U.S. Department of the Interior

U.S. Geological Survey

Glacial Geology and Aquifer 

Characteristics of the

Big River Area, Central 

Rhode Island

Water-Resources Investigations Report 01-4169

By JANET RADWAY STONE and DAVID C. DICKERMAN

Prepared in cooperation with the

RHODE ISLAND WATER RESOURCES BOARD

Stone and Dickerman 

— GLACIAL GEOLOGY AND AQUIFER CHARACTERISTICS OF THE BIG RIVER AREA, CENTRAL RHODE ISLAND 

— WRIR 01-4169

MASSACHUSETTS

CONNECTICUT

Big River 

Study Area

RHODE ISLAND
U.S. Department of the Interior

U.S. Geological Survey

Glacial Geology and Aquifer 

Characteristics of the

Big River Area, Central 

Rhode Island 

By JANET RADWAY STONE and DAVID C. DICKERMAN

Water-Resources Investigations Report 01-4169

Prepared in cooperation with the

RHODE ISLAND WATER RESOURCES BOARD

Northborough, Massachusetts

2002
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary 

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director 

For additional information write to: Copies of this report can be purchased 

Subdistrict Chief U.S. Geological Survey

Massachusetts-Rhode Island District Branch of Information Services

U.S. Geological Survey Box 25286

Water Resources Division Denver, CO 80225-0286

10 Bearfoot Road

Northborough, MA 01532

or visit our Web site at

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

CONTENTS

Introduction .......................................................................................................................................................................

Acknowledgments ...................................................................................................................................................

Previous Studies ......................................................................................................................................................

Topography and Drainage .......................................................................................................................................

Bedrock ...................................................................................................................................................................

Glacial Geology.................................................................................................................................................................

Distribution of Surficial Materials...........................................................................................................................

Till ...........................................................................................................................................................................

Meltwater Deposits..................................................................................................................................................

Glacial Lakes and Ice-Margin Positions during Deglaciation.................................................................................

Postglacial Deposits ................................................................................................................................................

Aquifer Characteristics......................................................................................................................................................

Till ...........................................................................................................................................................................

Stratified Deposits ...................................................................................................................................................

Hydraulic Properties of the Sand and Gravel Aquifer...................................................................................

Aquifer Tests .................................................................................................................................................

References .........................................................................................................................................................................

FIGURES

1, 2. Maps showing:

1. Location of study area and major drainages in the Big River area, Rhode Island ....................................

2. Glacial lakes and ice-margin positions during deglaciation, Big River area.............................................

TABLES

1. Surficial materials, well-construction characteristics, and hydraulic properties determined from aquifer 

tests in the Big River area, Rhode Island ............................................................................................................

CONVERSION FACTORS AND VERTICAL DATUM

CONVERSION FACTORS

VERTICAL DATUM

Sea Level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of the

United States and Canada, formerly called Sea Level Datum of 1929.

Multiply By To obtain

foot (ft) 0.3048 meter

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

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

inch (in.) 25.4 millimeter

mile (mi) 1.609 kilometer

square foot per day (ft2/d) 0.09290 square meter per day 

square mile (mi2) 2.590 square kilometer
Introd

Glacial Geology and Aquifer 

Characteristics of the

Big River Area, Central 

Rhode Island 

By Janet Radway Stone and David C. Dickerman

INTRODUCTION

The Rhode Island Water Resources Board 

(RIWRB), which is responsible for developing the 

State’s major water resources, is concerned that continued growth in demand for water in Rhode Island will 

severely stress water supplies. In the early 1960s, the 

State proposed construction of a surface-water reservoir in the Big River Basin in central Rhode Island to 

meet the growing water demands, but, to date (2001) 

the U.S. Environmental Protection Agency has not 

given approval for construction of this reservoir. As an 

alternative, the RIWRB would like to identify sites in 

the Big River area stream-aquifer system where highyield supply wells can be constructed to meet future 

water demands. A cooperative study was initiated 

during the summer of 1995 by the U.S. Geological 

Survey (USGS) and the RIWRB to evaluate ground 

water as a source of water supply in the Big River area.

This report presents the initial results of a multiyear investigation of the three-dimensional characteristics of the surficial aquifer system based on geologic 

and geophysical field studies, and provides information 

needed to protect, develop, and manage the Big River 

area stream-aquifer system. The Big River area 

includes the entire Big River drainage basin and part 

of the Mishnock River drainage basin (fig. 1) and 

covers approximately 35 mi2, including parts of the 

towns of Coventry, Exeter, and West Greenwich. Most 

of the Big River area is in Kent County, with a small 

part in Washington County; it encompasses part

Coventry Center, Hope Valley, Crompton, and S

7.5-minute quadrangles.

This investigation includes a characteriza

the geologic framework and an evaluation of th

hydraulic properties of the stream-aquifer syste

Big River area stream-aquifer system is the surfi

aquifer and the network of rivers, brooks, lakes

ponds that overlie and are in hydraulic connecti

the aquifer. The surficial materials units of the B

River area and the accompanying bedrock-surfa

contours (pl. 1) were delineated on the basis of 

collected during field mapping, seismic-refracti

surveys, ground-penetrating radar surveys, logs 

all available wells and test holes, and results of 

previous investigations.

 Some streams in the study area lose surf

water naturally to the underlying sand and grav

fer, whereas others lose water to the aquifer by i

infiltration of streamflow caused by ground-wat

withdrawals. Most large ground-water withdraw

from public-supply wells in the sand and gravel 

in the Mishnock River Basin. Minimal ground-

withdrawals take place in the Big River Basin, b

most of the land is designated as open space an

tected from development by State law. The prim

use of surface water in the study area is for recr

Water from the Flat River Reservoir, the largest 

surface-water body in the study area, is used on

recreational purposes.
2 Glacial Geology and Aquifer Characteristics of the Big River Area, Central Rhode Island

MASSACHUSETTS

CONNECTICUT

Big River 

Study Area

RHODE ISLAND

5

5

Island

Block

0 10 MILES

0 10 KILOMETERS

New Shoreham

41o15'

71o

07'30"

71o

15'

71o 71 22'30" o

30' 71o 71 37'30" o

45'

42o

00'

41o

52'30"

41o

45'

41o

30'

41o

37'30"

41o

22'30"

BLOCK ISLAND SOUND

RHODE ISLAND SOUND

ATLANTIC OCEAN

Burrillville

Smithfield

North

Cumberland

Lincoln

Johnston

Providence

Providence

North

Smithfield

Cranston

Warwick

West

Woonsocket

Coventry

West Greenwich

Exeter

Richmond

Hopkinton

Bristol

Warren

Barrington

Warwick

Providence

South

Kingstown

Greenwich

East

North

Kingstown

Narragansett

Pawtucket

East

Newport

Middletown

Portsmouth

Tiverton

Compton

Jamestown

Little

Charlestown

Westerly

Glocester

Scituate Foster

Falls

Central

Figure 1. Location of study area and major streams in the Big River area, Rhode Island.
Introd

 Acknowledgments

The authors express appreciation to Timothy 

Brown, General Manager, Kent County Water 

Authority for providing well logs, aquifer-test data, 

and pumpage records for water-supply wells in the 

Mishnock River Basin. Special acknowledgment is 

made to Patrick Craft, formerly with the USGS, who 

analyzed aquifer-test data and calculated hydraulic 

properties at six test sites. The authors also wish to 

thank Lance Ostiguy, USGS, who provided map digitization and GIS (geographic information systems) 

support, and Mark Bonito, USGS, for digital drafting.

Previous Studies

Surficial geologic maps have been published 

for the Hope Valley quadrangle (Feininger, 1962), 

Crompton quadrangle (Smith, 1956), and Slocum 

quadrangle (Power, 1957). These maps are based on a 

morphogenic classification of deposits, and generally 

show an accurate distribution of glacial till, glacial 

meltwater deposits, and postglacial deposits, but do 

not describe the thickness and textural distribution of 

the surficial materials. The surficial geology of the 

Coventry Center quadrangle was not previously 

mapped. The bedrock geology was mapped for the 

Coventry Center quadrangle (Moore, 1963), Hope 

Valley quadrangle (Moore, 1958), Crompton quadrangle (Quinn, 1963), and Slocum quadrangle (Power, 

1959). Many surficial geologic contacts and locations 

of nearly all bedrock outcrops shown on the surficial 

materials map (pl. 1) were taken from these earlier 

quadrangle studies. The bedrock geology of the area 

has been updated on the new Bedrock Geologic Map of 

Rhode Island by Hermes and others (1994). Groundwater maps have been published for the Crompton 

quadrangle (Allen and others, 1959), Hope Valley 

quadrangle (Bierschenk and Hahn, 1959), Slocum 

quadrangle (Hahn, 1959), and Coventry Center quadrangle (Mason and Hahn, 1960). Also, Gonthier (1966) 

conducted a water-resources investigation for th

Branch Pawtuxet River Basin, which includes t

River Basin.

Topography and 

Drainage

Landforms in the Big River study area co

of a series of north- to northwest-trending hills 

valleys. Most hills that form the drainage basin 

are higher than 400 ft in altitude; the highest po

at 600 ft on the top of Raccoon Hill. Valley bott

generally are below 300 ft, and contain a variet

glacial landforms such as flat-topped ice-contac

(kame) deltas, sinuous esker ridges, glacial lake

bottom plains, and postglacial wetlands and flo

plains. The lowest altitude in the area is 240 ft a

the Mishnock River where the river exits the dr

basin in the northeastern part of the area. The Bi

Basin drains to the north and includes seven str

ultimately tributary to the east-flowing Flat Riv

South Branch Pawtuxet River: Raccoon Brook 

north-flowing tributary to the south- and southe

flowing Nooseneck River; Congdon River is a n

flowing stream that joins the Nooseneck River t

the north-flowing Big River; Carr River and oth

north- and northwest-flowing tributaries join th

River in the central part of the study area. Bear 

flows north and east to join the Big River, and t

Mishnock River originates in a large wetland ar

flows northerly to the South Branch Pawtuxet R

The northern end of the Big River Valley now i

flooded by the Flat River Reservoir.

Bedrock

Bedrock controls the large-scale aspect o

landscape in the study area. The basin is underl

granitic rocks of the Scituate Igneous Suite (He

and others, 1994), formerly called Scituate gran
4 Glacial Geology and Aquifer Characteristics of the Big River Area, Central Rhode Island

gneiss (Quinn, 1971). The granite has undergone 

Paleozoic metamorphism and has a gneissic structure 

and texture. Although locally massive, in most places 

the rock is moderately foliated and compositionally 

layered. In the western part of the study area, the strike 

of foliation and layering generally is north-northeast 

with low (25–35 ̊) northwest dips; in the central part, 

the strike of foliation is north to north-northwest with 

steep (greater than 70 ̊) to vertical dip. In the easternmost part of the area, foliation trends are northeast to 

east-northeast with moderate (less than 40 ̊) northwest 

to north-northwest dips. Locally, Mesozoic-aged 

diabase dikes intrude the granitic rock. Ubiquitous 

fractures and joints cut the bedrock; cross-cutting 

fractures include near-horizontal unroofing joints and 

high-angle to vertical fractures generated by tectonic 

stresses. The orientation of dominant sets of high-angle 

fractures coupled with the orientation of foliation and 

layering in the bedrock control the erosional resistance 

of the rock, hence the trend and shape of bedrock hills 

and valleys. The bedrock valleys, which today are partially filled with glacial meltwater sediments, were 

developed from deeply weathered zones in the bedrock, modified by multiple episodes of continental 

glaciation as glacial ice preferentially plucked the 

fractured bedrock along zones of structural weakness.

Granitic bedrock in New England has extremely 

low primary porosity, and ground water is present only 

in fractures that cut the rock mass. Such bedrock is 

capable of providing enough water for domestic-well 

use and is, therefore, an important aquifer. The yield 

of water from bedrock wells is related to the number 

and connectivity of fractures that the well intersects. 

Reported yields of wells tapping bedrock in the study 

area range from less than 1 to 50 gal/min, with a 

median yield of 5 gal/min. Bedrock wells range from 

25 to 500 ft in depth, with a median well depth of 

200 ft (Gonthier, 1966).

The configuration of the bedrock surface in the 

valleys beneath surficial materials is shown on the plate 

(red contour lines) where it lies at or below 300 ft in 

altitude. Bedrock-surface contours were delineated on 

the basis of reported depths to bedrock or refusal at all 

available wells and test holes, as well as geologic inference based on a regional understanding of the thickness 

and distribution of surficial deposits. Depth to bedrock 

ranges from 0 to as much as 250 ft in the study area. 

The deepest bedrock valley lies below 100 ft in altitude 

in the Mishnock River Valley.

GLACIAL GEOLOGY

Glacial deposits overlie bedrock in the Bi

area (plate) and range from a few feet to more t

200 ft in thickness. Most of these materials are d

of the last two continental ice sheets that covere

England during the middle and late Pleistocene

deposits were laid down during the advance and 

of the last (late Wisconsinan) ice sheet, which r

its terminus on Long Island, N.Y., about 21,000 

ago, and was retreating northward through the B

River area by about 17,000 years ago (Stone and 

1986; Boothroyd and others, 1998). The glacial 

its are divided into two broad categories—glaci

and glacial meltwater deposits. Till was deposit

directly by glacier ice and is characterized as a 

sorted matrix of sand, silt, and clay with variab

amounts of pebbles, cobbles, and large boulder

cial meltwater deposits were laid down by meltw

lakes and streams in front of the retreating ice m

during deglaciation. These materials, also referr

glacial stratified deposits, consist of well-sorted 

poorly sorted layers of gravel, sand, silt, and cla

glacial sediments, primarily floodplain alluvium 

swamp deposits, are thin surface units and mak

lesser proportion of the surficial materials in the 

area. 

Distribution of Surficial 

Materials

The distribution of surficial materials tha

between the land surface (below the pedogenic 

horizon) and the bedrock surface is shown on th

(plate). Cross-sections A-A′, B-B′, C-C′, D-D′, a

(plate) illustrate the characteristic vertical succe

of glacial till, glacial meltwater deposits, and po

cial deposits. In upland areas, till is the major su

material: it is present as a discontinuous blanke

deposit of variable thickness over the bedrock s

In most places, till is less than 10 to15 ft thick; 

where till is thicker than 10 to15 ft are shown o

map by the dark gray color. Till is thickest in dr

such as Nooseneck Hill and Weaver Hill, and o

northwestern sides of bedrock hills, such as Hu

Hill. In the valleys, glacial meltwater deposits a

predominant surficial materials. These deposits 

ally overlie till; however, well logs indicate that 

some places till is not present in the subsurface 
Glacial Ge

meltwater deposits lie directly on bedrock. In the 

smaller valleys, like Raccoon Brook and Nooseneck 

River Valleys, meltwater deposits generally are 10 to 

40 ft thick. In the Big River, Carr River, and Mishnock 

River Valleys, meltwater deposits generally are 50 to 

100 ft thick and completely mask the till-draped 

bedrock surface. Postglacial materials locally overlie 

the glacial deposits in the study area. Alluvium underlies the floodplains of most rivers and brooks. Swamp 

deposits cover many floodplain surfaces and fill other 

poorly drained areas like kettle holes, where blocks of 

glacial ice, that were buried by meltwater sediments, 

subsequently melted.

Till

Glacial till generally is a compact, nonsorted 

mixture of sand, silt, clay and stones, laid down 

directly by glacial ice. Tills laid down during two separate episodes of continental glaciation are present 

throughout southern New England (Stone and Borns, 

1986; Melvin and others, 1992; Stone and others, 

1998), and both types are present in the study area. The 

lower (Illinoian-age) till is discontinuous and is present 

only in areas of thick till, such as drumlins and northwestern sides of bedrock hills. Although no exposures 

were observed in the Big River area during recent field 

mapping, lower till observed elsewhere in Rhode Island 

and Connecticut typically is gray to olive-gray, very 

compact mixture of pebbles, cobbles, and few boulders 

in a sandy matrix that contains up to 30–40 percent silt 

and clay; it commonly is stained with iron oxide. The 

upper parts of lower till sections contain distinct 

subhorizontal fissility; this fissility and a less welldeveloped, subvertical, iron- and manganese-stained 

joint system give the lower till an angular blocky 

structure.

The upper (late Wisconsinan age) till was deposited by the last ice sheet. Upper till exposures generally 

reveal compact, gray to gray-brown, non-oxidized, 

stony till with a sand/silt matrix. This till is interpreted 

to be a lodgment facies, which exhibits a weakly developed subhorizontal fissility. Where the upper till overlies the lower till, discrete pieces of the oxidized 

lower till occur as blocks within the matrix of the 

non-oxidized upper till. Locally, upper till is present as 

morainal deposits of ablation till. This material accumulated as a nonsorted mixture of sand, gravel, and silt 

with numerous large boulders directly at the ice front 

at sequential terminal positions during deglaciation. 

Ablation till typically is much less compact tha

lodgement till because the material was melted 

glacial ice at the margin during deglaciation rath

smeared beneath the great weight of the ice she

lodgment till. 

Meltwater Deposits

Glacial meltwater deposits were laid dow

during retreat of the last ice sheet through the Bi

area about 17,000 years ago. These sediments (

called glacial stratified deposits) consist of grav

sand, silt, and clay carried away from the ice fro

meltwater streams, which commonly flowed dir

indirectly into glacial lakes. The meltwater dep

consist of mappable bodies of coarse-grained se

(gravel, sand and gravel, and sand) and fine-gra

sediment (very fine sand, silt, and clay). Coarse

grained, poorly sorted, and relatively angular gr

and sand were deposited at, and proximal to, th

front. This material commonly was laid down o

ice at the glacier margin. Subsequent melting of 

produced “collapsed” ice-contact scarps and ke

holes in these proximal deposits. Finer-grained 

better-sorted gravel and sand was deposited fart

away from the ice margin, commonly in deltas t

graded into glacial lakes. Well-sorted, very fine 

silt, and clay settled out as bottom sediments in 

lakes. These bodies of contemporaneously depo

sediments, which grade from coarse grained ne

ice margin to fine grained in areas distal from th

are called morphosequences (Koteff and Pessl, 

Stone and others, 1992). Morphosequences in t

River area commonly are 0.25 to 1 mi long and 

present in the valleys in shingled form; that is—

coarse-grained, collapsed, ice-contact northern 

of one sequence is overlain by the fine-grained 

end of the next sequence to the north (see plate

tions A-A′, B-B′, C-C′). This shingled relation b

morphosequences is the result of sequential dep

related to systematic northward retreat of the ma

the ice sheet during deglaciation. Seven differen

of morphosequences are common in southern N

England and these have been defined in Stone a

others (1998) and Koteff and Pessl (1981).

The coarse-grained meltwater deposits in 

River area consist predominantly of a series of 

marginal deltaic and lacustrine-fan morphosequ

laid down sequentially in a series of glacial lake

plate, sections A-A′, and B-B′). Fine-grained me
6 Glacial Geology and Aquifer Characteristics of the Big River Area, Central Rhode Island

deposits consist of lake-bottom sediments laid down in 

deeper parts of the lake in front of the deltas and fans. 

In some places along the valley, successive deltas were 

built up against earlier ones, so that the surface gradient 

of the meltwater deposit is continuous from one deltaic 

morphosequence to the next. In other places, low areas 

underlain by lake-bottom sediments separate the deltaic sequences. Interfingering sand and gravel deposits 

and sand deposits are typical in the proximal areas of 

morphosequences, and interfingering sand deposits and 

fine deposits are common in distal parts.

Glacial Lakes and Ice-Margin 

Positions during Deglaciation

In order to map the distribution of coarse-grained 

and fine-grained meltwater deposits in an area and to 

predict textural variations in the subsurface, it is necessary to first understand ice-margin configurations and 

the associated depositional environments during retreat 

of the glacier. The highest level (altitude) at which glacial sands and gravels were deposited in particular valleys was controlled by the base level of the meltwater 

streams during the time of northward ice retreat 

through the area. In the north-draining Big River area, a 

series of glacial lakes controlled the levels of meltwater 

deposition as the ice margin retreated from south to 

north. Successive ice-margin positions, recorded by the 

proximal slopes of ice-marginal deltas and lacustrine 

fans, dammed these lakes. Lake levels were at successively lower altitudes as the wasting ice uncovered 

lower lake spillways. Ice-margin positions and the 

extent of individual glacial lake deposits are shown in 

figure 2. 

When the ice margin retreated northward across 

the southern part of the Big River drainage divide, 

small glacial lakes formed in the north-sloping 

Raccoon Brook and Congdon River Valleys, followed 

by a larger glacial lake in the Big River Valley. Meltwater was impounded in these valleys by the northerly 

retreating ice margin, and the earliest spillway for each 

lake was through bedrock-floored saddles on the 

drainage divide to the south. 

In the Raccoon Brook Valley, a small lak

fig. 2) controlled by a spillway at an altitude of 

across the drainage divide was a basin for delta

sediments. Deltaic sands and gravels reach 430 

altitude in the upper (southern) part of the valle

successively lower deposits at the northern end 

valley at 410 ft and 390 ft in altitude, were grad

lower levels of ponding controlled by spillways 

405 ft and 385 ft cut into thick till on the north 

Nooseneck Hill. 

In the upper Nooseneck River Valley, a sm

lake (nr, fig. 2) was impounded while ice remai

the lower Nooseneck Valley; because of the nor

ward lobation of the ice front, the upper valley b

ice free. Fluviodeltaic sands and gravels at 415–

in altitude were graded to a pond controlled by a 

spillway along the southern valley side.

West of Fish Hill, a small lake (fh, fig. 2) 

spilled across the lowest point (425 ft in altitud

local drainage divide between Nooseneck River 

Bear Brook. Ice-marginal delta deposits control

this level of ponding are at 435 ft. Meltwater ca

series of deep channels in the thick till across th

Fish Hill as it escaped from the valley along the 

the ice margin at successively lower altitudes. T

southernmost channels head at 435 ft, higher th

425-ft spillway that controlled the ponding in th

ley. The next two channels to the north head at 

and these served as lower spillways for the sma

the level of deltaic sand at the north end of the v

at 405 ft. The northernmost meltwater channel 

Fish Hill is at 385-ft altitude; when water could 

at this level, ponded conditions no longer were 

in the valley.

In the Congdon River Valley, a small glac

(cr, fig. 2) formed as soon as the ice margin retr

across the drainage divide; early ponding was c

trolled by a spillway across the divide in the Mo

Swamp Pond Valley at an altitude of 385 ft, wh

persisted in the Millbrook Pond Valley to the w

lower spillway at 365 ft across the divide in the 

valley controlled the lake level as successive ice

marginal deltas were built northward in the Con

River Valley. Non-collapsed delta surfaces are a

in the central part of the valley and 385 ft in the 

northern part. 
Glacial Ge

3 5 0

3 0 0

3 5 0

300

4 0 0

400

300

3 5 0

2 5 0

250

3 0 0

300

250

3 0 0

3 0 0

3 5 0

400

3 0 0

3 0 0

350

400

4 5 0

350

300

500

3 5 0

4 5 0

400

4 5 0

5 0 0

4 0 0

3 0 0

3 5 0

3 5 0

400

5 0 0

450

3 0 0

3 5 0

4 5 0

400

3 5 0

400

5 0 0

550

500

450

5 5 0

550

550

5 0 0

4 5 0

300

250 2 5 0

250

250

2 5 0

3 0 0 2 5 0

2 5 0

2 5 0

250

2 5 0

250

2 5 0

3 0 0

350

2 5 0

3 0 0

3 5 0

3

250

5 0 250

2 5 0

3 5 0

300

250

0 10,000 FEET

0 2 MILES

5,000

0 1 2 3 KILOMETERS

CONTOUR INTERVAL 50 FEET

NATIONAL GEODETIC VERTICAL DATUM OF 1929

1

450,000 460,000 470,000 480,000 

180,000

190,000

200,000

210,000

220,000

EXPLANATION

GLACIAL LAKE DEPOSITS

POSTGLACIAL DEPOSITS

Glacial Lake Mishnock deposits, Stage 2

Glacial Lake Mishnock deposits, Stage 1

Fish Hill ice-dammed pond deposits

Nooseneck River ice-dammed pond deposi

Raccoon Brook ice-dammed pond deposits

Congdon River ice-dammed pond deposits

Alluvium

Swamp

Ice-margin position, ticks point up ice

Glacial lake spillway (number is approxim

altitude in feet)

ICE MARGINS AND SPILLWAYS

GLACIAL TILL

Till, less than 15 feet thick

Till, greater than 15 feet thick

lm2

lm1

fh

nr

rb

cr

cr

lm1

lm1

lm2

fh

rb

nr

lm2

lm2

lm1

lm2

lm1

405

425

365 385

325

295 

405

385

405

405

415

385

W eaver 

Hill

Nooseneck

Hill

Raccoon

Hill

Hungry

Fish Hill

Hill

Hopkins

Hill

Crompton Qua

Slocum Quad

41o37’30" Coventry Center Quadrangle

Hope Valley Quadrangle

41o40’

41o35’

71o

40’ 71o

37’30" 71o

35’

Flat River Reservoir

Capwell Mill Pond

Carr

Pond Tarbox

 Pond

Lake

 Mishnock

Maple

Root

Pond

Reynolds

Pond

Millbrook

Pond

N o o s e n ec k

R i v e r

C o n g d o n

R i v e r

R i v e r

C a r r R i v e r

Mishnock

Swamp

Ol d

Hi c k o r y

B r o ok

M is h n o c k

R i v e r

Cedar

 Swamp

R a c c o o n

B r o o k

B e a r B r o o k

Tiogue

Lake

S o u t h Br a n c h

Pa w t u xe t

Ri v e r

Money Swamp

Pond

Dam

B ig

Rhode Island coordinate system,10,000 foot coordinate system used in digitization of map units and digital compositing of this map. 1927 North American datum.

Base topographic information derived from U.S. Geological 

Survey topographic quadrangle sheets:

Coventry Center, R.I., Photorevisions as of 1970,

Crompton, R.I., Photorevisions as of 1970,

Hope Valley, R.I., Photorevisions as of 1970, and

Slocum, R.I., Photorevisions as of 1970.

Source topographic sheets were Polyconic projection

Geologic interpretation by J.R. Stone

Big River 

Study Area

42ß00’

41ß30’

71ß15’

71ß45’

B L O C K I S L A N D S O U N D

MASSACHUSETT

C

S

ONNECTICUT

41ß45’

71ß30’

 30 KILOMETERS

0

0

20 MILES

RHODE ISLAND

Figure 2. Glacial lakes and ice-margin positions during deglaciation, Big River area, Rhode Island.
8 Glacial Geology and Aquifer Characteristics of the Big River Area, Central Rhode Island

In the Big River Valley, the first stage of glacial 

Lake Mishnock (lm1, fig. 2) developed as the ice 

margin retreated into the broader valley now occupied 

by the Big River and its eastern tributaries. Northerly 

retreat of the ice margin uncovered a 325-ft spillway 

across the drainage divide west of Hopkins Hill, and 

water levels fell about 40 ft from the level of ponding 

in the Congdon River Valley. The thickest and most 

extensive meltwater deposits in the study area are icemarginal deltas, lacustrine fans, and lake-bottom 

sediments of glacial Lake Mishnock. These deposits 

were laid down in association with at least six successive ice-margin positions (fig. 2). Delta-surface 

altitudes in this stage of Lake Mishnock are at 345 ft, 

and their topset-foreset contacts record a lake level of 

about 335 ft. Ice-marginal lacustrine fans deposited at 

the mouths of ice tunnels on the floor of the lake are 

present in several places within this stage of the lake. 

The top of these landforms did not build up to the lake 

surface, and therefore, lie below 345 ft. The southern 

half of section B-B′ (plate) crosses a well-developed 

series of four lacustrine fans and illustrates the “shingled” nature of coarser and finer sediments typical of 

successive ice-marginal morphosequences. 

As the ice retreated into the Mishnock River 

Valley, a lower spillway for stage 2 of glacial Lake 

Mishnock (lm2, fig. 2) was opened to the east, and the 

spillway across the drainage divide to the south was 

abandoned. Meltwater escaped briefly through a spillway at 295 ft across a till hill on the east side of the valley, and a few small deltas (included with stage 1 

deposits) at 305 ft were graded to this level in the lower 

Bear Brook Valley and on the east side of Hungry Hill. 

With further retreat, lower spillways to the east were 

uncovered at altitudes of 265 ft (east of map area) and 

245 ft; a few deltas associated with stage 2 are present 

in the map area and are at 275-ft altitude, but thick 

lake-bottom deposits predominate in the Mishnock 

Swamp area.

At the end of glacial retreat and meltwater deposition, all the glacial lakes were largely filled by the 

deltas and lake-bottom sediments that presently underlie the Big River study area. The altitude of the paleowater level in each lake is recorded by the unconformable contact between flat-lying, gravelly, fluvial topset 

beds and dipping, sandy, subaqueous foreset beds in 

the deltas. The topset-foreset contact beneath the flat, 

non-collapsed parts of delta surfaces commonly marks 

the boundary between gravel or sand and grave

and lower sand and silty sand beds (see plate, s

A-A′ through E-E′).

Postglacial Deposits

Postglacial deposits that consist of floodp

alluvium and swamp deposits accumulated afte

ciation of the valley was complete and glacial la

drained. Large blocks of detached glacial ice m

forming kettle-hole depressions, such as Mishn

Lake. At the same time, postglacial streams inci

glacial sediments, and an integrated drainage sy

developed. Rivers and streams incised rapidly, a

modern floodplain surfaces developed early afte

drainage. Alluvium underlying the floodplain su

consists of relatively thin sand, gravel, and silt 

(reworked glacial deposits) with minor amounts 

organic matter; thicker glacial deposits generall

underlie the alluvium. As postglacial vegetation 

into the region, organic debris accumulated as p

gyttja (freshwater organic-rich mud) in low-lyin

poorly drained areas and closed basins created b

melting of ice blocks. This peat and gyttja may 

much as 10 ft thick in the larger wetland areas.

AQUIFER 

CHARACTERISTICS 

Glacial stratified (meltwater) deposits and 

overlying, hydraulically connected network of r

brooks, lakes, ponds, and wetlands constitute th

stream-aquifer system in the Big River study ar

Hydraulic conductivity and transmissivity vary 

in the glacial stratified deposits and depend on t

grain-size distribution (texture) and stratificatio

characteristics (facies) in the stratified deposits.

Till

Till underlies most uplands in the Big Riv

and in many places extends beneath stratified d

in the valleys. The distribution of till is importa

because it affects the circulation of ground wate

ticularly rates of recharge to and discharge from 

underlying bedrock aquifer. Till generally is no
Glacial Ge

considered a reliable water-bearing unit because of 

small saturated thickness and low hydraulic conductivity; however, it does constitute an aquifer capable of 

yielding small amounts of water for domestic and agricultural use. Generally, till yields no more than 2 to 

3 gal/min to large-diameter wells (Hahn, 1959). Wells 

completed in till typically go dry during drought periods and may go dry annually during late summer or 

early fall.

Stratified Deposits

Stratified deposits underlie about 50 percent of 

the study area and reach a maximum known thickness 

of about 250 ft. Most stratified deposits occupy the two 

major north-south trending preglacial bedrock valleys, 

the preglacial Big River Valley to the west of Hungry 

Hill, and the preglacial Mishnock River Valley just east 

of Hungry Hill. Fine-grained stratified sediments 

(very fine sand, silts, and clay) have the lowest transmissivity, low water-bearing capacity, and may produce 

local semiconfining conditions in the aquifer. Thick, 

saturated coarse-grained stratified sediments (coarse 

gravel to fine sand) have the highest transmissivity and 

the capacity to yield large quantities of water to wells. 

These coarse-grained sediments form the sand and 

gravel aquifer, which is the only aquifer in the study 

area capable of producing yields of more than 

300 gal/min from individual wells. The aquifer is 

unconfined and is in hydraulic connection with rivers, 

brooks, lakes, ponds, and wetlands. Well yields depend 

on natural recharge to the sand and gravel aquifer, the 

hydraulic properties of the aquifer, and the degree of 

connection between the aquifer and overlying streams.

Hydraulic Properties of the 

Sand and Gravel Aquifer

The Big River area surficial materials map 

(plate) is a geohydrologic tool that can be used to identify sites in the stratified deposits that have the best 

potential to yield more than 300 gal/min to individual 

supply wells. Information shown on the map about the 

distribution and thickness of fine-grained and coarsegrained sediments in the stratified deposits was used to 

locate exploratory well sites. Six sites with the greatest 

potential for high yields were chosen, and aquifer tests 

were done to characterize hydraulic properties of the 

sand and gravel aquifer. Test wells were screene

a minimum depth of 55 to 75 ft to a maximum d

163 to 183 ft below the land surface. Test wells 

pumped for 2 days at rates of 325 to 920 gal/mi

water level responses were monitored in the pu

and surrounding observation wells. These hydra

responses were analyzed using the methods of M

(Barlow and Moench, 1999), and indicate that t

transmissivity (T) of the sand and gravel aquifer 

from 6,400 to 22,300 ft2/d (foot squared per day

Results of the analyses also show that the horiz

hydraulic conductivity (Kh) of the aquifer rang

94 to 281 ft/d, and the vertical hydraulic conduc

(Kv) ranges from 0.9 to 39.4 ft/d. All aquifer-te

are available in the Rhode Island Subdistrict Of

the USGS. The T, Kh, and Kv values summariz

table 1 are average values based on the total sat

thickness of the stratified deposits at each pump

well.

The sand and gravel aquifer hydraulically 

anisotropic and heterogeneous. The anisotropy 

chiefly to the small-scale interbedding of coarse

finer layers that is typical of glacial meltwater d

This interbedding causes ground water to flow e

the horizontal direction along coarser layers. Th

ence of finer beds above and below the coarser 

impedes flow in the vertical direction. Anisotro

may be due to the horizontal orientation of elon

plate-shaped grains, which causes the hydraulic 

ductivity of individual beds in the aquifer to be l

the vertical direction. Estimated ratios of horizo

vertical hydraulic conductivity for the aquifer r

from 5:1 to 125:1 (table 1), with higher ratios in 

preglacial Mishnock River Valley than in the Bi

Valley.

The heterogeneity of the aquifer is due to 

variation and geologic complexity of the glacia

water deposits. This heterogeneity must be con

when using the surficial materials map and bedr

surface contours (plate) to locate potentially fav

sites for new water-supply wells. Although wel

six aquifer-test sites tap thick sand and gravel d

differences in the three-dimensional distribution 

tural units in the aquifer near the sites are impo

The approximate area of pumping influence at e

pumped well is shown on the plate. The circula

of pumping influence were drawn using the dist

from the pumped well to the farthest observatio
10 Glacial Geology and Aquifer Characteristics of the Big River Area, Central Rhode Island

monitored during the aquifer test. The area of pumping 

influence for all aquifer-test sites extends into map 

units other than the one in which the pumped well is 

located.

 Aquifer Tests

At three of the six aquifer-test sites, WGW 355, 

410, and 411, wells penetrate proximal parts of morphosequences, and the entire thickness of the aquifer 

is sand and gravel (table 1). At two of the other three 

sites (WGW 354 and 356), the lower sections of sand 

and gravel, which are proximal parts of ice-marginal 

morphosequences, are overlain by fine-grained 

materials that are distal facies of later morphosequences. At these sites, much of the saturated thickness 

of the aquifer is fine-grained, poorly permeable material, and it is likely that most of the water pumped 

comes from the lesser thickness of the buried sand and 

gravel unit. The pumped well at site WGW 374 penetrates the core of an ice-marginal lacustrine fan deposit, 

which has a complex stratigraphy of coarser and finer 

units. The lower section of coarse-grained sand and 

gravel, in which the well is screened, is overlain by a 

50-ft section of fine-grained, poorly permeable material; however, the upper 100 ft of the section also is 

coarse-grained material consisting of interbedd

sand and gravel; this material may contribute to 

relatively high T calculated for this site. The Kh 

of 116 ft/d is a conservative estimate based on t

saturated thickness of 159 ft; it is likely that mos

water pumped comes from the lower 30-ft sand

gravel unit, and the Kh of this unit may be as hi

600 ft/d.

Sites WGW 355, 374, and 354 are within 

1,300 ft of each other in the preglacial Mishnoc

River Valley where bedrock is deepest and the s

rated thickness of the aquifer is greatest (genera

140 to 160 ft). Transmissivity values calculated 

from aquifer tests in this area are 14,600 ft2/d a

WGW 355, 18,400 ft2/d at WGW 374, and 22,3

at WGW 354. Sites WGW 354 and 374 have th

est estimated T values despite the fact that a lar

centage of the total saturated thickness at these 

composed of fine-grained materials, indicating 

Kh of the lower sand and gravel likely is much 

than those values for the entire saturated thickn

these sites. A low T value was calculated for sit

WGW 355 even though the saturated thickness 

well is entirely in sand and gravel. During the in

tion of WGW 355, coarse gravel was encounter

133 ft below land surface, and the well casing co

Table 1. Surficial materials, well-construction characteristics, and hydraulic properties determined from aquifer tests in 

River area, Rhode Island

[Surficial materials map unit: Map units are shown on the plate. b, saturated thickness at the pumping well; f, fine deposits; Kh, horizontal hydra

conductivity; Kv, vertical hydraulic conductivity; s, sand deposits, sg, sand and gravel; T, transmissivity; USGS, U.S. Geological Survey; WGW 3

Greenwich Well 354; in., inch; ft, foot; ft/d, foot per day; gal/min, gallons per minute; ft2/d, square foot per day]

USGS

well No. and

diameter

Surficial

materials

map unit

Depth of 

screened

interval

(ft)

Screen

slot

size

(in.)

Altitude

of 

screened

interval

(ft)

Pumping

rate

(gal/min)

b

(ft)

T

(ft2/d)

 Kh

(ft/d)

 Kv

(ft/d)

WGW 354 (8-in.) f / sg 120–125

125–135

135–140

0.100

.140

.150

143–123 350 137 22,300 163 3.3 

WGW 355 (8-in.) sg 113–115

115–123

123–133

.080

.100

.200

156–136 400 124 14,600 117 2.4 

WGW 374 (8-in.) sg / s / f / sg 163–183 .100 121–101 743 159 18,400 116 .9 

WGW 410 (10-in.) sg 60–80 .100 219–199 920 63 17,700 281 39.4 

WGW 356 (10-in.) s / f / sg 90–100

100–110

.020

.030

171–151 550 104 11,600 112 22.5 

WGW 411 (10-in.) sg 55–75 .050 203–183 325 67 6,400 94 9.4 
Glacial Geo

be advanced any deeper. It is likely that this site produced a lower T value than sites WGW 354 and 374 

because the base of the primary water-bearing unit at 

WGW 355 is about 30 ft below the bottom of the well 

screen, and that unit, composed mostly of gravel, was 

not fully tested.

Distances between sites WGW 410, 356, and 

411 in the Big River Valley are greater (3,000 to 

6,800 ft) than between sites in the Mishnock River 

Valley. In general, the saturated thickness of the aquifer 

is less than in the Big River Valley (generally 60 to 

100 ft). The southernmost aquifer-test site in the Big 

River Valley (WGW 410) is composed entirely of sand 

and gravel with a high calculated Kh of 281 ft/d. 

Because of the high Kh, this well could be pumped at 

a rate of 920 gal/min during a 2-day aquifer test; this 

rate was the highest tested. The T calculated for WGW 

410 is 17,700 ft2/d. Only the relatively small saturated 

thickness of the aquifer (63 ft) prevents this site from 

having the largest transmissivity of the six sites tested.

At site WGW 356, the lower section of sand and 

gravel in which the well is screened is the proximal 

facies of an ice-marginal morphosequence. This material is overlain by 55 ft of fine-grained distal facies of a 

later deposit. The Kh of 112 ft/d calculated for the 

entire saturated thickness of the aquifer at WGW 356 

probably is too low. It is likely that most of the water 

pumped from WGW 356 comes from the lower sandand-gravel unit which would have a higher Kh. The T 

calculated for the entire saturated thickness of the 

aquifer at WGW 356 is 11,600 ft2/d.

The stratified deposits at the northernmost aquifer-test site in the Big River Valley (WGW 411) are all 

sand and gravel (table 1). The hydraulic properties at 

this site are the lowest calculated for stratified deposits; 

this result is most likely because of the smaller saturated thickness and the presence of extensive finegrained deposits in the eastern part of the test site. Also, 

the coarse-grained deposits in the western part of the 

aquifer-test site are likely to have lower Kh than those 

at the other sites, because they are in a more ice-distal 

position within the morphosequence. The T calculated 

for the aquifer at site WGW 411 was 6,400 ft2/d and 

the Kh was 94 ft/d.

New exploratory well sites in coarse-grained 

stratified deposits in the Big River area with the potential to yield 300 gal/min or more to individual supply 

wells can be identified with greater precision by using 

the detailed textural delineation and information 

the depth to bedrock shown on the plate. This m

vides water-resource planners and water-supply 

managers with a unique geohydrologic tool tha

be used to help identify new sites for ground-w

development in the stratified deposits of the Big 

area stream-aquifer system.

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