1

U.S. Department of the Interior

U.S. Geological Survey

USGS Water-Resources Investigations Report 00–4245

December 2000

Figure 2. Location of the Fox River point-source discharge sites, dams, and the SMU 56/57

remediation project.

A Mass-Balance Approach for Assessing PCB Movement During

Remediation of a PCB-Contaminated Deposit on the Fox River, Wisconsin

The U.S. Geological Survey, in cooperation

with the Wisconsin Department of Natural Resources, collected water samples during the September 1–December 15, 1999 removal of sediment contaminated with polychlorinated biphenyls (PCBs) from a reach of the Lower Fox

River designated Sediment Management Unit

(SMU) 56/57. Results of analyses of the samples,

along with monitoring activities of several other

organizations, were used to delineate and compare PCB mass pathways during the cleanup

effort (fig. 1). Results indicate that the cleanup

at SMU 56/57 had the following effect on PCB

mass: dredging permanently removed more than

650 kg (1441 lb) of PCBs, transported 14.5 kg

(32 lb) downstream, and volatilized 2.6 kg (5.7

lb) to the atmosphere; associated activities on

the shore returned 0.1 kg (0.3 lb) to the river.

This report documents the USGS data-collection efforts and details the mass-balance approach for PCB pathway delineation.

Figure 1. Pathways of polychlorinated biphenyl (PCB) mass (Aroclor 1242) during

the September 1–December 15, 1999 remediation at SMU 56/57. Amounts are in

kilograms.

Introduction

Water quality and aquatic life in the

Lower Fox River, which flows from

Lake Winnebago to Green Bay (fig. 2),

have been affected by contaminants that

have accumulated in streambed sediments over the last several decades. The

Wisconsin Department of Natural Resources (WDNR) has determined that

contaminants released from Fox River

sediment deposits cause exceedances of

State water-quality standards and necessitate fish-consumption advisories. From

the perspective of human health and

ecological risk, polychlorinated biphenyls (PCBs) and mercury are the principal contaminants of concern. Sampling

has confirmed that sediment-associated

PCBs and mercury are accumulating

within the aquatic food chain and are

actively being transported within the

river and out into Green Bay and Lake

Michigan (Brazner and DeVita, 1998).

Green Bay

DePere

Menasha

Appleton

Kimberly

Kaukauna

Little

Rapids

Little

Chute Wrightstown

0 1 2 3 4 5 MILES

Neenah

Doty Island 

Little Lake Butte

des Morts 

Lake

Winnebago 0 1 2 3 4 5 KILOMETERS

88°30'

44°30'

44°15'

88°

Municipal areas

Point-source discharge site*

Dam

Acoustic

velocity flow

meter

SMU 56/57

dredge area

EXPLANATION

(USGS site 040851385)

Green Bay

Fox 

River 

study 

area

L a

k e

M i c h i g a n

*described in Steuer and others, 1995

WISCONSIN

N

Fox

River

 Lake

Winnebago

East

River

Removed permanently

from stream (trucked) Volatilized 2.6 kg

Fox River

Removed permanently

from stream (trucked)

Returned to 

river 

0.1 kg

Transported 

into dredged 

area 

Transported 

out of dredged

area

Net watercolumn load 

654 kg

20.9 kg

35.4 kg

14.5 kg

Volatilized (upstream from SMU 56/57) 3.7 kg Volatilized 2.7 kg
2

Figure 4. Fox River streamflow and sample-collection times on December 13, 1999.

Figure 3. Location of SMU 56/57 and samplecollection sites.

The Sediment Management Unit 56/57 (SMU 56/57) remediation

project was a joint effort between the State of Wisconsin and the

Fox River Group (FRG), a coalition of paper companies. A

primary purpose of the project was to remove PCB-contaminated

sediment by dredging and thereby generate information relevant to

the effectiveness of large-scale dredging and disposal of the

sediments (in this case, 7–11 million cubic yards) from the Lower

Fox River (ThermoRetec Consulting Corp., 1999; Blasland, Bouch,

and Lee, Inc., 1999; Montgomery Watson, 2000). A hydraulic

dredge was used to pipe a sediment slurry from the river bottom to

a settling basin; the onshore operation consisted of filter-pressing

the slurry, filtering the liquid effluent and returning it to the stream,

and trucking away the solids. In support of the sampling plan

designed by the FRG and WDNR, a mass-balance approach (a

combined examination of concentration and flow) was used to

determine the effectiveness of dredging in removing the PCBs

from the river environment.

Description of the study area

In 1995, sediment mapping by the WDNR in the 7-mile reach of

the Fox River between the De Pere dam and the river mouth

revealed a nearly continuous mass of soft sediment deposits. SMU

56/57 is approximately midway between the De Pere Dam and

Green Bay. A papermill is adjacent to SMU 56/57; its discharge

pipe is upstream from the dredged site and the upstream watercolumn sampling transect. A permeable silt curtain fabric was

deployed around the dredged area that allowed passage of water but

reduced transport of sediment and protected the papermill water

intake (fig. 3).

This area is a commonly used offloading area for coal ships. The

offloading slip is immediately downstream from SMU 56/57, and

the turning basin used by these deep-draft vessels is adjacent to the

deposit area (fig. 3). Fifteen coal ships offloaded cargo during the

15-week dredging operation.

SMU 56/57 has a surface area of approximately 9 acres with

overlying water depths of 2–14 ft. Maximum sediment thickness

was 16 ft with an overall average PCB concentration of 53 ppm

(parts per million). Maximum PCB concentration was 710 ppm,

the highest concentrations being in the top 2–5 ft. Total PCB mass

in the deposit was estimated to be between 2,090 and 3,000 kg

(4,600–6,600 lb) (Montgomery Watson, 2000; Blasland, Bouch,

and Lee, Inc., 1999).

 The lower 7-mile reach of the Fox River has an ever-changing

flow and depth oscillation commonly found in estuaries. Flow

reversals (from Green Bay toward De Pere Dam) are common in

this reach (fig. 4). A continuous streamflow record for the river at

SMU 56/57 was based on stream-velocity data collected at 15-

minute intervals with a double-path acoustic velocity meter located

approximately 2.7 mi downstream from the deposit and 0.8 mi

upstream from the river mouth at Green Bay (USGS site 040851385,

fig. 2). Because the dredging-site location was upstream from the

acoustic-velocity-meter site and the inflow point of the East River,

the daily mean streamflow was adjusted by a factor of 0.98 to

account for the basin area difference.

The average water depth in this reach of the river is a function

of Lake Michigan and Green Bay water levels, wind speed and

direction, and flow over the De Pere Dam (which depends on

precipitation and control at nine upstream dams). During 1999, the

river depth at the USGS acoustic-velocity-meter site varied by

more than 6 ft; during the dredging period (September 1– December 15, 1999) depth varied by more than 4.2 ft. River depth is

important to sediment and PCB transport in that, for a given flow,

water velocity increases as river depth decreases. An increase in

water velocity results, in turn, in an increase to the fourth power for

sediment resuspension (Jepsen and others, 1997).

Sampling methods

Water-column samples collected before, during, and after dredging operations were analyzed to support calculations of the mass

transport of PCBs. The samples were collected from four discrete

sites along an upstream transect and five sites on a downstream

transect (fig. 3). Site spacing was closest in areas of focused flow

(as determined by a portable Doppler flow meter). The southeast

side of the channel is the deeper part and contains most of the flow;

therefore, sample-collection sites are skewed toward that side. At

-10,000

-8,000

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

8,000

10,000

12:00 AM 4:00 AM 8:00 AM 12:00 PM 4:00 PM 8:00 PM

STREAMFLOW, IN CUBIC FEET PER SECOND

Streamflow

Upstream transect sub-site sample

Downstream transect sub-site sample

A1

A2

B

C

D

Downstream transect

Upstream transect

Turning

basin

(19 feet deep)

B

A

C

D Fox River

Papermill

discharge

Papermill

intake

Chicago Northwestern Railroad

FLOW

0 150 300 FEET

DOMINANT

1

7

14

2

2

1

2

7

8

9 13

7

10

9

3

9

13

17

A

EXPLANATION

Continuous

turbidity meter

(site contractor)

Silt curtain

Navigation channel

boundary

Water depth, in feet

Sample-collection

site

17

15

9

11

N

DEPOSIT

AREA

Coal vessel offload slip

Green

Bay

DePere

Study 

area
3

Figure 6. Mean total suspended solids concentrations and turbidity values for the site locations,

Fox River, Wis.

Mean turbidity (dredging period)

Mean total suspended solids (dredging period)

20

21

22

23

24

25

26

27

28

29

30

ABC D

Site

CONCENTRATION, IN MILLIGRAMS PER LITER

25

26

27

28

29

30

31

32

33

34

A1 A2 B C D

Site

Downstream transect

Upstream transect Downstream transect

Upstream transect

NEPHELOMETRIC TURBIDITY UNITS

each site, water was collected from two depths, at 20 percent and

80 percent of the total water depth. For a given transect (upstream

or downstream), water from the transect sites was composited

throughout the day to provide a representative PCB concentration

for each transect. During the dredging operation, each transect

(upstream and downstream) was sampled 2–3 times per sample

day, resulting in 36 sample (daily composite) pairs. In addition to

transect composites, discrete total suspended solids (TSS) samples,

and water-quality field measurements (temperature, turbidity, pH,

and specific conductance) were obtained from each site. At the

original downstream site A, it appeared that dredging could

produce a contamination plume that could remain close to shore

and not be collected. Therefore, section A was divided to create

sites A1 and A2, with collection volumes halved.

Water-column samples were collected over an 8–12 hour period

on each of 36 sample days during the 15-week dredging operation.

Efforts were made to collect water only during periods of outgoing

flow (fig. 4).

Upstream and downstream composite samples were analyzed

for 101 individual PCB congeners (dissolved and particulate),

TSS, dissolved organic carbon (DOC), and total organic carbon

(TOC). The dredging contractor also collected turbidity data

continuously at several sites during most of the dredging operation

(fig. 3).

Composite water-column samples (80-L volume) were filtered

through 0.7-μm glass fiber filters to determine particulate congener PCB concentrations. Filtrate was pumped through an absorbent resin column (that is, XAD-2) to concentrate PCBs for the

operationally defined “dissolved” phase. Complete procedures for

80-L PCB water-column samples are described in the dredgingproject quality assurance plan (Blasland, Bouck, and Lee, Inc.,

1999). Total PCB concentrations were computed by summing the

dissolved and particulate fractions; concentrations reported as

being less than the laboratory detection limit were given a zero

value. Daily mean river discharge was used in conjunction with the

water-column concentration data to compute daily TSS and PCB

loads.

On certain days, the entire sampling process was repeated to

produce sample duplicates for analysis of PCB (6 duplicates) and

TSS (3 duplicates). The purpose of the sample duplicates was to

assess the ability to detect real change in the

environment (that is, isolate laboratory and

sampling artifacts from environmental

change). The mean relative percent differences between sample duplicates were 5 percent for total PCB samples (combined dissolved and particulate phases); 10 percent for

composited TSS samples; and 12 percent for

discrete TSS samples. These duplicate results

are similar to those from previous sampling

efforts (Fox River Remediation Advisory

Team, 2000).

Suspended-solids transport during

dredging

 When averaged over the length of the

dredging operation, little difference was found

between the upstream and downstream TSS

and turbidity values. Periodic differences, however, were substantial (fig. 5). These differences were not consistent—at times net

TSS increased over the dredging area, and at other times it decreased.

 A consistent lateral pattern was evident at the upstream site (fig.

6). TSS concentrations were generally highest closest to the

papermill wastewater-treatment plant discharge pipe (570 lb/d),

and concentrations decreased away from this pipe.

The TSS concentrations at the sample-collection sites provided

insight regarding shipping operations. On the mornings of October

8 and November 3, 1999, coal-ship departure appeared to have

resuspended PCB-laden sediment (fig. 7). This increase in suspended sediment was in agreement with the continuous turbidity

data collected by the site contractor (Montgomery Watson, 2000).

A similar effect was observed on the two other days (October 14

and November 23) when PCB water-column samples were collected coincident with vessel movement.

Figure 5. Daily mean total suspended solids concentrations and turbidity

values for the upstream and downstream transects, Fox River, Wis.

Turbidity

Total suspended solids

0

10

20

30

40

50

60

70

CONCENTRATION, IN MILLIGRAMS PER LITER

Upstream transect; mean = 25.8 mg/L

Downstream transect; mean = 24.0 mg/L

Start of dredging

0

10

20

30

40

50

60

70

8/1/99 8/21/99 9/10/99 9/30/99 10/20/99 11/9/99 11/29/99

8/1/99 8/21/99 9/10/99 9/30/99 10/20/99 11/9/99 11/29/99

NEPHELOMETRIC TURBIDITY UNITS

Upstream

Downstream

Start of dredging
4

PCB concentration changes during dredging

After dredging started on September 1, a consistent PCB

concentration increase was evident at the downstream site (fig.

8A). The mean upstream concentration of PCB was 50.7 ng/L and

the downstream PCB concentration was 92.0 ng/L. The paired

upstream-downstream samples had a mean relative percent difference of 59 percent, substantially larger than the 5-percent difference between sample duplicates.

Initially, it seems contradictory that PCB concentration increased while suspended solids loading remained the same or

decreased (because of settling) during the dredging operation.

However, material exposed to or resuspended into the water

column during dredging increased the dissolved PCB concentration (fig. 8B), as well as the PCB concentration on a given particle

(fig. 8C). Therefore, even though the overall mass of particles

transported downstream did not increase, the PCB in solution and

transported on the particles did increase.

The TSS and PCB comparison (downstream minus upstream)

illustrates that TSS is not a reliable indicator of PCB transport

during a dredging operation. For example, from September 1 to

October 6, a period of negative TSS loading (less at the downstream than at the upstream site), the PCB loading was positive.

Thus, if one is to monitor PCB transport during a remediation

operation, sole reliance on turbidity or TSS measurements is

inadequate. One must also directly measure the concentration of

the contaminant of interest because exposed layers of contaminated sediment and exposed concentrated pore waters can contribute to particle- and dissolved-phase PCB concentrations in downstream waters. Concentration data, however, do not form a complete picture of the effects of dredging; the mass of transported

PCBs also must be taken into account.

Figure 7. Total suspended solids concentrations at the site locations on October 8 and

December 13, 1999, Fox River, Wis.

Figure 8. PCB concentrations at the upstream and downstream

transects before and during dredging operations, Fox River, Wis.

Downstream - November 3, 1999

Upstream - October 8, 1999 Upstream - November 3, 1999

Downstream - October 8, 1999

0

10

20

30

40

50

60

70

80

90

100

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36

TOTAL SUSPENDED SOLIDS

CONCENTRATION, IN MILLIGRAMS PER LITER

TOTAL SUSPENDED SOLIDS

CONCENTRATION, IN MILLIGRAMS PER LITER

Site A - deposit site

Site B

Site C

Site D

0

10

20

30

40

50

60

70

80

90

100

7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 Ship departure

PCB = 58.0 ng/L

PCB = 85.4 ng/L

7:00 8:12 9:24 10:36 11:48 13:00 14:12 15:24 16:36

7:00 8:12 9:24 10:36 11:48 13:00 14:12 15:24 16:36

PCB = 58.3 ng/L

PCB = 102.1 ng/L

0

20

40

60

80

100

120

140

0

20

40

60

80

100

120

140

Ship departure

TIME TIME

Total PCB - congener summation

Dissolved PCB

Particulate PCB

0

50

100

150

200

250

300

CONCENTRATION, IN NANOGRAMS PER LITER

Upstream transect

Downstream transect

Coal-vessel movement during samle collection

Coal-vessel movement before sample collection

Start of dredging

0

20

40

60

80

100

120

CONCENTRATION, IN NANOGRAMS PER LITER

Start of dredging

Start of dredging

0

1

2

3

4

5

6

7

8

CONCENTRATION, IN MICROGRAMS PER GRAM

8/1/99 8/21/99 9/10/99 9/30/99 10/20/99 11/9/99 11/29/99

Upstream transect

Downstream transect

Upstream transect

Downstream transect

A

B

C

DATE
5

PCB loading in the Fox River due to the dredging

operation

Putting the PCB concentration increase in a useful context

requires calculation of mass fluxes, such as the daily PCB load

(expressed as mass) to the water due to dredging operations and the

amount of PCB processed in the onshore operations. For a given

sample-collection day, the PCB load due to dredging operations

was calculated by multiplying daily streamflow by total PCB

concentration (summation of all congeners, dissolved and particulate).

A daily net PCB load due to dredging (fig. 9) was computed by

multiplying the difference between the downstream and upstream

PCB concentrations on a given sample day by the daily discharge.

Net PCB loads, in general, increased after November 15. This result

is consistent with a change in operations: the dredge had been

moved to an area of the deposit that contained higher PCB concentrations and was closer to the downstream transect (Blasland,

Bouck, and Lee, Inc., 2000). Additionally, streamflow increased

substantially after November 15 (fig. 10).

An initial overall PCB load estimate was calculated using the

median daily PCB load for the two intervals (before November 16

and after November 15). The median was used, rather than the

mean, because daily PCB loads were not normally distributed for

either interval. The median daily PCB loads for each interval (42.4

gm and 364.3 gm, respectively) were multiplied by the median

flows to provide initial load estimates of 3.2 kg and 10.9 kg,

respectively.

Further PCB loading analyses

examined relations with variables

that were measured daily (dredgeslurry settled-fraction concentrations and supernatant concentrations). Concentrations of the material being removed from the deposit or the amount of dredging

per day might be indicators as to

how much PCB was transported

downstream. Frequently monitored variables such as turbidity,

streamflow, and stream depth also

were examined. A usable regression relation could not be developed for the interval prior to November 16. For the dredging

interval after November 15, however, a regression was developed

in which four factors explained much of the variability (r2

 = 0.88):

daily PCB concentration of the incoming slurry mixture (settled

fraction (Set) and supernatant (Sup)), time spent dredging on a

given day (T), and stream depth (D).

The daily PCB loads resulting from this regression equation (fig.

9) were summed to arrive at a load of 13.7 kg for the postNovember 15 dredging period. The standard error was 25 percent

of the mean.

The final estimated PCB load (16.9 kg), combining the median

based pre-November 16 load (3.2 kg) with the regression-based

post-November 15 load (13.7 kg), was selected as a conservative

approach.

An estimated PCB load entering into the dredged area from

upstream (fig.1) was computed by applying the median daily

upstream PCB concentration (51.4 ng/L) to the median daily flow

(1,842 ft3/s) for the 106 days. The result was an estimated overall

PCB load of 24.5 kg entering the deposit cross-section from

upstream.

Congener distribution changed noticeably during dredging (fig.

11). Congeners 5/8, 4/10, and 6—congeners that readily volatilize

to the atmosphere—are noticeably less prevalent at the upstream

site than at the downstream site. Air monitoring during remediation

has shown that the river routinely volatilizes PCB to the atmosphere; thus depletion of these congeners is not surprising at the

upstream site. Sub-surface sediments and pore waters that are

newly exposed during the dredging may replenish these congeners,

as is reflected by concentrations at the downstream site.

The Fox River Mass Balance Study (Steuer and others, 1995)

estimated a PCB volatilization-to-advection ratio of 13 percent.

Applying this ratio to the upstream PCB advection (20.9 kg;

Aroclor*1242) yields an estimated 2.7 kg volatilization from the

Fox River upstream from SMU 56/57 during the dredging period.

Air monitoring at the shore-processing site indicated that between

0.3 to 4.9 kg of PCB volatilized from that facility during the 106

days of onshore processing (Blasland, Bouck, and Lee, Inc., 2000;

David Grande, Wisconsin Department of Natural Resources, written comm., 2000).

To put into context the PCB input to the water column during the

dredging operation (16.9 kg), one can consider PCB loading from

9/1/99 9/21/99 10/11/99 10/31/99 11/20/99 12/10/99

DAILY LOAD, IN GRAMS

-500

0

500

1,000

1,500

2,000

PCB load

Coal-vessel movement during sample

collection

Coal-vessel movement before sample

Daily PCB load regression

collection

Figure 9. Daily water-column PCB load in the deposit area during the dredging operation on the

Fox River, Wis.

Figure 10. Fox River daily streamflow and sample-collection days from

August 1, 1999, to March 31, 2000.

Daily PCB load (gm) = (-507.9 )(D) – (1237.9)(T) – (5.69)(Set) + (32.5)(Sup) + 293,703

-2,000

-1,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8/1/99 9/1/99 10/2/99 11/2/99 12/3/99 1/3/00 2/3/00 3/5/00

STREAMFLOW, IN CUBIC FEET PER SECOND

Streamflow

Sample day
6

Figure 12. Fox River PCB loading to Green Bay, April 1994 through

October 1995.

the river with no dredging taking place. The monthly river PCB

load is variable (fig. 12); in 1994-95, annual Fox River PCB

loading (congener summation) was 186 kg/yr (D.W. Hall, U.S.

Geological Survey, written commun., 1999).

PCB transport back into the river from the onshoreprocessing operation

After filter presses removed most solids from the incoming

slurry, the effluent was passed through sand and carbon filters

before being discharged back to the river at a rate of more than

700,000 gal/d. On five days, 80-L samples were collected by the

USGS (over an 8–12 hour period) from the shore-process-discharge pipe. Total PCB concentrations in the effluent ranged from

82 –676 ng/L with a mean concentration of 422 ng/L. These values

did not appear to be normally distributed. A conservative approach,

applying the median concentration (509 ng/L) to the effluent

volume discharged during the entire dredging operation (76,213,900

gallons), resulted in 0.147 kg of PCBs being returned to the river.

Of the 654 kg of PCBs that were processed onshore or held in the

settling basins (Montgomery Watson, 2000; Richard Weber, Montgomery Watson, written comm., 2000), less than 0.03 percent was

returned to the river. Additionally, the congener distribution (fig.

13) of these effluent samples was markedly different from that in

the water column samples—most of the more chlorinated congeners (higher health risk) had been removed. Thus, a very small PCB

mass was returned to the river, and this small mass was made up of

a less toxic PCB mixture.

Postdredging PCB concentrations and loads

Dredging was discontinued on December 15, 1999. Low temperatures and freezing water in pipelines, process equipment, and

the river surface required too many operating adjustments in all

aspects of the hydraulic-dredging, water-treatment, and dewatering processes for the operation to continue.

Three sets of water-column samples at the two transects were

collected after the termination of dredging. Net daily PCB transport decreased (range was –12 g/d to 2 g/d) from that during active

dredging. The dissolved-phase PCB concentration, however, still

increased substantially from upstream to downstream (fig. 14) due

to the deposit (a 15–21 percent increase). On two of the sampled

postdredging days, the particulate PCB concentration decreased

(as did TSS concentration) at the downstream site. Apparently, the

dredged area may be functioning, at least temporarily, as a depositional area. Daily mean flows during the postdredging sampling

were moderate—less than 3,000 ft3

/s (fig. 10)—and also may have

tended to promote deposition.

Even though a new sediment layer is exposed—with greater

PCB concentrations at the sediment surface than before the start of

dredging (thus the observed increase in dissolved PCB)—the

overall PCB concentration has decreased because of settling of

particles in the dredged area. These data do not indicate how long

this settling will continue, or at what rate of streamflow the

deposition will cease, or whether net scour of the exposed PCB

sediment will occur. The dredging operation was planned to

resume in summer or fall of 2000. The preceding observations were

based on three sets of data points; more postremediation sampling

would provide a stronger basis for conclusions.

Figure 11. Dissolved-phase PCB congener

distribution for the upstream and downstream

sites, Fox River, Wis.

0

2

4

6

8

10

12

14

16

PCB CONGENERS

PERCENTAGE OF CONGENER SUMMATION

Upstream

Downstream

 #3

 #4/10

 #5/8

 #6

 #7/9

 #15/17 #16/32

 #18 #19 #22

 #24/27

 #25 #26

 #28/31

 #33

 #37/42

 #40

 #41/71/64

#44

 #45 #46

 #47/48

 #49 #51

#52

 #53

 #56/60

 #63 #66

 #70/76

 #74

 #77/110

 #82 #83

#92/84

 #85 #87 #89 #91 #95 #97 #99

 #101 #118

#123/149

 #128

0

5

10

15

20

25

30

35

40

MONTHLY PCB LOAD, IN KILOGRAMS

Apr. 94

May 94

June 94

July 94

Aug. 94

Sept. 94

Oct. 94

Nov. 94Dec. 94

Jan. 95

Feb. 95

Mar. 95

Apr. 95

May 95

June 95

July 95

Aug. 95

Sept. 95

Oct. 95
7

Figure 14. Postdredging TSS and PCB concentration and PCB load in the

dredging-operation area, Fox River, Wis. (d/s, downstream; u/s, upstream).

Figure 13. Mean dissolved and

particulate effluent PCB congener

concentrations on the Fox River, Wis.

Adjusting water-column PCB concentrations to

allow comparison with onshore-sample PCB data

PCB aroclor analyses provided the foundation for the onshoreprocessing (slurry, trucked press cake) PCB concentrations

(Blasland, Bouck, and Lee, Inc., 1999). However, to reduce the

limits of detection, the 80-L water column samples were analyzed

on a congener-specific basis. The congener-specific analysis approach is expensive ($835 per sample); thus, only a few onshoreprocessing samples were analyzed to this level of detail. Most

samples collected onshore were examined with the less expensive

Aroclor-basis PCB analysis. Therefore, to compare water-column

results with the onshore-process PCB masses, a water-column

PCB Aroclor concentration had to be estimated (Aroclor*1242)

from the congener-specific data. This was done by an approach

developed in a previous remediation assessment (Fox River

Remediation Advisory Team, 2000). The conversion was based on

the dissolved (35 percent) and particulate (65 percent) average

phase distributions (figs. 8B and 8C) and the Aroclor/congener

sum ratios as calculated in the previous assessment.

The congener sum PCB load of 16.9 kg was adjusted to an

Aroclor*1242 basis as follows:

where 0.88 and 0.85 are the Aroclor/congener sum ratios for the

dissolved and particulate phases. Thus, the net water-column load

due to dredging is estimated to be 14.5 kilograms on an Aroclor*1242

basis. A similar conversion on the congener summation PCB load

entering the deposit area from upstream (24.5 kg) resulted in 20.9

kg PCB mass on an Aroclor*1242 basis.

Lessons learned

Commonly used techniques such as measurement of total suspended solids (TSS) and turbidity were inadequate to describe

transport of PCBs during a dredging operation in the Fox River.

Little or no measurable difference was found between the upstream

and downstream TSS concentrations (or loads) over the length of

the operation. However, neither turbidity nor TSS was sufficient to

predict PCB transport because of increased PCB concentration on

a particle and dissolved-phase PCB concentration. Approximately

35 percent of the PCB load at the downstream site was in the

dissolved phase. Results of the study described here indicate that

if chemical transport is to be quantified during a PCB remediation,

then monitoring of TSS and turbidity alone is not adequate.

The study illustrates the importance of collecting water-column

samples at numerous vertical and lateral locations to represent an

entire transect concentration. The study found lateral concentration differences that would skew a sample if the entire cross-section

was not adequately sampled. Additionally, in a dynamic situation

(dredging operation), even in a large river, sampling over a prolonged interval is necessary to obtain a representative daily concentration of a constituent of interest.

Aroclor*1242 PCB load = (0.35)(16.9 kg)(0.88) + (0.65)(16.9 kg)(0.85) = 14.5 kg , 

(Dissolved) (Particulate)

0

20

40

60

80

100

120

PCB CONGENERS

CONCENTRATION, IN NANOGRAMS PER LITER

Dissolved

Particulate

n = 5 samples

 #3

 #5/8

#7/9

 #16/32

 #19

 #24/27

 #26 #33 #40

#44

 #46

#49#52

 #56/60

 #66

#74

 #82

 #92/84

 #87 #91 #97

 #101

 #123/149

 #132/153/105

 #136

 #163/138

 #146 #158

 #170/190

 #172 #177 #180 #183 #193

 #208/195

 #198

#201

 #207

Postdredging - PCB or TSS load change (d/s - u/s)/(u/s) 

Net water-column PCB load (d/s - u/s)

-20

0

20

40

60

80

2/21/00 3/2/00 3/12/00 3/22/00 4/1/00

2/21/00 3/2/00 3/12/00 3/22/00 4/1/00

DAILY PCB LOAD,

 IN GRAMS

-40

-30

-20

-10

0

10

20

30

CONCENTRATION CHANGE, 

IN PERCENT

Dissolved PCB

Particulate PCB

Total suspended solids
8

Information

For information on this study or on other USGS programs

in Wisconsin, contact:

Author: Jeffrey J. Steuer

Printed on recycled paper

cubic foot per second (cfs) .02832 cubic meter per second

gallon (gal) 3.785 liter (L)

inch (in) 0.00003937 micron (μm)

pound (lb) 0.4536 kilogram (kg)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

acre 0.4047 hectare

Multiply by to obtain

CONVERSION FACTORS AND ABBREVIATIONS

Furthermore, the results of this study illustrate that a concentration-based approach to assessing remediation can be misleading.

Clearly, the water-column PCB concentration increased as a result

of dredging, but until this concentration is converted to a mass

basis, comparisons such as the following cannot be made: that the

PCB load into the water-column mass represented less than 2.5

percent of what was dredged from the deposit and approximately

9 percent of what was annually transported by the Fox River in

1994–95. The onshore-process effluent median PCB concentration of 509 ng/L may initially appear substantial, but when converted to a mass (0.147 kg), one can conclude that this is negligible

compared to the mass of PCBs that was permanently removed from

the deposit. Lastly, concentration-based approaches do not necessarily require a sample that represents an entire cross-section. Such

sampling, if done only on the deposit side of the river (fig. 6),

would have provided a biased data set.

Dredging ceased during arrival and departure of the coal vessels; ship movement apparently increased PCB transport in the

area. On four sampling days, vessels moved in or out of the area

shortly before or during sample collection (fig. 9). On the two days

when ship movement coincided with sample collection, the PCB

transport increase was more pronounced (400–600 g). The PCB

loading increase due to vessel movement was probably not sustained throughout the entire day; thus, applying a daily mean flow

to this concentration probably biased the resulting PCB load on the

high side. The concentration increase during vessel movement

(figs. 7 and 9), however, is substantially higher than the predredging

days in August or the postdredging days (fig. 14). Vessel movement is a continuing PCB transport mechanism regardless of

dredging operations.

In summary, hydraulic dredging, by means of a horizontal auger

cutter head and permeable silt curtain, resulted in a net PCB load

(Aroclor 1242) of 14.5 kg to the water column in the Fox River

while 654 kg were permanently removed from the deposit. At the

same time, less than 0.15 kg was discharged back to the water

column from the onshore processing (fig. 1). This is compared to

an annual load (congener summation) (1994–95) of 186 kg from

the Fox River into Green Bay.

References

Blasland, Bouck, and Lee, Inc., 1999, Draft quality assurance

project plan—environmental monitoring of SMU 56/57 demonstration project—Mass balance approach: Syracuse, New York

Blasland, Bouck, and Lee, Inc., 2000, Fox River dredging demonstration projects at sediment deposit N and sediment management unit 56/57: Syracuse, New York

Brazner, J., and DeVita, W., 1998, PCBs, DDE, and mercury in

young-of-the-year littoral fishes from Green Bay, Lake Michigan: Journal of Great Lakes Research v. 24, no. 1, p. 83–92.

Fox River Remediation Advisory Team, 2000, Evaluation of the

effectiveness of remediation dredging—The Fox River deposit

N demonstration project, November 1998–January 1999: University of Wisconsin–Madison, Water Resources Institute Special Report, WRI SR 00-01, http://www.dnr.state.wi.us/org/

water/wm/lowerfox/sediment/frratdepositnreport.pdf

Jepsen, R., Roberts, J., and Lick, W., 1997, Effects of bulk density

on sediment erosion rates: Water, Air and Soil Pollution, v. 99,

p. 21–31.

Montgomery Watson, 2000, Draft summary report—Sediment

removal demonstration project, sediment management unit 56/

57, Fox River, Green Bay Wisconsin: Project Number

1242291.01470101.

Stratus Consulting Inc. 1998, Fish consumption advisories in the

Lower Fox River/Green Bay assessment area: Boulder, Colo.,

prepared for U.S. Fish and Wildlife Service, U.S. Department of

the Interior, and U.S. Department of Justice, Final Report, Nov.

24.

Steuer, J.J., Jaeger, S., and Patterson, D., 1995, A deterministic

PCB transport model for the Lower Fox River between Lake

Winnebago and De Pere, Wisconsin: Wisconsin Department of

Natural Resources, Pub. WR 389-95, 283 p.

ThermoRetec Consulting Corp., 1999, Draft feasibility study,

Lower Fox River, Wisconsin: Project Number 3-3584-540.

Acknowledgments

Project development: Robert Paulson—Wisconsin Department

of Natural Resources; Peter Hughes—USGS.

Data collection: Brett Esser, Pitt Fagan, Gerald Goddard, Nick

Hanson, Eric Herro, David Housner, Peter Hughes, Steven March,

Daniel Olson, David Owens, Todd Stuntebeck.

Editorial and technical reviews: David Dolan—University of

Wisconsin; Michael Eberle and Leah Hout—USGS; Steven

Westenbroek—Wisconsin Department of Natural Resources.

Layout and illustrations: Michelle Greenwood and Aaron Konkol.

District Chief

U.S. Geological Survey

8505 Research Way

Middleton, WI 53562

(608) 828-9901

http://wi.water.usgs.gov/