Tier 2 Guideline Adjustment and Pathway Options for Contaminated Sites in Alberta

Once a site has been assessed against generic Tier 1 values, the next question is whether site-specific information can justify a different remediation objective without imposing land or water use restrictions. This course gives hands-on user guidance for that step. It identifies the site conditions that make Tier 2 mandatory, such as volatile sources near foundations, coarse or fractured materials and contamination close to surface water, and the conditions that rule Tier 2 out. It then works through each exposure pathway in turn, from direct soil contact and vapour inhalation to potable groundwater, aquatic life, livestock, irrigation and wildlife watering, setting out which can be excluded, which can be adjusted and which must always be treated as operative.

The second half focuses on Tier 2 Guideline Adjustment itself. It explains the three criteria that adjustable parameters must meet, the difference between primary and secondary adjustable parameters, and the limited cases where horizontal offsets are allowed. Practical requirements follow for measuring physical soil properties, hydrogeological conditions, source dimensions and receptor distances, including why single measurements and mean values are not acceptable. The course closes with recalculation of objectives using the Tier 1 models, determination of the governing objective, the Tier 2 decision process and the point at which Site-Specific Risk Assessment (SSRA) or Exposure Control becomes the better route.

What Will Be Covered:

• Site conditions that require a Tier 2 approach and conditions that preclude it

• Eligibility of each human health and ecological exposure pathway for exclusion or adjustment

• Exclusion of the potable groundwater pathway where no Domestic Use Aquifer (DUA) or an isolating layer is present

• The 300 m and 10 m offset rules for aquatic life and wildlife watering, including plume stability and Darcy velocity limits

• Livestock watering and irrigation pathways and the role of surficial dugouts on agricultural land

• Criteria for Tier 2 Guideline Adjustment and primary versus secondary adjustable parameters

• Data collection for soil properties, hydrogeological conditions, source dimensions and receptor distances

• Recalculation of soil and groundwater objectives and determination of the governing objective

• The Tier 2 decision process and when to move to Site-Specific Risk Assessment or Exposure Control