WATER TREATMENT: Revelstoke’s Greeley creek plant
Though membrane technology has been used in several water treatment plants in central and eastern Canada, Revelstoke's new water treatment plant is the first to use the technology in the west. Dayton ...
Though membrane technology has been used in several water treatment plants in central and eastern Canada, Revelstoke’s new water treatment plant is the first to use the technology in the west. Dayton & Knight consulting engineers of West Vancouver designed the plant after the town experienced problems in August 1995.
The water utility supplies over 7,000 people and had used the Greeley Creek mountain watershed as its principal source since 1930. So confident was the city that its water was of pristine quality, it appealed to the province when the B.C. Safe Drinking Water Act was imposed in 1992 because it did not feel it should have to use disinfection. The province had agreed to review the city’s request, but then in 1994 an outbreak of waterborne disease occurred, including giardiasis, cryptosporidiosis, yersiniosis and campylobacteriosis, which affected over 150 people.
As a first measure to solve the problem the utility added a gas chlorine system, at a dosage of about 2.5 mg/L, which eliminated 99.9% of the giardia cyst. However, the chlorine gave a taste to the water and people were concerned about the long-term health risks of the chemical. Also chlorine does not eliminate cysts, oocysts and the problem of high turbidity.
In 1998, therefore, after extensive reviews and public consultations, the city authorized the construction of the new supply plant. It still uses the Greeley Creek as a source, but has multiple barriers, membrane filtration and chlorine disinfection. The provincial Ministry of Health approved the design on the basis it gave the required 3-log giardia removal through membrane filtration, and the remaining required 1-log removal of the parasite by chlorination.
The building is a durable block structure covering 610 square metres. It houses the raw water strainers, membrane system, gas chlorination system and peak draw treated water pumps. It also contains an office and laboratory. It was carefully sited at an elevation so that the force of gravity eliminates the need for inlet pumping and gives the required transmembrane operating pressure. This strategy conserves energy and minimizes the impact on the distribution system gravity operating pressures. Also to save energy, heat from the compressor system partially heats the building.
The key components of the treatment system are oversized to allow for future capacity needs. There are five membrane units with 90 filter modules in each and a capacity of 16.7 ML/d of water. The US Filter/Memcor system includes polypropylene, hollow fibre micro membranes and a patented backwash system of compressed air and water. The clean-in-place (CIP) chemicals are Memclean, citric acid and sodium hydroxide.
For the landscaping, the team chose native trees, and low maintenance and drought-resistant plants. Earth-lined sedimentation ponds that ultimately feed back to Greeley Creek are used to treat and dispose of the plant’s filter backwash and waters.
The work involved upgrading the creek inlet works and settling basin, a new residual disposal system and a 910,000 litre clearwell. The team provided all the outside piping to integrate the plant to the existing transmission system, and developed the advanced SCADA control system.
Done on a fast-track, phased construction-management approach, the project started in July 1999 and was built and operational on schedule and below budget in 11 months, by June 2000.
The finished water has been extremely good with turbidity consistently less than 0.10 NTU and a 6-log removal of bacteria, giardia cysts and cryptosporidium oocysts. The chlorine dosage has been reduced to about 0.60 mg. Revelstoke users now have to pay more for their water — $225 a year per single family residence compared to $125 per year — but they have a reliable water source and one of the most cost-effective treatment plants in North America. Unit costs are about $0.30 per 1,000 litres. CCE
Client: City of Revelstoke
Prime consultant/civil, structural, mechanical, electrical, instrumentation, SCADA: Dayton & Knight, West Vancouver (Jack Bryck, P.Eng., Dennis Harrington, P.Eng. Ed Pratt, P.Eng., Doug Rhodes, P.Eng., Victor Wong, P.Eng., Sekip Okumus, P.Eng.)
Other key players: Bernd Hermanski Architects (building), Malcolm Pirnie (filter and process review), Maple Reinders (construction manager), US Filter/Memcor (equipment supplier)