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Last modified
10/26/2010 9:24:17 AM
Creation date
1/10/2008 10:43:49 AM
Metadata
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Template:
SWSI
Basin
Statewide
Title
SWSI Phase 1 Report - Section 3 Physical Environment of the Major River Basins
Date
11/15/2004
Author
CWCB
SWSI - Doc Type
Final Report
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Section 3 <br />Physical Environment of the Major River Basins <br />The unconfined alluvial aquifer of the Arkansas River, <br />comprised of glacial silts to large boulders, is primarily <br />recharged by surface water infiltration from the river as <br />well as from many ditches and canals. Irrigation also <br />plays a role in the recharge of the alluvial aquifer. Depth <br />of water in the lower valley generally ranges between 5 <br />and 30 feet and in the upper valley between 5 and <br />58 feet. Trends in hydrographs since the 1970s show a <br />general increase in the water table elevation, which can <br />be attributed to irrigation return flows. Irrigation is the <br />major use of the alluvial aquifer groundwater. However, <br />in Chaffee and Lake Counties, public water supply is the <br />primary use of alluvial groundwater. <br />The major aquifers of the Raton Basin include the Raton, <br />Vermejo, and Trinidad formations, and the Cuchara and <br />Poison Canyon formations. Sources of recharge for the <br />aquifers include runoff from the Sangre de Cristo <br />Mountains, precipitation infiltration, and infiltration from <br />streams and lakes. The depth to water generally <br />increases in the aquifers from northwest to southeast, <br />indicating a southeastern direction of groundwater flow. <br />In all areas but the southeast corner of the basin, water <br />can be encountered at less than 200 feet below ground <br />surface. <br />The Dakota-Cheyenne aquifer lies under the majority of <br />the Arkansas Basin. The stratigraphy of this unit ranges <br />from well-sorted sandstone to fine-grained shales. The <br />aquifer provides water for irrigation and domestic water <br />supply in the basin. Due to the diversity of the aquifer <br />stratigraphy, well yields can range from around 5 gpm to <br />over 1,000 gpm. <br />3.2.8 Arkansas Basin Water Quality <br />Surface water quality in the Arkansas Basin is "generally <br />good" and portions of the headwaters have been <br />designated by the State of Colorado as Outstanding <br />Waters. All streams, lakes, and reservoirs within Mount <br />Massive and Collegiate Peaks Wilderness Areas are <br />currently considered under the designation of <br />Outstanding Waters. However, there is some water <br />quality concern in the basin near the Arkansas River <br />headwaters in the historic mining districts and <br />downstream toward the Colorado-Kansas state line. The <br />major water quality issues in the basin are related to acid <br />mine drainage in the headwaters, and urban runoff and <br />salinity in the lower basin. Additionally, return flows from <br />agricultural and municipal water uses concentrate <br />naturally occurring salts, arsenic, and selenium in the <br />basin (CDPHE 2002). <br />Acid mine drainage was a significant problem in parts of <br />the Upper Arkansas River, especially along the <br />segments of the East Fork, St. Kevin's, and California <br />Gulches. Treatment plants have been constructed to <br />control discharge quality from the Yak Tunnel and the <br />Leadville Drain. Although much improvement has been <br />made, high metal concentrations are still observed. The <br />waters of Cripple Creek and Fourmile Creek are also <br />impaired as a result of historic mining (CDPHE 2002). <br />Urban areas are another contributor to water quality <br />degradation. Urban stormwater runoff can constitute a <br />majority of flow in parts of the basin during high flow <br />periods, while during low flow periods many of the <br />streams are dominated by M&I effluent (CDPHE 2002). <br />The High Plains aquifer is found in the eastern portion of <br />the basin and is considered a"Designated Basin" by the <br />State of Colorado. A Designated groundwater basin is <br />not adjacent to a continuously flowing natural stream or a <br />stream that fulfills a surface water right. A designated <br />groundwater basin is established by the Colorado <br />Groundwater Commission in accordance with Section <br />37-90-106 of the Colorado Revised Statutes. The High <br />Plains aquifer is a major source of water for southeast <br />Colorado. Because of this, groundwater withdrawals <br />have exceeded recharge since the early 1960s. The <br />depth of wells generally increases eastward toward the <br />Colorado-Kansas state line, and in the Arkansas Basin <br />the saturated thickness of the aquifer ranges between <br />zero and 50 feet. <br />~~ <br />Surface water quality trends were identified using data <br />from the USGS flow gage and water quality station on <br />the Arkansas River at Lamar from the years 1968 to <br />1998. Water quality trends suggest that total sulfate, <br />hardness (calcium carbonate), and conductivity are <br />decreasing slightly, while total alkalinity is increasing <br />(CDPHE 2002). Salinity appears to be increasing in the <br />downstream direction in the Arkansas River. A recent <br />study showed an increase from 300 parts per million <br />(ppm) total dissolved solids (TDS) east of Pueblo to <br />4,000 ppm near the state line (CGS 2003). <br />As discussed in Section 2.6, the TMDL process <br />evaluates and allocates pollutant loads in impaired <br />waters listed on the Colorado 303(d) list. Stream <br />~~ <br />Statew~itle Water Supply Inii'iative <br />.~-4 S:\REPORT\WORD PROCESSING\REPORT\S3 11-8-04-WITH PAGE BREAKS.DOC <br />
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