Shallow Groundwater and Soil Chemistry Response to Three Years of Subsurface Drip Irrigation Using Coalbed Methane Produced Water

Engle, Mark; Bern, Carleton R.; Boehlke, Adam; Geboy, Nicholas J.; Schroder, Karl; Zupancic, John W.

Disposal of produced waters in the Powder River Basin of Wyoming and Montana is a significant environmental issue for the development of coalbed methane (CBM). High sodium adsorption ratios (SAR) of the waters could degrade agricultural land, especially if directly applied to soil surface. One method of disposing of the produced water, while deriving beneficial use, is subsurface drip irrigation (SDI), where acidified CBM waters are applied year-round to cropland via buried tubing (0.92 m below ground surface).

This research examined the impacts to soil chemistry and shallow groundwater resulting from 3 years of SDI operation at a study site in Johnson County, Wyoming. The site spreads across an alluvial terrace system where depth to groundwater is generally shallow (~3 m). Excess irrigation water led to a rising water table, and even temporarily reached the depth of drip tubing. The rise corresponded to increasing groundwater salinity in some wells. Native magnesium-, sodium- and sulfate-bearing salts in soil contributed more to increased groundwater salinity than evaporated CBM water. Native salts have a laterally heterogeneous distribution in soils but redistribution by rising groundwater generates a more homogenous environment. Solutes in soil were also redistributed vertically, resulting in greatest salt concentrations in soil between drip tubing and the water table due to restricted drainage and root water uptake. Importantly, maximum soil SAR occurred around 0.75 m depth and little increase has occurred at the soil surface, illustrating natural buffering of the system. Results from this research suggest that SDI is a viable method for beneficial use of CBM produced waters, but like all technologies, requires proper management and monitoring.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013