<br />Section 3
<br />Physical Environment of the South Platte Basin and Denver/South Metro Counties
<br />
<br />The alluvial aquifer is estimated to contain as much as
<br />8.3 million AF in storage and is hydraulically connected
<br />to the river (CGS 2003). Therefore, groundwater
<br />withdrawals, of which the majority are junior in priority to
<br />most surface water rights, can greatly affect the flow of
<br />the lower South Platte River. This segment, which is
<br />downstream of metro Denver, gives rise to the need for
<br />well augmentation plans to protect senior water rights.
<br />
<br />In the lower South Platte River alluvium, there are
<br />approximately 10,880 permitted wells with yields ranging
<br />in capacity from 1 to 3,000 gpm. The average yield is
<br />430 gpm; however, 50 percent of the wells have a yield
<br />of 30 gpm or less, which is biased by domestic wells
<br />(CGS 2003).
<br />
<br />The Denver Basin aquifers, which cover approximately
<br />6,800 square miles, are comprised of the Dawson,
<br />Denver, Arapahoe, and Laramie-Fox Hills aquifers, are
<br />another important water resource for the South Platte
<br />Basin. The Denver Basin consists of Tertiary and
<br />Cretaceous age sedimentary rocks that supply
<br />groundwater for domestic, commercial, municipal,
<br />agricultural, and other users (CGS 2003).
<br />
<br />There are also five Designated Groundwater Basins in
<br />the South Platte Basin, which include the Upper Crow
<br />Creek, Camp Creek, Northern High Plains, Lost Creek,
<br />and Kiowa-Bijou. Designated groundwater is water that
<br />under natural conditions would not be used to recharge
<br />or supplement continuously flowing surface streams
<br />(Hobbs 2003).
<br />
<br />The Northern High Plains aquifer, which includes the
<br />Ogallala aquifer located in the Republican River Basin, is
<br />found in the eastern edge of Colorado in the High Plains
<br />region and is a major source of water for this agricultural
<br />region (CDPHE 2002). Groundwater withdrawals have
<br />exceeded recharge since the early 1960s. The mean well
<br />yield from this aquifer is 373 gpm and the median is
<br />20 gpm (CGS 2003).
<br />
<br />3.2.8 Water Quality
<br />
<br />There is a broad range of water quality in the South
<br />Platte Basin and Denver/South Metro Counties, ranging
<br />from high-quality mountain streams to those impacted
<br />due to urbanization and agricultural activities.
<br />
<br />The upper South Platte River watershed is an area that
<br />has been affected by historic mining districts (i.e.,
<br />
<br />S:\1177\Basin Reports\South Platte\S3_South Platte.doc
<br />
<br />Mosquito Creek), water resource development (i.e.,
<br />South Park Dams and water diversions), and severe
<br />sediment deposition from forest fires such as the recent
<br />Hayman, Buffalo Creek and Hi Meadows fires
<br />(CDPHE 2002).
<br />
<br />The middle reach of the watershed, from below Chatfield
<br />Reservoir to the confluence with the Cache la Poudre
<br />River, has experienced some of the most intense use
<br />and resultant impacts of any river in Colorado. This
<br />segment of the river has seen historic mining districts,
<br />explosive urban development, stormwater runoff,
<br />extensive hydrologic modification, urban and agricultural
<br />nutrient loading, and effects of Superfund sites.
<br />Pollutants that have impaired the waters of the South
<br />Platte Basin include nitrate, ammonia, and copper
<br />(CDPHE 2000). Furthermore, the South Platte River
<br />through and downstream of the Denver urban area
<br />exceeds E. coli standards (CDPHE 2002).
<br />
<br />The lower reach of the South Platte River, from the
<br />Cache la Poudre River to Julesburg, has been affected
<br />by upstream urbanization, historic agricultural land use,
<br />and waste disposal due to animal feeding operations.
<br />Non-point source pollution from pesticide and fertilizer
<br />runoff is the primary concern in this segment of the lower
<br />South Platte River (CDPHE 2002).
<br />
<br />Downstream of the Denver area, groundwater in the
<br />alluvial aquifer exceeds the nitrate limit for drinking water
<br />standards in some areas. The nitrate contamination not
<br />only affects the drinking water supply of several eastern
<br />plains cities, but can also be detrimental to certain crops
<br />when used for irrigation (CDPHE 2002).
<br />
<br />Groundwater in the alluvial aquifer near Denver contains
<br />approximately 1,000 parts per million (ppm) total
<br />dissolved solids (TDS). This concentration increases to
<br />about 4,000 ppm near Sterling. Surface water at the
<br />state line with Nebraska has an average TDS
<br />concentration of 1,300 ppm (CGS 2003). These
<br />concentrations are of concern because water containing
<br />greater than 2,000 ppm TDS is generally considered to
<br />be unsuitable for irrigation (CDPHE 2002).
<br />
<br />CONI
<br />
<br />3-9
<br />
|