WATER RESOURCE-WATER SUPPLY STUDY
OF THE
POTOMA.C ESTUARY
Technical Report 35
Environmental Protection Agency
Water Quality Office
April 1971
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Regional Center for Environmental Information
US EPA Region m
1650 Arch St.
Philadelphia, PA 19103
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Chesapeake Technical Support Laboratory
•Middle Atlantic Region
Water Quality Office
Environmental Protection Agency
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. A WATER RESOURCE-WATER SUPPLY STUDY
OF THE
• POTOMAC ESTUARY
Technical Report 35
• April 1971
Norbert A. Jaworski
_ Leo J. Clark
• Kenneth D. Feigner*
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*EPA, WQO, Washington, D. C.
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\i S. EPA Ragum HI
Ile.ovjnal Center for Environmental
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IidbO Arch Street (3PM52)
Philadelphia, PA 19108
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TABLE OF CONTENTS
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LIST OF TABLES ..............
LIST OF FIGURES ............. •
Chapter •
I INTRODUCTION 1-1
II SUMMARY AND CONCLUSIONS II - 1 I
III STUDY ARM DESCRIPTION ....... Ill - 1
A, Potomac River Tidal System ..... Ill - 1 I
Bo Hydrographie Analysis ...... Ill - 5 •
C, Proposed Reservoir Development . . . Ill - 8
D0 Water Resource Uses ....... Ill -12 I
1. Water Supply Use . Ill -12
a. Municipal Ill -12 I
b. Industrial ....... Ill -13 •
2. Recreation and Boating Ill -15
3« Commercial Fisheries ..... Ill -17 I
IV WASTEWATER LOADINGS AND RUNOFF CONTRIBUTIONS IV - 1
A. Wastewater Loadings and Trends ... IV - 1 I
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C0 Suburban and Urban Runoff ..... IV -12
D. Summary and Comparison of Nutrients, •
BOD, and Carbon Contributions ... IV -14
B. Potomac River Water Quality above
Great Falls ......... IV - 7
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TABLE OF CONTENTS (Continued)
I Chapter
• V WATER QUALITY CONDITIONS AND TRENDS . . . . V - 1
A. Bacterial Densities ....... V - 2
• B. Dissolved Oxygen V - 6
C. Silt and Debris . V -13
I D. Nutrients and Algal Growths ..... V -21
II. 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
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4. Algal Toxicity V -49
I VI DISSOLVED OXYGEN ENHANCEMENT ...... VI - 1
A. Study Approach ......... VI - 1
• B. DO Criteria .......... VI - 8
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3. Unfavorable Physical and Aesthetic
Characteristics of Algal Blooms . , V -48
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Chapter
VII
VIII
TABLE OF CONTENTS (Continued)
ALGAL GROWTH RESPONSE TO NUTRIENT CONTROL
A. Eutrophication Control Objectives .
Page
VII - 1
VII - 2
B. Nutrient Requirements to Prevent
Excessive Standing Crops of Blue-green
Algae VII - 5
!„ Algal Composition Analysis . VII - 8
20 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
60 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
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TABLE OF CONTENTS (Continued)
• Chapter
I 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
I 2. Carbon Chloroform Extraction . . . VIII -10
• 3o Chlorides and Total Dissolved Solids VIII -12
4* Pesticides and Herbicides . VIII -15
• IX POPULATION AND WASTEWATER PROJECTIONS . . . IX - 1
A. Population Projections ...... IX - 1
I B. Water Supply Requirements . IX - 6
• C. Wastewater Loadings ....... IX - 9
X WATER QUALITY SIMULATIONS ....... X - 1
I A. Water Quality Simulation Models ... X - 1
B. Alternative Wastewater Treatment Systems X - 5
| C. Wastewater Management Zones and Stream-
flow Criteria .00.0.0. X -16
• D. Ultimate Oxygen Demand . . . . . . X -20
E. Phosphorus .„.,...„.. X -2.6
• F. Nitrogen ........... X -33
IG. Chloride and Total Dissolved Solids
Simulations ......... X -37
_ 1. Estuary Water Supply Withdrawal . . X -37
* 20 Direct Reuse of Treated Wastewater X -47
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TABLE OF CONTENTS (Continued)
Cbaptey Page
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
A0 Seasonal Waste Treatment XII - 1
10 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
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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 Monoeacy River V -14
V - 2 Sediment Data, Northwest Branch Anacostia
River near Colesville, Maryland .... V -15
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Number
V - 3
V - 4
VII - 1
VII - 2
VII - 3
VII - 4
VIII - 1
IX - 1
IX - 2
IX - 3
IX - 4
IX - 5
IX - 6
IX - 7
LIST OF TABLES
Title
Oxygen Production and Respiration Rate
Survey, Upper and Middle Potomac Estuary,
1970 .............
Oxygen Product ion -Respiration Balances .
Subjective Analysis of Algal Control
Requirements ..........
Algal Composition Study, Upper Potomac
Estuary, 1970 ...........
Nitrogen Bioassay Summary, Potomac Estuary,
1970
Summary Data, Upper Rappahannock Estuary,
1970 „.,......,...
Heavy Metal Analyses of Sediment Samples,
August 18 - 20, 1970, Potomac Estuary . .
Data Summary Facility Service Areas .
Water Supply Requirements, Washington
Metropolitan Area .
Various Water Supply Demands, Washington
Metropolitan Area .........
Present Wastewater Loadings, Washington
Metropolitan Area .........
1980 \Vastewater Loadings, Washington
Metropolitan Area .........
2000 Wastewater Loadings, Washington
Metropolitan Area .........
2020 Wsstenvater Loadings, Washington
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P§ge
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TT
V -45
VII - 4
* ™
VII - 9
VII -16
VII -23
VIII - 9
IX - 2
IX - 7
IX - 8
IX -10
IX -11
IX -12
IX -13
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LIST OF TABLES
Number Title Page
X - 1 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
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LIST OF FIGURES
Number Title Page |
III - 1 Potomac River Tidal System ...... Ill - 3 m
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 ... 17-5
IV - 2 Nutrient Concentrations, Potomac River at Jj
Great Falls ........... IV - 8
V - 1 Total Coliform 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 Oxygen Concentration, Potomac 9
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 I
V - 9 Chemical Oxygen Demand of Sediments, Potomac
Estuary ............ V -20 •
V -10 Inorganic Phosphate Concentration as PO^,
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- I
1970 ............. V -26
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LIST OF FIGURES
Number Title Page
V -13 Phosphorus Concentration, Potomac Estuary,
Iv -a.,5 rnospnorus uoncenxration, rotomac Jisxuarj
September 28 - October 27, 1965 . . .
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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 Wastewater Nutrient Enrichment Trends and
Ecological Effects, Upper Potomac Tidal
River System . V -36
I V -21 Chlorophyll a, Potomac Estuary, Upper Reach,
1965-1966, 1969-1970 V -39
• V -22 Chlorophyll §_, Potomac Estuary, Middle and
Lower Reach, 1965-1966, 1969-1970 ... V -40
IV -23 DO Concentrations, Potomac Estuary,
August 19 - 22, 1968 ........ V -47
I VI - 1 A Schematic Diagram of Dissolved Oxygen
Interrelationships for the Three Major
Biological Systems . VI - 2
I VI - 2 DO Concentrations, Potomac Estuary,
September 22, 1968 VI - 4
VI - 3 DO Concentrations, Potomac Estuary,
August 12 - 17, 1969 ........ VI - 5
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Number.
VII - 1
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LEST OF FIGURES
Title
Nutrient -Chlorophyll Profiles, Potomac
Estuary, March-August 1965 .„„...
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.
Waste-water Service Areas, Washington
Metropolitan Area ....
Population Projections, Washington
Metropolitan Area
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
Estuary, Alternative III .
Wastewater Treatment Systems, Upper Potomac
Estuary, Alternative IV
Wastewater Treatment Systems, Upper Potomac
Estuary. Alternative V
Page
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VIII
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LIST OF FIGURES
Number Title Page
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
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1-1
CHARTER 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
I 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
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pollutants under various flow conditions, (6) an investigation of
alternative waste treatment plans, and (7) an estimate of the cost I
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 I
metropolitan area,,
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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
I using the estuary as a municipal water supply source. The latter
study was conducted in cooperation with the U. S. Army Corps of
g 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.
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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 63? miles •
of shoreline has barely been developed. •
5» In 1969, approximately 17-million pounds of fish, crabs, clams,
and oysters were taken from the Potomac tidal system with a dockside Jj
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 3ewer overflows, with a total flow of 325 mgd, contribute
450,000, 24,000, and 60,,000 Ibs/day of ultimate oxygen demand (UOD*), m
phosphorus, and nitrogen respectively to the waters of the upper
Potomac Estuary,
?<, TJnder low-flow conditions, the ultimate oxygen demand, phos- I
phorus, an.d nitrogen loadings from the upper basin and local runoff
were estimated as 66,000, 1,000, and 2,300 Ibs/day, respectively. I
8. The major sources of nutrients and ultimate oxygen demand in •
the Potomac Estuary are the local wastewater discharges. Under low-
flow conditions approximately 88, 90, and 96 percent of the ultimate I
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.
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At median freshwater inflows, approximately 62, 60, and 82 percent
respectively are from these wastewater discharges.
_ 9o Since the first sanitary surveys in 1913, the water quality of
* the upper Potomac Estuary has generally deteriorated. This is attributable
I 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-
tt tinuous wastewater effluent chlorination. At present, the largest
sources of bacterial pollution in the upper estuary are from sanitary
I 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„
• Ho 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
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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 I
including carbonaceous, nitrogenous, benthic, and algal demands indicate
that the nitrogenous demand is the greatest cause of dissolved oxygen I
deficit in the critical reach near the wastewater discharges and that A
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, approxijnately 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. I
15 o Since 1913, the wastewater discharge quantities have increased
over sevenfold from 42 to 325 mgd, the phosphorus load increased 22-fold f
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/day <, When ecological plant successions from a balanced toward I
an unbalanced system (primarily one dominated by blue-green algae) are
related to wastewater loading trends, it can be concluded that the j
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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
I 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
ft growth within the Tidal Basin. The effects of the massive blue-green
algal blooms in the middle and upper portions of the Potomac Estuary
I are (1) large increases of over 4.90,000 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 a
I 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 003 and 0*5 mg/1 as N and the upper limit of total phosphorus at
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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 j|
concentration apply to the embayments and middle portion of the estuary m
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.
19o Significant accumulations of various heavy metals in sediments I
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. tt
20„ Population and water supply needs have been projected as
follows: •
Water Supply Needs •
Xearr Population Yearly a,vgt Maximum Month MaximumDaily •
(mgd) (mgd) (mgd)
1969 2,700,000 370 470 660 |
1980 4,000,000 570 720 1000 -
2000 6,700,000 1010 1310 1820 •
2020 9,300,000 1570 2040 2820 I
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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*
1980 2000 2020
Recurrence Minimum Monthly For a 720 For a 1310 For a 2040
Interval Fresh Inflow mgd Need mgd Need mgd Need
(years) (mgd) (mgd) (mgd) (mgd)
5 1300 none 210 940
20 1170 none 340 1070
50 910 none 600 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 Floy BOD Nitrogen Phosphorus
(mgd) (Ibs/day) (ibs/day) (Ibs/day)
1969 325 483,500 63,500 27,300
1980 475 823,500 95,600 43,100
2000 860 1,463,500 155,700 70,300
2020 1,340 2,195,000 215,600 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
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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:
(l) Between the years 1980 and 2000, the Potomac (Dalles) 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. I
(4) Large wastewater volumes are projected in the Occoquan and
Pohick watersheds in the Virginia counties downstream from Washington, I
indicating a need for long-range water resources planning in this area. |
25o Three basic alternative wastewater treatment systems were
investigated to determine the effects of the discharge locations on j
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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 Mary land -B0 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
• invest igated., 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 „
•j 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
8 from the Chesapeake Bay is a function of (a) duration and magnitude
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11-10
of any selected flow, (b) location of the wastewater treatment facility
discharges, and (c) consumptive losses in the water distribution system, I
(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 I
(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 M
be used for a water supply source was determined by using a total
dissolved solids concentration in the blended water of 500 mg/1 maxi- I
mum as a criterion since this parameter was determined to be more
critical than chlorides. TDS water use increments* of 40 and 24-0 mg/1 |
I
* Water use increment is the amount that the concentration of TDS or
any other parameter is increased from the point of water intake to I
the point of discharge as a result of water supply treatment, J
municipal use, and wastewater treatment.
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1
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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
(5) For
(as observed
( cfs ) 40 mg/1 240 mg/1 40 mg/1 240 mg/1
500 >l66 >166 >166 >166
1250 90 35 140 45
2000 45 15 95 20
the year 2020 and using the upper position of the wedge
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
water supply
is given below as a function of freshwater flow before
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/1 240 mg/1 AQjflg^L 240 roe/1
(days (days) (days) (days)
45 15 18 18
>166 42 >l66 41
>166 >l66 >l66 >l66
(6) Since the projected water supply needs for the year 2020
1
1
1
cannot be met
completely either by withdrawals from the estuary or
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11-12
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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, I
27. Direct reuse of the renovated wastewater is another solution •
to meet water supply needs. This alternative has numerotis advantages
over withdrawals from the estuary because; I
(l) Any need for consideration of salt intrusion from the
Chesapeake Bay for water supply purposes is eliminated, I
(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 I
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.
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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
Zpne 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.
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11-14
30. For the three freshwater inflows (before water supply with-
drawal) investigated, i.e., 1800, 1100, and 4.00 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 6C0 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. I
31 o Allowable UOD loadings for the Piscataway and Gunston Cove
I
embayments have been developed for the projected wastewater volumes
and conditions specified in Number 29 and are given belows
MAXIMUM UOD LOADINGS FOR PISGATAWAY CREEK AND GUNSTON COVE
Piscataway Creek Gunston Cove I
Wastewater
Flow
(mgd)
24
49
79
Maximum
UOD Load
(Ibs/day)
10,000
11,000
12,000
Wastewater
Flow
(mgd)
50
103
170
Maximum
UOD Load
( Ibs/day
7,000
11,000
16,000
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32„ Since nitrification (the conversion of ammonia nitrogen to
nitrate nitrogen) has little effect on the oxygen resources of the J
estuary at temperatures below 15°C, nitrogen removal from the waste- •
water effluents to meet DO standards will be required whenever the
water temperature is above 15°C, usually during the months of April I
through October,
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11-15
In order to prevent formation of sludge deposits, to eliminate
MAXIMUM PHOSPHORUS LOADINGS FOR POTOMAC ESTUARY
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-
mm 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:
I
Zone Allowable Phosphorus
M (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
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34. Allowable phosphorus loadings for the Piscataway and Gunston
Cove embayments for phosphorus concentration in the receiving waters of
0.03 nig/1 as P are shown below as a function of wastewater flow:
PHOSPHORUS LOADINGS TO HVEAYMEMTS
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
Phosphorus Load
(Ibs/day)
35
60
140
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35o To prevent excessive algal growth and to enhance the water
quality in the upper and middle reaches of the estuary, it appears that p
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, I
the current phosphorus loading from all wastewater discharges in the
upper Potomac River Basin must be decreased from 6100 to 700 Ibs/day. 1
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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
I-a
I-b
I-c
II
III
(Upstream from Hains Point)
(Anacostia River)
(Hains Point to Broad Creek)
(Broad Creek to Indian Head)
(Indian Head to Smith Point)
Allowable Total Nitrogen
(Ibs/day)
1000
300
3400
5800
9000
37. Allowable total nitrogen loadings for the Piscataway and
Gunston Cove embayments based upon maintaining 0.3 rog/1 of inorganic
nitrogen under warm temperature conditions and for varying wastewater
flows follow:
NITROGEN LOADINGS TO EMBAYMENTS
Piscataway Creek
Gunston Cove
Wastewater
Flow
(mgd)
24
49
79
Maximum
Nitrogen Load
(Ibs/day)
120
170
270
Wastewater
Flow
(mgd)
50
103
170
Maximum
Nitrogen Load
(Ibs/day)
130
270
460
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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 I
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 M
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, tm
approaching ultimate wastewater renovation„ Unless this high degree of
removal is provided, effluents from Alexandria, Arlington, Piscataway, I
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 I
total average annual cost of $64,8 million. The unit treatment pro-
cesses assumed include activated sludge, biological nitrifieation-
denitrification, lime clarification, filtration, effluent aeration,
and chlorination.
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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
I Initial Capital
* Cost/PersonAear $17.0 $ 4.90 $ 7.30
•Operation and Maintenance
Cost/PersonAear $ 7.50 $ 8.60 $ 9.10
I Total Cost/PersonAear $24.50 $13.50 $16.40
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III-l
CHAPTER III
STUDY AREA DESCRIPTION
A0 POTOMAC RIVER TIDAL SYSTEM
The Potomac River Sasin^, with a drainage area of 14,670 square
M miles, is the second largest watershed in the Middle Atlantic States.
From its headwaters on the eastern slope of the Appalachian Mountains,
I 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
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III-2
remaining area of the tidal portion, which drains 3,216 square miles,
is sparsely populated. I
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: m
Reach, Description River Mile Volume
cu.ft.xlO9
Upper From Chain Bridge to 114.-4 to 73.8 9,3 •
Indian Head
Middle From Indian Head to 73.8 to 47.0 36.2 |
Rte. 301 Bridge
Lower From Rte. 301 Bridge 47.0 to 00.0 175.4 I
to Chesapeake Bay
The upper reach, although tidal, contains fresh water. The I
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. g
To facilitate determination of water quality control requirements,
the upper and middle reaches of the estuary have been segmented into I
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 I
May 8, 1969.
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<\
CHAIN BRIDGE
N
CHESAPEAKE
BAY
POTOMAC RIVER TIDAL SYSTEM
FIGURE III -1
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• E. HHHOGRAPHIC ANALYSIS
•j 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 cfa
• 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
I
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25 Percent
Quartile
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
Quartile
17,200
24,600
24,400
26,900
17,900
10,300
6,400
7,400
6,800
6,400
9,600
13,100
t,anuary
February
March
• April
May
8 June
• July
August
• September
October
| November
• December
In water resource management, especially for the water quality
I aspects, low-flow frequencies are used to determine assimilation and
transport capacities of receiving waters„ The low-flow frequency
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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- fl
consecutive-days-of-low-flow with a recurrence interval of once-in-10-
years. For the Potomac at Washington, this is 95-4 cfs (before the |
diversions for water supply). See Table III-2 for complete analyses _
of low-flow frequency information. *
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Table III-2
m MAGNITUDE AND FREQUENCY OF LOW FLOWS
• POTOMA.C RIVER NEAR WASHINGTON, D. C.
1930-1966 WATER YEARS
(Before Water Supply Diversions)
1
Period
1
1
^ (Consecutive days)
1
14
1
_ 60
90
• 120
183
1
Discharge for indicated recurrence interval
1.02 2.0 5,0 10.0
years years years years
(cfs)
3,440 1,620 1,150 954
3,350 1,700 1,210 1,000
4,470 1,890 1,340 1,130
6,620 2,300 1,540 1,260
8,630 2,660 1,740 1,420
8,770 3,110 2,060 1,670
11,200 4,280 2,800 2,220
I____
1
1
1
1
20,0 50,0
years years
814 6^0
862 730
976 8/.0
1,070 900
1,210 1,000
1,400 1,150
1,830 1,480
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III-8
C. PROPOSED RESERVOIR DEVELOPMENT I
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 I
(l) water supply, (2) water quality, (3) flood control, and
(4) recreational needs. |
The plan recommended a l6-reservoir system to provide for orderly M
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 g
were:
System
I Bloomington 8
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 I
the seven impoundments based on the 1967 cost index would be $204.4
million. See Table III-3 for individual reservoir cost. |
Using data from 1929 to 1968 and a river-flow mathematical model, _
the U. S. Army Corps of Engineers simulated the effects of the three *
reservoir systems on river flows over Great Falls. The low-flow j
frequency analysis for the three systems is given in Table III-4.
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FIGURE III-2
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Table III-3
RESERVOIR PROJECTS, STORAGE, AND COST*
1
1
1
Potomac River Basin
Project
Bloomington
Staunton
Sixes Bridge
Town Creek
North Mountain
Sideling Hill
Little Cacapon
Total
Total Storage
(acre-feet)
137,500
143,000
103,000
96,800
195,000
75,000
82,500
832,800
* Based on data supplied by the
District, September 1970
Total Initial
Cast ($)
90,400,000
22,870,000
20,510,000
13,190,000
24,450,000
13,600,000
19,350,000
Allocated Cost
Downstream Preserve Stream
Water Supply ($) Environment
30,000,000 36,800,000
756,000 3,473,000
1,112,000 5,005,000
2,039,000 4,136,000
3,953,000 7,312,000
2,753,000 5,557,000
3,872,000 7,857,000
$204,370,000 $44,485,000 $70,140,000
U. S. Army Corps
of Engineers, Baltimore
1
1
1
1
1
1
1
1
1
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1
1
1
1
1
•
1
1
1
w
1
1
1
1
1
1
1
1
LOT-FLOW
Table III -4
FREQUENCY ANALYSES FOR VARIOUS RESERVOIR
Potomac River near Washington
Reservoir System
Number I
Period Discharge in cfs for Indicated Recurrence
(days)
30
60
90
120
30
60
90
120
30
60
90
120
SISTEMS
Interval
(5 years) (10 years) ($0 years)
1600 1200
1900 1600
2100 1700
2600 2000
Number II
1900 1700
2000 1900
2200 2100
2600 2200
Number III
2000 1800
2150 2000
2300 2200
2800 2300
1000
1050
1100
1500
1200
1400
1500
1600
1400
1500
1600
1700
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111-12
D. WATER RESOURCE USES
Source Withdrawal
and used had the lows flows continued.
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1. Water Supply Use I
a. Municipal
The municipal water supply needs of the Washington metropolitan |
area are obtained from five major sources. The largest source is the M
Potomac River above Washington, D. C. For 1969-1970, water withdrawal
data for the five sources are presented below: I
Potomac River above Great Ealls 265
Patuxent River near Laurel 46 •
Goose Creek 6
Occoquan Creek 42 m
Wells and other minor sources 11 •
Total 370
Currently, there is no municipal water withdrawn from the freshwater I
portion of the Potomac Estuary. However, during the drought in the •
summer of 1969, an emergency estuary intake would have been constructed
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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,)
PEPCO Generating Station
(Alexandria, Va.)
VEPCOy Possum Point
(Quantico, Va.)
PEPCO, Sandy Point
PEPCO, Morgantown
(Charles Co., Md.)
Water
Usage
(mgd)
568
570
40
450
400
720
Receiving Water
Anacostia River
Anacostia River
Boundary Channel of
Potomac Estuary
Potomac Estuary
Potomac Estuary
Potomac Estuary
Potomac Estuary
Remarks
Also Uses
Cooling Towers'
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
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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.
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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
I numbers of tourists visit the numerous monuments, museums, public
buildings, and parks, to the remote park at Point Lookout near the
g Chesapeake Bay, the Potomac's amenities are widely used. These include
_ freshwater and tidal sport fishing, boating, hunting, swimming, camping,
* and picnicking.
I 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 1961 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]:
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III-16
I
1. Of the 63? 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 I
jellyfish than to a lack of suitable locations.
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III -17
3 . Commercial Fisheries
The Potomac River tidal system supports a substantial commercial
M fishery. There are approximately 160 species in the Potomac Estuary
ecosystem of which the anadromous* and the semi -ana dromous** speeies
I such as striped bass, shad, white and yellow perch, winter flounder,
and herring are the most significant economically,
g 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
I 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
I they been harvested commercially and the resource far exceeds the demand,,
The lower Potomac is a favorable habitat for the growth of blue crabs,
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 -ana dromous - fish which spend most of their lives in a brackish
• water and ascend freshwater streams to spawn
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111-18
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 I
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. I
Numerous fish kills have occurred in the Potomac Estuary in recent •
years, While 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. I
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1
1
1
•i
1
Species
Fish
• Crabs -
Hard
• Soft & Peeler
• Clam
Oyster
| Total
1
1
1
1
1
1
1
1
Table III-5
MARYLAND AND VIRGINIA LANDING OF FISH AND SHELLFISH
POTOMAC RIVER AND TRIBUTARIES
1969
Maryland Virginia Total
Pounds Value Pounds Value Pounds Value
1,250,668 $ 183,563 7,780,549 $ 347,974 9,031,217 $ 531,537
628,702 75,686 1,249,774 142,460 1,878,476 218,146
20,348 8,260 28,000 11,659 48,348 19,919
1,090,140 389,292 322,092 114,331 1,412,232 503,623
2,923,275 1,771,812 2,457,770 1,642,866 5,381,045 3,4H,678
5,913,133 $2,428,613 11,838,185 $2,259,290 17,751,318 $4,687,903
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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
B 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-l). Of the 325 mgd, 41.5, 23,1, and 35,4 percent
Gome from Maryland, Virginia, and the District of Columbia respectively,
I 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
m Ibs/day in 1913 to about 297,000 Ibs/day in the late 1950'se 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
jm 254,000 Ibs/day, which exceeds the current carbonaceous loading of
204,000 Ibs/day,
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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 (med)
0.109
0.221
0.786
0.214
0.111
0.700
0.410
1.000
0.300
1.400
Receiving
Water
Bull Run
Bull Run
Bull Run
Bull Run
Flatlick Ron
Bull Run
Giles Run
Marumsco Creek
Farm Creek
Potomac Estuary
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0.350
Upper Machodoc Creek
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400,000-
300,000-
o
•a
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
T
1940
YEAR
I
1950
I960
1970
FIGURE IV-I
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IV-6
I
Compared to the upper reach, which has a population served of
approximately 2.51 million, the middle and lower reaches serve a I
population of approximately 50,000. Most of the discharges in this
area are into tributary or embayment waters. •
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- IV-7
B. POTOMA.C RIVER WATER QUALITY ABOVE GREAT FALIS
I 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:
I
Parameter Cone ent rat ion
(fflg/1)
BCD5 2.60
TKN as N 0.61
• NC'2 + NOj as N 1,00
T, Phosphorus as P 0.13
• The observed data, as shown in Figure TV-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
8 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:
I Parameter Contribution
(Ibs/day)
_ T. Phosphorus as P 4,580
| Inorganic Phosphorus as P 2,650
TKN as N 22,410
I NH3 as N 4,590
N02 + N03 as N 36,700
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FIGURE IV-2
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IV-10
I
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 •
BODj 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 I
loadings into the Potomac from the upper basin are as follows:
Parameter Median Loading |
(Ibs/day)
BOD5 89,390 I
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. •
I
* Frequency percent is percentage of time in which a given parameter •
is equalled or exceeded I
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IV-12
C. SUBURBAN AND UEBAN RUNOFF I
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: •
Parajneter Lpadings
(Ibs/day)
BODj 12,500 •
TKN as N 2,560 •
NOa + N03 1,510
T, Phosphorus as P 850 I
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. 8
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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. m
95% 50% *
Low-Flow Condition Median-Flow Condition
Potomac R. Flow = 1200 cfs Potomac R. Flow = 6470 cfs •
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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 I
percentage from wastewater discharges (see Table IV-6).
Total From Percentage Total From Percentage
Parameter all Sources From Wastewater all Sources From Wastewater
T, Oxygen Demand
T. Carbon
T. Nitrogen
To Phosphorus
BOD5
(Ibs/day)
515,800
380,000
66,900
25,000
161, 580
(#)
88
55
90
96
87
(Ibs/day)
733,000
720,000
100,000
29,300
242,900
(*)
62
29
60
82
58
•
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CHAPTER V
I 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
I 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.
I 20 "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
I three channels is bad during hot weather, at times constituting a
M nuisance; but that, when the improvements now planned or under con-
struction are completed, these conditions should no longer exist."
I Not only has the water quality problem as stated above persisted,
conditions have deteriorated considerably.
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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 I
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 g
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. •
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tl» OCX B3d)
SWSIWS«O HHOJDOD
(1"001 83d)
SHStNTOUO HBQJVTOO
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FECAL COLIFORM DENSITIES
UPPER POTOMAC ESTUARY
100,000-
10,000-
CC. ,-*
1,000-
100-
• MEAN OF 10 SAMPLES — AUGUST 19-23, 1968
FLOW = 2.800 cf»
TEMP. = 27.5'C
AUGUST 17, 1970
FLOW = 2.500 cf»
TEMP. = 28.0'C
X Md. SHORE
D MAIN CHANNEL
O Va. SHORE
10
15
20
25
30
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35
RIVER MILES FROM CHAIN BRIDGE
FIGURE V-2
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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„
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V-6
B. DISSOLVED OXIGEN
Dissolved oxygen (DO) concentrations in the upper Potomac Estuary I
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. m
A significant increase in DO occurred in the early 1960's near
the Blue Plains outfall. However, with the population increase of the I
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. M
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 _
193&. 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 I
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 I
were recorded on all four cruises, even when the freshwater inflow was
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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
I of 2.0 mg/1, DO during the summer months of 1966 ranged from 0.5 to 3.0
M| mg/1 with an average of 1.5 mg/1. For the months of September through
December 1965, the DO concentrations remained depressed as a result of
• low-flow conditions. During December 1965, the DO was approximately
5.5 mg/1 even when the water temperature was less than 10°C<,
| The DO concentration for a given time and location can also vary
M over the cross -sect ion 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 photosynthetic production by dense
' algal growths . During hours of darkness , the DO dropped to less than
I 8,0 mg/1 in the embayment while it remained around 4.0 mg/1 in the
main Potomac.
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(•"I
N3OUO OJT1OSS*)
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= 8
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10
DO PROFILES
UPPER POTOMAC ESTUARY
1969
JUNE II,1969
R_OW=l800cfs
TEMP. = 26* C
JUNE 30.1969
FLOW = 940 cfs
TEMP. = 28.5* C
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
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•
V-13
C. SILT AND DEBRIS
I The upper Potomac Estuary has changed drastically during the
past hundred years. At one time, water covered what is now the
comer 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 :
• a0 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 1.9& 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
1034 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.
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Table V-2
SEDIMENT DATA
Northwest Branch Anacostia River near Coles ville, Maryland
_ (Drainage Area = 21.1 sq mi)
Year Total for Year Annual Yield
• (1000 Ibs) (1000 Ibs/sq mile)
1963 33,600 1,590
I 1964 23,200 1,090
1965 32,800 1,540
• 1966 28,800 1,360
• 1967 30,000 1,420
1968 21,100 1,000
I Average 28,300 1,341
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V-l6
Applying the Anacostia station average (1.34 million lbs/sq mi/yr)
to the entire Washington metropolitan area and a yield rate of 0.20 |
million lbs/sq mile to the lower coastal area, an estimate of the silt _
loading to the entire Potomac River is as follows: •
Average •
Annual |
Area Yield Drajjoage Area Loading
(1000 lbs/sq mi/yr) (sq mi) (1000 Ibs/yr) m
Upper Potomac
(above Great Falls) 190 11,640 2,200,000
Washington Area 1,340 714 957,000 •
Lower Coastal Area 200 2.326 465.000 •
Total 246* 14,670 3,622,000
^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.
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• 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.
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During periods of high runoff, large quantities of debris enter
the estuary from the upper basin as well as from the metropolitan area,
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V-18
Debris from the upper basin is typically trees, brush, leaves, and
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miscellaneous trash, and is usually partially decomposed. Debris from I
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. I
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 I
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 I
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. •
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V-21
D0 NUTRIENTS AND ALGAL GROWTH
I 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
I 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-1940 's. 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
I at Hains 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
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INORGANIC PHOSPHATE CONCENTRATION as PO4
POTOMAC ESTUARY
069-WTO
MAINS POINT
MILES BELOW CHAIN BRIDGE = 7.60
0.4-
02-
JAN. FEB.
APN T MAV ' JUN. ' JUL ' AUG. ' SEP. ' OCT NEW DEC JAN FEB.
1969 <_]—*-J370
JUN JIM. AUG. SEP.
3,4-
12-
M-
2.8-
Z&-
2A-
i2-
WOODROW WILSON BRIDGE
MILES BELOW CHAIN BRIDGE = 12.10
JAN FEB.
i „.„—I—^—r
APfi, ' MAV ' JUN. JUL. AUG.
out ' wou
' «• I
MM. I »
JM1
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ir
04-
03-
O2-
0.\-
JAN ' TO. MART A^. MW ' JUN. ' JUL. ' AUG. ' SEP. ' OCT. ' MOV DEC JAN. ^
SMITH POINT
MILES BELOW CHAIN BRIDGE = 46.80
APR. HAY ' JUN.
JAN. FEB.
*. MM JJN. JUL. ' ALJ& SER OCT NW. DEC,
, I JAN. '
8 *-U-«70
FEB. MAR. ' AMI M« JUH^1 JUU AUG. SER. T
1968 *--«70
tt7-
O6-
= O4-
5 O3-
02-
Q.\-
301 BRIDGE
MILES BELOW CHAIN BRIDGE = 6T7.40
0.7-
O6-
05-
JAN. FEB. MAR APR ' MAV ' JUN. JUL. AUG. SEP. OCT. MO\t DEC. [ JAN. ' FEB. MAR r APR. ' HHt *
PiNEY POWT
MLES BELOW CHAIN BROGC = 9920
AUG. SER
JAH FEB.
MAV JUN, JU. AUG. SEP. ' OCT.
DEC. \ JAN.
*-l9TO
1 rw - «« "J ^ - ^v—i—^r~r
FEB. ' MAR. ' APR. T MAV
JUN, ' JUL ' AUx ' SCR '
FIGURE V-IO
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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
I in greater detail later.
_ The total phosphorus concentration closely parallels that of
inorganic phosphorus. In the upper reach, the ratio of total phos-
fl phoras 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 (NOg) and nitrate (NO^) nitrogen at
Hains Point and Woodrow Wilson Bridge varies almost inversely to that of
I phosphorus (Figure V-ll). The N02 + N03 concentration was highest in
July and August 1969 and during the spring months of 1970. During these
g months, both high-flow periods, the phosphorus was lowest (Figure Y-10).
The increase of NC2 + 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 N03. 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.
-------
MAINS POINT
MLCS BELOW CHAIN BRIDGE = 7.SO
NITRATE and NITRITE NITROGEN as N
POTOMAC ESTUARY
B69-I970
1.0 -
QJ-
(15-
O4-
0.3-
02-
0.1 -
FEB. MM APR.
JUN. JUL AUG SEP. OCT. NOV. DEC | JAN. FEB. MAR. r APR.
. r JM
i •»-(-*• an
JUN. JUL. AUG.
WOODROW WILSON BRIDGE
WLES BELOW CHAIN BRIDGE * 12.»
+ j>
2 O8-
O4-
02-
JAN. FCB
""'APR. MAY ' JUN! fJUL!' AtJG.
-T—n:—r~——i—^r—r
INDIAN HEAD
MILES BELOW CHAIN BRIDGE = 30.60
u-
12 -
06-
&S-
O4-
03-
O2-
01-
FEB. MAA
MAY JUN. JUL AUG SEP OCT NOV DEC
•JAN.
WTO
FEB. MAR APR. MAY
JUL. AUG. SEP
SMITH POINT
MILES BELOW CHAIN BRIDGE = 46.60
05-
QA-
0.2-
01-
JAN. FEB. MAR. APR.
JUN. JUL. AUG
OCT. NOV.
T DEC. I J
«W*-U-»
MAY JUN, JUL ' AUG7 r »»r
301 BRIDGE
MILES BELOW CHAIN BADGE = 67.40
' 06-
05-
04-
O3-
02-
01-
JAN 'FEB. MAR.
JUN. JUL. AUG. SCR OCT NOV.
04-
-C
y 03-
PI^4EY POINT
MILES BELOW CHAIN BRIDGE = 90.20
JAN. FEB. «Mft
MAY JUN.
AUa SEP. * OCT. NOV.
' £J»
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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
I during the summer months is low because of nitrification.
During the summer and early fall months, the average ranges of pH,
8 alkalinity, and free dissolved C02 (measured by titration) for the five
M stations in the upper and middle reaches were:
Free Dissolved
m Location pH , Alkalinity QP2
• (units) (mg/1 as GaC03 (mg/l)
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 002 with a corresponding decrease in pH attri-
_ buted to wastewater discharges. There is a decrease in both alkalinity
* and 002 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.
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AMMONIA NITROGEN as N
POTOMAC ESTUARY
1969-1070
HAMS POMT
MLES BELOW CHAIN BNDGE = 7*0
APt) MAY ' JUN.
AUG. SEP. OCT NCW OK I JAN FEB. MM. APR.
WOOOROW WILSON BRIDGE
MLES BELOW CHAIN BRIDGE = 12.10
INDIAN HEAD
MILES BELOW CHAIN BRIDGE = 30.6O
SMITH POINT
MILES BELOW CHAIN BRIDGE = 46.60
Ftl. MAR ' APfl. MAY JUN. JUL. AUG. UP. OCT. NOV. DCC. 1 JAN. ' FEB. MAR APR MAY
3OI BRIDGE
MLES BELOW CHAN BRIDGE = 67.40
1 MAR. ' APR. ' MNT ' JUN ' JUL. ' AUO '
OCT. NCM. KC. I JAN. fCB
HNEY POINT
MLES BELOW CHAM BRIDGE < 89.20
i" ~ i—rr—i—-—i
OCT NW OK. JAN.
JUL AUG
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V-27
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2. Mathematical Models for Nutrienft 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-T7, V-l#, 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.
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m
d SV SnaOHdSOHd
FIGURE V-13
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f) 04 (VI CJ
(!/««•) *Od SV SnaOHdSOHd
FIGURE V-14
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$ £
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FIGURE V-15
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\— cc °°
Z < $
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.1-
.09-
.08-
.07-
.06-
.05-
.04-
.03-
.02-
1 .01-
i-
o>
~ .009-
.008-
.007-
.006-
.005-
.004-
.003-
.002-
.001-
EFFECT OF TEMPERATURE
ON
PHOSPHORUS DEPOSITION RATE
POTOMAC ESTUARY
11,000 cfs
8800 cfs
185 cfs
Kpl
KP2
(T, -T2)
9 - 1.084
Kp,20'C: 0.0225 (BASE e)
(SECOND-ORDER KINETICS)
T
10
15
i
20
T
25
TEMP.(O'C)
I i
30 35
FIGURE V-17
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0.4-
0.3-
0.2-
0.1-
.09-
.08-
.07-
.06-
.05-
.04-
.03-
2 JT .02-
x. X
.01-
.009-
.008-
.007-
.006-
.005-
.004-
.003-
.002-
.001-
EFFECT OF TEMPERATURE
ON
NITRIFICATION RATE
POTOMAC ESTUARY
NH-, —>• NCU-t- NO.,
i
10
Q- 1.188
KN= 0.068 (BASE e) at 20'C
(FIRST ORDER KINETICS)
I T
15 20
TEMPERATURE
CO
25
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35
FIGURE V-18
-------
0.2-
0.1-
.09-
.08-
.07-
.06-
.05-
.04-
.03-
.02-
.01-
.009-
.008-
.007-
.006-
.005-
.004-
.003-
.002-
.001-
EFFECT OF TEMPERATURE
ON
RATE OF NITROGEN UTILIZATION BY ALGAE
POTOMAC ESTUARY
NCL
ALGAL NITROGEN
e = 1.120
KN2 = 0.034 (BASE e) at ZO'C
(FIRST ORDER KINETICS)
10
\
15
I
20
I
25
30
TEMPERATURE
CO
T
35
FIGURE V-19
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m V-35
3. Ecological Trends as fielated 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 phytoplankton), mainly Anacystis sp.
are prevalent in the freshwater portion of the estuary. Large
I standing crops of this alga occur, especially during periods of
low flow, forming green mats of cells. The blue-green algae are
I 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 GymnQdinium sp. and Amphidinium 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
I have been implicated as stimulating this, with nitrogen and phos-
M phorus showing promise of being the most manageable.
The historical plant life cycles in the upper Potomac Estuary
I can be inferred from several studies. Gumming [7] surveyed the
estuary in 1913-1914 and noted the absence of plant life near the
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•
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
g 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
Anaeystis 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],
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V-38
I
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, g
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 (Myrlophyllum spicatum').
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. I
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HA1NS POINT
ML£S BELOW CHAN 8ROGC = 7.60
CHLOROPHYLL a
POTOMAC ESTUARY
UPPER REACH
PISCATAWAY CREEK
MILES BELOW CHAIN BRIDGE = 18.35
' SEP OCT ' mi. DECJW. Ftt
-------
SMfTM POINT
ML£S BELOW CHAM BWOGE *
CHLOROPHYLL o
POTOMAC ESTUARY
MOOLE ON* LOWER REACH
n:
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JAN FEB.
OCT. NOV. OCC. 1 JAM. FE6 MAR. APR.
FEB. MAR APR MAY JUN. JUL
PINEY POINT
MILES BELOW CHAIN BRIDGE = 99.20
OCT NOV IXC. I JAN. FEB. t*W. APfi. MAY JUN. JUL AUG. SEP.
JM. FCB
APR UAV JUN.
NOV OCC 1 JAN.
1969->-t-» 1970
FEB. MAR. AM.
JUN. JUL. ' AUO SE». '
FIOURC V-22
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• Prom 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.
I Laboratory and controlled field pond studies by Mulligan [15]
have shown similar results. Ponds receiving low-nutrient additions
I (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
8 reverted to its previous state. This observation was also supported
M by studies of Edmondson [16] on Lake Washington and Easier on the
Madison, Wisconsin lakes [17],
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V-42
I
E. EFFECTS OF EUTROPHICATION ON WATER QUALITY
The effects of nutrient enrichment and the resulting algal growths 8
are fourfold: (1) an increase in organic oxygen demanding load,
(2) an increase or decrease in dissolved oxygen caused by algal photo- 8
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 B
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below;
1° Increase in Organic Oxygenr DemandingLoad
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 8
60,000 Ibs/day of nitrogen discharged into the estuary from wastewater
treatment facilities is converted into algal cells. The combined 8
ultimate oxygen demand of nitrogen and carbon from these cells is •
approximately 4-90,000 Ibs/day. This load,, though dispersed over the
entire upper estuary, is nevertheless greater than the total oxygen 8
demand by all wastewater discharges into the upper estuary,
Laboratory studies on rate kinetics of the oxidation of algal ceils 8
at temperatures of 28 C to 30 C indicated that the reaction nates 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, 8
the embayments or along the shores as a result of wind action.
These concentrations of decaying algae produce noxious odors, 8
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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 mg/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 V-3 » A special respiration study was conducted on
| July 29, 1970, which indicated that .0010 mg Og/hr/ug of chlorophyll
mm respiration could be attributed to algae with the remainder due to
bacterial and other oxidation processes .
• With a euphotie zone of 2 feet, an average oxygen production of
.010 mg 02/hr/ug cf chlorophyll for 12 hours/day, an average respiration
8 of oOOlO 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
OXIGEN PRODUCTION AND RESPIRATION RATE SURVEY
Upper and Middle Potomac Estuary
Date
6-22
6-23
6-24
6-25
7-20
7-21
7-22
7-27
Water Chlorophyll a
Temp. Range
(°C) (ug/1)
26 40-110
27 70-120
27 54-HO
27 50- 60
28 30-100
27 30-143
26 30-140
28
1970
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 §,
.0023
.0011
.0024
.0033
.0022
.0016
.0017
.0010
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
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1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Water Column
(depth)
4
8
12
16
20
4
8
12
16
20
Table V-4
OXYGEN PRODUCTION-RESPIRATION BALANCES
Chlorophyll a = 100 ug/1
Oxygen Production = .010 mg/hr/ug chlorophyll for
Respiration = .0010 mg/hr/ug chlorophyll for 24
Eunhotic Zone of 2.0 feet
Increase in Oxygen
Averaged over Entire Decrease in
Water Column due to Oxygen due to
Photosynthesis Respiration
(ing/I/day)
6.0 2.4
3.0 2.4
2.0 2.4
1.5 2.4
1.2 2.4
Euphotie Zone of 4.0 feet
12.0 2.4
6.0 2.4
4.0 2.4
3.0 2.4
2.4 2.4
12 hours/day
hours/day
Net
(ing/I/day)
3 06
0.6
-0.4
-0.9
-1.2
+9.6
+3.6
+1.6
+0.6
0.0
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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 I
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 I
respiration and decay. The net oxygen production concept has been
incorporated into the DO budget model for the Potomac Estuary. I
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FIGURE V-23
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V-48
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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
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Basin.
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_ V-/.9
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— 4. Algal ToxicitY
• 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,
B 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
I 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.
I If the estuary is to be used as a water supply source, the
•j 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.
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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
M 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 EWQA Dynamic Quality
I Model consisting of the following five linkages :
(l) Oxidation of carbonaceous matter,
g (2) Oxidation of nitrogenous matter (ammonia and organic),
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(JJONfia QNVT)
(a3.LVM3.LSVM)
(a3iVM31SVM)
SJ.N3iainN TV11N3SS3 a3HlO
FIGURE VI-I
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VI-3
• (3) Oxygen production and respiration of simulated algal
• standing crops based upon nitrate utilization "by the
cells,
• (4) Benthie demand, and
(5) Reaeration from the atmosphere.
I 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°G ent Q (?1 - ?20)
™ Carbonaceous oxidation 0.170 1.047
8 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 ji
• 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 Oa/day sq. mi
* The model calculates reaeration as a function of depth and velocity
_ using any one of three formulations.
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FIGURE VI-3
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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 I
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, •
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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 27.8QC
March 7.8OC September 24.7°C
April 14.0°C October 18.4°C
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.
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VI-8
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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 |
(rog/1) (mg/1)
District of Columbia* 5.0 (Daily) 4.0 I
State of Maryland 5.0 (Monthly) 4.0
State of Virginia 5.0 (Daily) 4.0 •
* Except between the Rochambeau 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. ^
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VII-1
CHAPTER VII
ALGAL GROWTH RESPONSE TO NUTRIENT CONTROL
Reductions in the standing crop (biomass) of algae in the Potomac
I Estuary can be achieved by management, singly or in combinations, of
carbon, nitrogen, and phosphorus content. The decision as to which
I 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.
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VII-2
A. EUTRQPHICATION 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 v/ith 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 grovrths especially in v/aters 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 I
nitrogen from vrastewater 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 fishing, 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 I
upper estuary is to be used as a supplemental water supply.
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• VII-3
• To aid in defining an algal standing crop limit, a subjective
analysis using chlorophyll concentrations was developed incorporating
I conditions having possible effects on water quality. Four major
restraints to desired water uses are offered in this analysis (Table
I VII-1) 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 minimize 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.
I 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.
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• VII-5
m 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, Sawyer [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
M 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
M less than 0.03 mg/1, biologically healthy conditions will be maintained.
Jaworski efc al [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 rag/1 respectively, algal blooms
of approximately 50 ug/1 of chlorophyll a, would result. A chlorophyll g,
concentration of 50 ug/1 or over was considered indicative of excessive
^
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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 I
ei 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. I
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, I
5. Comparison with an estuary currently not eutrophic, and
6. Revie\? of historical nutrient and ecological trends in the
Potomac Estuary.
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• 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
I the saline portions. In a study undertaken by Carpenter, Pritchard,
and Whaley, oxygen concentrations of less than 1.0 mg/1 were found in
the area of the lower reach of the Potomac [97]. 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.
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VII-8
minimum of 4.5 rag/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.
I
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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 8.08$ •
Phosphorus 0.68$
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 a. contains the following:
Parameter Concentrafr ion I
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 I
algal bloom with a concentration of 100 ug/1 of chlorophyll §. requires a
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VII-10
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I
For the Potomac Estuary, which can be considered & 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. •
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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
H 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
I Bridge where 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 + N03 concentrations shown in Figures V-ll
• 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.
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VII-12
To determine if carbon was limiting algal growth in the bloom
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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:
I
Station Organic Carbon Inorganic Carbon •
(mg/1) (mg/1) I
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 8
inorganic carbon available for algal growth. As reported earlier,
with the free carbon dioxide in the water ranging between 6.0 and fj
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 •
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g -S
x
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50-
f-
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NUTRIENT-CHLOROPHYLL PROFILES
POTOMAC ESTUARY
MARCH — AUGUST , 1965
AUGUST 10. I96S
MARCH 24.1965
—I
2 0
40 60 60
MILES BELOW CHAIN BRIDGE
100
—I
120
FIGURE VII-I
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VII-14 I
Estuary from River Mile 20 to 60. The utilization of significant _
quantities of inorganic carbon as indicated by alkalinity was also ™
The 1965 data also demonstrated that another source of inorganic
carbon to the Potomac Estuary is recruitment from the Chesapeake Bay.
I
observed.
The basic difference between these sets of conditions vras that
the freshwater inflow during June and July 1965 was considerably less J
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. I
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 Jj
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- I
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 •
growth.
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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.
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VII-16
3. Bioassay Studies
To determine further v/hat nutrients were limiting algal growth in
the Potomac, bioassay tests as developed by Fitzgerald [28] [29 yrere
employed. Tests for both phosphorus and nitrogen were conducted in
the Potomac from Piscataway 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 grov/th as v/as 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
Station
Pis cataway
Indian Head
Possum Point
Smith Point
InJ/ater
NOp + N03
.110
.150
.001
.001
2.560
.084
.220
.150
Ammonia
Nitrogen AbsQ.rbed
(rrg N/hr/ug chforo)
+ -.0 7. 10 5
+ 6.0 x 10-5
+ 2.3 x 10-4
+ 1.3 x 1C~4
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• 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).
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4. Nutrient and Algal Modeling
VII-18
Recognizing the possibility that the Potomac becomes nitrogen
starved in late summer, an attempt was made to
surrogately mathe-
1
1
matically model algal growth based on the nitrogen cycle. The model,
similar to that proposed by Thomann et al [30]
as shown below:
Wastewater Ntti Kni v. NOo + NCh Kn? \
1
\ Kft4
is a feedback system
Organic Nitrogen
Expressed as
Chlorophyll a.
A
Km
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
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for summer conditions. The established rates (base e) are:
Kinetic Reaction Rates
Kni .30 - .40
Kn2 .07 - .09
Kn3 .01 - .05
Kn^. (not established)
The first two reactions including the rates Kii]_
fairly well verified as reported earlier and as
dieted profiles of NH3 and N02 + NO^ in Figures
(per day)
(per day)
(per day)
(per day)
and Kng have been
shown in the pre-
V-15 and V-l6. The
feedback link appears to play a minor part in the system during the
earlier summer months .
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VII-19
Predicted profiles using the surrogate algal model, as shown in
I
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, 1968, data as shown in
• Figure VII-2, the reduction of chlorophyll a. concentrations to 25 ug/1
would result in a maximum NC>2 + NC>3 concentration of 0.25 mg/1. For
I 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
M 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..
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VII-22
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5. Comparison With a Les_s-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 1970. 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 N02 + N03 between 0.1 to 0.3 mg/1,
the standing crop of algae will be minimal with a chlorophyll a. concen- I
tration of less than 4-0.0 ug/1.
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• Table VI I -4
SUMMARY DATA
_ Upper Rappahannock Estuary
• 1970
Date Inorganic N02 + N03 Chloro a Organic
IP as P04 Carbon
(mg/1) (mg/1) (ug/1) (mg/1)
• c-23 0.13 0.26 32 7.3
6-30 0.18 0.12 34 No Data
1 7-07 0.10 0.11 40 No Data
7-13* 0.33 0.64 8 7.8
1 7-21 0.15 0.27 70 5.0
• 7-29 0.22 0.39 17 9.7
* 8-28 0.14 0.21 39 17.9
• * High river discharge
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Inorganic
Carbon
(mg/1)
No Data
No Data
No Data
No Data
5.0
4.8
No Data
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VII-24
I
6. Review of Historical Nutrient and Ecplogjcal Trends, j.n 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 I
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 9
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. •
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C . CONTROLLABILITY OF VARIOUS NUTRIENTS
VII -25
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,
are listed
Month
nitrogen, and carbon attributable
below :
Mean
Monthly
Flow Percentage Currently
to wastewater discharges
from
Was t ewat er Dis cha TSQS
(°fs) Phosphorus Nitrogen Carbon
April
May
June
July
August
September
October
20,000 60
14,500 67
8,700 76
5 , 500 83
6,000 82
4,700 84
6,300 81
26
36
50
63
61
66
59
From the above tabulations, it can readily be seen
phosphorus be controlled by removal to the highest
removal) at
the wastewater treatment facility,
but
17
20
26
33
31
35
29
that not only can
degree (percentage
phosphorus can be
controlled earliest in the growing season. These tvro aspects enhance
the feasibility of phosphorus management.
While 82 to 96 percent of the phosphorus
can be controlled by removal at the wastewater
1 during median to low flows [52], an additional
1
entering the upper estuary
treatment facilities
reduction of phosphorus
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VII-26 •
concentration occurs during periods of high runoff within the upper «
estuary itself. As reported by Aalto et. aJL [8], large quantities of
phosphorus (over 100,000 Ibs/day) enter the upper estuary during high- 8
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. I
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 grov;ing 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
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• the Potomac Estuary, about 1,600 Ibs/day of nitrogen is obtained from
the atmosphere as compared to over 50,000 Ibs/day from v/astev/ater 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 '.Vis cons in [53] 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,
I 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 uastewater is 35 percent. Other major sources not included in
this figure are from the atmosphere, bacterial action in water, 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 C02 transfer from
the atmosphere is approximately 3,500,000,000 Ibs/day*. This source
from the atmosphere alone ma^es the possibility of effective carbon
p control doubtful at the present time since only about 100,000 Ibs/day
of carbon is discharged in v/astey/ater with over 330,000 Ibs/day from
• the upper basin.
• * The COo obtainable from the atmosphere v/as 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.
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VII-28
Another aspect of nutrient management is the transport and/or
carbon, is insignificant. Under these conditions, control of all
three nutrients in the \vastewater treatment process is feasible.
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deposit of the various nutrients along the longitudinal profile of
the estuary. Because of the great solubility in water, inorganic I
nitrogen and carbon are easily transported through the estuary
especially during high-flow periods in the winter and spring months. J
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 I
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 •
inflow thus the amount of inflow from the upper basin, especially
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80-
60-
40-
20-
5.0-
4.0-
3X>-
zS
«
2JD-
1JO-
2.0-
1.0-
10
CARBON . TKN & PHOSPHORUS IN SEDIMENTS
POTOMAC ESTUARY
AUGUST W-20. 1970
20
30 40 50 60
MILES BELOW CHAIN BRIDGE
70
80
90
100
FIGURE VII-4
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the Potomac Estuary:
Concentration Range.
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VII-30
D. NUTRIENT CRITERIA
There are no existing nutrient criteria specified by either the I
State of Maryland or the District of Columbia. To control algal grovrth,
the State of Virginia has set nutrient objectives for nitrogen and •
phosphorus of 1.0 and 0.2 mg/1 respectively in v/astewater 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
B
•
Inorganic Nitrogen 0,30 - 0.5 mg/1
Total Phosphorus 0.03 - 0.1 mg/1 I
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™ •
1 is lied at the present time. m
The lower values in these ranges are to be applied to the fresh-
water portion of Zone III -and to the embayment portions of the estuary I
in which the environmental conditions are more favorable toward algal
growth. The upper ranges of the criteria are more applicable to m
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 I
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 |
Maryland Point, there are primarily freshwater phytoplankton and zoo- tm
plankton populations. Above Maryland Point, the salinities are less
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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
8 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 tvro points of emphasis in estuarine
water quality management:
8 (l) Fairly discrete biotic provinces may be identified within a
tm 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 a
given estuary.
8 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
I 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
* Madison, Wisconsin [17] and Lake Washington [16] when wastewater dis-
• charges ere diverted from the lakes.
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VII-32 •
The criteria sho?/n above give maximum concentrations for both
nitrogen and phosphorus. Limits for both were incorporated for the |
following reasons: M
(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 I
is 10 times that for phosphorus (0.30 versus 0.03 mg/l) while the
nitrogen loading from the v/astevrater treatment facilities is 2.4 times I
that of phosphorus (60,000 versus 24,000 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 I
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 vrtiich in turn stimulates _
algal growth, and ™
(3) There is compatibility between v/astewater 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
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• Vll-33
• oxygen demand removal is required, whereas the control of algal standing
crops is predicated on phosphorus and nitrogen removal. To obtain a
I 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:
(l) by converting the unoxidized nitrogen to nitrates (commonly called
B 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.
B Thus with proper selection of wastewater treatment unit processes,
™ it is feasible not only to enhance the DO by removing the carbonaceous
I and nitrogenous UOD but also to reduce nuisance algal growth by removing
nutrients.
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VIII-1
CHAPTER VIII
I CONTROL CONSIDERATIONS FOR BACTERIAL DENSITIES, VIRUSES, HEAVY
METALS, AND OTHER WATER QUALITY PARAMETERS
B A. BACTERIAL DENSITIES
1. Indicator Organisms
8 Four bacterial organisms have been used as indicators of the
m sanitary water quality of the Potomac. These four are:
(1) Total coliform,
8 (2) Fecal coliform,
(3) Fecal streptococci, and
(4) Salmonella.
. In a 1969 report entitled l;Sanitary Bacteriology of the Upper Potomac
Estuary'1 by Lear and Jaworski [331, the folloying conclusions were
8 reached:
(l) High total coliform, fecal coliform, and fecal streptococci
densities were found in the Washington metropolitan area,
(2) Fecal col if orm/ fecal streptococci ratios indicated that most of
the bacterial pollution in the upper estuary was probably of human origin,
I (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 waters having high total and/or fecal coliform densities.
fl Data collected during 1969 [34] also reflected the earlier findings
including the salmonella isolations .
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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 wastewater outfalls. I
Hovrever, overflows from overloaded sanitary and combined sewers still
cause high fecal coliform densities as was shovm in Figure V-2. These •
high densities are a result of overflows of untreated wastewater _
entering the estuary near the confluence with Rock Creek. ™
The complete control of bacterial densities in the upper estuary B
cannot be realized until both continuous chlorination of wastewater
effluent is maintained and sanitary, combined and storm sewer over- •
flows are reduced or eliminated. Yi/hile 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 overflows of the combined sewer system, especially •
during the summer recreation period. This becomes increasingly serious
when the estuary is considered as a public water supply source. •
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VIII-3
2. Bacterial Standards
The bacterial water quality standards for the upper estuary are
I as given below:
Jurisdictipn Total Coliform Fecal Coliform
I Virginia 2400 MPN/100 ml 200 MPN/100 ml
(monthly avg.) (30-day log mean)
I Maryland 240 MPN/100 ml
(by survey)
•District of Columbia 1000 MPN/100 ml
(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.
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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 v/ater supply source. While no epidemic- I
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 \vater supply source. Since both wastewater effluents and |
overflows from storm, sanitary, and combined sewers contain viruses and tm
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/astev/ater treatment facilities in removing viral •
particles, and
(3) The effectiveness of water treatment processes in removing |
viruses .
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VIII-5
_ Studies regarding the viral removal effectiveness of wastewater and
water supply treatment processes have been undertaken by MQA's
I Advanced Waste Treatment Research Laboratory in Cincinnati, Ohio
and by the U. S. Army Corps of Engineers /'"respectively. The FtfQA
studies include an investigation of the effect of advanced v/aste
_ treatment processes on viruses. While a complete review is beyond
* the scope of this report, virus data on i/astev/ater 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
^ Y/ithout reaching free chlorine residual will not insure virus free
• effluents [36].
fl As one aspect of the cooperative study with FiQA 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
I
™ with the effectiveness of chlorination in deactivating various types
B of human enteric viruses.
A joint investigation by FWQA's Chesapeake Technical Support
I 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
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I
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 V/ater Intake
II Below Chain Bridge Near Site of Proposed Intake I
III Near Woodrow V/ilson Bridge Below Blue Plains g
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 p
with the Bacillus subtilis spore [3V] very promising as an indicator of
virus disinfection.
A committee report for the American Water Works Association [38] B
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. •
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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
concentrations of zinc and manganese were detected in the overlying
• waters of the estuary, considerable amounts of various heavy metals
by acid extraction from the sediments vrere 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
I 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,
M this heavy rnetal accumulation could develop into a serious water quality
management problem.
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in the sediments.
I
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VIII-8
Heavy metals in the sediments must also "be considered in the
disposal of dredged spoil. Dredging operations involving deepening I
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
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twice the recommended standard for CCE.
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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 I
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 v/ater temperature, reaching a high of 33°C.
Since the two areas periodically contain low dissolved oxygen I
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
I
sewers are eliminated.
2, Carbon Chloroform Extraction
Using carbon chloroform extraction (CCE) as an indicator of I
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. I
At times, the relative increase is high, approximately 400 ug/1 or 0.4 mg/1,
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FIGURE VIII-
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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 m
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 I
prototype were relatively uniform throughout the period. The mean
Potomac RiA/er 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 jl
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 I
these two points in time as illustrated in Figure VIII-2.
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VIII-13
The profile for July 7-8, 1965, was specified as the initial
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™ 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
I 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
c) 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
m in this report.
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O»
2
O
a
2
LU
U
O
O
til
9
cc
I
o
CHLORIDE CONCENTRATION
POTOMAC ESTUARY
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
LEGEND
CBI DATA. JULY 7-8.1965
x D.C. DATA. JULY 7-8, 1965
o CBI DATA. DEC. 1-2. 1965
o CTSL DATA, DEC. 1-2,1965
PROTOTYPE
MODEL
DEC. 1-2.1965 PROFILE
10 20
INITIAL PROFILE JULY 7-8, 1965
(ALSO MODEL)
30 40 50 60 70 80 90 100
MILES BELOW CHAIN BRIDGE
FIGURE VIII -2
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• 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.
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IX-1
CHAPTER IX
POPULATION AND WASTEWATER PROJECTIONS
A. POPULATION PROJECTIONS
I 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
mm were furnished by the Metropolitan Washington Council of Governments
(COG). Control populations for these benchmarks v/ere based on the
•
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"low -estimate" figures prepared for COG by Hammer, Green, Silar
Associates [39] . Distribution by individual service areas was essen-
tially determined from 1960-1968 population trends with consideration
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IX-3
given to land use potential and other attenuating factors. A similar
methodology was employed by FWQA-'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,
0 regional, and metropolitan area population trends.
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FIGURE IX-1
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POPULATION PROJECTIONS
WASHINGTON METROPOLITAN AREA
O
Q
d
z
i
TOTAL
—
1968
1
1980
BENCHMARK
2000
—
• —
2020
FIGURE IX -2
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IX-6 •
B. WATER SUPPLY REQUIREMENTS f
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 —
Water 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 J
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 1400 mgd or
90 percent. The Patuxent River currently supplies 42 mgd to the 9
Washington metropolitan area but will be unable to serve this area in •
the future due to projected needs within the Patuxent Basin [40].
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Table IX-3
VARIOUS WATER SUPPLY DEMANDS
Washington Metropolitan Area
Duration
Maximum Day
Maximum Five Day
Maximum Month
Maximum Two Months
Maximum Three Months
Maximum Six Months
Yearly Average
1980
(mgd)
1,001
950
723
712
695
634
556
2000
(mgd)
1,816
1,730
1,312
1,292
1,261
1,150
1,009
2020
(mgd)
2,822
2,680
2,038
2,007
1,960
1,788
1,568
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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
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for the 13 service areas
These data are presented
and 2020 respectively.
comprising the Washington metropolitan area.
in Tables IX-5, IX-6, and IX-7 for 1980, 2000,
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-
t ions :
Year Flow
1969 325
1980 473
2000 861
Before Treatment
BOD^ TKN as N T. P as P
( Ibs/day ) ( Ibs/day ) ( Ibs/day )
483,500 63,500 27,300
823,500 95,600 43,100
1,463,500 155,700 70,300
2020 1342 2,195,000 215,600 97,400
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.
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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
I a quality component that considers the basic transport mechanisms of
M 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 aa originally developed by Thomann [54] . This model was
• used to investigate seasonal variations in the nitrogen and phosphorus
distributions of the upper Potomac Estuary,
d A study investigating the relative merits of the FWQA Dynamic
M Estuary Model versus the tidal average approach has been made by
CTSL and a report of this investigation is currently in preparation.
I 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
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X-2
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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 B
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.
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rout MILE KUN
WASTEWATER PLANT NODES
NOOE PLANT
78 ARLINGTON
120 BLUC PLAINS
2 UPPER POTOMAC
81 ALEXANDRIA
I IB PISCATAWAV
7 PENTAGON
126 LOWER POTOMAC
IO6 ANACOSTIA
126 OCCOOUAN
31 tMTTWOMAN
96 PORT TOBACCO
LOWER MACHODOC CR
VEOCOM1CO RIVER
ST MAftYS RIVER
SMITH CR
CHESAPEAKE
SCHEMATIC OF POTOMAC ESTUARY
FOR FWQA DYNAMIC MODEL
-------
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55
fc
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CLQ:
RGURE X-2
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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 1980 2000 2020
I(mgd) (*ngd) (mgd)
Pentagon 111
_ Arlington 23 3? 45
| Blue Plains 285* 473 702
Alexandria 38 6l 83
I Piscataway 24 49 79
Lower Potomac 50 103 170
I OccocLuan 45 121 235
Mattawoman 5 9 13
Port Tobacco 0 6 11
Proposed capacity = 309 mgd
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE I
OCCOOUAN
OF COLUMBIA
(BLUE PLAINS)
FIGURE X-3
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WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE 1C
^DISTRICT OF COLUMBIA
(BLUE PLAINS)
.ATAWAY
IANACOSTIA
OCCOQUANV
FIGURE X-4
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE HI
UPPER POTOMAC \
WASHINGTON
7 /
ARLINGTON^ I / ^ /
/DISTRICT OF COLUMBIA
(BLUE PLAINS)
OCCOQUAN
FIGURE X-5
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WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE H
/DISTRICT OF COLUMBIA
'|[ V< (BLUE PLAINS)
'PISCATAWAY
FIGURE X-8
-------
WASTEWATER TREATMENT SYSTEMS
UPPER POTOMAC ESTUARY
ALTERNATIVE 31
,/DISTRICT OF COLUMBIA
(BLUE PLAINS)
'ANACOSTIA
OCCOQUAN
FIGURE X-7
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X-ll
Under Alternative I, the District of Columbia's Blue Plains
facility will also serve the upper Potomac area v/ithin 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
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to Blue Plains in the first two alternatives would be conveyed to the
upper Potomac plant.
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Table X-2
WASTEWATER FACILITIES AND PROJECTED FLOWS
Alternative II
Facility
Pentagon
Arlington
Anacostia
Blue Plains
Alexandria
Piscataway
Lower Potomac
Occoquan
Mattawoman
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
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_ Table X--3
| WASTEWATER FACILITIES AND PROJECTED FLOWS
Alternative III
Facility
• Pentagon
• Upper Potomac
Anacostia
I Arlington
Blue Plains
I
Alexandria
Piscatavray
Lower Potomac
• Occoquan
Mattawoman
Port Tobacco
* Proposed capacity = 309 mgd
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1980
(mgd)
1
0
0
23
285*
38
24
50
45
5
0
2000
(mgd)
1
38
126
37
309
61
49
103
121
10
6
2020
(mgd)
1
209
185
45
309
83
79
170
235
13
11
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x-u •
Alternative III is similar to the proposals in the "Memorandum _
of Understanding" with reference to the Washington metropolitan *
regional vfater pollution control plan as presented at a special •
session of the Potomac Hiver Washington Metropolitan Area Enforcement
Conference on October 13, 1970. In this memorandum, a maximum capacity •
of 309 ffigd 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. I
Alternative V, presented later in this report, is one variation \vith
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. I
This plan v;as 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, Lower Potomac, Occoquan, and Port Tobacco facilities I
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. I
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X-15
The estuary water supply intake was assumed to be one-half mile
belov/ Chain Bridge. In Figure X-l, the schematic diagram for the
• model, the water supply intake is at Node 114.
When the current wastewater collection and treatment facilities,
I projected populations, "Memorandum of Understanding," and water supply
• needs are reviewed, it can readily be observed that:
(l) Shortly after 1980, the Dulles Interceptor with its current
I 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-
struct ed in this region.
• (3) If the Dulles Interceptor is enlarged, wastewater treatment
capacity must be increased at either Blue Plains, Anacostia Valley,
| and Piscataway 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
I 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 v/atersheds .
_ 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.
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various bases such as population, drainage areas, and geographical
subdivisions.
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X-16
C. WASTEWATER MANAGEMENT ZONES AND STREAMFLOW CRITERIA
To facilitate determination of wastewater management requirements, I
the upper and middle estuary were initially divided into three 15-mile
zones with similar physical characteristics beginning at Chain Bridge. I
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 May 8, 1969, I
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 I
discharge can be obtained by prorating the total zonal poundage using
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1
1
1 9
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RIVER MILES FROM CHAIN BRIDGE = 0
PENTAGON
SU8ZONE la
ARLINGTON
SUBZONETb ZONE
DISTRICT OF/COLUMBIA
\L
ALEXAND
WESTGATE
SU8ZONEIc
t RIVER MILES FROM CHAM BRIDGE = IS
LITTLE HUWNG Cr-
I ANDREWS A.RB.
FORT BELVOIR
LOWER POTOMAC
PISCATAWAY Cr.
ZONE II
RIVER MILES FROM CHAIN BRIDGE = 30
WASTEWATER DISCHARGE ZONES
in UPPER POTOMAC ESTUARY
ZONE III
RIVER MILES FROM CHAIN BRDGE = 45
FIGURE X-8
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• 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
B also presented.
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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 I
|
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.
I
* The ultimate oxygen demand represents the sum of unoxidized carbon
and nitrogen I
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Table X-5
I 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
• (Ibs/day)
I-a 4,000
I l-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).
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X-22 •
Subzone I-c currently receives v/astewater effluents from 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- I
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
UOD 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
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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
(rngd) (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.
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•A."—£_Af. ^V
increase the downstream advective movement and the assimilative capacity .
of the Anacostia 'River. ™
Zone II of the Potomac Estuary currently receives effluents from I
the Piscataway and Lower Potomac wastewater treatment facilities via
the Piscataway Creek and Gunston Cove embayments. By 1980, a third J
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 I
(Alternative V) assumes that all effluents discharge directly into
the Potomac main channel whereas the other (Alternative I) assumes g
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 I
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 wastewater efflu-
ents projected in Alternative I, the maximum allowable UOD loadings •
will be reduced considerably when compared to Zone II loadings. The
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X-25
relative inability of these embayments to assimilate organic waste-
water is reflected in the data shown below:
UOD LOADINGS FOR PISCATAWAY CREEK AND GUNSTON COVE
Piscataway Creek Guns ton Cove
I Maximum Maximum
Flow UQD Load Flow UOD Load
(jngd) (Ibs/day) (mgd) (ibs/day)
• 2.L, 10,000 50 7,000
49 10,000 103 11,000
I 79 12,000 170 16,000
• Since the physical characteristics for each eiribayment 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 .
I There are at present no significant wastewater discharges within
Zone III of the Potomac Estuary; however, a treatment facility to serve
g the Oceoquan 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).
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X-26 •
E. PHOSPHORUS •
Simulation of phosphorus discharges in the Potomac Estuary was
made using the mathematical model with second-order reaction kinetics 8
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 rag/1 (P)
within Zone III and all embayments. All effluents were assumed to be of I
the same concentration. While various freshwater inflow rates (before
water supply diversions) between 300 cfs and 1800 cfs were investigated, 8
their effect on the allowable phosphorus loadings appeared to be quite
small.
The allowable phosphorus loading for Subzone I-c of the Potomac I
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- 8
gated. •
When Alternative III was considered, the limited waste assimilative
capacity of the Potomac Estuary in Subzone I-a near Chain Bridge became B
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 8
withdrawals are assumed, a certain portion of the phosphorus will be •
removed directly, thereby increasing the allowable load from wastewater
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Table X-6
I-a 200
I-b 85*
I-c 900
II 1500
III 2000
I PHOSPHORUS LOADINGS FOR POTOMAC ESTUARY
Freshwater Inflow = 300 cfs (after water supply diversion)
• Zone Allowable Phosphorus
(Ibs/day
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* The loading in this zone is sensitive to vrastewater flow as
• described in the text of this report.
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phorus analysis for Zone II.
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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 •
(efs) (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 I
loadings into Subzone I-b are also a function of \vastewater 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-- •
•
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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
Bis...Qharg.e_.Locatj.pn. Upper End of Embayment 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 Guiiston Cove, again assuming 1980 con-
ditions , follows:
Increase in Phosphorus Increase in Phosphorus
Pischarge Location Upper End of Embayment Lower End of Embayment
(mg/1) (mg/1)
Into Enihayment 8.62 0.61
Into Main Potomac 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 embayments.
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X-30
If discharges projected in Alternative I are made to the upper
I
end of the Piscatav/ay Creek and Gunston Cove embayments, the maximum
allowable phosphorus loadings are as follows: •
PHOSPHORUS LOADINGS TO EMBAYMENTS
Piscatav/ay Greek Gunston Cove
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Maximum Maximum
Flow Phosphorus Load Flow, Phosphorus Load
(mgd) (ibs/day) (mgd) (Ibs/day)
24 35 50 35 I
49 50 103 60 .
79 65 170 140 ™
The loadings given apply to these embayments only. A separate I
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. I
In order to realize the phosphorus criterion for Zone III of the
Potomac Estuary (0.03 mg/l), the maximum phosphorus loading from |
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• X-31
wastewater effluents within this zone was determined to be 2,000 Ibs/day
™ as shovffi in Table X-6.
• Using phosphorus as a tracer, simulation runs v/ere made to determine
hov; quickly an:," component in the v/astewater discharge could reach the
• proposed estuary water intake. Table X-7 sho7rs that in the extreme case
_ investigated, about L. days would elapse before detection there. For the
* projected year 2020, wastewater discharges and a river flow of 1800 cfs,
• the time would be increased to o days.
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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 Phosphorus at Water
-X-
— •*
10
.,._•*
9
5
8
5
4
an Increase
Intake
With a positive net inflow, there was no measurable intrusion into
the intake.
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•
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. With these levels of inorganic nitrogen,
M some algal growth will occur but nuisance conditions should be pre-
vented. The net estuary inflow, water supply withdrawal rates,
• population benchmarks, and alternative wastewater 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
I freshv/ater inflow of 300 cfs, Subzone I-a can receive and adequately
assimilate 1,000 Ibs/day of nitrogen from wastewater effluents. If
I 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.
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JMlTJttUiJUM IrUaUUNUt) J?Utt miUMAU JliJ'l'UAltl •
Freshwater Inflow = 300 cfs (after water supply diversion) •
Table X-8
NITROGEN LOADINGS FOR POTOMAC ESTUARY
§2Q§. Allowable Nitrogen •
(Ibs/day) |
I-a 1000 _
I-b 300* "
I-c 3400 •
II 5800
III 9000 |
I
The loading in this zone is sensitive to waste flow as des-
cribed in the text of this report. M
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1
1
1
1
1
1
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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 vrastewater 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 ffig/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 Guns ton 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-
1
1
1
1
1
1
water effluents to a level approaching the established criteria.
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X-36
For discharges made to the upper end of the embayments for
Alternative I, the maximum allowable nitrogen loadings are:
Piscataway
NITROGEN LOADINGS TO EMBAYMENTS
Gunston Cove
Flow
(mgd)
24
49
79
Maximum
Nitrogen Load
(Ibs/day)
120
170
270
Flow
(mgd)
50
103
170
Maximum
Nitrogen 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,
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X -37
G. CHLORIDE AND TOTAL DISSOLVED SOLIDS SIMULATIONS
1. Estuary V/ater 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 (1930-1931)
• 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 irainly a func-
tion of freshwater inflow rate and duration. The November 193-
profile shows the farthest upstream intrusion as a result of prolonged
low flows of less than 700 cfs from July through Ilovejvber. Al-Vbo'.rjr
• the drought conditions in September 1966 were more severe vlt: flo-s
of approximately 220 cfs, the duration »r;as shorter end ".-;ncG vise
• intrusion was not as great.
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FIGURE X-9
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• X-39
_ Using four historic low-flow conditions, the rate of intrusion was
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calculated as follows :
• Flows Upgtream 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 inflow on
the rate of the chloride intrusion from the Chesapeake Bay.
The intrusion of chlorides and total dissolved solids was simu-
• lated using the F.YQA. Dynamic Estuary Quality Model. For Alternatives I
and IV, the simulations were made assuning the following freshwater
| inflows and water supply withdrawals:
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« * Negative net flow represents withdrawal from estuary for water supply
Freshwater
Inflow at
Greai_Falls
(cfs)
Year 1980 1870
1120
?70
Year 2QQQ 1750
1000
250
Year 2020 1900
1150
400
Water Supply
Withdrawal
(cfs)
870
870
870
1500
1500
1500
2400
2400
2400
Net Flow Into
the Estuary*
(cfs)
+1000
+ 250
~ JOO
+ 250
- 500
-1250
- 500
-1250
-2000
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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 (IDS),
a relationship between TDS and chlorides was established from existing
data as follows:
TDS (mg/1) =1.69 Chlorides (mg/1) + 300
Boundary and loading conditions used in the simulations are itemized
below:
1966 Wedge 1965 Wedge
Chesapeake Bay chloride concentration 11000 mg/1 9000 mg/1
Chesapeake Bay TDS concentration
Freshwater inflow chloride concentration
Freshwater inflow TDS concentration
Wastewater TDS concentration*
18000 mg/1 14000 mg/1
30 mg/1
160 mg/1
300 mg/1
25 mg/1
40 mg/1
240 mg/1
15 mg/1
160 mg/1
300 mg/1
25 mg/1
40 mg/1
240 mg/1
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,
* The total TDS increase from water intake to wastewater discharge is
currently about 140 mg/1
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• X-41
I 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
I [45] in their preliminary report on the feasibility of the Potomac Estuary
as a supplemental water 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
I 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,
I 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:
Year Consumptive Loss
I (mgd)
1966* 44
- 1980 83
I 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
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X~42 I
This increased downstream discharge, coupled with the above increased
•
consumptive loss will reduce the net seaward flov; in the upper estuary
even without any water supply r/ithdrawal. •
2. The number of days that the estuary can be used for water supply
depends mainly on (a) duration and magnitude of drought conditions , •
(b) location of vrastewater treatment facility discharges, and (c) position
of the salt wedge before low-flov; conditions begin. •
3. The effect of the incremental increase in TDS in the ?;astewater •
on the concentration at Chain Bridge is not significant for the upper or
lower wedge positions for Alternative IV. The number of days that the •
estuary could be used for a v/ater 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 v/astewater •
discharge locations (Table X-9).
For the upper ^7edge position, as given in Table X-10, the effect of I
the concentration of TDS in the effluent is wore significant especially
for Alternative I and the year 2020. The tine 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 TDS criterion of 500 rig/1 in the blended water, •
Alternative I, and with less than 400 cfs coming over Great Falls before
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X-43
water supply withdrawal, the estuary could be used for water supply
for the following periods :
Year 40 mg/1 Increment.
(days of use)
1980 > 166
2000 90
2020 45
This reduction in usage between 1980 and 2020 is
240 mg/1 Increment
(days of use)
>166
35
15
primarily the result
of increased incursion due to reduced net seaward flow and increased
consumptive losses . For the lower position or the July 7-8, 1968,
location of the wedge and the other conditions given above, the estuary
could be used for water supply for the following
Year 40 mg/1 Increment
(days of use)
1980 > 166
2000 140
2020 95
The above reduction with time again reflects the
discharges and the increasing consumptive losses
periods :
240 ..mg/1 Increment
(days of use)
>166
45
20
increasing downstream
e
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
period) for both chlorides and TQ3 for all three
years 1980, 2000, and 2020.
of the simulation
population benchmark
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X-44 m
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 DAYS OF USE OF ESTUARY
I
Freshwater Inflc
Before
Water Supply
Withdrawal
(cfs)
400
1100
1800
yw Alternative I
Water Use Increment
of TDS
40 mg/1
( days )
45
>166
>l66
240 mg/1
( days )
15
42
>166
Alternative IV
Water Use Increment
of TE6
40 mg/1
( days )
18
>166
>166
240 mg/1
(days)
18
41
>166
since use of the estuary for water supply purposes is dependent on the
location and distribution of wastewater discharges.
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7. Since the projected water supply needs for the year 2020
cannot be met by either the upper basin with seven reservoirs or the m
estuary alone, both sources will be needed to supply the water needs •
for the Washington metropolitan area.
8. It is necessary to coordinate both the water supply and •
vrastewater treatment requirements for planning in the Washington area
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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 2000
Alt. I Alt. IV Alt. I Alt. IV
Freshwater Flow* 1000 cfs 250 cfs
Water Use Increment 40 mg/1 of TDS
TDS ( 500) mg/1 > 166 >l66 >l66 >l66
TDS (1000) mg/1 >166 >l66 > 166 >l66
TDS (1500) mg/1 > 166 > 166 >l66 >l66
Water Use Increment 240 mg/1 of TDS
TDS ( 500) mg/1 > 166 > 166 >l66 >l66
TDS (1000) mg/1 >166 >l66 > 166 >l66
TDS (1500) mg/1 > 166 >l66 >l66 >l66
Freshwater Flow 250 cfs -500 cfs
Water Use Increment 40 mg/1 of TDS
TDS ( 500) mg/1 >l66 >l66 >l66 12A
TDS (1000) mg/1 >166 >166 >166 >l66
TDS (1500) mg/1 >l66 >l66 >l66 >l66
Water Use Increment 240 mg/1 of TDS
TDS ( 500) mg/1 >l66 >l66 >l66 123
TDS (1000) mg/l >l66 >l66 >l66 >166
TDS (1500) mg/1 >l66 > 166 >l66 >l66
Freshwater Flow -500 cfs -1250 cfs
"/VB ter Use Increment 40 mg/1 of TDS
TDS ( 500) mg/1 >i66 118 130 58
TDS (1000) mg/1 >166 >l66 >l66 88
TDS (1500) mg/1 >l66 > 166 >l66 107
Water Use Increment 240 mg/1 of TDS
TDS ( 500) mg/1 83 117 126 57
TDS (1000) mg/1 >166 160 147 87
TDS (1500) mg/1 > 166 > 166 > 166 106
* Inflow to estuary after water supply withdrawal
2020
Alt. I
-500
>166
>166
>166
>166
>166
>166
-1250
>166
>166
>166
32
>166
>166
-2000
84
130
159
15
130
159
Alt. IV
cfs
132
>166
>166
162
>166
>l66
cfs
63
100
126
60
97
122
cfs
43
68
86
43
68
86
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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
TDS ( 500) mg/1 >l66 >l66
TDS (1000) mg/1 >166 >166
TDS (1500) mg/1 >l66 >l66
Water Use Increment 240 mg/1 of TDS
TDS ( 500) mg/1 >l66 >l66
TDS (1000) mg/1 >166 >166
TDS (1500) mg/1 >l66 >l66
Freshwater Flow 250 efs
Y/ater 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
Water Use Increment 240 mg/1 of TDS
IDS ( 500) mg/1 >166 >166
IDS (1000) mg/1 >166 >166
TDS (1500) .mg/1 >l66 >l66
.Freshwater Flow -500 cfs
Water Use Increment 40 mg/1 of TDS
7.DS ( 500) mg/1 >166 118
TDS (1000) mg/1 >166 >166
TDS (1500) mg/1 >l66 >l66
Water Use Increment 240 mg/1 of TDS
TDS ( 500) mg/1 83 11?
TDS (1000) mg/1 >166 160
TDS (1500) mg/1 >l66 >l66
* Inflow to estuary after water supply
2000
Alt. I
250
>166
>l66
>l66
>166
>166
>166
-500
>166
>166
>166
>166
>166
>l66
-1250
130
>166
>166
126
147
> 166
withdrawal
Alt. IV
cfs
>166
>166
>166
>l66
>166
>166
cfs
124
>166
>166
123
>166
>l66
cfs
58
88
107
57
87
106
2020
Alt. I
-500
>166
>166
>166
> 166
>166
>166
-1250
>166
>166
>l66
32
> 166
>166
-2000
84
130
159
15
130
159
Alt. IV
cfs
132
>166
>166
162
> 166
>166
cfs
63
100
126
60
97
122
cfs
43
68
So
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X-47
2. Direct Reuse of Treated Wastewater
In the system where treated waste-water 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, sijnulations were made with the direct
reuse system to determine the rate of buildup of both chlorides and TD6.
The results of these simulations for various flow conditions are presented
below:
Equilibrium Concentrations
Water from
Upper Basin
(cfs)
400
1150
1900
Water from
Direct Reuse
(cfs)
2000
1250
500
Chlorides max.
Concentration
(mg/D
140
42
22
40 mg/1 Of
TDS Increase
(mg/1)
360
203
171
240 mg/1 of
TE6 Increase
(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.
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X-48 I
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 TQS 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 seven-day-low-flow with a recurrence interval •
of once-in-50-years) or with approximately 70 percent of the water •
supply from renovated wastewater, the maximum TEG buildup would have
to be restricted to 140 mg/1. As reported earlier, this is the current I
buildup in the entire water use system.
Based on data obtained from the AWT pilot plant operation at •
Blue Plains [46], the TDS, 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 I
of the AWT treatment facilities, the 140 mg/1 increment can readily be
maintained. 8
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 I
spills, urban runoff, storm and combined sewer overflows with respect
to water supply is eliminated, I
(3) Restriction on the location of wastewater facilities with m
respect to water supply needs is eliminated,
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X-49
(4) With proper planning, the need for massive wastewater
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• 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.
B (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„
tm 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,
I a watershed between Baltimore and Washington.
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•
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
I plant at Blue Plains, Bishop [46] indicates that the following removal
rates can be anticipated from April to November (y/inter 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,
I (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
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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.
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• XI-3
B. WASTEIATER 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 mg/l). Capital costs and operation and maintenance (0 & M) costs
I 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 [48]. Where necessary, these costs were adjusted to reflect
• mid-1970 engineering indexes.
Cost data for specific years were determined by a computer sjrstems
I 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
• operation schemes included:
(l) Expenditures for new construction required in 1970, 1980, and
I 2000 are based upon design for conditions 10 or 20 years hence.
(2) In the case of existing treatment plants, construction of AWT
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units would begin in 1970 with 0 & M cost accruing from that time.
Other plants were assumed to be constructed in I960.
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u
UJ
0
Q
D
Q
U
1
U
p
V)
"1VO 0001/» - J.SOD J.N3WXV3dJ.
8 2
» o I
°. E
- O ~
• ; 0) ^
t • o-
u • .
« r -i.
_
8 !
" 8
j 2
* — f-
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s ^
8 P
o
o
O -^
g -o
o
x $ - J.SOD TVJJdVD
o
FIGURE Xl-l
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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
I 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
I 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
I time frame.
(7) The amortization of capital costs was assumed over a 20-year
I period with an interest rate of 5-1/8 percent.
m 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
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XI-6
population of six million people reduces to approximately $11 per person
per year, \7ith 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 (l) 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 $6 million from 2000-2020 can be realized.
Continued studies will be required to further define the temporal removal
requirements for nitrogen.
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Table XI -1
TOTAL WASTEWATER TREATMENT COST
1970-2020
Alternative III
Unit Process
Primary -secondary
Biological nitrification
Biological denitrification
Lime clarification
Dual media filtration
Effluent Aeration
Chlorination
Subtotal
Activated Carbon
Total
* Total present worth cost
expansion cost for Blue
TRY*
($ x 106)
457
247
133
370
101
10
22
1,340
360
1,700
TAAC**
($ x 106)
13.5
13.8
9.4
20.6
5.7
0.6
1.2
$64.8
20.1
$84.9
includes proposed secondary treatment
Plains
*•* Total average annual cost including operation
cost based on 12 months of operation
and maintenance
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Table XI-2
INITIAL CAPITAL CONSTRUCTION
AND
OPERATION AND MAINTENANCE COSTS
1970-1980, 1980-2000, and 2000-2020 Time Periods
UnitProcess
Primary-secondary
Biological nitrification
Biological denitrification
Lime clarification
Dual media filtration
Chlorination
Effluent aeration
Subtotal
Activated carbon
Total
1970-1980
Capital Other
1980-
Capital
($xlQ6) ($x!03) ($xlO&)
236.11 4H1.48 129.71
70.64 3968.66 84.53
62.11 427.29 71.84
69.31 8661.66 81.96
27.22 889.15 35.02
0.37 761.59 2.00
2.91 226.61 4.35
-2000
Other
($x!03)
7413.07
7097.46
759.32
15573.46
3064.69
1328.37
407.73
468.67 19176.44 409.49 35644.10
101.96 5931.92 118.38 10535.54
2000
Capital
($x!06)
371.11
167.63
148.24
166.12
66.09
3.55
6.90
929.64
243.40
-2020
Other •
($x!03) I
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 72372.97
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1
The tabulation below is a reduction of the initial
operation and maintenance costs to a per capita basis:
Item 1970-1980 1980-?000
Average Population 3,350,000 5,350,000
Total Initial Capital
Cost/Time Period $570,000,000 $528,000,000
Capital Cost/Person/Year $17.0 $4.9
0 & M CostAear $25,100,000 $46,200,000
0 & M Cost/Person/Year $7.5 $8.6
Total Cost/Person/Year $24.5 $13.5
The above summary, which does include replacement cost,
XI -9
capital and
2000-2020
8,000,000
$1,173,000,000
$7.3
$72,400,000
$9.1
$16.4
indicates that
the cost of Y/astewater treatment in the upper Potomac Estuary is about
$13 to $24/per person/per year. This expenditure, which includes the
1
1
1
1
1
1
1
1
cost of the activated carbon process, will renovate the
chemical and microbiological qualities meeting drinking
water to the
water standards
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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
I 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
B 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.
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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
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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.
I These criteria are approximately an order of magnitude lower than the
corresponding criteria for nitrogen. Because of these stringent criteria,
I 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.
m 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
im 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.
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FIGURE XII-I
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XII-5
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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
I As presented earlier in this chapter, the necessity for nitrogen
control in wastewater discharges to enhance the dissolved oxygen in
I 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,
I controllability becomes a significant factor.
Mathematical model studies were used to investigate the effects
I of seasonal and continuous nitrogen removal at the v/astewater
m 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).
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The controllable nitrogen from the wastewater 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
I estuary exceed 15°C, there may be a need for continuous control by
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XII-7
the year 2000.
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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 TES 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.
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- XII -9
2. Wastewater Discharges to the Embayments
I 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.
I 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,
I 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
I consideration of effluent dispersion devices to minimize local effects.
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I
* 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.
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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 [1].
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
substantually, 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.
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- 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 fleinhardt [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
I 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.
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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
M 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
I 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
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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 v/ere 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. Tomanio 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
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REFERENCES
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-------
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39. Metropolitan Washington Council of Governments, "Population Estimates
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at the Economic Commission for Europe, Czechoslovakia, May 2-18, 1971.
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52. Jaworski, N. A., Donald \V. Lear, Jr., Orterio Villa, Jr., "Nutrient
Management in the Potomac Estuary," Presented at the American Society
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January 19, 1971.
54. Thomann, Rovert V., "Mathematical Model for Dissolved Oxygen, Journal of
the Sanitary Engineering Division. ASCE. Vol. 89, No. SA5, October 1963.
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