Total petroleum hydrocarbon degradation and BTEX leaching in soils after application of oil-base drilling mud: Impact of application rate, rainfall regime, and time

Authors: WHITAKER, A - North Carolina State University; Penn, Chad

Submitted to: Modern Approaches in Oceanography and Petrochemical Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2018
Publication Date: 2/16/2018
Citation: Whitaker, A.H., Penn, C.J. 2018. Total petroleum hydrocarbon degradation and BTEX leaching in soils after application of oil-base drilling mud: Impact of application rate, rainfall regime, and time. Modern Approaches in Oceanography and Petrochemical Sciences. 1(2):1-13. https://doi.org/10.32474/MAOPS.2018.01.000107.
DOI: https://doi.org/10.32474/MAOPS.2018.01.000107

Interpretive Summary: Increases in oil and gas drilling have resulted in large quantities of oil base “mud” (OBM) to be disposed of. Land application of OBM to agricultural land is a common disposal technique that presents agronomic and environmental challenges since the material is rich in total petroleum hydrocarbons (TPH). Leaching of lower molecular weight hydrocarbons, mainly benzene, toluene, ethylbenzene, and xylene (BTEX), is a concern due to being somewhat soluble in water. The objective of this study was to determine the effect of rainfall amount, timing, and TPH loading rate on TPH degradation and BTEX leaching after OBM application. A soil column study was conducted where OBM was applied at five loading rates (0, 22,000, 45,000, 67,000, and 90,000 kg TPH/ha-1) and was subjected to four moisture regimes where different amounts of rainfall was simulated. Leachate was collected and tested for BTEX, and OBM samples were taken at different times and tested for TPH degradation and BTEX. After 60 days, a maximum TPH degradation of 35% was measured. The highest benzene concentrations measured in leachate were still below EPA drinking water quality standards. While increased application of OBM increased BTEX leaching, BTEX chemicals were no longer detectable after 28 days. Under these worst case conditions, there was little risk of BTEX leaching from land applied OBM. This research directly impacts the oil industry, agricultural producers, and environmental quality organizations.

Technical Abstract: Increases in oil and gas drilling have resulted in large quantities of oil base “mud” (OBM) to be disposed of. Land application of OBM to agricultural land is a common disposal technique that presents agronomic and environmental challenges since the material is rich in total petroleum hydrocarbons (TPH). Leaching of lower molecular weight hydrocarbons, mainly benzene, toluene, ethylbenzene, and xylene (BTEX), is a concern due to their relatively low octanol:water partition coefficients. The objective of this study was to determine the effect of rainfall regime and TPH loading rate on TPH degradation and BTEX leaching after OBM application. An OBM was characterized for TPH, BTEX, and trace metals. A soil column study was conducted where OBM was applied at five loading rates (0, 22,000, 45,000, 67,000, and 90,000 kg TPH/ha-1) and was subjected to four moisture regimes. OBM samples were taken at day 0, 7, 30, 60, and 91 to monitor TPH degradation. Leachate samples were taken at day 0, 14, 28, 35, 49, 56, 63, 77, and 84 to monitor electrical conductivity (EC), pH, metal concentrations, and BTEX concentrations. After 60 days, a maximum TPH degradation of 35% was measured. Leachate BTEX concentrations increased as TPH application rate increased and was mostly undetectable by day 28. Leachate EC increased over time and with increasing TPH rates. TPH rate had no effect on leachate pH. OBM loading rates had the greatest effect on TPH degradation and BTEX leaching. Under our experimental conditions, little risk of BTEX leaching from land applied OBM was observed.