SBCT Final EIS - Govsupport.us

Chapter 5 – Environmental Consequences5.2.2.3 Impacts from Live-Fire TrainingSignificant Impacts Mitigable to Less than SignificantImpact 2: Soil Erosion and Compaction. Weapons training would increase under implementation ofAlternative A, in the form of a greater number of various types of munitions fired by the additionalSBCT troops, including munitions for mobile gun systems, which are not currently used. Live-firetraining would occur at the BAX ranges at SBMP and PTA. SRTA training would also occur at theCACTF at KTA where the fire ignition potential is low. While weapons firing would typically occurin existing impact areas and the frequency of the training events would not change, surfacedisturbance caused by munitions impact would result in larger areas of bare ground than observedunder current conditions. Munitions impact can directly create craters and remove patches ofvegetation, which normally protect soil from erosion by slowing runoff, intercepting raindrops beforethey reach the soil surface, and anchoring the soil. Compaction in the craters caused by largerordnance explosions can alter the permeability and water-holding capacity of the soils and hardensilty clays affecting the ability of vegetation to recover in those areas. These direct impacts indirectlycreate large areas of bare ground that is susceptible to wind and water erosion, which can indirectlycause large-scale removal and redeposition of soils, gullying, or unstable slopes in areas of steepslopes and rapid runoff. Although weapons training events would be periodic, long-term impacts areexpected because soil disturbance typically requires time and effort to amend. Implementation of thesoil erosion control measures, implementation of standard BMPs, and revegetation and other landrestoration projects implemented by the LRAM program under the ITAM annual work plan(described previously) would reduce these impacts to less than significant.Detonation of munitions, smoking, use of welding torches, vehicle engines, and other training-relatedactivities can initiate wildland fires. The addition of a BAX range at both SBMR and PTA wouldincrease the use of larger caliber munitions. The BAX at PTA would be located in a previouslydisturbed site and oriented towards existing ordnance impact areas. Wildland fire caused by SBCTlive-fire training activities at the SBMP BAX, PTA BAX, and KTA could remove large areas ofvegetation that normally protect soil from erosion by slowing surface runoff, intercepting raindropsbefore they reach the soil surface, and anchoring the soil with roots. Vegetation removal resultingfrom wildland fires could result in increased soil erosion by water and wind, indirectly causing largescaleremoval and redeposition of soils, gullying, or unstable slopes in areas of steep slopes and rapidrunoff. The impact would be directly proportional to the size of the fire. Under natural conditions,wildland fires occur infrequently in Hawaii, partly due to lack of lightning. Thus, native plant speciesare not well adapted to fire. Fire and loss of soil could reduce native plant species and encourage fastgrowingnonnative species that recover quickly after fires. Some of these species may be moresusceptible, or even dependent, on fire so that the occurrence of wildland fires may help to increasethe chance of future wildland fires.The potential for erosion resulting from wildland fire started by weapons firing is expected to behighest at the SBMP BAX. Although wildland fires, particularly grass fires, could occur at PTA, theeffects on soil loss would be localized because much of the land contains shallow soil or exposed rockoutcrops. Removing grassland vegetation by fire would temporarily expose soils to increased watererosion, but perhaps even more so to wind erosion. Due to a lack of continually flowing streams, soilswould probably not migrate far from their upslope origins, but wind erosion could transport soilfurther from its original location. Many areas with soils on PTA are somewhat protected from watererosion because they are surrounded by rock outcrops. The potential for erosion resulting fromwildland fire is expected to be lowest at KTA because of the wetter climate than the other Hawaiiinstallations.February 2008 5-8 2/25th SBCT Final EIS