2016 American Water Works Association

Spotlight On . . . ABH AY TAD WAL KAR R.C. Harris Water Treatment Plant: A Civic Vision for Toronto’s Water Supply THE “PALACE OF PURIFICATION” IS A...
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Spotlight On . . .

ABH AY TAD WAL KAR

R.C. Harris Water Treatment Plant: A Civic Vision for Toronto’s Water Supply THE “PALACE OF PURIFICATION” IS AN ARCHITECTURAL LANDMARK IN TORONTO, ONT., CANADA, KNOWN FOR STUNNING ART DECO DESIGNS AND MODERN TREATMENT PROCESSES.

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he R.C. Harris Water Treatment Plant (Harris WTP), shown in the photograph on this page, is the largest water treatment facility in Toronto, Ont., Canada, producing up to 40% of Toronto’s water requirements. Located at the foot of Victoria Park Avenue, the plant is an architectural masterpiece, designed in the classical version of art deco style. The original 455-ML/d (100-mgd) plant was constructed from 1932 to 1941 by the City of Toronto. The photograph on page 94 shows lowering of one of the intake wells in 1933. Only the west half of the filter building, along with the pumping station and the service building, were constructed in the 1930s, however. The plant was enlarged from 1955 to 1958 when an identical east wing was added to the filter building, increasing the plant capacity to 910 ML/d at a cost of US$7.3 million. The expansion included building a second intake, doubling the filtration and settling areas, and installing major pumping and electrical equipment. The plant has since been re-rated at 950 ML/d. The consulting engineering firms of H.G. Acres Limited and Gore and Storrie Ltd. designed both the original plant and the additions, and also supervised the construction of both.

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Opposite page: The R.C. Harris Water Treatment Plant. Above: Filter building (on the left) with alum tower on the right.

The plant was named after Roland Caldwell Harris (see the photograph on page 94), who was the commissioner of works for the former City of Toronto from 1912 until his death in 1945. The name was bestowed upon the plant as a fitting memorial to Harris’ long and brilliant career in public service. As commissioner, Harris’ scope took in—and often integrated—water supply, sewerage and sewage treatment, roads, bridges, transit, and greenspaces, providing what architect Steven Mannell called “both service and amenity in monumental forms” (Reeves & Palassio 2008). At the Victoria Park site, Harris had a vision of building grand waterworks buildings, which in conjunction with the surrounding green-space and the beach, would constitute one of the most beautiful areas in Toronto (see the photograph on this page). Owing to

Harris’ foresight and that of his consultants, the original plant included all embedded piping for future enlargement, as well as space for future equipment. The waterworks projected the new face of the city outward, embodying a conscious sense of civic duty. Harris was also the manager of other legacy elements of the water supply system, including the Rosehill Reservoir and the High Level Pumping Station. In 1987, the plant became a literary landmark when it was mentioned in an acclaimed novel, In the Skin of a Lion, by Michael Ondaatje, who wrote, “Harris dreamed the marble walls, the copper-banded roofs.” Ondaatje, a Canadian writer and Booker Prize winner, referred to the plant as “the palace of purification.” On June 9, 2011, the Canada Post released a commemorative stamp of the Harris WTP, which was one of five buildings highlighted in

Canada for their important art deco designs. The plant has been declared a national historic site by the Canadian Society for Civil Engineering and is designated under the Ontario Heritage Act for architectural and historical significance. In 2013, the plant received the AWWA Water Landmark Award.

ARCHITECTURE The Harris WTP is an excellent large-scale example of how the art deco style could integrate late Romanesque revival and modern classical forms of architecture (e.g., round-arched openings, simplified pediments and pilasters). During the first phase of construction at the plant (1932 to 1937), art deco and modern classicism were popular styles for civic and semi-public buildings in North America. The plant is situated on Lake Ontario with a temple-like pavilion of the pumping station where low-lift

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Above: Lowering of the intake well in 1933. Right: Rowland Caldwell Harris (left) with his driver in 1933.

and high-lift pumps are located. The pumping station has a plaster ceiling 56 m long and 24 m wide, which was one of Canada’s largest when it was hung in 1937. Queenston limestone is used in the pilasters, carved panels, and stringcourse at the west end, the columns supporting the overhead traveling crane, the window surrounds, and on the walls above the Frontenac Cleartex herringbone tilework. Behind the east façade of the pumping station is the alum tower, topped by belvedere. A walkway and a stair climb the scope on the central axis of symmetry, leading to the entrance of the filter building. The ceremonial entrance to the filter building shown in the photograph on page 95 hints at the grandeur inside. The squared spiral staircase has treads and landings in Roman travertine, a marble stair string, and a wrought- and cast-iron balustrade with an ornate newel 94

post. The rotunda’s focal point is the signal pylon (see the photograph on page 95), which indicates time and filter backwash conditions. The pylon is built up with bands of Valternache (green-black) and Rosata Clair (honey-colored) marble and is inset with chrome-accented bronze panels. The floor under the pylon has a compass pattern composed of beige and black terrazzo (marble chip) fields, Valternache trim, and Lorado Chiaro (buff-colored) marble insets. The polygonal ceiling dome is embossed with geometric patterns and contains a spider’s web skylight. Each of the two filter operating galleries is more than 110 m long and provides access to 20 filters (see the center photograph on page 96). The floors and base heaters use the same materials found in the rotunda. The filter operating consoles still have the original Valternache and Rosata Clair facing and bronze

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doors (see the bottom photograph on page 96). A wealth of flattened, geometric art deco ornament in stone, brick, and metal is found throughout the plant. The use of rich materials like marble and bronze in the interior is both notable and characteristic of the times. A “Machine Age” capital and other decorative work in stone and brick on the wall of the pumping station express the building’s function (see the top photograph on page 96). While unusual for Toronto’s utilitarian structures, lavish treatment was typical in art deco–style filtration plants across North America. The intent was to create a water “showcase” for the public. As one commentator said of the Harris WTP in 1941, “The interior decoration of all buildings and the architectural features of the entire structure justify it being described as amongst the most modern and beautiful plants in America.”

Above: Ceremonial entrance to the filter building. Right: Rotunda with signal pylon.

PLANT PROCESSES The Harris WTP serves as one of the critical components of the Toronto water system. It is a conventional filtration plant that treats surface water from Lake Ontario. The unit treatment processes consist of screening, prechlorination, chemical coagulation, flocculation, sedimentation, filtration, corrosion control, chlorine disinfection, fluoridation, dechlorination, and chloramination. Raw water enters a surge well via two intake pipes and a single intake tunnel and is discharged to eight traveling screens. The screened water is pumped via six low-lift pumps to the mixing chambers for pretreatment. Chlorine can be dosed at the intake cribs and/or intake well prior to screening. Pretreatment consists of coagulant addition, flocculation, and clarification. Phosphoric acid, used for corrosion control of lead, can be applied downstream of the coagulant application point during warm water conditions to aid in aluminum residual control. Flocculation consists of 12 hydraulic spiral overand-under flow design tanks, with four sets of three cells in series in each tank. Following flocculation, the water enters the clarification process where solids settling occurs

in six horizontal cross-flow settling tanks. The clarified water then undergoes filtration via 40 dualmedia filters. In the reservoir, filtered water is dosed with chlorine for disinfection, hydrofluosilicic acid for fluoridation, and phosphoric acid for corrosion control. Dechlorination is provided using sodium bisulphite or sulphur dioxide at the reservoir exit. Ammonia is dosed at the reservoir outlet channel for chloramination. In 2004, the process control system at the plant was upgraded to a state-of-the-art supervisory control and data acquisition system that allowed for less attended operation while providing opportunities for greater efficiencies and process optimization.

RESIDUALS MANAGEMENT FACILITIES (RMF) In August 1999 Toronto Water completed the class environmental assessment to find the preferred solution for managing residuals from the Harris WTP. Before this, residuals from the water filtration process were returned to Lake Ontario without treatment. The recommended alternative involved the construction of underground equalization tanks and a pumping station at the Harris WTP, with a forcemain to a dedicated treatment facility at the nearby A s h b r i d g e s B a y Wa s t e w a t e r Treatment Plant site. As a result of public outcry in 1999 about the impact of aboveground structures at the Harris WTP

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Top: Carved feature portraying a pump impeller moving water. Center: Filter operating gallery. Bottom: Filter operating console with bronze doors.

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affecting its heritage and historical importance, and the increasing loads at the wastewater plant, a new approach was developed to manage the residuals. The new approach involved treating all residues at the Harris site in completely underground facilities (see the top photograph on page 97). This approach posed several significant challenges for the consultant and the contractor, including the requirement that the facility be constructed entirely below grade so as not to impact the heritage aspects of the Harris WTP (see the bottom photograph on page 97). Additionally the only available land for the RMF, with a footprint about the size of a Canadian Football League field, lay on a steep 30-degree slope between the existing filter building, the service building, and the 2,100-mm-diameter treated water conduits that carry water to the distribution system. Because of the importance of this plant to the city, no disruption in production could be tolerated, unless planned and coordinated several months in advance and only for short durations during the low-water-use seasons. As a result, the temporary shoring systems employed to support the adjacent structures during construction were a prime consideration in both the design and construction phases of the project. The primary shoring systems were a combination of conventional pile and lagging, conventional interlocking caisson walls, and the relatively new system of continuous flight auger interlocking walls. The continuous flight auger method minimizes soil loss during installation of the walls and so was used to shore the large excavation adjacent to the existing filter building, full underground reservoir, and the treated water conduits. Any significant movement of these facilities could have resulted in a disaster; therefore, the shoring in this location was subject to extremely stringent

FIGURE 1 allowable movement criteria and continuous monitoring. At its highest elevation, the completed structure is approximately 23 m above the deepest point in the RMF, the deepest point being approximately 7 m below lake level. The structure is a complex system of multi-level tankage and process galleries, reflecting the difficulty of trying to fit a new treatment train into a relatively small footprint on a sloping site. Careful staging of the work offered opportunities for collateral improvements in the heritage features—in particular, the loading area at the garages were expanded to include chemical handling. This allowed for the fountain terrace— which was located outdoors and had deteriorated over time—to be restored to its original design. The installation of the RMF was completed in 2008 at a cost of US$60 million. The facility consists of 10 decant tanks, four thickeners, and two centrifuges. Dewatered sludge is stored in bins and moved offsite for landfill disposal.

New approach for RMF

Clarification/ thickening/ storage Equalization/ decant tanks

Dewatering

Tracks through garage bays No. 3 and 4

THE R.C. HARRIS LEGACY For more than 20 years, Toronto Water has integrated heritage management principles into both capital projects and day-to-day operations as a result of a change in management philosophy. The intent has been to sustain existing architectural features and, wherever feasible, restore elements that have been modified or removed. Community support for this approach has been sustained through the R.C. Harris Public Advisory Committee, which meets regularly with the plant staff. Harris’ vision, sketched out in 1913, was to establish a safe and secure water supply system for Toronto while showcasing the importance of water. His legacy continues to live on for future generations.

ACKNOWLEDGMENT The author thanks Wayne Reeves, chief curator, Toronto, and Gord

Top: New approach for the residuals management facilities. Bottom: Large excavation adjacent to the filter building and full underground reservoir.

Mitchell, plant manager, Harris WTP, for their contributions to this article.

ABOUT THE AUTHOR Abhay Tadwalkar is the manager of operations efficiency at City of Toronto, 55 John St., Toronto, Ont., M5V 3C6 Canada; [email protected]. Tadwalkar is a registered professional engineer in Ontario. He has been with the City of Toronto for more than 30 years

and is in charge of process and energy optimization in both water and wastewater treatment plants. He is the past president of Ontario Water Works Association and is a member of the Water Research Foundation Tailored Collaboration Review Committee. http://dx.doi.org/10.5942/jawwa.2016.108.0146

REFERENCE Reeves, W. & Palassio, C., 2008. HTO: Toronto’s Water From Lake Iroquois to Lost Rivers to Low-Flow Toilets. Coach House Books, Toronto, p.112.

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