.
Interstate 10 Traffic Interchange at
Twin Peaks/Linda Vista
4-39
Project No.: NH-010-D (AIW)
TRACS No.: 10 PM 236 H5838 01D