NM 532 Curve Correction Project - New Mexico Department of ...

NM 532 Curve Correction Project Environmental Assessment
create challenging driving conditions. Along the existing alignment, the average grade of 8% would
remain the same except for minor modifications at curves. Extensive cut and fill construction activities
would be completed to correct curve geometrics, roadway grade, and slope stability conditions at the
Texas Turn, Axle Bend Curve, and Last Curve. Rock or slope protection would be used to create a
stabilized rock-cut face only if unstable rock is encountered. Rock would be excavated mechanically
without the use of explosives. RSS wall with rock-filled baskets would be installed at the curves. Less
long-term maintenance would be required.
4.3 Soils
Existing Conditions – Soils in the NM 532 Project Area are not well mapped. In general, the soils range
from deeper alluvial soils in valley bottoms to shallower, rocky soils on mountains side and ridge tops.
Because of the steeps slopes in many areas, the soils are subject to erosion, slippage, and landslides when
vegetation is removed.
Potential Effects and Mitigation Measures – During construction activities, soil excavation and
disturbance would occur. Approximately 10 acres would be affected. A Stormwater Pollution Prevention
Plan (SWPPP) containing Best Management Practices (BMPs) to reduce erosion would be prepared prior
to construction. Slope stabilization and drainage improvements would improve water quality through the
reduction of erosion and sediment transport.
4.4 Surface and Ground Water
Existing Conditions – The NM 532 Project Area is located within the Eagle Creek and Rio Ruidoso
watersheds of the Hondo basin. The North Fork of the Rio Ruidoso has headwaters in the western part of
the project area. Eagle Creek, south of NM 532, is a tributary of the Rio Ruidoso, which empties into the
Rio Hondo near the town of Hondo. A few drainage crossings may be jurisdictional waters subject to
Section 404 permits. Stream flows in Eagle Creek below South Fork can range from less than 1000 acrefeet
to 4000 acre-feet per year (Donohoe, 2004). Development is increasing the demand for surface and
ground water in the Ruidoso area. The 100-year floodplains are not well mapped in this area (Federal
Insurance Administration, 1977). The project area has an upland location and flooding is not a concern.
Potential Effects and Mitigation Measures – Reconstruction of the curves would correct drainage
issues at those locations; however, the existing drainage problems at other sections along NM 532 would
persist. Construction at Last Curve would not involve modification to the existing drainage culvert or
work within the Rio Ruidoso. Under current design, Section 404 permitting from the U.S. Army Corps of
Engineers (USACE) and Section 401 permitting from the New Mexico Environment Department
(NMED) would not be necessary. Wetlands at Last Curve are discussed under wetlands in the next
section. Since the area of disturbance exceeds one acre, the construction contractor will prepare a SWPPP
as part of obtaining coverage under a National Pollutant Discharge Elimination System (NPDES) general
construction activity permit. The SWPPP will include BMPs to minimize soil erosion and sediment
transport including mitigation measures to protect water quality. Temporary erosion and sediment control
plans will be included in the plan sets. Slope stabilization and drainage improvements would improve
water quality through the reduction of erosion and sediment transport.
4.5 Wetlands
Existing Conditions – Wetlands are identified by vegetation, soil, and hydrologic indicators diagnostic
of wetland conditions as defined in the 1987 Corps of Engineers Wetland Delineation Manual (USACE,
1987). Wetlands are present outside of the project area at Last Curve.
Potential Effects and Mitigation Measures – No wetlands are present at Texas Turn or Axle Bend
Curve, but wetlands are adjacent to Last Curve. Construction activities will avoid the wetlands at Last
Curve. Temporary fencing will be constructed around the wetlands to keep construction activities away
from the wetlands.
March 2013 10 CN 2101140