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"'~ "..~ ..',"::.-. \.~*.:' f\) 00 -.J ~... ../.;'"f., ~\>. ,'. ;:~" .:-....... (5) revegetation of spent shale; and (6) Miscellaneous plant uses (sanitary waste systems, etc.).l While upgrading, spent shale disposal, and revegetation account for the largest share of consumption, these six steps can differ substan- tially from one specific technology to the next (with some steps not even being present in certain technologies). Thus, estimates of water consumption vary by technology. Furthermore, estimates of consumption for a given tech- nology vary from one literature reference to thenext. As.a consequence. an estimate of the net annual consumption of water by a generic 50,000 barrel per day (bbl/day) surface retort plant must necessarily cover a range from about 3,500.to 9,000 acre-feet, although the majority of literature estilllates fall between about 5,000 .and 8,000 acre-feet. Until actual com- mercial operating experience is gained, it is unlikely that water consump- tion for surface retorting can be estimated with any greater accuracy. With respect to modified in-situ retorting processes, the portion of the shale rock that is initially mined out could be retorted on the sur- face. To the extent this were done, water would be consumed as in any other surface retorting process. Insofar as the in-situ retorting itself. is concerned, water is consumed through steam injection into the retort.2 5lllall amounts of water will also be consumed for dust control and miscel- laneous plant uses. If undertaken on-site, generation of electricity with off-gases and upgrading of the pyrolysis oils and tars would also cons~me water. As with surface retorting, literature estimates of net water consump- tion for modified in-situ retorting very by specific technology and even for a single technology. Clearly, however, modified in-situ facilities are apt to consume less water (exclusive of water consumed for any surface retorting of the initially mined out shale) than surface retorting. Literature estimates range from about 2,000 to 5,000 acre-feet per year , of'net consumption for a 50,000 bbl/d?y operation. The average value of iiterature estimates for annual consumption is about. 3,500 acre-feet. The prilllary reason modified in-situ technologies consume less water is that spent 'shale cooling, compaction, and disposal, and revegetation, would not be required. 1. As a seventh step, the off-gases could be used on-site to generate electricity, in which event water would be consumed for evaporative cooling. However, it appears from the available literature that all surface retorting technologies anticipate that the off-gases will be burned 10 order to heat the retort. This apparently would require little, if any, evaporative cooling. 2. As in surface retorting, modified in-situ retorting technologies generate water (not including excess mine drainage water and ground water seepage into the retort). The purpose of steam injection is to control the temperature of the retort. xxvii