Renovation of two large, above-ground EPCOR Utilities water reservoirs will extend the lives of these Edmonton landmarks a quarter century or more. The makeovers, involving primarily coating the inside walls of two 60-feet-high concrete tanks with a polyurea compound, are technically significant and will yield considerable cost-savings and environmental benefits
EPCOR has underground reservoirs at 10 other Edmonton sites, but none has the prominence of Tanks 1 and 2 with their large EPCOR logos and location adjacent to the Whitemud Freeway and busy 75 Street. The tanks, which stand on elevated land in the city's southeast, have become icons that Edmontonians use to give directions. Removing them would leave a hole in the cityscape and also in residents’ mindscape.
When the tanks were commissioned in 1963, EPCOR was using its centrally-located Rossdale water-treatment plant to serve Edmonton. Each Papaschase tank reservoir holds 25 mega litres (equal to the water in 10 Olympic swimming pools). Originally the reservoirs were front-line features that provided water pressure for fire-protection in the city’s outlying areas, and they distributed water during Rossdale shutdowns.
According to Gavin Post, P.Eng., EPCOR project manager for the current renovations, the tanks (and an adjacent belowground unit added in the 1980s) assumed more of a back-up role when a second water-treatment facility was completed, and when booster stations were added throughout Edmonton.
Their status as physical landmarks partly explains why EPCOR is going to some length to preserve the tanks. But the preservation also ties in nicely to EPCOR's business and environmental objectives. The company gains by not having to invest in a new facility, and spares itself and the public the disruption and environmental costs of disposing of tons of concrete.
Even so, explains Post, early on there was some thought that effervescence on the outside might doom the tanks. However, in 2009, EPCOR hired Stantec to conduct an assessment of the concrete. The work was combined with a cost-benefit assessment of refurbishing the tanks vs. removal and rebuilding at a cost of about $25 million each. Stantec determined the tanks had maintained their structural integrity and apart from some deterioration of the inside surface of the 12-18" thick walls, the concrete was in better-than-expected condition.
“That’s when we went the route of looking at a coating of the interior to provide an impermeable membrane,” says Post, who sees an analogy in procedures of inserting a membrane to extend the life of aging water mains. It was determined that at a cost of about $1 million per tank, they could be coated with an aliphatic polyurea coating system. EPCOR settled on this two-component polyurethane finish because of its toughness, flexibility and abrasion resistance – important because of the ice cover that moves up and down the tank during cold winter months. While the spray-on product had been used in other applications, it had not previously been used inside a confined tank.
“From a safety perspective, it has zero VOCs and it goes on as a 100-per-cent solid," says Post.
Led by the project contractor, PCL Construction Management, the project required careful choreography – starting with the installation of a new man-way for easier access through the side of the tank. Last September, Tank 1 was drained and dehumidifiers were brought in to dry the tank interior.
Once 11 kilometres of scaffolding on nine levels were erected in three weeks, pressure washing of the walls proceeded. To smooth out irregularities, the 27,000 square feet of inside wall surface were hand-trowelled with an epoxy filler before applying a primer.
As workers applied the lining, they were followed by an independent inspection team that checked that the membrane’s thickness met specifications of being between 60 and 80 mils and that there were no pinholes.
Liner application finished the first week of December. With the scaffolding removed, the tanks were disinfected before drawing in water to permit water-quality testing, including a blind-tasting-test panel, which gave a thumbs-up.
According to Post: “The plan is to move forward with the same procedure with Tank 2.” That work is expected to begin late 2013 or early 2014.
Refurbishing Tank 1 came in at just over $1 million and Post is confident that with this liner installed the tank will last another 25 years.
Nordahl Flakstad is an Edmonton-based freelance writer.