Scientific Investigations Report 2005-5219
In cooperation with the Minnesota Department of Natural Resources, the cities of Windom and Jeffers, Minnesota, the Red Rock Rural Water System, and the Cottonwood County Environmental Office
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Scientific Investigations Report 2005-5219
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Increased water demand in and around Windom led the U.S. Geological Survey, in cooperation with the Minnesota Department of Natural Resources, local water suppliers, and Cottonwood County, to study the hydrology of aquifers in the Des Moines River Valley near Windom. The study area is the watershed of a 30-kilometer (19-mile) reach of the Des Moines River upstream from Windom.
Based on stratigraphic analysis, two hydrologically and genetically separate surficial aquifers underlie the study area. The Windom aquifer has a saturated thickness of 34 meters (111 feet), and the Des Moines aquifer has a saturated thickness of 33 meters (108 ft). The surficial aquifers are relatively isolated from deeper aquifers by till, but some leakage probably occurs. Recharge to the aquifers is from areal recharge, from Cottonwood Lake, and from edge recharge. Pumping at the Windom well field induces substantial amounts of Cottonwood Lake water into the aquifer. During this study, the water level in a well located between two Red Rock wells and the river was lower than the river level during two periods. During those periods, water in the Des Moines River had the potential to recharge the aquifer. Discharge from the aquifers is primarily to municipal wells, the Des Moines River, and other surface waters.
Most of the ground-water samples collected in the study area consisted of calcium-magnesium bicarbonate waters. Corn and soybean herbicides and their degradates were detected at low concentrations in 14 of 27 ground-water samples and in all 3 river samples. Metolachlor ethane sulfonic acid was the most commonly detected compound and also was detected at the highest concentrations. Nutrient concentrations in ground-water samples were skewed low with high outliers, and nutrient concentrations in river samples generally were less than analytical reporting limits.
Nearly all recharge to the aquifer in the ground-water simulation was from edge recharge (80 percent). Calibrated net areal recharge ranged from 17 to 30 percent of the average annual precipitation. Isotopic composition of ground water and Cottonwood Lake water indicated about one-half of the water withdrawn from the Windom aquifer is from Cottonwood Lake.
Scenarios tested with the calibrated model involved increased ground-water withdrawals and changes in recharge to simulate drier or wetter weather conditions. Doubling the withdrawals from all wells in the model had a small effect except in the Windom well-field area. Maximum head declines in the Red Rock well field and the Jeffers city well were less than 40 centimeters (15 inches). In the Windom well field, the maximum head decline was 11 meters (36 feet). The Windom well field does not induce recharge from the Des Moines River. The addition of a new well that pumped 2,000 cubic meters per day (0.44 million gallons per day) in the Augusta Lake Valley area caused a 0.83-meter-deep (2.72-foot-deep) cone of depression that extended to the valley walls. The drought scenario and the high-precipitation scenario resulted in head changes in the northern part of the Augusta Lake Valley area, in the southwestern part of the Red Rock area, and near the valley edges.
Long-term withdrawals of water for public supplies may cause a net decrease in ground-water discharge to surface water. Water that does not evaporate, or that is not exported, is discharged to the Des Moines River but with changed water quality. Because ground-water and surface-water qualities in the study area are similar, the ground-water discharge probably has little effect on river water quality.
Abstract
Introduction
Study Area Description
Previous Studies
Acknowledgments
Study Design and Methods
Sample Collection and Quality Control
Water Levels and Stream Discharge
Aquifer-Property Tests and Recharge Estimates
Simulation of Ground-Water Flow
Hydrogeology
Geology
Surface Water
Ground Water
Description of Aquifers
Recharge and Discharge
Ground-Water Flow
Ground-Water/Surface-Water Interactions
Ground-Water Sources from Water Isotopes
Ground-Water Age from Dissolved Gasses
Water Quality
Nutrients
Herbicides and Their Degradates
Water-Quality Variability
Water-Quality Implications
Simulation of Ground-Water Flow
Model Description
Model Calibration and Sensitivity
Hypothetical Simulations
Increased Ground-Water Withdrawals
Drought
High Precipitation
Model Limitations
Effects of Ground-Water Withdrawals on Ground-Water/Surface-Water Interactions
Summary
References
Appendices
Local ground-water studies in the Des Moines River study area, southwestern Minnesota.
Number of samples analyzed for constituent groups, Des Moines River study area, southwestern Minnesota.
Water-quality sampling methods and quality control.
Figures
Map showing Des Moines River study area location, aquifer extent, and study sites, southwestern Minnesota.
Graph showing average annual precipitation cycles at Windom, Minnesota, 1971-2001.
Graph showing water uses and water sources in the Des Moines River study area, southwestern Minnesota, 2000.
Map showing aquifer thickness, Des Moines River study area, southwestern Minnesota.
Map showing water-table elevation, Des Moines River study area, southwestern Minnesota, September 30, 1999.
Graph showing ground-water levels, river levels, and precipitation near Windom, Minnesota, May-July 2000.
Graph showing isotopic compositions of ground-water samples and Cottonwood Lake, Des Moines River study area, southwestern Minnesota.
Graph showing nutrient concentrations in ground water and surface water, Des Moines River study area, southwestern Minnesota, 1999-2001.
Graph showing detected herbicide and degradate concentrations, Des Moines River study area, southwestern Minnesota, 1999-2000.
Graph showing variability of selected nutrient and chloride concentrations, Des Moines River study area, southwestern Minnesota, 1999-2000.
Graph showing variability of herbicide and degradate concentrations, Des Moines River study area, southwestern Minnesota, 1999-2000.
Map showing model grid and hydrologic stresses, Des Moines River study area, southwestern Minnesota.
Map showing difference between interpolated measured and simulated heads, Des Moines River study area, southwestern Minnesota.
Graph showing sensitivity of model input parameters, Des Moines River study area, southwestern Minnesota.
Map showing difference between calibrated model heads and simulated heads for a scenario in which withdrawals from existing wells were doubled, Des Moines River study area, southwestern Minnesota.
Map showing difference between calibrated model heads and simulated heads for a scenario in which a new well that pumped 2,000 cubic meters per day was added to the Augusta Lake Valley area, Des Moines River study area, southwestern Minnesota.
Map showing difference between calibrated model heads and simulated heads for a drought scenario, Des Moines River study area, southwestern Minnesota.
Map showing difference between calibrated model heads and simulated heads for a high-precipitation scenario, Des Moines River study area, southwestern Minnesota.
Tables
Annual water supply within the Des Moines River study area, 1989-2000.
Hydrologic properties for the Windom and Des Moines aquifers, Des Moines River study area, southwestern Minnesota.
Ground-water recharge dates and related well data, Des Moines River study area, southwestern Minnesota.
Herbicides and degradates for which water samples were analyzed, Des Moines River study area, southwestern Minnesota.
Measured and calibrated model input parameters, Des Moines River study area, southwestern Minnesota.
Measured and calibrated model values, Des Moines River study area, southwestern Minnesota.
Measured and simulated surface-water flows, October 8, 1997, Des Moines River study area, southwestern Minnesota.
Mass balances for calibrated model and hypothetical simulations, Des Moines River study area, southwestern Minnesota.
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