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Environmental Health - Toxic Substances


U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 3 of 3--Sursurface Contamination From Point Sources, Water-Resources Investigations Report 99-4018C

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Characterizing Recharge to Wells in Carbonate Aquifers Using Environmental and Artificially Recharged Tracers

By Earl A. Greene, USGS, WRD, Baltimore, MD


Stable environmental isotopes were used as tracers to identify the sources of recharge from sinking streams to wells and springs several kilometers downgradient in the karst Madison aquifer near Rapid City, South Dakota. Temporal sampling of steamflow above the swallets identified a distinct isotopic signature that was used to define the spatial dimensions of recharge to the aquifer. An artifical dye tracer (Rhodamine WT) was directly injected into a swallet at one of the sinking streams (Boxelder Creek) and traced to the city municipal well system to determine the flow paths and the volume of water that is contributed to the wells from this recharge source. Analysis of the breakthrough curves showed that first arrival of dye to the municipal well field is very rapid--between 26 and 49 days--and it takes up to 200 days after injection for the concentration of dye to reach background levels.

From these analyses it was possible to link sinking stream recharge to individual wells and springs in the Rapid City area and to illustrate the lateral movement of ground water across surface drainage divides. These results emphasize that when estimating areas of contributing recharge to wells in carbonate aquifers, water managers need to consider the lateral movement of ground-water flow from adjacent surface-drainage basins.

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