As regulators evaluate the environmental benefits or costs of removing dams blocking fish migration or collecting contaminated sediments, little thought is often given to the associated response of the adjacent shallow ground water system. Milltown Dam, built in 1907, blocks the Clark Fork and Blackfoot rivers just east of Missoula in western Montana. The reservoir contains at least 6.6 mcy of metal-contaminated sediment derived from a century of upstream mining operations.  Site remediation efforts are scheduled to excavate portions of the sediment and restore the river channels by removing the 9 m high dam in late 2008.  Predictions of reservoir drawdown impacts and dam removal on the adjacent water table position were modeled for the 20 km² area using a 3D finite difference code. The results suggest a complex pattern of water level change will occur. Managers are using model forecasts to proactively protect local ground water supplies by replacing or re-drilling wells at risk of having insufficient aquifer thicknesses to produce needed water.  The management’s risk based analysis relies on modeling results tied to a single conceptual model. On going work is evaluating how application of multiple conceptual models can be used to quantify prediction uncertainty and influence future management decisions.