EPA/600/A-93/212

                    DEVELOPMENT AND VALIDATION OF METHODS FOR REAL-TIME
            MEASUREMENT OF POLLUTANT TRANSPORT FROM AN URBANIZED ESTUARY
                                                    Gregory A. Tracey1
                                                      Charles James1
                                                     Gerald Hatcher1
                                                     William Nelson2
                                        'Science Applications International Corporation
                                                  Marine Services Branch
                                         c/o U.S. Environmental Protection Agency
                                                     27 Tarzwell Dr.
                                                  Narragansett, RI  02882

                                           2U.S. Environmental Protection Agency
                                      Environmental Research Laboratory- Narragansett
                                                     27 Tarzwell Dr.
                                                  Narragansett, RI  02882
                        ABSTRACT

       The potential remobilization of pollutants during dredging
and disposal of contaminated sediments is of principal concern to
environmental managers in the selection of dredging methods and
disposal options. In this study, we describe methods for estimation
of pollutant transport within New Bedford Harbor  (NBH), an
urbanized estuary  between  the cities  of  New Bedford  and
Fairhaven, MA. On eight separate dates corresponding to various
dredging activities, current velocity  and total suspended solids
(TSS) profiles were taken across  a narrow constriction (separating
the upper and lower harbor) in conjunction with chemical sampling
for dissolved and paniculate PCB analyses.  Three  methods of
estimating PCB transport were compared. In the "6-point" method,
current  measurements and  water samples  were taken at  three
discrete depths for two cross-channel locations. In the "transect"
method, continuous profiles of currents and suspended particulates
were   collected  at   five  cross-channel  locations.  In  the
"hypsographic" method, depth-volume relationships were derived
from NOAA bathymetry and USGS topography data bases, and
changes in tidal height were used to estimate transport.

       Event-based  (6-point  and  transect)  methods  yielded
comparable estimates of water transport, indicating that over the
duration  of the  ebb  or  flood  exchange,  the  flow field was
adequately  characterized  by  a limited number of sampling
locations. However, estimates of magnitude and direction of net
transport were observed with these methods differed from that of
the hypsographic method, indicating that event-based methods did
not adequately integrate the temporal variation in the flow field.
Significant differences were observed  between discrete- (6-point
method) and profile-based (transect method) TSS flux estimates,
indicating that the 6-point method did not adequately characterize
the spatial variation in TSS distribution under the Coggeshall St.
Bridge.  These results  suggest  that better  estimation of water
transport and TSS  flux would  be obtained by more elaborate
sample compositing procedures during each sampling event and
more frequent sampling events over the tidal cycle. The direction
of net PCB flux was consistent among methods on the  majority of
dates and predicted magnitudes varied less than two-fold. Estimates
of net corrected PCB flux for various  dates suggested significant
temporal variation independent of tidal asymmetry. Wind-driven
tidal asymmetry may be an important factor contributing to this
effect, and could alter transport by up to 80%. Best estimates of
net TSS flux, based on the transect method, ranged from  +3500
(up-harbor) to -3800 (down-harbor) kg cycle'1. Best estimates of
the net fluxes of particulate, dissolved and total PCBs were based
on the hypsographic method, and were observed to range from -31
to -98, +196 to -216, and +150 to -293 g cycle'1, respectively.
                     INTRODUCTION

       The  potential  remobilization   of  sediment-associated
contaminants during  dredging  and disposal of sediments  is of
principal concern to environmental managers in the selection of
dredging methods and disposal options. Predictive evaluation of
associated environmental impacts requires adequate assessment of
the amounts and  types of contaminants escaping the dredging and
disposal site. In this study, we examine methods for estimation of
particulate and contaminant transport within New Bedford Harbor,
an  urbanized estuary  between the cities of  New Bedford and
Fairhaven,  MA.  Sediments of upper New Bedford  Harbor are
highly contaminated (e.g. 500-100,000 ppm) with polychlorinated
biphenyls (PCBs) due primarily to the discharge from electrical
component manufacturing facilities (Weaver, 1984). Accordingly,
high contamination levels  have been observed in commercially
important fin- and shellfish species, resulting in  closure of the
fishery in the vicinity of the estuary.

       As a result of EPA Superfund site designation in 1982,
several options  for remediation of PCB's from  New  Bedford
Harbor were investigated. These  involved the construction of
containment facilities in the upper harbor  and the movement of
harbor sediments by various types  of dredges. During the study,
current velocity  and  total  suspended  solids (TSS)  data  were
collected in conjunction with chemical sampling for dissolved and
particulate PCB analyses in order to assess dredging efficiency and
to monitor the loss of PCBs into the lower harbor environment.

      The objectives of the present study are 1) to assess various
measurement methods  and  make recommendations for estimating
the flux of TSS and PCBs out of the upper harbor, 2) to provide
                                           0-7803-0202-8/91/0000-0501$1.00©1991 IEEE

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estimates of the amount and type of PCBs being transported, and
3) to assess the extent to which wind-related events may contribute
to these losses. It is  hoped that these results  will be useful in the
design of monitoring programs for estimation of paniculate or
chemical fluxes in general,  and for the remediation of the New
Bedford Harbor Superfund Site in particular.
               MATERIALS AND METHODS

Data collection

       The Coggeshall St. Bridge spans approximately 36 meters
across a relatively narrow and shallow constriction of Upper New
Bedford Harbor (Fig.  1).  This constriction served as a natural
boundary  across  which  the  flux  of  PCBs and  TSS  could be
measured. On 8 separate  dates corresponding to various phases of
the Pilot Dredging Project, sampling events were carried out under
the bridge at 5 equally-spaced time intervals between slack tides.
Each hourly sampling event commenced approximately 10 minutes
prior  to the hour and was completed about  10 minutes after the
hour.

Figure 1. Reference map for New Bedford Harbor, MA identifying
the remediation ("hot spot") and sampling (Coggeshall St. Bridge)
locations.
Figure 2. Sampling locations under the Coggeshall St. Bridge for
6-point and transect methods. Arrows indicate approximate depths
for surface,  middle and bottom discrete samples.
    Round Hill Pol
                                                Wilbur Roint
        Continuous profiles of current velocity and transmissivity
were taken at 5 separate transect points positioned approximately
6  meters apart on  the  bridge (Fig. 2). A  SEABIRD CTD
instrument equipped  with a  Marsh-McBirney  electromagnetic
current meter (model 501) and a SEATEC 25-cm transmissometer
was used. The  current meter was laboratory calibrated against a
laser  doppler  velocimeter (LDV)  installed  in a  20-m  flume
operated by Woods Hole Oceanographic Institution, and found to
be accurate to  + 1.0 cm  sec"1 over a range of 0 - 75 cm sec"1. In
order to determine a  relationship between transmissivity and total
suspended  solids (TSS), the transmissometer was placed in  a
stirred container with 0.45-^m filtered seawater and its response
to the addition of sediment collected from upper  New  Bedford
Harbor was measured. As sediment was added to the sea water,
the reduction in transmissivity was observed  and recorded. The
observed linear relationship (TSS = -0.19(% Trans.) - 16.5; r2 =
0.97) was used to convert field-measured transmissivity data to
total  suspended solids concentration.

      The SEABIRD system was deployed over the south side of
the bridge with a davit attached to a motor vehicle equipped with
              5     10     15    20    25     30    35
                   Distance from Cost Bank of Channel (m)
a power winch and camper. Real-time data collection was achieved
by  connecting  the SEABIRD data cable  and  deck unit to a
personal computer. The instrument sampling rate was pre-set at
12 samples sec"1, and  it was lowered at the rate of 0.25 m sec"1.
Transect data were stored in the form of raw data files containing
the water depth,  north  and east  current vectors,  and percent
transmissivity.  Because  the transmissometer required complete
submergence to give accurate results, it was necessary to neglect
the first 50 cm  of transmissivity data for each cast. Similarly, the
positioning of current, transmissivity and pressure probes on the
CTD housing restricted deepest measurements to within 30, 10 and
20  cm  of the  bottom,  respectively.  Data  were adjusted  for
positions of the probes relative to the pressure sensor.

       Water  samples for suspended  particulate and chemical
analyses were taken at the second and fourth transect location. A
1/2-inch teflon hose was attached to the CTD cage with inlet near
the current and  depth probe.  Samples were manually pumped with
a Viton-lined diaphragm pump  (Guzzler model, Ryan-Herco).
Previous studies of dissolved-particulate partitioning of metals had
shown this pump did not  significantly alter particle size-frequency
distribution  (Hunt, Battelle, pers.  comm.). Three depths were
sampled at each transect location. "Surface" and "bottom" samples
were collected  at 0.5  m  below the surface and 1.0 m above the
bottom, respectively. The "mid-depth"  sample was collected at a
depth equal to 1/2 of the total water column height at that time.

Chemical analyses

       A composite sampling strategy was used to reduce the
number  of  samples  for chemical  analyses. Potential spatial
variation in PCB distribution was incorporated by compositing of
water samples taken at the 6 discrete locations each hour. The six
samples were flow-weighted to adjust for potential depth-dependent
differences in transport according to the formula:
1.)
V,,d =
                                  x 6000 ml;
where V, „ is the volume of water from a given transect location (t)
and depth (d) added to the composite, Su is the current velocity at
a given transect (t) and depth (d), S^ is the sum of the 6 current
velocity measurements and 6000 ml was the desired  composite
sample size. In the rare case where current flow was opposite of
the expected direction, e.g. to the  north during  the ebb tide, Su
was set = 0. In these cases, Vu would equal 0, and no water from
the sample would contribute to the composites. After a sub-sample
of 500 ml was taken from the composite for TSS measurement,
                                                            502

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200 ml of the remaining sample was passed  through a 0.22-^m
filter. The procedure was repeated each hour until samples from
the 5  hourly composites  had been filtered,  thus integrating
temporal variation. At the end of the sample  day, the  filtered
material and  filtrate were analyzed for paniculate and dissolved
PCS concentration by methods outlined in Palmquist, ej ii.  (1987).
Total PCB concentration was quantified as the  total of Aroclors
1242  and 1254  in the dissolved and paniculate fractions, and
expressed in units of fig, L"1.

Transport analyses

       Three methods for estimating the net tidal transport cycle"1
were employed.  A tidal cycle is defined here as one consecutive
ebb and flood tide. The  methods  differ primarily in the  relative
characterization of spatial and temporal variability in the flow field
under the bridge.

       Six-point method. In the "6-point" method, water transport
(V) per tidal cycle was  estimated from the sum of products of
mean north current velocity (SJ and channel cross-sectional area
(A,) measured each hour  (t) according to the formula:

          2.)  V  = S,(S, x A,)  where (t  = 1,2,..,,5)

The cross-sectional area was found to increase linearly with water
depth  (y  =  34.4X-53.3; r3 =  0.99).  Only the north  current
velocity was used since the  harbor at the bridge  is oriented north-
south,  and thus any easterly component of the current would not
contribute to net transport. By convention, northerly currents (flow
to the north and into the upper harbor) were taken to be positive.

       Total TSS flux (T) for the ebb or flood tide was determined
in a manner similar to transport:

          3.)  T = S,(V, x T,) where (t =  1,2,...,5)

where  V, is  the  hourly  transport  estimate, and T, is the  mean
hourly TSS concentration determined from water  samples collected
at each of the 6 discrete depths.

       Transect method. In the "transect* method, hourly profile
data were used to create cross-sectional contours of north current
velocity and transmissivity.  A vendor-supplied  software package
(Surfer, Golden Software *) was used to transform the data into a
25 by 25 grid. A kriging  technique was selected  for final gridding
as the method tended to be less  influenced by noise or wide
fluctuations  in data than other methods (e.g. inverse distance).
Within the kriging routine,  an octal search method was  used to
select  profile data points for grid  value  calculation.  The octal
method forces  the gridding program to  search for  data both
vertically  within the  profile and  horizontally between adjacent
profiles in the data set. This approach was necessary to  remove
spatial bias which would otherwise arise because the profile data
were far more concentrated vertically  than horizontally.

       The   Surfer  program  automatically  scales  the  grid
dimensions to the maximum depth and channel width observed. A
"blanking" file was used to exclude  grid values outside of the
channel banks and thus restrict grid dimensions to the actual
channel bathymetry.  Representative  contour  plots of  current
velocity and transmissivity obtained from gridded files are found
in Figs. 3 and 4, respectively. The weighted  mean transport (m3
sec"') through all grid cells in the vertical cross-sectional plane was
calculated as the sum of products of current speed (m sec"1) x Area
(m1)  through  each  grid  cell. The calculation was based  on
Simpson's 3/8 Rule using the Util program included in the Surfer
package.  Transport estimates  were subsequently converted into
units of L hr'. Similarly, the weighted average TSS for each hour
was derived by calculating  the  sum  of products of  percent
transmissivity and grid cell area for all grids and dividing by the
channel cross-sectional area. Transmissivity data were converted
into TSS concentration (mg L"1) using the calibration equation. As
with  the  6-point method,  water transport and TSS flux  were
summed by hour to estimate total transport on the ebb  or  flood
tide.
Figure 3. Contour plot of current velocities (cm sec"1) under the
Coggeshall St. Bridge on 13 June 1988,  one hour after high tide.
Figure 4. Contour plot of transmissivity (%) under the Coggeshall
St. Bridge on 13 June 1988, one hour after high tide.
                 Cr- a m m CHon n w
       Hypsographic method. In  the  "hypsographic"  method,
tidal transport was calculated from tide gage data and  derived
hypsographic (tidal height - tidal volume)  relationships.  Harbor
bathymetry was obtained from the NOAA National Ocean Service
database system. Additional 7.5 minute (1:24,000) digital elevation
data were obtained from the USGS National Geographic Data
Center to provide coverage from mean low  water up to high tide,
These  databases  were  merged and gridded to  0.5 m  contour
intervals using the SEABEAM mapping programs at the Seafloor
Mapping Development Center, University of Rhode Island (Fig.
5),  Gridded data files were imported into the Surfer program to
determine water volumes associated with each 0,5 m change in
tidal height in order to construct a cumulative volume - tidal height
relationship (Fig. 6), A second order quadratic curve was fit to the
relationship.
                                                             503

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Figure 5. Three-dimensional representation of upper New Bedford
Harbor bathymetry up to 3 m above mean low water.
     --*>.
Figure 6. Water depth-tidal volume relationship for New Bedford
Harbor north of the Coggeshall St. Bridge.
   £2.0
          Y = 7.7x10' +  6.9x10°X  +  8.4x1oV
   o
   X
      -1.0   -0.5    0.0    0.5    1.0    1.5    2.0    2.5   3.0    3.5
          Tidal Height Relative  to Mean Low  Water (m)
                                                                 PCS flux calculations

                                                                        Total suspended solids flux was determined from the sum
                                                                 of products of hourly transport and TSS concentration as taken
                                                                 from either discrete water samples ("discrete" method) or from
                                                                 hourly transport and TSS concentration derived from continuous
                                                                 profile data ("profile" method). Dissolved, paniculate and  total
                                                                 PCB flux was estimated from the product of total tidal transport by
                                                                 either  the 6-point,  transect or  hypsographic method and  the
                                                                 composite sample PCB concentration for each tidal phase. In all
                                                                 cases, net flux was determined as the difference between ebb and
                                                                 flood fluxes. Net PCB flux estimates  were  also corrected for
                                                                 differences in tidal asymmetry according to the formula of Teeter
                                                                 (1987):
                                                                               4.)  Fc = (Ce - Cf) x ((T.
                                                                 where Fc is the corrected flux, Ce, Cf are the ebb and flood PCB
                                                                 concentrations (/ig L'1), respectively, and Te, Tf are the ebb and
                                                                 flood transport estimates (L cycle"1), respectively.

                                                                 Climatological analyses

                                                                        To  assess the potential effect  of wind events  on  water
                                                                 transport, wind data during a typical winter period were obtained
                                                                 from a weather station maintained at the New Bedford Harbor
                                                                 hurricane barrier. For this period, tide gage records were obtained
                                                                 and decomposed into tidal and non-tidal components using standard
                                                                 tidal analysis routines and NOAA tidal coefficients applicable for
                                                                 the lower harbor. The non-tidal component or tidal "residual" is
                                                                 that fraction  of the tidal  amplitude not due  to astronomical
                                                                 influences. Tidal residuals were compared against the wind data to
                                                                 elucidate climatological  effects  on tidal  height,  and hence,
                                                                 transport.
                                                                                           RESULTS

                                                                 PCB and TSS concentrations

                                                                        Ebb and flood tide  dissolved,  paniculate and  total  PCB
                                                                 concentrations are summarized in Table 1. The observed range of
                                                                 paniculate PCB concentrations on the ebb tide (0.07 - 0.32 fig L'1)
           Table 1. Summary of chemistry, transport and total suspended solids (TSS) measurements for 8 sampling dates
           during the New Bedford Harbor pilot dredging study.
Date
6/13/88
6/27/88
9/1/88
11/13/88
12/5/88
12/12/88
12/20/88
1/9/89
Tide
Ebb
Flood
Ebb
Flood
Ebb
Flood
Ebb
Flood
Ebb
Flood
Ebb
Flood
Ebb
Flood
Ebb
PI ortH
PCB Concentration,
lua I/'l
Diss.

0.15
0.17
0.44
0.05
0.28
0.06
0.22
0.16
0.03
0.00
0.02
0.29
0.16
0.11

Part.
0.19
0.12
0.32
0.12
0.27
0.20
0.15
0.03
0.13
0.04
0.07
0.02
0.24
0.16

Total
0.35
0.29
0.76
0.18
0.55
0.26
0.36
0.19
0.16
0.04
0.08
0.31
0.39
0.28

Water Transport,
(L x 10f)
e^Pt,
-973
787
-464
703
-880
1001
-751
597
-492
862
-1360
692
-1266
799
-842
Q Tl
Trsct

-929
860
-745
681
-844
841
-720
520
-650
820
-1193
640
-1209
807
-835
flST
. HVPS.
-808
985
-614
967
-850
961
-821
825
-461
667
-954
724
-943
826
-1128
1QA
Total sus
(ma
Discrete
15.7
7.4
15.5
13.1
8.1
6.2
4.1
2.4
6.2
2.0
2.6
1.7
4.6
6.1
10.4
i A n
. solids
Profile
9.0
10.9
8.9
8.4
9.9
7.3
4.4
4.7
5.4
3.6
6.2
8.2
8.4
9.9
10.7
i n R
                                                             504

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for each date exceeded flood concentrations (0.02 - 0.20 j*g L4) in
all   seven  cases.   For   dissolved   PCBs,   however,  flood
concentrations (0.00 - 0.29 jig L"1) exceeded the ebb concentration
(0.02  -  0.44  ng  L4)  on three of  seven  dates.  Total PCB
concentrations on the flood tide (0.04 -  0.31 £ig L"1) were less than
that of the ebb tide (0.08 - 0.76 pg L;1) on  six of seven dates.
Mean TSS concentrations measured from discrete water samples
(1.7 to 15.5 mg L4) varied by a factor  of two to three from those
estimated from transmissivity profiles  (4.7 to  10.9 mg L4). The
coefficient of variation  (CV) between estimates was 50.2%. This
difference most likely reflects varying degrees in spatial integration
of TSS distribution under the bridge by the two methods.

Water transport

       The transport of water under the Coggeshall St. Bridge  for
8 dates was observed to range from -1360 x 106 L on the ebb tide
to +1000 x 10* L on the flood tide (Table 1). The coefficient of
variation between 6-point and transect method  predictions was
small (13.9%), indicating close agreement among methods. The
coefficient of variation between 6-point and hypsographie methods
was 21.8%. A comparable variation  coefficient was observed
between  the transect  and hypsographie methods (23,4%). Thus,
better agreement was observed between event-based (6-point and
transect)  methods than was observed between event-based methods
and the hypsographie method.

TSS fluxes

       The net flux of total suspended  solids was calculated from
the product of hypsographie method-based water transport and TSS
concentration.  Using discrete depth-derived (6-point) TSS data,  net
TSS flux was found to be out of the upper harbor in six of eight
cases,  and ranged from +3200 to -5500 kg cycle'1 (Fig.  7).  In
contrast,  results using the profile-based (transect) method indicated
net TSS flux was into the upper harbor in five of eight cases, and
ranged from +3500 to -3800 kg cycle'1.

Figure 7. Net total suspended solids flux under the Coggeshall  St.
Bridge during the NBH Pilot Dredging Study.
net flux for this fraction was consistent among methods, being out
of the upper harbor on the majority (6 of 7) of dates, and predicted
magnitudes varied less than 50% among methods. Total PCB flux,
calculated as the sum of dissolved and particulate fluxes, ranged
from +150 to -440 g cycle"1 for the three methods (Fig. 10). The
direction of net transport was again out of the upper harbor and
consistent among methods on six of seven dates, while two-fold
variation in magnitude among methods was observed.

       Net PCB fluxes based on hypsographie method transport
estimates were corrected  for tidal asymmetry in order to assess
non-hydrologic related variability among sampling dates (Fig. 11).
Corrected dissolved  PCB flux was up-harbor on  two of seven
dates, ranging from +20 to +50 g cycle'1, and on five of seven
dates,  was  down-harbor  (-20 to -300  g cycle"1).  Corrected
particulate PCB flux was always down-harbor, ranging from -30
to -150 g cycle"1. Corrected total PCB flux was down-harbor on six
of seven dates, and ranged from +20 to -450 g cycle"1.

Figure  8. Comparison of  net particulate PCB flux under the
Coggeshall St.  Bridge during the NBH Pilot Dredging Study as
estimated by 6-point, transect, and hypsographie methods.
      30Q


    _ 200


    < 100
     -2OO

     -30O
Figure 9.  Comparison  of net dissolved  PCB flux  under the
Coggeshall St. Bridge during the NBH Pilot Dredging Study as
estimated by 6-point, transect and hypsographie methods.
PCB fluxes

       The net fluxes of dissolved, particulate and total PCBs were
calculated from  the product  of water transport for the three
methods and PCB concentration. The direction of net particulate
PCB flux  was consistently out of the upper harbor, and ranged
from -30 to -170 g cycle4 (Fig. 8). Factor of two to three variation
was found among methods for a given date. Net dissolved PCB
flux ranged from +200 to -290 g cycle'1 (Fig. 9).  The direction of
Climatological effects

       Relationships between wind stress and residual tidal height
were examined. Data were extracted from a July 1988 time series
for which  both  upper and lower  harbor  tide  gage data  were
available to investigate the possibility of tidal amplification in the
upper harbor relative to  the lower harbor. Differences in tidal
range between upper and lower harbors were minimal (Fig. 12).
Thus, the data indicate that no differential tidal forcing effects
were occurring in  the harbor.  Tidal residuals for a  winter time
                                                            505

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Figure 10. Comparison of net total PCB flux under the Coggeshall
St. Bridge during the NBH Pilot Dredging Study as estimated by
6-point, transect and hypsographie methods.
Figure 11. Comparison of net corrected dissolved, paniculate and
total PCB flux under the Coggeshall St. Bridge during the NBH
Pilot Dredging Study by the hypsographie method.
series were compared against wind data obtained during a period
for which  both  northerly and southerly  winds were  apparent
(January 7-14, 1988; Fig.  13). With the exception of the first 24
hr period, results show that wind events originating from  the north
(i.e. upward on plot) resulted in negative tidal residuals  of up to
-0.5 m, while southerly winds resulted in positive tidal residuals.
                       DISCUSSION

       In this study, various methods for estimating PCB and TSS
fluxes  out of upper  New  Bedford Harbor  were developed and
compared. This effort was undertaken in order to validate previous
flux  estimates,  as well as  to  recommend new approaches  to
estimating fluxes, if appropriate, when the remediation plan for the
harbor is developed.

Figure 12. Differences in tidal amplitude between upper and lower
New Bedford Harbor during July, 1988.
     -0.1 -I
         D   5  1O  55
Figure 13. Wind stress-tidal residual relationships for an eight day
winter storm period in New Bedford Harbor
    JT  20 H
        0
    -o
     J -20 -
                                                                     tf>
                                                                       -40 -J
                                                                                  7
                                                                                              >J
                                                                                24
                                                                                    I  | I
                                                                                     «8
                         •" I ' '  ' I I '  ' I ' '
                          72    96   120
                           Time (hoys)
T1
 H*
 •p-
166
Transport analyses

       Studies by Teeter (1987) observed net transport on three
dates to range from -250 to  +210 x  10* L. In the present study,
net transport  as  estimated  by the hypsographie method were
somewhat similar (-330 to + 350 x 10* L) but covered a broader
range in values. In both studies, depth-volume relationships were
used to calculate transport from tide height data. The difference in
observed ranges could  be partly due to a greater number of days
sampled in the present study, but also due to shape and slope of
the hypsographie curve itself. Based on limited data, Teeter's study
found a linear depth-volume relationship, whereas in the present
study, a second-order quadratic provided the best fit to the data.
With regard to slope, Teeter's study found tidal volume to change
by 800 x Itf L m4 of tide height, whereas in the present study the
volume is predicted to  change by  688 -  1110  x  106 L rrr1,
depending on  tidal height. These differences could account for
discrepancies in net transport estimates between studies.

TSS flux analyses

       The transect-based net fluxes  of TSS, which ranged from
+3500 to -3800  kg cycle"', are  comparable in magnitude with
studies by Teeter (1987) who  found  the net flux of TSS on two
dates to be about  +2100 kg  cycle4. Differences in the magnitude
of observed TSS flux  between studies may differ due both the
method of water sampling and water  transport estimates  as
discussed  above.  Our  study, however, has found that net TSS
transport may be either direction, a finding which may be due to
a greater  number of sampling  days incorporated into the present
study.

PCB flux analyses

       Fluxes of PCBs beneath the Coggeshall St. Bridge were
first investigated  in 1983 by  an EPA response  team  (USEPA
1983). From data  obtained in their study, the net  total PCB flux
was calculated to be -0.83 kg per tidal cycle, with a range of -0.62
to -1.20 kg (Teeter,  1987).  Additional studies were conducted in
1986 by the U.S. Army Corps of Engineers (Teeter, 1987). In that
study, PCB fluxes of -0.32 and -1.27 kg per tidal cycle were
observed.  In a study by Battelle (1990), a model was  used to
simulate PCB flux at the Coggeshall St. Bridge and predicted -0.22
kg  cycle"1.  Fluxes for total PCBs found  in  the present study
(+0.15 to -0.29 kg cycle"1) are low relative to  previous findings,
despite the fact that various dredging and construction activities
were occurring.  The  current  data  suggest that  no significant
                                                             506

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dredging-induced fluxes were occuring on these seven dates, and
that these  sampling periods  may  be representative  of baseline
conditions.

       Despite the correction for tidal asymmetry, net total PCB
fluxes were still observed to vary by up to an order of magnitude
among dates.  In addition,  paniculate  PCB fluxes were always
down-harbor while dissolved PCB fluxes were often up-harbor,
suggesting that down-harbor dissociation of PCBs from particulates
may have occurred and contributed to the up-harbor dissolved PCB
flux. Thus, factors controlling PCB concentration and partitioning
behavior would  appear to have a greater effect on net PCB flux
than does tidal asymmetry as previously reported (Teeter, 1987).

Climatological effects

       The extent to which  wind events affect net PCB flux out of
upper New Bedford Harbor by altering transport  was examined.
From a data set collected during a winter storm period, north wind
events were observed to cause lower tides in the region, while
south winds caused higher tides in the region. This effect is most
likely caused by seiching, or pushing of surface waters down wind,
and appeared to cause tidal  height at slack water to vary by up to
0.5 m. It is estimated that this residual could alter tidal transport
on a given ebb or flood tide by  an additional 320-580 x 106 L, or
80% of the tidal volume on a given tide.

Comparison of methods

       In this  study, it was assumed that  net water transport was
controlled primarily by changes in tidal height while the magnitude
of transport is dependent on the depth-volume relationship. The
upper  harbor  does  receive  some  freshwater  input from the
Acushnet River,  however even under high  flow conditions the flow
is a small fraction (e.g. 4.7%, Teeter, 1987) of the tidal volume.
Thus, both the magnitude and direction of net tidal transport can
be known with certainty given accurate tide gage and bathymetry
data.

       Tide gage data were available from the study site for each
sampling date  to provide estimates of tidal height differences to ±
0.1 m. The accuracy of these data was verified by comparisons of
soundings taken at the Coggeshall  St. Bridge and with  two tide
gages maintained at the  hurricane barrier  in the lower harbor.
Depth-volume  relationships   were  derived  from   controlled
bathymetric survey data with a single point precision of ± 0.3 m.
It is assumed  that the associated accuracy is substantially better
since the grid data were obtained  from  multiple soundings.  In
addition, high  resolution (1:24,000 scale)  USGS topographic data
specific for the study area were available to extend the bathymetric
data set  from  the  mean low  water  to  the observed tide height.
Thus,  we  are confident that  the  derived  hypsographic  curve
provides  the best estimates of net transport, and these data can be
used to evaluate 6-point and transect predictions.

       Good agreement was  observed between the 6-point and
transect method  predictions for  both the direction and magnitude
of transport, suggesting that the discrete sampling approach should
provide adequate spatial  integration of the  flow  field  during  a
given sampling event. However, a similar  comparison of TSS flux
estimates revealed substantial differences in  both direction and
magnitude between methods, indicating  the  limited  number  of
sampling locations incorporated into the  6-point method did not
adequately integrate the spatial differences  in suspended paniculate
concentrations  in  the channel. This  finding is consistent with
occasional  observations  significant  spatial  variability  in TSS
concentration  (e.g. Fig. 4), with highest concentrations being
restricted to surface waters and/or sides  of the channel.  These
results suggest future sampling designs should  include broader
spatial coverage than was done by the 6-point method in this study.

       Net transport predictions  by  the 6-point and  transect
methods were consistent with the hypsographic method only about
half of the time, indicating that the 6-point and transect  methods
lack sufficient temporal coverage to adequately  characterize net
transport. Future discrete sampling programs should be intensified
to include,  at a minimum, hourly sampling through the complete
tidal cycle.  Order-of-magnitude variation observed in net corrected
PCB flux between  dates suggests that temporal variability may be
important,  and should  also  be considered  in  future sampling
programs.
                      CONCLUSIONS

       1.)  Comparisons  of water  transport by the 6-point and
transect-based  methods  exhibited  good  agreement,   with the
coefficient of variation between methods being less than  14%. This
suggests that the flow field under the bridge at a given time may
be adequately characterized by the  6-point sampling strategy.

       2.) Discrete- (6-point method)  and profile-based (transect
method) estimates  of TSS  concentration  differed   greatly;  a
coefficient  of variation of 50% was observed between methods.
Given that  greater spatial measurement of TSS distribution under
the Coggeshall St. Bridge  was provided  by the profile-based
method, the results suggest that broader spatial coverage than that
obtained by the 6-point method will be required in future sampling
programs to estimate TSS and paniculate PCB net flux.

       3.) The direction of net transport predicted by event-based
(6-point and transect) methods and were often opposite to that
known  to  occur  from tidal  height observations.  This error is
attributed to poor temporal sampling of the tidal cycle and suggests
that broader temporal coverage should  be incorporated into event-
based sampling methods for elucidation of TSS and PCB fluxes.

       4.) Profile-based estimates  of  net TSS flux ranged  from
+3500  to  -3800  kg cycle'1. Hypsographic-based  net  fluxes of
paniculate, dissolved and total PCBs were observed to range from
-31 to  -98, +196  to  -216,  and  +150  to  -293  g  cycle'1,
respectively, and did not  indicate any dredging-induced effects.

       5.) Wind-driven tidal asymmetry was observed to cause up
to 0.5 m variation in tidal height.  This tidal residual  may cause
transport on the ebb and flood tides to increase by up to 80%, and
thus could also  similarly affect net  PCB flux.

       6.)  Hypsographic-based estimates of net corrected  PCB
flux, ranged from +20 to -450 g cycle"1 over seven dates.  This
suggests that factors  other than tidal asymmetry may  play  a
significant role  in PCB flux dynamics, and assessment  of day-to-
day variation in PCB fluxes should  be  an important component of
future sampling programs.
                                                             507

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                 ACKNOWLEDGEMENTS

      This manuscript is  ERLN contribution No. 1326. The
research was  supported  through EPA  contract 68-C1-Q005 to
Science Applications International Corporation, Ms, Patricia Cant,
Project Officer. The contents of the manuscript do not necessarily
reflect views  or  policies nor does mention of trade names or
commercial products constitute endorsement or recommendation
for use by the U.S. Environmental Protection Agency.
                  LITERATURE CITED
      Battelle, 1990. Modeling of the transport, distribution and
fate of PCBs and heavy metals in the Acushnet River/New Bedford
Harbor/Buzzards  Bay System.  Volume  II:  Final  Report to
EBASCO Services,  Boston, MA.

      Palmquist, R., K. Schweitzer, R. Bowen and R. Pruell,
1987.  New  Bedford  Harbor  Pilot  Study Pre-operational
Monitoring- Progress Report: Chemical analysis from the two pre-
operational water samplings conducted in  New Bedford Harbor
during July,  1987. EPA  Environmental Research Laboratory-
Narragansett Internal Report.

      Teeter, A. 1987. Baseline conditions for contaminant and
sediment migration,  New Bedford  Harbor,  Massachusetts.
USACE-Watenvays Experiment Station. Publ. No. WESHE-P,
1/26/87.

      USEPA,  1983. Aerovox PCB Disposal Site- Acushnet
River and New Bedford Harbor, MA: Tidal cycle and PCB mass
transport study, January 10-12, 1983. USEPA -Edison Laboratory,
Edison, NJ Final report 3/4/83

      Weaver, G.  1984. PCB contamination in and around New
Bedford, Massachusetts. Environ.  Sci. Technol. 18:22A-27A.
                                                          508

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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA/600/A-93/212 -
4. TITLE AND SUBTITLE DEVELOPMENT AND VALIDATION C
FOR REAL-TIME MEASUREMENT OF POLLUTANT TRANS
URBANIZED ESTUARY
F METHODS 5. REPORT DATE
PORT FROH AN
"' 	 *" ' "" 6. PERFORMING ORGANIZATION CODE
7^UTHOR(S). _ „,,,„,, 8. PERFORMING ORGANIZATION REPORT NO,
Uregory A. Tracey, Charles James, Gerald Hatcher,
William Nelson ERLN-1326
9. PERFORMING ORGANIZATION NAME AND ADDRESS
US EPA Environmental Research Laboratory
27 Tarzwell Drive
Narragansett, RI 02882
12. SPONSORING AGENCY NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
60-C1-QOQ5
13. TYPE OF REPORT AND PERIOD COVERED
Proceedinqs-peer reviewed
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
is. ABSTRACT The p^,^ remobilization of pollutants during dredging
and disposal of contaminated sediments is of principal concern to
environmental managers in the selection of dredging methods and
disposal options. In this study, we describe methods for estimation
of pollutant transport within New Bedford Harbor (NBH), an
urbanized estuary between the cities of New Bedford and
Fairhaven, MA. On eight separate dates corresponding to various
dredging activities, current velocity and total suspended solids
(TSS) profiles were taken across a narrow constriction (separating
the upper and lower harbor) in conjunction with chemical sampling
for dissolved and paniculate PCB analyses. Three methods of
estimating PCB transport were compared. In the "6-point" method,
current measurements and water samples were taken at three "~
discrete depths for two cross-channel locations. In the "transect"
method, continuous profiles of currents and suspended particulates
were collected at five cross-channel locations. In the
"hypsographic" method, depth-volume relationships were derived
from NOAA bathymetry and USGS topography data bases, and
changes in tidal height were used to estimate transport.
17_ KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
pollutant transport New Bedford Harbor
estuary Massachusetts
measurement dredging
total suspended solids
TSS
PCB
particulates
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
b.lDENTIFlEHS/OPEN ENDED TERMS C. COSATI Field/Croup

UNCLASSIFIED K
20. SECURITY CLASS (This page > 22. PRICE
UNCLASSIFIED
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