[en] This report describes the results of CHEMVAL Stage 1, an international chemical model verification exercise involving the active participation of 14 organisations within the CEC countries, Sweden, Switzerland and Finland. Five case systems were studied, namely, cement, clay, sandstone, granite and limestone. Overall, good agreement was obtained even for conceptually difficult geochemical simulations. Reasons for divergence in results have been explored and recommendations are made at the appropriate stages for enhancement of the thermodynamic database. A listing of the preliminary CHEMVAL Project Database is provided. (author)