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Open AccessArticle

A Generic Method for Predicting Environmental Concentrations of Hydraulic Fracturing Chemicals in Soil and Shallow Groundwater

1
CSIRO Land Water, Glen Osmond, SA 5064, Australia
2
CSIRO Land Water, Floreat, WA 6014, Australia
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Departamento de Engenharia Sanitária e Ambiental, Federal University of Santa Catarina, Florianópolis 88040, Brazil
4
Schmidt Institute of Physics of the Earth of Russian Academy of Sciences, Moscow 123242, Russia
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Department of Agriculture, Water and the Environment, Australian Government, Canberra 2600, Australia
*
Author to whom correspondence should be addressed.
Water 2020, 12(4), 941; https://doi.org/10.3390/w12040941
Received: 19 February 2020 / Revised: 22 March 2020 / Accepted: 23 March 2020 / Published: 26 March 2020
(This article belongs to the Section Water Quality and Ecosystems)
Source-pathway-receptor analyses involving solute migration pathways through soil and shallow groundwater are typically undertaken to assess how people and the environment could come into contact with chemicals associated with coal seam gas operations. For the potential short-term and long-term release of coal seam gas fluids from storage ponds, solute concentration and dilution factors have been calculated using a water flow and solute transport modelling framework for an unsaturated zone-shallow groundwater system. Uncertainty about dilution factors was quantified for a range of system parameters: (i) leakage rates from storage ponds combined with recharge rates, (ii) a broad combination of soil and groundwater properties, and (iii) a series of increasing travel distances through soil and groundwater. Calculated dilution factors in the soil increased from sand to loam soil and increased with an increasing recharge rate, while dilution decreased for a decreasing leak rate and leak duration. In groundwater, dilution factors increase with increasing aquifer hydraulic conductivity and riverbed conductance. For a hypothetical leak duration of three years, the combined soil and groundwater dilution factors are larger than 6980 for more than 99.97% of bores that are likely to be farther than 100 m from the source. Dilution factors were more sensitive to uncertainty in leak rates than recharge rates. Based on this dilution factor, a comparison of groundwater predicted environmental concentrations and predicted no-effect concentrations for a subset of hydraulic fracturing chemicals used in Australia revealed that for all but two of the evaluated chemicals the estimated groundwater concentration (for a hypothetical water bore at 100 m from the solute source) is smaller than the no-effect concentration for the protection of aquatic ecosystems. View Full-Text
Keywords: coal seam gas; hydraulic fracturing; source-pathway-receptor modelling; solute transport; soil and groundwater pathways; dilution factors coal seam gas; hydraulic fracturing; source-pathway-receptor modelling; solute transport; soil and groundwater pathways; dilution factors
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Mallants, D.; Bekele, E.; Schmid, W.; Miotlinski, K.; Taylor, A.; Gerke, K.; Gray, B. A Generic Method for Predicting Environmental Concentrations of Hydraulic Fracturing Chemicals in Soil and Shallow Groundwater. Water 2020, 12, 941.

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