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Water 2017, 9(6), 385;

Simulating the Fate and Transport of Coal Seam Gas Chemicals in Variably-Saturated Soils Using HYDRUS

CSIRO, Adelaide, SA 5000, Australia
University of California Riverside, Riverside, CA 92521, USA
Department of Earth Sciences, Utrecht University, 3512 JE Utrecht, The Netherlands
NIDES Interdisciplinary Center for Social Development, Federal University of Rio de Janeiro, Rio de Janeiro 21941-901, Brazil
Belgian Nuclear Research Centre, 2400 Mol, Belgium
Author to whom correspondence should be addressed.
Received: 16 April 2017 / Revised: 11 May 2017 / Accepted: 22 May 2017 / Published: 30 May 2017
(This article belongs to the Special Issue Water and Solute Transport in Vadose Zone)
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The HYDRUS-1D and HYDRUS (2D/3D) computer software packages are widely used finite element models for simulating the one-, and two- or three-dimensional movement of water, heat, and multiple solutes in variably-saturated media, respectively. While the standard HYDRUS models consider only the fate and transport of individual solutes or solutes subject to first-order degradation reactions, several specialized HYDRUS add-on modules can simulate far more complex biogeochemical processes. The objective of this paper is to provide a brief overview of the HYDRUS models and their add-on modules, and to demonstrate possible applications of the software to the subsurface fate and transport of chemicals involved in coal seam gas extraction and water management operations. One application uses the standard HYDRUS model to evaluate the natural soil attenuation potential of hydraulic fracturing chemicals and their transformation products in case of an accidental release. By coupling the processes of retardation, first-order degradation and convective-dispersive transport of the biocide bronopol and its degradation products, we demonstrated how natural attenuation reduces initial concentrations by more than a factor of hundred in the top 5 cm of the soil. A second application uses the UnsatChem module to explore the possible use of coal seam gas produced water for sustainable irrigation. Simulations with different irrigation waters (untreated, amended with surface water, and reverse osmosis treated) provided detailed results regarding chemical indicators of soil and plant health, notably SAR, EC and sodium concentrations. A third application uses the HP1 module to analyze trace metal transport involving cation exchange and surface complexation sorption reactions in a soil leached with coal seam gas produced water following some accidental water release scenario. Results show that the main process responsible for trace metal migration in soil is complexation of naturally present trace metals with inorganic ligands such as (bi)carbonate that enter the soil upon infiltration with alkaline produced water. The examples were selected to show how users can tailor the required model complexity to specific needs, such as for rapid screening or risk assessments of various chemicals nder generic soil conditions, or for more detailed site-specific analyses of actual subsurface pollution problems. View Full-Text
Keywords: HYDRUS; coal seam gas; contaminant transport; trace elements; HP1 HYDRUS; coal seam gas; contaminant transport; trace elements; HP1

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Mallants, D.; Šimůnek, J.; Genuchten, M.T.; Jacques, D. Simulating the Fate and Transport of Coal Seam Gas Chemicals in Variably-Saturated Soils Using HYDRUS. Water 2017, 9, 385.

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