Simulation of Ground-Water Flow and 

Areas Contributing Recharge to 

Production Wells in Contrasting 

Glacial Valley-Fill Settings, Rhode Island

By Paul J. Friesz and Janet R. Stone

Prepared in cooperation with the Rhode Island Department of Health

Scientific Investigations Report 2007–5133

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

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

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names 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:

Friesz, P.J., and Stone, J.R., 2007, Simulation of ground-water flow and areas contributing recharge to production 

wells in contrasting glacial valley-fill settings, Rhode Island: U.S. Geological Survey Scientific Investigations Report 

2007–5133, 50 p.
iii

Contents

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

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

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

Description of Study Sites and Previous Investigations ................................................................2

Numerical Modeling......................................................................................................................................4

Hydraulic Properties.............................................................................................................................5

Recharge Rates.....................................................................................................................................5

Harrisville Study Site.....................................................................................................................................5

Geology...................................................................................................................................................7

Hydrology ...............................................................................................................................................9

Ground-Water-Flow Model ...............................................................................................................15

Model Design..............................................................................................................................15

Simulation of Ground-Water Flow...........................................................................................19

Areas Contributing Recharge to Production Wells..............................................................20

Sensitivity and Uncertainty Analysis......................................................................................25

Richmond Study Site ...................................................................................................................................29

Geology.................................................................................................................................................29

Hydrology .............................................................................................................................................32

Ground-Water-Flow Model ...............................................................................................................33

Model Design..............................................................................................................................34

Simulation of Ground-Water Flow...........................................................................................37

Areas Contributing Recharge to Production Wells..............................................................39

Sensitivity and Uncertainty Analysis......................................................................................42

Summary and Conclusions.........................................................................................................................46

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

References Cited..........................................................................................................................................48
iv

Figures

1–4. Maps showing—

1. Study sites in Rhode Island and selected U.S. Geological Survey (USGS) long-term 

network streamflow-gaging stations and observation wells, and National 

Oceanic and Atmospheric Administration (NOAA) climatological stations ...............3

2. Production wells, section lines, selected borings and observation wells, 

model extent, and surficial geology, Harrisville study site, Rhode Island...................6

3. Data-collection network near production wells and water levels on 

June 24, 2005, Harrisville study site, Rhode Island..........................................................8

4. Bedrock-surface contours, Harrisville study site, Rhode Island.................................10

5. Geologic cross sections (lines of sections A-A’ and B-B’ are shown in figure 2),

Harrisville study site, Rhode Island .........................................................................................11

6–7. Graphs showing—

6. Water levels measured in observation well BUW187, 1997–2006 Harrisville study 

site, Rhode Island................................................................................................................13

7. Paired surface-water altitudes and ground-water altitudes at selected 

streambed piezometers in Batty Brook, 2004–2006 Harrisville study site, 

Rhode Island ........................................................................................................................14

8. Model-boundary types, recharge rates, simulated water-table contours for 

nonpumping, steady-state conditions, and spatial distribution of residuals

(measured-simulated), Harrisville study site, Rhode Island................................................17

9. Graph showing (A) Relation between simulated and measured ground-water 

levels and (B) residual (measured minus simulated) ground-water levels as a 

function of measured ground-water levels, Harrisville study site, Rhode Island............19

10–16. Maps showing.................................................................................................................................

10. Simulated area contributing recharge to the Harrisville well field at its 

average pumping rate of 224 gallons per minute, Harrisville study site, 

Rhode Island ........................................................................................................................21

11. Simulated area contributing recharge to the Harrisville well field at its 

maximum pumping rate of 600 gallons per minute, Harrisville study site, 

Rhode Island ........................................................................................................................22

12. Simulated traveltimes to the Harrisville well field at its maximum pumping 

rate of 600 gallons per minute, Harrisville study site, Rhode Island...........................24

13. Sensitivity analysis of the effects of multiplying the vertical hydraulic 

conductivity of streambed sediments at the well-field site by 0.5 and by 2, 

Harrisville study site, Rhode Island..................................................................................26

14. Sensitivity analysis of the effects of multiplying the hydraulic conductivity of

stratified deposits by 0.75 and by 1.25, Harrisville study site, Rhode Island .............27

15. Sensitivity analysis of the effects of multiplying recharge rates by 0.75 and 

by 1.25, Harrisville study site, Rhode Island ...................................................................28

16. Production wells, section lines, selected borings and observation wells, 

model extent, surficial geology, and bedrock-surface contours, Richmond study 

site, Rhode Island................................................................................................................30

17. Geologic cross sections showing Richmond study site, Rhode Island.............................31
v

Tables

1. Characteristics of the production wells for the Harrisville and Richmond study 

sites, Rhode Island .......................................................................................................................7

2. Streamflow and drainage-area characteristics of the Branch and Nipmuc River 

streamflow-gaging stations, Harrisville study site, Rhode Island......................................13

3. Summary of the long-term mean annual streamflow analysis for the temporary 

streamflow-gaging stations upstream of the well-field site, Harrisville study site, 

Rhode Island................................................................................................................................16

4. Summary of simulated values for hydraulic properties and recharge rates in the 

ground-water-flow model for the Harrisville study site, Rhode Island..............................16

5. Simulated steady-state average annual hydrologic budget for nonpumping 

conditions, Harrisville study site, Rhode Island.....................................................................20

6. Sizes of areas contributing recharge to the Harrisville production well field 

(Central Street) and the percentages of water withdrawn from different sources, 

Harrisville study site, Rhode Island .........................................................................................23

7. Streamflow and drainage-area characteristics of selected streamflow-gaging 

stations in and near the Richmond study site, Rhode Island ..............................................33

8. Summary of the long-term mean annual ground-water discharge analysis for 

partial-record sites, Richmond study site, Rhode Island.....................................................34

9. Summary of simulated values for hydraulic properties and recharge rates in the 

ground-water-flow model for the Richmond study site, Rhode Island..............................35

10. Simulated steady-state average annual hydrologic budget for nonpumping 

conditions, Richmond study site, Rhode Island.....................................................................38

11. Sizes of areas contributing recharge to the Richmond production well field and 

the percentages of water withdrawn from different sources, Richmond study site, 

Rhode Island................................................................................................................................39

18. Model-boundary types, recharge rates, simulated water-table contours for 

nonpumping, steady-state conditions, and spatial distribution of 

residuals (measured-simulated), Richmond study site, Rhode Island...............................36

19. Graphs showing (A) Relation between simulated and measured ground-water

levels and (B) residual (measured minus simulated) ground-water levels as a

function of measured ground-water levels, Richmond study site, Rhode Island............38

20–24. Maps showing—

20. Simulated area contributing recharge to the Richmond well field at 

337.5 gallons per minute, which is half of its maximum pumping rate of 

675 gallons per minute, Richmond study site, Rhode Island ...............................................40

21. Simulated area contributing recharge to the Richmond well field at its 

maximum pumping rate of 675 gallons per minute, Richmond study site,

Rhode Island................................................................................................................................41

22. Simulated traveltimes to the Richmond well field at its maximum pumping 

rate of 675 gallons per minute, Richmond study site, Rhode Island...................................43

23. Sensitivity analysis of the effects of multiplying the hydraulic conductivity of

stratified deposits by 0.75 and by 1.25, Richmond study site, Rhode Island.....................44

24. Sensitivity analysis of the effects of multiplying recharge rates by 0.75 and 

by 1.25,Richmond study site, Rhode Island ............................................................................45
vi

Conversion Factors, Datums, and Acronyms

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

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

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

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

Transmissivity

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

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

 °C=(°F-32)/1.8

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

(NGVD 29).

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

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

ABBREVIATIONS

MTBE methyl tert-butyl ether

RIDEM Rhode Island Department of Environmental Management

RIDOH Rhode Island Department of Health

USGS U.S. Geological Survey
Abstract

Areas contributing recharge and sources of water to a 

production well field in the Village of Harrisville and to a production well field in the Town of Richmond were delineated 

on the basis of calibrated, steady-state ground-water-flow 

models representing average hydrologic conditions. The study 

sites represent contrasting glacial valley-fill settings. The area 

contributing recharge to a well is defined as the surface area 

where water recharges the ground water and then flows toward 

and discharges to the well.

In Harrisville, the production well field is composed of 

three wells in a narrow, approximately 0.5-mile-wide, valleyfill setting on opposite sides of Batty Brook, a small intermittent stream that drains 0.64 square mile at its confluence with 

the Clear River. Glacial stratified deposits are generally less 

areally extensive than previously published. The production 

wells are screened in a thin (30 feet) but transmissive aquifer. 

Paired measurements of ground-water and surface-water levels 

indicated that the direction of flow between the brook and the 

aquifer was generally downward during pumping conditions. 

Long-term mean annual streamflow from two streams upgradient of the well field totaled 0.72 cubic feet per second.

The simulated area contributing recharge for the 2005 

average well-field withdrawal rate of 224 gallons per minute 

extended upgradient to ground-water divides in upland areas 

and encompassed 0.17 square mile. The well field derived 

62 percent of pumped water from intercepted ground water 

and 38 percent from infiltrated stream water from the Batty 

Brook watershed. For the maximum simulated well-field 

withdrawal of 600 gallons per minute, the area contributing 

recharge expanded to 0.44 square mile to intercept additional 

ground water and infiltration of stream water; the percentage 

of water derived from surface water, however, was the same 

as for the average pumping rate. Because of the small size 

of Batty Brook watershed, most of the precipitation recharge 

in the watershed was withdrawn by the well field at the 

maximum rate either by intercepted ground water or indirectly 

by infiltrated stream water. Because the production wells 

are screened in a thin and transmissive aquifer in a small 

watershed, simulated ground-water traveltimes from recharge 

locations to the discharging wells were relatively short: 

93 percent of the traveltimes were 10 years or less.

In Richmond, the production well field is composed 

of two wells adjacent to and east of the Wood River in a 

moderately broad, approximately 1.2-mile-wide, valley-fill 

setting. The wells are screened in a transmissive aquifer 

with saturated thickness greater than 60 feet. Streamflow 

measurements in Baker Brook, a tributary to the Wood River 

0.4 mile north of the well-field site, indicated that natural net 

loss of streamflow between the upland-valley contact and a 

downstream site was 0.12 cubic feet per second under average 

hydrologic conditions.

Simulated areas contributing recharge for the maximum 

well-field pumping rate of 675 gallons per minute and for 

one-half the maximum rate extended northeastward from the 

well field to ground-water divides in upland areas. The area 

contributing recharge also included a remote, isolated area on 

the opposite side of the Wood River from the well field. The 

model simulation indicated that the well field did not derive 

any of its water from the Wood River because of the large 

watershed and associated quantity of ground water available 

for capture by the well field.

The area contributing recharge for one-half the maximum 

rate was 0.31 square mile and the primary source of water 

to the well field was direct precipitation recharge. Fifteen 

percent of the water withdrawn from the production wells, 

however, was obtained from Baker Brook, indicating the 

importance of even small, distant tributary streams to the 

contributing area to a well. The area contributing recharge 

on the opposite side of the Wood River is a small upland till 

area. For the maximum pumping rate, the 0.66-square-mile 

area contributing recharge extended farther up and down the 

valley to intercept additional ground water and infiltration 

from Baker Brook; the percentage of pumped water derived 

from Baker Brook (10 percent), however, was less than for the 

lower pumping rate. The area contributing recharge across the 

Wood River included upland till and stratified deposits near 

the upland-valley contact. Because the Richmond well field is 

in a larger watershed with saturated sediments thicker than at 

the Harrisville site, the overall ground-water traveltimes are 

greater: only 54 percent of the traveltimes are 10 years or less.

Simulation of Ground-Water Flow and Areas Contributing 

Recharge to Production Wells in Contrasting Glacial 

Valley-Fill Settings, Rhode Island

By Paul J. Friesz and Janet R. Stone
2 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Hydrologic factors that most affected the simulated areas 

contributing recharge to production wells in the two contrasting valley-fill settings were recharge rates, the locations of 

upgradient ground-water divides, aquifer transmissivity, and, 

depending on the setting, the hydraulic connection between 

surface water and the aquifer. A well in the vicinity of a 

surface-water source may not always induce flow from that 

source, even if surface and ground waters are well connected, 

because the amount of water that a well draws from surface 

water also depends on the pumping rate and the quantity of 

ground water that the well can intercept. The area contributing recharge to a well also may include areas on the opposite 

side of a river from the well, despite the fact that the river is 

a major source of water in close proximity to the well. Under 

pumping conditions, precipitation recharge originating on the 

opposite side of a river may pass beneath the river and discharge to the well, although there may be little or no induced 

infiltration of river water. Areas contributing recharge can also 

extend into upland areas to ground-water divides and can also 

include isolated areas remote from a well.

Introduction

Accurate delineation of areas contributing recharge to 

production wells is an essential component of Federal, State, 

and local and strategies for the protection of drinking-water 

supplies from contamination (U.S. Environmental Protection 

Agency, 1991). The Source Water Assessment Program of 

the Rhode Island Department of Health (RIDOH), Office of 

Drinking Water Quality, was established by the 1996 Amendments to the Federal Safe Drinking Water Act. Since that time, 

RIDOH has assessed the susceptibility and risk of publicwater supplies to contamination and encourages land-use 

planning within the areas contributing recharge to a production 

well. The Rhode Island Department of Environmental Management (RIDEM), Office of Water Resources, has determined 

areas contributing recharge to most production wells in Rhode 

Island, but the RIDEM and RIDOH do not have a high degree 

of confidence in some of the contributing areas delineated for 

wells in complex hydrologic settings. Numerical groundwater-flow modeling, coupled with a particle-tracking 

technique, is a more advanced method for delineating areas 

contributing recharge than the analytical methods that have 

previously been used for this purpose.

The Village of Harrisville well field (Central Street) is 

an important ground-water supply in northwestern Rhode 

Island (fig. 1). The RIDOH determined this well field, 

screened in a thin, unconfined aquifer only 30 ft thick, to be 

at high risk of contamination (Clay Commons, Rhode Island 

Department of Health, written commun., 2004). A well 

field in the neighboring Village of Pascoag was abandoned 

in 2001 because of contamination from methyl tert-butyl 

ether (MTBE), thereby requiring Pascoag to connect to the 

Harrisville water supply. This action more than doubled the 

population served and caused the water system to operate near 

capacity. In addition, a second well field in Harrisville has 

had water-quality concerns (Clay Commons, Rhode Island 

Department of Health, written commun., 2004). This second 

well field is in a flood plain near the confluence of two rivers 

and is susceptible to flooding. In October 2005, flooding due 

to a major precipitation event required the town to discontinue 

operations at the well field for nine days; the Central Street 

well field was then the sole source of water supply.

The Town of Richmond well field in southwestern Rhode 

Island (fig. 1) was originally installed to provide water to a 

nearby village where residential wells had been contaminated. 

Population growth and development are expected to increase 

in the future in the surrounding area.

The production well fields in Harrisville (Central Street) 

and Richmond are near surface-water sources in glacial valleyfill settings, but these settings differ. These differences include 

aquifer thickness and width, the size of the area upgradient 

of the well field, and the size of the nearby stream. As part of 

the effort to protect the quality of the ground-water supplies 

in Rhode Island, the U.S. Geological Survey (USGS), in 

cooperation with the RIDOH, began a 2-year study in 2004 

to increase understanding of the geohydrology and of the 

important hydrologic factors required to properly delineate 

areas contributing recharge and the sources of water to the 

well fields in these contrasting glacial valley-fill settings.

Purpose and Scope

This report describes the geohydrology and the areas 

contributing recharge and sources of water to the Village 

of Harrisville production well field (Central Street), which 

is composed of three wells, and to the Town of Richmond 

production well field, which is composed of two wells. 

Numerical ground-water-flow models were developed 

and calibrated for each study site on the basis of geologic 

and hydrologic data collected during this and previous 

investigations. The simulated areas contributing recharge to 

the production wells and the associated simulated groundwater traveltimes from recharging locations to withdrawal 

points in these two glacial valley-fill settings are shown on 

maps for selected pumping rates and average, steady-state 

hydrologic conditions. Maps also show the effects of selected 

hydrologic properties and of recharge rates on the sizes, 

shapes, and locations of the delineated areas contributing 

recharge and on the sources of water to the production wells.

Description of Study Sites and 

Previous Investigations

The Harrisville study site is in the Clear River watershed 

in northwestern Rhode Island and the Richmond study site 

is in the Wood River watershed in southwestern Rhode 

Island (fig. 1). The climate is humid and temperate with an 

average annual temperature of about 50°F and average annual 

precipitation of 49 in. over the northern and 51 in. over the 
Introduction 3

Figure 1. Study sites in Rhode Island and selected U.S. Geological Survey (USGS) long-term network 

streamflow-gaging stations and observation wells, and National Oceanic and Atmospheric Administration 

(NOAA) climatological stations.

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:100,000, NAD 83

Pawcatuck

River

Harrisville

Study Site

Narragansett

Bay

Block Island Sound

Branch River

BURRILLVILLE

RICHMOND Wood River

Clear River

Richmond

Study Site

Study-site location

USGS streamflow-gaging

 station and identifier

USGS observation well

 and identifier

NOAA climatological

 station and identifier

EXPLANATION

71O45’

42O

41O30’

71O30’

0

0

10 MILES

10 KILOMETERS

MASSACHUSETTS

MASSACHUSETTS

CONNECTICUT

RHODE ISLAND

01111500

01111300 01111300

BUW187 BUW187

EXW6 01117800

01118000

01117468

01118300

01175670

374266

379423

374266

(latitude=42O15'54", 

longitude=72O

00'19")

(latitude=41O28' 29" 

longitude=71O

50' 05")
4 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

southern parts of the state on the basis of records from 1960 

through 2005 for the Woonsocket (379423) and Kingston 

(374266), Rhode Island, climatological stations (National 

Oceanic and Atmospheric Administration, 2006) (fig. 1).

Ground water at the study sites is stored and transmitted in surficial sediments of glacial origin—till and stratified 

deposits—and in the underlying bedrock. A thin, discontinuous layer of till deposited directly on the bedrock by glacial 

ice is composed of a poorly sorted mixture of sediments ranging in size from clay to boulders. Stratified deposits overlie the 

till in the valleys and consist of well-sorted, layered sediments 

ranging in size from clay to gravel deposited by glacial meltwater. The direction of ground-water flow is generally from 

the till in the uplands toward streams and stratified deposits 

in the valleys. The production wells are screened in coarsegrained stratified deposits composed of sand and gravel. Sand 

and gravel deposits are the primary aquifers in Rhode Island 

because of the higher storage and transmissive properties of 

these deposits compared to other geologic units.

The Harrisville study site is characterized by narrow 

river valleys approximately 0.5 mi wide bordered by steep 

hillslopes. The well field, which is in close proximity to a 

brook in a small watershed of the Clear River, is screened in 

thin and shallow saturated stratified sediments. Geologic and 

hydrologic information was available from regional USGS 

investigations of areas that include the study site. Previous 

studies of areas of the Clear River watershed (Hahn, 1961) 

and the Branch River watershed in Rhode Island (Johnston 

and Dickerman, 1974a) analyzed the ground-water and 

surface-water resources. Site-specific information from these 

regional investigations was available for the older production 

wells at the study site. A reconnaissance study of groundwater conditions in the area covered by the USGS Chepachet 

quadrangle, which includes the study site, was completed 

by Hahn and Hansen (1961). This study published a general 

map of the surficial geology with the approximate location 

of the contact between the stratified deposits and till; detailed 

mapping of the surficial deposits has not been completed for 

the area within the Chepachet quadrangle.

The Richmond study site is characterized by a moderately 

broad river valley approximately 1.2 mi wide bordered by tillcovered uplands. The well field is near the Wood River, a large 

tributary to the Pawcatuck River, and is screened deeper and 

in thicker saturated sediments than the well field at the Harrisville study site. Previous USGS investigations in the area 

covered by the USGS Hope Valley quadrangle, which includes 

the study site, include a reconnaissance of the ground-water 

conditions (Bierschenk and Hahn, 1959) and detailed mapping 

of the surficial deposits (Feininger, 1962). The first comprehensive investigation of the ground-water and surface-water 

resources of the lower Pawcatuck River watershed, which 

includes the Wood River watershed, was done by Gonthier 

and others (1974). More recently, a study on the availability of 

ground water in the upper Wood River watershed by Dickerman and Bell (1993) included a simplified two-dimensional 

flow model of the valley-fill deposits. An associated data 

report (Dickerman and others, 1989) compiled geologic and 

hydrologic data, including data from the previous studies.

Numerical Modeling

Many hydrologic features and processes may affect the 

size, shape, and location of the area contributing recharge 

to a well; this area is defined as the surface area where 

water recharges the ground water and then flows toward and 

discharges to the well (Reilly and Pollock, 1993). Features 

and processes such as ground-water systems with irregular 

geometry and complex lithology, or the interaction between 

individual pumping wells and hydrologic features such as 

surface-water bodies, are difficult to represent with analytical 

methods. Three-dimensional finite-difference numerical 

ground-water-flow models, however, can represent these 

and other geologic and hydrologic features and processes. 

Information provided by a numerical model on the source of 

water to a well can also be useful in the protection of public 

health in Rhode Island.

Ground-water-flow models based on the computer code 

MODFLOW-2000 (McDonald and Harbaugh, 1988; Harbaugh 

and others, 2000) and capable of simulating the response of 

the ground-water system to production-well withdrawals were 

developed for each of the two study sites. Areas contributing 

recharge and the sources of water to the production wells 

were determined on the basis of model simulations of average, 

steady-state hydrologic conditions and by use of the particletracking program MODPATH (Pollock, 1994). The particletracking program calculates ground-water-flow paths and 

traveltimes on the basis of the head distribution computed by 

the ground-water-flow simulation. Areas contributing recharge 

were delineated by forward tracking of particles from the top 

faces of model cells in recharging areas to the discharging 

wells. Particles were allowed to pass through model cells with 

weak sinks, which remove only a part of the water that flows 

into the cell.

Development of a ground-water-flow model required that 

the geometry and hydraulic properties of the ground-water 

system and fluxes into and out of the model be quantified. 

Model-input parameters were assigned from the literature 

or calibrated to water levels and streamflows. Models were 

calibrated by adjusting model-input parameters within reasonable ranges until the simulated water levels and streamflows approximated measured water levels and streamflows. 

Improvements in model-simulation results were achieved by 

minimizing the differences, or residuals, between simulated 

and measured values. Models, however, produce non unique 

solutions such that the same simulated response in water 

levels and streamflows may be obtained by using different 

combinations of hydraulic properties and recharge rates. This 

nonuniqueness was addressed by a sensitivity and uncertainty 

analysis for each study-site model to demonstrate how alternative but plausible model-input values affect the simulated areas 

contributing recharge to the well fields.
Harrisville Study Site 5

Hydraulic Properties

The hydraulic properties of glacial till are not well 

known. Aquifer tests and laboratory measurements indicated 

that hydraulic conductivity values for till in southern Rhode 

Island range from 0.07 to 41 ft/d with a median of 0.7 ft/d 

(Allen and others, 1966). Melvin and others (1992) summarized the hydraulic properties of till from previous studies in 

southern New England: for till derived from crystalline bedrock, horizontal hydraulic conductivities ranged from 0.004 to 

65 ft/d and vertical hydraulic conductivities ranged from 0.013 

to 96 ft/d. Porosity values determined from a limited number 

of measurements in southern Rhode Island by Allen and others 

(1963) ranged from 0.23 to 0.50 and averaged 0.30. Porosity values ranged from 0.22 to 0.41 and averaged 0.33 from 

a limited number of measurements in southern New England 

(Melvin and others, 1992).

Horizontal hydraulic conductivity values of glacial 

stratified deposits were estimated from lithology and available aquifer-test results at the production-well fields. Values 

determined from lithology were based on the relation between 

horizontal hydraulic conductivity and grain size determined 

by Rosenshein and others (1968) from aquifer-test results in 

southern Rhode Island. These values are 50 ft/d for fine sand, 

100 ft/d for sand, 200 ft/d for sand and gravel, and 500 ft/d for 

gravel. The vertical hydraulic conductivity averaged one-tenth 

the horizontal hydraulic conductivity on the basis of aquifertest analyses in southern Rhode Island by Dickerman (1984). 

The porosities of 24 stratified-sediment samples in southern 

Rhode Island reported by Allen and others (1963) ranged from 

0.26 to 0.42 with an average value of 0.34. LeBlanc (1987) 

reported a range of porosities from 0.35 to 0.40 for stratified 

deposits on western Cape Cod, Massachusetts.

Hydraulic properties of crystalline bedrock are generally 

low. Analysis of specific-capacity data from bedrock wells 

in eastern Connecticut indicated an average hydraulic 

conductivity of 0.5 ft/d (Randall and others, 1966). Lower 

values of 0.02 and 0.09 ft/d for crystalline bedrock in northern 

New Hampshire were determined through model calibration 

(Tiedeman and others, 1997). The range of porosity values for 

crystalline rock summarized in Meinzer (1923) range from 

0.0002 to 0.02.

The interaction between surface water and ground 

water requires a conductance term that incorporates the 

geometry and the vertical hydraulic conductivity of the 

bed sediments of the surface-water body. Reported vertical 

hydraulic conductivity values ranged from 0.1 to 17 ft/d for 

bed sediments in Rhode Island (Roshenshein and others, 

1968; Gonthier and others, 1974; Johnston and Dickerman, 

1974b) and Massachusetts (Lapham, 1989; de Lima, 1991; 

Friesz, 1996; Friesz and Church, 2001). The vertical hydraulic 

conductivity of coarse-grained sediments in these studies 

typically ranged from 1 to 3 ft/d and from 0.1 to 0.7 ft/d for 

fine-grained sediments.

Recharge Rates

Recharge in upland areas is primarily from direct 

infiltration of precipitation but may also include leakage 

from streams, ponds, and wetlands. Recharge rates in upland 

settings are not well understood and conceptually are highly 

variable, ranging from near zero in low-permeability tills on 

steep topography where the water table is near the land surface 

to values approaching mean annual runoff (precipitation minus 

evapotranspiration) in sandy tills on moderate slopes where 

the water table is perennially below the land surface.

The application of a mathematical relation derived from 

Connecticut streamflow records and geology indicated that 

ground-water discharge, a measure of effective recharge 

(ground-water recharge minus ground-water evapotranspiration), is about 35 percent of mean annual runoff for till areas 

(Mazzaferro and others, 1979). Computerized hydrographseparation techniques for long-term streamflow records 

from western Massachusetts and southeastern Rhode Island 

for watersheds covered predominantly by till (90 percent or 

greater) indicated effective recharge rates ranging from 

16–24 in/yr when mean annual runoff ranged from 27–

31 in/yr (Bent, 1995, 1999). For this study, effective recharge 

also determined by a computerized hydrograph-separation 

technique for streamflow draining a predominately till watershed in southeastern Connecticut near the Richmond study site 

fell within this range. 

Sources of recharge to valley-fill aquifers include direct 

infiltration of precipitation, runoff from adjacent upland 

hillslopes, and natural infiltration from streams that cross a 

valley from upland areas. In some cases, pumping by wells 

may also induce water from surface-water bodies. Conceptually, overland runoff is minimal in areas of stratified deposits, 

and recharge rates from direct infiltration of precipitation 

should approximate mean annual runoff rates (Lyford and 

Cohen, 1988). Runoff from adjacent upland hillslopes, either 

by ground water or surface water, can be a major source of 

recharge in a valley-fill setting depending on the size of the 

valley in comparison to the size of the upland area.

Harrisville Study Site

The Village of Harrisville production well field (Central 

Street) is in Batty Brook watershed, a small subbasin of 

the Clear River in the Town of Burrillville, northwestern 

Rhode Island (figs. 1 and 2). The well field consists of three 

production wells; the third well became active during this 

study in October 2004. The study area is characterized by 

narrow valleys approximately 0.5 mi wide bordered by steep 

hillslopes. The study area extends to features that serve as 

hydrologic boundaries in the numerical model: these features 

include the rivers and streams in the major valleys and upland 

topographical divides where surface-water and ground-water 

divides are most likely coincident. The study area is bordered 
6 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 2. Production wells, section lines, selected borings and observation wells, model extent, and surficial geology, Harrisville 

study site, Rhode Island.

Chepachet River

Pascoag

Reservoir

Branch River

Spring 

Lake

Pascoag 

Sucker Brook

River

Batty Brook

Nipmuc

River

Sucker 

Pond

Clear River

1 MILE

1 KILOMETER

.5

.5

0

0

A A'

01111300

BUW402

Till and bedrock outcrops PW1 

Model boundary

Boundary of Batty Brook watershed

Line of geologic cross section

Stratified deposits—Subdivided

 into depositional environments

 Glacial Lake Chepachet

 Sucker Pond-Batty Brook 

 ice-dammed pond deposits

 Clear River-Nipmuc River deposits

 Undifferentiated

Production well and

 identifier

Nipmuc River streamflow-

 gaging station

Long-term network

 observation well and identifier

Boring and identifier

EXPLANATION

A

A'

B

B'

41°56'

41°58'

71°42' 71°40'

Harrisville

Central St.

well field

Capped

landfills

Harrisville Eccleston

well field

BUW341 Village

center

Harrisville

Duck

Pond BUW302

BUW303

PW2

PW3

PW1

01111300

Pascoag

well field

BUW402

BUW401

BUW187

Glocester

Burrillville

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83

BUW187
Harrisville Study Site 7

on the west by the Pascoag, Clear, and Nipmuc Rivers, on the 

south by Sucker Brook, and on the east by the Chepachet and 

Branch Rivers. The study area is bordered on the southwest 

and the north by topographical divides. Land uses in and 

near Batty Brook watershed are primarily forest and rural 

residential except for a small sand and gravel operation 

near the well field. The urban center of Harrisville and two 

capped landfills are about 0.5 mi northwest and northeast, 

respectively, of the well field.

Characteristics of the three production wells, which are 

sited 50 to 160 ft from Batty Brook, are listed in table 1. The 

drilled wells are completed at, or just above, the top of the 

bedrock surface in a thin but transmissive aquifer consisting 

of coarse-grained stratified deposits. Well depths range from 

31.5 to 36 ft below land surface in about 30 ft of saturated 

sediments. Areas contributing recharge were determined for 

both the 2005 average well-field withdrawal rate, 224 gal/min, 

and the maximum well-field rate, 600 gal/min.

Water levels and streamflows were measured periodically 

from June 2004 to January 2006 to increase understanding 

of stream-aquifer interactions at the well-field site. The 

data-collection network included streambed piezometers, 

existing observation wells, and temporary streamflow-gaging 

stations (fig. 3). Seven streambed piezometers consisting of 

0.5-ft-long screens were driven to shallow depths beneath 

the stream. Streamflow-gaging stations, two upstream and 

one downstream of the well-field site, consisted of 90-degree 

v-notch weirs with continuous recorders; the weirs were able 

to capture most of the streamflow except during high flows 

and the downstream weir was affected by surface runoff from 

a road and parking lot. In addition to surface-water levels 

measured at the streambed-piezometer locations, a survey of 

surface-water altitudes in May and June 2005 was made at 

streams in Batty Brook watershed, at the Clear River at the 

confluence with Batty Brook (fig. 3), and at Sucker Pond. 

Lithologic logs and seismic-refraction surveys from local 

and state agencies and from USGS reports and files were 

compiled to define the bedrock surface and the grain size of 

stratified deposits.

Geology

The Harrisville study area is characterized by till-covered 

bedrock uplands cut by valleys that contain glacial-meltwater 

deposits of variable thicknesses (fig. 2). Postglacial sediments 

overlie glacial deposits in flood-plain and wetland areas. 

Bedrock beneath the study area consists predominately of late 

Proterozoic plutonic granite-gneiss rock units, with local more 

mafic intrusions, and layered gneissic and schistose rock units 

of the Blackstone Group and Absalona Formation (Quinn, 

1967). All of these rock units are part of the Avalon terrane 

(Hermes and others, 1994). Bedrock valleys partially filled 

with glacial meltwater sediments include the valley of the 

east-flowing Clear River and several north-draining tributary 

valleys, the largest of which contains the Chepachet River. The 

altitude of the bedrock surface beneath these valleys within 

Table 1. Characteristics of the production wells for the Harrisville and Richmond study sites, Rhode Island.

[Altitudes in feet relative to NGVD 29; USGS, U.S. Geological Survey; ft, foot; in., inch; gal/min, gallons per minute]

Name

Year 

drilled

Altitude of 

land surface

(ft)

Screen 

diameter

(in.)

Depth of screen top 

and bottom below 

land surface

(ft)

Screen altitude 

top and bottom

(ft)

Distance 

to stream

(ft)

Average 

pumping 

rate

(gal/min)

Maximum 

pumping 

rate

(gal/min)

USGS Local

Harrisville (Central Street)

BUW149 PW2 1958 325.9 12 21.5–32 304.4–293.9 50 173 2200

BUW359 PW3 1968 331.6 18 25.5–36 306.1–295.6 110 173 2200

BUW400 PW1 2003 341.0 18 26.5–31.5 314.5–309.5 160 178 3200

Total ......................................................................................................................... 224 600

Richmond

RIW815 PW1 1985 111.8 18 49.6–65 62.2–46.8 360 439 5450

RIW816 PW2 1995 107.4 8 42–54 65.4–53.4 580 Backup 5225

Total ......................................................................................................................... 39 675

1

 Average for year 2005.

2

 Rate used by Rhode Island Department of Environmental Management to determine contributing area by an analytical method.

3

 Estimated yield from well-completion log.

4

 Average for years 2000–04.

5

 Maximum rated capacity of pump.
8 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 3. Data-collection network near production wells and water levels on June 24, 2005, Harrisville 

study site, Rhode Island.

350.57

"

0

0 300 METERS

500

150

1,000 FEET

Stratified deposits 

Till and bedrock outcrops 

Production well and identifier 

Streambed piezometer and identifier—Altitude of

 water level measured on June 24, 2005, in feet

 above NGVD 29

Observation well—Altitude of water level

 measured on June 24, 2005, in feet above

 NGVD 29

Temporary streamflow-gaging station 

 and identifier

Stream-stage measurement site (in addition

 to piezometer and station sites)

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83

Clear River

Batty Brook

unnamed tributary

EXPLANATION

Pz2

340.31

01111321

01111320

01111323

447.45

350.57

328.70

327.86

327.14

321.16

PW2

319.66

pz5

pz3

324.53

329.84

331.93

335.41

330.22

PW1

PW1

327.53

329.12

326.32

pz7

PW3

328.59

pz1

322.48

pz4

334.06

pz6

340.31

pz2

01111320
Harrisville Study Site 9

the study area is shown on figure 4. Bedrock-surface contours 

were constructed on the basis of locations of bedrock outcrops, 

knowledge of bedrock structure, interpretation of glacial-till 

thickness from topography and aerial photographs, and available well data and seismic-refraction surveys.

The general distribution of glacial deposits was compiled 

from unpublished field maps (E. London, USGS, written 

commun., 2005) and analysis of aerial photographs. Glacial 

deposits include subglacially deposited till and stratified 

glacial-meltwater deposits. Stratified deposits generally were 

less areally extensive than previously published. Glacial 

deposits overlie the bedrock surface and range from a few 

feet to as much as 170 ft thick in parts of the Chepachet River 

valley. In the Sucker Pond valley south of the well field and in 

the Clear River valley north of the well field, glacial deposits are generally less than 80–90 ft thick. The distribution of 

surficial materials between the land surface and the bedrock 

surface is shown on cross sections A-A ́ and B-B ́ (fig. 5). The 

cross sections illustrate the characteristic vertical succession of 

glacial till, glacial-meltwater deposits (sand and gravel, sand) 

and postglacial deposits (alluvial). Most of these materials 

are deposits of the last two continental ice sheets that covered 

New England during the middle and late Pleistocene. Most 

were laid down during the advance and retreat of the last (late 

Wisconsinan) ice sheet, which reached its terminus on Long 

Island, N.Y., about 21,000 radiocarbon years ago, and was 

retreating northward through northern Rhode Island between 

16,500 and 16,000 radiocarbon years ago (Stone and Borns, 

1986; Stone and others, 2005).

Glacial till in the Harrisville study area was deposited 

directly by glacier ice and is characterized as a nonsorted, 

nonlayered, relatively compact mixture of sand, silt, and 

clay with variable amounts of stones and large boulders. Till 

blankets the bedrock surface in most places and is generally 

less than 10–15 ft thick. In many places within the area 

shown as “till and bedrock outcrops” (fig. 2), till is absent and 

bedrock is at the land surface. Till also commonly underlies 

glacial stratified deposits in the valleys where it is generally 

less than 10 ft thick.

Glacial-meltwater deposits that consist predominately 

of glaciodeltaic gravel, sand and gravel, and sand are in all of 

the valleys in the study area. Glacial lakes developed in these 

valleys as the ice-margin retreated through the area; meltwater 

deposits were laid down at successively lower altitudes, as 

lower meltwater pathways were uncovered to the north (see 

discussion of this meltwater depositional process in Stone 

and others, 2005). Glacial Lake Chepachet occupied the 

north-draining Chepachet River valley (fig. 2), and successive 

ice-marginal deltas deposited in this lake were controlled in 

altitude by a series of spillways over drainage divides to the 

south and east of the map area. The highest altitudes of deltas 

in the Sucker Brook and Chepachet River valleys are 505 ft. 

An ice-marginal delta deposited into glacial Lake Chepachet at 

the south end of Sucker Pond (see cross section A-A ́, fig. 5) 

reaches an altitude of 495 ft; this altitude was controlled by a 

485-ft-high spillway 2.2 mi southeast of Sucker Pond. Lower 

deltas built into glacial Lake Chepachet were controlled by a 

395-ft-high spillway across the eastern drainage divide.

A series of small ice-dammed lakes formed in the Sucker 

Pond-Batty Brook valley as the ice margin continued to retreat 

northward (fig. 2). The deltaic-surface altitudes of glacialmeltwater deposits surrounding Sucker Pond reach 475–

480 ft and include gravelly ice-channel fillings (or eskers); one 

of these ridges forms the Sucker Brook-Batty Brook surfacewater divide. These sediments were deposited in a small 

glacial lake dammed behind the 495-ft-high delta; meltwater spilled from this lake through a channel cut through the 

northeast edge of the delta. To the north in this valley, another 

delta with a noncollapsed surface altitude of 465 ft was graded 

to a small, ice-dammed pond controlled by a 465-ft-high 

spillway across the eastern divide of Batty Brook watershed. 

The northern ice-proximal part of this deltaic deposit, composed of collapsed, coarse gravel and sand, is tapped by the 

Harrisville production wells (fig. 5, section A-A ́). Deposits 

banked against the southern hillside of the Clear River valley 

have noncollapsed delta surfaces at an altitude of 415 ft and 

were graded to a level of ponding controlled by a 415-ft-high 

spillway across the eastern divide of Batty Brook watershed 

north of the earlier one.

Glacial-meltwater deposits in the Clear River valley 

(fig. 2) were deposited in a series of glacial ponds that developed because of sediment dams downstream and in the Branch 

River valley. Deltaic deposits in the valley along section line 

B-B ́ (fig. 5) are mostly noncollapsed, have surface altitudes of 

345–365 ft, and consist of horizontally bedded gravelly topset 

beds 5–15 ft in thickness overlying dipping sandy foreset beds 

as much as 90 ft thick.

Postglacial deposits locally overlie glacial deposits and 

include flood-plain alluvium along rivers and streams and 

organic peat and muck (wetland deposits) in low-lying closed 

depressions. These deposits are not shown on figure 2, but are 

illustrated on geologic sections (fig. 5). 

Hydrology

The production wells are in Batty Brook watershed, 

which drains 0.64 mi2 at its confluence with the Clear River 

(fig. 2). The Clear River flows east and joins the northeastdraining Chepachet River to form the Branch River. The north 

part of a north-south-trending valley between the Clear and 

Chepachet River watersheds is drained by Batty Brook, and 

the south part is drained by Sucker Pond and Sucker Brook, 

which flows into Chepachet River. Till uplands southwest 

and southeast of the well-field site also form watershed 

divides between the Clear and Chepachet River watersheds. 

The stream network shown in figure 2 is delineated at 

the 1:5,000 scale. Streams at the 1:24,000 scale did not 

adequately represent the stream network in the study area; 

these streams include several small tributaries in and near 

Batty Brook watershed. 
10 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 4. Bedrock-surface contours, Harrisville study site, Rhode Island.

PW1 

Stratified deposits

Till

Bedrock outcrops in study area

Model boundary

Bedrock-surface altitude—Contour 

interval is 20 feet

Production well and identifier

EXPLANATION

500

Glocester

Burrillville

71°42' 71°40'

41°56'

41°58'

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83

280

360

240

280

360

320

340

300

360

520

400

400

360 380

420

400

480

500

460

440

340

360

360

240

380

380

300

320

260

440

320

340

340

320

320

280

420

400

360

280

420

420

420

300

400

380

380

400

440

440

340

480

500 500

540

500

460

400

460

380

420

440

500

460

460

520

400

420

420

460

400

420

540

400

400

400

400

380

500

420

360

520

480

480

360

440

480

480

380

520

520

480

480

460

460

440

440

420

420

500

320

320

340

340

480

260

500 500

540

380

500

460

360

280

420

320

440

400

400

420

520

240

460

460

440

300

320

340

360

500

300

300

300

400

260

420

400

400

520

460

240

240

460

380 380

340

420

260

420

420

400

540

380

420

420

420

420

400

280

300

480

460

400

420

340

360

360

360

380

520

480

480

460

380

440

440

440

320

340

400

480

460

280

400

520

540

500

500

480

500

480

480

460

460

460

440

440

440

420

400

440

300

500

360

360 380

400

400

Chepachet River

Sucker 

Pond

Batty Brook

Branch River

Pascoag

Reservoir

Spring 

Lake

Pascoag 

Sucker Brook

River

Batty Brook

Sucker Brook

Sucker Brook

Nipmuc

River

Sucker 

Pond

PW3

PW1

PW2

Clear River

1 MILE

1 KILOMETER

.5

.5

0

0
Harrisville Study Site 11 Figure 5. Geologic cross sections (lines of sections A-A’ and B-B’ are shown in figure 2), Harrisville study site, Rhode Island.

500400300

200

A

North

A'

South

Clear River

B–B' Section 

Bend

Bend

Bend

Bend

Bend

Bend

BUW401

BUW402

Old railroad bed

PW2

PW3

PW1

Sucker Pond

ALTITUDE, IN FEET ABOVE NGVD 29

Production

well field}

B B'

East

ALTITUDE, IN FEET ABOVE

NGVD 29

400

300200

Bend

Bend

Clear River

A–A' Section 

BUW303

BUW302

BUW341 West

VERTICAL EXAGGERATION X 10

EXPLANATION

Open water bodyPostglacial alluvial depositsSand and gravel depositsSand depositsTill depositsBedrockProduction well screen and identifier

1 MILE

1 KILOMETER

.5

.5

0

0

Old railroad bed

PW2
12 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

The production wells are screened in thin but transmissive sand and gravel deposits on opposite sides of Batty 

Brook (figs. 2 and 5). Distances from the production wells to 

Batty Brook range from 50 ft for PW2 to 160 ft for PW1. The 

saturated thicknesses of the stratified deposits in Batty Brook 

watershed range from about 10 ft in its headwaters to 30 ft at 

the well-field site to about 50 ft in the valley axis of the Clear 

River. The average hydraulic conductivities of the stratified 

deposits determined from lithologic logs at and near each 

production well range from 210 ft/d at PW2 (Johnston and 

Dickerman, 1974a) to 140 ft/d at the new PW1. The average 

hydraulic conductivities calculated at PW3 and PW2 from 

specific-capacity data (Johnston and Dickerman, 1974a) were 

higher than hydraulic conductivity estimates from lithologic 

logs and ranged from 260 to 480 ft/d.

A hydrograph from USGS long-term observation well 

BUW187 in the upper part of Batty Brook watershed illustrates the seasonal variations in water levels typical of stratified deposits (figs. 3 and 6); also shown in figure 6 is the 

data-collection period compared to these seasonal fluctuations. 

Ground-water levels are generally highest in early spring and 

lowest in the fall. Ground-water level fluctuations are caused 

by increased recharge rates from late fall to spring when there 

is little or no evapotranspiration. The ground-water gradient in 

Batty Brook watershed is steep, even in the stratified deposits. 

The head difference between water levels at BUW187 and the 

well field is 118 ft and between the well field and the Clear 

River is 19 ft; these differences were measured over distances 

of 2,800 ft and 1,500 ft, respectively. 

Streamflow records from two nearby long-term streamflow-gaging stations provided a guide in assigning recharge 

rates in the study area (fig. 1 and table 2). The drainage area of 

the Branch River station (01111500) includes the model area 

and the Nipmuc River station (01111300) is 1.7 mi northwest 

of the well-field site. Mean annual streamflow (precipitation minus evapotranspiration) is equivalent to about 26 in/yr 

over the drainage areas. Mean annual ground-water discharge 

(effective recharge), calculated by use of the hydrographseparation technique PART (Rutledge, 1998), was about 19 to 

20 in/yr or 72 to 76 percent of total streamflow. These rates are 

an average over the entire watershed, including areas of stratified deposits, till, surface-water bodies, wetlands, and a variety 

of land uses. The difference between mean annual streamflow 

and ground-water discharge is surface runoff from areas that 

reject infiltration of precipitation; these areas include impervious surfaces, surface-water bodies, wetlands, and areas 

where the water table is at the land surface seasonally, such as 

some till areas. Batty Brook watershed consists primarily of 

permeable stratified deposits and adjacent upland hillslopes. 

A recharge rate of 26 in/yr over the 0.64-mi2 watershed is 

equivalent to 1.23 ft3/s or 552 gal/min. The 2005 well-field 

withdrawal rate of 224 gal/min is about 40 percent of the total 

water available in this small watershed, but the maximum 

well-field withdrawal rate of 600 gal/min exceeds it; thus, for 

the steady-state model simulation, the well field must derive 

part of its pumped water from outside Batty Brook watershed.

Ground water that discharges to streams in Batty Brook 

watershed is a potential source of water to the well field 

through streamflow loss, either naturally, induced by pumping 

of a well, or both. Natural streamflow loss may occur because 

the increased saturated thickness and hydraulic conductivity 

of the sand and gravel deposits at the well-field site may cause 

ground-water levels to be lower than the streambed. Paired 

water levels at streambed-piezometer sites and streamflows at 

the streamflow-gaging stations provide insights into streamaquifer interactions at the well-field site. The production wells, 

however, were operated on a varied pumping schedule, usually 

in a combination of two or more, or not at all. Well-field withdrawals were highest during the summer months, a period of 

generally minimal precipitation recharge.

Ground-water and surface-water levels were measured 

periodically at seven streambed-piezometer sites (PZ1–PZ7) 

upstream and downstream of the well field and between the 

wells (fig. 3); measurements were generally made when two 

or more of the wells were pumping. Paired measurements of 

ground-water and surface-water levels indicate the direction 

of flow between the stream and the underlying sediments 

(fig. 7); water levels at PZ3 site are typical of the streambed 

piezometers not shown (PZ1, PZ4, and PZ7). In general, 

paired water levels indicated that the direction of flow was 

downward except during periods of high seasonal recharge 

rates and low pumping rates. Measurements made at PZ2 show 

the response of water levels to the new production well PW1, 

which began pumping at the end of October 2004. Before 

pumping, water levels show a slight downward head gradient 

except after a precipitation event in late September 2004. Once 

the new production well began pumping, the downward head 

gradient increased.

In June 2005, water levels at the streambed-piezometer 

sites were measured during a period of normal pumping operation, then no pumping, followed by continuous pumping at 

all three production wells. On June 21, after about 14 hours 

of no pumping and 26 hours after minimal pumping, either 

the ground-water levels, except in PZ2, were equivalent to 

the surface-water levels, or the downward vertical gradients 

were less compared to the previous measurement made during 

pumping withdrawals. The succeeding four sets of measurements from June 21–24 at each piezometer during continuous 

pumping show an increase in the downward vertical gradient. 

Water levels measured in available observation wells between 

the production wells and the streambed piezometers after 

three days of continuous pumping indicate that the direction 

of ground-water flow was from the stream to the production 

wells (fig. 3). 

A comparison of instantaneous streamflow measurements 

made in June and July 2004, and of mean daily streamflow 

from the weirs upstream (01111320 and 01111321) and 

downstream (01111323) of the well-field site from November 

2004 to November 2005, indicated that during June, a month 

at or near long-term average ground-water levels (fig. 6), a 

net streamflow loss over the reach began and continued until 

ground-water levels returned to long-term average levels in 
Harrisville Study Site 13

Figure 6. Water levels measured in observation well BUW187, 1997–2006 (well location shown in figures 1 and 2), 

Harrisville study site, Rhode Island.

Table 2. Streamflow and drainage-area characteristics of the Branch and Nipmuc River streamflow-gaging stations, Harrisville study 

site, Rhode Island.

[USGS, U.S. Geological Survey. USGS station number: Locations shown on figures 1 and 2; mi2, square mile; ft3/s, cubic feet per second; in/yr, inches per 

year; PART (Rutledge, 1998) hydrograph-separation method. Ground-water discharge index is mean annual ground-water discharge divided by mean annual 

streamflow.]

USGS 

station 

number

Station name

Drainage 

area

(mi2)

Area of 

glacial 

stratified 

deposits 

(percent)

Period of record 

analyzed

Mean 

annual 

streamflow

(ft3/s)

Mean 

annual 

streamflow

(in/yr)

Mean 

annual 

groundwater 

discharge 

PART

(ft3/s)

Mean 

annual 

groundwater 

discharge 

PART

(in/yr)

Groundwaterdischarge 

index 

(percent)

01111300 Nipmuc River near 

Harrisville, R.I.

16.0 28 1965–90; 1994–03 30.6 26.0 22.1 18.8 72

01111500 Branch River at 

Forestdale, R.I.

91.2 30 1957–2003 177.6 26.4 135.3 20.2 76

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

444

445

446

447

448

449

450

WATER LEVELS, IN FEET ABOVE NGVD 29

MEAN WATER LEVEL FOR YEARS 1968–2005

Data-collection period

for this study

YEAR
14 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 7. Paired surface-water altitudes and ground-water altitudes at selected streambed piezometers in Batty Brook, 

2004–2006 (piezometer locations shown in figure 3), Harrisville study site, Rhode Island.

Brook dry and ground-water level

below screen bottom of 336.7 ft

9-9-05

9-9-05 9-9-05 Brook dry and ground-water level

below screen bottom of 317.1 ft

Brook dry and ground-water level

below screen bottom of 332.2 ft

Brook dry

S O N D J F M A M J J A S O N D J

2004 2005 2006

S O N D J F M A M J J A S O N D J

2004 2005 2006

O N D J F M A M J J A S O N D J

338

339

340

341

342

PZ2

333

334

335

336

337

PZ6

322

323

324

325

326

PZ3

318

319

320

321

322

PZ5

WATER LEVELS, IN FEET ABOVE NGVD 29

Surface-water level

Ground-water level

S

2004 2005 2006

S O N D J F M A M J J A S O N D J

2004 2005 2006

EXPLANATION
Harrisville Study Site 15

the fall after major precipitation events. The stream reach 

between stations returned to a net gaining stream in December 

2004, after major precipitation events in late November, 

early December, and October 2005, during which 16 in. of 

precipitation fell.

Field observations on two dates and streamflow at the 

weirs indicated that Batty Brook and the unnamed tributary 

are intermittent streams under the climatic and pumping 

conditions of 2005. Water levels at observation well BUW187 

during the summer were about 0.5 ft below long-term 

monthly means for the years 1968–2005. On July 29, 2005, 

streamflow in Batty Brook was completely lost to the stratified 

deposits between PW1 and PW3, but flow in the unnamed 

tributary flowed to its confluence with Batty Brook, past 

the downstream weir, and then intermittently thereafter to 

the Clear River. On September 9, 2005, flow in Batty Brook 

ceased about 350 ft upstream of the weir upstream of the wellfield site, and flow in the unnamed tributary was completely 

lost about 20 ft downstream of PZ7. Unpublished field notes 

from a previous USGS study (Johnston and Dickerman, 

1974a) also indicated intermittent-flow conditions in October 

1968, when long-term monthly mean ground-water levels 

were 1.5 ft below average. At that time, PW2 and a former 

production well on the opposite side of Batty Brook from 

PW2 were the only two production wells at the site. 

Net mean daily streamflow loss between gaging stations 

was generally 0.05 to 0.1 ft3/s (22 to 45 gal/min) from June 

to fall. If all streamflow lost to the stratified deposits between 

gaging stations is withdrawn by the well field, then streamflow 

loss is equivalent to 10 to 20 percent of the 2005 average 

pumping rate. Streamflow loss was greatest for several days 

after precipitation events caused the intermittent stream to 

flow continuously and ground-water levels were at their 

lowest; loss during these conditions was about 30 percent of 

the 2005 average rate.

Long-term average streamflow at the streamflow-gaging 

stations upgradient of the well field was estimated for a 

steady-state, nonpumping model calibration. Streamflows at 

the upgradient stations may be affected by pumping, but the 

affected flow is most likely within the uncertainty of the longterm average streamflow estimate. Mean daily streamflows 

greater than zero from November 1, 2004 to September 30, 

2005 at the upgradient weirs were related to concurrent mean 

daily streamflows at several nearby unregulated long-term 

streamflow-gaging stations in northern Rhode Island and 

central Massachusetts. Plots of log-transformed data were 

made to determine the quality and linearity of the relation. 

The Maintenance of Variance Extension, Type 1 (MOVE.1) 

technique developed by Hirsch (1982) was used to provide 

an equation that relates streamflow at the weirs to that at the 

long-term stations. The streamflow for only one long-term 

streamflow-gaging station correlated reasonably well with 

the streamflows measured at each weir most likely because 

long-term stations have drainage areas more than an order 

of magnitude larger than drainage areas of the weirs. Mean 

annual streamflow computed at the long-term station for 

complete years of record was entered into the equation to 

estimate the long-term mean annual streamflow at the weir. 

Estimated long-term average streamflows were 0.54 ft3/s for 

the Batty Brook site and 0.18 ft3/s for the unnamed tributary 

site. A detailed description of the MOVE.1 technique for 

streamflow analysis is described in Ries and Friesz (2000). 

Information concerning the analysis for each weir is 

summarized in table 3. 

At the maximum pumping rate, the Clear River is also 

a potential source of water to the well field. The production 

wells closest to the river, PW2 and PW3, are screened below 

the river altitude of 310.7 ft surveyed on May 19, 2005 

(table 1 and fig. 5). The quantity of river water available for 

infiltration for average annual conditions far exceeds the 

combined maximum pumping rates of the study-site well field 

(600 gal/min) and of the Harrisville Eccleston well field 

(400 gal/min; Dufresne-Henry, Inc., 2001) at the confluence of 

the Clear and Nipmuc Rivers (fig. 2). Mean annual streamflow 

and mean annual ground-water discharge (base flow) for the 

42.3-mi2 drainage area of the Clear River upstream of its confluence with Batty Brook are estimated to be 81 and 59 ft3

/s, 

respectively, on the basis of streamflow characteristics at the 

Nipmuc River station. The combined pumping rate for the two 

well fields (2.23 ft3/s) is 2.7 percent of mean annual streamflow and 3.8 percent of mean annual ground-water discharge.

Ground-Water-Flow Model

The ground-water-flow model for the Harrisville study 

site was designed to simulate long-term, steady-state groundwater levels, flow paths, and traveltimes. The model was 

calibrated to nonpumping conditions based on historical data 

and data collected during this study. A general calibration was 

first done for the model area, and then a detailed calibration 

was completed for Batty Brook watershed and adjacent areas. 

A small net increase in streamflow was assumed between 

the upgradient weirs and the Clear River during nonpumping 

conditions; the simulated area contributing recharge to 

the well field was nearly identical for either a small net 

streamflow gain or loss for nonpumping conditions. Model 

characteristics, including hydraulic properties and recharge 

rates, are summarized in table 4.

Model Design

Ground-water flow in the surficial deposits and the underlying bedrock was simulated by a two-layer numerical model 

with a uniformly spaced grid. The ground-water-flow model 

was calibrated to 53 ground-water altitudes and 2 long-term 

average streamflows in the stratified deposits and to a generally shallow water table that approximates the land-surface 

configuration in the till uplands. Ground-water levels in the 

uplands indicate a shallow water table ranging from 1 to 20 ft 

and averaging 6 ft below land surface in the USGS Chepachet 

quadrangle (Hahn and Hansen, 1961).
16 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Several available sets of ground-water levels were used 

to calibrate the model in the stratified deposits (fig. 8); these 

water levels were assumed to be unaffected or minimally 

affected by pumping wells. In Batty Brook watershed, 

measurements of four ground-water levels made on April 6, 

1985, by GZA GeoEnvironmental, Inc., (1985) and of five 

ground-water levels made on June 21, 2005, for this study are 

at or near long-term average annual conditions for USGS longterm observation well BUW187 and the Branch and Nipmuc 

River streamflow-gaging stations. During April, water levels 

would normally be at above-average conditions, but because 

of below-average precipitation in the months preceding April 

1985, water levels in observation well BUW187 were at 

average conditions. The April water levels are in the upper 

part of Batty Brook watershed. The 2005 water levels, four 

from observation wells near the well field and one from 

BUW187, were made about 14 hours after all the production 

wells stopped pumping and 26 hours after minimal pumping. 

The four observation wells near the well field were the farthest 

from the production wells that were available at the site. 

Water levels, which were measured during different pumping 

cycles in these four observation wells, indicated that water 

levels were unaffected or minimally affected by pumping. 

In addition, stage measurements made at the streambed 

piezometers and the weirs on June 21, 2005, were used to 

represent stream altitudes at the well site. 

In the remaining area of the model, 44 ground-water 

levels reported in previous USGS investigations (Hahn 

and Hansen, 1961; Johnston and Dickerman, 1974a) and 

at two contamination sites (Rhode Island Department of 

Environmental Management, 1995; Sage Environmental, 

2001) were used in model calibration. Most of these 

Table 3. Summary of the long-term mean annual streamflow analysis for the temporary streamflow-gaging stations upstream of the 

well-field site, Harrisville study site, Rhode Island.

[USGS, U.S. Geological Survey. USGS station number: Locations shown in figures 1 and 3; mi2, square mile; ft3/s, cubic feet per second]

USGS 

station 

number

Station name

Drainage 

area

(mi2)

Number of 

daily mean 

streamflows 

used in 

relation

Estimated 

long-term 

mean annual 

streamflow

(ft3/s)

Streamflow-gaging station 

used in relation

Correlation 

coefficient USGS 

station 

number

Station name

01111320 Batty Brook, upstream of 

Central Street, at Harrisville, R.I.

0.34 314 0.54 01111300 Nipmuc River near 

Harrisville, R.I.

0.89

01111321 Unnamed Tributary to 

Batty Brook at Harrisville, R.I.

.14 334 .18 01175670 Sevenmile River near 

Spencer, Mass.

.74

Table 4. Summary of simulated values for hydraulic properties 

and recharge rates in the ground-water-flow model for the 

Harrisville study site, Rhode Island.

Characteristics Simulated values

Hydraulic conductivity (feet per day)

Stratified deposits Sand and gravel at well field: 140

Remaining sediments: 10–80

Till Generally 3–4, ranged from 1–5

Bedrock .05

Ponds and lakes 1,000–5,000

Ratio of horizontal to vertical hydraulic conductivity

Stratified deposits 10:1

Till 10:1

Bedrock 1:1

Streambed vertical hydraulic conductivity (feet per day)

Coarse-grained deposits 1

Fine-grained deposits .1

Porosity

Stratified deposits 0.35

Till .35

Bedrock .02

Recharge rates (inches per year)

Stratified deposits 26

Upland hillslopes 26

Upland watersheds 16
Harrisville Study Site 17

Figure 8. Model-boundary types, recharge rates, simulated water-table contours for nonpumping, steady-state conditions, 

and spatial distribution of residuals (measured-simulated), Harrisville study site, Rhode Island.

Chepachet River

Pascoag

Reservoir

Branch River

Spring 

Lake

Pascoag 

Sucker Brook

River

Batty Brook

Nipmuc

River

Sucker 

Pond

Clear

River

EXPLANATION

1 MILE

1 KILOMETER

.5

.5

0

0

Glocester

Burrillville

500

340

460

460

480

420

440

460

380

480

400

420

440

460

480

500

540

520

480

460

380

360

440

420 400

440

500

520

380

360

340

320

320

360

380

400

420

440

400

540

520

480

460

380

360

440

420 400

440

500

520

540

520

480

460

380

380

380

360

360

340

340

320

320

440

400

420

440

500

520

360

380

400

420

440

460

480

400

400

420

440

460

440

420

440

460

480

480

500

520

380

480

480

500

Stratified deposits 

Till and bedrock outcrops

River cell

Stream cell

Model boundary

Simulated water-table

 contour—Interval is 20 feet

Production well and identifier PW1

Recharge rates, in inches 

 per year

 26 (stratified deposits)

 26 (upland hillslopes)

 16 (upland watersheds)

520

Residuals, in feet

Simulated heads greater

 than measured

 -15 to -10

 -10 to -5

 -5 to 0

 

Simulated heads less

 than measured

 0 to 5

 5 to 10

 10 to 15

 15 to 20

PW2

PW3

PW1

41°56'

41°58'

71°42' 71°40'

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83
18 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

water-level measurements were made from 1960 through 1968 

in the late spring and fall when hydrologic conditions are 

normally near average between seasonally high, early-spring 

water levels and low, late-summer water levels; however, 

the 1960–1968 water levels still represent a wide range of 

conditions. Unlike the water levels in Batty Brook watershed, 

the measuring-point altitude was based on land-surface 

altitude determined from the USGS Chepachet quadrangle. 

These altitudes are generally accurate within approximately ±5 

ft, but may be less accurate in areas of steep topography.

The two long-term average streamflows calculated at the 

streamflow-gaging stations upgradient of the well-field site 

were also used in model calibration. Streamflow at these two 

sites may have been affected by pumping withdrawals, but the 

affected flow is most likely within the uncertainty of the longterm average.

The ground-water-flow model extended to natural hydrologic boundaries beyond the likely area contributing recharge 

to the well field (fig. 8). This extent also minimized the effects 

of boundaries on simulated heads near ground-water divides 

separating Batty Brook from adjacent watersheds; pumping 

at the well field may shift the location of these divides. The 

lateral model boundaries included perennial streams: Pascoag, 

Clear, and Nipmuc Rivers on the west, Sucker Brook on the 

south, and Chepachet and Branch Rivers on the east. Elsewhere, the edge of the model extended to presumed groundwater divides in the till and bedrock uplands. The active model 

grid represented an area of 8.6 mi2, consisted of 549 rows and 

344 columns, and included a total of 192,598 cells with each 

cell 50 ft on a side. 

Vertical discretization was based on lithology. Layer 1, 

the top layer, represented surficial deposits. The bottom of 

layer 1 was the bedrock surface in the valleys (fig. 4); the 

uneven surface of the bedrock resulted in surficial deposits of 

variable thickness. The generally thin till in the valleys was 

incorporated into adjoining stratified deposits for assigning 

model-input parameters. In upland areas, the bottom of layer 1 

was set 15 ft below the land surface, which is consistent with 

typical till thicknesses in the study area (Hahn and Hansen, 

1961). Layer 2, the bottom layer, represents only bedrock. 

Bedrock was assigned a constant thickness of 200 ft throughout the model beneath the stratified deposits and till. 

Model layers were simulated by using a fixed 

transmissivity, including layer 1, because of the numerical 

instabilities caused by simulating a thin layer on the sides of 

steeply sloping hills. In addition, some layer 1 model cells, 

especially cells representing stratified deposits near the upland 

contact, may be unsaturated, either during nonpumping, 

steady-state conditions or because of the large pumping 

rates used in the calibrated model. In a fixed-transmissivity 

simulation, MODPATH particles can be tracked from an 

unsaturated cell representing an area of recharge to a discharge 

location. The top of the model grid, which is used to determine 

layer 1 transmissivity, is land surface in the uplands. In the 

valley, the top of the model grid represented the water table 

estimated from available ground-water levels and surfacewater elevations from surveys and topographical contours on 

the USGS Chepachet quadrangle. The top of the model grid 

was only used to calculate transmissivity; the model simulated 

the saturated thickness and water table.

Several types of boundary conditions were specified 

in the model to represent areas of discharge and sources 

of recharge (fig. 8). Interactions between surface water 

and ground water were simulated as head-dependent flux 

boundaries in layer 1. Streams that define the perimeter of 

the model were simulated by using the MODFLOW river 

package (Harbaugh and others, 2000). The Clear River, from 

its confluence with the Nipmuc River to where it forms the 

Branch River, and tributary streams with watersheds contained 

within the model were simulated by using the streamrouting package (Prudic, 1989) developed for MODFLOW. 

The stream-routing package accounts for gains and losses 

of water in each stream cell and routes streamflow from 

upstream to downstream cells. Streamflow loss to the aquifer, 

either naturally where the stream flows from low- to hightransmissive sediments or from induced infiltration due to 

pumping, would cease if simulated streamflow also ceases. 

Streams that flow into and out of ponds and lakes were 

simulated as flowing through these water bodies. The model 

contained a total of 1,177 river cells and 3,436 stream cells.

Surface-water altitudes for the head-dependent flux 

boundaries were determined from, or interpolated between, 

topographical contours intersecting streams and from pond 

and lake altitudes listed on the USGS Chepachet quadrangle. 

In addition, stage measurements made during this study in 

May and June 2005 at streambed piezometers, streamflow 

weirs, and surveyed water surfaces from 23 locations in Batty 

Brook, the unnamed tributary to Batty Brook, the Clear River 

at its confluence with Batty Brook, and Suckers Pond were 

used. Water depths and bed thicknesses of 1 ft were used to 

determine the top and bottom bed altitudes from surfacewater altitudes.

Simulated streams were assigned widths based on field 

measurements, observations, and estimates. Most simulated 

stream widths ranged from 3 to 5 ft for small tributaries to 

40 ft for the Clear River. In the vicinity of the well field, Batty 

Brook was simulated as 5 ft wide and the unnamed tributary to 

Batty Brook was simulated as 4 ft wide. 

Streams in the study area, including the Clear River 

downgradient of the well field and streams in Batty Brook 

watershed, are generally fast-moving with sand and gravel 

bed sediments. An exception to this in the well-field area is 

a small wetland through which the unnamed tributary flows 

downgradient of the weir. A vertical hydraulic conductivity 

value of 1 ft/d was used to represent coarse-grained bed 

sediments; a value of 0.1 ft/d, which is at the low end of 

reported values for fine-grained bed sediments, was used to 

represent wetland deposits beneath the unnamed tributary to 

Batty Brook. Streambed conductances simulated in the model, 

therefore, ranged from 20 ft2/d for the small stream flowing 

over the wetland near the well field to 2,000 ft2/d for the Clear 

River underlain by coarse bed sediments. 
Harrisville Study Site 19

Simulation of Ground-Water Flow

The altitude and configuration of the simulated water 

table for long-term, nonpumping, steady-state conditions are 

shown in figure 8. The simulated water-table contours and 

flow directions are consistent with the conceptual model of 

ground-water flow in the study area. Ground water flows from 

topographically high areas and discharges to streams and 

surface-water bodies. In the uplands, the water table generally 

parallels the land surface, and simulated ground-water divides 

generally coincide with watershed divides. The hydraulic 

gradient is steepest beneath the upland till and stratified 

deposits near the contact and flattens in the more transmissive 

valley-fill areas. 

A comparison of simulated to measured ground-water 

altitudes in the stratified deposits, shown in figure 9A, indicates a reasonable agreement. The mean absolute residual is 

Figure 9. (A) Relation between simulated and measured 

ground-water levels and (B) residual (measured minus 

simulated) ground-water levels as a function of measured 

ground-water levels, Harrisville study site, Rhode Island.

Recharge rates were distributed based on surficial geology and hydrography (fig. 8); recharge values used in the 

model are effective rates which account for the effects of 

ground-water evapotranspiration. A recharge rate of 

26 in/yr based on long-term averages at the Branch and 

Nipmuc River streamflow-gaging stations was applied to the 

stratified deposits. For impervious surfaces from which part or 

all of the precipitation is channeled to streams, this rate would 

have overestimated actual recharge. In the expected contributing area to the well field, however, these impervious areas are 

likely negligibly small. At the small sand and gravel operation 

near the well field where evapotranspiration rates may be less 

than rates in areas covered by vegetation, the model recharge 

rate may have underestimated the actual recharge. The same 

recharge rate, 26 in/yr, was applied to upland hillslopes that 

drain toward the valley with no streams or water bodies at 

their base. This rate represented both recharge in the uplands 

and surface runoff that recharges the stratified deposits near 

the valley-upland contact. Thus all water that is added to the 

ground-water system through precipitation was accounted 

for in the model. For upland watersheds and hillslopes 

with streams or water bodies at the valley-upland contact, a 

recharge rate of 16 in/yr was applied; this value is less than 

the basin-wide average effective recharge rate and is at the low 

end of recharge rates determined for till-dominated watersheds 

by computerized hydrograph-separation methods.

Horizontal hydraulic conductivity values were assigned 

on the basis of lithology. The final calibrated value for sand 

and gravel deposits at the well field was 140 ft/d. Initially 

one value was used to represent the remaining stratified 

deposits, which consist mostly of sand, and another value to 

represent till in the uplands. During model calibration, these 

surficial deposits were subdivided into additional hydraulic 

conductivity zones. In general, final hydraulic conductivity 

values for stratified deposits ranged from 10 ft/d near the 

upland-valley contact, where saturated thicknesses were about 

10 ft or less, to 80 ft/d in central areas of the valleys. Low 

hydraulic conductivity values were needed to simulate the 

relatively steep hydraulic gradient between the contact and 

the main valley streams. Areas of thin stratified deposits may 

overlie proportionally large quantities of till; this configuration 

lowers the overall transmissivity. In addition, little data was 

available to define the bedrock surface accurately in many 

areas of the modeled area especially along the valley edges. 

Final hydraulic conductivity values for upland till generally 

ranged from 3 to 4 ft/d. Bedrock was assigned a value of 

0.05 ft/d, which was not altered during model calibration. 

Model cells containing three large ponds and lakes in the 

upland and valley were assigned a high hydraulic conductivity 

ranging from 1,000 to 5,000 ft/d to simulate the flat gradient 

across these water bodies and realistic ground-water-flow 

patterns around the water bodies themselves.

460

460

430

430

400

400

370

370

340

340

310

310

280

20

15

10

5

0

-5

-10

-15

-20

280

280 310 340 370 400 430 460

SIMULATED WATER LEVEL, IN FEET RESIDUAL, IN FEET

MEASURED WATER LEVEL, IN FEET

A

B
20 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

amount (38 percent). These upland sources include lateral and 

vertical flow from till and bedrock (26 percent) and streamflow loss from tributary streams (12 percent).

Areas Contributing Recharge to 

Production Wells

Simulated areas contributing recharge to the Harrisville 

Central Street well field were determined on the basis of 

the calibrated steady-state model, for simulated pumping 

conditions, and tracking of pathlines with the MODPATH 

particle-tracking program. The locations and extents of the 

simulated areas contributing recharge to each production 

well pumping at the 2005 average rate and the maximum rate 

(table 1) are shown in figures 10 and 11. The total maximum 

pumping rate for the well field, 600 gal/min, is 2.7 times the 

total 2005 average rate of 224 gal/min. The total sizes of the 

areas contributing recharge to the well field and percentages of 

the total water withdrawn from each water source for the well 

field are listed in table 6.

4.5 ft, which is 3 percent of the total difference in groundwater altitude, 152.5 ft, measured at the observation wells. A 

comparison of residuals (fig. 9B) shows that the differences 

between simulated and measured water levels are generally 

randomly distributed around zero. The largest residuals occur 

near the boundary between the valley-upland contact (fig. 8) in 

areas with steep hydraulic gradients. The simulated direction 

of ground-water flow, however, is consistent with expected 

flow directions in these areas. Large residuals in these areas 

may be due to spatial variation in transmissivity and recharge 

rates along the edge of the valley that are not incorporated into 

the model. Other factors may include the accuracy in determining the exact location and measuring-point altitude from 

topographic maps for observation wells that were not surveyed 

to NGVD29.

In addition to ground-water altitudes and flow directions, 

simulated streamflows also were in good agreement with 

the long-term average streamflows determined for the two 

streamflow-gaging stations upgradient of the well field. The 

difference between simulated flow and estimated long-term 

average streamflow was 0.03 ft3/s for both the Batty Brook and 

unnamed tributary streamflow-gaging stations. By simulating the 2005 average pumping rates for each production well, 

simulated streamflows were reduced by 0.03 and 0.02 ft3/s at 

the Batty Brook and unnamed tributary stations, respectively. 

These reductions in simulated streamflow are most likely 

within the uncertainty of the calculated long-term average.

Simulated ground-water flow in the stratified deposits 

is nearly perpendicular to the main valley streams and nearly 

parallel to the small tributary streams that drain the uplands 

and become minimally gaining or losing as they flow over 

more transmissive stratified deposits; more ground water 

flows along deeper and longer flow paths to the main valley 

streams in these areas. An important simulated ground-water 

divide in the stratified deposits is between the Batty Brook and 

Sucker Pond watersheds. The simulated ground-water divide 

between these two watersheds is closer to Sucker Pond than 

Batty Brook because the stages of the most upstream reaches 

of Batty Brook are at an altitude lower than the stages of a 

tributary draining into Sucker Pond from the northwest and of 

the pond itself.

The simulated long-term nonpumping steady-state 

ground-water budget for the modeled area, summarized in 

table 5, indicates that precipitation recharge accounts for most 

of the total inflow (90 percent). Conceptually this percentage 

represents both direct infiltration of precipitation and surface 

runoff from hillslopes that recharges the valley near the contact. Streamflow loss from natural infiltration accounts for the 

remaining inflow (10 percent); most of this streamflow loss 

is from tributaries where they flow over the stratified deposits 

and at the downstream ends of ponds and lakes. Groundwater discharge is to the streams and surface-water bodies. 

The simulated water budget for only the stratified deposits is 

also shown in table 5. Precipitation recharge directly on the 

valley contributes most of the inflow (62 percent), but upland 

sources, either directly or indirectly, contribute a significant 

Table 5. Simulated steady-state average annual hydrologic 

budget for nonpumping conditions, Harrisville study site, 

Rhode Island.

[ft3/s, cubic feet per second]

Hydrologic budget component Flow rate (ft3/s)

Modeled area

Inflow

Recharge 14.2

Streamflow loss 1.6

Total inflow 15.8

Outflow

Streamflow 15.8

Total outflow 15.8

Glacial stratified deposits only

Inflow

Recharge 7.6

Streamflow loss 1.5

From till 2.5

From bedrock .6

Total inflow 12.2

Outflow

Streamflow 12.0

To till .1

To bedrock .1

Total outflow 12.2
Harrisville Study Site 21

Figure 10. Simulated area contributing recharge to the Harrisville well field at its average pumping rate of 

224 gallons per minute, Harrisville study site, Rhode Island.

Duck 

Pond

Batty Brook

Sucker

Pond

Nipmuc River

River

Clear

71°41' 71°40'

41°58'

41°57'

PW2

PW3

PW1

PW1 

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83

Stratified deposits

Till and bedrock

 outcrops

Simulated area contributing

 recharge to PW2

Simulated area contributing

 recharge to PW3

Simulated area contributing

 recharge to PW1

Model boundary

Production well and identifier

EXPLANATION

2,000 FEET

600 METERS

0

0
22 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 11. Simulated area contributing recharge to the Harrisville well field at its maximum pumping rate of 

600 gallons per minute, Harrisville study site, Rhode Island.

Duck 

Pond

Batty Brook

Sucker

Pond

Nipmuc River

71°41' 71°40'

41°58'

41°57'

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

PW2

PW3

PW1

River

Clear

2,000 FEET

600 METERS

0

0

PW1 

Stratified deposits

Till and bedrock

 outcrops

Simulated area contributing

 recharge to PW2

Simulated area contributing

 recharge to PW3

Simulated area contributing

 recharge to PW1

Model boundary

Production well and identifier

EXPLANATION
Harrisville Study Site 23

The total area contributing recharge for the average 

pumping rate covers about 0.17 mi2 and extends in a generally 

southward direction from the well field to ground-water 

divides in the uplands. The contributing area upgradient of 

the well field extends beneath and beyond small streams in 

two areas where the simulated stream does not capture all 

the water entering the model cell or the stream cell simulates 

as a slightly losing reach. The well field derived most of its 

water from direct precipitation recharge—intercepted ground 

water that normally discharges to streams—but 38 percent 

of the pumped water is from Batty Brook and its tributaries. 

The shape of the area contributing recharge and the source of 

water to an individual well are strongly affected by the other 

two pumping wells. The most upgradient well, PW1, derives 

a greater percentage of its water from ground water compared 

to the other two wells, whereas PW2, the most downgradient 

well, derives a greater percentage of its water from the streams 

than the other two wells. 

At the maximum withdrawal rate of 600 gal/min, the area 

contributing recharge is 0.44 mi2. The increased pumping rate 

is balanced by expansion of the area contributing recharge to 

intercept additional ground water that would have normally 

flowed to Batty Brook, its tributaries, and to the Clear River, 

and by inducing additional surface water, primarily from 

stream reaches of Batty Brook and the unnamed tributary in 

the vicinity of the well field. The percentage of pumped water 

derived from streamflow (37 percent), however, is about the 

same percentage as for the average pumping rate.

As was mentioned previously in the Hydrology section, 

the maximum pumping rate exceeds available recharge in 

the Batty Brook watershed. Thus, most of the precipitation 

recharge in the watershed is withdrawn by the well field at 

the maximum rate, either directly by intercepted ground water 

or indirectly by streamflow loss. More than 80 percent of the 

precipitation recharge that discharges to upstream reaches in 

Batty Brook watershed is withdrawn by the wells by inducing 

flow from stream reaches near the well field.

Similar to the average pumping rate, the shape of the 

contributing area and source of water to an individual well 

is strongly affected by nearby pumping. In contrast to the 

average pumping rate, however, the most downgradient well, 

PW2, derives a greater percentage of its water from ground 

water than the other two wells; the area contributing recharge 

to PW2 extends down valley toward the Clear River to capture 

ground water that would normally discharge to the Clear River 

and its tributaries. At the maximum pumping rate, it is the 

middle well PW3 that derives a greater percentage of its water 

from the stream than the other two wells.

Simulated traveltime estimates from recharging locations to the production wells for the maximum pumping rate, 

based on porosities of 0.35 for stratified deposits and till and 

0.02 for bedrock, are shown in figure 12. Traveltimes ranged 

from less than 6 months to more than 100 years; 93 percent 

of the traveltimes were 10 years or less. Water that recharges 

the stratified deposits at the well field from direct precipitation 

recharge and from streamflow loss has the shortest traveltimes, 

Table 6. Sizes of areas contributing recharge to the Harrisville production well field (Central Street) and the percentages of water withdrawn from different sources, Harrisville study site, Rhode Island.

[gal/min, gallons per minute; mi2, square mile]

Model scenario

Size of area 

contributing 

recharge

(mi2)

Direct precipitation 

recharge and 

upland runoff

(percent)

Infiltration of 

surface water

(percent)

224 gal/min 0.17 62 38

600 gal/min .44 63 37

600 gal/min and vertical hydraulic conductivity of streambed × 0.5 .52 75 25

600 gal/min and vertical hydraulic conductivity of streambed × 2 .37 52 48

600 gal/min and hydraulic conductivity of stratified deposits × 0.75 .44 63 37

600 gal/min and hydraulic conductivity of stratified deposits × 1.25 .44 62 38

600 gal/min and recharge rates × 0.75 .63 67 33

600 gal/min and recharge rates × 1.25 .37 67 33
24 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 12. Simulated traveltimes to the Harrisville well field at its maximum pumping rate of 600 gallons per minute, Harrisville 

study site, Rhode Island.

Duck 

Pond

Batty Brook

Sucker

Pond

Nipmuc River

River

Clear

Simulated traveltimes

Less than or equal to 0.5 year

Less than or equal to 1 year

Less than or equal to 2 years

Less than or equal to 4 years

Less than or equal to 10 years

Less than or equal to 50 years

Greater than 50 years

PW1 

Stratified deposits

Till and bedrock

 outcrops

EXPLANATION

Model boundary

Production well and 

identifier

PW2

PW3

PW1

71°41' 71°40'

41°58'

41°57'

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83 2,000 FEET

600 METERS

0

0
Harrisville Study Site 25

The hydraulic conductivity of the stratified deposits 

was decreased and increased by 25 percent. At this range 

of hydraulic conductivity, the simulated size of the area 

contributing recharge and the percentages of water from 

different sources withdrawn at the well field are the same 

as for the base-model simulations, but the location of the 

contributing area was slightly different (table 6 and fig. 14). 

By decreasing hydraulic conductivity of the stratified deposits, 

the hydraulic gradient between ground water and surface 

water increased, thereby increasing ground-water discharge to 

upstream reaches of Batty Brook watershed. Because of the 

stronger component of ground-water flow to these upstream 

reaches, the area contributing recharge to the well field shifted 

in a northward direction and included a small area in the till 

north of the Clear River. Increasing the hydraulic conductivity 

caused the opposite effect on the location of the contributing 

area: a stronger downvalley component of ground-water 

flow and less discharge to the upstream reaches, and thus a 

southward shift in the contributing area. 

Annual recharge rates were also decreased and increased 

by 25 percent across the modeled area. The area contributing 

recharge increased from 0.44 to 0.63 mi2 when recharge was 

reduced and decreased to 0.37 mi2 under higher recharge rates 

(table 6 and fig. 15). Surface-water infiltration for both lower 

and higher recharge rates was 33 percent of the total water 

pumped; this amount is 4 percent less than the base-model 

simulation. The reduced recharge rate resulted in the largest 

simulated contributing area to the well field for the range of 

model-input values considered. The area contributing recharge 

expanded in almost all directions from the opposite side of the 

Clear River north of the well field to an area that is within both 

till uplands and stratified deposits. Simulated recharge water 

that travels along both shallow and deep flow paths before 

discharging to the Clear River under nonpumping conditions 

travels instead beneath the Clear River to the well field under 

pumping conditions. A small quantity of pumped water (less 

than 1 percent) is also from the Clear River itself. The small 

streams in Batty Brook watershed were sensitive to the altered 

recharge rates; ground-water discharge to these streams 

upgradient of the well field at the lower recharge rate was less 

than one-half that at the higher rate. At the lower recharge 

rate, all available streamflow in Batty Brook and the unnamed 

tributary infiltrated, but because less ground water discharged 

to these streams upgradient of the well field under the reduced 

recharge rates, the percentage of surface water pumped at 

the well field was less. Hence, less streamflow near the well 

field also was a factor in the expanded contributing area in 

addition to the reduced recharge rate. In contrast, for simulated 

pumping wells that derived part of their water from nearby 

surface water, where the quantity of available surface water 

was large in comparison to the pumping rate, reduced recharge 

rates resulted in both an increase in contributing area and the 

percentage of surface-water infiltration (Friesz, 2004).

whereas recharge originating from areas near the ground-water 

divides in the southern part of Batty Brook watershed has the 

longest traveltimes.

The area contributing recharge to the Harrisville 

Eccleston well field extends in a generally westward direction from the Eccleston well field in the Clear River valley 

(Dufresne-Henry, Inc., 2001). The southeast extent of the 

Eccleston well-field contributing area, near Duck Pond 

(fig. 2), is about 0.7 mi from the western extent of the Harrisville Central Street well-field contributing area.

Sensitivity and Uncertainty Analysis

A sensitivity analysis of the effects of selected values 

of hydraulic properties and recharge on the simulated areas 

contributing recharge and the sources of water to the well field 

was done for the maximum well-field withdrawal rate of 

600 gal/min. Reasonable alternative values were chosen to 

provide insights into the effects of these values on the area 

contributing recharge to a well field in a small watershed in a 

narrow, valley-fill setting. The analysis provides an estimate of 

the uncertainty in the size, shape, and location of the contributing area by comparing it to the delineated contributing areas.

The hydraulic connection between streams in Batty 

Brook watershed and the aquifer was sequentially decreased 

by 50 percent and increased by a factor of 2 by altering the 

vertical hydraulic conductivity of streambed sediments. 

Changes were made only to stream cells in the vicinity of the 

well field in the area of infiltration so that approximately the 

same quantity of streamflow entered the well-field area and 

was available for infiltration. The reduced hydraulic connection between the stream and the aquifer caused the quantity 

of stream water withdrawn at the well field to decrease by 

12 percent (from 37 to 25 percent) and the area contributing 

recharge to the well field to increase from 0.44 to 0.52 mi2

(table 6 and fig. 13). The contributing area expanded primarily 

downvalley toward the Clear River and includes an isolated 

area on the opposite side and north of the river from the well 

field and south of a ground-water divide in the uplands. The 

area contributing recharge north of the Clear River includes till 

uplands and stratified deposits near the contact; this recharge 

travels along deeper and longer ground-water flow paths than 

recharging water that originates closer to the valley center. 

Under nonpumping conditions, this water would eventually 

discharge to the Clear River, but under pumping conditions 

is withdrawn by the well field. With an increased hydraulic 

connection, all available streamflow in Batty Brook and the 

unnamed tributary infiltrated; thus, the percentage of surface 

water withdrawn by the well field increased by 11 percent 

from 37 to 48 percent (table 6). The area contributing recharge 

decreased from 0.44 to 0.37 mi2 primarily in the downvalley 

direction from the well field (fig. 13).
26 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 13. Sensitivity analysis of the effects of multiplying the vertical hydraulic conductivity of streambed 

sediments at the well-field site by 0.5 and by 2, Harrisville study site, Rhode Island.

Stratified deposits

Till and bedrock outcrops

Delineated area contributing recharge

 to well field at maximum pumping rate

 of 600 gallons per minute

PW1 

Vertical hydraulic conductivity of 

 streambed sediments x 0.5

Vertical hydraulic conductivity of

 Streambed sediments x 2

Model boundary

Production well and identifier

Duck 

Pond

Batty Brook

Sucker

Pond

Nipmuc River

River

Clear

PW2

PW3

PW1

71°41' 71°40'

41°58'

41°57'

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

EXPLANATION

2,000 FEET

600 METERS

0

0
Harrisville Study Site 27

Figure 14. Sensitivity analysis of the effects of multiplying the hydraulic conductivity of stratified deposits by 

0.75 and by 1.25, Harrisville study site, Rhode Island.

Duck 

Pond

Batty Brook

Sucker

Pond

Nipmuc River

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

PW2

PW3

PW1

Stratified deposits

Till and bedrock

 outcrops

Delineated area contributing

 recharge to well field at

 maximum pumping rate of

 600 gallons per minute

Model boundary

Production well

 and identifier

EXPLANATION

PW1 

Hydraulic conductivity of 

 stratified deposits x 0.75

Hydraulic conductivity of 

 stratified deposits x 1.25

71°41' 71°40'

41°58'

41°57'

2,000 FEET

600 METERS

0

0

River

Clear
28 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 15. Sensitivity analysis of the effects of multiplying recharge rates by 0.75 and by 1.25, Harrisville study 

site, Rhode Island.

Duck 

Pond

Batty Brook

Sucker

Pond

Nipmuc River

PW2

PW3

PW1

71°41' 71°40'

41°58'

41°57'

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

2,000 FEET

600 METERS

0

0

Stratified deposits

Till and bedrock

 outcrops

Delineated area contributing 

 recharge to well field at

 maximum pumping rate of

 600 gallons per minute

Model boundary

Production well

 and identifier

EXPLANATION

PW1 

Recharge rates x 0.75

Recharge rates x 1.25

River

Clear
Richmond Study Site 29

Richmond Study Site

The Town of Richmond production well field is adjacent 

to the Wood River in southwestern Rhode Island (figs. 1 

and 16). The well field is in a broad (1.2-mi-wide) valleyfill setting bordered by extensive upland till and bedrock. 

The geographic extent of the study area includes perennial 

surface-water bodies and watershed divides that served as 

boundaries for the numerical model. These boundaries include 

Brushy Brook, Locustville Pond, and an unnamed tributary in 

the southwest; a section of the Wood River in the south; and 

watershed divides generally in the uplands where surfacewater and ground-water divides are most likely the same, in 

the southeast, east and west. The watershed boundary for the 

Wood River near Arcadia streamflow-gaging station forms 

the northern extent; this watershed boundary is in both upland 

and valley-fill deposits. The large model extent minimizes the 

effect of model boundaries on simulated heads near the area 

likely to be within the contributing area of the well field and 

incorporates uplands west and east of the well field directly 

in the model. Land use in the general area of the well field 

includes rural residential, agriculture, and forest. Some of the 

forestland is protected in Arcadia State Park Management 

Area. Land use also includes a sand and gravel mining 

operation about 0.4 mi northwest of the well-field site.

The Richmond production well field consists of two 

wells 360 ft and 580 ft east of the Wood River; characteristics 

of the supply wells are listed in table 1. The production wells 

are screened in the lower part of a coarse-grained sediment 

unit with saturated thickness greater than 60 ft. PW1 was 

constructed in 1985 to replace contaminated residential wells 

in the Village of Wyoming 1.5 mi south of the well-field site, 

whereas PW2, a small-diameter production well, was added in 

1995 as a backup to PW1. Areas contributing recharge were 

determined for the maximum well-field withdrawal rate of 

675 gal/min and, in addition, one-half the maximum withdrawal rate to determine the effects of pumping rates on the 

size and location of the contributing area.

Water levels and streamflows were measured periodically 

from May 2004 to July 2005 to provide information concerning average hydrologic conditions. Water-level measurements 

were made in existing observation wells and in the Wood 

River at the well-field site. Streamflow measurements were 

made at three sites in Baker Brook, which drains an upland 

watershed before flowing over the stratified deposits about 

0.4 mi north of the well field. Lithologic logs and seismicrefraction surveys, mainly from USGS reports and files, were 

compiled to define the altitude of the bedrock surface and 

sediment size of the stratified deposits.

Geology

In the Richmond study area, till-covered bedrock uplands 

border the Wood River valley and its tributary Brushy Brook 

valley. Glacial-meltwater deposits as much as 200 ft thick 

are in these valleys (fig. 16). Postglacial sediments overlie 

glacial deposits in flood-plain and wetland areas. Bedrock 

beneath the study area consists predominantly of Hope Valley 

alaskite gneiss in the southwestern part of the study area 

and the Scituate plutonic suite in the northeastern part of the 

area (Moore, 1958). These rock units were more recently 

characterized as late Proterozoic alaskite and granite gneisses 

of the Sterling and Esmond plutonic suites intruded by 

younger Devonian-age granite of the Scituate plutonic suite 

(Hermes and others, 1994). The bedrock valleys of the Wood 

River and Brushy Brook are partially filled with glacialmeltwater sediments, and the altitude of the bedrock surface 

beneath these valleys is shown on figure 16. Bedrock-surface 

contours were constructed on the basis of locations of bedrock 

outcrops, knowledge of bedrock structure, interpretation of 

glacial-till thickness from topography and aerial photographs, 

and all available well data and seismic-refraction surveys. 

The distribution of glacial deposits shown in figure 16 

was modified from Feininger (1962). Glacial deposits include 

subglacially deposited till and stratified glacial-meltwater 

deposits. These materials overlie the bedrock surface and 

range from a few feet to as much as 200 ft thick in parts of the 

Wood River valley. In the vicinity of the Richmond production 

well field, glacial deposits are generally about 75 ft in thickness. The distribution of surficial materials between the land 

surface and the bedrock surface is shown on cross sections 

C-C ́ and D-D ́ (fig. 17). The cross sections illustrate the characteristic vertical succession of glacial till, glacial-meltwater 

deposits (sand and gravel; sand; very fine sand, silt, and clay) 

and postglacial deposits (wetland and alluvial). Most of these 

materials are deposits of the last two continental ice sheets that 

covered New England during the middle and late Pleistocene. 

Most were laid down during the advance and retreat of the 

last (late Wisconsinan) ice sheet, which reached its terminus 

on Long Island, N.Y., about 21,000 radiocarbon years ago, 

and was retreating northward through southern Rhode Island 

between 18,000 and 17,000 radiocarbon years ago (Stone 

and Borns, 1986; Boothroyd and others, 1998; Stone and 

others, 2005). 

Glacial till in the map area was deposited directly by 

glacier ice and is characterized as a nonsorted, nonlayered, 

relatively compact mixture of sand, silt, and clay with 

variable amounts of stones and large boulders. Till blankets 

the bedrock surface in most places and is generally less than 

10–15 ft thick. Many places within the area shown as “till and 

bedrock outcrops” (fig. 16) are characterized by bedrock rather 

than till at the land surface. Till also commonly underlies 

glacial stratified deposits in the valleys where it is generally 

less than 10 ft thick.

Glacial-meltwater deposits in the Wood River valley with 

surface altitudes of about 135 ft in the southern part of the 

study area rising to about 185 ft in the northern part consist 

of gravel, sand and gravel, sand, and fine-grained materials. 

The surficial geologic map of the Hope Valley quadrangle 

(Feininger, 1962) describes the meltwater deposits in the study 

area as a single glaciofluvial unit deposited in large part on 
30 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 16. Production wells, section lines, selected borings and observation wells, model extent, surficial geology, and bedrocksurface contours, Richmond study site, Rhode Island.

95

160

40 0

0

40

40

40

40

40

0

0 80

40

60

40

120

120

100

120

120

120

100

80

120

160

100

100

80

100

120

120

160

160

160

160

120

160

160

40

80

100

100

80

80

120

120

160

120

100

160

160

80

100

120

160

120

120

120

120

40

40

40

40

0

0 0

120

100

80

160

160

40

80

120

160

80

80

40

120

120

100

100

120

100

160

160

160

100

160

80

80

160

100

100

160

120

0

0

40

0

40

40

40

80

120

160

520 16

40

40

40

0

0 80

40

120

80

100

160

HOW437

RIW721

RIW739

EXW551

EXW6 EXW490

RIW725

EXW479

HOW419

EXW489

EXW551

EXW6 EXW490

EXW479

RIW730

RIW725

HOW438 RIW721

RIW739

HOW419

HOW437 PW2

PW1

"

C C'

01117875

Till and bedrock outcrops 01117800

Wetland

Model boundary

Bedrock-surface altitude—Contour

 interval, in feet, is variable

Line of geologic cross section

Continuous streamflow-gaging 

 station and identifier

Partial-record streamflow-

 gaging station and identifier

Production well and identifier

Long-term network observation 

 well and identifier

Boring and identifier

PW1

EXW6

EXW490

Stratified deposits subdivided

 into morphosequences

Wood River valley

 sequence 

 1

 2

 3

 4

 5

 6

 7

Brushy Brook

 valley sequence 

 1

 2

Undifferentiated

EXPLANATION

Paris Brook

Wyoming

Pond

Browning

Mill 

Pond

Frying

Pan

Pond

Wood River

Roaring Brook

Wyoming

Pond

Locustville 

Pond

Parris Brook

Brushy Brook

Baker

Brook

Richmond

Exeter

Hopkinton

C'

D

D'

C 01117800

01117840

01117872

01117875

01117876

01117860

01117800

01117840

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83

41°32'

41°34'

71°44' 71°42' 71°40'

Village centerWyoming 0

0

.5

.5

1 MILE

1 KILOMETER
Richmond Study Site 31 Figure 17. Geologic cross sections (lines of sections C-C’ and D-D’ are shown in figure 16), Richmond study site, Rhode Island.

HOW-438

300200100

0

-100

ALTITUDE, IN FEET ABOVE NGVD 29

300200100

0

-100

ALTITUDE, IN FEET ABOVE NGVD 29

West

North South

D'

East

D

C'

C

Vertical exaggeration x 20

Bend

Bend

Bend

Bend

Bend

Bend

Bend

Bend

Section D-D' PW1

Section C-C'

Wood River

Wood River

Wood River

Wood River

Wyoming Pond

Wood River

Wood River

EXW 551

EXW 490

EXW 489

EXW 479

RIW 725

RIW 721

RIW 739

RIW 730 Projected

Streamflowgaging station

PW1

PW2

Production

well field

HOW-438

HOW-437

HOW-419

Production well

Open water bodyPostglacial wetland and alluvial depositsSand and gravel depositsSand depositsVery fine sand, silt, and clay depositsTill depositsBedrockProduction well screen and identifier

EXPLANATION

PW1

0

0

.5

.5

1 MILE

1 KILOMETER
32 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

stagnant ice and with an unpredictable, highly variable range 

in grain size. Recent analysis of these deposits on the basis 

of the regionally established geologic concepts of stagnationzone retreat and morphosequence deposition (Koteff and Pessl, 

1981; Stone and others, 2005) coupled with textural data 

derived from available well logs, however, allows for a more 

predictable and useful depiction of textural variations within 

these highly complex glacial-meltwater deposits. 

A series of ice-marginal, sediment-dammed ponds developed in the Wood River valley in which ice-marginal deltaic 

and lake-bottom sediments were deposited as the glacier front 

retreated northward through the area (see discussion of this 

meltwater depositional process in Stone and others, 2005). 

Section C-C ́ (fig. 17) shows the distribution of collapsed 

and noncollapsed gravelly deltaic-topset beds, sandy deltaicforeset beds, and fine-grained lake-bottom deposits of five 

shingled deposits (morphoseqences) related to five successive 

(from south to north) ice-margin positions in the valley. The 

Richmond production wells are screened in the coarse-grained 

ice-proximal part of the earliest morphosequence in this part 

of the valley; these coarse-grained deposits are overlain to the 

north and west by finer grained delta foreset sands and lakebottom fines of the next (younger) morphosequence to the 

north (see sections C-C ́ and D-D ́, fig. 17).

Postglacial deposits locally overlie glacial deposits and 

include flood-plain alluvium along rivers and streams and 

organic peat and muck (wetland deposits) in low-lying closed 

depressions. These deposits are illustrated on the geologic 

sections (fig. 17), but the alluvial deposits are not shown on 

the map (fig. 16).

Hydrology

The Richmond well field is adjacent to the Wood River, 

which drains a southward-trending valley (fig. 16). Stratified 

deposits form a moderately broad valley bounded on the 

west and east by till-covered bedrock uplands drained by 

numerous perennial streams. The stream network shown in 

figure 16 is delineated at the 1:24,000 scale except in and 

near the area expected to be within the contributing area of 

the well field, where the 1:5,000 scale network was used. This 

includes Baker Brook, where streams in the uplands were 

more extensive at the 1:5,000 scale, and a tributary north of 

Baker Brook, which was not in the 1:24,000-scale network. 

Two streams that flow into Browning Mill Pond, one of which 

is adjacent to Baker Brook watershed and the other a long 

stream, were also used in the ground-water flow model to 

simulate heads and flow directions in the uplands accurately. 

Dams built across streams created several ponds including 

Frying Pan Pond north and Wyoming Pond south of the wellfield site.

The production wells are screened in sand and gravel 

sediments east of the Wood River and north of a riparian 

wetland. The saturated thicknesses of the stratified deposits in 

the well-field area range from about 100 ft in the preglacialvalley axis west of the Wood River to more than 60 ft at the 

well-field site to zero near till and bedrock exposed within the 

valley east of the site. An average hydraulic conductivity of 

800 ft/d was estimated for these sand and gravel deposits from 

a short-term (45 hours) aquifer test at a well midway between 

the river and PW1, whereas the value estimated from the 

lithologic log was 200 ft/d (Dickerman and Bell, 1993).

A major potential source of water to the well field 

includes direct infiltration of precipitation. Streamflow records 

from three nearby long-term streamflow-gaging stations 

provided a guide in assigning recharge rates in the model area, 

(figs. 1 and 16, table 7). The drainage area of the Wood River 

at Hope Valley station (01118000) includes the model area, 

and the Wood River near Arcadia station (01117800) is at the 

northern model boundary. Both of the drainage areas for the 

Wood River stations include surficial deposits of till and 

stratified deposits. The Pendleton Hill Brook station, about 

8 mi southwest of the study site, drains a small, predominantly 

till watershed. Mean annual streamflow (precipitation minus 

evapotranspiration) is equivalent to about 29 in/yr over all 

three drainage areas. Mean annual ground-water discharge 

(effective recharge) for the Wood River stations computed by 

the hydrograph-separation method PART (Rutledge, 1998) 

was about 25 to 26 in/yr or 85 to 87 percent of total streamflow. Effective recharge for the Pendleton Hill Brook station 

was less, about 21 in/yr or 74 percent of total streamflow. 

These rates represent averages over the entire watershed, 

including areas of stratified deposits, till, surface-water bodies, 

wetlands, and a variety of land uses. The difference between 

mean annual streamflow and ground-water discharge is surface runoff from areas that reject infiltration of precipitation. 

These areas include impervious surfaces, surface-water bodies, 

wetlands, and areas where the water table is at the land surface 

seasonally, such as some till areas.

A second potential source of water to the well field is 

induced infiltration of river water from the nearby Wood River. 

A visual inspection of the riverbed sediments, along with measurements made by using a hand-held steel rod, indicated that 

the riverbed adjacent to the well field is composed of loose 

sand and gravel except near its banks, where fine-grained 

bottom sediments ranged from 0.6 to 1.6 ft thick. A cross 

section through the river 1,200 ft downstream of the well field 

by Gonthier and others (1974) showed similar results. The 

amount of river water available for infiltration under average 

annual conditions greatly exceeds the maximum withdrawal 

rate for the well field, 675 gal/min or 1.5 ft3/s. Mean annual 

streamflow (118 ft3/s) and ground-water discharge (100 ft3/s) 

for the 54.9-mi2 drainage area of the Wood River upstream 

of the well-field site are based on streamflow characteristics 

for the Wood River at Hope Valley station. The maximum 

withdrawal rate for the well field is less than 2 percent of these 

mean annual streamflow and ground-water-discharge rates. 

Drawdowns in observation wells, including one near the river 

during the aquifer test by Dickerman and Bell (1993), did not 

indicate any vertical leakage from surface water; however, this 

aquifer test was of short duration.
Richmond Study Site 33

Another potential source of water to the well field is natural or induced infiltration from tributaries that cross transmissive stratified deposits from upland areas, such as Baker Brook 

north of the well field. Streamflow measurements were made 

at three partial-record sites in Baker Brook: one site is at the 

valley-upland contact (01117872), and the other two sites are 

2,300 ft (01117875) and 3,200 ft (01117876) downstream of 

the contact (fig. 16). Ten sets of measurements made at the 

contact and the closer downstream site from May 2004 to July 

2005 indicated that net streamflow between sites ranged from 

0.04 ft3/s gain to 0.23 ft3/s loss. Additional measurements 

during the summer of 2004 at the farther downstream site near 

the confluence with the Wood River showed a maximum net 

loss of 0.32 ft3/s. At mean annual ground-water levels, based 

on long-term observation well EXW6 (fig. 16), net loss was 

0.12 ft3/s between the contact and the closer downstream site 

(with a range of 0.06 to 0.18 ft3/s net loss based on measurement accuracy). At near mean annual ground-water levels, 

loss ranged from 0.11 to 0.14 ft3/s. If the net loss of 0.12 ft3/s 

at average ground-water levels is applied to the total distance 

between the contact and the Wood River (3,300 ft), the total 

net loss for this reach is equivalent to 0.17 ft3/s, or 76 gal/min. 

Thus, the estimated net loss from Baker Brook as it flows over 

the stratified deposits corresponds to 11 percent of the maximum well-field withdrawal rate of 675 gal/min.

Streamflow measurements made at the upland-valley 

contact in Baker Brook and available streamflow measurements from the Parris Brook (01117840) and Roaring Brook 

(01117860) partial-record sites from previous and ongoing 

USGS studies (fig. 16) were related to concurrent mean daily 

streamflows for three nearby continuous-record stations to 

estimate the long-term mean annual ground-water discharges 

at the partial-record sites. Streamflow measurements were 

made several days after no precipitation and represent baseflow conditions. The long-term mean annual ground-water 

discharge estimate from Baker Brook was used in model 

calibration, and the Parris and Roaring Brook ground-waterdischarge estimates were used as inputs at the model edge. 

The Maintenance of Variance Extension, Type 1 (MOVE.1) 

method developed by Hirsch (1982) was used to provide an 

equation that relates ground-water discharge at the partialrecord sites to that at the long-term stations. Mean annual 

ground-water discharge calculated at the continuous stations 

by the hydrograph-separation method PART (Rutledge, 1998) 

was entered into the equation to determine the long-term mean 

annual ground-water discharges at the partial-record sites. 

The associated mean square error for each relation was used 

to combine the multiple estimates for each partial-record site 

into weighted-average estimates of mean annual ground-water 

discharge to obtain the single best estimate. Information about 

the analysis for each partial-record site is summarized in 

table 8. The mean annual ground-water discharge estimate for 

Baker Brook at the contact was 1.60 ft3/s.

Ground-Water-Flow Model

The ground-water-flow model for the Richmond study 

site was designed to simulate long-term, steady-state groundwater levels, flow paths, and traveltimes. The model was 

calibrated to nonpumping conditions based on historical data 

and data collected during this study. A general calibration was 

first done for the model area, and then a detailed calibration 

was completed for that part of the model expected to be within 

the contributing area of the well field. Model characteristics, 

including hydraulic properties and recharge rates, are summarized in table 9.

Table 7. Streamflow and drainage-area characteristics of selected streamflow-gaging stations in and near the Richmond study site, 

Rhode Island.

[USGS, U.S. Geological Survey. USGS station number: Locations shown on figures 1 and 16; mi2, square mile; ft3/s, cubic feet per second; in/yr, inches per 

year; PART (Rutledge, 1998) hydrograph-separation method. Ground-water discharge index is mean annual ground-water discharge divided by mean annual 

streamflow.]

USGS 

station 

number

Station name

Drainage 

area

(mi2)

Area of 

glacial 

stratified 

deposits

(percent)

Period of record 

analyzed

Mean 

annual 

streamflow

(ft3/s)

Mean 

annual 

streamflow

(in/yr)

Mean 

annual 

groundwater 

discharge 

PART

(ft3/s)

Mean 

annual 

groundwater 

discharge 

PART

(in/yr)

Groundwaterdischarge 

index

(percent)

01117800 Wood River near 

Arcadia, R.I.

35.2 23 1965–80; 1983–03 76.7 29.6 66.8 25.8 87

01118000 Wood River at 

Hope Valley, R.I.

72.4 26 1942–03 155.8 29.2 132.5 24.9 85

01118300 Pendleton Hill Brook 

near Clarks Falls, 

Conn.

4.02 8.4 1959–03 8.6 29.1 6.37 21.5 74
34 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

valley-upland contact and streamflow loss as Baker Brook 

crosses the valley to the Wood River were used in model 

calibration. The loss determined for Baker Brook as it crosses 

the valley was also applied to a nearby unnamed tributary 

north of Baker Brook.

The ground-water-flow model subdivided the study area 

of 13.1 mi2 into 283 rows and 207 columns and included a 

total of 109,551 active cells. Each cell was 100 by 100 ft 

square. The boundary of the model coincided with streams, 

ponds, or watershed divides (fig. 18). The large extent of 

the model minimized the effects of these boundaries on the 

contributing-area results. 

Vertical discretization of the three-layered model was 

based on lithology and production well-screen placements. 

The top two layers were simulated as water-table layers 

(convertible layers), which allow a model cell in an underlying 

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

dry. The bottom layer was simulated by using a fixed transmissivity. Layer 1, the top layer, represented stratified deposits 

in the valley and till and shallow bedrock in the uplands. In 

Model Design

Ground-water flow in the surficial deposits and the 

underlying bedrock was represented by a three-layered 

numerical model with a uniformly spaced grid. The numerical 

model was calibrated to 28 ground-water altitudes measured 

in the stratified deposits during February and March 1981 and 

December 1982 (Dickerman and others, 1989; Dickerman 

and Bell, 1993) near average ground-water and streamflow 

conditions and to two additional ground-water altitudes 

measured under near-average hydrologic conditions at the well 

field during this study on July 6, 2005. The July measurements 

were made 24 hours after minimal pumping at the well field. 

The model was calibrated to a generally shallow water table 

that approximates the land-surface topography in the till 

uplands. Ground-water levels in the uplands indicate a shallow 

water table averaging 16 ft below land surface in the USGS 

Hope Valley quadrangle (Bierschenk and Hahn, 1959). In 

addition to the ground-water altitudes, the long-term average 

ground-water discharge computed for Baker Brook at the 

Table 8. Summary of the long-term mean annual ground-water discharge analysis for partial-record sites, Richmond study site, 

Rhode Island.

[USGS, U.S. Geological Survey. USGS station number: Locations shown on figures 1 and 16; mi2, square mile; ft3/s, cubic feet per second]

USGS 

station 

number

Station name

Drainage 

area 

(mi2)

Number of 

measurements used 

in relation

Estimated 

long-term 

mean 

ground-water 

discharge

(ft3/s)

Streamflow-gaging stations 

used in relation

Correlation 

coefficient USGS 

station 

number

Station name

01117840 Parris Brook at Blitzkrieg 

Trail near Arcadia, R.I.

7.18 17 9.15 01117468 Beaver River near 

Usquepaug, R.I.

0.85

01117800 Wood River near 

Arcadia, R.I.

.93

01118300 Pendleton Hill Brook near 

Clarks Falls, Conn.

.96

01117860 Roaring Brook at Arcadia, R.I. 5.01 16 9.50 01117468 Beaver River near 

Usquepaug, R.I.

.85

01117800 Wood River near 

Arcadia, R.I.

.88

01118300 Pendleton Hill Brook near 

Clarks Falls, Conn.

.83

01117872 Baker Brook at KG Ranch 

Road near Hope Valley, R.I.

1.25 10 1.60 01117468 Beaver River near 

Usquepaug, R.I.

.96

01117800 Wood River near 

Arcadia, R.I.

.98

01118300 Pendleton Hill Brook near 

Clarks Falls, Conn.

.96
Richmond Study Site 35

the valleys, the bottom altitude of layer 1 was set at 65 ft or 

higher where it forms the geologic contact between stratified 

deposits and bedrock. The bottom of layer 1 was 50 ft below 

land surface in the uplands and near the edges of the valley 

where saturated stratified deposits are less than 10 ft thick; a 

relatively thick layer was used to increase numerical stability 

of the model. Layer 2, the middle layer, represented stratified 

deposits in the valley and bedrock in the uplands; layer 2 also 

included the production-well screens. The bottom altitude 

of layer 2 represented the bedrock surface in the valley at 

altitudes less than 65 ft and 100 ft below land surface in the 

uplands. Layer 3, the bottom layer, represented only bedrock. 

The bottom altitude of layer 3 is 200 ft below land surface in 

the uplands or the bedrock surface in the valley; thus, the total 

thickness of till and bedrock was assigned a constant value of 

200 ft throughout the model.

The interaction between surface water and ground water 

was simulated as a head-dependent flux boundary in layer 1 

primarily by using the stream-routing package (Prudic, 1989) 

developed for MODFLOW (fig. 18). The stream-routing package accounts for gains and losses of water in each stream cell 

and routes flow from upstream to downstream. Streams that 

flow in and out of ponds and lakes were simulated as flowing 

through these surface-water bodies. Ground-water discharges 

entering the model from areas not directly simulated were 

specified at the first boundary stream cell. Ground-water 

discharges were specified either by the long-term estimates 

based on the partial-record sites (table 8) or by areal estimates 

determined from the Wood River streamflow-gaging stations 

(table 7). The model contained 1,693 stream cells.

During model calibration the MODFLOW drain package 

(Harbaugh and others, 2000) was also used to simulate a 

head-dependent flux boundary where a small stream from the 

1:5,000 stream coverage drains an upland watershed adjacent 

to Baker Brook watershed and flows into Browning Mill Pond 

(fig. 18). Inclusion of this stream allowed for a more accurate 

representation of ground-water levels and flow patterns in the 

area. This stream was simulated with 46 drain cells.

Surface-water altitudes for the head-dependent flux 

boundary were interpolated from topographical contours 

Table 9. Summary of simulated values for hydraulic properties and recharge rates in the ground-water-flow model for the Richmond 

study site, Rhode Island.

Characteristics Simulated values

Hydraulic conductivity (feet per day)

Stratified deposits Sand and gravel: generally 200, ranged from 100–400

Sand: generally 100, ranged from 40–50 near edges of valley

Fine sand and silt: 50

Remaining sediments not subdivided: 80 in Wood River Valley and 100 in Brushy Brook Valley

Till and shallow bedrock Generally 2, ranged from 0.5–6

Bedrock .05

Ponds Ranged from 50 in uplands to 5,000 in valley

Ratio of horizontal to vertical hydraulic conductivity

Stratified deposits 10:1

Till 10:1

Bedrock 1:1

Streambed vertical hydraulic conductivity (feet per day)

Bed sediments 1

Porosity

Stratified deposits 0.35

Till .35

Bedrock .02

Recharge rates (inches per year)

Stratified deposits 29

Upland hillslopes 29

Upland watersheds 20

Valley-fill wetlands 22
36 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 18. Model-boundary types, recharge rates, simulated water-table contours for nonpumping, steady-state 

conditions, and spatial distribution of residuals (measured-simulated), Richmond study site, Rhode Island.

EXPLANATION

Stratified deposits

Till and bedrock outcrops

Wetland

Recharge rates, in inches

 per year

 29 (stratified deposits)

 22 (wetland in valley)

 29 (upland hillslopes)

 20 (upland watersheds)

Residuals, in feet

 Simulated heads greater

 than measured

 -5 to -4

 -4 to -2

 -2 to 0

 Simulated heads less

 than measured

 0 to 2

 2 to 4 520

PW1

01117875

Drain cell

Stream cell

Model boundary

Simulated water table—Contour

 interval, in feet, is variable

Production well and identifier

Partial-record streamflow-

 gaging station and identifier

0

0

.5

.5

1 MILE

1 KILOMETER

Base from U.S. Geological Survey, Rhode Island state 

plane projection, 1:24,000, NAD 83

95

41°32'

41°34'

71°44' 71°42' 71°40'

PW2

PW1

80

220

240

380

360

340

320

300

280

260

240

220

160

220

100

140

120

300

320

340

280

360

140160180

200

220

240

260

280

110

120

220

180 200

240

260

280

420

400380

360

340

320

300

160

180

200

220

240

140

160

180

200

380

360

160

140

80

380

360

340

320

300

280

260

240

240

220

220

220

140

140

160

160

160

180

180

200

220

240

260

180

180

200

200

440

420

400380

360

340

320

200

240

260

280

300

380 340

360

300 320

280

260

240

220

200

180

160

140

120

110

280

300

320

340

280

360

120

110

100

1002

140

80

80

140 160

200 180

220

220

240 260

280 300

320

340

Baker

Brook

Browning

Mill 

Pond

Baker

Brook

Wood River

Wyoming

Pond

Locustville

Pond

Frying

Pan

Pond

Parris Brook

Brushy Brook

Roaring

Brook

01117872

01117875

01117876
Richmond Study Site 37

(Wood River valley sequence 3) and immediately north (Wood 

River valley sequence 4) of the production well field. The 

remaining stratified deposits in the Wood River valley were 

simulated with one value, as were the stratified deposits in 

Brushy Brook valley. Final calibrated hydraulic conductivity 

values for the sand and gravel deposits were generally 200 

ft/d, but were as high as 400 ft/d for the sand and gravel deposits at the well field. Final values were generally 100 ft/d for 

sand and 50 ft/d for fine sand and silt. Final hydraulic conductivity values for upland till and shallow bedrock were generally 2 ft/d, but values ranged from 0.5–6 ft/d. Bedrock was 

assigned a value of 0.05 ft/d, and this value was not changed 

during model calibration. Ponds completely contained within 

the model were assigned high hydraulic conductivity values 

in comparison to surrounding materials to simulate minimal 

resistance to flow and the corresponding flat gradient across 

these water bodies. Final hydraulic conductivity values for the 

lithologic units and ponds are summarized in table 9.

Simulation of Ground-Water Flow

The altitude and configuration of the simulated water 

table for long-term, nonpumping, steady-state conditions 

are shown in figure 18 at 20-ft contour intervals except for a 

10-ft interval in the valley that includes the well-field area. 

The simulated water-table contours and flow directions are 

consistent with the conceptual model of ground-water flow in 

the study area. Ground water flows from topographically high 

areas and discharges to streams and ponds. In the uplands, 

the water table approximately parallels the land surface and 

simulated ground-water divides generally coincide with 

watershed divides. The water-table gradient is steepest in the 

till uplands and stratified deposits near the contact and flattens 

in the more transmissive valley-fill areas. 

Simulated ground-water flow in the stratified deposits 

is nearly perpendicular to the main valley streams, Wood 

River and Brushy Brook, except in areas where flow paths are 

affected by large ponds formed by dams, such as Frying Pan 

Pond north of the well-field site. Ground-water flow is nearly 

parallel to most of the small tributaries in the valley, which 

are minimally gaining or losing as they flow over transmissive 

stratified deposits. These ground-water-flow patterns are 

consistent with those shown on a water-table map for the 

stratified deposits drawn by Dickerman and Bell (1993).

The relation between simulated and measured groundwater altitudes in the stratified deposits indicates a reasonable 

agreement (fig. 19A). The mean absolute residual is 2.0 ft, 

which is less than 2 percent of the total difference in groundwater altitude, 112.7 ft, measured at the observation wells. 

A comparison of residuals indicates that the differences 

between simulated and measured water levels are generally 

randomly distributed around zero (fig. 19B). Simulated heads 

in some cases exceed measured heads (negative residuals) at 

low altitudes. These negative residuals are in areas that have 

steep hydraulic gradients near dams, where water levels are 

difficult to match, or near wetlands, which can reduce heads in 

intersecting streams and from pond altitudes shown on the 

USGS Hope Valley quadrangle. In addition, the stage of the 

Wood River measured at the well-field site on July 6, 2005, 

and 17 stage measurements reported by Dickerman and 

others (1989) and Dickerman and Bell (1993) at several 

sites including Baker Brook and additional sites for the 

Wood River were used. Both water depth and bed thickness 

were set equal to 1 ft so that the top and bottom bed altitude 

could be determined from surface-water altitudes. Tributary 

streams were simulated as 3 to 10 ft wide and the Wood River 

was simulated as 40 and 50 ft wide. A vertical hydraulic 

conductivity of 1 ft/d was used to represent bed sediments 

because most streams in the study area are fast-moving over 

coarse-grained sediments. Streambed conductances simulated 

in the model ranged from 300 ft2/d for the narrow tributaries to 

5,000 ft2/d for the Wood River.

Effective recharge rates, which account for ground-water 

evapotranspiration, were distributed based on surficial geology 

and hydrography (fig. 18). A recharge rate of 29 in/yr based 

on long-term averages at the Wood River streamflow-gaging 

stations was applied to the stratified deposits. Because the 

study area is generally rural, overland runoff is considered 

minimal in areas underlain by these deposits. The same 

recharge rate, 29 in/yr, was applied to upland hillslopes that 

drain toward the valley and have no streams or water bodies 

at their base. This rate accounts for both ground-water and 

surface-water runoff from the hillslopes that recharges the 

stratified deposits at and near the valley-upland contact. A 

recharge rate of 20 in/yr was applied to upland watersheds. 

This rate is less than the basin-wide average ground-water 

discharge (effective recharge) determined for the Wood 

River streamflow-gaging stations, about the same as the 

rate determined for Pendleton Hill Brook station, which 

drains a predominately upland watershed, and within the 

reported range of recharge rates determined for till-dominated 

watersheds by computerized hydrograph-separation methods.

Evapotranspiration rates in wetlands are poorly defined. 

Some studies have indicated that evapotranspiration rates from 

wetlands are higher and other studies that the rates are lower 

than evaporation rates from open-water bodies (Mitsch and 

Gosselink, 1993). For this study, an average evapotranspiration 

rate equivalent to evaporation from a shallow, open water 

surface was assumed to represent the wetlands in the valley 

adequately. A specified flux of 22 in/yr was applied to wetland 

areas by subtracting the evaporation rate from a free-water 

surface (29 in/yr) (Farnsworth and others, 1982) from the 

rate of precipitation for southern Rhode Island (51 in/yr). 

Conceptually, some of this water may infiltrate, particularly 

under pumping conditions, or move across the wetland as 

overland flow. The specified flux applied in upland wetlands 

was the same as recharge applied to the surrounding materials.

Hydraulic conductivity values were assigned on the basis 

of lithology. For the valley fill, the surficial materials map 

(fig. 16) and the geologic sections (fig. 17) provided a general framework for distributing hydraulic conductivity for 

the depositional sequence that includes the sequences at 
38 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

adjacent areas. Residuals in the remainder of the model show 

no discernible spatial trends (fig. 18).

Simulated streamflows also compared favorably with 

the long-term average ground-water discharge calculated for 

Baker Brook at the valley-upland contact and with streamflow loss measured downstream of this contact. Simulated 

streamflow at the contact was 1.62 ft3/s or 0.02 ft3/s more than 

the long-term average ground-water discharge at this site. 

Net simulated streamflow loss between the contact and the 

partial-record site 2,300 ft downstream was 0.09 ft3/s compared to 0.12 ft3

/s for the measured value, and simulated net 

loss between the contact and the Wood River was 0.14 ft3/s 

compared to the estimated loss of 0.17 ft3/s. Baker Brook, 

however, simulates as gaining flow for parts of the brook 

(7 of 42 stream cells) as it flows over the stratified deposits. 

The total simulated streamflow loss between the contact and 

the partial-record site and between the contact and the Wood 

River was 0.13 ft3/s and 0.19 ft3/s.

The simulated long-term nonpumping, steady-state 

ground-water budget for the study area (table 10) indicates that 

precipitation recharge provides 89 percent of the total inflow. 

Conceptually this percentage represents both direct infiltration 

of precipitation and surface runoff from upland hillslopes that 

recharges the valley near the contact. Streamflow loss from 

natural infiltration accounts for 11 percent of the total inflow; 

most of this streamflow loss is from tributaries where they 

flow over the stratified deposits and at the downgradient areas 

of the ponds. Ground water discharges through the streams 

and ponds. The simulated water budget for the stratified 

deposits only (table 10) indicates that precipitation recharge 

directly on the stratified deposits accounts for 58 percent of 

the inflow, but upland sources contribute a significant amount 

(42 percent). These upland sources include lateral and vertical 

flow from till and bedrock (30 percent) and streamflow loss 

from tributary streams (12 percent).

Figure 19. (A) Relation between simulated and measured 

ground-water levels and (B) residual (measured minus simulated) 

ground-water levels as a function of measured ground-water 

levels, Richmond study site, Rhode Island.

Table 10. Simulated steady-state average annual hydrologic 

budget for nonpumping conditions, Richmond study site, 

Rhode Island.

[ft3/s, cubic feet per second]

Hydrologic budget component Flow rate (ft3/s)

Modeled area

Inflow

Recharge 25.5

Streamflow loss 3.0

Total inflow 28.5

Outflow

Streamflow 28.5

Total outflow 28.5

Glacial stratified deposits only

Inflow

Recharge 13.9

Streamflow loss 2.9

From till 6.5

From bedrock .5

Total inflow 23.8

Outflow

Streamflow 23.6

To till .1

To bedrock .1

Total outflow 23.8

5

4

3

2

1

0

-1

-2

-3

-4

-5

A

B

200

200

180

180

160

160

140

140

120

120

100

100

80

80

80 100 120 140 160 180 200

MEASURED WATER LEVEL, IN FEET

RESIDUAL, IN FEET SIMULATED WATER LEVEL, IN FEET

LAYER 1

LAYER 2

LAYER 1

LAYER 2
Richmond Study Site 39

Areas Contributing Recharge to 

Production Wells

Areas contributing recharge to the Richmond well field 

were determined on the basis of the calibrated steady-state 

model for simulated pumping conditions and tracking of 

pathlines with the MODPATH particle-tracking program. 

The locations and extents of the simulated areas contributing 

recharge to each production well pumping at one-half the 

maximum well-field withdrawal rate (337.5 gal/min) and 

the maximum well-field rate (675 gal/min) are illustrated 

in figures 20 and 21 respectively; the sizes of the areas and 

percentages of the total water withdrawn from each water 

source for the well field are listed in table 11.

The simulated areas contributing recharge for both 

well-field withdrawal rates extend northeastward from the 

well field to the uplands and include small isolated areas. The 

area contributing recharge to PW1 at both pumping rates also 

includes an isolated area remote from the well field on the 

opposite side of the Wood River northwest of the well field. 

The area contributing recharge to PW2 does not overlie the 

well for either pumping rate, but instead precipitation recharge 

in the vicinity of PW2 flows above and around its screened 

interval to PW1. The well field does not derive any of its water 

from nearby Wood River, even at the maximum pumping rate, 

because of the relatively large area upgradient of the well 

field and the resulting quantity of ground water that can be 

intercepted by the well field. The area contributing recharge, 

however, does underlie Baker Brook, which contributes water 

to the well field and indicates the importance of even small 

tributary streams distant from a well field.

The total area contributing recharge for the lower 

pumping rate is 0.31 mi2. The well field derives most of its 

water from precipitation recharge; however, 15 percent of the 

withdrawn water is from Baker Brook as it flows from the 

upland-valley contact over the stratified deposits. PW1 derives 

a greater percentage of its water from surface-water infiltration 

than PW2. The area contributing recharge across the Wood 

River northwest of the well field is in an upland-till area near 

a ground-water divide. Particle tracks show that recharge 

originating in this till travels along deep ground-water-flow 

paths in the valley fill and, under pumping conditions, passes 

beneath the Wood River to PW1. Recharging water between 

this contributing area and the Wood River travels along 

shallow and intermediate-depth flow paths before discharging 

to the Wood River. At the higher pumping rate, the area 

contributing recharge (0.66 mi2) extends farther up and down 

the valley to capture enough water to balance the pumping 

rate. The size of the contributing area beneath Baker Brook 

increases, and thus the quantity of surface water withdrawn 

by the well field increases; the percentage of water pumped 

from this water source (10 percent), however, is less than at 

the lower pumping rate. PW1 and PW2 derive approximately 

the same percentage of their water from streamflow loss. At 

the increased pumping rate, the area contributing recharge to 

the well field from across the Wood River includes both till 

uplands and stratified deposits near the contact.

Table 11. Sizes of areas contributing recharge to the Richmond production well field and the percentages of water 

withdrawn from different sources, Richmond study site, Rhode Island.

[gal/min, gallons per minute; mi2, square mile]

Model scenario

Size of area 

contributing 

recharge

(mi2)

Direct precipitation 

recharge and 

upland runoff

(percent)

Infiltration of 

surface water

(percent)

337.5 gal/min 0.31 85 15

675 gal/min .66 90 10

675 gal/min and hydraulic conductivity of stratified deposits × 0.75 .68 94 6

675 gal/min and hydraulic conductivity of stratified deposits × 1.25 .64 87 13

675 gal/min and recharge rates × 0.75 .85 86 14

675 gal/min and recharge rates × 1.25 .54 93 7
40 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 20. Simulated area contributing recharge to the Richmond well field at 337.5 gallons per minute, which is half of its 

maximum pumping rate of 675 gallons per minute, Richmond study site, Rhode Island.

PW2 PW1

PW1 

EXPLANATION

Simulated area contributing

 recharge to PW1

Simulated area contributing

 recharge to PW2

Stratified deposits

Till and bedrock outcrops

Wetland

Model boundary

Production well and 

 identifier

71°43' 71°42' 71°41' 71°40'

41°33'

41°32'

41°31'

Locustville

Pond

Wyoming

Pond

Wood River

Baker

Brook

Frying

Pan

Pond

Browning

Mill 

Pond

0

0

.5

.5

1 MILE

1 KILOMETER

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

95
Richmond Study Site 41

Figure 21. Simulated area contributing recharge to the Richmond well field at its maximum pumping rate of 675 gallons 

per minute, Richmond study site, Rhode Island.

Locustville

Pond

Wyoming

Pond

Wood River

Frying

Pan

Pond

Browning

Mill 

Pond

95

PW2

PW1

Baker

Brook

71°43' 71°42' 71°41' 71°40'

41°33'

41°32'

41°31'

0

0

.5

.5

1 MILE

1 KILOMETER

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

PW1 

Simulated area contributing

 recharge to PW1

Simulated area contributing

 recharge to PW2

Stratified deposits

Till and bedrock outcrops

Wetland

Model boundary

Production well and 

 identifier

EXPLANATION
42 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Simulated traveltime estimates from recharging locations 

to the production wells for the maximum pumping rate, based 

on porosities of 0.35 for stratified deposits and till and 0.02 for 

bedrock, are shown in figure 22. Estimated traveltimes ranged 

from less than 1 year to more than 100 years; 54 percent of the 

traveltimes were 10 years or less, 83 percent were 20 years or 

less, and 98 percent were 50 years or less. Water that recharges 

the stratified deposits at the well field has the shortest traveltimes whereas water originating from recharge locations near 

upland ground-water divides has the longest traveltimes. The 

shortest ground-water traveltime from the area contributing 

recharge across the Wood River from the well field is about 

9 years. A small area of till and exposed bedrock surrounded 

by stratified deposits northeast of the well field affects the pattern of traveltimes by increasing traveltimes at and upgradient 

of this till area.

Sensitivity and Uncertainty Analysis

A sensitivity analysis of the effects of selected modelinput values on the simulated areas contributing recharge and 

the sources of water to the well-field was done for the maximum pumping rate of 675 gal/min. Reasonable alternative 

values were chosen to provide insights into the importance of 

these values on the area contributing recharge to a well field 

adjacent to a river in a relatively broad valley-fill setting. This 

analysis provides a measure of the uncertainty associated with 

the contributing area size, shape, and location by comparison 

to the delineated contributing area.

The hydraulic connection between the Wood River and 

the underlying aquifer was reduced by one-half and increased 

by a factor of 2 by altering the vertical hydraulic conductivity 

of riverbed sediments between Frying Pan Pond and Wyoming 

Pond. This range of vertical hydraulic conductivity resulted 

in areas contributing recharge nearly identical to the delineated contributing area because flow paths were similar and 

river water was not induced. Even by increasing the vertical 

hydraulic conductivity between the river and the aquifer by an 

order of magnitude from 1 ft/d to 10 ft/d, the well field did not 

derive any of its water from induced infiltration of river water. 

Thus, even at the maximum rate and with surface and ground 

waters well connected, the well field derived its water from 

intercepted ground water because of the large upgradient area.

The hydraulic conductivity of stratified deposits was 

decreased and increased by 25 percent. The sizes of the areas 

contributing recharge to the well field and the percentages 

of water drawn from different sources were slightly different from those calculated by the base model (table 11), but 

the locations of the contributing areas were shifted either 

downvalley or upvalley (fig. 23). For the decreased hydraulic 

conductivity, the simulated ground-water flow direction in the 

stratified deposits was more nearly perpendicular to the valley 

axis and the Wood River. This change caused the contributing 

area to shift downvalley or southward. Increasing the hydraulic 

conductivity caused the opposite effect because the flow direction had a stronger downvalley component that resulted in an 

upvalley or northward shift in the contributing area. The shift 

in the area contributing recharge is most evident for the contributing area northwest of the well field because flow directions are affected more on the west side of the Wood River and 

because of the long distance from recharging locations to the 

well field. Because the decreased hydraulic conductivity also 

raised simulated ground-water levels in the stratified deposits above those calculated by the base model, less tributary 

streamflow loss occurs and less of the pumped water is derived 

from Baker Brook. The increased hydraulic conductivity has 

the opposite effects on ground-water levels and streamflow 

loss; the well field derives more streamflow from Baker Brook 

and, because of the stronger downvalley component of groundwater flow, from the tributary north of the brook. These small 

changes in the proportion of tributary streamflow withdrawn 

by the well field cause corresponding small change in contributing-area size (table 11), which is mostly reflected in the 

contributing area across the Wood River.

Additional sensitivity tests were done by decreasing and 

increasing long-term average annual recharge rates by 

25 percent across the study area (table 11 and fig. 24). Because 

of the reduced recharge rates, the area contributing recharge 

to the well field expanded in almost all directions, increasing in size from 0.66 mi2

 to 0.85 mi2. The percentage of 

pumped water from tributary loss also increased, from 10 to 

14 percent, because the contributing area expanded beneath 

both Baker Brook and the stream north of the brook, simulated ground-water levels were lower than those calculated by 

the base model, and the quantity of tributary streamflow loss 

increased. The reduced recharge rate resulted in the largest 

simulated contributing area to the well field and the largest percentage from surface-water sources for the range of 

model-input values considered. Increasing the annual recharge 

rates by 25 percent caused the area contributing recharge to 

decrease to 0.54 mi2 and the percentage from Baker Brook to 

decrease to 7 percent.
Richmond Study Site 43

Figure 22. Simulated traveltimes to the Richmond well field at its maximum pumping rate of 675 gallons per minute, Richmond study 

site, Rhode Island.

71°43' 71°42' 71°41' 71°40'

41°33'

41°32'

41°31'

Locustville

Pond

Wyoming

Pond

Wood River

Frying

Pan

Pond

Browning

Mill 

Pond

0

0

.5

.5

1 MILE

1 KILOMETER

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

 Less than or equal to 20 years

 Less than or equal to 50 years

 Greater than 50 years

 Less than or equal to 1 year

 Less than or equal to 2 years

 Less than or equal to 5 years

 Less than or equal to 10 years 

 

EXPLANATION

PW1

Stratified deposits

Till and bedrock

 outcrops

Wetland

Model boundary

Production well and 

identifier

Simulated traveltimes

PW2 PW1

95

Baker

Brook
44 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Figure 23. Sensitivity analysis of the effects of multiplying the hydraulic conductivity of stratified deposits by 0.75 and by 

1.25, Richmond study site, Rhode Island.

71°43' 71°42' 71°41' 71°40'

41°33'

41°32'

41°31'

Locustville

Pond

Wyoming

Pond

Wood River

Frying

Pan

Pond

Browning

Mill 

Pond

0

0

.5

.5

1 MILE

1 KILOMETER

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83

PW1 

PW2 

95

Baker

Brook

Stratified deposits

Till and bedrock

 outcrops

Wetland

Delineated area contributing

 recharge to well field at

 maximum pumping rate of

 675 gallons per minute

Model boundary

Production well

 and identifier

EXPLANATION

PW1 

Hydraulic conductivity of 

 stratified deposits x 0.75

Hydraulic conductivity of 

 stratified deposits x 1.25
Richmond Study Site 45

Figure 24. Sensitivity analysis of the effects of multiplying recharge rates by 0.75 and by 1.25, Richmond study site, Rhode 

Island.

Locustville

Pond

Wyoming

Pond

Wood River

Frying

Pan

Pond

Browning

Mill 

Pond

PW1 

95

PW2 

Baker

Brook

Stratified deposits

Till and bedrock

 outcrops

Wetland

Delineated area contributing

 recharge to well field at

 maximum pumping rate of

 675 gallons per minute

Model boundary

Production well

 and identifier

EXPLANATION

PW1 

Recharge rates x 0.75

Recharge rates x 1.25

PW1 

71°43' 71°42' 71°41' 71°40'

41°33'

41°32'

41°31'

Base from U.S. Geological Survey, Rhode Island 

state plane projection, 1:24,000, NAD 83 0

0

.5

.5

1 MILE

1 KILOMETER
46 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Summary and Conclusions

Areas contributing recharge and sources of water to 

production well fields in the Village of Harrisville, Town of 

Burrillville, and in the Town of Richmond, Rhode Island, 

were determined on the basis of numerical steady-state 

ground-water-flow models representing long-term average 

hydrologic conditions. The U.S. Geological Survey (USGS), 

in cooperation with the Rhode Island Department of Health, 

Office of Drinking Water Quality, began a 2-year investigation 

in 2004 to increase understanding of the geohydrology and 

of the important hydrologic factors required to accurately 

delineate areas contributing recharge to the production 

wells. The production wells are screened in sand and gravel 

sediments in contrasting glacial valley-fill settings near 

potential surface-water sources. Differences between the 

settings include aquifer thickness and width, the size of 

the area upgradient of the well field, and the size of nearby 

streams. The area contributing recharge to a well is defined as 

the surface area where water recharges the ground water and 

then flows toward and discharges to the well.

In Harrisville, the production well field is composed of 

three wells in a narrow (approximately 0.5-mi-wide) valley-fill 

setting on opposite sides of Batty Brook, a small intermittent 

stream that drains 0.64 mi2 at its confluence with the Clear 

River. The areal distribution of glacial deposits determined 

from USGS field maps and analysis of aerial photographs 

indicated that stratified deposits generally were less extensive than previously published. The well field is screened 

in the ice-proximal part of a deltaic deposit composed of 

collapsed coarse sand and gravel; the aquifer is thin (30 ft) 

but transmissive at the well field. Paired measurements of 

ground-water and surface-water levels indicated the direction 

of flow between the brook and the aquifer was downward 

during pumping conditions, except during periods of high 

seasonal recharge rates and low pumping withdrawals. Mean 

daily streamflows measured upstream and downstream of the 

well field during 2004–2005 indicated that a net streamflow 

loss began near average hydrologic conditions and lasted until 

after major precipitation events in the fall; net loss during 

this period was about 10 to 20 percent of the 2005 average 

well-field pumping rate. Long-term mean annual streamflow 

upgradient of the well field is 0.54 ft3/s for Batty Brook and 

0.18 ft3/s for an unnamed tributary to Batty Brook.

Ground-water flow at the Harrisville study site was 

simulated by a two-layer model representing surficial deposits 

and the underlying bedrock. The model was calibrated 

by using 53 ground-water levels and 2 streamflows. The 

simulated nonpumping, steady-state hydrologic budget for the 

stratified deposits indicated that 62 percent of the inflow was 

from direct infiltration of precipitation and about 38 percent 

could be attributed to upland sources, either by infiltration 

from tributary streams (12 percent) or lateral and vertical flow 

from till and bedrock (26 percent).

The simulated area contributing recharge for the 2005 

average Harrisville well-field pumping rate of 224 gal/min 

extended upgradient to ground-water divides in the uplands 

and covered 0.17 mi2. The well field derived 62 percent of its 

water from intercepted ground water and 38 percent from infiltration from streams in Batty Brook watershed. The shape of 

the contributing area and the source of water to an individual 

well were strongly affected by the other two pumping wells: 

the farthest upgradient well derived a greater percentage of 

its water from intercepted ground water, whereas the farthest 

downgradient well derived a greater percentage of its water 

from stream infiltration. For the maximum well-field pumping 

rate of 600 gal/min, the area contributing recharge expanded 

to 0.44 mi2 and intercepted additional ground water and 

infiltration of stream water; the simulated percentage of water 

derived from surface water, however, was the same as for the 

average pumping rate. Because of the small size of the Batty 

Brook watershed, most of the precipitation recharge in the 

watershed was withdrawn by the well field at the maximum 

pumping rate either by intercepted ground water or indirectly 

by streamflow loss. In contrast to the simulation results for the 

average pumping rate, the farthest downgradient well derived 

a greater percentage of its water by capturing ground water 

that normally would have discharged to the Clear River and its 

tributaries, and the middle well derived the greater percentage 

of water from the stream. Because the production wells are 

screened in a thin and transmissive aquifer in a small watershed, simulated ground-water traveltimes from recharge locations to the discharging wells were relatively short: 93 percent 

of the traveltimes were 10 years or less.

Results of a sensitivity analysis of the area contributing 

recharge to the well field at its maximum pumping rate 

indicated that the size of the contributing area changed the 

most when the recharge rate and the hydraulic connection 

between streams and aquifer were changed. Reducing the 

recharge rate by 25 percent and the connection between 

streams and the aquifer by 50 percent resulted in the largest 

contributing areas for the range of model-input values 

considered; the areas contributing recharge included an area 

on the opposite side of the Clear River from the well field. At 

the reduced recharge rate, a small amount of pumped water 

(less than 1 percent) was from the Clear River itself.

In Richmond, a production well field in a moderately 

broad (approximately 1.2-mi-wide) valley-fill setting is composed of two wells adjacent to and east of the Wood River. 

The wells are screened in the coarse-grained ice-proximal part 

of a morphosequence with saturated thickness greater than 

60 ft. Streamflow measured in Baker Brook, a tributary to 

the Wood River 0.4 mi. north of the well-field site, indicated 

that the natural net streamflow loss between the upland-valley 

contact and a site 2,300 ft downstream is 0.12 ft3/s at average 
Acknowledgments 47

hydrologic conditions. Long-term mean annual ground-water 

discharge at the upland-valley contact is 1.60 ft3/s.

Ground-water flow was simulated at the Richmond study 

site by a three-layer model representing surficial deposits and 

bedrock. The model was calibrated by using 28 ground-water 

levels and 1 streamflow. The simulated nonpumping, steadystate water budget for the stratified deposits indicated that 58 

percent of the inflow was from direct recharge from precipitation and 42 percent could be attributed to upland sources, 

including infiltration from tributaries (12 percent) and runoff 

from till and bedrock (30 percent).

Simulated areas contributing recharge for the maximum 

Richmond well-field pumping rate of 675 gal/min and for 

one-half the maximum rate extended northeastward from the 

well field to ground-water divides in the uplands. The area 

contributing recharge also included a remote, isolated area 

on the opposite side of the Wood River from the well field. 

The area contributing recharge to the upgradient well did not 

include the area above it; instead, recharge in the vicinity of 

the well flows above and around its screen to the other well. 

Model simulations indicated that the well field did not derive 

any of its water from the Wood River, even when the hydraulic 

connection between the river and aquifer was increased by 

an order of magnitude, because of the large watershed and 

associated quantity of ground water that can be captured by 

the well field.

The area contributing recharge for one-half the maximum rate was 0.31 mi2

, and the well field derived most of its 

water from precipitation recharge; however, 15 percent was 

loss from Baker Brook, indicating the importance of even 

small, distant tributary streams to the contributing area to a 

well. The small area contributing recharge to the well field on 

the opposite side of the Wood River is in the till uplands. For 

the maximum well-field rate, the 0.66-mi2 area contributing 

recharge extended farther up and down the valley to intercept 

additional ground water and infiltration from Baker Brook; the 

percentage of pumped water derived from the brook (10 percent), however, was less than for the lower pumping rate. The 

area contributing recharge across the Wood River included 

upland till and stratified deposits near the upland-valley contact. Because the Richmond well field is in a larger watershed 

with saturated sediments thicker than at the Harrisville site, the 

overall ground-water traveltimes are greater: 54 percent of the 

traveltimes are 10 years or less, 83 percent are 20 years or less, 

and 98 percent are 50 years or less. The shortest traveltime 

from the area contributing recharge across the Wood River 

from the well field was 9 years.

A sensitivity analysis of the area contributing recharge 

to the well field when pumped at 675 gal/min indicated that 

the size of the contributing area changed the most when the 

recharge rate was modified. Reducing the recharge rate by 

25 percent resulted in the largest contributing area and 

included infiltration from Baker Brook and a second tributary 

stream that drains the uplands. When the hydraulic conductivity of the stratified deposits was varied by 25 percent, the 

size of the area contributing recharge did not change but the 

location shifted either up or down the valley. By increasing the 

hydraulic conductivity by 25 percent, the ground-water-flow 

direction had a stronger downvalley component that resulted 

in an upvalley shift in the contributing area and infiltration 

from the second tributary stream. The shift in the location of 

the area contributing recharge was most evident for the remote 

contributing area across the Wood River because of the long 

distance from recharge locations to the well field.

Recharge rate was the hydrologic factor that most 

affected the sizes of the areas contributing recharge to the production wells in both valley-fill settings. The locations of the 

areas contributing recharge in both settings were affected by 

the recharge rates, aquifer transmissivities, and the locations of 

upgradient ground-water divides. Depending on the setting and 

the pumping rate, a nearby surface-water body may also be a 

major factor affecting the size and location of the contributing area to a well. For a setting similar to the Harrisville study 

site, which has a small watershed area upgradient of the well 

field and a corresponding limited quantity of ground water that 

could be intercepted by the well, the quantity of surface water 

and the hydraulic connection between the surface water and 

the aquifer are important factors for determining the contributing area to a well. In a setting such as the Richmond study 

site, which has a large area upgradient of the well field, a well 

near a surface-water body may not always draw surface water, 

even when surface and ground waters are well connected; 

the amount of water that the well may draw from surface 

water can also depend on the pumping rate and the quantity 

of ground water that can be intercepted by the well. The area 

contributing recharge to a well also may include areas on the 

opposite side of a river, even with this major source of water 

in close proximity to the well; precipitation recharge originating on the opposite side of the river may pass beneath the river 

under pumping conditions and discharge to the well instead of, 

or including, induced infiltration of river water.

Acknowledgments

The authors express appreciation to Clay Commons 

(Source Water Assessment Coordinator, RIDOH, Office of 

Drinking Water Quality) for initiating and supporting the study 

and to Richard Amirault (RIDOH), Ernie Panciera (RIDEM), 

and Theodore Peters (RIDEM) for providing technical input 

during the course of the study. The authors also thank Paul 

Bisson (Superintendent, Harrisville Fire District) and his staff 

and Ronald Richard (Director, Richmond Water Supply System) for providing information on ground-water withdrawals 

and assisting in the coordination of field activities.
48 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

References Cited

Allen, W.B., Hahn, G.W., and Brackley, R.A., 1966, Availability of ground water, upper Pawcatuck River Basin, Rhode 

Island: U.S. Geological Survey Water-Supply Paper 1821, 

66 p., 3 sheets. 

Allen, W.B., Hahn, G.W., and Tuttle, C.R., 1963, Geohydrologic data for the upper Pawcatuck River Basin, Rhode 

Island: Rhode Island Water Resources Coordinating Board 

GWM-3, 1 sheet.

Bent, G.C., 1995, Streamflow, ground-water recharge and discharge, and characteristics of surficial deposits in Buzzards 

Bay Basin, southeastern Massachusetts: U.S. Geological 

Survey Water-Resources Investigations Report 95–4234, 

56 p.

Bent, G.C., 1999, Streamflow, base flow, and ground-water 

recharge in the Housatonic River Basin, western Massachusetts and parts of eastern New York and northwestern 

Connecticut: U.S. Geological Survey Water-Resources 

Investigations Report 98–4232, 68 p.

Bierschenk, W.H., and Hahn, G.W., 1959, Ground-water map 

of the Hope Valley Quadrangle, Rhode Island: Rhode 

Island Water Resources Coordinating Board GWM-6, 

scale 1:24,000.

Boothroyd, J.C., Freedman, J.H., Brenner, H.B., and Stone, 

J.R., 1998, The glacial geology of southern Rhode Island, 

in Murray, D.P. (ed.), 1998 New England Intercollegiate 

Geological Conference, 90th annual meeting, Kingston, 

R.I., October 9–11, 1998, Guidebook for fieldtrips in Rhode 

Island and adjacent regions of Connecticut and Massachusetts: trip C5, 25 p.

de Lima, V., 1991, Stream-aquifer relations and yield of 

stratified-drift aquifers in the Nashua River Basin, Massachusetts: U.S. Geological Survey Water-Resources Investigations Report 88–4147, 47 p.

Dickerman, D.C., 1984, Aquifer tests in the stratified drift, 

Chipuxet River Basin, Rhode Island: U.S. Geological Survey Water-Resources Investigations Report 83–4231, 39 p.

Dickerman, D.C., and Bell, R.W., 1993, Hydrogeology, water 

quality, and ground-water-development alternatives in the 

Upper Wood River ground-water reservoir, Rhode Island: 

U.S. Geological Survey Water-Resources Investigations 

Report 93–4119, 87 p.

Dickerman, D.C., Bell, R.W., Mulvey, K.D., Peterman, E.L., 

and Russell, J.P., 1989, Geohydrologic data for the upper 

Wood River ground-water reservoir, Rhode Island: Rhode 

Island Water Resources Board Water Information Series 

Report 5, 274 p., 2 pls.

Dufresne-Henry, Inc., 2001, Application to alter freshwater 

wetlands pursuant to the Rhode Island freshwater wetlands 

act—Eccleston public-water supply wellfield well development and pump station, Harrisville, Rhode Island: Westford, Mass., variously paged.

Farnsworth, R.K., Thompson, E.S., and Peck, E.L., 1982, 

Evaporation atlas for the contiguous 48 United States: 

U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, Technical Report NWS 33, 

26 p., 4 pls.

Feininger, T.G., 1962, Surficial geology of the Hope Valley 

quadrangle, Rhode Island: U.S. Geological Survey Geologic Quadrangle GQ-166, scale 1:24,000.

Friesz, P.J., 1996, Geohydrology of stratified drift and streamflow in the Deerfield River Basin, northwestern Massachusetts: U.S. Geological Survey Water-Resources Investigations Report 96–4115, 49 p., 1 pl.

Friesz, P.J., 2004, Delineation of areas contributing recharge 

to selected public-supply wells in glacial valley-fill and 

wetland settings, Rhode Island: U.S. Geological Survey 

Scientific Investigations Report 2004–5070, 57 p.

Friesz, P.J., and Church, P.E., 2001, Pond-aquifer interaction 

at South Pond of Lake Cochituate, Natick, Massachusetts: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4040, 42 p.

Gonthier, J.B., Johnston, H.E., and Malmberg, G.T., 1974, 

Availability of ground water in the Lower Pawcatuck River 

Basin, Rhode Island: U.S. Geological Survey Water-Supply 

Paper 2033, 40 p., 4 pls.

GZA GeoEnvironmental, Inc., 1985, Geohydrologic study for 

Sherlock Homes, Harrisville, Rhode Island: Providence, 

R.I., variously paged.

Hahn, G.W., 1961, Ground-water resources in the vicinity of Wallum Lake, Rhode Island: Rhode Island Water 

Resources Coordinating Board Geologic Bulletin No. 12, 

34 p., 4 pls.

Hahn, G.W., and Hansen, A.J., Jr., 1961, Ground-water map 

of the Chepachet Quadrangle, Rhode Island: Rhode Island 

Water Resources Coordinating Board GWM-15, scale 

1:24,000.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, 

M.G., 2000, MODFLOW-2000, The U.S. Geological 

Survey modular ground-water model-user guide to modularization concepts and the ground-water flow process: U.S. 

Geological Survey Open-File Report 00–92, 121 p.

Hermes, O.D., Gromet, P.L., Murray, D.P., and Hamidzada, 

N.A., 1994, Bedrock geologic map of Rhode Island; Rhode 

Island Map Series No. 1, University of Rhode Island, 

Kingston, R.I., scale 1:100,000.
References Cited 49

Hirsch, R.M., 1982, A comparison of four streamflow record 

extension techniques: Water Resources Research, v. 18, 

no. 4, p. 1081–1088.

Johnston, H.E., and Dickerman, D.C., 1974a, Availability 

of ground water in the Branch River Basin, Providence 

County, Rhode Island: U.S. Geological Survey WaterResources Investigations Report 18–74, 39 p., 1 pl.

Johnston, H.E., and Dickerman, D.C., 1974b, Availability of 

ground water in the Blackstone River area, Rhode Island 

and Massachusetts: U.S. Geological Survey WaterResources Investigations Report 4–74, 2 sheets.

Koteff, Carl, and Pessl, Fred, Jr., 1981, Systematic ice retreat 

in New England: U.S. Geological Survey Professional 

Paper 1179, 20 p.

Lapham, W.W., 1989, Use of temperature profiles beneath 

streams to determine rates of vertical ground-water flow and 

vertical hydraulic conductivity: U.S. Geological Survey 

Water-Supply Paper 2337, 35 p.

LeBlanc, D.R., 1987, Fate and transport of contaminants in 

sewage-contaminated ground water on Cape Cod, Massachusetts, in Franks, B.J., ed., U.S. Geological Survey 

program on toxic waste—Groundwater-contamination; 

Proceedings of the third technical meeting, Pensacola, Fla., 

March 23–27, 1987, U.S. Geological Survey Open-File 

Report 87–109, p. B3–B7.

Lyford, F.P., and Cohen, A.J., 1988, Estimation of water available for recharge to sand and gravel aquifers in the glaciated 

northeastern United States, in Randall, A.D., and Johnson, 

A.I., eds., Regional aquifer systems of the United States—

The northeast glacial aquifers: American Water Resources 

Association Monograph Series, no. 11, p. 37–61.

Mazzaferro, D.L., Handman, E.H., and Thomas, M.P., 1979, 

Water resources inventory of Connecticut, part 8, Quinnipiac River Basin: Connecticut Water Resources Bulletin, 

no. 27, 88 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular 

three-dimensional finite-difference ground-water flow 

model: U.S. Geological Survey Techniques of Water 

Resources Investigations, book 6, chap. A-1, 586 p.

Meinzer, O.E., 1923, The occurrence of ground water in the 

United States, with a discussion of principles: U.S. Geological Survey Water-Supply Paper 489, 321 p.

Melvin, R.L., de Lima, V., and Stone, B.D., 1992, The 

stratigraphy and hydraulic properties of tills in southern 

New England: U.S. Geological Survey Open-File Report 

91–481, 53 p.

Mitsch, W.J., and Gosselink, J.G., 1993, Wetlands, 2d ed.: 

New York, Van Nostrand Reinhold, 722 p.

Moore, G.E., 1958, Bedrock geology of the Hope Valley quadrangle, Rhode Island: U.S. Geological Survey Geologic 

Quadrangle Map GQ-105, scale 1:24,000.

National Oceanic and Atmospheric Administration, 2006, 

Annual climatological summary, accessed on June 2006, at 

http://hurricane.ncdc.noaa.gov/ancsum/ACS.

Pollock, D.W., 1994, User’s guide for MODPATH/MODPATH_PLOT, version 3: A particle tracking post-processing package for MODFLOW, the U.S. Geological Survey 

finite-difference ground-water flow model: U.S. Geological 

Survey Open-File Report 94–464, variously paged.

Prudic, D.E., 1989, Documentation of a computer program to 

simulate stream-aquifer relations using a modular, finitedifference, ground-water flow model: U.S. Geological 

Survey Open-File Report 88–729, 113 p.

Quinn, A.W., 1967, Bedrock geology of the Chepachet Quadrangle, Providence Co., Rhode Island: U.S. Geological 

Survey Bulletin 1241-G, map scale 1:24,000 with accompanying text, 26 p.

Randall, A.D., Thomas, M.P., Thomas, C.E., Jr., and 

Baker, J.A., 1966, Water resources inventory of Connecticut; Part 1, Quinebaug River Basin: Connecticut Water 

Resources Bulletin no. 8, 102 p.

Reilly, T.E., and Pollock, D.W., 1993, Factors affecting areas 

contributing recharge to wells in shallow aquifers: U.S. 

Geological Survey Water-Supply Paper 2412, 21 p.

Rhode Island Department of Environmental Management, 

1995, Site Inspection Prioritization Report for Burrillville 

Landfill Number 2, Burrillville, Rhode Island, variously 

paged.

Ries, K.G., III, and Friesz, P.J., 2000, Methods for estimating low-flow statistics for Massachusetts streams: U.S. 

Geological Survey Water-Resources Investigations Report 

00–4135, 81 p.

Rosenshein, J.R., Gonthier, J.B., and Allen, W.B., 1968, 

Hydrologic characteristics and sustained yield of principal 

ground-water units, Potowomut-Wickford area, Rhode 

Island: U.S. Geological Survey Water-Supply Paper 1775, 

38 p., 5 pls.

Rutledge, A.T., 1998, Computer programs for describing the 

recession of ground-water discharge and for estimating 

mean ground-water recharge and discharge from streamflow 

records-Update: U.S. Geological Survey Water-Resources 

Investigations Report 98–4148, 43 p.

Sage Environmental, 2001, Groundwater monitoring report, 

216 Main Street, Burrillville, Rhode Island: Pawtucket, 

R.I., variously paged.
50 Simulation of Ground-Water Flow and Areas Contributing Recharge to Production Wells in Glacial Valley-Fill Settings, R.I.

Stone, B.D., and Borns, H., 1986, Pleistocene glacial and 

interglacial stratigraphy of New England, Long Island, 

and adjacent Georges Bank and Gulf of Maine, in Sibrava, 

Vladimir, Bowen, D.Q., and Richmond, G.M., eds., Quaternary glaciations in the Northern Hemisphere: Oxford, 

United Kingdom, Pergamon Press, p. 39–52.

Stone, J.R., Schafer, J.P., London, E.H., DiGiacomo-Cohen, 

M.L., Lewis, R.S., and Thompson, W.B., 2005, Quaternary 

geologic map of Connecticut and Long Island Sound Basin: 

U.S. Geological Survey Scientific Investigations Map SIM2784, 1:125,000 scale, with accompanying text, 72 p.

Tiedeman, C.R., Goode, D.J., and Hsieh, P.A., 1997, Numerical simulation of ground-water flow through glacial deposits 

and crystalline bedrock in the Mirror Lake area, Grafton 

County, New Hampshire: U.S. Geological Survey 

Professional Paper 1572, 50 p.

U.S. Environmental Protection Agency, 1991, Protecting the 

nation’s ground water: EPA’s strategy for the 1990’s: U.S. 

Environmental Protection Agency, Office of the Administrator, Report 21Z-1020, 84 p.
For more information concerning the research in this report, contact:

Wayne H. Sonntag, Director

U.S. Geological Survey

Massachusetts-Rhode Island Water Science Center

10 Bearfoot Rd.

Northborough, MA 01532

or visit our Web site at:

http://ma.water.usgs.gov