Hydrochemical Analysis of Groundwater in Jewel Cave National Monument

Science Center Objects

The Issue: The park’s landscape and geomorphology is characterized as a carbonate karst environment, with sinking streams and fast connections between surface water and groundwater, resulting in high vulnerability of contamination to groundwater. Now that subterranean lakes have been discovered in Jewel Cave, understanding the groundwater connection of the lakes therein to the lakes in nearby Wind Cave is a priority for the National Park Service (NPS).

How USGS will help: In close cooperation with the NPS, the USGS is conducting a study of the hydrochemistry of Jewel Cave to better establish the relation and possible hydraulic connection between Jewel Cave and Wind Cave. 

New Year's Lake

New Year's Lake, a subterranean lake in Jewel Cave at a depth of more than 700 feet below land surface. NPS Photo

(Public domain.)

Problem: Until very recently, Jewel Cave was thought to contain little groundwater and no open lakes. Surprisingly, however, two subterranean lakes were discovered in the fall of 2015, as cave explorers pushed into the far reaches of the cave. These lakes probably represent the water table of the Madison aquifer, similar to lakes in Wind Cave, and therefore, may be hydraulically connected to lakes in Wind Cave. Understanding the hydrology of these lakes is a priority for the NPS, although little is known about them.

Objectives: The primary objective is to determine if hydrochemical samples in and near Jewel Cave are similar to any of the hydrogeologic domains that previously were established for the Wind Cave area, or if the samples are hydrochemically distinct or different from those domains. The second objective is to estimate the mixing proportions of different sources of water to the Jewel Cave lakes, if possible. 

Relevance and Benefits: Understanding the science of natural processes at our national parks and monuments is an important component to managing park resources and in educating the public regarding their treasured lands. The proposed work will benefit the nation by furthering the scientific understanding of Jewel Cave and how it interacts with the local and regional groundwater flow system. Park staff will have improved information for deciding what steps should be taken to protect park resources. Caves are important natural resources throughout the United States, and these methods, if applied elsewhere, could be useful for many public and private lands where groundwater interacts with caves. 

Approach: A groundwater flow and mixing analysis will be conducted. This will include principal-component analysis and end-member mixing applied to major ions and stable water isotopes. All data used in this study were previously published. This analysis will provide an assessment of Jewel Cave hydrology within the context of the surrounding southern Black Hills of South Dakota, which includes Jewel Cave National Monument and Wind Cave National Park. An additional mixing analysis will be conducted that includes strontium and uranium isotopes (87Sr/86Sr and 234U/238U). This second mixing analysis will consist of a smaller number of sampled sites than the analysis of major ions and stable isotopes but is expected to provide additional insights into groundwater mixing and flow related to Jewel Cave and Wind Cave. Comparison of the mixing analyses for the two different sample sets also might provide information regarding the uncertainty of estimated mixing proportions. Results will be published in a USGS series report, NPS series report, or suitable scientific journal.