SBCT Final EIS - Govsupport.us

Chapter 3 ⎯ Affected Environmentin stream discharge. Thus, more than 99 percent of the annual sediment load is transported during thesummer, and it is evenly distributed during this period (Anderson 1970).There are no streams within the DTA that have been designated as Wild and Scenic Rivers (NPS1999); however, the upper reach of the Delta River was designated as part of the National Wild andScenic River System in 1980. The Delta River designation terminates approximately 15 miles upstreamof DTA. The total length of Delta River within DTA boundaries is approximately 30 miles;however, no portion of this reach has been designated.Lakes are abundant on DTA, but information on their water quality is scarce. Water samples collectedfrom Bolio Lake had pH beyond acceptable alkalinity levels as defined by the State of Alaska and themajority of nitrogen occurred in organic form (USARAK 2004).Groundwater OccurrenceThe alluvial aquifer system underlying DTA is believed to comprise several aquifers that are separatedby leaky confining layers. However, data supporting this hypothesis are lacking and, as a result,this system is classified as a single aquifer with varying local confinement. Silty sediments and glacialtill may be the source of local confinement.The alluvial aquifer system underlying part of DTA is recharged through streambeds of Jarvis Creekand Delta River as well as other streams. The volume of groundwater recharge from DTA is directlyrelated to the amount of surface flow (Wilcox 1980). Recharge is greatest during annual high flow periods.Small amounts of infiltration of precipitation may also contribute to aquifer recharge.In the northern, western, and eastern portions of DTA East, as the aquifer approaches the surface andthe Tanana River, water is discharged from the alluvial aquifer system through a series of springs nearClearwater Creek and near the mouth of the Delta River. The annual groundwater discharge rate inDTA East is estimated to exceed 1,200 cubic feet per second not including the unmeasured seepagerates to the Tanana River (Wilcox 1980).Well data within DTA indicate that permafrost does not generally extend into the saturated zone andusually does not act as a confining layer. Stratification due to deposits of silt, sand, gravel, and boulderscauses permeability within the alluvial sequence to vary widely. Well yields in DTA are as highas 1,500 gallons per minute (Wilcox 1980).In this region, the water table is generally located closer to the land surface with increasing distancefrom the Alaska Range. The water table near eastern DTA slopes north with gradients ranging from 1to 25 feet per mile. Seasonal water table fluctuation varies from 20 to 60 feet in response to rechargefrom river and stream channels and from precipitation (Wilcox 1980).Groundwater QualityFew wells have been drilled on the installation, and data for groundwater quality are limited to areasin the immediate vicinity of Fort Greely. According to the available data, groundwater quality is goodat DTA. Water quality measurements were below concentrations recommended by the Alaska DrinkingWater Standards (USARAK 2004).February 2008 3–103 2/25th SBCT Final EIS