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CRITERIA FOR AQUIFER MAPPING
FROM HVCEO BULLETIN 37, 1985
1. Which governmental organizations contributed water resource information used in drawing the maps? The U.S. Geological Survey was the sole source of all water resource information used. The four USGS items used were (1) line of distinction between till and stratified drift, saturated thickness, transmissivity, and drainage divides derived from U.S.G.S. topographic maps.

2. Which boundary lines shown on the HVCEO maps may be readily confirmed through field observation? All lines shown are either contact lines between till and drift deposits, which are quite different in composition and discernible to a trained eye without chemical analysis, or drainage divides which are also readily defined by a civil engineer.

3. What was the process HVCEO used to plot the boundaries of primary recharge areas on the maps? According to the Ct. areawide Wastewater Treatment Management Planning Boards’ Nov. 1979 Guide to Groundwater and Aquifer Protection, "The boundary of the primary recharge area is based upon the type of surficial material and the thickness of saturated stratified rift". Primary recharge areas mapped by the HVCEO are defined among most of their length by the line of distinction between the two surficial materials known as till and stratified drift.

Where a stratified drift aquifer extended along a stream, valley beyond a pont where it is no longer favorable for groundwater development, its boundary was truncated by HVCEO using saturated thickness, transmissivity and drainage divides as criteria. Transmissivity is defined as the ability of an aquifer to transmit water.

Transmissivity values of 2,000 square feet per day or less and saturated thickness of 40 feet or less were used to estimated the vicinity of where the boundary would be drawn. Note that these values represent the lower end of scales for each criteria, as U.S.G.S. maps transmissivity up to 16,000 sq. ft. or greater an saturated thickness up to 160 feet.

This vicinity was then reduced to a specific line on the map by placing the boundary along the nearest drainage divide. The goal of this truncation was to logically and rationally reduce the size of aquifers needing protection so that the overall protection program would be more manageable by a municipality.

4. Since the map clearly shows stratified drift aquifer deposits, is the inclusion on the map of secondary recharge areas, not composed of stratified drift, a logical additional to the map? Water that replenishes the stratified drift primary recharge area is called " direct recharge". However, water that replenishes the till and bedrock secondary recharge area is also defined s "direct recharge", since this water moves laterally underground to enter the stratified drift aquifer.

The linking of both primary and secondary recharge area through the term "direct recharge" is made by the Connecticut Areawide Wastewater Treatment Management Planning Board in its 1979 Guide to Groundwater and Aquifer Protection.

5. Many of the boundaries shown on the maps represent drainage divides which are quite different from zoning’s traditional mapped features such as center lines of roadways, property lines, etc. Is this a precedent? No. The outer boundary of all secondary recharge areas and parts of the boundaries for primary recharge areas are mapped based upon the criteria of drainage divides. There is ample precedent, as the boundaries of water supply watersheds to which State Health regulations apply are also drainage divides.

6. Do the maps show the locations of all stratified drift aquifers within the Region? No. Rather, it shows only those determined to be "Priority Aquifers" having highest priority for immediate protective measures as listed in HVCEO’s Bulletin No. 5 entitled A Policy Direction for Groundwater Protection. Criteria used by HVCEO for placing only 12 of the 26 major aquifers in the 10 town Region on the priority list include proximity to area of need, potential well yield, an analysis of existing and potential land use over the aquifer, and existing pollution problems.

7. Does the U.S. Geological survey sanction use of the maps in its Water Resource Bulletins, reproduced as Section C of this Water Resource Atlas, as an appropriate base for local aquifer regulatory programs? According to a 1979 U.S.G.S. report entitled "Delineation of Recharge Areas for Stratified Drift Aquifers for Connecticut", the "areal extent of stratified drift deposits is shown. . .on 1:48,000 scale maps in the series of water resource inventories of Connecticut published by the State of Connecticut Water Resources Bulletins. . .Stratified drift areas can be obtained from this source. The extent of the aquifer can be considered to be the same as the extent of the stratified drift deposit."

MAPPING COMMENT FROM
1997 BETHEL, CT TOWN PLAN
There are other small stratified drift gravel deposits in Bethel, including along parts of Route 58. However, the statewide Connecticut Department of Environmental Protection led regional delineations of aquifer management areas did not include such smaller areas, as they were of insufficient depth or had overall limited transmissivity to be considered viable as public water supply system well sites.

This does not mean that groundwater quality protection there should be ignored; small bedrock wells will be drilled through the aquifer in those locations and thus such areas are in need of long term protection.

The approach of the 1980 and current groundwater protection program of Connecticut Department of Environmental Protection, Housatonic Valley Council of Elected Officials, and the United States Geological Survey is to only regulate what really needs to be regulated; minimize the boundaries as much as possible.

That is why the setting of aquifer boundaries in effect "chopped off" some aquifer areas of lesser value, such as along Route 58. It was felt that new restrictions on property use to preserve groundwater should be required only for aquifers that were known to be large enough to be of use to a public supply system.