TWENTY-PLUS YEARS OF TRYING TO UNDERSTAND SURFACE RUNOFF AND SHALLOW GROUNDWATER DYNAMICS IN THE SPRINGFIELD, MISSOURI URBAN AREA – COMBINING GEOPHYSICS, GEOCHEMISTRY, DYE-TRACING TOOLS AND MORE

Springfield, Missouri is built on land with many non-perennial streams, and known for springs, sinkholes, and caves. Local geology generally consists of granitic basement under about 2000 feet of mostly carbonate units. In Springfield, the Mississippian Burlington Formation (limestone) is most common at the surface. Beneath the Burlington lie the Elsey, Reeds Spring, and Pierson formations, each limestone with varying amounts of silica, often as chert nodules. These form the Springfield Aquifer hydrologic unit, with the Northview Formation, primarily shale, serving as ‘leaky aquitard’ separation from the Ozark Aquifer below (1000+ feet of Ordovician limestones and dolostones). Typical karst landscape issues, such as sinkholes and losing/dry streams, has led to sustained interest in understanding how the karst affects development and vice versa.

Previous studies (1970s to early 2000s) mapped karst features and documented dye traces. This provided the base for recent quantitative dye tracing, geophysical, and geochemical studies. Results from a few dozen MS thesis and undergrad projects, combined with caver insights published in Missouri Speleology (2018), suggest that much of the local karst landscape follows two common steps. The first step is where surface streams incise valleys and allow mass wasting to occur along the hillsides (be it landslides or simply creep). This mass wasting, facilitated by natural weathering at the soil- rock interface, leads to enlarged joints or fractures that are nearly vertical and often parallel to the stream valleys. Once opened, these joints often expose sub-horizontal bedding to surface runoff influx, where groundwater then seeps downward until it reaches the water table or finds a less-permeable horizon in the limestone, which becomes the second step. In this step, the waters typically begin more lateral (less vertical) flow, which begins to open a sub-horizontal drainage to the far edge of a hillside. This presentation will explain these processes and relate them to environmental studies in the Springfield Missouri urban area.