SBCT Final EIS - Govsupport.us

Chapter 5 – Environmental ConsequencesSBCT maneuver training activities are expected to cause significant disturbance to soils andvegetation due to intensified on and off-road maneuver training on the new BAX ranges at SBMP andPTA, the new training area at the Keamuku Parcel, and existing maneuver areas on DMR, and KTA,and SBMR. The surface disturbance caused by maneuver training would lead to increased soilerosion, compaction, and rutting in the training areas. Soil erosion impacts resulting from SBCTmaneuver training would be reduced with implementation of standard erosion control BMPs, and theland management practices mandated in the TRI, Sustainable Range Awareness Program (SRA), andLRAM programs of the USAG-HI ITAM annual work plan (described below), but not to less thansignificant levels.5.2.2.1 Impacts from Cantonment ConstructionThere is no cantonment construction required in USAG-HI to support the stationing of the 2/25 th .USAG-HI has adequate facilities on hand to support the SBCT and, in fact, was supporting theSBCT’s living, administrative, and vehicle maintenance requirements in 2007 prior to the unit’sdeployment.5.2.2.2 Impacts from Range ConstructionSignificant Impacts Mitigable to Less than SignificantImpact 1: Soil Erosion. Construction of PTA Trail would remove existing vegetation and disturbsoils, increasing the erosion potential. As proposed, much of the trail would be on steep slopes andwould be nearly straight up the fall line of the slope. The road would be a 24-foot-wide gravel bedwith 3-foot-wide shoulders, for a total width of 30 feet. The road may use existing road alignmentsand would be paved with asphalt on slopes greater than 10 percent. In effect, nearly all uphillsegments would be paved with asphalt, and traverses along elevation contours would be paved withgravel. During construction, erosion by both wind and water could occur. The largest impacts arelikely to be in steep slope areas containing fine loam soils, such as Waikoloa and Puu Pa sandy siltloams. This impact is considered potentially significant, but mitigable to less than significant duringconstruction with implementation of standard road construction BMPs. After construction of the PTATrail, however, the road could affect surface drainage in the long-term, both by focusing drainagecollected from impermeable surfaces onto adjacent lands and by interfering with natural drainagepatterns. Large runoff events could result in soil accumulation in culverts at gulch crossings, resultingin flooding and possible washouts of the roadway. Each of these situations could result in substantialsoil erosion and subsequent sedimentation on lands adjacent to the road. This is considered asignificant impact; however, implementation of mitigation measures makes this an unlikelypossibility.Construction of the BAX ranges at SBMR and PTA proposed for Alternative A is expected to causedirect, short-term, localized soil erosion impacts when ground surfaces are disturbed to construct livefirevillages, trench lines, stationary armor targets, machine gun bunkers, and other typical BAXfeatures. Each BAX range would cover approximately 2100 acres of land, although the BAX at PTAwould be established on top of the footprint of the existing Range 11T, which has already beendisturbed. Potential increases in soil erosion caused by range construction would be temporarybecause construction of the structures and other features associated with BAX ranges would createbare land only periodically. Additionally, the Army would construct stormwater runoff controlstructures as part of standard BMPs, which would divert water from the construction sites. Otherstandard range maintenance BMPs that would be implemented under Alternative A, such as roadgrading, target repair, and berm recontouring, would also reduce erosion. Compared to existingconditions, increased soil erosion resulting from range construction activities is expected to be short-February 2008 5-6 2/25th SBCT Final EIS