The “Triple Confluence Threat” to Groundwater Quality

This article summarizes my work on Karst, groundwater, rural private wells, and agricultural intensification. At the end of this article, you can find my main resources linked.

In short, I believe our region’s rural drinking water is at serious risk, especially for private homes relying on water from private wells. I believe that this threat is serious, may accumulate to billions of dollars in damages to homeowners, as well as sustained injury (e.g. kidney failure) and loss of life. After reviewing similar regions in North America, it is clear to me that contamination will happen – it is not a question of if, but of when. Also, communities will organize and governments will take action – either reactively after the damage is done, or proactively before widespread damage is done. With a first well cluster contaminated, I believe that communities should urgently wake up to protect our shared groundwater that so many of us rely on.

1. Issue

On the Silurian dolostone of Grey and Bruce counties, many rural households draw drinking water from private wells in fractured, often karstic bedrock with little or no soil cover. The areas currently experiences a shift of farming from pasture-based extensive agriculture toward annual cropping, feedlots, and intensive manure and fertilizer use. Ontario’s nutrient management rules are inadequate with respect to thin aquifer protection due to karst geology. Within the highly vulnerable aquifer areas that Source Protection identifies, its policies are limited to advisory and educational efforts. The province, counties and farm organizations should close this policy gap proactively before further contamination occurs .

2. Background: three factors that compound one another

Three factors compound the contamination risk in the Grey Bruce region:

1. Its aquifers have little natural protection. The Silurian dolostone that runs along the Niagara Escarpment to Tobermory is fractured and in many places karstic, . Water and contaminants can move rapidly from the surface to a well – within hours or days instead of years. Across much of the region, and especially on the Bruce Peninsula, overburden is very thin or absent (<1m) and fractured bedrock lies near the surface. Depth varies a great deal, though, and the regional assessment reports note that karst is “not well documented” and that more than a quarter of wells in the Grey Sauble area may be unrecorded [1]. For most rural households the dolostone is the only practical water source. The shale formations beneath it yield salt-contaminated water that is inadequate for human use.
2. A dense population of private wells. Over decades, farm severances created a large number of rural residential lots. Each is supplied by its own well and septic system. Responsibility for a private well, including testing and treatment, rests with the homeowner. The province pays for bacterial testing only, not nitrate or other chemicals [2].
3. A change in land use. As a generation of beef farmers retires and agricultural markets shift, much of the permanent pasture in Grey Bruce has been sold to cash-crop and larger livestock operations and converted into annual crops. This leaves the soil bare for longer and reduces the soil’s filtering capability. Some manure is also moved onto this land from operations in other regions, helping feedlot operators to meet nutrient management plan requirements. Practices that are defensible over deep overburden till were shown to deliver pathogens and nitrate directly to the aquifer and drinking water.

All of these processes occurred within regulatory limits and are legally supported. Drinking water risks emerge from their combination.

Health risks.

Two contaminants raise immediate concern for human health:

• Pathogens from manure. Pathogens mostly stem from sources such as manure spreading, storage, and feedlots. The risk is known in this region: In May 2000, E. coli O157:H7 and Campylobacter from cattle manure entered a shallow municipal well in fractured bedrock at Walkerton, in Bruce County. Seven people died and about 2,300 became ill [3].
• Nitrate. Diffuse sources from manure and commercial fertilizer are difficult to be traced to a single field. Health Canada sets a maximum acceptable concentration to 45 mg/L as nitrate (10 mg/L as nitrate-nitrogen), in order to protect bottle-fed infants from methaemoglobinaemia [4] and other general health concerns.

Kewaunee County, Wisconsin, offers the closest comparable evidence with the same Silurian dolostone and intense industrialization of agriculture. In a USGS–USDA study, 26–28% of private wells exceeded the nitrate standard of 10 mg/L nitrate-nitrogen, the same limit as Canada’s. Where there was less than 1.5 m of soil over bedrock, the exceedance rate rose to about 50%, compared with 23% where soil was deeper than 6.1 m. Nitrate and coliform contamination were associated with depth to bedrock and nearby agricultural land, not with septic systems. Among 131 wells tested for fecal source markers, 60% carried fecal markers of human or bovine origin [5]. A companion risk assessment estimated up to 301 cases of acute gastrointestinal illness per year from contaminated private wells in that one county, mostly from bovine sources [6].

3. Current framework and gaps

Four provincial policy statutes are most relevant. Neither one provides standards that address aquifer vulnerability over thin soils on karst.

1. Clean Water Act, 2006. Source protection plans must address significant drinking water threats, but only within protection zones around municipal wells and surface water intakes. Farm activities in highly vulnerable aquifers cannot be elevated to significant threat level [7]. Plan policies for activities above such aquifers therefore can only rely on education and outreach and carry no legal force. Private wells fall outside the Act unless a municipality brings them in explicitly (see Option 4).
2. Nutrient Management Act, 2002 and O. Reg. 267/03. The regulation does contain groundwater and depth-to-bedrock application standards (ss. 49–50). For example, certain solid non-agricultural source materials may not be applied over less than 50 cm of soil [8]. These standards have limited reach:
   • They apply mainly to farms required to hold a nutrient management strategy or plan, which are farms building or expanding livestock housing or manure storage, or those above 300 nutrient units, and to biosolids and other non-agricultural materials.
   • A farm that applies only commercial fertilizer generally falls outside the planning requirements.
   • The depth thresholds are measured in tens of centimetres. Wisconsin regulates up to six metres (see Section 4).
3. Farming and Food Production Protection Act, 1998. The Act protects farmers following normal farm practices from nuisance claims, but only for “disturbance,” defined as “odour, dust, flies, light, smoke, noise and vibration” [9]. It does not shield anyone from liability for contaminating a well. Its real constraint is section 6: no municipal by-law may restrict a normal farm practice, with normal not restricted above highly vulnerable aquifers [9]. Municipalities therefore cannot regulate nutrient application by by-law. A homeowner’s only remaining legal route is a private lawsuit, with the burden of proof to find the source with the harmed party. That is costly for pathogens and close to impossible for diffuse nitrate.
4. Environmental Bill of Rights, 1993. The EBR provides procedural rights, not a guarantee of clean water:
   • Any two Ontario residents may ask a ministry to review an existing regulation or policy, or the need for a new one (s. 61).
   • They may request an investigation of an alleged contravention (s. 74).
   • Residents may sue for significant harm to a public resource, which includes water, but only where an Act, regulation or instrument has been contravened. No damages are available, and class proceedings are barred (ss. 82–84, 93) [10].

   Where farm practices comply with the regulations, there is nothing to sue over. The most useful EBR tool here is the application for review.

In short, practices that are legal and “normal” can still contaminate an aquifer that has no protective cover, and no statute currently prevents that outcome.

4. A comparable approach: Wisconsin NR 151.075

Wisconsin faced the same problem on the same rock and decided to regulate. Since July 1, 2018, rule NR 151.075 has applied to any producer who mechanically applies manure on land over Silurian bedrock within 20 feet (about 6 m) of the surface, regardless of farm size [11]:

• Less than 2 ft (about 0.6 m) of soil. Mechanical manure application is prohibited.
• 2 to 20 ft. Requirements tighten as soil gets thinner:
  • depth to bedrock must be verified in the field;
  • fields must be ranked by pathogen-delivery risk;
  • no application on frozen or snow-covered ground, or when more than an inch of rain is forecast within 24 hours;
  • injection or incorporation within 24 hours;
  • limits on rate and timing, or pathogen treatment of the manure.

In 2021 the state agriculture department added a technical standard for verifying depth to bedrock [12]. The rule covers sixteen eastern Wisconsin counties. Kewaunee offers Ontario a tested template in comparable context, laying out agricultural restrictions according to how much soil protects the aquifer.

5. Options

The options run from least to most interventionist. They are not mutually exclusive.

1. Education and disclosure. Continue and amplify the extension work already under way (see Section 7). Ask municipalities and real estate boards to tell buyers of rural lots on Silurian bedrock about aquifer vulnerability, well testing and appropriate farm practices.
2. Monitoring. Add nitrate to the free provincial well-testing program, at least in mapped highly vulnerable aquifers. Expand provincial groundwater monitoring in karst areas. Map depth to bedrock at field scale, using Wisconsin’s verification standard as a model [12]. At present there is no early warning system for nitrate.
3. Funding for farm transition. Target federal–provincial cost-share funding under the Sustainable Canadian Agricultural Partnership to fields with the thinnest soils. Eligible practices would include conversion back to permanent pasture or perennial forage, managed grazing, cover crops, and better-sited manure storage. This gives farmers who carry the cost of protection a way to recover it, instead of leaving the conflict with their residential neighbours unresolved.
4. Including well clusters under the Clean Water Act. A municipal council can pass a resolution under s. 8(3) asking that other drinking water systems be added to the source protection plan’s terms of reference. Under O. Reg. 287/07, s. 4.1, this can include private wells that are part of a cluster of six or more wells, or are in a settlement area [13][14]. Contamination is not required first. Once a cluster is included, activities near it can be assessed as significant threats and managed through prohibitions or risk management plans. This is the strongest tool available to municipalities now, and it can be used before any harm occurs.
5. An EBR application for review. Any two residents can apply for a ministry review of O. Reg. 267/03, asking whether its depth-to-bedrock standards are adequate over Silurian karst [10].
6. Regulatory amendment. Revise ss. 49–50 of O. Reg. 267/03 so that, within mapped karst and thin-overburden areas, standards modelled on NR 151.075 apply to all mechanical manure application, and set nitrogen rate and timing standards for commercial fertilizer, whether or not a farm needs a nutrient management strategy.

6. Recommendation

Act now while prevention is still cheaper than remediation:

1. Bruce and Grey County councils, and their local municipalities, should identify qualifying well clusters in mapped highly vulnerable areas and pass s. 8(3) resolutions to bring them into the source protection plan (Option 4).
2. The Ministry of the Environment, Conservation and Parks and Public Health Ontario should add nitrate testing for private wells in highly vulnerable aquifers and fund a baseline well survey modelled on Kewaunee County (Option 2).
3. The Ministry of Agriculture, Food and Agribusiness should review O. Reg. 267/03 for Silurian karst, using NR 151.075 as the template, and pair any new standard with dedicated transition funding (Options 3 and 6).
4. Farm organizations and residents should make this a joint request. Farmers and their rural neighbours draw on the same aquifer, and a rule that both helped shape will hold up better than one imposed after a crisis.

7. Engagement to date

• Source Protection Committee. I presented these concerns to the Saugeen, Grey Sauble, Northern Bruce Peninsula Source Protection Committee. I previously supervised technical work for that region’s assessment reports (2009–2012).
• County councils. In September 2024 I delegated to Bruce County Council, and also to Grey County Council, recommending a proactive groundwater safety task force [15].
• Farm-sector outreach. After these presentations, source protection staff wrote an article on farming over karst, which the Grey County Federation of Agriculture brought to Rural Voice (Oct 2024, see impage below). My response to Mel Luymes was printed in Dec 2024 (scan). It was reported in Owen Sound Sun Times and was reprinted in the Ontario Farmer (later taken down again).
• Free well testing. The counties have lobbied for the province to keep free bacterial testing of private wells.

References

1. Grey Sauble Source Protection Area. Approved Assessment Report, Chapter 7, “Addressing Limitations” (2015). https://home.waterprotection.ca/wp-content/uploads/AR/GSCA/GSSPA_Ch7_2016_Final.pdf; Northern Bruce Peninsula Source Protection Area. Approved Assessment Report. https://home.waterprotection.ca/source-protection-plan/assessment-reports/northern-bruce-peninsula-source-protection-area-approved-assessment-report/
2. Public Health Ontario. “Protect Your Household: Test Your Private Drinking Water Source. It’s Fast and Free” (June 3, 2026). https://www.publichealthontario.ca/en/about/news/2026/06/well-water-testing
3. O’Connor, D. R. Report of the Walkerton Inquiry, Part One: The Events of May 2000 and Related Issues. Toronto: Ontario Ministry of the Attorney General, 2002.
4. Health Canada. Guidelines for Canadian Drinking Water Quality: Guideline Technical Document — Nitrate and Nitrite. Ottawa, 2013. https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-guideline-technical-document-nitrate-nitrite.html
5. Borchardt, M. A., J. P. Stokdyk, B. A. Kieke Jr., M. A. Muldoon, S. K. Spencer, A. D. Firnstahl, D. E. Bonness, R. J. Hunt, and T. R. Burch. “Sources and Risk Factors for Nitrate and Microbial Contamination of Private Household Wells in the Fractured Dolomite Aquifer of Northeastern Wisconsin.” Environmental Health Perspectives 129, no. 6 (2021): 067004. https://doi.org/10.1289/EHP7813
6. Burch, T. R., J. P. Stokdyk, S. K. Spencer, B. A. Kieke Jr., A. D. Firnstahl, M. A. Muldoon, and M. A. Borchardt. “Quantitative Microbial Risk Assessment for Contaminated Private Wells in the Fractured Dolomite Aquifer of Kewaunee County, Wisconsin.” Environmental Health Perspectives 129, no. 6 (2021): 067003. https://doi.org/10.1289/EHP7815
7. Ontario Ministry of Agriculture, Food and Rural Affairs. Source Protection Plans on the Farm. Factsheet 23-057 (2023). https://www.ontario.ca/files/2023-09/omafra-source-protection-plans-on-farm-23-057-en-2023-09-15.pdf
8. Ontario. O. Reg. 267/03 (General) under the Nutrient Management Act, 2002, ss. 49–50. https://www.ontario.ca/laws/regulation/030267; Ontario Ministry of Agriculture, Food and Agribusiness. “When farms require a nutrient management strategy (NMS), nutrient management plan (NMP) or non-agricultural source material (NASM) plan” (updated May 4, 2026). https://www.ontario.ca/page/when-farms-require-nutrient-management-strategy-nms-nutrient-management-plan-nmp-or-non
9. Ontario. Farming and Food Production Protection Act, 1998, S.O. 1998, c. 1, ss. 1, 2(1), 6(1). https://www.ontario.ca/laws/statute/98f01
10. Ontario. Environmental Bill of Rights, 1993, S.O. 1993, c. 28, ss. 61, 74, 82–84, 93. https://www.ontario.ca/laws/statute/93e28
11. Wisconsin Administrative Code, NR 151.075, “Silurian bedrock performance standards” (effective July 1, 2018). https://docs.legis.wisconsin.gov/code/admin_code/nr/100/151/II/075
12. Wisconsin Department of Agriculture, Trade and Consumer Protection. “DATCP Publishes Technical Standard for DNR Regional Manure Spreading Restrictions on Silurian Bedrock Areas” (August 6, 2021). https://datcp.wi.gov/Pages/News_Media/20210806DepthToBedrock.aspx
13. Ontario. Clean Water Act, 2006, S.O. 2006, c. 22, s. 8(3); O. Reg. 287/07 (General), s. 4.1. https://www.ontario.ca/laws/statute/06c22
14. Ontario Ministry of the Environment, Conservation and Parks. “Include optional drinking water sources in a source protection plan.” Best practices for source water protection (2021, updated November 2, 2023). https://www.ontario.ca/document/best-practices-source-water-protection/include-optional-drinking-water-sources-source
15. Bayshore Broadcasting. “Environmental Scientist Calls On Bruce County To Form Proactive Groundwater Safety Task Force” (September 10, 2024). https://www.bayshorebroadcasting.ca/2024/09/10/186973/