SBCT Final EIS - Govsupport.us

Chapter 5 – Environmental Consequencesthreshold for “severe”, estimated for the Keamuku Parcel at 50,000 MIMs). Based on a totalmaneuverable land area of 22,675 acres, Alternative A would result in about 1.52 MIMs per acre onthe Keamuku Parcel. There is currently no mounted maneuver training there. Uses that could affectsoil erosion include cattle grazing, civilian vehicle traffic, cinder cone quarrying operations, andperiodic burning by wildfires. In addition, the parcel has been used for military maneuver training inthe past (it is part of the Waikoloa Military Maneuver Area), and those past uses may have alreadyhad long-term effects on land condition, which is considered part of the baseline for this evaluation.Therefore, current conditions should not be assumed to reflect “natural” or undeveloped conditions.In the ATTACC modeling, it was assumed that nearly all of the land in the Keamuku Parcel ismaneuverable by Strykers. Therefore, the MIMs were distributed over the entire area of the parcel. Inpractice, however, it is likely that Strykers would follow routes that are neither over rock outcrops(which would be more difficult to traverse) nor over thick soft deposits, but would follow routes thatskirt the margins of outcrops where the soils are relatively thin and firm, with exception to theKeamuku Parcel. Thus, the effective maneuverable area may be smaller than that modeled, and theeffects on land condition may be more focused than assumed in the modeling. Although the averageMIMs per acre would be similar to those within the current PTA boundary, the Keamuku Parcel issteeper, contains highly erodible and compressible volcanic ash, and the erosion hazard is greater thanwithin the current PTA boundary. Stryker vehicle use of roads in this area could create conduits thatwould concentrate surface water flow and erode ash next to the roads. Vehicle maneuvering in thisarea could create tracks that act as potential preferential surface water pathways and severe erosionwould result.With the uncertainties of the model, the impact of soil loss from erosion caused by maneuver trainingactivities on SBMR, KTA, DMR, and PTA is expected to be significant over time because it couldresult in additional major soil erosion, such as that described for Range 10. Standard BMPs, the landmanagement practices mandated in the TRI, SRA, and LRAM programs of the USAG-HI ITAMannual work plan (described previously), and the additional mitigation measures described belowwould reduce the impacts, but not to less than significant levels in the event that all units are trainingat home station and not in deployment status.Regulatory and Administrative Mitigation 3: The Army would develop and implement a DuSMMoPfor the new training areas. The plan would address measures such as, but not limited to, restrictionson the timing or type of training during high-risk conditions, vegetation monitoring, soil monitoring,and buffer zones to minimize dust emissions in populated areas. The plan would determine howtraining would occur in order to keep fugitive dust emissions below CAA standards for PM 10 and soilerosion and compaction to a minimum. The Army would monitor the impacts of training activitiesthat emissions stay within the acceptable ranges as predicted and environmental problems do notresult from excessive soil erosion or compaction. The plan would also define contingency measures tomitigate the impacts of training activities that exceed the acceptable ranges for dust emissions or soilcompaction.Impact 4: Soil Compaction and Rutting.Soils in the training areas, particularly soils that have notpreviously been used for military vehicle maneuver training, are likely to become compacted by useof the SBCT vehicles, which could alter the permeability and water-holding capacity of the soils andharden silty clays. Reduced water-holding capacity and permeability adversely impacts the ability ofthe soils to support recovered vegetation. Because vegetation cover is a primary means of preventingsoil erosion, widespread compaction could indirectly lead to increased erosion and downstreamsedimentation. The compacted linear track ruts left by off-road vehicles could create preferentialpathways for surface runoff, which could also indirectly result in increased erosion along the tracksand subsequent downstream sedimentation.February 2008 5-12 2/25th SBCT Final EIS