Delineation of Areas Contributing 

Water to the Dry Brook Public-Supply 

Well, South Hadley, Massachusetts

By Stephen P. Garabedian and Janet Radway Stone

In cooperation with the

Drinking Water Program, Massachusetts Department of Environmental Protection

Water-Resources Investigations Report 03-4320

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested Citation:

Garabedian, S.P., and Stone, J.R., 2004, Delineation of areas contributing water to the Dry Brook public-supply well, 

South Hadley, Massachusetts: U.S. Geological Survey Water-Resources Investigations Report 03-4320, 52 p.

Cover photo: View of the Holyoke Range from Dry Brook Hill, South Hadley, Massachusetts. Photograph by 

Gene W. Parker, U.S. Geological Survey.

For additional information write to:

Chief, Massachusetts–Rhode Island District

U.S. Geological Survey

10 Bearfoot Road

Northborough, MA 01532

or visit our Web site at

http://ma.water.usgs.gov
 iii

Contents

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

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Description of Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Physiography and Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Bedrock Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Surficial Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Glacial Till. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Glacial Stratified Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Coarse-Grained Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Fine-Grained Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Streamflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Ground-Water Levels and Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Ground-Water Recharge and Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Aquifer Responses to Pumping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Simulation of Ground-Water Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Model Design and Boundary Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Hydraulic Properties and Recharge Rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Pumping Stresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Model Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Delineation of Areas Contributing Water to Dry Brook Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Sensitivity and Uncertainty Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Transient Analysis and Contributing Watersheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Suggestions for Future Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Figures

1–2. Maps showing:

1. Location of the Dry Brook study area, Hadley, Holyoke, and South Hadley, 

Massachusetts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2. Wells used in the study of the Dry Brook area, Hadley, Holyoke, and South Hadley. . . . . . . . . . . .4

3. Surficial materials map and locations of cross sections shown in figure 4, Dry Brook

study area, Hadley, Holyoke, and South Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4. Geologic cross sections, Dry Brook study area, Holyoke and South Hadley . . . . . . . . . . . . . . . . . . . . . . . 12
iv 

5. Map showing the altitude of the bedrock surface in the Dry Brook study area,

Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6. Photographs showing examples of glacial deposits in the Dry Brook study area, Hadley, 

Holyoke, and South Hadley: A, gravel and sand beds in an ice-marginal delta; B, flat-lying 

gravel topset beds overlying dipping sandy foreset beds in the Pearl City delta, South 

Hadley; C, glacial Lake Hitchcock varved silt (darker layers) and clay (lighter layers), 

and (D) typical red till in the Hartford Basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

7–8. Maps showing:

7. Locations of streamflow measurements for Elmer and Dry Brooks, Dry Brook study 

area, Hadley, Holyoke, and South Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8. Ground-water levels measured in the Dry Brook study area on November 16, 2000, 

Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

9–10. Graphs showing:

9. Ground-water levels measured in well GKW-68 in Granby . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

10. Ground-water levels measured in well SUW-81 compared to the stage of the 

Connecticut River at Montague. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

11. Map showing observation-well network for a 10-day aquifer test of Dry Brook well

(September 24, 1998–October 5, 1998), South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

12–14. Graphs showing:

12. Drawdowns in observation wells during the Dry Brook well 10-day aquifer test 

(September 24, 1998–October 5, 1998), South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

13. Drawdowns in observation wells during the Dry Brook well 10-day aquifer test 

(September 24, 1998–October 5, 1998) using relative time scale, South Hadley. . . . . . . . . . . . . . . 27

14. Connecticut River stage compared to water levels measured in observation 

wells SUW-84 and SUW- 51 during the Dry Brook well 10-day aquifer test,

South Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

15. Map showing the lateral extent of and boundary conditions for the MODFLOW model 

grid in the Dry Brook study area, Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

16. Geologic cross sections showing the vertical distribution of MODFLOW model layers in 

the Dry Brook study area, Holyoke and South Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

17. Map and graphs showing model-calibration results comparing observed and simulated 

drawdown at observation wells during the Dry Brook well 10-day aquifer test, South 

Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

18. Graph showing observed and simulated drawdowns at the end of the Dry Brook well 

10-day aquifer test in relation to radial distance from the well, South Hadley. . . . . . . . . . . . . . . . . . . . . . . 36

19–23. Maps showing:

19. Steady-state simulated water-level contours for layers 3 and 4 at a pumping rate 

of 40.0 cubic feet per minute in the Dry Brook study area, Hadley, Holyoke, and 

South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

20. Extent of the simulated area contributing water to the Dry Brook well at pumping 

rates of A, 40.0; and B, 122.2 cubic feet per minute, Hadley, Holyoke, and South 

Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

21. Sensitivity to various parameters of the simulated area contributing water 

to the Dry Brook well at a pumping rate of 122.2 cubic feet per minute for A, cases B 

and C; and B, cases D–H, Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

22. Simulated ground-water-level contours for layers 3 and 4 at a pumping rate 

of 122.2 cubic feet per minute after a transient, 180-day period of no recharge

and associated zone of ground-water flow towards the Dry Brook well,

Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
 v

23. Zone of contribution and associated watershed areas contributing water

to the Dry Brook well at a pumping rate of 122.2 cubic feet per minute,

Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Tables

1. Records of selected wells and test borings in the Dry Brook study area, Hadley, 

Holyoke, and South Hadley, Massachusetts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

2. Streamflow measurements for Elmer and Dry Brooks, South Hadley, September 8, 2000. . . . . . . . . . 20

3. Manual ground-water-level measurements in Dry Brook study area, South Hadley. . . . . . . . . . . . . . . 21

4. Aquifer properties and recharge rates for the Dry Brook study area, Hadley, Holyoke, 

and South Hadley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5. Comparison of observed to simulated drawdowns at the end of the 10-day Dry Brook 

well aquifer test (September 25, 1998–October 5, 1998), South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

6. Comparison of observed to steady-state simulated ground-water levels under an 

average pumping rate of 40.0 cubic feet per minute, Dry Brook study area, 

South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

7. Comparison of steady-state model-simulated water budgets under average and 

the Massachusetts Department of Environmental Protection’s approved-yield 

pumping rates, and various model-parameter test simulations for the Dry Brook 

study area, Hadley, Holyoke, and South Hadley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

CONVERSION FACTORS, VERTICAL DATUM, AND 

HORIZONTAL DATUM

Multiply By To obtain

inch (in.) 2.540 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square foot (ft2) 0.09290 square meter (m2)

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per minute (ft3/min) 0.02832 cubic meter per minute (m3/min)

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

inch per year (in/yr) 2.540 centimeter per year (cm/yr)

foot per minute (ft/min) 0.3048 meter per minute (m/min)

foot squared per minute (ft2/min) 0.09290 meter squared per minute (m2/min)

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD27).

Delineation of Areas Contributing 

Water to the Dry Brook Public-Supply 

Well, South Hadley, Massachusetts

By Stephen P. Garabedian and Janet Radway Stone

Abstract

Areas contributing water to the Dry Brook public-supply 

well in South Hadley, Massachusetts, were delineated with a 

numerical ground-water-flow model that is based on geologic 

and hydrologic information for the confined sand and gravel 

aquifer pumped by the supply well. The study area is along the 

Connecticut River in central Massachusetts, about 12 miles 

north of Springfield, Massachusetts. Geologic units in the study 

area consist of Mesozoic-aged sedimentary and igneous 

bedrock, late-Pleistocene glaciolacustrine sediments, and recent 

alluvial deposits of the Connecticut River flood plain. Dry 

Brook Hill, immediately south of the supply well, is a large 

subaqueous lacustrine fan and delta formed during the last 

glacial retreat by sediment deposition into glacial Lake 

Hitchcock from a meltwater tunnel that was likely near where 

the Connecticut River cuts through the Holyoke Range. The 

sediments that compose the aquifer grade from very coarse sand 

and gravel along the northern flank of the hill, to medium sands 

in the body of the hill, and to finer-grained sediments along the 

southern flank of the hill. The interbedded and overlapping finegrained lacustrine sediments associated with Dry Brook Hill 

include varved silt and clay deposits. These fine-grained 

sediments form a confining bed above the coarse-grained 

aquifer at the supply well and partially extend under the 

Connecticut River adjacent to the supply well.

Ground-water flow in the aquifer supplying water to Dry 

Brook well was simulated with the U.S. Geological Survey 

ground-water-flow modeling code MODFLOW. The Dry 

Brook aquifer model was calibrated to drawdown data collected 

from 8 observation wells during an aquifer test conducted by 

pumping the supply well for 10 days at a rate of 122.2 cubic feet 

per minute (ft3

/min; 914 gallons per minute) and to water levels 

collected from observation wells across the study area. 

Generally, the largest hydraulic conductivity values used in the 

model were in the sand and gravel aquifer near the Dry Brook 

well, which is consistent with the geologic information. Results 

of aquifer-test simulation indicated that spatially variable 

aquifer hydraulic properties and boundary conditions affected 

heads and ground-water flow near the well. A comparison and 

analysis of water-level fluctuations in study area wells to 

fluctuations in the Connecticut River indicated a hydraulic 

connection of the aquifer with the river, which is also consistent 

with geologic information. Simulated ground-water levels 

indicated that most ground water in the study area flowed 

toward and discharged to the Connecticut River and the Dry 

Brook well. Small amounts of ground water also discharged to 

smaller streams (Dry Brook and Bachelor Brook) in the study 

area.

Areas contributing water to the well were delineated 

with the MODPATH particle-tracking routine. Results of the 

contributing-area analysis indicated that the greatest sources of 

water to the well were recharge in the Dry Brook Hill area and 

infiltration of Connecticut River water in an area beyond the 

extent of the confining bed where the aquifer is in hydraulic 

connection with the river. The amount of water entering the Dry 

Brook well from recharge dominated at a lower pumping rate 

(40.0 ft3/min); about 90 percent of the pumped water originated 

from recharge and boundary flow, and infiltration from the 

Connecticut River supplied the remaining 10 percent. At a high 

pumping rate (122.2 ft3/min), however, about half of the water 

pumped from the Dry Brook well originated from recharge 

and boundary flow (49 percent), and half originated from 

infiltration of water from the Connecticut River (51 percent).

Results of a sensitivity analysis of the extent of areas 

contributing water to the Dry Brook well when pumped at 

122.2 ft3/min indicated that the size of these areas did not 

substantially change when aquifer properties were varied. In 

contrast, however, the size of these areas changed most when 

the recharge rate was modified. When the recharge rate was 

decreased by 25 percent, the extent of the area increased by 

about 200 feet farther to the south and east across Dry Brook 

Hill. When recharge was increased by 25 percent, the extent of 

the area decreased by about 200 feet on the south and east sides 

of Dry Brook Hill. The flow contribution from the Connecticut 

River increased to 60 percent of the total pumpage when the 

recharge was decreased by 25 percent, as compared to 43 

percent of the total pumpage when recharge was increased by 

25 percent. These results indicated Dry Brook Hill is important 

to the protection of the water quality in the Dry Brook well 
2 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

because this area contributes water under a number of simulated 

conditions, and is potentially vulnerable to contamination 

because of its permeable sandy soils and aquifer materials.

On the basis of this study, the important components 

needed in future studies to properly delineate areas contributing 

water to public-supply wells developed in confined aquifers 

include geologic information on the vertical and lateral 

extent of the confining beds and aquifer materials, and a 

conceptual model of ground-water flow in the aquifer based on 

hydrogeologic data that takes into consideration the movement 

of ground water from recharge to discharge areas. Other 

components include hydrologic data quantifying aquifer gains 

and losses of water from streams and ponds, and accurate 

estimates of recharge rates, which appear to be an important 

determinant of the extent of the areas contributing water to 

supply wells across Massachusetts, including those in confined 

ground-water-flow systems.

Introduction

An accurate delineation of the areas contributing water 

to public-supply wells is an important component of an

overall strategy of protecting ground-water resources from 

contamination (U.S. Environmental Protection Agency, 1987). 

The Drinking Water Program of the Massachusetts Department 

of Environmental Protection (MDEP) regulates public-water 

supplies throughout the State and encourages land-use planning 

within areas that contribute water to public-supply wells to 

prevent contamination of those supplies (Massachusetts 

Department of Environmental Protection, 1996). Although 

MDEP uses a number of available methods to delineate areas 

contributing water to public-supply wells, particularly for 

unconfined aquifers composed of sand and gravel, the issue of 

areas contributing water for wells completed in confined 

aquifers had not been adequately addressed by these methods. 

Consequently, the U.S. Geological Survey began a study in 

1999, in cooperation with MDEP, to investigate the factors 

needed to properly delineate areas contributing water to publicsupply wells developed in confined aquifers in Massachusetts. 

The area contributing water to the Dry Brook well in the town 

of South Hadley, MA (fig.1), was delineated as an example of 

this approach. South Hadley Fire District No. 2, which provides 

water to the northern portion of the town, owns and operates the 

well. The delineated areas will be used as part of the process 

needed to protect the water quality of the well. The results of 

this study also point out the important factors needed to 

properly delineate areas contributing water to public-supply 

wells developed in confined aquifers, and techniques used as 

part of this delineation can be used in similar hydrogeologic 

settings in Massachusetts and the Northeast United States.

Purpose and Scope

This report describes geologic and hydrologic information, 

along with the analysis applied to that information, used to 

delineate areas contributing water to the Dry Brook publicsupply well. The report presents geologic and hydrologic data, 

including the interpretations of geologic logs, ground-water 

levels, and streamflow measurements collected during the 

period of the study from October 1999 to November 2000. Data 

analysis included the preparation of geologic maps, geologic 

cross sections, a ground-water-flow model of the aquifer used 

for water supply in South Hadley, MA, and a particle-tracking 

analysis applied to the results of the flow model to delineate the 

areas contributing water to the supply well completed in the 

aquifer.

Description of Study Area

The study area is in the town of South Hadley in the 

Connecticut River Valley of central Massachusetts (fig. 1), but 

also includes portions of the towns of Hadley and Holyoke. The 

Dry Brook public-supply well (SUW-55) is about 200 ft from 

the Connecticut River, near the mouth of Dry Brook (fig. 2, 

table 1) in South Hadley, MA. Immediately north and west of 

the well are the Holyoke and Mt. Tom Ranges, bedrock ridges 

that divide the Connecticut River Valley. Immediately south of 

the well is Dry Brook Hill, a prominent deltaic sand and gravel 

deposit of late-Pleistocene age.

The climate of the area is moderately humid, with an 

average of 42 in. of precipitation per year. Precipitation is 

generally evenly distributed throughout the year, with slightly 

increased amounts during the fall and spring. Temperatures are 

moderate, with cold winters and temperate summers. Most 

evapotranspiration occurs during the warm-weather months 

from May through October, when vegetation actively removes 

water from the soil.

Acknowledgments

The authors thank Mr. William Selkirk of the South 

Hadley Fire District No. 2 for providing information about the 

operation of the Dry Brook public-supply well that was 

essential to the contributing-area analysis. Mr. Bruce Hansen, 

U.S. Geological Survey, collected hydrologic and geophysical 

data used as part of this study. Mr. Forest Lyford and Mr. Gene 

Parker, U.S. Geological Survey, provided field assistance for a 

number of activities during the project duration. Ms. Stacey 

Archfield, Ms. Elizabeth Farren, and Mr. Carl Carlson, U.S. 

Geological Survey, provided office support during the analysis 

of data used in this study.
Dry Brook

well

MASSACHUSETTS

Study Area

72o35'00" 72o

72o36'00" 34'00"

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

42o16'30"

42o

15'30"

42o

17'30"

CONNECTICUT RIVER

72o37'00"

Introduction 3

Figure 1. Location of the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.
67

H OLYOKE

SOUTH HADLEY

A D L E Y

CONNECTICUT RIVER

114

114

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

EXPLANATION

OBSERVATION WELL

AND NUMBER

South Hadley

Holyoke and Hadley

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

72o 72 35'00" o

36'00"

42o

15'30"

42o

17'30"

Brook

4 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 2. Wells used in the study of the Dry Brook area, Hadley, Holyoke, and South Hadley, Massachusetts.
Introduction 5

Table 1. Records of selected wells and test borings in the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.[Altitude relative to NGVD29. USGS, U.S. Geological Survey; ft, foot; gal/min, gallons per minute; <, actual value is less than value shown; --, unknown]

Local well

number

USGS 

well 

number

Date

drilled

Landsurface 

altitude

(ft)

Measuringpoint

altitude

(ft)

Borehole

depth

(ft)

Depth to

bedrock

or refusal

(ft)

Altitude

of bedrock

surface

(ft)

Screened

interval(s)

(ft)

Well

yield

(gal/min)

Remarks

Town of Hadley (HAW)

-- 1 12-01-50 145 -- 210 126 19 -- -- Domestic bedrock well.-- 2 -- 130 -- 96 -- <34 90–96 -- Domestic well.-- 19 9-08-72 110 -- 170 176 -66 163–170 745 Town of Hadley, test well.-- 32 3-06-63 108 -- 133 133 -25 127–133 15 Town of Hadley, test well.-- 33 3-08-63 110 -- 51 -- <59 43–51 -- Town of Hadley, test well.-- 34 3-34-63 100 -- 150 152 -52 141–150 40 Town of Hadley, test well.4-98 37 2-03-98 106.8 -- 144.8 144.8 -38 134–144 13 Town of Hadley, test well.7-98 38 6-05-98 130 -- 79.9 -- <50 71–76 2 Town of Hadley, test well.

Town of Holyoke (HUW)

HWPC 1 100 2-01-58 116 -- 69 -- <44 -- 425 Saines #16; Holyoke Power Company well.HWPC 2 101 8-01-58 113 -- 88 -- <25 73–88 610 Saines #17; Holyoke Power Company well.B1 102 -- 114.7 -- 150 -- <-35 -- -- Holyoke Power Company test boring.B2 103 -- 115 -- 124 119 -4 -- -- Holyoke Power Company test boring.B3 104 -- 110.1 -- 102.5 -- <7 -- -- Holyoke Power Company test boring.B4 105 -- 113.3 -- 110 105 8 -- -- Holyoke Power Company test boring.B5 106 -- 98.8 -- 101 -- <-2 -- -- Holyoke Power Company test boring.B6 107 -- 121.8 -- 12.1 7.1 115 -- -- Holyoke Power Company test boring.B7 108 -- 111.8 -- 99.7 94.7 17 -- -- Holyoke Power Company test boring.B8 109 -- 113.8 -- 100 -- <14 -- -- Holyoke Power Company test boring.B9 110 -- 117.4 -- 101 101 16 -- -- Holyoke Power Company test boring.B10 111 -- 118.8 -- 14.5 14.5 104 -- -- Holyoke Power Company test boring.B11 112 -- 113.7 -- 39.5 39.5 74 -- -- Holyoke Power Company test boring.B12 113 -- 111.9 -- 26.5 25.5 84 -- -- Holyoke Power Company test boring.B13 114 -- 117.5 -- 51.5 51.5 66 -- -- Holyoke Power Company test boring.B14 115 -- 121.7 -- 35 35 87 -- -- Holyoke Power Company test boring.
6 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts Town of South Hadley (SUW) TW11-60 51 7-22-60 109 111.08 121 121 -12 95–112 -- TW13-60 52 7-22-60 107 108.57 125 125 -18 118–125 50 TW10-60 53 7-20-60 105 105.46 137 137 -22 98–106 114–125 60 Exploration-well for Fire District 2 well. 8-inch test well 54 11-22-60 105 -- 114 -- <-9 100–112 300 8-inch test well. Dry Brook supply well 55 -- 105 -- 114 -- <-9 101–113 1080 At location of 10-60; 10-day aquifer test available. TW4-77 60 12-01-78 107 -- 184 184 -77 -- -- Also called 4-78; screened interval not reported. TW5-77 61 12-07-78 108 -- 218 218 -110 176–181 -- Also called 5-78. TW6-77 62 12-22-78 115 -- 176 176 -61 -- -- Also called 6-78; screened interval not reported. TW7-81 63 3-18-81 115 -- 196 196 -81 124–134 30 TW9-81 64 6-12-81 112 -- 103 103 <9 70–75 50 TW10-82 65 11-14-18 104 -- 162 162 -58 123–133 60 Also called 10-81. TW11-82 66 12-02-81 127 -- 220 220 -93 110–120 20 Also called 11-81. TW12-82 67 11-02-82 112 -- 189 189 -77 122–127 43 Screened interval not clear on log. TW13-82 68 11-15-82 112 -- 177 177 -65 131–136 50 TW14-82 69 11-22-82 114.3 115.05 241 241 -127 198–203 43 TW15-82 70 11-23-82 114 116.39 207 207 -93 85–90 33 Well filled with silt below 105 ft. TW1-94 71 12-13-94 120 -- 191 191 -71 145–155 7 TW2-94 72 12-28-94 125 -- 234 234 -109 143–153 38 Well screened temporarily at 182-192 ft. TW1-95 73 3-02-95 268.7 269.61 262 262 <7 -- -- Pipe driven to 235 ft; washed to 262 ft. TW2-95 74 3-23-95 264.1 265.90 293 293 -29 283–293 185 97-21 75 12-22-97 111 -- 140 140 -29 128–138 32 2-98 76 -- 109.1 -- 250 -- <-141 160–170 50 3-98 77 -- 111 -- 152 -- <-41 136–146 60 98-5 78 5-06-98 108.2 -- 140 -- <-32 130–140 55 98-6 79 6-02-98 110.1 -- 140 -- <-30 130–140 45 12-inch well 80 7-17-98 107.1 -- 130 -- <-23 105–130 --

TW3-95 81 -- 262.7 264.03 233 -- <30 222–233 -- No refusal.TW3-95B 81A 8-04-95 262 -- 294 289 -27 286–289 120 Located 25 ft east of TW3-95.TW4-95 82 10-31-95 264.3 265.92 293 293 -29 278–293 --TW9-97 83 1-29-97 115 117.77 52 52 63 39–49 -- Also called P-9.

Table 1. Records of selected wells and test borings in the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.—Continued[Altitude relative to NGVD29. USGS, U.S. Geological Survey; ft, foot; gal/min, gallons per minute; <, actual value is less than value shown; --, unknown]

Local well

number

USGS 

well 

number

Date

drilled

Landsurface 

altitude

(ft)

Measuringpoint

altitude

(ft)

Borehole

depth

(ft)

Depth to

bedrock

or refusal

(ft)

Altitude

of bedrock

surface

(ft)

Screened

interval(s)

(ft)

Well

yield

(gal/min)

Remarks
Introduction 7

Town of South Hadley (SUW)—Continued

TW7-97 84 2-03-97 115 116.39 136 136 -21 125–135 35 Also called P-7.TW6-97 85 2-11-97 116.9 118.56 128 -- <-11 112–122 50 Also called P-6.P-2 86 10-01-96 266.8 268.84 297 294 -27 -- --P-3 87 9-30-96 267.1 268.75 290 289 -22 -- --P-4A 88 4-03-97 215.9 218.49 247 -- <-31 237–247 -- Also called TW-4A.P-4B 94 1-27-97 208.5 212.05 -- -- -- -- -- Also called TW-4B; 100 ft west of P-4A.P-5 89 9-26-96 243.8 244.59 145 138 106 136–146 -- Partially screened in bedrock.P-8 90 4-11-97 265.3 267.29 298 298 -33 288–298 --P-10 91 3-26-97 262 -- 298 298 -36 288–298 --P-1 93 6-09-97 264.4 266.04 289 -- <-25 279–289 --T-1 100 -- 250 -- 142 139 111 -- -- Bedrock well.2 101 3-01-46 200 -- 202 34 166 -- 8 Domestic bedrock well.3 102 2-01-63 175 -- 145 3.5 171 -- 20 Domestic bedrock well.6 103 -- 190 -- 52 6 184 -- 5 Domestic bedrock well.7 104 -- 185 -- 107 6 179 -- 7 Domestic bedrock well.10 105 -- 122 -- 55 -- <67 -- 0.5 Domestic dug/augered well.18 106 -- 138 -- 180 -- < -42 -- 15 Domestic bedrock well.21 108 -- 190 -- 455 208 -18 -- 2.5 Domestic bedrock well.23 109 -- 183 -- 170 98 85 -- 8 Domestic bedrock well.25 110 -- 220 -- 85 25 195 -- 40–50 Domestic bedrock well.26 111 -- 230 -- 180 80 150 -- 15 Domestic bedrock well.27 112 -- 183 -- 330 135 48 -- 40 Domestic bedrock well.31 113 -- 111 -- 22 -- <89 -- -- Well point.34 114 -- 143 -- 80 3 140 -- 40 Domestic bedrock well.35 115 -- 195 -- 603 70 125 -- 4 Domestic bedrock well.37 116 -- 200 -- 174 80 120 -- 10 Domestic bedrock well.40 117 -- 168 -- 169 40 128 -- -- Domestic bedrock well (off figure 2).

Table 1. Records of selected wells and test borings in the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.—Continued[Altitude relative to NGVD29. USGS, U.S. Geological Survey; ft, foot; gal/min, gallons per minute; <, actual value is less than value shown; --, unknown]

Local well

number

USGS 

well 

number

Date

drilled

Landsurface 

altitude

(ft)

Measuringpoint

altitude

(ft)

Borehole

depth

(ft)

Depth to

bedrock

or refusal

(ft)

Altitude

of bedrock

surface

(ft)

Screened

interval(s)

(ft)

Well

yield

(gal/min)

Remarks
8 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Physiography and Geology 

The physiography of the area surrounding the Dry Brook 

public-supply well (figs. 1 and 3) is a result of the lithology and 

structure of igneous and sedimentary bedrock, the distribution 

of unconsolidated glacial sediments, and postglacial erosional 

and depositional processes. High hills in the western (Mt. Tom 

Range) and northern part (Holyoke Range) of the study area 

consist of erosionally resistant igneous bedrock (basalt and 

tuff); the highest peaks in these hills are just above 900 ft in 

altitude. In most places, relatively thin deposits of glacial 

till laid down beneath the last (late Wisconsinan) ice sheet 

blanket the bedrock. Lower lying areas are underlain by softer 

sedimentary bedrock (sandstone, siltstone, and shale) and by 

relatively thick deposits of glacial meltwater sediment (gravel, 

sand, silt, and clay) laid down in glacial Lake Hitchcock during 

the retreat of the last ice sheet. The bedrock surface lies as much 

as 125 ft below NGVD29 in parts of the area; surfaces of glacial 

lake deposits are generally between 

200 and 260 ft in altitude.

The Connecticut River, which developed on the drained 

glacial lake bed in postglacial time, flows through a steepwalled, narrow gap in the Holyoke and Mt. Tom Ranges, and 

has incised deeply into glacial Lake Hitchcock sediments along 

the reaches of its flood plain north and south of the gap. The 

flood plain lies generally between 110 to 120 ft in altitude along 

its course through the study area. Other postglacial streams, 

such as Elmer Brook, Bachelor Brook, and Stony Brook have 

also incised deeply into glacial lake sediments. The upper 

reaches of the Dry Brook valley consist of a narrow, steepwalled channel controlled by bedrock structure. From its 

headwaters, the stream descends 350 ft in altitude in less than 

a mile to a point at about 200 ft altitude where the valley 

widens as it enters the area underlain by glacial lake deposits. 

Downstream from this point, Dry Brook descends at a lesser, 

but still relatively steep gradient to about 100 ft altitude as it 

enters the Connecticut River. Maps and cross sections (figs. 3, 

4, and 5) illustrate the distribution of surficial geologic units and 

the configuration of the underlying bedrock surface in the study 

area.

Bedrock Geology

The bedrock geology of the area is shown on a geologic 

map of the Mt. Holyoke quadrangle (Balk, 1957) and on the 

Bedrock Geologic Map of Massachusetts (Zen and others, 

1983). A series of alternating units of early Jurassic-aged 

igneous and sedimentary bedrock underlie the study area. 

The area lies in the north-central part of a broad structural 

lowland in central Connecticut and Massachusetts known as 

the Hartford Rift Basin. In the vicinity of the South Hadley 

well field, the rock units strike northeast (parallel with the 

Mt. Holyoke ridge) and dip gently (15–20°) to the southeast. 

Northwest to southeast trending sections, B-B′, C-C′, and D-D′

(fig. 4), are drawn nearly perpendicular to the strike direction 

and show the entire stratigraphic section of rock units in the 

study area. (Note the gentle southeasterly dip appears much 

steeper on these sections because of the 8X vertical 

exaggeration.).

The lowest (oldest) bedrock unit in the study area is the 

Holyoke Basalt, a fine-grained, massive, dark greenish-gray 

columnar basalt (called diabase by Balk, 1957), interpreted 

to have formed as one or more ponded lava flows; the Holyoke 

Basalt is 300 to 400 ft thick in the Mount Holyoke quadrangle. 

The basalt is highly fractured by cooling joints that form 

columns in the rock; the columnar jointing is perpendicular 

to the bottom and top of the flow, or flows, producing large 

concentrations of high-angle fractures. Low-angle fractures, 

parallel to the top and bottom of the flow are also welldeveloped, but spaced wider than the high-angle fractures. 

The East Berlin Formation stratigraphically overlies the 

Holyoke Basalt and consists of reddish-brown arkosic 

sandstone and siltstone, gray sandstone and mudstone, and 

local black shale units; it is interpreted to have formed as lake 

beds. Balk (1957, p. 494) described the unit as about 150 ft thick 

in the study area, although he referred to it as the basal unit of 

the Longmeadow Sandstone. Fracturing in these sedimentary 

rocks typically includes through-going, low-angle, beddingparallel fractures and less extensive high-angle fractures that 

dip perpendicular to the bedding and have bedding-parallel 

strike; these high-angle fractures occur most frequently in

the coarser grained beds.
Physiography and Geology 9

Granby Basaltic Tuff and stratigraphically equivalent 

Hampden Basalt overlie the East Berlin Formation. The Granby 

Tuff–Hampden Basalt unit consists of chocolate brown, fine, 

medium, and coarse-grained, well stratified or massive tuff that 

locally incorporates sedimentary fragments and grades laterally 

into massive basalt. The unit is interpreted to have formed as 

lava flows, volcanic ash, and bedded volcanics. The Portland 

Formation (called Longmeadow Sandstone by Balk, 1957) is 

the youngest unit in the sequence, and in the study area consists 

of reddish-brown to pale-red arkose and siltstone, gray 

sandstone and siltstone, and black shale. The unit is interpreted 

to have formed as lake beds. Fracturing in these rocks is similar 

to that described for the East Berlin Formation.

Areas where bedrock is at or near land surface are 

indicated by map unit tb (fig. 3), and the configuration of the 

bedrock surface beneath thick surficial materials (where the 

bedrock lies at or below 200 ft altitude in the study area) is 

shown on figure 5. Locations of bedrock outcrops (from Balk, 

1957) and reported depths to bedrock in logs of wells and test 

holes were used to construct the bedrock-surface map (fig. 5). 

The bedrock surface beneath thick glacial deposits forms 

an irregularly shaped basin; the lithology and structure

of the underlying bedrock control the basin shape. Millions of 

years of differential erosion, accentuated by glacial plucking 

during Pleistocene glacial advances, has produced the 

configuration of the bedrock surface. The processes of erosion 

and plucking by glacial ice produced lows in the bedrock 

surface where the rock is softer and more highly fractured. 

The northeast-southwest trending lows in the bedrock surface 

(north and south of Dry Brook Hill) are scoured along the trends 

of the East Berlin and Portland Formations, which are less 

resistant sedimentary units; the more resistant Granby Tuff 

forms a higher ridge between these two lows in the bedrock 

surface. The northwest-southeast trending low in the bedrock 

surface that forms the gap in the Holyoke Range, through which 

the Connecticut River flows, extends beneath the west side of 

Dry Brook Hill and is most likely a fault or fracture zone.

Surficial Geology

The surficial geology of the Mt. Holyoke quadrangle was 

mapped and reported by Balk (1957), and the distribution of 

coarse- and fine-grained surficial materials in the region was 

described by Stone and others (1979), and Langer (1979). 

Marine seismic-reflection data from tracklines along the 

Connecticut River through the study area were presented by 

Hansen (1986). Many other earlier publications describe the 

deposits, depositional environments, and history of glacial Lake 

Hitchcock in the Connecticut Valley of central Massachusetts 

(Antevs, 1922; Jahns and Willard, 1942; Hartshorn and Koteff, 

1968; Gustavson and others, 1975; Ashley and others, 1982; 

Koteff and others, 1988; Ridge and Larsen, 1990), to name a 

few. Several theses done at the University of Massachusetts and 

Mt. Holyoke College have also addressed the geology and 

geohydrology of the South Hadley area (Saines, 1973; 

Jacobson, 1981; Donner, 1991; Delude, 1995; Rittenour, 1999).

Glacial deposits overlie the bedrock surface and range 

from a few feet to more than 250 ft thick in the study area. 

The surficial materials map (fig. 3) shows the distribution of 

surficial materials that lie between the land surface (below the 

pedogenic soil horizon) and the locally till-draped bedrock 

surface. Cross sections A-A′, B-B′, C-C′, D-D′, and E-E′ (fig. 4) 

illustrate the characteristic vertical succession of glacial till, 

glacial meltwater deposits, and postglacial deposits. Most of 

these materials are deposits of the last two continental ice sheets 

that covered New England during the middle and late 

Pleistocene. Most of the glacial deposits were laid down during 

the advance and retreat of the last (late Wisconsinan) ice sheet, 

which reached its terminus on Long Island, NY, about 21,000 

radiocarbon years ago, and retreated northward through the 

South Hadley area by about 14,000 radiocarbon years ago 

(Stone and Borns, 1986; Ridge and others, 1999; Stone, 1999). 

The glacial deposits are divided into two broad categories— 

glacial till and glacial stratified deposits. Glacier ice directly 

deposited the till, which is characterized as a nonsorted, 

nonlayered mixture of sand, silt, and clay with variable amounts 

of stones. During deglaciation, glacial stratified deposits were 

laid down by meltwater in lakes and streams in front of the 

retreating ice margin. These materials consist of well sorted to 

poorly sorted layers of gravel, sand, silt, and clay.

Postglacial sediments make up some of the surficial 

materials, and in the study area consist primarily of alluvial 

flood-plain deposits of the Connecticut River and its tributary 

streams–Bachelor Brook, Elmer Brook, Stony Brook, and Dry 

Brook. These sediments are inset into (and derived from) 

surrounding glacial deposits and in most places they are 

relatively fine grained, consisting of fine sand and silt. In the 

upper reaches of Dry Brook, alluvium is much coarser than 

most deposits and consists of cobble to boulder gravel and sand. 

For several hundred feet downstream from where Dry Brook 

exits its steep-walled bedrock canyon, the alluvium consists 

almost entirely of angular rock fragments.
Surficial materials mapping by J.R. Stone,

2000-01; modified from Balk, 1957

A'

A

D

E

B'

E'

D'

C'

a

f

f

a f

a

s

s tt

tt

s

s

sg

a

f

f

sg

sg

af

sg

f

f

s

s

sg

f

a

sg

f

a

a

tb tb

tb

tb

tb

s

s

a

sg

f

f

sg

f

a

11

110

1

101

1

80

3

51

53

5

100

111

112

38

33

2

1

102

106

101

32

1

1

112

1

109

72 66

110

60

61

64

62 71

70

69

68

7

63

113

14

SOUTH HADLEY

HADLEY

HOLYOKE

Dry

Elmer

Bachelor

Brook

Brook

Brook

Dry Brook Hill

72o35'00" 72o 72 34'00" o36'00"

42o16'30"

42o15'30"

72o37'00"

42o17'30"

Base from U.S. Geological Survey digital raster data,1:24,000,

topographic quadrangle, Mt. Holyoke, 1964, photorevised 1979,

North American datum 1927, Polyconic projection, zone 18

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

300

10 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 3. Surficial materials map and locations of cross sections shown in figure 4, Dry Brook study area, Hadley, Holyoke, 

and South Hadley, Massachusetts.
Physiography and Geology 11

111

s

f

sg

af

f

a

a a

sg sg

s

sg

s

f

sg

f

s

sg

f

A A'

tt tb

DESCRIPTION OF MAP UNITS

POSTGLACIAL DEPOSITS

Artificial Fill—Composed predominantly of earth materials emplaced along large road and railroad embankments

Flood plain Alluvium—Composed of sand, silt, and local gravel, with varying amounts of organic material. Alluvium is beneath

the modern flood plain surfaces along the Connecticut River, Dry Brook, Elmer Brook, Bachelor Brook, and Stony Brook. In the

steep-gradient section of Dry Brook, alluvium is composed predominantly of boulder-cobble gravel. Along the smaller streams,

alluvium is generally thin (<10 ft thick) and overlies thicker glacial stratified deposits indicated by letter symbol (see description

below); along the Connecticut River, alluvium is as much as 50 ft in thick.

GLACIAL STRATIFIED DEPOSITS

Gravel, sand, silt, and clay particles (as defined in the adjacent particle-size diagram), that occur in layers and are classified into three

textural units on the basis of grain-size distribution—sand and gravel deposits, sand deposits, and fine deposits. The texture of glacial

stratified deposits is described throughout their entire vertical extent either as a single textural unit or two or more units in various orders

or superposition, referred to as “stacked units.” Areas where sand and gravel deposits underlie sand or fines are shown by the orangedotted pattern on the cross sections. Contacts between subsurface textural units are not mapped with as great an accuracy and detail as

those at the surface. All units of glacial stratified deposits overlie glacial till and (or) bedrock, which are not included in the stacked unit.

Coarse Deposits

Sand and gravel—Composed of mixtures of gravel and sand particles within individual layers and as alternating layers; sand and

gravel layers range from 25- to 50-percent gravel particles and from 50- to 75-percent sand particles. Layers are well to poorly

sorted; bedding may be distorted by postdepositional collapse (proximal deltaic and fluvial deposit and delta topset beds).

Typical hydraulic conductivity is 100 to 500 feet per day.

Sand—Composed mainly of very coarse to fine sand particles; coarser layers may contain up to 25-percent gravel particles,

generally granules and pebbles; finer layers may contain some very fine sand, silt, and clay. Layers are commonly well sorted

(delta foreset beds, distal lacustrine fan deposits and distal fluvial deposits). Typical horizontal hydraulic conductivity is 25 to

250 feet per day.

Fine Deposits

Fines (very fine sand, silt, and clay)—Composed of well sorted, thin layers of alternating silt and clay and (or) thicker layers of

very fine sand and silt; locally may contain lenses of coarser material (lake-bottom deposits). Typical horizontal hydraulic

conductivity is less than 5 feet per day.

Stacked Map Units

Sand and gravel overlying sand—Sand and gravel is generally less than 20 feet thick, horizontally bedded and overlies thicker,

inclined layers of sand (deltaic deposits).

Sand and gravel overlying sand overlying fines—Sand and gravel is generally less than 20 feet thick, horizontally bedded and

overlies thicker inclined beds of sand, which in turn overlie thinly bedded fines of variable thickness (deltaic deposits overlying

lake-bottom sediment).

Sand overlying fines—Sand is of variable thickness, commonly in inclined foreset beds and overlies thinly bedded fines of

variable thickness (distal deltaic deposits overlying lake-bottom sediment).

Fines overlying sand and gravel—Fines of variable thickness overlies sand and gravel of variable thickness (lake-bottom

sediments overlying collapsed ice-marginal deltaic or lacustrine fan deposits).

GLACIAL DEPOSITS (NONSTRATIFIED)

Till—Nonsorted, nonstratified, generally compact mixture of grain sizes ranging from clay to large boulders; matrix is largely

sand particles containing up to 25-percent silt and clay. Till blankets the bedrock surface in most places and underlies glacial

stratified deposits but is not included in the stacked units. In most of the map area (unit tb), till is less than 10 feet-thick and

bedrock is exposed at land surface in many places, particularly on steep hillsides. Shading indicates areas where till is greater

than 10 feet thick (unit tt). Hydraulic conductivity is generally less than 1 foot per day.

MAP SYMBOLS

Contact between map units, dashed where inferred

Line of geologic section shown in figure 4.

OBSERVATION WELL AND NUMBER

EXPLANATION

Figure 3—Continued. Surficial materials map and locations of cross sections shown in figure 4, Dry Brook study area, 

Hadley, Holyoke, and South Hadley, Massachusetts.
84

52

85

88

81

87

65

66

Bachelor Brook

Dry Brook

?

?

-100

0

100

200

300

400

500

A

WEST

A'

EAST

Former lakebottom surface

Holyoke Basalt

101

CONNECTICUTRIVER

C-C'

B-B'

D-D'

BEND IN SECTION

East Berlin

Formation

Granby

Basaltic

Tuff

BEND IN SECTION

Interstate 91

BEND IN SECTION

BEND IN SECTION

Dry Brook

Valley

? ?

?

?

Former level

of glacial

Lake Hitchcock

51

108

FEET

53

B

NORTH

B'

SOUTH

Holyoke Basalt Portland

Formation

CONNECTICUT RIVER

BEND IN SECTION

East Berlin

Formation

Granby

Basaltic

Tuff

VERTICAL EXAGGERATION X 8

FEET

BEND IN SECTION

A-A'

E-E'

0

0 200 300 100 400 METERS

500 1,000 1,500 2,000 FEET

-100

-200

0

100

200

300

???

Dry Brook Hill

EXPLANATION

51

FLOOD-PLAIN

ALLUVIUM

SAND AND GRAVEL

DEPOSITS

SAND DEPOSITS

FINES DEPOSITS

Fine to very fine sand

and silt

Very fine sand, silt and

clay

TILL

BEDROCK

Sedimentary rock

Igneous rock

INFERRED CONTACT

WELL LOCATION AND

IDENTIFIER

12 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 4. Geologic cross sections, Dry Brook study area, Holyoke and South Hadley, Massachusetts.
Dry Brook Hill

-100

-200

0

100

200

300

C

NORTH C'

SOUTH

Holyoke Basalt East Berlin

Formation

Granby

Basaltic

Tuff

Portland Formation

CONNECTICUT RIVER

BEND INSECTION

BEND INSECTION

BEND IN SECTION

Bachelor Brook

105

101

A-A'

91748682

73 E-E'

FEET

61 Projected

62

Dry Brook

Hill

-100

-200

0

100

200

300

D

NORTH

D'

SOUTH

VERTICAL EXAGGERATION X 8 Dry Brook

Elmer Brook

Bachelor Brook

Gravel pit

Route 47

A-A'

E-E'

0

0 100 200 300 400 METERS

500 1,000 1,500 2,000 FEET

FEET

Holyoke Basalt

?

?

?

83

89

69 Projected

East Berlin

Formation

Granby

Basaltic

Tuff

Portland

Formation

?

BEND INSECTION

Physiography and Geology 13

Figure 4—Continued. Geologic cross sections, Dry Brook study area, Holyoke and South Hadley, Massachusetts.
EXPLANATION

FLOOD-PLAIN ALLUVIUMSAND AND GRAVEL DEPOSITSSAND DEPOSITS

FINES DEPOSITS

 Fine to very fine sand and silt Very fine sand, silt and clayTILL

BEDROCK

 Sedimentary rock Igneous rockWELL LOCATION AND IDENTIFIER

70

-100-200

0

300200100

E

WEST

E'

EAST

D-D'

C-C'

B-B'

Elmer Brook

VERTICAL EXAGGERATION X 8

CONNECTICUT 

RIVER

Portland Formation

00 200 300 100 400 METERS 

500 1,000 1,500 2,000 FEET

Granby Basaltic Tuff Granby Basaltic Tuff Granby Basaltic Tuff

Interstate 91

FEET

Former level of glacial lake Hitchcock

73

70 Projected

Dry Brook Hill

14 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts Figure 4—Continued. Geologic cross sections, Dry Brook study area, Holyoke and South Hadley, Massachusetts.
-50

-100

-150

-150

150

200

200

0

10

150

0

50

0

200

250 200

200

0

SOUT DLEY

HADLEY

HOLYOKE

Dry

Elmer

Brook

Brook

Brook

Dry Brook Hill

EXPLANATION

200

<50

72o35'00" 72o34'00"

42o16'30"

42o15'30"

72o37'00"

42o17'30

Base from U.S. Geological Survey digital raster data,1:24,000,

topographic quadrangle, Mt. Holyoke, 1964, photorevised 1979,

North American datum 1927, Polyconic projection, zone 18

ETERS

1,000 FEET

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Bachelor

Dry Brook well

Figure 5. Altitude of the bedrock surface in the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.

Physiography and Geology 15
16 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Glacial Till

In the study area, till was deposited predominantly as 

lodgment till beneath the ice sheet. The color and texture of 

the till vary locally and are related to the type of bedrock in 

northerly adjacent areas from which the till was derived. No 

exposures of till were available for examination in the Dry 

Brook area at the time of this study; however, till in the region 

is typically reddish-brown in areas of sedimentary bedrock 

and varies to grayish brown near basalt ridges. The material 

(fig. 6D) consists of a nonsorted, nonlayered mixture of grain 

sizes with a matrix of 50- to 60-percent sand, 30- to 40-percent 

silt, and 10- to 15-percent clay; larger rock fragments generally 

constitute 10 to 20 percent of the total volume of material and 

include angular blocks of sandstone, basalt, tuff, and erratic 

clasts of metamorphic rock (Melvin and others, 1992). Till is 

relatively thin (less than 20 ft thick) over most of the study area, 

and is absent where bedrock crops out at land surface in many 

places. Locally, however, till is thicker than 20 ft (unit tt, fig. 3). 

Several NNW–SSE trending hills in the area are drumlins 

composed entirely of glacial till; these include Prospect Hill just 

east of Mt. Holyoke College and two hills southeast of Stony 

Brook in South Hadley, MA.

Glacial Stratified Deposits

In the study area, stratified deposits were laid down by 

meltwater as lacustrine fans, deltas, and lake-bottom sediments 

in glacial Lake Hitchcock, an extensive proglacial lake that 

occupied the Connecticut Valley for several thousand years as 

the last ice sheet retreated from central Connecticut northward 

through Massachusetts to the vicinity of Burke, VT (Koteff and 

others, 1988; Koteff and Larsen, 1989; Stone and others, in 

press). These meltwater deposits overlie the glacially scoured 

and till-draped bedrock surface at altitudes below 260 ft, 

controlled by the level of Lake Hitchcock at the time the ice 

retreated through the South Hadley area. Sediments range from 

a few to more than 300 ft in thickness and include coarsegrained and fine-grained sedimentary facies (fig. 6). Various 

sedimentary facies that constitute glacial meltwater deposits in 

southern New England are described in detail by Stone and 

others (in press).

Coarse-Grained Deposits

Coarse-grained stratified deposits (fig. 6A and B) consist 

of gravel and sand with local diamict sediment in ice-proximal 

(northerly) parts, and grade to finer gravels and sand within 

short distances in distal (southerly) directions. The principal 

unit of coarse-grained glacial stratified deposits in the study 

area underlies Dry Brook Hill to the southeast of the Dry Brook 

supply well. Dry Brook Hill is an ice-marginal delta built into 

glacial Lake Hitchcock at a time when the ice margin stood 

along the north and northwest side of the Holyoke Range and a 

narrow tongue of ice protruded through the gap (fig. 1; Saines, 

1973; Donner, 1991). Deposition of this feature began when 

sediment-laden meltwater discharged (under hydrostatic head) 

from a subglacial tunnel onto the floor of Lake Hitchcock and 

constructed a subaqueous lacustrine fan. Deposition continued 

after fan sediments had reached lake level and the final 

construction of the landform was accomplished by delta 

progradation southeasterly into the lake. The interpretation of 

well logs and test borings, and three-dimensional reconstruction 

of the distribution of sedimentary facies (fig. 4) within 

Dry Brook Hill, provide evidence that the deltaic landform 

has a core of lacustrine fan beds in the northwest and 

central parts, although these beds have not been exposed. 
A.

C. D.

B.

Physiography and Geology 17

Figure 6. Examples of glacial deposits in the Dry Brook study area, Hadley, Holyoke, and South Hadley, 

Massachusetts: A, gravel and sand beds in an ice-marginal delta; B, flat-lying gravel topset beds overlying 

dipping sandy foreset beds in the Pearl City delta, South Hadley; C, glacial Lake Hitchcock varved silt (darker 

layers) and clay (lighter layers); and D, typical red till in the Hartford Basin.

The northwest side of Dry Brook Hill is underlain by coarse, 

poorly sorted gravel and sand that extends beneath subsequently 

deposited glacial lake clays in Dry Brook Valley at the 

northwest base of the hill. These gravels compose the highly 

productive aquifer tapped by the Dry Brook supply well (fig. 4, 

sections B-B′ and D-D′). The eastern and southern sides of Dry 

Brook Hill, underlain by sands and clays, are the frontal foreset 

slopes of the delta.

The steep western slope of Dry Brook Hill is an erosional 

scarp, cut first by water spilling from Lake Hitchcock north of 

the Holyoke Range, after the southern basin of the lake had 

drained (Stone and Ashley, 1995; Stone, 1999), and later by the 

ancestral Connecticut River as it continued to incise the entirely 

drained lake bed. A small portion of the delta remains on 

the west side of the river as a 245-ft hill on west side of I-91 

(figs. 3 and 4, section A-A′). The Dry Brook delta plain has a 

surface altitude of 265 to 270 ft; a sand and gravel excavation 

cut into the delta surface (fig. 3) exposes 10 to 12 ft of flat-lying 

layers of gravel and sand (topset beds) overlying about 30 ft of 

easterly dipping sandy layers (foreset beds). The contact 

between the topset and foreset beds marks the level (altitude) of 

the glacial lake at the time the delta was constructed. Figure 6B

shows the topset-foreset contact in the Pearl City delta about 

2 mi east of Dry Brook Hill. The altitude of the topset-foreset 

contact in the Dry Brook delta is 255 ft (Jacobson, 1981). In the 

southern and eastern parts of Dry Brook Hill, distal sandy beds 

interfinger with and overlie fine-grained glaciolacustrine 

sediments.

Fine-Grained Deposits

Fine-grained glaciolacustrine deposits in the study area 

consist of finely laminated silt, clay, and minor fine sand in 

couplets (varves) ranging from 0.4 to 1.6 in. thick, each couplet 

representing annual deposition into Lake Hitchcock (fig. 6C). 

These sediments are gray in upper parts of the lacustrine 

sections but locally are red, especially in lower parts of 

lacustrine sections; deposits range from a few feet to as much as 

200 ft in thickness. These varved silt and clay sediments settled 

out in relatively still, deep water as the ice margin retreated 

farther to the north. Each silt-clay couplet (fig. 6C) represents 

deposition in the glacial lake during one year; the silt layer was 

deposited during the spring-summer melt season, and the clay 

slowly settled out of the water column during the winter when 

the lake was frozen.
18 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Glaciolacustrine silt and clay deposits underlie and 

interfinger with sand beds of the Dry Brook delta in central and 

southern parts of Dry Brook Hill. In some places, lenses of 

coarser grained lacustrine sediment consisting of alternating 

layers of very fine to fine sand and silt lie beneath and within 

the varved silt and clay sections (fig. 4, sections D-D′ and E-E′). 

North of the hill and at the site of the Dry Brook supply well, 

silt and clay deposits overlie collapsed, ice-marginal gravels 

and sands of the Dry Brook delta and lacustrine fan beds. 

Beneath lake-bottom surfaces (at 175–205 ft altitude) east and 

south of Dry Brook Hill, lacustrine varved silt and clay grade 

upward to a coarser, sandy material deposited in shallow water 

as the glacial lake filled with sediment and eventually drained. 

These sandy lake-bottom deposits consist of well-sorted fine to 

medium sand. This 5- to 20-ft thick facies gradationally overlies 

the finer-grained silt-clay facies.

Hydrology

The surface- and ground-water hydrology of the study area 

is dominated by topography, underlying geologic materials, and 

the Connecticut River. The source of all water in the area is 

precipitation, which averages about 42 in. per year. Generally, 

because of steep slopes and thin soil cover, much of the 

precipitation occurring on the Holyoke and Mt. Tom Ranges 

runs off quickly during and immediately after precipitation. On 

Dry Brook Hill, however, much of the precipitation infiltrates 

through the sandy soils on the higher elevations of the hill. 

Lacustrine silts and clays (varves) that impede infiltration occur 

along the flanks and lower elevations of the hill, creating 

surface runoff during precipitation. The Dry Brook supply well 

is completed in the sand and gravel aquifer that underlies the 

lacustrine sediments near the mouth of Dry Brook. This sand 

and gravel aquifer is physically contiguous with coarse 

sediments in Dry Brook Hill. Water in the study area (not 

pumped from wells) will generally flow to the Connecticut 

River under natural conditions.

Streamflow

Four streams flow in the vicinity of the Dry Brook supply 

well: Dry Brook, Elmer Brook, Bachelor Brook, and the 

Connecticut River. The smallest of the streams is Dry Brook 

(fig. 7), which drains 0.8 mi2 at its confluence with the 

Connecticut River. Flow measurements of Dry Brook on 

September 8, 2000 (table 2, fig. 7), indicate rapid gains and 

losses in flow along the stream length. For example, Dry Brook 

gained flow in its upper reach, and then rapidly lost all flow 

after exiting from a bedrock gorge as it came in contact with 

rubble and cobble streambed materials (alluvium). Flow then 

gained downstream from the alluvial fan at the mouth of the 

gorge for a distance of about 3,000 ft, where it began to lose 

flow again into the sandy material in the streambed. On the date 

of these measurements, all flow was lost at the point where Dry 

Brook reached Massachusetts Route 47. The streamflows 

measured in Dry Brook on this date (0.01–0.07 ft3

/s) are small 

relative to the annual median flow estimated for a drainage 

basin of this size (0.7 ft3

/s), indicating that these flows are at the 

lowest range for this stream. The annual median flow was 

estimated for Dry Brook using the Streamstats Internet 

application developed to estimate streamflow duration statistics 

for Massachusetts streams (Ries and Friesz, 2000).

Although these observations of gains and losses along Dry 

Brook indicate a significant interaction between surface and 

ground water along Dry Brook, most of the lower reach of Dry 

Brook is underlain by varved lacustrine sediments, which are 

exposed in the streambed just north of Route 47 (figs. 3, 4, 

section D-D′ ). Most likely much of the water that infiltrates 

along the lower reach of Dry Brook flows laterally through the 

alluvial materials in the streambed as underflow to discharge to 

the Connecticut River at the confluence. It is also possible, 

however, that some water from Dry Brook infiltrates to and 

through the fractured bedrock and lacustrine sediments to 

recharge the sand and gravel aquifer at depth.

Elmer Brook flows along the eastern flank of Dry Brook 

Hill and drains 4.0 mi2

 at its confluence with Bachelor Brook 

(fig. 7). Streamflow measurements also were made on Elmer 

Brook on September 8, 2000 (table 2). These measurements 

indicate that Elmer Brook did not gain or lose much water under 

the hydrologic conditions on that date along the reach that runs 

from north to south along the east side of Dry Brook Hill 

(table 2, fig. 7). The measured flows (1.79–1.89 ft3/s) are 

smaller than the estimated annual median flow (4.0 ft3

/s; Ries 

and Freeze, 2000), which is indicative of the low-flow 

conditions on this date. Elmer Brook will gain substantial 

amounts of water from surface runoff during rainfall because 

the lacustrine sediments (fig. 4, section D-D′ ) exposed in 

the streambed and in the hillside above the brook will limit 

infiltration. These sediments also likely cause the small 

change in streamflow because they transmit and discharge 

small amounts of ground water during periods between 

rainfall events, and much of that flow would be lost as 

evapotranspiration to the heavy vegetation on the slopes 

above the brook.

The largest streams in the study area are Bachelor Brook 

and the Connecticut River. Bachelor Brook flows along the 

southern flank of Dry Brook Hill (fig. 7) and is a tributary of the 

Connecticut River. Bachelor Brook drains about 32 mi2 and has 

an estimated median flow of 32 ft3/s (Ries and Freze, 2000). 

The Connecticut River is the largest stream in central New 

England and has an average flow of about 14,000 ft3/s at the 

streamflow-gaging station at Montague City, MA, about 22 mi 

upstream from the study area. The river continues to gain flow 

from several large tributaries as it crosses central Massachusetts 

and averages about 17,000 ft3/s at the streamflow-gaging 

station near the State line at Thompsonville, Connecticut, about 

20 mi downstream of the study area. Streamflow in the 

Connecticut River is highly regulated by releases from several 

upstream dams, used primarily for hydroelectric power 

generation and flood control. These releases can cause large and 

rapid fluctuations in the Connecticut River stage and flow.
1

2

3

A

B

C

4

5

6

Elmer Brook

measurement

locations

Dry Brook

measurement

locations

Elmer

Bro

o

k

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

72o 72 35'00" o36'00"

HADLEY

HOLYOKE

CONNECTIC

UT

RIVER

42o16'00"

42o

17'00"

Dry

Brook

Hydrology 19

Figure 7. Locations of streamflow measurements for Elmer and Dry Brooks, Dry 

Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.

Ground-Water Levels and Flow

Ground-water levels measured as part of this study are 

shown in table 3, and water levels measured on November 16, 

2000, are shown on figure 8. Wells in table 3 are listed with two 

names, one of which is assigned by the USGS (for example, 

SUW-85), and the other a local name assigned at the time of 

installation (for example, TW6-97). In the following 

discussion, the USGS names will be used for consistency. 

Ground-water measurements made in the study area 

(table 3, fig. 8) indicate that ground-water levels were generally 

higher than 100 ft above NGVD29 under Dry Brook Hill, and 

less than that immediately around the Dry Brook supply well 

(SUW-55, fig. 2), because of drawdown caused by pumping at 

the supply well. The water levels measured at well SUW-89 

near the center of Dry Brook Hill are higher than those closer 

to the Connecticut River (table 3, fig. 8). The altitude of the 

Connecticut River in the vicinity of Dry Brook Hill is about 
Table 2. Streamflow measurements for Elmer and Dry Brooks, 

South Hadley, Massachusetts, September 8, 2000.

[See figure 7 for locations of measurements. ft3/s, cubic foot per second]

Location Flow rate

(ft3

/s) Comments

Dry Brook

1 (upstream) 0.01 Stream begins at seep

2 .03

3 .04

4 0 Lost all flow at alluvial fan

5 .07

6 (downstream) 0 Lost all flow at Massachusetts 

Highway Route 47

Elmer Brook

A 1.79

B 1.84

C 1.89

20 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

100 ft. These water-level data indicate that, in general, ground 

water in this area flows towards the Connecticut River. In 

addition, because the water levels measured in wells near the 

Dry Brook supply well were below the stage of the Connecticut 

River, water may also flow from the river to the supply well 

when the well is pumped. 

Ground-water levels vary seasonally, with highest 

levels in the late spring and lowest levels in early fall. This 

pattern of ground-water levels is caused by increased recharge 

rates during the period from late fall through spring when 

evapotranspiration rates are lowest. The seasonal variation in 

ground-water level can be seen in data from a nearby USGS 

observation well completed in a glacial outwash aquifer in 

Granby, MA (fig. 9; Socolow and others, 2002). Water levels 

measured during the study period (October 1999 through 

November 2000) were typical of the normal range of water 

levels expected for surficial aquifers in central Massachusetts 

(fig. 9).

The stage of the Connecticut River also affects groundwater levels in the study area. The continuous measurement of 

water levels in well SUW-81 (fig. 2) near the river, and the 

variations in stage of the Connecticut River at the Montague 

(Massachusetts) station about 22 mi upstream of the Dry Brook 

area, are shown in figure 10. There are no dams that impound 

the river between this station and the study area. In addition, 

there are no major tributaries that enter the river in this reach. 

The stage of the Connecticut River adjacent to Dry Brook Hill 

would be expected to follow the rise and fall in river stage at the 

Montague station with a 1- to 2-day time lag in stage response. 

Although upstream reservoirs heavily regulate the Connecticut 

River on a daily basis, the flows in the river are highest in the 

spring after the snow melts (fig. 10). The good correlation 

between these two hydrographs indicates a hydraulic 

connection between the ground-water system under Dry Brook 

Hill and the river.

Ground-Water Recharge and 

Discharge

The rate of ground-water recharge in the study area was 

assumed to vary with the topography (slope), texture (grain 

size) of the soil, and the type of underlying rock or sediments. 

Recharge was assumed to be greatest, about 24 in/yr, on the 

northern part of Dry Brook Hill and other locations where the 

sediments are the coarsest in the study area. This recharge 

amount represents about half of the available precipitation. 

Recharge was assumed to be about 12 in/yr in areas along the 

flanks of the Holyoke Range, where steep slopes and bedrock at 

or near the surface increase surface runoff of precipitation. 

In areas underlain by lacustrine silts and clays (varves), 

particularly where these sediments are thick in the area 

immediately around the Dry Brook well, recharge was assumed 

to be 6 in/yr. Recharge rates of 22 in/yr for stratified deposits 

and 8 in/yr for till were used in a similar study in Connecticut 

for an area underlain by Mesozoic-aged bedrock and glacial 

sediments (Starn and others, 2000). As noted previously, 

most ground water in the study area discharges to streams 

or is pumped from wells. A small amount of ground-water 

discharge is lost by evapotranspiration, primarily in low-lying 

areas where seeps and springs feed streams, creating wet soils 

and wetlands.

Aquifer Responses to Pumping

An aquifer test was conducted for 10 days (September 25, 

1998–October 5, 1998) by pumping the Dry Brook well 

(SUW-55, fig. 2) at an average rate of 914 gal/min (Tighe 

and Bond, 1999). The Dry Brook supply well is completed 

in the sand and gravel aquifer below about 100 ft of lacustrine 

silts and clays; these overlying fine-grained sediments locally 

confine the aquifer tapped by the supply well (fig. 4, sections 

A-A′ and B-B′). The extent of the confined portion of the sand 

and gravel aquifer is shown on figure 11; however, the sand and 

gravel aquifer extends beyond the area shown in figure 11 and 

is either unconfined or overlain by the Connecticut River 

beyond the confining bed (figs. 3 and 4).

Ground-water levels measured during the aquifer test in 

wells near the Dry Brook well and open to the aquifer (fig. 11) 

are shown in figure 12. A small amount of precipitation 

(0.25 in.) fell on the third day of the test (September 27, 1998), 

but did not appear to affect the confined aquifer responses. The 

responses are shown as drawdowns, which are the water-level 

declines observed in the wells from the beginning of the aquifer 

test. The drawdowns observed in these wells indicated a variety 

of responses to the stress caused by the pumping at the Dry 

Brook well. The largest drawdowns generally were in wells 

closest to the pumped well, the closest of which is SUW-53, 

only 2 ft away from the pumped well within the pump house. 
Table 3. Manual ground-water-level measurements in Dry Brook study area, South Hadley, Massachusetts.

[DTW and Altitude: Relative to NGVD29. DTW, depth to water; USGS, U.S. Geological Survey; --, no measurement]

Local

well

name

USGS

number

(SUW)

Measuringpoint

altitude

Date of measurement

10-22-1999 11-19-1999 1-06-2000 2-24-2000 4-06-2000

DTW Altitude DTW Altitude DTW Altitude DTW Altitude DTW Altitude

TW11-60 51 111.08 13.84 97.24 -- -- -- -- -- -- -- --

TW13-60 52 108.57 13.51 95.06 -- -- -- -- -- -- -- --

TW14-82 69 115.05 11.84 103.21 -- -- -- -- -- -- -- --

TW15-82 70 116.39 11.26 105.13 11.30 105.09 11.37 105.02 -- -- 10.54 105.85

TW1-95 73 269.61 168.36 101.25 -- -- -- -- -- -- 165.38 104.23

TW2-95 74 265.90 164.06 101.84 -- -- -- -- -- -- 160.27 105.63

TW3-95 81 264.03 164.55 99.48 164.78 99.25 161.95 102.08 164.42 99.61 156.96 107.07

TW9-97 (P9) 83 117.77 19.66 98.11 19.83 97.94 13.23 104.54 -- -- 13.16 104.61

TW6-97 (P6) 85 118.56 20.64 97.92 20.79 97.77 17.46 101.10 -- -- 12.71 105.85

P-2 86 268.84 166.53 102.31 166.56 102.28 166.38 102.46 -- -- 163 105.84

P-3 87 268.75 166.16 102.59 166.25 102.50 165.85 102.90 166.36 102.39 163.89 104.86

P-4A 88 218.49 119.49 99.00 -- -- -- -- -- -- 111.47 107.02

P-5 89 244.59 136.79 107.80 137.02 107.57 137.08 107.51 -- -- 136.53 108.06

P-8 90 267.29 165.3 101.99 165.41 101.88 164.54 102.75 165.42 101.87 162.11 105.18

P-1 93 266.04 164.36 101.68 164.54 101.50 -- -- -- -- 160.34 105.70

P-4B 94 212.05 113.95 98.10 114.19 97.86 -- -- -- -- 105.65 106.40

Local

well

name

USGS

number

(SUW)

Measuringpoint

altitude

Date of measurement

6-08-2000 8-10-2000 9-21-2000 11-16-2000

DTW Altitude DTW Altitude DTW Altitude DTW Altitude

TW11-60 51 111.08 -- -- -- -- -- -- -- --

TW13-60 52 108.57 -- -- -- -- -- -- -- --

TW14-82 69 115.05 9.8 105.25 -- -- -- -- 11.18 103.87

TW15-82 70 116.39 9.2 107.19 9.86 106.53 10.25 106.14 10.79 105.60

TW1-95 73 269.61 166.55 103.06 167.58 102.03 167.94 101.67 167.78 101.83

TW2-95 74 265.90 164.3 101.60 163.04 102.86 163.19 102.71 163 102.90

TW3-95 81 264.03 160.53 103.50 163.68 100.35 163.58 100.45 162.73 101.30

TW9-97 (P9) 83 117.77 15.91 101.86 17.52 100.25 19.69 98.08 17.96 99.81

TW6-97 (P6) 85 118.56 16.4 102.16 18.34 100.22 20.03 98.53 17.9 100.66

P-2 86 268.84 164.3 104.54 165.69 103.15 165.98 102.86 166.2 102.64

P-3 87 268.75 163.92 104.83 165.04 103.71 165.34 103.41 165.37 103.38

P-4A 88 218.49 -- -- -- -- -- -- -- --

P-5 89 244.59 135.88 108.71 136.28 108.31 136.26 108.33 136.42 108.17

P-8 90 267.29 162.74 104.55 164.2 103.09 164.4 102.89 164.32 102.97

P-1 93 266.04 -- -- -- -- -- -- -- --

P-4B 94 212.05 109.53 102.52 -- -- 112.87 99.18 111.91 100.14

Hydrology 21
73

101.83

87

103.38

74

102.90

100.14

86

102.64

81

101.30

83

99.81

85

100.66

89

90 108.17

102.97

70

105.60

69

103.87

55 Dry Brook well

EXPLANATION

OBSERVATION WELL AND NUMBER

GROUND-WATER LEVEL, IN FEET RELATIVE TO

NGVD29

101.83

73

CONNECTICUT

RIVER

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

Dry Brook

Elmer Brook

94

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

72o 72 35'30" o36'00"

42o16'30"

42o17'00"

SOUTH

HADLEY

HOLYOKE

Bachelor Brook

22 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 8. Ground-water levels measured in the Dry Brook study 

area on November 16, 2000, Hadley, Holyoke, and South Hadley, 

Massachusetts.

There were, however, some exceptions. For example, 

drawdown after 10 days for well SUW-84, 150 ft from the 

pumped well, was significantly greater than drawdown in well 

SUW-52, which is also 150 ft from the pumped well. The same 

was true for well SUW-83, which is 600 ft away from the 

pumped well, but had drawdown after 10 days that was greater 

than drawdown in well SUW-85, which is about 300 ft from 

the supply well (fig. 11). Data in figure 11 indicate that the 

drawdown cone was likely elongated in a northern direction 

towards well SUW-83. Deviations from radially concentric 

drawdown conditions would likely be caused by variations in 

aquifer properties and (or) type of aquifer boundary.

In addition to these likely deviations from ideal conditions, 

variations in the drawdown responses over time differ at the 

observation wells. Although the thick overlying varved clays 

should confine the aquifer yielding water to the well (fig. 11), 

most of the drawdowns observed in the observation wells 

indicated some type of stabilization of the confined-storage 

drawdown response a few minutes to a few tens of minutes after 

the beginning of the test (fig. 12). To separate the effect of 

distance from the pumped well from other effects, the 

drawdown responses were plotted against time divided by the 

square of radial distance (fig. 13). In the ideal case (Theis-type, 

or confined- aquifer conditions with uniform hydraulic 

properties), drawdown responses observed in wells with 

different radial distances from the pumped well should be 

identical when plotted in this fashion.

Drawdown reponses over time vary significantly between 

the observation wells, even after distance is considered (fig. 13). 

For example, the early confined response is substantially 

different at each of the observation wells, with SUW-83 

responding most rapidly, and SUW-53 responding the slowest. 
Datacollection

period for

study

D

1992

M J SD

1993

M J SD

1994

M J SD

1995

M J SD

1996

M J SD

1997

M J SD

1998

M J SD

1999

M J SD

2000

M J SD

2001

MJS

3 230

4 229

5 228

6 227

7 226

8 225

9 224

10 223

11 222

TREND LINE AND DATA POINTS

WATER LEVEL, IN FEET BELOW LAND SURFACE

WATER LEVEL, IN FEET ABOVE NGVD29

Hydrology 23

Figure 9. Ground-water levels measured in well GKW-68 in Granby, Massachusetts.

The sluggish relative early response in SUW-53 may be at least 

partially attributed to borehole storage effects, in which the 

early drawdown in the pumped well deviates from the ideal 

response because a real (but finite) amount of water in the well 

reduces the water-levels declines in, and immediately around, 

the pumped well. Also, Tighe and Bond (1999, p. 3–6) reported 

that data from observation wells SUW-51, -52, and -53 may be 

limited in their use because of the age (approximately 40 years) 

and suspected deterioration of well screens in these wells. The 

potential deterioration of the well screens in SUW-51, -52, 

and -53 is likely the cause of their poor early response, in which 

they clearly lag behind responses in the newer wells. Early 

drawdown responses generally extend most rapidly to the north 

towards SUW-83 and northwest to SUW-84, relative to the 

response in well SUW-85 (fig. 13).

There appears to be an intermediate time stabilization of 

the drawdown that is likely caused by vertical drainage from 

either leaky confining beds above the pumped well, or from the 

unconfined part of the aquifer southeast of the pumped well 

(fig. 4, section B-B′). Later drawdown responses vary in the 

observation wells, but generally increase steadily over time 

(figs. 12, 13). The type of aquifer boundary closest to the well 

likely affects these later responses (fig. 11). For example, 

the later increase in drawdown (fig. 13) at SUW-83 is nearly 

double that in other observation wells. This greater slope in the 

drawdown curve at later time is likely caused by the truncation 

of the aquifer near SUW-83 (fig. 4, section D-D′), effectively 

creating a no-flow boundary. In contrast, the slope of the later 

drawdown curves for SUW-84 and SUW-52 are less than those 

for either SUW-51 or SUW-85. These decreased drawdown 

slopes are because of the closer proximity of these wells to 

the Connecticut River. A close examination of cross sections 

A-A′ and B-B′ (fig. 4, sections A-A′ and B-B′) indicates that the 

aquifer is hydraulically connected to the Connecticut 

River west of the Dry Brook supply well either directly 

(southwest) or through overlying alluvium (west and 

northwest). The stage of the Connecticut River should not 

change in response to leakage through the sediments to the 

supply well because of the large amount of flow in the river 

relative to the rate of pumping by the well.
1999 2000

SO N D J FM A M J J A S ON D

110

105

100

95

90

85

80

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD29

TRANSDUCER DATA

MANUAL MEASUREMENTS

SUW-81

Connecticut River

24 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 10. Ground-water levels measured in well SUW-81 compared to the stage of the Connecticut River at Montague, 

Massachusetts. Connecticut River stage 75 feet above arbitrary datum.

Examination of the drawdown response in well SUW-53 

(fig. 13) shows four segments of the curve, each with a different 

slope. Although the typical unconfined response will involve 

three segments, early confined, intermediate (vertical) drainage 

stabilization, and later unconfined (Neuman, 1972), the fourth 

(last) segment of the drawdown curve for SUW-53 would 

appear to be due to an aquifer boundary. In this case, because 

the fourth response segment shows a stabilization of drawdown, 

a positive (recharge) boundary is indicated. As noted 

previously, the aquifer is likely hydraulically connected to the 

Connecticut River, and river water infiltrates the aquifer near 

the Dry Brook well when it is pumped. River leakage, therefore, 

stablizes ground-water levels in that part of the aquifer when the 

well is pumped.

Ground-water levels also responded to Connecticut River 

stage fluctuations during the aquifer test, similar to that noted 

for SUW-81 (fig. 10). On a daily basis, upstream hydroelectric 

dams release water for power generation, creating fluctuations 

in river stage. These rises in river stage cause a subsequent 

rise in ground-water levels in the aquifer near the river. For 

example, the water level in well SUW-84 (fig. 11) rose about 

0.2 ft in response to a 1-ft rise in the Connecticut River stage 

(Tighe and Bond, 1999), about 5,700 minutes after the start 

of the test (fig. 14). The stage of the Connecticut River was 

measured near the Dry Brook well during the 10-day aquifer 

test. In comparison, a muted water-level response of about 

0.02 ft to this rise in river stage was recorded in well SUW-51, 

and the peak response in this well occurred after that in well 

SUW-84 (fig. 14) because it is further from the river (fig. 11). 
5.89

H

O

LY

O

K

E

SOUTH

HADLEY

54

EXPLANATION

OBSERVED DRAWDOWN AT THE END OF

THE 10-DAY AQUIFER TEST, INTERVAL IS 5 FEET

APPROXIMATE EXTENT OF CONFINED AQUIFER

OBSERVATION WELL

DRAWDOWN VALUES

CONNECTICUT

RIVER

500 1,000 FEET

150 300 METERS

0

0

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,

1:25,000, topographic quandrangle, Mt. Holyo e,

1964, photorevised 1979, North American datum

1927, Polyconic projection, zone 18

42o16'45"

42o17'00"

72o36'00" 72o35'45"

Hydrology 25

Figure 11. Observation-well network for a 10-day aquifer test of Dry Brook well (September 25, 

1998–October 5, 1998), South Hadley, Massachusetts (Tighe and Bond, 1999).
0.01

0.1

1.0

10.0

100.0

0.1 1 10 100 1,000 10,000 100,000

TIME, IN MINUTES

SUW-51

SUW-52

SUW-85

SUW-84

SUW-83

SUW-53

SUW-86

SUW-88

DRAWDOWN, IN FEET

Pumping rate, 914 gallons per

minute (122.2 cubic feet per minute)

26 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 12. Drawdowns in observation wells during the Dry Brook well 10-day aquifer test (September 25, 1998–October 5, 

1998), South Hadley, Massachusetts (Tighe and Bond, 1999).

The difference in time to the peak response at these two 

wells can be used to estimate the distance to the point where the 

aquifer is exposed to the river bottom, by applying an equation 

developed for the analysis of tidal effects on coastal aquifers 

(Todd, 1980; p. 243–245, eq. 6.17):

tL x t0 ( ) S ⁄ 4πT 1 2⁄ = , (1)

where

tL is the time lag between a change in river stage and the 

aquifer response;

x is the distance from river to observation well;

t0 is the tidal period, the time from peak to peak;

S is the aquifer storage coefficient; and

T is the aquifer transmissivity.

Taking the ratio of lag time for two observation wells creates the 

following relation:

tL1 tL2 x1 x2 ⁄ = ⁄ , (2)

in which the numbered subscripts refer to the two different 

wells. The use of this relation eliminates the need for estimates 

of aquifer properties or of the tidal period. This approach is 

based on the assumption, however, that the aquifer properties 

are constant in the area between the river and the two wells. 

The time at the peak stage of the Connecticut River was 

5,700 minutes, and peak responses at wells SUW-84 and -51 

occurred at 5,920 and 6,040 minutes from the beginning of the 

aquifer test (fig. 14), respectively; therefore, response times 

were 220 minutes for SUW-84 and 340 minutes for SUW-51. 
0.01

0.1

1

10

100

0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100 1,000

TIME, (IN MINUTES) DIVIDED BY RADIAL DISTANCE (IN FEET) SQUARED

DRAWDOWN, IN FEET

SUW-51

SUW-52

SUW-85

SUW-84

SUW-83

SUW-53

SUW-86

SUW-88

Pumping rate, 914 gallons per

minute (122.2 cubic feet per minute)

Hydrology 27

Figure 13. Drawdowns in observation wells during the Dry Brook well 10-day aquifer test (September 25, 1998–

October 5, 1998) using relative time scale, South Hadley, Massachusetts.

The distance from the river bank to SUW-51 is 440 ft, and is 

80 ft for SUW-84 (fig. 11). The ratio of distances from the river 

to the wells for SUW-51 to SUW-84 (5.50) is significantly 

different than the ratio of the lag times (1.55); however, it is 

likely that this difference is because the aquifer is not exposed 

to the river at the bank, and there is some distance from the 

river’s edge to where the aquifer is hydraulically connected to 

the river. This distance (d) can be calculated from the ratio of lag 

times as follows:

x1 x2 ( ) 440 + d ( ) 80 + d t = L1 ⁄ = ⁄ tL2 ⁄ = 1.55 , (3)

which, after algebraic manipulation, gives the result that d is 

575 ft, about two thirds the distance across the Connecticut 

River at this location. This indicates a hydraulic connection 

between the Connecticut River and the aquifer that is consistent 

with the interpretation that the confining bed in the immediate 

area around Dry Brook well pinches out underneath the river as 

shown in geologic cross sections A-A′ and B-B′ (fig. 4, sections 

A-A′ and B-B′and fig. 11).

The Dry Brook well aquifer test was conducted at 

the same time as another aquifer test which used a well on 

Hockanum Flat in the northernmost part of South Hadley near 

Russell Cove, north and west of the Dry Brook well (fig. 1). 

No interference effects were noted at either well during the 

coincident 10-day aquifer tests. An earlier set of 48-hour aquifer 

tests conducted separately on Dry Brook and Hockanum 

Flat wells also indicated no drawdown (interference response) 

between the well fields, indicating a hydraulic separation 

between the two areas (Tighe and Bond, 1999). These results 

indicate either a pinch-out of the aquifer pumped by the 

Dry Brook well to the northwest because of the bedrock 

structure or limits of the surficial materials (figs. 3 and 4, 

section B-B′), and (or) a hydraulic connection to the 

Connecticut River of the aquifer areas with well fields such 

that declines in water levels in the aquifer(s) are localized 

around the pumped wells.
93.50

94.00

94.50

95.00

95.50

96.00 SUW 51

89.50

90.00

90.50

91.00

91.50

92.00

SUW 84

CONNECTICUT RIVER STAGE

99

99.5

100

100.5

101

0 2,000 4,000

5,700

6,000 8,000 10,000 12,000 14,000 16,000

ALTITUDE, IN FEET ABOVE NGVD29

TIME, IN MINUTES

98.5

28 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 14. Connecticut River stage compared to water levels 

measured in observation wells SUW-84 and SUW-51 during the 

Dry Brook well 10-day aquifer test, South Hadley, 

Massachusetts.
Simulation of Ground-Water Flow 29

Simulation of Ground-Water Flow

Ground-water flow in the surficial and bedrock aquifers 

supplying water to the Dry Brook well was simulated with 

numerical methods of analysis. Numerical methods have 

advantages over analytical methods in that boundary and initial 

conditions, along with aquifer properties, can be varied across 

the area of interest, increasing the degree to which the models 

represent the conditions in aquifer systems. The numerical 

method used in these analyses is the MODFLOW model, a 

three-dimensional finite-difference simulator documented by 

McDonald and Harbaugh (1988) and Harbaugh and McDonald 

(1996).

The approach to analysis included several steps. First, a 

long-term average flow condition was simulated in the aquifer 

at the Dry Brook site as a steady-state condition. The result from 

the steady-state simulation then provided a stable initial 

condition for the second step, simulation of the Dry Brook 

aquifer test. These steps were then repeated as calibration of the 

aquifer properties proceeded, with the goal of improving the 

degree of representativeness for each set of changes in aquifer 

conditions made during model calibration. Aquifer properties 

were changed during model calibration to produce simulated 

hydrologic conditions similar to those observed in the aquifer 

under average conditions (steady-state simulations), and to 

conditions observed during the Dry Brook aquifer test (transient 

simulations). After steady-state and transient calibration steps 

were completed, a steady-state version of the model was used to 

simulate the area contributing water to the Dry Brook supply 

well.

Model Design and Boundary Conditions

The model grid covers a 7,000-ft-by-7,000-ft area centered 

on the northwestern edge of Dry Brook Hill (fig. 15). The model 

area was subdivided into 20-ft (square) cells (or blocks), 

creating a mesh of 350 blocks on each (horizontal) side; figure 

15 shows every fifth block division, or groups of 5×5 blocks. 

The model has four layers, which for most of the modeled area 

are composed of surficial sediments in the upper three layers 

and a bottom layer that represents the Mesozoic-aged bedrock 

(fig. 16). The upper three layers were simulated as water-table 

layers, or as convertible layers, which allow a cell in an 

underlying layer to become a water-table layer if the cell above 

becomes dewatered (dry). The bottom layer (four), representing 

fractured Mesozoic-aged bedrock, was assumed to have a fixed 

transmissivity. Ground water in the Mesozoic-aged bedrock 

likely flows primarily through fractures, and these fractures 

were assumed to be continuous enough that an equivalent 

porous-media approach would provide a good representation 

and simulation of flow in the bedrock aquifer. For those 

portions of the simulated area that are underlain solely by 

bedrock (along Mt. Tom and the Holyoke Range, see figs. 3 and 

15), all four model layers are used to represent ground-water 

flow in the bedrock. The top altitude of each layer was set equal 

to the bottom altitude of the layer above, and the top of layer 1 

was generally set to land surface. These top and bottom surfaces 

were allowed to vary spatially across the modeled area (fig. 

16A, B). For example, the upper two layers in the area 

immediately around the Dry Brook well were used to represent 

the confining bed composed of varved lacustrine sediments, the 

third layer was used to represent the sand and gravel aquifer 

pumped by the Dry Brook supply well, and layer 4 was used 

to represent the Mesozoic-aged bedrock beneath the aquifer 

(fig. 16A).

Boundary conditions for the model included no-flow 

boundaries at the bottom of layer 4 and specified ground-waterflow conditions along the perimeter, particularly along the flank 

of the Holyoke Range north of the Dry Brook well and Mt. Tom 

Range west of the Connecticut River. Specified flows on the 

lateral boundary of the model were incorporated into the 

recharge rate. These flows enter the aquifer at that point of the 

uppermost active node on the model boundary. Specified 

ground-water-flow rates were 7.5 ft3/min along the northern 

boundary of the model and 9.9 ft3/min on the western boundary 

(fig. 15). The flows on the northern boundary of the model were 

distributed in three zones that include areas west of Dry Brook 

(3.1 ft3

/min), Dry Brook alluvium (2.6 ft3/min), and east of Dry 

Brook (1.8 ft3/min). These specified ground-water boundary 

flows are small in comparison to the estimates of median flow 

for the Dry Brook drainage basin (24 ft3/min at the model 

boundary), but are reasonable when the steep mountain slopes 

and thin soils that limit the infiltration of precipitation are 

considered. Other model boundaries included specified-head 

conditions that represent the Connecticut River in layer 1, and 

river nodes that act as drains (but as not sources of water) along 

Dry Brook, Elmer Brook, Bachelor Brook, and in a steep gully 

ascending the northeastern flank of Dry Brook Hill (fig. 15).
72o 72 35'00" o

36'00"

42o16'30"

42o17'30"

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

HADLEY

HOLYOKE

SOUTH HADLEY

EXPLANATION

MODEL GRID SPECIFIED-HEAD NODE RIVER NODE SPECIFIED-FLOW

BOUNDARY NODE

30 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 15. The lateral extent of and boundary conditions for the MODFLOW model grid in the Dry Brook study area, 

Hadley, Holyoke, and South Hadley, Massachusetts.
Simulation of Ground-Water Flow 31

FLOOD-PLAIN ALLUVIUM

SAND AND GRAVEL DEPOSITS

SAND DEPOSITS

EXPLANATION

FINE TO VERY FINE SAND AND SILT

BEDROCK

Sedimentary rock

Igneous rock

C

O

NNE

C

TIC

U

T

RIVER

Layer 3

Holyoke Basalt

East Berlin

Formation

Not to scale

-100

0

100

200

300

400

CONNECTICUTRIVER

SECTION B-B'

BEND IN SECTION

BEND IN SECTION

Dry Brook

Valley

VERTICAL EXAGGERATION X 8 Interstate 91

A

WEST

A'

EAST

500

FEET

Granby

Basaltic

Tuff

Layer 3

Layer 4

Layer 4

ALTITUDE, IN FEET RELATIVE TO NGVD29

BEND IN SECTION

Layer 1 Layer 1

Layer 2

Bottom of model layer 4

MODEL

BOUNDARY

BEND IN SECTION 55 Dry Brook well

Figure 16. Geologic cross sections showing the vertical distribution of MODFLOW model layers in the Dry Brook study area, 

Holyoke and South Hadley, Massachusetts.
Layer 1

Layer 2

Layer 3

Layer 4

Layer 1

Layer 2

Layer 3

Layer 4

Bachelor Brook

Dry Brook

B

NORTH

B'

SOUTH

Holyoke Basalt

Portland

Formation

CONNECTICUT RIVER

BEND IN SECTION

East Berlin

Formation

Granby Basaltic Tuff

(Hampton Basalt)

VERTICAL EXAGGERATION X 8 BEND IN SECTION SECTION A-A'

FEET

-100

-200

0

100

200

300

FLOOD-PLAIN ALLUVIUM

SAND AND GRAVEL DEPOSITS

SAND DEPOSITS

TILL

EXPLANATION

VERY FINE SAND, SILT AND CLAY

BEDROCK

Sedimentary rock

Igneous rock

Not to scale

ALTITUDE, IN FEET RELATIVE TO NGVD29

MODEL

BOUNDARY

Dry Brook Hill

32 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 16. Geologic cross-sections showing the vertical distribution of MODFLOW model layers in the Dry Brook study area, 

Holyoke and South Hadley, Massachusetts.—Continued

Hydraulic Properties and Recharge Rates

The hydraulic properties of the model were varied 

horizontally and vertically to represent the surficial sediments 

and bedrock in the study area (table 4, fig. 3). In general, the 

largest horizontal hydraulic conductivities (along model layers) 

were for the sand and gravel aquifer around the Dry Brook well 

(0.5 ft/min, 720 ft/d). Most of the sand and gravel aquifer was 

assigned a horizontal hydraulic conductivity of 0.12 ft/min 

(173 ft/d) to 0.08 ft/min (115 ft/d). The values of horizontal 

hydraulic conductivity in the aquifer decreased as the sediments 

became finer to the southeast across Dry Brook Hill (fig. 3) 

and to the northeast up Dry Brook. The smallest hydraulic 

conductivity values were for the varved lacustrine silts and 

clays (1.0×10-3 ft/min, 1.4 ft/d), followed by Mesozoic-aged 

bedrock in the upper three layers (3.0×10-3 ft/min, 4.3 ft/d), and 

by fine sands (2.5×10-2 ft/min, 36 ft/d). These rates are similar 

to those used in a study in Connecticut for an area underlain by 

Mesozoic-aged bedrock and glacial sediments (Starn and 

others, 2000). The transmissivity value used for layer 4 varied 

as the thickness changed across the modeled area (fig. 16), 

but was relatively uniform under the surficial sediments 

(0.3 ft2/min, 432 ft2/d) because the thickness of the active-flow 

zone in the Mesozoic-aged bedrock aquifer was assumed to be 

100 ft. The largest transmissivities were in layer 3 (the pumped 

zone); these values were about 18 ft2/min (26,000 ft2

/d) 

immediately around the Dry Brook well, but typically ranged 

from less than 1 to greater than 9 ft2/min (1,000–13,000 ft2

/d) 

in the area a few hundred feet around the well. Variations in 

aquifer thickness and hydraulic conductivity cause the 

variability of layer 3 transmissivity, which agrees well with 

previously determined values for this aquifer (Saines, 1973; 

Delude, 1995).
Table 4. Aquifer properties and recharge rates for the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.

[Sediment or rock type: See figure 3. ft, foot; ft/min, foot per minute, in/yr, inch per year]

Sediment or rock type

Horizontal hydraulic

conductivity

(ft/min)

Vertical hydraulic

conductivity

(ft/min)

Ratio of vertical to

horizontal hydraulic

conductivity

Recharge rate

(in/yr)

Mesozoic bedrock 3.0×10-3 3.0×10-4

Alluvium 8.0×10-2 2.0×10-2

Sand and gravel1 0.5, 1.2×10-1 3.0×10-2

Sand 8.0×10-2 2.0×10-2

Fines (fine sand to silt) 3 2.0×10-2, 2.5×10-2 1.0×10-3, 2.5×10-3

Varves (very fine sand to clay) 1.0×10-3 1.0×10-5

Simulation of Ground-Water Flow 33

1

The horizontal hydraulic conductivity for 30 ft around Dry Brook well was set to 0.5 ft/min.; for all other sand and gravel sediment, the horizontal hydraulic 

conductivity was set to 1.2×10-1 ft/min.

2The recharge rate for alluvium along Elmer and Dry Brooks was set to 12 in/yr; the rate for all other alluvium was set to 24 in/yr.

3The horizontal hydraulic conductivity in an area of fine sediment north of Dry Brook well was set to 2.0x10-2 ft/min, the vertical hydraulic conductivity in this 

area was set to 1.0×10-3 ft/min, so that the ratio of vertical to horizontal hydraulic conductivity was 0.05. The horizontal hydraulic conductivity of all other areas 

of fine sediment was set to 2.5×10-2 ft/min, the vertical hydraulic conductivity was set to 2.5×10-3 ft/min, and the ratio of vertical to horizontal hydraulic 

conductivity was 0.01.

0.1 12

0.25 212, 24

0.25 24

0.25 24

0.05, 0.1 12

0.01 6

The largest value of vertical hydraulic conductivity used

in the model was for the sand and gravel at 3.0×10-2 ft/min 

(table 4). This value produced an average vertical to horizontal 

hydraulic conductivity anisotropy ratio of 0.25 for this sediment 

type. The smallest values of vertical hydraulic conductivity 

used in the model were those for vertical flow through the 

varved lacustrine sediments (1.0×10-5 ft/min); intermediate 

values were used for vertical flow in the Mesozoic-aged 

bedrock (3.0×10-4 ft/min) and for vertical flow in the fine sand 

and silty sediments (2.5×10-3 ft/min). The vertical to horizontal 

hydraulic conductivity anisotropy ratios ranged from 0.01 to 

0.25 for these sediments and rock types (table 4). Vertical 

conductances for flow between model layers were calculated 

(external from the model) by using the vertical hydraulic 

conductivities for the two adjacent layers decribed previously, 

half the adjacent layer thicknesses, and the equation for the 

harmonic mean (McDonald and Harbaugh, 1988, section 5). 

Streambed leakances were set to a uniform value of 10 ft/min/ft 

for Dry Brook, Elmer Brook (and tributaries), and Bachelor 

Brook. Storage coefficients were varied across the study area 

from 0.25 in areas of unconfined conditions to 1.0×10-4 for 

confined conditions in the upper two layers. The storage 

coefficients used for the sand and gravel aquifer and the finegrained sediments in layer 3 were 3.0×10-4 and 3.0×10-5, 

respectively. The storage coefficient used for the bedrock 

aquifer in layer 4 was set to 1.0×10-5.

A spatially varying recharge rate was applied across 

the modeled area: 24 in/yr (3.8×10-6 ft/min) in areas underlain 

by sand, 12 in/yr (1.9×10-6 ft/min) in areas underlain by 

Mesozoic-aged bedrock and fine-grained sediments (fine sand 

and silt), and 6 in/yr (9.5×10-7 ft/min) in areas underlain by 

lacustrine (varved) silts and clays (fig. 3, table 4). These 

recharge rates are similar to those used in a study in Connecticut 

for an area underlain by Mesozoic-aged bedrock and glacial 

sediments (Starn and others, 2000). The option of recharge 

entering the highest active cell at any given location was used 

to ensure that recharge continued to enter the simulated aquifer 

even if overlying model cells became dry and inactive.

Pumping Stresses

Pumping in the simulations was limited to the Dry Brook 

well, in layer 3 of the model. Pumping rates for the Dry Brook 

well were specified as either zero, 40.0 ft3/min (299 gal/min), 

or 122.2 ft3

/min (914 gal/min). These rates correspond to a preaquifer test condition (zero), the average pumping rate for water 

supply during the year 2000 (Mr. William Selkirk, South 

Hadley Fire District No. 2, written commun., 2002), and an 

average pumping rate during the aquifer test. Although there are 

several rural water-supply wells for homes in the study area, the 

amount of pumpage by these wells would be expected to be 

small (less than 1 gal/min on a sustained 24-hour basis), and 

most of the water would be returned to the ground through onlot septic systems. For these reasons, the pumpage by these 

wells was not included as part of the aquifer simulation.
34 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Model Calibration

The Dry Brook aquifer model was calibrated with 

information from the 10-day aquifer test (Tighe and Bond, 

1999) by adjusting model parameters (hydraulic conductivity 

and storage coefficients) until a reasonable match to the aquifertest results was achieved (fig. 17). The aquifer test was 

simulated by using two stress periods, an initial period of 10 

days in which the Dry Brook well was not pumped, and a 

second period of 10 days in which the well was pumped at a 

constant rate of 122.2 ft3

/min (914 gal/min). Simulated and 

observed drawdown at the end of the 10-day aquifer test were 

compared (table 5). The differences between simulated and 

observed drawdowns at the end of the aquifer test were 1 ft or 

less for all but one of the wells shown in figure 17. Some of 

these differences were positive and others were negative. The 

average difference is 0.21 ft, and the average of the absolute 

values of these differences is 0.67 ft. As was noted, observed 

early drawdowns were likely less than simulated drawdowns 

for the older wells, SUW-51, -52, and -53 (fig. 17), because 

corroded well screens prevented these wells from rapidly 

responding to changing head conditions in the aquifer.

A comparison of observed and simulated drawdowns 

at the end of the 10-day aquifer test for the Dry Brook well 

(table 5), when plotted in relation to radial distance, is shown in 

figure 18. The relative sequence of observed drawdowns (from 

largest to smallest–SUW-53, SUW-84, SUW-52, SUW-51, 

SUW-83, SUW-85, SUW-88, SUW-86) is similar to the 

sequence of simulated drawdowns (SUW-53, SUW-84, 

SUW-52, SUW-51, SUW-85, SUW-83, SUW-88, SUW-86). 

For the ideal case of uniform aquifer hydraulic properties, along 

with boundary and confining conditions, drawdowns are 

expected to decrease with increased radial distance. As stated 

previously, however, the magnitudes of the observed 

drawdowns do not uniformly decrease with radial distance from 

the pumped well. Drawdown at wells SUW-84 and 

SUW-52 are significantly different, even though these wells 

are at the same radial distance from the pumped well; the 

same is true for wells SUW-51 and SUW-85, (fig. 18). 

The transmissivity value calculated by using the trend line 

in figure 18 and the distance-drawdown method of analysis 

(Fetter, 2001) is 6.4 ft2/min, which is similar to the values 

used in this and previous studies. The storage coefficient 

calculated by using this method is 0.04, a value that is low for 

an unconfined system and high for a confined system, indicative 

of the partially confined condition of the sand and gravel aquifer 

pumped by the Dry Brook well.

The largest difference between simulated and observed 

drawdowns is for observation well SUW-83, located 600 ft 

from the pumped well and farthest from the river of all 

observation wells. In addition, wells north and west of the 

pumped well (SUW-83 and SUW-84) had observed drawdowns 

that plot above the trend line, whereas the wells south and east 

of the pumped well (SUW-52, SUW-85) had drawdowns that 

plot below this trend line (fig. 18). The calibrated model 

reasonably simulates the drawdown variations, as shown in 

figure 18, and simulated drawdowns generally cluster near the 

observed drawdowns but are closer to the overall trend line than 

the observed drawdowns. The conclusion that can be drawn, 

therefore, is that these deviations in drawdowns from the ideal 

case are most likely caused by spatially varying boundary 

conditions, hydraulic properties, and confining conditions for 

the aquifer.

In addition to simulating the aquifer test, steady-state 

model simulations were conducted by using the average 

pumping rate for the Dry Brook well during the year 2000, 

40.0 ft3/min (299 gal/min) and the results were compared to 

ground-water levels obtained over the period of data collection. 

Ground-water-level contours from steady-state model 

simulations are shown in figure 19, and a comparison of 

observed and simulated water levels is shown in table 6. These 

results are based on a steady-state simulation that has a different 

constant-stage condition for the Connecticut River than that 

used for the 10-day aquifer test. The Connecticut River stage 

near the Dry Brook well during the 10-day aquifer test was 

about 99.5 ft above NGVD29 (fig. 14), whereas it was 

estimated that the average Connecticut River stage was 

101.25 ft above NGVD29 during the data-collection period. 

This latter value was used as the constant head for the 

Connecticut River during steady-state simulations for 

comparison to ground-water-level values collected during the 

study, and was assumed to be close to the average boundary 

condition for the Dry Brook aquifer.

A comparison of ground-water levels indicates that the 

simulated steady-state water levels were, on average, within 

half a foot of the observed water levels, and that the majority of 

the simulated water levels at the observation wells were within 

the range of the water levels observed in these wells (table 6). 

The average difference between the observed ground-water 

levels and simulated ground-water levels is 0.36 ft, and the 

average of the absolute values of these differences is 1.22 ft. 

The ground-water levels measured on November 16, 2000, 

were compared to the simulated ground-water levels because 

the observed ground-water levels were collected at a time when 

the water-level conditions observed in SUW-81 were closest to 

their average for the study period (fig. 10). Ground-water levels 

in SUW-81 ranged over 7 ft during the study period because of 

seasonal changes in recharge and and the effect of stage changes 

in the Connecticut River.

The ground-water-level contours for model layers 3 and 4 

are shown in figure 19; however, in some locations layer 3 was 

dry (for example, in the northeast portion of Dry Brook Hill) 

and layer 4 was the only active layer. These contours show that 

ground water generally moves from topographically higher 

areas to discharge at the Connecticut River, and the contours 

also show the effect of ground-water pumping at the Dry Brook 

well on the overall flow pattern and local head distribution. The 

effect of the plunging ridges of bedrock (figs. 3 and 4) can also 

be observed in the higher ground-water levels north and east of 

Dry Brook. The ground-water gradients become much less 

steep southwest of the Dry Brook well across Dry Brook Hill as 

the sediments become thicker and more permeable.
S

U

W-52

0.01

0.101.00

10.00

0.1 1 10 100 1,000 10,000 100,000

TEEF NI , N WOD WARD

TIME, IN MINUTES

S

U

W-84

0.010.101.00

10.00

0.1 1 10 100 1,000 10,000 100,000

TEEF NI , N WOD WARD

TIME, IN MINUTES

S

U

W-85

0.010.101.00

10.00

TEEF NI , N WOD WARD

TEEF NI , N WOD WARD

OBSER

VED

D

R

A

W

D

O

W

N

SIM

ULA

TED

D

R

A

W

D

O

W

N

EX

TEN

T

OF C

O

NFINED

A

Q

UIFER

0.1 1 10 100 1,000 10,000 100,000

TIME, IN MINUTES

0.01

0.10

1.00

10.00

100.00

0.1 1 10 100 1,000 10,000 100,0000.1 1 10 100 1,000 10,000

TIME, IN MINUTES

TEEF NI , N WOD WARD

S

U

W-53

S

U

W-51

0.01

0.10

1.00

10.00

0.01

0.101.00

10.00

0.1 1 10 100 1,000 10,000 100,000

S

U

W-83

TEEF NI , N WOD WARD

TIME, IN MINUTES

TIME, IN MINUTES

3

CONNECTICUT RIVER

EXPLA

N

ATIO

N

100,000

Simulation of Ground-Water Flow 35 Figure 17. Model-calibration results comparing observed and simulated drawdown at observation wells during the Dry Brook well 10-Day aquifer test, South Hadley, Massachusetts.
Table 5. Comparison of observed to simulated drawdowns at the end of the 10-day Dry Brook well aquifer test (September 25, 1998–

October 5, 1998), South Hadley, Massachusetts.

[Radial distance: Distance in feet from the Dry Brook Well, as reported by Tighe and Bond, 1999. USGS, U.S. Geological Survey; ft, foot]

Local well

number

USGS well

number

(SUW)

Radial

distance

(ft)

Observed

drawdown

(ft)

Simulated

drawdown

(ft)

Difference between

observed and

simulated

(ft)

TW11-60 51 300 6.29 6.17 0.12

TW13-60 52 150 6.55 7.17 -.62

2 inch (TW10-60) 53 2 17.71 17.87 -.16

TW9-97 (P9) 83 600 5.89 3.70 2.19

TW7-97 (P7) 84 150 10.00 9.05 .95

TW6-97 (P6) 85 300 3.66 4.71 -1.05

P-2 86 2,300 .09 .08 .01

P-4A (TW-4A) 88 1,400 .93 .70 .23

Average .......................................................................................................... 0.21

Average of absolute values ............................................................................ 0.67

1 10 100 1,000 10,000

SUW-88

20

18

16

14

12

10

8

6

4

2

0

Distance-drawdown analysis:

∆ s = 7 feet, r0 = 2,300 feet;

T = 6.4 ft2/min = 9,200 ft2/min

S = 0.04

DRAWDOWN, IN FEET

OBSERVED DRAWDOWN

SIMULATED DRAWDOWN

RADIAL DISTANCE, IN FEET

EXPLANATION

SUW-86

SUW-53

SUW-85 SUW-83

SUW-51 SUW-52

SUW-84

36 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 18. Observed and simulated drawdowns at the end of the 

Dry Brook well 10-day aquifer test in relation to radial distance 

from the well, South Hadley, Massachusetts. ∆s is the change in 

drawdown over one logarithmic interval of radial distance; r0 is the 

intercept of radial distance, at zero drawdown; T is the aquifer 

transmissivity; and S is the aquifer storage coefficient.
Dry Brook

well

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

EXPLANATION

Dry

Brook

108

110

100

120

130

140

104

102

102

106

120

110

Layer 4

72o 72 35'30" o 72 36'00" o

36'30"

42o16'30"

42o

17'00"

Elmer Brook

Simulation of Ground-Water Flow 37

Figure 19. Steady-state simulated water-level contours for layers 3 and 4 at a pumping rate of 40.0 cubic feet per minute 

in the Dry Brook study area, Hadley, Holyoke, and South Hadley, Massachusetts.
Table 6. Comparison of observed to steady-state simulated ground-water levels under an average pumping rate of 40.0 cubic feet per 

minute, Dry Brook study area, South Hadley, Massachusetts.

[Range of observed water levels: Measured water levels shown in table 3. USGS, U.S. Geological Survey; ft, foot; --, not measured]

Local well

number

USGS well

number

(SUW)

Range of observed

water levels

Observed water 

levels on

11-16-2000

(ft)

Steady-state 

simulated water 

levels

(ft)

Difference

between observed

and simulated

water levels

(ft)

TW11-60 -- --

TW13-60 -- --

TW14-82 103.87 -1.31

TW15-82 105.60 -.04

TW1-95 101.83 .06

TW2-95 102.90 1.19

TW3-95 101.30 -.31

TW9-97 (P9) 99.81 -2.08

TW6-97 (P6) 100.66 .18

P-2 102.64 1.11

P-3 103.38 1.13

P-5 108.17 4.70

P-8 102.97 1.10

P-1 -- --

P-4B 100.14 -1.39

Average .................................................................................................................... 0.36

Average of absolute values ...................................................................................... 1.22

38 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

1

Within range of observed water levels.

51 97.24 100.38

52 95.06 99.48

69 103.21–105.25 1105.18

70 105.02–107.19 1105.64

73 101.25–104.23 1101.77

74 101.60–105.63 1101.71

81 99.25–107.07 1101.61

83 97.94–104.61 1101.89

85 97.77–105.85 1100.48

86 102.28–105.84 1101.53

87 102.39–104.86 102.25

89 107.51–108.71 103.47

90 101.87–105.18 1101.87

93 101.50–105.70 1101.70

94 97.86–106.40 1101.53

The ground-water-level contours indicate vertical head 

differences between layers 3 and 4 immediately around the Dry 

Brook well caused by sustained pumping at the well (fig. 19). 

Other locations with vertical head differences are east and 

southeast of the Dry Brook well, where 2- to 4-ft differences 

indicate upward flow from layer 4 to layer 3, the layer that was 

pumped (fig. 19). Simulated ground-water levels above stream 

stage indicate that ground water discharges to the lower ends of 

Dry Brook and Bachelor Brook, and to the Connecticut River. 

The close agreement of observed to simulated heads, along with 

the flow directions that are hydrologically reasonable, support 

the conclusion that the model as calibrated is a reasonable 

representation of the ground-water-flow system in the Dry 

Brook study area.

Delineation of Areas Contributing 

Water to Dry Brook Well

Areas contributing water to the Dry Brook public-supply 

well were delineated by using the calibrated steady-state 

ground-water-flow model with the MODPATH particletracking routine and the MODPLOT graphical routine 

available for the MODFLOW model (Pollock, 1994). For this 

application, the area contributing water to the Dry Brook well is 

defined as the surface area where water that eventually flows to 

the well enters the ground-water system (Reilly and Pollock, 

1993; Franke and others, 1998; U.S. Geological Survey, 2003, 

Office of Ground Water Technical Memorandum No. 2003.02). 

Areas contributing water to the Dry Brook well were delineated 

by using the average rate of pumping in 2000 (40.0 ft3/min, 

299 gal/min) and the MDEP-approved yield (122.2 ft3/min, 914 

gal/min; Joseph Cerutti, Massachusetts Department of 

Environmental Protection, written commun., 2000) (fig. 20). 

The MDEP-approved yield is about three times greater than the 

average rate of pumping in 2000. The maps (fig. 20A, B) show 

the distribution of starting positions for model-simulated 

particles entering the ground-water system as recharge or 

boundary flow that were forward-tracked through the aquifer, 

and that leave the system through pumping from the Dry Brook 

well. These particles are simulated points that travel along flow 

paths in the ground-water system as determined by the threedimensional MODFLOW model of the ground-water system in 

the area of the Dry Brook well.

A comparison of the water budgets for these two 

simulations is shown in table 7. The two sources of water flow 

to the supply well include water originating as either recharge 

and boundary flow, or infiltration from the Connecticut River. 
1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

Bachelor Brook

SOUTH

HADLEY

HOLYOKE

EXPLANATION

CONNECTICUT

RIVER

Dry Brook

Elmer Brook

SIMULATED AREA CONTRIBUTING WATER TO DRY BROOK

WELL AT PUMPING RATE OF 40.0 CUBIC FEET PER

MINUTE (299 GALLONS PER MINUTE)

. 72o 72 35'30" o

36'00"

42o16'30

42o17'00

72o36'30"

Delineation of Areas Contributing Water to Dry Brook Well 39

Figure 20. Extent of the simulated area contributing water to the Dry Brook well at pumping rates of A, 40.0; and B, 122.2 

cubic feet per minute, Hadley, Holyoke, and South Hadley, Massachusetts.
1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

Bachelor Brook

SIMULATED AREA CONTRIBUTING WATER TO DRY BROOK

WELL AT PUMPING RATE OF 122.2 CUBIC FEET PER

MINUTE (914 GALLONS PER MINUTE)

EXPLANATION

CONNECTICUT

RIVER

Elmer Brook

SOUTH

HADLEY

HOLYOKE

B. 72o 72 35'30" o

36'00"

42o

16'30"

42o

17'00"

72o36'30"

40 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 20. Extent of the simulated area contributing water to the Dry Brook well at pumping rates of A, 40.0; and B, 122.2 cubic 

feet per minute, Hadley, Holyoke, and South Hadley, Massachusetts.—Continued
Table 7. Comparison of steady-state model-simulated water budgets under average and the Massachusetts Department of 

Environmental Protection’s approved-yield pumping rates, and various model-parameter test simulations for the Dry Brook study area, 

Hadley, Holyoke, and South Hadley, Massachusetts

[In cubic feet per minute (not all totals equal the sum of items due to round-off error). A, MDEP-Approved Yield, “base case”; B, “base case” recharge × 1.25; C, 

“base case” recharge × 0.75; D, “base case” hydraulic conductivity × 1.2; E, “base case” hydraulic conductivity × 0.8; F, “base case” vertical hydraulic 

conductivity × 4.0; G, “base case” vertical hydraulic conductivity × 2.0; H, “base case” vertical hydraulic conductivity × 0.5. MDEP, Massachusetts Department 

of Environmental Protection]

Model budget component Average 

pumping A B C D E F G H

IN (inflow to the modeled area)

Constant heads (Connecticut River) 4.19 61.82 53.03 72.73 60.48 63.67 70.91 66.51 57.53

Recharge 103.40 103.40 129.25 77.55 103.40 103.40 103.40 103.40 103.40

Boundary flow 17.41 17.41 21.76 13.06 17.41 17.41 17.41 17.41 17.41

Total IN 125.00 182.63 204.05 163.34 181.29 184.48 191.72 187.32 178.34

OUT (outflow from modeled area)

Constant heads (Connecticut River) 68.96 46.60 61.65 32.43 46.30 46.78 55.38 51.11 42.49

Wells 40.00 122.20 122.20 122.20 122.20 122.20 122.20 122.20 122.20

River leakage (small streams) 16.08 13.83 20.23 8.77 12.92 15.50 14.21 14.02 13.65

Total OUT 125.04 182.63 204.09 163.40 181.42 184.48 191.79 187.33 178.35

Total IN – Total OUT -.04 .00 -.04 -.06 -.13 .00 -.07 -.01 -.01

Percent discrepancy -.03 .00 -.02 -.04 -.07 .00 -.04 .00 .00

Delineation of Areas Contributing Water to Dry Brook Well 41

Water entering the Dry Brook well from recharge and boundary 

flow dominates at a lower pumping rate (40.0 ft3/min); about 

90 percent of the pumped water originates from this source, 

and infiltration from the Connecticut River supplies the 

remaining 10 percent. At a higher pumping rate (122.2 ft3/min), 

in contrast, about half of the water pumped from the Dry Brook 

well originates from recharge and boundary flow (49 percent), 

and half originates from the infiltration of water from the 

Connecticut River (51 percent). Tripling the pumping rate from 

40.0 to 122.2 ft3/min, therefore, increases the amount of water 

entering the aquifer from the Connecticut River by nearly 

15 times the amount entering at the lower pumping rate, a 

difference of 57.6 ft3

/min. The assumption that the water 

entering the model from the constant-head cells that represent 

the Connecticut River is pumped from the Dry Brook well was 

tested by reducing the pumping rate at the well to zero. Under 

this tested condition, no water entered the aquifer from the 

constant-head cells, because the Connecticut River stage is the 

lowest water level in the study area when the well is not 

pumped. Generally, as the pumping rate at the Dry Brook well 

increases, more Connecticut River water infiltrates into the 

aquifer and is a source of water for the Dry Brook supply well.

A comparison of the two areas contributing water to the 

Dry Brook well indicates that, although the area contributing 

water increased in size as the pumping rate was increased from 

40.0 to 122.2 ft3/min, the overall increase in area was not as 

proportionally large as the increase in flow from the 

Connecticut River (fig. 20, table 7). The amount of water 

pumped by the Dry Brook well originating from recharge 

and boundary flow under average pumping conditions 

(40.0 ft3/min) is 35.8 ft3/min, whereas under MDEP-approved 

yield conditions (122.2 ft3

/min), that amount increases to 

60.4 ft3/min, about 70 percent greater than the amount under 

average conditions. Most of this increased recharge will enter 

the aquifer from the area of Dry Brook Hill, because this is 

where the soils are most permeable. In addition, the large gap in 

the area contributing water immediately around the Dry Brook 

well at the lower pumping rate is absent at the higher pumping 

rate. This gap is caused by the lacustrine sediment (varves) 

confining layer, which inhibits vertical flow, forcing recharge 

in this area to discharge to the lower end of Dry Brook and the 

Connecticut River. Water will flow vertically at the larger 

pumping rate, however, and some portion of the recharge in the 

area around the well will discharge from the well. At the larger 

pumping rate, the size of the area under the Connecticut River 

from which water will flow to the well increases, and the size of 

the area contributing water to the well from west of the river 

also increases (fig. 20).

Sensitivity and Uncertainty Analysis

The model sensitivity to recharge, boundary flows, and 

horizontal and vertical hydraulic conductivity was tested by 

increasing and decreasing these values to determine how these 

changes affect the simulated ground-water levels and flows. 
42 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

These results were also used to provide an estimate of 

uncertainty that can be expected within a reasonable range of 

accuracy of the model parameter values. Uncertainties 

associated with the contributing-area analysis were also 

evaluated by varying the model parameters within reasonable 

limits to simulate new areas contributing water to the well for 

comparison to the contributing area from the calibrated model.

Results of sensitivity tests that included increasing 

and decreasing the recharge and boundary flow rates by 25 

percent when pumping the Dry Brook well at the higher rate 

(122.2 ft3

/min) are shown on figure 21A (cases B and C, 

respectively). These results indicated that the area contributing 

water to Dry Brook well is robust, with relatively small changes 

under conditions of varied recharge. Under these conditions, the 

overall area increased or decreased by about 200 ft from the 

base condition further to the south and east across Dry Brook 

Hill, and the contribution from the Connecticut River increased 

to 60 percent of the pumpage when the recharge was decreased, 

as compared to 43 percent of the pumpage under higher 

recharge conditions (table 7). Although the amount of ground 

water discharged to Dry Brook and Bachelor Brook in the study 

area was small, it was sensitive to changes in the recharge rates, 

with discharge to these streams at the higher recharge value 

more than double that at the lower recharge value (table 7).

Other sensitivity tests of the model were conducted by 

increasing or decreasing the horizontal hydraulic conductivity 

by 20 percent uniformly across the area and all layers (cases D 

and E, respectively, fig. 21B). These simulation results 

indicated a small overall change in the size of the area 

contributing water, particularly in the eastern portion along 

Elmer Brook, where the size of the contributing area increased 

or decreased by 100 ft or less. The overall size of the area 

contributing water generally increased as the hydraulic 

conductivity was increased, and the area decreased slightly as 

the hydraulic conductivity was decreased. This effect is caused 

by expansion of the cone of depression created by pumping at 

the Dry Brook well. The cone of depression expands outward as 

the hydraulic conductivity increases (see fig. 8.6 in Freeze and 

Cherry, 1979). As with reduced recharge, the contribution of 

flow to the well from the Connecticut River increased slightly 

when hydraulic conductivity was decreased, from 51 percent 

in the base case to 52 percent. The larger hydraulic gradient 

that develops around the Dry Brook well as the hydraulic 

conductivity is decreased, and drawdowns are increased, causes 

this small effect. The contribution of flow to the well from the 

Connecticut River decreased as hydraulic conductivity was 

increased, to 50 percent of the total pumpage (table 7).

Additional sensitivity tests were simulated in which the 

vertical hydraulic conductivity of the model was increased by 

factors of 4 and 2, and decreased by 50 percent (cases F, G, and 

H, respectively, fig. 21B). The first two simulations greatly 

increase vertical ground-water flow in the model. The size of 

the area contributing water on Dry Brook Hill changed very 

little under these three simulations, but the size of the area 

across the Connecticut River, west of the Dry Brook well, was 

significantly affected (fig. 21B). The amount of water 

contributed by the river to the Dry Brook well decreased to 47 

percent when the vertical conductance was decreased by 50 

percent, and the amount increased to 52 and 54 percent when 

this parameter was increased by factors of 2 and 4, respectively 

(table 7). The effect of pumping ground water on the west side 

of the Connecticut River was also tested. When a simulated well 

in the flood plain directly across the Connecticut River from the 

Dry Brook well was pumped at a steady rate of 40.0 ft3

/min 

(299 gal/min), the steady-state modeling results indicated that 

the size of the area that had contributed water from the west side 

of the river to Dry Brook well was substantially reduced. This 

result indicates that the additional pumping from this well 

captures most of the water that, under the simulated conditions 

shown in figure 20, would have traveled to the Dry Brook well 

from the west side of the Connecticut River.

Transient Analysis and Contributing 

Watersheds

The MDEP wellhead-protection guidelines state that the 

contributing area to a well should be determined at the end of a 

transient 180-day period of no recharge from precipitation 

(Massachusetts Department of Environmental Protection, 

1996). The possible effects of an extended period of no recharge 

on contributing areas was determined by using a transient 

analysis of ground-water flow in the study area. For this 

analysis, the steady-state ground-water levels for average 

recharge conditions while pumping at the MDEP-approved 

yield were used as starting water levels for a transient 180-day 

period of no recharge while continuing to pump at the MDEPapproved yield. The storage properties used to simulate the 10-

day aquifer test were also used to simulate the 180-day period 

of no recharge. The resulting ground-water levels after the 

simulated 180-day period of no recharge are shown in figure 22, 

and were used to identify the zone in which ground water 

flowed toward the Dry Brook well during this period. This 

approach is commonly used to define wellhead-protection 

zones for public-supply wells in Massachusetts (Joseph Cerutti, 

Massachusetts Department of Environmental Protection, oral 

commun., 2003). Declines in simulated aquifer heads under 

these conditions were generally less than 5 ft in layer 3, and 

were only 0.55 ft for the Dry Brook well.
72o

36'30"

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

EXPLANATION

HOLYOKE

Dry Brook

72o 72 35'30" o36'00"

42o16'30"

42o

17'00"

Elmer Brook

A.

Delineation of Areas Contributing Water to Dry Brook Well 43

Figure 21. Sensitivity to various parameters of the simulated area contributing water to the Dry Brook well at a 

pumping rate of 122.2 cubic feet per minute for A, cases B and C; and B, cases D–H, Hadley, Holyoke, and South Hadley, 

Massachusetts.
Dry Brook

well

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

EXPLANATION

Dry Brook

Elmer Brook

72o 72 35'30" o

36'00"

42o16'30"

42o

17'00"

HOLYOKE

B. 72o

36'30"

44 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Figure 21—Continued. Sensitivity to various parameters of the simulated area contributing water to the Dry Brook well at 

a pumping rate of 122.2 cubic feet per minute for A, cases B and C; and B. cases D–H, Hadley, Holyoke, and South Hadley, 

Massachusetts.
Dry Brook

well

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

EXPLANATION

Dry

Brook

100

130

120

106

104

102

102

102

10

1

4

06

108

110

110

Elmer Brook

72o 72 35'30" o36'00"

42o16'30"

42o

17'00"

72o36'30"

Delineation of Areas Contributing Water to Dry Brook Well 45

Figure 22. Simulated ground-water-level contours for layers 3 and 4 at a pumping rate of 122.2 cubic feet per minute 

after a transient, 180-day period of no recharge and associated zone of ground-water flow towards the Dry Brook well, 

Hadley, Holyoke, and South Hadley, Massachusetts.
46 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

The simulated potentiometric surface for layer 3 at the end 

of the transient 180-day period of no recharge indicated the size 

of the area in which water flows toward Dry Brook well 

expanded about 500 ft (fig. 22) as compared to the area 

delineated under steady-state conditions (fig. 20B), but had a 

shape similar to the steady-state area. Although the size of the 

simulated area in which ground water flows towards Dry Brook 

well expanded during the 180-day period, and flow was 

reversed near the previously determined ground-water divides, 

the distance that water traveled during the period of flow 

reversal was likely to be short because of low hydraulic 

gradients near the divide. During wet periods, the ground-water 

divides would shift closer to the pumped well and flow would 

again reverse near the divides away from the well. The net 

effect would be little or no change from average conditions in 

the area contributing water. Reilly and Pollock (1995) 

demonstrated that half-year cyclic changes in recharge 

generally caused minor differences from average conditions in 

areas contributing water and in ground-water flow paths. This 

analysis, however, does delineate an expanded area around the 

supply well that could provide additional water-quality 

protection.

The steady-state zone of contribution for the Dry 

Brook well at the MDEP-approved yield (122.2 ft3/min) 

incorporates the area contributing water to the Dry Brook 

well within the model boundaries (fig. 20B), the associated 

watersheds draining to this area, and the area through which this 

water flows to the well (fig. 23). The primary area contributing 

water for the Dry Brook well is shown on figure 23, and the 

associated watersheds that contribute water to the well 

primarily by overland flow and a minor amount as subsurface 

flow are also shown on this figure. The slopes in the watershed 

areas are generally steep, and much of the precipitation in these 

areas may not infiltrate, but instead flow directly to Dry Brook 

or the Connecticut River. As discussed, simulation of water 

sources to the Dry Brook well at the MDEP-approved-yield 

conditions shown in figure 23 indicates that about half of the 

water pumped from the Dry Brook well entered the groundwater system from the Connecticut River, and half entered the 

ground-water system as recharge and boundary flow, most of 

which entered from Dry Brook Hill. Dry Brook Hill is 

important to the protection of the water quality in the Dry Brook 

well because this area contributes water under both higher and 

lower pumping scenarios, and is potentially vulnerable to 

contamination because of its permeable sandy soils and aquifer 

materials.

The aquifer pumped by the Dry Brook well is partially 

confined by very fine-grained (varved) lacustrine sediments, 

which overlie the area around the well. Although relatively little 

water passes through the confining bed (about 1 ft3/min under 

the MDEP-approved yield), the confining bed overlying the 

Dry Brook well is included in the zone of contribution because 

water passes underneath this area as it travels from where it 

enters the aquifer to the well. An estimate of the time that it 

would take for water to travel vertically from the land surface to 

the Dry Brook well can be made by using simulation results 

with pumping at the MDEP-approved yield and the following 

equation:

Time of travel = z v⁄ nz

2 Kv = ⁄ ( ) dh , (4)

where

z is the vertical distance (100 ft),

v is the velocity of ground water,

n is the porosity (0.5),

Kv is the vertical hydraulic conductivity (10-5 ft/min), and 

dh is the vertical head difference (17.8 ft).

The resulting travel time is about 50 years, indicating that 

although the confining bed likely protects the water quality 

of the aquifer from immediate degradation by surface 

contamination, long-term migration of persistent contaminants 

from the surface is possible if those contaminants are present. 

This calculation of time of travel assumes conservative 

(nonreactive) transport at the point of greatest head difference in 

the vertical; and because the head differences would be less at 

greater distances from the Dry Brook well, the time required for 

water to travel through the confining bed is likely to be greater 

than 50 years.
EXPLANATION

AREA CONTRIBUTING WATER TO

DRY BROOK WELL

WATERSHED AREA CONTRIBUTING

WATER TO DRY BROOK WELL

Dry Brook

well

72o 72 34'00" o36'00"

1,000

300 600 METERS

0

0

2,000 FEET

CONTOUR INTERVAL 10 FEET

NATIONAL GEODETIC VERTICAL DATUM 1929

Base from U.S. Geological Survey digital raster data,1:25,000,

topographic quandrangle, Mt. Holyoke, 1964,

photorevised 1979, North American datum 1927,

Polyconic projection, zone 18

42o

16'30"

42o

17'30"

RIVER

HADLEY

HOLYOKE

Delineation of Areas Contributing Water to Dry Brook Well 47

Figure 23. Zone of contribution and associated watershed areas contributing water to the Dry Brook well at a pumping 

rate of 122.2 cubic feet per minute, Hadley, Holyoke, and South Hadley, Massachusetts.
48 Delineation of Areas Contributing Water to the Dry Brook Public-Supply Well, South Hadley, Massachusetts

Suggestions for Future Study

The simulation results discussed above demonstrate the 

potential importance of drawdown observations from wells 

across the Connecticut River from the Dry Brook well for 

any additional aquifer tests conducted at the Dry Brook well. 

Water-level observations in this area would increase 

understanding of the degree to which the Connecticut River 

affects head conditions in the aquifer and ground-water flows 

under the river to the well. For example, if it can be shown that 

drawdown from pumping the Dry Brook well at a relatively 

high rate does not propagate under the river, as was the case for 

the Hockanum Flat test well located about 2,000 ft north of the 

Dry Brook well (Tighe and Bond, 1999), then this would be 

important information for any subsequent interpretation of the 

hydrogeologic conditions in this part of the aquifer. Future 

investigations of ground-water flow in the study area would 

benefit from additional water-level measurements in the Dry 

Brook Hill area, along with obtaining additional information on 

the hydraulic characteristics of the Mesozoic-aged bedrock 

underlying the hill.

On the basis of this study, the important components 

needed in future studies to properly delineate areas contributing 

water to public-supply wells developed in confined aquifers 

include geologic information on the vertical and lateral 

extent of the confining beds and aquifer materials, and a 

conceptual model of ground-water flow in the aquifer based on 

hydrogeologic data that takes into consideration the movement 

of ground water from recharge to discharge areas. Other 

components include hydrologic data quantifying aquifer gains 

and losses of water from streams and ponds, and accurate 

estimates of recharge rates, which appear to be an important 

determinant of the extent of the areas contributing water to 

supply wells across Massachusetts (Lyford and others, 2003), 

including those in confined ground-water-flow systems.

Summary and Conclusions

Areas contributing water to the Dry Brook publicsupply well in South Hadley, MA, were delineated by using a 

numerical ground-water-flow model that was based on exisiting 

and newly developed geologic and hydrologic information for 

the confined sand and gravel aquifer tapped by the supply well. 

This study was undertaken in 1999 by the U.S. Geological 

Survey, in cooperation with the Massachusetts Department of 

Environmental Protection, to investigate the factors needed to 

properly delineate areas contributing water to public-supply 

wells developed in confined aquifers in Massachusetts. 

The study area is along the Connecticut River in central 

Massachusetts, about 12 mi north of Springfield, MA. Geologic 

units in the study area consist of Mesozoic-aged sedimentary 

and igneous bedrock, late-Pleistocene glaciolacustrine 

sediments, and recent alluvial deposits of the Connecticut River 

flood plain. Dry Brook Hill, immediately south of the supply 

well, is a large subaqueous lacustrine fan and delta formed 

during the last glacial retreat by sediment deposition into glacial 

Lake Hitchcock from a meltwater tunnel that was likely near 

where the Connecticut River cuts through the Holyoke Range. 

The sediments that compose the aquifer grade from very coarse 

sand and gravel along the northern flank of the hill to medium 

sands in the body of the hill, to finer-grained sediments along 

the southern flank of the hill. The interbedded and overlapping 

fine-grained lacustrine sediments associated with Dry Brook 

Hill include varved silt and clay deposits. These fine-grained 

sediments form a confining bed above the coarse-grained 

aquifer at the supply well and partially extend under the 

Connecticut River adjacent to the supply well.

Ground-water flow in the aquifer supplying water to the 

Dry Brook well was simulated with the USGS ground-waterflow modeling code MODFLOW. The Dry Brook aquifer 

model was calibrated by using drawdown data collected in

8 observation wells during an aquifer test conducted by 

pumping the supply well for 10 days at a rate of 122.2 ft3

/min. 

(914 gal/min) and by using water levels collected in observation 

wells across the study area. Generally, the largest hydraulic 

conductivities were in the sand and gravel aquifer in the 

immediate vicinity of the well, which is consistent with the 

geologic information. Results of aquifer-test simulation 

indicated heads and ground-water flow near the Dry Brook well 

are affected by spatially variable aquifer hydraulic properties 

and boundary conditions. A comparison and analysis of groundwater-level fluctuations in study-area wells to fluctuations in 

the Connecticut River indicated a hydraulic connection of the 

aquifer with the river, which is also consistent with geologic 

information. Simulated ground-water levels indicated that most 

ground water in the study area flows towards and discharges to 

the Connecticut River and the Dry Brook well. Small amounts 

of ground water also discharge to smaller streams in the study 

area (Bachelor Brook and Dry Brook).

Delineation of areas contributing water to the well was 

completed by using the MODPATH particle-tracking routine. 

Results of the contributing-area analysis indicated that the 

greatest sources of water to the well were recharge in the Dry 

Brook Hill area and infiltration of Connecticut River water in an 

area beyond the extent of the confining bed where the aquifer is 

hydraulically connected to the river. Water entering the Dry 

Brook well from recharge and boundary flow dominates at a 

lower pumping rate (40.0 ft3/min); about 90 percent of the 

pumped water originates from this source, and infiltration from 

the Connecticut River supplies the remaining 10 percent. At a 

higher pumping rate (122.2 ft3/min), in contrast, about half of 

the water pumped from the Dry Brook well originates from 

recharge and boundary flow, and half originates from the 

infiltration of water from the Connecticut River. Tripling the 

pumping rate from 40.0 to 122.2 ft3/min increases the amount 

of water entering the aquifer from the Connecticut River by 

nearly 15 times the amount entering at the lower pumping rate.
References Cited 49

Results of the sensitivity analysis of the extent of areas 

contributing water to the Dry Brook well indicated that the size 

of these areas did not substatially change when aquifer 

properties were varied; however, the size of these areas changed 

the most when the recharge rate was changed. When the 

recharge rate was decreased by 25 percent, the extent of the area 

increased by about 200 feet farther to the south and east across 

Dry Brook Hill. When recharge was increased by 25 percent, 

the extent of the area decreased by about 200 ft on the south and 

east sides of Dry Brook Hill. The contribution from the 

Connecticut River increased to 60 percent of the total pumpage 

when the recharge was decreased as compared to 43 percent of 

the total pumpage under higher recharge conditions. These 

results indicated Dry Brook Hill is important to the protection 

of the water-quality in the Dry Brook well because this area 

contributes water under a number of simulated conditions, and 

is potentially vulnerable to contamination because of its 

permeable sandy soils and aquifer materials.

On the basis of this study, the important components 

needed in future studies to properly delineate areas contributing 

water to public-supply wells developed in confined aquifers 

include geologic information on the vertical and lateral 

extent of the confining beds and aquifer materials, and a 

conceptual model of ground-water flow in the aquifer based on 

hydrogeologic data that takes into consideration the movement 

of ground water from recharge to discharge areas. Other 

components include hydrologic data quantifying aquifer gains 

and losses of water from streams and ponds, and accurate 

estimates of recharge rates, which appear to be an important 

determinant of the extent of the areas contributing water to 

supply wells across Massachusetts, including those in confined 

ground-water-flow systems.

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