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Hydrogeology and Quality of Ground Water in the Upper Arkansas River Basin from Buena Vista to Salida, Colorado, 2000-2003

By Kenneth R. Watts

Available 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

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The citation for this report, in USGS format, is as follows:
Watts, K.R., 2005, Hydrogeology and quality of ground water in the upper Arkansas River Basin from Buena Vista to Salida, Colorado, 2000-2003: U.S. Geological Survey Scientific Investigations Report 2005-5179, 61 p.

Abstract

The 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 Contents

Abstract

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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