AWWA ACE54529

The Town of Gillam, Manitoba, Canada is located approximately 1,100 kilometers north of Winnipeg, the capital city of the Province of Manitoba. The approximate longitude and latitude of the community is 9442' W, and 5621' N, respectfully. The current population of the Town is approximately 2,000 people. The original water treatment plant serving the Town was constructed in 1966 and was designed to treat approximately 1,800 m 3 /d of raw water from the Nelson and Kettle Rivers. The Town has experienced winter frost penetration of up to 3.65 m in depth and extreme minimum air temperatures of minus 46 degrees C. To cope with these temperature extremes the residents had been required to bleed their water services to prevent freezing. The Town had also bled dead-end mains to prevent freezing within the distribution system. A consequence of the required bleeding was that the average treated water demand within the Town in the years 1992 to 1995 was 2,500 m 3 /d. This equates to an average per capita demand of approximately 1,250 L/capita/d, three to four times what would normally be expected. The 1992-1995 maximum day demand was 3,750 m 3 /d, far exceeding the capacity of the water treatment plant and resulting in a deterioration of treated water quality. An action plan was developed to deal with the deteriorating water quality within the Town and the treated water wasted due to bleeding. The plan included the following key elements: design and construction of a new water treatment system capable of meeting the current maximum day demands; identification of the minimum required recirculation flow and temperature from the water treatment plant to prevent system freezing; identification of potential water distribution supply and return loops from the water treatment plant to reduce the bleeding of water; and, identification of water distribution system improvements to provide complete water distribution recirculation and fire protection. During the conceptual design stage, conventional treatment including flocculation, gravity settling and filtration wasinitially considered. However, following pilot testing and cost comparisons of the available options, the Town of Gillam decided to proceed with the design and construction of a new treatment plant system based on Dissolved Air Flotation (DAF) technology. The higher loading rates (7 m/hr.) and smaller retention time required by the DAF system also allowed the existing building to be modified and reused whereas conventional gravity settling would have required an expansion of the existing facility. To identify the minimum required recirculation flow and temperature of the water leaving the treatment plant; a model of the distribution system was created. The model was used to provide water travel times within the distribution system during various demand conditions and to ensure the required fire flow requirements were achieved. Water travel times were extracted from the model and used to calculate the heat loss within the distribution system. The modeling exercise resulted in the recommendation to heat the water leaving the water treatment plant to 4 degrees C and maintain a minimum recirculation flow of 24 L/s. The design temperature of the water returning to the water treatment plant was 0.5C. As a result of the constructed water treatment plant and distribution system improvements, the average day demand based on available data from 1998 to present is approximately 1,100 m 3 /d; a 55 percent reduction in average day demand. Treated water quality is excellent and freezing has not been an issue. Includes 2 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2001

Number of Pages:

18

File Size:

1 file , 1.6 MB