SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected Environmentnizes 31 soil series and associations and four major landscape types on PCMS (DECAM 2002a).Soils range from shallow to deep and are well drained. The soils are formed primarily from shale,sandstone, and limestone. Each of the four landscape types on PCMS has a characteristic pattern andcoverage of soils, which are briefly described below. Additional information on the PCMS soil typescan be found in the INRMP, and specific information can be obtained from the NRCS soil surveys forLas Animas County.Flat to sloping plains in the western portion of the PCMS contain soils formed in wind-deposited lipswith intermittent small ridges of limestone that outcrop in some areas (DECAM 2002a). These soilsare generally silty, weakly developed, and calcareous throughout. The dominant soils in this landscapeare loamy plains on upland flats, saline overflow in the depressions and along intermittentdrainages, and sandy plains in sand dunes. This landscape is characterized by medium stability, withmoderate soil losses from water erosion and high soil losses from wind in areas where soil is disturbed(DECAM 2002a).Limestone ridges cross the northwestern corner of the PCMS. Major soils found in this landscape arelimestone breaks on steep sideslopes and saline overflow along intermittent drainages. These soils areunstable, experiencing moderate to high water erosion and moderate wind erosion in disturbed areas(DECAM 2002a).The upland valley that crosses the installation from southwest to northeast, between limestone ridgesand the Purgatoire River, contains soils that range from wind-deposited silty soils in flat areas toclayey soils formed from weathered shale in broad depressions. Major soils in this landscape consistof loamy plains, alkaline plains, and saline overflow. Soils in this landscape are characterized by mediumto low stability, moderate water erosion, and high wind erosion rates in disturbed areas.Soils occurring in the landscape where the Purgatoire River and the associated side canyons form aseries of rock-strewn cliffs and rolling mesa tops are predominantly loamy plains and sandstonebreaks interspersed with rock outcrops with some areas of loamy plains, saline overflow, and saltmeadow soil types. These soils are moderately stable and water erosive in gently sloping areas, butare unstable and severely erosive in steep areas. Soil loss from wind erosion is low on almost all disturbedsoils in this landscape.Erosion ManagementThe PCMS currently follows regulations and implements the same management plans that were discussedpreviously for FTC. Banksloping to reclaim incised erosion courses is a type of project implementedby DECAM and ITAM specifically to areas affected by training activities on PCMS. Themain dirt roads in the training areas are maintained by contractors or in-house personnel (USACE2007a).Chemical Constituents in SoilChemical constituents in soils on PCMS include naturally occurring selenium, similar to FTC, whichwas described above in Section 3.3.1.1.Geologic Hazards and SeismicityThe Great Plains Physiographic Province may be seismically active. According to the CGS, some ofthe 90 potentially active faults in Colorado may be near the Raton Basin (CGS 1999). USGS andCGS databases indicate that faults in the area could have a low to moderate potential to cause damagingearthquakes (USGS 2005, CGS 1999). It is estimated that there are several thousand faults withinFebruary 2008 3–142 2/25th SBCT Final EIS