  The groundwater flow system in the Culebra Dolomite Member (Culebra) of the
Permian Rustler Formation is a potential radionuclide release pathway from the
Waste Isolation Pilot Plant (WIPP), the only deep geological repository for
transuranic waste in the United States. In early conceptual models of the
Culebra, groundwater levels were not expected to fluctuate markedly, except in
response to long-term climatic changes, with response times on the order of
hundreds to thousands of years. Recent groundwater pressures measured in
monitoring wells record more than 25 m of drawdown. The fluctuations are
attributed to pumping activities at a privately-owned well that may be
associated with the demand of the Permian Basin hydrocarbon industry for water.
The unprecedented magnitude of drawdown provides an opportunity to
quantitatively assess the influence of unplanned anthropogenic forcings near
the WIPP. Spatially variable realizations of Culebra saturated hydraulic
conductivity and storativity were used to develop groundwater flow models to
estimate a pumping rate for the private well and investigate its effect on
advective transport. Simulated drawdown shows reasonable agreement with
observations (average Model Efficiency coefficient = 0.7). Steepened hydraulic
gradients associated with the pumping reduce estimates of conservative particle
travel times across the domain by one-half and shift the intersection of the
average particle track with the compliance boundary by more than two
kilometers. The value of the transient simulations conducted for this study lie
in their ability to (i) improve understanding of the Culebra groundwater flow
system and (ii) challenge the notion of time-invariant land use in the vicinity
of the WIPP.
