In Mississauga the City frames the hydrogeological report around one practical question: what groundwater will the building have to deal with, during construction and after. A hydrogeological study in Mississauga follows the City's Transportation and Works terms of reference, tests water against the City's storm sewer limits if dewatering is planned, and has to respect the Region of Peel's rule that groundwater never goes to the sanitary sewer.
What this means for your project in Mississauga
- Most Mississauga studies support buildings with underground levels: they set the seasonal high water table, construction dewatering needs and how the foundation will drain afterwards.
- The City's Transportation and Works Department sets the report requirements; the Region of Peel controls discharges to its sewers; Credit Valley or Toronto and Region Conservation Authority comments on natural features.
- Plan for at least three months of water level readings from at least three monitoring wells before the report can be finished.
- The local factor most likely to affect scope and cost: where dewatering water can go. With sanitary sewers closed to groundwater, the water must meet the City's storm sewer limits or be treated.
Mississauga groundwater data
Calculated from public provincial datasets for City of Mississauga. Each value names its source; links are under Sources at the end of the page.
| Median static water level | 4.6 m below ground (662 records reporting depth and water level) |
|---|---|
| Well records | 12,493 records (all types) |
| Active Permits to Take Water | 19 permits; largest purpose categories: Construction 7, Dewatering Construction 5, Commercial 3 |
| Active construction and dewatering permits | 13 of 19 active Permits to Take Water |
| Conservation authority | Credit Valley Conservation (64.8% of area); Toronto and Region Conservation Authority (30.9% of area); Conservation Halton (4.2% of area) |
| Provincial plan areas | Greenbelt 2% of area |
| Sewer discharge | Groundwater drainage may not connect to sanitary sewers (Peel By-law 53-2010, s. 15); storm discharge tested against City By-law 0046-2022 (Region of Peel) |
Source: Well Records (Water Well Information System), MECP (WWIS_2026a), retrieved 2026-10-14.
Source: Permit to Take Water, MECP (PermitsToTakeWater_26-01), retrieved 2026-10-14.
Source: Conservation Authority Administrative Area, Ontario GeoHub, retrieved 2026-10-14.
Source: Oak Ridges Moraine (ORM) Planning Area, Ontario GeoHub; Greenbelt Outer Boundary, Ontario GeoHub; Niagara Escarpment Plan Boundary, Ontario GeoHub; retrieved 2026-10-14.
Figures count records inside the municipal boundary that report a value; well locations and values are as submitted by well contractors, and MECP notes inaccuracies exist. How these figures are calculated.
13 of the 19 active Permits to Take Water in Mississauga are for construction or dewatering, the largest share of any category, and smaller takings registered on the EASR are not counted. The city's 12,493 well records are mostly test holes, monitoring and dewatering wells (86.9% of those with a recorded use), so depth figures are left out of the panel; the median static water level is 4.6 m below ground.
The City's terms of reference
Mississauga's hydrogeological report terms of reference (July 2023) explain the purpose plainly: subsurface conditions may require temporary discharge to City or Region sewers during construction, and mitigation to redirect permanent groundwater flow around foundations. The report may be required for a consent, official plan or zoning amendment, plan of subdivision or site plan.
| Requirement | Detail |
|---|---|
| Monitoring wells | Normally at least three to determine flow direction; fewer only with a qualified person's rationale |
| Water levels | At least three monthly measurements over at least three months |
| Aquifer testing | Pumping or slug tests for hydraulic conductivity and transmissivity, plus drawdown analysis |
| Development details | Number of buildings, sub-grade depth and sub-surface structure area, land use |
| Water quality | Inorganics, dissolved and total metals, SAR and EC; all Storm Sewer Use By-law 0046-2022 parameters if storm discharge is proposed |
| Recommendations | Construction dewatering, permanent foundation drainage discharge, groundwater control, seasonal high water table, and PTTW or EASR needs |
Two administrative points catch applicants out. The consultant must locate all underground utilities before drilling, and the report needs a reliance clause or letter on the City's template authorizing the City to rely on it.
Peel's Wastewater By-law and groundwater
The Region of Peel's Wastewater By-law 53-2010 governs discharges to Regional sewers in Mississauga, Brampton and Caledon. For groundwater it is strict. Section 15 prohibits connecting a building's groundwater drainage system, directly or indirectly, to the sanitary sewer connection, and "indirectly" includes groundwater leaking in through open joints in private sewer connections. Groundwater must be conducted away from the building so it does not accumulate or affect neighbours, and the owner installs and maintains the system at their own expense. Discharging storm water or uncontaminated water to a sanitary sewer is prohibited except in an emergency with the Commissioner's approval, or with prior written approval for a non-emergency discharge. The Region also publishes hydrogeologic reporting guidelines for serviced developments (revised July 2009), which set out its expectations for groundwater quality, groundwater levels and nearby wells.
For a Mississauga building this narrows the options. Long-term foundation drainage goes to a storm system, or the building is designed watertight so there is little to drain. Construction dewatering goes to storm sewers where the City allows it, which is why the terms of reference tie water quality testing to the storm sewer by-law. The hydrogeological report's estimates of long-term flow and its water quality results decide which route is realistic.
Temporary discharge to City storm sewers
Any construction or maintenance work that discharges surface runoff or groundwater to the City's storm system needs a stormwater temporary discharge approval under Storm Sewer Use By-law 0046-2022. The application form covers water pumped from wells or excavations, ponds and storage tanks, and the City asks applicants to allow ten business days after a complete submission. The package includes:
- A site plan, and pre-treatment system specifications where treatment is planned
- A pre-discharge sample analysed by an accredited laboratory for the by-law's Part IV parameters
- The Permit to Take Water where one applies, and the Region's dewatering approval if water also goes to Regional infrastructure
- A certificate of insurance and a contingency plan in case the City ends the approval
Conditions follow the approval: the City sets the maximum discharge rate from the capacity of the receiving sewer, may ask for ongoing sampling, and does not allow pumping during or within 24 hours of a storm that discharges to that sewer. A spill or non-compliance means stopping the discharge immediately. For a hydrogeologist, the useful link is that the report's pre-development water quality results and flow estimates are the starting point for this application.
Hydrogeological study cost in Mississauga
| Study | Starting point | Full span |
|---|---|---|
| Construction dewatering study | $9,000 – $14,000 | $9,000 – $62,500 |
| Discharge permit and foundation drainage | $3,500 – $6,000 | $3,500 – $15,500 |
| Hydrogeological report for a planning application | $12,000 – $18,000 | $12,000 – $150,000 |
| Permit to Take Water application study | $12,000 – $20,000 | $5,500 – $31,000 |
These are indicative ranges based on typical scopes, the same province-wide ranges the estimator uses, not prices specific to Mississauga. Locally, the work is reviewed by the City of Mississauga, the Region of Peel and Credit Valley or Toronto and Region Conservation and, for water takings, the ministry, and the scope they ask for is what moves a quote. The City's minimum of three monitoring wells and three months of readings, plus storm sewer testing where dewatering is planned, sets the baseline scope. Excludes well drilling, government application fees and HST. Worked scenarios are in the cost guide for Ontario studies.
Projects that need a hydrogeological study in Mississauga
- Mid-rise and high-rise buildings. Seasonal high water table, construction dewatering volumes and a permanent drainage strategy that keeps groundwater out of sanitary sewers.
- Infill and consents. The City lists consent to sever among the applications that may need a report.
- Redevelopment of commercial and industrial land. Groundwater quality against storm sewer limits, alongside any environmental site assessment.
Working with a hydrogeologist in Mississauga
Mississauga's terms of reference normally expect at least three monitoring wells and at least three months of water levels with monthly readings, so a consultant needs the site plan and the proposed underground levels at the start. Transportation and Works staff review the report, and the City asks for a reliance clause or letter on its own template so it can rely on the findings; ask whoever prepares the hydrogeological assessment in Mississauga to include it in the proposal. Where dewatering is planned, water quality is tested against the City's storm sewer limits, because Peel keeps groundwater out of sanitary sewers. The professional named in the reliance letter can be checked on Ontario's register of practising geoscientists or, for an engineer, PEO's online search of licence holders.
Where Mississauga dewatering needs a provincial filing too, how to register EASR dewatering, step by step walks through it.
Mississauga questions
How many monitoring wells does Mississauga expect?
Normally at least three, so that groundwater flow direction can be determined. The City's terms of reference allow a qualified person to justify fewer wells because of site constraints, using other information to estimate flow direction. Static water levels are to be collected over at least three months, with at least three monthly measurements.
What is the reliance letter, and why does the City want one?
Mississauga asks for the hydrogeological report to come with a clause or separate letter authorizing the City to rely on its findings and recommendations, using the City's approved template in Section 5, Appendix 1 of the Transportation and Works Development Requirements Manual. Confirm it is in the consultant's scope.
Which water quality parameters do we need to test?
Mississauga's terms of reference ask, at minimum, for inorganic parameters, dissolved and total metals, and sodium adsorption ratio and electrical conductivity. If the plan is to discharge dewatering water to City storm sewers, the results must also be compared with every chemical parameter listed in the City's Storm Sewer Use By-law 0046-2022.
Can a new building drain groundwater to the sanitary sewer in Peel?
No: section 15 of the Region of Peel's Wastewater By-law (53-2010) says a groundwater drainage system must not be connected directly or indirectly to a sanitary sewer connection, and that groundwater must instead be conducted away from the building. The owner installs and maintains the drainage system at their own expense.
Does a consent to sever need a hydrogeological report in Mississauga?
It can: the City lists consent to sever alongside official plan and zoning amendments, plans of subdivision and site plan control as applications that may need one.
Which conservation authority reviews Mississauga sites?
It depends on which way the site drains. The Credit River side of the city, about 64.8% by area, belongs to Credit Valley Conservation; the eastern watersheds, about 30.9%, to Toronto and Region; and a sliver in the west to Conservation Halton.
Studies for Mississauga sites
- Construction Dewatering Assessment
Groundwater inflow estimates and dewatering rates for excavations, basements and servicing trenches.
- Groundwater Discharge Permits & Foundation Drainage
Approvals for discharging pumped groundwater to municipal sewers, during construction and over the long term.
- Development Hydrogeological Study
Groundwater assessments that support subdivision, site plan and zoning applications.
- Permit to Take Water & EASR
Work out whether a water taking needs an EASR registration or a Permit to Take Water.
- Hydrogeological study cost guide
Ranges for every study type, side by side.
Near Mississauga
Sources
- Wastewater By-law 53-2010 (opens in a new tab), Region of Peel.
- Well Records: Water Well Information System (WWIS_2026a) and county Well Record Data Reports (WW_Reports_2026a) (opens in a new tab), Government of Ontario (MECP), Ontario Data Catalogue.
- Permit to Take Water dataset (PermitsToTakeWater_26-01) (opens in a new tab), Government of Ontario (MECP), Ontario Data Catalogue.
- Conservation Authority Administrative Area (opens in a new tab), Ontario GeoHub.
- Oak Ridges Moraine (ORM) Planning Area (opens in a new tab), Ontario GeoHub.
- Greenbelt Outer Boundary (opens in a new tab), Ontario GeoHub.
- Niagara Escarpment Plan Boundary (opens in a new tab), Ontario GeoHub.
- Terms of Reference: Hydrogeological Report (July 2023) (opens in a new tab), City of Mississauga, Transportation and Works.
- Guidelines for Hydrogeologic Assessment and Reporting Requirements, New Developments on Municipal Services (revised July 2009), Public Works Design, Specifications and Procedures Manual (opens in a new tab), Region of Peel.
- Stormwater temporary discharge approval and Storm Sewer Temporary Discharge Approval Form 2873 (Storm Sewer Use By-law 0046-2022) (opens in a new tab), City of Mississauga.
- Public Register (registered members) (opens in a new tab), Professional Geoscientists Ontario.
- Search for licence holders and engineering interns (opens in a new tab), Professional Engineers Ontario.
- Municipal Boundary - Lower and Single Tier (opens in a new tab), Ontario GeoHub.
- OHN Waterbody, 2M generalized layer (provincial hydrography dataset) (opens in a new tab), Ontario GeoHub.
- O. Reg. 63/16: Registrations under Part II.2 of the Act - Water Taking (consolidated to e-Laws currency date October 9, 2026) (opens in a new tab), Government of Ontario (e-Laws).