Danbury, CT Water Supply Resource Inventory

Emergency Planning
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Each of the ten municipal plans of conservation and development has policies towards aquifers and water supply watersheds. Danbury's and the other nine have been copied and placed into one regional file to facilitate comparisons.

1) Sugar Hollow Aquifer: In the southernmost section of Danbury, primarily to the east of Route 7 and shared with Ridgefield and Redding, is located the Sugar Hollow Aquifer. This resource includes an area of 310 acres of saturated thickness of ten feet or greater. (All acreages below represent this same variable).

Pond over Danbury's Sugar Hollow Aquifer.
Photo courtesy of Rick Gottschalk.

2) Kenosia Aquifer: Moving north up Route 7 and located under the Danbury Airport and Danbury Fair Mall is the large Kenosia Aquifer, 1,640 acres, extending to the north side of Lake Kenosia and then westerly along I-84 to the intersection of Route 6 and Aunt Hack Road.

3) Still River West Aquifer: The next aquifer in Danbury is in the center of the City. This is the 1,120 acre Still River West Aquifer. Centered on White Street, it extends north on the east side of Main Street to I-84. On its south side it follows Main Street into Rogers Park, also continuing easterly along the railroad right of way and along Shelter Rock Road.

4) Great Plain Aquifer: Then due north is the Great Plain Aquifer, with an area of saturated thickness of ten feet or greater of about 290 acres. Its location is along the relatively level land along Great Plain Road, east of Danbury Town Park and north of I-84.

5) Still River Middle Aquifer: To the east of this resource is the Still River Middle Aquifer. This aquifer begins in the I-84 & Route 7 interchange area and extends northeasterly along the Still River between Federal Road and Route 7.

6) East Swamp Aquifer: Turning to the south along the Danbury - Bethel border, the East Swamp Aquifer enters from Bethel. It follows Limekiln Brook and extends north to Newtown Road and almost reaches I-84 Exit 8. There are 870 acres of saturated area of ten feet or greater.

7) Sympaug Brook Aquifer: To the south, a very small portion of the Sympaug Brook Aquifer crosses over from Bethel along Route 53.


Almost 42% of Danbury's total land area is in use as public water supply watershed. This includes both Danbury's own substantial watersheds and those in use for other communities. Some of the water drained from these lands is used as water supply within Danbury and some drains out of the town and is used elsewhere.

While Danbury has its own well defined internal need for additional water supply, its supply system may also be a source for other communities, as shown in this 2006 HVCEO report.

Danbury, the Housatonic Valley Region’s central city, ranks third of the ten municipalities in the region in terms of total land area used for water supply drainage, following Redding's 87% and then Ridgefield at 62%.

Danbury's zoning regulations maintain a protective overlay zone for the existing water supply watersheds within the City. Not just Danbury’s own water supply watersheds are covered but those of Bethel, New York City and the Aquarion Water Company as well.

As a result, development applications and permits are subject to some limitations and additional scrutiny. A citywide hazardous substance management ordinance complements the zoning overlay.

1) Croton River Watershed: The extreme northwestern corner of the City, about 1,000 acres of land, drains westward towards the East Branch of the Croton River in Town of Southeast, N.Y. This is part of the Croton River Watershed.

The East Branch Reservoir in nearby New York State.

Water from this area flows to the East Branch Reservoir and from there to the Croton Reservoir for consumption in New York City and environs. This use of Danbury’s water by New York City for water supply purposes began back in 1842.

2) Kenosia Watershed: The Kenosia Watershed in western Danbury is centered along the I-84 corridor. This supply shed designation dates from 1984 when Danbury added piping to make it possible to use surface water in Lake Kenosia for supplemental water supply, pumping it only on rare occasions northward to the West Lake Reservoir.

The Lake Kenosia diversion is designed as a flood skimming operation and therefore Lake Kenosia storage is not utilized in the calculations of safe yield. The pump station has the capacity to divert up to 9 million gallons per day from Lake Kenosia to West Lake Reservoir, but only during the non-swimming season, and only when West Lake Reservoir does not fill from other water supply watersheds.

The area of Lake Kenosia water supply watershed in Danbury is about 3,020 acres. Additional upland acreages for this watershed are located to the southwest, within adjacent Ridgefield, CT and in adjacent New York State.

In 1997 an important state policy change was made regarding the status of the Kenosia Water Supply Watershed. Rather than identifying on the State Plan Map that area’s remaining vacant lands along I-84 as in the Conservation Category, these would now be classified as part of the Urban Growth Category, thereby allowing state support for more intensive development than if Conservation.

OPM staff notes from 1997 identify the following summary of public comment on the issue and resulting OPM recommendation:

“Issue: Change the Lake Kenosia, Class II public water supply area in western Danbury along I-84 from Conservation to a Growth Area. The Housatonic Valley Economic Development Partnership has designated this section of Danbury as the area of greatest economic development importance within the region. Lake Kenosia can only be used in a water supply emergency. Withdrawal is limited to the winter months and the water supply has not been used since it was first designated in 1981.

The City has enacted strict controls on the type of development that may take place in the watershed of Lake Kenosia. Stormwater drainage requires pretreatment. A maximum of 50% of a lot may be developed if there are environmentally sensitive areas on the lot. A watershed management plan is in preparation. If Lake Kenosia is permanently lost as an emergency water supply source, there are other sources within the region that may be substituted in the future.”

The OPM staff record continuing, “Recommendation: It is recommended that the Class II type lands within the Lake Kenosia watershed between the water body and the New York border be changed from Conservation to Growth because: 1) this area is of the very highest importance to the region’s economic health; 2) the very low marginal value of the water resources for drinking water purposes; 3) adopted water supply plans call for expanding drinking water resources in other areas, and 4) extensive implementation of local regulations that focus on the continued protection of water resources from the impacts of new development.”

3) Kohanza Brook Watershed: The Kohanza Brook Watershed (West Lake Reservoir system) occupies much of western and northwestern Danbury. The best landmark to serve as a dividing line with the Padanaram Brook Watershed (Margerie System) is the ridge along which runs Route 39. The Boggs Pond Reservoir, feeding into West Lake Reservoir, dates from 1905.

Danbury's West Lake Reservoir.
Photo courtesy of Rick Gottschalk.

According to the Danbury Water Department's 6/2003 Water Supply Plan, "The safe yield of the West Lake System is 4.9 million gallons per day. The West Lake System consists of West Lake Reservoir, Boggs Pond, Upper and Lower Kohanza Reservoirs, Lake Kenosia Diversion, and the Kenosia Well Field."

4) Padanaram Brook Watershed: The Padanaram Brook Watershed (Margerie Reservoir System) occupies much of western and northwestern Danbury. Margerie Reservoir itself was built in 1935 and went into operation in 1937.

According to the Danbury Water Department’s 6/2003 Water Supply Plan, "The safe yield of the Margerie surface water supply system is 3.3 million gallons per day. The Margerie system consists of Margerie Reservoir, King Street Diversion, East Lake Reservoir, and Padanaram Reservoir. The proposed Ball Pond Brook and Lake Candlewood Diversions would be included in this system in the future."

See also the CT Department of Public Health's assessment report for the Kohanza Brook and Padanaram Brook Watersheds.

5) Ball Pond Brook Watershed: Ball Pond Brook runs easterly through New Fairfield to Candlewood Lake. Its drainage area includes Short Woods Brook as a major tributary. The entire Ball Pond Brook Watershed occupies a large central portion of New Fairfield but only about 125 acres in Danbury. This is along Bear Mountain Road near the New Fairfield Town Line.

For many years the waters of Ball Pond Brook have been under consideration as a future supplemental source for Danbury's nearby Margerie Reservoir.

6) Candlewood Lake Watershed: If Danbury ever taps Candlewood Lake as a water supply source then that part of the Candlewood Lake Watershed that lies within Danbury, primarily the vicinity of Danbury Bay, would also become existing, rather than potential, water supply watershed.

7) Saugatuck River Watershed: All of the land in the southern panhandle of Danbury, on the south side of the divide from the City’s Still River Watershed, is part of the Saugatuck River Watershed draining to the Saugatuck Reservoir in Redding. The total land area in Danbury drained south to the Saugatuck Reservoir is about 2,780 acres.

8) Sympaug Brook Watershed: Also in southern Danbury, on the Still River side of the drainage divide and near the Bethel Line, are found Mountain Pond, draining down to Eureka Lake, and their associated water supply watershed areas. These small reservoirs in the Sympaug Brook Watershed are owned by the Bethel Water Department and contribute water to the Town of Bethel to the east.

Their drainage area occupies only about 400 acres of southeastern Danbury. Some additional acreage right on the Danbury-Bethel Line is part of the Murphy’s Brook drainage area, a reserve supply on occasion pumped from the Brook up to Eureka Lake.


The Connecticut Department of Environmental Protection (CT DEP) has developed water quality standards in conjunction with the principles of the federal Clean Water Act.

As a result each stream or water body in the Region has two classifications, one for existing use, and one for ultimate future use, written in a existing/future format such as "B/A" or "A/AA". The highest standards are reserved of existing and potential water supply areas, which are AA.

The DEP seeks to bring every water body in the State to a minimum classification of "B" or better, which would not be suitable for human consumption without treatment, but could be suitable for recreational use, fish and wildlife habitat, agricultural and industrial supply, and other legitimate uses.

There is a non degradation policy such that stream now AA or A cannot be reduced to B to allow discharges from industries or treatment plants. The classification system and application to Danbury is summarized below:

Class AA: Designated uses are existing or proposed drinking water supply, fish and wildlife habitat, some recreational use, agricultural and industrial supply. Discharges severely restricted.

Class A: Designated uses is potential drinking water supply; fish and wildlife habitat; recreational use; agricultural and industrial supply and other legitimate uses including navigation. Discharges severely restricted. No reclassification of A or AA allowed down to B.

Class B: Designated uses are varied and include discharges from industrial and municipal wastewater treatment facilities providing Best Available Treatment and Best Management Practices are applied. All water bodies must eventually reach the minimum standards of the B classification.

Classes C and D: Indicates unacceptable quality, the goal is Class B or Class A and DEP will issue orders to require improvement.

1. Candlewood Lake due to wastewater pumped up from the Housatonic River: B/B.

2. Eureka Lake and tributaries: AA/AA.

3. Hudson River tributaries reaching into northwestern Danbury from New York State: AA/AA.

4. Kohanza Reservoir and upstream tributaries: AA/AA.

5. Kenosia Lake tributaries: AA/AA.

6. Limekiln Brook flowing from the Bethel Line northerly to the Still River: C/B. Also an unnamed tributary stream on the west side of old Danbury landfill flowing northerly to Limekiln Brook: B/B .

7. Margerie Reservoir and tributaries: AA/AA .

8. Padanaram Brook and tributaries north of Padanaram Reservoir: AA/AA. Then Padanaram Brook from Margerie Reservoir Brook south to Patch Street: B/A, and third Padanaram Brook from Patch Street south to the Still River: B/B.

9. Saugatuck Reservoir tributaries reaching north from Redding into Danbury: AA/AA.

10. Still River from Lake Kenosia easterly to Padanaram Brook: B/A. Then the Still River from Padanaram Brook easterly to Limekiln Brook: B/B. And next the Still River from Limekiln Brook (where Danbury Sewer Treatment Plant effluent enters) north to the Brookfield Line: C/B.

11. Sympaug Brook flowing from the Bethel Line north to the Still River: B/B.

12. West Lake Reservoir and tributaries: AA/AA.

13. Unnamed brook in Rogers Park flowing south into Bethel to join Reservoir Brook: B/A.

14. All other streams in Danbury such as Great Plain Brook, Miry Brook, Parks Pond Brook, etc: A/A.



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