SUBSURFACE MAP OF THE OZARK CONFINING UNIT IN A SPECIAL USE DRILLING AREA OF SOUTHWESTERN MISSOURI

Historic contamination in Southwestern Missouri from a variety of sources, including the Tri-State Mining District, has led to groundwater contamination in portions of the Springfield Plateau Aquifer. Because of this, a two county area in the region is designated as a special use drilling area. Migration of contaminated groundwater to the lower Ozark Aquifer, the principal aquifer in the Springfield Plateau groundwater province, is limited by the Ozark Aquifer Confining Unit (OACU). The “Subsurface map of the Ozark Confining Unit in a special use drilling area of southwestern Missouri” delineates the upper and lower elevations of the OACU throughout the special drilling area for the purpose of improving water well construction standards in Jasper and Newton Counties. The data is being used to draft regulations that will prevent aquifer mixing, thereby preserving the quality of the Ozark Aquifer.

The data for this map is sourced from stratigraphic well logs for public wells created by geologists and drilling logs from domestic water well construction records. Using ArcGIS software, top and bottom elevations of the OACU at each well location were calculated by subtracting formation depths below ground surface from an NED 10 meter elevation raster data set. The confining unit surfaces were then interpolated from formation elevations using a natural neighbor algorithm. The interpolated surfaces were evaluated to determine the maximum depth a well could be drilled to prevent penetration of the OACU and to establish minimum casing depth values to adequately seal through the OACU by ¼-section area within a public land survey system section. The values were then normalized for elevation changes within each ¼-section area. This data will be used to designate casing depths for wells drilled into the Ozark Aquifer and to establish depth limitations for wells drilled into the Springfield Plateau Aquifer by ¼-section throughout the special use drilling area.