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Hydrogeology and Quality of Ground Water in the Upper Arkansas River Basin from Buena Vista to Salida, Colorado, 2000-2003By Kenneth R. WattsAvailable from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Scientific Investigations Report 2005-5179, 61 p., 21 figs.—ONLINE ONLY
This document also is available in pdf format: The citation for this report, in USGS format, is as follows:
AbstractThe upper Arkansas River Basin between Buena Vista and Salida, Colorado, is a downfaulted basin, the Buena Vista-Salida structural basin, located between the Sawatch and Mosquito Ranges. The primary aquifers in the Buena Vista-Salida structural basin consist of poorly consolidated to unconsolidated Quaternary-age alluvial and glacial deposits and Tertiary-age basin-fill deposits. Maximum thickness of the alluvial, glacial, and basin-fill deposits is about 5,000 feet, but 95 percent of the water-supply wells in Chaffee County are no more than 300 feet deep. Hydrologic conditions in the 149-square mile study area are described on the basis of hydrologic and geologic data compiled and collected during September 2000 through September 2003. The principal aquifers described in this report are the alluvial-outwash and basin-fill aquifers. An estimated 3,443 wells pumped about 690 to 1,240 acre-feet for domestic and household use in Chaffee County during 2003. By 2030, projected increases in the population of Chaffee County, Colorado, may require use of an additional 4,000 to 5,000 wells to supply an additional 800 to 1,800 acre-feet per year of ground water for domestic and household supply. The estimated specific yield of the upper 300 feet of the alluvial-outwash and basin-fill aquifers ranged from about 0.02 to 0.2. Current (2003) and projected (2030) ground-water withdrawals by domestic and household wells are less than 1 percent of the estimated 472,000 acre-feet of drainable ground water in the upper 300 feet of the subsurface. Locally, little water is available in the upper 300 feet. In densely populated areas, well interference could result in decreased water levels and well yields, which may require deepening or replacement of wells. Infiltration of surface water diverted for irrigation and from losing streams is the primary source of ground-water recharge in the semiarid basin. Ground-water levels in the alluvial-outwash and basin-fill aquifers vary seasonally with maximum water levels occurring in the early summer after snowmelt runoff peaks. Because of the drought during 2002, relatively large declines in ground-water levels occurred in about one-half of the monitored wells. Differences in water-level altitudes in shallow and deep wells indicate the potential for downward flow in upland areas and support results of preliminary cross-sectional models of ground-water flow. The apparent mean age of ground-water recharge ranged from about 1 to more than 48 years before 2001. The older (pre-1953) water was from wells that were located in ground-water discharge areas. Ground-water flow in the Buena Vista-Salida structural basin drains eastward toward the Arkansas River and, locally, toward the South Arkansas River. Ground water in the alluvial-outwash and basin-fill aquifers generally is calcium-bicarbonate water type with less than 250 milligrams per liter dissolved solids. Nitrate concentrations generally were less than 1 to 2 milligrams per liter and do not indicate widespread contamination of ground water from surface sources. Table of ContentsAbstract Introduction Purpose and Scope Hydrologic Setting Climate and Runoff Population, Water Supply, and Wells Water Rights and Augmentation Plans Acknowledgments Methods Water-Level Measurements Sample Collection and Processing Hydrogeology Geologic Setting Bedrock Basin-Fill Deposits Glacial Outwash and Till Alluvial Deposits Hydrogeologic Setting Hydrologic Properties Estimated Specific Yield Specific Capacity of Wells Alluvial-Outwash Aquifer Till Aquifer Basin-Fill Aquifer Bedrock Aquifer Preliminary Conceptual and Cross-Sectional Models of Ground-Water Flow Conceptual Model Cross-Sectional Models Water Levels Alluvial-Outwash and Till Aquifers Basin-Fill Aquifer Bedrock Aquifer Configuration of the Water Table Depth to Water Direction of Ground-Water Flow Effects of the 2002 Drought on Water Levels Age of Ground-Water Recharge Sustainability of Ground-Water Supplies Ground-Water Storage Potential Effects of Increased Ground-Water Use Estimated Withdrawals and Consumptive Use by Domestic and Household Wells, 2003-2030 Well Density and Well Interference Water Quality Alluvial-Outwash Aquifer Physical Properties and Chemical Characteristics Water Type Indicators of Anthropogenic Effects on Water Quality Basin-Fill Aquifer Physical Properties and Chemical Characteristics Water Type Indicators of Anthropogenic Effects on Water Quality Comparison of Water Quality between the Alluvial-Outwash and Basin-Fill Aquifers Summary References Cited Glossary |
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