This report describes site investigations conducted at two tailings impoundments to develop baseline hydrological data for the evaluation of these waste management practices. The impoundments are associated with a lead mine and mill in Missouri and a gold mine and mill in South Dakota. The overall objectives of the investigations were to estimate the rate of seepage, to evaluate water quality impacts, and to obtain a better definition of the hydrogeology in the immediate area of the dams. Water table contour maps were prepared, water balance calculations were made, pump tests were conducted, water quality samples were collected and analyzed, and pertinent existing data were assembled and evaluated. Results of the study were largely inconclusive with regard to determination of water quality impacts due to seepage and estimation of theoretical seepage rates by water balance calculation. They have, however, provided additional insight into understanding the complex hydrogeological systems at these sites.