This report sets forth the technical progress under the cooperative agreement for the third three-month period (April 1--June 30, 1994) of Phase I of the overall program. Preliminary environmental risk assessment on the FGD by-products to be placed underground is well underway. The initial mixes for pneumatic and hydraulic placement have been selected and are being subject to TCLP, ASTM, and modified SLP shake tests as well as ASTM column leaching. All TCLP data on the pneumatic mixes has been collected and analyzed, and data compilation and analysis for other materials and tests is underway. The TCLP results show that all individual materials in the pneumatic placement mixes, and the mixes themselves, are non-hazardous in character and very unlikely to have any adverse effects on groundwater at the underground placement site. Based on available information, including well logs obtained from Peabody Coal Company, a detailed study of the geology of the placement site has been completed. The study shows that the disposal site in the abandoned underground mine workings at depths of between 325 and 375 feet are well below potable groundwater resources. This, coupled with the benign nature of the residues and residues mixtures, should alleviate any concern ofmore » the effects of underground placement on groundwater resources.« less