I-10 Twin Peaks Traffic Interchange, Environmental Assessment

Affected Environment and Environmental Impacts October 2005
would be designed and constructed as all-weather roadways designed to withstand
a 100-year flood event.
To mitigate the impacts to the floodplain from the preferred alternative, several
mitigative measures would be implemented. These include:
• The Town of Marana would widen the low flow channel of the Santa Cruz
River to prevent an unacceptable rise in floodwater elevations within the
100-year floodplain.
• Prior to the removal of vegetation during construction, the Town of Marana
would develop a revegetation plan (See Biological Resources Section, page
4-25).
• During final design, the Town of Marana would give the local floodplain
administrator the opportunity to review project plans.
Section 404/401 of the Clean Water Act
Section 404 of the Clean Water Act (CWA) establishes a permit program for
activities that would discharge dredged or fill material into "waters of the United
States." This permit program is authorized by the Corps. "Waters of the United
States" is a broad term that includes: (1) waters, lakes, rivers, and streams that are
navigable waters of the United States, including adjacent wetlands: (2) tributaries
to navigable waters of the United States, including adjacent wetlands: and (3) other
waters, such as isolated wetlands and intermittent streams, the degradation or
destruction of which could affect interstate commerce.
Existing Conditions
Jurisdictional waters of the U.S. in the study area were delineated by the Town of
Marana for the proposed improvements and for private development projects in the
area. These delineations were compiled and submitted to the Corps for
concurrence. The Corps concurred with these delineations, which appear in Figure
4-3. As presented in Figure 4-3, three major jurisdictional waters and several
minor tributaries were delineated. Two of the waters flow through box culverts
beneath I-10, the eastbound and westbound frontage roads, and the UPRR. The
third water is the low flow channel of the Santa Cruz River. The total area of
jurisdictional waters within the project area is 47.39 acres.
Impacts
No Build Alternative
Under the no build alternative, no affects to Waters of the U. S. would occur.
Preferred Alternative
Waters of the U.S. would be impacted by the preferred alterative. The bridge
spanning the Santa Cruz River and the widening of the low flow channel in the
Santa Cruz River would impact Waters of the U.S. In addition, redirection of a
Interstate 10 Traffic Interchange at
Twin Peaks/Linda Vista
4-19
Project No.: NH-010-D (AIW)
TRACS No.: 10 PM 236 H5838 01D