The critical issue facing the Des Moines Water Works since the initial design of the Maffitt Reservoir Well-Field on the Raccoon River is the limited saturated thickness of the underlying alluvial aquifer. The key to productivity of the well field is inducing infiltration from the Raccoon River. Barr first conducted a pre-design study to understand the hydrogeologic environment of the alluvial aquifer.
Using existing and new data and transient simulations of the aquifer tests, we then designed and calibrated a regional groundwater flow model with two highly discretized, linked local models. The local models were required for evaluating the design of new radial collector wells. We also performed a predictive uncertainty analysis of the productivity of the expanded well field. Barr then used the groundwater flow models from calibration and the predictive analysis to design two new radial collector wells and estimate the expanded well field capacity under a number of scenarios. The estimates indicated that the client would likely not be able to produce the desired amount from the expanded well field under all conditions, so they are now focusing on other sources of supply.