Technical Reports 37-45 Volume 5

U.S. ENVIRONMENTAL PROTECTION AGENCY Annapolis Field Office Annapolis Science Center Annapolis, Maryland 21401 TECHNICAL REPORTS Volume 5 ------- ------- Table of Contents Volume 5 37 Nutrient Transport and Dissolved Oxygen Budget Studies in the Potomac Estuary 39 Preliminary Analyses of the Wastewater and Assimilation Capacities of the Anacostia Tidal River System 41 Current Water Quality Conditions and Investigations in the Upper Potomac River Tidal System 43 Physical Data of the Potomac River Tidal System Including Mathematical Model Segmentation 45 Nutrient Management in the Potomac Estuary ------- PUBLICATIONS U.S. ENVIRONMENTAL PROTECTION AGENCY REGION III ANNAPOLIS FIELD OFFICE* VOLUME 1 Technical Reports 5 A Technical Assessment of Current Water Quality Conditions and Factors Affecting Water Quality in the Upper Potomac Estuary 6 Sanitary Bacteriology of the Upper Potomac Estuary 7 The Potomac Estuary Mathematical Model 9 Nutrients in the Potomac River Basin 11 Optimal Release Sequences for Water Quality Control in Multiple Reservoir Systems VOLUME 2 Technical Reports 13 Mine Drainage in the North Branch Potomac River Basin 15 Nutrients in the Upper Potomac River Basin 17 Upper Potomac River Basin Water Quality Assessment VOLUME 3 Technical Reports 19 Potomac-Piscataway Dye Release and Wastewater Assimilation Studies 21 LNEPLT 23 XYPLOT 25 PLOT3D * Formerly CB-SRBP, U.S. Department of Health, Education, and Welfare; CFS-FWPCA, and CTSL-FUQA, Middle Atlantic Region, U.S. Department of the Interior ------- VOLUME 3 (continued) Technical Reports 27 Water Quality and Wastewater Loadings - Upper Potomac Estuary during 1969 VOLUME 4 Technical Reports 29 Step Backward Regression 31 Relative Contributions of Nutrients to the Potomac River Basin from Various Sources 33 Mathematical Model Studies of Water Quality in the Potomac Estuary 35 Water Resource - Water Supply Study of the Potomac Estuary VOLUME 5 Technical Reports 37 Nutrient Transport and Dissolved Oxygen Budget Studies in the Potomac Estuary 39 Preliminary Analyses of the Wastewater and Assimilation Capacities of the Anacostia Tidal River System 41 Current Water Quality Conditions and Investigations in the Upper Potomac River Tidal System 43 Physical Data of the Potomac River Tidal System Including Mathematical Model Segmentation 45 Nutrient Management in the Potomac Estuary VOLUME 6 Technical Reports 47 Chesapeake Bay Nutrient Input Study 49 Heavy Metals Analyses of Bottom Sediment in the Potomac River Estuary ------- VOLUME 6 (continued) Technical Reports 51 A System of Mathematical Models for Water Quality Management 52 Numerical Method for Groundwater Hydraulics 53 Upper Potomac Estuary Eutrophication Control Requirements 54 AUT0-QUAL Modelling System Supplement AUT0-QUAL Modelling System: Modification for to 54 Non-Point Source Loadings VOLUME 7 Technical Reports 55 Water Quality Conditions in the Chesapeake Bay System 56 Nutrient Enrichment and Control Requirements in the Upper Chesapeake Bay 57 The Potomac River Estuary in the Washington Metropolitan Area - A History of its Water Quality Problems and their Solution VOLUME 8 Technical Reports 58 Application of AUT0-QUAL Modelling System to the Patuxent River Basin 59 Distribution of Metals in Baltimore Harbor Sediments 60 Summary and Conclusions - Nutrient Transport and Accountability in the Lower Susquehanna River Basin VOLUME 9 Data Reports Water Quality Survey, James River and Selected Tributaries - October 1969 Water Quality Survey in the North Branch Potomac River between Cumberland and Luke, Maryland - August 1967 ------- VOLUME 9 (continued) Data Reports Investigation of Water Quality in Chesapeake Bay and Tributaries at Aberdeen Proving Ground, Department of the Army, Aberdeen, Maryland - October-December 1967 Biological Survey of the Upper Potomac River and Selected Tributaries - 1966-1968 Water Quality Survey of the Eastern Shore Chesapeake Bay, Wicomico River, Pocomoke River, Nanticoke River, Marshall Creek, Bunting Branch, and Chincoteague Bay - Summer 1967 Head of Bay Study - Water Quality Survey of Northeast River, Elk River, C & D Canal, Bohemia River, Sassafras River and Upper Chesapeake Bay - Summer 1968 - Head ot Bay Tributaries Water Quality Survey of the Potomac Estuary - 1967 Water Quality Survey of the Potomac Estuary - 1968 Wastewater Treatment Plant Nutrient Survey - 1966-1967 Cooperative Bacteriological Study - Upper Chesapeake Bay Dredging Spoil Disposal - Cruise Report No. 11 VOLUME 10 Data Reports 9 Water Quality Survey of the Potomac Estuary - 1965-1966 10 Water Quality Survey of the Annapolis Metro Area - 1967 11 Nutrient Data on Sediment Samples of the Potomac Estuary 1966-1968 12 1969 Head of the Bay Tributaries 13 Water Quality Survey of the Chesapeake Bay in the Vicinity of Sandy Point - 1968 14 Water Quality Survey of the Chesapeake Bay in the Vicinity of Sandy Point - 1969 ------- VOLUME 10(continued) Data Reports 15 Water Quality Survey of the Patuxent River - 1967 16 Water Quality Survey of the Patuxent River - 1968 17 Water Quality Survey of the Patuxent River - 1969 18 Water Quality of the Potomac Estuary Transects, Intensive and Southeast Water Laboratory Cooperative Study - 1969 19 Water Quality Survey of the Potomac Estuary Phosphate Tracer Study - 1969 VOLUME 11 Data Reports 20 Water Quality of the Potomac Estuary Transport Study 1969-1970 21 Water Quality Survey of the Piscataway Creek Watershed 1968-1970 22 Water Quality Survey of the Chesapeake Bay in the Vicinity of Sandy Point - 1970 23 Water Quality Survey of the Head of the Chesapeake Bay Maryland Tributaries - 1970-1971 24 Water Quality Survey of the Upper Chesapeake Bay 1969-1971 25 Water Quality of the Potomac Estuary Consolidated Survey - 1970 26 Water Quality of the Potomac Estuary Dissolved Oxygen Budget Studies - 1970 27 Potomac Estuary Wastewater Treatment Plants Survey 1970 28 Water Quality Survey of the Potomac Estuary Embayments and Transects - 1970 29 Water Quality of the Upper Potomac Estuary Enforcement Survey - 1970 ------- 30 31 32 33 34 Appendix to 1 Appendix to 2 3 4 VOLUME 11 (continued) Data Reports Water Quality of the Potomac Estuary - Gilbert Swamp and Allen's Fresh and Gunston Cove - 1970 Survey Results of the Chesapeake Bay Input Study - 1969-1970 Upper Chesapeake Bay Water Quality Studies - Bush River, Spesutie Narrows and Swan Creek, C & D Canal, Chester River, Severn River, Gunpowder, Middle and Bird Rivers - 1968-1971 Special Water Quality Surveys of the Potomac River Basin Anacostia Estuary, Wicomico .River, St. Clement and Breton Bays, Occoquan Bay - 1970-1971 Water Quality Survey of the Patuxent River - 1970 VOLUME 12 Working Documents Biological Survey of the Susquehanna River and its Tributaries between Danville, Pennsylvania and Conowingo, Maryland Tabulation of Bottom Organisms Observed at Sampling Stations during the Biological Survey between Danville, Pennsylvania and Conowingo, Maryland - November 1966 Biological Survey of the Susquehanna River and its Tributaries between Cooperstown, New York and Northumberland, Pennsylvnaia - January 1967 Tabulation of Bottom Organisms Observed at Sampling Stations during the Biological Survey between Cooperstown, New York and Northumberland, Pennsylvania - November 1966 VOLUME 13 Working Documents Water Quality and Pollution Control Study, Mine Drainage Chesapeake Bay-Delaware River Basins - July 1967 Biological Survey of Rock Creek (from Rockville, Maryland to the Potomac River) October 1966 ------- VOLUME 13 (continued) Working Documents 5 Summary of Water Quality and Waste Outfalls, Rock Creek in Montgomery County, Maryland and the District of Columbia - December 1966 6 Water Pollution Survey - Back River 1965 - February 1967 7 Efficiency Study of the District of Columbia Water Pollution Control Plant - February 1967 VOLUME 14 Working Documents 8 Water Quality and Pollution Control Study - Susquehanna River Basin from Northumberland to West Pittson (Including the Lackawanna River Basin) March 1967 9 Water Quality and Pollution Control Study, Juniata River Basin - March 1967 10 Water Quality and Pollution Control Study, Rappahannock River Basin - March 1967 11 Water Quality and Pollution Control Study, Susquehanna River Basin from Lake Otsego, New York, to Lake Lackawanna River Confluence, Pennsylvania - April 1967 VOLUME 15 Working Documents 12 Water Quality and Pollution Control Study, York River Basin - April 1967 13 Water Quality and Pollution Control Study, West Branch, Susquehanna River Basin - April 1967 14 Water Quality and Pollution Control Study, James River Basin - June 1967 15 Water Quality and Pollution Control Study, Patuxent River Basin - May 1967 ------- VOLUME 16 Working Documents 16 Water Quality and Pollution Control Study, Susquehanna River Basin from Northumberland, Pennsylvania, to Havre de Grace, Maryland - July 1967 17 Water Quality and Pollution Control Study, Potomac River Basin - June 1967 18 Immediate Water Pollution Control Needs, Central Western Shore of Chesapeake Bay Area (Magothy, Severn, South, and West River Drainage Areas) July 1967 19 Immediate Water Pollution Control Needs, Northwest Chesapeake Bay Area (Patapsco to Susquehanna Drainage Basins in Maryland) August 1967 20 Immediate Water Pollution Control Needs - The Eastern Shore of Delaware, Maryland and Virginia - September 1967 VOLUME 17 Working Documents 21 Biological Surveys of the Upper James River Basin Covington, Clifton Forge, Big Island, Lynchburg, and Piney River Areas - January 1968 22 Biological Survey of Antietam Creek and some of its Tributaries from Waynesboro, Pennsylvania to Antietam, Maryland - Potomac River Basin - February 1968 23 Biological Survey of the Monocacy River and Tributaries from Gettysburg, Pennsylvania, to Maryland Rt. 28 Bridge Potomac River Basin - January 1968 24 Water Quality Survey of Chesapeake Bay in the Vicinity of Annapolis, Maryland - Summer 1967 25 Mine Drainage Pollution of the North Branch of Potomac River - Interim Report - August 1968 26 Water Quality Survey in the Shenandoah River of the Potomac River Basin - June 1967 27 Water Quality Survey in the James and Maury Rivers Glasgow, Virginia - September 1967 ------- VOLUME 17 (continued) Working Documents 28 Selected Biological Surveys in the James River Basin, Gillie Creek in the Richmond Area, Appomattox River in the Petersburg Area, Bailey Creek from Fort Lee to Hopewell - April 1968 VOLUME 18 Working Documents 29 Biological Survey of the Upper and Middle Patuxent River and some of its Tributaries - from Maryland Route 97 Bridge near Roxbury Mills to the Maryland Route 4 Bridge near Wayson's Corner, Maryland - Chesapeake Drainage Basin - June 1968 30 Rock Creek Watershed - A Water Quality Study Report March 1969 31 The Patuxent River - Water Quality Management - Technical Evaluation - September 1969 VOLUME 19 Working Documents Tabulation, Community and Source Facility Water Data Maryland Portion, Chesapeake Drainage Area - October 1964 Waste Disposal Practices at Federal Installations Patuxent River Basin - October 1964 Waste Disposal Practices at Federal Installations Potomac River Basin below Washington, D.C.- November 1964 Waste Disposal Practices at Federal Installations Chesapeake Bay Area of Maryland Excluding Potomac and Patuxent River Basins - January 1965 The Potomac Estuary - Statistics and Projections - February 1968 Patuxent River - Cross Sections and Mass Travel Velocities - July 1968 ------- VOLUME 19 (continued) Working Documents Wastewater Inventory - Potomac River Basin - December 1968 Wastewater Inventory - Upper Potomac River Basin - October 1968 VOLUME 20 Technical Papers - 1 A Digital Technique for Calculating and Plotting Dissolved Oxygen Deficits 2 A River-Mile Indexing System for Computer Application in Storing and Retrieving Data (unavailable) 3 Oxygen Relationships in Streams, Methodology to be Applied when Determining the Capacity of a Stream to Assimilate Organic Wastes - October 1964 4 Estimating Diffusion Characteristics of Tidal Waters - May 1965 5 Use of Rhodamine B Dye as a Tracer in Streams of the Susquehanna River Basin - April 1965 6 An In-Situ Benthic Respirometer - December 1965 7 A Study of Tidal Dispersion in the Potomac River February 1966 8 A Mathematical Model for the Potomac River - what it has done and what it can do - December 1966 9 A Discussion and Tabulation of Diffusion Coefficients for Tidal Waters Computed as a Function of Velocity February 1967 10 Evaluation of Coliform Contribution by Pleasure Boats July 1966 ------- VOLUME 21 Technical Papers 11 A Steady State Segmented Estuary Model 12 Simulation of Chloride Concentrations in the Potomac Estuary - March 1968 13 Optimal Release Sequences for Water Quality Control in Multiple-Reservoir Systems - 1968 VOLUME 22 Technical Papers Summary Report - Pollution of Back River - January 1964 Summary of Water Quality - Potomac River Basin in Maryland - October 1965 The Role of Mathematical Models in the Potomac River Basin Water Quality Management Program - December 1967 Use of Mathematical Models as Aids to Decision Making in Water Quality Control - February 1968 Piscataway Creek Watershed - A Water Quality Study Report - August 1968 VOLUME 23 Ocean Dumping Surveys Environmental Survey of an Interim Ocean Dumpsite, Middle Atlantic Bight - September 1973 Environmental Survey of Two Interim Dumpsites, Middle Atlantic Bight - January 1974 Environmental Survey of Two Interim Dumpsites Middle Atlantic Bight - Supplemental Report - October 1974 Effects of Ocean Disposal Activities on Mid- continental Shelf Environment off Delaware and Maryland - January 1975 ------- VOLUME 24 1976 Annual Current Nutrient Assessment - Upper Potomac Estuary Current Assessment Paper No. 1 Evaluation of Western Branch Wastewater Treatment Plant Expansion - Phases I and II Situation Report - Potomac River Sediment Studies in Back River Estuary, Baltimore, Maryland Technical Distribution of Metals in Elizabeth River Sediments Report 61 Technical A Water Quality Modelling Study of the Delaware Report 62 Estuary ------- NUTRIENT TRANSPORT AND DISSOLVED OXYGEN BUDGET STUDIES IN THE POTOMAC ESTUARY October 1972 Technical Report 37 Annapolis Field Office Region III Environmental Protection Agency ------- ------- Annapolis Field Office Region III Environmental Protection Agency NUTRIENT TRANSPORT AND DISSOLVED OXYGEN BUDGET STUDIES IN THE POTOMAC ESTUARY Technical Report 37 October 1972 Leo 0. Clark Norbert A. Jaworski* Supporting Staff: Johan A. Aalto, Director, AFO Orterio Villa, Jr., Chief, Laboratory Development Section * Environmental Protection Agency National Environmental Research Center Corvallis, Oregon ------- ------- TABLE OF CONTENTS Page PREFACE iii LIST OF TABLES vi LIST OF FIGURES vii Chapter I. INTRODUCTION I - 1 A. PURPOSE AND SCOPE I - 1 B. ACKNOWLEDGEMENTS 1-3 II. SUMMARY AND CONCLUSIONS II - 1 III. DESCRIPTION OF STUDY AREA Ill - 1 IV. SOURCES OF NUTRIENTS AND OXYGEN DEMANDING SUBSTANCES . IV - 1 A. WASTEWATER LOADINGS IV - 1 B. CONTRIBUTIONS FROM THE UPPER POTOMAC RIVER BASIN . IV - 3 C. SUBURBAN AND URBAN RUNOFF IV - 7 V. FRAMEWORK FOR ANALYSIS V - 1 A. WATER QUALITY DATA V - 1 B. CHEMICAL, PHYSICAL AND BIOLOGICAL REACTIONS. . . V - 3 1. Nitrogen V - 3 2. Phosphorus V-6 C. MATHEMATICAL MODELING TECHNIQUES V - 9 VI. NITROGEN ASSIMILATION AND TRANSPORT VI - 1 A. TEMPORAL AND SPATIAL DISTRIBUTION VI - 1 B. DETERMINATION OF REACTION RATES AND TEMPERATURE EFFECTS VI - 7 1. Nitrification VI - 7 2. Algal Uptake VI - 23 IV ------- PREFACE The ability to simulate, mathematically, the historical dissolved oxygen (DO) distribution in a watercourse is quite an achievement, especially when most of the known components of the DO budget are quantitatively defined and incorporated in the analysis. This ability is in fact required to predict future changes, including standards compliance, in the dissolved oxygen content of a lake, stream, or estuary due to municipal or industrial growth. While the classical Streeter-Phelps study of the Ohio River in 1924 initially established the basic relationships governing dissolved oxygen, the evaluation of the oxygen budget is no longer based solely on the biochemical oxyged demand (BOD) and reaeration. Sanitary engineers have intruded into the biologist's domain by attempts to determine in mathematical terms the effects of nutrient materials, specifically nitrogen and phosphorus, on the density and extent of algal blooms and the algae's subsequent effect on the DO budget. A strong interdependence exists among nitrogen, phosphorus, algae and dissolved oxygen, and although only a rudimentary approach was ventured, the Annapolis Field Office (AFO) of the Environmental Protection Agency (EPA) has mathematically modeled this interrelation- ship in the upper Potomac Estuary. ------- TABLE OF CONTENTS Page Chapter VI. NITROGEN ASSIMILATION AND TRANSPORT (Continued) C. SIMULATION OF NITROGEN TRANSPORT THROUGH AN ANNUAL CYCLE VI - 25 D. CHLOROPHYLL PREDICTIONS BASED ON NITROGEN ASSIMILATION BY THE BIOMASS VI - 31 VII. PHOSPHORUS ASSIMILATION AND TRANSPORT VII - 1 A. TEMPORAL AND SPATIAL DISTRIBUTION VII - 1 B. DETERMINATION OF LOSS RATE AND TEMPERATURE EFFECTS VII - 5 C. SIMULATION OF PHOSPHORUS TRANSPORT THROUGH AN ANNUAL CYCLE VII - 21 D. CHLOROPHYLL PREDICTIONS BASED ON PHOSPHORUS ASSIMILATION BY THE BIOMASS VII - 27 VIII. DISSOLVED OXYGEN BUDGET VIII - 1 A. FORMULATION OF SOURCES AND SINKS VIII - 1 B. SIMULATION AND MODEL VERIFICATION STUDIES . . . VIII - 6 C. SENSITIVITY ANALYSIS VIII - 17 1. Effects of Oxidation Rates (Carbon and Nitrogen) VIII - 17 2. Effects of Photosynthesis and Respiration Rates VIII - 18 3. Effects of Benthic Demand Rate VIII - 19 4. Effects of Reaeration Rate VIII - 19 D. NUTRIENT REGENERATION - SPECIAL DO MODEL .... VIII - 26 IX. ADDITIONAL STUDY REQUIREMENTS IX - 1 BIBLIOGRAPHY ------- LIST OF TABLES Chapter Page IV - 1 Wastewater Loadings to the Upper Potomac Estuary and Tributaries IV - 2 IV - 2 Upper Potomac River Basin Contributions (Above Great Falls) February 1969 through February 1970 . IV - 6 IV - 3 Urban and Suburban Runoff Contributions to Upper Potomac Estuary IV - 8 VIII - 1 Oxygen Production and Respiration Rate Survey, Upper and Middle Potomac Estuary, 1970 . . . . VIII - 4 ------- LIST OF FIGURES Number III - IV - V - V - V - VI - VI - VI - VI - VI - VI - VI - VI - VI - VI - VI - VI - 1 1 1 2 3 1 2 3 4 5 6 7 8 9 10 11 12 Description Potomac Estuary Location Map Nutrient Concentrations, Potomac River at Great Falls Simplified Nitrogen Cycle Simplified Phosphorus Cycle Simplified DO Budget for Dynamic Estuary Model • Ammonia Nitrogen Isopleth, Potomac Estuary, 1969-70 Data Nitrite + Nitrate Nitrogen Isopleth, Potomac Estuary, 1969-70 Data Organic Nitrogen Isopleth, Potomac Estuary, 1969-70 Data Nitrogen Concentration, Potomac Estuary, September 6-13, 1966 Nitrogen Concentration, Potomac Estuary, August 31 - September 23, 1965 Nitrogen Concentration, Potomac Estuary, October 7, 1968 Nitrogen Concentration, Potomac Estuary, January 25, 1966 Nitrogen Concentration, Potomac Estuary, September 28-30, 1970 Nitrogen Concentration, Potomac Estuary, September 20-21 ,1967 Nitrogen Concentration, Potomac Estuary, August 5, 1968 . Nitrogen Concentration, Potomac Estuary, October 15-16, 1969 Nitrogen Concentration, Potomac Estuary, August 19-22, 1968 Page III - IV - V - V - V - VI - VI - VI - VI - VI - VI - VI - VI - VI - VI - VI - VI - 3 5 5 8 11 4 5 6 9 10 11 12 13 14 15 16 17 VII ------- LIST OF FIGURES Number Description Page VI - 13 Nitrogen Concentration, Potomac Estuary, December 9, 1969 VI - 18 VI - 14 Nitrogen Concentration, Potomac Estuary, November 24, 1969 VI - 19 VI - 15 Nitrogen Concentration, Potomac Estuary, August 12-14, 1969 . VI - 20 VI - 16 Nitrogen Concentration, Potomac Estuary, April 21, 1966 VI - 21 VI - 17 Effect of Temperature on Nitrification Rate, Upper Potomac Estuary VI - 22 VI - 18 Effect of Temperature on Algal Nitrogen Utilization Rate, Upper Potomac Estuary . . VI - 24 VI - 19 Annual Nitrogen Profiles, Potomac Estuary at Hains Point VI - 26 VI - 20 Annual Nitrogen Profiles, Potomac Estuary at Piscataway Creek VI - 27 VI - 21 Annual Nitrogen Profiles, Potomac Estuary at Indian Head VI - 28 VI - 22 Annual Nitrogen Profiles, Potomac Estuary at Maryland Point VI - 29 VI - 23 Annual Nitrogen Profiles, Potomac Estuary at Piney Point VI - 30 VI - 24 Chlorophyll Concentrations, Potomac Estuary, September 6-9, 1966 VI - 33 VI - 25 Chlorophyll Concentrations, Potomac Estuary, October 7, 1968 VI - 34 VI - 26 Chlorophyll Concentrations, Potomac Estuary, September 28-30, 1970 VI - 35 VI - 27 Chlorophyll Concentrations, Potomac Estuary, September 20-21, 1967 VI - 36 vm ------- LIST OF FIGURES Number Description Page VI - 28 Chlorophyll Concentrations, Potomac Estuary, August 5, 1968 VI - 37 VI - 29 Chlorophyll Concentrations, Potomac Estuary, October 15-16, 1969 VI - 38 VI - 30 Chlorophyll Concentrations, Potomac Estuary, August 19-23, 1968 VI - 39 VI - 31 Chlorophyll Concentrations, Potomac Estuary, August 12-14, 1969 VI - 40 VII - 1 Inorganic Phosphorus Isopleth, Potomac Estuary, 1969-70 Data VII - 3 VII - 2 Total Phosphorus Isopleth, Potomac Estuary, 1969-70 Data VII - 4 VII - 3 Phosphorus Concentration, Potomac Estuary, September 6-13, 1966 VII - 6 VII - 4 Phosphorus Concentration, Potomac Estuary, June 30 - July 1, 1969 VII - 7 VII - 5 Phosphorus Concentration, Potomac Estuary, January 25, 1966 VII - 8 VII - 6 Phosphorus Concentration, Potomac Estuary, September 23, 1968 VII - 9 VII - 7 Phosphorus Concentration, Potomac Estuary, September 28 - October 27, 1965 VII - 10 VII - 8 Phosphorus Concentration, Potomac Estuary, October 27, 1969 VII - 11 VII - 9 Phosphorus Concentration, Potomac Estuary, September 20-21, 1967 VII - 12 VII - 10 Phosphorus Concentration, Potomac Estuary, October 15-16, 1969 VII - 13 VII - 11 Phosphorus Concentration, Potomac Estuary, August 19-22, 1968 VII - 14 ------- LIST OF FIGURES Number VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Description Phosphorus Concentration, Potomac Estuary, November 19, 1969 Phosphorus Concentration, Potomac Estuary, December 9, 1969 Phosphorus Concentration, Potomac Estuary, June 9, 1966 Phosphorus Concentration, Potomac Estuary, August 12-19, 1969 Phosphorus Concentration, Potomac Estuary, April 21, 1966 Effect of Temperature on Phosphorus Loss Rate, Upper Potomac Estuary Annual Phosphorus Profiles, Potomac Estuary at Hains Point Annual Phosphorus Profiles, Potomac Estuary at Piscataway Creek Annual Phosphorus Profiles, Potomac Estuary at Indian Head Annual Phosphorus Profiles, Potomac Estuary at Maryland Point Annual Phosphorus Profiles, Potomac Estuary at Piney Point Predicted Chlorophyll Profiles Based Upon Various Phosphorus Assimilation Rates, Upper Potomac Estuary (September 1966) Predicted Chlorophyll Profiles Based Upon Various Phosphorus Assimilation Rates, Upper Potomac Estuary (October 1968) Predicted Chlorophyll Profiles Based Upon Various Phosphorus Assimilation Rates, Upper Potomac Estuary (September 1967) Page VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - VII - 15 16 17 18 19 20 22 23 24 25 26 29 30 31 ------- LIST OF FIGURES Number Description Page VII - 26 Predicted Chlorophyll Profiles Based Upon Various Phosphorus Assimilation Rates, Upper Potomac Estuary (October 1969) ... VII - 32 VIII - 1 Benthic Uptake, Potomac Estuary .... VIII - 5 VIII - 2 Dissolved Oxygen Profiles, Upper Potomac Estuary, September 6-13, 1966 VIII - 8 VIII - 3 Dissolved Oxygen Profiles, Upper Potomac Estuary, June 30 - July 12, 1969 .... VIII - 9 VIII - 4 Dissolved Oxygen Profiles, Upper Potomac Estuary, August 31 - September 23, 1965 • • VIII - 10 VIII - 5 Dissolved Oxygen Profiles, Upper Potomac Estuary, September 20-21, 1967 VIII - 11 VIII - 6 Dissolved Oxygen Profiles, Upper Potomac Estuary, October 15-16, 1969 VIII - 12 VIII - 7 Dissolved Oxygen Profiles, Upper Potomac Estuary, July 22, 1968 VIII - 13 VIII - 8 Dissolved Oxygen Profiles, Upper Potomac Estuary, August 19-22, 1968 VIII - 14 VIII - 9 Dissolved Oxygen Profiles, Upper Potomac Estuary, August 12-14, 1969 VIII - 15 VIII - 10 Dissolved Oxygen Profiles, Upper Potomac Estuary, September 28-30, 1970 VIII - 16 VIII - 11 Effects of Carbonaceous Oxidation Rate, DEM DO Simulations VIII - 20 VIII - 12 Effects of Nitrogenous Oxidation Rate, DEM DO Simulations VIII - 21 VIII - 13 Effects of Photosynthesis Rate, DEM DO Simulations VIII - 22 ------- LIST OF FIGURES Number Description Page VIII - 14 Effects of Respiration Rate, DEM DO Simulations VHI ' 23 VIII - 15 Effects of Benthic Rate, DEM DO Simulations VI11 - 24 VIII - 16 Effects of Reaeration Rate Formulation, DEM DO Simulations VIII - 25 VIII - 17 Special DEM DO Simulation, Upper Potomac Estuary, September 1970 VIII - 28 xn ------- I - 1 CHAPTER I INTRODUCTION A. PURPOSE AND SCOPE The importance of mathematical models as a water quality manage- ment "tool" is widely acknowledged. Models have evolved from the one dimensional steady-state type capable of simulating only relatively conservative constituents such as tracer dye or chlorides to time- dependent models linking BOD and DO and finally to multi-constituent models capable of (1) elaborate "feedback" linkage between the various constituents, (2) not only first-order kinetics but any mathematically describable reaction, and (3) incorporating tidal aspects to permit "real-time" hydraulic and quality predictions. The purpose of this report is to present the approach taken by AFO to model a portion of the nitrogen cycle, phosphorus deposition, and the occurrence of algal blooms as measured by chlorophyll a_; as well as the effects of carbonaceous, nitrogenous, and benthic oxygen demand; algal photosynthesis, respiration and decay; and reaeration on the dissolved oxygen resources in the upper Potomac Estuary. Basically, this approach entailed a feedback model similar to the one proposed by Thomann [1] and a procedure whereby individual reaction rates, based on a visual comparison of observed and simulated data, were estimated. Upon determining the appropriate rates, the models' reliability to predict DO distributions was investigated. The EPA Dynamic Estuary Model [2] was modified to incorporate the necessary reactions describing nitrogen and phosphorus transport and ------- I - 2 most sources and sinks of dissolved oxygen. This model was used pri- marily to simulate short-term, pseudo-steady-state conditions. DECS III, an average tidal model, [3] was used to simulate nitrogen and phosphorus behavior over an annual cycle. Both of these models successfully simulated (1) a tracer dye distribution following a 13-day continuous release and (2) seasonal chlorinity changes in the Potomac Estuary [4] prior to the more complex modeling discussed in this report. In addition, the two models were used to investigate the role of nutrients in the eutrophication process and to establish maximum allowable nutrient and ultimate oxygen demand loadings for different zones of the Potomac Estuary [5]. The entire Potomac Estuary is included in the framework of the mathematical models. Since uncertainties arise when applying either model to the mesohaline portion of the estuary, most of the analyses will pertain to the freshwater region of the Potomac with the major emphasis placed on the critical area immediately downstream from Washington, D. C. ------- I - 3 B. ACKNOWLEDGEMENTS Special recognition has been given to the Steuart Petroleum Company, Piney Point, Maryland, for their extensive cooperation and assistance in performing all sampling during AFO's 1969-70 nutrient transport study of the Potomac Estuary. This report could not have been completed as promptly without such sampling assistance. ------- ------- II - 1 CHAPTER II SUMMARY AND CONCLUSIONS During 1970, the Annapolis Field Office embarked on a mathematical modeling study of the Potomac Estuary utilizing a 1965-70 data base to (1) predict nitrogen and phosphorus distributions during both a relatively short time period (steady-state) and over an annual cycle, (2) define the various reaction rates, including temperature effects, directly influencing nutrient transport, (3) evaluate the role of both nitrogen and phosphorus in the existing eutrophication problem and develop predictive capabilities for algal standing crop, (4) formulate a DO budget model incorporating algal effects in addition to biological oxidation and reaeration and (5) determine the maximum allowable load- ings of nitrogen, phosphorus and carbon (BOD) that will maintain water quality commensurate with existing standards. The findings evolved during data analysis, model development and verification are as follows: 1) There are currently eighteen wastewater treatment facilities in the Washington Metropolitan Area that discharge total BOD5, phosphorus (P) and nitrogen (N) loadings to the upper Potomac Estuary of 143,000 Ibs/day, 25,000 Ibs/day, and 60,000 Ibs/day, respectively. 2) During the period from February 1969 to February 1970 the average nutrient contributions from the upper Potomac River Basin were, phosphorus (as P), 4,580 Ibs/day, and nitrogen (as N), 59,000 Ibs/day. These loadings correspond to an average freshwater flow of 6,900 cfs. ------- II - 2 3) The median loadings contributed from urban and suburban runoff to the upper Potomac Estuary are given below: Parameter Loading (Ibs/day) BOD 12,500 5 Phosphorus (P) 850 Nitrogen (N) 4,070 4) Using weekly nitrogen data collected in the Potomac Estuary from February 1969 to July 1970 the following conclusions were drawn: a) Maximum ammonia concentrations of 2.0 mg/1 were observed on numerous occasions near the major wastewater discharges. A drastic reduction in ammonia, attributable to nitrification, occurred between the Woodrow Wilson Bridge and Indian Head under high temperature con- ditions. b) The reduction in ammonia concentrations were accompanied by high levels of nitrate nitrogen, often approaching 2.0 mg/1. Farther downstream, between Indian Head and Smith Point, a significant decrease in nitrate, due to biological (algal) uptake, occurred during the summer and fall months. c) Organic nitrogen concentrations were extremely high (3.0 mg/1) in the Potomac during the late summer and early fall when algal blooms were profuse. 5) Utilizing the EPA Dynamic Estuary Model and data from thirteen intensive sampling runs conducted under steady-state conditions, nitri- fication rates required for model verification varied from 0.005/day ------- II - 3 to 0.4/day depending on temperature. At 20°C, the nitrification rate was 0,084/day (base e). 6) Reasonable agreement between the thirteen sets of observed nitrate data and model predictions was obtained when algal uptake rates varied from 0.01/day to 0.13/day with a 20°C value of 0.037/day (base e). A definite temperature vs algal uptake rate relationship was again indicated. 7) A modified version of DECS III that incorporated the veri- fied reaction rates and temperature effects discussed above accurately simulated the basic seasonal trends and spatial distributions of ammonia and nitrate nitrogen observed during the period February 1969 to July 1970. 8) A modified version of the EPA Dynamic Estuary Model which con- verted losses of nitrate nitrogen to algal biomass based upon ele- mental composition ratios was used to predict bloom conditions in the Potomac as measured by chlorophyll a^. Eight separate sets of chlorophyll data representing different flow and temperature conditions were simu- lated satisfactorily with this model, thus indicating the importance of inorganic nitrogen as a possible growth-rate-limiting nutrient. 9) Phosphorus data measured weekly in the Potomac Estuary during 1969-70 revealed the following: a) The distribution of both inorganic and total phosphorus was markedly similar during the study period. Maximum concentrations of 2.0 mg/1 and 4.0 mg/1, respectively, were recorded between Bellevue and Piscataway Creek with concentrations diminishing farther downstream. ------- II - 4 b) Although high freshwater flow periods contributed an ex- cessive phosphorus load, the adsorption of phosphorus onto silt particles accompanying these high flows and its eventual deposition actually reduced the phosphorus content in the upper Potomac Estuary. c) During high temperature periods, inorganic phosphorus concentrations decreased appreciably downstream from Piscataway Creek as a result of biological uptake by phytoplankton and chemical deposition, 10) A modified version of the DEM having second order kinetics was utilized to simulate fourteen sets of prototype data and evaluate the phosphorus loss rate. Based on these simulation studies the loss rates required for model verification ranged from 0.005 gr/day to 0.04 gr/day, varying with temperature. The rate derived from a regression analysis for 20°C was 0.0218 gr/day. 11) A modified version of DECS III that again incorporated second order kinetics and the verified rates given above adequately simulated the interseasonal phosphorus distributions throughout the Potomac Estuary as observed between February 1969 and July 1970. 12) A series of model runs (DEM) that related phosphorus loss to algal productivity was made in order to delineate biological uptake from physical deposition of phosphorus and to acquire a better under- standing of the significance of phosphorus as a possible growth-rate- limiting nutrient. Based on these runs, it appeared that only 10 to 20 percent of the phosphorus losses were attributable to uptake by algal cells whereas 80 to 90 percent represented deposition to the bottom sediments. ------- II - 5 13) The DO budget model employed by AFO in its study of the Potomac Estuary consisted of the following five linkages: a) oxidation of carbonaceous matter b) oxidation of nitrogenous matter c) oxygen production and respiration of simulated algal standing crops based upon the nitrogen cycle d) benthic demand, and e) atmospheric reaeration 14) The aforementioned DO model proved capable of simulating nine different observed conditions between 1965 and 1970 when fresh- water flows and temperature ranged from 185 cfs to 8800 cfs, and 19°C to 30°C, respectively. In order to achieve a meaningful verification of this model it was necessary to base all simulation runs on the following reaction rates and other related assumptions: Process a) Carbonaceous oxidation - 0.17 (base e - 20°C) b) Nitrogenous oxidation - 0.084 (base e - 20°C) c) Reaeration - O'Connor-Dobbins Formulation d) Algal oxygen production rate - 0.012 mgOa/hr/yg chloro a_ e) Algal respiration rate - 0.0008 mg02/hr/yg chloro a^ f) Euphotic Zone - 2 feet g) Respiration Depth - VJ1 depth of water column h) Algal oxygen production period - 12 hours i) Algal respiration period - 24 hours j) Benthic demand - 1.0 gr02/meter2/day ------- II - 6 15) In order to determine the relative importance of the various rates incorporated in the DO budget model, a detailed sensitivity analysis was performed. The following conclusions were drawn based upon the results of this sensitivity analysis: a) The predicted critical DO deficit is markedly sensitive to the carbonaceous oxidation rate assigned in the model. Since the mass of unoxidized nitrogen in the Potomac is considerably less than that of carbon, the model predictions for DO were not significantly affected when a comparable range in nitrification rates was inputted. b) Increasing the algal photosynthesis rate or decreasing the respiration rate produced basically comparable results insofar as model predictions are concerned. Both the critical deficit and that portion of the predicted profile representing DO recovery were drastically affected when a change in either rate was instituted. c) A displacement of the entire predicted DO profile by a substantial amount was noted when different benthic demand rates were used indicating significant model sensitivity. d) Various expressions for computing the reaeration rate (i.e. O'Connor-Dobbins, Churchill and Langbein's Egs) were used in the model; however, no changes in predicted DO data were detected. ------- Ill - 1 CHAPTER III DESCRIPTION OF STUDY AREA The Potomac River Basin, with a drainage area of 14,670 square miles, is the second largest watershed in the Middle Atlantic States. From its headwaters on the eastern slope of the Applachian Mountains near the historic Fairfax Stone, the Potomac flows first northeasterly then generally southeasterly some 400 miles to the Chesapeake Bay. The Potomac traverses the Piedmont Plateau until it reaches the Fall Line near Washington, D. C. Below the Fall Line, the Potomac is tidal, ex- tending 114 miles southeastward and discharging into the Chesapeake Bay. The tidal portion is several hundred feet in width in 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 maintained upstream from the mouth to Washington. Except for this channel and a few short reaches where depths up to 100 feet occur, the tidal portion is relatively shallow with an average depth of approximately 18 feet. The mean tidal range is approximately 1.4 feet near the Chesapeake Bay and 2.9 feet in the vicinity of Washington. The lag time for the tidal phase between Chesapeake Bay and Washington is approximately 6.5 hours. The entire Potomac Estuary is characterized by numerous tidal embayments, generally less than 5 feet in depth, some of which are quite large in area. Of the 3.3 million people living in the basin, approximately ------- Ill - 2 2.8 million reside in the upper portion of the Potomac Estuary within the Washington Metropolitan Area. The lower area of the tidal portion, which drains 3,216 miles, is sparsely populated. The upper reach, although tidal, contains fresh water. The mid- dle reach is normally the transition zone from fresh to brackish water. The lower reach is saline with chloride concentrations near the Chesa- peake Bay ranging from approximately 7,000 to 11,000 mg/1. Because of minimal regulation, the Potomac is characterized by flash floods and extremely low flows. The average freshwater flow of the Potomac River near Washington, before diversions for municipal water supply, is 10,800 cubic feet per second (cfs) with a median flow of 6,500 cfs. Detailed physical data for the Potomac Estuary, including model segmentation geometry, have been presented in a previous report [6], ------- / \ N \ ANACOSTIA RIVCM GUNSTON COVE OCCOQUAN BA- POSSUM POINT LEGEND • MAJOR WASTE TREATMENT PLANTS A GAGING STATION - WASHINGTON, D.C A DISTRICT OF COLUMBIA B ARLINGTON COUNTY C ALEXANDRIA SANITATION AUTHORITY 0 FAIRFAX COUNTY - WESTGATE PLANT E FAIRFAX COUNTY - LITTLE HUNTING CREEK PLANT F FAIRFAX COUNTY - OOGUE CREEK PLANT G WASHINGTON SUBURBAN SANITARY COMMISSION - PISCATAWAY M ANDREWS AIR FORCE BASE - PLANTS ONE FOUR I FORT BELVOIR - PLANTS ONE TWO I PENTAGON K FAIRFAX COUNTY - LOWER POTOMAf LOCATION MAP CHCSAPfAKC BAY MITW POINT — POTOMAC ESTUARY FIGURE TH-I ------- ------- IV - 1 CHAPTER IV SOURCES OF NUTRIENTS AND OXYGEN DEMANDING SUBSTANCES A. WASTEWATER LOADINGS A total domestic wastewater flow of approximately 337 mgd is dis- charged into the Potomac River tidal system upstream from Indian Head, Maryland. Nineteen facilities currently serve approximately 2.6 million people in the Washington Metropolitan Area with the largest facility being the Blue Plains plant of the District of Columbia. Of the 337 mgd, 40.0, 26.0, and 34.0 percent originate in Maryland, Virginia, and the District of Columbia, respectively. The current BOD and nutrient loadings from each treatment facility are presented in Table IV-1. The total loadings into the upper Potomac Estuary from wastewater sources are (1) BOD5 - 143,000 Ibs/day, (2) Total Phosphorus (P) - 25,000 Ibs/day, (3) Total Nitrogen (N) - 60,000 Ibs/day. There are 82 wastewater point-source discharges in the Potomac Estuary between Indian Head, Maryland, and the Chesapeake Bay. The estimated BOD, phosphorus as P, and nitrogen as N loadings from these sources are 4,000, 500, and 1,000 Ibs/day, respectively. Compared to the upper reach, with a population of approximately 2.6 million, the wastewater facilities in the middle and lower reaches serve a population of approximately 50,000 and consequently account for a small percent- age of the total loadings to the Potomac Estuary. Most of the discharges in this area are into tributary or embayment waters. ------- ^ re -o 00 n O LO O CVJ CD CM ~ r— O O O CVJ 0 CM O t o CM O in o 1— CVJ co oo •a- oo i— CO LO CO —< a: OJ 2 TO 01 --S =J -a >, i. oj TO O •!-> T3 -r re ~^ a. aj m ISt I- £ O 1— r— a. """ I— ^ T3 TO oo a) -u •O •-> -^ •r- TO oo r— OJ l"l O i- r— -O C OJ -^ 0) •"->>> Q- TO fT3 CO QJ -O 3 S- ~^ CO •-» 00 c .a = •— >> •O TO OJ "O ^_> v^_ TO uo OJ .a L. •— t— — ' LO a o ao -o — . 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O CNJ CO i — « — OJ ^O i— CO r^ j-^ ^- CM C~t C^ O •"" f~~ f^ OJ ^£> CO r— »— <— OJ ro 00 •— O O O OJ OJ fj> CT» o ro ^~ ^- oj ^- !— A » c\ cr> i— CT^ O O O r— •— LT> ^" CJ^ ^f OJ oj ro ^~ O in u"> oj CNJ •— ^o ur> vr> >JD oo r— ro ro VO O •— O in a o o 01 O CO • Cu "O O oj z: o i- 0 •— OJ c - >-i o c re « >-> i— i I-H o 1 -O OJ 1 &- 31 OJ OJ OJ CU TI X O +J +J +J 4-> OJ re c ••- -i- ••- -t- oo M- i — recocococo ire i. (0 -f- «t CO •i- > T3 1— -H I— ------- IV - 3 B. CONTRIBUTIONS FROM THE UPPER POTOMAC RIVER BASIN During the period of February 1969 to February 1970, the follow- ing average concentrations of BOD5 and nutrients in the freshwater flow entering the upper Potomac Estuary were measured. Parameter Concentration fing/Tl BOD5 2.60 TKN as N • 0.61 N02 + N03 as N 1.00 Phosphorus as P 0.13 Detailed analyses of the freshwater inflows from the upper Potomac River Basin at Great Falls were conducted during 1969 and 1970. The observed data, as shown in Figure IV-1, indicate the wide range of nutrient concentrations for the period of June 1969 to July 1970. The river discharge was considerably higher during the 1970 period of the study than it was for the 1969 thus resulting in higher N02 + N03 concentrations. Concentrations of TKN and phosphorus appeared to de- crease during periods of high flow, except during periods of intense runoff. The monthly nutrient contributions from the upper basin during the period of February 1969 through February 1970 are presented in Table IV-2. For this 13-month period, the average daily contributions of nutrients are given below: ------- IV - 4 Parameter Contribution (Ibs/day) Total Phosphorus as P 4,580 Inorganic Phosphorus as P 2,650 TKN as N 22,410 NH as N 4,590 3 NO + NO as N 36,700 2 3 ------- in 3 d - != S z o u 8s > I- a: UJ U 5 < 2 5 Q. a ------- ------- ro O + 1/1 rO CM O to O 00 o oo CM o oo LO o LO r-. CM 0 CTl r- o CTl oo CM O r- CTl •* o oo o CM CO o o o 0 to CO 0 oo CTi to o o CTl CO o CO CTl 00 o CT! CTl o o to CO (/I to CO (T3 T3 O o co ft LO O 00 o ft LO o LO CO o r-. o * CM O CTi o CTi CM O r-.. co #1 co CM f\ CM CO o o IT) o ID 01 n ID O CTl o CTl LO -o _a o oo CM CM o CO to CM o 0 r-v CM CM o oo ID £Z o CO ID ^ 0 ID 00 o to CM to CM o 00 to 2 0 0 CM 00 o o 00 ) o CTl CO LO CM o 00 00 CO o s o CM CM 00 •z. o ca H—t a: o i~^ en o o r— 0) "Z. ro CM t—i U_ I OO QJ a> a: i- •— LU o -Q > ro i—i CU I— C£. > O o .a •=r < cn £ CTi ID CTi to O ro C tO rO 3 CD L. i. O o x: c Q. •—i to o ro o o P-» CM CM r— O O cn o co LO o o o un o o CM co CM CO CM CM i— o o CO O CTl tO * * CM LO O un in O Lf) 10 n CM o D- o: a. a. 0 -C O.O- V) O IO .C ro s/day IT) CTi CD O LT> »l LD O •51- 0 co O 10 LO CM •— 0 CD i— LO o CM CTl f\ CM O 00 ID Lf) 0 CO CM 0 CO 00 0 UD CO CO LO o o to o o 00 o o o o o CTl ft ro o o CM ft CM O O CM O O O ft 00 o o CO O O O o CTi O O CTi 8 «=»- O o CTi CM r- i— i— r— CM ro 3 S- _a CU o i- ro O) c =3 3 O) 3 cu •i cu 4-> Q. cu oo S- s- cu CU -Q JQ E O CU 4J > o o o -z. 0) CU O cu Q ro 3 to 3 S- -Q a> cu cn ro cu ------- ------- IV - 7 C. SUBURBAN AND URBAN RUNOFF A regression analysis of the river discharge and contributory loadings was applied to data from the Rock Creek and Anacostia River watersheds in the District of Columbia. Based on these regression studies and flow duration curves, yield rates in terms of Ibs/day/sq mi were determined. These rates were used for the suburban areas in Vir- ginia and Maryland as shown in Table IV-3. For the District of Columbia, additional data on stormwater and urban runoff were obtained from a study of Washington overflows [7]. The median loadings contributed from urban and suburban areas to the upper Potomac Estuary (Table IV-3) are tabulated below: Parameter Loadings (Ibs/day) BOD5 12,500 TKN as N 2,560 N02 + N03 1,510 T. Phosphorus as P 850 The total Ibs/day loadings of BOD and nutrients from suburban and urban runoff were fairly low when compared to those contributed from the upper Potomac Basin. However, the yield rates, except for nitrites and nitrates, were significantly higher for the urban and suburban area than for the upper Potomac Basin. This indicates that as an area becomes more populated, the amount of BOD, phosphorus, and TKN contributions will probably also increase. ------- ------- o: i — Q; J3 t— CO ra Z r— I— O r- CJ ro O ro z: QJ rD s- Qi CJ3 DQ a: ca Z3 oo Q ^. c: ro o cr: ., — +J "O rO > — S- O) Q •>- 03 O) i- , rO •o oo -Q o- 00 ro T3 CO ro -o CO .0 i cr co "^ ro TO CO -Q ^ ro "O CO -Q E CT 00 ^^ >> -5 ^^ 00 .Q ro ^^ CO -Q .,_ E CT 00 >i TD CO -Q 4~> c~ O> U ^_ QJ CL i — e r^j- oo C- O Ln OJ OJ 0 ^j- LO o o r-- o 1 0 •* o oo o o LO LO LO LO en 1 — o o OJ ^ 1 — o oo OO LO Oo LO oo -a c rO >, S- rO 51 O O oo LD cr> o o ^ , — o OJ oo o o LO f— 1^- 1 — o LO 00 o o r- 0 LO OJ LO O'') o OJ «* OJ , — o OJ o LD o 0 o OJ o LO oo o 1 — o LO en OJ LO oo 0 o OJ CTi o ^)- LO o o •—^ CTi 0 •* o oo o o ^ ^ LO LD LO i — O o o ' — 0 oo oo LO o o oo ro •r— C CT> S_ •i — > O o en OJ LD 0^ O LO CTl O OJ OO O LO 1 — r-~ i — o o oo o o r- o LO o o oo o LO OO OJ , — o co 1 — o LO CD o LD o OJ o o 00 o o LO CTi O O oo 0 o CT> OO CTi OJ LO O O LO OJ 0 CTl , — " 0 o r^ ,_r OJ ^f r^. OJ O o ! •N •— ^- r~^ r- LO OJ LD +J O •i — ^_> CO • f— Q O O OJ LD O O •— O o LO o ' — CO o o 3~ LO <• LO O O OJ oo OJ oo o LO OJ LD rO _a j r~ O 3 0 o o o OO CO «3- o CTi 0 LO , — 0 LO o •cf o LO OJ 0 o LO CT, OJ LO o o LO LO LO CO OO LD O O •^ OJ OJ p-v oo , — oo o o CT. i — •— LD LD LD r— O 0 oo f- oo OJ LO >=+ LO 1 — I-- ro ^_> o 1— O O LO OO o LO r^ •— o LO LO OJ 00 LO oo o LO , 1 — • — OJ 0 LO co o OJ <— o 1 — 1 — o CO 0 , — 1 — LO , — o CO •* r — , LO o o oo 1 — LO OJ o o CTi OJ 1 — o LO CTi , — r-^. •a O) a> 01 s_ o T3 O) CT a> CO ro cr CO -a cu o o to s- en ro -C o •r— -3. o 0) o <- OJ Q. ai ------- ------- V - 1 CHAPTER V FRAMEWORK FOR ANALYSIS A. WATER QUALITY DATA Since 1965, the Annapolis Field Office has conducted water quality sampling in the Potomac Estuary. Initially, most of the data were col- lected in the critical upper reach near Washington, D. C., but the area of concern has progressively lengthened to include the middle reach, where the most serious algal problems occur, and more recently the almost continuously saline lower reach. The frequency and duration of sampling generally followed one of two patterns: (1) an intensive type survey, hopefully performed during steady-state conditions, composed of multiple sampling runs carried out each day for approximately a week's duration or (2) weekly or bi- weekly sampling over an annual cycle. The importance of the first sampling method is that relatively short-term intensive data can be employed to obtain reaction rates and, thus, be used for model verification during a period of somewhat constant temperature and freshwater flow. The EPA estuary model, due to its hydraulic solution, particularly lends itself to steady-state flow analysis. In order to verify a mathematical model over a larger time scale, to predict seasonal variations in the nitrogen and phosphorus transport mechanism, and to investigate the effects of seasonal wastewater treatment requirements, AFO with the cooperation of Steuart Petroleum Company conducted a weekly nutrient sampling program of the entire Potomac Estuary from February 1969 to May 1970. These data ------- V - 2 will be discussed in a later section of this report. All of the intensive data have been published in separate reports [8] [9] [10]. In addition to AFO sampling, data collected by the District of Columbia's Department of Sanitary Engineering in weekly cruises in the upper Potomac Estuary were also evaluated. Certain data, which were collected during appropriate steady-state periods, were used in the rate determination and model verification studies presented in this report. ------- V - 3 B. CHEMICAL, PHYSICAL, AND BIOLOGICAL REACTIONS 1. Nitrogen Figure V-l schematically shows the major reactions of the nitrogen cycle in an aquatic environment. Organic nitrogen derived primarily by biological action has many forms, with the more common being pro- teins, amines, purines, and urea. While certain forms (fibrous proteins) are resistant to biological degradation, others may be decomposed by biological action or, in the case of urea, hydrolyzed enzymatically into ammonia and carbon dioxide. Ammonia nitrogen can be introduced into natural waters by sewage effluents or agricultural runoff. In addition, ammonia is released by biological decomposition of organic matter. Since it is extremely soluble in water, ammonia concentrations can become quite large. Am- monia is characterized by significant sorption (physical and chemical) properties, but more important is the fact that it can be resynthesized to organic nitrogen by aquatic plants or oxidized to nitrites by auto- trophic bacteria (nitrosomonas). This latter reaction, known as nitri- fication, is highly dependent on temperature and pH and will proceed only under aerobic conditions. It has been reported [11] that this phase of nitrification requires 3.43 grams of oxygen for 1 gram of ammonia nitrogen to be oxidized to nitrite. In addition to the oxidation of ammonia, nitrites are also formed by the reduction of nitrates. Further reduction by heterotrophic bac- teria (denitrification) results in the release of nitrogen gas. Nitrite ------- V - 4 nitrogen is very unstable since it can be readily oxidized by Nitro- bacter bacteria to nitrates. Consequently, high concentrations of nitrite are not normally found in surface waters. Approximately 1.14 grams of oxygen are required to oxidize one gram of nitrite nitrogen. Nitrate nitrogen represents the completely oxidized form of nitro- gen in the nitrogen cycle. Its major external sources in a watercourse are wastewater effluents and agricultural runoff. The nitrate form is quite soluble in water and concentrations can reach high levels, par- ticularly since it does not adsorb on particulate matter and is chem- ically relatively nonreactive. In addition to the reduction of nitrate by heterotrophic bacteria at low DO levels (0-2 mg/1), it may also be used by phytoplankton as a nutrient source. The assimilated nitrate nitrogen is converted to organic nitrogen in the plant's cells. Upon death, the cellular material releases organic nitrogen which completes the nitrogen cycle. From the standpoint of mathematical modeling the Potomac Estuary, there are two aspects of the nitrogen cycle that deserve special atten- tion: (1) the reduction in dissolved oxygen by bacterial oxidation of unoxidized nitrogen forms (ammonia + organic nitrogen) and (2) the assimilation of inorganic nitrogen forms by phytoplankton during their growth phase. * Commonly measured as total Kjeldahl nitrogen ------- UJ _l U u z u o o cr a LJ a. I CO o o 10 o cr ii i l§ o cc 13 < z — UJ 1 o £ ct LU z o l/l o a. O O CE Q UJ a FIGURE v-i ------- ------- V - 6 2. Phosphorus Since the advent of synthetic detergents, phosphorus levels in the natural environment have increased drastically and its role in the eutrophication process has received considerable attention. Shown in Figure V-2 is a schematic representation of a simplified phosphorus cycle with pertinent chemical, physical, and biological reactions. Although large quantities of mineral phosphates are present on the earth's surface, they are relatively insoluble in water. Phosphorus in the aquatic environment can basically be categorized as either inorganic or organic. As shown in Figure V-2, inorganic phos- phorus can be subdivided into: (1) particulate, (2) soluble ortho, and (3) soluble poly and pyro. The major contributor of soluble inor- ganic phosphorus is wastewater effluents. Prior to the inception of synthetic detergent use orthophosphate constituted most of the total phosphorus present in sewage, with the remainder being primarily dis- solved and suspended organic compounds. Since that time, however, the cleansing agents polyphosphate and pyrophosphate have become predomi- nant factors in water quality management. In addition to sewage sources, both inorganic and organic phosphorus (soluble and particulate) may be contributed in much smaller quantities by agricultural and other types of land runoff. Polyphosphate and pyrophosphate are readily hydrolyzed to the orthophosphate form. Various sorption phenonmena can convert soluble orthophosphates to a particulate form or vice versa. Of the different ------- V - 7 forms of inorganic phosphorus, only soluble orthophosphate can be bio- logically assimilated by phytoplankton. A portion of the particulate phosphorus is deposited in the bottom sediments. A quantitative appraisal of phosphorus recycling has not been undertaken, but it appears that the sediment adsorbs more phosphorus than it releases. The organic phosphorus component also contains soluble and parti- culate phosphorus which undergo chemical and physical reactions similar to their inorganic counterparts. The oxidation of organic soluble phos- phorus into an inorganic form is a relatively minor sink of DO. The cells of plants and animals convert inorganic phosphorus to an organic form; when these cells die, a certain portion is probably deposited. Biological decomposition of the remainder results in additional soluble and particulate organic phosphorus, and because of "luxury" uptake, some soluble inorganic phosphorus. Phosphorus cycle factors of special concern in mathematical modeling studies are the gross deposition rate and the quantity bio- logically taken up by algae. While other aspects are also important, they are not as easily defined. ------- LJ d u cr O CL CO O CL Q LJ CL :E to FIGURE V-2 ------- ------- V - 9 C. MATHEMATICAL MODELING TECHNIQUES Water quality simulations discussed in this report were made using the EPA Dynamic Estuary Model (DEM) and DECS III (Thomann Model). Relatively steady-state conditions over a 2 or 3 week period were simulated with the DEM, whereas DECS III was used to simulate inter-seasonal conditions. The DEM is a real time system incorporating hydraulic and quality com- ponents. Both of these components utilize the same two-dimensional net- work of interconnecting junctions and channels. The hydraulic solution describes tidal movement, while the quality solution considers the basic transport mechanisms of advection and dispersion as well as the per- tinent sources and sinks of each constituent. The DEM can concurrently simulate six different constituents. They may be either conservative or nonconservative and may be interrelated in any mathematical linkage. A detailed description of this model is available from EPA [2]. The application and verification of the DEM in simulating dye and chloride data in the Potomac Estuary and a detailed sensitivity analysis of the various input parameters have also been documented [4]. Several modifications were made to the DEM in order to simulate nutrient transport and historical dissolved oxygen distributions. A schematic diagram of the basic feedback linkage employed by the DEM to predict algal growth based on the nitrogen cycle and the effects of algae and other sources and sinks on the DO budget are shown in Figure V-3. One version of the DEM included five nitrogen reactions: (1) bacterial nitrification of ammonia to nitrite and nitrate, (2) phyto- plankton utilization of inorganic nitrogen, (3) release of organic ------- V - 10 nitrogen by the death of phytoplankton, (4) deposition of organic nitrogen, and (5) decomposition of organic nitrogen to ammonia. More- over, the following DO budget linkages were included in a separate model: (1) oxidation of carbonaceous matter, (2) oxidation of nitro- genous matter (ammonia and organic), (3) oxygen production by photo- synthesis and utilization by respiration of simulated algal standing crops based upon the nitrogen cycle, (4) benthic demand, and (5) re- aeration from the atmosphere. All model reactions were based on a mass balance basis. The mass conversion factors (nitrogen to chlorophyll a_) were determined by algal composition analyses performed in the laboratory [5]. The rates used in the DO budget analysis were obtained primarily from field studies. Besides changing the various reaction rates temporally, a modification was made in the DO model to allow for spatial variations in the photosynthetic, respirational and benthic rates as well as the depth of the euphotic zone. Simulations of phosphorus transport in the Potomac Estuary were based on second-order reaction kinetics. As will be discussed in a subsequent section of this report, adequate agreement between observed and predicted phosphorus profiles could not be obtained using a first- order system for deposition rates. Consequently, the DEM was modified to handle second and other order reactions. Linkage between algal growth and phosphorus loss in the model was performed similarly to that of the nitrogen cycle, e.g., mass balance analysis. ------- WASTEWATER NH3 A SIMPLIFIED DO BUDGET FOR DYNAMIC ESTUARY MODEL O O O Kn A o 0 z DO -> NO2 + NO3 Kn4 ORGANIC NITROGEN EXPRESSED AS CHLOROPHYLL a. A Kn3 TO THE SEDIMENTS FIGURE V-3 ------- ------- V - 12 The DECS III model is based on a tidal average time-dependent solution of the basic mass balance equations as originally developed by Thomann [12]. These equations are expressed in finite difference form by segmenting the estuary under study. Since this model is nontidal, a dispersion coefficient is introduced to account for tidal dispersion and advection in addition to eddy and molecular diffusion. The quantitative appraisal of this coefficient becomes extremely difficult. AFO's experience in verifying DECS III for historical dye and chloride data and the estimation of dispersion coefficients for several reaches of the Potomac Estuary as a function of freshwater inflow is available in another report [4]. The major disadvantage of using DECS III is its limitation to a two- constituent linkage. Therefore, neither the complete nitrogen cycle nor the DO budget could be simulated. To help alleviate this problem, ammonia nitrogen and nitrate nitrogen replaced BOD and DO, respectively, in the original version of the model. The reaeration component sign was changed; it thus behaved as a sink of N03 instead of a source of DO. This loss would, of course, correspond to the biological uptake of N03 by algae. In such a manner, two nitrogen fractions could be properly represented. Two other modifications were made to DECS III to permit the simu- lations given in this report: (1) the inclusion of second-order re- action kinetics for the analysis of phosphorus transport and (2) the inclusion of a mathematical expression relating dispersion coefficient ------- V - 13 to freshwater flow. This latter addition was necessary since the sim- ulation period was long in duration and was characterized by extreme flow differences. ------- VI - 1 CHAPTER VI NITROGEN ASSIMILATION AND TRANSPORT A. TEMPORAL AND SPATIAL DISTRIBUTION The concentrations and forms of nitrogen in the Potomac Estuary are dependent upon wastewater loadings, temperature, freshwater inflow, and biological activity. The weekly nitrogen data collected by AFO from February 1969 to July 1970 are presented in isopleth form in Fig- ure VI-1 (Ammonia Nitrogen), VI-2 (Nitrite + Nitrate Nitrogen), and VI-3 (Organic Nitrogen). As shown in Figure VI-1, ammonia concentrations of 2.0 mg/1 were fairly common in the upper estuary in 1969 as a result of wastewater discharges. The rapid decrease in concentrations between the Woodrow Wilson Bridge (River Mile 12) and Indian Head (River Mile 31) is in- dicative of nitrification or the conversion of ammonia nitrogen to ni- trite and nitrate nitrogen. Based upon the data shown in Figure VI-1, the rate of this reaction appears to be definitely related to tempera- ture. During the warm summer months, for example, ammonia concentrations in the vicinity of Dogue Creek (River Mile 22) were about 0.5 mg/1, whereas concentrations during winter and spring periods averaged 1.0 - 1.5 mg/1. The almost immediate effects of nitrification would indicate that the upper Potomac Estuary behaves as a "continuous-culture system." It should also be noted that changes in freshwater flow rates had a ------- VI - 2 relatively minor effect on the ammonia nitrogen levels upstream from Mains Point (River Mile 7.6). The concentrations of nitrite and nitrate nitrogen at any given time will be a function of (1) nitrification rate and (2) nitrate uptake by algal cells. Figure VI-2 shows maximum nitrite and nitrate nitrogen concentrations (1.5 - 2.0 mg/1) throughout much of the summer and fall of 1969 and again in January 1970. These high levels generally pre- vailed between Woodrow Wilson Bridge and Indian Head where rapid reduction in ammonia levels was observed. Besides the conversion of ammonia from wastewater effluents, a considerable amount of nitrate nitrogen enters the upper Potomac Estuary during periods of high freshwater flow. This contribution would account for the high concentrations in January 1970, a low-temperature, minimal nitrification period. The significant decrease in nitrite and nitrate nitrogen between Indian Head and Smith Point (River Mile 46) in the summer and early fall of 1969 was caused by algal uptake of nitrogen. This reaction, like nitrification, appears to be related to temperature as evidenced by the greater persistence of nitrate nitrogen during colder periods. From a water quality management standpoint, the virtual disap- pearance of inorganic nitrogen in the critical algal growing areas suggests that this nutrient may become the major factor in limiting algal growth in the middle reach of the Potomac Estuary. The distribution of organic nitrogen in the Potomac Estuary during 1969-70 is shown in Figure VI-3. These iso-concentration lines were ------- VI - 3 based on differencing the total Kjeldahl nitrogen (TKN) and ammonia nitrogen data. As shown in Figure VI-3, organic nitrogen is quite plentiful in the Potomac Estuary, especially during the late summer and early fall of 1969. Maximum concentrations, exceeding 3.0 mg/1, were observed in the middle estuary throughout most of September 1969 with the lower reach having levels nearer 2.0 mg/1. These extremenly high levels of organic nitrogen resulted from the profuse algal blooms which were visually observed and measured at greater than 100 yg/1 chlorophyll a_. The maximum recorded chlorophyll value during this critical period was 445 yg/1. Algal composition studies conducted by AFO [5] indicate that water with an algal bloom of 100 yg/1 chloro- phyll a^ contains about 1.0 mg/1 of organic nitrogen. Relatively high organic nitrogen concentrations (1.5 - 2.0 mg/1) continued in the upper and middle estuary through October 1969. Similar concentrations were again observed in June and July 1970 when a reap- pearance of algal blooms occurred. It would appear from a comparison of the ammonia nitrogen and organic nitrogen data that the rate of decomposition of organic nitro- gen is much slower than the rate of bacterial nitrification, since or- ganic nitrogen is the predominant form of nitrogen in the middle and lower estuary. ------- ------- X h- UJ a 5 If 13 LJ „ O a: o 2 - I Z O o 2 8 2 2 390IUS NIVH3 MCH38 S31I" FIGURE Vl-l ------- ------- LJ a o U 2 < ; 5 «> o 2 BOQIHfl NIVHO MCH38 S3HH FIGURE VI-2 ------- ------- a! 8 S 8 8 ------- ------- VI - 7 B. DETERMINATION OF REACTION RATES AND TEMPERATURE EFFECTS 1. Nitrification The rate at which ammonia nitrogen (NH3) is biochemically oxidized to nitrite and nitrate nitrogen (N02 + NOa), commonly referred to as the nitrification rate, was determined for the Potomac Estuary by using the aforementioned version of DEM to simulate numerous observed con- ditions representing a variety of temperatures and freshwater inflows. The prototype behavior was established using intensive-type sampling data collected during relatively steady-state flow periods. These data indicated that ammonia was being rapidly depleted, especially when high temperatures prevailed, and that a subsequent increase in nitrate concentrations could be expected. Because of this and the fact that maximum depletion occurred upstream from the major algal blooms, it was apparent that nitrification, and not biological uptake by phytoplankton, was primarily responsible for the loss of ammonia. Various reaction rates were inputted to the Dynamic Estuary Model until a reasonable simulation of each of the observed ammonia profiles was achieved. The final profiles obtained with the model along with the appropriate nitrification rates are shown in Figures VI-4 through VI-16. As can be seen in the figures, peak ammonia concentrations and spatial gradients were generally simulated satisfactorily. In order to establish a relationship between nitrification rate and temperature, a regression analysis was performed utilizing the thir- teen separate sets of data discussed above. The linear relationship ------- VI - 8 resulting from this analysis is presented in Figure VI-17. At 20°C, the nitrification rate is 0.084/day (base e). ------- ( I / 6ui] FIGURE VI-4 ------- ------- o £ 1? lT> >- (O a: o> CO C\J CL LJ 1/1 z o 1 ^t CVJ 1 <\J tvj 1 • q <\i I i 00 l£) 1 I 1 <* N O 1 CD d 1 1C d ^ d i (VJ d --t- o d (\| / 6iu) FIGURE VI-5 ------- ------- o Q r o CD UJ FIGURE VI-6 ------- ------- I FIGURE VI-7 ------- ------- o LJ 8 o (- o> o f> Z ^ fe ui P a ofe o a: § a. 2 m ii (VI c X. OBSERVED 1 1 I (/) z O 1- u MODEL PR ED m UJ o Q in cc i o o _ O I oo lp cvi oo d OJ o d d (I/6m) FIGURE VI-8 ------- ------- cc > z UJ O o o z UJ o cc 9 IT OQ FIGURE VI-9 ------- ------- z \- 2 5 O Z 0 O o o K Z O cc CD o LJ _J 2 FIGURE VI-10 ------- ------- o Q I o o FIGURE VI-I I ------- ------- > = z o f. O g o> O tO (vi 2 LJ 8s * z ^ UJ O O Q. O CC K Z I/I vD < H / / 1 I 1 0, O "t -s o ro u O Q cr CD u _o o (VI 00 op o (O o • ------- ------- a £T o> z < 5 i/> UJ _j 2 (,/Bui) FIGURE VI-13 ------- ------- o • in m o o o 8 < o, ra f> UJ ------- ------- It 1 "* O 00 c < -in > 3 "o 8 9 cc a z Uo UJ _j 2 I * FIGURE VI-15 ------- ------- 0 o . (0 10 O> g z _ N ------- ------- 1.0 EFFECT b.F TEMPERATURE ON NITRIFICATION RATE UPPER POTOMAC ESTUARY NH3 •- N02+NO3 REGRESSION DATA: CORRELATION COEF. r 0.886 " I" =6.3430 «* DEGREES OF FREEDOM = (M-2) = 11 O.I 0.01 • e> = 1.155 Kn, = 0.084 (BASE e)e 20° C (FIRST-ORDER KINETICS) 0.001 10 IS 20 TEMP C 25 30 35 FIGURE VI-17 ------- ------- VI - 23 2. Algal Uptake The predicted formation of nitrate nitrogen by the nitrification process was found to be quite high when compared with actual sampling data. It was, therefore, necessary to apply a decay mechanism to account for the nitrate uptake by phytoplankton and effect a better comparison. The appropriate reaction rates were determined utilizing the mathematical model and a trial and error approach similar to the one described for nitrification in the preceding section. Figures VI-4 through VI-16 show observed and predicted nitrate profiles for the upper Potomac Estuary at different temperature and flow conditions. Also shown are the algal uptake rates used in the model. The figures indicate that reasonable agreement between proto- type and model data was obtained. The effect of temperature on the rates of algal nitrogen utili- zation is presented in Figure VI-18. A regression analysis was per- formed on the data and the results are statistically valid. At 20°C, the rate of nitrogen uptake by algae is 0.037/day (base e). ------- ------- 1.0 -i EFFECT 6F TEMPERATURE ON ALGAL NITROGEN UTILIZATION RATE UPPER POTOMAC ESTUARY NO3—•• ALGAL NITROGEN REGRESSION DATA: CORRELATION COEF = 0.899 "t" = 6.8092* DEGREES OF FREEDOM r (M-2) = II o.i - I ------- ------- VI - 25 C. SIMULATION OF NITROGEN TRANSPORT THROUGH AN ANNUAL CYCLE The two primary reactions involving nitrogen, i.e. nitrification and algal uptake of inorganic nitrogen, were incorporated in the DECS III version of the Thomann Model to simulate nitrogen transport in the Potomac Estuary throughout an annual cycle. Observed data collect- ed weekly from February 1969 to July 1970 was used for comparison pur- poses and model verification. The reaction rates and temperature effects developed from the preceding nitrogen verification runs were used in the model with cer- tain modifications. These modifications generally consisted of re- ducing the nitrification rates to reflect (1) low DO concentrations and (2) high freshwater inflows. The former would inhibit biological oxidation by the aerobic nitrifying bacteria and the latter would cause a flushing action resulting in a lag time for repopulation of the nitrifiers which must be anticipated. In the case of biological uptake rates, a downward attenuation was performed when and where algal standing crop levels were believed to be abnormally low. Observed and predicted nitrogen profiles (both ammonia and ni- trate nitrogen) are presented in Figures VI-19 to VI-23 for five dif- ferent sampling stations in the Potomac Estuary. An examination of the data indicates that the basic seasonal and spatial distributions were simulated surprisingly well. In view of limitations in observed data and simplification in the model itself, a closer agreement, especially in short-term fluctuations, was not really expected. ------- ------- O z Z K UJ < O §1 S I i (M O Z Q UJ OBSERV PJ 0 Q Ld PREDIC1 m I Z a UJ OBSERV I" z 0 UJ PREDIC1 FIGURE VI-19 ------- ------- 31 "-i z 52 Ld0- R O) i O) ------- ------- 2 is! UJ i i' if r- y o: Q UJ Ld (/> QC CD FIGURE VI-21 ------- ------- co o a d < cr SH! O* 1 H£ S <. UJ i< i i UJ CC. CO O ^~ u a UJ cr a. FIGURE VI-22 ------- ------- u. >- _ I c °> C < 1 _ So 2 < o 0~ z O Ul cr UJ (/> O Q U f— u Q i.t 0; Q. m X Z a UJ > a: UJ 00 m O l" Z o p_ y a Ul a: a FIGURE VI-23 ------- ------- VI - 31 D. CHLOROPHYLL PREDICTIONS BASED ON NITROGEN ASSIMILATION BY THE BIOMASS Subsequent to application of the Dynamic Estuary Model for deter- mining reaction rates involving nitrogen in the Potomac Estuary, the next logical step pursued was to mathematically "link" the nitrogen cycle with algal production. The purpose of extending the DEM in this manner was essentially twofold: (1) to determine whether nitrogen was indeed the growth-rate-limiting nutrient in the middle estuary as in- dicated by other methods of analysis and (2) to establish permissible nitrogen concentrations and loadings for the maintenance of a balanced ecological system. In order to simulate the standing crop of algae as measured by chlorophyll a^ the DEM was modified to convert losses of nitrate nitro- gen to algal biomass. As indicated previously, it appeared that biolog- ical assimilation of ammonia nitrogen was minimal since nitrification occurring upstream from bloom areas reduced its availability during high temperature periods. The mass conversion factor was estimated, from 1970 algal composition analysis data, to be 90.0. This in- ferred that a 1.0 mg loss of nitrate would create a chlorophyll a^mass of 90 pg. Practically complete utilization of nitrogen by the algal cells was assumed. Figures VI-24 through VI-31 present observed and predicted chlorophyll a^ profiles for the upper 40 miles of the Potomac Estuary based on the "surrogate" version of the DEM. Also shown are the flows, temperatures, and decay rates for which these data apply. From these mathematical model runs, it.appears that the standing crop of algae, ------- VI - 32 as measured by chlorophyll a^, can be predicted using the nitrogen cycle, and that the availability of nitrogen may be the factor con- trolling algal growth in the critical area of the Potomac Estuary. To achieve a satisfactory comparison between the observed and predicted chlorophyll data shown in Figures VI-24 to VI-31, it was necessary to incorporate a decay rate in the model ranging from about 0.01 to 0.07/day. This decay probably represents death and/or deposition of the algal cells. The decay rates needed for the various model runs did not appear to be closely related to temperature or the quantity of algae in the system. ------- in 2 O St o: id a: O < O^ \j ------- ------- CO z O CL UJ < U ^ O UJ 5 U r- a. O CE O _i I U O o oj g U. (J p 6 (VI ii a: o o (M 5 ------- ------- 93-IA 38D9IJ m o o -1 on O n z 00 X ro o M u U) o o Ul o \ \ O I r~ O 8 -D -0 O I o m O c O > m O z CO ------- ------- en O o O m in 5 o I a. r\> o ' rv, «" O I r- O -o a? Q O OJ o o in • OJ o o — <)•_ X X o. a. a o 3? -I 3 m - £ .T) II H O M O z Co 00 o o ------- ------- 9Z -IA 3Un9IJ (/Xg/l) o 1 — N l/l O 01 O O O o O 1 1 1 1 1 1 1 \\ (/> CD n O n i ro o OJ o A O O X O -o 3) Q O 00 2 > o s C! C ^ o I 2 > o 5 m ^ z H 33 O z Co ------- ------- 6Z-IA 01 o I in O L in - CO m I n I S o rvj in • w _ in in O I o § 8 5 § IO 3 o > m < -i ------- ------- OC-IA 3MD9IJ in ro o o 2 o o f\) in V o I in o I 00 o o t/i ro cj rn o> O § I o 5 0 ^ § O z CO ------- ------- IC-IA 01 - z F 5 o o o oo o o I o o I UI o I fy> O O I r > O <•> ro 01 in OB 00 O O O O Ul 3 r\> O — u> o O I c? O ro 5 "s 5 § S H Z c O 15 O Z ------- ------- VII - 1 CHAPTER VII PHOSPHORUS ASSIMILATION AND TRANSPORT A. TEMPORAL AND SPATIAL DISTRIBUTION Like nitrogen, the distribution of phosphorus in the Potomac Estuary is strongly dependent upon such factors as temperature, bio- logical activity, and freshwater flow rates. Figure VII-1 shows, by means of an isopleth, the spatial distribution of inorganic phosphorus during 1969 and 1970. Of special importance are the maximum concen- trations of 2.0 to 2.5 mg/1 (as PO^) which were observed between Bell- evue (River Mile 10) and Piscataway Creek (River Mile 18) during the low-flow periods of June, July, October, and early November 1969. The month of August (1969) was characterized by abnormally high flows and low phosphorus levels, the result of phosphorus deposition by adsorp- tion onto silt particles during high flow periods. A similar occurrence had been observed previously (March 1967) and it was concluded that, while periods of high freshwater inflows con- tribute an excessive phosphorus load, the overall effects of adsorption and deposition produce a net decrease in phosphorus during these peri- ods in the upper Potomac Estuary. Inorganic phosphorus concentrations upstream from Hafns Point (River Mile 7.6) were usually less than 0.5 mg/1. Downstream from Piscataway Creek, inorganic phosphorus levels decreased appreciably during high temperature periods due to continued deposition and bio- ------- VII - 2 logical uptake by phytoplankton. During low temperature periods, when biological activity was at a minimum, the decrease in inorganic phos- phorus levels in the middle estuary was considerably less pronounced. The entire lower half of the estuary normally contained less than 0.5 mg/1 of inorganic phosphorus. The total phosphorus (inorganic plus urganic) data collected during the 1969-70 survey are shown in Figure VII-2. A comparison of Figures VII-1 and VII-2 will reveal similar patterns in the spatial and temporal distribution of total and inorganic phosphorus. For example, maximum concentrations of total phosphorus (3.5 - 4.0 mg/1 as POit), as well as inorganic phosphorus, were observed between Bellevue and Piscataway Creek during low-flow periods. During high flows, total phosphorus concentrations were much lower because of the aforementioned deposition process. Although variations in total phosphorus concentrations generally corresponded to those of inorganic phosphorus, there were slight dif- ferences in the ratios. In the upper reach of the Potomac Estuary, the ratio of total phosphorus to inorganic phosphorus ranged from 1.1 to 1.5, while the ratio in the middle reach normally varied from 1.5 to 2.0. This difference in a high productivity area may be due to the biological conversion of soluble inorganic phosphorus to cellular organic forms. ------- MILES BtLOW CHAIN BRIDGE 8 5 8 e O 2 O •jo cn o T) ------- ------- MILES BELOW CHAIN BRIDGE "3 S I "V -O O I O •o r ------- ------- VII - 5 B. DETERMINATION OF LOSS RATE AND TEMPERATURE EFFECTS Water quality sampling data collected in the upper Potomac Estuary from fourteen separate surveys were used for purposes of Dynamic Estuary Model verification, and more specifically, to determine the magnitude of the overall phosphorus loss rate. During these model studies, no distinction was made as to the relative importance of (1) deposition to bottom muds and (2) biological uptake by algal cells. All of the sampling data were collected under relatively steady-state flow con- ditions, ranging from 185 cfs to 11,000 cfs. A range in water temper- e e atures, from 1.0 C to 28.5 C, was also represented. Figures VII-3 through VII-16 depict the observed total phosphorus and inorganic phosphorus profiles in the upper 45 miles of estuary, as well as the model predictions for total phosphorus. The close re- lationship between observed TP and Pi data eliminated the necessity for separate simulations. An examination of these figures will indicate that the magnitude of peak concentrations and the rate of decrease in phosphorus downstream from those peaks were accurately simulated. In order to obtain this agreement with the model, it was necessary to utilize second-order kinetics having the following form: St--"'• where c = concentration t = time and k = reaction rate (gr/day) The reaction rates required for model verification were greatly affected by temperature, as can be seen in Figure VII-17. ------- ------- I OJ I CO I o T ------- ------- o o Ul O LU (ft o a i 5 3 LJ CD o o d sv FIGURE VII-4 ------- ------- UJ O o 3 bJ m 10 UJ sv FIGURE VII-5 ------- ------- ."1 _0 in <> -s .m K M ffl z .in _o I CM I (O I O I 10 r M CO <\J O rj I 10 I (M I CO O O (!/•«) Od SV SnaOHdSOHd FIGURE VII-6 ------- ------- at CD < o Ul J Z FIGURE VII-7 ------- ------- £ z 5 FIGURE VII-8 ------- ------- o 01 z I U U g i a D 5 UJ O I I O ro CM (\l (V (I/6) Od SV SndOHdSOHd FIGURE VII-9 ------- ------- 5 UJ 00 1/1 LJ (!/•«) Od SV SnaOHdSOHd FIGURE VII-10 ------- ------- o I- o: Z \| 00 a\|i §(/) \|_ < o o (0 PJ (M £ CO _o o (M i I u CO 1/1 UJ .o I (M m I ------- ------- cc z 5 oo uj S <° O g 2. § '"> O i a _o 1 1 M - 1 (M — 1 03 O 1 «t O O O in g Ul CO in UJ .in _o 0d SV Sn«OHdSOHd FIGURE VII-II ------- ------- I UJ _J FIGURE VII-IZ ------- ------- I 3 (!/•«) Od SV SnaOHdSOHd FIGURE VII-13 ------- ------- C) PJ PJ (VJ (!/•«) Od SV SnMOHdSOHd FIGURE VII-14 ------- ------- z o _•• K- < QL \- LJ O > < 0) -J 10 • Ol M u O O 00 00 " \ o • <6 (M '< i t- o II a 0 UJ ^ (Vj D ° ^ § U 5 UJ O a. _o o IM g ffl z UJ m 10 UJ .in _o 1 I 1 1 1 1 (!/•«) Od SV SnHOHdSOHd 1 oo o xf o FIGURE VII-15 ------- ------- z o cr l- >• z 2p ui < O ? §ln £ UJ £ o o o o . — "fr <0 o X O UJ z o o Q _o o ro O (M i 5 I UI CD l/l UJ _ o I in I f I o I IO I n I o I ID I M I CO (V (!/•) MDd SV SndOHdSOHd o o FIGURE VII-16 ------- ------- O.I - EFFECT OF TEMPERATURE ON PHOSPHORUS LOSS RATE UPPER POTOMAC ESTUARY REGRESSION DATA; CORRELATION COEF - 0.899 "t"= 7.0951** DEGREES OF FREEDOM = (M-2) = 12 aoi - Kpl _0(T,-T2) KP2 Q> - 1.078 Kp,20°C = 0.0218 (BASE e) (SECOND-ORDER KINETICS) aooi 10 is 20 TEMP "C 25 30 35 FIGURE VII-17 ------- ------- VII - 21 C. SIMULATION OF PHOSPHORUS TRANSPORT THROUGH AN ANNUAL CYCLE The mass transport and spatial distribution of total phosphorus over an annual cycle must be known and predictable if the role of phosphorus in the eutrophication process and a management program for wastewater treatment are to be determined. Because of its importance, AFO endeavored to mathematically model phosphorus transport in the Potomac Estuary during a 15-month period in 1969 and 1970, This period was characterized by both high and low summer flows and offered an ideal situation for simulation. A modified version of the Thomann Model (DECS III) which incorporated second-order kinetics and the phosphorus loss rated developed in the preceding section was used for this simulation. Observed and predicted phosphorus (TPOi) data are shown for five selected stations in Figures VII-18 through VII-22. A comparison of the two profiles in each figure will indicate that the basic temporal distribution, including seasonal trends, was simulated reasonably well. Some difficulty was experienced in simulating phosphorus under excessive algal productivity conditions. This problem can be evidenced in Figures VII-19 (Piscataway Creek), VII-20 (Indian Head) and VII-21 (Maryland Point). In order to improve the predictive capability of the model during these periods, such factors as the extent of phos- phorus regeneration following the death of algal cells and the quantity of phosphorus exchange with the bottom sediments during different flow conditions would have to be quantitatively defined. ------- ------- Q- ? «? h: ° OL. < r- O >_ 2 i i - as i m o o o "od FIGURE VII -18 ------- ------- «/> a oc s: g i o> (O at 2; O il o in o' (\|/6ui) - "Od -IV101 FIGURE VII-\|9 ------- ------- LJ to o > ~r ~ E < (/) D O) (O o> 2 in d o o TV1O1 FIGURE VII-20 ------- ------- 00 d o d -1VJ.01 FIGURE VII-21 ------- ------- o cr a. Q. < £ to r> o> < 2 3 2 i o Z a. (I/Bui) ''Od 1V1OJ. FIGURE VI I-22 ------- ------- VII - 27 D. CHLOROPHYLL PREDICTIONS BASED ON PHOSPHORUS ASSIMILATION BY THE BIOMASS To delineate that portion of the previously computed loss rate representing biological uptake of phosphorus by algal cells from other processes and to better understand the phosphorus contribution to eutro- phic conditions in the Potomac Estuary, an attempt was made to predict chlorophyll levels based upon various phosphorus conversion or assimi- lation factors. A special version of the DEM that correlated algal production, as measured by chlorophyll a_, with inorganic phosphorus up- take was used for simulation under four historical conditions. Mass relationships between the two were determined from algal chemical com- position analysis. Figures VII-23 to VII-26 show observed chlorophyll profiles and those obtained from the model assuming phosphorus conversion factors of (1) 10 percent, (2) 25 percent, (3) 50 percent, and (4) 75 percent. The data pertain to late summer and early fall periods during which freshwater flows varied from 185 to 2,200 cfs. As can be seen, the model predictions indicate that only about 10 to 20 percent of the phosphorus losses from the aqueous system can be accounted for by uptake of algal cells. Therefore, the remaining 80-90 percent must be associated with the deposition of phosphorus or some other physical process. Analyses of the bottom muds in the upper estuary further substantiate the fact that large quantities of phosphorus are indeed being lost to sediments. Insofar as eutrophication is concerned, it appears that there is an abundance of phosphorus in the critical algal growing areas of the Potomac Estuary. Since the standing crop of blue-green algae was pre- ------- VII - 28 dieted from the nitrogen cycle, and only a 50 percent utilization of the available phosphorus produced excessive chlorophyll when com- pared to observed data, and for other reasons enumerated by Jaworski et al. [5], nitrogen is probably the growth-rate-limiting nutrient in the middle portion of the estuary at the present time. However, this presumption does not lessen the need to control phosphorus to the maximum extent possible, including loadings from wastewater treatment facilities, in the Potomac Estuary for several reasons: (1) the potential for controlling phosphorus is extremely great, especially during high flow periods (2) rapid phosphorus transport and mobility and uncertainty of its recycling ability and (3) phosphorus criteria for eutrophication control are considerably more stringent than nitrogen criteria for comparable reaches of the estuary. ------- to UJ Sc ce a: CD o UJ m o o o o ------- ------- UJ (\/6l1) mAHdOdOIHO FIGURE VII-24 ------- ------- (\/6ri) FIGURE VII-25 ------- ------- LJ 5 cr z o LJ cc - X Q. O CC O I U Q LJ O U Q 7Z OC (T Q. O LJ to CD to LJ Oi (O (J cn LJ U e> CE CD U CD _0 o m (M o o t\j I o in I o o I o in (\|/6Tf) D TUHdOaCTIHD FIGURE VII-26 ------- ------- VIII - 1 CHAPTER VIII DISSOLVED OXYGEN BUDGET A. FORMULATION OF SOURCES AND SINKS A schematic diagram of the dissolved oxygen budget incorporated, in the AFO mathematical model of the Potomac Estuary is shown in Figure V-3. As can be seen, the model consisted of the following five linkages: 1. Oxidation of carbonaceous matter, 2. Oxidation of nitrogenous matter (ammonia and organic nitrogen), 3. Oxygen production and respiration of simulated algal standing crops based upon the nitrogen cycle, 4. Benthic demand, and 5. Atmospheric reaeration. One important limitation of the DO model presented above is that it neglected the oxygen demand of dying and decomposing algae. An effect such as this may be included relatively easily by regenerating the oxidizable carbon and nitrogen "tied-up" in plant cells and was con- sidered in a subsequent version of the model discussed later in this report. Although this DO sink may be significant in the fall months when algal death is prevalent, the extremely low chlorophyll decay rates required for most model verification runs (Chapter VI) and the apparent success of the existing model in simulating various DO conditions ------- VIII - 2 suggests that it is negligible during the natural growth phase of the algae's life cycle when compared to other major sinks of oxygen. The basic coefficients and assumptions employed in the DO budget model were: Rate (base e) Temperature Coefficient Process at 20°C 9 (Tt - T20) Carbonaceous oxidation 0.170 1.047 Nitrogenous oxidation 0.084 1.16 Reaeration from the Atmosphere 1.021 Algal oxygen production rate = 0.012 mg 02/hr/yg chlorophyll a^ Algal respiration rate = 0.0008 mg 02/hr/yg chlorophyll a_ Euphotic zone = 2 feet Respiration depth = full depth of water column Algal oxygen production period = 12 hours Algal respiration period = 24 hours Benthic demand rate =1.0 grams Oz/sq. meter/day All of the above rates were established through field and laboratory studies, with the exception of the nitrogenous oxidation rate which was determined from modeling of the nitrogen cycle as presented in Chapter VI. Light and dark bottle studies were conducted at various locations in the upper and middle Potomac Estuary during June-July, 1970, to * Based on O'Connor-Dobbins velocity and depth formulation ------- VIII - 3 estimate the oxygen production and respiration rates for a known stand- ing crop of algae. The data collected during this survey are shown in Table VIII-1. A considerable amount of data relating to light penetra- tion (Secchi Disk) was available for the entire Potomac Estuary. The assumed depth of the euphotic zone was based upon an analysis of this data. Finally, a benthic respirometer was used by AFO in the upper estuary to obtain benthic oxygen demand rates. These data, which are shown in Figure VIII-1, indicate that benthic uptake rates vary spatial- ly, with the maximum rate occurring near the District of Columbia's Blue Plains Sewage Treatment Plant (River Mile 10.4). ------- ------- Table VIII-1 OXYGEN PRODUCTION AND RESPIRATION RATE SURVEY Upper and Middle Potomac Estuary 1970 Date 6-22 6-23 6-24 6-25 7-20 7-21 7-22 7-27 Water Temp. (°0 26 27 27 27 28 27 26 28 Chlorophyll a_ Range (ng/1) 40-110 70-120 54-110 50-60 30-100 30-143 30-140 _ Light Intensity Range (foot candles) 250-300 200-300 200-300 200-300 250-400 200-300 100-200 _ Oxygen Production mg/hr/yg of Chlorophyll a .0073 .0084 .0087 .0121 .0130 .0130 .0146 .0060 Respiration mg/hr/yg of Chlorophyll a .0023 .0011 .0024 .0033 .0022 .0016 .0017 .0010 ------- ------- UJ {3 z o U Q. 00 in OJ o Q UJ O Ul ------- ------- VIII - 6 B. SIMULATION AND MODEL VERIFICATION STUDIES Eight separate intensive sampling runs conducted in the upper Potomac Estuary between 1965 and 1969 were used, initially, to verify the DO budget model, including the various reaction rates and assump- tions presented in the previous section. Each run represented approx- imately a 20- to 30-day period under relatively steady-state conditions. The flows for the eight sets of sampling data ranged from 185 cfs to 8,800 cfs. Figures VIII-2 through VIII-9 show the observed DO profiles and those predicted by the mathematical model. As can be seen, favorable agreement was obtained in every case. Although the two sets of pro- files did not coincide exactly, the magnitude and location of the criti- cal DO deficit and the general rate of depression and recovery appear- ed to be simulated reasonably well using the aforementioned coefficients The critical deficit was primarily the result of the oxidation of carbonaceous and nitrogenous material in the wastewater effluents; the rate and extent of DO recovery was influenced greatly by the net effect of algal photosynthesis and respiration. The pronounced decrease in DO predicted by the model in the ex- treme upper portion of the estuary during lower flow periods could have been due to the very deep holes in this area, which lowered the reaeration capacity and magnified the effects of algal respiration. As a further test of the model's capability to predict dissolved oxygen distribution in the Potomac Estuary, a completely independent ------- VIII - 7 and more recent (September 1970) condition was simulated. The sampling data collected by AFO on September 9, served to define the initial conditions. Data collected 20 days later and compared to model pre- dictions after a comparable time period were used as a basis for veri- fication. The freshwater flow during this period ranged from 1,200 cfs to 1,900 cfs (1,500 cfs average), and the reaction rates and assumptions incorporated in the other eight runs were applied without change. The results of this simulation are shown in Figure VIII-10. Generally, good agreement was obtained between observed and predicted data describing the rate of oxygen depletion, the magnitude and location of the critical deficit, and the initial stage of recovery. The considerable diver- gence in the later stages of recovery may be ascribed to the extensive algal death and decomposition which normally occurs in that area of the estuary during late September. As stated previously the additional oxygen demanding load resulting from the biological decay of algal cells and nutrient regeneration had not been incorporated into this version of the model, and consequently, the secondary DO depressions that at times exist in the Potomac Estuary were not accurately simulated. ------- 10 ------- ------- co UJ Ld O in UJ U g g O a. Q LJ tr > J^ co Q '-•O'O FIGURE VIII-4 ------- ------- LJ _J Lu > 0 5 a: < Q. O O LJ O c/) O a 0. Q. 15 i /6m - FIGURE VIII- 5 ------- ------- to Ul to UJ 2 i o < - S- 8 = I/BUI —-Q' FIGURE VIM - 6 ------- ------- o -Ifi O O LJ O K ff < z S O {/} C/^ 5 3 > e j o a § < o u 1- L) O 2 1 1 1 W cc 3 ± i z 1 1 _o (£ CD 10 I "PJ U O O : "(VJ _o \/6m -' FIGURE VIII-7 ------- ------- o "in CO LJ O ------- ------- o> §< UJ O < Q - u cr > u _j a o 5 to ^ 3 J > E d s D O > < 0 u 1_ o Q UJ CE a 1 I I u O < ------- ------- o ~ O O E 7 LJ I o. oo (VI UJ x Z o» o m S 8 aui O _• Z (VI -J UJ u. g- LJ _J U. > CO g o a to 5 1 ------- ------- VIII - 17 C. SENSITIVITY ANALYSIS A study was performed to determine the Potomac Estuary DO model's sensitivity to the various input rates. A knowledge of the relative importance of each rate in the DO budget offers assistance for (1) model verification, (2) the design of field and laboratory studies to define a particular rate by suggesting the necessary de- gree of accuracy required, and (3) the relation of the gross effect of each rate to the estuary's physical and biological parameters such as depth, surface area, and algal productivity. The general approach adopted in this sensitivity analysis was to assume two values for each rate—one approximately one-half and the other twice the verified value. All of the model runs simulated the October 1969 loading condition that had been previously verified. 1. Effects of Oxidation Rates (Carbon and Nitrogen) The simulated DO profiles based on carbonaceous and nitrogenous oxidation rates of O.I/day and 0.3/day are shown in Figures VIII-11 and VIII-12. Figure VIII-11 illustrates the considerable effect that the carbonaceous rate exerts on the DO distribution, and in particular on the magnitude of the maximum deficit. Increasing the oxidation rate threefold results in a lowering of the critical sag point from 4.0 mg/1 to 0.2 mg/1. A comparison of Figures VIII-11 and VIII-12 clearly shows that the DO model is markedly less sensitive to the rate of nitrogenous oxida- tion than to the carbonaceous rate. A variation in K comparable to ------- VIII - 18 that of K produced a change in the critical DO deficit of only about L. 1.0 mg/1. The reason for this difference in model sensitivity can be attributed to the greater masses of carbon in the system, and hence a greater range in the amount of oxidized material and DO demand for a given range in rates. 2. Effects of Photosynthesis and Respiration Rates The effects of changing the algal photosynthesis or respiration rates in the DO model are quite extreme, particularly in the recovery region of the upper Potomac Estuary where algal growth is usually ex- cessive. As shown in Figures VIII-13 and VIII-14, the model predictions behaved similarly when either the photosynthesis rate was increased or the respiration rate was decreased. According to the DO profiles in Figure VIII-13, increasing the rate of photosynthesis fourfold, from 0.006 to 0.024 mg 02/hr/yg chlorophyll, increased the critical sag point by 4.0 mg/1 and greatly accelerated the rate and degree of DO recovery. Figure VIII-14 shows a similar oc- currence when the respiration rate was lowered from 0.0016 to 0.0004 mg 02/hr/yg chlorophyll. It should be noted that the maximum chlorophyll concentrations observed during the simulation period were approximately 100 yg/1. Of course, both the individual effects of photosynthesis and respiration as well as the net effect will be dependent upon the quantity of algae present. The model's sensitivity to euphotic depth was also investigated and the results closely paralleled to those presented for the photosynthesis rates. ------- VIII - 19 3. Effects of Benthic Demand Rate Since the units of benthic demand rate include an areal term (ft2), its effects are closely related to the surface area of the Potomac Es- tuary. Figure VI11-15 illustrates the resulting DO profiles when ben- thic rates of 0.0 and 2.0 gr/meter2/day were assigned. As can be seen, the higher rate significantly lowered the entire profile with the most pronounced differences occurring in the wider downstream areas. However, it did not drastically alter the DO gradients or the rates of depression and recovery. 4. Effects of Reaeration Rate Of the various DO budget components investigated in this sensi- tivity analysis, the method by which the reaeration rate is computed, i.e. O'Connor-Dobbins equation, Churchill equation, or USGS (Langbein) equation, was the least important in terms of affecting model output. In fact, the three profiles shown in Figure VIII-16 are coincident, in- dicating that any of the more commonly used equations for determining reaeration rates should prove equally successful. ------- ------- o - o CM y b> LJ cr z g § x o U2 o> — to ^ to g> O o & < o U- o to H U UJ _ o \ \ T o T 01 —r 00 I T UI 9 cr m m (VI o S O UJ OQ . O u> l/6ui FIGURE VIII- II ------- ------- LJ CE Z o 9 x Si 2 * 1§ CO h- U LJ 0> 10 O) u o T o o o o oi o> N in '•* o '•* o K in m ~ z •4 0 o UP u _J I Lo \|/6ui -O'O FIGURE VIII-12 ------- ------- UJ * oc .«•> 8 5 OoP " O O 0- t- K z o o iT t- I T Q. Q. — tD 1/1 2>x I Q CL Q U. 2 o ^ Q U UJ u. u. UJ o o UJ O O i u o o •<\J tf) - cca FIGURE VIII—13 ------- ------- UJ oc. z J5 2 I cr Q. i /\ i/) LU OL U_ 0 (A \- o LJ L_ _i D 2 ^C. 1/1 ci Ci 2 UJ Q < Q 0) «O O) 1^: U O UJ f V \ \ UJ O g ce . m CD tvj z < o $ o •8 in UJ _l I 00 to in FIGURE VIII-14 ------- ------- u 5 CC 10 u o I S j« I- -j 5 Z 3 ° U 2 g OQ to o> Q ci o 12 u. U. I/BUI _ - i in lO CQ O 3 S to Ul -J i FIGURE I- 15 ------- ------- Z o o: O u s tr z O a: LJ < UJ a: o to U UJ 10 z o s — o» «/> (O O) O Q 2 UJ a o o o CO UJ O Q cr m ^^ 5 i u UJ o m U i . o o O) CO {VJ FIGURE VIII-16 ------- ------- VIII - 26 D. NUTRIENT REGENERATION - SPECIAL DO MODEL Realizing the inherent limitations of the dissolved oxygen model heretofore discussed, a further revision of the DEM to incorporate organic nitrogen and nutrient regeneration was investigated. Unfor- tunately, these inclusions complicated the "feedback-feedforward" link- age within the model somewhat and created a problem by simultaneously evaluating several reaction rates. Prior to this, there had been only a single unknown rate to be evaluated through each series of model veri- fication runs. A considerable amount of background information re- lating to the nutrient regeneration process was, however, provided by Jewell [13]. Organic nitrogen was treated in two distinct forms in the model: (1) dissolved or soluble and (2) particulate. The latter, or course, would comprise organic nitrogen within algal cellular material. The dissolved fraction was "decayed" by first-order kinetics to ammonia nitrogen (hydrolysis), while a portion of the particulate form was regenerated to inorganic nitrogen (NH3) and carbon (BOD), thereby cre- ating an additional oxygen demand. Based on a subjective appraisal of existing information, it was assumed that 50 percent of the organic nitrogen and carbon in the dead algal cells, as computed from the mass of chlorophyll decayed, was regenerated; the remaining 50 percent was assumed to be deposited to the bottom sediment. Ratios of chlorophyll to nitrogen and chlorophyll to carbon were estimated using 1970 algal composition analysis data. ------- VIII - 27 Upon completion of this "surrogate" DO model and estimation of the necessary reaction coefficients, a verification run was performed based on September 1970 data. This particular set of data was selected because it pertained to a time of year when algal death was prevalent, as indicated by the relatively high chlorophyll decay rate (0.07/day) required for model verification. Furthermore, a review of Figure VIII-10 shows that the recovery portion of the observed DO profile was not accurately simulated with the existing DO model, presumably because the effects of nutrient regeneration were omitted. Figure VIII-17 illustrates the improved comparison that resulted from predictions using the mathematical model described herein. Both the rate of recovery and the secondary DO sag farther downstream were satisfactorily simulated. Due to an inadequacy of organic nitrogen data and uncertainties in decay rates, no serious attempt was made to verify the model for prediction of this parameter. ------- d o 2 o « cr LJ Q. a to \|/6ui - PlGURE I- 17 ------- ------- IX - 1 CHAPTER IX ADDITIONAL STUDY REQUIREMENTS Recognizing the basic limitations of existing data and their subsequent effects on model structure and verification, the following areas are suggested for continued study of the Potomac Estuary: 1. The use of either laboratory or field studies to acquire a better understanding of algal decomposition rates and extent of nutrient regeneration, 2. The use of either laboratory or field studies to determine nutrient transfer rates between the bottom sediments and the overlying water for consideration in the overall nitrogen and phosphorus budgets, 3. Perform additional algal composition studies (laboratory) during various times of the year in order to relate biological uptake rates of both nitrogen and phosphorus to seasonal bloom conditions, 4. Develop techniques to acquire a better understanding of the nutrient-phytoplankton relationship in the saline portion of the Potomac Estuary where water quality stresses are becoming increasingly pro- nounced and where biological communities are quite different from those encountered upstream, and 5. Incorporation of data from the above, and other special studies, into a truly biological model; one not only capable of predicting algal standing crop levels but also capable of simulating algal species succession, including their causes and effects, zooplankton grazing ------- IX - 2 rates and other well established biological reactions. The develop- ment of this type of model would not only serve a definite purpose in the Potomac Estuary, but more importantly it would provide a signifi- cant foundation for any mathematical modeling effort in the Chesapeake Bay itself. ------- BIBLIOGRAPHY 1. Thomann, R. V., Donald J. O'Connor and Dominic M. Di Torro, "Modeling of the Nitrogen and Algal Cycles in Estuaries," presented at the Fifth International Water Pollution Research Conference, San Francisco, California, July 1970. 2. Feigner, K. and Howard S. Harris, Documentation Report, FWQA Dynamic Estuary Model, FWQA, U. S. Department of the Interior, July 1970. 3. Jeglic, J. M., "Mathematical Simulation of the Estuarine Be- havior," Contract to FWQA by General Electric, 1967. 4. Clark, L. J. and Kenneth D. Feigner, "Mathematical Model Studies of Water Quality in the Potomac Estuary," AFO, Region III, EPA, March 1972. 5. Jaworski, N. A., Leo J. Clark, and Kenneth D. Feigner, "A Water Resource-Water Supply Study of the Potomac Estuary," CTSL, MAR, WQO, EPA, April 1971. 6. Jaworski, N. A. and Leo J. Clark, "Physical Data Potomac River Tidal System Including Mathematical Model Segmentation," CTSL, MAR, FWQA, 1970. 7. Private communication with Roy Weston Consulting Engineering Firm currently investigating the storm and combined sewer contribution under contract to FWQA. 8. "Water Quality Survey of the Potomac Estuary-1965-1966 Data Report," CTSL, MAR, FWPCA. 9. "Water Quality Survey of the Potomac Estuary - 1967 Data Report," CTSL, MAR, FWPCA. 10. "Water Quality Survey of the Potomac Estuary - 1968 Data Report," CTSL, MAR, FWPCA. 11. Manhattan College, New York, N. Y., "Mathematical Modeling of Natural Systems" - 1971 Course Manual. 12. Thomann, Robert V., "Mathematical Model for Dissolved Oxygen," Journal of the Sanitary Engineering Division ASCE, Vol. 89. No. SA5, October 1963. ------- 13. Jewell, W. 0., "Aerobic Decomposition of Algae and Nutrient Regeneration," A Doctoral Dissertation, Stanford, University, June 1968. ------- Chesapeake Technical Support Laboratory Middle Atlantic Region Federal Water Quality Administration U. S. Department of the Interior PRELIMINARY ANALYSES OF THE WASTEWATER AND ASSIMILATION CAPACITIES OF THE ANACOSTIA. TIDAL RIVER SYSTEM Norbert A. Jaworski Leo J. Clark Kenneth D. Feigner* Technical Report No. 39 April 1970 Federal Water Quality Administration, Washington, D. C« ------- TABLE OF CONTENTS Page LIST OF TABLES ............... iv LIST OF FIGURES .............. v Chapter I INTRODUCTION ........ 1-1 II SUMMARY AND CONCLUSIONS ......... II - 1 III DESCRIPTION OF THZ STUDY AREA ....... Ill - I A. General ............. HI - 1 B. Stream Flow Analysis . „ . . Ill - 2 C. Water Quality Conditions ....... Ill - 3 1. Dissolved Oxygen and Biochemical Oxygen Demand ............ Ill - 3 2, Bacteriological Densities ...... Ill - 7 3. Nutrients , . «, . . „ . „ . . . in - 11 4. Sediments and Turbidity . Ill - 14. D. Population and Wastewater Projections . . . Ill - 16 1. Anacostia Valley ......... Ill - 16 2. District of Columbia ....... Ill - 17 IV. WASTEWATER ASSIMILATION AND TRANSPORT ANALYSIS . IV - 1 A, Stream Flow - Wastewater Flow Analysis . « . IV - 2 B. Residence or Flushing Time ....... IV - 5 C. Tidal Hydrodynamics . , . . . . . . . IV - 8 D0 Self-Purification and the Dissolved Oxygen Budget ............. IV - 17 ------- TABLE OF CONTENTS (Continued) Chapter IV. WASTEWATER ASSIMILATION AND TRANSPORT ANALYSIS (Cont.) IV - 1 E. Nutrients and Algal Growth IV - 20 F. Treatment at the Blue Plains Plant vs Constructing a Facility in the Anacostia Valley IV - 21 G0 Continuing Studies . IV - 23 REFERENCES APPENDIX A. Anacostia River Study B. Nutrient Concentrations at Bladensburg Bridge Road, Anacostia River, 1966 C. Anacostia River, Kingroan Lake, June 26-27, 1969 111 ------- LIST :? TABLED Number Description 1 Mean Monthly River Discharge. , „ . „ „ Ill - 2 IT Nutrient Cone em rat ions and Loadings, Eladensburg Foad Bridge, Anacostia River , 1966 ..„..,,".„..... .131 - 12 III Anacostia Tidal River System, L. C, Water Pollution Control Pivif ion Data , Monthly Report, June 1969 ........... II! - 13 IV Mathemat icdl Model Segmentation, Anacostia Tid%l Fiver SvrteTn, Mean Water D&ra „ IV _ IV ------- Number I II III IV V VI VII VIII IX XI XII IJST Of FI Description Upper Potomac and Anaeostia Tidal River System Dissolved Oxygen Concentration, Anacostia Tidal River System, 1969 „,..„..„.. BOD Concentration, Ana?ostia Tidal River System, 1969 ..,,., 0 ...,„.... ^ecal Coliform Densities, Anacostia Tidal River System, E'.C,-Md. Line, 1969 .- „ , „ . „ . Fecal Coliform Tensities, Anacc£.ia Tidal River System, Pennsylvania Avenue, 1969 , . . . . Fecal Coliform Densities, Ana^ostia Tidal River System, South Capitol Street, 1959 Turbidity Concentration, Anacostia lidal River System, 1969 . . ,.,..... Mathematical Model Segments, Anascstia Tidal River System .-.,„<,..... Residence Time for ^noos V/astevva+er Flows, Anacostia Tidal River System „„.... Dispersion Coefficient vz Flow, Anacostia Tidal River System, 1969 C. C. Alkalinity Data . . . Simulated Profiles for Various Dispersion Coefficients of a Conservative Pollutant Dis- charged at a Hate cf 1000 Its/day into the Anacostia Tidal River System Above C.C.-Md, Line, Q = 58 cfs „...„,..... Simulated, Profiles For '-'arious Dispersion CoefficientuS of & '"'cnaervative Pollutant Dis- charged at a Rate of 1000 Ibs/day into the Anacostia lidal River System Above P.C.-Md. Line, Q = 108 cfs ......... Page I - 3 III - 5 III - 6 III - 8 III - 9 III - 10 IV - 3 IV - 7 IV - 11 IV - 12 IV - 13 ------- LIST OF FIGURES (Continued) Number Description XIII Simulated Profiles For Various Dispersion Coefficients of a Conservative Pollutant Dis- charged at a Rate of 1000 Ibs/day into the Anacostia Tidal Biver System Above D.C.-Md. Line, Q = 208 cfs .......... IV - H XIV Simulated Profiles For Various Wastewater Dis- charge Rates For Calculated Dispersion Coefficients of a Conservative Pollutant Discharged at a Rate of 1000 Ibs/day into the Anacostia Tidal River System Above D.C.-Md. Line ............... IV - 15 XV Simulated Profiles for Various Dispersion Coefficients of a Nonconservative Pollutant Discharged at a Rate of 1000 Ibs/day Into the Anacostia Tidal River System Abnve the D.C.-Md. Line, Q = 108 cfs, Decay Rate = 0.3 (base e). . IV - 16 XVI Simulated Profiles For a Conservative and Non- Conservative Pollutant Discharged at a Rate of 1000 Ibs/day into the Anacostia Tidal River System Above the P«,C.-Md, Line, Wastewater now = 100 mgd, River 0. = 8 cfs ...... IV - 18 VI ------- I - 1 CHAFFER I INTRODUCTION To provide information to assist in decision making as requested by Assistant Secretary of the Interior Carl Klein, a study of waste- water assimilation and transport capabilities of the tidal portion of the Anacostia River was initiated by the Chesapeake Technical Support Laboratory (CTSL) during April of 1970, This study was designed to investigate the effects of a wastewater discharge into the Anacostia River at or near the site of the abandoned Washington Suburban Sanitary Commission (WSSC) Plant near Bladensburg, Maryland. Currently, waste- water flows from the Anacostia Valley are conveyed to the Blue Plains Treatment Plant of the District of Columbia. The Blue Plains plant is presently overloaded and plans are currently being developed to expand the facility. If this plant is to accomodate the projected wastewater volumes using current renovation processes, more land will be required for expansion. Other alternatives could be process changes that would allow increased volumes to receive required treatment within the same area or development of facilities to treat the wastewater at other locations such as the Anacostia Valley. The major emphasis of this study was to determine the effect of a wastewater discharge on the water quality in the tidal portion of the Anacostia in the vicinity of the D. C.-Maryland Line (See Figure I). ------- 1-2 Presented in this report are: (l) an assessment of the current water quality conditions, (2) a hydrologic analysis, and (3) prelimi- nary results of the assimilation and transport capacities of the Anacostia tidal system. ------- 8 fi g tr \| /\ \ \ °c>\^ \ Vv \ \ ------- II - 1 "HAP.7ER J.T A''E' "'ONC1T':5I-"MS A preliminary analysis tf the waitewat-'-r assimilation and trans- port, capacities of the tid.^1 portion of the Ana cos tie River has been made. The findings of rhi.- r^pcrt, which a."; limited '•;• predicting the possible effect on water quality in the Anaoostia tidal river system of dicchifging trfited wastewater fr..-m a service •-r«a comprising the Anacasti'-t Valley ar- Msryjsin'i, are sxunmarizt-d belcw, lo The Anacostia watershed, tributary - the Potomac Estuary ne^r Washington, £•„ Oe, ha? a dr^in^ge are of 18/+ sqioarf mile-, 30 square miles within th° Distrirr of '"^.'.'mtia and 1^4 square mile? within the State of Maryland, 2, The mean stream fl.w in -:he Irnsin is -9bout 122 :f-- ar-i the 7-day low fl:v with a r^'urr^n:^ ir;t--ri/al of i-'.nce-in-ten-year;- is 8 cfs. 3, The lower pert ion rf >>e Ar.dcratis River is a tidal freshwater system having a mean volune of aboxit f4.0,OOC«,OGC Cubic fe»t. 4- Based on 1969 sampling dbta, tne rater quality rond.ition? in the tidal river under £iojmner ccrditi.-.^- are typified ty; a0 Low dissolved : yyg^r. c;nr:^ntra.t icns often falling below ?.0 mg/1, b. High fecal :c,ifora rlen^a'ifts c-ften above 10,000 MPN/100 mi c,, High turbidity level.- especially d-oring periods cf high runoff, and ------- 11-2 d. High nutrient concentrations. While some of the above water qualiiy indicators which fall below accepted stream standards can be attributed to urban runoff, the most pronounced degradation results from storm sewer and combined sewer overflows and defective sanitary sewer systems. 5. The projected populations and wastewater flows of the water quality renovation facility investigated, at a site above the D.C.-Md, border and serving the Anacostia Vnlley in Maryland, are given below. Wastewater Flows Year 1970 1980 2000 2020 PQ-pulation 466,ooo 061,000 744,000 83';,000 55 78 88 99 o, A comparison of the projected wastewater flows to the Blue Plains Treatment Plant of the District of Columbia excluding Anacostia flows and. the flows from the Anacostia Valley is shown below: Year 1970 1980 2000 Blue Plains (med) 177 231 331 Ana cost ia Valley 78 88 % of Blue Plains Flow liqgd) 31 34 27 ------- Year 1980 2000 2020 Stream Flow (cfs) 8 8 8 Wastewater Flow (mgd) 78 88 99 II - 3 7. The ratio of projected Anacostia wastewater flows to the designated low stream flow criterion of 8 cfs, as presented below, vividly shows that most of the advective flow in the tidal system would be from the wastewater renovation facility. Ratio of Wasteyater/Stream Flow 15.1 17.0 19.? 8. Mathematical model investigations of the Anacostia River indicate that wastewater assimilation and transport capabilities for large advective flews are mcst sensitive to the decay rate of a pollutant and not to the dispersion effect of the tidal system. The sensitivity of the decay rate is a result of the long detention time of the tidal system while the effect of the dispersion coeffici- ent is diminished by the pronounced advective movement. 9. Based on mathematical model studies and analysis of 1969 water quality data., it was concluded that the tidal system capability to assimilate oxygen demanding wastewater is currently being exceeded and that any wastewater discharged would have to be of better quality than that currently existing in the Anacostia. 10. The discharge cf low turbidity effluents into the highly turbid Anacostia is expected to create nuisance algal blooms due to increased light penetration. Therefore, a high degree of nutrient removal will also be required. ------- Before Treatment (me/1) 200,0 11.0 2200 Effluent Criteria fffK/U- 2.0 - 4,0 0,1 0.5 - 0,2 - 1,0 Percent Removal Rapee 98 98 96 - 99 - 99 - 98 TJ - 4 11„ Incorporating the need for enhancing the dissolved oxygen levels, preventing nuisance algal growth, and considering the large flow of wastewater compared to stream flow, effluent standards were used to determine wastewater renovation requirements. Renovation requirements for a discharge into the Anacostia are presented below: Parameter BOD5 T. Phosphorus as P T. Nitrogen as N 12. An important requirement of the renovation process is an aerated effluent. Since most of the net advective flow will be wastewater, the effluent must have as a minimum 4.0 mg/1 of dissolved oxygen to meet the DC', standard in the /macostia at the discharge site, 13. If the wastewater were subjected to high carbonaceous and nitrogenous BOD removal and if the effluent is aerated to 6.0 mg/1, the present water quality of the Anaeostia River would be enhanced. The additional 2,0 mg/1 in the effluent is expected to ruise the DO to meet the standard of 4,0 mg/1 at the critical point downstream,, 14. The greatest uncertainty, even at high removal requirements, is the algal growth potential. The effluent, which would be the result of ultimate wastewater treatment (UWT) and would be considered suitable for many water uses, might still contain nutrients at con- centrations capable of producing excessive algal blooms. ------- II - 5 15. A dye tracer study was conducted in late April 1970, during preparation of this report, to ascertain tidal dispersion character- istics and residence times in the'Anacostia tidal system. Other continuing studies will involve (l) water quality interactions between Kingman Lake and the Anacostia Fiver, and (2) reaeration rates and benthic oxygen demands along the Anacostia. Results of these studies will be reported in progress statements of the Potomac Washington Metropolitan Area Enforcement Conference, ------- Ill -1 CHAPTER III DESCRIPTION OF THE STUDY AREA A. GENERAL The Anacostia watershed, tributary to the Potomac River, lies within Montgomery and Prince Georges Counties in Maryland and the District of Columbia. The drainage area of the basin is 184 square miles and presently contains a population of approximately 993,000. The tidal portion of the river extends from the Potomac River near Hains Point to the confluence of the Northeast and Northwest Branches, a distance of 8.75 miles. The mean volume of the tidal portion of the Anacostia is approximately 540,000,000 cubic feet. The nontidal portion of the watershed has a drainage area of 125 square miles. The 196? population of the nontidal area was approxi- mately 466,000. The river mile locations of pertinent land features of the tidal system are presented below: Item River Mile Hains Point 0.00 Douglas Bridge 1,45 llth and 12th Street Bridge 2.45 Sousa Bridge 3.10 Lower End of Kingman Lake 3.80 East Capitol Street Bridge 4.35 Benning Road Bridge 4.90 Upper End of Kingman Lake 5.65 U. S. Route 50 Bridge 6.90 WSSC Marina 8.10 Bladensburg Road Bridge 8.45 Confluence of Northeast and Northwest Branches 8.75 ------- 5, STREAM FLOW ANALYSIS The nontidal stream flew _f the Anaco^tia River comes primarily from the Northeast and Northwest Branches. Mean monthly flows of the two branches and their tots it -^re presented in Table I. Title I Mean Monthly River Discharge Northeast Pr_ Northwest Er. Total l cfs) (cfs) Mon^h January Kebruary March April May -June July August September October November December ' cfs : 89.6 110,4 128.0 108.2 78,6 57.5 48.1 66 . 4 42- D 44.5 63.4 75.3 51.6 141.2 U.I 174/, 73.4 201.4 64.1 172.3 50.9 129.5 39.7 97,2 32.6 80.7 40.8 107.2 28.1 70.7 24.8 69,3 38.0 101.4 43.0 118.3 The average daily discharge of the combined branches is .1.22 cfs with a 7-day low-flow recurring once-in-ten-years of 8 cfs. While the average flow is 122 :fs, the median flow fthat flow occurring 50 percent of the time) is 66 cfs, indicating that stream discharge is flashy. ------- I C . WAT ER QUAL ETY COND 1 1 1 ONc The water quality condition of the tidal portion cf the Anacostia is monitored by the Department of Sanitary Engineer-ing, District of Columbia and by the Chesapeake Technical Support Laboratory, Federal Water Quality Administration, Special studies of the entire basin were conducted by CTSL in 1967 said ±969. The major sources of water quality degradation are land runoff, storm drainage, defective sanitary sewers, and •jombi.r.ed sewers., There are no significant discharges from wnstewater treatment facilities in the basin, 1« Dissolved Oxygen and Biochemical Oxygen _ Demand The dissolved oxygen (DO) concentration in 1969 was depressed below 5.0 mg/1 in most cf the tidal system during most of July, August, and September. As can be seen in Figure II, the lowest con- centration, between 1,0 ' ------- Ill - 4 The water quality standard for DO for this reach of the Anacostia is a minimum of 3.0 mg/1 with an average of 4.0 mg/1. This standard was not met in July, August, and September of 1969 in the tidal portion of the Anacostia. June 1969 surveys indicated the same to be true for the Kingman Lake area and the Pennsylvania Avenue sampling point. ------- Figure II ------- o I O) «0 I r- ------- Ill - 7 Jb 2. Bacteriological k Figures IV, V, and VI present the fecal colifonn densities for the water quality sampling stations at the D.C.-Md. Line, Pennsylvania Avenue, and South Capitol Street Bridge. The data obtained by the District of Columbia Department of Sanitary Engineering indicate that fecal densities are higher near the D.C.-Md. Line. Densities over 10,000 MPN per 100 ml were measured frequently at the D.C.-Md. Line during 1969. Data for the Kingman Lake study also indicate high fecal densities with counts ranging from 2,100 to 93,000. The fecal coliform standards, which are a geometric mean of 1000/100 ml and 10 percent of samples not to equal or exceed 2000/100 ml, are not currently being met in the tidal portion. Daring the survey of the entire watershed in 1967, the Sligo Creek station at Chillum Manor and the Northwest Branch at Queens Chapel Road had the highest bacterial densities. Of the fifteen stations sampled, none had consistently higher densities than were found at the stations located in the tidal portion of the basin during 1969 (See Appendix A). This indicates, that the high densities in the tidal portion are from local sources such as the sewer systems and not runoff originating in the upper drainage area. ------- 100.000-1 FECAL COLIFORM DENSITIES ANACOSTIA TIDAL RIVER SYSTEM O.C.- MO. LINC 1969 I 0.000- 1,000- 100- r ii i r T i i I I I I JAN FEB. MAR APR. MAY JUN JUL AUG. SER OCT NOV DEC. Fi P\ i rp TV ------- 100.000 FECAL COLIFORM DENSITIES ANACOSTIA TIDAL RIVER SYSTEM PA AVE. 1969 (Z40.0OO) 10.000- I.OOO- ------- 100,00'! 10.000- 1,000- FECAL COLIFORM DENSITIES ANACOSTIA TIDAL RIVER SYSTEM S CAP. STREET 1969 ,(240.000) IAN. FEB. MAR. APR. MAY JUM JUL AUG SEP. OCT NOV. DEC. Figure VJ ------- Ill - 11 3. Nutrients During the 1966 nutrient survey of the Potomac River Basin, phos- phorus and nitrogen concentration data were obtained by CTSL, FWQA (See Appendix B). For 1966, the mean monthly nutrient concentrations and their loadings are summarized in Table II„ As presented in Table II, the average concentrations of phosphorus as PO^, N03 as N, and TKN as N were 0,80, 0.86, and 1.24 mg/1 for the Bladensburg station during 1966. The resulting loadings for the stations in 1966 were 3r;4, 513 > and 633 Ibs/day of phosphorus as PO^, N03 and TKN, respectively, Phosphorus concentrations as high as 8.7 mg/1 as PC/ have been observed in the tidal portion near the D.C.-Md. Line. This large increase, especially during high flows, can be attributed to defective sewerage systems of the Washington Suburban Sanitary Oommission. Data for the month of -rune 1969, presented in Table III, document these high concentrations. Associated with decreases in turbidity or suspended sediments in the tidal system is a decrease in phosphorus which is also shown in Table III,, This adsorption phenomenon of phosphorus or,to silt particles has also been demonstrated recently in both laboratory and field measurement by the Chesapeake Technical Support Laboratory as part of a nutrient transport study in the Potomac Estuary. ------- rtj F> CO H OS «a; EH SB n3 § > 0) H bO "fl J O O -— N S w w 0) S O > -H _C~} P fl O S t— f~-OOOVOONONl~--4 OOONLA CO!AVDOO-4-4OJO^— ^— LAOJ OOVDVOOI^OJHHLA-40OOJ H H H -4-4OLAiHOOOOJVOCOLAON -d-Lr\-4-4-HHOOOO-4VO-4-LA HHHHiHHHHOHHO LAiAON-VOaNOOJOO-=f-HOJ HO-4-4--4--4LA-H/OJH-4-CO OOO.]^-^?-! r-)HHOO t^-OJOOOOHVOOJOjOt^t—- O H H 0s, VD 5 ^ 5dpoa) d^^^^aHbppHPt-o cd fl3 co PH cc! ^3 jij 3 ^) o o cy h)Ssi W) H aJ C~J ^) P (U fl > S ------- TABLE III Anacostia Tidal River System B.C. Water Pollution Control Division Data MONTHLY REPORT June 1969 Sampling Station D. C. Line Ben. Rd. E. Cap. St. Pa. Ave. llth St. S. Cap. St. Wash. Ch. Total,P as PO 6.10 4.81 2.74 1.16 1.03 1.09 0.81 TKN as N (mg/1) 2.14 2.23 2.18 1.85 1.97 2.15 1.73 N02+N0 as N 0.59 0.41 0.40 0.30 0.33 0.20 0.31 NH -N (ml/1) 1.18 0.63 1.10 1.80 l.8o 1.41 0.86 Turb (units) 226 197 161 53 40 18 9 ------- Ill - 14 4o Sediments and Turbidity The Anacostia River can usually be characterized as a muddy stream. Daring periods of high stream flow, large quantities of silt and debris are carried downstream to the Potomac, Sediment data obtained by US OS for the Colesville, Maryland station, located in the Northwest Branch, indicate concentrations over 4,300 ppm at times. The 196? to 1968 sediment yield for the Colesville station, which has a drainage area of 21,1 square miles, is giver, below; Biver Discharge Sediment Year (of s -day.) (tons/year) 1963 5337 16811 1964 6844 11596 1965 5068 15889 1966 5137 14402 1967 6738 15009 1968 6188 10498 Using an average sediment t"linage of 14,OCG at this station, the esti- mated silt contribution for the entire watershed is about 114,000 tons/year. The effect of the sediment loadings en the turbidity in the tidal system is shown in Figure vjl. The higher concentrations of turbidity near the D_C.-Mdn Line are decreased significantly downstream, especially at the South Capitol Street Bridge station. The decrease in turbidity is also reflected in the monthly summary as shown in Table III. ------- 2 H h- 55; ££ LJ > U I -3> "• O) ^ 8* = > >- t < Q P CD V) a o 3 o r o a. UJ Ul cr u ^n o o a UJ in CD OOOOQ T—i—T~T—n—FT—i—r aooooooooc OO — o Figure VII ------- Ill - 16 D. POPULATION AND WASTEWATER PROJECTIONS 1. Anacostia Valley The area which could be served by a wastewater renovation facility located upstream from the D.C.-Md, Line would be the Anacostia Valley located in Prince Georges and Montgomery Counties. Population pro- jections for the Anacostia and Beaverdam Valleys of the two counties have been developed jointly by the Washington Suburban Sanitary Commission and the Maryland-National Capital Park and Planning Commission and are given below: Year 19o7 1980 2000 Capacity Montgomery (Anacostia.1 131,400 167,800 228,600 453,400 Prince Georges (Anacostia) (Beaverdam) 197,400 237,700 313,800 390,500 64,200 81,800 100,900 122,700 Total Populat ion 393,000 487,300 643,300 966,600 These figures were obtained from the current "Ten Year Water and Sewerage Plan" of the Washington Suburban Sanitary Commission for Prince Georges County. Data from a 1968 report prepared for WSSC by Whitman, Requardt, and Associates indicate that the population for the Anacostia. Valley is con- siderably higher. Their analysis shows the following: Year 1968 500,000 1980 850,000 2000 1,000,000 ------- Ill - 17 A request was made to the Maryland-National Capital Park and Planning Commission to update their projections. Their recent projections are given below: Year Population 1970 466,000 1980 661,000 2000 744,000 2020 837,000 Utilizing an average of the wastewater volumes and constituents obtained in the 1969 surveys ( 1 ] and the above populations, dis- charge volumes, BOD, phosphorus and nitrogen loadings before treatment were projected as follows: Phosphorus T. Nitrogen Year 1970 1980 2000 2020 Population 466,000 661,000 744,000 837,000 Volume (med) 55 78 88 99 BOD (Ibs/day 69,200 99,150 111,600 125,550 as P (Ibs/day) 4,320 5,949 6,696 7,533 as N (Ibs/dav) 9,830 13,881 15,624 17,577 2. District of Columbia The projected population, wastewater volume, and BOD loadings, as determined by Metcalf and Eddy, Engineers, in February 1969 for the Blue Plains Treatment Plant of the District of Columbia are presented below: Year 1970 1980 2000 Population 1,750,000 2,227,000 3,122,000 Volume (mgd) 232 309 419 BOD Clbs/dav) 304,000 490,000 718,000 Suspended Solids 378,000 537,000 843,000 ------- Ill - 18 If the wastewater from the Anacostia Valley is treated by a separate facility, the following reductions in flow at the Blue Plains Treatment Plant were estimated: Year Blue Plains* Anacostia Valley % of Blue Plains (mgd) (mgd) Flow 31 34 27 * Excluding Anacostia Flows 1970 1980 2000 177 231 331 55 78 88 ------- rv - i CHAPTER IV WASTEWATER ASSIMILATION AND TRANSPORT ANALYSIS The five major physical factors which govern the wastewater assimilation and transport capabilities are: 1. Stream flow conditions including flow-wastewater volume ratio, 2. Residence flushing time of the tidal system, 3. Tidal hydrodynamics including dispersion, 4. Reaeraticn and decay rates on dissolved oxygen budget, and 5. Turbidity and algal growth. Factors which affect the assimilation and transport capacities other than waste loadings are; I. Storm sewer dischargee, 2e Combined sewer discharges located between East Capitol Street and Souea Bridges and near the llth Street Bridge, 3. Defective sanitary sewerage systems, 4. Benthic demand of organic deposits in the bottom muds, and 5. Land runoff. Water quality data presented ir, the previous chapter indicate that under current sanitary practice.?, the tidal portion of the Anacostia River is receiving more oxygen demanding wastes than it can assimilate during the months of July, Augost, and September. While nutrient concentrations, both nitrogen and phosphorus, are manyfold above the minimum level associated with excessive algal blooms, ------- rv - 2 the growths are not as pronounced as those of the 1950's as reported by Bartsch [ 2 } and Stotts and Longwell [ 3 ]. Reduction in algal growths can be primarily attributed tc lack cf light penetration resulting from high turbidities and to the elimination of discharges from the Bladensburg waste-water treatment facility of WSSC0 Preliminary analysis of the assimilation and transport capacity of the tidal system was made using two separate mathematical models developed by Ihomann [ /i ] and by Water Resources Engineers, Inc., (WRE) [ 5 L The segmentation of the tidal system for the Thomann model is shown in Figure VIII. with detailed data presented in Table IV„ Detailed explanation of the two mathematical models is beyond the scope of this report. A., STREAM FLOW - vfASTEWATER. FLOW ANALYSIS Water quality standards are applicable to river discharges equal to or greater than the 7-day low flow with a recurrence inter- val of once-in-ten-years „ For- the Anacostia tidal system this flow is 8 cfs. For 1968 and the three population benchmarks, the wastewater and river discharges including the ratio of west-ewater stream discharge are presented below: Year 1970 1980 2000 River Discharge-* (cfs) 8 8 3 Wastewater Discharge (med) 55 78 88 Ratio of Waste to/Stream 19.6 15.1 17.0 Dis charge 2020 8 99 19.2 * 7-day low flow with recurrence interval of once-in-ten-years ------- \ if) Z Z LJ UJ 0 £ (T o < o o I I Figure VIII ------- £?, o M t; fH v>. EH oj frr? CO w T 5 >> CO > M H ,_q 5; u g a. l— i O 03 CC pa g -o' 3r "-i ^ ON fv. ^ -r' -7 _T ir^ CV ON -r, r-j j- ^ ^ ..-» CM C1 a") --< ON o o CvJ CX CM CM Cki '-1 — f ~-> --> H H vC1 -~ CQ o ^ c -t x, c cv o J- ^ ON cv --c r^ I---! cc -d- '- f^~ vi o O co --t <•"> (M rv~. ."v. CM (v. —J r-J '-i —i r-J C lACOOrCCTN^^O ^ ,— 0 -X' -f • C-- ~f -^ rv"> -,0 CO u^ vi~ -JT , — I iT~' ^C ^~~ T4 O 3 CO •— 1 CTs ^ CT -• . ' • y^ O CO 1 1 1 O O O O O C 1 ^. '" O O O O O .TO CO - J ^ r^ r^ f c J." r~~ (^ C vM ^X i~Vj VA ' v\ ^ ^O ' " \ 'v" "" ' i'1O CV ' o o o C' c r- -r> c -r o o o c O 0 i/N J-x U.-V u~. LTN u- ^> C u'v r- O A. '-T^. CV O-' ^ ^~ ^ f" L~< -^r '^^ ^O OO -v^, ^ ,„ J .'\| J o o c r; o o " c ^ c <^ o o C uT' J> ." _,- ..^ J~ S O 'J~' O O LP -~ CV CM '-J ^- h- fv- t" -" PO '•^ ^ CV , — : , — f — i , i O O O C '"^ O v . o' .' ..r C L"v O vC ON O C — i <_T O N- r^; — 1 ^ ^ LA ir- h- h- (>... t-- •— 1 -T U-. r-J r-J 0 0^ H •H fi ort ,cg * * ------- IV - 5 B. RESIDENCE OP FLUSHING TJME Assuming a base flow of 8 cfs and wastewater discharges of 50, 100. and 150 mgd and the volume cf the tidal system of 540,000,,000 cubic feet, the residence time of the Anacostia as given below has been computed by a volume displacement analysis and by using the WRE mathematical model; River Flow (cfs) 8 3 * , V O Wastewater Dia Lst&l 0 77 IK 2:>L charge (mgd j 0 50 100 150 Computed Total Residence Flow Time ( cfs .' vdays ; 8 781 35 7 < 162 38 < ------- IV - 6 Therefore, there will be very little effect under low flow conditions on the oxygen resources of the .main Potomac from a discharge in the Anacostia at the site investigated. ------- o 9NINIVW3M % ------- IV - C. TIDAL HYDRODYNAMICS The cross-sectional area of the Anacostia tidal system can be mathematically expressed by the following equation: A - A /»ax Ax - Ac e where: Ax = cross-section at point x Ao = cross-section at x = o a = exponent (slope of curve describing A as function of x) x - distance along the river Using the above expression, the steady-state equation for a conserva- tive substance was used to determine the dispersion coefficient required in the Thoinann mathematical model. The equation is given below: Cx = Co e Q (l-e-ax) a A0 E where: Cx = concentration at point x Co = concentration at x = o E = dispersion coefficient Other variables as previously defined Two methods of determining the dispersion coefficients are by use of either salinity or dye tracer data. However, since this area is not saline and since the dye study, which was initiated in the latter part of April 1970 would not be completed in time for this report, alkalinity data were utilized for dispersion studies. The ------- IV - 9 natural alkalinity difference of about 50 mg/1 between the Potomac and the Anacostia was adequate for this purpose and incorporated into the above formulations. Dispersion coefficients, for the various jnodel segments throughout a range of river discharges, are given in Figure X. For total river discharges of 58, 108, and 208 cfs, the effect of the dispersion coefficient on the simulated profiles using the Thomann steady state model can be seen in Figures XI, XII, and XIII, respec- tively. At the higher flows, the effect on the simulated profile is not as significant as during lower flows. Figure XIV shows simulated profiles for various wastewater dis- charge rates using the Thomann model with the dispersion coefficients as given in Figure X and considering a conservative pollutant. A sharp decrease in the simulated profile occurs at model segment 8 or at the lower end of Kingman Lake. The volume of the tidal system increases rapidly in this reach„ Simulated profiles for a nonconservative pollutant such as BOD, as presented in Figure XV, show an even smaller response to the dis- persion coefficient. The sensitivity of the nonconservative simulated profile to the decay rate of a pollutant is also an indication of a high residence time in the tidal system. Expanded scale simulated profiles for conservative and noncon- servative pollutants are shown in Figure XVI. A 1000 Ibs/day discharge at the site investigated will increase the concentrations of conservative and nonconservative pollutants in model segment 8 to ------- IV - 10 approximately 0.5 and 0.2 mg/1, respectively. Dissolved oxygen in this segment is the most depressed, often with concentrations near 1.0 rng/1 under summer conditions. ------- DISPERSION COEFFICIENT v» FLCW ANACOSTIA TIDAL RIVER SYSTEM 1969 DC ALKALINITY DATA INTERFACE NUMBER 10 RIVER DISCHARGE - 100 IOOC ------- H3AIH DVWOiOd ------- - CO JO re XIi ------- M3AIH DVWOlOd U4 T O. .^ H-, i^.^' O ;,) ,,; « fc: 1 o — in o 6 - li n W UJ 0 (\j UJ I m ci c vO UJ C C (I/6") INVinTOd JO NOUV«iN3DNOD Figure ''III ------- H3AI« DVWOlOd- ( I/6") INVinnOd JO NOliVMiN3DNCO Figure ------- M3AW DVWOlOd (!/••) INVimiOd JO NOI.WUN3DNOD Figure XV ------- IV - 17 D. SELF-PURIFICATION AND THE DISSOLVED OXYGEN BUDGET In the tidal system, carbonaceous and nitrogenous BOD from land runoff, storm sewers, defective sanitary systems was large enough at times to depress tire DC below 2.0 aig/1 in the area of Klngman Lake. Preliminary model .studies Vising the Y/RE hydrodynamic model indi- cate that even with large wastewater discharges, there would be no appreciable increase in self-purification or reaeration rates because of insignificant changes in the advective tidal velocities,, Hence, it appears that a discharge into the Anacostia would have to contain a BOD (both carbonaceous and nitrogenous) concentration equal to or lower than that currently found in the tidal system. For the critical months, the effluent should be renovated to have a BCD5 of 2.0 to 4.0 and an unoxidized nitrogen concentration of 0.5 to 1.0 mg/1. Another important aspect of the v/astev.^ter treatment facility in terms of watej: quality enhan:ement. of the receiving water will be the DO in the final effluent. For a wastewater discharge of 100 mgd, nearly all of the advective rivrer flow will be from the wastewater. Therefore, a minimum of -4.0 mg/1 should be maintained in the final effluent at =511 times. If & c 0 mg/1 concentration of DO is maintained in the effluent, along with a low oxygen demand, the wastewater could enhance present water quality in the Anacostia River. An example of this enhancement c^n be readily shown by utilising the simulated curves in Figure XVJ. With an effluent DC' of 4.0 mg/1, the DO at the critical sag point will be increased by 2.0 mg/1 (0.5 x 4.0) with resulting DO being about 3,0 mg/1. If the effluent ------- H3AIH DVWOlOd -w«\| (PM* i" $ < * !' ^ M s K LU CC. I ------- IV - 19 has 6.0 ing/1,--or approximately 5,000 Ibs/day of oxygen, the DO at the critical point will be increased by approximately 3.0 mg/1. This assumes that reaeration from the atmosphere is equal to the oxygen demand of the wastewater (The DO during the summer months of 1969.was about 1.0 mg/1 in this area). The resulting DO in the system from the 6.0 mg/1 would then be approximately 4.0 mg/1 (3.0 + 1.0), thus meeting the DO water quality standard. ------- IV - 20 E. NUTRIENTS AND ALGAL GROWTH As indicated earlier in this chapter, algal growths were abundant in the Anacostia in the 1950's. Lark of nuisance blooms during the spring and summer months in the I960'? appear to have been a result of low light penetration snd the elimination of the Bladensburg Wastewater Treatment Facility. If a wastewater effluent of 100.mgd of highly treated effluent including low turbidities were to be discharged into the Anacostia above the D,,r. .-Md. Line, a significant increase in light penetration will occur. Such an increase could cause nuisance algal growth in the Anacostia„ To reduce the incidence and magnitude of nuisance algal growth in the upper Potomac tidal system, upper limits of 0.1 and 0.5 mg/1 of phosphorus as P and nitrogen respectively were used to calculate maximum permissible nutrient loadings from wastewater discharges. Since most of the a directive flow would be from wastewater, the nutrient concentrations in any Anaeostia effluent should be similar to these limits. Allowing for possible continued reduction in light penetration, a range of these nutrient limits was utilized. The phosphorus limits vsed were 0,1 t.c 0.2 mg/1 with nitrogen limits of 0.5 to 1.0 mg/1. ------- IV - 21 F. TREATMENT' AT THE BLUE PLAINS PLANT VERSUS CONSTRUCTING A FACILITY IN THE ANACQSTIA VALLEY The Potomac River-Washington Metropolitan Area Enforcement Con- ference on May 8, 1969, agreed upon a BOD loading of 16,500 Ibs/day, a nitrogen loading of 8,000 Ibs/day, and a phosphorus loading of 740 Ibs/day. Based on 1968 contributions, the Blue Plains Treatment Plant was allocated 12,700, 6,130, and 560 Ibs/day of BODj, nitrogen, and phosphorus, respectively. Using the current loading rates and popu- lation projections, the removal percentage and effluent concentrations were determined as given below: 1970 1980 2000 Q = 232 mgd Q = 309 ffigd Q = 419 nigd Cone. Cone. Cone. Removal Effl. Removal Effl. Removal Effl. (%} (we/I) (%} (me/1) (%) (me/1) BOD5 Nitrogen Phos . as P 95.8 Sf>.6 96.6 6,50 3.20 0.28 97 90 97 4.90 2,40 0.22 98 93 98 3.60 1.80 0.16 The effluent from the 419 mgd facility would have to be renovated to such a high degree, except for nitrogen, that it could be considered as approaching ultimate was tews ter treatment (IJWT). Ultimate wastewater treatment 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 intended use of the water resource due to the lack of needed assimilative or transport capability of the stream. ------- 200.0 11.0 22.0 2.0 0.1 0.5 - 4.0 - 0.2 - 1.0 98 - 99 98 - 99 96 - 98 IV - 22 Wastewater constituents before treatment, effluent concentrations, and percent removal requirements for a discharge into the Anacostia at the site investigated are presented below: Wastewater Constituents Effluent Percent Parameter Before Treatment Concentrations Removal (mg/l) (mg/l) Requirements BOD5 T. Phosphorus as P T. Nitrogen as N In incorporating UWT into a water quality management program, the effluent standard concept is utilized. For receiving waters such as the tidal portion of the Anacostia River, this concept appears to be realistic under present conditions to enhance the dissolved oxygen resources and to prevent nuisance algal growths. If an effluent of this quality is maintained during the critical times of the year, the UWT concept cnn be applied to the tidal portion of the Anacostia River. With this concept, the effluent will be of higher quality than the existing water quality in the Anacostia and thus will enhance the water quality providing a positive water quality management approach. Even with the high waste removal requirements, a major uncertainty is the possibility of nuisance algal blooms stimulated by favorable growing conditions in the tidal system. Data obtained by CTSL from the tidal waters of the Anacostia, which are shallow, with little ------- IV - 23 freshwater inflow and insignificant transport indicate that such areas have higher growths at the same nutrient levels for a given area than along the main stem of the Potomac. While light penetration inhibition may reduce this potential somewhat in the Anacostia, nevertheless, the potential remains. Discharges into the main Potomac have a decreased algal growth potential per square foot area because of the greater depths. G. Continuing Studies Additional studies relating to (l) tidal dispersion characteristics of the Anacostia River, (2) water quality interactions between Kingman Lake and the Anacostia River, and (3) further definition of the DO budget including reaeration rates and benthic demands are already in progress or will be initiated by CTSL in the coming months. As mentioned earlier in this report, a dye tracer investigation of the Anacostia River was conducted from April 22-28, 1970. While the data collection phase of this study has not been completed, preliminary analyses indicate that (1) dye movement and residence time closely parallels mathematical model predictions, and (2) a considerable dye buildup was observed in Kingman Lake which further demonstrates that its water quality is significantly dependent on the Anacostia's quality. The final results of this dye study will be incorporated into the next progress report for the Potomac River-Washington Metropolitan Area Enforcement Conference. They will also be published in a separate report entitled "Potoraac-Anacostia Rivers Dye Studies." ------- REFERENCES 1. Jaworski, N. A, "Water Quality and Wastewater Loadings Upper Potomac Estuary During 1969," Chesapeake Technical Support Laboratory, Federal Water Pollution Control Administration, Technical Report No. 27, November 1969. 2. Bartsch, A. F., "Bottom and Plankton Conditions in the Potomac River in the Washington Metropolitan Area," Appendix A, A report on water pollution in the Washinton metropolitan area, Interstate Commission on the Potomac River Basin, 1954. 3. Stotts, V. D. and Longwell, J. R., "Potomac River Biological Investigation, 1959," Supplement to technical appendix to part VII of the report on the Potomac River Basin studies, U. S. Dept. HEW, 1962. 4. Thomann, Robert V., "Mathematical Model for Dissolved Oxygen," Journal of thjg Sanitary Engineering Divisionf American Society of Civil Engineers, Proceedings Paper 3680, Vol. 89, No. SA5, October 1963. 5. Orlob, G. T., R. P. Shubinski and K. D. Feigner, "Mathematical Modeling of Water Quality in Estuarial Systems," Proceedings of the National Symposium of Estuarine Pollution, Stanford University, August 1967. ------- PH 3£K 0) -H PH Mn >~H £ o S-( o f H P^ o A ""} oooo o ~orc o ON O O h- CV 01 CM r-l O CV! O "O CVi H r>. ,"- .^ OJ ^ H v x-' H ^ \' c o o o o c- o o o o o o o o^ .j-\ r- o o o co oj o a> N »-f cv o-i ro [--" S-T - -~ oA~ r-! -1 V i - - -H r-H r~-\i co a-NVT' O o c, >r, ..« O ^i i;: of\| ... i .... t •/) (i"i ,rx i -L <\i rH -i CV , -] J ; •" < CO H ~~- j N 1-4 <"1 OJ O O ~~ rx Q ,-- QQ >~! 0 fT.) [—\| Bl? GO H C/) W ua n h> > 1 Hi W t" U-J ON <! H M frt F-I S: ro •A ,-. w; iH\| • • • • • - ... CO LI R i ICO c\i N- -4- t-N ur; C C LO ON J- h-J H cq H H to tr: F.-i O ' 1 t f ' r£ i ; n H' T, i" 1^- V.) _J .I-1 O -"> r-i 0 H r5 "---^ > .r> CM CM H O O 01 0" CO L'\ 01 ^n 1? "^7 ? CO CO OO CO ------- Fecal Coliform MPN 0 "f-i ^ •H P- r-J ^ o s O • • H i> CO E ft • H m H ^-~ CO CO S H PQ S ll a O £31 1 ^ Bw r- i C] (!) ft Q> d a? cd P CO EH O 0 O C 0 O ONCO CO r— OO f— -4 H -H H A OO-CN O O O O 0 O O O O OJ ON ON O O £-- N- f— oo oo H AHH OJ O LACO OO OJ OO 1 CO P< H -t o o o co pa E5 DO O t^--4 OJ H OJ H - g O K ° § £> OO LA h- H I M 4- -4- CO H -4 g OJ OJ H H H W PP 0 S § PM S O Q M LA, O OJ OJ VO O VO OJ LA -4 OO t~- f- LA H O ON ON O VO OO -4- -4 O CO O O rH OJ H H H r-\| H H t--OO ON O H H H H OJ OJ I i i i i ooooo ooooo OOOOOO-if N-OOONONON f— OO OO oo H rH ^J-Ot— 00 H" OOOOO OOOOO OO-4-ONO ONCOONOJO O OJ H LA OJ rH -4-OOOO OOJCO-4CO LArjOHLA OJH -4" ^^ H H OOOOO CODO-4-vO-4-O CO 4-N-HOO^ 3 VOOJVOVO S 4-VOVDOOt^-O H OO VO ONH O OOCO -4- -4" -4- H VD -4 -4 VO OO t— OJ ^-t^-OOJVO COVOVON-CO b-H-4-COO -40OLALAOO X)OOCT\ONON OOJrHOH H H H H H t^-CO ON O H -4 LAVO N-OO HHHOJOJ OJOJOJOJOJ 1 1 1 1 1 till! —T -^ -^" -^ -~~f --^" -^* -^j" ^r -^5" - ooooo VO O OJ O H -4" LA OO OJ OO OOOOO CO O t— O VO -4" OO H OO-4 OO H 00 -4- -4" CO -O VO OJ -4- -4" O oo ^H > OJ OJ O VO H 1 t1— LA O LA, 3 H P CO h^ O H ONCO H i 30 CO VO LAVO OJ H H OJ H O I EH CO oo S ^ 0 f^H vD -4^ LA O C— 4- LA OO-4" VO H 00 LA. t— CO OJ H OOCO O -4" H OJ H H OJ H H H H H 4" lAVO t~CO OJ OJ OJ OJ OJ 1 1 1 1 1 4- -4 ^4- -4- -4" OOOOO oo oo ooco ON OJ H i-l -4 -4- 00 OOOOO O OO OOCO ON t-- 00 H -4- t-- OO -4 -4 O i I OJ OJ VO O VO -4- 1-4- i ON O H O -4 -4- -4- oo VD ONCO VD LA OJ H H OJ OJ e O OJ ON O OJ -4- OO OJ t— t^- H H rO 4^ ON OJ H ON oo o3 d (•— OJ C— VO CO -P 0) O OJ H O r-\ ------- £• !H H O (D CM g; t) -H E d\ , i ^r VL" 1^ rJ^i fn O O o CQ e • ft • H w H ^-J CQ CQ S H § ef CO \|K tQ I") H EH EH 0< Hg. 0) H a -} 1 H W o W >D CO OO LA LA W 4- -4" O VD O I1 O ON 00 OJ -4- OJ te O H H U CO O J3 O CO O CO CQ o co o VD VD VD LA OO O -4- CO O LA t— b--4" H t^- H OO oo t— b- ro H VD LA CO CO O CO CM H ON CM -4- LAVD t>-CO CM CM CM CM CM I I I I I 80 o o o o o o o ON O O O O O ON O CO O VO O LA LA ON H VD CM O O 0 O O O O O O O ON O O O O O ON O O O VO O OO OOCO H VD H CM -4- •v "s H oo 0 -4- 0 OJ-4- -4- CM OOVO DO CM O VD -4- X) OO OJ ON O K H H M PH § o P-* O VD LAVO LA 5 OOCO OJ ON H PP LA-4" OO LA-4" S P 2j PQ X> CM LA LA CO OO OO-4- OO t— LA LA LA CO .A O VD -4" VO -4" N- N- CM N- CM VD N- ON O OOCO ONOO CM OO OJ ON ON H H H 4- LAVD !>-CO OJ OJ CM CM CM I 1 1 1 I O 0 O O O CO O O Q O H O CM O O ON t-^ 00 t^~ H VD O O O O O O O O O O CO O O O O -4- VO -4- O CM oo^i- CM H OO CM -4- CO -4- O VO CM -4" VD LA ON CM -* CO O VD OO -4" CO O LA H -3- 00 00 CM pt] 8 S pq O LA OO h- O •O f— ON h— CM O 4- oo ooco oo B CO CO 00 H CO LA CM ON CM CM LA CM O O O O O vO ON LA ONVD CM OO OO-4- CM LA r-f VD O ON O VD H H CO ^O t— i-~CO ON •4- LAVD t--CO CM OJ CM CM CM 1 I I t I O O O O 0 OO O OO CM CO H t- OO-4- J- H lA OO O O O O O CM O O O O -4- O OO O O LA OO H OO-4- H H CM -4- CM CO O O CM LA CM CO CO H H H H H W • i— O VD O CO H H H K i K u X) CO oo oo ON & ------- Fecal CoHform MEN N& UIJOJT-] O 0 O^\ i./- cj qp > CO B P-, • H rn I ""-s^ C/J rn ^^ 3 O bD co co 6 p< SIP ffl H § . II o^L S^ 0) H fl ------- EH PQ < vp to t> O fi3 O O ONO LT\-4-COCOOO O LT\LT\OJ-4- OJ f— CO b— CO H LTN-cJ- O LT\CO H OJHOJt^ OO 00 H -=!• LA H H OJ O VDOOOOj OHOJOJ HOJOJOOHOJOJOOHHOJOOHOJOOHOJOHOJOJOHOHOJOJO I I i I l i I i i I i I I I i i i i i I I i i I i I i i i i i H H H OJ OJ OJ OJ OJ OOOOOOOOOOOO-J--^- LALALALAVOVOVOVO f— t^-CACAON^O ------- T( w > O ^H •H H 0 Sampling Date OOOOOOOOOOO i — i cj v£j cvi o c\l t^x O v^) ON co O OJ CO O^ i — i CO t1 — CO M3 ^" C — H-J-oomoooooo OOOOOOOOOOO LT\OJ t~— ON OJ H-^"-? 1ALT\LT\ ocuoo-^-oooooo OOOOOOOOOOO t^~ LT\ ON ^5 CW O — d" LT\ ^\ VO ON LTN-^J" LT\ -^" ^^" O"N CO LTN CJN CTN VD OJOOOOOOOOOH LT\ O ^ O ~^~ E' — VO VO VO t1 — LTs LfN OO LT\ IT\ CO t— VO LA -if -it CO H ITs H HOJOJOHHOOHCMCVl i i i i i i i i i i i OOOi-jHHOJCVJOJOJCVJ HHHr-HHHrHHHHH ------- >H K £) FH £ pg - p , £> f-i K i3 -P ?H d) p^ «J 0) o ^j fH OJ -P -P -P ft 0) Oj JD CD \|^ (U-4 pr^ ct O £H -H 0) 4J ^.Q u5 S 4-5 p CO & 0) t(J) cd EH CO EH OJ H a a> ft a) -P E .^j eS S cfl P CO EH §000000000 OOOOOOOOO OOOOOooooOO OO J" J" -^" LT\-^ ^t J" _^- OO CTxOJOJOJHOJ OJ- oooooooooo 8 ooooooooo ooooooooo ooooooooooooO ooooro CT\ ON -j- ^d/ _H/ ON .-th ON -H/ -~j- OJ J-COCOOO-4- OJ-VDVDCO -d- H CVJ VO H OO 00 J- OO OJ t~- t— LA LA-d-'-H/ VO -=t -4" LA lAVO rH 00 J- ^1- H LA^t CO OJ-OJOJHOJHr-IOJH OCOOJOiAOJOOOO -4" OOOJ OOOJ-:!-- OOOOOO VOU5M3VDVOVD^OVOVOVO LA OJ OJ OO U"\ LA O OO ON O ON ON O"N ON ON ON O 0s* ON G> OJOJOJOJOJOJOOCUOJOO LA OJ OJ 1 1 1 O O O VO ^3- H H H , H OJ OO.-3- LA^O l^-OO ON O H "^ OOlAOOt^t— t— -4- OO LA-* OO OO OJ O lA J- OO O HOOOOOOOOOOOJOJOJOJ HHHHHHHHHH VO OJ 1 VD . r^ 0) ^ 0) CO € 3 g 10 •rl fl 0} ® O c°s •H 0 t> -p •H -P H O fl 0 S -P , -P !H -P CD 0 > X O O Tj r^ O ^ H -P -H =H 0 O W -N •^ ti f"H JH i — I O CU f a CO ------- APPENDIX C (continued) Station Description; 1 Intersection of stream and Anacostia, north of Worth Kingman Lake bridge. 2 Kingman Lake, north of northmost island. 3 Kingman Lake, northeast corner of third northmost island, first above bridge, h Kingman Lake, just north of Banning bridge. 5 Kingman Lake, west side of island, between stone outfall and drainpipe. 6 Klngraan Lake, east side of southmost island. 7 Kingman Lake, just south of East Capitaol Street Bridge. 8 Kingman Lake, north of locks, east of hospital. 9 Anacostia River, south of locks. 10 Anacostia River, south of Benning bridge. ------- Chesapeake Technical ^uprori. l,abora;o> Kiddle Atlantic Region Federal Water ', ualicy Administration U. S. Derartrrent of the Interior CURRENT WATER QUALITY CONDITIONS AND INVESTIGATIONS IN THE UPPER POTOMAC RIVER TIDAL SYSTEM Teci.T.ical Report No. kl Johan A. Aalto, Chief, CTSL Norbert A. Jaworski, Ph.D. Donald W. Lear, -jr., Ph.D. May 1970 ------- TABLE OF CONTENTS fc • Page L LIST OF FIGURES ..................... iv 3fc }. LIST OF TABLES ..................... v 'In Chapter I INTRODUCTION ................... I- 1 " II SUMMARY ..................... II- 1 III DESCRIPTION AND LOCATION INDEX OF THE * POTOMAC RIVER TIDAL SYSTEM ........... Ill- 1 A. General Description ............. Ill- 1 «w B. Location Indexes .............. Ill- 1 ' 1. Reaches of Potomac River Tidal System . . Ill- 3 2. Zones of Upper Potomac Tidal System . . . Ill- 3 ** IV WATER QUALITY CONDITIONS ............ IV- 1 A. Upper Potomac River Tidal System ...... IV- 1 te B. Potomac Tributaries ............. IV- 5 * V CURRENT ACTIVITIES ............... V- 1 m A. Wastewater Composition ............ V- 3 I » 1. Historical Trends ............ V- 3 t 2. Evaluation of Sources .......... V- 3 » B. Nutrient Response Studies .......... V- 7 ' 1. Biological Discontinuity Studies ..... V- 7 2. Ecological Treads as Related to i Nutrient Loadings ........... V- 9 ii ------- TABLE OF CONTENTS (Continued) Chapter REFERENCES V CURRENT ACTIVITIES (Cont.) C. Nutrient Transport .............. V-14 D. Dissolved Oxygen Budget ............ V-18 E. Embayment Studies .............. V-19 iii ------- LIST OF FIGURES Number 1 Wastewater Discharge Zones in Upper Potomac Estuary Ill- 2 II Potomac River Tidal System Ill- 4 III Nutrient Enrichment Trends and Ecological Effects in the Upper Potomac Tidal River System V-10 TV Total P as PO. Isopleth V-15 iv ------- ------- LIST OF TABLES Number I Zones of Upper Potomac Estuary Ill- 5 II Fecal Coliform Densities - Upper Potomac River Tidal System IV- 3 III Fecal Coliform Summary - Potomac Tributaries IV- 6 IV Wastewater Loading Trends - Washington Metropolitan Area V- 5 V BOD,, Carbon, Nitrogen arid Phosphorus - Summary of Contributions V- 6 VI River Discharge and Phosphorus Loading . . . V-16 ------- I- 1 CHAPTER I ,(, INTRODUCTION During the November 1969 progress meeting of the Potomac Washington Metropolitan Area Enforcement Conference, information was presented on water quality conditions and wastewater loadings in the upper Potomac tidal system during 1969- At the spring meeting of the Interstate Commission on the Potomac River Basin (ICPRB) at Indian Head, Maryland, April 16-17, lv^70, a summary statement was presented giving data on waste loadings, water quality, and studies by the Chesapeake Technical Support Laboratory on the middle and lower Potomac estuaries as part of the joint stud;/ proposed in Recommendation Ik of the conference. A detailed oral presentation was also given by Dr. Lear on the "Ecology of a Eutrophic Estuarine Discontinuity." Since there were no significant changes in water quality conditions and wastewater loadings as of November 1969> this report will concentrate on the status of investigations currently being conducted by the Chesa- peake Technical Support Laboratory. Specific references will be made to the Potomac-Pi scataway and the Artacostia wastewater assimilation and transport studies. Separate reports on both of these studies have been prepared and are available. ------- IT- 1 CHAPTER II .SUMMARY Based on data obtained by rc-rjonnel of the U. S. Geological Survey, Dalecarlia Filtration Plant, U. 5. Army Corps of Engineers, D. C. Depart- ment of Sanitary Engineering (DCDSE), D. C. Department of Public Health (DCDPH), Chesapeake Technical Support Laboratory (CTSL) of the Federal Water Quality Administration (FWQA) and the several wastewater treatment agencies in the Washington metropolitan area, a statement on current water condition- and investigations of the upper Potomac Eiver tidal system was prepared and is summarized below: 1. Fecal coliform densities in the area of Woodrow Wilson Bridge continue to be significantly lower as a result of the increased chlori- nation of treated waste discharges initiated in June-September 1969- For example, during the months oi Tare, July, and August 196}* the median density was about 90,000 MPN/100 ml, while from September 19b9 to April 1970, over 50 percent of the samples had fecal coliform densities less than 1000. 2. High fecal coliform densities were prevalent at times of high stream flow in the portion of the Potomac from Chain Bridge to Memorial Bridge, which it atove the major wastewater discharges. These high densities can be attributed to a combination of land runoff from the upper Potomac basin, urban runoff, storm sewers and combined sewer overflows. 3- Tributaries of the Potomac in the Washington metropolitan area also contained very high fecal coniform densities at times. Cabin John ------- II- 2 Creek had consistently high counts in 1969 with 25 out of 23 samples showing fecal coliform densities over 10,000. k. A Potomac Estuary Technical Committee was formed to provide guidance and coordination in the study of water quality problems of the upper Potomac River tidal system. 5. Studies by CTSL are continuing in three major areas: (l) nutrient ecological responses, (2) nutrient transport, and (3) oxygen budget resources. fj, During Februar,, and Mar..:, in 19^9 and again in 197(3? extensive rnytoj'laiihtoi' blooms were detected in the Potomac from Smith Point to Gunston Cove. "'. Under 5j_jmner ci>: di tior.r massive blooms of blue-;r',-cn algae were prevalent from Fort Washington to Maryland Point. T; e de.':sities of these blooms were about ;> to 10 'Ames ',hat reported in mos'- otf er e~j troi >h. i c warer5, . 3. Preliminary resiJ.ts of ecological studies of the Potomac est-iary in the area immediately above tne Rout;e 301 Potomac River Bridge indicate that the decrease in ohe macsive blae-green algae, Anac^stis, is inter- related to (l) the increase of saliraty from about 2,000 to 10.000 ;-i.:i. (2) the decline ir. nutrients, mainly phosphorus and nitrogen, and (3) the competition for available nutrients by the dominant marine communities in the area below the Route 301 Bridge. 9- Since the late 1930'3 the amount of phosphorus entering -one Potomac from wastewater discharges in the Washington metropolitan area has increased aboat tenfold and nitrogen increased about fivefold. ------- II-3 The amount of BOD (carbon) since then,, although increasing to about 200,000 Ibs/day in 1957, has decreased to about 129,000 Ibs/day in 1969. 10. The major shift from the balanced ecological communities in the Potomac toward nuisance blue-green algal growths appears to be related to increases in nitrogen and phosphorus, and not BOD (carbon). This shift in ecological communities has also been simulated in controlled studies. 11. Nutrient data Irom March 196'? suggest that while large phosphorus loadings enter the Potomac estuary during extremely high discharge from the river upstreain, the effect appears 10 be a decrease rather than an increase in concentration in the upper Potomac tidal system. Most of the phosphorus which entered the tidal system from the upper basin, plus some in the system from the wastewater discharges, was adsorbed and depos- ited in the bottom sediments of the estuary. 12. Studies of nitrification rates suggest that the oxidation of ammonia nitrogen is r.ot a significant factor in the oxygen budget when the water temperature is below 10° C. Studies are continuing to determine the effects of nitrogen on the eutrophication aspects. 13- Dye and mathematical model investigations of the Piscataway embayments and the Anacostia tidal system indicate that wast,ewater assimi- lation and transport rates are very low. Wastewater discharges into the embayments of the Potomac may require higher removal rates than those required by the enforcement conference. Ik. An analysis of each individual embayment will be required before wastewater treatment levels can be determined. ------- Ill- 1 CHAPTER III DESCRIPTION AND LOCATION INDEX OF THE POTOMAC RIVER TIDAL SYSTEM A. , GENERAL DE3CRIPTI01I The Potomac River Basin is the second largest watershed in the Middle Atlantic States. Its tidal portion begins at Little Falls in the Washington metropolitan area and extends 11^ miles southeastward to the Chesapeake Bay. The tidal system is several hundred feet in width at its head near Washington and t-roade-is to nearly six miles at Its mouth. A shipping channel with a nil r.imurn depth of 2k feet is maintained upstream to Washington. Except for the channel and a few short reaches where depths up to 100 feet are found, the tidal system is relatively shallow with an average deptn of about IB feet. Effluents from "twelve major wastewater treatment plants, with a thirteenth under construction, serving a population of about 2,500,000 people, are discharged into the upper tidal system. The locations of the discharges from these treatment facilities are shown in Figure I. B. LOCATION INDEXES To achieve uniformity in locating water quality sampling stations, wastewater effluents and related activities, a detailed location index was developed for the entire Potomac River tidal system. A starting point at the confluence of the Potomac with the Chesapeake Bay was established. Uniform river mile locations using statute miles have been developed for the primary sampling stations, landmarks, navigation buoys, etc. The data will be published by the CTSL in the near future. ------- ZONE I MILES fVjM ' HAiN 6RIDGF - 15 ANDREWS A.F.B. MILES 'ROM CHAIN 3RIDGE : 0 (STRICT OF COLUMBIA ZONE II P .'LR MILES FROM CHAIN BRIDGE - 30 WASTEWATER DISCHARGE ZONES ' m UPPER POTOMAC ESTUARY ZONE III MILES FROM CHAIN BRlOGE = 45 FIGURE-I ------- * III- 3 * 1. Reaches of Potomac River Tidal System For discussion ana investigative purposes, the tidal portion of the Potomac River has been divided into three reaches as shown in Figure II and described below: t ~^ Reach Description Hiver Miles Volume ft I \ cu. ft. x 10° JH« "^ t i ' Upper From Chain Br. to Uk.k to 73-8 93-50 Indian Head /' Middle From Indian Head to 73-8 to Vf.O 362.28 Rt. 301 Bridge » Lower From Rt. 301 Bridge Vf.O to 00.0 175^-7^ to Chesapeake Bay n The upper reach, although tidal, contains fresh water. The middle reach is normally the transition zone from fresh to brackish water. In tof the lower reach, chloride concentrations near the Chesapeake Bay range from about 7,000 to 11,000 mg/1. M 2. Zones of Upper Potomac Tidal System w To facilitate determination of water' quality control requirements, the upper estuary was segmented by the CTSL into 15 mile zones beginning * at Chain Bridge. Establishment of zones similar in physical character- istics allows flexibilitv in developing control needs. This zone concept Mr was adopted by the conferees of the Potomac Enforcement Conference on ^ May 8, 1969. River mile distances from both the Chesapeake Bay and Chain Bridge " for the upper three zones are given in Table I as well as in Figure II. ------- Ill- 4 CHAIN WIOOC N POTOMAC RfVER TIDAL SYSTEM FIGURE -H ------- Ill- 5 8 Q K E & CO M f-i •H O ^ cu d CM O O tNl (1 ) CLJ vL/ •+-( H O 3 i 21 d fH W > ^ (U 6 cd O 0) h P^ CM «8 w 0) ^J o 0) M -J •H Q £, o « M CM d •t~i cd ,— pM O t « 0 "cS E ^ •H o W c^l d •H 0} d O d o •H 0) -p d t^ ft o d -H rs) o5 fn o CQ 45 _fr -J- -3- ON -=J- CT\ •3N 00 vD " O D O lA O :r\ H OO -=J- ~4 -J" -^" -4- '7\ -4- H O 0 C O LT\ O H ro -P o d •P O O TH ^ 4J Tj -P O 0) ------- / CHAPTER IV WATER QUALITY CCSDITIONS A. UPPER POTOMAC RIVER TIDAL SYSTEM During the November 19&9 progress meeting, it vas reported that there had been a significant reduction in the fecal coliform densities in the area of Woodrow Wilson Bridge [1]. This was a result of the Installation of effluent chlorination facilities at all major wastewater treatment plants during June-September 1969. Fecal coliform records at four stations in the Washington metro- politan area of the Potomac River, as summarized in Table II, support this November conclusion. Fecal coliform densities continued to be high during periods of considerable runoff in the area from Chain Bridge to Hains Point. These high counts can be attributed to (l) land runoff from above and below Chain Bridge, (2) storm sewer discharge, and (3) malfunctioning sanitary sewer systems. Nevertheless, there continues to be a significant reduction in fecal coliforms from previous years in the treatment plant discharge area. As an example, in 1965 the median fecal coliform counts near Woodrow Wilson Bridge was about 90;COO MPN/100 ml for the months of June, July and August, Since September 1969, over 50 percent of the samples had fecal coliform counts of less than 1000. There has been no significant change in dissolved oxygen readings in the Potomac estuary since November 1969- During the winter and spring ------- IV- ?. months, freshwater flows were near or above normal with the April flows: at about twice the median flow. As a result of the higher flows and low winter and spring temperatures, the dissolved oxygen (DO) concentrations were above 8.0 rag/1. DO concentrations were about 5.0 mg/1 for the first week of Kay 1970 with a river di;--charge of 15/000-20,000 cfs . This can be compared Lo DO concentrations of less than 1.0 mg/1 at the Woodrow Wilson Bridge j •:. early May 19^ when a fish Kill occurred. ------- IV- 3 TABLE II FECAL COLIFORM DENSITIES MPN/100 ml Upper Potomac River Tidal System B.C. Water Pollution Control Division Data April 1969 - April 1970 Date 4- 7 4-21 5- 5 5-12 6- 2 6-18 6-23 6-30 7- 7 7-14 7-28 8-11 8-18 8-25 9- 1 9- 8 9-15 9-25 9-29 10- 6 Chain Bridge -- -- -- -- — — -- -- — 23 4,300 4,300 1,100 1,500 230 2,400 15,000 150 360 730 Memorial Bridge 930 210 150 150 240,000 9,300 2,400 750 11,000 36 240,000 4,300 3,000 360 230 93,000 4,300 230 23 no Opposite Blue Plains 910 93,000 2,300 73,000 4,300 9,300 230 360 2,300 230 93,000 7,300 1,500 910 360 7,200 9,300 2,100 230 730 W.Wilson Bridge 9,100 360 3,600 -- 2,300 3,600 2,300 3,600 4,300 1,500 24,000 11,000 36c 230 230 9,300 9,300 360 230 360 ------- TABLE II (continued) IV- 4 Date 10-20 10-29 11- 3 11-11 11-17 11-24 12- 1 12- '8 12-15 2- 2 2- 9 2-16 2-23 3- 2 3-16 3-23 3-30 4- 6 4-13 ^hain Bridge 23 23 L-) ^3 93 930 ^,300 po cj 2,400 1,200 24,000 ^,300 2,400 2,400 150 73 930 4,300 2,400 Memorial Bridge 23 36 930 93 430 4,300 73 24,000 1,500 110, 000 2,400 15,000 2,400 230 430 930 2,400 430 430 Opposite Blue Plains 9,300 230 930 1,500 ^,300 930 910 36 2,400 110, 000 ^,300 46,000 9,300 240 1,500 230 9,300 430 36 W.Wilson T) • ~t jjridge 360 23 910 36 23 ~ ~J 150 150 43 11,000 110, 000 9,300 92,000 2,400 23 1,500 4,300 15,000 430 ~J v 430 ------- IV-5 t' B. POTOMAC TRIBUTARIES In the previous section, fecal coliform counts were shown to be high during times of high runoff. Sampling data for tributaries of the Potomac taken by the D. C. Department of Public Health in 1969 also show high counts as given in Table III. The locations of the six stations in the table are: Tributary Sampling Point Miles from Potomac Cabin John (Md.) G. Washington Parkway 0-3 Rock Run (Md.) David Taylor Model Basin 0.7 Seneca Creek (Md.) River Road 0.7 Broad Run (Va.) Leesburg Turnpike 2.0 Sugarland Run (Va.) Leesburg Turnpike 0.5 Difficult Run (Va.) Old Georgetown Road 1.0 For the months of June, July, August, and September, high i'ecal coliform densities were observed for all six stations. The data for the Cabin John station show high densities' the year round, suggesting a periodically overloaded sanitary sewerage system in this watershed. Data for other urban streams in the Washington metropolitan area, such as Rock Creek as reported by Aalto, et al [2j, and Anacostia River by Jaworski et aJL [3], also indicated high fecal coliform densities. While increases in fecal coliforms occur during periods of high flow, the large increases were usually associated with either combined sewer overflows or defective sewerage systems. ------- TV- TABLE III FECAL COLIFORM SUMMARY - MFN/100 ml Potomac Tributaries D.C. Department of Public Health Data 1969 Date 01-08 01-15 02-05 02-12 02-19 04-09 04-16 04-23 04-30 05-07 05-14 05-21 06-04 06-11 06-18 07-09 07-23 08-13 08-27 Cabin John 250,000 + 250,000+ 250,000+ 400, 000 25, ooo 25,000 250,000 25,000 250, ooo 250, ooo 25,000 200, 000 250, ooo 6,000 25,000 25, 000 ^ 25, ooo 170, ooo 120, 000 Reck Run 25, ooo 6,000 1,200 400, OCO 2,500 250 1,200 7,000 4,000 12, 000 500 250 30, ooo 600 2,500 6, ooo 30,000 25,000 60,000 Seneca Creek — 5,000 400 400, 000 1,200 250 1,200 2,500 500 6,000 1,700 200, 000 250, ooo 4,000 2,500 1,700 250, 000+ 6,000 25,000+ Broad Run 600 4, 000 500 250 600 400 250 2,500 4oo _- 1,300 1,200 60,000 600 4,000 25, 000+ 60, 000 2,500 4,000 Sugar land Run 4,000 17,000 10, 000 — .. 2,500 4,000 2,500 3,000 6,000 6,000 5,000 120, 000 25,000 4,000 40, 000 250, 000+ 25, 000 120, COO Difficult Run 250 6,000 1(00 4 00 600 400 600 7, 000 6oc 1, 20-'1 6,000 60, ooo 120,000 4, noo 4, ooo 1, 700 250, 000+ 4, ooo 7 12, 000 ------- iv- r TABLE III (Continued) Seneca Sugarland Difficuli Date Cabin John Rock Bun Creek Broad Run Run Run 09-03 09-10 09-24 10-01 10-08 10-22 n-o4 12-09 12-16 4,000,000+ 4, 000, 000 120,000 12,000 25,000 12,000 12,000 1,600 4,000 400, 000+ 6,000 6,000 40,000 6,000 4,000 0 2,500 60 250, 000+ 25,000+ 3,500 1,700 4,000 6,000 200 7,000 400 7,000 4,000 1,100 2,900 1,700 4,000 50 1,200 1,700 250, 000+ 6,000 12, 000 25, ooo 60,000 250, 000+ 4,000 40,000 4,000 250, 000+ 12, 000 1,700 2,500 7,000 4,000 2,500 1,700 1,700 ------- V- 1 CHAPTER V CURRENT ACTIVITIES Studies to investigate the nutrients that stimulate algal growth and to determine the major driving forces producing dissolved oxygen stresses are continuing. The objectives of the ecological, nutrient transport, and dissolved oxygen budget studies are to: (l) determine the extent of present water quality degradation, (2) develop predictive capabilities for stresses from projected loadings, (3) determine the corrective actions required, and (k) evaluate the detailed ecological pattern during changes resulting from selective nutrient reductions . Other tidal waters of the Chesapeake Bay are also currently being monitored to provide a basis for comparison. These waters include the Patuxent, Rappahannock, Chester, and Severn Rivers, and the upper Chesapeake Bay itself. To provide input and guidance for the CTSL program in studying the Potomac, a Potomac Estuary Technical Coordination Committee (PETCC) was formed, with the first meeting held in November 19&9• Members of PETCC include individuals from Maryland Department of Water Resources, Maryland State Department of Health, ICPRB, Maryland-National Capital Parks and Planning Commission, Virginia Water Control Board, Virginia Department of Economic Development, DCDPH, DCDSE, U.S. Army Corps of Engineers, and FWQA. ------- V- This chapter presents specific areas currently being investigated. Included are recent findings within each of five study areas: wastewater composition, nutrient response, nutrient transport, dissolved oxygen budget, and discharges into embayments. ------- V- 3 A. WASTEWATER COMPOSITION 1. Historical Trends While the population in the Washington metropolitan area increased eightfold from 1913 to 1969 as shown in Table IV, the phosphorus content in the waste discharges increased almost twentyfold. For the same time period the nitrogen loadings have increased about ninefold, from 6,kOO to 52,000 Ibs/day, while the BOD's have increased from >8,000 to over 200,000 Ibs/day in the late 1950's. Since I960 the BOD loading has been reduced to 129,000 Ibs/day. The twentyfold increase is a result of the rapid increase in use of detergents high in phosphorus content since the 19^0's in place of the soap products formerly used in household cleaning usage. At the present time approximately 50 to TO percent of all phosphorus in municipal waste discharges can be attributed to the use of detergents [17] 2. Evaluation of Sources As previously reported [l] CTSL conducted a nutrient survey of the upper estuary during 1969 to determine the relative contributions of critical water quality parameters from the upstream freshwater inflow and wastewater discharges in the metropolitan area. The loadings for the first eight months are given in Table V and a summary of the relative percentages follows: ------- v- u Parameter Freshwater Inflow Wastewater Discharge % of total% of total BOD 45 55 Organic Carbon 68 32 Inorganic Carbon 89 11 Total Carbon 80 21 Total Phosphorus 1^ 86 Total Nitrogen 3^ 66 This summary shows that the parameters in order of most amenable to control measures using wastewater treatment are: (l) phosphorus, (2) nitrogen, and (3) BOD. ------- V- 5 TABLE IV ' Wastewater Loading Trends Discharge to Potomac Washington Metropolitan Area Year •""•»••»• 1913 1932 1944 1954 1957 I960 1965 1968 1969 Population of Service Area - ___ 320, 000 575,000 1,149,000 1,590,000 1,680,000 1,860,000 2,100,000 2,415,000 2,480,000 Wastewater Flow _. (mgd) ^ 42 75 167 195 210 222 285 334 Qiift jK5 BOD _ (Ibs/day) __ 58,000 103,000 141,000 200,000 204,000 110,000 125,000 130,000 129,000 T. Nitrogen as N _ (Ibs/day) 6,400 11,500 22,980 31,800 33,600 37,200 42,000 53,000 52,000 T. Phosphor as PO, 4 ( Ibs/day) 3,300 6,000 12.000 / v v 16, 700 _7 1 v v 26,000 s v 30, 000 57,000 6l, 000 64, ooo ------- H 05 P O EH 0 O •f\ O 00 O r. r OO OO OJ O O O rH OO ^ 0 o 0 6 OJ OO O 0 o 0 O VO H -=f iTN OJ '"O 8 „ IT\ H O 0 O O •\ »\ 00 CO V- 6 !, OJ 0) bO 05 c3 o> 'o -p c/i W -H cd M O u~\ OO C\J H O OJ o H C\J H OJ O O no no O O OJ 00 O O co p; o s T, O 01 !_ IXJ ^ '>, (U PH O M <7\ -P > _H H JS \|~1 p rH ,£T Vs << W to 03 r! M W -P D H ^ W CO >i O C3 1 ^ O o 0 < fH f'j O >i — f /it f-i a) "Pj DC S <, PH 05 is ^" o '"J -P - -H O C O D pq M (D -p CD of 1 O O Q O O O LT\ O O OO GC H H -3" CO 03 s, ^ Q) d) 'U <~CJ ~""--. "^-^ & to w bp Q ^ E i-l rH t! O ' X! CO o \ CJ •H § SO o o o cH O d fr^ fQ H § H OJ "J «5 - crt (o -„ 03 ^-J H "H O £^ a o •H 08 bO ^ O § ON CO VD O a >-, ell* T3 -^^^ W A^ rH ci o 1 0 H $ O EH 8 VO OO CO o5 ^ d^ r-w .^^^ CO o H co rH O w 1 -P O E-i O O CO H CO 05 .^ (Tf r3 ^ CO ,£> H OJ -P 5 j T •H "r CO ------- V- 7 B. NUTRIEM1 RESPONSE STUDIES During 19^9, field investigations were continued to further define the nutrient requirements (carbon, nitrogen and phosphorus) for producing nuisance algal growths. Considerable efforts were spent in defining eutrophic conxli.tdrcfas- iri the salinity transition zone. In the freshwater portions of the tidal'system, large blooms of phytoplankton were observed in February and March of 1969 and again in 1970. Water temperatures at the beginning of these blooms were about k° C. These blooms were primarily in areas between HmJth Point and Gunston Cove. Under 1969 summer and fall conditions as in previous years, large populations of blue-green algae, primarily Anacystis sp., were prevalent. An important aspect of these algal growths was that the "standing crop" as measured by chlorophyll a nad concentrations ranging from approxi- mate!;,' 75 "to over 200 ^ug/1. This is about five to ten times that reportedly observed in most other eutrophic waters [15] Ll6] . The algal populations in t; e saline water areas were not as dense as those in the fresh water areas. Nevertheless in summer large popu- lations of the dinoflagellates Gymnodinium sp. and Amphidinium sp. occurred producing the phenomenon known as "red tides." 1. Biological Discontinuity Studies During the summer of 1969? a special ecological study was under- taken in a 20-mile portion of uie Potomac estuary just upstream from the Potomac River Bridge at Morgantown. This area has been observed for several years [10] to be the lower limit in terms of distance from ------- V- 8 (Jhain Bridge of massive blue-green algal blooms. The major purpose of this intensive study was to determine why algal blooms apparently decreased at this location. The area of investigation was found to be a reach of rapidly increasing salinity downstream, the "salt wedge". An obvious bio- logical discontinuity was found in this reach with marine organisms dominant at the lower end. Tentative conclusions from this study indicate: 1. The massive blooms or the blue-green alga Anacystis currently terminate in this reach for three interrelated reasons: (l) the increase of salinity from approximately 2 to 12 parts per thousand, (2) a decline in nutrients, especially nitrogen and phosphorus, and (3) the competition for available nutrients by the essentially marine dominated biological community in the lower reach is apparently successful under present conditions. 2. These observations may be useful for predicting the time, duration and extent of a possible similar invasion of blue-green algae in other fresh water tributaries at the head of the Chesapeake Bay, especially the Sassafras, Bohemia, Elk, and Northeast Rivers. 3- When firmer conclusions can be drawn from continued obser- vations, the effects of disposal of nutrients from treated sewage into saline waters as compared to fresh waters may assist in optimizing the increase in estuarine water productivity by controlled addition of nutrients, or at least minimize any stress to the estuarine system caused by these additions. ------- ------- I I' V- 9 5. Single sets of daily observations were difficult to interpret, but the aggregate of 15 cruises over a six weeks period showed some statistically significant patterns. 2- geological Trends as Related to Nutrient Loadings A review of past eutrophic trends with estimated nutrient loadings from wastewater discharges into the Potomac was made. In Table IV it can readily be seen that while the present BOD (carbon) loading is the same as in the late 1930's, there is about ten times a;j much phosphorus and five tjme^ as much nitrogen now being discharged. The effect of these increased nutrient loadings can be seen in Figure III. The change in the ecology from 1913 has been dramatic. Several nutrients and growth stimulants have been implicated as causes of this accelerated eutrophication with nitrogen and phosphorus showing promise of being the most manageable. The historical plant life cycles in the upper Potomac estuary can be inferred from several studies. Cumming [k\ surveyed the estuary in 1913-191^, and noted the absence of plant life'neai- the major waste outfalls with "normal" amounts of rooted aquatic plants on the flats or shoal areas below ;-he urban area. No nuisance levels of rooted aquatic plants or phytoplankton blooms were noted. In the 1920's an infestation of water chestnut appeared. This was controlled by mechanical removal [5] . In September and October of 1952, another survey of the reaches near the metropolitan area, made by Bartsch [6], revealed that vegetation ------- xroe v-io 8 CM e r-i rn » i ffffl i TOCfc Si s o - y tv' GB i O ra ft •rl -H I .0 10 4> '.o L 3 cj 0> H i:! ft ,a 1) -< 6 2J •rl -ri f! <& 'i O I «J -H c: q H r ••* :* B -i H ,ij • xi rs»»»»»»M»HN -n £0 a> w a} <- 4> £ ,•* 'o w) (U aj i.- on n r".' 10 ,p Ov H O ON H ,0 - a- H O UJ- ON § H O H H 000 \c> LT> -JT O O no c\J SB '.-'9SoJU fu FIGURE -nr ------- V-ll in the area was virtually nonexistent. No dense phytoplankton blooms were reported, although the study did not include the areas downstream where they were subsequently found. In August and September of 1959, a survey of the area was made by Stotts and Longwell [j]. Blooms of the nuisance blue-green alga Anacystis were reported in the Anacostia and Potomac Rivers near Washington, D. C. In 1958, nuisance conditions of the rooted aquatic plant water milfoil developed in the Potomac estuary. The growth increased to major proportions by 1963, especially in the embayments from Indian Head downstream [81. These dense stands of rooted aquatic plants which rapidly invaded the system also dramatically disappeared in 1965 and 1966. The decrease was presumably due to a natural virus [9]. Subsequent and continuing observations by the CTSL have confirmed persistent massive summer blooms of the blue-green alga Anacystis at nuisance concentrations from the metropolitan area downstream at least as far as Maryland Point [10]. Data as presented below for comparable flow and temperature conditions for September-October 1965 and October 1969 indicate that algal populations have not only increased in density but have become more widespread. ------- V-12 Potomac Estuary River Miles from Chlorophyll a - ,ug/l Location Chain Bridge Sept. 15,Oct. 19,Oct. 1U-16, 1965 196? 1969** Piscataway 18.35 k$ 90 Jk Indian Head 30.60 36 75 120 Smith Point 45.80 6l 56 70 * Single sample ** Average of a minimum of 5 samples While data are limited for 1965, based upon these data and field obser- vations the increase in nuisance algae appears to be significant. Sampling difficulty makes it impossible to quantify the increase at the present time, These biological observations can be interpreted as an ecological succession. The initial response to a relatively light over-enrichment was the growth of water chestnut, which when removed allowed the increas- ing nutrient load to be incorporated Into the rooted aquatic plant water milfoil (Myriophyllum spicatum). The water milfoil dieoff 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 and decay. From these considerations it would appear that nuisance conditions did not increase directly with an increase in nutrients as indicated by the concentrations of phosphorus and nitrogen. Instead, the nutrient increase encouraged a given species to dominate the plant life in the aquatic environment. With a further increase in nutrients this species ------- V-13 was rather rapidly replaced in turn by another dominating nuisance form. This is indicated in Figure III where the massive persistent blue-green algal blooms were associated with large increases in phosphorus and nitrogen enrichment in the upper reaches of the Potomac River tidal system. The persistent massive algal blooms have been occurring since the early 1960's even though the amount of carbon (BOD) has been reduced by almost 50 percent. Laboratory and controlled field pond studies by Mulligan [11] have indicated similar results. Ponds receiving low nutrient additions (phosphorus and nitrogen) had submerged aquatic weeds. Continuous blooms of algae occurred in the ponds having high nitrogen and phosphorus concentrations. An important aspect of Mulligan's studies is that when the aquatic resources were returned to their natural state, the eco- system returned to its natural state. This is also supported by studies of Edmondson [12] on Lake Washington and Hasler on the Madison, Wisconsin lakes [ Ik]. ------- V-lk C. NUTRIENT TRANSPORT A one-year- cooperative sampling program with Steuart Petroleum Company has been completed. The survey was designed to determine the i nutrient movement throughout the entire tidal system. Since 1969 was a nontypical stream flow year, the study was extended into 1970. Nutrient data from 1969 taken at Great Falls, Maryland, indicated that large quantities of nutrients enter the tidal system during periods of high stream flow. A study of a high runoff period in 1967 revealed a significant phenomenon. Figure TV shows that the total phosphorus concentration on the early days of March was about 0.150 mg/1 at Chain Bridge increasing to over 1.0 mg/1 at Woodrow Wilson Bridge as result of wastewater discharges. At the same time the concentrations at Piscataway and Indian Head were l.k and 1.0 mg/1, respectively. On March 7 and 8, the river discharge increased rapidly to about 139,000 cfs (Table VT). This resulted in a discharge on March 8 of over 1,208,000 Ibs/day of phosphorus into the tidal system. However, when the concentrations in the entire upper tidal sje tern are compared to early March, a general overall decrease in phosphorus can be observed. Phosphorus concentrations during high flows are accom- panied by high sediment loads and when they enter the slow moving tidal system, much of phosphorus was adsorbed onto the sediment particles and was removed from water as the sediment settled. CTSL conducted labora- tory studies using Potomac River samples to confirm this removal of phosphorus by adsorption. ------- 55-1 50- 45i 40- TOTAL P«P04 ISOPUETH (mg/l) POTOMAC TIDAL RIVER SYSTEM INDIAN HEAD NOODROW WILSON BRIDGE 0 I 2 34 5 6 7 6 9 10 II 12 13 14 15 MARCH IM7 FIGURE -35 ------- V-I6 TABLE VI RIVER DISCHARGE AND PHOSPHORUS LOADING Potomac River at Washington, D. C. March 1 to 14, 1967 Date River discharge (cfs) T. Phosphorus T. Phosphorus as PO, (Ibs/day) 3- 1 3- 2 3- 3 3- 4 3- 5 3- 6 3- 7 3- 8 3- 9 3-10 3-11 3-12 3-13 3-14 7,690 7,010 7,230 7,270 7,620 8,590 63,100 133,000 139,000 76,400 46,700 36,500 29,500 25,100 0.153 -- 0.155 0.132 0.225 0.177 1.316 1.701 0.936 0.717 0.578 0.355 0.264 -- 6,280 -- 5,990 5,130 9,150 8,120 44,800 1,208,000 694,800 292,500 144,200 69,200 41,588 -- ------- V-17 A more sophisticated mathematical model has been recently adapted to the Potomac Estuary to increase sensitivity in simulating the move- ment of nutrients and other pollutants. Once this capability has been developed and verified, technical areas to be investigated will include: 1. Sensitivity of nutrient concentrations in the upper, middle, and lower reaches to loadings in the upper reach, including contributions from land runoff, 2. The flow probability to be used in determining maximum permissible nutrient levels, including transport, such as seven-day-ten-year flow or the mean monthly flow, 3- Ecological,nutrient transport and nutrient response studies will be necessary to determine whether or not the same nitrogen, phosphorus and carbon removal levels are required during twelve months of the year in order to enhance the water quality in the upper, middle, and lower reaches. 4. Effects of withdrawal of water from the upper portion of Zone I as a supplemental water supply for the Wa&nington metropolitan area on the allowable nitrogen, phosphorus, and carbon loadings from wastewater discharges, and 5• Development of seasonal nutrient loadings for Zones II and III of the upper reach and for -che middle and lower reaches of the tidal system. ------- V-18 D. DISSOLVED OXYGEN BUDGET Investigations of the oxygen budget axe in three areas: (l) carbonaceous and nitrogenous oxygen demand from wastewater discharges, (2) oxygen production by phytoplan.-cton, and (3) increased organic carbon and nitrogen loadings from phytoplankton, primarily in the middle and lower reaches. During 1969, preliminary CTSL studies were in the first two areas. Preliminary analyses of nitrogen data from the past five years indicate that nitrification (the oxidation of NH_to WO ) becomes a minor factor i <••. the oxyger. budget at water temperatures below 10°C. This observatjo" would s't^ges . t,hat nitrogen removal from wastewater for the maintenance of oxygen standards would not be required at temperatures below 10°C. 'The need for nitrogen removal for the control of eutrophication is still being Investigated as previously reported. Effects of organic loadings on the dissolved oxygen budget in the middle and lower reaches is being intensively studied during 1970. During the summer months, dissolved oxygen in the lower reach is often depressed at greater depths, attrib ited partially to the decay of organic matter, main!., phytoplar-. ------- V-19 E. EMBAYMENT STUDIES Except for the Blue Plains facility of the District of Columbia, all major wastewater discharges are into embayments of the Potomac River tidal system. As an interim measure to protect the embayments, the conferees at the Potomac Enforcement Conference applied the Zone I removal percentages to wastewater discharges in Zone II. A study of the wastewater assimilation and transport capacity of the Piscataway embayment was recently completed [13J- One of the findings of the study was that this embayment has little capacity to a~c ImllaU; aud transport tri-aied wastewater. The stud,'/ further Indicated if the same nutrient levels were to be maintained in the embayments- as in the Potomac, only a limited poundage of the waste constituents could be discharged into the embayment if low nutrient levels are to be maintained. Moreover, if the plant were to be expanded to 30 mgd, a higher degree of removal than that currently agreed upon (96$ for BOD^, 91$ for phosphorus, and 85$ for nitrogen) would "be required if the lower- nutrient levels are ^o be maintained. Preliminary analysis of the Anacostia River tidal system also indicates a limited assimilation and transport capability [3'- In this embayment, complete renovation or ultimate wastewater treatment (UW1?) will be required if there are to be any large discharges in the upper portion of the Anacostia tidal system. Based on the Piscataway and Anacostia studies, a re-examination of the removal requirements for embayment discharges is required. The ------- V-20 "real time" mathematical model previously mentioned includes all the major embayments. To complete the analysis, a dye release in each embayment will be required to verify predictive coefficients. Nutrient response characteristics of the waters of the various embayments are currently being investigated by CTSL. Limited data attained in 1968 and 1969 indicate greater standing crops of algal populations in the embayment for given nutrient levels than in the main stem of the tidal river. The sampling program for the embay- menis, especially Piscataway, Dogue, Gunston Cove, Occoquan-Belmont, and Mattawoman was initiated in February 1970 to further explore these observations. ------- REFERENCES 1. Jaworski, N.A., Aalto, J.A., Lear, D.W., and Marks, J.W., "Water Quality and Wastewater Loadings Upper Potomac Estuary During 1969," Technical Report No. 27, CTSL, FWPCA, MAP, November 1969- 2. Aalto, J.A., Jaworski, N.A., and ochremp, W.H., "A Water Quality Study of the Rock Creek Watershed," CB-SRBP Working Document No. 30, FWPCA, MAR, March 1969, 3- Jaworski, II.A., Clark, L.J., Feigner, K.D., "Preliminary Analyses of the Wastewater and Assimilation Capacities of the Anacostia Tidal Hiver System," Technical Report No. 39, CTSL, FWQA, MAR, April 1970. if. Gumming, H.3., "Investigation of the Pollution and Sanitary Conditions of the Potomac Watershed," USPHS Hygiene Laboratory Bulletin IQk, 1916. '>. Ljvermore, D.!1'1. and WunderlJch, W.E., "Mechanical Removal of Organic Production from Waterways," Eutrophication; Causes, Conseguenc es, Correct1ves, National Academy of Sciences, Washington, B.C., 1969. 6. Bartsch, A.F., "Bottom and Plankton Conditions in the Potomac River in the Washington Metropolitan Area," Appendix A, A report on water pollution in the Washington metropoli -can area, Interstate Commission on the Potomac River Basin, 1954. 7. Stotts/ V.D. and Longwell, J.R., "Potomac River Biological Investigation 1959," Supplement to technical appendix to part VII of the report on the Potomac River Basin studies, U. S. Dept. of H3W, 1962. 8. Eiser, H.J., "Status of Aquatic Weed Problems.in ^Tidewater Maryland, Spring 1965," Maryland Department of Chesapeake Bay Affairs, 8 pp mimeo. 1965. 9. Bayley, S.f Rabin, H., and Southwick, C.H., "Recent Decline in the Distribution and Abundance of E-urasian Watermilfoil in Chesapeake Bay," Chesapeake Science 9(3): 173-181, 1968. 10. Jaworski, U.A., Lear, D.W., a-d Aalto, J.A., "A Technical Assessment of Current Water Quality Conditions and Factors Affecting Water Quality in the Upper Potomac Estuary," Technical Report No. 5, CTSL, FWPCA, MAR, 1969. ------- 11. Mulligan, H.T., "Effects of Nutrient Enrichment on Aquatic Weeds and Algae," The Relationship of Agriculture to Soil and Water Pollution Conference Proceedings, Cornell University, New York, January 19-21, 1970. 12. Edmondson, W.T., "The Response of Lake Washington to Large Changes in its Nutrient Income," International Botanical Congress, Seattle, Washington, 1969. 13. Jaworski, N.A., Johnson, James H., "Potomac-Piscataway Dye Releases and Wastewater Assimilation Studies," Technical Report No. 19, CTSL, FWPCA, MAR, December 1969. Ik. Hasler, A.D., "Culture Eutrophication is Reversible," BioScience, Vol. 19, No. 3> May 1969. 15. Brezanik, W.H., Morgan, W.H., Shannon, E.E., and Putnam, H.D., "Eutrophication Factors in North Central Florida Lakes," Florida Engineering and Industrial Experiment Station, Bulletin Series No. 134, Gainesville, Florida, August, 1969. 16. Welch, E.B., "Phytoplankton and Related Water Quality Conditions . in an Enriched Estuary," JWPCF, Vol.40, pp 1711-1727, October 1968. 17- Task Group Report on Nitrogen and Phosphorus in Water Supplies, JAWWA, Vol. 59, No. 3. PP 344^366, March 1967. ------- Chesapeake Technical Support Laboratory Middle Atlantic Region Federal Water Quality Administration U. S. Department of the Interior PHYSICAL DATA POTOMAC RIVER TIDAL SYSTEM INCLUDING MATHEMATICAL MODEL SEGMENTATION Technical Report No. 43 Norbert A. Jaworski Leo J. Clark ------- INTRODUCTION In its continuing water quality studies of the Potomac, the Chesapeake Technical Support Laboratory (CTSL) found it necessary to systematically and accurately define the physical character- istics of the estuary. Factors of major importance are: surface and cross-sectional areas, volumes, and distances between "bridges, buoys, prominant landmarks and other reference points. This type of data is not only essential for mathematical modeling studies but also to interpret field survey information. River mileages were measured along the main channel using a set of dividers on U.S. Geological Survey 7-5 minute quadrangle maps. For convenience, a.11 distances were measured from Chain Bridge rather than from a reference point at the mouth of the Potomac. A reference point at the confluence of the Potomac with the Chesapeake Bay was established (See Figure II). Uniform river mile locations using statute miles were determined for the primary sampling stations, landmarks, navigation buoys, etc., and are presented in this report. Cross-sections were plotted at intervals from 0.5 to 3.0 miles from soundings shown on U.S. Coast and Geodetic Survey charts and the plots planimetered to determine cross-section areas. Surface areas were also planimetered directly from USC&GS charts. Segment volumes were obtained by multiplying the average cross-sectional areas by the length. ------- Although much of the data presented in this report applies to a predetermined segmentation for mathematical model studies, it is general in nature and thus adaptable to other needs. Hopefully, these basic data will be used by other agencies involved with the Potomac Estuary to eliminate duplication of effort. ------- GENERAL DESCRIPTION OF THE POTOMAC RIVER TIDAL SYSTEM The Potomac River basin is the second largest watershed in the Middle Atlantic States. Its tidal portion begins at Little Falls in the Washington metropolitan area and extends Ilk miles southeastward to the Chesapeake Bay. The tidal portion is several hundred feet in width at its head at Washington and broadens to nearly six miles at its mouth. A shipping channel with a minimum depth of 24 feet is maintained upstream to Washington. Except for this channel and a few short reaches where depths up to 100 feet can be found, 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 lA feet near the Chesapeake Bay. The lag time for the tidal phase between Washington and the Chesapeake Bay is about 6.5 hours. Effluents from twelve major wastewatcr treatment plants, with a thirteenth under construction, serving a population of about 2,500,000, are discharged into the upper tidal system. The locations of the discharges from these treatment facilities are shown in Figure I and presented in Table I. ------- ------- / \ RIVER MILES FROM CHAIN BRIDGE = 0 Mt£S FROM CHAIN BftOGC - IS ZONE II RIVER MILES FROM CHAIN BRIDGE ; 30 FORT 8EIVO1R LOWER POTOMAC WASTEWATER DISCHARGE ZONES UPPER POTOMAC TIDAL RIVER SYSTEM FIGURE I ------- TABLE I Major Wastewater Discharge Locations Upper Potomac Estuary Facility Combined D.C. system sewer overflow Pentagon Arlington District of Columbia Alexandria Fairfax-West Gate Piscataway Andrews AFB No. 1 Andrews AFB No. 2 Fairfax Hunting Cr . Fairfax Dogue Creek Fairfax Lower Potomac Ft. Belvoir No. 1 Ft. Belvoir No. 2 Distance Receiving from Stream Chain Bridge Potomac Es tuary Potomac Estuary Four Mile Run Potomac Estuary Hunting Creek Hunting Creek Embayment Piscataway Embayment Piscataway Creek Piscataway Creek Little Hunting Creek Dogue Creek Pohick Gunston Cove Guns ton Cove 4.0 5-8 10.4 12.4 12.8 18.3 18.3 18.3 20.0 22.5 24.5 24.5 24.5 Expanded Thomann Model Segment 4 6 12 13 15 16 22 22 22 24 27 28 28 28 FWQA Model Segment 5 7 78 129 81 16 118 118 118 25 84 128 85 85 * If discharge is into an embayment distance is to midpoint of embayment All distances in statute miles ------- A. Reaches of Potomac River Tidal System For discussion and investigative purposes, the tidal portion of the Potomac River Was divided into three reaches as shown in Figure II and described below: Reach Description River Miles Volumen cu.ft.xlCr Upper From Chain Bridge to 114.4 to 73-8 93-50 Indian Head Middle From Indian Head to 73.8 to 47.0 362.28 Rt. 301 Bridge Lower From Rt. 301 Bridge 47.0 to 00.0 1754.74 to Chesapeake Bay The upper reach, although tidal, contains fresh water. The middle reach is normally the transition zone from fresh to brackish water. In the lower reach, chloride concentrations near the Chesa- peake Bay range from about 7,000 to 11,000 mg/1. B. Zones of Upper_Potomac Tidal System To facilitate determination of water quality control requirements, the upper estuary was segmented by the CTSL into 15 mile zones beginning at Chain Bridge. Establishment of zones similar in physical character- istics allows flexibility in developing control needs. This zone concept was adopted by the conferees of the Potomac Enforcement Conference on May 8, 1969. River mile distances from both the Chesapeake Bay and Chain Bridge for the upper three zones are given in Table II as well as in Figure II. ------- POTOMAC RIVE* intoai BAY RIVER MILE 00- POTOMAC RIVER TIDAL SYSTEM FIGURE - U ------- CQ H O H O H B PH I & § CQ O N (D a	------- MATHEMATICAL MODEL INVESTIGATIONS Two approaches have been adopted to simulate water quality conditions in the Potomac Estuary. The first was the "average" tidal model developed "by Dr. Robert Thomann at New York University. The second and the more recent approach is the FWQA Dynamic Estuary or "real time" tidal model originally developed by Water Resources Engineers of Walnut Creek, California under contract to U.S. Public Health Service, FWQA, and the State of California. Details of both approaches have been adequately documented and are available from the authors or FWQA. A report comparing the two approaches in simulating the movement of pollutants in the Potomac Estuary is currently being prepared by CTSL. Originally, the Potomac Estuary was divided into 28 segments for the Thomann Model. To add greater sensitivity in analyzing field data and reaction rates, the estuary divisions were further increased to 73 segments. For the FWQA Model, three networks have "been developed, one corresponding to the 73-segment FWQA Model with embayment segmen- tation added to give a total of ihl segments, and a detailed network of 766 segments. In this report, segmentation data for both versions of the Thomann and the main stem of 73 node FWQA models were presented. ------- Detailed data on the other system are available from C'TSL upon request. For the main Potomac, nodes for the FWQA Model were placed at the interfaces of the Thomann Model segments. In Figures VII and VIII are exhibited the segmentation for the Thomann approach for the Anacostia and Potomac Tidal River Systems with Figure IX presenting a schematic of the FWQA Potomac Estuary Model. The lower 11 segments of the FWQA Model are not incorporated into the current working system. ------- DATA FORMAT The remainder of this report presents the following: A. Sampling Stations and Landmark Locations Table Number 1. CTSL Sampling Stations III 2. D. C. Water Pollution Control Division Sampling Stations IV 3• Bridges V U. Potomac Estuary Buoys to Reference Water Quality Sampling ' VI 5. Mileage Location of Prominent Reference Points along the Potomac Estuary VII Figure 1. Sampling Stations Potomac Estuary III B. Mathematical Model and Physical Data Table 1. Thomann Model, Segment Geometry, Potomac Estuary Mean Low Water Data (Excluding Embayments) VIII 2. Thomann Model, Segment Geometry, Potomac Estuary Mean Water Data (Excluding Embayments) IX 3. Thomann Model, Segment Volumes (including Embayments) X k. Thomann Model, Revised Potomac Estuary Geometry for Expanded Segmented System, Mean Water Data (Excluding Embayments) XI 5• Mathematical Model Segmentation, Anacostia Tidal River System, Mean Water Data XII ------- Table (continued) Number 6. FWQA Network Data, Potomac Estuary (Excluding Embayments) XIII J. Enibayment Data, Potomac Estuary XIV 8. Mathematical Model Plotting Positions for the Potomac Estuary XV Figure Number 1. Cumulative Surface Area Versus Distance, Potomac Estuary Mean High Water Data ; TV 2. Cumulative Volume Versus Distance, Potomac Estuary Mean Water Data V 3- Cross-sectional Area Versus Distance, Potomac Estuary Mean Water Data VI k. Thomann Mathematical Model Segments, Potomac Estuary VII 5- Thomann Mathematical Model Segments, Anacostia Tidal River VIII 6. Schematic of Potomac Estuary Network for the FWQA. Dynamic Model IX ------- TABLE III CTSL SAMPLING STATIONS Station Number 1 1A 2 2A 3 3A 4 4A 5 5A 6 7 8 8A 9 10 10A 11 12 13 ik Location Key Bridge Memorial Bridge l4th Street Bridge Potomac Park Hains Point Hunters Point Bellevue Goose Island Woodrow Wilson Bridge Rosier Bluff Broad Creek Piscataway Creek Dogue Creek Guns ton Cove Hallowing Point Indian Head Occuquon Bay Possum Point Sandy Point Smith Point Maryland Point Buoy Reference N "6" C "1" - N "4" C "11" - C "9" FLR - 23' Bell R "8" - N "6" c "87" N "86" FL "77" FL "67" R "64" FL "59" N "54" N "S2" R "44" N "40" N "30" G "21" Miles below Chain Bridge 3-35 4.85 5-90 6.70 7.60 8.70 10.00 11.05 12.10 13-55 15.20 18.35 22.30 2^.30 26.90 30.60 32.15 38.00 42.50 46.80 52.40 ------- CTSL SAMPLING STATIONS Station Number 15 15A 16 17 18 19 20 21 22 23 24 25 Location Nanjemoy Creek Port Tobacco 301 Bridge Bluff Point or Stony Pt. Colonial Beach/Kettle Bottom Shoals Vicomico River Kingcopsico Ragged Point Piney Point Point Lookout Smith Point Point Lookout Buoy Reference N "10" C "3" BW - MO(A) "H" FL "25" C "15" BWN "52" B BW "51" B FR "0" FR A FL "4" Bell BWN "43" B BWN "57" B Miles below Chain Bridge 58.55 63-75 67.40 73.45 76.60 82.00 90.25 95-42 99-20 107.41 118 . 00 114.85 ------- TABLE IV D. C. WATER POLLUTION CONTROL DIVISION SAMPLING STATIONS Station Number 1 2 3 4 5 6 7 8 9 10 11 12 13 Ik 15 16 17 18 19 20 21 22 Location Chain Bridge Fletcher's Boat House Three Sisters Island Roosevelt Island Memorial Bridge Highway Bridge Potomac Park Hains Point Giesboro Park Above WPCP (Blue Plains) Opposite WPCP " Below WPCP Woodrow Wilson Bridge Ft. Foote Ft. Washington Marshall Hall . Hallowing Point Indian Head. St. Neck Sandy Point Smith Point Maryland Point Buoy Reference Sewer outlet N "6" N "4" N "3" N "11" FLR 4 sec "23" Sewer outlet N "8" N "86" N "87" C "79" N "69" FL "59" N "54" N "46" N "41" N "30" G "21" Miles below Chain Bridge o.oo 1.40 2.75 4.25 4.85 5-90 6.70 7.20 8.20 10.20 10.40 10.70 12.10 14.45 17-95 21.80 26.90 30.60 35-20 42.50 45.80 52.40 ------- TABLE V BRIDGES Location or Name Chain Bridge Key Bridge Theodore Roosevelt Bridge Memorial Bridge 14th Street Bridges a. George Mason "b. Rochambeau Woodrow Wilson Bridge 301 Bridge Miles "below Chain Bridge 0 3-35 ^.U5 1+.85 5-90 6.05 12.10 67.40 ------- TABLE VT POTOMAC ESTUARY BUOYS USED TO REFERENCE WATER QUALITY SAMPLING Buoy River Miles from Chain Bridge N "12" 5.15 RN "10" 5.75 N "6" 6.70 C "1" 7.87 I "V 7.20 C "3" 7-20 N "2" 7-72 c "ii" 8.50 c "9" 8.95 C "1" 9.15 N "2" 9.25 23' Bell 10.01 R "8" 10.75 N "6" 11.30 N "V 11.70 R "2" 13.05 C "87" 13-95 N "86" ill-.95 R "84" 15.95 C "83" 17.13 ------- POTOMAC ESTUARY BUOYS USED TO REFERENCE WATER QUALITY SAMPLING (Cont.) Buoy River Miles from Chain Bridge C "81" 17.40 C "79 17-95 FL "77" 18.50 C "75" 19.00 C "73" 19.90 FL "71" 20.99 C "69" 21.55 FL "67" 22.30 N "66" 23.05 R "64" 2k.25 R "62" 24.90 c "61" 26.40 FL "59" 26.90 R "60" 27.00 C "57" 27.70 N "54" 30.60 N "52" 32.15 R "44" 37.90 N "4o" 42.50 N "30" 45.80 ------- POTOMAC ESTUARY BUOYS USED TO REFERENCE WATER QUALITY SAMPLING (Cont.) Buoy River Milejs from Chain Bridge N "24" 50.20 G "21" 52.40 N "16" 55.00 N "10" 58.55 C "3" 63-75 FL "29" 70.65 BW MO(A) "H" 73.45 FL "25" 76.60 C "15" 82.00 B¥W "52" B 90.25 BW SI B 95-42 FR "D" FR A 99.20 FL "4" Bell 107-41 EWN "57" B 114.85 BWN "43" B 118.00 ------- TABLE VII MILEAGE LOCATION OF PROMINENT REFERENCE POINTS ALONG THE POTOMAC ESTUARY (excluding those used as sampling stations) Landmark Points Miles below Chain Bridge Mai-bury Point 10.55 Fox Ferry Point 7-50 Jones Point 12.34 Indian Queen Point 14.90 Hatton Point 17-30 Sheridon Point 18.65 Mockley Point 18.60 Bryan Point 19.80 Ferry Point 21.90 Whitestone Point 24.10 Pomonkey Point 26.40 Sycamore Point 29.80 High Point 31-30 Deep Point 34.00 Cockpit Point 35-90 Douglas Point 43-90 Simms Point 46.80 Marlboro Point 49-35 Blossom Point 59-10 Upper Cedar Point 60.10 ------- MILEAGE LOCATION OF PROMINENT REFERENCE POINTS ALONG THE POTOMAC ESTUARY (excluding those used as sampling stations) Landmark Points Miles below Chain Bridge Mathias Point 62.70 Persimmon Point 66.20 Lower Cedar Point 68.80 Stony Point 72.70 Swan Point 7^.20 White Point 75.00 Gum Bar Point 76.00 Church Point 77.00 Cobb Point 80.25 Waterloo Point 84.30 Crunch Point 88.10 Ragged Point 95-^0 Deep Point 102.80 Kitts Point 105.20 Lawson Point 106.60 ------- >H Cd •a; 13 (H CO - W M -s e, H t= -p O <-H 'O QJ O O -p !<„ P 0) J-t J-.J <- ^ rH O rH OJ OJ OJ OJ OJ -.Q CO O O r°\ '"^ tO rH PA Xf CO r-A CO OJ xf xf CO CO PA 0"^ LT\ xf O rH rH CM CM °\ xf CM r^, c^\ rH xf rH xT -"' "O rH UA ^f '0 rH O fO OA O U\ [- Nf O vf 0 O CO O T^ O "C1 V"J rH UA C^N Xf XT O '7~ "•- 'f~> rH O 0 O O O O O O J O O O .H OJ O O ^ OJ xf OJ OJ i", f\ v^ §OOOOO o o o o o rH rH OJ O O m NT OJ OJ "A r^ rH CM f"\ Xf iTv VO O O CO rH uT\ O O O rH CO OJ ;> '^O -»t c\ OJ CO Qs r-\| CO UA OJ OA VO rH O O f-A xf C"~\ LT\ xf >O CO "•A CO 0s c""\ co O Q> OJ -O VO r> !> VD O C^N r- r^ xf co co rA OJ ["•- y^ r^ ^o^ vo ^v ^ rH rH CO tr\ rH O co ->j ir\ O ^D UA OJ rH -r\ r^\ 0s O O xf O r- v O iT\ ir\ CC7 C O fA CO CXI rH r^ o vo in O o cv1 O O i-t TO [^ CM rH 0"^ c^i ii""i O UTN i — i r"A f-~v i — 1 r^\ o r"\ -^ ir\ rH rH rH rH rH OJ rH O O O O O O O LTV O O UA UA O ir\ C-A LT\ C^\ rH OJ O rH "^ O O O O O f\ xT xT ;J O 'JO O OJ rH §000000 IT, O O U~N ur\ O OJ c"\ 0^ O O O 0s (-A xf xf D -O CO "N t~- CO O O i— f OJ t^A rH rH rH rH t^\ [> OJ rH 0 0 > -^ o VO f"\ O <^\ !> CO OJ CO O rH rH 'vD vo ^f O) rH vn rH UlA O OJ UA VO CO 0s C""\ rH rH OJ O '^D OJ xf OJ r"\ rH rH rH [> CO O O CO O OJ C^ Xf OJ ,^> O C"\ CO i/\ [--. 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O -H O 0) 0] rC r* 0) CO o o ho - ,31 rH >> S hp O H C 4 W CO CO UA 0 c? rH I O to o rH r1^ O rr\ J 0 u^ CO O 0 to .0 ^t- rH hi •H O o •H g O o 0) >-l m 8 rH 1 rH UA O rH > r^\ UA c^- 0 Nf rv^ 0 C^ VO to to OJ 01 0 r4 0 •d w 8 s rH 1 0 B rH VD ^ 0 J 8 vO o 0 C\J 8 rH CO OJ rl O > « C 8 o o rH rH ^A rH O O .0 cu CM ,_H O •o OJ r^x O OJ CO CM I 0 rH rH £ ------- TABLE XV MATHEMATICAL MODEL PLOTTING POSITIONS FOR MAIN STEM OF POTOMAC ESTUAKY Segment Number 1 2 3 4 5 6 1 8 9 10 n 12 13 ik 15 16 17 18 Thomann Model (miles) 0.7^ 2.15 3-09 3-7^ k.kQ 5-37 6.2k 7.10 8.00 8.54 9.05 9.68 10.55 11.63 12.50 13.24 1k. 20 15-03 FWQA Model (miles) 0* 1.48 2.82 3-30 4.13 4.83 5.90 6.57 7.61 8.37 8.70 9.4o 9-97 11.12 12.12 12.87 13-61 14.77 * Junction 114 ------- Segment Number 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 10 Thomann Model (miles) 15-79 16.61 17.42 18.20 18.98 19.96 20.92 21.84 28.13 24.82 26.32 27.74 29.06 30.12 31.04 32.06 33.46 35-26 37-34 39.38 41.45 43-63 FWQA. Model (miles) 15.27 16.30 16.92 17.92 18.48 19.^7 20.44 21.39 22.30 23.96 25=67 26.95 28.52 29.58 30.66 31.42 32.70 34.22 36.21 38.76 4o.6o 42.90 ------- Segment Number 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Thomann Model (miles) 45.73 47.97 50.37 52.11 55-29 57-95 60.30 62.88 66.24 67.82 69.35 71.96 73.85 76.04 78.34 80.31 82.13 84.09 86.26 88.36 FWQA. Model (miles) 44.95 47.08 49-44 51.87 53-92 57-24 59-24 61.94 64.39 66.67 68.53 69.75 71.75 73^54 74.83 76.85 78.77 80.42 82.75 84.76 ------- Segment dumber 61 62 63 6k 65 66 67 68 69 70 71 72 73 Thomann Model (miles) 90.10 91.56 93-20 96.48 97-19 99-71 101.89 103.67 105.83 107.81 109.87 111.72 113.84 FWQA Model (miles) 86.96 88.23 89.88 91.52 93.16 96.21 98.21 100.17 102.16 104.31 106.31 108.12 110.02 ------- MAJOR WASTE THEATIfcHT KANTS A BBTWCT Or COJUHI* » MLMGflON COUNTY C 4LCXAMMA SAWWRY AUTHOMTY 0 KMVAX COUMTY - WtSHiATt PLANT t HWTAX COUKTV - UTTU HUNTHO CREEK PLAWT r mMmx COUKTV - OOGUE CWEK PLANT G WUHMGTON SUtUV -MTrUf/ COMMOOON - PSOTWCW H ANDREWS AR FORCE BASE - PtAKTS ! ind ' I TOOT eavOfl - PLANTS \ mi Z J PENTAGON POTOMAC ESTUARY SAMPLING STATIONS FIGURE nr ------- o CO Q in < bJ cc. < >• o: < 13 1- IO u 1 cr LJ I -8 ------- LU O il CO O -BZ 5 ------- = V3MV 1VNOI1D3S SSOMD ------- THOMANN MATHEMATICAL MODEL SEGMENTS LOCATION MAP ORIGINAL 28 SEGMENTS EXPANDED 73 SEGMENTS SCALE ffl MILES POTOMAC ESTUARY ------- \ Z 2 u u 3 5 w QC QC * p y < K- P tn O U ® Figure VIII ------- CHAIN BRIDGC FOUR MILE RUN WASTEWATER PLANT NODES NODE PLANT "78 ARLINGTON 129 BLUE PLAINS I 6 WESTGATE 81 ALEXANDRIA MB PI SCAT AWAY 84 OOGUE CR 128 LOWER POTOMAC SCHEMATIC OF POTOMAC ESTUARY FOR FWQA DYNAMIC MODEL ------- Chesapeake Technical Support Laboratory Middle Atlantic Region Water Quality Office Environmental Protection Agency NUTRIENT MANAGEMENT IN THE POTOMAC ESTUARY Technical Report 45 January 1971 Norbert A. Jaworski Donald W. Lear, Jr. Orterio Villa, Jr. To be presented at the American Society of Limnology and Oceanography Symposium on Nutrients and Eutrophication: "The Limiting Nutrient Controversy," February 11-13, 1971, Michigan State University, East Lansing,Michigan ------- TABLE OF CONTENTS INTRODUCTION . . . 1 Brief Description of the Study Area 1 CURRENT WATER QUALITY CONDITIONS 5 ECOLOGICAL TRENDS AS RELATED TO NUTRIENT ENRICHMENT . . 15 NUTRIENT SOURCES AND CONTROLLABILITY 19 NUTRIENT TRANSPORT AND ALGAL STANDING CROP MATHEMATICAL MODELS .......... 25 EUTROPHICATION CONTROL 43 ESTABLISHMENT OF NUTRIENT CRITERIA 46 1. Algal Composition Analysis 47 2. Analysis of Data on an Annual Cycle and Longitudinal Profile Basis 48 3. Bioassay Studies 50 4. Algal Modeling 52 5. Comparison with a Non-eutrophic Estuary ... 52 6. Review of Historical Nutrient and Ecological Trends in the Potomac Estuary 53 7. Specific Criteria 54 a. Freshwater Portion 54 b. Me?ohaline Portion 55 WASTEWATER TREATMENT' REQUIREMENTS 57 A WATER QUALITY MANAGEMENT PROGRAM 60 REFERENCES ------- ------- LIST OF FIGURES Figure Description 1 A map of the Potomac Estuary showing wastewater treatment facilities and predominant landmarks. 4 2 Inorganic phosphorus concentration as PC>4 for various stations in the Potomac Estuary from February 1969 through September 1970. 7 3 Nitrate and nitrite nitrogen concentration for various stations in the Potomac Estuary from February 1969 through September 1970. 8 4 Ammonia nitrogen concentration for various stations in the Potomac Estuary from February 1969 through September 1970. 10 5 Chlorophyll §. concentrations for stations in the upper reach of the Potomac Estuary, 1965-1966 and 1969-1970. 13 6 Chlorophyll g. concentration for stations in middle and lower level of the Potomac Estuary, 1965-1966 and 1969-1970. H 7 Wastewater nutrient enrichment trends and ecological effects on the upper Potomac Tidal River System, 1913-1970. 16 8 Phosphorus concentration in the Potomac Estuary before, during, and after a period of intensive runoff. 22 9 Average observed and predicted phosphorus concentration in the Potomac Estuary, September 25-October 27, 1965. 26 10 Average observed and predicted phosphorus concentration in the Potomac Estuary, January 25, 1966. 27 11 Effect of temperature in the phosphorus deposition rate, Potomac Estuary. 28 ------- Figure Description Page 12 Simplified nitrogen cycle used in modeling the nitrogen and algal standing crops in the Potomac Estuary. 32 13 Average observed and predicted ammonia and nitrite + nitrate concentration in the Potomac Estuary, September 9-13, 1966. 33 14 Average observed and predicted ammonia and nitrite + nitrate concentration in the Potomac Estuary, August 17-22, 1968. 34 15 Effect of temperature on the rate of nitrification, Potomac Estuary. 35 16 Effect of temperature on the rate of nitrogen utilization by algae, Potomac Estuary. 36 17 Average observed and predicted chlorophyll a. concentration, Potomac Estuary, September 6-7, 1966. 38 18 Average observed and predicted chlorophyll a. concentration, Potomac Estuary, August 19-23, 1968. 39 19 Average observed and predicted dissolved oxygen concentration, Potomac Estuary, September 22, 1968. 40 20 Average observed and predicted dissolved oxygen concentration, Potomac Estuary, August 12-17, 1969. 41 21 Wastewater discharge zones in the upper Potomac Estuary. 62 ------- LIST OF TABLES Table Description Page 1 Summary of nutrient sources entering the upper and middle reaches of the Potomac Estuary. 20 2 Data summary of algal chemical composition studies Potomac Estuary, June-October 1970. 31 3 Subjective analysis of algal control requirements. 45 ------- INTRODUCTION Historically, since the first sanitary survey was made in 1913 [30], the water quality of the upper Potomac Estuary has been degraded as a result of the discharge of either untreated or partially treated munici- pal wastewater from the Washington Metropolitan Area. Early surveys indicated that high coliform densities and low dissolved oxygen content were the two major water quality problems of the upper estuary. In the past decade, large nuisance populations of blue-green algae have also added to the water quality management problems of the upper and middle reaches of the estuary„ Initially, as part of the Chesapeake Bay-Susquehanna River Basins Comprehensive Planning Project* and now as an integral part of the Potomac Enforcement Conference, field water quality studies were under- taken, beginning in 1965, to define wastewater treatment requirements. The studies and concepts used to formulate a nutrient management pro- gram for the Potomac Estuary are presented in this, paper, Brief Description of the Study Area The Potomac River Basin, with a drainage area of 14,670 square miles, is the second largest watershed in the Middle Atlantic States. From its headwaters on the eastern slope of the Appalachian Mountains, The Chesapeake Bay-Susquehanna River Basin Comprehensive Project was initiated by the Division of Water Supply and Pollution Control of the Public Health Service, U0 S. Department of Health, Education, and Welfare. ------- 2 the Potomac flows first northeasterly then generally southeasterly in direction some 400 miles to the Chesapeake Bay. Upstream from Washington, D. C., the Potomac traverses the Piedmont Plateau to the Coastal Plain at the Pall Line. Below the Fall Line, the Potomac is tidal extending 114 miles southeastward and discharges 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 where depths up to 100 feet can be found, the tidal portion is relatively shallow with an average depth of approximately 18 feet. Of the 3.3 million people living in the entire basin, approxi- mately 2.8 million reside in the upper portion of the Potomac Estuary within the Washington Metropolitan Area. The lower areas of the tidal portion, which drains 3,216 square miles, are sparsely populated. ------- 3 For purposes of discussion and investigation, the tidal portion of the Potomac River (Figure l) has been divided into the three reaches described below: Reach Description River Mile* Volume (mi. below Chain Br.) (cu.ft.xlO8) Upper From Chain Bridge to 0.0 to 30.0 93.50 Indian Head Middle From Indian Head to 30.0 to 67.0 362.28 Rte. 301 Bridge Lower From Rte. 301 Bridge to 67.0 to 114.4 1754.74 Chesapeake Bay * All river miles are referenced to Chain Bridge which is located at the upper end of the tidal portion of the Potomac River. The upper reach, although tidal, is essentially fresh water. The middle reach is normally the transition zone from fresh to brackish water. The lower reach is mesohaline with chloride concentrations near the Chesapeake Bay ranging from approximately 7,000 to 11,000 mg/1. The average freshwater flow of the Potomac River near Washington before diversions for municipal water supply is 10,800 cubic feet per second (cfs) with a median flow of 6,500 cfs. The flow of the Potomac is characterized by flash floods and extremely low flows. ------- -IfiBSL MAJOR VStt TREATMENT PLANT A ocmcr or OOUJMM • AMJWION COOTY C ALCXAtCMt MMMV AUTHOMTY D MMX OXMTT- WCSRM1 PLANT c HMWW COUNTY - urru; HUNTMG CREEK PLANT t INMM OXMTY- OOGUC OCEK PONT G MMMICTON 1UMM SANTABV COMMSSKM - PBCAWMW H AMMCWS AD rancc MSC - PLANTS i «< 4 I KMT KLVOR - PLANTS l mt 2 J PENTAOON POTOMAC ESTUARY Figure 1 ------- 5 CURRENT WATER QUALITY CONDITIONS In the upper reach, approximately 325 million gallons per day (mgd) of wastewater is discharged mainly from municipal treatment facilities currently serving approximately 2.5 million people in the Washington Metropolitan Area. The largest wastewater treatment facility is the Blue Plains plant of the District of Columbia which serves approximately 1.8 million people. Wastewater discharged from the 18 facilities cur- rently contributes 450,000, 24,000, and 60,000 Ibs/day of ultimate oxygen demand* (UOD), phosphorus** and nitrogen respectively, to the waters of the upper estuary. The quantities of wastewater discharged into the middle and lower reaches is less than 5.0 mgd and thus very insignificant when compared to the upper reach. Low dissolved oxygen (DO) concentrations, often less than 1.0 mg/1 during summer, occur in the upper reach as a result of the oxidation of 200,000 and 240,000 Ibs/day of carbonaceous and nitrogenous UOD res- pectively. Since the summer of 1969, the high fecal coliform densities (over 50,000 MPN/100 ml) previously observed near the wastewater dis- charges have been significantly reduced (less than 1,000 MPN/100 ml) by effective continuous chlorination. * Ultimate oxygen demand is basically the sum of 1.45 times the 5-day biochemical oxygen demand and 4.57 times the unoxidized nitrogen. ** Phosphorus concentrations or loadings in this paper are given as phosphorus (P) except when specifically designated as PO, ------- 6 The concentrations or forms of phosphorus and nitrogen in the Potomac Estuary are a function of wastewater loadings, temperature, freshwater inflow, distance from the Chain Bridge, and biological activity. As shown in Figure 2, the inorganic phosphorus varied considerably for the six stations presented from March 1969 through September 1970. The concentration at Hains Point, which is located at the upper end of the tidal excursion of the major wastewater discharges, was fairly uniform averaging 0.1 mg/1 as P (0.3 mg/1 as PO^). At Woodrow Wilson Bridge, which is located below the Blue Plains wastewater discharge, the inorganic phosphorus increased appreciably with concentrations over 0.8 mg/1 (2.5 mg/1 as PO^) occuring during low-flow periods as those in the months of May-July 1969, October-November 1969, and September 1970. The remaining four downstream stations had progressively lower concentrations. The total phosphorus concentration closely parallels that of inorganic phosphorus. In the upper reach, the ratio of total phos- phorus to inorganic phosphorus ranges from 1.1 to 1.5. The ratio is higher in the middle reach normally varying from 1.5 to 2.0 with the lower reach having a range from approximately 2.0 to 2.5. The concentration of nitrite and nitrate nitrogen at Hains Point and Woodrow Wilson Bridge varies almost inversely with that of phos- phorus (Figure 3). The N02 + NO-j concentrations as a result of land runoff were the highest during periods of high river flows as in July ------- INORGANIC PHOSPHATE CONCENTRATION POTOMAC CSTUMVr HAMS PQMT UUS KCOW CHNM OCT ' MX ' ICC. JHL MOOOROW MLSON IMDGC MUS KUW CHAM MOGC » BJO JO. ML. IMMAN KAD JIM JUL •tflt ' JLM, ' JUt- ' >. SKHTH POINT «CLOW CHMN M«OGC • 4.0 MA JUN J«M. ' fST nou. 2 ------- NITRATE a* NITRITE NITROGEN POTOMAC ESTUARY N MAIN'. PCHWT «f5 K10W CHAM IMOGC » T«0 WOODROW WILSON BR1D6E MUS KLOW CHAIN IMDGC • 12 10 INDIAN HLAO MIUS PMLOW CHAIN BRIDGC « 30.60 tf» OC SMITH POINT WLfS BCLOW CHAIN BRKXiC • «.80 JU AUC i BRIDGE: MMS KtOW CHAIN WDOt • 6T40 JU. AiA. Iff T OCT NOV. PtNfV POI^'T MUS WLOW CHAM M>GC • M.20 •Sl^^ KC. T JMt^ •M i I • •» ------- and August 1969, and during the late winter and early spring months of 1969 and 1970. During these flow conditions, the inorganic phosphorus concentration was lowest (Figure 2). The increase of N02 + N03 at Indian Head as compared to Woodrow Wilson Bridge in May-June 1969, September-November 1969, and July 1970 is the result of the conversion of ammonia (from the wastewater treat- ment plant discharges) to nitrates. The low concentration of N02 + N03 in the summer months at Smith Point is caused by uptake of algal cells as described later in this report. During winter months, algal utili- zation is much less thus the concentrations of nitrates are high as in the months of January through April 1970. At Piney Point, concentrations of NOa + N03 are usually less than 0.1 mg/1 on an annual basis. As shown in Figure 4, 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, ammonia concentrations at Indian Head during the summer months are low due to nitrification. » ------- ------- and August 1969, and during the late winter and early spring months of 1969 and 1970. During these flow conditions, the inorganic phosphorus concentration was lowest (Figure 2). The increase of N02 + N03 at Indian Head as compared to Woodrow Wilson Bridge in May-June 1969, September-November 1969, and July 1970 is the result of the conversion of ammonia (from the wastewater treat- ment plant discharges) to nitrates. The low concentration of N02 + N03 in the summer months at Smith Point is caused by uptake of algal cells as described later in this report. During winter months, algal utili- zation is much less thus the concentrations of nitrates are high as in the months of January through April 1970. At Piney Point, concentrations of N02 + NO^ are usually less than 0.1 mg/1 on an annual basis. As shown in Figure 4, 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, ammonia concentrations at Indian Head during the summer months are low due to nitrification. , ------- AMMONIA NITROGEN as N POTOMAC ESTUARY WOOOftOW VMLSON SMDGE ifiOH CHMN moat • a.e ------- 11 JSL- (units) 7.5 7.0 7.2 7.5 7.5 - 8.0 - 7.5 - 8.0 - 8.2 - 8.0 Alkalinity COp (mg/1 as CaCO^) 80 90 70 60 65 - 100 - 110 - 90 - 85 - 85 (mg/1) 2 8 6 2 7 - 4 - 12 - 10 - 8 - 8 During the summer and early fall months, the average ranges of pH, alkalinity, and free dissolved C02 (measured by titration) for the five stations in the upper and middle reaches were: Free Dissolved Location Chain Bridge W. Wilson Bridge Indian Head Maryland Point Rte. 301 Bridge In the vicinity of the Woodrow Wilson Bridge, there is an increase in both alkalinity and C02 with a corresponding decrease in pH attri- buted to wastewater discharges. There is a decrease in both alkalinity and COa 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. Salinity concentration as well as nutrient enrichment from waste- water discharges has a pronounced effect on the ecology of the estuary. Under summer and fall conditions, large populations of blue-green algae, primarily Anacystis sp. (Microcystis), are prevalent from the metro- politan area as far downstream as Maryland Point. Under warm temperature and low-flow conditions, large standing crops of this alga develop forming "green mats" of cells. Chlorophyll a ------- 12 concentrations (a measure of algal standing crop) range from approxi- mately 50 to over 200 ug/1 in these areas of dense growth which at times encompass approximately 50 miles of the upper and middle reaches of the estuary. These high chlorophyll levels are 5 to 10 times those reportedly observed in other eutrophic waters [5] [32]. During a dense bloom, the dry weight of cells ranges from 10 to 25 mg/1 which is almost twice those reported for the Madison, Wisconsin lakes [22]. Chlorophyll a determinations for the upper reach and for the middle and lower reaches of the Potomac Estuary are presented in Figures 5 and 6, respectively. At Indian Head and Smith Point for 1965-1966 and 1969-1970, the chlorophyll a. concentrations indicate that algal popu- lations have not only increased in density in the latter years but have become more persistent over the annual cycle. At both stations, higher values of chlorophyll were measured during the 1969-1970 sampling cruises than during the 1965-1966 cruises even though flow conditions were more stable in 1965-1966. The occurrence of a spring bloom of diatoms was observed in 1969 and 1970 but not during the 1965-1966 cruises. In the mesohaline portion of the lower reach of the Potomac Estuary, the,algal populations are not as dense as in the freshwater portion. Nevertheless at times, large populations of marine phyto- plankton (primarily the dinoflagellates Gymnodinium sp. and Anrohidinium sp.) occur producing what are known as "red tides." ------- ------- MAINS POINT WLES BELOW CHAM (DOGE =760 CHUOROPHYLL a POTOMAC ESTUARY U»>P€R REACH PISCATAWAY CREEK MLES KLOW CHAIN BRIDGE ' .» ------- SMITH PONT MLES BCLOW CH/MN MDGC • CHUDfiQPHYLL a POTOMAC ESTUARY MBOUE •- LOWER MCACM OCT MOV 301 BRIDGE. MLES KLDW CHAIN BRIDGE * 67 4Q PtNCY POINT MLE.S BUOW CHAIN BRlOot = M 20 ------- 15 ECOLOGICAL TRENDS AS RELATED TO NUTRIENT ENRICHMENT Since the first observations reported in 1913, the effect of the increased nutrients on the ecology of the upper Potomac Estuary has been dramatic (Figure ?)„ Historical invasions of nuisance plant growths in the upper Potomac Estuary can be inferred from several studies. Gumming [6] surveyed the estuary in 1913-1914 and noted the absence of plant life near the 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 phyto- planlrton blooms were noted „ In the 1920's, an infestation of water chestnut appeared in the waters of the Chesapeake Pay including the Potomac Estuary, This infestation was controlled by mechanical removal [23], In September and October 1952, another survey of the reaches near the metropolitan area made by Eartsch [2] revealed that vegetation in the area was virtually nonexistent. While no massive phytoplankton blooms were reported, there was a noticeable increase in blue-green algae and diatoms when compared to the 1913-1914 studies,. In August and September 1959, a survey of the area was made by Stotts and Longwell [28]„ Blooms of the nuisance blue-green alga Anacystis were reported in the Anacostia and Potomac Rivers near Washington„ In 1958 a rooted aquatic plant, water milfoil, developed in the waters of the Chesapeake Bay including the Potomac Estuary and created ------- D •» NO98VO DINV9MO I UJ O I o 2 UJ O I ------- 17 nuisance conditions. The growth increased to major proportions by 1963, especially in the embayments from Indian Head downstream [8] and then dramatically disappeared beginning in late 1965. The decrease was presumably due to a natural virus [3]. Subsequent and continuing observations by the Chesapeake Technical Support Laboratory (CTSL) staff have confirmed persistent massive summer blooms of the blue-green algaJjaafiXfliifi. Nuisance concentrations occur from the Washington Metropolitan Area downstream as far as Maryland Point [16]. From the above considerations, it would appear that nuisance conditions did not develop linearly with an increase in nutrients . Instead, the increase in nutrients appeared to favor the growth and thus the domination by a given species . As nutrients increased further, the species in turn was rapidly replaced by another dominant form. For example, water chestnut was replaced by water milfoil which in turn was replaced by Figure 7 indicates that the massive blue-green algal blooms now occurring every summer since I960 are associated with large phosphorus and nitrogen loading increases in the upper reaches of the Potomac River tidal system. The blooms have persisted since the early I960 'a although the amount of organic carbon from wastewater has been reduced by almost 50 percent of that discharged prior to I960. Moreover, the organic carbon loadings being discharged now are equal to those that were discharged in the early 1940 's when there were no reported nuisance ------- 18 conditions as a result of algal growth. These observations tend to suggest that the ecological changes have been caused by increases in nitrogen and phosphorus and not by organic carbon. ------- 19 NUTRIENT SOUHCE5 AND CONTROLLABILITY A complete analysis of the nutrient sources in the upper Potomac Estuary has been made by Jaworski ei si [17]„ A summary of the three major sources is presented in Table 1 for low- and median-flow conditions. For low- and median-flows, the contribution from wastewater discharges of the three nutrients on a percentage basis is presented below: Percentage from Wastewater Discharges Excluding Air-Water Interface Including Air-Water Interface Median Flow () Carbon Nitrogen Phosphorus 29 60 82 to to to Low Flow () 55 90 96 Median Flow 00 12 59 82 to to to Low Flow () 15 89 96 From the above tabulation, it can be concluded that the order of control- lability of nutrients by wastewater treatment is (1) phosphorus, (2) nitrogen, and (3) carbon. While 82 to 96 percent of the phosphorus entering the upper estuary can be controlled by removal at the wastewater treatment facilities, an additional reduction of phosphorus concentration occurs during periods of high runoff within the upper estuary itself. As reported by Aalto e% aj. [1], large quantities of phosphorus (over 100,000 Ibs/day) enter the upper estuary during high-flow periods at concentrations over 0.5 mg/1 (1.5 mg/1 as PO/;) during the rising portion of the river discharge hydrograph. However, high silt concentrations also accompany high flows. ------- SUMwJlv; w>' r'i'r.'i. fiiVC SGUHCiiS Upper arid .Middle )> i^v.s :;f the Potomac Estuary (Potomac Rivei Discharge t •- I'^cdngtoi!, D G, - 1200 cfs) l£ ""i '•'urflsv y-:.;' fit..:-Water Carbon Nitrogen Phosphorus 170,000 6,700 1 .000 60000 000 (Ibs/day) 9SO,,000'W- 0 (Potomac Hivei Dx.^charge ct Waojiington, D. C. = 6500 CAS) Carbon 350,000 j.bO.,000.- 950,000"* Nitrogen 40,000 60,,000 1^600*** Phosphorus >,3CO 2-4,000 0 * Of the 160,000 Ibs/day, 60/..00 .i;}s/d,-%y ave discharged as inorganic carbon •** The potential G02 obtainable from tLe atmosphere was determined by using only 0.1 percent of the iTai%dfer rate of 0,,6 mg/cm2/min as indicated by Riley and Skirrow [15] Based on a nitrogen fixation i-ane -jf five Ibs/'aere/year as reported by Hutchinson [14] ------- 21 Large amounts of phosphorus &:& s^^t"! -upon ths s;i-it particles and removed from the water system as sedimentation occurs in the upper reach of the estuary. This deposition vras also Disarmed in the summer of 1970 (Figure 8)0 During the month of June, the average flow of the Potomac at Washington was approximately 6,,000 cfs with a dally contribution of approximately 2,000 Ibs/day of phosphorus to the ipper Sfctuary, During the period from July 10 to July 11, 1970, the flow increased to over 47.,000 cfs contributing over 70,000 Ihs/da." of phosphorus. By July 13, the flow decreased to less than 19,000 cfe with the flow on July 22 being less than 5,000 cfs and the phosphorus contribution decreased to less than 3,000 Ibs/day. Although thare was some dilution of high phosphorus concentrations, the large sediment load reduced tne overall phosphorus concentration by a minimum of 20 percent in the reaches upstream and downstream from the major wastewater sources at River Mile 12,0. (See profiles for July 13 and July 22, 1970) 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 slgal growing season and the large losses to the sediments during high- flow periods made phosphorus an ideal nutrient to manage. In periods of extremely high runoff, the concentration of nitrate in the waters entering the Potomac Estuary from the upper basin also increases; and at timesf over 300,000 Ibs/day of nitrogen enters the ------- o o: z s. O 0 o f- 2 „ o a z 1 1 o £ Q 5 -} i • i 8 a eg M S 1 1 1 ------- 23 upper estuary. During the months of June through Octobers when blue- green algal growths become a nuisance,, the contribution from the upper basin is small when compared to that from wastewater discharges (See Table l). Based on data as presented in Table 1, the amount of atmospheric nitrogen from rainfall, dustfall, and fixation by algae is approxi- mately 1,600 Ibs/day for the upper and middle Potomac Estuary. Extension of recent data from studies at the University of Wisconsin [31] indicate that approximately 5,000 Ibs/day of nitrogen could be fixed by blue-green algae in the upper and middle reaches of the Potomac Estuary,, Nevertheless, compared to all other sources, the contribution from the atmosphere including that by nitrogen fixing algae appears to be insignificant, Thus, during the summer months, algal control by management of nitrogen appears to be a feasible alternative to phosphorus control. Under summer flow conditions, the alkalinity in runoff from the upper basin ranges from 80 to 100 mg/1, with wastewater discharges ranging from 100 to 150 mg/1. Including runoff and wastewater dis- charge sources only, approximately 60 to 70 percent of the total carbon entering the upper estuary is in the inorganic form. Using only 0,1 percent of the transfer rate, the amount of carbon (C02) potentially available from the atmosphere is approximately ^ 950,000 Ibs/day (Table 1). With the upper reach of the estuary well ------- mixed due to tidal action, recruitment of carbon from benthic decompo- sition also appears to be another significant source of inorganic carbon. Data indicate that waters of the lower reach of the Potomac Estuary and Chesapeake Bay are high in alkalinity and inorganic carbon. As the salt wedge moves upstream, there appears to be some recruitment of alkalinity and inorganic carbon from the Chesapeake Bay into the lower and middle reaches of the Potomac Estuary [17J. When all potential sources are considered, it appears that the management of carbon for algal control is not a feasible alternative at the present time. ------- 25 NUTRIENT TRANSPORT AND ALGAL STANDING CROP MATHEMATICAL MODELS In investigating the role of nitrogen and phosphorus on the eutrophic conditions in the Potomac Estuary, a detailed study of the movement of these nutrients was made using a "real time" dynamic water quality estuary mathematical model [10]. Models were also developed for algal standing crops and dissolved oxygen. Phosphorus movement in the estuary was simulated by using a depo- sition formulation based on second order reaction kinetics. As shown in Figures 9 and 10, the model accurately predicts the rate of phos- phorus deposition. Figure 11 indicates that the deposition rate is greatly affected by temperature. Analyses of the bottom muds of the estuary also indicate that large quantities of phosphorus are being lost to sediments in the vicinity of the wastewater discharges. To determine if the phosphorus loss is related to algal growths, algal standing crops were predicted using a surrogate phosphorus mathematical model. In the model, the loss in phosphorus was con- verted to algal standing crops using a chlorophyll a/phosphorus weight relationship as given in Table 2. Based on six simulated standing crop studies, it appears that only 10 to 30 percent of the phosphorus losses from the aqueous system can be accounted for by uptake of algal cells. In investigating the role of nitrogen in water quality management, a feedback system of the nitrogen cycle was incorporated into the dynamic estuary mathematical model similar to that proposed by Thomann Si &1 [29]. The model, as shown in Figure 12, consists of six possible ------- ------- 8 I UJ 00 UJ _J Z ( I/.•••) Od $V SnMOMdSOHd FIGURE 9 ------- S i 5 1 LJ CD J 2 (!/•") Od SV SnWOHdSOHd FIGURE 10 ------- .OS .08 .07 .06 .05 .04 EFFECT OF TEMPERATURE ON PHOSPHCJRUS DEPOSITION RATE POTOMAC ESTUARY 11,000 cf» .03 saoocfs .02- 185 cf» 01- '08- \|Q7- 06- 05- (T«~v 9 : 1.064 04- 03- 02- Kp.20'C: 0.0225 (BASE •) (SCCON D — ORDER KINETICS ) T~ 5 10 -1 T" 15 20 TEMP.(0,C) T" 25 —I 1 30 35 FIGURE 11 ------- 29 reactions: (l) chemical and biological decomposition of organic nitrogen to ammonia, (2) bacterial nitrification of ammonia to nitrite and nitrate, (3) phytoplankton utilization of ammonia, (4) phytoplankton utilization of nitrite and nitrate, (5) deposition of organic nitrogen, and (6) the death of the phytoplankton. With the area near Woodrow Wilson Bridge being light limited with respect to algal growths, the rate of phyto- plankton utilization of ammonia appears to be less than that in the area near Indian Head. For summer temperatures of 26°C to 29°C, first-order kinetic reaction rates have been established for the various processes given below: Nitrification by bacteria 0.30 to 0.40 Nitrogen utilization by phytoplankton 0.07 to 0.09 Deposition of algal cells 0.005 to 0.05 The first two processes (nitrification and nitrogen utilization) including the reaction rates have been well established as shown in the predicted profiles (Figures 13 and 14). The effect of temperature on the nitrification process and the rate of nitrogen utilization by algal cells has also been formulated as shown in Figures 15 and 16. Initial simulations indicate that the rate of recycling of nitrogen was not significant in the freshwater portions. As can be seen in Figures 13 and 14, there is a discontinuity in the nitrogen cycle at Nthe point of saline intrusion. This discontinuity appears to be a result of the transformation from fresh to mesohaline organisms. It appears that ------- 30 the rate of decomposition of organic nitrogen is much slower than the rate of bacterial nitrification or the rate of nitrogen uptake by algal cells in that the predominant form of nitrogen in the middle and lower estuaries is organic. ------- Table 2 DATA SUMMARY OF ALGAL CHEMICAL COMPOSITION STUDIES Potomac Estuary June - October 1970 Nutrient Btff, pf Nutrient ing, of Nutrient ug of Chlorophyll a mg. of S. Solids Carbon 0.045 0.331 Nitrogen 0.010 0.073 Phosphorus 0.001 0.006 ------- to LJ O to tr c o LJ CO to LU o to -o g LJ I CO O CO cr LJ 1 LU to LU ^L. Z LJ O LJ t K Z tr z O u. tr , 8 1 z o 3 i 1 s a CO FIGURE 12 ------- u \n oo O 2 _j u u. t- O Q Cf. CD u I Ul CO bJ -J 2 • ------- z o 2 UJ O oo <£ 0) (M 00 O) ^ O o «M I 6 P 3 O cc (M in m "(VI .o CJ O o IT 03 I 1 LJ i _0 (VJ oo d ------- 0.4 0.3- EFFECT OF TEMPERATURE ON NITRIFICATION RATE POTOMAC ESTUARY 0.2- 0.1- .09- .08- .07- .06- .05- .04- .03- .02- .01- X>9- )08- >07- 06- 05- 04- 9=1.186 Kj^z Ouoea (BASE •) at 2O'C (FIRST ORDER KINETICS) 03- 02- 01- "T 5 T" 10 -i r 15 20 TEMPERATURE CO "T" 25 "T" 30 35 FIGURE 15 ------- EFFECT OF TEMPERATURE ON RATE OF NITROGEN UTILIZATION BY ALGAE POTOMAC ESTUARY NO3—»- ALGAL NITROGEN 9 - 1.120 KN2 = 0.034 (BASE •) at 20C (FIRST ORDER KINETICS) 20 I 25 TEMPERATURE CO 30 35 FIGURE 16 ------- 37 Using the weight ratio of nitrogen to chlorophyll a (Table 2) and the nitrogen model rates indicated above, the dynamic model was expanded to predict the concentration of chlorophyll a based on the utilization of inorganic nitrogen. In Figures 17 and 18, predicted profiles using the surrogate algal model and observed data are presented. The predicted maximum concentrations compare closely to the observed data in both dis- tribution and magnitude. Eight other model predictions have been made and will be described fully in a report currently being prepared by CTSL. A DO budget has been incorporated into the dynamic water quality model consisting of the following five linkages: (1) Oxidation of carbonaceous matter, (2) Oxidation of nitrogenous matter (ammonia and organic), (3) Oxygen production and respiration of simulated algal standing crops based upon the nitrogen cycle, (4) Benthie demand, and (5) Reaeration from the atmosphere. The model, which is also described in the CTSL report currently in preparation, 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, (Figures 19 and 20 res- pectively) demonstrate that the model can predict DO responses over a wide range of freshwater inflows. ------- ------- B* r Si TIAHdOWOTHO FIGURE 16 ------- \| FIGURE 19 ------- _ m t; . id b O o O T i i i i i I I V")10 00 LJ o (M to 3 - o FIGURE 20 ------- 42 The basic coefficients used in the DO budget model were: Rate (base e) Temperature Coeffici- Process at 20 C ent Q (Tl - T20) Carbonaceous oxidation 0.230 1.047 Nitrogenous oxidation 0.068 1.188 Algal utilization of nitrogen 0.034 1.120 Reaeration from the atmosphere * 1.021 The remaining processes in the DO budget are given below: Algal oxygen production rate = 0.012 mg Oa/hr/ug chlorophyll a Algal respiration rate = 0.008 mg 02/hr/ug chlorophyll §. Euphotic zone = 2 feet Respiration depth = full depth of water column Algal oxygen production period = 12 hours Algal respiration period = 24 hours Benthic demand rate = 1.0 gr 02/day sq meter The five linkages provide a mechanism for not only investigating the effects of the various components on the dissolved oxygen budget but also for establishing the algal standing crop limits and nutrient criteria. * Based on a velocity and depth formulation ------- 43 EUTROPHICATION CONTROL For purposes of water quality management, the upper Potomac Estuary may be considered eutrophic when undesired standing crops become the predominant plant life as is now occurring with the nuisance blue-green alga species. The major objectives for controlling the blue- green algal standing crop in the upper estuary are fourfold; • ' 1. To reduce the dissolved oxygen (DO) depression caused by res- piration and the decay of algal growths especially in waters over 10 feet in depth„ At times, DO depressions of more than 3.0 mg/1 below saturation occur even during daylight hours. 2, To minimize the increase of ultimate oxygen demand which is a result of the conversion of inorganic carbon and nitrogen to oxi- dizable organic compounds by algal cells. 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 dioring 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 odors caused by blue-green algae if the upper estuary is to be used as a supplemental water supply«, ------- •44 To aid in defining an algal standing crop limit, a subjective analysis using chlorophyll concentrations was developed incorporating conditions having possible effects on water quality. Four major interferences are offered in this analysis (Table 3) including the desired reduction in the chlorophyll standing crop for each of the parameters. The desired maximum limit of 0.5 mg/1 DO below saturation was set 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. Of the four interferences, the most stringent reduction percentage is in the control of growths to prevent nuisance conditions. From the above analysis, a 75 to 90 percent reduction in chlorophyll concentration will be required in the Potomac Estuary, or chlorophyll levels of approximately 25 ug/1. ------- to UN vo o* o • o 5? o •p I tfN • H 8 9 a § I ------- 46 .» ESTABLISHMENT OF NUTRIENT CRITERIA Various investigators studying algal growth requirements have discussed 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 [27] recommended limits of inorganic nitrogen and inorganic phosphorus of 0.35 and 0.02, respectively. Mackenthun [24] 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 [9]. No recommendations for inorganic nitrogen were presented other than that the naturally occurring ratio of nitrogen to phosphorus should not be radically changed. Pritchard [25], studying the Chesapeake Bay and its tributaries, suggests that if total phosphorus concentrations in estuarine waters are below 0.03 mg/1, biologically healthy conditions will be maintained. Pritchard suggested no limit for nitrogen. Jaworski et al [16], reviewing historical data for the upper Potomac Estuary, indicated that if the concentrations of inorganic phosphorus and inorganic nitrogen were at or above 0.1 and 0.5, respectively, algal blooms of approximately 50 ug/1 would result. Chlorophyll a. of 50 ug/1 or over was considered indicative of excessive algal growths. Studies of the James River Estuary, a sister estuary to the Potomac, by Brehmer and Haltiwanger [4] indicate that nitrogen appears to be the rate limiting nutrient. ------- Recently, the management of carbon in controlling algal blooms has been suggested by Kuentzel [20] and Lange [21]„ Studies by Kerr ei si [191 also suggest that inorganic carbon is apparently directly responsible for increased algal populations in waters that they have studied. The Kerr studies indicate that the addition of nitrogen and phosphorus indirectly increases algal growth by stimulating growth of large heterotroph^c bacterial populations. No criteria for nitrogen, phosphorus, of carbon were indicated by Kerr. ion to the data reviewed above and that cited by numerous stigators not reported, six methods were used to develop the nutrient requirements for the Potomac Estuary. The six were: 1. Algal chemical composition analyses, 2. Analysis of the nutrient data on an annual cycle and profile basis, 3o Nutrient bioassay, 40 Nutrient and algal mathematical modeling, 5. Comparison with an estuary currently not eutrophic, and 6. Review of historical nutrient and ecological trends in the Potomac Estuary. 1. Algal Composition Analysis An analysis of the chemical composition of blue-green algae in the Potomac was made during the summer months of 1970. Summary data in terms of micrograms of chlorophyll a and grams of suspended solids are presented in Table 2. ------- ------- 4B Baaed on data in Table 2, an algal bloom of 100 ug/1 chlorophyll contains the following: 5. Solids 14.2 ag/1 Carbon 4.5 mg/1 Nitrogtn 1.0 mg/1 Phosphorus 0.1 ng/1 For tha Potomac Eatuary, which can ba oonsidared a alow-moving oontinuoua culture system, ooncantrations equal to or lass than 1.12 mg/1 of carbon, 0.25 ng/1 of nitrogen, and .025 ng/1 of phos- phorus would ba thaorrtioally required to maintain a 25 ug/1 chlorophyll 4 laval. Upper limits of nutrianta using this mathod should ba oonaidarad miniaal conoantrationa, ainoa no loaa to aadiaanta ia assumed, 2 An>l.¥Mij of Dit> an an Aimml Qvola >nd Longitudinal Pmftl* BaaiM Nutrianti not rajtovad fron tha watara ara it ill oapabla of tup- porting tha growth of algaa and othar organiaaa if thara ia an adaquata aupply of tha raaaining autrianta in tha aoallaat quantity naadad for growth* Using tha disappaaranoa of a apacifio nutriant both aaasooally and along longitudinal profilas, insight can ba gainad as to tha possibility that tha nutriant ia limiting algal growth. This taauffjaa that othar anviromantal factors do not rastriot growth. Ami Indian Kaad to flaith Point, which is tha am of pronounoad algal growth! thara is ovar 0.15 ag/1 of phosphorus in tha watara avan undar mxitum bloom conditions, (In Figura 2, inorganic phosphorus ------- 49 concentrations are given.) Data indicated that in the upper and middle reaches of the Potomac, phosphorus is in excess and thus is not rate limiting. In the lower reach near Piney Point, the total phosphorus concentration is often 0.04 mg/1 and thus phosphorus could be limiting for this reach. When the N02 + N03 and NH3 concentrations shown in Figures 3 and 4 are reviewed, it is evident that 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-nAugust 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 a major factor in limiting algal growth in the middle and lower estuary. To determine if carbon was limiting algal growth in the bloom area of the Potomac Estuary, a review of historical alkalinity data was made. Total and inorganic carbon analyses were also conducted during the latter part of 1969 and throughout 1970. During August and September 1970, river flows were low with air temperatures reaching 95°F during most of the days in September. Dense algal blooms extended from Hains Point to Smith Point. Carbon ------- 50 concentrations obtained during a sampling cruise on September 20, 1970, were as follows: Station Organic Carbon Inorganic Carbon (55713 Hains Point 7.2 12.2 Wilson Bridge 10.2 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 obtained during the mid-day hours of September 20, 1970, indicate that large quantities of inorganic carbon were available for algal growth even during periods of dense blooms. The 1969 data, historical alkalinity data, and other 1970 cruise data also substantiate the September 1970 findings. 3 . Bj.oassay Studies To determine further what nutrients were limiting algal growth in the Potomac, bioassay tests as developed by Fitzgerald [11] [12] were 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 ------- 51 in the range of 10 mg N/hr/ug chlorophyll a. The cells had adequate nitrogen available for growth as was also indicated by the high nitrate concentration in the water, especially at the upper stations above Indian Head. Tests for the latter part of July and August exhibited rates of absorption that were approximately twice as high for the Indian Head station as for the lower station at Maryland Point. In addition, when compared to the earlier data, the absorption rates were considerably higher ranging in the area of 10 mg N/hr/ug chlorophyll §_„ 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. N02 + NO-} Ammonia Station In Water In Water Nitrogen Absorbed (mg/l) (mg/i) (mg N/hr/ug chloro) Piscataway .110 2.560 + 6,0 x 10"5 Indian Head .150 .684 + 6,0 x 10"5 Possum Point .001 .220 + 2.3 x 10"4 Smith Point .001 .150 + 1.3 x 10"4 The higher rates of ammonia absorption for Possum and Smith Points and the low concentration of inorganic nitrogen indicates that this reach of the Potomac is becoming nitrogen limited. Two tests, an extraction procedure and an enzymatic analysis [12], were used to determine if algal growth was phosphorus limited. The phosphorus extraction bioassay studies indicated very little difference ------- ------- but i; ------- ------- i aese •.. ri t.«-. enhancement o; trends j r ne .. , an envarurum.irt occune'i - f '• wEii tor e-it .f 'b, .ra ')•' •O'-fj .-.t-eate • e;5t> j ui • w b 1 ch has ,-' cuTTfcv' T. the wastewa L> from fres/iH f ': ,1 •. rapid in erv.m-' •/•" ..-• iferyland Poizi . •',•.• plankton pop", lat'i . . two part ^ pt i the1 -< •• of the t.cunei.t .01= •• approximating i \,,\~-'\ Bas ed on ! •'.-: a- growth oi 'iiassj ;;-- :<•.. freshwater port j'uiifj, were often encount.t » These obdt?rv«i • - water quality n.enngM (1 ) FV< J.rJ \ ,i''-\ given reacJi of th- r-, ">n.' ht- f ) / .simi'p transition • (--spond 4 rig 10 ,'••'-luiLe rc-fach at. })"! H;;k'ton BJirt '^OO- : • .! e;; .4 re Lest: ( ban i" i:'iMC f.e •; h" k)wer end •:;. M -.ppears That the 1' f- • r;.' v < -es tri CH ,? J to the ------- ------- (2) There is. nut ri ent parairt v, e j f-: given est'iar.v« Therefore, at tr.e p/v.^-.r.-1 established iur c^t: ifteaho -., .. • 56 ze on i/1 portions of a -.'t •; '-?;tev-i8 nave been -t QUO. " E? ------- WASTEWATER TREATMENT REQUIREMENTS Under controlled cond.itJorr:, ;s r-vi-nrted oy varictis investigators, reductions in the standing ^rop of al/rv; r-tn :,<=• Chawed by the manage- merit of either carbon, -nJtropen, o:c phosphorus or by o corrni nation of these basic nutrients. The ncc^s u>.r: as to which nutrient or nutrients in a natural system should, be control led by removal from point sources may depend upor many fsc-t na jr/ciudiiTg the four listed below: 1. Level of algal rea-ucticn requvrad to minimize adverse effects on water quality,, 2. Minimuii' nutrjenl requirements to /naiintain a given algal standing crop, 3, Controllability and mobility of a given nutrient within the system, and 4. The overall vrater <.uf«Vit,y management needs, such as DO enhancement, eutrophicatlon reversal, and reduction of potentially toxic matter including heavy mi;,^"i:j. In establishing !,he overs.n wutftewater uianage/nent prograwi for the Potomac Estuary, tiif> IUM,, i Ui-ni,- A.-r- ;:oth nitx-ogen and phosphorus were ------- 58 Limits for both were Incorporated for the following reasons ° (l) Since the flow of the Potomac Paver is very flashy, neither phosphorus nor nitrogen can be controlled thrcsughout the estuary at all times. To reduce eutrophicaiicn i>>. the entire estuary for years having average or above average flow conditions, phosphorus control appears to be more feasible. However, in, the middle and upper estuary during low-flow years, nitrogen control appears to be more effective. This is because the nitrogen criterion for restricting algal growth is ten times that for phosphorus (0.^0 versus 0.03 mg/l) while the nitrogen loading from the wastewater treatment facilities is 2.4 times 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 a fourfold advantage in removing nitrogen over that of phosphorus. (2) Various investigators report that increases in nitrogen and/or phosphorus can increase heterotropbic activity which in turn stimulates algal growth, and (3) There is compatibility between wastewater treatment require- ments for dissolved oxygen enhancement and eutrophication control. Compatibility of treatment requirements is probably one of the most important considerations of the four factors influencing the selection of wastewater treatment unit processes. For example, to maintain the dissolved oxygen standard In the upper estuary under summer conditions, a high degree of carbonaceous and nitrogenous ------- 59 oxygen demand removal is required, whereas the control of algal standing crops is predicated on phosphorus and nitrogen removal. To obtain a high degree of carbonaceous oxyger. demand removal, a chemical coagulation unit process is usually required beyond secondary treatment. This unit process will also remove a high percentage of phosphorus. The removal of the nitrogenous demand can be satisfied by one of two methods: (1) by converting the unoxidized nitrogen to nitrates (commonly called nitrification), or (2) by removal of nitrogen completely. If a unit process such as biological nitrification- denitrification is employed, both the DO and algal requirements for nitrogen can be met. Thus with proper selection of wastewater treatment unit processes, it is feasible not only to enhance the DO by removing the carbonaceous and nitrogenous UOD but also to reduce nuisance algal growth by removing nutrients. ------- 60 A WATER QUALITY MANAGEMENT PROGRAM The conferees of the Potomac River-Washington Metropolitan Area Enforcement Conference agreed on May 8, 1969, to limit the amount of UOD, phosphorus, and nitrogen which could be discharged into the upper estuary from wastewater treatment facilities. The water quality management program currently being developed recognizes a need not only for high degrees of wastewater treatment for the removal of carbonaceous and nitrogenous UOD but also a need for the control of eutrophicat ion. Segmenting the upper estuary into three 15-mile zones (Figure 21), maximum Ibs/day loadings were established for Zone I equivalent to 96 percent removal of BODj, 96 percent of phosphorus, and 85 percent of nitrogen. These percent removals were also adopted for discharges in Zone II until firmer loadings could be developed. Since May 1969, more detailed loadings have been developed and presented to the conference in the December 1970 progress meeting [18]. The program calls for the construction of advanced wastewater treatment facilities by 1977 capable of removing the above designated percentages of carbon, nitrogen, and phosphorus, with possible advancement of the construction deadline to December 1974. Present worth cost of the additional wastewater treatment required, including operation, maintenance, and amortization for the time period 1970 to 2020 has been estimated to be $1.2 billion with a total average annual cost of $54.8 million. The unit processes assumed include ------- / \ RIVER MILES FROM CHAIN BRIDGE = 0 (STRICT OF COLUMBIA ALEXANDRIA WESTGATE RIVER MILES FROM CHAIN BRIDGE - IS LITTLE HUNTING Cr. ANDREWS A.F.B. PISCATAWAY Cr. ZONE II RIVER MILES FROM CHAIN BRIDGE - 30 WASTEWATER DISCHARGE ZONES in UPPER POTOMAC ESTUARY ZONE III RIVER MILES FROM CHAIN BRIDGE - 45 FORT BELVOIR LOWER POTOMAC FIGURE 21 ------- 61 activated sludge, biological nitrification-denitrification, lime clari- fication, filtration, effluent aeration and chlorination. On a per capita basis, the cost of the wastewater removal program is estimated to be approximately $13.50 to $!8.30/person/year0 The program being developed will not only enhance the water quality of the estuary to meet minimum designated standards but will render it a feasible source of municipal water supply. Studies indicate that either indirect or direct reuse of renovated waste- water is a viable alternative in meeting the water supply needs for the Washington, V. C. Metropolitan Area [15] [17]. ------- REFERENCES 1. Aalto, J. A., N. A0 Jaworski, and Donald W. Lear, Jr., "Current Water Quality Conditions and Investigations in the Upper Potomac River Tidal System," CTSL, MAR, FWQA, U. S. Department of the Interior, Technical Report No. 41, May 1970. 20 Bartsch, A. F., "Bottom and PlaTikton Conditions in the Potomac River in the Washington Metropolitan Area," Appendix A, A report on water pollution in the Washington metropolitan area, Interstate Commission on the Potomac River Basin, 1954. 3, Bayley, S., H. Rabin, and C0 H. Southwick, "Recent Decline in the Distribution and Abundance of Eurasian Watermilfoil in Chesapeake Bay," Chesapeake Science, Vol. 9, No. 3, 1968. 4. Brehmer, M. L. and Samuel 0. Haitiwanger, "A Biological and Chemical Study of the Tidal James River," Virginia Institute of Marine Science, Gloucester Point, Virginia, November 15, 1966, 5. Brezanik, W. H., W. H. Morgan, E. E. Shannon, and H. D. Putnam, "Eutrophication Factors in North Central Florida Lakes," Florida Engineering and Industrial Experiment Station, Bulletin Series No. 134, Gainesville, Florida, August 1969, 6. Gumming, H. S., ".'nvestigation of the Pollution and Sanitary Conditions of the ?otomac Watershed," Appendix to USPHS Hygiene Laboratory Bulletir 104, 1916. 7. Edmondson, W. T., 'The Response of Lake Washington to Large Changes in its Nutrient Income," International Botanical Congress. 1969. 8. Elser, H. J., "Status of Aquatic Week Problems in Tidewater Maryland, Spring 1965," Maryland Department of Chesapeake Bay Affairs, 8 pp mimeo, 1965. 9. Federal Water Pollution Control Administration, "Water Quality Criteria," Report of the National Technical Advisory Committee to the Secretary of the Interior, April 1, 1968„ 10. Feigner, K. and Howard S. Harris, Documentation Report, FWQA Dynamic Estuary Model, FWQA, U. S. Department of the Interior, July 1970. 11. Fitzgerald, George P., "Detection of Limiting on Surplus Nitrogen in Algae and Aquatic Weeds," Journal of Phvcology. Vol. 2, No. 1 1966. ------- 12. Fitzgerald, George P. and Thomas C. Kelson, "Extractive and Enzymatic Analyses for Limiting on Surplus Phosphorus in Algae," Journal on Fhycology. Vol. 2, No. 1, 1966. 13. Easier, A. D., "Culture Eutrophication is Reversible," Bioscience. Vol. 19, No. 5, May 1969, 14, Hutchinson, G. E., A Treatise on Limnology. Vol. 1, John Wiley and Sons, Inc., New York, 1957. 15. Hydroscience, Inc., "The Feasibility of the Potomac Estuary as a Supplemental Water Supply Source," prepared for N.E.W.S. Water Supply Study, North Atlantic Division, U. S. Army Corps of Engineers, March 1970. 16. Jaworski, N. A0, D. W. Lear, And J. A. Aalto, "A Technical Assess- ment of Current Water Quality Conditions and Factors Affecting Water Quality in the Upper Potomac Estuary," CTSL, FWPCA, MAR, U. S. Department of the Interior, 1969. 17. Jaworski, N. A., Leo J. Clark, and Kenneth D. Feigner, "A Water Resource - Water Quality Study of the Potomac Estuary," CTSL, FWQA, Environmental Protection Agency, Technical Report No. 35, 1970. (In Preparation) IS. Jaworski, N. A., Johan A. Aalto, Leo J. Clark, and Donald W. Lear, Jr., "Summary Statement on Potomac Estuary Water Quality Studies for the December 8 and 9, 1970 Progress Meeting of the Potomac Metropolitan Area Enforcement Conference," CTSL FWQA., Environmental Protection Agency, December 1970. 19. Kerr, Pat C,, Dorris F. Parie, and D. L. Bruckway, "The Inter- relation of Carbon and Phosphorus in Regulating Hetrotrophic and Autotrophic Populations in Aquatic Ecosystems," Southeast Water Laboratory, FWQA, U.S. Department of the Interior, 1970. 20. Kuentzel, L. E., "Bacteria, C02 and Algal Blooms," Journal Water Pollution Control Federation. 21, 1737-1749, 1969. 21. Lange, W., "Effect of Carbohydrates on Symbolic Growth of Planktonic Blue-Green Algae with Bacteria," Nature 215, 1277-1278, 1967. 22. Lawton, G. W., "The Madison Lakes Before and After Diversion," Trans. I960 Seminar on A^gae and Metropolitan Wastes, pp 108-117, Robert A. Taft Sanitary Engineering Center, Tech. Report W61-3, 1961. ------- 23. Livermore, D. F. and W. E. Wanderlich, "Mechanical Removal of Organic Production from Waterways," Eutrophication: Causest Conse- quences j. Correct!vesf National Academy of Sciences, 1969. 24. Mackenthun, K. M. "Nitrogen and Phosphorus in Water/1 USPHS, Department of Health, Education and Welfare, 1965. 25. Pritchard, Donald W., "Dispersion and Flushing of Pollutants in Estuaries," Journal of the Hydraulics Division American Society of Civil Engineers. Vol. 95, No. HY1, January 1969. 26. Riley, J. P. and G. Skirrow, Chemical Oceanography. Vol. 1, Academic Press, London and New York, 1965. 27. Sawyer, C. N., "1969 Occoquan Reservoir Study," Metcalf and Eddy, Inc. for the Commonwealth of Virginia Water Control Board, April 1970. 28. Stotts, V. D. and J. R. Longwell, "Potomac River Biological Investi- gation 1959," Supplement to technical appendix to Part VII of the report on the Potomac River Basin studies, U. S. Department of Health, Education and Welfare, 1962. 29. Thomann, R. 0., Donald J. O'Connor, and Dominic M. DiTorro, "Modeling of the Nitrogen and Algal Cycles in Estuaries," presented at the Fifth International Water Pollution Research Conference, San Francisco, California, July 1970. 30. U. S. Public Health Service, "Investigation of the Pollution and Sanitary Conditions of the Potomac Watershed," Hygienic Laboratory Bulletin No. 104, Treasury Department, February 1915. 31. University of Wisconsin, Private Communication with George P. Fitzgerald, January 19. 1971. 32. Welch, E. B., "Phytoplankton and Related Water Quality Conditions in an Enriched Estuary," Journal Water Pollution Control Federation. Vol. 40, pp 1711-1727, October 1968. -------


U.S. ENVIRONMENTAL PROTECTION AGENCY
       Annapolis Field Office
      Annapolis Science Center
     Annapolis, Maryland  21401
         TECHNICAL REPORTS
           Volume 5

-------

-------
                       Table of Contents


                           Volume 5
37         Nutrient Transport and Dissolved Oxygen Budget
           Studies in the Potomac Estuary
39         Preliminary Analyses of the Wastewater and Assimilation
           Capacities of the Anacostia Tidal  River System
41         Current Water Quality Conditions and Investigations
           in the Upper Potomac River Tidal System
43         Physical Data of the Potomac River Tidal System
           Including Mathematical Model Segmentation
45         Nutrient Management in the Potomac Estuary

-------
                            PUBLICATIONS

                U.S.  ENVIRONMENTAL PROTECTION AGENCY
                             REGION III
                       ANNAPOLIS FIELD OFFICE*


                              VOLUME 1
                          Technical  Reports


 5         A Technical  Assessment of Current Water Quality
           Conditions and Factors Affecting Water Quality in
           the Upper Potomac Estuary

 6         Sanitary Bacteriology of the Upper Potomac Estuary

 7         The Potomac Estuary Mathematical Model

 9         Nutrients in the Potomac River Basin

11         Optimal  Release Sequences for Water Quality Control
           in Multiple Reservoir Systems

                              VOLUME 2
                          Technical  Reports


13         Mine Drainage in the North Branch Potomac River Basin

15         Nutrients in the Upper Potomac River Basin

17         Upper Potomac River Basin Water Quality Assessment

                              VOLUME  3
                          Technical  Reports

19         Potomac-Piscataway Dye Release and Wastewater
           Assimilation Studies

21         LNEPLT

23         XYPLOT

25         PLOT3D


     * Formerly CB-SRBP, U.S. Department of Health, Education,
       and Welfare; CFS-FWPCA, and CTSL-FUQA,  Middle Atlantic
       Region, U.S. Department of the Interior

-------
                             VOLUME 3   (continued)

                         Technical Reports


27         Water Quality and Wastewater Loadings - Upper Potomac
           Estuary during 1969


                             VOLUME 4
                         Technical Reports


29         Step Backward Regression

31         Relative Contributions of Nutrients to the Potomac
           River Basin from Various Sources

33         Mathematical Model Studies of Water Quality in the
           Potomac Estuary

35         Water Resource - Water Supply Study of the Potomac
           Estuary

                             VOLUME 5
                         Technical Reports


37         Nutrient Transport and Dissolved Oxygen Budget
           Studies in the Potomac Estuary

39         Preliminary Analyses of the Wastewater and Assimilation
           Capacities of the Anacostia Tidal River System

41         Current Water Quality Conditions and Investigations
           in the Upper Potomac River Tidal System

43         Physical Data of the Potomac River Tidal System
           Including Mathematical Model Segmentation

45         Nutrient Management in the Potomac Estuary


                             VOLUME 6

                         Technical Reports


47         Chesapeake Bay Nutrient Input Study

49         Heavy Metals Analyses of Bottom Sediment in the
           Potomac River Estuary

-------
                                  VOLUME  6  (continued)

                              Technical  Reports

     51          A System of Mathematical Models for Water Quality
                Management

     52         Numerical  Method for Groundwater Hydraulics

     53         Upper Potomac Estuary Eutrophication Control
                Requirements

     54         AUT0-QUAL Modelling System

Supplement      AUT0-QUAL Modelling System:  Modification for
   to 54        Non-Point Source Loadings

                                  VOLUME  7
                              Technical  Reports

     55         Water Quality Conditions in the Chesapeake Bay System

     56         Nutrient Enrichment and  Control Requirements in the
                Upper Chesapeake Bay

     57         The Potomac River Estuary in the Washington
                Metropolitan Area - A History of its Water Quality
                Problems and their Solution

                                  VOLUME  8
                              Technical  Reports

     58         Application of AUT0-QUAL Modelling System to the
                Patuxent River Basin

     59         Distribution of Metals in Baltimore Harbor Sediments

     60         Summary and Conclusions - Nutrient Transport and
                Accountability in the Lower Susquehanna River Basin

                                  VOLUME  9
                                 Data Reports

                Water Quality Survey, James River and Selected
                Tributaries - October 1969

                Water Quality Survey in the North Branch Potomac River
                between Cumberland and Luke, Maryland - August 1967

-------
                            VOLUME 9  (continued)
                           Data Reports


           Investigation of Water Quality in Chesapeake Bay and
           Tributaries at Aberdeen Proving Ground, Department
           of the Army, Aberdeen, Maryland - October-December 1967

           Biological Survey of the Upper Potomac River and
           Selected Tributaries - 1966-1968

           Water Quality Survey of the Eastern Shore Chesapeake
           Bay, Wicomico River, Pocomoke River, Nanticoke River,
           Marshall Creek, Bunting Branch, and Chincoteague Bay -
           Summer 1967

           Head of Bay Study - Water Quality Survey of Northeast
           River, Elk River, C & D Canal, Bohemia River, Sassafras
           River and Upper Chesapeake Bay - Summer 1968 - Head ot
           Bay Tributaries

           Water Quality Survey of the Potomac Estuary - 1967

           Water Quality Survey of the Potomac Estuary - 1968

           Wastewater Treatment Plant Nutrient Survey - 1966-1967

           Cooperative Bacteriological Study - Upper Chesapeake Bay
           Dredging Spoil Disposal - Cruise Report No. 11

                            VOLUME 10
                           Data Reports

 9         Water Quality Survey of the Potomac Estuary - 1965-1966

10         Water Quality Survey of the Annapolis  Metro Area - 1967

11         Nutrient  Data on Sediment  Samples of the Potomac Estuary
           1966-1968

12         1969  Head  of  the Bay Tributaries

13         Water Quality Survey of the Chesapeake Bay in the
           Vicinity  of Sandy  Point -  1968

14         Water Quality  Survey of the Chesapeake Bay in the
           Vicinity  of Sandy  Point -  1969

-------
                             VOLUME  10(continued)

                           Data Reports

15         Water Quality Survey of the  Patuxent River -  1967

16         Water Quality Survey of the  Patuxent River -  1968

17         Water Quality Survey of the  Patuxent River -  1969

18         Water Quality of the Potomac Estuary Transects,
           Intensive and Southeast Water Laboratory Cooperative
           Study - 1969

19         Water Quality Survey of the  Potomac  Estuary Phosphate
           Tracer Study - 1969

                             VOLUME  11
                            Data Reports

20         Water Quality of the Potomac Estuary Transport  Study
           1969-1970

21         Water Quality Survey of the Piscataway Creek Watershed
           1968-1970

22         Water Quality Survey of the Chesapeake Bay in the
           Vicinity of Sandy Point - 1970

23         Water Quality Survey of the Head of the Chesapeake Bay
           Maryland Tributaries - 1970-1971

24         Water Quality Survey of the Upper Chesapeake Bay
           1969-1971

25         Water Quality of the Potomac Estuary Consolidated
           Survey - 1970

26         Water Quality of the Potomac Estuary Dissolved  Oxygen
           Budget Studies - 1970

27         Potomac Estuary Wastewater Treatment Plants Survey
           1970

28         Water Quality Survey of the Potomac Estuary Embayments
           and Transects - 1970

29         Water Quality of the Upper Potomac Estuary Enforcement
           Survey - 1970

-------
   30


   31


   32
   33
   34
Appendix
  to 1
Appendix
  to 2
    3


    4
                  VOLUME 11  (continued)
                 Data Reports

Water Quality of the Potomac Estuary - Gilbert Swamp
and Allen's Fresh and Gunston Cove - 1970

Survey Results of the Chesapeake Bay Input Study -
1969-1970

Upper Chesapeake Bay Water Quality Studies - Bush River,
Spesutie Narrows and Swan Creek, C & D Canal, Chester
River, Severn River, Gunpowder, Middle and Bird Rivers -
1968-1971

Special Water Quality Surveys of the Potomac River Basin
Anacostia Estuary, Wicomico .River, St. Clement and
Breton Bays, Occoquan Bay - 1970-1971

Water Quality Survey of the Patuxent River - 1970

                  VOLUME 12

               Working Documents

Biological Survey of the Susquehanna River and its
Tributaries between Danville, Pennsylvania and
Conowingo, Maryland

Tabulation of Bottom Organisms Observed at Sampling
Stations during the Biological Survey between Danville,
Pennsylvania and Conowingo, Maryland - November 1966

Biological Survey of the Susquehanna River and its
Tributaries between Cooperstown, New York and
Northumberland, Pennsylvnaia - January 1967

Tabulation of Bottom Organisms Observed at Sampling
Stations during the Biological Survey between Cooperstown,
New York and Northumberland, Pennsylvania - November 1966

                  VOLUME 13
               Working Documents

Water  Quality and Pollution Control Study, Mine Drainage
Chesapeake  Bay-Delaware River Basins - July 1967

Biological  Survey of Rock Creek (from Rockville, Maryland
to  the Potomac River)  October 1966

-------
                             VOLUME   13   (continued)

                          Working  Documents

 5         Summary of Water Quality  and  Waste Outfalls,  Rock  Creek
           in Montgomery County, Maryland and the  District  of
           Columbia - December 1966

 6         Water Pollution Survey  -  Back River 1965 -  February  1967

 7         Efficiency Study of the District  of Columbia  Water
           Pollution Control  Plant - February 1967

                             VOLUME   14
                          Working Documents

 8         Water Quality and Pollution Control  Study -  Susquehanna
           River Basin from Northumberland to West Pittson
           (Including the Lackawanna River Basin)   March  1967

 9         Water Quality and Pollution Control  Study, Juniata
           River Basin - March 1967

10         Water Quality and Pollution Control  Study, Rappahannock
           River Basin - March 1967

11         Water Quality and Pollution Control  Study, Susquehanna
           River Basin from Lake Otsego,  New York, to Lake  Lackawanna
           River Confluence, Pennsylvania -  April  1967

                             VOLUME  15

                          Working Documents

12         Water Quality and Pollution Control  Study, York  River
           Basin - April 1967

13         Water Quality and Pollution Control  Study, West  Branch,
           Susquehanna River Basin - April 1967

14         Water Quality and Pollution Control  Study, James River
           Basin - June 1967

15         Water Quality and Pollution Control  Study, Patuxent  River
           Basin - May 1967

-------
                             VOLUME 16

                          Working Documents

16         Water Quality and Pollution Control  Study,  Susquehanna
           River Basin from Northumberland, Pennsylvania,  to
           Havre de Grace, Maryland - July 1967

17         Water Quality and Pollution Control  Study,  Potomac
           River Basin - June 1967

18         Immediate Water Pollution Control  Needs, Central  Western
           Shore of Chesapeake Bay Area (Magothy,  Severn,  South,  and
           West River Drainage Areas)  July 1967

19         Immediate Water Pollution Control  Needs, Northwest
           Chesapeake Bay Area (Patapsco to Susquehanna Drainage
           Basins in Maryland) August 1967

20         Immediate Water Pollution Control  Needs - The Eastern
           Shore of Delaware, Maryland and Virginia -  September 1967

                             VOLUME 17
                           Working Documents

21         Biological Surveys of the Upper James River Basin
           Covington, Clifton Forge, Big Island, Lynchburg, and
           Piney River Areas - January 1968

22         Biological Survey of Antietam Creek and some of its
           Tributaries from Waynesboro, Pennsylvania to Antietam,
           Maryland - Potomac River Basin - February 1968

23         Biological Survey of the Monocacy River and Tributaries
           from Gettysburg, Pennsylvania, to Maryland Rt. 28 Bridge
           Potomac River Basin - January 1968

24         Water Quality Survey of Chesapeake Bay in the Vicinity of
           Annapolis, Maryland - Summer 1967

25         Mine Drainage Pollution of the North Branch of Potomac
           River - Interim Report - August 1968

26         Water Quality Survey in the Shenandoah River of the
           Potomac River Basin - June 1967

27         Water Quality Survey in the James and Maury Rivers
           Glasgow,  Virginia - September 1967

-------
                             VOLUME  17   (continued)

                           Working Documents

28         Selected Biological  Surveys in the James River Basin,
           Gillie Creek in the  Richmond  Area, Appomattox River
           in the Petersburg Area, Bailey Creek from Fort Lee
           to Hopewell - April  1968

                             VOLUME  18
                           Working Documents

29         Biological  Survey of the Upper and Middle Patuxent
           River and some of its Tributaries - from Maryland
           Route 97 Bridge near Roxbury Mills to the Maryland
           Route 4 Bridge near Wayson's Corner, Maryland -
           Chesapeake Drainage Basin - June 1968

30         Rock Creek Watershed - A Water Quality Study Report
           March 1969

31         The Patuxent River - Water Quality Management -
           Technical Evaluation - September 1969

                             VOLUME 19
                          Working Documents

           Tabulation, Community and Source Facility Water Data
           Maryland Portion, Chesapeake Drainage Area - October 1964

           Waste Disposal Practices at Federal  Installations
           Patuxent River Basin - October 1964

           Waste Disposal Practices at Federal  Installations
           Potomac River Basin below Washington, D.C.- November 1964

           Waste Disposal Practices at Federal  Installations
           Chesapeake Bay Area of Maryland Excluding Potomac
           and Patuxent River Basins - January 1965

           The Potomac Estuary - Statistics and Projections -
           February 1968

           Patuxent River - Cross Sections and Mass Travel
           Velocities - July 1968

-------
                            VOLUME  19 (continued)

                         Working Documents

          Wastewater Inventory - Potomac River Basin -
          December 1968

          Wastewater Inventory - Upper Potomac River Basin -
          October 1968

                            VOLUME 20
                         Technical Papers -

 1         A  Digital Technique for Calculating and Plotting
          Dissolved Oxygen Deficits

 2         A  River-Mile  Indexing System for Computer Application
          in Storing and Retrieving Data      (unavailable)

 3         Oxygen  Relationships in Streams, Methodology to be
          Applied when  Determining the Capacity of a Stream to
          Assimilate Organic Wastes - October 1964

 4         Estimating Diffusion Characteristics of Tidal Waters -
          May  1965

 5         Use  of  Rhodamine B Dye as a Tracer in Streams of the
          Susquehanna River Basin - April 1965

 6         An In-Situ Benthic Respirometer - December 1965

 7         A  Study of Tidal Dispersion in the Potomac River
          February  1966

 8         A  Mathematical Model for the Potomac River - what it
          has  done  and  what it can do - December 1966

 9         A  Discussion  and Tabulation of Diffusion Coefficients
          for  Tidal Waters Computed as a  Function of Velocity
          February  1967

10         Evaluation of Coliform  Contribution by Pleasure Boats
          July 1966

-------
                            VOLUME  21
                         Technical Papers

11         A Steady State Segmented Estuary Model

12        Simulation of Chloride Concentrations in the
          Potomac Estuary - March 1968

13        Optimal Release Sequences for Water Quality
          Control in Multiple-Reservoir Systems - 1968

                            VOLUME  22
                         Technical  Papers

          Summary Report - Pollution of Back River - January 1964

          Summary of Water Quality - Potomac River Basin in
          Maryland - October 1965

          The Role of Mathematical  Models in the Potomac River
          Basin Water Quality Management Program - December 1967

          Use of Mathematical Models as Aids to Decision Making
          in Water Quality Control  - February 1968

          Piscataway Creek Watershed - A Water Quality Study
          Report - August 1968


                            VOLUME  23
                        Ocean Dumping Surveys

          Environmental Survey of an Interim Ocean Dumpsite,
          Middle Atlantic Bight - September 1973

          Environmental Survey of Two Interim  Dumpsites,
          Middle Atlantic Bight - January 1974

          Environmental Survey of Two Interim Dumpsites
          Middle Atlantic Bight - Supplemental Report -
          October 1974

          Effects of Ocean Disposal Activities on Mid-
          continental Shelf Environment off Delaware
          and Maryland - January 1975

-------
                            VOLUME 24

                           1976 Annual
               Current Nutrient Assessment - Upper Potomac Estuary
               Current Assessment Paper No.  1

               Evaluation of Western Branch  Wastewater Treatment
               Plant Expansion - Phases I and II

               Situation Report - Potomac River

               Sediment Studies in Back River Estuary, Baltimore,
               Maryland

Technical      Distribution of Metals in Elizabeth River Sediments
Report 61

Technical      A Water Quality Modelling Study of the Delaware
Report 62      Estuary

-------
NUTRIENT TRANSPORT AND DISSOLVED
  OXYGEN BUDGET STUDIES IN THE
         POTOMAC ESTUARY

           October 1972
        Technical  Report 37
      Annapolis Field Office
            Region III
 Environmental Protection Agency

-------

-------
                 Annapolis Field Office
                       Region III
             Environmental Protection Agency
            NUTRIENT TRANSPORT AND DISSOLVED
              OXYGEN BUDGET STUDIES IN THE
                     POTOMAC ESTUARY
                   Technical Report 37

                      October 1972
                      Leo 0. Clark
                  Norbert A. Jaworski*
                    Supporting Staff:

              Johan A. Aalto, Director, AFO
Orterio Villa, Jr., Chief, Laboratory Development Section
            * Environmental Protection Agency
         National  Environmental  Research Center
                    Corvallis, Oregon

-------

-------
                         TABLE OF CONTENTS
                                                               Page

PREFACE                                                         iii

LIST OF TABLES                                                   vi

LIST OF FIGURES                                                 vii

Chapter

   I.  INTRODUCTION	     I -  1

       A.  PURPOSE AND SCOPE	     I -  1

       B.  ACKNOWLEDGEMENTS   	     1-3

  II.  SUMMARY AND CONCLUSIONS	    II -  1

 III.  DESCRIPTION OF STUDY AREA    	Ill -  1

  IV.  SOURCES OF NUTRIENTS AND OXYGEN DEMANDING SUBSTANCES  .    IV -  1

       A.  WASTEWATER LOADINGS	    IV -  1

       B.  CONTRIBUTIONS FROM THE UPPER POTOMAC RIVER BASIN  .    IV -  3

       C.  SUBURBAN AND URBAN RUNOFF	    IV -  7

   V.  FRAMEWORK FOR ANALYSIS	     V -  1

       A.  WATER QUALITY DATA	     V -  1

       B.  CHEMICAL, PHYSICAL AND BIOLOGICAL REACTIONS.  .   .     V -  3

           1.  Nitrogen	     V -  3

           2.  Phosphorus	     V-6

       C.  MATHEMATICAL MODELING TECHNIQUES  	     V -  9

  VI.  NITROGEN ASSIMILATION AND TRANSPORT   	    VI -  1

       A.  TEMPORAL AND SPATIAL DISTRIBUTION 	    VI -  1

       B.  DETERMINATION OF REACTION RATES AND  TEMPERATURE
           EFFECTS	    VI -  7

           1.  Nitrification	    VI -  7

           2.  Algal Uptake	    VI - 23
                                 IV

-------
                           PREFACE

     The ability to simulate,  mathematically,  the  historical  dissolved
oxygen (DO) distribution in a  watercourse is  quite an  achievement,
especially when most of the known components  of the DO budget are
quantitatively defined and incorporated in the analysis.   This ability
is in fact required to predict future changes, including  standards
compliance, in the dissolved oxygen content of a lake, stream, or
estuary due to municipal or industrial  growth.
     While the classical Streeter-Phelps study of the  Ohio River
in 1924 initially established  the basic relationships  governing
dissolved oxygen, the evaluation of the oxygen budget  is  no longer  based
solely on the biochemical oxyged demand (BOD)  and reaeration.
Sanitary engineers have intruded into the biologist's  domain by attempts
to determine in mathematical terms  the effects of nutrient materials,
specifically nitrogen and phosphorus, on the density and  extent of
algal blooms and the algae's subsequent effect on the  DO  budget.
A strong interdependence exists among nitrogen, phosphorus, algae
and dissolved oxygen, and although only a rudimentary  approach was
ventured, the Annapolis Field Office (AFO) of the Environmental
Protection Agency  (EPA) has mathematically modeled this interrelation-
ship in the upper Potomac Estuary.

-------
                         TABLE OF CONTENTS

                                                               Page

Chapter

  VI.  NITROGEN ASSIMILATION AND TRANSPORT (Continued)

       C.  SIMULATION OF NITROGEN TRANSPORT THROUGH AN
           ANNUAL CYCLE	      VI  -  25

       D.  CHLOROPHYLL PREDICTIONS BASED ON NITROGEN
           ASSIMILATION BY  THE BIOMASS	      VI  -  31

 VII.  PHOSPHORUS ASSIMILATION AND TRANSPORT  	     VII  -   1

       A.  TEMPORAL AND SPATIAL DISTRIBUTION  	     VII  -   1

       B.  DETERMINATION OF LOSS RATE AND TEMPERATURE EFFECTS     VII  -   5

       C.  SIMULATION OF PHOSPHORUS TRANSPORT THROUGH AN
           ANNUAL CYCLE	     VII  -  21

       D.  CHLOROPHYLL PREDICTIONS BASED ON PHOSPHORUS
           ASSIMILATION BY  THE BIOMASS	     VII  -  27

VIII.  DISSOLVED OXYGEN BUDGET    	    VIII  -   1

       A.  FORMULATION OF SOURCES AND SINKS	VIII  -   1

       B.  SIMULATION AND MODEL VERIFICATION STUDIES   .   .   .    VIII  -   6

       C.  SENSITIVITY ANALYSIS	VIII  -  17

           1.   Effects of Oxidation Rates (Carbon and
               Nitrogen)	VIII  -  17

           2.   Effects of Photosynthesis and Respiration
               Rates	VIII  -  18

           3.   Effects of Benthic Demand Rate	VIII  -  19

           4.   Effects of Reaeration Rate	VIII  -  19

       D.  NUTRIENT REGENERATION - SPECIAL DO MODEL ....    VIII  -  26

  IX.  ADDITIONAL STUDY REQUIREMENTS 	      IX  -   1

       BIBLIOGRAPHY

-------
                        LIST OF TABLES

Chapter                                                        Page

  IV - 1    Wastewater Loadings to the Upper Potomac Estuary
           and Tributaries	      IV - 2

  IV - 2   Upper Potomac River Basin Contributions (Above
           Great Falls) February 1969 through February 1970 .      IV - 6

  IV - 3   Urban and Suburban Runoff Contributions to Upper
           Potomac Estuary    	      IV - 8

VIII - 1    Oxygen Production and Respiration Rate Survey,
           Upper and Middle Potomac Estuary, 1970  .   .   .   .    VIII - 4

-------
LIST OF FIGURES
Number
III -
IV -

V -
V -
V -
VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -


1
1

1
2
3
1

2

3

4

5

6

7

8

9

10

11

12

Description
Potomac Estuary Location Map 	
Nutrient Concentrations, Potomac River at Great
Falls 	
Simplified Nitrogen Cycle 	
Simplified Phosphorus Cycle 	
Simplified DO Budget for Dynamic Estuary Model •
Ammonia Nitrogen Isopleth, Potomac Estuary,
1969-70 Data 	
Nitrite + Nitrate Nitrogen Isopleth, Potomac
Estuary, 1969-70 Data 	
Organic Nitrogen Isopleth, Potomac Estuary,
1969-70 Data 	
Nitrogen Concentration, Potomac Estuary,
September 6-13, 1966 	
Nitrogen Concentration, Potomac Estuary,
August 31 - September 23, 1965 	
Nitrogen Concentration, Potomac Estuary,
October 7, 1968 	
Nitrogen Concentration, Potomac Estuary,
January 25, 1966 	
Nitrogen Concentration, Potomac Estuary,
September 28-30, 1970 	
Nitrogen Concentration, Potomac Estuary,
September 20-21 ,1967 	
Nitrogen Concentration, Potomac Estuary,
August 5, 1968 . 	
Nitrogen Concentration, Potomac Estuary,
October 15-16, 1969 	
Nitrogen Concentration, Potomac Estuary,
August 19-22, 1968 	
Page
III -

IV -
V -
V -
V -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

VI -

3

5
5
8
11

4

5

6

9

10

11

12

13

14

15

16

17
      VII

-------
                        LIST  OF  FIGURES

Number                    Description                          Page

  VI - 13   Nitrogen  Concentration,  Potomac  Estuary,
            December  9,  1969	      VI - 18

  VI - 14   Nitrogen  Concentration,  Potomac  Estuary,
            November  24, 1969	      VI - 19

  VI - 15   Nitrogen  Concentration,  Potomac  Estuary,
            August 12-14, 1969    .	      VI - 20

  VI - 16   Nitrogen  Concentration,  Potomac  Estuary,
            April  21, 1966	      VI - 21

  VI - 17   Effect of Temperature on Nitrification  Rate,
            Upper  Potomac Estuary	      VI - 22

  VI - 18   Effect of Temperature on Algal Nitrogen
            Utilization  Rate, Upper  Potomac  Estuary   .   .      VI - 24

  VI - 19   Annual Nitrogen Profiles,  Potomac  Estuary  at
            Hains  Point     	      VI - 26

  VI - 20   Annual Nitrogen Profiles,  Potomac  Estuary  at
            Piscataway Creek	      VI - 27

  VI - 21   Annual Nitrogen Profiles,  Potomac  Estuary  at
            Indian Head	      VI - 28

  VI - 22   Annual Nitrogen Profiles,  Potomac  Estuary  at
            Maryland  Point	      VI - 29

  VI - 23   Annual Nitrogen Profiles,  Potomac  Estuary  at
            Piney  Point     	      VI - 30

  VI - 24   Chlorophyll  Concentrations,  Potomac  Estuary,
            September 6-9, 1966	      VI - 33

  VI - 25   Chlorophyll  Concentrations,  Potomac  Estuary,
            October 7, 1968	      VI - 34

  VI - 26   Chlorophyll  Concentrations,  Potomac  Estuary,
            September 28-30,  1970	      VI - 35

  VI - 27   Chlorophyll  Concentrations,  Potomac  Estuary,
            September 20-21,  1967	      VI - 36
                             vm

-------
                        LIST  OF  FIGURES

Number                    Description                          Page

  VI - 28   Chlorophyll  Concentrations, Potomac Estuary,
            August 5,  1968	      VI - 37

  VI - 29   Chlorophyll  Concentrations, Potomac Estuary,
            October 15-16, 1969	      VI - 38

  VI - 30   Chlorophyll  Concentrations, Potomac Estuary,
            August 19-23,  1968	      VI - 39

  VI - 31   Chlorophyll  Concentrations, Potomac Estuary,
            August 12-14,  1969	      VI - 40

 VII -  1   Inorganic  Phosphorus  Isopleth, Potomac Estuary,
            1969-70 Data	     VII -  3

 VII -  2   Total  Phosphorus  Isopleth, Potomac Estuary,
            1969-70 Data	     VII -  4

 VII -  3   Phosphorus Concentration, Potomac Estuary,
            September  6-13, 1966	     VII -  6

 VII -  4   Phosphorus Concentration, Potomac Estuary,
            June  30 -  July 1, 1969	     VII -  7

 VII -  5   Phosphorus Concentration, Potomac Estuary,
            January 25,  1966	     VII -  8

 VII -  6   Phosphorus Concentration, Potomac Estuary,
            September  23,  1968	     VII -  9

 VII -  7   Phosphorus Concentration, Potomac Estuary,
            September  28 - October  27, 1965	     VII - 10

 VII -  8   Phosphorus Concentration, Potomac Estuary,
            October 27,  1969	     VII - 11

 VII -  9   Phosphorus Concentration, Potomac Estuary,
            September  20-21,  1967	     VII - 12

 VII - 10   Phosphorus Concentration, Potomac Estuary,
            October 15-16, 1969	     VII - 13

 VII - 11   Phosphorus Concentration, Potomac Estuary,
            August 19-22,  1968	     VII - 14

-------
LIST OF FIGURES
Number
VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -


VII -


VII -



12

13

14

15

16

17

18

19

20

21

22

23


24


25


Description
Phosphorus Concentration, Potomac Estuary,
November 19, 1969 	
Phosphorus Concentration, Potomac Estuary,
December 9, 1969 	
Phosphorus Concentration, Potomac Estuary,
June 9, 1966 	
Phosphorus Concentration, Potomac Estuary,
August 12-19, 1969 	
Phosphorus Concentration, Potomac Estuary,
April 21, 1966 	
Effect of Temperature on Phosphorus Loss Rate,
Upper Potomac Estuary
Annual Phosphorus Profiles, Potomac Estuary at
Hains Point 	
Annual Phosphorus Profiles, Potomac Estuary at
Piscataway Creek 	
Annual Phosphorus Profiles, Potomac Estuary at
Indian Head 	
Annual Phosphorus Profiles, Potomac Estuary at
Maryland Point 	
Annual Phosphorus Profiles, Potomac Estuary at
Piney Point 	
Predicted Chlorophyll Profiles Based Upon Various
Phosphorus Assimilation Rates, Upper Potomac
Estuary (September 1966) 	
Predicted Chlorophyll Profiles Based Upon Various
Phosphorus Assimilation Rates, Upper Potomac
Estuary (October 1968) 	
Predicted Chlorophyll Profiles Based Upon Various
Phosphorus Assimilation Rates, Upper Potomac
Estuary (September 1967) 	
Page

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -

VII -


VII -


VII -


VII -


15

16

17

18

19

20

22

23

24

25

26


29


30


31

-------
                        LIST  OF  FIGURES

Number                    Description                          Page

 VII - 26   Predicted Chlorophyll  Profiles  Based Upon
            Various Phosphorus Assimilation Rates,
            Upper Potomac Estuary  (October  1969)   ...       VII - 32

VIII -  1   Benthic Uptake,  Potomac  Estuary     ....      VIII -  5

VIII -  2   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, September 6-13, 1966   	      VIII -  8

VIII -  3   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, June 30  - July  12,  1969    ....      VIII -  9

VIII -  4   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, August  31 - September  23,  1965   •   •      VIII - 10

VIII -  5   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, September 20-21,  1967	      VIII - 11

VIII -  6   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, October  15-16,  1969    	      VIII - 12

VIII -  7   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, July 22, 1968    	      VIII - 13

VIII -  8   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, August  19-22, 1968	      VIII - 14

VIII -  9   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, August  12-14, 1969	      VIII - 15

VIII - 10   Dissolved Oxygen  Profiles, Upper  Potomac
            Estuary, September 28-30,  1970	      VIII - 16

VIII - 11   Effects of Carbonaceous  Oxidation Rate, DEM
            DO Simulations	      VIII - 20

VIII - 12   Effects of Nitrogenous Oxidation  Rate, DEM
            DO Simulations	      VIII - 21

VIII - 13   Effects of Photosynthesis  Rate, DEM
            DO Simulations	      VIII - 22

-------
                        LIST OF  FIGURES

Number                    Description                          Page

VIII - 14   Effects of Respiration  Rate, DEM
            DO Simulations	     VHI ' 23

VIII - 15   Effects of Benthic Rate, DEM
            DO Simulations	     VI11 - 24

VIII - 16   Effects of Reaeration Rate Formulation, DEM
            DO Simulations	     VIII - 25

VIII - 17   Special DEM DO Simulation, Upper Potomac
            Estuary, September 1970	     VIII - 28
                               xn

-------
                                                              I - 1
                           CHAPTER I
                         INTRODUCTION
A.  PURPOSE AND SCOPE
     The importance of mathematical models as a water quality manage-
ment "tool" is widely acknowledged.  Models have evolved from the one
dimensional steady-state type capable of simulating only relatively
conservative constituents such as tracer dye or chlorides to time-
dependent models linking BOD and DO and finally to multi-constituent
models capable of (1) elaborate "feedback" linkage between the various
constituents, (2) not only first-order kinetics but any mathematically
describable reaction, and (3) incorporating tidal aspects to permit
"real-time" hydraulic and quality predictions.
     The purpose of this report is to present the approach taken by
AFO to model a portion of the nitrogen cycle, phosphorus deposition,
and the occurrence of algal blooms as measured by chlorophyll a_; as
well as the effects of carbonaceous, nitrogenous, and benthic oxygen
demand; algal photosynthesis, respiration and decay; and reaeration
on the dissolved oxygen resources in the upper Potomac Estuary.
Basically, this approach entailed a feedback model similar to the one
proposed by Thomann [1] and a procedure whereby individual reaction
rates, based on a visual comparison of observed and simulated data,
were estimated.  Upon determining the appropriate rates, the models'
reliability to predict DO distributions was investigated.
     The EPA Dynamic Estuary Model [2] was modified to incorporate the
necessary reactions describing nitrogen and phosphorus transport and

-------
                                                               I - 2
most sources and sinks of dissolved oxygen.   This model  was used pri-
marily to simulate short-term, pseudo-steady-state conditions.   DECS
III, an average tidal model, [3] was used to simulate nitrogen and
phosphorus behavior over an annual  cycle.  Both of these models
successfully simulated (1) a tracer dye distribution following a
13-day continuous  release and (2)  seasonal  chlorinity changes in the
Potomac Estuary [4] prior to the more complex modeling discussed in
this report.  In addition, the two  models were used to investigate
the role of nutrients in the eutrophication  process and to establish
maximum allowable nutrient and ultimate oxygen demand loadings for
different zones of the Potomac Estuary [5].
     The entire Potomac Estuary is  included  in the framework of the
mathematical models.  Since uncertainties arise when applying either
model to the mesohaline portion of  the estuary, most of the analyses
will pertain to the freshwater region of the Potomac with the major
emphasis placed on the critical area immediately downstream from
Washington, D. C.

-------
                                                              I  -  3
B.   ACKNOWLEDGEMENTS



     Special  recognition has been given to the  Steuart Petroleum



Company, Piney Point, Maryland,  for their extensive cooperation and



assistance in performing all sampling during AFO's 1969-70 nutrient



transport study of the Potomac Estuary.  This report could not have



been completed as promptly without such sampling assistance.

-------

-------
                                                              II  -  1
                          CHAPTER II
                    SUMMARY AND CONCLUSIONS
     During 1970, the Annapolis Field Office embarked on a mathematical
modeling study of the Potomac Estuary utilizing a 1965-70 data base
to (1) predict nitrogen and phosphorus distributions during both a
relatively short time period (steady-state) and over an annual cycle,
(2) define the various reaction rates, including temperature effects,
directly influencing nutrient transport, (3) evaluate the role of both
nitrogen and phosphorus in the existing eutrophication problem and
develop predictive capabilities for algal standing crop, (4) formulate
a DO budget model incorporating algal effects in addition to biological
oxidation and reaeration and (5) determine the maximum allowable load-
ings of nitrogen, phosphorus and carbon (BOD) that will maintain water
quality commensurate with existing standards.  The findings evolved
during data analysis, model development and verification are as follows:
     1)  There are currently eighteen wastewater treatment facilities
in the Washington Metropolitan Area that discharge total BOD5, phosphorus
(P) and nitrogen (N) loadings to the upper Potomac Estuary of 143,000
Ibs/day, 25,000 Ibs/day, and 60,000 Ibs/day, respectively.
     2)  During the period from February 1969 to February 1970 the
average nutrient contributions from the upper Potomac River Basin
were, phosphorus (as P), 4,580 Ibs/day, and nitrogen (as N), 59,000
Ibs/day.  These loadings correspond to an average freshwater flow of
6,900 cfs.

-------
                                                               II  -  2
      3)  The median loadings  contributed  from urban  and  suburban

runoff to the upper Potomac Estuary are  given  below:


           Parameter                    Loading
                                       (Ibs/day)

           BOD                          12,500
              5
           Phosphorus (P)                  850
           Nitrogen (N)                   4,070

      4)  Using weekly nitrogen data collected in the Potomac Estuary

from February 1969 to July 1970 the following  conclusions were drawn:

          a)  Maximum ammonia  concentrations of 2.0 mg/1  were observed

on numerous occasions near the major wastewater discharges.   A drastic

reduction in ammonia, attributable to nitrification,  occurred between

the Woodrow Wilson Bridge and  Indian Head under high  temperature con-

ditions.

          b)  The reduction in ammonia concentrations were accompanied

by high levels of nitrate nitrogen, often approaching 2.0 mg/1.

Farther downstream, between Indian Head  and Smith Point,  a significant

decrease in nitrate, due to biological (algal) uptake, occurred during

the summer and fall months.

          c)  Organic nitrogen concentrations  were extremely high (3.0

mg/1) in the Potomac during the late summer and early fall when algal

blooms were profuse.

      5)  Utilizing the EPA Dynamic Estuary Model and data from thirteen

intensive sampling runs conducted under steady-state conditions, nitri-

fication rates required for model verification varied from 0.005/day

-------
                                                              II - 3
to 0.4/day depending on temperature.  At 20°C, the nitrification rate
was 0,084/day (base e).
     6)  Reasonable agreement between the thirteen sets of observed
nitrate data and model predictions was obtained when algal uptake
rates varied from 0.01/day to 0.13/day with a 20°C value of 0.037/day
(base e).  A definite temperature vs algal uptake rate relationship
was again indicated.
     7)  A modified version of DECS III that incorporated the veri-
fied reaction rates and temperature effects discussed above accurately
simulated the basic seasonal trends and spatial distributions of
ammonia and nitrate nitrogen observed during the period February 1969
to July 1970.
     8)  A modified version of the EPA Dynamic Estuary Model which con-
verted losses of nitrate nitrogen to algal biomass based upon ele-
mental composition ratios was used to predict bloom conditions in the
Potomac as measured by chlorophyll a^.  Eight separate sets of chlorophyll
data representing different flow and temperature conditions were simu-
lated satisfactorily with this model, thus indicating the importance
of inorganic nitrogen as a possible growth-rate-limiting nutrient.
     9)  Phosphorus data measured weekly in the Potomac Estuary during
1969-70 revealed the following:
         a)  The distribution of both inorganic and total phosphorus
was markedly similar during the study period.  Maximum concentrations
of 2.0 mg/1 and 4.0 mg/1, respectively, were recorded between Bellevue
and Piscataway Creek with concentrations diminishing farther downstream.

-------
                                                              II  -  4
         b)  Although high freshwater flow periods contributed an ex-
cessive phosphorus load, the adsorption of phosphorus onto silt particles
accompanying these high flows and its eventual  deposition actually
reduced the phosphorus content in the upper Potomac Estuary.
         c)  During high temperature periods, inorganic phosphorus
concentrations decreased appreciably downstream from Piscataway Creek
as a result of biological uptake by phytoplankton and chemical deposition,
    10)  A modified version of the DEM having second order kinetics
was utilized to simulate fourteen sets of prototype data and evaluate
the phosphorus loss rate.  Based on these simulation studies the
loss rates required for model verification ranged from 0.005 gr/day to
0.04 gr/day, varying with temperature.  The rate derived from a
regression analysis for 20°C was 0.0218 gr/day.
    11)  A modified version of DECS III that again incorporated second
order kinetics and the verified rates given above adequately simulated
the interseasonal phosphorus distributions throughout the Potomac
Estuary as observed between February 1969 and July 1970.
    12)  A series of model runs (DEM) that related phosphorus loss to
algal productivity was made in order to delineate biological uptake
from physical deposition of phosphorus and to acquire a better under-
standing of the significance of phosphorus as a possible growth-rate-
limiting nutrient.  Based on these runs, it appeared that only 10 to
20 percent of the phosphorus losses were attributable to uptake by algal
cells whereas 80 to 90 percent represented deposition to the bottom
sediments.

-------
                                                              II  -  5
    13)  The DO budget model  employed by AFO in its study of the
Potomac Estuary consisted of the following five linkages:
         a)  oxidation of carbonaceous matter
         b)  oxidation of nitrogenous matter
         c)  oxygen production and respiration of simulated algal
             standing crops based upon the nitrogen cycle
         d)  benthic demand,  and
         e)  atmospheric reaeration
    14)  The aforementioned DO model  proved capable of simulating
nine different observed conditions between 1965 and 1970 when fresh-
water flows and temperature ranged from 185 cfs to 8800 cfs, and 19°C
to 30°C, respectively.  In order to achieve a meaningful verification
of this model it was necessary to base all simulation runs on the
following reaction rates and other related assumptions:
     Process
         a)  Carbonaceous oxidation - 0.17 (base e - 20°C)
         b)  Nitrogenous oxidation -  0.084 (base e - 20°C)
         c)  Reaeration - O'Connor-Dobbins Formulation
         d)  Algal oxygen production  rate - 0.012 mgOa/hr/yg chloro a_
         e)  Algal respiration rate - 0.0008 mg02/hr/yg chloro a^
         f)  Euphotic Zone -  2 feet
         g)  Respiration Depth - VJ1 depth of water column
         h)  Algal oxygen production  period - 12 hours
         i)  Algal respiration period - 24 hours
         j)  Benthic demand - 1.0 gr02/meter2/day

-------
                                                              II  -  6
    15)  In order to determine the relative importance of the various
rates incorporated in the DO budget model, a detailed sensitivity
analysis was performed.   The following conclusions were drawn based
upon the results of this sensitivity analysis:
         a)  The predicted critical DO deficit is markedly sensitive
to the carbonaceous oxidation rate assigned in the model.  Since the
mass of unoxidized nitrogen in the Potomac is considerably less than
that of carbon, the model predictions for DO were not significantly
affected when a comparable range in nitrification rates was inputted.
         b)  Increasing the algal  photosynthesis rate or decreasing
the respiration rate produced basically comparable results insofar as
model predictions are concerned.  Both the critical deficit and that
portion of the predicted profile representing DO recovery were drastically
affected when a change in either rate was instituted.
         c)  A displacement of the entire predicted DO profile by a
substantial amount was noted when different benthic demand rates
were used indicating significant model sensitivity.
         d)  Various expressions for computing the reaeration rate
(i.e. O'Connor-Dobbins, Churchill  and Langbein's Egs) were used in
the model; however, no changes in predicted DO data were detected.

-------
                                                             Ill - 1

                          CHAPTER III
                   DESCRIPTION OF STUDY AREA
     The Potomac River Basin, with a drainage area of 14,670 square
miles, is the second largest watershed in the Middle Atlantic States.
From its headwaters on the eastern slope of the Applachian Mountains
near the historic Fairfax Stone, the Potomac flows first northeasterly
then generally southeasterly some 400 miles to the Chesapeake Bay.  The
Potomac traverses the Piedmont Plateau until it reaches the Fall Line
near Washington, D. C.  Below the Fall Line, the Potomac is tidal, ex-
tending 114 miles southeastward and discharging into the Chesapeake Bay.
     The tidal portion is several hundred feet in width in 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 maintained
upstream from the mouth to Washington.  Except for this channel and a  few
short reaches where depths up to 100 feet occur, the tidal portion is
relatively shallow with an average depth of approximately 18 feet.  The
mean tidal range is approximately 1.4 feet near the Chesapeake Bay and
2.9 feet in the vicinity of Washington.  The lag time for the tidal
phase between Chesapeake Bay and Washington is approximately 6.5 hours.
The entire Potomac Estuary is characterized by numerous tidal embayments,
generally less than 5 feet in depth, some of which are quite large in
area.
     Of the 3.3 million people living in the basin, approximately

-------
                                                             Ill  - 2

2.8 million reside in the upper portion of the Potomac Estuary within
the Washington Metropolitan Area.   The lower area of the tidal portion,
which drains 3,216 miles, is sparsely populated.
     The upper reach, although tidal, contains fresh water.   The  mid-
dle reach is normally the transition zone from fresh to brackish  water.
The lower reach is saline with chloride concentrations near the Chesa-
peake Bay ranging from approximately 7,000 to 11,000 mg/1.
     Because of minimal regulation,  the Potomac is characterized  by
flash floods and extremely low flows.  The average freshwater flow of
the Potomac River near Washington, before diversions for municipal
water supply, is 10,800 cubic feet per second (cfs) with a  median flow
of 6,500 cfs.
     Detailed physical data for the Potomac Estuary, including model
segmentation geometry, have been presented in a previous report [6],

-------
                        /      \

          N
           \
ANACOSTIA RIVCM
        GUNSTON COVE
  OCCOQUAN BA-
POSSUM POINT
                         LEGEND
                 •   MAJOR WASTE TREATMENT PLANTS
                 A   GAGING STATION - WASHINGTON, D.C
                 A   DISTRICT OF COLUMBIA
                 B   ARLINGTON COUNTY
                 C   ALEXANDRIA SANITATION AUTHORITY
                 0   FAIRFAX COUNTY - WESTGATE PLANT
                 E   FAIRFAX COUNTY - LITTLE HUNTING CREEK PLANT
                 F   FAIRFAX COUNTY - OOGUE CREEK PLANT
                 G   WASHINGTON SUBURBAN SANITARY COMMISSION - PISCATAWAY
                 M   ANDREWS AIR FORCE BASE - PLANTS ONE FOUR
                  I   FORT BELVOIR - PLANTS ONE TWO
                  I   PENTAGON
                 K   FAIRFAX COUNTY - LOWER POTOMAf
                                             LOCATION MAP
                                                                                               CHCSAPfAKC
                                                                                                   BAY
                                                                                        MITW POINT —
                               POTOMAC     ESTUARY
                                                                                          FIGURE TH-I

-------

-------
                                                              IV  -  1
                          CHAPTER IV
     SOURCES OF NUTRIENTS AND OXYGEN DEMANDING SUBSTANCES
A.  WASTEWATER LOADINGS
     A total domestic wastewater flow of approximately 337 mgd is dis-
charged into the Potomac River tidal system upstream from Indian Head,
Maryland.  Nineteen facilities currently serve approximately 2.6 million
people in the Washington Metropolitan Area with the largest facility
being the Blue Plains plant of the District of Columbia.   Of the 337 mgd,
40.0, 26.0, and 34.0 percent originate in Maryland, Virginia, and the
District of Columbia, respectively.   The current BOD and  nutrient
loadings from each treatment facility are presented in Table IV-1.   The
total loadings into the upper Potomac Estuary from wastewater sources
are  (1) BOD5 - 143,000 Ibs/day, (2)  Total Phosphorus (P)  - 25,000 Ibs/day,
(3) Total Nitrogen (N) - 60,000 Ibs/day.
     There are 82 wastewater point-source discharges in the Potomac
Estuary between Indian Head, Maryland, and the Chesapeake Bay.  The
estimated BOD, phosphorus as P, and nitrogen as N loadings from these
sources are 4,000, 500, and 1,000 Ibs/day, respectively.   Compared to
the upper reach, with a population of approximately 2.6 million, the
wastewater facilities in the middle and lower reaches serve a population
of approximately 50,000 and consequently account for a small percent-
age of the total loadings to the Potomac Estuary.  Most of the discharges
in this area are into tributary or embayment waters.

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                                                              IV - 3
B.  CONTRIBUTIONS FROM THE UPPER POTOMAC RIVER BASIN
     During the period of February 1969 to February 1970, the follow-
ing average concentrations of BOD5 and nutrients in the freshwater
flow entering the upper Potomac Estuary were measured.
         Parameter                       Concentration
                                             fing/Tl
         BOD5                               2.60
         TKN as N           •                0.61
         N02 + N03 as N                     1.00
         Phosphorus as P                    0.13
     Detailed analyses of the freshwater inflows from the upper Potomac
River Basin at Great Falls were conducted during 1969 and 1970.  The
observed data, as shown in Figure IV-1, indicate the wide range of
nutrient concentrations for the period of June 1969 to  July 1970.  The
river discharge was considerably higher during the 1970 period of
the study than it was for the 1969 thus resulting in higher N02 + N03
concentrations.  Concentrations of TKN and phosphorus appeared to de-
crease during periods of high flow, except during periods of intense
runoff.
     The monthly nutrient contributions from the upper  basin during the
period of February 1969 through February 1970 are presented in Table IV-2.
For this 13-month period, the average daily contributions of nutrients
are given below:

-------
                                                     IV - 4
Parameter                         Contribution

                                     (Ibs/day)


Total Phosphorus as P                  4,580


Inorganic Phosphorus as P              2,650


TKN as N                              22,410


NH  as N                               4,590
  3

NO  + NO  as N                        36,700
  2     3

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-------
                                                              IV - 7
C.  SUBURBAN AND URBAN RUNOFF
     A regression analysis of the river discharge and contributory
loadings was applied to data from the Rock Creek and Anacostia River
watersheds in the District of Columbia.  Based on these regression
studies and flow duration curves, yield rates in terms of Ibs/day/sq mi
were determined.  These rates were used for the suburban areas in Vir-
ginia and Maryland as shown in Table IV-3.  For the District of Columbia,
additional data on stormwater and urban runoff were obtained from a
study of Washington overflows [7].
     The median loadings contributed from urban and suburban areas to
the upper Potomac Estuary (Table IV-3) are tabulated below:
              Parameter                       Loadings
                                              (Ibs/day)
              BOD5                              12,500
              TKN as N                           2,560
              N02 + N03                          1,510
              T. Phosphorus as P                   850
     The total Ibs/day loadings of BOD and nutrients from suburban and
urban runoff were fairly low when compared to those contributed from the
upper Potomac Basin.  However, the yield rates, except for nitrites and
nitrates, were significantly higher for the urban and suburban area than
for the upper Potomac Basin.  This indicates that as an area becomes more
populated, the amount of BOD, phosphorus, and  TKN contributions will
probably also increase.
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                                                              V  -  1
                           CHAPTER V
                    FRAMEWORK FOR ANALYSIS
A.  WATER QUALITY DATA
     Since 1965, the Annapolis Field Office has conducted water quality
sampling in the Potomac Estuary.   Initially, most of the data were col-
lected in the critical upper reach near Washington, D.  C., but the area
of concern has progressively lengthened to include the  middle reach,
where the most serious algal problems occur, and more recently the almost
continuously saline lower reach.
     The frequency and duration of sampling generally followed one of
two patterns:  (1) an intensive type survey, hopefully  performed during
steady-state conditions, composed of multiple sampling  runs carried
out each day for approximately a  week's duration or (2) weekly or bi-
weekly sampling over an annual cycle.  The importance of the first sampling
method is that relatively short-term intensive data can be employed to
obtain reaction rates and, thus,  be used for model verification during
a period of somewhat constant temperature and freshwater flow.  The EPA
estuary model, due to its hydraulic solution, particularly lends itself
to steady-state flow analysis.  In order to verify a mathematical model
over a larger time scale, to predict seasonal variations in the nitrogen
and phosphorus transport mechanism, and to investigate  the effects of
seasonal  wastewater treatment requirements, AFO with the cooperation of
Steuart Petroleum Company conducted a weekly nutrient sampling program
of the entire Potomac Estuary from February 1969 to May 1970.  These data
-------
                                                             V - 2
will be discussed in a later section of this  report.   All  of the
intensive data have been published in separate reports [8] [9]  [10].
     In addition to AFO sampling,  data collected by the District  of
Columbia's Department of Sanitary  Engineering in weekly cruises in the
upper Potomac Estuary were also evaluated.   Certain data,  which were
collected during appropriate steady-state periods, were used in the
rate determination and model verification studies presented in  this
report.
-------
                                                              V  -  3
B.  CHEMICAL, PHYSICAL, AND BIOLOGICAL REACTIONS
1.  Nitrogen
     Figure V-l  schematically shows  the major reactions  of the  nitrogen
cycle in an aquatic environment.   Organic nitrogen derived primarily
by biological action has many forms, with the more common being pro-
teins, amines, purines, and urea.   While certain  forms (fibrous proteins)
are resistant to biological degradation, others may be decomposed by
biological action or, in the case  of urea, hydrolyzed enzymatically  into
ammonia and carbon dioxide.
     Ammonia nitrogen can be introduced into natural  waters by  sewage
effluents or agricultural runoff.   In addition, ammonia  is released  by
biological decomposition of organic  matter.   Since it is extremely
soluble in water, ammonia concentrations can become quite large.   Am-
monia is characterized by significant sorption (physical  and chemical)
properties, but more important is  the fact that it can be resynthesized
to organic nitrogen by aquatic plants or oxidized to nitrites by auto-
trophic bacteria (nitrosomonas).   This latter reaction,  known as nitri-
fication, is highly dependent on  temperature and  pH and  will proceed
only under aerobic conditions.  It has been reported [11] that  this  phase
of nitrification requires 3.43 grams of oxygen for 1  gram of ammonia
nitrogen to be oxidized to nitrite.
     In addition to the oxidation  of ammonia, nitrites are also formed
by the reduction of nitrates.  Further reduction  by heterotrophic bac-
teria (denitrification) results in the release of nitrogen gas.  Nitrite
-------
                                                              V  -  4
nitrogen is very unstable since it can be readily oxidized by Nitro-
bacter bacteria to nitrates.   Consequently, high concentrations  of
nitrite are not normally found in surface waters.  Approximately 1.14
grams of oxygen are required  to oxidize one gram of nitrite nitrogen.
     Nitrate nitrogen represents the completely oxidized form of nitro-
gen in the nitrogen cycle.  Its major external  sources in a watercourse
are wastewater effluents and  agricultural runoff.  The nitrate form is
quite soluble in water and concentrations can reach high levels, par-
ticularly since it does not adsorb on particulate matter and is  chem-
ically relatively nonreactive.  In addition to the reduction of nitrate
by heterotrophic bacteria at  low DO levels (0-2 mg/1), it may also be
used by phytoplankton as a nutrient source.  The assimilated nitrate
nitrogen is converted to organic nitrogen in the plant's cells.   Upon
death, the cellular material  releases organic nitrogen which completes
the nitrogen cycle.
     From the standpoint of mathematical modeling the  Potomac Estuary,
there are two aspects of the  nitrogen cycle that deserve special atten-
tion:  (1) the reduction in dissolved oxygen by bacterial oxidation
of unoxidized nitrogen forms  (ammonia + organic nitrogen)* and (2) the
assimilation of inorganic nitrogen forms by phytoplankton during their
growth phase.
*  Commonly measured as total Kjeldahl nitrogen
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                                                              V  -  6
2.  Phosphorus
     Since the advent of synthetic detergents,  phosphorus  levels  in
the natural environment have increased drastically and  its  role  in the
eutrophication process has received considerable attention.   Shown in
Figure V-2 is a schematic representation of a simplified phosphorus
cycle with pertinent chemical, physical, and biological  reactions.
Although large quantities of mineral  phosphates are present on the
earth's surface, they are relatively insoluble  in water.
     Phosphorus in the aquatic environment can  basically be categorized
as either inorganic or organic.   As shown in Figure V-2,  inorganic phos-
phorus can be subdivided into:  (1) particulate, (2)  soluble ortho,
and (3) soluble poly and pyro.  The major contributor of soluble  inor-
ganic phosphorus is wastewater effluents.  Prior to the  inception of
synthetic detergent use orthophosphate constituted most  of the total
phosphorus present in sewage, with the remainder being  primarily  dis-
solved and suspended organic compounds.   Since  that time,  however, the
cleansing agents polyphosphate and pyrophosphate have become predomi-
nant factors in water quality management.  In addition  to  sewage  sources,
both inorganic and organic phosphorus (soluble  and particulate)  may  be
contributed in much smaller quantities by agricultural  and other  types
of land runoff.
     Polyphosphate and pyrophosphate are readily hydrolyzed to the
orthophosphate form.  Various sorption phenonmena can convert soluble
orthophosphates to a particulate form or vice versa.  Of the different
-------
                                                              V  -  7
forms of inorganic phosphorus,  only soluble orthophosphate  can  be bio-
logically assimilated by phytoplankton.   A portion of the particulate
phosphorus is deposited in the  bottom sediments.   A quantitative appraisal
of phosphorus recycling has not been undertaken,  but it appears that
the sediment adsorbs more phosphorus than it releases.
     The organic phosphorus component also contains soluble and parti-
culate phosphorus which undergo chemical  and physical reactions similar
to their inorganic counterparts.  The oxidation of organic  soluble phos-
phorus into an inorganic form is a relatively minor sink of DO.  The
cells of plants and animals convert inorganic phosphorus to an  organic
form; when these cells die, a certain portion is  probably deposited.
Biological decomposition of the remainder results in additional soluble
and particulate organic phosphorus, and because of "luxury" uptake, some
soluble inorganic phosphorus.
     Phosphorus cycle factors of special  concern  in mathematical
modeling studies are the gross  deposition rate and the quantity bio-
logically taken up by algae.  While other aspects are also  important,
they are not as easily defined.
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-------
                                                              V - 9
C.  MATHEMATICAL MODELING TECHNIQUES
     Water quality simulations discussed in this report were made using
the EPA Dynamic Estuary Model (DEM) and DECS III (Thomann Model).  Relatively
steady-state conditions over a 2 or 3 week period were simulated with
the DEM, whereas DECS III was used to simulate inter-seasonal conditions.
The DEM is a real time system incorporating hydraulic and quality com-
ponents.  Both of these components utilize the same two-dimensional net-
work of interconnecting junctions and channels.  The hydraulic solution
describes tidal movement, while the quality solution considers the basic
transport mechanisms of advection and dispersion as well as the per-
tinent sources and sinks of each constituent.  The DEM can concurrently
simulate six different constituents.  They may be either conservative
or nonconservative and may be interrelated in any mathematical linkage.
A detailed description of this model is available from EPA [2].  The
application and verification of the DEM in simulating dye and chloride
data in the Potomac Estuary and a detailed sensitivity analysis of the
various input parameters have also been documented [4].
     Several modifications were made to the DEM in order to simulate
nutrient transport and historical dissolved oxygen distributions.  A
schematic diagram of the basic feedback linkage employed by the DEM
to predict algal growth based on the nitrogen cycle and the effects of
algae and other sources and sinks on the DO budget are shown in Figure
V-3.  One version of the DEM included five nitrogen reactions:  (1)
bacterial nitrification of ammonia to nitrite and nitrate, (2) phyto-
plankton utilization of inorganic nitrogen, (3) release  of organic
-------
                                                               V - 10
nitrogen by the death of phytoplankton, (4) deposition of organic
nitrogen, and (5) decomposition of organic nitrogen to ammonia.   More-
over, the following DO budget linkages were included in a separate
model:  (1) oxidation of carbonaceous matter, (2) oxidation of nitro-
genous matter (ammonia and organic), (3) oxygen production by photo-
synthesis and utilization by respiration of simulated algal standing
crops based upon the nitrogen cycle, (4) benthic demand, and (5) re-
aeration from the atmosphere.
     All model reactions were based on a mass balance basis.  The mass
conversion factors (nitrogen to chlorophyll a_) were determined by
algal composition analyses performed in the laboratory [5].  The
rates used in the DO budget analysis were obtained primarily from field
studies.  Besides changing the various reaction rates temporally, a
modification was made in the DO model to allow for spatial variations
in the photosynthetic, respirational and benthic rates as well as the
depth of the euphotic zone.
     Simulations of phosphorus transport in the Potomac Estuary were
based on second-order reaction kinetics.  As will be discussed in a
subsequent section of this report, adequate agreement between observed
and predicted phosphorus profiles could not be obtained using a first-
order system for deposition rates.  Consequently, the DEM was modified
to handle second and other order reactions.  Linkage between algal growth
and phosphorus loss in the model was performed similarly to that of the
nitrogen cycle, e.g., mass balance analysis.
-------
WASTEWATER
   NH3
   A
 SIMPLIFIED   DO  BUDGET
             FOR
DYNAMIC  ESTUARY   MODEL
     O
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ORGANIC  NITROGEN
 EXPRESSED  AS
 CHLOROPHYLL a.
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                                 TO THE  SEDIMENTS
                                 FIGURE V-3
-------
-------
                                                               V  -  12
     The DECS III model  is based on a tidal  average  time-dependent
solution of the basic mass balance equations as  originally developed
by Thomann [12].   These  equations are expressed  in finite  difference
form by segmenting the estuary under study.   Since this  model  is  nontidal,
a dispersion coefficient is introduced to account for tidal  dispersion
and advection in addition to eddy and molecular  diffusion.  The
quantitative appraisal of this coefficient becomes extremely difficult.
AFO's experience in verifying DECS III for historical dye  and  chloride
data and the estimation  of dispersion coefficients for several  reaches  of
the Potomac Estuary as a function of freshwater  inflow is  available
in another report [4].
     The major disadvantage of using DECS III is its limitation to a  two-
constituent linkage.  Therefore, neither the complete nitrogen cycle
nor the DO budget could  be simulated.  To help alleviate this  problem,
ammonia nitrogen and nitrate nitrogen replaced BOD and DO, respectively,
in the original version  of the model.  The reaeration component sign
was changed; it thus behaved as a sink of N03 instead of a source of  DO.
This loss would, of course, correspond to the biological uptake of N03
by algae.  In such a manner, two nitrogen fractions  could  be properly
represented.
     Two other modifications were made to DECS III to permit the  simu-
lations given in this report:  (1) the inclusion of second-order  re-
action kinetics for the  analysis of phosphorus transport and (2)  the
inclusion of a mathematical expression relating  dispersion coefficient
-------
                                                               V -  13







to freshwater flow.   This latter addition was necessary since the sim-



ulation period was long in duration and was characterized by extreme



flow differences.
-------
                                                              VI  -  1
                          CHAPTER VI
              NITROGEN ASSIMILATION AND TRANSPORT
A.  TEMPORAL AND SPATIAL DISTRIBUTION
     The concentrations and forms of nitrogen in the Potomac Estuary
are dependent upon wastewater loadings, temperature, freshwater inflow,
and biological activity.  The weekly nitrogen data collected by AFO
from February 1969 to July 1970 are presented in isopleth form in Fig-
ure VI-1 (Ammonia Nitrogen), VI-2 (Nitrite + Nitrate Nitrogen), and
VI-3 (Organic Nitrogen).
     As shown in Figure VI-1, ammonia concentrations of 2.0 mg/1  were
fairly common in the upper estuary in 1969 as a result of wastewater
discharges.  The rapid decrease in concentrations between the Woodrow
Wilson Bridge (River Mile 12) and Indian Head (River Mile 31) is in-
dicative of nitrification or the conversion of ammonia nitrogen to ni-
trite and nitrate nitrogen.  Based upon the data shown in Figure VI-1,
the rate of this reaction appears to be definitely related to tempera-
ture.
     During the warm summer months, for example, ammonia concentrations
in the vicinity of Dogue Creek (River Mile 22) were about 0.5 mg/1,
whereas concentrations during winter and spring periods averaged 1.0 -
1.5 mg/1.  The almost immediate effects of nitrification would indicate
that the upper Potomac Estuary behaves as a "continuous-culture system."
It should also be noted that changes in freshwater flow rates had a
-------
                                                              VI  -  2
relatively minor effect on the ammonia  nitrogen  levels  upstream  from
Mains Point (River Mile 7.6).
     The concentrations of nitrite and  nitrate nitrogen at any given
time will be a function of (1) nitrification rate and (2)  nitrate uptake
by algal cells.   Figure VI-2 shows maximum nitrite and  nitrate nitrogen
concentrations (1.5 - 2.0 mg/1) throughout much  of the  summer and fall
of 1969 and again in January 1970.  These high levels generally  pre-
vailed between Woodrow Wilson  Bridge and Indian  Head where rapid reduction
in ammonia levels was observed.  Besides the conversion of ammonia
from wastewater effluents, a considerable amount of nitrate nitrogen
enters the upper Potomac Estuary during periods  of high freshwater
flow.  This contribution would account  for the high concentrations in
January 1970, a low-temperature, minimal nitrification  period.
     The significant decrease  in nitrite and nitrate nitrogen between
Indian Head and Smith Point (River Mile 46) in the summer and early fall
of 1969 was caused by algal uptake of nitrogen.   This reaction,  like
nitrification, appears to be related to temperature as  evidenced by
the greater persistence of nitrate nitrogen during colder periods.
     From a water quality management standpoint, the virtual disap-
pearance of inorganic nitrogen in the critical algal growing areas
suggests that this nutrient may become  the major factor in limiting
algal growth in the middle reach of the Potomac Estuary.
     The distribution of organic nitrogen in the Potomac Estuary during
1969-70 is shown in Figure VI-3.  These iso-concentration lines  were
-------
                                                              VI - 3
based on differencing the total Kjeldahl nitrogen (TKN) and ammonia
nitrogen data.  As shown in Figure VI-3, organic nitrogen is quite
plentiful in the Potomac Estuary, especially during the late summer and
early fall of 1969.  Maximum concentrations, exceeding 3.0 mg/1, were
observed in the middle estuary throughout most of September 1969 with
the lower reach having levels nearer 2.0 mg/1.  These extremenly high
levels of organic nitrogen resulted from the profuse algal blooms
which were visually observed and measured at greater than 100 yg/1
chlorophyll a_.  The maximum recorded chlorophyll value during this
critical period was 445 yg/1.  Algal composition studies conducted
by AFO [5] indicate that water with an algal bloom of 100 yg/1 chloro-
phyll a^ contains about 1.0 mg/1  of organic nitrogen.
     Relatively high organic nitrogen concentrations (1.5 - 2.0 mg/1)
continued in the upper and middle estuary through October 1969.  Similar
concentrations were again observed in June and July 1970 when a reap-
pearance of algal  blooms occurred.
     It would appear from a comparison of the ammonia nitrogen and
organic nitrogen data that the rate of decomposition of organic nitro-
gen is much slower than the rate of bacterial nitrification, since or-
ganic nitrogen is  the predominant form of nitrogen in the middle and
lower estuary.
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                                                              VI  -  7
B.  DETERMINATION OF REACTION RATES AND TEMPERATURE EFFECTS
1.  Nitrification
     The rate at which ammonia nitrogen (NH3) is biochemically oxidized
to nitrite and nitrate nitrogen (N02 + NOa), commonly referred to as
the nitrification rate, was determined for the Potomac Estuary by using
the aforementioned version of DEM to simulate numerous observed con-
ditions representing a variety of temperatures and freshwater inflows.
The prototype behavior was established using intensive-type sampling
data collected during relatively steady-state flow periods.  These
data indicated that ammonia was being rapidly depleted, especially
when high temperatures prevailed, and that a subsequent increase in
nitrate concentrations could be expected.   Because of this and the
fact that maximum depletion occurred upstream from the major algal
blooms, it was apparent that nitrification, and not biological uptake
by phytoplankton, was primarily responsible for the loss of ammonia.
     Various reaction rates were inputted  to the Dynamic Estuary Model
until a reasonable simulation of each of the observed ammonia profiles
was achieved.  The final  profiles obtained with the model  along with the
appropriate nitrification rates are shown  in Figures VI-4 through VI-16.
As can be seen in the figures, peak ammonia concentrations and spatial
gradients were generally simulated satisfactorily.
     In order to establish a relationship  between nitrification rate
and temperature, a regression analysis was performed utilizing the thir-
teen separate sets of data discussed above.  The linear relationship
-------
                                                             VI - 8

resulting from this  analysis  is  presented  in  Figure  VI-17.   At  20°C,
the nitrification rate is  0.084/day  (base  e).
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UPPER POTOMAC ESTUARY
    NH3	•- N02+NO3
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                                                                FIGURE  VI-17
-------
-------
                                                              VI - 23

2.  Algal Uptake
     The predicted formation of nitrate nitrogen by the nitrification
process was found to be quite high when compared with actual sampling
data.  It was, therefore, necessary to apply a decay mechanism to
account for the nitrate uptake by phytoplankton and effect a better
comparison.  The appropriate reaction rates were determined utilizing
the mathematical model and a trial and error approach similar to the
one described for nitrification in the preceding section.
     Figures VI-4 through VI-16 show observed and predicted nitrate
profiles for the upper Potomac Estuary at different temperature and
flow conditions.  Also shown are the algal uptake rates used in the
model.   The figures indicate that reasonable agreement between proto-
type and model data was obtained.
     The effect of temperature on the rates of algal nitrogen utili-
zation is presented in Figure VI-18.  A regression analysis was per-
formed on the data and the results are statistically valid.  At 20°C,
the rate of nitrogen uptake by algae is 0.037/day (base e).
-------
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    1.0 -i
     EFFECT  6F TEMPERATURE


                ON


ALGAL NITROGEN UTILIZATION  RATE


     UPPER  POTOMAC  ESTUARY


     NO3—•• ALGAL NITROGEN
               REGRESSION  DATA:

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                   "t" = 6.8092**

                   DEGREES OF FREEDOM r (M-2) = II
    o.i -
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-------
-------
                                                              VI  -  25

C.  SIMULATION OF NITROGEN TRANSPORT THROUGH AN ANNUAL CYCLE
     The two primary reactions involving nitrogen, i.e.  nitrification
and algal uptake of inorganic nitrogen, were incorporated in the DECS
III version of the Thomann Model  to simulate nitrogen transport in
the Potomac Estuary throughout an annual cycle.  Observed data collect-
ed weekly from February 1969 to July 1970 was used for comparison pur-
poses and model verification.
     The reaction rates and temperature effects developed from the
preceding nitrogen verification runs were used in the model  with cer-
tain modifications.  These modifications generally consisted of re-
ducing the nitrification rates to reflect (1) low DO concentrations
and (2) high freshwater inflows.   The former would inhibit biological
oxidation by the aerobic nitrifying bacteria and the latter would
cause a flushing action resulting in a lag time for repopulation of
the nitrifiers which must be anticipated.  In the case of biological
uptake  rates, a downward attenuation was performed when and where
algal  standing crop levels were believed to be abnormally low.
     Observed and predicted nitrogen profiles (both ammonia and ni-
trate nitrogen) are presented in  Figures VI-19 to VI-23 for five dif-
ferent sampling stations in the Potomac Estuary.  An examination of
the data indicates that the basic seasonal and spatial distributions
were simulated surprisingly well.  In view of limitations in observed
data and simplification in the model  itself, a closer agreement,  especially
in short-term fluctuations, was not really expected.
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-------
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                                                              VI - 31

D.  CHLOROPHYLL PREDICTIONS BASED ON NITROGEN ASSIMILATION BY THE BIOMASS
     Subsequent to application of the Dynamic Estuary Model for deter-
mining reaction rates involving nitrogen in the Potomac Estuary, the
next logical step pursued was to mathematically "link" the nitrogen
cycle with algal production.  The purpose of extending the DEM in this
manner was essentially twofold:  (1) to determine whether nitrogen was
indeed the growth-rate-limiting nutrient in the middle estuary as in-
dicated by other methods of analysis and (2) to establish permissible
nitrogen concentrations and loadings for the maintenance of a balanced
ecological system.
     In order to simulate the standing crop of algae as measured by
chlorophyll a^ the DEM was modified to convert losses of nitrate nitro-
gen to algal biomass.  As indicated previously, it appeared that biolog-
ical assimilation of ammonia nitrogen was minimal  since nitrification
occurring upstream from bloom areas reduced its availability during
high temperature periods.  The mass conversion factor was estimated,
from 1970 algal composition analysis data, to be 90.0.  This in-
ferred that a 1.0 mg loss of nitrate would create a chlorophyll a^mass
of 90 pg.  Practically complete utilization of nitrogen by the algal
cells was assumed.
     Figures VI-24 through VI-31  present observed and predicted
chlorophyll a^ profiles for the upper 40 miles of the Potomac Estuary
based on the "surrogate" version  of the DEM.  Also shown are the flows,
temperatures, and decay rates for which these data apply.  From these
mathematical model runs, it.appears that the standing crop of algae,
-------
                                                               VI - 32

as measured by chlorophyll a^, can be predicted using the nitrogen
 cycle, and that the availability of nitrogen may be the factor con-
 trolling algal growth in  the critical area of the Potomac  Estuary.
     To achieve a satisfactory comparison between the observed and
 predicted chlorophyll data shown in Figures VI-24 to VI-31,  it was
 necessary to  incorporate  a decay rate in  the model ranging from  about
 0.01 to 0.07/day.  This decay probably  represents death and/or
 deposition of the algal cells.  The decay rates needed for the various
 model runs did not appear to be closely related to temperature or the
 quantity of algae in the  system.
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                                                              VII  -  1

                          CHAPTER VII
             PHOSPHORUS ASSIMILATION AND TRANSPORT
A.  TEMPORAL AND SPATIAL DISTRIBUTION
     Like nitrogen, the distribution of phosphorus in the Potomac
Estuary is strongly dependent upon such factors as temperature, bio-
logical activity, and freshwater flow rates.   Figure VII-1  shows,  by
means of an isopleth, the spatial distribution of inorganic phosphorus
during 1969 and 1970.  Of special importance  are the maximum concen-
trations of 2.0 to 2.5 mg/1  (as PO^) which were observed between Bell-
evue (River Mile 10) and Piscataway Creek (River Mile 18) during the
low-flow periods of June, July, October, and  early November 1969.   The
month of August (1969) was characterized by abnormally high flows  and
low phosphorus levels, the result of phosphorus deposition by adsorp-
tion onto silt particles during high flow periods.
     A similar occurrence had been observed previously (March 1967)  and
it was concluded that, while periods of high  freshwater inflows con-
tribute an excessive phosphorus load, the overall effects of adsorption
and deposition produce a net decrease in phosphorus during these peri-
ods in the upper Potomac Estuary.
     Inorganic phosphorus concentrations upstream from Hafns Point
(River Mile 7.6) were usually less than 0.5 mg/1.  Downstream from
Piscataway Creek, inorganic  phosphorus levels decreased appreciably
during high temperature periods due to continued deposition and bio-
-------
                                                              VII  -  2

logical  uptake by phytoplankton.   During low temperature periods,  when
biological activity was at a minimum,  the decrease in inorganic  phos-
phorus levels in the middle estuary was considerably less pronounced.
The entire lower half of the estuary normally contained less  than  0.5
mg/1 of inorganic phosphorus.
     The total phosphorus (inorganic plus urganic) data collected
during the 1969-70 survey are shown in Figure VII-2.  A comparison
of Figures VII-1 and VII-2 will  reveal similar patterns in the spatial
and temporal  distribution of total  and inorganic phosphorus.   For
example, maximum concentrations  of total phosphorus (3.5 - 4.0 mg/1  as
POit), as well as inorganic phosphorus, were observed between  Bellevue
and Piscataway Creek during low-flow periods.  During high flows,  total
phosphorus concentrations were much lower because of the aforementioned
deposition process.
     Although variations in total  phosphorus concentrations generally
corresponded  to those of inorganic phosphorus, there were slight dif-
ferences in the ratios.  In the upper reach of the Potomac Estuary,
the ratio of total phosphorus to inorganic phosphorus ranged  from 1.1
to 1.5, while the ratio in the middle reach normally varied from 1.5
to 2.0.  This difference in a high productivity area may be due to
the biological conversion of soluble inorganic phosphorus to  cellular
organic forms.
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                                                               VII  -  5

B.  DETERMINATION OF LOSS RATE AND TEMPERATURE EFFECTS
     Water quality sampling data collected in the upper Potomac Estuary
from fourteen separate surveys were used for purposes  of Dynamic Estuary
Model verification, and more specifically, to determine the magnitude
of the overall phosphorus loss rate.   During these model  studies, no
distinction was made as to the relative importance of  (1) deposition  to
bottom muds and (2) biological uptake by algal cells.   All  of the
sampling data were collected under relatively steady-state  flow con-
ditions, ranging from 185 cfs to 11,000 cfs.  A range  in water temper-
                e         e
atures, from 1.0 C to 28.5 C, was also represented.
     Figures VII-3 through VII-16 depict the observed  total phosphorus
and inorganic phosphorus profiles in  the upper 45 miles of  estuary, as
well as the model predictions for total phosphorus.  The close re-
lationship between observed TP and Pi data eliminated  the necessity
for separate simulations.  An examination of these figures  will indicate
that the magnitude of peak concentrations and the rate of decrease
in phosphorus downstream from those peaks were accurately simulated.
In order to obtain this agreement with the model, it was necessary  to
utilize second-order kinetics having  the following form:

         St--"'•
           where     c = concentration
                     t = time
            and      k = reaction rate (gr/day)
     The reaction rates required for  model verification were greatly
affected by temperature, as can be seen in Figure VII-17.
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PHOSPHORUS  LOSS RATE
UPPER POTOMAC ESTUARY
             REGRESSION  DATA;
                CORRELATION COEF - 0.899
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                DEGREES OF FREEDOM = (M-2) = 12
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                                   FIGURE VII-17
-------
-------
                                                               VII - 21

C.  SIMULATION OF PHOSPHORUS TRANSPORT THROUGH AN ANNUAL CYCLE
     The mass transport and spatial distribution of total phosphorus
over an annual cycle must be known and predictable if the role of
phosphorus in the eutrophication process and a management program for
wastewater treatment are to be determined.  Because of its importance,
AFO endeavored to mathematically model phosphorus transport in the
Potomac Estuary during a 15-month period in 1969 and 1970,  This
period was characterized by both high and low summer flows and offered
an ideal situation for simulation.  A modified version of the Thomann
Model (DECS III) which incorporated second-order kinetics and the
phosphorus loss rated developed in the preceding section was used for
this simulation.
     Observed and predicted phosphorus (TPOi*) data are shown for five
selected stations in Figures VII-18 through VII-22.  A comparison of
the two profiles in each figure will indicate that the basic temporal
distribution, including seasonal trends, was simulated reasonably well.
     Some difficulty was experienced in simulating phosphorus under
excessive algal productivity conditions.  This problem can be evidenced
in Figures VII-19 (Piscataway Creek), VII-20 (Indian Head) and VII-21
(Maryland Point).  In order to improve the predictive capability of
the model during these periods, such factors as the extent of phos-
phorus regeneration following the death of algal cells and the quantity
of phosphorus exchange with the bottom sediments during different
flow conditions would have to be quantitatively defined.
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                                                               VII - 27

D.  CHLOROPHYLL PREDICTIONS BASED ON PHOSPHORUS ASSIMILATION BY THE BIOMASS
     To delineate that portion of the previously computed loss rate
representing biological uptake of phosphorus by algal cells from other
processes and to better understand the phosphorus contribution to eutro-
phic conditions in the Potomac Estuary, an attempt was made to predict
chlorophyll levels based upon various phosphorus conversion or assimi-
lation factors.  A special version of the DEM that correlated algal
production, as measured by chlorophyll a_, with inorganic phosphorus up-
take was used for simulation under four historical conditions.  Mass
relationships between the two were determined from algal chemical com-
position analysis.
     Figures VII-23 to VII-26 show observed chlorophyll profiles and
those obtained from the model assuming phosphorus conversion factors of
(1) 10 percent, (2) 25 percent, (3) 50 percent, and (4) 75 percent.  The
data pertain to late summer and early fall periods during which freshwater
flows varied from 185 to 2,200 cfs.  As can be seen, the model predictions
indicate that only about 10 to 20 percent of the phosphorus losses from
the aqueous system can be accounted for by uptake of algal cells.
Therefore, the remaining 80-90 percent must be associated with the
deposition of phosphorus or some other physical process.  Analyses
of the bottom muds in the upper estuary further substantiate the fact
that large quantities of phosphorus are indeed being lost to sediments.
     Insofar as eutrophication is concerned, it appears that there is
an abundance of phosphorus in the critical algal growing areas of the
Potomac Estuary.  Since the standing crop of blue-green algae was pre-
-------
                                                             VII - 28

dieted from the nitrogen cycle, and only a 50 percent utilization
of the available phosphorus produced excessive chlorophyll  when com-
pared to observed data, and for other reasons enumerated by Jaworski
et al. [5], nitrogen is probably the growth-rate-limiting nutrient in
the middle portion of the estuary at the present time.  However, this
presumption does not lessen the need to control phosphorus  to the
maximum extent possible, including loadings from wastewater treatment
facilities, in the Potomac Estuary for several reasons:   (1) the
potential for controlling phosphorus is extremely great, especially
during high flow periods (2) rapid phosphorus transport and mobility
and uncertainty of its recycling ability and (3) phosphorus criteria
for eutrophication control are considerably more stringent  than nitrogen
criteria for comparable reaches of the estuary.
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-------
                                                              VIII - 1








                         CHAPTER VIII





                    DISSOLVED OXYGEN BUDGET





A.  FORMULATION OF SOURCES AND SINKS



     A schematic diagram of the dissolved oxygen budget incorporated,



in the AFO mathematical model of the Potomac Estuary is shown in



Figure V-3.  As can be seen, the model consisted of the following



five linkages:



     1.  Oxidation of carbonaceous matter,



     2.  Oxidation of nitrogenous matter (ammonia and organic nitrogen),



     3.  Oxygen production and respiration of simulated algal standing



         crops based upon the nitrogen cycle,



     4.  Benthic demand, and



     5.  Atmospheric reaeration.




One important limitation of the DO model presented above is that it



neglected the oxygen demand of dying and decomposing algae.  An effect



such as this may be included relatively easily by regenerating the



oxidizable carbon and nitrogen "tied-up" in plant cells and was con-



sidered in a subsequent version of the model discussed later in this



report.  Although this DO sink may be significant in the fall months



when algal death is prevalent, the extremely low chlorophyll decay rates



required for most model verification runs (Chapter VI) and the apparent



success of the existing model in simulating various DO conditions
-------
                                                              VIII  -  2

suggests that it is negligible during the natural  growth phase of the
algae's life cycle when compared to other major sinks of oxygen.
     The basic coefficients and assumptions employed in the DO budget
model were:
                            Rate (base e)     Temperature Coefficient
Process                        at 20°C             9 (Tt - T20)
Carbonaceous oxidation         0.170                 1.047
Nitrogenous oxidation          0.084                 1.16
Reaeration from the
Atmosphere                       *                   1.021
Algal oxygen production rate = 0.012 mg 02/hr/yg chlorophyll  a^
Algal respiration rate = 0.0008 mg 02/hr/yg chlorophyll a_
Euphotic zone = 2 feet
Respiration depth = full depth of water column
Algal oxygen production period = 12 hours
Algal respiration period = 24 hours
Benthic demand rate =1.0 grams Oz/sq. meter/day
All of the above rates were established through field and laboratory
studies, with the exception of the nitrogenous oxidation rate which
was determined from modeling of the nitrogen cycle as presented in
Chapter VI.
     Light and dark bottle studies were conducted at various locations
in the upper and middle Potomac Estuary during June-July, 1970, to


* Based on O'Connor-Dobbins velocity and depth formulation
-------
                                                              VIII - 3

estimate the oxygen production and respiration rates for a known stand-
ing crop of algae.   The data collected during this survey are shown in
Table VIII-1.  A considerable amount of data relating to light penetra-
tion (Secchi Disk)  was available for the entire Potomac Estuary.  The
assumed depth of the euphotic zone was based upon an analysis of this
data.  Finally, a benthic respirometer was used by AFO in the upper
estuary to obtain benthic oxygen demand rates.  These data, which are
shown in Figure VIII-1, indicate that benthic uptake rates vary spatial-
ly, with the maximum rate occurring near the District of Columbia's
Blue Plains Sewage  Treatment Plant (River Mile 10.4).
-------
-------
                Table VIII-1

OXYGEN PRODUCTION AND RESPIRATION RATE SURVEY
      Upper and Middle Potomac Estuary
                    1970
Date
6-22
6-23
6-24
6-25
7-20
7-21
7-22
7-27
Water
Temp.
(°0
26
27
27
27
28
27
26
28
Chlorophyll a_
Range
(ng/1)
40-110
70-120
54-110
50-60
30-100
30-143
30-140
_
Light
Intensity
Range
(foot candles)
250-300
200-300
200-300
200-300
250-400
200-300
100-200
_
Oxygen
Production
mg/hr/yg of
Chlorophyll a
.0073
.0084
.0087
.0121
.0130
.0130
.0146
.0060
Respiration
mg/hr/yg of
Chlorophyll a
.0023
.0011
.0024
.0033
.0022
.0016
.0017
.0010
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                                                              VIII - 6

B.  SIMULATION AND MODEL VERIFICATION STUDIES
     Eight separate intensive sampling runs conducted in the upper
Potomac Estuary between 1965 and 1969 were used, initially, to verify
the DO budget model, including the various reaction rates and assump-
tions presented in the previous section.  Each run represented approx-
imately a 20- to 30-day period under relatively steady-state conditions.
The flows for the eight sets of sampling data ranged from 185 cfs to
8,800 cfs.
     Figures VIII-2 through VIII-9 show the observed DO profiles and
those predicted by the mathematical model.  As can be seen, favorable
agreement was obtained in every case.  Although the two sets of pro-
files did not coincide exactly, the magnitude and location of the criti-
cal DO deficit and the general rate of depression and recovery appear-
ed to be simulated reasonably well using the aforementioned coefficients
The critical deficit was primarily the result of the oxidation of
carbonaceous and nitrogenous material in the wastewater effluents; the
rate and extent of DO recovery was influenced greatly by the net
effect of algal photosynthesis and respiration.
     The pronounced decrease in DO predicted by the model in the ex-
treme upper portion of the estuary during lower flow periods could
have been due to the very deep holes in this area, which lowered the
reaeration capacity and magnified the effects of algal respiration.
     As a further test of the model's capability to predict dissolved
oxygen distribution in the Potomac Estuary, a completely independent
-------
                                                              VIII  -  7

and more recent (September 1970)  condition  was  simulated.   The sampling
data collected by AFO on September 9,  served  to define  the  initial
conditions.   Data collected 20 days later and compared  to model  pre-
dictions after a comparable time  period were  used as  a  basis  for veri-
fication.
     The freshwater flow during this period ranged from 1,200 cfs to
1,900 cfs (1,500 cfs average), and the reaction rates and assumptions
incorporated in the other eight runs were applied without change.  The
results of this simulation are shown in Figure  VIII-10.  Generally, good
agreement was obtained between observed and predicted data  describing
the rate of oxygen depletion, the magnitude and location of the critical
deficit, and the initial stage of recovery.  The considerable diver-
gence in the later stages of recovery may be  ascribed to the  extensive
algal death and decomposition which normally  occurs in  that area of
the estuary during late September.  As stated previously the  additional
oxygen demanding load resulting from the biological decay of  algal  cells
and nutrient regeneration had not been incorporated into this version
of the model, and consequently, the secondary DO depressions  that at
times exist in the Potomac Estuary were not accurately  simulated.
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-------
                                                              VIII  - 17

C.  SENSITIVITY ANALYSIS
     A study was performed to determine the Potomac Estuary DO
model's sensitivity to the various input rates.  A knowledge of the
relative importance of each rate in the DO budget offers assistance
for (1) model verification, (2) the design of field and laboratory
studies to define a particular rate by suggesting the necessary de-
gree of accuracy required, and (3) the relation of the gross effect
of each rate to the estuary's physical and biological parameters such
as depth, surface area, and algal productivity.
     The general approach adopted in this sensitivity analysis was
to assume two values for each rate—one approximately one-half and the
other twice the verified value.  All of the model runs simulated the
October 1969 loading condition that had been previously verified.
1.  Effects of Oxidation Rates (Carbon and Nitrogen)
     The simulated DO profiles based on carbonaceous and nitrogenous
oxidation rates of O.I/day and 0.3/day are shown in Figures VIII-11
and VIII-12.  Figure VIII-11  illustrates the considerable effect that
the carbonaceous rate exerts  on the DO distribution, and in particular
on the magnitude of the maximum deficit.  Increasing the oxidation
rate threefold results in a lowering of the critical sag point from
4.0 mg/1 to 0.2 mg/1.
     A comparison of Figures  VIII-11 and VIII-12 clearly shows that the
DO model is markedly less sensitive to the rate of nitrogenous oxida-
tion than to the carbonaceous rate.  A variation in K  comparable to
-------
                                                              VIII  - 18







that of K  produced a change in the critical  DO deficit of only about
         L.


1.0 mg/1.  The reason for this  difference in  model  sensitivity can



be attributed to the greater masses of carbon in the system, and hence



a greater range in the amount of oxidized material  and DO demand for



a given range in rates.



2.  Effects of Photosynthesis and Respiration Rates



     The effects of changing the algal photosynthesis or respiration



rates in the DO model are quite extreme, particularly in the recovery



region of the upper Potomac Estuary where algal growth is usually ex-



cessive.  As shown in Figures VIII-13 and VIII-14,  the model predictions



behaved similarly when either the photosynthesis rate was increased



or the respiration rate was decreased.



     According to the DO profiles in Figure VIII-13, increasing the rate



of photosynthesis fourfold, from 0.006 to 0.024 mg  02/hr/yg chlorophyll,



increased the critical sag point by 4.0 mg/1  and greatly accelerated



the rate and degree of DO recovery.  Figure VIII-14 shows a similar oc-



currence when the respiration rate was lowered from 0.0016 to 0.0004



mg 02/hr/yg chlorophyll.  It should be noted that the maximum chlorophyll



concentrations observed during the simulation period were approximately



100 yg/1.  Of course, both the individual effects of photosynthesis



and respiration as well as the net effect will be dependent upon the



quantity of algae present.



     The model's sensitivity to euphotic depth was  also investigated



and the  results closely paralleled to those presented for the



photosynthesis rates.
-------
                                                              VIII - 19

3.  Effects of Benthic Demand Rate
     Since the units of benthic demand rate include an areal term (ft2),
its effects are closely related to the surface area of the Potomac Es-
tuary.  Figure VI11-15 illustrates the resulting DO profiles when ben-
thic rates of 0.0 and 2.0 gr/meter2/day were assigned.  As can be
seen, the higher rate significantly lowered the entire profile with the
most pronounced differences occurring in the wider downstream areas.
However, it did not drastically alter the DO gradients or the rates of
depression and recovery.
4.  Effects of Reaeration Rate
     Of the various DO budget components investigated in this sensi-
tivity analysis, the method by which the reaeration rate is computed,
i.e. O'Connor-Dobbins equation, Churchill equation, or USGS (Langbein)
equation, was the least important in terms of affecting model  output.
In fact, the three profiles shown in Figure VIII-16 are coincident, in-
dicating that any of the  more commonly used equations for determining
reaeration rates should prove equally successful.
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-------
                                                              VIII  - 26

D.  NUTRIENT REGENERATION - SPECIAL DO MODEL
     Realizing the inherent limitations of the dissolved oxygen model
heretofore discussed, a further revision of the DEM to incorporate
organic nitrogen and nutrient regeneration was investigated.   Unfor-
tunately, these inclusions complicated the "feedback-feedforward" link-
age within the model somewhat and created a problem by simultaneously
evaluating several reaction rates.  Prior to this, there had  been only
a single unknown rate to be evaluated through each series of  model  veri-
fication runs.  A considerable amount of background information re-
lating to the nutrient regeneration process was, however, provided  by
Jewell [13].
     Organic nitrogen was treated in two distinct forms in the model:
(1) dissolved or soluble and (2) particulate.  The latter, or course,
would comprise organic nitrogen within algal cellular material.  The
dissolved fraction was "decayed" by first-order kinetics to ammonia
nitrogen (hydrolysis), while a portion of the particulate form was
regenerated to inorganic nitrogen (NH3) and carbon (BOD), thereby cre-
ating an additional oxygen demand.  Based on a subjective appraisal of
existing information, it was assumed that 50 percent of the organic
nitrogen and carbon in the dead algal cells, as computed from the mass
of chlorophyll decayed, was regenerated; the remaining 50 percent was
assumed to be deposited to the bottom sediment.  Ratios of chlorophyll
to nitrogen and chlorophyll to carbon were estimated using 1970 algal
composition analysis data.
-------
                                                              VIII  - 27

     Upon completion of this "surrogate" DO model  and estimation of
the necessary reaction coefficients, a verification run was  performed
based on September 1970 data.   This particular set of data was selected
because it pertained to a time of year when algal  death was  prevalent,
as indicated by the relatively high chlorophyll decay rate (0.07/day)
required for model verification.  Furthermore, a review of Figure
VIII-10 shows that the recovery portion of the observed DO profile
was not accurately simulated with the existing DO  model, presumably
because the effects of nutrient regeneration were  omitted.
     Figure VIII-17 illustrates the improved comparison that resulted
from predictions using the mathematical model described herein.  Both
the rate of recovery and the secondary DO sag farther downstream were
satisfactorily simulated.  Due to an inadequacy of organic nitrogen
data and uncertainties in decay rates, no serious  attempt was made  to
verify the model for prediction of this parameter.
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                                                                                                                I- 17
-------
-------
                                                              IX - 1
                          CHAPTER IX

                 ADDITIONAL STUDY REQUIREMENTS

     Recognizing the basic limitations of existing data and their
subsequent effects on model structure and verification, the following
areas are suggested for continued study of the Potomac Estuary:
     1.  The use of either laboratory or field studies to acquire a
better understanding of algal decomposition rates and extent of nutrient
regeneration,
     2.  The use of either laboratory or field studies to determine
nutrient transfer rates between the bottom sediments and the overlying
water for consideration in the overall nitrogen and phosphorus budgets,
     3.  Perform additional algal composition studies (laboratory)
during various times of the year in order to relate biological uptake
rates of both nitrogen and phosphorus to seasonal bloom conditions,
     4.  Develop techniques to acquire a better understanding of the
nutrient-phytoplankton relationship in the saline portion of the Potomac
Estuary where water quality stresses are becoming increasingly pro-
nounced and where biological  communities are quite different from those
encountered upstream, and
     5.   Incorporation of data from the above, and other special studies,
into a truly biological  model; one not only capable of predicting algal
standing crop levels but also capable of simulating algal  species
succession,  including their causes and effects, zooplankton grazing
-------
                                                              IX  -  2
rates and other well  established biological  reactions.   The  develop-
ment of this type of  model  would not only serve  a definite purpose  in
the Potomac Estuary,  but more importantly it would provide a signifi-
cant foundation for any mathematical modeling effort in  the  Chesapeake
Bay itself.
-------
                           BIBLIOGRAPHY
 1.  Thomann, R.  V.,  Donald J.  O'Connor  and  Dominic  M.  Di  Torro,
     "Modeling of the Nitrogen  and Algal  Cycles  in Estuaries,"
     presented at the Fifth International  Water  Pollution  Research
     Conference,  San  Francisco, California,  July 1970.

 2.  Feigner, K.  and  Howard S.  Harris, Documentation Report,  FWQA
     Dynamic Estuary  Model, FWQA,  U.  S.  Department of the  Interior,
     July 1970.

 3.  Jeglic, J.  M., "Mathematical  Simulation of  the  Estuarine Be-
     havior," Contract to FWQA  by  General  Electric,  1967.

 4.  Clark, L. J. and Kenneth D. Feigner,  "Mathematical  Model
     Studies of Water Quality in the  Potomac Estuary,"  AFO,  Region
     III, EPA, March  1972.

 5.  Jaworski, N. A., Leo J.  Clark, and  Kenneth  D. Feigner,  "A
     Water Resource-Water Supply Study of the Potomac Estuary,"
     CTSL, MAR,  WQO,  EPA, April 1971.

 6.  Jaworski, N. A.  and Leo J. Clark,  "Physical Data Potomac River
     Tidal System Including Mathematical  Model Segmentation," CTSL,
     MAR, FWQA,  1970.

 7.  Private communication  with Roy Weston Consulting Engineering
     Firm currently investigating  the storm  and  combined sewer
     contribution under contract to FWQA.

 8.  "Water Quality Survey  of the  Potomac  Estuary-1965-1966  Data
     Report," CTSL, MAR, FWPCA.

 9.  "Water Quality Survey  of the  Potomac  Estuary -  1967 Data Report,"
     CTSL, MAR,  FWPCA.

10.  "Water Quality Survey  of the  Potomac  Estuary -  1968 Data Report,"
     CTSL, MAR,  FWPCA.

11.  Manhattan College, New York,  N.  Y.,  "Mathematical  Modeling of
     Natural Systems" - 1971  Course Manual.

12.  Thomann, Robert  V., "Mathematical Model  for Dissolved Oxygen,"
     Journal of the Sanitary Engineering  Division ASCE,  Vol.  89.
     No.  SA5, October 1963.
-------
13.   Jewell,  W.  0.,  "Aerobic  Decomposition of Algae and Nutrient
     Regeneration,"  A  Doctoral  Dissertation, Stanford, University,
     June 1968.
-------
         Chesapeake Technical Support Laboratory
                  Middle Atlantic Region
          Federal Water Quality Administration
             U. S. Department of the Interior
              PRELIMINARY ANALYSES OF THE

              WASTEWATER AND ASSIMILATION

                   CAPACITIES OF THE

              ANACOSTIA. TIDAL RIVER SYSTEM

                  Norbert A. Jaworski
                      Leo J. Clark
                   Kenneth D. Feigner*

                Technical Report No. 39
                       April 1970
Federal Water Quality Administration, Washington, D. C«
-------
                            TABLE OF CONTENTS

                                                                   Page

LIST OF TABLES ...............           iv

LIST OF FIGURES   ..............            v

Chapter

    I   INTRODUCTION ........   	            1-1

   II   SUMMARY AND CONCLUSIONS  .........           II -  1

  III   DESCRIPTION OF THZ STUDY AREA  .......          Ill -  I

        A.  General  .............          HI -  1

        B.  Stream Flow Analysis .   „   .   .	          Ill -  2

        C.  Water Quality Conditions   .......          Ill -  3

            1.  Dissolved Oxygen and Biochemical Oxygen
                Demand  ............          Ill -  3

            2,  Bacteriological Densities ......          Ill -  7

            3.  Nutrients  ,   .  «,   .   .   „   .   „   .   .   .          in - 11

            4.  Sediments and Turbidity   .                         Ill - 14.

        D.  Population and Wastewater Projections   .   .   .          Ill - 16

            1.  Anacostia Valley .........          Ill - 16

            2.  District of Columbia   .......          Ill - 17

   IV.   WASTEWATER ASSIMILATION AND TRANSPORT ANALYSIS    .           IV -  1

        A,  Stream Flow - Wastewater Flow Analysis  .   «   .           IV -  2

        B.  Residence or Flushing Time .......           IV -  5

        C.  Tidal Hydrodynamics  .   ,   .   .   .   .   .   .   .           IV -  8

        D0  Self-Purification and the  Dissolved  Oxygen
            Budget   .............           IV - 17
-------
                            TABLE OF CONTENTS (Continued)
Chapter

  IV.   WASTEWATER ASSIMILATION AND TRANSPORT ANALYSIS (Cont.)      IV -  1

        E.  Nutrients and Algal Growth	          IV - 20

        F.  Treatment at the Blue Plains Plant vs
            Constructing a Facility in the Anacostia
            Valley	          IV - 21

        G0  Continuing Studies   .	          IV - 23

REFERENCES

APPENDIX

        A.  Anacostia River Study

        B.  Nutrient Concentrations at Bladensburg Bridge
            Road, Anacostia River, 1966

        C.  Anacostia River, Kingroan Lake, June 26-27,
            1969
                                    111
-------
                              LIST :? TABLED


Number                         Description

   1         Mean Monthly River Discharge.  ,  „  .  „  „           Ill -  2

  IT         Nutrient Cone em rat ions and Loadings,
             Eladensburg Foad Bridge, Anacostia River ,
             1966  ..„..,,".„.....           .131 - 12

 III         Anacostia Tidal River System, L. C, Water
             Pollution Control Pivif ion Data , Monthly
             Report,  June 1969 ...........           II! - 13
  IV         Mathemat icdl Model Segmentation, Anacostia
             Tid%l Fiver SvrteTn, Mean Water D&ra    „               IV _
                                    IV
-------
Number

   I

  II


 III


  IV


   V


  VI


 VII


VIII


  IX
  XI
 XII
                IJST Of FI

                  Description

Upper Potomac and Anaeostia Tidal River System

Dissolved Oxygen Concentration, Anacostia Tidal
River System, 1969   „,..„..„..

BOD Concentration, Ana?ostia Tidal River System,
1969  ..,,.,   0   ...,„....

^ecal Coliform Densities, Anacostia Tidal River
System, E'.C,-Md. Line, 1969   .-   „   ,   „   .   „   .
Fecal Coliform  Tensities, Anacc£*.ia Tidal River
System, Pennsylvania Avenue, 1969   ,   .   .   .   .
Fecal Coliform Densities, Ana^ostia Tidal River
System, South Capitol Street, 1959  	
Turbidity Concentration, Anacostia lidal River
System, 1969   .   .      ,.,.....
Mathematical Model Segments, Anascstia Tidal
River System   .-.,„<,.....
Residence Time  for ^noos V/astevva+er Flows,
Anacostia Tidal River System  „„....
Dispersion Coefficient vz Flow, Anacostia Tidal
River System, 1969 C. C. Alkalinity Data  .   .   .

Simulated Profiles for Various Dispersion
Coefficients of a Conservative Pollutant Dis-
charged at a Hate cf 1000 Its/day into the
Anacostia Tidal River System Above C.C.-Md,
Line, Q = 58 cfs „...„,.....
Simulated, Profiles For '-'arious Dispersion
CoefficientuS of & '"'cnaervative Pollutant Dis-
charged at a Rate of 1000 Ibs/day into the
Anacostia lidal River System Above P.C.-Md.
Line, Q = 108 cfs   .........
Page

  I -  3


III -  5


III -  6


III -  8


III -  9


III - 10
 IV -  3
                                                                    IV -  7
                                                                    IV - 11
                                                                    IV - 12
                                                                    IV - 13
-------
                             LIST OF FIGURES (Continued)

Number                         Description

XIII         Simulated Profiles For Various Dispersion
             Coefficients of a Conservative Pollutant Dis-
             charged at a Rate of 1000 Ibs/day into the
             Anacostia Tidal Biver System Above D.C.-Md.
             Line, Q = 208 cfs   ..........        IV - H

 XIV         Simulated Profiles For Various Wastewater Dis-
             charge Rates For Calculated Dispersion
             Coefficients of a Conservative Pollutant
             Discharged at a Rate of 1000 Ibs/day into the
             Anacostia Tidal River System Above D.C.-Md.
             Line ...............        IV - 15

  XV         Simulated Profiles for Various Dispersion
             Coefficients of a Nonconservative Pollutant
             Discharged at a Rate of 1000 Ibs/day Into the
             Anacostia Tidal River System Abnve the D.C.-Md.
             Line, Q = 108 cfs, Decay Rate = 0.3 (base e).  .        IV - 16

 XVI         Simulated Profiles For a Conservative and Non-
             Conservative Pollutant Discharged at a Rate of
             1000 Ibs/day into the Anacostia Tidal River
             System Above the P«,C.-Md,  Line, Wastewater
             now = 100 mgd,  River 0. =  8 cfs ......        IV - 18
                                    VI
-------
                                                                  I - 1
                                CHAFFER I



                               INTRODUCTION






     To provide information to assist in decision making as requested



by Assistant Secretary of the Interior Carl Klein, a study of waste-



water assimilation and transport capabilities of the tidal portion of



the Anacostia River was initiated by the Chesapeake Technical Support



Laboratory (CTSL) during April of 1970,  This study was designed to



investigate the effects of a wastewater discharge into the Anacostia



River at or near the site of the abandoned Washington Suburban Sanitary



Commission (WSSC) Plant near Bladensburg, Maryland.  Currently, waste-



water flows from the Anacostia Valley are conveyed to the Blue Plains



Treatment Plant of the District of Columbia.



     The Blue Plains plant is presently overloaded and plans are



currently being developed to expand the facility.  If this plant is



to accomodate the projected wastewater volumes using current renovation



processes, more land will be required for expansion.  Other alternatives



could be process changes that would allow increased volumes to receive



required treatment within the same area or development of facilities



to treat the wastewater at other locations such as the Anacostia



Valley.



     The major emphasis of this  study was to determine the effect of



a wastewater discharge on the water quality in the tidal portion



of the Anacostia in the vicinity of the D.  C.-Maryland Line (See



Figure I).
-------
                                                                  1-2





     Presented in this report are: (l) an assessment of the current



water quality conditions, (2) a hydrologic analysis, and (3) prelimi-



nary results of the assimilation and transport capacities of the



Anacostia tidal system.
-------
    8
fi
      g

    tr
    |
                                /\
                                     \
\
°c>\^
*\
Vv
\
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-------
                                                                   II - 1






                                 "HAP.7ER J.T




                                  A''E' "'ONC1T':5I-"MS






     A preliminary analysis tf the waitewat-'-r assimilation and trans-




port, capacities  of the tid.^1 portion of the Ana cos tie  River has been




made.  The  findings of rhi.- r^pcrt, which a."; limited  '•;• predicting




the possible  effect on water quality in the Anaoostia  tidal river




system of dicchifging trfited wastewater fr..-m a service  •-r«a comprising




the Anacasti'-t Valley ar- Msryjsin'i, are sxunmarizt-d belcw,




     lo   The  Anacostia watershed, tributary *- the  Potomac Estuary ne^r




Washington, £•„ Oe,  ha? a dr^in^ge are* of 18/+ sqioarf mile-, 30 square




miles within  th°  Distrirr  of '"^.'.'mtia and 1^4 square mile? within the




State of Maryland,




     2,  The  mean stream fl.w in -:he Irnsin is -9bout 122  :f-- ar-i the




7-day low fl:v with a r^'urr^n:^ ir;t--ri/al of i-'.nce-in-ten-year;- is 8




cfs.




     3,  The  lower  pert ion rf >>e Ar.dcratis River is a tidal freshwater




system having a mean volune of aboxit f4.0,OOC«,OGC Cubic fe»t.




     4-  Based on 1969 sampling dbta, tne rater quality  rond.ition? in




the tidal river under £iojmner ccrditi.-.^- are typified ty;




         a0   Low  dissolved : yyg^r. c;nr:^ntra.t icns often falling below




              ?.0  mg/1,




         b.  High fecal :c,ifora rlen^a'ifts c-ften above 10,000 MPN/100 mi




         c,,  High turbidity level.- especially d-oring periods cf high




              runoff,  and
-------
                                                                 11-2
         d.  High nutrient concentrations.

     While some of the above water qualiiy indicators which fall below

accepted stream standards can be attributed to urban runoff, the most

pronounced degradation results from storm sewer and combined sewer

overflows and defective sanitary sewer systems.

     5.  The projected populations and wastewater flows of the water

quality renovation facility investigated, at a site above the D.C.-Md,

border and serving the Anacostia Vnlley in Maryland, are given below.

                                          Wastewater Flows
Year

1970

1980

2000

2020
PQ-pulation

 466,ooo

 061,000

 744,000

 83';,000
55

78

88

99
     o,  A comparison of the projected wastewater flows to the Blue

Plains Treatment Plant of the District of Columbia excluding Anacostia

flows and. the flows from the Anacostia Valley is shown below:
Year

1970
1980
2000
Blue Plains
(med)
177
231
331
                                 Ana cost ia Valley
                                         78

                                         88
                                        % of Blue
                                        Plains Flow
                                           liqgd)

                                             31

                                             34

                                             27
-------
Year
1980
2000
2020
Stream
Flow
(cfs)
8
8
8
Wastewater
Flow
(mgd)
78
88
99
                                                                 II - 3


     7.  The ratio of projected Anacostia wastewater flows to the

designated low stream flow criterion of 8 cfs, as presented below,

vividly shows that most of the advective flow in the tidal system

would be from the wastewater renovation facility.

                                                   Ratio of
                                            Wasteyater/Stream Flow


                                                    15.1

                                                    17.0

                                                    19.?

     8.  Mathematical model investigations of the Anacostia River

indicate that wastewater assimilation and transport capabilities

for large advective flews are mcst sensitive to the decay rate of

a pollutant and not to the dispersion effect of the tidal system.

The sensitivity of the decay rate is a result of the long detention

time of the tidal system while the effect of the dispersion coeffici-

ent is diminished by the pronounced advective movement.

     9.  Based on mathematical model studies and analysis of 1969

water quality data., it was concluded that the tidal system capability

to assimilate oxygen demanding wastewater is currently being exceeded

and that any wastewater discharged would have to be of better quality

than that currently existing in the Anacostia.

    10.  The discharge cf low turbidity effluents into the highly

turbid Anacostia is expected to create nuisance algal  blooms due to

increased light penetration.  Therefore, a high degree of nutrient

removal will also be required.
-------
Before
Treatment
(me/1)
200,0
11.0
2200
Effluent
Criteria
fffK/U-
2.0 - 4,0
0,1
0.5
- 0,2
- 1,0
Percent
Removal
Rapee
98
98
96
- 99
- 99
- 98
                                                                 TJ - 4






    11„  Incorporating the need for enhancing the dissolved oxygen



levels, preventing nuisance algal growth, and considering the large



flow of wastewater compared to stream flow, effluent standards were



used to determine wastewater renovation requirements.  Renovation



requirements for a discharge into the Anacostia are presented below:








Parameter



BOD5




T. Phosphorus as P



T. Nitrogen as N



    12.  An important requirement of the renovation process is an



aerated effluent.  Since most of the net advective flow will be



wastewater, the effluent must have as a minimum 4.0 mg/1 of dissolved



oxygen to meet the DC', standard in the /macostia at the discharge site,



    13.  If the wastewater were subjected to high carbonaceous and



nitrogenous BOD removal and if the effluent is aerated to 6.0 mg/1,



the present water quality of the Anaeostia River would be enhanced.



The additional 2,0 mg/1 in the effluent is expected to ruise the DO



to meet the standard of 4,0 mg/1 at the critical point downstream,,



    14.   The greatest uncertainty, even at high removal requirements,



is the algal growth potential.  The effluent, which would be the



result of ultimate wastewater treatment (UWT) and would be considered



suitable for many water uses, might still contain nutrients at con-



centrations capable of producing excessive algal blooms.
-------
                                                                 II - 5






    15.  A dye tracer study was conducted in late April 1970, during




preparation of this report, to ascertain tidal dispersion character-



istics and residence times in the'Anacostia tidal system.  Other




continuing studies will involve (l) water quality interactions between




Kingman Lake and the Anacostia Fiver, and (2) reaeration rates and



benthic oxygen demands along the Anacostia.  Results of these studies




will be reported in progress statements of the Potomac Washington




Metropolitan Area Enforcement Conference,
-------
                                                                Ill -1
                               CHAPTER III

                      DESCRIPTION OF THE STUDY AREA


A.  GENERAL

     The Anacostia watershed, tributary to the Potomac River, lies

within Montgomery and Prince Georges Counties in Maryland and the

District of Columbia.  The drainage area of the basin is 184 square

miles and presently contains a population of approximately 993,000.

     The tidal portion of the river extends from the Potomac River

near Hains Point to the confluence of the Northeast and Northwest

Branches, a distance of 8.75 miles.  The mean volume of the tidal

portion of the Anacostia is approximately 540,000,000 cubic feet.

The nontidal portion of the watershed has a drainage area of 125

square miles.  The 196? population of the nontidal area was approxi-

mately 466,000.

     The river mile locations of pertinent land features of the

tidal system are presented below:

Item                                               River Mile

Hains Point                                           0.00
Douglas Bridge                                        1,45
llth and 12th Street Bridge                           2.45
Sousa Bridge                                          3.10
Lower End of Kingman Lake                             3.80
East Capitol Street Bridge                            4.35
Benning Road Bridge                                   4.90
Upper End of Kingman Lake                             5.65
U. S. Route 50 Bridge                                 6.90
WSSC Marina                                           8.10
Bladensburg Road Bridge                               8.45
Confluence of Northeast and Northwest Branches        8.75
-------
5,  STREAM FLOW ANALYSIS

     The nontidal stream flew _f the Anaco^tia River comes primarily

from the Northeast and Northwest Branches.  Mean monthly flows of the

two branches and their tots it -^re presented in Table I.


                                 Title I

                       Mean Monthly River Discharge

                   Northeast Pr_          Northwest Er.         Total
                                              l cfs)             (cfs)
Mon^h
January
Kebruary
March
April
May
-June
July
August
September
October
November
December
' cfs :
89.6
110,4
128.0
108.2
78,6
57.5
48.1
66 . 4
42- D
44.5
63.4
75.3
                                               51.6             141.2

                                               U.I             174/,

                                               73.4             201.4

                                               64.1             172.3

                                               50.9             129.5

                                               39.7              97,2

                                               32.6              80.7

                                               40.8             107.2

                                               28.1              70.7

                                               24.8              69,3

                                               38.0             101.4

                                               43.0             118.3

     The average daily discharge of the combined branches is .1.22 cfs

with a 7-day low-flow recurring once-in-ten-years of 8 cfs.  While

the average flow is 122 :fs, the median flow fthat flow occurring 50

percent of the time) is 66 cfs, indicating that stream discharge is

flashy.
-------
                                                                 I
C .  WAT ER QUAL ETY COND 1 1 1 ONc




     The water quality condition of  the tidal portion  cf  the Anacostia




is monitored by the Department of Sanitary Engineer-ing, District  of




Columbia and by the Chesapeake Technical Support Laboratory, Federal




Water Quality Administration,  Special studies  of the  entire basin




were conducted by CTSL in 1967 said ±969.




     The major sources of water quality degradation are land runoff,




storm drainage, defective sanitary sewers, and  •jombi.r.ed sewers.,




There are no significant discharges from wnstewater treatment facilities




in the basin,




1«  Dissolved Oxygen and Biochemical Oxygen _ Demand




     The dissolved oxygen (DO) concentration in 1969 was  depressed




below 5.0 mg/1 in most cf the tidal system during most of July,




August, and September.  As can be seen in Figure II, the  lowest con-




centration, between 1,0 '
-------
                                                                Ill - 4






     The water quality standard for DO for this reach of the Anacostia



is a minimum of 3.0 mg/1 with an average of 4.0 mg/1.  This  standard



was not met in July, August, and September of 1969 in the tidal  portion



of the Anacostia.  June 1969 surveys indicated the same to be true  for



the Kingman Lake area and the Pennsylvania Avenue sampling point.
-------
Figure II
-------

o

I
O)

«0

I
r- 
-------
                                                                              Ill - 7
Jb

             2.  Bacteriological
k
                  Figures IV, V, and VI present the fecal colifonn densities for

             the water quality sampling stations at the D.C.-Md. Line, Pennsylvania

             Avenue, and South Capitol Street Bridge.  The data obtained by the

             District of Columbia Department of Sanitary Engineering indicate that

             fecal densities are higher near the D.C.-Md. Line.  Densities over

             10,000 MPN per 100 ml were measured frequently at the D.C.-Md. Line

             during 1969.

                  Data for the Kingman Lake study also indicate high fecal densities

             with counts ranging from 2,100 to 93,000.  The fecal coliform standards,

             which are a geometric mean of 1000/100 ml and 10 percent of samples not

             to equal or exceed 2000/100 ml, are not currently being met in the

             tidal portion.

                  Daring the survey of the entire watershed in 1967, the Sligo Creek

             station at Chillum Manor and the Northwest Branch at Queens Chapel Road

             had the highest bacterial densities.  Of the fifteen stations sampled,

             none had consistently higher densities than were found at the stations

             located in the tidal portion of the basin during 1969 (See Appendix A).

             This indicates, that the high densities in the tidal portion are from

             local sources such as the sewer systems and not runoff originating in

             the upper drainage area.
-------
100.000-1
 FECAL COLIFORM DENSITIES

ANACOSTIA TIDAL  RIVER SYSTEM

          O.C.- MO. LINC

              1969
I 0.000-
 1,000-
   100-
           r     ii      i     r    T    i      i     I     I      I     I
       JAN  FEB.   MAR  APR.  MAY   JUN   JUL   AUG.  SER  OCT   NOV  DEC.


                                                             Fi P\ i rp TV
-------
100.000
 FECAL COLIFORM  DENSITIES
ANACOSTIA TIDAL RIVER SYSTEM
            PA AVE.
             1969
           (Z40.0OO)
 10.000-
 I.OOO-
-------
100,00'!
10.000-
 1,000-
                         FECAL  COLIFORM  DENSITIES

                        ANACOSTIA TIDAL RIVER SYSTEM
                                   S CAP. STREET
                                        1969
                                            ,(240.000)
       IAN.  FEB.   MAR.   APR.  MAY   JUM  JUL    AUG   SEP.   OCT    NOV.   DEC.
                                                              Figure  VJ
-------
                                                                Ill - 11





3.  Nutrients



     During the 1966 nutrient survey of the Potomac River Basin, phos-




phorus and nitrogen concentration data were obtained by CTSL, FWQA



(See Appendix B).  For 1966, the mean monthly nutrient concentrations



and their loadings are summarized in Table II„



     As presented in Table II, the average concentrations of phosphorus



as PO^, N03 as N, and TKN as N were 0,80, 0.86, and 1.24 mg/1 for the



Bladensburg station during 1966.  The resulting loadings for the



stations in 1966 were 3r;4, 513 >  and 633 Ibs/day of phosphorus as PO^,



N03 and TKN, respectively,



     Phosphorus concentrations as high as 8.7 mg/1 as PC/ have been



observed in the tidal portion near the D.C.-Md. Line.  This large



increase, especially during high flows, can be attributed to defective




sewerage systems of the Washington Suburban Sanitary Oommission.  Data



for the month of -rune 1969, presented in Table III, document these high



concentrations.



     Associated with decreases in turbidity or suspended sediments



in the tidal system is a decrease in phosphorus which is also shown



in Table III,,  This adsorption phenomenon of phosphorus or,to silt



particles has also been demonstrated recently in both laboratory and



field measurement by the Chesapeake Technical Support Laboratory as



part of a nutrient transport study in the Potomac Estuary.
-------










rtj
F>
CO H
OS
«a; EH
SB
n3
§ > 0)
H bO
"fl J
O O -— N
S w w
0) S O
> -H



_C~}
P
fl
O
S
t— f~-OOOVOONONl~--4 OOONLA
CO!AVDOO-4-4OJO^— ^— LAOJ
OOVDVOOI^OJHHLA-40OOJ
H H H

-4-4OLAiHOOOOJVOCOLAON
-d-Lr\-4-4-HHOOOO-4VO-4-LA
HHHHiHHHHOHHO

LAiAON-VOaNOOJOO-=f-HOJ
HO-4-4--4--4LA-H/OJH-4-CO
OOO.]^-*^?-! r-)HHOO




t^-OJOOOOHVOOJOjOt^t—- O
H H 0s, VD 5  ^ 5dpoa)
d^^^^aHbppHPt-o
cd fl3 co PH cc! ^3 jij 3 ^) o o cy
h)Ssi W)
H aJ
C~J ^)
P (U
fl >
S
-------
                 TABLE III

       Anacostia Tidal River System
B.C. Water Pollution Control Division Data

              MONTHLY REPORT
                June 1969
Sampling
Station
D. C. Line
Ben. Rd.
E. Cap. St.
Pa. Ave.
llth St.
S. Cap. St.
Wash. Ch.
Total,P
as PO
6.10
4.81
2.74
1.16
1.03
1.09
0.81
TKN as N
(mg/1)
2.14
2.23
2.18
1.85
1.97
2.15
1.73
N02+N0
as N
0.59
0.41
0.40
0.30
0.33
0.20
0.31
NH -N
(ml/1)
1.18
0.63
1.10
1.80
l.8o
1.41
0.86
Turb
(units)
226
197
161
53
40
18
9
-------
                                                                Ill - 14


 4o  Sediments and Turbidity

     The Anacostia River  can usually be characterized as a muddy stream.

 Daring periods of high stream flow, large quantities of silt and debris

 are carried downstream to the Potomac,

     Sediment data obtained by US OS for the Colesville, Maryland station,

 located in the Northwest  Branch, indicate concentrations over 4,300 ppm

 at times.  The 196? to 1968 sediment yield for the Colesville station,

 which has a drainage area of 21,1 square miles, is giver, below;


                             Biver Discharge              Sediment
 Year                            (of s -day.)	             (tons/year)

 1963                              5337                      16811

 1964                              6844                      11596

 1965                              5068                      15889

 1966                              5137                      14402

 1967                              6738                      15009

 1968                              6188                      10498

 Using an average sediment t"linage of 14,OCG at this station, the esti-

 mated silt contribution for the entire watershed is about 114,000

 tons/year.

     The effect of the sediment  loadings en the turbidity in the tidal

 system is shown in Figure vjl.  The higher concentrations of turbidity

 near the D_C.-Mdn Line are decreased significantly downstream,

 especially at the South Capitol  Street Bridge station.  The decrease

 in turbidity is also reflected in the monthly summary as shown in

Table III.
-------
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8* =
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a  o
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                                            r

o a.
   UJ
   Ul
   cr
   u
   ^n
                                             o
                                             o
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                                             UJ
                                             in
                                             CD
             OOOOQ
                                T—i—T~T—n—FT—i—r
                                aooooooooc
                                         OO
                                         — o
                                  Figure VII
-------
                                                                Ill - 16






D.  POPULATION AND WASTEWATER PROJECTIONS



1.  Anacostia Valley



     The area which could be served by a wastewater renovation facility



located upstream from the D.C.-Md, Line would be the Anacostia Valley



located in Prince Georges and Montgomery Counties.  Population pro-



jections for the Anacostia and Beaverdam Valleys of the two counties



have been developed jointly by the Washington Suburban Sanitary



Commission and the Maryland-National Capital Park and Planning Commission



and are given below:
Year
19o7
1980
2000
Capacity
Montgomery
(Anacostia.1
131,400
167,800
228,600
453,400
Prince Georges
(Anacostia) (Beaverdam)
197,400
237,700
313,800
390,500
64,200
81,800
100,900
122,700
Total
Populat ion
393,000
487,300
643,300
966,600
These figures were obtained from the current "Ten Year Water and



Sewerage Plan" of the Washington Suburban Sanitary Commission for



Prince Georges County.



     Data from a 1968 report prepared for WSSC by Whitman, Requardt, and



Associates indicate that the population for the Anacostia. Valley is con-



siderably higher.  Their analysis shows the following:



Year
1968                      500,000



1980                      850,000



2000                    1,000,000
-------
                                                                Ill - 17





A request was made to the Maryland-National Capital Park and Planning




Commission to update their projections.  Their recent projections



are given below:




Year                    Population




1970                      466,000



1980                      661,000



2000                      744,000



2020                      837,000



     Utilizing an average of the wastewater volumes and constituents



obtained in the 1969 surveys ( 1 ] and the above populations, dis-



charge volumes, BOD, phosphorus and nitrogen loadings before treatment



were projected as follows:



                                              Phosphorus   T. Nitrogen
Year
1970
1980
2000
2020
Population
466,000
661,000
744,000
837,000
Volume
(med)
55
78
88
99
BOD
(Ibs/day
69,200
99,150
111,600
125,550
as P
(Ibs/day)
4,320
5,949
6,696
7,533
as N
(Ibs/dav)
9,830
13,881
15,624
17,577
2. District of Columbia
     The projected population, wastewater volume, and BOD loadings, as



determined by Metcalf and Eddy, Engineers, in February 1969 for the



Blue Plains Treatment Plant of the District of Columbia are presented



below:
Year
1970
1980
2000
Population
1,750,000
2,227,000
3,122,000
Volume
(mgd)
232
309
419
BOD
Clbs/dav)
304,000
490,000
718,000
Suspended Solids
378,000
537,000
843,000
-------
                                                                Ill - 18
     If the wastewater from the Anacostia Valley is treated by a

separate facility, the following reductions in flow at the Blue

Plains Treatment Plant were estimated:

Year      Blue Plains*     Anacostia Valley        % of Blue Plains
             (mgd)         	(mgd)	        	Flow	

                                                         31

                                                         34

                                                         27


* Excluding Anacostia Flows
1970
1980
2000
177
231
331
55
78
88
-------
                                                                 rv - i
                                CHAPTER IV



              WASTEWATER ASSIMILATION AND TRANSPORT ANALYSIS






     The five major physical factors which govern the wastewater



assimilation and transport capabilities are:



     1.  Stream flow conditions including flow-wastewater volume



         ratio,



     2.  Residence flushing time of the tidal system,




     3.  Tidal hydrodynamics including dispersion,



     4.  Reaeraticn and decay rates on dissolved oxygen budget, and



     5.  Turbidity and algal growth.




Factors which affect the assimilation and transport capacities other



than waste loadings are;



     I.  Storm sewer dischargee,



     2e  Combined sewer discharges located between East Capitol



         Street and Souea Bridges and near the llth Street Bridge,



     3.  Defective sanitary sewerage systems,



     4.  Benthic demand of organic deposits in the bottom muds, and



     5.  Land runoff.



Water quality data presented ir, the previous chapter indicate that



under current sanitary practice.?,  the tidal portion of the Anacostia



River is receiving more oxygen demanding wastes than it can assimilate



during the months of July, Augost, and September.



     While nutrient concentrations, both nitrogen and phosphorus, are



manyfold above the minimum level associated with excessive algal blooms,
-------
                                                                  rv -  2
the growths are not as pronounced as those of the  1950's as reported
by Bartsch  [ 2 } and Stotts and Longwell  [ 3 ].  Reduction in algal
growths can be primarily attributed tc lack cf light penetration
resulting from high turbidities and to the elimination of discharges
from the Bladensburg waste-water treatment facility of WSSC0
     Preliminary analysis of the assimilation and  transport capacity
of the tidal system was made using two separate mathematical models
developed by Ihomann [ /i ] and by Water Resources  Engineers, Inc.,
(WRE) [ 5 L  The segmentation of the tidal system for the Thomann
model is shown in Figure VIII. with detailed data presented in
Table IV„  Detailed explanation of the two mathematical models is
beyond the scope of this report.
A.,  STREAM FLOW - vfASTEWATER. FLOW ANALYSIS
     Water quality standards are applicable to river discharges
equal to or greater than the 7-day low flow with a recurrence inter-
val of once-in-ten-years „  For- the Anacostia tidal system this flow
is 8 cfs.
     For 1968 and the three population benchmarks, the wastewater and
river discharges including the ratio of west-ewater stream discharge
are presented below:
Year
1970
1980
2000
River
Discharge-*
(cfs)
8
8
3
Wastewater
Discharge
(med)
55
78
88
Ratio of Waste to/Stream
19.6
15.1
17.0
Dis charge



2020          8              99                        19.2
* 7-day low flow with recurrence interval of once-in-ten-years
-------
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                                                                  IV - 5






B.  RESIDENCE OP  FLUSHING TJME



     Assuming a base flow of 8 cfs and wastewater discharges of 50, 100.



and 150 mgd  and the  volume cf the tidal system of 540,000,,000 cubic feet,



the residence time of the Anacostia as given below has been computed by



a volume displacement analysis and by using the WRE mathematical model;
River
Flow
(cfs)
8
3
*
, V
O
Wastewater
Dia
Lst&l
0
77
IK
2:>L
charge
(mgd j
0
50
100
150
Computed
Total Residence
Flow Time
( cfs .' vdays ;
8 781
35 7 <
162 38
<
-------
                                                                  IV - 6
Therefore, there will be very little effect under low flow conditions



on the oxygen resources of the .main Potomac from a discharge in the



Anacostia at the site investigated.
-------
                                               o
9NINIVW3M %
-------
                                                                 IV -

C.  TIDAL HYDRODYNAMICS
     The cross-sectional area of the Anacostia tidal system can be
mathematically expressed by the following equation:
     A   -  A  /»ax
     Ax  -  Ac e
     where:
     Ax  =  cross-section at point x
     Ao  =  cross-section at x = o
     a   =  exponent (slope of curve describing A as function of x)
     x   -  distance along the river
Using the above expression, the steady-state equation for a conserva-
tive substance was used to determine the dispersion coefficient
required in the Thoinann mathematical model.  The equation is given
below:
     Cx  =  Co e    Q       (l-e-ax)
                 a   A0 E
     where:
     Cx  =  concentration at point x
     Co  =  concentration at x = o
     E   =  dispersion coefficient
     Other variables as previously defined
     Two methods of determining the dispersion coefficients are by
use of either salinity or dye tracer data.  However, since this area
is not saline and since the dye study, which was initiated in the
latter part of April 1970 would not be completed in time for this
report, alkalinity data were utilized for dispersion studies.  The
-------
                                                                IV - 9






natural alkalinity difference of about 50 mg/1 between the Potomac and



the Anacostia was adequate for this purpose and incorporated into the



above formulations.  Dispersion coefficients, for the various jnodel



segments throughout a range of river discharges, are given in Figure X.



     For total river discharges of 58, 108, and 208 cfs, the effect of



the dispersion coefficient on the simulated profiles using the Thomann



steady state model can be seen in Figures XI, XII, and XIII, respec-



tively.  At the higher flows, the effect on the simulated profile is




not as significant as during lower flows.



     Figure XIV shows simulated profiles for various wastewater dis-




charge rates using the Thomann model with the dispersion coefficients



as given in Figure X and considering a conservative pollutant.  A



sharp decrease in the simulated profile occurs at model segment 8 or



at the lower end of Kingman Lake.  The volume of the tidal system



increases rapidly in this reach„



     Simulated profiles for a nonconservative pollutant such as BOD,



as presented in Figure XV, show an even smaller response to the dis-



persion coefficient.  The sensitivity of the nonconservative simulated



profile to the decay rate of a pollutant is also an indication of a



high residence time in the tidal system.



     Expanded scale simulated profiles for conservative and noncon-



servative pollutants are shown in Figure XVI.  A 1000 Ibs/day discharge



at the site investigated will increase the concentrations of



conservative and nonconservative pollutants in model segment 8 to
-------
                                                                 IV - 10





approximately 0.5 and 0.2 mg/1, respectively.  Dissolved oxygen in this




segment is the most depressed, often with concentrations near 1.0 rng/1



under summer conditions.
-------
          DISPERSION COEFFICIENT  v»  FLCW
            ANACOSTIA  TIDAL RIVER SYSTEM
                 1969 DC ALKALINITY DATA
	INTERFACE NUMBER
              10
              RIVER DISCHARGE -
100
IOOC
-------
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                              (I/6")  INVinTOd  JO NOUV«iN3DNOD
                                                                    Figure  ''III
-------
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( I/6") INVinnOd JO NOliVMiN3DNCO
                                   Figure 
-------
                                 M3AW DVWOlOd

(!/••) INVimiOd JO NOI.WUN3DNOD
                                  Figure  XV
-------
                                                                 IV - 17






D.  SELF-PURIFICATION AND THE DISSOLVED OXYGEN BUDGET



     In the tidal system, carbonaceous and nitrogenous BOD from land



runoff, storm sewers, defective sanitary systems was large enough



at times to depress tire DC below 2.0 aig/1 in the area of Klngman Lake.



     Preliminary model .studies Vising the Y/RE hydrodynamic model indi-



cate that even with large wastewater discharges, there would be no



appreciable increase in self-purification or reaeration rates because



of insignificant changes in the advective tidal velocities,,  Hence, it



appears that a discharge into the Anacostia would have to contain a



BOD (both carbonaceous and nitrogenous) concentration equal to or lower



than that currently found in the tidal system.  For the critical months,



the effluent should be renovated to have a BCD5 of 2.0 to 4.0 and an



unoxidized nitrogen concentration of 0.5 to 1.0 mg/1.



     Another important aspect of the v/astev.^ter treatment facility in



terms of watej: quality enhan:ement. of the receiving water will be the



DO in the final effluent.  For a wastewater discharge of 100 mgd,



nearly all of the advective rivrer flow will be from the wastewater.



Therefore, a minimum of -4.0 mg/1 should be maintained in the final



effluent at =511 times.  If & c 0 mg/1 concentration of DO is maintained



in the effluent, along with a low oxygen demand, the wastewater could



enhance present water quality in the Anacostia River.



     An example of this enhancement c^n be readily shown by utilising



the simulated curves in Figure XVJ.  With an effluent DC' of 4.0 mg/1,



the DO at the critical sag point will be increased by 2.0 mg/1



(0.5 x 4.0) with resulting DO being about 3,0 mg/1.  If the effluent
-------
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s

K
                                                                                                 LU

                                                                                                 CC.

                                                                                                 I
                                                                                                 
-------
                                                                 IV - 19
has 6.0 ing/1,--or approximately 5,000 Ibs/day of oxygen, the DO at the




critical point will be increased by approximately 3.0 mg/1.  This



assumes that reaeration from the atmosphere is equal to the oxygen



demand of the wastewater (The DO during the summer months of 1969.was



about 1.0 mg/1 in this area).  The resulting DO in the system from



the 6.0 mg/1 would then be approximately 4.0 mg/1 (3.0 + 1.0), thus



meeting the DO water quality standard.
-------
                                                                  IV - 20






E.  NUTRIENTS AND ALGAL GROWTH




     As indicated earlier in this chapter, algal growths were abundant




in the Anacostia in the 1950's.  Lark of nuisance blooms during the




spring and summer months in the I960'? appear to have been a result of




low light penetration snd the elimination of the Bladensburg Wastewater




Treatment Facility.




     If a wastewater effluent of 100.mgd of highly treated effluent




including low turbidities were to be discharged into the Anacostia




above the D,,r. .-Md. Line, a significant increase in light penetration




will occur.  Such an increase could cause nuisance algal growth in




the Anacostia„




     To reduce the incidence and magnitude of nuisance algal growth




in the upper Potomac tidal system, upper limits of 0.1 and 0.5 mg/1




of phosphorus as P and nitrogen respectively were used to calculate




maximum permissible nutrient loadings from wastewater discharges.




Since most of the a directive flow would be from wastewater, the




nutrient concentrations in any Anaeostia effluent should be similar




to these limits.  Allowing for possible continued reduction in




light penetration, a range of these nutrient limits was utilized.




The phosphorus limits vsed were 0,1 t.c 0.2 mg/1 with nitrogen




limits of 0.5 to 1.0 mg/1.
-------
                                                                 IV - 21


F.  TREATMENT' AT THE BLUE PLAINS PLANT VERSUS CONSTRUCTING A FACILITY
    IN THE ANACQSTIA VALLEY

     The Potomac River-Washington Metropolitan Area Enforcement Con-

ference on May 8, 1969, agreed upon a BOD loading of 16,500 Ibs/day,

a nitrogen loading of 8,000 Ibs/day, and a phosphorus loading of 740

Ibs/day.  Based on 1968 contributions, the Blue Plains Treatment Plant

was allocated 12,700, 6,130, and 560 Ibs/day of BODj, nitrogen, and

phosphorus, respectively.  Using the current loading rates and popu-

lation projections, the removal percentage and effluent concentrations

were determined as given below:

                  1970              1980                2000
               Q = 232 mgd       Q = 309 ffigd         Q = 419 nigd
                      Cone.             Cone.               Cone.
            Removal   Effl.   Removal   Effl.    Removal    Effl.
              (%}     (we/I)    (%}     (me/1)     (%)      (me/1)
BOD5
Nitrogen
Phos . as P
95.8
Sf>.6
96.6
6,50
3.20
0.28
97
90
97
4.90
2,40
0.22
98
93
98
3.60
1.80
0.16
     The effluent from the 419 mgd facility would have to be renovated

to such a high degree, except for nitrogen, that it could be considered

as approaching ultimate was tews ter treatment (IJWT*).
  Ultimate wastewater treatment 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
  intended use of the water resource due to the lack of needed
  assimilative or transport capability of the stream.
-------
200.0
11.0
22.0
2.0
0.1
0.5
- 4.0
- 0.2
- 1.0
98 - 99
98 - 99
96 - 98
                                                                 IV - 22


     Wastewater constituents before treatment, effluent concentrations,

and percent removal requirements for a discharge into the Anacostia at

the site investigated are presented below:

                Wastewater Constituents       Effluent         Percent
Parameter         Before Treatment          Concentrations      Removal
                       (mg/l)	        (mg/l)        Requirements

BOD5

T. Phosphorus
   as P

T. Nitrogen
   as N

     In incorporating UWT into a water quality management program, the

effluent standard concept is utilized.  For receiving waters such as

the tidal portion of the Anacostia River, this concept appears to be

realistic under present conditions to enhance the dissolved oxygen

resources and to prevent nuisance algal growths.

     If an effluent of this quality is maintained during the critical

times of the year, the UWT concept cnn be applied to the tidal portion

of the Anacostia River.  With this concept, the effluent will be of

higher quality than the existing water quality in the Anacostia and

thus will enhance the water quality providing a positive water quality

management approach.

     Even with the high waste removal requirements, a major uncertainty

is the possibility of nuisance algal blooms stimulated by favorable

growing conditions in the tidal system.  Data obtained by CTSL from

the tidal waters of the Anacostia, which are shallow, with little
-------
                                                                 IV - 23






freshwater inflow and insignificant transport indicate that such areas




have higher growths at the same nutrient levels for a given area than



along the main stem of the Potomac.  While light penetration inhibition




may reduce this potential somewhat in the Anacostia, nevertheless, the



potential remains.  Discharges into the main Potomac have a decreased



algal growth potential per square foot area because of the greater



depths.




G.  Continuing Studies



     Additional studies relating to (l) tidal dispersion characteristics



of the Anacostia River, (2) water quality interactions between Kingman



Lake and the Anacostia River, and (3) further definition of the DO



budget including reaeration rates and benthic demands are already in



progress or will be initiated by CTSL in the coming months.



     As mentioned earlier in this report, a dye tracer investigation of



the Anacostia River was conducted from April 22-28, 1970.  While the



data collection phase of this study has not been completed, preliminary



analyses indicate that (1) dye movement and residence time closely



parallels mathematical model predictions, and (2) a considerable dye



buildup was observed in Kingman Lake which further demonstrates that



its water quality is significantly dependent on the Anacostia's quality.



The final results of this dye study will be incorporated into the next



progress report for the Potomac River-Washington Metropolitan Area



Enforcement Conference.   They will also be published in a separate



report entitled "Potoraac-Anacostia Rivers Dye Studies."
-------
                                REFERENCES

1.  Jaworski, N. A, "Water Quality and Wastewater Loadings Upper
    Potomac Estuary During 1969," Chesapeake Technical Support
    Laboratory, Federal Water Pollution Control Administration,
    Technical Report No. 27, November 1969.

2.  Bartsch, A. F., "Bottom and Plankton Conditions in the Potomac
    River in the Washington Metropolitan Area," Appendix A, A report
    on water pollution in the Washinton metropolitan area, Interstate
    Commission on the Potomac River Basin, 1954.

3.  Stotts, V. D. and Longwell, J. R., "Potomac River Biological
    Investigation, 1959," Supplement to technical appendix to part
    VII of the report on the Potomac River Basin studies, U. S.
    Dept. HEW, 1962.

4.  Thomann, Robert V., "Mathematical Model for Dissolved Oxygen,"
    Journal of thjg Sanitary Engineering Divisionf American Society
    of Civil Engineers, Proceedings Paper 3680, Vol. 89, No. SA5,
    October 1963.

5.  Orlob, G. T., R. P. Shubinski and K. D.  Feigner, "Mathematical
    Modeling of Water Quality in Estuarial Systems," Proceedings of
    the National Symposium of Estuarine Pollution, Stanford
    University, August 1967.
-------
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-------
                            APPENDIX C (continued)


Station Description;

          1          Intersection of stream and Anacostia,  north of
                      Worth Kingman Lake bridge.
          2          Kingman Lake,  north of northmost island.
          3          Kingman Lake,  northeast corner of third northmost
                      island,  first above bridge,
          h          Kingman Lake,  just north of Banning bridge.
          5          Kingman Lake,  west side of island,  between stone outfall
                      and drainpipe.
          6          Klngraan Lake,  east side of southmost island.
          7          Kingman Lake,  just south of East Capitaol Street Bridge.
          8          Kingman Lake,  north of locks, east of hospital.
          9          Anacostia River, south of locks.
         10          Anacostia River, south of Benning bridge.
-------
Chesapeake Technical ^uprori. l,abora;o>
         Kiddle Atlantic Region
 Federal Water ', ualicy Administration
  U. S. Derartrrent of the Interior
   CURRENT WATER QUALITY CONDITIONS

      AND INVESTIGATIONS IN THE

   UPPER POTOMAC RIVER TIDAL SYSTEM


       Teci.T.ical Report No. kl
     Johan  A.  Aalto,  Chief,  CTSL
     Norbert A.  Jaworski,  Ph.D.
     Donald W. Lear,  -jr.,  Ph.D.

              May 1970
-------
                                        TABLE OF CONTENTS

fc

  *•
                                                                           Page

L
*           LIST OF FIGURES   .....................      iv
  3fc

}.            LIST OF TABLES    .....................       v


  'In          Chapter


                I    INTRODUCTION  ...................       I- 1


  *"           II    SUMMARY   .....................      II- 1


              III    DESCRIPTION AND LOCATION INDEX OF THE
  **                   POTOMAC RIVER TIDAL SYSTEM  ...........    Ill- 1


                     A.  General Description  .............    Ill- 1
  «w
                     B.  Location Indexes   ..............    Ill- 1


  '                       1.  Reaches of Potomac River Tidal System   .  .    Ill- 3


                         2.  Zones of Upper Potomac Tidal System  .  .  .    Ill- 3


   **           IV    WATER QUALITY CONDITIONS   ............      IV- 1


                     A.  Upper Potomac River Tidal System    ......      IV- 1

   te
                     B.  Potomac Tributaries  .............      IV- 5


 *              V    CURRENT ACTIVITIES   ...............       V- 1
   m

                     A.  Wastewater Composition ............       V- 3
 I
   *»                    1.  Historical Trends  ............       V- 3


  t                       2.  Evaluation of Sources  ..........       V- 3

   *»
                     B.  Nutrient Response Studies  ..........       V- 7


  '                       1.  Biological Discontinuity Studies  .....       V- 7
   **

                         2.  Ecological Treads as Related to
  i                             Nutrient Loadings   ...........       V- 9
                                                 ii
-------
                                      TABLE OF CONTENTS (Continued)
**         Chapter
              REFERENCES
              V     CURRENT ACTIVITIES (Cont.)




                    C.  Nutrient Transport  ..............     V-14




                    D.  Dissolved Oxygen Budget ............     V-18




                    E.  Embayment Studies   ..............     V-19
                                                iii
-------
                             LIST OF FIGURES

Number
  1          Wastewater Discharge Zones in
               Upper Potomac Estuary	   Ill- 2

 II          Potomac River Tidal System   	   Ill- 4

III          Nutrient Enrichment Trends and
               Ecological Effects in the Upper
               Potomac Tidal River System   	     V-10

 TV          Total P as PO.  Isopleth	     V-15
                                iv
-------
-------
                             LIST OF TABLES
Number

  I          Zones of Upper Potomac Estuary   	    Ill-  5

 II          Fecal Coliform Densities - Upper
               Potomac River Tidal System  	     IV-  3

III          Fecal Coliform Summary -
               Potomac Tributaries    	     IV-  6

 IV          Wastewater Loading Trends - Washington
               Metropolitan Area   	     V-  5

  V          BOD,, Carbon, Nitrogen arid Phosphorus  -
               Summary of Contributions  	     V-  6

 VI          River Discharge and Phosphorus Loading   .  .  .     V-16
-------
                                                                  I- 1
                                CHAPTER I
 ,(,



                               INTRODUCTION






     During the November 1969 progress meeting of the Potomac Washington




Metropolitan Area Enforcement Conference, information was presented on




water quality conditions and wastewater loadings in the upper Potomac




tidal system during 1969-  At the spring meeting of the Interstate




Commission on the Potomac River Basin (ICPRB) at Indian Head, Maryland,




April 16-17, lv^70, a summary statement was presented giving data on




waste loadings, water quality, and studies by the Chesapeake Technical




Support Laboratory on the middle and lower Potomac estuaries as part




of the joint stud;/ proposed in Recommendation Ik of the conference.  A




detailed oral presentation was also given by Dr.  Lear on the "Ecology




of a Eutrophic Estuarine Discontinuity."




     Since there were no significant changes in water quality conditions




and wastewater loadings as of November 1969> this report will concentrate




on the status of investigations currently being conducted by the Chesa-




peake Technical Support Laboratory.  Specific references will be made to




the Potomac-Pi scataway and the Artacostia wastewater assimilation and




transport studies.  Separate reports on both of these studies have been




prepared and are available.
-------
                                                                 IT- 1




                               CHAPTER II




                                .SUMMARY






     Based on data obtained by rc-rjonnel of the U. S. Geological Survey,




Dalecarlia Filtration Plant, U. 5. Army Corps of Engineers, D. C. Depart-




ment of Sanitary Engineering (DCDSE), D. C. Department of Public Health




(DCDPH), Chesapeake Technical Support Laboratory (CTSL) of the Federal




Water Quality Administration (FWQA) and the several wastewater treatment




agencies in the Washington metropolitan area, a statement on current




water condition- and investigations of the upper Potomac Eiver tidal




system was prepared and is summarized below:




     1.  Fecal coliform densities in the area of Woodrow Wilson Bridge




continue to be significantly lower as a result of the increased chlori-




nation of treated waste discharges initiated in June-September 1969-




For example, during the months oi Tare, July, and August 196}* the median




density was about 90,000 MPN/100 ml, while from September 19b9 to April




1970, over 50 percent of the samples had fecal coliform densities less




than 1000.




     2.  High fecal coliform densities were prevalent at times of high




stream flow in the portion of the Potomac from Chain Bridge to Memorial




Bridge, which it atove the major wastewater discharges.  These high




densities can be attributed to a combination of land runoff from the




upper Potomac basin,  urban runoff, storm sewers and combined sewer




overflows.




     3-  Tributaries  of the Potomac in the Washington metropolitan area




also contained very high fecal coniform densities at times.   Cabin John
-------
                                                                 II- 2



Creek had consistently high counts  in 1969 with 25 out of 23 samples




showing fecal  coliform densities  over 10,000.




     k.  A Potomac Estuary Technical  Committee was formed to provide




guidance and coordination in the  study of water quality problems of




the upper Potomac River tidal system.




     5.  Studies by  CTSL are continuing in three major areas: (l)




nutrient ecological  responses,  (2)  nutrient transport, and (3) oxygen




budget resources.




     fj,  During Februar,,  and Mar..:,  in 19^9 and again in 197(3? extensive




rnytoj'laiihtoi'  blooms were detected  in the Potomac from Smith Point to




Gunston Cove.




     "'.  Under 5j_jmner  ci>: di tior.r  massive blooms of blue-;r',-cn algae were




prevalent from Fort Washington  to Maryland Point.   T; e de.':sities of




these blooms were about ;> to 10 'Ames  ',hat reported in mos'- otf er




e~j troi >h. i c warer5, .




     3.  Preliminary resiJ.ts  of ecological studies of the  Potomac est-iary




in the area immediately above tne Rout;e 301 Potomac River  Bridge indicate




that the decrease in ohe macsive  blae-green algae,  Anac^stis, is inter-




related to (l) the increase  of  saliraty from about 2,000 to 10.000 ;-i.:i.




(2) the decline ir. nutrients, mainly  phosphorus and nitrogen, and (3) the




competition for available nutrients by the  dominant marine communities




in the area below the Route  301 Bridge.




     9-  Since the late  1930'3  the amount  of phosphorus  entering -one




Potomac from wastewater  discharges in the  Washington metropolitan area




has increased aboat tenfold and nitrogen increased about fivefold.
-------
                                                                 II-3




The amount of BOD (carbon) since then,, although increasing to about




200,000 Ibs/day in 1957, has decreased to about 129,000 Ibs/day in 1969.




     10.  The major shift from the balanced ecological communities in




the Potomac toward nuisance blue-green algal growths appears to be




related to increases in nitrogen and phosphorus, and not BOD (carbon).




This shift in ecological communities has also been simulated in controlled




studies.




     11.  Nutrient data Irom March 196'? suggest that while large phosphorus




loadings enter the Potomac estuary during extremely high discharge from




the river upstreain,  the effect appears 10 be a decrease rather than an




increase in concentration in the upper Potomac tidal system.  Most of




the phosphorus which entered the tidal system from the upper basin,  plus




some in the system from the wastewater discharges,  was adsorbed and depos-




ited in the bottom sediments of the estuary.




     12.  Studies of nitrification rates suggest that the oxidation of




ammonia nitrogen is r.ot a significant factor in the oxygen budget when




the water temperature is below 10°  C.  Studies are continuing to determine




the effects of nitrogen on the eutrophication aspects.




     13-  Dye and mathematical model investigations of the Piscataway



embayments and the Anacostia tidal system indicate that wast,ewater assimi-




lation and transport rates are very low.  Wastewater discharges into the




embayments of the Potomac may require higher removal rates than those




required by the enforcement conference.




     Ik.  An analysis of each individual embayment will be required before




wastewater treatment levels can be determined.
-------
                                                                 Ill- 1
                              CHAPTER III
                     DESCRIPTION AND LOCATION INDEX
                  OF THE POTOMAC RIVER TIDAL SYSTEM
A. , GENERAL DE3CRIPTI01I

     The Potomac River Basin is the second largest watershed in the

Middle Atlantic States.  Its tidal portion begins at Little Falls in

the Washington metropolitan area and extends 11^ miles southeastward

to the Chesapeake Bay.

     The tidal system is several hundred feet in width at its head near

Washington and t-roade-is to nearly six miles at Its mouth.  A shipping

channel with a nil r.imurn depth of 2k feet is maintained upstream to

Washington.  Except for the channel and a few short reaches where depths

up to 100 feet are found,  the tidal system is relatively shallow with

an average deptn of about IB feet.

     Effluents from "twelve major wastewater treatment plants, with a

thirteenth under construction, serving a population of about 2,500,000

people, are discharged into the upper tidal system.  The locations of

the discharges from these treatment facilities are shown in Figure I.

B.  LOCATION INDEXES

     To achieve uniformity in locating water quality sampling stations,

wastewater effluents and related activities, a detailed location index

was developed for the entire Potomac River tidal system.  A starting point

at the confluence of the Potomac with the Chesapeake Bay was established.

Uniform river mile locations using statute miles have been developed for

the primary sampling stations, landmarks, navigation buoys, etc.  The

data will be published by  the CTSL in the near future.
-------
                                             ZONE  I
                                  MILES fVjM  ' HAiN  6RIDGF - 15
                                          ANDREWS A.F.B.
                                  MILES  'ROM CHAIN 3RIDGE : 0
                        (STRICT OF COLUMBIA
                                             ZONE   II
                             P .'LR MILES  FROM CHAIN BRIDGE - 30
WASTEWATER DISCHARGE ZONES
   '  m UPPER  POTOMAC ESTUARY
ZONE   III
                                 MILES FROM  CHAIN  BRlOGE = 45
                                           FIGURE-I
-------
*                                                                          III-  3


 *         1.  Reaches of Potomac River Tidal System

               For discussion ana investigative purposes, the tidal portion of

          the Potomac River has been divided into three reaches as shown in

          Figure II and described below:
 t
      *~^     Reach         Description           Hiver Miles        Volume  ft
 I         \                                                      cu. ft.  x 10°
 JH«          "^
  t          i
            '   Upper      From Chain Br. to      Uk.k to 73-8           93-50
                            Indian Head

 *   /'       Middle     From Indian Head to     73-8 to Vf.O          362.28
                            Rt. 301 Bridge

 »             Lower      From Rt. 301 Bridge     Vf.O to 00.0         175^-7^
                            to Chesapeake Bay

 n             The upper reach, although tidal, contains fresh water.  The middle

          reach is normally the transition zone from fresh to brackish water.  In

  tof
          the lower reach, chloride concentrations near the Chesapeake Bay range

          from about 7,000 to 11,000 mg/1.
 M
          2.  Zones of Upper Potomac Tidal System

  w            To facilitate determination of water' quality control requirements,

          the upper estuary was segmented by the CTSL into 15 mile zones beginning

  *       at Chain Bridge.  Establishment of zones similar in physical character-

          istics allows flexibilitv in developing control needs.  This zone concept
  Mr
          was adopted by the conferees of the Potomac Enforcement Conference on

  ^       May 8, 1969.

               River mile distances from both the Chesapeake Bay and Chain  Bridge

  *"       for the upper three zones are given in Table I as well as in Figure II.
-------
                                               Ill- 4
CHAIN WIOOC
    N
         POTOMAC RfVER TIDAL SYSTEM
                                            FIGURE -H
-------
                                                                     Ill- 5
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-------
                              /
                                CHAPTER IV
                         WATER QUALITY CCSDITIONS

A.  UPPER POTOMAC RIVER TIDAL SYSTEM
     During the November 19&9 progress meeting, it vas reported that
there had been a significant  reduction  in the fecal coliform densities
in the area of Woodrow Wilson Bridge [1].  This was a result of the
Installation of effluent chlorination facilities at all major wastewater
treatment plants during June-September 1969.
     Fecal coliform records at four stations in the Washington metro-
politan area of the Potomac River, as summarized in Table II, support
this November conclusion.  Fecal coliform densities continued to be high
during periods of considerable runoff in the area from Chain Bridge to
Hains Point.  These high counts can be attributed to (l) land runoff
from above and below Chain Bridge, (2) storm sewer discharge, and (3)
malfunctioning sanitary sewer systems.
     Nevertheless,  there continues to be a significant reduction in fecal
coliforms from previous years in the treatment plant discharge area.  As
an example,  in 1965 the median fecal coliform counts near Woodrow Wilson
Bridge was about 90;COO MPN/100 ml for the months of June, July and August,
Since September 1969, over 50 percent of the samples had fecal coliform
counts of less than 1000.
     There has been no significant change in dissolved oxygen readings in
the Potomac estuary since November 1969-  During the winter and spring
-------
                                                                  IV-  ?.
months, freshwater flows were near or above normal with the April  flows:




at about twice the median flow.  As a result of the higher flows and  low




winter and spring temperatures, the dissolved oxygen (DO) concentrations




were above 8.0 rag/1.




     DO concentrations were about 5.0 mg/1 for the first week of Kay  1970




with a river di;--charge of 15/000-20,000 cfs .  This can be compared Lo




DO concentrations of less than 1.0 mg/1 at the Woodrow Wilson Bridge  j •:.




early May 19^ when a fish Kill occurred.
-------
                                                    IV-  3

                  TABLE II
    FECAL COLIFORM DENSITIES MPN/100 ml
     Upper Potomac River Tidal System
B.C. Water Pollution Control Division Data
         April 1969 - April 1970
Date
4- 7
4-21
5- 5
5-12
6- 2
6-18
6-23
6-30
7- 7
7-14
7-28
8-11
8-18
8-25
9- 1*
9- 8
9-15
9-25
9-29
10- 6
Chain Bridge
--
--
--
--
—
—
--
--
—
23
4,300
4,300
1,100
1,500
230
2,400
15,000
150
360
730
Memorial Bridge
930
210
150
150
240,000
9,300
2,400
750
11,000
36
240,000
4,300
3,000
360
230
93,000
4,300
230
23
no
Opposite
Blue Plains
910
93,000
2,300
73,000
4,300
9,300
230
360
2,300
230
93,000
7,300
1,500
910
360
7,200
9,300
2,100
230
730
W.Wilson
Bridge
9,100
360
3,600
--
2,300
3,600
2,300
3,600
4,300
1,500
24,000
11,000
36c
230
230
9,300
9,300
360
230
360
-------
TABLE II (continued)
                                   IV- 4
Date
10-20
10-29
11- 3

11-11
11-17
11-24
12- 1

12- '8
12-15
2- 2
2- 9
2-16
2-23
3- 2
3-16
3-23
3-30
4- 6

4-13
^hain Bridge
23
23
L-)
^3
93
930
^,300
po
cj
2,400
1,200
24,000
^,300
2,400
2,400
150
73
930
4,300


2,400
Memorial Bridge
23
36

930
93
430
4,300

73
24,000
1,500
110, 000
2,400
15,000
2,400
230
430
930
2,400

430
430
Opposite
Blue Plains
9,300
230

930
1,500
^,300
930

910
36
2,400
110, 000
^,300
46,000
9,300
240
1,500
230
9,300

430
36
W.Wilson
T) • ~t
jjridge
360
23

910
36
23
*~ ~J
150

150
43
11,000
110, 000
9,300
92,000
2,400
23
1,500
4,300
15,000

430
~J v
430
-------
                                                                             IV-5
t'            B.   POTOMAC TRIBUTARIES
                  In the previous section,  fecal coliform counts were shown to be




             high during times of high runoff.   Sampling data for tributaries of




             the Potomac taken by the D.  C.  Department of Public Health in 1969




             also show high counts as given in  Table III.   The locations of the




             six stations in the table are:




                  Tributary              Sampling Point         Miles from Potomac




             Cabin John (Md.)        G. Washington Parkway             0-3




             Rock Run (Md.)          David  Taylor Model Basin          0.7




             Seneca Creek (Md.)      River  Road                        0.7




             Broad Run (Va.)         Leesburg Turnpike                 2.0




             Sugarland Run (Va.)     Leesburg Turnpike                 0.5




             Difficult Run (Va.)     Old  Georgetown Road               1.0




                  For the months of June, July,  August,  and September,  high i'ecal




             coliform densities were observed for all six stations.   The data for the




             Cabin John station show high densities' the year round,  suggesting a




             periodically overloaded sanitary sewerage system in this watershed.




                  Data for other urban streams  in the Washington metropolitan area,




             such as Rock Creek as reported by  Aalto,  et al [2j,  and Anacostia River




             by  Jaworski et aJL [3],  also  indicated high fecal coliform densities.




             While increases in fecal coliforms  occur during periods  of high flow,




             the large increases were usually associated with either  combined sewer




             overflows or defective sewerage systems.
-------
                                             TV-
             TABLE III

 FECAL COLIFORM SUMMARY - MFN/100 ml

        Potomac Tributaries
D.C. Department of Public Health Data
               1969
Date
01-08
01-15
02-05
02-12
02-19
04-09
04-16
04-23
04-30
05-07
05-14
05-21
06-04
06-11
06-18
07-09
07-23
08-13
08-27
Cabin John
250,000 +
250,000+
250,000+
400, 000
25, ooo
25,000
250,000
25,000
250, ooo
250, ooo
25,000
200, 000
250, ooo
6,000
25,000
25, 000 ^
25, ooo
170, ooo
120, 000
Reck Run
25, ooo
6,000
1,200
400, OCO
2,500
250
1,200
7,000
4,000
12, 000
500
250
30, ooo
600
2,500
6, ooo
30,000
25,000
60,000
Seneca
Creek
—
5,000
400
400, 000
1,200
250
1,200
2,500
500
6,000
1,700
200, 000
250, ooo
4,000
2,500
1,700
250, 000+
6,000
25,000+
Broad Run
600
4, 000
500
250
600
400
250
2,500
4oo
_-
1,300
1,200
60,000
600
4,000
25, 000+
60, 000
2,500
4,000
Sugar land
Run
4,000
17,000
10, 000
— ..
2,500
4,000
2,500
3,000

6,000
6,000
5,000
120, 000
25,000
4,000
40, 000
250, 000+
25, 000
120, COO
Difficult
Run
250
6,000
1(00
4 00
600
400
600
7, 000
6oc
1, 20-'1
6,000
60, ooo
120,000
4, noo
4, ooo
1, 700
250, 000+
4, ooo
7
12, 000
-------
                                                             iv- r

                              TABLE III (Continued)

                                Seneca              Sugarland  Difficuli
Date    Cabin John   Rock Bun   Creek    Broad Run     Run        Run
09-03
09-10
09-24
10-01
10-08
10-22
n-o4
12-09
12-16
4,000,000+
4, 000, 000
120,000
12,000
25,000
12,000
12,000
1,600
4,000
400, 000+
6,000
6,000
40,000
6,000
4,000
0
2,500
60
250, 000+
25,000+
3,500
1,700
4,000
6,000
200
7,000
400
7,000
4,000
1,100
2,900
1,700
4,000
50
1,200
1,700
250, 000+
6,000
12, 000
25, ooo
60,000
250, 000+
4,000
40,000
4,000
250, 000+
12, 000
1,700
2,500
7,000
4,000
2,500
1,700
1,700
-------
                                                                 V- 1



                                CHAPTER V




                            CURRENT ACTIVITIES





     Studies to investigate the nutrients that stimulate algal




growth and to determine the major driving forces producing dissolved




oxygen stresses are continuing.  The objectives of the ecological,




nutrient transport, and dissolved oxygen budget studies are to:




(l) determine the extent of present water quality degradation, (2)




develop predictive capabilities for stresses from projected loadings,




(3) determine the corrective actions required, and (k) evaluate the




detailed ecological pattern during changes resulting from selective




nutrient reductions .




     Other tidal waters of the Chesapeake Bay are also currently being




monitored to provide a basis for comparison.  These waters include




the Patuxent, Rappahannock, Chester, and Severn Rivers, and the upper




Chesapeake Bay itself.




     To provide input and guidance for the CTSL program in studying




the Potomac, a Potomac Estuary Technical Coordination Committee (PETCC)




was formed, with the first meeting held in November 19&9•   Members of




PETCC include individuals from Maryland Department of Water Resources,




Maryland State Department of Health, ICPRB,  Maryland-National Capital




Parks and Planning Commission, Virginia Water Control Board, Virginia




Department of Economic Development, DCDPH, DCDSE, U.S. Army Corps of




Engineers, and FWQA.
-------
                                                                 V-
     This chapter presents specific areas currently being investigated.




Included are recent findings within each of five study areas: wastewater




composition, nutrient response, nutrient transport, dissolved oxygen



budget, and discharges into embayments.
-------
                                                                 V- 3
A.  WASTEWATER COMPOSITION




1.  Historical Trends




     While the population in the Washington metropolitan area increased




eightfold from 1913 to 1969 as shown in Table IV, the phosphorus content




in the waste discharges increased almost twentyfold.  For the same time




period the nitrogen loadings have increased about ninefold, from 6,kOO




to 52,000 Ibs/day, while the BOD's have increased from >8,000 to over




200,000 Ibs/day in the late 1950's.  Since I960 the BOD loading has been




reduced to 129,000 Ibs/day.




     The twentyfold increase is a result of the rapid increase in use




of detergents high in phosphorus content since the 19^0's in place of




the soap products formerly used in household cleaning usage.  At the




present time approximately 50 to TO percent of all phosphorus in




municipal waste discharges can be attributed to the use of detergents [17]




2.   Evaluation of Sources




     As previously reported [l] CTSL conducted a nutrient survey of the




upper estuary during 1969 to determine the relative contributions of



critical water quality parameters  from the upstream freshwater inflow




and wastewater discharges in the metropolitan area.   The loadings for the




first eight months are given in Table V and a summary of the relative




percentages follows:
-------
                                                                 v- u


Parameter                 Freshwater Inflow            Wastewater Discharge
                             % of total% of total

BOD                              45                             55

Organic Carbon                   68                             32

Inorganic Carbon                 89                             11

Total Carbon                     80                             21

Total Phosphorus                 1^                             86

Total Nitrogen                   3^                             66

     This summary shows that the parameters in order of most amenable to

control measures using wastewater treatment are: (l) phosphorus, (2) nitrogen,

and (3) BOD.
-------
                                            V- 5
           TABLE IV
' Wastewater Loading Trends*
     Discharge to Potomac
Washington Metropolitan Area


Year
*•""*•»••»•
1913
1932
1944
1954
1957
I960
1965
1968
1969

Population
of
Service
Area
- 	 ___
320, 000
575,000
1,149,000
1,590,000
1,680,000
1,860,000
2,100,000
2,415,000
2,480,000

Wastewater
Flow

_. (mgd) ^
42
75
167
195
210
222
285
334
Qiift
j*K5
BOD

_ (Ibs/day) __
58,000
103,000
141,000
200,000
204,000
110,000
125,000
130,000

129,000
T. Nitrogen
as N
_ (Ibs/day)
6,400
11,500
22,980
31,800
33,600
37,200
42,000
53,000

52,000
T. Phosphor
as PO,
4
( Ibs/day)
3,300
6,000
12.000
/ v v
16, 700
_7 1 v v
26,000
s v
30, 000
57,000
6l, 000

64, ooo
-------
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-------
                                                                V-  7





B.  NUTRIEM1 RESPONSE STUDIES




     During 19^9, field investigations were continued to further define




the nutrient requirements (carbon, nitrogen and phosphorus) for producing




nuisance algal growths.  Considerable efforts were spent in defining




eutrophic conxli.tdrcfas- iri the salinity transition zone.




     In the freshwater portions of the tidal'system, large blooms of




phytoplankton were observed in February and March of 1969 and again in




1970.  Water temperatures at the beginning of these blooms were about




k° C.  These blooms were primarily in areas between HmJth Point and




Gunston Cove.




     Under 1969 summer and fall conditions as in previous years, large




populations of blue-green algae, primarily Anacystis sp., were prevalent.




An important aspect of these algal growths was that the "standing crop"




as measured by chlorophyll a nad concentrations ranging from approxi-




mate!;,' 75 "to over 200 ^ug/1.   This is about five to ten times that




reportedly observed in most other eutrophic waters [15] Ll6] .




     The algal populations in t; e saline water areas were not as dense




as those in the fresh water areas.  Nevertheless in summer large popu-




lations of the dinoflagellates Gymnodinium sp.  and Amphidinium sp.




occurred producing the phenomenon known as "red tides."




1.   Biological Discontinuity Studies




     During the summer of 1969? a special ecological study was under-




taken in a 20-mile portion of uie Potomac estuary just upstream from




the Potomac River Bridge at Morgantown.  This area has been observed




for several years [10] to be the lower limit in terms of distance from
-------
                                                                V- 8





(Jhain Bridge of massive blue-green algal blooms.   The major purpose of



this intensive study was to determine why algal blooms apparently




decreased at this location.



     The area of investigation was found to be a  reach of rapidly



increasing salinity downstream, the "salt wedge".  An obvious bio-




logical discontinuity was found in this reach  with marine organisms




dominant at the lower end.



     Tentative conclusions from this study indicate:



     1.  The massive blooms or the blue-green alga Anacystis currently



terminate in this reach for three interrelated reasons: (l) the increase



of salinity from approximately 2 to 12 parts per  thousand, (2) a decline



in nutrients, especially nitrogen and phosphorus, and (3) the competition



for available nutrients by the essentially marine dominated biological



community in the lower reach is apparently successful under present



conditions.



     2.  These observations may be useful for predicting the time,



duration and extent of a possible similar invasion of blue-green algae



in other fresh water tributaries at the head of the Chesapeake Bay,



especially the Sassafras, Bohemia, Elk, and Northeast Rivers.



     3-  When firmer conclusions can be drawn from continued obser-



vations, the effects of disposal of nutrients from treated sewage into



saline waters as compared to fresh waters may assist in optimizing the



increase in estuarine water productivity by controlled addition of



nutrients, or at least minimize any stress to the estuarine system



caused by these additions.
-------
-------
 I
I*'
                                                                              V-  9


                  5.   Single  sets  of daily observations were  difficult  to  interpret,


             but the  aggregate  of  15 cruises  over a  six weeks period showed some


             statistically significant patterns.


             2-   geological Trends as Related to Nutrient Loadings


                  A review of past eutrophic  trends  with estimated nutrient loadings


             from wastewater  discharges  into  the Potomac was  made.   In  Table IV it


             can readily be seen that while the present BOD (carbon)  loading is the


             same as  in the late 1930's, there is about ten times a;j  much  phosphorus


             and five tjme^ as  much nitrogen  now being discharged.


                  The effect  of these increased nutrient loadings can be seen  in


             Figure III.   The change in  the ecology  from 1913 has been  dramatic.


             Several  nutrients  and growth  stimulants have been implicated  as causes


             of  this  accelerated eutrophication with nitrogen and phosphorus showing


             promise  of being the  most manageable.


                  The historical plant life cycles in the upper Potomac estuary can


             be  inferred from several studies.  Cumming [k\ surveyed  the estuary in


             1913-191^, and noted  the absence  of plant life'neai- the  major  waste


             outfalls  with "normal"  amounts of rooted aquatic plants  on the flats


             or  shoal  areas below  ;-he urban area.  No nuisance levels of rooted


             aquatic  plants or phytoplankton blooms were noted.


                  In  the 1920's an infestation of water chestnut appeared.   This was


             controlled by mechanical removal  [5] .


                  In September and October  of  1952, another survey of the reaches


             near  the  metropolitan area, made by Bartsch [6],  revealed that  vegetation
-------
                                                            xroe
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                                                                                                     FIGURE -nr
-------
                                                                V-ll





in the area was virtually nonexistent.  No dense phytoplankton blooms




were reported, although the study did not include the areas downstream




where they were subsequently found.




     In August and September of 1959, a survey of the area was made




by Stotts and Longwell [j].   Blooms of the nuisance blue-green alga




Anacystis were reported in the Anacostia and Potomac Rivers near




Washington, D. C.




     In 1958, nuisance conditions of the rooted aquatic plant water




milfoil developed in the Potomac estuary.  The growth increased to




major proportions by 1963, especially in the embayments from Indian




Head downstream [81.




     These dense stands of rooted aquatic plants which rapidly invaded




the system also dramatically disappeared in 1965 and 1966.  The decrease




was presumably due to a natural virus [9].




     Subsequent and continuing observations by the CTSL have confirmed




persistent massive summer blooms of the blue-green alga Anacystis at



nuisance concentrations from the metropolitan area downstream at least




as far as Maryland Point [10].




     Data as presented below for comparable flow and temperature




conditions for September-October 1965 and October 1969 indicate that




algal populations have not only increased in density but have become




more widespread.
-------
                                                                V-12

 Potomac Estuary     River Miles  from          Chlorophyll a  - ,ug/l
    Location           Chain Bridge    	
                                      Sept. 15,Oct. 19,Oct. 1U-16,
                                        1965	196?*	1969**

 Piscataway               18.35          k$           90          Jk

 Indian  Head              30.60          36           75         120

 Smith Point              45.80          6l           56          70

     *  Single sample

    **  Average of a minimum of 5 samples

 While data are limited for 1965, based upon these data and field obser-

 vations the increase in nuisance algae appears to be significant.  Sampling

 difficulty  makes it impossible  to  quantify the increase at the present time,

     These  biological observations can be interpreted as an ecological

 succession.  The initial response to a relatively light over-enrichment

was the growth of water chestnut, which when removed allowed the increas-

 ing nutrient load to be incorporated Into the rooted aquatic plant water

milfoil (Myriophyllum spicatum).  The water milfoil dieoff 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 and decay.

     From these considerations it would appear that nuisance conditions

did not increase directly with an increase in nutrients  as indicated by

the concentrations of phosphorus and nitrogen.  Instead,  the nutrient

increase encouraged a given species  to dominate the plant life in the

aquatic environment.   With a further increase in nutrients this species
-------
                                                               V-13
was rather rapidly replaced in turn by another dominating nuisance form.




This is indicated in Figure III where the massive persistent blue-green




algal blooms were associated with large increases in phosphorus and




nitrogen enrichment in the upper reaches of the Potomac River tidal




system.  The persistent massive algal blooms have been occurring since




the early 1960's even though the amount of carbon (BOD) has been reduced




by almost 50 percent.




     Laboratory and controlled field pond studies by Mulligan [11] have




indicated similar results.  Ponds receiving low nutrient additions




(phosphorus and nitrogen) had submerged aquatic weeds.  Continuous




blooms of algae occurred in the ponds having high nitrogen and phosphorus




concentrations.  An important aspect of Mulligan's studies is that when




the aquatic resources were returned to their natural state,  the eco-




system returned to its natural state.  This is also supported by studies




of Edmondson [12] on Lake Washington and Hasler on the Madison,  Wisconsin




lakes [ Ik].
-------
                                                                V-lk




 C.  NUTRIENT TRANSPORT



     A one-year- cooperative sampling program with Steuart Petroleum



 Company has been completed.  The survey was designed to determine the
                           i


 nutrient movement throughout the entire tidal system.  Since 1969



 was a nontypical stream flow year, the study was extended into 1970.



     Nutrient data from 1969 taken at Great Falls, Maryland, indicated



 that large quantities of nutrients enter the tidal system during



 periods of high stream flow.  A study of a high runoff period in 1967



 revealed a significant phenomenon.  Figure TV shows that the total



 phosphorus concentration on the early days of March was about 0.150 mg/1



 at Chain Bridge increasing to over 1.0 mg/1 at Woodrow Wilson Bridge



 as result of wastewater discharges.   At the same time the concentrations



 at Piscataway and Indian Head were l.k and 1.0 mg/1, respectively.



     On March 7 and 8, the river discharge increased rapidly to about



139,000 cfs (Table VT).  This resulted in a discharge on March 8 of



over 1,208,000 Ibs/day of phosphorus into the tidal system.



     However,  when the concentrations in the entire upper tidal sje tern



are compared to early March,  a general overall decrease in phosphorus



 can be observed.   Phosphorus concentrations during high flows are accom-



panied by high sediment loads and when they enter the slow moving tidal



 system,  much of phosphorus was adsorbed onto the sediment particles and



was removed from water as the sediment settled.   CTSL conducted labora-



tory studies using Potomac River samples to confirm this removal of



phosphorus by adsorption.
-------
55-1
50-
45i
40-
 TOTAL  P«P04 ISOPUETH
           (mg/l)
POTOMAC TIDAL RIVER SYSTEM
                                                   INDIAN HEAD
                                                NOODROW WILSON BRIDGE
   0   I    2   34   5   6   7    6    9   10   II   12   13   14   15
                            MARCH  IM7
                                                                 FIGURE -35
-------
                                                                V-I6
                                TABLE VI
                RIVER DISCHARGE AND PHOSPHORUS LOADING
                  Potomac River at Washington, D.  C.
                        March 1 to 14,  1967
Date       River discharge

                (cfs)
T. Phosphorus
T.  Phosphorus
    as PO,
  (Ibs/day)
3- 1
3- 2
3- 3
3- 4
3- 5
3- 6
3- 7
3- 8
3- 9
3-10
3-11
3-12
3-13
3-14
7,690
7,010
7,230
7,270
7,620
8,590
63,100
133,000
139,000
76,400
46,700
36,500
29,500
25,100
0.153
--
0.155
0.132
0.225
0.177
1.316
1.701
0.936
0.717
0.578
0.355
0.264
--
6,280
--
5,990
5,130
9,150
8,120
44,800
1,208,000
694,800
292,500
144,200
69,200
41,588
--
-------
                                                                V-17




     A more sophisticated mathematical model has been recently adapted




to the Potomac Estuary to increase sensitivity in simulating the move-




ment of nutrients and other pollutants.  Once this capability has been




developed and verified, technical areas to be investigated will include:




     1.  Sensitivity of nutrient concentrations in the upper, middle,




and lower reaches to loadings in the upper reach, including contributions




from land runoff,




     2.  The flow probability to be used in determining maximum permissible




nutrient levels, including transport, such as seven-day-ten-year flow or




the mean monthly flow,




     3-  Ecological,nutrient transport and nutrient response studies will




be necessary to determine whether or not the same nitrogen, phosphorus




and carbon removal levels are required during twelve months of the year




in order to enhance the water quality in the upper, middle, and lower




reaches.




     4.  Effects of withdrawal of water from the upper portion of Zone I




as a supplemental water supply for the Wa&nington metropolitan area on




the allowable nitrogen, phosphorus, and carbon loadings from wastewater




discharges,  and




     5•  Development of seasonal nutrient loadings for Zones II and III




of the upper reach and for -che middle and lower reaches of the tidal



system.
-------
                                                                V-18





 D.   DISSOLVED OXYGEN BUDGET




      Investigations of the oxygen budget axe in three areas: (l)




 carbonaceous and nitrogenous oxygen demand from wastewater discharges,




 (2)  oxygen production by phytoplan.-cton, and (3) increased organic




 carbon and nitrogen loadings from phytoplankton, primarily in the




middle and lower reaches.  During 1969, preliminary CTSL studies




were  in the first two areas.




      Preliminary analyses of nitrogen data from the past five years




indicate that nitrification (the oxidation of NH_to WO ) becomes a




minor factor i <••. the oxyger. budget at water temperatures below 10°C.




This observatjo" would s't^ges .  t,hat nitrogen removal from wastewater




for the maintenance of oxygen standards would not be required at




temperatures below 10°C.  'The need for nitrogen removal for the control




of eutrophication is still being Investigated as previously reported.




     Effects of organic loadings on the dissolved oxygen budget in the




middle and lower reaches is being intensively studied during 1970.




During the summer months, dissolved oxygen in the lower reach is often




depressed at greater depths,  attrib ited partially to the decay of




organic matter,  main!.,  phytoplar-.
-------
                                                                V-19





E.  EMBAYMENT STUDIES




     Except for the Blue Plains facility of the District of Columbia,




all major wastewater discharges are into embayments of the Potomac




River tidal system.  As an interim measure to protect the embayments,




the conferees at the Potomac Enforcement Conference applied the Zone I




removal percentages to wastewater discharges in Zone II.




     A study of the wastewater assimilation and transport capacity




of the Piscataway embayment was recently completed [13J-  One of the




findings of the study was that this embayment has little capacity to




a~c ImllaU; aud transport tri-aied wastewater.  The stud,'/ further Indicated




if the same nutrient levels were to be maintained in the embayments- as




in the Potomac, only a limited poundage of the waste constituents could




be discharged into the embayment if low nutrient levels are to be




maintained.  Moreover, if the plant were to be expanded to 30 mgd, a




higher degree of removal than that currently agreed upon (96$ for BOD^,




91$ for phosphorus, and 85$ for nitrogen) would "be required if the lower-




nutrient levels are ^o be maintained.



     Preliminary analysis of the Anacostia River tidal system also




indicates a limited assimilation and transport capability [3'-  In this




embayment, complete renovation or ultimate wastewater treatment (UW1?) will




be required if there are to be any large discharges in the upper portion




of the Anacostia tidal system.




     Based on the Piscataway and Anacostia studies, a re-examination of




the removal requirements for embayment discharges is required.  The
-------
                                                                V-20





"real time" mathematical model previously mentioned includes all the



major embayments.  To complete the analysis, a dye release in each




embayment will be required to verify predictive coefficients.



     Nutrient response characteristics of the waters of the various



embayments are currently being investigated by CTSL.  Limited data



attained in 1968 and 1969 indicate greater standing crops of algal



populations in the embayment for given nutrient levels than in the



main stem of the tidal river.  The sampling program for the embay-




menis, especially Piscataway, Dogue,  Gunston Cove, Occoquan-Belmont,



and Mattawoman was initiated in February 1970 to further explore



these observations.
-------
                                 REFERENCES
  1.  Jaworski, N.A., Aalto,  J.A., Lear,  D.W., and Marks, J.W.,
     "Water  Quality and Wastewater Loadings  Upper Potomac  Estuary
     During  1969," Technical Report No.  27,  CTSL, FWPCA, MAP,
     November 1969-

  2.  Aalto,  J.A., Jaworski,  N.A., and  ochremp, W.H.,  "A Water
     Quality Study of the Rock Creek Watershed,"  CB-SRBP Working
     Document No. 30, FWPCA, MAR, March  1969,

  3-  Jaworski, II.A., Clark,  L.J., Feigner, K.D.,  "Preliminary
     Analyses of the Wastewater and Assimilation  Capacities of
     the Anacostia Tidal Hiver System,"  Technical Report No. 39,
     CTSL, FWQA, MAR, April  1970.

  if.  Gumming, H.3., "Investigation of  the Pollution and Sanitary
     Conditions of the  Potomac Watershed," USPHS Hygiene Laboratory
     Bulletin IQk, 1916.

  '>.  Ljvermore, D.!1'1. and WunderlJch, W.E., "Mechanical  Removal of
     Organic Production from Waterways," Eutrophication; Causes,
     Conseguenc es, Correct1ves, National Academy of Sciences,
     Washington, B.C., 1969.

 6.  Bartsch, A.F., "Bottom and Plankton Conditions in  the Potomac
     River in the Washington Metropolitan Area," Appendix A, A
     report on water pollution in the Washington metropoli -can area,
     Interstate Commission on the Potomac River Basin, 1954.

  7.  Stotts/ V.D. and Longwell, J.R.,   "Potomac River Biological
     Investigation 1959," Supplement to technical appendix to part
     VII of the report on the Potomac River Basin studies, U. S.
     Dept. of H3W, 1962.

 8.  Eiser, H.J., "Status of Aquatic Weed Problems.in ^Tidewater
     Maryland,  Spring 1965," Maryland Department of Chesapeake Bay
     Affairs, 8 pp mimeo.  1965.

 9.  Bayley,  S.f  Rabin,  H.,  and Southwick,  C.H.,  "Recent Decline
     in the Distribution and Abundance of E-urasian Watermilfoil in
     Chesapeake Bay,"  Chesapeake Science 9(3): 173-181, 1968.

10.  Jaworski,  U.A., Lear,  D.W.,  a-d Aalto,  J.A.,  "A Technical
     Assessment of Current Water Quality Conditions  and Factors
     Affecting Water Quality in the  Upper Potomac  Estuary,"
     Technical Report  No.  5,  CTSL, FWPCA, MAR, 1969.
-------
11.  Mulligan, H.T., "Effects of Nutrient Enrichment on Aquatic Weeds
     and Algae," The Relationship of Agriculture to Soil and Water
     Pollution Conference Proceedings, Cornell University, New York,
     January 19-21, 1970.

12.  Edmondson, W.T., "The Response of Lake Washington to Large
     Changes in its Nutrient Income," International Botanical Congress,
     Seattle, Washington, 1969.

13.  Jaworski, N.A., Johnson, James H., "Potomac-Piscataway Dye
     Releases and Wastewater Assimilation Studies," Technical Report
     No. 19, CTSL, FWPCA, MAR, December 1969.

Ik.  Hasler, A.D., "Culture Eutrophication is Reversible," BioScience,
     Vol. 19, No. 3> May 1969.

15.  Brezanik, W.H., Morgan, W.H., Shannon, E.E., and Putnam, H.D.,
     "Eutrophication Factors in North Central Florida Lakes," Florida
     Engineering and Industrial Experiment Station, Bulletin Series
     No. 134, Gainesville, Florida, August, 1969.

16.  Welch, E.B., "Phytoplankton and Related Water Quality Conditions
   .  in an Enriched Estuary," JWPCF, Vol.40, pp 1711-1727, October 1968.

17-  Task Group Report on Nitrogen and Phosphorus in Water Supplies,
     JAWWA, Vol. 59, No. 3.  PP 344^366, March 1967.
-------
Chesapeake Technical Support Laboratory
         Middle Atlantic Region
 Federal Water Quality Administration
   U. S. Department of the Interior
          PHYSICAL DATA
    POTOMAC RIVER TIDAL SYSTEM
   INCLUDING MATHEMATICAL MODEL
           SEGMENTATION
      Technical Report No.  43
        Norbert A.  Jaworski
           Leo J. Clark
-------
                              INTRODUCTION






     In its continuing water quality studies of the Potomac, the




Chesapeake Technical Support Laboratory (CTSL) found it necessary




to systematically and accurately define the physical character-




istics of the estuary.  Factors of major importance are: surface




and cross-sectional areas, volumes, and distances between "bridges,




buoys, prominant landmarks and other reference points.   This type




of data is not only essential for mathematical modeling studies but




also to interpret field survey information.




     River mileages were measured along the main channel using a




set of dividers on U.S. Geological Survey 7-5 minute quadrangle




maps.  For convenience, a.11 distances were measured from Chain Bridge




rather than from a reference point at the mouth of the Potomac.  A




reference point at the confluence of the Potomac with the Chesapeake




Bay was established (See Figure II).  Uniform river mile locations




using statute miles were determined for the primary sampling stations,




landmarks, navigation buoys, etc., and are presented in this report.




     Cross-sections were plotted at intervals from 0.5 to 3.0 miles




from soundings shown on U.S. Coast and Geodetic Survey charts and




the plots planimetered to determine cross-section areas.  Surface




areas were also planimetered directly from USC&GS charts.  Segment




volumes were obtained by multiplying the average cross-sectional




areas by the length.
-------
     Although much of the data presented in this  report applies to




a predetermined segmentation for mathematical model studies,  it is




general in nature and thus adaptable to other needs.   Hopefully,




these basic data will be used by other agencies involved with the




Potomac Estuary to eliminate duplication of effort.
-------
         GENERAL DESCRIPTION OF THE POTOMAC RIVER TIDAL SYSTEM





     The Potomac River basin is the second largest watershed in the




Middle Atlantic States.  Its tidal portion begins at Little Falls in




the Washington metropolitan area and extends Ilk miles southeastward




to the Chesapeake Bay.




     The tidal portion is several hundred feet in width at its head




at Washington and broadens to nearly six miles at its mouth.  A




shipping channel with a minimum depth of 24 feet is maintained upstream




to Washington.  Except for this channel and a few short reaches where




depths up to 100 feet can be found, 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 lA feet near the Chesapeake Bay.  The lag time




for the tidal phase between Washington and the Chesapeake Bay is about




6.5 hours.




     Effluents from twelve major wastewatcr treatment plants, with a




thirteenth under construction, serving a population of about 2,500,000,




are discharged into the upper tidal system.  The locations of the




discharges from these treatment facilities are shown in Figure I and




presented in Table I.
-------
-------
                        /       \
                                            RIVER MILES FROM  CHAIN BRIDGE = 0
                                                Mt£S FROM  CHAIN BftOGC - IS
                                                           ZONE  II
                                            RIVER  MILES FROM CHAIN  BRIDGE ; 30
   FORT 8EIVO1R
LOWER  POTOMAC
                 WASTEWATER  DISCHARGE ZONES
              UPPER POTOMAC  TIDAL  RIVER  SYSTEM
                                                           FIGURE I
-------
                                TABLE I

                 Major Wastewater Discharge Locations
                         Upper Potomac Estuary
Facility
Combined D.C.
system sewer
overflow
Pentagon
Arlington
District of
Columbia
Alexandria
Fairfax-West
Gate
Piscataway
Andrews AFB
No. 1
Andrews AFB
No. 2
Fairfax
Hunting Cr .
Fairfax
Dogue Creek
Fairfax Lower
Potomac
Ft. Belvoir
No. 1
Ft. Belvoir
No. 2
Distance
Receiving from
Stream Chain Bridge
Potomac
Es tuary
Potomac
Estuary
Four Mile Run
Potomac
Estuary
Hunting Creek
Hunting Creek
Embayment
Piscataway
Embayment
Piscataway
Creek
Piscataway
Creek
Little Hunting
Creek
Dogue Creek
Pohick
Gunston Cove
Guns ton Cove
4.0
5-8

10.4
12.4
12.8
18.3
18.3
18.3
20.0
22.5
24.5
24.5
24.5
Expanded
Thomann Model
Segment
4
6
12
13
15
16
22
22
22
24
27
28
28
28
FWQA
Model
Segment
5
7
78
129
81
16
118
118
118
25
84
128
85
85
* If discharge is into an embayment distance is to midpoint of embayment
  All distances in statute miles
-------
A.  Reaches of Potomac River Tidal System

     For discussion and investigative purposes,  the tidal portion of

the Potomac River Was divided into three reaches as shown in

Figure II and described below:

     Reach          Description          River Miles       Volumen
                                                        cu.ft.xlCr

   Upper        From Chain Bridge to   114.4 to  73-8       93-50
                  Indian Head

   Middle       From Indian Head to     73.8 to  47.0      362.28
                  Rt. 301 Bridge

   Lower        From Rt. 301 Bridge     47.0 to  00.0     1754.74
                  to Chesapeake Bay

     The upper reach, although tidal, contains fresh water.  The

middle reach is normally the transition zone from fresh to brackish

water.  In the lower reach, chloride concentrations near the Chesa-

peake Bay range from about 7,000 to 11,000 mg/1.

B.  Zones of Upper_Potomac Tidal System

     To facilitate determination of water quality control requirements,

the upper estuary was segmented by the CTSL into 15 mile zones beginning

at Chain Bridge.  Establishment of zones similar in physical character-

istics allows flexibility in developing control needs.  This zone concept

was adopted by the conferees of the Potomac Enforcement Conference on

May 8, 1969.

     River mile distances from both the Chesapeake Bay and Chain Bridge

for the upper three zones are given in Table II  as well as in Figure II.
-------
              POTOMAC RIVE* intoai
                                             BAY
                              RIVER MILE 00-
POTOMAC RIVER TIDAL SYSTEM
                                      FIGURE - U
-------
       CQ
       H

       O
H     O
H     B
       PH
       I
       &
       §
       CQ
       O
       N


(D
a

-------
MATHEMATICAL MODEL INVESTIGATIONS




     Two approaches have been adopted to simulate water quality




conditions in the Potomac Estuary.  The first was the "average"




tidal model developed "by Dr. Robert Thomann at New York University.




The second and the more recent approach is the FWQA Dynamic Estuary




or "real time" tidal model originally developed by Water Resources




Engineers of Walnut Creek, California under contract to U.S. Public




Health Service, FWQA, and the State of California.




     Details of both approaches have been adequately documented and




are available from the authors or FWQA.  A report comparing the two




approaches in simulating the movement of pollutants in the Potomac




Estuary is currently being prepared by CTSL.




     Originally, the Potomac Estuary was divided into 28 segments




for the Thomann Model.  To add greater sensitivity in analyzing




field data and reaction rates, the estuary divisions were further




increased to 73 segments.




     For the FWQA Model, three networks have "been developed, one




corresponding to the 73-segment FWQA Model with embayment segmen-




tation added to give a total of ihl segments, and a detailed network




of 766 segments.




     In this report, segmentation data for both versions of the




Thomann and the main stem of 73 node FWQA models were presented.

-------
Detailed data on the other system are available from C'TSL upon




request.  For the main Potomac, nodes for the FWQA Model were




placed at the interfaces of the Thomann Model segments.




     In Figures VII and VIII are exhibited the segmentation for the




Thomann approach for the Anacostia and Potomac Tidal River Systems




with Figure IX presenting a schematic of the FWQA Potomac Estuary




Model.  The lower 11 segments of the FWQA Model are not incorporated




into the current working system.

-------
DATA FORMAT

     The remainder of this report presents the following:

A.  Sampling Stations and Landmark Locations

                     Table                                   Number

     1.  CTSL Sampling Stations                               III

     2.  D. C. Water Pollution Control Division
           Sampling Stations                                   IV

     3•  Bridges                                                V

     U.  Potomac Estuary Buoys to Reference Water
           Quality Sampling         '                           VI

     5.  Mileage Location of Prominent Reference
           Points along the Potomac Estuary                   VII

                     Figure

     1.  Sampling Stations Potomac Estuary                    III

B.  Mathematical Model and Physical Data

                     Table

     1.  Thomann Model, Segment Geometry, Potomac
           Estuary Mean Low Water Data (Excluding
           Embayments)                                       VIII

     2.  Thomann Model, Segment Geometry, Potomac
           Estuary Mean Water Data (Excluding
           Embayments)                                         IX

     3.  Thomann Model, Segment Volumes  (including
           Embayments)                                          X

     k.  Thomann Model, Revised Potomac Estuary
           Geometry for Expanded Segmented System,
           Mean Water Data (Excluding Embayments)              XI

     5•  Mathematical Model Segmentation, Anacostia
           Tidal River System, Mean Water Data                XII

-------
                 Table (continued)                      Number

6.  FWQA Network Data, Potomac Estuary
      (Excluding Embayments)                             XIII

J.  Enibayment Data, Potomac Estuary                       XIV

8.  Mathematical Model Plotting Positions
      for the Potomac Estuary                              XV

                 Figure                                 Number

1.  Cumulative Surface Area Versus Distance,
      Potomac Estuary Mean High Water Data                ; TV

2.  Cumulative Volume Versus Distance,
      Potomac Estuary Mean Water Data                       V

3-  Cross-sectional Area Versus Distance,
      Potomac Estuary Mean Water Data                      VI

k.  Thomann Mathematical Model Segments,
      Potomac Estuary                                     VII

5-  Thomann Mathematical Model Segments,
      Anacostia Tidal River                              VIII

6.  Schematic of Potomac Estuary Network
      for the FWQA. Dynamic Model                           IX

-------
      TABLE III




CTSL SAMPLING STATIONS
Station
Number
1
1A
2
2A
3
3A
4
4A
5
5A
6
7
8
8A
9
10
10A
11
12
13
ik
Location
Key Bridge
Memorial Bridge
l4th Street Bridge
Potomac Park
Hains Point
Hunters Point
Bellevue
Goose Island
Woodrow Wilson Bridge
Rosier Bluff
Broad Creek
Piscataway Creek
Dogue Creek
Guns ton Cove
Hallowing Point
Indian Head
Occuquon Bay
Possum Point
Sandy Point
Smith Point
Maryland Point
Buoy Reference



N "6"
C "1" - N "4"
C "11" - C "9"
FLR - 23' Bell
R "8" - N "6"

c "87"
N "86"
FL "77"
FL "67"
R "64"
FL "59"
N "54"
N "S2"
R "44"
N "40"
N "30"
G "21"
Miles below
Chain Bridge
3-35
4.85
5-90
6.70
7.60
8.70
10.00
11.05
12.10
13-55
15.20
18.35
22.30
2^.30
26.90
30.60
32.15
38.00
42.50
46.80
52.40

-------
CTSL SAMPLING STATIONS
Station
Number
15
15A
16
17
18
19
20
21
22
23
24
25
Location
Nanjemoy Creek
Port Tobacco
301 Bridge
Bluff Point or Stony Pt.
Colonial Beach/Kettle
Bottom Shoals
Vicomico River
Kingcopsico
Ragged Point
Piney Point
Point Lookout
Smith Point
Point Lookout
Buoy Reference
N "10"
C "3"

BW - MO(A) "H"
FL "25"
C "15"
BWN "52" B
BW "51" B
FR "0" FR A
FL "4" Bell
BWN "43" B
BWN "57" B
Miles below
Chain Bridge
58.55
63-75
67.40
73.45
76.60
82.00
90.25
95-42
99-20
107.41
118 . 00
114.85

-------
               TABLE IV

D. C. WATER POLLUTION CONTROL DIVISION
            SAMPLING STATIONS
Station
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
Ik
15
16
17
18
19
20
21
22
Location
Chain Bridge
Fletcher's Boat House
Three Sisters Island
Roosevelt Island
Memorial Bridge
Highway Bridge
Potomac Park
Hains Point
Giesboro Park
Above WPCP (Blue Plains)
Opposite WPCP "
Below WPCP
Woodrow Wilson Bridge
Ft. Foote
Ft. Washington
Marshall Hall .
Hallowing Point
Indian Head.
St. Neck
Sandy Point
Smith Point
Maryland Point
Buoy Reference


Sewer outlet



N "6"
N "4" N "3"
N "11"
FLR 4 sec "23"
Sewer outlet
N "8"

N "86" N "87"
C "79"
N "69"
FL "59"
N "54"
N "46"
N "41"
N "30"
G "21"
Miles below
Chain Bridge
o.oo
1.40
2.75
4.25
4.85
5-90
6.70
7.20
8.20
10.20
10.40
10.70
12.10
14.45
17-95
21.80
26.90
30.60
35-20
42.50
45.80
52.40

-------
                            TABLE V



                            BRIDGES
Location or Name




Chain Bridge




Key Bridge




Theodore Roosevelt Bridge




Memorial Bridge




14th Street Bridges




     a.  George Mason




     "b.  Rochambeau




Woodrow Wilson Bridge




301 Bridge
Miles "below Chain Bridge




           0




        3-35



        ^.U5




        1+.85








        5-90




        6.05




       12.10




       67.40

-------
                              TABLE VT
                     POTOMAC ESTUARY BUOYS USED
                TO REFERENCE WATER QUALITY SAMPLING

Buoy                         River Miles from Chain Bridge
N "12"                                   5.15
RN "10"                                  5.75
N "6"                                    6.70
C "1"                                    7.87
I "V                                    7.20
C "3"                                    7-20
N "2"                                    7-72
c "ii"                                   8.50
c "9"                                    8.95
C "1"                                    9.15
N "2"                                    9.25
23'  Bell                                10.01
R "8"                                   10.75
N "6"                                   11.30
N "V                                   11.70
R "2"                                   13.05
C "87"                                  13-95
N "86"                                  ill-.95
R "84"                                  15.95
C "83"                                  17.13

-------
                     POTOMAC ESTUARY BUOYS USED
              TO REFERENCE WATER QUALITY SAMPLING (Cont.)

Buoy                        River Miles from Chain Bridge
C "81"                                  17.40
C "79                                   17-95
FL "77"                                 18.50
C "75"                                  19.00
C "73"                                  19.90
FL "71"                                 20.99
C "69"                                  21.55
FL "67"                                 22.30
N "66"                                  23.05
R "64"                                  2k.25
R "62"                                  24.90
c "61"                                  26.40
FL "59"                                 26.90
R "60"                                  27.00
C "57"                                  27.70
N "54"                                  30.60
N "52"                                  32.15
R "44"                                  37.90
N "4o"                                  42.50
N "30"                                  45.80

-------
                      POTOMAC ESTUARY BUOYS USED
              TO REFERENCE WATER QUALITY SAMPLING (Cont.)

Buoy                       River Milejs from Chain Bridge
N "24"                                 50.20
G "21"                                 52.40
N "16"                                 55.00
N "10"                                 58.55
C "3"                                  63-75
FL "29"                                70.65
BW MO(A) "H"                           73.45
FL "25"                                76.60
C "15"                                 82.00
B¥W "52" B                             90.25
BW SI B                                95-42
FR "D" FR A                            99.20
FL "4" Bell                           107-41
EWN "57" B                            114.85
BWN "43" B                            118.00

-------
                                TABLE VII

             MILEAGE LOCATION OF  PROMINENT   REFERENCE POINTS
                         ALONG THE POTOMAC ESTUARY
                (excluding those used as sampling stations)
Landmark Points                           Miles below Chain Bridge

Mai-bury Point                                       10.55

Fox Ferry Point                                      7-50

Jones Point                                         12.34

Indian Queen Point                                  14.90

Hatton Point                                        17-30

Sheridon Point                                      18.65

Mockley Point                                       18.60

Bryan Point                                         19.80

Ferry Point                                         21.90

Whitestone Point                                    24.10

Pomonkey Point                                      26.40

Sycamore Point                                      29.80

High Point                                          31-30

Deep Point                                          34.00

Cockpit Point                                       35-90

Douglas Point                                       43-90

Simms Point                                         46.80

Marlboro Point                                      49-35

Blossom Point                                       59-10

Upper Cedar Point                                   60.10

-------
            MILEAGE LOCATION OF  PROMINENT  REFERENCE POINTS
                        ALONG THE POTOMAC ESTUARY
               (excluding those used as sampling stations)


Landmark Points                          Miles below Chain Bridge

Mathias Point                                      62.70

Persimmon Point                                    66.20

Lower Cedar Point                                  68.80

Stony Point                                        72.70

Swan Point                                         7^.20

White Point                                        75.00

Gum Bar Point                                      76.00

Church Point                                       77.00

Cobb Point                                         80.25

Waterloo Point                                     84.30

Crunch Point                                       88.10

Ragged Point                                       95-^0

Deep Point                                        102.80

Kitts Point                                       105.20

Lawson Point                                      106.60

-------






















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                         TABLE XV

         MATHEMATICAL MODEL PLOTTING POSITIONS FOR
               MAIN STEM OF POTOMAC ESTUAKY
Segment
Number
1
2
3
4
5
6
1
8
9
10
n
12
13
ik
15
16
17
18
Thomann
Model
(miles)
0.7^
2.15
3-09
3-7^
k.kQ
5-37
6.2k
7.10
8.00
8.54
9.05
9.68
10.55
11.63
12.50
13.24
1k. 20
15-03
FWQA
Model
(miles)
0*
1.48
2.82
3-30
4.13
4.83
5.90
6.57
7.61
8.37
8.70
9.4o
9-97
11.12
12.12
12.87
13-61
14.77
* Junction 114
-------
Segment
Number
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
1*0
Thomann
Model
(miles)
15-79
16.61
17.42
18.20
18.98
19.96
20.92
21.84
28.13
24.82
26.32
27.74
29.06
30.12
31.04
32.06
33.46
35-26
37-34
39.38
41.45
43-63
FWQA.
Model
(miles)
15.27
16.30
16.92
17.92
18.48
19.^7
20.44
21.39
22.30
23.96
25=67
26.95
28.52
29.58
30.66
31.42
32.70
34.22
36.21
38.76
4o.6o
42.90
-------
Segment
Number
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Thomann
Model
(miles)
45.73
47.97
50.37
52.11
55-29
57-95
60.30
62.88
66.24
67.82
69.35
71.96
73.85
76.04
78.34
80.31
82.13
84.09
86.26
88.36
FWQA.
Model
(miles)
44.95
47.08
49-44
51.87
53-92
57-24
59-24
61.94
64.39
66.67
68.53
69.75
71.75
73^54
74.83
76.85
78.77
80.42
82.75
84.76
-------
Segment
dumber
61
62
63
6k
65
66
67
68
69
70
71
72
73
Thomann
Model
(miles)
90.10
91.56
93-20
96.48
97-19
99-71
101.89
103.67
105.83
107.81
109.87
111.72
113.84
FWQA
Model
(miles)
86.96
88.23
89.88
91.52
93.16
96.21
98.21
100.17
102.16
104.31
106.31
108.1*2
110.02
-------
                       MAJOR WASTE  THEATIfcHT  KANTS
                     A BBTWCT Or COJUHI*
                     » MLMGflON COUNTY
                     C 4LCXAMMA SAWWRY AUTHOMTY
                     0 KMVAX COUMTY - WtSHiATt PLANT
                     t HWTAX COUKTV - UTTU HUNTHO CREEK PLAWT
                     r mMmx COUKTV - OOGUE CWEK PLANT
                     G WUHMGTON SUtUV  -MTrUf/ COMMOOON - PSOTWCW
                     H ANDREWS AR FORCE BASE - PtAKTS *! ind '*
                     I TOOT  eavOfl - PLANTS *\ mi *Z
                     J PENTAGON
POTOMAC      ESTUARY
         SAMPLING   STATIONS
                                                    FIGURE  nr
-------
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= V3MV 1VNOI1D3S SSOMD
-------
                    THOMANN MATHEMATICAL MODEL SEGMENTS
                                                   LOCATION MAP
ORIGINAL 28 SEGMENTS
EXPANDED 73 SEGMENTS
                        SCALE ffl MILES
            POTOMAC    ESTUARY
-------
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w
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     QC
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                                                            Figure VIII
-------
             CHAIN BRIDGC
FOUR MILE RUN
                                            WASTEWATER  PLANT  NODES

                                            NODE      PLANT

                                             "78       ARLINGTON
                                            129       BLUE PLAINS
                                             I 6       WESTGATE

                                             81        ALEXANDRIA
                                            MB       PI SCAT AWAY
                                             84       OOGUE CR

                                            128       LOWER  POTOMAC
                                      SCHEMATIC  OF  POTOMAC  ESTUARY
                                            FOR  FWQA  DYNAMIC  MODEL
-------
                         Chesapeake Technical Support Laboratory
                                  Middle Atlantic Region
                                   Water Quality Office
                            Environmental Protection Agency
                                 NUTRIENT MANAGEMENT

                                        IN THE

                                   POTOMAC ESTUARY


                                 Technical Report 45



                                     January 1971
                                 Norbert A. Jaworski

                                 Donald W. Lear, Jr.

                                 Orterio Villa, Jr.


To be presented at the American Society of Limnology and Oceanography
Symposium on Nutrients and Eutrophication:  "The Limiting Nutrient
Controversy," February 11-13, 1971, Michigan State University, East
Lansing,Michigan
-------
                           TABLE OF CONTENTS
 INTRODUCTION   .   .   .	         1

     Brief Description  of the Study Area	         1

 CURRENT WATER  QUALITY CONDITIONS   	         5

 ECOLOGICAL TRENDS AS RELATED TO NUTRIENT  ENRICHMENT  .   .        15

 NUTRIENT SOURCES AND CONTROLLABILITY   	        19

 NUTRIENT TRANSPORT AND ALGAL STANDING  CROP MATHEMATICAL
  MODELS   ..........   	        25

 EUTROPHICATION CONTROL	        43

 ESTABLISHMENT  OF NUTRIENT CRITERIA	        46

     1.  Algal Composition Analysis	        47

     2.  Analysis of Data on an Annual Cycle and
           Longitudinal Profile Basis     	        48

     3.  Bioassay Studies	        50

     4.  Algal Modeling	        52

     5.  Comparison with a Non-eutrophic Estuary  ...        52

     6.  Review of Historical Nutrient and Ecological
           Trends in the Potomac Estuary    	        53

     7.  Specific Criteria	        54

         a.  Freshwater Portion	        54

         b.  Me?ohaline Portion	        55

WASTEWATER TREATMENT' REQUIREMENTS	        57

A WATER QUALITY MANAGEMENT PROGRAM	        60

REFERENCES
-------
-------
                            LIST OF FIGURES

Figure                        Description


   1       A map of the Potomac Estuary showing wastewater
           treatment facilities and predominant landmarks.          4

   2       Inorganic phosphorus concentration as PC>4 for
           various stations in the Potomac Estuary from
           February 1969 through September 1970.                    7

   3       Nitrate and nitrite nitrogen concentration for
           various stations in the Potomac Estuary from
           February 1969 through September 1970.                    8

   4       Ammonia nitrogen concentration for various stations
           in the Potomac Estuary from February 1969 through
           September 1970.                                         10

   5       Chlorophyll §. concentrations for stations in the
           upper reach of the Potomac Estuary, 1965-1966
           and 1969-1970.                                          13

   6       Chlorophyll g. concentration for stations in
           middle and lower level of the Potomac Estuary,
           1965-1966 and 1969-1970.                                H

   7       Wastewater nutrient enrichment trends and
           ecological effects on the upper Potomac Tidal
           River System, 1913-1970.                                16

   8       Phosphorus concentration in the Potomac Estuary
           before, during, and after a period of intensive
           runoff.                                                 22

   9       Average observed and predicted phosphorus
           concentration in the Potomac Estuary,
           September 25-October 27, 1965.                          26

  10       Average observed and predicted phosphorus
           concentration in the Potomac Estuary,
           January 25, 1966.                                       27

  11       Effect of temperature in the phosphorus
           deposition rate, Potomac Estuary.                        28
-------
Figure                        Description                         Page

  12       Simplified nitrogen cycle used in modeling the
           nitrogen and algal standing crops in the
           Potomac Estuary.                                        32

  13       Average observed and predicted ammonia and
           nitrite + nitrate concentration in the
           Potomac Estuary, September 9-13, 1966.                  33

  14       Average observed and predicted ammonia and
           nitrite + nitrate concentration in the
           Potomac Estuary, August 17-22, 1968.                    34

  15       Effect of temperature on the rate of
           nitrification, Potomac Estuary.                         35

  16       Effect of temperature on the rate of nitrogen
           utilization by algae, Potomac Estuary.                  36

  17       Average observed and predicted chlorophyll a.
           concentration, Potomac Estuary,
           September 6-7, 1966.                                    38

  18       Average observed and predicted chlorophyll a.
           concentration, Potomac Estuary,
           August 19-23,  1968.                                     39

  19       Average observed and predicted dissolved
           oxygen concentration, Potomac Estuary,
           September 22,  1968.                                     40

  20       Average observed and predicted dissolved
           oxygen concentration, Potomac Estuary,
           August 12-17,  1969.                                     41

  21       Wastewater discharge zones  in the upper
           Potomac Estuary.                                        62
-------
                            LIST OF TABLES

Table                         Description                       Page


  1      Summary of nutrient sources entering the upper
         and middle reaches of the Potomac Estuary.               20

  2      Data summary of algal chemical composition
         studies Potomac Estuary, June-October 1970.              31

  3      Subjective analysis of algal control requirements.       45
-------
                              INTRODUCTION


     Historically, since the first sanitary survey was made in 1913  [30],

the water quality of the upper Potomac Estuary has been degraded as a

result of the discharge of either untreated or partially treated munici-

pal wastewater from the Washington Metropolitan Area.  Early surveys

indicated that high coliform densities and low dissolved oxygen content

were the two major water quality problems of the upper estuary.  In the

past decade, large nuisance populations of blue-green algae have also

added to the water quality management problems of the upper and middle

reaches of the estuary„

     Initially, as part of the Chesapeake Bay-Susquehanna River Basins

Comprehensive Planning Project* and now as an integral part of the

Potomac Enforcement Conference, field water quality studies were under-

taken, beginning in 1965, to define wastewater treatment requirements.

The studies and concepts used to formulate a nutrient management pro-

gram for the Potomac Estuary are presented in this, paper,

Brief Description of the Study Area

     The Potomac River Basin, with a drainage area of 14,670 square

miles, is the second largest watershed in the Middle Atlantic States.

From its headwaters on the eastern slope of the Appalachian Mountains,
  The Chesapeake Bay-Susquehanna River Basin Comprehensive Project was
  initiated by the Division of Water Supply and Pollution Control of
  the Public Health Service, U0 S. Department of Health,  Education,
  and Welfare.
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                                                                        2



the Potomac flows first northeasterly then generally southeasterly in



direction some 400 miles to the Chesapeake Bay.



     Upstream from Washington, D. C., the Potomac traverses the Piedmont



Plateau to the Coastal Plain at the Pall Line.  Below the Fall Line, the



Potomac is tidal extending 114 miles southeastward and discharges 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 where depths up to 100 feet can be found, the tidal



portion is relatively shallow with an average depth of approximately



18 feet.



     Of the 3.3 million people living in the entire basin, approxi-



mately 2.8 million reside in the upper portion of the Potomac Estuary



within the Washington Metropolitan Area.  The lower areas of the



tidal portion, which drains 3,216 square miles, are sparsely populated.
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                                                                        3

     For purposes of discussion and investigation, the tidal portion

of the Potomac River (Figure l) has been divided into the three

reaches described below:


     Reach         Description            River Mile*          Volume
                                     (mi. below Chain Br.)  (cu.ft.xlO8)

     Upper     From Chain Bridge to       0.0  to   30.0        93.50
                 Indian Head

     Middle    From Indian Head to       30.0  to   67.0       362.28
                 Rte. 301 Bridge

     Lower     From Rte. 301 Bridge to   67.0  to  114.4      1754.74
                 Chesapeake Bay


* All river miles are referenced to Chain Bridge which is located at the
  upper end of the tidal portion of the Potomac River.


     The upper reach, although tidal,  is essentially fresh water.  The

middle reach is normally the transition zone from fresh to brackish

water.  The lower reach is mesohaline  with chloride concentrations near

the Chesapeake Bay ranging from approximately 7,000 to 11,000 mg/1.

     The average freshwater flow of the Potomac River near Washington

before diversions for municipal water  supply is 10,800 cubic feet per

second (cfs) with a median flow of 6,500 cfs.  The flow of the Potomac

is characterized by flash floods and extremely low flows.
-------
                      -IfiBSL
                      MAJOR V*Stt  TREATMENT  PLANT*
                     A ocmcr or OOUJMM
                     • AMJWION COOTY
                     C ALCXAtCMt MMMV AUTHOMTY
                     D MMX OXMTT- WCSRM1 PLANT
                     c HMWW COUNTY - urru; HUNTMG CREEK PLANT
                     t INMM OXMTY- OOGUC OCEK PONT
                     G MMMICTON 1UMM  SANTABV COMMSSKM - PBCAWMW
                     H AMMCWS AD rancc MSC - PLANTS *i «< *4
                     I KMT  KLVOR - PLANTS *l mt *2
                     J PENTAOON
POTOMAC     ESTUARY
                                                    Figure  1
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                                                                        5

CURRENT WATER QUALITY CONDITIONS

     In the upper reach, approximately 325 million gallons per day (mgd)

of wastewater is discharged mainly from municipal treatment facilities

currently serving approximately 2.5 million people in the Washington

Metropolitan Area.  The largest wastewater treatment facility is the

Blue Plains plant of the District of Columbia which serves approximately

1.8 million people.  Wastewater discharged from the 18 facilities cur-

rently contributes 450,000, 24,000, and 60,000 Ibs/day of ultimate

oxygen demand* (UOD), phosphorus** and nitrogen respectively, to the

waters of the upper estuary.  The quantities of wastewater discharged

into the middle and lower reaches is less than 5.0 mgd and thus very

insignificant when compared to the upper reach.

     Low dissolved oxygen (DO) concentrations, often less than 1.0 mg/1

during summer, occur in the upper reach as a result of the oxidation of

200,000 and 240,000 Ibs/day of carbonaceous and nitrogenous UOD res-

pectively.  Since the summer of 1969, the high fecal coliform densities

(over 50,000 MPN/100 ml) previously observed near the wastewater dis-

charges have been significantly reduced (less than 1,000 MPN/100 ml) by

effective continuous chlorination.
*  Ultimate oxygen demand is basically the sum of 1.45 times the 5-day
   biochemical oxygen demand and 4.57 times the unoxidized nitrogen.

** Phosphorus concentrations or loadings in this paper are given as
   phosphorus (P) except when specifically designated as PO,
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                                                                        6



     The  concentrations  or forms  of phosphorus and nitrogen  in  the  Potomac



 Estuary are  a  function of wastewater loadings, temperature,  freshwater



 inflow, distance  from the Chain Bridge, and biological activity.  As



 shown  in  Figure 2, the inorganic  phosphorus varied considerably for the



 six stations presented from March 1969 through September 1970.  The



 concentration  at  Hains Point, which is located at the upper  end of  the



 tidal  excursion of the major wastewater discharges, was fairly  uniform



 averaging 0.1  mg/1 as  P  (0.3 mg/1 as  PO^).  At Woodrow Wilson Bridge,



 which  is  located  below the Blue Plains wastewater discharge, the



 inorganic phosphorus  increased appreciably with concentrations  over



 0.8 mg/1  (2.5  mg/1 as  PO^) occuring during low-flow periods  as  those



 in the months  of May-July 1969, October-November 1969, and September



 1970.  The remaining  four downstream  stations had progressively lower



 concentrations.



     The  total phosphorus  concentration closely parallels that  of



 inorganic phosphorus.  In the upper reach, the ratio of total phos-



 phorus to inorganic phosphorus ranges from 1.1 to 1.5.  The ratio is



 higher in the middle reach normally varying from 1.5 to 2.0 with the



 lower reach having a range from approximately 2.0 to 2.5.



     The  concentration of  nitrite and nitrate nitrogen at Hains Point



and Woodrow Wilson Bridge  varies almost inversely with that of phos-



phorus (Figure 3).  The N02 + NO-j concentrations as a result of land



runoff were the highest during periods of high river flows as in July
-------
              INORGANIC   PHOSPHATE   CONCENTRATION
                                POTOMAC CSTUMVr
HAMS PQMT
   UUS KCOW CHNM
                                    OCT  '  MX  '  ICC.   JHL
MOOOROW MLSON IMDGC
   MUS KUW CHAM  MOGC » BJO
                                                                                  JO*.   ML.
IMMAN KAD
             JIM    JUL
                                                                           •tflt  '  JLM, '  JUt-  '  **>.
SKHTH POINT
       «CLOW CHMN M«OGC • 4*.*0
       MA*    JUN
                                                     J«M.  '  fST
                                                                                                nou.  2
-------
                                 NITRATE   a*  NITRITE  NITROGEN
                                              POTOMAC  ESTUARY
N
 MAIN'.  PCHWT
    «*f5  K10W CHAM IMOGC » T«0
 WOODROW  WILSON  BR1D6E
    MUS KLOW  CHAIN IMDGC •  12 10
 INDIAN  HLAO
    MIUS PMLOW  CHAIN BRIDGC « 30.60
                                                  tf»    OC*
SMITH  POINT
    WLfS  BCLOW CHAIN BRKXiC • «.80
                                      JU     AUC
  i  BRIDGE:
   MMS KtOW CHAIN WDOt  • 6T40
                                     JU.    AiA.    Iff  T  OCT     NOV.
PtNfV  POI^'T
   MUS WLOW  CHAM *M>GC • M.20
                                                               •Sl^^ KC.  T  JMt^
                                                                     •M i I • •»
-------
and August 1969, and during the late winter and early spring months of
1969 and 1970.  During these flow conditions, the inorganic phosphorus
concentration was lowest (Figure 2).
     The increase of N02 + N03 at Indian Head as compared to Woodrow
Wilson Bridge in May-June 1969, September-November 1969, and July 1970
is the result of the conversion of ammonia (from the wastewater treat-
ment plant discharges) to nitrates.  The low concentration of N02 + N03
in the summer months at Smith Point is caused by uptake of algal cells
as described later in this report.  During winter months, algal utili-
zation is much less thus the concentrations of nitrates are high as in
the months of January through April 1970.  At Piney Point, concentrations
of NOa + N03 are usually less than 0.1 mg/1 on an annual basis.
     As shown in Figure 4, 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, ammonia concentrations at Indian
Head during the summer months are low due to nitrification.
                     »
-------
-------
and August 1969, and during the late winter and early spring months of



1969 and 1970.  During these flow conditions, the inorganic phosphorus



concentration was lowest (Figure 2).



     The increase of N02 + N03 at Indian Head as compared to Woodrow



Wilson Bridge in May-June 1969, September-November 1969, and July 1970



is the result of the conversion of ammonia (from the wastewater treat-



ment plant discharges) to nitrates.  The low concentration of N02 + N03



in the summer months at Smith Point is caused by uptake of algal cells



as described later in this report.  During winter months, algal utili-



zation is much less thus the concentrations of nitrates are high as in



the months of January through April 1970.  At Piney Point, concentrations



of N02 + NO^ are usually less than 0.1 mg/1 on an annual basis.



     As shown in Figure 4, 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, ammonia concentrations at Indian



Head during the summer months are low due to nitrification.
                     *,
-------
                                                AMMONIA NITROGEN  as N
                                                     POTOMAC ESTUARY
WOOOftOW VMLSON SMDGE
      ifiOH CHMN moat • a.e
-------
                                                                       11
JSL-
(units)
7.5
7.0
7.2
7.5
7.5
- 8.0
- 7.5
- 8.0
- 8.2
- 8.0
Alkalinity COp
(mg/1 as CaCO^)
80
90
70
60
65
- 100
- 110
- 90
- 85
- 85
(mg/1)
2
8
6
2
7
- 4
- 12
- 10
- 8
- 8
     During the summer and early fall months, the average ranges of pH,

alkalinity, and free dissolved C02 (measured by titration) for the five

stations in the upper and middle reaches were:

                                                    Free Dissolved
Location


Chain Bridge

W. Wilson Bridge

Indian Head

Maryland Point

Rte. 301 Bridge


     In the vicinity of the Woodrow Wilson Bridge, there is an increase

in both alkalinity and C02 with a corresponding decrease in pH attri-

buted to wastewater discharges.  There is a decrease in both alkalinity

and COa 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.

     Salinity concentration as well as nutrient enrichment from waste-

water discharges has a pronounced effect on the ecology of the estuary.

Under summer and fall conditions, large populations of blue-green algae,

primarily Anacystis sp. (Microcystis), are prevalent from the metro-

politan area as far downstream as Maryland Point.

     Under warm temperature and low-flow conditions, large standing

crops of this alga develop forming "green mats" of cells.  Chlorophyll a
-------
                                                                       12
concentrations (a measure of algal standing crop) range from approxi-



mately 50 to over 200 ug/1 in these areas of dense growth which at



times encompass approximately 50 miles of the upper and middle reaches



of the estuary.  These high chlorophyll levels are 5 to 10 times those



reportedly observed in other eutrophic waters [5] [32].  During a dense



bloom, the dry weight of cells ranges from 10 to 25 mg/1 which is almost



twice those reported for the Madison, Wisconsin lakes [22].



     Chlorophyll a determinations for the upper reach and for the middle



and lower reaches of the Potomac Estuary are presented in Figures 5 and



6, respectively.  At Indian Head and Smith Point for 1965-1966 and



1969-1970, the chlorophyll a. concentrations indicate that algal popu-



lations have not only increased in density in the latter years but have



become more persistent over the annual cycle.  At both stations, higher



values of chlorophyll were measured during the 1969-1970 sampling



cruises than during the 1965-1966 cruises even though flow conditions



were more stable in 1965-1966.  The occurrence of a spring bloom of



diatoms was observed in 1969 and 1970 but not during the 1965-1966



cruises.



     In the mesohaline portion of the lower reach of the Potomac



Estuary, the,algal populations are not as dense as in the freshwater



portion.  Nevertheless at times, large populations of marine phyto-



plankton (primarily the dinoflagellates Gymnodinium sp. and Anrohidinium



sp.) occur producing what are known as "red tides."
-------
-------
MAINS  POINT
   WLES BELOW  CHAM  (DOGE =760
CHUOROPHYLL  a
POTOMAC ESTUARY
    U»>P€R REACH
PISCATAWAY  CREEK
   MLES KLOW CHAIN BRIDGE ' *.»
-------
 SMITH  PONT
    MLES  BCLOW CH/MN  MDGC •
  CHUDfiQPHYLL  a
  POTOMAC  ESTUARY
MBOUE  •-*  LOWER MCACM
                                                       OCT    MOV
301  BRIDGE.
   MLES KLDW  CHAIN  BRIDGE * 67 4Q
PtNCY  POINT
   MLE.S BUOW  CHAIN  BRlOot = M 20
-------
                                                                        15
 ECOLOGICAL TRENDS AS RELATED TO  NUTRIENT  ENRICHMENT



     Since the  first observations  reported  in  1913,  the effect  of the



 increased nutrients on the  ecology of the upper Potomac Estuary has



 been dramatic (Figure ?)„   Historical invasions of nuisance plant



 growths  in the  upper Potomac Estuary can  be  inferred from several



 studies.  Gumming  [6] surveyed the estuary  in  1913-1914 and noted



 the absence  of  plant life near the 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 phyto-



 planlrton blooms were noted „



     In  the  1920's, an infestation of water  chestnut appeared in the



 waters of the Chesapeake Pay including the Potomac Estuary,  This



 infestation  was controlled  by mechanical  removal [23],



     In September and October 1952, another  survey of the reaches near



 the metropolitan area made by Eartsch [2] revealed that vegetation



 in the area  was virtually nonexistent.  While  no massive phytoplankton



 blooms were  reported, there  was a  noticeable increase in blue-green



 algae and diatoms when compared to the 1913-1914 studies,.



     In August  and September 1959, a survey  of the area was made by



Stotts and Longwell [28]„  Blooms  of the nuisance blue-green alga



Anacystis were  reported in the Anacostia and Potomac Rivers near



Washington„




     In 1958 a rooted aquatic plant, water milfoil,  developed in the



waters of the Chesapeake Bay including the Potomac Estuary and created
-------
                                              D •» NO98VO DINV9MO
I
UJ
O
I
o
2
UJ


O

I
-------
                                                                       17

nuisance conditions.  The growth increased to major proportions by 1963,
especially in the embayments from Indian Head downstream [8] and then
dramatically disappeared beginning in late 1965.  The decrease was
presumably due to a natural virus [3].
     Subsequent and continuing observations by the Chesapeake Technical
Support Laboratory (CTSL) staff have confirmed persistent massive summer
blooms of the blue-green algaJjaafiXfliifi.  Nuisance concentrations occur
from the Washington Metropolitan Area downstream as far as Maryland
Point [16].
     From the above considerations, it would appear that nuisance
conditions did not develop linearly with an increase in nutrients .
Instead, the increase in nutrients appeared to favor the growth and
thus the domination by a given species .  As nutrients increased further,
the species in turn was rapidly replaced by another dominant form.  For
example, water chestnut was replaced by water milfoil which in turn was
replaced by
     Figure 7 indicates that the massive blue-green algal blooms now
occurring every summer since I960 are associated with large phosphorus
and nitrogen loading increases in the upper reaches of the Potomac River
tidal system.  The blooms have persisted since the early I960 'a although
the amount of organic carbon from wastewater has been reduced by almost
50 percent of that discharged prior to I960.  Moreover, the organic
carbon loadings being discharged now are equal to those that were
discharged in the early 1940 's when there were no reported nuisance
-------
                                                                       18
conditions as a result of algal growth.  These observations tend to



suggest that the ecological changes have been caused by increases in



nitrogen and phosphorus and not by organic carbon.
-------
                                                                       19





NUTRIENT SOUHCE5 AND CONTROLLABILITY



     A complete analysis of the nutrient sources in the upper Potomac



Estuary has been made by Jaworski ei si [17]„  A summary of the three



major sources is presented in Table 1 for low- and median-flow conditions.



For low- and median-flows, the contribution from wastewater discharges



of the three nutrients on a percentage basis is presented below:




                 Percentage from Wastewater Discharges



            Excluding Air-Water Interface   Including Air-Water Interface
Median Flow
(*)
Carbon
Nitrogen
Phosphorus
29
60
82
to
to
to
Low Flow
(*)
55
90
96
Median Flow
00
12
59
82
to
to
to
Low Flow
(*)
15
89
96
From the above tabulation, it can be concluded that the order of control-



lability of nutrients by wastewater treatment is (1) phosphorus,



(2) nitrogen, and (3) carbon.



     While 82 to 96 percent of the phosphorus entering the upper estuary



can be controlled by removal at the wastewater treatment facilities, an



additional reduction of phosphorus concentration occurs during periods of



high runoff within the upper estuary itself.  As reported by Aalto e% aj.



[1], large quantities of phosphorus (over 100,000 Ibs/day) enter the



upper estuary during high-flow periods at concentrations over 0.5 mg/1



(1.5 mg/1 as PO/;) during the rising portion of the river discharge



hydrograph.  However, high silt concentrations also accompany high flows.
-------
                       SUMwJlv; w>' r'i'r.'i. fiiVC SGUHCiiS

             Upper arid .Middle )> i^v.s  :;f the Potomac Estuary
        (Potomac Rivei Discharge t •-  I'^cdngtoi!,  D  G, - 1200 cfs)

                    l£ ""i              '•'urflsv y-:.;'          fit..:-Water
Carbon

Nitrogen

Phosphorus
170,000

  6,700

  1 .000
                                         60000
                                            000
                                                          (Ibs/day)

                                                           9SO,,000'W-
0
        (Potomac Hivei Dx.^charge c*t Waojiington,  D. C. = 6500 CAS)

Carbon             350,000             j.bO.,000.-            950,000"*

Nitrogen            40,000              60,,000              1^600***

Phosphorus           >,3CO              2-4,000                  0


  * Of the 160,000 Ibs/day, 60/..00 .i;}s/d,-%y  ave  discharged as inorganic
    carbon

 •** The potential  G02 obtainable from tLe atmosphere was determined by
    using only  0.1 percent of the iTai%dfer  rate of 0,,6 mg/cm2/min as
    indicated by Riley and Skirrow [15]

    Based on a  nitrogen fixation i-ane -jf five Ibs/'aere/year as reported
    by Hutchinson  [14]
-------
                                                                       21






Large amounts of phosphorus &:*& s^^t"! -upon ths s;i-it particles and



removed from the water system as sedimentation occurs in the upper reach



of the estuary.



     This deposition vras also Disarmed in the summer of 1970 (Figure 8)0



During the month of June, the average flow of the Potomac at Washington




was approximately 6,,000 cfs with a dally contribution of approximately



2,000 Ibs/day of phosphorus to the ipper Sfctuary,  During the period



from July 10 to July 11, 1970, the flow increased to over 47.,000 cfs



contributing over 70,000 Ihs/da." of phosphorus.  By July 13, the flow



decreased to less than 19,000 cfe with the flow on July 22 being less



than 5,000 cfs and the phosphorus contribution decreased to less than



3,000 Ibs/day.



     Although thare was some dilution of high phosphorus concentrations,



the large sediment load reduced tne overall phosphorus concentration



by a minimum of 20 percent in the reaches upstream and downstream from



the major wastewater sources at River Mile 12,0.  (See profiles for



July 13 and July 22,  1970)  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 slgal  growing season and the large



losses to the sediments during high- flow periods made phosphorus an



ideal nutrient to manage.



     In periods of extremely high runoff, the concentration of nitrate




in the waters entering the Potomac Estuary from the upper basin also



increases; and at timesf over 300,000 Ibs/day of nitrogen enters the
-------
o
o:

z
s.
O
0
o
f-
2
„*
o
a

z
1
1
o
£
Q

5
-}
i
•
i
8
a
eg
M

S
1
1
1
    
-------
                                                                      23
upper estuary.  During the months of June through Octobers when blue-


green algal growths become a nuisance,, the contribution from the upper


basin is small when compared to that from wastewater discharges (See


Table l).


     Based on data as presented in Table 1, the amount of atmospheric


nitrogen from rainfall, dustfall, and fixation by algae is approxi-


mately 1,600 Ibs/day for the upper and middle Potomac Estuary.


Extension of recent data from studies at the University of Wisconsin


[31] indicate that approximately 5,000 Ibs/day of nitrogen could be


fixed by blue-green algae in the upper and middle reaches of the


Potomac Estuary,,  Nevertheless, compared to all other sources, the


contribution from the atmosphere including that by nitrogen fixing


algae appears to be insignificant,  Thus, during the summer months,


algal control by management of nitrogen appears to be a feasible


alternative to phosphorus control.


     Under  summer flow conditions,  the alkalinity in runoff from the


upper basin ranges from 80 to 100 mg/1, with wastewater discharges


ranging from 100 to 150 mg/1.  Including runoff and wastewater dis-


charge sources only, approximately 60 to 70 percent of the total carbon


entering the upper estuary is in the inorganic form.


     Using only 0,1 percent of the transfer rate, the amount of carbon


(C02) potentially available from the atmosphere is approximately
                                                                    ^

950,000 Ibs/day (Table 1).  With the upper reach of the estuary well
-------
mixed due to tidal action, recruitment of carbon from benthic decompo-



sition also appears to be another significant source of inorganic



carbon.



     Data indicate that waters of the lower reach of the Potomac Estuary



and Chesapeake Bay are high in alkalinity and inorganic carbon.  As the



salt wedge moves upstream, there appears to be some recruitment of



alkalinity and inorganic carbon from the Chesapeake Bay into the lower



and middle reaches of the Potomac Estuary [17J.  When all potential



sources are considered, it appears that the management of carbon for



algal control is not a feasible alternative at the present time.
-------
                                                                        25
 NUTRIENT TRANSPORT AND ALGAL STANDING CROP MATHEMATICAL MODELS



      In investigating the role of nitrogen and phosphorus  on the



 eutrophic conditions  in the Potomac  Estuary,  a detailed study of the



 movement of these nutrients was made using a  "real  time" dynamic



 water quality estuary mathematical model  [10]. Models  were  also



 developed for algal standing crops and dissolved  oxygen.



      Phosphorus movement in the estuary was simulated by using a depo-



 sition formulation based on second order  reaction kinetics.  As  shown



 in Figures  9 and  10,  the model accurately predicts  the  rate  of phos-



 phorus deposition.  Figure 11 indicates that the  deposition  rate is



 greatly affected  by temperature.   Analyses of  the bottom muds  of the



 estuary also indicate that large  quantities of phosphorus are  being



 lost  to sediments in  the vicinity of the  wastewater discharges.



      To determine if  the phosphorus  loss  is related to  algal growths,



 algal standing crops  were predicted  using a surrogate phosphorus



 mathematical model.   In the model, the loss in phosphorus was  con-



 verted to algal standing crops  using  a chlorophyll  a/phosphorus



 weight relationship as  given in Table  2.   Based on  six  simulated



 standing  crop studies,  it  appears  that only 10 to 30 percent of the



 phosphorus  losses from  the aqueous system can  be accounted for by



 uptake of algal cells.



      In  investigating the  role  of  nitrogen in  water quality management,



 a feedback  system of the nitrogen  cycle was incorporated into the



dynamic estuary mathematical model similar to that proposed by Thomann



Si &1 [29].  The model, as shown in Figure  12,  consists of six possible
-------
-------
                                                                8

                                                                I
                                                                UJ
                                                                00


                                                                UJ
                                                                _J

                                                                Z
( I/.•••)  Od  $V SnMOMdSOHd
                                                    FIGURE  9
-------
                                                            S


                                                            i

                                                            5



                                                            1
                                                            LJ
                                                            CD
                                                            J

                                                            2
(!/•")   Od SV SnWOHdSOHd
                                               FIGURE 10
-------
.OS


.08


.07


.06



.05




.04
            EFFECT OF TEMPERATURE

                       ON

        PHOSPHCJRUS  DEPOSITION  RATE

                 POTOMAC  ESTUARY
11,000 cf»
.03
                                                            saoocfs
.02-
                                                      185 cf»
01-
'08-


|Q7-


06-



05-
                                  (T«~v
                                               9 : 1.064
04-
03-
02-
                                           Kp.20'C: 0.0225 (BASE •)

                                           (SCCON D — ORDER KINETICS )
            T~
             5
                       10
                -1	T"
                15          20
                   TEMP.(0,*C)
T"
 25
—I	1
 30         35
    FIGURE  11
-------
                                                                       29





reactions:   (l) chemical and biological decomposition of organic nitrogen



to ammonia,  (2) bacterial nitrification of ammonia to nitrite and nitrate,



(3) phytoplankton utilization of ammonia, (4) phytoplankton utilization



of nitrite and nitrate, (5) deposition of organic nitrogen, and (6) the



death of the phytoplankton.  With the area near Woodrow Wilson Bridge



being light limited with respect to algal growths, the rate of phyto-



plankton utilization of ammonia appears to be less than that in the area



near Indian Head.



     For summer temperatures of 26°C to 29°C, first-order kinetic



reaction rates have been established for the various processes given



below:



     Nitrification by bacteria                  0.30  to  0.40



     Nitrogen utilization by phytoplankton      0.07  to  0.09



     Deposition of algal cells                  0.005 to  0.05




The first two processes (nitrification and nitrogen utilization)



including the reaction rates have been well established as shown in



the predicted profiles (Figures 13 and 14).  The effect of temperature



on the nitrification process and the rate of nitrogen utilization by



algal cells has also been formulated as shown in Figures 15 and 16.



     Initial simulations indicate that the rate of recycling of nitrogen



was not significant in the freshwater portions.  As can be seen in



Figures 13 and 14, there is a discontinuity in the nitrogen cycle at Nthe



point of saline intrusion.  This discontinuity appears to be a result of



the transformation from fresh to mesohaline organisms.  It appears that
-------
                                                                      30
the rate of decomposition of organic nitrogen is much slower than the
rate of bacterial nitrification or the rate of nitrogen uptake by algal
cells in that the predominant form of nitrogen in the middle and lower
estuaries is organic.
-------
                                Table 2

                          DATA SUMMARY OF

                   ALGAL CHEMICAL COMPOSITION STUDIES

                            Potomac Estuary
                          June - October 1970


Nutrient                     Btff, pf Nutrient                ing, of Nutrient
                           ug of Chlorophyll a              mg. of S. Solids


Carbon                            0.045                          0.331

Nitrogen                          0.010                          0.073

Phosphorus                        0.001                          0.006
-------
 to
 LJ
 O
to

tr
 c
 o
LJ


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to
LU
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to
-o
 g

LJ


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CO
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cr
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1

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to
               LU
               ^L.
                   Z
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                   O
               LJ   t
               K   Z
               tr

               z
               O
               u.
               tr
                     ,
                   8
                   1
              z   o
              3   i
                                                    1
                                                         s

                                                                            a

                                                                            CO
                                                                     FIGURE   12
-------
 u
\n
oo
O  2
_j  u
u.  t-
                                                                                     O

                                                                                     Q

                                                                                     Cf.
                                                                                     CD
                                                                                     u


                                                                                     I
                                                                                     Ul
                                                                                     CO
                                                                                     bJ

                                                                                     -J


                                                                                     2

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-------
z
o
2
UJ
O
oo
<£
0)
(M
00
         O)
                                  ^  O
                                  o
«M
    I  6
    P  3
O
cc
                                                     (M
                                                                                                            in
                                                                                                   m
                                                                                                  "(VI
                                                                                                           .o
                                                                                                            CJ
                                                                             O
                                                                             o

                                                                             IT
                                                                             03



                                                                             I
                                                                                                                  1
                                                                                                                  LJ


                                                                                                                  i
                                                                                                           _0
          (VJ
                                                                      oo

                                                                      d
                                                                      
-------
 0.4
 0.3-
EFFECT    OF  TEMPERATURE
               ON
    NITRIFICATION   RATE
       POTOMAC   ESTUARY
 0.2-
 0.1-
.09-
.08-
.07-
.06-

.05-

.04-


.03-



.02-
.01-
X>9-
)08-
>07-
06-

05-

04-
                   9=1.186
                   Kj^z Ouoea (BASE •)  at 2O'C
                   (FIRST ORDER  KINETICS)
03-
02-
01-
              "T
              5
T"
 10
-i	r
 15          20
  TEMPERATURE
     CO
"T"
 25
"T"
 30
                                                                                     35
                                                                           FIGURE  15
-------
            EFFECT   OF TEMPERATURE
                        ON
RATE   OF  NITROGEN   UTILIZATION   BY  ALGAE
                 POTOMAC ESTUARY
                NO3—»- ALGAL  NITROGEN
                                9 - 1.120
                                KN2 = 0.034 (BASE •) at 20*C
                                (FIRST ORDER KINETICS)
                               20
 I
25
                      TEMPERATURE
                         CO
30         35

 FIGURE 16
-------
                                                                       37






     Using the weight ratio of nitrogen to chlorophyll a (Table 2) and



the nitrogen model rates  indicated above, the dynamic model was expanded



to predict the concentration of chlorophyll a based on the utilization



of inorganic nitrogen.  In Figures 17 and 18, predicted profiles using



the surrogate algal model and observed data are presented.  The predicted



maximum concentrations compare closely to the observed data in both dis-



tribution and magnitude.  Eight other model predictions have been made



and will be described fully in a report currently being prepared by CTSL.



     A DO budget has been incorporated into the dynamic water quality



model consisting of the following five linkages:



     (1)  Oxidation of carbonaceous matter,



     (2)  Oxidation of nitrogenous matter (ammonia and organic),



     (3)  Oxygen production and respiration of simulated algal standing



          crops based upon the nitrogen cycle,



     (4)  Benthie demand, and



     (5)  Reaeration from the atmosphere.



The model, which is also  described in the CTSL report currently in



preparation, 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, (Figures 19 and 20 res-



pectively) demonstrate that the model can predict DO responses over a



wide range of freshwater  inflows.
-------
          
-------
B*
                              r
                              Si
                     TIAHdOWOTHO
                                         FIGURE  16
-------
          |
FIGURE  19
-------
                                                                         _ m

    t;  *.
    id  b
O
o
                                              O
                T     i      i     i      i     i      I     I

                                      V*")10
                                        00
                                                                            LJ
                                                                            o
                                                                          (M
                                                                            to

                                                                            3
                                                                        - o
                                                                   FIGURE  20
-------
                                                                        42


The basic coefficients used in the DO budget model were:


                                      Rate  (base e)   Temperature Coeffici-
          Process                     at 20 C         ent Q  (Tl - T20)

     Carbonaceous oxidation              0.230               1.047

     Nitrogenous oxidation               0.068               1.188

     Algal utilization of nitrogen       0.034               1.120

     Reaeration from the atmosphere       *                 1.021

The remaining processes in the DO budget are given below:

     Algal oxygen production rate = 0.012 mg Oa/hr/ug chlorophyll a

     Algal respiration rate = 0.008 mg 02/hr/ug chlorophyll §.

     Euphotic zone = 2 feet

     Respiration depth = full depth of water column

     Algal oxygen production period = 12 hours

     Algal respiration period = 24 hours

     Benthic demand rate = 1.0 gr 02/day sq meter

The five linkages provide a mechanism for not only investigating the

effects of the various components on the dissolved oxygen budget but

also for establishing the algal standing crop limits and nutrient

criteria.
* Based on a velocity and depth formulation
-------
                                                                        43





EUTROPHICATION CONTROL



     For purposes of water quality management, the upper Potomac



Estuary may be considered eutrophic when undesired standing crops



become the predominant plant life as is now occurring with the nuisance



blue-green alga species.  The major objectives for controlling the blue-



green algal standing crop in the upper estuary are fourfold;



  •  ' 1.  To reduce the dissolved oxygen (DO) depression caused by res-



piration and the decay of algal growths especially in waters over 10



feet in depth„  At times, DO depressions of more than 3.0 mg/1 below



saturation occur even during daylight hours.



     2,  To minimize the increase of ultimate oxygen demand which is



a result of the conversion of inorganic carbon and nitrogen to oxi-



dizable organic compounds by algal cells.  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 dioring 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 odors caused by blue-green algae if the upper estuary is to be used



as a supplemental water supply«,
-------
                                                                        •44
     To aid in defining an algal standing crop limit, a subjective



analysis using chlorophyll concentrations was developed incorporating



conditions having possible effects on water quality.  Four major



interferences are offered in this analysis (Table 3) including the



desired reduction in the chlorophyll standing crop for each of the



parameters.



     The desired maximum limit of 0.5 mg/1 DO below saturation was



set 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.



     Of the four interferences, the most stringent reduction percentage



is in the control of growths to prevent nuisance conditions.  From



the above analysis, a 75 to 90 percent reduction in chlorophyll



concentration will be required in the Potomac Estuary, or chlorophyll



levels of approximately 25 ug/1.
-------
        to
                 UN
                 vo
        o*
                 o
                  •
                                              o

                                              5?
                                              o
                                              •p
I

        tfN
         •

        H
        8
9

a
                    §


                                                    I
-------
                                                                      46

                                                               .»
ESTABLISHMENT OF NUTRIENT CRITERIA

     Various investigators studying algal growth requirements have

discussed 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  [27] recommended

limits of inorganic nitrogen and inorganic phosphorus of 0.35 and 0.02,

respectively.  Mackenthun [24] 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 [9].  No recommendations for

inorganic nitrogen were presented other than that the naturally

occurring ratio of nitrogen to phosphorus should not be radically

changed.

     Pritchard [25], studying the Chesapeake Bay and its tributaries,

suggests that if total phosphorus concentrations in estuarine waters

are below 0.03 mg/1, biologically healthy conditions will be maintained.

Pritchard suggested no limit for nitrogen.  Jaworski et al [16], reviewing

historical data for the upper Potomac Estuary, indicated that if the

concentrations of inorganic phosphorus and inorganic nitrogen were at

or above 0.1 and 0.5, respectively, algal blooms of approximately 50 ug/1

would result.  Chlorophyll a. of 50 ug/1 or over was considered indicative

of excessive algal growths.   Studies of the James River Estuary, a sister

estuary to the Potomac, by Brehmer and Haltiwanger [4] indicate that

nitrogen appears to be the rate limiting nutrient.
-------
      Recently, the management of carbon in controlling algal blooms



 has been suggested by Kuentzel [20]  and Lange [21]„   Studies by Kerr



 ei si [191  also suggest that inorganic carbon is  apparently directly



 responsible for increased algal populations in waters that  they have



 studied. The Kerr studies indicate  that the addition of nitrogen and



 phosphorus  indirectly increases algal growth by stimulating growth of



 large heterotroph^c bacterial populations.   No criteria for nitrogen,



 phosphorus, of carbon were indicated by Kerr.



              ion to the data reviewed above and that  cited  by numerous



     stigators not reported,  six methods were used to  develop the  nutrient



 requirements for the Potomac Estuary.   The  six were:



      1.   Algal chemical composition  analyses,



      2.   Analysis of the nutrient  data on an annual cycle and profile



          basis,



      3o   Nutrient bioassay,



      40   Nutrient and algal  mathematical modeling,



      5.   Comparison with an  estuary  currently not eutrophic,  and



      6.   Review  of historical nutrient and  ecological trends  in the



          Potomac Estuary.



 1.  Algal Composition Analysis



     An  analysis of the  chemical composition of blue-green algae  in the



 Potomac  was  made during  the  summer months of 1970.  Summary  data  in terms



 of micrograms  of chlorophyll a and grams  of  suspended solids are presented



in Table 2.
-------
-------
                                                                        4B
Baaed on data  in Table 2, an algal bloom of 100 ug/1 chlorophyll
contains the following:
              5. Solids                    14.2 ag/1
              Carbon                        4.5 mg/1
              Nitrogtn                      1.0 mg/1
              Phosphorus                    0.1 ng/1
For tha Potomac Eatuary, which can ba oonsidared a alow-moving
oontinuoua culture system, ooncantrations equal to or lass than
1.12 mg/1 of carbon, 0.25 ng/1 of nitrogen, and .025 ng/1 of phos-
phorus would ba thaorrtioally required to maintain a 25 ug/1
chlorophyll 4 laval.  Upper limits of nutrianta using this mathod
should ba oonaidarad miniaal conoantrationa, ainoa no loaa to
aadiaanta ia assumed,
2   An>l.¥Mij of Dit> an an Aimml Qvola >nd Longitudinal Pmftl* BaaiM
     Nutrianti not rajtovad fron tha watara ara it ill oapabla of tup-
porting tha growth of algaa and othar organiaaa if thara ia an adaquata
aupply of tha raaaining autrianta in tha aoallaat quantity naadad
for growth*  Using tha disappaaranoa of a apacifio nutriant both
aaasooally and along longitudinal profilas, insight can ba gainad as
to tha possibility that tha nutriant ia limiting algal growth.  This
taauffjaa that othar anviromantal factors do not rastriot growth.
     Ami Indian Kaad to flaith Point, which is tha am of pronounoad
algal growth! thara is ovar 0.15 ag/1 of phosphorus in tha watara avan
undar mxitum bloom conditions,  (In Figura 2, inorganic phosphorus
-------
                                                                       49
concentrations are given.)  Data indicated that in the upper and middle



reaches of the Potomac, phosphorus is in excess and thus is not rate



limiting.  In the lower reach near Piney Point, the total phosphorus



concentration is often 0.04 mg/1 and thus phosphorus could be limiting



for this reach.



     When the N02 + N03 and NH3 concentrations shown in Figures 3 and 4



are reviewed, it is evident that 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-nAugust 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 a major factor in limiting algal growth in the middle and lower



estuary.



     To determine if carbon was limiting algal growth in the bloom area



of the Potomac Estuary, a review of historical alkalinity data was made.



Total and inorganic carbon analyses were also conducted during the latter



part of 1969 and throughout 1970.



     During August and September 1970, river flows were low with air



temperatures reaching 95°F during most of the days in September.



Dense algal blooms extended from Hains Point to Smith Point.  Carbon
-------
                                                                        50
concentrations obtained during a sampling cruise on September 20, 1970,

were as follows:

Station                        Organic Carbon        Inorganic Carbon
                                  (55713
Hains Point                         7.2                    12.2

Wilson Bridge                      10.2                    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 obtained during the mid-day hours of September 20, 1970,

indicate that large quantities of inorganic carbon were available for

algal growth even during periods of dense blooms.  The 1969 data,

historical alkalinity data, and other 1970 cruise data also substantiate

the September 1970 findings.

3 .  Bj.oassay Studies

     To determine further what nutrients were limiting algal growth

in the Potomac, bioassay tests as developed by Fitzgerald [11] [12]

were 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
-------
                                                                        51
in the range of 10   mg N/hr/ug chlorophyll a.  The cells had adequate

nitrogen available for growth as was also indicated by the high nitrate

concentration in the water, especially at the upper stations above

Indian Head.

     Tests for the latter part of July and August exhibited rates of

absorption that were approximately twice as high for the Indian Head

station as for the lower station at Maryland Point.  In addition, when

compared to the earlier data, the absorption rates were considerably

higher ranging in the area of 10   mg N/hr/ug chlorophyll §_„

     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.
                                  N02 + NO-}              Ammonia
Station          In Water         In Water          Nitrogen Absorbed
                  (mg/l)           (mg/i)          (mg N/hr/ug chloro)

Piscataway         .110             2.560              + 6,0 x 10"5

Indian Head        .150              .684              + 6,0 x 10"5

Possum Point       .001              .220              + 2.3 x 10"4

Smith Point        .001              .150              + 1.3 x 10"4

The higher rates of ammonia absorption for Possum and Smith Points and

the low concentration of inorganic nitrogen indicates that this reach

of the Potomac is becoming nitrogen limited.

     Two tests, an extraction procedure and an enzymatic analysis [12],

were used to determine if algal growth was phosphorus limited.  The

phosphorus extraction bioassay studies indicated very little difference
-------
-------
but i;
-------
-------
      i aese  •.. ri t.«-.




enhancement  o;




trends  j r   ne .. ,




an  envarurum.irt




occune'i  -   f *'•
                                                                     wEii  tor
                                                                e-it .f 'b,   .ra




                                                                ')•'  •O'-fj  .-.t-eate




                                                                • e;5t> j ui • w b 1 ch has




                                                                  ,-' cuTTfcv'  T. the
wastewa L>
from fres/i*H f ':    ,1 •.




rapid in  erv.m-'  •/•"  ..-•




iferyland  Poizi  .  •',•.•




plankton  pop", lat'i  . .




two part ^  pt i  the1 -< ••




of  the t.cunei.t  .01= ••




approximating  i   \,,\~-'\




      Bas ed on  ! •'.-:  a-



growth oi  'iiassj ;;--  :<•..




freshwater port j'uiifj,



were often encount.t »




      These obdt?rv«i • -




water quality n.enngM




      (1 )   FV< J.rJ \  ,i''-\




given reacJi of  th-  r-,
                       ">n.'
                              ht-
                                                           f ) /  .simi'p  transition




                                                             •  (--spond 4 rig 10




                                                             ,'••'-luiLe rc-fach at.




                                                           })"! H;;k'ton BJirt '^OO-




                                                           :  • .!  e;; .4 re  Lest:  ( ban




                                                           i" i:'iMC f.e •; h" k)wer end
 •:;.    M  -.ppears  That  the




1' f- • r;.' v  < -es tri CH ,? J to the




 
-------
-------
      (2)  There  is.



nut ri ent parairt v, e j f-:




given  est'iar.v«
Therefore, at tr.e p/v.^-.r.-1
established iur  c^t:  ifteaho -., .. •
                                                                              56
              ze on



     i/1  portions of a
-.'t  •; '-?;tev-i8 nave been




-t QUO. "  E?
-------
WASTEWATER TREATMENT REQUIREMENTS



      Under controlled cond.itJorr:, ;*s  r-vi-nrted  oy varictis investigators,



reductions in the standing ^rop of al/rv;  r-tn :,<=•  Chawed by the manage-



merit  of  either carbon, -nJtropen, o:c phosphorus or by o corrni nation of



these basic nutrients.  The ncc^s u>.r:  as to which nutrient or nutrients



in a  natural system should, be control led  by removal from point sources



may depend upor many fsc-t na jr/ciudiiTg the four  listed below:



      1.  Level of algal rea-ucticn requvrad to minimize adverse effects



on water quality,,



      2.  Minimuii' nutrjenl requirements to /naiintain a given algal



standing crop,



      3,  Controllability and mobility of a given nutrient within the



system,  and



      4.  The overall vrater <.uf«Vit,y management needs,  such as DO



enhancement,  eutrophicatlon reversal, and reduction of potentially



toxic matter including heavy mi;*,^"i:j.



      In  establishing !,he overs.n wutftewater uianage/nent prograwi for



the Potomac Estuary, tiif> IUM,, i Ui-ni,-  A.-r- ;:oth nitx-ogen and phosphorus



were
-------
                                                                       58





Limits for both were Incorporated for the following reasons °



      (l)  Since the flow of the Potomac Paver is very flashy, neither



phosphorus nor nitrogen can be controlled thrcsughout the estuary at



all times.  To reduce eutrophicaiicn i>>. the entire estuary for years




having average or above average flow conditions, phosphorus control



appears to be more feasible.  However, in, the middle and upper estuary




during low-flow years, nitrogen control appears to be more effective.



This  is because the nitrogen criterion for restricting algal growth



is ten times that for phosphorus (0.^0 versus 0.03 mg/l) while the



nitrogen loading from the wastewater treatment facilities is 2.4 times



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



a fourfold advantage in removing nitrogen over that of phosphorus.




      (2)  Various investigators report that increases in nitrogen and/or



phosphorus can increase heterotropbic activity which in turn stimulates



algal growth, and



      (3)  There is compatibility between wastewater treatment require-



ments for dissolved oxygen enhancement and eutrophication control.



     Compatibility of treatment requirements is probably one of the



most important considerations of the four factors influencing the



selection of wastewater treatment unit processes.  For example, to



maintain the dissolved oxygen standard In the upper estuary under



summer conditions, a high degree of carbonaceous and nitrogenous
-------
                                                                       59
oxygen demand removal is required, whereas the control of algal



standing crops is predicated on phosphorus and nitrogen removal.



To obtain a high degree of carbonaceous oxyger. demand removal, a



chemical coagulation unit process is usually required beyond secondary



treatment.  This unit process will also remove a high percentage of



phosphorus.  The removal of the nitrogenous demand can be satisfied



by one of two methods:  (1) by converting the unoxidized nitrogen to



nitrates (commonly called nitrification), or (2) by removal of nitrogen



completely.  If a unit process such as biological nitrification-



denitrification is employed, both the DO and algal requirements for



nitrogen can be met.



     Thus with proper selection of wastewater treatment unit processes,



it is feasible not only to enhance the DO by removing the carbonaceous



and nitrogenous UOD but also to reduce nuisance algal growth by



removing nutrients.
-------
                                                                       60
A WATER QUALITY MANAGEMENT PROGRAM



     The  conferees of the Potomac River-Washington Metropolitan Area



Enforcement Conference agreed  on May  8, 1969, to limit the amount of



UOD, phosphorus, and nitrogen  which could be discharged into the upper



estuary from wastewater treatment facilities.  The water quality




management program currently being developed recognizes a need not



only for  high degrees of wastewater treatment for the removal of



carbonaceous and nitrogenous UOD but also a need for the control of



eutrophicat ion.



     Segmenting the upper estuary into three 15-mile zones (Figure 21),



maximum Ibs/day loadings were  established for Zone I equivalent to



96 percent removal of BODj, 96 percent of phosphorus, and 85 percent



of nitrogen.  These percent removals were also adopted for discharges



in Zone II until firmer loadings could be developed.



     Since May 1969, more detailed loadings have been developed and



presented to the conference in the December 1970 progress meeting [18].



The program calls for the construction of advanced wastewater treatment



facilities by 1977 capable of removing the above designated percentages



of carbon, nitrogen, and phosphorus,  with possible advancement of the



construction deadline to December 1974.



     Present worth cost of the additional wastewater treatment required,



including operation, maintenance,  and amortization for the time period



1970 to 2020 has been estimated to be $1.2 billion with a total average



annual cost of $54.8 million.   The unit processes  assumed include
-------
                            /          \
                                                 RIVER MILES FROM  CHAIN BRIDGE = 0
                                            (STRICT OF  COLUMBIA
                       ALEXANDRIA
                          WESTGATE
                                                  RIVER MILES  FROM  CHAIN  BRIDGE - IS
              LITTLE HUNTING  Cr.
                                                                ANDREWS A.F.B.
                                PISCATAWAY  Cr.
                                                                   ZONE   II
                                                 RIVER MILES  FROM  CHAIN   BRIDGE - 30
                   WASTEWATER   DISCHARGE  ZONES
                        in  UPPER POTOMAC ESTUARY
ZONE  III
                                                 RIVER MILES  FROM  CHAIN  BRIDGE - 45
   FORT  BELVOIR
LOWER POTOMAC
                                                                         FIGURE  21
-------
                                                                       61
activated sludge, biological nitrification-denitrification, lime clari-



fication, filtration, effluent aeration and chlorination.  On a per



capita basis, the cost of the wastewater removal program is estimated



to be approximately $13.50 to $!8.30/person/year0



     The program being developed will not only enhance the water




quality of the estuary to meet minimum designated standards but will



render it a feasible source of municipal water supply.  Studies



indicate that either indirect or direct reuse of renovated waste-



water is a viable alternative in meeting the water supply needs for



the Washington, V. C. Metropolitan Area [15] [17].
-------
                                REFERENCES


 1.  Aalto, J. A., N. A0 Jaworski, and Donald W. Lear, Jr., "Current
     Water Quality Conditions and Investigations in the Upper Potomac
     River Tidal System," CTSL, MAR, FWQA, U. S. Department of the
     Interior, Technical Report No. 41, May 1970.

 20  Bartsch, A. F., "Bottom and PlaTikton Conditions in the Potomac
     River in the Washington Metropolitan Area," Appendix A, A report
     on water pollution in the Washington metropolitan area, Interstate
     Commission on the Potomac River Basin, 1954.

 3,  Bayley, S., H. Rabin, and C0 H. Southwick, "Recent Decline in the
     Distribution and Abundance of Eurasian Watermilfoil in Chesapeake
     Bay," Chesapeake Science, Vol. 9, No. 3, 1968.

 4.  Brehmer, M. L. and Samuel 0. Haitiwanger, "A Biological and
     Chemical Study of the Tidal James River," Virginia Institute of
     Marine Science, Gloucester Point, Virginia, November 15, 1966,

 5.  Brezanik, W. H., W. H. Morgan, E. E. Shannon, and H. D. Putnam,
     "Eutrophication Factors in North Central Florida Lakes," Florida
     Engineering and Industrial Experiment Station, Bulletin Series
     No. 134, Gainesville, Florida, August 1969,

 6.  Gumming, H. S., ".'nvestigation of the Pollution and Sanitary
     Conditions of the ?otomac Watershed," Appendix to USPHS Hygiene
     Laboratory Bulletir 104, 1916.

 7.  Edmondson, W. T., 'The Response of Lake Washington to Large Changes
     in its Nutrient Income," International Botanical Congress. 1969.

 8.  Elser, H. J., "Status of Aquatic Week Problems in Tidewater
     Maryland, Spring 1965," Maryland Department of Chesapeake Bay
     Affairs, 8 pp mimeo, 1965.

 9.  Federal Water Pollution Control Administration,  "Water Quality
     Criteria," Report of the National Technical Advisory Committee to
     the Secretary of the Interior, April 1, 1968„

10.  Feigner, K. and Howard S. Harris, Documentation Report, FWQA
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11.  Fitzgerald, George P., "Detection of Limiting on Surplus Nitrogen
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12.  Fitzgerald, George P. and Thomas C. Kelson, "Extractive and
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13.  Easier, A. D., "Culture Eutrophication is Reversible," Bioscience.
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14,  Hutchinson, G. E., A Treatise on Limnology. Vol. 1,  John Wiley
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15.  Hydroscience, Inc., "The Feasibility of the Potomac  Estuary as a
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16.  Jaworski, N. A0, D. W. Lear, And J. A. Aalto, "A Technical Assess-
     ment of Current Water Quality Conditions and Factors Affecting
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17.  Jaworski, N. A., Leo J. Clark, and Kenneth D. Feigner, "A Water
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IS.  Jaworski, N. A., Johan A. Aalto, Leo J. Clark, and Donald W. Lear, Jr.,
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     Area Enforcement Conference," CTSL FWQA., Environmental Protection
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19.  Kerr, Pat C,, Dorris F. Parie, and D. L. Bruckway, "The Inter-
     relation of Carbon and Phosphorus in Regulating Hetrotrophic and
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20.  Kuentzel, L. E., "Bacteria, C02 and Algal Blooms," Journal Water
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21.  Lange, W., "Effect of Carbohydrates on Symbolic Growth of Planktonic
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22.  Lawton, G. W., "The Madison Lakes Before and After Diversion,"
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23.  Livermore, D. F. and W. E. Wanderlich, "Mechanical Removal of
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24.  Mackenthun, K. M. "Nitrogen and Phosphorus in Water/1 USPHS,
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25.  Pritchard, Donald W., "Dispersion and Flushing of Pollutants in
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26.  Riley, J. P. and G. Skirrow, Chemical Oceanography. Vol. 1,
     Academic Press, London and New York, 1965.

27.  Sawyer, C. N., "1969 Occoquan Reservoir Study," Metcalf and Eddy,  Inc.
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28.  Stotts, V. D. and J. R. Longwell, "Potomac River Biological Investi-
     gation 1959," Supplement to technical appendix to Part VII of the
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29.  Thomann, R. 0., Donald J. O'Connor, and Dominic M. DiTorro, "Modeling
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30.  U. S. Public Health Service, "Investigation of the Pollution and
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31.  University of Wisconsin, Private Communication with George P.  Fitzgerald,
     January 19. 1971.

32.  Welch, E. B., "Phytoplankton and Related Water Quality Conditions  in
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