Changes in Groundwater Quality and Subsurface Hydrology during the Rocky Mountain 1 Underground Coal Gasification Test, Hanna, Wyoming. Topical Report

摘要

Groundwater sampling and potentiometric surface monitoring was performed during the Rocky Mountain 1 (RM1) underground coal gasification (UCG) test. Observable hydrologic and groundwater quality changes were restricted to the Hanna No. 1 coal seam. Substantial head declines (120 ft) in the coal occurred by the end of the test. Head fluctuations in the coal aquifer was directly correlated to cavity pressures. A cone of depression in the potentiometric surface of the coal centered around the cavities and was maintained for the entire test. Spatial variations in fluid pressure and hydraulic conductivity are the primary factors that explain hydrologic responses to the RMI UCG test. Product gas was released into the coal seam; however, the only significant effect was the decline of groundwater pH from 8.5 to 6.5. Observed increases in sulfate, total dissolved solids, and ammonia were caused by groundwater migration. High concentrations in the water condensate of product gas and low concentrations in coal groundwater suggest that ammonia, sulfide, phenols, and total organic carbon did not migrate away from the immediate vicinity of the cavity. Coal groundwater quality was not significantly degraded during the RM1 test.