Arkansas Basin_Water Supply and Needs

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Section 3 Physical Environment of the Arkansas Basin IJIII depth of wells generally increases eastward toward the Colorado-Kansas state line, and in the Arkansas Basin the saturated thickness of the aquifer ranges between zero and 50 feet. 3.2.8 Water Quality Surface water quality in the Arkansas Basin is "generally good" and portions of the headwaters have been designated by the State of Colorado as Outstanding Waters. All streams, lakes, and reservoirs within Mount Massive and Collegiate Peaks Wilderness Areas are currently considered under the designation of Outstanding Waters. However, there is some water quality concern in the basin near the Arkansas River headwaters in the historic mining districts and downstream toward the Colorado-Kansas state line. The major water quality issues in the basin are related to acid mine drainage in the headwaters, and urban runoff and salinity in the lower basin. Additionally, return flows from agricultural and municipal water uses concentrate naturally occurring salts, arsenic, and selenium in the basin (CDPHE 2002). Acid mine drainage was a significant problem in parts of the Upper Arkansas River, especially along the segments of the East Fork, St. Kevin's, and California Gulches. Treatment plants have been constructed to control discharge quality from the Yak Tunnel and the Leadville Drain. Although much improvement has been made, high metal concentrations are still observed. The waters of Cripple Creek and Fourmile Creek are also impaired as a result of historic mining (CDPHE 2002). Urban areas are another contributor to water quality degradation. Urban stormwater runoff can constitute a majority of flow in parts of the basin during high flow periods, while during low flow periods many of the streams are dominated by M&I effluent (CDPHE 2002). Surface water quality trends were identified using data from the USGS flow gage and water quality station on the Arkansas River at Lamar from the years 1968 to 1998. Water quality trends suggest that total sulfate, hardness (calcium carbonate), and conductivity are decreasing slightly, while total alkalinity is increasing (CDPHE 2002). Salinity appears to be increasing in the downstream direction in the Arkansas River. A recent study showed an increase from 300 parts per million CDIVI 3-4 (ppm) total dissolved solids (TDS) east of Pueblo to 4,000 ppm near the state line (CGS 2003). The TMDL process evaluates and allocates pollutant loads in impaired waters listed on the Colorado 303( d) list. Stream segments in need of TMDLs, and those of concern with inadequate quantity or quality of data to assess impairment, are compiled into Regulation 93 and Regulation 94 lists, respectively. Figure 3-7 identifies the locations of surface waters in the Arkansas Basin that are listed on Colorado's 2002 303( d) list. Stream segments proposed for listing on the 303( d) list and the Monitoring and Evaluation list are described in Colorado Water Quality Control Commission (WQCC) Regulations 93 and 94. The state's 2004 proposed 303( d) list incorporates several additions from the 2002 list. It includes numerous stream segments of the mainstem and its tributaries listed for selenium, primarily in the middle and lower (eastern) portions of the basin. Proposed 2004 higher-priority listings in the basin are primarily associated with metals constituents in the upper basin. Groundwater in the upper Arkansas River Valley is generally suitable for use as potable water supply with a few exceptions caused by acid rock drainage and septic system effluent contamination. Groundwater in the lower Arkansas Basin alluvial aquifer is considered to be of fairly good quality (CGS 2003). However, similar to the river, the groundwater increases in salinity with distance downstream. Groundwater or surface water with TDS concentrations greater than 2,000 ppm is generally considered to be unsuitable for irrigation without further treatment (CDPHE 2002). 3.2.9 Areas of Environmental Concern, Special Attention Areas, and Threatened and Endangered Species A major concern for the Upper Arkansas River Valley is the acid-mine drainage from many of the historic mining locations surrounding the headwaters of the Arkansas River (CGS 2003). One of these sites is the California Gulch Superfund site near Leadville, Colorado. Large volumes of mining waste were left at the site due to the intense historical mining activities, contaminating soils and surface water runoff (U .S. Environmental Protection Agency [EPA] 2003). In 1990, the Yak Tunnel Treatment o :\SHAWN\ARKANSAS\S3 _ARKANSAS. DOC