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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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* 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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39. Metropolitan Washington Council of Governments, "Population Estimates
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52. Jaworski, N. A., Donald \V. Lear, Jr., Orterio Villa, Jr., "Nutrient
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