As part of the redevelopment of a former heavy industrial site into a mixed-use residential and commercial project in Gatineau (Quebec), along the Ottawa River, HDS Environment conducted toxicological and ecotoxicological risk assessments, along with an impact analysis on groundwater and surface water. The study aimed to confirm the feasibility of leaving certain contaminated soils in place under existing structures while implementing mitigation and monitoring measures.
The site contained contaminated soils exceeding applicable limit values for future use. However, several contaminated zones were located beneath existing buildings (including several heritage structures) where demolition was not an option. This limited conventional remediation paths and required a demonstration through risk assessment.
The approach had to consider numerous exposure pathways (on-site and off-site), specifically mechanisms related to dust/resuspension and transfers to other media, involving both human receptors (workers, residents) and ecological receptors (vegetation, invertebrates, birds, small mammals).
The study had to be integrated into a previously submitted and revised remediation plan, providing a robust and documented demonstration to secure ministerial approval. It also required distinguishing between contaminants that could be managed via risk assessment and those requiring conventional treatment.
HDS compiled and interpreted over ten years of environmental soil and groundwater data to identify contaminants manageable through risk assessment. The evaluation integrated on-site and off-site exposure scenarios for workers and residents, utilizing a conceptual exposure model and a conservative approach based on robust statistics (e.g., 95% Upper Confidence Limit).
HDS performed an ecological characterization of the sector and structured the analysis by receptors (plants, invertebrates, birds, small mammals). Laboratory bioassays (plants and invertebrates) and tissue analysis were used to complement the modeling, anchoring the interpretation in observable and measurable biological effects.
Following the compilation and interpretation of all results, HDS proposed a mitigation plan to manage the contaminated soils left in place. This plan integrated containment measures, land-use restrictions, and environmental monitoring. Additionally, HDS supported the client in administrative dealings with various stakeholders (Ministry, municipality, public meetings, etc.) to ensure project acceptance.
The risk assessment confirmed the feasibility of a safe and acceptable redevelopment by reducing the need for widespread excavation, particularly in areas constrained by heritage buildings. This allowed the project to move forward with a realistic, technically defensible management strategy to revitalize the neighborhood.
The process provided a clear profile of risks (human health, ecology, water), supported by conservative assumptions, conceptual models, and bioassays. The mitigation recommendations translated these results into concrete measures, facilitating their integration into the remediation plan for final approval.
By combining containment, use restrictions, and a monitoring program (including registries), the project secures the long-term management of soils left in place. This ensures risk control over time while protecting future users and the surrounding receiving environment.
HDS reduces the environmental impact of road de-icing salts for a public agency: audits of 10 CEMS, water sampling, and action plans.
Industrial hygiene services provided by HDS for a northern mining company: assessment of living and production facilities to ensure compliance.
