Impact of Applying Spent Bentonite Drilling Mud on Soil Properties.

The US shale oil and gas industry uses horizontal directional drilling (HDD) to install pipelines under ecologically sensitive areas (wetlands, rivers, etc.) or heavily used commercial infrastructure (railroad, highways). HDD operations produce spent bentonite drilling mud as a waste product. Using the spent bentonite mud as a soil amendment is a cost-effective way for its disposal. We examined the potential impact of spent HDD mud on properties of 17 different soils amended with the mud at different application rates (up to 10%, dry weight basis). Soil solution was analyzed for total dissolved solids, sodium and ionic and elemental composition, and SAR. Although soil salinity and SAR increased with application rate, they remained below levels considered detrimental to yield of sensitive plants or to soil structure.