Assessment of Water Supply Contamination Due to Underground Coal Gasification

A site has been chosen in northwestern New Mexico for a proposed underground coal gasification zone and the groundwater. There is no major aquifer in the region of the Fruitland Formation subbituminous coal seam (500 ft.), although the zone is saturated and a transmissivity of 0.6 feet ²day ^-l  has been determined. The groundwater is of poor quality having a pH ÷ lO, conductivity ÷ 6 mmho, total dissolved solids ÷ 3900 ppm, alkalinity ÷ l700 ppm CaC0 ₃, and hardness ÷ 50 ppm. Na, K, Mg, Ca are the major metal contaminants with environmentally significant ions present on the ppb level (As, Pb, Cd, Be, Cu, etc.). The major anionic species are Cl ^–, F ^–, SO ₃ ^2-, S ^2-, and HCO ₃ ^–. Deep water samples effervesce when brought to the surface, smelling strongly of H ₂S. X-ray diffraction and petro graphic examinations of the overburden, parting, and underburden indicate the major minerals to be quartz, feldspars, kaolinite, and montmorillonite. The sediment is fine grained, horizontally stratified, and fractured with fracture filling by calcite and/or gypsum; it also contains a large amount of organic matter. Major and trace element analyses of the sediment finds, aside from Si and Al, Na, Mg, K, Ca, and Fe as the major constituents of this material. The baseline results for the major and trace metal analyses of the groundwater and mineral material, anionic analyses of the groundwater, and trace organic analyses of the groundwater is discussed. A brief description of the local environment is given.

Project No. B-061-NMEX, 1345641, 1423641