When managing a site in Ontario, it is essential to understand Ontario Regulation 153/04 and the environmental due diligence it requires.

What Is A CSM?

A Conceptual Site Model (CSM) is one of the requirements that shapes the Environmental Site Assessment (ESA) process (both Phase I and II) and is required for a Record of Site Condition (RSC). Essentially, a CSM is a summary of conditions at a site which:

1. Identifies the type of all potential sources of contamination

3. Identifies the location of all potential sources of contamination
4. Identifies how and where people, plants or animals may be exposed to the contamination

Why You May Need A CSM:

The CSM clearly articulates the project team’s (including Qualified Person, project engineers, field scientists, and others) understanding of the site’s environmental system framework, impacts and associated potential risks.

Initially, this understanding is a well-supported hypothesis based on available data coupled with an honest recognition of all significant gaps in the model, relying heavily upon the use of assumptions. As additional data is collected and the team’s understanding is refined, the hypothesis moves toward a well-understood and defensible model that can be confidently relied upon for remedial decision-making.

The CSM serves three purposes:

1. Creates a descriptive interpretation of the site using all available and relevant site data, including a comprehensive explanation of distribution/delineation of contaminants of concern (COCs), the source area(s), geologic/hydrogeologic conditions, fate and transport of COCs, potential health and/or environmental risks associated with COCs and remedial measures installed and/or planned to remediate COCs and their associated potential risks;

2. Highlights data gaps that may affect the understanding of the site conditions as the team moves towards site assessment, remediation, and closure;

3. Forms the basis for development, refinement and implementation of the site closure approach and selection of a remediation strategy.

The CSM is primarily a descriptive written document which is submitted as part of a RSC and is supported by maps, drawings, site plans, and cross-sections. These are especially helpful on complex or large sites where the volume of information may be overwhelming or hard to interpret.

What AEL Recommends Including In A CSM:

AEL recommends that the following site-specific information, as well as all necessary supporting data, is included in the CSM:

1. A brief background section identifying site location, uses, ownership; regulatory framework; cleanup responsibilities, and/or any other introductory items that could be pertinent to the overall closure process:

2. Identification and characterization of the possible sources of contaminants, and their features;

3. Identification of COCs and geochemical factors affecting fate and transport and/or remedy selection;

4. Understanding of the lithologic, stratigraphic, and hydrogeologic aspects of the subsurface;

5. Delineation of the COCs in the subsurface;

6. Understanding of fate and transport of the COCs;

7. Identification of potential receptors (human and ecological) and the potential risks associated with the presence or transport of the COCs on those potential receptors;

8. Identification of data gaps that could significantly affect remedy selection and design, and/or site closure; and

9. Description of the past/current/planned remedial action(s) and an evaluation of their effectiveness.

Important CSM Considerations:

One other important consideration when beginning to develop a CSM is to identify the goals that the site owner has for the site. As an RSC is generally required when a site transitions from a less sensitive to more sensitive land use, it can be helpful to explain what the site will be used for. Understanding these goals and communicating them clearly to the project team will ensure that the RSC process leads to achieving the site owner’s goals.

Looking Ahead:

Over time, the CSM will be refined. The data gaps will be addressed, new site data will be incorporated and used to accept or reject assumptions made in the CSM.

Having a clear understanding of the requirements and purposes of a CSM is critical to successfully navigating the RSC process under Ontario Regulation 153.

If you still have questions about CSM, feel free to contact us.