By Lexi McFarlane, Times Chronicle
The water quality of Osoyoos Lake, as well as ground water sources, was the focus of a lengthy discussion at Osoyoos Council on Tuesday during a briefing by Carollo Engineers as the Town inches forward on a new treatment plant that will be located on Strawberry Creek Rd.
Stephen Horsman, of the firm Carollo Engineers, detailed the state of Osoyoos’s water program to Council with a thorough presentation analyzing pilot testing results for Osoyoos’s water systems.
The findings came from over a year’s worth of research, gathering data, and understanding the system itself. The overall process was first initiated back in 2018, when Osoyoos gave approval to an assessment for water supply options.
Four main areas of concern were identified by the report, those being water quality, capacity, reliability, and future growth. The water quality issue is one Horsman says is “not uncommon”, that being the discolouration of water through manganese breaking out from water-treatment solutions, and entering Osoyoos’s ground water supply. These instances lead to boil-water advisories being put in place,
“The challenge with manganese is that it builds up over time,” Horsman explained. “So it accumulates within your distribution system, and changes in water quality, (for example) the addition of an oxidant such as chlorine, would allow that manganese to come out of solution, and show up in your water.”
The testing performed by Carollo’s team on Osoyoos Lake included a four-step process, designed to replicate realistic lake-water conditions and how they react to different water treatment options. Testing was done over the course of a year, meeting Health Canada requirements which Mayor Sue McKortoff alluded to, as she sought to clarify that results were shared with the federal body.
“Have they been provided with the results, and are they okay with it?” McKortoff asked.
“We’ve included them in regular updates through the pilot-testing period,” Horsman said, also confirming that, once a full report has been finalized, it will also be given to Health Canada.
The process began by establishing a standard “baseline performance” along with identifying areas where operations could be limited. Equipment calibration also factored heavily into the startup process. Phases 2 and beyond centred around a “dissolved air flotation” (DAF) process, which evaluated how much treatment of the water with coagulants and polymer was required.
Phase 3 evaluated how well different types of filters worked in the DAF process, including a granular activated carbon (GAC) filter which operates similarly to a Brita filter, and helps with organics reduction. The final step covered the best chemistry for water treatment solutions, and evaluating the different filters.
In response to a question from Councillor Johnny Cheong, Horsman confirmed the tests were run in series, rather than parallel.
“With the Phase 2 testing, we really just looked at the DAF performance without much consideration for how the filter was operating behind it, and then once we ran the filter, we left a baseline DAF operation to test the loading conditions. And then, in the final phase, we (completely) tested them both in-series… so we structured our testing to look at them both independently initially, and then collectively.”
Results of the testing found that the best performance of the DAF process occurred with loading rates around 29 metres per hour, but could still handle as high as 39 metres per hour. In more simple terms, Horsman said, the capacity for water filtration was shown to be much higher than what was initially proposed.
“Within these water quality parameters, we were able to really push this filter, almost two times what was initially proposed,” Horsman explained. “And showing quite stable, quite reliable filter performance at higher loading rates.”With the standards established, however, came a caution that there would be a need to be prepared for more variable conditions. In particular, cold-water conditions did affect the filter performance, so variations in temperature would need to be considered. Water Councillor Bob Appleby made a note of this when asking for more insight.
“You tested water at 14 metres, and at 30 metres; what was the difference in average temperature of those two sources?” Appleby asked.
“That can be 15 to 20 degrees (difference), under those (lake turnover) conditions,” Horsman said. “The cold-water temperature is usually a little more stable at the 30 metre depth, so you get less fluctuation from those seasonal lake turnover events, whereas at the 14 metre depth, you’re going to see that surface water influence, so you’re going to see generally quite a bit higher temperatures.”
A water treatment plant that Osoyoos has been looking to build would need to consider those variances, along with how to work the selected filters into its design and have a residuals handling process. It would need to open with a 25 mega-litre per day (MLD) capacity, meeting current 20 MLD demand, with room to expand and also have built-in redundancy requirements in case of maintenance.
Tyler Madsen, the Town’s Director of Operational Services, confirmed that a specific site is already in mind, and that these results will help complete the design process.
“The site that (has been) selected is up on Strawberry Creek Road, on Town of Osoyoos-owned property,” Madsen said.
Cheong also wondered if the Town would need to have a reserve package as part of a future treatment plant to address algae blooms, should those ever emerge.
“When you’re investing in this type of infrastructure… the addition of (the package) would be prudent,” Horsman confirmed. “It’s probably a risk-based decision for the Town, whether they build it into the facility or include a provision to expand the facility, to accommodate it in the future.”
The ultimate cost of the future water treatment facility has not yet been estimated, though in response to Councillor Jim King, it was noted there’s different cost estimate tiers for a future plant.
“In Class C, it’s in the order of a plus-30 to plus-40 per cent cost certainty,” Horsman said. “The costing that you’ve done to date is a Class 4-level estimate, and that has pretty high error bars on it. So, as you move higher up in classes, you have more cost certainty.”
No action was required from Council at this point in time, as Carollo’s team will continue to gather information to further the design process. Further results will be delivered to Council at a future date when they become available.
