Environmental Science & Engineering - www.esemag.com - May 2005
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Designing a multi-purpose pumping and storage facility


Finished main pump room.
The Airport Road Reservoir and Pumping Station project was designed to supply enough water storage and pumping capacity to serve both the Regional Municipality of Peel and the Regional Municipality of York’s future water demand needs. These huge Ontario regions both have rapidly increasing populations.

The pumping station was proposed to pump to three separate pressure districts, Peel 4E, Peel 5E, and York. The facility was designed to provide adequate and safe drinking water to both municipalities’ residents, in a costeffective and timely manner. The client’s objective was to design a reservoir and pumping station that could meet the supply needs for the receiving water systems for projected flows in the year 2011 (Phase I), but also have the capability of upgrading the capacity to meet the ultimate design flows projected for the year 2036 (Phase II).

The client also had more specific objectives for the design of the pumping station itself. A hydraulic transient analysis was conducted on the entire water system, from the incoming water supply to the outgoing discharge pressure zones. This analysis looked into potential hydraulic transient issues, proposed surge control schematics, and proposed pump and valve operation. The pumping station included a surge protection system to minimize the impacts of potentially destructive forces due to high and low pressures in the discharge pipes. Emergency power was also included in the design to ensure the pumping station could continue to supply water in the event of power failures.

MacViro’s solution to the storage and pumping capacity needed to meet the future demands was to design a 52.5 megalitre reservoir footprint to supply the pumping station with an uninterrupted water supply. The reservoir was designed to meet the Phase II flows of 633 ML/d, but was only constructed to meet the design flows for Phase I of 316 ML/d. This resulted in the construction of two out of the three reservoir cells totaling 35 ML.

The pumping station was designed in a similar fashion to meet the pumping requirements for Phase II, but only constructed to meet the design flow for Phase I. The pumping station design is essentially three separate pumping stations housed under the same roof. This design costs much less than building three separate stations, since many components required to run a pumping station can be used by all three systems. There are three sets of pumps individually sized to meet the demands of the three individual pumping zones. All of the pumps share a common reservoir, suction is through two separate 1800 mm suction headers, and discharge is through three individual discharge headers (1800 mm, 1500 mm, and 900 mm).

Installation of piping and equipment in the main pump room.
Matching the pump motor drive efficiencies and large hydraulic head variations required variable frequency drives (VFD) to be installed. Pump selection and operation will be based on obtaining the best efficiencies and having gradual changes in flow to match the demand for York and Peel 4E. The Owner’s recognition of the operational flexibility advantages for this approach resulted in the addition of a VFD for Peel 5E.

The pumping system is protected from high surge pressures, due to power failure, in two ways. Lower pressure Peel systems (4E and 5E) are protected from high surge pressures by using four surge anticipating valves, two on each system. The York system, which has significantly higher surge pressures, is protected by using two 225m3 surge tanks. These tanks act as an air cushion to dissipate high water pressures and minimize downsurge effects in the pipelines.

Two 1825 KW diesel generators provide emergency power to the station in case of a power failure. The generators supply power to all essential equipment needed to run the pumping station. The generators were sized to provide power to run only two pumps on each pumping system.

Two chemical disinfection systems were designed to disinfect the water both coming into the reservoir and leaving the pumping station. A chlorine injection system with 16,000 L of storage for Phase I was designed to deliver chlorine, in the form of sodium hypochlorite, to the inlet of the reservoir and the discharge of the Peel 4E, Peel 5E, and York systems. An ammonia injection system with 16,000 L of storage for Phase I was designed to deliver ammonia to the York system only. This provides chlorine and ammonia in the York system, which combine to form chloramines for maintenance of a chloramine residual in the distribution system.

The station’s design allows for future expansion and installation of equipment to meet the Phase II design flows. Connection points and extra room were included to allow for the additional pumps, valves, piping, generators, chemical storage, and reservoir storage required for Phase II.

The communities that are being supplied by the Airport Road Pumping Station are rapidly growing, as are their water demands. Communities to the north, in both municipalities, rely heavily on well water. As the population grows, these wells will not be able to keep up with the demand. The Airport Road Pumping Station will start to supply communities that were originally on well water. This will allow the Yonge St. aquifer and the Oak Ridges Moraine watershed abstractions to be reduced.

Technical excellence and innovation
The use of an 800 tonne hydraulic crane, one of three in Canada, to drop equipment into the buildings saved months of inactive building time. Since the construction started in September 2003, there was a need to pour concrete foundations and erect building walls before the winter months would slow construction. It was decided to completely erect the pumping station walls before installing any equipment. Since much of the equipment was too large to fit through the pumping station service bay doors, and maneuver in place, the hydraulic crane allowed the equipment to be dropped into the pumping station through the roof opening.

In order to design an efficient and safe pumping station, a hydraulic transient analysis was used to model the proposed pumping station’s operation. The transient analysis was used to ensure that potential hydraulic transient issues pertaining to the environment, public health and safety, infrastructure risk management, energy efficiency and optimal pumping operation were identified and addressed. These issues included: Other objectives of the hydraulic transient analysis were to develop a surge control scheme that would protect the pumping station and the discharge feedermains from the high and low pressures induced by the emergency pump shut-down and start-up. It also outlined pump and valve operation procedures to provide efficient operation, while minimizing pressure surges related to starting and stopping equipment.

With regards to the low water level and suction conditions, the design of the reservoir was unique. It was designed to allow the reservoir to be drained down to almost entirely empty. The recessed suction lines allow the reservoir low water level to be set at the reservoir floor elevation. A typical reservoir would only allow the water level to drop to a few metres above the floor level before adverse conditions around the suction lines would occur. Since the Airport Road Reservoir can be lowered to essentially empty it takes advantage of the entire reservoir capacity.

Level of complexity
One of the most important obstacles to be overcome was the time constraint on the entire project. A reservoir and pumping station of this size would typically require three years to plan, design, and construct. The timeframe from the initial planning stages to final construction of the Airport Road Reservoir and Pumping Station was a mere one and a half years. Much of the design of the pumping station took place while construction of the reservoir and pumping building was in progress. An initial design was implemented and the construction started. Final design details were attended to during construction.

This reservoir and pumping station are complex compared to other more typical pumping stations. The complexity is due to the fact that one pumping station must pump to three separate systems. The station was simplified by housing all three systems in the same building and allowing them to share common resources (chemicals, emergency power, water supply) but they must be independently controlled by separate interfaces. Control sequences and programming for three separate pumping systems were provided. They all use common resources.

Hydraulic transient analyses were complex to perform due to the unique design of the pumping station and the three discharge pressure zones. Under normal circumstances, the transient analysis would be simple and straightforward, using just one discharge and one pressure zone. The Airport Road Pumping Station analysis needed to take into consideration three pressure zones consisting of over 19 pumping stations and reservoirs, and all of the interconnecting piping.

The inlet structure of the reservoir is a very unique design. The incoming water supply conditions posed a design problem, since the Airport Road Reservoir was at the same elevation as the incoming water line. Water needed to be pumped to a high point and allowed to flow by gravity to the reservoir.

If the reservoir water level was very low, the incoming water line could possibly run dry, due to gravity emptying the pipeline. This condition would pose a water quality issue, and “repriming” of the pipeline would be needed. To avoid this potential problem, the reservoir inlet structure was designed to keep the incoming pipeline flooded and pressurized to maintain water quality. The 16 metre high inlet structure provides 16 metres of head inside of the incoming pipeline. The height of the inlet structure water level can be regulated through three electrically operated weir gates.

The level of redundancy for the suction headers requested by the client added to the complexity of the facility. The client wanted to have the ability to continue pumping even if a suction header had to be taken out of service. For this reason, two suction headers were designed to take water from alternating reservoir cells.

Conclusion
The new facility will achieve sustainability of our natural resources by reducing the demand for water on the natural aquifers and water tables, and by reducing the number of households that rely on groundwater. The pumping station and reservoir were strategically located in an area that would not pose any negative impacts on agriculture, hydrology, landforms, soils, or fisheries.

An Environmental Assessment Report for the York/Peel feedermain and an Environmental Study Report for the Northeast Brampton Water Supply were conducted to ensure that environmental principles were followed. The location was chosen to minimize environmental impacts, based on the findings of the two reports. Feedermains leaving the pumping station were mainly constructed on road right-of-ways and through existing pipeline corridors to avoid any environmentally sensitive areas.

The emergency power system has been equipped with load monitoring and peak shaving capabilities to become a Provincial Smart Energy plant. The Airport Road Pumping Station can monitor power consumption levels on the power grid and start the diesel generators to reduce the power consumption of the pumping station during high demand periods. The current diesel generators are also capable of bi/fuel power generation using natural gas. This capability for use of the generator with natural gas will also allow for reduced air emissions.

For more information, contact Jeff Radley, e-mail: jradley@macviro.com.

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