Soil Science Society of America

Hydraulic properties of a sandy loam soil following spent drilling mud application on native prairie

Water-based drilling mud (WBM) systems are used by the petroleum industry during drilling of oil and natural gas wells. Provincial regulations in western Canada allow disposal of spent WBM on cropland and sometimes native prairie at low rates. There is concern, however, that application of drilling waste on native prairie in semiarid climates may alter soil properties, which may adversely affect soil biophysical processes and overall ecosystem productivity. This study was initiated to examine the effects of single and multiple applications of differential rates (0, 40, and 80 m3 ha–1) of summer-applied WBM on hydraulic conductivity (K{psi}) and macropore indices. Results from unconfined, steady-state infiltration measurements taken at –0.03- and –0.01-m supply pressure potentials ({psi}) at the soil surface provide evidence of a significant alteration of these hydraulic parameters with excessive (80 m3 ha–1) drilling mud application. Across the {psi} range investigated, K{psi} measured 5 to 7 wk after a single mud application and the effective water-transmission macroporosity ({theta}{Delta}{psi}) calculated using the K{psi} decreased by 54 and 61%, respectively, at 80 m3 ha–1 compared with the control (0) and 40 m3 ha–1 rates. Corresponding decreases 5 to 8 wk after a third annual mud application were 62 and 72%. While the rate effect had disappeared 1 yr after the single application, the effect of three annual applications persisted into the following summer. By modifying soil hydrophysical properties, excessive drilling mud applications may adversely affect the soil water balance and alter the plant community structure in this sensitive ecosystem, with important implications on overall biological productivity.

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