The Piceance basin of northwestern Colorado contains rich deposits of oil shale in sedimentary rocks of the Parachute Creek Member of the Green River Formation. Plans for mining these deposits in Federal prototype lease tracts C-a and C-b require ground water to be pumped to allow the construction of underground retorts for use in extracting the shale oil. The possible adverse effects of mine pumping and resaturation of spent shale in an abandoned mine were investigated by studying the geochemistry of the aquifers and by use of ground water quality modeling techniques.