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
Characterizing Recharge to Wells in Carbonate Aquifers Using Environmental
and Artificially Recharged Tracers
By Earl A. Greene, USGS, WRD, Baltimore, MD
ABSTRACT
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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