U.S. ENVIRONMENTAL PROTECTION AGENCY
Annapolis Field Office
Annapolis Science Center
Annapolis, Maryland 21401
TECHNICAL REPORTS
Volume 4
-------
-------
Table of Contents
Volume 4
29 Step Backward Regression
31 Relative Contributions of Nutrients to the
Potomac River Basin from Various Sources
33 Mathematical Model Studies of Water Quality
in the Potomac Estuary
35 Water Resource - Water Supply Study of the
Potomac Estuary
-------
-------
PUBLICATIONS
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION III
ANNAPOLIS FIELD OFFICE*
VOLUME 1
Technical Reports
5 A Technical Assessment of Current Water Quality
Conditions and Factors Affecting Water Quality in
the Upper Potomac Estuary
6 Sanitary Bacteriology of the Upper Potomac Estuary
7 The Potomac Estuary Mathematical Model
9 Nutrients in the Potomac River Basin
11 Optimal Release Sequences for Water Quality Control
in Multiple Reservoir Systems
VOLUME 2
Technical Reports
13 Mine Drainage in the North Branch Potomac River Basin
15 Nutrients in the Upper Potomac River Basin
17 Upper Potomac River Basin Water Quality Assessment
VOLUME 3
Technical Reports
19 Potomac-Piscataway Dye Release and Wastewater
Assimilation Studies
21 LNEPLT
23 XYPLOT
25 PLOT3D
* Formerly CB-SRBP, U.S. Department of Health, Education,
and Welfare; CFS-FWPCA, and CTSL-FWQA, Middle Atlantic
Region, U.S. Department of the Interior
-------
VOLUME 3 (continued)
Technical Reports
27 Water Quality and Wastewater Loadings - Upper Potomac
Estuary during 1969
VOLUME 4
Technical Reports
29 Step Backward Regression
31 Relative Contributions of Nutrients to the Potomac
River Basin from Various Sources
33 Mathematical Model Studies of Water Quality in the
Potomac Estuary
35 Water Resource - Water Supply Study of the Potomac
Estuary
VOLUME 5
Technical Reports
37 Nutrient Transport and Dissolved Oxygen Budget
Studies in the Potomac Estuary
39 Preliminary Analyses of the Wastewater and Assimilation
Capacities of the Anacostia Tidal River System
41 Current Water Quality Conditions and Investigations
in the Upper Potomac River Tidal System
43 Physical Data of the Potomac River Tidal System
Including Mathematical Model Segmentation
45 Nutrient Management in the Potomac Estuary
VOLUME 6
Technical Reports
47 Chesapeake Bay Nutrient Input Study
49 Heavy Metals Analyses of Bottom Sediment in the
Potomac River Estuary
-------
VOLUME 6 (continued)
Technical Reports
51 A System of Mathematical Models for Water Quality
Management
52 Numerical Method for Groundwater Hydraulics
53 Upper Potomac Estuary Eutrophication Control
Requirements
54 AUT0-QUAL Modelling System
Supplement AUT0-QUAL Modelling System: Modification for
to 54 Non-Point Source Loadings
VOLUME 7
Technical Reports
55 Water Quality Conditions in the Chesapeake Bay System
56 Nutrient Enrichment and Control Requirements in the
Upper Chesapeake Bay
57 The Potomac River Estuary in the Washington
Metropolitan Area - A History of its Water Quality
Problems and their Solution
VOLUME 8
Technical Reports
58 Application of AUT0-QUAL Modelling System to the
Patuxent River Basin
59 Distribution of Metals in Baltimore Harbor Sediments
60 Summary and Conclusions - Nutrient Transport and
Accountability in the Lower Susquehanna River Basin
VOLUME 9
Data Reports
Water Quality Survey, James River and Selected
Tributaries - October 1969
Water Quality Survey in the North Branch Potomac River
between Cumberland and Luke, Maryland - August 1967
-------
VOLUME 9 (continued)
Data Reports
Investigation of Water Quality in Chesapeake Bay and
Tributaries at Aberdeen Proving Ground, Department
of the Army, Aberdeen, Maryland - October-December 1967
Biological Survey of the Upper Potomac River and
Selected Tributaries - 1966-1968
Water Quality Survey of the Eastern Shore Chesapeake
Bay, Wicomico River, Pocomoke River, Nanticoke River,
Marshall Creek, Bunting Branch, and Chincoteague Bay -
Summer 1967
Head of Bay Study - Water Quality Survey of Northeast
River, Elk River, C & D Canal, Bohemia River, Sassafras
River and Upper Chesapeake Bay - Summer 1968 - Head ot
Bay Tributaries
Water Quality Survey of the Potomac Estuary - 1967
Water Quality Survey of the Potomac Estuary - 1968
Wastewater Treatment Plant Nutrient Survey - 1966-1967
Cooperative Bacteriological Study - Upper Chesapeake Bay
Dredging Spoil Disposal - Cruise Report No. 11
VOLUME 10
Data Reports
9 Water Quality Survey of the Potomac Estuary - 1965-1966
10 Water Quality Survey of the Annapolis Metro Area - 1967
11 Nutrient Data on Sediment Samples of the Potomac Estuary
1966-1968
12 1969 Head of the Bay Tributaries
13 Water Quality Survey of the Chesapeake Bay in the
Vicinity of Sandy Point - 1968
14 Water Quality Survey of the Chesapeake Bay in the
Vicinity of Sandy Point - 1969
-------
VOLUME 10(continued)
Data Reports
15 Water Quality Survey of the Patuxent River - 1967
16 Water Quality Survey of the Patuxent River - 1968
17 Water Quality Survey of the Patuxent River - 1969
18 Water Quality of the Potomac Estuary Transects,
Intensive and Southeast Water Laboratory Cooperative
Study - 1969
19 Water Quality Survey of the Potomac Estuary Phosphate
Tracer Study - 1969
VOLUME 11
Data Reports
20 Water Quality of the Potomac Estuary Transport Study
1969-1970
21 Water Quality Survey of the Piscataway Creek Watershed
1968-1970
22 Water Quality Survey of the Chesapeake Bay in the
Vicinity of Sandy Point - 1970
23 Water Quality Survey of the Head of the Chesapeake Bay
Maryland Tributaries - 1970-1971
24 Water Quality Survey of the Upper Chesapeake Bay
1969-1971
25 Water Quality of the Potomac Estuary Consolidated
Survey - 1970
26 Water Quality of the Potomac Estuary Dissolved Oxygen
Budget Studies - 1970
27 Potomac Estuary Wastewater Treatment Plants Survey
1970
28 VJater Quality Survey of the Potomac Estuary Embayments
and Transects - 1970
29 Water Quality of the Upper Potomac Estuary Enforcement
Survey - 1970
-------
30
31
32
33
34
Appendix
to 1
Appendix
to 2
3
4
VOLUME 11 (continued)
Data Reports
Water Quality of the Potomac Estuary - Gilbert Swamp
and Allen's Fresh and Gunston Cove - 1970
Survey Results of the Chesapeake Bay Input Study -
1969-1970
Upper Chesapeake Bay Water Quality Studies - Bush River,
Spesutie Narrows and Swan Creek, C & D Canal, Chester
River, Severn River, Gunpowder, Middle and Bird Rivers -
1968-1971
Special Water Quality Surveys of the Potomac River Basin
Anacostia Estuary, Wicomico .River, St. Clement and
Breton Bays, Occoquan Bay - 1970-1971
Water Quality Survey of the Patuxent River - 1970
VOLUME 12
Working Documents
Biological Survey of the Susquehanna River and its
Tributaries between Danville, Pennsylvania and
Conowingo, Maryland
Tabulation of Bottom Organisms Observed at Sampling
Stations during the Biological Survey between Danville,
Pennsylvania and Conowingo, Maryland - November 1966
Biological Survey of the Susquehanna River and its
Tributaries between Cooperstown, New York and
Northumberland, Pennsylvnaia - January 1967
Tabulation of Bottom Organisms Observed at Sampling
Stations during the Biological Survey between Cooperstown,
New York and Northumberland, Pennsylvania - November 1966
VOLUME 13
Working Documents
Water Quality and Pollution Control Study, Mine Drainage
Chesapeake Bay-Delaware River Basins - July 1967
Biological Survey of Rock Creek (from Rockville, Maryland
to the Potomac River) October 1966
-------
VOLUME 13 (continued)
Working Documents
5 Summary of Water Quality and Waste Outfalls, Rock Creek
in Montgomery County, Maryland and the District of
Columbia - December 1966
6 Water Pollution Survey - Back River 1965 - February 1967
7 Efficiency Study of the District of Columbia Water
Pollution Control Plant - February 1967
VOLUME 14
Working Documents
8 Water Quality and Pollution Control Study - Susquehanna
River Basin from Northumberland to West Pittson
(Including the Lackawanna River Basin) March 1967
9 Water Quality and Pollution Control Study, Juniata
River Basin - March 1967
10 Water Quality and Pollution Control Study, Rappahannock
River Basin - March 1967
11 Water Quality and Pollution Control Study, Susquehanna
River Basin from Lake Otsego, New York, to Lake Lackawanna
River Confluence, Pennsylvania - April 1967
VOLUME 15
Working Documents
12 Water Quality and Pollution Control Study, York River
Basin - April 1967
13 Water Quality and Pollution Control Study, West Branch,
Susquehanna River Basin - April 1967
14 Water Quality and Pollution Control Study, James River
Basin - June 1967 ,
15 Water Quality and Pollution Control Study, Patuxent River
Basin - May 1967
-------
VOLUME 16
Working Documents
16 Water Quality and Pollution Control Study, Susquehanna
River Basin from Northumberland, Pennsylvania, to
Havre de Grace, Maryland - July 1967
17 Water Quality and Pollution Control Study, Potomac
River Basin - June 1967
18 Immediate Water Pollution Control Needs, Central Western
Shore of Chesapeake Bay Area (Magothy, Severn, South, and
West River Drainage Areas) July 1967
19 Immediate Water Pollution Control Needs, Northwest
Chesapeake Bay Area (Patapsco to Susquehanna Drainage
Basins in Maryland) August 1967
20 Immediate Water Pollution Control Needs - The Eastern
Shore of Delaware, Maryland and Virginia - September 1967
VOLUME 17
Working Documents
21 Biological Surveys of the Upper James River Basin
Covington, Clifton Forge, Big Island, Lynchburg, and
Piney River Areas - January 1968
22 Biological Survey of Antietam Creek and some of its
Tributaries from Waynesboro, Pennsylvania to Antietam,
Maryland - Potomac River Basin - February 1968
23 Biological Survey of the Monocacy River and Tributaries
from Gettysburg, Pennsylvania, to Maryland Rt. 28 Bridge
Potomac River Basin - January 1968
24 Water Quality Survey of Chesapeake Bay in the Vicinity of
Annapolis, Maryland - Summer 1967
25 Mine Drainage Pollution of the North Branch of Potomac
River - Interim Report - August 1968
26 Water Quality Survey in the Shenandoah River of the
Potomac River Basin - June 1967
27 Water Quality Survey in the James and Maury Rivers
Glasgow, Virginia - September 1967
-------
VOLUME 17 (continued)
Working Documents
28 Selected Biological Surveys in the James River Basin,
Gillie Creek in the Richmond Area, Appomattox River
in the Petersburg Area, Bailey Creek from Fort Lee
to Hopewell - April 1968
VOLUME 18
Working Documents
29 Biological Survey of the Upper and Middle Patuxent
River and some of its Tributaries - from Maryland
Route 97 Bridge near Roxbury Mills to the Maryland
Route 4 Bridge near Wayson's Corner, Maryland -
Chesapeake Drainage Basin - June 1968
30 Rock Creek Watershed - A Water Quality Study Report
March 1969
31 The Patuxent River - Water Quality Management -
Technical Evaluation - September 1969
VOLUME 19
Working Documents
Tabulation, Community and Source Facility Water Data
Maryland Portion, Chesapeake Drainage Area - October 1964
Waste Disposal Practices at Federal Installations
Patuxent River Basin - October 1964
Waste Disposal Practices at Federal Installations
Potomac River Basin below Washington, D.C.- November 1964
Waste Disposal Practices at Federal Installations
Chesapeake Bay Area of Maryland Excluding Potomac
and Patuxent River Basins - January 1965
The Potomac Estuary - Statistics and Projections -
February 1968
Patuxent River - Cross Sections and Mass Travel
Velocities - July 1968
-------
VOLUME 19 (continued)
Working Documents
Wastewater Inventory - Potomac River Basin -
December 1968
Wastewater Inventory - Upper Potomac River Basin -
October 1968
VOLUME 20
Technical Papers^
1 A Digital Technique for Calculating and Plotting
Dissolved Oxygen Deficits
2 A River-Mile Indexing System for Computer Application
in Storing and Retrieving Data (unavailable)
3 Oxygen Relationships in Streams, Methodology to be
Applied when Determining the Capacity of a Stream to
Assimilate Organic Wastes - October 1964
4 Estimating Diffusion Characteristics of Tidal Waters -
May 1965
5 Use of Rhodamine B Dye as a Tracer in Streams of the
Susquehanna River Basin - April 1965
6 An In-Situ Benthic Respirometer - December 1965
7 A Study of Tidal Dispersion in the Potomac River
February 1966
8 A Mathematical Model for the Potomac River - what it
has done and what it can do - December 1966
9 A Discussion and Tabulation of Diffusion Coefficients
for Tidal Waters Computed as a Function of Velocity
February 1967
10 Evaluation of Coliform Contribution by Pleasure Boats
July 1966
-------
VOLUME 21
Technical Papers
11 A Steady State Segmented Estuary Model
12 Simulation of Chloride Concentrations in the
Potomac Estuary - March 1968
13 Optimal Release Sequences for Water Quality
Control in Multiple-Reservoir Systems - 1968
VOLUME 22
Technical Papers
Summary Report - Pollution of Back River - January 1964
Summary of Water Quality - Potomac River Basin in
Maryland - October 1965
The Role of Mathematical Models in the Potomac River
Basin Water Quality Management Program - December 1967
Use of Mathematical Models as Aids to Decision Making
in Water Quality Control - February 1968
Piscataway Creek Watershed - A Water Quality Study
Report - August 1968
VOLUME 23
Ocean Dumping Surveys
Environmental Survey of an Interim Ocean Dumpsite,
Middle Atlantic Bight - September 1973
Environmental Survey of Two Interim Dumpsites,
Middle Atlantic Bight - January 1974
Environmental Survey of Two Interim Dumpsites
Middle Atlantic Bight - Supplemental Report -
October 1974
Effects of Ocean Disposal Activities on Mid-
continental Shelf Environment off Delaware
and Maryland - January 1975
-------
VOLUME 24
1976 Annual
Current Nutrient Assessment - Upper Potomac Estuary
Current Assessment Paper No. 1
Evaluation of Western Branch Wastewater Treatment
Plant Expansion - Phases I and II
Situation Report - Potomac River
Sediment Studies in Back River Estuary, Baltimore,
Maryland
Technical Distribution of Metals in Elizabeth River Sediments
Report 61
Technical A Water Quality Modelling Study of the Delaware
Report 62 Estuary
-------
Chesapeake Technical Support Laboratory
Middle Atlantic Region
Federal Water Pollution Control Administration
U.S. Department of the Interior
Technical Report No. 29
STEP BACKWARD REGRESSION
by
Gary I. Seiner*
August 1969
^Revised by Paul R. Dorn
Johan A. Aaltos Chief8 CTSL
Herbert A. Jaworski, Chief, Engineering Section
Richard Burkett, Draftsman
-------
TABU: OF CONTENTS
Page
Program . ° 1
Abstract ....... 1
Description , 2
Restrictions .... 5
Program Run Preparation 6
JOB card 7
System Control Cards .10
Header Card . 13
Options IH
Column Identifier Cards . ...... 15
Row Selector Cards , 16
Column Selector Cards ... 17
Minimum Number of Variables Card . . 18
Residual Start Card 19
Output . 20
Sample Output . ........ 21
-------
-------
PROGRAM; STEP BACKWARD REGRESSION
ABSTRACT; This program performs a multiple regression analysis and
provides related statistics on a STATPAC data matrix or on a subset
of that matrix formed by the selection of rows and columns of the
matrix. If desired, the regression may proceed stepwise where, at
each step, the least significant independent variable is deleted
from the regression equation. The regression residuals may also be
computed.
-------
BESTRICTIONS;
The input matrix may have a maximum size of 99999 rows and
199 columns. The maximum size of the subset selected for a re-
gression analysis is 99999 rows and 99 columns.
-------
PROGRAM RUE PREPARATION;
The follawing is a complete deck setup for this program;
1. JOB card
2. System control cards
3- Header card
It-. Column selector cards*
5. Row selector cards*
6. Minimum number of variables card *
T. Residual start card*
8. Delimeter
*0ptional--see the individual sections on the various cards.
If more than one run is to be performed, repeat cards 3-7 as
necessary; the final card should "be delimiter card.
-------
JOB CARD:
The JOB card cannot be catalogued and is installation as well
as machine dependent. Below is the specification for the 360/Model
65 located in the Department of the Interior building, in Washing-
ton, D.C. The structure of the JOB card changes occasionally, and
one should check with the computer center "before using the below
form.
Card 1 -
Card Columns Contents
1-2 //
3 Center Code:
D = Denver, Colorado
F = Flagstaff, Arizona
I = Crystal Plaza, Virginia
M = Menlo Park, California
R = Rolls, Missouri
W = Washington, B.C.
4 - 5 Agency Code
6-8 User registration code.
9-10 User's ID, May be changed by the user as
desired. Do not use the same two charac-
ters for different jobs run during the
same day.
11 Blank.
12 - 14 JOB (i.e. the word JOB).
-------
-------
Card Columns Contents
1.5 Blank.
16 ( (Left parenthesis)„
17 - 20 Program Number
21 , (Comma)„
22 - 25 Auxiliary account number.
26 .» (Comma).
27 - 30 Estimated execution time in minutes. Re-
quires four numeric digits.
31 , (Comma).
32 - 35 Estimated lines of print expressed in
thousands of lines. Requires four
numeric digits„
36 , (Comma).
3? - 1*0 Estimated number of cards to be punched.
Requires four numeric digits.
41 , (Comma),
42 Reserved for future use; must "be a I
punch.
43 , (Comma).
44 Reserved for future use; must "be a 1
punch.
4,5 , (Comma).
46 Type of Run:
C = Compile only
T = Test of program
P = Production use of program
-------
9
Card Columns
47
48 - 49
Contents
50
51
52
53 -
62
63
64
72
- 71
(Comma),
Number of lines per page. A value of
zero suppresses page overflow tests „ If
this field (and the preceding comma) is
eliminated, a default option of 6l lines
per page is used. In this case the
following fields are shifted left 3 col-
umns. (Except columns 62-72.)
) (Right parenthesis)„
, (Comma).
1 (Apostrophe).
Name of the user-
1 (Apostrophe).
, (Comma).
Blank.
X (The letter X).
Card 2 -
Card Columns
1-2
3 - 15
16 - 25
26
27 - 33
34 - 72
II
Blank.
MSGEEVEL-1
, (Comma),
CLASS=C
Blank.
Contents
-------
10
SYSTEM CONTROL CARDS;
Cards 1 & 2;
(a) If the object deck is used -
1
//"bEXECbLIHKFORT ^REGION. GO=252K /TIME. G0=J
//IKEDoSYSBTbDDb*
where J is the time required to run the program(in minutes). The
'b' stands for a blank space. Next comes the object deck (includ-
ing its delimiter).
(b) If the source deck is used -
1
//bEXECbFORTGCLG, PARM.FORT=' DECK', REGION. GO=252K ,TIMB. G0=J
//FORT.SYSlNbDDb*
where J is as before. Next comes the source deck (including its
delimeter).
Cards 3 & ki
(a) If the data resides on the disc SYSDK -
1 PASS
//GO. PT10F001bDDbDSN=&NAME ,UNIT=SYSDY ,DISP=(OLD .>HS][BTE ^DELETE),
//bDCB=(RECFM=VB,IEECL=RRR.,BIKSIZE=BBBB)
where SsNAME is the name of the storage space. (The '&' signifies
the storage is temporary--it only exists for the extent of the job.)
PASS is used if the data file is used later on; otherwise use DELETE.
The letters 'RRR' and 'BBBB' are computed as follows:
RRR » 8M + 2k where M = number of columns in the data matrix.
BBBB = K(RRR) + k where K is an integer chosen so that the
positive difference (7200-BBBB) is as small as possible.
-------
11
(b) If the data resides on magnetic tape -
1
=( ,SL) ,,VOLUME=( ,HRTAIN, , ,
//bDISP«(OIJ),KEEP) ,DSP=STAPAC
where 'THYYY' in the first tape card represents a six digit in-
put tape number (leading zeros must be given).
The letters 'RRR' and 'BBBB' are as before,
When a tape is used, a tape setup card is required. Its form is:
Card Columns Contents
1-9 /*MESSAGE
10 - 12 Blank.
13 - 20 The same characters as in columns 3-10
of the JOB card.
21 - 22 Blank.
23 - 2? SETUP.
28 - 29 Blank.
30 - 36 The number of the tape used.
37 - 38 /9
If the tape is written on as well as read,, in column 39; place
an R (for ring in). This card should be placed right after the JOB
card. (This card's format is particular to the 360/65 in Washington,
B.C.)
-------
-------
12
Card 5:
1
//GOoSYSINbDIJb*
-------
HEADER CARDs
13
Columns
1-30
Format Entj
7A4,A2 TITIE
31-38
39-43
VT-56
T3-TT
15
13
1011
15
INPUT ID
INFJT N
INPUT M
OPTION
FROH
T8-8Q
13
PROM
Description
Up to 30 characters of alphanumeric
information used to title the out-
put for this data set. It is also
used when listing the total number
of plots created. It is not'used
on the graph.
Up to 8 characters of alphanumeric
information used to identify the
input data set.
The number of rows in the input
data matrix. (Right justified.)
The number of columns in the in-
put data matrix. (Right justified,
199-)
See the following sheet.
The number of pairs of row numbers
needed to select the desired rows
of the input matrix. If blank,
all rows are included„ If not
blank, this number must be right
justified and row selector cards
must be included.
The number of pairs of column num-
bers needed to select the desired
columns in the input data matrix.
(if blank, all columns are inclu-
ded. If not blank, this number
must be right justified and column
selector cards must be provided.)
-------
OPTIONS -
0 - No stepwise deletion of variables
OPTION( 1) -}_ _ Deletion of least significant variable occurs
until the program reaches minimum specified,
0 - No action taken.
OPTIOW( 2) -JL _ Residual analysis performed starting with all
variables present; continues until stepwise
deletion stops.
OPTION( 3) -2 - Residual analysis performed starting with num-
ber of variables specified on Residual start
card.
0 - Indeterminants not allowed in the selected data
OPTION( 4) -i _ observations having indeterminants in selected
data are skipped.
OPTIONf 5) _° - No action taken
^ ^' 1 - Residual analysis doen using antilog transform
of dependent variable.
OETION( 6) - NOT USED
0!TION( 7) - NOT USED
0!TION( 8) - NOT USED
0 - Input tape unit is 10.
OPTION( 9) -]__9 Thls is the input tape unit.
0 - Use the variable identifiers on the STATPAC tape
OPTION(10) -]_ _ Read in new varia-bie identifiers from cards.
-------
COLUMN IDENTIFIER CARDS:
These cards are used only if OPTION(lO)=l on the header
card. They permit the user to associate an eight character
identifier with each column in the data matrix. Ten identi-
fiers can "be used per card; if more then ten identifiers are
needed, they are continued on another card. The numbers above
the eight card column fields indicate the columns in the data
matrix the identifiers are associated with. One identifier
must be specified for each column in the output data matrix.
-------
16
ROW SELECTOR CARDS;
These cards are used only if FRON on the header card is
not blank. The number entered in the field FRON specifies how
many pairs of row numbers are used to select desired rows of a
data matrix. Each pair specifies the rows FROM and including
the first member of the pair TO and including the last member
of the pair will be selected. The pairs must be entered
starting in the left most field of the card and continuing a-
cross eight pairs per card If more pairs are used, continue
on another card. The first member of the pair is entered under
the word "FROM" and the second member of the pair entered under
"TO." Except for the selection of a single row (where the "TO"
portion is left blank) the row numbers must form an increasing
sequence, i.e., rows must be selected in the order they appear
in the data matrix.
-------
17
COLUMN SEUSCTOB CARDS;
These cards are used only if ERON on the header card is
not blank. The number entered in the field PROW specifies
how many pairs of column numbers are used to select desired
columns of a data matrix. The instructions for their use is
identical to the select row cards except that thirteen pairs
per card are used and the columns need not be selected in in-
creasing order.
-------
18
MINIMUM NUMBER OF VARIABLES CARD;
This card is used if OPTIOH(3,) is non-zero. It gives the
minimum number of variables (including the dependent variable)
at which stepwise deletion is to cease.
Its format is:
Columns Format Entry Description
1 - h Ik K The minimum number of variables
(including the dependent variable
on which the regression is to be
performed. The stepwise deletion
stops when M' is less than K.
(K must be punched right justified.)
-------
-------
19
RESIDUAL START CARD;
This card is used if OETION(2) is a two, and OPTION(l) is
non-zero. It gives the number of variables (including the de-
pendent variables) at which residual analysis is to be performed,
Its format is the same as the MINIMUM NUMBER OF VARIABLES CARD.
-------
20
OUTPUT:
Output to this program is a printed table of means, standard
deviations, variance-covariance,, the correlation matrix, mul-
tiple correlation coefficients (and degrees freedom), regress-
ion coefficients,, regression weights, regression constants,,
standard errors of the regression weights and tests of signi-
ficance, variables deleted (if any), residuals and sums of
the squares of the residuals if requested, and the standard
error of the estimate of the dependent variable.
-------
21
Appendix; Sample Output
-------
Or
«5
>
O
i"
a ~
o
u
0
"' X
>•- a
o
-------
of u
OJ LU
a; tr.
o o
u. o
o c-
LJ a
o > •"..
LU
nor
o
o
o
•n D
v- >
o r>
-------
O
in
o
o
o
o
CJ
o
o
o
O rt O CC O
I u. \f\ Uj rj
UJ o
^ D cc rs 10
< 2- • 2- .
—• CJ O
Cf "» ^|
< o o
> tf or
-------
O
O
O
r -t o
o o
7.
o or o UL r-
•« in o u * r J
»- an o a.' —
< ) o y u^
-J II -• D ro
nt
O
O
-------
i O
o
-• I
o o
' h?
•3
U
UJ
o
u.
c
a. c
1 X u. V- C5
• o u *^
. —• uj S n
« u: O r o C ' C~
"C O O O <_> JL -<
) j O
• 7* Uj 7* u' ^' u. |
'< O FNJ CJ O C U)
. t/1 l/^ CO JJ LO CX °Q
m i/l —^ 1/1 < (j-
u/ »iu "U-tiir1
O X. O LI ^* •
O I
o
C' r?
Q
r*
O
-------
ee-c-c'C'i-'oc'r o o o c o c
i i i i I i i i i i i i i i i
U-> a
a u
C
I
UJ
IT
C-J
(V,
c z
V Ul
OC »_;
< 0
a
•a
iv, r- e i i t i i i i i i i i i
u Ij 1. u I' L L U U " U I. U L. L: u
r u* C' ^3 ^, f^ ^? a fv, "• • "^ ^ ^ O 3T c
^TsTi/- A. /*-^H^r-rri'-1j-r--^.r- "^C
"VJ C' tr ^ ' <7 ^ C fvj (Y f^ - C ^ — * i.* -*
Jf-j^C-C^Vy-^-— f" rv, .C ~ C1 — ^C
fv. — ~
I I I I I
O
,c
o c c- c •:• r~- c- c '.' c~ o c- <• roc '_ c c
a-
^T-
o
o
r~
o
a-
o-
a-
LL) O
C -J
Z U-
o
2" O-
-------
-------
RELATIVE CONTRIBUTIONS OF NUTRIENTS
TO THE POTOMAC RIVER BASIN
FROM VARIOUS SOURCES*
Technical Report No. 31
January 1970
-------
-------
Chesapeake Technical Support Laboratory
Middle Atlantic Region
Federal Water Pollution Control Administration
U.S. Department of the Interior
RELATIVE CONTRIBUTIONS OF NUTRIENTS
TO THE POTOMAC RIVER BASIN
FROM VARIOUS SOURCES*
Technical Report No. 31
Norbert A. Jaworski
and
Leo J. Hetling**
January 1970
* Presented at the Cornell Agricultural Waste Management
Conference, January 19-21, 1970, Rochester, New York
** Director, Research Unit, Division of Environmental
Health Services, New York State Department of Health
-------
-------
TABLE OF CONTENTS
Page
LIST OF TABLES 11
LIST OF FIGURES ill
INTRODUCTION 1
A DESCRIPTION OF THE POTOMAC RIVER BASIN 2
NUTRIENT SOURCES 4
A. Sampling Programs It-
's. Wastewater Loadings in the Potomac Basin 7
C. Land Runoff and Other Sources 9
D. Relative Contribution of Loadings 18
E. Temporal Variations 21
F. Comparison to Other River Basins in the
Middle Atlantic Region 27
G. Hudson River Basin System 31
SUMMARY AND CONCLUSIONS 33
REFERENCES 36
-------
ii
LIST OF TABLES
Number Table
I Nutrient Loadings from Wastewater Discharges 8
by Sub-Regions
II Nutrient Loadings from Watersheds with 12
Varying Land Use
III Comparison of Annual Average Nutrient 13
Concentrations and Loadings
IV Estimated Nutrient Loadings from Land IT
Runoff - Potomac River Basin
V Estimated Total Potomac Basin Nutrient 20
Loading
VT Comparison of Nutrient Loadings in Hudson 32
and Potomac River Basins
-------
ill
LIST OF FIGURES
Number Figure
1 Major Municipal Wastewater Discharges
Potomac River Basin 3
2 Nutrient Network - Potomac River Basin 5
3 Chesapeake Bay Nutrient Input Stations 6
k Land Use Comparison - Total Phosphorus PO,
Potomac River Basin 1966 10
5 Land Use Comparison - NOp+NO,, as N - Potomac
River Basin 1966 J 11
6 South Branch Potomac River at Petersburg,
West Virginia - TKN, N02+N0 and PO^ vs
River Discharge -* 15
7 Potomac River Basin Nitrate Nitrogen Loadings
at Great Falls, Maryland 19^7-196? 23
8 Nutrient Loadings and River Discharges -
Potomac River at Great Falls, Md. 1966 2k
9 Phosphorus Loadings - Potomac River at
Great Falls, Md. 1969 25
10 Nitrogen Loadings - Potomac River at
Great Falls, Md. 1969 26
11 Chesapeake Bay Nutrient Inputs - Total P0>
as PO. - Monthly average 28
12 Chesapeake Bay Nutrient Inpurs - N02+N0_ as N
Monthly average 29
13 Chesapeake Bay Nutrient Inputs - TKN as N
Monthly average 30
-------
-------
INTRODUCTION
The ujper Potomac estuary iz highly eutrophic. During the
rummer months, large blooms of nuisance blue-green algae, mainly
mlcroc.ystis, occur in the fresh water portion of the upper estuary.
A relationshii between high nutrient content and the accelerated
eutrophication i •> the Potomac estuary has been established [1].
To aid in developing the water resources of the Potomac River
ha^;iii, an investigation was initiated in 1906 to determine nutrient
sources including temporal and spaMal distributions. The analyses
was expanded in 1^)08 to determine the amount of nutrients entering
'he Potomac Basin fron. al^ major wastewater discharges. The scope
of the program was exjanded to include several other basins in the
Middle Atlantic Region during 1^9-
-------
A DESCRIPTION OF THE POTOMAC RIVER BASIN
The Potomac River Basin has a drainage area of 14,670 square
miles and encompasses parts of Pennsylvania, Maryland, West Virginia,
and Virginia and all of the District of Columbia. The major sub-basins,
including their drainage areas, are:
3ub-Basin Drainage Area
(square miles)
(l) ^henaridoah River 3,05^
(2) South Branch lA93
(3) North Branch 1,328
(k) Monocacy River 970
(5) Cacapon River 683
(6) Conococheague Creek 563
(7) Opequon Creek 3^5
(8) Antietam Creek 292
A map of the basin is presented in Figure I.
Of the 3 million people living in the basin, about 2.5 million,
or 83 percent, live in the Washington, D. C. metropolitan area. The
industrial development is primarily concentrated in the North Branch
of the Potomac near Luke and Cumberland, Maryland, and in the South
Fork of the Shenandoah near Front Royal and Waynesboro, Virginia.
Land use in the sub-basins is either predominately forest, agri-
cultural or urban. In the entire Potomac Basin, it has been estimated
that the land use is 5 percent urban, 55 percent forest and ^0 percent
agricultural including pasture lands.
The Potomac and its tributaries are characterized by flash floods
and extremely low flows . The average discharge of the Potomac River
at Washington, D. C. is about 11,000 cubic feet per second (cfs).
-------
8
3,
-------
NUTRIENT SOURCES
A. Sampling Programs
During the 1966 calendar year, a ^O-station stream sampling
network was monitored weekly for nitrogen and phosphorus as shown
in Figure 2. Weekly analyses of nutrients from 13 wastewater
discharges in the upper basin were initiated during the latter part
of l mill iop gallons
per day (mgd) were sampled.
In 19^'9» a sampling network, as shown in Figure 3j was developed
to determl >, e the nutrient loading Into the Chesapeake Bay. The
weekly anal/sis included two forms of carbon, three of phosphorus
and four of nitrogen taken at sampling stations just above the
non-tidal portions of the respective basins.
-------
-------
CHESAPEAKE BAY NUTRIENT INPUT STATIONS
c
CHESAPEAKE BAY
SCALE IN MILES
6 5 10 IS 20 25
POTOMAC AT
ODEA
FIGURE 3
-------
A- o? "• ",<•*•; , ' -.ere were a • "o vastewatpr discharges
Jn the upper Potomac River basin, Dur: itr 19faP>, 80,^30 Ibs/day of
t otal /:hoj. . I i^T'is am] t •• . --V lb;./ria',r r.ot.fil K,]nldah2 r.Itroff-n were
dlschargrd ' •" *-h« '•.urf'Pcip waters. As nan be seen in Table T, the
jRi'ffo^i (-."I- '--p,1;' "MI: •• . • '\f Piitoma" c>0 f-r." '.?< from the Washington,,
I;. C. area r'or a •,".-. r^d popiilat io:i c^' 2,903,^00, this reduces to
0.02^ and 0.020 Ibs /Capita/day of phosphorus and nitrogen, respectively.
Nutr^M load.J;.y; from industrial wastewater discharges are
about 7,700 Jbs/day ot total PO, and h/iOC Ibs/day of TKN. The indus-
u
irjal contribution;: to wastewater nutrient loadings in the basin are
about 10 jtro"',', or .re. 4 ota,l PO, (TFO^ ) and about 7 percent of the
total nitrogen. The amount of N0p+N0^ nitrogen in both the industrial
and municipal wastewater discharges is insignificant.
-------
8
TABLE I
NUTRIENT LOADINGS FROM WASTEWATER DISCHARGES
BY SUB-REGIONS*
Sub-Region Population
Served
North Branch
South Branch and
Upper Region
Opequon
Conococheague and
Upper Middle Region
Antietim and Middle
RegJ OP.
Shenandoah
Ca^octin Creeks
Md. and Va.
Mor.ocacy
Lower Fresh Water
Region
Potomac Estuary 2
TOTAL 2
79,200
17,300
3^,800
26,900
61,500
108,500
5,^00
62,500
7,^00
,500,000
,903,500
LOADING AFTER TREATMENT
BOD TKN TPO^
Ib s /day 1 b s /day Ib s /day
55,300
2,720
3,vro
U.250
7,980
31,800
7^0
U,220
200
130,000
21*0,680
1,750
•370
v-'O
(10
R90
u,8'>0
i i U
1,380
i 00
53,000
63 , 660
M50
460
1,100
1,0-0
2,380
6,360
220
1,830
180
62,000
80,U30
* A Sub-region may include discharges to the small tributaries and
to the main stem of the Potomac.
-------
C. Land Runoff and Other Sources
To determine the amount of nutrients entering the Potomac from
land runoff, analyses of loadings from areas with three distinct land
uses (forest, agricultural, and urban) were made [2]. Using the
Catoctin Creek (Maryland) watershed basin as primarily agricultural,
the Patterson Creek watershed as forested, and Bock Creek watershed
as urban, the effect of land uses on the contribution of nutrients
to surface waters is illustrated in Figures k and 5- These three
areas receive a relatively small wastewater volume.
On an annual basis, the concentration of nutrients was consist-
ently higher from agricultural areas. As summarized in Table IT, it
can be seen that the runoff from agricultural areas yields about
twice the nitrogen and phosphorus as does the forested area.
Summary of the nutrient data for the major sub-tasins, as
presented in Table ITI, indicates that the phosphorus conc.entra4 ions
were at least three times greater in the Monocacy Fiver, Opequon
Creek, and Antietan Creek sub-basins than in the remaining five sub-
basins. These three sub-basins, while primarily agricultural, also
receive considerable quantities of municipal wastewater. These higher
concentrations are also reflected in large PO. yields of i'rom 3-6 to
^.8 Ibs/day/sq. mi., as shown in Table III.
The Conococheague, Antietam, Opequon, and Mor.o^a..y sub-basins had
average concentrations of N0?+N0.- nitrogen of 1.1* mg/1 and greater.
The Conococheague and Monocacy sub-basins had nitrine and nitrate
yields of over 10 Ibs/day/sq.mi., almost twofold larger than that of
the remaining four sub-basins. This is mainly from agricultural drainage.
-------
8
T
a a:
Ul °
S J
2»
"Od
'Od IViOi
Figure 4
-------
Figure 5
-------
12
M
M
W
PQ
-l
§
B
M
:?
fH efl
W 4'
S3 o{
CO M
$ vo
B VO
'-£ ON
1 - , — |
^"•'
O
F' I
T)
O
g
h-l
&
•H
&
f$ . •
0*
to tn
«! "\
§ ^
w
^j.
fZ -H
W
flj ^^
w
m ^\
i ^
H" id
OJ ~\
O 03
^ n
H
— '
^^
^ -g
0
i-l-j O^
w
V) '~^-.
«5 >>
•S
o •--.
P-l M
^ S,
1) , — .
Kn
QU
03 CS5 -H
a 03 E
•H Sj
cd <4 o^
0) 0)
J2 to
m T) !D
^ rt
o efl -d
4-1 d
S 5
_ ^ [*""• ^~~
odd
O O t—
OJ VD CM
LT\ OO iH
O H H
CT\ CT\ t—
N- 0 t^-
CM H
W X -p -H .'i; • Ai --N
MOJW -POlO 0>C
0)0)0) oai-H aic8
•P ?H £n O JH ^i At JH .^
-POO 4JO5> OU^i
ft — O •— - K — '
-------
13
co
£5
is
8!
•H
K
O
£
fn
4)
to
a)
!H
O
as
CO
a)
O*
fi
OT
I
CO
S
o1
0)
cs'' aJ
a1
m
•H C
W O
05 T*
rO -P
I 03
rQ -P
^ CO
CO —
-
00
f-
VD
OJ
N-
VD
(M
ro
CO
[--
oo
OJ
ON
-H
LA
LA
CM
OJ
ro
CO
OJ
oo
(0
o
-P
OJ
LA
OJ
LA
LA
VD
OO
VC'
ON
OJ
LA
CO
o
LA
-4"
O
O
CO
£
ON
-4-
CO
H
oo
LA
on
ON
LA
MD
OJ
VO
OJ
OJ
t-—
OJ
ON
VD
o
s
•H •>
K ^d
o
>> -H
(J ^
0) 0)
o tJ
O H
•H H
K «J
O
o3 -P
fa flj
O 0)
-P fn
PH ^—--
•H
H
&
O
ca
i
o>
03
05
-------
The large variations in NOp+NO- nitrogen can be attributed to
high mobility of NO ion as reported by Wadleigh [3] and Bailey O].
Figure 6 for the South Branch station at Petersburg demonstrates
that the concentration of nitrates is directly related to river
discharge while concentrations of TKN and PO. are indirectly related
For the 35 stations in the non-tidal portion of the basin,
regression analyses were made using both linear and lo>/ transforms
The lop branr;forms appeared to yield the best correlation resulting
in the following expression:
C = aQb
where:
C - concentration of PO, , TKN, or N0_+N0 (mg/l)
Q = stream flow (cfs)
a = a constant
b = an exponent
Usjny the slope of the concentration-discharge relationship (the
exponent b) and knowing the specific location of the sampling point
in reJatiou to the municipal or industrial waste outfalls, a quanti-
zation of the sources of the nutrients can be obtained. For example,
all stations,except one below an industrial outfall discharging
nitrates, had a positive slope ranging from about 0.3 to 0.7 with an
average of 0.L) suggesting that most of the inorganic nitrogen comes
from land and other sources and not from wastewater discharges.
-------
lO.Or
SOUTH BRANCH POTOMAC RIVER
AT
PETERSBURG, WEST VIRGINIA
TKN. N02+N03 and P04 V». RIVER DISCHARGE
1000
10.000
RIVER DISCHARGE ef»
Figure 6
-------
16
The concentrations of phosphorus'and TKN for most of the non-
tidal stations had either slightly positive or negative slopes
indicating a diluting effect. The correlation coefficients for these
two parameters were low, probably due to seasonal and flushing effects
which were not incorporated into the regression studies.
A review of the slopes of the coneentration-flow relationships
for stations above and below waste outfalls definitely supports the
finding:; oi.' Bailey [k] who indicated that (l) nitrate nitrogen has
high mobilii,;/ in soil, (2) PO, and TKN are not readily leached, and
(3) nutrient concentrations appeal- to be ai't'ected by stream transport
mechanisms.
Using tre same land use designations that the U. S. Corps of
Engineers developed in their 19t>8 stud,/ [6], the nutrient loading from
land runoff was determined (Table IV) . It should be noted that the
largest contribution of nutrients, at out ;'-'5 percent, is from agri-
cultural r.r.olM even though only 38 percent of the basin is farmed or
in pasture lands.
-------
IT
C
•H
•H ON
« H
O
-p
fr;
CO
a5
J§
EH
H,
to
Oj
oo
o
£^
+
g™
O
°3
$
6^
&
0)
1
0)
to
!=>
£3
(rt
t— i
•H
fi
0*
to
, — „
•g
0*
CO
t>.
«5
id
to
f
<-\
%
"a
^-
to
o
H
•rH
C71
07
t
w
H
CO
CO
o
*x
-*
t"-
o
0
o
-
ir\
CO
O
^O
^
4
H
" — '
•H
H
to
§
CO
H
81
LT\
^
en
H
^1 °
1 CO
W| LTN
*
0)
^
-P
1
0
•H
H
S)
<
o
~3"
OJ
m
-4-
o
8
OJ
*s
\^Q
H
O
OJ
0
o
-4-
LT\
O
8
H
co"
•P
to
^
o
fc
H
H
LT\
r-
o
0
ON
H
•-.
OJ
O
m
8
CO
H
rH
o
on
t—
0)
£>
^
ON
CO
CO
•s
K
m
LfN
O
O
no
^j-
»s
ro
l/N
CO
ON
-*'
OJ
-3-
sf
^
0
o
M3
-^
H
c!
•H
q5
m
•d
-p
o
EH
§
-p
I
•o
cd
O
fn
O
-P
O
W
0!
O
d
0)
to
o
•H
!n
-------
18
D. Relative Contribution of Loadings
Utilizing the wastewater data of 1968 and stream flow conditions
of 1966, the total nutrient loadings to the surface waters of the
basin have been estimated as presented in Table V. The delineation
of the sources indicates the following:
1. Of the 92,872 Ibs/day of total phosphorus as PO,,
87 percent was from wastewater discharges.
2. About 67 percent of the total phosphorus was from
wastewater discharges in the upper Potomac estuary.
3- The total loading of nitrogen as N was about 125,000
Ibs/day, of which approximately ;?! percent or
63,i->80 Ibs/day originated from wastewater discharges.
H. About ^3 percent of the total nitrogen loading was from
wastewater discharges in the upper Potomac estuary.
The above delineation clearly indicates for the Potomac River
basin the ma.'iOr sources of phosphorus is from wastewater. The major
source of nitrogen in 1966 was also from wast-ewater discharge. Land
runoff from the agricultural areas had the nighest yield of nitrogen
per square r..;ie. Moreover, the concentration of nitrate-nitrogen
appears also to be greatly affected by stream flow conditions.
Data i'or the first eight months of 19'"'9 indicate that over
Bo percent of phosphorus and (~>6 percent of the nitrogen entering the
Potomac estuary was from wastewater discharges in the Washington, B.C.
area [7]- Even though the first six months of 19^9 had stream flows
-------
19
below normal with the latter period having above or normal flow
conditions, the data supports the 1966 findings that the major
source of nutrients in the Potomac is from wastewater discharges.
-------
20
-p
o
-p
ON
00
o
o
H
3
1
O
00
MD
vo
ON
en
oo
ir\
•s
pi
-p
O
-P
O
O
-p
o
•H
en
55 \O
FQ \D
a\
O r-H
<£
£
fe
CQ
0}
oo
§
,, — s
>>
^
~-^^
w
rQ
H
O
oo
^t-
* »,
or^
ITS
0
oo
J-
OO
LT\
P4
I
H
O
W
El
B
M
t--
oo
O
O
•
g,
•H
W
0)
0)
I
-p
w
0)
O x-s
^ b
05
D'J Tj
03 ~^.
CO
-* ^3
S d
rH v — ^
EH
O CM
r>o ^J-
-* J-
•s »\
eg SI
CO
f-
oo
CM
ON
0)
o
o
CO
0)
-p
0)
-p
to
a]
Vl
o
c
s
K
C
•H
M
O
?H
•P
•H
S
f
O
fe
+
O
-p
-------
21
E. Temporal Variations
An important aspect of the nutrient control problem is the
annual variation in nutrient contributions from the various sources,
especially from land runoff. The nitrate-nitrogen loadings from the
years 1947-196? for the Potomac River at Great Falls show a definite
seasonal pattern (Figure 7)• The seasonal loading variations closely
parallel those of river discharge that is high in the spring months,
low in the summer and fall, and somewhat higher than fall in the
wi nter months.
The relationship between river discharge and nutrient loadings
is vividly demonstrated in Figure 8 for the Potomac at Great Falls.
During the high discharge rate in February and March of 1966, the
N0p+N0~ and TPO, loadings were also the largest while in August,
when the flow was very low, the nutrient loadings were likewise
smalJ .
In mid-September of 1966, there was considerable precipitation
throughout the basin. This resulted in a high nutrient loading in
September as also seen in Figure 8.
An important aspect of -the temporal variations in nutrient
loadings is nutrient transport. This is especially pronounced for
phosphorus. As can also be seen in Figure 3, during August, less
than 100 Ibs/day of TPO, entered the estuary even though over
1
-------
22
onto sediment particl-es or utilized by aquatic life. At times of
high stream flows, much of the phosphorus is re-suspended and trans-
ported downstream.
The high loadings of TPO; • in mid*September were due to flushing
of the river channel system by.the high stream flows. The high
inorganic nitrogen loadings in September can be readily attributed to
flushing of the land as previously indicated.
The various forms of phosphorus and nitrogen for the Potomac
River at Great Falls during the first 10 months of 19&9 are presented
in Figures 9 and 10. Figure 9 shows that only about 25 percent of
the total phosphorus is in the dissolved reactive form. This suggests
that most of the phosphorus originating from the upper basin was or
has become attached to silt particles.
Similar to Figures 6 and 7, the N0p+N0_ nitrogen as shown in
Figure 10 demonstrates the dependence of this form of nitrogen on
river discharge. Fraction analyses of the TKN form indicates that
over 50 percent is in the particulate state.
The wide variations in nutrient loadings in the Potomac River
at Great Falls demonstrates the need to sample at various river
discharges continuously over an annual cycle before a delineation
of nutrient sources can be made. Moreover, as shown in Figure 8,
sampling only during summer flow conditions can yield misleading
conclusions as to the temporal distribution, relative sources and
transport mechanism of nutrients.
-------
CON
Figure 7
-------
NUTRIENT LOADINGS and RIVER DISCHARGES
POTOMAC RIVER a* GREAT FALLS. Md.
-*-
Figure 8
-------
Id
5
g 5
'I' 39MVHDSIO M3AIM
FIGURE - 9
-------
z
r
n i i i i
I IT i rt
<3
HOUSE - 10
-------
27
F. Comparison to Other River Basins in the Middle Atlantic Region
Figures 11, 12 and 13 present a six month comparison of nutrient
concentrations for five river basin systems as part of a nutrient
input study of the Chesapeake Bay system. The mean monthly concen-
tration of phosphorus is highest for the Patuxent Basin and lowest
for the Susquehanna with the Potomac being second highest (Figure ll).
Except for the Patuxent, all have concentrations usually less than
0.5 rug/I.
In terms of N0p+N0_ nitrogen, the Patuxent is the highest
(Figure 12). This is mainly due to high ratio of sewage to stream
flow in this small basin. The concentrations, usually less than
0.5 mg/1, were the lowest for the Rappahannock Basin with Potomac
being comparable to the other basins of its size, ranging from about
0.5 to 0.75 mg/1.
TKN nitrogen concentrations in the Patuxent were the highest
with the Potomac being second highest. For the three remaining basins,
the concentration varied from about 0.3 to 1.0 mg/1.
-------
I/)
CE
uj
i
UJ
I
00
O
U
O
1
10
O
q
•*'
q
o
0d
FIGURE- II
-------
a
z
P s
=> c
Z O
CO
UJ
U
a
UJ
I
U
UJ
<
>
I
I-
2
U cr
i
LJ
in
(Vj
q
i/)
N
o
10
ci
cc
uj
UJ
cr
UJ
m
U
o
I/)
q
o
FIGURE- 12
-------
I
a
z
i-
z
UJ
i 3
o
UJ
> *- -J
< * I
CD K Z
O
U ^
ui
a
UJ
X
u
a:
ui
GO
O
o
UI
-, 1 , r ,
ui o
OJ N
\ 1 ' — 1
in
r — ' 1
Q
— i r^ 1
m
o'
-4
c
FIGURE- 13
-------
31
G. Hudson River Basin System
In order to determine if the relatively high percentage of
nutrients from wastewater in the .Potomac Basin vas unique or
whether it Js more generally true that wastevater discharges are
the most significant contributors of nutrients to the aquatic
ecosystem in the Middle Atlantic Region, a comparison of the
nutrient sources was made for the Hudson River Basin. This basin
Is relatively comparable to the Potomac in size, land use patterns
and population (both over-all density and distribution). It is
also more highly industralized.
A complete description of the Hudson River Basin and its
nutrient loading was recently presented by Tofflemire and Hetling
L8]. As a result of this study, it was estimated that the total
phosphorus as PO. discharged to the Hudson Rive.r Basin above the
New York City line is approximately 72,000 Ibs/day, 73% of which
is from wastewater discharges. The corresponding total for nitrogen
as N is 125,570 Ibs/day with 63/0 coming from wastewater.
A comparison of the Hudson River estimates with those found
for the Potomac is given in Table VI. The Hudson results give
added support to the Potomac findings that, for the large river
basins in the Middle Atlantic Region, the major source of nutrients
is wastewater discharges.
-------
Source
Wastewater
Land Runoff
Total Basin
Source
Wastewater
Land Runoff
Total Basin
TABLE VI
COMPARISON OF NUTRIENT LOADINGS
IN HUDSON AN) POTOMAC RIVER BASINS
Total Phosphorus as PO,
Potomac Basin
(Ibs/day) 4
80,430 87
12,442 13
92,872 100
Total Nitrogen as N
Potomac Basin
63,680 51
61,269 49
124,949 100
Hudson Basin
'(Ibs/day) %
52,000 73
19,420 37
71,600 100
Hudson Basin
78,500 63
47,070 37
125,570 100
-------
33
SUMMARY AND CONCLUSIONS
Results of the initial phase of the nutrient investigations
in the Potomac River system, which have been expanded to include
other river basins and which are being continued by the CTSL, are
summarized below:
1. The annual average concentration of phosphorus as PO, in
the major sub-basins varied from a minimum of 0.09 mg/1 in the
South Branch to a maximum of 1.9 mg/1 in the Antietam watershed.
2. The annual average concentration of N02+N0 nitrogen as N
in the major sub-basins varied from 0.3 mg/1 in the South Branch to
2.2 mg/1 in Opequon Creek.
3- The annual average concentrations of phosphates, total
Kjeldahl nitrogen (TKN) and NO + NO nitrogen in the freshwater
stream flow entering the estuary near Washington, D. C., were 0.3,
0.3, and O.y mg/1, respectively.
k. About 92,700 Ibs/day of total phosphorus as PO, entered
the surface waters of the Potomac in 1966, of which 87 percent
resulted from wastewater discharges.
5. The average 1966 loading of total nitrogen as N from all
sources to the surface waters of the basin was about, 125,000 Ibs/day,
of which 63,680 Ibs/day, or 5! percent, were from wastewater discharges.
6. Seasonal variations in inorganic nitrogen loadings are much
more pronounced when compared to phosphorus. This is mainly attributed
-------
to.a direct relationship between stream flow and inorganic nitrogen
concentration for the stations in the non-tidal portion of the basin
while phosphorus generally has an inverse relationship.
J. Prom an analysis of watersheds with varying land uses and
receiving little or no wastewater discharges, the average annual
yields per square mile for the entire basin was 0.8 Ibs/day of
phosphorus PO, , 5-0 Ibs/day of NCL+NO nitrogen as N, and 0.5 Ibs/day
of TKN.
8. Of the 6l,2TO Ibs/day of total nitrogen from land runoff,
about 35>000 Ibs/day or 65 percent, were from agricultural areas which
comprise only 38 percent of the total drainage area in the basin.
9- Nutrient yields were over twofold greater from areas which
were predominately agricultural than from forested areas.
10. Similar to 1966 findings, data for the first eight months
of 1969 corroborate that the major source of nutrients is from waste-
water discharge with the largest contribution originating in the
Washington, D. C. area.
11. During low flow conditions a significant proportion of the
phosphorus entering the surface water from the various sources in
the upper basin is retained in the stream channel. At high stream
flow, it appears that a large proportion of this phosphorus is
"flushed" out of the stream channel and transported downstream.
12. The wide variation in nutrient loadings clearly demonstrates
the need to sample more frequently over a vide range of stream flows
before a precise identification of nutrient sources can be made.
-------
13. In the Hudson River Basin, wastewater discharge contributes
about 73 percent of the phosphorus and 63 percent of the nitrogen.
lU. A comparison of sources of nutrients in the Hudson River
Basin to those found in the Potomac supports the contention that for
large drainage basins in the Middle Atlantic Region the major source
of nutrients to the aquatic ecosystem is from wastewater discharges.
-------
36
REFERENCES
1. Jaworski, N.A., Lear, D.W., and Aalto, J.A., "A Technical
Assessment of Current Water Quality Conditions and Factors
Affecting Water Quality in the Upper Potomac Estuary,"
Technical Report No. 5, CTSL, MAR, FWPCA, March 1969.
2. Jaworski, N.A., Villa, 0., and Hetling, L.J., "Nutrients in
the Potomac River Basin/' Technical Report No. 9, CTSL, MAR,
FWPCA, May 1969.
3. Wadleigh, C.H., "Wastes in Relation to Agriculture and
Forestry/' U.S. Department of Agriculture, Washington, D.C.,
March 1968.
k. Bailey, G.W., "Role of Soils and Sediment in Water Pollution
Control, Part One," Southeast Water Laboratory, FWPCA,
March 1968.
5- Jaworski, N.A., "Nutrients in the Upper Potomac River Basin,"
Technical Report No. 15, CTSL, MAR, FWPCA, August 1969.
6. U.S. Army Corps of Engineers, "Potomac River Basin Report,"
Volume 1, Part 1, North Atlantic Division, Baltimore, Md., 1963.
7. Jaworski, N.A., "Water Quality and Wastewater Loadings Upper
Potomac Estuary During 1969," Technical Report No. 27, CTSL,
MAR, FWPCA, November 1969.
8. Tofflemire, T.J. and Hetling, Leo J., "Pollution Sources and
Loads in the Lower Hudson River," presented at the Second
Annual Symposium on Hudson River Ecology, New York University
Medical Center, Institute of Environmental Medicine, Sterling
Forest, New York, October 3969.
-------
35
13. In the Hudson River Basin., wastewater discharge contributes
about 73 percent of the phosphorus and 63 percent of the nitrogen.
lU. A comparison of sources of nutrients in the Hudson River
Basin to those found in the Potomac supports the contention that for
large drainage basins in the Middle Atlantic Region the major source
of nutrients to the aquatic ecosystem is from wastewater discharges.
-------
36
REFERENCES
1. Jaworski, N.A., Lear, D.W., and Aalto, J.A., "A Technical
Assessment of Current Water Quality Conditions and Factors
Affecting Water Quality in the Upper Potomac Estuary,"
Technical Report No. 5, CTSL, MAR, FWPCA, March 1969-
2. Jaworski, N.A., Villa, 0., and Hetling, L.J., "Nutrients in
the Potomac River Basin," Technical Report No. 9, CTSL, MAR,
FWPCA, May 1969.
3. Wadleigh, C.H., "Wastes in Relation to Agriculture and
Forestry," U.S. Department of Agriculture, Washington, D.C,,
March 1968.
^. Bailey, G.W., "Role of Soils and Sediment in Water Pollution
Control, Part One," Southeast Water Laboratory, FWPCA,
March 1968.
5. Jaworski, N.A., "Nutrients in the Upper Potomac River Basin,"
Technical Report No. 15, CTSL, MAR, FWPCA, August 1969.
6. U.S. Army Corps of Engineers, "Potomac River Basin Report,"
Volume 1, Part 1, North Atlantic Division, Baltimore, Md., 1963.
7- Jaworski, N.A., "Water Quality and Wastewater Loadings Upper
Potomac Estuary During 1969," Technical Report No. 27, CTSL,
MAR, FWPCA, November 1969.
8. Tofflemire, T.J. and Hetling, Leo J., "Pollution Sources and
Loads in the Lower Hudson River," presented at the Second
Annual Symposium on Hudson River Ecology, New York University
Medical Center, Institute of Environmental Medicine, Sterling
Forest, New York, October 1969.
-------
Annapolis Field Office
Region III
Environmental Protection Agency
MATHEMATICAL MODEL STUDIES OF WATER QUALITY
IN THE
POTOMAC ESTUARY
Technical Report 33
March 1972
Leo J. Clark
Kenneth D. Feigner*
*Environmental Protection Agency, Office of Water Programs,
Washington, D. C.
-------
PREFACE
During 1969, two independent but coordinated studies were under-
taken by the U. S. Department of the Interior, (FWQA)* and the Corps of
Engineers to ascertain the feasibility of using the upper Potomac Estuary
as a supplemental water supply source for the Washington Metropolitan Area.
Another of the primary requirements for the FWQA study was determination
of maximum allowable pollutant loadings to achieve and maintain the adopted
water quality standards. Current water quality conditions in the upper
estuary have been adequately defined by extensive sampling, but prediction
of the effects of large freshwater withdrawals and the corresponding
increases in wastewater flows on water quality was also required.
The Chesapeake Technical Support Laboratory (CTSL)** has employed
mathematical modeling techniques to predict water quality behavior in the
Potomac Estuary for various hydraulic conditions and wastewater loading
schemes. While existing estuary models have proven to be flexible and
versatile tools, verification for a particular system was necessary
before reliable predictions could be made. This report presents CTSL's
findings based upon simulation studies in the Potomac Estuary using two
of the more commonly known mathematical models: (1) DECS III***, and
(2) the FWQA Dynamic Estuary Model. The former model employs an average
tidal solution whereas the latter is based upon a real-time solution.
* Now the Environmental Protection Agency
** Presently known as Annapolis Field Office
*** Hereafter referred to as the Thomann Model
-------
TABLE OF CON-TENTS
Page
PREFACE iii
LIST OF TABLES vii
LIST OF FIGURES viii
Chapter
I. INTRODUCTION I - 1
A. Purpose and Scope I - 1
B. Acknowledgements 1-3
II. SUMMARY AND CONCLUSIONS II - 1
III. DESCRIPTION OF STUDY AREA Ill - 1
IV. DESCRIPTION OF MATHEMATICAL MODELS .... IV - 1
A. Thomann Model IV - 1
B. Dynamic Estuary Model IV - 5
V. MATHEMATICAL MODEL SIMULATIONS OF 1969-1970
DYE RELEASES V - 1
A. Thomann Model V - 1
1. Simulations and Verification ... V - 1
a. Potomac Dye Study V - 1
b. Anacostia Dye Study V - 12
B. FWQA's Dynamic Estuary Model V - 19
1. Simulations and Verification ... V - 19
a. Potomac Dye Study V - 19
b. Anacostia Dye Study V - 28
iv
-------
TABLE OF CONTENTS
Chapter Page
VI. OTHER MATHEMATICAL MODEL SIMULATIONS VI - 1
A. Simulation of 1965 Dye Release VI - 1
1. Thomann Model VI - 1
2. Dynamic Estuary Model VI - 6
B. Chloride Simulations - 1966 and 1969 ... VI - 11
1. Thomann Model VI - 11
C. Simulation of 1965 Chlorides VI - 16
1. Dynamic Estuary Model VI - 16
VII. COMPARATIVE SENSITIVITY EVALUATIONS - THOMANN AND
DYNAMIC ESTUARY MODELS VII - 1
A. Decay Rate of Pollutant VII - 1
B. Segment Length VII-5
1. Thomann Model VII-5
2. Dynamic Estuary Model VII-5
C. Dispersion Coefficient • VII - 10
1. Thomann Model VII - 10
a. Point Discharges VII - 10
b. Chloride Distributions VII - 15
2. Dynamic Estuary Model VII - 18
a. Point Discharges VII - 18
b. Chloride Distributions VII - 20
D. Advective Transport VII - 25
1 . Thomann Model VII - 25
2. Dynamic Estuary Model VII - 28
-------
TABLE OF CONTENTS
Chapter Page
VII. COMPARATIVE SENSITIVITY EVALUATIONS - THOMANN AND
DYNAMIC ESTUARY MODELS (Continued)
E. River Flow and Dispersion Coefficients (Thomann
Model) VII - 30
F. Manning Coefficient and Tidal Effects (Dynamic
Estuary Model) VII - 33
VIII. ENGINEERING CONSIDERATIONS VIII - 1
A. Dispersion and Advection VIII - 1
B. Model Comparison VIII - 5
APPENDIX A.- 1
A. Potomac Dye Study - 1969 A - 1
1. Release Conditions A - 1
2. Monitoring System A - 4
a. Longitudinal Stations (Slack Tide) . . A - 4
b. Lateral and Vertical Stations .... A - 4
3. Presentation of Data A - 6
a. Tidal Conditions and Hydrology ... A - 6
b. Dye Movement A - 12
c. Loss Rate Determination A - 20
B. Anacostia Dye Study - 1970 A - 23
1. Release Conditions A - 23
2. Monitoring System A - 24
3. Presentation of Data A - 26
a. Tidal Conditions and Hydrology ... A - 26
b. Dye Movement A - 28
c. Loss Rate Determination A - 32
BIBLIOGRAPHY
vi
-------
LIST OF TABLES
Number
VII -
Appendi
1
X
1
2
3
4
5
6
7
Effects of Manning Coefficients on Tides
Dye Injection Data, Blue Plains, November
1969 . . . . .
Longitudinal Sampling Stations, Potomac
River
Longitudinal Sampling Stations, Anacostia
River
Summary of Dye Concentration Data - Potomac
Estuary, November 1969, High Slack Tide Data
Summary of Dye Concentration Data - Potomac
Estuary, November 1969, Low Slack Tide Data
Summary of Dye Concentration Data - Anacostia
River, April-May, 1970, High Slack Tide Data
Summary of Dye Concentration Data - Anacostia
River, April-May, 1970, Low Slack Tide Data
Page
VII
A
A
A
A
A
A
A
- 33
- 2
- 5
- 25
- 34
- 35
- 36
- 37
Vll
-------
LIST OF FIGURES
Number
I -
III -
III -
III -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
1
1
2
3
1
2
3
4
5
6
7
8
9
10
11
12
Description
Potomac River Tidal System
Cross-sectional Area vs Distance, Potomac
Estuary, Mean Water Data
Accumulative Volume vs Distance, Potomac
Estuary, Mean Water Data .
Accumulative Surface Area vs Distance,
Potomac Estuary, Mean High Water Data
Thomann Mathematical Model Segments, Potomac
Estuary
Thomann Model Dye Simulation and Verification,
Uoper Potomac Estuary, November 6, 1969
Thomann Model Dye Simulation and Verification,
Upper Potomac Estuary, November 7, 1969
Thomann Model Dye Simulation and Verification,
Upper Potomac Estuary, November 10, 1969
Thomann Model Dye Simulation and Verification,
Upper Potomac Estuary, November 12, 1969
Thomann, Model Dye Simulation and Verification,
Upper Potomac Estuary, November 17, 1969
Temporal Dye Profiles, Upper Potomac Estuary,
Thomann Model
Thomann Model Dye Simulation and Verification,
Anacostia River, April 23, 1970
Thomann Model Dye Simulation and Verification,
Anacostia River, April 27, 1970
Thomann Model Dye Simulation and Verification,
Anacostia River, April 29, 1970
Thomann Model Dye Simulation and Verification,
Anacostia River, May 4, 1970
Thomann Model Dye Simulation and Verification,
Anacostia River, May 7, 1970
Page
I -
III -
III -
III -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
2
3
4
5
2
6
1
8
9
10
11
13
14
15
16
17
vm
-------
LIST OF FIGURES
Number
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
V -
VI -
VI -
VI -
13
14
15
16
17
18
19
20
21
22
23
1
2
3
Description
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Upper Potomac Estuary, November 6,
1969 ...
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Upper Potomac Estuary,
November 10, 1969
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Upper Potomac Estuary,
November 12, 1969 . . . ....
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Upper Potomac Estuary.
November 17, 1969
Temporal Dye Profiles, Upper Potomac Estuary,
FWQA Dynamic Estuary Model (High Water Slack Data)
Temporal Dye Profiles, Upper Potomac Estuary,
FWQA Dynamic Estuary Model (Low Water Slack Data)
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Anacostia River, April 23, 1970.
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Anacostia River, April 27, 1970. •.
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Anacostia River, April 29, 1970.
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Anacostia River, May 4, 1970.
FWQA Dynamic Estuary Model Dye Simulation and
Verification, Anacostia River, May 7, 1970.
Thomann Model Dye Simulation and Verification,
1965 Dye Release, June 14, 1965
Thomann Model Dye Simulation and Verification,
1965 Dye Release, June 22, 1965
Thomann Model Dye Simulation and Verification,
1965 Dve Release, June 26, 1965
Page
V
V
V
V
V
V
V
V
V
V
V
VI
VI
VI
- 21
- 22
- 23
- 24
- 25
- 26
- 30
- 31
- 32
- 33
- 34
- 2
- 3
- 4
IX
-------
LIST OF FIGURES
Number
VI -
VI -
VI -
VI -
VI -
VI -
VI -
VI -
VI -
VII -
VII -
VII -
4
5
6
7
8
9
10
11
12
1
2
3
Description
Thomann Model Dye Simulation and Verification,
1965 Dye Release, July 1, 1965
FWQA Dynamic Estuary Model Dye Simulation and
Verification, 1965 Dye Release, June 14, 1965 .
FWQA Dynamic Estuary Model Dye Simulation and
Verification, 1965 Dye Release, June 26, 1965 .
FWQA Dynamic Estuary Model Dye Simulation and
Verification, 1965 Dye Release, July 1, 1965
FWQA Dynamic Estuary Model Dye Simulation and
Verification, 1965 Dye Release, July 8, 1965
Thomann Model Chloride Simulation and Verifi-
cation, 1966 Chloride Data, Potomac Estuary at
Possum Point, Va
Thomann Model Chloride Simulation and Verifi-
cation, 1969 Chloride Data, Potomac Estuary at
Nanjemoy Creek
Thomann Model Chloride Simulation and Verifi-
cation, 1969 Chloride Data, Potomac Estuary at
Wicomico River
FWQA Dynamic Estuary Model Chloride Simulation and
Verification, Potomac Estuary, July-December 1965
Effects of Decay Rates, Dynamic Estuary Model
Effects of Decay Rates , Thomann Model ....
Effects of Segmentation, Thomann Model Dye
Page
VI
VI
VI
VI
. VI
VI
VI
VI
VI
. VII
. VII
- 5
- 7
- 8
- 9
- 10
- 1?
- 14
- 15
- 17
- 2
- 3
Simulations, November 6, 1969 VII - 7
VII - 4 Effects of Segmentation, Thomann Model Dye
Simulations, November 12, 1969 VII - 8
VII - 5 Effects of Segmentation, Thomann Model Dye
Simulations, November 17, 1969 VII - 9
-------
LIST OF FIGURES
Number Description Page
VII - 6 Effects of Dispersion Coefficient, Thomann
Model Dye Simulations, November 6, 1969 . . . VII - 11
VII - 7 Effects of Dispersion Coefficient, Thomann
Model Dye Simulations, November 12, 1969 . . . VII - 12
VII - 8 Effects of Dispersion Coefficient, Thomann
Model Dye Simulations, November 17, 1969 ... VII - 13
VII - 9 Effects of Dispersion Coefficient, Thomann
Model Chloride Simulations, Potomac Estuary at
Nanjemoy Creek v II - 16
VII - 10 Relationship of Dispersion Coefficient to
Chlorides Based upon 1969 (3,000 - 5,000 cfs)
Data VII - 17
VII - 11 Effects of Dispersion Constant (CiJ on Dynamic
Estuary Model Simulations, Point Discharge . . VII - 19
VII - 12 Effects of Dispersion Constant (Cj on Dynamic
Estuary Model ,Chloride Simulations VII - 21
VII - 13 Effects of Advection Factor (a), Thomann Model
Dye Simulations, November 6, 1971 VII - 26
VII - 14 Effects of Advection Factor (a), Thomann Model
Dye Simulations, November 12, 1969 VII - 27
VII - 15 Effects of Advective Solution Technique,
Dynamic Estuary Model,Chloride Simulations . . VII - 29
VII - 16 Dispersion Coefficient vs Flow, Thomann Model,
Upper Potomac Estuary VII - 31
Appendix
A - 1 Tidal Data, Potomac Estuary at Washington,
November 1969 A - 7
A - 2 Tidal Data, Potomac Estuary at Washington,
November 1969 4-8
A - 3 Tidal Data, Potomac Estuary at Washington,
November 1969 A ~ 9
xi
-------
LIST OF FIGURES
Number Page
A - 4 Freshwater Flows, Potomac River at Great Falls,
November 1969 A - 10
A - 5 Dye Isopleth, Upper Potomac Estuary, Low Slack
Data, November 1969 A - 14
A - 6 Dye Isopleth, Upper Potomac Estuary, High Slack
Sampling Data, November 1969 A - 15
A - 7 Transect Dye Sampling Summary, Upper Potomac
Estuary, November 11, 1969 A - 16
A - 8 Transect Dye Sampling Summary, Upper Potomac
Estuary, November 18, 1969 A - 17
A - 9 Transect Dye Sampling Summary, Upper Potomac
Estuary, November 20, 1969 A - 18
A - 10 Dye Loss Rate, Upper Potomac Estuary, November
1969 A - 21
A - 11 Freshwater Flows, Anacostia River, April-May
1970 A - 27
A - 12 Dye Isopleth, Anacostia River, High Slack
Sampling, April-May 1970 A - 29
A - 13 Dye Isopleth, Anacostia River, Low Slack
Sampling, April-May 1970 A - 30
A - 14 Dye Loss Rate, Anacostia River, April-May 1970 . A - 33
A - 15 Transect # 1 - Key Bridge A - 38
A - 16 Transect # 2 - 14th Street Bridge A - 39
A - 17 Transect * 3 - Mains Point A - 40
A - 18 Transect * 3A - Hunter Point A - 41
A - 19 Transect * 4 - Bellevue A - 42
-------
LIST OF FIGURES
Number Description Page
A - 20 Transect # 4A - Goose Island A - 43
A - 21 Transect # 5 - Woodrow Wilson Bridge .... A - 44
A - 22 Transect # 5A - Rosier Bluff A - 45
A ,. 23 Transect # 6 - Broad Creek A - 46
A - 24 Transect # 7 - Piscataway Creek A - 47
A - 25 Transect # 8 - Dogue Creek A - 48
A - 26 Transect # 8A - Gunston Cove A - 49
A - 27 Transect # 9 - Hallowing Point A - 50
A - 28 Transect # 10 - Indian Head A - 51
XI 1 1
-------
I - 1
CHAPTER I
INTRODUCTION
A. PURPOSE AND SCOPE
Mathematical models are becoming an increasingly important "tool"
for predicting, under a variety of conditions, water quality behavior
in an estuary. The purpose of this report is to present recent CTSL
studies on use of these models in the Potomac Estuary, specifically,
the Thomann Model (time-dependent version) and the FWQA Dynamic Estuary
Model.
Numerous computer runs were made with both models in an attempt to
make a reasonably accurate simulation of dye profiles observed in the
Potomac Estuary following a 13-day continuous release during November 1969
and of observed dye profiles in the Anacostia River following a 7-day con-
tinuous release during April 1970. In addition to model verification,
consideration was given to: (1) a comparison of modeling approaches,
(2) the limitations of each model, (3) input data requirements, and (4) a
detailed sensitivity analysis to determine which input parameters had the
greatest effect on model output. Hopefully, investigations of each of
these factors will assist in future modeling efforts by defining the
limitations and applicability of each model and also by indicating where
expenditures for necessary data refinement are warranted.
While mathematical models have been developed for the entire Potomac
Estuary, most studies in this report pertain to the 40-mile reach of the
upper estuary extending from Key Bridge to Sandy Point (Figure 1-1).
-------
POTOMAC RIVER TIDAL SYSTEM
lEOtNO
A USGS STREAM GAGl
D USC & GS TIDAL GAG£
SCAL£ N HLCS
POTOMAC ESTUARY
FIGURE
-------
I - 3
B. ACKNOWLEDGEMENTS
The assistance and cooperation extended by the personnel at the
District of Columbia's Blue Plains Sewage Treatment Plant, the Washington
Suburban Sanitary Commission, and the U. S. Geological Survey, Washington,
D. C. contributed to successful completion of this study and is gratefully
acknowledged.
-------
II - 1
CHAPTER II
SUMMARY AND CONCLUSIONS
In its continuing study of the Potomac Estuary, the Chesapeake
Technical Support Laboratory (CTSL) has utilized mathematical models
to predict water quality response to given hydrographic, demographic,
and other physical, chemical, and biological constraints. In the course
of model application, many problems associated with verification became
evident almost immediately. The findings and conclusions which evolved
during CTSL verification studies of both a nontidal model (Thomann) and
a tidal or real-time model (FWQA Dynamic Estuary) for the Potomac are
reported as follows:
1. The primary model verification effort involved simulation of a
13-day continuous dye release during November 1969 in which 4,454 pounds
of diluted (6 percent) Rhodamine WT dye were discharged into the Potomac
Estuary at the District of Columbia's Blue Plains Sewage Treatment Plant.
2. Using dispersion coefficients varying from 2.0 mi^/day to 5.0
mi^/day, the Thomann Model appeared to simulate the 1969 Potomac dye study
satisfactorily in terms of peak concentrations and longitudinal dye dis-
tribution. Shortcomings found in the Thomann Model simulations were pro-
nounced "peaking" during the early phase of the release and insufficient
movement of peak dye concentration. Both of these problems were probably
caused by the basic analytical (nontidal) solution employed by this model
since refinement in the segmentation did not appear to overcome them.
-------
It - 2
3, A comparison of observed spatial profiles and those obtained
from the Dynamic Estuary Model indicated that, except for minor
differences in peak dye concentrations near the release point and the
rate of downstream transport, the Dynamic Estuary Model was also ade-
quately verified using the 1969 Potomac dye study data. For this
verification, the dispersion coefficient ranged from about 1.0 to
2.0 mi2/day depending on the existing tidal velocities and depths.
4. In order to define the mass transport characteristics of the
Anacostia Tidal River better and also to provide data upon which confir-
mation of dispersion rates and other model input for this tidal system
could be based, a 7-day continuous dye release was conducted during
April 1970 at the Bladensburg Marina, above the D. C.-Maryland line.
5. With the exception of inadequate downstream movement of the
simulated peak concentration, both the Dynamic Estuary and Thomann Models
appeared to be capable of closely predicting the observed dye distribution
in the Anacostia River.
6. A Potomac dye study conducted in 1965 was successfully simulated
with both the Dynamic Estuary and Thomann Models. The substantially lower
freshwater inflows which occurred during this study resulted in the use of
lower dispersion coefficients (1.0 - 2.0 mi^/day) for the Thomann Model.
The dispersion coefficients remained the same in the DEM.
-------
II - 3
7. Based on all of the dye simulation studies, it can be concluded
from the standpoint of model verification that, in general, maximum
difficulty was experienced in the immediate area of the release point.
However, this could have been expected since complete mixing had not yet
occurred in the prototype but had to be assumed in both of the models
(neither model can treat vertical concentration gradients), and because of
the difficulty in selecting representative sampling points.
8. Chloride profiles observed in the Potomac Estuary during 1966
and 1969 were simulated using the Thomann Model. Historical station
data, showing annual fluctuations in observed and predicted chlorides,
indicated very good agreement when dispersion coefficients ranged
between 1.5 - 14.0 mi^/day during relatively low-flow periods and 2.0 -
20.0 mi^/day during the higher flow periods of 1966 and when they ranged
between 2.0 - 16.0 mi^/day for the entire year of 1969.
9. The following conclusions can be drawn based upon the chloride
simulations performed with the Thomann Model:
a. A considerable range in the dispersion coefficients can be
expected where there are great salinity increases in a longitudinal
direction. The pronounced gradients, rather than the actual salinity
concentrations, require much larger dispersion coefficients for the
Thomann Model if meaningful data are to be obtained.
b. Dependence of dispersion coefficients on freshwater inflow rates
was not as evident for chloride as it was for dye simulations. In fact, an
apparent anomaly appeared since maximum chloride intrusion occurred in the
-------
II - 4
Potomac Estuary during low-flow periods whereas the use of high dis-
persion coefficients normally associated with high-flow periods was
required in the model to produce similar results. Thus, the dispersion
term in the Thomann Model may have to be evaluated and related to flow
in a different manner for constituents dispersing upstream than for
those dispersing primarily downstream.
10. The observed chloride data, measured longitudinally during a
period of relatively steady-state flow (July-December 1965), were
simulated in the Dynamic Estuary Model. Special problems involving both
the advection and dispersion components arose, probably as a result of the
unusually high concentration gradients.
11. The following conclusions can be drawn based upon the chloride
simulations performed with the Dynamic Estuary Model:
a. The dispersion term employed in the Dynamic Estuary Model (C4)
must be increased over an order of magnitude in the seaward portion of the
model network to reflect the increasing chloride concentration gradients
and to obtain sufficient mass transfer across the seaward boundary. The
approximate range in dispersion coefficients used for simulation of
chlorides was from 1.0 mi^/day to 20.0 mi^/day for representative depths
and tidal velocities.
b. Determination of the proper amount of constituent advected from
one node to another in the model becomes quite critical in areas with high
concentration gradients. The quarter-point solution method for advective
transport, which generally produces acceptable accuracy and low numerical
-------
II - 5
mixing, did not yield satisfactory comparisons for chloride simulations
in the Potomac. The use of a third-point advective concentration within
a given channel was found to yield more favorable results.
12. Undoubtedly, many of the difficulties associated with application
of either the Thomann or Dynamic Estuary Model to simulate the movement of
chlorides are the result of representing a three-dimensional stratified
system with a one-dimensional model. This further points out the importance
of hydrodynamic behavior and the fallacy of using a model to solve a problem
for which it was not designed.
13. In order to determine where additional refinement of model input
may be warranted, a detailed sensitivity analysis of several factors
pertinent to the Thomann and/or Dynamic Estuary Models was performed.
14. Based upon the results of this sensitivity analysis with the
Thomann ,Model, the following represent a listing, in decreasing importance,
of the sensitivity of each variable:
a. Dispersion coefficient (K),
b. Decay rate,
c. Segmentation, and
d. Proportionality factor (a) used for advective transport.
15. Of the various input parameters investigated for the Dynamic
Estuary Model, the decay rate and the solution technique for advective
transport appeared to be the most sensitive in affecting the model's
predictions. With the exception of simulating salinity (chlorides),
the least sensitivity was identified with the dispersion coefficient.
-------
II - 6
While the hydraulic solution was relatively sensitive to the Manning
roughness coefficients, the quality predictions were insensitive to them
as well as to the tidal range specified at the seaward boundary. Based
on limited data, it appeared that the Dynamic Estuary Model was con-
siderably more sensitive to network detail than the Thomann Model.
16. Utilizing an approach where simulated data from both tidal and
nontidal models were compared, relationships of dispersion coefficients
(as used in the Thomann Model) to freshwater flows were formulated for
the Potomac Estuary. For the flow range investigated (930 cfs ^o 20,000
cfs) it was determined that dispersion coefficients (K) varied directly
with flow in accordance with the following equations:
Upstream from B1ue P1 aJ ns
K = 0.195 Q°'34
Blue Plains to Occoquan Bay
K = 0.027 Q°-63
where:
K = dispersion coefficient (mi^/day) and
Q - freshwater flow (cfs).
17. The primary disadvantage of the Thomann Model or any nontidal
model is the greater significance of dispersion coefficients for an
estuarine system and the need to relate them to freshwater flows, sal in;
gradients, and other factors.
18. Another deficiency encountered with the Thomann Model, as evi
denced by certain chloride simulations and the sensitivity analysis was
-------
II - 7
the apparent deemphasis of both tidal and nontidal advective transport
as a result of the model's strong dependence on dispersion. Moreover,
the fact that a flow sequence is routed through the system instantaneously
indicates that the hydraulic conditions influencing advection are based
strictly on a velocity (Q/A) relationship and not on volume displacement.
19. Other important disadvantages of the Thomann Model are its
inability to (1) branch in a lateral direction and (2) link more than two
constituents.
20. Significant advantages of the Thomann Model over the FWQA Dynamic
Estuary Model as both models are presently programmed are (1) its less
stringent input requirements, (2) its ability through the Namelist I/O
option to change input variables, such as flow on a daily basis, and
thereby readily simulate interseasonal conditions, and (3) the capability
of running several alternative data decks back-to-back with a minimum of
effort. In short, one can generate considerably more data in much less
time with the Thomann Model.
21. In addition to more demanding input requirements, another dis-
advantage of the Dynamic Estuary Model is the fact that it is quite costly
and time consuming to link different hydraulic conditions if simulation of
seasonal or annual quality characteristics is desired.
-------
II - 8
22. Because the Dynamic Estuary Model is a "real-time" system, it
can predict the effect of tidal exchange and excursion on the distribution
of a pollutant as well as other intratidal cycle variations in water
quality and it is significantly less dependent on an empirically derived
dispersion term. Other major advantages of this model are its ability to
branch in a lateral direction and thereby allow simulation of water quality
behavior within embayments and to consider six separate constituents
either dependency or independently of one another.
-------
Ill - 1
CHAPTER III
DESCRIPTION OF THE STUDY AREA
The Potomac River Basin, draining 14,170 square miles, is the
second largest watershed in the Middle Atlantic States. Its tidal
portion begins at Little Falls in the Washington Metropolitan Area
and extends 114 miles southeastward to the Chesapeake Bay. The
section of the estuary discussed in detail in this report is the
40-mile reach extending from Key Bridge in Washington to Sandy Point
which is located downstream from Quantico, Virginia (Figure 1-1).
The estuary is less than 200 feet wide near its upper end at
Chain Bridge and widens to approximately 4,000 yards at Sandy Point.
A shipping channel with a minimum depth of 24 feet is maintained from
Washington to the Chesapeake Bay. The major embayments along the upper
Potomac Estuary and their surface areas are:
Embayments Surface Area
PI ?
Occoquan-Belmont Bays 218 x 10 ft
Mattawoman Creek 75 x 106 ft2
Gunston Cove 65 x 106 ft
Piscataway Creek 36 x 106 ft2
Anacostia River 31 x 106 ft
Quantico Creek 30 x 106 ft2
Except for the main channel and a small reach below Chain Bridge where
depths up to 80 feet occur, the estuary is relatively shallow with an
average depth of about 15 feet. The embayments generally have average
depths of 5 feet or less.
-------
Ill - 2
The upper 20 miles of the study reach (Chain Bridge to Marshall
Hall) contain fresh water whereas the lower 20 miles (Marshall Hall to
Sandy Point) form the transition zone from fresh to brackish water.
The average tidal range at Washington is 2.9 feet, with high and low
water occurring about +6 and +7 hours respectively.*
Physical data for the entire Potomac Estuary are summarized in
Figure III-l (cross-sectional area versus distance below Chain Bridge),
Figure III-2 (accumulative volume versus distance below Chain Bridge),
and Figure III-3 (accumulative surface area versus distance below Chain
Bridge). More detailed information was recently published by CTSL in a
separate report [1].
* Referenced to Piney Point (River Mile 99)
-------
= V3MV TVNOU33S SSOiD
-------
8
-o
a
o
-8z
-8
-------
o
-8
-------
-------
IV - 1
CHAPTER IV
DESCRIPTION OF MATHEMATICAL MODELS
A. THOMANN MODEL
The Thomann Model [4] was originally developed in 1963 as a one-
dimensional, steady-state, BOD-DO model specifically for the Delaware
Estuary. A time-dependent version of this model [5] and a chloride
model [6] were developed in 1966-1967 by General Electric under con-
tract to the Federal Water Pollution Control Administration.* Each of
the above models was applied to the Potomac Estuary shortly after
development.
The time-dependent Thomann Model employs a segmented network of
the water body under consideration and utilizes a finite difference
approach to solve the basic mass balance equations. For the case of
BOD and DO, these equations can be written as follows:
nan a,] + c^-.] = EJ,]
HAH [c,] t [£.] - [r, cs, * P, - d, L,]
where [I JJ denotes a square matrix of order n and [ ] denotes a column
vector of dimension n (n is equal to the number of segments in the system),
The total number of equations and unknowns equals 2n. The components
of matrices A and B are defined as:
a. Q + E
A = R - ' J i
V i-i Bi, i-r M.
V.
Now Environmental Protection Agency
-------
IV - 2
dj
A - - Ei + 1 "*1 *
A
i , i + 1 i , i + 1 \Tj
The remainder of the terms are defined below:
L = BOD
C = DO
J- = forcing function or loading in section i
r. =? reaeration coefficient
J
C = saturation value of DO
d. = decay coefficient
J
P.. = other sources and sinks of oxygen
V. = volume of segment i
Q. = net flow
\J
E.J = eddy exchange coefficient
a. • <(>. = advection factors
I J 5 I
Of special importance are the eddy exchange coefficient and the
advection factors. The eddy exchange coefficient is used to describe the
tidal and other nonadvective effects on the transport of a constituent.
Between sections i and i + 1, it can be computed as follows;
F = i , J x i , j ,
i, j 1 /. . , v x 27.878 x 10°
2 ai Li + 1;
-------
IV - 3
where:
K. . = eddy diffusion coefficient between sections i and i + 1
"i > J
(mi2/day)
A. . = cross-sectional area at the boundary of segments i and
' > J
i + 1, and
L. = length of segment i
The purpose of the advection factor is to serve as a means of com-
puting the concentration of a constituent at the interface of two segments
by "weighing" the concentrations in these two adjacent segments. In order
to guarantee positivity in the solution, the advection factor takes on the
following definition:
Ei - 1 ' Ei '
Qi - 1 , J ' Qi , J
'i > J
if . . > 0.5 then . . = 0.5
< i J ' > J
for the first section:
in which case a = 1.0 (pure advection). If the concentrations in
the adjoining sections are to be weighed equally (pure dispersion both c
and a are 0.5.
-------
IV - 4
The simultaneous, linear, first-order differential equations
employed by the Thomann Model express the time rate of change of
pollutant concentration as a function of the advection and dispersion
components at each segment interface and sources and sinks within each
segment. These equations are numerically integrated by a fourth-order
Runge-Kutta procedure whereby the truncation error is kept within some
preset allowable value by constant adjustment of the time step size.
The solution yields a mean tide concentation of a particular consti-
tuent for every segment.
Since the Thomann Model does not have a "real-time" solution where
tidal movement is explicitly considered in the mass transfer equations,
the dispersion coefficient (K) must be an "all-inclusive" term that can
grossly represent tidal behavior. Another source of uncertainty is
numerical dispersion which is introduced by the assumption of a completely
mixed finite volume.
-------
IV - 5
B. FWQA DYNAMIC ESTUARY MODEL
The DEM represents the two-dimensional flow and mass transfer within
an estuary by a network of interconnecting junctions and channels.
Uniformity must be assumed only in the vertical direction. The hydraulic
component of the model essentially solves the equations describing the
propagation of a long wave (tidal) through a shallow water system. When
the tidal conditions such as amplitude, period, etc. existing at the sea-
ward boundary are known, this solution can be obtained from the one-
dimensional form of the equations of motion and continuity. The equation
of motion is:
3u 3u „, , 3H
3t = ~U97 -K/U/U -9 a?
where:
u = velocity along x axis
x = distance along x axis
H = water surface elevation
g = acceleration of gravity
K = frictional resistance coefficient
t = time
The equation of continuity can be expressed as:
-------
IV - 6
The equation of motion is applied to the channel elements to predict
velocity and flow and the continuity equation is associated with the
junctions and accounts for tidal fluctuations in the water surface elevation
(head) and corresponding changes in volume. Both of these differential
equations are converted to finite difference form and solved by numerical
integration techniques (predictor-corrector method) to yield a "real-time"
hydraulic solution. The time step used is normally very small, i.e., 1-5
^minutes, as dictated by the network and by numerical stability. The solution
will converge for a given set of boundary conditions (including tides and
freshwater flow rates) to a dynamic equilibrium having velocities, flows,
and heads repeated at intervals equal to the specified tidal period.
The quality component of the FWQA model incorporates the two basic
transport mechanisms; namely, advection and diffusion, and requires the
dynamic steady-state hydraulic solution as input. Advective transport is
primarily a hydraulic mechanism that moves the constituent in the direction
of flow. It can be represented by the following two equations:
3C _ ,. 3C
at 3x
or in terms of mass and in finite difference form
where:
c* = concentration in advected water
U = channel velocity, and
A = channel area
-------
IV - 7
The determination of c* can present special problems such as computa-
tional instability and "numerical mixing." Previous studies have
indicated that an advected concentration equal to that at one-quarter of
the channel length, measured in the direction of decreasing gradient,
generally proved satisfactory.
Diffusion (eddy) is represented in the model as a physical-chemical
transport mechanism dependent only upon concentration gradients. Mathe-
matically, it can be expressed as:
l£ = % 32C
3t 3x^"
or again in terms of mass
AM _ v. Ac
At ~ ™ x
where:
Ac = concentration gradient within a channel
x = channel length, and
K = diffusion coefficient
The diffusion coefficient has a dimension of length squared over
time and can be defined by the following equation:
K = Ci,/U/R
where:
C4 = a constant
U = mean channel velocity, and
R = hydraulic radius of channel.
-------
IV - 8
As currently programmed, a maximum of six constituents can be
handled simultaneously in the FWQA model. They may be either conser-
vative or nonconservative and may be interrelated in any mathematically
describable fashion. Recent modifications have enabled this model to
quantitatively consider terms other than carbonaceous BOD oxidation and
reaeration in the DO budget. For example, nitrification, benthic oxygen
demand, and phytoplankton photosynthesis and respiration have also been
included.
The model will compute constituent concentrations throughout the
system by means of a numerical integration solution of the above finite
difference equations describing advection and diffusion as well as those
expressing degradation and the constituent's other sources and sinks.
While maintaining mass continuity, the solution proceeds from channel to
channel and junction to junction performing the appropriate transfers
over a specified time step.
In order to minimize "induced dispersion" or numerical mixing, ample
consideration should be given to the network layout and to selection of the
time step. Ideally, the ratio of fluid displacement (LJAt) to the channel
length (x) should approach unity.
-------
V - 1
CHAPTER V
MATHEMATICAL MODEL SIMULATIONS OF 1969-1970 DYE RELEASES
A. THOMANN MODEL
1. Simulations and Verification
a. Potomac Dye Study
It should be noted at the outset that all mathematical model verifi-
cations involving the 1969 dye release data were based upon a dye loss
rate of 0.03 per day as computed in Section A-3c of the Appendix. While
other values for loss rate were considered in the Thomann and Dynamic
Estuary models, the most favorable output was obtained with the 0.03 per
day rate. Moreover,si nee neither background nor boundary data were
collected prior to this dye study, the upper and lower boundary concen-
trations as well as a uniform background concentration of 0.1 ppb were
arbitrarily specified in both models to compensate for differences between
observed and discharged dye quantities. An evaluation of the sampling
data collected from areas where dye was nonexistent and from background
data collected during the 1965 Potomac dye study provided some insight
into the magnitude of these concentrations.
The expanded segmented network used for the Potomac Estuary Thomann
Model is shown in Figure V-l. Model simulations discussed in this section
were made using the upper 35 segments between Chain Bridge and Mattawoman
Creek.
During the simulation and verification studies, special consideration
was given to the following:
1) Advection factors (, a), and
2) Dispersion coefficient (K).
-------
A/
THOMANN MATHEMATICAL MOOtl SI .McN'S
ORIGINAL 28 SEGMENTS
EXPANDED 73 SEGMENTS
SCAU N ML£S
POTOMAC ESTUARY
FIGURE V-i
-------
V - 3
As described previously, the advective proportionality factors are
used to determine the constituent concentration at a segment interface
as a function of the concentrations in the adjoining segments. This
concentration, when multiplied by a net flow across the interface, yields
the quantity of constituent advected from one segment to another. Theo-
retically, a must range between 1.0 (nontidal or pure advection system)
and 0.5 (pure tidal system with no net adve,ctive flow). In the original
Thomann time-dependent model, was computed from the ratio E/Q, where
E is the eddy exchange coefficient (ft^/day) and Q is net flow and a was
equal to 1 - . Since there was no stipulation on the magnitude of a, a
program modification was made to maintain its value between these specified
limits. A sensitivity analysis of cc on model predictions is presented in
Chapter VI.
The major problem involved with verifying the Thomann Model was esti-
mating the longitudinal dispersion coefficient (K). This is a complex
parameter affected by (1) freshwater inflow rates, (2) salinity gradients,
(3) estuary geometry, and (4) tidal conditions.
The relationship between freshwater flow rates and dispersion coeffi-
cients is presented in Chapter VI. Salinity has a very pronounced effect
on dispersion due to density gradients causing significant changes in the
boundary shear velocity distribution. As reported by Harleman [7], dis-
persion coefficients calculated for freshwater and high salinity areas in
a constant area estuary (Rotterdam Waterway) were 0.5 mi2/day and 40 mi^'
respectively.
-------
V - 4
The geometry of the channel and the tidal conditions also affect the
extent of dispersion although quantitative relationships among the three
have not been determined in this report. A sensitivity analysis of the
dispersion coefficient in the Thomann Model is presented in Chapter VI.
In an attempt to verify the Thomann Model, several runs were made
using the 1969 dye release data, each with different dispersion coeffici-
ents. The most favorable agreement between observed and simulated
spatial profiles was noted utilizing the coefficients shown below:
Segment Time Period
Numbers November 1-5 November 6-30
1 - 13 (upstream of
discharge) K = 2.0 K = 3.0*
14 - 37 (downstream of
discharge) K = 3.0 K = 5.0*
* Dispersion coefficients were increased after November 5, to reflect
the increased freshwater inflows and were increased farther down-
stream to reflect geometry and salinity changes.
The simulated spatial profiles obtained from the Thomann time-
dependent model and the observed profiles at high- and low-slack tide
are shown in Figures V-2 through V-6 for 5 different days of the study
period. Major emphasis during model verification studies was placed
upon closely simulating dye peaks, both spatially and in magnitude, and
achieving similarly shaped curves. It was also important that simulated
profiles generally fall within high- and low-slack water observed data
since they do represent mean tide conditions. As can be seen in these
figures, acceptable agreement between prototype and model data was
-------
V - 5
generally obtained but certain discrepancies did arise. The primary
shortcoming in the Thomann Model simulations appeared to be the
pronounced "peaking" that occurred during the early period of the
study. The simulated profiles for November 6 (Figure V-2), November 7
(Figure V-3), and November 10 (Figure V-4) show extremely sharp and
somewhat greater peaks as compared to prototype data. Another diffi-
culty encountered with some of the Thomann Model simulations was
insufficient downstream movement of peak concentrations. This is
evident in Figures V-3, V-5, and V-6.
A refinement in the estuary segmentation did not resolve the above
problems. Increasing the dispersion coefficient lowered the peaks but
the configuration of the curve was adversely affected for model verifi-
cation. It appeared that all of the problems associated with simulation
of dye peaks were created by the nontidal approach or the analytical
mathematical solution of the basic equations employed by the Thomann
Model.
A station history or temporal verification of the dye release data
with the Thomann Model simulations discussed previously is shown for four
selected sampling stations in Figure V-7.
-------
r
15
y
LL
cr
I
2
Q;
UJ
Q.
\
X
B ^
1 i
§ S
i i i
*J "1 *
d d d
(qdd)
31Q
3
OJ
d
\
\
\
\
\
d i
-------
s
d
(<*")
3AO
3 §
-------
-------
1-3
9 >•
I 2
S < ;
i I s
* 2 8
S
I
I
I
-------
O
m 2
-------
5?
UJ
o *
2 a
5 &
UJ D
I-
cr
CD
z
O
to
d o
in uj
i 5
P a
§ >
CO (T
r
q
r ONOO
CO
z o
< o
I <0
1 :
fO "> i.
^ s.
z - /
0 z /c
t- QC
< y <
H >
to tr ^ ,
<]
0
O
3
i
c
c
3
1 1
q - c
- 0
CM
tf>
5
a
11
UJ
Z
. g t-
)
>
O
z
$
o
a<
to
M
CTi uj
5 i
l- tr
r
o
; ONOO
r-
l
H
UJ
(T
n
o
o
(M
I
Z
O (-
qdd•ONOD
10
UI
Z
-------
V - 12
b. Anacostia Dye Study
The segmented network applied to the Anacostia tidal system for
modeling purposes is presented in Figure V-l. The problem of veri-
fying the Thomann Model based upon 1970 Anacostia dye study data was
again essentially one of evaluating a dispersion coefficient to yield
the best agreement between observed and simulated data. The dye loss
rate was specified as 0.05 per day for all simulation runs. After
several trial runs, it appeared that a K value of 0.7 mi^/day produced
the most satisfactory results. Attempting to vary the dispersion
coefficient longitudinally or relating it to freshwater flow, as was
done with the Potomac, did not seem to improve the simulated data.
Observed spatial profiles and simulated data from the Thomann Model
are shown in Figures V-8 through V-12. An analysis of these figures
indicates that the basic configurations of the two curves are generally
similar for various times in the study, especially those portions
representing the leading edge of the dye cloud. Moreover, relatively
close agreement was obtained between observed and simulated peak dye
concentrations insofar as magnitude was concerned. Again, a major
shortcoming of the Thomann Model predictions, which can be seen in
several of the figures, was an insufficient rate of longitudinal peak
movement.
The net advective transport of the dye cloud's centroid was not
accurately simulated with the range of dispersion coefficients investi-
gated. As was noted with the Potomac dye study, the effects of such
factors as extreme and "flashy" flow variation and unusually high or
-------
THOMANN MODEL DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
APRIL 23. 1970
9-
8-
7 -
6-
a.
a.
Jjg
O
4-
3-
2-
LOW SLACK (OBSERVED)
HIGH SLACK (OBSERVED)
MEAN TIDE (PREDICTED)
456
MILES FROM POTOMAC
1
FIGURE .Z-8
-------
THOMANN MODEL DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
APRIL 27, 1970
10-
9-
8-
7-
6-
4-
3-
2-
LOW SLACK (OBSERVED)
HIGH SLACK (OBSERVED)
MEAN TIDE (PREDICTED)
I
2
I
3
r i i
456
MILES FROM POTOMAC
I
7
FIGURETT-9
I
8
-------
THOMANN MODEL DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
APRIL 29. 1970
-LOW SLACK (OBSERVED)
lO-i
9-
8-
7-
6-
-o
a
a
'5-
4-
3-
2-
HIGH SLACK (OBSERVED)
MEAN TIDE (PREDICTED)
\
I
3
I I I
456
MILES FROM POTOMAC
I
9
FIGURE 1- 10
-------
9-
8 -
7-
6-
5-
Q
4-
3-
2-
THOMANN MODEL DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
MAY 4. 1970
10-1
LOW SLACK (OBSERVED)
MEAN TIDE (PREDICTED)
\ I I i
3456
MILES FROM POTOMAC
I
7
FIGURE 3C- I
-------
THOMANN MODEL DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
MAY 7. 1970
10-1
9-
8-
7-
6-
>- 5
o
4-
3-
2-
I-
HIGH SLACK (OBSERVED)
MEAN TIDE ( PREDICTED )
I I I
456
MILES FROM POTOMAC
FIGURE 3T-I2
-------
V - 18
low tides with the corresponding changes in tidal excursion and advection
which generally accompany a long-term study are not adequately incorpo-
rated in the nontidal model and while the dispersion coefficient does
exert considerable influence, there are limitations present.
-------
V - 19
B. FWQA's DYNAMIC ESTUARY MODEL
1. Simulations and Verification
a. Potomac Dye Study
The network of junctions comprising the Dynamic Estuary Model for
the main Potomac are basically the same as those shown in Figure V-l.
The simulation data presented herein pertain to the 35 junctions
upstream from Occoquan Bay.
The verification of the Dynamic Estuary Model based upon 1969 dye
study data initially required a reliable representation of the hydro-
dynamics during the study period. For sake of convenience, only two
hydraulic conditions were simulated. The period from November 1-5
assumed an average flow of 1,886 cfs. The remainder of November was
assigned an average flow of 3,974 cfs. The actual tidal record at
Piney Point, Maryland, (near the seaward boundary) was obtained from the
U. S. Coast and Geodetic Survey for the month of November. A somewhat
typical tide, having a period of 12.5 hours, was selected and assumed to
recur continuously throughout the study period. Hydraulic runs using
different Manning coefficients were tried until the simulated tidal data
at Washington, including ranges and phasing, compared favorably with
corresponding observed data. Predicted tidal data at intermediate
stations throughout the estuary were also compared with observed data for
hydraulic verification.
-------
V - 20
Insofar as the quality program is concerned, consideration was
given to (1) appropriate dye loading rate, and (2) dispersion term
C4*. Since dye loading rates were computed fpr each 4-hour interval
of the 13-day release period, a similar procedure was used in the model.
Simulations were based on varying the dye concentrations in the effluent
every 4 hours until the 13th day when the dye release was shut off
entirely. While the dispersion coefficient is relatively unimportant
in this model as compared to the Thomann Model, the initial value of
2.5 used for Ci» was considered too low and was subsequently increased an
order of magnitude to 25. For a tidal velocity of 1.5 ft/sec and a
channel depth of 15 feet, a d, of 25.0 would translate to a dispersion
2
coefficient of 1.7 mi /day. This value yielded better results and
additional refinement in the dispersion coefficient did not appear
warranted.
The simulated dye profiles obtained from the Dynamic Estuary Model
for the conditions and assumptions described above are shown in Figures
V-13 through V-16. Also shown are high- and low-slack water sampling
data for the same 4 days of the study period. The spatial profiles
depicted in these figures indicate that the model was predicting dye
movement and concentration buildups satisfactorily. While simulated
As indicated previously, the actual dispersion coefficient is computed
internally from the relationship
E i C^ U d
where C4 is a constant, U is the mean velocity, and d is the depth
-------
l±J
§1
2 5
fc£
CC f- o>
LJ «« 5
^> Ul »
ft Q
UJ z
<
O ^
O
-------
o
"•*
U 2
s
Q
6
I 1 I
3 3 *
« in ">
i * 1
o Q
C U
=
«) ^ 2
as Z 2
O (/)!/)
O
o
\
\
\
-------
g " fc s
fc 5" a-
w *" ~
y z 1 i
5 92 i
^ i- Q- Sr
- 5
a
-3AQ
-------
IN
5 £i
4 S
ill 1
* ^
5 a ^ sj
5 3 9J 5i
B in
Hll
Q 0
Q Q Ul "
I
\
I
o
-3AQ
-------
CO
UJ
_J
\J_
2
a.
UJ
>
TEMPORAL D
>
ae
<
D
Si
UJ
0
^2
§
O.
a:
UJ
|
_i
2
•^
i
UJ
FWQA DYNAMIC
WOODROW WILSON BRI
1
V
f
(V
V
— 1 1
-8
" I
O
~f\J
UJ
K
_0
z
<
X
\;
17
\?
^
'(
O
n
i«
>
<
0 Q
o
oj
|
^
_o
'
\ i
o o o
t-
I
UJ
-------
g
£
_o
f)
O
g
I
o
' 3NOD
i
2
o
z
1
o
"n
i
>
UJ
cc
o
o
o
_o
I
o
2
oo
in O
qdd •
O
a
to
2
<
I
o
I
o
10
I
uj
Ul
cc.
u
i
o
_O
_o
o
"n
i
_0
\l
UJ
_o
I
o
qdd
qdd '
-------
V - 27
maximum dye concentrations were generally higher than prototype data,
they were not characterized by the pronounced "peaking" which occurred
with Thomann Model simulations and their spatial position agreed
favorably with observed data. The other consistent difference between the
observed and simulated profiles was the insufficient downstream dye trans-
port by the model over a given time interval. It is interesting to note
that a "real-time" solution permitted the effects of a short term dye
slug to be simulated as can be seen in Figure V-15. Considering the
difficulty of model verification by a comparison of spatial profiles for
specific slack-tide periods, the Dynamic Estuary Model has demonstrated
the capability to simulate the hydraulic and quality behavior in the Potomac
acceptably utilizing 1969 dye study data. Similar agreement between model
and prototype data can be shown when temporal variations are considered.
Data of this type (station histories) are presented in Figures V-17 and
V-18.
-------
V - 28
b. Anacostia Dye Study
The physical network of junctions applied to the Anacostia tidal
river for the Dynamic Estuary Model is shown in Figure V-l. This network
is identical to the one used in the Thomann Model and is comprised of 15
junctions with lengths averaging approximately 1/2 mile.
For all hydraulic simulations during the study period, an average
Potomac tide (12.5-hour period) was estimated from data recorded by the
U. S. Coast and Geodetic Survey at Piney Point. Some degree of hydro-
dynamic verification was lacking due to the absence of tidal gaging
stations in the Anacostia River. Visual observations of the tidal range
near the point of dye release and the model's tidal range predictions
appeared to be of similar magnitude; however, it could not be deter-
mined whether the simulation of tidal phasing and duration of rise and
fall throughout the Anacostia, or even the assumed Manning roughness
coefficients were accurate.
The dye study period was divided into four separate hydraulic
components as follows:
Average Average
Time Period Potomac Flow Anacostia Flow
April 20-28 30,000 180
April 29-May 11 15,000 83
May 12-18 7,800 145
May 19-28 6,800 72
-------
V - 29
The quality program for the Anacostia study was based on a constant
dye loading rate of 8.1 Ibs/day, a dye loss rate of 0.05/day and a uni-
form background concentration of 0.10 ppb. Moreover, the dispersion
term, d*, was assigned a value of 25.0. The dye profiles observed during
various days of the study and corresponding simulated data from the
Dynamic Estuary Model are shown in Figures V-19 through V-23. While the
general longitudinal dye distribution predicted by the model compared
favorably with prototype data, several figures were characterized by
insufficient downstream movement of simulated peak concentrations. On
one occasion (Figure V-19), the magnitude of the simulated peak was
excessive. A further evaluation of the input factors which may have
influenced these differences such as network geometry or dye loading
rates was made but with no apparent success. It appeared that a lack
of tidal data during the study period may have been partially respon-
sible, otherwise a better hydraulic representation would have been
obtained. Another possible cause of the differences noted could have
been the flow averaging concept used for each hydraulic simulation.
This averaging may tend to disregard or minimize the effects of the
"flashy" flows that occurred during the early phase of the study.
Improved agreement may have been realized in both models had trans-
ect sampling data been collected to correlate mid-channel concentrations
with cross-sectional averages. Normally, the differences resulting from
this omission would be especially acute near the release point where
incomplete mixing could be expected and where most of the model verifi-
cation difficulties were encountered.
-------
10-
9-
7-
a.
a.
O
FWQA DYNAMIC ESTUARY MODEL
DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
APRIL 23. 1970
OBSERVED LOW SLACK DATA
OBSERVED HIGH SLACK DATA
SIMULATED LOW SLACK DATA
SIMULATED HIGH SLACK DATA
T 1 1 T
3456
MILES FROM POTOMAC
FIGURE V-19
-------
-Q
a
a
I
U
10-
9-
8-
7-
6-
5-
4-
3-
2-
I-
FWQA DYNAMIC ESTUARY MODEL
DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
APRIL 27, 1970
•- OBSERVED LOW SLACK DATA
OBSERVED HIGH SLACK DATA
SIMULATED LOW SLACK DATA
SIMULATED HIGH SLACK DATA
1 1 I
456
MILES FROM POTOMAC
FIGURE V-20
-------
8-1
FWQA DYNAMIC ESTUARY MODEL
DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
APRIL 29, 1970
OBSERVED LOW SLACK DATA
OBSERVED HIGH SLACK DATA
SIMULATED LOW SLACK DATA
SIMULATED HIGH SLACK DATA
7-
6-
I 5-
4-
3-
2-
I I I
456
MILES FROM POTOMAC
FIGURE V-21
-------
FWQA DYNAMIC ESTUARY MODEL
DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
MAV 4 . 1970
OBSERVED LOW SLACK DATA
SIMULATED LOW SLACK DATA
3-1
2-
a
a
456
MILES FROM POTOMAC
FIGURE V-22
-------
FWQA DYNAMIC ESTUARY MODEL
DYE SIMULATION AND VERIFICATION
ANACOSTIA RIVER
MAY 7 . 1970
OBSERVED HIGH SLACK DATA
SIMULATED HIGH SLACK DATA
3-1
2-
I
LJ
Q
4 5
MILES FROM POTOMAC
FIGURE V-23
-------
VI - 1
CHAPTER VI
OTHER MATHEMATICAL MODEL SIMULATIONS
A. SIMULATION OF 1969 DYE RELEASE
The 1965 dye release data were incorporated in a series of model
runs for verifying both the Thomann and Dynamic Estuary mathematical
models under a different hydraulic regime than that which occurred
during the November 1969 dye study. The freshwater inflow rates during
the 1965 study period (June 10-July 15) averaged about 2,000 cfs, or
approximately one-half of the average November 1969 flows. Because of
this lower flow, the appropriate dispersion coefficients required to
verify the Thomann Model were expected to be significantly different.
1. Thomann Model
Figures VI-1 through VI-4 show the observed high- and low-slack
water sampling data for various days and the corresponding simulated
mean tide data using the Thomann Model. A dispersion coefficient of
2.0 mi2/day was used initially when flows were relatively high, and 1.0
mi2/day for the remainder of the study period when flows were much
lower. Although other dispersion coefficients and different spatial
variations were investigated for model verification, the above values
appeared to yield the closest agreement. It should be noted that these
coefficients were considerably higher than those obtained by Hetling and
O'Connell [3] using an analog computer solution based on temporal or
"station history" verification. Their computed dispersion coefficients
varied between 0.2 - 0.6 mi2/day for a similar reach of the upper Potomac
Estuary.
-------
. in
(M
V3
2
Q 3
(O
O)
1
1
1 1
O
I
I-
00
d
ID
O
-------
o
cc
Id
O
UJ
2 «£
o g
§ £
i *
<7> Q
• i *n
uj (o
^ o>
ID
*
(VI
(M
LJ
z
o
I
y S
00
(M
<\J
A
(VJ
f-fO
•«§
cr
o
3
.ID UJ
— CD
_<*)
oo
O
o
o
-------
o
L_
LJ
>
Q
Z
^
z
o
^
1
K^
z>
s
co
LxJ
£T
s
s
/
/
1
1
1
UJ | /
(0 /
< 1 /
UJ \ 1
-1 jOl 1
LJ $' \
QC -.\ \
10 v \
PO \ >
£s \/
Q- /\
/ \
s /
O> /
«•>
I
a;
o
-------
*
o
o *
3
I 3 Z
i o
<
o
U.
CC
I—
<
u
O
-Ol
- 9
00
CD z
P- 5
"I
to uJ
- 00
lij
_ —I
i
.<*>
-.
t
H
UJ
cr
O
-------
VI - 6
2. Dynamic Estuary Model
Two separate hydraulic conditions were assumed for the Dynamic
Estuary Model when attempting to simulate the 1965 dye study data.
Prior to June 23, the freshwater flow was assigned an average value of
2,687 cfs. The second hydraulic condition, which represented the
remainder of the study period, was based on a constant flow of 1,451
cfs. In general, a steadily declining flow was experienced during this
dye study.
The simulated 1965 dye profiles (high- and low-slack water) that
resulted from using the Dynamic Estuary Model along with observed data
are shown in Figures VI-5 through VI-8 for several days of the study
period. An examination of these figures showed relatively close agree-
ment in the spatial position, shape, and peak dye concentrations between
the prototype and model data. However, in order for the observed and
simulated dye mass characteristics to compare favorably, it was necessary
to treat the dye as a conservative substance since applying a decay rate
of either 0.034/day or 0.02/day in the model reduced the dye concentrations,
and thus the mass, beyond an acceptable level. As will be pointed out in
a subsequent chapter, the effects of decay rate are quite significant.
The reason that this problem occurred in the mass balancing of prototype
and model data cannot be explained except that the indeterminate fluores-
cent contribution from algae may have been responsible.
-------
r
k
(O
"^
5 2
O b
2
>- ^
0^ Q;
< Ul UJ
£><
LJ Z £
O £
Q D
2
< ^
a ui
o
00
2
o
_J
I/)
o
_J
Q
Ul
UJ
in
CD
O
1
1
•«».
\-
O
|
tf>
O
I
0
Ul
w
m
O
1
1
I
1
1
g
o
§
-J
in
!
Q
Ul
_l
2
I
x:
^
_
i/>
i
c
I
Q
S
_
i?
O o O
in ^ r»)
<1dd - NOI1VH1N3DNCO 3AQ
PJ
"
ro
"
-------
£ t
< £
—5 -T LJ
.-*'>(/)
t— <
tO Q UJ
UJ Z CJ
<
(M
o
oq
d
r-.
O
-------
Q O
O p
25
>- u.
5 c
< i
D :
Z o: 2
U
M
z b
r-
Uo
CO
UJ
O
cr
OQ
I
O
o o o o o
qdd -NOIiV«iN3DNOO 3AQ
ra —. q
c> ° o
-------
_ NOIlVaiN3DNOD 3AQ
-------
VI - 11
B. CHLORIDE SIMULATIONS - 1966 AND 1969
1. Thomann Model
Further simulation and verification studies with the Thomann Model
were made using 1966 and 1969 chloride data from the Potomac Estuary.
It was believed that chloride data would provide a sound basis for
estimating dispersion characteristics throughout the entire estuary
rather than just the upper portion for which dye data was available.
Moreover, the effects of density gradients created by varying chloride
concentrations on dispersion rates could be evaluated.
The most complete temporal record of 1966 chloride concentrations
in the Potomac was provided by the Virginia Electric and Power Company
generating plant at Possum Point. These data along with the simulated
chloride profiles at two representative model segments are shown in
Figure VI-9. Observed and simulated profiles show reasonable agreement
except for the almost continuous cyclic variation in the observed data.
Two sets of dispersion coefficients were used in the Thomann Model for
the 1966 chloride simulations. One set ranging from 2.0 - 20.0 mi^/day
was selected for the period January-May when freshwater inflows were
usually between 11,000 and 14,000 cfs. The other set which ranged from
1.5 - 14.0 mi^/day was used for the remainder of the year for 1,000 -
7,000 cfs inflows. The high range, of course, applied to the seaward
portion of the estuary where maximum density differences could be
expected.
-------
o
l/&»-S30IH01HO
-------
VI - 13
Chloride concentrations at the upper boundary (Chain Bridge) were
determined from D. C. Department of Sanitary Engineering sampling data.
Seaward boundary values were correlated to U. S. Coast and Geodetic
Survey data collected at Solomons, Maryland. Supplemental sampling
data were obtained from a Potomac nutrient study conducted by the
Chesapeake Bay Institute. The concentration of chlorides in wastewater
discharges was assumed to be 40 mg/1.
A comparison of simulated and observed profiles showing 1969 chloride
distributions is given in Figures VI-10 and VI-11 for sampling stations
in the middle and lower reaches of the Potomac Estuary. The data as
presented in these figures indicate relatively close agreement between model
predictions and observed chloride profiles, again except for the day-to-day
fluctuations in the observed data. Various sets of dispersion coefficients
were tried in verifying the 1969 chloride data and the best agreement was
obtained by using one set of coefficients ranging from 2.0 - 16.0 mi'2/day.
It should be noted that use of a single set of coefficients departs from
previous Thomann Model simulation studies discussed in this report wherein
dispersion was found to be directly related to freshwater flow rates.
While flows varied greatly during 1969, attempts to refine the dispersion
coefficients to reflect these flow changes did not prove successful.
-------
If
3 Q
t >
5 IT
D ^
3 £
O
o
UJ
UI
cr
O
I 8 S
i 5 g j
z z o ^
1 g ^ >
i ^ ° I
o>
-------
I
o
0
o
o
o
o
8
§ 1
o c
§ ?
5 °
> §
1
O
§
i
o
o.
— h
o
•» -saaiac»D
-------
VI - 16
C. SIMULATION OF 1965 CHLORIDES
1. Dynamic Estuary Model
To demonstrate the Dynamic Estuary Model's capability of simulating
changing salinity conditions in the Potomac Estuary, an historical period
(July-December 1965) was selected for which sufficient data were available
to establish the salinity distribution throughout the system at two
different points in time and for which flow rates were relatively uniform.
The mean Potomac River flow over Great Falls remained near 1,300 cfs
during this 5-month period with the mean monthly flows varying between
1,018 and 1,585 cfs. Data were available to establish the salinity pro-
file in the main stem of the Potomac near the start of the period
(July 7-8, 1965) and also near the end (December 1-2, 1965). These data
were converted to chloride concentrations and were then utilized to
establish visual "best fit" profiles for these two points in time as
illustrated in Figure VI-12. No attempt was made to relate any specific
data point to the tidal phase at the time of sampling, e.g., high- or low-
slack water conditions; hence, the concentrations were assumed to be
representative of the mean concentration over a full tidal cycle.
The profile for July 7-8, 1965, was specified as the initial profile
in the model. For this simulation, the network extended to Piney Point,
near River Mile 99. The specified chloride concentration at the seaward
boundary was changed during the simulation to correspond to the change
noted in the prototype during the same period, i.e., the concentration
-------
II. 000-,
10,000-
9000-
8000-
7000-
J 6000-
O 5000-
_j
u
4000-
3000-
2000-
1000 -J
FWQA DYNAMIC ESTUARY MODEL
CHLORIDE SIMULATION AND VERIFICATION
POTOMAC ESTUARY
JULY—DECEMBER , 1965
MILES BELOW CHAIN BRIDGE
FIGURE VI - 12
-------
VI - 18
was increased from 8,400 mg/1 to 10,930 mg/1 in increments of 55 mg/1
every 3 days. A uniform flow of 1,300 cfs in the Potomac River was
maintained in both the hydraulic and quality simulations.
The chloride profile predicted by use of the model after the
147-day simulation period is illustrated in Figure VI-12 along with that
measured in the prototype. As can be seen, the upstream movement of the
"salt wedge" and the spatial chloride distribution in the Potomac Estuary
were successfully simulated for this 5-month condition.
In the course of model verification, certain unexpected problems
arose which were related to the basic transport mechanisms, advection, and
dispersion. These problems were evidently the result of simulating a con-
stituent having an extremely high concentration gradient. For example,
the standard one-quarter point method, i.e., the assigning of an advective
concentration equal to that at one-quarter of the channel length measured
in the direction of decreasing gradient, did not prove adequate. Although
this solution technique for advective transport is acceptable in terms of
numerical mixing, accuracy, and stability when simulating dye or other
constituents with a small concentration gradient, the one-third point
method yielded the best results with chlorides. A discussion of the
Dynamic Estuary Model's sensitivity to the advective transport solution is
included in Chapter VII.
The chloride simulation presented in Figure VI-12 was based on d+
values of 15.0 (above River Mile 55), 80.0 (River Mile 55 to River Mile 70)
and 250.0 (River Mile 70 to River Mile 99). Unlike previous simulations
-------
VI - 19
where the rate of dispersion was considered constant throughout the system,
it appeared that a strong relationship existed between dispersion rates
and increased salinity gradients as suggested by Harleman [7]. A dis-
cussion of this aspect is also presented in Chapter VII.
It should be noted that an improved representation of the chloride
distribution with less difficulty in defining the transport components
of the model, including the transfer of chlorides across the seaward
boundary, might have been realized had the model network been more refined
in the lower portions of the Potomac Estuary. Almost all channels in this
area were much wider than they were long, a distortion which could con-
ceivably influence the chloride predictions obtained using the Dynamic
Estuary Model.
-------
VII - 1
CHAPTER VII
COMPARATIVE SENSITIVITY EVALUATIONS
THOMANN AND DYNAMIC ESTUARY MODELS
A. DECAY RATE OF POLLUTANT
The purpose of investigating the role of decay rate during mathe-
matical modeling studies in the Potomac was essentially twofold: (1) to
ascertain the effects of decay on the simulated distribution (steady
state) of a pollutant by using both the Thomann and Dynamic Estuary Models
and (2) to compare profiles from the two models for similar loading rates
and freshwater flows for determining whether the predicted results agree,
and what effect, if any, does decay rate exert on this agreement.
Figures VII-1 and VII-2 present steady-state simulated profiles from
the Dynamic Estuary and Thomann Models, respectively, for decay rates
varying from 0.0 to 0.4/day (base e), for a constant loading of 100,000
Ibs/day, and for a flow of 4,430 cfs. As can be seen in these figures,
each model's predictions are highly sensitive to the magnitude of the
decay rate and each behaves similarly, i.e., lower peak concentrations
and less mass transport, particularly downstream, as the decay rate
increases. The major change in profiles occurs between decay rates of
0.0 (conservative) and O.I/day. A further increase diminishes the effects
of the decay rate in both models.
By comparing Figures VII-1 and VII-2, it is clearly evident that
many similarities existed in the predictions from both models. Of
particular importance was the close agreement obtained in peak magnitudes
-------
(0
o
u.
UJ
2 o
-------
UJ
*!
(/> O
UJ
-------
VII - 4
for each of the decay rates investigated. Moreover, the general shape
and position of the profiles did not differ appreciably over this com-
plete range in decay rates, indicating that either model can be used
to simulate a given constituent regardless of its decay rate. As was
noted previously when simulating dye data, the major difference between
the two models' predictions was the pronounced peaking with the Thomann
Model whereas the DEM "smoothed" the gradients considerably in the area
of maximum concentration.
-------
VII - 5
B. SEGMENT LENGTH
1. Thomann Model
A certain degree of refinement in the segmentation and the associ-
ated physical data of an estuary is necessary; however, the CTSL studies
in the Potomac using the Thomann Model suggest that overrefinement of the
geometry may be a wasted effort. Figures VII-3, VII-4, and VII-5 show
simulated 1969 dye data for two separate networks that were applied to the
Potomac Estuary. According to these figures, there is relatively low
model sensitivity to the length of segments. The original 28-segment sys-
tem, from which 15 segments were used for this analysis, produced basically
the same profiles as the expanded system for 3 different days during the
dye study period. The only differences noted were (1) slightly higher peak
concentrations, and (2) slight downstream displacement of entire profile.
The foregoing results remain true for decay rates of either 0.03 or 0.3
per day.
The effects of "induced dispersion" due to averaging concentrations
throughout the larger volumes and longer distances in a coarse network
appeared to be minimal.
2. Dynamic Estuary Model
A detailed investigation was not undertaken to determine the sensi-
tivity of the Dynamic Estuary Model to network detail. In fact, the
114-node network used for all DEM simulations throughout this report was
initially laid out for the Thomann Model. In order to avoid the time-
consuming task of developing the additional data required for a new
-------
VII - 6
network, the original segmentation, except for embayments, was used with-
out basic change in the DEM. Subsequent simulations have indicated that
this degree of refinement was adequate to reproduce the hydrodynamic and
quality behavior in the prototype. A single run based upon a 28-node
network, also specifically designed for the Thomann Model, showed that a
network with this coarse detail could not accurately simulate tidal move-
ment in the Potomac Estuary.
-------
M
ui G
z z
?, £
-------
If
H K
UJ UJ
2 Z
2 ft
_
II
1 ^
2 S
B
z
LLJ <
t I
U I
1 -3AQ
-------
Z
O o
in ?
» °S
u. ui 5
o a 2
u
H- z
U- o
UJ ±
* *
I 1
UJ UJ
I 5
I
-------
VII - 10
C. DISPERSION COEFFICIENT
1. Thomann Model
a. Point Discharges
Of the various input parameters investigated, the Thomann Model
appeared to be most sensitive to the dispersion coefficient (K),
especially when simulating constituents having low decay rates. The
importance of this term is evident from an examination of Figure VI1-6,
VII-7, and VII-8 wherein simulated 1969 dye profiles are shown for K
values ranging from 0.5 mi^/day to 10.0 nn'2/day for all segments. The
higher dispersion coefficients indicated greater upstream and downstream
dye movement. Moreover, higher coefficients greatly decreased concen-
tration peaks to compensate for the additional mass of dye at the leading
and trailing edges. On November 17 (Figure VII-8), for example, dye peaks
of 0.8 ppb, 0.7 ppb, 0.5 ppb, and 0.4 ppb were predicted for dispersion
coefficients of 0.5, 2.0, 5.0, and 10.0 respectively. The remaining 2 days
of the study for which data were plotted indicated similar results.
The spatial position of peak concentrations was also affected by the
dispersion coefficient. As can be seen in Figures VII-7 and VII-8,
increased dispersion coefficients resulted in a lower rate of downstream
movement of the concentration peak.
The range in dispersion coefficients selected for this sensitivity
analysis may have been extreme, but it nevertheless showed that a
relatively accurate estimate of the dispersion coefficient was required
for the Thomann Model either by conducting a dye study or by using some
-------
o
-S >
u
3
8
-s
-------
-------
rS
I tO 1
r- m 4:
-------
VII - 14
natural tracer. The relationship of dispersion coefficient to fresh-
water inflow, salinity, and possibly the physical characteristics of the
system should also be defined prior to extensive model use.
For nonconservative constituents such as BOD, the effects of decay
somewhat overcome the influence of dispersion coefficient in the Thomann
Model.
-------
VII - 15
b. Chloride Distributions
The effects of using three different sets of dispersion coefficients
in the Thomann Model to simulate the annual (1969) chloride distribution
at Nanjemoy Creek are shown in Figure VII-9. Increasing the previously
P
verified dispersion coefficients of 2.0 to 16.0 mi^/day by an order of
magnitude resulted in a profound change in chloride concentrations.
Instead of the model predicting chloride concentrations between 3,000
and 5,000 mg/1, which were comparable to observed values, the chloride
levels were generally in the range of 7,000 to 9,000 mg/1. Similar
differences could be expected at most other locations along the Potomac
Estuary.
The third profile shown in Figure VII-9, based on a constant dis-
persion coefficient of 2.0 mi^/day, indicates the considerable effect
that changing chloride gradients exert on Thomann Model simulation
studies. Under this assumption, a minimal amount of chlorides
(< 500 mg/1) were transported up the Potomac Estuary from Chesapeake Bay.
It can be concluded that the Thomann Model's sensitivity to dispersion
is at least equally as great for simulating chlorides as it is for point-
source discharges.
The relationship of dispersion coefficient and chloride concentrations
established from Thomann Model simulations and actual data collected in
1969 during a relatively steady-state flow period (3,000 cfs-5,000 cfs)
can be seen in Figure VII-10.
-------
I
o
CO
z
UJ
o
52 ^
Q _) <
g
I ,'
I
o
8
8
q
d
-------
-J.N3IDUJ3O? NOISM3dSIO
UJ
O
o
o
<
o
z -5
y §
u. m
u.
u I
O o
§
z 2
(T «
UJ
a z
o
5 %
u. o
O »
o
5
K
D
O
-------
VII - 18
2. Dynamic Estuary Model
Studies with the Dynamic Estuary Model in the Potomac Estuary
indicate that the quality solution is relatively insensitive to the
dispersion constant (C4) when considering point discharges in the
freshwater portion of the system. On the other hand, the simulation
of salinity intrusion with this model indicated a significantly
greater sensitivity to the dispersion term. The difficulty encountered
with proper assignment of the dispersion term in high salinity areas is
due in part to representing a vertically stratified system with a one-
dimensional model.
a. Point Discharges
The effect of the dispersion constant, d,, on the steady-state
distribution resulting from a point discharge of 100,000 Ibs/day at
Blue Plains is indicated in Figure VII-11. These studies were con-
ducted with a 4,430 cfs freshwater inflow and mean tidal conditions.
As would be expected, increasing the dispersion constant generally
lowers the peak concentration and reduces the concentration gradient
somewhat. These comparisons indicate that the predicted distribution
resulting from a point discharge is relatively insensitive to the dis-
persion term in the Dynamic Estuary Model. Because this model simulates
advective transfers and mixing resulting from tidal action, there is
significantly less dependence on a dispersion term than that shown with
the Thomann Model.
-------
~ z
2
S g
III
o o 5
K
£E > Z
SI 5
— ^,
O uj <
0 z
UJ O
o
o
•s§
o 9
o 9
iri o
Aj u)
-------
VII - 20
b. Chloride Distributions
As a second test of the significance of the dispersion term C4 in
the Dynamic Estuary Model, an attempt was made, as discussed in the pre-
ceding chapter, to simulate changing salinity conditions in the Potomac
Estuary during the July 1965 to December 1965 period.
The profiles representing prototype conditions for July 7-8, 1965,
and December 1-2, 1965, are shown in Figure VII-12. The initial simu-
lation was completed with the dispersion constant Ci» equal to 2.5 for
the entire system (labeled model prediction number 1 in Figure VII-12).
A second simulation with d* increased to 25.0 (model prediction number 2
in Figure VII-12) resulted in only a slightly better agreement. From
these two simulations, it was apparent that the model was significantly
misrepresenting the rate of chloride incursion as well as the chloride
distribution through the system. The discrepancies could be attributable
to any of several causes, including:
1) Network layout - a brief discussion of the effect of network
layout on model predictions is presented in other sections of
this report. No further attempt to determine the effect of the
network layout on chloride intrusion was made. It remains as a
possible significant cause of the poor simulation agreements.
2) Prototype data - insufficient and/or inadequate data to
establish prototype behavior can present appreciable problems
in model verification. For this comparison, however, the data
-------
12,000-1
10,000-
8000-
6000-
O
i
UJ
Q
CC
3
X
o
4000-
2000-
EFFECTS OF DISPERSION CONSTANT ( C4 ) ON
DYNAMIC ESTUARY MODEL CHLORIDE SIMULATIONS
If 1 1 1 1
40 50 60 70 80 90
1 1
100 HO
MILES BELOW CHAIN BRIDGE
FIGURE VII-12
-------
VII - 22
were considered sufficient to adequately define the profiles
and to dismiss the prototype data as a major cause of the
discrepancies.
3) Advective transport techniques - the techniques utilized for
advective transport within the quality model can significantly
affect the rate of movement and the profile of any quality
constituent but particularly one which has steep concentration
gradients such as salinity. This "numerical mixing" phenomenon
is discussed in detail in the DEM Documentation Report [8].
4) Dispersion - although previous applications [8] of the Dynamic
Estuary Model indicated that transport due to dispersion was
relatively insignificant when compared to advective transport,
recent studies by Harleman [7] demonstrated that the dispersion
term can be very important in those portions of an estuary with
vertical or longitudinal concentration gradients. For this
reason the sensitivity of the dispersion term on model pre-
dictions was further investigated.
The studies by Harleman [7] indicate that dispersion in areas with
perceptible salinity gradients is many times greater than dispersion in
areas with uniform salinity. To evaluate the significance of this
phenomenon in the Dynamic Estuary Model, it was necessary to incorporate
the ability to vary the constant C4 with distance from the seaward boun-
dary. For this study, the estuary was divided into three zones With a
different constant for each. The C4 constant was assigned a relatively
-------
VII - 23
low value in both the upstream and middle reaches but was increased
substantially in the seaward reach. In one simulation (labeled model
number 3 in Figure VII-12) C4 was assigned a value of 2.5 in the upper
40 miles of the estuary, 25.0 in the next 20 miles, and a value of 250.0
between River Miles 60 to 96 (the seaward boundary for the model). This
simulation demonstrated the marked effect of increasing the dispersion
term. The final simulation presented (model number 4 in Figure VII-12)
was a result of utilizing a d, value of 15.0 in the upper 55 miles of
the estuary, 80.0 in the next 15 miles, and 250.0 in the downstream
29 miles (River Miles 70-99). Further refinement and adjustment of
these dispersion terms undoubtedly would have resulted in even more
favorable agreement between model and prototype behavior. However,
because of uncertainties in the prototype data base, the uncertainty of
the model network effect and other factors, further refinement in this
one aspect of the model did not appear warranted. The conclusion
reached from this study was that a significant transfer of chloride
across the seaward boundary above and beyond that entering the model via
the advective transport mechanism is necessary to adequately simulate
chloride distributions in the Potomac. This was demonstrated in this
study by substantially increasing the dispersion term in the downstream
portions of the estuary. Thus the dispersion term appears to be the
important factor in predicting the distribution and rate of transfer of
a water quality constituent having the ocean as its major source such
as chlorides. It should be kept in mind that no specific study was
-------
VII - 24
conducted to determine the effect of the network layout on the rate of
advective transfer across the seaward boundary. Whether or not this
is a significant factor in the case of the Potomac system has yet to be
demonstrated.
It is also possible that the dispersion constants determined in this
analysis are applicable only for the flow and tidal conditions existing
at the time. No specific analysis was conducted to determine whether
these constants are appropriate for other freshwater flow conditions.
-------
VII - 25
D. ADVECTIVE TRANSPORT
1. Thomann Model
As mentioned previously, the advective proportionality factor (a)
should theoretically range between 0.5 and 1.0 depending on the relative
importance of dispersion and advection for a given estuary. In the
Thomann Model, it is computed as a function of the eddy exchange coef-
ficient and flow. Simulated dye profiles based upon a values of 0.5,
0.75, and 1.0 for all model segments with other variables held constant
are shown in Figures VII-13 and VII-14. As can be seen in both of these
figures, the three profiles almost coincide indicating that the model is
quite insensitive to a. Decreasing a results in slightly higher peak
concentrations accompanied by less upstream movement. The configuration
of the profile's leading edge is unaffected.
In addition to dye simulations, the effects of a on chloride
modeling was also investigated. The considerably higher concentration
gradient found in the longitudinal chloride distribution did not appear
to increase the Thomann Model's sensitivity to the advective component
of mass transport as was noted with the dispersion component for similar
conditions.
Based upon the above discussion, it would seem that the advective
transport mechanism plays an insignificant role in the Thomann Model.
-------
r°
-------
f- 3AC
-------
VII - 28
2. Dynamic Estuary Model
The effectiveness of the method utilized for advective transport
determination in the Dynamic Estuary Model was demonstrated by simu-
lating a somewhat shorter historical salinity incursion period than that
utilized to demonstrate the effect of the dispersion term. For this
analysis, the chloride conditions in the Potomac during the period
October 19 through December 2, 1965, were used as a basis for comparing
two different solution techniques. The effect of changing the concen-
tration in the advected water from that computed at a channel's quarter
point to that computed at the upstream third point is illustrated in
Figure VII-15. As can be noted, the quarter-point method significantly
increases the predicted upstream incursion and tends to flatten the
gradient more than the third-point method. While the third-point method
produces the more favorable comparison with prototype behavior, it should
not be interpreted as the "best" the model can do since the- comparisons
could have been improved by use of appropriate dispersion constants
throughout the estuary (as discussed in a previous section). The curves are
included only to illustrate the effect of the advective solution technique.
It is apparent that the model predictions are sensitive to the method used
for advective transport; however, the effect is more pronounced for water
quality constituents with substantial concentration gradients such as
chloride. For other water quality constituents with less significant
gradients, the predictions are much less sensitive to the solution technique
used.
-------
2000-1
10000-
8000-
6000
D>
a.
O
I
u
4000
2000-
EFFECTS OF ADVECTIVE SOLUTION TECHNIQUE
DYNAMIC ESTUARY MODEL
CHLORIDE SIMULATIONS
OCT. 19-20, 1965(OBSERVED)
•- DEC 1-2 , I965(OBSERVED)
1/4 POINT (PREDICTED)
1/3 POINT (PREDICTED)
30
40
\ ITT
50 60 70 80
MILES BELOW CHAIN BRIDGE
90
FIGURE VII-15
100
\
HO
-------
VII - 30
E. RIVER FLOW AND DISPERSION COEFFICIENTS (THOMANN MODEL)
To increase the predictive reliability of the Thomann Model in the
upper Potomac Estuary, the effect of freshwater inflows on dispersion
coefficients was investigated. The simulation of November 1969 and
June 1965 dye study data indicated that a direct relationship existed
whenever flows were between 1,400 and 4,000 cfs. The increased inflows
which occurred during the study periods required higher dispersion
coefficients in order to obtain a satisfactory agreement between proto-
type and model data. Moreover, a study in the Delaware Estuary by
Paulson [9] also indicated that dispersion increased directly with flow.
This relationship may be partly due to the dissipation of the larger energy
levels associated with greater flows.
The approach adopted for this analysis was a comparison of simulated
data from the tidal and nontidal models for the upper 30 miles of the
Potomac Estuary. The data generated by the "real-time" tidal model was
used as a basis for determining when the most favorable predictions,
hence most applicable dispersion coefficients, occurred with the Thomann
Model. Four separate flow conditions, ranging from 930 cfs to 20,000 cfs,
were investigated. For each inflow, an arbitrary loading at Blue Plains
of 100,000 Ibs/day with a decay rate of O.I/day (base e) was assumed.
Initial and boundary concentrations were set to zero in both models and
simulations continued in time until steady-state conditions were observed.
The dispersion coefficients yielding the best data with the Thomann
Model are plotted as a function of flow in Figure VII-16.
-------
Q
to >•
> a
*dl
Z Q to
UJ O u
y2^
^ -^ Ld
If |
cr
Q.
o
o
I — I - 1 - 1 I T
—i—i—i—i—r
o
o
o
o
o
q
o
i
g
o
8
AVa/S3-|m'DS (X) 1N3IDIJJ30D NOISdldSIO
FIGURE VI! -16
-------
VII - 32
As can be seen in Figure VI1-16, there were two different K
versus Q relationships—one applied to the model segments upstream
from the discharge point and the other to the segments between the
discharge point and the Occoquan Bay. The effects of flow on the
dispersion coefficient were more pronounced in the downstream direction
but nevertheless a direct relationship between the two existed upstream
as well. For the higher flow conditions, it appeared that the increased
downstream advective movement overshadowed the effects of upstream
dispersion resulting from the higher coefficients.
-------
VII - 33
F. MANNING COEFFICIENT AND TIDAL EFFECTS (DYNAMIC ESTUARY MODEL)
Studies were made with the Dynamic Estuary Model to ascertain the
effects of Manning's roughness coefficient (n) on the steady-state
hydraulic solution and its subsequent effects on the quality program.
Moreover, two different tidal conditions (mean annual and mean spring
tide) were simulated hydraulically to determine the sensitivity of tidal
input on quality predictions.
The following table contains various sets of Manning coefficients
for the main Potomac and the corresponding dynamic steady-state tides
predicted at Washington. For purposes of comparison, the mean tide
which was used for this investigation had an average range at Washington
of 2.9 feet and phasing differences referenced to Piney Point of 6.4 hours
and 7.1 hours for high and low water, respectively. At Piney Point, the
average tidal range was 1.4 feet.
Table VII-1
Effects of Manning Coefficients on Tides
"n"
(decreasing downstream)
.023 -
.020 -
.025 -
.025 -
.020 -
.020 -
.020 -
.019
.020 -
.022 -
.017 -
.017 -
.016
.017
.020
.015
.014
Tidal
Range
TftTJ
2.60
2.23
2.48
2.13
2.73
2.85
High and Low
Lag Times
(hrs.
5.80 -
6.05 -
5.80 -
6.10 -
5.85 -
5.90 -
.)
7.00
7.10
7.00
7.15
7.00
7.00
-------
VII - 34
It is evident from the above data that tidal range was more
sensitive to channel roughness than tidal phase. The greater roughness
values slowed the tidal movement and thereby produced greater lag times
and lower ranges. The best agreement was obtained with "n" ranging from
.020 to .014. While the hydraulics were relatively sensitive to Manning
coefficients, quality program output based upon two different sets of
coefficients indicated that simulated concentrations were essentially
unchanged. An attempt to overrefine Manning coefficients does not appear
warranted from the standpoint of required predictive capability.
In addition to the use of mean tidal figures previously discussed,
numerous simulation studies were made for the Potomac using the mean
spring tidal figures. This particular tide has a range of 1.6 feet at
Piney Point and 3.3 feet at Washington. The most favorable simulation
of the spring tide again occurred with Manning coefficients varying from
.020 to .014. The predicted quality data in the upper Potomac Estuary
resulting from the use of mean spring tidal figures did not differ
appreciably from a mean annual tide hydraulic condition. Maximum concen-
tration differences were less than 10 percent.
-------
VIII - 1
CHAPTER VIII
ENGINEERING CONSIDERATIONS
A. DISPERSION AND ADVECTION
The mathematical model simulation studies discussed in this report
indicated that dispersion coefficients were particularly significant
when a "tidal-averaging" concept was used. Since lateral differences
in tidal velocities are the predominant driving force in physical dis-
persion, a nontidal system must include a gross term approximating the
total effect of various individual dispersion components.
The dispersion coefficient employed in the Thomann Model was hard
to evaluate. Two large scale dye studies were conducted in the upper
Potomac Estuary in an attempt to characterize dispersion, but the results
appear to contain discrepancies. The 1969 dye study yielded dispersion
coefficients of 2.0 and 3.0 mi2/day for 1,900 cfs and 3.0 and 5.0 mi2/day
for 4,000 cfs. For a similar reach of the Potomac, values of 2.0 mi2/day
(3,200 cfs) and 1.0 mi2/day (1,600 cfs) provided the best agreement
between observed and simulated 1965 dye study data. While it can be
concluded that dispersion coefficients in the Thomann Model for a point-
source discharge appeared to be directly related to freshwater inflow
rates, the probable magnitudes to be assigned for predictive studies using
fairly conservative constituents are difficult to determine. It should be
noted that the aforementioned dye studies produced only approximate values
of dispersion which have limited application. When constituents exhibiting
significant degradability are simulated, i.e., K > O.I/day, the effects of
-------
VIII - 2
dispersion in the nontidal modeling approach will be decreased because
the natural decay process dominates the effects of transport and pri-
marily governs the constituent distribution.
Simulation of chloride data also created problems because
dispersion coefficients appear to be greatly influenced by salinity
gradients. The 1966 and 1969 chloride simulations, as presented in
Chapter VI, again indicated wide variation in dispersion coefficients
both spatially and temporally. From the dispersion standpoint, the 1966
chloride simulations yielded results comparable to those of the dye
studies, i.e., dispersion coefficients were found to be directly pro-
portional to freshwater inflow. However, the 1969 chloride simulations
showed a different relationship. In order to realize basic agreement
between simulated profiles and observed data, dispersion coefficients
were held constant for the entire year of simulation regardless of fresh-
water inflow rates. Not only did this approach differ with the direct K
versus Q relationship developed in Chapter VII for a point discharge but
with the logical definition of dispersion as applied to chloride intrusion
as well. It would appear that the true dispersion coefficients for a
tracer discharged into the upper reaches of the Potomac Estuary and
dispersing primarily in a downstream direction are directly proportional
to inflow rates because advection and diffusion forces have accumulative
effects. Dispersion coefficients for chlorides and other constituents
dispersing upstream should then be inversely proportional to flow;
although this was not reflected in the Thomann Model simulations presented
-------
VIII - 3
in this report. Since chloride intrusion is in an upstream direction
and the forces of advection and diffusion oppose each other, it is
reasonable to assume that during low-flow periods, maximum intrusion
would result. To duplicate similar performance in the model, high
dispersion coefficients were necessary to simulate the downstream
movement of the chloride wedge.
Discrepancies in the interrelationship between dispersion, advec-
tion and flow on the hydrodynamic behavior and the relative insensitivity
of the advective proportionality factor suggest that tidal and nontidal
advection is deemphasized in the Thomann Model. The method by which
this model handles incoming flows may be responsible for deficiencies
in the basic transport mechanisms of dispersion and advection. A given
flow sequence, for example, is assumed to occur instantaneously through-
out the system, indicating that the hydraulics are strictly a function
of velocity (Q/A) and not volume displacement. It can be concluded
that continual refinement of the dispersion coefficient and a sound
understanding of how it is affected by various factors within a given
system are mandatory when applying the Thomann Model to any great extent.
The simulations for a point-source discharge conducted using the
Dynamic Estuary Model indicated that a much more accurate representation
of advection and dispersion can be expected. The insensitivity of this
model to the dispersion component and the relative importance of tidal
-------
VIII - 4
and advective forces were indications that the DEM more realistically
approximates the hydrodynamic behavior of the prototype.
In the case of chlorides or other constituents entering the Potomac
Estuary from the Chesapeake Bay, caution must be exercised when assigning
the dispersion term C4 in areas with large concentration gradients. The
chloride simulations performed with the DEM showed that dispersion can
be directly related to the concentration gradient and furthermore that the
advective concentration is quite important. Whether this can be attributed
to the coarse network used or some other peculiarity in the solution tech-
nique has not been adequately determined. Since this model employs a
"real-time" system, it is essential that the total quantity of constituent
crossing the seaward boundary over a complete tidal cycle be accurately
represented, even if this is done by drastically increasing dispersion.
-------
VIII - 5
B. MODEL COMPARISON
As discussed in previous sections of this report, the primary dis-
advantage of the Thomann Model, or any other nontidal model, is the
difficulty in selection of appropriate dispersion coefficients. Costly
dye studies and field data collection can provide an approximation of
this coefficient but the accuracy necessary for various predictive water
quality studies will probably remain to be developed. Other important
disadvantages of the Thomann Model are its inability to (1) branch in a
lateral direction, (2) link more than two constituents, and (3) simulate
the effects of tides on the distribution of a constituent.
The major advantages of the Thomann Model over the FWQA Dynamic
Estuary Model as presently programmed are (1) less stringent input require-
ments, (2) its ability through Namelist I/O option to change input
variables, such as flow on a daily basis, and thereby readily simulate an
entire year's or season's characteristics, and (3) the capability of
running several different data decks "back-to-back" without having to
resubmit the whole program. In light of the above, one can investigate
many more alternatives in much less time with the Thomann Model which is
important when time is critical.
Except as noted earlier, the Dynamic Estuary Model does not appear
to be very sensitive to the dispersion coefficient since tidal effects
are included. Furthermore, the short time step which can be used in the
real-time quality solution enables this model to make a better prediction
for constituents having a relatively fast reaction rate. Nitrification
-------
VIII - 6
analysis, for example, may be better investigated with the Dynamic Estuary
Model. Recent refinement in the quality program has added several
additional source and sink terms in DO budget analyses. The effects of
algal photosynthesis and respiration based upon conversion of inorganic
nitrogen to chlorophyll a_, nitrogenous oxygen demand, benthic oxygen
demand, and modifications to the reaeration term have been programmed into
the model and should definitely increase its capability in predicting DO
concentrations in eutrophic estuarine waters. Another recent innovation
was the expansion of the first-order reaction system to any order system.
This was the outcome of preliminary phosphate simulation data analysis
which indicated that a second-order reaction was more applicable. A
report currently being prepared by CTSL [10] describes such nutrient
and DO simulation studies. Source and sink terms in the DO budget have
not been delineated to this extent in the Thomann Model nor can chloro-
phyll levels be simulated by linkage with the nitrogen cycle.
When initially applying the Dynamic Estuary Model to a given system,
reasonable care is required in simulating the hydraulics to avoid major
errors in the quality predictions. The values assumed for Manning rough-
ness coefficients are particularly important since they influence both
the tidal range and phasing. An optimum set of coefficients with verifi-
cation based upon USC&GS tidal data should be determined by trial and
error procedures prior to any quality simulations. Another factor
warranting consideration in the hydraulic model is the time step used
for the solution. In order to minimize hydrodynamic instability, a
-------
VIII - 7
stability criterion which relates channel length, wave celerity, and tidal
velocity to the time step, must be satisfied. Once the stability criterion
is met, selecting shorter time intervals would not improve the hydraulic
predictions significantly.
A discussion of both models' sensitivity to the physical network
detail was previously presented. The Thomann Model, possibly because of
its averaging effect over long time periods, does not appear to be very
sensitive to degree of segmentation. For the Potomac Estuary, segment
lengths of 1 to 3 miles were adequate. The Dynamic Estuary Model appears
to be considerably more sensitive to the refinement of the network based
upon limited data pertaining to the two networks originally developed for
the Thomann Model. However, it should be recognized that input require-
ments and computer time and output increase in proportion to the number of
channels and junctions selected. Time and resource restraints must be
weighed against accuracy of data required before an evaluation of the
required network can be made.
Practically all of the prototype dye data were reasonably simulated
with the Thomann and Dynamic Estuary Models. With sufficient manipulation
of dispersion coefficients, it was possible to make reasonable simulations
of the 1966 and 1969 Potomac Estuary chloride distributions using the
Thomann Model and of a 5-month transient chloride condition (1965) using
the DEM. From an engineering viewpoint, it is preferable to refine the
hydrodynamics of a system by utilizing a real-time solution (such as the
Dynamic Estuary Model) rather than to represent a gross tidal mixing
-------
VIII - 8
phenomenon with an empirically derived dispersion coefficient appli-
cable only over a narrow range of prototype conditions. This is
particularly significant when attempting to predict water quality
behavior for future conditions significantly different from any
experienced historically and for which the validity of the dispersion
coefficients is uncertain. From a practical standpoint, however, the
Thomann Model does offer expediency with minimum effort.
-------
A - 1
APPENDIX
A. POTOMAC DYE STUDY - 1969
1. Release Conditions
A 6-percent solution of Rhodamine WT dye was discharged continu-
ously into the upper Potomac Estuary from November 2-14, 1969, via the
District of Columbia's Blue Plains Sewage Treatment Plant outfall. This
outfall extends to the main shipping channel approximately 900 feet from
the eastern shore at a point 10.4 miles downstream from Chain Bridge. The
dye solution was discharged into the elutriation washwater discharge sump
which drains directly to the outfall. Initially, dye was pumped at a rate
of 120 ml/min but a pump failure occurred during the second day of the
study. It was therefore decided to use a siphoning procedure for the
remaining 12 days.
Due to the imprecision of siphoning, it was necessary to recalibrate
the discharge rate of 120 ml/min several times each day. As an additional
check, the rectangular tank in which the dye solution was mixed was
accurately measured to determine changes in the volume of dye. Volume
changes for each 4-hour period of the study were recorded and subsequently
converted to a mass basis. Table 1 presents volumes, discharge rates and
related factors for the 13-day release period. Except for November 3 when
a pump failure occurred and November 11-12 when a line became clogged, the
dye injection rates (as shown in Table 1) were relatively uniform. During
this release period, a total of 269 pounds of pure dye (4,454 pounds of
6-percent dye solution) was discharged to the Potomac Estuary.
-------
O C
O n
.S
V
II
CO
- tl o1
•< 5 •
tl
+>
fl
tHOOO OJ O «H -O O »T\ C^\-vTiHOrHC\J
r-\ r^ f\ ry o O irv CO -N* to u^ CO O O O 00
r*-\ r^ f\ r'N O O rH OJ vo f\j fN r\j c»\ c*\ t- rH
J f"\ O O1- "* r- r-l *0 <\| O 0s O
f\ CO f\ W ^CvVO'T'^^O f\ tf\ O»- Ol H ^
v r"\ ->f f\ r-\ CO -4- C\J m,
<*\ O »Tv >* O OJ -* O C
-*>t^f^- ir\ Q o r- T^ r- co r-
ir\ ur\ ir\ ITN rH O O NT O •>* '"
rH OJ
*O
^- -\o vo eo
o w H r-i p
rHrHi-ifu
- r- \o c-
- to r- 6
to c- to o o «>
rn o w H o >»
r-lfHiHr-lr-IN
«o r- C~ ^9 ?M S
cr S to >B *\ o
-
\ O CO *T» OJ O OJ t
r ^ r^ r*> o rH •
r ^ •< -^ ^* o (
tf\m«fstf\ rHOO>ArHtfN ^O>f\^OKOr-lt*\ tKifN^fScO^ v^>VOt-^25>T\^J Co^COOJ^CSO l
O O O O O O C\J O fH O O O O O i-I O O O O O O O O CD O O O f4 tD O i-J O O C3 <
3
-------
rH O
g*
Vi O
o •
•
a -
^3
to
s't:
i -H
I!
y*
C5'
~*f 0s vO OJ Oj O O O O £- OJ f*\ OJ
r*"\ "*i rH r^ r^- o o o o to t^- Nf f- i
- -tf <*> rH »
I O OOO-*i-CTvOj rH(
i C"v O CVI «% r\CM OJ <
^ oj H H o o o^ o t
rH rH rH
oOrH^r^o o o o
t^O^O 0s f\ ^ rH rH Q Q Q Q "^ O °J rHPAOJCr-°J
rHojoj ojo^ojojo ooocor--^ ojvosta^cj
rHrHrHrHrH rH rHOJ
OJr>>fCT*rH»r\ rH^TsOCT^
r- \Q \o S"
\ CO rH Co M*\ OJ CO •
P?5j!
rH rH CO
&\O
CO OJ r
_ . J f\ rH rH
03 «0 O r^t^
I O C"\ P4
»T\ O f\J
<\l V O
i-H OJ
rH OJ O
H C*\ OJ (
-
- tf\ r^
I fo Ki
r- to o 1-1
•*f*\r\ c\i
?J rg (\i oj
CT^ O^ C~ CO -^ 0s ^ (7* ^O rH C^ *fN ^ y~* f\J C^ OJ CvJ O O O O O O "^ OJ t^~ ""* C^- O C^ O O O C^-
yDVOQOC^O^yD \OlO"Ar^\r^f<^ r^rHrr\rHrHO OOO>TNOOJ rHf'NOJrHOJrH OOOOO
O O O O O O O O O O O O O* O rH O O O O O O O O rH O O O O rH rH rH rH rH rH O
r*- oj ^ &* oj ifv <*\ oj o (*\ co v^ -^ cu ^D *«o ^o r^- co o ^
- ,.... ___ <*\r\OJ rHrHOOCjl I I lOCJ^CQ tQCOOOr^^O»fN ^C^f^NOj
•f\tr\«~\tf\tf\tf\ if\'*-4'^*tfNtf\>r\ ir\»fNirvtr\tf\i i i i if\ >*•><• •^sr^>4'>t''^'
OJOJOJOJOJOJ OJOJOJOJOJOJOJ OJOJOJOJOJ OJOJOJ OloJOJOJOJOl
i-4-cor- cooc^-'^oojco oj
kO>OJ-** r^-rH-NtO^jOrHC'N
< CO CO PMT\ OJ rH O (
I O O O O V\ O 1
V ifN if\ tfN lf\ C\J f\ 1
* O^ O^ O^ ^ (J* CO I
888SJ
t *f> -rf- f*> OJ rH O
OOrHrHCUOJ OOrHrH OJOJ oSHrHOjo5 OOrHrHOJOJ OOrHrHOJCM OOHi
I I I I II I I I I I I I I I I I I 1 1 1 I I I III
8O Q Q Q o O O O O O O O O O O Q O O O O O C
o o o o o o o o o o o o o o o o o o o o o c
5OOrH rHOJ OOOrHrHOJ OOOrHrHOJ OOOrHrHCV
188!
» OJ vo (
188!
13%:
o
rH
I 7
OJ
T
-------
A - 4
2. Monitoring System
a. Longitudinal Stations (Slack Tide)
Longitudinal sampling in the Potomac Estuary from Key Bridge to
Sandy Point during high- and low-slack tide periods was conducted by
CTSL. Data from 10 low-slack sampling runs and eight high-slack runs
were obtained during the period November 3-December 1. A tabulation of
the data as analyzed by the U. S. Geological Survey is included in this
appendix.
Surface samples at mid-channel were collected from 18 stations for
longitudinal monitoring of the dye release. A listing of these stations
is given in Table 2.
b. Lateral and Vertical Stations
To determine the lateral and vertical mixing of the dye, transect
sampling was conducted by CTSL at 14 stations, all of which coincided
with the longitudinal sampling stations. These transect stations are
shown in Table 2.
Five transect sampling runs were made during the period November
4-20. Due to the considerable amount of time required for transect
sampling, it was not possible to limit sampling to slack-tide periods.
Cross-sectional area profiles showing the sampling grids used for each
station are presented in the appendix. As can be seen from these profiles,
eight to 17 samples were collected at each station. It should be noted
that many of the transects extended into the major embayments.
-------
Table 2
LONGITUDINAL SAMPLING STATIONS
Potomac River
Station Miles Below
Number Location Chain Bridge
1 * Key Bridge 3.35
1A Memorial Bridge 4.85
2 * 14th Street Bridge 5.90
2A Buoy N "6" 6.70
3 * Hains Point . 7.60
3A Hunter's Point 8.70
4 * Bellevue 10.00
4A* Goose Island 11.05
5 * Woodrow Wilson Bridge 12.10
5A Rosier Bluff 13.55
6 * Broad Creek 15.20
7 * Piscataway Creek 18.35
8 * Dogue Creek 22.30
8A* Gunston Cove 24.30
9 * Hallowing Point 26.90
10 * Indian Head 30.60
11 Possum Point 38.00
12 Sandy Point 42.50
* Also transect stations
-------
A - 6
3. Presentation of Data
a. Tidal Conditions and Hydrology
The tidal conditions in the upper Potomac Estuary at Washington,
D. C. are monitored routinely by the U. S. Coast and Geodetic Survey.
Figures 1, 2, and 3 present actual tidal data at Washington for
most of November 1969 and the mean tidal height at this station for the
entire period of record.
As can be seen in Figures 1 through 3, there were three dis-
tinct tidal conditions during November. The first 3 days of the month
were characterized by atypically high tides with considerable fluctuations
in the tidal range. The predominately northwesterly winds which occurred
on November 3-6 were responsible for the steadily decreasing tidal levels
shown during this period. These extremely low tides had a pronounced
effect on the downstream movement of dye. The remaining 3 weeks showed
generally normal tidal ranges with average heights approximating the
mean-tide condition. The slight decrease in tidal levels on November 19-21
was again attributed to high northwesterly winds.
Average daily flows measured at Great Falls during November 1969 are
shown in Figure 4. Freshwater inflows to the upper Potomac Estuary,
like tides, were influenced greatly by climatological conditions. As
indicated in Figure 4, two separate flow regimes occurred. The period
November 1-5 had an average flow of 1,886 cfs whereas during the remainder
of the month, the average flow was 3,974 cfs. Daily flows within each
period were uniform, however.
-------
- 00
iJ - 1HOI3H
FIGURE - A I
-------
FIGURE - A 2
-------
I
O)
to
Ol
_ r-
(VJ
cc
Ul
CO
u
I
O.
I
Ol
I
CO
I
(O
I
10
- 1H9I3H
o
f>J
_ Ol
o
FIGURE - A 3
-------
5000-
FRESHWATER FLOWS
POTOMAC RIVER AT GREAT FALLS
NOVEMBER. 1969
O
_j
u.
o
z
•<*
ui
Z
4500-
4000-
3500-
3000-
2500-
2000-
1500-
1000-
500-
0--
i i I I
5
rill
10
I I I I I 1 I I
15 20
NOVEMBER 1969
I I I I I I T
25 30
FIGURE - A 4
-------
A - 11
Freshwater inflows account for the net advective downstream move-
ment in a tidal system. They can also greatly affect its dispersion
characteristics. Because of their importance, freshwater flows must be
defined and incorporated into the hydrodynamics of a tidal system if
mathematical model simulation studies are to be successful.
-------
A - 12
b. Dye Movement
The upper Potomac Estuary dye data obtained from longitudinal
sampling stations between Key Bridge and Possum Point are presented in
isopleth form in Figure 5 (low-slack data) and Figure 6 (high-slack
data). Although dye was discharged at River Mile 10.4, Figure 5
indicates that maximum dye buildup occurred between River Mile 14 and
15. Dye concentrations between 1.0 and 2.0 ppb were observed in this
area on November 5, three days after dye was initially discharged. The
fact that dye peaks were located 5 miles downstream from the discharge
point may have been due to (1) dye injected at a 14-foot depth with
samples collected at the surface, (2) freshwater inflows which caused
net downstream advective movement, (3) sampling performed at low-slack
tide when maximum downstream movement could be expected. The effects
of item (3) are evident when Figures 5 and 6 are compared. The high-
slack tide data shown in Figure 6 indicate that maximum dye concentrations
(> 1.0 ppb) occurred between River Mile 8 and 11, or approximately a
complete tidal excursion range upstream from the low-slack tide peaks.
Longitudinal dye movement can be readily identified in the two
isopleths. The dye cloud spread rapidly between Hains Point and
Piscataway Creek as shown in Figure 5. In 3 days, it moved approxi-
mately 5 miles upstream beyond the 14th Street Bridge and approximately
14 miles downstream to Gunston Cove. This represented movement rates of
1.7 mi/day and 4.7 mi/day, respectively. The especially high downstream
movement can be attributed to the very low tides observed during this
-------
A - 13
period (see previous section). Downstream movement rates beyond
November 5 can be estimated from the slopes of the concentration lines
shown in Figures 5 and 6. The rates generally range from approximately
0.8 mi/day to 1.2 mi/day with an average of 1.1 mi/day. These rates
apply only to a freshwater inflow of 4,000 cfs.
Dye was initially detected at Indian Head on November 15 and at
Possum Point on November 19. Both time periods yield an average down-
stream movement rate of approximately 1.6 mi/day. An instantaneous dye
release study conducted in the upper Potomac Estuary by the U. S.
Geological Survey in August 1965 [2] showed the average velocity of net
downstream movement of the dye mass centroid to be 0.6 mi/day. It should
be noted, however, that the tides were relatively stable during the USGS
study and that freshwater flows at Great Falls varied between 700 and
1,200 cfs, considerably smaller flows than those encountered during the
1969 dye study. The rates of movement of the leading edge and the centroid
of the dye mass may also differ appreciably.
Data collected from the three complete transect runs—November 11, 18,
and 20--between the 14th Street Bridge and Indian Head are plotted in
Figures 7, 8, and 9. The ranges in dye concentration at each transect
station and in the major embayments, mean concentrations at each transect
(excluding embayments), and mid-channel concentrations are shown in these
figures. Mid-channel stations correspond with the longitudinal sampling
-------
A - 14
stations discussed previously. The stations comprising a transect
were selected in such a way that each would have about equal weight
in terms of the cross-sectional area and the flow represented.
In most cases, the total dye concentration range for a given
transect was within 0.3 ppb which indicated that considerable lateral
and vertical mixing had actually occurred. According to Figures 7 and
9, the dye concentration ranges measured in Broad Creek, Piscataway
Creek, Dogue Creek, and Gunston Cove were generally representative of
data collected at comparable main-channel stations. The extent of dye
intrusion into these embayments was substantial, further indicating that
tidal exchanges between the main channel and adjoining embayments should
definitely be considered and, if possible, incorporated in mathematical
modeling studies.
To assist in the interpretation of simulated and observed data for
model verification purposes, an analysis was made of the average concen-
tration for transect and mid-channel (surface) values. Figures 7, 8, and
9 generally show relatively small differences (< 0.5 ppb) between these
two sets of data. Therefore, it would appear to be valid to compare the
model predictions for a given segment with the results obtained from
longitudinal sampling within that segment. Where larger deviations between
mean and mid-channel concentrations were noted, no significant conclusions
could be drawn concerning their relative magnitudes.
-------
3
JDOIdB NIVHD MO138 S31IW
FIGURE - A 5
-------
-8
30
-------
TRANSECT DYE SAMPLING SUMMARY
UPPER POTOMAC ESTUARY
NOVEMBER II. 1969
-O-i
.9-
.8 -
.7-
.6-
S.5H
.4-
.2-
Q— CONCENTRATION RANGE FOR TRANSECT
Q — CONCENTRATION RANGE FOR EMBAYMENT ONLY
X—MEAN CONCENTRATION (EXCLUDING EMBAYMENT)
A— MID-CHANNEL CONCENTRATION
0
n
6
(D
o
(i
a
9
{2
t)
C)
I
4
I
12
T I I
16 20 24
MILES BELOW CHAIN BRIDGE
28 32
FIGURE - A 7
-------
TRANSECT DYE SAMPLING SUMMARY
UPPER POTOMAC ESTUARY
NOVEMBER 18, 1969
1.0 -I
O—CONCENTRATION RANGE FOR TRANSECT
Q—CONCENTRATION RANGE FOR EMBAYMENT ONLY
X—MEAN CONCENTRATION (EXCLUDING EMBAYMENT)
A—MID-CHANNEL CONCENTRATION
.9-
.8 -
.7-
.6-
o.
Q.
i -H
.4-
.3-
.2
Q
o
i
12
I
16
I
MILES
I
20 24
.OW CHAIN BRIDGE
I
28
FIGURC - A 8
I
32
-------
TRANSECT DYE SAMPLING SUMMARY
UPPER POTOMAC ESTUARY
NOVEMBER 20. 1969
I.O-
.9-
.8 -
.7 -
.6-
£.5-
o
.4-
.3 -
.2 -
CONCENTRATION RANGE FOR TRANSECT
CONCENTRATION RANGE FOR EMBAYMENT ONLY
MEAN CONCENTRATION (EXCLUDING EMBAYMENT)
MID-CHANNEL CONCENTRATION
[]
(\
()
8
8
o
*
i^
4
I IJ I I I
12 16 20 24
M _b BELOW CHAIN BRIDGE
I I
28 32
FIGURE - A 9
-------
A - 20
c. Loss Rate Determination
The dye loss rate considers not only a decay or adsorption phenomenon
but also reflects the inability to detect dye at low concentrations. It
was estimated by computing the rate of change in the total dye mass as
measured throughout the upper estuary during an 18-day period immediately
following the dye release. Longitudinal sampling data, supplemented by
two sets of transect data, were converted from concentrations to mass
loadings per lineal foot of estuary according to the following equation:
Mass (Ibs/lineal ft.) = C x ^Qg 62'4
where: C = dye concentration (ppb) for a given sampling station
A = cross-sectional area (ft2) at the sampling station
62.4 = mass of 1 cubic foot of water, and
1()9 = conversion factor
The mass loadings obtained were plotted as a function of distance and
fitted with smooth curves. The areas under these curves were planimetered
to determine the total dye mass observed at a given time. As shown in
Figure 10, all such dye masses for the 18-day period appear to follow
a first-order reaction. The slope of the resulting line, which is the dye
loss rate, was calculated to be 0.030 per day (base e). A 1965 upper
Potomac Estuary dye study by Hetling and O'Connell [3] yielded a dye loss
rate of 0.034 per day (base e) which was calculated utilizing a similar
approach.
-------
A - 21
The dye masses computed from measured data were always greater
than the actual masses discharged during the release period. By the
end of the release period (November 14), approximately 350 pounds of
dye were computed to be in the estuary whereas only 269 pounds had been
discharged. This 80-pound difference, excluding dye losses to November
14, can perhaps be attributed to (1) naturally occurring background
fluoresence which was not defined quantitatively, (2) possible unrepre-
sentative sampling, especially near the injection site, or (3) inaccuracy
in analysis. For purposes of computing dye loss rate, these factors
should have a uniform relationship over the entire sampling period.
-------
O)
(M
CC
h-
to
LJ
10
01
O
O O
Ld
s
o
Q.
DC
LJ
Q.
a
a:
LJ
CD
z
LJ
O
I
I
O
o
O
I
o
o
in
-CO
o
o
3xa
FIGURE - A 10
-------
A - 23
B. ANACOSTIA DYE STUDY - 1970
1. Release Conditions
A 20-percent solution of Rhodamine WT dye was discharged continu-
ously into the Anacostia River from April 22-28, 1970, to determine the
advective transport characteristics of the Anacostia tidal system and to
provide additional data upon which mathematical model verification studies
could be based. The dye was discharged into the main channel of the
Anacostia River approximately 1 foot below the low water surface at the
Washington Suburban Sanitary Commission's marina in Bladensburg, Maryland
(River Mile 8.1). This area exhibits an average tidal range of approxi-
mately 3 feet but nontidal conditions exist 1/2 mile upstream.
A diaphragm type controlled volume pump, precalibrated to discharge
40 Ibs/day, was utilized for this study. The container of dye was placed
on a scale so that weight could be read and recorded several times each
day as a further check of the actual mass pumped. A total of 280 pounds
of the 20-percent dye solution or 56 pounds of pure dye was discharged
to the Anacostia during this study.
-------
A - 24
2. Monitoring System
Longitudinal monitoring of the dye cloud was performed daily during
periods of high- and low-slack water. Coverage extended from the conflu-
ence of the Northeast and Northwest Branches to the mouth of the Anacostia
River at Mains Point. Thirteen high-slack and 10 low-slack water
sampling runs were made during the period April 22-May 27. All samples
were analyzed by CTSL using a Turner fluorometer modified with a high
sensitivity kit to obtain concentrations as low as 0.1 ppb. The sampling
data is shown in this appendix.
There were 19 stations routinely sampled. All samples were collected
at mid-channel and within 1 foot of the surface. A description of these
stations is presented in Table 3.
In addition to the stations given in Table 3, several samples were
collected within Kingman Lake to determine the effect of tidal exchange
between this embayment and the main stem Anacostia River. -However, neither
lateral nor vertical sampling was routinely performed at any of the sampling
stations. As was discussed in a previous chapter on model verification, the
lack of transect data raised some doubt as to the representativeness of
those stations actually sampled.
-------
Table 3
LONGITUDINAL SAMPLING STATIONS
Anacostia River
Station
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
16
17
18
19
20
Location
Ha ins Point
Mouth of Washington Channel ....
Opposite U. S. Naval Station ....
Upstream from Buzzard Point ....
Douglass Bridge
Opposite Washington Naval Yard
llth Street Bridge
Sousa Bridge
Southern Entrance to Kingman Lake
East Capitol Street Bridge
Benning Bridge
Northern Entrance to Kingman Lake
Opposite Kenilworth Aquatic Gardens .
Route 50 Bridge
Upstream from Unnamed Tributary
Southern Edge of Marina
Bladensburg Road Bridge
Northwest Branch at Rhode Island Avenue
Bridge
Northeast Branch at Baltimore Avenue
Bridae
Miles Upstream
from Mouth
0.00
-
0.55
1.00
1 .45
1.95
2.45
3.10
3.75
4.35
4.90
5.65
6.25
6.90
7.45
7.95
8.45
9.00
-------
A - 26
3. Presentation of Data
a. Tidal Conditions and Hydrology
There are no tidal monitoring stations in the Anacostia River and
consequently detailed tidal data during the dye study were not obtained.
It has been reported by the U. S. Coast and Geodetic Survey that the
mean tidal range at both Benning Bridge and Anacostia Bridge is 2.9 feet.
The observed tidal range at the Bladensburg marina, which is farther
upstream, was also estimated to be approximately 3 feet. Time differences
for Benning Bridge referenced to the Washington gage average +16 minutes
for high water and +04 minutes for low water.
Average daily flows entering the tidal portion of the Anacostia
River were measured by USGS gaging stations on the Northwest Branch
at Hyattsville and the Northeast Branch at Riverdale. The flows for the
study period are shown in Figure 11. Except for the initial 9 days when
flows averaged 180 cfs, the freshwater inflows were generally between 60
and 100 cfs. Unusually high flows, i.e., 200-500 cfs, also occurred
during the study but they were "flashy" in nature.
-------
A - 28
b. Dye Movement
The Anacostia River dye data obtained from the sampling stations
outlined previously are presented in isopleth form in Figure 12
(high-slack data) and Figure 13 (low-slack data). As can be seen in
Figure 12, maximum dye concentrations were observed at River Mile 7.5
on April 27-28, which were the last two days of dye discharge. Concen-
trations in this area were initially 6 to 7 ppb but as the study
progressed, dye concentrations exceeded 10 ppb. Figure 13 also showed
a maximum dye buildup of similar magnitude on April 27-28 but at River
Mile 6.9. Evidently, the 0.6 mile difference can be attributed to the
tidal excursion between slack water periods. The relatively high fresh-
water flows that occurred prior to April 28 were probably responsible
for the net advective downstream movement of the dye peak from River Mile
8.1 to River Mile 7.5 or 6.9, depending on the tidal phase.
The longitudinal dye movement occurred quite rapidly between the
point of injection and the southern entrance to Kingman Lake. Under
low-slack conditions, when maximum downstream movement could be expected,
dye concentrations exceeding 1.0 ppb were observed at that downstream
station the second day (April 23) after discharge started. This trans-
lates to a velocity of approximately 2.5 mi/day. The rate of dye movement
decreased farther downstream due to a significant increase in the volume
of the Anacostia River. From April 23 to May 4, the average rate of
downstream movement based upon the slopes of the concentration lines
shown in Figure 13 was approximately 0.3 mi/day for the existing flows.
-------
L
_| U
CE 5?
1°
is
C/) 2
UJ <
o:
Q.
E
1
1
1 1 1 1 1 1
o o o o o o
^ 00
-------
A - 29
During this period, the leading edge of the dye cloud progressed down-
stream to the mouth of the Anacostia River.
As shown in Figures 12 and 13, there was very little upstream
movement of the dye which is attributable to the fact that tidal effects
do not extend much above the discharge point. Moreover, the trailing
edge of the dye cloud appeared to move downstream at a slightly greater
rate than the leading edge. The samples collected within Kingman Lake
indicated that comparable amounts of dye were present there as in
adjacent reaches of the main stem Anacostia River. The tidal and mass
exchange between these two bodies of water therefore appears to be quite
significant.
-------
O ^ O
ID 10 ui in
3DN3mjNOD DVWOlOd
m
(M
o
FIGURE - A 12
-------
DYE ISOPLETH
ANACOSTIA RIVER
LOW SLACK SAMPLING
APRIL-MAY , 1970
Z2
APRIL
1970
MAY
FIGURE - A 13
-------
c. Loss Rate Determination
An estimate of the dye loss rate in the Anacostia River was obtained
using a method similar to that discussed previously for the Potomac dye
study. The total quantities of dye observed during a 25-day period
following the release are shown in Figure 14. The dye loss rate for the
Anacostia study which again followed first-order kinetics was computed to
be 0.050/day.
Although 56 pounds of dye were discharged during the study period,
the initial mass of dye observed .in the Anacostia River was approximately
63 pounds. A relatively higti natural background concentration (0.1 - 0.3
ppb) was measured prior to dye injection and may be responsible for this
7-pound difference.
-------
lOO-i
DYE LOSS RATE
ANACOSTIA RIVER
APRIL-MAY, 1970
SLOPE (D)-- 0.050 DAY — BASE t
FIGURE - A 14
-------
*
CTi
<-O
cn
S_
OJ
_p
s
_^.
o
•--
'
i-.'
rr*
-^
Lu
,~ "
"' ra
O O
o a.)
Tf Q_ -o
• f~ ,- •
UJ 1 1 — jQ
,Q n; .v Ci
rr) 4-> c •--'
J — • T <"O
t — ^ ^_
L/-I
e
• -- "c->
*•' 'C
;? ~L
t_>
ctr
r
-.,
r )
OJ
"V
en
O
;>>
i.
rn
c:'
£s
1 o
i—
O
e^£
00
CO
o
4-> ~^
Q •—
CO
o
0
CM
r—
•
0
LD
CO
0
CM
LO
0
t-~
I"-;
0
r^
r—
•
•—
O
co
o
0
CO
CD
O
"3]
O
,_
0
CD
i —
O
•
CD
,
O
o
,_
o
•
0
1
1
1
'
oo
o
"^
o
CM
0
r—
CM
0
0
CM
0
^.
CM
•
O
LO
LO
•
0
CM
CO
o
CM
co
o
LO
co
o
, —
CO
•
o
o
co
0
0
co
o
CO
CO
CD
^.
LO
0
CTI
r^
•
O
LO
•— ;
o
^
t—
•
0
CO
i —
•
0
o
^-~
x^-
I—
0
^-
o
o
CO
o
o
t
r~
•
o
LO
r—
•
0
0
LO
o
LO
LO
0
LO
U3
0
LO
LO
•
o
LO
•*
o
CO
LO
o
LO
LO
o
01
CM
•
CD
CM
o
•
o
CO
•— ;
o
,
o
•
o
1
1
1
1
CM
^~
^
o
CM
•
0
01
o
o
o
CO
^o
o
co
LO
•
o
LO
LO
o
r^
o
, —
o
0
LO
r—
•
0
CO
0
•
0
1
1
1
1
^3-
^~
"^
CM
o
o
LO
l—f
o
LO
CM
o
CTi
CO
•
o
CTi
CO
•
o
LO
CO
o
CTI
LO
o
o
uO
0
CO
CM
•
0
CM
CM
o
LO
<—
0
p^
CD
o
CO
CD
O
CM
O
0
,
0
o
f*^
^~
""•»
1
1
'
CM
CM
0
l
CO
o
00
CO
•
o
o
LO
•
o
1
LO
o
•3-
LO
o
LO
**•
o
,
CO
o
^J-
CM
o
LO
1—
o
CO
r—
0
LO
o
o
CM
o
o
«;:j-
0
o
CO
o
.
0
CM
0
•
o
CTi
r—
"^
o
r—
c
Li
0
c
«;
o
c
r-
c-
c
c
o
c
c
r—
c
o
c
c
t—
c
c
r™
c
•^,
r\
0
3
3
J
3
1-
J
3
si
*
3
3
J
•
3
3
3
0
3
3
3
3
(A
'!/>
j*
fO
C
n3
OJ
-Q
00
3 OO
•^ ^..".-3
j
-------
CM
i —
r—
i
0
i —
en
•X
en
LO
UJ
O O3
O •*— ' e^C
E 03 LO
0 Q
i ^
O Ol
LO O- "O
•r— ' — *
CD 1 1 — J3 LO
r— Q.
-0 03 -*: Q.
03 4-> O - — -
^"** 'O f"O
Q r—
o
c~
O)
t — \
ro
14-
0
^
S-
ro
CO
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
p
i
i
i
i
I
1
i
i
i
i
LO
ro
0
CM
ro
•
0
VO
r—
O
o
1 —
•
o
CM
f—
CD
1
1
1
1
1
1
1
1
1
1
1
1
CM
0
0
CM
0
o
CM
CM
•
0
ro
0) o
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
1
i
i
i
i
_
ro
•
O
0
CTl
•
o
^t-
0
CM
ro
ro
•—
LO
CO
.
O
ro
r^
•
, —
r*^
^o
0
f—
ro
•
1 —
CJ1
CM
.
O
co
1 —
•
o
LO
1 —
•
o
o
CM
o
«.,.
CM
•
O
LO
o
1 —
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
i
0
ro
CD
*3"
cc
o
CO
CTi
O
CM
CTl
•
O
CM
LO
•
O
r^.
r\
0
r--
o
•
0
o
i —
0
CM
r—
•
0
CO
o
•
o
(^
f~^
o
00
o
•
0
<*D
0
"•^
co
o
•
o
CM
o
0
LO
o
•
o
CM
CM
0
1 —
LO
O
CM
CO
o
en
* —
0
CTl
<^"
•
0
^o
ro
•
CD
CTi
(Ni
-
o
<^-
r-~
•
o
LO
"—
o
CTi
CM
•
o
LO
CM
•
o
*^3~
CM
•
o
I—
CM
•
0
^J-
CM
•
CD
cc
ro
•
0
LO
ro
•
o
co
CM
•
o
LO
CM
~-^
to
to
fO
c
03
-------
CO
^ «=f
fO r— ~
J
£ 00
Q. i—
•=!!
1
s- oj
O) r—
•r—
Oi
ro i —
•i— ro i —
4-* 4-*
in ro
0 Q
O
ro O) CD
C -0 i—
£ -Q
1 O-
_*: o_
ro O — - cn
4-> ro
ro r—
Q CO
C -C:
O CTl CO
•1 — *l —
rO
$_
4-*
C
cu r~~
c
o
o
CO
ru
o
t-
O LO
rO
E
CO
CO
00
1 —
in
c:
0
4J
ro
4-J
CO
•x * co
r~.
•X -X r—
•x * i—
CO r— CO
LO CO CO
O OO O
co r*~^ co
LO ID O
r— CD 00
i — ^f" CO
CO LO O
OO ^3- OO
i— co
r- «* O
oo r-. co
00
CO O O
i— CO i—
00
LO LT) O
i — CO O
,
•3- o o
r— OO CO
^ co «a-
i— i— CO
CO LO i —
i—r—00
«^J~ CO ^J~
i—i—OO
•^- oo co
I— r— i—
1 -X -X
1 -X -X
1 -X -X
1 * *
OO CVJ OJ
ro ^^^ "*-~» **^*
O "st" «=!• ^3"
o
1 —
CO
^1
CO
o
CO
o
co
00
o
cn
CO
o
oo
CO
o
CO
00
o
r-.
co
o
LO
—
00
cn
CO
co
OJ
co
oo
OJ
•~;
•X
-X
^
LO
oo
•^^^
*3"
1
1
-X
CD
LO
CO
cn
o
CO
o
CD
,3-
o
CO
CO
LO
cn
OJ
o
CO
00
o
o
oo
LO
oo
,
o
o
,
oo
LO
^
r~~
00
00
r—
OJ
^
OO
CO
OJ
r-^.
OJ
^^^
«d-
,
'
•X
r^
r-.
CO
[H
LO
^
LO
^
co
«^-
0
o
^j-
rv^
cn
00
CO
•—
oo
cn
•—
OJ
cn
, —
cn
•—
,_
OJ
LO
LO
CO
r^.
•— ;
•x
^.
•~;
^.
i —
CO
OJ
-* —
<^-
,
1
•X
r^
co
•—
o
CO
LO
OJ
CO
LO
, —
CO
,3-
co
CO
CO
^J-
LO
CO
o
CO
oo
cn
OJ
oo
,
0
oo
o
i —
,_
•^-
CO
00
•X
_
CO
•X
cn
oo
•-.
«d~
(
i
•X
-X
1 —
•—
CO
CO
CO
co
r^-
CO
co
cn
CO
CO
co
CO
CO
CO
oo
^j-
co
00
00
CO
, —
oo
cn
i —
CO
oo
00
C1
•-;
-x
•X
-X
CD
CO
^•^
«sf
(
1
-X
r—
OO
o
CO
,-J.
LO
O
O
,_
CD
CO
,_
cn
i —
,_
o
LO
•-
^.
LO
,—
r~^
•*
r—
OO
0
—
co
^
i —
"^
to
*"]
o
00
,_
• —
CO
CD
--^
LO
t
1
1
-X
•X
cn
r—
CO
cn
CO
oo
co
cn
CO
oo
oo
r~
CO
CO
, —
,3-
CO
i —
CO
cn
CO
CO
00
LO
CO
r—
^
00
CO
00
f^
0
•* —
LO
1 1 1
1 1 1
' * '
•x oo -x
•x oo oo
LO cn o
OO i — OJ
^i-oo
CO OO OO
LO r- CO
•Bj- CVJ i —
CD co cn
LO OO r—
r- •— 00
CO OJ r—
CO O OO
CO 00 r—
O CD 4:
r-^ oo
oo t-~~ -x
CO r-
^J" «^- ^C
«^- 1 —
LO 1— *
CO i—
LO -X -X
00
-X -X -X
r— -X -X
oo
-X -X *
oo oo r^-
i— OJ 00
~*h-> ^^- ^^-
LO LO LO
"
c-
ro
4->
(/)
i/l
0)
1
.
"^
-------
f^».
QJ
»—
.0
(O
^~
O
CM
cn
co
r^
"~
0
cn to
r\
% *t
(
•r-
i.
CL co
ro
O ro O
U Q i—
ro
c~ cLJ x — ^
«=t -0 -0
•r- Q-
i 1— Q. cn
—
ro ^
•*-* O
ro ro
Q •—
00 CO
C
0 2
•r- O
ro
i— r*"^>
4_}
c:
CD
O
c
O to
o
Q
LO
M-
O
ro ^-
E
oo
CO
CM
^
to
o
£>
ro
1 *
OO
* cn i
"""]
-K CO 1
-K CM *
CM O «»•
tD LO CO
LO 00 to
CO ^J- f —
O i— 00
co co o
co r^. CM
CM ^3- LO
LO •* O
• . •
co r-~ to
CM o r-.
• * .
CM LO ^T
oo o LO
r-. LO o
co ^J-
^j- •cj- LO
CM cn CM
• . •
i — CO
LT) CM CM
i — to to
...
CM
LO i — tO
i— CO O1
...
r—
to oo co
"""I """I """I
LD tO O
i— i— cn
• • •
LD LO i —
i — i — tO
•3- CO r—
i — i — LO
* * *
* * cn
•~;
cu CM co r^
•»-> CM CM CM
O _,. «* *J-
1
1
o
-^
LO
LO
O
tO
r-
CM
oo
LO
O
•
^
crv
.
LO
co
CO
•
LD
r—
CM
.
«^-
CM
CM
•
CO
«^-
CM
•
CM
00
LD
CO
O
r-^
oo
LO
,3-
LO
CO
r~-
^.
CM
oo
CM
^"
1
-K
-K
.-
CO
0
LO
cn
.
LO
CM
to
^J.
cn
.
LO
«^J-
co
.
^j-
to
CM
.
CO
co
«=}-
.
CM
f^
CO
LO
o
r-^
CM
LO
LD
^
O
CM
O
CO
cn
CM
.3-
1
*
*
*
r-
o
CM
00
.
ro
cn
CM
^
LD
•
CO
0
O
.
^j-
LD
r-^
CO
to
to
.
CM
cn
CO
en
CO
^
cn
^
r^.
LD
00
CO
•~;
o
CO
^J-
1
'
1
r-
r—
CM
CO
i —
^f-
•
CO
r—
.
CM
«^-
CM
•
CM
CM
to
*
CM
CO
CO
.
CO
CO
CM
to
cn
CM
CO
*
to
to
CM
LO
cn
CM
*
,
CD
LO
1
1
,
*
*
1—
^J"
CO
.
CO
•
CM
LD
•
CO
o
.
1 —
o
f^
.
•—
CM
01
.
r—
^J-
oo
CM
to
r-'
CM
CO
"~
cn
cn
LO
cn
^
^;
^.
o
LD
'
,
CM
*
*
,-
CO
cn
•
^
•
CM
to
•
LO
cn
»
o
LO
•
•—
r*>^
LO
.
f—
i-~
to
to
CO
^
LO
cn
CM
oo
LD
co
CM
LD
O
LD
1
1
r~
r-
CM
CM
CO
•
CM
.
,_
CM
•
O
CM
•
cn
•
0
CM
•
px.
•"";
CM
CM
*
oo
,-j.
1
LO
•"^
CM
O1
LO
d)
_J
*
-------
o
O
a
5
a
5
-------
UJ
O
9
a:
CD
UJ
UJ
a:
CO
I/)
(D
Z
_
Q.
2
<
in
OJ
O
ui
in
z
<
a:
i-
LJ
a:
r
o
I
CO
I
•
I
-O
(\J
1J - Hld3Q
FIGURE A-16
-------
Q
2
O
_
a
5
2
<
h-
u
UJ
co
Z
<
cc
LJ
QC
i
GO
T
•
-------
I/)
z
o
I
IO
o
z
_l
Q.
Q
2
O
Q.
CC
LJ
t-
h-
u
UJ
cc
h-
<
UJ
r
o
I
•*
OJ
O
•s
o
.o
o
o
-o
00
O
-o
I/)
Q
I
I-
Q
s
o
o
o
o
(VI
UJ - Hid3Q
FIGURE A-18
-------
IO
z
o
o
-8
Q.
2
UJ
I-
o
UJ
cr
I-
UJ
cr
h-
to
a
O
Z
(J
o
.o
o
o
-o
00
o
-o
co
Q
I
I
O
-o
o
-o
fVJ
I
to
I
•*
(VJ
(M
- Hld3C]
FIGURE A-19
-------
z
o
13
Z
a
a
z
CO
CO
O
O
(D
U
LL)
CO
Z
<
a:
LJ
a
CO
a
u
I
o
I
VO
O
-o
o
-o
1-8
o
•o
I
I
o
o
(VJ
o
o
- Hld3Q
FIGURE A-ZO
-------
z
o
o
a:
Q
O
i
lO
z
o
O
Z
a
u
Ul
LJ
tr
1>
(D
Z
o
.o
o
.o
o
u
.8
IO
I
fe
$
o
• o
<£>
UJ - Hld3Q
FIGURE A-21
-------
o
a
D
CO
a:
UJ
O
cc
o
UJ
cr
UJ
a:
to
a
Z
o
o
o
o
o
•
.8
o
o
O
co
>
I
I
o
•o
-8
o
o
(\J
-o
o
I
CO
I
10
(M
- Hid3Q
FIGURE A-22
-------
to
-z.
o
o
-O
<
i/l
o
_o
*^00
(M
UJ
LU
o:
U
O
O
^•*
(\J
CD
(O
*
U
U
cc.
h-
<
Ul
cc
CO
Q.
D
O
Z
U
0
\~°
r
-------
UJ
UJ
tr
O
I
£
U
-------
to
o
O
z
_
a
Ul
LJ
(T
U
LJ
Z>
O
O
Q
00
A
U
UJ
i/>
Z
<
a:
L8
CO
M
.8
CVJ
• <
00
LJ
a:
a.
D
o
2
U
i
CO
<0
- Hld3Q
•
-------
o
£
10
z
a
5
u
z
D
<
00
U
Ul
o
.o
o
-8
o
_o
C\J
O
o
•QO
I
fe
Ul
-------
I-
z
2
z
o
10
z
o
o
z
_1
a
2
O)
(J
UJ
cc
h-
UJ
cr
I
I
- Hid3Q
FIGURE A-27
-------
a
I
LJ
I
a
z
O
*
a:
h-
u
cr
to
a
o
.o
o
o
o
to
I
o
>-
I
I-
Q
O
-O
00
-o
I
o
00
I
IO
I
Tt
(VI
- Hld30
FIGURE A-28
-------
BIBLIOGRAPHY
1. Jaworski, N. A., L. J. Clark, "Physical Data Potomac River Tidal
System Including Mathematical Model Segmentation," CTSL, MAR,
FWQA, 1970.
2. U. S. Geological Survey, "Movement of a Solute in the Potomac River
Estuary at Washington, D. C. at Low Inflow Conditions," 1969.
3. Hetling, L. J., R. L. O'Connell, "A Study of Tidal Dispersion in
the Potomac River," CTSL, MAR, FWQA, 1966.
4. Thomann, Robert V., "Mathematical Model for Dissolved Oxygen,"
Journal of the Sanitary Engineering Division, ASCE, Vol. 89. No. SA5,
October 1963.
5. Jeglic, J. M., "Mathematical Simulation of the Estuarine Behavior,"
Contract to FWQA by General Electric, 1967.
6. Jeglic, J. M., "Mathematical Simulation of the Estuarine Chloride
Distribution," Contract to FWQA by General Electric, 1967.
7. Harleman, D. R. F., "One-Dimensional Mathematical Models in State of
the Art of Estuary Models," Contract to FWQA by Tracer, Inc., 1971.
8. Feigner, K. D. and H. S. Harris, Documentation Report, FWQA Dynamic
Estuary Model, FWQA, July 1970.
9. Paulson, R. W., "Variation of the Longitudinal Dispersion Coefficient
in the Delaware River Estuary as a Function of Freshwater Inflow,"
Water Resources Research, Volume 6, April 1970, Number 2.
10. Clark, L. J. and N. A. Jaworski, "Nutrient Transport and Dissolved
Oxygen Budget Studies in the Potomac Estuary," CTSL, MAR, FWQA,
(In Preparation).
-------
Chesapeake Technical Support Laboratory
Middle Atlantic Region
Water Quality Office
Environmental Protection Agency
A WATER RESOURCE-WATER SUPPLY STUDY
OF THE
POTOMAC ESTUARY
Technical Report 35
April 1971
Norbert A. Jaworski
Leo J. Clark
Kenneth D. Feigner*
*EPA, WQO, Washington, D. C.
-------
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES . . .
Chapter
I INTRODUCTION 1-1
II SUMMARY AND CONCLUSIONS II - 1
III STUDY AREA DESCRIPTION Ill - 1
A. Potomac fiiver Tidal System Ill - 1
B,, Hydrographic Analysis Ill - 5
C. Proposed Reservoir Development . . . Ill - 8
D, Water Resource Uses Ill -12
1. Water Supply Use Ill -12
a. Municipal Ill -12
b. Industrial Ill -13
2. Recreation and Boating - III -15
3o Commercial Fisheries Ill -17
IV WASTEWATER LOADINGS AND RUNOFF CONTRIBUTIONS IV - 1
A. Wastewater Loadings and Trends ... IV - 1
B0 Potomac River Water Quality above
Great Falls IV - 7
C0 Suburban and Urban Runoff IV -12
D. Summary and Comparison of Nutrients,
BOD, and Carbon Contributions ... IV -14
ii
-------
TABLE OF CONTENTS (Continued)
Chapter Page
V WATER QUALITY CONDITIONS AND TRENDS .... V - 1
A. Bacterial Densities V - 2
B. Dissolved Oxygen V - 6
C. Silt and Debris V -13
D. Nutrients and Algal Growths V -21
1. Nutrient Concentrations in the Potomac
Estuary . V -21
2. Mathematical Models for Nutrient
Transport V -27
3. Ecological Trends as Related to
Nutrient Loadings V -35
E. Effects of Eutrophication on Water Quality V -42
1. Increase in Organic Oxygen Demanding
Load V -42
2. Algal Oxygen Production and Respiration V -43
3. Unfavorable Physical and Aesthetic
Characteristics of Algal Blooms . . V -48
4. Algal Toxicity V -49
VI DISSOLVED OXYGEN ENHANCEMENT VI - 1
A. Study Approach VI - 1
B. DO Criteria VI - 8
iii
-------
Chapter
VII
VIII
TABLE OF CONTENTS (Continued)
ALGAL GROWTH RESPONSE TO NUTRIENT CONTROL
A. Eutrophication Control Objectives .
VII - 1
VII - 2
B. Nutrient Requirements to Prevent
Excessive Standing Crops of Blue-green
Algae VII - 5
!„ Algal Composition Analysis .... VII - 8
2. Analysis of Data on an Annual Cycle
and Longitudinal Profile Basis . . VII -11
3o Bioassay Studies . „ VII -16
4, Nutrient and Algal Modeling . . . VII -18
5. Comparison With a Less-stressed
Estuary VII -22
6. Review of Historical Nutrient and
Ecological Trends in the Potomac
Estuary VII -24
C. Controllability of Various Nutrients . . VII -25
D. Nutrient Criteria VII -30
CONTROL CONSIDERATIONS FOR BACTERIAL DENSITIES,
VIRUSES, HEAVY METALS, AND OTHER WATER
QUALITY PARAMETERS VIII - 1
A. Bacterial Densities VIII - 1
1. Indicator Organisms VIII - 1
2. Bacterial Standards VIII - 3
B. Viruses VIII - 4
C. Heavy Metals VIII - 7
IV
-------
TABLE OF CONTENTS (Continued)
Chapter Page
VIII CONTROL CONSIDERATIONS FOR BACTERIAL DENSITIES,
VIRUSES, HEAVY METALS, AND OTHER WATER
QUALITY PARAMETERS (Continued) VIII - 1
D. Other Water Quality Indicators .... VIII -10
1. Thermal VIII -10
2. Carbon Chloroform Extraction . . . VIII -10
3. Chlorides and Total Dissolved Solids VIII -12
4. Pesticides and Herbicides .... VIII -15
IX POPULATION AND WASTEWATER PROJECTIONS ... IX - 1
A0 Population Projections ...... IX - 1
B. Water Supply Requirements IX - 6
C. Wastewater Loadings IX - 9
X WATER QUALITY SIMULATIONS X - 1
A. Water Quality Simulation Models ... X - 1
B. Alternative Wastewater Treatment Systems X - 5
C. Wastewater Management Zones and Stream-
flow Criteria . X -16
D. Ultimate Oxygen Demand X -20
E. Phosphorus . „ X -26
F. Nitrogen X -33
G. Chloride and Total Dissolved Solids
Simulations X -37
1. Estuary Water Supply Withdrawal . . X -37
2, Direct Reuse of Treated Wastewater X -47
-------
TABLE OF CONTENTS (Continued)
Chapter
XI WASTEWATER TREATMENT FACILITIES AND COSTS XI - 1
A. Treatment Considerations XI - 1
B. Wastewater Treatment Costs .... XI - 3
XII IMPLEMENTATION TO ACHIEVE WATER QUALITY
STANDARDS XII - 1
A. Seasonal Waste Treatment XII - 1
1. Ultimate Oxygen Demand .... XII - 1
2. Phosphorus XII - 2
3. Nitrogen XII - 5
B. Location of Wastewater Discharges . . XII - 8
1. Wastewater Assimilation Versus
Salinity Intrusion XII - 8
2. Wastewater Discharges to the
Embayments XII - 9
C. Flow Regulation for Water Supply and
Water Quality Control XII -10
ACKNOWLEDGEMENTS
REFERENCES
vi
-------
LIST OF TABLES
Number Page
III - 1 Zones of the Upper and Middle Reaches of
the Potomac Estuary ........ Ill - 4
III - 2 Magnitude and Frequency of Low Flows,
Potomac River near Washington, D. C.,
1930-1966 Water Years Ill - 7
III - 3 Reservoir Projects, Storage, and Cost,
Potomac River Basin Ill -10
III - 4 Low-flow Frequency Analyses for Various
Reservoir Systems, Potomac near Washington III -11
III - 5 Maryland and Virginia Landings Fish and
Shellfish, Potomac River and Tributaries,
1969 ............. Ill -19
IV - 1 Wastewater Loadings to the Upper Potomac
Estuary and Tributaries, Great Falls to
Indian Head, 1970 IV - 2
IV - 2 Wastewater Loading Trends, Washington
Metropolitan Area IV - 3
IV - 3 Upper Potomac River Basin Contributions
(Above Great Falls), February 1969 through
February 1970 IV - 9
IV - 4 Nutrient and BOD Contributions from the
Upper Potomac River Basin above Great
Falls, Maryland IV -11
IV - 5 Urban and Suburban Runoff Contributions to
Upper Potomac Estuary (Great Falls to
Indian Head) IV -13
IV - 6 Summary of Contributions of Nutrients, BOD,
and Carbon IV -15
V - 1 Sediment Data, Potomac River Basin Below
Confluence of Monocacy River V -14
V - 2 Sediment Data, Northwest Branch Anacostia
River near Colesville, Maryland .... V -15
VII
-------
LIST OF TABLES
Number Title
V - 3 Oxygen Production and Respiration Rate
Survey, Upper and Middle Potomac Estuary,
1970 V -44
V - 4 Oxygen Production-Respiration Balances . . V -45
VII - 1 Subjective Analysis of Algal Control
Requirements VII - 4
VII - 2 Algal Composition Study, Upper Potomac
Estuary, 1970 VII - 9
VII - 3 Nitrogen Bioassay Summary, Potomac Estuary,
1970 ............. VII -16
VII - 4 Summary Data, Upper Rappahannock Estuary,
1970 0 ............ VII -23
VIII - 1 Heavy Metal Analyses of Sediment Samples,
August 18 - 20, 1970, Potomac Estuary . . VIII - 9
IX - 1 Data Summary Facility Service Areas ... IX - 2
IX - 2 Water Supply Requirements, Washington
Metropolitan Area IX - 7
IX - 3 Various Water Supply Demands, Washington
Metropolitan Area IX - 8
IX - 4 Present Wastewater Loadings, Washington
Metropolitan Area IX -10
IX - 5 1980 Wastewater Loadings, Washington
Metropolitan Area IX -11
IX - 6 2000 Wastewater Loadings, Washington
Metropolitan Area IX -12
IX - 7 2020 Wastewater Loadings, Washington
Metropolitan Area IX -13
Vlll
-------
LIST OF TABLES
Number Title Page
X - I Wastewater Facilities and Projected Flows,
Alternative I X-5
X - 2 Wastewater Facilities and Projected Flows,
Alternative II X -12
X - 3 Wastewater Facilities and Projected Flows,
Alternative III X -13
X - 4 Zones of the Upper and Middle Reaches of
the Potomac Estuary ........ X -17
X - 5 UOD Loadings for Potomac Estuary .... X -21
X - 6 Phosphorus Loadings for Potomac Estuary. . X -27
X - 7 Intrusion Times for Phosphorus into Estuary
Water Intake X -32
X - 8 Nitrogen Loadings for Potomac Estuary . . X -34
X - 9 Time, In Days, To Reach Indicated Concen-
tration of Total Dissolved Solids in
Estuary at Proposed Water Intake near
Chain Bridge X -45
X -10 Time, In Days, To Reach Indicated Concen-
tration of Total Dissolved Solids in
Estuary at Proposed Water Intake near
Chain Bridge X -46
XI - 1 Total Wastewater Treatment Cost, 1970-2020,
Alternative III XI - 7
XI - 2 Initial Capital Construction and Operation
and Maintenance Costs, 1970-1980, 1980-
2000, and 2000-2020 Time Periods .... XI - 8
IX
-------
LIST OF FIGURES
Number Title
III - 1 Potomac River Tidal System ...... Ill - 3
III - 2 Planned Development for the Proposed Seven
Reservoir System, Potomac River Basin . . Ill - 9
IV - 1 UOD Loading Trends to Potomac Estuary From
Washington, D. C. Metropolitan Area ... IV - 5
IV - 2 Nutrient Concentrations , Potomac River at
Great Falls . . ......... IV - 8
V - 1 Total Goliform Organisms, Upper Potomac
Estuary, 1938-1970 Summer Averages ... V - 3
V - 2 Fecal Coliform Densities, Upper Potomac
Estuary . . . . ........ V - 4
V - 3 Dissolved Oxygen Concentration, Upper Potomac
Estuary, 1938-1970 ......... V-8
V - 4 DO Profiles, Upper Potomac Estuary, 1969 V - 9
V - 5 Dissolved Oxygen Concentration, Potomac
Estuary at Woodrow Wilson Bridge, 1965 .. V -10
V - 6 Dissolved Cbcygen Concentration, Potomac
Estuary at Woodrow Wilson Bridge, 1966 . 'V -11
V - 7 DC Contour (mg/l) Piscataway Embayment-
Potomac Estuary, June 22, 1970 ..... V -12
V-8 Benthal Uptake, Potomac Estuary .... V -19
V - 9 Chemical Oxygen Demand of Sediments, Potomac
Estuary ...... ...... V -20
V -10 Inorganic Phosphate Concentration as .
Potomac Estuary, 1969-1970 ...... V -22
V -11 Nitrate and Nitrite Nitrogen as N, Potomac
Estuary, 1969-1970 ... ...... V -24
V -12 Ammonia Nitrogen as N, Potomac Estuary, 1969-
1970 ............. V -26
-------
LIST OF FIGURES
Number Tj,tle gage
V -13 Phosphorus Concentration, Potomac Estuary,
September 28 - October 27, 1965 .... V -28
V -14 Phosphorus Concentration, Potomac Estuary,
January 25, 1966 V -29
V -15 Nitrogen Concentration, Potomac Estuary,
September 6-13, 1966 V -30
V -16 Nitrogen Concentration, Potomac Estuary,
August 19 - 22, 1968 V -31
V -17 Effect of Temperature on Phosphorus
Deposition Rate, Potomac Estuary .... V -32
V -18 Effect of Temperature on Nitrification Rate,
Potomac Estuary V -33
V -19 Effect of Temperature on Rate of Nitrogen
Utilization by Algae, Potomac Estuary . . V -34
V -20 Waste-water Nutrient Enrichment Trends and
Ecological Effects, Upper Potomac Tidal
River System V -36
V -21 Chlorophyll a, Potomac Estuary, Upper Reach,
1965-1966, 1969-1970 ' V -39
V -22 Chlorophyll g., Potomac Estuary, Middle and
Lower Reach, 1965-1966, 1969-1970 ... V -40
V -23 DO Concentrations, Potomac Estuary,
August 19 - 22, 1968 V -47
VI - 1 A Schematic Diagram of Dissolved Oxygen
Interrelationships for the Three Major
Biological Systems VI - 2
VI - 2 DO Concentrations, Potomac Estuary,
September 22, 1968 VI - 4
VI - 3 DO Concentrations, Potomac Estuary,
August 12 - 17, 1969 VI - 5
XI
-------
LIST OF FIGURES
Number
VII
VII
VII
VII
VIII
VIII
IX
IX
X
X
X
X
X
X
X
- 1
- 2
- 3
- 4
- 1
- 2
- 1
- 2
- 1
- 2
_ -j
- 4
- 5
- 6
- 7
Title
Nutrient -Chlorophyll Profiles, Potomac
Chlorophyll Concentration, Potomac Estuary,
August 19 - 23, 1968
Chlorophyll Concentration, Potomac Estuary,
September 6-7, 1966
Carbon, TKN and Phosphorus in Sediments,
Potomac Estuary, August 19 - 20, 1970 . .
Carbon Chloroform Extract, Potomac Estuary,
1963-1968 . .
Chloride Concentration, Potomac Estuary.
Wastewater Service Areas, Washington
Metropolitan Area
Population Projections, Washington
Schematic of Potomac Estuary for FWQA
Dynamic Model ...
Schematic of Water Flow, Water Quality
Simulation .
Wastewater Treatment Systems, Upper Potomac
Estuary, Alternative I
Wastewater Treatment Systems, Upper Potomac
Estuary, Alternative II .
Wastewater Treatment Systems, Upper Potomac
Wastewater Treatment Systems, Upper Potomac
Estuary, Alternative IV
Wastewater Treatment Systems, Upper Potomac
Estuary. Alternative V
Page
VII
VII
VII
VII
VIII
VIII
IX
IX
X
X
X
X
X
X
X
-13
-20
-21
-29
-11
-14
- 4
- 5
_ ^
- 4
- 6
- 7
- 8
- 9
-10
Xll
-------
LIST OF FIGURES
Number Title
X - 8 Wastewater Discharge Zones in Upper Potomac
Estuary X -18
X - 9 Observed Chloride Profiles for Low Flow
Conditions X -38
XI - 1 Activated Sludge Cost XI - 4
XII - 1 Annual Phosphorus Profiles, Potomac Estuary
at Indian Head XII - 4
XII - 2 Simulated Annual Nitrogen, Potomac Estuary
at Indian Head XII - 6
xiii
-------
1-1
CHAPTER I
INTRODUCTION
At the third session of the Conference on the Matter of Pollution
of the Interstate Waters of the Potomac River and Its Tributaries in
the Washington Metropolitan Area held April 2, 3, 4 and again on
May 8, 1969, the conferees agreed upon 15 recommendations to enhance
the water quality of the Potomac and to assure adequate sewerage
services for the area.
At the progress evaluation meeting of the conference held on
November 6-7, 1969, a technical advisory committee was established
to determine the studies required to evaluate water quality management
needs of the upper estuary.
In November 1969, the Assistant Secretary of the Interior also
requested a study of the water supply potential of the upper Potomac
Estuary. Incorporating both the suggestions of the Potomac Enforcement
Technical Advisory Committee and the request of the Assistant Secretary
of the Interior, a detailed water quality-water resources study of the
Potomac Estuary was undertaken by the Chesapeake Technical Support
Laboratory.
The study included (l) an evaluation of pollution sources including
nutrients, (2) the development and refinement of mathematical models to
predict the effects of the various pollutants on water quality, (3) the
projection of water supply needs and wastewater loadings, (4) an evalu-
ation of the estuary as a potential water supply source, (5) the
determination of the maximum pound loadings by zone for the various
-------
1-2
pollutants under various flow conditions, (6) an investigation of
alternative waste treatment plans, and (7) an estimate of the cost
of wastewater treatment required to maintain water quality standards.
During this study, close cooperation was maintained with the
North Atlantic Division of the U. S. Army Corps of Engineers who were
investigating the water supply potential of the upper Potomac Estuary
as part of their Northeast Water Supply Study (NEWS) for the Washington
metropolitan area0
-------
II-1
CHAPTER II
SUMMARY AND CONCLUSIONS
A detailed study of the interrelationships among wastewater
discharges, water supply withdrawals, freshwater inflow, and water
quality in the Potomac Estuary was undertaken in November 1969. This
study had two purposes: (l) to refine the allowable oxygen demanding
and nutrient loadings previously established for Zones I, II, and III
of the upper Potomac Estuary and (2) to determine the feasibility of
using the estuary as a municipal water supply source. The latter
study was conducted in cooperation with the U. S. Army Corps of
Engineers. The study findings as related to wastewater management
are presented below:
1. The Potomac River Basin has a drainage area of 14,670 square
miles. The average discharge rate of the Potomac River at Great Falls
is 10,780 cubic feet per second (cfs) with a minimum of 610 cfs and a
maximum of over 484,000 cfs.
2. Of the present 3.3 million population in the Potomac River
Basin, 2.8 million live within the study area which encompasses the
entire Washington metropolitan region.
3. The present municipal water use within the study area is
370 mgd with 72 percent (265 mgd) supplied from the Potomac River
above Washington. The industrial water use is 2,750 mgd with cooling
water for electric power production accounting for 99 percent.
-------
II-2
4. Recreational facilities on or near the Potomac Estuary include
a national park, three state parks, seven fish and game areas and 226
county recreational sites. A recent study by the Bureau of Outdoor
Recreation indicated that the recreational potential of the 637 miles
of shoreline has barely been developed.
5. In 1969, approximately 17-million pounds of fish, crabs, clams,
and oystere were taken from the Potomac tidal system with a dockside
value of some $4.7 million, A study in 196l indicated that about $0.6
million was spent during 6 months of sport fishing in the Potomac
Fstuary, There are approximately 95 marina facilities in the tidal
Potomac which accommodate over 5,200 recreational watercraft.
60 Effluents from the 18 major wastewater treatment facilities
and combined sewer overflows, with a total flow of 325 mgd, contribute
450,000, 24,000, and 60,000 Ibs/day of ultimate oxygen demand (UOD*),
phosphorus, and nitrogen respectively to the waters of the upper
Potomac Estuary„
7» Under low-flow conditions, the ultimate oxygen demand, phos-
phorus, and nitrogen loadings from the upper basin and local runoff
were estimated as 66,000, 1,000, and 2,300 Ibs/day, respectively.
8. The major sources of nutrients and ultimate oxygen demand in
the Potomac Estuary are the local wastewater discharges. Under low-
flow conditions approximately SB, 90, and 96 percent of the ultimate
oxygen demand, nitrogen, and phosphorus are from treated waste effluents,
* UOD - Ultimate Oxygen Demand is defined as the sum of 1.45 times the
5-day biochemical oxygen demand and 4.57 times the unoxidized nitrogen.
-------
II -3
At median freshwater inflows, approximately 62, 60, and 82 percent
respectively are from these wastewater discharges.
9. Since the first sanitary surveys in 1913, the water quality of
the upper Potomac Estuary has generally deteriorated. This is attributable
to the increased pollution originating in the Washington area.
10. Fecal coliform densities have recently proved an exception to
the general degradation as shown by the water quality indicators. Since
the summer of 1969, the high fecal coliform densities previously found
near the waste discharge points have been significantly reduced by con-
tinuous wastewater effluent chlorination. At present, the largest
sources of bacterial pollution in the upper estuary are from sanitary
and combined sewer overflows, where at times about 10 to 20 mgd of
untreated sewage enters the estuary because of inadequate sewer and
treatment capacities„
To achieve the adopted fecal coliform water quality standards,
there must be both continuous disinfection of wastewater effluents
and elimination or drastic reduction in overflows from sanitary and
combined sewers.
11„ The most pronounced effect of thermal discharges is in the
Anacostia tidal river where a five-degree rise above ambient water
temperature frequently occurs and readings as high as 33°C have been
recorded during the summer months.
12. Since 1938, dissolved oxygen levels in the upper estuary had
been decreasing. A slight upward trend occurred in the early 1960's
-------
II-4
due to the provision of a higher degree of wastewater treatment. However,
with increasing population, the amount of organic matter discharged has
increased to a record high in 1970 resulting in a critical dissolved
oxygen stress in the receiving water. In recent years, dissolved oxy-
gen concentrations of less than 1.0 mg/1 have occurred during low-flow,
high-temperature periods.
13. Mathematical model simulation of the dissolved oxygen budget
including carbonaceous, nitrogenous, benthic, and algal demands indicate
that the nitrogenous demand is the greatest cause of dissolved oxygen
deficit in the critical reach near the wastewater discharges and that
algal growths have the greatest effect on DO from Piscataway to Indian
Head, at times depressing it below 5.0 mg/1.
14. On the average, approximately 3-billion pounds per year of
sediments enter the Potomac Estuary of which 2.2-billion pounds per
year originate in the upper Potomac River Basin. The sediment yield
from the Washington area on a Ibs/sq mi/yr basis is about seven times
greater than that from the upper basin.
15 o Since 1913, the wastewater discharge quantities have increased
over sevenfold from 42 to 325 mgd, the phosphorus load increased 22-fold
from 1,100 to 24,000 Ibs/day; nitrogen ninefold, from 6,400 to 60,000
Ibs/day; and carbon approximately twofold, from 40,000 to 100,000
Ibs/dayo When ecological plant successions from a balanced toward
an unbalanced system (primarily one dominated by blue-green algae) are
related to wastewater loading trends, it can be concluded that the
-------
II-5
ecological successions are the result of increases in nutrients.
Moreover, it appears that the ecological changes are due primarily
to the large increases in phosphorus and nitrogen.
16. In recent years, large populations of blue-green algae, often
forming thick mats, have been observed in the Potomac Estuary from the
Potomac River Bridge (Route 301) to the Woodrow Wilson Bridge during
the months of June through October. In September of 1970, after a
period of low-stream flow and high temperatures, the algal mats
extended upstream beyond Hains Point and included the first nuisance
growth within the Tidal Basin. The effects of the massive blue-green
algal blooms in the middle and upper portions of the Potomac Estuary
are (l) large increases of over 490,000 Ibs/day in total oxygen demand,
(2) an overall decrease in dissolved oxygen due to algal respiration in
waters 12 feet and greater in depth, (3) creation of nuisance and
aesthetically objectionable conditions, and (4) reduction in the feasi-
bility of using the upper estuary as a potable water supply source
because of potential toxin, taste, and odor problems.
17, To reduce the effects of excessive algal blooms on water
quality and designated beneficial uses, it has been determined that
during the summer months, the standing crop should be reduced to a
minimum of 75 to 90 percent of the current level or to a chlorophyll §.
concentration at or below 25 ug/1.
18. From six independent methods of analysis, it appears that if
the upper concentration limit of inorganic nitrogen is maintained bet-
ween Oo3 and 0.5 mg/1 as N and the upper limit of total phosphorus at
-------
II-6
0.03 to 0.1 mg/1 as P, the algal standing crop can be maintained below
nuisance levels under summer conditions. The lower limits of nutrient
concentration apply to the embayments and middle portion of the estuary
where growing conditions are more favorable, whereas the higher concen-
trations are applicable to the upper portion of the estuary where lack
of light penetration limits algal growth.
19. Significant accumulations of various heavy metals in sediments
have been detected near the major wastewater discharges. A study of the
possible long-term toxic effects of these heavy metals on the biota of
the Potomac Estuary, especially shellfish, is essential.
20. Population and water supply needs have been projected as
follows:
Water Supply Needs
lear
1969
1980
2000
2020
Populat ion
2,700,000
4,000,000
6,700,000
9,300,000
Yearly avg.
(mgd)
370
570
1010
1570
Maximum Month
(mgd)
470
720
1310
2040
Maximum Daily
(mgd)
660
1000
1820
2820
-------
II-7
21. Even with the seven proposed upper Potomac River Basin reser-
voirs operational, the following withdrawals will be required from the
estuary or from direct wastewater reuse to meet the water supply
requirements:
Low-flow Characteristics Before Withdrawal from the Potomac Estuary
Water Supply Diversion or from Direct Reuse*
Recurrence
Interval
(years)
5
20
50
Minimum Monthly
Fresh Inflow
(mgd)
1.300
1170
910
1980
For a 720
mgd Need
(mgd)
none
none
none
2000
For a 1310
med Need
(mgd)
210
340
600
2020
For a 2040
med Need
(mgd)
940
1070
1330
* Withdrawal based on minimum 30-day low flow concurrently with a
maximum 30-day water supply withdrawal and a 200 mgd minimum base
flow over Great Falls into the estuary.
22, The projected wastewater volumes and loading characteristics
before treatment are as follows:
Year
1969
1980
2000
2020
Flow
(mgd)
325
475
860
1,340
BOD
(Ibs/day)
483,500
823,500
1,463,500
2,195,000
Nitrogen
(Ibs/day)
63,500
95,600
155,700
215,600
Phosphorus
(Ibs/day)
27,300
43,100
70,300
97,400
23. To aid in determining the allowable pollutant loadings from
wastewater discharges, mathematical models have been developed and
verified for predicting (l) phosphorus transport, (2) nitrogen trans-
port and assimilation, (3) effects of benthic, carbonaceous, and
nitrogenous oxygen demand, including the effects of algal photosynthesis
-------
II-8
and respiration on the dissolved oxygen budget, and (4) chloride and
total dissolved solid intrusions from the Chesapeake Bay, and their
buildup as a result of water supply withdrawals from the estuary.
24. Based upon the study of projected wastewater quantities and the
recently adopted metropolitan Washington wastewater treatment implemen-
tation schedule, the following can be concluded:
(1) Between the years 1980 and 2000, the Potomac (Dulles) Interceptor,
with its current capacity of 65 mgd, will be overloaded,
(2) To provide for future wastewater collection and treatment
facilities in areas currently projected to be served by the Potomac
Interceptor, either the capacity of the interceptor would have to be
significantly increased or additional wastewater treatment facilities
constructed on the Potomac River above Washington.
(3) With the Blue Plains wastewater treatment capacity limited
to 309 mgd, a need exists not only for one or more facilities to
serve the Anacostia Valley but also to serve a portion of the upper
Potomac area currently served by Blue Plains via the Dulles Interceptor.
(4) Large wastewater volumes are projected in the Occoquan and
Pohick watersheds in the Virginia counties downstream from Washington,
indicating a need for long-range water resources planning in this area.
25. Three basic alternative wastewater treatment systems were
investigated to determine the effects of the discharge locations on
-------
II-9
receiving water quality including chloride and total dissolved solid
intrusions, as follows:
(l) Alternative I consisted of the following plants: Pentagon,
Arlington, Blue Plains, Alexandria, Piscataway (also serving Andrews
Air Force Base), Lower Potomac (serving Pohick, Accotink, Dogue, and
Little Hunting Creek watersheds including Fort Belvoir), Mattawoman,
Neabsco (serving the Occoquan watershed), and Port Tobacco.
(2) Alternative II consisted of the nine treatment plants as in
Alternative I plus a facility serving the Anacostia Valley and located
just above the Maryland-D. C. Line, and
(3) Alternative III consisted of the same facilities as Alternative
II plus an upper Potomac plant discharging near Chain Bridge and serving
the upper Potomac region.
Two other systems designated as Alternatives IV and V were also
investigated. These were identical to III, except that for Alternative
IV, all effluents were assumed to be discharged into the main channel
of the Potomac; while for Alternative V, all effluents were assumed to
be conveyed downstream to a common discharge point below Indian Head,
Maryland.
26. Data from the chloride, total dissolved solids, and other
simulations where the estuary was used as a potable water supply source
indicate the following:
(1) The position of the salt wedge with respect to intrusion
from the Chesapeake Bay is a function of (a) duration and magnitude
-------
11-10
of any selected flow, (b) location of the wastewater treatment facility
discharges, and (c) consumptive losses in the water distribution system.
(2) Even with no water supply withdrawals from the estuary, for
comparable flow conditions, intrusion of chlorides and total dissolved
solids from the Chesapeake Bay will occur farther upstream in the future
as a result of the greater percentages of wastewater discharged down-
stream into the salt wedge and the projected increases in consumptive
loss, with the latter having the most pronounced effect.
(3) The number of days during which the estuary can be used for
water supply depends upon (a) the position of the wedge prior to the
withdrawal, (b) magnitude of the withdrawal, (c) freshwater inflow
during withdrawal, (d) location of the wastewater discharges, and
(e) the increase in chlorides and total dissolved solids as a result
of water use.
(4) The maximum possible number of days that the estuary could
be used for a water supply source was determined by using a t6tal
dissolved solids concentration in the blended water of 500 mg/1 maxi-
mum as a criterion since this parameter was determined to be more
critical than chlorides, TDS water use increments* of 40 and 240 mg/1
* Water use increment is the amount that the concentration of TDS or
any other parameter is increased from the point of water intake to
the point of discharge as a result of water supply treatment,
municipal use, and wastewater treatment.
-------
11-11
were applied at both the upstream and downstream location extremes of
the saltwater wedge to give the results in the table below:
Alternative I
Maximum Days of Use of Estuary
Upper Position Lower Position
Water Withdrawal of Wedge of Wedge
Year From Estuary Water Use Increment Water Use Increment
1980
2000
2020
(cfs)
500
1250
2000
40 mg/1
>166
90
45
240 mg/1
>166
35
15
40 mg/1
>166
140
95
240 mg/1
>166
45
20
(5) For the year 2020 and using the upper position of the wedge
(as observed in early September 1966—the lowest flow on record), the
number of days that the estuary can be used as a water supply and yet
maintain a maximum 500 mg/1 total dissolved solids standard in the
blended water is given below as a function of freshwater flow before
water supply diversions:
Maximum Days of Use of Estuary
Alternative I Alternative V
Freshwater Flow Water Use Increment Water Use Increment
(cfs)
400
1100
1800
40 mg/1
(days
45
>166
>166
240 me/1
( days )
15
42
>166
40 mg/1
(days)
18
>166
>166
240 mg/1
( days )
18
41
>166
(6) Since the projected water supply needs for the year 2020
cannot be met completely either by withdrawals from the estuary or
-------
11-12
from the seven proposed upper basin reservoirs for drought periods
extending over a month, both sources will eventually be needed to
meet the future water requirements for the Washington metropolitan
area. It appears that an increase of approximately 860 cfs (from 940
to 1800 cfs) in the Potomac River discharge at Washington will be
required to maintain an acceptable blended water with respect to
total dissolved solids for a 240 mg/1 water reuse increase. If the
increase is less than 240 mg/1, the flow regulation requirements will
decrease„
(7) While other aspects of water supply requirements such as
viruses and carbon chloriform extractables need to be considered in
more detail, it appears that the estuary can be used as a supplementary
water supply source if wastewater discharges and water supply withdrawals
are subjected to adequate treatment.
27. Direct reuse of the renovated wastewater is another solution
to meet water supply needs. This alternative has numerous advantages
over withdrawals from the estuary because:
(l) Any need for consideration of salt intrusion from the
Chesapeake Bay for water supply purposes is eliminated,
(2) Localized runoff and combined sewer overflows will not
degrade the high quality renovated water,
(3) The need for flow regulation from upstream reservoirs to meet
the projected Washington area water supply requirements is reduced to
a total flow of approximately 1100 cfs (before water supply diversion)
or an increase of about 150 cfs above unregulated conditions.
-------
11-13
Excluding the psychological objections to treated wastewater reuse
and the problems of physical transport of the wastewater to the water
intake, the major disadvantage, especially from the technical viewpoint,
would be the need to maintain the present maximum total dissolved solids
buildup of 140 mg/1 through the water supply treatment, water use, and
wastewater renovation processes whenever more than 80 percent of the
water supply is taken directly from renovated wastewater.
28. When the water resource needs of the entire basin are considered,
the long-range solution to the water supply-wastewater disposal problem
may initially be a combination of water supply withdrawals from the
estuary and flow regulation, with direct reuse becoming increasingly
feasible by early in the 21st Century.
29. The maximum allowable ultimate oxygen demand loadings have
been determined as given below for various zones and subzones of the
upper estuary for a 29°C temperature, a freshwater inflow after water
supply diversion of 300 cfs, a DO of 6 mg/1 in the treated effluent,
and based upon maintaining 5 mg/1 DO in the receiving waters.
MAXIMUM UOD LOADINGS FOR POTOMAC ESTUARY
Zone Allowable UOD*
(Ibs/day)
I-a (Upstream from Hains Point) 4,000
I-b (Anacostia River) 3,000
I-c (Hains Point to Broad Creek) 75,000
II (Broad Creek to Indian Head) 190,000
III (Indian Head to Smith Point) 380,000
* These loadings are the maximum allowable loadings for each zone assuming
adjacent zones are loaded to their maximum capacities.
-------
II-U
30. For the three freshwater inflows (before water supply with-
drawal) investigated, i.e., 1800, 1100, and 400 cfs, the maximum UOD
loadings were not affected significantly except for Alternative III
which included a treated waste discharge in Zone I-a near Chain Bridge,
When the DO in the effluents in mathematical model simulations was
decreased from 6.0 to 2.0 mg/1, the most pronounced effect was in Zone I-c
in which the UOD loading decreased from 75,000 to 56,000 Ibs/day.
31o Allowable UOD loadings for the Piscataway and Gunston Cove
embayments have been developed for the projected wastewater volumes
and conditions specified in Number 29 and are given below:
MAXIMUM UOD LOADINGS FOR PISGATAWAY CREEK AND GUNSTON COVE
Piscataway Creek
Wastewater Maximum
Flow UOD Load
(mgd) (Ibs/day)
24 10,000
49 11,000
79 12,000
Gunston Cove
Wastewater Maximum
Flow UOD Load
(mgd) (Ibs/day)
50 7,000
103 ,11,000
170 16,000
32. Since nitrification (the conversion of ammonia nitrogen to
nitrate nitrogen) has little effect on the oxygen resources of the
estuary at temperatures below 15°C, nitrogen removal from the waste-
water effluents to meet IX) standards will be required whenever the
water temperature is above 15°C, usually during the months of April
through October.
-------
11-15
In order to prevent formation of sludge deposits, to eliminate
objectionable floating matter, and to prevent low DO concentrations
during periods of ice cover, a minimum of 70-percent UOD removal and an
effluent concentration of less than 15 mg/1 suspended solids are required
year-around for all discharges.
33. Using an average freshwater inflow of 300 cfs to the Potomac
Estuary after water supply diversions, the allowable loadings of phos-
phorus by zones were determined based on maintaining an average maximum
of 0.067 mg/1 as P in Zones I and II, and 0.03 mg/1 as P in Zone III for
algal control. The allowable loadings are presented below:
MAXIMUM PHOSPHORUS LOADINGS FOR POTOMAC ESTUARY
Zone Allowable Phosphorus
(Ibs/day)
I-a (Upstream from Hains Point) 200
I-b (Anacostia River) 85
I-c (Hains Point to Broad Creek) 900
II (Broad Creek to Indian Head) 1500
III (Indian Head to Smith Point) 2000
-------
II-16
34. Allowable phosphorus loadings for the Piscataway and Gunston
Cove embayments for phosphorus concentration in the receiving waters of
0.03 mg/1 as P are shown below as a function of wastewater flow:
PHOSPHORUS LOADINGS TO EMBAYMENTS
Piscataway Creek Gunston Cove
Wastewater
Flow
(mgd)
24
49
79
Maximum
Phosphorus Load
(Ibs/day)
35
50
65
Wastewater
Flow
(mgd)
50
103
170
Maximum
PhosjchoTus Load
(Ibs/day)
35
60
140
35. To prevent excessive algal growth and to enhance the water
quality in the upper and middle reaches of the estuary, it appears that
it will be necessary to remove phosphorus on a continuous or a year-
around basis for discharges into the upper estuary. Moreover, the
control of at least 50 percent of the phosphorus load originating in
the upper Potomac River Basin appears necessary if the aforementioned
phosphorus criteria are to be achieved. To accomplish this reduction,
the current phosphorus loading from all wastewater discharges in the
upper Potomac River Basin must be decreased from 6100 to 700 Ibs/day.
-------
11-17
36. Using a freshwater inflow of 300 cfs and average maximum
inorganic nitrogen concentrations of 0.5, 0.4, and 0.3 mg/1 in Zones I,
II, and III, respectively, for algal control, the maximum nitrogen
loadings for warm temperature conditions were determined as follows:
NITROGEN LOADINGS FOR POTOMAC ESTUARY
Zone Allowable Total Nitrogen
(Ibs/day)
I-a (Upstream from Hains Point) 1000
I-b (Anacostia River) 300
I-c (Hains Point to Broad Creek) 3400
II (Broad Creek to Indian Head) 5800
III (Indian Head to Smith Point) 9000
37. Allowable total nitrogen loadings for the Piscataway and
Gunston Cove embayments based upon maintaining 0.3 mg/1 of inorganic
nitrogen under warm temperature conditions and for varying wastewater
flows follow:
NITROGEN LOADINGS TO EMBAYMENTS
Piscataway Creek Gunston Cove
Wastewater Maximum Wastewater Maximum
Flow Nitrogen Load Flow Nitrogen Load
(mgd) (Ibs/day) (mgd) (ibs/day)
24 120 50 130
49 170 103 270
79 270 170 460
-------
11-18
38. Considering the present difficulty in controlling nitrogen in
the upper basin and its transport characteristics in the estuary, it
appears that the need for nitrogen removal for algal control at waste-
water treatment plants will be limited to those periods when the water
temperature exceeds 15°C, normally from April through October. With
the large projected increases in nitrogen from wastewater discharges,
there may be a need for year-around nitrogen control by the year 2000.
39. Because of the lack of transport and assimilative capacity in
the upper portions of small tidal embayments and also because of ideal
algal growing conditions, maximum concentrations of UOD, phosphorus and
nitrogen in effluents discharged to these areas should be less than 10.0,
0.2, and 1.0 mg/1, respectively. A detailed analysis for each embayment
is required to determine the minimum cost of either extending the dis-
charge outfall to the main channel of the Potomac or discharging within
the embayment and providing a very high degree of wastewater treatment,
approaching ultimate wastewater renovation. Unless this high degree of
removal is provided, effluents from Alexandria, Arlington, Piscataway,
and the Lower Potomac facilities should be discharged into the main
channel of the Potomac Estuary.
40. The present worth cost of additional wastewater treatment
from the year 1970 to 2020, including operation, maintenance, and
amortization costs, has been estimated to be $1.34 billion with a
total average annual cost of $64.8 million. The unit treatment pro-
cesses assumed include activated sludge, biological nitrification-
denitrification, lime clarification, filtration, effluent aeration,
and chlorination.
-------
11-19
41. The cost of wastewater treatment on a per capita basis is
as follows:
Item 1970-1980 1980-2000 2000-2020
Average Population 3,350,000 5,350,000 8,000,000
Initial Capital
Cost/Person/Year $17.0 $ 4.90 $ 7.30
Operation and Maintenance
Cost/PersonAear $ 7.50 $ 8.60 $ 9.10
Total Cost/PersonAear $24.50 $13.50 $16.40
-------
III-l
CHAPTER III
STUDY AREA DESCRIPTION
A. POTOMAC RIVER TIDAL SYSTEM
The Potomac River Basin, with a drainage area of 14,670 square
miles, is the second largest watershed in the Middle Atlantic States.
From its headwaters on the eastern slope of the Appalachian Mountains,
the Potomac flows first northeasterly then generally southeasterly in
direction some 400 miles to the Chesapeake Bay.
Above Washington, D, C., the Potomac traverses the Piedmont
Plateau to the Coastal Plain at the Fall Line. Below the Fall Line,
the Potomac is tidal and extends -114 miles southeastward to its dis-
charge point into the Chesapeake Bay.
The tidal portion is several hundred feet in width at its upper-
most reach near Washington and broadens to nearly six miles at its
mouth. A shipping channel with a minimum depth of 24 feet is main-
tained upstream to Washington. Except for this channel and a few
short reaches with depths up to 100 feet, the tidal portion is
relatively shallow with an average depth of about 18 feet.
The mean tidal range is about 2.9 feet in the upper portion near
Washington and about 1.4 feet near the Chesapeake Bay. The lag time
for the tidal phase between Washington and the Chesapeake Bay is
about 6.5 hours.
Of the 3.3 million people living in the entire basin, approxi-
mately 2.8 million reside in the Washington metropolitan area. The
-------
III-2
remaining area of the tidal portion, which drains 3,216 square miles,
is sparsely populated.
For purposes of discussion and investigation, the tidal portion
of the Potomac River has been divided into three reaches as shown in
Figure III-l and described below:
Reach
Upper
Middle
Lower
Description
From Chain Bridge to
Indian Head
From Indian Head to
Rte. 301 Bridge
From Rte. 301 Bridge
River Mile
114.4 to 73.8
73.8 to 47.0
47.0 to 00.0
Volume
cu.ft.xlO9
9.3
36.2
175.4
to Chesapeake Bay
The upper reach, although tidal, contains fresh water. The
middle reach is normally the transition zone from fresh to brackish
water. The lower reach is saline with chloride concentrations near
the Chesapeake Bay ranging from about 7,000 to 11,000 mg/1.
To facilitate determination of water quality control requirements,
the upper and middle reaches of the estuary have been segmented into
15-mile zones of similar physical characteristics beginning at Chain
Bridge.
River mile distances from both the Chesapeake Bay and Chain Bridge
for the three upper zones are given in Table III-l. This zone concept
was adopted by the conferees at the Potomac Enforcement Conference on
May 8, 1969.
-------
CHAIN BRIDGE
A/
.CHESAPEAKE
BAY
POTOMAC RIVER TIDAL SYSTEM
FIGURE III -1
-------
0)
r-t
o
cd
tsi
0)
c
CH O
O 1X1
0) *•
CO
O
•
O
o
*
ITN
•sl-
rH
H
CO
O
O
O
O
O
QJ 0)
bp <1)
•3^ ^
•H o
FH
« TJ
o
•p -a
cd
>4 (1)
o
•H
cq
0)
W
CS
13 CO
Pi
-------
III-5
B. HYDROGRAPHIC ANALYSIS
The major source of freshwater inflow into the Potomac Estuary
is from the upper Potomac River Basin. The average flow, measured
at Great Falls before diversions for municipal water supply for the
period from 1930-1968, was 10,768 cfs with a minimum flow of 610 cfs
that occurred on September 10, 1966.
The monthly flow characteristics for the Potomac at Great Falls
are tabulated below for the reference period of 1931-1960.
Month
January
February
March
April
May
June
July
August
September
October
November
December
25 Percent
Quart ile
7,600
8,700
13,900
12,800
8,800
6,100
3,500
2,700
2,000
2,000
3,000
3,800
Mean
Flow
(cfs)
13,600
16,600
21,100
20,000
14,500
8,700
5,500
6,000
4,700
6,300
6,600
9,900
75 Percent
Quart ile
17,200
24,600
24,400
26,900
17,900
10,300
6,400
7,400
6,800
6,400
9,600
13,100
In water resource management, especially for the water quality
aspects, low-flow frequencies are used to determine assimilation and
transport capacities of receiving waters. The low-flow frequency
-------
III-6
utilized for water quality control in the Potomac Estuary as set by
the State of Maryland and the District of Columbia is the seven-
consecutive-days -of -low-flow with a recurrence interval of once-in-10-
years. For the Potomac at Washington, this is 954 cfs (before the
diversions for water supply). See Table III-2 for complete analyses
of low-flow frequency information.
-------
Table III-2
MAGNITUDE AND FREQUENCY OF LOW FLOWS
POTOMAC RIVER NEAR WASHINGTON, D. C.
1930-1966 WATER YEARS
(Before Water Supply Diversions)
Period
(Consecutive days)
7
14
30
60
90
120
183
1.02
years
3,440
3,8^0
4,470
6,620
8,630
8,770
11,200
Discharge
2.0
years
1,620
1,700
1,890
2,300
2,660
3,110
4,280
for indicated recurrence interval
5.0
years
(cfs)
1,150
1,210
1,340
1,540
1,740
2,060
2,800
10.0
years
954
1,000
1,130
1,260
1,420
1,670
2,220
20.0
years
814
862
976
1,070
1,210
1,400
1,830
50.0
years
670
730
8/.0
900
1,000
1,150
1,480
-------
Ill-8
C. PROPOSED RESERVOIR DEVELOPMENT
In 1956, the U. S. Army initiated a study of the water resources
of the Potomac River Basin. The result of this study was a plan for
development of water and related land resources of the basin including
(l) water supply, (2) water quality, (3) flood control, and
(4) recreational needs.
The plan recommended a l6-reservoir system to provide for orderly
development, conservation, and utilization of the basin water resources
to meet the needs of the next 50 years [1]. To provide additional
water supply resources for the Washington metropolitan area, three
alternative reservoir systems were suggested. These three systems
were:
System
I Bloomington
II Bloomington, Verona, and Sixes Bridge
III Bloomington, Verona, Sixes Bridge, Town Creek,
North Mountain, Sideling Hill, and Little
Cacapon
The locations of the seven reservoirs in System III plus the two
existing impoundments are shown in Figure III-2. The initial cost of
the seven impoundments based on the 1967 cost index would be $204.4
million. See Table III-3 for individual reservoir cost.
Using data from 1929 to 1968 and a river-flow mathematical model,
the U. S. Army Corps of Engineers simulated the effects of the three
reservoir systems on river flows over Great Falls. The low-flow
frequency analysis for the three systems is given in Table III-4.
-------
FIGURE III - 2
-------
Project
Bloomington
Staunton
Sixes Bridge
Town Creek
North Mountain
Sideling Hill
Little Cacapon
Total
Table III-3
RESERVOIR PROJECTS, STORAGE, AND COST*
Potomac River Basin
Total Storage Total Initial
Allocated Cost
(acre-feet)
137,500
143,000
103,000
96,800
195,000
75,000
82,500
832,800
Cost ($)
90,400,000
22,870,000
20,510,000
13,190,000
24,450,000
13,600,000
19,350,000
$204,370,000
Downstream
Water Supply
30,000,000
756,000
1,112,000
2,039,000
3,953,000
2,753,000
3,872,000
$44,485,000
Preserve Stream
($) Environment
36,800,000
3,473,000
5,005,000
4,136,000
7,312,000
5,557,000
7,857,000
$70,140,000
Based on data supplied by the U. S. Army Corps of Engineers, Baltimore
District, September 1970
-------
Table III-4
LOW-FLOW FREQUENCY ANALYSES FOR VARIOUS RESERVOIR SYSTEMS
Potomac River near Washington
Reservoir System
Number I
Period
(days)
30
60
90
120
30
60
90
120
30
60
90
120
Discharge
(5 years)
1600
1900
2100
2600
1900
2000
2200
2600
2000
2150
2300
2800
in cfs l"or Indicated
(10 years)
1200
1600
1700
2000
Number II
1700
1900
2100
2200
Number III
1800
2000
2200
2300
Recurrence Inter^
(50 yea]
1000
1050
1100
1500
1200
1400
1500
1600
MOO
1500
1600
1700
-------
111-12
D. WATER RESOURCE USES
1. Water Supply Use
a. Municipal
The municipal water supply needs of the Washington metropolitan
area are obtained from five major sources. The largest source is the
Potomac River above Washington, D. C. For 1969-1970, water withdrawal
data for the five sources are presented below:
Source Withdrawal
(mgd)
Potomac River above Great Ealls 265
Patuxent River near Laurel 46
Goose Creek 6
Occoquan Creek 42
Wells and other minor sources 11
Total 370
Currently, there is no municipal water withdrawn from the freshwater
portion of the Potomac Estuary. However, during the drought in the
summer of 1969, an emergency estuary intake would have been constructed
and used had the lows flows continued.
-------
111-13
b. Industrial
In the Washington metropolitan area, the amount of water used for
manufacturing is insignificant. The major industrial use is as cooling
water.
There are currently six major cooling water users in the Potomac
River tidal system with another being proposed near Sandy Point. The
total cooling water use is 2,748 mgd as follows:
Facility
PEPCO at Benning Rd.
(Washington, D. C.)
PEPCO, Buzzard Point
(Washington, D. C.)
Virginia Heating
(Arlington, Va.)
PEPGO Generating Station
(Alexandria, Va.)
VEPCO, Possum Point
(Quantico, Va.)
PEPCO, Sandy Point
PEPCO, Morgantown
(Charles Co., Md.)
Water
Usage
(mgd)
568
570
40
450
400
Receiving Water
Anacostia River
Anacostia River
Boundary Channel of
Potomac Estuary
Potomac Estuary
Potomac Estuary
Remarks
Also Uses
Cooling Towers
720
Potomac Estuary
Potomac Estuary
Proposed
Facility
Ultimate Usage
to be 1440 mgd
Total 2,748
Navigational use of the Potomac Estuary waters is primarily to pro-
vide commercial transport via river barges. Two commercial firms
presently transport various petroleum products from tank farms located
-------
111-14
in the lower Potomac and in the Chesapeake Bay proper to the Washington
metropolitan area.
Sand and gravel mining is also a water related industrial use of
the estuary bed. Currently, dredging for this purpose is being con-
ducted in the estuary below Indian Head, Maryland.
-------
111-15
2. Recreation and Boating
Aside from enhancing the suburban environment, the water and land
resources of the Potomac Estuary and its tributaries contribute to the
aesthetics of the nation's capital. From Washington, where large
numbers of tourists visit the numerous monuments, museums, public
buildings, and parks, to the remote park at Point Lookout near the
Chesapeake Bay, the Potomac's amenities are widely used. These include
freshwater and tidal sport fishing, boating, hunting, swimming, camping,
and picnicking„
At the present time, there are approximately 95 marina facilities
in the Potomac River tidal system. These marinas offer slips and moorings
to accommodate over 5,200 recreational watercraft. They also provide
boat rentals and launching areas for small craft.
Expanses of open water below Washington with large populations of
several popular species have stimulated the growth of sport fishing
in the Potomac Estuary. A study in 1959-1961, estimated that 101,000
angler trips produced approximately 1,200,000 fish weighing almost
642,000 pounds [2].
The most popular fish caught are striped bass, bluefish, spot, and
perch„ For a 5-month period during the 196l survey, an estimated
$594,000 was spent by Potomac Estuary anglers [2].
A recent study by the Bureau of Outdoor Recreation indicated the
following regarding recreational facilities and the potential of the
Potomac Estuary [3]:
-------
111-16
1. Of the 637 miles of shoreline and 207,000 acres of water sur-
face, which are rich in natural resources, the recreational potential
has barely been touched.
2. At the present time, there is one national park, three state
parks, three state forests, seven game and fish areas, and 226 county
recreation sites in the estuary drainage area. Most of these areas
are located inland without direct access to the water.
3. The recreational potential remains relatively undeveloped
because of poor access to many shoreline areas and because extensive
acreage is controlled by private and government interests.
4. There are few public beaches, but lack of such development
is probably due more to poor water quality and the hazard of stinging
jellyfish than to a lack of suitable locations.
-------
Ill-17
3. Commercial Fisheries
The Potomac River tidal system supports a substantial commercial
fishery. There are approximately 160 species in the Potomac Estuary
ecosystem of which the anadromous* and the semi-anadromous** species
such as striped bass, shad, white and yellow perch, winter flounder,
and herring are the most significant economically.
Another group of commercially important fish species spawns and
winters outside of the Chesapeake Bay in the Atlantic Ocean and utilizes
the Potomac for a nursery area and feeding ground. Included in this
group are the menhaden, croaker, silver perch, sea trout, and drum.
Oysters are indigenous to the lower reaches of the Potomac Estuary.
These reaches are considered prime shellfish waters.
Soft clams, like oysters, are indigenous to the Chesapeake Bay and
occur in the same general areas. Only in recent years, however, have
they been harvested commercially and the resource far exceeds the demand.
The lower Potomac is a favorable habitat for the growth of blue crats,
As juveniles, the young crabs feed and grow in the estuary before com-
pleting their life cycle at the mouth of the Chesapeake Bay.
* Anadromous - fish which spend most of their lives in the ocean and
ascend freshwater streams and rivers to spawn
** Semi-anadromous - fish which spend most of their lives in a brackish
water and ascend freshwater streams to spawn
-------
Ill-18
In 1969, approximately 9 million pounds of fish, 1.9 million
pounds of crabs, 1.4 million pounds of clams, and 5.3 million pounds
of oysters were harvested from the waters of the Potomac and its
tributaries [4]. The dockside value of the 1969 harvest was computed
to be over $4.6 million. See Table III-5.
There are currently about 29,000 acres of oyster beds in the
Potomac Estuary and its embayments. Of these, approximately 970
acres, mainly in the embayments, are closed because of high bacterial
densities resulting from domestic sewage pollution.
Numerous fish kills have occurred in the Potomac Estuary in recent
years. IHIhile the cause of many of these kills is unknown, several have
been attributed to low dissolved oxygen concentrations resulting from
domestic waste discharges such as the large kill near Washington during
May 1969.
-------
Table III-5
MARYLAND AND VIRGINIA LANDINGS OF FISH AND SHELLFISH
POTOMAC RIVER AND TRIBUTARIES
1969
Maryland Virginia Total „
Species Pounds Value Pounds Value Pounds Value
Fish
Crabs -
Hard
Soft & Peeler
Clam
Oyster
1,250,668
628,702
20,348
1,090,140
2,923,275
$ 183,563
75,686
8,260
389,292
1,771,812
7,780,549
1,249,774
28,000
322,092
2,457,770
$ 347,974
142,460
11,659
114,331
1,642,866
9,031,217
1,878,476
48,348
1,412,232
5,381,045
$ 531,537
218,146
19,919
503,623
3,414,678
Total 5,913,133 $2,428,613 11,838,185 $2,259,290 17,751,318 $4,687,903
-------
IV-1
CHAPTER IV
WASTEWATER LOADINGS AND RUNOFF CONTRIBUTIONS
A. WASTEWATER LOADINGS AND TRENDS
In the upper reach from Great Falls to Indian Head, Maryland, a
domestic wastewater flow of approximately 325 mgd is discharged into
the Potomac River tidal system. Eighteen facilities currently serve
approximately 2.5 million people in the Washington metropolitan area
with the largest facility being the Blue Plains Plant of the District
of Columbia (Table IV-1). Of the 325 mgd, 41.5, 23.1, and 35.4 percent
come from Maryland, Virginia, and the District of Columbia respectively.
An analysis of the loading trends since 1913 indicates that waste-
water volumes have increased eightfold, from 42 to 325 mgd. Similar
trends have occurred for total nitrogen and phosphorus with 10-fold
and 24-fold increases respectively (Table IV-2).
Of major significance has been the increase in ultimate oxygen
demand (UOD) loadings. The carbonaceous UOD increased from 84,000
Ibs/day in 1913 to about 297,000 Ibs/day in the late 1950's. With
the construction of the secondary treatment facilities, including
completion of the Blue Plains Plant of the District of Columbia, the
carbonaceous loading was reduced to 110,000 Ibs/day. The nitrogenous
loading has increased steadily from 1913 to the present loading of
254,000 Ibs/day, which exceeds the current carbonaceous loading of
204,000 Ibs/day.
-------
S
I
O O
OJ vj-
rH >n
OJ OJ OJ
Q O O
VO «0 V£>
<*N OJ O
f-
c"N
sphoru
reated
&
(-H
?S
a
EH
m o O
\O U"N C—
O
!fc
I rH
Solids
Tte
Suspended
rea
FH
t)
rH
•3
H
^— *
t
O O O
rH O O
C"\ <^\ f-
& 8 8 8
•3 rH -J- f-
fc
O
H I
g
I
'b
Bf
•O
885
CQ
rQ
S 1-0
' Iff
r^\ vr\
ON CVJ
8O O O T\
O g CVJ >*"
§
8 8
VD OJ
O O O •* O O O
OJ OJ «0
O rH
Q O O
O C^ to
O
-*
rH
. A
8f\ O
l-t rH
O O O
to i-t i-H
to O H
ff- rH OJ §
8
O
iH
r-t
O
«
8 8
m O O O O
SvS o r- rH
MD c^ in to
>T\ O O O
rH O O
•* o ><•
^T VO f*N
oj' d oJ
8
8 8
VD >!•
O c^ CO
H V rH
OJ
O O
t*N CT^
tO rH
-*
if
drlrlt)B*
M M !>
M M M
3"
CO Q
C««H & *PP •««s»>fli!aSi'2 M
Ba°43l&§§ iilJiegsf.?....
•S-stJ^ISfiBollA-i^ igw^^ss
•H §!3" s KB a a««accotowoj
iHttrlSCdECr-l-^VltH +J H rl O C C ^ H r. r. f> f> h 1C) -H
S--H 01 10-H CO •§ -5 > • -ri Tl It T< 1-1 >13
s£«d«si3j*fi«tS££a*5
o S +»
bo* o
H "O m
§ § 8
-------
18888888888
^s. MOO*r\^oOwrH rH O
8
J"^
*I| 888888
« «\ •* -» O f- «r\ w
ba.8
vo iH f\
rH CM
rA r.
»*\ N\
R
«
. *> z
I *>
H3a
g5
•-f O
Q T)
O 0)
fi H
-H
&T>
•H
•a H
M
t^
q
o
S'S
r—1 I
&«
g §
c-\ \o
OJ OJ OJ OJ
w -t^ T"
•Qgfl
5 JH 5
g
-------
IV-4
As can be seen in Figure IV-1, the current total oxygen demanding
carbonaceous and nitrogenous loading is over 450,000 Ibs/day, the
highest loading rate ever discharged into the estuary although the
percent removal of 5-day BOD has remained at about 70 percent. Since
I960, the increase in wastewater volumes and the continual increase
in nitrogenous UOD has resulted in a total oxygen demanding load to
the estuary similar to that which occurred before the secondary treat-
ment facility at Blue Plains was completed in the late 1950's.
There are 82 wastewater point source discharges into the middle
and lower reaches of the Potomac Estuary and their tributaries. The
estimated BOD, total phosphorus as P, and nitrogen as N are 4,000, 500,
and 1,000 Ibs/day, respectively.
The major sources of domestic wastewater discharges are listed
below:
Mannassas Park No. 1
Mannassas Park No. 2
Manassas
Greenbrier
Fairfax-Flatlick
Greater Manassas S. D.
Lorton Reformatory
Marumsco
Featherstone, Va.
Marine Corps Schools
(Quantico, Va.)
Naval Weapons Laboratory
(Dahlgren, Va.)
Wastewater
Volume (mg d)
0.109
0.221
0.786
0.214
0.111
0.700
0.410
1.000
0.300
1.400
0.350
Receiving
Water
Bull Run
Bull Run
Bull Run
Bull Run
Flatlick Run
Bull Run
Giles Run
Marumsco Creek
Farm Creek
Potomac Estuary
Upper Machodoc Creek
-------
400,000-
3 00,000-
200,000-
100,000-
UOD LOADING TRENDS
TO
POTOMAC ESTUARY
FROM
WASHINGTON D C METROPOLITAN AREA
TOTAL OF CARBONACEOUS AND NITROGENOUS
NITROGENOUS UOD
1910
1920
1930
I
1940
YEAR
7
1950
I I
I960 1970
FIGURE IV-
-------
IV-6
Compared to the upper reach, which has a population served of
approximately 2.51 million, the middle and lower reaches serve a
population of approximately 50,000. Most of the discharges in this
area are into tributary or embayment waters.
-------
IV-7
B. POTOMAC RIVER WATER QUALITY ABOVE GREAT FALLS
Detailed analyses of the freshwater inflow from the upper Potomac
River Basin at Great Falls were conducted during 1969 and 1970. During
the period of February 1969 to February 1970, the following were the
average measured concentrations of BOD^ and nutrients :
Parameter Concentration
BOD5 2.60
TKN as N 0.6l
N02 + N03 as N 1,00
T0 Phosphorus as P 0.13
The observed data, as shown in Figure IV-2, show the wide range of
nutrient concentrations for the period of June 1969 to July 1970. The
river discharge was considerably higher during the 6 months of 1970 than
for the last 7 months of 1969. This resulted in higher N02 + NO-^ concen-
trations „ Concentrations of TKN and phosphorus appeared to decrease
during the higher flow periods except during periods of intense runoff [5]
The contributions from the upper basin in Ibs/day during the period
of February 1969 through February 1970 are presented in Table IV-3, For
the 13 -month period, the average daily contributions of nutrients were
tabulated and are given below:
Parameter Contribution
(Ibs/day)
T. Phosphorus as P 4,580
Inorganic Phosphorus as P 2,650
TKN as N 22,410
NH3 as N 4,590
N02 + N03 as N 36,700
-------
I/)
3 -
-
^ K
Z o
o \-
z <
O Q,
O ui
>
h~ ^
UJ U
•o: <
O
r~
01
^ a>
a.
-------
o o
5 — 1 C"°~
t-l ON
& rH
S &
O 10 £l
0 rH ,0
| ft)
i— "1 U/
fc*' CO ^i
P§ «j P
«D 0) O
rH pi f-! £
Q pfj p^f Cj
m F> -P
HMO)
W > ON
OVO
0 ,0 ON
|j <^rH
P «J
O . r~{
g
P4 .O
0 Q)
P_j fjr_j
!=>
f\ *— «
O £»
53 o
+ * \.
^s,
CO W
AJ rrt .C
0 r-
x—.
Cfl
co
s-l
CO
§5
C | s S
Oi
CQ
C>
•U p -C
tlD «H ^^N,
h O W
O & ^Q
fj fi^ (--
rH 03 •---
O
p ^~
0 ">
rd CC
TO ^v
o to a
H
SCO
CM
EH ^
i
oooooooo
tOt>ir\HONt>rr\->l-
oc*N,r^cJNtQONOO
C>-\if\rHl>OJ-VOVO xtOJVO
OJVOOJHI>tOVO^t
OJ CM OJ H CM rH
OOOOOOOO
[>- ^~ CM O C'A ^" O WA
OCMrHON-^UAOO
** »s ^ »V **
CM 0^ CM CM H
UAOOOOOOO
ONO^tC^vVOOrHCM
^^" IA f^- £^- VfN. [^- C*™\ ON
^l-ir\^}-OJrHHifNOJ
OOOOOOOO
OOOOOOOO
r^ ^t" o ON CM ^i~ O O'N,
votoc^r^ojojtoxr
f-,
& ^|
M O "H d) r*5 p -P
^3r>GrH&)P(
O
3
CVN
O
OJ
OJ
CM
to
o
CM
§
VO
rH
O
O
CM
October
o
to
vo
o
C'N
O
O
to
rH
rH
O
H
to
O
UA
OJ
g
VO
c^
November
o
o
-sf
ON
O'N,
O
o
rH
ir\
0
ON
to
CM
O
to
ON
•v
OJ
O
CM
ITN
O
o
C--
December
o
to
vo
to
o
ir\
ON
VO
O
!>
to
to
VO
C^>
o
ON
-
-------
IV-10
A regression analysis of the river discharge and contribution
loadings was made. Utilizing the flow duration curve for the Potomac
River near Washington and the regression equation between river dis-
charge and loadings, the contribution of phosphorus, nitrogen, and
BOD/, was determined for three frequency periods: 5%, 50%, and 95% of
the time (Table IV-4). Based on this analysis, 50 percent of the time,
which corresponds to a median river discharge of 6,470 cfs, the nutrient
loadings into the Potomac from the upper basin are as follows:
Parameter Median Loading
(Ibs/day)
BOD5 89,390
TKN as N 16,850
N02 + N03 as N 19,830
Phosphorus as P 4,350
Total Carbon as C 480,000
Data for the 5-percent duration or 34,000 cfs, as also given in
Table IV-4, show higher loading rates and thus higher total loadings.
Conversely, for the 95-percent duration of the 1200 cfs discharge rate,
the loading rates are lower as are the loadings. For water quality
control purposes, the 50- and 95-percent duration times are more
applicable since they occur under critical summer conditions.
* Frequency percent is percentage of time in which a given parameter
is equalled or exceeded
-------
aj o
O O
-sf
1
FH
rH
£>
cd
EH
IZ5
M
ro
^n
pQ
pj
P
rt
o
$3
PI
@
Pn
P-i
t=>
g
EH
6
§
0
M
1
a
&
o
Q
§
£-^
5s
Q
O
«
Z
CO
CO VO (^ 0s
f> H TO rH
rH C*N
•g
CO
\ vo to j>
CO
cd o o o
~\ tf\ to o^
CQ - -v *
^3 TO VO >!•
rH O H
cd
J2
S
EH
•H
S
CO
\ 0 i> c^
^ . . .
T3 to H O
CO
^
S5
CO
cd
>j O O O
cd vo c^\ vo
TJ if\ to OJ
'*\^ *v *s *«
CQ £> O^ rH
rO D^ rH
rH OJ
ol'a
+ j CO
1 j OJ !> rH
cd
T3 >t rH O
\ OJ
CO
H
P-.
CO
•>
£> O --t
rH H
^
fj
o
^
8
E
<
EH
•H
e
CQ
\ TO CO to
tVO c^ O
rH O O
^N^
CQ
rH
•a CD
O b
-p h f
cd CD ct
*H I> ,C
O -H O
O p"I 0
CQ -r
^
8O O
!> O
H
£
U> O if\
u^\ 0^
exceeded
^
O
•o
0)
H
H
%
cu
CQ
•rH
CT1
1
rrj
\^
CQ
ft
rH
•0
H
•H
cT
O
•H
.g
*
^
O
0)
5
-p
C,_(
O
-p
C
OJ
o
CO
p(
0)
X!
EH
*
-------
IV-12
C. SUBURBAN AND URBAN RUNOFF
An analysis similar to that used for the Potomac at Great Falls was
applied to data on Rock Creek and the Anacostia River. Based on these
regression studies and flow duration curves, yield rates in terms of
Ibs/day/sq mi were determined as given in Table IV-5. These rates were
used for the suburban areas in Virginia and Maryland.
For the District of Columbia, data on stormwater and urban runoff
were obtained from a study of Washington overflows [6], The rates and
flow frequency percentages based upon the Rock Creek and the Anacostia
River drainage areas were used.
The median loadings contributed from urban and suburban areas to
the upper Potomac Estuary are tabulated below:
Parameter Loadings
(Ibs/day)
BOD5 12,500
TKN as N 2,560
N02 + N03 1,510
T. Phosphorus as P 850
The total loadings (Ibs/day) of BOD and nutrients from suburban and
urban runoff were fairly small when compared to those from the upper
Potomac Basin. However, yield rates (Ibs/day/sq mi) for the urban and
suburban area, except for nitrites and nitrates, were significantly
higher (Table IV-5). This indicates that as population in an area
increases, the BOD, phosphorus, and TKN loadings from urban runoff will
probably also increase.
-------
I 8 8 8
5 8
o1
a o \o
CM O
MD rH
o O H o \f> to oo
r^rHCV rH C> i-l M3 >A
s O rH
o ^o to
••
0" O O O O C
>> O f\ O O r-
.§ ^ '"X
SO O O f1- to c^
O^ <— I
8
8 8
r- >»•
O" lf\ rH O
m \O t- cu
CM
>f\ rH O
8 S 8
•s
0)
u
H
S
I
rH CM_
CM" o
8 8
C"\ SO
•o
^
"o
g
8
o o o
r-v O rH
r^ r-I O
^r <*\ o
C-- CM >!•
CM p CM
CM
•H O
II
oS
w.
O
m
I
CMCMCM QQQ CMCMCM
tf\ l/N ITN O O O ^O ^O ^O
rH rH •>*
r- t> a
0
& K
.1 ?
*
€ 43
*fcf
+> O 3
-------
IV-14
D. SUMMARY AND COMPARISON OF NUTRIENTS, BOD, AND CARBON CONTRIBUTIONS
For the 50- and 95-percent flow durations, the largest source of
BOD and nutrients is from wastewater discharges in the Washington area.
As summarized below, under low-flow conditions, wastewater discharges
contributed over 55 percent of all four parameters.
95$ 5056
Low-Flow Condition Median-Flow Condition
Potomac R. Flow = 1200 cfs Potomac R. Flow = 6470 cfs
Total From Percentage Total From Percentage
Parameter all Sources From Wastewater all Sources From Wastewater
(Ibs/day) (%) (Ibs/day)
T. Oxygen Demand 515,800 88 733,000 62
T. Carbon 380,000 55 720,000 29
T. Nitrogen 66,900 90 100,000 60 •
T. Phosphorus 25,000 96 29,300 82
BOD5 161,580 87 242,900 58
Even under median-flow conditions, the contribution of total oxygen
demand, total nitrogen, and total phosphorus is largest from the waste-
water treatment facilities. At the 5-percent frequency or for a Potomac
flow of 34,600 cfs, only in the case of phosphorus (52$) is the largest
percentage from wastewater discharges (see Table IV-6).
-------
8
c\
6 CM ir>
e»\ 8 8 c\i vo
O
f-
00 C- >fN rH
v£> O VO ^»
01 >r oi r-
C~ CVJ Ol i-H 00 <\l Q"* 0s CM r^- 00 tfN O^ «>
rHrHrHiA UN *O Kl >A CO 00 CO lA ft CT-
>> Q
0 O
•o o
0) rH \O O
rH rH ^t Oj
2 S oi ^* S
rH VO O O
r4 ~t PJ
o o ^r
^ o evl
y>
1
3
S M
00 ^
(
11
1
0
rH
ffl
+J
O
rH
Vl
O
Vt.
4
^s.
m
xS
iH
B\D f
r*\ C
o ^o y
8 § \
>r\ 0s C
->r VD c
rH
""S CT^ CO tf\ Q^ t*"
U OJ O r-t O iH
•X 0 C- UN •* >t
3 8 8 888
J f\ f*N *f\ O O
-^- r^\ CM O O
° ^ rH C-N <^
O 0s ^D t^ ^O CJ^ r*\
-* CM O O CM O O
O CO O CO O HJ
^J rH m O
r-«
Ob.
to r-
ai vo
•g VO f-
I §
St- VO rH
O CO »H
y~\ OJ O cvj
8 8
8 8
^ O O
H r\ O
g §
« g
. 9 ft
•S S 8
a s £
m H H t-i H
t^ o
•-» 00
CV1 ^f
O
01
«O
g § 9 -a
£ 3 S £
•A 1 1 1
« € S t5
H H H H
C
bO
H H
.33
•o +»
JS
C « o
tl
M OJ
a 3 rn"
<^5sl si'
<~
o
a
«»
-------
V-l
CHAPTER V
WATER QUALITY CONDITIONS AND TRENDS
The water quality problems resulting from discharge of municipal
wastewater into the Potomac Estuary are not new. The first three
conclusions of a study conducted in 1913 [7], which are as applicable
today as they were then, are listed below:
1. "That at no point above Washington is the water of the
Potomac River safe for use as a public water supply without reasonable
treatment.
2. "That portions of the main or Georgetown Channel, between
the Chain Bridge and the junction of the main channel with Anacostia
River and Washington Channel, are so heavily polluted that the water
is unsafe for bathing purposes. The water from this section supplies
the Tidal Basin.
3. "That the conditions of that area in Anacostia River in the
neighborhood of the sewage-pumping station and at the junction of the
three channels is bad during hot weather, at times constituting a
nuisance; but that, when the improvements now planned or under con-
struction are completed, these conditions should no longer exist."
Not only has the water quality problem as stated above persisted,
conditions have deteriorated considerably.
-------
V-2
A. BACTERIAL DENSITIES
Bacterial densities in the Potomac Estuary have been determined
routinely since 1938. Total coliform counts in the Potomac at Three
Sisters Island have remained fairly constant for the past 20 years
at about 2,000 MPN/100 ml during the summer months (Figure V-l). In
contrast, total coliform densities in the estuary have increased to
over 2,000,000 in 1966 and then decreased to less than 7,000 in 1970
near the Blue Plains Sewage Treatment Plant. The reduction in recent
years can be attributed in part to an increase in overall wastewater
treatment efficiency including chlorination, and to higher river flows.
During 1969, continuous year-around chlorination of final effluents
was initiated at all major plants. This appears to be the most signifi-
cant single factor in the reduction of bacterial densities in the estuary
near Washington. As shown in Figure V-2, there has been a corresponding
reduction in fecal coliform counts under similar flow and temperature
conditions in August 1968 and August 1970.
The highest fecal coliform densities in 1968 were found between
River Mile 10 and 15 in the vicinity of the major wastewater discharges.
In August 1970, the highest densities were found at River Mile 7 in the
vicinity of Hains Point. At times, 10 to 20 mgd of untreated sewage is
discharged into the estuary as a result of inadequate sewerage and
treatment plant capacity at Blue Plains. Urban runoff from the Anacostia
River and Rock Creek basins also add to the fecal coliform problem.
-------
II*- 001 «3d)
SWS1NV9UO WHOJITOO
-------
FECAL COLIFORM DENSITIES
UPPER POTOMAC ESTUARY
100,000-
10,000-
cr ,,
8 N i.ooo;
£~
100-
MEAN OF 10 SAMPLES — AUGUST 19-23. 1968
FLOW = 2.800 cf>
TEMP. = 27.5'C
AUGUST 17, 1970
FLOW = 2300 cf»
TEMP. = 28.0'C
X Md. SHORE
D MAIN CHANNEL
o Vo. SHORE
I
10
15
20
25
30
35
RIVER MILES FROM CHAIN BRIDGE
FIGURE V-2
-------
V-5
At the Fort Washington monitoring station, total coliform densities
during the summer months have remained fairly constant except for recent
downtrends (see Figure V-l). These downtrends can also be attributed
to recent chlorination of treatment plant effluents.
-------
V-6
B. DISSOLVED OXTGEN
Dissolved oxygen (DO) concentrations in the upper Potomac Estuary
have also been routinely monitored since 1938. As shown in Figure V-3,
there has been a continuous downward trend in DO in the Potomac Estuary
near and below the wastewater discharges.
A significant increase in DO occurred in the early 1960's near
the Blue Plains outfall. However, with the population increase of the
past decade and little or no increase in treatment plant capacities,
DO in the Blue Plains vicinity during the summer months is now approaching
the levels of the late 1950's.
With increased loadings to existing waste treatment plants and
additional facilities being located farther downstream, the number of
miles affected by wastewater effluents has increased. As presented in
Figure V-3, the minimum 28-day DO concentrations at Fort Washington
have decreased from approximately 5.0 mg/1 to less than 4.0 mg/1 since
1938. Currently, about 20 miles of the estuary has a DO concentration of
less than 5.0 mg/1 (the water quality standard for that reach of the
Potomac) during low-flow periods.
The DO concentration at any given location in the estuary is a
function of many factors including biological activity, freshwater
inflow, temperature, wastewater loadings, and tidal stage. On four
sampling cruises made during the summer months of 1969, the locations
and readings of the minimum concentration of DO varied as shown in
Figure V-4. Minimum dissolved oxygen readings of less than 2.0 mg/1
were recorded on all four cruises, even when the freshwater inflow was
-------
V-7
as high as 8,890 cfs. Increases in freshwater inflows caused the point
of minimum DO to move downstream as evidenced when the DO profiles for
June 30 and August 14 are compared.
Data for the Potomac Estuary at the Woodrow Wilson Bridge (Figures
V-5 and V-6) show the typical annual variation in DO. During the summer
of 1965, DO concentrations ranged from 0.5 to 3.5 mg/1 with an average
of 2.0 mg/1. DO during the summer months of 1966 ranged from 0.5 to 3.0
mg/1 with an average of 1.5 mg/1. For the months of September through
December 1965, the DC concentrations remained depressed as a result of
low-flow conditions. During December 1965, the DC was approximately
5.5 mg/1 even when the water temperature was less than 10°C0
The DO concentration for a given time and location can also vary
over the cross-section of the estuary. In the Piscataway embayment,
DO varied from 4.0 to 12.0 mg/1 during a sampling cruise made on
June 27, 1970. At the same time, the main channel of the Potomac
Estuary showed a fairly uniform DO (about 4.0 mg/l) as a result of
tidal mixing (see Figure V-7). The higher DO concentrations in the
embayment were attributed to the photosyr.thetic production by dense
algal growths. During hours of darkness, the DO dropped to less than
8.0 mg/1 in the embayment while it remained around 4.0 mg/1 in the
main Potomac.
-------
•OOOCO 03A10590
-------
DO PROFILES
UPPER POTOMAC ESTUARY
1969
JUNE II, 1969
/' FLOW=l800cfs
x TEMP. = 26* C
JUNE 30,1969
FLOW = 940cfs
TEMP. = 28 5* C
x 8
Ol
O
Q 6
0
10
JULY 24, 1969
FLOW = 3200 cfs
TEMP. = 27* C
SURFACE
BOTTOM
W.WILSON BRIDGE
AUGUST 14.1969
FLOW = 8890 cfs
TEMP.= 27*C
10 20
RIVER MILES FROM CHAIN BRIDGE
30
FIGURE V-4
-------
UJ
O £
*z
e 1
Z d
Ld £
o
Ld
<3
ce
o
O in
O to
o:
o 5
> IS
'I Ld
°§
CL
S
O.)
i.'
i
o
o
-5
§
—
of
<
o
o
o
I
q
a.
LJ
CO
O
LJ
£
m
LJ
u.
oa
FIGURE V-5
-------
o
b:
. •
:'
g
<
) •.. ;;: ••• •" ' "
CD
S ' ' • . .
z ' '-.
- •'•-.-.
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
O O O OOQOOOOOO
05 w ~ •* CJ O 00 <£)'•* N O'
0.) (I/6-")
3aniVci3dW3i oa
FIGURE V-6
-------
fc5
U
I,
a g
UJ CJ
O <
w CD
o u
1
o
-8
(O
I
O
IO
r
•*
to
Hld3Q
FIGURE V-7
-------
V-13
C. SILT AND DEBRIS
The upper Potomac Estuary has changed drastically during the
past hundred years. At one time, water covered what is now the
corner of Seventeenth Street and Constitution Avenue. Potomac Park
and Hains Point did not exist. Tidewaters covered the present site
of National Airport and Boiling Field. The Anacostia River was a
broad stream with extensive mud flats. Many of the tidal flats of
the upper Potomac were formed by sediments and have been transformed
by dredged material into the present Washington area waterfronts.
The silt in the Potomac Estuary can be attributed to three
sources:
a. Above Great Falls, mainly forested;
b. Washington metropolitan area, mainly urban;
c. Coastal area, mainly rural.
For the water years 196l through 1968, the average sediment
yield of the upper Potomac above Great Falls was 1.98 billion Ibs/year
(Table V-l). The highest percentage of the annual contribution occurred
during either February or March with the maximum month values ranging
from 51 percent to 90 percent of the total annual load.
The Northwest Branch of the Anacostia River near Colesville,
Maryland with a drainage area of 21.1 square miles showed an annual
yield ranging from 1.0 to 1.6 million Ibs/sq mile with an average of
1.34 million Ibs/sq mi/yr (Table V-2). This is about seven times
greater than that from the upper basin which averages about 0.190
million Ibs/sq mi/yr.
-------
Tl
H
0)
S
0<
CO
ft
o
CM
O
H
ft
CM
CM
rH
CM
TV
O
ON
TJ ~
t>-
CM
•
--t
CO
VO
TV
t»
•
O
TV
TO
fi
fl
o
0
A
o
I
Q>
cd
0)
fc
-P tJO
cd -O
T3 -H
CM
H
VO
H
TV
O
H
O
MD
ON
TO
*
co cd
-------
Table V-2
SEDIMENT DATA
Northwest Branch Anacostia River near Colesville, Maryland
(Drainage Area = 21.1 sq. mi)
Year Total for Year Annual Yield
(1000 Ibs/sq mile)
1,590
1,090
1,540
1,360
1,420
1,000
Average 28,300 1,341
1963
1964
1965
1966
1967
1968
(1000 Ibs)
33,600
23,200
32,800
28,800
30,000
21,100
-------
V-16
Applying the Anacostia station average (1.34 million Ibs/sq mi/yr)
to the entire Washington metropolitan area and a yield rate of 0.20
million Ibs/sq mile to the lower coastal area, an estimate of the silt
loading to the entire Potomac River is as follows:
Yield Drainage Area
(1000 Ibs/sq mi/yr)
190
1,340
200
246*
(sq mi)
11,640
714
2r326
14,670
Average
Annual
Loading
(1000 Ibs/yr)
2,200,000
957,000
465.000
3,622,000
Upper Potomac
(above Great Falls)
Washington Area
Lower Coastal Area
Total
^Average Annual Yield
The upper basin is the greatest source of sediments.
In addition to the obvious silting of navigation channels, sedi-
ments have other relationships to water quality management problems,
some which are favorable and some unfavorable. During periods of
high flow and suspended sediment load, the Potomac contains corres-
pondingly greater quantities of organic carbon, nitrogen and phosphorus.
The suspended and adsorbed pollutants are deposited as the silt settles,
primarily in the upper 20 miles of the Potomac Estuary. During high
runoff periods, the upper 10 to 20 miles is chocolate brown in color
and aesthetically objectionable. Since the high silt loadings usually
occur during the spring months when fish are spawning in the estuary,
the silt may cover freshly laid eggs, thus reducing the effective
spawning area in the upper estuary.
-------
V-17
While silt transports a considerable amount of adsorbed nutrients
during high-river flows, the overall effect is to reduce the nutrient
concentration in the estuary, especially phosphorus. Sampling before
and after a period of extremely high runoff in March 1967, as reported
by CTSL [8], confirmed this observation. Silt also tends to cover
much of the organic matter deposited from wastewater discharges.
This covering generally reduces the availability of nutrients and
oxygen demanding material from bottom deposits.
It was observed by CTSL on numerous occasions that suspended
sediments contribute to algal control in the upper estuary. During
the summer months, runoff resulting from heavy rainfall usually causes
high turbidity in the upper estuary which restricts light penetration
in the water and reduces algal growth even though all other environ-
mental conditions may be favorable.
During the low-flow periods of 1966 and 1970, a reduction in
turbidity in the upper estuary along with other favorable environmental
condtions caused a significant increase in nuisance algal blooms near
and above Woodrow Wilson Bridge [52]. These nuisance blooms can be
expected to become more frequent as the silt control program becomes
more effective unless there is a simultaneous adequate removal of
nutrients from wastewater effluents.
During periods of high runoff, large quantities of debris enter
the estuary from the upper basin as well as from the metropolitan area.
-------
V-18
Debris from the upper basin is typically trees, brush, leaves, and
miscellaneous trash, and is usually partially decomposed. Debris from
the metropolitan area not only enters the estuary from local streams
but also from storm sewers and often contains paper, vegetable and
fruit peelings, styrofoam cups, etc. It appears that better solid-
waste management practices would decrease the amount of local debris
entering the estuary.
The effect of the increased silt and debris organic loadings on
the oxygen resources of the estuary has not been well defined. Based
upon DO studies made during a period of heavy precipitation, it appeared
that increased flows and the resulting dilution minimized any immediate
effect on the oxygen budget. Most of the organic matter carried into the
estuary by silt and debris settles and contributes to the benthic oxygen
demand. CTSL studies in the Potomac Estuary indicated that oxygen uptake
from benthic deposits was about twice as large in areas with treated
waste sludge deposits than in other areas of the upper estuary (Figure
V-8). Analysis of sediments for chemical oxygen demand (COD), as pre-
sented in Figure V-9, shows a fairly close relationship between COD
and benthic demand. From COD and uptake data, it appears that the
effect of sludge deposits and other suspended solids from wastewater
on the oxygen resources is much greater than the effect from the
organic solids in silt and debris.
-------
i
LJ
5
LJ
U
O
>- fc
DC i
13
z
UJ
IO
*«•>
. .
-------
LJ
< I
P ^
CL p:
3 a
S
Z
o
in
o
LJ
S
o:
tr
8
o
u
cr
1
2
I
I
o
1-8
oo
-8
-SB
I
O)
I
00
I
r-
T
(O
I
't
i
ro
(M
-S
-00
-to
-
-------
V-21
D. NUTRIENTS AND ALGAL GROWTH
As discussed previously in this report, the major source of nitrogen
and phosphorus in the upper Potomac Estuary is from the wastewater dis-
charges in the Washington area. Total phosphorus has increased about
22-fold, from 1,100 Ibs/day in 1913 to 24,000 Ibs/day in 1970, with
total nitrogen loadings increasing from 6,400 to 60,000 Ibs/day. A
greater increase for phosphorus reflects not only an increase in popu-
lation but also the increased use of detergents. The current carbon
loadings are about 100,000 Ibs/day, approximately the same as they were
in the mid-19401s. The decrease in organic carbon in the early 1960's
was a result of the completion of present treatment facilities at Blue
Plains.
1. Nutrient Concentrations in the Potomac Estuary
The concentrations and forms of phosphorus and nitrogen in the
Potomac Estuary are a function of wastewater loadings, temperature,
freshwater inflow, and biological activity. As shown in Figure V-10,
the inorganic phosphorus varied considerably for the six stations
sampled from March 1969 through September 1970. The concentration
at Mains Point, located at the upper end of the tidal excursion of
the major wastewater discharges, was fairly uniform averaging about
0.3 mg/1. At Woodrow Wilson Bridge, located below the Blue Plains
wastewater discharge, the inorganic phosphorus increased appreciably
with concentrations over 2.5 mg/1 during periods of low flow such as
those that occurred in July to October 1969 and September 1970. The
-------
INORGANIC PHOSPHATE CONCENTRATION «
POTOMAC ESTUARY
HAMS POMT
MCES BELOW CHAIN BMDGC » 7.60
JUN JUC MJG SEP. 'OCT ' NOV. DCC. I JAN. Ftt.
WOODROW WILSON BRIDGE
MLES BELOW CHAW BRIDGE *
APB. ' MAY JUN. JUL. ' AUG. ' SEP. ' OCt
1 - I '
MB«4-»I
1.2-
LO -
INWAN HEAD
JUN. JUL ' AUG. XP OCT. NOU
07-
= 06-
f 05-
OJ-
03-
02-
01-
SMITH POINT
MLES BELOW CHAIN BRIDGE * 4640
or-
06-
!03-
02-
Ol-
FU. MAM. AM. MAY JUN.
301 BRIDGE
SCR OCT. NOV. DGC. JtM.
• mo
C. Jt
B i I •
AML MW JIM.
MAY JUN.
AUG. ' sa ' OCT. NOU ' occT 1 J«t ' roT
m0-*-!-*• «7o
07-
06-
oft-
e O*-
- os-
02-
PINEY PONT
MLES BELOW CHAM BROGC a 99.20
Am. MAY JUN
AUG. SCR OCT. NOU
JAN. FEI.
-------
V-23
remaining four downstream stations had concentrations progressively
smaller.
It was observed that much of the phosphorus is deposited into
the upper estuary even during high flows such as those in August 1969
and April 1970. During periods of high freshwater inflow, the sediment
appears to adsorb more phosphorus than it releases. This is discussed
in greater detail later.
The total phosphorus concentration closely parallels that of
inorganic phosphorus. In the upper reach, the ratio of total phos-
phorus to inorganic phosphorus ranges from 1.1 to 1.5. The ratio is
higher in the middle reach normally varying from 1.5 to 2.0 with the
lower reach having a range from approximately 2.0 to 2.5.
The concentration of nitrite (N02) and nitrate (N03) nitrogen at
Hains Point and Woodrow Wilson Bridge varies almost inversely to that of
phosphorus (Figure V-ll). The N02 + N03 concentration was highest in
July and August 1969 and during the spring months of 1970. During these
months, both high-flow periods, the phosphorus was lowest (Figure V-10).
The increase of N02 + N03 at Indian Head as compared to Woodrow Wilson
Bridge in May-June 1969, September-November 1969, and July 1970 was a
result of the conversion of ammonia from the wastewater treatment plant
discharges to NO^. The extremely low concentration of N02 + N03 in the
summer months at Smith Point was caused by uptake by algal cells [52].
During winter months algal utilization is lower [52], thus the concen-
trations of nitrates are high, as in January and April 1970. At Piney
Point, concentrations of N02 + N03 are usually less than 0.1 mg/1.
-------
Li-
U-
13-
12-
+ r«H
£-~07-
O5-
O4-
03-
02-
MAINS POINT
MUS BELOW CHAIN WKXJE •
NITRATE
-------
V-25
As shown in Figure V-12, the concentration of ammonia nitrogen
is also affected by flow and temperature conditions. Although large
quantities of ammonia are discharged from wastewater treatment facilities
into the Potomac near Woodrow Wilson Bridge, the ammonia at Indian Head
during the summer months is low because of nitrification.
During the summer and early fall months, the average ranges of pH,
alkalinity, and free dissolved C02 (measured by titration) for the five
stations in the upper and middle reaches were:
Free Dissolved
Location _piL_ Alkalinity CO?
(units) (mg/1 as CaC03 (mg/T)
Chain Bridge 7.5 - 8.0 80-100 2 - 4
W. Wilson Bridge 7,0 - 7.5 90 - 110 8 - 12
Indian Head 7.2-8.0 70-90 6-10
Maryland Point 7.5-8.2 60-85 2-8
Rte. 301 Bridge 7.5-8.0 65-85 7-8
In the vicinity of the Woodrow Wilson Bridge, there is an increase
in both alkalinity and C02 with a corresponding decrease in pH attri-
buted to wastewater discharges. There is a decrease in both alkalinity
and C02 with a corresponding increase in pH at the Indian Head and
Maryland Point stations which are due to algal growths. In the lower
estuary, the alkalinity and C02 increases while pH decreases. The
algal standing crops are considerably smaller in this reach.
-------
«^OJ-
* I 07-
04-
OS-
o.*-
O3-
02-
01-
00-
AMMONIA MTROGEN a
POTOMAC ESTUMtV
NW-V7D
N
WOODROW WILSON BRIDGE
ML£S BELOW CHAM WUX3E > 12.10
SMITH POINT
MILES BELOW CHAIN BRIDGE * 4C.80
n
0.7-
OJt-
05-
=_04-
03-
M-
0.1-
301 BRIDGE
ML£S BELOW CHAM BRIDGE * 67.40
A
^/v^x^
(U-
O7-
(U-
O5-
M"
tft I 1 • <
PMEY POINT
MLES BELOW OiWN MDGE - M.ZO
FIGURE V-12
-------
V-27
2. Mathematical Models for Nutrient Transport
Mathematical models for predicting the movement and transport
of phosphorus and nitrogen have been developed by CTSL. A detailed
report of the modeling of nutrient transport is in preparation.
Some of the model's predictions for phosphorus are shown in Figures
V-13 and V-14 and for nitrogen in Figures V-15 and V-l6.
The effects of temperature on nutrient transport, deposition,
and utilization by the biota were determined by CTSL. The rates of
phosphorus loss, ammonia utilization, and nitrate algal uptake as a
function of temperature are shown in Figures V-17, V-18, and V-19,
respectively.
These models, which considered the effects of temperature on
the algal productivity rates, were used to investigate the role of
nutrients in eutrophication. The models were also used to establish
maximum allowable nutrient loadings by zones as presented later in
this report.
-------
O
cr
o
D
Ul
in
-------
in
_o
H
1 1 1 1 1 1 1 1 1 1 1 1 1
ID
"5
5
-IT)
_O
If)
SV
FIGURE V-14
-------
LJ rf >o
Z u -.
8^1
z 11
£ o
*» V
« a
ii u
^ a*
O 2
CO
o 5
g"
1
Tl-
(VI
M
(VJ
O
rvi
op
—
(O
—
•*.
—
i
CM
—
q
—
1
oo
ci
1
IO
o
•*
o
1
M
O
C
c
(l/6ul) N39OHJ.IN
FIGURE V-15
-------
Z
U ^
O fe
Z u
fi °
o <
Ld O
O Q.
O
tr
oo
u>
o>
(VI
CM
O
j: o
(M N
n "
(M
o
(M
oo
m
o
9
00
2
-S
to
UJ
.j
5
_o
-in
(O
M
00
O
-------
. I-
.09-
.08-
.07-
.06-
.05-
.04-
.03-
.02-
5 .01-
- .009-
O.
.008-
.007-
.006-
.005-
.004-
.003-
.002-
001-
EFFECT OF TEMPERATURE
ON
PHOSPHCJRUS DEPOSITION RATE
POTOMAC ESTUARY
11.000 cf»
8800 cf>
185 cf»
bf ** I *» tT —T \
r\ p I fl I **'
R72
0 : 1.084
Kp.20'Cr 0.0225 (BASE •)
(SECOND-ORDER KINETICS)
10
15 20
TEMP. to:c)
25
30 35
FIGURE V-17
-------
0.4-
0.3-
0.2-
^
O.M
.09-
.08-
.07-
.06-
.05-
.04-
.03-
.02-
.01-
.009-
.008-
.007-
.006-
.005-
.004-
.003-
.002-
.001-
EFFECT OF TEMPERATURE
ON
NITRIFICATION RATE
POTOMAC ESTUARY
NH,
NO2+ NO3
0 = 1.188
KN= 0.068 (BASE «) a* 20'C
(FIRST ORDER KINETICS)
10
I I
15 20
TEMPERATURE
CO
I
25
I
30
I
35
FIGURE V-18
-------
0.2-
0.1-
.09-
.08-
.07-
.06-
.05-
.04-
.03-
.02-
.01-
.009-
.008-
.007-
.006-
.005-
.004-
.003-
.002H
.001
EFFECT OF TEMPERATURE
ON
RATE OF NITROGEN UTILIZATION BY ALGAE
POTOMAC ESTUARY
NO —*• ALGAL NITROGEN
9 = 1-120
KN2 = 0.034 (BASE •) at 20*C
(FIRST ORDER KINETICS)
I
10
I
15
I
20
25
I
30
I
35
TEMPERATURE
CO
FIGURE V-19
-------
V-35
3. Ecological ^rends as Related to Nutrient Loadings
The Potomac tidal system is saline in the lower reach with the
middle reach brackish and the upper reach fresh water. These dif-
ferences in salinity as well as nutrient enrichment by wastewater
discharges have a pronounced effect on the ecology of the estuary.
Under summer and fall conditions, large populations of blue-green
algae (a pollution tolerant phytoplanlcton), mainly Anacvstis sp.
are prevalent in the freshwater portion of the estuary. Large
standing crops of this alga occur, especially during periods of
low flow, forming green mats of cells. The blue-green algae are
apparently not readily grazed by the higher trophic forms and
therefore are often considered a "dead end" of the normal food chain.
In the saline portion of the Potomac Estuary, the algal popu-
lations are not as dense as in the freshwater portion. Nevertheless,
at times large populations of marine phytoplankton, primarily the
algae Gvmnodinium sp. and Amnhidinium sp., occur producing massive
growths known as "red tides."
The effect of the increases in nutrient loadings from wastewater
since 1913 on the dominant plant forms in the upper estuary has been
dramatic (Figure V-20). Several nutrients and other growth factors
have been implicated as stimulating this, with nitrogen and phos-
phorus showing promise of being the most manageable.
The historical plant life cycles in the upper Potomac Estuary
can be inferred from several studies. Gumming [7] surveyed the
estuary in 1913-1914 and noted the absence of plant life near the
-------
O «» NO9HVD DINV9MO
I I
01
O
ul
o:
(E
IU
1 2
u x
Z &
Ul 3
a
z
tr:
u
t
1
LJ
10
1
t-
D
Z
H
(/)
¥
O
a:
V
4
V—
J«rt
a. ui
O
O
z
0
O
0
o"
IO
o
o
q
o
(M
O
o
o
in
*
N «
0
8
iff
—
0
8
o"
CO
0 N39OM1IN ~lViOl
O
8
o
o
o
o
m"
o
O 0
8
in
d «° SnMOHdSOHd IVIOI
FIGURE V-20
-------
V-37
major waste outfalls with "normal" amounts of rooted aquatic plants on
the flats or shoal areas below the urban area. No nuisance levels of
rooted aquatic plants or phytoplankton blooms were noted.
In the 1920"s, an infestation of water chestnut appeared in the
waters of the Chesapeake Bay including the Potomac Estuary. This
infestation was controlled by mechanical removal [9].
In September and October 1952, another survey of the reaches
near the metropolitan area made by Bartsch [10] revealed that vege-
tation in the area was virtually nonexistent. No dense phytoplankton
blooms were reported although the study did not include the downstream
areas where they were subsequently found.
In August and September 1959, a survey of the area was made by
Stotts and Longwell [11]. Blooms of the nuisance blue-green alga
Anacystis were reported in the Anacostia and Potomac Rivers near
Washington.
In 1958 a rooted aquatic plant, water milfoil, developed in the
Potomac Estuary and created nuisance conditions. The growth increased
to major proportions by 1963, especially in the embayments from Indian
Head downstream [12].
These dense strands of rooted aquatic plants, which rapidly
invaded the system, dramatically disappeared in 1965 and 1966. The
decrease was presumably due to a natural virus [13].
-------
V-38
Subsequent and continuing observations by CTSL have confirmed per-
sistent massive summer blooms of the blue-green alga Anacystis in
nuisance concentrations of greater than 50 ug/1 from the metropolitan
area downstream at least as far as Maryland Point [14]. Chlorophyll a
determinations (a gross measure of algal standing crop) in the upper
reach and in the middle and lower reaches of the Potomac Estuary are
presented in Figures V-21 and V-22 respectively.
Chlorophyll a at Indian Head and Smith Point for 1965-1966 and
1969-1970, as presented in Figures V-21 and V-22 respectively, indi-
cate that algal populations have not only increased in density but
have become more persistent over the annual cycle. At both stations,
higher values of chlorophyll were measured during the 1969-1970
sampling cruises. The occurrence of a spring bloom of diatoms was
observed in 1969 and 1970. This had not been observed during the
1965-1966 cruises.
These biological observations over the years appear to indicate
a species succession. The initial response to a relatively light
overenrichment [9] was the growth of water chestnut which when
removed allowed the increasing nutrient load to be taken up into
the rooted aquatic plant, water milfoil (Myriophvllum snicatum).
The die-off of water milfoil then allowed the nutrients to be
competitively selected by the blue-green alga Anacystis. Since
Anacystis is apparently not utilized in the normal food chain, huge
mats and masses accumulate, die off, and decay.
-------
HAMS POMT
MLES KU3W CHAM BBCG£ s 7.60
CHUOROPHYLL a
POTOMAC ESTUARY
UPPER REACH
-------
SMITH POINT
MLES KLOW CHAM MMI « 4140
CHLOROPHYLL a
POTOMAC ESTUARY
MDOLE t* LOWE* REACH
SI-
HAY JUN
ni*
»•«—I—••*>
JM. JUL MJG.
301 BRIDGE
MLES BELOW CHAIN BRIDGE < 67.40
JAN FEL
APR MAY JIM
OCT MOV oec S*.
IBM *-!-* KflO
AUG. SCf
WNEY POINT
MILES BELOW CHAM BRIDGE = M.20
JUN. JUL
SCR OCT NOW DEC | JAN.
IM9 *
r-p
»»-!—•«
~>—r^;—>—™—'
-------
V-41
From the above considerations, it would appear that nuisance
conditions did not develop linearly with an increase in nutrients.
Instead, the increase in nutrients appeared to favor the growth and
thus the domination by a given species. As nutrients increased
further, the species in turn was rapidly replaced by another dominant
form. For example, water chestnut was replaced by water milfoil
which in turn was replaced by Anacystis.
Figure V-20 indicates that the massive blue-green algal blooms
were associated with large phosphorus and nitrogen loading increases
in the upper reaches of the Potomac River tidal system. The massive
algal blooms have persisted since the early 1960's even though the
amount of organic carbon from wastewater discharges has been reduced
by almost 50 percent.
Laboratory and controlled field pond studies by Mulligan [15]
have shown similar results. Ponds receiving low-nutrient additions
(phosphorus and nitrogen) contained submerged aquatic weeds. Con-
tinuous blooms of algae appeared in the ponds having high nitrogen
and phosphorus concentrations. An important observation in Mulligan's
studies was that when the water quality was returned to its original
state by reduction of nutrient concentrations, the ecosystem also
reverted to its previous state. This observation was also supported
by studies of Edmondson [16] on Lake Washington and Easier on the
Madison, Wisconsin lakes [17].
-------
V-42
E. EFFECTS OF EUTROPHIGATION ON WATER QUALITY
The effects of nutrient enrichment and the resulting algal growths
are fourfold: (l) an increase in organic oxygen demanding load,
(2) an increase or decrease in dissolved oxygen caused by algal photo-
synthesis or respiration, (3) the creation of nuisance and aesthetically
objectionable conditions, and (4) the possible toxic effects on other
plants and aquatic life. Each of the effects is discussed separately
below;
1» Increase in Organic Oxygen Demanding Load
Algal cells convert inorganic carbon and nitrogen into organic
compounds and result in an appreciable oxygen demanding load after
their death. For example, under summer conditions, all of the
60,000 Ibs/day of nitrogen discharged into the estuary from wastewater
treatment facilities is converted into algal cells. The combined
ultimate oxygen demand of nitrogen and carbon from these cells is
approximately 490,000 Ibs/day. This load, though dispersed over the
entire upper estuary, is nevertheless greater than the total oxygen
demand by all wastewater discharges into the upper estuary.
Laboratory studies on rate kinetics of the oxidation of algal cells
at temperatures of 28°C to 30 C indicated that the reaction rates for
the oxygen demanding process vary from 0.16 to 1.25 per day. The
increase in organic oxygen demanding loads is often concentrated in
the embayments or along the shores as a result of wind action.
These concentrations of decaying algae produce noxious odors.
-------
V-43
2. Algal Oxygen Production and Respiration
As shown in Figure V-7, the DO concentration in the Piscataway
embayment was 12 mg/1 which was about 4 nig/1 above saturation capacity
at the observed water temperature. This increase in DO above satura-
tion capacity is due to oxygen produced by algal cells. The total
oxygen production of a community as a result of the photosynthetic
activity is a function of algal biomass and population composition,
light intensity, and temperature. In the upper and middle Potomac
Estuary, light penetration is usually limited to the upper 2 to 4
feet of the water column.
Bacterial and algal respiration occur simultaneously with the
oxygen production process. Since the upper estuary is well mixed,
this respiration process occurs over the entire water column. During
the months of June and July 1970, oxygen production and respiration
rate studies were made in the upper and middle Potomac Estuary as
presented in Table Y-3„ A special respiration study was conducted on
July 29, 1970, which indicated that .0010 mg 02/hr/ug of chlorophyll
respiration could te attributed to algae with the remainder due to
bacterial and other oxidation processes.
With a euphctic zone of 2 feet, an average oxygen production of
.010 mg 02/hr/ug cf chlorophyll for 12 hours/day, an average respiration
of 0001Q mg 02/hr/ug of chlorophyll for 24 hours/day, and an average
chlorophyll concentration of 100 ug/1, the oxygen balance for various
water columns is given in Table V-4. The data indicate that for a
-------
Table V-3
OXYGEN PRODUCTION AND RESPIRATION RATE SURVEY
Upper and Middle Potomac Estuary
1970
Date
6-22
6-23
6-24
6-25
7-20
7-21
7-22
7-27
Water
Temp.
(°c)
26
27
27
27
28
27
26
28
Chlorophyll a
Range
(ug/1)
40-110
70-120
54-110
50- 60
30-100
30-143
30-140
_
Light
Intensity
Range
(foot candles)
250-300
200-300
200-300
200-300
250-400
200-300
100-200
_
Oxygen
Production
mg/hr/ug of
Chlorophyll a
.0073
.0084
.0087
.0121
.0130
.0130
.0146
.0060
Respiration
mg/hr/ug of
Chlorophyll a.
.0023
.0011
.0024
.0033
.0022
.0016
.0017
.0010
-------
Table V-4
OXTCEN PRODUCTION-RESPIRATION BALANCES
Chlorophyll a = 100 ug/1
Oxygen Production = .010 mg/hr/ug chlorophyll for 12 hours/day
Respiration = .0010 mg/hr/ug chlorophyll for 24 hours/day
Euphotic Zone of 2.0 feet
Increase in Oxygen
Averaged over Entire Decrease in
Water Column due to Oxygen due to
Water Column Fhotosynthes is Respiration Net
(depth)
4
8
12
16
20
4
8
12
16
20
(mg/l/day)
6.0
3.0
2.0
1.5
1.2
Euphotic Zone
12.0
6.0
4.0
3.0
2.4
2.4
2.4
2.4
2.4
2.4
of 4.0 feet
2.4
2.4
2.4
2.4
2.4
(mg/l/day)
3.6
0.6
-0.4
-0.9
-1.2
+9.6
+3.6
+1.6
+0.6
0.0
-------
V-46
water depth greater than 10 feet, respiration would be larger than
production, thus resulting in a negative net balance on the oxygen
resources of the system.
If the euphotic zone were increased to 4 feet, there would be a
net oxygen production for water columns of 24 feet or less. Conversely,
if the depth of the euphotic zone were 1 foot, there would be a net
oxygen production for water approximately 6 feet and less in depth.
The DO budget in the Potomac Estuary is affected by algal pro-
duction and respiration as shown in Figure V-23. The net result of
oxygen production and demand by algal respiration and decay is a
reduction of the oxygen resources. This DO depression is approxi-
mately 2.0 mg/1 in the estuary and can be attributed to algal
respiration and decay. The net oxygen production concept has been
incorporated into the DO budget model for the Potomac Estuary.
-------
j; o
8 «
oo r-
(VJ CM
O
00
-------
V-48
3. Unfavorable Physical and Aesthetic Characteristics of Algal Blooms
When algal blooms become extensive, large mats are formed causing
what appears to be a coating of green paint on the water surface. In
embayments such as Gunston Cove, Piscataway and Dogue Creeks, these mats
usually concentrate in the vicinity of marinas not only coating the
hulls of boats but also emitting an obnoxious odor when the cells die
and decay.
Along the Potomac shorelines, rows of algal mats are often formed
by wind action. These windrows of algae render the shoreline unsuitable
for swimming and recreation.
In September 1970, after a period of low flows, the algal blooms
became quite prominent in the area of Woodrow Wilson Bridge. After a
week of temperatures in the 90's Fahrenheit, an algal mat developed in
the Tidal Basin. The dense growth of algae was physically removed to
minimize the obnoxious odors emanating from the decaying mats. This
was the first known occurrence of a heavy algal bloom in the Tidal
Basin.
-------
V-49
4. Algal Toxicitv
It has been postulated that some algal species cause gastric
disturbances in human beings who ingest infested water. Under cer-
tain conditions, several species of blue-green algae produce toxic
organic compounds that can kill fish, birds, and domestic animals
[21]. Of the 10 such known genera, three (Anabaena, Oscillatoria,
and Anacystis) grow profusely in the upper Potomac Estuary.
At the present time, the effects of toxins from blue-green algae
on other forms of life in the waters of the Potomac Estuary are not
well established. In the summer of 1970, the blue crab harvest in
an area of heavy algal blooms was reduced because of undesirable
tastes and odors. It was also reported that several people became
ill after eating crabs from this area. Crabbing in the lower Potomac,
where there are no blue-green algal blooms, was not affected. It is
postulated that the objectionable taste and odor of the crabs was
related to the blue-green algae.
If the estuary is to be used as a water supply source, the
possibility of the effect of toxins from blue-green algae must be
considered. The genera currently found in the Potomac have known
species which are toxin producers and as mentioned previously are
also known to affect the taste and odor of seafood.
-------
VI-1
CHAPTER VI
DISSOLVED OXYGEN ENHANCEMENT
A. STUDY APPROACH
The concentration of dissolved oxygen in the upper estuary is
a function of environmental conditions, biological population and
activity, and concentration and composition of organic matter in the
system. A schematic diagram shown in Figure VI-1, originally pre-
sented by Torpey [18], demonstrates the interrelationships of the
oxidation of carbonaceous and nitrogenous components of organic
matter by bacteria, and photosynthetic activity by phytoplankton,
and dissolved oxygen.
The three biological systems having the greatest effect on the
DO are the bacteria which oxidize the carbonaceous matter, the bac-
teria which oxidize the nitrogenous matter, and the phytoplankton
which grow as a result of nutrient enrichment. In the upper Potomac
Estuary, these three biological systems can and do occur simultaneously
in the same area. The predominance of one or all of the three systems
depends not only on the source of organic matter (wastewater effluents)
but also on such environmental factors as temperature, light penetration,
and freshwater inflow.
A DO budget has been incorporated into the FWQA Dynamic Quality
Model consisting of the following five linkages:
(l) Oxidation of carbonaceous matter,
(2) Oxidation of nitrogenous matter (ammonia and organic),
-------
I
CO CO
Z 2
O if
% £
H ui<"
y cc
< 2
X
O
§
co
CO
5
CD
CC
O
(JJONfia QNVT)
noaOHDVB - DIHLN38)
(a30.VM3J.SVM)
QNVT)
N39AXO
QNV1)
(a3i.VM3.LSVM)
Noaavo DINVOWO
(Dia3HdSOWlV)
(a31VM31SVM)
(JJONOH ONV1)
Noaavo
JLH9H
NHS
(QNnoaoxova -
(JdONOa QNVT)
(a31VM31SVM)
TVI1N3SS3 a3H10
FIGURE VI-I
-------
VI -3
(3) Oxygen production and respiration of simulated algal
standing crops based upon nitrate utilization by the
cells ,
(4) Benthic demand, and
(5) Reaeration from the atmosphere.
The model, which is described in a CTSL report currently in pre-
paration, has been verified for flow ranges from 212 to 8800 cfs .
The average observed and predicted DO concentrations for the
periods of September 22, 1968, and August 12-19, 1969, as shown in
Figures VI -2 and VI -3 respectively, demonstrate that the model can
predict DO responses over a wide range of freshwater inflows.
The basic coefficients used in the DO budget model are:
Rate (base e) Temperature Coeffici-
Process at 20°C ent 9(^1- ?2Q)
Carbonaceous oxidation 0.170 1.047
Nitrogenous oxidation 0.068 1.188
Algal utilization of nitrogen 0.034 1.120
Reaeration from the atmosphere * 1.021
The remaining processes in the DO budget are given below:
Algal oxygen production rate = 0.012 mg 02/hr/ug chlorophyll §.
Algal respiration rate = 0.0008 mg 02/hr/ug chlorophyll a
Euphotic zone = 2 feet deep
Respiration depth = full depth of water column
Algal oxygen production period = 12 hours
Algal respiration period = 24 hours
Benthic demand rate = 1.0 gr 02/day sq mi
* The model calculates reaeration as a function of depth and velocity
using any one of three formulations.
-------
o
_ o
I
o>
I
CO
-------
(VI
u
O
o
1
o
I
10
Ul
_ o
FIGURE VI-3
-------
VI-6
Details of the effect of these parameters on the DO budget will also
•be given in the CTSL report now in preparation.
The major area of depressed oxygen during low-flow periods is
from Hains Point to about Gunston Cove. In this area, the major
source of the oxygen depression is from wastewater effluent. The
total daily oxygen demanding loads from these discharges are as
follows:
Carbonaceous = 200,000 Ibs/day
Nitrogenous = 250,000 Ibs/day
Under these flow conditions, approximately 65,000 Ibs/day of car-
bonaceous and nitrogenous oxygen demand enter the upper estuary from
land runoff. From the above, it can be concluded that the current
nitrogenous demand has the greatest effect on the oxygen resources
of the estuary with carbonaceous demand being slightly lower.
However, the rate at which the demand (carbonaceous and nitro-
genous) is exerted varies significantly depending upon temperature.
At a 28°C temperature, the demand rates are equal at 0.34 day (base e);
while at 15°C, the carbonaceous demand rate is 0.18 with the nitro-
genous demand dropping to 0.03. See Figure V-18 for nitrification rates.
Simulation runs with the model indicate that while nitrification
continues to occur at temperatures of 15°C or lower, it plays a minor
role in the overall DO budget of the upper Potomac Estuary.
-------
VI-7
For 22 years of record, mean monthly water temperatures in the
upper estuary have been determined as given below:
January 2.5°C July 28.1°C
February 3.3°C August 27.8OC
March 7.8QC September 24.7°C
April 14.0°C October 18.400
May 20.4°C November 11.5°C
June 25.9°C December 4.8°C
Based upon the above tabulation and the study discussed above, it
appears that nitrification control for DO enhancement is required
only for the months of April through October. This is developed
further in Chapter XII.
-------
VI-8
B. DO CRITERIA
Water quality standards for dissolved oxygen have been adopted
by the States of Maryland and Virginia and by the District of Columbia.
For the waters of the Potomac, the standards are as given below:
Jurisdiction Average DO Minimum DO
(mg/1) lmg/1)
District of Columbia* 5.0 (Daily) 4.0
State of Maryland 5.0 (Monthly) 4.0
State of Virginia 5.0 (Daily) 4.0
* Except between the Rocbambeau Memorial and Prince Georges County
(Maryland) line where the average is 4.0 and the minimum DO is 3.0.
These DO .standards were used as criteria in this study.
-------
VII-1
CHAPTER VII
ALGAL GROWTH RESPONSE TO NUTRIENT CONTROL
Reductions in the standing crop (biomass) of algae in the Potomac
Estuary can be achieved by management, singly or in combinations, of
carbon, nitrogen, and phosphorus content. The decision as to which
nutrient or nutrients to control may depend upon several factors
especially the four listed below:
1. Level of algal reduction required to minimize the effect on
water quality such as DO and recreational water use,
2. Maximum nutrient concentration allowable to maintain a maxi-
mum permissible algal standing crop,
3. Controllability and mobility of a given nutrient, and
4. The overall water quality objectives, such as DO enhancement,
eutrophication reversal, or reduction of potentially toxic matter
including heavy metals.
The four factors listed above were used not only to establish the
nutrient criteria but also to develop the overall wastewater manage-
ment program for the Potomac Estuary.
-------
VII-2
A. EUTRQEHICATION CONTROL OBJECTIVES
For purposes of water quality management, the upper Potomac
Estuary may be considered eutrophic when undesired standing crops
become the predominant plant life as is now occurring with the nuisance
blue-green alga species. The major objectives for controlling the blue-
green algal standing crop in the upper estuary are fourfold:
1. To reduce the dissolved oxygen (DO) depression caused by res-
piration and the decay of algal growths especially in waters over 10
feet in depth. At times, DO depressions of more than 3.0 mg/1 below
saturation occur even during daylight hours.
2. To minimize the increase of ultimate oxygen demand (UOD)
resulting from the conversion by algal cells of inorganic carbon and
nitrogen from wastewater to oxidizable organic compounds. Currently,
more UOD is added to the upper Potomac Estuary in the summer months as
a result of algal growth than from wastewater discharges.
3. To enhance the aesthetic conditions in the upper estuary. Large
green mats develop during the months of June through October and create
objectionable odors, clog marinas, cover beaches and shorelines, and in
general reduce the potential of the estuary for recreational purposes
such as fishing1, boating, and water skiing.
4. To reduce any potential toxin problem and objectionable taste
and odor problems related to excessive blue-green algal crops if the
upper estuary is to be used as a supplemental \vater supply.
-------
VII-3
To aid in defining an algal standing crop limit, a subjective
analysis using chlorophyll concentrations was developed incorporating
conditions having possible effects on water quality. Four major
restraints to desired water uses are offered in this analysis (Table
VII-l) including the required reduction in the chlorophyll standing
crop for each of the parameters.
The desired maximum limit of 0.5 mg/1 DO below saturation was
selected by CTSL to allow for assimilation of waste discharges and
naturally occurring oxygen demanding pollutants. To minimise the
effects of increased organic loads and sludge deposits caused by
algal growths, an upper limit of 5.0 mg/1 of total oxygen demand is
proposed.
Of the four restraints, the most stringent reduction percentage
is for control of growths to prevent nuisance conditions. From the
above analysis, a 75 to 90 percent reduction in chlorophyll concen-
tration will be required in the Potomac Estuary, or chlorophyll
levels of approximately 25 ug/1.
-------
H
;
M
M
>
0
rH
r~i
"cd
H
co
Eg
^H
CM
M
s
8
>-H
§
S
O
o
d
c5
K-5
<
Er-,
0
CO
M
B
!H
^^
&£}
™>
M
e
K)
CQ
CO
fi
O
•H
-P
O
S P
t3 O
££
0 ty
ho P
cd -H
-p T3
fl fi
0 cd
0 -p
Pi CO
0
CL, -p
fl
T) 0
0 fH
P. P
•H "
3 0
0*
0 VH
tti 0
tfN
to
U"\
vo
-P
•H
%
h4
'O S
0 3
Pi B
CQ X
si
<^
^
*>fN
*
O
*.
CQ
-P
PS
•r-
S
^
cn
•p
P!
•H
$-i cd
O Pi
-P
>> CQ
-p 0
•H fCj
rH
cd 0
( y i ^
£-f Pi
0 0
-P -P
cc cd
^3
TJ
0
CQ
cd
O
SM
o
•H
CQ
CQ
0
ft
£~5
O
Q
q
Q
•H
-P
fi
^
_{_>
fU
CO
B
•H
-P
cd
•H
Qt
CQ
0
PS
•a
§
r*i
cd
o
0
P.
O
to
1
lf\
\Q
•!^
%
O
•
ITV
, — |
^
o
o
-p
ITl
rH
0
CQ
cd
fn
o
P!
M
^_l
0
H
^"s^
tip
S
d
0
ho
r?
o
1 — 1
cd
b
EH
P!
•H
0
CQ
cd
0
o
a
t-i
Q
o
m
CD
-P
£3
-H
H
[ID
f^
*H
rc3
cd
O
l_Zj
up
•H
TJ
pj
CO
S
Q
O
0
tf\
/*w
&
H
"ho
jj
U^\
nj
I — 1
^-v^
b£
^
rH
/ V
i
£l
o
o
rH
^5
r^-4
P
0
rH
r£*
O
O
•H
-P
-P
CQ
0
o
O
H
P4
cd
A
-t-z
rt
0
-P
cd
S
hO
0
Pi
cd
S
0
•H
-P
cd
Pi
40
K
0
o
P;
o
o
cdl
rH
rH
£
ft
0
£-J
o
1 — t
'o
«\
CO
g
•H
-p
•H
13
PI
O
O
B
0
0
rH
-Q
0
O
cj
cd
CQ
-H
r$
^
0
T3
P5
*
rt
P
rH
0
O
in
0
•P
n
i
•H
-P
0
[L|
0
^>
0
Q)
ho
B
J>
-------
VII-5
B. NUTRIENT REQUIREMENTS TO PREVENT EXCESSIVE STANDING CROPS OF BLUE-
GREEN ALGAE
Various investigators studying algal growth requirements have dis-
cussed the concentrations of nitrogen and phosphorus needed to stimulate
algal blooms. In a recent study of the Occoquan Reservoir, located on a
tributary of the Potomac Estuary, Sa-wyer [19] recommended limits of
inorganic nitrogen and inorganic phosphorus of 0.35 and 0.02 mg/1,
respectively. This reservoir has blue-green algal blooms under summer
conditions attributed to wastewater effluents discharged into tributaries
flowing into the reservoir. Mackenthun [20] cites data indicating upper
limits of inorganic nitrogen at 0.3 mg/1 and inorganic phosphorus at
0.01 mg/1 at the start of the growing season to prevent blooms. FWQA's
Committee on Water Quality Criteria recommends an upper limit of 0.05
mg/1 of total phosphorus for estuarine waters [21]. No recommendations
for inorganic nitrogen were made other than that the ratio of nitrogen
to phosphorus should not be radically changed from that naturally
occurring.
Pritchard [22], studying the Chesapeake Bay and its tributaries,
suggests that if total phosphorus concentrations in estuarine waters are
less than 0.03 mg/1, biologically healthy conditions will be maintained.
Jaworski e_£. ajl [14], reviewing historical data for the upper Potomac
Estuary, suggest that if the concentration of inorganic phosphorus and
inorganic nitrogen were at 0.1 and 0.3 mgA respectively, algal blooms
of approximately 50 ug/1 of chlorophyll §. would result. A chlorophyll a
concentration of 50 ug/1 or over was considered indicative of excessive
-------
VII-6
algae. Studies of the James River Estuary, a sister estuary to the
Potomac, by Brehmer and Haltiwanger [23] indicate that nitrogen appears
to be the rate limiting nutrient.
Recently, the management of carbon in controlling algal blooms
has been suggested by Kuentzel [24] and Lange [25]. Studies by Kerr
et al [26] also suggest that inorganic carbon is apparently directly
responsible for increased algal populations in waters they have
studied. The Kerr studies indicate that the addition of nitrogen and
phosphorus indirectly increases algal growth by stimulating growth of
large heterotrophic populations. No concentration criteria for either
nitrogen, phosphorus, or carbon were suggested to prevent excessive
algal blooms.
In addition to the review of data cited above and other numerous
articles not reported, six considerations were used to develop the
nutrient requirements for the Potomac Estuary. The six were
1. Algal composition analyses,
2. Analysis of the nutrient data on an annual cycle and profile
basis,
3. Nutrient bioassay,
4, Nutrient and algal mathematical modeling,
5. Comparison with an estuary currently not eutrophic, and
6. Review of historical nutrient and ecological trends in the
Potomac Estuary.
-------
VII-7
A comprehensive approach to algal growth control was taken to include
all three reaches of the estuary: the fresh water, the brackish, and
the saline portions. In a study undertaken by Carpenter, Pritchard,
and Whaley, oxygen concentrations of less than 1.0 mg/1 v/ere found in
the area of the lower reach of the Potomac [27]. Comparable areas of
the Chesapeake Bay, in terms of salinity and vertical stratification,
did not show depletions to less than 1.0 mg/1. In terms of plankton
counts and chlorophyll, their study indicated that the lower reach of
the Potomac was more eutrophic than comparable waters of the Chesapeake
Bay.
-------
VII-8
1. Algal Composition Analysis
In a previous chapter, the need to control algal growth was estab-
lished. The three major nutrients in blue-green algal cells are carbon,
nitrogen, and phosphorus. The chemical composition by weight of
Anacystis, which is the most common algae in the Potomac as reported by
Lawrence [21], is presented below:
Carbon 46.46$
Nitrogen 8. (
Phosphorus CM
Elemental analysis of the blue-green algae in the Potomac was made during
the summer months of 1970 [53] and the data on carbon, nitrogen, and
phosphorus ratios in terms of micrograms of chlorophyll a. and grams of
suspended solids are presented in Table VII-2. These data indicate that
water with an algal bloom of 100 ug/1 chlorophyll §. contains the following;
Parameter Concentration
S. Solids 14.2 mg/1
Carbon 4.5 mg/1
Nitrogen 1.0 mg/1
Phosphorus 0.1 mg/1 (0.3 mg/1 as PO^)
Assuming that all nutrients can be utilized by the algal cells, an
algal bloom with a concentration of 100 ug/1 of chlorophyll a requires a
minimum of 4.5 mg/1 of carbon, 1.0 mg/1 of nitrogen, and 0.10 mg/1 of
phosphorus (0.30 mg/1 of PO^) in the supporting water.
-------
03
t=>
E-i
CO
O
I—I
EH
r?
cd
-P
.3
w LJ-
-P C>
8£
o
fH
J CD
9 &
9 P<
^^
O rH
S'
O
•H
& «0
S O
cd o
CO t-1
VO VO
C x-CO i-H rH
.£ p • o o
^ ft CO
CT
cc
1 s
-3 o en ex)
S -N H O O
g 0 .d 0 0
(P " '
EH!
VO OJ
O CO VO VO
.;: • o o
.p S CO • •
^ & pT
S
a g
f^l O O! O
S rH rH O
,5 ^ O O
"" s; o • •
o $
fn CO C1- VO
o cd • OA OA
.;: o co
i§ m !~
Si £ >0
f 0 fH
j: ,0 o o -o-
r* PH H VO VO
^ CO J3 O CD
o o • •
&i up
fa,
t) -p
I I £
O PH
-pi a
O CO £S
PH -r-f -p
*n3 *H
C C fi
O M CO
Ol O O
-p OJ OJ
ITN r-l OJ
rH 1 i-H OJ
O O O
oj -sf vo OA
O O O O
o o o o
CO OA «A
•^3" t OA O
O O O
• » •
V) OO to O!
O O O O
^J" rH
• •
tO --t UA
«A 1 Nf OJ
O O O
-P rH CvJ
O -p co -P iti -p cO
P 1 f~| fY^ ^j f^^ fj pT^
•rl -H >H
t3 O CO O CQ O CQ
fl PH £: PH |3 PH &
>J> T3 t-J T3 rH TJ rH
.^d cO ijgi cO .-^ cO f^
1^ co- — co — ' co —
~-t -vf VO VO
OJ OJ OJ OJ
II 1 1
!> to to to
1 OA 1 I rH
O O
OJ OA OJ OJ OA
SO O O O
o o o o
• • * * •
OJ OA
1 S ! ' B
* •
O OJ O vo O
8rH O O rH
O O O 0
* • • » •
CJ^ r^
: t> i i OA
• «
o o o o o
• • • • *
rH OJ
-P
^rj T^ T^ p
cd cd cd *H
CD 0 0) O
c a s § o
cd cd cd p
M M I-H PH >
^3
CO
TJ
•H
•H
13
PH
o
-P
S
•H
C O
a *
CQ 4°
PJ rt
CO
-------
VII-10
For the Potomac Estuary, which can be considered a slow-moving
continuous culture system during the summer, a carbon concentration
equal to or less than 1.1 mg/1, 0.25 mg/1 of nitrogen, and 0.08 mg/1
(0.027 mg/1 as P) of phosphate would be theoretically required to
maintain a 25 ug/1 chlorophyll a level (or one quarter of the nutrient
content in a bloom of 100 ug/l). These should be considered maximum
concentrations since no recycling is assumed.
-------
VII-11
2. Analysis of Data on an Annual Cycle and Longitudinal Profile Basis
Using the disappearance of a specific nutrient both seasonally
and along longitudinal profiles, insight can be gained as to the possi-
bility of this nutrient becoming algal growth rate limiting. This
assumes that other environmental factors do not restrict growth.
Figure V-10 in Chapter V shows that there was over 0.2 mg/1 of
available phosphorus as PO^ in the critical reaches above Route 301
Bridge v/here there is substantial algal growth. From Indian Head to
Smith Point, the area of pronounced algal growth, there was over 0.4
mg/1 of inorganic phosphorus in the waters even under maximum bloom
conditions. These data indicate that in the upper and middle reaches
of the Potomac, phosphorus is in excess of 0.30 mg/1 as PO^ and thus
not rate limiting. In the lower reach around Piney Point, the inorganic
phosphorus was often as high as 0.1 mg/1 and thus phosphorus could be
limiting for this reach.
When the NH3 and N02 + NO^ concentrations shown in Figures V-11
and V-12 are reviewed, it is evident that in the later summer months
practically all of the inorganic nitrogen had disappeared in the reach
between the Smith Point and Route 301 Bridge stations by late July 1969
and by mid-August 1970. This depletion occurred even though the summers
of 1969 and 1970 had relatively high flows. Based upon the disappearance
of inorganic nitrogen, it appears that nitrogen becomes the major factor
in limiting algal growth in the middle reach of the estuary.
-------
VII-12
To determine if carbon was limiting algal growth in the bloom
area of the Potomac, total and organic carbon analyses were made during
September 1970. (Flows during August and September 1970 were low with
air temperatures reaching 95°F during the last week of September.)
Dense algal blooms extended from Hains Point to Smith Point. Carbon
concentrations obtained during a sampling cruise on September 20, 1970,
were as follows:
Station Organic Carbon Inorganic Carbon
(mg/1) (mg/D
Hains Point 7.2 12.2
Wilson Bridge 10.5 15.4
Piscataway 10.5 8.6
Indian Head 10.5 15.0
Smith Point 8.5 7.7
Route 301 Bridge 6.1 6.1
The above data, which were obtained during the mid-day hours of
September 20, 1970, indicate that there were large quantities of
inorganic carbon available for algal growth. As reported earlier,
with the free carbon dioxide in the water ranging between 6.0 and
10.0 at the point of maximum growth (Indian Head), it appears that
there is an excess of inorganic carbon available for algal growths.
A review of nutrient data for the summer of 1965 yielded similar
results. As can be seen in Figure VII-1, there was complete utilization
of nitrate nitrogen between March and August by biota in the Potomac
-------
NUTRIENT -CHLOROPHYLL PROFILES
POTOMAC ESTUARY
MARCH — AUGUST , IB65
^ lOO-i
§}
SO-
|J
AUGUST 10. IM5
MARCH 24.IVCS
40 6O 80
MILES HLOW CHAIN MI06C
VII-I
-------
VII-14
Estuary from River Mile 20 to 60. The utilization of significant
quantities of inorganic carbon as indicated by alkalinity was also
observed.
The basic difference between these sets of conditions was that
the freshwater inflow during June and July 1965 was considerably less
than in 1970. The increase in freshwater inflow in 1970 was enough
to keep the Potomac high in nitrogen until late August and to maintain
a minimum of 5.0 mg/1 of carbon throughout the estuary.
From the 1965 data, it can be concluded that: (l) phosphorus is
excessive in the upper and middle reaches of the estuary with very low
concentrations in the lower reach, (2) inorganic nitrogen has the
largest decrease and virtually disappears, with the lower 60 miles of
the estuary almost void of nitrogen in August, (3) the significant
loss of total alkalinity (a measure of inorganic carbon) occurred in
approximately 15-20 miles of the middle portion of the estuary. How-
ever, there was a residual of about 3.0 to 5.0 mg/1 of inorganic carbon,
and (4) based on the above, it appears that nitrogen in the middle reach
and possibly both nitrogen and phosphorus in the lower reach was con-
trolling the growth of algae. All three nutrients are in excess in
the upper reach with light penetration being the limiting factor of
grovrth.
The 1965 data also demonstrated that another source of inorganic
carbon to the Potomac Estuary is recruitment from the Chesapeake Bay.
-------
VII-15
This source of inorganic carbon appears to be a very important part of
the entire carbon balance especially in the middle and lower portion
of the estuary. In this area, which as previously indicated is more
eutrophic than comparable areas of the Chesapeake Bay, the control of
algae may be limited to management of nitrogen and phosphorus.
-------
VII-16
3. Bioassay Studies
To determine further what nutrients were limiting algal growth in
the Potomac, bioassay tests as developed by Fitzgerald [28] [29: were
employed. Tests for both phosphorus and nitrogen were conducted in
the Potomac from Plscataway Creek to Route 301 Bridge for the period
June through October 1970.
Using the rate of ammonia absorption by algal growths, it is
possible to determine if the algal cells have surplus nitrogen or if
they are nitrogen starved. Tests made during June and early July
indicate that ammonia was either released or absorbed at a low rate
in the range of 10~° mg N/hr/ug chlorophyll a. The cells had adequate
nitrogen available for growth as was also indicated by the high nitrate
concentration in the water, especially at the upper stations above
Indian Head.
Bioassay tests for October 13, 1970, as tabulated below, show a
significant increase in ammonia absorption rates between the Piscataway
station and the Smith Point station farther downstream,
Table VII-3
NITROGEN BIOASSAY SUMMARY
Potomac Estuary
1970
NH3 NOp + N03 Anmonia
Station .InJ.Yater lil_i''!§.ter _ Nitrogen Absorbed
(r'g/l) U'g/1) (rug N/hr/ug chloro)
Piscatawav .110 2.560 + i,.0 :'. 10 5
Indian Head .150 .084 + 6.0 x 10~5
Possum Po-Int .001 .220 + 2.3 x 10~4
Smith Point .001 .150 + 1.3 x 10"^
-------
VII-17
The higher rates of ammonia absorption for Possum and Smith Points and
the low concentration of inorganic nitrogen indicate that this reach
of the Potomac is becoming nitrogen limited.
Two tests, an extraction and an enzymatic analysis [29], were
used to determine if algal growth was phosphorus limited. The phos-
phorus extraction bioassay studies indicated very little difference
between amounts of phosphorus released at the upstream and downstream
stations. Tests for alkaline phosphatase, an enzyme indicator of
phosphorus starved algal cells, were all negative. These two tests
also confirmed the observation, discussed in the previous section,
that the phosphorus content in the upper and middle estuary was
excessive (over 0.15 mg/1 as P).
-------
VII-18
4. Nutrient and Algal Modeling
Recognizing the possibility that the Potomac becomes nitrogen
starved in late summer, an attempt was made to surrogately mathe-
matically model algal growth based on the nitrogen cycle. The model,
similar to that proposed by Thomann et §JL [30] is a feedback system
as shown below:
Organic Nitrogen
Expressed as
V/astewater NH3 Kn^ -^ NOj + N03 Kng \ Chlorophyll a
t
To the sediments
This system was incorporated into the dynamic estuary model [41] and
was utilized to establish the first-order rates for the feedback system
for summer conditions. The established rates (base e) are:
Kinetic Reaction Rates
Kni .30 - .40 (per day)
Kno .07 ~ .09 (per day)
Kn3 .01 - .05 (per day)
Kn^ (not established) (per day)
The first two reactions including the rates Kn]_ and Kn2 have been
fairly well verified as reported earlier and as shown in the pre-
dicted profiles of NH3 and N02 + N03 in Figures V-15 and V-16. The
feedback link appears to play a minor part in the system during the
earlier summer months.
-------
VII-19
Predicted profiles using the surrogate algal model, as shown in
Figures VII--2 and VII-3, matched the observed data quite closely with
respect to location of maximum concentration and general shape of the
profile. Other model predictions and a complete description of the
model are also currently being prepared by CTSL.
From these mathematical model runs, it appears that the standing
crop of the blue-green alga can be predicted using the nitrogen cycle.
This further supports the premise that the availability of nitrogen
appears to be controlling the standing crop of algae.
Using the model and the August 19-23, 1963, data as shown in
Figure VII-2, the reduction of chlorophyll a. concentrations to 25 ug/1
would result In a maximum N02 + N03 concentration of 0.25 mg/1. For
the September 6-9, 1966, data as shown in Figure VII-3, an upper
limit of 0.38 mg/1 of nitrogen would be required to reduce the chloro-
phyll level to 25.0 ug/1. From the modeling analysis, it appears that
if the inorganic nitrogen is between 0.2 and 0.4 mg/1 the blooms can
be held below the maximum level of 25 ug/1 of chlorophyll a..
-------
o
O Z> <5
o ft 8
Old I
0>
* I
I1
Q
i
o
in
i
8
i
o
m
LJ
o
z
I
o
8
I
u. O
0 -HAHdOHCriHO
FIGURE VII -2
-------
o
8
u
(O
!§!
O o-
ac
Q
8
(\/*r1)
I
S
•8
z
$
o
-o
— m
o
FIGURE VII-3
-------
VII-22
5. Comparison With a Less-Stressed Estuary
To investigate further the nutrient requirements for algal growth,
seven sampling cruises of the upper 30 miles of the Rappahannock
Estuary were made in 19VO. As shown in Table VII-4, the estuary con-
tains relatively high concentrations of both organic and inorganic
carbon with low nitrates and inorganic phosphates. This is due in part
to an industrial discharge which is low in nitrogen and phosphorus but
high in organic carbon. The data suggest that if inorganic phosphate
is approximately 0.1 to 0.2 mg/1 and NO? + N03 between 0.1 to 0.3 mg/1,
the standing crop of algae will be minimal with a chlorophyll a. concen-
tration of less than 40.0 ug/1.
-------
Table VII-4
SUMMARY DATA
Upper Rappahannock Estuary
Date
^-23
::-30
7 -07
7-13*
7-°l
7-29
3~?8
Inorganic
P as P04
(mg/1)
0.13
0.18
0.10
0.33
0.15
0.22
0.14
N02 + N03
(mg/1)
0.26
0.12
0.11
0.64
0.27
0.39
0.21
1970
Chloro a
(ug/1)
32
34
40
8
70
17
39
Organic
Carbon
(rag/1)
7.3
No Data
No Data
7.8
5.0
9.7
17.9
Inorganic
Carbon
(mg/1)
No Data
No Data
No Data
No Data
5.0
4.8
No Data
* High river discharge
-------
VII-24
6• Review of Historical Nutrient and Ecological Trends in the Potomac
Estuary
As reported in Chapter V, there appears to be a definite relation-
ship between the ecological and nutrient enrichment trends in the upper
Potomac (Figure V-20). Prior to the 1920's, the phosphorus loading was
1,100 Ibs/day or 4 percent of today's loading. Similarly, the nitrogen
loading was 6,400 Ibs/day or 10 percent of today's wastewater contri-
bution.
The concentration in the upper estuary under summer conditions for
the period before 1920 was estimated to be 0.12 to 0.20 mg/1 of PO^
with inorganic nitrogen ranging from 0.15 to 0.30 mg/1. With a reversion
to these concentrations, not only should there be a significant reduction
in the blue-green algal population, but there should also be a general
reversal in the ecological community succession.
-------
VII-25
C. CONTROLLABILITY OF VARIOUS NUTRIENTS
As discussed previously, the three major sources of nutrients in
the upper estuary are (l) wastewater discharges, (2) the upper
basin, and (3) Washington urban and suburban drainage.
For the 7 months during which algal growths are most prolific
and affected by changes in nutrient contributions, the percentages of
phosphorus, nitrogen, and carbon attributable to wastewater discharges
are listed below:
Month
April
May
June
July
August
September
October
Mean
Monthly
Flow
(cfs)
20,000
14,500
8,700
5,500
6,000
4,700
6,300
Percentage
Phosphorus
60
67
76
83
82
84
81
Currently from Wastewater
Nitrogen
26
36
50
63
61
66
59
Discharges
Carbon
17
20
26
33
31
35
29
From the above tabulations, it can readily be seen that not only can
phosphorus be controlled by removal to the highest degree (percentage
removal) at the wastewater treatment facility, but phosphorus can be
controlled earliest in the growing season. These two aspects enhance
the feasibility of phosphorus management.
While 82 to 96 percent of the phosphorus entering the upper estuary
can be controlled by removal at the wastewater treatment facilities
during median to low flows [52], an additional reduction of phosphorus
-------
VII-26
concentration occurs during periods of high runoff within the upper
estuary itself. As reported by Aalto ei §1 [8], large quantities of
phosphorus (over 100,000 Its/day) enter the upper estuary during high-
flow periods at concentrations over 0.5 mg/1 (1.5 mg/1 as PO^) during
the rising portion of the river discharge hydrograph. However, high
silt concentrations also accompany high flows. Large amounts of phos-
phorus are sorbed upon the silt particles and removed from the water
system as sedimentation occurs in the upper reach of the estuary.
Although there was some dilution of high phosphorus concentrations,
the large sediment load reduced the overall phosphorus concentration by
a minimum of 20 percent in the reaches upstream and downstream from the
major wastewater sources [52]. This reduction during periods of high
flow would tend to add to the controllability of phosphorus as tabulated
earlier. The high percentage from wastewater discharges, especially
during the early months of the algal growing season and the large losses
to the sediments during high-flow periods made phosphorus an ideal
nutrient to manage.
The tabulation also indicates that over 60 percent of the nitrogen
originates in the wastewater discharges during the critical months of
July through October. The previous table does not include nitrogen
recruitment from the atmosphere or by either bacterial or algal fixation.
Hutchinson [31] reported that about 5 Ibs/acre/year of nitrogen is
drawn from the atmosphere. Using this rate for the upper 60 miles of
-------
VII-?,'
the Potomac Estuary, about 1,600 Ibs/day of nitrogen is obtained front
the atmosphere as compared to over 50,000 Ibs/day from v/astewater dis-
charges. Thus it can be concluded that nitrogen fixation is a minor
source of nitrogen in the Potomac Estuary. Extension of recent data
from studies at the University of Wisconsin F53] indicate that approxi-
mately 5,000 Ibs/day of nitrogen could be fixed by blue--green algae in
the upper and middle reaches of the Potomac Estuary. Nevertheless,
compared to all other sources, the contribution from the atmosphere
including that by nitrogen fixing algae appears to be insignificant.
Thus, during the summer months, algal control by management of nitrogen
appears to be a feasible alternative to phosphorus control.
Also in the above tabulation, the maximum percentage of carbon
from Y/astewater is 35 percent. Other major sources not included in
this figure are from the atmosphere, bacterial action in -rater, and
bacterial action in the sediments. The quantity of carbon (002)
exchanged at the air-water interface is a function of the transfer
rates, concentration of C02 in the air, pH of water, and the alkalinity
of the water. For the Potomac, the maximum potential (Xb transfer from
the atmosphere is approximately 3,500,000,000 Ibs/day*. This source
from the atmosphere alone ma'kes the possibility of effective carbon
control doubtful at the present time since only about 100,000 Ibs/day
of carbon is discharged in v/astev/ater with over 330,000 Ibs/day from
the upper basin.
The CO? obtainable from the atmosphere was determined by using a
transfer rate of 0.6 mg/cm2/min [32] for an upper estuary surface
area equal to 2.0 x 109 ft2.
-------
VII-28
Another aspect of nutrient management is the transport and/or
deposit of the various nutrients along the longitudinal profile of
the estuary. Because of the great solubility in water, inorganic
nitrogen and carbon are easily transported through the estuary
especially during high-flow periods in the winter and spring months.
The large quantities of phosphorus and organic carbon which
originate in wastewater discharges do not move as easily through the
estuary. Large quantities of phosphorus and organic carbon are lost
to sediments. Analysis of the sediment confirms the deposit of both
carbon and phosphorus (Figure VII-4).
A review of the management requirements for the estuarine reaches
was made to determine if management of any single nutrient by waste-
water treatment processes can achieve the water quality standards.
For the lower and middle reaches, because of the large carbon supply
intrusion from the Chesapeake Bay, the management of nitrogen and
phosphorus appears to be a feasible approach. Management of the
upper estuary is limited primarily to nitrogen and phosphorus control
except during periods of extremely low flow when it is anticipated
that the estuary will be used for a supplementary water supply. When
the estuary is being so used, there will be little or no freshwater
inflov; thus the amount of inflow from the upper basin, especially
carbon, is insignificant. Under these conditions, control of all
three nutrients in the wastewater treatment process is feasible.
-------
80
60-
II
Po
20-
CARBON, TKN & PHOSPHORUS IN SEDIMENTS
POTOMAC ESTUARY
AUGUST 18-20. WTO
5.0-
4.0-
30-
^?
z
c
IjO-
1X1-
10
ao
30
40 50 60
MILES BELOW CHAIN BRIDGE
70
80
90
100
FTGURE VII-4
-------
VII-30
D. NUTRIENT CRITERIA
There are no existing nutrient criteria specified by either the
State of Maryland or the District of Columbia. To control algal growth,
the State of Virginia has set nutrient objectives for nitrogen and
phosphorus of 1.0 and 0.2 mg/1 respectively in wastewater effluent.
Based upon the methodology reported in the previous section, the
following nutrient criteria were developed in Section VII-B with the
objective of reversal of eutrophication in the freshwater portions of
the Potomac Estuary:
Parameter Concentration Range
Inorganic Nitrogen 0.30 -- 0.5 mg/1
Total Phosphorus 0.03 - 0.1 nig/1
Since there was over 5.0 mg/1 of inorganic carbon in the estuary, even
under maximum bloom conditions, no criteria for carbon could be estab-
lished at the present time.
The lower values in these ranges are to be applied to the fresh-
v;ater portion of Zone III and to the embayment portions of the estuary
in whicn the environmental conditions are more favorable toward algal
growth. The upper ranges of the criteria are more applicable to
Zone I of the Potomac Estuary which has a light-limited euphotic zone
of: usually less than 2 feet.
Studies of the Potomac Estuary showed a relatively sharp transition
from freshwater to a typical mesohaline environment as indicated by the
rapid increase in salinity. At the upper end of the 22-mile reach at
Laryland Point, there are primarily freshwater phytoplankton and zoo-
plankton populations. Above Maryland Point, the salinities are less
-------
VII-31
than two parts per thousand. At low flows, marine forms dominate the
lower end of the transition zone at the Route 301 Bridge with salinities
in summer approximating 12 parts per thousand.
Based on the past 5 years of field studies, it appears that the
growth of massive blue-green algal mats are apparently restricted to the
freshwater portions. In the mesohaline environment, dinoflagellates
were often encountered in "red tide" proportions.
These observations lead to tuo points of emphasis in estuarine
water quality management:
(l) Fairly discrete biotic provinces may be identified within a
given reach of the estuary, responding differently to a given stress.
(2) There is insufficient evidence to date to generalize on
nutrient parameters and hypertrophic conditions in all portions of s
given estuary.
Therefore, at the present time, no specific nutrient criteria have been
established for the mesohaline portion of the Potomac Estuary.
These criteria, along with a high degree of carbon removal for
enhancement of dissolved oxygen would not only lead to a reversal of
nutrient buildup in the estuary but also creation of an environment
conducive to reversal of the aquatic plant succession that has occurred
in the Potomac. This reversal has occurred in the lakes surrounding
L'iadison, Wisconsin [17] and Lake Washington [16] when wastewater dis-
charges . ere diverted from the lakes.
-------
VII-32
The criteria shown above give maximum concentrations for both
nitrogen and phosphorus. Limits for both were incorporated for the
following reasons:
(l) Since the flow of the Potomac River is very flashy, neither
phosphorus nor nitrogen can be controlled throughout the estuary at
all times. To reduce eutrophication in the entire estuary for years
having average or above average flow conditions, phosphorus control
appears to be more feasible. However, in the middle and upper estuary
during low-flow years, nitrogen control appears to be more effective.
This is because the nitrogen criterion for restricting algal growth
is 10 times that for phosphorus (0.30 versus 0.03 mg/l) while the
nitrogen loading from the wastewater treatment facilities is 2.4 times
that of phosphorus (60,000 versus 2/4,000 Ibs/day). Considering only the
magnitude of the limiting nutrient concentrations and the magnitude of
the percentage of the wastewater contribution, this results in more than
a fourfold advantage in removing nitrogen over that of phosphorus.
(2) Various investigators report that increases in nitrogen and/or
phosphorus can increase heterotrophic activity which in turn stimulates
algal growth, and
(3) There is compatibility between wastewater treatment require-
ments for dissolved oxygen enhancement and eutrophication control.
Compatibility of treatment requirements is probably one of the
most important considerations of the four factors influencing the
selection of wastewater treatment unit processes. For example, to
maintain the dissolved oxygen standard in the upper estuary under
summer conditions, a high degree of carbonaceous and nitrogenous
-------
VII-33
oxygen demand removal is required, whereas the control of algal standing
crops is predicated on phosphorus and nitrogen removal. To obtain a
high degree of carbonaceous oxygen demand removal, a chemical coagulation
unit process is usually required beyond secondary treatment. This unit
process will also remove a high percentage of phosphorus. The removal
of the nitrogenous demand can be satisfied by one of two methods:
(1) by converting the unoxidized nitrogen to nitrates (commonly called
nitrification), or (2) by removal of nitrogen completely. If a unit
process such as biological nitrification-denitrification is employed,
both the DO and algal requirements for nitrogen can be met.
Thus v/ith proper selection of wastewater treatment unit processes,
it is feasible not only to enhance the DO by removing the carbonaceous
and nitrogenous UOD but also to reduce nuisance algal growth by removing
nutrients.
-------
VIII-1
CHAPTER VIII
CONTROL CONSIDERATIONS FOR BACTERIAL DENSITIES, VIRUSES, HEAVY
METALS, AND OTHER WATER QUALITY PARAMETERS
A. BACTERIAL DENSITIES
1. Indicator Organisms
Four bacterial organisms have been used as indicators of the
sanitary water quality of the Potomac. These four are:
(1) Total coliform,
(2) Fecal coliform,
(3) Fecal streptococci, and
(4) Salmonella.
In a 1969 report entitled "Sanitary Bacteriology of the Upper Potomac
Estuary" by Lear and Jaworski [33], the folloi;7ing conclusions were
reached:
(l) High total coliform, fecal coliform, and fecal streptococci
densities were found in the Washington metropolitan area,
(2) Fecal coliform/fecal streptococci ratios indicated that most of
the bacterial pollution in the upper estuary vras probably of human origin,
(3) A potential health hazard existed in the Washington area in
that salmonella organisms were readily and regularly isolated in waters
of the estuary, and
(4) In general, greater incidence of salmonella recovery occurred
in 'vaters having high total and/or fecal coliform densities.
Data collected during 1969 [34] also reflected the earlier findings
including the salmonella isolations.
-------
VIII-2
As reported earlier, all discharges from wastewater facilities in
the upper estuary were being chlorinated as of September 1969. This has
dramatically reduced fecal coliform densities near the v/astewater outfalls,
However, overflows from overloaded sanitary and combined sewers still
cause high fecal coliform densities as was shown in Figure V-2. These
high densities are a result of overflov/s of untreated wastewater
entering the estuary near the confluence with Rock Creelc.
The complete control of bacterial densities in the upper estuary
cannot be realized until both continuous chlorination of wastev/ater
effluent is maintained and sanitary, combined and storm sewer over-
flov/s are reduced or eliminated. While the storm sewers increase
bacterial indicator densities in the estuary significantly, the
increased flows tend to reduce their populations by dilution and to
disperse them downstream. Apparently, the more persistent bacterial
problems result from overflov/s of the combined sevrer system, especially
during the summer recreation period. This becomes increasingly serious
./hen the estuary is considered as a public water supply source.
-------
VIII-3
2. Bacterial Standards
The bacterial water quality standards for the upper estuary are
as given below:
Jurisdiction Total Coliform Fecal Coliform
Virginia 2400 MPN/100 ml 200 MPN/100 ml
(monthly avg.) (30-day log mean)
Maryland 240 MPN/100 ml
(by survey)
District of Columbia 1000 MPN/100 nil
(geometric mean)
For the shellfish producing area of the Potomac, a total coliform
density of 70 MPN/100 ml is used by both the States of Maryland and
Virginia.
-------
VIII-4
B. VIRUSES
The role of water as a vector in the dissemination of viruses is
not well understood. However, enteric viruses are present in sewage
effluents and can find their ways into public water supplies [35].
In the Potomac Estuary, the problem of viruses and associated
health hazards has three aspects that must be considered: (l) the
lower portion of the estuary is a prime shellfish area, (2) the entire
estuary is an ideal recreational use area, and (3) the upper estuary
has been proposed as a public water supply source. While no epidemio-
logical evidence exists relating waste discharges to the first two
aspects presented, a potential hazard does exist at present and will
probably become greater as the population increases.
The viral problem will be of major concern if the estuary is to
be used as a water supply source. Since both wastewater effluents and
overflows from storm, sanitary, and combined sewers contain viruses and
do enter the estuary, the need to determine the threat to public health
remains.
To evaluate this health hazard, a three-phase investigation is
required to determine:
(l) The existing virus population along the longitudinal dimension
of the estuary,
(2) The role of v/astewater treatment facilities in removing viral
particles, and
(3) The effectiveness of water treatment processes in removing
viruses.
-------
VIII-5
Studies regarding the viral removal effectiveness of wastewater and
water supply treatment processes have been undertaken by fWQA's
Advanced Waste Treatment Research Laboratory in Cincinnati, Ohio
and by the U. S. Army Corps of Engineers,"respectively. The RVQA
studies include an investigation of the erTect of advanced waste
treatment processes on viruses. While a complete review is beyond
the scope of this report, virus data on v/astewater as reported by
Berg [35] indicates that AWT units are approximately 90 percent
effective in removing viruses. An evaluation of virus hazards by
the American Society of Civil Engineers indicated that chlorination
without reaching free chlorine residual will not insure virus free
effluents [36],
As one aspect of the cooperative study with FWQA on the feasi-
bility of the estuary as a supplemental water supply, the U. S. Army
Corps of Engineers investigated the effectiveness of water supply
*
treatment processes on virus removal. The study dealt primarily
V
with the effectiveness of chlorination in deactivating various types
of human enteric viruses.
A joint investigation by FWQA's Chesapeake Technical Support
Laboratory and the Cincinnati Advanced Waste Treatment Research
Laboratory to determine existing viral populations in the estuary was
undertaken. Preliminary results from the first set of samples taken
-------
VIII-6
during the low-flow period of September 1970 for the stations presented
below were negative.
Number Station Location
I Great Falls at Current Water Intake
II Below Chain Bridge Near Site of Proposed Intake
III Near Woodrow Wilson Bridge Below Blue Plains
This study is being continued and will be repeated under various
temperature and flow conditions.
There are no water quality standards for viruses at present. Use
of various indicator organisms such as coliforms have been suggested
with the Bacillus subtilis spore [37] very promising as an indicator of
virus disinfection.
A committee report for the American Water Works Association [38]
summarized their study findings by stating: "There is no doubt that
water can be treated so that it is always free from infectious micro-
organisms—it will be biologically safe. Adequate treatment means
clarification (coagulation, sedimentation, and filtration), followed
by effective disinfection." They further concluded that there is
i»,
considerable room for research, both laboratory and epidemologic, to
determine if there is a problem in virus disease transmission by water.
-------
VIII-7
C. HEAVY METALS
A cooperative program with the laboratory at the U. S. Naval
Ordnance Station in Indian Head, Maryland, to determine periodically
the heavy metal occurrence in the Potomac Estuary waters and sedi-
ments was initiated during the summer of 1970. While only small
i
concentrations of zinc and manganese v/ere.detected in the overlying
waters of the estuary, considerable amounts of various heavy metals
"by acid extraction from the sediments were recorded.
From the sediment analysis (Table VIII-l), it can be seen that
there are significant increases of lead, cobalt, chromium, cadmium,
copper, nickel, zinc, silver, and barium in the upper estuary near
the Woodrow Wilson Bridge. Since concentrations of metal are
greatest near the sewage outfalls where other components of waste-
water such as phosphorus and carbon are also highly concentrated,
it can be concluded that the heavy metals originate in the waste-
water discharges. Some accumulations such as cadmium could also be
from urban and suburban runoff.
The effect of these heavy metal accumulations on the ecology of
the estuary is indeterminate. Since the lower estuary is a prime
shellfish production area, a study of the possible availability and
effects of the apparently small but continuous discharges of heavy
metals on the water quality and biota should be undertaken. With
wastewater loadings projected to increase over fourfold and with
increases in the number of discharge points farther down the estuary,
this heavy metal accumulation could develop into a serious water quality
management problem.
-------
VIII-8
Heavy metals in the sediments must also be considered in the
disposal of dredged spoil. Dredging operations involving deepening
and widening of the channels near Washington, construction of piers
and marinas, etc. disturb the sediments and require disposal of the
dredged spoil. These activities should also be monitored especially
where there are known high concentrations of potentially toxic metals
in the sediments.
-------
o
OJ
(D
ra
EH ^
*!
|p S^
ft
ft
N ft
W %
ft
O ft
ft
O ft
ft
o §
O ft
ft
O ft
ft
& ft
0
H
£-(
u
CM
SO
ON
O
0
-4-
LA
O
O
H
SO
O
%
-<
CO
ON
-4-
01
I-
s
ro
SO
LA
LA
-4-
ON
OJ
H
CO
OO
-4-
LA
ON
3
O
ON
H
OJ
so
ON
ON
o
01
o
IA
ON
ro
oo
V
9
•H
£
-» SO
ON -4-
H
OO b-
-* ON
ro oo
H rH
O CO
CO OO
SO CM
CTs O
rH
rH CO
LA LA
rH H
-4- OJ
H H
(^ -3"
t— CO
CM 01
OO b-
ON ON
CM LA
LA CM
S? S
% $
CO CO
ON UN
o-l -4-
O -4-
OJ OJ
CO ON
OO OO
H -4-
rH 00
-4- eg
t— CO
-4" OO
CO ON
ON ro
OJ ro
CO OO
CO ON
CM 00
rH SO
ON ON
t— ON
rH H
o
d O
£ 8
ON H
-* SO
o
0
H
LA
so
H
so
oo
3
co
t—
rH
CM
OO
ON
oo
r-
oo
t-
"
CM
SO
-4-
0
rH
CM
ON
SO
OJ
ON
ro
O
O
.4-
rH
SO
CO
t—
c-
co
LA
-4-
oo
ON
OO
OJ
d
§8
ON
(U
£
•d
O ON
CO CM
LA LA
-4- OO
CO OO
rH rH
CO CVI
CM
CO OO
Oj co
CO 00
$ 21
CM O
00 01
ON ON
OO CM
t*- OO
ON -4-
ON so
IV- 0
H LA
-4- -4-
ON SO
ro O
CM LA
CM OJ
ON CO
b- ON
-4- H
LA rH
LA OO
-4- t—
so -=t
rH H
OJ ON
CO -4-
OO LA
SO -4-
SO ON
CO SO
ON t—
-4- CM
LA O
ON CO
ON t—
rH rH
a a*
SO CM
CO SO
H ro
LA ro
CD
D
Q
>, V
oj D
§ rj
OS V
o rd
pj Q
SO CO
rH 21
ON b-
ON -4-
O ON
H O
CM SO
CM r-H
so op
CO CO
SO CM
ON S-
SO CM
ro oo
t— oo
ON -4-
CM CM
O ON
° ^
LA O
S S
CM O
8 ON
CO
J- -4-
CO OO
ON ON
rH 00
CM CM
0 0
oj1 %
SO -=f
oo O
LA CO
OO LA
rH rH
SO t—
ON CO
3 S
t- CM
ON ON
LA LA
01 01
& *
LA OO
H H
cj cs
SO ON
LA LA
OO OO
.p
£*
•H
O
1 |
« H
ON OO
LA CO
i-l CM
H t-
H r-l
0 .4-
00 H
00 [-
OO O
H
OO LA
LA SO
CO ^t
CM OI
oo co
t— SO
SO CO
ro ro
SO -4-
® ^
»- OI
* ON
SO so
OO ON
ON -4"
ro ON
r-H
-4- b-
co b-
LA b-
OI OJ
ON CO
ro b-
01 CM
I- O
ON ON
O oo
b- LA
rH OJ
H H
b- so
b- I—
-4- ^t
cS tt
LA rH
OJ 00
O\ LA
CO CO
t— t—
rH H
CJ> d>
fL fi
LA LA
OO CO
+3
C -P
•H a
PH O
01 rg
§f4
gj
SO O
t- o
CM H
so so
rH H
CO ON
rH rH
SO SO
CO SO
CO LA
H rH
CM OI
CO rH
H CM
LA t—
O CM
-4- -4-
ON CO
ON SO
3 rl
oj as
GO CO
3> ^
H
b- CO
01 OJ
O H
SO ON
00 OJ
SO rH
LA O
01 SO
CM O
OO CM
LA H
ON -4-
t— O
ro LA
SO CO
CT\ O
ON ON
CM OJ
b- ON
ON OO
ON ON
rH H
a> en
LA SO
ON sS
LA CM
CO -4^
-p
d
•H
-P O
•rH
O 13
1 I
LA ^*
CO O
rH rH
ro ON
LA b-
rH 0
CO O
H
SO O
CM H
b- 0
CO LA
0 -*
H rH
LA CTs
00 ON
r-H CO
oo O
H O
ON LA
CO rH
H
LA SO
H so
rH CM
CO O
-4- 01
O C^
r? ON
H ON
-4- -4-
CO SO
r-H
ON O
H -4-
OJ
J- CO
SO -4-
SO O
b- rH
ro ON
co ON
LA b-
OO
O ON
ON ON
rH LA
OJ
& $
oo oo
H
a> a
IA ON
CO ON
H b-
ro
9)
CO -H
H K
CO
co
ON
rH
V
^
OH
O
O
to
•H
ft
S3
SO SO
CO H
SO O
00 ON
OO b—
H 0
-4- O
CM H
CO
H -4-
CM -4-
SO OO
rH
^ C^
ON rH
O b~
oo O
co co
b- ON
rH H
CM
CM CO
0 -4-
LA O
S-4-
OI
CO O
-4- -4-
OI
H CO
CO -4-
CO LA
r-H
b- O
LA -4-
OI
SO H
00 -4-
& *-
ON O
LA ON
ON t—
OO
^t 00
CO ON
LA LA
H
O OO
ON ON
ON LA
o> a>
o
CO
ON O
rH
Ij
a -p
•H El
^ 1
S £
g«
S 5
•P O
O ru
d) +5
+3 U)
0) rd
•d fl
-------
VIII-10
D. OTHER WATER QUALITY INDICATORS
Other water quality parameters are temperature, color, odor, taste,
total dissolved solids, carbon chloroform.extractions, pesticides, and
herbicides.
1. Thermal
The most pronounced effect of thermal discharges on elevation of
ambient water temperature can be found in the reach of the Potomac between
Hains Point and Woodrow Wilson Bridge and in the Anacostia River near the
Benning and East Capitol Street Bridges. Of these two areas, the rise in
the Anacostia is the greatest with a 5-degree rise occurring above the
ambient water temperature, reaching a high of 33°C.
Since the two areas periodically contain low dissolved oxygen
concentrations, the effect of the elevated temperature is difficult to
assess. Future thermal control may be required to provide a more
favorable environment for aquatic life and to enhance dissolved oxygen
when the wastewater plants are upgraded and the overflows from combined
sewers are eliminated.
2. Carbon Chloroform Extraction
Using carbon chloroform extraction (CCE) as an indicator of
potentially toxic organic materials, it can be seen in Figure VIII-1
that there is a significant increase in the waters between Great Falls
and Memorial Bridge upstream from the combined sewer overflow discharges.
At times, the relative increase is high, approximately 400 ug/1 or 0.4 mg/1,
twice the recommended standard for CCE.
-------
FIGURE VIII-I
-------
VIII-12
If the estuary is to be used for a water supply, a more detailed
analysis of CCE should be undertaken. A study of the effects of water
supply withdrawals on CCE should also be initiated.
3. Chlorides and Total Dissolved Solids
Of the remaining parameters, increases in total dissolved solids
and chlorides are major considerations in the use of the estuary as
a water supply. The concentrations of total dissolved solids and
chlorides at the proposed intake are functions of concentrations in
the freshwater flow, location of the salt wedge, and total increase
of each parameter resulting from water treatment, domestic use, and
waste treatment. Water quality simulations for both parameters were
made using the FWQA Dynamic Estuary Mathematical Model.
To demonstrate the model's capability to simulate changing salinity
conditions in the estuary, a test condition was selected for which suf-
ficient data were available to establish the salinity gradient through
the system at two different points in time. An historic period (July
through December 1965) was selected for which flow conditions in the
prototype were relatively uniform throughout the period. The mean
Potomac River flow over Great Falls remained near 1300 cfs with the
mean monthly flows varying between 1018 and 1586 cfs during this period.
Chloride and salinity data were available to establish the salt
wedge position in the main stem of the Potomac near the start of this
period (July 7-8, 1965) and near the end (December 1-2, 1965). These
data were utilized to establish visually the "best fit" profiles for
these tv/o points in time as illustrated in Figure VIII-2.
-------
VIII-13
The profile for July 7-8, 1965, was specified as the initial
profile in the model. For the simulation, the network extended to
Piney Point near River Mile 96. The specified chloride concentration
at the seaward boundary was changed during the simulation in corres-
pondence to the change noted in the prototype during the same period,
i.e., the concentration was increased from 8400 mg/1 to 10930 mg/1 in
small steps (increased 55 mg/1 every 3 days). A uniform flow of 1300
cfs in the Potomac River was maintained throughout the simulation.
The chloride profile predicted by the mathematical model after the
147 day simulation period is also illustrated in Figure VIII-2 along
with that measured in the estuary. The predicted and observed profiles,
which overlap, indicate that the model can accurately simulate the
intrusion of chloride from the Chesapeake Bay.
The simulation was completed utilizing a dispersion coefficient
ranging from approximately 0.5 square miles per day (175 square feet
per second) in the upper 55 miles of the estuary, 5.0 square miles
per day (1600 ft2/sec) in the next 15 miles, and 12.5 mi2/day (4000
ft^/sec) in the lower 26 miles of the estuary. These coefficients are
of the order of magnitude suggested by Harleman [49] for the freshwater
and salinity incursion zones, respectively, of estuary. These coeffici-
ents were utilized for the chloride and TDS simulations presented later
in this report.
-------
CHLORIDE CONCENTRATION
POTOMAC ESTUARY
'2
O
UJ
* >
"Z
o
o
Id
o
3
X
u
11000
10000
9000
3000
7000
6000
5000
•4000
3000
2000
1000
LEGEND
• CBI DATA. JULY 7-8.1965
x D.C. DATA. JULY 7-8. 1965
a CBI DATA. DEC. 1-2.1965
o CTSL DATA. DEC. 1-2,1965
PROTOTYPE
MODEL
DEC. 1-2. 1965 PROFILE
10
INITIAL PROFILE JULY 7-8. 1965
(ALSO MODEL)
30 40 50 60 70
MILES BELOW CHAIN BRIDGE
80
90
100
FIGURE VIII-2
-------
VIII-15
4. Pesticides and Herbicides
Samples taken from six points in the Potomac Estuary were analyzed
for 12 hydrocarbon pesticides in August 1969. None of these compounds
were found at detectable concentrations in the samples nor in a 24-hour
composite sample taken from the Blue Plains Sewage Treatment Plant
effluent [341. Since there is considerable agricultural use of pesti-
cides and herbicides within the Potomac River Basin at certain times
of the year, further EPA surveys to include those seasons of use are
indicated as well as a data search of investigations by other agencies.
-------
IX-1
CHAPTER IX
POPULATION AND WASTEWATER PROJECTIONS
A. POPULATION PROJECTIONS
To facilitate the determination of wastewater loading rates and
water supply requirements for the entire Washington metropolitan area,
population projections were developed for 13 service areas. Deline-
ation of watersheds within each service area is presented in Table
IX-1.
Population data for the Virginia and Maryland portions of the
Washington metropolitan area along with the District of Columbia are
shown in Figure IX-2 for the three benchmarks investigated. Summarized
below are the total population projections for the Washington metro-
politan area:
Year Population
1969 2,800,000
1980 4,000,000
2000 6,700,000
2020 9,300,000
Population projections for the benchmark years of 1980 and 2000
were furnished by the Metropolitan Washington Council of Governments
(COG). Control populations for these benchmarks were based on the
"low-estimate" figures prepared for COG by Hammer, Green, Siler
Associates [39]. Distribution by individual service areas was essen-
tially determined from 1960-1968 population trends with consideration
-------
o
•g
•a
o
I
I I
cd
I I
o
iH
g
•a «
0) -H
O
o
o
-H
t.
*
*
0 •o o -a
3131
& & & &
Jf
I I
o, P,
+> o>
o
t-»
(4
m
•H
Q
1
I
o
s
MM>>MI-11-(M
M (H M > W M M
M > M M
-------
IX-3
given to land use potential and other attenuating factors. A similar
methodology was employed by JWQA-'s Middle Atlantic Region economists
to develop population estimates for the year 2020 benchmark except that
the control figure was derived from a long-term relationship of national,
regional, and metropolitan area population trends.
-------
FIGURE IX-1
-------
10-
POPULATION PROJECTIONS
WASHINGTON METROPOLITAN AREA
o
ci
9-
8-
7-
10
O
2
i-
O
Q.
O
4-
3-
2-
I-
1968
1980
2000
2020
BENCHMARK
FIGURE IX -2
-------
IX-6
B. WATER SUPPLY REQUIREMENTS
Data pertaining to current water supply demands and per capita
usage were obtained from the major water suppliers in the metropolitan
area and served as a baseline for the water supply projections shown
in Table IX-2. The total projected average yearly water requirements
for the three benchmarks are presented as follows:
Year Projected Usage
1969, 370 mgd
1980 556 mgd
2000 1009 mgd
2020 1568 mgd
V/ater supply requirements for shorter demand periods are delineated
in Table IX-3.
The per capita water use was assumed to increase through the year
2020 at a rate of one gpcd/year. Allowing for the maximum dependable
yield of other existing sources of water such as Occoquan and Goose
Creeks, it appears that all of the District of Columbia's water supply
and a major portion of the water supply for the metropolitan area within
Virginia and Maryland must be provided by a combination of the Potomac
River and the upper Potomac Estuary. Of the total projected 2020 demand,
these latter sources are expected to supply approximately 1/400 mgd or
90 percent. The Patuxent River currently supplies 42 mgd to the
Washington metropolitan area but will be unable to serve this area in
the future due to projected needs within the Patuxent Basin [40].
-------
&i
3!
0)
bp
3
I|S
0)
99
•H «o^
«J T?
S «> &
O| M +»•— .
OJ| 0) 01
PH *
g
•H 13
t^
CO
&.
0)
bo
oT
o) -o
H *-->
a
*
0)
•H m^_^
a) *5
QIC d a
Oj t) bo
cdl o> 01
&< >
I,
•p g
"3 oi
gl CO
PH
c
ni^
•g MM
&H 4^ ^— •*
«J
*
0)
5Sf
•H a
Ql «| trl
«lo ^ 5,
aj o bo
0) $^^
g^
+> f>
«H M
g.CO
01
a bo
•P 01
iH 03
3^?
v S
0) «"^
OS -ttt
vp o
^ CO
iH rH C3'-N
^ -p ^ *S>
+J O 4) B
to *
•H -a
II
P,
8
rt
O
OJ
§
irT
c\T cvT
8 8
O^ "^
ON CO
rH rH
0 0
H r-*
§o
o
**D
-*P Nf
5 5
8 8
r-l r-l
8 8
r-I to"
1-1
§ §
80
o
i—( TO
r-l
I 1
8
5
§
•s
*r\
oT
8
rH
0
,
^
^o
^0
8
•0
ir\
g
><•
OJ
8
8
o
r--
§
8
cu
1
-------
Table IX-3
VARIOUS WATER SUPPLY DEMANDS
Washington Metropolitan Area
Duration 1980 2000 2020
(mgd) (mgd) (mgd)
Maximum Day 1,001 1,816 2,822
Maximum Five Day 950 1,730 2,680
Maximum Month 723 1,312 2,038
Maximum Two Months 712 1,292 2,007
Maximum Three Months 695 l,26l 1,960
Maximum Six Months 634 1,150 1,788
Yearly Average 556 1,009 1,568
-------
IX-9
C. WASTEWATER LOADINGS
Utilizing the population projections discussed previously and the
current waste flows and loading rates for each existing treatment
facility as shown in Table IX-4, future wastewater trends were developed
for the 13 service areas comprising the Washington metropolitan area.
These data are presented in Tables IX-5, IX-6, and IX-7 for 1980, 2000,
and 2020 respectively. It can be seen from these tables that the BOD,
nitrogen and phosphorus loadings before treatment are projected to
increase drastically. The table below summarizes these loading condi-
tions :
Before Treatment
1969 325
1980 473
2000 861
2020 1342
Wastewater flows were adjusted upward to reflect the additional
per capita water usage. Consumptive losses were maintained at approxi-
mately 14 percent. In the case of Federal installations, waste flow
was computed by assuming a per capita contribution of 100 gpd. The
per capita BOD load was also increased slightly in accordance with
historical loading trends while current per capita nitrogen and phos-
phorus loadings were held constant for each of the benchmark years.
BOD*;
(ibs/day)
483,500
823,500
1,463,500
2,195,000
TKN as N
(Ibs/day)
63,500
95,600
155,700
215,600
T. P as P
(Ibs/day)
27,300
43,100
70,300
97,400
-------
>
a. o o
a-H^a
NJ-CQ
IH Q ,0
OJ ft rH
OH f-l-^
4) >j
-p co a
co a TJ
h •>!" CQ
Pi rX rH
0 & —
•P *-*
•r- 1 TJ t>J
& 8 •§
W
0) S rH
0^ CH • *
T) '"^
"£ -8
n*^
S £-,_
a
P T>'->
PI o a
a 1-3 T3
o ^\
rW CT,S
OJ O rH
0, CQ^--
1 ^5
H O tO
S d
a *
•p 5
•H H
O 4) P.
-p HO
M CO ~~^r
oj a
OH s=
C
5
•H T3
•P 0)
a >
t3 OJ
& w
o
OH
11
CO
4) OT?
IH v5
<
>>
4?
•rl
rH
•H
O
rS
§
o
S
rH
OJ
O
O
^
o
OJ
o
8
rH
OJ
8
§
VO
O~
rH
0
8
rH
C
Pent ago
to
o
in
^p
o^
1^
0
8
to
Nf
-sf
rH
O
8
c*C
?
g
o
p-
OJ
o
o-
rH
g
1
O
o
«N
VO
in
0
0
0
•*
o
OJ
o
0
p-
c^
to
8
C'N
to
rH
VD
rH
OJ
O
«
Q
1
d
r.
IH
to
O
8
o
o
o
8
0
o
8
o
OJ
8
"
S
ITS
O
S
0
o
+9
a
1
a
z
8
o
0
^
VO
m
8
o
g
^
vo
o
OJ
0
8
£>
c^\
^
00
g
o
0
m
rH
§
rH
OJ
a
•H
_o
rH
O
o
fc
•p
Distric
rH
8
o
o
vo"
-^-
0
0
§
"\
>»•
o
OJ
o
g
CO
OJ
0
o
s
r-H
8
<-N
(TN
OJ
a
•H
rl
Alexand
p-OtOrHO(»\O(Hr-l
CJOjrHOJoJrAcvxajoj
OOOOOOOOC5
ooooooooo
O^ O *n rH iH C^\ O P* O*^ 1
C*S rH
inoto-^tOQvr^ooj
O O O f~^ O c~l O O O
ooooooooo
OOOCVTvOtfNU^iO
NtlTiOrHrHCViVO-^^O 1
rH VO I> ^ rH O
t^N rH
SrH T\OJM3MDOOO
ooooooooo
QOQ^OOCOQO
OOOOrHVD ** O O
U^O^OJrHi-COOrHiTx
rH VO rH ^ ->T rH r^v
rH
r*\vo QQQOOJr^c^
0s O O O O <*\ OJ VO c\l 1
go|S$oogg
-stOOJCovOoOvO -*4"
~^~ ir\ co if\ o c*\ co
OJ lA OJ OJ rH
rH
OOOvOc^OHOO
HmOOOr^OJOOJ
rH
1
M 0
§O M g
ft Q rH OJ O
H ^J- Ti O 93 -P
4) -p H • • O
-p ••aboooocH
a OOP!? z z
BB Z Z tO -H 4> rl
P -p p M In 4)
CO EQCL) •CbO'rf'rts
CO^^EjbjSpOOOO
^ g<;HflC8,HlHP-Prl
•HCO'^'O^-H-Hrlt-.-H
a -H q s a a ,« p p a
C(X.H
o to c«>
8 8 8
o o o*
O O w^v
OJ fX O>
a 8 8
o o o
O O OJ
C*N rH
VO O C*\
O rH O
d o o'
m in OJ
in in
rH (•*>
888
§* *
o o
in vo
oj" c^C
O O vn
0 0 0
g
•H
•P
0
•p
to
c a IH IH M
3 OJ M rH
£ G 4) 41 OJ
o a -p •*> -p
vH iH -H *H
rH -O tO CO (O
? M
S
8
o
tfx
o
OJ
o
OJ
o
OJ
o
OJ
8
rH
8
o
HH
41
p
•H
CO
o
o^"
in
OJ
IW
OJ
+>
-------
8rH
+» if
+* tH J3
s •i
3 <->
S-S'S
^9
tSBi
!S1
f H j!
S £
S^T;
P< O 40
*a1
0) H rH
0t v_x
3 &
(0 iA t3
2 S oT
C rH
5 C
tit
•AM
rl O .O
0) O r-l
PL, £Q % *•
g
* t5
3" ^o
a +> elf
< J'"'
58
3 «lL
rl 0-55
££
•H TJ
CO t*
S.«
CU
+»
iH
rH
C
S 3
to" to"
8 8
0 0
P- O
tA VQ
IA v\
OJ oj
O O
0 0
So
OJ
O f*>
OJ OJ
OJ OJ
0 O
S S
>r\ \o
OJ C\J
O O
rH rl
O CO
•Nt H
c*\ to
rH rH
OJ OJ
. ,
- g
0 0
03 tf
i i
+? -B
o o
PL. 0,
rl rl
II
rH
to"
8
0
9
lf\
§
o
H
rH
rH
"A
OJ
OJ
O
to
>A
OJ
o
rH
to
IA
OJ
3
*
O
O
§
rH
C*-
o
5
i
o
OJ
r^N
OJ
OJ
OJ
O
«
rH
8
8
VO
O
rH
•
^
§
Sf
I
§
,_!
™
8
o
E;
rH
tr\
a
o
*TN
rH
*rT
P'N
rH
8J
o
£\
^
o
rH
«>
OJ
^
rH
VO
3
4)
rH
rH
01
Anacoeti
o
VO
O
8
o
o
-*
§
o
g
VO
IA
o
OJ
o
o
to
OJ
OJ
8
g
o
to
OJ
CM
$
5
Arlingtc
»
to
OJ
m
8
O
>r\
OJ
§
o
o
OJ
^
rH
OJ
OJ
0
o
o
rt
O
to
rH
to
j_
SI
CO
*H
rQ
i
s
o
District
5
»r\
8
o
to
to
r->
§
O
vS
rH
^
81
o
H
O
OJ
0
8
IA*
rH
s2
'A
Alexandi
S
»r\
8
o
to
6
-*
§
o
s
CD
IA
OJ
OJ
o
^
^
o
rH
8
r-l
f*\
H
£
a
41
i
H
rH
=S
i
Cameron
o
r\
in
O
8
0
o
p-
^
o
8
o
o
r>
Vr
OJ
rH
O
OJ
OJ
OJ
8
g
O
rH
rH
2
fr
Piacatai
to
S?
_^.
"
8
0
to
R
S
§
0
>A
OJ
r\
OJ
OJ
o
VO
VO
o
rH
rx
O^
f*\
•K
O
1
J
^
rH
WN
8
o
fe
§
o
s
EN
t^-
SI
o
UN
to
f\
0
rH
cu
<^v
O
lA
r-i
3
a
0
i
5
^.
v\
8
o
g
o"
rH
§
O
r-N
VD
Q
OJ
OJ
o
OJ
r\
in
o
rH
vS
y
rH
rH
a
^
1
o
iH
ft
8
O
tfN
§
o
R
C*N
OJ
OJ
OJ
0
8
rH
0
to
to
IA
0
rH
•
O
Q
•S
&
i
R
8
o
o
o
0
o
0
o
0
o
rH
o
8
g
o
rH
Sj
0
0
S
3
rH
CO
S3
O r^ *^ ^f ^0
a OJ rH 3 J..
53 81 o a 8
o o o o o
8 'rH ri S g
O ^D O O O
rH H OJ ^ >T»
tj O tj O O
o o o o o
o o \o o o
»Tv rH rH OJ C"-
,-T rH tT\
E> -vf CO O O
rH ^ rH (T\ OJ
0 O O O O
Q O t O O
O- rH O C^ >t
O O O O C\J
8 8 8 S ft
§8888
O o r** oj o^
a- I-H] -^ co
rH
g
•H
a
to
g
O rH 01
rH >»• -H
• • O O
O 0 u Z Z
2 2 1 * "
§ 1 1 1 1
1 1 III
S04 03 iT\
f*\
8 8 S S
O* O C3 CJ
VO OJ r^ OJ
r*N rH
OJ (*N t*\ O
rH Q C*N Q
O O O Si
O O O O
§O r> OJ
Q
rH ^t
«O r*\ O
rH O OJ
0 O O O
O O 'rH
O O O
8888
rH rH H rH
§o o o
O O rH
O rH
r»*\ -^~
c
•H
«
to
o -o
II M a a &
IS 5 5 5 5
rH -O tO tO tO tO
1"
g
-------
i-l O O
CJ> r^ c«"\
Ov CU T\
C- TV ir\ cu
oj in -*vb
D to
to
fc
VD to O
to
s
9
$ TJ^N
> ir\ «"\ u"\ C"* r\ >r\ ir\ o *r\ *f\ u~\ u"\ tf\OO(*\ OOO
JS-JjS 3883 8888 888 888 8888 8 8 8
o' o' o' o* o' o* o' o' o* o* o* o'o'o' o' o' o° o' o' o' o"
•
§00 <*\ O
O to O
O O Q* CL
i! Cf ?5
S
s s§
oJ H
o|
CM|
^
g m oooo oooo
to! H-d
•o -^
> r^\OO-^ OJO>^\O
•P a»C\jQi>'«tQOCo^p^-
0 tf\ ^ O O C*- tfN O O^ ~*^ O^
H o at CT^CO^DOJ r^r^ojr^
+3 ^ Q ON \^ ;^~ r^\ CD O "^
G H H OJ OJ
& — *
3'°'-
P*0o >4--vt^t^l; >J-C\J->tNt
JT ^5 T3 OJCMOJCM OJCMCMCM
if\m OOOO* OOOO
h Q jo
£§Ci
§
0) rH
bDfe^"^ ^OC^^O UNtOrHO^
J) +» S" t-v rH rH rH VO C-- O* O*
> a) — VN O -J- CM CA \O CM
<* 01 rH rH
0 O O OOO
C'N O >f r^ to to
o vo ^o to oj oj
CO "^ "^ V\ rH C^
1A VD to rH rH CM
rH OJ
~^ O^ "^ ^ *^ ~^"
CM rH OJ OJ OJ OJ
OOOOOO
r> O CM O rH TV
r-l 0 Q O O
•* TV i-H rH CM t-
rH rH C^
*>* TV C^. -^ CO O O
CM O rH rH rH (^ OJ
OOOO OOO
if\ O O O C; O O
OOOO O O CM
«•
« S 8 8
oooo
O O rH
p\ <* O
d o o
8
OOO OOO
rH rH rH rH
O Q O Q Q
CT1 O O O O
8888
Q
O
O rH
rH t-
0*
of
H O
CM r-v
»
8
O)
rH
8
8
£
2 3
5 J<
•P «i
3
if
£ S § S
O M m
I*
O< Q
s-
t<
<
, I
* 3
f s o s;._.
II
I! f *F
m m 6 a 6 -p
•H rH S -H 5 ffl
Q <; o a, J a
• o
>£ °
VI
• o
-------
t> cd ci ^ S o*» w jf\
jf o o c*\ "-O ^o *-* w
i fi • Q ^ r**> r\ O*- ff*
; H 3 « •>}• H •* cvi
£ «
O
R 8
«
ft.
-
O
C
8p"\ r°*\ r*4 r*\ P**\ P**\ f*\ p"^ P*\ f\ f*\ c*\ f\ (*\ p*^ oj cy Q oj w w O to o
O O O O O O O O O O O O O O O O O O O O O O O ^
0*0*0*0' oooo d o o o o o d o* CD* CD* odd d d d d
SET"! c- Rj «s
B\ « • •>
CvJ^t OOC^-Q cuir\r^c\ic^Ch
to^tf^o^ i-< *\ to N to H
to tf>
vi> ^f
S o^
l*\ to O ^O rH VN f^
i-l <»\ c^ CM
ir\OOvo OOO
a a a s a a a a a s a aaa. a 8 a a a ar s
f*\ C*\
O C\
O O
OOOO OOOO OOO OOO OOOO OOO OOOO
"O ""^
• >>
•g ?
• jS^
COB
4*03,2
*^ NjOO
OOO \Q O
«\f*\«* OI>A
* "
r\ «\ ej ev O vo cv i- •>
-
»
8 5? 4 38 8
oooo oooo o o o o o o oooo ooo
« S 8 8
oooo
»T\rH C-^OCVJ
13 S » Z
WNOOO ^OO OOi-l
H'f-ICT>i-l Ot^^* (»\>»O
£>O*O'CDOO**-OC\J tOHOr^Ot^ C*-OOO P*
tO 00
to t\I
cj S
p^ O *f* ^O "^ **"^
p"\ (M v\ r^ to to
C\J C«i tO OJ OJ "*
*r\ o* ¥\ p«-
3 *"*
8 S
jS
0>
i
s.,-
I".
« c"
•rt O
lg
«; > a
" 3 o SS
S
CO
=8
I! 1
"O
c
o ^ * S
+> +»
8 i
iH f) O £ to
g
*
f, ia ^ 5H
0) O f>
8£
ts -8
5 -
II
I ^
i 5
& &
3§
ra
IX,
-H tn O
^S
co
e>*
1
2 £
1?
«i
I
il
*s 2
•g-s «
J» t-l
S
M M M t>
M M M
» 5 5
-H -H -H
U3
-------
X-l
CHAPTER X
WATER QUALITY SIMULATIONS
A. WATER QUALITY SIMULATION MODELS
Water quality simulations for this report were made using the
FWQA Dynamic Estuary Model (DEM) and DECS III. The DEM, which was
used to evaluate allowable wastewater loadings and chloride intrusion
as discussed subsequently in this chapter, is a real-time system
incorporating a hydraulic component that describes tidal movement and
a quality component that considers the basic transport mechanisms of
advection and dispersion as well as the pertinent sources and sinks
of each constituent. The ability to utilize a two-dimensional network
of interconnecting junctions and channels makes it possible to include
the embayments directly in the flow network. A detailed description
of the model is available from FWQA [41]. DECS III is based on a
time-dependent tidal average solution of the basic mass balance
equations as originally developed by Thomann [541. This model was
used to investigate seasonal variations in the nitrogen and phosphorus
distributions of the upper Potomac Estuary.
A study investigating the relative merits of the FWQA Dynamic
PJstuary Model versus the tidal average approach has been made by
CTSL and a report of this investigation is currently in preparation.
A schematic diagram of the Potomac Estuary used in the Dynamic
Estuary Model is given in Figure X-l. The location nodes for the
existing discharges and proposed locations for future discharges
-------
X-2
are also shown in this figure. A similar segmentation of the main
Potomac was also used for DECS III.
In simulating the various water quality constitutents, a water
flow system as shown in Figure X-2 was incorporated into the Dynamic
Estuary Model. This feature was necessary to simulate conservative
constituents such as chlorides and total dissolved solids.
-------
CHAIN WtlOOC
WASTEWATER PLANT NODES
NODE PLANT
78 MUMGTON
i2» ILUC PLAINS
2 UWtR POTOMAC
PISCATAWAY
PENTAGON
LOWEM POTOMAC
ANACOSTIA
MATTMOMAN
PORT TOBACCO
LOWEH MACHOOOC Ci
MANVS RIVEH
CHtSAPEAKf KAV
SCHEMATIC OF POTOMAC ESTUARY
FOR FWQA DYNAMIC MODEL
-------
* §
7,
0
H
Ul
FIGURE X-2
-------
X-5
B. ALTERNATIVE WASTEWATER TREATMENT SYSTEMS
As shown in Figures X-3, X-4, and X-5, three basic alternative
wastewater treatment systems were investigated. A fourth system,
similar to Alternative III except for a facility on Rock Creek, was
also investigated; however, the population projections indicated
that the expanded Blue Plains, Upper Potomac, and Anacostia plants
could readily serve the Rock Creek area and this alternative was
subsequently omitted. Alternative discharge locations for two of the
above schemes were considered in the mathematical model simulation
and are presented in Figures X-6 and X-7.
Alternative I consisted of nine wastewater treatment plants in
the upper Potomac Estuary. The projected waste flows for each of
these facilities are shown in the following table:
Table X-l
WASTEWATER FACILITIES AND PROJECTED FLOWS
Alternative I
Facility
Pentagon
Arlington
?lue Plains
Alexandria
Piscataway
Lower Potomac
Occoquan
Mattawoman
Port Tobacco
* Proposed capacity = 309 mgd
.980
mgd)
I
23
285*
-38
24
50
45
5
0
2000
(mgd)
1
37
473
61
49
103
121
9
6
2020
(mgd)
1
45
702
83
79
170
235
13
11
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE I
OCCOQUAN
OF COLUMBIA
(etUE PLAINS)
FIGURE X - 3
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE Tt
^'DISTRICT OF COLUMBIA
(BLUE PLAINS)
FIGURE X-4
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE HI
UPPER POTOMAC \
WASHINGTON
OCCOQUAN
FIGURE X-5
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE 31
OF COLUMMA
(BLUE PLAINS)
OCCOQUAN
FIGURE X-e
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE 3C
OAWAY
OCCOQUAN
FIGURE X-7
-------
X-ll
Under Alternative I, the District of Columbia's Blue Plains
facility will also serve the upper Potomac area within Virginia and
Maryland, the Anacostia Valley, and the Rock Creek Basin. In this
alternative, it is assumed that the expansion at Blue Plains is not
restricted. In all three alternatives, Alexandria's facility will
also serve the Cameron Run and Belle Haven areas, Piscataway will
serve Andrews Air Force Base, and the Lower Potomac plant will
serve Fort Belvoir. The existing Fairfax Dogue and Little Hunting
Creek plants are to be abandoned and the waste transported to the
Lower Potomac facility.
Alternative II was identical to Alternative I except that a
wastewater plant was assumed on the Anacostia River. This facility
will only serve the Anacostia Valley. It was also assumed that the
Blue Plains treatment plant would be expanded to accomodate the
remainder of the flow. The facilities and wastewater flows associ-
ated with Alternative II are shown in Table X-2.
Table X-3 shows wastewater facility data corresponding to
Alternative III which assumes another plant built in 1980 to serve
the upper Potomac area. In Alternative III, the maximum size of Blue
Plains is limited to 309 mgd. The Anacostia facility would serve the
Anacostia Valley and the remainder of the flow shown as transported
to Blue Plains in the first two alternatives would be conveyed to the
upper Potomac plant.
-------
Table X-2
WASTEWATER FACILITIES AND PROJECTED FLOWS
Alternative II
Facility
Pentagon
Arlington
Anacostia
Blue Plains
Alexandria
Pis cataway
Lower Potomac
Gccoquan
Mattaworaan
Port Tobacco
* Proposed capacity = 309 mgd
1980
(mgd)
1
23
0
285*
38
24
50
45
5
0
2000
(mgd)
1
37
126
347
61
49
103
121
10
• 6
2020
(mgd)
1
45
185
518
83
79
170
235
13
11
-------
Table X-3
WASTEWATER FACILITIES AND PROJECTED FLOWS
Alternative III
Facility
Pentagon
Upper Potomac
Anacostia
Arlington
Blue Plains
Alexandria
Piscatav/ay
Lower Potomac
Occoquan
Mattawoman
Port Tobacco
* Proposed capacity =309 mgd
1980
(ngd)
1
0
0
23
285*
38
24
50
45
5
0
2000
(rogd)
1
38
126
37
309
61
49
103
121
10
6
2020
(mgd)
1
209
185
45
309
83
79
170
235
13
11
-------
x-u
Alternative III is similar to the proposals in the "Memorandum
of Understanding" with reference to the Washington metropolitan
regional water pollution control plan as presented at a special
session of the Potomac River Washington Metropolitan Area Enforcement
Conference on October 13, 1970. In this memorandum, a maximum capacity
of 309 mgd for the Blue Plains facility was proposed. It also required
the appropriate parties to provide another regional plant or plants to
accomodate the projected increases in wastewater volumes.
While there can be numerous variations of Alternative III in
respect to flow distribution, the basic layout concept is fundamental.
Alternative V, presented later in this report, is one variation with
discharge points to the main Potomac.
Alternative IV, which is identical with Alternative I for waste-
water treatment plant location, differs in that the effluents from
the upper six plants are conveyed downstream as far as Occoquan Bay.
This plan was investigated to determine the effects of discharges
lower in the estuary on its use as a water supply source (Figure X-6).
Alternative V was developed to investigate the effects of dis-
charging the effluents directly into the main Potomac instead of the
embayments. This alternative, which is identical to Alternative III
in facility locations has the Anacostia, Arlington, Alexandria,
Piscataway, Lov/er Potomac, Occoquan, and Port Tobacco facilities
discharging into the Potomac main channel. The Blue Plains, Upper
Potomac, and Mattawoman facilities either do or were assumed to dis-
charge into the main channel.
-------
X-15
The estuary water supply intake was assumed to be one-half mile
below Chain Bridge. In Figure X-l, the schematic diagram for the
model, the water supply intake is at Node 11/4.
When the current wastewater collection and treatment facilities,
projected populations, "Memorandum of Understanding," and water supply
needs are reviewed, it can readily be observed that:
(1) Shortly after 1980, the Dulles Interceptor with its current
capacity of 64 mgd will be overloaded.
(2) To provide for future wastewater collection and treatment
services in the upper Potomac, either the Dulles Interceptor should
be significantly enlarged or wastewater treatment facilities con-
structed in this region.
(3) If the Dulles Interceptor is enlarged, wastewater treatment
capacity must be increased at either Blue Plains, Anacostia Valley,
and Pis cata-.vay or a combination of all three.
(4) With the current capacity limitation of 309 mgd at Blue
Plains, it appears that treatment facilities will be needed not only
in the upper Potomac but also in the Anacostia Valley.
(5) Large wastewater volumes will be generated in the lower
counties of Virginia, mainly in the Occoquan and Pohick watersheds.
The above five observations indicate that consideration in
selection of wastewater management programs should not only include
treatment facilities but also collection systems. This is discussed in
greater detail later in this report when the water supply aspects are
presented.
-------
X-16
C. WASTEWATER MANAGEMENT ZONES AND STREAMFLOW CRITERIA
To facilitate determination of wastewater management requirements,
the upper and middle estuary were initially divided into three 15-mile
zones with similar physical characteristics beginning at Chain Bridge.
This allowed greater flexibility in developing control needs.
River mile distances for the three upper zones, from both the
Chesapeake Bay and Chain Bridge, are given in Table X-4. The zonal
concept was adopted by the Conferees at the Potomac Enforcement
Conference Progress Meeting on Fay 8, 1969.
More recent studies have suggested that Zone I be divided into
three subzones as shown in Figure X-8. The three subzones are
described as follows:
Subzone Description
I-a Potomac Estuary from Chain Bridge to Hains Point,
a distance of 7.6 miles
I-b Anacostia tidal river from Bladensburg, Maryland to the
confluence with the Potomac, a distance of 9.0 miles
I-c Potomac Estuary from Hains Point to Broad Creek, a
distance of 7.4 miles
Discharges to embayments are also considered in this report.
Using the zonal concept, a total maximum loading for a specific
pollutant is given for each zone. Allocation of pound loading for each
discharge can be obtained by prorating the total zonal poundage using
various bases such as population, drainage areas, and geographical
subdivisions.
-------
o
4)
> N
ofl
CO
<
0)
1-1
,0
0)
Q
2
t P
§1^
tsi rt o
„
•H
f-<
m -o
«3
5?
•gl
o 3
•»* ^
a.
•o
«"a
a «
s^
•H al
-------
RIVER MILES FROM CHAIN BRIDGE = 0
PENTAGON
SUBZONE la
ARLINGTON
SUBZONE Xb ZONE
N^ "^ /
DISTRICT OF/COLUMBA
ALEXANO
WESTGATE
SUBZONE I e
* RIVER MILES FROM CHAM BRIDGE = IS
LITTLE HUNTNG Cr-
ANDREWS A.FB.
FORT BELVOIR
LOWER POTOMAC
P1SCATAWAY Cr.
ZONE II
RIVIH MIUES FROM CHAIN BRIDGE = 30
WASTEWATER DISCHARGE ZONES
in UPPER POTOMAC ESTUARY
ZONE III
RIVER MILES FROM CHAIN BRDGE = 45
FIGURE X-8
-------
X-19
The 7-day-low-flow into the Potomac Estuary, with a recurrence
interval of once-in-10-years, is 95-4 cfs before water supply diversion.
Since the need for water supply is projected to utilize all of the
river flow during critical flow conditions by 1980, a design flow of
300 cfs was used in determining wastewater loadings. This minimum
flow serves to maintain an ecological balance in critical stream
segments during low-flow periods as well as preserve the aesthetic
appearance of this historic area. Where applicable, effects of flow
changes including withdrawal from the estuary for water supply are
also presented.
-------
X-20
D. ULTIMATE OXYGEN DEMAND
The interrelationship between ultimate oxygen demand* (UOD) and
dissolved oxygen (DO) in the Potomac Estuary was determined using a
verified mathematical model. Studies included investigations of
alternative wastewater treatment schemes, UOD loading rates, and net
flows into the estuary for the three benchmark years. Maximum allowable
UOD loadings in pounds per day, based upon compliance with existing DO
stream standards were established for each of the zones including the
embayments.
In developing the allowable UOD loadings, the reaction kinetics,
as given in Chapter VI, were used, including the following DO criteria:
Parameter Value
Water temperature 29.0°C
DO standard (average) 5.0 mg/1
DO saturation at 29°C 7.7 mg/1
Background DO deficit 0.7 mg/1
Allowable deficit 2.0 mg/1
Included in the 0.7 mg/1 DO deficit for background are the effects
of algal growth and benthic demand. In using this deficit, it was
assumed that the algal populations were under control and that the
benthic demand resulting from wastewater sludge deposits had been
substantially reduced from existing conditions. The UOD loadings were
based upon maintaining 5.0 mg/1 of DO averaged over the tidal cycle.
* The ultimate oxygen demand represents the sum of unoxidized carbon
and nitrogen
-------
Table X-5
UOD LOADINGS FOR POTOMAC ESTUARY
Based Upon Maintaining 5.0 mg/1 DO
Freshwater Inflow = 300 cfs (after water supply diversion)
Water temperature = 29°C
Zone Allowable UOD
(Its/day)
I-a 4,000
I-b 3,000*
I-c 75,000
II 190,000
III 380,000
The loading increases with increase in waste flow (See text for
more details).
-------
X-22
Subzone I-c currently receives waste-water effluents fron the Blue
Plains Sewage Treatment Plant which serves the District of Columbia
and surrounding portions of Maryland and Virginia, and from sewage
treatment plants in Arlington, Alexandria, and Fairfax County,
Virginia. As shown in Table X-5, a maximum UOD loading of approxi-
mately 75,000 Ibs/day may be discharged into Subzone I-c regardless
of the alternative investigated.
The effect of eliminating effluent aeration as a treatment process
was determined for Subzone I-c. If a dissolved oxygen concentration of
2.0 mg/1 instead of 6.0 mg/1 in the wastewater is assumed, the allowable
UOD loading in Subzone I-c would be about 60,000 Ibs/day, or a reduction
of 20 percent.
Two other subzones within Zone I, Subzone I-a of the Potomac Estuary
in the vicinity of Chain Bridge and Subzone I-b of the Anacostia tidal
river, were evaluated separately for Alternatives II and III because
their waste assimilative capacities are quite limited. The allowable
QOD loading for Subzone I-a based upon a freshwater flow of 200 to 300
cfs is 4000 Ibs/day. The lack of adequate transport under low-flow
conditions, and more important, the limited reaeration capability due
to the considerable depth of water in this area greatly reduce the
maximum allowable UOD loadings in the Potomac near Chain Bridge. CTSL
mathematical modeling studies have shown that the allowable UOD load
to this portion of the estuary increases substantially with increasing
water supply flow withdrawals. This relationship, which is due to
-------
X-23
the direct removal of UOD before it is exerted in the receiving water,
is shown below:
Net Flow
into the
Estuary* Allowable UOD
(cfs) (Ibs/day)
+ 250 -4000
- 500 6000
-1250 12000
-2000 18000
The allowable UOD loadings in Subzone I-b, which is the upper
Anacostia tidal river (Alternative II), are given for the three
waste flow conditions as follows:
Wastewater
Flow Allowable UOD
(mgd) (Ibs/day)
68 3000
126 6000
185 9000
Again the absence of adequate transport and dilution restricts
the waste assimilative capacity of the Anacostia tidal river. The
increase in the allowable UOD shown above can be attributed to the
progressive increase in wastewater discharges which greatly exceeds
the natural inflow to the Anacostia tidal system in importance. In
effect, the proposed wastewater discharge would substantially
Negative net flows represent water supply withdrawal from the estuary
assuming that all freshwater inflow from the upper basin, except for
a base flow of 200 mgd, has already been diverted.
-------
X-24
increase the downstream advective movement and the assimilative capacity
of the Anacostia -River._
Zone II of the Potomac Estuary currently receives effluents from
the Piscataway and Lower Potomac wastewater treatment facilities via
the Piscataway Creek and Gunston Cove embayments. By 1980, a third
facility serving Mattawoman Creek basin in Charles County will also
discharge into Zone II near Indian Head. Two basic schemes were
investigated to determine UOD loadings in this zone. One scheme
(Alternative V) assumes that all effluents discharge directly into
the Potomac main channel whereas the other (Alternative I) assumes
that the Piscataway Creek and Gunston Cove embayments continue to
receive treated effluents from their respective wastewater plants.
According to Table X-5, the maximum UOD which can be discharged
into Zone II and still permit the DO standard of 5.0 mg/1 to be
realized is 190,000 Ibs/day. It should be noted that prior to
determination of this allowable load, the residual or carryover
effects of Zone I and Zone III loadings upon Zone II were determined
and included.
If Piscataway Creek and Gunston Cove receive the wastev/ater efflu-
ents projected in Alternative I, the maximum allowable UOD loadings
will be reduced considerably when compared to Zone II loadings. The
-------
X-25
relative inability of these embayments to assimilate organic waste-
water is reflected in the data shown below:
UOD LOADINGS FOR PISCATAVIIAY CREEK AND GUNSTON COVE
Piscata
Flow
(mgd)
24
49
79
wav Creek
Maximum
UOD Load
(Ibs/day)
10,000
10,000
12,000
Guns ton Cove
Maximum
Flow UOD Load
(mgd) (Ibs/day)
50 7,000
103 11,000
170 16,000
Since the physical characteristics for each embayment vary widely,
it must be emphasized that separate determinations of loadings will be
required for embayments other than those given above.
Because of the stringent loading requirements associated with
discharges to embayments, it would appear advisable to discharge
wastewater effluents directly to the Potomac (as in Alternative V) and
utilize the additional dilution and transport capability it affords.
There are at present no significant wastewater discharges within
Zone III of the Potomac Estuary; however, a treatment facility to serve
the Occoquan watershed in Virginia has been proposed for construction
by 1980. Moreover, it was assumed that a facility at Port Tobacco,
Maryland, would also be in existence prior to the year 2000. With
Zone II receiving its allowable UOD load (190,000 Ibs/day) and deducting
the necessary carryover effects, the allowable UOD loading for Zone III
was estimated at 380,000 Ibs/day (Table X-5).
-------
X-26
E. PHOSPHORUS
Simulation of phosphorus discharges in the Potomac Estuary was
made using the mathematical model with second-order reaction kinetics
previously described. Included in the model was a phosphorus deposition
rate of 0.05 mg/day at a temperature of 29°C. The allowable phosphorus
loadings in pounds per day were determined based on maintaining an average
of 0.067 mg/1 of phosphorus (P) within Zones I and II and 0.03 mg/1 (P)
within Zone III and all embayments. All effluents were assumed to be of
the same concentration. While various freshwater inflow rates (before
water supply diversions) between 300 cfs and 1800 cfs were investigated,
their effect on the allowable phosphorus loadings appeared to be quite
small.
The allowable phosphorus loading for Subzone I-c of the Potomac
Estuary is 900 Ibs/day as shown in Table X-6. It should be noted
that this loading remains about the same for each alternative investi-
gated.
When Alternative III was considered, the limited waste assimilative
capacity of the Potomac Estuary in Subzone I-a near Chain Bridge became
evident. For a freshwater flow of 300 cfs, the allowable phosphorus
loading to this area was determined to be 200 Ibs/day. If water supply
withdrawals are assumed, a certain portion of the phosphorus will be
removed directly, thereby increasing the allowable load from wastev/ater
-------
Table X-6
PHOSPHORUS LOADINGS FOR POTOMAC ESTUARY
Freshwater Inflow = 300 cfs (after water supply diversion)
Zone Allowable Phosphorus
(Ibs/day
I-a 200
I-b 85*
I-c 900
II 1500
III 2000
* The loading in this zone is sensitive to wastewater flow as
described in the text of this report.
-------
X-28
effluents. The relationship of allowable phosphorus load to rate of
withdrawal is presented in the following table:
Net Flow Into Allowable Phos-
Estuary phorus Loadings
(cfs) (Ibs/day)
+ 300 200
- 500 300
-1250 400
-2000 500
For Alternative II, which includes a discharge into the Anacostia
River, simulation runs indicate that the minimum transport and dilution
greatly restricts the allowable phosphorus load that may be discharged
into the Anacostia tidal system. As in the case of UOD, the phosphorus
loadings into Subzone I-b are also a function of wastev/ater as follows:
Wastewater Allowable Phos-
Flow phorus Loadings
(mgd) (Ibs/day)
68 85
126 135
185 180
As shown in Table X-6, the allowable phosphorus loading into
Zone II of the Potomac is 1500 Ibs/day. The appropriate carryover
effects from both Zones I and III were incorporated into the phos-
phorus analysis for Zone II.
-------
X-29
When wastewater effluents are discharged into the embayments of
Zone II, there is a much larger increase in phosphorus concentration
for a given phosphorus loading. As an example, assuming 1980 waste-
water flow data and a 1000 cfs inflow, if the effluent contains 10 mg/1
of phosphorus, the result in the Piscataway embayment would be as
follows:
Increase in Phosphorus Increase in Phosphorus
Discharge Location Upper_End of Emba.vment Lower End of Embayment
(mg/1) (mg/1)
Into Embayment 3.93 1.22
Into Main Potomac 0.78 0.92
A similar tabulation for Gunston Cove, again assuming 1980 con-
ditions , follows:
Increase in Phosphorus Increase in Phosphorus
Discharge Location Upper.End of Embayment Lower End of Embayment
(mg/1) (rag/1)
Into iJmbayment 8.62 O.ol
Into Main Potoraac 0.49 0.62
The above tabulations clearly show that concentrations in the upper
end of the embayments can be drastically reduced by diverting discharges
to the main Potomac. However, they also show that the phosphorus concen-
trations in the lower end of the embayments are considerably less affected,
This can be attributed to the tidal exchange between the main Potomac and
the erabayments.
-------
X-30
If discharges projected in Alternative I are made to the upper
end of the Piscataway Creek and Gunston Cove embayments, the maximum
allowable phosphorus loadings are as follows:
PHOSPHORUS LOADINGS TO EMBAmENTS
Piscataway Creek Gunston Cove
Maximum Maximum
How Phosphorus Load Flow Phosphorus Load
(mgd) (Ibs/day) (mgd) (Ibs/day)
24 35 50 35
49 50 103 60
79 65 170 140
The loadings given apply to these embayments only. A separate
determination will be required for other embayments because of different
physical configuration. The effect of the main Potomac on the embayments
was previously demonstrated by Jaworski and Johnson in a preliminary study
of the Piscataway embayment [-42].
It can be concluded that there is a significant advantage in dis-
charging wastewater effluents into the main channel (Zone II) from the
standpoint of phosphorus buildup. Moreover, it appears that with the
lack of transport in the embayments, the allowable phosphorus concen-
tration in discharges to the embayments begins to approach the developed
criteria.
In order to realize the phosphorus criterion for Zone III of the
Potomac Estuary (0'.03 mg/1), the maximum phosphorus loading from
-------
X-31
wastewater effluents within this zone was determined to be 2,000 Ibs/day
as shovrn in Table X-6.
Using phosphorus as a tracer, simulation runs were made to determine
ho.v quickly any component in the >,rastewater discharge could reach the
proposed estuary water intake. Table X-? shors that in the extreme case
investigated, about 4 days vraxild elapse before detection there. For the
projected year 2020, wastewater diseharces and a river flow of 1800 cfc,
the time would be increased to o days.
-------
Table X-7
INTRUSION TIMES FOR PHOSPHORUS INTO ESTUARY WATER INTAKE
Wastewater Alternative I
Year
1980
1980
1980
2000
2000
2000
2020
2020
2020
Net
Inflow
+1250
+ 250
- 500
+ 500
- 500
-1000
- 500
-1500
-2000
Days Required to Detect
in Phos -chorus at Water
— *
— *
10
.-_•*
9
5
8
5
4
an Increase
Intake
* With a positive net inflow, there was no measurable intrusion into
the intake.
-------
X-33
F. NITROGEN
Inorganic nitrogen was simulated using a mathematical model which
had already been verified based upon observed data. For purposes of
developing zonal loadings, the total inorganic nitrogen was assumed
to behave conservatively. Since nitrogen appears to be limiting the
rate of algal growth in Zones II and III, more stringent criteria
were adopted for those areas. The upper nitrogen concentration limits
used for Zones I, II, and III were 0.5, 0.4, and 0.3 mg/1 respectively
at a temperature of 29°C. V/ith these levels of inorganic nitrogen,
some algal growth will occur but nuisance conditions should be pre-
vented. The net estuary inflow, water supply withdrawal rates,
population benchmarks, and alternative vrastewater treatment schemes
incorporated in the analysis of nitrogen were identical to those used
for determining phosphorus loadings.
The allowable nitrogen loading for Subzone I-c of the Potomac
Estuary is 3,400 Ibs/day (Table X-8). For Alternative III and a
freshwater inflow of 300 cfs, Subzone I-a can receive and adequately
assimilate 1,000 Ibs/day of nitrogen from wastewater effluents. If
nitrogen is removed from this portion of the estuary via water supply
withdrawals, the allowable nitrogen loadings will, of course, increase
in a manner similar to that shown previously for UOD and phosphorus.
-------
Table X-8
NITROGEN LOADINGS FOR POTOMAC ESTUARY
Freshwater Inflow = 300 cfs (after water supply diversion)
Zone Allowable Nitrogen
(Ibs/day)
I-a 1000
I-b 300*
I-c 3400
II 5800
III 9000
* The loading in this zone is sensitive to waste flow as des-
cribed in the text of this report.
-------
X-35
Allowable nitrogen loadings for Subzone I-b, which is the upper
Anacostia tidal river, are also a function of wastewater flow and are
as follows:
Flow,, Allowable Nitrogen
(mgd) (Ibs/day)
68 300
126 550
185 800
With all major wastewater effluents discharging to the main
channel, Zone II of the Potomac Estuary can receive 5800 Ibs/day of
inorganic nitrogen (Table X-8) and still maintain the criterion of
0.4 mg/1. As shown in Table X-8, the allowable nitrogen loading for
Zone III of the Potomac is 9000 Ibs/day.
The importance of nitrogen as a potential rate-limiting nutrient
within Zone II must be considered when evaluating the loading require-
ments for embayments such as Piscataway Creek and Gunston Cove. As in
the case of phosphorus, the lack of movement from the head end of the
embayments necessitates reducing the nitrogen concentration in waste-
water effluents to a level approaching the established criteria.
-------
X-36
For discharges made to the upper end of the embayments for
Alternative I, the maximum allowable nitrogen loadings are:
NITROGEN LOADINGS TO EMBABffiNTS
Piscatawav Gunston Cove
Flow
(mgd)
24
49
79
Maximum
Nitroeen Load
(Ibs/day)
120
170
270
Flow
(mgd)
50
103
170
Maximum
Nitrosen Load
(Ibs/day)
130
270
460
Independent determinations of nitrogen loadings must be made
for other embayments because of varying hydrography and tidal
characteristics. In view of this stringent allowable loading, a
definite advantage is evident in discharging into the main channel.
-------
X-37
G. CHLORIDE AND TOTAL DISSOLVED SOLIDS SIMULATIONS
1. Estuary Water _Supply Withdrawal
In March 1969, Hetling [43] investigated the possible use of the
upper Potomac Estuary as a water supply source, primarily from the
chloride intrusion aspect. From this study, it was concluded that
(l) under most critical summer-flow conditions on record (1930'-193l)
and the year 2010 demand, the estuary could be used for potable water
supply purposes, and (2) if the wastewater is discharged out of the
basin, such as to the Chesapeake Bay, the water supply potential of
the estuary is reduced considerably. In light of the large projected
wastewater volumes in the lower counties of Virginia along the upper
Potomac, a review of the possible intrusion of chlorides and total
dissolved solids into the estuary water intake was undertaken.
Data in Figure X-9 indicate that the chloride intrusion from
Chesapeake Bay varies appreciably. This variation is rrainly a func-
tion of freshwater inflow rate and duration. The November 19J\-
profile shows the farthest upstream intrusion as a result of prolonged
low flows of less than V'OO efs from July through Uover/oer. -^I'L/JO1:;-^
the drought conditions in September 19fco were more severe \ J.hV "leys
of approximately 220 cfs, the duration 'ras shorter and 'i;nce 'Lhc
intrusion was not as great.
-------
FIGURE X-9
-------
X-39
Using four historic low-flow conditions, the rate of intrusion was
calculated as follows:
Flows Upstream Movement
(cfs) (miles/day)
5000 0.00
1100 0.07
580 0.21
214 0.71
The above tabulation clearly shows the effect of freshwater inflov.' on
the rate of the chloride intrusion from the Chesapeake Bay.
The intrusion of chlorides and total dissolved solids was simu-
lated using the RVQA Dynamic Estuary Quality Model. For Alternatives I
and IV, the simulations were made assuming the following freshwater
inflows and water supply withdrawals:
Year 1980
Year 2000
Year 2020
Freshwater
Inflow at
Great Falls
(cfs)
1870
1120
3'/0
1750
1000
250
1900
1150
400
Water Supply
Withdrawal
(cfs)
870
870
870
1500
1500
1500
2400
2400
2400
Net Flow Into
the Estuary*
(cfs)
+1000
+ 250
- 500
+ 250
- 500
-1250
- 500
-1250
-2000
* Negative net flow represents withdrawal from estuary for water supply
-------
X-40
Two sets of initial conditions were used for each simulation:
(l) an initial chloride wedge position as observed on September 13, 1966,
and (2) a less severe condition using July 7-8, 1965, observations. The
upper end of the chloride wedges under these two conditions is shown in
Figure X-9.
To obtain the initial conditions for total dissolved solids (TDS),
a relationship between TDS and chlorides was established from existing
data as follows:
IDS (mg/1) =1.69 Chlorides (mg/l) + 300
Boundary and loading conditions used in the simulations are itemized
below:
Chesapeake Bay chloride concentration
Chesapeake Bay TDS concentration
Freshwater inflow chloride concentration
Freshwater inflow TDS concentration
Wastewater TDS concentration*
Water use chloride increment
Water use TDS increment (Run l)
Water use TDS increment (Run 2)
Currently the average concentration of chlorides and TDS in the waste-
water effluents are about 40 and 300 mg/1, respectively. The above
40 and 240 increments for TDS are well within the range of accepted
concentrations in the effluent of 200 to 400 mg/1. In this study,
1966 Wedge
11000 mg/1
18000 mg/1
30 mg/1
160 mg/1
300 mg/1
25 mg/1
40 mg/1
240 mg/1
1965 Wedge
9000 mg/1
14000 mg/1
15 mg/1
160 mg/1
300 mg/1
25 mg/1
40 mg/1
240 mg/1
* The total TDS increase from water intake to wastewater discharge is
currently about 140 mg/1
-------
X-41
maximum upper limits for municipal water supply of 250 and 500 mg/1 of
chlorides and TDS respectively in the blended mix of estuary water and
freshwater inflow were used as recommended by the U. S. Public Health
Service [44],
With the concentration of TDS in both the estuary and the wastewater
effluent higher than for chlorides, the restricting limitation on the use
of the estuary is TDS. This finding is also supported by Hydroscience
[45J in their preliminary report on the feasibility of the Potomac Estuary
as a supplemental v/ater supply source.
Summaries of the results of the TDS simulations for the initial con-
ditions of July 7-8, 1965, and September 13, 1966, are given in Tables X-9
and X-10. Based on data summarized in these two tables as well as from
other simulations runs, it can be concluded that:
1. Even with no water supply withdrawals from the estuary, chloride
and TDS intrusion will occur farther upstream in the Potomac Estuary as a
result of the larger percentages of total wastewater volumes discharged
farther downstream and projected increases in consumptive loss. Currently,
less than 20 mgd is discharged into saline waters. By 2020, approximately
31 percent of the wastewater or over 400 mgd will be discharged into the
saltwater wedge. The consumptive loss, which is water supply withdrawal
minus wastewater discharge, is projected to increase as shown below:
Yegr Consumptive Loss
(mgd)
1966* 44
1980 83
2000 148
2020 226
* During the month of August in which the flow into the estuary was 538 cfs,
the consumptive loss was about 13.5 percent
-------
X-42
This increased downstream discharge, coupled with the above increased
consumptive loss will reduce the net seaward flow in the upper estuary
even without any water supply withdrawal.
2. The number of days that the estuary can be used for v/ater supply
depends Fa inly on (a) duration and magnitude of drought conditions,
(b) location of wastewater treatment facility discharges, and (c) position
of the salt wedge before low-flow conditions begin.
3. The effect of the incremental increase in TDS in the waste-water
on the concentration at Chain Bridge is not significant for the upper or
lov/er -..-edge positions for Alternative IV. The number of days that the
estuary could be used for a water supply did not vary if 40 or 240 mg/1
was used. The major effect on the concentration was the intrusion from
the Chesapeake Bay which is controlled by freshwater inflow and wastewater
discharge locations (Table X~9),.
For the upper wedge position, as given in Table X-10, the effect of
the concentration of IDS in the effluent is more significant especially
for Alternative I and the year 2020. The tiuie was reduced by 24 days
when the TDS increment was increased from 40 to 240 mg/1.
4. V.'ith the salt wedge in the upper position as of September 13,
1966, using the TBS criterion of 500 r.ig/1 in the blended water,
Alternative I, and with less than 400 cfs coming over Great Falls before
-------
X-43
water supply withdrawal, the estuary could be used for water supply
for the following periods:
Year 40 me/1 Increment 240 me/1 Increment
(days of use) (days of use)
1980 > 166 > 166
2000 90 35
2020 45 15
This reduction In usage between 1980 and 2020 is primarily the result
of increased incursion due to reduced net seaward flow and increased
t 166 > 166
2000 140 45
2020 95 20
The above reduction with time again reflects the increasing downstream
discharges and the increasing consumptive losses.
5. Assuming about 1800 cfs freshwater inflow and the September
13, 1966, initial wedge location, the estuary can be used as a water
supply source for over 166 days (the upper limit of the simulation
period) for both chlorides and TDS for all three population benchmark
years 1980, 2000, and 2020.
-------
X-44
6. The number of days that the estuary can be used as a water
supply for the year 2020 beginning with the September 13, 1966, wedge
location as a function of freshwater flow is given below:
MAXIMUM MYS OF USE OF ESTUARY
Freshwater Inflow Alternative I Alternative IV
Before Water Use Increment Water Use Increment
Water Supply of TDS of TDS
Withdrawal
(cfs)
400
1100
1800
40 mg/1
( days )
45
>166
>l66
240 mg/1
( days )
15
42
>166
40 mg/1
( days )
18
>166
>166
240 mg/1
(days)
18
41
>166
7. Since the projected water supply needs for the year 2020
cannot be met by either the upper basin with seven reservoirs or the
estuary alone, both sources will be needed to supply the water needs
fcr the Washington metropolitan area.
8. It is necessary to coordinate both the water supply and
vrastewater treatment requirements for planning in the Washington area
since use of the estuary for water supply purposes is dependent on the
location and distribution of wastewater discharges.
-------
Table X-9
TIME, IN DAYS, TO REACH INDICATED
CONCENTRATION OF TOTAL DISSOLVED SOLIDS
IN ESTUARY
AT PROPOSED WATER INTAKE NEAR CHAIN BRIDGE
(Initial Conditions as of July 7-8, 1965)
1980
Freshwater Flow*
Alt. I
Alt. IV
1000 cfs
Water Use Increment 40 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
>166
>166
>166
Water Use Increment 240 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
Freshwater Flow
>166
>166
>166
250
Water Use Increment 40 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
>166
>166
>166
Water Use Increment 240 mg/1
TDS (500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
freshwater Flow
>166
>166
>166
-500
of TDS
>166
>166
>166
of TDS
>166
>l66
>166
cfs
of TDS
>166
>166
>166
of TDS
>166
>166
>166
cfs
2000
Alt. I
250
>166
>166
>166
>166
>166
>166
-500
>166
>166
>166
>166
>166
>166
-1250
Alt. IV
cfs
>166
>166
>166
>166
>166
>166
cfs
124
>166
>166
123
>166
>166
cfs
Ait. :
>l66
>166
>166
>166
>l66
>166
>166
>166
>166
32
>166
>166
2020
I Alt. IV
-500 cfs
132
>166
>166
162
>166
>l66
-1250 cfs
63
100
126
60
97
122
-2000 cfs
V.'ster Use Increment 40 mg/1 of TDS
IDS ( 500) mg/1 >l66 118
1JO
-------
Table X-10
TIME, IN BAYS, TO REACH INDICATED
CONCENTRATION OF TOTAL DISSOLVED SOLIDS
IN ESTUARY
AT PROPOSED WATER INTAKE NEAR CHAIN BRIDGE
(Initial Conditions as of September 13, 1966)
1280.
2000
2020
Alt. I
Alt. IV
Alt. I
Alt. IV
Alt. I
Alt. IV
Freshwater Flow*
1000 cfs
250 cfs
-500 cfs
Water Use Increment 40 mg/1 of TDS
TDS ( 500) mg/1 >l66 >l66
TDS (1000) mg/1 >166 >166
TDS (1500) mg/1 >l66 >l66
ti'ater Use Increment 240 mg/1 of TDS
IDS ( 500) mg/1 >166 >166
TDS (1000) mg/1 >166 >166
LD3 (1500) mg/1 >l66 >l66
>166
>l66
>l66
>166
>l66
>166
>166
>166
>166
>166
>166
>166
>166
>166
>16'6
> 166
>l66
>166
132
>166
>156
162
> 166
>l66
Freshwater Flow
250 cfs
-500 cfs
-1250 cfs
V/ater Use Increment 40 mg/l of TDS
TDS ( 500) mg/1
IDS (1000) mg/1
IDS (1500) mg/1
Water Use Increment 240 rcg/1 of TDS
>00) mg/1 >166 >166
>166 >166
>166
>166
>l66
>166
>166
>l66
>166
>166
>l66
>l66
124
>166
>166
>166
>166
>166
TIS (1000) mg/1
TJS (1500) mg/1
>166
>166
>166
>166
>166
123
>l66
> 166
32
> 166
>166
63
100
126
60
97
122
-------
Tci.'blc> X- -10
fj':\l'A}} It VdYS, TO K/.AOK li'DIOAT^D
oo/:CtvOj'uAv;KK>; o/ TOivu, jxf^oLY.jn) CO/.TIXJ
AT i'i?avo3;-:D vAyxi; IKTAKM KJ-:/J{ cMitf }irax;^;
(initial Cloaca tu OIL.-; as of fkrptc.rfjcr .13, 1966)
.(.' .C'O-
T f- . I
l-iS
TD3
T.>3
0'D:i
',/li^t
T.D3
T.JX3
TC-3
"103
Frcs
,L /i C-' J?
?E£5
T.Bo
T.DS
TIo
Jnev
'.i.' u3
TD3
T.03
TTo
i-re.
Tr.cr
TiO
T.t/V>
T.u.
Til,::,-
TiX;
'•.-.•;•',
1 .1 - *
hv ' l->.r
-::-.;.-. ;.er
\ x* /
(1003)
(1500)
(2000)
:-r,. ":!•.; or
( 500)
(1000)
(1500)
(2000)
h^ator
e-i-^nt
( 500)
(HO DO)
(.1500)
(2000)
e.r.oat '
( 503)
(-'030)
(1500)
(2000)
":.;; ',--.-r
(' 500)
')':(-r'^J(
} ' ^ A \
v-;o,-o)
: ,• ' •"• i
( V03)
( ' , ')-;}
t i %
v '-''',' ';
Alt .
}'U.OW
Incrccmer'a;
xi 66
X166
>l66
XL66
Increraerrb
X166
Xi.66
xi 66
X166
Flo-.-r
^0 rng/1
>166
>166
X166
xv66
•>];.Q m:r/l
Xi.66
X166
Xi.66
Xi.66
i'.l o-.f
-0 r.-Vl
v_->/
Xi.66
X166
X166
X166
-)',n - ^-/i
83
Xi66
xi 66
Xi 66
3980
I Alt. p
1030 cTs
hO it.-/.!
X166
X166
>166
Xi 66.
2'iO j.^-./.l.
Xi 66 '
X166
xi.66
X166
250 el's
Xi.66
X166
Xi.66
Xi.66
Xi 66
Xi 66
X166
Xi 66
-500 c,7.
Y'.
-i 06
3.29
l':-5
yl;
1 06
129
t';>
jTi-l L'
Xi 66
X165
X166
Xi.66
XL66
>165
Xi 66
Xi.66
>166
X166
X166
Xi.66
5Y
Xi.66
Xi 66
Xi.66
Y8
132
165
Xi.66
,
26
.'i 03
.1 ': 0
>:i 66
2.000
I Alt. N
250 cis
X166
>i66
>l65
>166
>166
X166
Xi 66
Xi 66
-500 ci's
YO
110
:i35
15Y
YO
110
135
-.3250 cr«
•28^
j'5
58
YO
28
V;
58
YO
Alt .
xi.66
X166
Xi 66
Xi 66
XL66
>166
X166
Xi.66
X166
XL66
X166
XI 66
28
Xi 66
Xi.66
X166
39
Y8
100
122
-15
60
83
103
2020
1 Alt J//
-500 cfs
Y-L
115
150
- X166
Y-i
a 15
Xi.66
-1250 cl-s
28
),y
61
Y8
28
60
Y6
-2500 el's
2-';
39
-'Y
-,'s
;_c)
-------
-------
Table X-10
TIME, IN DAYS, TO REACH INDICATED
CONCENTRATION OF TOTAL DISSOLVED SOLIDS
IN ESTUARY
AT PROPOSED WATER INTAKE NEAR CHAIN BRIDGE
(Initial Conditions as of September 13, 1966)
1980
Alt. I Alt. IV
Freshwater Flow* 1000 cfs
Water Use Increment 40 mg/1 of TDS
77JS ( 500) mg/1 >166 >l66
7D3 (1000) mg/1 >166 >166
126 (1500) mg/1 >166 >166
Vi'ater Use Increment 240 mg/1 of TDS
IDS ( 500) mg/1 >l66 >l66
IDS (1000) mg/1 >l66 >166
ID3 (1500) mg/1 >l66 >l66
Freshwater Flow 250 cfs
i'/ater Use Increment 40 mg/1 of TDS
TDS ( 500) mg/1 >l66 >l66
IDS (1000) mg/1 >166 >166
TDS (1500) mg/1 >l66 >l66
\/ate," U?e Increment 240 mg/1 of TDS
irs ( 500) mg/1 >l66 >l66
776 (1000) mg/1 >166 >l66
"X (1500'; mg/l >166 >166
'.resb.water Flow -500 cfs
Y/>ter Use Increment 40 mg/1 of TDS
::,;' i 500) mg/1 >166 118
I~£ (1000) mg/1 >166 >166
7.TS (1500) mg/1 >l66 >l66
','/at,er Ifee Increment 240 mg/1 of TDS
TDt> ( 500) mg/1 83 11?
IuS (1000) mg/1 >l66 160
70S (1500) mg/1 >166 >166
2000
Alt. I
250
>166
>166
>166
>166
>166
>166
-500
>166
>166
>l66
>166
>l66
>166
-1250
130
>166
>166
126
147
>166
Alt. IV
cfs
>166
>166
>166
>l66
>166
>166
cfs
124
>166
>166
123
>l66
>l66
cfs
58
S8
107
57
87
106
2020
Alt. I Alt. IV
>166
>166
>l66
>166
>166
>166
>166
>166
>166
32
> 166
> 166
o/.
130
159
15
130
159
-500 cfs
132
>166
>166
162
> 166
>l66
-1250 cfs
63
100
126
60
97
122
-2000 cfs
43
68
00
43
•^ ; o
36
Inflow to estuary after water supply withdra\val
-------
Table X-9
TIME, IN DAYS, TO REACH INDICATED
CONCENTRATION OF TOTAL DISSOLVED SOLIDS
IN ESTUARY
AT PROPOSED WATER INTAKE NEAR CHAIN BRIDGE
(Initial Conditions as of July 7-8, 1965)
1980
Freshwater Flow*
Alt. I
1000
Water Use Increment 40 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
>166
>166
>166
Water Use Increment 240 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
Freshwater Flow
>166
>166
>166
250
Water Use Increment 40 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
>166
>166
>166
Water Use Increment 240 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
freshwater Flow
>166
>166
>166
-500
"tfster Use Increment 40 mg/1
TDS ( 500) mg/1
TDS (1000) mg/1
TD3 (1500) mg/1
>l66
>166
>l66
Water Use Increment 240 mg/1
IDS ( 500) mg/1
TDS (1000) mg/1
TDS (1500) mg/1
83
>l66
>166
Alt. IV
cfs
of TDS
>l66
>166
>166
of TDS
>166
>166
>166
cfs
of TDS
>166
>166
>166
of TDS
>166
>166
>166
cfs
of TDS
118
>166
>166
of TDS
117
160
>166
2000
Alt. I
250
>166
>166
>166
>166
>166
>166
-500
>166
>166
>166
>166
>166
>166
-1250
130
>166
>166
126
147
>166
Alt. IV
cfs
>166
>166
>166
>166
>166
>166
cfs
124
>166
>166
123
>166
>166
cfs
58
88
107
57
87
106
2020
Alt. I Alt. IV
>166
>166
>166
>166
>166
>166
>166
>166
>166
32
>166
>166
84
130
159
15
130
159
-500 cfs
132
> 166
>166
162
>166
>166
-1250 cfs
63
100
126
60
97
122
-2000 cfs
43
68
86
43
68
86
Inflow to estuary after water supply withdrawal
-------
X-47
2. Direct Reuse of Treated Wastewater
In the system where treated wastewater is discharged into the fresh-
water estuary, intrusion of salt from Chesapeake Bay is one of the major
restrictions if the upper estuary is to be used as a potable water supply.
The direct reuse system (that is, going directly from the advanced waste-
water treatment facility to the water supply facility) removes this
restriction.
Using the water requirements for the year 2020 and conditions as
defined in the previous section, simulations were made with the direct
reuse system to determine the rate of buildup of both chlorides and TDS.
The results of these simulations for various flow conditions are presented
below:
Equilibrium Concentrations
V/ater from Water from Chlorides max. 40 mg/1 of 240 mg/1 of
Upper Basin Direct Reuse Concentration TDS Increase TGB Increase
(cfs)
400
1150
1900
(cfs)
2000
1250
500
(mg/1)
140
42
22
(mg/1)
360
203
171
(mg/1)
1360
421
233
The equilibrium concentrations or maximum concentrations to which the
system would build up with partial direct recycling usually were
reached in less than 20 days except for the first flow condition (400 cfs
from Great Falls) in which 40 days were required.
-------
X-48
The above tabulation indicates that direct reuse is a feasible
solution to the future water supply needs of the Washington metro-
politan area with respect to TE6 and chlorides. The only restriction
is that with over 80 percent of the water supply from renovated waste-
water, the maximum combined buildup in TDS from both the water supply
and wastewater treatment facilities has to be less than 65 mg/1. For
a flow of 670 cfs (the s even-day-lo?/~f low with a recurrence interval
of once-in-50-years) or with approximately 70 percent of the water
supply from renovated wastewater, the maximum TDS buildup would have
to be restricted to 1-40 mg/1. As reported earlier, this is the current
buildup in the entire water use system.
Based on data obtained from the AIT pilot plant operation at
Blue Plains [46], the TES, excluding the bicarbonate system, is not
anticipated to increase and in fact may decrease,, Since the bicarbonate
concentration can be controlled by proper selection of unit processes
of the AWT treatment facilities, the 140 mg/1 increment can readily be
maintained.
The direct reuse concept has the following advantages:
(l) Effects of intrusion from the Chesapeake Bay are eliminated,
(2) Need for the protection of the upper estuary from accidental
spills, urban runoff, storm and combined sewer overflows with respect
to water supply is eliminated,
(3) Restriction on the location of wastewater facilities with
respect to water supply needs is eliminated,
-------
X-49
(4) With proper planning, the need for massive wastewater
collection and water distribution systems can be reduced. For example,
both facilities can be located in the upper Potomac area with reuse
being instituted whenever needed. During high-flow periods, the
effluent may be discharged into the Chesapeake and Ohio Canal and
conveyed past the downstream water intake.
(5) The need for the proposed upstream impoundments for water
supply in the Washington area would be eliminated.
The major disadvantages are:
(l) Ammonia nitrogen conversion or removal will be required at
temperatures approaching 5°C. Technology for this requirement is not
fully developed at the present time.
(2) With the potential buildup of TDS, unit process will have
to be carefully selected.
(3) A high degree of operation efficiency, including "fail safe"
concepts, must be maintained at both the wastewater and the water
supply facilities.
The direct reuse concept has great potential. However, there are
many aspects which need to be investigated. These concepts could also
be readily applied to small areas such as the Occoquan watershed, a
sub-basin of the Potomac below Washington, and the Patuxent River Basin,
a watershed bet?/een Baltimore and Washington.
-------
-------
XI-1
CHAPTER XI
WASTEWATER TREATMENT FACILITIES AND COSTS
A. TREATMENT CONSIDERATIONS
To meet the carbon (UOD), nitrogen, and phosphorus requirements
previously specified, a high degree of wastewater treatment will be
required for Zone I. Based upon the performance of the FWQA. pilot
plant at Blue Plains, Bishop [46] indicates that the following removal
rates can be anticipated from April to November (winter operation
reliability has not been demonstrated):
Parameter After Treatment, % Removal
BOD5 <2.0 >99
Nitrogen as N 1.0 - 2.0 90 - 95
Phosphorus as P < 0.1 > 99
To achieve the above removals, the following unit process sequence
could be selected:
(l) Primary settling and activated sludge,
(2) Biological nitrification,
(3) Biological denitrification,
(4) Lime treatment,
(5) Dual media filtration,
(6) Effluent breakpoint chlorination, and
(7) Effluent aeration.
The above unit processes can produce an effluent which will meet
the removal requirements for phosphorus and ultimate oxygen demand.
However, with respect to nitrogen removal for algal control, it appears
-------
XI-2
that the requirement cannot be readily met. Since over 99 percent of
phosphorus can be removed, it appears that with a combination having a
high percentage of carbon removal and 90 percent nitrogen removal, such
as the preceeding seven unit processes can provide, both the DO enhance-
ment and algal control will be realized. At present, the need for
activated carbon adsorption has not been adequately demonstrated.
An important aspect of wastewater treatment will be the additional
effluent aeration required, especially in Zone I, or for large dis-
charges into small embayments. For example, a discharge of 185 mgd
into the Anacostia River will be over 35 times greater than the
freshwater inflow during low-flow periods. Hence, to maintain a DO
level of 5.0 mg/1, the discharge will have to have at least 5.0 mg/1
of DO. The unit process for this effluent quality is included in all
costs presented in this report.
Additional removal of inorganic nitrogen and carbon could be
provided by activated carbon. The activated carbon beds become media
for bacterial growths which convert some of the organic nitrogen to
ammonia. The ammonia can then be removed by additional chlorination.
Since the continued effectiveness of this additional nitrogen removal
process is not well established, the effectiveness or the need for
carbon adsorption as an additional wastewater unit process has not at
present been established. Its utility appears to be more predicated on
the use of the estuary as a water supply than for wastewater treatment.
-------
XI-3
B. WASTEWATER TREATMENT COSTS
Cost estimates for conventional secondary treatment and six
advanced waste treatment (AWT) processes were developed for 15 present
and planned facilities. The AWT processes considered include lime
clarification with dual media filtration (for phosphorus removal and
for additional carbon removal), carbon adsorption, biological nitrifi-
cation and denitrification (for removal of ammonia and nitrate nitrogen
respectively), and effluent aeration (to increase the DO from 1.0 to
6.0 rag/1). Capital costs and operation and maintenance (0 & M) costs
for each process were obtained chiefly from the Bechtel Corporation's
report [47] on AWT at Blue Plains and cost data prepared by Smith and
McMichael [4.8]. Where necessary, these costs were adjusted to reflect
mid-1970 engineering indexes.
Cost data for specific years were determined by a computer systems
program which incorporated equations describing the dollar per unit
discharge relationship. One of the cost curves used is shown in
Figure XI-1. Basic assumptions and alternative amortization and plant
operat i on s chemes included:
(l) Expenditures for new construction required in 1970, 1980, and
2000 are based upon design for conditions 10 or 20 years hence.
(2) In the case of existing treatment plants, construction of AWT
units would begin in 1970 with 0 & M cost accruing from that time.
Other plants were assumed to be constructed in 1980.
-------
•"1V£> OOOI/» - J.SOO XN3WJLV3MJ.
8 o
J
I
1
- J.SOO TVXIdVO
O
HGURE Xl-l
-------
XI-5
(3) If a new AWT plant is to be constructed in 1970, a 15-percent
replacement of this plant would be necessary by 1980 in addition to
required expansion. For the year 2000 construction, it was assumed that
the entire original plant built in 1970 and 30 percent of the plant
built in 1980 would be replaced.
(4) If a new AWT plant is to be constructed in 1980, 30-percent
replacement would be provided for the year 2000 along with expansion to
meet 2020 needs.
(5) With the exception of Arlington, conventional treatment units
at the existing plants were considered to be new in 1970. The current
capacity at Piscataway was assumed to be 30 mgd since construction of
additional facilities is well under way.
(6) 0 & M costs for AWT units were based on 6-month and 12-month
operating periods and the average projected waste flows for the specific
time frame.
(7) The amortization of capital costs was assumed over a 20-year
period with an interest rate of 5-1/8 percent.
Table XI-1 presents a summary of the treatment cost data for the
upper Potomac Estuary through the year 2020.
Using Alternative III, the total present worth cost of wastewater
treatment expenditures from 1970 to 2020 was determined to be $1,340
million (Table XI-l). If activated carbon is added, the cost will
increase to $1,700 million. The annual cost basis for an average
-------
XI-6
population of six million people reduces to approximately $11 per person
per year. With the activated carbon units, the cost increases to
$14 per person per year.
Capital cost expenditures and 0 & M costs are presented by unit
process for-the three periods (1) 1970-1980, (2) 1980-2000, and
(3) 2000-2020 in Table XI-2. As can be seen in the table, the largest
capital costs of the total initial cost of $2,272 million are $737 million
for secondary and $463 million for activated carbon unit process, with
the 0 & M cost being largest for the lime clarification and activated
carbon processes.
With nitrification and denitrification required for only 7 months
out of 12, an annual 0 & M savings of $3 million from 1970-1980,
$4 million from 1980-2000, and $6 million from 2000-2020 can be realized.
Continued studies will be required to further define the temporal removal
requirements for nitrogen.
-------
Table XI-1
TOTAL WASTEWATER TREATMENT COST
1970-2020
Alternative III
Unit Process
Primary -s e condary
Biological nitrification
Biological denitrification
Lime clarification
Dual media filtration
Effluent Aeration
Chlorination
Subtotal
Activated Carbon
TRY*
($ x 106)
457
2/47
133
370
101
10
22
1,340
360
TAAC**
($ x 106)
13.5
13.8
9.4
20.6
5.7
0.6
1.2
$64.8
20.1
Total 1,700 $84.9
* Total present worth cost includes proposed secondary treatment
expansion cost for Blue Plains
** Total average annual cost including operation and maintenance
cost based on 12 months of operation
-------
Table XI-2
INITIAL CAPITAL CONSTRUCTION
AND
OPERATION AND MAINTENANCE COSTS
1970-1980, 1980-2000, and 2000-2020 Time Periods
Unit Process
Primary-secondary
Biological nitrification
Biological denitrification
Lime clarification
Dual media filtration
Chlorinat ion
Effluent aeration
Subtotal
Activated carbon
Total
1970-1980
Capital Qtfoer
($x!06) ($x!03)
236.11
70.64
62.11
69.31
27.22
0.37
2.91
468.67
101.96
4H1.48
3968.66
427.29
8661.66
889.15
761.59
226.61
19176.44
5931.92
1980-2000
Capital Other
($xltf>) ($x!03)
129.71
84.53
71.84
81.96
35.02
2.00
4.35
409.49
118.38
7413.07
7097.46
759.32
15573.46
3064.69
1328.37
407.73
35644.10
10535.54
2000-2020
Capital Other
($x!06) ($x!03)
371.11
167.63
148.24
166.12
66.09
3.55
6.90
929.64
243.40
11512.23
11044.23
1197.80
24560.32
4510.30
2165.03
739.27
55729.18
16643.79
570.63 25108.36 527.87 46179.64 1173.04 72372.9?'
-------
XI -9
The tabulation below is a reduction of the initial capital and
operation and maintenance costs to a per capita basis:
Item 1970-1980 1980-gQOO 2000-2020
Average Population 3,350,000 5,350,000 8,000,000
Total Initial Capital
Cost/Tijue Period $570,000,000 $528,000,000 $1,173,000,000
Capital Cost/Person/Year $17.0 $4.9 $7.3
0 & M CostAear $25,100,000 $46,200,000 $72,400,000
0 & M Cost/Person/Year $7.5 $8.6 $9.1
Total Cost/Person/Year $24.5 $13.5 $16.4
The above summary, which does include replacement cost, indicates that
the cost of waste-water treatment in the upper Potomac Estuary is about
$13 to $24/per person/per year. This expenditure, which includes the
cost of the activated carbon process, will renovate the water to the
chemical and microbiological qualities meeting drinking water standards,
-------
-------
XII-1
CHAPTER XII
IMPLEMENTATION TO ACHIEVE WATER QUALITY STANDARDS
A. SEASONAL WASTE TREATMENT REQUIREMENTS
1. Ultimate Oxygen Demand
The maximum allowable UOD loadings presented in Chapter X for
the three upper zones of the Potomac Estuary apply under warm
temperature conditions. The effects of nitrogenous oxygen demanding
substances on the dissolved oxygen budget were determined to be quite
significant when water temperatures exceed 15°C. At the present time,
approximately 250,000 Ibs/day of nitrogenous oxygen demand is dis-
charged in wastewater effluents as compared to about 200,000 Ibs/day
of carbonaceous demand. Therefore, during very warm periods when
nitrification rates are high, the nitrogenous component of UOD exerts
a greater effect on the dissolved oxygen resources than the carbona-
ceous material. In order to comply with the allowable UOD loadings
shown previously, it is necessary to reduce drastically both the
nitrogen and carbon levels at the wastewater treatment plants whenever
temperatures exceed 15°C.
During cold weather periods when the ambient water temperature
is less than 15°C, the effects of nitrification on the dissolved
oxygen budget become negligible as reported in Chapter VI. Therefore,
the need for removal or oxidation of ammonia in wastewater discharges
is not required during these periods.
-------
XII-2
To prevent the accumulation of sludge deposits in the vicinity of
sewage treatment outfalls during cooler weather and to maintain high
DO levels under ice cover, a high degree of removal of suspended solids
and carbonaceous oxygen demanding material must be continued. Suspended
solids concentrations in the effluent should not exceed 15 mg/1, and a
minimum of 90 percent of the carbonaceous oxygen demand should be removed
on a year-around basis. Currently, about 72 percent of the UOD load before
wastewater treatment is carbonaceous and the remaining 28 percent nitroge-
nous. Based upon this proportion of carbonaceous and nitrogenous
components in raw sewage, the requirement for carbonaceous removal would
translate to 70-percent UOD removal.
Since the quantity of dilution flows in the upper end of the tidal
embayments is greatly limited, continuous aeration of major wastewater
effluents discharged to these areas will be required.
2. Phosphorus
Of the various nutrients that have been associated with the eutro-
phication problem in the upper and middle reaches of the Potomac Estuary,
phosphorus has been found to be most controllable, not only on a seasonal
basis but on an annual basis as well. As presented in Chapter VII,
approximately 60 to 96 percent of the total phosphorus load to the
Potomac Estuary can be controlled depending upon the existing flow
conditions. An additional reduction in the uncontrollable phosphorus
load from the upper basin occurs in the upper estuary as a result of
-------
XII-3
phosphorus being sorbed upon silt particles accompanying high flows,
which is then removed by sedimentation.
The phosphorus criteria required to prevent nuisance algal blooms
from occurring, as developed in Chapter VII, varied from 0.03 to 0.1 mg/1.
These criteria are approximately an order of magnitude lower than the
corresponding criteria for nitrogen. Because of these stringent criteria,
particularly in the lower zones of the estuary, and the possibility of
recycling previously deposited phosphorus from the bottom muds (this con-
tribution has not been quantitatively defined), year-around phosphorus
removal at the wastewater treatment facilities in the upper estuary will
be necessary.
The mathematical model used to predict the annual distribution of
phosphorus in the critical algal growing areas was verified based upon
extensive phosphorus data collected from February 1969 to September 1970.
The close agreement between observed and predicted phosphorus profiles
during this period for the Potomac Estuary at Indian Head is shown in
Figure XII-1. Also shown in Figure XII-1 are the predicted annual
phosphorus profiles resulting from year-around removal in the upper
estuary, assuming (l) no control and (2) 50-percent control of the
phosphorus load originating in the upper Potomac River Basin. It can
be concluded after an examination of Figure XII-1 that both phosphorus
removal on a year-around basis in the estuary and partial control of
the incoming load will be required if the recommended phosphorus
criteria are to be achieved.
-------
_J ^
== UJ
u. i
0 2
O H-
TT *O
£ u
i O
ui
(0
§
I I I I I I I I I I I I
to^<\iai«o*
evi«vi<\i«si — — — — — bdd
o:
u
a
a
0.0
i£
at
UI
o
UI
Q
o
o
3
«
«
o
UJ
«
-------
XII-5
In order to realize a 50-percent reduction in the current phosphorus
load from the upper Potomac River, the wastewater contribution of 6100
Ibs/day must be reduced to 700 Ibs/day.
3. Nitrogen
As presented earlier in this chapter, the necessity for nitrogen
control in wastewater discharges to enhance the dissolved oxygen in
the Potomac Estuary is restricted to that time of year when water
temperatures exceed 15°C. When evaluating inorganic nitrogen treat-
ment requirements for the prevention of excessive algal blooms,
controllability becomes a significant factor.
Mathematical model studies were used to investigate the effects
of seasonal and continuous nitrogen removal at the wastewater
facilities in the upper Potomac Estuary. Figure XII-2 shows the
predicted annual nitrogen profiles for the Potomac Estuary at Indian
Head, using the verified mathematical model, assuming (l) no nitrogen
removal, (2) nitrogen removal during periods with temperatures above
15°C (April-November), and (3) year-around nitrogen removal. These
profiles show that the recommended nitrogen criteria can be obtained
during the critical growing periods with either seasonal or continuous
nitrogen removal. Though it would be desirable to continuously main-
tain nitrogen concentrations at or below these criteria, the high flows
from the upper basin during the winter and spring months contribute
high nitrogen loadings which increase the nitrogen concentrations above
acceptable levels regardless of treatment practices (Figure XII-2).
-------
LJ
Q-
UJ <
O 5
O z
tr -
o:
<
Q
ul
UJ
U
<
I
O
Q.
r
q
i r
I T I I
(M
i I
^
^
o>
IO
01
r
•* <\J O
6 6 6
FIGURE XII-2
-------
XII-7
The controllable nitrogen from the waste-water treatment sources
in the Washington metropolitan area is currently limited to about
60 percent of the total contribution from all sources. If nitrogen
loadings increase as projected, the controllable amounts will also
increase. Thus it appears that while nitrogen removal for algal
control could be limited to periods when water temperatures in the
estuary exceed 15°C, there may be a need for continuous control by
the year 2000.
-------
XII-8
B. LOCATION OF WASTEWATER DISCHARGES
1. Wastewater Assimilation Versus Salinity Intrusion
Projected wastewater loadings are highest in Zone I, with allow-
able UOD, nitrogen, and phosphorus loadings the lowest of all three
zones. The concentration of wastewater discharges in Zone I will
require much higher removal rates there than will be necessary in
Zones II and III.
When the high degree of wastewater treatment is considered, it
would appear to be advantageous to discharge effluents farther down-
stream in the estuary. The assimilation and transport capacity in
Zone II is about four times that of Zone I. However, when the estuary
is considered as a water supply source, no major effluent discharges
from the Washington metropolitan area should occur below the middle of
Zone II (or below Gunston Cove). This downstream discharge limit is
required to keep the salt wedge from moving upstream and causing
chloride and TDS intrusion at the water intake.
If direct water reuse is eventually adopted, greater use of
the assimilative and transport capacity of the estuary can be realized.
Moreover, the farther down the estuary residual nutrient loads are
discharged, the less favorable conditions will be for blue-green
algae because of higher salinity.
-------
XII-9
2. Wastewater Discharges to ^he Embaymen.ts
All present treated waste effluents except that from Blue Plains
discharge into the tidal portion of various embayments. As presented
in the previous chapter, a high degree of UOD, nitrogen, and phosphorus
removal will be required if the present embayment discharge practice
is continued.
Based upon detailed analyses, including dye studies, of the
Anacostia, Piscataway, and Gunston Cove tidal embayments, it appears
that major discharges into the upper portion of small tidal embayments
should have a maximum concentration of UOD, phosphorus, and nitrogen
of 10, 0.2, and 1.0 mg/1, respectively. Effluents from these facilities
will require renovation to approach ultimate wastewater renovation*
(UWR) levels. Unless UWR is provided, effluents from Alexandria,
Arlington, Piscataway, and the Lower Potomac facilities should be
discharged into the main channel of the Potomac Estuary.
A detailed investigation is essential for each embayment to
determine which option provides the lesser cost, an outfall to the
main channel of the river or UWR. Future studies should also include
consideration of effluent dispersion devices to minimize local effects.
Ultimate wastewater renovation can be defined as renovation of the
wastewater to such a degree that it can be discharged into the
receiving stream in unlimited quantities without restriction of the
designated water resource use due to the lack of needed assimilative
or transport capability of the stream. This implies that the quality
of the effluent from a UWR plant conforms to the stream standards of
the receiving waters.
-------
XII-10
C. FLOW REGULATION FOR WATER SUPPLY AND WATER QUALITY CONTROL
In the original plan for reservoir development in the upper Potomac
River Basin, the U. S. Army Corps of Engineers recommended 16 impound-
ments including the large Seneca Dam [1]. These 16 reservoirs would
regulate the flow of the Potomac at Washington to maintain an approxi-
mate 4600 cfs minimum and would provide the maximum daily water supply
needs of the basin up to the year 2020. When the Seneca Reservoir is
excluded, the remaining 15 impoundments would increase the dependable
low flow to approximately 3600 cfs. This would be an adequate flow to
meet the maximum monthly water supply demand for the Washington
metropolitan area up to the year 2020.
In the original Corps of Engineers' plan, approximately $210
million or 42 percent of the $500 million construction cost was charged
to water quality control. Of this $210 million water quality control
construction cost, approximately $130 million was required to maintain
Potomac Estuary water quality [I].
Davis [50], in his study of the water quality management problems
of the Potomac Estuary, suggested that mechanical reoxygenation and
low-flow augmentation provided the least costly solution to maintain
a specific dissolved oxygen (DO) level. Although the costs for
individual wastewater processes as presented by Davis have increased
substantially, later investigations have indicated that algal control
and nitrification requirements are presently the two most important
considerations in water quality management for the upper estuary.
-------
XII-11
Nevertheless, the Davis studies demonstrate that DO standards could be
maintained with a high degree of wastewater treatment at lower cost
and with greater dependability than by flow regulation alone.
As summarized by Reinhardt [51], a program of water resource
management must be flexible in order to make use of modern technological
developments to meet current wastewater treatment requirements. The
requirements developed in this study reflect not only a need for high
carbonaceous BOD removals but also for nutrient removals to control
algal growth. Low-flow augmentation for nutrient control will not be
effective since the total nutrient loading in pounds per day entering
the estuary is the primary factor to be considered in algal control.
This insensitivity to flow is especially pronounced in the middle
reach where the volume of the estuary is large, advective movement
slight, and algal growing conditions ideal.
The maximum waste loadings and treatment costs presented in
Chapters X and XI will not be greatly affected by flow regulation
considerations, even with construction of either 15 or 16 reservoirs.
It appears that the major advantage of flow regulation is for water
supply purposes and not for water quality management.
-------
-------
ACKNOWLEDGEMENTS
The assistance and cooperation of various governmental and
institutional agencies greatly facilitated the collection and
evaluation of the data presented in this report. While every
agency contacted provided valuable assistance, the cooperation of
the following merit special recognition:
Maryland Department of Water Resources
Maryland State Department of Health
Virginia State Water Control Board
Virginia Department of Conservation and Economic Development
District of Columbia, Department of Environmental Health
District of Columbia, Department of Sanitary Engineering
County of Fairfax, Virginia
City of Alexandria, Virginia
County of Arlington, Virginia
Washington Suburban Sanitary Commission
Andrews Air Force Base
Department of the Army, Fort Belvoir
Washington Aqueduct and North Atlantic Division, U. S. Army
Corps of Engineers
U. S. Geological Survey, Department of the Interior
Metropolitan Washington Council of Governments
Interstate Commission on the Potomac River Basin
-------
The assistance and guidance given by Dr. George P. Fitzgerald,
Research Associate, University of Wisconsin, a special consultant to
the Chesapeake Technical Support Laboratory is sincerely appreciated.
The suggestions of the Potomac Enforcement Conference Technical
Advisory Committee were also helpful in formulating this study.
The authors also wish to acknowledge the assistance of all staff
members of the Chesapeake Technical Support Laboratory, especially
Mary F. Tornanio who helped in preparing this report, and the following:
Johan A. Aalto, Chief, Chesapeake Technical Support Laboratory
Donald W. Lear, Jr., Chief, Ecology Section, CTSL
James W. Marks, Chief, Laboratory Section, CTSL
Orterio Villa, Jr., Chief Chemist, CTSL
Margaret S. Mason, Typist
Margaret B. Munro, Typist
Richard Burkett, Draftsman
Gerard R. Donovan, Jr., Draftsman
Frederick A. Webb, Draftsman
-------
REFERENCES
1. U. S. Army Corps of Engineers, "Potomac River Basin Report,"
Vol. 1 - Vol. VIII, North Atlantic Division, Baltimore District,
February 1963.
2. FrisMe, C. M. and D. E. Ritchie, "Sport Fishing Survey of the Lower
Potomac Estuary, 1959-1961," Chesapeake Science. Vol. 4, No. 4,
December 1963.
3. U. S. Department of the Interior, "The Potomac - A Model Estuary,"
Bureau of Outdoor Recreation, July 1970.
4. U. S. Department of the Interior, "Maryland and Virginia Landings
Annual Summary," Bureau of Commercial Fisheries, Fish and Wildlife
Service, 1969.
5. Jaworski, N. A., "Nutrients in the Upper Potomac River Basin," CTSL,
MAR, FWPCA, U. S. Department of the Interior, August 1969.
6. Private communication with Roy Weston Consulting Engineering Firm
currently investigating the storm and combined sewer contribution
under contract to FJVQA..
7. U.S. Public Health Service, "Investigation of the Pollution and
Sanitary Conditions of the Potomac Watershed," Hygienic Laboratory
Bulletin No. 104, Treasury Department, February 1915.
8. Aalto, J. A., N. A. Jaworski, and Donald W. Lear, Jr., "Current
Water Quality Conditions and Investigations in the Upper Potomac
River Tidal System," CTSL, MAR, FWQA, U. S. Department of the Interior,
Technical Report No. 41, May 1970.
9. Livemore, D. F. and W. E. Wanderlich, "Mechanical Removal of Organic
Production from Waterways," Eutrophication: Causes, Consequences.
Correctives. National Academy of Sciences, 1969.
10. Bartsch, A. F., "Bottom and Plankton Conditions in the Potomac River
in the Washington Metropolitan Area," Appendix A, A report on water
pollution in the Washington metropolitan area, Interstate Commission
on the Potomac River Basin, 1954.
11. Stotts, V. D. and J. R. Longwell, "Potomac River Biological Investi-
gation 1959," Supplement to technical appendix to Part VII of the
report on the Potomac River Basin studies, U. S. Department of Health,
Education and Welfare, 1962.
-------
12. Elser, H. J., "Status of Aquatic Week Problems in Tidewater Maryland,"
Spring 1965, Maryland Department of Chesapeake Bay Affairs, 8 pp mimeo,
1965.
13. Bayley, S., H. Rabin, and C,. H. Southwick, "Recent Decline in the
Distribution and Abundance of Eurasian Watermilfoil in Chesapeake Bay,"
Chesapeake Science, Vol. 9, No. 3, 1968.
14. Jaworski, N. A., D. W, Lear, Jr., and J. A. Aalto, "A Technical Assessment
of Current Water Quality Conditions and Factors Affecting Water Quality
in the Upper Potomac Estuary," CTSL, FWPCA, MAR, U. S. Department of the
Interior, March 1969.
15. Mulligan, H. T., "Effects of Nutrient Enrichment on Aquatic Weeds and
Algae," The Relationship of Agriculture to Soil and Water Pollution
Conference Proceedings, Cornell University, January 1970.
16. Edmondson, W. T., "The Response of Lake Washington to Large Changes in
its Nutrient Income," International Botanical Congress. 1969.
17. Hasler, A. D., "Culture Eutrophication is Reversible," Bioscience.
Vol. 19, No. 5, May 1969.
18. Torpey, W. N., "Efforts of Reducing the Pollution of Thames Estuary,"
Water and Sewage Works. July 1968.
19. Sawyer, C. N., "1969 Occoquan Reservoir Study," Metcalf and Eddy, Inc.
for Commonwealth of Virginia Water Control Board, April 1970.
20. Mackenthun, K. M., "Nitrogen and Phosphorus in Water," U. S. Public
Health Service, Department of Health, Education and Welfare, 1965.
21. Federal Water Pollution Control Administration, "Water Quality Criteria,"
Report of the National Technical Advisory Committee to the Secretary of
the Interior, April 1, 1968.
22, Pritchard, Donald W., "Dispersion and Flushing of Pollutants in Estuaries,"
Journal of the Hydraulics Division. ASCE. Vol. 95, No. HY1, January 1969.
23. Brehmer, M0 L. and Samuel 0. Haltiwanger, "A Biological and Chemical Study
of the Tidal James River," Virginia Institute of Marine Science,
Gloucester Point, Virginia, November 15, 1966.
24. Kuentzel, L. E0, "Bacteria, COg and Algal Blooms," Journal Water Pollution
Control Federation. 21, 1737-1749, 1969.
25„ Lange, W., "Effect of Carbohydrates on Symbolic Growth of Planktonic Blue-
Green Algae with Bacteria," Nature 215, 1277-1278, 1967.
-------
26. Kerr, Pat C., Dorris F. Paris, and D. L. Bruckway, "The Interrelation
of Carbon and Phosphorus in Regulating Heterotrophic and Autotrophic
Populations in Aquatic Ecosystems," Southeast Water Laboratory, FtfQA,
U. S. Department of the Interior, 1970.
27. Carpenter, J. H., D. W. Pritchard, and R. C. Whaley, "Observation of
Eutrophication and Nutrient Cycles in Some Coastal Plain Estuaries,"
Eutrophication: Causest Consequences, and Correctives. National
Academy of Sciences, 1969.
28. Fitzgerald, George P., "Detection of Limiting on Surplus Nitrogen in
Algae and Aquatic Weeds," Journal of Phycology. Vol. 2, No. 1, 1966.
29. Fitzgerald, George P. and Thomas C. Nelson, "Extractive and Enzymatic
Analyses for Limiting on Surplus Phosphorus in Algae," Journal of
Phycology. Vol. 2, No. 1, 1966.
30. Thomann, R. V., Donald J. O'Connor, and Dominic M. DiTorro, "Modeling
of the Nitrogen and Algal Cycles in Estuaries," presented at the
Fifth International Water Pollution Research Conference, San Francisco,
California, July 1970.
31. Hutchinson, G. E., A Treatise on Limnology. Vol. 1, John Wiley & Sons,
Inc., New York, 1957.
32. Riley, J. P. and Skirrow, G., Chemical Oceanography. Vol. 1, Academic
Press, London and New York, 1965.
33. Lear, D. W., Jr. and N. A. Jaworski, "Sanitary Bacteriology of the
Upper Potomac Estuary," CTSL, MAR, FWPCA, U. S. Department of the
Interior, Technical Report No. 6, March 1969.
34. Jaworski, J. A., "Water Quality and Wastewater Loadings, Upper Potomac
Estuary, Spring 1969," CTSL, MAR, FWPCA, U. S. Department of the
Interior, Technical Report No. 27, November 1969.
35. Berg, Gerald, "An Integrated Approach to the Problem of Viruses in
Water," Proceedings of the National Specialty Conference of Disinfection,
University of Massachusetts, July 1970.
36. Committee on Environmental Quality Management," Engineering Evaluation
of Virus Hazard in Water," Journal of Sanitary Engineering Division.
ASCE. Vol. 96, No. SA1, February 1970.
37. Toenniessen, G. H. and J. Donald Johnson, "Heat Schocked Bacillus
Subtilis Spores as an Indication of Virus Disinfection," Journal of
the American Water Works Association. Vol 62, No. 9, September 1970.
38. Committee Report, "Viruses In Water," Journal of the American Water
Works Association. Vol. 6l, No. 10, October 1969.
-------
39. Metropolitan Washington Council of Governments, "Population Estimates
and Forecasts, Selected Jurisdictions, Washington Metropolitan Area,"
1969.
40. Chesapeake Technical Support Laboratory, "The Patuxent River, Water
Quality Management Technical Evaluation," MAE, FWPCA, U. S. Department
of the Interior, September 1969.
41. Feigner, K. and Howard S. Harris, Documentation Report, FWQA. Dynamic
Estuary Model, FWQA, U. S. Department of the Interior, July 1970.
42. Jaworski, N. A. and James H. Johnson, Jr., "Potomac-Piscataway Dye
Releases and Wastewater Assimilation Studies," CTSL, MAR, FWQA.,
U. S. Department of the Interior, December 1969.
43. Hetling, Leo J., "Simulation of Chloride Concentration in the Potomac
Estuary," CB-nSRBP Technical Paper No. 12, MAR, FWPCA, U. S. Department
of the Interior, March 1968.
44. U. S. Public Health Service, "Drinking Water Standards," Revised 1962,
U. S. Department of Health, Education and Welfare, 1962.
4^. Hydroscience, Inc., "The Feasibility of the Potomac Estuary as a
Supplemental Water Supply Source," prepared for N.E.W.S. Water Supply
Study, North Atlantic Division, U. S. Army Corps of Engineers, March
1970.
46. Private communication with D. Fred Bishop, FWQA, Blue Plains Advanced
Wastewater Treatment Pilot Plant, Washington, D. C., March 1970.
47. Bechtel Corporation, "Preliminary Cost Estimates for a Blue Plains
Advanced Waste Treatment Plant," prepared for FWQA, U. S. Department
of the Interior, July 1970.
48. Smith, Robert and Walter F. McMichael, "Cost and Performance Estimates
for Tertiary Wastewater Treatment Processes," Taft Center, FWQA, U. S.
Department of the Interior, Cincinnati, Ohio, June 1969.
49. Harleman, D. R. F., "One-Dimensional Mathematical Models in State of
the Art of Estuary Models," Contract to FWQA by Tracer, Inc. (In
preparation).
50. Davis, Robert K., "The Range of Choice in Water Management, A Study of
Dissolved Oxygen in the Potomac Estuary," Johns Hopkins Press, Baltimore,
Maryland, 1968.
51. Reinhardt, H. R., "The Potomac River Basin, A Case Study of Environmental
Problems Impeding Effective Water Resource Management," To be presented
at the Economic Commission for Europe, Czechoslovakia, May 2-18, 1971.
-------
52. Jaworski, N. A., Donald V/. Lear, Jr., Orterio Villa, Jr., "Nutrient
Management in the Potomac Estuary," Presented at the American Society
of Limnology Symposium on Nutrients and Eutrophication, Michigan
State University, East Lansing, Michigan, February 1971 (CTSL, MAR,
WQO, Environmental Protection Agency, Technical Report No. 45).
53. University of Wisconsin, Private Communication with George P. Fitzgerald,
January 19, 1971.
54. Thomann, Rooert V., "Mathematical Model for Dissolved Oxygen, Journal of
the Sanitary Engineering Division. ASCE. Vol. 89, No. SA5, October 1963.
-------
-------
|