2011 Synthesis of SAR/Hydraulic Conductivity Data from Multiple Column Studies Coupled with Three-Dimensional Transport Modeling to Support Framework for Subsoil SAR Guidelines

Increases in Sodium Adsorption Ratio (SAR) may result in swelling and/or dispersion of clayey soils and consequent loss of hydraulic conductivity.  This may lead to reduced infiltration or ‘hard-pan’ with elevated SAR in root-zone soils, or detrimental changes in water-table (water-logging) with elevated SAR in subsoil.  Equilibrium Environmental has been involved in numerous (and ongoing) column studies for evaluating the effects of EC/SAR combinations on hydraulic conductivity for a variety of soil types.  This project proposes to synthesize the results of these numerous column studies to generate an algorithm for predicting the relative loss of hydraulic conductivity based on EC, SAR, and soil type.  The potential effects of these hydraulic conductivity losses on water table can then be modeled in three dimensions using a program such as MODFLOW as a function of factors such as impact depth and size, and original water table level.  Ultimately, SAR/EC combinations which do not produce unacceptable changes in modeled water table could be used as a framework for subsoil SAR guidelines.  This project builds on previous SAR research performed by Equilibrium in conjunction with PERD and AUPRF funding as well as synergizing with various SAR risk assessments for the oil and gas industry.  Where supplementary analytical work is required from associated column experiments, in-kind support from Exova in terms of preferred analytical rates is available.

Industry would benefit from this project in terms of reduced investigation and remediation costs as well as improved environmental performance.  Subsoil SAR currently has inadequately refined guidelines which may lead to over-remediation of certain sites or the inability to generate effective remediation or risk management plans on other sites due to a lack of appropriate risk-based guidelines.  Risk-based subsoil SAR guidelines could be based on factors such as soil type, EC, impact depth, dimensions, and background salinity depending on the desired degree of conservatism and guideline complexity.  Results from this project will be presented to PTAC and Alberta Environment including recommendations for subsoil SAR guidelines.

Policy issue: Additional Science for the Refinement of Regulatory Guidelines/Directives/Policies/Criteria.

Knowledge gap:  Several funded projects in the previous years have addressed various salinity-related projects, with various aspects of subsoil SAR being significant knowledge gaps in this area.