This paper addresses the extent of water resources impacts that western coal regions are experiencing as a result of surface coal mining activities, focusing primarily on the Powder River Coal Region. Hydrologic effects of coal mining are described and applicable federal regulations are summarized, including those relating specifically to western alluvial valleys. The cumulative impacts from extensive mining in the Powder River basin have not been assessed. However, in general insufficient field data has been collected to date to permit verification of the occurrence and geographic extent of the adverse impacts on western aquifers that have been predicted. Preliminary mine spoil leaching experiments have produced waters of similar quality to those found in the field under background conditions. The paper makes several recommendations for future research efforts that would assist in further characterizing the extent of the problem and the cumulative effects of large scale western surface mining activities. Judging the potential for preserving aquifers in western areas where intensive coal development is scheduled requires more detailed site specific documentation in light of existing regulatory programs.