MGS geologists presented research at the 15th Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst, April 2-6, 2018
April 6, 2018
Factors affecting karst spring turbidity in eastern Washington County, Maryland
David K. Brezinski, Johanna Gemperline, Rebecca Kavage Adams, and David W. Bolton
ABSTRACT
Infrequent and episodic turbidity events within the karst spring at the Albert Powell Trout Hatchery in Maryland’s eastern Great Valley threatened late winter fry populations. Turbidity events in early winter 2016–2017 prompted detailed geologic, dye tracing, and resistivity studies. The hatchery spring lies at the juncture of a northeast trending thrust fault and a northwest trending cross strike fault. Dye tracing study along these structures produced mixed results. Fluorescein tracing, injected 1,500 m north, and upstream of the spring was used to test the conductivity along the Beaver Creek fault and Beaver Creek. This dye was not conclusively identified at any of the surrounding recovery sites. Rhodamine WT injected more than a kilometer northwest of the spring, and along the trend of the cross fault, was detected at both the hatchery spring and surrounding recovery sites after about one week. 2D resistivity studies attempting to identify subsurface voids along the cross-fault trend show a high resistivity anomaly possibly indicating an air-filled void and warrant further investigation. The study suggests that while faulting plays a role in direction of ground water movement, turbidity events appear to be most prone during periods of lowered flow.
Further investigation: In March 2018, expanded resistivity (ER) and induced polarization (IP) surveys were performed 50m north using 2D and quasi-3D processing to increase the depth and width of the imaging and better constrain the location and orientation of the void imaged in ER Survey 1. A resistive zone appears in the middle of the profile at 6-30m depth, suggesting the anomaly in ER Survey 1 trends north/northeast underneath a visible ridge, is larger and deeper than was first imaged, and decreases in size to the northeast. It dips southeast (following bedrock orientation) and is broken by a northwest dipping zone of lower resistivity values that may be fractured bedrock at northeast striking joints. Corresponding IP surveys show highly chargeable material from 30-40m in depth below the bedrock, which is indicative of a clay-rich zone, possibly a clay-filled void.
This interdisciplinary biennial conference series is the most important international meeting that concentrates on the practical application of karst science. Geologists, engineers, and geographers, who study how and where karst develops and how sinkholes form, interact with engineers and planners, who apply this information to building and maintaining society’s infrastructure while protecting our environment.
The conference is managed by the National Cave and Karst Research Institute, which partnered with the Karst Waters Institute to offer this 2018 meeting. Given its location in the Great Valley of the Appalachians, one of the premier karst regions of the USA, the conference also included the 3rd Appalachian Karst Symposium.
Conference topics included: Karst Development & Mapping, Pro-Active and Remedial Engineering in Karst Terrain, Karst Water Resource Management.
