WESTLOCK - A recent update to the Town of Westlock's sewer master plan concluded that the two main problems in the system right now are capacity issues and stormwater getting into sewer pipes.
The study, by MPE Engineering, and accompanying recommendations, which were presented to town council at a committee of the whole meeting Feb. 18, are based on a model of sewer flow through the town’s system.
Data from the sewers was collected using a rain gauge and five flow monitors from August to November 2016, and May to September 2017. To calibrate the computer model, MPE also used historical data from a July 7-8, 2004 storm, classified as a one-in-five-year event.
Based on the model — which doesn’t reflect actual flows in every case since only five monitors were placed in the town — the mains that run along Highway 18 west of 108 Ave, north on 106 Ave, west again on 102 St. and north on 105 Ave. experience high utilization (the pipe is used above capacity).
Scott Kusalik, engineer with MPE, explained that this particular line of pipe takes the bulk of flow from the east side of Westlock.
Prominently, and most pressingly for town officials and people living in that area, manholes there are surcharging. This means that the fluid level is at surface, or within 1.5 meters of the surface.
The other high-utilization area is north of the west industrial park close to 113A St.
One problem that leads to sanitary flow issues is the inflow and infiltration of stormwater into the sewer system, but engineers said the causes are unknown.
Since the variables around stormwater infiltrating the sewer system aren’t clear either (how much and where), town officials will focus on getting a program going, at the recommendation of the engineers, to identify the areas where stormwater gets in and measure it.
Director of operations Grant Gyurkovits said the best time to start measurements is in the spring.
“It seems that’s our initial priority and (immediate) action item out of this master plan update … There are some fairly cost-effective ways where we can make an estimate on where our infiltration is coming from,” added CAO Simone Wiley after the meeting.
Fixing infiltration could alleviate capacity issues and reduce the need to follow all related recommendations in the master plan.
In their report, MPE engineers provided two options that would fix surcharging in manholes on the east side of town, while taking into account current development trends for the town at a rate of 1.1 per cent population growth. New developments like Westgate Business Park and Greenfield Estates were also considered.
The option they recommend would have a new 450 mm pipe going across a quarter section directly north of town and the replacement of some pipes in eastern Westlock with even larger pipes. It would solve all the surcharging and utilization issues on the east side.
However, it doesn’t address surcharging out of the west industrial park because the proposed trunk will intercept all the flow from the east side of town and divert it to the existing pipe that runs along the town’s northern boundary, explained Kusalik.
The sanitary sewer mains converge northwest of town and lead to the wastewater treatment plant two kilometres outside of town.
This particular upgrade would cost the town $9.5 million.
Existing pipe conditions
Between Aug. 1-8, 2018, 2.6 kilometres of sewer piping (out of the town’s total 56.7-kilometre system), was flushed and most of it inspected via CCTV.
MPE’s review of the footage determined that most of the inspected mains were in fair to poor condition.
They are rated on defects like cracks, joint offsets, broken pipe, fractures. The majority of the older pipe in Westlock is clay pipe, which Kusalik said would have been used in the 1950s and 60s, meaning it’s close to the end of its serviceable life.
“It doesn’t speak to the entire condition of the system because we’re only investigating less than one per cent of the actual distance of mains in Westlock,” he added.
The pipes were chosen with input from town staff, based on their GIS and record drawing data.
Sags in the pipes are not included in the structural condition ratings, but MPE made note of them because they typically occur at the joints when the pipes are not laid flat (at the same grade as the adjacent ones).
“In some of the cases, the pipes with ratings of one and two had severe sags in them,” said Kusalik.
MPE recommended the town prioritize the pipes in worst condition for repair, noting that this condition is not atypical for a town like Westlock.
Replacing all the pipes in fair and poor condition comes at a cost of nearly $3 million, although there is overlap between the pipes included in this repair-only part of the recommendation and the $9.5 million system upgrade.
“What we need to do is review that information that they have. I personally haven’t seen the sags or the holes in the pipes. I need to prioritize those problem areas. They may see that there’s a problem but it’s not affecting anything that can’t wait … or (there might be something) that I feel should be brought to council in a more immediate setting,” said Gyurkovits.
Decisions remain to be made about potential work on the inspected infrastructure in poor condition, based both on MPE recommendations and administration’s own filed knowledge.
Continuous inspection of the mains is also recommended, especially a year or two ahead of planned roadwork.
There also exists a correlation between commercial areas and grease zones in the sanitary system. The best way to prevent grease entering the pipes is a grease trap program.
“That’s not news to anyone. It’s kind of been an ongoing council request to administration that we put a program in place to inspect the traps in these businesses or to make sure that they have them in the first place,” said Wiley.
Andreea Resmerita, TownandCountryToday.com
Follow me on Twitter @andreea_res
