Potential beneficial uses of coalbed natural gas (CBNG) water.

The CBNG well water is typically managed by discharging into nearby disposal ponds. The CBNG well water could potentially be very useful in the water-limited regions (e.g., arid and semi-arid), but beneficial uses may be hindered by water quality problems. Objectives of this research were to: (1) examine trend analysis of nine years of CBNG well water at discharge (outfall) points and in corresponding disposal ponds, (2) evaluate geochemical processes, (3) identify potential water quality issues, and (4) find potential beneficial uses. The CBNG well water at discharge points and in corresponding disposal ponds was measured on-site for pH and electrical conductivity (EC). These water samples were also analyzed in the laboratory for calcium (Ca), sodium (Na), magnesium (Mg), potassium (K), iron (Fe), aluminum (Al), copper (Cu), arsenic (As), selenium (Se), cadmium (Cd), and barium (Ba). Total dissolved solids (TDS) were calculated from EC measurements. The sodium adsorption ratio (SAR) was calculated from Na, Ca, and Mg concentrations. Trend analyses of outfalls and disposal ponds were conducted separately so that the differences in trends could be compared. Trends in CBNG well water at discharge points are not always the same as trends in CBNG disposal ponds: environmental and geochemical processes play an important role in the water quality of these well waters. Overall trend analyses suggest that CBNG well water at discharge points in all basins of the Powder River Basin meets beneficial use criteria, except for SAR and to some extent EC, for aquatic life, livestock and wildlife watering, and irrigation. The CBNG well water in disposal ponds across all basins meets criteria for all beneficial uses except for As, pH, SAR, and to some extent EC for irrigation, aquatic life, and livestock and wildlife watering.