SBCT Final EIS - Govsupport.us

Chapter 5 – Environmental ConsequencesCompaction is likely to occur in moist soils containing clays, which comprise most of KTA. DrumRoad would be used under Alternative A to transport vehicles and Soldiers to KTA. 3,384 acres areproposed as new off-road maneuver areas under the Alternative A. ATTACC modeling resultssuggest that a proportion of the land area in the maneuver areas could be affected by compaction frommaneuver training. Together, the impacts of soil compaction from maneuver training activities onKTA are expected to be significant. These impacts would occur in addition to the ongoing erosionand compaction stresses due to documented public access and unauthorized use of portions of KTA.Regulatory and Administrative Mitigation 4: Standard mitigation funded and implemented under theannual ITAM and SRA program work plans, with particular attention to areas where soilcharacteristics, depth, soil moisture, or other existing conditions preclude susceptibility to compactionand rutting, would reduce the soil compaction impacts on KTA, but not to less than significant levels.AEC should provide guidance in implementing the SRA program and oversee SRA programimplementation and documentation. COE should review design plans to check that mitigationidentified in the annual ITAM and SRA program work plans is accounted for.Significant Impacts Mitigable to Less than SignificantImpact 5: Soil Compaction and Rutting. As described above, soils in the training areas, particularlysoils that have not previously been used for military vehicle maneuver training, are likely to becomecompacted by use of the Stryker vehicles, which could alter the permeability and water-holdingcapacity of the soils and harden silty clays. Soil compaction may also affect vegetation recovery andcreate preferred drainage pathways along which erosion and subsequent downslope sedimentationmay be enhanced.Soils on existing road surfaces in the SRAA may be susceptible to compaction and rutting. Over thelong term, use of Dillingham Trail by heavy vehicles may lead to compaction of the road surface andformation of ruts that interfere with proper drainage.The Waikoloa and Waimea soils in the Keamuku Parcel are vulnerable to compaction because theycontain a high percentage of fine materials. However, soils throughout PTA tend to have lowmoisture content. Therefore, the Waikoloa and Waimea soils are likely to be moderately vulnerable tocompaction except shortly after storm events. Once compacted, the soils may remain compacted for along time. Significant soil compaction is expected to occur in the Keamuku Parcel because this areahas not been previously subjected to a high degree of vehicle use.The impacts of compaction and rutting are considered to be potentially significant on PTA, SBMP,and DMR under the Alternative A depending on the soil characteristics and amount of the landaffected because ATTACC modeling suggested that a large portion of the land in the maneuver areascould be affected by maneuver training.Regulatory and Administrative Mitigation 5: Standard mitigation funded and implemented underannual ITAM and SRA program work plans, with particular attention to areas where soilcharacteristics, depth, soil moisture, or other existing conditions preclude susceptibility to compactionand rutting, would reduce impacts to less than significant levels on all ranges except portions of KTA,as described above.Impact 6: Increased Potential for Slope Failure Resulting from Road Use. Slope failure is thecollapse of soils on a steep slope when the internal friction of the materials supporting the slope isexceeded by the weight of the materials. Slope failure can be initiated by increasing the loading at thetop of the slope, by deeper weathering of the materials in the slope, and by vibration. TheFebruary 2008 5-13 2/25th SBCT Final EIS