Town of Port Hawkesbury

Drinking Water

INTRODUCTION

The Town of Port Hawkesbury's water is supplied from the Landry Lake Watershed. Landry Lake is located on the Port Malcolm Road east of the WTP in Point Tupper. The Landry Lake Watershed is operated and maintained by the Nova Scotia Department of Transportation and Public Works. The Landry Lake pumping station pumps water from the lake into an above ground storage tank. The water flows by gravity from the storage tank to the Town of Port Hawkesbury's Water Treatment Plant (WTP). The water that is supplied to the WTP is untreated and is called "raw water".

HISTORY

Prior to the Town of Port Hawkesbury using Landry Lake as the main source for water supply, the water was supplied by numerous wells located around the Town. Due to a limited water supply and increased demand due to Town growth there was a need for an alternate source of Water. In 1971 the Town constructed a new WTP in Point Tupper.

The 1971 WTP was an up flow clarifier treatment plant. At that time the plant was designed to treat 500,000 gallons of water/day. In 1986 there was an addition of two treatment filters to meet the water demands of the Town. The addition of the two new filters increased the WTP's capacity from the 500,000 gallons to 1,000,000 gallons per/day.

The Town of Port Hawkesbury built a new WTP in 1996. A complete new plant was built and attached to the old WTP building. The new WTP is a dissolved air flotation (DAF) technology. The process was first used for drinking water in Sweden in 1960. When the DAF unit was put in service the old up flow clarifier plant was taken out of service. With the addition of the new DAF treatment plant the Town could now treat up to 1,500,000 gallons of water per/day.

TREATMENT SYSTEM THEORY AND OPERATION

The raw water enters the WTP by gravity from an above ground storage tank. The raw water first passes through a fine screen to remove any large particles in the raw water. The water flows from the screen to a flocculation tank (floc tank). Flocculation is designed to create a large number of smaller floc particles that can be floated to the surface. Between the screen and floc tank there is chemical addition to the water. Aluminum sulfate (alum) is added so the fine particles coagulate together to form larger floc. Alum lowers the pH of water so there is also the addition of soda ash to raise the pH. The water flows from the floc tank to the gravity sand filter. An air and water mixture (dissolved air) is pumped in an upward direction at the entrance to the filter. The upward motion of dissolved air brings the floc that formed in the floc tank to the surface of the filter. The floc is then removed from the surface by mechanical skimming. The water remaining in the filter must exit downward through the filter media where particles adhere to the filter media. The filtered water flows from the bottom of the filter to a below ground storage tank (clear-well).

The filter media is made up of different media densities (dual filter). The media system has to be periodically cleaned to remove the particles. This cleaning of the media is called "back washing". Backwashing is pumping the clean water from the clear well back through the media from bottom of the filter. An air alone cycle is also used in a similar manner in the backwash cycle. When the filter is cleaned it is introduced back into the system to begin filtering water once again.

Between the filter and clear-well caustic soda, phosphate and chlorine are added. Caustic soda is added for additional pH control, phosphate is added for corrosion prevention and chlorine is added for disinfection of the water. The clear-well is used as a storage tank and also as a chlorine contact chamber. Sufficient retention time in the clear-well is needed to allow the chlorine to be in contact with the water for disinfection. The treated water is pumped from the clear-well to the distribution system. Fluoride is added to the distribution treated water as it exits the WTP and enters the distribution system. Fluoride is added to help prevent tooth decay.

DISTRIBUTION SYSTEM

The Town of Port Hawkesbury's water distribution system consists of three above ground storage tanks (two are currently in service), 27-30 miles of distribution piping, valves, hydrants etc. and one booster station with chlorine injection. Distribution piping ranges in size from 4 inch to 14 inch in diameter.

Under normal operating conditions the treated water is pumped into the distribution system approximately 18 hours a day from the WTP. The WTP will run 24 hours per/day under heavy demand periods such as with a water break. The Town pumped an average of 640,000 us gallons of water into the distribution system per/day in the year 2005. The water is pumped either directly to a consumer or by gravity from a storage tank. The water tanks are operated in a manner to ensure a good turnover of water in each tank daily.

The distribution system is divided into three zones. The three zones are high, intermediate and low. Each zone is either pressured by the WTP pumps or from one of the storage tanks. The storage tanks provide the pressure just by the elevation of the water in the tank. The storage tanks serve as storage and also as a water supply for fighting fires.

The Town operates a booster station to boost the pressure in one of the zones. The pressure is increased by additional pumping of the water. There is also chlorine injection at the booster station. The chlorine injection ensures that there is an adequate chlorine residual maintained in that zone.

The Town of Port Hawkesbury has partnered with the County of Inverness in respect to their Water and Wastewater systems. The County is erecting a water tower in Port Hastings and connecting to the Town of Port HawkesburyÙs water distribution system. The Town of Port Hawkesbury will supply water to Port Hastings and surrounding area in addition to the Town of Port Hawkesbury.