The raw water source for our drinking water is the South Saskatchewan River which runs through Medicine Hat. The quality of the water in the river fluctuates seasonally meaning the treatment plant process must adapt with each fluctuation. Due to the fluctuations of the water quality in the South Saskatchewan River, the quality of the water taken in from the river generally falls in the following ranges:
- Turbidity - 1 to 10,000 NTU
- pH – 6.5 to 8.5
- Total Hardness - 130 to 270 mg/l (7.6 to 15.8 grains)
- Alkalinity - 120 to 240 mg/l
- Temperature - 1 to 24 oC
The treatment process begins at the bottom of the South Saskatchewan River with the raw water intakes.
Raw Water Intakes
There are a number of different intakes located along the bottom of the South Saskatchewan River, with the first being constructed in 1912. The purpose of an intake is to draw water from the lowest possible depth in the river to ensure we will be able to continue to draw water in the event of drought conditions.
Raw Water Pumps
Raw Water Pumps, aka low lift pumps, transfer the untreated water from the intakes into the Water Treatment Plant for processing. There are multiple low lift pumps located in close proximity to the river to allow for flexibility where we draw river water into the plant. Intakes and pumps are equipped with screen mechanisms to prevent the passage of trash, logs or other foreign materials into the plant.
The latest raw water pumping station is equipped with self-cleaning traveling screens which are cleaned automatically, whereas the older designs still require manual cleaning. The main low lift pump, referred to as #5LL, is a vertical turbine pump with a rated capacity of 65 million litres per day.
Solids Contact Units
Designed to treat the river water entering the plant, the Solids Contact Units (SCU’s) act as the primary treatment mechanisms for the City‘s Water Treatment Plant. The Plant is currently equipped with multiple SCU’s to accommodate seasonal flow variability and redundancy.
River water entering an SCU slows down as it passes through the various chambers housed within the unit. Aluminum Sulphate (Alum), referred to as a coagulant, is added to assist particulates found in the river water to clump together becoming heavier. These heavier particles, referred to as floc, settle while the clear water rises to the top of the unit around the perimeter where it is sent on to the filtration part of the treatment process.
Dual Media Filtration
The filters used in the Plant are called dual media because they consist of anthracite and crushed quartz. These filters are supported by an underdrain system to allow the water to drain from the filter while retaining the media. The purpose of filtration is to remove very fine particulate impurities from the water being treated as these particulates have the ability to shield microorganisms from chlorine disinfection. A common misconception of filtration is that particles are removed mainly via a “straining” process; however this is not the case. Filtration is essentially both a physical and chemical process.
In 2000, the Plant was retrofitted to allow for the feed of a polymer filter aid. As a result, filter effluent (discharge) particulate quality is among the best in Western Canada with turbidity levels consistently in the 0.03-0.05 NTU range with the regulatory requirement being below 0.3 NTU. The City of Medicine Hat Water Treatment Plant’s “in-house standard” for filtered water quality is below 0.1 NTU 100% of the time, so before any filter is put back into service, it is “filtered to waste” until effluent quality is lower than 0.1 NTU which is well below the regulatory requirement.
Baffled Clearwell System
The filtered water is transferred to the Baffled Clearwell system next. The clearwell is a multi-chambered storage system, much like a maze, where chlorine is administered and given enough contact time with the filtered water to disinfect prior to sending it onto UV disinfection. The contact time with the chlorine is essential to ensure that the potable water supply remains free of any disease-causing microorganisms as it continues through the distribution system. A minimum chlorine residual of 0.1 milligrams per litre (mg/L) is required to remain in the treated water distribution system at all times.
Ultraviolet Light Disinfection System
Part of the 2008 expansion was the installation of three Ultraviolet (UV) reactors in place of the Secondary Clearwell to enhance the disinfection and treatment of the clear water. UV disinfection is a revolutionary new concept in water treatment. It is a flexible, safe and cost-effective technology that effectively inactivates any disease-causing microorganisms found in raw water.
During the winter months, one reactor is in service, whereas during the peak summer demand a second reactor is used as needed. The third reactor unit is kept as a back-up should it be required. UV is particularly effective in the deactivation of Giardia and Cryptosporidium. UV disinfection systems are completely safe for human use and have been proven through many years of scientific study.
High Lift Pumps
The last stop for the treated water before leaving the Treatment Plant is the High Lift Pumping facility. Treated, also referred to as potable, water is sent to the distribution system by way of the High Lift Pumps. Currently, there are five vertical turbine pumps (with near future addition of a sixth) within the facility. Of the five pumps, two pumps are 450 horsepower pumps moving the water at 256 litres per second and the other three pumps are 850 horsepower pumps moving the water at 516 litres per second. Control of these pumps is through a sophisticated control network based on observed water demands throughout the City at any given time. These pumps distribute the water to our various reservoirs and booster stations via a network of water mains and pressure regulating valves.
Normal winter operation includes the alternation of one small and one large pump. During peak summer demand, all three large pumps can be used in succession producing in excess of 1500 litres per second or over 125 million litres per day.
Chemicals used in the City of Medicine Hat Water Treatment Process
Aluminum Sulphate (alum) – a coagulant, added in the Solids Contact Unit, which causes very fine particles found in the raw water to clump or floc together into larger, heavier particles to settle out.
Caustic Soda (Sodium Hydroxide) – used primarily to adjust pH to prevent excessive corrosion within the distribution system. When large amounts of coagulant chemicals are used, like alum, the pH of finished water may be suppressed enough that it warrants the feed of caustic soda to bring the pH back up. In general, caustic soda is only required during periods of high spring runoff. Spring run-off water is generally higher in turbidity which means additional alum is used in the treatment process, therefore requiring the addition of caustic soda.
Chlorine – a disinfectant used to destroy pathogenic organisms in water. Prior to chlorination practices (early 1900’s), outbreaks of cholera, typhoid and dysentery were regular occurrences resulting in tens of thousands of deaths annually. Chlorination of water supplies has been the most significant public health accomplishment during the last 100+ years.
Polymer – a medium chain cationic polymer is used primarily as a filter aid. The function of a polymer is to bind small suspended particles to larger chemical flocs for easier settling and removal from water.
Potassium Permanganate – a strong chemical oxidizer used primarily for the treatment of taste and odour. It is used to oxidize iron, manganese and sulphide compounds in the raw water. The addition of this chemical must be very precise and quantified through laboratory tests prior to adjusting the feed rates. An overfeed of the chemical will produce an intense purple or pink colour in the water whereas an underfeed may result in taste and odour episodes.
Powdered Activated Carbon (PAC) – removes contaminants from water via “adsorption” and is also effective in taste and odour control. Feed rates must be monitored closely as PAC has the ability to penetrate filter beds in an overfeed situation. PAC is also effective in removing organic contaminants from raw water.
Sodium Bisulphate (SBS) – used to remove chlorine from Plant wastewater prior to discharge back into the South Saskatchewan River. Residual Chlorine can have a negative impact on aquatic life.
Note: Alum, Polymer, Powdered Activated Carbon and Potassium Permanganate are consistently added during the treatment process but are removed prior to entering the distribution system. Chlorine is the only chemical added which remains in the finished water; the amount of which is carefully regulated by Alberta Environment and Parks. Chlorine provides a barrier of protection against contamination within the distribution system.