SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected Environment(DECAM 2002a). Water rights directly support the training mission by ensuring adequate water supplyfor the support and rehabilitation of natural resources on FTC and to provide training capabilitiesand fire suppression.3.3.2.2 Pinon Canyon Maneuver SiteSurface WaterThe PCMS is located in the Purgatoire watershed of the Arkansas River basin and includes severalmajor drainages. Water from the PCMS ultimately drains into the Arkansas River via the PurgatoireRiver or the Big Arroyo drainage. A figure depicting surface water features at PCMS is available inthe PCMS Transformation EIS (USACE 2007b).The majority of the drainages at the PCMS flow from the northwest to the southeast and drain into thePurgatoire River, which flows to the northeast along the southern and eastern boundaries of thePCMS. The Purgatoire River and its tributaries within the PCMS have periodic high flows, includingthe potential for flash floods. Smaller creeks and drainages might be dry much of the year. The BigArroyo drainage system is located in the northwest region and flows northeast into Timpas Creek,which is approximately 3 miles northwest of the PCMS.Floodplains have not been mapped on the PCMS. However, flash floods occur intermittently duringheavy rainfall events, typically between May and October (DECAM 2002a). Flood-prone areas occuralong the drainages in the training areas. The cantonment is not subject to flooding (USACE 2007b).Surface Water QualityTo control and monitor sediment transport and loading, as a part of USACE Section 404 regionalpermit, the USGS operates approximately 70 erosion control reservoirs, a streamflow gauge on thePurgatoire River, and five streamflow sediment gauges on Purgatoire River tributaries that drain morethan 60 percent of the PCMS. The erosion control reservoirs are used to assess sediment yields fromsmall watersheds in the training areas, while the streamflow sediment gauges quantify water andsediment leaving the PCMS (DECAM 2002a).The USGS has monitored water quality, including sediment yield, at the PCMS since 1983 in cooperationwith the Army and FTC. Statistical analysis comparing water quality data from periods beforemilitary training activities with those from periods after the training demonstrated no statistically significanteffect on water quality in the Purgatoire River (USGS 1993). Another study sought to evaluateerosion and sedimentation for potential TMDL compliance (USDA 2001b). The TMDL study didnot result in a TMDL for sedimentation, but it outlined further steps for study.Even though the quality of surface water at the PCMS is generally high it is not a source of domesticwater supply (DECAM 2002a).Groundwater OccurrenceThe majority of regional groundwater at or near the PCMS occurs in the Dakota Sandstone and thePurgatoire Formation (DECAM 2002a), which are part of the Arkansas River basin. Much of the ArkansasRiver basin has a hydraulic head difference in the deep bedrock aquifers that is lower than thatin the shallow formations. This indicates that the deep bedrock aquifers are not in communicationwith the shallow formations.February 2008 3–145 2/25th SBCT Final EIS