An evaluation of the groundwater obtained both from the Rawlins No. 1 underground coal gasification (UCG) reactor and from nearly hydrology wells was conducted to determine the effects of UCG on groundwater. This study held to the following conclusions: 1) Hydraulic communication between the G-seam coal and the overlying sandstone strata has occurred; 2) phenol concentration in the wells surrounding the reactor increasing during the test but quickly decreased to pretest levels in the post test sample; 3) minerals saturation indices calculated from the analytical data show that the cavity rater is oversaturated with respect to gypaum while the nearby well water is saturated with respect to calcite and dolomite; 4) analytical data on the cavity water indicate that, except for sulfate, all the significant parameters are either within pretest levels or lower.