Water authorities in mining regions are frequently concerned with the potential hydrologic impacts of active and abandoned mine workings on water quantity and quality of public well water supplies. During active mining, wellhead protection of public supply wells focuses on water quantity issues, as the capture zone for the mine changes with the advancement of mine workings. When mine workings are abandoned, water within the flooded workings can become acidic and a potential source of contamination to public groundwater supplies. To address this issue, the US Bureau of Mines is identifying and assessing various hydrogeologic and mining variables that are important in delineating wellhead protection zones around public supply wells in mining regions. Researchers are monitoring hydrologic conditions between an active underground coal mine and three municipal wells in Pennsylvania. Active mining occurs outside of a 1,800 foot radial protection zone established around the wells. Municipal water pumping rates, groundwater inflow rates into the mine, and other pertinent hydrologic conditions are monitored and incorporated into hydrologic simulations of the site. Results from monitoring and simulations indicate that the hydrologic impact of active mining on nearby well water supplies depends principally on the method of extraction, whether primary or secondary mining, and the proximity of fractured stream valleys to mine workings and public supply wells.