Alternative Process for Developing a Tier 2 SSRO

Gladys Stephenson
GL 09-9193-50

Currently, there is a provision in the draft Alberta Tier 2 guidance document for development of a Tier 2 sitespecific remedial objective(s) (SSRO) for PHCs in soil; however, in practice only the pass/fail approach applied to remediated PHC-contaminated soils has been used successfully to secure site closure. The current pass/fail process involves a post-remediation ecotoxicity assessment to demonstrate minimal risk to ecological receptors via the soil contact exposure pathway for in situ contamination. The objective of this project is to review the results of a minimum of 10 Tier 2 pass/fail ecotoxicity assessments to determine a process for deriving SSROs should the site samples fail to satisfy the Tier 2 criteria for specific land uses.

Depending on the size and complexity of a site, members of the oil and gas industry can pay up to 160K for an ecotoxicity assessment of a remediated site with PHC contamination. Should the ecotoxicity assessment indicate that the soils on the site do not satisfy the “pass/fail” criteria, further remedial activities are required for those soils with the hope that they will then pass a second ecotoxicity assessment. The Tier 2 ecotoxicity assessment generates between 11 (minimum requirement) and 36 endpoints depending primarily on the number of site soil samples tested. The proposed project will develop a process to derive SSROs for the PHC fractions of concern using A) endpoint sensitivity distributions of the geometric means for all endpoints; and B) general linear or non-linear models to integrate data and predict impairment concentrations for sites with multiple contaminants of concern (COCs). The program will include a process for verifying the efficacy of the derived SSRO in order to mitigate the necessity for a second ecotoxicity assessment for the same site samples. The process should overcome some of the current limitations inherent in the current Tier 2 pass/fail approach and reduce remedial costs. If accepted and effective, the process could impact the current regulatory remediation guidelines.

Policy Issue
Risk Assessment Cost Reduction. Identify areas where the board application of risk assessment strategies may reduce the required management/remediation efforts.

Knowledge Gap
Application of different measures of bioavailability to support the derivation of risk-based (Tier 2) remedial benchmarks for PHC contaminated sites.

Final Report