U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5015

Prepared in cooperation with the New York City Department of Environmental Protection

Preliminary Analysis of the Hydrologic Effects of Temporary 

Shutdowns of the Rondout-West Branch Water Tunnel on the 

Groundwater-Flow System in Wawarsing, New York
A

B

C

D

E

Cover.A, Basement pumpage discharging to a flooded street in Wawarsing, New York; B, U.S. 

Geological Survey scientists measuring groundwater levels in Wawarsing, New York; C, Basement 

flooding in Wawarsing, New York; D, U.S. Geological Survey observation well drilling in Wawarsing, 

New York; and E, Rondout Reservoir, located in the Towns of Wawarsing and Neversink, New 

York. (Background photograph of Rondout Reservoir courtesy of New York City Department of 

Environmental Protection.)
Preliminary Analysis of the Hydrologic 

Effects of Temporary Shutdowns of the 

Rondout-West Branch Water Tunnel on the 

Groundwater-Flow System in Wawarsing, 

New York

By Frederick Stumm, Anthony Chu, Michael D. Como, and Michael L. Noll

Prepared in cooperation with the 

New York City Department of Environmental Protection

Scientific Investigations Report 2012–5015

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Stumm, Frederick, Chu, Anthony, Como, M.D., and Noll, M.L., 2012, Preliminary analysis of the hydrologic effects of 

temporary shutdowns of the Rondout-West Branch Water Tunnel on the groundwater-flow system in Wawarsing, 

New York: U.S. Geological Survey Scientific Investigations Report 2012–5015, 48 p., at http://pubs.usgs.gov/

sir/2012/5015/.
iii

Contents

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

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

Objectives and Approach ....................................................................................................................4

Purpose and Scope ..............................................................................................................................4

Previous Studies ...................................................................................................................................4

Rondout-West Branch Tunnel ............................................................................................................4

Precipitation...........................................................................................................................................5

Hydrogeology..................................................................................................................................................5

Unconsolidated Deposits ..................................................................................................................12

Bedrock ................................................................................................................................................12

Catskill Aqueduct Construction Observations ......................................................................13

Rondout West–Branch Water Tunnel Construction Observations ....................................13

Hydrology ......................................................................................................................................................13

Groundwater-Flow System ................................................................................................................17

Long-Term Water-Level Monitoring .................................................................................................17

Potentiometric Surface in the Bedrock Aquifer ...................................................................20

Water Table in the Unconsolidated Aquifer ..........................................................................26

Hydrologic Effects of Temporary Shutdowns ..........................................................................................26

Tunnel-Leakage Influences on the Bedrock Aquifers ..................................................................26

Tunnel Leakage to the Unconsolidated Aquifers ..........................................................................33

Groundwater Temperature ................................................................................................................39

Summary........................................................................................................................................................46

Acknowledgments.......................................................................................................................................47

References Cited..........................................................................................................................................47

Figures

 1. Map showing location of Wawarsing study area including Summitville, 

Port Jervis Trough (Kingston to Port Jervis), the four reservoirs (Cannonsville, 

Pepacton, Neversink, and Rondout), the Delaware Aqueduct, and the Kensico 

Reservoir in New York ..................................................................... 2

 2. Map showing locations of bedrock and unconsolidated-aquifer wells, 

production wells, and selected surface-water sites within the study area, 

Town of Wawarsing, Ulster County, New York .......................................... 6

 3A. Map showing locations of observation wells, production wells, and surfacewater sites; Roundout–West Branch Tunnel geology; and water-inflow rates 

documented during tunnel construction within the study area, Town of 

Wawarsing, Ulster County, New York ................................................... 8

 3B. Cross section of geology observed during New York City Board of Water 

Supply test borings and Rondout West–Branch Tunnel construction from 

A to A’ within the study area, Town of Wawarsing, Ulster County, New York ...... 10

 4. Graph showing annual precipitation as recorded by the National Weather 

Service at Central Park, New York County, New York during 1869–2010 ............ 12
iv

5. Map showing topography and locations of bedrock and unconsolidated aquifer

observation wells, production wells, and selected surface-water sites within the

study area, Town of Wawarsing, Ulster County, New York ........................... 14

6. Graphs showing water-level and precipitation data for three unconsolidatedaquifer wells, two bedrock wells, and a surface-water site within the study 

area, Town of Wawarsing, Ulster County, New York: A, Unconsolidated-aquifer 

well U-1626, October 21, 2008–November 16, 2010; B, bedrock production well 

U-1629, October 22, 2008–November 16, 2010; C, surface-water site at U.S 

Geological Survey lake gage 01366807, November 20, 2008–November 16, 2010; 

D, unconsolidated-aquifer well U-1627, October 21, 2008–December 1, 2010; 

E, unconsolidated-aquifer well U-1642, September 14, 2008–June 22, 2010; and 

F, bedrock well U-1628, February 24, 2009–December 1, 2010 ........................ 18

7. Hydrogeologic section B to B’ showing difference in water levels between 

the unconsolidated and bedrock aquifers, Town of Wawarsing, Ulster County, 

New York .................................................................................... 21

8. Map showing elevation of the potentiometric surface in the bedrock aquifer 

within the study area, Town of Wawarsing, Ulster County, New York, March and 

April 2010 .................................................................................... 22

9. Map showing elevation of the potentiometric surface in the bedrock 

aquifer within the study area, Town of Wawarsing, Ulster County, New York, 

November 2010 .............................................................................. 24

10. Map showing elevation of the water table in the unconsolidated aquifer 

within the study area, Town of Wawarsing, Ulster County, New York, March and 

April 2010 .................................................................................... 28

11. Map showing elevation of the water table in the unconsolidated aquifer 

within the study area, Town of Wawarsing, Ulster County, New York, 

November 2010 .............................................................................. 30

12. Graphs showing the potentiometric-surface elevation in bedrock wells, the 

water level in the Rondout-West Branch Tunnel, and precipitation within the study 

area, Town of Wawarsing, Ulster County, New York: A, well U-1628, October 25,

2009–February 06, 2010; B, well U-1625, October 25, 2009–February 06, 2010; and 

C, well U-1653, November 10, 2009–February 06, 2010 ................................. 32

13. Map showing maximum water-level response to influence of tunnel leakage on 

the bedrock aquifer within the study area, Town of Wawarsing, Ulster County, 

New York, 2009-10 ........................................................................... 34

14. Map showing tunnel-leakage influence delay time on water levels in bedrock

wells within the study area, Town of Wawarsing, Ulster County, New York, 

2009-2010 .................................................................................... 36

15. Graphs showing the water-table elevation in unconsolidated aquifer wells, 

tunnel water level, and precipitation data within the study area, Town of 

Wawarsing, Ulster County, New York: A, well U-1627, October 25, 2009–

February 06, 2010; B, well U-1637, January 14, 2010–February 06, 2010; and 

C, well U-1641, October 25, 2009–February 06, 2010 .................................... 38

16. Map showing maximum water-level response to influence of tunnel leakage 

on the unconsolidated aquifer within the study area, Town of Wawarsing, 

Ulster County, New York .................................................................. 40

17. Map showing tunnel-leakage influence delay time on water levels in

unconsolidated-aquifer wells and surface-water sites within the study area, Town

of Wawarsing, Ulster County, New York, 2009–10 ....................................... 42

18. Map showing groundwater temperature in bedrock wells within the study area,

Town of Wawarsing, Ulster County, New York, August 2010 ........................... 44
v

Tables

1. Site information for groundwater wells and selected surface-water sites within the 

study area, Town of Wawarsing, Ulster County, New York ........................... 16

Conversion Factors, Datum, and Abbreviations

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

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

Specific capacity

gallon per minute per foot [(gal/min)/ft)] 0.2070 liter per second per meter [(L/s)/m]

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

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) 

except in figure 5, where it is referenced to the North American Datum of 1927 (NAD 27).

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

*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

List of Acronyms and Abbreviations

BLS below land surface

E. coli Escherichia coli 

GPS Global Positioning System

NOAA National Oceanic and Atmospheric Administration

NWS National Weather Service

NYCBWS New York City Board of Water Supply

NYCDEP New York City Department of Environmental Protection

NYSDEC New York State Department of Environmental Conservation

RWB Rondout–West Branch

USGS U.S. Geological Survey
Preliminary Analysis of the Hydrologic Effects of 

Temporary Shutdowns of the Rondout–West Branch 

Water Tunnel on the Groundwater-Flow System in 

Wawarsing, New York

By Frederick Stumm, Anthony Chu, Michael D. Como, and Michael L. Noll

Abstract

Flooding of streets and residential basements, and 

bacterial contamination of private-supply wells with 

Escherichia coli (E. coli) are recurring problems in the 

Rondout Valley near the Town of Wawarsing, Ulster County, 

New York. Leakage from the Rondout-West Branch (RWB) 

Water Tunnel and above-normal precipitation have been 

suspected of causing elevated groundwater levels and 

basement flooding. The hydrology of a 12-square-mile 

study area within the Town of Wawarsing was studied 

during 2008–10. A network of 41 wells (23 unconsolidatedaquifer and 18 bedrock wells) and 2 surface-water sites 

was used to monitor the hydrologic effects of four RWB 

Water Tunnel shutdowns. The study area is underlain by 

a sequence of northeast-trending sedimentary rocks that 

include limestone, shale, and sandstone. The bedrock contains 

dissolution features, fractures, and faults. Inflows that ranged 

from less than 1 to more than 9,000 gallons per minute from 

the fractured bedrock were documented during construction 

of the 13.5-foot-diameter RWB Water Tunnel through the 

sedimentary-rock sequence 710 feet (ft) beneath the studyarea valley. Glacial sediments infill the valley above the 

bedrock sequence and consist of clay, silt, sand, and gravel. 

The groundwater-flow system in the valley consists of both 

fractured-rock and unconsolidated aquifers. Water levels in 

both the bedrock and unconsolidated aquifers respond to 

variations in seasonal precipitation. During the past 9 years 

(2002–10), annual precipitation at Central Park, N.Y., has 

exceeded the 141-year mean.

Potentiometric-surface maps indicate that groundwater in 

the bedrock flows from the surrounding hills on the east and 

west sides of the valley toward the center of the valley, and 

ultimately toward the northeast. On average, water levels in 

the bedrock aquifer had seasonal differences of 5.3 ft. Analysis 

of hydrographs of bedrock wells indicates that many of these 

wells are affected by the RWB Tunnel leakage. Tunnelleakage influences (water-level and temperature changes) in 

the bedrock aquifer were measured at distances up to 7,000 ft 

from the RWB Tunnel. Water levels in the bedrock changed 

as much as 12 ft within 0.5 hour during tunnel shutdowns. 

Nine of the 10 wells that responded to the shutdowns showed 

a water-level response of 5 ft or greater. Changes in water 

levels ranged from 1.5 to 12 ft, with tunnel-leakage influence 

delay times ranging from 0.5 to 60 hours. Many of the longest 

tunnel-influence delay times and smallest water-level changes 

were in wells located closest to the tunnel in shale. Tunnelinfluence response of the bedrock aquifer is consistent with 

its preliminary characterization as an anisotropic aquifer with 

greater transmissivity along bedding strike than across bedding 

strike. This tunnel-influence response is also consistent 

with the likely presence of discrete high-transmissivity 

networks along fractured limestone beds that have undergone 

dissolution. A lack of bedrock observation wells in half of the 

study area hampered a more thorough analysis of the extent of 

leakage from the RWB Tunnel in the study area.

On average, water levels in the unconsolidated aquifer 

had a seasonal difference of 5 ft. Some unconsolidated-aquifer 

wells indicated water-level changes due to tunnel leakage. The 

locations of unconsolidated-aquifer wells with measurable 

water-level changes due to tunnel leakage correlated with 

those in the bedrock. Water levels in the unconsolidated 

aquifer changed as much as 2.5 ft within 18 hours of tunnel 

shutdowns, but water-level changes in some unconsolidatedaquifer wells were smaller or nonexistent.

Introduction

Seasonal flooding of streets and residential basements 

and bacterial contamination of private-supply wells with 

Escherichia coli (E. coli) are recurring problems in the 

Rondout Valley near the Town of Wawarsing, Ulster County, 

New York (fig. 1). Street flooding may be related to the low 

infiltration rates of local soils and ineffective stormwaterdrainage networks. The E. coli contamination of shallow 
2 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Cannonsville

Reservoir

Pepacton

Reservoir

Neve

Rese

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

SULLIVAN

COUNTY

 DELAWARE

COUNTY

Port 

0 12.5 25 50 MILES

0 12.5 25 50 KILOMETERS

EXPLANATION

Delaware Aqueduct

76° 

42°

41°

N

PENNSYLVANIA

Figure 1. Location of Wawarsing study area including Summitville, Port Jervis Trough (Kingston to Port Jervis), the four 

reservoirs (Cannonsville, Pepacton, Neversink, and Rondout), the Delaware Aqueduct, and the Kensico Reservoir in New York.
Abstract 3

P

O R T

J E R V I S

T

R

O

U

G

H

LONG ISLAND SOUND

on

oir

Neversink

Reservoir

Rondout

Reservoir

Wawarsing

study area

Kensico

Reservoir

Central

Park

Roseton 

ULSTER 

COUNTY

AN

Y

ORANGE

COUNTY

WESTCHESTER

COUNTY

ROCKLAND

COUNTY

DUTCHESS

COUNTY

PUTNAM

COUNTY

Port Jervis

Summitville

Kingston 

Hu

ds

o

n

Riv

e

r

74°

NEW JERSEY

CONNECTICUT

NEW YORK

AREA OF

DETAIL

Figure 1. Location of Wawarsing study area including Summitville, Port Jervis Trough (Kingston to Port Jervis), the four reservoirs 

(Cannonsville, Pepacton, Neversink, and Rondout), the Delaware Aqueduct, and the Kensico Reservoir in New York.—Continued
4 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

wells appears to be related to elevated water-table levels and 

the presence of clay in the shallow subsurface in some areas. 

Basement flooding is related to the local water-table elevation, 

its proximity to basement-floor elevations, and local variations 

in subsurface geology. To investigate the possible relation 

between basement flooding and leakage from the adjacent 

New York City Rondout-West Branch (RWB) Water Tunnel, 

the U.S. Geological Survey (USGS), in cooperation with 

the New York City Department of Environmental Protection 

(NYCDEP), began a study in the fall of 2008 to characterize 

the groundwater-flow system in the area. The study area 

within the town of Wawarsing is about 12 square miles (mi2

) 

and includes parts of the hamlets of Napanoch to the south and 

Kerhonkson to the north (fig. 2).

Objectives and Approach

The objective of the study was to characterize the 

groundwater-flow system of the study area, including an 

investigation of the hydrologic connection between the flow 

system and the RWB Tunnel.

The approach of the study included—

1. development of a groundwater-level monitoring network 

for the unconsolidated and bedrock aquifers;

2. monitoring of groundwater levels seasonally and during 

temporary RWB Tunnel shutdowns;

3. compilation of hydrogeologic data from RWB Tunnel 

construction and well drilling;

4. collection and analysis of geochemical isotope and agedating tracers in the groundwater and surface water, and

5. collection and analysis of surface and borehole 

geophysical surveys.

Purpose and Scope

This report (1) describes the hydrologic characteristics 

of the unconsolidated and bedrock aquifers in the study area; 

(2) compares the water-level elevations in the RWB Tunnel 

shaft during temporary shutdowns with measured groundwater 

elevations in observation, private-supply, and production 

wells; and (3) presents a preliminary analysis of the relation of 

water levels, amplitudes of water-level changes, and tunnelinfluence delay times in the well network to water levels in the 

RWB Tunnel shaft during temporary tunnel shutdowns.

Previous Studies

Several published reports describe the surficial and 

bedrock geology and hydrology of the area. Frimpter 

(1970, 1972) compiled well-drilling logs and described the 

unconsolidated deposits and bedrock in Orange and Ulster 

Counties. Berkey (1911) described the unconsolidated 

deposits, bedrock, and possible faults in the Rondout Valley. 

Fluhr and Terenzio (1973, 1984) described the geologic results 

of exploration drilling and tunnel construction by the New 

York City Board of Water Supply (NYCBWS) in the study 

area. Caldwell (1989) mapped the surficial geology of the 

study area and Reynolds (2007) described the unconsolidated 

aquifers in the area. Fisher and others (1970) mapped the 

bedrock geology of the study area. Bartosik (2005) described 

the post-glacial history of the study-area valley. Berkey and 

Fluhr (1936), Dibbell (1944), and the New York City Board 

of Water Supply (1940, 1941) described the construction, 

geology, and hydrology of the RWB Tunnel in the study 

area. This data set was invaluable in understanding geologic 

contacts, faults, and groundwater inflow from the bedrock 

surrounding the tunnel.

Rondout-West Branch Tunnel

The RWB Tunnel delivers water from four interconnected 

reservoirs that constitute the Delaware System: the 

Cannonsville, Pepacton, Neversink, and Rondout Reservoirs 

(fig. 1). Separate tunnels from the Cannonsville, Pepacton, and 

Neversink Reservoirs deliver water to the Rondout Reservoir, 

which is then collected in the Rondout Reservoir and sent 

through the RWB Tunnel toward New York City. Construction 

of the RWB Tunnel portion of the Delaware System began in 

1937 and was completed in 1944 (New York City Department 

of Environmental Protection, 2010; Merguerian, 2000). 

The reservoirs were built and put on line in stages, with 

the Rondout Reservoir being the first completed, in 1950. 

The Neversink, Pepacton, and Cannonsville Reservoirs 

were completed and added to the Delaware System in 1954, 

1955, and 1964, respectively (New York City Department of 

Environmental Protection, 2010). The RWB Tunnel supplies 

roughly half of the 1.03 billion gallons of water per day 

delivered, on average, to New York City (New York City 

Department of Environmental Protection, 2010).

The RWB Tunnel underlies the central part of the 

study area at an average depth of 710 ft below the valley 

floor. During the construction of the RWB Tunnel, 

groundwater inflows ranging from less than 1 to more than 

9,000 gallons per minute (gal/min) were found at fractures, 

fault zones, solution features, and geologic contacts beneath 

the study area (Dibbell, 1944; New York City Board of Water 

Supply, 1941) (figs. 3A and 3B). At least five faults were 

identified in the bedrock encountered beneath the study area. 

Sections of highly weathered rocks had been mechanically 

broken up, and crush zones and dissolution features were 

encountered. Steel reinforcements were required to stabilize 

the tunnel throughout most of the Rondout Valley. The 

excavated tunnel was lined with concrete to a 13.5-ft finished 

diameter. More than 20,000 bags of concrete were needed 

to stabilize one section of the tunnel, where inflow exceeded 

9,000 gal/min, during construction (New York City Board 
Hydrogeology 5

of Water Supply, 1941). In that part of the tunnel, a special 

reinforced section (steel interliner) was required (fig. 3A). 

Estimated leakage out of the RWB Tunnel is 15 to 35 million 

gallons per day (Mgal/d) (James Canale, New York City 

Department of Environmental Protection, written commun., 

2011; DiNapoli, 2007) (fig. 1).

Flooded basements, unusual changes in the water 

levels in homeowners’ wells, and new springs were first 

reported by Wawarsing residents in 1992. In 2003 and 2009, 

an autonomous underwater vehicle was used to inspect the 

interior of the RWB Tunnel. It recorded 8,200 linear feet of 

cracking throughout the tunnel (James Canale, New York City 

Department of Environmental Protection, written commun., 

2011). Most of the cracking was found in the sections of 

the tunnel that are within the limestone units at Roseton and 

Wawarsing, N.Y.

Periodic construction, maintenance, and repairs of the 

tunnel infrastructure have required that flow through the tunnel 

be temporarily reduced or substantially lowered (“shutdowns”) 

for short periods of time, during which residents have claimed 

to observe a reduction in basement flooding and lower 

water levels in private-supply wells. This report outlines the 

hydrologic response of groundwater in the unconsolidated 

and bedrock aquifers to four temporary shutdowns of the 

RWB Tunnel that occurred during October–December 2008, 

November 2009, December 2009, and January 2010.

Precipitation

The National Weather Service (NWS) has recorded 

daily precipitation since 1869 in Central Park in New York 

City (National Oceanic and Atmospheric Administration, 

2010). The 141-year record indicates that the mean annual 

precipitation is 45.10 inches (in.) (fig. 4). Long-term 

precipitation records are available for the areas surrounding 

the study area, but the higher elevation (about 1,245 ft) of 

one site, gaps in data, and lack of long-term measurements at 

most sites reduce their applicability to the study area. Randall 

(1996) studied precipitation variations in upstate (northern) 

New York and found that the Wawarsing study area received 

an average of about 44 in. of precipitation annually from 1951 

to 1980. During this same period, precipitation in Central Park 

averaged 44.55 in. Comparing the Central Park data with the 

shorter records from nearby weather stations indicates only 

slight variations due to localized storms. The Central Park data 

were used in the hydrologic analysis in this study because of 

the high quality of the long-term records that correlate closely 

with the less extensive local data.

The annual precipitation in Central Park has exceeded 

the long-term mean every year from 2002 through 2010 

(fig. 4). This is the first time in the 141-year record that annual 

precipitation has exceeded the annual mean for 9 consecutive 

years. During the same 9 years, many long-term precipitation 

records were broken. The NWS has determined the wettest 

years, months overall, months, seasons, and individual days 

for the Central Park weather station (fig. 4). The years 2007, 

2006, and 2003 were the fourth wettest (61.70 in.), seventh 

wettest (59.90 in.), and eighth wettest (58.56 in.) years 

during the 141-year record, respectively. October 2005 and 

April 2007 were the second and fifth wettest months overall, 

respectively. February 2010 and 2008 were the third and 

tenth wettest Februarys, respectively. March 2010 and 2001 

were the wettest and sixth wettest Marches, respectively. 

April 2007 was the second wettest April. April 15, 2007, was 

the second wettest day ever recorded for Central Park, with 

7.57 in. of precipitation. June 2003, 2009, and 2006 were the 

wettest, second wettest, and sixth wettest Junes, respectively. 

September 2004 was the third wettest September recorded; 

October 2005 was the wettest October; and December 2009 

and December 2008 were the fourth and eighth wettest 

Decembers, respectively.

The NWS defines spring as including March, April, and 

May; summer includes June, July, and August; fall includes 

September, October, and November; and winter includes 

December, January, and February. The spring of 2007; the 

summers of 2003, 2006, 2007, and 2009; the falls of 2005 

and 2006; and winter 2009-10 were all among the 10 wettest 

seasons ever recorded in Central Park (National Oceanic and 

Atmospheric Administration, 2010). 

These high precipitation values may be related to a 

change in climate, but their impact has been to increase 

water levels in the unconsolidated and bedrock aquifers and 

contribute to surface flooding when the rate of precipitation 

exceeds the rate at which the water can be drained away from 

roadways or can infiltrate into (recharge) surficial deposits 

in Wawarsing.

Hydrogeology

The study area consists of a relatively flat, glaciated 

valley with isolated kames and glacial-lake deltas that rise 

about 70 ft above the surrounding valley floor (fig. 5). The 

Port Jervis Trough (fig. 1) is a deep, glaciated valley that 

extends about 100 miles southward from Kingston, N.Y. (Van 

Diver, 1989). In New York, the trough extends northward 

about 34 mi from Port Jervis to Kerhonkson, and separates 

the Shawangunk Mountains to the east from the Catskill Front 

(eastern side of the Catskill Mountains) to the west (Reynolds, 

2007). Both Soren (1961) and Frimpter (1972) reported that 

the outwash in the northern extension of this trough from the 

Orange–Sullivan County line northward to Summitville is 

much coarser than at Port Jervis (figs. 1 and 2). The valley 

slopes northward and contains thick deposits of lacustrine clay 

and silt as well as both unconfined and locally confined sand 

and gravel aquifers. 

Sedimentary bedrock crops out and rises above the valley 

floor, forming a boundary along its eastern and western sides 

(fig. 5). The surrounding bedrock uplands rise about 150 ft 

above the valley to the west and about 300 ft to the east. The 
6 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

U-1654

U-1660

U-1657

U-1635

U-1639

U-1637

U-1641

U-1652

U-1646 U-1644 U-1672

U-1634

U-1669

U-1671

U-1670

U-1673

U-1655

U-1658

U-1661

U-1674

U-1624

U-1664

U-1627

U-1650

U-1636

U-1629

U-1648

U-1645

U-1649 

01366807

U-1626

U-1643

U-1663

U-1628

U-1625

U-1656 U-1638

U-1642

U-1651

A

B

B'

Figure 2. Locations of bedrock and unconsolidated-aquifer wells, production wells, and selected surface-water sites 

within the study area, Town of Wawarsing, Ulster County, New York. (For location map, see figure 1.)
Hydrogeology 7

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

EXPLANATION

Line of section

Bedrock observation well and identifier

Unconsolidated-aquifer observation well and identifier

Production well and identifier

Surface-water site

U.S. Geological Survey downstream order identifier

New York State identifier

U-1631

U-1627

U-1629

01366807

U-1674

A A ́

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

-1654

60

57

U-4862

U-1662

U-1659

U-1640

U-1647

U-3772

U-1044

U-1653

U-1650

-1636

U-1631

-1626

U-1643

-1663

U-1630

1628

A ́

B'

Figure 2. Locations of bedrock and unconsolidated-aquifer wells, production wells, and selected surface-water sites within 

the study area, Town of Wawarsing, Ulster County, New York. (For location map, see figure 1.)—Continued
8 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

Steel interliner

A

Figure 3A. Locations of observation wells, production wells, and surface-water sites; Roundout–West Branch Tunnel 

geology; and water-inflow rates documented during tunnel construction within the study area, Town of Wawarsing, Ulster 

County, New York. (Tunnel geology and groundwater-inflow data from Dibbell, 1944) (For location map, see figure 1.)
Hydrogeology 9

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE ROAD

EXPLANATION

Line of section

Bedrock observation well

Unconsolidated-aquifer observation well

Production well

Surface-water site

Water inflow, in gallons per minute

2–10

10–100

100–1,000

9,100

Rock Type/Formation

Shale (Ashokan)

Shale (Hamilton-Marcellus)

Limestone (Onondaga)

Shale (Esopus-Schoharie)

Shaly limestone (Port Ewen)

Limestone (Becraft)

Limestone (New Scotland)

Limestone (Coeymans)

Limestone (Manlius)

LS/SS/SH (Binnewater)

SH/LS (High Falls)

Limestone (Wawarsing Wedge)

Sandstone (Shawangunk)

Shale (Hudson River)

Helderberg

Group

A A ́

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

A ́

Figure 3A. Locations of observation wells, production wells, and surface-water sites; Roundout–West Branch Tunnel geology; 

and water-inflow rates documented during tunnel construction within the study area, Town of Wawarsing, Ulster County, New York. 

(Tunnel geology and groundwater-inflow data from Dibbell, 1944) (For location map, see figure 1.)—Continued
10 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

A 

Figure 3B. Cross section of geology observed during New York City Board of Water Supply test borings and Rondout 

West–Branch Tunnel construction from A to A’ within the study area, Town of Wawarsing, Ulster County, New York. (Location 

is shown in figure 3A.) (The Helderberg Group has been divided into the Port Ewen, Becraft, New Scotland, and Coeymans 

Formations.) (Modified from Berkey and Fluhr, 1936.)
Hydrogeology 11

A ́

Figure 3B. Cross section of geology observed during New York City Board of Water Supply test borings and Rondout 

West–Branch Tunnel construction from A to A’ within the study area, Town of Wawarsing, Ulster County, New York. 

(Location is shown in figure 3A.) (The Helderberg Group has been divided into the Port Ewen, Becraft, New Scotland, and 

Coeymans Formations.) (Modified from Berkey and Fluhr, 1936.).—Continued
12 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

(45.10 inches)

Year

0

10

20

30

40

50

60

70

80

90

Total annual precipitation, in inches

186918721875187818811884188718901893189618991902190519081911191419171920192319261929193219351938194119441947195019531956195919621965196819711974197719801983198619891992199519982001200420072010

Figure 4. Annual precipitation as recorded by the National Weather Service at Central Park, New York County, New York, during 

1869–2010 (National Oceanic and Atmospheric Administration, 2010). (Solid black line indicates annual mean precipitation during 

the 141-year period of observation.)

uplands have thin veneers of glacial and alluvial deposits 

with exposed bedrock outcrops. The valley is underlain by 

unconsolidated glacial deposits that vary in thickness from less 

than 10 to more than 300 ft.

Unconsolidated Deposits

The valley in the study area is underlain by gravel, 

sand, silt, and clay of Pleistocene and Holocene age. The 

unconsolidated deposits include till, lacustrine silt and clay, 

lacustrine delta sediments, kame and outwash sand and gravel, 

and alluvium (Cadwell, 1989). Frimpter (1972), Bartosik 

(2005), and Reynolds (2007) describe discontinuous sand 

and gravel aquifers buried beneath the glacial-lake sediments. 

Geologic data from 14 observation wells drilled by the USGS 

for this study indicate highly variable deposits ranging from 

sand and gravel to silt and clay. The lacustrine silt and clay 

locally exceed 140 ft in thickness.

Bedrock

A complex series of sedimentary bedrock units of Silurian 

and Devonian age underlies the unconsolidated deposits in the 

study area (Fisher and others, 1970). In descending order as 

described by Berkey and Fluhr (1936), Dibbell (1944), and the 

New York City Board of Water Supply (1940), these include 

the Marcellus Shale, Onondaga Limestone, Esopus-Schoharie 

Shale, Helderberg Limestones (Port Ewen-Becraft, New 

Scotland, and Coeymans), Manlius Limestone, Binnewater 

Limestone and Sandstone, High Falls Shale and Limestone, 

Wawarsing Wedge complex, Shawangunk Sandstone, and 

Hudson River Shale. The Wawarsing Wedge, which consists 

mostly of limestone with minor shale and sandstone, pinches 

out to the north. The sedimentary bedrock units and their 

bedding generally strike northeast and dip about 45 degrees to 

the northwest (fig. 3B). Dibbell (1944) and the New York City 

Board of Water Supply (1940) describe the bedrock sequences 
Hydrology 13

below the study area as having sections with substantial 

fracturing and faulting. In limestone, dissolution along such 

secondary features and selected beds greatly increases aquifer 

transmissivity. Many of the bedrock flow zones produced 

volumes of groundwater in the range of thousands of gallons 

per minute in the study area during construction of the RWB 

Tunnel (fig. 3). In limestone, dissolution along such secondary 

features and selected beds greatly increases transmissivity in 

the direction of strike (northeast-southwest), resulting in an 

anisotropic aquifer in which transmissivity is much greater 

along the bedding strike than across it.

Catskill Aqueduct Construction Observations

During the exploration and construction of the Catskill 

Aqueduct about 10 miles (mi) northeast of the study area, 

nearly all of the bedrock units found in Wawarsing were 

encountered except the Wawarsing Wedge (Berkey, 1911). 

Caves and cavities filled with clay were discovered in test 

borings for the Catskill Aqueduct (Fluhr and Terenzio, 1973). 

During exploration drilling, a void 28 ft in length was detected 

200 ft below land surface (Berkey, 1911). The Onondaga 

Limestone was described as being cavernous in many places, 

and members of the Helderberg and Manlius Limestones 

exhibited a tendency to develop cavernous structures (Berkey 

and Fluhr, 1936). In the Manlius Limestone, the most 

characteristic features were solution joints that in some places 

enlarged to cave-like form (Berkey, 1911). Several clay-filled 

spaces several feet wide were encountered during construction 

at about the -100-ft elevation (Berkey, 1911). The Binnewater 

Sandstone and the High Falls Shale were found to be more 

porous and transmissive than other formations in the area, 

especially along bedding planes (Berkey, 1911; Berkey and 

Fluhr, 1936). During construction of the aqueduct, vertical 

and horizontal clay-filled cavities and joints were encountered 

over a 500-ft zone in the Helderberg Limestone (Fluhr and 

Terenzio, 1973). Several vertical chimneys or caves several 

feet wide crossed the tunnel at a 45-degree angle and extended 

high into the roof of the tunnel (Fluhr and Terenzio, 1973).

Rondout West–Branch Water Tunnel 

Construction Observations

The Catskill Aqueduct served as an indicator of what 

might be expected in the RWB Tunnel (Fluhr and Terenzio, 

1973). The major difficulties in construction of the tunnel 

occurred over a 500-ft section between the Helderberg 

Limestone and the Shawangunk Formation (Fluhr and 

Terenzio, 1973). Grouting proved unsuccessful in stopping 

inflows of groundwater from the Manlius Limestone (Fluhr 

and Terenzio, 1973). Several severely decayed bands with 

solution cavities produced large quantities of water (more 

than 9,000 gal/min) in the Binnewater Sandstone and the High 

Falls Shale (Dibbell, 1944; Fluhr and Terenzio, 1973; New 

York City Board of Water Supply, 1940 and 1941). Many 

solution cavities, decayed or leached limestone, fault crush 

zones, and prominent solution features were described during 

construction of the steel interliner for the tunnel (Dibbell, 

1944; New York City Board of Water Supply, 1940). The 

steel interliner was required within parts of the Manlius, 

Binnewater, High Falls, Wawarsing, and Shawangunk 

Formations (Dibbell, 1944; New York City Board of Water 

Supply, 1941) (fig. 2). Berkey (1911) states that formations 

that are porous or soluble and are subject to enforced seepage 

(from a pressurized tunnel) may become progressively 

more porous with time due to tunnel leakage. He describes 

blocks of the Manlius and Coeymans Limestones used in 

the Delaware and Hudson Canal that exhibited dissolution 

etching up to 1 in. deep resulting from contact with surface 

waters after only 35 to 40 years (Berkey, 1911). On the basis 

of the geologic core, the geologic descriptions of the tunnel 

excavation, and the large groundwater inflows, the bedrock 

within the study area can be highly transmissive locally as a 

result of a combination of fault crush zones, large fractures, 

and large dissolution features or cavities in some areas. The 

limestone bedrock demonstrates a potential for dissolution 

from leaking tunnel water (acidic surface water) without the 

normal buffering effects that reduce the acidity and dissolution 

potential of water recharged under natural conditions.

Water from the RWB Tunnel appears to be leaking from 

cracks in the concrete liner installed during construction in 

1937–44. The cracks may allow pressurized tunnel water 

to flow behind and (or) through the liner where voids may 

exist and into the transmissive solution cavities in limestone, 

fractures, faults, and geologic contacts. Sustained leakage 

of pressurized tunnel water through limestone that has been 

subject to dissolution may further enhance the transmissivity 

of the limestone as a result of additional dissolution 

surrounding the tunnel liner.

Hydrology

In October 2008, the USGS began measuring 

groundwater levels in two private-supply unconsolidatedaquifer wells and in two bedrock wells (one private-supply 

and one production well). By July 2010, the groundwatermonitoring network had been expanded to 41 wells and 

2 surface-water sites. Of the 41 wells, 23 are screened 

in unconsolidated deposits and 18 are cased through the 

unconsolidated deposits and completed as an open hole in 

bedrock. Water levels measured in the bedrock wells represent 

composite hydraulic heads and are largely controlled by the 

most transmissive zones. The two surface-water sites consist 

of a lake-level gage at the northwestern part of the lake at 

Lippman Park (USGS lake-level gage 01366807), and a 

possible limestone sinkhole (pond-level gage) located in an 

open field (U-1674) (fig. 2; table 1).
14 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1927

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

U-1654

U-1660

U-1657

U-1635

U-1639

U-1637

U-1641

U-1652

U-1646 U-1672 U-1644

U-1634

U-1669

U-1671

U-1670

U-1673

U-1655

U-1658

U-1661

U-1674

U-1624

U-1664

U-1627

U-1650

U-1636

U-1629

U-1648

U-1645

U-1649

01366807

U-1626

U-1663

U-1628

U-1625

U-1656 U-1638

U-1642

U-1651

Figure 5. Topography and locations of bedrock and unconsolidated-aquifer observation wells, production wells, and 

selected surface-water sites within the study area, Town of Wawarsing, Ulster County, New York.
Hydrology 15

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

EXPLANATION

Bedrock observation well and identifier

Unconsolidated-aquifer observation well and identifier

Production well and identifier

Surface-water site

U.S. Geological Survey downstream-order identifier

New York State identifier

U-1631

U-1627

U-1629

01366807

U-1674

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

660

657

U-4862

U-1662

U-1659

U-1640

U-1647

U-3772

U-1044

U-1653

U-1650

-1636

U-1631

1626

U-1643

1663

U-1630

628

Figure 5. Topography and locations of bedrock and unconsolidated-aquifer observation wells, production wells, and selected 

surface-water sites within the study area, Town of Wawarsing, Ulster County, New York.—Continued
16 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Table 1. Site information for groundwater wells and selected surface-water sites within the study area, Town of Wawarsing, Ulster 

County, New York.—Continued

[NYSDEC, New York State Department of Environmental Conservation; USGS, U.S. Geological Survey; NAVD 88, North American Vertical Datum of 1988; 

NA, not applicable; °,',", degrees, minutes, seconds; --, no data]

Well identifier

Latitude 

north

Longitude 

west

Elevation

(feet above NAVD 88) Depth

(feet below 

land surface 

March–

April 

2010)

Depth

(feet below 

land surface 

November 

2010)

Aquifer 

NYSDEC USGS Measuring 

point

Land 

surface 

U-1044 414615074201201 41°46'15" 74°20'12" 277.97 276.1 7.3 9.6 Bedrock

U-1624 414531074210401 41°45'31" 74°21'04" 285.25 283.2 17.2 23.5 Bedrock

U-1625 414546074205301 41°45'46" 74°20'53" 279.55 278.4 -2.6* -1.6* Bedrock

U-1626 414534074205001 41°45'34" 74°20'50" 276.45 275.7 1.4 5.4 Unconsolidated

U-1627 414543074205501 41°45'43" 74°20'55" 279.26 279.3 4.5 8.9 Unconsolidated

U-1628 414534074205101 41°45'34" 74°20'51" 277.45 275.7 4.2 7.3 Bedrock

U-1629 414535074212001 41°45'35" 74°21'20" 301.73 300.1 11.5 15.6 Bedrock

U-1630 414550074203002 41°45'50" 74°20'30" 267.17 266.1 -1.1* -- Bedrock

U-1631 414553074202701 41°45'53" 74°20'26" 261.93 262.5 -- -2.5* Bedrock

U-1635 414435074213601 41°44'35" 74°21'36" 278.46 276.5 9.7 12.4 Unconsolidated

U-1636 414549074204201 41°45'49" 74°20'42" 279.49 278.4 2.3 16.9 Bedrock

U-1637 414506074210801 41°45'06" 74°21'08" 264.27 264.5 2.6 5.1 Unconsolidated

U-1638 414526074210101 41°45'26" 74°21'01" 350.23 349.1 84.1 87.6 Unconsolidated

U-1639 414441074212601 41°44'41" 74°21'26" 276.44 275.6 11.9 14.1 Unconsolidated

U-1640 414546074201001 41°45'46" 74°20'10" 253.07 253.6 4.5 6.6 Unconsolidated

U-1641 414506074210802 41°45'06" 74°21'08" 264.37 264.5 0.2 2.5 Unconsolidated

U-1642 414527074210401 41°45'27" 74°21'04" 323.47 323.7 26.2 32.2 Unconsolidated

U-1643 414550074203001 41°45'50" 74°20'30" 267.80 267.4 5.9 -- Unconsolidated

U-1644 414519074212501 41°45'18" 74°21'25" 269.71 268.4 44.0 51.1 Bedrock

U-1645 414535074210601 41°45'35" 74°21'06" 289.19 288.2 9.4 14.3 Bedrock

U-1646 414518074212202 41°45'18" 74°21'22" 266.57 266.9 1.1 2.5 Unconsolidated

U-1647 414614074194501 41°46'14" 74°19'45" 279.96 279.1 7.0 13.1 Bedrock

U-1648 414547074205201 41°45'47" 74°20'52" 280.17 278.9 -- 5 Bedrock

U-1649 414549074205101 41°45'49" 74°20'51" 301.07 299.4 20.5 24.1 Bedrock

U-1650 414553074203201 41°45'53" 74°20'32" 263.47 263.9 2.0 5.2 Unconsolidated

U-1651 414528074210501 41°45'28" 74°21'05" 316.63 315.2 38.8 45.3 Bedrock

U-1652 414518074212201 41°45'18" 74°21'22" 266.80 267.0 2.3 4.0 Unconsolidated

U-1653 414611074201201 41°46'11" 74°20'12" 278.21 276.2 7.5 9.8 Bedrock

U-1654 414457074205301 41°44'57" 74°20'53" 284.25 281.8 -- 19.6 Unconsolidated

U-1655 414421074222801 41°44'21" 74°22'28" 297.60 298.1 -- 14.9 Unconsolidated

U-1656 414527074210402 41°45'27" 74°21'04" 323.52 324.0 -- 61.1 Unconsolidated
Hydrology 17

Groundwater-Flow System

Major users of municipal water in the study area include 

the Village of Ellenville (4,323), Eastern/Ulster Correctional 

Facility (3,000), Kerhonkson Water District (500), Napanoch 

Water District (400), and various small private suppliers 

(811), totaling about 9,000 municipal groundwater users 

(New York State Department of Health, 1982). U.S. Census 

data in 2010 indicate that the total population of the Town of 

Wawarsing is 13,157 (United States Census Bureau, 2010). 

Within the study area, most households rely on individual 

private-supply wells in either the unconsolidated or bedrock 

aquifers. The transmissivity of the unconsolidated aquifer near 

Ellenville appears to be very high, as evidenced by a yield of 

1,000 gal/min during test pumping of a 39-ft-deep production 

well for the Village of Ellenville (Frimpter, 1972).

Manual measurements of groundwater levels were 

completed monthly. Precision global positioning system 

(GPS) surveying was used to establish benchmarks in the 

study area and to measure the elevations of monitored wells. 

Nearby wells and doublets were optically leveled and tied 

into the GPS elevations to within 0.003 ft. Hydraulic heads 

and vertical gradients for the measured wells were calculated 

using these precision elevations. Of the 41 wells, 29 are 

equipped with digital data loggers with pressure transducers 

that record groundwater levels and temperature hourly. 

Sixteen data loggers are in the unconsolidated-aquifer wells 

and 13 are in bedrock wells (fig. 2); one of these recorders 

is an electromagnetic flowmeter and pressure transducer that 

measures the discharge from flowing artesian bedrock well 

U-1631 (hydraulic head in this well is above the top of the 

well) in gallons per minute at hourly intervals (fig. 2). The 

well discharges groundwater at an average rate of 70 gal/min, 

which is directed by a 4-in.-diameter pipe toward the front of 

the private property to a ditch along the nearby roadway.

Long-Term Water-Level Monitoring

At three wells (U-1626, U-1627, and U-1629) and a lakelevel gage (01366807), water levels were measured manually 

at monthly intervals and digitally at hourly intervals beginning 

in October/November 2008 (fig. 6). The lake-level gage is 

located in the northwestern part of a modified body of water 

called Lippman Lake, which receives runoff and base flow 

from several small streams that flow from the adjacent hills. 

Runoff from the lake discharges to a culvert when the lake 

level is high (fig. 2). Wells U-1626 and U-1627 are shallow 

Table 1. Site information for groundwater wells and selected surface-water sites within the study area, Town of Wawarsing, Ulster 

County, New York.—Continued

[NYSDEC, New York State Department of Environmental Conservation; USGS, U.S. Geological Survey; NAVD 88, North American Vertical Datum of 1988; 

NA, not applicable; °,',", degrees, minutes, seconds; --, no data]

Well identifier

Latitude 

north

Longitude 

west

Elevation

(feet above NAVD 88) Depth

(feet below 

land surface 

March–

April 

2010)

Depth

(feet below 

land surface 

November 

2010)

Aquifer 

NYSDEC USGS Measuring 

point

Land 

surface 

U-1657 414458074205401 41°44'58" 74°20'54" 275.29 276.1 -- 5.4 Unconsolidated

U-1658 414420074222501 41°44'20" 74°22'25" 298.94 297.7 -- 28.9 Bedrock

U-1659 414546074201002 41°45'46" 74°20'10" 253.09 253.6 -- 3.3 Unconsolidated

U-1660 414458074205402 41°44'58" 74°20'54" 275.63 276.1 -- 12.7 Unconsolidated

U-1661 414421074222701 41°44'21" 74°22'27" 298.05 297.6 -- 35.9 Bedrock

U-1662 414610074201201 41°46'10" 74°20'12" 276.27 276.7 -- 13.6 Unconsolidated

U-1663 414545074205201 41°45'45" 74°20'52" 274.79 275.2 -- 4.9 Unconsolidated

U-1664 414535074211601 41°45'35" 74°21'16" 300.09 297.4 12.4 14.7 Unconsolidated

U-3772 414539074193301 41°45'39" 74°19'33" 285.43 283.5 -- -5.6 Bedrock

U-4862 414616074190601 41°46'16" 74°19'06" 270.79 269.0 25.8 29.5 Unconsolidated

**U-1674 414414074221801 41°44'14" 74°22'17" 280.41 NA NA NA NA

NA **01366807 41°45'50" 74°21'11" 302.60 NA NA NA NA

*

 Estimated.

** Surface-water site.
18 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

A. U-1626 (Unconsolidated)

264

266

268

270

272

274

276

278

0

Precipitation, in inches

1

2

3

4

5

Water level

Precipitation

EXPLANATION

B. U-1629 (Bedrock)

Water level, in feet above NAVD 88

Water level, in feet above NAVD 88

278

280

282

284

286

288

290

292

0

Precipitation, in inches

1

2

3

4

5

C. 01366807 (Lake)

Water level, in feet above NAVD 88

294

296

298

300

302

304

306

308

Date

0

Precipitation, in inches

1

2

3

4

5

07/01/200808/01/2008

09/01/2008

10/01/200811/01/200812/01/200801/01/2009

02/01/200903/01/2009

04/01/2009

05/01/200906/01/2009

07/01/200908/01/2009

09/01/2009

10/01/200911/01/2009

12/01/2009

01/01/2010

02/01/2010

03/01/2010

04/01/2010

05/01/201006/01/201007/01/2010

08/01/2010

09/01/2010

10/01/201011/01/2010

12/01/2010

Figure 6. Water-level and precipitation data for three unconsolidated-aquifer wells, two bedrock wells, and a surface-water 

site within the study area, Town of Wawarsing, Ulster County, New York: A, Unconsolidated-aquifer well U-1626, October 21, 

2008–November 16, 2010; B, bedrock production well U-1629, October 22, 2008–November 16, 2010; C, surface-water site at U.S 

Geological Survey lake gage 01366807, November 20, 2008–November 16, 2010; D, unconsolidated-aquifer well U-1627, October 

21, 2008–December 1, 2010; E, unconsolidated-aquifer well U-1642, September 14, 2009–June 22, 2010; and F, bedrock well U-1628, 

February 24, 2009–December 1, 2010. (Precipitation data from National Oceanic and Atmospheric Administration station in Central 

Park, N.Y.; for locations, see figure 1).
Hydrology 19

D. U-1627 (Unconsolidated)

264

266

268

270

272

274

276

278

0

Precipitation, in inches

1

2

3

4

5

Water level

Precipitation

EXPLANATION

E. U-1642 (Unconsolidated)

Water level, in feet above NAVD 88

Water level, in feet above NAVD 88

290

292

294

296

298

300

302

304

0

Precipitation, in inches

1

2

3

4

5

F. U-1628 (Bedrock)

Water level, in feet above NAVD 88

260

262

264

266

268

270

272

274

Date

0

Precipitation, in inches

1

2

3

4

5

07/01/200808/01/2008

09/01/2008

10/01/200811/01/200812/01/200801/01/2009

02/01/200903/01/2009

04/01/2009

05/01/200906/01/2009

07/01/200908/01/2009

09/01/2009

10/01/200911/01/2009

12/01/2009

01/01/2010

02/01/2010

03/01/2010

04/01/2010

05/01/201006/01/201007/01/2010

08/01/2010

09/01/2010

10/01/201011/01/2010

12/01/2010

Figure 6. Water-level and precipitation data for three unconsolidated-aquifer wells, two bedrock wells, and a surface-water 

site within the study area, Town of Wawarsing, Ulster County, New York: A, Unconsolidated-aquifer well U-1626, October 21, 

2008–November 16, 2010; B, bedrock production well U-1629, October 22, 2008–November 16, 2010; C, surface-water site at U.S 

Geological Survey lake gage 01366807, November 20, 2008–November 16, 2010; D, unconsolidated-aquifer well U-1627, October 

21, 2008–December 1, 2010; E, unconsolidated-aquifer well U-1642, September 14, 2009–June 22, 2010; and F, bedrock well U-1628, 

February 24, 2009–December 1, 2010. (Precipitation data from National Oceanic and Atmospheric Administration station in Central 

Park, N.Y.; for locations, see figure 1).—Continued
20 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

(10-ft-deep) dug wells in the unconsolidated aquifer (figs. 2 

and 6). Well U-1629 is a 118-ft-deep production well open to 

bedrock (figs. 2 and 6). Well U-1629 is pumped during late 

March through mid-November but is not pumped during the 

winter (fig. 6). Drawdown in well U-1629 due to pumping can 

exceed 12 ft, below the depth of the digital recorder (fig. 6). 

Seasonal variations in the bedrock water levels are monitored 

during the recovery peaks. Hydrographs of wells screened in 

the unconsolidated aquifer (U-1626, U-1627, and U-1642), the 

bedrock aquifer (U-1628 and U-1629), and the lake-level gage 

indicate fluctuations in the water levels throughout the study 

period (October 2008—November 2010) (fig. 6).

In general, during the study period water levels were 

highest in two time periods—(1) March, April, and May, and 

(2) December and January (fig. 6.). During these periods, 

snow melt and elevated precipitation coupled with minimal 

evapotranspiration recharge the aquifers and raise the lake 

level. March 2010 was the wettest March recorded at the 

Central Park weather station since 1869 (National Oceanic and 

Atmospheric Administration, 2010). In June 2009, however, 

unusually high water levels were recorded in many of the 

network wells, producing an outlier in the seasonal waterlevel patterns (fig. 6). The high water levels were caused 

by the extremely large amount of precipitation measured in 

June 2009, one of the 10 wettest Junes since 1869 (National 

Oceanic and Atmospheric Administration, 2010). Water 

levels typically are lowest in August, September, and October 

(fig. 6). The hydrographs indicate discharge from the aquifers 

due to reduced precipitation, increased consumptive use, 

and increased evapotranspiration from the aquifers (seasonal 

effects). Water levels in both the unconsolidated-aquifer and 

bedrock wells are closely correlated with precipitation (fig. 6). 

The large influence of precipitation on groundwater levels in 

the study area can be seen in long-term hydrographs (fig. 6). 

Punctuated shutdowns of the RWB Tunnel revealed that 

leakage from the tunnel affected the aquifers both regionally 

and locally, as discussed in detail farther on in this report.

The hydrograph of well U-1642, a USGS observation 

well screened in the unconsolidated aquifer, was an exception 

to these patterns, however (fig. 6). The localized mounding of 

groundwater due to the presence of unique geologic deposits 

in that area is described in detail farther on in this report.

In the unconsolidated aquifer, variations in precipitation 

and seasonal effects caused water levels to range seasonally 

from 3.5 ft (in well U-1652) to 6.5 ft (in well U-1626) (figs. 2 

and 6). On average, water levels in the unconsolidated aquifer 

had a seasonal difference of 5 ft (fig. 7). Seasonal differences 

in water levels in wells in the bedrock aquifer ranged from 

1.5 ft (in well U-3772) to 9.5 ft (in well U-1645) (fig. 2). On 

average, water levels in the bedrock aquifer had a seasonal 

difference of 5.3 ft (fig. 6).

In general, groundwater flows through a network of 

interconnected fractures in bedrock from higher elevations 

in the surrounding hills toward the center of the valley. 

The unconsolidated aquifer receives recharge as a result of 

infiltration throughout the valley. Water levels in Lippman 

Lake responded similarly to precipitation changes, but with 

smaller amplitudes (fig. 6). Field observations and survey 

measurements indicate that overflow of the lake to a culvert 

is minimal and occurs only when the lake stage exceeds an 

elevation of 298.2 ft. Water levels in nearby unconsolidatedaquifer wells indicate that recharge (subsurface leakage) from 

the lake to the shallow aquifers occurs locally throughout 

the year.

Potentiometric Surface in the Bedrock Aquifer

Most of the recharge to the bedrock aquifer probably 

occurs through outcrops of fractured bedrock at the higher 

elevations in the hills that surround the study-area valley. In 

some bedrock wells the potentiometric surface was higher 

than the top of the well casing, resulting in flowing artesian 

conditions (fig. 7). Results of a synoptic measurement 

in March/April 2010 indicate that the elevation of the 

potentiometric surface of the bedrock aquifer ranges from 

288.6 ft (11.5 ft below land surface (BLS)) at well U-1629, 

along the base of the surrounding hills on the west side of 

the valley, to 267.2 ft (-1.1 ft BLS (flowing artesian well)) 

at well U-1630 in the north-central part of the valley (fig. 

8). An exception was a cone of depression at well U-1644, 

where water-level elevations were only 224.4 ft (44.0 ft BLS), 

probably as a result of pumping from a low-transmissivity 

bedrock unit, possibly the Esopus Shale. Similar conditions 

were measured at this well in November 2010, but water 

levels were slightly lower (fig. 9).

In November 2010, an anomaly in groundwater-elevation 

contours was observed along Route 209 near wells U-1651, 

U-1628, and U-1625 (a flowing artesian well) (fig. 9). Higher 

water levels in these wells are indicated by comparing the 

local changes in contour lines to those in the regional trend.

 In November 2010, the head differential between wells 

U-1629 (in bedrock) and U-1664 (in the unconsolidated 

aquifer) was upward at 1.8 ft. This was the smallest head 

differential measured in any bedrock/unconsolidated-aquifer 

doublet. Upward flow gradients of 9.7, 6.8, 2.8, 5.1, 7.0, 

and 3.3 ft were measured at wells U-1625, U-1630, U-1636, 

U-1649, U-1651, and U-1653, respectively (figs. 7, 8, and 9). 

With the exception of one doublet, flow gradients from the 

bedrock to the unconsolidated aquifers at all bedrock wells 

influenced by tunnel leakage were upward with values that 

ranged from 1.6 to 5.4 times that measured at well U-1629. 

Because the groundwater in the bedrock in the vicinity of 

well U-1629 is not influenced by leakage from the RWB 

Tunnel, the head difference at this well may represent a 

normal hydraulic gradient between the bedrock and the 

unconsolidated deposits in this part of the valley. Four bedrock 

wells in the study area are flowing artesian wells (U-1625, 

U-1630, U-1631, and U-3772), with water levels above land 

surface (figs. 8 and 9). These conditions and the larger-thannormal upward flow of water measured at other bedrock wells 

indicate a significant flow-gradient potential from the bedrock 

to the unconsolidated deposits in parts of the study area. The 
Hydrology 21

U-1627

U-1625

BEDROCK BEDROCK

UNCONSOLIDATED AQUIFER

Land surface

Typical

basement

Water table–March/April 2010

Water table–November 2010

B e d r o c k p o t e n t i o m e t r i c s u r f a c e

Artesian-flowing

bedrock well

Elevation, in feet above NAVD 88

285

280

275

270

265

260

255

Water-level

range

Water-level

range

Depth to water

4.48 feet Depth to water

8.87 feet

Vertical exaggeration x10

B B’

Figure 7. Hydrogeologic section B to B’ showing the difference in water levels between the unconsolidated and bedrock 

aquifers, Town of Wawarsing, Ulster County, New York. (Location is shown in figure 2.)
22 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

271.5

276.4

266

276.

278.9

281*

278.8

288.6

224.4

ND

ND

250

240

290

280

270

260

270

280

?

?

?

?

?

?

?

260

ND

U-163

U-1624

U-1628

U-1625

U-1629

U-1658

U-1661

U-1648

U-1644

U-1645

U-1649

U-1651

U-1672

U-1634

U-1669

U-1671

230

270

Figure 8. Elevation of the potentiometric surface in the bedrock aquifer within the study area, Town of Wawarsing, 

Ulster County, New York, March and April 2010.
Hydrology 23

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

Water-level elevation in bedrock wells—Shows 

equipotential surface of hydraulic head. Dashed 

where inferred. Hachures indicate depression.

Contour interval is 10 feet

Observation well—Upper number represents New York

State well identifier. Lower number, where present, indicates 

water-level elevation in feet above NAVD 88. ND indicates 

that no data were available at time of study. Asterisk (*) 

indicates estimated value

Production well—Upper number represents New York State 

well identifier. Lower number, where present, indicates 

water level elevation in feet above NAVD 88 

EXPLANATION

U-3772

ND

U-1629

289

270

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

271.5

76.4

ND

272.1

268.7

267.2

276.1

8.9

?

?

?

?

? ? ?

ND

U-1636

U-1647

U-1630

U-1628

U-3772

U-1653

649

U-1631

1651

Figure 8. Elevation of the potentiometric surface in the bedrock aquifer within the study area, Town of Wawarsing, 

Ulster County, New York, March and April 2010.—Continued
24 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

268.4

269.9

259.7

261.5

275.3

280* 273.9

284.5

217.3

268.8

261.7

274

U-1636

U-1624 

U-1628

U-1625

U-1629

U-1658

U-1661

U-1648

U-1644

U-1645

U-1649

U-1651

U-1672

U-1634

U-1669

U-1671

240

230

250

220

260

27

26

240

250

260

270

280

280

?

?

?

?

?

?

?

? ?

?

270

Figure 9. Elevation of the potentiometric surface in the bedrock aquifer within the study area, Town of Wawarsing, Ulster 

County, New York, November 2010. 
Hydrology 25

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

Water-level elevation in bedrock wells—Shows 

equipotential surface of hydraulic head. Dashed 

where inferred. Hachures indicate depression. 

Contour interval is 10 feet

Observation well—Upper number represents New York 

State well identifier. Lower number, where present, indicates 

water-level elevation in feet above NAVD 88. ND indicates 

that no data were available at time of study. Asterisk (*) 

indicates estimated value

Production well—Upper number represents New York 

State well identifier. Lower number, where present, indicates 

water-level elevation in feet above NAVD 88 

EXPLANATION

U-1653

266.4

U-1629

284.5

270

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

8.4

281.7

266.0

266.4

ND

265*

U-1647

U-1630

628

U-3772

U-1653

U-1631

280

270

260

260

270

280

?

?

?

? ?

?

Figure 9. Elevation of the potentiometric surface in the bedrock aquifer within the study area, Town of Wawarsing, Ulster 

County, New York, November 2010. —Continued
26 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

cross section shown in figure 7 illustrates the large difference 

in water levels between the unconsolidated and bedrock 

aquifers along Route 209 in Wawarsing, N.Y. The extent of 

this upward flow gradient in the eastern half of the study area 

is unknown because no bedrock observation wells were drilled 

for this study, and no private-supply bedrock wells were 

available in that part of the study area.

Water Table in the Unconsolidated Aquifer

Analyses of hydrographs indicate that the water-table 

elevation in the unconsolidated aquifer fluctuates in response 

to seasonal variations in precipitation, evapotranspiration, 

pumpage, and, in some wells, leakage from the tunnel through 

the underlying bedrock. The elevation of the water table in 

March/April ranged from 285 ft (12.4 ft BLS) at well U-1664 

at the western edge of the valley to 243.2 ft (25.8 ft BLS) 

at well U-4862 near the central part of the valley, where 

groundwater discharges to the Rondout Creek (fig. 10). A 

similar (but lower) water-table configuration was measured in 

November 2010 (fig. 11). Groundwater in the unconsolidated 

aquifer generally flows from the surrounding hills east and 

west of the valley and from the southwest part of the valley 

toward the central and ultimately northeastern part of the 

valley (figs. 10 and 11).

Water levels were higher than the regional trend at wells 

U-1626, U-1638, and U-1656 in March/April 2010 (figs. 2 

and 10). A similar high groundwater-level condition was 

observed in November 2010 (fig. 11). It is not clear whether 

this condition is related to the underlying bedrock water-level 

anomaly or to underlying lacustrine silt and clay (figs. 10 

and 11).

An area of anomalously high groundwater levels with 

perched-like conditions (elevated groundwater separated 

from the regional water table) was observed at well U-1642, 

a shallow USGS observation well (figs. 6 and 11). Measured 

water-level elevations at U-1642 were consistently about 

29 ft higher than those in the deeper nearby wells U-1638 

and U-1656 (figs. 2 and 11). Water-level elevations in well 

U-1642 do not correlate with those in the underlying regional 

groundwater-flow system and do not respond to changes in 

RWB tunnel pressure. The hydrograph from well U-1642 

shows a limited and delayed response of water levels to 

variations in precipitation (fig. 6). Analysis of the dates of 

seasonal low and high water levels in well U-1642 indicates a 

1-month lag compared to those in other unconsolidated-aquifer 

wells in the area and regionally (fig. 6). Vertical gradients 

in the unconsolidated aquifer in November 2010 at doublets 

U-1652 and U-1646, U-1641 and U-1637, and U-1659 and 

U-1640 were all upward, with head differences of 1.4, 2.6, 

and 3.3 ft, respectively (figs. 2, 10, and 11). In contrast, the 

vertical gradient in the unconsolidated aquifer within the area 

of anomalously high water levels (perched-like conditions) 

at doublet U-1642 and U-1656 was downward, with a head 

difference of 28.6 ft (figs. 2, 10, and 11). This is the largest 

vertical head difference in any unconsolidated-aquifer well 

doublet within the study area. The large head differences, 

downward flow direction, lack of daily variations in water 

levels, lack of response to changes in RWB Tunnel pressure, 

and lag in seasonal low and high water levels compared to the 

regional aquifer response indicate that the anomalously high 

water levels (perched-like conditions) in this area probably 

are caused by the large amount of clay underlying this hilly 

deltaic deposit. Fine-grained sediments in this deposit appear 

to be responsible for springs that discharge from the upper 

slopes of this feature during seasonal (spring) periods of high 

precipitation. The upward flow gradients in the unconsolidated 

aquifer were greatest in the central parts of the valley where 

shallow groundwater discharges to the Rondout Creek and the 

aquifer is thickest (figs. 10 and 11).

Hydrologic Effects of 

Temporary Shutdowns

Since October 2008, the NYCDEP has shut down the 

RWB Tunnel four times: October 25–November 26, 2008; 

November 5–19, 2009; December 4–16, 2009; and January 

13–26, 2010. During each shutdown, the tunnel pressure was 

slowly reduced from about 600 ft to about 75 ft elevation over 

a period of time that ranged from 34 to 56 hours, as measured 

in a nearby tunnel shaft. The repressurization process was 

accomplished in the same manner, by increasing the pressure 

in the RWB Tunnel from about 75 ft to about 600 ft elevation, 

over a period of time that ranged from 43 to 54 hours. Six 

of the eight cycles of depressurization and subsequent 

repressurization of the tunnel took place during a precipitation 

event (rainfall). Because the two events coincided, it was 

difficult to separate natural (precipitation) from artificial 

(RWB Tunnel leakage) recharge or discharge influences on 

water levels in the bedrock and unconsolidated aquifers.

Tunnel-Leakage Influences on the 

Bedrock Aquifers

Leakage from the RWB Tunnel increased water levels 

in wells in the bedrock aquifers for a distance of more than 

7,000 ft from the tunnel. Three bedrock wells (U-1625, 

U-1653, and U-1628) were selected to illustrate the tunnelinfluence response of the bedrock aquifers to RWB Tunnel 

shutdowns in 2009 and 2010 (figs. 2 and 12).

Bedrock well U-1625 is located about 1,820 ft from 

the RWB Tunnel and is a flowing artesian private-supply 

well (figs. 2 and 12). Drawdowns in this well were minimal 

compared to those measured in other bedrock wells with 

similar pumps as a result of the high transmissivity of 

the local bedrock aquifer (fig. 12). The specific capacity 

and transmissivity at well U-1625 were estimated to 

be 4.62 gallons per minute per foot ((gal/min)/ft) and 

1,325 feet squared per day (ft2

/d), respectively. Specific 
Hydrologic Effects of Temporary Shutdowns 27

capacity and transmissivity of the bedrock at well U-1625 

were estimated using the hourly recorded water-level-elevation 

data from the digital data logger during a period that the RWB 

Tunnel was in operation under “normal,” or typical (stable) 

tunnel pressures between shutdowns. The largest drawdown 

in the dataset was selected as the maximum drawdown for 

the test. The duration of the aquifer test was assumed to 

be the 1-hour period between measurements. Because the 

rate of withdrawal from the well could not be measured, it 

was estimated to be the pump’s maximum rating of 12 gal/

min. The aquifer-test data were processed using a computer 

program (Bradbury and Rothschild, 1985) to calculate the 

transmissivity of the bedrock. Because of the uncertainties in 

pumping rates, pumping duration, and maximum drawdown, 

the calculated specific capacity and transmissivity of the well 

are considered to be estimates.

Analysis of the hydrographs recorded during the 

tunnel shutdowns indicates the bedrock aquifer in this area 

responds within about 0.5 hour of tunnel depressurization 

or repressurization (fig. 12). During the shutdowns, water 

levels decreased between 8 and 12 ft. The rapid response 

times to changes in tunnel pressure, the large changes in 

water level, and the long distance from the tunnel indicate 

that the fractures in this formation may be well connected 

with extremely high transmissivity. An interconnected 

fracture system affected by dissolution with large storage and 

transmissivity characteristics may exist locally in this aquifer.

Bedrock well U-1653 is located about 5,680 ft from 

the RWB Tunnel and was formerly an industrial-supply well 

(figs. 2 and 12). Analysis of the hydrograph from this well 

indicates that water levels decrease an average of 10 to 11 

ft during tunnel shutdowns (fig. 12). In general, the bedrock 

aquifer in this area responds to changes in RWB Tunnel 

pressure within 6 to 8 hours. Like the water-level record 

from well U-1625, the record from well U-1653 indicates the 

presence of a well-connected and highly transmissive fracture 

network 

A third bedrock well, U-1628, located 945 ft from the 

RWB Tunnel is a private-supply well (figs. 2 and 12). The 

hydrograph from well U-1628 shows pumping drawdowns of 

4 to 6 ft (fig. 12), which indicate a moderately transmissive 

fracture network. Changes in the RWB Tunnel pressure 

caused water levels in this well to decrease 5 to 6 ft during 

the shutdowns, with a tunnel-influence delay time of about 

48 hours (fig. 12). This delay time indicates that the fracture 

network in this bedrock unit is less transmissive than those in 

wells U-1625 and U-1653.

Monitoring groundwater elevations in bedrock wells 

U-1624, U-1625, U-1628, U-1629, U-1630, U-1631, U-1645, 

U-1647, U-1649, and U-1653 at hourly intervals provided 

data on the magnitude and time delay of the tunnel-leakage 

influence on water levels in the bedrock underlying the study 

area (figs. 12, 13, and 14). Analysis of water levels in the 

bedrock wells during the four tunnel shutdowns indicates 

significant decreases in water levels followed by increases 

during repressurization (fig. 12). Most of these wells were 

instrumented during the second, third, and fourth shutdowns. 

The maximum water-level changes in the bedrock aquifers 

in the study area during tunnel shutdowns were contoured 

to determine patterns within the study area (fig. 13). Waterlevel changes during the shutdowns ranged from 12 ft at well 

U-1625 to 1.5 ft at well U-1645, with well U-1629 indicating 

no measurable influence from tunnel leakage (fig. 13).

Water-level-difference contours in figure 13 indicate 

that the areas of major changes in bedrock water levels due 

to tunnel influence were on either side of an area of lowest 

changes in water levels, at wells U-1645, U-1624, and 

U-1628. This area of lowest water-level response to tunnel 

influence may coincide with the Esopus Shale (figs. 3A, 3B, 

and 13). The larger water-level responses to tunnel influence 

on either side of these wells appear to correlate with the 

presence of limestone units in contact with the shale (figs. 

3A, 3B, and 13). Water levels in well U-1629 indicated no 

tunnel-influence response although this well was among those 

closest to the RWB Tunnel. Wells U-1653 and U-1647 were 

the farthest measured wells from the RWB Tunnel (about 

5,680 and 7,100 ft, respectively), but they indicated waterlevel responses to tunnel influence (tunnel leakage) (fig. 13). 

Because no bedrock observation wells are located on the east 

side of the valley, it was not possible to determine the waterlevel responses to tunnel influence in half of the study area. 

One new private-supply bedrock well in the northeastern 

part of the study area, U-3772, was added to the monitoring 

network in November 2010, after the fourth shutdown 

(January 2010). Because no tunnel shutdowns have occurred 

since January 2010, it is unclear whether the bedrock in this 

part of the study area is influenced by leakage from the RWB 

Tunnel. Additional monitoring during shutdowns would help 

to determine whether tunnel leakage affects water levels in 

this area.

Analysis of the hydrographs from bedrock wells during 

tunnel shutdowns indicated tunnel-leakage influence delay 

times that ranged from about 0.5 to 60 hours (fig. 14). Tunnelinfluence delay times were shortest at wells U-1625 (about 

0.5 hour), U-1649 (14 hours), and U-1653 (7 hours) (fig. 14). 

Tunnel-influence delay times at most bedrock wells influenced 

by tunnel leakage ranged from 21 to 33 hours (fig. 14). The 

longest tunnel-influence delay times were not in the wells 

farthest from the tunnel, which indicates the presence of a 

complex, transmissive bedrock fracture network. Tunnelinfluence delay times were longest (48, 48, and 60 hours, 

respectively) in bedrock wells U-1628, U-1624, and U-1631 

(fig. 14). Wells U-1628 and U-1624 were among the four wells 

closest to the tunnel.

The hydrologic response of the bedrock aquifer to tunnel 

shutdowns is consistent with its preliminary characterization 

as an anisotropic aquifer with greater transmissivity along 

bedding strike than across bedding strike. The response is also 

consistent with the presence of a discrete high-transmissivity 

network, likely along fractured limestone beds that have been 

affected by dissolution (Freeze and Cherry, 1979).
28 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

298.9

01366807

285

U-1664

274.3

U-1626

ND

U-1663

274.8

U-1627

ND

U-1655

ND

U-1674

266.8

U-1635 263.7

U-1639

261.9

U-1637

264.7

U-1652

ND

U-1654

ND

U-1657

U

2

U-164

261.5

265

U-1638

U-1656

U-1642*

ND

270

290

280

?

?

?

?

Figure 10. Elevation of the water table in the unconsolidated aquifer within the study area, Town of Wawarsing, Ulster 

County, New York, March and April 2010.
Hydrologic Effects of Temporary Shutdowns 29

Figure 10. Elevation of the water table in the unconsolidated aquifer within the study area, Town of Wawarsing, Ulster 

County, New York, March and April 2010.—Continued

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

D

663

249.1

U-1640

U-1662

ND

U-4862

243.2

D

657

U-1650

261.9

U-1643

261.5

EXPLANATION

Water level-elevation in unconsolidated-aquifer wells 

and selected surface-water sites—Shows equipotential 

surface of hydraulic head. Dashed where inferred. 

Contour interval is 10 feet

Observation well—Upper number represents New York 

State well identifier. Lower number, where present, indicates 

water-table elevation in feet above NAVD 88. ND indicates 

that no data were available at time of study. Asterisk (*) 

indicates data not plotted

Surface-water site—Lower number, where present, 

indicates water-table elevation, in feet above NAVD 88.

ND indicates that no data were available at time of study

U.S. Geological Survey downstream-order identifier

New York State identifier

Areal extent of anomalously high water levels—

Perched-like conditions

U-1646

265

01366807

290

U-1674

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

280

270

270

260

260

250

240

0

?

? ? ?

?

?

?

?

?

?

?
30 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

298.3

01366807

282.7

U-1664 270.3

U-1626

270.3

U-1663

270.4

U-1627

283.2

U-1655

276.7

U-1674

264.1

U-1635

261.5

U-1639

259.4

U-1637

263

U-1652

262.2

U-1654

263.4

U-1660

261.9

U-1638

U-1656

U-1642*

262.9

260

270

280

290

290

280

270

?

?

?

Figure 11. Elevation of the water table in the unconsolidated aquifer within the study area, Town of Wawarsing, Ulster 

County, New York, November 2010.
Hydrologic Effects of Temporary Shutdowns 31

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

0.3

663

247

U-1640

U-1662

263.1

U-4862

239.5

263.4

-1660

U-1650

258.7

U-1643

ND

EXPLANATION

Water-level elevation in unconsolidated-aquifer wells 

and selected surface-water sites—Shows equipotential 

surface of hydraulic head. Dashed where inferred. 

Contour interval is 10 feet

Observation well—Upper number represents New York 

State well identifier. Lower number, where present, indicates 

water-table elevation in feet above NAVD 88. ND indicates 

that no data were available at time of study. Asterisk (*) 

indicates data not plotted

Surface-water site—Lower number indicates watertable elevation, in feet above NAVD 88

U.S. Geological Survey downstream-order identifier

New York State identifier

Areal extent of anomalously high water levels—

Perched-like conditions

U-1654

262.2

01366807

290

U-1674

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

280

270

260

250

290

240

260

250

270

280

?

?

?

?

? ? ? ? ?

?

?

?

Figure 11. Elevation of the water table in the unconsolidated aquifer within the study area, Town of Wawarsing, Ulster 

County, New York, November 2010.—Continued
32 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

A. U-1628

260

262

264

266

268

270

272

0

Precipitation, in inches

1

2

3

4

5

B. U-1625

Water level, in feet above NAVD 88

Water level, in feet above NAVD 88

262

264

266

268

270

272

274

276

0

Precipitation, in inches

1

2

3

4

5

C. U-1653

Water level, in feet above NAVD 88

Water level in tunnel, in feet above NAVD 88

Water level in tunnel, in feet above NAVD 88

Water level in tunnel, in feet above NAVD 88

256

258

260

262

264

266

268

270

0

100

200

300

400

500

600

700

0

100

200

300

400

500

600

700

0

100

200

300

400

500

600

700

Date

0

Precipitation, in inches

1

2

3

4

5

02/07/2010

10/25/2009

11/01/2009

11/08/2009

11/15/2009

11/22/2009

11/29/2009

12/06/2009

12/13/200912/20/2009

12/27/2009

01/03/2010

01/10/2010

01/17/201001/24/201001/31/2010

EXPLANATION

2 3 4

2 3 4

2 3 4

Water level

Water level in tunnel

Precipitation

2 Tunnel shutdown sequence number

Figure 12. Graphs showing the potentiometric-surface elevation in bedrock wells, the water level in the Rondout-West Branch 

Tunnel, and precipitation within the study area, Town of Wawarsing, Ulster County, New York: A, well U-1628, October 25, 2009–

February 06, 2010; B, well U-1625, October 25, 2009–February 06, 2010; and C, well U-1653, November 10, 2009–February 06, 2010. 

(Precipitation data from National Oceanic and Atmospheric Administration station in Central Park, N.Y.; tunnel water-level data 

from New York City Department of Environmental Protection; for locations, see figure 1.)
Hydrologic Effects of Temporary Shutdowns 33

Tunnel Leakage to the Unconsolidated Aquifers 

Observation and private-supply wells in the 

unconsolidated aquifers were monitored to determine 

the extent of the influence of RWB Tunnel leakage in the 

unconsolidated aquifer overlying the bedrock. The presence of 

an upward flow gradient from the underlying bedrock aquifer 

to the unconsolidated aquifer greater than that due to natural 

conditions indicates that transmissive bedrock fractures that 

crop out on the bedrock surface (beneath the unconsolidated 

aquifer) potentially can transmit water from the RWB Tunnel 

to the unconsolidated aquifer above.

If the delay between tunnel leakage and the response of 

the bedrock aquifer averages more than 20 hours, the tunnelinfluence delay time for the unconsolidated aquifer likely is 

even longer. This additional delay is due to the dispersion of 

inflow (from the underlying bedrock), which is dependent 

on the transmissivity and storativity of the unconsolidated 

aquifer, making it difficult to quantify tunnel leakage that 

has been discharged from the underlying bedrock aquifer to 

the unconsolidated aquifer. The occurrence of precipitation 

during or soon after repressurization of the RWB Tunnel is an 

obstacle to quantifying potential leakage from the tunnel to the 

unconsolidated aquifer.

Water leaking from the RWB Tunnel has been 

documented to enter the adjacent bedrock in Roseton and 

Wawarsing, N.Y. (James Canale, New York City Department 

of Environmental Protection, written commun., 2011). Data 

from this study indicate that this leakage causes water levels in 

the bedrock aquifer in Wawarsing to increase as much as 12 ft. 

Measuring the extent of tunnel leakage to the unconsolidated 

aquifer is difficult as a result of (1) the large influence of 

recharged precipitation, (2) the dispersion of tunnel-leakage 

inflow from the bedrock aquifer into the unconsolidated 

aquifer (porous media), and (3) the limited number of 

screened unconsolidated wells available in which to measure 

water levels.

The large influence of precipitation on water levels in 

the unconsolidated aquifer can be seen in the hydrograph 

from well U-1627 (fig. 15). Rain events greater than about 

1 in. cause measurable increases in the water levels in the 

unconsolidated aquifer. The hydrograph of well U-1627 

indicates this increase as an upward spike (recharge) followed 

by a slow decline (discharge) (fig. 15).

To illustrate the influence of precipitation on groundwater 

levels in the unconsolidated aquifer, a multiday storm was 

analyzed during “normal,” or typical (stable) tunnel pressures 

between shutdowns. The storm produced 2.05 in. of rainfall 

over a 3-day period from December 25 to 27, 2009 (fig. 15). 

Daily rainfall totals on December 25, 26, and 27 were 0.24, 

1.48, and 0.33 in., respectively (National Oceanic and 

Atmospheric Administration, 2010). Water levels at well 

U-1627 in the unconsolidated aquifer began to rise from 

an elevation of 271.3 ft (8.0 ft BLS) on December 27 and 

reached a peak elevation of 272.7 ft (6.6 ft BLS) on December 

28 (fig. 15). The water-table elevation rose 1.4 ft as a result 

of recharge of precipitation from the storm. Water-table 

responses to precipitation indicate rapid changes in water 

levels in parts of the unconsolidated aquifer within the study 

area. When combined with localized constrained (shallow 

permeable layers underlain by clay) aquifer effects, seasonally 

large amounts of precipitation can cause large increases in 

groundwater levels.

To properly separate the effects of recharging 

precipitation from tunnel-leakage inflows (from the underlying 

bedrock aquifer) in the unconsolidated aquifer requires tunnel 

depressurizations and repressurizations to occur during dry 

periods. During the second tunnel shutdown (November 

5–12, 2009), depressurization did occur during a dry period. 

The weather was also dry during the repressurization of the 

third shutdown (December 4–16, 2009). These events were 

used to determine the influences of tunnel leakage on the 

unconsolidated aquifer.

Unconsolidated-aquifer well U-1627 is located 1,460 ft 

from the RWB Tunnel (fig. 2). The well is a limited-use 

private-supply well that was dug in the shallow part of the 

aquifer. The hydrograph of water levels in well U-1627 and 

the water levels in the RWB Tunnel during the last three of the 

four tunnel shutdowns investigated in this study are shown in 

figure 15.

The deflection of the hydrograph at the beginning of 

shutdowns 2 and 4 and the continued drop in water levels 

during the shutdowns indicate the influence of leakage 

from the tunnel on the unconsolidated aquifer in this area. 

During shutdown 3, precipitation occurred during the 

depressurization, in the middle, and toward the end of the 

shutdown (fig. 15). A spike of precipitation-induced recharge 

can be seen in the middle of shutdown 3; however, the 

weather was dry during the repressurization in shutdown 3, 

and a distinct increase in water levels was detected (fig. 15). 

The hydrograph shapes are distinctively different during 

recessional discharge after precipitation than during tunnel 

depressurization (fig. 15). Similar effects were observed at 

unconsolidated-aquifer well U-1626, although the amplitude 

was much smaller because the well is shallower than well 

U-1627 and the depth to bedrock is greater (about 50 to 60 ft 

BLS) (fig. 2).

To determine the effect of the inflows from the RWB 

Tunnel into the unconsolidated aquifer in areas with greater 

depths to bedrock, the USGS drilled a deep and a shallow 

unconsolidated-aquifer observation-well doublet (U-1637 and 

U-1641) in the center of the valley (fig. 2). An unpublished 

USGS seismic survey completed in 2008-09 indicated a depth 

to bedrock of about 310 ft at these wells. Well U-1641 was 

drilled to a depth of 134 ft BLS and U-1637 to a depth of 

27 ft BLS. A hydrograph of well U-1641 indicates a decrease 

in water levels of 2 to 2.5 ft during each of the last three 

shutdowns with clearly defined troughs similar to those seen in 

bedrock hydrographs (figs. 12 and 15). Tunnel-influence delay 

time was only about 18 hours, indicating that the bedrock, 

which is about 170 ft deeper than well U-1641, probably 

contains highly transmissive fractures or features that respond 
34 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

ND

U-1658

ND

U-1661

ND

U-1644

5

U-1624

9

U-1630

ND ND

U-1636 U-1648

9

U-1649

12

U-1625

5.5

U-1628

1.5

U-1645

0

U-1629

10*

U-1651

5

0

10

?

?

?

?

10

5

?

10

Figure 13. Maximum water-level response to influence of tunnel leakage on the bedrock aquifer within the study area, 

Town of Wawarsing, Ulster County, New York, 2009–10.
Hydrologic Effects of Temporary Shutdowns 35

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

5

624

ND

U-3772

10

U-1647

9*

U-1631

9

U-1630

10.5

U-1653

Maximum-tunnel leakage influence in bedrock 

wells—Shows lines of equal tunnel influence. 

Dashed where inferred. Hachures indicate depression. 

Contour interval is 5 feet

Observation well—Upper number represents New York

State well identifier. Lower number, where present, 

indicates tunnel-leakage influence, in feet. ND indicates 

that no data were available at time of study.

Asterisk (*) indicates estimated value

Production well—Upper number represents New York 

State well identifier. Lower number, where present, 

indicates tunnel-leakage influence, in feet

EXPLANATION

U-1647

10

U-1629

0

10

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

5

0

?

?

10

?

?

10

Figure 13. Maximum water-level response to influence of tunnel leakage on the bedrock aquifer within the study area, 

Town of Wawarsing, Ulster County, New York, 2009–10. —Continued
36 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

R

PORT

BEN

ROAD

STATE

ROUTE

20 9

0.5

14

NA

48

25

U-1636

U-1624

U-1625

U-1629

U-1658

U-1661

U-1648

U-1644

U-1645

U-1649

U-1651

ND

ND

ND

ND

ND ND

2

48

U-1

U-1628

Figure 14. Tunnel-leakage influence delay time on water levels in bedrock wells within the study area, Town of Wawarsing, 

Ulster County, New York, 2009–2010.
Hydrologic Effects of Temporary Shutdowns 37

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

Observation well—Upper number represents New York 

State well identifier. Lower number, where present, indicates 

tunnel-influence delay time in hours. NA indicates that 

water levels in well are unaffected by tunnel influence. 

ND indicates that no data were available at time of study

Production well—Upper number represents New York 

State well identifier. Lower number, where present, indicates 

tunnel-influence delay time in hours. NA indicates that

water levels in well are unaffected by tunnel influence

Tunnel-influence delay time, in hours

EXPLANATION

U-1653

7

U-1629

NA

No data

0–20

21–40

41–60

Not affected

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

ND

60

24

7

33

U-1647

U-1630

U-3772

U-1653

U-1631

Figure 14. Tunnel-leakage influence delay time on water levels in bedrock wells within the study area, Town of Wawarsing, 

Ulster County, New York, 2009–2010.—Continued
38 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

A. U-1627

256

258

260

262

264

266

268

0

Precipitation, in inches

1

2

3

4

5

B. U-1637

Water level, in feet above NAVD 88

Water level, in feet above NAVD 88

264

266

268

270

272

274

276

278

0

Precipitation, in inches

1

2

3

4

5

C. U-1641

Water level, in feet above NAVD 88

Water level in tunnel, in feet above NAVD 88

Water level in tunnel, in feet above NAVD 88

Water level in tunnel, in feet above NAVD 88

256

258

260

262

264

266

268

270

0

100

200

300

400

500

600

700

0

100

200

300

400

500

600

700

0

100

200

300

400

500

600

700

Date

0

Precipitation, in inches

1

2

3

4

5

EXPLANATION

02/07/2010

10/25/2009

11/01/2009

11/08/2009

11/15/2009

11/22/2009

11/29/2009

12/06/2009

12/13/200912/20/2009

12/27/2009

01/03/2010

01/10/2010

01/17/201001/24/201001/31/2010

2 3 4

2 3 4

2 3 4

Water level

Water level in tunnel

Precipitation

2 Tunnel shutdown sequence number

Storm—December 25–27, 2009

Figure 15. Graphs showing the water-table elevation in unconsolidated-aquifer wells, tunnel water level, and precipitation 

data within the study area, Town of Wawarsing, Ulster County, New York: A, well U-1627, October 25, 2009–February 

06, 2010; B, well U-1637, January 14, 2010–February 06, 2010; and C, well U-1641, October 25, 2009–February 06, 2010. 

(Precipitation data from National Oceanic and Atmospheric Administration station in Central Park, N.Y.; tunnel water-level 

data from New York City Department of Environmental Protection; for locations, see figure 1.)
Hydrologic Effects of Temporary Shutdowns 39

quickly to changes in tunnel pressure (fig. 15). A bedrock 

observation well at this location was not available to verify 

this hypothesis. Small daily increases and decreases in the 

water levels in wells U-1641 and U-1637 over several hours 

are caused by the nearby pumping of production wells at the 

Eastern/Ulster Correctional Facility (U-1670 and U-1673) 

(figs. 2 and 15).

In contrast to well U-1641, well U-1637, at the 

same location, was screened in a shallower part of the 

unconsolidated aquifer (figs. 2 and 15). The hydrograph of 

well U-1637 begins during the depressurization stage of 

the fourth and last tunnel shutdown on January 15, 2010 

(fig. 15). The shallower part of the unconsolidated aquifer 

shows a smaller water-level response to tunnel influence than 

the deeper part (fig. 15). The fourth RWB Tunnel shutdown 

lowered the water table 0.8 ft. The shallower part of the 

aquifer responded later (longer delay time) and with a smaller 

water-level response to tunnel influence than the deeper 

portion, reflecting the dispersion in the unconsolidated aquifer 

(fig. 15).

A contour map of the maximum measured influence 

of leakage from the RWB Tunnel into the unconsolidated 

aquifer is shown in figure 16. The aquifer appears to dissipate 

(disperse) the transmitted leakage or pressure wave from the 

underlying bedrock to a larger area with small amplitudes in 

the unconsolidated aquifer. Influences of the RWB Tunnel 

shutdowns were detected in unconsolidated-aquifer wells 

U-1626, U-1627, U-1637, U-1638, U-1641, and U-1650 

(fig. 16).

No measurable water-level response to RWB 

Tunnel shutdowns were detected in digital recorders at 

unconsolidated-aquifer wells U-1640, U-1642, U-1652, 

U-4862, and USGS lake-level gage 01366807 (fig. 2). These 

wells are screened at various depths and are located in separate 

areas of the study area. This absence of response indicates 

that the influences from tunnel leakage occur in isolated 

locations in the study area; however, the absence of wells in 

the eastern part of the area limits the ability to determine the 

influences from tunnel leakage in half of the study area. New 

observation-well drilling and monitoring during future tunnel 

shutdowns would provide valuable information about this part 

of the study area.

Analysis of digitally and manually obtained water 

levels in the unconsolidated-aquifer wells during the four 

tunnel shutdowns indicates measurable decreases in the 

water table during depressurizations, followed by increases 

during repressurizations (figs. 15 and 16). Precipitation has a 

large influence on water levels in the unconsolidated aquifer, 

and nearly every tunnel shutdown began and ended during 

a precipitation event (figs. 12 and 15). Tunnel shutdown 3 

offered better conditions for assessing the influence of tunnel 

leakage on groundwater levels than did the other tunnel 

shutdowns. The maximum changes in water levels in the 

unconsolidated aquifer ranged from 0.1 ft at well U-1650 to 

2.5 ft at well U-1641 (fig. 16); however, it is estimated that 

inflows of tunnel leakage caused an increase of 0.1 to 0.5 ft 

in water levels in the unconsolidated aquifer in the vicinity 

of wells U-1627 and U-1626 (fig. 16). The water-leveldifference contours in figure 16 correlate with recharge to the 

unconsolidated aquifer from the underlying bedrock resulting 

from tunnel leakage (fig. 13). The changes were greatest 

along Port Ben Road (wells U-1641 and U-1637), where 

USGS seismic surveys and drilling indicated greater depths 

to bedrock (figs. 15 and 16). The location of wells U-1637 

and U-1641 is adjacent to the section of the RWB Tunnel that 

required the steel interliner due to poor bedrock quality and 

large groundwater inflows (more than 9,000 gal/min) during 

construction (figs. 2 and 3A).

The tunnel-influence delay time in the unconsolidated 

aquifer ranged from about 18 hours at wells U-1627 and 

U-1641 to 54 hours at well U-1650 (fig. 17). Generally, 

the tunnel-influence delay time was shortest in the wells 

displaying the largest water-level responses to tunnel influence 

(largest amplitude) and longest in the wells showing the 

smallest water-level responses to tunnel influence (smallest 

amplitude). Water-level amplitudes may be underestimated at 

some of the unconsolidated-aquifer wells that were dug wells 

because these wells may be less effectively connected with the 

aquifer than screened wells. Shallow wells in areas of thick 

overburden may be a poor indicator of possible influences 

from tunnel leakage because of the dispersion effect. Several 

of the unconsolidated-aquifer observation wells that indicated 

larger water-level response to tunnel influence were screened 

deeper in the aquifer.

In general, the largest influence on water levels regionally 

was precipitation, but pumpage and (or) tunnel leakage had 

large influences in some wells locally. In the spring, when 

water levels are highest, the water table is in direct contact 

with some basements locally, causing basement flooding. 

During the summer and late fall, water levels decrease an 

average of 5 ft and are below most basements, resulting in 

a lack of basement flooding. In the unconsolidated aquifer, 

elevated water levels due to tunnel-leakage influence, when 

combined with seasonally high water levels, can exacerbate or 

create localized basement flooding (fig. 7).

Groundwater Temperature

The digital data loggers installed in wells also record 

water temperature. Bedrock groundwater temperature within 

the study area indicates areas of lower temperature that 

correlate with areas of short tunnel-influence delay time and 

large water-level changes during tunnel shutdowns (figs. 13, 

14, and 18). During a synoptic water-level measurement in 

August 2010, groundwater temperature in the bedrock wells 

was measured manually using a submersible probe. When 

depths to groundwater exceeded 25 ft, temperature data were 

collected using digital data loggers. Bedrock groundwater 

temperature ranged from 50 to 56 degrees Fahrenheit (°F) 

throughout the study area (fig. 18). Water in the Rondout 

Reservoir downtake (primary reservoir inflow to RWB Tunnel) 
40 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

NA

01366807

ND

U-1664

0.1*

U-1626

ND

U-1663

0.5*

U-1627

ND

U-1655

ND

U-1635

ND

U-1639

2.5

U-1641

NA

U-1652

ND

U-1654

ND

U-1660

U-1650

0.1

0.3

U-1638

NA

U-1642

ND

U-1674

2.5

2.0

0.5

1.5

1.0

0.5

?

?

Figure 16. Maximum water-level response to influence of tunnel leakage on the unconsolidated aquifer within the study 

area, Town of Wawarsing, Ulster County, New York.
Hydrologic Effects of Temporary Shutdowns 41

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

6

3

NA

U-1640

U-1662

ND

U-4862

NA

D

654

0

U-1650

0.1

U-1643

ND

EXPLANATION

Maximum response to tunnel shutdown in unconsolidatedaquifer wells and at selected surface-water sites due to 

tunnel influence—Shows lines of equal tunnel influence. 

Dashed where inferred. Contour interval is 0.5 feet

Observation well—Upper number represents New York 

State well identifier. Lower number, where present, 

indicates tunnel-leakage influence in feet. NA indicates 

that water levels in the well are unaffected by tunnel 

influence. ND indicates that no data were available 

at time of study. Asterisk (*) indicates estimated value

Surface-water site—NA indicates that water levels are 

unaffected by tunnel influence. ND indicates that no data 

were available at time of study

U.S. Geological Survey downstream-order identifier

New York State identifier

U-1654

ND

01366807

2.0

U-1674

Areal extent of anomalously high water levels—

Perched-like conditions

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

Figure 16. Maximum water-level response to influence of tunnel leakage on the unconsolidated aquifer within the 

study area, Town of Wawarsing, Ulster County, New York.—Continued
42 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

NA

01366807

ND

U-1664

18

U-1626

ND

U-1663

18

U-1627 

ND

U-1655

ND

U-1674

ND

U-1635

ND

U-1639

18

U-1641

NA

U-1652

ND

U-1654

ND

U-1660

U-1650

54

U

N

ND

U-1638

NA

U-1642 

40

20

?

?

?

?

?

?

Figure 17. Tunnel-leakage influence delay time on water levels in unconsolidated-aquifer wells and surface-water sites 

within the study area, Town of Wawarsing, Ulster County, New York, 2009–10.
Hydrologic Effects of Temporary Shutdowns 43

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

6

63

ND

U-1640

U-1662

ND

U-4862

NA

54

U-1650

54

U-1643

ND

Line of equal tunnel-influence delay time in 

unconsolidated-aquifer wells and at selected 

surface-water sites—Dashed where inferred. 

Hachures indicate depression. Contour interval 

is 20 hours

Observation well—Upper number represents New York 

State well identifier. Lower number, where present, 

indicates tunnel-influence delay time, in hours. 

NA indicates that water levels in well are unaffected 

by tunnel influence. ND indicates that no data were 

available at time of study

Surface-water site—NA indicates that water levels are 

unaffected by tunnel influence. ND indicates that no data 

were available at time of study

U.S. Geological Survey downstream-order identifier

New York State identifier

EXPLANATION

U-1650

54

20

01366807

U-1674

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

?

?

Figure 17. Tunnel-leakage influence delay time on water levels in unconsolidated-aquifer wells and surface-water sites 

within the study area, Town of Wawarsing, Ulster County, New York, 2009–10.—Continued
44 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

Base from U.S. Geological Survey Digital Data 1:100,000 series

Lambert Conformal Conic Projection

North American Datum of 1983

H A M L E T B O U N D A R Y

NAPANOCH

Lippman

 Park Lake

Honk Lake

ELLENVILLE

74°22' 

41°

46'

41°

44'

PORT

BEN

ROAD

STATE

ROUTE

20 9

?

?

?

54

53

?

?

52

?

?

??

?

52

?

51 50

? 53

ND

52

53

52

ND

U-1636

U-1629

U-1648

U-1645

U-1649

50

U-1625

53.8

54

U-1658

U-1661

51

52

U-1624

U-1628

U-1651

52

ND

U-1644

Figure 18. Groundwater temperature in bedrock wells within the study area, Town of Wawarsing, Ulster County, New 

York, August 2010.
Hydrologic Effects of Temporary Shutdowns 45

RONDOUT - WEST BRANCH TUNNEL

KERHONKSON

74°18'

Rondout

Cre e k

ROUTE 44

FOORDMORE RO A D

EXPLANATION

Line of equal temperature—Shows groundwater 

temperature from bedrock wells. Dashed where 

inferred. Hachures indicate depression. Contour 

interval is 1 degree Fahrenheit

Observation well—Upper number represents New 

York State well identifier. Lower number, where 

present, indicates groundwater temperature, in 

degrees Fahrenheit. ND indicates that no data 

were available at time of study

U-1647

56

55

0 0.25 0.5 1 MILE

0 0.25 0.5 1 KILOMETER

56

55

54

53

52

51

?

?

? ? ? ?

?

?

?

?

?

51 50

6

9

51

U-1647

U-3772

U-1653

53 56

24

28

50 

53

U-1630

U-1631

Figure 18. Groundwater temperature in bedrock wells within the study area, Town of Wawarsing, Ulster County, New York, 

August 2010.—Continued
46 Effects of Shutdowns of the Rondout–West Branch Water Tunnel on the Groundwater-Flow System in Wawarsing, New York

was sampled five times during the study and its geochemistry 

was determined; the temperatures of these samples averaged 

51.3°F (RWB Tunnel water temperature). Groundwater 

temperatures in wells U-1625, U-1630, U-1649, and U-1651 

were the lowest among those in the monitored bedrock wells 

(fig. 18). The temperature anomalies delineated on the bedrock 

water-temperature map (fig. 18) are consistent with the 

leakage of colder tunnel water into the surrounding fracturedbedrock groundwater-flow system along highly transmissive 

sections. Bedrock wells with the coldest groundwater 

temperatures were the same wells that have the largest waterlevel changes and shortest delay times due to tunnel influences 

(figs. 13, 14, and 18). The low temperatures (51°F) measured 

at well U-3772 indicate that tunnel leakage may occur in other 

parts of the study area where there are no observation wells. 

Additional work in this part of the study area would provide 

information on the extent of RWB Tunnel leakage.

Analysis of groundwater temperatures in shallow 

unconsolidated-aquifer wells indicates no clear patterns. The 

variable depth, construction characteristics of the wells, and 

the close proximity of groundwater in the unconsolidated 

aquifer to the atmosphere produce large variations in 

temperature that would tend to obscure influences of 

tunnel leakage.

Summary

Leakage from the Rondout-West Branch (RWB) 

Water Tunnel and above-normal precipitation have been 

suspected of causing elevated groundwater levels and 

basement flooding in the Town of Wawarsing, New York. The 

hydrology of a 12-square-mile study area within the Town 

of Wawarsing was studied during 2008-10. A network of 

41 wells (23 unconsolidated-aquifer and 18 bedrock wells) 

and 2 surface-water sites was used to monitor the hydrologic 

effects of four RWB Tunnel shutdowns. Inflows from the 

fractured bedrock that ranged from less than 1 to more than 

9,000 gallons per minute (gal/min) were documented during 

construction of the 13.5-foot (ft)-diameter RWB Water Tunnel 

through the sedimentary-rock sequence 710 ft beneath the 

study-area valley.

The study area contains unconsolidated overburden 

aquifers and bedrock aquifers. The groundwater in the 

unconsolidated aquifer flows from the surrounding hills 

east and west of the valley and from the southwest of the 

valley toward the central and ultimately northeastern part 

of the valley. The groundwater in the bedrock aquifer flows 

through a network of interconnected bedrock fractures from 

higher elevations in the surrounding hills toward the center of 

the valley.

Water levels indicate that groundwater flows upward 

from the bedrock to the unconsolidated aquifer under natural 

conditions with a head difference of 1.8 ft. However, most 

of the bedrock wells had upward flow gradients 1.6 to 

5.4 times the normal gradient. This represents a significant 

flow-gradient potential of RWB Tunnel leakage to the 

overlying unconsolidated aquifer. In general, water levels in 

the unconsolidated and bedrock aquifers are highest in two 

time periods—March, April, and May, and December and 

January. Water levels are lowest during August, September, 

and October. One area of anomalously high groundwater 

levels (perched-like conditions) was observed in the vicinity 

of well U-1642. The highest vertical gradient observed in 

any unconsolidated-aquifer well doublet was measured at 

wells U-1642 and U-1656 as a result of a large mound of clay 

underlying a hilly deltaic deposit.

Since 2002, annual precipitation in the region has 

exceeded the long-term mean of the 141-year record in Central 

Park, N.Y. This unusually high precipitation causes increased 

groundwater levels and contributes to surface flooding when 

the rate of precipitation exceeds the rate at which water can 

drain away from roadways or infiltrate into (recharge) the 

surficial deposits. Water levels in the unconsolidated and 

bedrock aquifers varied seasonally as a result of the effects 

of precipitation, evapotranspiration, and pumpage. In the 

unconsolidated aquifer, seasonal effects caused water-level 

differences to range seasonally from 3.5 ft (U-1652) to 6.5 ft 

(U-1626). On average, the seasonal water-level difference 

in the unconsolidated aquifer is 5 ft. Seasonal water-level 

differences in the bedrock aquifer ranged from 1.5 ft (U-3772) 

to 9.5 ft (U-1645). On average, the seasonal water-level 

difference in the bedrock aquifer is 5.3 ft. Seasonal water-level 

differences in the bedrock aquifer were larger than those in the 

unconsolidated aquifer.

During the exploration and construction of the Catskill 

Aqueduct 10 miles north of the RWB Tunnel, caves, cavities, 

cavernous structures, faults, fractures, and solution joints were 

encountered in the limestone bedrock. The same bedrock 

units were found during the exploration and construction of 

the RWB Tunnel. Groundwater inflows from the limestone 

exceeded 9,000 gal/min in places during tunnel construction. 

Grouting proved unsuccessful in the Manlius Limestone. 

Solution cavities, decayed or leached limestone, fractures, 

fault crush zones, and prominent solution features were 

encountered during the construction of the RWB Tunnel.

RWB Tunnel leakage caused water levels in some 

bedrock wells to increase. During tunnel shutdowns, water 

levels in the bedrock decreased within 0.5 to 60 hours. 

Bedrock water levels declined from 1.5 to 12 ft during tunnel 

shutdowns at wells up to 7,000 ft from the tunnel. Tunnelinfluence delay times at most affected bedrock wells ranged 

from 21 to 33 hours. Water levels in some unconsolidatedaquifer wells responded to tunnel leakage from the underlying 

bedrock. Maximum water-level changes in the unconsolidated 

aquifer due to tunnel leakage ranged from 0.1 to 2.5 ft. Areas 

in the unconsolidated aquifer that were influenced by tunnel 

leakage correlated with areas of bedrock wells influenced by 

tunnel leakage.

Bedrock groundwater temperature during the synoptic 

measurements made in August 2010 ranged from 50 to 
References Cited 47

56 degrees °F throughout the study area. The Rondout 

Reservoir downtake temperatures average 51.3°F. Bedrock 

wells with the coldest groundwater temperatures were the 

same wells that have the largest water-level changes and 

shortest delay times due to tunnel influences.

Given the historical descriptions of solution features, 

cavities, and fault crush zones, leakage from the RWB Tunnel 

has the potential to reach highly transmissive areas in the 

bedrock sequence and to cause the rapid change in water 

levels in the bedrock aquifer up to 7,000 ft from the tunnel. 

The concept of a highly transmissive, interconnected 

network of fractures within the bedrock is supported by 

the bedrock water-level and temperature data collected. In 

general, the largest influence on water levels regionally was 

precipitation, but pumpage and (or) tunnel leakage were 

large influences in some wells locally. Precipitation and 

other seasonal effects have the largest influence on water 

levels in the unconsolidated aquifer. Tunnel leakage from 

the bedrock was measurable in the unconsolidated aquifer. 

In the unconsolidated aquifer, elevated water levels due to 

tunnel-leakage influence, when combined with seasonally 

high water levels, can exacerbate or create localized basement 

flooding. A larger network of wells in both the bedrock and 

unconsolidated aquifers would provide additional data that 

could increase understanding of this complex system, and 

would also allow for verification of areas of tunnel leakage 

and the extent of hydrogeologic deposits. Additional data 

are needed about the bedrock fracture patterns, bedrock 

fracture transmissivity, solution-cavity locations, and water 

levels in areas of the valley where observation wells are 

currently lacking.

Acknowledgments

The authors thank the residents of the Town of 

Wawarsing for providing access to their properties and 

private-supply wells during this study. Without their 

assistance, the groundwater data collected for this study would 

have been limited to data from the 14 U.S. Geological Survey 

(USGS) unconsolidated-aquifer wells. We also thank Ira 

Stern and James Canale of the New York City Department of 

Environmental Protection for their technical support. Thanks 

are extended to Town of Wawarsing Supervisor Leonard M. 

Distel for his technical assistance and access to town property. 

The authors thank James Johnson and Eric Greppo of the New 

York State Department of Corrections for providing access 

to observation wells at the Eastern New York Correctional 

Facility in Napanoch, N.Y. Malcolm Pirnie, Inc., shared 

their research on the monitoring of springs within the study 

area. Special thanks are extended to Paul Heisig and Richard 

Reynolds of the USGS for their help in establishing part of the 

groundwater network and for their technical support. Thanks 

are also extended to Jason Finkelstein of the USGS for his 

geographic information system (GIS) support.

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For additional information write to: 

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U.S. Geological Survey 

425 Jordan Road

Troy, NY 12180

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Stumm and others—Effects of Shutdowns of the Rondout-West Branch Water Tunnel on Groundwater Flow in Wawarsing, New York—Scientific Investigations Report 2012–5015

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