Sediment Issue 

Measuring Contaminant Resuspension 

Resulting from Sediment Capping 

Purpose 

Introduction

 Site Descriptions 

Methods 

Results and Discussion

 Boston Harbor

 Eagle Harbor 

Conclusions 

References 

Purpose 

The National Risk Management Research Laboratory (NRMRL) of the U.S. Environmental 

Protection Agency (U.S. EPA) is developing 

effective, inexpensive remediation strategies for 

contaminated sediments. This program theme 

includes the evaluation of capping to contain/stabilize contaminated sediments. Studies were conducted by NRMRL to evaluate the resuspension 

of surface materials contaminated with polycyclic 

aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). This information, along 

with U.S. EPA’s sediment guidance document (1), 

is intended to: a) be used as a reference for site 

managers and U.S. EPA decision makers who are 

considering the environmental impacts of capping 

contaminated sediments, and b) provide a better 

understanding of the techniques and mechanisms 

that can be applied to minimize the resuspension 

of contaminated material during capping. 

Monitoring the Water Column During Capping Activities at Boston Harbor 

The results of two NRMRL studies undertaken to evaluate solids 

resuspension before, during, and after capping of contaminated 

sediments are summarized below. These two studies were both 

conducted at marine sites. One study was carried out at the 

Boston Harbor/Mystic River Site in cooperation with U.S. EPA 

Region 1 and the U.S. Army Corps of Engineers (USACE). The 

other study took place at the Wyckoff/Eagle Harbor Superfund Site 

off Bainbridge Island, WA, in cooperation with U.S. EPA Region 

10 and USACE. 

Introduction 

During sediment capping activities, clean material is commonly released from a barge at the water surface and falls through the water 

column to the sediment surface, providing an uncontaminated surface sediment layer (2). Information on the potential release of insitu contaminated sediment during and after capping operations is 

sparse; therefore, NRMRL conducted studies as reported in Lyons 

et al. (2) in order to develop a better understanding of the amount 

of contaminants released into the surrounding water column 

before, during, and after capping. These studies evaluated whether 

the placement of conventional sand caps results in the disturbance 

of contaminated surface sediments and thus the release of contaminants into the surrounding water column through resuspension. 
Two sites were examined where different capping methods 

(see Table 1 below) were employed for dissimilar sediment 

types (2). Data associated with the sites indicated that: 

• The resuspension of contaminated sediments was measur

able, remaining in the ng/L range (for contaminants in 

the water column), when capping was conducted over 

uncapped sediments. 

• The magnitude of contaminant resuspension decreased 

with successive capping layers, suggesting the greatest 

potential for resuspension occurred when capping native 

uncapped contaminated material. 

• After capping operations ceased, turbidity plumes dis

sipated rapidly (generally within hours) due to deposition 

and off-site transport. 

Site Descriptions 

Table 1 summarizes characteristics of the study sites, 

including capping techniques, source of capping materials, 

and contaminants-of-concern (COCs) at the study sites. 

For the Boston Harbor Site, confined aquatic disposal 

(CAD) cell M8, measuring 213 m by 61 m, was excavated to a depth of 27 m and had an estimated capacity 

of 118,500 m3

 of dredged material. CAD cell M19, the 

­

­

Table 1. Description of Study Sites.

larger of the two cells measuring 244 m by 91 m, was excavated to a depth of 24 m and had an estimated capacity 

of 136,900 m3

. The area monitored for the Eagle Harbor 

study covered an area of approximately 150 m by 275 m. 

Methods 

An aquatic monitoring tool was towed behind a boat to 

collect and integrate in-situ measurements with continuous 

water collection to monitor the effects of sediment suspension during capping operations. Aquatic monitoring of 

the capping events was conducted using the Battelle Ocean 

Sampling System (BOSS) deployed from a survey vessel. 

The BOSS is an integrated profiling system comprised of 

an underwater sensor unit, an electromechanical profiling 

cable for delivery of real-time data and continuous water 

samples to the shipboard laboratory, and a customized 

profiling winch and handling system, as shown in Figure 1. 

The BOSS in-situ sensor package (housed inside a towfish) 

includes a conductivity, temperature, and depth (CTD) 

sensor; a turbidity sensor; an Acoustic Doppler Current 

Profiler for vertical profiles of horizontal currents; and a 

TeflonTM/titanium pumping system for sample collection, 

which delivered water samples to the onboard laboratory at 

12 L/min through a TeflonTM line. The survey vessel towed 

the BOSS at a depth of approximately 1 to 2 m above the 

sediment surface to optimize detection of resuspended 

sediments. 

Study Site Location Sediment Type Capping Capping Material COCs Contaminant ConcentraTechnique tions in Sediment 

Prior to Capping 

CAD cells (M8 and 

Boston Harbor/ 

Mystic River 

Site 

Boston, 

MA 

M19) filled with 

dredged sediments, 

typically 85-100% 

silt/clay with in-situ 

Pushing an open 

hopper dredge with 

a tugboat over the 

area to be capped 

Sand dredged from the Cape 

Cod Canal having modal 

grain size of 0.25 mm diameter with an average of less 

PCBs 

PAHs 

Average total PCBs and total 

PAHs were 220 μg/kg and 

64,478 μg/kg, 

respectively (4) 

solids ranging from than 1% fines (3) 

30-55% (3) 

Clean quarry sand with the Total PAH concentrations 

following properties: 81.1% reported as 1,273 ± 2,116 

Wyckoff/Eagle 

Harbor 

Superfund 

Site 

Bainbridge 

Island, 

WA 

Bedded (specifics 

about sediment 

unknown) 

High-pressure 

washing of 

sediments off the 

surface of a barge 

over the area to be 

capped 

passed through a #10 mesh 

but retained on a #40 mesh 

(0.43- to 2.0-mm-diameter 

medium sand); 9.5% passed 

through a #40 mesh but was 

retained on a #200 mesh 

(0.075- to 0.43-mm-diameter 

PAHs 

mg/kg in the upper 10 cm 

of three sediment cores 

collected within 91 m of 

the site; farther from the 

site, total PAH concentrations decreased to 18.3 ± 

6.6 mg/kg in the upper 10 

fine sand); and 0.6% passed cm of three sediment cores 

through a #200 mesh (less collected 305 m from the 

than 0.075-mm-diameter silt site (5) 

or clay) (2) 

2 
Figure 1. BOSS and On-Board Components. 

A differential Global Positioning System (developed by 

Northstar) was interfaced with the BOSS computer to 

provide vessel positioning information during sampling 

operations. 

In order to evaluate the amount of contaminants released 

into the surrounding water column before, during, and 

after capping, water samples collected by the BOSS were 

analyzed for total PCBs (i.e., sum of 18 PCB congeners 

[t-PCBs]), total PAHs (i.e., sum of 16 priority PAH 

analytes [t-PAHs]), and total suspended solids (TSS). 

If suspended sediment was visibly present in the water sample, a quartz glass fiber filter (1.0 μm) was used to remove 

larger sediment particles because they were considered to 

represent cap material, and because sediments greater than 

1.0-μm in diameter would settle relatively quickly in the 

immediate vicinity of the capping area. Smaller particles 

that passed through the filters were more likely to undergo 

long-range transport from the site. 

Samples were collected before, during, and after capping 

activities and were generally defined as: 

• Pre-Capping Survey: samples taken several days or 1 week 

before capping initiated 

• Pre-Capping Event: samples taken approximately 1 hour 

before each capping event 

• Capping Event: samples taken during capping (i.e., each 

time a lift of capping material applied) 

• Post-Capping Event: samples taken approximately 1 hour 

after each capping event 

• Post-Capping Survey: samples taken days to months after 

capping was completed 

The sampling events and sample schedule for each of the 

studies are summarized in Table 2. 

3 
4 

Figures 2 and 3 show the target BOSS transects and target typical monitoring event during capping. Actual 

sampling locations used for background surveys and active transects differed significantly based on the barge locamonitoring events (i.e., during capping) at Boston Harbor tion, capping operations, and turbidity plume migration. 

and Eagle Harbor, respectively. The top transect represents the daily Pre-Capping and Post-Capping background 

monitoring events. The bottom transect represents a 

Figure 2. Transect Line and Sampling Station Locations for BOSS 

Surveys and Monitoring at Boston Harbor. Figure 3. Transect Line and Sampling Station Locations for BOSS 

Surveys and Monitoring at Eagle Harbor. 

Table 2. Survey Event and Sample Schedule. Reprinted with permission from (2). Copyright 2006, American Society of Civil Engineers. 

Number of 

Type of Event Events Total Samples 

Boston Harbor Sample Schedule 

CAD Cell M19 CAD Cell M8 

Pre-Capping Survey 1 5 5 10 

Pre-Capping Events 1 – 4

Capping Events 1 – 4

Post-Capping Events 1 – 4 

4 

4 

4 

3 

9 

3a 

-­

-­

-­

12 

36 

10 

Pre-Capping Events 5 – 8

Capping Events 5 – 8

Post-Capping Events 5 – 8 

4 

4 

4 

-­

-­

-­

3 

9 

12 

36 

12 

Post-Capping Survey

Total 

1 5 

3 

5 

10 

138 

Eagle Harbor Sample Schedule 

Capped Area 

Pre-Capping Surveyb 1 3 3 

Day 1, Capping Events 1-3

Day 2, Capping Events 1-3

Day 3, Capping Events 1-3 

3 

3 

3 

6 to 9c 

6 to 9c 

6 to 9c 

24 

24 

24 

Days 1-3, Post-Capping Events 3 3 9 

Post-Capping Survey 1 15 15 

Total 108 

a - Sampler struck bottom immediately following sample collection for the first Post-Capping Event 3 sample, and system components fouled with mud. As a result, 

the second and third samples for Post-Capping Event 3 could not be collected.

b - Pre-capping samples were collected by divers during a separate site investigation, and the AMT was not used for the pre-capping survey. 

c - Nine samples were collected daily during Transects 1 and 2, and six samples were collected daily during Transect 3. 
 

5 

Figure 4. Boston Harbor Turbidity and TSS Maps for Cell M19. 

TSS values were based on turbidity readings and correlations derived from measured turbidity and TSS samples. Reprinted with permission from (2). Copyright 2006, American Society of Civil Engineers. 

Figure 5. Average t-PAH Concentrations at Boston Harbor Cell 

M19. Error bars represent the standard error. *Elevated concentration 

for Pre-Capping Event 2 is attributed to the engine turbulence of a large 

container ship that docked near Cell M19 during sampling. 

Reprinted with permission from (2). Copyright 2006, American Society of 

Civil Engineers. 

Figure 6. Average t-PCB Concentrations at Boston Harbor Cell 

M19. Error bars represent the standard error. *Elevated concentration for Pre-Capping Event 2 is attributed to the engine turbulence of a 

large container ship that docked near Cell M19 during sampling. 

Reprinted with permission from (2). Copyright 2006, American Society of 

Civil Engineers. 

Results and Discussion 

Boston Harbor 

Two-dimensional turbidity maps using levels detected 

by the BOSS were generated to depict turbidity levels in 

the area where capping took place, as shown in Figure 4. 

Turbidity data generated by the BOSS in-situ sensors were 

calibrated using TSS concentrations measured in the water 

samples. Cells M8 and M19 produced similar turbidity 

and TSS data; however, only results for CAD Cell M19 

are depicted in Figure 4. The highest turbidity and corresponding TSS concentrations were noted during the first 

capping event, followed by progressively decreasing turbidity and TSS during subsequent events. This observation 

clearly indicates that the amount of bed sediment resuspended decreased with each successive capping event. 

In order to quantify changes in contaminant concentrations in the water column caused by capping activities, 

analytical results of water samples collected before, during, 

and after capping activities were compared. As indicated 

previously, results obtained for both CAD Cells M8 and 

M19 were similar; therefore, only results from Cell M19 

are presented here. Figures 5 and 6 indicate that the t-PAH 

and t-PCB concentrations collected during Capping Event 

1 were much greater than for any of the successive capping 

events, suggesting that the greatest release of contaminants 

* 

* 
 

occurred when cap material was placed on previously 

uncapped sediment. Statistical comparisons among the 

four capping events were conducted by omitting the data 

from the Pre-Capping and Post-Capping Events and using 

Tukey multiple comparisons at a fixed significance level of 

0.10. For t-PAHs, Capping Event 1 concentrations were 

significantly greater than those for Capping Events 2, 3, 

and 4, and there were no significant differences between 

Capping Events 2, 3, and 4. For t-PCBs, Capping Event 

1 concentrations were significantly greater than those for 

Capping Events 2 and 3. Capping Event 4 concentrations 

could not be distinguished from those for Capping Events 

1, 2, and 3, and resided somewhere between these three 

capping events. 

Turbidity concentration plots for Capping Events 1 

through 4, the Pre-Capping Survey, and the Post-Capping 

Survey for Cell M19 and water sample locations are plotted 

in Figure 4. The relationship between contaminant concentrations and turbidity was analyzed by plotting t-PAH 

and t-PCB against TSS concentrations for water samples 

collected during capping operations. The correlation 

coefficients (r2

 values) for the best-fit linear regression lines 

were calculated (2). Despite the visual observation that 

higher TSS/turbidity concentrations during Capping Event 

1 coincided with higher t-PAH and t-PCB concentrations, 

as shown in Figures 5 and 6, a strong correlation between 

high TSS concentrations and high organic contaminant 

concentrations could not be determined statistically. It is 

likely that the contribution of bed sediments to TSS and 

turbidity was overshadowed by the TSS from the cap material. 

Eagle Harbor 

TSS concentrations measured in the water samples and turbidity data generated by the BOSS in-situ sensors were used 

to develop two-dimensional turbidity maps, shown in Figure 7, to display turbidity levels in the area where capping 

took place. Elevated turbidity levels were observed at varying distances and along different directions from the barge, 

extending beyond the boundaries of the study area based 

on analysis of samples collected outside the study area. The 

Post-Capping Event map in Figure 7 shows that turbidity 

levels quickly decreased to near Pre-Capping Event transect 

levels within 1 to 2 hours after capping. As with Boston 

Harbor, the contribution of TSS from the cap material 

itself may have partially overshadowed the contribution of 

bed sediments to elevated turbidity and TSS levels. Nonetheless, in the vicinity of the capping operations, turbidity 

and TSS levels were highest during Capping Events 1 and 

2, indicating decreased turbidity with successive capping 

events. These data suggest that the measured turbidity includes a significant contribution from in-situ sediment, and 

not only capping material during the initial capping events. 

Average t-PAH concentrations measured for the successive 

sampling events conducted over the 3-day Eagle Harbor monitoring period are shown in Figure 8. Elevated 

contaminant concentrations were observed during capping operations, which appeared to decrease with each 

successive capping day and dissipated after capping was 

completed. Such rapid dissipation likely was the result of 

the combined effects of sedimentation and off-site plume 

t= -1 hr 

t= 0 hr
 

Lift 1
 

t= +3 hr
 

Lift 2
 

t= +4 hr
 

Lift 3
 

t= +5 hr 

Figure 7. Turbidity and TSS Maps for Eagle Harbor Day 3. TSS 

values were based on turbidity readings and correlations derived 

from measured turbidity and TSS samples. Reprinted with permission 

from (2). Copyright 2006, American Society of Civil Engineers. 

6 
Figure 8. Average t-PAH Concentrations at Eagle Harbor. Error 

bars represent standard deviations. Reprinted with permission from (2). 

Copyright 2006, American Society of Civil Engineers. 

migration. A two-way analysis of variance was conducted 

to determine whether there were statistically significant differences between different days or sampling events within a 

single day using the raw data, log-transformed data, and a 

significance level of 0.10. Because of high data variability, 

no statistically significant differences were found between 

the four sampling events (i.e., samples collected during 

Capping Events 1, 2, and 3, and the post-capping sample) 

within any single day for Days 1, 2, and 3, and no differences existed between Days 1, 2, and 3. 

Scatter graphs plotting t-PAHs against TSS were generated 

to determine the relationship between contaminant concentration and turbidity. During the first survey day, 

r

2

 values ranged from 0.72 through 0.95, indicating a correlation between turbidity and t-PAHs. However, r2

 values 

decreased during subsequent capping surveys and, by the 

third day, r2

 values were less than 0.54, indicating that a 

correlation between turbidity and t-PAHs was lacking. As 

with Boston Harbor, it is suspected that the suspended solids generated by the cap material overshadowed the solids 

resulting from suspension of contaminated bed sediments 

during subsequent capping events (i.e., after capping events 

1 and 2). 

Conclusions 

A comparison of sampling results at Boston Harbor and 

Eagle Harbor is provided in Table 3. COC levels were 

below detection limits or at very low levels at both sites 

before capping. The highest resuspension of contaminated 

material was seen during the first capping event at both 

sites. In general, contaminant resuspension, although 

substantially higher than observed during pre-capping 

sampling, was relatively low for all capping events during 

both surveys, where contaminant concentrations remained 

in the low ng/L range for most samples. Resuspension of 

TSS and COCs occurred continuously throughout capping 

operations but dissipated to background levels in a matter 

of hours following cessation of capping activities. 

Data generated during these two studies have helped to 

achieve a better understanding of the amounts and patterns 

of contaminants released into the surrounding water column resulting from the capping events. Data from Boston 

Harbor and Eagle Harbor indicate that the resuspension of 

contaminated sediments was measurable, but relatively low, 

when capping was conducted over uncapped sediments. 

Based on the results of the two studies summarized here, 

resuspension during capping may be reduced by placing cap material in lifts in which the first lift provides 

a uniform layer of clean material using techniques that 

minimize potential disturbance. The data presented here 

suggest that subsequent lifts could be placed more aggressively once the contaminated sediment is covered. 

References

(1) United States Environmental Protection Agency. 2005. Contaminated Sediment Remediation Guidance for Hazardous Waste Sites, 

OSWER 9355.0-85, EPA540/R05/012. December. (http://www.

epa.gov/superfund/resources/sediment/pdfs/guidance/pdf). 

(2) Lyons, T., J.A. Ickes, V.S. Magar, M. ASCE, C.S. Albro, L. Cumming, B. Bachman, T. Fredette, T. Myers, M. Keegan, K. Marcy, 

and O. Guza. 2006. Evaluation of Contaminant Resuspension 

Potential during Cap Placement at Two Dissimilar Sites. J. Environ. 

Eng., 132 (4): 505-514. 

(3) U.S. Army Corps of Engineers. 1988. Navigation Improvement 

Study Feasibility Report and Environmental Assessment. Boston Harbor, Massachusetts. Mystic River, Chelsea River and Reserved Channel. 

New England Division, Waltham, MA. 

Table 3. Concentrations of Suspended Contaminated Sediments Before, 

During, and After Capping. 

(4) U.S. Army Corps of Engineers. 1999. Chemistry 

Data Report – Boston Harbor Navigation and Berth 

Dredging, Boston Harbor. August 5. 

(5) Brenner, R.C., V.S. Magar, J.A. Ickes, J.E. Abbott, 

S.A. Stout, E.A. Crecelius, and L.S. Bingler. 2002. 

Characterization and Fate of PAH-Contaminated 

Sediments at the Wyckoff/Eagle Harbor Superfund 

Site. Environ. Sci. Technol., 36 (12): 2605–2613. 

Boston Harbor Eagle Harbor 

Monitoring Event PCB (ng/L) PAH (ng/L) PAH (ng/L) 

Before Capping BDL 46 – 59 46 – 73 

During Capping BDL – 84 65 – 5,242 20 – 3,872 

After Capping 0.4 – 1.5 41 - 83 38 - 159 

BDL - below detection limits 

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