Summary

Description

This data set provides information for evaluation of streamflow loss as mechanism of transport of potential contaminants when assessing sensitivity of ground-water to contamination in Lawrence County, SD. This data set is a result of a larger work (WRIR 00-4103 cited above), which includes a paper plate titled: "Map showing sensitivity of ground-water to contamination in Lawrence County, South Dakota." Thirty drainage basins upstream from outcrops of the Minnekahta Limestone, Minnelusa Formation, or Madison Limestone were delineated using digital elevation models (DEM) for the study area and GIS algorithms for the analysis of watersheds. Streamflow loss is an important source of recharge to the Minnekahta, Minnelusa, and Madison aquifers. Precipitation that falls on outcrop areas could transport a contaminant to the water table by direct infiltration, but in many instances the runoff moving to a streamflow-loss zone is a more important mechanism of potential ground-water contamination. Water from streamflow loss in the study area is more likely to enter rapid flowpaths through the unsaturated zone and aquifer media because of solution openings. An additional data set listed in cross-references (sd_lcsens_lz) shows the locations of the streamflow loss zones. An attribute file describes selected characteristics of the drainage basins and includes a site identifier that can be related to the loss_zones. The source data includes digital data that characterizes the geology of the Black Hills area, which has been compiled at 1:100,000 scale and published in 1999 as part of the Black Hills Hydrology Study. USGS digital elevation models were used to describe land-surface altitudes. The drainage area data set has been archived at the USGS Water Resources National Spatial Data Information Node.