Sediment Quality and Polychlorinated 

Biphenyls in the Lower Neponset River, 

Massachusetts, and Implications for 

Urban River Restoration

By Robert F. Breault, Matthew G. Cooke, and Michael Merrill

Prepared in cooperation with the

Massachusetts Executive Office of Environmental Affairs

Department of Fish and Game Riverways Program, and the 

U.S. Environmental Protection Agency

Scientific Investigations Report 2004-5109 

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

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

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

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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

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

endorsement by the U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Breault, R.F., Cooke, M.G., and Merrill, Michael, 2004, Sediment quality and polychlorinated biphenyls in the lower 

Neponset River, Massachusetts, and implications for urban river restoration: U.S. Geological Survey Scientific 

Investigations Report 2004-5109, 48 p.
 iii

Contents

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

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

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Study Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Water Depths and Sediment Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Sample-Collection Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Sample-Collection Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Chemical Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Data-Analysis Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Bias and Variability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Data Representativeness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Sediment Quality and Implications for River Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Concentrations of Elements Compared to Background Concentrations . . . . . . . . . . . . . . . . . . . . . 18

Organic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Comparison of Sediment Chemistry in the Lower Neponset River to that in 

Other Urban Rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Contaminated Bottom-Sediment Toxicity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Benthic Organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Comparison between Upstream and Downstream Sediment Chemistry. . . . . . . . . . . . . . . . . . . . . 30

Implications of Sediment Contamination for Waste Disposal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Polychlorinated Biphenyls in Water, Sediment, and Fish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Polychlorinated Biphenyl Source Identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Polychlorinated Biphenyl Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Aquatic-Life Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Human Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Figures

1. Map showing the study area, sediment-grab and sediment-core sampling 

locations, and the locations where PISCES polychlorinated biphenyl passive 

samplers were deployed, lower Neponset River, Massachusetts . . . . . . . . . . . . . . . . . . . . . . . . .2

2, 3. Photographs showing: 

2. Walter Baker impoundment, lower Neponset River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

3. Tileston and Hollingsworth Dam and impoundment, lower Neponset River . . . . . . . . . . .5

4. Schematic of a typical polychlorinated biphenyl : A, more substituted; and 

B, less substituted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

5. Photograph showing former Jenkins Dam impoundment, known as the braided 

channel, lower Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
iv 

6–8. Maps showing:

6. Water depths and sediment thickness measured in the Walter Baker 

impoundment, lower Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

7. Water depths and sediment thickness measured in the Tileston and 

Hollingsworth impoundment, lower Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

8. Sediment thickness measured in the braided channel, lower Neponset River . . . . . . . 11

9. Sediment-core log showing visual interpretation of sediment type and length of 

sediment cores collected from the lower Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

10–12. Graphs showing:

10. Concentrations of A, elements; and B, organic compounds (by type) measured 

in grab and core samples collected from the lower Neponset River . . . . . . . . . . . . . . . . 20

11. Population statistics for element and organic compound concentrations 

measured in grab samples collected from the lower Neponset River in 

comparison to other urban rivers in the United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

12. Relative amount of enrichment of elements and organic compounds from 

three urban rivers tributary to Boston Harbor—the lower Neponset River, the 

upper Mystic River, and the lower Charles River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

13. Bar chart showing estimated sediment toxicity to Hyalella azteca and 

Chironomus spp. with respect to consensus-based freshwater sediment-quality 

guidelines from samples collected from the lower Neponset River . . . . . . . . . . . . . . . . . . . . . . 29

14–16. Graphs showing:

14. Comparison of concentrations of selected A, elements; and B, organic 

compounds in sediment collected from the lower Neponset River with 

human-health guidelines for direct contact with and incident ingestion of 

contaminated soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

15. Sediment-type summary statistics for grab and core samples collected from 

the lower Neponset River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

16. Comparison of elements and organic compound concentrations in sediment 

collected from the lower Neponset River with Commonwealth of 

Massachusetts guidelines for the reuse and disposal of contaminated soil . . . . . . . . . 33

17. Bar chart showing polychlorinated biphenyl congener patterns of commercially 

available Aroclors by International Union of Pure and Applied Chemistry 

number (IUPAC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

18. Graph showing differences in polychlorinated biphenyl congener patterns between 

duplicate samples collected from the lower Neponset River. . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

19–24. Bar charts showing: 

19. Polychlorinated biphenyl concentrations and between-station root mean 

square differences of congener patterns measured in PISCES passive 

samplers, Mother Brook and the Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

20. Average relative polychlorinated biphenyl congener concentrations in selected 

PISCES samples collected from the lower Neponset River by International 

Union of Pure and Applied Chemistry (IUPAC) number . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

21. Average relative polychlorinated biphenyl congener concentrations in 

selected grab samples collected from the lower Neponset River by 

International Union of Pure and Applied Chemistry (IUPAC) number. . . . . . . . . . . . . . . . 41

22. Average relative polychlorinated biphenyl congener concentrations in 

selected core samples collected from the lower Neponset River by 

International Union of Pure and Applied Chemistry (IUPAC) number. . . . . . . . . . . . . . . . 42
 v

23. Estimated water-column concentrations of total polychlorinated biphenyls 

(ΣPCBs) collected from the lower Neponset River in comparison to U.S. 

Environmental Protection Agency freshwater continuous chronic 

criteria for ΣPCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

24. Toxic equivalency of total polychlorinated biphenyls relative to 2,3,7,8-

tetrachlorodibenzo-p-dioxin (TCDD) collected from the lower Neponset River . . . . . . .45

Tables

1. Sediment-grab and sediment-core sampling locations and time of sampling, from 

the Walter Baker impoundment, Tileston–Hollingsworth impoundment, and 

braided channel, lower Neponset River, Massachusetts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

2. Laboratories and analytical methods used in this study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

3. Location and details of polychlorinated biphenyl sampling by means of PISCES 

passive samplers, lower Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

4. Common sources and (or) uses of selected constituents typically found in rivers 

that drain urban and industrial areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

5. Estimated number of samples needed to calculate average concentrations within 

a 25-percent range of acceptable error for elements, and within a 50-percent range

of acceptable error for organic compounds, with 90-percent confidence for the 

lower Neponset River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

6. Median background concentrations of elements measured in sand, silt, and clay

samples collected from Massachusetts, Connecticut, Maine, New Hampshire,

New York, and Rhode Island as part of the National Uranium Resource Evaluation

Hydrogeochemical and Stream Sediment Reconnaissance Program . . . . . . . . . . . . . . . . . . . .19

7. Measured total polychlorinated biphenyl (ΣPCB) concentrations, by congener 

analysis in PISCES samplers, estimated ΣPCB water-column concentrations, and 

estimated ΣPCB concentrations in fish tissue, lower Neponset River . . . . . . . . . . . . . . . . . . . .38

8. Total polychlorinated biphenyl concentrations by congener analysis in selected 

grab and core samples, lower Neponset River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
vi 

Conversion Factors and Abbreviations

Temperature in degrees Celsius (°C) may be converted to

degrees Fahrenheit (°F) as follows:

°F = 1.8°C + 32

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

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 

(NAD 83).

Concentrations of sediment-quality constituents are give in percent (%), parts per million (ppm), 

and parts per billion (ppb). Concentrations of water-quality constituents are given in nanograms 

per hexane sample (ng/hexane sample).

Multiply By To obtain

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

cubic yard (yd3) 0.7646 cubic meter (m3)

foot (ft) 0.3048 meter (m)

gallon (gal) 3.785 liter (L)

inch (in.) 25.4 millimeter (mm)

pound, avoirdupois (lb) 0.4536 kilogram (kg)

ACOE Army Corps of Engineers

BAF bioaccumulation factor

BCF bioconcentration factor

CCC continuous chronic criterion

DDD dichlorodiphenyldichloroethane

DDE dichlorodiphenyldichloroethylene

DDT dichlorodiphenyltrichloroethane

MDEP Massachusetts Department of 

Environmental Protection

FCM food-chain multiplier

FDA Food and Drug Administration

GPS global positioning system

GIS geographic information system

HSSR Hydrogeochemical and Stream 

Sediment Reconnaissance

IUPAC International Union of Pure and 

Applied Chemistry

MDC Metropolitan District Commission

MDL method detection limit

μm micrometer

mg/L milligram per liter

mL milliliter

MRL minimum reporting level

ng/L nanogram per liter

NAQWA National Water-Quality 

Assessment

NETLAB New England Testing Laboratory

NURE National Uranium Resource 

Evaluation

PAH polyaromatic hydrocarbon

PES performance evaluation sample

PCB polychlorinated biphenyl

PEC probable effect concentration

pg/L picogram per liter

RMSD root mean square difference

SOP standard operating procedure

TCLP toxicity characteristic leaching 

procedure

TCDD 2,3,7,8-tetrachlorodibenzo-pdioxin

TEQ toxic equivalency

TIN triangular irregular network

USEPA U.S. Environmental Protection 

Agency

USGS U.S. Geological Survey
Sediment Quality and Polychlorinated 

Biphenyls in the Lower Neponset River, 

Massachusetts, and Implications for 

Urban River Restoration

By Robert F. Breault1, Matthew G. Cooke1, and Michael Merrill2

Abstract

Efforts to restore fish passage, habitat, and recreational 

use of the Neponset River, a tributary to Boston Harbor, 

Massachusetts, have raised concerns about the sediment, 

water, and biota quality of the river. Consequently, the U.S. 

Geological Survey, in cooperation with the Massachusetts 

Executive Office of Environmental Affairs Department of Fish 

and Game Riverways Program and the U.S. Environmental 

Protection Agency, studied sediment and water quality, with a 

specific focus on polychlorinated biphenyls, in the Neponset 

River.

Sediment samples were collected throughout the Neponset 

River and tested for elements and organic compounds including 

polyaromatic hydrocarbons, organochlorine pesticides, and 

polychlorinated biphenyls. Although enriched compared to 

background concentrations, sediment quality in the Neponset 

River was generally better than that of other urban rivers in the 

United States, except with respect to one constituent, polychlorinated biphenyls. Concentrations of lead, some polyaromatic 

hydrocarbons, and polychlorinated biphenyls in the sediment 

may be toxic to aquatic organisms and may pose a risk to human 

health. The sediment quality also fails to meet the minimum 

requirements set by the Commonwealth of Massachusetts for 

lined landfill disposal.

The locations of the source(s) of polychlorinated biphenyls 

to the Neponset River were determined by means of congener 

analysis from PISCES passive water-column samplers. The 

PISCES data indicate a sharp increase in polychlorinated 

biphenyl concentrations and a substantial shift in congener 

pattern downstream of one PISCES sampling location near 

Fairmont Avenue, Boston, Massachusetts. This result indicates 

that the area upstream of this sampling location may be the 

location of a historical source of polychlorinated biphenyls to 

the Neponset River. The present (2003) source to the water 

column may likely be PCB contaminated sediment.

Introduction

In 1998, then Department of the Interior Secretary Bruce 

Babbitt reported that throughout its history America had 

constructed 75,000 dams. As Babbitt wrote, this number is “the 

equivalent of one [dam being built] every day since Jefferson 

wrote the Declaration of Independence” (Babbitt, 1998). These 

dams were built for many reasons, including flood control, 

power production, navigation, and water supply, but many of 

them no longer serve their intended purpose. As the dams have 

aged, many have fallen into states of disrepair. An accidental 

breach or catastrophic failure of a dam may represent a 

substantial threat to public safety and to the environment in the 

vicinity of the dam.

Dams also interfere with many natural processes. Blocking 

fish passage is perhaps the most widely recognized environmental effect of dams, but the reservoirs that dams create also 

inundate wetlands and terrestrial ecosystems; with dams, rivers 

become fragmented, and peak flows and other hydrologic characteristics are changed. Dams also change sediment regimes in 

a river by trapping most of the sediment in impoundments 

behind the dams (Heinz Center, 2002). For these and other 

reasons, restoring urban rivers by removing dams has gained 

prominence as a viable alternative to other restoration strategies 

within the environmental community.

The Neponset River, a tributary to Boston Harbor, has 

been dammed in some fashion for the past 350 years (fig. 1). 

Historically, the river supported abundant populations of 

American shad (Alosa sapidissima) and river herring [alewife, 

(Alosa pseudoharengus)] and blueback herring (Alosa 

aestivalis). While the estuary continues to support an important 

fishery of rainbow smelt (Osmerus mordax), dams in the lower 

Neponset River block passage for shad and herring. Following 

a habitat survey in 1995, the Massachusetts Fisheries began to 

stock both shad and herring upstream of the two remaining 

dams in anticipation of fish passage (U.S. Army Corps of 

Engineers, written commun., 2002). 1U.S. Geological Survey.

2Massachusetts Executive Office of Environmental Affairs Department of 

Fish and Game Riverways Program.
2 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

BGY-114 BGY-114

M2Y-002 M2Y-002

M2Y-001 M2Y-001

BGY-113 BGY-113

BGY-111 BGY-111

BGY-110 BGY-110

BGY-109 BGY-109

BGY-108 BGY-108

BGY-114

M2Y-002

M2Y-001

BGY-113

BGY-111

BGY-110

BGY-109

BGY-108

Tileston and Hollingsworth Tileston and Hollingsworth 

Impoundment Impoundment

Tileston and Hollingsworth 

Impoundment

0 100 200 METERS 200 METERS

0 300 600 FEET 600 FEET 

0 100 200 METERS

0 300 600 FEET 

Fowl Meadow Nepons

et River

Mother Brook

Charles

Riv

er

Paul's Bridge

Fairmont Ave.

Reservation

Park

Martini Shell

Incinerator 

Road

BGY-107

BGY-106

BGY-105

BGY-104

BGY-102

BGY-101

BGY-100

BGY-103

Boston

Needham

Dedham

Westwood

Brookline

0 50 MILES

0 50 KILOMETERS

41 ̊30'

70 ̊00'

0 50 MILES

0 50 KILOMETERS

41 ̊30'

70 ̊00'

0 50 MILES

0 50 KILOMETERS

41 ̊30'

70 ̊00'

50,000

950,000

900,000

800,000

850,000

100,000 150,000 200,000

Study Area

250,000

300,000

73 ̊00'

42 ̊30'

42 ̊00'

71 ̊00'

72 ̊00'

MASSACHUSETTS

288,835

889,459

892,459

71O10'

42O

15'

42O

20'

Base map coverages from MassGIS, NAD 83 Lambert Conformal Polyconic projection, 

Massachusetts coordinate system mainland zone in meters

Figure 1. The study area, sediment-grab and sediment-core sampling locations, and the locations where PISCES polychlorinated biphenyl
Introduction 3

passive samplers were deployed, lower Neponset River, Massachusetts.
4 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Environmental managers and local advocates have 

proposed river-restoration efforts, such as channel restoration 

for habitat improvements and fish-passage alternatives, 

including the installation of engineered fishways, dam 

breaching, and removal of the most downstream dams on the 

lower Neponset River—the Walter Baker Dam (fig. 2) and the 

Tileston and Hollingsworth Dam (fig. 3; U.S. Army Corps of 

Engineers, written commun., 2002). Fish passage at these dams 

would open access to more than 17 mi of riverine habitat to 

migratory fish and help increase recreational use of the lower 

Neponset River, that section of the river from Fowl Meadow to 

the Walter Baker Dam in Milton, MA (U.S. Army Corps of 

Engineers, written commun., 2002).

Like most urban rivers in the Northeast, the Neponset 

River has a long industrial history. Industrialization and subsequent urbanization began in the Neponset River Basin as early 

as 1630. By the mid 1700s, the Neponset River drained one of 

the most heavily industrialized drainage basins in the Nation 

(U.S. Army Corps of Engineers, written commun., 2002). 

Industrial activity continued on the Neponset River until 1965, 

when the last major industrial facility relocated from the lower 

section of the river. This industrial past, combined with the 

urbanization that continues in the drainage basin, has likely 

contaminated bottom sediment throughout the river. 

The Neponset River has also been altered by flood-control 

measures. Most of these were implemented following the flood 

of 1955, which damaged many of the dams along the river and 

flooded much of southern New England (National Weather 

Service, 2002). After the flood, the Metropolitan District 

Commission (MDC) took ownership of the dams along the 

river; and by the late 1950s and early 1960s, the MDC had 

removed the two damaged Mattapan Dams and the Jenkins 

Dam. Around this same time, the MDC also rebuilt the Walter 

Baker and Tileston and Hollingsworth Dams. The MDC also 

straightened large river reaches, dredged and deepened the main 

channel, and armored and steepened the river banks with 

concrete and dredge spoils. More information concerning the 

history of flood control in the Neponset River Basin can be 

found on the World Wide Web at www.state.ma.us/dfwele/ 

River/NeponsetFish/Neponset-Historical-Photos.htm.

Figure 2. Walter Baker impoundment, lower Neponset River, Massachusetts.
Introduction 5

Figure 3. Tileston and Hollingsworth Dam and impoundment, lower Neponset River, 

Massachusetts.

Many studies have focused on the Neponset River, but few 

have addressed the question of its sediment quality. In 2002, the 

U.S. Army Corps of Engineers (ACOE) completed a study on 

the environmental effects of dam removal that focused on fish 

passage and habitat restoration (U.S. Army Corps of Engineers, 

written commun., 2002). Although this study was not primarily 

focused on sediment quality, two bottom-sediment cores were 

collected—one from the Walter Baker impoundment, and one 

from the Tileston and Hollingsworth impoundment. These 

bottom-sediment cores were enriched in many contaminants, 

most notably polychlorinated biphenyls (PCBs).

In any river, high concentrations above background levels 

of any elements and organic compounds in bottom sediment are 

a concern. As long as the contaminated sediments stay in the 

river, they remain non-point sources of contaminants. Through 

the processes of entrainment, resuspension, or chemical and 

biological transformation, the contaminated sediments may 

directly cause adverse biological effects to benthic (bottomdwelling) organisms, or indirectly affect pelagic (swimming) 

organisms (Baudo and Muntau, 1990; Sly, 1994). Consumption 

of these contaminated organisms can pose health risks to 

predatory fish, wildlife, and humans. Direct contact with or 

accidental ingestion of contaminated sediments may also pose 

health risks to humans.

Whether a river is restored through dam removal, other 

restoration efforts, or a combination of dam removal and other 

methods, data indicating the quality and quantity of bottom 

sediment are needed as the basis for informed sedimentmanagement decisions. These data are especially important in 

the case of dam removal. Because the physical and chemical 

properties of most contaminants favor solid phase (or sediment) 

associations (Horowitz, 1991), accumulated fine-grained 

bottom sediment usually are associated with contaminants. 

These contaminants include elements and organic compounds, 

which can enter a river through waste disposal, urban runoff, 

sanitary sewers, atmospheric deposition, and inadvertent spills. 

As the contaminated sediments travel downstream, they 

commonly accumulate in the slack water behind dams.
6 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Among the contaminants that may accumulate in sediments are PCBs, a group of organic compounds consisting of a 

biphenyl ring structure with 1 to 10 attached hydrogen or 

chlorine atoms (fig. 4). Individually, these different compounds 

are called congeners. These congeners are designated by an 

IUPAC (International Union of Pure and Applied Chemistry) 

number from 1 to 209 (also known as a PCB number), with 1 

indicating the lowest number of attached chlorine atoms (and 

the highest number of hydrogen atoms) and 209 the highest 

number of attached chlorine atoms (and the lowest number of 

hydrogen atoms). Specific mixtures of congeners, called 

Aroclors, were commercially manufactured and sold in the past. 

The composition of each Aroclor depended on the intended 

commercial use, but consisted of 60 to 90 congeners. These 

mixtures were identified by four digits (for example, 1232, 

1242, and 1254), which indicate the number of carbon atoms 

(the first two digits) and the percentage of chlorine substituted 

for hydrogen by weight (the second two numbers). For 

example, Aroclor 1254 contains 12 carbon atoms and 54 

percent substituted chlorine (Wisconsin Department of Natural 

Resources, 2000). Over 700,000 tons (1.4 billion pounds) of 

PCBs were sold in North America between the 1930s and the 

late 1970s (North American Commission for Environmental 

Cooperation, 1996).

Increased public dialogue about restoration of the 

Neponset River, combined with extensive dam construction, the 

long history of industrialization and urbanization along the 

river, and a preliminary knowledge of the occurrence and 

geographic distribution of sediment contamination, including 

PCBs, in the lower Neponset River, prompted this study of 

bottom sediment quality and quantity. The U.S. Geological 

Survey (USGS) completed this study during 2002–03 in 

cooperation with the Massachusetts Executive Office of 

Environmental Affairs Department of Fish and Game 

Riverways Program, and the U.S. Environmental Protection 

Agency (USEPA).

Purpose and Scope

 This report presents maps of water depths (or bathymetry) 

and thickness of impounded (and previously impounded) 

bottom sediment in the study area and describes the collection 

of 20 sediment-grab samples (top 4 in. of sediment), 31 

sediment-core samples (depth composited from 5–50 in., 

depending on the total depth of the sediment), and 12 measurements of PCB concentrations in the water column by means of 

a passive water-sampling system (PISCES). The report 

discusses the occurrence and geographic distribution of 

elements and organic compounds in the bottom sediment, as 

well as the potential adverse effects that these contaminants 

pose to aquatic organisms and humans. Throughout this report, 

the implications of these sediment data are discussed in terms of 

sediment-management options, such as sediment removal, and 

other river-restoration methods. Finally, this report details 

possible past and present source areas of polychlorinated 

biphenyls (PCBs) to the water, biota, and sediment of the lower 

Neponset River.

Study Methods

Water depths were measured in two impoundments 

(Walter Baker and Tileston and Hollingsworth). Sedimentthickness data were collected in these impoundments and 

within the former Jenkins Dam impoundment (referred to as the 

braided channel, fig. 5). Sediment-grab samples (top 4 in.) were 

collected randomly throughout the study area (table 1). 

Sediment cores (cores extended through the entire thickness of 

fine-grained sediment) were collected randomly within areas of 

sediment deposition just upstream of the Walter Baker and 

Tileston and Hollingsworth Dams and within the braided 

channel. All sediment samples were analyzed for elements, 

organic compounds, and physical properties (table 2).

Water Depths and Sediment Thickness

Water depths were measured on December 18 and 19, 

2002. For these 2 days, the discharge measured at the USGS 

streamflow-gaging station Neponset River at Milton Village, 

Massachusetts (011055566), averaged about 690 ft3/s. This 

amount is about four times the mean discharge (168 ft3/s) for 

this station, on the basis of 6 years of record. Water depths, 

however, were adjusted to full pool equivalence by subtracting 

the difference between the height of the water measured at the 

time of sampling and the dam elevation (head).

An echo sounder was used to measure water depths. 

Water-depth data were recorded simultaneously with positional 

data taken with a global positioning system (GPS). A steel rod, 

manually pushed into the bottom sediment, was used to collect 

sediment-thickness data. These manual sediment-thickness 

measurements were made at over 200 locations.

H

H

H

H

H

H H Cl

Cl Cl

Cl

Cl

C C

C

C C

C

C C

C

C C

C

C C

C

C C

C

C C

C

C C

C

Cl Cl

Cl Cl

Cl

H

H

H

A.

B.

Figure 4. Schematic of a typical polychlorinated biphenyl: A, more substituted; and 

B, less substituted.
Introduction 7

Figure 5. Former Jenkins Dam impoundment, known as the braided channel, lower 

Neponset River, Massachusetts.

A combination of the triangular irregular network 

(TIN) data model and topogrid functions of ESRI’s 

ARC/INFO geographic information systems (GIS) software 

(Environmental Research Institute, Inc., Version 7.11) were 

used to map channel morphology and bottom-sediment 

thickness from water-depth and sediment-thickness data. The 

TIN data model of ARC/INFO was used to determine water and 

sediment volumes (figs. 6–8). 

On average, water depth in the Tileston and Hollingsworth 

impoundment was the deepest measured in the Neponset River 

(about 8.8 ft), with a maximum depth of 15 ft. Maximum water 

depth in the Walter Baker impoundment was 9.3 ft, with an 

average depth of about 7.3 ft. Where measured, sediment 

thickness averaged from about 1.1 to 1.4 ft. Maximum measurements of sediment thickness were 5.8, 7.6, and 9.7 ft in the 

braided channel, and Walter Baker, and Tileston and 

Hollingsworth impoundments, respectively.

The braided-channel area of the Neponset River contains 

about 49 percent (or about 790,000 ft3) of the total bottomsediment volume measured, the Tileston and Hollingsworth 

impoundment contains about 38 percent (or about 620,000 ft3), 

and the Walter Baker impoundment contains about 13 percent 

(less than 210,000 ft3). This sediment volume (about 1.6 million 

ft3) is the equivalent of the volume of about 6,000 dump trucks, 

each containing 10 yd3.

Sample-Collection Design

In October 2002, sediment-grab samples (from the top 

4 in. of sediment) were collected (table 1; fig. 1) from 20 

randomly selected locations between Fowl Meadow and the 

Walter Baker Dam. A subroutine within ARC/INFO GIS 

software (Scott, 1990) was used to select the 20 sampling 

locations. A GPS unit was then used to navigate to these 

locations in the study area. For comparison to the samples 

collected within the study area, one sediment-grab sample, a 

composite of eight randomly collected dredge samples, was 

collected in the estuarine part of the lower Neponset River, just 

downstream of the Walter Baker Dam.

Sediment-core samples were collected between December 

2002 and February 2003 (table 1). A stratified randomsampling design, incorporating many of the same methods used 

to develop the sediment-grab sampling design, was used to 

collect the 31 sediment cores. Sediment-core sampling locations were limited to areas of sediment deposition just upstream 

of the Walter Baker and Tileston and Hollingsworth Dams and 

within the braided channel (fig. 1). A GPS unit was used to 

locate the sampling locations in the study area.
8 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Table 1. Sediment-grab and sediment-core sampling locations and time of sampling, from the Walter Baker impoundment, Tileston–

Hollingsworth impoundment, and braided channel, lower Neponset River, Massachusetts.

[Locations shown on figure 1. USGS, U.S. Geological Survey]

USGS

number Date and time State plane coordinates

Easting Northing

Sediment-Grab Sampling Locations

BGY-100 10-02-02 8:18 231,148.63 887,168.62

BGY-101 10-02-02 9:00 230,958.07 887,519.43

BGY-102 10-02-02 10:00 230,706.00 887,978.52

BGY-103 10-02-02 10:20 230,731.99 888,380.45

BGY-104 10-02-02 11:00 231,078.47 889,012.78

BGY-105 10-02-02 11:20 231,354.79 889,173.03

BGY-106 10-02-02 12:00 231,530.63 889,402.57

BGY-107 10-02-02 12:30 231,745.45 889,724.80

BGY-112 10-02-02 13:00 232,093.67 890,114.60

M2Y-003 10-02-02 15:30 232,401.00 890,087.87

BGY-115 10-02-02 16:00 232,487.18 890,108.19

BGY-116 10-02-02 12:30 233,296.44 890,561.52

M2Y-004 10-02-02 15:00 233,157.71 890,327.50

BGY-117 10-02-02 12:00 233,813.96 890,830.16

BGY-118 10-02-02 11:15 233,817.19 890,953.21

BGY-119 10-02-02 11:00 234,314.76 891,002.36

BGY-121 10-02-02 10:30 234,494.85 890,994.46

BGY-124 10-02-02 10:00 234,604.62 891,046.12

M2Y-012 10-02-02 9:30 235,025.07 891,176.71

BGY-133 10-02-02 9:00 235,501.41 891,208.91

Sediment-Core Sampling Locations

Walter Baker Impoundment

BGY-130 12-18-02 10:30 235,413.94 891,208.50

BGY-131 12-18-02 11:00 235,482.25 891,217.13

BGY-132 12-18-02 11:30 235,495.30 891,225.00

BGY-134 12-18-02 13:00 235,529.78 891,208.25

BGY-135 12-18-02 12:00 235,536.77 891,229.69

BGY-136 12-18-02 12:30 235,548.88 891,226.88

BGY-137 12-18-02 13:30 235,562.39 891,239.94

BGY-138 12-18-02 14:00 235,562.86 891,209.63

Sediment-Core Sampling Locations

Braided Channel

M2Y-005 1-09-03 10:00 234,365.02 890,968.13

BGY-120 1-08-03 10:45 234,429.17 891,022.19

M2Y-006 1-08-03 11:15 234,450.80 890,997.69

M2Y-007 1-08-03 12:15 234,503.42 891,012.81

BGY-122 1-08-03 12:45 234,556.05 891,066.13

BGY-123 1-09-03 10:35 234,592.81 891,117.31

BGY-125 1-09-03 11:00 234,664.19 891,139.69

M2Y-008 1-09-03 12:00 234,681.48 891,081.31

BGY-126 1-09-03 12:25 234,747.09 891,118.06

BGY-127 1-18-03 13:00 234,756.28 891,142.00

BGY-128 1-09-03 13:30 234,800.27 891,151.38

BGY-129 1-09-03 14:00 234,824.05 891,170.13

M2Y-009 2-11-03 11:45 234,880.64 891,127.25

M2Y-010 2-11-03 12:00 234,889.30 891,164.00

M2Y-011 2-11-03 11:00 234,995.98 891,181.31

Sediment-Core Sampling Locations

Tileston–Hollingsworth Impoundment

BGY-108 12-19-02 10:30 231,991.86 890,013.13

BGY-109 12-19-02 11:30 232,021.58 890,061.19

BGY-110 12-19-02 12:00 232,046.48 890,090.88

BGY-111 12-19-02 12:30 232,058.72 890,102.25

BGY-113 12-19-02 13:00 232,098.48 890,116.69

M2Y-001 12-19-02 13:15 232,120.33 890,110.13

BGY-114 12-19-02 14:15 232,129.95 890,144.19

M2Y-002 12-19-02 13:45 232,130.39 890,118.00

USGS

number Date and time State plane coordinates

Easting Northing
Introduction 9

Table 2. Laboratories and analytical methods used in this study.

[NETLAB, New England Testing Laboratory; TCLP, toxicity characteristic leaching procedure; USEPA, U.S. Environmental Protection Agency; USGS, U.S. 

Geological Survey]

Constituent Sample type Laboratory Analytical technique

Inorganic elements Bottom sediment XRAL Inductively coupled plasma mass spectroscopy

TCLP trace metals Bottom sediment USEPA Inductively coupled plasma mass spectroscopy

Reactive sulfides Bottom sediment NETLAB Titrimetry

Polyaromatic hydrocarbons Bottom sediment USEPA Gas chromatography with electron-capture detection

Hydrocarbons Bottom sediment USEPA Gas chromatography with flame-ionization detection

Organochlorine pesticides Bottom sediment USEPA Gas chromatography with electron-capture detection

Polychlorinated biphenyls Bottom sediment USEPA Gas chromatography with electron capture

Polychlorinated biphenyls Bottom sediment AXYS Analytical Low-resolution quadrupole mass selective detection

Polychlorinated biphenyls Hexane AXYS Analytical Low-resolution quadrupole mass selective detection

Grain-size distribution Bottom sediment USGS Gravimetry

Total solids Bottom sediment USEPA Gravimetry

235,267 235,417 235,567

891,121

891,271

0

0 150

50 100 METERS

300 FEET

2

4

6

2

2

2

BOTTOM ELEVATION, IN FEET ABOVE

NGVD 29

14–12.1

12–10.1

10–8.1

LINE OF EQUAL THICKNESS OF

IMPOUNDED SEDIMENT—Interval is 2 feet.

EXPLANATION

2

Base map from MassGIS digital orthophoto, Massachusetts coordinate system, 

in meters 1:5,000, NAD 83, Zone 19

8–6.0

Less than 6

Figure 6. Water depths and sediment thickness measured in the Walter Baker impoundment, lower Neponset River, 

Massachusetts.
10 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

4

2

2

889,714

890,114

231,686 232,086

100 METERS

300 600 FEET

0

0

BOTTOM ELEVATION, IN FEET 

ABOVE NGVD 29

36–32.1

32–28.1

28–24.1

24–22

LINE OF EQUAL THICKNESS OF 

IMPOUNDED SEDIMENT—Contour

interval is 2 feet.

2

Base from MassGIS digital orthophoto, Massachusetts coordinate 

system, in meters 1:5,000, NAD 83, Zone 19

EXPLANATION

Figure 7. Water depths and sediment thickness measured in the Tileston and Hollingsworth impoundment, 

lower Neponset River, Massachusetts.

In August 2002, samples for analysis of PCBs in the water 

column were collected according to a deterministic sampling 

design (fig. 1). PCB passive samplers (PISCES) were placed at 

12 locations throughout the study area. Samplers were also 

placed upstream and downstream of Mother Brook, as well as 

within Mother Brook, a tributary to the Neponset River that 

diverts water from the Charles River and a possible source of 

PCBs (fig. 1).

Sample-Collection Techniques

In water deeper than about 5 ft, a stainless-steel Eckman 

dredge was used to collect sediment-grab samples. In water less 

than 5 ft deep, a stainless-steel scoop or stainless-steel spoon 

was used to collect sediment-grab samples. A minimum of three 

samples were collected at each sampling location to better 

characterize conditions at the site (Baudo and Mantau, 1990). 

Any water trapped in either the dredge, scoop, or spoon was 

decanted off after most of the fines had settled. The top 4 in. (if 

available) of the sample was either removed from the dredge or 

scooped from the sediment surface and placed in a pre-cleaned 

stainless-steel bowl and homogenized with a stainless-steel 

spatula in the field, with the exception of the sediment-grab 

sample collected downstream of the Walter Baker Dam. This 

sample was scooped from the dredge by using a nylon spoon 

and homogenized in a pre-cleaned Teflon bag. 

After homogenization, sediment-grab samples were sieved 

through a 6-mm sieve (the sediment-grab sample collected 

downstream of the Walter Baker Dam was not sieved). Subsamples were collected, placed in pre-cleaned containers, and 

stored on ice for overnight delivery to the appropriate laboratory (table 2). In the field, all sediment-sampling equipment 

was cleaned between samplings by scrubbing the equipment 

with a nylon brush and phosphate-free detergent and then 

copiously rinsing it with native water.
Introduction 11

2

3 3

1 2

1 2

32

4

2

2 3 3

3

1

12

3

4

5

4

2

4

3

3

1

1

3

2

3

2

3

2

3

2

1

2

4 3

1

3

2

1

1

2

1

4

4 2

3

1

2

2

2

3

3

3

2

2

2

2

2 1

1

1

1

2 3

4

2

3

1

1

4

1

1

1

3

3

3

3 3

3 2 2 1

12

2 3

1

EXPLANATION

WATERLINE OF EQUAL THICKNESS OF FORMERLY IMPOUNDED SEDIMENT—Contour interval is 1 foot.

234,435 234,635 234,835 235,035

891,159

890,959

Base map coverages from MassGIS, NAD 83, Lambert Conformal Polyconic projection, Massachusetts coordinate system mainland zone in meters

0

0

300 FEET

100 METERS

Figure 8. Sediment thickness measured in the braided channel, lower Neponset River, Massachusetts.
12 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Because of the large range of sediment sizes in the 

lower Neponset River (silt and clay to boulders), sieving was 

necessary. Sieving allows for more reproducible sampling 

results and data comparability among sampling locations 

(Haökanson, 1984). Use of a relatively large sieve size (6 mm) 

compared to other sieving procedures ensures that chemical 

data represent the “true” chemistry of the sample as opposed to 

the chemistry of a particular narrow size fraction (for example, 

less than 63 micrometers); secondly, ACOE has predicted that 

sediment of about 6 mm in size or smaller may be resuspended 

following dam removal (U.S. Army Corps of Engineers, written 

commun., 2002); and finally, because sediment-toxicity 

guidelines are developed on the basis of chemical data for 

unsieved samples, comparison with finely sieved data may be 

inappropriate.

A hand corer with a disposable 2.5-in. inside-diameter 

Lexan core barrel was used to collect sediment cores. The core 

barrel was pushed or hammered into the sediment until it could 

be driven no farther. The cores were then retrieved, capped, 

labeled, and transported upright to the USGS laboratory in 

Northborough, Massachusetts. They were visually inspected, 

and the lithologic characteristics (fig. 9) were logged in a 

notebook. The cores were then extruded into pre-cleaned Teflon 

bags and homogenized with a nylon spoon. Subsamples were 

collected and placed in pre-cleaned containers for delivery to 

the appropriate laboratory (table 2). Lexan core barrels were 

rinsed with native water before samples were taken. Teflon bags 

were pre-cleaned by rinsing with methanol, 5-percent 

hydrochloric acid, and copious amounts of deionized water.

The methods of Litten and others (1993) were used to 

collect PCB samples with PISCES passive water-column 

samplers. The samplers were filled with 0.2 L of hexane and 

hung from buoys that were anchored to the river bottom. After 

about 17 days, the samplers were collected, and their contents 

were poured into 250-mL amber glass bottles (table 3). Before 

the samplers were deployed, they were rinsed with phosphatefree detergent followed by a deionized water rinse; they then 

were allowed to air dry. When dry, the samplers were rinsed 

with acetone then rinsed three times with hexane. The 

polyethylene membranes were cleaned by 7-hr Soxhlet 

extraction (solid-liquid extraction using Soxhlet apparatus) 

with hexane. Once cleaned, the samplers were wrapped in 

hexane-rinsed aluminum foil until they were deployed.

Chemical Analysis

Sediment samples were analyzed for a suite of elements 

and organic compounds commonly found in rivers that drain 

historically industrial and urban watersheds (table 4). XRAL 

Laboratory of Ontario, Canada, analyzed the sediment samples 

by inductively coupled plasma emission spectroscopy for trace 

elements and by infrared spectroscopy for total organic carbon. 

The USEPA New England Regional Laboratory of Chelmsford, 

Massachusetts, also analyzed sediment samples for a suite of 

organic compounds, including PCBs and organochlorine 

pesticides; five sediment-grab samples were analyzed for 

polyaromatic hydrocarbons (PAHs). In addition, the USEPA 

also tested selected sediment cores for toxicity characteristic 

leaching procedure (TCLP) metals, including arsenic, barium, 

cadmium, chromium, lead, mercury, selenium, and silver.

The New England Testing Laboratory (NETLAB) of 

North Providence, Rhode Island, used methods in accordance 

with Massachusetts methodology (Massachusetts Department 

of Environmental Protection, 1998) to analyze sediment-core 

samples for extractable petroleum hydrocarbons. The single 

longest cores from each impoundment and from the braided 

channel were selected for reactive sulfide analysis, which was 

completed by NETLAB. Grain-size distributions were 

measured by the USGS Sediment Laboratory in Louisville, 

Kentucky.

AXYS Analytical Services of Sydney, British Columbia, 

Canada, completed analysis for PCBs. PISCES passive watercolumn samples were analyzed for 209 individual PCB compounds or congeners. Aroclor concentrations were estimated 

from PCB congener data. Aroclors, mixtures of PCB congeners 

produced commercially and used by many industries, are the 

likely source of PCB congeners in the river today. Five sediment samples were also tested for PCB congeners by AXYS 

Analytical Services. Those samples were selected on the basis 

of PISCES PCB congener data and were from sample locations 

upstream and downstream of a suspected PCB source. Colman 

(2000) gives a detailed description of Aroclor and PCB 

congener chemical analysis.
Introduction 13

50

45

40

35

30

25

20

15

10

5

0

DEPTH, IN IN

CHE

S

BGY-135BGY-138BGY-136BGY-130

BGY-132

BGY-134

BGY-131BGY-137

BGY-123

M2 Y-009

M2Y-007

BGY-127

BGY-122

BGY-120

M2Y-010

BGY125M2YBGY-128 006M2Y-005

BM2Y-011

GY129

M2Y-008

BGY-126

BGY-114

BGY-111BGY-110

BGY-113M2Y-001

BGY-109

M2Y-002

BGY-108

Tileston and Hollingsworth Braided Channel Walter Baker

Figure 9. Sediment-core log showing visual interpretation of sediment type and length of sediment cores, collected from the 

lower Neponset River, Massachusetts.

Data-Analysis Methods

A variety of statistical methods was used to summarize 

sediment-quality data. Particular attention was given to censored data, defined as concentrations less than the detection 

limit. If constituent concentrations were added to give a total 

concentration, censored data were set to zero, with two exceptions: (1) all of the individual values to be added are censored, 

and (2) the values are being added in order to calculate the 

probable effect concentration (PEC) quotient. In these cases, 

(1) the reported detection limit was substituted for the censored 

data, (2) censored data were set equal to one-half the reported 

detection limit, unless all of the constituents added were 

reported as less than detection, in which case detection limits 

were added, respectively.

The USGS Method Detection Limit (MDL) program 

(part of S-Plus statistical software) was used to calculate 

summary statistics for constituents with censored data; a 

minimum of three observations are required to determine 

summary statistics by means of the MDL program, where a logprobability method is used for determining summary statistics. 

Helsel and Cohn (1998) describe these statistical methods in 

detail. In instances where the MDL program was not appropriate (for example, if there were fewer than three observations), simple population statistics were calculated with 

Microsoft Excel by using the methods described previously for 

censored data.
14 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Table 3. Location and details of polychlorinated biphenyl sampling by means of PISCES passive samplers, lower Neponset River, 

Massachusetts.

[PCB, polychlorinated biphenyls; °C, degrees Celsius; μS/cm, microsiemens per centimeter]

Station name Sample

number

Date and time 

deployed

Date and time

retrieved

Number

of days

deployed

Specific

conductance

(μS/cm)

Temperature

(°C)

State plane coordinates

Easting Northing

Paul’s Bridge 17 8-06-02 10:00 8-23-02 11:00 17.04 398 26.3 231,138.43 887,163.84

18 8-06-02 10:00 8-23-02 11:00 17.04 398 26.3

Martini Shell 19 8-06-02 10:30 8-23-02 11:30 17.04 567 26.6 230,732.06 888,141.67

20 8-06-02 10:30 8-23-02 11:30 17.04 567 26.6

Incinerator Road 23 8-06-02 11:30 8-23-02 12:20 17.03 441 29.0 227,337.28 889,542.08

24 8-06-02 11:30 8-23-02 12:20 17.03 441 29.0

Reservation Park 21 8-06-02 11:00 8-23-02 11:50 17.03 486 29.0 230,572.10 888,943.01

22 8-06-02 11:00 8-23-02 11:50 17.03 486 29.0

Fairmont Avenue 15 8-03-02 11:30 8-20-02 12:00 17.02 492 26.3 231,474.16 889,338.38

16 8-03-02 11:30 8-20-02 12:00 17.02 492 26.3

Tileston–Hollingsworth 

Dam upstream

13 8-03-02 10:55 8-20-02 11:45 17.03 503 25.9 232,116.15 890,101.56

14 8-03-02 10:55 8-20-02 11:45 17.03 503 25.9

Tileston–Hollingsworth 

Dam downstream

11 8-03-02 10:30 8-20-02 11:30 17.04 512 25.8 232,343.06 890,111.39

12 8-03-02 10:30 8-20-02 11:30 17.04 512 25.8

Kennedy playground 9 8-03-02 10:00 8-20-02 11:00 17.04 528 24.8 233,281.86 890,518.50

10 8-03-02 10:00 8-20-02 11:00 17.04 528 24.8

Ryan playground 7 8-03-02 8:30 8-20-02 10:45 17.09 540 24.1 234,089.63 891,067.10

8 8-03-02 8:30 8-20-02 10:45 17.09 540 24.1

Braided channel 5 8-03-02 9:05 8-20-02 10:30 17.06 538 24.3 234,555.98 891,005.87

6 8-03-02 9:05 8-20-02 10:30 17.06 538 24.3

Central Avenue 3 8-03-02 8:05 8-20-02 9:30 17.06 537 23.7 235,216.89 891,176.52

4 8-03-02 8:05 8-20-02 9:30 17.06 537 23.7

Baker Dam 1 8-03-02 7:45 8-20-02 9:00 17.05 520 24.6 235,565.80 891,213.10

2 8-03-02 7:45 8-20-02 9:00 17.05 520 24.6
Introduction 15

Table 4. Common sources and (or) uses of selected constituents typically found in rivers that drain urban and industrial drainage 

basins.

[BHC, 1,2,3,4,5,6-hexachlorocyclohexane; DDD, dichlorodiphenyldichloroethane; DDE, dichlorodiphenyldichloroethylene; 

DDT, dichlorodiphenyltrichloroethane]

Constituent Common source or urban uses

Inorganic Elements

Calcium auto exhaust, brakes, deicers

Magnesium .....do.

Phosphorus auto exhaust, fuel, lubricants, industrial and 

municipal runoff, wastewater

Potassium auto exhaust, deicers

Sodium .....do.

Antimony flame retardants, car batteries

Arsenic production of pesticides and herbicides

Barium motor vehicle brake linings

Beryllium ceramics, steel

Bismuth malleable irons, medicine

Cadmium Ni-Cd batteries, televisions

Chromium bricks, stainless steel

Cobalt jet engines, gas turbine engines

Copper boats, wires

Lanthanum battery electrodes, lighter flints

Lead batteries

Lithium .....do.

Manganese batteries, steel

Molybdenum aircraft parts, electrical parts

Nickel electronics, automobiles

Scandium high-intensity lights

Silver batteries, electronics, electrical parts

Strontium greases, pyrotechnics

Tin electronics, food packing, plumbing

Titanium automobiles, construction, plastics

Tungsten electrical parts, electronics

Vanadium batteries, electronics

Yittrium television sets

Zinc paints, plastic, textiles, electronics

Zirconium production of steel, photography

Polyaromatic Hydrocarbons

Acenaphthene automobile exhaust

Acenaphthylene production of dyes, plastics, pesticides

Anthracene .....do.

Benzo(a)anthracene automobile exhaust

Benzo(a)pyrene .....do.

Benzo(b)fluoranthene automobile exhaust

Benzo(ghi)perylene .....do.

Benzo(k)fluoranthene automobile exhaust, motor oil

Chrysene combustion of coal and petroleum products

Dibenzo(a,h)anthracene automobile exhaust

Polyaromatic Hydrocarbons—Continued

Fluoranthene automobile exhaust

Fluorene production of dyes, plastics, pesticides

Indeno(1,2,3-cd)pyrene automobile exhaust

Naphthalene coal tar, gasoline and diesel fuels

Phenanthrene production of dyes, plastics, pesticides, 

explosives, and drugs

Pyrene production of dyes, plastics, pesticides

Organochlorine Pesticides

4,4′-DDD pesticide for vegetables and tobacco

4,4′-DDE breakdown product of DDT

4,4′-DDT pesticide for livestock and crops

Aldrin termite control

Alpha Chlordane household insecticide

alpha-BHC insecticide

beta-BHC .....do.

delta-BHC .....do.

Dieldrin .....do.

Endosulfan I insecticide for crops

Endosulfan II .....do.

Endosulfan sulfate .....do.

Endrin .....do.

Endrin aldehyde pesticide to control birds, rodents, insects 

Endrin ketone .....do.

gamma Chlordane insecticide for fire-ant control, lawns

gamma-BHC pesticide for crops

Heptachlor insecticide for home, buildings, corn crops

Heptachlor epoxide .....do.

Methoxychlor insecticide for crops, livestock, household

Chlordane (technical) insecticide for home lawns, gardens, crops

Toxaphene pesticide for crops

Polychlorinated Biphenyls

Aroclor (1016) hydraulic fluids, rubber plasticizer, and 

adhesives

Aroclor (1221) .....do.

Aroclor (1232) .....do.

Aroclor (1242) .....do.

Aroclor (1248) .....do.

Aroclor (1254) .....do.

Aroclor (1260) .....do.

Aroclor (1262) .....do.

Aroclor (1268) .....do.

Constituent Common source or urban uses
16 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

The statistic root mean square difference (RMSD; eq. 1) 

was used to compare differences in PCB congener patterns, 

referred to as "fingerprints" (Colman, 2000). Individual 

congener concentrations at a given sampling location were first 

divided by summed congener concentrations at that sampling 

location, excluding censored values, to yield a normalized 

concentration (Colman, 2000). The RMSD is defined as the 

square root of the sum of squared differences of normalized 

concentrations of the same congener in two different samples. 

The two different samples could be duplicates collected at the 

same site or samples collected from adjacent sites. 

(1)

where

Differences in congener patterns between sampling locations 

were considered important when the differences in the RMSD 

values for samples collected in different sampling locations 

(intercomparison) were greater than differences in RMSD 

values for duplicate samples collected at the same sampling 

location (intracomparison).

Bias and Variability

Water-quality and sediment-quality data are subject to 

bias (or systematic error) and variability (or random error) 

during sample collection, processing, and analysis. The 

nature and magnitude of bias and variability can be determined 

by analysis of quality-control samples including blanks, 

field duplicates, laboratory duplicates, matrix spikes, matrixspike duplicates, and performance-evaluation samples (PES). 

With a few exceptions, bias and variability in this study 

were generally within acceptable limits (Charles Porfert, 

U.S. Environmental Protection Agency, written commun., 

2002). Most notable is the potential contamination bias 

introduced by the equipment used for collection and processing 

of sediment-grab samples (stainless-steel dredge, bowl, and 

spoon). The analysis of PES indicates that sediment-grab 

samples may be enriched in chromium (values not reported 

here) caused by contamination bias. As a result of these 

findings, the standard operating procedure (SOP) for sedimentcore sampling was changed to include scooping sediment from 

the dredge that does not come in contact with any part of the 

dredge, using a nylon spoon (opposed to a stainless-steel 

spoon), and compositing in disposable pre-cleaned Teflon bags 

(in place of the stainless-steel bowl). It should be noted that the 

amount of contamination bias was relatively low compared to 

the concentrations of chromium measured in the sediment cores 

(processed by using the modified procedure); however, to 

prevent misinterpretation of the data, chromium values were not 

included.

The variability caused by sample collection, processing, 

and analysis needs particular attention when PCB congener 

patterns are compared. For this reason, duplicate samples were 

collected at each of the PISCES-sampling stations. Generally, 

duplicate samples were in good agreement with respect to total 

PCB (ΣPCB) concentrations and congener patterns, with one 

exception. One of the duplicate samplers (sample number 7) 

installed at the Ryan Playground sampling location appeared to 

have leaked during deployment. This problem was noted during 

retrieval and likely caused the observed concentration difference between the samples. The congener patterns did not appear 

to be affected by this problem.

Data Representativeness

Because sediment-management decisions will likely be 

made by regulatory agencies on the basis of data presented in 

this report, the data must be representative of conditions present 

in the river. The data collected should accurately describe the 

physical and chemical conditions in the river, or else more data 

will need to be collected before sediment-management 

decisions can be made.

With some simple statistics and the acceptance of a few 

general assumptions, equation 2 (Haökanson, 1984) can be used 

to test data representativeness. These assumptions include: 

(1) the variability of the collected data approximates the “true” 

variability; (2) sediment-sampling techniques and analysis were 

adequate (that is, bias and variability were within acceptable 

limits); and (3) physical and chemical data are approximately 

normally distributed. After accepting these assumptions, the 

number of sediment samples needed to calculate a representative mean value (for those properties and constituents listed in 

table 2) were calculated at the 90-percent confidence level, with 

equation 2 (table 5):

(2)

where

RMSD is the root mean square difference;

A and B are normalized concentrations of the same 

congener in two different samples; and

n is the number of congener pairs compared.

RMSD ∑( ) A B– 2

n ------------------------

0.5

=

Ni is the number of data (or samples) for property or 

constituent i;

tc is the value of student’s t for desired two-sided 

confidence interval c with n-1 degrees of freedom 

where n is the number of samples;

sx,i is the measured variance for property or constituent i; 

is the average concentration measured of property or 

constituent i; and

y is the acceptable error, in percentage of the mean; 

25 percent is considered acceptable for elements, and 

50 percent is considered acceptable for organic 

compounds.

Ni

tc s × x i ,

y x × i

----------------- ⎝ ⎠ ⎛ ⎞ 2

= + 1

xi
Introduction 17

Table 5. Estimated number of samples needed to calculate average concentrations within a 25-percent range of acceptable error for 

elements, and within a 50-percent range of acceptable error for organic compounds, with 90-percent confidence for the lower Neponset 

River, Massachusetts.

[BHC, 1,2,3,4,5,6-hexachlorocyclohexane; DDD, dichlorodiphenyldichloroethane; DDE, dichlorodiphenyldichloroethylene; DDT, dichlorodiphenyltrichloroethane; T&H, Tileston–Hollingsworth]

Constituent Sediment

grab

Sediment cores

Walter

Baker

Braided

channel T&H

Total organic carbon 62 14 3 3

Inorganic Elements

Calcium 5 4 2 2

Magnesium 7 3 2 3

Sodium 6 2 9 13

Potassium 4 4 7 11

Phosphorus 14 18 3 2

Aluminum 5 22 3 5

Antimony 1 1 14 1

Arsenic 125 30 5 5

Barium 8 9 3 5

Beryllium 4 8 4 5

Bismuth 1 1 1 1

Cadmium 42 35 6 4

Chromium 22 5 14 7

Cobalt 7 4 3 4

Copper 45 20 4 3

Iron 6 2 5 4

Lanthanum 3 4 2 3

Lead 50 23 4 3

Lithium 9 9 3 5

Manganese 30 3 11 3

Molybdenum 42 14 24 19

Nickel 10 7 181 133

Scandium 6 12 3 6

Silver 15 19 5 8

Strontium 5 7 2 3

Tin 98 143 5 3

Titanium 3 2 3 2

Tungsten 1 1 1 1

Vanadium 5 34 3 2

Yittrium 4 6 2 4

Zinc 29 31 2 3

Zirconium 5 3 5 6

Polyaromatic Hydrocarbons

Acenaphthene 24 50 3 7

Acenaphthylene 12 35 19 50

Anthracene 16 116 2 3

Benzo(a)anthracene 13 13 3 7

Benzo(a)pyrene 13 20 3 14

Benzo(b)fluoranthene 14 13 4 2

Benzo(ghi)perylene 13 1 4 116

Benzo(k)fluoranthene 12 27 3 56

Chrysene 12 116 3 50

Dibenzo(a,h)anthracene 13 1 1 1

Fluoranthene 12 5 3 4

Fluorene 15 10 4 50

Indeno(1,2,3-cd)pyrene 13 1 2 1

Naphthalene 13 1 148 1

Phenanthrene 20 5 3 4

Pyrene 11 4 2 4

Organochlorine Pesticides

4,4′-DDD 1 10 6 7

4,4′-DDE 1 8 23 6

4,4′-DDT 1 116 3 1

Aldrin 1 1 1 1

Alpha Chlordane 1 116 11 2

alpha-BHC 1 1 1 1

beta-BHC 1 1 1 1

delta-BHC 1 1 1 1

Dieldrin 1 1 1 1

Endosulfan I 1 1 1 1

Endosulfan II 1 1 1 1

Endosulfan sulfate 1 1 1 1

Endrin 1 116 1 89

Endrin aldehyde 1 1 1 1

Endrin ketone 1 1 1 1

Constituent Sediment

grab

Sediment cores

Walter

Baker

Braided

channel T&H
18 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

In general, enough data were collected and data were 

representative (the data can be used to calculate a mean value at 

the 90-percent confidence level) of those areas for which cores 

were collected. Similarly, the number of sediment-grab samples 

generally is appropriate, with a few notable exceptions. The 

combination of good (bias and variability within acceptable 

limits) and representative (enough or sufficient amount) 

sediment-quality data, combined with appropriate sampling 

techniques and data-analysis methods, indicate that the data 

interpretation will yield meaningful results that can be used to 

make sediment-management decisions when options for river 

restoration are considered.

Sediment Quality and Implications for 

River Restoration

Before sediment-management decisions are made and 

river-restoration efforts begin, it is useful to define objectives 

for managing and monitoring sediment quality. By determining 

these objectives, environmental managers can make more 

informed decisions about dam removal and sediment 

management. Sediment-quality objectives may include 

reducing element and organic-compound concentrations to 

“background” concentrations (those concentrations not affected 

by anthropogenic activities), or to levels equal to or below other 

criteria. Comparisons between measured bottom-sediment 

contaminant concentrations and background concentrations, 

concentrations from other urban rivers, and concentrations 

established by sediment-quality guidelines may also help 

decisionmakers determine the best approach to managing 

sediment for river restoration.

Concentrations of Elements Compared to 

Background Concentrations

With the concerns described above in mind, concentrations of elements measured in sediment samples from the lower 

Neponset River were compared to median concentrations 

measured in sediment collected from streams in Connecticut, 

Maine, Massachusetts, New Hampshire, New York, and Rhode 

Island. These sediment samples were collected between 1977 

and 1980 as part of the National Uranium Resource Evaluation 

(NURE) program, specifically the Hydrogeochemical and 

Stream Sediment Reconnaissance (HSSR) program (Smith, 

1998) and reanalyzed by the National Geochemical Survey 

using modern (2000) methods (Grossman, 1998; U.S. 

Geological Survey, 2003). A brief history of this program, as 

well as tabulated data, are available on the World Wide Web 

(U.S. Geological Survey, 2004).

The NURE HSSR program SOP instructed researchers to 

collect bottom-sediment samples from small "uncontaminated" 

streams (Ferguson and others 1977). In other words, samples 

were purposely collected in areas assumed to be unaffected by 

humans; therefore, element concentrations measured from these 

sediment samples may approximate "non-urban background" 

concentrations of New England streams.

Table 5. Estimated number of samples needed to calculate 

average concentrations within a 25-percent range of acceptable 

error for elements, and within a 50-percent range of acceptable 

error for organic compounds, with 90-percent confidence for the 

lower Neponset River, Massachusetts.—Continued

[BHC, 1,2,3,4,5,6-hexachlorocyclohexane; DDD, dichlorodiphenyldichloroethane; DDE, dichlorodiphenyldichloroethylene; DDT, dichlorodiphenyltrichloroethane; T&H, Tileston–Hollingsworth]

Constituent Sediment

grab

Sediment cores

Walter

Baker

Braided

channel T&H

Organochlorine Pesticides—Continued

gamma Chlordane 1 1 9 1

gamma-BHC 1 1 1 1

Heptachlor 1 1 1 1

Heptachlor epoxide 1 1 1 1

Methoxychlor 137 1 1 1

Polychlorinated Biphenyls

Aroclor (1016) 1 1 1 1

Aroclor (1221) 1 1 1 1

Aroclor (1232) 1 1 1 1

Aroclor (1242) 30 17 7 2

Aroclor (1248) 1 1 1 1

Aroclor (1254) 23 16 6 3

Aroclor (1260) 18 19 5 3

Aroclor (1262) 1 1 1 1

Aroclor (1268) 1 1 1 1

Chlordane (technical) 1 1 1 1

Toxaphene 1 1 1 1
Sediment Quality and Implications for River Restoration 19

The samples collected by NURE HSSR and the samples 

collected in this study were processed by different methods 

(Ferguson and others 1977). The NURE HSSR samples were 

sieved with a 150-micrometer sieve; however, samples 

collected in this study were not sieved. This difference in 

methods could artificially bias concentrations because finegrained sediments have much larger surface area per unit 

weight than coarse sediments (Horowitz, 1991); therefore, finegrained sediments have more area for contaminants to adhere.

Enrichment factors were calculated by dividing element 

concentrations measured in bottom-sediment samples collected 

from the lower Neponset River by median background 

concentrations (table 6) measured as part of the NURE 

HSSR program. An enrichment factor greater than one indicates 

that the constituent concentration is greater than background 

concentration for that constituent; an enrichment factor less 

than one indicates the opposite. An enrichment factor of 

one indicates that the measured concentration is equal to 

background concentration.

There are, however, potential problems associated with the 

interpretation of calculated enrichment factors. Many natural 

factors can cause bottom sediments to be enriched with 

elements. Some of these factors include differential weathering 

(related to solubilities of individual elements), physical and 

chemical fractionation (for example, winnowing of fines), the 

mineralogy of atmospheric dust, and biogenic dust (Reimann 

and De Caritat, 2000); therefore, researchers may erroneously 

conclude that enrichment is caused by human activity, when it 

may actually be caused by natural processes. Nonetheless, 

enrichment factors might serve as a good first approximation to 

estimate how anthropogenic activity has affected sediment 

quality.

With the above discussion in mind, some element concentrations in grab samples, which represent more recent 

deposition, collected from the lower Neponset River were 

generally (at more than one-half of the sampling sites) enriched 

(fig. 10). Of particular concern are nickel (nickel concentrations 

were greater than the background concentration for nickel at 90 

percent of the grab-sampling locations), copper (85 percent), 

zinc (80 percent), lead (70 percent), and molybdenum (65 

percent) concentrations. Of those grab-sampling stations where 

samples had enrichment factors greater than one, the 

enrichment factors for copper, lead, and zinc averaged about 

four. The sample collected from location BGY-121 was, on 

average, the most enriched. Specifically, arsenic, copper, 

phosphorus, lead, molybdenum, nickel, and zinc concentrations 

were all higher than background concentrations at this station.

Table 6. Median background concentrations of elements 

measured in sand, silt, and clay samples collected from 

Massachusetts, Connecticut, Maine, New Hampshire, New York, 

and Rhode Island, as part of the National Uranium Resource 

Evaluation Hydrogeochemical and Stream Sediment 

Reconnaissance Program.

[--, no data; ppm, parts per million]

Constituent Concentration

Calcium, in percent 1.2

Magnesium, in percent .48

Sodium, in percent 1.4

Potassium, in percent 1.4

Phosphorus, in percent .06

Aluminum, in percent 5.1

Arsenic, in ppm 7.6

Barium, in ppm 345

Beryllium, in ppm 2

Chromium, in ppm 54

Cobalt, in ppm 8

Copper, in ppm 10

Iron, in percent 2.5

Lanthanum, in ppm 44

Lead, in ppm 30

Lithium, in ppm 15

Manganese, in ppm 815

Molybdenum, in ppm 1.2

Nickel, in ppm 12

Scandium, in ppm 9

Silver, in ppm 3

Strontium, in ppm 143

Tin, in ppm --

Titanium, in percent .53

Tungsten, in ppm --

Vanadium, in ppm 53

Yittrium, in ppm 23

Zinc, in ppm 48
20 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004

BGY-116

BGY-117BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012BGY-133

BGY-100BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112M2Y-003

BGY-115M2Y-004BGY-116

BGY-117

BGY-118

BGY-119

BGY-121BGY-124

M2Y-012BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

Arsenic (grab) Arsenic (core)

30

24

18

12

6

0

Cadmium (grab) Cadmium (core)

5

4

3

2

1

0

CONCENTRATION, IN PARTS PER MILLION

STATION NUMBER

STATION NUMBER

Chromium 

(core)

1,200

960

720

480

240

0

<3 <1

<1<1<1<1<1<1<1<1<1<1<1<1<1<1<1<1<1<1

<3<3<3<3<3<3<3<3<3<3<3<3<3<3<3

A.

Figure 10. Concentrations of A, elements; and B, organic compounds (by type) measured in grab and core samples collected from 

the lower Neponset River, Massachusetts (<, actual value is less than value shown).
Sediment Quality and Implications for River Restoration 21

A.—Continued

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

M2Y-003

BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012

BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012

BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105BGY-106

BGY-107

BGY-112

M2Y-003

BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012

BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

350

280

210

140

70

0

Copper (grab) Copper (core)

800

640

480

320

160

0

Lead (grab)

Nickel (grab)

Lead (core)

Nickel (core)

500

400

300

200

100

0

CONCENTRATION, IN PARTS PER MILLION

STATION NUMBER STATION NUMBER

Figure 10—Continued. Concentrations of A, elements; and B, organic compounds (by type) measured in grab and core samples 

collected from the lower Neponset River, Massachusetts (<, actual value is less than value shown).
22 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

A.—Continued

CONCENTRATION, IN PARTS PER MILLION

STATION NUMBER STATION NUMBER

0.25

0.20

0.15

0.10

0.05

0

1,200

960

720

480

240

0

1.5

1.2

0.9

0.6

0.3

0

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012

BGY-133

BGY-100

BGY-101

BGY-102BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119BGY-121

BGY-124

M2Y-012BGY-133

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012

BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

Phosphorus (grab) Phosphorus (core)

Zinc (grab) Zinc (core)

Silver (grab) Silver (core) <.2 <.2

Figure 10—Continued. Concentrations of A, elements; and B, organic compounds (by type) measured in grab and core samples 

collected from the lower Neponset River, Massachusetts (<, actual value is less than value shown).
Sediment Quality and Implications for River Restoration 23

B.

12,000

24,000

36,000

48,000

60,000

0

50,000

100,000

150,000

200,000

250,000

0

80

160

240

320

400

0

2,500

5,000

7,500

10,000

12,500

0

12,000

24,000

36,000

48,000

60,000

0

0

20

40

60

80

100

Polyaromatic Hydrocarbons (grab)

Polychlorinated Biphenyls (grab)

Chlordane (core)

CONCENTRATION, IN PARTS PER BILLION

Total Extractable Hydrocarbons (core)

Polychlorinated Biphenyls (core)

DDT (core)

*

*

** * ** * * ***** ** BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

M2Y-003

BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012

BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012BGY-133

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

M2Y-003BGY-115

M2Y-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

M2Y-012BGY-133

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

BGY-108 BGY-109 BGY-110 BGY-111 BGY-113 M2Y-001 BGY-114 M2Y-002 M2Y-005 BGY-120 M2Y-006 M2Y-007 BGY-122 BGY-123 BGY-125 M2Y-008 BGY-126 BGY-127 BGY-128 BGY-129 M2Y-009 M2Y-010 M2Y-011 BGY-130 BGY-131 BGY-132 BGY-134 BGY-135 BGY-136 BGY-137 BGY-138

<1,530<1,440<1,440

<220<220<220<220<220<220<220<220<220<220<220<220<220<220<220<220<220<220<30<30<30<30<30<30<30<30<30<30<30

<1,440<1,440<1,440

No sample

Figure 10—Continued. Concentrations of A, elements; and B, organic compounds (by type) measured in grab and core samples 

collected from the lower Neponset River, Massachusetts (<, actual value is less than value shown).
24 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Similar to the grab samples, core samples, which represent 

both recent and historical deposition, are enriched with 

elements. Cobalt, iron, lithium, magnesium, molybdenum, and 

potassium, whose concentrations in the core samples were 

similar to their concentrations in the grab samples, and all other 

elements in core samples with calculated enrichment factors 

greater than one were more enriched in core samples than they 

were in grab samples. In addition to potentially toxic chemicals 

that were enriched at more than one-half of the grab-sampling 

sites [nickel (100 percent of the sites), copper (100 percent), 

lead (100 percent), and zinc (100 percent)], chromium (100 

percent), cobalt (84 percent), molybdenum (100 percent), 

phosphorus (90 percent), and vanadium (68 percent) concentrations were enriched at more than one-half of the core-sampling 

sites. In the core samples, copper, on average, had the greatest 

degree of enrichment (average enrichment factor 13), followed 

by lead (12), and chromium (9.5).

Sediment cores collected from the Walter Baker impoundment were, on average, more enriched than sediment cores 

collected from the Tileston and Hollingsworth impoundment 

and the braided channel area. Of all samples from coring locations, the sample collected from location M2Y-006 (braided 

channel) was the most enriched. Specifically, chromium, 

cobalt, copper, phosphorus, molybdenum, nickel, lead, and zinc 

concentrations were all higher than background concentrations 

at this station.

Enrichment factors calculated for core samples were 

expected to be greater than those calculated for grab samples. 

Sediment cores were not collected throughout the study area. 

Instead, they were collected specifically from current and 

former impoundments where contaminants may have accumulated in fine-grained sediment. Additionally, because sediment 

cores indicate contamination that has accumulated over the 

history of an impoundment, the sediment cores collected from 

the lower Neponset River represent historical input of contaminants to the river, which may have been substantially greater 

than current (2003) inputs.

Simply comparing enrichment factors between grab 

samples and core samples, however, allows only generalizations about sediment quality in the study area. The comparison 

does not definitively indicate whether sediment quality is 

improving, getting worse, or remaining constant. If more 

definitive information about the history of sediment quality in 

the lower Neponset River is needed, then it would be necessary 

to complete a detailed paleolimnological study, which would 

include the collection, analysis, and dating of sediment cores; 

such work was beyond the scope of this study.

Organic Compounds

In contrast to the natural occurrence of elements in bottom 

sediments, many organic compounds in bottom sediment can 

originate only as a result of human activities. A clear understanding of detection rates, however, requires an understanding 

of the implications of the detection or non-detection of a 

chemical. Essentially, a detection indicates only that the 

constituent concentration is greater than the minimum reporting 

level (MRL) for a given analytical method. A non-detection, 

however, can indicate two possibilities: (1) the chemical is not 

present in the sample, or (2) the chemical is present in the 

sample at a concentration less than the MRL. Non-detection of 

a constituent, therefore, does not unequivocally demonstrate the 

absence of that constituent. Knowing this fact is particularly 

important when analyzing organic compound data. Because 

of interferences from coeluting compounds (compounds 

that cannot be separated from the analyte during the sample 

analysis), the MRLs for organic compounds can differ among 

some samples (even when the same method is used). This 

aspect of the MRLs can create a situation in which a constituent 

is undetected in one sample but detected in another. In this 

section, constituent concentrations reported as "less than 

detection" were considered to be absent from the sample. It is 

important to note that this assumption can substantially affect 

data interpretation.

With this in mind, a few of the PAHs for which analysis 

was completed were detected in all of the sediment samples 

(fig. 10). Similarly, PCBs3 were also detected in all but six grab 

samples. Of the PCB Aroclors tested, only three were detected: 

1242, 1254, and 1260. The other Aroclors were not detected in 

any of the samples. Except for two detections of Methoxychlor 

from grab samples collected at the most downstream part of the 

study area (stations BGY-124 and BGY-133), there were 

almost no detections of organochlorine pesticides in the grab 

samples. There were, however, many detections of these 

pesticides in the core samples. Most notably, Chlordane, DDT 

(dichlorodiphenyltrichloroethane), and its isomers DDD 

(dichlorodiphenyldichloroethane) and DDE (dichlorodiphenyldichloroethylene), were detected in many samples.

Concentrations of PAHs and PCBs in grab samples indicated great spatial variability. Among locations where organic 

compounds were detected in the grab samples, the Walter Baker 

impoundment yielded sediment with the highest concentrations 

of ΣPAHs (sum of 16 PAHs); high ΣPAHs in the Walter Baker 

impoundment may result because of the railroad bridge that 

spans the river just upstream of the impoundment. Interestingly, 

the ΣPCB concentration (sum of Aroclors 1242, 1254, and 

1260) measured in the grab samples collected at sampling 

location BGY-105 was the hightest from all of the sampling 

locations (Breault and Cooke, 2004). The PISCES watercolumn data collected from this stretch of the river also 

indicated a major source of PCBs.

Organic compound concentrations measured in core 

samples were generally much higher than concentrations 

measured in grab samples, the only exception being PAH 

concentrations, which were similar in core and grab samples. 

3Discussions about PCB Aroclors or ΣPCB concentrations (sum of 

Aroclors 1242, 1254, and 1260) in sediment samples refer to those PCBs 

analyzed by the U.S. Environmental Protection Agency, unless otherwise 

noted.
Sediment Quality and Implications for River Restoration 25

Similar PAH concentrations were expected because combustion sources continue to enrich the upper layers of sediment 

with PAHs (VanMetre and others, 2000).

On average, the sediment cores collected from the Tileston 

and Hollingsworth impoundment had the highest concentrations of ΣDDT (sum of DDT, DDE, and DDD) and ΣPCBs. 

Sediment cores collected from the braided channel, on average, 

had the highest concentrations of ΣChlordane (sum of alphaChlordane, gamma-Chlordane, and Chlordane-technical); 

however, sediment collected from the Walter Baker impoundment may have an average ΣChlordane concentration of equal 

or greater magnitude (estimated ΣChlordane concentration 

equal to less than 220 ppb).

Of all the core-sampling locations, location M2Y-010 

(braided channel) yielded sediment samples with the highest 

concentrations (about four times the average) of ΣDDT and 

ΣChlordane. The highest concentration of ΣPCBs (about four 

times the average) was detected in the sample from location 

M2Y-002 (Tileston and Hollingsworth impoundment).

As with the elements, the greater number of detections and 

higher concentrations of some organic compounds in core 

samples than in grab samples was expected. More detections 

were expected in cores because the cores were specifically 

collected from the impoundments, or former impoundments 

(for example, braided channel), which are depositional areas. In 

contrast, many of the surficial grab samples were collected from 

the higher velocity, free-flowing reaches, which tended to have 

particles of a coarser grain size. Also, the use and disposal of 

some organic compounds was more prevalent in the past than in 

recent years. In fact, general use of DDT was banned in the 

United States in 1972 (U.S. Environmental Protection Agency, 

1972). In 1988, the USEPA banned all uses of Chlordane 

(Agency for Toxic Substances and Disease Registry, 1995a). 

It is important to note that the history of sediment distribution in the Neponset River has been changed by dredging and 

channelization that took place in the 1950s and 1960s. Although 

beyond the scope of this study, it is likely that much of the early 

contamination (before the 1960s) is present in the banks and 

upland soils that surround the river, where the dredged sediment 

was disposed.

Comparison of Sediment Chemistry in the 

Lower Neponset River to that in Other 

Urban Rivers

One goal of river restoration is to restore a river to its 

"natural" state, the condition present before human activities 

affected the river. For this goal to be achieved, metal 

concentrations, for example, might be reduced to background 

levels, or all synthetic organic compounds might be removed 

from the river. This goal, however, is often unrealistic for rivers 

that drain heavily urban and industrial areas, such as the area 

drained by the Neponset River. In these cases, it may be 

important to define alternative goals for urban-river restoration. 

For example, the sediment quality of a particular river might be 

improved enough to match that of rivers in other similarly urban 

areas. 

To help define the effort needed to restore the sediment 

quality of the lower Neponset River to that of other urban rivers, 

concentrations of elements and organic compounds measured in 

grab samples collected from the Neponset River were compared 

with those collected from other urban rivers throughout the 

conterminous United States as part of the National WaterQuality Assessment (NAQWA) Program of the USGS (Rice, 

1999; fig. 11). Element concentrations in grab samples from the 

Neponset River are generally less than or equal to element 

concentrations in sediment collected from other urbanized, 

free-flowing rivers, with the exception of molybdenum and 

silver. Of the organic compound concentrations tested, concentrations of PAHs and PCBs were much higher in the samples 

from the Neponset River. In fact, median PCB concentrations 

measured in grab samples from the Neponset River are over 120 

times greater than those collected from the NAQWA urban 

rivers.

Although a comparison of contaminant concentrations 

from the Neponset River to those of other urban rivers from 

across the United States is valuable, a better comparison might 

be that of concentrations from the Neponset River to those of 

other urban rivers in Massachusetts. Better yet, a comparison 

of concentrations with those from the other two dammed 

rivers tributary to Boston Harbor would be the most valuable 

comparison (Breault and others, 2000). The element and 

organic compound concentrations in bottom sediment in the 

Neponset, upper Mystic, and lower Charles Rivers are shown in 

figure 12. Generally, element concentrations are lower in the 

Neponset River than in the lower Charles and upper Mystic 

Rivers. Organic compound concentrations in the Neponset are 

generally lower than in the lower Charles River and upper 

Mystic River, which has concentrations higher than the Charles 

River, although PCB concentrations are similar in the Charles 

and Neponset Rivers. No PCBs were detected in the upper 

Mystic River.

These comparisons are useful, but different sampling 

methods, sample preparation, and laboratory analytical 

methods also may contribute to the observed differences in 

concentrations, particularly in the case of the NAQWA 

samples. Sediment samples collected by the NAQWA Program 

for trace metal and organic compound analysis were sieved 

through a 63-mm sieve and a 2-mm sieve, respectively. Knowledge of this sieving is important because contaminants are 

often associated with the "finer" fraction; therefore, constituent 

concentrations measured by the NAQWA Program may be 

biased high relative to the Neponset River sediment samples. In 

addition, the chemical-analysis methodology used by the 

NAQWA Program includes a more robust digestion than that 

used in this study. A comparatively stronger digestion may also 

bias the NAQWA Program data high relative to the Neponset 

River sediment samples.
26 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

90th Percentile

75th Percentile

25th Percentile

Average

50th Percentile (Median)

10th Percentile

SILVER

ARSENIC

CADMIUM

CHROMIUM

COPPER

LEAD

NICKEL

PHOSPHORUS

ZINC

1,000

100

CONCENTRATIONS, IN PARTS PER MILLION

CONCENTRATIONS, IN PARTS PER BILLION

10

1

0.1

0.01

CHLORDANE

DDT

PAHs

PCBs

0.01

0.1

1

10

100

1,000

10,000

100,000

NS <

<

<

EXPLANATION

Number of sediment-grab samples

NS

NEPONSET RIVER

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

NO SAMPLE

LESS THAN DETECTION LIMIT

(NAQWA)

(NEP.)

(NAQWA)

(NEP.)

(NAQWA)

(NAQWA)

(NAQWA)

(NEP.)

(NAQWA)

(NEP.)

(NAQWA)

(NEP.)

(NAQWA)

(NEP.)

(NAQWA)

(NEP.)

(NAQWA)

(NEP.)

(NAQWA)

(NAQWA)

(NEP.)

(20)

(42)

(20)

(42)

(20)

(42) (20) (42)

(20)

(42)

(20)

(42)

(20)

(42)

(20)

(42)

(42)

(42)

(42)

(5)

(42)

(20)

(42)

(NEP.)

(NAQWA)

(NEP.) (42)

Figure 11. Population statistics for element and organic compound concentrations measured in grab samples collected from the 

lower Neponset River, Massachusetts, in comparison to other urban rivers in the United States.
Sediment Quality and Implications for River Restoration 27

1

0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0

Mystic River

Neponset River

Charles River

Benzo(a)pyrene

Benzo(k)fluoranthene

Benzo(a)anthracene

Benzo(ghi)perylene

Benzo(b)fluoranthene

Chrysene

Pyrene Fluoranthene

Anthracene Indeno(1,2,3-cd)pyrene

Phenanthrene

Naphthalene

Fluorene

Acenaphthylene

Acenaphthene

Mystic River

Neponset River

Charles River

4-4' DDD

Dibenzo(a,h)anthracene

Total PCBs

Total PAHs

0

1

0.80.60.4

0.2

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

0.8

0.60.4

0.2

0

1

Silver

Cadmium

Lead

Copper

Zirconium BariumScandium and Vanadium

Zinc

Tin

Cobalt

Strontium

Manganese

Titanium

Bismuth, Molybdenum,

Antimony, and Tungsten

Beryllium

Lanthanum

Yttrium

Arsenic

Nickel

Figure 12. Relative amount of enrichment of elements and organic compounds from three urban rivers tributary to Boston 

Harbor—the lower Neponset River, the upper Mystic River, and the lower Charles River, Massachusetts. 

Comparisons of data from grab samples collected from 

throughout the lower Neponset River (Paul’s Bridge to the 

Walter Baker Dam) and other urban rivers, including those 

tributary to Boston Harbor, give insight into the overall sediment quality of the Neponset River. Some parts of the river, 

however, are highly contaminated with PCBs, in particular the 

impounded and formerly impounded reaches. It may be useful, 

therefore, to compare PCB concentrations measured in the 

Neponset River sediment to concentrations in sediment from 

other rivers with known PCB contamination. One such river is 

the Housatonic River, in western Massachusetts. From 1932 to 

1977, at least 10,000 kilograms of PCBs were discharged to the 

Housatonic River (Gay and Frimpter, 1984). In the most heavily 

contaminated sections of the Housatonic River, PCB concentrations average about 1,500,000 ppb, with a maximum of 

54,000,000 ppb (U.S. Environmental Protection Agency, 

2002). Although these concentrations are higher than those in 

the Neponset River, concentrations downstream of the most 

heavily contaminated section of the Housatonic River are 

comparable to those in the Neponset River. In Woods Pond, the 

first impoundment downstream of the heavily contaminated 

area on the Housatonic River, sediment PCB concentrations 

ranged from less than the detection limit to 220,000 ppb (U.S. 

Environmental Protection Agency, 2003a). In the Neponset 

River, PCB concentrations are of similar magnitude; these 

concentrations averaged about 140,000, 30,000, and 32,000 ppb 

in cores from the Tileston and Hollingsworth impoundment, 

braided channel, and Walter Baker impoundment, respectively.

Contaminated Bottom-Sediment Toxicity

Water-resource managers and environmental constituencies often use the terms "fishable" and "swimmable" to 

describe the goals of river restoration. In practice, for a river 

to be fishable and swimmable, the water and sediment quality 

must (1) allow for a healthy and diverse fish population, and 

(2) be safe enough for humans to swim in the river. If achieving 

a fishable and swimmable Neponset River is the goal of river 

restoration, then sediment quality must be quantified in terms of 

potential adverse effects to aquatic organisms and humans, 

particularly if environmental managers choose the "no-action" 

sediment-management option, in which sediment is allowed to 

remain and is not removed, contained, remediated, or released.
28 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Benthic Organisms

One way to assess whether a river can support a healthy 

and diverse population of fish is to test the health of their food 

source, particularly benthic organisms. Benthic organisms (for 

example, amphipods, mussels, and worms), upon which some 

fish feed, are those organisms that live and feed on the river 

bottom, where they come in direct contact with contaminated 

sediment. Contaminants can accumulate in the tissues of these 

organisms as they ingest sediment contaminated with elements 

and organic compounds or sorb these containments directly 

from sediment and water (Forstner and Whittman, 1983). 

Eventually, the accumulation of these constituents in benthic 

organisms can cause physiological problems and death. 

Subsequent ingestion of contaminated benthic organisms by 

other organisms higher in the food chain (for example, fish) can 

cause similar health effects.

The potential toxicity of Neponset River sediment to 

benthic organisms can be estimated by comparing measured 

contaminant concentrations to a set of sediment-quality 

guidelines known as PECs. Concentrations greater than the 

PECs are known to cause toxicity because of their effect on the 

survival or growth of laboratory test organisms, such as the 

amphipod Hyalella azteca, and the insect larva Chironomus 

spp. The predicted potential for toxicity depends on the 

organism and the test conditions. First, a measured contaminant 

concentration is divided by its corresponding PEC to yield a 

PEC quotient. In this study, the PEC quotients for up to three 

types of contaminants (trace metals, ΣPAHs, and ΣPCBs) were 

computed and then averaged for each sample according to 

equation 3:

, (3)

where

Finally, the average PEC quotients are compared to PECquotient ranges associated with different toxicity potentials 

(Ingersoll and others, 2000).

The potential for toxicity was determined for the top 

2–4 in. of bottom sediment, which can be considered the 

biologically active sediment layer (Baudo and Muntau, 1990). 

The potential for toxicity by test organisms (Hyalella azteca

and Chironomus spp.) and test conditions (10- to 14-day test 

and 28- to 42-day test) at each site is shown in figure 13. The 

potential for toxicity in figure 13 refers to the potential for 

toxicity compared to a control or reference sediment (Ingersoll 

and others, 2000). For example, a sediment sample with an 

estimated potential toxicity of 20 percent means that 20 out of 

100 toxicity tests are likely to show some level of toxicity for 

the concentration of contaminants measured in that sediment 

sample for a particular organism and a particular set of test 

conditions.

The predicted potential of toxicity ranged from about 13 

percent to 100 percent among the sampling locations (fig. 13). 

Trace elements and the PAHs accounted for some level of 

toxicity at every sediment-sampling location for which they 

were tested; however, PCBs were most responsible for 

predicted toxicity, on average. The largest PEC quotient was 

calculated for sediment-sampling location BGY-105. In fact, 

PCBs accounted for most (96 percent) of the PEC quotient at 

this location. 

This evaluation of potential toxicity is an informal 

screening to distinguish groups of chemicals, and locations, 

that are likely to be associated with adverse biological effects. 

This treatment of the data is intended to supplement, not 

substitute, direct measures of sediment toxicity.

Humans

River-restoration efforts often focus on bringing people 

and river together. When a river is restored, access to it 

improves, recreational opportunities increase, and more people 

fish and swim in the river. As people interact with the river, they 

will likely come in contact with sediment. Consequently, 

information about human health risks associated with direct 

contact or incidental ingestion of contaminated sediment is 

important for water-resources management.

Potential human-health effects caused by direct contact 

with or incidental ingestion of contaminated sediment can be 

indirectly assessed by comparing sediment-contaminant 

concentrations with exposure-based guidelines. Such guidelines, however, do not exist for aquatic sediment, but they do 

exist for contaminated upland soil. In the absence of aquaticsediment guidelines, comparison with direct-contact, exposurebased soil standards may suffice (Massachusetts Department of 

Environmental Protection, 1996; method 2, soil category S-1).

Soil standards exist for many of the constituents tested; but 

in the sediment samples (grabs and cores), only a few of the 

constituents were detected at concentrations equal to or greater 

than the soil standards. Of the elements, beryllium, chromium, 

lead, and nickel had concentrations closest to the soil standards. 

Beryllium and lead concentrations measured at about 40 

percent of the sites were greater than the soil standards (fig. 14).

is equal to the average PEC quotient for sample x;

Cx, y is equal to the concentration of contaminant type y in 

sample x. Contaminant types are the PAHs, PCBs, 

or the trace elements arsenic (As), cadmium (Cd), 

copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn);

PECy is equal to the PEC for contaminant y (Ingersoll and 

others, 2000); and

n is equal to the number of contaminant types available 

for sample x.

Qx

Cx y,

PECy

∑-------------

nx

= ------------------

Qx
Sediment Quality and Implications for River Restoration 29

POTENTIAL TOXICITY, IN PERCENT

100

90

80

70

60

50

40

30

20

10

0

BGY-100

BGY-101

BGY-102

BGY-103

BGY-104

BGY-105

BGY-106

BGY-107

BGY-112

MY2-003

BGY-115

MY2-004

BGY-116

BGY-117

BGY-118

BGY-119

BGY-121

BGY-124

MY2-012

BGY-133

Chironomus 

spp.

10- to

14-day test

Hyalella azteca 

10- to 

14-day test

Hyalella azteca 

28- to 42-day test

Figure 13. Estimated sediment toxicity to Hyalella azteca and Chironomus spp. with respect to consensus-based 

freshwater sediment-quality guidelines from samples collected from the lower Neponset River, Massachusetts.

Measurements of organic compound concentrations are 

more important in terms of (1) the number of constituents, and 

(2) the magnitude of concentrations greater than the soil 

standards. Of particular importance are PCBs (PCB concentrations measured at about 67 percent of the sites were greater 

than the soil standard) and some of the PAHs listed by the 

Department of Health and Human Services as known animal 

carcinogens: benzo(a)anthracene (55 percent of the sites), 

benzo(b)fluoranthene (59 percent), and benzo(a)pyrene (57 

percent) (Agency for Toxic Substances and Disease Registry, 

1995b) (fig. 14).

Comparing sediment concentrations to soil-based, humanhealth standards likely overestimates the potential humanhealth risk. As people wade or swim near contaminated sediment, the sediment is washed quickly from their skin. On the 

other hand, people exposed to contaminated soils have extended 

contact time with the soil; therefore, the contaminant is more 

likely to enter the body (Clifford Opdyke, U.S. Army Corps of 

Engineers, written commun., 2004). Nonetheless, the comparison can provide a sense of the risk associated with contacting 

the sediment. These comparisons, however, are not intended to 

replace direct measures of the health risk.
30 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

BERYLLIUM

ANTIMONY

ARSENIC

CHROMIUM

LEAD

1,000

100

10

1

0.1

0.01

CONCENTRATION, IN PARTS PER MILLION

CONCENTRATION, IN PARTS PER BILLION

BENZO(A)

ANTHRACENE

BENZO(B)

FLUORANTHENE

BENZO(K)

FLUORANTHENE

BENZO(A)

PYRENE

POLYCHLORINATED 

BIPHENYLS

1,000,000

100,000

10,000

1,000

100

10

90th Percentile

75th Percentile

25th Percentile

Average

50th Percentile (Median)

10th Percentile

EXPLANATION

IDENTIFIER

Tileston and Hollingworth 

impoundment

Braided channel (former 

Jenkins impoundment) HUMAN HEALTH STANDARD 

FOR UPLAND SOIL

Walker Baker 

impoundment

Grab samples

T 

J 

B

G

(T)(J)(B)

(J)

(T) (J)(B)

(T)(J)

(B)

(T)(J)

(B)

(T)

(J)

(B)

(G) (G)

(G)

(G)

(G)

(G)

(T)

(J)

(B)

(G)

(G)

(G)

(G)

(T)

(J)

(B)

(J)

(B)

(T)

(J)

(B)

(T)

A. Elements B. Organic compounds

Figure 14. Comparison of concentrations of selected A, elements; and B, organic compounds in sediment collected from 

the lower Neponset River, Massachusetts, with human health guidelines for direct contact with and incident ingestion of 

contaminated soils.

Comparison between Upstream and 

Downstream Sediment Chemistry

With comparisons between sediment-quality data and 

background concentrations, concentrations from other urban 

rivers, and concentrations set forth in aquatic life guidelines, 

water-resources managers can begin to make informed 

decisions about sediment management. One possible management option is natural sediment redistribution. With this option, 

the deltaic deposits trapped behind a dam would be released 

partially and slowly after dam deconstruction or breaching and 

allowed to naturally redistribute downstream. A decision to 

redistribute the sediment, however, would have to be based on 

information about sediment quality downstream of the dam that 

traps the contaminated sediment. To meet this need, eight grab 

samples were collected from the estuarine portion of the river 

downstream of the Walter Baker Dam, where any released 

sediment would initially be deposited and from which tidal 

action could then distribute the sediment farther downstream. 

Detailed sediment-transport models would be needed to determine the ultimate distribution of these sediments, but that work 

was beyond the scope of this study. The detailed grain-size 

distribution data collected in this study (fig. 15), however, could 

serve as the basis for any future modeling of sediment transport.
Sediment Quality and Implications for River Restoration 31

EXPLANATION

90th Percentile

75th Percentile

25th Percentile

Average

50th Percentile (Median)

10th Percentile

Tileston and Hollingsworth 

Impoundment (Core) 

Braided Channel (former Jenkins 

Dam Impoundment) (Core)

Walter Baker Impoundment (Core) 

Entire Neponset River (Grab)

100

80

60

40

20

0

100

80

60

40

20

0

Pebble

Granule

Medium Sand

Coarse Sand

Fine Sand

Very Fine Sand

Medium Silt

Coarse Silt

Fine Silt

Very Fine Silt

Clay-1

Clay-2

Pebble

Granule

Medium Sand

Coarse Sand

Fine Sand

Very Fine Sand

Medium Silt

Coarse Silt

Fine Silt

Very Fine Silt

Clay-1

Clay-2

CUMULATIVE WEIGHT, IN PERCENT CUMULATIVE WEIGHT, IN PERCENT

Pebble

Granule

Coarse sand

Medium sand

Fine sand

Very fine sand

Coarse silt

Medium silt

Fine silt

Very fine silt

Clay-2

Clay-1

> Greater than

< Less than

>4.75

4.73–2.00

2.00–0.43

0.43–0.25

0.25–0.08

0.08–0.06

0.06–0.031

0.031–0.016

0.016–0.008

0.008–0.004

0.004–0.002

<0.002

MATERIALS MILLIMETERS

Figure 15. Sediment-type summary statistics for grab and core samples collected from the lower Neponset River, Massachusetts. 

The eight samples were composited into one and analyzed 

for a suite of elements and organic compounds (these data are 

published in a companion report by Breault and Cooke, 2004). 

As the data indicate, the sediment quality downstream of 

the Walter Baker Dam was generally better than that of the 

sediment quality upstream of the dam, in the braided channel, 

and behind the Tileston and Hollingsworth Dam. The likely 

reason for this difference in sediment quality is that much of the 

past and present contamination is trapped upstream of the dam. 

Additionally, any contaminated sediment that does make it into 

the estuary may be flushed by tidal action or diluted by cleaner 

sediment brought in with the tides.

If the sediments upstream of the Walter Baker Dam were 

purposefully or accidentally released, the sediment quality just 

downstream of the dam might be severely affected. Ultimately, 

the release of large volumes of contaminated sediment may 

adversely affect sediment quality in the downstream estuarine 

part of the river and in Boston Harbor (fig. 1).
32 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Implications of Sediment Contamination for 

Waste Disposal

Contaminated sediment may also be completely or 

partially removed from a river, but this managment option is 

often the most costly. The costs associated with sediment 

removal often increase exponentially with the type and amount 

of contamination. The relation between cost and contamination 

mostly results because of costs associated with sediment 

disposal, rather than with sediment removal. For example, 

uncontaminated sediment may be reused as capping material at 

lined landfills. Contaminated sediment cannot be used for 

similar purposes, so it must be disposed of so that it does not reenter the environment. 

The Massachusetts Department of Environmental Protection (MDEP) has set maximum allowable contaminant concentrations of some chemicals in sediments to be disposed of as 

capping material at lined landfills. By comparing the measured 

concentration to this maximum concentration, the appropriate 

disposal option of the sediment can be determined 

(Massachusetts Department of Environmental Protection, 

1997). Sediment with contaminant concentrations greater than 

these values usually requires special disposal, but sediment with 

concentrations below these values may not. 

Generally, contaminant concentrations measured in 

sediment cores collected from the Neponset River were less 

than concentrations required for disposal of sediment in a lined 

landfill, with one exception (fig. 16). The PCB concentrations 

measured in sediment cores from the Walter Baker and Tileston 

and Hollingsworth impoundments and from the braided channel 

were greater than the allowable concentrations for PCBs. In 

fact, PCB concentrations were, on average, about 30 times 

greater than the concentration prescribed by the MDEP.

Although it is helpful to compare contaminant concentrations to those values set by the MDEP, other methods can help 

predict the consequences of different modes of sediment 

disposal. Specifically, the TCLP and reactive sulfide test can be 

used to determine the likelihood of sediment contamination 

entering the environment from a landfill. In the TCLP, sediment 

samples are subjected to conditions similar to those found in 

landfills. By doing this test, researchers determine the concentration of chemicals, if any, that may leach to the environment 

under those conditions. Reactive sulfide testing determines if 

exposure of sediment to slightly acidic precipitation causes a 

release of hydrogen sulfide gas (H2S).

TCLP results of selected sediment cores from the 

Neponset River indicate that some trace metals (barium and 

lead) are likely to leach from these sediments (laboratory blanks 

showed a bias for barium; however, this bias was about three 

times less than the measured concentrations). In contrast, it 

appears that under normal environmental conditions, no H2S 

would be released from these sediments.

Polychlorinated Biphenyls in 

Water, Sediment, and Fish

For many years, environmental managers have suspected 

that the Neponset River was contaminated with PCBs. Consequently, the ACOE collected sediment samples from the 

Neponset River and tested them for PCBs (U.S. Army Corps of 

Engineers, written commun., 2002). The data from these tests 

indicated that sediment in the Neponset River, at least in the 

areas tested, is contaminated with PCBs.

One method of successfully sampling for PCBs in the 

water column is to use PISCES passive-water-column samplers 

(Litten and others 1993; Colman, 2002). These samplers, which 

are deployed in the river, absorb PCBs from the water column 

across a semipermeable membrane; therefore, these samplers 

collect a time-integrated sample (over the time of deployment) 

of the PCBs dissolved in the water that passes the sampling 

point.

Using passive-water-column sampler methodology to 

detect PCBs has many advantages that other methods (for 

example, sampling sediment and fish tissue) lack. These 

include: (1) water-column samples generally have lower 

detection limits because of fewer chemical interferences; 

(2) dissolved PCB concentrations are an indirect measure of 

bioavailable PCBs in the aquatic environment; and (3) PCB 

concentration variability measured in water-column samples is 

not affected by external factors such as grain size or organic 

carbon content (in sediment samples), or weight, age, sex, 

and lipid content (in fish-tissue samples) (Colman, 2002).

Two techniques can be used to analyze PCB data: Aroclor 

or congener analysis. Aroclors are analyzed by testing for 

characteristic congeners, and then by using a mathematical 

algorithm to estimate the concentrations of other congeners. 

These data are reported in terms of Aroclor concentration. The 

problem with measuring PCBs by testing for Aroclors arises 

when congener patterns deviate from those of the original 

Aroclor (fig. 17). For example, once an Aroclor enters the 

environment, individual congeners can be preferentially 

(1) degraded by microbial action, (2) chemically weathered, or 

(3) physically changed in such a way that the original congener 

pattern for that Aroclor is lost (Butcher and others, 1997). In 

contrast, a congener analysis tests for the presence of individual 

congeners.

Because the advantages of using congener analysis usually 

outweigh those of Aroclor analysis, congener analysis of the 

PISCES passive-water-column samples was used. All of the 

sediment samples were analyzed for PCBs by Aroclor analysis, 

but a few sediment samples were also analyzed for PCB 

congeners.
Polychlorinated Biphenyls in Water, Sediment, and Fish 33

90th Percentile

75th Percentile

25th Percentile

Average

50th Percentile (Median)

10th Percentile

(T)

(B)

(J)

(T)

(B)

(J)

(T)

(B)

(T) (J)

(B)

(J)

(T)

(B)

(J)

(T)

(B) (J) (T)

EXPLANATION

IDENTIFIER

Tileston and Hollingworth 

impoundment

Braided channel (former 

Jenkins impoundment)

Walker Baker impoundment

GUIDELINE FOR UPLAND

REUSE AND DISPOSAL

T

J

B

CONCENTRATION, IN PARTS PER MILLION

ARSENIC

CADMIUM

CHROMIUM

LEAD

TOTAL

PETROLEUM 

HYDROCARBONS

POLYCHLORINATED

BIPHENYLS

0.1

1

100

1,000

10

10,000

Figure 16. Comparison of elements and organic compound concentrations in sediment 

collected from the lower Neponset River, Massachusetts, with Commonwealth of Massachusetts 

guidelines for the reuse and disposal of contaminated soil.
34 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration Aroclor 1016 Aroclor 1248

RELATIVE POLYCHLORINATED BIPHENYL CONCENTRATION, IN PERCENT 15

5

10

0

15

5

10

0

1

2

3 4&10

5&86 7&9

11 12&1314

15 16&3217

18

19 20&21&3322 23&34

24&2725

26

28

29

30

31

35

36

37

38

39

40 41&64&68&71 42&59

43&4944

45

46 47&48&7550

51 52&7353

54

55 56&6057

58 61&74

62&6563 66&8067

69 70&7672

77

78

79

81

82 83&10884 85&120

86&97 87&115&116 88&121 89&90&10191

92 93&9594

96 98&10299

100

103

104 105&127

106&118

107&109 110 111&117 112

113

114

119

122

123

124

125

126

128

129

130 131&142

132&168 133 134&143

135&144 136

137 138&163&164 139&149 140

141

145

146

147

148

150

151

152

153

154

155

156

157 158&160 159

161

162

165

166

167

169 170&190 171 172&192 173 174&181 175

176

177

178

179

180 182&187 183

184

185

186

188

189

191

193

194

195 196&203 197

198

199

200

201

202

204

205

206

207

208

209

POLYCHLORINATED BIPHENYL CONGENER IUPAC NUMBER

16.9

Figure 17. Polychlorinated biphenyl congener patterns of commercially available Aroclors by International Union of Pure and Applied Chemistry number (IUPAC).
Polychlorinated Biphenyls in Water, Sediment, and Fish 35

Aroclor 1254

1

2

3 4&10

5&86 7&9

11 12&1314

15 16&3217

18

19 20&21&3322 23&34

24&2725

26

28

29

30

31

35

36

37

38

39

40 41&64&68&71 42&59

43&4944

45

46 47&48&7550

51 52&7353

54

55 56&6057

58 61&74

62&6563 66&8067

69 70&7672

77

78

79

81

82 83&10884 85&120

86&97 87&115&116 88&121 89&90&10191

92 93&9594

96 98&10299

100

103

104 105&127

106&118

107&109 110 111&117 112

113

114

119

122

123

124

125

126

128

129

130 131&142

132&168 133 134&143

135&144 136

137 138&163&164 139&149 140

141

145

146

147

148

150

151

152

153

154

155

156

157 158&160 159

161

162

165

166

167

169 170&190 171 172&192 173 174&181 175

176

177

178

179

180 182&187 183

184

185

186

188

189

191

193

194

195 196&203 197

198

199

200

201

202

204

205

206

207

208

209

RELATIVE POLYCHLORINATED BIPHENYL CONCENTRATION, IN PERCENT

POLYCHLORINATED BIPHENYL CONGENER IUPAC NUMBER

Aroclor 1260

15

5

10

0

15

5

10

0

Figure 17—Continued. Polychlorinated biphenyl congener patterns of commercially available Aroclors by International Union of Pure and Applied Chemistry

number (IUPAC).
36 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Polychlorinated Biphenyl Source 

Identification

To determine the causes of a change in congener 

pattern, it is necessary to examine the changes in patterns in 

the PISCES data and in the sediment data, and to examine 

the changes from one location to another. Because changes 

in congener patterns could be caused by slight variations in 

the positioning of PISCES samplers in the water column 

(Colman, 2000), or by sediment heterogeniety, it is first 

necessary to determine congener-pattern variability, if any, 

between duplicate samples collected at a single location.

Differences in congener patterns between duplicate 

samples were quantified by comparing the RMSDs of 

normalized congener concentrations. The RMSD values 

for PISCES duplicate pairs ranged from 0.06 to 0.3 percent 

(fig. 18). Colman (2000) reports a similar range of RMSDs 

for similar total (Σ) PCB concentrations in the Millers River 

of central Massachusetts. The RMSD values for sedimentsample duplicate pairs averaged about 0.2 percent.

The second step in determining the locations of 

potential PCB sources to a river is to compare RMSD values 

from adjacent PISCES sampling stations. RMSD values are 

plotted in downstream order in figure 19. RMSD values 

from adjacent PISCES sampling stations were determined 

to be statistically different (α=0.05) by using the student’s 

t-test function of S-Plus 2000 statistical software (for two 

samples, assuming equal variance). The means for the t-test 

were from pooled RMSD values of the duplicate pairs 

(n=12) and RMSD values calculated for adjacent PISCES 

sampling stations (n=2); sample 1 at one station was compared to sample 1 of another station and sample 2 of the first 

station was compared to sample 2 of the second station.

In this case, the PISCES data show a substantial change 

in congener pattern, as measured by the RMSD, between the 

Fairmont Avenue and the two upstream sampling locations, 

Reservation Park on Mother Brook, and Martini Shell on the 

Neponset River (fig. 19). Two scenarios could account for 

the congener-pattern change measured in the PISCES 

samples in this location: (1) a historic PCB source is 

between the Fairmont Avenue and the Martini Shell or 

Reservation Park locations and the original congener pattern 

has not been altered; or (2) a historic PCB source was 

upstream of Martini Shell or Reservation Park. PCBs from 

this source were transported in the water column 

downstream to Fairmont Avenue, and ultimately settled 

there in the sediment. Once deposited, microbial action may 

have degraded the historic PCB pattern, thereby causing the 

observed pattern change. Because anaerobic degradation by 

microbial processes favors substitution of chlorine atoms by 

hydrogen atoms (Wisconsin Department of Natural Resources, 

2000), this process would explain the preeminence of mono- and 

dichlorobiphenyls in PISCES samples downstream of Fairmont 

Avenue (fig. 20).

Analysis of the sediment data, however, suggests a third 

possibility. The change in congener pattern may be caused by both 

a change in PCB source and anerobic degradation of that source. 

The congener pattern from the sediment sample collected at site 

BGY-104, just upstream of Fairmont Avenue, is distinctly 

different than the pattern observed in the sample collected at site 

BGY-105, between site BGY-104 and Fairmont Avenue (figs. 21 

and 22). This difference cannot be explained by microbial 

degradation; therefore, the congener pattern in the sample from site 

BGY-105 may be indicative of a major source of PCBs to the river. 

In contrast, the congener-pattern change observed in some 

sediment samples downstream of BGY-105 can be explained by 

the process of anaerobic degradation. However, the samples 

collected from stations M2Y-012, BGY-133, and BGY-128 

complicate this interpretation, because the congener patterns in 

these samples most closely resemble that from BGY-105. It is 

likely that conditions at these stations (including the ΣPCB 

concentration) are not conducive to anaerobic degradation, and 

that sediment in these samples was contaminated by the same PCB 

source as the sample from BGY-105. It is also possible that PCBs 

consisting mostly of a single congener may have been directly 

released into the Neponset River. More detailed studies are 

required for positive identification of the historical source(s) of 

PCBs to this part of the river.

0.5

0.4

0.3

0.2

0.1

0

0 1,000 2,000 3,000 4,000 5,000

CONCENTRATION OF MEAN SUM OF POLYCHLORINATED 

BIPHENYLS, IN NANOGRAMS PER HEXANE SAMPLE

ROOT MEAN SQUARE DIFFERENCE, IN PERCENT

Paul's Bridge

Martini Shell

Reservation Park

Fairmont 

Avenue Tileston and Hollingsworth 

Impoundment Upstream

Tileston and Hollingsworth 

Dam Downstream

Kennedy

Playground

Braided

Channel

Central 

Avenue

Walter Baker Dam

Figure 18. Differences in polychlorinated biphenyl congener 

patterns between duplicate samples collected from the lower 

Neponset River, Massachusetts.
Polychlorinated Biphenyls in Water, Sediment, and Fish 37

PAUL'S BRIDGE

MARTINI SHELL

FAIRMONT AVE.

TILESTON AND

HOLLINGSWORTH 

DAM UPSTREAM

TILESTON AND

HOLLINGSWORTH 

DAM DOWNSTREAM

RYAN 

PLAYGROUND

KENNEDY 

PLAYGROUND

BRAIDED CHANNEL

CENTRAL AVE.

WALTER BAKER DAM

10

8

6

4

2

0

5,000

4,000

3,000

2,000

1,000

0

RESERVATION PARK

ROOT MEAN SQUARE DIFFERENCE, 

IN PERCENT

CONCENTRATION OF MEAN SUM OF POLYCHLORINATED 

 BIPHENYLS, IN NANOGRAMS PER HEXANE SAMPLE

ROOT MEAN SQUARE DIFFERENCE, 

IN PERCENT

EXPLANATION

ROOT MEAN SQUARE DIFFERENCE, IN RELATIVE

CONCENTRATION PERCENT

CONCENTRATION OF MEAN SUM OF POLYCHLORINATED BIPHENYLS, 

IN NANOGRAMS PER HEXANE SAMPLE

DOES NOT INCLUDE SAMPLE 7 *

*

6,177 5,000

4,000

3,000

2,000

1,000

0

10

8

6

4

2

0

FAIRMONT AVE.

INCINERATOR 

ROAD

 CONCENTRATION OF MEAN SUM OF 

POLYCHLORINATED BIPHENYLS, 

IN NANOGRAMS PER HEXANE SAMPLE

Mother 

Brook

Figure 19. Polychlorinated biphenyl concentrations and between-station root mean square differences of congener 

patterns measured in PISCES passive samplers, Mother Brook and the lower Neponset River, Massachusetts.

Whatever the case, it appears that presently (2003) the 

majority of dissolved PCBs in the Neponset River continue to 

be released into the river from the existing sediment 

downstream of Fairmont Avenue. This is demonstrated by the 

fact that congener patterns from PISCES samples and from 

sediment samples are similar in this reach of the river. As PCBs 

enter a river, they attach to fine-grained sediment suspended in 

the water column. These particles move downstream in the 

flowing water and ultimately settle in slack pools. The PCBs 

that accumulate in the sediment eventually move from the 

sediment back into the water column (Chambers, 1999). 

Although some sediment samples were analyzed for PCB 

congener data (table 8), more detailed studies are required to 

identify the present-day source(s) and their importance to 

water-column PCBs contamination. 
38 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Table 7. Measured total polychlorinated biphenyl (ΣPCB) concentrations, by congener analysis in PISCES samplers, estimated ΣPCB 

water-column concentrations, and estimated ΣPCB concentrations in fish tissue, lower Neponset River, Massachusetts.

[Because the food chain multiplier for primary consumers equals 1, bioconcentration values are identical to primary consumer values. ΣPCBs, sum of the 209 

polychlorinated biphenyls; mg/kg/kg lipid, milligram per kilogram per kilogram lipid; ng, nanogram; ng/L, nanogram per liter; --, no data]

Station Sample

number

ΣPCB by

congener

(ng/hexane

sample)

Water-column 

estimated 

concentration

(ng/L)

Bioaccumulation (mg/kg/kg lipid)

Primary 

consumers

Secondary 

consumers

Predators

Paul’s Bridge 17 112 2.0 4.0 52.3 91.2

18 257 4.7 8.6 110.8 192.3

Martini Shell 19 142 2.5 4.8 61.3 106.6

20 115 2.0 3.5 44.5 77.1

Incinerator Road 23 -- -- -- -- --

24 29 .4 .8 10.5 18.0

Reservation Park 21 102 1.5 2.0 24.2 41.1

22 108 1.6 2.1 25.5 43.3

Fairmont 15 5,253 95 27.3 264.2 405.8

16 3,595 65 18.8 179.6 272.2

Tileston–Hollingsworth 

Dam upstream

13 2,330 43 14.9 147.3 230.2

14 2,652 49 18.9 198.3 320.6

Tileston–Hollingsworth 

Dam downstream

11 4,719 89 32.8 341.0 544.5

12 4,382 82 29.6 309.1 499.4

Kennedy playground 9 2,373 48 16.8 170.7 271.9

10 1,706 34 11.0 107.6 168.4

Ryan playground 7 1,304 28 8.7 82.8 127.6

8 6,177 131 44.4 434.6 677.1

Braided channel 5 3,381 71 27.1 264.0 406.6

6 4,541 95 37.1 363.6 561.7

Central Avenue 3 2,956 65 29.2 297.3 466.2

4 3,144 69 30.0 302.4 472.4

Baker Dam 1 1,790 37 16.0 161.3 251.8

2 1,874 38 17.0 172.3 270.4
Polychlorinated Biphenyls in Water, Sediment, and Fish 39

1

2

3 4&10

5&86 7&9

11 12&1314

15 16&3217

18

19 20&21&3322 23&34

24&2725

26

28

29

30

31

35

36

37

38

39

40 41&64&68&71 42&59

43&4944

45

46 47&48&7550

51 52&7353

54

55 56&6057

58 61&74

62&6563 66&8067

69 70&7672

77

78

79

81

82 83&10884 85&120

86&97 87&115&116 88&121 89&90&10191

92 93&9594

96 98&10299

100

103

104 105&127

106&118

107&109 110 111&117 112

113

114

119

122

123

124

125

126

128

129

130 131&142

132&168 133 134&143

135&144 136

137 138&163&164 139&149 140

141

145

146

147

148

150

151

152

153

154

155

156

157 158&160 159

161

162

165

166

167

169 170&190 171 172&192 173 174&181 175

176

177

178

179

180 182&187 183

184

185

186

188

189

191

193

194

195 196&203 197

198

199

200

201

202

204

205

206

207

208

209

Martini Shell, mainstem Neponset RiverReservation Park, Mother BrookFairmont Avenue, mainstem Neponset River

 CONCENTRATION, IN PERCENT POLYCHLORINATED BIPHENYL RELATIVE 

POLYCHLORINATED BIPHENYL CONGENER IUPAC NUMBER

0

1510

5

0

1510

5

0

1510

5

35.419.4

Figure 20. Average relative polychlorinated biphenyl congener concentrations in selected PISCES samples collected from the lower Neponset River, Massachusetts, by 

International Union of Pure and Applied Chemistry (IUPAC) number.
40 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

Polychlorinated Biphenyl Toxicity

Numerous studies have shown that PCBs pose a risk to 

fish, wildlife, and humans, by causing a variety of health 

effects, including cancer (U.S. Environmental Protection 

Agency, 1996). Numerical standards for aquatic-life protection 

(aquatic-life criteria) and human health (toxic equivalency 

factors) can help determine the health risks associated with PCB 

exposure. These aquatic-life criteria and human-health 

guidelines are available for dissolved PCB concentrations. 

Because PISCES passive-water-column samplers concentrate 

PCBs from the dissolved phase, data from the samples can be 

used to estimate dissolved PCB concentrations (table 7; 

Colman, 2000). These data can then be used to estimate 

exposure-based health risks.

The relation between PCB concentrations in the samples 

from PISCES passive-water samplers and the concentrations of 

dissolved PCBs in the water column is as follows (John Hassett, 

State University of New York–Syracuse, written commun., 

2000; equation 4):

(4)

where

Estimated ΣPCB dissolved concentrations ranged from 

less than 0.5 ng/L at Incinerator Road in Mother Brook to a 

maximum concentration of 131 ng/L in the Neponset River at 

the Ryan Playground PISCES sampling location (sample 

number 8 in table 7) (fig. 23). On average, ΣPCB water-column 

concentrations were about 1.17 ng/L on Mother Brook. On the 

Neponset River, upstream and downstream of the Fairmont 

Avenue sampling location, concentrations were about 2.8 and 

66 ng/L, respectively (excluding sample number 7).

Aquatic-Life Criteria

As aquatic organisms, for example, predatory fish, eat 

other aquatic organisms, such as smaller fish or benthic 

organisms that feed and live on bottom sediments contaminated 

with PCBs, the predatory organism can become contaminated 

(Oliver and Niimi, 1985). Aquatic organisms may also become 

contaminated directly from the water column by absorbing 

dissolved PCBs through gill membranes (Björk and Gilek, 

1999). Through this process, PCBs can become more 

concentrated in fish tissue (bioaccumulation) than in the water 

or sediment. As of December 1998, bioaccumulation of PCBs 

in fish tissue was responsible, at least in part, for the 679 fishconsumption advisories that were issued in the United States. 

Only one other constituent, mercury, accounts for more fishconsumption advisories than PCBs (U.S. Environmental 

Protection Agency, 1999).

The USEPA publishes numerical standards that relate 

chronic toxicity to concentrations of PCBs dissolved in the 

water column. Presently (2003), the freshwater continuous 

chronic criterion (CCC) for aquatic organisms is 14.0 ng/L 

(U.S. Environmental Protection Agency, 2003b). The USEPA 

defines the CCC as the highest constituent concentration to 

which an aquatic organism can be exposed indefinitely without 

causing adverse biological effects. Aquatic organisms exposed 

for any length of time to PCB levels greater than the CCC may 

develop impaired reproductive-, endocrine-, and immunesystem function, increased lesions and tumors, or they may die 

(U.S. Environmental Protection Agency, 1999).

Generally, estimated dissolved ΣPCB concentrations in 

Mother Brook and upstream of the Fairmont Avenue station on 

the Neponset River were less than the CCC for PCBs (fig. 23). 

Downstream of the Fairmont Avenue sampling station, 

estimated dissolved ΣPCB concentrations were greater than the 

CCC for PCBs. Therefore, PCBs would not be expected to 

cause adverse biological effects in Mother Brook or in the 

Neponset River upstream of the Fairmont Avenue sampling 

station, but exposure to PCBs downstream of that station may 

cause adverse biological effects to aquatic organisms or 

wildlife. 

Although PCBs in aquatic organisms were not directly 

measured, bioconcentration factors (BCFs) and 

bioaccumulation factors (BAFs) can be used to estimate orderof-magnitude concentrations expected in tissue samples. These 

factors represent ratios that might be expected between 

contaminant concentrations in tissue and contaminant 

concentrations in water. The mode of exposure determines 

which ratio (BCF or BAF) is most appropriate to use. A BCF is 

used to estimate contaminant concentrations in tissue that result 

from contaminated water in equilibrium with gill membranes 

and skin (U.S. Environmental Protection Agency, 1993). Direct 

ingestion and the uptake of contaminants through the food chain 

is accounted for in the BAF (U.S. Environmental Protection 

Agency, 1995).

Table 8. Total polychlorinated biphenyl concentrations by 

congener analysis in selected grab and core samples, lower 

Neponset River, Massachusetts.

[dup, duplicate; ΣPCBs, total polychlorinated biphenyls; ppb, parts per billion]

USGS number ΣPCB

(ppb)

USGS

number

ΣPCB

(ppb)

BGY-102 29 M2Y-002 230,845

BGY-104 1,054 BGY-128 66,053

BGY-105 13,843 M2Y-012 4,670

BGY-106 16,293 BGY-133 5,841

BGY-112 16,458 BGY-137 79,182

BGY-102-dup 28 BGY-128-dup 59,660

Cw is the concentration of the congener in water, in 

nanograms per liter;

Ms is the mass of the congener measured in the PISCES 

sample, in nanograms per hexane sample;

A is the surface area of the semipermeable membrane, in 

square centimeters;

T is water temperature, in degrees Kelvin; and,

t is the exposure time, in days.

Cw

Ms

A e

–6.591

T ---------------- + 19.269 ⎝ ⎠ ⎛ ⎞

× × t

= ----------------------------------------------------
Polychlorinated Biphenyls in Water, Sediment, and Fish 41

1

2

3 4&10

5&86 7&9

11 12&1314

15 16&3217

18

19 20&21&3322 23&34

24&2725

26

28

29

30

31

35

36

37

38

39

40 41&64&68&71 42&59

43&4944

45

46 47&48&7550

51 52&7353

54

55 56&6057

58 61&74

62&6563 66&8067

69 70&7672

77

78

79

81

82 83&10884 85&120

86&97 87&115&116 88&121 89&90&10191

92 93&9594

96 98&10299

100

103

104 105&127

106&118

107&109 110 111&117 112

113

114

119

122

123

124

125

126

128

129

130 131&142

132&168 133 134&143

135&144 136

137 138&163&164 139&149 140

141

145

146

147

148

150

151

152

153

154

155

156

157 158&160 159

161

162

165

166

167

169 170&190 171 172&192 173 174&181 175

176

177

178

179

180 182&187 183

184

185

186

188

189

191

193

194

195 196&203 197

198

199

200

201

202

204

205

206

207

208

209

BGY-104

BGY-105

BGY-106

RELATIVE POLYCHLORINATED BIPHENYL CONCENTRATION, IN PERCENT

0

1510

1510

5

5

1510

5

0

0

POLYCHLORINATED BIPHENYL CONGENER IUPAC NUMBER

Figure 21. Average relative polychlorinated biphenyl congener concentrations in selected grab samples collected from the lower Neponset River, Massachusetts, by International Union of Pure and Applied Chemistry (IUPAC) number.
42 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

1

2

3 4&10

5&86 7&9

11 12&1314

15 16&3217

18

19 20&21&3322 23&34

24&2725

26

28

29

30

31

35

36

37

38

39

40 41&64&68&71 42&59

43&4944

45

46 47&48&7550

51 52&7353

54

55 56&6057

58 61&74

62&6563 66&8067

69 70&7672

77

78

79

81

82 83&10884 85&120

86&97 87&115&116 88&121 89&90&10191

92 93&9594

96 98&10299

100

103

104 105&127

106&118

107&109 110 111&117 112

113

114

119

122

123

124

125

126

128

129

130 131&142

132&168 133 134&143

135&144 136

137 138&163&164 139&149 140

141

145

146

147

148

150

151

152

153

154

155

156

157 158&160 159

161

162

165

166

167

169 170&190 171 172&192 173 174&181 175

176

177

178

179

180 182&187 183

184

185

186

188

189

191

193

194

195 196&203 197

198

199

200

201

202

204

205

206

207

208

209

M2Y-002

BGY-128

BGY-137

RELATIVE POLYCHLORINATED BIPHENYL CONCENTRATION, IN PERCENT

15

5

10

0

15

5

10

0

25 21

15

5

10

0

POLYCHLORINATED BIPHENYL CONGENER IUPAC NUMBER

Figure 22. Average relative polychlorinated biphenyl congener concentrations in selected core samples collected from the lower Neponset River, Massachusetts, by International Union of Pure and Applied Chemistry (IUPAC) number. 
Polychlorinated Biphenyls in Water, Sediment, and Fish 43

140

100

80

120

60

40

0

20

INCINERATOR ROAD

RESERVATION PARK

FAIRMONT AVENUE

TILESTON AND HOLLINGSWORTH

DAM DOWNSTREAM

TILESTON AND HOLLINGSWORTH DAM UPSTREAM

KENNEDY 

PLAYGROUND

RYAN PLAYGROUND

BRAIDED CHANNEL

CENTRAL AVENUE

WALTER BAKER DAM

PAUL'S BRIDGE

MARTINI SHELL

CONCENTRATION OF POLYCHLORINATED 

BIPHENYLS, IN NANOGRAMS PER LITER (ng/L)

EXPLANATION

ESTIMATED CONCENTRATION 

OF POLYCHLORINATED 

BIPHENYLS IN THE WATER 

COLUMN 

U.S. ENVIRONMENTAL 

PROTECTION AGENCY 

CONTINUOUS CHRONIC 

CRITERION (14 ng/L)

SAMPLER LEAKED

SAMPLE NUMBER

(17)(18) (19)(20) (24) (21)(22)

(15)

(16)

(13)

(14)

(11)

(12)

(8)

(5)

(6)

(3) (4)

(1)

(1)

(2)

(9)

(10) (7)

Figure 23. Estimated water-column concentrations of total polychlorinated biphenyls (ΣPCBs) collected from the lower 

Neponset River, Massachusetts, in comparison to the U.S. Environmental Protection Agency freshwater continuous chronic 

criterion for ΣPCBs.

Octanol-water partition coefficients (Kow), which are 

measures of the tendency for a chemical to partition to a 

substance other than water (for example, tissue), can be used to 

estimate lipid-normalized BCFs as

(5)

where

Congener-specific Kow values estimated by Hawker and 

Connell (1988) were used to calculate BCFs for each congener. 

In the case of coeluting congeners, an average Kow value was 

used.

Unlike BCFs, the biomagnification of a contaminant as it 

moves through the food chain is accounted for in the BAF. For 

example, largemouth bass (Micropterus salmoides), a predator, 

is expected to have higher ΣPCB concentrations in its tissues 

than those found in the fish eaten by the largemouth bass. To 

account for this increase, PCB congener concentrations are 

multiplied by a food-chain multiplier (FCM) as

(6)

where

In this calculation, USEPA-derived FCMs for three 

feeding levels were used: (1) primary consumers (herbivores 

and suspension feeders), (2) secondary consumers (small fish), 

and (3) predators (fish) (U.S. Environmental Protection 

Agency, 1993). These FCMs generally increase with feeding 

level and congener Kow values; however, some superlipophilic 

congeners (Kow greater than 6.5) have slightly lower FCM 

values. Because large molecules cannot readily pass through 

gill membranes, these congeners biomagnify to a lesser degree 

through the food chain (Oliver and Niimi, 1985).

BCFi is the lipid-normalized BCF for congener i, in 

microgram congener per kilogram lipid per 

microgram per liter congener concentration in 

water; and,

Kow, i is the octanol-water partition coefficient for congener 

i.

BCFi ≈ Kow i ,

BAFi is the BAF for congener i, in microgram congener per 

kilogram lipid per microgram per liter congener 

concentration in water; and, 

FCM is the food-chain multiplier for a given feeding level.

BAFi = FCM K× ow i ,
44 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

With equation 7, BCFs and BAFs were used to estimate 

lipid-normalized ΣPCB in primary consumers, secondary 

consumers, and predators (table 7):

(7)

where

A previous study of fish fillets (edible fish parts) contaminant concentrations completed by the MDEP and other State 

agencies measured ΣPCB concentrations of about 1.4 ppm 

(average 4.0 g lipid or 0.56 percent lipid) in a composite of 

brown bullhead (Ameiurus nebulosus), a secondary consumer 

(Massachusetts Department of Environmental Protection, 

1994). These fish were collected far upstream of the study area, 

but were said also to represent the upper part of the study area 

(Paul’s Bridge to the Tileston and Hollingsworth Dam). Largemouth bass (Micropterus salmoides), a predator, were also 

collected and analyzed. A concentration of 0.17 ppm was 

measured in a composite of largemouth bass fillets (average 

2.2 g lipid or 0.18 percent lipid). 

The Massachusetts Department of Public Health issues 

fish-consumption advisories for fish with measured PCB 

concentrations in their tissue of about 2 ppm, the U.S. Food and 

Drug Administration (FDA) and USEPA "action level" for 

PCBs (U.S Food and Drug Administration, 2001). Consequently, a fish advisory was issued for the consumption of 

brown bullhead collected from the Neponset River between the 

Hollingsworth and Vose Dam (Walpole, MA) to the Tileston 

and Hollingsworth Dam (Hyde Park, MA).

Estimated average ΣPCB concentrations (calculated by 

using an average lipid mass of 4.0 g) in secondary consumers 

ranged from about 0.1 ppm in Mother Brook and 0.3 ppm 

upstream of Fairmont Avenue to about 1.0 ppm downstream of 

Fairmont Avenue on the Neponset River. Similar concentrations were estimated for predatory fish in Mother Brook 

(0.1 ppm), and upstream (0.3 ppm) and downstream (0.8 ppm) 

of Fairmont Avenue on the Neponset River (average lipid mass 

of 2.2 g). Estimated ΣPCB concentrations in the river reach 

from Paul’s Bridge to the Tileston and Hollingsworth Dam 

were similar to those measured, and averaged about 0.4 ppm for 

both secondary consumers and predatory fish. Estimates of 

ΣPCB concentrations (lipid normalized) in tissue samples for 

other feeding levels and modes of exposure by PISCES 

sampling station are given in table 7.

Another comparison can be made with fish-tissue ΣPCB 

concentrations measured in fish from the Housatonic River. 

White suckers (Catostomus commersoni), a bottom-feeding 

fish, were collected as part of the NAQWA Program and 

analyzed for PCBs. The average of the whole-body (entire fish) 

ΣPCB concentrations measured in white suckers from the 

Housatonic River ranged from 12 to 72 ppm (Coles, 1998). This 

range is higher than the whole-body concentrations estimated 

for small fish in the PCB contaminated area of the Neponset 

River (9.0 ppm, based on a lipid mass of 35 g or 5.3 percent 

lipid). This concentration range is not surprising, because PCB 

contamination in the Housatonic River is greater and more 

widespread than the Neponset River.

Many factors affect PCB concentrations in aquatic 

organisms, particularly fish, including the character of the river, 

temperature, and organic carbon concentrations (Cook and 

Burkhard, 1998). A study that involves the collection and 

analysis of aquatic organisms would help to determine definitively how PCB contaminated sediment and water affect biota 

in the lower Neponset River.

Human Health

Dioxin and "dioxin-like" compounds are a group of 

structurally similar organic compounds that act by a similar 

cellular mechanism to cause comparable biological and toxic 

effects (U.S. Environmental Protection Agency, 2001). Of the 

30 dioxin or dioxin-like compounds in the environment, the 

most toxic is 2,3,7,8-tetrachlorodibenzo-p-dioxin (often 

referred to as 2,3,7,8-TCDD, TCDD, or dioxin; Murphy, 1986). 

Human exposure to high levels of TCDD causes a variety of 

ailments, including chloracne, porphyria (skin and nerve 

damage), liver damage, and psychiatric disturbances 

(International Agency for Research on Cancer, 1997).

Of the 209 PCB congeners, 13 are considered dioxin-like; 

that is, they cause toxic effects similar to TCDD. Because of 

this similarity, the USEPA has developed an approach in which 

PCB toxicity can be estimated relative to TCDD to produce a 

"toxic equivalency" (fig. 24). Equation 8 was used to calculate 

the toxic equivalency (TEQ) for dissolved PCB congener 

concentrations (calculated by equation 4): 

(8)

where

The toxic equivalency factors were derived by the World Health 

Organization in 1997, and are considered applicable for human 

and wildlife species (Van den Berg and others, 1998).

ΣPCB is the estimated concentration of PCBs, in milligrams 

per kilogram (or parts per million) per kilogram 

lipid;

Ci is the estimated concentration of PCB congener i in 

the water, in nanograms per liter;

Yi is either the BCF or BAF for congener i, in 

microgram congener per kilogram lipid per 

microgram per liter congener concentration in 

water.

∑PCB

Ci

1,000

------------- × Yi

1,000 = ------------------------

TEQi is the toxic equivalency of congener i, in picograms 

per liter (pg/L);

Ci is the concentration of congener i, in water, in pg/L;

TEFi is the toxic equivalency factor for congener i.

TEQi Ci × TEFi

i = 1

k

= ∑
Summary 45

(17)

(18)

(19) (20)

(24)

(21)(22)

(15)

(16)

(13)

(14)

(11)

(12)

(9)

(10)

(7)

(8)

(5)

(6)

(3)

(4)

(1) (2)

(2)

EXPLANATION

TOXIC EQUIVALENCY OF 

POLYCHLORINATED 

BIPHENYLS

U.S. ENVIRONMENTAL 

PROTECTION AGENCY 

HUMAN HEALTH STANDARD 

(0.005 ng/L)

SAMPLER LEAKED

SAMPLE NUMBER

TOTAL TOXIC EQUIVALENCY, IN PICOGRAMS PER LITER 

(RELATIVE TO 2,3,7,8-tetrachlorodibenzop-dioxin)

0.05

0.04

0.03

0.02

0.01

0.06

0

INCINERATOR ROAD

RESERVATION PARK

FAIRMONT AVENUE

TILESTON AND 

HOLLINGSWORTH

DAM DOWNSTREAM

TILESTON AND 

HOLLINGSWORTH

DAM UPSTREAM

KENNEDY 

PLAYGROUND

RYAN PLAYGROUND

BRAIDED CHANNEL

CENTRAL AVENUE

WALTER BAKER 

DAM

PAUL'S BRIDGE

MARTINI SHELL

Figure 24. Toxic equivalency of total polychlorinated biphenyls relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) 

collected from the lower Neponset River, Massachusetts.

Estimated water-column PCB concentrations, expressed 

as TCDD, were greater than the USEPA human-health standard 

(0.005 pg/L), with the exception of the sample from the 

Incinerator Road location. The largest total TEQ was calculated 

for PCB congener concentrations measured just downstream of 

the Tileston and Hollingsworth Dam. At this station, the TEQ 

was about 10 times greater than the standard. This assessment 

of PCB toxicity does not include any toxicity caused by 

"nondioxin-like” PCB congeners. Moreover, analysis used by 

this study may underestimate some “dioxin-like” congener 

concentrations.

Interestingly, TEQs normalized by ΣPCB concentrations 

indicate that PCBs from upstream of Fairmont Avenue are 

much more toxic than PCBs downstream of Fairmont Avenue. 

This finding indicates that either the major source of PCB 

contamination near Fairmont Avenue was relatively non-toxic, 

compared to PCBs from upstream sources, or that dechlorination has reduced the toxicity of the original PCB source.

Summary

Evaluation of fish-passage alternatives, including dam 

removal or breaching for the purposes of increasing fish 

passage and river restoration of the Neponset River in 

Massachusetts has raised concerns about the quality and 

quantity of bottom sediment. Of particular concern is the wellknown presence of elevated concentrations of polychlorinated 

biphenyls (PCBs) in the bottom sediment of the river. In 

response to these concerns, the U.S. Geological Survey, in 

cooperation with the Massachusetts Executive Office of 

Environmental Affairs Riverways Program, and the U.S. 

Environmental Protection Agency, tested sediment and water 

quality in the lower Neponset River.

Bottom-sediment quality was measured by collecting 

sediment-grab samples (top 4 in.) from the outlet of Fowl 

Meadow, Canton, MA, to the Walter Baker Dam, Milton, MA, 

and sediment cores (extending the length of impounded 

sediment) from two impoundments (Walter Baker and Tileston 

and Hollingsworth), and from within the former Jenkins Dam 

impoundment, known as the braided channel. Sediment 

samples were analyzed for elements and organic compounds 

(including PAHs and PCBs) and for physical properties such as 

grain-size distribution. Bottom-sediment quantity was 

measured by manual measurements of sediment thickness. Data 

on bottom-sediment quality and quantity will help waterresources managers make informed decisions regarding dam 

removal and other river-restoration efforts.
46 Sediment Quality and PCBs in the Lower Neponset River, MA, and Implications for Urban River Restoration

The source of PCB contamination was determined by 

comparing PCB concentrations and PCB congener patterns (or 

"fingerprinting") analyzed from samples collected with 

PISCES passive-water-column samplers. PISCES passivewater-column samplers were deployed at 12 locations along the 

Neponset River, retrieved about 2 weeks later, and their 

contents were analyzed for 209 PCB congeners. Congener 

patterns, in combination with PCB concentrations measured in 

sediment-grab samples, may provide insight into past and 

present PCB source(s).

Bottom-sediment samples (grab and core) collected from 

the Neponset River are generally enriched in elements and 

organic compounds when compared to "nonurban-background" 

concentrations. Although enriched relative to background, most 

constituent concentrations were equal to or less than those 

found in other urban rivers, with the notable exception of PCBs. 

Some chemicals, particularly PCBs, are in sufficiently high 

concentrations in sediment samples collected from the 

Neponset River to pose a threat to benthic organisms and 

potentially to cause human health risks if humans come in 

contact with the sediment.

PCB fingerprinting techniques indicate a significant 

change in congener pattern between two sampling locations. 

These data may possibly be used to locate the original source of 

PCB contamination to the river. Presently (2003), it appears that 

PCBs in the Neponset River are from PCB contaminated sediment from Fairmont Avenue downstream. PCB concentrations 

in the water column downstream of this area persist at 

potentially toxic levels to fish, wildlife, and humans.

The data and analysis presented in this report will help 

water-resources managers evaluate the advantages and limitations of various sediment-management options. Sediment 

removal or redistribution may increase the risk of introducing 

buried contaminants back into the environment. On the other 

hand, the contaminated sediment left in place may serve as a 

continuing future source of contaminants to the water column 

and biota living in and around the river. In either case, contaminated sediment and water in settings like the Neponset River 

have substantial implications for the restoration of urban rivers 

and dam deconstruction. 

Acknowledgments

The authors express their gratitude to the following people 

for their cooperation and assistance with sampling: USGS 

colleagues Stacey Archfield, John Colman, Andrew Massey, 

Timothy McCobb, Vicky-Rose Siegel, Jason Sorenson; for 

technical and editorial assistance, the authors thank USGS 

colleagues Mary Ashman, James Coles, Leslie DeSimone, 

Gregory Granato, Christine Mendelsohn, Steven Smith, Marcus 

Waldron, Anne Weaver, and Peter Weiskel; and Karen Pelto 

(Massachusetts Executive Office of Environmental Affairs 

Department of Fish and Game), Steven Lipman (Massachusetts 

Department of Environmental Protection), and David Larson 

and Clifford Opdyke (U.S. Army Corps of Engineers); for 

assistance with laboratory analysis and operations, the authors 

thank William Andrade, Thomas Faber, Robert Maxfield, and 

Charles Porfert (U.S. Environmental Protection Agency); 

Libby Shrieve (USGS Sediment Laboratory); and Joseph Foley 

(New England Testing Laboratory).

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