Water quality monitoring at the Hoe Creek test site: review and preliminary conclusions

It has been shown that underground coal gasification (UCG) may introduce a broad range of residual products into the groundwater of a coal aquifer. Sorption of many contaminants by the coal itself is an important factor in restricting the migration of these contaminants in the groundwater. However, our field studies at the Lawrence Livermore National Laboratory (LLNL) Hoe Creek site in northeastern Wyoming have shown that sorption of organic compounds by coal is not as effective as expected, perhaps because the coal surface area is limited. Furthermore, if severe roof collapse has taken place during gasification, non-coal aquifers located above the gasified coal seam may become interconnected with the cavity. Contaminants may enter these non-coal aquifers, in which sorption is even less effective. The Hoe Creek II and III experiments have enabled us to study the contamination of a sand aquifer located above a gasified coal seam in a hydrological recharge area. The preliminary results indicate that the water in the overlying sand aquifer is much less contaminated with organic compounds than that in the gasified