Sault Ste. Marie Drinking Water System

Sault Ste. Marie's Drinking Water System

The Sault Ste. Marie Drinking Water System (SSM DWS) serves a population of approximately 66,000 (within the Urban Service Line area) of the City of Sault Ste. Marie and Batchewana First Nation. The typical annual water volume of water distributed each year is approximately 11.5 million cubic meters per with a maximum peak day is in the range of 45,000 cubic meters.

Water for the greater Sault Ste. Marie area is presently obtained from two independent sources. One source of supply is from six deep wells in 4 pumping stations located at the Steelton Pump Station, Goulais Pump Station, Shannon Pump Station and Lorna Pump Station. The water pumped from the wells is treated utilizing chlorine gas for primary and secondary disinfection.  Water quality and quantity within the aquifer are both excellent with very little fluctuation of both throughout the year.

The second supply source is surface water from Lake Superior at Gros Cap. The raw water from Lake Superior is pumped to the twin control tanks on Marshall Drive and then flows by gravity through a concrete watermain to the Water Treatment Plant (filtration plant).  Surface water at the treatment plant consists of direct filtration - incorporating chemically assisted coagulation, flocculation and dual media filtration but with no sedimentation. The plant is located on the south side of Second Line between Town Line Road and Carpin Beach Road immediately east of the Little Carp River. The plant is rated at 40,000 m3 per day but is capable of operating at higher levels for extended periods at times of high demand, subject to contact time limitations.

Sault Ste. Marie also treats the water to adjust pH by either adding soda ash (to raise pH) or injecting carbon dioxide (to lower pH) depending on the water source and the water’s natural characteristics.  This allows for stabilized pH throughout the distribution prior to the addition of blended phosphate for corrosion control.

The complete water supply system is monitored and controlled through a SCADA system from the Control Room at the Water Treatment Plant.

Distribution System

The distribution system is divided into two pressure zones (Pressure Zone Map); one below the escarpment and the second above. A 27,275 m3 reservoir located on Second Line west of Highway 17 North provides balancing storage for the pressure zone (Zone 1) below the escarpment. Pressure for Zone 2, above the escarpment, is provided by a 9,000 m3 reservoir located on Peoples Road at Coronation Drive. There are four identified booster pumping stations which provide water pressure for their respective areas. These include the Zone II Booster, Coronation St. Booster, Crimson Ridge Booster, and the People's Road Booster.

The sizes of the mains vary from 900 mm diameter to 50 mm diameter, providing a total length of approximately 470 km of distribution mains. The approximate breakdown of major pipe materials includes 51% cast iron, 26% ductile iron, 14 % PVC, and 9% concrete pressure pipe.

Gros Cap Raw Water Pumping Station

Water is received from an intake extending into Lake Superior, which is then gravity-fed to the raw water pumping station.  Water passes through a screening process to remove debris and is pumped to two large tanks on Marshall Drive.  The raw water pumping station has four pumps to maintain preset levels at the Marshall Drive tanks.  The station also has a diesel generator for backup power in the event of an outage.

Marshall Drive Raw Water Tanks

The Marshall Drive tanks receive raw lake water from the Gros Cap Pumping Station and discharges via gravity to the Water Treatment Plant on Second Line.

The Water Filtration Plant Process

The Plant consists of the following components:

Pressure Reducing Station 

The raw water entering the plant inlet first passes through a raw water isolation valve and then through the raw water pressure reducing valve which lowers the incoming water pressure to 125 kPa.  Under normal operations, water then flows thorough the intake energy recovery turbine system and into the low lift well.

Low Lift Pumping 

Two low-lift well cells contain four low-lift pumps, two in each cell. The low-lift pumps serve to pump water from the low-lift well to the flocculation tanks. Each low lift pump is equipped with a pressure relief valve, which serves to relieve excess discharge pressure back to the low lift well. The discharge pipe for each low lift pump is also equipped with an inline blender, which allows for thorough mixing of the aluminum sulfate which is added to the discharge flow of each pump.  The discharge flow from the low lift pumps flows through a common discharge header, then through the raw water flow control valve, and finally, onto the flocculation tanks. The raw water flow control valve varies the flow into the flocculation tanks to maintain a constant level in the filter inlet trough.

Coagulation and Flocculation

The raw water entering the plant contains suspended solid particles that must be removed from the water as part of the treatment process. Aluminum sulfate is added to carrier water that is added to the raw water discharge from the low lift pumps as a coagulant, which encourages the suspended solids in the water to clump together into larger particles called “floc”. The larger floc particles are then easily removed from the water by the filters.

Flocculation Tanks

Water from the low-lift pumps flows into four flocculation tanks. The flocculation tanks provide retention time to allow floc particles to develop. Each of the flocculation tanks is equipped with a variable speed mixer, which slowly stirs the water to aid in the formation of floc particles. Manual gate valves located at the inlet and outlet of each flocculation tank allow for the tanks to be operated as four individual tanks in parallel or as a pair of tanks in parallel, each with two cells in series. Water exiting the flocculation tanks flows into the filter inlet trough.

Filtration

The filter inlet trough feeds all four filters. The water slowly enters each filter through its dedicated inlet valve and flows down through the filter media (anthracite and sand), then out through the filtrate valve. Filtered water then flows from the filters into the chlorine contact chamber, where post-chlorination takes place, and then on to the clearwells.

Backwashing

The filters periodically require cleaning by backwashing and surface washing. A backwash cycle is a sequence of steps where the inlet valve is closed to allow clean filter water to be drained from the filter before closing the filtrate valve. The water flow through the filter is then reversed with potable water from the WTP main reservoir. The water is forced back up through the filter media by the backwash pumps in order to remove accumulated floc particles; the anthracite surface of the filter is washed as well by spray arms fed by the surface wash pumps. Used wash water flows into troughs near the top of the filter media and then into the two hydraulically connected wastewater settling tanks.

High Lift Pumping

Water exiting the chlorine contact chamber flows into the two clearwells, which provide extra chlorine contact time for disinfection of the water. From the clearwells, the treated water flows into the WTP main reservoir, which feeds the high lift pumps. There are three high lift pumps, which supply water to storage reservoirs within the distribution system. The water main from the high lift pumps also supplies water to the City’s West end.

Surge tanks are connected to the west end of the high lift discharge header to buffer the water surge from high lift pump operation.

Corrosion Control Plan

PUC implemented a corrosion control plan in 2015 to reduce lead uptake in the drinking water.  Sault Ste. Marie’s drinking water system is comprised of multiple water sources mixing surface water and ground water supplies.  pH stabilization is achieved to a target of 7.6 by the addition of soda ash at the surface water plant to increase pH, while the east wells utilize carbon dioxide to lower pH.  Blended phosphates are then added at all sites as a corrosion inhibitor to mitigate lead leaching from plumbing or service lines containing lead.

Sault Ste. Marie Well supply

The surface water facility provides approximately half of the daily water supply.  Fifty percent is also drawn from six deep wells in four pumping stations - Steelton Pump Station, Goulais Pump Station, Shannon Pump Station and Lorna Pump Station. The water pumped from the wells is treated utilizing chlorine gas for primary and secondary disinfection.  The well water is also adjusted with required chemicals stated in the corrosion control plan. Water quality and quantity within the aquifer are both excellent with very little fluctuation of both throughout the year.

Water Storage Reservoirs, Booster Stations and Pressure Reducing Station

Sault Ste. Marie has three pressure zones which are maintained by having two distribution storage facilities and four booster stations.  The drinking water system also has one pressure reducing station to adjust pressure to a lower elevation area.