Day County Study

Project Description

New exploratory test-hole drilling, well installation, and geologic mapping within Day County are currently proceeding. Day County primarily resides within the Prairie Coteau region of South Dakota and was extensively glaciated during the Quaternary period. Drilling test holes has proven to be challenging due to the glacial drift thickness ranging from 300 to 800 feet and unstable subsurface materials encountered across the county. An abundance of historical test-hole data, aquifer maps, and previous publications are used to produce an updated set of 1:100,000-scale maps of the surface geology, aquifer materials, and bedrock geology. These updated maps will be complemented with a report, further detailing the complex geology and hydrology within Day County. Subsurface information is obtained through drilling test holes accompanied by a written descriptive analysis of the materials drilled. GIS analysis and field survey methods are used in conjunction with the test-hole data to yield a thorough investigation of Day County.

Following is a recent test hole map in relation to a preliminary aquifer map. Recent aquifer materials analysis is providing a refined delineation of the Lynn Aquifer and the Sweetwater Channel.

Pictured below is a bedrock elevation model generated from historical and recent test-hole data. Extensive drilling is still required in central and eastern Day County to gain a clear understanding of the bedrock topography and buried ancient channel aquifers within the county.