HR: 0800h
AN: H51A-0339    [Abstracts]
TI: Predicting Long-Term Well Performance in the Piedmont Using Short-Term Hydraulic Well Tests: Preliminary Findings
AU: * Hisz, D
EM: dhisz@clemson.edu
AF: Clemson University, Geological Sciences 340 Brackett Hall, Clemson, SC 29634 United States
AU: Murdoch, L
EM: lmurdoc@clemson.edu
AF: Clemson University, Geological Sciences 340 Brackett Hall, Clemson, SC 29634 United States
AB: A reliable estimate of the physically sustainable discharge of a well is a fundamental aspect affecting management of water resources, but there are surprisingly few analyses describing on how to make such an estimate. Pumping from a water well will go through three basic stages: an early storage-release stage, a late boundary-interaction stage, and an intermediate transition stage. Well behavior during the storage-release stage is characterized by most hydraulic well tests. Some wells may remove water from storage in an aquifer for a long time, so understanding this early stage may be all that is necessary for a practical characterization of those wells. Wells that are completed in deep confined aquifers or in shallow unconfined aquifers that are far from streams may behave this way, for example. The long-term operation of many water wells, particularly wells in the Piedmont, probably occurs during the transition or boundary-interaction stages, so understanding these effects will be important when predicting long-term performance. Wells go to steady state because they change the balance of flow into, or out of the aquifer. Under most conditions in the Piedmont, a well will not change the flow into an aquifer by distributed recharge, but it can change the flow out by altering discharge of groundwater to streams. We have been using the effects of streams on short-term hydraulic well tests to predict long-term performance during pumping. Preliminary results using an analytical solution suggest that stream interaction probably affects most wells in the Piedmont and that some short-term well tests are sensitive to this effect. A simple analytical solution that assumes an idealized boundary successfully predicts the apparent steady state performance of a well at the Clemson University in western South Carolina. A more detailed analysis that considers a variable strength of interaction between a stream and a well extends the versatility of this method to a wide range of conditions. The analytical solutions neglect effects of saprolite, a high-porosity layer overlying fractured rock throughout the Piedmont. Numerical simulations have been used to show that saprolite can mask the effect of a stream boundary by lengthening the storage-release stage. Ultimately, however, the high storage capacity of saprolite probably has a minor effect on steady-state performance of wells in fractured rock.
DE: 1816 Estimation and forecasting
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1849 Numerical approximations and analysis
SC: Hydrology [H]
MN: Fall Meeting 2005