[en] The FASTCHEM (Fly Ash and FGD Sludge Transport and Geochemistry) computational package simulates the subsurface transport of solutes, encompassing hydrology and geochemistry in a series of related by independent modules. The FASTCHEM package comprises the hydrological codes EFLOW and ETUBE, the geochemical code ECHEM, the coupled geohydrochemical transport code EICM, and their associated file processor codes. This document describes the geochemical data used by the FASTCHEM package. The geochemical data discussed in this report were categorized as measured thermochemical data, estimated ion-exchange and specific-ion adsorption data, and measured kinetic data. The measured thermochemical (i.e., aqueous speciation and solubility) data have been derived primarily from the existing MINTEQ thermochemical database and modified using thermodynamic data compiled and measured as part of EPRI Projects RP2485-3 and RP2485-8. In establishing the database for the FASTCHEM package, the reactions and rate constants were checked for consistency. Identifiers denoting the sources of the data were added. Interim models describing ion-exchange and specific-ion adsorption reactions were included in the FASTCHEM database. The ion-exchange database was developed for reactions on smectite clays as a framework for estimating thermochemical data that are not yet available. The specific-ion adsorption database includes reactions for the adsorption of selected elements on hydrous ferric oxide. 159 refs., 26 figs., 21 tabs