U.S. Department of the Interior

U.S. Geological Survey

Pond-Aquifer Interaction at 

South Pond of Lake Cochituate, 

Natick, Massachusetts

By PAUL J. FRIESZ and PETER E. CHURCH

Water-Resources Investigation Report 01-4040

Prepared in cooperation with the

U.S. ENVIRONMENTAL PROTECTION AGENCY

and the U.S. ARMY

Northborough, Massachusetts

2001
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 c

Chief, Massachusetts-Rhode Island District U.S. Geolog

U.S. Geological Survey Branch of Information Services

Water Resources Division Box 25286

10 Bearfoot Road Denver, CO 80225-0286

Northborough, MA 01532

or visit our Web site at

http://ma.water.usgs.gov
Contents III

CONTENTS

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

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

Geographic Setting...................................................................................................................................................... 2

Geologic Setting.......................................................................................................................................................... 4

Pond Characteristics.............................................................................................................................................................. 4

Surface Geophysical Techniques................................................................................................................................. 5

Bathymetry and Morphometry .................................................................................................................................... 5

Thickness of Fine-Grained Bottom Sediments ........................................................................................................... 6

Pond-Aquifer Interaction....................................................................................................................................................... 8

Natick Springvale Wellfield......................................................................................................................................... 8

Geohydrology of Wellfield Area ................................................................................................................................. 10

Temperature Profiles and Stable Isotope Techniques.................................................................................................. 14

Vertical Ground-Water Flow and Vertical Hydraulic Conductivity of Pond-Bottom Sediments ................................ 15

Pond Leakance ............................................................................................................................................................ 19

Isotopic Composition of Pond Water and Ground Water .................................................................................. 19

Characterizing Interaction of Pond Water and Ground Water........................................................................... 23

Summary and Conclusions.................................................................................................................................................... 26

References Cited ................................................................................................................................................................... 28

Appendix A. Pond stage and water levels in piezometers and observation wells, South Pond of 

Lake Cochituate, Natick, Massachusetts................................................................................................................. 33

Appendix B. Water temperature in South Pond and in piezometers NCW83 and NCW85, September and 

October 1998, Lake Cochituate, Natick, Massachusetts......................................................................................... 37

Appendix C. Temperature, specific conductance, delta deuterium, and delta oxygen-18 in water, 

February 1998 to July 1999, South Pond of Lake Cochituate, Natick, Massachusetts........................................... 41

PLATE

(in back pocket)

1. Map showing bathymetry and thickness of fine-grained bottom sediments, South Pond of 

Lake Cochituate, Natick, Massachusetts.

FIGURES

1. Map showing location and physical setting of the four ponds that form Lake Cochituate (South, Carling, 

Middle, and North), Natick public-supply wellfields, and the U.S. Army facility, Natick, Massachusetts .......... 3

2. Ground-penetrating radar record and interpretation (line of section A-A′ shown on pl. 1), South Pond 

of Lake Cochituate................................................................................................................................................. 7

3. Continuous seismic-reflection record and interpretation (line of section B-B′ shown on pl. 1), South 

Pond of Lake Cochituate ....................................................................................................................................... 8

4. Orthophotomap showing location of Natick Springvale public-supply wells, data-collection network, 

and selected observation wells and borings, South Pond of Lake Cochituate....................................................... 9

5. Graph showing daily pumping rates for each active public-supply well—NCW1, NCW2, and 

NCW3—and total daily pumping rate at the Natick Springvale wellfield from January 1998 to July 1999, 

South Pond of Lake Cochituate ............................................................................................................................. 11

6. Cross section showing lithology, public-supply wells, data-collection network and water levels on 

November 16, 1998 (line of section C-C′ shown in fig. 4), South Pond of Lake Cochituate................................ 12

7. Hydrograph showing stage of South Pond and water levels in pond-bottom piezometers, 

Lake Cochituate ..................................................................................................................................................... 13
IV Contents

8–12. Graphs showing:

8. (A) Temperature of South Pond adjacent to NCW83, (B) measured bihourly temperature profiles 

in NCW83 for the 24-hour period beginning at 2 p.m. September 18, 1998, and (C) simulated 

temperature envelopes for vertical flow rates of 0, 0.5, 1.0, 1.5 feet per day, Lake Cochituate.................... 17

9. (A) Temperature of South Pond adjacent to NCW85, (B) measured bihourly temperature profiles 

in NCW85 for the 24-hour period beginning at 1 a.m. October 17, 1998, and (C) simulated 

temperature envelopes for vertical flow rates of 0, 0.5, 1.0 feet per day, Lake Cochituate........................... 18

10. Temporal variation in delta oxygen-18 of pond water, ground water, water from observation wells 

between South Pond and Natick Springvale wellfield, and water from the public-supply wells, 

February 1998 to July 1999, Lake Cochituate .............................................................................................. 20

11. Relation between delta oxygen-18 and delta deuterium in pond water, ground water, and water from 

the public-supply wells, South Pond of Lake Cochituate, and the local meteoric water line for 

Concord, Massachusetts, 1998–99 ................................................................................................................ 22

12. Mixing line based on a two-component mixing model using average isotope values for pond water, 

ground water, and water from the public-supply wells. Mixing-line result and uncertainty analysis 

indicate that 64 percent ±15 percent at the 95-percent confidence interval of water withdrawn at the 

Natick Springvale public-supply wells is derived from pond water ............................................................. 26

TABLES

1. Characteristics of the Natick Springvale public-supply wells, piezometers, and observation wells, South 

Pond of Lake Cochituate, Natick, Massachusetts................................................................................................... 10

2. Sampling site characteristics and water-quality constituents in a ground-water inflow area to South Pond 

of Lake Cochituate, December 1997 and December 1998 ..................................................................................... 23

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

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. 

ABBREVIATIONS

Multiply By To obtain

calorie per cubic centimeter degree Celsius (cal/cm3- ̊C) 62.43 British thermal unit per cubic foot degree Fahrenheit

calorie per second centimeter degree celsius (cal/s-cm- ̊C) 243.9 British thermal unit per hour foot degree Fahrenheit

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

cubic foot per year (ft3/y) 0.02832 cubic meter per year

foot (ft) 0.3048 meter

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

foot per nanosecond (ft/ns) 0.3048 meter per nanosecond

foot per second (ft/s) 0.3048 meter per second

inch (in.) 25.4 millimeter

mile (mi) 1.609 kilometer

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

square foot (ft2) 0.09290 square meter

square mile (mi2) 2.590 square kilometer

Temperature in degrees Fahrenheit ( ̊F) can be converted to degrees Celsius ( ̊C) 

as follows:  ̊C = 5/9 ( ̊F - 32).

cm2/s square centimeter per second

g/cm3 gram per cubic centimeter

kHz kilohertz

MHz megahertz

μS/cm microsiemens per centimeter

δ18Ο delta oxygen-18

δD delta deuterium
Abstract 1

Pond-Aquifer Interaction at 

South Pond of Lake Cochituate, 

Natick, Massachusetts

By Paul J. Friesz and Peter E. Church

Abstract

A U.S. Army facility on a peninsula in 

South Pond of Lake Cochituate was designated 

a Superfund site by the U.S. Environmental 

Protection Agency in 1994 because contaminated 

ground water was detected at the facility, which is 

near the Natick Springvale public-supply wellfield. The interaction between South Pond and the 

underlying aquifer controls ground-water flow patterns near the pond and determines the source of 

water withdrawn from the wellfield.

A map of the bathymetry and the thickness 

of fine-grained pond-bottom sediments was 

prepared on the basis of fathometer, groundpenetrating radar, and continuous seismic-reflection surveys. The geophysical data indicate that 

the bottom sediments are fine grained toward the 

middle of the pond but are coarse grained in 

shoreline areas. 

Natick Springvale wellfield, which consists 

of three active public-supply wells adjacent to 

South Pond, is 2,200 feet downgradient from the 

boundary of the Army facility. That part of South 

Pond between the Natick Springvale wellfield 

and the Army facility is 18 feet deep with at least 

14 feet of fine-grained sediment beneath the pondbottom. Water levels from the pond and underlying 

sediments indicate a downward vertical gradient 

and the potential for infiltration of pond water near 

the wellfield. Head differences between the pond 

and the wellfield ranged from 1.66 to 4.41 feet 

during this study. The velocity of downward flow 

from South Pond into the pond-bottom sediments, 

determined on the basis of temperature profiles 

measured over a diurnal cycle at two locations 

near the wellfield, was 0.5 and 1.0 feet per day. 

These downward velocities resulted in vertical 

hydraulic conductivities of 1.1 and 2.9 feet per day 

for the pond-bottom sediments.

Naturally occurring stable isotopes of 

oxygen and hydrogen were used as tracers of pond 

water and ground water derived from recharge of 

precipitation, two potential sources of water to a 

well in a pond-aquifer setting. The isotopic composition of pond water varied seasonally and was 

distinctly different from the isotopic composition 

of ground water. The isotopic composition of 

shallow water beneath and adjacent to South Pond 

near the wellfield corresponds to the temporal 

variation of pond water, indicating that nearly all 

water at shallow depths was derived from pond 

water. A two-component mixing model based on 

the average stable isotope values of the source 

waters indicated that 64 ±15 percent at the 95-

percent confidence interval of the water withdrawn 

at the public-supply wells was derived from the 

pond; pond water accounted for most of the uncertainty in the result. The rate of infiltration of pond 

water into the aquifer and discharging to the wellfield was 1.0 million gallons per day at the average 

pumping rate.
2 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

INTRODUCTION 

South Pond of Lake Cochituate is located in an 

urbanized setting in Natick, Mass., in the eastern part 

of the state (fig. 1). The watershed of South Pond 

includes the town centers of Natick and Framingham. 

Inflow to the pond includes both ground water and surface water. Land-uses in the immediate vicinity of the 

pond include recreational, residential, commercial, 

and industrial, including the U.S. Army Soldier and 

Biological Chemical Command Soldier Systems 

Center hereafter referred to as the Army facility. The 

Army facility began research and development activities in 1954 on a peninsula in South Pond. Elevated 

concentrations of the solvents tetrachloroethene (PCE) 

and trichloroethene (TCE) have been found in ground 

water at the Army facility and in the immediate vicinity 

of the facility (Arthur D. Little, Inc., 1998).

The Army facility was designated a Superfund 

site in 1994 by the U.S. Environmental Protection 

Agency (USEPA) under the Comprehensive Environmental Response, Compensation, and Liability Act of 

1980 because of the detection of contaminated ground 

water at the facility and its proximity to public-supply 

wellfields for the town of Natick (fig. 1). One of these 

public-supply wellfields, the Natick Springvale wellfield, is adjacent to South Pond downgradient of the 

Army facility (Gay, 1985; Arthur D. Little, Inc., 1998). 

The town of Natick, which has been withdrawing water 

from the Natick Springvale wellfield since 1903, 

obtains approximately 50 percent of its water supply 

from this wellfield during the summer months and 

approximately 30 percent during the remaining months 

of the year (Ronald Pong, Tata & Howard, Inc., oral 

commun., 2000). PCE and TCE have been detected in 

this water (Engineering Technologies Associates, Inc., 

1997). Numerous ground-water studies concerning this 

Superfund site either have been completed (Weston 

Geophysical Corporation, 1995; Arthur D. Little, Inc., 

1996, 1998, Engineering Technologies Associates, Inc., 

1997), or are on-going, including numerical model 

simulations of the ground-water flow system that 

encompasses South Pond.

The interaction between surface water (the pond) 

and ground water (the underlying aquifer), which is not 

well understood at South Pond, is an important control 

on local ground-water flow patterns and could affect 

public water supplies and contaminant transport. The 

degree of hydraulic connection between the pond 

and the aquifer affects both ground-water flow and 

contaminant transport paths as well as the tendency for 

pumping to induce infiltration of pond water into the 

aquifer. The quantity of ground-water inflow and pondwater infiltration, and the size and shape of the area of 

the aquifer contributing water to and receiving water 

from the pond, can be affected by the degree of hydraulic connection. An increased understanding of pondaquifer interaction requires knowledge of several physical characteristics and hydrologic processes, including 

the geometry of the pond, the nature of pond-bottom 

sediments, and pond leakance near the wellfield.

The U.S. Geological Survey (USGS), in cooperation with the USEPA and the U.S. Army, began a 

study in December 1997 to improve the understanding 

of pond-aquifer interaction at South Pond of Lake 

Cochituate. This report presents the results of this study 

in (1) a map of the bathymetry and the thickness of 

fine-grained pond-bottom sediments in South Pond, 

and (2) a description of a quantitative analysis of pond 

leakance and associated hydraulic properties of pondbottom sediments near the Natick Springvale wellfield. 

These results are based on surface geophysical surveys, 

water-level measurements, vertical profiles of water 

temperature, and analyses of water samples collected 

from South Pond and the underlying aquifer from 

December 1997 to July 1999.

Geographic Setting

Lake Cochituate, which consists of four ponds 

connected by shallow, narrow waterways, is located in 

the towns of Natick, Framingham, and Wayland, Mass., 

16 mi west of Boston (fig. 1). Lake Cochituate lies in 

the Sudbury River Basin; cochituate means “swift 

river” in the Algonquin language (Wilbur, 1978) and 

refers to Cochituate Brook (Schaller and Prescott, 

1998), which connects the lake to the Sudbury River. 

Water flows generally northward through the four 

ponds from South Pond to Carling, Middle, and North 

Ponds before discharging into Cochituate Brook. Small 

dams built in the nineteenth century at the outlet of the 

lake to increase lake storage raised the natural lake 

level by 13 ft. The drainage area of Lake Cochituate at 

its outlet is 17.7 mi2, including 0.92 mi2 of lake surface 

(Gay, 1985).
Introduction 3

150

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Snake Brook

AREA SHOWN

IN FIGURE 4

AREA SHOWN

ON PLATE

90

9

27

MASSACHUSETTS

0

0

50 KILOMETERS

50 MILES

100,000 200,000

300,000

900,000

800,000

Boston

208,500

897,000

895,500

894,000

210,000 211,500

892,500

Base from MassGIS digital terrain model, 1,500 meter grid based

on Massachusetts coordinate system. Contour interval 10 feet 0 1,000 2,000 3,000 4,000 FEET

0 250 500 750 1,000 METERS

Cours e Brook

FISK POND

SOUTH

POND U.S. ARMY

FACILITY

MIDDLE

POND

NORTH POND

FRAMINGHAM

NATICK

Coch ituate Brook

Beaverdam Brook

Pegan Bk.

WAYLAND

DUG POND

DUDLEY

POND

Sudburty River

L A K E C O C H I T U A T E

CARLING

POND

Natick Evergreen

Wellfield

Natick Evergreen

Wellfield

Natick Springvale

Wellfield ellfield

Figure 1. Location and physical setting of the four ponds that form Lake Cochituate (South, 

Carling, Middle, and North), Natick public-supply wellfields, and the U.S. Army facility, Natick, 

Massachusetts.
4 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

Lake Cochituate was used as a source of water 

supply for Boston from 1848 to 1931, and until 1947 

it served as a standby supply when its use was discontinued because of deteriorating water quality (Gay, 

1985). Subsequent development in the basin, especially 

along the lake shore, continued to affect the water quality of the lake. The USGS conducted a study in the late 

1970s (Gay, 1981 and 1985) to determine the inflow 

and outflow of water and nutrients to the lake. Results 

of that study indicated that the quantity of nutrients 

entering the lake would sustain and continue the 

mesotrophic conditions of the lake. The lake is now 

part of Cochituate State Park and is used for recreational activities such as fishing, swimming, and 

boating.

Water enters the pond as precipitation falling 

directly on the pond surface and from ground-water 

and surface-water inflow. Most of the water entering 

Lake Cochituate, and thus South Pond, is surface water 

from Fisk Pond (Gay, 1985). Beaverdam Brook and 

Course Brook drain a predominantly urban environment and flow into Fisk Pond, which in turn flows into 

the southern end of South Pond (fig. 1). Pegan Brook 

drains the town center of Natick and flows directly into 

the southeastern end of South Pond. Most of the land 

adjacent to South Pond contains storm sewers that 

empty directly into the pond (Gay, 1985, pl. 1). Water 

leaves South Pond through evaporation off the pond 

surface, surface-water outflow to Carling Pond to the 

north, and pond-water seepage to the aquifer induced 

by pumping at the Natick Springvale wellfield.

Geologic Setting

Lake Cochituate is underlain by a north-south 

trending bedrock valley ranging in depth from 0 to 

200 ft below the land surface (Gay, 1985). The bedrock 

is primarily granodiorite, but gabbro and diabase are 

present beneath the easternmost shore of South Pond 

and these rocks crop out near this shoreline (Nelson, 

1975).

Sediments of glacial origin—till and stratified 

drift—overlie the bedrock. Till is composed of poorly 

sorted mixtures of sediment ranging in size from clay 

to boulders deposited directly on bedrock. Stratified 

drift consists of well-sorted, layered sediments ranging 

in size from clay to gravel deposited by glacial meltwater in a variety of environments including glacial 

ice-contact, deltaic, and lacustrine. Surficial deposits of 

till are limited to the east part of the watershed whereas 

stratified drift covers most of the watershed (Nelson 

1974a,b). 

The four ponds of Lake Cochituate were formed 

by the melting of large blocks of ice that remained in 

the deep bedrock valley during deglaciation. Clay, silt, 

sand, and gravel carried in meltwater from the retreating glacier were deposited around and on top of the 

blocks of ice, subsequently forming the bank and 

bottom sediments of the lake when the ice melted (Gay, 

1985). A thin elongated swamp area, consisting of peat 

and organic-rich sediment, is present along the northwestern shore of the east part of South Pond (Nelson, 

1974b).

POND CHARACTERISTICS

A map of the bathymetry and the thickness of 

fine-grained pond-bottom sediments of South Pond of 

Lake Cochituate was prepared from results of surface 

geophysical surveys. The bathymetry defines the spatial relation of the pond-bottom sediment to the surrounding aquifer. Surficial sediment samples were 

collected with a hand-held dredge sampler in the center 

of the central and eastern parts of the pond, and observations of shoreline sediments were noted to aid in 

subsequent interpretation of the data. Collection of sediment cores from pond-bottom sediments to validate 

the surface geophysical interpretations was beyond the 

scope of this study. 

Fine-grained sediments, which are less permeable than coarse-grained sediments, are defined for this 

report as consisting primarily of fine sand, silt and clay, 

or organic-rich fine sand, silt and clay, or both. Groundwater inflow and pond-water infiltration is most likely 

to occur in areas of permeable, coarse-grained pondbottom sediments. Surficial sediment samples indicated that a black, organic-rich, fine-grained sediment 

covers the bottom of the center of the central and eastern parts of the pond. Fine-grained, organic-rich 

sediment would be expected to occur more in the deep 

parts of the pond than along the pond shore because 

wave action prevents deposition of this fine-grained 

sediment in shallow water.
Pond Characteristics 5

Surface Geophysical 

Techniques

Water depth was determined using a fathometer 

and the thickness of fine-grained pond-bottom 

sediment was delineated using ground-penetrating 

radar and continuous seismic reflection. For each surface geophysical technique, a signal is transmitted 

through the water and is reflected back to the surface 

when an interface of materials having different physical properties is encountered. The strength and traveltime of the reflected signal is detected by a receiving 

antenna at the surface where it is recorded and displayed as a graphic image. Depth of the interface and 

the thickness of the materials can be interpreted from 

the traveltimes of the reflected signal. The groundpenetrating radar and continuous seismic-reflection 

records were interpreted from the pattern of the 

reflected signal and its corresponding geologic interpretation described in Beres and Haeni (1991). In general, horizontal laminar reflections are indicative of 

fine-grained sediments, whereas hummocky and chaotic reflections are associated with coarse-grained 

materials. The effectiveness of these surface geophysical techniques in measuring water depth and lake and 

river bottom sediment thickness has been shown by 

Haeni and others (1987), Beres and Haeni (1991), 

Placzek and Haeni (1995), and Haeni (1996).

Horizontal location points along the surface geophysical survey lines are shown on plate 1. Horizontal 

positions were determined using a global positioning 

system. Transects were run across the pond and parallel 

to the shoreline.

Fathometer surveys were made on June 24 and 

25, and November 19, 1998. The fathometer transmits 

high-frequency acoustic energy which is reflected at 

the water-sediment interface because of contrasting 

acoustic properties. A velocity of sound of 4,800 ft/s 

was assumed for freshwater. In addition to providing 

information on water depths, fathometer surveys 

also were used to confirm the location of the watersediment interface along parts of the groundpenetrating radar and continuous seismic-reflection 

records where this interface was not clearly defined 

on these records.

Ground-penetrating radar surveys were made on 

June 22 and 23, 1998. Ground-penetrating radar transmits short pulses of radio-frequency electromagnetic 

energy, which is reflected from pond-bottom layers of 

different electrical properties. Penetration of the radar 

waves into pond-bottom layers may be limited by conductive gases, fluids, and sediments. In addition, a deep 

water column may impede penetration of the radar 

waves into the bottom layers or even to the pond 

bottom itself. For this study, a transmission frequency 

of 100 MHz was selected; radar wave velocity for the 

fine-grained sediments beneath the pond bottom used 

in this study was 0.16 ft/ns. The theory and operation 

of the ground-penetrating radar method is discussed in 

Haeni and others (1987) and in Davis and Annan 

(1989).

Continuous seismic-reflection surveys were 

completed on June 24 and 25, 1998, approximately 

along the same survey lines as the ground-penetrating 

radar. Sound-source energy is reflected back to the surface from pond-bottom layers of contrasting acoustic 

properties. Some factors limiting the penetration of 

sound-source energy into sediments are the presence of 

very coarse sediments, such as cobbles and boulders, 

and gases within organic material; however, this 

method is not limited by conductive materials or a deep 

water column. For this study, a 7.0 kHz acoustic transducer was selected, and sediment thicknesses were estimated using a sound velocity of 5,000 ft/s for saturated 

unconsolidated sediments. A complete description of 

the theory and operation of this method is given in 

Sylwester (1983) and Placzek and Haeni (1995). 

Bathymetry and 

Morphometry

A bathymetric map of South Pond was drawn 

using 10-foot intervals and is referenced to a common 

water-surface elevation of 137.2 ft above sea level measured on November 19, 1998 (pl. 1). The maximum 

measured water depth of 68.0 ft is in the center of the 

central part of South Pond, but the water is less than 

10 ft deep in a large area of the eastern part of the pond. 

The pond bottom slopes steeply near the east shoreline 

in the central part of the pond. The mean water depth of 

South Pond is 19.8 ft and its surface area is 0.39 mi2. 

Additional morphometric characteristics of South Pond 

are listed on plate 1.
6 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

Thickness of Fine-Grained 

Bottom Sediments

Ground-penetrating radar surveys penetrated 

bottom sediments of sufficient thickness for interpretation in the shallow parts of South Pond: the north, 

south, east, and along the perimeter of the pond. But 

even along sections of these survey lines, groundpenetrating radar did not fully penetrate the sediment 

to the interface between fine- and coarse-grained 

sediment. The maximum water depth at which radar 

waves penetrated the full water column, but not any 

substantial sediment thickness, was about 24 ft. Deeper 

penetration of pond-bottom sediments at this water 

depth is restricted by the conductance of the pond 

water, which was approximately 230 μS/cm during the 

ground-penetrating radar survey. A representative 

example of a ground-penetrating radar record along 

with the corresponding interpretation is shown in 

figure 2 (section line A-A′, pl. 1). The record indicates 

coarse-grained sediments in an area of water less than 

10 ft deep in the southwestern half of the profile. Finegrained sediments are present in most of the northeastern half of the profile, where the pond ranges in depth 

from 10 to 18 ft. Thickness of the fine-grained 

sediments is interpreted to be greater than 10 ft beneath 

the deep water along the profile, as indicated by the 

maximum depth of the sloping radar reflections. Pondbottom sediments are coarse-grained over a short distance at the most northeastern part of this profile in the 

shallow water near the shoreline. The channel-shaped 

radar reflection present below the coarse-grained 

sediments in the southwestern part of this profile may 

indicate the location of a former ice-block depression.

In general, continuous seismic-reflection records 

of good quality were recovered in the north part of 

South Pond and in parts of survey lines south of the 

peninsula and the perimeter of the pond. The continuous seismic-reflection signals did not penetrate the 

pond bottom in the eastern or central part of the pond, 

most likely because gases within the fine-grained 

organic sediments prevented the penetration of soundsource energy. In areas where seismic-reflection 

records of good quality were recovered, the penetration 

of the sound-source energy was usually limited by 

entrapped gases at depth. A continuous seismicreflection record between the Natick Springvale wellfield and the Army facility, typical of records in the 

north part of the pond, is shown in figure 3 (section line 

B-B′, pl. 1). This record was interpreted as showing 0 to 

14 ft of fine-grained sediment over coarse-grained 

material. In the center part of the profile, however, 

entrapped gases at about 6 ft beneath the water and 

fine-grained sediment interface prevented further penetration. For purposes of interpretation, the thickness 

of fine-grained sediment was assumed to be equal 

to or greater than the maximum depth measured 

on either side of the entrapped gases. The groundpenetrating radar record collected along this same 

section of South Pond provided data with better resolution that was more useful in determining the presence 

of fine-grained sediments along the shoreline sections 

than the continuous seismic reflection; however, 

because of deep water in the center of the profile, the 

ground-penetrating radar survey provided insufficient 

penetration into these sediments.

Results of the interpreted ground-penetrating 

radar and continuous seismic-reflection records are 

summarized on plate 1. Lines of equal thickness of 

fine-grained sediment were drawn at various intervals. 

Lines of equal thickness were not drawn in the central 

part of the pond because of inadequate data; however, 

the interpreted records did not indicate the presence 

of fine-grained sediments along the perimeter of the 

central part of the pond.

Results indicate, in general, thick fine-grained 

sediments towards the middle of the pond where surveys provided data. In most cases, the full thickness of 

the fine-grained sediments was not penetrated; thicknesses in the center of South Pond in the north, south, 

and east exceed the thickest contour drawn. The thickest fine-grained sediments measured were in the east 

part of the pond. Arthur D. Little, Inc., (1998) reported 

that lithologic logs collected adjacent to this part of the 

pond contained peat and organic-rich sediments that 

may be indicative of an ancient wetland. An area in the 

middle of the pond where no substantial fine-grained 

sediment is present is that near the confluence with 

Pegan Brook. According to the fathometer surveys, the 

eastern extent of the pond, before construction of the 

dams raised the water-surface elevation by 13 ft, would 

be in this area. In addition, maps of Natick drawn in 

1750 and 1829, before the water surface was raised, 

showed this area as the eastern extent of the pond; thus, 

the sediments along the shore of South Pond may have 

been coarse grained before the water level was raised. 

Shoreline areas of South Pond consisted of little or no 

fine-grained sediments; conceptually, ground water 

flows into the pond and pond water infiltrates the aquifer mainly through these shoreline areas.
Pond Characteristics 7

Fine-grained sediment

Water Surface

Pond bottom

Pond bottom

Coarse-grained sediment

C

Fine-grained sediment

Possible former ice

block depression

Coarse-grained sediment

C

Fine-grained sediment

Possible former ice

block depression

VERTICAL EXAGGERATION APPROXIMATELY X 50

APPROXIMATE HORIZONTAL DISTANCE

A 

ONE-WAY TRAVEL TIME, 

IN NANOSECONDS

0

75

150

225

00 30 60 90 120 METERS

100 200 300 400 FEET

Figure 2. Ground-penetrating radar record and interpretation (line of section A-A′ shown on pl. 1), South Pond of Lake Cochituate.
8 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

Penetration limited Penetration limited

by entrapped gases by entrapped gases

0

0 15 30

50 100 150 200 FEET

12

10

8

6

4

2

0

B B'

ONE WAY TRAVELTIME, IN MILLISECONDS

45 60 METERS

Penetration limited

by entrapped gases

Approximate horizontal distance

60

50

40

30

20

10

DEPTH BELOW WATER SURFACE, IN FEET

0

VERTICAL EXAGGERATION X 6.2

Coarsegrained

sediment

Fine-grained sediment Fine-grained sediment

?

Pond bottom Pond bottom

Coarsegrained

sediment

?

Water Surface

Coarsegrained

sediment

POND-AQUIFER 

INTERACTION

The water withdrawal from a well in a pondaquifer setting can be from two sources—ground 

water derived from recharge of precipitation and leakance of pond water, which may be enhanced by 

pumping of the well. If the pond is a source, then the 

area contributing ground water to the well is likely to 

be less than if the source is ground water only. Water 

levels, water-temperature profiles, and stable isotopes 

of water were used to determine hydraulic properties 

of South Pond bottom sediments and pond leakance 

near the Natick Springvale wellfield.

Natick Springvale Wellfield

The Natick Springvale wellfield is on a peninsula 

bordered by South Pond, Carling Pond, and Middle 

Pond (figs. 1 and 4). Surface water flows in a clockwise 

direction around the peninsula through open channels 

connecting the ponds beneath Route 9 and a railroad. 

Land use in the vicinity of the wellfield includes residential, commercial, and industrial and Route 9, a 

major four-lane highway. The northern boundary of the 

Army facility lies about 2,200 ft southeast of the wellfield. Figure 4 shows the location of the public-supply 

wells in relation to the three ponds and the datacollection network along with selected observation 

wells and borings.

Figure 3. Continuous seismic-reflection record and interpretation (line of section B-B′ shown on pl. 1), South Pond of 

Lake Cochituate.
Pond-Aquifer Interaction 9

C

C'

South Pond near NCW77

C C'

EXPLANATION

OBSERVATION WELL 

 OR BORING AND NUMBER

PUBLIC-SUPPLY WELL AND NUMBER

SURFACE-WATER SITE

LINE OF CROSS SECTION–See figure 6

210,600 210,900

894,600

894,300

894,000

Orthophoto mosaic base by Massachusetts Executive Office of Environmental Affairs; aerial photographs from 1997

500-meter grid based on Massachusetts state plane projection

NCW59 MW202B

NCW77,78,83

NCW79,80

NCW1

NCW86,87

NCW2

NCW4

NCW96

NCW3

NCW84,85

NCW26

NCW63

South Pond

Carling Pond

Middle Pond

NCW2

NCW26

Figure 4. Location of Natick Springvale public-supply wells, data-collection network, and selected observation 

wells and borings, South Pond of Lake Cochituate.
10 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

The Natick Springvale wellfield consists of four public-supply wells; three of the 

four wells, NCW1, NCW2, and NCW3 were 

active during this study. NCW1 was constructed in 1903 and is an open-ended 30-

foot diameter dug well completed 23 ft 

below the land surface. NCW2 and NCW3 

were constructed in 1946 and 1954, respectively; NCW2 consists of a 16.5-inch diameter 20-foot long screen completed from 42 to 

62 ft below land surface whereas NCW3 

consists of an 18-inch diameter 20-foot long 

screen completed from 55 to 75 ft below land 

surface. In addition to the active publicsupply wells, the data-collection network in 

the vicinity of the wellfield included the 

pond and four piezometer clusters. Two piezometer clusters (NCW77, 78, 83 and 

NCW84, 85) were driven into the pondbottom sediments near the shoreline. Two 

existing piezometer clusters were located 

adjacent to the pond (NCW79, 80) and near 

the public-supply wells (NCW86, 87). The 

active public-supply wells and the datacollection network were used to measure 

water-levels and temperature profiles and to 

collect water samples. NCW83 was used 

only to measure temperature profiles because 

the screen ruptured during installation and 

the bottom of the casing filled with sediments. Characteristics of the public-supply 

wells and the data-collection network near 

the wellfield are included in table 1.

Daily pumping rates for each publicsupply well and the total daily pumping rate 

for the wellfield from January 1998 to July 

1999 are shown in figure 5. The three active 

public-supply wells operated on a variable 

pumping schedule. The public-supply wells 

were operated alone, or in combination of 

two or more, or not at all. Pumping rates 

averaged 1.6 Mgal/d from January 1998 to 

July 1999, and ranged from a minimum average daily pumping rate of 0.8 Mgal/d for 

January 1998 to a maximum average daily 

pumping rate of 2.4 Mgal/d for both May 

and June 1999. NCW1, which was operated 

infrequently during this study, supplied only 

six percent of the total water pumped from the wellfield. A new 

supply well screened at a similar depth as NCW2, 3, and 4, is 

scheduled to be drilled adjacent to NCW1 and then NCW1 will be 

used to supplement pumpage when needed (Phil Plaisted, Natick 

Water Division, oral commun., 2000).

Geohydrology of Wellfield Area

Thickness of stratified drift in the Natick Springvale wellfield area is approximately 200 ft on the basis of lithologic logs 

collected by Gay (1985) 2,100 ft north and by Arthur D. Little, 

Inc., (1998) 2,000 ft southeast of the wellfield. A geologic section 

showing the spatial relation among the public-supply wells, 

selected piezometers, and the northern part of South Pond is shown 

in figure 6. Lithologic logs available from the wellfield indicate the 

public-supply wells are screened in sand and gravel sediments. 

1Depth or altitude of bottom of well casing (no screen) below land surface (ft).

Table 1. Characteristics of the Natick Springvale public-supply wells, 

piezometers, and observation wells, South Pond of Lake Cochituate, 

Natick, Massachusetts

[Locations shown on figure 4 and plate 1. USGS, U.S. Geological Survey; ft, foot; 

--, information not available or applicable]

Name Altitude

of land

surface

or pond

bottom

(ft)

Altitude of

measuring

point

(ft)

Depth of 

screen top 

and bottom 

below land 

surface or 

pond bottom

(ft)

Altitude

of screen

interval

(ft)

USGS Local

Public-supply wells

NCW1 Springvale 1 145 -- 123 1122

NCW2 Springvale 3 148 -- 42.5–62.5 105.5–85.5

NCW3 Springvale 4 148 -- 55.4–75.4 92.6–72.6

NCW4 Springvale 5 147 -- 45.0–65.0 102.0–82.0

Piezometer and observation wells

NCW77 -- 136.6 138.58 3.0–3.5 133.6–133.1

NCW78 -- 136.6 138.64 5.9–6.4 130.7–130.2

NCW79 PZ7A 142.89 143.92 4–9 138.9–133.9

NCW80 PZ7B 142.89 143.76 35–40 107.9–102.9

NCW81 MW11A 166.76 166.30 25–35 141.8–131.8

NCW82 MW92B 165.58 165.33 61–71 104.6–94.6

NCW83 -- 136.6 138.86 111.3 1125.3

NCW84 -- 136.0 138.75 2.2–2.7 133.8–133.3

NCW85 -- 135.9 138.96 11.9–12.4 124.0–123.5

NCW86 -- 146.9 147.91 35–40 111.9–106.9

NCW87 -- 146.8 149.72 61–66 85.8–80.8
Pond-Aquifer Interaction 11

0

1.0

0.5

0

2.0

0.5

1.0

1.5

0

2.0

0.5

1.0

1.5

J FMAM J J A SOND J FMAM J J

1998 1999

0

4.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

PUMPING RATE, IN MILLION GALLONS PER DAY

NCW1

NCW2

NCW3

TOTAL (NCW1,2,3)

Figure 5. Daily pumping rates for each active public-supply well—NCW1, NCW2, and NCW3—and total daily 

pumping rate at the Natick Springvale wellfield from January 1998 to July 1999, South Pond of Lake Cochituate.
12 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

160

120

80

40

0

-40

-80

0

0 90 180 270 360 METERS

300 600 900 1,200 FEET

NCW2 NCW3 (PROJECTED)

NCW26

NCW96 (PROJECTED)

NCW87

NCW77

NCW1(PROJECTED)

NCW79

MW202B

Sand and gravel

Fine sand, silt,

and clay

Fine sand, silt, and clay

Bedrock

C C'

ALTITUDE IN FEET ABOVE SEA LEVEL

133.69

133.59

135.96

136.14

137.18

135.90

135.78

135.78

South Pond

NCW78

NCW83

NCW80

NCW86

no data

VERTICAL EXAGGERATION X 7.5

EXPLANATION

CONTACT LINE–Dashed

 where approximately located

WELL SCREEN–Number 

 is water level on 

 November 16, 1998.

 Public-supply wells are 

 shown in blue

These coarse-grained sediments range in thickness 

from 65 ft at NCW1 to 78 ft at NCW96, overlie fine 

sand, silt, and clay, and appear to extend laterally 

beneath South Pond with unknown thickness. Interpretation of fathometer records indicates that the maximum water depth of the northern part of South Pond is 

about 18 ft. As discussed previously, results from the 

ground-penetrating radar and continuous seismicreflection records indicate that the shoreline areas consist of coarse-grained sediments whereas fine-grained 

pond-bottom sediments of at least 14-foot thickness 

underlie this northern section of South Pond.

A comparison of the stage of South Pond to 

ground-water levels beneath the pond at both pondbottom piezometer clusters indicates a vertical downward gradient and thus the potential for pond water to 

infiltrate the aquifer (fig. 7). Water levels measured on 

November 16, 1998, at the pond and at piezometers 

between the pond and the public-supply wells 

along the geologic section are shown in figure 6. 

Figure 6. Lithology, public-supply wells, data-collection network and water levels on November 

16, 1998 (line of section C-C′ shown in figure 4), South Pond of Lake Cochituate.
Pond-Aquifer Interaction 13

J FMAM J J A SOND J FMAM J J

1998 1999

134

140

135

136

137

138

139

WATER LEVELS, IN FEET ABOVE SEA LEVEL

EXPLANATION

SOUTH POND OF LAKE COCHITUATE

NCW77 (Screen altitude 133.1 to 133.6) 

NCW78 (Screen altitude 130.2 to 130.7)

SOND J FMAM J J

1998 1999

134

140

135

136

137

138

139

WATER LEVELS, IN FEET ABOVE SEA LEVEL

NCW84 (Screen altitude 133.3 to 133.8)

NCW85 (Screen altitude 123.5 to 124.0)

Figure 7. Stage of South Pond and water levels in pond-bottom piezometers, Lake Cochituate.
14 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

Water levels indicate ground-water flow was from the 

direction of the pond toward NCW87 in the middle of 

the public-supply wells. The head difference between 

the pond and NCW87 was 3.59 ft on November 16, 

1998; head differences ranged from 1.66 to 4.41 ft 

between these two measuring points for the period of 

record. Water levels consistently showed a vertical 

downward gradient (fig. 7) and decreasing levels from 

the pond to the public-supply wells (appendix A).

Pumping at the public-supply wells may affect 

water levels and flow beneath and across South Pond 

from the wellfield. Water levels in NCW59 and 

NCW63 (Gay, 1985) and in MW202B (Arthur D. 

Little, Inc., 1998) (fig. 4) also indicated a potential for 

infiltration of pond water. On the east side of South 

Pond, water levels in NCW59 and MW202B were 

lower than the pond surface; west of South Pond, water 

levels in NCW63 for 6 months of the year were lower 

than the pond. Gay (1985) suggested that water may be 

infiltrating along the shoreline areas near these observation wells and flowing beneath the shallow, northern 

part of South Pond through permeable aquifer material.

Temperature Profiles and 

Stable Isotope Techniques

Temperature profiles: Vertical profiles of 

ground-water temperature have been used in numerous 

studies to indirectly determine the rate of vertical 

ground-water flow and vertical hydraulic conductivity 

in sediments beneath surface water because heat can be 

transmitted both by conduction and by the movement 

of water. Suzuki (1960) developed, and Stallman 

(1965) modified, a one-dimensional analytical equation 

for the simultaneous flow of heat and ground water 

beneath a waterbody whereby the surface-water 

temperature varies sinusoidally. The period of surfacewater temperature variation can be relatively short 

(daily) or long (annually). The generalized form of 

Stallman’s (1963) analytical equation was solved 

numerically by Lapham (1989), who found that the 

shape of the temperature envelope, the minimum and 

maximum temperature at any given depth, defined by 

temperature profile measurements over either a daily or 

annual cycle, is indicative of the direction and rate of 

ground-water flow beneath surface-water bodies. On 

the basis of this work, Lapham (1989) found that 

downward flow of ground water increases the depth 

affected by the surface-water temperature variation 

compared to heat conduction alone, and upward flow of 

ground water decreases the depth of influence.

The rate of vertical ground-water flow is calculated by comparing temperature envelopes determined 

from measured temperature profiles to simulated temperature envelopes determined by the numerical model. 

The ground-water flow rate in the model is varied until 

the best visual match between the measured temperature envelopes and simulated temperature envelopes is 

obtained. Vertical hydraulic conductivity is then calculated from Darcy’s Law, by using the ground-water 

flow velocity simulated by the model and the measured 

vertical hydraulic gradient across the sediments. The 

upper thermal boundary of the model is represented 

by the temporal variation in surface-water temperature 

using a harmonic function, and the lower thermal 

boundary is represented by the temperature of ground 

water at a given depth. If surface-water temperature 

varies sinusoidally, then the temperature envelope 

will be symmetrical around the mean surface-water 

temperature. The numerical model assumes vertical 

steady-state ground-water flow and transient heat flow. 

Assumptions of the model also include that there is no 

internal heat gained or lost and that sediments are 

homogenous. A detailed description of the method and 

model assumptions is included in Lapham (1989).

Lapham (1989) applied the temperature profile 

technique to determine rates of ground-water flow and 

vertical hydraulic conductivity beneath perennial 

streams in the Northeast. One of these streams was 

near a wellfield, where diurnal variation in stream and 

ground-water temperature was used to determine the 

rate of induced infiltration of water from the stream 

into the aquifer caused by pumping the wells. The temperature profile technique also was used to determine 

the ground-water inflow rate to a lake (Krabbenhoft 

and Babiarz, 1992) and a wetland (Hunt and others, 

1996) in Wisconsin.

Temperature profiles were measured at the study 

site hourly from September 18–23, 1998, in piezometer 

NCW83 and from October 16–22, 1998, in piezometer 

NCW85. Temperature of the pond adjacent to the piezometers also was measured hourly during these periods. Temperature was measured in the pond water and 

at varying depths in the piezometers using thermistors 

recorded by a data logger; precision of the thermistors 

was about ±0.1 ̊C. Water in the piezometers was 

assumed to be in thermal equilibrium with adjacent 

sediments and ground water. 
Pond-Aquifer Interaction 15

Stable isotopes: Stable isotopes of oxygen and 

hydrogen in water can be used to investigate pondaquifer interactions if the isotopic composition of the 

pond water and of ground water upgradient from the 

pond are isotopically distinct. Ground water upgradient 

of the pond, which is not in contact with pond water, 

has an isotopic composition of precipitation recharge. 

The isotopes oxygen and hydrogen, because they are 

constituents of the water molecule itself, can be used 

as natural tracers of different water sources (Gat and 

Gonfiantini, 1981) and thus provide insights into the 

effects of pumping wells on ground-water flow in a 

pond-aquifer setting. The isotope technique can be 

used to detect the presence of pond-derived water in the 

aquifer and to quantify the mixing of different water 

sources at the public-supply wells or at other sampling 

points in the aquifer. Studies that have successfully 

used oxygen and hydrogen isotopes to investigate 

surface-water and ground-water interactions near 

pumping wells include Stichler and others (1986), 

Dysart (1988), McCarthy and others (1992), and 

Boyd (1998).

The contribution of pond water and ground water 

at a sampling location can be calculated using a twocomponent mixing model. If pond water and ground 

water have distinct isotopic signatures, they will define 

the end-points of a mixing line on a graph on which the 

oxygen isotopes are plotted against the hydrogen isotopes. Water consisting of a specific mixture of pond 

water and ground water will plot at a certain point on 

the mixing line between the end-points. The location of 

the water sample along this mixing line can then be 

used to identify the contribution from each water 

source.

Water samples for isotopic analysis were collected from South Pond and from selected piezometers 

and wells from December 1997 to July 1999; locations 

of these sampling sites near the Natick Springvale 

wellfield are shown in figure 4, and sampling sites on 

the peninsula where the Army facility is located are 

shown on plate 1. Isotopic composition of pond water 

was represented by samples collected at the pond 

surface near NCW77 and NCW67. Isotopic composition of ground water was represented by samples collected at wells on the peninsula where the Army facility 

is located. Water-table maps constructed by Arthur D. 

Little, Inc. (1998), indicate that this peninsula is 

upgradient of the pond. Water samples were collected 

from selected wells between South Pond and the 

public-supply wells and from the public-supply wells 

themselves. Water samples were collected at nonpumping wells after an equivalent of at least three volumes 

of water in the well casing had been removed and 

temperature and specific conductance stabilized.

Water samples were collected and stored in glass 

bottles with polyseal caps to prevent evaporation. The 

samples were analyzed for their isotopic values at the 

U.S. Geological Survey Isotope Fractionation Project 

Laboratory in Reston, Virginia. Oxygen isotope ratio 

values of the water samples were determined using a 

carbon dioxide equilibration technique (Epstein and 

Mayeda, 1953) and the hydrogen isotope ratio values 

were determined using a hydrogen equilibration technique (Coplen and others, 1991). The isotopic composition of the water samples is defined in delta (δ) 

notation: δ18Ο for the oxygen isotopes and δD for the 

hydrogen isotopes. δ-notation is reported in parts-perthousand (per mil) difference in the ratio of the least 

abundant isotope (oxygen-18 or deuterium) to the most 

abundant isotope (oxygen-16 or protium) in a sample 

relative to the same ratio in Vienna Standard Mean 

Ocean Water (V-SMOW). The analytical precision of 

the oxygen and hydrogen isotope results is ±0.2 and 

±2 per mil, respectively, at the 95 percent confidence 

interval (Tyler Coplen, U.S. Geological Survey, written 

commun., 1999).

Vertical Ground-Water Flow and 

Vertical Hydraulic Conductivity of 

Pond-Bottom Sediments

Diurnal, rather than annual, variations in pond 

and ground-water temperature were analyzed to determine rates of vertical ground-water flow and vertical 

hydraulic conductivity in sediments beneath South 

Pond because pumping rates at the wellfield vary 

during the year. Steady-state hydraulic conditions were 

assumed during collection of the temperature profiles 

because the public-supply wells were expected to be 

operating continuously at a constant rate. This was the 

case for the first four days of data-collection at NCW85 

(when the pumping rate was a constant 2.1 Mgal/d), the 

period in which the temperature profiles were analyzed. However, pumping rates varied from day to day 

during data-collection at NCW83. During the 24-hour 

period in which the temperature profiles were analyzed, pumping rates at the wellfield decreased from 

1.7 to 1.2 Mgal/d, thus the rate of vertical ground-water 

flow may have varied during the period analyzed. 
16 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

Another assumption of the model, vertical flow of heat 

and fluid, was assumed to apply at shallow depths 

beneath the pond.

Temperature of South Pond adjacent to piezometer NCW83 from September 18–23, 1998, and adjacent 

to piezometer NCW85 from October 16–22, 1998, is 

shown in figures 8A and 9A. During these periods of 

data collection, the stage of the pond was such that piezometer NCW83 was approximately 0.5 ft from the 

pond shore in about 0.3 ft of pond water, and piezometer NCW85 was approximately 10 ft from the shore in 

about 1.5 ft of water. Pond-water temperature varied in 

a generally sinusoidal pattern at NCW83 during the 

first four days of data-collection and at NCW85 during 

the period of data-collection. The amplitude of this 

temperature fluctuation varied each day. In addition, 

the amplitude of the temperature fluctuation of the 

pond water was less at NCW85 than at NCW83 

because of less variability in air temperature and 

because piezometer NCW85 was in deeper pond water. 

Temperature profiles at NCW83 during the first 24 

hours of data collection (beginning at 2 p.m. on 

September 18) were chosen to define the diurnal temperature envelope because: (a) ground-water temperature profiles were nearly symmetrical around the mean 

surface-water temperature, (b) thermistors were calibrated at the beginning but not at the end of data collection, so that corrections in temperature drift could not 

be made, and (c) one of the thermistors at shallow 

depth beneath the pond-bottom malfunctioned after 

this 24-hour period. Temperature profiles at NCW85 

collected on October 17 (beginning at 1 a.m.) were 

chosen to define the diurnal temperature envelope for 

the same reasons as (a) and (b) listed above for 

NCW83, and because the amplitude of the surfacewater fluctuation was greatest during this 24-hour 

period of the temperature record. Bihourly temperature 

profiles and resulting daily temperature envelopes for 

these 24-hour periods in NCW83 and NCW85 are 

shown in figures 8B and 9B (temperature values are 

listed in appendix B). The temperature profiles are 

drawn by linear interpolation between temperature 

measurements. The water level in piezometer NCW83 

was below the pond bottom during data collection, thus 

the first ground-water temperature measurement was at 

a depth of about 0.9 ft below the pond. The temperature 

envelopes indicate that the magnitude of the daily temperature variation decreases rapidly with increasing 

depth beneath the pond bottom.

Limited field data were available for estimating 

hydraulic and thermal properties of the sediments. 

Pond-bottom sediments consist of sand, gravel and 

cobbles; because these sediments were not suited for 

collection of core samples and because the model 

assumes homogenous sediments across the vertical 

thickness that is simulated, average physical and thermal properties for coarse-grained sediments were 

assumed to adequately represent these sediments. The 

following average physical and thermal properties for 

coarse-grained sediments, reported in Lapham (1989), 

were used as inputs to the model: wet-bulk density 

2.0 g/cm3; thermal conductivity 0.0043 cal/s-cm- ̊C; 

volumetric heat capacity 0.65 cal/cm3- ̊C; and thermal 

diffusivity 0.0066 cm2/s.

Temporal variation in temperature of the pond 

at NCW83 for the 24-hour period beginning at 2 p.m. 

September 18 was represented in the model sinusoidally using a mean stream temperature of 22.1 ̊C and a 

semiamplitude of 2.6 ̊C. Simulated temperature envelopes using downward rates of ground-water flow of 0, 

0.5, 1.0, and 1.5 ft/d are shown in figure 8C. The simulated temperature envelope defined by a velocity of 

0 ft/d represents heat conduction only. A comparison 

between the simulated temperature envelopes for heat 

conduction alone and the measured temperature envelope indicates the direction of ground-water flow is 

downward because the measured temperature envelope 

is elongated in the vertical direction. This conclusion 

supports the hydraulic-gradient measurements that 

show pond water to be infiltrating the aquifer along this 

part of the shoreline. The best overall match between 

the measured temperature envelope and the simulated 

temperature envelopes was obtained with a downward 

flow of about 1.0 ft/d; however, temperature variations 

at shallow depths agree best with a downward flow rate 

of about 0.5 ft/d, and temperature variations at deep 

depths agree with a downward rate of about 1.5 ft/d, 

indicating possible heterogeneity in the pond-bottom 

sediments, which is not simulated in the model.
Pond-Aquifer Interaction 17

24-hour period modeled

DATE

1926202122232425

TEMPERATURE, IN DEGREES CELSIUS

19 

20 21 22 23 

TEMPERATURE, IN DEGREES 

0

10

2468

19 25 20 21 22 23 24

TEMPERATURE, IN DEGREES CELSIUS

0

10

2468

DEPTH BELOW POND BOTTOM, IN FEET

(A)

(B) (C)

Sept. 18 Sept. 19 Sept. 20 Sept. 21 Sept. 22 Sept. 23 

0 ft/d

1.5 ft/d

1.0 ft/d

0.5 ft/d

MEASURED TEMPERATURES SEPTEMBER 18–19, 1998

SIMULATETEMPERAENVELOP

SOUTH 

Figure 8. (

A) Temperature of South Pond adjacent to NCW83, (

B) measured bihourly temperature profiles in NCW83 for the 24

beginning at 2 p.m. September 18, 1998, and (

C) simulated temperature envelopes for vertical flow rates of 0, 0.5, 1.0, 1.5 feet 

Cochituate.
18 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts 24-hour period modeled 1219131415161718

TEMPERATURE, IN DEGREES CELSIUS

13 19 14 15 16 17 18

TEMPERATURE, IN DEGREES CELSIUS

0

10

2468

DEPTH BELOW POND BOTTOM, IN FEET

13 

14 15 16 17 

TEMPERATURE, IN DEGREES CE

0

10

2468

(B)

(A)

(C) 0 ft/d

1.0 ft/d

0.5 ft/d

DATE

Oct. 16 Oct. 17 Oct. 18 Oct. 19 Oct. 20 Oct. 21 Oct. 22 

MEASURED TEMPERATURES OCTOBER 17-–18, 1998

SIMULATETEMPERAENVELOP

SOUTH 

Figure 9. (

A) Temperature of South Pond adjacent to NCW85, (

B) measured bihourly temperature profiles in NCW85 for the 24

beginning at 1 a.m. October 17, 1998, and (

C) simulated temperature envelopes for vertical flow rates of 0, 0.5, 1.0 feet per day
Pond-Aquifer Interaction 19

A vertical head difference of 1.11 ft between 

water levels in the pond and in NCW77, located next to 

NCW83, was measured at the beginning of the 24-hour 

period on September 18, 1998. This head difference 

equals a hydraulic gradient of 0.35 foot per foot across 

the first 3.2 ft of pond-bottom sediments. Using the 

measured hydraulic gradient of 0.35 foot per foot and a 

downward rate of ground-water flow of 1.0 ft/d determined from the temperature envelopes, a vertical 

hydraulic conductivity calculated using Darcy’s Law 

was 2.9 ft/d for the 3.2 ft of pond-bottom sediment.

Temporal variation in pond temperature at 

NCW85 for the 24-hour period beginning at 1 a.m. 

October 17 was represented in the model sinusoidally 

using a mean stream temperature of 15.7 ̊C and a semiamplitude of 0.9 ̊C. Simulated temperature envelopes 

using downward rates of ground-water flow of 0, 0.5, 

and 1.0 ft/d are shown in figure 9C. A comparison 

between the measured temperature envelope and the 

simulated temperature envelopes indicates that the 

direction of ground-water flow at the site appears to be 

downward; the best match between measured and simulated envelopes results in a downward rate of groundwater flow of about 0.5 ft/d. This conclusion supports 

the hydraulic-gradient measurements at the site that 

induced infiltration is occurring. Because of the ±0.1 ̊C 

precision of the thermistors, however, temperature profiles measured during a larger diurnal surface-water 

variation than 1.8 ̊C would be needed to accurately 

determine the downward rate of ground-water flow for 

this site.

A vertical head difference of 1.08 ft between 

water levels in the pond and in NCW84, located adjacent to NCW85, was measured on October 16, 1998. 

This head difference equals a hydraulic gradient of 

0.45 foot per foot beneath the top 2.4 ft of pond-bottom 

sediments. Using the measured hydraulic gradient of 

0.45 foot per foot and a downward rate of ground-water 

flow of 0.5 ft/d determined from the temperature envelopes, a vertical hydraulic conductivity of 1.1 ft/d for 

the 2.4 ft of pond-bottom sediment was calculated 

using Darcy’s Law. The temperature profile results 

indicate that the pond-bottom sediments at the two 

locations have similar vertical hydraulic conductivities.

Pond Leakance

Leakance of pond water into the aquifer, naturally or induced by pumping at a well, or both, may be 

quantified at a measuring point in the aquifer on the 

basis of stable isotopes of oxygen and hydrogen in 

water. Knowledge of the isotopic composition of pond 

water and ground water, and its temporal and spatial 

variability, is needed because average isotopic values 

of these source waters represent the end-points in a 

two-component mixing model. The accuracy of the 

estimated contribution from each water source at a 

sampling site is dependent on the average isotopic 

composition at the site and on the accuracy of the average isotopic composition determined for the water 

sources. Pond data collected at South Pond near 

NCW77 and ground-water data collected at MW92B 

and MW11A were used to represent the average 

isotopic composition of these water sources.

Temporal variation in isotopic composition was 

determined on the basis of δ18Ο values; δD indicates, 

in general, similar trends. The isotopic composition 

for each sample, along with relevant water-quality 

parameters, is listed in appendix C.

Isotopic Composition of Pond 

Water and Ground Water

Differences in the isotopic compositions of water 

samples can be an indication that they are from different sources, or that they represent a mixture of waters 

from those sources. In this study, the isotopic composition of water samples from South Pond and from 

nearby wells were compared to determine the degree of 

interaction between the two sources. Of particular relevance is whether the isotopic composition data would 

indicate any leakage of water from South Pond into the 

underlying aquifer. The temporal variability in δ18Ο of 

South Pond near NCW77 and of ground water at observation wells MW92B and MW11A for the period of 

record is shown in figure 10. The isotopic composition 

of pond water varies seasonally and is enriched in δ18Ο

relative to ground water.
20 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

FMAMJ J ASOND J FMAMJ J

1998 1999

-10

-5-9-8-7-6

DELTA OXYGEN-18, IN PER MIL

NCW3

NCW2

NCW1

NCW80

NCW79

NCW77

MW92B

POND 

WATER

MW11A

Figure 10. Temporal variation in delta oxygen-18 of pond water, ground water, water from observation wells between South Pond and N

and water from the public-supply wells, February 1998 to July 1999, Lake Cochituate.
Pond-Aquifer Interaction 21

Several climatic and hydrologic factors affect the 

isotopic composition of pond water. The isotopic composition of precipitation varies seasonally, primarily 

due to changes in atmospheric temperature (Gat, 1980), 

and as a result, the isotopic composition of surfacewater runoff to South Pond also varies seasonally. The 

δ18Ο of bulk precipitation samples collected approximately monthly from July 1998 to September 1999 in 

Concord, Mass., 10 miles north of South Pond, ranged 

from -11.2 per mil in winter to -3.26 per mil in summer; the isotopic composition of South Pond reflects 

this seasonal trend. Gay (1985) calculated the water 

balance for Lake Cochituate for climatic year 1978 and 

determined that inflow to the lake is dominated by surface-water runoff (about 82 percent) and precipitation 

(about 9 percent) and that the water-residence time is 

relatively short at 7 months. Evaporation from the pond 

surface is a process that can modify the isotopic composition of pond water and, because evaporation rates 

vary through the year and because of the relatively 

short water-residence time of the lake, also can contribute to the seasonal variation in the isotopic composition 

of South Pond. Evaporation can cause an enrichment in 

δ18Ο and δD in the pond water. A detailed discussion 

of the factors that influence the isotopic composition of 

surface-water bodies can be found in Dincer (1968).

The δ18Ο and δD of pond water and ground 

water, and the local meteoric water line (LMWL) for 

Concord, Mass., are plotted in figure 11. The LMWL 

was defined on the basis of rainfall-dominated precipitation samples. The slope of the LMWL of 7.22 differs 

from the global meteoric water line (GMWL) of 8, 

probably because of the limited number and range of 

data points used to calculate the linear regression of δD 

against δ18Ο. Water that has been affected by evaporation will plot to the right of the LMWL along what is 

called an evaporation line. The evaporation line has a 

less steep δD/δ18O slope, usually between 4 and 6, than 

the meteoric water line because evaporation causes an 

increased relative enrichment of oxygen-18 than of 

deuterium in the residual water (Gat, 1981b). The isotopic composition of ground water plots near the 

LMWL, indicating that water recharging the aquifer 

was unaffected by evaporation. Several of the pond 

water samples, however, appear to have been affected 

by evaporation. The isotopic composition of the 

pond water from mid-summer through mid-fall, during 

and immediately following the highest monthly evaporation rates, generally was the most affected by 

evaporation.

All these interdependent factors—the seasonal 

variation in the isotopic composition of precipitation, 

surface-water inflow as the dominant component of the 

water budget, the relatively short water-residence time 

of the lake, and the seasonal variation in evaporation 

rates—caused δ18Ο of pond water to increase, in general, from spring to summer and decrease from autumn 

to winter. An exception to this general trend was 

observed from mid-June to mid-July 1998. A major 

storm from June 13–16, 1998, produced 7.91 in. of precipitation at the Natick climatological station (U.S. 

Department of Commerce, National Oceanic and 

Atmospheric Administration, 1998), caused the δ18Ο

of pond water to decrease before returning to the general trend of increasing during the warm weather 

months. This temporary decrease in δ18Ο of pond 

water indicates that this large precipitation event was 

depleted in δ18Ο compared to the isotopic composition 

of pond water.

Annual variation in the isotopic composition of 

pond water also was evident. Isotopic composition of 

pond water near NCW67 in December 1997 (table 2; 

location shown on pl. 1) was similar to the isotopic 

composition of pond water near the Natick Springvale 

wellfield in December 1998 (fig. 10). If the isotopic 

composition of pond water from the central part of 

South Pond can be used to represent pond water from 

the northern part, then the isotopic composition of 

pond water in late autumn of 1997 was similar to that 

in late autumn of 1998. However, a comparison of 

common months of data from February through July 

show that the isotopic composition of pond water for 

1999 was more enriched than 1998 values (fig. 10). As 

a result of below average precipitation, streamflows 

and ground-water levels in eastern Massachusetts were 

generally normal to below normal during autumn 1998 

and winter 1999, and below normal during spring and 

summer 1999 (Socolow and others, 2000). Thus, the 

isotopic composition of pond water in 1999 may not 

reflect long-term climatic and hydrologic conditions 

affecting the pond. 
22 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

The δ18Ο of pond water ranged from a minimum 

of -8.34 per mil in April 1998 to a maximum of 

-5.63 per mil in July 1999. The average isotopic composition of the pond water used in a two-component 

mixing model is discussed in a subsequent section of 

this report.

Isotopic composition of water from wells 

MW92B and MW11A indicates a minimal temporal 

variability in upgradient ground water compared to 

pond water. Isotopic composition of ground water 

should reflect the approximate average annual isotopic 

composition of recharge derived from precipitation 

(Gat, 1981a). Because precipitation is available to 

recharge the aquifer from autumn, after the soil 

moisture deficit has been satisfied, through late spring 

when evapotranspiration exceeds precipitation, the 

isotopic composition of ground water should be 

depleted in δ18Ο and δD compared to the average 

annual isotopic composition of precipitation.

Well MW92B consists of a 10-foot screen centered about 38 ft below the water table. δ18Ο of ground 

water at this site ranged from -9.14 to -9.00 per mil, 

which is virtually constant because these values are 

within the analytical precision. Average values for the 

period of record were -9.09 per mil for δ18Ο and 

-58.0 per mil for δD. Well MW11A consists of a 10-

foot screen installed across the water table. δ18Ο of 

ground water at the top of the aquifer is slightly 

-12 -11 -10 -9 -8 -7 -6 -5

DELTA OXYGEN-18, IN PER MIL

-75

-25

-70

-65

-60

-55

-50

-45

-40

-35

-30

DELTA DEUTERIUM, IN PER MIL

LOCAL METEORIC WATER LINE

 FOR CONCORD, MASSACHUETTS

PRECIPITATION AT CONCORD, MASSACHUSETTS

POND WATER

 SOUTH POND NEAR NCW77 (AUG.–NOV.)

 SOUTH POND NEAR NCW77 (DEC.–JUL.)

GROUND WATER–Upgradient of Pond

 MW11A

 MW92B

PUBLIC-SUPPLY WELLS

 NCW1

 NCW2

 NCW3

δD = 7.22 δ180 + 8.52

 (n = 11; R2 = 0.96)

Figure 11. Relation between delta oxygen-18 and delta deuterium in pond water, ground water, and water 

from the public-supply wells, South Pond of Lake Cochituate, and the local meteoric water line for Concord, 

Massachusetts, 1998–99.
Pond-Aquifer Interaction 23

enriched compared to that of water deeper in the aquifer at MW92B, and also shows some temporal variability which ranges from -9.00 to -8.32 per mil. The 

isotopic composition of ground water at MW11A for 

the period of record averaged -8.68 per mil for δ18Ο

and -55.9 per mil for δD. Mixing of recharge water 

from different ground-water flow paths may account 

for these differences between sites.

Because the isotopic composition of ground 

water at the water table and deeper in the aquifer differed slightly, additional water samples were collected 

from seven wells upgradient of the pond in December 

1998 to determine the spatial variability of upgradient 

ground water. These samples, along with three groundwater samples also upgradient of the pond collected in 

December 1997, are shown in table 2. δ18Ο ranged 

from -8.88 to -8.08 per mil; there was no observable 

pattern in the vertical or areal distribution in the aquifer. Seven of the ten values are within the range of 

values found at MW92B and MW11A for the period of 

record, however, indicating that the average isotopic 

composition of ground water at MW92B and MW11A 

should adequately represent the isotopic composition 

of ground water in a two-component mixing model.

Characterizing Interaction of Pond 

Water and Ground Water

The temporal variation in δ18Ο of water from 

sampling points between South Pond and the Natick 

Springvale public-supply wells, and from the publicsupply wells themselves, are shown in figure 10. The 

temporal variation in δ18Ο of water from shallow 

depths beneath and adjacent to South Pond at NCW77 

and NCW79 generally corresponds to the seasonal 

variation in δ18Ο of pond water; isotopic composition 

of shallow water from NCW78 indicates the same 

results and is listed in appendix C. This confirms the 

results of the previously discussed hydraulic-gradient 

and temperature-profile data that pond water is infiltrating the aquifer near the wellfield. Isotope results further indicate that nearly all water at these shallow 

depths is derived from pond water.

Table 2. Sampling site characteristics and water-quality constituents in a ground-water inflow area to South Pond of Lake 

Cochituate, December 1997 and December 1998, Natick, Massachusetts

[Locations shown on plate 1. USGS, U.S. Geological Survey; ft, foot; δD, delta deuterium; δ18O, delta oxygen-18; μS/cm, microsiemens per centimeter at 25 

degrees Celsius;  ̊C, degrees Celsius; NA, not applicable, --, information not available or applicable]

Name Altitude

of land

surface

or pond

bottom

(ft)

Altitude of

measuring

point

(ft)

Depth of

screen top

and bottom 

below land

surface or

pond bottom

(ft)

Altitude

of screen

interval

(ft)

Date

Temperature

( ̊C)

Specific

conductance

(μS/cm)

δD

(per

mil)

δ18O

(per

USGS Local mil)

December 1997

South Pond near 

NCW67 -- -- -- -- -- Dec. 19 3.2 402 -47.8 -6.90

NCW67 -- 136.3 138.33 3.0–3.5 133.3–132.8 Dec. 11 6.1 347 -53.8 -8.39

NCW69 PZ3A 138.93 140.00 4–9 134.93–129.93 Dec. 8 11.4 317 -53.2 -8.36

NCW76 MW90B 150.18 150.18 47–57 103.18–93.18 Dec. 9 12.8 1,010 -54.7 -8.34

December 1998

NCW88 MW10A 161.47 161.10 25–35 136.47–126.47 Dec. 8 13.8 120 -54.1 -8.24

NCW89 MW10B 161.62 161.20 34–54 127.62–107.62 Dec. 10 12.0 1,862 -57.3 -8.80

NCW90 MW11B 166.92 166.61 48–68 118.92–98.92 Dec. 14 13.6 1,008 -54.0 -8.21

NCW91 MW4 142.30 144.40 6–16 136.30–126.30 Dec. 9 14.0 1,458 -56.3 -8.88

NCW92 MW201A 153.87 153.61 17–27 136.87–126.87 Dec. 11 12.2 162 -54.9 -8.68

NCW93 MW201B 153.62 153.32 53–73 100.62–80.62 Dec. 10 11.2 294 -55.9 -8.76

NCW94 MW205B 172.95 172.72 60–70 112.95–102.95 Dec. 10 11.8 592 -52.0 -8.08
24 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

In contrast, the isotopic composition of water 

samples from shallow depths near the pond collected in 

a ground-water inflow area in December 1997 show 

different results (table 2). Water samples from shallow 

depths beneath and adjacent to the pond at NCW67 

and NCW69 are isotopically distinct from pond water 

and are nearly identical to ground water at MW90B 

approximately 600 ft upgradient. Thus, the isotope 

results indicate that at this ground-water inflow area to 

the pond, all water is derived from ground water, even 

at shallow depths near the pond.

Isotope results from a study of a Minnesota lake 

unaffected by pumping wells (Kendall and others, 

1997), which used a closely spaced vertical sampling 

network below the ground-water inflow and lake-water 

outflow areas of the lake, showed that water sources 

changed abruptly from predominantly ground water at 

about 8 in. below the lake bottom to surface water at 

the lake-sediment contact in the ground-water inflow 

area. Beneath the lake-water outflow area, the isotope 

results showed that the source of water gradually 

changed from surface water to an increasing percentage of ground water with depth. This pattern contrasts 

with that observed at the Natick Springvale wellfield 

area, where pumping wells induce infiltration of pond 

water into the aquifer, causing all water at shallow 

depths to be derived from pond water.

Water from NCW80 and from the public-supply 

wells, which are screened at greater depths and farther 

from South Pond than the shallow piezometers, is 

generally depleted in δ18Ο compared to pond-water 

values and enriched compared to ground-water values 

(fig. 10). The isotopic composition of water from the 

public-supply wells also is shown in figure 11 and 

values are clustered generally between pond-water and 

ground-water values. Therefore, water at NCW80 and 

the public-supply wells is interpreted to consist of a 

mixture of pond water and ground water.

The δ18Ο of water from public-supply wells 

NCW2 and NCW3 showed minimal temporal fluctuation; δ18Ο ranged from -7.88 to -7.45 per mil at NCW2 

and from -7.69 to -7.19 per mil at NCW3. The isotopic 

composition of water from these two public-supply 

wells showed a slight enrichment in the second half of 

the data set versus the first half but these differences are 

close to the analytical precision. The average isotopic 

composition of water from NCW2 was -7.64 per mil 

for δ18Ο and -49.5 per mil for δD and from NCW3 the 

average isotopic composition was -7.49 per mil for 

δ18Ο and -49.3 per mil for δD. Because these averages 

from NCW2 and NCW3 are nearly equivalent, an average of the two wells was used to represent the isotopic 

composition of the two public-supply wells in a twocomponent mixing model. The ranges and averages of 

isotopic values at these two public-supply wells are 

similar to those values from NCW80 located between 

the public-supply wells and the pond, and screened at 

an altitude slightly higher than NCW2 and NCW3. The 

isotopic composition of water from NCW1, however, 

which was sampled only three times (May to July 

1998) and which draws water from near the water 

table, may not be represented by the long-term data 

collected at the other two public-supply wells, which 

are screened deeper in the aquifer. The public-supply 

well that will be installed adjacent to NCW1 will probably yield water with an isotopic composition similar 

to that at NCW2 and NCW3, because the proposed 

screen interval will be near the same depth as in these 

two wells.

Even though the isotopic composition of pond 

water fluctuates seasonally, the isotopic composition of 

water from the public-supply wells, which is partly 

derived from the pond, shows little temporal variability. 

This temporal constancy in the isotopic composition of 

water at the public-supply wells is probably partly due 

to the mixing of pond water of varying isotopic composition at the public-supply wells. Infiltration of pond 

water induced by the public-supply wells occurs at different points along the pond bottom and thus at different distances from the public-supply wells. Traveltimes 

vary along the different flow paths between the pond 

and well screens, and because pumping rates also vary, 

traveltimes along the same flow path can change. The 

isotopic composition of water from the public-supply 

wells did not show any seasonal variability offset from 

the seasonal variability of pond water that would allow 

an estimate of traveltime of pond water to the wells. 

Calculation of an average linear velocity on the basis of 

Darcy’s Law and a range in parameter values of 100 to 

200 ft/d for hydraulic conductivity, 0.3 to 0.4 for porosity, and 2- to 4-foot head difference between the pond 

and the public-supply wells resulted in estimates of 

traveltime ranging from 1 to 8 months for pond water 

infiltrating near NCW77 to reach the public-supply 

wells. Because infiltration of pond water occurs at various distances from the public-supply wells than infil-
Pond-Aquifer Interaction 25

tration at NCW77—possibly even the opposite 

shoreline—traveltimes of pond-derived water could 

range from days to more than a year. Thus, water at the 

public-supply wells can consist of pond water that infiltrated the pond bottom at different times and with different isotopic compositions. The temporal constancy 

in the isotopic composition of the public-supply wells 

also is due to the temporal constancy of ground water, 

the other source of water to the public-supply wells.

Average isotope values for the period of data 

collection represented the isotopic composition of 

ground water and also water from the public-supply 

wells in a two-component mixing model because of 

the minimal temporal variability in the isotopic composition of these waters. The isotopic composition of 

ground water, represented by MW92B and MW11A, 

averaged -8.89 ±0.12 per mil for δ18Ο (95-percent confidence interval used for the isotope averages) and 

-57.0 ±0.8 per mil for δD. The isotopic composition of 

water from the public-supply wells, represented by 

NCW2 and NCW3, averaged -7.57 ±0.04 per mil for 

δ18Ο and -49.4 ±0.3 per mil for δD. Pond water, however, was represented in the mixing model by an annual 

mean isotopic composition because of the relatively 

large temporal variability in its isotopic composition 

and because of the difficulty in choosing a period that 

best represents the bulk of pond-derived water pumped 

at the public-supply wells. The annual mean was determined by first obtaining 12 monthly values and then 

averaging the months: if more than one isotope value 

occurred in a month, these values were first averaged, 

and if isotope values occurred in the same month 

but different years, the two monthly averages were 

then averaged to obtain one monthly average. The 

95-percent confidence interval was determined from 

the 12 monthly average observations. The annual mean 

isotopic composition of pond water was -6.92 ±0.42 

per mil for δ18Ο and -44.8 ±1.9 per mil for δD.

Average isotopic composition used to represent 

each source water and the average isotopic composition 

of water from the public-supply wells are shown in 

figure 12. The mixing line based on these averages 

indicates that 64 percent of the water pumped from the 

public-supply wells is derived from the pond. The 

uncertainty of the mixing-line result was quantitatively 

assessed using a equation described by Genereux 

(1998). This equation relates the uncertainty of the 

mixing-line result to the range defining the end-points 

of the mixing line and to the uncertainties of the mean 

values determined for each of the water sources and for 

the water from the public-supply wells. The equation 

described by Genereux (1998) is shown with subscripts 

consistent to this study:

,

where W represents the uncertainty and C represents 

the mean isotopic composition in the variable in the 

subscripts. The subscripts gw, pw, and w represent 

ground water, pond water and water from the publicsupply wells, in units of per mil, and the subscript f

represents the fraction or percentage of pond water 

calculated from the mixing line. The 95-percent 

confidence interval was used for the uncertainty values. 

The solution of the equation indicates that the 

uncertainty of the mixing-line result of 64 percent is 

±15 percent at the 95-percent confidence interval. 

Because the mean isotopic composition of pond water 

shows the greatest variability, and because it accounts 

for more than half the water withdrawn at the publicsupply wells, this end-member value accounted for 

most (96 percent) of the total uncertainty in the mixingline result. Thus, additional isotope data collected from 

South Pond over the long-term could substantially 

reduce the uncertainty of the mixing-line result.

The average pumping rate, 1.6 Mgal/d, which 

also includes water withdrawals at NCW1, can be multiplied by the percentage of pond-derived water at the 

public-supply wells to determine the quantity of pond 

water infiltrating the aquifer and discharging to the 

wellfield. The estimate of infiltration of pond water is 

1.0 Mgal/d, and the corresponding estimate of water 

derived from ground water is 0.6 Mgal/d.

The land-surface area of the peninsula where the 

public-supply wells are located is about 997,000 ft2, 

and the long-term annual recharge from precipitation is 

about 2 ft for eastern Massachusetts (Randall, 1996). 

W f

Cgw Cw –

Cpd Cgw ( ) – 2 --------------------------------W pd 



 2

=

Cw Cpd –

Cpd Cgw ( ) – 2 --------------------------------Wgw

2

+

1

Cpd Cgw – ------------------------Ww

2







+

1/2
26 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

-10.0 -9.5 -9.0 -8.5 -8.0 -7.5 -7.0 -6.5 -6.0

DELTA OXYGEN-18, IN PER MIL

POND WATER........................

GROUND WATER..................

 (MW11A AND MW92B)

WATER FROM SUPPLY WELLS....

 (NCW2 AND NCW3)

±95-PERCENT

CONFIDENCE LIMITS

MEAN ±95-PERCENT

CONFIDENCE LIMIT

Delta Oxygen-18

 -6.92±0.42

 -8.89±0.12

 -7.57±0.04 

Delta Deuterium

-44.8±1.9

-57.0±0.8

-49.4±0.3

-60

-42

-58

-56

-54

-52

-50

-48

-46

-44

DELTA DEUTERIUM, IN PER MIL

0

64

100

Percentage of pond water at public-supply wells

Therefore, the quantity of water from precipitation 

recharge on the peninsula is about 1,990,000 ft3/yr, or 

0.04 Mgal/d. If the contributing area of the publicsupply wells includes this peninsula, and if all the 

water that recharges the peninsula from precipitation is 

withdrawn at the public-supply wells, then the peninsula contributes only 7 percent of ground water 

pumped from the public-supply wells. Thus, most of 

the ground-water component of water withdrawn at the 

public-supply wells originates outside this peninsula. 

Further hydrologic work is needed to define the complete contributing area to the Natick Springvale wellfield.

SUMMARY AND 

CONCLUSIONS

Lake Cochituate lies in the Sudbury River Basin 

in eastern Massachusetts and consists of four ponds 

connected by shallow waterways. The southernmost 

pond, South Pond, has a surface area of 0.39 mi2 and is 

located in an urbanized setting in Natick, Mass.. Inflow 

and outflow to the pond include ground water and surface water. A U.S. Army facility on a peninsula in 

South Pond was designated a Superfund site by the 

U.S. Environmental Protection Agency in 1994 

because of contaminated ground water detected at the 

facility and its proximity to the Natick Springvale 

public-supply wellfield. Pond-aquifer interaction is an 

Figure 12. Mixing line based on a two-component mixing model using average isotope values for pond 

water, ground water, and water from the public-supply wells. Mixing-line result and uncertainty analysis 

indicate that 64 percent ±15 percent at the 95-percent confidence interval of water withdrawn at the Natick 

Springvale public-supply wells is derived from pond water.
Summary and Conclusions 27

important control on local ground-water flow patterns 

and determines the source of water withdrawn from the 

wellfield. An increased understanding of pond-aquifer 

interaction requires knowledge of several physical 

characteristics and hydrologic processes including the 

geometry of the pond, nature of pond-bottom sediments, and pond leakance near the wellfield.

A map of the bathymetry and the thickness of 

fine-grained pond-bottom sediments was prepared on 

the basis of fathometer, ground-penetrating radar, and 

continuous seismic-reflection records. The maximum 

measured water depth when the pond surface was at an 

elevation of 137.2 ft above sea level was 68.0 ft; mean 

water depth was 19.8 ft. Thick fine-grained pondbottom sediments are found towards the middle of the 

pond, but in most cases the records did not fully penetrate the sediment to the interface between fine- and 

coarse-grained sediments. Thickest fine-grained pondbottom sediments were in the eastern part of the pond, 

an area of relatively shallow water. Maximum water 

depth of South Pond between the Natick Springvale 

wellfield and the Army facility is 18 ft, with finegrained sediments of at least 14 ft thick beneath the 

pond bottom. Shoreline areas of the pond consist of 

predominantly coarse-grained sediments, indicating 

that the exchange of ground water and pond water most 

likely occurs through these areas.

The Natick Springvale wellfield is adjacent to 

South Pond, 2,200 ft from the boundary of the Army 

facility. The wellfield consists of three active publicsupply wells screened in sand and gravel sediments 

that appear to extend beneath the pond. Potential 

sources of water to public-supply wells in a pondaquifer setting include pond water and ground water 

derived from precipitation recharge. Water levels from 

the pond and at shallow depths beneath the pond indicate a downward vertical gradient and the potential for 

pond water to infiltrate the aquifer. In addition, water 

levels from the pond and between the pond and the 

public-supply wells indicate ground-water flow was 

from the direction of the pond to the public-supply 

wells. Head differences between the pond and an 

observation well in the middle of the public-supply 

wells ranged from 1.66 to 4.41 ft during the study.

Temperature profiles collected hourly over a 

daily cycle and water levels were used to calculate vertical ground-water flow and vertical hydraulic conductivity of pond-bottom sediments at two locations near 

the Natick Springvale wellfield. Measurements were 

collected from the two locations during different pumping rates. The temperature profiles indicated that the 

magnitude of the daily temperature variation at a given 

depth decreased rapidly with increasing depth beneath 

the pond bottom. Simulated temperature profiles using 

a numerical model that solves for the simultaneous 

flow of fluid and heat were compared to the measured 

temperature profiles to determine the rate of groundwater flow. The velocity of downward ground-water 

flow at one location was determined to be 1.0 ft/d and 

the corresponding vertical hydraulic conductivity was 

computed to be 2.9 ft/d across 3.2 ft of pond-bottom 

sediment. The second location had a downward velocity of ground-water flow of 0.5 ft/d and corresponding 

vertical hydraulic conductivity of 1.1 ft/d across 2.4 ft 

of sediment. These temperature profile results indicate 

that the pond-bottom sediments at the two locations 

have similar vertical hydraulic conductivities.

Stable isotopes of oxygen and hydrogen were 

used as natural tracers of the different source waters to 

detect the presence and quantity of pond water in the 

aquifer. Isotopic composition of pond water varied seasonally and annually and was distinctly different from 

the isotopic composition of ground water. The temporal 

variability was probably due to several interdependent 

climatic and hydrologic factors including the temporal 

variability in the isotopic composition of precipitation 

and in evaporation rates, surface water as the dominant 

component of the water budget, and the short waterresidence time of the pond. Isotopic composition of 

ground water and water from the public-supply wells 

showed little temporal variability. There was some spatial variability in ground water; however, there was no 

vertical or areal pattern in the spatial variation.

The isotopic composition of shallow water 

beneath and adjacent to South Pond near the publicsupply wells corresponds to the temporal variation of 

pond water, indicating that nearly all water at shallow 

depths was derived from pond water, and confirming 

that the hydraulic gradient and temperature profile 

results that this is an area of pond outflow. In contrast, 

the isotopic composition of water at shallow depths in a 

ground-water inflow area to the pond was isotopically 

distinct from the pond water. Isotopic composition of 

water from the public-supply wells was generally intermediate between the isotopic composition of pond 

water and ground water, indicating that water from the 
28 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

public-supply wells was a mixture of these source 

waters. A mixing line based on a two-component 

mixing model was used to determine the contribution 

from each source water at the public-supply wells. 

Average isotopic values for the period of record represented the isotopic composition of ground water and 

water from the public-supply wells whereas pond water 

was represented by an annual mean isotopic composition because of the relatively large variability in its isotopic composition. The position along the mixing line 

of the isotopic composition of water withdrawn from 

the public-supply wells indicated that 64 percent of 

water withdrawn from these wells was derived from 

pond water. An uncertainty analysis of the mixing-line 

result indicated that this estimate is ±15 percent at the 

95-percent confidence limit; pond water accounted for 

most of the total uncertainty in the mixing-line result 

because the mean isotopic composition of pond water 

shows the greatest variability and because it accounts 

for more than half of the water withdrawn at the publicsupply wells. Based on the average pumping rate at the 

wellfield, 1.6 Mgal/d, infiltration of pond water into the 

aquifer and discharging to the wellfield was calculated 

to be 1.0 Mgal/d.

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Appendix A
Appendix A 33

Appendix A. Pond stage and water levels in piezometers and observation wells, South Pond of Lake Cochituate, Natick, 

Massachusetts—Continued

Date

Water levels, in feet above sea level

South Pond NCW77 NCW78 NCW79 NCW80 MW11A MW92B NCW84 NCW85 NCW86 NCW87

1-07-98 137.76 137.36 136.87 -- -- -- -- -- -- -- --

1-09-98 138.13 137.78 137.33 137.48 137.22 -- -- -- -- -- --

2-09-98 137.54 137.24 136.92 136.94 136.76 -- -- -- -- -- --

2-20-98 138.06 137.84 137.48 137.52 137.28 -- 138.22 -- -- -- --

3-12-98 138.28 137.71 137.34 137.38 137.15 139.99 137.50 -- -- -- --

3-13-98 138.08 137.47 137.17 137.18 136.99 -- -- -- -- -- --

4-08-98 137.69 136.98 136.81 136.81 136.67 -- -- -- -- -- --

4-23-98 137.53 136.94 136.78 136.75 136.65 -- -- -- -- -- --

5-07-98 137.89 137.05 136.73 136.75 136.58 -- -- -- -- -- --

5-20-98 137.51 137.16 137.03 137.16 137.06 -- -- -- -- -- --

5-26-98 137.26 136.22 136.00 135.94 135.78 -- -- -- -- -- --

6-09-98 137.61 137.09 136.91 136.87 136.81 140.98 137.75 -- -- -- --

6-12-98 137.55 136.92 136.71 136.70 136.60 -- -- -- -- 136.10 135.80

6-17-98 138.94 -- -- 138.27 138.01 -- -- -- -- 135.91 135.78

7-02-98 138.40 137.68 137.29 137.37 137.09 -- -- -- -- 135.42 135.35

7-10-98 137.33 136.04 135.88 135.79 135.64 141.72 137.75 -- -- 134.16 134.10

7-16-98 137.13 135.67 135.54 135.43 135.28 -- -- -- -- 133.17 133.07

7-28-98 137.18 136.02 135.93 135.88 135.77 -- -- -- -- 134.17 134.08

8-12-98 137.40 136.62 136.51 136.44 136.38 141.18 137.54 -- -- 135.25 135.19

8-26-98 137.51 136.66 136.49 136.45 136.35 -- -- -- -- 133.96 134.22

8-27-98 137.38 136.75 136.63 136.59 136.51 -- -- -- -- 134.61 134.52

9-01-98 136.96 136.15 136.02 135.94 135.87 -- -- -- -- 135.31 135.30

9-09-98 136.75 135.70 135.59 135.49 135.36 -- -- 135.54 135.49 133.02 132.92

9-14-98 136.72 135.95 135.87 135.78 135.68 -- -- 135.85 135.82 -- --

9-16-98 136.75 135.52 135.40 135.27 135.09 140.48 136.92 135.32 135.27 132.75 132.64

9-18-98 136.74 135.63 135.52 135.38 135.25 -- -- 135.49 135.45 133.80 133.73

9-23-98 137.08 136.20 136.00 135.93 135.81 -- -- 135.96 135.93 135.22 135.21

9-25-98 137.07 136.10 135.92 135.82 135.71 -- -- 135.84 135.82 133.63 133.66

10-01-98 137.00 135.84 135.67 135.57 135.41 -- -- 135.62 135.57 133.22 133.12

10-05-98 136.93 135.82 135.66 135.57 135.41 -- -- 135.62 135.58 133.74 133.67

10-06-98 136.91 135.75 135.59 135.51 135.38 -- -- 135.52 -- 133.69 133.62

10-09-98 137.42 136.22 135.72 135.69 135.45 -- -- 135.67 -- 133.13 133.03

10-16-98 137.74 137.03 136.69 136.75 136.51 -- -- 136.66 -- 134.20 134.08

10-21-98 137.44 136.73 136.55 136.55 136.44 140.25 137.56 136.51 -- 135.25 135.32

10-22-98 137.39 136.64 136.42 136.46 136.29 -- -- 136.36 136.30 134.17 134.07

Appendix A. Pond stage and water levels in piezometers and observation wells, South Pond of Lake Cochituate, Natick, 

Massachusetts

[--, no data]
34 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

11-02-98 137.28 136.36 136.16 136.11 135.98 -- -- 136.14 136.08 133.88 133.78

11-16-98 137.18 136.14 135.96 135.90 135.78 140.08 137.29 135.91 135.86 133.69 133.59

11-19-98 137.16 -- -- -- -- -- -- -- -- -- --

11-30-98 137.13 136.02 135.84 135.76 135.64 -- -- 135.80 135.75 133.65 133.55

12-18-98 137.11 136.27 136.11 136.07 135.95 -- -- 136.09 136.04 134.61 134.55

12-30-98 137.19 136.38 136.16 136.12 136.01 -- -- 136.15 136.09 133.97 133.88

1-27-99 137.98 137.58 137.12 137.30 136.97 -- -- 137.78 -- 134.79 134.62

2-11-99 137.64 137.04 136.78 136.81 136.63 -- -- 137.47 -- 134.60 134.51

3-03-99 137.74 136.97 136.56 136.65 136.41 139.73 137.74 137.30 -- 134.09 133.99

3-25-99 137.68 137.08 136.96 136.95 136.84 -- -- 136.91 -- 135.42 135.35

4-14-99 137.36 136.75 136.61 136.59 136.49 -- -- 136.56 -- 135.34 135.26

5-06-99 137.07 135.78 135.57 135.44 135.28 -- -- 135.45 -- 132.95 132.85

6-02-99 137.18 136.10 135.85 135.80 135.61 139.68 137.24 135.69 -- 133.20 133.09

7-13-99 136.65 135.29 135.13 134.97 134.76 -- -- 135.00 -- 132.37 132.24

Appendix A. Pond stage and water levels in piezometers and observation wells, South Pond of Lake Cochituate, Natick, 

Massachusetts—Continued

Date

Water levels, in feet above sea level

South Pond NCW77 NCW78 NCW79 NCW80 MW11A MW92B NCW84 NCW85 NCW86 NCW87
Appendix B
Appendix B 37

Appendix B. Water temperature in South Pond and in piezometers NCW83 and NCW85, September and October 1998, Lake 

Cochituate, Natick, Massachusetts

[--, no data]

Date Time South 

Pond

Depth below pond bottom (feet)

0.9 1.2 1.7 2.2 3.2 4.2 5.7 7.7

NCW 83

9-18-98 1400 24.8 22.1 22.1 22.2 22.2 22.3 22.2 22.1 22.1

9-18-98 1500 24.7 22.2 22.1 22.2 22.2 22.3 22.2 22.1 22.1

9-18-98 1600 24.2 22.4 22.2 22.2 22.1 22.3 22.3 22.1 22.1

9-18-98 1700 23.3 22.5 22.2 22.2 22.0 22.3 22.3 22.1 22.1

9-18-98 1800 22.8 22.7 22.2 22.3 22.1 22.3 22.3 22.1 22.1

9-18-98 1900 22.0 22.8 22.3 22.3 22.2 22.3 22.3 22.1 22.0

9-18-98 2000 21.7 22.8 22.4 22.3 22.2 22.3 22.3 22.1 22.0

9-18-98 2100 21.1 22.8 22.4 22.4 22.3 22.3 22.3 22.1 22.1

9-18-98 2200 21.4 22.7 22.5 22.4 22.3 22.3 22.3 22.1 22.1

9-18-98 2300 20.6 22.6 22.4 22.4 22.3 22.3 22.3 22.1 22.1

9-19-98 0 20.0 22.6 22.4 22.4 22.4 22.3 22.3 22.1 22.1

9-19-98 100 19.9 22.4 22.3 22.3 22.3 22.2 22.3 22.1 22.0

9-19-98 200 19.8 22.3 22.3 22.2 22.3 22.2 22.2 22.1 22.0

9-19-98 300 19.2 22.2 22.2 22.2 22.2 22.2 22.2 22.1 22.0

9-19-98 400 19.4 22.1 22.2 22.1 22.2 22.2 22.2 22.1 22.0

9-19-98 500 19.4 22.0 22.1 22.0 22.1 22.2 22.2 22.1 22.0

9-19-98 600 19.5 21.9 22.1 21.9 22.1 22.1 22.1 22.1 22.0

9-19-98 700 19.9 21.9 22.1 22.0 22.1 22.1 22.1 22.1 22.0

9-19-98 800 20.5 21.6 22.0 21.9 22.1 22.1 22.1 22.1 22.0

9-19-98 900 21.5 21.6 21.9 21.9 22.0 22.1 22.1 22.1 22.0

9-19-98 1000 22.0 21.4 21.9 21.8 22.0 22.1 22.1 22.1 22.0

9-19-98 1100 22.6 21.4 21.8 21.8 22.0 22.0 22.1 22.1 22.0

9-19-98 1200 23.4 21.4 21.8 21.8 21.9 22.1 22.1 22.1 22.0

9-19-98 1300 23.5 21.5 21.8 21.8 22.0 22.1 22.0 22.1 22.0

9-19-98 1400 23.5 21.6 21.7 -- 21.9 22.1 22.1 22.1 22.0
38 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

Appendix B. Water temperature in South Pond and in piezometers NCW83 and NCW85, September and October 1998, Lake 

Cochituate, Natick, Massachusetts—Continued

Date Time South

Pond

Depth below pond bottom (feet)

0.2 0.5 1.0 1.5 2.5 4.0 6.0

NCW 85

10-17-98 100 15.1 15.3 15.6 15.7 15.8 15.7 15.6 15.9

10-17-98 200 15.1 15.2 15.5 15.7 15.8 15.6 15.6 15.9

10-17-98 300 15.0 15.2 15.5 15.7 15.8 15.6 15.6 15.9

10-17-98 400 14.9 15.1 15.5 15.6 15.7 15.6 15.6 15.9

10-17-98 500 14.9 15.1 15.5 15.6 15.7 15.6 15.6 15.9

10-17-98 600 14.8 15.1 15.4 15.7 15.7 15.6 15.6 15.9

10-17-98 700 14.8 15.1 15.4 15.6 15.7 15.6 15.6 15.9

10-17-98 800 14.8 15.1 15.4 15.6 15.7 15.6 15.6 15.9

10-17-98 900 14.9 15.1 15.4 15.6 15.6 15.6 15.6 15.9

10-17-98 1000 15.1 15.1 15.4 15.5 15.6 15.6 15.6 15.9

10-17-98 1100 15.2 15.3 15.4 15.5 15.6 15.6 15.6 15.9

10-17-98 1200 15.7 15.3 15.4 15.5 15.6 15.6 15.6 15.9

10-17-98 1300 16.6 15.7 15.4 15.5 15.6 15.6 15.6 15.9

10-17-98 1400 16.4 16.2 15.5 15.5 15.6 15.6 15.5 15.8

10-17-98 1500 16.6 16.4 15.6 15.6 15.6 15.5 15.6 15.8

10-17-98 1600 16.7 16.3 15.8 15.6 15.6 15.5 15.5 15.8

10-17-98 1700 16.4 16.2 15.8 15.7 15.6 15.5 15.5 15.8

10-17-98 1800 16.3 16.3 15.9 15.7 15.6 15.5 15.5 15.8

10-17-98 1900 16.2 16.2 15.9 15.7 15.5 15.5 15.5 15.8

10-17-98 2000 16.0 16.1 16.0 15.8 15.5 15.5 15.5 15.8

10-17-98 2100 16.1 16.0 16.0 15.8 15.5 15.5 15.5 15.8

10-17-98 2200 16.0 16.0 15.9 15.8 15.5 15.5 15.5 15.8

10-17-98 2300 15.9 16.0 15.9 15.8 15.5 15.5 15.5 15.8

10-18-98 0 15.8 15.9 15.9 15.8 15.6 15.5 15.5 15.8

10-18-98 100 15.8 15.8 15.9 15.8 15.5 15.5 15.5 15.8
Appendix C
Appendix C 41

Date Time

Temperature

( ̊C)

Specific

conductance

(μS/cm)

δD

(per

mil)

δ18O

(per

mil)

South Pond near NCW77

2-20-98 1255 3.2 350 -51.9 -8.29

3-13-98 1250 6.2 360 -53.1 -8.32

4-08-98 1227 11.0 366 -54.5 -8.34

4-23-98 1016 14.1 361 -52.3 -7.93

5-07-98 1035 17.0 326 -48.3 -7.66

5-26-98 1102 21.6 288 -47.0 -7.20

6-09-98 1326 22.3 302 -44.6 -6.95

6-17-98 1148 20.1 224 -40.4 -6.57

7-02-98 1230 24.6 238 -43.8 -6.80

7-16-98 1053 27.3 250 -45.7 -7.02

7-28-98 1035 26.0 266 -45.4 -6.72

8-12-98 1235 25.9 277 -44.4 -6.49

8-27-98 1300 27.7 297 -42.7 -6.14

9-09-98 1228 22.6 287 -41.4 -6.15

9-23-98 1105 21.3 291 -41.8 -6.16

10-06-98 1345 18.3 295 -40.6 -6.06

10-22-98 1212 14.3 263 -42.5 -6.45

11-02-98 1320 11.7 272 -42.9 -6.34

11-16-98 1140 8.7 286 -45.7 -6.70

11-30-98 1229 7.4 297 -44.5 -6.80

12-18-98 1042 4.9 303 -44.2 -6.89

12-30-98 1101 2.6 306 -46.0 -6.97

1-27-99 1214 3.0 260 -44.5 -7.10

2-11-99 1114 2.5 310 -43.5 -7.26

3-03-99 1206 4.0 349 -47.0 -7.58

3-25-99 1110 6.4 424 -46.1 -7.56

4-14-99 1426 10.7 418 -45.3 -7.47

5-06-99 1215 14.6 415 -45.1 -7.24

6-02-99 1310 25.7 401 -42.2 -6.42

7-13-99 1050 24.8 415 -37.5 -5.63

NCW1

5-07-98 1446 11.6 420 -51.2 -7.82

7-02-98 1440 12.8 416 -49.1 -7.61

7-16-98 0959 13.8 550 -50.0 -7.94

NCW2

2-20-98 1400 11.1 524 -49.8 -7.66

3-13-98 1351 10.1 510 -50.2 -7.69

4-08-98 1426 11.7 506 -50.1 -7.63

4-23-98 1430 11.3 504 -51.5 -7.75

5-07-98 1441 11.9 514 -51.7 -7.77

NCW2—Continued

5-26-98 1213 13.1 515 -51.2 -7.88

6-17-98 1132 12.4 535 -50.4 -7.69

7-02-98 1435 12.7 517 -49.8 -7.70

7-16-98 0954 13.3 521 -47.8 -7.69

7-28-98 0926 13.0 497 -49.9 -7.63

8-27-98 1045 13.0 494 -49.8 -7.73

9-09-98 1035 12.7 496 -50.3 -7.68

9-23-98 1008 12.0 466 -49.8 -7.67

10-06-98 1215 11.8 499 -49.4 -7.70

10-22-98 1032 12.1 496 -48.3 -7.55

11-02-98 1417 12.3 498 -48.9 -7.59

11-16-98 1041 12.0 504 -49.4 -7.54

11-30-98 1146 12.1 511 -50.6 -7.62

12-30-98 1154 11.8 501 -48.3 -7.61

1-27-99 1318 11.9 498 -48.7 -7.59

3-03-99 1450 11.5 496 -47.8 -7.45

5-06-99 1130 11.7 502 -48.3 -7.49

6-02-99 1225 12.7 500 -48.1 -7.60

7-13-99 1155 11.9 520 -47.7 -7.51

NCW3

2-20-98 1356 10.8 489 -49.0 -7.56

3-13-98 1345 8.5 460 -51.0 -7.60

4-08-98 1422 11.1 473 -51.0 -7.63

4-23-98 1425 12.6 492 -50.8 -7.62

5-07-98 1433 15.2 483 -50.2 -7.67

5-26-98 1240 14.3 465 -49.8 -7.69

6-17-98 1124 15.7 456 -49.4 -7.62

7-02-98 1445 13.4 447 -48.4 -7.52

7-16-98 0947 14.4 444 -50.2 -7.52

7-28-98 1110 15.6 415 -50.2 -7.40

8-27-98 1210 14.2 458 -49.5 -7.60

9-09-98 1138 14.1 456 -50.3 -7.52

9-23-98 1001 13.7 479 -48.8 -7.52

10-06-98 1206 13.4 464 -48.3 -7.56

10-22-98 1044 13.2 448 -48.8 -7.37

11-02-98 1414 13.3 433 -47.4 -7.30

11-16-98 1035 13.7 443 -48.6 -7.35

11-30-98 1141 13.8 452 -48.9 -7.42

1-27-99 1312 12.6 417 -47.9 -7.32

3-03-99 1448 12.4 409 -49.0 -7.38

Date Time

Temperature

( ̊C)

Specific

conductance

(μS/cm)

δD

(per

mil)

δ18O

(per

mil)

Appendix C. Temperature, specific conductance, delta deuterium, and delta oxygen-18 in water, February 1998 to July 1999, 

South Pond of Lake Cochituate, Natick, Massachusetts

[δD, delta deuterium; δ18O, delta oxygen-18; μS/cm, microsiemens per centimeter at 25 degrees Celsius;  ̊C, degrees Celsius]
42 Pond-Aquifer Interaction at South Pond of Lake Cochituate, Natick, Massachusetts

NCW3—Continued

5-06-99 1125 12.2 446 -48.2 -7.42

6-02-99 1220 13.7 453 -49.5 -7.53

7-13-99 1150 13.0 468 -47.8 -7.19

NCW77

2-20-98 1442 3.4 405 -54.1 -8.16

3-13-98 1309 4.3 383 -53.7 -8.31

4-08-98 1356 11.0 374 -54.7 -8.32

5-07-98 1351 17.1 334 -50.6 -7.63

5-26-98 1117 20.2 290 -47.3 -7.12

7-02-98 1259 22.9 247 -44.4 -6.73

7-16-98 1110 26.5 251 -47.0 -7.00

8-27-98 1315 26.0 287 -42.7 -6.23

9-23-98 1148 20.4 292 -42.7 -6.11

10-22-98 1226 14.1 275 -41.8 -6.47

11-30-98 1241 8.0 303 -43.9 -6.76

12-30-98 1110 1.5 306 -48.0 -7.21

1-27-99 1232 2.4 266 -43.3 -7.05

NCW78

2-20-98 1501 3.3 375 -52.3 -8.13

3-13-98 1325 4.8 386 -55.2 -8.32

4-08-98 1411 10.0 381 -53.3 -8.29

5-07-98 1408 16.1 344 -48.7 -7.70

5-26-98 1131 19.0 298 -46.7 -7.29

7-02-98 1318 23.1 248 -43.2 -6.80

7-16-98 1122 24.7 252 -46.6 -7.10

8-27-98 1330 24.8 284 -44.9 -6.38

9-23-98 1214 20.9 288 -42.0 -6.08

10-22-98 1240 14.8 250 -42.9 -6.41

11-30-98 1254 8.7 296 -45.1 -6.78

12-30-98 1122 3.1 319 -46.0 -6.89

1-27-99 1244 1.6 254 -45.0 -7.09

NCW79

2-20-98 1312 5.9 200 -55.5 -8.67

3-13-98 1414 4.7 365 -55.1 -8.22

4-08-98 1330 12.0 380 -54.6 -8.36

5-07-98 1314 15.5 326 -50.0 -7.59

5-26-98 1149 19.2 297 -46.8 -7.12

6-17-98 1224 20.2 228 -42.1 -6.56

7-16-98 1140 24.8 276 -46.8 -7.01

8-27-98 1228 24.6 302 -42.8 -6.23

9-23-98 1044 21.4 370 -43.5 -6.37

10-22-98 1114 14.7 268 -42.8 -6.37

Date Time

Temperature

( ̊C)

Specific

conductance

(μS/cm)

δD

(per

mil)

δ18O

(per

mil)

NCW79—Continued

11-30-98 1204 9.3 300 -44.2 -6.72

12-30-98 1044 3.9 316 -44.4 -6.98

1-27-99 1151 3.0 87 -48.7 -7.89

NCW80

2-20-98 1428 5.2 428 -47.4 -7.35

3-13-98 1428 5.9 432 -48.7 -7.39

4-08-98 1318 9.6 440 -51.0 -7.61

5-07-98 1326 12.3 431 -51.0 -7.58

5-26-98 1201 14.3 440 -49.6 -7.71

6-17-98 1242 17.6 416 -49.5 -7.45

7-16-98 1159 19.7 420 -49.3 -7.49

8-27-98 1244 19.7 438 -50.5 -7.70

9-23-98 1102 17.0 429 -49.7 -7.62

10-22-98 1131 14.4 433 -49.5 -7.70

11-30-98 1218 11.7 431 -50.4 -7.70

12-30-98 1054 8.7 417 -49.8 -7.54

1-27-99 1204 3.2 385 -48.4 -7.25

3-03-99 1329 5.7 398 -46.5 -7.31

MW11A

3-12-98 1146 13.5 325 -53.8 -8.53

5-05-98 0830 14.3 312 -52.8 -8.53

6-09-98 1031 13.4 337 -55.1 -8.71

7-10-98 1104 13.1 364 -53.2 -8.32

8-12-98 1142 13.0 343 -54.2 -8.54

9-16-98 1515 13.3 383 -57.3 -8.76

10-21-98 1108 13.2 384 -58.9 -8.98

11-16-98 1412 13.5 384 -58.4 -9.00

12-09-98 0850 14.0 310 -58.5 -8.93

3-03-99 1016 13.8 331 -58.7 -8.85

6-02-99 1055 13.9 333 -54.6 -8.34

MW92B

2-20-98 0935 15.7 144 -57.7 -9.12

3-12-98 1033 15.2 126 -56.9 -9.08

5-06-98 1425 16.7 129 -58.6 -9.14

6-09-98 1124 15.8 146 -57.4 -9.04

7-10-98 1218 15.9 143 -58.1 -9.05

8-12-98 1105 15.9 150 -57.2 -9.11

9-16-98 1435 16.1 150 -57.9 -9.09

10-21-98 1158 15.4 148 -57.7 -9.00

11-16-98 1510 15.1 152 -58.8 -9.14

12-15-98 1525 15.4 125 -57.9 -9.11

3-03-99 1058 15.3 145 -58.9 -9.02

6-02-99 1010 16.0 152 -58.4 -9.12

Date Time

Temperature

( ̊C)

Specific

conductance

(μS/cm)

δD

(per

mil)

δ18O

(per

mil)

Appendix C. Temperature, specific conductance, delta deuterium, and delta oxygen-18 in water, February 1998 to July 1999, 

South Pond of Lake Cochituate, Natick, Massachusetts—Continued