SBCT Final EIS - Govsupport.us

Chapter 4 − Impact MethodologyUnified Soil Classification System (USCS) and ecological land surveys (geomorphologic andvegetation surveys for each unit). Resulting soil property maps were generated in GIS bysuperimposing the vegetation and USCS soil maps (USARAK 2004). The model results were used todetermine limitations based on potential impacts to soil resources resulting from operation of militarycombat vehicles, including Stryker vehicles. The 2006 BAX and CACTF FEIS supplemented thetrafficability model results from the 2004 USARAK Transformation FEIS by incorporating additionalinformation on soil properties in the DTA, using information from the NRCS Soil Survey of theDTA, which was initiated in 1999 and completed in 2004 (USDA 2005). Soil trafficability is theprimary factor used in Chapter 5 of this EIS to evaluate the potential damage to soils caused by offroadmilitary Stryker vehicle maneuvers on DTA. The results of the studies are summarized below asthey relate to the trafficability of specific areas within the DTA.Slopes in the DTA East rarely exceed 30 percent in the areas studied for trafficability of soils formilitary vehicle maneuvers; therefore, the presence of wetlands was the primary factor used fordetermining trafficability in the 2006 BAX and CACTF FEIS. Wetlands, which are characterized bysaturated soils, and slopes steeper than 30 percent are considered not trafficable. Trafficability alsovaries by season on DTA. During the summer season, soils are often saturated, and the ability of wetsoils to support off-road vehicle maneuvers is very low. During the winter (November to April), soilsthat may not be trafficable during summer do not limit off-road vehicle maneuvers, because frozensoils can support more than the required maneuver capacity regardless of soil type. Maneuvercapacity was evaluated by estimating the number of vehicle passes each alternative site could sustainover the summer season without becoming impassible. An area containing a higher percentage oftrafficable soils was considered to have increased maneuver capacity and lower expected erosion rates(USAGAK 2006a). Military vehicle MIMs were also calculated for each area studied. The study alsodescribed how certain wet soils in areas could be manipulated to provide increased maneuver capacityby filling and hardening an area. The trafficability, maneuver capacity of soils, and the militaryvehicle MIMs in the DTA that were calculated for the proposed action of the 2006 BAX and CACTFFEIS are summarized below as the baseline conditions to assess the net difference in vehiclemaneuver impact that would result from transformation of the existing IBCT unit on DTA to anSBCT unit.The portion of DTA west of the Delta River is considered by USARAK to be “NO GO” year roundbecause of lack of access across the Delta River. The area east of the river is more maneuverable andthe “NO GO” areas are characterized by thick forest and wet areas along the floodplains of JarvisCreek and the Delta River. About 86,000 MIMs annually are estimated for current vehicle maneuverson DTA East as a whole, which is 69 percent of capacity in the summer and 1.2 percent of capacity inthe winter.The DTA East was distinguished by several sub-areas, including the North Texas Range, theDonnelly Drop Zone, and the Eddy Drop Zone, with BAX and CACTF areas within each sub-area.Most of the soils on the Eddy Drop Zone were considered trafficable and able to support militaryvehicle training maneuvers year-round. The proposed BAX maneuver area could support 10,001Stryker vehicle passes in the summer season without becoming impassible. Winter season trainingwas not considered affected by trafficability.The Donnelly Drop Zone did not contain enough trafficable soils to support year-round militaryvehicle training maneuvers without site modification (filling and hardening activities). The proposedBAX maneuver area could only support 988 Stryker vehicle passes in the summer season withoutbecoming impassible. Winter season training was not considered affected by trafficability.February 2008 4–6 2/25th SBCT Final EIS