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Condensed from a presentation at NEGSA 2007, from bedrock mapping by Thompson (2006) and surficial mapping by DeSimone (2006):
Groundwater Resources of Woodstock, Vermont
by Laurence Becker, David DeSimone, Peter Thompson, and Marjorie Gale

Abstract

The Town of Woodstock requested surficial and aquifer mapping from the Vermont Geological Survey to aid in groundwater protection and planning, which are priorities in the Woodstock Municipal Plan and the Two Rivers-Ottauquechee Regional Plan. Bedrock mapping was included since many residential wells penetrate bedrock.

The Waits River Formation consists of interbedded garnet schist and punky-weathering sandy marble and underlies much of the town. This bedrock was easily abraded by glacier ice and hills were rounded and veneered with till. Marble layers are more permeable than schists. Where the layers are nearly horizontal, bedrock wells penetrate alternating schist and marble and thus are likely to yield more water. Where the layers are more vertical, wells may show exceptionally high or low yields. A few high-yield wells in the SW corner of town tap well jointed, dense Barnard Volcanics. Two dominant joint sets, oriented roughly east-west and northeast, may explain the course of the Ottauquechee River and may also control the location of glacially scoured pockets in bedrock. Lineaments that are coincident with joint sets measured in the field may help locate future productive wells

As part of the surficial mapping project, data from well logs were consulted to evaluate yield, recharge potential to aquifers, delineate the extent of overburden aquifers, and to determine the 3-D distribution of glacial deposits. Thin till predominates in the upland region. Ice contact deposits, chiefly sand and gravel, occur primarily as isolated kamic deposits including minor kame terraces along the major valleys. Valleys contain thick overburden, primarily till, with glacially over deepened valley pockets. Beneath this till is a gravel unit yielding water to wells from a confined aquifer. The stratigraphy of these gravel wells is commonly capped by a fluvial terrace or flood plain unit of sand and gravel representing an unconfined aquifer.

Maps that combine information from the bedrock and surficial studies help to identify areas where thin till with relatively high recharge potential coincide with areas underlain by more permeable, moderately inclined marble layers. Derivative groundwater resource maps and recharge area maps are the result of these studies.

CLICK ON THE IMAGES BELOW TO ENLARGE THEM (PDF FILES). Paper copy of 12 plates may be purchased for $60.00 or $10.00 per map. Click here to download digital data (Geodatabase)


Bedrock Geologic Map of Woodstock, Vermont (Thompson, 2006)
A-A'
Cross-sections A-A' and B-B' show 3 fold generations (F1, F2, and F3).
Woodstock is on the east flank of the Green Mountain anticlinorium,
in a structural saddle between the north-plunging end of the Chester
dome and the south-plunging end of the Pomfret dome.
(Thompson, 2006)



Cross-section B-B'. The domes (D3) deform an older set of folds that are overturned toward the east. (Thompson, 2006)


Map of zone of steeply dipping bedrock
and high (>20gpm) and low (<2gpm) yield
wells. (Thompson, 2006)

Structural domains, bedding formlines, and photolinears Well yields -Domain A: 0-500 gpm with a mean value of 22 gpm; Domain B: 0-200 gpm with a mean value of 15 gpm; Domain C: 0-200 gpm with a mean value of 19 gpm.(Thompson, 2006)

Surficial Geologic Map of Woodstock,
Vermont (DeSimone, 2006)

Depth to Bedrock and Well Locations

Recharge Potential to Bedrock
Aquifers (DeSimone, 2006)

Recharge Potential to Shallow (unconfined) Aquifers (DeSimone, 2006)

Recharge Potential to Buried (confined) Aquifers (DeSimone, 2006)


Ice Margins and Striations (DeSimone, 2006)


Depths of all (517) located wells are shown. Total well depth ranges from 20-1022’ with a mean depth of 332’.


Well yields from 517 wells range from
0-500 gpm with a mean value of 17 gpm.
Most wells in Woodstock are in the
Waits River Fm.

 

Generalized Geologic 
	Map of Vermont - 1970 - click for larger map image

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