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Danbury’s water system has adequate sources of supply to meet current demands, but the margin of safety of 16% for 2004 and 2005 was very close to the 15% margin of safety recommended by the Department of Public Health and the Department of Public Utility Control. The margin of safety varied from 6% to 9% between 2000 and 2002. As the system is served by surface supplies, the production can exceed the safe yield to meet projected maximum month and peak day demands through 2050.

The existing safe yield is 8.7 MGD, consisting of 4.9 MGD from the West Lake system (West Lake Reservoir, Boggs Pond, Upper and Lower Kohanza Reservoirs, and Lake Kenosia Diversion), 3.3 MGD from the Margerie Lake system (Margerie Lake Reservoir, East Lake and Padanaram Reservoirs and King Street Diversion) and 0.5 MGD from the Osborne Street Well. The 2005 average day consumption was 7.48 MGD and 8.21 MGD in 2001.

An additional 1.0 MGD would be needed to provide a 15% margin of safety for projected average day demands of 8.41 MGD in 2020, and an additional 2.0 MGD for projected average day demands of 9.29 MGD in 2050. These figures to not include additional sales to surrounding Towns.

When the dams and dike for Margerie Reservoir and West Lake Reservoir were reconstructed several years ago, provisions were made to allow for the eventual raising of West Lake Reservoir 5 feet and Margerie Reservoir 3 feet. This was to provide additional storage for diversions from adjacent watersheds.

West Lake Reservoir Dam was constructed to the full height. Margerie Reservoir Dam and Dike were constructed wide enough to allow raising, but were not constructed to the full height. The spillway training wall was constructed to the full height.

At West Lake Reservoir, water is currently diverted from Lake Kenosia and the Kenosia Well Field. Raising West Lake Reservoir 5 feet would increase the storage capacity and the safe yield by 0.6 MGD to 5.5 MGD. The pumping stations and pipelines are already in place and operating. The additional costs would be for raising the spillway and raising Middle River Road along the reservoir. This cost is estimated at about $7.0 million.

At Margerie Reservoir the potential diversion would be from Lake Candlewood and would require construction of a pumping station and pipeline. This is a proposal with a long history. Raising Margerie Reservoir 3 feet would provide additional storage and would further increase the safe yield. The cost of raising the dam and dike would be about $1.4 million.

SEE MAP OF POTENTIAL DIVERSION

As Lake Candlewood is a privately owned hydro storage reservoir, Danbury would have to negotiate an agreement with the owner for access to the lake and purchase of the water.

The costs for the Lake Candlewood Diversion pipeline and pumping station were estimated at $3.6 million. The diversion from Lake Candlewood assumes no pumping from Memorial Day to Labor Day.

The table below shows the approximate safe yields of the Margerie System with a 30-inch pipeline and 5, 10 or 15 MGD pumping capacity from Lake Candlewood, both with and without raising the reservoir.

APPROXIMATE SAFE YIELD
OF MARGERIE SYSTEM IN MGD

As the Margerie Water Filtration Plant has a design capacity of 5.5 MGD, it would require expansion to accommodate the higher flows. The plant was built with provisions for adding two additional filters and an additional dissolved air floatation clarifier. These additions would increase the capacity to 8.25 MGD. The cost of the expansion has not been determined, but would be several million dollars.

A Comprehensive Water Distribution Study of the Danbury System was prepared in 1987. Along with internal improvements, recommendations were made for distribution improvements to allow Danbury to provide "up to 3.0 MGD to surrounding towns to the east." Neither the distribution system study nor the distribution system models have been updated.

These proposed improvements included: 1,600 feet of 20-inch main in Hayestown Avenue; 4,700 feet of 24-inch main in Tamarack Avenue, Sherry Lane, and Wixon Road; and 9,800 feet of 20-inch in Great Plain Road, Stadley Rough Road, Rockwell Road, Rubson Drive, cross country, Old Brookfield Road, and Federal Road to the Brookfield town line. To date, of the 16,100 feet needed, only about 1,200 feet or 7.5% has been installed, this in Federal Road near Brookfield.

The estimated cost of the remaining water mains would be about $3,200,000. If the quantity of water to be provided is significantly less than 3.0 MGD the costs would also be lower. This is due to the fact that the need for much of the pipeline would be eliminated as existing pipelines could be used, or the pipe sizes reduced.

The end of the 20-inch Danbury water main in Federal Road is currently about 700 feet from the Brookfield town line. This main is fed by two 12-inch mains within the Danbury Distribution system.

All costs were updated with Engineering News Record Construction Cost Index of 7422 for July 2005.

TOTAL DANBURY SYSTEM SAFE YIELD

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