Chapman Creek Water Treatment Plant

OVERVIEW

The SCRD supplies water to approximately 22,000 customers on the Sunshine Coast, with over 90% of this water coming from Chapman Creek. The new Water Treatment Plant is adjacent to the existing Selma Park Zone 2 reservoir. Until Spring 2004, surface water from Chapman Creek received little treatment, with sedimentation and chlorine addition only.

The water quality of Chapman Creek is good for most of the year, however colour and turbidity levels exceed drinking water guidelines during spring runoff and following heavy rainfalls. As well, the water is very corrosive to piping. On an untreated surface water source like Chapman Creek, there is also the potential for waterborne diseases including giardiasis (beaver fever) and cryptosporidiosis.

The Chapman Creek Water Treatment Plant was placed into operation in March 2004. The total construction cost was $7 million. $3.8 million was paid through a Canada/BC Infrastructure grant. The water treatment process consists of chemical injection and rapid mixing, coagulation and flocculation, clarifying by floatation, filtration and disinfection. Ultra violet light is used as the primary disinfection system followed by chlorine disinfection.

Benefits of the new water treatment plant include:
• Reduction of colour due to organic material
• Increased protection from bacteria and viruses
• Reduction in the amount of chlorine required for disinfection.

The water treatment plant supplies safe and excellent quality water to residents and visitors to the Sunshine Coast.
Water flows from the intake on Chapman Creek through an existing sedimentation box, where the water flow is slowed to allow settling of sand which can be manually flushed out. Water then travels by gravity pipeline for approximately one kilometer to a new raw water pumping station.

This pumping station consists of three low lift pumps which supply all the flow to the new treatment plant. Each pump has a capacity of 16ML/day and operates on variable speed drives. Two pumps only can operate together. The raw water is pumped to the main treatment plant building which is adjacent to the existing 13 ML Selma Zone 2 reservoir.

PLANT PROCESS

Ever wonder how your water gets cleaned? Where does it go once its pulled from Chapman Creek? Click here to see an illustration of our water treatment plant! (Not to scale)

The water treatment plant process consists of chemical injection and rapid mixing, coagulation and flocculation, clarifying by flotation, filtration and disinfection. Treated water is discharged into the adjoining reservoir prior to entering the distribution system.

Rapid Mixing
Raw water enters the plant by a 600 mm water main and passes through a flow meter which measures total flow and is used to adjust the chemical feed amounts. The plant uses aluminum sulphate (alum) as a coagulant, which is injected at the head of the plant. The liquid alum is rapidly mixed in the water by a pump and diffuser. Water then flows to a flow splitter box where soda ash is injected. The soda ash solution increases the low pH of the raw water.

The flow splitter box divides the water flow into two pre-treatment process trains. Each train consists of two flocculation tanks and one DAF tank. Following this are four filters. During lower flows from October to April, one process train and two filters are in operation; with both trains and four filters required for the spring and summer month's operations.

Coagulation and Flocculation
Alum is used as the coagulant, which results in the clumping together of fine particles which cause colour and turbidity, into larger particles called floc. Once the alum has been injected into the raw water, the water enters the flocculation tanks where it is gently mixed. The flocculators are mechanical paddle mixers with one mixer in each tank. The first tank mixing is done at about twice the speed as the second tank. Detention time at maximum flow is 23 minutes.

Flocculation Tanks 4 (2 per train)
Volume per cell 110 m3
Water depth 4.40 m
DAF Clarification

Water leaves the flocculation tanks entering into the bottom of the dissolved air flotation (DAF) tanks. There is a slanted baffle plate in the first section of each DAF tank where aerated water in injected from recycled lines. Millions of microscopic air bubbles (20-50 micron diameter) are released and float to the surface of the DAF floating the floc particles to the water surface. This floc is skimmed by a continuously rotating skimmer brush and sent to waste. Clean water is collected at the bottom of the DAF through launder pipes that lead to the filter influent channel.

DAF Clarification
DAF tanks 2 (1 per train)
DAF size 5m x 9.5m
Water depth 3.9 m
Surface loading 12.2 m/hr
Maximum flow 13.9 ML/day/chamber

Filters
Water is diverted to any of the four filters from the filter distribution channel. Polymer is added as a filter aid and also added to backwashed waste water. The rapid rate filters are gravity down flow filters with dual media - 500mm of anthracite on top of 250 mm of sand. The filters are backwashed from a submersible pump pumping treated water and air scoured by one of two blowers.

Filters
Filters 4
Filter size 6.1m x 3.6m
Water depth 3.0 m
Filter media 500mm anthracite
250mm sand
Disinfection

UV light is used as the primary disinfection system just before the treated water leaves the plant. Chlorine gas is the secondary disinfectant, added first in the filter distribution chamber before water enters the filters, and then also in the effluent chamber as the treated water leaves the plant prior to flowing into the 13 ML reservoir. Chlorine is also added as required as the treated water leaves the reservoir for the distribution system.

Soda ash is also injected in the effluent chamber once the treatment process is complete, again to raise the pH of the treated water.

Residuals
The treatment process produces sludge from the removal of colour and turbidity in the DAF and filter processes. Floc from the DAF process and backwash waste from the filters is flushed by gravity to the old open water reservoir 1.5 km from the water treatment plant. The old reservoir was converted to a sludge settling basin where the water is decanted and piped to an adjacent gravel and sand operation.

Plant Controls
Two new standby diesel generators are available for automatic switchover in case of a power outage. A 450kW generator powers the main plant with a 100kW unit powering the raw water pump station. An existing 35kW generator powers the chlorine building in case of a power outage.
The new plant has a networked SCADA system allowing for onsite plant operation with data logging and report generation, and remote monitoring and alarming through the SCRD monitoring system.

Staffing
The plant is operated with one operator on day shift, seven days a week. There are four trained operators who share the work on a rotational basis throughout the year.

The Chapman Creek Water Treatment Plant was commissioned in March 2004, supplying safe and excellent quality water to Sunshine Coast residents and visitors.