Hydrogeological Study Halton Hills

Georgetown and Acton well fields

Halton Region's 2025 annual reports describe two groundwater systems in the town. According to the 2025 Georgetown report, part of Georgetown has been on Lake Ontario water since November 5, 2024; the rest is supplied by nine wells in three well fields, Cedarvale (four), Princess Anne (three) and Lindsay Court (two), with the Cedarvale water treated at the Georgetown Water Treatment Plant by greensand filtration and ultraviolet disinfection. The 2025 Acton report says all of Acton's supply comes from six wells in the Davidson, Fourth Line and Prospect Park well fields, with iron and manganese removal at Prospect Park.

Under Ontario's source protection program, municipal wells have wellhead protection areas, where activities such as fuel storage, chemical handling and septic systems can be significant drinking water threats. For a business, a subdivision or a site alteration near a well field, the hydrogeological study and the source water protection screening should be scoped together at pre-consultation.

Keeping recharge in Acton and Georgetown

The source protection plan protects the amount of water reaching these aquifers as well as its quality. The CTC Source Protection Region's water balance guidance (version 2.1, 2019) lists the Tier 3 water budget areas where wellhead protection areas for quantity (WHPA-Q) were delineated: Acton is a Significant Groundwater Quantity Threat Area, rated significant, and Georgetown a Future Significant Groundwater Threat Area, rated moderate.

In WHPA-Q2 areas with significant threats, policy REC-1 of the CTC Source Protection Plan, in effect since December 31, 2015 and amended in March 2019, requires:

• Best management practices such as low impact development, with the goal of maintaining pre-development recharge, on new development and site alteration (voluntary for farm uses where impervious surfaces are no more than 10% of the lot)
• A water balance assessment for site plan and subdivision applications for major residential, commercial, industrial or institutional development (site plans for one single family dwelling or land zoned agricultural excluded)
• Maintaining recharge on site as far as feasible, and off-site recharge enhancement within the same WHPA-Q2 where it cannot
• Where the site is also in an issue contributing area for sodium, chloride or nitrates, a water balance that addresses water quality as well (minor variances excluded)

For an Acton property, that makes infiltration testing and a pre- and post-development water balance part of most applications. For Georgetown, ask at pre-consultation whether the moderate-risk designation brings any of these requirements to your site.

Private wells and septic systems

Outside the serviced communities, Halton's hydrogeological study guidelines apply: development must be self-sustaining on individual well and septic services, and communal systems are not permitted in private servicing areas. A Stage 1 study pumps test wells for at least six hours, checks for interference in private wells within 250 m, and calculates the density the site can support from nitrate dilution at the property limits; a Stage 2 study confirms a well on each lot before a subdivision of more than two lots is registered. Our guide to how a D-5-4 nitrate assessment works explains the nitrate method behind Stage 1. The guidelines were written under the Regional Official Plan, which became a local plan of the Town on July 1, 2024, so confirm with Town planning staff how they apply.

Escarpment, watersheds and sewers

About 28.2% of Halton Hills is in the Niagara Escarpment Plan area, where the Niagara Escarpment Commission issues development permits, and the Halton guidelines note the Commission may have its own study requirements. Credit Valley Conservation covers about 51.5% of the town and Conservation Halton about 46.3%. In the serviced areas, construction dewatering cannot go to Regional sanitary sewers without the Commissioner's written authorization under Halton's Sewer Use By-law 2-03.

Projects that need a hydrogeological study in Halton Hills

• Rural severances and estate subdivisions. Halton Stage 1 and Stage 2 studies, test wells and nitrate dilution.
• Development near the Georgetown or Acton well fields. Source water protection screening alongside the hydrogeological study.
• Georgetown and Acton subdivisions. Groundwater levels, water balance and construction dewatering.
• Farm and commercial water supplies. Pumping tests and Permits to Take Water above 50,000 L/day.

Working with a hydrogeologist in Halton Hills

Start by placing the property on three maps, because each one adds a reviewer or a requirement. Near the Acton or Georgetown well fields, source protection screening comes first, and in Acton a site plan or subdivision usually needs infiltration testing and a pre- and post-development water balance, so allow for both in the budget. On the escarpment, ask the Niagara Escarpment Commission early whether its development permit brings its own study requirements. The watershed decides whether Credit Valley Conservation or Conservation Halton comments, and in the serviced areas any construction dewatering needs the Region's written authorization before it reaches a sanitary sewer. With the Regional Official Plan now a Town plan, confirm at pre-consultation who reviews the hydrogeology, and give the consultant any existing well records so the hydrogeological assessment in Halton Hills can build on them. Before the work starts, confirm the hydrogeologist's licence through the register kept by Professional Geoscientists Ontario.

For a single severance rather than a subdivision in Halton Hills, our article on whether a lot severance needs a hydrogeological study covers the first questions.