Madison Aquifer Study in the Rapid City Area

Executive Summary

The U.S. Geological Survey (USGS) and the city of Rapid City have had a long-term cooperative relationship to conduct hydrologic investigations to better understand the complex system that supplies water to Rapid City and the surrounding area. Rapid City has become a regional water supplier and demand for water within and beyond the city limits continues to increase steadily due to rapid population growth. As such, sound scientific information is needed to assess the consequences of future development and drought on water supplies and to maintain the delivery of high-quality water. This collaborative study plan is designed to assist the City with hydrologic data and additional interpretive information to better provide a sustainable, high-quality water supply. City water supplies are obtained from wells completed in the Madison and Minnelusa aquifers, collection galleries in the alluvium along Rapid Creek, and surface water from Rapid Creek.

The Madison and Minnelusa aquifers are vital water supplies for Rapid City and the surrounding areas. The Madison aquifer is especially vulnerable to contamination in the Rapid City area because of (1) bedrock outcrop areas west of Rapid City; (2) direct connections to potential surface contaminants through streamflow loss zones; and (3) fast travel paths through solution-enhanced openings and fractures. Collection galleries in the Rapid Creek alluvium also are supplied in part by springflow originating from the bedrock aquifers. Evaluations related to meeting future water supply demands and protecting these aquifers from contamination requires a better understanding of the characteristics of these important aquifers. These long-term objectives are being accomplished with a variety of hydrologic investigations conducted by the USGS.

A detailed description of the Madison and Minnelusa aquifers in the Rapid City area is available in “Long, A.J., and Putnam, L.D., 2002, Flow-system analysis of the Madison and Minnelusa aquifers in the Rapid City area, South Dakota--Conceptual Model: U.S. Geological Survey Water-Resources Investigations Report 02-4185, 100 p., 3 pl.”

Objectives

The objectives of the study include maintaining a water-level monitoring network, conducting aquifer tests, analyzing ground-water flow paths using environmental and anthropogenic tracers, compiling and evaluating water budgets, and developing conceptual and numerical models of the aquifers.