oEPA
United States
Environmental Protection
Agency
Office of Marine
and Estuarine Protection
Washington DC 20460
EPA 430/09-88-001
September 1987
Water
A Simplified Deposition
Calculation (DECAL) for
Organic Accumulation Near
Marine Outfalls
-------
EPA Contract No. 68-01-6938
TC-3953-31
Final Report
A SIMPLIFIED DEPOSITION CALCULATION (DECAL)
FOR ORGANIC ACCUMULATION NEAR MARINE-OUTFALLS
for
Marine Operations Division
Office of Marine and Estuarine Protection
U.S. Environmental Protection Agency
Washington, DC 20460
September 1987
by
Tetra Tech, Inc.
11820 Nortfcup Way, Suite 100
Bellevue, Washington 98005
-------
CONTENTS
Page
LIST OF FIGURES iv
LIST OF TABLES vi
ACKNOWLEDGEMENTS vii
EXECUTIVE SUMMARY viii
I. INTRODUCTION 1
I!. OVERVIEW 3
COASTAL TRANSPORT 3
PARTICLE TRANSPORT AND ORGANIC CARBON CYCLES 5
ENVIRONMENTAL QUALITY 7
III. MODEL DEVELOPMENT 8
MODELING FRAMEWORK 8
MODEL FORMULATION 13
IV. MODEL RESULTS AND DISCUSSIONS 22
SAMPLE CALCULATIONS 22
VERIFICATION STUDIES 25
V. EXTENSION OF THE MODEL FOR PREDICTING CHEMICAL CONTAMINATION 34
MODEL FORMULATION 35
MODEL CALCULATIONS 37
VI. CONCLUSIONS 45
REFERENCES 47
APPENDIX A - REVIEW OF PARTICLE DEPOSITION MODELS A-l
-APPENDIX B - USER'S GUIDE FOR THE DECAL MODEL: TOOL #61 ON THE
OCEAN DATA EVALUATION SYSTEM (ODES) B-l
ii
-------
APPENDIX C - MASS CONSERVATION EQUATIONS AND STEADY-STATE SOLUTIONS
FOR PARTICLE CONCENTRATIONS IN THE LOWER WATER COLUMN C-l
APPENDIX D - MASS CONSERVATION EQUATIONS AND STEADY-STATE SOLUTIONS
FOR CHEMICAL CONTAMINANT CONCENTRATIONS IN THE LOWER
WATER COLUMN . 0-1
iii
-------
- FIGURES
Number Page
1 Simplified diagram of niunicipal~~effluent transport in coastal
waters 11
2 Simplified diagram of particle transport and organic carbon
cycles 12
3 Settling flux of organic carbon from the surface layer
as a function of the phytoplankton productivity rate (Ptotal)
4 Suspended oarticle concentration, deposition rate, and organic
accumulation gv/en by the model as an example case Z3
5 Deposition rates near the Orange County outfall along the
60-m isobath based on model predictions and field estimates 28
6 Organic accumulation near the Orange County outfall along the
60-m isobath based on model predictions and field estimates 29
7 Deposition rates near the Los Angeles County outfall along the
60-m isobath based on model predictions and field estimates 31
8 Organic accumulation near .the Los Angeles County outfall
along the 60-m isobath based on model predictions and field
estimates 33
9 Chemical deposition rates near the Los Angeles County outfall
along the 60-m isobath based on model results 38
10 Lead accumulation in surface sediments near the Los Angeles
County outfall along the 60-m isobath based on model results
and field estimates 41
11 Copper accumulation in surface sediments near the Los Angeles
County outfall along the 60-m isobath based on model results
and field estimates _ 42
12 Cadmium accumulation in surface sediments near the Los Angeles
County outfall along the 60-m isobath based on model results
and field estimates 43
B-l Simplified diagram of municipal effluent transport in coastal
waters B-2
iv
-------
B-2 Simplified diagram of particle transport and organic carbon
cycles " B-3
B-3 Record of current velocity data for currents off Newport
Beach, California B-7
B-4 Power spectral density distributions of currents off Newport
Beach, California . 8-8
B-5 Cumulative variance distributions of currents off Newport
Beach, California B-9
B-6 Cumulative probability curves for nontidal currents off
Newport Beach, California B-ll
B-7 DECAL contour plot of total deposition rate of waste particles
for the sample calculations B-21
3-8 DECAL contour plot of waste parncie deposition rate for the
sample calculations 3-22
-------
TABLES
Number • Page
1 Time-scale estimates for coastal transport and particle
dynamics 9
2 Power law relationship for coagulation/settling kinetics
from Farley and Morel (1986) 14
VI
-------
ACKNOWLEDGEMENTS
This technical document was completed by Tetra Tech, Inc. staff for the
U.S. Environmental Protection Agency under the 301(h) Post-Decision Technical
Support Contract No. 68-01-6938, Ms. Allison J. Duryee and Mr. Barry Burgan,
Project Officers. The report was authored by Dr. Kevin J. Farley. Drs.
W.P. Muellenhoff and A.M. Soldate, Jr. provided . techni cal editing and
produced the final document.
Comments and suggestions cf Professors Francois M.M. Morel and ,<«=it:i C.
StoTzenbach of the Massachusetts Institute of Technology, Dr. William 0.
Grant of the Woods Hole Oceanographic Institute, Dr. Thomas O'Connor of the
U.S. Department of Commerce, National Oceanic and Atmospheric Administration,
and Drs. John Paul and Donald Baumgartner of the U.S. Environmental Protec-
tion Agency are appreciated. Thanks are also extended to Drs. Tereah
Hendricks and Jack Anderson of the Southern California Coastal Water
Research Project for providing access to current meter data and to Tetra
Tech staff members who participated in this study (particularly Mr. Michael
Morton and Dr. Mark Clark for their work in analyzing current meter data).
VII
-------
EXECUTIVE SUMMARY
The' deposition calculation (DECAL) presented in this report provides a
simple model for predicting particle deposition and accumulation of organic
material in sediments near municipal ocean outfalls. The model has been
formulated on the basis of coastal transport, particle transport, and
organic carbon cycles, and includes the effects of coagulation and settling
of effluent particles and natural organic material.
inout parameters ror cne model induce rhe discharge flow rare, r.ne
effluent solids concentration, the outfall cliff user location and geometry,
the density structure and depth of the water column, the phytopl ankton
productivity rate, and a simplified description of ocean currents. Three
modeling coefficients are required for calculating particle deposition and
organic accumulation in surface sediments. They are the second-order
coagulation/settling rate coefficient, the decomposition rate coefficient
for suspended organic material, and the interfacial removal rate coefficient
for sedimented organic material.
Model predictions for particle deposition and organic accumulation in
sediments near the Orange County and Los Angeles County outfalls compare
well with field estimates at both outfall locations. These results demon-
strate the applicability of the model in predicting deposition and accumula-
tion near relatively deep outfall outfalls in the Southern California Bight.
For outfalls in shallower waters (where.wave-induced currents may redis-
tribute sedimented organic material), model calculations can be used to
determine initial deposition patterns and to provide conservative estimates
for organic accumulation in sediments. Additional verification studies,
however, should be performed for deep outfalls in other geographic areas and
for shallow outfall locations.
vm
-------
The DECAL model has been extended to predict metal and trace organic
chemical accumulations in sediments. Preliminary modeling results for metal
accumulations near the Los Angeles County outfall compare well with field
estimates, and suggest that deposited metals are retained in sediments near
the outfall (probably in the form of metal sul fides) _ and are buried in
time. Similar model calculations for the accumulation of trace organic
chemicals could be performed to examine the importance of chemical trans-
formations in sediments.
DECAL calculations for accumulation of organics and chemicals in
sediments can be used for predicting environmental impacts from ocean
outfalls regulated under Section 301(h) of the Clean Water Act. The model
can also be usea to heio design monuonrg programs, -25:30;-sr, -".ru.-e
monitoring strategies, and analyze field data for chemical enrichment and
biological impacts. Applicability of the model calculations, however, is
dependent upon the availability of valid input data (particularly ocean
currents), and the assignment of appropriate modeling coefficients.
Therefore, care must be exercised in analyzing current meter records, and
further modeling coefficient studies may be required. In addition, detailed
examinations of sediment processes should be considered to determine the
individual roles of microbial decomposition and burial in removing organic
material from surface sediments. The actual removal pathway (decomposition,
burial, resuspension/transport, or combination thereof) is important in
evaluating the long-term environmental impacts of municipal discharges to
coastal waters.
«•
A review of several particle deposition models is provided in Appendix
A, and Appendix B is a users guide for the OECAL model on the U.S. EPA Ocean
Data Evaluation System (ODES Tool No. 61).
IX
-------
I. INTRODUCTION
Assessment "of the fate of discharged_wastes is an important part of
determining the impacts of municipal discharges from ocean outfalls. For
example, these assessments are used to:
• Predict environmental effects of planned improved discharges,
especially involving outfall relocations
» Evaluate transport of the wastefield relative to special
habitats such as kelp beds or coral reefs
• Specify monitoring station locations in areas of predicted
sediment deposition.
Such assessments have been limited, however, by the lack of a generally
applicable model that predicts the farfield fate of discharged effluent in
the marine environment.
This report describes a simple model to predict the fate of municipal
wastewaters in the marine environment, including particulate matter and
toxic chemicals. The model development involved the following tasks:
t Evaluate physical/chemical processes affecting particle
settling characteristics in marine waters
• Develop a simple mathematical formulation to describe the
above relationship
t Construct a model for predicting particle deposition, organic
accumulation, and toxics concentrations near ocean outfalls
-------
• Incorporate the model into the Ocean Data Evaluation System
(ODES).
_____ •
As a result of the first task, this report provides an overview of
coastaj transport, particle transport, and organic carbon cycles in marine
waters. A mathematical model is -then described to predict particle deposi-
tion and organic accumulation in surface sediments. Calculations are
provided for the Orange County and Los Angeles County outfalls, followed by
discussions of the modeling results. Extension of the model for predicting
metal and trace organic chemical accumulations in sediments is also pre-
sented.
-------
II. OVERVIEW
Particle deposition and organic accumulation near ocean outfalls are
controlled by coastal transport, particle transport, and organic carbon
cycles. A1 summary of these processes is presented, followed by a brief
discussion of particle deposition and its relationship to environmental
quality.
COASTAL TRANSPORT
Outfalls extending 0-10 km from shore are used to discharge municipal
wastewater to coastal environments. Buoyancy of the wastewater in seawater
results in seawater entrainment and a vertical rise of the wastewater plume.
Entrainment factors of the order of 100 are common and time scales character-
izing the buoyancy rise are relatively short (minutes to hours) for present
designs of outfall diffusers. During stratification periods (Richardson
numbers ca. 10 ), wastewater plumes are trapped below the sharp density
gradients of the pycnocline region. Subsequent transport and dilution of
the wastefield are controlled by ocean currents and mixing processes.
Fluid motions in coastal waters are driven by surface waves, tidal
oscillations, wind-driven currents, and large-scale mean circulation. Wave
motions at the surface are characterized by orbital velocities on the order
of 1 m/sec and periods of 5-10 sec. Since wave motions conform closely to
irrotational flow over most of the water column, wave-induced transport of
pollutants is generally of minor importance._ Near the surface, waves may
play a significant role in enhancing air/sea exchange through surface
renewal, wave breaking, and sea spray. Exchange and resuspension at the
water/sediment interface are determined to a large extent by wave-induced
2
shear stresses (on order 1 dyne/cm ).
-------
In many coastal locations, tidal oscillations are a significant part of
the observed currents. Tidal motions typically follow elliptical paths,
with the major axis paralleling the shoreline. Osc-i-1 lation periods range
from 12 to 25 h depending upon the relative strength of the main tidal
components. For typical tidal velocities (5-15 cm/sec) the major axis of
the tidal excursion ellipse is several kilometers; the minor axis vanes-
with offshore distance, increasing from zero at the coast. Since outfalls
are fixed in space, the effect of tidal motion is to distribute the diluted
7
effluent over the tidal excursion ellipse (1-5 km ).
Nontidal flows are generally dominated by wind-driven (or pressure
gradient-driven) currents. The currents exhibit significant variation,
often reversing direction in cycles of 4-8 days according to the passage of
weather systems. Long quiescent periods are also observed. Wind-driven
currents range in magnitude from 5 to 15 cm/sec and typically flow parallel
to the coast. Cross-shore motions, which show significant variation with
depth, also occur and are associated with the cross-shore component of the
wind stress and Coriolis effects. During stratification periods, cross-shore
motions may induce upwelling or downwelling.
Large-scale mean circulation on the shelf is characterized by longshore
velocities typically ranging from 1 to 3 cm/sec. This long-term motion is
induced by a sea level slope determined by deep oceanic gyres and modified
by setup from a mean wind stress.
Turbulent energy production at or near the surface and seafloor bound-
aries is responsible for vertical mixing in coastal waters. In the absence
2
of density gradients, vertical diffusivities of 10-50 cm /sec are typical.
During stratification periods, turbulent fluctuations propagating from the
boundaries are dampened by stabilizing density gradients. Low diffusivities
in the pycnocline region (0.1-1.0
of surface and lower layer waters.
2
in the pycnocline region (0.1-1.0 cm /sec) can severely limit the exchange
Horizontal dispersion is determined by turbulent fluctuations as well as
by vertical variations in horizontal velocities associated with shear flow.
-------
Dispersion has been observed to increase with length scale, typically
expressed by a 4/3 power law (Brooks 1960; Okubo and Osmidov 1970; Okubo
1971)_. Over length scales" of 1-10 km, horizontal dTs'persion coefficients
4 2
are on the order of 10 cm /sec.
PART4CLE TRANSPORT AND ORGANIC CARBON CYCLES
Mass concentrations of particles in coastal waters typically range from
a few tenths to a few milligrams per liter. The particles consist primarily
of organic material derived from phytoplankton production or (for this
•
study) discharged from municipal outfalls. In many coastal locations,
terrestrial inputs and bottom resuspension may also be important.
Phytoplankton activity is generally confined to surface layers and is
controlled by light, availability of major nutrients, trace metal concen-
trations, and temperature-dependent, metabol ic processes. Productivity
rates for total organic carbon are typically observed in the range of
0.2-2.0 gC-m -day (Suess 1980; Eppley et al. 1983). A large portion of
the production consists of particles, ranging in size from a few nanometers
for colloidal exudates to a few microns for plankton cells. Values of
0.05-0.10 g POC/cm have been reported for particulate organic carbon/
particle volume ratios (Eppley et al. 1977) indicating a high water content
for plankton cells and detrital material. The dry weight composition is
primarily protein amino acids and carbohydrates. Lipid content of phyto-
plankton is typically less than 20 percent (Parsons et al. 1977).
Primary losses of particles from surface layers are through microbial
degradation and coagulation/settling. In shallow waters, particle removal
by direct contact (coagulation) with the bottom may also be important.
Decomposition of natural organic particles occurs at rates on the order of
O.-l/day; lipids may degrade more slowly. In oligotrophic waters, over
90 percent of the organic material may be returned to the nutrient pool by
degradation processes. In highly eutrophic waters, a large fraction of the
organic material -is transported to lower water layers by coagulation/
settling. Zooplankton may play an important role in both coagulation/
-------
settling (through the formation of fecal pellets) and degradation (by acting
as grinding mills to reduce larger particTes to colloidal or dissolved
organic material ).
Mass concentrations of effluent particles (ca. 50-200 mg/L) discharged
from submerged outfalls are rapidly diluted by plume entrainment and are
2
then distributed over the tidal excursion ellipse (1-5 km ). Primary treated
effluent consists mostly of biological material with large amounts of
bacteria and bacterial fragments. Organic composition of effluent is similar
%
to natural particles; lipid content of 20-25 percent has been reported (Myers
1974). Smaller quantities of inorganic material are also present in treated
wastewater.
During stratification periods, effluent particles are typically trapped
below the pycnocline where they add to concentrations of natural particles
that have settled out of surface waters. Decomposition rates of the organic
material are on the order of O.I/day. Reduced metabolic rates may occur
below the pycnocline due to lower temperatures. Particle deposition rates
are often controlled by coagulation/settling kinetics and strongly depend on
the aggregation of effluent particles and natural particles. Particle
removal by contact (coagulation) with sediments is also possible and is
affected by bottom boundary flow and turbulent mixing rates.
Reported estimates of deposition rates are in the range of 0.25
-2 -1
g-m -day (dry wt) for "natural" waters off southern California (Emery
1960) to 6.0 g-nf -day (dry wt) for municipal effluent particles in the
vicinity of the Los Angeles County outfall (Galloway 1972). Particles
deposited at the water/sediment interface are generally mixed with surface
sediments to a depth of 1 to 10 cm by bottom shear (induced by waves and
currents) and bioturbation. Removal of organic material from surface
sediments is attributed to decomposition and burial. Interfacial turnover
rates for the removal of organic material in "natural" sediments are in the
range of 0.01-0.025 cm/day (from field estimates of Hopkinson 1985 and
references therein). The observed turnover rates are based on steady-state"
assumptions and include the effects of decomposition of easily degradable
6
-------
organic material (e.g., carbohydrates, amino acids), decomposition of more
refractory compounds (e.g., complex lipids, humic substances), and burial of
organic material as the sediment interface progresses upwards with time
(i.e., with the accumulation of particles). Resuspension events which are
typically associated with storms may disrupt accumulated sediments.
f
ENVIRONMENTAL QUALITY
Dissolved oxygen concentrations are often used as a measure of environ-
mental quality for coastal waters. In surface waters, dissolved oxygen is
usually saturated or oversaturated due to phytoplankton production and
air/sea gas exchange. In lower waters, microbial degradation of naturally-
occurring organic material and effluent organic material results in a net
consumption of oxygen. During stratification periods, oxygen resuoply from
surface waters is limited by low diffusivities in the pycnocline region.
Decreased oxygen concentrations in the range of 4-7 mg/L are typically
observed below the pycnocline; anoxic conditions are extremely rare [e.g.,
New York Bight, 1976 (Gross 1983)].
Organic enrichment in surface sediments near municipal outfalls is
generally accompanied by increased heterotrophic activity (and oxygen
consumption). In areas of high organic deposition, oxygen demand in surface
sediments may exceed the rate of oxygen resupply from overlying waters and
result in anoxic conditions. Structural alterations in benthic communities
are likely and may be related to the production of toxic hydrogen sulfide by
anaerobic microbes (Smith and Greene 1976). Alternatively, benthic communi-
ties may be affected by the enrichment of metals and trace organic compounds
in deposition areas near municipal outfalls. Thus, understanding particle
deposition and organic accumulation in marine sediments is of primary
importance in assessing the environmental effects of a coastal municipal
discharge.
-------
III. MODEL DEVELOPMENT
A simplified model for particle deposition and organic accumulation in
coastal waters is developed in the following paragraphs. Coastal transport,
phytoplankton dynamics, microbi'al degradation, and coagulation/settling of
natural particles and effluent particles are considered. Since model
•
applications are examined for deep outfall sites (ca. 60 m) off Southern
California, the model is presented for stratified water columns. The
production of natural particles is attributed to carbon fixation by phyto-
olankton and is expressed by .Tieasursd productivity races. Bonn natural
particles and effluent particles are considered to be comprised of organic
material, and organic decomposition is expressed by a first-order decay rate
(Stumm and Morgan 1981). Details of coagulation/settling kinetics are
discussed later in the report. Sediment resuspension and particle removal
by contact with the bottom are not expected to be significant for deep
outfall sites and are not included in the model.
MODELING FRAMEWORK
As a first step in constructing a simplified model for particle depo-
sition and organic accumulation, coastal process time scales were examined.
For the transport and mixing of effluent in coastal waters, time scales range
from a few minutes for plume entrainment to several weeks for large-scale
mean circulation (Table 1). Time estimates of 8 h to 10 days are given for
water column processes associated with particle "dynamics and organic
decomposition. With the exception of mixing in surface sediment layers,
sediment processes are described by time scales of 3-100 days during
accumulation periods.
Although time scales for many processes overlap, the following approxi-
mations have been made to simplify the modeling analysis. For water column
calculations, time scales of one to several days are considered most
8
-------
TABLE 1. TIME-SCALE ESTIMATES FOR COASTAL TRANSPORT
AND PARTICLE DYNAMICS
TIME SCALE (DAYS}
1.0 10 100
COASTAL TRANSPORT
1. Plume Entramment
2. Tidal Oscillations
3 Wind-Driven Currents
4 Large-Scale Circulation
5. Vertical Diffusion:
- In surface and lower waters
- Through the pycnocline
6. Horizontal Dispersion
WATER COLUMN PROCESSES
7. Phytoplankton Productivity
8 Organic Decomposition
9. Coagulation/Settling Kinetics
SEDIMENT PROCESSES
10. Mixing of Surface Sediments
11. Decomposition of Deposited
Organic Material
12. Burial of Surface Sediments
13. Frequency of Resuspension
Events
-------
important in describing particle dynamics and organic decomposition. Plume
entrainment, tidal oscillations, and mixing in the surface and lower waters
are characterized by smaller time scales and are assumed instantaneous. In
the model, these processes are averaged over the daily cycle. Conversely,
diffusion, through the pycnocline and horizontal dispersion are characterized
.by larger time scales and are not-considered significant over travel
distances of 10-ZO km.
Based on the above simplifications, the vertical structure of the water
column is described by a well-mixed surface and lower layer, separated by a
pycnocline region (Figure 1). For a surfacing waste•plume, a single
well-mixed layer can be assumed. The daily averaged discharge of effluent is
considered to be uniformly distributed over the tidal excursion Ellipse.
The concept of uniformly distributing a waste over an "extended source"
region was previously used by Csanady (1983). In defining dimensions of the
extended source, it is convenient to visualize the diffuser moving through a
stationary water body in the opposite direction of tidal currents (Csanady
1983).. Nontidal flow by wind-driven currents and large-scale mean circula-
tion are important in providing dilution waters to the extended source
region and in advecting effluent from this region.
A schematic of particle dynamics and organic accumulation (which is
consistent with the daily averaging of transport processes) is presented in
Figure 2. In the surface layer, "natural" particle concentrations are
controlled by phytoplankton production, organic decomposition, and coagu-
lation/settling. Advective transport of surface waters does not play a
significant role since natural concentrations are expected to be relatively
uniform over distances of 10-20 km. In the lower layer, discharged effluent
particles add to concentrations of natural particles that have settled from
surface waters. Removal mechanisms in the lower layer include organic
decomposition, coagulation/settling, and advective transport! Removal of
organic material from surface sediments is attributed to decomposition and
burial and is described by an interfacial turnover rate.
10
-------
SIGMA-T
VERTICALLY
WELL MIXED
TIDAL MOTION
VERTICALLY
WELL MIXED
TIDAL MOTION
/////////r
MUNICIPAL
EFFLUENT
NONTIDAL FLOW
NONTIDAL
FLOW
DIFFUSER
EXTENDED
SOURCE
REGION
NONTIDAL
FLOW
TIDAL
MOTION
Figure 1. Simpiffied diagram of municipal effluent transport in coastal
waters.
11
-------
PHYTOPLANKTON
PRODUCTION
NATURAL
PARTICLES
' COAGULATION/SETTLING
•>> DECOMPOSITION
DECOMPOSITION
. DECOMPOSITION
COAGULATION/SETTLING
DECOMPOSITION
AND BURIAL
^
TOTAL SOLIDS
NATURAL
PARTICLES
WASTE
PARTICLES
fe-
DECOMPOSITION
AND BURIAL
Figure 2. Simplified diagram of particle transport and organic carbon
cycles.
12
-------
MODEL FORMULATION
The mathematical formulation for calculating particle deposition and
organic accumulation presented in this report is based on the modeling
framework presented in Figures 1 and 2. Coagulation/settling kinetics are
herein described by a simplified expression developed by Farley and Morel
(1986). Their results show that the mass removal rate of solids, dC/dt, can
be described as the sum of three power laws:
-- 2'3l'91'3
each term of which corresponds to a oarf cuUr coacuTation nee Nanism:
differential settling, shear, and Brownian motion. Empirical relationships
for the coefficients Bds> B$h, and Bb are also provided as functions of
system parameters (Table 2).
Relationships given by Farley and Morel (1986) are expressed in terms of
floe densities and are applicable to the wet weight of suspended particles.
An equivalent expression for mass removal can be written in terms of dry
weight concentrations as follows:
dt
where C now represents dry weight concentration; and f is the conversion
from dry weight to wet weight and is given
fluid density, Pf, and floe porosity, e, as:
from dry weight to wet weight and is given in terms of particle density,p ,
()
In applying Equation 2 to coastal waters, only the differential settling
term and the shear term are expected to be important for mass concentrations
13
-------
TABLE 2. POWER LAW RELATIONSHIP FOR COAGULATION/SETTLING KINETICS
FROM FARLEY AND MOREL (1986)
- 3. C2'3 - 3 C1'9 - 3, C1'3
ds in b
dt
. «« «
d. • ' °e ab ad« ds
1.33
where C is the aasa concentration of particles, expressed in terms of wet weight; Bja,
Bsh. 3b «• th« sedimentation rate coefficients corresponding to coagulation by dif-
ferencial seeding, shear, and Brownlan notion; ajs. asn, Ob •« ehe efficiencies of
particle collision; Kj,, K«OI Kg are dimension*! parameters for the collision fre-
quency functions
ZW 3-1 C -1 /* \l/3 g (0-0.)
S"~lcmMC 1;Ksh'7l"c ' : K^« 'I —I |c»'lsec'
/ 6 N 1/3 g (Oe-0j)
(S/h) is the dlaensional parameter for Stokes settling In a vertically homogeneous
water column of depth, h
S/h -
1
61T2
1/3 g (pe- Pf)
[ca"2sec"1]
3v hP
f
k Is Che Boltraann constant; T Is ehe absolute temperature; u and v are the dynamic
and kinematic viscosities of the fluid; G is the shearing race of ehe fluid; g is ehe
gravitational acceleration; pe is Che floe density
pe • (l-«) pp + ePf
e is che floe porosity; Pp and Pf are the particle and fluid density.
14
-------
greater than 0.1 mg/L (dry wt). Removal rates can therefore be approximated
reasonably well by a second-order expression:
-- = -BC2 (4)
The coefficient, B, is then given as:
Bds C * f- Bsh C ' ,5,
where B. and 8 . are given in Table 2; f is given by Equation 3; and
is an average (or representative) dry weight concentration.
For water column concentrations of 'particles, the governing mass
conservation equation is then given as:
_3C_ TRANSPORT . - _ . _ -2 ,
3t * FLUXES - S - kdC - BC (6)
where 3C/3t is the time rate of change in mass concentration; transport
fluxes are associated with nontidal advection (Figure 1); S represents
sources of particles (e.g., phytoplankton productivity and municipal
effluent in the extended source region); k.C is the decomposition of organic
2
particles by first-order decay and BC is the second-order approximation for
coagulation/settling kinetics (Equation 4).
Surface Layer
For "natural" particle concentrations in the surface layer, transport
fluxes are not important (since concentrations are considered spatially
uniform) and particle product.!' on__!s_expressed by measured productivity
rates. The mass conservation equation is given as:-
15
-------
-2 -1
where ptota| represents phytoplankton productivity in gC-m -day ; 2.5 is
taken as the stoichiometric conversion of gC to g (dry wt); and h is the
surface layer depth. Using typical values for coastal waters, the reaction
half-lime of Equation 7 is given as a few days and steady-state approxima-
tions are often reasonable.
The flux of organic carbon settling through the pycnocline can be
expressed as:
Psed = BCV2-5
-2 -1
whene ? . is in umco of gC-m -day . Substituting tail's sxprgssion
the steady-state form of Equation 7. yields a simple relationship for P . as
a function of the productivity rate:
(9)
10 B
where kdnu/B is the only adjustable parameter.
2
To estimate k
-------
O.I/sec, which is roughly equivalent to an energy dissipation rate of
-42 3
10 cm /sec . A collision efficiency of 0.3 is assumed for coagulation
(Farley and Morel 1986) and particle concentrations are estimated in the
range of 0.5 mg/L (dry wt). For an average surface layer depth of 30 m, the
calculated value for,B equals 2-10 L-mg -sec (dry wt).
Results for the settling flux of organic carbon as a function of the
productivity rate (Equation 9) are given by the solid curve in Figure 3 for
the values of k., h , and B presented above. The predicted curve is shown
to compare very well with field estimates for stations in the Southern
California Bight and Monterey Bay (Eppley et al. 1983). Field estimates for
settling fluxes of organic carbon in the Gulf of Panama and the Central
Norcn Pacific fail below the solid curve ana may be e.xplainea oy mgner
decomposition rates (associated with higher temperatures) or deeper surface
layers.
Lower Layer
Calculations for particle concentrations in the lower layer are
developed in similar fashion from Equation 6. Here, sources of particles
include effluent input and the settling of natural particles from the surface
layer (Figure 2). Transport fluxes are considered in the lower layer to
account for the advection of effluent from the extended source region.
A summary of mass conservation equations and steady-state solutions for
suspended particle concentrations is presented in Appendix C for background
conditions (no effluent input), for the extended source region, and for the
region downcurrent of the extended source (see Figure 1). Note that in
these equations the second-order approximation for coagulation/settling
kinetics is assumed to be valid for overlying water layers, and is based on
the expectation of higher particle concentrations in the lower water laye'r
due to sewage discharge.
Solutions presented in Appendix C are dependent on dimensions of the
extended source region and nontidal advection. This information is obtained
17
-------
10 -i
2*
CD
T3
CM
u
2
x
D
_l
U.
O
UJ
0)
10 -
10 -
DATA FROM EPPLEY ET AL. 1983
• S. CALIFORNIA BIGHT
O S CALIFORNIA BIGHT
Q MONTEREY BAY
A CENTRAL N. PACIFIC
O GULF OF PANAMA
EQUATION 9
hu = 30m
kd = 0.1/day
B = 2x 10"6Lymg-sec
10
-1
10V
10'
PRODUCTIVITY RATE (gC/m2-day) -
Figure 3. Settling flux of organic carbon from the surface layer (Psed)
as a function of the phytoplankton productivity rate (P{ . .).
18
-------
from analysis of current records where harmonics for the main tidal com-
ponents are given as:
u
tidal
tidal
cos
cos
2»t
Zirt
Tj
.
uj
rvj
(10)
(11)
where U-, V. are amplitudes of the tidal oscillations in the x and y
•direction; T. is the oscillation period; and
-------
Fs(t) = B hLC2 (14)
where F (t) is the sediment flux rate in g-m -day (dry wt); and h. is the
height of the lower water layer in meters. For a fixed sediment location
(x, y), the deposition rate varies throughout the tidal cycle as overlying
waters move relative to the sediments. At any instant in time, the depo-
sition rate is expressed in terms of the water column coordinate system
(x1,y') using Equations 12 and 13, where x,y now represent coordinates for a
fixed sediment location. Daily-averaged deposition rates to the sediments
are then computed from flux rates in Equation 14 by numerically integrating
2 ?4-h pen'!cd.
In the surface sediments, the mass conservation equation for organic
accumulation is given as:
dCs - F - K C (15)
- S S S
where C$ is the organic accumulation in units of g/L; hg is the mixing
depth for surface sediments; Fs is the daily-averaged deposition rate in
-2 -1
g-m -day (dry wt); and K is an apparent interfacial removal rate
coefficient for sedimented organic material and includes the effects of
decomposition and burial. Steady-state solution for organic accumulation is
given as:
Cs(x,y) = Fs /Ks (16)
where an approximate value for K is given as 0.015 cm/day, based on steady-
state estimates of organic carbon turnover rates in surface sediments (from
field studies of Hopkinson 1985 and references therein). The time to reach
steady state is estimated from the mixing depth of surface sediments
(1-10 cm) and the interfacial removal rate coefficient for organic material
(0.01-0.025 cm/day) and is expected to range from a month to several years.
20
-------
Steady-state sediment calculations will therefore be most applicable to
sites where redistribution of sedimented material (by resuspension) is not
likely to occur at frequent intervals.
21
-------
IV. MODEL RESULTS AND DISCUSSIONS
Sample calculations and' verification studies are presented in the
following sections to demonstrate the general behavior of the model and its
predictive capabilities.
SAMPLE CALCULATIONS
Sample calculations are presented for a 10 m /sec discharge of primary
effluent, containing 100 mg/i_ of participate material. The outfall ciiffuspr
is submerged in 60 m of water, is 1,000 m long, and is oriented at an angle
of 30° to the longshore direction. The water column is divided into a
surface and lower layer by a sharp density gradient at the mid-depth.
Phytoplankton productivity in the surface waters is described by an average
-2 -1
rate of 1.0 gC-m -day . Short-term oscillatory currents are described by
a semi-diurnal tide. The tidal currents in both the longshore and cross-
shore direction have amplitudes of 0.1 m/sec and are 30° out of phase.
Nontidal flow is considered constant in time with a current velocity of
0.03 m/sec in the longshore direction.
The decomposition rate of suspended organic material is taken as
O.I/day. The second-order rate coefficient for the coagulation/settling of
particles is again given as 2-10 L-mg -sec (dry wt). This value is
based on previous calculations and is consistent with results from settling
column tests for several primary effluents. Removal of organic material in
surface sediments is described by an interfacial rate coefficient of
0.015 cm/day.
Model results for total suspended particle concentrations in the lower
layer, deposition rates, and organic accumulation in sediments are shown in
Figure 4. For suspended concentrations, background values for "natural"
particles are calculated as 0.46 mg/L in surface waters and 0.25 mg/L in
22
-------
a) SUSPENDED PARTICLE CONCENTRATION
. 0 2.5 km
EXTENDED SOURCE REGION
.63 :— .56 -r .50 r- .44
BACKGROUND CONCENTRATION = 0.25 mg/L
b) DAILY-AVERAGED DEPOSITION RATE
BACKGROUND DEPOSITION RATE - 0.35 g/m2-day
c) ORGANIC ACCUMULATION IN SEDIMENTS
BACKGROUND ORGANIC ACCUMULATDN - 2.3 g/L
Figure 4. _ Suspended particle concentration, deposition rate, and
organic accumulation given by the model as an example case.
23
-------
lower waters. In the lower waters, effluent particles discharged from the
outfall are mixed throughout an extended area by tidal oscillations
(Figure 4a). in the "extended source" region, total particle concentrations
are increased due to the municipal effluent. For this calculation, particle
concentrations in the extended source region are largely controlled by
farfield dilution (which in turn is controlled by nontidal currents, the
maximum excursion distance of the extended source perpendicular to the
nontidal currents, and the height of the lower layer). Downcurrent of the
extended source region, particle concentrations decrease due to deposition
and organic decomposition.
The background deposition rate for "natural" particles is calculated as
-2 -1
0.35 g-m -day (Figure 4b) ana is roughly equivalent to the reported
estimate of Emery (1960). In the vicinity of the outfall, daily-averaged
deposition rates are enhanced and are as much as eight times the background
rate. Since deposition rates are described by a second-order dependency of
particle concentrations, enhancement in deposition rates is more pronounced
than increases in suspended particle concentrations.
In the cross-shore direction, waste particles are deposited over fairly
large distances (Figure 4b). This lateral spreading, along with cross-shore
gradients in the deposition rate, is the result of oscillatory tidal motion
of the water column over the fixed sediment layer. Tidal effects also occur
in the longshore direction, as evidenced by the deposition of waste particles
upcurrent of the diffuser. In the downcurrent direction, nontidal advection
plays the predominant role in determining deposition patterns. For the area
mapped in Figure 4b, 30 percent of the waste particles are deposited in
sediments. The remainder is either decomposed in the water column
(26 percent) or advected further downcurrent (44 percent).
As shown in Figure 4c, steady-state distributions for organic accumu-
lations in sediments mimic deposition patterns. Accumulations of organic
material in sediments are calculated as 2.3 g/L for background conditions to
-a maximum of 18.4 g/L near the outfall. Assuming a sediment water content
24
-------
of 0.5 and a particle density for sediments of 2.6 g/cm , the results for
organic content would range from 0.2 to 1.4 percent on a dry weight basis.
•
VERIFICATION STUDIES
Model veri f.ication studies are presented for the Orange County and Los
Angeles County outfalls to demonstrate the predictive capabilities of the
deposition calculation. Methods used to calculate model parameters -are
first described. A detailed description of modeling the Orange County
outfall and comparison of model and field deposition and organic accumulation
rates is followed by a similar description for the Los Angeles County
outfall .
For both the Orange County and Los Angeles County outfalls, field
estimates of predicted model parameters are derived from July 1977 data
(Word and Mearns 1979) and May 1980 • data (Swartz et al. 1985). Field
estimates of inorganic deposition rates were obtained by assuming that for
steady-state conditions, BOOs measurements for the upper 2 cm of sediment are
related to deposition rates as follows:
W _
Fs = BOD5 Ps - Rs (ps-^) 1.07 g02/g dry wt 5 days (17)
where Fs is the deposition rate in g/mz/day; BOOs is given as mg 02 demand/kg
of dry sediment; Rs is the sediment dry wtrwet wt ratio and is given as kg
of dry sediment/kg of wet sediment; ps is the particle density for sediments
and is taken as 2.6 g/cm3; P^ is the density of seawater; hs is the size (or
depth) of the sediment sample in m; 1.07 is a stochiometric conversion
factor; and 5 days is the specified time for the BODs measurement. Fie-ld
estimates of organic accumulation in sediments were obtained from COO and
volatile solids measurements for the upper 2 cm of sediment as follows:
Rsps°w 10"3
r • b 5 w
s Ps - Rs (ps-pw) 1.07 g02/g dry wt
25
-------
or
A
C ' 10
s Ps - Rs ( ps-pw)
where._Cs is the organic accumulation in sediment..in g/L; COD is given as mg
Og demand/kg of dry sediment; VS is given in terms of percent dry wt.
For Orange County, the wasteflow rate and effluent solids concentration
are given as 8.2 m /sec and 140 mg/L, respectively, based on 1977-1980
discharge conditions (Schafer 1979, 1980). The wastewater is discharged
through a 90° dogleg diffuser, having dimensions of 960 m in the cross-shore
direction (188° N) and 860 m in the longshore direction (278° N). Water
depth at the discharge site is approximately 60 m. Based on observed
density gradients, the water column is divided into a surface and lower
layer at the mid-depth. Pnytoplankton productivity in the surface layer is
-2 -1
described by an average rate of 2.0 gC-m -day and is based on observations
of increased productivity near other large outfalls off Southern California
(Thomas 1972).
Model parameters for tidal and nontidal flow were obtained from analysis
of current meter data (see Ocean Currents in Appendix B for details). The
current meter data were collected by Southern California Coastal Water
Research Program (SCCWRP) personnel from 2/2/81 to 7/21/81 at a depth of 40 m
in 55 m of water near the Orange County outfall. These data were assumed to
be representative of lower layer flow. A spectral analysis of the data
indicates that short-term oscillatory motion is dominated by semidiurnal
tidal currents. Tidal amplitudes of 6.5 cm/sec in the longshore (278° N)
direction and 6.0 cm/sec in the cross-shore (188° N) direction_were deter-
mined by assuming that all short-term variance (i.e., having periods less
than 1 day) is associated with semidiurnal tidal motion. Phase shifts for
tidal velocities in the longshore and cross-shore directions were assigned
as 45° and 0°, resulting in an elliptical tidal motion. This motion is
considered to represent average conditions for spreading the sewage over an
extended source region.
26
-------
Nontidal flows were- determined from a 24-h running average of the
current meter record. Nontidal flows in the cross-shore direction were
found to be small and were considered negligible for model application.
Nontidal flows in the longshore direction ranged from 0 to 20 cm/sec, often
reversing in direction in cycles of 4-8 days. From a cumulative distribution
plot, we found that nontidal flows are described by an average upcoast
(278° N) velocity of 9.0 cm/sec occurring 67 percent of the time, and an
average downcoast velocity (98° N) of 5.1 cm/sec occurring 33 percent of the
time. For model application, nontidal flows were assumed to follow the
local bathymetry.
Model predictions for deposition rates near the Orange County outfall
were performed using a decomposition rate of O.I/day in the surface layer
and 0.05/day in the lower layer (to account for cooler water temperatures
below the pycnocline). As in previous calculations, the second-order rate
coefficient for the coagulation/settling of particles was set as 2-10
L-mg~ -sec" (dry wt). Model predictions for deposition rates in the
longshore direction are given by the solid line in Figure 5 and are in
reasonable agreement with estimates from field data taken along the 60-m
isobath. Note that deposition of effluent particles is predicted in both the
upcoast and downcoast direction due to reversals in the nontidal flow.
Results of the deposition calculation also indicate that 34 percent of the
effluent particles are deposited within 20 km of the outfall. The remainder
is either decomposed in the water column (11 percent) or advected from the
study area (55 percent).
Model predictions were also performed for organic accumulation in
surface sediments near the Orange County outfall using a interfacial rate
coefficient of 0.015 cm/day for the removal of organic material in surface
sediments. Results are presented in Figure 6 for organic accumulation in
the longshore direction and are in good agreement with field estimates for
accumulation along the 60-m isobath. Model predictions in Figures 5 and 6
were also compared to "calculated results for phytoplankton productivity
-2 -1
rates of 1.0 and 2.0 gC-m -day (with no effluent particles). Results
27
-------
ro
00
10%
>» I
00
•o
CM
E
5
UJ
z
g
H
(0
O
Q.
LU
Q
I
10 -
10
o_
-15
FIELD ESTIMATES FROM BOD5
MEASUREMENTS (JULY 1977)
kd = 0 OS/day (LOWER LAYER)
B = 2 x 10~6 L/mg-sec
(with no effluent)
LOCATION OF DIFFUSER
.day.
(with no effluent)
-10
-5
r
5
10
15
i
20
DISTANCE (km)
Figure 5. Deposition rates near the Orange County outfall along the 60-m isobath based on
model predictions and field estimates.
-------
ZCB
^^^
o
io-
O UJ
PC/)
z <
Is
10-
• FIELD ESTIMATES FROM COD
MEASUREMENTS (JULY 1977)
o FIELD ESTIMATES FROM
VOLATILE SOLIDS
MEASUREMENTS (JULY 1987)
Ks = 0015 cm/day
P'?«?!.'.20.??m day
(with no effluent)
LOCATION OF DIFFUSER
F*total = 1 OgC/ni - day (wiih no effluent)
-15
-10
-5
i
0
10
i
15
20
DISTANCE (km)
Figure 6. Organic accumulation near the Orange County outfall along the 60-m isobath based
on model predictions and field estimates.
-------
indicate that for Orange County the discharge of effluent particles and
enhanced productivity near the outfall are both important in determining the
deposition and accumulation of organic material in sediments.
Similar calculations were performed for the Los Angeles County outfall.
For Los Angeles County, the wasteflow rate and the effluent solids concen-
tration are given as 20 m /sec and 165 mg/L, respectively, based on 1977-
1980 discharge conditions (Schafer 1979, 1980). The effluent is discharged
from two operating diffusers. For model application, the diffusers are
approximated by a 2,750-m continuous line source (based on endpoints of the
•
diffusers) in the longshore direction (278° N). Water depth at the discharge
site is approximately 60 m. Based on observed density gradients, the water
column is divided into a surface and lower layer at cne mid-aepch. Phyto-
plankton productivity in the surface layer is described by an average rate
-2 -1
of 2.0 gC-m -day , base<
the outfall (Thomas 1972).
-2 -1
of 2.0 gC-m -day , based on observations of increased productivity near
Model parameters for tidal and nontidal flow were again obtained from an
analysis of current meter data. The current meter data were collected by
SCCWRP personnel from 4/16/79 to 9/18/79 at a depth of 41 m in 56 m of water
near the Los Angeles County outfall. An analysis of the data indicates that
short-term oscillatory motion is dominated by semidiurnal tidal currents,
with amplitudes of 7.0 cm/sec in both the longshore (278° N) and cross-shore
(188° N) directions. Phase shifts for the tidal velocities in the longshore
and cross-shore directions were assigned as 45° and 0°, respectively.
Nontidal flow is described by an average upcoast (278° N) velocity of
5.5 cm/sec occurring 100 percent of the time.
For model application, coefficients were again set at O.I/day and
0.05/day for the decomposition rate in the surface layer and lower layer,
respectively; at 2-10~ L-mg~ -sec" (dry wt) for the second-order coagu-
lation/settling rate; and at 0.015 cm/day for the removal rate of organic
material from surface sediments. Predictions for organic deposition rates
near the Los Angeles County outfall are presented in Figure 7 and are in
good agreement with field estimates for deposition rates along the 60-m
30
-------
DEPOSITION RATE (g/m2-day
• FIELD ESTIMATES FROM BOD5
MEASUREMENTS (JULY 1977)
o FIELD ESTIMATES FROM BOD-
MEASUREMENTS (MAY 1980)
kd = 0 05/day (LOWER LAYER)
B = 2x 10'6 L/mg-sec
total
(with no ellluenl)
P.o.al -'OgC/taf-day
(will) no effluent)
LOCATION OF DIFFUSERS
-15
-10
-5
0
5
10
15
20
DISTANCE (km)
Figure 7. Deposition rates near the Los Angeles County outfall along the 60-m isobath based
on model predictions and field estimates.
-------
isobath. Note that the maximum deposition rate near the Los Angeles County
outfall is 3-4 times greater than the predicted deposition rate near the
Orange County outfall. This is primarily due to the higher effluent particle
discharge rate of 3,300 g/day from Los Angeles County vs. 1,150 g/day from
Orange County. For Los Angeles County, results of the deposition calcula-
tion also' indicate that 63 percent of the effluent particles are deposited
within 20 km of the outfall. The remainder is either decomposed in the
water column (12 percent) or advected out of the study area (25 percent).
(Note that the deposited material is subject to further decomposition in the
sediments and burial).
Model predictions for organic accumulation in surface sediments near the
Los Angeles County outfall are shown in Figure 8. Again, the results
compare quite well with field estimates, and are 3-4 times greater than the
prediction for organic accumulation in 'surface sediments near the Orange
County outfall. Calculated results for phytoplankton productivity rates of
-2 -1
1.0 and 2.0 gC-m -day '(with no effluent) are also given in Figures 7
and 8. For Los Angeles County, the large discharge of effluent particulates
plays the predominant role in determining the deposition and accumulation of
organic material in sediments near the outfall.
32
-------
to
co
-I Z
25
3 ?^
UJ
O O
cc
103-
10-
-15
I
LOCATION OF DIFFUSERS
i
-10
. FIELD ESTIMATES FROM COD
MEASUREMENTS (JULY 1977)
A FIELD ESTIMATES FROM
VOLATILE SOLIDS
MEASUREMENTS (JULY 1977)
o FIELD ESTIMATES FROM
VOLATILE SOLIDS
MEASUREMENTS (MAY 1980)
Ks =001 5 cm/day
p,p,ai .:.20.9C/m;day..
(with no ellluenl)
P . =10gC/m -day (with no effluent)
-5.
10
15
I
20
DISTANCE (km)
Figure 8. Organic accumulation near the Los Angeles County outfall along the 60-m isobath
based on model predictions and field estimates.
-------
V. EXTENSION OF THE MODEL FOR PREDICTING CHEMICAL CONTAMINATION
The accumulation of metals and trace organic chemicals in sediments is
dependent on the partitioning of the chemical between the dissolved and
particulate phase, particle deposition rates, and removal processes in the
sediments. A model for predicting particle deposition rates has been
presented in the previous sections. In this section, the deposition model
is extended to include calculations for the deposition and accumulation of
chemical contaminants in sediments. Descriptions for the partitioning
benavior o-f chemicals in tne water column ana removal processes in the
sediments are discussed below.
Several approaches can be used in modeling the partitioning behavior of
chemicals in the water column. They include instantaneous (or equilibrium)
partitioning, complete stabilization of the chemical in the particulate
phase, and kinetic release of chemicals into solution by desorption/dissolu-
tion reactions. For this model formulation, equilibrium partition coeffi-
cients are used to describe the dissolved/particulate interactions in the
water column. It should be noted, however, that using the equilibrium
partitioning approach with a very high partition coefficient is equivalent
to assuming complete stabilization of the chemical in the particulate phase
or slow kinetic release of particle-bound chemicals.
Removal rates for metals and trace organic chemicals from sediments may
be controlVed by burial of surface sediments by new deposits, desorption/
dissolution reactions (possibly related to the oxidation of sulfide, the
decomposition, of organic material, or diffusion across the water/sediment
interface), or chemical transformations (e.g., hydrolysis, microbial
degradation). As a first approximation, the removal of chemicals from
surface sediments is described in this model by a first-order rate law and
an interfacial removal rate coefficient. _
34
-------
MODEL FORMULATION
. Following the modeling approach presented in the previous sections, the
governing mass conservation equation for a trace chemical in the water
column is given as:
3C . TRANSPORT _ <. RM2_ ,7fn
~3~r + FLUXES " S " BM F (20)
where 3C/3t is the time rate of change of the total concentration of a
chemical in the water column; transport fluxes are associated with nontidal
advection (see Figure 1); S represents sources of the chemical (e.g.,
7
effluent in the extended source region); and BM T is the deposition rate for
the chemical and is dependent on the second-order rate coefficient for the
coagulation/settling of particles (B), the mass concentration of suspended
particles (M), and the particulate concentration of the chemical (r). In
addition to deposition, chemical transformations (e.g., hydrolysis reactions)
may occur in the water column and can be included in the"mass conservation
equation.
In solving Equation 20, it is necessary to specify a relationship for
the total chemical concentration and the particulate chemical concentration.
Here, the total chemical concentration is given by the summation of the
particulate and dissolved fractions:
C = TM + Cdis (21)
where C is the total chemical concentration in ug/L; r is the particulate
concentration of the chemical in mg/g; M is the mass concentration of
suspended particles in mg/L; and Cdis is the dissolved chemical concentration
in ug/L. For equilibrium conditions, the particulate concentration can be
expressed in terms of the dissolved concentration:
r=10-6KC • (22)
35
-------
where K is the equilibrium partitioning coefficient and is given in units
of L/kg. Substituting Equations 21 and 22 into Equation 20 yields the
expression:
_c 2 _
3C + TRANSPORT . 1Q B KPM C ,,,.
3t FLUXES - - -6 (23)
Mass conservation equations and steady-state solutions for chemical concen-
trations in the lower water column are developed based on Equation 23 and
are presented in Appendix D for the extended source region and for the region
downcurrent of the extended source (see Figure 1).
Chemical deposition rates are determined from suspended particle
concentrations and the dissol ved/particulate distribution of the chemical in
the overlying waters and are given as:
Fs(t) = B h,_M2r (24)
where F (t) is the deposition flux rate of the chemical at any instant in
-2 -1
time and is given in units of mg-m -day ; and h, is the height of the
lower water layer in meters. Substituting Equations 21 and 22 into
Equation 24 yields a relationship for the deposition rate in terms of the
total chemical concentration:
- 10~6- KC
F.(t) = Bh.M* § (25)
5 L 1 + lO'VM
For a fixed sediment location (x,y), the deposition rate varies throughout
the tidal cycle as overlying waters move relative to" the sediments. The
deposition rate can be expressed in terms of the water column coordinate
system (x',y') using Equations 12 and 13, where x,y represent coordinates
for a fixed sediment location. Daily-averaged deposition rates to the
36
-------
sediments are then computed from flux rates in Equation 25 by numerically
integrating a 24-h period.
In the surface sediments, the mass, conservation equation for the
accumulation of a metal or a trace organic chemical is given as:
h dCs = F - K C (26)
S dt s r s
where C is the accumulation of the chemical in the surface sediments in
units of ug/L; h is the mixing depth for 'surface sediments; Fs is the
-2 -1
daily-averaged deposition rate in mg-m -day ; and K is an apparent
interfacial removal rate coefficient for the chemical in surface sediments
and includes tne effects of burial, desorption/aissolution reactions, and
chemical transformations. Steady-state solution for accumulation of the
chemical in the surface sediments is given as:
Cs(x,y) = Fs /Kp (27)
Appropriate values for Kp will be discussed in the following section.
MODEL CALCULATIONS
Sample calculations for chemical deposition rates were performed for the
Los Angeles County outfall for several partition coefficients and a 1 ug/L
effluent concentration of a chemical contaminant. Calculated results for
the longshore distribution of chemical deposition rates are presented in
Figure 9. The results clearly show that the magnitude of chemical deposition
is significantly affected by the choice of partition coefficient. For a low
partition coefficient (<104), a large fraction of the trace chemical is
dissolved in the water column and very little is deposited in the sediments.
For a high partition coefficient (>10^), the discharged chemical is almost
entirely associated with the particulate phase and ca. 25 percent of the
chemical is deposited within 20 km of the outfall. (Note that this latter
case of a high partition coefficient represents maximum deposition rates for
37
-------
LOCATION OF DIFFUSERS
co
00
LU
Z
o
E £
c/> -o
?~
&• P
UJ fc
Q O)
O
O
10
-3
-15
-10
-5
0
10
i
15
i
20
DISTANCE (km)
Figure 9. Chemical deposition rates near the Los Angeles County outfall along the 60-m
isobath based on model results.
-------
the trace chemical and is equivalent to assuming complete stabilization of
the chemical in the particulate phase.)
Values for partition coefficients are determined by the specific
behavior of the metal or the trace organic chemical. "Coefficients for trace
organic chemicals are typically described by octanol/water partitioning
behavior and the organic content of suspended particles (Karickhoff et al.
1979). For metals, partitioning behavior is largely controlled by the
formation of organic and inorganic complexes in seawater, the precipitation/
dissolution of oxidized and possibly reduced species (if redox species are
kinetically stable over periods of several days), and the sorption of metals
on organic and inorganic surfaces. Partition coefficients for metals are
difficult to assign, but can be estimated from laboratory data, field data,
or chemical calculations. For example, in this report the relative magni-
tudes for the partitioning for metals have been estimated from reported
ocean residence times (Balistrieri et al . 1981), which indicate that
partition coefficients for metals can vary over several orders of magnitude
as follows: lead > copper >» cadmium. This result is used below in
examining metal accumulations in sediments.
The accumulation of 'metals in sediments near the Los Angeles County
outfall were examined to test the applicability of the modeling approach
presented in this report. Model predictions for lead, copper, and cadmium
accumulations in surface sediments are compared to estimates based on field
data taken in July 1977 (Word and Mearns 1979) and in May 1980 (Swartz et
al . 1985). Field estimates were obtained from lead, copper, and cadmium
measurements for the upper 2 cm of sediment as follows:
where Cs is the metal accumulation in sediment in mg/L; (Metal) is the
observed metal concentration in the upper 2 cm of sediment in mg/kg (dry wt);
Rs is the sediment dry~wtrwet wt ratio and is given as kg of dry sediment/kg
of wet sediment; Ps is the particle density for sediments and is taken as
39
-------
Z.6 g/cnv3; and Pw is the density of seawater. Values for (Metal) and Rs are
from Word and Mearns (1979) for the July 1977 field estimates, and from
Swartz et al. (1985) for the May 1980 field estimates.
The effluent lead concentration was taken as 145 ug/L, based on 1977-
1980 discharge conditions (Schafer 1979, 1980), and the partition coefficient
was assumed to be greater than 10 . Background concentrations of the metal
were neglected in this examination. The rate coefficient for the removal of
lead from surface sediments, K , was adjusted to match the calculated
results with field estimates. Results are presented in Figure 10 for the
longshore distribution of lead accumulation using a value of 0.007 cm/day
for Kp.
Similar calculations were performed for copper, using an effluent
concentration of 220 ug/L (Schafer 1979; 1980) and assuming that the
partition coefficient is greater than 10 . A good comparison of calculated
results and field estimates was again obtained using a value of 0.007 cm/day
for
-------
FIELD ESTIMATES FROM LEAD
MEASUREMENTS (JULY 1977)
O)
2«o
H H
< 2
-I UJ
O
O
Q
UJ
< UJ
§<
< u.
UJ CE
-" r>
(A
103n
10'-
o FIELD ESTIMATES FROM LEAD
MEASUREMENTS (MAY 1980)
Kf= 0007 cm/day
Kp> 107f'Ukg
Ce()| =0 145mg/L
LOCATION OF DIFFUSERS
-15
-10
-5
i
5
10
15
20
DISTANCE (km)
Figure 10. Lead accumulation in surface sediments near the Los Angeles County outfall
along the 60-m isobath based on model results and field estimates.
-------
• FIELD ESTIMATES FROM COPPER
MEASUREMENTS (JULY 1977)
0)
o
o
UJ
„ UJ
c o
£<
O
o
DC
10
2_
10'-
o FIELD ESTIMATES FROM COPPER
MEASUREMENTS (MAY 1980)
LOCATION OF DIFFUSERS
-15
-10
i
-5
10
Kf = 0007 cm/day
K > 107L/kg
0220rrig/L
I
15
20
DISTANCE (km)
Figure 11. Copper accumulation in surface sediments near the Los Angeles County outfall
along the 60-m isobath based on model results and fluid estimates.
-------
z P
o S
o o
O UJ
< (/)
•5 UJ
O OC
o w
z
10_
LOCATION OF DIFFUSERS
-15
-10
-5
• FIELD ESTIMATES FROM CADMIUM
MEASUREMENTS (JULY 1977)
o FIELD ESTIMATES FROM CADMIUM
MEASUREMENTS (MAY 1980)
10
DISTANCE (km)
K = 0 007 cm/day
Celfl -°°27mg/L
i
15
i
20
Figure 12. Cadmium accumulation in surface sediments near the Los Angeles County outfall
along the 60-m isobath based on model results and field estimates.
-------
copper. A large fraction of the cadmium is therefore expected to remain in
the water column (probably in the form of cadmium complexes), and will be
advected away from the discharge site.
> Observed distributions for trace organic accumulations (e.g., PCBs,
DOT) are similar to distributions of chemical deposition rates in Figure 9.
For PCBs and DDT, both burial and the formation of metabolites of the parent
compounds are expected to be important removal processes in the sediments.
Removal rate coefficients should therefore be greater than 0.007 cm/day.
Further investigations, however, are necessary to determine extent of
metabolite production in sediments near the Los Angeles County outfall.
44
-------
VI. CONCLUSIONS
The model presented in this report provides a simple and realistic
calculation for predicting particle deposition and organic accumulation in
surface sediments near municipal ocean outfalls. The model is formulated
based on coastal transport, particle transport, and organic carbon cycles,
and inc-ludes the effects of coagulation and settling of effluent particles
and natural organic material.
Input parameters for the model include the cischarge flow race and the
effluent solids concentration, the outfall diffuser location and geometry,
the density structure and depth of the water column, the phytoplankton
productivity rate, and a simplified description of ocean currents. Three
modeling coefficients are required for calculating particle deposition and
organic accumulation in surface sediments. They are the second-order
coagulation/settling rate coefficient, the decomposition rate coefficient
for suspended organic material, and the interfacial .removal rate coefficient
for sedimented organic material. Values for the first two coefficients are
obtained from results of theoretical and laboratory studies, while the
removal rate coefficient for sedimented organic material is assigned based
on field studies of organic turnover rates in surface sediments.
Model predictions for particle deposition and organic accumulation in
sediments near the Orange County and Los Angeles County outfalls were
performed using predetermined values for the modeling coefficients.
Predicted results compared well with field estimates at both outfall
locations, demonstrating the applicability of the model in predicting
deposition and accumulation near deep municipal outfalls. For municipal
outfalls in shallower waters (where resuspension may play an active role in
redistributing sedimented organic material), model calculations can be used
in determining initial deposition patterns and in providing conservative
estimates for organic accumulation in sediments. Additional verification
45
-------
studies, however, should be performed for deep outfalls in other geographic
areas and for shallow outfall locations.
Extension of the model for predicting metal and trace organic chemical
accumulations in sediments has also been presented. For chemical calcula-
tions, -equilibrium partition coefficients are used to describe dissolved/
particulate interactions in the water column. The removal of chemicals from
surface sediments is approximated using an interfacial removal rate coeffi-
cient. Preliminary model results for metal accumulations near the Los
Angeles County outfall compare favorably with field estimates. These
%
results suggest that deposited metals are retained in sediments near the
outfall (probably in the form of metal sul fides) and are buried in time.
Similar model calculations for the accumulation of trace organic chemicals
should be performed to examine the importance of chemical transformations in
sediments.
Model calculations for organic accumulations and chemical accumulations
in sediments can be used in predicting environmental impacts from municipal
discharges, in designing monitoring programs and establishing future
monitoring strategies, and in analyzing field data for chemical enrichment
and biological impacts. Applicability of the model calculations however
will depend on the availability of input data (particularly for ocean
currents), and the assignment of modeling coefficients. Future efforts
should therefore be directed at the analysis of long-term current meter
records, and at additional studies of modeling coefficients. In addition,
detailed examinations of sediment processes should be performed to determine,
the individual roles of microbial decomposition and burial in removing
organic material from surface sediments. The actual removal pathway
(decomposition vs. burial) will be .-important in determining the long-term
environmental impacts of sewage discharge.
46
-------
REFERENCES
Balistrieri, L., P.G. Brewer, and J.W. Murray. 1981. Scavenging residence
times of trace metals and surface chemistry of sinking particles in the deep
ocean. Deep-Sea Res. 28A:101-121.
Brandsma, M.G., and T.C. Sauer, Jr. 1983. The OOC model: prediction of
short term fate of drilling mud in the ocean. Vot. 2:57-106. In: An
Evaluation of Effluent Dispersion and Fate Models for OCS Platforms. A.K.
Runchal (ed). Prepared for U.S. Department of Interior, Minerals Management
Service.
Brooks, N.H. 1960. Diffusion of sewage effluent in an ocean-current. In:
Proceedings of the 1st International Conference on Waste Disposal in the
Mar-ne Environment, Berkeley, CA. July 1959. Pe^gamon °ress, New York, NY.
Chen, C.W., O.J. Smith, J.D. Jackson, and J.D. Hendr.ick. 1975. Organic
sediment model for wastewater outfall. In: Proceedings of the Symposium on
Modeling Tecniques, ASCE, San Francisco, CA.
Csanady, G.T. 1983. Dispersal by randomly varying currents. J. Fluid
Mechanics 132:375-394.
CRC. 1981. Handbook of chemistry and physics. 61st Edition. CRC Press,
Inc., Boca Raton, FL.
Emery, K.O. 1960. The sea off southern California. John Wiley and Sons,
New York, NY.
Eppley, R.W., W.G. Harrison, S.W. Chisholm, and E. Stewart. 1977. Particu-
late organic matter in surface waters off southern California and its
relationship to phytoplankton. J. Mar. Res. 35:671-696.
Eppley, R.W., E.H. Renger, and P.R. Betzer. 1983. The residence time of
particulate organic carbon in the surface layer of the ocean. Deep-Sea
Res. 30:311-323.
Farley, K.J., and F.M.M. Morel. 1986. The role of coagulation in the
kinetics of sedimentation. Environ. Sci. Technol. 20:187-195.
Farley, K.J. 1985. A simplified deposition calculation (DECAL) for organic
solids accumulation near sewage outfalls. Draft Report. Prepared for U.S.
Environmental Protection Agency, Washington, DC. Tetra Tech, Inc., Bellevue,
WA.
Galloway, J.N. 1972. Man's alteration of the natural geochemical cycle of
selected trace metal-s. _Ph.-D-. Dissertation. University of California, San
Diego. 143 pp.
47
-------
Gross, M.G. 1983. The coastal ocean: the regional background. pp.
93-128. In: Ocean Disposal of Municipal Wastewater: Impacts on. the Coastal
Environment. E.P. Meyers and E.T. Harding (eds). Massachusetts Institute
of Technology, Sea Grant College Program, Cambridge, MA.
Hendricks, T.J. 1974. The fate of trace metals and particulates. In:
Southern Cali-fornia Coastal Water Research Project 1974 Annual Report. W.
Bascom (ed). El Segundo, CA.
Hendricks, T.J. 1983. Numerical model of sediment quality near an ocean
outfall. Final Report. NOAA Grant #NA80RAD0041. Southern California
Coastal Water Research Project Authority, Long Beach, CA.
Hopkinson, C.S., Jr. 1985. Shallow-water benthic and pelagic metabolism:
evidence of heterotrophy in the nearshore Georgia Bight. Mar. Biol .
87:19-32.
Hunt, J.R. 1982. Partite dynamics in seawater; implications for predicting
the fate of discharged parades. Environ. Sci. Technol. 16:303-309.
Karickhoff, S.W., D.S. Brown, and T.A. Scott. 1979. Sorption of hydrophobic
pollutants on natural sediments. Water Res. 13:241-248.
Koh, R.C.Y. 1982. Initial sedimentation of waste particulates discharged
from ocean outfalls. Environ. Sci. Technol. 16:757-763.
Mercier, R.S. 1984. The reactive transport of suspended particles:
mechanisms and modeling. Ph.D. Thesis. Massachusetts Institute of Tech-
nology, Cambridge, MA.
Metcalf & Eddy, Inc. 1972. Wastewater engineering: collection, treatment,
disposal. McGraw-Hill, Inc. New York, NY. 782pp.
Meyers, E.P. 1974. The concentration and isotopic composition of carbon in
marine sediments affected by a sewage discharge. Ph.D. Dissertation.
California Institute of Technology, Pasadena, CA. 178 pp.
Morel, F.M.M., and S.L. Schiff. 1980. Geochemistry of municipal waste in
coastal waters. R.M. Parsons Laboratory Technical Report 259. Massachusetts
Institute of Technology, Cambridge, MA.
Oicubo, A. 1971. Ocean diffusion diagrams. Deep-Sea Res. 18:789-802.
Okubo, A., and R.V. Osmidov. 1970. Empirical dependence of the coefficient
of horizontal turbulent diffusion in the ocean of the scale of phenomenon in
question. Izd. Acad. of Sciences USSR, Atmospheric and Ocean Physics: 6.
Parsons, T.R., M. Takahashi, and B. Margrave. 1977. Biological ocean-
ographic processes. 2nd Edition. Pergamon Press, New York, NY. 332 pp.
Runchal, A.K. 1983. The drift model: thoery and development of the model.
Vol. 2:157-173. In: An Evaluation of Effluent Dispersion and Fate Models
48
-------
for OCS Platforms. A.K. Runchal (ed). Prepared for U.S. Department of the
Interior, Minerals Management Service.
Schafer, H.A. 1979. Characteristics of municipal wastewater discharges,
1977. pp. 97-102. In: Southern California Coastal Water Research Project
1978-Annual Report. W. Bascom (ed). El Segundo, CA.
Schafer, H.A. 1980. Characteristic's of municipal wastewater. pp. 235-Z40.
In: Southern California Coastal Water Research Project- Biennial Report,
1979-1980. W. Basconf'Ted). Long Beach, CA.
Seuss, E. 1980. Participate organic carbon flux .in the oceans—surface
productivity and oxygen utilization. Nature 288:260-264.
Smith, R.W., and C.S. Greene. 1976. Biological communities near submarine
outfall. J. Water Pollut. Control Fed. 48:1894-1912.
Stull, J.K., R.B. Baird, and T.C. Heesen. 1986. Marine sediment core
profiles of trace constituents, offshore of a deep wastewater outfall. J.
Water Pollut. Control Fed". 58:985-991.
Stumm, W., and J.J. Morgan. 1981. Aquatic chemistry: an introduction
emphasizing chemical equilibrium in natural waters. 2nd Edition. John
Wiley and Sons, New York, NY. 780 pp.
Suess, E. 1980. Participate organic carbon flux in the oceans—surface
productivity and oxygen utilization. Nature 288:260-264.
Swartz, R.C., D.W. Schults, G.R. Ditsworth, W.A. DeBen, and F.A. Cole.
1985. Sediment toxicity, contamination, and macrobenthic communities near a
large sewage outfall, pp. 152-175. In: Validation and Predictability of
Laboratory Methods for Assessing the Fate and Effects of Contaminants in
Aquatic Ecosystems. ASTM STP 865. T.P. Boyle (ed). American Society for
Testing and Materials, Philadelphia, PA.
Thomas, W.H. 1972. Nutrients, chlorophyll, and phytoplankton productivity
near southern California sewage outfalls. Univ. of Calif. Inst.
Mar. Res. Ref. No. 72-19. 77 pp.
f +
U.S. Environmental Protection Agency. 1982. Revised Section 301(h)
technical support document. EPA-430/9-82-011. Washington, DC.
Word, J.Q., and A.J. Mearns. 1979. 60-meter control survey off southern
California. TM 229. South. Calif. Coastal Water Res. Proj., El Segundo,
CA. 58 pp.
Wu, F., and T. Lueng. 1983. Modified Koh-Chang model, pp. 107-126. In:
An Evaluation of Effluent Dispersion and Fate Models for OCS Platforms,
Volume 2 - Contributed Papers. A.K. Runchal (ed). Prepared for U.S.
Department'of the Interior, Minerals Management Service by MBC Applied
Environmental Sciences, and Analytic and Computational Research, Inc.
49
-------
APPENDIX A
REVIEW OF PARTICLE DEPOSITION MODELS
-------
REVIEW OF PARTICLE DEPOSITION MODELS
Various models" of particle deposition in coastal waters have been
proposed for examining municipal effluent (and sludge) discharges from
submerged outfalls. A comparison of frequently cited models with DECAL is
given below.
— %
CHEN ET AL. 1975
i. Particle deposition rates are described by a fixed distribution of
apparent settling rates for effluent particles. Decomposition of organic
particles in the water column is not considered significant.
2. Horizontal transport of particles by ocean currents is described by a
mean flow and a spreading (dispersion) coefficient to account for
"random" components of currents. Vertical diffusion is not considered
significant. Wastefield height above the bottom is obtained from
calculations for plume height of rise.
3. Solution for the particle transport equation is obtained analytically
(using integral calculus). Superpositioning is used in the solution for
a continuous waste discharge.
4. Organic decomposition in sediments is described by first-order decay.
Resuspension and redistribution of sedimented material is empirically
described by a sediment diffusion mechanism.
U.S. ENVIRONMENTAL PROTECTION AGENC.Y_1982 [REVISED 301(h) TSD]
1. Particle deposition rates are described by a fixed distribution of
apparent settling rates for effluent particles. Decomposition of organic
particles in the water column is not considered significant.
A-l
-------
2. Horizontal transport of particles is described by mean currents in each
of four directions (upcoast, downcoast, onshore, offshore). Horizontal
dispersion and vertical diffusion are not considered significant.
Wastefjeld height above the' bottom is obtained from calculations for
plume height of rise.
3. Solution for the particle transport equation is obtained analytically.
4. Organic decomposition in sediments i's described by first-order decay.
Sediment accumulation calculations are performed for steady-state or for
a prescribed accumulation period (e.g., 90 days).
KOH 1982
1. Particle deposition rates are described by a fixed distribution of
apparent settling rates. Decomposition of organic particles in the water
column is not considered significant.
2. Temporal variations in ocean currents (for periods less than 11 days) are
attributed to horizontal dispersion. Net-flow is not considered. A
vertical diffusion coefficient is assigned. Wastefield height above the
bottom is obtained from calculations for plume height of rise.
3. Solution for the particle transport equation is obtained analytically.
Superpositioning is used in the solution for a continuous waste dis-
charge. Steady-state deposition patterns are calculated.
4. Sediment calculations_are not performed.
HENDRICKS 1983
1. Particle deposition rates are described by a fixed distribution of
apparent settling rates. Decomposition of organic particles in the water
column is not considered significant.
A-2
-------
2. Long-term drift velocities are obtained from progressive vector diagrams
of ocean currents. Horizontal dispersion and vertical diffusion are not
considered significant. Wastefield height is assigned.
3. Solution for the particle transport equation is obtained analytically.
A numerical algorithm is used in tracking the fate of effluent particles.
4. A second model (submodel) is available to simulate bottom processes
(resuspension and redistribution of sediments, complete decomposition of
labile material in sediments). The bottom processes model is empirically
derived from observations near the Los Angeles County outfall.
OECAL MODEL
1. Particle deposition rates are determined from coagulation and settling
kinetics and are described by a second-order dependency on mass concen-
tration. Particle interactions of effluent- and phytoplankton-derived
material are taken into account. Carbon fixation by phytoplankton is
expressed by measured productivity rates. Decomposition of organic
material in the water column is described by first-order decay.
2. Based on time scale arguments, coastal transport is simplified by
averaging over a daily period. Hence, the vertical structure of the
water column is described by a well-mixed surface and lower layer,
separated by a pycnocline region. In the lower layer, the daily-averaged
discharge of effluent is distributed over an extended area by tidal
oscillations. Nontidal flow by wind-driven currents and large-scale mean
circulation advect diluted wastewater from the discharge area.
3. Solution for the particle transport equation is obtained analytically.
A numerical algorithm is used in computing daily-averaged deposition
rates.
A-3
-------
4. Organic decomposition in sediments is described by an apparent first-
order decay. Steady-state calculations for sediment accumulation are
recommended.
Previous models for particle deposition^ (Chen et al. 1975; U.S. Envi-
ronmental Protection Agency 1982; Koh 1982; Hendricks 1983) differ primarily
in their descriptions of ocean currents (see item 2 in model summaries).
Other differences also exist (e.g., Chen et al. and Hendricks address the
resuspension and redeposition of sedimented material using very different
empiricisms).
In the previous models, particle deposition rates are described by a
fixed distribution of apparent settling rates. (The same Description for
particle deposition rates is employed in the drilling mud models of Brandsma
and Sauer 1983; Wu and Leung 1983; and Runchal 1983.) The settling rates
are typically obtained from observations in laboratory settling columns
under quiescent conditions. Observed settling rates in laboratory columns
however should not be considered adequate in describing the deposition of
sewage particles in coastal waters. Coagulation plays an important role in
determining deposition rates and direct extrapolation of apparent rates in
laboratory columns to field conditions is not appropriate.
Mathematical descriptions for particle coagulation are complex and are
not easily incorporated in particle deposition models for coastal waters.
However, simplified descriptions for the coagulation and settling of
particles have been developed from theoretical and laboratory studies (Morel
and Schiff 1980; Hunt 1982; Farley and Morel 1986). In these formulations,
particle deposition is approximately described by a second-order dependency
on mass concentration.
Describing particle deposition by a second-order rate law represents a
major change from previous modeling approaches. Modification of an existing
model was not performed since the incorporation of second-order deposition
requires new analytical solutions of the particle transport equation and
since superpositioning (used in the solutions of Chen et al. and Koh) is not
' A-4
-------
valid for second-order (nonlinear) equations. Work in the 301(h) Post-
Decision study has therefore focused on the development of a new deposition
model (see DECAL model summary). In the DECAL model, ocean transport is
___ •
specified based on expected time scales for particle deposition.
The new deposition model (flECAL) provides a simple calculation for
organic accumulation in both "natural" coastal waters and in the vicinity of
coastal municipal outfalls. Refinement in the present modeling approach to
include more detailed descriptions of coastal • transport and parti.cle
dynamics is possible and would require numerical solution of the particle
transport equation (e.g., see Mercier 1984).
A-5
-------
APPENDIX B
USER'S GUIDE FOR THE DECAL MODEL:
TOOL #61 ON THE OCEAN DATA EVALUATION SYSTEM (ODES)
-------
INTRODUCTION
Environmental effects associated with the discharge of- effluent- in
marine water's are often linked to the distribution of organic material in
sediments. Tool #61 on the Ocean Data Evaluation System (ODES) provides the
user with a simple model calculation for predicting particle deposition and
organic sediment accumulation in the vicinity of municipal ocean outfalls.
Model results can be used in predicting environmental effects from effluent
discharge, in designing monitoring programs and establishing future moni-
toring strategies, and in analyzing field data for chemical enrichment and
biological impacts. "
MODEL DESCRIPTION
Deposition and accumulation of organic material in coastal waters is
controlled by fluid transport, particle transport, and organic carbon
cycles. Modeling these processes in detail is extremely complex. For DECAL
calculations, the modeling approach has been simplified by assuming that
removal of organic material from the water column primarily occurs within
the time scale of one to several days.
Based on the above simplification, the fluid transport is approximated
by averaging over a daily period. Hence, the vertical structure of the water
column is described by a well-mixed surface and lower layer, separated by a
pycnocline region (Figure B-l). (For a surfacing waste plume, a single
well-mixed layer can be assumed.) In the lower layer, the daily-averaged
discharge of effluent is distributed over an extended area by tidal oscilla-
tions. Nontidal flows by wind-driven (or pressure-driven) currents and
large-scale mean circulation play a key role in advecting diluted effluent
from the discharge area.
Particle dynamics and organic carbon cycling are also described by
daily-averaged rates (Figure B-2). In the surface layer, carbon fixation by
phytoplankton is expressed by measured productivity rates and is attributed
to production of particulate material (either by formation of particles or
B-r
-------
SIGMA-T
NONTIDAL FLOW
VERTICALLY
WELL MIXED
TIDAL MOTION
VERTICALLY
WELL MIXED
TIDAL MOTION
MUNICIPAL
EFFLUENT
NONTIDAL
FLOW
DIFFUSER
EXTENDED
SOURCE
REGION
TIDAL
MOTION
Figure B-1. Simplified diagram of municipal effluent transport in coastal
waters.
B-2
-------
PHYTOPLANKTON
PRODUCTION
NATURAL
PARTICLES
DECOMPOSITION
COAGULATION/SETTLING
DECOMPOSITION
DECOMPOSITION
COAGULATION/SETTLING
DECOMPOSITION
AND BURIAL
TOTAL SOLIDS
NATURAL
PARTICLES
WASTE
PARTICLES
_>.
DECOMPOSITION
AND BURIAL
Figure B-2. Simplified diagram of particle transport and organic carbon
cycles.
B-3
-------
adsorption of dissolved organic material on surfaces). Removal of organic
material from the surface layer is described by a first-order decomposition
rate, and a second-order approximation for coagulation/settling kinetics.
Effluent particles discharged in the lower layer are added to concentrations
of phytopl ankton-derived material that has settled from surface waters.
5-
Removal of organic material from the lower layer is also described by a
first-order decomposition rate, and a second-order approximation for
coagulation/settling kinetics.
Removal of organic material deposited in the surface sediments is
attributed to decomposition and burial, and is described by a first-order
removal rate. Resuspension events are not considered. Hence, the DECAL'
model is most aoolicable to sediment accumulation periods. The model can
also be used in approximating the potential for organic sediment accumulation
during periods when resuspension (and possibly redistribution of sedimented
material) is likely, recognizing that the actual accumulation is likely to
be less. A more complete description of the model is given in the report
"A Simplified Deposition Calculation (DECAL) For Organic Solids Accumulation
Near Marine Outfalls."
MODEL INPUT
Input parameters to DECAL include wasteflow characteristics, outfall
diffuser location and geometry, background oceanographic information, and
ocean currents. A description of input parameters, including suggested
procedures for obtaining input values, is given below:
Wasteflow Characteristics
Values for the discharge flow rate and the effluent solids concen-
trations are required for DECAL calculations. Depending on the specific
application, the user may obtain values for these inputs from effluent moni-
toring data, design specifications for effluent discharge, or NPDES permit
linrrts. Discharge ra4:es_for 301(h) applicants range from 0.1 to 23 m /sec.
Average suspended solids concentrations range from 30 to 200 mg/L.
B-4
-------
Outfall Diffuser Location and Geometry
OECAL calculations are performed for a specified study area. The study
area is rectangular in shape and is specified by its length, width, and
orientation from true North. The outfall diffuser is located within the
study area by specifying the" diffuser length, orientation, and di stance "from
the study area boundaries. Outfall diffusers are typically on the order of
100 m in length for every m^/sec of wasteflow.
Background Oceanographic Information
Values for the total water column depth, the height of the lower layer,
and the rate of phytoplankton production are required for OECAL calcula-
tions. For major outfalls in the Southern California Bight, total water
column depths of 60 m are common. On the East Coast, municipal ocean
outfalls are typically located in shallower waters.
For discharged sewage that is trapped below the surface waters of the
ocean by strong density gradients, the height of the lower layer is given as
the height-of-rise of the waste plume or the pycnocline height. (Note that
the plume height of rise can be obtained from plume model calculations; ODES
Tool #60.) For surfacing waste plumes, the height of the lower layer is
equal to the total water column depth. Phytoplankton production, which is
given as daily-averaged productivity rates, can be estimated using carbon
uptake measurements and is typically observed in the range of 0.2-2.0
'" (Suess 1980; Eppley et al . 1983).
Ocean Currents
For OECAL model calculations, ocean currents are described by short-term
(tidal) oscillations and long-term (nontidal) flows. A simplified descrip-
tion for tidal and nontidal flow can be obtained from an analysis of current
meter records. A sample analysis is discussed for current meter measurements
B-5
-------
taken' off Newport Beach by the Southern California Coastal Water Research
Project (SCCWRP).
The current meter at Newport Beach was in place from 2/2/81 to 7/21/81
at a depth of ^0 m in 55 jn of water. The data was transposed by SCCWRP
personnel into current velocities along the major and- minor axis of flow.
Monthly records of current velocity data along the major (longshore) and
minor (cross-shore) axis of flow are shown in Figure B-3 for currents off.
Newport Beach (6/25 to 7/27/81). The monthly records were analyzed by first
computing power spectral density distributions. Each monthly record was
divided into four segments to increase confidence in the spectral estimates.
Results for longshore and cross-shore currents off Newport Beach are shown
in Figure B-4. Both- spectra show a significant peak at approximately
2 cycles/day, indicating the dominance of a semidiurnal tidal oscillation.
Cumulative variance distributions were obtained by integrating the
spectral results and are shown in Figure B-5 for currents off Newport Beach.
For DECAL model applications, all variance associated with periods of less
than a day is attributed to the dominant tidal component. Amplitudes for
the tidal motion were obtained by comparing variance estimates from the
current velocity data to computed variance for ideal oscillatory motion.
For an oscillating current, the tidal velocity is given as
utidal = Ucos
where U is the amplitude of the tidal oscillation; t is time; T is the
oscillation period; and o> is the phase shift. The variance for an arbitrary
number of tidal cycles (n) is then given as
variance - -^- |" U2cos2 f-2^- + *\ dt - U2/2 (B2)
j-r"
11 J(
For the Newport Beach data, amplitudes for the tidal oscillation are
6.5 cm/sec and 6.0 cm/sec, respectively, in the longshore and cross-shore
direction. Phase shifts for tidal velocities in the longshore and cross-
B-6
-------
Newport Beach: 6/2S to 7/27/81 • meter/water depth = 40/56 m
o
0)
V)
£
u
O
O
UJ
UJ
cc
O
X
-------
Newport Beach: 6/25 to 7/27/81 - meter/water depth =. 40/56 m
POWER SPECTRAL DENSITY
(cm/sec)2 / (cycles/day)
POWER SPECTRAL DENS
(cm/sec)2 / (cycles/day)
I
I
' ^
„.
I
^
s^
•
—
•
w— — — . —
3
10
12 14
16
FREQUENCY (cycles/day)
Spectral Plot of Hendricks raw data set NB81040V.176 (Longshore)
Newport Beach: 6/25 to 7/27/81 - meter/water depth » 40/56 m
8
10 12
14
16
FREQUENCY (cycles/day)
Spectral Plot of Hendricks raw data set NB81040V.176 (Cross-shore)
Figure B-4. Power spectral density distributions of currents off
Newport Beach, California.
B-8
-------
Newport Beach: 6/25 to 7/27/81 - meter/water depth = 40/56 m
1
CUMULATIVE VARIANCE (cm/sec)2 CUMULATIVE VARIANCE (cm/sec)2
— ^ — * M ro — * — •• ro i\> to
O Ul O (It & Ut O OU1001
1
Y ' : :
/
'
1
1
/
/
/
1
|
I :
i I
% !
1
5123456 3
PERIODS (days)
Integrated Spectral Plot of Hendricks raw data set
NB81 040V. 176 (Longshore)
Newport Beach: 6/25 to 7/27/81 - meter/water depth - 40/56 m
/
/
I
i
i
0
^-
12345678
PERIODS (days)
Integrated Spectral Plot of Hendricks raw data set
NB81 040V. 176 (Cross-shore)
Figure B-5. Cumulative variance distributions of currents off
Newport Beach, California.
B-9
-------
shore direction are assigned as 45° and 0°, resulting in an elliptical tidal
motion. This is motion is considered to represent average conditions for
spreading the sewage over the extended source region.
A 24.75-h running average of the monthly velocity records was also
computed and wa-s used in describing nontidal flow. Averaging results for
currents off Newport Beach are shown by the "smoothed" lines in Figure 8-3.
The currents range from 0 to 20 cm/sec and exhibit significant variation,
often reversing direction in cycles of 4-8 days according to the passage of
weather systems.
Cumulative probability (frequency) of occurrence is computed using
running averages for nontidal flows. The cumulative prooaoility curves for
currents off Newport Beach from 2/2 to 7/27/81 are given in Figure B-6. As
shown, nontidal flows in the cross-shore direction are typically small and
are considered negligible for DECAL model applications. Nontidal flows in
the longshore direction are specified by dividing the cumulative probability
curve into intervals of average velocity and percent occurrence. For
currents off Newport Beach, an average upcoast and average downcoast
velocity is considered for OECAL model input of nontidal flows.
Simplified descriptions for currents off Newport Beach (2/2 - 7/27/81)
and Palos Verdes (4/16 - 9/18/79) are included in an ODES on-line dictionary
and are easily accessible for DECAL model applications. The user also has
the option of entering his own information on currents. Information on
currents should be based on long records of current meter measurements. For
future field studies, we recommend collecting current meter data at the
mid-depth of the lower layer over a full year.
MODELING COEFFICIENTS
Three modeling coefficients are required for DECAL model calculations.
They are the second-order coagulation/settling rate coefficient, the
decomposition rate coefficient for suspended organic material, and the
interfacial removal rate coefficient for sedimented organic material.
B-10
-------
1.0
0.9
-; o.a
Newport Beach: 2/2 to 7/27/81 - meter/water depth = 40/55 m
D
O
CD
<
m
O
IT
CL
UJ
>
"5.
z>
O
CO
CD
O
DC
0.
UJ
> 0.4
H
*5 0.3
0.7
0.6
0.5
0.2
0.1
RUNNING AVER
— Avg. vel. = 4.31
AGE VELOCITIES
cm/sec
| Avg. pos. vel. - 9.03 cm/sec ;..-•'
"'--- ! ' : /
1 1 '
tj
\ 1 ,' '
|
I
I/I ! ! i
V '
/ i i ;
• 1 • 1
/ i
yf Avg. neg. vel. = -5.12 cm/sec :
/' 1 !
_.-^_ >
-25 -20 -15 -10 -5
10
20 25
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
LONGSHORE VELOCITY (cm/sec)
Hendrick's Combined Data Sets
NB81040V.033 - NB81040B.176
Newport Beach: 2/2 to 7/27/81 - meter/water depth - 40/55 m
RUN
~Avg.
NING
vel. .
AVER/
0.50 c
*GEVE
m/sec
10CIT
/
4
IES yf
/ i
/Avg. pos
/
i
i
1
;
. vel. =
/ Avg. neg. vel. - -1.87
7"
2.31 cm/sec
cm/sec
i
-25 -20 -15 -10 -5
10
15 20 25
CROSS-SHORE VELOCITY (cm/sec)
Hendrick's Combined Data Sets
NB81040V.033 - NB81040B.176
Figure B-6. Cumulative probability curves for nontidal currents off
Newport Beach, California.
B-ll
-------
Default values for the modeling coefficients are given in the prompting
sequence. They have been obtained as follows:
For the second-order coagulation/settling rate coefficient, a value was
obtained from results of theoretical and laboratory studies (Farley and
Morel 1986) and the following parameters. For natural organic particles'and
sewage organic material, dry density is estimated to be 1.5 g/cm based on
reported values for protein amino acids and carbohydrates (CRC Handbook of
Chemistry and Physics 1981). A floe porosity of 0.8 is assumed (Farley
and Morel 1986). Fluid properties include temperature (T = 20° C),
2 3
viscosity (v = 0.01 cm /sec), and density ( pf = 1.025 g/cm ). The Boltzmann
-16
constant and gravitational acceleration are given as 1.38-10 erg/0 K and
2
980 cm/sec . The fluid shearing rate is taken as O.I/sec, which is roughly
-42 3
equivalent to an energy dissipation rate of 10 cm /sec . A collision
efficiency of 0.3 is assumed for coagulation (Farley and Morel 1986). The
second-order rate coefficient is calculated as i
an estimated particle concentration of 1.0 mg/L.
second-order rate coefficient is calculated as 2-10 L-mg -sec based on
The default value for the decomposition rate of organic material in the
water column is given as O.I/day. This value is based on laboratory studies
for the decomposition of readily-degradable fractions (e.g., carbohydrates
and amino acids) of effluent organic material (Metcalf & Eddy 1972). The
interfacial removal rate coefficient for sedimented organic material is
given as 0.015 cm/day. This value is based on steady-state estimates of
organic carbon turnover rates in surface sediments (for field studies of
Hopkinson 1985 and references therein) and is includes the effects of
decomposition in surface sediments and burial.
MODEL OUTPUT
Output for the DECAL is given as sets of contour plots for suspended
particle concentrations in the lower water layer, for the daily-averaged
deposition rates of organic material, or for organic accumulation in
sediments.
B-12
-------
The following is a sample terminal session with ODES Tool #61 showing
typical prompts and output. User responses are underlined.
B-13
-------
* ODES *
— ODES~~Envi ronmental Decision Support Tool #61 — -
** SIMPLIFIED DEPOSITION CALCULATION (DECAL) **
* This tool provides you with a simple model calculation for predicting
particle deposition and organic accumulation in the vicinity of sewage
outfalls during sediment accumulation periods. Processes incorporated in
the model include coastal transport, phytoplankton production, coagula-
tion/settling of natural organic material and sewage particles and
microbial degradation." further details of the model are discussed in the
report "A Simplified Deposition Calculation (DECAL) for Organic Accumula-
tion Near Marine Outfalls."
— You will first be asked to specify input parameters for the DECAL
model which include wasteflow characteristics, outfall diffuser
location and geometry, background oceanographic information, and
values for three modelling coefficients.
— You will also be asked to specify the types of contour plots you
would like to produce.
— ODES will then run the model to calculate predicted particle deposi-
tion and organic accumulation, and will produce the selected plots.
> Please hit RETURN to continue or enter B (Basic Options)>
* ODES will now ask you to specify two wasteflow characteristics:
(1)'discharge flow rate in cubic meters per second; and (2) effluent
solids concentration in milligrams per liter.
> Enter discharge flow rate (m3/sec)> 10
> Enter effluent solids concentration (mg/L)> 100
B-14
-------
ODES will now ask you to specify the study area and diffuser location. For
model calculations, the diffuser is located within a rectangular grid. You
wi-11 be asked to enter the orientation and size of the study area by
specifying the clockwise rotation of the Y-axis (in degrees) from true
North, and the length (in km) of the X-axis (XL) and Y-axis (YL). You
will also be asked to'specify the location of one end of the diffuser
(point A) in terms of its distance from the origin (0,0), the length of
the diffuser (in m) (AB), and the orientation of the of the diffuser in
relation to the X-axis (angle C). If you choose, you can hit RETURN after
each prompt to .use the indicated default value.
Study Area and Diffuser Location
km YL + + + + +
B
0 X > XL km
> Enter Y-axis rotation (deg from true North) (default=0)> 0
> Enter X-axis length of study area (km) (default=20 km)> 20
> Enter Y-axis length of study area (km) (default=20 km)> U
> Enter X distance from origin (km) (default=10.00)> 7
> Enter Y distance from origin (km) (default=5.5)> 5.5
> Enter length of diffuser (m) (default=1000.)> 1000
> Enter orientation of diffuser (deg from X-axis)(default=0)> 30
* ODES will now ask you to specify background oceanographic information. You
must enter a value for each parameter as no default values are provided.
> Enter the total water column depth (m)> 60
* You will now be asked to specify the height of the lower water layer (in
meters). This value is given as the height-of-nse of the waste plume, or
the pycnocline height.
> Enter height of the lower water layer (m)> 30
> Enter phytoplankton productivity (gC/m2-day)> 1.0
B-15
-------
* Ocean currents are described by short-term harmonic (tidal) motions and
long-term advective flows. You can choose to enter your own information
or use the information from one of several ODES files:
E = ENTER own information
U = USE information from an ODES File
> Enter E (enter information) or U (use ODES File)> U
* You will now be asked to specify the ODES Current File you want to use by
entering its 7-character ODES code, or you can enter H to look up valid
codes.-
> Enter a File by its 7-character code, or H> H
ODES
— ODES On-line Dictionary —
* The On-Line Dictionary stores the name and the 7-character Current File
Code stored in the ODES Database. You can search for a name, or part of a
name, or a 7-character code.
> SEARCH FOR>
CODE CURRENT FILE NAME
PV79041 = PALOS VERDES 4/16-9/18/79 (41/56 M)
SAMPLE1 = SAMPLE CALCULATIONS IN DECAL REPORT
NB81041 = NEWPORT BEACH 2/2-7/21/81 (40/55 M)
> Search for another CURRENT? (Y/N)> N
* Returning to Tool #61...
* You will now be asked to specify the ODES Current File you want to use by
entering its 7-character ODES code, or you can enter H to look up valid
codes."
> Enter a File by its 7-character code, or H> SAMPLEI
B-16
-------
* If you wish, you can review a detailed description of file SAMPLE1
before continuing.
> Do you want to review the detailed description? (Y/N)> Y_
CURRENT FILE CODE: SAMPLE1
CURRENT FILE NAME: SAMPLE CALCULATIONS IN DECAL REPORT
DESCRIPTION:
The following description of currents was used in sampl«e calculations in
the report "A Simplified Deposition Calculation (DECAL) for Organic Accumula-
tion Near Marine Outfalls." Short-term oscillatory currents are attributed
to a semidiurnal tidal component in both the longshore (90° N) and cross-
shore (0° N) direction. Amplitudes of the tidal currents are 0.1 m/sec in
both the longshore and cross-shore directions. Phase shifts of tidal
velocities in the longshore and cross-shore direction are taken as 210° and
180°, respectively. Long-term (nontidal) flow is considered constant in time
with a current velocity of 0.03 m/sec in the longshore direction.
> Please press RETURN to continue >
* Calculations can be performed for steady-state or time-dependent sediment
accumulations. You will now be asked to specify steady-state or time-
dependent sediment accumulations. If you select time-dependent accumula-
tions you will.be asked to enter the duration of the accumulation period.
S = Steady-state sediment accumulations
T = Time-dependent sediment accumulations
> Enter S (Steady-state) or T (Time-dependent)> S
B-17
-------
* ODES will now ask you to specify three modelling coefficients that are
required for the OECAL calculation. You can select the default val-ues by
hitting RETURN when asked to enter a value.
* You will be asked to enter the second order coagulation/settling rate
coefficient in L/mg(dry wt)-sec.
> Enter this coefficient (default=2E-6 L/mg(dry wt)-sec)>
* You will be asked to enter the first order decomposition rate coefficient
for suspended organic material in L/day.
~ •
> Enter this coefficient (default=0.1/day)>
* You will be asked to enter the interfacial removal rate coefficient for
sedimented organic material in cm/day.
> Enter this coefficient (default=0.015 cm/day)>
* ODES will now list the values you have specified for ths model and allow
you to change the selections before the job is submitted. ODES will
display the values on several pages. To view the next page enter C, to
change a value enter its number, and to submit the job enter S.
* These are the values you have specified:
WASTEFLOW CHARACTERISTICS
1) Discharge flow rate in m3/sec: 10.
2) Effluent solids concentration in mg/L: 100.
STUDY AREA AND DIFFUSER LOCATION
3) Y-axis rotation from true North, in degrees: 0.0
4) Study area length, X-axis in km: 20.0
5) Study area length, Y-axis in km: 11.
6) Diffuser distance from 0, X-axis in km: 7.
7) Diffuser distance from 0, Y-axis in km: 5.5
8) Length of diffuser in m: 1000.
9) Orientation of diffuser in degrees: 30: -
OCEANOGRAPHIC INFORMATION
10) Total water column depth in m: 60.
11) Water depth below pycnocline in m: 30.
12) Phytoplankton productivity in gC/m2-day: 1.0
CONTINUED...
B-18
-------
> Enter a number, C to continue, or S to submit> C_
OCEAN CURRENTS - Short-term harmonic (tidal) motion
- - f
13) Orientation of principal axis, in degrees: 0.000
14) Harmonic constituents described by ODES FILE SAMPLE1
maj axis maj-phase min axis min-phase
period amplitude shift amplitude shift
(hours) (m/sec) (degrees) (m/sec) (degrees)
14-1) 12. 0.1 210.0 0.1 180.0
OCEAN CURRENTS - Long-term advective (nontidal) flows
15) Flow conditions described by
direction probability
velocity of flow of occurence
(m/sec) (degrees) (percent)
15-1) 0.03 90.0 100.
16) Sediment accumulations: STEADY-STATE
17) Duration' of accumulation period in days: N/A
MODELING COEFFICIENTS
18) Second order coagulation/settling rate coefficient: .000002
19) First order organic material decomposition rate coefficient: .1
20) Interfacial removal rate coefficient for sedimented organic
material: .015
> Enter a number, C to relist, or S to submit> S
* You will now be asked to select the type of contour plots you want to
produce. Each option below produces two contour plots:
1) Total Suspended Particles and
Waste Suspended Particles; or
2) Total Deposition Flux of Particles and
Deposition Flux of Waste Particles; or
3) Total Organic Accumulation in Sediments and
Organic Accumulation of Waste Particles.
> Please enter a set of contour plots by number (1, 2, or 3)> 2
B-19
-------
* If you have a Tektronix 4010 (or compatible) graphics device, you can
display the output from ODES Tool 61 in high-quality graphics format.
> Do you want to produce high-quality graphics? (Y/N) Y_
* ODES will assume you have a Tektronix 4010 (or compatible) graphics device.
> Do you have a TEK4010? (Y/N)> Y
> Enter a 1-8 character name for your graphic) SAMPLE 1
* You may enter a 1-40 character footnote that will appear on your graphic
and accompanying back-up tables.
> Do you wish to enter a footnote? (Y/N)> N
* Thank you.
************************
JOB 5391 KVF61 SUBMITTED
************************
* Please record the above job number for subsequent retrieval. Jobs usually
take 5-10 min to run.
The output plots (Figures B-7 and B-8) and summary data from this job are
provided below.
B-20
-------
ODES TOOL 61: DECAL MODEL
Total Deposition Rate Of Waste Particles g/m**2-day
1
LLl
O
z
^
1-
C/3
Q
>
\ i •
10 -
9 -
8 -
-
6 -
5 -
4 -
3 -
2 -
1 -
0.
(
-~
/'' ^""^
l\\ ^"T .."^ ~"
N, *Miy ~J ^2 _^~~^ •'
Xv*"- — *•• — "" ^ ___.
\vO>v_ . — "^""^ """
\*x i""""
_
i i i i i i i i i
) 2 4 6 8 10 12 14 16 18 2(
X-DISTANCE (km)
CONTOUR KEY (g/m2- day)
0.3413
1.0239
1.7065
2.3891
3.0717
Background Rate: 0.3413
Figure B-7. DECAL contour plot of total deposition rate of waste particles
for the sample calculations.
B-21 —
-------
ODES TOOL 61: DECAL MODEL
Total Deposition-Rate Of Waste Particles g/m**2-day
E"
i
LJJ
O
Z
^
h-
52
Q
>•
1 1 •
10 -
9 -
8 -
7 -
6 -
5 -
4 -
3 -
2 -
1 -
(
- .
•
,'
\t f^IT"^- — ~.. ~~"*
»<\'^^"^,1 , _J
'yv. — .^** — »--~ "
X>N . — — '"
i i i i i i i i i
) 2 4 6 8 10 12 14 16 18 2(
X-DISTANCE (km)
CONTOUR KEY (g/m - day)
0.6826
1.3652
2.0478
Figure B-8. DECAL contour plot of waste particle deposition rate for the
sample calculations.
B-22
-------
ODES: OCEAN DATA EVALUATION SYSTEM
DEVELOPED BY: AMERICAN MANAGEMENT SYSTEMS, INC. & TETRA TECH, INC.
DEVELOPED FOR: OFFICE OF MARINE AND ESTUARINE PROTECTION, U.S. EPA
CAUTION: DATA ARE FROM SOURCES OF VARYING QUALITY
JOB NAME: KVF61 SUBMITTED AT 11:13:07 ON 10/03/86
ODES TOOL 61: A SIMPLIFIED DEPOSITION CALCULATION
WASTEFLOW CHARACTERISTICS
1) DISCHARGE FLOW RATE IN M3/SEC: 10.000
2) EFFLUENT SOLIDS CONCENTRATION IN MG/L: 100.00
STUDY AREA AND DIFFUSER LOCATION
3) STUDY AREA ORIENTATION, YAXIS ORIENTATION
IN DEGREES FROM TRUE NORTH: .OOOOOE+00
4) STUDY AREA LENGTH, X-AXIS IN KM: 20.000
5) STUDY AREA LENGTH, Y-AXIS IN KM: 11.000
6) DIFFUSER DISTANCE FROM 0, X-AXIS IN KM: 7.00
7) DIFFUSER DISTANCE FROM 0, Y-AXIS IN KM: 5.50
8) LENGTH OF DIFFUSER IN M: 1000.0
9) ORIENTATION OF DIFFUSER IN DEGREES FROM THE X-AXIS: 30.000
GEOGRAPHIC INFORMATION
10) TOTAL WATER COLUMN DEPTH IN M: 60.000
11) HEIGHT OF LOWER WATER LAYER IN M: 30.000
12) PHYTOPLANKTON PRODUCTIVITY IN GC/M2-DAY: 1.0000
13) PRINCIPAL AXIS FOR CURRENTS IN DEGREES
FROM TRUE NORTH: 90.000
14) SHORT-TERM (TIDAL) CURRENTS DESCRIBED BY:
PERIOD X-AMPLITUDE X-PHASE SHIFT Y-AMPLITUDE Y-PHASE SHIFT
(HOURS) (M/SEC) (DEGREES) (M/SEC) (DEGREES)
14-1) 12.0 .10000 210.00 .10000 180.00
15) LONG-TERM ("NON-TIDAL) CURRENTS DESCRIBED BY:
VELOCITY DIRECTION PERCENT OCCURRENCE
(M/SEC) • (DEGREES)
15-1) .30000E-01 90.000 100.00
16) STEADY-STATE SEDIMENT ACCUMULATION
17) DURATION OF SEDIMENT ACCUMULATION PERIOD IN DAYS: N/A
B-23
-------
MODELING COEFFICIENTS
18) SECOND-ORDER COAGULATION/SETTLING
RATE COEFFICIENT: .20000E-05 L/MG-DAY
19) FIRST-ORDIR ORGANIC MATERIAL
DECOMPOSITION RATE COEFFICIENT: .10000 /DAY
20) INTERFACIAL REMOVAL RATE COEFFICIENT
FOR SEDIMENTED ORGANIC MATERIAL: .15000E-01 CM/DAY
**END OF FILE**
B-24
-------
APPENDIX C
MASS CONSERVATION EQUATIONS AND
STEADY-STATE SOLUTIONS FOR PARTICLE CONCENTRATIONS
IN THE LOWER WATER COLUMN
-------
MASS CONSERVATION EQUATIONS AND STEADY-STATE SOLUTIONS
FOR PARTICLE CONCENTRATIONS IN THE LOWER WATER COLUMN
This appendix provides the differential conservation equations and
their steady-state solutions used to determine mass concentrations of
suspended particles in the lower water column in the background (i.e., in
the absence of any effluent suspended solids particles), in the extended
source region, and downcurrent of the extended source.
Tne background mass concentration of suspended oarticles (CD) satisfies
the equation:
dt
= 2'5 Psed/hL - kdCb - BCb
which has steady-state solution:
28
1 -
10 B
0.5
In the extended source region, the mass concentration of suspended
particles (Ce) satisfies the equation:
C. -
which has steady-state solution:
ZB
1 -
0.5
C-l
-------
where: a = 2.5 PCQj/h. + ^a b + ^w w
sed ~h~A — ~h~A —
Yes nLAes
b -
hLAes
Downcurrent of the extended source region, the mass concentration of
suspended particles (C
-------
t = time
psed = the flux of organic carbon settling from the surface layer,
which is a function of the productivity rate (see Equation 9-)
kd = the decomposition rate coefficient for suspended organic material
B = the second-order coagulation/settling rate coefficient
HL = the height of the lower layer
Aes = the area of the extended source region
Oa = the nontidal flow through the extended source region, which is
dependent on the nontidal currents, the width of the extended
source region perpendicular to the nontidal currents, and the
height of the lower layer
ua = the velocity of the nontida'l flow
Qw - the effluent discharge flow rate
Cw = the mass concentration of particles in the effluent
s = the distance downcurrent of the extended source region.
C-3
-------
APPENDIX D
MASS CONSERVATION EQUATIONS AND
STEADY-STATE SOLUTIONS FOR CHEMICAL CONTAMINANT
CONCENTRATIONS IN THE LOWER WATER COLUMN
-------
MASS CONSERVATION EQUATIONS AND STEADY-STATE SOLUTIONS FOR CHEMICAL
CONTAMINANT CONCENTRATIONS IN THE LOWER WATER COLUMN
This appendix provides the differential equations and their steady-
state solutions used to determine the total mass concentrations of a
chemical contaminant in the lower water column in the extended source region
and downstream of the extended source region. %
In the extended source region, the total mass concentration of a
chemical contaminant (Ce) satisfies the equation:
.5
dt
hLAes
IP"6 B K
Ce
10~6 K
which has steady-state solution:
0 0
vw vw
"L*eS
Va *
\Aes
10"6 B Kp M2
1 + l(f6 K M
1 « JLU N 1 1
where: M
e
b
2B
1 -
hLAes
D-l
-------
Downcurrent of the extended source region, the total mass concentration
of a chemical contaminant (C
-------
In the above formulas:
j-
Ce = the total mass concentration of the chemical contaminant in the
extended source region
C,j = the total mass concentration of the chemical contaminant" down-
current of the extended source region
Mb = the mass concentration of background particles in the lower layer
Me = the mass concentration of suspended particles in the extended
source region
M
------- |