HVCEO - Housatonic Valley Council of Elected Officials

MINOR AQUIFERS IN
BRIDGEWATER, CONNECTICUT

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HISTORIC BASE LINE DATA: 1980 HVCEO
REPORT ON BRIDGEWATER'S MINOR AQUIFERS
In 1980 the Board of Selectman in the Town of Bridgewater recognized the need to identify major aquifers within their borders as possible emergency water supply sources. It was thought that development of groundwater sources for public use might require easements to purchase of the lands directly overlying these resources. At the request of the selectmen, HVCEO prepared the text below:

An aquifer is a geologic unit containing and transmitting water. It is not an underground stream or lake as popularly misconceived. Aquifers occur in two types of geologic units: bedrock and surficial deposits which overlie bedrock.

Bedrock aquifers are the principal sources of water for residential use in areas not served by a public water supply. The entire Town of Bridgewater is underlain by metamorphic and igneous crystalline rocks (mostly gneisses and schists) which contain and transmit water in open fractures. These joints and fractures generally do not occur below a depth of 300 feet.

Yields from wells tapping bedrock will depend upon the number and size of fractures intersected by a well. In general, approximately 90% of the bedrock wells will yield approximately 2 gallons per minute. Obviously, these crystalline bedrock aquifers cannot be considered as a townwide emergency water supply source.

Aquifers also occur in surficial material which overlies the bedrock such as glacial till, which occurs on uplands, and stratified drift, which is defined as glacial meltwater deposits of mostly sand and gravel which occur in river and stream valleys. Glacial till, deposited directly by the ice, is a heterogeneous mixture of material ranging in size from clay to large boulders.

Most of Bridgewater is underlain by glacial till with some upland areas covered with at least 40'. These surficial deposits result in low water yields as their saturated thickness is minimal and the material does not easily transmit water. Accordingly, these areas are limited to on-site domestic use.

Stratified drift aquifers occur in two types of hydrogeologic settings: headwater aquifers which occur in small stream basins or the headwaters of larger streams and those deposits that occur contiguous to intermediate and large streams. Only a small amount of streamflow is available for induced recharge in the former setting and, therefore, sustained large yields may not be adequate.

The Town of Bridgewater, due to its natural topography, contains only headwater aquifers. These deposits, however, represent the most viable alternatives for townwide purposes in emergency situations as sustained large yields would probably not be a necessity.

Well yields from stratified drift will depend upon several factors: saturated thickness, the areal extent of the deposit, grain size, and the recharge potential to the aquifer including direct infiltration from precipitation (primary recharge), lateral groundwater flow from upland areas (secondary recharge), and induced recharge (surface water flowing towards a well).

Coarse grained stratified drift aquifers, comprised mostly of sand an gravel, are very porous and contain large volumes of water. Additionally, groundwater flows through these deposits with relative ease. Though capable of yielding upwards of 50-2000 gallons per minute, Bridgewater’s aquifers are restricted to the lower end of the range due to their size and hydrogeologic setting.

Based upon a preliminary investigation and available sources, there are five known stratified drift areas in the Town. Because specific hydrogeologic data is lacking for these deposits, a qualitative ranking has been made based upon the following criteria: areal extent, potential for induced recharge, proximity to developed areas, and feasibility to convey water from the site. The stratified drift deposits are ranked in descending order of favorability.

1. HITCHCOCK MILL BROOK AREA. This land parcel is bordered on the east by Christian Street, on the south by Rock Hill Road and is drained by Hitchcock Mill Brook. The stratified drift generally occurs along land contiguous to the brook including the swamp land adjacent to Christian Street and Rock Hill Road.

Access a legend for the map above
Source of Map: Water Resources Inventory of CT, Part 6, Upper Housatonic River Basin, by the
U. S. Geological Survey and the CT Department of Environmental Protection, 1972.

THIS IS AN EARLY (1972) GENERALIZED MAP OF ESTIMATED AQUIFER BOUNDARIES ONLY;
COMPARE IT TO LATER DATE USGS SURFICIAL MATERIALS MAP

The saturated thickness is estimated at greater than 10 feet but, as is true with all deposits within town, the transmissivity is unknown. (Transmissivity is the rate at which water passed through a unit width of aquifer under a unit hydraulic gradient and, therefore, is an indicator of the ability of an aquifer to yield water).

The major advantage of this aquifer is its proximity to the Center of Bridgewater and other developed areas. However, pumping would be required if the intention was to convey water to the Center. Areas south of Hitchcock Brook along Northrup Street could be gravity fed.

This aquifer is inferred to be of coarse-grained composition. “Inferred” means it is thought to be coarse-grained but hydrogeologic data are incomplete and verification requires further investigation and, therefore, it has the potential of yielding useable amounts of water. Accordingly, on-site investigations would be necessary for this site and all other sites.

The following opinion about this resource was supplied directly from the U.S. Geological Survey: (1) The area is underlain by a relatively small stratified-drift deposit, but we have no subsurface data from which to determine if the thickness and composition are favorable for ground-water development.

(2) The stratified drift is of very limited areal extent and the upstream drainage area of Mill Brook is also very small. Both factors would limit ground-water availability significantly, even if the saturated thickness is greater than 10 feet and the materials are coarse grained.

In summary, this area does not appear to have potential for serving as a source of public supply."

2. CLATTER VALLEY AREA. This stratified drift deposit is essentially bisected by Town Farm Brook with approximately 60% of the aquifer lying in New Milford and the balance in Bridgewater. the aquifer extends up the narrow valley drained by the watercourse east of Wolf Pit Mountain. Most of the aquifer has a minimum of 10 feet saturated thickness. This aquifer is also inferred to be of course grained composition.

Town Farm Brook, with a relatively limited flow rate, would provide some induced recharge if a well was located adjacent to the watercourse. The Brook’s water quality would not present a problem as it currently has a Class A standard (suitable for potable purposes) and drains Reservoir No. 4 in New Milford.

These are two limitations to this area: (1) proximity to presently developed areas; and (2) conveying the water to other areas would require a pumped system resulting in a high capital investment and maintenance costs.

3. IRON ORE HILL ROAD AREA. This deposit occurs on a gently west facing slope of land contiguous to Lake Lillinonah in the vicinity of Iron Ore Hill Road. Development of this aquifer may result in induced recharge from Lake Lillinonah.

The quality of these waters (currently Class D) would not permit consumption for potable purposes. This fact, coupled with the area’s location to the rest of the Town, limited access, and steep slopes reduces the viability of this site as an emergency water supply source. Use of this site, additionally, would also require consultation with the Connecticut Light and Power Company.

4. SECOND HILL BROOK AREA. This stratified drift deposit occurs beneath land contiguous to Second Hill Brook in the northeastern part of Bridgewater, near the intersection of Roxbury Road and Route 67. Second Hill Brook is a tributary of the Shepaug River.

The Brook has a relatively low flow rate due to the small basin size and, therefore, represents little potential for sustained induced recharge. The actual areal extent and textural composition of this deposit is unknown.

5. SHEPAUG RIVER SHORELAND. Several areas contiguous to the Shepaug River are believed to contain stratified drift deposits. Access is not currently available and conveyance of water to other points of town would necessitate a pumping system due to the steep slopes of adjacent lands. Additionally, these areas are relatively remote from the predominant share of the population.

CONCLUSIONS. The Town of Bridgewater should concentrate on acquiring easements to or purchase of lands with the best opportunities for groundwater development. The “Hitchcock Hill Brook Area” and the “Clatter Valley Area” are the optimum sites based upon this preliminary analysis. Land use above and adjacent to these areas should be limited to residential use with strict enforcement of the sanitary code to avoid possible groundwater contamination.

Bridgewater’s 1967 Plan of Development recommended two other potential groundwater sites as sources of water on a townwide consumption scale: 1) near Curtis Road and Hatshop Hill Road on Mead Corners and 2) springs on Route 133 near Cemetery Swamp. Present data does not depict any stratified drift in these areas. However, as is true with all sites, on-site investigation is needed to verify the potential of these sites as well as those outlined above.

Finally, wells or a well field tapping bedrock have been known to yield sufficient volumes of water. This situation can occur if there is a high degree of interconnection between the open fractures. However, water quality may become a problem if contaminated water enters these fractures are there is little opportunity for bedrock to attenuate contaminants, particularly pathogens.

UPDATE ON AQUIFERS
BY 1989 HVA REPORT
In 1989 the Housatonic Valley Association prepared a detailed Groundwater Action Plan for Bridgewater. While water quality protection was seen as vital for public health, stratified drift aquifer deposits were found to be so meager that they would play no role in future water supply.

According to the HVA Plan “Bridgewater’s water resources are limited, and most residents rely on private wells drilled in bedrock. Meanwhile, the few sand and gravel (stratified drift) aquifers in town are not large enough to support a public water system.”

Therefore the HVA Plan advised a variety of bedrock aquifer protection strategies, but not a classic stratified drift aquifer protection district with a distinct boundary line, as operating in Brookfield, Newtown and Ridgefield.