- © 2016 Association of Environmental & Engineering Geologists
Detailed karst terrain assessments require the identification and survey of surface features such as closed depressions, sinkholes, and cave entrances. Typically, surveys are carried out at sites encompassing several hundred acres or less; however, the traditional methods have proven impractical from a time and expense viewpoint for extensive, regional-level surveys in well-developed karst terrain. This subject survey covered a 76-mi (122.3-km) length of a natural gas transmission pipeline. The goal of the study was to assist the United States Fish and Wildlife Service in assessing habitat vulnerability for the Madison Cave Isopod, a federally protected threatened species found only in phreatic ground water of the Great Valley of Virginia and West Virginia. The survey used an integrated approach involving the evaluation of topographic maps, digital elevation models, shaded relief maps, satellite imagery, and historic aerial photographs to identify “concentrations” of karst features. Ground surveys were then undertaken by walking sections of the pipeline right-of-ways that occurred within karst concentrations, and documenting the features using GPS instrumentation. The karst survey encompassed 48,640 acres (19.2 hectares), and was the largest utility-associated karst assessment ever conducted in the Commonwealth of Virginia. Approximately 216 closed depressions and 28 cave entrances were located, identified, and described based on their geology, physical appearance, and drainage characteristics. The use of an integrated approach significantly reduced the time and cost of the study. The study’s findings and recommendations have been used to develop conservation-based avoidance and minimization measures intended to limit the impact to the species’ habitat.