A Phase I ESA and a Phase II ESA answer different questions. Here's what each involves — and the situations in Ontario where a Phase II, and a Record of Site Condition, become mandatory.
An Environmental Site Assessment (ESA) asks one practical question: is this property higher- or lower-risk for contamination? In Ontario it answers that in two stages, and the two stages do different jobs.
A Phase I ESA is a paper-and-eyes review: a search of historical and public records, a site visit, and interviews. Its job is to find out whether any potentially contaminating activity, past or present, has created an area of potential environmental concern. It involves no sampling. A Phase II ESA is the intrusive follow-up — boreholes, monitoring wells, and sampling of soil and groundwater (and, where relevant, sediment, surface water, or soil vapour) to confirm whether contaminants are actually present, and whether they exceed the applicable standards.
| Phase I ESANon-intrusive | Phase II ESAIntrusive | |
|---|---|---|
| Question | Is there a reason to suspect contamination? | Is contamination actually present, and how much? |
| Method | Records review, site reconnaissance, interviews | Boreholes, monitoring wells, soil & groundwater sampling |
| Sampling | Desktop study only | Soil and groundwater — plus sediment, surface water or soil vapour where relevant |
| Output | Potentially contaminating activities and areas of potential environmental concern (APECs) | Measured concentrations compared against the applicable site condition standards |
| Standard | CSA Z768 & O. Reg. 153/04 | CSA Z769 & O. Reg. 153/04 |
The whole point of a Phase I ESA is to answer one question — is this property higher- or lower-risk for contamination? Where it finds a real risk, the Phase I must recommend a Phase II, and for a Record of Site Condition that Phase II is mandatory.
A qualified person must call for a Phase II ESA whenever the Phase I finds any one of three things: the property is an enhanced-investigation property (used, now or in the past, for an industrial operation, a service garage, a fuel or gasoline outlet, or a dry cleaner); a contaminating activity on the property itself, such as a fuel or oil tank, a past spill, or chemical storage; or a contaminating activity off the property that has created an area of potential environmental concern on it. Any single one of the three is enough — they do not all have to apply.
These triggers become a legal requirement when the property needs a Record of Site Condition (see below). A Phase II can also be ordered directly by the Ministry, and is very often required by a lender, a purchase agreement, or a municipal planning condition.
Under O. Reg. 153/04 (section 32), a Phase II ESA is required — not optional — whenever any one of these applies.
| Mandatory trigger | What it looks like on a property |
|---|---|
| An enhanced-investigation usesubject to limited exceptions | Any current or former use of the property (in whole or in part) as an industrial operation, a service garage, a fuel or gasoline outlet (a bulk liquid dispensing facility), or a dry-cleaning operation. |
| A contaminating activity on the property | A fuel or heating-oil tank (above or below ground), chemical, solvent or waste storage, or a past spill or discharge on the site. |
| An off-site activity that has reached the property | A contaminating activity on a neighbouring property that has created an area of potential environmental concern on this one. |
Ontario’s RSC rules changed on 23 October 2025: an RSC can no longer be filed on the basis of a Phase I ESA alone, and certain commercial-to-residential building conversions are now exempt from filing (O. Reg. 236/25, adding s. 11.1 to O. Reg. 153/04). Rules and standards change — confirm the current requirements for your property with a qualified person.
A Record of Site Condition is the province’s formal sign-off that a property is clean enough for its intended use. Under the Environmental Protection Act, one must generally be filed before a property changes to a more sensitive use — commercial or industrial land becoming residential, parkland, institutional, or agricultural — and it is often required before a building permit can be issued.
How long it takes: a Phase II ESA is usually about one to two months. A straightforward Record of Site Condition can take several months from start to filing; where contamination has to be cleaned up, or a risk assessment prepared, the full process commonly runs from roughly four months to well over two years. Provincial review timelines vary — it pays to build this into the schedule early.
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How we help
We complete the Phase I ESA and, if it flags a concern, the Phase II sampling — giving you and your lender a clear picture before you commit.
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As qualified persons we run the Phase I and Phase II, guide any cleanup, and file the Record of Site Condition so your building permit can proceed.
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We scope the assessment to exactly what the authority requires and respond to their comments so the condition is cleared.
← BackAn ESA is only worth what the person signing it can stand behind. Under O. Reg. 153/04 the work has to be led by a qualified person — a licensed professional engineer or geoscientist who meets the regulation’s experience and insurance requirements — and that is who runs your file here, not a technician with a review at the end.
We carry the work through end to end: the Phase I risk screen, the Phase II drilling and sampling where a trigger is present, remediation or risk assessment where the standards are exceeded, and the Record of Site Condition filed on the provincial registry and defended if the Ministry audits it. One team, one chain of accountability.
It also helps that the drilling is ours. On most sites the Phase II boreholes and the geotechnical investigation can be planned as a single program — one mobilization, one drilling cost, and no risk of the environmental and geotechnical pictures of the same ground disagreeing with each other.
A Phase I ESA is a non-intrusive review — historical and public records, a site visit, and interviews — that identifies past and present potentially contaminating activities and any resulting areas of potential environmental concern. It involves no sampling. A Phase II ESA is intrusive: it samples soil and groundwater (and, where relevant, sediment, surface water, or soil vapour) to confirm whether contaminants are actually present and whether they exceed the applicable site condition standards.
When a Phase I ESA finds any one of three things: (1) the property is an enhanced-investigation property — used, now or in the past, for an industrial operation, a service garage, a fuel or gasoline outlet, or a dry cleaner; (2) a contaminating activity on the property itself, such as a fuel or oil tank, a past spill, or chemical storage; or (3) a contaminating activity off the property that has created an area of potential environmental concern on it. Any one of the three makes a Phase II mandatory for a Record of Site Condition (O. Reg. 153/04, section 32), and a Phase II can also be ordered directly by the Ministry.
Usually, yes. A fuel or heating-oil storage tank — above or below ground, in use or abandoned — is a potentially contaminating activity. If a Phase I ESA finds a tank, or evidence of a former one, it is treated as an area of potential environmental concern, which makes a Phase II ESA mandatory before a Record of Site Condition can be filed. Former gas stations, garages, dry cleaners, and industrial uses trigger a mandatory Phase II in the same way.
Under the Environmental Protection Act, an RSC must generally be filed before changing a property from a less sensitive to a more sensitive use — typically commercial or industrial to residential, parkland, institutional, or agricultural — a change often tied to a building permit. As of 23 October 2025, an RSC can no longer be filed on the basis of a Phase I ESA alone, and certain commercial-to-residential building conversions are now exempt, so confirm the current rules for your project.
No. If the Phase I ESA finds no potentially contaminating activity and no area of potential environmental concern, no Phase II is required. A Phase II is triggered only when the Phase I identifies a concern that needs to be confirmed by sampling.
The assessment must be led by a qualified person as defined in the regulation — a licensed professional engineer or professional geoscientist who meets the experience and insurance requirements set out in that regulation.
Yes — Phase I and Phase II ESAs, Record of Site Condition support, and remediation planning, across Markham, the GTA, and Ontario.
General educational information only — not engineering advice for a specific property, and no substitute for the current regulations or the requirements of the conservation authority or approval body having jurisdiction. Standards, allowances, and criteria vary by watershed and authority; confirm for your site with a qualified professional.
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