Integrated modelling for exposure assessment: A methodology applied to assessing the impact of produced water on Sable Bank (Scotian Shelf, Canada)

Produced water is the largest volume waste stream component of the offshore oil and gas industry. Produced water is a complex, and variable mixture of metals, dispersed hydrocarbons, dissolved hydrocarbons, and organic acids. The prediction of chemical fate and effects in the marine environment is extremely important to mitigate adverse effects on the Scotian Shelf. Modelling provides an examination of dispersion and possible environmental partitioning. The modelling results indicated the spatial extent of contamination (exposure) and the marine communities that should be examined during monitoring studies.; The integrated exposure modelling approach for this study followed the ecological risk assessment framework (EPA, 1998). This study was used to develop an iterative modelling approach that allowed the characterization of risk for the local marine ecosystem based on toxic endpoints and effects.; Analysis of environmental effects is developed through an integrated exposure modelling approach. The CORMIX was used to model hydrodynamic dispersion, which described the physical pathways a wastewater plume followed for the Sable Island Bank region of the Scotian Shelf. Fugacity modelling was used to considered the physical-chemical properties of toxic components of produced water, namely benzene and naphthalene. The partitioning model described likely partitioning in environmental media—water, suspended sediment, biota and sediment based on advection times.; Dispersion and partitioning indicated that the risk for adverse effects from produced water was small. Rapid dilution of the produced water constituents led to low risk after a distance of about 1.0 meter for all modelling cases. The persistence of benzene and naphthalene were also seen to be of low risk to the benthic boundary layer. This led to the conclusion that risk to marine biota in the water column from produced water effluent on the Scotian Shelf is low.