SBCT Final EIS - Govsupport.us

Chapter 5 – Environmental ConsequencesSoil loss from continued use of the military vehicles on trails within and leading to PTA would occur.Without pavement or drainage improvements, dust erosion impacts would continue, as wouldpotential impacts from erosion by surface runoff. The impacts are not considered to be significantrelative to long-term soil loss or erosion because the trail occupies a relatively small amount ofacreage. Trails would continue to be maintained as needed to ensure that it remains passable.Regulatory Administrative Mitigation 3: ATTACC modeling indicates that current land conditionresults in negligible soil erosion impacts at DMR and PTA, and that damage that occurs under currenttraining conditions at SBMR and KTA is significant but mitigable to less than significant levels withapplication of the USAG-HI ITAM Program. Although ATTACC modeling identifies the currentimpacts of maneuver training overall on SBMR as “moderate”, the INRMP for installations on Oahusuggests that significant soil erosion has occurred in the past in certain ridge top areas at SBMR andcurrent conditions are not sustainable, as land condition has continued to decline. Under the NoAction Alternative, no additional lands would be available to enable training to be rotated to otherareas while the damaged land recovers. Those areas are expected to be addressed through the ITAMprocess and will gradually recover under improved land management. Therefore, impacts areconsidered to be less than significant with implementation of mitigation measures.Impact 4: Increased Potential for Slope Failure. The PTA Trail would not be improved, and thepotential for slope failure would continue. Slope failure is considered a potentially significant, butmitigable to less than significant impact.Regulatory Administrative Mitigation 4: Slope failure has not been identified as a noticeable problemfrom road usage under existing conditions. However, with regular monitoring and early maintenanceof the roadways and adjacent slopes as mandated in the USAG-HI ITAM annual work plan, projectrelatedimpacts would be reduced to less than significant.Less Than Significant ImpactsSoil Compaction and Rutting. Soils in training areas would be subject to existing levels ofcompaction. Most of these effects have already occurred, although continued maneuver trainingwould reduce the ability of soils to recover from these effects, and impacts would be less thansignificant.Volcanic and Seismic Hazards. The potential for strong ground motion or volcanic eruptions thatcould present a hazard to people or property would be the same as that described for the AlternativeA. The impacts would be greatest at PTA, but they are not expected to be significant, because existingwarning systems would provide sufficient warning of an eruption such that personnel and equipmentwould likely have time to evacuate from the path of a lava flow. The hazards associated with futureearthquakes at PTA are considered less than significant because structures at the ranges andcantonment have been designed to withstand the expected range of seismic shaking and because thearea is underlain by thin soils and hard rock, which, unlike thick alluvial deposits, transmits ratherthan amplifies seismic wave energy.February 2008 5-197 2/25th SBCT Final EIS