SBCT Final EIS - Govsupport.us

Chapter 5 – Environmental Consequencesintensity of ground shaking in a reasonably strong earthquake would be moderate to minor because ofits distance from the source of the earthquakes. There is very little risk of renewed volcanic activityon Oahu, so the hazard to personnel on the ranges at SBMP and KTA are considered less thansignificant.As described previously, existing warning systems are generally expected to provide sufficientwarning of a volcanic eruption in the vicinity of PTA, such that personnel and equipment wouldlikely have time to evacuate from the path of a lava flow. The hazards associated with lava flows orearthquakes at PTA, therefore, are considered less than significant.5.2.2.4 Impacts from Maneuver TrainingSignificant ImpactsImpact 3: Soil Erosion. Mounted and dismounted maneuver training using Stryker vehicles isexpected to damage or remove vegetation and disturb soils to an extent that would substantiallyincrease soil erosion rates and alter drainage patterns in the training areas, which could lead togullying, and indirectly to downstream sedimentation, particularly when the vehicles travel off-road.While some of the off-road maneuvering would occur on existing maneuver areas, there would beseveral areas used for maneuvering that have not been previously used. Stryker vehicles tend to usetrails much more than off-road travel, unlike current maneuver training at USAG-HI, because of theirhigh speed and ability to cover greater distances. Because of their weight and wheel size of theStryker vehicles, however, the off-road maneuvering that they would conduct could cause significantdisturbance to soils and vegetation, increasing the potential for soil erosion. As discussed in Chapter4, ATTACC model used calculated MIMs to predict effects to land condition as a result of Strykervehicle maneuver training under Alternative A. Calculated MIMs were compared to predictedcarrying capacity (also measured in MIMs) of each training area to come up with a predicted landcondition, which was defined as the threshold of significance for training in each area and wasclassified as “mild”, “moderate”, and “severe”.Off-road maneuvering by Stryker vehicles is expected to occur on 2,223 acres of existing maneuverarea on SBER. Limited off-road maneuvering is anticipated at SBMR and the existing acreage atSRAA. ATTACC model results suggested that land conditions from maneuver training activitieswould decline in both the SRAA and SBER from “moderate” and “minor”, respectively, to “severe”.Land in the SRAA is currently used for pineapple cultivation. The modeling assumed that thepineapple crops would be removed and maneuver training would be unrestricted over the entireaccessible areas where slopes are less than 30 percent, which was determined would severely degradethe land condition. Under Alternative A, Stryker vehicles would generally use the existing roads.Relative to the assumption in the model, land disturbance would be limited to the existing roadsinstead of the entire range area; however, damage to the road areas would increase because vehicleuse would be concentrated onto a smaller area and effects to soils from the Stryker vehicle arerelatively greater than those from vehicles used for existing USAG-HI maneuver training. While thisdisturbance would not destroy as much vegetative cover as disturbance to off-road areas would, itcould disturb the soils underlying the roads, causing ruts and gullies to form, which in turn could leadto the indirect effect of increased surface water runoff and soil erosion off of the road surface. Theannual training load at SBMR would increase from 16,740 MIMs to approximately 31,259 MIMs(about a 118 percent increase). The land condition in SBER was similarly projected to decline from“moderate” to “severe” without mitigation under Alternative A because maneuver training with theStryker vehicles would be focused in the relatively small portion where slopes are less than 30percent.February 2008 5-10 2/25th SBCT Final EIS