Headline News

Mono considers options to improve drinking water system, reduce arsenic

July 9, 2026   ·   0 Comments

By JAMES MATTHEWS

Mono has identified a need to re-evaluate its water supply in relation to changes in provincial standards for arsenic concentrations in potable water,

In light of planned and approved growth, the municipality will consider reducing arsenic concentrations that exceed the maximum allowable concentration limits.

When the town’s wells were commissioned, the maximum acceptable concentration (MAC) for arsenic, as stipulated in the Ontario Drinking Water Quality Standards (ODWQS), was 0.025 mg/L, and all the wells were comfortably within this limit.

Accordingly, the Island Lake Drinking Water System (DWS) does not have treatment in place for arsenic.

Four of the five wells in the Island Lake DWS are in compliance, but all five wells have raw water concentrations of arsenic that are reported to be above half of the MAC, which is now five micrograms per litre or 0.005 mg/L.

Additional care and monitoring are required when arsenic levels exceed the half MAC.

According to a presentation from R.J. Burnside and Associates, arsenic levels tend to fluctuate and may increase over time, posing a threat to the town’s Island Lake DWS and a major concern for the municipality.

“There is a slight trend upward is what we’ve been seeing over the years,” said Matt Paznar of R.J. Burnside. “There isn’t anything too major. But they do seem to be averaging slightly higher over time.”

Sometimes one of the wells (Coles Well Production Well 1) has had arsenic concentrations exceeding the 10 micrograms per litre MAC. As such, Coles Well PW1 was taken offline in late 2017, causing a loss of raw water supply to the system and thereby reducing the firm capacity of the Island Lake DWS.

The Ministry of the Environment, Conservation and Parks (MECP) requested that the town implement measures to restore the potable water supply that comply with the ODWQS, including reducing arsenic concentrations.

Paznar said there are three broad categories of technical solutions to the arsenic problem. Remove arsenic from the raw water using a water treatment plant. Seek hydrogeological solutions, such as drawing water from aquifers with lower arsenic levels, or address the potential for fluctuations and/or increases in arsenic concentration in existing wells. And obtain water from the supply of a different municipality.

“The preferred alternative may include a combination of solutions, implemented in a staged approach if required,” he said.

The preferred alternative is to drill new wells and connect Island Lake and Cardinal Woods drinking water systems together, to be implemented in the following stages:

Stage 1: Drill two new wells at the Klondyke Gravel Pit site (Klondyke Test Well site), complete with a building that provides the required disinfection, and connect to the Cardinal Woods DWS (immediate);

Stage 2: Connect the Island Lake and Cardinal Woods systems together by a transmission main to form one drinking water system (short-term);

Stage 3: Decommission Coles PW1 (the well is currently above the arsenic limits and has been out of service since 2017) (short-term); and

Stage 4: Reduce reliance on remaining Island Lake DWS wells by decommissioning all but the largest capacity wells when there is an adequate supply of non-arsenic water and/or arsenic limits are further reduced in the future (long-term).

“So not everything will happen right away,” Paznar said. “It will be done likely over a seven to 10 year range depending on the growth that the town sees.”

The preferred alternative is the only one that can supply enough raw water to meet the existing demands; accommodates all anticipated growth within the town in proximity to both existing systems; does not require reliance on the Island Lake DWS wells that have naturally occurring concentration of arsenic; meets the current provincial drinking water standards for the concentration of arsenic in the drinking water as well as treatment (i.e., disinfection only); has the lowest capital, operation and maintenance (O&M), and 20-year net present value (NPV) estimated costs and is easy to implement and operate; and meets the problem/opportunity statement.

He said Mono will need more water storage when the population increases by 1,300 people. That may require a new water tower at the Klondyke test well site.

“That would be the long-term plan for the drinking water systems for the Town of Mono at this time,” Paznar said.

Readers Comments (0)