Does My Severance Need a Hydrogeological Study?
A landowner’s guide to the questions that decide it, before you file the consent application.
Whether a severance needs a hydrogeological study comes down to three things: how the new lot will get water and treat sewage, how big the lots are, and what your municipality's Official Plan says. If you can answer those before you file the consent application, you will know whether to budget for a study and how much field work it is likely to need.
The short answer
| Your situation | Likely answer |
|---|---|
| New lot on municipal water and municipal sewer | Usually no study under the provincial guidelines; confirm with the municipality |
| New lot on a private well and septic system, under 1 ha | Usually yes, covering both the well and the septic system |
| New lot on a private well and septic system, 1 ha or more | Often a shorter study; the well still has to be shown to work |
| Several lots from one parcel, or an area with known well problems | Yes, and expect closer review |
Question 1: how will the new lot be serviced?
The two provincial guidelines that severance studies follow are both about private services. Guideline D-5-5 covers private wells: can each lot get enough water of acceptable quality? Guideline D-5-4 covers individual on-site sewage systems: will nitrate from the septic system stay within acceptable limits in the groundwater? If the new lot connects to municipal water and sewer, neither question arises, although a municipality can still ask for groundwater information for other reasons, such as a basement close to the water table.
Question 2: how big are the lots?
Lot size decides how far the septic assessment has to go. Under D-5-4, lots of one hectare or more are considered acceptable in most cases, and a development whose lots average one hectare, with none under 0.8 ha, may not need a detailed assessment if a qualified consultant shows the area is not hydrogeologically sensitive. That opinion is still a short study, and it does not replace the well test. Below those sizes, the consultant has to show that septic effluent is isolated from the aquifers people drink from, or predict the nitrate concentration at the property boundary.
Question 3: what does your Official Plan say?
D-5-4 applies formally to developments of more than five units, but it encourages municipalities to apply it to consents, and many have written their own triggers. A few examples from Official Plans and guidelines we have read:
| Municipality | Local rule |
|---|---|
| Ottawa | A hydrogeological report is required before lot creation; at least one well is tested, and up to one test well per lot where results are marginal (City of Ottawa Hydrogeological and Terrain Analysis Guidelines, 2021, section 4) |
| Belleville | A study may be required for a consent on private services in an area of known groundwater concern, or where 5 or more dwellings or lots of 4 ha or less lie within 300 m of the new lot (Belleville Official Plan, s. 7.2.1 c) |
| Kawartha Lakes | Hamlet lots on private services should be at least 4,000 m², with a D-5-5 study as the basis for density (Kawartha Lakes Official Plan, s. 19.3.13) |
| District of Muskoka | An assessment is generally required on groundwater for more than five lots with some under 1.0 ha, in areas of known water shortage or quality concerns, or on a lot under 1.0 ha where cumulative impacts are a concern (Muskoka Official Plan s. D15.5) |
Belleville's test is worth copying even where it does not apply: counting the homes and small lots within 300 m of your proposed lot line is a quick way to see whether the neighbourhood is already dense on wells and septic systems.
What the study would actually test
- The well. A pumping test of at least six hours at a fixed rate, recovery monitoring, and a water sample taken near the end of the test, analysed for physical, chemical and bacteriological parameters.
- The septic system. Whether effluent is isolated from supply aquifers and, if not, whether nitrate-nitrogen at the downgradient property boundary stays at or below 10 mg/L.
- The surroundings. Land uses within at least 500 m and, where they exist, nearby wells surveyed and sampled.
Our severance hydrogeological study page sets out the test rates, the three D-5-4 steps and what a study typically costs.
How to find out for your lot
- Read the servicing policies. Search your municipality's Official Plan for "hydrogeological", "private services" and "consent". Rural and hamlet designations usually carry the triggers.
- Book pre-consultation. Ask the planner three things: is a hydrogeological study required, does it need to cover the retained lot as well as the new one, and will it be peer reviewed.
- Gather what exists. Well records for wells on and near the property, any septic permit, and a sketch of where the new lot, house, well and septic bed would go.
- Check the lot layout. Under 1 ha, or close to many existing homes, expect the full septic assessment. Adjusting the lot line before filing can sometimes change that.
Related questions
The land I am severing already has a house with a well. Does that help?
Often: Guideline D-5-5 requires at least one test well on the site, new or existing, and allows existing wells nearby to be used where they meet the guideline's requirements. An existing drilled well with a record and good access can sometimes be tested instead of drilling a new one, which shortens the field work.
Who decides whether my consent needs a study?
The municipality or planning board that approves the consent decides, often with its own peer reviewer. D-5-4 notes that the ministry does not normally review proposals of five or fewer lots and encourages municipalities to apply the guideline to consents and severances, which is why the local Official Plan and pre-consultation matter more than the provincial text.
Can I leave the study until after the consent is approved?
Usually not: D-5-5 asks that the availability of a potable water supply be determined as early as possible in the severance approval process, and some municipalities say so directly: Ottawa staff may recommend preparing the hydrogeological report before the application where an area has known issues.
The new lot will have municipal water but a septic system. Which guideline applies?
Only the septic guideline applies: D-5-5 deals with private wells, so a lot on municipal water does not need a well test; D-5-4 deals with individual on-site sewage systems, so the question of nitrate reaching groundwater can still be asked if the lot is small or the area is sensitive.
Where to go next
- Severance Hydrogeological Study (D-5-4 / D-5-5): scope, cost and what the reviewer checks
- Hydrogeological study Belleville: local rules, data and costs
- Hydrogeological study Kawartha Lakes: local rules, data and costs
- Hydrogeological study Ottawa: local rules, data and costs
- Water balance assessments explained
- D-5-4 nitrate impact assessment explained
Sources
- D-5-5 Private wells: water supply assessment (opens in a new tab), Government of Ontario (MECP).
- D-5-4 Individual on-site sewage systems: water quality impact risk assessment (opens in a new tab), Government of Ontario (MECP).
- Hydrogeological and Terrain Analysis Guidelines (March 2021) (opens in a new tab), City of Ottawa.
- Official Plan, By-law 2021-180 (office consolidation, July 2026) (opens in a new tab), City of Belleville.
- Official Plan, 2012 (March 2025 office consolidation) (opens in a new tab), City of Kawartha Lakes.
- Muskoka Official Plan (office consolidation, June 2025), sections C2.6 Lake System Health and D15.5 individual on-site services (opens in a new tab), District Municipality of Muskoka.