IMPACTS OF COALBED NATURAL GAS CO-PRODUCED WATER ON CROPLAND IRRIGATED SOILS IN THE POWDER RIVER BASIN,

Water quality is a major concern with regard to development of coalbed natural gas (CBNG) in the Powder River Basin. Large quantities of water are being produced and discharged as a by-product in the process of releasing natural gas from coal. Current practices of discharging large volumes of water into drainage channels or using it to irrigate cropland areas has the potential to elevate salinity and sodicity in soils. Elevated salinity affects the ability of plants to uptake water to facilitate biochemical processes such as photosynthesis and plant growth. Elevated sodicity in irrigation water adversely affects soil structure necessary for water infiltration, nutrient supply, and aeration. Salinity and sodicity concentrations are important in that a sodic soil can maintain its structure if the salinity level is maintained above the threshold electrolyte concentration. In this study, cropland soil and CBNG water were treated with gypsum and sulfur. Plots were monitored to evaluate the effects of gypsum and sulfur on pH, electrical conductivity (EC), sodium adsorption ratio (SAR), and sulfate concentrations. Changes in soil chemistry due to the addition of different qualities of irrigation waters such as CBNG water and soil amendments were monitored using a split plot experiment. The CBNG water used for irrigation had an EC of 1380 µS cm -1 and SAR of 24.3 mmol 1/2 L -1/2 . Baseline and post treatment soil samples were collected to a depth of 60 cm within each study plot, analyzed, and characterized for chemical parameters. Comparisons between baseline and post irrigation soil chemistry data after one season indicated treatment of the irrigation water statistically increased (P<0.05) the rate at which Na + is moved through the profile. The addition of gypsum and sulfur as a water treatment and a soil amendment was the most effective in maintaining low SAR at the soil surface. Both EC and SAR statistically increased with all treatments in the top two sampling depths. Applying a leaching fraction at the end of each irrigation season should be tested for its effectiveness at moving Na + below the