CCME Updates Canadian Groundwater Quality Guidelines
CCME Updates Canadian Groundwater Quality Guidelines
The Canadian Council of Ministers of the Environment (CCME, 2026) has released an updated version of the Canadian Groundwater Quality Guidelines for the Protection of Environmental and Human Health. These guidelines provide a nationally consistent framework for assessing and remediating groundwater contamination at contaminated sites to be protective of human health and the environment.
Groundwater quality is a key consideration during environmental site assessments, risk assessments, brownfield redevelopment, and remediation planning. The updated guidelines reflect advances in contaminant transport modelling, toxicology, groundwater management, and vapour intrusion science since the publication of the previous CCME protocol.
This article provides an overview of why the new groundwater quality guidelines were developed, summarizes the key updates, and discusses what they mean for environmental practitioners.
Why were the new groundwater quality guidelines released?
The 2015 publication of the CCME Protocol for the Derivation of Groundwater Quality Guidelines for Use at Contaminated Sites has since been superseded by methodological improvements reflecting advances in groundwater fate and transport modelling, vapour intrusion assessment, toxicological science, and environmental risk evaluation. CCME (2021) initially implemented this updated approach in the development of its groundwater and soil guidelines for perfluorooctanesulfonic acid (PFOS) and has subsequently expanded its application to establish guidelines for 99 additional contaminants of concern.
Beyond expanding contaminant coverage, the update improves consistency across jurisdictions, better identifies situations where free-phase product may be present, and refines vapour intrusion evaluation to reflect current human health and ecological risk assessment practices.
What information does the guideline provide?
For each of the 99 contaminants, the CCME evaluates multiple human health and ecological groundwater exposure pathways and selects the most conservative (lowest) value as the final guideline. Values are calculated based on land use, and where applicable, soil texture (coarse versus fine grained).
As with the 2021 PFOS groundwater guidance, these guidelines support contaminated site assessment and are expected to be adopted or referenced by provincial and territorial regulators over time.
Key updates in the new guidelines
While the overall purpose of the guidelines remains unchanged, several important scientific and technical updates have been incorporated. Three of the most significant changes are summarized below.
- New groundwater management limits based on contaminant solubility
One of the most significant additions is the introduction of groundwater management limits for each contaminant. These limits are based on aqueous solubility and are intended to identify situations where free-phase product (non-aqueous phase liquid, or NAPL) may be present.
As a general guideline:
- Contaminants expected to form a light non-aqueous phase liquid (LNAPL) should generally not exceed 50% of their aqueous solubility.
- Contaminants expected to form a dense non-aqueous phase liquid (DNAPL) should generally not exceed 10% of their aqueous solubility.
CCME further clarifies that a contaminant’s potential to exist as DNAPL should be evaluated based on its density rather than its molecular weight.
These management limits are screening tools that identify the potential presence of free-phase product, which may require additional investigation and invalidate assumptions used in groundwater transport modelling.
- Updated groundwater transport modelling
One of the more technical updates involves how contaminant transport is modelled during guideline development.
Previous groundwater quality guidelines modelled contaminant transport to a theoretical worst-case, steady-state condition, which could span tens of thousands of years for slow-moving contaminants. The updated guidelines use the same Domenico (1987) model but apply a fixed 500-year modelling period instead.
CCME’s rationale for this approach is that remediation decisions should not be driven by contaminant impacts that may not occur for centuries, recognizing continued advances in remediation technologies and natural attenuation.
While this represents a more realistic approach to groundwater contaminant migration, it also means the new guidelines are intended to represent protection within a defined 500-year assessment period rather than under all future conditions.
- A more chemical-specific approach to vapour intrusion
The updated guidelines also introduce a more refined approach to evaluating indoor air exposure from groundwater vapour intrusion. Previous commercial and industrial guideline development generally applied dose-averaging with a standard exposure term (ET=0.27) to account for intermittent workplace exposure. Under the new groundwater guideline protocol, the CCME instead evaluates dose averaging on a chemical specific basis.
For contaminants with toxicity reference values associated with reproductive or developmental effects, no dose averaging is used as a precautionary measure (ET=1). For other threshold contaminants, the CCME compares calculated indoor air concentrations against available air quality benchmarks from California and Ontario. Where calculated concentrations exceed these benchmarks, or where suitable benchmarks are unavailable, no dose averaging is applied (ET=1). Dose averaging (ET=0.27) is utilized only where available evidence demonstrates that this approach remains protective.
As a result, dose averaging is no longer applied uniformly. For contaminants with more sensitive toxicological endpoints, the updated methodology may produce more conservative groundwater guideline values than those derived under the previous approach.
What do these updates mean for environmental professionals?
The CCME’s (2026) Canadian Groundwater Quality Guidelines present the current best practices for contaminated site assessment and groundwater risk evaluation in Canada.
Environmental consultants, risk assessors, developers, and regulators should be aware that the updated guidance:
- Introduces groundwater management limits to help identify potential free-phase product.
- Incorporates updated contaminant transport modelling based on a 500-year assessment period.
- Applies a more refined, chemical-specific approach to vapour intrusion assessment.
- Reflects current toxicological information and human health risk assessment practices.
- Provides a stronger scientific foundation for groundwater assessment across Canada.
As Canadian provinces and territories review and adopt these guidelines, practitioners should become familiar with the changes and consider how they may influence future environmental investigations, remediation planning, and contaminated site risk assessments.
Resources
CCME. 2021. Scientific Criteria Document for the Development of the Canadian Soil and Groundwater Quality Guidelines for the Protection of Environmental and Human Health. Perfluorooctane Sulfonate (PFOS). PN 1625. ISBN 978-1-77202-075-5. Available at: https://ccme.ca/en/res/pfossoilandgroundwaterqualityguidelinesscden.pdf
CCME. 2026. Canadian Groundwater Quality Guidelines for the Protection of Environmental and Human Health. PN 1660 ISBN 978-1-77202-102-8. Available at: https://ccme.ca/en/res/canadiangroundwaterqualityguidelines-en.pdf