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What’s in a Hydrogeological Report

A section-by-section reading guide, with an annotated mock-up of a typical report.

A hydrogeological report follows a fairly standard order, because most municipal terms of reference ask for the same building blocks. Knowing what each section is for helps you check a draft before it goes to the municipality, and spot the gaps reviewers most often send back. The mock-up below shows where each part usually sits; the numbers match the sections that follow.

Annotated mock-up of a hydrogeological report (illustrative) An illustrative report page with numbered parts: a summary box with key numbers, a site plan showing monitoring wells and the study area, a table of water levels by date, a cross-section of soil layers with the water table, an impact assessment section and a signature and seal block. Not a real report. ILLUSTRATIVE MOCK-UP: NOT A REAL REPORT 1 Summary of key numbers 2 Study area and site plan 3 Boreholes and monitoring wells 4 Water levels over the seasons 5 Cross-section and water table 6 Impacts and mitigation 7 Signature and seal
Illustrative mock-up only. Not a real site or report; the layout varies by consultant and by what the terms of reference ask for.

Annotated mock-up of a hydrogeological report (illustrative)

Scroll sideways to see the whole diagram, or turn your phone for a wider view.

1. Summary of key numbers

The first page should let a reviewer find the answers without reading the whole report. Hamilton's urban guidelines are the most specific on this: the executive summary has to give the number of wells, flow direction, the highest measured and estimated seasonal high water levels in metres above sea level and below ground, the lowest finished floor, dewatering volumes and peak flow, groundwater quality against the sewer limits, and whether an EASR registration or Permit to Take Water applies.

2. Purpose, site and study area

This section says what the report supports (a severance, a site plan, a dewatering registration), names the terms of reference it follows and describes the site and proposal. York Region's terms of reference for hydrogeological reports set the study area as the largest possible zone of influence of the groundwater taking or source of contamination, with existing conditions described within 500 m. Clearview's terms of reference ask for water wells within 500 m plotted from the provincial records. A study area that stops at the property line is a common reason for a report to come back.

3. Field program: boreholes and monitoring wells

Here the report lists what was drilled, where and why, with the borehole logs and well construction details in an appendix. Expect the number and depth of wells to follow the local rules. Brampton's terms of reference ask for at least three monitoring wells reaching at least 2 m below the lowest proposed structure, and Hamilton sets minimum well counts by building type. A site plan should show every borehole and well, the property lines, the proposed buildings and the study area.

4. Groundwater levels and flow

A table of water levels in each well on each date, the groundwater elevations, and a contour map or arrows showing flow direction. This is where the seasonal high comes from, so the monitoring period matters: York Region asks for four-season monitoring including seasonally and historically high levels, and Lake Simcoe Region Conservation Authority's hydrogeology page says it generally expects at least 12 continuous months to support a planning application. Where the record is shorter, the report should explain how the seasonal high was estimated.

5. Geology, testing and water quality

The cross-sections show the soil and rock layers, the aquifers and the water table against the proposed excavation. The hydraulic testing that follows turns those layers into numbers: Richmond Hill's requirements ask for single-well response tests in the formations dewatering will affect, and longer pumping tests where yield or interference is the question. Water quality results, compared with the relevant standards or sewer limits, decide where pumped water can be discharged and whether treatment is needed.

6. Impact assessment and mitigation

This is the part the reviewer reads most closely. Depending on the project it covers:

  • dewatering rates and the zone of influence, with the assumptions shown;
  • effects on nearby private and municipal wells;
  • effects on wetlands, streams and recharge, often with a water balance;
  • settlement of nearby buildings and municipal services;
  • septic system impact under D-5-4 where on-site sewage systems are proposed.

Each predicted effect should be paired with a measure (waterproofing or a cut-off wall, sentry wells, a monitoring plan) and a contingency if monitoring shows the prediction was wrong.

7. Conclusions, qualifications and sign-off

The report ends with clear conclusions and recommendations, then the author's qualifications and seal. York Region and Richmond Hill both require the report to be stamped by a licensed professional geoscientist or an exempted professional engineer. LSRCA adds a useful test for the whole document: another qualified person should be able to recreate the work from the report alone, which means every input, assumption and calculation is shown.

A quick check before you submit

  • Does the summary answer the reviewer's questions on page one?
  • Does the study area extend beyond the property to the zone of influence and nearby wells?
  • Is the monitoring period long enough for the local terms of reference, and is the seasonal high explained?
  • Do the wells reach the depths required below the lowest proposed floor?
  • Is every impact paired with mitigation and a contingency?
  • Is it stamped by the right professional?

For what goes into scoping and pricing a study for planning approval, see the development hydrogeological study page.

Related questions

How long is a typical hydrogeological report?

It depends on the study and the terms of reference. The body is often short compared with the appendices, which carry the borehole logs, well records, monitoring data, test analyses and laboratory certificates that support it. Reviewers check the appendices, so they are not padding.

Can I reuse an old report for a new application?

Sometimes, with an update, because some municipalities limit how old a study can be: Innisfil's terms of reference treat a study as valid for up to 18 months from its date. Older monitoring data may need to be supplemented if site conditions or regulations have changed.

What does "seasonal high" mean in the summary?

Seasonal high means the highest groundwater level expected during the year, usually in spring. It decides basement and foundation design, how deep infiltration features can go and whether dewatering is needed, so reviewers look for it to be measured over enough of the year or estimated with a clear method.

Where to go next

Sources

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