Water Quality Modeling

Application to Estuaries, Volume III

Wu-Seng Lung

• Publisher: CRC Press
• Year: 2021
• eBook ISBN: 9781000447576
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

This volume to discussing the various aspects of estuarine water quality modeling. Topics considered include fundamental principles, estuarine mass transport, BOD/DO and eutrophication model kinetics, kinetics on toxicants, and sediment-water interactions. The book also discusses mixing zone modeling and how to integrate estuarine hydrodynamic and water quality models. Many case studies demonstrating successful model applications are discussed.

Chapter 1
INTRODUCTION TO ESTUARINE WATER QUALITY MODELING

I. INTRODUCTION

In Volume I of this series: Transport and Surface Exchange in Rivers,¹ McCutcheon stated that models are necessary to both describe and predict water quality conditions. The same statement applies to estuaries. To put it into a perspective and to appreciate the need for estuarine water quality models, it is necessary to examine the water quality pollution control approaches that have been tried in the U.S. for the past two decades.

Before 1972, water pollution control efforts were based on achievement of ambient water quality standards.² Although this approach was economically efficient, it proved virtually impossible to administer, because of the difficulties in translating ambient standards into end-of-pipe effluent limits for individual dischargers, wasteload allocations (WLA). The result was regulatory frustration and very little cleanup. One of the factors that contributed to the frustration was that the “translating” technology, water quality modeling, was not ready at that time.

In 1972, the Federal Water Pollution Control Act was amended to require, at a minimum, a level of control based on available treatment technology. Under this approach, the need to determine impact on the ambient environment was largely eliminated. Instead, regulators had to determine appropriate control technology which is a much simpler technical task. The result was substantial reduction in pollution, even if this was achieved in areas in which cleanup was not needed to meet water quality goals. This was technology-based approach to water pollution control. Over the next half dozen years, secondary treatment was promulgated as the minimum level for all POTWs (publicly owned treatment works) on the assumption that the expected water quality responses were worth the expenditure. Wasteload allocation was used specifically for those instances where there was some doubt that the water quality standards could be achieved by secondary treatment alone.

The pendulum continued to swing between wasteload allocation and effluent requirements.³ In 1977, the Clean Water Act was passed. Water quality criteria for toxic substances were prepared and, in 1979, the EPA indicated that any requests for construction grants for advanced waste treatment must be rigorously justified through a cost-benefit analysis. It was clear by 1982 that EPA strongly favored water quality-based effluent limitations, rather than technology-based limits, as a basic water quality pollution control strategy, thereby reversing the trend. By that time, water quality modeling technology had advanced significantly and was ready to address a variety of water quality problems. This history indicates a clearer recognition of the importance of a rational approach to water quality management has finally emerged. Thus, contemporary water quality management programs are an integrated system of basic effluent requirements, supplemented by specific analyses of individual situations to arrive at a meaningful allowable discharge.

In the 1990s, wasteload allocation continues to be an important part of this overall process.³ In fact, the Water Quality Planning and Management Regulation (40 CFR 130) links a number of Clean Water Act sections, including sections 303(d), to form the water quality-based approach to protecting and cleaning up the nation’s waters. One of permit writers’ goals is to determine what effluent composition will protect aquatic organisms and human health. Exposure assessment includes defining how much of the waterbody is subject to the exceedance of criteria, for how long, and how frequently. The first step is to evaluate the effluent plume dispersion. If mixing is not rapid and complete, and if state water quality standards allow a mixing zone, the wasteload allocation should include a mixing zone analysis.

TABLE 1
History of Water Pollution Control and Water Quality Modeling Applications

Year	Water pollution control	Water quality modeling applications
Pre-1970	To achieve ambient water quality standards
	Impossible to administer (translating ambient standards into end-of-pipe effluent limits)	BOD/DO modeling
1970	EPA established	Aquatic plants/nutrient Eutrophication modeling
1972	Federal Water Pollution Control Act amended	Hydrothermal modeling
	NPDES permit program for municipal and industrial discharges (technology-based control)
	Substantial reduction in pollut...

Table of contents

• Cover
• Title Page
• Copyright Page
• Dedication
• Author
• Preface
• Contents
• 1. INTRODUCTION TO ESTUARINE WATER QUALITY MODELING
• 2. FUNDAMENTALS OF ESTUARINE MODELING
• 3. QUANTIFYING ESTUARINE MASS TRANSPORT
• 4. WATER COLUMN KINETICS I: DISSOLVED OXYGEN AND EUTROPHICATION
• 5. WATER COLUMN KINETICS II: TOXIC SUBSTANCES
• 6. MODELING SEDIMENT-WATER INTERACTIONS
• 7. INTEGRATING HYDRODYNAMIC AND WATER QUALITY MODELS
• 8. ESTUARINE MIXING ZONE ANALYSIS
• INDEX