Prepared in cooperation with the

New York State Department of Environmental Conservation

Hydrogeology of the West Branch Delaware River 

Basin, Delaware County, New York

Scientific Investigations Report 2013–5025

U.S. Department of the Interior

U.S. Geological Survey
Cover. Groundwater discharging from bedrock fractures exposed in a roadcut of Catskill Mountain Series rocks (upper Walton 

Formation), Ulster County, New York. Deeper springs emerging from fractures or bedding planes in bedrock are used extensively 

throughout the Catskill Mountain region for domestic and municipal water supplies, and provide a major contribution to the base flow 

of streams in the region. Photo by Jason Zatorsky, U.S. Geological Survey, January 2003.
Hydrogeology of the West Branch 

Delaware River Basin, Delaware County, 

New York

By Richard J. Reynolds

Prepared in cooperation with the

New York State Department of Environmental Conservation

Scientific Investigations Report 2013–5025

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Reynolds, R.J., 2013, Hydrogeology of the West Branch Delaware River basin, Delaware County, 

New York: U.S. Geological Survey Scientific Investigations Report 2013–5025, 26 p., http://pubs.usgs.gov/

sir/2013/5025/.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Previous Studies ...................................................................................................................................3

Hydrogeology..................................................................................................................................................4

Deglaciation of the West Branch Delaware River Basin...............................................................4

Surficial Geology...................................................................................................................................5

Till....................................................................................................................................................5

Colluvium.......................................................................................................................................7

Ice-Contact Stratified Drift.........................................................................................................7

Kames................................................................................................................................... 7

Kame Terraces ....................................................................................................................7

Kame Deltas.........................................................................................................................7

Kame Moraines...................................................................................................................8

Outwash, Alluvium, and Inwash................................................................................................8

Outwash................................................................................................................................8

Alluvium................................................................................................................................8

Inwash ..................................................................................................................................9

Bedrock Geology...................................................................................................................................9

Stratigraphy ..................................................................................................................................9

Structure and Folding..................................................................................................................9

Faults and Jointing ....................................................................................................................11

Stress Relief Fracturing ............................................................................................................11

Well Yields...................................................................................................................................11

Saline Groundwater ..................................................................................................................12

Groundwater Flow System.......................................................................................................13

Springs.........................................................................................................................................13

Marcellus Shale.........................................................................................................................15

Stratified-Drift Aquifers .....................................................................................................................17

Upper West Branch Delaware River......................................................................................18

Middle West Branch Delaware River.....................................................................................18

Lower West Branch Delaware River......................................................................................19

Precipitation, Runoff, and Evapotranspiration...............................................................................19

Sources of Stream Base Flow ..........................................................................................................20

Base Flow in Relation to Geology ....................................................................................................22

Bedrock as a Source of Base Flow ........................................................................................22

Thick Till Deposits as a Possible Source of Base Flow.......................................................23

Summary........................................................................................................................................................23

Selected References...................................................................................................................................24
iv

Figures

1. Map showing the location of the West Branch Delaware River Basin in

southeastern New York ...............................................................................................................2

2. Map showing distribution of major bedrock units within the West Branch Delaware

River Basin in southeastern New York. ..................................................................................10

3. Generalized geologic section showing features of stress-relief fracturing. ...................12

4. Conceptual diagram of groundwater flow within bedrock and stratified-drift

aquifers within the West Branch Delaware River Basin in southeastern New York......14

5. Graph showing yield of 178 springs in Delaware County, New York, as a function of

altitude. ........................................................................................................................................15

6. A, Geophysical log showing typical gamma log response and B, photograph

showing typical stratigraphy of the Marcellus Shale in New York. ..................................16

7. Map showing the distribution of mean annual precipitation and runoff for 1951–80

within the West Branch Delaware River Basin.....................................................................20

Tables

1. Thickness of and depth to the Marcellus Shale in selected deep test holes in

Delaware County, New York .....................................................................................................17

2. Hydrogeologic characteristics of 13 Catskill drainage basins within the Delaware

River Basin in southeastern New York....................................................................................21
v

Conversion Factors and Datum

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second (ft3

/s) 28.32 foot per second (m3/s)

cubic foot per second per square 

mile [(ft3

/s)/mi2]

0.01093 cubic meter per second per square kilometer 

[(m3/s)/km2]

gallon per minute (gal/min) 0.06309 liter per second (L/s)

gallon per day per foot (gal/d/ft) 0.0001437 liter per second per meter (L/s/m)

gallon per day per square mile 

[(gal/d)/mi2

]

0.001461 cubic meter per day per square kilometer 

[(m3/d)/km2]

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

million gallons per day (Mgal/d) 3,785 cubic meter per day (m3

/d)

million gallons per day per square 

mile [(Mgal/d)/mi2

]

1,461 cubic meter per day per square kilometer 

[(m3/d)/km2]

Specific capacity

gallon per minute per foot [(gal/

min)/ft)]

0.2070 liter per second per meter [(L/s)/m]

Hydraulic conductivity*

foot per day (ft/d) 0.3048 meter per day (m/d)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity**

foot squared per day (ft2

/d) 0.09290 meter squared per day (m2/d) 

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83) 

and the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the vertical datum.

*Hydraulic conductivity: The standard unit for hydraulic conductivity is cubic foot per day per 

square foot of aquifer cross-sectional area (ft3/d/ft3). In this report, the mathematically reduced 

form, feet per day (ft/d), is used for convenience.

**Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot 

times foot of aquifer thickness [(ft3

/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.
vi

Abbreviations

GIS geographic information system

NRCS Natural Resources Conservation Service

NYSDEC New York State Department of Environmental Conservation

USGS U.S. Geological Survey
Hydrogeology of the West Branch Delaware River Basin, 

Delaware County, New York

By Richard J. Reynolds

Abstract

In 2009, the U.S. Geological Survey, in cooperation with 

the New York State Department of Environmental Conservation, began a study of the hydrogeology of the West Branch 

Delaware River (Cannonsville Reservoir) watershed. There 

has been recent interest by energy companies in developing 

the natural gas reserves that are trapped within the Marcellus Shale, which is part of the Hamilton Group of Devonian 

age that underlies all the West Branch Delaware River Basin. 

Knowing the extent and thickness of stratified-drift (sand and 

gravel) aquifers within this basin can help State and Federal 

regulatory agencies evaluate any effects on these aquifers 

that gas-well drilling might produce. This report describes the 

hydrogeology of the 455-square-mile basin in the southwestern Catskill Mountain region of southeastern New York and 

includes a detailed surficial geologic map of the basin.

Analysis of surficial geologic data indicates that the most 

widespread surficial geologic unit within the basin is till, 

which is present as deposits of ablation till in major stream 

valleys and as thick deposits of lodgment till that fill upland 

basins. Till and colluvium (remobilized till) cover about 89 

percent of the West Branch Delaware River Basin, whereas 

stratified drift (outwash and ice-contact deposits) and alluvium 

account for 8.9 percent. The Cannonsville Reservoir occupies 

about 1.9 percent of the basin area. Large areas of outwash 

and ice-contact deposits occupy the West Branch Delaware 

River valley along its entire length. These deposits form a 

stratified-drift aquifer that ranges in thickness from 40 to 50 

feet (ft) in the upper West Branch Delaware River valley, from 

70 to 140 ft in the middle West Branch Delaware River valley, 

and from 60 to 70 ft in the lower West Branch Delaware River 

valley.

The gas-bearing Marcellus Shale underlies the entire 

West Branch Delaware River Basin and ranges in thickness 

from 600 to 650 ft along the northern divide of the basin to 

750 ft thick along the southern divide. The depth to the top of 

the Marcellus Shale ranges from 3,240 ft along the northern 

basin divide to 4,150 ft along the southern basin divide.

Yields of wells completed in the aquifer are as high as 

500 gallons per minute (gal/min). Springs from fractured sandstone bedrock are an important source of domestic and small 

municipal water supplies in the West Branch Delaware River 

Basin and elsewhere in Delaware County. The average yield of 

178 springs in Delaware County is 8.5 gal/min with a median 

yield of 3 gal/min. An analysis of two low-flow statistics indicates that groundwater contributions from fractured bedrock 

compose a significant part of the base flow of the West Branch 

Delaware River and its tributaries.

Introduction

The West Branch Delaware River (Cannonsville Reservoir) watershed occupies a drainage area of approximately 

455 square miles (mi2

) in the Catskill Mountain region of 

southeastern New York. The watershed encompasses all but 

1 mi2

 of the West Branch Delaware River Basin, as measured 

at the U.S. Geological Survey (USGS) streamgaging station 

at Stilesville (01425000) about 17.8 miles (mi) upstream from 

the confluence of the West and East Branch Delaware Rivers at Hancock, New York. In this report, the West Branch 

Delaware River Basin refers to the 455 mi2

 of the basin that 

lies upstream from the Cannonsville Reservoir and does not 

include the 211 mi2

 between the reservoir and the downstream 

confluence of the West and East Branch Delaware Rivers. The 

location of the West Branch Delaware River Basin is shown in 

figure 1.

The West Branch Delaware River valley, upstream of the 

Cannonsville Reservoir, extends for 59 mi from the Cannonsville Reservoir Dam to the river’s headwaters near Stamford, 

N.Y., and supplies municipal groundwater to the villages 

of Delhi, Hobart, Stamford, and Walton (fig. 1) and to the 

Bloomville Water District, collectively serving a population 

of more than 11,000 people (New York State Department of 

Health, 1982). The stratified drift within this valley consists 

of outwash and ice-contact deposits of sand, gravel, silt, and 

clay, and fine-grained lacustrine deposits, locally mantled by 

postglacial alluvium. The outwash and ice-contact deposits 

together constitute the principal stratified-drift (sand and 

gravel) aquifer in this valley and may reach thicknesses of up 

to 140 feet (ft) in places, such as near Hawleys, N.Y. In the 

lowest reach of the valley, some of the valley fill consists of 

low permeability lacustrine silt and clay, which are the result 
2 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

75°30' 75°15' 75° 74°45' 74°30'

42°30'

42°15'

RENSSELAER SCHOHARIE

PUTNAM

ORANGE

WESTCHESTER

COLUMBIA GREENE

DUTCHESS

ULSTER

NEW JERSEY

CONNECTICUT

Base from U.S. Geological Survey digital data, 1:100,000, 1983

NEW YORK

OTSEGO ALBANY

DELAWARE

SULLIVAN

ROCKLAND

PENNSYLVANIA

West Branch

Delaware River

basin

0 6 123 36 MILES

0 12 36 KILOMETERS

75° 74°30' 74°

42°30’

42°

41°30'

73°30'

DELAWARE

SCHOHARIE

OTSEGO

CHENANGO

BROOME

Cannonsville

Reservoir

Deposit

West Br anch De laware R iver

EXPLANATION

West Branch Delaware River 

basin boundary

Streamgage and station number

Village

014200103

Pinesville

Hawleys

Hamden DeLancey

01422500

0142900

East Delhi

Bloomville

South Kortright

Beerston

Apex

Hamlet

Walton

Delhi

Hobart

Stamford

0 20 MILES

0 20 KILOMETERS

5 10 15

5 10 15

Figure 1. The location of the West Branch Delaware River Basin in southeastern New York.
Introduction 3

of remnant glacial lakes. In other areas, permeable ice-contact 

sand and gravel are buried beneath large thicknesses of silt and 

clay or till, forming confined aquifers. Each of these hydrogeologic situations has specific implications for the availability of groundwater for public supply. In addition, groundwater 

in the water-table aquifer is hydraulically connected to the 

river within the valley and discharges to the river to sustain 

base flow during periods of little or no precipitation.

Recently, there has been interest by energy companies 

in developing the natural gas reserves that are trapped within 

the Marcellus Shale, which is part of the Hamilton Group of 

Devonian age that underlies all of the West Branch Delaware 

River Basin. Concern has been expressed by local interest 

groups that gas-well drilling might have adverse effects on 

both the sand and gravel and the bedrock aquifers that overlie 

the Marcellus Shale, including contamination of overlying 

aquifers with hydrocarbons, depletion of groundwater in 

productive aquifers used to supply hydrofracturing operations 

with subsequent effect on nearby domestic wells, and possible 

groundwater contamination from specialized drilling fluids. 

Knowing the character, extent, and thickness of stratified-drift 

aquifers within this basin can help State and Federal regulatory agencies in the evaluation of potential effects on these 

aquifers that gas-well drilling might produce.

In 2009, the U.S. Geological Survey (USGS), in cooperation with the New York State Department of Environmental 

Conservation (NYSDEC), began a study of the hydrogeology of the West Branch Delaware River Basin (Cannonsville 

Reservoir watershed) that entailed delineating the surficial 

geology of the basin, describing the extent and thickness of 

the stratified drift aquifer within the valley, and describing 

the general hydrogeology of the underlying bedrock units and 

their relation and effect on stream base flow.

Purpose and Scope

The primary objective of this study was to define the 

hydrogeology of the valley-fill aquifer system in the West 

Branch Delaware River valley, above the Cannonsville Reservoir. This was accomplished through the delineation of surficial geologic units within the basin, compilation of well and 

test-hole data from several databases (including the NYSDEC 

well database), and subsequent creation of geographic information system (GIS) datasets of surficial geology, locations of 

wells and test holes, and bedrock geology.

The mapped area consists of all or part of eighteen 

7.5-minute quadrangles and covers an area of 455 mi2

. The 

map was derived from several sources: (1) digital soils maps 

of Delaware County produced by the Natural Resources 

Conservation Service (NRCS) of the U.S. Department of 

Agriculture, (2) maps and illustrations from unpublished 

doctoral dissertations by Kirkland (1973) and Ozvath (1985); 

and (3) unpublished reconnaissance-level surficial geologic 

maps at 1:62,500 scale, prepared during a previous USGS 

study (Soren, 1963) of the groundwater resources of Delaware 

County (Julian Soren, U.S. Geological Survey, unpub. maps, 

1958). Surficial geology was superimposed on topography 

mapped at 1:24,000 scale; the mapping included upland areas 

that are adjacent and tributary to the main valley-fill aquifers

This report (1) describes the distribution and character of 

surficial geologic units throughout the West Branch Delaware 

River Basin, (2) outlines the deglacial chronology that led to 

the deposition of successive stratified-drift units in the main 

valley, (3) discusses the approximate thickness and character 

of stratified-drift aquifers within three reaches of the West 

Branch Delaware River, (4) describes the general stratigraphy 

and hydrogeology of the bedrock that underlies the basin, and 

(5) gives available information on the thickness and depth to 

the Marcellus Shale that underlies the entire basin.

Previous Studies

Several investigators have studied various hydrologic 

and geologic aspects of the Delaware River Basin in New 

York. Rich (1935) studied the surficial geology of the western 

and central Catskill Mountains, including the eastern third of 

the West Branch Delaware River Basin, and reported evidence of two distinct drift sheets, which he termed “early” 

and “late” Wisconsinan. Later investigations of the glacial 

geology within this basin included doctoral dissertations 

by Kirkland (1973) and Ozvath (1985). Kirkland’s study 

encompassed most of the West Branch Delaware River Basin, 

whereas Ozvath’s study included only the westernmost part of 

the basin.

Investigations by the USGS in the 1950s and early 

1960s, in cooperation with the New York State Department of 

Conservation (superceded by NYSDEC in 1970), produced 

a report on the groundwater resources of Delaware County 

(Soren, 1963), which includes the West Branch Delaware 

River Basin. Geotechnical and engineering studies conducted 

by the New York City Board of Water Supply, in conjunction 

with the planned construction of the Cannonsville Reservoir, 

were summarized in Fluhr (1953) and Fluhr and Terenzio 

(1984). N.M.Perlmutter and E.H. Salvas (U.S. Geological 

Survey, written commun., 1957) described various aspects 

of groundwater in the New York part of the Delaware River 

Basin; their findings were later incorporated into a larger 

USGS study of the entire Delaware River Basin conducted in 

the early 1960s by Parker and others (1964). As part of that 

same basinwide USGS study, Hely and Olmsted (1963) investigated the relation between low-flow statistics and watershed 

characteristics in the entire Delaware River Basin. A comparison study of Delaware and Susquehanna River Basin streams 

by Coates (1971) investigated the relation of bedrock type 

and joint spacing, extent of valley-fill stratified sediments, and 

several geomorphic indices to stream base flow, and provided 

streamflow and low-flow statistics for all gaged streams in the 

Delaware River Basin in New York. Most recently, Reynolds 

(2004) delineated the surficial geology of the Pepacton Reservoir watershed in the East Branch Delaware River Basin and 
4 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

observed that the magnitude of base flows in this basin correlated positively with the extent and massiveness of sandstone 

relative to shale and siltstone bedrock, as measured by Coates 

(1971), but—contrary to the results of studies elsewhere in the 

glaciated Northeast—did not correlate with the extent of stratified valley-fill sediments. Reynolds (2000) also delineated 

the surficial geology of the Beaver Kill Basin to the south and 

noted that 90-percent flow duration was substantially larger 

and base-flow recessions generally more sustained in this 

watershed than elsewhere in the Delaware River Basin, which 

could be attributed to a larger water input from precipitation 

and to the underlying massive sandstone, which contains 

extensive water-bearing fractures.

Hydrogeology

The thickness, type, and areal extent of surficial geologic 

units within the West Branch Delaware River Basin are the 

direct result of the mode of deglaciation and largely determine the groundwater productivity and storage in the valleyfill aquifer.

Deglaciation of the West Branch Delaware 

River Basin

The style of deglaciation that occurred in the West 

Branch Delaware River Basin resulted in the deposition of 

large volumes of sand and gravel both as ice-contact features, 

and as valley-train outwash throughout the entire 59-mi-long 

valley from Stamford to Deposit, N.Y. Ice retreat in the valley 

of the West Branch Delaware River was characterized by a 

series of ice-tongue detachments that resulted in six zones of 

stagnant ice (Ozvath, 1985). These stagnant-ice zones ranged 

in length from 10 to 15 mi each, and together indicate six 

fluvial morphosequences (Koteff, 1974), in which a complete 

morphosequence consists of outwash grading upstream to 

pitted outwash, and then to kame moraine or kame terrace. 

Deglaciation in the more sinuous East Branch Delaware River 

to the south, in contrast, occurred through the ablation of 

stagnant-ice masses, which in turn resulted in a succession 

of proglacial lakes in the lower reaches of the East Branch 

Delaware River valley. In these morphosequences, a kame 

moraine marks the end position of a detached ice tongue, 

whereas upstream kame terraces were constructed by meltwater streams flowing between the melting ice tongue and the 

valley wall. These morphosequences range from 10 to 15 mi in 

length and their depositional features were formed at both the 

end and valley-side margins of an ice tongue that had become 

detached from the main ice sheet and began to stagnate (melt). 

Kirkland (1979) identified six of these well-defined morphosequences in the West Branch Delaware River valley from 

Deposit to Stamford. Although much of the evidence, especially kame moraines, for these six morphosequences have 

been either eroded or buried by subsequent deposition, a study 

by Ozvath (1985) identified several kame moraines in the West 

Branch Delaware River valley that serve to locate former ice 

margins and thus corroborate Kirkland’s deglaciation model. 

Ozvath (1985) and Kirkland (1979) agreed that, with few 

exceptions, all the stratified drift exposures in the West Branch 

Delaware River valley indicate continuous deposition by glacial meltwater flowing downvalley (southwest). The distribution of outwash and ice-contact deposits (plate 1) supports this 

finding, as do the logs of wells in the valley that consistently 

show coarse-grained sand and gravel down to bedrock in 

places along the entire 59-mi stretch of valley. There are a few 

depositional features known as kame deltas, however, which 

indicate that small, short-lived proglacial lakes existed in 

several places along the West Branch Delaware River. These 

lakes typically formed between a detached ice block located 

at a sharp curve or narrowing of the river valley, causing a 

temporary lake to form and extend upstream to the retreating 

ice tongue. Ozvath (1985) identified a kame delta about 1 mi 

north of Delhi and another pair 2 mi southwest of Delhi that 

give evidence for temporary glacial lakes in this reach. One 

lake level stood at about 1,400 ft and stretched from a dam of 

stagnant ice at Delhi about 2 mi upstream to East Delhi, where 

the lake level is also seen in a deltaic complex. The existence 

of this lake is supported by the logs of two wells (D–2208 and 

D–1442) in this reach that show thicknesses of about 60 to 

75 ft of lacustrine silt within the valley fill. Further downvalley two kame deltas near Pinesville and one on the south side 

of the sharp “S” bend in the river southwest of Walton, record 

a temporary proglacial lake level of 1,280 ft (Ozvath, 1985). 

The ice dam that produced this lake was most likely located 

in the sharp “S” bend southwest of Walton. The logs of two 

wells (D–102 and D–175) in Walton and one (D–1337) south 

of Walton at Beerston, N.Y., show thicknesses of lacustrine silt 

and clay ranging from 40 to more than 100 ft, thus confirming 

the existence of this short-lived proglacial lake.

Ozvath and Coates (1986) have correlated two of Kirkland’s (1973) six ice-marginal positions in the West Branch 

Delaware River valley to nearby ice-marginal positions in 

the Susquehanna River valley, which have radiocarbon dates 

associated with them. These radiocarbon dates place, by 

inference, the ice tongue in the West Branch Delaware River 

valley at Walton approximately 16,650 years before present 

(B.P.; plus or minus 1,800 years) and at Delhi approximately 

14,860 years B.P (plus or minus 800 years). These data therefore suggest that the rate of retreat of the ice tongue along the 

central reach of the West Branch Delaware River valley was 

extremely slow, taking on the order of 1,800 years to retreat 

the 16 mi from Walton to Delhi. This pace would have allowed 

plenty of time for the small localized proglacial lakes to 

accumulate up to 100 ft of fine-grained sediment that are now 

evident in the several well logs mentioned above.
Hydrogeology 5

Surficial Geology

A primary objective of this study was to produce a generalized surficial geologic map of the West Branch Delaware 

River Basin above the Cannonsville Reservoir Dam that can 

be used to identify the location and extent of stratified-drift 

aquifers within the drainage area of the Cannonsville Reservoir. The surficial geologic map (plate 1) includes all or 

part of eighteen 7.5-minute quadrangles and represents an 

area of 455 mi2

. The map is based on the interpretation of 

surficial units derived from three primary sources: (1) digital 

soils maps of Delaware County produced by the NRCS in 

Walton; (2) plates and illustrations in doctoral dissertations 

by Kirkland (1973) and Ozvath (1985); and (3) unpublished 

reconnaissance-level surficial geologic maps at 1:62,500 scale 

prepared as part of a previous USGS study by Soren (1963). 

To compile this map, an analysis of the GIS coverage of 

NRCS soils units for the study area showed that there were 

154 individual soil types within the basin. These 154 soil types 

were used to identify their parent materials, on the basis of the 

soils descriptions given in the NRCS soils report. The individual soil types were each assigned a color based on its assigned 

parent material and then aggregated by common parent material in a GIS coverage to identify 11 surficial geologic map 

units: alluvium, alluvium over outwash, alluvial fans, artificial 

fill, kame sand and gravel, outwash and (or) kame sand and 

gravel (undifferentiated), outwash sand and gravel, peat and 

muck, exposed bedrock, till and thick till, and till and (or) colluvium (undifferentiated). The map units were plotted as overlays to 1:24.000-scale topographic maps within the basin and 

were checked to determine whether the unit contacts generally 

conformed to topography. In addition, morphostratigraphic 

units delineated either by Kirkland (1973) or by Ozvath (1985) 

in valley sections were compared with those derived from the 

soils units and with field notes and observations (Julian Soren, 

U.S. Geological Survey, unpub. maps, 1958). Generally, the 

contacts of surficial geologic units as delineated from the soils 

data conformed very well to the topography. Areas identified 

as kame sand and gravel plotted where they were expected 

to be, that is, on valley-side terraces. Areas of valley train 

outwash, alluvium, and alluvial fans were also well delineated from the soils data. Similarly, areas of thick lodgment 

till (greater than 5 ft) in upland valleys or colluvium were 

located in upland tributaries and on the sides of steep valley 

walls, where they would also be expected. The soils-derived 

surficial geologic map in this report is in good agreement with 

similar mapping of surficial geologic units by Kirkland (1979) 

and Ozvath (1985) and compares well with unpublished field 

mapping (Julian Soren, U.S. Geological Survey, unpub. maps, 

1958). In some cases, the exact origin of a morphostratigraphic 

unit could not be determined from the soils data; for example, 

whether a sand and gravel unit was derived from ice-contact 

material or from outwash. Similarly, the soils data could sometimes not be used to help differentiate between areas of till 

and colluvium (remobilized till). The ambiguities of these two 

mapping units are indicated in the map explanation.

The four major categories of surficial (unconsolidated) 

sediments within the West Branch Delaware River Basin 

are till, ice-contact stratified drift, outwash, and postglacial 

alluvium. Till is, by far, the most widespread surficial unit 

within the basin and is mapped (plate 1) as three distinct units: 

thin till over bedrock (ground moraine), thick till, and undifferentiated till and colluvium. Ice-contact stratified drift occurs 

as small, isolated kames, kame terraces, kame moraines, and 

kame deltas emplaced along the sides of the West Branch 

Delaware River valley and some of the river’s larger tributaries. Outwash and postglacial alluvium form a narrow deposit 

of coarse gravel and sand that floors the West Branch Delaware River valley and some of its major tributaries. Bedrock 

is commonly exposed along steep hillsides and ridgetops. 

The origin and distribution of these major units are discussed 

below.

Till

Till, the predominant surficial geologic unit within the 

West Branch Delaware River Basin, covers approximately 

89 percent of the area within the basin. Till occurs within the 

basin as (1) thin till over bedrock (ground moraine), (2) thick 

till of varying origins, and (3) undifferentiated till and colluvium, which is till that has moved downslope and has been 

redeposited. The predominance of till in the uplands of the 

West Branch Delaware River Basin is the direct result of the 

mode of deglaciation, the steep topography, and the limited 

volume of external meltwater that entered the basin during 

deglaciation. Deglaciation in the West Branch Delaware River 

Basin progressed as a series of six morphosequences, which 

resulted in the deposition of large amounts of ice-contact 

sand and gravel in the valley bottoms, ablation till in tributary 

valleys, and previously deposited lodgment till in the uplands 

(Kirkland, 1973; Ozvath, 1985). Conversely, deglaciation in 

the East Branch Delaware River Basin progressed as “icestagnation” retreat, which resulted in large masses of ablation 

till being deposited along the East Branch Delaware River 

valley bottom, sides, and tributary valleys. Ozvath (1985) 

refers to ablation till as “valley diamicton” and ascribes its 

deposition to the resedimentation of supraglacial and englacial 

debris during ice melting. Large masses of ablation till in the 

western Catskill Mountains are commonly associated, and 

may interfinger with, ice-contact stratified-drift, especially in 

the smaller tributary valleys. This interfingering is a result of 

the multiple depositional processes (resedimentation, meltwater runoff, and slope colluviation) that occurred during ice 

ablation, which resulted in wide variability in till composition (Ozvath, 1985). The ablation till in the western Catskill 

Mountains has been described as a massive, matrix-supported 

deposit of sand, silt, and gravel with clasts ranging up to boulder size, and is much less compact than the upland lodgment 

till (ground moraine).

Deposits of ablation till in the West Branch Delaware 

River Basin and in much of the western Catskill Mountains 

form a variety of recognizable landforms, such as drumlin-like 
6 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

hills, morainal loops, ridges, knobs, and lateral embankments 

(large deposits of ablation till containing some stratified 

beds that were emplaced along the lower valley walls). Rich 

(1935) was the first to recognize these ablation till features and 

ascribed their occurrence to deposition by active ice margins. 

Later investigators, notably Kirkland (1973) and Ozvath 

(1985), maintained that these features resulted from the disintegration of stagnant ice within the stream valleys, especially 

valleys that are oriented perpendicular to the southwestward 

direction of continental ice flow, or that are extremely sinuous in their course. Ozvath (1985) first used the term “lateral 

embankments” and suggested that they represented supraglacial and englacial debris that collected in troughs between the 

ablating ice and the valley wall. Large lateral embankments of 

ablation till are present in many of the small valleys tributary 

to the West Branch Delaware River, as well as many other 

streams in the western Catskill Mountains, and typically fill 

the original bedrock valley to a level that has caused the present-day stream course to shift considerably from the original 

bedrock thalweg (Reynolds, 2000; Randall, 2001). A notable 

example of just such an occurrence is located in the West 

Branch Delaware River valley, about 1 mi east of Walton. 

Here a large lateral embankment composed of ablation till and 

(or) colluvium is emplaced along 1.5 mi of the steep southern 

valley wall. This material has pushed the course of the West 

Branch Delaware River northward on the order of 1,000 ft. A 

single well (D–174) south of the river penetrates 170 ft of till 

and (or) colluvium, is completed in a confined sand and gravel 

aquifer, and approximates the location of the bedrock thalweg. 

Some of these lateral embankments may consist partly or 

entirely of resedimented till. Rich (1935) first described and 

mapped “thick drift” deposits of “non-morainic” or ablation 

till in the Catskill Mountains and noted that the till in the lee 

(southern) side of spurs on valley walls can be so thick as 

to block the mouths of tributaries and shift them downvalley. Coates (1966) was the first to use the term “till shadows” 

for thick deposits of lodgment till that were deposited on 

the southern, or lee, side of bedrock hills with respect to ice 

flow and later (1981) showed how these till shadows on the 

south sides of hills in the Appalachian Plateau had shifted the 

thalwegs of small upland valleys. Large masses of till, whether 

as lateral embankments or till shadows, can be hydrologically 

important, in that they can overlie and confine saturated sand 

and gravel deposits to form locally confined aquifers. Randall (2001) noted that thick till shadows that locally protrude 

into valley bottoms in the Catskill Mountains are actually 

products of upland depositional processes and are not related 

to the deglaciation of the valleys, but rather to the glaciation 

of the adjacent uplands. The sand and gravel aquifers that 

are confined by these masses of till are presumably of small 

areal extent, and may or may not be hydraulically connected 

to the valley-fill aquifers that occupy most of the valleys in 

the Catskill Mountains. An example can be found in the log 

of well D–990, located in a small upland tributary known as 

Arbuckle Hollow, a tributary to Bagley Brook, approximately 

3.5 mi east of the village of De Lancey. This well penetrates 

95 ft of boulder till and then 19 ft of sand and gravel before 

continuing into the underlying bedrock.

Some of the thickest deposits of till in the West Branch 

Delaware River Basin are deposits of lodgment till that fill 

upland bedrock valleys and hollows in the headwaters of 

upland tributaries (Ozvath, 1985). These deposits are the 

result of ice movement over the divides that separate the West 

Branch Delaware River Basin from the Susquehanna River 

Basin to the northwest and the East Branch Delaware River 

Basin to the southeast. These thick deposits of till are the 

product of three glacial processes: (1) the dropout of subglacial debris as glacial ice moved over lee side depressions, (2) 

the meltout of debris from active ice, and (3) the meltout of 

debris from stagnant basal ice (Ozvath, 1985). Lodgment till 

in upland valleys and on south-facing slopes can exceed 60 ft 

in thickness (Soren, 1963); elsewhere, till is deposited as a 

veneer of ground moraine, which generally does not exceed 

6 ft in thickness. One of the thickest till deposits in the West 

Branch Delaware River Basin is present at Tunis Lake in the 

headwaters of the Little Delaware River where two wells 

penetrate 184 ft (D–423) and 234 ft (D–2171) of boulder till in 

what appears to be a former glacial meltwater channel (or col) 

that breaches the divide between the West Branch Delaware 

River Basin to the north and the East Branch Delaware River 

Basin to the south. Lodgment till and ground moraine in the 

West Branch Delaware Basin range in matrix composition 

from sandy silt to silty loam, with minor amounts of clay and 

are poorly sorted, with embedded clasts as large as gravel size 

(Ozvath, 1985).

The upland ground moraine and thick till shadows were 

probably deposited by and beneath the ice sheet as the ice 

advanced and consist of numerous pebble- and cobble-sized 

clasts in a compact matrix of sandy silt to silty loam with 

minor amounts of clay (Ozvath, 1985, p. 48). Ground moraine 

is poorly sorted, poorly permeable, and non-water-yielding 

to drilled wells. The colluvium mapped on plate 1 consists of 

upland till redeposited by gravity near the base of steep slopes 

and is similar in texture. The ablation till exposed near land 

surface on the lower slopes and bottoms of many small valleys 

was inferred by Ozvath (1985) to have melted out of stagnant ice masses, in part reworked by meltwater, and to have 

been commonly redeposited by landslides as the remaining 

underlying ice melted. Although ablation till also consists of 

abundant clasts in a matrix of loamy silt to silty sand, it is usually coarser grained and less compact than the upland ground 

moraine. Ablation till commonly contains isolated stringers 

or lenses as much as 1.5 ft thick that range from sandy silt to 

sand to fine gravel, and at some locations it grades imperceptibly into very poorly sorted sand and gravel (Ozvath, 1985, 

p. 60–62). These sand and gravel lenses described by Ozvath 

would probably increase the small yields of large-diameter 

shallow, dug wells, but are too thin to perceptibly enhance 

the yield of drilled wells. Ozvath (1985) reported that 20 to 

80 percent of the clasts in the ablation till are rounded, because 

of fluvial transport, and inferred that they were derived from 
Hydrogeology 7

stream gravels present in these valleys prior to the advance of 

the ice.

Colluvium

Colluvium is one of the major surficial geologic units 

in the West Branch Delaware River Basin, covering about 

2.7 percent of the basin (plate 1). Colluvium is prevalent 

along steep upland slopes in the West Branch Delaware River 

Basin, including steep valley walls that border sections of the 

West Branch Delaware River valley and its larger tributaries. 

Ozvath (1985) lists three types of colluvium common to the 

western Catskill Mountains: (1) remobilized till, (2) talus, and 

(3) landslides. Remobilized till forms gently sloping, hummocky deposits at the base of steep hillsides and is derived 

from lodgment till that has moved gradually downslope under 

the influence of gravity during periglacial conditions. Talus 

consists of angular, boulder-sized slabs of bedrock that became 

dislodged from outcrops on steep valley walls or cliffs and 

accumulated at the base of the slope. Landslides are abrupt 

downslope movements of large masses of earth material that 

form convex mounds of colluvium at the base of steep slopes, 

and leave corresponding concave depressions in the hillside, 

directly upslope from where the material was removed. Large 

glacial or postglacial deposits of colluvium can partly block 

a valley in much the same way that a lateral embankment or 

till shadow can and thus can alter the course of a modern-day 

stream. The previously discussed lateral embankment of till 

and colluvium in the West Branch Delaware River valley just 

east of Walton is a good example of stream alteration. Colluvium that consists of remobilized till can cover and obscure 

older sand and gravel or thick till deposits on the valley floor 

and locally confine groundwater in the underlying aquifer.

Ice-Contact Stratified Drift

Geomorphic features within the West Branch Delaware 

River Basin that consist of ice-contact stratified drift include 

kames, kame terraces, kame deltas, and kame moraines. These 

units (plate 1) were deposited as prominent features of six 

deglacial morphosequences that mark the steady northeastward progression of the receding ice tongue from Deposit to 

Stamford, a distance of 59 mi. Ice-contact sand and gravel 

deposits, together with locally overlying outwash, form the 

bulk of the stratified-drift aquifer in the West Branch Delaware 

River valley. Proper classification of ice-contact deposits usually requires suitable field exposures of their internal sedimentary structures in order to differentiate between kame terraces, 

kame deltas, and kame moraines. Kirkland (1979) and Ozvath 

(1985) remarked on the lack of field exposures of ice-contact 

deposits, created by gravel mining or borrow pits, in the West 

and East Branch Delaware Rivers; this lack of field exposures 

made it difficult for both investigators to classify some of the 

features that they had mapped as ice-contact material. Similarly, the NRCS soils data used to create the current surficial 

geologic map (plate 1) do not identify the geomorphology of 

parent material for soils derived from ice-contact deposits. 

Therefore, the unit identified as “kame sand and gravel” on 

plate 1 cannot be classified further (that is; kame moraine, 

kame terrace, kame delta) based on the current availability of 

data. A discussion of the geomorphology of each type, however, is useful to the understanding of the differences in the 

mode of deposition between them.

Kames

Kames are small, rounded hills up to 60 ft in height and 

800 ft in width that occupy the valley floor or lower hillslopes 

of a valley. Kames consist of englacial or supraglacial debris 

released by ice melting, then briefly transported by meltwater, 

and then deposited as poorly sorted gravel or sand. A wide 

range in grain size, sorting, and roundness is typical and 

reflects the rapid changes in the rates of meltwater flow and 

sediment release in the glacial environment (Ozvath, 1985).

Kames can be indicative of areas that are favorable for 

water-supply development where they are largely saturated or 

hydraulically connected to saturated ice-contact stratified drift 

at depth or to adjacent or overlying saturated outwash. Surface 

exposures of kames, even if mostly unsaturated, can act as 

recharge areas for saturated ice-contact deposits at depth.

Kame Terraces

Kame terraces are large deposits of fluvially deposited 

ice-contact sediments that once occupied the area between 

the bedrock valley wall and the ablating ice tongue within the 

valley. Kame terraces within the West Branch Delaware River 

Basin can have surface altitudes as high as 100 ft above the 

valley floor and can be as much as 1,000 ft wide and up to 

a 0.5 mi long. Many kame terraces have been partly eroded 

by postdepositional slumping or floods. Kame-terrace sediments within the West Branch Delaware River Basin range 

from silt to cobble-sized gravel and are crossbedded locally. 

Ozvath (1985) identified four common sediment facies within 

kame terraces in the western Catskill Mountains, all of which 

indicate deposition in a braided glacial-stream environment. 

As a product of this fluctuating depositional environment, 

kame terrace sediments can be characterized by large and 

abrupt changes in grain size between adjacent beds, crossbedding, truncated beds, and various deformation features, such as 

faults, folds, slumps, and till inclusions. Kame terraces constitute much of the valley-fill aquifer in the West Branch Delaware River Basin and also provide surface pathways where 

recharge can migrate downward to reach confined portions of 

the valley fill aquifer.

Kame Deltas

Kame deltas are terrace-like deposits of stratified sand, 

gravel, silt, and clay that were deposited by meltwater into a 

proglacial lake. Ozvath (1985) recognized two forms of kame 

deltas in the western Catskill Mountains—those that flank a 
8 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

valley wall (terraces), and those that extend across the valley. 

Kame deltas emplaced as flanking terraces were deposited in 

lakes that developed between the valley wall and the ablating 

ice tongue, whereas cross-valley kame deltas were deposited 

in proglacial lakes that developed between the toe of the ice 

tongue and older downvalley deposits. Kame deltas, whose 

nearly flat upper surfaces were graded to a former lake level, 

typically consist of three units of sedimentation: topset beds, 

foreset beds, and bottomset beds. Topset beds consist of coarse 

sediment deposited at or above lake level in the channels of 

meltwater streams. They overlie steeply inclined foreset beds, 

which consist of sediment deposited at the leading edge of a 

delta as it advances into a proglacial lake. The foreset beds 

overlap bottomset beds, which are fine-grained sediments 

deposited on the floor of the proglacial lake. Foreset and 

topset beds of kame deltas can contain considerable amounts 

of coarse sand and gravel, but their altitudes are typically 

above the modern stream grade and, therefore, are largely 

unsaturated and generally do not support large groundwater 

development. Kame deltas may, however, represent potential 

groundwater recharge areas for saturated ice-contact deposits at depth. Kame deltas are recognized in only a few short 

reaches of the West Branch Delaware River valley where 

small glacial lakes were impounded by downstream dams 

composed of detached blocks of glacial ice. Ozvath (1985) 

identified several kame deltas in the vicinity of Delhi and 

Walton—two are located on either side of the sharp “S” bend 

in the river, southwest of Walton, and two more flank the sharp 

southward bend in the river just westward of the confluence 

with the Little Delaware River near Delhi. The logs of several 

wells in both of these locations show substantial thicknesses of 

fine-grained lake-bottom sediments, which appear to confirm 

the existence of two small glacial lakes.

Kame Moraines

Kame moraines are ice-contact landforms that are closely 

associated with a temporary pause in the retreat of the ice 

front within a valley; they also are known as outwash heads. 

Kame moraines generally consist of extremely coarse-grained 

(to boulder size), poorly sorted gravel that was deposited by 

fast-moving meltwater streams close to the ice. These deposits 

generally show deformation features from ice shove and can 

contain till clasts. Kame moraines indicate the location of a 

former ice-margin position within the valley, and generally 

grade downvalley into outwash deposits. In the West Branch 

Delaware River Basin, kame moraines range in height from 

50 to 200 ft above the present flood plain and are commonly 

located near the junctions with tributary valleys. The common 

occurrences of kame moraines at the junctions with tributary 

valleys suggest that their locations were controlled by the 

availability of the extra sediment load produced by the tributary streams (Kirkland, 1979; Ozvath, 1985).Though not as 

well sorted as kame terraces and kame deltas, kame moraines 

may have potential for groundwater development, especially 

midvalley, where they are overlapped by and buried beneath 

later outwash and alluvium and are mostly saturated. Kirkland 

(1979) identified multiple sets of kame moraines, each keyed 

to an individual morphosequence in the West Branch Delaware 

River Basin; however, some of these were later reclassified by 

Ozvath (1985) as either kame deltas or kame terraces.

Outwash, Alluvium, and Inwash

Outwash

Outwash consists of well-sorted, coarse-grained sediments deposited by meltwater streams issuing from the ice 

front. The relatively steep stream gradients within the West 

Branch Delaware River Basin, combined with variable meltwater flows and an abundance of coarse-grained sediments, 

resulted in high-energy, braided streams that deposited tens of 

feet of coarse sand and gravel outwash. This outwash accumulated on the valley floor as the ice receded and formed what is 

known as a valley train. Floods and meltwater drainage commonly reworked and redistributed the outwash and adjacent 

ice-contact deposits during late glacial and postglacial time 

to form a veneer of alluvium over the outwash. Deposits of 

valley train outwash and alluvium in the West Branch Delaware River valley are generally less than 2,000 ft wide but 

can be as much as a 0.5 mi wide at major valley confluences. 

Outwash, particularly where underlain by ice-contact sand and 

gravel, forms the principal stratified-drift aquifer in the basin. 

Outwash,or alluvium underlain by outwash,also floors the 

larger tributaries to the West Branch Delaware River, except 

in the upper reaches of the tributaries, but these deposits rarely 

exceed 1,000 ft in width.

The thickness and horizontal continuity of outwash 

within the West Branch Delaware River Basin are highly 

variable as a result of the locally varying amounts of meltwater and sediment that were available within the basin. Where 

outwash is present in tributary valleys, it typically forms only 

a veneer over older deposits of ablation till and ice-contact 

stratified drift. Within the West Branch Delaware River valley, 

the logs of wells that report fine-grained lacustrine sediments 

beneath the surficial outwash deposit indicate that the combined thickness of alluvium and outwash ranges from 20 to 

40 ft thick near Delhi, 20 to 50 ft thick near Walton, and 20 to 

65 ft thick at Deposit.

Alluvium

Alluvium consists primarily of postglacial, fluvially 

deposited sediment ranging in size from silt, to fine to coarse 

sand, and to fine gravel, generally less than 10 ft in thickness, 

and is present as overbank deposits on flood plains. Alluvium 

is derived from reworked and fluvially sorted outwash, icecontact, and till deposits, and is generally confined to modern 

flood plains within a valley or deposited as alluvial fans where 

small tributaries enter major valleys. Alluvium is generally 

permeable and on valley floors, typically overlies and grades 

downward into outwash. Because it can be difficult to distinguish alluvium from the underlying outwash in a valley, both 
Hydrogeology 9

Kirkland (1979) and Ozvath (1985) generally depict outwash 

and alluvium as one unit. In tributary valleys where ice-contact deposits line the valley wall, these same deposits can be 

expected to underlie the alluvium toward the center of the valley. Elsewhere in tributary valleys, alluvium generally overlies 

deposits of ablation till. Areas of alluvium delineated on plate 

1 are based on NRCS soil types that are derived from alluvium, and the thickness of the alluvium is usually much less 

than 10 ft. Alluvial fans, however, are composed of tens of feet 

of postglacial alluvium and form rounded, fan-shaped deposits 

where tributary streams enter the larger valleys. Alluvial fans 

are mapped separately on plate 1 because they can be major 

sources of additional recharge to the underlying valley-fill 

aquifer though streambed infiltration losses where the stream 

crosses the alluvial fan.

Inwash

Inwash deposits are stratified accumulations of sand 

and gravel deposited into valleys by tributaries of nonglacial 

origin. Inwash commonly takes the form of an alluvial fan 

and may have been deposited atop outwash, or against stagnant ice, where it coalesced with a developing kame terrace. 

Inwash deposits are typically found in upland headwaters, 

where outwash deposits would not be expected. Scattered 

deposits of inwash are found in the upper reaches of some of 

the tributaries to the West Branch Delaware River. Because the 

soil types that are derived from inwash are much the same as 

those that are derived from outwash, inwash is not delineated 

as a separate unit on plate 1 but is labeled as outwash instead.

Bedrock Geology

The bedrock that underlies the West Branch Delaware 

River Basin not only provides groundwater to bedrock wells 

but is a major contributor of groundwater flow (base flow) to 

the West Branch Delaware River and its tributaries.

Stratigraphy

The entire Catskill Mountain region, including the West 

Branch Delaware River Basin, is underlain by the informally 

named Catskill Mountain series (Mather, 1840; Chadwick, 

1936) of Upper Devonian age; the series is as much as 6,000 ft 

thick and consists of marine and nonmarine red and gray sandstones, shales, and conglomerates. Bedrock layers throughout 

the Appalachian Plateau dip gently southward, as shown by 

the southward progression from older to younger formations 

in figure 2, but bedrock in Delaware County is also deformed 

by broad folds whose axes trend east–northeast, so gentle dips 

to the northwest and southeast are commonly observed (Soren, 

1963). The Catskill Mountains were formed from the dissection of a bedrock plateau by streams and glacial erosion. The 

highest hilltops and ridges, which form the principal drainage divides, are underlain by various beds of siliceous rocks 

that are highly resistant to erosion, whereas the lower hilltops 

and ridges are capped by various sandstone units that also are 

highly resistant. The valleys are developed along the strike 

of less competent siltstones and shales, gentle anticlines, and 

fracture zones (Soren, 1963).

Fisher and others (1970) and Rickard (1975) have divided 

the nonmarine red and gray sandstones and shales of the 

Catskill Mountain series, or Catskill facies (Rickard, 1975), in 

the West Branch Delaware River Basin into five major formations—the Honesdale, Slide Mountain, and upper Walton 

Formation of the West Falls Group, the lower Walton Formation of the Sonyea Group, and the Oneonta Formation of the 

Genesee Group (Rickard, 1975, plate 3). The stratigraphically 

higher (and younger) Honesdale and Slide Mountain Formations occupy the ridgetops of the drainage divide between the 

West Branch Delaware River Basin and the East Branch Delaware River Basin just south of the Cannonsville Reservoir. 

The upper Walton Formation occupies the southern uplands 

within the West Branch Delaware River Basin and its ridges 

also form part of the drainage divide between the West and 

East Branch Delaware Rivers. The lower Walton Formation 

underlies the lower slopes and valleys of the main tributaries 

south of Delhi, whereas the Oneonta Formation underlies the 

upper West Branch Delaware River and its tributaries from 

Delhi northeastward to its headwaters just beyond Stamford 

(Fisher and others, 1970). The areal distribution of these major 

bedrock formations within the West Branch Delaware River 

Basin is illustrated in figure 2.

Structure and Folding

The Catskill Mountain series rocks in Delaware County 

lie in broad, low folds, striking in a northeasterly direction 

within a larger synclinal structure whose trough axis plunges 

slightly southwestward and appears to lie wholly within Delaware County (Soren, 1963). The East and West Branch Delaware Rivers lie along low anticlines with a syncline occupying 

the intervening uplands. Soren (1963) observed anticlinal folds 

along highway exposures near the Pepacton Reservoir and 

near the village of Apex, N.Y., in the West Branch Delaware 

River Basin. Woodward (1957) estimated that the axis of the 

folding is approximately 75° N to 80° E, and appears to extend 

across Delaware County. The limbs of the folds dip at low 

angles, generally less than 5 degrees (°), to the southeast and 

northwest (Soren, 1963). The steepest dips measured by Soren 

(1963) were at outcrops at Delhi, in the bed of Steele Brook, 

where gray shale beds of the lower Walton Formation dip 

about 12° to the northwest, and along State Highway 10, north 

of Apex, N.Y., where an anticlinal fold whose limbs dip 8° to 

the northwest and 5° to the southeast, is exposed. As Soren 

(1963) points out, folds can affect the occurrence and movement of groundwater. The inclination of beds in the limbs of 

folds and along the plunge of the folds can produce artesian 

pressures in more permeable beds of sandstone lying between 

shale beds of lower permeability. Beds of lower permeability, 

such as shales, can also serve as barriers to the movement of 

groundwater between adjacent folds.
10 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

Base from U.S. Geological digital data, 

Universal Transverse Mercator projection, zone 18

North American Datum 1983

01424997

01425000

01423900

01423000 0142400103 01422747

01424108

01422389

01422500

01422738

01421900

01421618 01421614

01421610

75°15' 75° 74°45'

42°30'

42°15'

EXPLANATION

Streamgage and station number

West Branch Delaware River basin boundary

Streamgage basin drainage divide

Bedrock units—Oldest to youngest, in descending order

Oneonta Formation—shale, sandstone, conglomerate

Unadilla, Laurens, New Lisbon, and Gilboa Formations—shale, siltstone, sandstone

Moscow Formation—shale and sandstone

Panther Mountain Formation—shale, siltstone, sandstone

Enfield and Kattel Formations—shale, siltstone, sandstone

lower Walton Formation—shale, sandstone, conglomerate

Honesdale Formation—sandstone, shale

Slide Mountain Formation—sandstone, shale, conglomerate

upper Walton Formation—shale, sandstone, conglomerate

0 7.5 15 MILES

0 7.5 15 KILOMETERS

Geology from Fisher and others (1970)

01421614

LOCATION MAP

NEW YORK

Figure 2. Distribution of major bedrock units within the West Branch Delaware River Basin in southeastern New York. Bedrock units 

listed in descending order from oldest to youngest.
Hydrogeology 11

Faults and Jointing

Little surface evidence of faulting has been reported 

in the West Branch Delaware River Basin and in Delaware 

County in general, because of a lack of marker beds and a 

scarcity of accessible rock outcrops (Soren, 1963). Soren 

(1963) observed a thrust fault with a displacement of several feet in the anticlinal fold seen north of Apex. This fault 

displayed a dip of about 15° to the northeast. Soren (1963) 

also noted that the bedrock in Catskill Mountain series rocks 

in Delaware County is strongly jointed (fractured), with sets 

of closely spaced joints observed in shales, and joints with 

spacings of several feet in the thicker sandstones. Two vertical 

joint sets strike northeast and northwest, respectively, with the 

planes of the joint sets nearly perpendicular to the bedding 

plane in the rock. A third joint set, which is parallel to the bedding plane, intersects the two vertical joints sets, and all three 

appear in most of the beds of Catskill Mountain series rocks. 

The two vertical joint sets are roughly perpendicular—one 

striking northeast, from 15° N to 35° E, and the other striking 

northwest, from 25° N to 80° W (N.M. Perlmutter and E.H. 

Salvas, U.S. Geological Survey, written commun., 1957). 

These roughly orthogonal vertical fracture sets facilitated the 

quarrying of bedrock from hillsides by glacial ice to produce 

horizontal surfaces and ledges bounded by nearly vertical 

cliffs, commonly tens of feet high (Soren, 1963; Parker and 

others, 1964). The joint sets also serve to increase the permeability of the rock and are the reason for the relatively high 

yields of bedrock wells in this region. Bedding plane openings, or joints, are important contributors to the secondary 

porosity of the bedrock, as are the vertical joints and fractures 

that intersect these bedding plane openings. The continuity 

and connectivity of these features and their ability to transmit 

water (transmissivity) are important factors in determining the 

larger scale transmissivity and storage capacity of the bedrock 

aquifer. The sandstones and shales of the Catskill Mountain 

series rocks in the West Branch Delaware River Basin show 

typical sedimentary rock structure and range from thin shale 

layers up to 3⁄8-inch (in.) thick, to individual beds of sandstone 

more than 4 in. thick (Soren, 1963). The beds of the Catskill 

Mountain series have been characterized as poor to moderately good aquifers whose well yields can vary widely within 

hundreds of feet (Parker and others, 1964). In general, the 

sandstone beds are much more permeable than are the shale 

beds, although some massive sandstone units are so completely cemented and lacking in fractures that they transmit 

little water (Parker and others, 1964).

Stress Relief Fracturing

Stress relief in valleys has been shown to be the principal factor in enhancing the secondary permeability of clastic 

sedimentary rocks (Wyrick and Borchers, 1981). Stress relief 

refers to the fracturing, arching, and faulting of sedimentary 

rocks beneath a bedrock valley floor and along the valley walls 

in response to the removal of rock by erosional processes. The 

removal of rock to produce a bedrock valley creates tensional 

forces along the valley walls and resultant upward forces on 

the bedrock that directly underlies the valley floor (fig. 3). 

These forces typically produce vertical tensile fractures in 

bedrock on the valley walls and vertical fracturing, low-angle 

faulting, and arching of beds beneath the valley floor. The 

tensile fractures on the valley walls can result in blocky or 

steep cliffs with nearly vertical faces, especially in structurally competent rocks such as massive sandstones, whereas 

the vertical and horizontal compressional forces on the rock 

underlying the valley floor typically produce arching of beds 

and associated vertical fracturing. There is ample evidence of 

stress relief fracturing in the valleys of the Catskill Mountain 

region. Soren (1963) reported anticlinal crests (folds) in the 

East and West Branch Delaware Rivers near the Pepacton 

Reservoir and near Apex. Heisig (1999) depicted stratigraphy 

(based on natural gamma radiation logs) in the Batavia Kill 

valley near Windham, N.Y., east of the West Branch Delaware River Basin that appears to show arching of beds (or 

an anticlinal structure) beneath the thalweg of the bedrock 

valley there. According to Woodward (1957), the East and 

West Branch Delaware Rivers lie along anticlinal folds whose 

orientation (75° N to 80° E) nearly matches the orientation of 

the valleys. On the basis of this evidence, it can be reasonably 

assumed that vertical fracturing is present in bedrock beneath 

the West Branch Delaware River valley and many of its larger 

tributaries. Valley-bottom and valley-side fracturing caused 

by stress relief improves the secondary permeability of rock 

to the extent that yields from bedrock wells in these areas are 

typically higher than those of wells drilled into the upper hillsides or hilltops. The general features of stress relief fracturing 

are illustrated in figure 3.

Well Yields

Records of 199 wells drilled into the Catskill Mountain 

series within Delaware County indicate well depths ranging 

from 18 to 687 ft, with a median depth of 158 ft (Soren, 1963); 

most well depths range from 100 to 300 ft. Yields range from 

0 to 450 gallons per minute (gal/min), with a median yield 

of about 15 gal/min. Specific capacities range from less than 

0.2 to 4 gal/min per foot [(gal/min)/ft] of drawdown (N.M. 

Perlmutter and E.H. Salvas, U.S. Geological Survey, written 

commun., 1957). The maximum known yield from a bedrock 

well in the West Branch Delaware River Basin (400 gal/min) 

is from well D–420, a 10-in.-diameter well that is 172 ft deep 

and is completed in the lower Walton Formation, which underlies most of the West Branch Delaware River valley. Similarly, 

the maximum known yield (550 gal/min) from a bedrock well 

within Delaware County is from well D–15, a 12-in.-diameter 

industrial well completed in sandstone and shale near Sidney, 

N.Y. (within the Susquehanna River Basin). Eight bedrock 

wells (D–33, D–88, D–90, D–91, D–102, D–103, D–353, and 

D–420) in the West Branch Delaware River Basin have yields 

that exceed 100 gal/min. These high-yielding bedrock wells 

are all situated on the valley floor where overlying sand and 
12 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

Land surface

Colluvium and till

Top of rock

Compression fractures

Alluvium

Sand and gravel

Tensile fractures

Fractures due to arching Open bedding planes

Compressional stress

Resultant stress

Sandstone

Shale

Shale

Colluvium

and till

Figure 3. Generalized geologic section showing features of stress-relief fracturing. From Wyrick and Borchers (1981, fig. 3.2–2).

gravel deposits likely enhance the well yields. Wells that are 

completed in the Catskill Mountain series and are situated on 

valley floors commonly exhibit artesian flow because potentiometric heads in the underlying bedrock are typically above 

land surface in these locations. Data from exploratory borings 

made in the 1930s and 1940s along the routes of the nearby 

East and West Delaware Aqueducts indicate artesian flow at 

several borings in valley floor and lower hillside settings with 

a potentiometric surface more than 10 ft above land surface 

(Reynolds, 2000).

Saline Groundwater

Groundwater from the Catskill Mountain series generally is of excellent quality and is typically used for domestic, 

industrial, and municipal supplies without treatment (Parker 

and others, 1964). Hardness ranges from very soft to moderately hard, and dissolved solids concentrations are generally 

low. Iron concentrations are typically low (0.01–0.17 milligram per liter [mg/L]), but can be elevated locally (Parker and 

others, 1964).

Despite the documented high quality of groundwater 

from the Catskill Mountain series, saline groundwater has 

been reported at depth within the West Branch Delaware River 

Basin and within the Schoharie Creek Basin to the east. Soren 

(1963) reported two bedrock wells, both located on the floor 

of the West Branch Delaware River valley, which produced 

water with elevated chloride concentrations. Water from a 

bedrock well at Deposit (D–114), which is 208 ft deep, yielded 

water with a chloride concentration of 310 mg/L when first 

drilled in 1946. Also in 1946, well D–102 at Walton (420 ft 

deep) initially had a chloride concentration of 800 mg/L, but 

had a chloride concentration of only 126 mg/L when it was 

resampled in 1957. Many of the deep bedrock wells drilled 

into the Catskill Mountain series rocks also produce naturally 

occurring methane gas, in addition to producing saline water. 

Well D–32, a 505-ft-deep bedrock well on the valley floor 

just southwest of Delhi, produced flammable gas (methane) 

and hydrogen sulfide gas when drilled in 1941, reportedly 

produced a gas flame 3 to 5 ft high for more than a year after 

being abandoned, and was finally cemented shut in 1947 

(N.M. Perlmutter and E.H. Salvas, U.S. Geological Survey, 

written commun., 1957). Newland and Hartnagle (1932) 

reported that a brine spring existed in the Elk Creek valley, 

about 4 mi north of Delhi as early as 1833. A subsequent boring to 394 ft at this location produced enough brine for the 

commercial manufacture of salt, and small amounts of natural 

gas were observed in the water. In 1864, an exploratory well 

was drilled near the site of the original spring (MacDonald 

test hole; plate 1) to a depth of 750 ft. Insufficient natural gas 

was found for the well to be economically developed, and the 

well was abandoned. In 1924, however, the gas pressure on 

the well was tested at 25 pounds per square inch, and Newland 

and Hartnagle (1932) estimated that the well could produce 

enough gas to supply a single home for several years. N.M. 

Perlmutter and E.H. Salvas (U.S. Geological Survey, written 

commun., 1957) also reported a 462-ft-deep bedrock well in 

central Sullivan County, N.Y., that produced natural gas (methane) and saline water from a gray shale unit. All these wells 

probably intersect marine shales of the Catskill Mountain 
Hydrogeology 13

series and tap naturally occurring brine (connate water). Saline 

groundwater has also been reported in deep wells completed in 

Catskill Mountain series rocks within the adjacent Schoharie 

Creek Basin to the east. Heisig (1999) reported three bedrock 

wells within the Batavia Kill valley near Windham that produce very saline groundwater from depths ranging from 420 

to 489 ft. Several bedrock wells within the Batavia Kill valley 

were geophysically logged in that study and water samples 

were obtained at selected intervals within the boreholes with 

a down-hole point sampler. Dissolved chloride concentrations 

in groundwater entering the boreholes from fractures ranged 

from 370 to 13,000 mg/L (Heisig, 1999, app. B). However, 

not all deep bedrock wells that intercept saline water at depth 

produce nonpotable water because considerable mixing generally occurs within the borehole. Moreover, the location of the 

well with respect to the valley will affect the flow within the 

borehole. Wells that are located high on the valley walls or on 

hilltops are generally in areas of groundwater recharge where 

the vertical gradient, and thus the flow within the well bore, 

are downward. Conversely, wells on the valley floor are in 

areas of groundwater discharge where the vertical gradient, 

and thus the flow within the well bore, are upward. Bedrock 

wells located on valley floors and that intercept saline groundwater at depth, therefore, usually yield water that gradually 

becomes nonpotable through the upward movement of saline 

water within the well bore. In a study of wells that penetrated 

either saline water or gas in the Upper Devonian bedrock 

of Chemung, Tioga, and Broome Counties, N.Y., Williams 

(2010) found that the base of freshwater circulation (that is, 

the top of saline water) appeared to be about 800 ft below land 

surface in upland settings, but only 200 ft below land surface 

on the valley floors. At depths greater than 200 ft below the 

valley floors groundwater in the Upper Devonian bedrock, and 

in some places in the immediate overlying glacial drift, was 

saline. The frequency of occurrence of methane gas increased 

with depth in the bedrock, with some pockets of gas present above the base of the freshwater circulation (Williams, 

2010). The two bedrock wells (D–102 at Walton and D–114 at 

Deposit) that have penetrated saline water in the West Branch 

Delaware River Basin appear to show a similar depth of freshwater circulation below the valley floor.

Groundwater Flow System

The sequence of permeable sandstone units alternating 

with less permeable shale units within the Catskill Mountain 

series forms a series of stacked aquifers separated by confining units of varying thickness, but generally thinner than the 

aquifer units. Weathering, glacial loading and unloading, and 

stress relief through the erosion of bedrock in the valleys have 

made exposed rock and rock nearest to the mountainsides 

typically more jointed and fractured than the unexposed rock 

deep within each mountain or ridge. This enhanced jointing increases the secondary permeability in these areas and 

allows groundwater in the highly jointed sandstone to flow 

readily to points of discharge (springs) along the hillside, just 

above confining shale beds, as illustrated in figure 4. A small 

unsaturated zone develops in the upper part of each sandstone 

unit near the hillside, although the entire rock section within 

the core of the mountain is saturated. Thus, the mountainsides 

commonly exhibit a stepwise pattern of steep sandstone faces 

with springs at their bases, separated by gentler slopes of 

shale. Horizontal joints and permeable bedding-plane fractures 

typically form at the contact between lithologically dissimilar 

rock units; therefore, groundwater within a saturated sandstone 

unit typically discharges at the contact with the underlying 

shale unit as a contact spring. These springs can be ephemeral 

features that flow during only the wet spring season (March 

and April), but may flow continuously if the saturated zone 

above the springs is thick enough. These sandstone units 

also are saturated but less fractured or jointed where they 

extend into the core of the mountain, and groundwater within 

these units moves mainly as slow, diffuse flow through small 

intergranular spaces and small, discontinuous fractures and, 

therefore, probably contributes little to contact springs.

Groundwater within saturated sandstone in valley 

segments that contain thick deposits of ablation till occurs 

generally under confined conditions, with groundwater levels 

typically rising to above land surface in bedrock wells on or 

near the valley floor. For example, records of two test holes 

drilled into sandstone and basal till along the route of the East 

Delaware Aqueduct crossing of Beaver Kill at Lewbeach in 

adjacent Sullivan County indicate that artesian flow from a 

3-in.-diameter casing was as much as 18 gal/min, and heads 

ranged from 12 to 13 ft above the valley floor (Reynolds, 

2000). The large head difference between the water table in 

the valley and the potentiometric surface of the confined, fractured sandstone at depth may indicate low vertical hydraulic 

conductivity within the bedrock or within a till confining unit 

between the bedrock and the outwash and may explain the 

relatively high base flows of streams in this region.

Springs

Springs are a source of domestic groundwater supplies 

for much of the rural population of the West Branch Delaware 

River Basin, and much of the Catskill Mountain region. Well 

and spring inventories were conducted by the USGS during 

previous groundwater investigations of Delaware County 

(Soren, 1963) and the Delaware River Basin in New York 

(N.M. Perlmutter and E.H. Salvas, U.S. Geological Survey, 

written commun., 1957). Perlmutter and Salvas inventoried 

about 300 springs that discharge from the Catskill Mountain 

series rocks in the Appalachian Plateau, which includes both 

the West and East Branch Delaware River Basins and most of 

adjoining Sullivan County. Nearly all these springs were situated on hillsides, originated from bedding-plane openings or 

other fractures, and discharged only 2 to 3 gal/min, although 

a few exhibited discharge rates as high as 106 gal/min (N.M. 

Perlmutter and E.H. Salvas, U.S. Geological Survey, written 

commun., 1957, p. 21). Soren (1963) published records of 184 

representative springs in Delaware County, nearly all of which 
14 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York EXPLANATION Sandstone—Fractured; saturated where shaded. Forms a regional, confined aquifer in the Catskill Mountain region Shale—Forms confining beds within bedrock aquifer Ice-contact deposits—Kame terraces or kame moraines compsed chiefly of sand and gravel emplaced against the valley wall; saturated where shaded. Outwash—Valley train outwash and alluvium; saturated where shaded.

Water table

Spring discharge – Contact springs at the base of sandstone unitsGroundwater flow—Generalized direction of groundwater flow within zone of saturationUnsaturated flow—Generalized direction of unsaturated flow in fractured bedrockDownvalley flow—Indicated flow into the page (downvalley)

Till—Forms a veneer at the toe of steep bedrock faces

Runoff

Runoff

2,2002,1002,0001,9001,8001,7001,6001,500

Altitude, in feet above NGVD 29

NOT TO SCALE

Outwash

Stream

Modified from Kipp and others, 1983.

Ice-contactdeposits

est Branch Delaware River Basin in southeastern New Conceptual diagram of groundwater flow within bedrock and stratified-drift aquifers within the W Figure 4.

York. From Reynolds (2000, fig. 8).
Hydrogeology 15

1,000

1,500

2,000

2,500

0 20 40 60 80 100

Altitude, in feet above NGVD 29

Yield, in gallons per minute

Figure 5. Yield of 178 

springs in Delaware 

County, New York, as a 

function of altitude. Data 

are from Soren (1963). 

NGVD 29, North American 

Vertical Datum of 1929.

discharged from Catskill Mountain series sandstones. Most 

of these springs were used as domestic supplies for homes 

and farms, although some were used for public water supplies for several villages. Yields of 178 of these springs were 

measured by the USGS from October 1948 through February 

1949; the highest yield (100 gal/min) was from a group of 

three springs that supply the village of Downsville, N.Y., in 

the East Branch Delaware River Basin. The average yield for 

these 178 springs, which include 11 public-water supplies, 

was 8.5 gal/min, with a median yield of 3 gal/min, although 

most of the domestic springs had yields of less than 5 gal/min. 

Records of these 178 springs show that they range in altitude from 1,000 ft to 2,360 ft above the National Geodetic 

Vertical Datum of 1929 (NGVD 29), with a mean altitude of 

1,676 ft. A plot of yield as a function of altitude for these 178 

springs (fig. 5) indicates that most of the yields were less than 

10 gal/min and that most of the springs are at altitudes ranging 

between 1,400 and 2,000 ft above NGVD 29.

Many small villages within the West Branch Delaware 

River Basin still rely on springs as their primary source of 

water, but often use wells as an auxiliary supply. Soren (1963) 

reported that, in 1960, more than half of the small municipalities (17 out of 31) within Delaware County relied on springs 

to supply all or part of their drinking water, and water-use data 

for 2000 (New York State Department of Health, written commun., 2000) indicated that there were 15 small municipalities 

in Delaware County that continue to obtain all or part of their 

water needs from springs. Several small villages in the West 

Branch Delaware River Basin still use springs for all or part 

of their municipal supply. For example, De Lancey relies on 

three springs, with an average yield of 10 gal/min, to serve 

a population of 135. Similarly, the Hamden Water District 

relies on four springs to serve a population of 150 people, 

and the village of Bloomville, N.Y., relies on a combination 

of springs and wells to supply a population of 300 (Soren, 

1963; New York State Health Department, 1982). All these 

municipal-supply springs issue from fractured Catskill 

Mountain series sandstones. The prolific use of springs for 

domestic and municipal water supplies in the Catskill Mountain region appears to indicate a lesser dependence on drilled 

wells for drinking water than in other parts of New York. The 

abundance of springs issuing from Catskill Mountain series 

sandstones reflects the relatively high secondary permeability of these rocks because of the presence of both vertical 

and bedding-plane fracture sets and the effect of stress-relief 

fracturing on the valley walls. The abundance of springs has a 

pronounced effect on the base flow of tributary streams within 

the West Branch Delaware River Basin, as many of the small 

tributaries originate as spring discharge from hillsides (N.M. 

Perlmutter and E.H. Salvas, U.S. Geological Survey, written 

commun., 1957).

Marcellus Shale

The Marcellus Shale, a black, organic-rich, gas-bearing 

shale that forms the basal member of the Middle Devonian 

Hamilton Group in New York, is one of several black shales 

that occupy the Appalachian Plateau. The Marcellus Shale 

extends from northeastern Kentucky into West Virginia, northeastward through Pennsylvania and northwest Maryland, and 

into the Southern Tier of New York, as well as Delaware and 

Sullivan Counties in New York. The Marcellus Shale is the 

most widespread Devonian gas-bearing shale sequence in New 

York and consists of black “sooty” shale with some interbedded gray shales and dark gray to black limestones (DeWitt 

and others, 1993). The Marcellus Shale reaches a thickness of 

about 1,000 ft in central Pennsylvania and thins to the north, 

west, and south (DeWitt and others, 1993). However, the net 

thickness of organic-rich black shales within the Marcellus is 

considerably less—approximately 250 ft in eastern Bradford 

County, Pa., and Tioga County, N.Y., and only about 150 ft 

thick in Delaware County (Milici and Swezey, 2006). The 

Marcellus Shale has been further subdivided into two gasbearing black shale units—the Oatka Creek Shale Member 

and the lowermost Union Springs Member—both of which are 
16 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

Union Springs Member

Cherry Valley Limestone

Oatka Creek Shale Member

High gamma

radiation

High gamma

radiation

B. Marcellus shale stratigraphy

A. Geophysical log

Depth, in feet below land surface

Figure 6. A, Geophysical log showing typical gamma log response and B, photograph showing typical stratigraphy of the Marcellus 

Shale in New York. The shaded portion of the gamma response curve represents an upward shift in scale to 200 to 400 American 

Petroleum Institute (API)units and indicates the high gamma radiation response characteristic of black shales. Geophysical log modified 

from Lash and Engelder (2009); photograph by J.H. Williams, U.S. Geological Survey.

separated by the intervening Cherry Valley Limestone Member 

(fig 6). The base of the Marcellus Shale conformably overlies 

the Onondaga Limestone (Rickard, 1975).

New developments in horizontal drilling and hydraulic 

fracturing have made the Marcellus Shale the newest exploitable source of natural gas in the Northeastern United States. 

There is, however, concern among State regulatory agencies 

and the general public in New York and Pennsylvania about 

the possible contamination of stratified-drift and bedrock aquifers from proposed gas well drilling operations. Along with the 

natural gas, the wells would produce highly mineralized brine 

from the Marcellus Shale, large volumes of drilling fluids 

with numerous additives, and drill cuttings. The chemical and 

radiologic qualities of these fluids and solids have not been 

well documented, but will have to be dealt with at the drill 

site and during transportation and disposal (Soder and Kappel, 

2009). Therefore, State, county, and municipal, governmental 

agencies are seeking information that will help them discern if 

these drilling operations may contaminate overlying aquifers 

that supply potable water.

Ten deep exploratory test holes that encircle the West 

Branch Delaware River Basin give information on both the 

thickness and depth to the Marcellus Shale (table 1). The 

thickness of the Marcellus Shale (Marcellus Formation of the 

Hamilton Group; Rickard, 1975) ranges from about 600 to 

650 ft along the northern watershed divide with the adjacent 

Susquehanna River Basin (test holes Fowler Finch 1, Hazlett 

Merrit 1, and Hirsch K1) to about 750 ft along the southern 

divide with the East Branch Delaware River Basin (test holes 

Holdridge Charles 1, Lanzilotta 1, and Weickert F1) and thins 

slightly to about 660 ft further westward (test hole Campbell). 

The depth to the top of the Marcellus Shale ranges from about 

2,600 to 2,900 ft in the Ouleout Creek and Treadwell Creek 

valleys to the north (test holes Leslie Caroline E1 and Hazlett 

Merrit 1) to 3,240 ft in the uplands near the northern watershed divide (test hole Hirsch K1). Similarly, the depth to the 
Hydrogeology 17

top of the Marcellus Shale along the southern divide with the 

East Branch Delaware River Basin ranges from about 3,500 

to 4,150 ft in three upland test holes (Holdridge Charles 1, 

Lanzilotta 1, and Weickert F1). The greatest depth to the Marcellus Shale of about 4,390 ft is seen at the Campbell HA test 

hole southeast of De Lancey in the uplands of the East Branch 

Delaware River Basin. Two test holes (Grant 6 and Grant C1a) 

in the Ouleout Creek valley to the north indicate that the thickness of the Union Springs Member of the Marcellus Shale is 

about 28 ft thick in this location.

Stratified-Drift Aquifers

The location and thickness of stratified-drift aquifers in 

the West Branch Delaware River Basin are directly related to 

the distribution of outwash and ice-contact deposits. In general, the upper and middle reaches of the West Branch Delaware River contain thick sections of outwash and sand and 

gravel, with thick beds of fine-grained lacustrine sediments 

appearing in only the lowermost valley reach. The unconsolidated sediments in the small tributary valleys become less 

stratified and sorted as the valley size decreases and generally include large thicknesses of till, and what little stratified 

drift is present consists of poorly sorted ice-contact material 

(Ozvath and Coates, 1986). The main valley of the upper West 

Branch Delaware River (Stamford to Delhi) and middle West 

Branch Delaware River (Delhi to Walton), however, contains 

large amounts of ice-contact sand and gravel and outwash 

that together form productive sand and gravel aquifers that 

are generally under water-table (unconfined) conditions. The 

lowermost reach of the West Branch Delaware River (Walton 

to Deposit) contains an additional thin, basal sand and gravel 

aquifer confined beneath thick sequences of lacustrine clay, 

silt, and fine sand. The distribution, thickness, and composition of the stratified-drift aquifers in each of these valley segments are discussed below.

Upper West Branch Delaware River

The upper West Branch Delaware River, the 20-mi reach 

from the river’s headwaters near Stamford to the confluence 

with the Little Delaware River at Delhi (pl. 1), is characterized 

by long stretches of valley filled with ice-contact features such 

as kame terraces and kame moraines, bisected by a narrow 

ribbon of valley-train outwash. The valley fill in this section 

consists mostly of ice-contact sand and gravel, overlying a 

basal till, all of which is overlain by valley-train outwash. The 

valley floor in this stretch, as throughout most of the West 

Branch Delaware River valley, averages about 2,500 ft in 

width. The thickness of the valley fill, which includes fine- and 

coarse-grained sediments, ranges from 130 ft at Hobart (well 

D–51, a supply well for the Hobart Water Company) to 119 ft 

at Bloomville (well D–503), and to 142 ft at East Delhi (well 

D–2208). Each of these three wells is located where a major 

upland tributary valley joins the West Branch Delaware River 

valley; the limited well data suggest that depth to bedrock is 

greatest near such junctions. For example, near Delhi where 

Table 1. Thickness of and depth to the Marcellus Shale in selected deep test holes in Delaware County, New York. 

[Data are from New York State Museum Empire State Oil and Gas Information System (ESOGIS) database, 2010, http://esogis.nysm.nysed.gov/esogis/index.

cfm. Horizontal datum is North American Datum of 1983 (NAD 83). The bottom of the Marcellus Shale is the Cherry Valley Limestone Member of the Marcellus Shale (Rickard, 1975). NGVD 29, North American Vertical Datum of 1929; NA, not applicable]

Well name Latitude Longitude

Hole 

depth, 

in feet

Depth to 

Marcellus 

Shale

top, in feet

Depth to

Marcellus 

Shale

bottom, in 

feet

Marcellus

thickness,

in feet

Land surface

altitude, in 

feet above

NGVD 29

Marcellus 

Shale

top altitude, 

in

feet above

NGVD 29

Marcellus 

Shale

bottom

altitude, in 

feet above

NGVD 29

Lanzilotta 1 42.27354 -74.62734 9,075 3,560 4,305 745 1,835 -1,725 -2,470

Fowler Finch 1 42.31691 -75.23368 7,973 3,376 3,973 597 1,658 -1,718 -2,313

Campbell HA 42.18284 -74.92141 10,992 4,393 5,055 662 1,776 -2,617 -3,279

Hirsch K1 42.37398 -75.04223 5,327 3,240 3,884 644 1,990 -1,250 -1,894

MacDonald 42.33135 -74.87257 750 NA NA NA 1,570 NA NA

Hazlett Merrit 1 42.34249 -75.0814 4,570 2,920 3,575 655 1,457 -1,463 -2,118

Weickert F1 42.29766 -74.62458 6,740 3,512 4,250 738 1,999 -1,513 -2,251

Holdridge Charles 1 42.18614 -74.68299 6,681 4,151 4,905 754 1,704 -2,447 -3,201

Leslie Caroline E1 42.39048 -75.04415 7,952 2,625 3,260 635 1,485 -1,140 -1,775

Grant 6 42.39777 -75.05277 5,600 3,348 3,375 1

27 1,595 -1,753 -1,780

Grant C1a 42.39906 -75.05232 5,580 3,393 3,421 1

28 1,635 -1,758 -1,786

1

Thickness of the Union Springs black shale unit overlying the Onondaga Limestone.
18 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

only small tributaries enter, the floor of the West Branch Delaware River valley narrows to about 1,000 feet, and several 

wells document a range in aquifer thickness from 42 (well 

D–861) to 72 ft (well D–984).

Communities within this reach that obtain municipal 

water from wells that are screened in the valley-fill aquifer 

include Delhi and Hobart. Two supply wells in Delhi (D–256 

and D–286) are 50 ft deep, are screened in ice-contact sand 

and gravel, and yield 500 gal/min. Hobart has a 130-ft-deep 

well screened in ice-contact sand and gravel that yields 

100 gal/min.

Although most of the valley in the Stamford-Delhi reach 

of the river is filled with ice-contact sand and gravel and 

outwash, limited amounts of fine-grained lacustrine sediment, 

deposited in short-lived proglacial lakes, exist within the valley fill. For example, the log of well D–1442 at East Delhi, 

near the confluence of Elk Creek, shows 40 ft of alluvium 

and outwash, overlying a 60-ft section of silt, which in turn 

overlies at least 13 ft of confined ice-contact sand and gravel. 

Depth to bedrock in this area is approximately 140 ft. The log 

of nearby well D–2208 similarly shows 20 ft of alluvium and 

outwash, overlying 117 ft of silt and clay, which in turn overlies 5 ft of ice-contact sand and gravel atop bedrock. This well 

produces 45 gal/min from this thin confined aquifer.

Middle West Branch Delaware River

The middle West Branch Delaware River, the 16-mi reach 

from Delhi southwest to Walton (pl. 1), is also characterized 

by large kame terraces and kame moraines along both valley 

walls, with narrow valley-train outwash and alluvium in the 

center. As in the upper reach, the valley fill consists mostly 

of ice-contact sand and gravel that overlies a discontinuous 

basal till, all of which is overlain by valley-train outwash. The 

valley width ranges from about 3,000 ft at the confluence of 

the Little Delaware River just south of Delhi to about 4,500 

ft at De Lancey at the confluence of Bagley Brook to almost 

5,200 ft at Walton where West Brook and East Brook converge 

with the West Branch Delaware River. Some of the thickest 

outwash deposits in the West Branch Delaware River valley 

are located in these areas where tributary valleys provided 

pathways for sediment-laden glacial meltwater to contribute large volumes of outwash. In contrast, the valley width 

decreases to less than 1,000 ft just east of Walton where a 

large deposit of colluvium at the base of the south valley wall 

has buried the main bedrock channel and moved the course of 

the river northward. This mass of colluvium is identified in the 

log of well D–174, which penetrates 170 ft of till (interpreted 

as remobilized till and colluvium) and is completed in a thin, 

confined sand and gravel layer. The thickness of the valleyfill aquifer ranges from about 70 ft just south of Delhi (wells 

D–420 and D–421) to between 90 ft (well D–88) and 110 ft 

(well D–1604) near De Lancey to more than 140 ft (wells 

D–1393 and D–506) near the hamlet of Hawleys, N.Y. The 

6-mi valley reach from Hawleys west to Walton is flanked 

with large kame terraces on both valley walls, and the aquifer 

thickness ranges from 80 to 90 ft (wells D–173 and D–848) 

and composes almost entirely ice-contact sand and gravel. The 

aquifer thins to less than 20 ft where the valley width narrows to less than 1,000 ft about 1 mi east of Walton because 

of a large mass of colluvium that has diverted the course of 

the river northward and filled the bedrock thalweg with more 

than 170 ft of material (well D–174). Well yields from the 

valley-fill aquifer range up to 500 gal/min for two 12-in.-

diameter supply wells (D–256 and D–286) for Delhi that are 

screened in ice-contact sand and gravel. Other municipalities that rely on groundwater from the valley-fill aquifer are 

Hamden (well D–254) and Walton (wells D–253 and D–493). 

Numerous commercial dairy-processing facilities in the valley 

also require large well yields, as exemplified by a 65-ft-deep, 

510-gal/min supply well (D–261) at Walton.

Just south of Delhi, the Little Delaware River enters the 

main West Branch Delaware River valley. Limited well data 

in the Little Delaware River valley indicate that the valley fill 

consists mostly of till and isolated ice-contact deposits with 

an overlying veneer of alluvium, and ranges in thickness from 

80 (well D–1914) to 27 ft (well D–754). One of the thickest 

till deposits in the entire West Branch Delaware River Basin, 

however, occurs in the headwaters of the Little Delaware 

River at Tunis Lake where two wells penetrate 184 ft (well 

D–423) and 234 ft (well D–2171) of boulder till in what 

appears to be a former glacial meltwater channel (or col) that 

breaches the divide between the West Branch Delaware River 

Basin and the East Branch Delaware River Basin to the south.

Lower West Branch Delaware River

The lower West Branch Delaware River, the 23-mi reach 

from Walton to Deposit (20 mi to the Cannonsville Reservoir 

Dam), is the most sinuous of the three reaches and is mostly 

occupied by the Cannonsville Reservoir. Upstream from the 

reservoir, the valley fill is characterized by broad outwash 

terraces overlain by postglacial alluvium. Small kame terraces are emplaced along the valley sides, especially along the 

inside bends in the river. At Walton, a large remnant outwash 

terrace occupies the valley between the river and the south 

valley wall. South of Pinesville, a large kame terrace similarly 

occupies the sharp inside bend in the river. The Cannonsville 

Reservoir has covered any glacial deposits that were formerly 

exposed in this reach. The valley width varies from about 

1 mi at Walton to about 3,000 ft at Beerston to about 1,000 ft 

in the upper reaches of the reservoir. Well data in this reach 

are sparse, but what data there are indicate that the valleyfill aquifer here varies in thickness from about 70 ft (wells 

D–261 and D–262) at Walton to more than 60 ft at Pinesville (well D–1150) to a 30-ft-thick aquifer confined beneath 

90 ft of lacustrine clay at Beerston (well D–1337). Logs of 

wells that are located beneath the Cannonsville Reservoir 

show that the thickness of the valley fill there (as measured 

from preconstruction land surface altitudes) ranges from 80 

ft (well D–105) at the reservoir’s eastern end to 125 ft (well 

D–353) at the former location of the hamlet of Cannonsville 
Hydrogeology 19

approximately 3.5 mi upstream from the dam. The appearance 

of lacustrine clay, silt, and fine sand in some well logs (well 

D–403) in the lower section of the West Branch Delaware 

River valley gives evidence of previous proglacial lakes. The 

majority of well logs under the Cannonsville Reservoir, however, indicate that the valley fill there is predominantly sand 

and gravel overlying till (wells D–111 and D–399) or in some 

locations all till (well D–353). Downstream from the Cannonsville Reservoir, well logs in the valley between the dam 

and nearby Deposit indicate depths to bedrock ranging from 

115 to 150 ft (wells D–284 and D–1570). Logs of wells in this 

area also indicate thick sequences of fine-grained lacustrine 

sediments overlain by outwash and underlain by ice-contact 

sand and gravel. For example, the log of well D–1570 shows 

45 ft of outwash sand and gravel overlying 70 ft of fine sand, 

which grades down into 15 ft of clay, all of which is underlain by 20-ft of basal gravel. Other wells in the area show a 

similar sequence of outwash overlying lacustrine sediments, 

all underlain by a thin basal sand and gravel aquifer (wells 

D–1133, D–1613, D–1797, and D–1832). In some localities, 

the confined aquifer may be absent.

As in the middle and upper reaches, the valley-fill aquifer 

in the lower reach of the West Branch Delaware River is very 

transmissive and is able to support high-yielding municipal 

supply wells. For example, well D–284 is a 120-ft-deep supply 

well for Deposit that is screened in the thin, confined basal 

sand and gravel aquifer and produces 500 gal/min. Three other 

supply wells, located in adjacent Broome County (BM–452, 

BM–453, and BM–454), for Deposit similarly have yields 

ranging from 200 to 500 gal/min.

To summarize, along the main West Branch Delaware 

River valley, a well drilled anywhere in areas mapped as kame 

sand and gravel, outwash, or outwash and alluvium on plate 1 

(except close to the till-mantled valley walls) is likely to penetrate at least 10 and perhaps 100 ft or more of permeable sand 

and gravel that could yield 100 gal/min or more to a properly 

constructed well. In tributary valleys, by contrast, even in 

areas where kame sand and gravel or alluvium are mapped 

at land surface, wells are likely to penetrate mostly till above 

bedrock; highly productive aquifers are uncommon. Maximum long-term aquifer yield to a local array of gravel wells 

will depend on the availability of infiltration from low flows 

of the Delaware River and on the volume of water stored in 

the aquifer, which can be estimated from streamflow records, 

approximate calculations such as those presented by MacNish 

and Randall (1982), or from detailed site investigations.

Precipitation, Runoff, and Evapotranspiration

Data from three precipitation stations, one each at 

Deposit, Walton, and Delhi, were obtained for each year from 

2001 to 2010 from the Northeast Regional Climate Center 

database at Cornell University (http://climod.nrcc.cornell.

edu/). The mean annual precipitation for these three stations 

for the 10-year period was as follows: Deposit, 47.05 in.; 

Walton, 50.36 in.; and Delhi, 51.90 in. Similarly, the 30-year 

mean precipitation (1971–2000) for each of these stations was 

as follows: Deposit, 43.4 in.; Walton, 46.69 in.; and Delhi, 

43.20 in. The most recent 10-year precipitation means show 

an increase in average annual precipitation as one moves 

upvalley (east) from Deposit to Delhi, while the 30-year mean 

values show the Walton station as having a higher mean than 

the other two. The 1971–2000 mean values are similar to 

slightly higher than values interpolated from the areal distribution of mean annual precipitation over the West Branch 

Delaware River Basin for 1951–80 (Randall, 1996). Therefore, 

the contours of mean annual runoff and evapotranspiration 

depicted in Randall (1996) can still be considered reasonably 

valid through 2000. The distribution of mean annual precipitation and runoff for 1951–80 within the West Branch Delaware 

River Basin is shown in figure 7, which shows that the longterm mean annual precipitation ranges from about 44 to 46 in. 

in the high terrain near the divides that bound the basin on the 

northwest and southeast, but is close to 43 in. near the axis 

of the basin (Randall, 1996). Long-term mean annual runoff 

within the basin ranges from 22 inches per year (in/yr) at the 

western end of the basin (near Deposit) to 26 in/yr along the 

southern uplands and in the eastern headwaters (fig. 7). Mean 

evapotranspiration is approximately 19 in/yr throughout the 

West Branch Delaware River Basin (Randall, 1996).

Sources of Stream Base Flow

Previous studies of the Beaver Kill Basin (Reynolds, 

2000) and the Pepacton Reservoir Basin (Reynolds, 2004) 

have shown that the streams within these basins exhibit some 

of the highest base flows in the Catskill Mountain region. 

A high base flow (that is, dry weather flow) for a stream 

generally indicates that the basin contains a large amount of 

groundwater in storage, generally in saturated stratified drift 

within the valley and (or) in fractured bedrock aquifers. A 

common statistic that indicates the magnitude of groundwater 

storage within a given basin is the duration of base-flow recession. Coates (1971) developed base-flow recession curves for 

13 stream subbasins in the Delaware River Basin and for 12 

stream subbasins in the Susquehanna River Basin and from 

these curves, calculated two indices to measure the duration 

of base-flow recession for each stream: (1) the number of days 

required for flow to decline from its mean annual value to 10 

percent of that value and (2) the number of days required for 

flow to decline from 1 cubic foot per second per square mile 

[(ft3

/s)/mi2] to 0.1 (ft3/s)/mi2. Hydrogeologic characteristics for 

the 13 Catskill Mountain stream subbasins are listed in table 2.

Three stream subbasins gaged by the USGS within 

the West Branch Delaware River Basin—the West Branch 

Delaware River near Delhi (01421900), Little Delaware River 

near Delhi (01422500), and Trout Creek near Trout Creek, 

N.Y. (0142400103)—were evaluated and are shown in bold 

typeface in table 2. The two indices of base-flow recession 

show that all three of these streams have some of the longest 
20 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

base-flow recessions in the Catskill Mountains—33, 28, and 

29.7 days, respectively—to decline from 1 (ft3

/s)/mi2 to 0.1 

(ft3

/s)/mi2 (table 2). Only four other subbasins—Beaver Kill 

at Craigie Claire, Beaver Kill at Cooks Falls, Mill Brook, and 

East Branch Delaware River—display substantially longer 

base-flow recessions with 37.6, 36.7, 36.1, and 34.7 days, 

respectively. A long base-flow recession indicates that groundwater is supplying the base flow during long precipitation-free 

periods. Another commonly used measure of base flow and 

flow duration is Q90, which is the discharge that is exceeded 90 

percent of the time. Values of Q90 for the 13 Catskill Mountain 

subbasins are shown in table 2 in two formats: first as a percentage of mean annual discharge, then as normalized to basin 

size and expressed as cubic feet per second per square mile. 

The Q90 for the West Branch Delaware River is 8.5 percent 

of the mean annual discharge, for the Little Delaware River 

Basin is 7.8 percent of mean annual discharge, and for Trout 

Creek is 11 percent of mean annual discharge. Similarly, the 

Q90 normalized to basin size is equivalent to 0.145 (ft3

/s)/mi2

in the West Branch Delaware River Basin, 0.141 (ft3

/s)/mi2

in the Little Delaware River Basin, and 0.201 (ft3

/mi2) in the 

Trout Creek Basin. These values of Q90, in percent of mean 

annual discharge and in cubic feet per second per square mile, 

are similar to or greater than values for the 12 streams evaluated in the Susquehanna River Basin (Coates, 1971), and are 

similar to 6 other streams in the Delaware River Basin (table 

2). These values are, however, substantially less than the Q90

values for four streams in the eastern part of the East Branch 

Delaware River Basin, all of which drain the highest part of 

the Catskill Mountains, where mean precipitation and runoff 

EXPLANATION

USGS streamgage and station number

Mean annual precipitation 1951−80, in inches

Mean annual runoff 1951−80, in inches

West Branch Delaware River basin boundary

Streamgage basin drainage divide

Streams

Cannonsville Reservoir

42

24

Base from U.S. Geological Survey digital data, 

Universal Transverse Mercator projection, zone 18

North American Datum 1983

01424997

01425000

01423900

01423000

01422747

0142400103

01424108

01422389

01422500

01422738

01421900

01421618

01421610

01421614

26

24

24

22

42

46

44

75°15' 75° 74°45'

42°30'

42°15' 44

42

0 7.5 15 MILES Climate data from Randall (1996)

0 7.5 15 KILOMETERS

LOCATION MAP

NEW YORK

Figure 7. The distribution of mean annual precipitation and runoff for 1951–80 within the West Branch Delaware River Basin.
Hydrogeology 21

Table 2. Hydrogeologic characteristics of 13 Catskill drainage basins within the Delaware River Basin in southeastern New York.[Data are from Coates (1971) and reproduced from Reynolds (2000). Locations are shown in figure 1. Streams within the West Branch Delaware River basin shown in bold typeface. ft, feet; (ft3/s)/mi2, cubic 

feet per second per square mile; in., inches; max., maximum; mi2, square miles; precip., precipitation; Q , flow at 90 percent duration] 90

Flow duration (Q )† Baseflow recession, in days 90 Area of Mean Basin Max. Mean annual Normalized to stratified Sandstone annual Mean annual Normalized to To 10 percent of Massiveness Basin area, in basin discharge, in decline from 1.0 drift, in index,a in precip., in discharge, in basin size, in mean annual indexb mi2 relief (ft3/s)/mi2 to 0.1, in percent of percent in. percent (ft3/s)/mi2 discharge (ft3/s)/mi2 basin

Terry Clove 14.1 1,290 44.0 1.88 10.0 .188 13.5 16.5 4.3 79 73

Mill Brook 25.0 2,420 48.8 2.27 12.0 .272 26.5 36.1 2.9 91 88

Coles Clove 28.0 1,460 44.0 2.03 10.0 .203 17.7 21.0 5.7 79 73

Tremper Kill 33.0 2,045 43.7 1.88 10.0 .188 13.2 25.2 5.5 88 79

Platte Kill 34.7 2,055 43.0 1.82 9.0 .164 17.7 18.5 4.5 78 71

Trout Creek 49.5 1,280 43.4 1.83 11.0 .201 22.5 29.7 7.6 78 68

Little Delaware River 49.8 1,965 42.7 1.81 7.8 .141 22.7 28.0 3.6 64 51

Willowemoc Creek near 63 1,960 52.0 2.42 16.0 .387 22.1 32.0 4.4 91 88

Livingston Manor*

Oquaga Creek 66 1,040 43.0 1.78 8.5 .151 17.5 22.9 5.2 84 72

Beaver Kill at Craigie 82 2,495 51.8 2.55 14.0 .357 30.3 37.6 5.0 98 96

Claire

West Branch Delaware 142 1,835 41.5 1.70 8.5 .145 27.5 33.0 12.2 64 53

River

East Branch Delaware River 163 2,595 44.0 1.89 10.0 .189 27.1 34.7 5.0 78 70

Beaver Kill at Cooks Falls* 241 2,727 50.1 2.34 16.0 .374 31.5 36.7 6.0 89 82

 Mean 76.5 1,930 45.5 2.01 11.0 .228 23.1 28.6 5.5 81 74

†Q90 is the stream discharge that is exceeded 90 percent of the time.aSandstone index is the average percentage of sandstone found within measured stratigraphic sections with each basin (Coates, 1971).bMassiveness index is the percentage of rock units in observable outcrops that exhibit joint-free exposures of greater than 1-ft in thickness (Coates, 1971).*Includes Willowemoc Creek drainage. Beaver Kill and Willowemoc Creek are treated as separate basins above their confluence at Roscoe, N.Y., and as a combined basin downstream from their confluence.
22 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

are much higher than in the West Branch Delaware River 

Basin (Randall, 1996). The difference in base flows between 

the West and East Branch Delaware River Basins, therefore, 

may be related to differences in the percentage of massive 

sandstone present in each basin and to the corresponding 

degree of jointing and fracturing of the sandstone (Base Flow 

in Relation to Geology section).

Base Flow in Relation to Geology

Stream base flows in the glaciated Northeastern United 

States that are well sustained and (or) that are relatively large 

in terms of volume per square mile of basin area have generally been ascribed to the discharge of groundwater stored in 

stratified-drift aquifers that occupy the valley bottoms or to 

partly saturated ice-contact deposits emplaced against valley 

walls (Coates, 1971; Randall and Johnson, 1988; Wandle and 

Randall, 1994; Randall, 2010). Coates (1971) delineated the 

percentage of land area occupied by stratified drift (valley fill) 

within each of the13 Catskill Mountain subbasins he studied 

and found that stratified drift composes 12.2 percent of the 

West Branch Delaware River Basin, 7.6 percent of the Trout 

Creek Basin, and 3.6 percent of the Little Delaware River 

Basin (table 2). The percent area of stratified drift for the West 

Branch Delaware River Basin is the highest of the 13 Catskill 

Mountain subbasins studied by Coates (1971), yet it does not 

display the highest base flow, as measured by both Q90 flow 

duration and the length of base flow recession. The other 

Catskill Mountain subbasins studied by Coates (1971) in the 

East Branch Delaware River Basin had lower percentages of 

stratified drift compared with those of the West Branch Delaware River Basin, but had higher, more sustained base flows 

(table 2). These findings indicate that most of the base flow in 

the East Branch Delaware River Basin must be coming from 

storage in aquifers other than that composed of stratified drift.

Bedrock as a Source of Base Flow

Groundwater discharge from bedrock is a major contributor to stream base flow in Catskill Mountain region streams, 

particularly in the West Branch Delaware River, East Branch 

Delaware River, and Beaver Kill subbasins (Coates, 1971; 

Reynolds, 2000; Reynolds, 2004). Bedrock in the Catskill 

Mountains consists of sandstone, shale, and siltstone, of which 

sandstone is the predominant rock type and the most permeable because of its extensive jointing. Coates (1971) developed 

two indices that describe the amount of sandstone present and 

the degree of jointing within the sandstone for each of the 13 

Catskill Mountain subbasins that he studied (table 2). The first, 

defined by Coates as the “sandstone index”, is the average 

percentage of sandstone present within measured stratigraphic 

sections within each subbasin. The second, defined by Coates 

as the “massiveness index”, is a measure of sandstone competency and fabric and is the percentage of rock thickness, as 

seen in outcrops, in which the spacing between bedding-plane 

fractures exceeds 1 ft. Coates (1971) observed that the joints 

in the sandstones of the Catskill Mountains are less numerous 

but larger and more continuous than those in the shale and 

siltstone bedrock of the Susquehanna River Basin to the west. 

He concluded that most of the sandstone within the 13 Catskill 

Mountain subbasins that he studied is massive and therefore 

would tend to have large, continuous joints that serve to easily 

transmit groundwater. The highest sandstone indices of the 13 

Catskill Mountain subbasins studied by Coates (1971) were in 

the Beaver Kill and Willowemoc Creek subbasins (98 percent 

for the Beaver Kill and 91 percent for Willowemoc Creek); 

these two subbasins also had the highest massiveness indices 

(96 percent for the Beaver Kill and 88 percent for Willowemoc 

Creek) (Reynolds, 2000, table 1).

Among the other East Branch Delaware River subbasins 

that were analyzed by Coates (1971), the Mill Brook Basin 

had the highest sandstone index (91 percent) and the highest 

massiveness index (88 percent); the Tremper Kill Basin had 

the next highest sandstone and massiveness indices of 88 and 

79 percent, respectively (table 2). The remaining four East 

Branch Delaware River subbasins had sandstone indices of 

78 to 79 percent and massiveness indices of 70 to 73 percent 

(Reynolds, 2000). The high percentage of sandstone in all 

eight of the East Branch Delaware River subbasins is consistent with the values of Q90 as a percent of mean annual 

discharge, which range from 9 to 12 percent of mean annual 

discharge (table 2), despite the small amounts of stratified drift 

within these subbasins—not more than 6 percent, and less 

than 5 percent in most of the subbasins (Reynolds, 2000, table 

1). In comparison, the sandstone indices for the three West 

Branch Delaware Basins—West Branch Delaware River, Little 

Delaware River, and Trout Creek—are 64, 64, and 78 percent, 

respectively, whereas the corresponding massiveness indexes 

are 53, 51, and 68, respectively. This finding indicates that 

there appears to be less sandstone bedrock within the West 

Branch Delaware River Basin compared with the East Branch 

Delaware River Basin to the south. Furthermore, the overall lower massiveness index for the sandstone in the West 

Branch Delaware River Basin indicates that the sandstone 

there appears to be less massive and therefore may have fewer 

continuous water-bearing joints than does the sandstone in the 

East Branch Delaware River Basin to the south. Coates (1971) 

has shown through statistical analysis that the sandstone 

index and the massiveness index show close correlation with 

the Q90. Each index was correlated with (1) Q90 divided by 

mean annual discharge and (2) Q90 divided by drainage area; 

the correlation coefficients (R2

) were 0.76 for the sandstone 

index and 0.79 for the massiveness index, relative to either 

base-flow term (Coates, 1971, table 6; Reynolds, 2000). This 

positive relation supports the theory that the sustained base 

flows in the West and East Branch Delaware River Basins may 

be wholly or partly derived from groundwater discharge from 

the jointed-sandstone aquifer, albeit to a greater degree in the 

East Branch Delaware River Basin. The same conclusion can 

be said for the adjacent Beaver Kill and Willowemoc Creek 

Basins to the south (Reynolds, 2000).
Summary 23

Thick Till Deposits as a Possible Source of Base 

Flow

The thick till that covers many upland areas in the West 

and East Branch Delaware River Basins could be considered 

as a potential source of sustained stream base flow, simply 

because the till covers most of the basin. However, recent 

studies in New York and New England have shown that the 

groundwater in thick till deposits does not contribute appreciably to the base flow of streams in glaciated basins. Randall 

and Johnson (1988) presented four low-flow equations, each 

one developed from a separate low-flow study in the glaciated 

Northeastern United States, to estimate the average minimum 

7-day low flow, known as the 7Q10. All four equations include 

independent variables that account for the area covered by 

stratified drift, the area covered by till, the mean runoff or the 

mean altitude, and the area occupied by wetlands (Randall and 

Johnson, 1988, table 1). In each of these studies, the regression 

coefficients for the area covered by stratified drift was from 9 

to 25 times larger than that for the area covered by till. Regression coefficients for stratified drift ranged from 0.46 to 2.16, 

whereas those for till ranged from 0.05 to 0.10. These small 

coefficients for till indicate that the till within a basin makes 

only a minor groundwater contribution to streamflow.

A study by Wandle and Randall (1994) on the effects of 

surficial geology, lakes, swamps, and annual water availability 

on the low flows of streams in central New England reached 

similar conclusions regarding the relative effects of till and 

stratified drift on base flow. The regression equations developed in that study to estimate 7Q10 for high- and low-relief 

areas of central New England indicated that groundwater 

discharge from coarse stratified drift was from 4 to 8 times 

greater than the groundwater discharge from till. Tills of New 

England generally have a much lower clay content and, thus, 

greater permeability than those of New York; this conclusion 

would imply that the relative amount of groundwater discharged to streams from tills in New York would be much less 

than in New England.

The results of these Randall and Johnson (1988) and 

Wandle and Randall (1994) (1) indicate that the thick upland 

deposits of till within the West and East Branch Delaware 

River Basins probably contribute little groundwater discharge 

to the base flow of streams and (2) provide additional evidence 

that the relatively high base flows of streams in the Catskill 

Mountain region are at least partly derived from groundwater 

discharge from the underlying fractured and jointed sandstone.

Summary

In 2009, the U.S. Geological Survey, in cooperation with 

the New York State Department of Environmental Conservation, began a study of the hydrogeology of the West Branch 

Delaware River Basin (Cannonsville Reservoir watershed). 

There has been recent interest by energy companies in 

developing the natural gas reserves that are trapped within 

the Marcellus Shale, which is part of the Hamilton Group 

of Middle Devonian age that underlies all the West Branch 

Delaware River Basin. Knowing the extent and thickness of 

stratified-drift (sand and gravel) aquifers within this basin can 

help State and Federal regulatory agencies to evaluate any 

potential effects to these aquifers that gas-well drilling might 

produce.

The West Branch Delaware River Basin (Cannonsville 

Reservoir watershed) drains about 455 mi2

 of the southwestern Catskill Mountains. The most widespread geologic unit 

within the basin is till and colluvium, which occurs as masses 

of ablation till in major stream valleys and as thick deposits of 

lodgment till and colluvium that partly fill upland basins. Till 

and colluvium cover approximately 89 percent of the basin, 

and stratified drift, which consists of alluvium, outwash, and 

ice-contact deposits, accounts for 8.9 percent. The Cannonsville Reservoir occupies about 1.9 percent of the basin area. 

Outwash and ice-contact (kame) deposits occupy the West 

Branch Delaware River valley for its entire 59-mi length from 

Deposit, New York, to the river’s headwaters near Stamford, 

N.Y. These deposits form a stratified-drift aquifer that ranges 

in thickness from 40 to 50 feet (ft) in the upper reach of the 

West Branch Delaware River valley (from Stamford to Delhi, 

N.Y.), from 70 to 140 ft in the middle reach of the valley (from 

Delhi to Walton, N.Y.), and from 60 to 70 ft thick in the lower 

reach of the valley from Walton to Deposit, N.Y. Well yields 

from the valley-fill aquifer commonly exceed 100 gallons per 

minute (gal/min) and reach up to 500 gal/min. Thick deposits 

of lodgment till, some more than 200 ft in thickness, partly fill 

upland tributary valleys and hollows. The valley train outwash 

that overlies ice-contact deposits thoughout the basin increases 

in thickness downvalley from a maximum of 40 ft at Delhi to 

50 ft at Walton and to 65 ft at Deposit. Localized deposits of 

fine-grained lacustrine sediments, up to 100 ft thick, within the 

valley fill just east of Delhi and southwest of Walton indicate 

the former locations of proglacial lakes.

The Catskill Mountain series rocks that underlie the West 

Branch Delaware River Basin are jointed by three distinct 

joint sets, two vertical joint sets that trend northwestward and 

northeastward, and a horizontal set that lies parallel to the 

bedding plane. These joint sets greatly increase the secondary permeability of the rock and thus increase the storage 

and movement of groundwater within the rock. Yields from 

bedrock wells completed in the sandstone and shale bedrock 

within the West Branch Delaware River Basin range from 0 

to 400 gal/min, with eight wells having yields in excess of 

100 gal/min, and one well having a yield of 400 gal/min. The 

median yield for 199 bedrock wells completed in Catskill 

Mountain series rocks in Delaware County is 15 gal/min.

Springs are still an important source of domestic water 

supply within the West Branch Delaware River Basin, as well 

as all of Delaware County, and several villages within the 

West Branch Delaware River Basin use springs as all or part 

of their municipal supply. The average yield of 178 springs 
24 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

in Delaware County is 8.5 gal/min, with a median yield of 

3 gal/min. The highest measured spring yield was 100 gal/min.

The gas-bearing Marcellus Shale underlies the entire 

West Branch Delaware River Basin, as well as the remainder of Delaware County. Data from 10 deep test holes that 

encircle the West Branch Delaware River Basin indicate that 

the Marcellus Shale ranges in thickness from 600 to 650 ft 

along the northern divide with the adjacent Susquehanna River 

Basin to about 750 ft thick along the southern divide with the 

East Branch Delaware River Basin. The depth to the top of the 

Marcellus Shale ranges from 2,600 to 2,900 ft in two upland 

tributaries to the adjacent Susquehanna River Basin to 3,240 ft 

along the northern divide of the West Branch Delaware River 

Basin, and ranges from 3,500 to 4,150 ft along the southern 

divide of the West Branch Delaware River Basin.

The long-term mean annual precipitation within the West 

Branch Delaware River Basin ranges from 42 inches per year 

(in/yr) at its western end near Deposit to 44 in/yr at the river’s 

headwaters near Stamford, although the average precipitation 

for the most recent 10-year period (2001–2010) ranged from 

47 to almost 52 in/yr. Long-term mean annual runoff within 

the West Branch Delaware River Basin ranges from 22 in/yr 

at the western end of the basin to 26 in/yr along the southern 

uplands and in the eastern headwaters. Long-term evapotranspiration is approximately 19 in/yr throughout the West Branch 

Delaware River Basin.

Two statistical indicators of base flow, the duration of 

base-flow recession in days and the discharge that is exceeded 

90 percent of the time (Q90), were tabulated and compared 

for 13 streams in the Catskill Mountain region. Three gaged 

streams within the West Branch Delaware River Basin 

displayed base-flow recessions that were longer than those 

for most streams in the Catskill Mountain region—ranging 

from 22.5 to 27. 5 days—but were substantially shorter than 

those for two streams in the Beaver Kill Basin to the south 

(36.7 and 37.6 days) and for two streams in the adjacent 

East Branch Delaware River Basin (34.7 and 36.1 days). 

Similarly, the Q90 for the three West Branch Delaware River 

Basin streams ranged from 7.8 to 11 percent of mean annual 

discharge, whereas streams in the East Branch Delaware 

River and Beaver Kill Basins displayed Q90 values ranging 

from 9 to 16 percent of mean annual discharge. Two indices 

(Coates, 1971) that describe the amount of sandstone present 

in measurable rock outcrops—the sandstone and massiveness 

indices—were substantially lower for the three subbasins in 

the West Branch Delaware River Basin than for subbasins 

in the adjacent East Branch Delaware River and Beaver Kill 

Basins to the south. These data support the theory that the sustained base flows in the West and East Branch Delaware River 

Basins, as well as the Beaver Kill Basin to the south, may be 

wholly or partly derived from groundwater discharge from the 

jointed-sandstone aquifer, albeit to a much lesser degree in the 

West Branch Delaware River Basin.

Selected References

Chadwick, G.H., 1936, History and value of the name 

“Catskill” in geology: New York State Museum Bulletin 

No. 307, 116 p.

Coates, D.R., 1966, Glaciated Appalachian plateau-till shadows on hills: Science, v.152, p. 1617–1619.

Coates, D.R., 1971, Hydrogeomorphology of Susquehanna 

and Delaware basins, in Morisawa, Marie, Quantitative 

geomorphology—Some aspects and applications—Proceedings of the second annual geomorphology symposia series, 

Binghamton, New York, October 15–16, 1971: Binghamton, N.Y., State University of New York at Binghamton, 

p. 273–306.

De Witt, Wallace, Jr., Roen, J.B., and Wallace, L.G., 1993, 

Stratigraphy of Devonian black shales and associated rocks 

in the Appalachian basin, in Roen, J.B., and Kepferle, R.C., 

eds., Petroleum geology of the Devonian and Mississippian black shale of eastern North America: U.S. Geological 

Survey Bulletin, 1909–B, p. B1–B57.

Fisher, D.W., Isachsen, Y.W., and Rickard, L.V., 1970, 

Geologic map of New York: New York Museum and 

Science Service Map and Chart Series No. 15, 5 sheets, 

1:250,000 scale.

Fluhr, T.W., 1953, Geology of New York City’s water supply 

system, a progress report: The Municipal Engineers Journal, 

v. 39, 4th quarter, p. 125–145.

Fluhr, T.W., and Terenzio, P.E., 1984, Engineering geology of 

the New York City water supply system: New York State 

Geological Survey Open-File Report 05.08.001, 184 p.

Gubitosa, Matthew, 1980, Glacial geology of the Hancock 

area, western Catskills, New York: State University of New 

York at Binghamton master’s thesis, 102 p.

Hely, A.G., and Olmsted, F.H., 1963, Some relations between 

streamflow characteristics and the environment in the Delaware River region: U.S. Geological Survey Professional 

Paper 417B, 25 p.

Heisig, P.M., 1999, Water resources of the Batavia Kill basin 

at Windham, Greene County, New York: U.S. Geological 

Survey Water Resources Investigations Report 98–4036, 

96 p.

Heisig, P.M., 2004, Hydrogeology and water quality of the 

Pepacton Reservoir watershed in Southeastern New York, 

part 4 of Quantity and quality of ground-water and tributary 

contributions to stream base flow in selected main-valley 

reaches: U.S. Geological Survey Scientific Investigations 

Report 2004–5018, 21 p.
Selected References 25

Kipp, J.A., Lawrence, F.W., and Dinger, J.S., 1983, A conceptual model of ground-water flow in the Eastern Kentucky 

Coal Field, in Graves, D.H., ed., Symposium on surface 

mining, hydrology, sedimentology, and reclamation, 

Lexington, Kentucky, November 27–December 2, 1983: 

Lexington, University of Kentucky, p. 543–548.

Kirkland, J.T., 1973, Glacial geology of the western Catskills: 

State University of New York at Binghamton, Doctoral dissertation, 104 p.

Kirkland, J.T., 1979, Deglaciation events in the western 

Catskill Mountains, New York: Geological Society of 

America Bulletin, v.90, p. 521–524.

Koteff, Carl, 1974, The morphologic sequence concept and 

deglaciation of southern New England, in Coates, D.R., ed., 

Glacial geomorphology: Binghamton, State University of 

New York Publications in Geomorphology, p. 121–144.

Lash, G.G., and Englander, Terry, 2009, The Middle Devonian 

Marcellus Shale—A record of eustasy and basin dynamics 

(abstract and poster), in American Association of Petroleum 

Geologists Annual Meeting, Denver, Colo., June 7–10, 

2009: American Association of Petroleum Geologists, 

accessed 1/20/2011, at http://www.searchanddiscovery.net/

documents/2009/090805lash/ndx_lash.pdf.

MacNish, R.D., and Randall, A.D., 1982, Stratified-drift aquifers in the Susquehanna River basin, New York: New York 

State Department of Environmental Conservation Bulletin 

75, 68 p.

Mather, W.W., 1840, Fourth annual report of the geologist 

of the first geological district of the state of New York, 

in Fourth annual report: New York Geological Survey, 

p. 212–258.

Milici, R.C., and Swezey, C.S., 2006, Assessment of Appalachian basin oil and gas resources—Devonian shale—Middle 

and Upper Paleozoic total petroleum system: U.S. Geological Survey Open File Report 2006–1237, 70 p.

Natural Resources Conservation Service, 1999, Digital soils 

map of Delaware County, New York: U.S. Department of 

Agriculture, accessed at http://soildatamart.nrcs.usda.gov

on 11/2008.

Newland, D.H., and Hartnagle, C.A., 1932, Review of natural 

gas and petroleum developments in New York State: New 

York State Museum Bulletin 295, p. 101–184.

New York State Department of Health, 1982, New York State 

atlas of community water system sources: New York State 

Department of Health, 79 p.

Ozvath, D.L., 1985, Glacial geomorphology and late Wisconsinan deglaciation of the western Catskill Mountains, New 

York: State University of New York at Binghamton doctoral 

dissertation, 181 p.

Ozvath, D.L., and Coates, D.R., 1986, Woodfordian stratigraphy in the western Catskill mountains, in Cadwell, D.H., 

The Wisconsinan stage of the first geologic district, eastern 

New York: New York State Museum Bulletin No. 455, 

p. 109–120.

Parker, G.G., Hely, A.G., Keighton, W.B., Olmsted, F.H., and 

others, 1964, Water resources of the Delaware River basin: 

U.S. Geological Survey Professional Paper 381, 200 p.

Parker, J.M., III, 1942, Regional systematic jointing in 

slightly deformed sedimentary rocks: Geological Society of 

America Bulletin v. 53, p. 381–408.

Randall, A.D., 1996, Mean annual runoff, precipitation, and 

evapotranspiration in the glaciated northeastern United 

States, 1951–80: U.S. Geological Survey Open-File Report 

96–395, 2 sheets, scale 1:1,000,000.

Randall, A.D., 2001, Hydrogeologic framework of stratifieddrift aquifers in the glaciated northeastern United States: 

U.S. Geological Survey Professional Paper 1415–B, 179 p.

Randall, A.D., 2010, Low flow of streams in the Susquehanna 

River basin of New York: U.S. Geological Survey Scientific 

Investigations Report 2010–5063, 57 p.

Randall, A.D., and Johnson, A.I., 1988, The northeast glacial 

aquifers RASA project—An overview of results through 

1987, in Randall, A.D., and Johnson, A.I., eds., Regional 

aquifer systems of the United States-the northeast glacial 

aquifers: American Water Resources Association Monograph Series no. 11, p. 1–15.

Reynolds, R.J., 2004, Hydrogeology and water quality of the 

Pepacton Reservoir watershed in southeastern New York—

Part 2. Hydrogeology, stream base flow, and groundwater 

recharge: U.S. Geological Survey Scientific Investigations 

Report 2004–5134, 31p.

Reynolds, R.J., 2000, Hydrogeology of the Beaver Kill basin 

in Sullivan, Delaware, and Ulster counties, New York: U.S. 

Geological Survey Water Resources Investigations Report 

00–4034, 23 p.

Rich, J.L., 1935, Glacial geology of the Catskills: New York 

State Museum Bulletin no. 299, 180 p.

Rickard, L.V., 1975, Correlation of the Silurian and Devonian 

rocks in New York State: New York State Museum and Science Service Map and Chart Series no. 24, 16 p.

Soder, D.J., and Kappel, W.M., 2009, Water resources and 

natural gas production from the Marcellus Shale: U.S. Geological Survey Fact Sheet 2009–3032, 6 p.

Soren, Julian, 1963, The ground-water resources of Delaware 

County, New York: New York State Department of Conservation Bulletin GW–50, 59 p.
26 Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York

Ver Straeten, C.A., Griffing, D.H., and Brett, C.E., 1994, The 

lower part of the Middle Devonian Marcellus “Shale”, 

central to western New York State; stratigraphy and depositional history, in Brett, C.E., and Scatterday, James, eds., 

Field trip guidebook: New York State Geological Association Guidebook, 66th Annual Meeting, Rochester, N.Y., 

p. 271–321.

Wandle, S.W., and Randall, A.D., 1994, Effects of surficial 

geology, lakes and swamps, and annual water availability 

on low flows of streams in central New England, and their 

use in low-flow estimation: U.S. Geological Survey Water 

Resources Investigations Report 93–4092, 57 p.

Williams. J. H., 2010, Evaluation of well logs for determining the presence of freshwater, saltwater, and gas above the 

Marcellus Shale in Chemung, Tioga, and Broome Counties, 

New York: U.S. Geological Survey Scientific Investigations 

Report 2010–5224, 27 p.

Woodward, H.P., 1957, Structural elements of the northeastern 

Appalachians: American Association of Petroleum Geologists Bulletin, v. 41, no. 7, p. 1429–1440.

Wyrick, G.G., and Borchers, J.W., 1981, Hydrologic effects 

of stress-relief fracturing in an Appalachian valley: U.S. 

Geological Survey Water Supply Paper 2177, 51 p.
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

New York Water Science Center

425 Jordan Road

Troy, NY 12180-8349

dc_ny@usgs.gov

or visit our Web site at

http://ny.water.usgs.gov
Reynolds—Hydrogeology of the West Branch Delaware River Basin, Delaware County, New York—Scientific Investigations Report 2013–5025