English

Abstract

Significant quantities of water are being produced and discharged as a by-product of coalbed natural gas (CBNG) development in the Powder River Basin (PRB). Elevated salinity and sodicity in CBNG water has become a major concern, particularly with regard to its use or disposal. If land applied, elevated salinity and/or sodicity in CBNG water may adversely affect soil physical properties such as structure, infiltration, permeability, and aeration. Soil chemical properties impacted by CBNG water utilized for irrigation include changes in nutrient supply, modification of the soil exchange complex with dispersion, and pH effects. A sodic soil has been shown to maintain good soil structure if the salinity level is maintained above the threshold electrolyte concentration (TEC). In this study, cropland that was irrigated with Piney Creek (control) and CBNG waters were sampled two years after CBNG water irrigation and compared to baseline and post irrigation data to evaluate changes in soil physical and chemical properties. CBNG water was treated with gypsum (CaSO4●2H2O), sulfur (S) via a S burner, or both, and soils were amended with CaSO4●2H2O, elemental S, or both (GS). Changes in soil physical and chemical properties were monitored using a split plot experiment. Single ring infiltration experiments were conducted within each plot to determine if infiltration rates were affected by water type and/or water and soil treatments. A significant decrease in infiltration rate was observed for plots irrigated with CBNG water without soil amendments or water treatments. Soil samples were taken and analyzed for chemical parameters including pH, electrical conductivity (EC) and sodium adsorption ratio (SAR) before CBNG water application and two seasons following final CBNG water application. Decreases in EC and SAR were determined for most CBNG irrigated plots. Higher EC levels were detected in S and GS plots due to delayed microbial conversion of S. It appears Na + is moving through the soil profile with all soil amendment and water treatment combinations; however, CBNG-GSB+GS treatment results in the lowest SAR in the A and Bt1 horizons.