Inorganic constituents present in UCG process effluents can be strongly correlated with changes in coal and overburden mineralogy. An analysis of the Hanna, Wyoming, UCG she provides insight on how inorganic constituents enter the system. A comparison of preburn versus post burn mineralogy indicates that carbonates, clay minerals, micas, and sulfurous minerals hreak down structurally because of high temperatures. This decomposition releases calcium. magnesium, silica, and nluminum for rebonding in high-temperature stable silicate and aluminosilicate minerals. It also releases constituents such as iron sodium, sulfur, ann boron into the UCG process effluent. Other constituents such as calcium, copper, magnesium, manganese, potassium, and sodium are predominantly introduced into the groundwater by leaching. Groundwater quality data and analysis of other process effluents support these interpretations. Complete chemical and mineralogical characterization of the coal, coal ash, and immediate overburden is an important tool in determining inorganic constituents that affect groundwater quality at UCG sites. Early planning offers substantial economic incentives by allowing treatment while the constituents are confirmed are confined to the cavity before migration affects much larger areas.