vvEPA
United States
Environmental
Protection Agency
Office of Water
(4601)
EPA815-D-03-009
June 2003
Draft
LONG TERM 2 ENHANCED SURFACE WATER
TREATMENT RULE
TOOLBOX GUIDANCE MANUAL
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Note on the Long Term 2 Enhanced Surface Water Treatment Rule Toolbox
Guidance Manual, June 2003 Draft
Purpose: The purpose of this guidance manual, when finalized, is solely to provide technical
information on applying the "Toolbox" of Cryptosporidium treatment and management strategies
that are part of the upcoming Long Term 2 Enhanced Surface Water Treatment Rule
(LT2ESWTR). EPA is developing the LT2ESWTR to reduce the risk of Cryptosporidium and
other microbial pathogens in drinking water. This regulation would require certain public water
systems to provide additional treatment for Cryptosporidium by implementing one or more
options from the Toolbox. Chapter 1 of this manual contains additional information about this
regulation.
This guidance is not a substitute for applicable legal requirements, nor is it a regulation itself.
Thus, it does not impose legally-binding requirements on any party, including EPA, states, or the
regulated community. Interested parties are free to raise questions and objections to the
guidance and the appropriateness of using it in a particular situation. Although this manual
covers many aspects of implementing Toolbox options, the guidance presented here may not be
appropriate for all situations, and alternative approaches may provide satisfactory performance.
The mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
Authorship: This manual was developed under the direction of EPA's Office of Water, and was
prepared by The Cadmus Group, Inc and Carollo Engineers. Questions concerning this
document should be addressed to:
Mike Finn
U.S. Environmental Protection Agency
Mail Code 4607M
1200 Pennsylvania Avenue NW
Washington, DC 20460-0001
Tel: (202) 564-5261
Fax: (202) 564-3767
Email: fmn.michael@epa.gov
Request for comments: EPA is releasing this manual in draft form in order to solicit public
review and comment. The Agency would appreciate comments on the content and organization
of technical information presented in this manual. Please submit any comments no later than 90
days after publication of the Long Term 2 Enhanced Surface Water Treatment Rule proposal in
the Federal Register. Detailed procedures for submitting comments are stated below.
Procedures for submitting comments: Comments on this draft guidance manual should be
submitted to EPA's Water Docket. You may submit comments electronically, by mail, or
through hand delivery/courier.
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To submit comments using EPA's electronic public docket, go directly to EPA Dockets at
http://www.epa.gov/edocket, and follow the online instructions for submitting comments.
Once in the system, select "search," and then key in Docket ID No. OW-2002-0039.
• To submit comments by e-mail, send comments to OW_Docket@epa.gov, Attention Docket
ID No. OW-2002-0039. If you send an e-mail comment directly to the Docket without going
through EPA's electronic public docket, EPA's e-mail system automatically captures your e-
mail address, which is included as part of the comment that is placed in the official public
docket.
• To submit comments on a disk or CD ROM, mail it to the address identified below. These
electronic submissions will be accepted in WordPerfect or ASCII file format. Avoid the use
of special characters and any form of encryption.
To submit comments by mail, send three copies of your comments and any enclosures to:
Water Docket, Environmental Protection Agency, Mail Code 4101T, 1200 Pennsylvania
Ave., NW, Washington, DC, 20460, Attention Docket ID No. OW-2002-0039.
To submit comments by hand delivery or courier, deliver your comments to: Water Docket,
EPA Docket Center, Environmental Protection Agency, Room B102, 1301 Constitution
Ave., NW, Washington, DC, Attention Docket ID No. OW-2002-0039.
Please identify the appropriate docket identification number in the subject line on the first page
of your comment. If you submit an electronic comment, please include your name, mailing
address, and an e-mail address or other contact information in the body of your comment. Also
include this contact information on the outside of any disk or CD ROM you submit, and in any
cover letter accompanying the disk or CD ROM.
For public commenters, please note that EPA's policy is that public comments, whether
submitted electronically or in paper, will be made available for public viewing in EPA's
electronic public docket as EPA receives them and without change, unless the comment contains
copyrighted material, confidential business information, or other information whose disclosure is
restricted by statute.
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Contents
Figures x
Tables xii
Acronyms xiv
Chapter 1: Introduction
1.1 Objectives 1-1
1.2 Organization 1-2
1.3 Existing Regulations and Treatment Requirements 1-3
1.3.1 Surface Water Treatment Rule 1-3
1.3.2 Interim Enhanced Surface Water Treatment Rule 1-3
1.3.3 Stage 1 Disinfectants and Disinfection Byproducts Rule 1-4
1.3.4 Long Term 1 Enhanced Surface Water Treatment Rule 1-5
1.4 Microbial-Disinfection Byproduct Rule Summary 1-5
1.4.1 Stage 2 Disinfectant and Disinfection Byproduct Rule 1-5
1.4.2 Long Term 2 Enhanced Surface Water Treatment Rule 1-6
1.4.2.1 Filtered Systems 1-6
1.4.2.2 Unfiltered Systems 1-9
1.4.2.3 Uncovered Finished Water Reservoirs 1-10
1.5 Summary of Mcrobial Toolbox Options 1-11
1.6 Disinfection Profiling and Benchmarking 1-13
1.6.1 Creating a Disinfection Profile 1-15
1.6.2 Disinfection Benchmark 1-15
1.7 Implementation Schedule 1-16
Chapter 2: Watershed Control Program
2.1 Introduction 2-1
2.1.1 Credits 2-1
2.2 What Kinds of PWSs Should Implement Watershed Control Programs? 2-2
2.2.1 Case Studies of Existing Watershed Control Programs 2-2
2.2.2 What Are The Advantages and Di sadvantages of a
Watershed Control Program? 2-5
2.2.2.1 Advantages 2-5
2.2.2.2 Disadvantages 2-6
2.2.3 What If I Already Have a Watershed Control Program? 2-6
2.3 How Do I Apply for Approval? 2-7
2.3.1 Notifying the State of Intention to Participate 2-7
2.3.2 Initial Approval of Watershed Control Program Plan 2-7
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2.3.2.1 Vulnerability Analysis, Including Area of Influence 2-7
2.3.2.2 Analysis of Control Measures 2-8
2.3.2.3 Watershed Control Plan 2-8
2.3.2.4 Approval and Conditional Approval 2-8
2.3.3 Maintaining Approval of Watershed Control Program 2-8
2.3.3.1 Submit Annual Status Report 2-9
2.3.3.2 Conduct State-Approved Watershed Sanitary Survey 2-9
2.3.3.3 Request Review and Re-Approval 2-9
2.4 Developing the Watershed Control Program Plan 2-10
2.4.1 Vulnerability Analysis 2-10
2.4.1.1 What Should Be Included in a Vulnerability Analysis? 2-10
2.4.1.2 How Should I Identify the Area of Influence? 2-11
2.4.1.3 What and Where Are the Potential or Existing Sources of
Cryptosporidium? 2-14
2.4.1.4 How Do Fate and Transport Affect the Way Cryptosporidium
Impacts My Water Supply? 2-17
2.4.1.5 What Role Should Monitoring Play in a Vulnerability Analysis? 2-19
2.4.2 Analysis of Control Measures 2-21
2.4.2.1 How Should I Build Partnerships with Other Stakeholders? 2-22
2.4.2.2 What Regulatory and Other Management Strategies Are
Available to Me? 2-22
2.4.2.3 How Should Point Sources Be Addressed? 2-25
2.4.2 A WhatBMPs Can Help Alleviate Nonpoint Sources? 2-27
2.4.3 Writing the Watershed Control Plan 2-32
2.4.4 How States Should Assess Plans 2-32
2.5 Maintaining Approval of a Watershed Control Program 2-37
2.5.1 Annual Watershed Control Program Status Report 2-37
2.5.2 State-Approved Watershed Sanitary Survey 2-38
2.5.3 Request for Re-Approval 2-39
2.5.3.1 Describe Implementation of Plan 2-39
2.5.3.2 Describe How System Is Addressing Any Problems 2-40
2.5.3.3 Describe Need for Changes in Plan 2-40
2.5.4 Guidance to States on Re-Approval 2-40
Chapter 3: Alterative Source/Intake
3.1 Introduction 3-1
3.2 Changing Sources 3-2
3.2.1 Advantages and Disadvantages 3-2
3.2.2 Evaluation of Source Water Characteristics for Existing Treatment
Requirements 3-2
3.3 Changing Intake Locations 3-3
3.3.1 Applicability 3-3
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3.3.1.1 Advantages and Disadvantages 3-3
3.3.2 Reservoirs and Lakes 3-3
3.3.2.1 Depth 3-4
3.3.2.2 Stratification and Mixing 3-4
3.3.2.3 Proximity to Inflows 3-4
3.3.3 Streams and Rivers 3-5
3.3.3.1 Depth 3-5
3.3.3.2 Flow and River Hydraulics 3-5
3.3.3.3 Upstream Sources of Contamination 3-5
3.3.3.4 Seasonal Effects 3-5
3.4 Changing Timing of Withdrawals 3-6
3.4.1 Toolbox Selection Considerations 3-6
3.4.1.1 Advantages and Disadvantages 3-6
Chapter 4: Bank Filtration
4.1 Introduction 4-1
4.2 LT2ESWTR Compliance Requirements 4-2
4.2.1 Credits 4-3
4.2.2 Monitoring Requirements 4-4
4.3 Toolbox Selection Considerations 4-5
4.3.1 Advantages and Disadvantages 4-5
4.3.1.1 Removal of additional contaminants 4-5
4.3.1.2 Clogging of pores 4-7
4.3.1.3 Scour 4-8
4.3.1.4 Additional Treatment Steps 4-9
4.4 Site Selection and Aquifer Requirements 4-9
4.4.1 Selected Bank Filtration Sites 4-11
4.4.2 Aquifer Type 4-12
4.4.2.1 Unconsolidated, Granular Aquifers 4-12
4.4.2.2 Karst, Consolidated Clastic, and Fractured Bedrock Aquifers 4-12
4.4.2.3 Partially Consolidated, Granular Aquifers 4-13
4.4.3 Aquifer Characterization 4-13
4.4.3.1 Coring 4-14
4.4.3.2 Sieve Analysis 4-15
4.4.4 Site Selection as it Relates to Scour 4-16
4.4.4.1 Stream Channel Erosional Processes 4-16
4.4.4.2 Unsuitable Sites 4-17
4.5 Design and Construction 4-22
4.5.1 Well Type 4-23
4.5.2 Filtrate Flow Path and Well Location 4-25
4.5.2.1 Required Separation Distance between a Well and the
Surface Water Source 4-25
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4.5.2.2 Locating Wells at Greater than required distances from the
Surface Water Source 4-26
4.5.2.3 Delineating the edge of the Surface Water Source 4-29
4.5.2.4 Measuring Separation Distances for Horizontal Wells and Wells
that are neither Horizontal nor Vertical 4-31
4.6 Operational Considerations 4-32
4.6.1 HighRiver Stage 4-32
4.6.2 Implications of Scour for Bank Filtration System Operations 4-32
4.6.3 Anticipating high flow events / flooding 4-33
4.6.4 Possible Responses to Spill Events and Poor Surface Water Quality 4-33
4.6.5 Maintaining Required Separation Distances 4-33
Chapter 5: Presedimentation
5.1 Introduction 5-1
5.2 LT2ESWTR Compliance Requirements 5-2
5.2.1 Credits 5-2
5.2.2 Monitoring Requirements 5-2
5.2.3 Calculations 5-2
5.3 Toolbox Selection Considerations 5-3
5.3.1 Source Water Quality 5-3
5.3.2 Advantages and Disadvantages of Installing a Presedimentation Basin 5-4
5.4 Types of Sedimentation Basins 5-4
5.4.1 Horizontal Flow 5-7
5.4.1.1 Rectangular 5-7
5.4.1.2 Circular 5-7
5.4.2 Upflow Clarifier 5-7
5.4.3 Reactor Clarifier 5-7
5.4.4 High Flow Rate Designs 5-8
5.4.5 Ballasted Flocculation 5-8
5.5 Design and Operational Issues 5-8
5.5.1 Redundancy 5-8
5.5.2 Short Circuiting 5-8
5.5.3 Sludge Removal 5-9
5.5.4 Coagulant Addition and Dose Ranges of Common Coagulants 5-9
Chapter 6: Lime Softening
6.1 Introduction 6-1
6.2 LT2ESWTR Compliance Requirements 6-2
6.2.1 Credit for Cryptosporidium Removal 6-2
6.2.2 Reporting Requirements 6-3
6.3 Spilt-Flow Processes 6-3
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Chapter 7: Combined and Individual Filter Performance
7.1 Introduction 7-1
7.2 LT2ESWTR Compliance Requirements 7-2
7.2.1 Treatment Credit 7-2
7.2.2 Monitoring Requirements 7-2
7.2.2.1 Combined Filter Effluent 7-2
7.2.2.2 Individual Filter Effluent 7-3
7.2.3 Turbidity Monitors 7-3
7.2.3.1 Methods 7-4
7.2.3.2 Maintenance and Calibration 7-4
7.2.3.3 Quality Assurance / Quality Control (QA/QC) 7-6
7.3 Reporting Requirements 7-6
7.3.1 Combined Filter Performance 7-6
7.3.2 Individual Filter Performance 7-6
7.4 Process Control Techniques 7-7
7.4.1 Chemical Feed 7-11
1 A.I.I Type of Chemical and Dose 7-11
7.4.1.2 Mixing 7-11
7.4.1.3 Streaming Current Detectors and Zeta Potential Monitors 7-12
7.4.2 Flocculation 7-13
7.4.3 Sedimentation 7-13
7.4.4 Filtration 7-14
7.4.4.1 Flow Split 7-15
7.4.4.2 Filter Beds 7-15
7.4.4.3 Backwashing 7-15
7.4.4.4 Filter to Waste 7-16
7.4.4.5 Backwash Recycle 7-17
7.4.4.6 Filter Assessments 7-17
7.4.5 Hydraulic Control 7-17
7.5 Process Management Techniques 7-17
7.5.1 Standard Operating Procedures (SOPs) 7-17
7.5.2 Prevention and Response Plan for Loss of Chemical Feed 7-18
7.5.3 Adequate Chemical Storage 7-18
7.5.4 Voluntary Programs 7-18
7.5.4.1 Partnership for Safe Water 7-19
7.5.4.2 Composite Correction Program (CCP) 7-20
Chapter 8: Bag and Cartridge Filters
8.1 Introduction 8-1
8.2 LT2ESWTR Compliance Requirements 8-2
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8.2.1 Credits 8-2
8.2.2 Reporting Requirements 8-3
8.2.3 Integration Into a Treatment Process Train 8-3
8.3 Toolbox Selection Considerations 8-5
8.3.1 Advantages 8-5
8.3.2 Disadvantages 8-6
8.4 Challenge Testing 8-6
8.4.1 Testing Conditions 8-7
8.4.1.1 Full Scale Filter Element 8-7
8.4.1.2 Challenge Paniculate 8-7
8.4.1.3 Feed Concentration 8-7
8.4.1.4 Time Periods of Challenge Testing 8-8
8.4.1.5 Water Quality of Challenge Test Solution 8-8
8.4.1.6 Maximum Design Flow Rate 8-9
8.4.1.7 Challenge Particulate Seeding Method 8-9
8.4.1.8 Challenge Test Solution Volume 8-10
8.4.1.9 Sampling 8-11
8.4.2 Calculation of Log Removal 8-12
8.4.3 Modifications to Filtration Unit after Challenge Test 8-13
8.5 Design Considerations 8-14
8.5.1 Water Quality 8-17
8.5.2 Size of Filter System and Redundancy 8-17
8.5.3 Design Layout 8-17
8.5.4 Filter Cycling 8-18
8.5.5 Pressure Monitoring, Valves, and Appurtenances 8-18
8.5.6 Air Entrapment 8-18
8.5.8 NSF Certification 8-19
8.6 Operational Issues 8-19
8.6.1 Pressure Drop (Inlet/Outlet Pressures) 8-19
8.6.2 Monitoring 8-19
Chapter 9: Second Stage Filtration
9.1 Introduction 9-1
9.2 LT2ESWTR Compliance Requirements 9-1
9.2.1 Credits 9-1
9.2.2 Reporting Requirements 9-2
9.3 Toolbox Selection Considerations 9-2
9.3.1 Advantages 9-3
9.3.2 Disadvantages 9-3
9.4 Design and Operational Considerations 9-4
9.4.1 Hydraulic Requirements 9-4
9.4.2 Backwashing 9-4
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9.4.3 Turbidity Monitoring 9-5
Chapter 10: Chlorine Dioxide
10.1 Introduction 10-1
10.2 Log Inactivation Requirements 10-2
10.2.1 CT Calculation 10-3
10.3 Monitoring Requirements 10-6
10.3.1 LT2ESWTR 10-6
10.3.2 Stage 1 DBPR 10-7
10.4 Unfiltered System LT2ESWTR Requirements 10-8
10.5 Disinfection With Chlorine Dioxide 10-8
10.6 Toolbox Selection Considerations 10-9
10.6.1 Advantages 10-9
10.6.2 Disadvantages 10-9
10.7 Design Considerations 10-10
10.7.1 Designing to Lowest Temperature 10-10
10.7.2 Point of Addition 10-11
10.8 Operational Considerations 10-11
10.9 Safety Issues 10-12
10.9.1 Chemical Storage 10-12
10.9.2 Acute Health Risks of Chlorine Dioxide 10-12
Chapter 11: Ozone
11.1 Introduction 11-1
11.2 Credits 11-2
11.3 CT Determination 11-4
11.3.1 Measuring C for T10 and CSTRMethods 11-6
11.3.2 T10 Method 11-6
11.3.3 CSTRMethod 11-9
11.3.4 Extended CSTR Approach 11-12
11.4 Monitoring Requirements 11-13
11.4.1 LT2ESWTR 11-13
11.4.2 Stage 1 DBPR 11-13
11.5 Unfiltered System LT2ESWTR Requirements 11-13
11.6 Toolbox Selection 11-14
11.6.1 Advantages 11-14
11.6.2 Disadvantages 11-14
11.7 Disinfection With Ozone 11-15
11.7.1 Chemistry 11-15
11.7.2 Byproduct Formation 11-16
11.7.2.1 Bromate and Brominated Organic Compounds 11-17
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11.7.2.2 Non-Brominated Organic Compounds 11-17
11.8 Design 11-17
11.8.1 Generators and Contactors 11-17
11.8.2 Point of Addition 11-17
11.8.3 Biologically Active Filters 11-18
11.8.3.1 Media for Biologically Active Filters 11-18
11.8.3.2 Operating Biologically Active Filters 11-19
11.9 Safety Considerations in Design 11-19
11.10 Operational Issues 11-20
11.10.1 Ozone Demand 11-20
11.10.2 pH 11-21
11.10.3 Temperature 11-21
11.10.4 Maintaining Residual Disinfectant in the Distribution System 11-21
11.11 Request for Comment on Segregated Flow Analysis 11-21
Chapter 12: Demonstration of Performance (DOP): Microbial Removal
12.1 Introduction 12-1
12.2 LT2ESWTR Compliance Requirements 12-2
12.2.1 Credits 12-2
12.2.2 Reporting Requirements 12-3
12.3 Toolbox Selection Considerations 12-3
12.3.1 Overview of the Demonstration Protocol 12-4
12.4 DOP Criteria Development 12-5
12.4.1 Process Evaluation Criteria 12-6
12.4.1.1 Treatment Objectives 12-6
12.4.1.2 Influent Water Quality Characteristics 12-7
12.4.1.3 System Flow Rate 12-7
12.4.1.4 Plant Operating Conditions 12-7
12.4.2 Selection of Performance Indicators 12-8
12.4.2.1 Surrogate Parameters for Cryptosporidium 12-8
12.4.2.2 Long-Term Performance Indicators 12-9
12.4.3 Full-Scale Versus Pilot-Scale Testing 12-9
12.5 Demonstration Protocol 12-11
12.5.1 DOP Test Matrix 12-11
12.5.2 DOP Monitoring Plan 12-12
12.5.2.1 Sampling Location 12-14
12.5.2.2 Monitoring Parameters 12-14
12.5.2.3 Monitoring Frequency 12-14
12.5.2.4 Quality Assurance/Quality Control 12-14
12.5.3 DOP Implementation 12-14
12.5.3.1 Sample Collection Methods 12-15
12.5.3.2 Analytical Methods 12-15
12.5.3.3 Microbial Dosing 12-16
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12.5.3.4 Documentation of WTP Operating Conditions 12-16
12.5.4 Data Analysis and Reporting 12-17
12.5.4.1 Evaluation of Performance 12-17
12.5.4.2 Reporting for the OOP 12-17
12.5.4.3 Ongoing Reporting 12-18
Chapter 13: Ultraviolet Light
13.1 Introduction 13-1
13.2 Log Inactivation Requirements 13-1
13.2.1 Monitoring Requirements 13-1
13.2.2 Reporting Requirements 13-2
13.3 Toolbox Selection Considerations—Advantages and Disadvantages 13-2
13.4 Design and Operational Considerations 13-3
Chapter 14: Membrane Filtration
14.0 Membrane Filtration 14-1
14.1 Introduction 14-1
14.2 Log Inactivation Requirements 14-1
14.3 Toolbox Selection Considerations 14-1
14.4 Design Considerations 14-2
14.5 Operational Considerations 14-2
Appendix A: Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
Appendix B: Ozone CT Methods
Appendix C: Measuring Ozone Residual
Appendix D: Derivation of Extended CSTR Equations
Appendix E: Watershed Control Best Management Practices (BMPs)
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Figures
Chapter 1: Introduction
Figure 1.1 Systems Required to Develop a Disinfection Profile and Benchmark 1-14
Chapter 2: Watershed Control Program
Figure 2.1 Ground Water/Surface Water Interaction 2-13
Chapter 3: Alterative Source/Intake
Chapter 4: Bank Filtration
Figure 4.1 Generalized Depiction of Stream Channel Lateral Migration 4-21
Figure 4.2 Taking a Water Level Reading 4-22
Figure 4.3 Schematic Showing Generalized Flow and Required Separation Distance
to a Vertical Well 4-24
Figure 4.4 Schematic Showing Generalized Flow and Required Separation Distance
to a Horizontal Well With Three Laterals 4-25
Figure 4.5 The Streambed of a Perched Stream Is Well above the Water Table 4-27
Chapter 5: Presedimentation
Chapter 6: Lime Softening
Figure 6.1 Typical Two-Stage Lime Softening Process 6-2
Chapter 7: Combined and Individual Filter Performance
Chapter 8: Bag and Cartridge Filters
Figure 8.1 Schematic of Treatment Process with Bag/Cartridge Filters 8-4
Figure 8.2 Bag/Cartridge Filters in Series 8-4
Figure 8.3 Bag/Cartridge Filter with UV System 8-5
Figure 8.4 Single Filter Vessel 8-14
Figure 8.5 Manifold Bag Filter Design 8-15
Figure 8.6 Multiple Filter Vessel 8-16
Chapter 9: Second Stage Filtration
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Chapter 10: Chlorine Dioxide
Figure 10.1 CT Calculation Example Schematic 10-5
Chapter 11: Ozone
Figure 11.1 Reaction Pathways of Ozone in Water 11-16
Chapter 12: Demonstration of Performance (DOP): Microbial Removal
Figure 12.1 Flowchart for DOP Protocol 12-5
Chapter 13: Ultraviolet Light
Chapter 14: Membrane Filtration
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Tables
Chapter 1: Introduction
Table 1.1 Bin Requirements for Filtered Plants 1-8
Table 1.2 LT2ESWTR Treatment Requirements for Unfiltered Systems 1-10
Table 1.3 Summary of Microbial Toolbox Options with Available Log Credits and
Design/Implementation Criteria 1-11
Table 1.4 Compliance Dates 1-17
Chapter 2: Watershed Control Program
Table 2.1 Assessment Criteria for Use By States When Reviewing
Watershed Control Program Plans 2-34
Chapter 3: Alterative Source/Intake
Chapter 4: Bank Filtration
Table 4.1 Selected Bank Filtration Systems in Europe and the United States 4-11
Chapter 5: Presedimentation
Table 5.1 Influent and Effluent Turbidity Values Resulting in 0.5 Log Reduction 5-4
Table 5.2 Comparison of Sedimentation and Clarifier Types 5-6
Chapter 6: Lime Softening
Chapter 7: Combined and Individual Filter Performance
Table 7.1 Maintenance and Calibration Activities for On-line Turbidimeters 7-5
Table 7.2 Maintenance and Calibration Activities for Bench Top Turbidimeters 7-5
Table 7.3 Performance Limiting Factors
(Adapted from the Composite Correction Program) 7-8
Table 7.4 Effluent Turbidity Goals for the Sedimentation Process 7-14
Chapter 8: Bag and Cartridge Filters
Chapter 9: Second Stage Filtration
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Chapter 10: Chlorine Dioxide
Table 10.1 CT Values (mg-min/1) for Cryptosporidium Inactivation by C1O2 10-4
Table 10.2 Distribution System Monitoring Requirements at Each Plant 10-7
Chapter 11: Ozone
Table 11.1 CT Values for Cryptosporidium Inactivation by Ozone 11-3
Table 11.2 Applicable Methods and Terminology for Calculating the
Log-Inactivation Credit 11-5
Table 11.3 Correlations to Predict C* Based on Outlet Concentration 11-6
Table 11.4 Inactivation Coefficients for Cryptosporidium., Log base 10 (L/mg-min) 11-10
Chapter 12: Demonstration of Performance (DOP): Microbial Removal
Table 12.1 Filtration Plant Types Eligible for DOP 12-1
Table 12.2 Example DOP Test Matrix 12-12
Table 12.3 Example DOP Monitoring Plan 12-13
Chapter 13: Ultraviolet Light
Chapter 14: Membrane Filtration
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Acronyms
AFOs Animal Feeding Operations
AOC Assimilable Organic Carbon
ASTM American Society for Testing and Materials
BMPs Best Management Practices
CAFOs Concentrated Animal Feeding Operations
CCP Composite Correction Program
CFE Combined Filter Effluent
C102 Chlorine Dioxide
CPE Comprehensive Performance Evaluation
CSO Combined Sewer Overflow
CSTR Continuous Stirred Tank Reactor
CT Disinfectant Concentration x Contact Time
CTA Comprehensive Technical Assistance
CWSs Community Water Systems
DAF Dissolved Air Flotation
DBFs Disinfection Byproducts
DBPR Disinfection Byproducts Rule
DEM Digital Elevation Model
DOP Demonstration of Performance
E. coli Escherichia coli
EDTA Ethylenediamine Terra-Acetic Acid
EM Electromagnetic
EPA U.S. Environmental Protection Agency
FEMA Federal Emergency Management Agency
GAC Granular Activated Carbon
GIS Geographical Information System
GPR Ground Penetrating Radar
GWUDI Ground Water Under the Direct Influence of Surface Water
HAA Haloacetic acid
HAAS The sum of five HAA species [monchloroacetic acid, dichloroacetic acid,
trichloroacetic acid, monobromoacetic acid, dibromoacetic acid]
HOT Hydraulic Detention Time
HPCs Heterotrophic Plate Counts
HUC Hydrologic Unit Code
IDSE Initial Distribution System Evaluation
IESWTR Interim Enhanced Surface Water Treatment Rule
IFE Individual Filter Effluent
IP Induced Polarisation
k* Ozone decay rate
k10 Log base ten lethality coefficient
LRAA Locational Running Annual Average
LTIESWTR Long Term 1 Enhanced Surface Water Treatment Rule
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LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule
MCL Maximum Contaminant Level
M-DBP Microbial and Disinfection Byproduct
MF/UF Microfiltration and Ultrafiltration
mL Milliliters
MRDLs Maximum Residual Disinfectant Levels
MS4s Municipal Separate Storm Sewer Systems
MTBE Methyltertiarybutylether
NHDES New Hampshire Department of Environmental Services
NOM Natural Organic Matter
NPDES National Pollutant Discharge Elimination System
NRCS Natural Resources Conservation Service
NTNCWSs Nontransient Noncommunity Water Systems
NTU Nephelometric Turbidity Units
OSHA Occupational Safety and Health Administration
PCR Polymerase Chain Reaction
PWS Public Water System
QA Quality Assurance
QA/QC Quality Assurance/Quality Control
RAA Running Annual Average
SCD Streaming Current Detectors
SDWA Safe Drinking Water Act
SF A Segmented Flow Analysis
SMP Standard Monitoring Program
SOCs Synthetic Organic Compounds
SOPs Standard Operating Procedures
SP Self-Potential
SPDES State Pollution Discharge Elimination System
SSDR Stock Solution Delivery Rate
S S O s Sanitary Sewer Overflows
SSS System-Specific Study
Stage 1 DBPR Stage I Disinfection Byproducts Rule
SWTR Surface Water Treatment Rule
TCE Trichloroethylene
TEM Pusle-transient Electromagnetic
TFCVI Trihalomethane
TNCWSs Transient Noncommunity Water Systems
TOC Total Organic Carbon
TTHM Total Trihalomethanes
UFRVs Unit Filter Run Volumes
UPS Uninterruptible Power Supply
USD A U. S. Department of Agriculture
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USGS U.S. Geological Survey
UV Ultraviolet Light
UV254 Ultraviolet Light at a wavelength of 254 nm
WTP Water Treatment Plant
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1.0 Introduction
In establishing drinking water regulations for microbial and disinfection byproduct (M-DBP)
control, the U.S. Environmental Protection Agency (EPA) is promoting a multi-barrier approach for
treating drinking water. A multi-barrier treatment process provides a number of protective "layers"
against contamination by using more than one method of prevention and treatment to remove or
inactivate microorganisms and minimize disinfection byproducts (DBFs). To that end, EPA is publishing
this guidance to help public water systems (PWSs) choose appropriate combinations of treatment
processes for compliance with the Long Term 2 Enhanced Surface Water Treatment Rule
(LT2ESWTR).
The LT2ESWTR focuses on improved control of microbial contamination, specifically the
protozoan parasite Cryptosporidium. Differing from previous drinking water regulations, the
LT2ESWTR requirements for each system are based on the PWS's vulnerability to contamination, as
measured by the occurrence of Cryptosporidium in the source water. This "Microbial Framework"
strategy stems from a recognition that only some systems may need to provide additional protection
against Cryptosporidium and that such decisions should be made on a system-specific basis.
With this approach, systems initially conduct source water monitoring to determine average
Cryptosporidium concentrations (small filtered systems first monitor for E. coli to determine if
Cryptosporidium monitoring is required). Based on their monitoring results, systems are classified into
different categories (or bins). The bins indicate the additional Cryptosporidium treatment
requirements, if any, that must be met to comply with the rule. Systems required to provide additional
treatment will choose from a "toolbox" of options consisting of treatment technologies, process
optimization techniques, and management techniques to meet the requirements. Thus, this approach
requires enhanced Cryptosporidium treatment for systems with higher vulnerability to
Cryptosporidium contamination and provides several options for those systems to achieve compliance.
These options are described in this manual.
1.1 Objectives
The primary objectives of this manual are to provide guidance to public water systems for
selecting appropriate toolbox options and achieving compliance for each option. To accomplish these
objectives, this manual will describe each toolbox option in terms of achieving Cryptosporidium
treatment credit(s) and discuss design and operational issues systems should consider for each option.
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1.2 Organization
This manual consists of fifteen chapters and appendices:
Chapter 1
Chapters 2-14
Introduction - The remainder of this chapter summarizes the LT2ESWTR,
presents the bin classifications for conventional treatment plants, direct
filtration plants, and plants with other treatment technologies (i.e., softening,
slow sand filtration, and diatomaceous earth filtration), and defines those
processes in the context of the LT2ESWTR.
Toolbox Options - These chapters describe each toolbox option and how
systems can implement these options to achieve the associated
Cryptosporidium treatment credit. Where applicable, basic design criteria
are recommended to achieve a given log removal. Each chapter contains
its own list of references.
Appendix A Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
describes the different elements of a site specific study to generate a set of
chlorine dioxide or ozone CT values for that site and discusses some of the
issues involved in the statistical analysis of the results.
Appendix B Ozone CT Methods - describes the Segmented Flow Analysis and Extended-
CSTR methods to calculate the CT inactivation credits with ozone.
Appendix C Measuring Ozone Residual - discusses ozone residual sample collection,
measurement, and online ozone residual analyzer calibration.
Appendix D Derivation of SFA and Extended CSTR Equations - provides derivations for
the Segmented Flow Analysis equation and the equation used to calculate k*.
Appendix E Watershed Control Best Management Practices (BMPs^ - provides a list of
programmatic resources and guidance available to assist systems in building
partnerships and implementing watershed protection activities.
1.3 Existing Regulations and Treatment Requirements
The following sections describe the predecessors to the LT2ESWTR, along with the Stage 1
Disinfectants and Disinfection Byproducts Rule (DBPR), which was promulgated to reduce the
formation of DBFs in the plant and distribution system.
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1.3.1 Surface Water Treatment Rule
Under the 1989 Surface Water Treatment Rule (SWTR) (54 FR 27486), EPA established
treatment requirements for all PWSs using surface water or ground water under the direct influence of
surface water (GWUDI) as a source. The requirements are intended to protect against the adverse
health effects associated with Giardia lamblia, viruses, and Legionella and include the following:
• Maintenance of a disinfectant residual in water entering and within the distribution system.
• Removal/inactivation of at least 99.9 percent (3 log) of Giardia and 99.99 percent (4 log)
of viruses.
• Filtration, unless systems meet specified avoidance criteria.
• For filtered systems, a turbidity limit for the combined filter effluent of 5 nephelometric
turbidity units (NTUs) at any time and a limit of 0.5 NTU in 95 percent of measurements
each month for treatment plants using conventional treatment or direct filtration (with
separate standards for other filtration technologies). These requirements were superseded
by the 1998 IESWTR and the 2002 LT1ESWTR.
• Watershed control programs and water quality requirements for unfiltered systems.
1.3.2 Interim Enhanced Surface Water Treatment Rule
The Interim Enhanced Surface Water Treatment Rule (IESWTR) (63 FR 69478) applies to
PWSs serving at least 10,000 people and using surface water or GWUDI as a source. These systems
were to comply with the IESWTR by January 2002. The requirements and guidelines include:
• Removal of 99 percent (2 log) of Cryptosporidium for systems that provide filtration
• For treatment plants using conventional treatment or direct filtration, a turbidity performance
standard for the combined effluent of filters of 1 NTU as a maximum and 0.3 NTU as a
maximum in 95 percent of monthly measurements, based on 4-hour monitoring (these limits
supersede the SWTR turbidity limits)
• Continuous monitoring of individual filter effluent turbidity in conventional and direct
filtration plants and recording of turbidity readings every 15 minutes
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A disinfection benchmark to assess the level of microbial protection provided before
facilities change their disinfection practices to meet the requirements of the Stage 1 DBPR
Inclusion of Cryptosporidium in the definition of GWUDI and in the watershed control
requirements for unfiltered PWSs
All new finished water reservoirs must be covered.
1.3.3 Stage 1 Disinfectants and Disinfection Byproducts Rule
Pursuant to requirements under the Safe Drinking Water Act (SDWA), EPA developed
interrelated regulations to control microbial pathogens and disinfectants/DBPs in drinking water. These
rules, collectively known as the M-DBP rules, are intended to address complex risk trade-offs between
the two different types of contaminants. EPA promulgated the IESWTR concurrently with the Stage 1
DBPR so that systems could coordinate their responses to the risks posed by DBFs and microbial
pathogens.
The 1998 Stage 1 DBPR (63 FR 69390) applies to all community water systems (CWSs) and
nontransient noncommunity water systems (NTNCWSs) that add a chemical disinfectant to their water.
Certain requirements in the rule also apply to transient noncommunity water systems (TNCWSs).
Surface water and GWUDI systems serving at least 10,000 people were required to comply with the
rule by January 2002. All other systems (including ground water systems) must comply by January
2004.
The Stage 1 DBPR sets maximum residual disinfectant levels (MRDLs) for chlorine,
chloramines, and chlorine dioxide; and maximum contaminant levels (MCLs) for total trihalomethanes
(TTHM), haloacetic acids (HAAS), bromate, and chlorite. The MRDLs and MCLs, except those for
chlorite and chlorine dioxide, are calculated as running annual averages. For conventional filtration
systems, enhanced coagulation/softening is the best available treatment technique for removal of DBF
precursors.
1.3.4 Long Term 1 Enhanced Surface Water Treatment Rule
The Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) (67 FR 1811) was
promulgated in 2002 and extends most of the requirements of the IESWTR to surface water and
GWUDI systems serving fewer than 10,000 people.
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1.4 Microbial-Disinfection Byproduct Rule Summary
In keeping with a phased M-DBP strategy, EPA developed the Stage 2 DBPR and
LT2ESWTR. These rules are summarized below.
1.4.1 Stage 2 Disinfectant and Disinfection Byproduct Rule
The requirements of the Stage 2 DBPR apply to all community water systems (CWSs) and
nontransient noncommunity water systems (NTNCWSs)—both ground and surface water
systems—that add a disinfectant other than ultraviolet light (UV), or that deliver water that has been
treated with a disinfectant other than UV.
Initial Distribution System Evaluations
The Stage 2 DBPR is designed to reduce DBF occurrence peaks in the distribution system by
changing compliance monitoring requirements and the procedure for determining compliance.
Compliance monitoring will be preceded by an initial distribution system evaluation (IDSE) to identify
compliance monitoring locations that represent high TTHM and HAAS levels. The IDSE consists of
either a standard monitoring program (SMP) or a system-specific study (SSS). NTNCWSs serving
fewer than 10,000 people are not required to perform an IDSE, and other systems may receive
waivers from the IDSE requirement.
Compliance Determination and Schedule
The Stage 2 DBPR changes the way sampling results are averaged to determine compliance.
The determination for the Stage 2 DBPR is based on a locational running annual average (LRAA) (i.e.,
compliance must be met at each monitoring location) instead of the system-wide running annual average
(RAA) used under the Stage 1 DBPR.
The Stage 2 DBPR will be implemented in two phases, Stage 2A and Stage 2B. Under Stage
2A, all systems must comply with TTHM/HAA5 MCLs of 120/100 |ig/L measured as LRAAs at each
Stage 1 DBPR monitoring site, while continuing to comply with the Stage 1 DBPR MCLs of 80/60
jig/L measured as RAAs. Under Stage 2B, systems must comply with TTHM/HAA5 MCLs of 80/60
|ig/L at locations identified under the IDSE.
Compliance Monitoring
Systems will continue to monitor at their Stage 1 DBPR compliance monitoring sites for the
Stage 2A DBPR. The Stage 2B DBPR compliance monitoring sites will be determined from the results
of the IDSE. Stage 2B compliance monitoring requirements (number of sites and frequency of
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sampling) will be similar to the Stage 1 DBPR requirements for most, but not all, systems. Some small
systems will have to add an additional monitoring location if their highest TTHM and highest HAAS site
do not occur at the same location.
Significant Excursion Evaluations
Because Stage 2 DBPR MCL compliance is based on an annual average of DBF
measurements, a system could from time to time have DBF levels significantly higher than the MCL
(referred to as a significant excursion) while still being in compliance. This is because the high
concentration could be averaged with lower concentrations at a given location. If a significant excursion
occurs, a system must conduct a significant excursion evaluation and discuss the evaluation with the
State no later than the next sanitary survey.
1.4.2 Long Term 2 Enhanced Surface Water Treatment Rule
1.4.2.1 Filtered Systems
The LT2ESWTR requires systems that use a surface water or GWUDI source (referred to
collectively in this manual as surface water systems) and provide filtration to conduct source water
monitoring to determine average Cryptosporidium concentrations, unless they have historical
Cryptosporidium data equivalent to what is required under the LT2ESWTR (40 CFR 141.701(a)).
Based on its average source water Cryptosporidium concentration, a system will be classified in one of
four possible bins. A system's bin assignment determines the extent of any additional Cryptosporidium
treatment requirements. The rule requires systems to comply with additional treatment requirements by
using one or more management or treatment techniques from the toolbox of options (40 CFR
141.720(b)). The process is described in more detail below; the full monitoring requirements are
described in the Source Water Monitoring Guidance Manual for Public Water Systems for the
Long Term 2 Enhanced Surface Water Treatment Rule (USEPA 2003).
Monitoring Requirements
The LT2ESWTR specifies two monitoring schemes for filtered systems serving at least 10,000
people. The first is that the system collect at least 24 samples, but not more than 47 samples, over a 2-
year period and base the bin assignment on the maximum running annual average (RAA) (40
CFR141.709(b(l)). (The first RAA will be the average of the results of the first 12 months of
monitoring; the second RAA will be the average of results from months 2-13, the third will be the
average of concentrations from months 3-14, etc.) Alternatively, systems may collect two or more
samples per month over the 2-year period and use the average of all samples to determine bin
placement (40 CFR 141.709(b(l))).
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For filtered systems serving fewer than 10,000 people, the LT2ESWTR requires those systems
to first monitor for E. coli (or an indicator approved by the State) at least every two weeks for 12
months; based on the results, they may be required to conduct Cryptosporidium monitoring at least
twice a month for 12 months (40 CFR 141.701(e)). Systems that, based on their E. coli results, do not
have to monitor Cryptosporidium are placed in Bin 1 (see Table 1.1). Systems that must conduct
Cryptosporidium monitoring include the following (40 CFR 141.702(b)):
• Systems that use lakes or reservoirs as sources and that have an average E. coli
concentration of more than 10 E. coli per 100 milliliters (mL).
• Those systems that use flowing streams as sources and that have an average E. coli
concentration of more than 50 E. coli per 100 mL.
For those systems triggered into Cryptosporidium monitoring, bin assignment is based on the average
Cryptosporidium concentration of the 24 required samples (40 CFR 141.709(b(3))).
Bin Classification
Table 1.1 presents the bin classifications and their corresponding additional treatment
requirements for all filtered systems (40 CFR 141.709 and 40 CFR 141.720). Systems with average
Cryptosporidium concentrations of less than 0.075 oocysts per liter are placed in Bin 1, for which no
additional treatment is required. For concentrations of 0.075 or more, additional treatment is required
on top of that required by existing rules. The additional treatment required for each bin, specified in
terms of log removal, depends on the type of treatment already in place in the system.
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Table 1.1 Bin Requirements for Filtered Plants1
If your
Cryptosporidium
concentration
(oocysts/L) is...
< 0.075
>0.075and < 1.0
> 1.0 and <3.0
>3.0
Your bin
classification
is...
1
2
3
4
And if you use the following filtration treatment in full
compliance with existing regulations, then your additional
treatment requirements are...
Conventional
Filtration
Treatment
(includes
softening)
No additional
treatment
1 log
treatment2
2 log
treatment3
2. 5 log
treatment3
Direct
Filtration
No
additional
treatment
1.5 log
treatment2
2. 5 log
treatment3
Slog
treatment3
Slow Sand or
Diatomaceous
Earth
Filtration
No additional
treatment
1 log treatment2
2 log treatment3
2.5 log
treatment3
Alternative
Filtration
Technologies
No additional
treatment
As determined
by the State2'4
As determined
by the State3'5
As determined
by the State3'6
(40 CFR 141.709 and 40 CFR 141.720)
Systems may use any technology or combination of technologies from the microbial toolbox.
Systems must achieve at least 1 log of the required treatment using ozone, chlorine dioxide, UV, membranes,
bag/cartridge filters, or bank filtration.
Total Cryptosporidium treatment must be at least 4.0 log.
Total Cryptosporidium treatment must be at least 5.0 log.
Total Cryptosporidium treatment must be at least 5.5 log.
Additional Treatment Requirements
The total Cryptosporidium treatment required for Bins 2, 3, and 4 is 4.0 log, 5.0 log, and 5.5
log, respectively. The additional treatment requirements in Table 1.1 are based on a determination that
conventional, slow sand, and diatomaceous earth filtration plants in compliance with the IESWTR
or LT IESWTR achieve an average of 3 log removal of Cryptosporidium (the 2 log credit for
Cryptosporidium under the IESWTR and LT IESWTR is based on the minimum removal expected
with these types of filtration). Therefore, conventional, slow sand, and diatomaceous earth filtration
plants will require an additional 1.0 to 2.5 log additional treatment to meet the total removal
requirement, depending on the bin they are placed in.
Conventional treatment is a treatment train with coagulation, flocculation, sedimentation, and
granular media filtration. Sedimentation is defined in 40 CFR 141.2 as a process for removal of solids
before filtration by gravity or separation. Solid/liquid separation processes with solids removal
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capability include gravity sedimentation (traditional, plate, tube, ballasted sand), dissolved air flotation
(DAF), solids contact clarifiers, and buoyant and non-buoyant media clarifiers.
Direct filtration plants have coagulation, flocculation, and filtration processes, like
conventional treatment, but lack a sedimentation process. By providing a second pathogen barrier, a
sedimentation basin enhances the overall removal efficiency and stability of the treatment train. EPA
has determined that direct filtration plants achieve an average 2.5 log removal of Cryptosporidium.
Consequently, under the LT2ESWTR, direct filtration plants in Bins 2-4 must provide 0.5 log more in
additional treatment than conventional plants to meet the total Cryptosporidium removal requirement.
The LT2ESWTR specifies that a State may award greater credit to a system demonstrating
through a State-approved protocol that it reliably achieves a higher level of Cryptosporidium removal
(40 CFR 141.727(c)). Conversely, a State may award less credit to a system where the State
determines, based on site-specific information, that the system is not achieving the degree of
Cryptosporidium removal indicated in Table 1.1 (40 CFR 141.727(c)).
For systems using alternative filtration technologies, such as bag or cartridge filters, the
LT2ESWTR specifies that the State will determine additional treatment requirements based on the
credit awarded to a particular technology. The additional treatment must be such that plants in Bins
2,3, and 4 achieve the total required Cryptosporidium reductions of 4.0, 5.0, and 5.5 log, respectively
(40 CFR 141.720).
Systems in Bin 2 can meet additional Cryptosporidium treatment requirements by using an
option or combination of options in the toolbox (40 CFR 141.720(b)). In Bins 3 and 4, systems must
achieve at least 1 log of the additional treatment requirement through use of ozone, chlorine dioxide,
ultraviolet light, membrane filtration, bag filtration, cartridge filtration, or bank filtration (40 CFR
141.720(c)).
1.4.2.2 Unfiltered Systems
All existing requirements for unfiltered systems under the SWTR (40 CFR, parts 141.71 and
72(a)) remain in effect. This includes disinfection to achieve at least 3 log inactivation of Giardia and 4
log inactivation of viruses and to maintain a disinfectant residual in the distribution system (e.g., free
chlorine or chloramines). The IESWTR and LT1ESWTR did not change the disinfection requirements
for unfiltered systems.
Under the LT2ESWTR, unfiltered systems are required to monitor their source water for
Cryptosporidium to determine the amount of treatment required (40 CFR 141.701(d)). Systems
serving 10,000 or more people must monitor at least once a month for two years (40 CFR
141.701(e)). Systems serving fewer than 10,000 people must monitor at least twice a month for one
year (40 CFR 141.701(e)). All small unfiltered systems must monitor Cryptosporidium; there is no
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exception based on E. coli monitoring results as there is for small filtered systems. These monitoring
requirements are described in detail in the Source Water Monitoring Guidance Manual (USEPA 2003).
The arithmetic mean concentration of all Cryptosporidium samples taken is used to determine
the amount of treatment required, as shown in Table 1.2 (40 CFR 141.721(a)). If the mean
concentration is less than or equal to 0.01 oocysts/L, the system must provide 2 log inactivation of
Cryptosporidium (40 CFR 141.721(b)). If the mean concentration of Cryptosporidium exceeds
0.01 oocysts/L, the system must provide at least 3 log inactivation of Cryptosporidium (40 CFR
Table 1.2 LT2ESWTR Treatment Requirements for Unfiltered Systems
Average Cryptosporidium Concentration
(oocysts/liter)
<0.01
>0.01
Additional Cryptosporidium Inactivation
Requirements
2 log1
Slog1
'Overall disinfection requirements must be met with a minimum of two disinfectants.
The LT2ESWTR requires unfiltered systems to meet overall disinfection requirements (i.e.,
Cryptosporidium., Giardia, and virus inactivation) using a minimum of two disinfectants (40 CFR
141.721(d)). Disinfectants that can be used to meet this requirement include ozone, ultraviolet (UV)
light, and chlorine dioxide. (Refer to the UV Guidance Manual for rule requirements and guidance
regarding UV systems.) Further, each of the two disinfectants must achieve by itself the total
inactivation required for one of the three pathogen types. For example, a system could use UV light to
achieve 2 log inactivation of Cryptosporidium and Giardia, and use chlorine to inactivate 1 log
Giardia and 4 log viruses. In this case chlorine would achieve the total inactivation required for
viruses, while UV light would achieve the total inactivation required for Cryptosporidium and Giardia,
and the two disinfectants together would meet the overall treatment requirements for viruses, Giardia,
and Cryptosporidium.
1.4.2.3 Uncovered Finished Water Reservoirs
The LT2ESWTR requires systems with uncovered finished water reservoirs to cover the
uncovered finished water reservoir, treat the reservoir discharge to the distribution system to achieve a
4 log virus inactivation, or implement a risk mitigation plan (40 CFR 141.724). The LT2ESWTR
specifies that risk mitigation plans address physical access, surface water run-off, animal and bird
waste, and continuous water quality assessment (40 CFR 141.724(a)(3))).
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1.5 Summary of Microbial Toolbox Options
The LT2ESWTR requires systems to use one or more of the microbial toolbox options
described in Table 1.3 (40 CFR 141.722). Components of the toolbox include watershed control
programs, alternative sources, pretreatment process, additional filtration barriers, inactivation
technologies, and enhanced plant performance. The intent of the toolbox is to provide systems with
flexibility in selecting cost-effective LT2ESWTR compliance strategies.
In most cases, systems will receive presumptive log credit for a toolbox option by
demonstrating compliance with required design and implementation criteria. The demonstration of
performance option allows States to approve a treatment credit greater than the presumptive log credit
based on a site-specific or technology-specific demonstration of performance (40 CFR 141.727(c)).
Systems may use a combination of toolbox options to achieve the required log treatment. For
example, a conventional filtration system assigned to Bin 3, requiring an additional 2 log treatment, can
implement ozone with a contact time and concentration yielding 1.5 log credit and achieve the
requirements for combined filter performance, thus receiving an additional 0.5 log credit for a total of 2
log credit.
Table 1.3 Summary of Microbial Toolbox Options with Available Log Credits and
Design/Implementation Criteria
Toolbox Option
Cryptosporidium Treatment Credit with Design and Implementation
Criteria
Source Toolbox Components
Watershed
control program
0.5 log credit for State approved program comprised of EPA specified elements.
Specific criteria are in 40 CFR 141.725(a). See Chapter 2 of this manual.
Alternative
source/ intake
management
No presumptive credit. Systems may conduct simultaneous monitoring for
LT2ESWTR bin classification at alternative intake locations or under alternative
intake management strategies. See 40 CFR 141.725(b). See Chapters.
Pre-Filtration Toolbox Components
Bank filtration
0.5 log credit for 25 foot setback; 1.0 log credit for 50 foot setback. Aquifer must
be unconsolidated sand containing at least 10% fines. Average turbidity in wells
must be <1 NTU. Systems with existing wells must monitor well effluent to
determine bin classification and are not eligible for presumptive credit. See 40
CFR 141.726(c). See Chapter 4.
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Toolbox Option
Cryptosporidium Treatment Credit with Design and Implementation
Criteria
Presedimentation
basin with
coagulation
0.5 log credit for new basins with continuous operation and coagulant addition.
Basins must achieve 0.5 log turbidity reduction based on the monthly mean of
daily measurements in 11 of the 12 previous months. All flow must pass through
basins. Systems with existing pre-sed basins must monitor after basins to
determine bin classification and are not eligible for presumptive credit. See 40
CFR 141.726(a). See Chapter 5.
Two-stage lime
softening
0.5 log credit for two-stage softening with coagulant addition. Coagulant must be
present in both clarifiers and includes metal salts, polymers, lime, or magnesium
precipitation. Both clarifiers must treat 100% of flow. See 40 CFR 141.726(b).
See Chapter6.
Treatment Performance Toolbox Components
Combined filter
performance
0.5 log credit for combined filter effluent turbidity < 0.15 NTU in 95% of samples
each month. See 40 CFR 141.727(a). See Chapter 7.
Individual filter
performance
1.0 log credit for individual filter effluent turbidity < 0.1 NTU in 95% of daily
maximum samples each month (excluding 15 minutes following backwash) and
no filter >0.3 NTU in two consecutive measurements taken 15 minutes apart. See
40 CFR 141.727(b). See Chapter 7.
Demonstration of
performance
Credit based on a demonstration to the State through State-approved protocol.
See 40 CFR 141.727(c). See Chapter 12.
Additional Filtration Toolbox Components
Bag filters
1 log credit with demonstration of at least 2 log removal efficiency in challenge
test; Specific criteria are in 40 CFR 141.728(a). See Chapters.
Cartridge filters
2 log credit with demonstration of at least 3 log removal efficiency in challenge
test; Specific criteria are in 40 CFR 141.728(a). See Chapters.
Membrane
filtration
Log removal credit up to the lower value of the removal efficiency demonstrated
during the challenge test if verified by direct integrity testing. See 40 CFR
141.728(b). See the Guidance Manual for Membrane Filtration.
Second stage
filtration
0.5 log credit for a second separate filtration stage; treatment train must include
coagulation prior to first filter. No presumptive credit for roughing filters. See 40
CFR 141.728(c). See Chapter 9.
Slow sand filters
2.5 log credit for second separate filtration process. No disinfectant residiual
present in influent. See 40 CFR 141.728(d). See Chapter 9.
Inactivation Toolbox Components
Chlorine dioxide
Log credit based on demonstration of compliance with CT tables. See 40 CFR
141.729(b). See Chapter 10.
Ozone
Log credit based on demonstration of compliance with CT tables. See 40 CFR
141.729(c). See Chapter 11.
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uv
Log credit based on demonstration of compliance with UV dose table; reactor
testing required to establish validated operating conditions. See 40 CFR
141.729(d). See UV Guidance Manual.
1.6 Disinfection Profiling and Benchmarking
The purpose of a disinfection benchmark is to ensure that when a system makes a change to its
disinfection processes, it does not compromise the adequacy of existing microbial protection. A
disinfection profile is a graphical representation of a system's level of Giardia lamblia and viral
inactivation measured during the course of 1 or more year(s). A benchmark is the lowest monthly
average of microbial inactivation during the disinfection profile period. This tool was introduced in the
IESWTR (63 FR 69478 December 16, 1998) as a means for ensuring maintenance of microbial
protection when systems made changes to address DBF control for the Stage 1 DBPR. The
LT2ESWTR also includes a disinfection benchmark to ensure that any significant treatment change,
whether for byproduct control under the Stage 2 DBPR, improved Cryptosporidium control under the
LT2ESWTR, or both, does not significantly compromise existing Giardia and virus protection.
The profiling and benchmarking requirements under the LT2ESWTR are similar to those
promulgated under IESWTR and LT1ESWTR and are applicable to: 1) systems required to conduct
Cryptosporidium source water monitoring and 2) small surface water systems that do not have to
conduct Cryptosporidium source water monitoring and have Stage 1 DBPR TTHM annual average
results of at least 56 jig/L or HAAS annual average results of at least 42 jig/L (40 CFR 141.711).
Figure 1.1 presents a flow chart that can be used to determine if a system must develop a disinfection
profile and benchmark. The LT2ESWTR requires these systems to prepare a disinfection profile that
characterizes current levels of Giardia lamblia and virus inactivation throughout the plant over the
course of one year (40 CFR 141.713). The profile may be developed using equivalent historical data.
Subsequently, if a system proposes to make a significant change to its disinfection practice, then the
LT2ESWTR requires the system to calculate a disinfection benchmark and consult with the State
regarding how the proposed change will affect that benchmark (40 CFR 141.714).
Detailed guidance for conducting a disinfection profile and calculating a benchmark is provided
in the IESWTR Disinfection Profiling and Benchmarking Guidance Manual for systems serving at least
10,000 people and the LT IESWTR Disinfection Profiling and Benchmarking Guidance Manual for
systems serving less than 10,000 people. A summary of the steps required to create a disinfection
profile and calculate a benchmark are listed in the following two subsections.
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Chapter 1 - Introduction
Figure 1.1 Systems Required to Develop a Disinfection Profile and Benchmark
Does
system provide at least
5.5 log treatment
for Crypto?
Is system
a NTNCWS or
CWS?
Does system
have equivalent
historical disinfection
profile data?
Does system
serve > 10,000
people?
Does system
ovide filtration?
Is system's E.coli
>10/100 ml (for
reservoirs/lakes) or>50/100 ml
(for flowing stream)?
Is system s
TTHM >0.056mg/l_or
5 >0.042 mg/
Perform disinfection
profiling starting at 24
months after promulgation
Perform disinfection
profiling starting at 54
months after promulgatio
Perform disinfection
profiling starting at 42
months after promulgation
Is system
planning a significant
change in
isinfection?
No further
action
required
Calculate disinfection benchmark
for both Giardia and viruses
No disinfection \
profile I
required I
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Chapter 1 - Introduction
1.6.1 Creating a Disinfection Profile
The following steps describe how to calculate the Giardia lamblia and vims inactivations over
a one year period:
1) Collect disinfectant residual, temperature, and pH (if chlorine is used) data daily for large
systems and weekly for small systems for 12 consecutive months. The data should be
collected after injection of the disinfectant and prior to the first customer (or next
disinfectant injection point if applicable) during peak hourly flow.
2) Determine disinfectant contact time during peak hourly flow conditions measured between
the point of application and the point of residual measurement.
3) Calculate CTcalc (product of disinfectant residual concentration and contact time) and from
the CT tables determine the CT99 9 Giardia and CT99 99 virus. (Chapter 12 contains more
detailed information on calculating CT.)
4) Calculate the estimated log inactivation for Giardia and viruses according to the following
equations:
Log inactivation of Giardia = 3.0 x CTcalc / CT99 9 Giardia
Log inactivation of viruses = 4.0 x CTcalc / CT99 99 virus
5) Plot the total log inactivations from each day or week on a graph (Giardia and virus data
on separate graphs). The resulting graph of 365 days or 52 weeks of data is the
disinfection profile.
1.6.2 Disinfection Benchmark
A system that is required to develop a disinfection profile and that plans to make a significant
change to its disinfection practice must calculate a benchmark and notify the State prior to making the
change (40 CFR 141.714(a)). The LT2ESWTR defines significant changes to disinfection practices as
changing the point of disinfection, the type of disinfectant, the process used, or other changes identified
by the State.
The benchmark is a system's lowest monthly average microbial inactivation based on the
disinfection profile. If the benchmark is substantially greater than the required inactivation (3.0 log
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Chapter 1 - Introduction
Giardia and 4.0 log virus), then a system may consider decreasing the amount of disinfectant added,
contact time, or altering other disinfection practices, as long as it notifies the State.
1.7 Implementation Schedule
For those systems requiring additional treatment, the LT2ESWTR requires compliance by [72
months after promulgation] for systems serving 10,000 or more people and [102 months after
promulgation] for systems serving less than 10,000 people (40 CFR 141.701(e)). States may grant an
extra two years to systems that need to make capital improvements in order to meet the requirements.
However, some toolbox options have additional requirements that must be met at an earlier date. Table
1.4 lists the requirements and compliance dates for each toolbox option for large and small systems,
respectively.
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Chapter 1.0 - Introduction
Table 1.4 Compliance Dates1
Toolbox Option
Systems must submit the following
information
Schedule
Systems serving > 10,000
people
Systems serving < 10,000
people
Watershed Control
Program (WCP)
Notify State of intention to develop WCP
No later than [date 48 months
after date of publication of final
rule in the Federal Register]
No later than [date 78 months
after date of publication of final
rule in the Federal Register]
Submit initial WCP plan to State
No later than [date 60 months
after date of publication of final
rule in the Federal Register]
No later than [date 90 months
after date of publication of final
rule in the Federal Register]
Annual report and State-approved watershed
survey report
By a date determined by the
State, every 12 months, beginning
on [date 84 months after date of
publication of final rule in the
Federal Register].
By a date determined by the
State, every 12 months, beginning
on [date 114 months after date of
publication of final rule in the
Federal Register].
Request for re-approval and report on the
previous approval period.
Six months prior to the end of the
current approval period or by a
date previously determined by the
State.
Six months prior to the end of the
current approval period or by a
date previously determined by the
State.
Presedimentation
(new basins)
Monthly verification of:
• Continuous basin operation
• Treatment of 100% of the flow
• Continuous addition of a coagulant
• At least 0.5 log removal of influent turbidity
based on the monthly mean of daily turbidity
readings for 11 of the 12 previous months
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 72 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 102 months after date of
publication of final rule in the
Federal Register]
Bank filtration
Initial demonstration of
• Unconsolidated, predominantly sandy aquifer
• Setback distance of at least 25 ft. (0.5 log) or
50ft. (1.0 log)
Initial demonstration no laterthan
[date 72 months after date of
publication of final rule in the
Federal Register]
Initial demonstration no laterthan
[date 102 months after date of
publication of final rule in the
Federal Register]
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Chapter 1.0 - Introduction
Toolbox Option
Two-stage lime
softening
Combined filter
performance
Individual filter
performance
Membrane
filtration
Systems must submit the following
information
If monthly average of daily max turbidity is
greater than 1 NTU, then system must report
result and submit an assessment of the cause
Monthly verification of:
. Continuous operation of a second clarification
step between the primary clarifier and filter
• Continuous presence of a coagulant in both
primary and secondary clarifiers
. Both clarifiers treat 100% of the plant flow
Monthly verification of:
• Combined filter effluent (CFE) turbidity levels
less than or equal to 0.15 NTU in at least 95
percent of the 4 hour CFE measurements
taken each month
Monthly verification of:
• Individual filter effluent (IFE ) turbidity levels
less than or equal to 0.1 NTU in at least 95
percent of all IFE measurements taken each
month based on daily maximum (excluding 15
min period following start-up after backwash)
• No individual filter greaterthan 0.3 NTU in two
consecutive readings 15 minutes apart
Results of verification testing demonstrating:
• Removal efficiency established through
challenge testing that meets rule criteria
• Integrity testing and associated baseline
Schedule
Systems serving > 10,000
people
Report within 30 days following
the month in which monitoring
was conducted, beginning [date
72 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 72 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 72 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 72 months after date of
publication of final rule in the
Federal Register]
No later than [date 72 months
after date of publication of final
rule in the Federal Register]
Systems serving < 10,000
people
Report within 30 days following
the month in which monitoring
was conducted, beginning [date
1 02 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 1 02 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 1 02 months after date of
publication of final rule in the
Federal Register]
Within 10 days following each
month in which the monitoring
was conducted, beginning on
[date 1 02 months after date of
publication of final rule in the
Federal Register]
No later than [date 102 months
after date of publication of final
rule in the Federal Register]
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Chapter 1.0 - Introduction
Toolbox Option
Systems must submit the following
information
Schedule
Systems serving > 10,000
people
Systems serving < 10,000
people
Monthly report summarizing any direct integrity
tests above the control limit, any indirect integrity
monitoring results triggering direct integrity
testing and the corrective action that was taken.
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
Bag filters and
cartridge filters
Demonstration that the following criteria are met:
• Process meets the definition of bag or cartridge
filtration
• Removal efficiency established through
challenge testing that meets rule criteria
• Challenge test shows at least 2 log removal for
bag filters and 3 log removal for cartridge filters
No later than [date 72 months
after date of publication of final
rule in the Federal Register]
No later than [date 102 months
after date of publication of final
rule in the Federal Register]
Monthly verification that 100% of flow was
filtered.
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
Second stage
filtration
Monthly verification that 100% of flow was
filtered.
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
Slow sand
filtration
Monthly verification that 100% of flow was
filtered.
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
Chlorine dioxide
Summary of CT values for each day based on
Tables in 40 CFR 141.729(b).
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
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Toolbox Option
Systems must submit the following
information
Schedule
Systems serving > 10,000
people
Systems serving < 10,000
people
Ozone
Summary of CT values for each day based on
Tables in 40 CFR 141.729(c).
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
UV
Validation test results demonstrating operating
conditions that achieve required UV dose.
No later than [date 72 months
after date of publication of final
rule in the Federal Register]
No later than [date 102 months
after date of publication of final
rule in the Federal Register]
Monthly report summarizing the percentage of
water entering the distribution system that was
not treated by UV reactors operating within
validated conditions.
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
Demonstration of
Performance
Results from testing following a State approved
protocol.
No later than [date 72 months
after date of publication of final
rule in the Federal Register]
No later than [date 102 months
after date of publication of final
rule in the Federal Register]
As required by the State, monthly verification of
operating within conditions of State approval for
demonstration of performance credit.
Within 10 days following the
month in which monitoring was
conducted, beginning [date 72
months after date of publication of
final rule in the Federal Register]
Within 10 days following the
month in which monitoring was
conducted, beginning [date 102
months after date of publication of
final rule in the Federal Register]
1(40CFR141.730)
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2.0 Watershed Control Program
2.1 Introduction
A well-designed watershed control program can result in a reduction of overall microbial risk.
The risk reduction is associated with the implementation of practices that reduce Cryptosporidium as
well as other pathogens. Further, knowledge of the watershed and factors affecting microbial risk,
including sources of pathogens, fate and transport of pathogens, and hydrology, can also help a system
reduce microbial risk.
There are many potential sources of Cryptosporidium in watersheds, including sewage
discharges and nonpoint sources associated with animal feces. The feasibility, effectiveness, and
sustainability of control measures to reduce Cryptosporidium contamination of water sources will be
site-specific. Consequently, the watershed control program credit centers on systems working with
stakeholders in the watershed to develop a site-specific program, and State review and approval are
required. This section is intended to assist water systems in developing their watershed control
programs and States in assessing and approving these programs.
A watershed control program can serve an additional purpose—it can also be a component of
a comprehensive source water protection program that addresses chemical and microbial contaminant
threats. Much of the background information and preparation needed to develop a watershed control
program and comprehensive source water protection program are already complete as a result of the
source water assessments required under the 1996 Amendments to the Safe Drinking Water Act.
Section 1453 of the Act required States to conduct source water assessments for all public water
systems, including delineating the "boundaries of the areas providing source waters for PWSs and
identifying the origins of regulated and certain unregulated contaminants in the delineated area to
determine the susceptibility of the PWSs to such contaminants." Information resulting from these
assessments should be available from the States. Information may also be available in systems that
have had watershed sanitary surveys done. These surveys are required as part of the Interim Enhanced
Surface Water Treatment Rule (IESWTR), and some States have required them for years.
2.1.1 Credits
Filtered systems that develop a State-approved watershed control program designed to reduce
the level of Cryptosporidium in the watershed can receive a 0.5 log credit towards the
Cryptosporidium treatment requirements under the LT2ESTWR (40 CFR 141.722). The watershed
control program credit can be added to the credit awarded for any other toolbox component.
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The list below provides the organization for the rest of this chapter.
2.2 What Kinds of PWSs Should Implement Watershed Control Programs - discusses
case studies of watershed control programs in place at different PWSs around the
Unites States; describes advantages and disadvantages of implementing a watershed
control program; and what to do if your system already has a watershed control
program.
2.3 How Do I Apply for Approval - discusses procedure systems must follow to apply for
approval to implement a watershed control program. The following procedures are
described: notifying the State of intent to participate; initial approval of watershed
control program; and maintaining approval of watershed control program.
2.4 Developing the Watershed Control Program Plan - discusses the factors systems
should consider in determining the impact Cryptosporidium has on their water quality,
along with descriptions of best management practices systems can use to protect their
source water from Cryptosporidium. The following four areas are discussed:
vulnerability analysis; analysis of control measures; writing the watershed control plan;
and how States should assess plans.
2.5 Maintaining Approval of a Watershed Control Program - discusses annual watershed
control program status report. State approved watershed sanitary survey, request for
re-approval, and guidance to States on re-approval.
2.2 What Kinds of PWSs Should Implement Watershed Control Programs?
Many types of systems can benefit from a watershed control program. This section contains
case studies of watershed control programs in place at different PWSs around the United States.
These studies show how systems of different sizes and source water types and with varying regulatory
authority have adopted watershed control programs to fit their specific needs. This section also
describes advantages and disadvantages of implementing a watershed control program.
2.2.1 Case Studies of Existing Watershed Control Programs
Watershed control programs should be based on site-specific conditions. A successful
program will address the unique combination of land use, land ownership, zoning, regulatory controls,
contaminant sources, and natural characteristics of the watershed being considered. The size,
ownership, and jurisdictional nature of the water utility will also affect the role it plays in the watershed
control program (AWWARF 1991).
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As shown by the case studies below, successful watershed control programs will vary
significantly in their approach to source protection. The systems in the case studies did not focus
specifically on Cryptosporidium but on controlling microbial point and non-point sources and other
contaminants. However, many of the elements noted in these case studies may be useful in watershed
control programs addressing Cryptosporidium. For more case studies, see Protecting Sources of
Drinking Water: Selected Case Studies in Watershed Management (U.S. EPA 1999a).
Burlington, Vermont
Medium Surface Water PWS, Watershed Located in Multiple Jurisdictions
The City of Burlington has a population of 40,000 and is located on the shore of Lake
Champlain, a 120-mile long, 12-mile wide lake that is the source of drinking water for the city and
other municipalities. In such a large watershed with multiple landowners, it is difficult to control
activities that affect water quality. Burlington addresses microbial pollution through a combination of
land use control, reduction in combined sewer overflow, watershed restoration, and outreach.
Through Act 250, the State of Vermont regulates land use near lake shores and rivers,
accounting for new wastewater treatment plants and sewer systems, timber management, impervious
surface area, water withdrawal by ski areas for snowmaking, and other issues. To address combined
sewer overflow problems that were affecting Lake Champlain water quality, the city increased the
capacity of its main wastewater treatment plant and extended the outfall far into the lake to dilute the
effluent. The city separated the sanitary and storm sewers at its smaller plants. Two streams feeding
into the lake that suffer from poor water quality are currently undergoing restoration, including
retrofitting of existing storm water detention ponds, channel stabilization to prevent erosion, and
outreach to change pet waste management, lawn care, and other practices (U.S. EPA 200la).
Manchester, New Hampshire
Large Surface Water System Where State Plays an Active Role
The City of Manchester gets its water from Lake Massabesic, which is located approximately
three miles east of downtown Manchester. Management of the water supply is primarily under the
jurisdiction of the Manchester Water Works. The lake has a surface area of about 2,500 acres and a
gross storage capacity of nearly 15 billion gallons. For more than 120 years, this reservoir has served
Manchester and five other communities. The Lake Massabesic water supply is supplemented by
Tower Hill Pond, which has a gross storage capacity of 1.3 billion gallons. Manchester controls
microbial pollution by restricting land use in the portions of the watershed controlled by the water
works and the State.
The watershed area for the supply covers 42 square miles with over 25 percent owned and
managed by the New Hampshire Department of Environmental Services (NHDES). The NHDES
monitors these areas and controls recreational use through regulations posted in the surrounding area,
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Chapter 2 - Watershed Control Program
which are enforced by a staff of watershed patrol officers. These regulations strictly prohibit such
activities as waste disposal, horseback riding, boating, or any other activity that would immediately or
indirectly endanger the surface water quality. Other areas of the watershed are primarily monitored by
the Manchester Water Works and have regulated levels of outdoor recreation. Activities such as
mountain biking or the establishment of docks and moorings are subject to review and permitting by this
agency. Parts of Lake Massabesic closest to the intake are closed to all activity.
The NHDES has provided funding to the Manchester Water Works for the protection of its
watershed, specifically funding the installation of a storm water treatment facility and a project to
address erosion and sedimentation. DES also provided funding for emergency planning, wellhead
protection management plans, drainage mapping, storm water best management practices, and public
outreach and education. The source of all this funding was the source water protection-related set-
asides from the Drinking Water State Revolving Fund (U.S. EPA 2001b).
Springfield, Missouri
Large GWUDI and Surface Water System with Rapidly Urbanizing Watershed
Springfield is a city of approximately 150,000 residents located in southwestern Missouri.
Much of Springfield's bedrock is limestone and dolomite, and karst features are very pronounced.
There are numerous losing streams, springs, and large concentrations of sinkholes in the area. The
city's drinking water is provided by City Utilities of Springfield, a municipally-owned utility. The city
uses a combination of springs, wells, reservoirs, and the James River to supply its daily demand of
approximately 30 MGD.
The three primary threats to Springfield's water quality that have been identified by its
watershed committee are: 1) urbanization in the watershed; 2) wastewater treatment in suburban and
rural areas, which consists primarily of septic systems on karst terrain; and 3) agriculture, especially
animal waste from concentrated beef and dairy cattle operations. Agricultural and urban BMPs are the
primary methods used to address microbial contaminants.
In 1984 a citizen-based Watershed Management Coordinating Committee was established to
guide and oversee water protection efforts. The group later incorporated as a non-profit organization
and renamed itself the Watershed Committee of the Ozarks. The committee's operating budget is
provided by Greene County (in which much of the watershed lies), the City of Springfield (containing
the bulk of the water users), and City Utilities (U.S. EPA 2001 c).
In 2001, the Committee hosted a workshop on conservation development and better site
design for Springfield and Greene County planning and zoning staff members, hosted a workshop on
agricultural best management practices (BMPs) for farmers, helped local developers incorporate
stormwater BMPs and better site design into their developments, and helped local farmers install
alternative watering facilities. The Committee currently has grants under Section 319 of the Clean
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Chapter 2 - Watershed Control Program
Water Act to restore several of the area's watersheds. One of these grants involves a study of the
current and future loading rates of sediment and nutrients and future construction of a wetland or
forebay to treat runoff from the Valley Water Mill watershed as it enters the reservoir. Another project
for the Little Sac River Watershed, which provides 85 percent of Springfield's water, has just gotten
underway (Watershed Committee of the Ozarks 2001).
2.2.2 What Are The Advantages and Disadvantages of a Watershed Control
Program?
2.2.2.1 Advantages
Although the costs associated with implementing a particular toolbox option are system-
specific, a watershed control program can cost less than options that require additional technology be
installed. This is especially the case if other stakeholders contribute time and resources to the
watershed control program. Stakeholders could include concerned citizens along with other
municipalities, other agencies in the same municipality, and county or State employees. Watershed
control programs that involve land acquisition or purchase of easements, however, may be as or more
expensive than installing treatment.
Funding is available to implement many aspects of a watershed control program. For example,
the Clean Water Act authorizes State revolving fund loans to upgrade wastewater treatment plants and
provides grants (under Section 319) for control of nonpoint source pollution. The Farm Bill of 2002
authorizes several billion dollars for management of agricultural pollution. Drinking Water State
Revolving Funds are also available to a limited extent for source water protection. Each State may set
aside as much as 15 percent of its grant each year to provide loans for source water protection
activities, including land or easement acquisition, implementation of incentive-based voluntary source
water protection programs, and implementation of wellhead protection programs.
In addition, much of the information required to implement a watershed program, such as a
contaminant source inventory and delineation of the watershed, will already be available as a result of
the source water assessment conducted under the 1996 Safe Drinking Water Act Amendments.
Section 1453 directs States to have completed source water assessments of PWSs by 2003. Although
source water assessment programs vary from State to State, they will all provide much of the
information required to implement a watershed program, allowing systems to incorporate existing
information into their watershed control plans at minimal cost.
Flexibility is another advantage of a watershed control program. A watershed control program
allows a system to design a suite of pollution management measures tailored to the physical, political,
and economic characteristics of the local environment. This enables systems to focus resources on, and
restrict costs to, actions that address the highest priority contaminants.
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The reduction and prevention of source water contamination by microbial pathogens may also
serve other public health and ecological goals, such as use of the water body for fishing and swimming,
reduction of ground water contamination, and protection of aquatic habitats and the species that
depend on such habitats for survival.
2.2.2.2 Disadvantages
There are some circumstances where a watershed control program may not be successful.
Systems should consider the following potential pitfalls in deciding whether to adopt a watershed
control program. Because Cryptosporidium occurs in low concentrations and is difficult to detect
using existing analytical methods, it can be hard to determine whether concentrations have decreased as
a result of a watershed control program. In addition, microbiological contaminants are frequently
related to nonpoint sources, and control of these sources is often highly dependent on changing the
behaviors of large groups of people. In a voluntary program (e.g., if the water system has no authority
to regulate land use and is encouraging landowners to voluntarily take action), it is difficult to determine
whether individuals are making the recommended changes necessary to control contaminants. Although
the required annual watershed survey will assist in evaluating progress, systems that implement
watershed control programs will need to be creative in finding ways to gauge the success of their
programs.
A successful watershed control program requires the cooperation of a variety of stakeholders;
however, it may be difficult to get agreement or participation from these stakeholders. Alternatively,
stakeholder groups may agree to perform certain activities, such as outreach, but could lose funding and
be unable to follow through on their commitments. Systems that have concerns about the likelihood of
building strong relationships with their stakeholders may decide that a watershed control program is not
appropriate for them. In some watersheds, depending on size of the watershed control program and
the ability to share costs with others, significant PWS staff time may be required to oversee a program.
These costs may be prohibitive for some systems.
Urban growth and land development can affect the success of a watershed control program. If
growth occurs too quickly and there are insufficient controls on development, the subsequent decline in
water quality can cancel out or even outstrip any improvement resulting from the watershed program.
In high-growth areas, PWSs should make sure that the community is willing to support restrictions on
development.
2.2.3 What If I Already Have a Watershed Control Program?
Systems that already have a watershed control program in place are permitted to choose this
option; however, they will have to amend and strengthen their programs to get the log removal credit.
This is because the credit, for all systems, is based on control measures that are in addition to the
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Chapter 2 - Watershed Control Program
program already in place. To get the additional credit, a system with an existing watershed control
program could, for example, increase public outreach efforts or toughen land use ordinances that affect
water quality. Systems with existing programs must still go through the entire application process.
2.3 How Do I Apply for Approval?
After notifying their States of their intention to participate, systems must include several items in
their watershed control program plans. In addition to the plan itself, systems must submit a vulnerability
analysis and an analysis of the interventions they considered in developing the plan. The procedure,
based on the preamble to the LT2ESWTR, is provided below (U.S. EPA 2002a).
2.3.1 Notifying the State of Intention to Participate
Systems must notify their States of their intention to implement a watershed control program
within one year of learning their initial bin assignment based on Cryptosporidium monitoring (40 CFR
141.725(a)(l)). The application and plan must be submitted for approval within two years after initial
bin assignment (40 CFR 141.725(a)(2)).
2.3.2 Initial Approval of Watershed Control Program Plan
Initial State approval of a system's watershed control program will be based on State review of
the system's proposed watershed control plan and supporting documentation, including a vulnerability
analysis and analysis of the proposed control measures (40 CFR 141.725(a)(3)). The initial approval
will be valid until the system completes the second round of Cryptosporidium monitoring (systems
begin a second round of monitoring six years after the initial bin assignment) (40 CFR 141.725(a)(4)).
At the very latest, systems must begin implementing the program 42 months (three and a half years)
after the end of the source water monitoring period (40 CFR 141.701). The program elements are
summarized below and described in more detail in section 2.4.
2.3.2.1 Vulnerability Analysis, Including Area of Influence
The application must include an analysis of the system's source water vulnerability to the
different sources of Cryptosporidium identified in the watershed. The vulnerability analysis must
characterize watershed hydrology and identify an "area of influence on source water quality" (the area
to be considered in future watershed surveys). The analysis must also address sources of
Cryptosporidium, seasonal variability, and the relative impact of the sources of Cryptosporidium on
the system's source water quality (40 CFR 141.725(a)(3)(i)).
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2.3.2.2 Analysis of Control Measures
The application must present an analysis of control measures that could address the sources of
Cryptosporidium contamination identified in the vulnerability analysis. The analysis of control
measures must discuss the effectiveness of each measure in reducing Cryptosporidium in source water
(40CFR141.725(a)(3)(ii)).
2.3.2.3 Watershed Control Plan
The watershed control plan must be submitted within two years of initial bin assignment. It must
address goals and define and prioritize specific actions to reduce source water Cryptosporidium levels.
The plan must explain how actions are expected to contribute to specified goals; identify partners and
their roles, resource requirements, and commitments; and include a schedule for plan implementation
(40CFR141.725(a)(3)(iii)).
2.3.2.4 Approval and Conditional Approval
The State must review each system's proposed watershed control program plan and either
approve, reject, or conditionally approve the plan. If the plan is approved, or if the system agrees to
implementing the State's conditions for approval, the system will be awarded 0.5 log Cryptosporidium
removal credit to apply toward additional treatment requirements.
2.3.3 Maintaining Approval of Watershed Control Program
Systems that have obtained State approval of their watershed control programs are required to
meet the following additional requirements within each approval period to maintain compliance with
their programs and continue their eligibility for the 0.5 log removal credit.
• Submit an annual watershed control program status report to the State during each year of the
approval period (40 CFR 141.725(a)(4)(i)).
• Conduct an annual State-approved watershed sanitary survey and submit the survey report to
the State (40 CFR 141.725(a)(4)(ii)).
The annual status reports, watershed control plan, and annual watershed sanitary surveys must
be made available to the public upon request. These documents must be in plain language format and
include criteria by which to evaluate the success of the program in achieving plan goals. The State may
withhold portions of the annual status report, watershed control plan, and watershed sanitary survey
based on security considerations (40 CFR 141.725(a)(4)(iii)).
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The initial State approval of the system's watershed control program is valid until the system
completes the required second round of Cryptosporidium monitoring (40 CFR 141.725(a)(4)). To be
reapproved and to continue receiving 0.5 log treatment credit, the system must submit to the State an
application for review and re-approval of the watershed control program six months before the initial
approval period ends (40 CFR 141.725(a)(4)(iii)).
2.3.3. 1 Submit Annual Status Report
The annual watershed control program status report must be submitted during the last three
months of each year of the approval period, or by a date determined by the State. The report must
describe the system's implementation of the approved plan and assess the adequacy of the plan for
meeting the system's goals. It also must explain how the system is addressing any shortcomings in plan
implementation, including those previously identified by the State or by the system during a watershed
survey. If the system made any substantial changes to its approved program, it must describe the
changes and explain the reason for making them. If the change is likely to reduce the level of source
water protection, the system must explain what actions it will take to mitigate the effects (40 CFR
2.3.3.2 Conduct State-Approved Watershed Sanitary Survey
The State-approved watershed survey must be conducted annually according to State
guidelines and by persons approved by the State to conduct watershed surveys. A report on the results
of the survey must be submitted to the State annually. The survey must cover the area of the watershed
that was identified in the approved watershed control program plan as the area of influence and must
focus on assessing the priority activities identified in the plan and on identifying any significant new
sources of Cryptosporidium (40 CFR 141.725(a)(4)(ii)). More information on watershed surveys is
provided in section 2.5.2.
2.3.3.3 Request Review and Re-Approval
The system must request a review of its watershed control program by the State at least six
months before the approval period expires or by a date previously determined by the State. The
request must summarize activities and issues identified during the approval period and must include a
revised plan that addresses activities for the next approval period. The revised plan must detail any
proposed changes to the existing State-approved program. As with the initial request for State
approval, the plan must address goals, prioritize specific actions intended to reduce source water
Cryptosporidium, explain how these actions are expected to contribute to the achievement of goals,
identify partners and their roles and resource requirements, and provide a schedule for plan
implementation (40 CFR 141.725(a)(4)(iii)).
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2.4 Developing the Watershed Control Program Plan
The following subsections discuss the factors systems should consider in determining the impact
Cryptosporidium has on their water quality, along with descriptions of best management practices
systems can use to protect their source water from Cryptosporidium.
2.4.1 Vulnerability Analysis
2.4. 1. 1 What Should Be Included in a Vulnerability Analysis?
The vulnerability analysis must address the vulnerability of each source to Cryptosporidium in
the watershed upstream of the drinking water intake. It must include the following (40 CFR
• A characterization of the watershed hydrology
• Identification of an area of influence (the area to be considered in future watershed surveys)
outside of which there is no significant probability of Cryptosporidium or fecal
contamination affecting the drinking water intake
• Identification of potential and actual sources of Cryptosporidium contamination
• Determination of the relative impact of the sources of Cryptosporidium contamination on
the system's source water quality
• An estimate of the seasonal variability of such contamination
Systems may be able to use the results of the source water assessments conducted under the
Safe Drinking Water Act Amendments of 1996 in your vulnerability analysis. Most States will have
completed source water assessments of surface water systems by the end of 2003. These assessments
establish a foundation for the vulnerability analysis: they delineate the watershed, providing a starting
point for defining the area of influence, and they inventory and rank the susceptibility of the water supply
to actual and potential contamination sources. Some States involved PWSs in conducting source
inventories and susceptibility analyses, so some PWSs may already have this information on hand. The
assessments covered all contaminants in a watershed, including Cryptosporidium (U.S. EPA 1997).
In some cases, if sufficiently detailed, the source water assessments may fully satisfy the analytical needs
of the watershed control plan's vulnerability analysis.
Other source and watershed information may be available from sanitary surveys conducted for
the IESWTR and the Long Term 1 Enhanced Surface Water Treatment Rule (these rules require
sanitary surveys at least every three years for community water systems and at least every five years for
noncommunity water systems). Guidance is available at
http://www.epa.gov/safewater/mdbp/pdf/sansurv/sansurv.pdf The California-Nevada section of the
American Water Works Association and the California Department of Health Services Division of
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Drinking Water and Environmental Management also have developed guidance specifically for
watershed sanitary surveys.
2.4.1.2 How Should I Identify the Area of Influence?
The area of influence for which the vulnerability analysis is performed should be determined by
several factors, including hydrology, location of Cryptosporidium sources, fate and transport, and
pathogen loading . If watershed monitoring data are not available, it may be necessary to conduct
some monitoring to determine the most problematic areas of the watershed.
In a small watershed, the geography and hydrology may not be important in determining the
most sensitive areas, since the distance to the water source or streams feeding into the source is small.
In such cases, all potential sources of Cryptosporidium contamination should be evaluated based on
the characteristics of the source and the likelihood of Cryptosporidium release to a water body.
Delineation
As part of the source water assessments, States delineated the watershed surrounding each
PWS's source. These delineations may be used as a starting point for determining the area of influence.
To delineate watersheds, some States started with watersheds as catalogued by the U.S. Geological
Survey (USGS) (Horsley and Witten 2001). The USGS has assigned each watershed and its
subwatersheds in the United States a hydrologic unit code (HUC). Because the HUC subwatersheds
can be quite large, and a PWS's source may come from only a section of the watershed, or portion of
a hydrologic unit, sometimes only the part of the watershed upstream of the PWS's intake was
mapped. Sometimes watersheds were further segmented into "critical areas" within which more
detailed assessments were performed.
Some States delineated critical areas based on setbacks from the edge of the source water and
all tributaries feeding into the source water. Others defined critical areas based on a fixed distance or
time-of-travel from the intake (upstream of the intake or in all directions from the intake) (Horsley and
Witten 2001).
Systems that need to delineate their watersheds or subwatersheds for the first time and do not
have geographical information system (GIS) available can do so easily with topographic maps. The first
step is to find the source (including tributaries) and the water treatment plant intake on the map. Each
of the contour lines (which is actually not a line but a closed shape) around the source connects points
of equal elevation. Upstream, the elevation indicated by each contour line increases with distance from
the source. All precipitation falling within a zone of increasing elevation around the source will flow
towards the source. Where the contour elevations stop increasing and begin decreasing is the break
point. On the other side of the break point, water is flowing into a different watershed. The area
delineated by connecting the break points is the watershed (AWWA 1999). See
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http://www.terrene.org/fl6.pdffor an illustrated fact sheet on delineation. If the intake is not at the
downstream end of the watershed, it is only necessary to delineate the area upstream of the intake.
Systems with GIS can follow the same process using digital elevation model (DEM) data rather
than contour lines.
Within the watershed, systems may wish to delineate the area of concern based on fixed
distances from the shore of the source or based on time of travel (see box).
PWSs using ground water under the
direct influence of surface water (GWUDI) as a
source can delineate an area of influence by
combining a delineation of the watershed
influencing the ground water source with a
delineation of the wellhead protection area.
Watershed Hydrology
Once the watershed has been
delineated, PWSs should examine the hydrology
of their watersheds to help determine the area of
influence. The vulnerability analysis submitted to
the State must contain information on the
watershed's hydrology.
Stream discharge can affect the
transport of sediment and Cryptosporidium
oocysts, especially during and after storms.
When more rain falls than can be
absorbed immediately by the soil, soil cover, or
impervious surface, water will pond on the
surface. With increasing rainfall, the water will
flow to a lower level on the surface, to a river,
lake, or reservoir, as shown in Exhibit 2.1. As
water travels, it may pick up contaminants on
the soil surface (e.g., Cryptosporidium oocysts
from deposited fecal matter). These particles
are then suspended in the runoff and can be
transported to surface water supplies. The
microorganisms (including parasitic protozoa)
Delineation Based on Travel Time
In its watershed control program, the New York
City Department of Environmental Protection
delineated an area around its reservoirs that has a
60-day residence time 95 percent of the time
(Klett 1996). Within this zone, the department
limits the operation and construction of
wastewater treatment plants. The residence time
was calculated using the formula T=V/Q, where
T=time, V=volume of the reservoir, and Q=flow out
of the reservoir. Determining residence time
experimentally would have been too time-
consuming and expensive.
The department adjusted the actual reservoir
volume in its calculations to reflect changes over
time. First, it accounted for de facto changes in
volume resulting from stratification (i.e., during the
summer there is little vertical mixing, so the
volume of the bottom layer of the reservoir never
enters into the T=V/Q equation). Where the
entrance to an aqueduct transporting water from a
reservoir was significantly upgradient of the
reservoir dam, the volume of the water
downgradient of the aqueduct also was
subtracted, because water moving through the
reservoir may enter the aqueduct without ever
reaching the downgradient area. The department
also adjusted for changing reservoir volumes
caused by rising and falling water levels.
If the calculated residence time of a reservoir
close to New York City was less than 60 days,
the residence time of the next upstream reservoir
was added. Once a 60-day time was achieved,
the watershed around each of the reservoirs (or
parts of the reservoirs) was delineated based on
surrounding topography.
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associated with the soil can be transported as individual organisms, aggregates of organisms, or within
an aggregate of soil particles and organisms.
Exhibit 2-1. Ground Water/Surface Water Interaction
Precipitation
Well
Runoff
Recharge
Ground Water / Surface Water
Interaction
Septic
,., fS System
Road with
Catch Basin
Aquifer
Ground water that is considered to be under the direct influence of surface water (GWUDI) is
usually immediately adjacent to surface water or to the discharge point of a spring. These ground water
supplies are considered especially vulnerable to contamination by parasitic protozoa. GWUDI may be
contaminated by direct infiltration of oocysts from the surface as a result of rain, but, more commonly,
ground water is contaminated as a result of the action of pumping wells (see Exhibit 2-1). Given
sufficiently high pumping rates, wells can locally reverse the direction of ground water flow. In such
cases, surface water is induced to flow from a river, lake, or reservoir into the adjacent ground water,
where it may be extracted by one or more pumping wells. If the surface water is contaminated with
oocysts, the adjacent ground water may also become contaminated.
Water quality flow models analyze specific hydrologic, geographic, and water quality
parameters to estimate the travel time needed for contaminants to reach a drinking water intake and the
amount of contamination at that intake. Surface runoff models may also be used to assess the potential
impact of individual Cryptosporidium sources, and to identify watershed areas with the greatest
potential impact on source water quality. Models should always be validated for the settings in which
they are used.
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PWSs should also consider topography and soil type, which can affect hydrology. Areas with
steep slopes may experience a higher percentage of overland flow or runoff (as opposed to infiltration
and subsurface flow) and have faster overland flow rates during rainfall than flat areas.
Cryptosporidium may be more likely to be transported to water bodies in such areas, although if the
topography is very steep, livestock that carry Cryptosporidium may not be present. Impermeable or
compacted soil, impervious surfaces, unvegetated areas, and a high water table can also affect overland
flow. Riparian zones can be considered sensitive areas simply due to their proximity to streams that
feed into source waters. They are also subject to erosion. PWSs should also factor soil types into their
decisions; areas with high clay content may be more impermeable or more subject to erosion and can
contribute to high turbidity.
2.4.1.3 What and Where Are the Potential or Existing Sources of
Cryptosporidium?
All Cryptosporidium sources must be reported in the vulnerability analysis (40 CFR
141.725(a)(3)(i)). Systems may be able to use source inventory data collected as part of the source
water assessment program. Most States are asking systems to assist with identifying significant
potential contaminant sources (Horsley and Witten 2001), either through field verification or through
review of inventory databases or other information. Therefore, some PWSs should already have this
information available. States will also be assessing the risk of each source or category of sources,
primarily through numerical ranking systems and matrices; systems will have this information at their
disposal as well. It is possible that the inventory and ranking of potential sources may not be detailed
enough for a Cryptosporidium watershed control program, but they should provide a good starting
point.
After noting sensitive areas based on topography and geology, systems should determine
whether these areas coincide with land use that could contribute to microbiological contamination.
Reviewing land use and zoning maps helps target areas for further investigation or for prediction of
future sources and loading. PWSs should then search local data sources, such as health department
data on septic systems, and review recent sanitary survey results. Furthermore, they should obtain data
on point sources such as wastewater treatment plants that require EPA or State permits, e.g., National
Pollutant Discharge Elimination System (NPDES). NPDES information (also called water discharge
permit or PCS data) is available on EPA's Envirofacts website at
http://www.epa.gov/enviro/indexJ ava.html. After identifying potential sources of contaminants,
systems should field verify the locations of these point and nonpoint sources.
The paragraphs below summarize existing research on Cryptosporidium sources and
associated land use in watersheds. Because most studies of Cryptosporidium occurrence involve
sampling at water system intakes, little information is available about occurrence of Cryptosporidium
within watersheds and transport of oocysts to surface water supplies. The studies described are site-
specific; it is important to investigate these relationships in one's own watershed as well.
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Land Use
The character (topography, plant cover) and land uses (urban, farming) within a watershed also
influence the occurrence or concentration of Cryptosporidium in surface water (Hansen and Ongerth
1991). Oocyst concentrations can be as much as 10 times higher in urban and agricultural watersheds
(Hansen and Ongerth 1991, Stern 1996) than in undeveloped ones. However, such differences may be
site-specific—in streams in an agricultural watershed in southern Ontario, no connection was found
between Cryptosporidium concentration and sources or land use such as wastewater treatment plants,
combined sewer overflows, livestock, crops, houses, wildlife, and campgrounds (Fleming et al. 1999).
Sources
Many land uses in a watershed have the potential to introduce Cryptosporidium into water
supplies. These include point sources—combined sewer overflows, wastewater treatment plants, and
concentrated animal feeding operations—and nonpoint sources, including livestock, wildlife, pets, storm
water runoff, and septic systems. Seasonal variations in precipitation may affect Cryptosporidium
concentrations as well. Point and nonpoint sources of Cryptosporidium are described below.
Point Sources
Point sources such as combined sewer overflow (CSO) outfalls, which are common in older
municipalities, can be a significant source of oocysts, depending on the weather and the endemic rate of
cryptosporidiosis. CSOs contain raw sewage diluted by storm water. In one study, Cryptosporidium
concentrations at CSO outfalls on the Allegheny River in Pittsburgh during storms ranged from 0 to
3,000 oocysts/100 L, with a geometric mean of 2,013 oocysts/100 L (States et al. 1997).
Wastewater treatment plants may also contribute to oocyst loads, depending on the amount of
treatment provided. Primary treatment can remove as little as 27 percent of oocysts from effluent
(Payment et al. 2001); most plants in the United States provide secondary treatment, so removal should
be better. In the Netherlands, it is estimated that 85 percent of Cryptosporidium oocysts occurring in
surface water are discharged in wastewater treatment plant effluent (Medema and Schijven 2001). In
one study in Pittsburgh, oocysts were detected in 33 percent of samples with a geometric mean
concentration of 924 oocysts/100 L over 24 months of sampling (States et al. 1997). In another study
near Philadelphia, concentrations ranged from 33 to 2,490 oocysts per 100 L (67 percent of samples
were positive); downstream from the plant, concentrations ranged from 325 to 825 oocysts per liter
(Crockett and Haas 1997).
Concentrated animal feeding operations (CAFOs) can be a significant source of animal waste,
which can contaminate source water in two ways. If not properly managed, waste can leak or
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overflow from waste storage lagoons, feedlots, or other facilities. In addition, waste applied as fertilizer
to fields can run off into drinking water sources or source tributaries, especially if overapplied.
Nonpoint Sources
Agriculture can also be a nonpoint source of Cryptosporidium. On a stream running through a
small dairy farm before feeding into the Allegheny River, Cryptosporidium was detected in 82 percent
of samples (States et al. 1997), with a geometric mean concentration of 42 oocysts/100 L. Twice
during the 24-month study, concentrations of more than 1,000 oocysts/100 L were observed. In an
agricultural area in Canada, drain tiles contained average concentrations of 771 oocysts/100 L.
Concentrations were high even in tiles on farms without bams (these farms were assumed not to have
livestock present). Oocysts were also present in some samples in liquid swine manure storage lagoons
(Fleming et al. 1999).
Cattle are thought to be significant sources of oocysts. Cryptosporidium infection rates in cattle
depend on animal age. Calves, particularly those less than one or two months old, have the highest rates
(infection rates in different studies range from 2 to 39 percent of calves) (Wade et al. 2000, Sischo et
al. 2000, Huetink et al. 2001).
Cryptosporidium may directly enter surface water via waterfowl. Oocysts have been found in
Canada goose feces collected in the environment (Graczyk et al. 1998). Canada geese, some of which
no longer migrate, could cause considerable contamination of surface water sources and uncovered
finished water reservoirs.
Other wildlife may also be a source of Cryptosporidium, though the impact on source water
may not be as direct. Deer, muskrat, and other small mammals were shown to carry Cryptosporidium
in upstate New York (Perz and Le Blancq 2001). In one study of California ground squirrels, 16
percent of squirrels sampled were found to shed an average of 50,000 oocysts per gram of feces
(Atwill et al. 2001). The infection rate in each species and the species present in each watershed will
vary, so the contribution from wildlife will also differ from watershed to watershed.
Although little research has been performed on the overall prevalence of Cryptosporidium in
pets, Cryptosporidium has been detected in dogs and cats, although pets usually carry strains that are
rarely detected in humans. Several studies have shown dogs to be significant carriers of Giardia, fecal
coliform, and other bacteria (Schueler 1999), and these microbes have been found in storm water,
suggesting that Cryptosporidium may also be present in urban watersheds and storm water runoff.
Low levels of Cryptosporidium may also enter surface water through septic systems and
subsequent subsurface transport (Lipp et al. 2001).
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Cryptosporidium sources can be identified through polymerase chain reaction (PCR) analysis
of Cryptosporidium DNA. PCR can be used to determine the species or genotype of
Cryptosporidium; many genotypes or species are typically, although not exclusively, found in specific
hosts, such as cattle, dogs, and humans. In mixed-use watersheds, this information can help determine
whether Cryptosporidium in the source water could have come from agricultural runoff, combined
sewer overflows, or stormwater runoff.
Influence of Precipitation
Systems should determine the extent to which Cryptosporidium occurrence in their watershed
coincides with extreme rainfall—68 percent of waterborne disease outbreaks between 1948 and 1994
were shown to be associated with heavy precipitation (Curriero et al. 2001). Cryptosporidium
occurrence may also be related to seasonal variations in infection among livestock, but any correlation
is site-specific and depends on the source. In a study in six watersheds, Sobrinho et al. (2001) found
no substantial difference between Cryptosporidium detection rates during "event" (rainfall, high
turbidity, melting snow and spring runoff) and "non-event" sampling when all data were taken together.
However, for three of the watersheds, when examined individually, detection within each watershed
was significantly higher during event sampling.
Both Cryptosporidium detection and concentrations at six watersheds were highest between
the months of October and April, with March experiencing a detection rate of more than 30 percent
and oocyst concentration of about 0.038 oocysts/L (Sobrinho et al. 2001).
Other studies have noted a connection between rainfall and "extreme runoff' events in
tributaries to drinking water sources (Kistemann et al. 2002). One study noted a decrease in farm
stream concentrations of Cryptosporidium with an increase in 5-day cumulative precipitation
(probably because continued rainfall washed most of the Cryptosporidium downstream) (Sischo et al.
2000).
2.4.1.4 How Do Fate and Transport Affect the Way Cryptosporidium
Impacts My Water Supply?
Transport of oocysts in surface water and ground water and survival of oocysts all affect the
potential impact of Cryptosporidium on water supplies. The behavior of oocysts in each medium is
described below.
Transport in Surface Water
The buoyancy of oocysts in water depends on their attachment to other particles. Oocysts that
are not bound to particles have a tendency to float, even after being centrifuged (Swabby-Cahill et al.
1996). Cryptosporidium oocysts have a very low density (about 1.05 g/cm3) and a very low settling
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rate (2 mm per hour or less), which suggests that sedimentation without coagulation may not be an
effective means of oocyst removal (Gregory 1994). Oocysts attached to wastewater effluent particles
may settle more quickly than those that are freely suspended and sedimentation velocity increases with
particle size (Medema et al. 1998). In source waters, many oocysts are likely to be adsorbed to
organic or other suspended material and would probably settle more quickly than free-floating oocysts
(Medema et al. 1998).
Cryptosporidium is thought to be easily transported over land. Because oocysts are
approximately the size of clay/silt particles, the amount of kinetic energy needed to entrain and suspend
oocysts in overland flow may be quite small (Walker et al. 1998).
Transport In Ground Water
Surface water sediments and the aquifer matrix material may play significant roles in minimizing
oocyst transport to water supply wells; however, it is difficult to isolate the effect of these materials on
transport. For example, if oocysts are not detected in a sample, it could be because they are not
present in the aquifer or that they are present but were not recovered in the laboratory. Or it could be
that fractures or dissolution conduits in the aquifer allow ground water and oocysts to effectively bypass
the protective action of most of the aquifer matrix.
It is known that Cryptosporidium can be transported through soil and ground water
(Mawdsley et al. 1996; Hurst 1997). For instance, in one study examining riverbank filtration, oocysts
were recovered at a well 200 feet from the Ohio River (Arora et al. 2000). Movement of C. parvum
through soil and ground water is affected by sedimentation and filtration of the surrounding soil and
aquifer matrix (Brush et al. 1999; Harter et al. 2000). Adsorption of oocysts to matrix particles also
affects filtration. Adsorption depends on the electrical charge of the organism and of the surrounding
matrix. A charge on the oocyst can change the effective diameter of the oocyst; however, the charge is
difficult to ascertain because it can be altered by the purification method used to recover oocysts in the
laboratory (Brush et al. 1998).
Factors other than adsorption and micropore size may influence the oocyst movement. C.
parvum transport in one study was greater in a silty loam and a clay loam soil than in a loamy sand soil
(Mawdsley et al. 1996); this contradicts other evidence suggesting that clay soils exhibit greater
adsorption and smaller micropores than sandy soils. The authors used intact soil cores (rather than
columns created in the laboratory) to maintain the natural soil structure and macropores, and they
concluded that the rapid flow of water through macropores largely bypasses the filtering and adsorptive
effects of the soil and increases the risk of Cryptosporidium transport to ground water (Mawdsley et
al. 1996).
Survival in the Environment
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Several factors influence oocyst survival. This section presents the findings from several studies
describing oocyst inactivation due to temperature and dessication.
Before oocysts enter a water source, they may be vulnerable to dessication. Robertson et al.
(1992) reported that air drying an oocyst suspension at room temperature for 4 hours eliminated
viability. Oocysts in fecal material, however, are protected from desiccation, so their viability in the
environment is prolonged (Rose 1997). In addition, Cryptosporidium in liquid swine manure has been
shown to remain viable despite the high ammonia content of the manure (Fleming et al. 1999).
However, Olson et al. (1999) found that oocyst survival appears to be better in soil than in feces.
Once initial contamination has occurred, water can remain a source of viable oocysts for days
(Heisz 1997; Lisle and Rose 1995). Lisle and Rose reported a duration of 176 days to produce die-
off rates of 96 percent in tap water and 94 percent in river water under laboratory conditions. After 2
days, only 37 percent of the oocysts in tap water were nonviable, suggesting that oocysts that reach the
distribution system might be viable.
Olson et al. (1999) compared oocyst survival at temperatures and in media likely to occur in
the natural environment. They examined survival in -4°, 4°, and 25° C. Unlike Giardia, which died off
quickly at low temperatures, Cryptosporidium oocyst survival was best at -4°C, with close to 50
percent of oocysts remaining viable for 12 weeks. Survival was lowest at 25°C, but oocysts were still
viable at six weeks. Survival rates were best in water and worst in feces.
Loading
Once you have gathered information about Cryptosporidium sources and the likelihood of the
oocysts reaching your source water (based on watershed characteristics and fate and transport), you
should determine the amount and proportion of oocysts that each source is expected to contribute to
the overall Cryptosporidium load. Loading can be calculated fairly easily for constant point sources
such as wastewater treatment plants but is more difficult for farms and urban runoff; monitoring and
water quality modeling may be necessary (see section below on monitoring).
2.4.1.5 What Role Should Monitoring Play in a Vulnerability Analysis?
The vulnerability analysis is required to address sources of Cryptosporidium, seasonal
variability, and the relative impact of the sources of Cryptosporidium on a system's source water
quality (40 CFR 141.725(a)(3)(i)). While you may already have some knowledge of potential
Cryptosporidium sources through land use information or discharge permit data, monitoring can help
you determine the extent to which these sources are impacting your source and can help you target
portions of your watershed for extra protection or BMP implementation. Although not required as part
of the vulnerability analysis, monitoring throughout your watershed for Cryptosporidium (or indicators
of fecal contamination) is the best way to measure the success of a watershed control program.
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Monitoring data collected during the vulnerability analysis provide a baseline against which you can
compare data gathered during implementation of the watershed program. Some PWSs, as well as the
USGS and local universities, may already have some water quality or streamflow data available.
Watershed monitoring can help narrow down the locations of some sources and determine the
load contributed by each source. The Philadelphia Water Department, for example, planned a four-tier
study to determine why there was such a large difference in protozoan levels at two plants using the
same source (the Schuylkill River) but located 2.5 miles apart (Crockett and Haas 1997) (see sidebar).
Because Cryptosporidium occur in low
concentrations and are difficult to detect, it may
be helpful to monitor other parameters in
addition to or instead of Cryptosporidium.
While E. coli concentrations often do not
correlate with Cryptosporidium levels, they are
good indicators of fecal contamination. Fecal
coliform bacteria have traditionally used as
water quality indicators, but E. coli is thought to
be more closely linked to fecal contamination.
Turbidity does not always indicate fecal
contamination; often, increased turbidity is
simply a product of high sediment levels.
However, turbidity may indicate the presence of
a water quality problem, where additional
research is necessary to determine its cause.
Monitoring should be conducted
regularly. Because nonpoint sources of
microbiological contamination discharge
primarily during wet weather flows, monitoring
during or soon after these events is also
important. When combined with stream
discharge data, rates of storm-related
Cryptosporidium transport and loading can be
calculated. The monitoring frequency should be
such that seasonal variability in
Cryptosporidium levels is observable.
There are two types of watershed monitoring for stream networks. First, basinwide monitoring
involves monitoring just upstream of the confluence of two streams (AWWARF 1991). Conducted at
stream junctions throughout the watershed, basinwide monitoring helps give a general picture of the
Monitoring to Locate Cryptosporidium
Sources
To determine the source of
Cryptosporidium contamination in the
Schuylkill River, the Philadelphia Water
Department decided to focus on a creek
feeding into the Schuylkill just before the
Queen Lane plant (Crockett and Haas
1997). This creek has several wastewater
treatment plants in its upper reach and
farms and parks along its lower reach. In
the first phase, the water department
tested the Queen Lane intake during dry
flow. It then sampled a site along the
creek downstream of the wastewater
treatment plants and one downstream of
the farms during various weather
conditions. In the third tier of sampling, the
department sampled wastewater effluent
and additional sites up- and downstream
of some of the wastewater treatment
plants during different weather events.
Lastly, the department planned to focus on
the prevalence of Cryptosporidium and
Giardia in livestock and wildlife along the
creek. Results are discussed in section
2.4.1.3.
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water quality and helps isolate the stream reaches contributing to contamination. Second, site-specific
monitoring involves monitoring just upstream and downstream of a suspected or known point or
nonpoint source, as the Philadelphia Water Department did (Crockett and Haas 1997). Such
monitoring is appropriate where impacted stream reaches have already been identified. The results of
any monitoring should enable the system to compare the relative contribution of various sources to the
overall Cryptosporidium occurrence in the watershed and their effect on water quality.
Monitoring in a reservoir or lake, if applicable, can help systems determine the fate of
Cryptosporidium once it flows from a stream into the lake, or once it enters the lake directly from land
immediately adjacent to the lake. Sampling patterns should depend on the shape and depth of the lake.
A round lake should be sampled at several locations and depths near the center of the lake; a long lake
should be sampled in a transect along its long axis (AWWARF 1991). More specific monitoring may
be needed to answer more detailed questions on fate and transport. For instance, does
Cryptosporidium concentration decrease due to sedimentation or dilution? How long does it take for
Cryptosporidium to flow from one end of the reservoir to the intake?
PWSs may find it helpful to use a geographic information system (GIS) to analyze their water
quality and contaminant source data. For systems that have Arc View software, BASINS 3.0, a
software and GIS package developed by EPA, can assist systems with integrating local data and
nationally available pre-formatted spatial data (e.g., watershed hydrologic unit codes (HUCs), digital
elevation model (DEM) data, roads, NPDES permit data, and Clean Water Needs Survey data on
wastewater treatment plants). BASINS also includes a model for determining nonpoint source loading
and other models for loading and transport, as well as tools for assessing contamination from various
sources.
2.4.2 Analysis of Control Measures
The analysis of control measures submitted with the watershed control plan must address the
relative effectiveness of each measure at reducing Cryptosporidium loading to the source water, along
with the sustainability of each measure (40 CFR 141.725(a)(3)(ii)).
Control measures may include 1) the elimination, reduction, or treatment of wastewater or
storm water discharges, 2) treatment of Cryptosporidium contamination at the sites of the waste
generation or storage, 3) prevention of Cryptosporidium migration from sources, or 4) any other
measures that are effective, sustainable, and likely to reduce Cryptosporidium contamination of source
water. If you do not own or otherwise have authority over the Cryptosporidium sources in your
watershed, you may need to develop and maintain partnerships with landowners within the watersheds.
These could include other municipal governments, farmers, wastewater treatment plant operators,
regional planning agencies, and others. Examples of these partnerships and possible control measures
for different sources are described in the following sections; further detail is provided in Appendix E.
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2.4.2.1 How Should I Build Partnerships with Other Stakeholders?
Many watershed management practices cannot be implemented by water systems alone. For
example, agricultural BMPs must be implemented by farmers; stormwater BMPs are implemented by
developers, manufacturers, and government agencies. Parts of your watershed may be in different
municipalities. Therefore, it is imperative that PWSs work with these and other stakeholders to solicit
their input and earn their cooperation.
The type of partnership you build depends on each type of stakeholder. With government
agencies you might need to sign memoranda of agreement or make other formalized arrangements. For
some types of stakeholders it may be more appropriate or efficient to reach out to technical assistance
providers such as cooperative extension agents or association representatives and provide them with
information to distribute. Ultimately, however, you must reach out to individual stakeholders, because
people who don't know about the watershed control program will not be as likely to do their part.
Increasingly, PWSs are incorporating more intensive stakeholder participation into their
planning whenever possible. They have found that dialogue with stakeholders is more likely to result in
an acceptable solution than situations in which systems simply inform stakeholders that they already
know the best way to address a problem (AWWARF 2001). The book Guidance to Utilities on
Building Alliances with Watershed Stakeholders (AWWARF 2001) explains how to present issues
to stakeholders, how to target stakeholders, and how to structure your partnership with stakeholders.
2.4.2.2 What Regulatory and Other Management Strategies Are Available
to Me?
For systems in watersheds where most of the land is privately owned, land use regulations may
be the best way to control pollution, especially in heavily developed or growing areas. Examples of
possible regulations include septic system requirements, zoning ordinances specifying minimum lot sizes
or low-impact development, limits on discharge from wastewater treatment plants and other facilities,
pet waste cleanup ordinances, and requirements for permits for certain land uses. Your ability to
regulate land use will depend on the authority granted to your municipality by the State, the ownership
of your system (public or private), and the support of your local government and the public. Regulatory
authority, steps for designing a regulation that can withstand lawsuits, and types of land use regulations
are described in the paragraphs below.
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Determining Authority to Regulate
The ability of a municipality to pass a land use ordinance or other law to help reduce
contamination may depend on the authority the State grants to the local government in the State
constitution or through legislation, although States normally do not interfere with the actual land use and
zoning rules (AWWARF 1991). Privately owned water systems may need to ask the cooperation of
the local government to get source water regulations passed. Publicly owned PWSs face less of a
hurdle, although winning support of the local government may still be difficult.
If the area of influence on water quality extends throughout several municipalities, it can be
difficult to standardize watershed control practices throughout the watershed. The legal framework
used will depend on who has jurisdiction over land use in the watershed and on the authority of the
water system (AWWARF 1991). For example, some States may create agencies authorized to
promulgate and enforce watershed protection regulations, or interstate agencies may be created to
regulate watersheds where watersheds cross State boundaries. County governments in some States
may have some zoning authority and may be able to assist with enforcement of some regulations
affecting source water (e.g., septic systems).
Where PWSs do not have regulatory or enforcement authority, they should work with other
local governments' PWSs and agencies in their watersheds to sign memoranda of agreement or
understanding, in which each entity agrees to meet certain standards or implement certain practices.
Zoning
Early zoning laws simply prohibited certain land uses that would be considered nuisances in
certain areas. Later, zoning ordinances became more specific; further restrictions were imposed on the
permitted uses, such as limits on building or population density, percentage of impervious surface area,
building height, and minimum distance of buildings from property boundaries. Most zoning ordinances
have grandfather clauses that allow nonconforming uses to continue. Ordinances may also allow the
zoning authority to grant variances if the topography or size of a lot make it difficult to comply with a
zoning requirement.
To make sure a zoning law can withstand a legal challenge, it is important to make sure the
appropriate procedures are followed and that the law has sufficient scientific basis (AWWA 1999).
First, be sure you have the authority to regulate. Make sure the rule is specific enough. Comply with
all administrative procedure requirements; failure to do so is the most common reason for rules being
revoked. The ordinance should conform to the objectives of the watershed control program plan,
which should contain enough data to illustrate how the ordinance will affect water quality.
Ordinances should also be designed to withstand a takings lawsuit (AWWA 1999). The fifth
amendment to the U.S. Constitution states that private property may not be taken for public use without
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just compensation. Any physical invasion without consent is always considered a taking, even if the
landowner retains ownership of the land. Installation of a monitoring well or stream gauge without
consent is an example of a taking.
To prevent takings claims, the municipality should show the need for the regulation and a
connection between the ordinance and the expected result (AWWA 1999). This proof should be
based on a scientific analysis beginning with an accurate delineation of the watershed or wellhead
protection area/recharge area.
Following the delineation, determine the impact the regulation will have by mapping current and
projected development under current zoning requirements. Then map current and projected
development for the proposed ordinance and determine the potential pollutant load under each scenario
(AWWA 1999). Local groups or universities may be able to provide pollutant data and assist with
modeling. This "buildout analysis" will help you show that your proposed ordinance advances a
legitimate government interest and how the effect of the ordinance is proportional to the impact of land
use in your watershed.
Types of Ordinances
Watershed ordinances usually apply within an "overlay district," which may be the area of
influence you determined for your watershed control plan. All existing zoning or land use regulations
apply within that area, but additional requirements apply within the overlay district. Within your
watershed, particularly within the area of influence, there are many different kinds of regulatory controls
you may wish to consider:
• Large-lot or low-density zoning.
• Limits on certain types of land use except by special permit.
• Impact fees.
• Submission and approval of a watershed protection plan or impact study as a condition for
development of a subdivision or apartment complex.
• Performance standards, which permit development but limit the impact of the development.
More detail on each of these types of ordinances is found in Appendix E. Examples of source
water protection ordinances can be found on EPA's website at
http://www.epa.gov/owow/nps/ordinance/osm7.htm.
Land Acquisition/Conservation Easements
Acquisition of watershed land by the utility or its affiliated jurisdiction is often the most effective
approach to protecting the water source. EPA's Drinking Water State Revolving Fund allows a
percentage of the fund to be set aside for land acquisition associated with watershed protection.
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Land trusts and conservancies can help systems purchase land to protect drinking water quality,
especially when government agencies are unable to move quickly enough to buy land when it becomes
available. Trusts can buy and hold land from multiple landowners on behalf of a water system until the
system can assemble funding to purchase it from the trust. The Trust for Public Land
(http ://www.tpl .org^ can provide more information.
Trusts also can work with landowners to buy or have landowners donate conservation
easements. An easement is a legal document that permanently limits the development of a piece of
land, even after the land is sold or otherwise changes ownership. See
http://www.landtrust.org/ProtectingLand/EasementInfo.htm for frequently asked questions about
easements and for an example of a model easement for use in the State of Michigan. The Land Trust
Alliance (http://www.lta.org). a trade organization for land trusts, has published handbooks on designing
and managing conservation easement programs.
Other government agencies, such as the U.S. Forest Service or State natural resource
departments, may be able to buy parcels in your watershed if you are unable to afford to purchase all
the land that needs to be protected.
2.4.2.3 How Should Point Sources Be Addressed?
Changes in farming practices and in wastewater treatment technologies in the past decade have
resulted in new management strategies for agricultural and urban point sources. The following sections
briefly describe solutions for agricultural, wastewater, and stormwater point sources; detailed
descriptions are provided in Appendix E. As part of your application for watershed control program
approval, you must submit an analysis of control measures that can mitigate sources of
Cryptosporidium such as these (40 CFR 141.725(a)(3)(ii)). Loans from the Clean Water State
Revolving Fund can be used to fund projects associated with wastewater treatment and watershed and
estuary management. See www.epa.gov/owm/cwfinance/cwsrf/index.htm for more information.
Concentrated Animal Feeding Operations
Animal feeding operations (AFOs) are facilities where animals are confined for 45 days or
more a year and where no vegetation grows in the area used for confinement. This includes farms
where animals graze the majority of the year but are confined and fed during the winter for at least 45
days. Some AFOs are also considered concentrated animal feeding operations (CAFOs) (see
Appendix E). EPA recently issued a rule that changed the requirements on CAFOs that must apply for
National (or State) Pollutant Discharge Elimination System (NPDES) permits (U.S. EPA 2003). The
new CAFO rule requires CAFOs to implement nutrient management plans that affect manure handling,
storage, and land application. These plans will include best management practices (BMPs) primarily
designed to reduce nitrate and phosphorus contamination but which will at the same time reduce
pathogen contamination. Elements of this plan may include limiting the manure land application rate,
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instituting buffer zones where manure is applied, ensuring adequate manure and wastewater storage,
and others.
Wastewater Treatment Plants
All wastewater treatment plants in the United States are required to provide secondary
treatment (U.S. EPA 2001e). Most plants are also required to disinfect their effluent before
discharging. However, conventional chlorine disinfection in wastewater plants is ineffective against
Cryptosporidium. Some wastewater treatment facilities are beginning to implement treatment similar to
that used for drinking water treatment (e.g., advanced treatment, including chlorine disinfection,
filtration, and dechlorination). PWSs should identify all wastewater treatment plants in their watersheds
and determine what their permit effluent limits are and whether the limits are being met.
Combined Sewer Overflows
Combined sewers carry both sewage and storm water to wastewater treatment plants. During
storms, the volume of water in combined sewers may become too great for wastewater plants to treat.
As a result, the excess sewage and storm water are released untreated into surface water through
CSOs. CSOs are most common in older cities in the northeastern and midwestern United States and
can be a significant contributor of Cryptosporidium to urban watersheds.
There are three major structural solutions to the problem of CSOs:
• Separate combined sewers into sanitary and storm sewers, where sanitary sewers flow to
the wastewater treatment plant and storm sewers release to surface water.
• Increase the capacity of the wastewater treatment plant so that it is able to treat combined
sewage from most storms.
• Build aboveground covered retention basins or to construct underground storage facilities
for combined sewage to hold the sewage until the storm has passed and can be treated
without overloading the plant.
Although CSOs are not regulated directly under their own program, EPA has a CSO control
policy (U.S. EPA 1994) which encourages minor improvements to optimize CSO operation, and CSO
management may be written into NPDES or State Pollution Discharge Elimination System (SPDES)
permits. Minor improvements include maximizing in-line storage within the sewer system, reducing
inflow, and treatment of CSO outfalls.
Sanitary Sewer Overflows
Watersheds with separate sanitary and storm sewer systems may still have water quality
problems. Sanitary sewer overflows (SSOs) occur when untreated and mostly undiluted sewage backs
up into basements, streets, and surface water. SSOs discharging to surface water are prohibited under
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the Clean Water Act. Insufficient maintenance and capacity and illegal connections are some of the
primary causes of SSOs.
SSOs can be reduced by cleaning and maintaining the sewer system; reducing inflow and
infiltration by repairing leaking or broken service lines; increasing sewer, pumping, and/or wastewater
treatment plant capacity; and constructing storage for excess wastewater (U.S. EPA 2001f). EPA is
proposing a rule that will require sewer systems to implement capacity assurance, management,
operation, and maintenance programs and will require public notification of overflow events. This
information will assist PWSs in addressing SSO point sources.
Municipal Separate Storm Sewer Systems
Municipal separate storm sewer systems (MS4s) in areas with populations of more than
100,000 are also required to obtain NPDES permits. Information on storm sewer outfall locations,
volume discharged, conventional pollutant loads, and existence of illicit discharges is submitted as part
of the permit application process (U.S. EPA 1996). In addition, these MS4s must develop
management plans addressing items such as outfall monitoring, structural and nonstructural BMPs to be
implemented, and identification and elimination of illicit discharges. Illicit discharges to MS4s include
any non-stormwater discharges, such as discharges that should be connected to sanitary sewers (e.g.,
water from sinks, floor drains, and occasionally toilets), illegal dumping of sewage from recreational
vehicles, sanitary sewer overflow backing up through manhole covers into storm drains, effluent from
failing septic systems, water from sump pumps, etc.
Small MS4s (serving areas with populations of less than 100,000), with some exceptions, are
subject to NPDES permit requirements if they are located in "urbanized areas" as determined by the
Bureau of the Census. Those MS4s subject to NPDES permits must implement "control measures" in
six areas, including a plan for eliminating illicit discharges (U.S. EPA 2000b).
PWSs should work with all MS4 utilities in the area of influence to gather existing information
about storm water contamination. MS4 utilities may need to install or retrofit structural BMPs, such as
retention ponds, to reduce contamination.
2.4.2.4 What BMPs Can Help Alleviate Nonpoint Sources?
The following sections briefly describe BMPs for agricultural, forestry, and urban sources of
Cryptosporidium; detailed descriptions are provided in Appendix E. Your watershed control program
plan must discuss how these or any other BMPs you choose will be implemented in the area of
influence. EPA Section 319 grants and Clean Water State Revolving Fund loans can be used for
nonpoint sources and watershed management purposes.
Agricultural BMPs
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Management Programs
The U.S. Department of Agriculture recommends the following "control points" for controlling
pathogens (USDA 2000):
• Preventing initial infection by controlling pathogen import to the farm
Controlling the reproduction and spread of the pathogen throughout the farm
• Managing waste
• Controlling pathogen export from the farm
PWSs should work with local soil conservation districts or cooperative extensions for technical
assistance with BMPs.
BMPs that can reduce pathogen loading include the following:
Composting
• Waste management (manure storage and land application)
• Grazing management
• Feedlot runoff diversion
• Buffer or filter strips
Composting
Can effectively reduce pathogen concentrations
• Entire waste mass should be uniformly treated and there should be no cold spots
Buffer Strips
• Provide buffer between area of manure application or grazing and adjacent streams or
lakes
• USDA (2000) recommends that buffer and filter strips be considered secondary practices
for pathogen control and be used in conjunction with control measures
Grazing Management
• Managed grazing can be cheaper and less environmentally damaging than confined feeding
and unmanaged grazing. It decreases feed, herbicide, equipment, and fertilizer costs, while
reducing erosion and increasing runoff infiltration and manure decomposition rates (Ohio
State University Extension, undated).
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• In managed, or rotational, grazing, a sustainable number of cattle or other livestock graze
for a limited time (usually 2-3 days) on each pasture before being rotated to the next
pasture.
Manure Storage
• Manure storage facilities allow farmers to wait until field conditions are more suitable for
land application.
• Manure storage facilities should be designed to prevent discharge through leaching or
runoff. They should be lined, and if possible, covered. Facilities that are not covered
should be designed to contain precipitation and runoff from a 25-year 24-hour storm.
Land Application of Manure
Several precautions taken in manure application can prevent runoff from entering surface
water, reducing the likelihood of Cryptosporidium contamination.
• Manure should not be applied to frozen ground or before predicted rainfall, or near
tile drains or dry wells or to land subject to flooding.
For pastures to be used for grazing, waste should be stored for at least 60 days and
then applied at least 30 days before the scheduled grazing period, to avoid infection
of the animals.
Feedlot Runoff Diversion
• Diverting clean water before it drains into the feedlot can significantly reduce the amount of
wastewater that needs to be managed.
• All roofs that could contribute to feedlot runoff should have -
• gutters
• downspouts
outlets that discharge away from the feedlot
Forestry BMPs
• Logging can cause increased erosion, leading to increased runoff and making it more likely
that Cryptosporidium present in wildlife will reach the source water. Logging can also
cause elevated sediment levels, resulting in high turbidity, which affects water treatment
efficiency. Examples of forestry BMPs are listed below -
filter strips
streamside or riparian management zones
• logging roads should be constructed to minimize runoff
• road runoff should be diverted away from streams and prevented from channelizing
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• loggers should minimize soil disturbance and compaction on skid trails
Urban/Suburban BMPs
See http://www.epa.gov/owm/mtb/mtbfact.htm for fact sheets on technologies and BMPs
municipalities can use to reduce contamination from wastewater and stormwater.
Buffer Zones
• For watersheds in urban areas, buffer zones help to protect development on the floodplain
from being damaged when the water is high, as well as protect the stream from the effects
of the development.
• The extent to which buffer zones reduce Cryptosporidium loading is not well understood;
therefore, they should be used to augment, rather than replace, other watershed
management practices.
Dry Detention Basins
• Dry detention basins temporarily store stormwater runoff and release the water slowly to
allow for settling of particulates and the reduction of peak flows.
Infiltration Devices
• Infiltration devices remove pathogens and particles by adsorption onto soil particles and
filtration as the water moves through the soil to the ground water. Infiltration devices
include (NALMS 2000) -
• infiltration basins
• infiltration trenches
• dry wells
Sancf Filters
• Sand filters can be used to treat storm water runoff from large buildings and parking lots.
Wet Retention Ponds
• Ponds can effectively reduce suspended particles and, presumably, some pathogens, by
settling and biological decomposition.
There is concern, however, that ponds attract wildlife that may contribute additional fecal
pollution to the water, rather than reducing contamination.
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Constructed Wetlands
Constructed subsurface flow wetlands (where wetland plants are not submerged) can
reduce Cryptosporidium and bacteria concentrations in wastewater (Thurston et al. 2001).
• Wetlands may also be useful for treating storm water or other polluted water.
Runoff Diversion
Structures can be installed in urban settings to divert clean water flow before it reaches a
contamination source. Structures that channel runoff away from contamination sources
include stormwater conveyances, such as -
• swales
gutters
• channels
• drains
• sewers
Pet Waste Management
• Municipalities can implement pet waste management programs to encourage pet owners to
properly collect and dispose of their animals' waste.
Water Conservation
• Can help preserve the amount of water available for use, especially during times of drought.
Can also decrease the amount of wastewater and stormwater generated, thereby protecting
the quality of the water supply (U.S. EPA 2002d)
• The following are examples of water conservation methods -
• low-flow toilets and showerheads
• reducing lawn watering
Low Impact Development
• Low impact development tries to reduce the amount of impervious cover, increase natural
lands set aside for conservation, and use pervious areas for more effective stormwater
treatment of residential and commercial developments.
Septic Systems
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• Failing septic systems can result in clogging and overflow of waste onto land or into surface
water.
• Water systems should work closely with the local regulatory authority to ensure that septic
system codes are being properly enforced and to strengthen codes where necessary.
• Utilities should encourage residents with septic systems in the watershed to understand their
systems and the proper maintenance that their systems require. Cooperative extensions can
work with residents on this issue.
Wildlife BMPs
Steps taken to prevent wildlife from contaminating source water vary with the source and
type of wildlife. The following are examples of wildlife BMPs -
• boats with noisemakers to scare seagulls and geese away
fences on the water's edge to keep out larger land animals and humans
2.4.3 Writing the Watershed Control Plan
Your plan must establish goals and define and prioritize specific actions to reduce source water
Cryptosporidium levels. The plan must explain how the actions are expected to contribute to the goals,
identify watershed partners and their roles, identify resource requirements and commitments, and
include a schedule for plan implementation (40 CFR 141.725(a)(3)(iii)).
The Center for Watershed Protection provides basic templates to help with design of
watershed protection programs, including steps systems can take in seven areas: watershed planning,
land conservation, buffer zones, stormwater BMPs, non-stormwater discharges, watershed stewardship
programs, and unique tools (e.g., spill response). Templates are available at
www. stormwatercenter.net.
2.4.4 How States Should Assess Plans
Vulnerability Analysis
The vulnerability analysis should evaluate the potential for the water supply to draw water
contaminated with Cryptosporidium. Cryptosporidium prevalence and the natural sensitivity of the
water source should be considered together to determine the potential susceptibility of the drinking
water source to contamination. The utility should define an area of influence for its water supply and
provide an explanation of the assumptions that guided the delineation of that area of influence. The
vulnerability analysis should take into account hydrologic and hydrogeologic factors, intake location,
fate and transport characteristics of Cryptosporidium oocysts, and characteristics of potential sources
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of Cryptosporidium in the area of influence. In addition, the vulnerability analysis should address the
prevalence of different Cryptosporidium sources within the area of influence. Some assessment
criteria that States can use during their review of vulnerability analyses are provided in Table 2.1.
Additional criteria may be appropriate, based on site-specific characteristics of the area of influence
and sources of Cryptosporidium contamination.
Identification and Analysis of Control Measures
The water supply must identify what measures could be taken to reduce or eliminate sources of
Cryptosporidium identified in the vulnerability analysis (40 CFR 141.725(a)(3)(ii)). These control
measures should be discussed in enough detail that the water supply has demonstrated it has a realistic
understanding of what would be needed to implement the measures. The water supply should include
an accurate estimate of control measure costs, as well as discussion of the political feasibility of
implementation. Thoughtful estimates should be included of how much time the implementation of
specific control measures would take, including any special considerations, such as seasonal
restrictions.
In addition, the system must address how implementation of the control measures will impact
Cryptosporidium loading in the watershed (40 CFR 141.725(a)(3)(ii)). The utility should discuss the
degree to which control measures would control specific sources of Cryptosporidium. It should also
provide context of the overall impact of the implementation of the control measures, addressing which
control measures will be applied to Cryptosporidium sources that are significant in size or close to the
water supply intake, and how effective the utility thinks they will be. Some assessment criteria that
States can use during their review of the utility's discussion of control measures are provided in Table
2.1.
The Watershed Protection Plan
The watershed protection plan must address goals and define and prioritize specific actions to
reduce source water Cryptosporidium levels. The plan must explain how actions are expected to
contribute to the specified goals, identify partners and their roles, describe resource requirements and
commitments, and include a schedule for plan implementation (40 CFR 141.725(a)(3)(iii)). Some
assessment criteria for States to use during the review of watershed protection plans are provided in
Table 2.1.
Cryptosporidium control measures included in watershed protection plans may include such
diverse activities as structural BMPs, land use control regulations, and public education. Each of the
activities should have a timetable for implementation, a budget, and details about how the activity will be
implemented.
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Utilities will have the maximum opportunity to realize their watershed protection goals if they
have complete ownership of the watershed. Utilities should include in their watershed protection plan a
description of efforts that will be made to obtain ownership, such as any special programs or budget.
When complete ownership of the watershed or area of influence is not practical, the system should
explain what efforts will be made to gain ownership of critical elements, such as reservoir or stream
shoreline and access areas.
Where ownership of land is not possible, utilities should describe plans to obtain written
agreements that recognize the watershed as part of a public water supply. As much as possible,
maximum flexibility should be given to the utility to control land uses which could have an adverse effect
on the water quality. Utilities should include with these descriptions an explanation of how they will
ensure that landowners will comply with the agreements.
Watershed control plans must identify watershed partners and their roles (40 CFR
141.725(a)(3)(iii)). Plans should document the efforts to be made to establish voluntary local
partnerships, including solicitation of private individuals living within the defined area of influence who
are likely to be affected by decisions made as part of the watershed protection program, whose
participation is important for the success of the program. Plans should also document how members of
municipal or other local governments or political subdivisions of the State that have jurisdiction over the
area of influence will participate in the watershed protection effort. Watershed protection plans should
include descriptions of how the proposed local partnership has or will identify and account for any
voluntary or other activities already underway in the area of influence that may reduce or eliminate the
likelihood that Cryptosporidium will occur in drinking water.
Table 2.1 Assessment Criteria for Use By States When Reviewing Watershed
Control Program Plans
Assessment Criteria
Addressed in
Sufficient Detail?
Vulnerability Analysis
Has the area of influence been delineated in appropriate detail, taking into consideration
available information about Cryptosporidium fate, transport and local hydrogeo logical
characteristics? Have sensitive areas been identified?
Is the scale of the delineation appropriate for the watershed plan? Does it provide a level
of detail sufficient for effective decisions to be made?
Has the intake location been identified relative to the water body?
Is any information available about time of travel in the watershed?
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Assessment Criteria
Does it seem that all activities within the watershed that could result in Cryptosporidium
contamination of the water supply have been identified and located?
Have contaminant sources been located and described relative to the drinking water
source intake location?
Have the likelihood and timing of releases of contamination been addressed?
Are there permitted wastewater discharges (NPDES) of concern? If there are wastewater
treatment plants in the area of influence, systems should include information about their
size, discharge quantity, and whether there has been any recent significant noncompliance
with permit conditions.
Are sludge disposal areas identified and characterized? Are there any locations in the
watershed where biosolids have been applied? Have they been identified? When in the
year are they applied?
Have stormwater discharges been located? Are there any discharges directly into the
surface water supply?
Have septic systems been identified and located? What information is available about
their age, condition, design, and siting?
Has land use zoning been characterized?
If land uses in the watershed include agriculture, have the types of farming been
identified? Are feedlots located? Are fields where manure is spread identified?
Have Concentrated Animal Feeding Operations (CAFOs) been identified and located?
Have natural sources of Cryptosporidium been identified and located?
Have recreational areas (e.g., campgrounds, trailer parks) been identified and located?
Has any on-site landfilling, land treating, or surface impounding of waste other than
landscape waste or construction and demolition debris taken place, and will such
circumstances continue?
Does the vulnerability analysis address the effectiveness of physical barriers (e.g.,
geology, hydraulic conditions, intake structure and location) at preventing the movement
of contaminants to the drinking water source?
Have tributaries or areas of the reservoir with high bacterial readings been identified? If
so, where are they located relative to the drinking water intake?
If Cryptosporidium monitoring data exist for the watershed, have results been addressed
and discussed?
Have recreational uses of the surface water supply been identified? Has the effect of
those uses on Cryptosporidium loading been addressed?
Addressed in
Sufficient Detail?
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Assessment Criteria
Are there portions of the watershed with high percentages of impervious surfaces which
might lead to increased stormwater runoff?
Is water quality monitoring and assessment information (305(b) Report) available?
Have existing best management practices or controls been identified and located?
Is there any information available about the effectiveness of current pollution prevention
activities?
Addressed in
Sufficient Detail?
Potential Control Measures to Control Cryptosporidium Contamination
Do the control measures proposed specifically address the reduction of Cryptosporidium
contamination?
Would the implementation of the proposed control measures take place in areas where
there would be an impact on Cryptosporidium loading into the water supply?
Do the proposed control measures seem economically and politically feasible?
If the proposed control measures are ongoing, has the utility explained how they would be
sustained?
Is the water utility in a position where it could implement the control measures itself, or
would other parties be responsible?
If other parties would be responsible for implementation, are those parties motivated and
reliable? What agreements between the utility and those parties exist that document
implementation responsibilities?
How does the utility track control measures implemented by other parties?
Has the water system responded adequately to concerns expressed about the source or
watershed area in past inspections and sanitary surveys?
Watershed Control Program Plan
Does the plan specifically address potential and existing Cryptosporidium sources in the
watershed?
Have the proposed actions in the plan been clearly defined and sufficiently addressed?
Does the plan explain how the actions described are expected to contribute to specified
goals?
Does the plan prioritize its proposed efforts? Does it define short-term and long-term
actions and prioritize them?
Does the plan include cost estimates for implementation of proposed actions?
Does the plan include, in detail, what other resources will be required to implement the
watershed control measures? Does it identify the source(s) of those resources?
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Assessment Criteria
Does the plan include an implementation schedule?
Does the plan assign responsibilities for implementing short-term and long-term actions?
How reliable are the organizations that will be carrying out the source protection
activities?
Has an individual been identified as the responsible party for the plan?
Will the entire watershed for the source be protected? Will the utility try to purchase all
land within the watershed? If not, will critical elements of the watershed be protected or
purchased by the utility?
If the water system cannot purchase portions of the watershed, does it propose to have
written agreements with the landowners concerning land use?
Where access is limited, will the watershed be inspected regularly for new potential and
actual sources of contamination?
Does the plan address all existing regulations for the watershed or area of influence?
Does or will the water system employ adequately qualified personnel to identify watershed
and water quality problems? Who is given responsibility to correct these problems?
Have the stakeholders in the watershed or area of influence been identified?
Were stakeholders involved with the plan's development?
Is it proposed that the water system will actively interact with other agencies that have
control or jurisdiction in the watershed? Are their policies or activities consistent with the
water system's goal of reducing source water Cryptosporidium levels?
How does the watershed protection plan propose to coordinate protection efforts? Will
there be a committee of stakeholders?
How will the utility track progress of the implementation of the watershed controls? Does
the plan describe how the utility intends to measure the success of projects?
Addressed in
Sufficient Detail?
2.5 Maintaining Approval of a Watershed Control Program
2.5.1 Annual Watershed Control Program Status Report
The annual watershed control program status report must describe the water system's
implementation of the approved plan and assess the adequacy of the plan for meeting the system's
stated goals. The annual report must explain how the system is addressing any shortcomings in plan
implementation, including those previously identified by the State or by the system during a watershed
survey. If the system needs to make substantial changes to its approved program, it must explain the
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nature of those changes and why they are being made. If the changes are likely to reduce the level of
source water protection, the water utility must explain what actions it will take to mitigate the effects (40
CFR 141.725(a)(4)(i)). If there have been any changes to components of the program, such as
partnerships or stakeholder groups that have been created or have dissolved, the annual report should
include this information, along with a description of how the change will affect the watershed control
program plan.
The annual status report must describe progress being made implementing individual control
measures (40 CFR 141.725(a)(4)(i)). Progress should be compared with the original timetable
provided in the watershed control program plan. Implementation delays should be explained, and
actions to prevent further delays should be proposed.
The original watershed control program plan should include specific measures by which the
utility can evaluate the effectiveness of the program. Annual status reports should provide updates on
those measures of program effectiveness as the watershed practices are implemented. The report
should address progress being made on high priority activities and, to the extent possible, evaluate
whether projects are achieving their objectives. The report should also identify emerging issues and
incorporate them into the watershed protection program. Since annual status reports must be available
to the public on request, reports must be written in plain language format (40 CFR 141.725(a)(4)(iv)).
2.5.2 State-Approved Watershed Sanitary Survey
The annual watershed sanitary survey must be conducted according to State guidelines and by
persons approved by the State to conduct watershed surveys. The survey must encompass the area of
influence. At a minimum, the watershed survey must assess the priority activities identified in the plan
and identify any significant new sources of Cryptosporidium (40 CFR 141.725(a)(4)(ii)). States
developing a watershed sanitary survey program may wish to use the watershed sanitary survey manual
developed by the California Department of Health Services, and the California/Nevada Section of
AWWA (the manual is available from the California/Nevada Section).
The watershed survey should be conducted by competent individuals such as engineers,
sanitarians, or technicians with experience in the operation of water systems and a sound understanding
of public health principles and waterborne diseases. Other means of assessing inspector qualifications
include whether the inspector has attended formal training sessions, whether he or she has documented
on-the-job training, whether the training received is appropriate for the type and size of system being
surveyed, and whether the inspector is knowledgeable about State and federal drinking water
regulations.
The annual watershed survey should address the following areas:
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• Review the effectiveness of the watershed control program to date
• Identify any new significant actual or potential sources of Cryptosporidium
Verify and re-evaluate the vulnerability analysis
Verify that the utility has control over watershed areas and activities specified as its
responsibility in the Watershed Protection Plan
• Confirm that public access is properly restricted from areas identified in the Watershed
Protection Plan
• Confirm that fencing and postings have not been vandalized or removed
• Identify any significant hydrological changes in the watershed that could affect
Cryptosporidium loading
Inspect the intake structure and identify any modifications to its location or design
A final survey report must be submitted to the State for approval (40 CFR 141.725(a)(4)(ii)).
The report should be completed as soon as possible after the survey is conducted. The length of the
report will depend on the findings of the survey and the size and complexity of the watershed. The
survey report should include: 1) the date of the survey; 2) who was present during the survey; 3) survey
findings; 4) recommended improvements to the identified problems; and 5) the dates for completion of
any improvements.
The annual watershed survey reports must be written in a plain language format. Survey results
must be made available to the public upon request. The State may withhold portions of the survey
report based on security considerations (40 CFR 141.725(a)(4)(iv)).
2.5.3 Request for Re-Approval
If the water system intends to continue to receive 0.5 log Cryptosporidium removal credit
beyond the approval period, it must submit a written request for review and re-approval of the
watershed control program. The request must be provided to the State at least six months before the
current approval period expires or by a date previously determined by the State. The request must
include a summary of activities and issues identified during the previous approval period and a revised
plan that addresses activities for the next approval period, including any new actual or potential sources
of Cryptosporidium contamination and details of any proposed or expected changes to the existing
State-approved program. The revised plan must address goals, prioritize specific actions to reduce
source water Cryptosporidium, explain how actions are expected to contribute to achieving goals,
identify partners and their roles, describe resource requirements and commitments, and include a
schedule for further plan implementation (40 CFR 141.725(a)(4)(iii)).
2.5.3.1 Describe Implementation of Plan
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The request for re-approval should build upon progress that has been made during the previous
watershed protection period. It must update program goals and priorities for Cryptosporidium control
measures and explain how proposed actions will contribute to specified goals. The request for re-
approval must include involved parties and their roles, resource requirements and commitments, and
schedules for implementation. New actual or potential sources of Cryptosporidium contamination
identified in previous annual watershed surveys must be addressed, (40 CFR 141.725(a)(4)(iii)). Each
new watershed control measure introduced should have a timetable for implementation, a budget, and
details about how the activity will be implemented. The request for re-approval should also include
updated measures by which the utility can evaluate the effectiveness of the program.
2.5.3.2 Describe How System Is Addressing Any Problems
As part of the request for re-approval, the water system should identify any unresolved
problems it encountered during the previous watershed protection period that interfered with achieving
the stated watershed protection goals. The system should address how it intends to resolve the
problems or change the watershed protection plan to work around the problems. If the changes
proposed are likely to reduce the level of source water protection, the utility should explain what
actions it will take to mitigate the effects.
2.5.3.3 Describe Need for Changes in Plan
Many watershed protection plans will require periodic revisions to ensure that their actions and
priorities remain up-to-date. As part of the request for program re-approval, the utility should describe
what changes need to be made to the watershed protection plan and explain why those changes should
be made. Any new control measure introduced should be accompanied by a budget, timetable for
implementation, and details about how the measure will be implemented. The utility should include an
explanation of how and why the watershed protection plan's priorities may change for the next
approval period. The utility should also define measures by which it will evaluate the effectiveness of
the revised program.
2.5.4 Guidance to States on Re-Approval
The State should consider several sources of information when reviewing requests for re-
approval. It should refer to a system's annual watershed control program status reports to evaluate
whether progress made so far is acceptable and that previous timetables have been accurate. The
State should review whether the identified responsible parties are participating reliably and in a timely
manner.
The State should review the annual watershed surveys to ensure that newly discovered actual
or potential sources of Cryptosporidium contamination have been addressed in the request for re-
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approval and feasible control measures have been proposed. The State should also refer to the most
recent sanitary survey conducted of the water system to see that source protection concerns regarding
pathogen contamination are being addressed. States can use the watershed control program plan
assessment criteria provided in Table 2.1 to guide their review of the proposed changes to the plan.
As part of the re-approval process, States should consider whether a utility's measures of
program effectiveness for the previous approval period were useful and accurate. If not, States should
ensure that the request for re-approval includes improved ways to measure program effectiveness.
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Management. Office of Water. EPA 816-R-98-016. April.
http://www.epa.gov/safewater/swp/swpcases.pdf Accessed December 10, 2002.
U.S. EPA 1999b. Funding Decentralized Wastewater Systems Using the Clean Water State Revolving
Fund. Office of Water (4204). EPA 832-F-99-001. 4 pages.
http://www.epa.gov/owm/cwfinance/cwsrf/septic3.pdf Website accessed March 2003.
U.S. EPA 1999c. Combined Sewer Overflow Management Fact Sheet: Sewer Separation. Office of
Water. EPA 832-F-99-041. September, http://www.epa.gov/npdes/pubs/sepa.pdf Website accessed
March 2003.
U.S. EPA. 2000a. Wastewater Technology Fact Sheet: Granular Activated Carbon Adsorption and
Regeneration. Office of Water. EPA 832-F-00-017. September.
http://www.epa. gov/owmitnet/mtb/carbon_absorption.pdf
U.S. EPA 2000b. Storm Water Phase H Final Rule: Small MS4 Storm Water Program Overview.
Fact Sheet 2.0. Office of Water. EPA 833-F-00-002. www.epa.gov/npdes/pubs/fact2-0.pdf Website
accessed March 2003.
U.S. EPA 2000c. Wastewater Technology Fact Sheet. Wetlands: Subsurface Flow. Office of Water
EPA 832-F-00-023. September. http://www.epa.gov/owm/mtb/wetlands-subsurface_flow.pdf
Website accessed March 2003.
U.S. EPA. 200 la. Case Study of Local Source Water Protection Program—Burlington, Vermont.
Web page updated May 11, 2001. http://www.epa.gov/safewater/protect/casesty/burlingtonx.html.
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U.S. EPA. 2001b. Case Study of Local Source Water Protection Program—Manchester, New
Hampshire. Web page updated November 26th, 2002.
http://www.epa.gov/safewater/protect/casesty/manchester.html. Accessed on December 12th, 2002.
U.S. EPA. 2001c. Case Study of Local Source Water Protection Program—Springfield, Missouri.
Web page updated November 26th, 2002.
http://www.epa.gov/safewater/protect/casesty/springfield.html.
U.S. EPA. 2001d. "Proposed Revisions to CAFO Regulations (January 12, 2001; 66 FR2960):
Frequently Asked Questions." http://www.epa.gov/npdes/pubs/cafo_faq.pdf. Downloaded February,
2002.
U.S. EPA. 2001e. "Secondary Treatment Standards."
http://cfpub.epa.gov/npdes/techbasedpermitting/sectreat.cfm?program_id=15. Last updated February
21, 2001. Downloaded January 22, 2002.
U.S. EPA 200If. Sanitary Sewer Overflows Frequently Asked Questions. Office of Wastewater
Management. Web page updated March 20, 2001.
http://cfpub.epa.gov/npdes/faqs.cfm?program_id=4. Website accessed January 2002.
U.S. EPA. 2002a. Preamble to Long Term 2 Enhanced Surface Water Treatment Rule. Draft.
November 6, 2002.
U.S. EPA. 2002b. Occurrence and Exposure Assessment for Long-Term 2 Enhanced Surface
Water Treatment Rule. Draft. Prepared by The Cadmus Group, Inc., Arlington, VA. March 2002.
U.S. EPA 2002c. Polluted Runoff (Nonpoint Source Pollution: Managing Nonpoint Source Pollution
from Forestry. Pointer No. 8. EPA 841-F-96-004H. Office of Wetlands, Oceans, and Watersheds.
www.epa.gov/owow/nps/facts/points.htm. Last modified August 28, 2002. Website accessed March
2003.
U.S. EPA. 2002d. "Public Education and Outreach on Storm Water Impacts: Water Conservation
Practices for Homeowners." http ://cfpub.epa.gov/npdes/stormwater/menuofbmps/edu_l 3.cfm. Last
updated November 25, 2002. Downloaded December 10, 2002.
U.S. EPA 2003. National Pollutant Discharge Elimination System Permit Regulation and Effluent
Limitation Guidelines and Standards for Concentrated Animal Feeding Operations (CAFOs). Federal
Register 68(29): 7176-7274. February 12.
Vendrall, P.F., K.A. Teague, and D.W. Wolf. 1997. Pathogen indicator organism die-off in soil.
ASA Annual Meeting, Anaheim, CA.
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Wade, S.E., H.O. Mohammed, and S.L. Schaaf. Prevalence of Giardia sp., Cryptosporidium
parvum and Cryptosporidium andersoni (syn. C. muris) in 109 dairy herds in five counties of
southeastern New York. Veterinary Parasitology 93(1): 1-11.
Walker M.J., C.D. Montemagno, and M.B. Jenkins. 1998. "Source water assessment and nonpoint
sources of acutely toxic contaminants: A review of research related to survival and transport of
Cryptosporidium parvum:' Wat. Resour. Res. 34(12): 3383-3392.
Watershed Committee of the Ozarks. 2001. 2001 Annual Report.
www.watershedcommittee.org/publications/annual_reports/2001/200l_annual_report.htm. Accessed
December 12, 2002.
Young, R.A. et al. 1980. Effectiveness of vegetated buffer strips in controlling pollution from feedlot
runoff. J. Environ. Oual. 9:483-487.
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3.0 Alternative Source/Intake
3.1 Introduction
Changing the water source or intake location can improve source water quality and reduced
treatment requirements for the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR).
The rule states that systems may be classified in a bin based on monitoring of an alternative source or
intake location or monitor using an alternative procedure for managing the timing of withdrawal; this
monitoring must be conducted concurrently with their existing intake or withdrawal practice. After
monitoring, a system would then choose which source, intake location, or intake procedure it will use
based on bin classification results. (40 CFR 141.725(b)(l))
Applicability
The LT2ESWTR specifies the sample locations for systems with presedimentation basins
and raw water off-stream storage (40 CFR 141.704). These locations are after the basins;
therefore, this option should not be considered by systems with those treatment processes.
Since the LT2ESWTR requires that alternative monitoring must be conducted concurrently
with source water monitoring (40 CFR 141.725(b)(l)), this toolbox option needs to be evaluated
prior to the start of source water monitoring.
This chapter discusses the concurrent monitoring options of changing sources, moving the plant
intake, and managing the timing or level of withdrawal and is organized as follows:
3.2 Changing Sources - discusses factors to be considered in changing sources, including
advantages and disadvantages and influence of source water characteristics on existing
treatment requirements.
3.3 Changing Intake Locations - discusses the applicability of changing the intake locations
and variables affecting Cryptosporidium concentrations in reservoirs, lakes, streams,
and rivers.
3.4 Changing Timing of Withdrawals - describes different approaches, and advantages and
disadvantages to changing the timing of withdrawals.
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3.2 Changing Sources
In order to be able to relocate an intake to a different source, a system would need to
identify an unallocated source within a reasonable distance of its treatment plant. The new source
would require sufficient unallocated flow to meet the system's needs, including those for peak flow and
future growth. The effect of the different water quality on the existing treatment process should also be
considered.
3.2.1 Advantages and Disadvantages
The main advantage of changing sources as an approach to dealing with higher
Cryptosporidium levels in a current source is avoiding the addition of a new treatment process. The
capital expense of a new well or new intake may be less than the expenses associated with installing
and operating a new treatment technology. In addition to having a lower Cryptosporidium
concentration, the new source may also have better water quality that could reduce treatment costs.
Systems should assess any potential new source to ensure its integrity, quantity, and quality. In
addition, switching to a new source often requires approval by the State.
A disadvantage associated with changing sources is that the different source water may respond
differently to the treatment train already existing at the plant. This may require changes in plant
operating procedures, such as changing the type and amount of coagulant added, the length of filtration
runs, and the dose of disinfectant added. Another disadvantage is that the source may be lower in
Cryptosporidium concentration but have higher concentrations of other contaminants. There may also
be legal and environmental issues associated with tapping a new source. Plant standard operating
procedures (SOPs) should be updated if a new source is added. Finally, the cost of installing a new
intake and transmission line should be considered; depending on the location of the source or intake in
relation to the plant or to existing transmission lines, a new source/intake could be more expensive than
other toolbox options.
3.2.2 Evaluation of Source Water Characteristics for Existing Treatment
Requirements
If a new source is to be introduced to an existing treatment plant, the treatability of the new
water by the existing process should be considered. For example, in a conventional treatment train
consisting of coagulation, sedimentation, and dual media filtration, each source water will have unique
coagulation properties depending on its characteristics. Organic content, alkalinity, and pH all affect the
coagulation process. Consequently, water quality parameters including pH, alkalinity, total organic
carbon (TOC), UV254, turbidity, and iron and manganese concentrations should be measured and
evaluated against the existing water and the treatment train. If coagulation is used as a part of the
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treatment process, jar tests should be conducted to determine the coagulation and settling properties of
the new water and to aid in calculating the required dose of coagulant. (See American Water Works
Association (AWWA) Manual M37, Operational Control of Coagulation and Filtration Processes
for more information on jar testing.) Pilot plant studies can also help determine the treatability of a
proposed new source.
3.3 Changing Intake Locations
Another method for reducing Cryptosporidium source concentrations is to move the intake
within the same source. This could involve relocating an intake within a source or changing the depth
from which the intake draws.
3.3.1 Applicability
Relocating an intake can be a good strategy if an obvious source of Cryptosporidium is
present which can easily be avoided by moving the location of the intake. One example of such a
situation is if an intake could be moved upstream of a municipal wastewater discharge in a river, where
it had previously been located downstream of the discharge.
3.3.1.1 Advantages and Disadvantages
One advantage of moving the location of an intake is its potentially low relative cost, if the
distance the intake must be moved is relatively short. This option could be particularly attractive if an
existing intake structure can be used to withdraw water from a different depth, resulting in decreased
Cryptosporidium concentrations.
Disadvantages could include significant amounts of excavation and piping, as well as additional
pumping if the intake must be relocated a considerable distance. Also, altering the intake may not bring
the desired reduction or provide any additional protection against future increases or spikes in
Cryptosporidium concentration.
3.3.2 Reservoirs and Lakes
Several variables can affect the concentration of Cryptosporidium at a particular location in a
reservoir or lake, including the intake depth, the way in which the lake mixes, the thermal properties of
the lake, and the proximity of the intake to streams and other discharges. It is recommended that a
water system develop an SOP for water withdrawal based on the specific conditions of the waterbody
being used as the source.
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3.3.2.1 Depth
The intake depth can significantly change the quality of the water being drawn and used. In
general, shallow intakes are more likely to draw water exposed to recreational activity and surface
water runoff. Deeper intake locations are often more protected from sources of Cryptosporidium,
unless an intake location is so deep that it draws water containing re-suspended material from the lake
or reservoir bottom. Water systems are often well-advised to draw water from intermediate depths,
where they can avoid higher oocyst concentrations that may exist near the lake or reservoir surface, and
also avoid particles that may be stirred up near the bottom.
3.3.2.2 Stratification and Mixing
Another factor that can affect the depth profile of Cryptosporidium in a lake or reservoir is the
amount of stratification or mixing present. Larger lakes and reservoirs often stratify, especially in the
summer months, forming a hypolimnion (a cold lower layer) and an epilimnion (a warm upper layer)
separated by a thermocline. There is very little mixing between these layers when a lake is strongly
stratified. Particles may settle through the layers, but there is little other mixing. The epilimnion is often
well mixed because of the mixing action of wind. Therefore, it is likely that Cryptosporidium may be
present at uniform concentrations throughout the epilimnion. Cryptosporidium oocysts that have
attached to particles and settled will have a concentration gradient in the hypolimnion. The shape of any
concentration gradient will depend on local conditions such as temperature, stream inflows, and particle
settling rates. Lakes or reservoirs that are strongly stratified and have a high input of organics can often
develop anoxia in the hypolimnion. Therefore, all water quality parameters should be considered
before determining the depth from which to draw the water. Extremely high withdrawal rates may
provide enough energy to overcome stratification and draw from the layer outside of where the intake is
located.
3.3.2.3 Proximity to Inflows
The proximity of the intake to stream inflows may affect the quality of the intake. Streams
carrying agricultural or urban runoff can cause water quality degradation if located too close to a source
water intake. States et al. (1998) reported an increase in Cryptosporidium concentrations with wet
weather events, particularly as the sampling location became closer to the contamination source.
Kortmann (2000) reported a system substantially reduced coliform bacteria in their source water by
moving their intake further away from a stream which drained an agricultural area and by installing an
artificial partition in the reservoir to limit the exchange of water between the stream input and the rest of
the lake.
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3.3.3 Streams and Rivers
There are several factors to consider when deciding where to locate an intake on a river
including depth, flow hydraulics, seasonal effects, and upstream sources of contamination.
3.3.3.1 Depth
Depth is not as likely to affect Cryptosporidium concentrations in small rivers and streams as it
is in lakes and reservoirs. Fast moving or shallow streams are likely to be fairly mixed across all
depths. In contrast, deeper and slower moving rivers may be less mixed and may show some
concentration gradient of Cryptosporidium with unattached oocysts being greater near the surface and
oocysts attached to particles being greater near the bottom. In rivers and streams, intakes located near
the bottom are more likely to draw sediment and other particles resuspended from the bottom.
3.3.3.2 Flow and River Hydraulics
Hydraulics of the river and the flow around the intake are extremely important in determining
the quality of water that enters the system. In general, portions of a stream or river with lower velocities
and less turbulence will contain less sediment and possibly less Cryptosporidium oocysts. Care should
also be taken to make sure that the design of the intake does not cause turbulence which might stir up
sediments.
3.3.3.3 Upstream Sources of Contamination
Any potential sources of contamination upstream of a new intake should be identified and their
impact considered with respect to both biological and chemical contamination. Contaminant sources of
particular concern for Cryptosporidium include animal feeding operations and sewage outfalls. If an
intake cannot be located upstream of such a source, then locating it as far as possible downstream to
allow time for particles to settle may be the next best alternative. Analyses of the vulnerability of a
stream source should be made on a regular basis. Any changes in the vulnerability of a source to
Cryptosporidium or other contaminants should be reported to the primacy agency.
3.3.3.4 Seasonal Effects
Cryptosporidium concentrations tend to be higher during runoff events, particularly in the
spring. Although it is probably not feasible to cease withdrawals during such incidents, it may be
possible to alter flow rates and coagulant doses to offset the effect of such events.
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3.4 Changing Timing of Withdrawals
The LT2ESWTR allows the option of changing the timing of withdrawals to obtain a lower
source water concentration of Cryptosporidium for bin assignment (40 CFR 141.725(b)(l)). For
implementation of this option, the system must then continue to draw source water in the same manner
as conducted for Cryptosporidium source water monitoring (40 CFR 141.725(b)(3)). The operating
conditions under which the samples were collected for the LT2ESWTR must be reported and
submitted to the State with the monitoring results (40 CFR 141.725(b)(2)).
3.4.1 Toolbox Selection Considerations
As stated above, the change in timing must be consistent during Cryptosporidium monitoring
and during routine operation after monitoring. Additionally, the LT2ESWTR does not allow source
water monitoring to deviate from a predetermined schedule by more than 2 days, unless extreme
conditions or situations arise that prevent sampling (40 CFR 141.703(b) and (c)). Given these
limitations, the following provides examples of recommended and not recommended approaches.
Recommended Approaches
• Changing the timing of withdrawal on a daily basis (e.g., from the afternoon to morning to
avoid suspended material stirred up by recreational water use).
• Use a water quality indicator to avoid short-term increases in Cryptosporidium due to
short-term weather or source water contamination events. For example, if a system
routinely experiences a spike in turbidity and subsequently, Cryptosporidium, for a 12-24
hour period following a storm event, then the system may choose to set up a monitoring
plan that delays withdrawal for a 24 hour period when detecting a spike in turbidity.
Approaches Not Recommended
• Limiting withdrawal in response to seasonal effects or weather effects lasting on the order of
days. This would be a difficult monitoring strategy to follow and stay in compliance with the
2 day sampling window.
3.4.1.1 Advantages and Disadvantages
The advantage of changing the timing of withdrawals is it requires no treatment changes, only a
change in operations. For systems with multiple sources it also allows the greatest flexibility in meeting
water quality goals.
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A disadvantage of relying on changing withdrawals to lower Cryptosporidium concentrations is
that it may result in decreased flexibility, since systems must follow the same withdrawal practices they
did during Cryptosporidium source water monitoring. If electing to practice a withdrawal approach
that defers withdrawal during likely Cryptosporidium events, then a system may need some raw water
storage capacity.
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References
Gregory, J. 1994. "Cryptosporidium in water: Treatment and monitoring methods." Filtr. Sep. 31(3):
283-289.
Kortmann, R.W. 2000. Reservoir management approaches exemplified." Proceedings of American
Water Works Association Water Quality Technology Conference.
Kortmann, R.W. 1989. Raw water quality control: an overview of reservoir management techniques.
Journal of the New England Water Works Association. December 1989. pp. 197-220.
Swabby-Cahill, K.D., G.W. Clark, and A.R. Cahill. "Buoyant qualities of Cryptosporidium parvum
oocysts." AWWA Water Quality Technology Conference. Boston: AWWA, 1996.
Walker M.J., C.D. Montemagno, and M.B. Jenkins. 1998. "Source water assessment and nonpoint
sources of acutely toxic contaminants: A review of research related to survival and transport of
Cryptosporidium parvum'' Wat. Resour. Res. 34(12): 3383-3392.
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4.0 Bank Filtration
4.1 Introduction
Bank filtration is a surface water pretreatment process that uses the bed and bank of a river (or
lake) and the adjacent aquifer as a natural filter. In optimal locations and under optimal conditions, bank
filtration is suitable for accomplishing sufficient Cryptosporidium removal to partially meet the
requirements of the Long Term 2 Enhanced Surface Water Treatment Rule. To accomplish this, a
pumping well located in the adjacent aquifer induces surface water infiltration through the bed and bank.
Bank filtration differs significantly from artificial recharge and from aquifer storage and recovery, both of
which rely on engineering works to move water into specially constructed and maintained recharge
basins or wells for infiltration into or replenishment of the aquifer. Although microorganism removal can
occur in such engineered systems, they are not bank filtration. This is because bank filtration relies
solely on the natural properties of the surface water bed and aquifer, unmodified by engineered works
or activity, except for the recovery of ground water via a pumping well.
A significant proportion of microorganisms and other contaminants are removed by contact
with the aquifer material as the water travels to the well through the subsurface. Flow to the well may
be horizontal or vertical, but more typically will take a variable path with both horizontal and vertical
components. The water which has been induced to infiltrate through the river's bed and bank is known
as "bank filtrate." It will be mixed with ambient ground water that has taken a different and typically
longer path to the well. The ambient ground water may have originated as bed or bank infiltration from
an upstream portion of the river or from a lake. It may have originated from infiltrating precipitation.
Regardless, ambient ground water is likely to contain different contaminants and contaminant
concentrations than bank filtrate because its origin and flow pathways differ significantly. Ambient
ground water should not be assumed to be uncontaminated.
Aquifers suitable for bank filtration are composed of unconsolidated, granular material (i.e.,
grains) and have open, interconnected pores that allow ground water to flow. Pathogen removal is
enhanced when fine-grained sediment is present along the flow path. Geologic units consisting primarily
of fine-grained (e.g., clay-sized) materials will have higher removal but will be incapable of yielding
economically significant water flow rates. In aquifers containing both sand-sized and finer grains, the
presence of fine grains increases the possibility that pathogens will encounter a grain surface. This is
because flow is slower and flow paths are longer than they would be in aquifers without such fine
grains. Microorganisms will be removed from flow as they contact and attach to grain surfaces.
Although microorganism (e.g., Cryptosporidium) detachment can occur, it usually does so at slow
rates (Harter et al, 2000). When little or no detachment occurs or when detachment is slow,
microorganisms can become non-viable while attached to grain surfaces. Thus, bank filtration provides
physical removal, and in some cases, inactivation, to remove pathogens from water supplies.
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The purposes of this chapter are: 1) to clarify the requirements of the LT2ESWTR related to
receiving Cryptosporidium removal credit for the use of bank filtration systems 2) to present the
current state-of-the-science, advantages and disadvantages of Cryptosporidum removal by bank
filtration; 3) to explain how local geologic and hydrologic conditions affect the functioning and
effectiveness of bank filtration systems; and 4) to provide suggestions for optimal operation of bank
filtration systems.
This chapter is organized as follows:
4.2 LT2ESWTR Compliance Requirements - describes requirements for receiving
Cryptosporidium removal credits related to the proposed installation of bank filtration
wells.
4.3 Toolbox Selection Considerations - describes the advantages and disadvantages of
using bank filtration as a pretreatment technology.
4.4 Site Selection and Aquifer Requirements - characterizes surface water and aquifer
types that are suitable for bank filtration.
4.5 Design and Construction - describes the types of wells eligible for bank filtration credits
and the locations at which such wells are best placed.
4.6 Operational Considerations - describes issues relevant to the optimal operation of
bank filtration systems in order to protect public health.
4.2 LT2ESWTR Compliance Requirements
Systems that propose to install bank filtration wells to meet any additional treatment
requirements imposed by the LT2ESWTR may be eligible for 0.5 or 1.0 log Cryptosporidium removal
credit (40 CFR 141.726(c)). Systems meeting all regulatory requirements (e.g. systems with
conventional or direct filtration that meet the well siting requirements) receive Cryptosporidium log
removal credit prior to construction of the production wells. For those systems which already use bank
filtration as a component of their treatment process and which also have existing conventional or direct
filtration treatment, the LT2ESWTR requires source water monitoring of produced water from the bank
filtration well. This will determine the initial bin classification for these systems. Because their source
water monitoring accounts for any bank filtration treatment, these systems are not eligible for
subsequent additional bank filtration credits (40 CFR 141.704).
Systems using ground water under the direct influence (GWUDI) of surface water or bank
filtered water without additional filtration must take source water samples in the surface water to
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determine bin classification (40 CFR 141.704). This applies to systems using an alternative filtration
demonstration to meet the Cryptosporidium removal requirements of the IESWTR or LT1ESWTR
(40 CFR 141.173(b) and 141.552(a)). As a result, the requirements and guidance provided in this
chapter do not apply to existing primacy agency actions providing alternative filtration
Cryptosporidium removal credit for IESWTR or LT IESWTR compliance.
4.2.1 Credits
The LT2ESWTR specifies the following design requirements for systems to receive log removal
credit for bank filtration (40 CFR 141, Subpart W, Appendix A):
• Wells must draw from granular aquifers that are comprised of clay, silt, sand, or pebbles
or larger particles. Minor cement may be present.
The aquifer material must be unconsolidated, with subsurface samples friable upon touch.
• Granular aquifers formed by alluvial or glacial processes are eligible for bank filtration
credit.
• Granular aquifers, either unconsolidated or partially consolidated, and mapped as
earlier than Quaternary alluvium, must be considered on a case-by-case basis by the
state to determine if they are too cemented, and therefore too fractured, to provide
sufficient natural filtration.
• Wells located in consolidated clastic aquifers (e.g., conglomerates), fractured bedrock
aquifers, and karst limestone aquifers are not eligible for bank filtration credit.
Only horizontal and vertical wells are eligible for bank filtration log removal credit.
Other ground water collection devices such as infiltration galleries and spring boxes are
ineligible.
Systems using horizontal or vertical wells located at least 25 feet from the surface water
source are eligible for a 0.5 log removal credit and those located at least 50 feet from the
surface water source are eligible for a 1.0 log removal credit.
• Systems with vertical wells must identify the distance to surface water using the
floodway boundary or 100 year flood elevation boundary as delineated on Federal
Emergency Management Agency (FEMA) Flood Insurance Rate maps. If the
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floodway boundary or 100 year flood elevation boundary is not already delineated,
systems must determine the floodway or 100 year flood elevation boundary using
methods substantially similar to those used in preparing FEMA Flood Insurance Rate
maps.
• Systems with horizontal wells must measure the distance from the normal flow stream
bed to the closest horizontal well lateral.
Systems must characterize the aquifer at the proposed production well site to determine
aquifer properties.
At a minimum, the aquifer characterization must include the collection of relatively
undisturbed continuous core samples from the surface to a depth at least equal to the
projected bottom of the well screen for the proposed production well.
The recovered core length must be at least 90 percent of the total depth to the
projected bottom of the well screen and each sampled interval must be a composite of
no more than 2 feet in length.
• Each composite sample must be examined to determine if at least 10 percent of the
grains in that interval are less than 1.0 mm in diameter. Each composite sample with at
least 10 percent of the grains less than 1.0 mm in diameter is considered an interval with
sufficient fine-grained material to provide adequate removal.
• An aquifer is eligible for removal credit if at least 90% of the composited intervals
contain sufficient fine-grained material as defined previously.
4.2.2 Monitoring Requirements
The LT2ESWTR requires systems to monitor turbidity in bank filtration wells to provide
assurance that the assigned log removal credit is appropriate. The LT2ESWTR specifically requires the
following monitoring (40 CFR 141.726(c)(l)):
• Turbidity measurements must be performed on representative water samples from each
wellhead every four hours that the bank filtration system is in operation or more frequently if
required by the state.
• Continuous turbidity monitoring at each wellhead may be used if the system validates the
continuous measurement for accuracy on a regular basis using a protocol approved by the
state.
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If the monthly average of daily maximum turbidity values at any well exceeds 1 NTU, the
system must report this finding to the state within 30 days. In addition, within 30 days of
the exceedance the system must conduct an assessment to determine the cause of the high
turbidity levels and submit that assessment to the state for a determination of whether any
previously allowed credit is still appropriate.
4.3 Toolbox Selection Considerations
Bank filtration is best suited to systems that are located adjacent to rivers with reasonably good
surface water quality and that plan to use bank filtration as one component of their treatment process.
For systems that can meet the aquifer requirements (section 4.4) and the design criteria (section 4.5),
bank filtration can be an efficient, cost-effective pretreatment option to improve water quality (Berger,
2002). Medema et al. (2000) and Wang et al (2000, 2002) documented high removal of
Cryptosporidium indicator organisms at production well sites in The Netherlands and in Louisville,
Kentucky. There was very little occurrence of Cryptosporidium in river water at the Kentucky site and
no Cryptosporidium was found in the well water at either site. The amount of Cryptosporidium
removal at either site is unknown.
The efficient removal of indicator organisms at the Netherlands site was likely due to the
relatively impermeable, fine-grained layer of river sediment present, as well as the effect of pyrite
oxidizing to ironhydroxides. Ironhydroxides may enhance the attachment of microorganisms to riverbed
sediments (Medema et a/, 2000). In Louisville, Kentucky, an alluvial aquifer was chosen for the bank
filtration site. Wang et al (2000, 2002) found that removal of particles increased with filtration distance
of the riverbank filtration process, although most of the removal occurred at the surface of the riverbed,
within the first two feet of filtration. Wang et al (2002) attributed the removal in their bank filtration
system to a combination of mechanical filtering and biological activity (e.g., biofiltering) at the surface of
the riverbed.
As discussed in section 4.4, only certain sites are suitable for bank filtration. It is important to
understand the type of bed and aquifer material present, the dynamics of groundwater flow, and the
potential for scouring of riverbed materials at a potential bank filtration site. The degree to which the
bed and banks of surface water bodies may effectively filter Cryptosporidium may vary not only only
from site to site, but also at a single site over time.
4.3.1 Advantages and Disadvantages
4.3.1.1 Removal of additional contaminants
The two research sites with published data (Medema et al., 2000; Wang et al., 2000; Wang et
al., 2002; Berger, 2002) have reported that bank filtration is effective at removing Cryptosporidium.
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Bank filtration has also been shown at some sites to be an effective technology for attenuating a variety
of additional microorganisms as well as particulates, ammonia, nitrate, pesticides (e.g., atrazine), heavy
metals, ethylenediamine tetra-acetic acid (EDTA), alkylated and chlorinated benzenes and other
organic contaminants, and disinfection by-product precursors (DBFs) in the form of natural organic
matter (NOM) (Schijven et al., 2003; Tufenkji et al, 2002; Ray et al, 2002; Kuehn and Mueller,
2000). Bank filtration achieves the removal of these diverse contaminants by facilitating or enhancing
physical and chemical filtering, sorption, reduction/oxidation, precipitation, ion exchange, and
biodegradation (Schijven et al., 2003; Ray et al., 2002; Tufenkji et al., 2002). Bank filtration further
reduces contaminant concentrations and especially shock contaminant loads from spills and intentional
acts by providing for the multidimensional dispersion and dilution of contaminants (Ray et al., 2002).
The degree to which any particular contaminant will be removed via bank filtration depends on
site-specific conditions. For example, under aerobic conditions, ammonia is often completely
transformed, whereas such removal may not occur under more reducing conditions. Oxygen is usually
significantly depleted within 5-15 feet of the riverbed, due to microbial activity in this zone. As
infiltrating water becomes increasingly depleted of organic matter due to degradation, microbial activity
diminishes, and the aquifer may be reaerated at a certain distance from the riverbed (Tufenkji et al.,
2002). The anaerobic part of the aquifer was observed to remove up to 99% of polar organic
contaminants at a site in central Germany (Juttner, 1995). Miettinen et al (1994) found that almost 90%
of the high molecular weight fraction of NOM had been removed at a bank filtration site in Finland.
The reduction in some treatment costs made possible by bank filtration results from a reduced
need for other treatment technologies. When bank filtration decreases the concentration of dissolved
organic carbon reaching a treatment plant, costs are lowered because a decreased proportion of
dissolved contaminants needs to be adsorbed onto activated carbon filters. Thus, each filter is capable
of operating for a longer period of time, and fewer replacement filters are needed. Particle and
microorganism removal during bank filtration allows for more efficient filtration, use of membranes, and
disinfection during subsequent treatment steps. The removal of ammonia means that the additional
treatment step of oxidizing ammonia with chlorine may be unnecessary. The removal of nitrate when
water is induced to flow through anaerobic areas may eliminate the need for expensive ion exchange or
reverse osmosis treatment processes (Kuehn and Mueller, 2000). Finally, because it is effective at
biodegrading many contaminants, bank filtration reduces the need for adding large quantities of
flocculants to drinking water, thereby reducing both costs and the unhealthful effects of water treatment
residuals (Kuehn and Mueller, 2000).
Another advantage of bank filtration as a pretreatment technology is that it acts to equalize
fluctuations in contaminant concentrations observed in surface waters. This is due to the effects of
dilution and dispersion which serve to spread peaks in contaminant concentrations over space and time
by the time they reach wells. Contaminant concentration peaks may be due to variations in river water
levels, seasonal effects, and runoff, in addition to spills, terrorist acts and emissions by municipal and
industrial institutions (Kuehn and Mueller, 2000). Bank filtration also smooths out fluctuations in water
temperature. Bank filtration is continuously active, and the decreased amplitude of the contaminant
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peak by the time it reaches a well (an inherent result of subsurface transport through porous material)
allows for easier and less expensive treatment by utilities with limited capabilities. In addition, the time
lag between contamination of surface water and arrival of contaminant at a well would give utilities more
of an opportunity to respond to a threat or an accidental spill. Kuehn and Mueller (2000) estimate that
in many modern bank filtration systems bank filtrate spends anywhere from 5 to 15 days in the
subsurface before reaching supply wells. At one site in the Netherlands, bank filtrate was estimated to
spend 45-65 days in the subsurface before reaching the supply well (Medema, et al., 2000).
Residence time depends on site-specific hydrogeology as well as bank filtration system design.
The removal of NOM during bank filtration is useful because NOM occurrence can result in
the production of harmful disinfection byproducts, as discussed above. In addition, moderate to high
concentrations of NOM in drinking water can result in unpleasant taste and odor. Finally, NOM
removal via bank filtration can also aid in the removal of a large variety of additional organic and
inorganic contaminants. These contaminants are sometimes made more mobile in surface and ground
waters due to a partitioning process whereby they are attached to NOM, which is relatively mobile,
and thereby carried along a flow path. The removal of NOM and associated contaminants prior to
above-ground treatment is likely to lessen the overall cost of water treatment at a given facility.
4.3.1.2 Clogging of pores
Clogging of the surface water - ground water interface has the potential to be a problem with
any riverbank filtration system, and results from physical, chemical, and biological processes. Partial
clogging during riverbank filtration system operation is likely to be unavoidable (Wang et al., 2001),
however its effects are not always deleterious. The disadvantage of clogging is that it can reduce
hydraulic conductivity of the local riverbed and the aquifer, thereby temporarily or permanently reducing
well yields. On the other hand, a limited accumulation of fine-grained sediments and the accompanying
development of a biologically active zone can enhance pathogen removal. Indeed, this enhanced
removal is a basic principle behind riverbank filtration as a water treatment technology. An optimal
amount of clogging is beneficial because it can reduce the size of large pores or reduce entrances to
pores in a stream bed or aquifer. Pore size reduction and decreased hydraulic conductivity also result in
longer travel times which can result in additional pathogen inactivation. Transport of fewer pathogens is
also likely because there are more opportunities for pathogen contact with aquifer grain surfaces.
Physical clogging of the surface water - ground water interface results from the deposition of
fine-grained, suspended sediment at the interface and in the near surface pores. The deposition and
growth of microorganisms also contribute to physical clogging. This clogging may be exacerbated
during periods of low surface water discharge, and is most apparent near the river's edge where flow
velocities are generally lower than at the center of the river. Chemical clogging can result from
precipitation of dissolved surface water constituents and may occur near the interface or anywhere
along the flowpath. This is due to the change in geochemical conditions as infiltrating water enters the
riverbed and aquifer. Factors to be considered when evaluating the potential for chemical clogging
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include electrolyte concentration, pH, redox potential, presence of dissolved or colloidal organic matter,
and the mineralogy and surface characteristics of stream bed and aquifer solids.
Finally, biological or microbial clogging can result from the accumulation of bacterial cells in
pore spaces, the production of extra-cellular polymers, the release of gaseous byproducts from
denitrifying bacteria and methanogens, and the microbially mediated accumulation of insoluble
precipitates (Vandevivere et al, 1995; Baveye et al, 1998). Biogenic gas bubbles have the effect of
blocking or partially blocking water flow through pores in much the same way that solid particles do
(Orlob and Radhakrishna 1958; Oberdorfer and Peterson 1985; Sanchez de Lozada et al., 1994).
Insoluble sulfide salts can cause clogging due to the activity of sulfate reducing bacteria, whereas iron
hydroxide and manganese oxide deposition can be brought on by bacterial iron metabolism
(Vandevivere et al., 1995; Baveye et al., 1998). Biological clogging is most likely to occur near the
surface water - ground water interface where nutrients are most available.
Some or all of these processes may act at a particular site to lower hydraulic conductivity and
thus decrease flow velocities. For example, several months of pumping from a new riverbank filtration
well in Louisville, Kentucky resulted in a significant decline in well production, presumably due to a
70% reduction in leakance from the river to the adjacent aquifer. The reduced well yields were
attributed to the physical clogging of riverbed sediments (Schafer, 2000). The disadvantage of reduced
well yields accompanies the advantages of increased microbial inactivation rates due to lower flow
velocities (and thus longer residence times in the aquifer) as well as increased removal of pathogens due
to smaller pores.
4.3.1.3 Scour
Both the positive and negative effects of clogging on riverbank filtration system performance
may be diminished following periodic flooding. Scour refers to the erosion of the river's bed and
banks, and depends on both flood conditions and the resistance of the bed and bank material that has
been deposited at a particular site. During flooding the river channel may be scoured, and fine
sediments at the surface water - ground water interface mobilized.
Much of the removal of the contaminants and microbes discussed above occurs during the first
few centimeters of the flow path, due to the significant filtering and sorptive capabilities of sediments in
the riverbed. These sediments are often organic-rich, highly biologically active, and fine-grained. The
effectiveness of bank filtration, however, may be temporarily threatened during high flows if this active
layer is washed away or scoured. EPA suggests the potential for stream channel scour be evaluated
during riverbank filtration site selection (section 4.4). Section 4.5 provides further discussion of scour
and its implications for riverbank filtration system operation.
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4.3.1.4 Additional Treatment Steps
In addition to clogging and scour, there are several disadvantages to bank filtration which
utilities may wish to consider and balance against the advantages and cost savings described in section
4.3.1. One disadvantage is that an additional aeration step may be required during water treatment due
to the possible depletion of oxygen as biological activity consumes oxygen during riverbank filtration
pretreatment (Kuehn, et al, 2000). This oxygen depletion may lead to extremely anaerobic conditions
over a portion of the flow path, which may sometimes result in the release of iron and manganese from
the bank sediment into the flowing water. This process occurs due to a redox reaction which reduces
iron and manganese to their water-soluble forms. This condition may necessitate the removal of these
metals during subsequent treatment steps (Kuehn, et al., 2000; Tufenkji et al., 2002).
On the other hand, if the flow path between the riverbank and the well is long enough, iron and
manganese may precipitate onto the sediments in the subsurface before ever reaching the well (Tufenkji
et al., 2002). The aquifer becomes reaerated with increasing distance from the riverbed. This is one
reason for locating riverbank filtration wells greater than 25 or 50 feet from the river, as discussed in
section 4.5.2.2. Even though most contaminant removal occurs during the first few centimeters of
subsurface transport, the reaeration and associated precipitation reactions in the aquifer may
significantly improve water quality before it reaches the well (Tufenkji et al., 2002). The location of the
aerated and anaerobic portions of the aquifer vary seasonally due to variable microbial activity and
changing pumping rates.
Finally, riverbank filtration is ineffective at removing a few persistent compounds, primarily non-
polar organic compounds and highly soluble chemical contaminants such as methyltertiarybutylether
(MTBE) and trichloroethylene (TCE), which would need to be addressed during subsequent treatment
steps. In addition, when bank filtration is used to induce infiltration of highly contaminated surface
water, it may be important to include additional adsorption steps during later treatment (Kuehn, et al.,
2000).
4.4 Site Selection and Aquifer Requirements
Unconsolidated, granular aquifers with sufficient amounts of fine-grained material (see section
4.4.2) are eligible for Cryptosporidium removal credits under the LT2ESWTR. Partially consolidated,
granular aquifers may also be eligible for removal credits. Each granular aquifer proposed as a bank
filtration site is to be evaluated on a case-by-case basis with regard to its grain size distribution and
degree of cementation. For example, a partially consolidated, granular aquifer may be too cemented,
and thus perhaps too fractured, to provide adequate pathogen removal. Geophysical methods,
discussed in section 4.5.2.2, may be helpful in determining the degree of fracturing of such aquifers.
This section characterizes river and aquifer types that may be suitable for bank filtration surface
water treatment. A list of selected sites in the United States and Europe which have used bank filtration
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is provided for reference. No information is available for these sites, however, regarding whether they
would meet the siting criteria in the LT2ESWTR. Some common aquifer types that are clearly not
appropriate for this technology are described as well. Finally, site-specific aquifer criteria which shall
be met in order for systems to receive Cryptosporidium removal credits are outlined in section 4.4.3.
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4.4.1 Selected Bank Filtration Sites
Table 4.1 Selected Bank Filtration Systems in Europe and the United States
Site Location
Europe
Torgau, Germany
Mockritz, Germany
United States
Cincinnati, OH
Columbus, OH
Louisville, KY
Terra Haute, IN
Jacksonville, IL
Galesburg, IL
Henry, IL
Mt. Carmel, IL
Quincy, IL
Sacramento, CA
Sonoma County, CA
Independence, MO
Lincoln, NB
Kennewick, WA
Kalama, WA
St. Helens, OR
Kansas City, KS
Sioux Falls, OK
Well Type*
V
V
V
H
H
H
H
H
V
V
H
H
H, V
Hf
H, V
H
H
H
H
H
Number of
Wells
42
74
10
4
1 +
1
1
1
1
1
1 +
1
5(H) + 7(V)
1
2 (H) + 44 (V)
1
1
3
1
1 +
Maximum Capacity
mgd (ms/s)
39.7(1.737)
28.8(1.260)
40.0(1.750)
40.0(1.750)
20.0(0.875)
12.0(0.525)
8.0(0.350)
10.0(0.438)
0.7(0.030)
1.0(0.044)
10.0(0.438)
10.0(0.438)
85.0(3.727)
15.0(0.656)
35.0 (H) (1.530)
3.0(0.130)
2.6(0.110)
5.0(0.219)
40.0(1.750)
40.0(1.750)
River System
Elbe
Elbe
Great Miami
Scioto/Big Walnut
Ohio
Wabash
Illinois
Mississippi
Illinois
Wabash
Mississippi
Sacramento
Russian
Missouri
Platte
Columbia
Kalama
Columbia
Missouri
Missouri
* H-horizontal, V-vertical
f Gravel-packed Laterals
Reprinted from Journal AWWA, Vol.94, No.
Waterworks Association.
4 (April 2002), by permission. Copyright © 2002, American
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4.4.2 Aquifer Type
4.4.2.1 Unconsolidated, Granular Aquifers
Unconsolidated, granular aquifers can be composed of a wide range of sediment sizes including
clay, silt, sand, and larger particles. They may also exhibit minor cementation, but subsurface samples
are typically friable (readily crumbled by hand). To be eligible for bank filtration credits under the
LT2ESWTR, Unconsolidated granular aquifers are expected to contain a sufficient amount of fine-
grained sediments to achieve adequate pathogen removal and/or inactivation (section 4.4.3 prescribes
the amount deemed sufficient). In aquifers with these characteristics, the flow path is tortuous at the
micro-scale (Figure 4.3), providing many opportunities for removal of microorganisms by straining or
by their attachment to grain surfaces.
Many alluvial aquifers contain significant amounts of well-sorted, fine-grained sediments.
Alluvial aquifers are produced by fluvial depositional processes and are adjacent to modern streams.
Aquifers formed in glacial deposits may also contain sufficient amounts of fine-grained material. These
may be "till" deposits, which have a wide range of poorly sorted sediment sizes, or glacial outwash
deposits that are formed by meltwater and often contain well-sorted, sand-sized sediments. Any of
these alluvial or till aquifers would be likely to be suitable for a bank filtration system. On the other
hand, coarse gravel aquifers produced by the rapid drainage of glacial lakes, or in outwash
environments that deposit little fine-grained material, may not be eligible for bank filtration credits unless
sieve analysis shows sufficient fine-grained material as discussed in section 4.4.3.2.
Alluvial aquifers may be identified on detailed hydrogeologic maps simply as "Quaternary
alluvium", indicating both their genesis and relative age. Glacial deposits are documented on surficial
geology maps and, where aquifer-forming, may be identified on large-scale hydrogeologic maps.
4.4.2.2 Karst, Consolidated Clastic, and Fractured Bedrock Aquifers
In karst, consolidated clastic, and fractured bedrock aquifers, ground water velocities are fast,
and flow paths may be direct, allowing microbial contaminants to travel rapidly to a well with little
removal or inactivation. Therefore, these aquifer types are not eligible for bank filtration treatment
credits.
Karst may be broadly defined as a region where the dissolution of calcitic or other soluble
bedrock, primarily limestone (calcium carbonate), produces a unique subsurface drainage network and
associated surface landforms. Ground water movement in karst aquifers differs from that in porous,
granular aquifers in that flow in the former occurs predominantly in conduits and dissolution-enlarged
fractures. Consequently, there is little physical removal of microbes and other particles by filtration and
few opportunities for microbes to come in contact with the surfaces of aquifer materials. Furthermore,
rapid flow creates conditions where inactivation is less likely to occur before ground water reaches a
well.
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Although fractures have a role in ground water movement through any aquifer, fractures provide
the dominant flow-path in fractured consolidated clastic and fractured bedrock aquifers. Most
consolidated aquifers can be presumed to be fractured. Similar to solution conduits in karst aquifers,
fractures in consolidated aquifers provide preferential flow paths that may transmit ground water at high
velocities, and in a relatively direct flow path to a well, with little time or opportunity for inactivation or
removal of microbial pathogens. Wells located in these aquifers would not be eligible for bank filtration
credit.
4.4.2.3 Partially Consolidated, Granular Aquifers
Granular aquifers formed by marine processes earlier than Quaternary alluvial or glacial
deposition may be partially consolidated by natural cement that fills pores, connects grains, and makes
the aquifer material less friable. Partially consolidated, granular aquifers are present within the Atlantic
Coastal Plain, Gulf Coast Lowland, Texas Coastal Upland, and Mississippi Embayment aquifer
systems (USGS 1998). When significant proportions of cement are present, fractures are more likely
to exist. As in consolidated aquifers, fractures in partially consolidated, granular aquifers create direct
paths for microbial contamination that minimize the natural filtration capabilities of the aquifer system.
EPA suggests that partially consolidated aquifers be evaluated at the proposed well location to
determine if they may be too cemented, and thus perhaps too fractured, to provide sufficient natural
filtration.
The degree of cementation can be evaluated by a variety of methods. Geologic material
collected from below the aquifer's weathered zone that is friable upon touch is likely to be adequate for
bank filtration purposes. Another test for the degree of cementation includes the slaking test, which
involves alternate wetting and drying of the sample in water, or in salt or alcohol solutions. Finally, a
triaxial compression test can be used to measure strain in three mutually perpendicular directions. Less
cemented samples will be more deformable during such tests.
4.4.3 Aquifer Characterization
Systems seeking Cryptosporidium removal credit are required to characterize the aquifer
properties between their surface water source and their well. The aquifer characterization will include,
at a minimum, core sampling to determine grain size distribution. This data will establish whether enough
fine-grained sediment is present to provide adequate filtration. The following procedure outlines the
steps necessary to perform such a characterization, which will ultimately determine eligibility for bank
filtration treatment credits under the LT2ESWTR.
1) Collect relatively undisturbed continuous core samples from the surface to a depth at least
equal to the projected bottom of the well screen for the proposed production well.
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2) Determine if recovered core consists of at least 90% of the interval from the surface to the
planned location of the well screen bottom. If core recovery is insufficient, another well
core must be obtained.
3) Examine each 2 foot long composite sample of recovered core in a laboratory using sieve
analysis to determine grain size distribution. Core intervals are typically 2 feet long for a
conventional split-spoon sampler and 3 or 4 feet long for soil probes (e.g., a Giddings-type
soil probe).
4) If more than 10 percent of the sediments in each 2 foot long composite sample are less
than 1.0 mm in diameter (very coarse sand), then the core interval from which it was taken
is noted as containing a sufficient quantity of fine-grained material to provide adequate
pathogen removal.
5) To receive Cryptosporidium removal credit, at least 90 percent of the analyzed
composited core intervals from the sampled aquifer will meet criterion number (4) above.
4.4.3.1 Coring
The collection of relatively undisturbed cores in unconsolidated aquifers can be quite difficult,
especially when gravel-sized clasts are present. The two most important criteria for successful test
drilling to obtain a core are sample accuracy and drilling speed. Borehole stability is a major problem in
drilling in an unconsolidated gravelly formation. Rotary core drilling is particularly suited to drilling in
unconsolidated formations because the drilling fluid, which cools the drill bit and carries up the core,
also acts to stabilize the borehole (Driscoll, 1986).
Other drilling methods require the installation of a casing to stabilize the borehole, a process
which slows down the speed of drilling. Rotary core drilling is the fastest method for drilling in an
unconsolidated formation. One disadvantage to rotary core drilling is the separation of different sized
core particles as they rise (smaller particles rise faster) and cross-contamination by overlying borehole
material. An experienced driller can avoid cross contamination by using the dual-wall method of rotary
core drilling. In the dual-wall method, the core is pushed up the inner pipe of the drill rather than
traveling in the space between the drill and the borehole wall (Driscoll, 1986). Shallow wells will have
fewer particle size separation problems than deeper wells.
Auger drilling is another method for drilling test wells. In this method an earth auger is screwed
into the earth by rotation. Auger drilling in an unconsolidated formation is slower than rotary core
drilling, due to the necessary installation of casing to support the borehole. Sampling with augers can
provide reliable samples from any depth. A split spoon sampler can be used wherein a split spoon is
driven to the bottom of the hole. The depth to which an auger can drill is dependent on the size of the
rig. The maximum drilling depth possible for a small drill rig is approximately 250 ft. (Driscoll, 1986).
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Information about drilling and finding a driller can be found through the National Groundwater
Association (NGWA) website: http://www.ngwa.org/. In addition, the EnviroDirectory™ provides
listings for laboratories and drillers in New England, the Mid-Atlantic, and the Great Lakes regions
(www. envirodirectory. com).
4.4.3.2 Sieve Analysis
The American Society for Testing and Materials (ASTM) has a published standard for
conducting sieve analysis, the Standard Test Method for Sieve Analysis of Fine and Coarse
Aggregates: Standard C 136-1 (ASTM, 2003).
Sieve analysis is used to determine the particle size distribution of a sample of dry aggregate of
known mass by passing the sample through a series of sieves with progressively smaller openings.
Sieve analysis requires the following equipment:
1. A balance, accurate to 0. Ig or 0.1% of test load for fine aggregate, or accurate to 0.5g or
0.1% of test load for a mixture of fine and coarse aggregate
2. Stackable sieves
3. A mechanical sieve shaker (for sample sizes greater than 20kg)
4. An oven capable of maintaining 110 ± 5°C (230 ± 9°F)
In the first step of sieve analysis the sample is dried using the oven. Once dry, its weight is
measured and recorded. While the sample dries, sieves are selected with suitable openings to furnish
the information required. For bank filtration related sieve analyses, it is only necessary to determine
what percentage of the sample is less than 1.0mm; however, it is recommended that sieves covering a
range of sizes be used so as to prevent the overloading of any one sieve. Once the sample is dry and
the sieves are stacked in order of decreasing mesh size, the sample is placed in the top sieve and sieving
either by machine or hand begins. Sieving should be continued until no more than 1% by mass of the
material retained on an individual sieve will pass through that sieve during 1 minute of continuous hand
sieving. Finally the mass on each sieve is weighed. The total mass of the material after sieving should
correspond closely with the original mass of the sample. Using the mass for each size increment and the
total mass of the sample, the size distribution of the sample can be determined (ASTM, 2003).
Further information about sieve analysis can be found at the ASTM web site (www.astm.org).
A multi-media sieve analysis demonstration can be found at Geotechnical, Rock and Water Resources
Library (GROW)
(http://www.grow.arizona.edu/geotechnical/virtual_labs/sieveanalysis/sieveanalysisexp.shtmiy
ASTM also provides a search engine which allows the user to search for laboratories that perform
sieve analyses (http://astm.365media.com/astm/labs/). The EnviroDirectory™ provides listings for
laboratories and drillers in New England, the Mid-Atlantic, and the Great Lakes regions
(www. envirodirectory. com).
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4.4.4 Site Selection as it Relates to Scour
Stream channel scour may often be an important consideration in choosing sites that are suitable
for riverbank filtration. This section discusses stream channel erosional processes in general, as well as
reasons sites with certain characteristics may be unsuitable for riverbank filtration. Section 4.6
discusses the implications of periodic scour for riverbank filtration system operations. Detailed
information on fluvial erosional processes can be obtained from any of a number of texts on fluvial
geomorphology, hydrology, and river hydraulics (e.g., Leopold et al., 1964; Ritter et al, 1995; Chow
1964).
4.4.4.1 Stream Channel Erosional Processes
This discussion focuses on the dominant erosional processes of alluvial rivers because, given the
LT2ESWTR's aquifer requirements, such rivers may be among the most suitable for bank filtration
credits. Although many lake banks are also suitable sites for bank filtration, lakes will not be discussed
in detail in this section. Lake bank filtration settings typically do not change rapidly with time and
climate. Their hydrologic properties are not highly variable and thus do not require the detailed
evaluation discussed here for riverbank filtration settings.
The width, depth, and gradient of an undisturbed alluvial river has typically adjusted to
prevailing discharge conditions and sediment loads such that no net erosion or deposition occurs over
long time periods (Mackin 1948; Leopold and Maddock 1953). The quasi-equilibrium condition of
such rivers, which are referred to as "graded streams" (Mackin 1948), may be disrupted over short time
periods (e.g., due to floods), when erosion or deposition may be considerable.
The dominant scouring process in alluvial rivers is lateral migration. This process is responsible
for the stream meanders visible on many floodplains, and is accomplished by the progressive erosion of
the outside bank of a river bend with concurrent deposition on the inside bank. Because erosion is
generally matched by deposition in this process, channel dimensions do not change significantly over
time, and the net result is migration of the channel across the floodplain (Figure 4.1). Stream channel
meanders are characteristic of many alluvial rivers and are indicative of a graded stream.
Downcutting, another type of scour that can occur in fluvial environments, is the vertical erosion
of the streambed. Downcutting is fairly uncommon in alluvial rivers except during floods or if the stream
is not graded. The long-term dynamic equilibrium of a graded stream can be disrupted by a variety of
changing hydrologic and geologic conditions and especially by anthropogenic activity. Human activities
in a watershed or river channel may alter the conditions to which an alluvial river has become adjusted,
initiating a period of readjustment marked by either progressive downcutting or aggradation
(deposition).
Urbanization generally increases the proportion of impervious surface in a watershed, increasing
flood volumes during precipitation events because less water is able to infiltrate the land surface and
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recharge ground water (Jacobsen et al., 2001). Increased flood volumes may cause higher water levels
in a river channel, increasing the shear stress on the channel bed and causing scour (Booth, 1990).
Downcutting may continue until the channel gradient, and/or channel dimensions, become adjusted to
the new flooding regime.
Impoundment is another activity that may disrupt the quasi-equilibrium state of a graded river
and initiate readjustment of the channel. The sharp decrease in sediment supply, which commonly
occurs subsequent to dam and reservoir construction, may initiate downcutting in the reach immediately
downstream until the channel adjusts to the lightened sediment load. This has been observed
downstream of many dams throughout the world. One of the most dramatic examples is the 7.5 meters
of channel-bed degradation that occurred twelve kilometers downstream of the Hoover Dam after its
completion in 1935 (Williams and Wolman, 1984).
The construction of artificial levees (raised banks along a stream channel) also may result in
flooding downstream. Levees allow greater quantities of water to be carried by the stream, thus
decreasing the probability of flooding in the vicinity of the levee, but increasing flood hazards
downstream (Montgomery, 2000). Even if flooding downstream does not result, the high flows
downstream may cause downcutting of the river, removal of fine-grained bed material, and thus a threat
to the protectiveness of a riverbank filtration system. Another possible effect of levees is an increase in
sedimentation in the channel. Sediment that would otherwise be deposited on the floodplain may be
trapped within the channel. This can raise the channel bottom and thus raise stream stage or the
elevation of the water surface in the channel (Montgomery, 2000). The consequences of this for a
riverbank filtration system are variable. Increased sedimentation may lead to clogging and/or decreased
well yields. On the other hand, higher stream stages may result in flooding and scour along certain
portions of the river as the channel adjusts to a new equilibrium condition. Understanding the impact of
current or planned upstream activities can be an important part of site selection for a riverbank filtration
system.
4.4.4.2 Unsuitable Sites
As discussed in section 4.4.2.2, some sites may be ineligible for bank filtration credit due to the
type of aquifer adjacent to the river. The following section, however, focuses on importance of
understanding the nature of the surface water- ground water interface at a potential bank filtration site.
In some localities, frequent scour, the absence of a sufficiently fine-grained interface, and/or the coarse-
grained or fractured aquifer materials may suggest that a certain river or reach is not the best possible
location for a bank filtration system. A system may choose to evaluate such situations on a site-by-site
basis, however, except as specified in the LT2ESWTR, EPA does not require such evaluations or any
particular decisions made on the basis of such evaluations. EPA recommends, however, that this
information be considered in order to ensure that bank filtration systems are protective of public health.
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Data from studies of aerobic and anaerobic spore (indicator organism) removal in bank
filtration systems indicate that much of the removal of spores between a surface water body and a bank
filtration pumping well takes place at the surface water-ground water interface and in the aquifer
material proximal to that interface. The interface, which lines the bottom of the riverbed, is typically
comprised of very fine-grained, biologically-active material a few inches to a foot in thickness. Some
rivers, however, (especially many in the western United States) lack this fine-grained bed and the
important organic-rich materials or silts usually associated with the surface water - ground water
interface (Ray et al., 2002). For this reason, such rivers should be evaluated carefully to determine if
bank filtration is a suitable treatment technology.
Other rivers may sometimes possess this important layer of fine-grained sediment for the first
few inches or feet from the surface water source, but may at other times be subject to periodic scour.
The nature and performance of the surface water-ground water interface on such rivers may be altered
temporarily by flood scour, specifically during the high river stages that occur periodically throughout
the year. This situation is most likely to occur on uncontrolled rivers. Higher flow velocities in the
river and increased bedload transport at such times mobilizes fine sediments (which were deposited
when discharges were lower). (Note that bedload transport is the carrying of heavy, coarse sediments
by saltation along the stream bed rather than by suspension. Saltation is the process in which particles
jump from one point to the next along the stream bed.) Lower log removals are thus expected to occur
during floods. If such situations are expected to occur very frequently, and if a system cannot envision
a way of managing the system so as to adequately protect its water supply during such events, sites on
such rivers may be inappropriate for riverbank filtration. On the other hand, through careful
management it may be feasible to protect drinking water wells from the potentially negative
consequences of occasional scour, as discussed in section 4.6.2.
EPA recommends that the potential for scouring be considered during site selection. If a site
that undergoes occasional scour is selected for riverbank filtration, the system may wish to locate its
wells at greater than the required separation distance from the surface water body, as discussed in
section 4.5.2.2. Such a solution helps to ensure the protection of public health. The drawback of this
solution to the problem of scour, however, is that wells located at very great distances from surface
water sources are drawing in more ambient ground water and less riverbank filtrate than wells located
closer to the river or lake. One result of this is that the yield to the wells is likely to be smaller when the
wells are located far from the surface water source.
The potential for scour can be evaluated initially by examining the past frequency of high flow
and flood events. Data on flood history and discharge is typically available from the US Geological
Survey, the Army Corps of Engineers, the US Bureau of Reclamation and the Department of
Homeland Security (formerly FEMA). State and county highway and transportation departments
typically evaluate river scour to determine the safety of bridge supports. A more comprehensive
evaluation of the potential for scour can be conducted when the effect of past and current human
activities (as discussed in section 4.4.4.1) is considered in comparison to the history of flood events.
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Sources of high flow and flood data
USGS
Main Page: http://water.usgs.gov
The National Flood Frequency (NFF) Program:
http://water.usgs.gov/pubs/wri/wri024168/pdf/entirereport.pdf
• A computer program developed by the USGS for estimating the magnitude and frequency of
floods for ungaged sites. Since 1993, updated equations have been developed by the USGS for
various areas of the nation. These new equations have been incorporated into an updated
version of the NFF Program.
USGS Fact Sheets (listed by state):
http://water.usgs.gov/wid/index-state.html
• Includes NFF program methods for estimating flood magnitude and frequency (in rural and
urban areas) for: AL, AZ, AR, CA, CN, HI, LA, MD, MO, NV, NM, NC, OK, SC, SD, TX
UT, VT, VA, and WA. These fact sheets describe the application of the updated NFF
Program to various waterways within the specific State. Includes maps of each of the above
state's hydrologic regions, as well as regression equations and statistics.
WaterWatch:
http://water.usgs.gov/cgi-bin/dailvMainW?state=us&maptvpe=flood&webtvpe=map
• Map of current flood and high flow conditions in the United States. The map shows the
location of streamgages where the water level is currently at or above flood stage (*) or at
high flow (•). The high flow conditions are expressed as percentiles that compare the current
(i.e., within the past several hours) flow value to historical daily mean flow values for all days
of the year. The real-time data used to produce the maps have not been evaluated or edited.
Army Corps of Engineers
Main Page: http://www.usace.army.mil/
• Flood control and management pages. For example, river and reservoir reports including flood
level data are available for the St. Louis district of Missouri (see example below)
(http://mvs-wc.mvs.usace.armv.mil/dresriv.htmiy
Mississippi River:
Gage
Station
6 am
Levels
24-hr
Change
National Weather Service River Forecasr
Next 3 Days
Hood
Level
Gage Zero
Record
Level
309.0
301.2
Hannibal
Dam 22 tw
16.9
15.9
-0.2
-0.3
16.6 16.1 15.6
15.8 15.3 14.7
16.0
16.0
449.3
446.1
31.80
29.58
US Bureau of Reclamation
Main Page: http://www.usbr.gov/main/
Dams and Reservoirs Page: http://www.usbr.gov/dataweb/html/dam selection.html
• The project DataWeb provides the most current information on the bureau's projects, facilities,
and programs including dam and reservoir information for western states. This data can be
obtained by selecting a dam or from the State and Region maps.
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The Department of Homeland Security (formerly FEMA)
Main Page: http://www.fema.gov/
Flood Hazard Mapping: http://www.fema.gov/fhm/
• The flood maps describe where the flood risks are, based on local hydrology, topology,
precipitation, flood protection measures such as levees, and other scientific data. Fee to obtain
maps.
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Figure 4.1 Generalized Depiction of Stream Channel Lateral Migration
Net at
(a)
A
t,
Location of river at time, 10
of at I,
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(a) Map of a Stream Meander; (b) Cross-section of the Channel from A-A' with Channel Positions at 3
Successive Times (t0, t,, and t2); (c) Map of Stream Meander Showing Location After Migration
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4.5 Design and Construction
This section describes the type of wells eligible for bank filtration credits under the
LT2ESWTR. Because specific well construction requirements (e.g., casing depths) vary by state and
with geologic conditions, this guidance will address these issues only briefly where appropriate.
Readers are referred to the agency within their state that makes regulations or recommendations
regarding well construction for details on issues such as casing depths, annular seals, drilling methods,
filter packs, etc. Other good general references on well construction include Driscoll (1986) and
USEPA (1975).
Figure 4.2 Taking a Water Level Reading
The pump house for the horizontal collector well caisson is in the background.
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4.5.1 Well Type
Only vertical and horizontal wells are eligible for bank filtration credits. Other types of
ground water collection devices may not provide adequate filtration of pathogens. For example, a
spring box is a ground water collection device located at the ground surface and is designed to contain
spring outflow and protect it from surface contamination until the water is used. Spring boxes are found
where local hydrogeologic conditions have focused ground water discharge into a smaller area (i.e., a
spring) and at a faster volumetric flow rate than elsewhere. Often, localized fracturing or dissolution-
enhanced channels are the cause of the focused discharge to the spring. As noted in section 4.4.2.2,
fractures and dissolution channels have significant potential to transport microbial contaminants. Thus,
spring boxes are not eligible for bank filtration credit.
Infiltration galleries (or filter cribs) are also not eligible for bank filtration credits. Infiltration
galleries are designed to collect water infiltrating from the surface, or to intercept ground water flowing
naturally toward surface water, using a slotted pipe installed horizontally in a trench and backfilled with
granular material (Symons et al., 2000). An infiltration gallery is not bank filtration because the material
overlying an infiltration gallery may be engineered to optimize oocyst removal. Bank filtration systems
are defined as relying solely on the natural properties of the system to remove microbial contaminants.
An infiltration gallery may, however, be eligible for Cryptosporidium removal credit as an alternative
treatment technology [40 CFR 141.73(d)].
Horizontal and vertical wells are both eligible for bank filtration credits. They are distinguished
from each other by the orientations of their well screens, and the important implications this has for their
well hydraulics (Figure 4.3 and 4.4). Collector horizontal wells are constructed by the excavation of a
central vertical caisson or pipe. One or more laterals (i.e., collector lateral well screens) extend
horizontally from the caisson bottom and may be very long. Laterals may extend radially in all
directions - resulting in a radial collector well- or primarily in the direction of the river (Driscoll, 1986;
Ray, 200 la). The lateral well screens are often installed near the bottom of the formation, allowing a
greater proportion of the saturated thickness of the aquifer to be used. A greater proportion of
pathogens and other contaminants are removed when the distance between the surface water body and
the laterals is increased (Ray, 2001a). Section 4.5.2.2 contains a discussion of when it may be
appropriate to locate wells at separation distances greater than those required by the LT2ESWTR.
Laterals may extend underneath a surface water body in the United States. This is generally not how
horizontal wells are placed in Europe (Ray 200la) because in Europe such wells are required to meet a
55-60 day average travel time requirement. An example of a pump house for a horizontal collector well
in Louisville, KY is shown in Figure 4.2. It is elevated to prevent flood waters from entering it.
The choice between using a vertical or horizontal well for a bank filtration system depends on
the site hydrogeology and the pumping requirements. For systems with large production requirements
(e.g., many Public Water Systems) or for pumping in shallow alluvial aquifers, horizontal wells may be
preferred because they are designed to capture large volumes of surface water recharge with little
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drawdown (Driscoll, 1986). Vertical wells with large production requirements are not well suited to
shallow alluvial aquifers because the necessary low drawdown cannot be sustained (Ray, 200la).
Finally, a comparison of construction expense with the costs of well maintenance may play a
role in the choice of well type. Horizontal collector wells are substantially more costly than vertical wells
(Driscoll, 1986). However, moderately large utilities may need many smaller capacity vertical wells to
match the capacity of a horizontal well. The maintenance of these vertical wells may require significant
effort and expense (Ray, 2001a). In such cases, horizontal collector wells may be preferred.
Figure 4.3 Schematic Showing Generalized Flow and Required Separation
Distance to a Vertical Well
h
Minimum 25 Feet
for Log Removal Credits^
Vertical
Pumping
Well
Mapped Floodway or 100-Year Floodplain
Bedrock
/
(Inset shows tortuous ground water flow at the micro-scale.)
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Figure 4.4 Schematic Showing Generalized Flow and Required Separation
Distance to a Horizontal Well With Three Laterals
Horizontal
Pumping
Well
Minimum 25
Feet for Log
Removal Credits
Bedrock
4.5.2 Filtrate Flow Path and Well Location
For systems to receive Cryptosporidium log removal credits, the ground water flow path
length between the edge of the surface water body and the well is expected to be sufficient for effective
oocyst removal. This section discusses EPA's requirements for appropriate flow path lengths, and
associated well locations, for the log removal credits available under the LT2ESWTR. The ground
water flow path length necessary to receive credits is specified for both vertical and horizontal wells. A
discussion of how to obtain information necessary to define the edge of the surface water body is also
included.
4.5.2.1 Required separation distance between a well and the surface water
source
Cryptosporidium oocyst removal may vary significantly throughout the year in many bank
filtration systems. At most typical bank filtration locations, high log removal rates (e.g. 3.5 log removal
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over 13m) may be expected with the surface water discharges that predominate during most of the
year. During short flood periods, however, there may be substantially lower removal (e.g. 0.5 to 1.0
log removal over 13m) due to scouring of the surface water-ground water interface, as discussed
below in section 4.6.2. In summary, a number of different factors may contribute to increased risk of
Cryptosporidium reaching wells. These factors include the presence of coarse-grained aquifer or
stream bed sediments, high river velocities, and frequent scouring of riverbeds. Given the need to
protect water supplies during periods of high surface water discharge with their potentially lower log
removal capabilities, the LT2ESWTR rule language (40 CFR 141.726(c)) provides 0.5 log removal
credit for systems with bank filtration wells located greater than 25 feet from a surface water source
and 1.0 log removal credit for wells located greater than 50 feet from a surface water source.
4.5.2.2 Locating wells at greater than required distances from the surface
water source
Given the dynamic nature of riverbanks and aquifer systems, including scouring processes, as
discussed in section 4.3.1.3, it may sometimes be advisable to place bank filtration wells at distances
greater than 25 or 50 feet from a surface water source. This extra precaution may also be advisable
when a system is uncertain as to whether the riverbed and bank contain sufficient fine-grained material
to provide adequate removal of Cryptosporidium oocysts. That is, EPA is requiring the separation
distances of 25 feet and 50 feet for the log removal credits discussed above, but greater separation
distances may result in additional public health protection at some sites. The disadvantage of using
greater separation distances between the surface water source and the bank filtration well is that water
yields to the well will be decreased. When a system makes a decision to place wells at a greater
distance from a surface water source than EPA requires, it will need to balance the sacrifice in well
yield with the added public health protection.
The remainder of section 4.5.2.2 discusses geophysical methods which may be of use in
constructing a conceptual model of subsurface flow conditions in riverbank filtration systems. By
obtaining hydrogeologic information through geophysical or other means (e.g., pre-existing
hydrogeologic or geologic maps), systems can determine the degree to which local conditions may
affect Cryptosporidium removal at the bank filtration site. For example, if mapping the bedrock-
alluvial interface and the water table at a particular site indicates that the aquifer is fairly thin, it is unlikely
that infiltrating river water will be diluted by much ambient ground water. In such a case it may be
advisable to locate wells at greater than the required distance from the surface water source. On the
other hand, if detailed hydrogeologic investigations indicate that the aquifer contains a large proportion
of fine-grained sediments, it would not be advisable to locate the well at greater than the required
distance from the surface water source, because the aquifer is already likely to be an efficient pathogen
filter, and it would be inadvisable to further sacrifice well yields.
When the aquifer contains fine-grained material, it is possible that well over-pumping may break
the hydraulic connection between ground water and surface water, yielding a variably saturated zone
underneath a perched stream, as shown below in Figure 4.5. Formation of such a variably saturated
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zone during periods of high pumping can greatly alter the existing ground water flow paths. New
ground water flow paths could result in marked changes in water quality. For example, surface water
infiltration could occur further upstream, resulting in a longer ground water flow path for infiltrating
surface water flowing towards the well. The increase in flow path-length could improve water quality.
Alternatively, the result of over-pumping could be decreased water quality. This may occur because
the decreased thickness of the saturated aquifer - due to the formation of a large variably saturated
zone - may cause faster ground water flow (assuming pumping rates remain constant). Faster ground
water flow provides less time for contaminant attenuation within the aquifer. Finally, the variably
saturated zone itself, to the extent that it transmits water, can improve water quality because
contaminant attenuation is usually increased under variably saturated conditions. If possible, the
potential for formation of a variably saturated zone can be investigated in order to provide additional
information regarding the desirability of locating wells at greater than required distances from the surface
water source.
Figure 4.5 The Streambed of a Perched Stream Is Well above the Water Table
Geophysical methods generally do not disturb subsurface materials. They are often less
expensive than labor-intensive digging of trial pits or drilling of boreholes. Furthermore, the useful
information gleaned by using geophysical methods can aid in choosing the best locations for wells
(Reynolds, 1997). Geophysical methods include gravity and magnetic methods, seismic methods,
electrical methods, and ground penetrating radar.
Hydrogeophysical methods can be used in pre-existing boreholes, thereby providing high
resolution data for a very localized area around the borehole. Alternatively, surface geophysical
methods can be used to obtain more generalized information over a large area, including information on
the depth to the water table, the depth to bedrock, and stratigraphy (Hubbard, 2003). The discussion
below provides only a generalized overview of currently available geophysical methods. More detailed
information can be obtained from texts by Hearst (2000), Reynolds (1997), Rubin and Hubbard
(2003), Keys (1990) and Burger (1992).
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Gravity surveying measures variations in the acceleration due to the Earth's gravitational field
which are caused by density variations in subsurface rocks. Subsurface cavities can be detected with
this technology, however sites with such cavities would not be suitable for bank filtration. Reynolds
(1997) states that gravity methods are fairly uncommon in hydrogeological work compared to electrical
methods. On the other hand, in the Arizona district of the United States Geological Survey, gravity
methods have been in use for over 15 years to evaluate changes in water storage in aquifers. These
methods can detect water table elevation changes of as little as a few inches (Callegary, 2003). Thus,
gravity methods may be useful at riverbank filtration sites for assessing the depth to water table, aquifer
thickness, and seasonal effects on the dilution of infiltrating river water with ambient groundwater.
Magnetic surveying or magnetic anomolies can also be used in hydrogeologic investigations. For
example, clay infilling bedrock cavities can be detected due to slight changes in the magnetic
susceptibility of clay and most bedrock (Reynolds, 1997).
Seismic methods are widely used in hydrogeologic investigations. Applied seismology involves
generating a signal through an explosion or other method at a specific time. The generated seismic
waves travel through the subsurface, are reflected and refracted back to the surface, and the return
signals are detected on monitoring instruments. The amount of time that elapses is the basis for
determining the nature of subsurface layers/materials (Reynolds, 1997). Reynolds (1997) provides a
detailed example of the use of seismic refraction surveying for locating the bedrock/alluvial interface at
one particular site.
Seismic methods can be used to:
• estimate depth to bedrock (ideal for riverbank filtration applications)
determine the nature of bedrock (e.g., cavernous) or location of cavities. Note that karst
buried by alluvium may contain unexpected ground water flowpaths.
• determine the location of faults that may juxtapose bedrock against alluvial material
• determine stratigraphy (useful where sands and clays may be interlayered)
determine porosity
determine ground water particle velocities (an important parameter for riverbank filtration
systems)
Electrical resistivity methods are used extensively in downhole logging to identify hydrogeologic
units that will produce high flow rates. Electrokinetic surveying makes use of electrodes implanted at
the ground surface to identify the location of the water table. This may be useful at riverbank filtration
sites, where water table layer and depth to bedrock can be used to determine aquifer thickness - an
important parameter in determining how much dilution of bank filtrate with ambient groundwater is
occurring. A more recent development is the use of electrokinetic methods to measure flowrates in
boreholes (Reynolds, 1997).
The spontaneous polarisation or self-potential (SP) method is conducted by measuring
differences in ground electrical potential at different locations, but is still fairly uncommon. Another
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electrical method, the induced polarisation (IP) method can be used to detect ground water and water
tables, however electromagnetic induction methods are generally considered more practical for these
purposes in the field. Contaminated ground water within subsurface clays can also sometimes be
detected with the IP method (Reynolds, 1997).
Electromagnetic (EM) methods have been used in groundwater investigations to delineate
contaminant plumes, and thus can be useful in conceptualizing flow systems in a riverbank filtration
context when the quality of infiltrating river water is especially poor. Pulse-transient EM (TEM) surveys
(a type of EM method) may be useful in conceptualizing flow for riverbank filtration systems where
infiltrating water quality is poor. It may also be useful in monitoring the quality of infiltrating water.
When data is available from both borehole and surface instruments, EM and electrical methods
can be used to map subsurface geology such as the locations of coarse-grained and fine-grained units.
Ground penetrating radar (GPR) has been used as a surface method for contaminant plume
mapping and monitoring pollutants in groundwater. To operate such a system, a signal generator,
transmitting and receiving antennae, and a receiver must be used. Radiowaves are generated, which
travel in a broad beam at high speeds. Energy is lost or attenuated depending on the subsurface
materials through which the waves travel. GPR has proven valuable in mapping sediment sequences,
and can be used to investigate sediments through freshwater up to 27 m deep (Reynolds, 1997). Thus,
it may be of use in gaining information about the composition of riverbeds, and for monitoring the effects
of scour on riverbed composition. GPR can also be used to locate water tables, delineate sedimentary
structures which may contain pockets of coarse-grained alluvium, and determine the spatial extent and
continuity of buried clay and peat layers within subsurface deposits. Borehole radar can also be used
for hydrogeologic investigations.
Before choosing a specific geophysical method it may be important to consider the following:
desired level of resolution, area of coverage, site-specific conditions and their influence on the
applicability of the method, possible non-uniqueness of the geophysical attribute, resources needed to
interpret the geophysical data, and possible integration with direct measurements. In general, mapping
the water table and finding the depth to bedrock are considered standard hydrogeophysical
procedures. Other applications such as estimating permeabilities or porosities are at an earlier stage of
development and may not yet be appropriate for routine use at riverbank filtration sites (Hubbard,
2003).
4.5.2.3 Delineating the edge of the surface water source
The flow paths due to induced infiltration to a vertical well have both vertical and horizontal
components, and are tortuous at the micro-scale (Figure 4.3). Such flow will typically have a significant
horizontal component, especially if the vertical well is screened in a shallow, unconsolidated, alluvial
aquifer that is eligible for bank filtration credits. Therefore, for the purpose of receiving log removal
credits, the flow path length to a vertical well is to be determined using the measured horizontal distance
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from the edge of the surface water body to the well intake. The edge of the surface water body is
defined as the edge of either the 100-year floodplain or the floodway, discussed below. The 100-year
floodplain is defined by its boundary - the flood elevation that has a one percent chance of being
equaled or exceeded each year.
As a first step, utilities may use the online maps available at the following website to get a
general idea of the mapped extent of the 100-year floodplain in their area:
http://www.esri.com/hazards/makemap.html. In order to satisfy the requirements of the LT2ESWTR for
the location of the wells of a bank filtration system, however, an official Federal Emergency
Management Agency (FEMA) (now part of the Department of Homeland Security) flood hazard map
must be used. Such maps can be ordered in either paper or digital formats from FEMA. The following
website can be used to order these maps: http://msc.fema.gov/MSC/.
Although in some areas of the United States the mapped extent of the 100-year floodplain may
be more easily accessible than the mapped extent of the floodway, some utilities may choose to use the
edge of the floodway as a starting point for measuring separations distances to wells because it typically
allows wells to be placed slightly closer to the river and is thus a somewhat less restrictive requirement.
The floodway is a regulatory concept, and is defined as that portion of the overbanks that must be kept
free from encroachment to discharge the one percent annual chance flood (i.e. the 100-year flood)
without increasing flood levels by more than 1.0 foot. It is determined by specified methods according
to FEMA guidelines, as described below.
For many areas, the mapped extent of the floodway will also be drawn on the flood hazard map
obtained by FEMA. The utility may choose to use the edge of the floodway rather than the edge of the
100-year floodplain for the purpose of determining the required separation distance between a river
and a riverbank filtration well. If the mapped extent of the floodway is unavailable, the utility may opt to
perform the mapping using one of a number of hydraulic models approved by FEMA. A list of these
approved models is available at http://www.fema.gov/mit/tsd/en_hydra.htm. EPA recommends using
the US Army Corps of Engineers' HEC-RAS model for mapping floodway limits. The HEC-RAS
software, User's Manual, Applications Guide, and Hydraulic Reference Manual are available for free
downloading from http://www.hec.usace.army.mil/software/soflware_distrib/index.html.
When a utility elects to determine the edge of the floodway, and to model the floodway
boundaries if they are not available from FEMA, the preferred encroachment method within HEC-RAS
is Method 4. Method 4 can be summarized as follows, according to FEMA's Map Assistance Center
(2003):
The Method 4 encroachment operates by analyzing the hydraulic conveyance for the unencroached
one percent annual chance floodplain at each cross section, then equally reducing the conveyance
from both overbank areas by moving toward the stream channel from the edge of the floodplain
until the resulting water-surface elevation is one foot higher than the unencroached elevation, and
the resulting encroached conveyance is approximately equal to the unencroached conveyance. The
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new left and right cross-section limits are assumed to be vertical walls. Finally, a backwater energy
balance is calculated using the new cross sections, which results in the encroached or floodway
water-surface profile. The floodway modeling process requires adjustments and rerunning of the
model because the final calculationis the backwater energy balance between new cross sections.
Many times the 1.0-foot target cannot be achieved exactly at each cross section because of energy
balance considerations. Floodplain geometry, constrictions at culvert and bridge crossings, and
constrictions from other man-made obstructions in the floodplain may require adjustments to the
encroachment widths to stay at or below the 1.0-foot maximum water-surface increase. Chapter
10 of the HEC-RAS User's Manual includes a discussion of performing a floodway encroachment
analysis.
In most areas, however, EPA expects that utilities will find it preferable and simpler to use the
previously mapped limits of the 100-year floodplain to determine the edge of the river for riverbank
filtration separation distances.
4.5.2.4 Measuring separation distances for horizontal wells and wells that
are neither horizontal nor vertical
As noted in section 4.5.1, horizontal wells may have laterals that extend underneath a surface
water body. The flow direction for induced infiltration to a horizontal well that extends under a surface
water body is predominately downward. Therefore, the flow path length to a horizontal well is the
measured vertical distance from the bed of the river under normal flow conditions to the closest
horizontal well lateral's intake (Figure 4.4).
Some wells may be constructed so that the well is neither truly horizontal nor truly vertical. In
these cases, there is greater uncertainty about the definition of separation distance from surface water.
For simplicity, if the well if closer to being a vertical well than to being a horizontal well (i.e. the well is
oriented at greater than a 45 degree angle to a horizontal line), the separation distance is defined for the
purposes of this toolbox option to be the horizontal distance from the edge of the river to the closest (in
terms of horizontal distance) intake on the well. Similarly, if the well is closer to being a horizontal well
as opposed to a vertical well, separation distance is defined as the shortest possible vertical distance
from the riverbed to an intake on the well. To ensure that the assigned log removal credit is realized,
systems are expected to perform continuous turbidity monitoring for all wells that receive a credit.
Continuous turbidity monitoring is discussed in section 4.2.2.
4.6 Operational Considerations
4.6.1 High River Stage
When the river stage (i.e. the elevation of the water surface) is high, the increased head gradient
between the river and the adjacent aquifer results in increased infiltration and increased ground water
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flow rates. This condition can be expected to occur periodically throughout the year at many sites, and
will generally be associated with reduced log removals (Gollnitz, 1999; Ray, 200 Ib). High river stage
is often associated with scouring of riverbed sediments. Nevertheless, even when scour does not
occur, the high ground water velocities associated with high river stage can be a significant threat to a
riverbank filtration system.
One solution to this problem is that pumping rates can be temporarily decreased during periods
of high river flow (Medema et al, 2000). Decreased pumping rates will in turn decrease the head
gradient between the river and the well, thereby decreasing subsurface velocities, increasing residence
times, and facilitating pathogen inactivation.
4.6.2 Implications of Scour for Bank Filtration System Operations
Periodic, short-term flood scour can have both negative and positive impacts on the
performance of a bank filtration system. As noted in section 4.5.2 above, lower log removals of
oocysts are expected during floods because higher river shear velocities and associated increases in
bedload transport mobilize fine sediments deposited when discharges were lower.
Removal of fine sediments opens large pore spaces, increasing the hydraulic conductivity across
the surface water-ground water interface (Gollnitz, 1999; Ray, 200la; Ray, 200Ib). Unfortunately,
this potentially increases the number of pathogens transported. Furthermore, the microbial activity and
unique geochemical environment of the riverbed, which serves to facilitate the removal of pathogens via
sorption and other processes, may not be present for short periods following flood scour. Recent work
in Germany (Baveye et al., 2003) suggests that the biologically active zone is re-established very
quickly after scour, perhaps within 3 days, at least when measured in terms of the ability to degrade
certain organic compounds. Limited scour can reduce clogging at the surface water-ground water
interface and improve well yields (Wang et al., 2001). The continuous turbidity monitoring required by
the LT2ESWTR for bank filtration credits can be used to help systems manage the threat posed by
periodic, short-term flood scour.
When high river stages or high turbidity levels indicate that flood scour may be occurring and
compromising the effectiveness of a bank filtration system, pumping rates can be decreased. This will
lead to lower velocities and longer subsurface residence times, thereby increasing the protectiveness of
the system (Medema et al., 2000; Juhasz-Holterman, 2000).
4.6.3 Anticipating high flow events / flooding
Many factors are involved in increasing the probability that a flood will occur. Intense rainfall is
the most apparent factor, however the geomorphology of a watershed is important in determining how
quickly water will enter a stream system after a rainfall event, as well as how quickly water will enter a
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major river from smaller tributaries. Systems can anticipate that a high flow event will occur if a rapid
spring thaw follows a winter of unusually heavy snowfall. It is also important to be aware of recent
changes in vegetation due to wildfires or urbanization. When vegetation is removed or decreased there
are fewer barriers to rapid surface runoff, plant roots no longer keep soil loose and permeable (thus
more compact soils will be less able to decrease surface runoff), and plants themselves will be
unavailable to take in a certain proportion of precipitation (Montgomery, 2000). Therefore, systems
may wish to monitor for pathogens more frequently or change pumping regimes in riverbank filtration
systems when high flows are anticipated.
4.6.4 Possible responses to spill events and poor surface water quality
One response to a serious water quality threat is to stop pumping from all bank filtration
production wells. Other pumping regime changes can also be implemented to reduce risks, including
decreasing the number of hours the system is in operation each day. For systems that have a number of
wells in operation, it may be advisable to increase pumping rates for wells further from the surface
water source and decrease pumping rates for wells that are closer (Juhasz-Holterman, 2000). Juhasz-
Holterman (2000) recommended that this kind of change be implemented seasonally at a site in the
Netherlands. Her study of the site's hydrology indicated that during the winter months pumping wells
were more vulnerable to contamination due to "short-circuited" flow paths from the polluted river
through the subsurface. Her solution involved both restricting extraction rates to a few hours a day
(which was acceptable due to decreased demand during the winter months) as well as an altered
pumping regime which relied more on wells located further from the river.
4.6.5 Maintaining required separation distances
Alluvial rivers that are experiencing active, progressive erosion as an adjustment to new
flooding regimes or sediment loads, or in relation to natural lateral migration, may pose serious, longer-
term challenges to bank filtration systems. For example, significant log removal reductions may be
more frequent in an urbanizing basin as a consequence of more frequent flooding and associated
scouring. In extreme cases, long term degradation of the bed or banks may reduce the threshold
separation distances between the surface water source and bank filtration well. Recall that these
separation distances - 25 feet for 0.5 log removal credit and 50 feet for 1.0 log removal credit - are
required to receive log removal credits under the LT2ESWTR.
Systems may wish to assess their sites for active, progressive erosion. Lateral migration rates
can be calculated using sequential aerial photography and/or topographic maps, if available. Systems
without such data may need to obtain the needed information by conducting sequential field surveys of
the floodplain area proposed for the site. This will require a far more lengthy investigation period.
Progressive downcutting could also be measured with sequential field surveys of the channel bed
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elevation over a period of years. Regardless of the method used, the threshold separation distances
between the surface water source and the bank filtration well must be maintained.
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References
ASTM (American Society for Testing and Materials), 2003. Standard Test Method for Sieve Analysis
of Fine and Coarse Aggregates - Standard C 136-1.
Baveye, P., P. Vandevivere, B. L. Hoyle, P.C. DeLeo, and D. Sanchez de Lozada. 1998.
Environmental impact and mechanisms of the biological clogging of saturated soils and aquifer materials.
Critical Reviews in Environmental Science and Technology. 28(2): 123-191.
Baveye, P., Berger, P., Schijven, J., and Grischek, T. 2003. Research needs to improve knowledge of
bank filtration removal of pathogens, in Riverbank Filtration: Improving Source Water Quality,
edited by Ray, C., Melin, G. and Linsky, R., Kluwer, Dordrecht,
Berger, P. 2002. Removal of Cryptosporidium Using Bank Filtration in Riverbank Filtration:
Understanding Contaminant Biogeochemistry and Pathogen Removal, C. Ray (ed.). The
Netherlands: Kluwer Academic Publishers, p. 85-121.
Burger, H.R., D.C. Burger, and R.H. Burger, 1992. Exploration Geophysics of the Shallow
Subsurface. Upper Saddle River, NJ: Prentice Hall.
Booth, D.B. 1990. Stream-channel incision following drainage basin urbanization. Water Resources
Bulletin 26(3): 407^17.
Callegary, James, United States Geological Survey, personal communication, 3/03.
Chow, V.T. 1964. Handbook of Applied Hydrology. New York: McGraw Hill.
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Dunne, T., and Leopold, L.B. 1978. Water in Environmental Planning. New York: W.H. Freeman and
Company. 818 pp.
FEMAMap Assistance Center. 2003. Personal communication.
Juttner, F. 1995. Elimination of terpenoid odorous compounds by slow sand and river bank filtration of
the Ruhr River, Germany. Water Science & Technology. 31: 211-217.
Goldenberg, L.C., I. Hutcheon, N. Wardlaw, and A.J. Melloul. 1993. Rearrangement of fine particles
in porous media causing reduction of permeability and formation of preferred pathways of flow:
experimental findings and a conceptual model. Transport in Porous Media 13: 221-237.
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Gollnitz, W.D. 1999. Induced infiltration rate variability and water quality sampling issues.
Proceedings of the International Riverbank Filtration Conference. November 4-6, 1999. Louisville,
Kentucky.
Harter, T., S. Wagner, and E. R. Atwill, 2000. Colloid Transport and Filtration of Cryptosporidium
parvum in Sandy Soils and Aquifer Sediments, Environmental Science and Technology, 34(1), pp.
62-70.
Hearst, J.R., P.H. Nelson, and F.L. Paillet, 2000. Well Logging for Physical Properties: A
Handbook for Geophysicists, Geologists, and Engineers, 2nd Edition. New York: Wiley.
Hubbard, Susan M., Lawrence Berkeley National Laboratory, personal communication, 3/03.
Hubbs, S., J.Z. Wang, and R. Song. 2001. Use of Riverbank Filtration to Meet the Requirements of
SWTR and DBF Rules. Presentation at the American Water Works Association Water Quality
Technology Conference, November 11-15, Nashville, TN.
Jacobson, R.B., S.R. Femmer, and R.A. McKenney. 2001. Land-use Changes and the Physical
Habitat of Streams : a review with emphasis on studies within the U.S. Geological Survey Federal-State
cooperative program. U.S. Geological Survey Circular 1175. Reston, VA.: U.S. Geological Survey.
63pp.
Juhasz-Hoterman, M.H. A. 2000. Reliable drinking water by bank filtration along the river Maas
(Meuse), by knowledge of the system combined with simple resources, in Proceedings of
International Riverbank Filtration Conference, Nov. 2-4, Duesseldorf., W. Julich and J. Schubert
(eds.), International Arbeitgemeinschaft der Wasserwerke im Rheineinzugsgebiet, Amsterdam.
Jiittner, F. 1999. Efficacy of bank filtration for the removal of fragrance compounds and aromatic
hydrocarbons. Water Science Technology 40(6): 123-128.
Keys, W.S., 1990, Borehole geophysics applied to groundwater investigations: U.S. Geological
Survey, Techniques of Water-Resources Investigations of the U.S. Geological Survey, Book 2,
Collection of Environmental Data, Chapter E2, 150 p.
Kuehn, W. and U. Mueller. 2000. Riverbank filtration: an overview. AWWA Journal. 92(12): 60-69.
Leopold, L.B. and Maddock, T. 1953. The Hydraulic Geometry of Stream Channels and Some
Physiographic Implications. U.S. Geological Survey Professional Paper 252. Washington: U.S.
Government Printing Office.
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Leopold, L.B., M.G. Wolman, and J.P. Miller. 1964. Fluvial Processes in Geomorphology. San
Francisco: W H Freeman and Co.
Mackin, J.H. 1948. Concept of the graded river. Geological Society of America Bulletin 59:
463-512.
Medema, G.J., M.H.A. Juhasz-Hoterman, and J.A. Luitjen. 2000. Removal of micro-organisms by
bank filtration in a gravel-sand soil, in Proceedings of International Riverbank Filtration
Conference, Nov. 2-4, Duesseldorf, W. Julich and J. Schubert (eds.), International
Arbeitgemeinschaft der Wasserwerke im Rheineinzugsgebiet, Amsterdam.
Miettinen, IT., PJ. Martikainen, T. Vartiainen. 1994. Humus transformation at the bank filtration
water plant. Water Science & Technology, 30 (10): 179.
Montgomery, Carla W., 2000. Environmental Geology, updated 5th edition. Boston: McGrawFfill.
Oberdorfer, J.A. and F.L. Peterson. 1985. Waste-water injection: geochemical and biogeochemical
clogging processes. Ground Water 23: 753-761.
Orlob, G.T. and G.N, Radhakrishna. 1958. The effects of entrapped gases on the hydraulic
characteristics of porous media. Transactions of the American Geophysical Union 39: 648-659.
Purdue University. 2001. Well Water Location and Condition on the Farm. Available on the Internet
at: http://www.epa.gov/seahome/well/src/titie.htm, accessed November 27, 2002.
Ray, C., T. Grischek, J. Schubert, J. Wang, and T. Speth. 2002. A perspective of riverbank filtration,
J. AWWA, 94(4): 149-160.
Ray, C. 2001a. Riverbank filtration: an analysis of parameters for optimal performance. Proceedings
of the Annual Conference of the American Water Works Association. June 17-21, 2001.
Washington, DC.
Ray, C. 2001b. Modeling riverbank filtration systems to attenuate shock loads in rivers. Proceedings
of the Annual Conference of the American Water Works Association. June 17-21, 2001.
Washington, DC.
Reynolds, J.M., 1997. An Introduction to Applied and Environmental Geophysics. New York:
Wiley.
Ritter, D.F., C.R. Kochel, and J.R. Miller. 1995. Process Geomorphology. 3rd edition. Dubuque,
Iowa: Wm. C. Brown Publishers.
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Rubin Y. and S. Hubbard, 2003. Hydrogeophysics. Kluwer.
Sanchez de Lozada, D., P. Vandevivere, P. Baveye, and S. Zinder. 1994. Decrease of the hydraulic
conductivity of sand columns by Methanosarcina barkeri. World Journal of Microbiology and
Biotechnology 10: 325-333.
Schafer, D. 2000. Groundwater modeling in support of riverbank infiltration for Louisville Water
Company, in Proceedings of International Riverbank Filtration Conference, Nov. 2-4,
Duesseldorf, W. Julich and J. Schubert (eds.), International Arbeitgemeinschaft der Wasserwerke im
Rheineinzugsgebiet, Amsterdam.
Schijven, J., Berger, P., Miettenen, I. 2003. Removal of viruses, bacteria, protozoa and toxins using
bank filtration, in Riverbank Filtration: Improving Source Water Quality, edited by Ray, C., Melin, G.
and Linsky, R, Kluwer, Dordrecht,
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for Well Construction and Ground Water Protection. Available on the Internet at:
http://www.dnr.state.oh.us/water/pubs/pdfs/wellconguide.pdf.accessed November 27, 2002.
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may inexpensively clean up poor-quality raw surface water. Environmental Science and Technology.
36: 422A - 428A.
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570/9-75-001. Washington, D.C. 156 pp.
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saturated soils and aquifer materials: Evaluation of mathematical models. Water Resources Research
31(9): 2173-2180.
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Wang, J.Z., S.A. Hubbs, and M. Unthank. 2001. Factors Impacting the Yield of Riverbank Filtration
Systems. Presentation at the American Water Works Association Water Quality Technology
Conference, November 11-15, Nashville, TN.
Wang, J.Z., R. Song, and S.A. Hubbs. 2000. Particle removal through riverbank filtration process, in
Proceedings of the International Riverbank Filtration Conference., Nov. 2-4, Duesseldorf, W.
Julich and J. Schubert (eds.), International Arbeitgemeinschaft der Wasserwerke im
Rheineinzugsgebiet, Amsterdam.
Wang, J.Z., Hubbs, S.A. and Song, R. 2002. Evaluation of Riverbank Filtration as a Drinking Water
Treatment Process, American Water Works Association Research Foundation Report 90922, 145 p.
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precursors and pathogens during riverbank filtration at three midwestern drinking water utilities, in
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Geological Survey Professional Paper 1286. Washington: U.S. Government Printing Office.
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5.0 Presedimentation
5.1 Introduction
Presedimentation is a preliminary treatment process used to remove gravel, sand, and other
material from the raw water and dampen particle loading fluctuations to the rest of the treatment plant.
This toolbox option is applicable to new sedimentation basins only; systems with existing
presedimentation basins that are required to conduct source water monitoring for Cryptosporidium
must collect samples after the basins for the purposes of bin classification (40 CFR 141.726(a)).
Sedimentation processes are common in the water treatment process and much design and
operational information is available. However, the use of an additional sedimentation basin in series, or
a pre-sedimentation basin at the head of the treatment plant is not as common as the standard
sedimentation basin, and little information is available. Therefore, the guidance provided in this chapter
is based on the design and operational principles of sedimentation processes.
This chapter on presedimentation is organized as follows:
5.2 LT2ESWTR Compliance Requirements - This section describes the criteria
presedimentation basins must achieve in order to receive Cryptosporidium removal
credit.
5.3 Toolbox Selection Considerations - This section assists systems in determining whether
the presedimentation toolbox option is a viable and beneficial option for meeting the
LT2ESWTR bin requirements.
5.4 Types of Presedimentation Basins - This section compares several sedimentation basins
and clarifiers in terms of structure and factors affecting settling efficiency.
5.5 Design and Operating Issues - This section discusses typical design and operational
issues including redundancy, short circuiting, sludge removal, and coagulant addition.
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5.2 LT2ESWTR Compliance Requirements
5.2.1 Credits
Presedimentation basins with coagulant addition may receive 0.5 log Cryptosporidium removal
credit under the LT2ESWTR if they meet the following criteria (40 CFR 141.726(a)):
• The presedimentation basin must be in continuous operation and must treat all of the flow
reaching the filters.
• A coagulant must be continuously added to the presedimentation basin (or prior to) while
the plant is in operation.
The presedimentation basin must achieve 0.5 log (68 percent) turbidity reduction on an
average monthly basis, for at least 11 of the 12 previous months. For those systems not
operating year-round, the 0.5 log turbidity reduction must be met for all but any one of the
operating months, based on the last 12 consecutive months.
Systems with existing presedimentation basins must monitor for Cryptosporidium
after the presedimentation basin and prior to the main treatment plant for the
purpose of determining bin assignment and cannot receive presedimentation
credit towards Cryptosporidium removal to meet the bin requirements (40 CFR
141.704(b)).
5.2.2 Monitoring Requirements
Systems must measure presedimentation basin influent and effluent turbidity at least once per
day, or more frequently as determined by the State (40 CFR 141.726(a)).
5.2.3 Calculations
For compliance with the LT2ESWTR, the log turbidity reduction must be calculated as a
monthly mean, from readings collected daily, according to the following equation (40 CFR
141.726(a)).
Log Reduction =
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Log10(Monthly Average Influent Turbidity) - Log10(Monthly Average Effluent Turbidity)
Or if calculated as a percent,
Percent Reduction =
(Monthly Average Influent Turbidity) - (Monthly Average Effluent Turbidity) x 100
(Monthly Average Influent Turbidity)
Example Calculation
Average influent turbidity = 16.3 NTU
Average effluent turbidity = 4.2 NTU
Log Reduction = Log10(16.3) - Log10(4.2) = 0.59
Percent Reduction = (16.3-4.2)716.3 = 74.2%
5.3 Toolbox Selection Considerations
The purpose of this section is to assist systems in determining whether the presedimentation
toolbox option is a viable and beneficial option for meeting the LT2ESWTR bin requirements. There
are two general aspects for systems to evaluate when considering this toolbox option:
1) Can the turbidity removal requirements be met consistently over the expected range of raw
water conditions?
2) What are the advantages and disadvantages of installing a presedimentation basin?
For presedimentation, the first question is driven by source water particle load and how much
of that load a proposed sedimentation basin would remove. Before researching potential
presedimentation designs, a system should determine if their source water has a high enough turbidity on
a consistent basis. Section 5.3.1 discusses the source water characteristics necessary to meet the
compliance requirements. Section 5.3.2 discusses the advantages and disadvantages of adding a
presedimentation process to the treatment train.
5.3.1 Source Water Quality
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To meet the 0.5 log turbidity removal requirement, the source water should have consistently
high turbidity. When influent turbidity is low, most presedimentation basins will have difficulty achieving
0.5 log reduction. For example, if a system has an average of 10 NTU source water turbidity for a few
months of the year, the average effluent turbidity would have to be 3.2 NTU for those months, which
could be difficult for some systems to achieve. Table 5.1 lists influent and effluent turbidity values that
yield 0.5 log reduction.
Table 5.1 Influent and Effluent Turbidity Values Resulting in 0.5 Log Reduction
Monthly Average Turbidity (NTU)
Influent
2
5
10
20
30
40
Effluent
0.6
1.6
3.2
6.3
9.5
12.6
Monthly Average Turbidity (NTU)
Influent
50
60
70
80
90
100
Effluent
15.8
19.0
22.1
25.3
28.5
31.6
5.3.2 Advantages and Disadvantages of Installing a Presedimentation Basin
The presedimentation process can reduce influent fluctuations in particle loading, flow, and
other water quality parameters. An additional sedimentation process in series provides increased
operational flexibility to handle rapid changes in influent turbidity. It also allows for enhanced
performance of subsequent processes in the treatment plant. Although, if the presedimentation effluent
turbidity is too low, the second sedimentation process may not be able to provide significant removal
since removal performance is enhanced by increased particle load.
As with the addition of many unit processes, the two major disadvantages are capital costs and
land requirements. The requirement of coagulant addition may increase chemical costs, although the
amount added in the next stage could be reduced. Whether these chemical costs offset each other is
site-specific.
5.4 Types of Sedimentation Basins
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There are several types of sedimentation basins (also called clarifiers) used for drinking water
treatment. Selection of a basin for presedimentation should be based on turbidity removal capability
and meeting the flow and space requirements of the facility. The focus of this chapter is on guidance for
complying with the LT2ESWTR, therefore the discussion in this section is limited to factors affecting
settling efficiency, as measured by turbidity removal. Further information on design can be found in the
following literature:
• Water Quality and Treatment—A Handbook of Community Water Supplies, 5th ed.
(AWWA 1999)
• Integrated Design and Operation of Water Treatment Facilities, 2nd ed. (Kawamura
2000)
Table 5.2 provides a comparison of several sedimentation basins and clarifiers. It is likely that
only horizontal clarifiers would be chosen for presedimentation, since they are less complex in operation
compared to the others (i.e., upflow, high rate, reactor, and ballasted sand clarifiers). The table
includes the additional types since some plants that choose to employ the presedimentation toolbox
option may elect to use their current sedimentation basin for presedimentation and construct a new
basin for primary sedimentation. The performance advantages and disadvantages listed in the table
relate to settling efficiency or indications for potential process upset. These were derived from
Integrated Design and Operation of Water Treatment Facilities (Kawamura 2000) and are
characteristic of sedimentation processes, not specifically presedimentation processes. The remainder
of this section provides short descriptions of different clarifier types.
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Table 5.2 Comparison of Sedimentation and Clarifier Types
Type
Performance Advantages
Performance Disadvantages
Applicable for Presedimentation and Sedimentation
Horizontal Flow (general)
Rectangular Basin
Circular Basin
-Easy to operate and maintain
-Tolerant to shock loads
-Good for handling large flows
-Easy sludge removal
-Can obtain high clarification
efficiency
-Subject to wind and density
currents (causing short-circuiting)
-Designs with trays have shown poor
settling efficiency
-Greater potential for hydraulic
imbalance in comparison to
rectangular basin (not good for
removing alum floes)
Applicable for Sedimentation
Upflow Clarifier (general)
Center Feed
Peripheral Feed
High Rate Settlers
(horizontal flow or upflow)
Reactor Clarifiers
(general)
High recirculation and
mechanical sludge plow
Sludge blanketzone and
mechanical sludge plow
Ballasted sand
-High clarification efficiency
-Easy sludge removal
-Good for source water with high
solids
-Increases the hydraulic load
capability and settling efficiency of
horizontal flow basins and clarifiers
-Good clarification due to seeding
effect
-Tolerant to shock loads
-Good turbidity removal
-Can handle higher flows with very
low detention times (on the order of
minutes)
-Can handle shock particle loads
without increasing coagulant dose
-Quick process startup
-Need constant flow rate and water
quality
-Limitations on size
-Short circuiting
-Potential short-circuiting
-Can form scales (calcium
carbonate) which clog flow
-Poorflocculation possible
-Need constant flow rate and water
quality
-Requires greater operator skill
-Dependent on one drive unit
-Limitations on size
-Very sensitive to shock loads
-Requires 2-4 days to build sludge
blanket
-Short detention time means not
much time for process adjustments
Note: Adapted from "Integrated Design and Operation of Water Treatment Facilities." Kawamura (2000).
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Sedimentation processes can be categorized in three general types: horizontal flow basins or
clarifiers, upflow clarifiers, and reactor clarifiers. High rate settlers are modified horizontal or upflow
clarifiers with plate or tube modules placed into the basin to increase the settling area. An additional
design described in this chapter that differs from the three general types is ballasted sand or high-rate
microsand process (a proprietary design).
5.4.1 Horizontal Flow
5.4.1.1 Rectangular
In rectangular sedimentation tanks the water flows in one end and ideally proceeds through the
basin in a plug flow manner. A uniform distribution at the inlet is an important design factor.
Rectangular basins can be susceptible to density currents that cause short circuiting. These basins are
easy to operate, have low maintenance costs, offer predictable performance under most conditions, and
are most tolerant to shock loads. High rate settlers can be easily installed to improve settling efficiency.
Rectangular basins are particularly well suited for large systems compared to circular basins that require
additional space and yard piping for equivalent flow.
5.4.1.2 Circular
The flow in circular basins is more commonly from a center feed well, radially outward to the
peripheral weirs. In comparison to rectangular basins, circular basins will have more land between the
basins and also require more yard piping. Circular basins have easy sludge removal, can obtain high
clarification efficiency, and are adaptable to high rate settling modules. However, if flow distribution
from the inlet is not uniform, the settling efficiency will be hindered. These basins are not as
hydraulically stable as rectangular basins.
5.4.2 Upflow Clarifier
In upflow clarifiers the influent enters at the bottom and clarified water flows upward while the
solids settle to the bottom. As with horizontal flow basins, upflow clarifiers can also be modified with
high rate settling modules. Upflow clarifiers can provide higher clarification efficiency than horizontal
flow, however, they are more sensitive to shock loads than horizontal flow basins.
5.4.3 Reactor Clarifier
Reactor clarifiers use the seeding concept to improve settling. The water flows through the
sludge layer so particles can coalesce with already formed floes. Two common designs of reactor
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Chapter 5 - P re sedimentation
clarifiers are slurry recirculation and sludge blanket clarifiers. Both operate on a center feed system
with built-in flocculation zones. The process is more complex than traditional horizontal or upflow
clarifiers. Reactor clarifiers can provide high clarification efficiency but at the cost of flexibility—the
source water quality and hydraulic loads must be constant.
5.4.4 High Flow Rate Designs
High rate settlers are modules of inclined tubes or plates that are installed in horizontal flow
(plates only) or simple upflow clarifiers. They provide increased surface area for particles to settle and
reduce settling time. Kawamura (2000) noted poor performance occurred when flow distribution was
uneven and flocculation was poor.
5.4.5 Ballasted Flocculation
Ballasted flocculation is a high-rate, physical-chemical clarification process that uses sand to
improve the settling of flocculated particles. The floe attaches to the surface of a sand particle, which
has a settling time 20 to 60 times faster than an alum floe (Kawamura 2002), thus creating a high-rate
settling process. Because of the increased settling rate, the space required is much less than other
clarifiers.
5.5 Design and Operational Issues
5.5.1 Redundancy
As stated earlier, for compliance with the LT2ESWTR, all flow must be treated by the
presedimentation process to receive Cryptosporidium treatment credit (40 CFR 141.726(a)).
Systems should consider the need for redundancy in the design of a presedimentation process. Smaller
systems or systems with a demand much lower than the design capacity may be able to shut down the
water treatment plant for presedimentation basin maintenance activities and, thus, not require additional
basins for redundancy. However, systems that operate on a continuous basis do not have that flexibility
and should have a plan for staying in compliance while a basin is shut down.
5.5.2 Short Circuiting
A common issue that must be considered in the design and operation of presedimentation
basins is short-circuiting. If a portion of flow does not receive close to the intended treatment (in this
case, detention time), then the effluent turbidity is likely to be higher than anticipated. Several factors
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affect short-circuiting including even distribution of flow at the inlet, density or temperature differentials
between influent and basin water, surface currents, and basin cleaning and sludge removal.
A proper design of the inlet is one of the most important design factors. In addition to flow
short-circuiting, a poorly designed inlet can lead to overall hydraulic instability in the settle zone.
Installation of perforated baffles is a simple and effective method for even flow distribution from the inlet
to the basin.
Temperature differentials and high wind velocities could induce circular currents in the vertical
direction of the basin. Influent water warmer than the basin water will rise to the surface and reach the
outlet of the sedimentation basin much faster than the intended detention time of the basin. Influent
water colder than the basin water will dive to the bottom of the basin and flow along the bottom of the
basin and rise to the top of the basin at the outlet, thereby reaching the outlet of the sedimentation basin
much faster than the intended detention time of the basin. Above ground tanks built of steel are more
susceptible to temperature differentials from exposure to the sun and heat transfer.
The degradation of effluent water quality due to wind is more noticeable in circular or square
sedimentation basins of diameters greater than 100 - 115 feet. When using long, shallow rectangular
settling basins, effects of wind induced currents can be minimized by ensuring that the longitudinal axis
of the basin is perpendicular to the prevailing wind direction. In addition to causing flow short-
circuiting, currents can also scour settled solids, causing resuspension of settled solids and increasing
effluent turbidity.
5.5.3 Sludge Removal
Sludge build-up in the tank decreases the volume of the sedimentation basin and reduces the
settling time in the basin. Additionally, as sludge builds up, particles become more susceptible to
resuspension during sludge removal, increasing the effluent turbidity. Sedimentation basins with high rate
settlers accumulate sludge rapidly, and therefore require continuous sludge removal.
5.5.4 Coagulant Addition and Dose Ranges of Common Coagulants
Current operational practice of presedimention processes often focus on mitigating shock loads
in the raw water supply (such as turbidity spikes due to precipitation in river source waters). However,
during periods of low influent turbidity less attention may be given to the actual performance of the
basin, resulting in less than 0.5 log turbidity reduction through the basin. To receive the credit, the
presedimentation basin may need to be operated more stringently, including the addition of coagulant.
The coagulant dose required to treat an influent stream depends on the chemical composition of the
influent, the characteristics of the colloids and suspended matter in the influent, the addition of a
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coagulant aid, the water temperature, and mixing conditions. Coagulant dose and other water
chemistry parameters of the coagulation and sedimentation processes are system-specific. Jar test
procedures for evaluating the appropriate coagulants, dosages, and other chemical attributes for a
treatment train are provided in AWWA's Operational Control of Coagulation and Filtration
Processes.
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References
AWWA. 2000. Operational Control of Coagulation and Filtration Processes, AWWA Manual M37,
Second Edition, pp. 1-34.
Kawamura, Susumu. 2000. Integrated Design and Operation of Water Treatment Facilities. John
Wiley & Sons, Inc.
USEPA. 1998. Optimizing Water Treatment Plant Performance Using the Composite Correction
Program, pp. 233-236.
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6.0 Lime Softening
6.1 Introduction
Lime softening is a drinking water treatment process that uses chemical precipitation with lime
and other chemicals to reduce hardness and to enhance clarification prior to filtration. Lime softening
can be categorized into two general types: (1) single stage softening that is used to remove calcium
hardness and (2) two-stage softening that is used to remove magnesium hardness and high levels of
calcium hardness. A single stage softening plant includes a primary clarifier and filtration components.
A two stage softening plant has an additional clarifier located between the primary clarifier and filter.
Within these general categories there are several possible treatment schemes; however, describing each
is beyond the scope of this chapter.
This toolbox option is practical for lime softening plants that either have a two stage process or
could upgrade to a two stage process. The advantage of using this toolbox option to achieve
compliance with the LT2ESWTR is that systems will have the treatment process in place or if an
upgrade or modification is needed, it could benefit the treatment of other contaminants. A disadvantage
for softening plants is a potential reduced flexibility in the treatment train since all water must be treated
by both stages.
Since the water systems considering this toolbox option will most likely have a lime softening
process in place, this section does not provide design or operational information. Instead, this section
focuses on the requirements that lime softening systems must meet to receive Cryptosporidium removal
credit and how those requirements can be met with general process modifications. The chapter is
organized into two sections:
6.2 LT2ESWTR Compliance Requirements - describes the criteria that plants must meet in
order to receive additional credit for Cryptosporidum removal, and reporting
requirements to maintain compliance.
6.3 Split Flow Processes - addresses compliance issues for split flow processes.
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6.2 LT2ESWTR Compliance Requirements
6.2.1 Credit for Cryptosporidium Removal
The LT2ESWTR requires plants to meet the following criteria in order to receive 0.5 log credit
towards additional Cryptosporidium treatment requirements (40 CFR 141.726(b)):
• The plant must have a second clarification step between the primary clarifier1 and filter
which is operated continuously. For split treatment processes, only the portion of flow
going through two clarification stages can receive credit. If a portion of flow bypasses one
stage, additional treatment must be provided to the bypassed portion (see section 6.3).
• A coagulant must be present in both clarifiers. Precipitation of metal salts (e.g., magnesium
hydroxide or excess lime) could be considered a coagulant for the second clarifier.
Figure 6.1 shows a typical two stage lime softening process. Lime or lime and soda ash are
added at the first stage. To receive treatment credit for this type of process, both stages of clarification
must have a coagulant present.
Figure 6.1 Typical Two-Stage Lime Softening Process
Lime
1
Flocculation and
Sedimentation Basin
C02
Recarbonation
Soda As
T
Flocculation and
Sedimentation Basin
T
Recarbonation
Filters
Primary Clarifier
coagulant must be present
Secondary Clarifier
coagulant must be present
For purposes of compliance with the lime-softening toolbox option, "clarifier" is used as a general term for
processes with settling.
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6.2.2 Reporting Requirements
The LT2ESWTR requires monthly verification and reporting of the following conditions for
systems using the lime softening option (40 CFR 141.730):
Continuous operation of a second clarification step between the primary clarifier and filter
• Continuous presence of coagulant in the first and second stage clarifiers
• Both clarifiers treat 100 percent of the plant flow
In addition, EPA recommends submitting a schematic of the treatment process to the State,
clearly identifying the two stages of clarification. EPA also recommends that systems monitor the
coagulant dosages (or concentration) in the secondary clarifier on a daily basis, for the first year, and
record the average and minimum coagulant concentrations. This data can assist the State in assessing
whether the system operates in compliance at all times.
6.3 Spilt-Flow Processes
Split-flow processes divert a portion of the flow from either the first or second stage of the
process and then blend the two streams together further downstream. Only the portion of flow that
receives the two stages of treatment would be eligible for the 0.5 log credit. In these situations, systems
would either have to: 1) eliminate the bypass and direct the entire flow through both stages, or 2) treat
the bypassed portion with another toolbox option, such as chlorine dioxide, membranes, or ozone to
receive 0.5 log credit for that stream.
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7. Combined and Individual Filter Performance
7.1 Introduction
Turbidity is an optical property that measures the amount of light scattered by suspended
particles in a solution. It can detect a wide variety of particles in water (e.g. clay, silt, mineral particles,
organic and inorganic matter, and microorganisms), but cannot provide specific information on particle
type, number, or size. Therefore, the U.S. Environmental Protection Agency (EPA) recognizes that
turbidity reduction is not a direct indication of pathogen removal, but is an effective indicator of process
control.
The Surface Water Treatment Rule (SWTR), Interim Enhanced SWTR (IESWTR), and Long
Term 1 Enhanced SWTR (LT IESWTR) all motivate public water systems to achieve a certain level of
finished water quality by requiring them to meet specified filtered water turbidity limits. Under the
IESWTR and LT1ESWTR, combined filter effluent turbidity in conventional and direct filtration plants
must be less than or equal to 0.3 NTU in 95 percent of samples taken each month and must never
exceed 1 NTU. These plants are also required to conduct continuous monitoring of turbidity for each
individual filter, and provide an exceptions report to the State or regulating agency when certain criteria
for individual filter effluent turbidity are exceeded.
The LT2ESWTR awards additional Cryptosporidium treatment credit to certain plants that
maintain finished water turbidity at levels significantly lower than currently required. This credit is not
available to membrane, bag/cartridge, slow sand, or diatomaceous earth plants, due to the lack of
documented correlation between effluent turbidity and Cryptosporidium removal in these processes.
This remainder of this chapter is organized as follows:
7.2 LT2ESWTR Compliance Requirements - describes the conditions for receiving
Cryptosporidium removal credit and monitoring requirements for maintaining
compliance.
7.3 Reporting Requirements - describes the routine reporting requirements that systems
must follow to receive credit.
7.4 Process Control Techniques - discusses modifications or operational aspects that
provide the tightened process control needed to meet the turbidity requirements for this
toolbox option.
7.5 Process Management Techniques - describes standard operating procedures, response
plans for loss of chemical feed, adequate chemical storage, and voluntary programs that
encourage full process control from administration to operation and maintenance.
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7.2 LT2ESWTR Compliance Requirements
7.2.1 Treatment Credit
For systems using conventional or direct filtration treatment to obtain an additional 0.5 log
Cryptosporidium removal credit, the LT2ESWTR requires the combined filter effluent (CFE) turbidity
measurements taken for any month at each plant are less than or equal to 0.15 NTU in at least 95
percent of the measurements (40 CFR 141.727(a)).
Alternatively, the LT2ESWTR allows systems using conventional or direct filtration treatment to
claim an additional 1.0 log Cryptosporidium removal credit for any month at each plant that meet both
of the following individual filter effluent (IFE) turbidity requirements (40 CFR 141.727(b)):
1) IFE turbidity must be less than 0.1 NTU in at least 95 percent of the maximum daily values
recorded at each filter in each month, excluding the 15 minute period following return to
service from a filter backwash
AND
2) No individual filter may have a measured turbidity greater than 0.3 NTU in two consecutive
measurements taken 15 minutes apart.
Systems may not claim credit for combined filter performance AND individual filter
performance in the same month (40 CFR 141.727(a)).
7.2.2 Monitoring Requirements
For both the CFE and IFE options, compliance with the LT2ESWTR is determined by sample
measurements taken for the IESWTR and LT1ESWTR (40 CFR 141.727(a) and (b)). In other
words, the LT2ESWTR does not require any additional monitoring from the IESWTR and
LT1ESWTR.
7.2.2.1 Combined Filter Effluent
The monitoring frequency and compliance calculation requirements for the CFE option are that
CFE turbidity must be measured at 4-hour intervals (or more frequently) and 95 percent of the
measurements from each month must be less than or equal to 0.15 NTU (40 CFR 141.727(a)).
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7.2.2.2 Individual Filter Effluent
The monitoring frequency and compliance calculation requirements for the IFE option are that
IFE turbidity must be measured every 15 minutes (excluding the 15 minute period following return to
service from a filter backwash) and 95 percent of the measurements from each month must be less than
or equal to 0.1 NTU (40 CFR 141.727(b)).
The LT2ESWTR specifies no individual filter may have a measured turbidity greater than 0.3
NTU in two consecutive measurements taken 15 minutes apart (40 CFR 141.727(b)). If the individual
filter is not providing water which contributes to the CFE (i.e., it is not operating, is filtering to waste, or
its filtrate is being recycled) the system does not need to report the turbidity for that specific filter.
7.2.3 Turbidity Monitors
An important aspect of awarding additional removal credit for lower finished water turbidity is
the performance of turbidimeters in measuring turbidity below 0.3 NTU. The EPA believes that
currently available turbidity monitoring equipment is capable of reliably assessing turbidity at levels
below 0.1 NTU, provided instruments are well calibrated and maintained. EPA strongly recommends
systems that pursue additional treatment credit for lower finished water turbidity to develop the
procedures necessary to ensure accurate and reliable measurement of turbidity at levels of 0.1 NTU
and less, and believes these procedures to be essential to maintain toolbox credit.
Turbidimeter maintenance should include frequent calibration by the manufacturer's methods as
well as frequent verification, in order to measure accurately in the low turbidity ranges required for this
toolbox option. Chapter 3 of the LT1ESWTR Turbidity Provisions Guidance Manual describes the
sampling methods, operation, maintenance, and calibration for turbidimeters and discusses quality
assurance and quality control measures. This section summarizes the information from that chapter,
including the approved methods, commonly used turbidimeters, calibration standards, and important
factors of maintaining turbidimeters. Systems are encouraged to review Chapter 3 of the LT1ESWTR
Turbidity Provisions Guidance Manual to ensure their operation, maintenance, and calibration
practices meet or exceed those recommended by EPA.
[insert web address for LT1 Guidance Manual]
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7.2.3.1 Methods
Currently, EPA has approved three methods for the measure of turbidity (described in 40 CFR
141.74).
• EPA Method 180.1
• Standard Method 213 OB
Great Lakes Instrument Method 2
These methods are summarized in Appendices C, D, and E of the LT1ESWTR Turbidity Provisions
Guidance Manual.
7.2.3.2 Maintenance and Calibration
Maintenance and calibration of both benchtop and on-line turbidimeters are fully described in
the LT1ESWTR Turbidity Provisions Guidance Manual. It is very important to follow the
manufactures procedures for maintenance and calibration of turbidimeters, as they vary between
manufacturers. Tables 7.1 and 7.2 list several maintenance and calibration activities common among
manufacturers for on-line and bench top turbidimeters. These activities should be conducted for all
turbidimeters to ensure proper operation on a consistent basis.
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Table 7.1 Maintenance and Calibration Activities for On-line Turbidimeters
Activity
Inspect for cleanliness
Verify sample flow rate
Verify calibration with primary standard,
secondary standard or by comparison with
bench-top1
Clean and calibrate with primary standard
Verify alarm settings and response to
alarms
Replace lamp
Recommended Frequency
Weekly
Weekly
For CFE credit: Weekly on CFE turbidimeter
and monthly on all IFE turbidimeters
For IFE credit: Weekly on both CFE and
turbidimeters
IFE
Quarterly2
Quarterly
Annually
1The sampling and comparative process of using a bench top turbidimeter is likely to introduce
unacceptable levels of error into the verification process. Therefore, EPA recommends using a primary or
secondary standard over the bench top for calibration.
frequency should be increased if verification indicates greater than a +/-10 percent deviation from
secondary standard.
Table 7.2 Maintenance and Calibration Activities for Bench Top Turbidimeters
Activity
Inspect for cleanliness
Verify calibration with secondary standard
Clean and calibrate
Replace lamp
Recommended Frequency
Daily
Weekly
Quarterly1
Annually
frequency should be increased if verification indicates greater than a +/-10 percent deviation from
secondary standard.
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In addition to those activities listed in the tables, the following documentation or record keeping
items should be developed and kept up to date.
• Log of turbidimeter maintenance and calibration
QA/QC plan for accuracy and consistency
• Standard operating procedures
7.2.3.3 Quality Assurance / Quality Control (QA/QC)
Systems should develop a QA/QC plan for measuring turbidity. This plan should include
written standard operating procedures (SOPs) to ensure that operation, maintenance, and calibration
activities are carried out in a consistent manner, and that each activity is understood by all that are
involved. At a minimum, systems should develop SOPs for cleaning turbidimeters, creating Formazin
Standards, calibrating turbidimeters, and referencing index samples.
For bench top turbidimeters, measurement errors can be introduced by dirt, scratches, or
condensation on the glassware, air bubbles in the sample, and particle settling. Operators should
strictly follow manufactures procedures for sampling and maintenance.
7.3 Reporting Requirements
7.3.1 Combined Filter Performance
In order to receive the 0.5 log removal credit for the LT2ESWTR, a water system must submit
monthly verification of CFE turbidity levels less than or equal to 0.15 NTU in at least 95 percent of the
4-hour CFE measurements taken each month (40 CFR 141.730).
7.3.2 Individual Filter Performance
For the 1.0 log removal credit under the LT2ESWTR, a water system must report monthly
verification of IFE turbidity levels less than or equal to 0.1 NTU in at least 95 percent of all maximum
daily IFE measurements taken each month for each filter (excluding the 15 minute period following
startup after backwash), and monthly verification that there were no IFE measurements greater than 0.3
NTU in two consecutive readings 15 minutes apart for any filter (40 CFR 141.730).
As requirements of the IESWTR and the LT1ESWTR, water systems must report monthly that
they have conducted individual filter turbidity monitoring. Systems are required to report actual IFE
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measurements only if they have exceeded one of the IFE turbidity triggers. Systems that would apply
successfully for the 1.0 log Cryptosporidium removal credit for LT2ESWTR compliance would not,
by definition, be systems that were required to report IFE measurements under the earlier regulations.
A system must, therefore, submit additional information about IFE turbidity measurements in order to
receive the 1.0 log credit.
7.4 Process Control Techniques
To meet the lower finished water turbidity requirements, systems will need a high level of
process control from the source water intake to the filters. The Guidance Manual for Compliance
with the IESWTR: Turbidity Provisions (EPA 1999) discusses many design and operational aspects
water systems should consider for achieving low effluent turbidity. Chapter 4 of that manual provides
design and operational modifications systems can use to optimize their process for compliance with the
LT2ESWTR toolbox requirements. This chapter of the Toolbox Guidance Manual builds on that
information, by highlighting those modifications or operational aspects that provide the tightened
process control needed to meet the turbidity requirements for this toolbox option. To meet the lower
finished water turbidity requirements of the CFE or IFE performance standards, systems will need
consistent process performance and the ability to maintain the high filtered water quality under sub-
optimal conditions and changing water quality.
The IESWTR guidance manuals are available on EPA's website at:
www.epa.gov/safewater/mdbp/implement.html.
Design and operational factors are not the only considerations for maintaining the high filtered
water quality standards; all areas of a water system must be dedicated towards the process optimization
goal, including administration and maintenance. This toolbox option will require continuing effort and
commitment from management and operations staff. Table 7.3 lists several factors in the areas of
administration, design, operation, and maintenance that may limit a system's ability to continually meet
the LT2ESWTR lower finished water turbidity requirements. This table demonstrates the importance
of considering the capabilities of the entire water system. This table was adapted from the Composite
Correction Program, an EPA program for optimizing water treatment plant performance (discussed in
section 7.5.4.2).
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Table 7.3 Performance Limiting Factors
(Adapted from the Composite Correction Program)
ADMINISTRATION
Plant Administrators
Policies
Familiarity with Plant Needs
Supervision
Planning
Complacency
Reliability
Source Water Protection
Do existing policies orthe lack of policies discourage staff members from making
required operation, maintenance, and management decision to support plant
performance and reliability?
Do administrators lack first-hand knowledge of plant needs?
Do management styles, organizational capabilities, budgeting skills, or
communication practices at any management level adversely impact the plant to the
extent that performance is affected?
Does the lack of long range planning for facility replacement or alternative source
water quantity or quality adversely impact performance?
Does the presence of consistent, high quality source water result in complacency
within the water utility?
Do inadequate facilities or equipment, or the depth of staff capability, present a
potential weak link within the water utility to achieve and sustain optimized
performance?
Does the water utility lack an active source water protection program?
Plant Staff
Number
Plant Coverage
Personnel Turnover
Compensation
Work Environment
Certification
Does a limited number of staff have a detrimental effect on plant operations or
maintenance?
Does the lack of plant coverage result in inadequate time to complete necessary
operational activities? (Note: This factor could have significant impact if no
alarm/shutdown capability exists - see design factors).
Does high personnel turnover cause operation and maintenance problems that affect
process performance or reliability?
Does a low pay scale or benefit package discourage more highly qualified persons
from applying for operator positions or cause operators to leave after they are trained?
Does a poor work environment create a condition for "sloppy work habits" and lower
operator morale?
Does the lack of certified personnel result in poor O&M decisions?
Financial
Operating Ratio
Coverage Ratio
Reserves
Does the utility have inadequate revenues to cover operation, maintenance, and
replacement of necessary equipment (i.e., operating ratio less than 1.0)?
Does the utility have inadequate net operating profit to cover debt service requirements
(i.e., coverage ratio less than 1.25)?
Does the utility have inadequate reserves to cover unexpected expenses or future
facility replacement?
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DESIGN
Source Water Quality
Microbial
Contamination
Does the presence of microbial contamination sources in close proximity to the water
treatment plant intake impact the plant's ability to produce an adequate treatment
barrier?
Unit Process Adequacy
Intake Structure
Presedimentation Basin
Raw Water Pumping
Flow Measurement
Chemical Storage and Feed
Facilities
Flash Mix
Flocculation
Sedimentation
Filtration
Disinfection
Sludge/Backwash Water
Treatment and Disposal
Does the design of the intake structure result in excessive clogging of screens, build-
up of silt, or passage of material that affects plant equipment?
Does the design of an existing presedimentation basin or the lack of a
presedimentation basin contribute to degraded plant performance?
Does the use of constant speed pumps cause undesirable hydraulic loading on
downstream unit processes?
Does the lack of flow measurement devices or their accuracy limit plant control or
impact process control adjustments?
Do inadequate chemical storage and feed facilities limit process needs in a plant?
Does an inadequate mixing result in excessive chemical use or insufficient
coagulation to the extent that it impacts plant performance?
Does a lack of flocculation time, inadequate equipment, or lack of multiple flocculation
stages result in poor floe formation and degrade plant performance?
Does the sedimentation basin configuration or equipment cause inadequate solids
removal that negatively impact filter performance?
Do filter or filter media characteristics limit the filtration process performance?
Do the disinfection facilities have limitations, such as inadequate detention time,
improper mixing, feed rates, proportional feeds, or baffling, that contribute to poor
disinfection?
Do inadequate sludge or backwash water treatment facilities negatively influence plant
performance?
Plant Operability
Process Flexibility
Process Controllability
Process Instrumentation
/Automation
Standby Units
Flow Proportioning
Does the lack of flexibility to feed chemicals at desired process locations or the lack
of flexibility to operate equipment or processes in an optimized mode limit the plant's
ability to achieve desired performance goals?
Do existing process controls or lack of specific controls limit the adjustment and
control of a process over the desired operating range?
Does the lack of process instrumentation or automation cause excessive operator
time for process control and monitoring?
Does the lack of standby units for key equipment cause degraded process
performance during breakdown or during necessary preventive maintenance activities?
Does inadequate flow splitting to parallel process units cause individual unit overloads
that degrade process performance?
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Alarm Systems
Alternate Power Source
Laboratory Space and
Equipment
Sample Taps
Does the absence or inadequacy of an alarm system for critical equipment or
processes cause degraded process performance?
Does the absence of an alternative power source cause reliability problems leading to
degraded plant performance?
Does the absence of an adequately equipped laboratory limit plant performance?
Does the lack of sample taps on process flow streams prevent needed information
from being obtained to optimized performance?
OPERATION
Testing
Process Control Testing
Representative Sampling
Does the absence or wrong type of process control testing cause improper operational
control decisions to be made?
Do monitoring results inaccurately represent plant performance or are samples
collected improperly?
Process Control
Time on the Job
Water Treatment
Understanding
Application of Concepts and
Testing to Process Control
Does staff's short time on the job and associated unfamiliarity with process control
and plant needs result in inadequate or improper control adjustments?
Does the operator's lack of basic water treatment understanding contribute to
improper operational decisions and poor plant performance or reliability?
Is the staff deficient in the application of their knowledge of water treatment and
interpretation of process control testing such that improper process control
adjustments are made?
Operational Resources
Training Program
Technical Guidance
Operational
Guidelines/Procedures
Does inadequate training result in improper process control decisions by plant staff?
Does inappropriate information received from a technical resource (e.g., design
engineer, equipment representative, regulator, peer) cause improper decision or
priorities to be implemented?
Does the lack of plant-specific operating guidelines and procedures result in
inconsistent operational decision that impact performance?
MAINTENANCE
Maintenance Program
Preventive
Corrective
Housekeeping
Does the absence or lack of an effective preventive maintenance program cause
unnecessary equipment failures or excessive downtime that results in plant
performance or reliability problems?
Does the lack of corrective maintenance procedures affect the completion of
emergency equipment maintenance?
Does a lack of good housekeeping procedures detract from the professional image of
the water treatment plant?
Maintenance Resources
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Materials and Equipment
Skills or Contract Services
Does the lack of necessary materials and tools delay the response time to correct
plant equipment problems?
Do plant maintenance staff have inadequate skills to correct equipment problems or
do the maintenance staff have limited access to contact maintenance services?
7.4.1 Chemical Feed
There are two main considerations for the chemical application of a coagulation and flocculation
treatment process:
• Are the chemicals and their dose optimum for the treatment process?
• Are they properly mixed or dispersed at the right point in the system?
7.4.1.1 Type of Chemical and Dose
Optimizing the coagulation and flocculation for the range of water quality and demand
experienced by the plant is a key factor in improving the overall treatment performance and ensuring
process control. One method commonly used to evaluate the type and dose of coagulant and other
chemical additives is the jar test (AWWA 2000a).
To provide the process control necessary for producing consistently low filter water turbidity,
systems should establish SOPs for changing chemical additions when raw water quality changes
significantly. The SOPs should list the appropriate chemicals to be added and the dose according to
specified raw water conditions. Jar tests or other chemical evaluations should be conducted with raw
water samples representing conditions from high water quality to the worst-case scenario and should
reasonably represent the treatment process.
7.4.1.2 Mixing
Adding coagulants at the proper location and providing the right amount of mixing is critical to
the coagulation and flocculation processes.
• Metal salts such as alum and ferric chloride should be added at the point of highest mixing.
• Low weight polymers can be added with the metal salts or at a second stage mixing
process.
• High weight polymers should be added at a point of gentle mixing.
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The coagulation process occurs rapidly; therefore, it is important that the coagulant is well-dispersed
and distributed across the width of the flow stream at the point of addition. Flash mixers are necessary
for coagulants requiring instantaneous mixing. Systems with mechanical mixers for these types of
coagulants should consider changing to a design that provides more uniform dispersion as studies have
indicated that mechanical mixers experience short circuiting and frequent maintenance requirements
(Kawamura 2000). Kawamura rated several flash mixer designs according to (in order of importance)
effectiveness, reliability, minimal maintenance, and cost:
1) Diffusion mixing by pressured water j ets
2) In-line static mixing
3) In-line mechanical mixing
4) Hydraulic mixing
5) Mechanical flash mixing
6) Diffusion by pipe grid
The mixing speed should be adjustable and changed with flow and raw water conditions as necessary.
Cold water is more viscous and may require a higher mixing energy. Highly turbid or colored water
may also require more mixing power to properly disperse the coagulant. For flash mixing, Kawamura
(2000) recommends G x t values of 300 to 1600, where G is the mixing energy (expressed in seconds"
*) and t is time (seconds).
7.4.1.3 Streaming Current Detectors and Zeta Potential Monitors
The coagulation process should be monitored continuously, with real time output. Streaming
current detectors (SCDs) can provide on-line coagulation control, by measuring the net surface charge
of the particle and ionic species in a sample of water. Through jar testing or other coagulant studies, the
charge measurement is correlated to the optimal coagulation conditions. The SCDs are typically
located directly after coagulant addition to allow the operator time to adjust the dose of the coagulant
before filtration. This quick response can prevent process upsets due to fluctuations in influent water
quality.
Source waters high in iron or manganese concentrations and the use of treatment chemicals with
iron salts or potassium permanganate can extensively increase maintenance requirements (AWWA,
2000a). Additionally, use of powdered activated carbon can increase maintenance requirements.
AWWA recommends comparing the SCD measurements to jar tests and zeta potential monitoring
results on a regular basis (AWWA, 2000a).
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Zeta potential monitors also indicate particle surface charge and can be used in the same
manner as SCDs.
7.4.2 Flocculation
The purpose of the flocculation process is to aggregate the particles into larger groups of
particles or "floes" that will settle in the subsequent sedimentation process. Through gentle and
prolonged agitation, the suspended particles collide with each other and form floes. The mixing must be
thorough enough to provide opportunities for the particles to collide but also gentle enough to prevent
the flocculated particles from breaking apart. It is likely, however, that some floe breakup will occur.
As aggregates grow in size, they are more likely to break up due to the shearing forces in the mixing
chamber. In this situation the aggregation and breakup can occur simultaneously leading to a steady-
state distribution of floe sizes.
The key factors of an effective flocculation process include: adequate mixing, low floe breakup,
and plug flow conditions. The following guidance can help to achieve these conditions:
Tapered mixing is most appropriate with variable G values ranging from 70 sec"1 to 15 sec"
i
• If flow is split between two flocculators, they should be mixing at the same speed.
Coagulant dosages are most likely optimized to one speed.
• Basin inlet and outlet conditions should prevent floe breakup.
• Baffling should be adequate to provide plug flow conditions.
7.4.3 Sedimentation
The purpose of the sedimentation process is to enhance filtration by removing the flocculated
particles. As with other unit processes, the sedimentation process must be optimized and provide a
consistent settled water quality. The key factors of a good settling process include:
• Minimization of short circuiting.
Sludge removal equipment should not resuspend particles or produce currents in the water.
• Surface loading rate, or overflow rate, needs to provide enough settling time. If flocculated
particles are not settling it could be a function of particle density or the surface loading rate.
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Continuous or frequent turbidity monitoring of settled water.
To provide a consistent well-clarified water from the sedimentation basin, the operating
parameters of the sedimentation basin may need to be adjusted with significant fluctuations in raw water
quality. For example, if a runoff event causes a spike in turbidity the particles may need more time to
settle, and by decreasing the flow through the basin it is possible to achieve the desired level of
clarification. Table 7.4 lists sedimentation basin effluent turbidity goals for several State and industry
optimization programs. Operators need knowledge and authority to modify the coagulation and
flocculation processes or reduce the flow to the plant when settled water quality goals are not being
met. For long-term process control, tracking seasonal raw water quality changes and their impacts on
the settling process can provide valuable information for optimizing the overall sedimentation process.
Table 7.4 Effluent Turbidity Goals for the Sedimentation Process
Optimization Program
California - Cryptosporidium Action Plan
Texas
Partnership for Safe Water / EPA Composite
Correction Program (CCP)
Sedimentation Basin or Clarifier Effluent
Turbidity Goal
1 to 2 NTU
<2NTU
1 NTU for raw water conditions of < 10 NTU
2 NTU for raw water conditions of > 1 0 NTU
The sludge blanket level is also an important factor for optimum settling conditions. A water
system should have SOPs for sludge draw-off that include routine checks of the sludge pumping lines.
Sludge pumping lines can plug, causing disruption of the sludge blanket and consequently disrupting the
settling process.
7.4.4 Filtration
Filtration is the last step in the particle removal process. Although filter performance is a
function of the coagulation, flocculation, and sedimentation processes, proper filter operation is needed
to provide the high quality finished water required for this toolbox option. The following factors should
be considered when optimizing or evaluating filtration performance.
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7.4.4.1 Flow Split
Systems should evaluate the flow distribution to the filters to ensure there is an even load across
all filters under the range of expected operating conditions (e.g., filter out of service, backwash).
7.4.4.2 Filter Beds
The filters should be operated with a design capacity that considers at least one filter as a
reserve. The reserve filter is put on-line to maintain flow stability to the filters; if this is not possible,
flow to the filters should be reduced. This will allow consistent flow when one filter is backwashed or
taken out of service for maintenance.
Media loss or disturbance can lead to particles passing through the filters. The filter should be
inspected on a regular basis to detect changes in the media. Media should be inspected to ensure
depths of media are proper, the media are evenly distributed, and the size distribution of the media are
still to specifications. Media samples can be taken with a coring device or by excavation for the
inspection. If media are lost or damaged, they should be replaced. Underdrains should also be
examined regularly to be sure they are not damaged and causing disturbances to the media or allowing
particles and media to pass out of the filter.
7.4.4.3 Backwashing
Backwashing is an integral part of the filtration process. Two important operating parameters
for backwashing are the backwash flow rate and frequency of cycles. Other factors relating to
backwash that affect filter effluent quality are hydraulic surges and filter start-up or "ripening".
Flow rate
Systems should determine the appropriate flow that will clean the filter and prevent mudball
formation, but will not upset the filter media and subject the underdrain to sudden momentary pressure
increases. Typical flow rates are 15 to 20 gpm/ft2 which result in 15 to 30 percent bed expansion.
Frequency
Although the filter effluent turbidity is the indicator for pathogen control and the determining
factor for compliance, other operating parameters should be used to determine when backwash is
needed. Emelko et al. (2000) performed filtration studies where pathogen breakthrough occurred
towards the end of the filter cycle before an increase in turbidity was detected. Their studies emphasize
the need to evaluate and optimize backwashing cycles with respect to filter effluent water quality. Most
systems use filtration time, headloss, effluent turbidity, or effluent particle counts to indicate when
backwashing is needed. For improved process control, it may be beneficial to use all indicators.
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Systems with multiple filters also should evaluate the hydraulic surges resulting from
backwashing. The timing of individual filter backwash cycles should be considered with respect to the
other filters, particularly adjacent filters. Consider the following two examples:
• If a large system with 50 filters backwashed 10 filters at the same time, this would cause a
20 percent increase in flow to the other filters. In this situation, the system could backwash
fewer filters at one time or reduce the flow to the filters to avoid the filter overload.
• When one filter is backwashed, a hydraulic surge can be experienced by an adjacent filter.
Improving filter effluent during start-up
It is very important for systems to conduct a full evaluation of their backwashing process and
operational variations to optimize the process. At the process optimization level, systems must eliminate
turbidity spikes in the filter effluent resulting from the backwashing process—it only takes a few high
turbidity readings to cause non-compliance. The following operational practices may provide improved
filter effluent during start-up:
• Ramping the backwash rate down in increments to allow better media gradation
• Resting a filter after backwash for several minutes or up to several hours before putting the
filter in service
• Adding a polymer to the backwash water
Slowly increasing the hydraulic load on the filter as it is brought back on line
7.4.4.4 Filter to Waste
During the beginning of a filter cycle the filter is "ripening" and the effluent turbidity is usually
higher. To avoid sending this poorer quality water to the CFE stream, the filter effluent produced
during the first few minutes of a filter cycle can be sent to waste (filter to waste) or recycled to the head
of the plant. Some systems filter to waste or recycle until the filter effluent reaches the desired level of
turbidity. Practicing filter to waste produces an overall higher quality water and may be necessary to
maintain a CFE or IFE below 0.15 NTU.
7.4.4.5 Backwash Recycle
Plants that recycle the backwash water to the head of the plant should evaluate the impacts the
backwash stream has on the coagulation, flocculation, and sedimentation processes. For example, the
operator should know how the coagulation and flocculation processes need adjusting when there is a
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change in recycle flow. Ideally, the impacts of the recycle flow on these processes should be
minimized.
For systems that recycle, the Filter Backwash Rule requires spent filter backwash, thickener
supernatant, or liquids from dewatering processes to be returned through all the processes of a
system's existing conventional or direct filtration treatment train (40 CFR 141.76(c)). The rule allows
for alternative recycle locations with State approval (40 CFR 141.76(c)).
7.4.4.6 Filter Assessments
Filter assessments can provide valuable information for optimizing the performance of a filter.
The IESTWR and LT1ESWTR require systems to conduct an individual filter self-assessment if a filter
exceeds specified effluent turbidity criteria. However, systems seeking Cryptosporidium treatment
credit for lower finished water turbidity should also consider conducting filter assessments to evaluate
operating parameters and optimize filter performance. Chapter 5 of the IESWTR Turbidity Guidance
Manual describes how to conduct an individual filter self- assessment.
7.4.5 Hydraulic Control
Proper hydraulic control throughout the treatment process is essential. In the coagulation and
sedimentation processes it is important to minimize short circuiting so the majority of the water receives
the designed coagulation and sedimentation treatment. Hydraulic surges can cause greater turbulence
that may break up flocculating particles and resuspend settling particles. In the subsequent filtration
process, hydraulic surges can cause particle breakthrough anytime during the filtration cycle. Systems
should look at historical water demand data and other conditions that adversely affect the system's
ability to control filter performance (e.g., backwashing, changes in flow). With these data, they should
develop operating plans to address the condition and allow control of the filter effluent quality.
7.5 Process Management Techniques
7.5.1 Standard Operating Procedures (SOPs)
Developing SOPs for all aspects of the operation and maintenance of a water system is
essential for running a high quality system. SOPs provide the basis for ensuring that activities are
accomplished in a consistent manner. They should be kept as simple as possible in order to ensure that
each operator is consistent in carrying out the task at hand. The title of the procedure should be clear,
concise, and descriptive of the equipment, process, or activity. SOPs should be developed with input
from staff, thus enabling them to understand and implement procedures in compliance with applicable
requirements.
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7.5.2 Prevention and Response Plan for Loss of Chemical Feed
Loss of chemical feed is a common cause of increased turbidity through the treatment
processes. Plants should have equipment and SOPs for preventing such occurrences or reacting to
them rapidly if they do occur. The following items are necessary to prevent an upset in water quality
due to a chemical feed failure.
• SOPs to verify doses with feed response time (lag time) accounted for
• Redundant feeds
• Routine maintenance of all chemical feed parts (e.g., pump, feed line)
• Inventory of spare parts available so repairs can be made quickly
• Pump or feed failure alarms
• Process monitors detecting chemical feed failure (e.g., streaming current, zeta potential, and
pH monitors)
7.5.3 Adequate Chemical Storage
Sufficient chemical storage is necessary to ensure continued operation of the plant at proper
dosages, including enough to run at higher dosages if an unexpected turbidity spike should occur in the
raw water. Care must also be taken, however, to follow manufacturer's suggestions on the useful life of
the chemical. Many coagulants will degrade over time and will not perform properly and may even
cause increased turbidity if allowed to age too long. Storage tanks should also be designed so that
there are no dead spaces where chemicals may accumulate with much longer residence times than the
hydraulic residence time of the tank.
7.5.4 Voluntary Programs
EPA, State regulatory agencies, AWWA, and other drinking water organizations have
established voluntary programs for systems to ensure the delivery of safe water to their customers.
These programs often focus on optimizing the treatment process and identifying the limiting factors of
performance. Consequently, they are excellent aids for systems considering this toolbox option. This
section discusses two programs, the Partnership for Safe Water and the Composite Correction
Program (CCP). (The CCP is also promoted as part of the Partnership for Safe Water).
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7.5.4.1 Partnership for Safe Water
The Partnership for Safe Water is a voluntary cooperative effort between EPA, AWWA, and
surface water systems. The goal of the program is to "provide a new measure of safety to millions of
Americans by implementing prevention programs where legislation or regulation does not exist. The
preventive measures are based around optimizing treatment plant performance, and thus increasing
protection against microbial contamination in America's drinking water supply."
(http://www.awwa.org/partner/partnerl.htm).
For further information about the Partnership for Safe Water and how to join, see
AWWA's website: http://www.awwa.org/partner/partnerl.htm
Water systems that participate in the program go through four phases:
Phase I: Commitment - operators and management indicate their willingness to complete the
program through phase in.
Phase II: Data Collection and Analysis - the water system must collect one year of raw, settled,
and filter effluent turbidity data and submit to AWWA for analysis.
Phase HI: Self Assessment - allows the system to examine the capabilities of the existing plant's
operation and administration and identify factors that limit performance.
Phase IV: Procedures and Applications Package - systems demonstrate they addressed areas
of limited performance and produce high quality water as measured by filter effluent turbidity.
Through the efforts of monitoring, data analysis, and evaluating the capabilities of unit
processes, significant improvements in water quality can be achieved. In the Partnership's 2001 Annual
report, AWWA reported an increase from 20 percent to 32 percent of plants completing Phase n with
finished water turbidity levels less than 0.1 NTU (based on 95th percentiles). At the beginning of Phase
HI, approximately 51 percent of plants reported 95th percentile turbidity less than 0.1 NTU, and after
completing Phase m approximately 70 percent of plants achieved less than 0.1 NTU.
7.5.4.2 Composite Correction Program (CCP)
The CCP was developed in 1988 to optimize surface water treatment plant performance with
respect to protection from microbial pathogens. The program consists of two parts, the comprehensive
performance evaluation (CPE) and comprehensive technical assistance (CTA). The CPE is a thorough
review and analysis of a facility's design capabilities and associated administrative, operational, and
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maintenance practices as they relate to achieving optimum performance from the facility. It can be
conducted by the system or by a third party over a period of roughly 3 to 4 days. The CTA builds on
the results of the CPE by addressing the combination of factors that limit a facility's performance. If
conducted by a third party, it should be implemented by a third party who is in a position to pursue
corrective actions in all areas, including politically sensitive, administrative, or operational limitations.
EPA published a handbook, Optimizing Water Treatment Plant Performance Using the
Composite Correction Program (1998), that fully describes the goals, methods, and procedures of
the CCP. To obtain a copy, call the EPA Safe Drinking Water Hotline at 1-800-426-4791.
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References
American Water Works Association. 2000a. Operational Control of Coagulation and Filtration
Processes, 2nd Edition. American Water Works Association.
American Water Works Association. 2000. Water Quality and Treatment 5th Edition. McGraw
Hill.
Kawamura, Susumu. 2000. Integrated Design and Operation of Water Treatment Facilities. John
Wiley & Sons, Inc.
USEPA. 1998. Optimizing Water Treatment Plant Performance Using the Composite Correction
Program. Office of Water and Office of Research and Development. EPA 625/6-91/027.
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8.0 Bag and Cartridge Filters
8.1 Introduction
Under the LT2ESWTR, bag and cartridge filters are defined as pressure driven separation
processes that remove particles larger than 1 jim using an engineered porous filtration medium
(generally a fabric material) through either surface or depth filtration (40 CFR 141.2). Typically, small
systems use bag and cartridge filters for protozoa or other particle removal. The pore sizes in the filter
bags and cartridges designed for protozoa removal are small enough to remove protozoan cysts and
oocysts but generally large enough that viruses, bacteria, and fine colloidal clays could pass through.
The distinction between bag filters and cartridge filters is based on the type of filtration media
used and the manner in which the devices are constructed. Bag filters are typically constructed of a
non-rigid, fabric filtration media housed in a pressure vessel in which the direction of flow is from the
inside of the bag to the outside. Cartridge filters are typically constructed as rigid or semi-rigid,
self-supporting filter elements housed in pressure vessels in which flow is from the outside of the
cartridge to the inside. A pressure vessel may contain either single or multiple filters in a series or in
parallel.
As the water flows through a bag or cartridge filter, particles collect on the filter and the
difference in pressure from the inlet to the outlet, termed "pressure drop," increases. Once a "terminal
pressure drop" is reached, the bag or cartridge filter must be replaced. Bag and cartridge filters are
disposable and designed to be easily replaced; however, a few cartridge filter devices are reportedly
designed to be cleaned and operated through multiple filtration cycles.
This chapter provides background information on the treatment performance, design, and
operation of bag and cartridge filters, with emphasis on those issues that a system should consider for
integrating bag or cartridge filters into its treatment process to comply with the LT2ESWTR. This
chapter is organized as follows:
8.2 LT2ESWTR Compliance Requirements - describes criteria and reporting requirements
that systems must meet to receive Cryptosporidium treatment credit.
8.3 Toolbox Selection Considerations - describes the advantages and disadvantages of
integrating a bag and cartridge filtration process for compliance with the LT2ESWTR.
8.4 Challenge Testing - describes the challenge testing that a bag or cartridge filter must
pass to be awarded Cryptosporidium treatment credit for the LT2ESWTR.
8.5 Design Considerations - discusses influent water quality, size of filter system and
redundancy, layout features, filter cycling, pressure monitoring, valves and
appurtenances, air entrapment, and NSF certification.
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8.6 Operational Issues - discusses pressure drop across the filter, and monitoring to assess
performance and indicate possible process upsets with the bag or cartridge filter or
other upstream processes.
8.2 LT2ESWTR Compliance Requirements
8.2.1 Credits
Bag and cartridge filtration processes that meet the EPA definition and demonstrate
Cryptosporidium removal through challenge testing may receive the following Cryptosporidium
removal credit for the LT2ESWTR (40 CFR 141.728(a)):
• 1 log removal for bag filtration showing a minimum of 2 log removal in challenge testing
• 2 log removal for cartridge filtration showing a minimum of 3 log removal in challenge
testing
A 1 log factor of safety is applied to the allowable removal credit over that demonstrated by
challenge testing because bag and cartridge filters cannot have their integrity directly tested; hence, there
are no means of verifying their removal efficiency during routine use.
Recently, some cartridge filtration devices have been developed for drinking water treatment
using membrane media, which can be direct integrity tested. These membrane cartridge filters (MCFs)
could be considered a membrane filtration process for the purpose of compliance with the LT2ESWTR
treatment requirements for Cryptosporidium (i.e., the MCF process would be eligible for the same
credit, and subject to the same requirements, as a membrane filtration process). A direct integrity test
is a physical test applied to a membrane unit to identify and isolate integrity breaches (i.e., one or more
leaks that could result in contamination of the filtrate). Manufacturers can provide information on direct
integrity testing and whether it is feasible with their products. Refer to the EPA Membrane Filtration
Guidance Manual for direct integrity testing and other membrane filtration requirements.
States may choose to award removal credits in excess of 1 and 2 log for bag and cartridge
filtration, respectively, if challenge testing demonstrates that the process can reliably achieve a greater
removal efficiency.
8.2.2 Reporting Requirements
All reporting requirements for the Surface Water Treatment Rule (SWTR), Interim
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Enhanced Surface Water Treatment Rule (IESWTR), and Long Term 1 Enhanced Surface Water
Treatment Rule (LT IESWTR) are still applicable; the LT2ESWTR does not modify or replace any
previous rule requirements. The location of filter effluent turbidity monitoring for compliance with the
IESWTR and LT IESWTR does not change with the installation of a bag or cartridge filter as a
secondary filtration process. That is, a system would still monitor filter effluent turbidity after the
primary filters for compliance with the IESWTR and LT IESWTR.
The LT2ESWTR requires an initial report be submitted by [72 months after rule promulgation]
for large systems and [102 months after rule promulgation] for small systems that demonstrates the
following (40 CFR 141.730):
• Process meets the definition of a bag or cartridge filter
• Removal efficiency from challenge testing (described in section 8.4) that must show at least
2 log removal for bag filters and 3 log removal for cartridge filters
For routine compliance reporting, the rule requires verification that all flow was treated by the
bag or cartridge filter (40 CFR 141.730). One possible approach States may elect to use for flow
verification is to have operators certify each month that all flow was treated by the filter. States may
require additional reporting at their discretion. Section 8.6 provides recommendations for filter effluent
and process monitoring.
8.2.3 Integration Into a Treatment Process Train
To achieve compliance with the IESWTR and LT IESWTR, all plants (except those meeting
the filter avoidance criteria in 40 CFR 141.71) must have a filtration process approved by the State.
Approved processes receive 2 log Cryptosporidium removal credit under the IESWTR and
LT IESWTR. For compliance with additional treatment requirements for the LT2ESWTR, bag and
cartridge filters should be added as an additional filtration process following the existing primary
filtration (see Figures 8.1 and 8.2). The bag and cartridge filters provide additional removal of the
smaller contaminants and any contaminants that break through the granular media filters during the end
of a run cycle or process upsets.
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Figure 8.1 Schematic of Treatment Process with Bag/Cartridge Filters
Raw
water
-crl
Bag or Cartridge Filter
Coagulation Flocculation
Sedimentation
Granular Filters Service pump
(if needed)
Distribution
System
High service pump
Clearwell
For those systems using a bag or cartridge filter process to meet LT1ESWTR requirements,
thus serving as the primary filtration process, it may be possible to configure the bag or cartridge filters
in a series (see Figure 8.2).
Figure 8.2 Bag/Cartridge Filters in Series
Raw
water
— >
Prim
Cart
k.
ary Bag or Secondary Bag or
•idge Filter(s) Cartridge Filter(s)
Distribution
System
High service pump
Clearwell
Another possible configuration is a bag or cartridge filter followed by a UV system (see Figure
8.3). This configuration would allow removal of particles and microbial pathogens as well as
inactivation of Cryptosporidium, Giardia, and viruses. In this case, the bag or cartridge filter would
serve as the primary filter and thus, be subject to SWTR, IESWTR, and LT1ESWTR requirements,
while the UV system would be subject to the LT2ESWTR requirements. Refer to EPA's UV
Disinfection Guidance Manual for information regarding UV systems and associated requirements
withLT2ESWTR.
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Figure 8.3 Bag/Cartridge Filter with UV System
Distribution
System
High service pump
Bag or Cartridge
Filter(s)
UV System
Clearwell
Other factors that should be considered when developing a treatment process scheme include
available space, hydraulic profile, and point of disinfection. Space requirements are small for bag and
cartridge filter systems, but extra space for maintenance activities should be accounted for in the
planning process. Because a significant head loss is associated with an additional filtration process, a
utility should consider its hydraulic profile when integrating new filters into an existing process sequence.
Although the addition of a new bag filtration process does not necessarily require that the point of
primary disinfection be changed, some bag filtration applications chlorinate prior to the bag filtration
process to minimize biofilm growth on the bags. However, if considering a process train with a bag or
cartridge filter as the primary filter, as in Figure 8.3, chlorinating prior to filtration will likely cause higher
disinfection byproduct formation compared to post-filter chlorination since the filtration process will
remove some organic material.
8.3 Toolbox Selection Considerations
This section describes the advantages and disadvantages of integrating a bag and cartridge
filtration process for compliance with the LT2ESWTR.
8.3.1 Advantages
The advantages of bag and cartridge filtration processes include low maintenance requirements,
relatively low capital cost, minimal operator skill and attention required, and low space requirements.
The only routine maintenance required is filter replacement when a defined terminal pressure drop or
other operating parameter, such as filter age or volume treated, is reached. The operation of these
systems is straightforward and requires little technical skill. In addition, the filter materials are relatively
inexpensive and the housing system is not complex, resulting in relatively low capital costs.
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8.3.2 Disadvantages
A disadvantage of bag and cartridge filtration processes is most filters must be replaced instead
of regenerated. For larger flows, or water with higher particle loads, frequent filter replacement
increases operation and maintenance costs. Additional pumps may be required to provide needed
pressure. Also, redundancy should be built into the process design, increasing costs.
8.4 Challenge Testing
Manufacturers commonly rate fabric filters by pore size or pore distribution. However, there is
no industry standard for measuring or reporting these characteristics. This lack of standardization
causes problems for establishing design criteria to ensure that a given bag or cartridge filter will
effectively remove a given percentage of Cryptosporidium. Furthermore, an oocyst has different
structural characteristics than the markers used to determine pore size; thus, the rate of rejection may
differ for an oocyst versus the test markers used to determine pore size or molecular weight cutoff. To
compensate for these factors of uncertainty for Cryptosporidium removal, the LT2ESWTR requires
bag or cartridge filters to be challenge tested—a process in which a known quantity of
Cryptosporidium oocysts (or an acceptable surrogate) is added to the filter influent and the effluent
concentration is measured to determine the removal capabilities of the filter (40 CFR 141.728(a)). This
testing is product-specific, not site-specific, meaning it does not have to be tested at every water system
seeking removal credit. Instead, a manufacturer (or independent third party) would challenge test each
of its products in order to obtain a 1 or 2 log Cryptosporidium removal rating.
For compliance with the LT2ESWTR, EPA defined a set of test conditions that must be met for
an acceptable challenge test. These conditions provide only a framework for the challenge test and
States may develop additional testing requirements. The EPAMembrane Filtration Guidance
Manual contains detailed guidance on developing challenge test protocol and conducting the test for
membrane processes that relate to these requirements. Additionally, NSF International, in cooperation
with EPA, developed the Protocol for Equipment Verification Testing for Physical Removal of
Microbiological and Particulate Contaminants with a chapter for testing bag and cartridge filters.
Although the protocol was developed for compliance with the SWTR, some1 testing principles still
apply.
Section 8.4.1 describes the test conditions required by the LT2ESWTR (40 CFR 141, Subpart
W, Appendix B). Section 8.4.2 shows how to calculate the log removal value for challenge testing
Specific sections of the EPA/NSF ETV Protocol that provide guidance for developing and conducting a
challenge test for LT2ESWTR include: section 10.4, Pre-Filter Water Quality Analysis; section 11.0, Operating
Conditions; section 12.3, Workplan; section 13.0, Data Management; and section 14.0, QA/QC.
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results. Section 8.4.3 discusses modifications to the filter unit (e.g., change in filter media) occurring
after challenge testing that may require additional challenge testing.
8.4.1 Testing Conditions (141, Subpart W, Appendix B)
8.4.1.1 Full Scale Filter Element
Challenge testing must be conducted on a full-scale filter element identical in material and
construction to the filter elements proposed for use in full-scale treatment facilities. For this challenge
testing, a filter element consists of the filter media, filter housing, and inlet and outlet piping.
8.4.1.2 Challenge Particulate
Challenge testing must be conducted using Cryptosporidium oocysts or a surrogate which is
removed no more efficiently than Cryptosporidium oocysts. The organism or surrogate used during
challenge testing is referred to as the "challenge particulate." The concentration of the challenge
particulate must be determined using a method capable of discreetly quantifying the specific organism or
surrogate used in the test, and gross measurements such as turbidity cannot be used. Key physical
characteristics to be considered for identifying an acceptable surrogate include size, shape, surface
charge, and mono-dispersion (i.e., particles remain discrete in solution and do not aggregate).
Chapter 3 of EP A's Membrane Filtration Guidance Manual describes the characteristics of
acceptable surrogates and lists potential and inert surrogates for Cryptosporidium. Examples of
possible microbial surrogates are P. dimunita and Serratia marcessans.
8.4.1.3 Feed Concentration
In order to demonstrate a removal efficiency of at least 2 or 3 log for bag or cartridge
filters, respectively, it may be necessary to seed the challenge particulate into the test solution. A
criticism of this approach is that the seeded levels are orders of magnitude higher than those
encountered in natural waters, which could lead to artificially high estimates of removal efficiency. To
address this issue, EPA set a limit on the maximum feed concentration applied to a filter during the
challenge study. The limit is based on the detection limit of the challenge particulate:
Cartridge filters: Maximum Feed Concentration = 3.16 x 104 x Filtrate Detection Limit
Bag filters: Maximum Feed Concentration = 3.16 x 103 x Filtrate Detection Limit
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These concentrations allow the demonstration of up to 3.5 log removal for bag filters and 4.5 log
removal for cartridge filters during challenge testing, if the challenge paniculate is removed to the
detection limit.
8.4.1.4 Time Periods of Challenge Testing
The challenge test must run until "terminal pressure drop" is reached. Terminal pressure drop is
a parameter specified by the manufacturer which establishes the end of the useful life of the filter.
However, continuous challenge paniculate feed is not required (i.e., intermittent seeding is permitted).
At a minimum, removal efficiency must be determined during three periods over the filtration cycle:
1) Within 2 hours of start-up after a new bag or cartridge filter has been installed.
2) When the pressure drop is between 45 and 55 percent of the terminal pressure drop.
3) At the end of the run after the pressure drop has reached 100 percent of the terminal
pressure drop.
The rule does not specify the number of samples that must be collected during each of the three
periods. Because the effluent concentration is often very low and near the detection limit, it may be
beneficial to collect more effluent than influent samples to obtain a more accurate removal efficiency. If
one sample has an uncharacteristically high concentration this can result in a low log removal value
(LRV) that is not necessarily representative of the filter's removal efficiency.
8.4.1.5 Water Quality of Challenge Test Solution
Water quality can have a significant impact on the removal of particulate contaminants, such as
Cryptosporidium. In general, bag and cartridge filters in water treatment do not experience influent
turbidity concentrations much greater than 10 NTU; and for the application of the LT2ESWTR, will
receive filtered water and thus, very low turbidity.
A clean-water challenge test will generally provide the most conservative estimate of removal
efficiency. However, since the challenge test must run until terminal head loss is reached, the challenge
test solution will need to contain some solids to cause the head loss build-up across the filter, but not an
excessive amount that will cause a rapid build-up. Particulate foulants that may be appropriate to add
to the test solution include clay particles (such as bentonite or kaolin) or carbon powder, as long as they
are not excessively fine-sized.
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The following are recommended for the challenge test solution:
• High quality water with a low to moderate concentration of suspended solids should be
used as the challenge solution. Suspended solids concentration should be high enough to
achieve a reasonable rate of headloss buildup, but not so high that the headloss builds up
too rapidly to conduct the challenges at the various headloss levels.
• No oxidants, disinfectants, or other pretreatment chemicals should be added to the test
solution.
• Characterized with respect to basic water quality parameters, such as pH, turbidity,
temperature, and total dissolved solids.
For the initial sampling conducted at zero percent headloss (see section 8.4.1.8), no particulate
foulant needs to be added to the test solution. This can be accomplished if the foulant is injected into
the feed stream, rather than fed in batch. In this case the foulant feed pump would not be turned on
until the zero percent challenge is completed. If the particulate foulant is added in batch, then the zero
percent headloss challenge must be completed before five percent of the terminal headloss is reached.
8.4.1.6 Maximum Design Flow Rate
The challenge test must be conducted at the maximum design flow rate specified by the
manufacturer.
8.4.1.7 Challenge Particulate Seeding Method
There are two basic approaches to seeding: batch seeding and in-line injection. In batch
seeding, all of the challenge particulates are introduced into the entire volume of test solution and mixed
to uniformity. In-line injection allows for the continuous or intermittent introduction of challenge
particulates into the feed stream entering the bag or cartridge system. While both methods are
acceptable, intermittent, in-line injection may the most practical seeding method for the testing.
Batch seeding requires the entire test solution to be contained in a reservoir and for the
reservoir to be well mixed to ensure a uniform concentration of the seeded particles. Generally, batch
seeding is used for small scale systems that only require relatively small amounts of feed solution for
testing.
While, in-line injection of the challenge particle can be either continuous or intermittent, the
intermittent feed may be more practical to conduct the challenge test at the required periods (i.e., a
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minimum of beginning, middle, and end-of-run; see section 8.4.1.4). It is vital that equilibrium is
achieved during each seeding event prior to the collection of feed and filtrate samples.
In-line injection delivers the challenge particles from a concentrated stock solution with a
known feed concentration (Cstock). The concentration of the stock solution should be 50 to 200 times
the desired concentration in the test feed solution (Cfeed). The stock solution delivery rate (SSDR) for
in-line injection is calculated using the equation below:
SSDR = (Cfeed x Qfeed ) / Cstock Equation 8-1
Where: SSDR = stock solution deliver rate (gpm)
Cfeed = feed solution concentration (# or mass / volume)
Qfeed = feed flow (gpm)
CstoCk = stock solution concentration (# or mass / volume)
The stock solution should be continuously mixed to ensure a uniform concentration of particles are
injected into the feed stream.
In-line injection requires additional equipment, such as chemical feed pumps, injection ports and
in-line mixers. A more detailed description of in-line injection is available in the Membrane Filtration
Guidance Manual (USEPA, 2003).
8.4.1.8 Challenge Test Solution Volume
The total volume of test solution required for the challenge should be the same for the different
challenge particle seeding methods. However, the seeded test solution volume can differ for the
different methods.
In general, the volume of the test solution depends on filtrate flow rate, test duration, and hold-
up volume of the test system and can be calculated by the following equation.
Vtest = (Qf x T + Vsys ) x SF Equation 8-2
Where:
Vtest = Volume of test solution (gallons)
Qf = Filtrate flow rate (gallons per minute)
T = Duration of test (minutes)
Vsys = Volume of solution contained within the filter unit(gallons)
SF = Safety factor (dimensionless)
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To calculate the total volume of test solution, the T value in the above equation is the time between the
initiation of flow to the filter unit to the time the last sample is drawn when terminal headloss is reached.
For batch seeding and continuous in-line injection tests, the seeded test solution volume (Vseeded) is the
same as the total test solution volume.
For intermittent, in-line injection, the seeded test solution volume can be considerably less than
that required for batch seeding. To calculate this smaller volume, the equation above can be modified
as follows:
VSeeded = (Qf x Tseed + Vsys + Veq) x SF Equation 8-3
Where:
deeded = seeded test solution volume (gallons)
Veq = volume required to reach feed equilibrium (gallons)
Tseed = Duration of sampling (minutes)
The equilibrium volume (Veq) is the quantity of seeded test solution needed to pass through the filter to
reach a stable feed concentration of the challenge particle. In general, filtrate sampling cannot begin
until this volume has passed through the system. A common assumption is that a minimum of three to
five system volumes are needed to reach equilibrium (i.e., Veq >3 Vsys). The duration of the test, T,
does not include time needed to reach equilibrium, as this is accounted for by Veq. Thus, T represents
the time necessary to conduct the actual sampling as discussed in section 8.4.1.9). Section 3.10.5 of
the Membrane Filtration Guidance Manual (USEPA, 2003) contains a detailed example of
challenge test solution design.
For in-line injection of the challenge particles the volume of stock solution needed can be
calculated from the seeded test volume as follows:
Vstock = Deeded x Cfeed) / (Cstock) Equation 8-4
Where:
Vstock = volume of stock solution (gallons)
Vseeded = seeded test solution volume (gallons)
Cfeed = feed solution concentration (# or mass / volume)
Cstock = stock solution concentration (# or mass / volume)
8.4.1.9 Sampling
An effective sampling program depends on a detailed sampling plan and the use of appropriate
sampling methods, locations, and QA/QC measures.
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Samples can be collected using either grab or composite sampling methods. Grab samples
consist of pre-determined amounts of water taken from the feed or filtrate streams, while composite
samples are of the entire process stream. It is likely that grab sampling methods will be used in the
challenge test. Good sampling practices include flushing samples taps, using clean sample containers
and preventing cross contamination of samples. QA/QC measures include clearly identifying samples,
collecting duplicates and using blanks. The time of filtrate sampling should be based on the initiation of
seeding for a given sampling period and flow rate. The influent should be sampled just prior to entering
the filter (but at least 10 pipe diameters downstream of the particle injection point and in-line mixers).
Sampling of the filtrate should occur immediately following the filter, but after any filtrate side
instrumentation that may be affected by the sampling.
Sample port design is an important consideration and should ensure that a representative
sample is obtained. Poorly designed ports contain large volumes where stagnation may occur (e.g.,
large valves and long sample tubes) and pull the sample from the edge of the pipe. A well designed
port has a sample quill that extends into the center of the pipe to draw a more representative sample.
Chapter 3 of the Membrane Filtration Guidance Manual (USEPA, 2003) contains
additional information on developing sampling plans and provides schematics of typical sampling
apparatuses.
8.4.2 Calculation of Log Removal
To determine the maximum feed concentration, use Equation 8-5. To determine the log
removal efficiency of the filter process tested, calculate the log removal using Equation 8-6.
Maximum Feed Concentration = 3.16x 106x (Filtrate Detection Limit) Equation 8-5
LRV = Log10(Feed Concentration) - Log10(Filtrate Concentration) Equation 8-6
The feed and filtrate concentrations must be expressed in the same units (number of challenge
particulate per unit volume). If the challenge particulate is not detected in the filtrate, then the filtrate
concentration is set equal to the detection limit.
Example 1 - Determining maximum allowable filtrate concentration
If the detection limit of the surrogate test is 2 units/L then the maximum feed concentration is
3.16xl06x(2) = 6.32xl06
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Example 2 - Calculating the LRV
Feed Concentration 20,000 units/L
Filtrate Concentration 3 units/L
LRV = Log(20,000) - Log(3)
LRV = 4.30-0.48 = 3.82
The LT2ESWTR does not specify how the feed and effluent concentration must be determined.
One possible approach is to use the average of all the feed samples and average of all the filtrate
samples. A more conservative approach would be to use the lowest feed concentration and highest
filtrate concentration from each filter run.
A challenge test will likely evaluate multiple filters. An LRV must be calculated for each filter
tested. The final log removal efficiency assigned to the filter process tested depends on the number of
filters tested:
• If fewer than 20 filters were tested during a challenge study, then the lowest LRV observed
would be the removal efficiency assigned to the process.
• If 20 filters were tested during challenge testing, then the removal efficiency assigned for the
process is the 10th percentile of the LRVs observed during the challenge study. (The
percentile is defined by [i/(n+l)] where / is the rank of n individual data points ordered
lowest to highest. If necessary the system may calculate the 10th percentile using linear
interpolation.)
8.4.3 Modifications to Filtration Unit after Challenge Test
If any significant modifications to the filter unit are made after challenge testing, additional
challenge testing is required to demonstrate removal efficiency of the modified unit. Significant
modifications specified by the rule are, but not limited to:
Changes to the filtration media (e.g., different fabric, change in the filter manufacturing
process)
• Changes to the configuration of the filtration media
• Modifications to the sealing system
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8.5 Design Considerations
Bag and cartridge filter systems may contain anywhere from one to over twenty filter units.
There is no maximum number of filters a system can include; however, membrane or other filtration
processes become more practical for larger flows since bag and cartridge filters are generally replaced
instead of backwashed or regenerated. A single filter unit is comprised of the filter media (bag or
cartridge), housing, and associated piping and valves. Figure 8.4 shows a typical single filter vessel
(housing).
Figure 8.4 Single Filter Vessel
:;; t Adjustable IS" Standsrd
-. 1119" Foot [%-irt
Source: U.F. Strainrite
Systems with multiple filters may be designed as a manifold with connective piping between the
individual filters in separate housing or alternatively as multiple filters in a single housing. Figures 8.5
and 8.6 show the manifold design and multiple filter vessel design, respectively.
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Figure 8.5 Manifold Bag Filter Design
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Source: U.F. Strainrite
The designs of bag and cartridge filters are not complex, however, there are a couple of key
issues that should be taken into consideration. First, the filter units must be designed integrally with their
respective housing systems. Poor fittings can cause leaks and premature failure. Manufacturers can
provide individual filter units that can be retrofitted into the existing process or complete filter houses
that are skid mounted. It is important to adhere to the manufacturer's instructions on filter
installation.
Second, the overall water treatment process design should minimize sudden changes in
pressures applied to the bag or cartridge filters. Each time the flow to the filter is interrupted and then
restarted, a sudden increase in pressure can occur across the filter unit unless steps are taken to allow
for gradual pressure ramp-up. The particle load in the filter effluent often increases when the filter cycle
begins. A study by McMeen (2001) reported that the increase in particle load could be occurring due
to the seal at the top of the filter failing when the pressure suddenly increases. Bag filters are especially
susceptible to cycling because these pressure fluctuations also increase wear on the fabric and seams,
causing premature failure. Section 8.5.4 provides recommendations for reducing filter cycling.
Figure 8.6 Multiple Filter Vessel
55 lit"
DMuser
utlet
Hydraulic tid'
operiini jick
12 3/4" Foot Print
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8.5.1 Water Quality
As previously described, systems seeking compliance with the LT2ESWTR will most likely
integrate a bag or cartridge filter process after the primary filtration process. As a result, influent water
quality, with respect to high paniculate levels, should not be an issue. However, for systems with
existing processes that use coagulants, the presence of residual coagulant in the primary filter effluent
may clog the pores of a bag or cartridge filter. Although this will not impair removal efficiency for
Cryptosporidium, it will shorten the time until the terminal pressure drop is reached, thus reducing filter
life.
Another water quality issue is the potential for biofilm growth on the bag or cartridge filter
media. Systems can add a disinfectant prior to the bag or cartridge filters to prevent biofilm growth.
(The filters must be compatible with the disinfectant.)
8.5.2 Size of Filter System and Redundancy
Systems should be adequately designed to handle maximum day or maximum instantaneous
flow, depending on the existing treatment process design. Prolonged operation at maximum flow
velocity wears the filter media at a higher rate than operating at lower flow velocities. The total volume
throughput is greater when operating at a flow velocity lower than maximum flow velocity rated for the
filter.
A minimum of two bag or cartridge filter housings should be provided to ensure continuous
water treatment in the event of failure in the filter operation. For water systems that do not require
continuous operation, a State may approve a single filter housing operation. Redundancy in pumps is
also recommended to ensure continuous operation.
8.5.3 Design Layout
Design layout features that should be considered for most designs are as follows:
• Piping should be designed to allow isolation of the individual filter units or vessels for
maintenance and filter replacement
Common inlet and outlet headers for the filter units
• Sufficient available head to meet the terminal pressure drop and system demand
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8.5.4 Filter Cycling
Filter cycling refers to the starting and stopping of the pump or filter operation. This can be
problematic with bag filter processes (cartridge filters are not known to have this problem) in which
water is pumped directly from the source to the filter, and then out to the distribution system. In these
situations, the filters operate on demand, similar to wells for small systems, and the sudden increase in
pressure across the filter causes premature wear and filter failure. For LT2ESWTR compliance,
systems with bag filters in a series or followed by UV disinfection should consider the following
recommendations for controlling the flow into the filter process to minimize filter cycling.
• Lengthen the filter runs by reducing the flow as much as possible through the filter.
• Install or divert the flow to a storage facility (e.g., pressure tank, clearwell) after the bag
filtration process. The stored water can supply the frequent surges in demand and thus
reduce the bag or cartridge filter cycling.
During filter start-up and other hydraulic surges, bag and cartridge filters often experience an
increase in filter effluent turbidity. Systems should consider the following options to improve filtered
water quality:
• Design for filter to waste capability. EPA strongly recommends filtering to waste for the
first five minutes of the filter cycle.
• Install a slow opening and closing valve ahead of the filter to reduce flow surges.
8.5.5 Pressure Monitoring, Valves, and Appurtenances
As previously mentioned, once the terminal pressure drop has been reached, the filter should be
replaced. At a minimum, pressure gauges should be located before and after the bag or cartridge filter
system and should be monitored at least daily. A valve or flow restricter should be installed on the inlet
header pipe of the filters to maintain flows below the maximum operating flow for the filters.
8.5.6 Air Entrapment
An automatic air release valve should be installed on the top of the filter housing to release any
air trapped in the filter. These valves should be checked routinely and properly maintained.
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8.5.8 NSF Certification
All components used in the drinking water treatment process should be evaluated for
contaminant leaching and certified under ANSI/NSF Standard 61.
8.6 Operational Issues
8.6.1 Pressure Drop (Inlet/Outlet Pressures)
The pressure drop across the filter directly relates to the amount of particle build-up on the filter
material and to the time when the filter should be replaced. Typical pressure drops across a clean filter
are 1 to 2 psig (pounds per square inch-gauge) and can increase to a differential of 20 to 30 psig when
the terminal pressure drop is achieved. The pressure differential does not increase linearly with run
time; the differential pressure increases at a faster rate with the duration of the run or as more material
accumulates on the filter. The time between filter replacement is primarily dependent on flow rate, but
also on influent water quality and filter material (i.e., size of pores).
The differential pressure between the inlet and outlet header should be monitored to determine
when the filter needs replacement. An alarm could also be linked to the pressure gauge to ensure the
operator is alerted.
8.6.2 Monitoring
In addition to monitoring the pressure drop across the filter, the influent and effluent turbidity or
particle count should be monitored to assess performance and indicate possible process upsets with the
bag or cartridge filter or other upstream processes. The recommended monitoring frequency depends
on the influent water quality and its variability. At a minimum, the pressure differential and effluent
turbidity should be checked daily. During the initial start-up phase of a newly integrated bag or
cartridge filtration system, monitoring should be more frequent and then can be reduced once the
operator becomes familiar with the system. If continuous monitoring of turbidity and/or pressure
differential is employed, the output from the sensors should be sent to an alarm to warn operators of
sudden changes in operation, or if the filter element needs replacing.
EPA recognizes turbidity has limitations as an indicator of filter failure or pathogen
breakthrough. However, in the absence of a better indicator, monitoring both influent and effluent
turbidity over a full run (i.e., from start to end of the filter life) can provide a performance baseline. The
baseline can then be used to indicate process upsets. This method may not be applicable to all systems;
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since the bag or cartridge filter influent will be filtered water, the difference between influent and effluent
turbidity may be too low to provide meaningful data.
Particle counters can be another valuable monitoring tool. If available, periodic checks of
influent and effluent particle counts are also recommended to ensure the filter is removing particles in the
appropriate size range (i.e., 4-6 microns).
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References
McMeen (2001). Alternate Filtration: Placing New Technology in an Old Regulatory Box.
American Water Works Association, Membrane Conference Proceedings.
NSF International. (2000). Protocol for Equipment Verification Testing for Physical Removal of
Microbiological andParticulate Contaminants. 40CFR35.6450.
USEPA (2002). Draft Membrane Filtration Guidance Manual, April 2002 draft.
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9.0 Second Stage Filtration
9.1 Introduction
The LT2ESWTR 40 CFR 141.728(c) describes second stage filtration as the use of a rapid
sand, dual media, granular activated carbon (GAC), or other fine grain media unit process applied in a
separate stage following rapid sand or dual media filtration. Applying an additional layer of media, such
as a GAC cap, on an existing single stage filtration unit does not qualify for this credit.
This chapter is organized as follows:
9.2 LT2ESWTR Compliance Requirements - discusses criteria and reporting requirements
that systems must meet to receive Cryptosporidium removal.
9.3 Toolbox Selection Considerations - discusses issues specific to second stage filtration
that water systems should consider when selecting toolbox options.
9.4 Design and Operational Considerations - discusses hydraulic issues, backwashing, and
turbidity monitoring for systems that integrate a second stage filtration in their treatment
train.
9.2 LT2ESWTR Compliance Requirements
9.2.1 Credits
Under the LT2ESWTR, a system that employs a second, separate filtration stage meeting the
following criteria may receive 0.5 log credit for Cryptosporidium removal (40 CFR 141.728(c)).
The first stage of filtration is preceded by a coagulation step
• The second stage of filtration is comprised of rapid sand, dual media, GAC, or other fine
grain media
• Both filtration stages treat 100 percent of plant flow
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Under the LT2ESWTR, a system integrating a slow sand filtration process for the second stage
of filtration meeting the following criteria can receive 2.5 log credit for Cryptosporidium removal (40
CFR141.728(d)).
• No disinfectant residual is present in the influent to the slow sand filtration process
• Both filtration stages treat 100 percent of plant flow
9.2.2 Reporting Requirements
To receive Cryptosporidium removal credit for compliance with the LT2ESWTR, systems
must report the following monthly (40 CFR 141.730):
• Verification that 100 percent of finished water was treated by two stages of filtration.
Actual data or information required to report is determined by the State. EPA recommends
plant piping schematics be initially reported followed by monthly operator certification.
Reporting for LT2ESWTR does not take the place of the IESWTR and LT1ESWTR reporting
requirements. Specifically, the turbidity of the combined and individual filter effluent from the first
filtration stage must be reported as required by the IESWTR and LT1ESWTR (40 CFR 141.74, 40
CFR 141.174(a), 40 CFR 141.551, and 40 CFR 141.560).
9.3 Toolbox Selection Considerations
Plants already employing a second unit process that meets the requirements for this toolbox
option (e.g., GAC columns to meet dissolved organic or taste and odor treatment goals) are in the ideal
position to seek credit. Other plants that have enough excess filtration capacity or unused filter beds
(e.g., built in anticipation of unrealized plant expansions), may be able to convert piping to enable these
filters to operate in series for relatively low cost. However, many plants will find that integrating second
stage filtration into an existing treatment train poses significant additional space, capital, and hydraulic
requirements. These systems may want to consider this option if the additional treatment provides other
benefits. For example, systems that use chloramination and/or ozone could run the second stage under
biological filtration conditions to reduce assimilable organic carbon (AOC), which promotes biofilm
growth and nitrification (for chloraminating systems) in the distribution system.
Additionally, plants experiencing taste and odor problems or dissolved organic contaminants in
their raw water might consider installing GAC columns to alleviate these problems and also receive the
Cryptosporidium removal credit.
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Slow sand filtration plants who wish to consider this toolbox option should either have sufficient
excess filtration capacity to allow filters to operate in series (with possible piping modifications) or have
sufficient land area to build additional filters.
9.3.1 Advantages
The advantages of a second stage filtration process are the same for both rapid and slow sand
plants and include operator familiarity with the process, ease of operation, and potential to reduce
disinfection byproducts. For plants with existing processes and infrastructure meeting the two-stage
requirements, implementation costs are likely to be relatively low.
9.3.2 Disadvantages
The disadvantages associated with second stage filtration apply primarily to those plants that do
not have existing processes in place or cannot easily convert built-in infrastructure. In addition to the
capital cost for new filters, these plants may need the following improvements to integrate a second
stage of filtration:
• Space if there is currently no room for expansion in the existing plant grounds
• Additional pumping to compensate for head loss associated with an additional filtration
process
• Increased backwash supply and treatment
For those plants that have existing infrastructure available for a second stage of filtration, they
still may have to account for an increased volume of backwash and loss of head due to the second
stage.
Systems with rapid sand filtration plants that are considering integrating slow sand filtration into
their treatment process should be aware of the following differences in operation and performance of
slow sand plants compared to rapid sand plants:
• More space required for slow sand plants
• Decreased filtering performance with cold temperatures
• Maintenance of filters requires draining and scraping a thin layer off the top of the filter
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9.4 Design and Operational Considerations
The design of the second stage is site-specific and depends on existing infrastructure (e.g., some
systems may have enough filtration capacity to operate filters in series) and space and hydraulic
requirements. EPA does not specify or restrict certain configurations, beyond the requirement that all
flow must be treated by both stages. Systems that have existing filters not in use or not used to capacity
may reconfigure the piping to operate in series. Media sizing for the second stage is also not specified;
however, typical design standards for regular or deep bed filters should be followed. If the filter effluent
from the first stage is not combined prior to second stage, the turbidity monitoring for IESWTR and
LT1ESWTR may have to be conducted on individual filters. For these cases, systems need to consult
with the State to develop a new IESWTR or LT IESWTR filter effluent monitoring plan.
9.4.1 Hydraulic Requirements
Additional pumps may be needed to provide the necessary head between the first and second
stages of filtration. The number of pumps and total number of filters should allow for redundancy, to
ensure that sufficient treatment capacity is in place to treat all the plant flow in the event of equipment
breakdown or maintenance. However, the filter loading rate to the second stage does not necessarily
need to be the same as for the first stage. The water influent to the second stage should be significantly
cleaner, and may enable higher loadings. Final design loading rates should be determined in
consultation with the State.
If the filter effluent from the first stage filters is not combined and sent to the second stage filters
via a distribution box or other flow equalization device, plant operation may be more complex. For
example, if the effluent from one first stage filter is sent to just one second stage filter, then as the flow
from first filter decreases (or headloss through it increases), flow through the second filter will also
decrease, unless automatic effluent control valves are installed on the second stage filter. Also, in this
case, whenever the first stage filter is backwashed, the second stage filter will also be out of service.
9.4.2 Backwashing
Consistent with the Filter Backwash Recycling Rule, the filter backwash from the second stage
(as well as the first stage) must be recycled to the head of the plant if it is recycled. The existing
backwashing capacity may be limited and need to be increased. There may be insufficient finished
water storage to supply backwash water or there may need to be additional pumping capacity,
depending upon the design of the additional filtration stage (e.g., if the existing filters have a small area
and the new filters are significantly larger, the existing backwash pumps may not be able to supply
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water at a high enough flow to properly expand the filter bed). It is likely that the second stage filters
would need to be backwashed less frequently than the first stage ones, due to the lower solids loading.
Filter ripening and/or filter-to-waste times for the second filtration stage will most likely differ
from the first stage.
9.4.3 Turbidity Monitoring
EPA recommends monitoring the turbidity of the individual filters in the second stage in order to
be able to identify any possible filter upset situations. Depending on the first filtration stage effluent
quality, it may be difficult to see a significant difference in the second stage effluent. If the combined
second stage filter effluent is the only process stream monitored, it is unlikely that an upset in one
second stage filter could be detected.
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10.0 Chlorine Dioxide
10.1 Introduction
Chlorine dioxide is used for disinfection, taste and odor control, and iron and manganese
removal. Chlorine dioxide is effective for inactivation of bacteria, viruses, and protozoa, including
Cryptosporidium while forming fewer halogenated byproducts than chlorine. It is stable only in dilute
aqueous solutions and must be generated on-site. It can be generated using a variety of starting
materials including chloride, chlorite, or chlorate.
The Surface Water Treatment Rule (SWTR) and subsequent Stage 1 Disinfection Byproducts
Rule (Stage 1 DBPR) and Interim Enhanced Surface Water Treatment Rule (IESWTR) all recognize
the ability of chlorine dioxide to inactivate pathogens. As a result, there is much information and
guidance available on the application of chlorine dioxide for disinfection, particularly in the following two
guidance manuals:
• Guidance Manual for Compliance with the Filtration and Disinfection Requirements
for Public Water Systems Using Surface Water Sources (USEPA 1991) (commonly
referred to as the Surface Water Treatment Rule Guidance Manual).
- Describes how to calculate the CT value (CT is described in the next sub-section) for a
given disinfectant, including methodologies for determining the residual concentration
(C) and contact time (T).
- Includes CT values for log-inactivation of Giardia and viruses.
• Alternative Disinfectants and Oxidants Guidance Manual (USEPA 1999).
- Provides full descriptions of:
• chlorine dioxide chemistry
• on-site generation
• primary uses and points of applications
• pathogen inactivation and disinfection efficiency
• byproduct production
• analytical methods
• operational considerations
The SWTR and Alternative Disinfectants and Oxidants Guidance Manuals are available on
EPA's website, http://www.epa.gov/safewater/mdbp/implement.html.
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The purpose of this chapter is to (1) describe what systems need to do to achieve
Cryptosporidium inactivation treatment credit for disinfecting with chlorine dioxide, (2) discuss design
and operational considerations that will assist water systems in deciding whether this toolbox option is a
practical option for them, and (3) discuss key issues associated with using chlorine dioxide as a
disinfectant. This chapter is organized as follows:
10.2 Log Inactivation Requirements - describes the concentration and time variables of the
CT parameter, presents the chlorine dioxide CT table for Cryptosporidium, and
provides a sample CT calculation.
10.3 Monitoring Requirements - describes monitoring requirements of both LT2ESWTR and
Stage 1 DBPR.
10.4 Unfiltered Systems LT2ESWTR Requirements - describes the level of
Cryptosporidium inactivation unfiltered systems must provide, and monitoring
requirements that must be met.
10.5 Disinfection with Chlorine Dioxide - describes chlorine dioxide chemistry and
disinfection with chlorine dioxide.
10.6 Toolbox Selection Considerations - discusses the advantages and disadvantages of
disinfection with chlorine dioxide.
10.7 Design Considerations - di scusses effects of temperature and the point of chlorine
dioxide addition on achieving the required CT value.
10.8 Operational Considerations - discusses water quality parameters that affect the
disinfection ability of chlorine dioxide.
10.9 Safety Issues - describes considerations for chemical storage and discusses the acute
health risks of chlorine dioxide.
10.2 Log Inactivation Requirements
Systems can achieve anywhere from 0.5 to 3.0 log Cryptosporidium inactivation with the
addition of chlorine dioxide. The amount of Cryptosporidium inactivation credit a system may receive
is determined by the CT provided in the treatment process (40 CFR 141.729(b)). This methodology
provides a conservative characterization of the dose of chlorine dioxide necessary to achieve a
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specified inactivation level of Cryptosporidium. CT is the product of the disinfectant concentration and
disinfectant contact time and is defined in the LT2ESWTR (40 CFR 141.729(a)):
CT = Disinfectant (mg/L) x Contact Time (minutes)
• "T" is the time (in minutes) it takes the water, during peak hourly flow, to move from the
point of disinfectant application to a point where, C, residual concentration is measured
prior to the first customer, or between points of residual measurement.
• "C" is the concentration of chlorine dioxide present in the system, expressed in mg/L.
The concept of regulating surface water treatment disinfection processes through CT was first
introduced in the SWTR. Tables of Giardia and virus log inactivations correlated to CT values,
commonly referred to as CT tables, were presented in the SWTR Guidance Manual. For the
LT2ESWTR, EPA developed CT tables for the inactivation of Cryptosporidium. Alternatively, a
system may conduct a site-specific study to determine the CT values necessary to meet a specified log
inactivation, using State approval (40 CFR 141.729(b)(4)). Appendix A provides guidance for
conducting a site-specific study.
10.2.1 CT Calculation
The methodology and calculations for determining CT have not changed from the SWTR to the
LT2ESWTR requirements. This section briefly reviews how CT is used to determine log-inactivation
for the SWTR and presents the chlorine dioxide CT table for Cryptosporidium inactivation. Refer to
the SWTR Guidance Manual for descriptions of measuring C and determining T.
Summary of CT Determination and Corresponding Log-inactivation as Presented in the SWTR
Guidance Manual
CT can be calculated for an entire treatment process or broken into segments and summed for
a total CT value. C is measured at the end of a given segment. T is generally estimated by methods
involving established criteria (flow, volume, and contactor geometry) or tracer studies. The following
steps describe the CT calculation from measured C and T values for a segment of the entire treatment
process:
1) Calculate CTcalc by multiplying the measured C and T values.
2) From the CT tables, find the CT value for the log inactivation desired, this is CTtable.
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3) Calculate the ratio of CTcalc/CTtable for each segment.
4) If a system has multiple segments, sum the CTcall/CTtable ratios for a total inactivation ratio.
5) If the ratio of CTcalc/CTtable is at least 1, then the treatment process provides the log
inactivation that the CTtable represents (log inactivation desired from step #2).
Table 10.1 CT Values (mg-min/l) for Cryptosporidium Inactivation by CIO2
Log
credit
0.5
1.0
1.5
2.0
2.5
3.0
Water Temperature, °C1
<=0.5
319
637
956
1275
1594
1912
1
305
610
915
1220
1525
1830
2
279
558
838
1117
1396
1675
3
256
511
767
1023
1278
1534
5
214
429
643
858
1072
1286
7
180
360
539
719
899
1079
10
138
277
415
553
691
830
15
89
179
268
357
447
536
20
58
116
174
232
289
347
25
38
75
113
150
188
226
1CT values between the indicated temperatures may be determined by interpolation
Example CT Calculation
A plant draws 1.5 MGD of 5 degrees Celsius water from a stream, adding 1.8 mg/1 of chlorine
dioxide at the intake. The water travels through 2 miles of 12 inch pipe to a settling tank. The detention
time in the tank, as determined by a tracer study, is 150 minutes. After the tank, it travels through
another 12-inch pipe to the plant. Figure 10.1 provides a schematic of an intake, piping, and tank. The
concentration of chlorine dioxide at each point is measured as follows:
Cinitiai = 1-8 mg/1
Centering tank = L 6 mg/1
Qeaving tank = 0.8 mg/1
'leaving :
2nd pipe = 0.2 mg/1
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Figure 10.1 CT Calculation Example Schematic
Cin = 1.8 mg/l
Transmission Line
2 miles
Segment 1
Segment 2
Segment 3
The residence times of the two sections of pipe are determined assuming plug flow. Therefore
the time for each section is calculated as follows:
! = (A^Lj/Qj) = (7ir2L1/Q1)*(7.48 gal./l ft.3)*(MG/l, 000,000 gal.)*(l,440 min./day)
where:
A is the cross-sectional area of the pipe in square feet
• Q is the volumetric flow rate in MGD
• L is the length of pipe in feet
• r is the radius of the pipe in feet.
Therefore the times for the two sections of the pipe are as follows:
Tj = 2 mi.*(5,280 ft./mi.)*7i*(0.5 ft.)2*(0.0108 MG*sec/ft.3*day)/(1.5 MGD) = 59.7 min.
T3 = 0.25 mi.*(5,280 ft./mi.)*7i*(0.5 ft.)2*(0.0108 MG*sec/ft.3*day)/(1.5 MGD) = 7.4 min.
The T10, or time for 90 percent of a tracer to pass through the section for the tank is as follows:
T7 = 150 minutes
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CT Calculation:
Step 1 . Calculate CT for each segment.
The concentrations and times for each segment are known. The T's are calculated above and
the C is the concentration measured at the end of each segment. The CT for each segment is
calculated as follows:
CT1 = (1.6mg/l)x (59.5 min.) = 95.2 mg x min./l
CT2 = (0.8 mg/1) x (150 min.) = 120 mg x min./l
CT3 = (0.2 mg/1) x (7.4 min.) = 1.5 mg x min./l
Step 2. Look up CTtable in Table 10.1. For 5°C and 0.5 log inactivation,
CTtable = 214 mgxmin./l.
Step 3. Calculate the ratio of CTcalc/CTtable for each segment.
! = 95.2/214 = 0.44
(CTcalyCTtable)2= 120 7214 = 0.56
(CTcal/CTtable)3= 1.5/214 = 0.01
Step 4. Sum the CTcalc/CTtable for each segment.
(CTcal/CTtable)total = 0.44 + 0.56 + 0.01 = 1.01
Determine Log Inactivation:
If the result of Step 4 is greater than 1, the log inactivation associated with the CTtable values is
achieved. If the result is less than 1, that level of log inactivation is not achieved (if the log
inactivation was less than 1.0, the calculations should be repeated at a lower log inactivation).
In this example, the sum of the CTcal(/CTtable for all the segments is greater than 1, so the system
qualifies for a 0.5 log Cryptosporidium inactivation.
10.3 Monitoring Requirements
10.3.1 LT2ESWTR
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The LT2ESWTR requires daily CT monitoring (40 CFR 141.730), which must be done
during peak hourly flow. Since systems may not know when the peak hourly flow will occur, EPA
recommends monitoring on an hourly basis. Contact time does not have to be determined on a daily
basis, only concentration does. Contact time is determined using the peak hourly flow. Systems should
reevaluate contact time whenever they modify a process and the hydraulics are affected (e.g., add a
pump for increased flow, reconfigure piping).
The chlorine dioxide concentration should be measured using approved analytical methods,
either DPD, (Standard Method 4500-C1O2 D) or Amperometric Method II, (Standard Method 4500-
C1O2 E). Details on these methods can be found in Standard Methods for the Examination of
Water and Wastewater, 20th edition, American Public Health Association, 1998.
Note, if a system is required to develop a disinfection profile under the LT2ESWTR and
changes its disinfection process, the LT2ESWTR requires the system to calculate a disinfection profile
and benchmark (40 CFR 141.714(a)) (see Chapter 1, section 1.6 for details).
10.3.2 Stage 1DBPR
The Stage 1 DBPR requires all systems using chlorine dioxide for disinfection or oxidation to
monitor daily for chlorine dioxide and chlorite at the distribution system entry point. In addition,
systems must take monthly chlorite samples at three locations in the distribution system. Table 10.2 lists
the chlorine dioxide and chlorite distribution system monitoring requirements.
Table 10.2 Distribution System Monitoring Requirements at Each Plant
Location
Frequency
Chlorite
Distribution System Entry Point
Distribution System Sample Set of 3:
1 Near First Customer
1 In Middle of the Distribution System
1 At Maximum Residence Time
Daily
Monthly
Chlorine Dioxide
Distribution System Entry Point
Daily
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If the chlorine dioxide maximum residual disinfectant level (MRDL) of 0.8 mg/L or the chlorite
maximum contaminant level (MCL) of 1.0 mg/L is exceeded in any of the samples, additional
monitoring is required (see the Stage 1 DBPR, 40 CFR141.132(b) for further information). The
monthly monitoring requirements for chlorite may be reduced if all chlorite samples are below the MCL
fora 1-year period.
10.4 Unfiltered System LT2ESWTR Requirements
The LT2ESWTR requires unfiltered systems to provide at least 2.0 log Cryptosporidium
inactivation (40 CFR 141.721(b)). If their source water Cryptosporidium concentration is greater
than 0.01 oocyst/liter, then systems must provide 3.0 log Cryptosporidium inactivation (40 CFR
141.721(b)). The requirements of the previous SWTR regulations still apply— achieve 3 log
inactivation of Giardia and 4 log inactivation of viruses and maintain a disinfectant residual in the
distribution system (e.g., free chlorine or chloramines). LT2ESWTR also requires that a minimum of
two disinfectants be used to meet overall disinfection requirements.
The monitoring requirements described in section 10.3 apply to unfiltered systems.
Additionally, the LT2ESWTR requires unfiltered systems to meet the Cryptosporidium log-inactivation
requirements determined by the daily CT value every day the system serves water to the public, except
one day per calendar month (40 CFR 141.721(c)). Therefore, if an unfiltered system fails to meet
Cryptosporidium log-inactivation two days in a month, it is in violation of the treatment technique
requirement.
10.5 Disinfection With Chlorine Dioxide
Chlorine dioxide (C1O2) is an uncharged compound of chlorine in the +IV oxidation state. It is a
relatively small, volatile, and highly energetic molecule, and a free radical even in dilute aqueous
solutions. At high concentrations, it reacts violently with reducing agents. However, it is stable in dilute
solution in a closed container in the absence of light. When an aqueous solution is open to the
atmosphere, chlorine dioxide readily comes out of solution. Aqueous solutions of chlorine dioxide are
also susceptible to photolytic decomposition, depending on the time of exposure and intensity of UV
light.
Disinfection of protozoa is believed to occur by oxidation reactions disrupting the permeability
of the cell wall (Aieta and Berg 1986). Chlorine dioxide functions as a highly selective oxidant due to
its unique, one-electron transfer mechanism where it is reduced to chlorite (C1O2") (Hoehn et al. 1996).
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In drinking water, chlorite (C1O2") is the predominant reaction end product, with approximately
50 to 70 percent of the chlorine dioxide converted to chlorite and 30 percent to chlorate (C1O3") and
chloride (C1-) (Werdehoff and Singer 1987). This has a significant impact on disinfection capabilities
for drinking water, since chlorite is a regulated drinking water contaminant with an MCL of 1.0 mg/L.
Based on a 50 to 70 percent conversion of chlorine dioxide to chlorite, the maximum dose is limited to
1.4 to 2.0 mg/1 unless the chlorite is removed through subsequent treatment processes.
10.6 Toolbox Selection Considerations
10.6.1 Advantages
There are several advantages to using chlorine dioxide as a primary disinfectant. Chlorine
dioxide is approximately four times as effective as chlorine for the inactivation of Giardia and is a
stronger disinfectant than chlorine for bacteria (White 1999). However, free chlorine is more effective
for the inactivation of viruses. Other advantages of disinfection with chlorine dioxide include:
• A high oxidizing potential allows it to oxidize other compounds such as manganese and
some taste and odor compounds.
• Chlorine dioxide does not form regulated halogenated organic byproducts.
• The effect of pH on the disinfection ability of chlorine dioxide is much smaller than for other
disinfectants.
• Chlorine dioxide has shown a synergistic effect when combined with other disinfectants
such as ozone, chlorine, and chloramines that leads to greater inactivation with the
disinfectants added in series than by either disinfectant individually.
10.6.2 Disadvantages
A major disadvantage of chlorine dioxide is the byproduct formation of chlorite and chlorate.
Section 10.6 describes the dose limits of chlorine dioxide due to the formation of chlorite. Other
disadvantages of disinfection with chlorine dioxide include:
• Difficulty in maintaining an effective residual. Additionally, residual will be lost in the filters.
• It decomposes upon exposure to sunlight, flourescent light bulbs, and UV disinfection
systems.
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• Ability to disinfect is reduced under colder temperatures.
• If the ratio of reactants in the chlorine dioxide generator is incorrect, excess aqueous
chlorine can remain, which can form halogenated disinfection byproducts.
Chlorine dioxide must be generated on-site.
• There may be a need for three-phase power which may not be compatible with some water
systems.
• Chlorine dioxide can be explosive at high temperatures or pressures.
Storage of sodium chlorite solution can be problematic due to crystallization at low
temperatures or high concentrations and stratification at temperatures below 40"F (or
4"C).
• High cost of chemicals.
• Dialysis patients are sensitive to higher chlorite levels and should be notified if chlorine
dioxide is going to be added where it has not routinely been used.
Training, sampling, and analysis costs are high.
Systems considering using chlorine dioxide as a disinfectant should perform chlorine dioxide
demand/decay tests on the water being considered for disinfection (raw water or filter effluent) under
normal and poor water quality conditions. If chlorine dioxide is added where the demand is 1.4 mg/1 or
greater, the system may have difficulty complying with the chlorite MCL. If the raw water has a chlorine
dioxide requirement greater than 1.4 mg/1, chlorine dioxide might still be able to be used for post
disinfection since the oxidant demand will be less after the filters.
10.7 Design Considerations
10.7.1 Designing to Lowest Temperature
As the water temperature declines, chlorine dioxide becomes less effective as a disinfectant.
LeChevallier et al. (1997) found that reducing the temperature from 20 degrees Celsius to 10 degrees
Celsius reduced disinfection effectiveness by 40 percent. Since the treatment achieved for chlorine
dioxide addition is temperature dependent, systems need to consider the variability in water
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temperature to ensure they meet the CT level for the minimum treatment needed for compliance. For
example, if a system is required to provide an additional 1 log Cryptosporidium treatment and plans to
achieve that with chlorine dioxide alone, then it should determine the CT required for the lowest water
temperature experienced and ensure it can meet those CT requirements.
10.7.2 Point of Addition
There are two main considerations for determining locations of chlorine dioxide addition for the
purpose of Cryptosporidium inactivation—contact time and chlorine dioxide demand. Additionally,
systems using ozone should consider that ozone will degrade chlorine dioxide. The application point for
chlorine dioxide should be well upstream of the ozone process or just after the ozone process.
Contact Time
There must be substantial contact time with a residual concentration. The CT requirements for
Cryptosporidium are much higher than for Giardia and viruses and when designing to the lowest
water temperatures, the resulting contact time requirements are relatively high for even the 0.5 and 1.0
log inactivation. Chlorine dioxide readily degrades when exposed to light from flourescent lamps or the
sun, therefore all the available concentration in open basins will most likely not be utilized for
disinfection. For most systems, the point of application will be either at the raw water intake or after
the filters, whichever can provide the necessary contact time.
Oxidant Demand
The oxidant demand of the water affects chlorite and chlorate byproduct formation (section
10.6). If the chlorine dioxide requirement of the raw water is greater than 1.4 mg/L then chlorite
concentration will likely exceed the MCL. However, chlorine dioxide could be added after the filters
where the oxidant demand is frequently lower and, therefore, a lower dose of chlorine dioxide would
result in a lower byproduct concentration of chlorite.
10.8 Operational Considerations
Of all the water quality parameters, water temperature has the strongest effect on the
disinfection ability of chlorine dioxide. The concentration of suspended matter and pH also have an
effect, but to a lesser extent than temperature. Although the disinfection potential of chlorine dioxide is
not strongly affected by pH, studies have shown that chlorine dioxide disinfection is better under higher
pH (LeChevallier et al. 1997).
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Suspended matter and pathogen aggregation affect the disinfection efficiency of chlorine
dioxide. Protection from chlorine dioxide inactivation due to bentonite was determined to be
approximately 11 percent for water with turbidity values less than or equal to 5 NTU and 25 percent
for turbidity between 5 and 17 NTUs (Chen et al. 1984).
Based on the research discussed above, the optimal conditions for Cryptosporidium
disinfection with chlorine dioxide are low turbidity, high pH, and high temperature.
10.9 Safety Issues
Because chlorine dioxide can be explosive and pose acute
health risks to those exposed to gaseous chlorine dioxide, a safety
plan should be developed that includes precautions for generation,
handling, storage, and emergency response.
Airborne concentrations
greater than 10 percent
may cause explosions.
10.9.1 Chemical Storage
Most chlorine dioxide generators use sodium chlorite solutions as a raw material. If sodium
chlorite solutions are accidently acidified or exposed to a reducing agent, uncontrolled production and
release of gaseous chlorine dioxide can result. In addition to being toxic, if the gaseous chlorine dioxide
reaches concentrations greater than 10 percent, it can spontaneously explode.
Sodium chlorite should be stored away from other chemicals, particularly any acid solutions or
chemicals that could act as reducing agents. Construction materials in sodium chlorite storage areas, as
well as chlorine dioxide generating areas, should be fire resistant such as concrete. Sodium chlorite
fires burn especially hot and produce oxygen as a byproduct, so special fire fighting techniques are
required to extinguish the fire. These firefighting techniques should be part of the safety plan and proper
equipment and supplies should be stored nearby. Temperatures in storage and generation areas should
be kept below 130 degrees Celsius.
10.9.2 Acute Health Risks of Chlorine Dioxide
Exposure to gaseous chlorine dioxide can cause shortness of breath, coughing, respiratory
distress, and pulmonary edema. The Occupational Safely and Health Administration (OSHA)
permissible exposure limit (PEL) is 0.1 ppm. Areas where chlorine dioxide is generated and stored
should have appropriate monitoring to detect leaks of chlorine dioxide or other chlorine containing
chemicals into the air. Proper ventilation and scrubbing systems should be installed. First aid kits and
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respirators should also be accessible outside the building. Operators should be trained to use the
respirators.
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References
APHA. 1998. Standard Methods for the Examination of Water and Wastewater, 20th edition,
American Public Health Association.
Aieta, E., and J.D.Berg. 1986. "A Review of Chlorine Dioxide in Drinking Water Treatment. " J.
AWWA. 78(6):62-72.
Chen, Y.S.R., OJ. Sproul, and A.J. Rubin. 1984. "Inactivation of Naegleria Gruberi cysts by
Chlorine Dioxide." EPA Grant R808150-02-0, Department of Civil Engineering, Ohio State
University.
Hoehn, R.C., A.A. Rosenblatt, and DJ. Gates. 1996. "Considerations for Chlorine Dioxide Treatment
of Drinking Water." Conference proceedings, AWWA Water Quality Technology
Conference, Boston, MA.
LeChevallier, M.W., et al. 1997. "Chlorine Dioxide for Control of Cryptosporidium and Disinfection
Byproducts." Conference proceedings, 1996 AWWA Water Quality Technology Conference
Part II, Boston, Massachusetts.
USEPA 1999. Alternative Disinfectants and Oxidants Guidance Manual. Washington, D.C.
USEPA, 1991. Guidance Manual for Compliance with the Filtration and Disinfection Requirements for
Public Water Systems Using Surface Water Sources. Washington, D.C.
Werdehoff, K.S, and P.C. Singer. 1987. "Chlorine Dioxide Effects on THMFP, TOXFP and the
Formation of Inorganic By-Products" J. AWWA. 79(9): 107.
White, Geo. Clifford. 1999. Handbook of Chlorination and Alternative Disinfectants, 4th edition,
John Wiley & Sons, Inc.
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11.0 Ozone
11.1 Introduction
Ozone is commonly used in drinking water treatment for disinfection and taste and odor control.
Ozone is a strong oxidant that can inactivate microorganisms, including Cryptosporidium, and also
oxidize and break down natural organic matter. It exists as a gas at room temperature and must be
generated on-site. Ozone reacts rapidly with organic and inorganic compounds and does not maintain
a residual over the time scales associated with secondary disinfection.
The Surface Water Treatment Rule (SWTR) and subsequent Stage 1 Disinfectants and
Disinfection Byproducts Rule (DBPR) and Interim Enhanced SWTR (ESWTR) all recognize the
capability of ozone to inactivate pathogens. As a result, there is much information and guidance
available on the application of ozone for disinfection, particularly in the following two guidance manuals:
• Guidance Manual for Compliance with the Filtration and Disinfection Requirements
for Public Water Systems Using Surface Water Sources (USEPA 1991) (commonly
referred to as the Surface Water Treatment Rule Guidance Manual).
- Describes how to calculate the CT value for ozone (CT is described in the next
section), including methodologies for determining the residual concentration (C) and
contact time (T).
- Includes ozone CT values for log-inactivation of Giardia and viruses.
• Alternative Disinfectants and Oxidants Guidance Manual (USEPA, 1999).
- Provides full descriptions of:
• ozone chemistry • byproduct production
• on-site generation • analytical methods
• primary uses and points • operational considerations
of application
The Surface Water Treatment Rule Guidance Manual and Alternative Disinfectants and
Oxidants Guidance Manual are available on EPA's website:
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The purpose of this chapter is to (1) describe what systems need to do to receive
Cryptosporidium treatment credit for disinfecting with ozone, (2) discuss design and operational
considerations that will assist water systems in deciding whether this toolbox option is a practical option
for their system, and (3) discuss key issues associated with using ozone as a disinfectant. This chapter
is organized as follows:
11.2 Credits - discusses Cryptosporidium inactivation credit systems can receive with the
addition of ozone, and relates CT to Cryptosporidium inactivation credit.
11.3 CT Determination - summarizes how CT is used to determine log inactivation credit for
the SWTR and highlights the changes in CT calculation methodologies from the SWTR
to the LT2ESWTR.
11.4 Monitoring Requirements - discusses monitoring requirements of both LT2ESWTR and
Stage 1 DBPR.
11.5 Unfiltered Systems LT2ESWTR Requirements - discusses Cryptosporidium
inactivation requirements that unfiltered systems must meet.
11.6 Toolbox Selection - discusses the potential advantages and disadvantages of ozone
processes.
11.7 Disinfection with Ozone - describes reaction pathways of ozone in water, and inorganic
and organic byproduct formation.
11.8 Design - discusses similarities and differences of different types of ozone generators and
contactors, general considerations in determining the locations of ozone addition, and
filter media and operating conditions of biologically active filters.
11.9 Safety Considerations in Design - discusses various safety considerations that should be
taken into account in the design of ozone generators.
11.10 Operational Issues - discusses how ozone disinfection and CT calculation are affected
by ozone demand, pH, temperature, and residual disinfectant in the distribution system.
11.2 Credits
Systems can receive between a 0.5 to 3.0 log Cryptosporidium inactivation credit with the
addition of ozone, depending on the ozone dose applied. The value of the Cryptosporidium
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inactivation credit that a system receives is determined by the CT or inactivation provided in the
treatment process. CT values are established to provide a conservative characterization of the dose of
ozone necessary to achieve a specified inactivation of Cryptosporidium. CT is defined as the product
of the disinfectant concentration and disinfectant contact time:
CT = Disinfectant (mg/L) x Contact Time (minutes)
• "T" is the time it takes the water to move from the point where the initial disinfectant
residual concentration is measured to the point where the final disinfectant residual
concentration is measured in a specified disinfectant segment
• "C" is the measured concentration of dissolved ozone in mg/L
The concept of regulating surface water treatment disinfection through CT was first introduced
in the SWTR. Tables relating Giardia and virus log inactivations with associated CT values, commonly
referred to as CT tables, were presented in the SWTR Guidance Manual. For the LT2ESWTR, EPA
developed CT values for Cryptosporidium inactivation by ozone (Table 11.1).
Table 11.1 CT Values for Cryptosporidium Inactivation by Ozone (40 CFR 141.730)
Log
credit
0.5
1.0
1.5
2.0
2.5
3.0
Water Temperature, °C1
<=0.5
12
24
36
48
60
72
1
12
23
35
46
58
69
2
10
21
31
42
52
63
3
9.5
19
29
38
48
57
5
7.9
16
24
32
40
47
7
6.5
13
20
26
33
39
10
4.9
9.9
15
20
25
30
15
3.1
6.2
9.3
12
16
19
20
2.0
3.9
5.9
7.8
9.8
12
25
1.2
2.5
3.7
4.9
6.2
7.4
1CT values between the indicated temperatures may be determined by interpolation.
If a utility believes that the CT values presented in Table 11.1 do not accurately represent the
conditions needed to achieve the desired level of inactivation in their system, they have the option of
conducting a site specific study to generate a set of CT tables for their facility. The study would involve
measuring actual Cryptosporidium inactivation performance under site conditions. If accepted by the
State, the CT tables generated by the site study would replace the tables given in this guidance for the
site at which the study was performed. Guidance on site specific studies of Cryptosporidium
inactivation is presented in Appendix A.
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11.3 CT Determination
The recommended methodologies and calculations for determining CT have two modifications
from the SWTR to the LT2ESWTR.
• For Cryptosporidium., EPA recommends that no inactivation credit be granted for the
first dissolution chamber due to the higher CT requirements of Cryptosporidium compared
to Giardia and virus. (This differs from the SWTR guidance manual, where EPA
recommends granting inactivation Giardia and virus credit for first chamber of an ozone
contactor, provided that the residual ozone concentration measured at the outlet from the
first contact chamber met minimum concentration levels.) The relatively small CT values
normally achieved due to oxidant demand in the first dissolution chamber and the resources
required for routine ozone monitoring would likely offset the benefit from the small
Cryptosporidium credit achieved.
• If no tracer study data are available for determining T, EPA recommends using the
continuous stirred tank reactor (CSTR) approach (described below) or the Extended-
CSTR approach (described in Appendix B). The T10/T ratios based on baffling
characteristics presented in Table C-5 of the SWTR Guidance Manual are based on
hydraulic studies of clearwells and basins. At this time, EPA is not aware of similar studies
for ozone contactors that could be used to develop comparable recommendations.
This guidance manual presents three methods for calculating CT:
• T10
Continuous stirred tank reactor (CSTR)
• Extended-CSTR
These methods differ in the level of effort associated with them and, in general, the ozone dose
required to achieve a given level of inactivation. Selecting the appropriate method(s) to use depends on
the configuration of the ozone contactor and amount of process evaluation and monitoring that a system
wishes to undertake. Combinations of two or more methods may also be used. For example,
contactors with multiple segments may have one or two segments with their CT calculated using either
the T10 or CSTR methods, while the CT for the remaining segment is calculated using the Extended-
CSTR approach. The T10 and CSTR are the simplest methods and are described in this chapter.
Appendix B provides more information for choosing the appropriate method and detailed guidance for
the Extended-CSTR method. A fourth method, the Segmented Flow Analysis approach, is under
consideration by EPA, but the details of the approach are not final. EPA is requesting comment on the
approach and any appropriate safety factors to ensure the inactivation credit calculated using the
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method is actually achieved (see section 11.11 for comment requests). Table 11.2 summarizes the
current methods, including describing the situations when their use is appropriate.
Table 11.2 Applicable Methods and Terminology for Calculating the
Log-lnactivation Credit
No Tracer Data
.2
"ro
Q
(D
o
ro
H
o
z
Section
Description
Terminology
Method for Calculating
Log-lnactivation
Restrictions
Chambers where ozone is added
First chamber
Other chambers
First Dissolution
Chamber
Co-Current or
Counter-Current
Dissolution
Chambers
No log-inactivation credit
is recommended
CSTR Method in each
chamber with a measured
effluent ozone residual
concentration
None
No credit is given to a
dissolution chamber unless a
detectable ozone residual has
been measured upstream of
this chamber
Reactive Chambers
> 3 consecutive
chambers
< 3 consecutive
chambers
Extended-CSTR
Zone
CSTR Reactive
Chamber(s)
Extended-CSTR Method
in each chamber
CSTR Method in each
chamber
Detectable ozone residual
should be present in at least 3
chambers in this zone,
measured via in-situ sample
ports. Otherwise, the CSTR
method should be applied
individually to each chamber
having a measured ozone
residual
None
Chambers where ozone is added
First chamber
Other chambers
First Dissolution
Chamber
Co-Current or
Counter-Current
Dissolution
Chambers
No log-inactivation is
credited to this section
T10orCSTR Method in
each chamberwith a
measured effluent ozone
residual concentration
Not applicable
No credit will be given to a
dissolution chamber unless a
detectable ozone residual has
been measured upstream of
this chamber
Reactive Chambers
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> 3 consecutive
chambers
< 3 consecutive
chambers
Extended-CSTR
Zone
T10 or CSTR
Reactive
Chamber(s)
Extended-CSTR Method
in each chamber
T10orCSTR Method in
each chamber
Detectable ozone residual
should be present in at least 3
chambers in this zone,
measured via in-situ sample
ports. Otherwise, the T1 0 or
CSTR method should be
applied to each chamber
having a measured ozone
residual
None
The remainder of this section describes how to calculate C for the T10 and CSTR methods and
then describes the T10 and CSTR methodologies.
11.3.1 MeasuringCforT10 and CSTR Methods
The methods for determining C have not been modified from those presented in the SWTR
Guidance Manual. The two methods for determining C are:
1) Direct measure of the concentration profile of dissolved ozone in each contact chamber
(described in section O.3.2 of the SWTR Guidance Manual)
2) Indirect prediction of the average C based on dissolved ozone measurements at the contact
chamber outlet (described in section O.3.3 of the SWTR Guidance Manual)
For the second method, predicting the average C based on outlet measurements, the
correlations presented in Table 11.3 are to be used for estimating C based on Cin and Cout
measurements, based on the flow configuration within the contact chamber. To be granted inactivation
credit for a chamber, its final ozone concentration should be above the detection limit (i.e., have a
positive Cout value).
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Table 11.3 Correlations to Predict C* Based on Outlet Concentration
Turbine
t^out
Co-Current Flow
Coutor(Cin+C0ut)/2
Counter-Current
Flow
Cout/2
Reactive Flow
t^out
* C - Characteristic concentration, used for CT calculation
Cout - Ozone residual concentration at the outlet from the chamber
Cin - Ozone residual concentration at the inlet to the chamber
11.3.2 T10 Method
The T10 method is appropriate for contactors with hydraulic conditions resembling plug flow.
Using the T10 approach, the contact time (T) is the time at which 90 percent of the water in the
contactor or segment has passed through the contactor. EPA recommends that tracer studies be used
to determine the T10 for ozone contactors. The SWTR Guidance Manual describes how to conduct a
tracer test.
CT can be calculated for an entire treatment process (e.g., an entire ozone contactor) or
broken into segments (e.g., individual contact chambers) and summed for a total CT value for all
segments. C is measured either at the end of a given segment or both the beginning and end of the
segment.
The following steps describe the CT calculation from measured C and T values for a segment
or the entire treatment process:
1) Calculate CTcalc by multiplying the measured C and T values.
2) From the CT table (Table 11.1), find the CT value for the log inactivation credit desired,
this is CTtable.
3) Calculate the ratio of CTcall/CTtable for each segment.
4) If a system has multiple segments, sum the CTcall/CTtable ratios for a total inactivation ratio.
5) If the ratio of CTcall/CTtable is at least 1, then the treatment process provides the level of log
inactivation that CTtable represents (log inactivation credit desired from step #2).
Example CT Calculation and Log Credit Determination using the T10 Method
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A water system employs a 4 chamber ozone contactor to achieve a 0.5-log Cryptosporidium
inactivation credit. The contactor is designed and operated as shown in the following diagram.
C4out = 0.0 mg/L
1
Chamber 1
Counter-Current
Oc°°
• »
9 O O
a a •
Chamber 2
Co-Current
O o °O O O
a a a • •
J
Chamb
Counter-
QO °o
• • — a-
1
Chamber 3
Counter-Current
Q 0 °0 0 0
• • a • a
Chamber 4
Reactive Flow
t
C10ut= 1.2 mg/L =
The water temperature is 5 degrees Celsius. Each chamber has a volume of 1,000 gallons.
Results from a tracer test showed the T10 for the entire contactor (i.e. through all 4 chambers) was 24
minutes.
The first step is to determine the ozone concentration for each chamber (segment). EPA
recommends that inactivation credit not be granted for the first chamber, therefore concentrations are
only calculated for Chambers 2, 3, and 4. Using Table 1 1 .2, C can be determined with the following
equations:
Chamber 2
Chamber 3
Chamber 4
C = (Ci
^"^ ^"^OV
c = cni.
Cout)/2 or C = C
out
11
Therefore for:
Chamber 2: C = (1.2 + 0.8) / 2 = 1.0 mg/L (this equation gives the higher C value)
Chamber 3: C = 0.9 / 2 = 0.45 mg/L
Chamber 4: C = 0.0mg/l
2) Calculate the T for each chamber.
The T10 of all four chambers is divided proportionally by volume among the four chambers.
This method cannot be used if the chambers with final concentrations of zero (non-detectable) are 50
percent or greater than the entire volume of the chambers. Only the last chamber had a non-detectable
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final concentration and that chamber is 25 percent the volume of all the chambers. Therefore the T10
can be extrapolated among the chambers to estimate individual T10 values.
T10 of each chamber = ^(V^/VT) = 24(1,000 gallons/4,000 gallons) = 6 min.
(In this example, the volume of each chamber is same therefore the T10 of each chamber is
simply one-fourth of the total T10.)
3) Calculate the CT for each chamber
Chamber 1: not calculated
Chamber 2: CT =1.0 mg/L x 6 min = 6.0 mg-min/L
Chamber 3: CT = 0.45 mg/L x 6 min = 2.7 mg-min/L
Chamber 4: CT = 0 mg/L x 6 min = 0 mg-min/L
4) Identify the CTtable for the log inactivation credit desired for each chamber. Calculate the
ratio of CTcalc to CTtable, and sum the ratios to get a total log inactivation ratio.
Chamber 2
Chambers
Chamber 4
CT^c
6.0
2.7
0
CTtabie for0.5-log
7.9
7.9
7.9
Total Log Inactivation Ratio
Ratio of CT^/CTfcbfe
0.76
0.34
-
1.10
The log inactivation ratio is at least 1, therefore this system achieves 0.5 log Cryptosporidium
inactivation credit.
11.3.3 CSTR Method
The CSTR method is recommended for contactors that experience significant back mixing or
when no tracer data is available. This method uses the hydraulic detention time of the ozone contactor,
as described below, for estimating the contact time. The CSTR method should be applied to the
individual chambers in the contactor.
For the CSTR approach, the CT table is not directly used and instead log inactivation is
calculated with the following equation:
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-Log (Mo) = Log (1 + 2.303k10 x C x HDT) Equation 11-1
where:
-Log (I/I0) = the log inactivation
k10 = log base ten inactivation coefficient (L/mg-min)1
C = Concentration from Table 11-2 (mg/L)
HDT = Hydraulic detention time (minutes)
Table 11.4 presents the k10 values for Cryptosporidium (k10 values are calculated from the CT table).
Table 11.4 Inactivation Coefficients for Cryptosporidium, Log base 10 (L/mg-min)
km
Water Temperature, °C
<=0.5
0.0417
1
0.0430
2
0.0482
3
0.0524
5
0.0629
7
0.0764
10
0.101
15
0.161
20
0.254
25
0.407
To interpolate between the temperatures in the table, the following equation can be used:
k10 = 0.0397 x (1.09757)1 Equation 11-2
In order to apply Equation 11-1, both C and HDT must be known. These two parameters can
be determined for individual chambers or for zones consisting of multiple, adjacent chambers. In
general, if the concentration is measured at 3 or more points in the contactor the Extended-CSTR
method will be used, so the CSTR method likely will not be applied when 3 or more zones (excluding
the first dissolution chamber) are defined.
EPA recognizes that, for many situations, either the CSTR and T10 method can be used to
calculate inactivation credit, and that they may generate two different estimates of log inactivation. EPA
recommends that systems use, and States accept, the higher estimate of the log inactivation credit.
However, systems should select one method to be used and use that method consistently.
Example - CT Calculation and Log Credit Determination using the CSTR Method with the
concentration measured for each chamber
\w is calculated from the CT table with the following equation: Log inactivation = k10 x CT
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A system employs a three chamber ozone contactor, with ozone addition in the first two
chambers. The second chamber is a counter-current flow dissolution chamber with influent and effluent
ozone concentrations of Cin = 0.3 mg/L and Cout = 0.3 mg/L. The effluent ozone concentration in the
third, reactive chamber is Cout = 0.2 mg/L. At 10° C, k10 = 0.1005 L/mg-min. The HDT for each
chamber = 20 minutes.
Chamber 1
Counter-Current
O o O O O
• • . . t
+
Chamber 2
Counter-Current
0 o °0 0 0
.. • . .
Chamber 3
Reactive Flow
t
C3out- 0.2 mg/L
C1out= 0.3 mg/L = C
2in
C2out = 0.3 mg/L
1) Determine the C values for each chamber
Chamber 1 No inactivation credit recommended
Chamber 2 C = Cout/2 = 0.3/2 = 0.15 mg/L
Chamber 3 C = Cout = 0.2 mg/L
2) Calculate the log inactivation for each chamber using Equation 11-1
Chamber 2 Log inactivation = Log(l + 2.303x0.1005x0.15x20) = 0.23
Chamber 3 Log inactivation = Log(l + 2.303xQ. 1005x0.20x20) = 0.28
3) Sum the log inactivations to determine the log credit achieved.
The total log-inactivation across the contactor is 0.23 + 0.28 = 0.51 log inactivation,
therefore 0.5 log credit achieved.
Example - CT Calculation and Log Credit Determination using the CSTR Method with the
concentration not measured for each chamber
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A system employs a four chamber ozone contactor, with ozone addition in the first two
chambers. The second chamber is a counter-current flow dissolution chamber with influent and effluent
ozone concentrations of Cin = 0.3 mg/L and Cout = 0.3 mg/L. The effluent ozone concentration in the
third, reactive chamber is unknown, and in the fourth, reactive chamber is 0.1 mg/L. At 10° C, k10 =
0.1005 L/mg-min. The HDT for each chamber = 20 minutes. Chambers 3 and 4 are considered one
zone, and the effluent concentration of Chamber 3 is assumed to be equal to that of Chamber 4.
C1 out= 0.3 mg/L = C2in C2 out = 0.3 mg/L
Chamber 1
Counter-current
o
O f
o o <
0
3°°o
4
Chamber 2
Counter-current
o o
o o o o° o
a ° °o o
i
Chambers
Reactive Flow
\
Chamber 4
Reactive Flow
4out
= 0.1 mg/L
1)
Determine the C values for each chamber
Chamber 1 No inactivation credit recommended
Chamber 2 C = C2 out/2 = 0.3 / 2 = 0.15 mg/L
Chamber 3 C = C4 out = 0.1 mg/L
Chamber 4 C = C4 out = 0.1 mg/L
2) Calculate the log inactivation for each chamber using Equation 11-1
Chamber 2 Log inactivation = Log(l + 2.303x0.1005x0.15x20) = 0.23
Chamber 3 Log inactivation = Log(l + 2.303x0.1005x0.1x20) = 0.17
Chamber 4 Log inactivation = Log(l + 2.303x0.1005x0.1x20) = 0.17
3) Sum the log inactivations to determine the log credit achieved.
The total log-inactivation across the contactor is 0.23 + 0.17 + 0.17 = 0.57 log
inactivation, therefore 0.5 log credit achieved.
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11.3.4 Extended CSTR Approach
The Extended CSTR approach requires the measurement of the ozone concentration at a
minimum of three points within the contactor These data are used to develop a predicted ozone
concentration profile through the contactor. The Extended CSTR approach generally results in lower
doses of ozone resulting in the same level of inactivation, when compared to the CSTR method.
Appendix B provides a complete description of the Extended CSTR approach.
11.4 Monitoring Requirements
11.4.1 LT2ESWTR
The LT2ESWTR (40 CFR 141.730) requires daily CT monitoring conducted during peak
hourly flow (40 CFR 141.729(a)). Since systems may not know when the peak hour flow will occur,
EPA recommends monitoring on an hourly basis. Contact time does not have to be determined on a
daily basis, only concentration. Systems should reevaluate contact time whenever they modify a
process and the hydraulics are affected (e.g., add a pump for increased flow, reconfigure piping).
The concentration of ozone must be measured with the indigo colorimetric method, Standard
Method 4500-O3 B (40 CFR 141.729(a)). Details on these methods can be found in Standard
Methods for the Examination of Water and Wastewater, 19th edition, American Public Health
Association, 1995. Appendix C provides information on sample collection, preparation and stability of
reagent, and calibration and maintenance of online monitors.
11.4.2 Stage 1DBPR
The Stage 1 DBPR requires all systems using ozone for disinfection or oxidation to take at least
one bromate sample per month for each treatment plant using ozone (See the Stage 1 DBPR, 40 CFR
141.132(b) for further information). Samples must be taken at the distribution system entry point when
the ozone system is operating under normal conditions. Systems may reduce monitoring from monthly
to quarterly if the system demonstrates that the annual average raw water bromide concentration is less
than 0.05 mg/1, based on monthly measurements for one year. The MCL for bromate if 10 |ig/l based
on a running annual average.
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11.5 Unfiltered System LT2ESWTR Requirements
The LT2ESWTR requires unfiltered systems to meet the following requirements (40 CFR
141.721(b)and(c)):
• Provide at least 2.0 log Cryptosporidium inactivation
• If their source water Cryptosporidium concentration is greater than 0.01 oocyst/liter then
the system must provide 3.0 log Cryptosporidium inactivation
• Use a minimum of two disinfectants to meet overall disinfection requirements
The requirements of the previous SWTR regulations still apply— achieve 3 log inactivation of
Giardia and 4 log inactivation of viruses, and maintain a disinfectant residual in the distribution system
(e.g., free chlorine or chloramines).
The monitoring requirements described in section 11.4 apply to unfiltered systems.
Additionally, unfiltered systems must meet the Cryptosporidium log-inactivation requirements every
day the system serves water to the public, except one day per calendar month (40 CFR 141.721(c)).
Therefore, if an unfiltered system fails to meet Cryptosporidium log-inactivation two days in a month, it
is in violation of the treatment technique requirement.
11.6 Toolbox Selection
Selecting ozone disinfection to receive Cryptosporidium inactivation credit for compliance with
the LT2ESWTR has cost, operational, and upstream and downstream process implications. The ozone
CT requirements for Cryptosporidium inactivation are significantly higher than for Giardia and virus,
and capital requirements could be substantial for a system seeking higher than 0.5 credit. As a result,
ozone is likely a better option for systems that will benefit from its other treatment effects. This section
discusses the potential advantages and disadvantages of ozone processes.
11.6.1 Advantages
Ozonation reduces many other contaminants and improves process performance, both directly
and indirectly. The indirect benefits are those where other aspects of the treatment process can be
improved or changed, resulting in a higher finished water quality. The advantages of ozone use include:
Total organic carbon (TOC) reduction
• Iron, manganese, and sulfide oxidation
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• Taste, odor, and color control
Trihalomethane (THM) and haloacetic acid (HAA) reduction with reduction in chlorine use
• Biological stability with biological filtration
11.6.2 Disadvantages
Considering only benefits from Cryptosporidium inactivation credit, the capital, operational,
and maintenance costs are relatively high compared to other toolbox options for similar credit,
especially for systems treating colder water. Other disadvantages include:
• Higher level of maintenance and operator skill required.
• Additional safety and containment issues with ozone contactors.
• Possible need for three-phase power which may not be compatible with some water
systems.
• Bromate formation (bromate is a regulated DBF).
• Upstream processes can cause fluctuations in ozone demand, thus affecting ozone residual
control.
• Assimilable organic carbon (AOC) production, which can contribute to biofilm growth in
the distribution system if not removed.
• High capital requirements to achieve CT requirements with low water temperatures (below
10 °C).
11.7 Disinfection With Ozone
11.7.1 Chemistry
Ozone decomposes spontaneously during water treatment by a complex mechanism that
involves the generation of hydroxyl free radicals (Hoigne and Bader 1983a and 1983b; Glaze et al.
1987). The hydroxyl free radicals are among the most reactive oxidizing agents in water, with reaction
rates on the order of 1010 - 1013 M'1 s'1 (Hoigne and Bader 1976). The half-life of hydroxyl free
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radicals is on the order of microseconds. Concentrations of hydroxyl free radicals can never reach
levels above 10'12 M (Glaze and Kang 1988).
When ozone is added to water, it reacts through two possible pathways (see Figure 11.1):
• Direct oxidation of compounds by molecular ozone in the aqueous phase.
Oxidation of compounds by hydroxyl free radicals produced during the decomposition of
ozone.
As indicated in Figure 11.1, the direct reaction with molecular ozone is relatively slow
compared to the hydroxyl reaction. However, the reaction with many aqueous species is still very rapid
compared to other disinfectants. The reaction mechanisms for microbial inactivation are poorly
understood, and there is conflicting research regarding the pathway more responsible for disinfection.
Park et al. (2001) researched the ozone reaction mechanisms using natural waters. The authors
described the ozone consumption rate with two steps: an initial rapid consumption step (ozone
consumed after a few seconds) followed by a slower ozone decay step. Results showed the ozone
consumption in the initial rapid reactions increased with increasing ozone dose (for raw water only; sand
filtered water showed no change) and increasing TOC levels. However, the slower decay reaction
rates decreased with increasing ozone dose. Consequently, the decay reaction was slower at higher
applied ozone doses. This is of importance for considerations to ozone dose requirements and residual
maintenance.
Figure 11.1 Reaction Pathways of Ozone in Water
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Direct Pathway
Slower
3 (aqueous)
Selective
Oxidation of Substrate and
Microbial Inactivation
Byproducts
Indirect Pathway
OH
Fast
Non- Selective
Oxidation of Substrate and
Microbial Inactivation
Byproducts
Fast
CO32andHCO3
co3- •
and HCO3 *
Byproducts
Direct oxidation is the dominant pathway at neutral pH and lower. While the direct pathway is
minor in the initial reaction, it becomes more dominant in the slower decay stages. At higher pH levels,
the formation of the hydroxyl radical is favored. Advanced oxidation processes induce conditions that
favor the hydroxyl radical formation and increase the rate of ozone decomposition. (See Chapter 7 of
the Alternative Disinfectants Guidance Manual for information on advanced oxidation processes).
11.7.2 Byproduct Formation
Reactions between ozone and natural organic matter (NOM) can form a variety of organic
byproducts including aldehydes, ketones, and acids. Inorganic byproducts are also formed. Bromide
reacts with ozone and hydroxyl radicals to form bromate, a regulated drinking water contaminant with
an MCL of 10 ug/1. Brominated organic compounds can also be formed, such as bromoform and
dibromoacetic acid, which are also regulated through the total trihalomethanes (TTHMs) and haloacetic
acids (HAAS) MCLs under the Stage 2 DBPR.
11.7.2.1 Bromate and Brominated Organic Compounds
Bromate and brominated organic compound formation is dependent on water quality and
treatment conditions, and only occurs in waters with bromide ion present. Bromate concentration
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increases with increasing pH, carbonate alkalinity, bromide concentration, ozone dose, and
temperature. However, attempts at reducing bromate formation by lowering pH may increase the
formation of brominated organic byproducts. The source water bromide concentration is an important
factor when considering adding ozone to a treatment process.
11.7.2.2 Non-Brominated Organic Compounds
Ozone reacts with NOM and breaks larger organic molecules down into simpler, more
biodegradable compounds such as aldehydes, ketones, and acids. These biodegradable organic
molecules are a food source for microorganisms and can affect biological growth in the distribution
system. Escobar and Randall (2001) conducted a case study at a ground water treatment plant that
was adding ozone to improve the aesthetic quality of the water. They found that the assimilable organic
carbon (AOC; the fraction of total organic carbon that is most readily utilized by bacteria)
concentrations significantly increased in the distribution system, however, with diligent maintenance of
chlorine residual biological growth was suppressed. Biofilters can be used to reduce the AOC
entering the distribution system. (Section 11.9.3 describes biofilters and their operation.)
11.8 Design
11.8.1 Generators and Contactors
There are several types of ozone generators and contactors. All generators use oxygen as a
raw material and convert it to ozone using electrochemical reactions. They differ from each other in the
source of oxygen used and the configuration of generator elements. Generators can use either air or
pure oxygen as an oxygen source. The Alternative Disinfectants and Oxidants Guidance Manual
describes the type of generators and contactors in detail.
11.8.2 Point of Addition
Raw water quality, turbidity, and ozone demand are commonly used to assess the possible
locations for adding ozone. The Alternative Disinfectants and Oxidants Guidance Manual
describes the water quality characteristics, advantages, and disadvantages of feed points at a raw water
location, after sedimentation, and after first-stage filtration of a two-stage process. The general
considerations are:
• Placing the ozone addition point further downstream ozone, particularly after physical
removal processes, generally reduces both the ozone demand and byproduct formation.
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• Adding ozone ahead of filtration allows any biodegradable organics, formed from the
ozonation of more recalcitrant TOC, to be removed by subsequent biological activity in the
filters. Also, solid-phase manganese and iron formed through oxidation by ozone can also
be removed by the filters.
In general, applying ozone prior to coagulation can enhance clarification. Applying prior to
filtration can also improve filtration performance; however these effects are site-specific and are likely
to depend on ozone dose.
Detrimental impacts on filtration operation have also been reported. Bishop et al. (2001)
investigated the effects of ozone on filtration with a raw water of moderate turbidity, TOC, iron, and
manganese concentrations. With ozone doses of 0.5 to 1.0 mg/L, turbidity increased in the contactors
with visible floe formation. At lower ozone doses, 0.16 to 0.35 mg/L, the turbidity still increased, but
not as much as the higher ozone dose. Because of the higher filter loadings, the duration of filter cycles
decreased. The authors believed the increased turbidity was partially due to solid-phase manganese
formation, and also likely due to the organic matter and residual metals.
11.8.3 Biologically Active Filters
When ozone oxidizes organic matter, the AOC in the water typically increases. Some systems
use biologically active filters to remove the AOC prior to chlorination and entry to the distribution
system. Microbes present in the upper portion of the filters consume the AOC, mineralizing them to
carbon dioxide and water, and reducing the amount available to microorganisms in the distribution
system (e.g. microorganisms in pipeline biofilm) and for DBF formation.
11.8.3.1 Media for Biologically Active Filters
Any filter media which has sufficient surface area for microbes to attach to can be used for
biological filtration. Slow sand, rapid sand, and GAC filters have all been successfully used for
biologically active filtration. Research indicates that both sand/anthracite and sand/GAC filters can
support the total amount of biomass to sufficiently remove organic components (LeChevallier et al.
1992; Krasner et al. 1993; Coffey et al. 1995). Wang and Summers (1996) and Zhang and Huck
(1996) have shown that the contact time with the biofilm is more important than the mass of biofilm
above a minimum level of biomass. Generally, the longer the contact time the greater the removal of
AOC. However, the increase in removal is not a linear-relationship; the removal rate decreases at
extended contact times (Zhang & Huck 1996). DBF precursors most often take longer to biodegrade
making extended contact times necessary if this is the process goal. This can be achieved with deep
anthracite filter beds or GAC filters (Prevost et al. 1990). The adsorption capacity of GAC provides a
longer time for the organic compounds to be consumed by the biomass as the particles are adsorbed by
the GAC (LeChevallier et al. 1992).
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11.8.3.2 Operating Biologically Active Filters
It is not necessary to seed a biological filter in order to obtain the necessary biological growth.
The organisms naturally present in the system are sufficient to obtain the needed growth. The only
additional requirement is to provide the conditions for biological growth. These conditions include
necessary food sources, sufficient dissolved oxygen, nutrients, proper pH and temperature. The
products from ozone and NOM reactions will provide the needed food for the microorganisms to
grow. The reaction of ozone also produces oxygen as one of its products, so the dissolved oxygen
concentration should be sufficiently high. Generally the pH and nutrient levels in most waters will also
be sufficient to allow the necessary growth. Organic removal will generally be higher at higher
temperatures. Several studies have found significantly decreased removal at temperatures below 15
degrees Celsius (Krasner et al. 1993; Coffey et al. 1995; Daniel and Teefy 1995).
In order to maintain biological growth, a disinfectant other than ozone cannot be added prior to
the filters. GAC filters can reduce small disinfectant residuals through reaction with the carbon,
however, this can lead to physical breakdown of the GAC and more frequent media replacement.
Using chlorinated or chloraminated backwash water can also be a concern. Studies have shown mixed
results with chlorinated backwash water, with some showing no effect and others showing significantly
reduced removal (Miltner et al. 1996; Miltner et al. 1995; Hacker et al. 1994; Reckhow et al. 1992;
McGuire et al. 1991). Short vigorous backwashes with a relatively low chlorine dose may be more
effective in maintaining biological filtration than less vigorous backwashes at longer times with higher
chlorine doses (Urfer et al. 1997).
11.9 Safety Considerations in Design
Ozone is a corrosive gas and according to Occupational Safety and Health Administration
(OSHA) Standards, exposure to airborne concentrations should not exceed 0.1 mg/L (by volume)
averaged over an eight-hour work shift.
Ozone generators should be housed indoors for protection from the environment, and to
protect personnel from leaking ozone in the case of a malfunction. Ventilation should be provided to
prevent excess temperature rise in the generator room, and to exhaust the room in the case of a leak.
Adequate space should be provided to remove the tubes from the generator shell and to service the
generator power supplies. Off-gas destruct units can be located outside if the climate is not too
extreme. If placed inside, an ambient ozone detector should be provided in the enclosure. All rooms
should be properly ventilated, heated, and cooled to match the equipment-operating environment.
11.10 Operational Issues
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When using ozone for disinfection, it is important to evaluate all the factors that could affect the
CT achieved. For example, if raw water quality fluctuates and ozone demand increases, without
adjusting the ozone dose, the residual concentrations will decrease. The system is now at risk of not
achieving the required level of CT. The ozone demand, pH, and temperature of the raw water, under
worst-case to best-case conditions, should be evaluated to determine their effect on ozone disinfection.
Systems should develop standard operating procedures (SOPs) for addressing changes in raw water
quality. The remainder of this section discusses the how these factors affect ozone disinfection and the
CT calculation.
11.10.1 Ozone Demand
The following water quality constituents contribute to ozone demand:
• Natural organic matter (NOM)—Ozone will oxidize organic matter, which includes
compounds causing taste and odor. As discussed in section 11.8.2 organic byproducts are
also produced.
Synthetic organic compounds (SOCs)—Some SOCs can be oxidized and mineralized
under favorable conditions.
• Bromide—Ozone will oxidize bromide forming, hypobromous acid, hypobromite ion,
bromate ion, brominated organics, and bromamines.
• Bicarbonate or carbonate ions—The hydroxyl radical reacts with bicarbonate and
carbonate ions and form carbonate radicals.
Ozone demand is particularly important to the CT calculation since it directly affects the residual
ozone used in the CT calculation. Ozone concentrations in water are generally monitored continuously
using an aqueous ozone residual monitor, and confirmed periodically using the batch indigo method. As
the ozone demand changes, the amount of ozone applied can be adjusted to maintain the desired CT.
11.10.2 pH
The pH of water does not have a significant effect on ozone disinfection capabilities. However,
there is strong impact of pH on ozone demand and decay rate. As pH increases, the hydroxyl radical
decomposition pathway is favored and the initial demand and rate of decay increase substantially.
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11.10.3 Temperature
The CT requirements are based on temperature; as temperature decreases, the CT required to
achieve a given level of inactivation increases. Conversely, the rate of ozone decay decreases as
temperature decreases, generally resulting in a higher CT for a given ozone dose. The ozone process
should be designed to provide the necessary log inactivation under all conditions. Standard operating
procedures (SOPs) should also describe process adjustments required to operate at the lowest water
temperatures experienced by the system in the past 10 years.
11.10.4 Maintaining Residual Disinfectant in the Distribution System
It is necessary to maintain a residual in the distribution system to prevent microbial regrowth.
Because of the reactive nature of ozone, its residual tends to dissipate within minutes and cannot be
relied upon to maintain a disinfectant throughout the distribution system. Therefore, a secondary
disinfectant must be used, usually either chlorine or chloramines.
11.11 Request for Comment on Segregated Flow Analysis
As mentioned in section 11.3, EPA is evaluating the segregated flow analysis (SFA) to estimate
CT for ozone disinfection. The SFA approach is based on an assumption that the residence time
distribution (RTD) of an ozone contactor is sufficient to completely describe the hydrodynamics within
the contactor (i.e., zero micro-mixing occurs). If micro-mixing does occur, then the SFA approach
may overestimate the inactivation of microorganisms. The degree to which inactivation may be
overestimated depends on several factors including the predicted ozone decay, the predicted
inactivation, and the extent that the hydrodynamics within the contactor deviate from ideal plug-flow
conditions (as indicated by the RTD).
Incorporating micro-mixing calculations into the SFA is quite complicated, and likely
impractical for many systems. EPA requests comments on the SFA approach and the following
questions:
1. Should the impact of micro-mixing be considered?
2. Can a worst case scenario, incorporating reactor configuration, reaction kinetics and complete
micro-mixing be developed?
3. Can appropriate safety factors be established to ensure the SFA approach does not overestimate
inactivation?
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References
Bishop, M. M., Qiao, F., Iversen, G., and Carter, G.C. 2001. "Intermediate Ozonation for
Cryptosporidium Inactivation and Effects on Filtration". AWWA WQTC Proceedings.
Coffey, B.M., S.W. Krasner, M.J. Sclimenti, P.A. Hacker, and J.T. Gramith. 1995. A Comparison of
Biologically Active Filters for the Removal of Ozone By-Products, Turbidity and Particles. In Proc.
AWWA WQTC. Denver, CO: AWWA.
Daniel, P., and S. Teefy. 1995. Biological Filtration: Media, Quality, Operations, and Cost. In Proc.
AWWA Annual Conf. Denver, CO: AWWA.
Escobar 1C. and A.Randall. 2001. "Case Study: Ozonation and Distribution System Biostability." J.
Glaze, W.H., et al. 1987. "The Chemistry of Water Treatment Processes Involving Ozone, Hydrogen
Peroxide, and Ultraviolet Radiation." Ozone Sci. Engrg. 9(4): 33 5.
Glaze, W.H., and J.W. Kang. 1988. "Advanced Oxidation Processes for Treating Groundwater
contaminated with TCE and PCE: Laboratory Studies." J. AWWA. 88(5): 57- 63.
Hacker, P.A., C. Paszko-Kolva, M.H. Stewart, R.L. Wolfe, and E.G. Means. 1994. Production and
Removal of Assimilable Organic Carbon Under Pilot-Plant Conditions through the Use of Ozone and
PEROXONE. Ozone Sci. Eng., 16(3): 197-212.
Hoigne J., and H. Bader. 1983 a. "Rate Constants of Reaction of Ozone with Organic and Inorganic
Compounds in Water - 1. Non-dissociating Organic Compounds." Water Res. 17:173-183.
Hoigne J., and H. Bader. 1983b. "Rate Constants of Reaction of Ozone with Organic and Inorganic
Compounds in Water - n. Dissociating Organic Compounds." Water Res. 17: 185-1 94.
Hoigne J. and H. Bader. 1976. Role of Hydroxyl Radical Reactions in Ozonation Processes in
Aqueous Solutions, Water Res. 10: 377.
Krasner, S.W., W.H. Glaze, H.S. Weinberg, et al. 1993. "Formation of Control of Bromate During
Ozonation of Water Containing Bromide." J. AWWA. 85(5):62.
LeChevallier, M.W., W.C. Becker, P. Schorr, and R.G. Lee. 1992. "Evaluating the Performance of
Biologically Active Rapid Filters." J. A WWA . 84(4) : 1 3 6- 1 46 .
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Chapter 11 - Ozone
McGuire, MJ. et al. 1991. Pilot-scale Evaluation of Ozone and PEROXONE (90951). AWWARF.
Denver, CO.
Mltner, R.J., R.S. Summers, N.R. Dugan, M. Koechling, and D.M. Moll. 1996. A Comparative
Evaluation of Biological Filters. In Proc. AWWA WQTC. Denver, CO: AWWA.
Mltner, R.J., R.S. Summers, and J.Z. Wang. 1995. Biofiltration Performance: Part 2, Effect of
Backwashing. Jour. AWWA, 87(12):64.
Park, H., Hwang, T., Kang, L, Choi, H, and Oh, H. 2001. "Characterization of Raw Water for the
Ozone Application Measuring Ozone Consumption Rate". Water Research (35) (11) p. 2607-2614.
Prevost, M., R. Desjardins, D. Duchesne, and C. Poirier. 1990. Chlorine Demand Removal by
Biological Activated Carbon Filtration in Cold Water. In Proc. AWWA, WQTC. Denver, CO:
AWWA.
Reckhow, D.A., I.E. Tobiason, M.S. Switzenbaum, R. McEnroe, Y. Xie, X. Zhou, P. McLaughlin,
and HJ. Dunn. 1992. "Control of Disinfection Byproducts and AOC by Pre-Ozonation and
Biologically Active In-Line Direct Filtration." Conference proceedings, AWWA Annual Conference,
Vancouver, British Columbia.
Urfer, D., P.M. Huck, S.DJ. Booth, and B.M. Coffey. 1997. Biological Filtration for BOM and
Particle Removal: A Critical Review. Jour. AWWA, 89(12):83.
Wang, J., and R.S. Summers. 1996. Biodegradation Behavior of Ozonated Natural Organic Matter in
Sand Filters. Rev. Sci. Eau, 1:3.
Zhang, S., and P.M. Huck. 1996. Biological Water Treatment: A Kinetic Modeling Approach. Wat.
., 30(5): 1195.
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12.0 Demonstration of Performance (OOP):
Microbial Removal
12.1 Introduction
The purpose of the "demonstration of performance" (DOP) toolbox component is to allow a
system to demonstrate that a plant, or a unit process1 within a plant, should receive a higher
Cryptosporidium treatment credit than is presumptively awarded under the LT2ESWTR. Presumptive
treatment credits are applicable to granular media filtration plant types indicated in Table 12.1 that
comply with the provisions of the Interim Enhanced Surface Water Treatment Rule (IESWTR) and
Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) (40 CFR 141.720). These
credits are also applicable to unit processes in the microbial toolbox when they meet specified design
and operational criteria, as discussed in other chapters of this manual.
Table 12.1 Filtration Plant Types Eligible for DOP
Plant Type
Conventional
Slow Sand Filtration
Diatomaceous Earth
Softening/Granular Media
Filtration
Direct Filtration
Minimum Elements of Process Train
Coagulation/Flocculation
Sedimentation
High Rate Granular Media Filtration
Slow Sand Filtration
Diatomaceous Earth Filtration
Single-Stage Lime Softening
High Rate Granular Media Filtration
Coagulation/Flocculation
High Rate Granular Media Filtration
Where a system can demonstrate that a plant, or a unit process within a plant, consistently
achieves a Cryptosporidium treatment efficiency greater than the presumptive credit specified in the
LT2ESWTR, the State may allow the system to receive a higher Cryptosporidium treatment credit for
compliance with the LT2ESWTR (40 CFR 141.727(c)). To demonstrate the higher level of
Cryptosporidium treatment, systems should conduct a site-specific study using a protocol approved by
the State. This study should account for all expected operating conditions and, at the discretion of the
EPA requests comment on how a system would conduct a DOP of a unit process while ensuring the other
parts of the treatment process were achieving their assumed Cryptosporidium treatment. For example, maximizing
removal in a pre-sedimentation basin can cause reduced removal in the subsequent sedimentation basin and filters.
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State, determine ongoing monitoring and/or performance requirements to ensure conditions under which
the DOP was awarded are maintained during routine operations.
In general, the term "treatment" in the LT2ESWTR refers to both physical removal and
inactivation of Cryptosporidium. Treatment credits discussed in this chapter pertain to physical
removal by the process trains listed in Table 12.1 (or individual components of these trains), pre-
sedimentation, bank filtration, secondary filtration, and two-stage softening. Treatment credits for
physical removal by membranes and bag and cartridge filtration are addressed in the Membrane
Filtration Guidance Manual and Chapter 8 of this manual, respectively. Inactivation of
Cryptosporidium by chlorine dioxide, ozone, and UV may also be used to provide additional
treatment credits, as discussed in Chapters 10, 11, and 13 of this manual.
This chapter provides guidance for implementing the DOP toolbox option and is organized as
follows:
12.2 LT2ESWTR Compliance Requirements - discusses DOP treatment credit with respect
to other toolbox options and reporting requirements.
12.3 Toolbox Selection Considerations - describes selection considerations for plants to
consider before conducting a DOP study, the duration of a DOP study, and an
approach for conducting a DOP study.
12.4 DOP Criteria Development - discusses key issues of DOP design including process
evaluation criteria, selection of performance indicators, and full-scale versus pilot-scale
testing.
12.5 Demonstration Protocol - discusses the minimum elements that should be included in
the DOP protocol - DOP test matrix, DOP monitoring plan, DOP implementation, and
data analysis and reporting.
12.2 LT2ESWTR Compliance Requirements
12.2.1 Credits
The LT2ESWTR does not specify how treatment performance must be demonstrated; however
the protocol used must be approved by the State (40 CFR 141.727(c)). Determination of an increased
Cryptosporidium treatment credit will be made by the State.
The LT2ESWTR does not allow systems to claim presumptive credit for the toolbox options
listed below, if that component is included in the DOP credit (40 CFR 141.727(c)(2)).
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• Presedimentation • Membrane filters
• Two-stage lime softening • Bag and cartridge filters
• Bank filtration • Second stage filtration
• Combined or individual filter
performance
For example, if a plant receives a DOP credit for a treatment train, the system may not also receive
credit for a presedimentation basin or achieving the lower finished water turbidity of the combined filter
performance option.
States may award a lower level of Cryptosporidium treatment credit towards compliance for
the LT2ESWTR to a system where, based on site-specific information, a plant or a unit process
achieves a Cryptosporidium treatment efficiency less than a presumptive credit specified in the
LT2ESWTR (40 CFR 141.727(c)(l)).
12.2.2 Reporting Requirements
The LT2ESWTR requires results from the testing be submitted no later than [date 72 months
after promulgation] for large systems and [date 102 months after promulgation] for small systems (40
CFR 141.730).
The State may require systems to report operational data on a monthly basis to verify that
conditions under which DOP credit was awarded are maintained during routine operation (40 CFR
141.730).
12.3 Toolbox Selection Considerations
The DOP toolbox option is intended for plants that operate at a high level of performance. A
system should review existing performance data to verify that it can meet high performance levels under
a range of operating conditions (including filters out of service, returning to service, and flow rate
changes) before conducting a DOP study. EPA recommends systems achieve less than 0.1 NTU in
each individual filter effluent as an indicator for considering whether the DOP option is practical.
Before applying the DOP approach to an individual unit process, facilities should carefully
consider the potential advantages and disadvantages of such an approach. The microbial toolbox
allows for treatment credits for unit processes based on specified design and/or operational criteria
described in other chapters of this manual. It is possible that a detailed DOP program may result in a
lower credit than already granted by the LT2ESWTR.
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A DOP study should be conducted for a minimum of one year. Systems should have a
contingency plan for achieving compliance with the LT2ESWTR if the DOP does not provide the
anticipated credit.
12.3.1 Overview of the Demonstration Protocol
This chapter presents one approach for conducting a DOP study. Other approaches or
modifications to this approach may be approved by the State. Major elements of the DOP protocol
include the following:
• Development of DOP evaluation criteria and test matrix
• DOP implementation
• Data analysis and reporting
Figure 12.1 presents a flowchart relating these elements to the overall microbial toolbox framework.
Each of these topics is discussed in detail in this chapter.
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Chapter 12 - Demonstration of Performance (DOP): Microbial Removal
Figure 12.1 Flowchart for DOP Protocol
BIN CLASSIFICATION
MICROBIAL TOOLBOX
SIKAItbY
ADD DISINFECTION
OR
ALTERNATIVE
PHYSICAL REMOVAL
TECHNOLOGIES
DOP EVALUATION
CHIItHIAANU ItS I
MATRIX
DOP IMPLEMENTATION
T
DATA ANALYSIS
AND
REPORTING
REQUEST TREATMENT CREOfT
\
\
\
DEMON3TATION
OF PERFORMANCE
POP)
/ CONVENTIONAL
/ FILTRATION
/ TECHNOLOGIES
12.4 DOP Criteria Development
Source water Cryptosporidium levels and water quality characteristics vary from system to
system. Accordingly, DOP programs should be tailored to address site-specific process issues
associated with each water treatment plant (WTP). Major questions that should be resolved during the
design of the DOP include (but are not limited to) the following:
• What are the governing process evaluation criteria and treatment objectives?
• What microorganism or surrogate parameters) should be used to demonstrate removal
efficiency of Cryptosporidium^
• Should the DOP be conducted at full-scale or pilot-scale?
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Each of these questions is addressed in the following sections.
12.4.1 Process Evaluation Criteria
Process evaluation encompasses the treatment objectives of the plant, influent water quality,
system demand, and operating conditions or treatment techniques. The DOP plan should address all
critical operating conditions, whether conducted in full-scale or pilot-scale. Influent water quality, flow
rates, process configurations, and operating conditions need to be clearly defined during the
development of the DOP plan. Common process evaluation criteria are discussed in this section.
12.4.1.1 Treatment Objectives
The DOP toolbox option primarily relates to Cryptosporidium removal by physical methods
such as clarification and filtration. However, WTPs are tasked to remove or control multiple
contaminants in the source water besides Cryptosporidium. The impact of operational strategies and
treatment methods for other contaminants on the efficiency of Cryptosporidium removal should be
considered during the DOP criteria development stage. The system should not change its operational
strategy between the DOP study conditions and routine operation after the study has ended—the DOP
credit is based on the operational strategy used in the study. For example, a system that uses enhanced
coagulation throughout the study period should also use it during routine operation for compliance with
the LT2ESWTR.
Other examples of treatment techniques that can affect Cryptosporidium removal and thus
should be considered in the development stage include the following:
• Prechlorination may be used to enhance floe formation (and Cryptosporidium removal) in
filtration trains. However, prechlorination may also promote trihalomethane (THM) and
haloacetic acid (HAA) formation. Therefore, prechlorination doses used during the DOP
study should be set to balance floe and disinfection byproduct formation. Operational
guidelines should be documented in the DOP plan.
Granular media filter run times may be extended to increase unit filter run volumes (UFRVs)
and filter efficiency. However, increased UFRVs also increase the potential for
Cryptosporidium breakthrough. Maximum UFRVs should be established to minimize
Cryptosporidium breakthrough.
• Alternative coagulation strategies may be used to enhance Cryptosporidium removal in
granular media filters but may also result in post-filtration flocculation that can cause
deposition or scaling in water distribution systems. Coagulant dosing rates should be set
during the DOP study to minimize downstream floe formation.
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Additionally, if a treatment process or plant technique is used intermittently for a seasonal or
sporadically occurring contaminant, this treatment should also be used as needed during the DOP
study, consistent with routine operation.
12.4.1.2 Influent Water Quality Characteristics
Source water quality characteristics that may affect Cryptosporidium removal efficiencies
should be identified. These will depend on the treatment processes employed and may include (but are
not limited to) turbidity, pH, alkalinity and temperature. Critical (or worst-case) ranges for these
parameters that are anticipated over the plant design life or permit period should be clearly defined.
The demonstration study should include tests run under the worst-case source water conditions. In
pilot-scale DOP studies, raw source water can be modified to simulate worst-case water qualities.
12.4.1.3 System Flow Rate
The system flow rate or range of flow rates to be evaluated during the DOP should be clearly
defined. Where possible, plant performance should be demonstrated for the critical flow condition that
defines permitted plant capacity (e.g., peak instantaneous flow or peak daily flow). For full-scale
studies, this may not be feasible for facilities that operate significantly below permitted or maximum
capacity. For pilot-scale studies, the range of system unit process flow rates should replicate the full-
scale low, intermediate, and maximum flow and recycles rates.
12.4.1.4 Plant Operating Conditions
WTP operations can vary significantly over the course of the demonstration period due to
various factors including, but not limited to, raw water quality, system flow rate, and maintenance
activities. The critical operating conditions that may impact Cryptosporidium removal at the WTP
should be defined. Issues to consider include the following:
• What are the normal and worst-case operating conditions for each unit process with
respect to Cryptosporidium removal?
• How many process trains or elements are normally in service? How will the plant perform
when units are out of service for maintenance and repair, thereby increasing unit process
flow rates (particularly in filters)?
• What is the process control strategy for chemical addition? How does this relate to
Cryptosporidium removal?
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• What is the process control strategy for filter operations? How does this relate to
Cryptosporidium removal?
• How will the plant's recycle, backwash, and filter-to-waste schemes affect
Cryptosporidium removal?
In the case of pilot-scale studies, performance demonstrations should replicate full-scale
operating conditions in any respect that may influence Cryptosporidium removal.
12.4.2 Selection of Performance Indicators
Although the LT2ESWTR mandates treatment controls for Cryptosporidium, it is not currently
feasible to demonstrate actual Cryptosporidium removal at full-scale facilities. In most cases, influent
Cryptosporidium levels are not consistently high enough to demonstrate significant (such as 4 log)
removal across the process train. Raw water spiking of Cryptosporidium is not a feasible option at
full-scale facilities due to the potential health risk to system users and the number of oocysts required.
Consequently, alternative indicators of Cryptosporidium removal will be needed for facilities that plan
to conduct DOP studies at full-scale.
12.4.2.1 Surrogate Parameters for Cryptosporidium
EPA has reviewed a number of studies that suggest aerobic bacteria spores are a suitable
indicator of Cryptosporidium removal in conventional treatment trains (coagulation, flocculation,
sedimentation and filtration). Some characteristics of aerobic spores (as summarized by Cornwell et
al., 2001) are:
• Naturally occurring (Nieminski and Bellamy 2000, Jakubowski et al. 1996).
• Do not pose health risks (Jakubowski et al. 1996, Rice et al. 1996).
• Can be detected at low concentrations (< 1 cfu/100 mL).
• Are slightly smaller than Cryptosporidium oocysts (Rice et al., 1996).
• Spore removal by water treatment is a conservative indicator of Cryptosporidium removal
(Rice et al. 1996, Dugan et al. 1999, Nieminski and Bellamy 2000, Emelko 2001).
• Reduction of indigenous spores by inactivation is expected to be negligible in comparison
with removal of spores by physical processes (Jakubowski et al. 1996, Rice et al. 1996).
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• Aerobic spores do not undergo re-growth during treatment.
Although aerobic spores appear to be a suitable indicator for Cryptosporidium removal in
filtration plants, raw source water spore concentrations will likely not be high enough throughout the
study period to demonstrate high log removal across a full-scale treatment train.
The State may accept alternative indicators for Cryptosporidium; however, they should not be
more easily removed than Cryptosporidium. The surrogate parameter should give a direct view of
removal and should be an element that is not created in the plant (e.g., particle counts caused by
chemical precipitation). Furthermore, the method of measurement should be sensitive enough to detect
temporal variations in the parameter. Parameters such as turbidity or particle counts may be used in the
DOP study, but are not suitable as stand-alone surrogates.
12.4.2.2 Long-Term Performance Indicators
As discussed previously, plants that implement a DOP plan should document long-term
performance of filtration facilities for turbidity and/or particle count reduction. While turbidity and
particle counts are not suitable as stand-alone indicators for full-scale Cryptosporidium removal, such
data can be used to identify changes in the filtration performance.
It is recommended that individual filter efficiency be monitored frequently to identify differences
in individual filter performance. This will allow the plant to assess temporal variations in filter effluent
quality and will provide improved process control.
12.4.3 Full-Scale Versus Pilot-Scale Testing
In general, full-scale testing is preferred over pilot-scale testing since the performance of
existing process trains is demonstrated directly. However, full-scale studies may not be feasible for
many facilities for the following reasons:
• Influent Cryptosporidium levels will not be high enough to demonstrate high log removal.
Likewise, influent aerobic spore concentrations may not be high enough to demonstrate
significant log removal.
• Full-scale spiking with aerobic spores may not be feasible due to larger flows.
• Facilities may operate well below design or permitted flow capacity for the entire study
period.
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• Demonstration of worst-case operating conditions at full-scale may be difficult to plan,
especially with regard to raw water quality and flow rates.
The major concern with the use of pilot-scale testing is the uncertainty associated with scale-up
of pilot results to predict the performance of full-scale systems. Other potential limitations of pilot-scale
studies are:
• Pilot-scale data generally represent steady-state conditions; however, sudden changes in
flow or water quality may have a significant effect on Cryptosporidium removal; such
changes are difficult to capture in a pilot-scale plant.
• Pilot-scale plants generally have much tighter process controls and higher levels of attention
than full-scale plants; and thus, may not be indicative of actual full-scale performance.
• A pilot-scale plant cannot represent expected individual differences between multiple filters
in a full-scale plant.
• Particle loadings to the treatment process in a pilot-scale study may be much higher than
actual full-scale loadings, and thus, may not represent actual operating conditions.
• It may be too difficult to construct a pilot plant that represents the entire full-scale process
train.
Pilot system dimensions and flow rates should be sufficiently large to minimize scale-up issues.
Some recommended guidelines for pilot filter sizing include the following (USEPA 1991):
• Unit filtration rate in the pilot system should be identical to that of the full-scale plant.
• Pilot filter diameter should be greater than or equal to 100 times the media diameter.
• Media diameter and depth should be identical to that of the full-scale system.
Pilot systems should also incorporate all major process elements of the full-scale process train,
including chemical addition systems and recycle streams. Such systems must be able to simulate flow
rate and water quality perturbations (i.e., temporal disturbances to steady state conditions).
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Chapter 12 - Demonstration of Performance (DOP): Microbial Removal
12.5 Demonstration Protocol
Once the DOP criteria have been developed, the DOP protocol can be formulated. This
section outlines the minimum elements that should be included in the DOP protocol. Participation from
the governing regulatory agency should be solicited during the DOP protocol development phase.
12.5.1 DOP Test Matrix
The first step in the formulation of the specific DOP protocol is the development of a matrix of
test conditions to be evaluated during the DOP period. These test conditions should be formulated to
assess Cryptosporidium removal (or other suitable parameters) under a range of normal and worst-
case scenarios. The DOP matrix should clearly define specific test scenarios to be evaluated,
incorporating the following criteria:
• Source water quality ranges- including minimum/maximum limits for critical water quality
parameters that influence Cryptosporidium removal in the plant.
• Influent flow rates- including the maximum flow rate that defines plant capacity.
• Operating scenarios- including all operations that may cause process upset in the treatment
train (e.g., events that cause temporal changes in water quality, and flow loadings to
process units). These operations include, but are not limited to: filter backwashing, filter-to-
waste practices, intermittent recycles, returning filters to service, and routine maintenance
practices.
Critical influent flow ranges and operating conditions should be identified during the DOP
criteria development phase, as described in section 12.2. The demonstration period should be at least
one year, and should encompass all critical operating conditions. An example test matrix format is
presented in Table 12.2.
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Table 12.2 Example DOP Test Matrix
Scenario
S1
S2
S3
S4
S5
Condition
(Normal or
Worst-Case)
Normal
Normal
Worst Case A
Worst Case B
Worst Case C
Influent Concentration
Range
Surrogate
Average
Average
Average
High
Low
Turbidity
Average
Average
Average
High
Low
Flow
Rate
Range
Average
Average
High
Average
Average
Units in
Servic
e
4 (All)
3
3
3
3
Backwash
Conditions
Date of
Scenario
Test
12.5.2 DOP Monitoring Plan
The DOP involves sampling and analysis of Cryptosporidium indicators in the raw source
water and filtration train effluent over the course of a demonstration period defined by the DOP test
matrix. Once the test matrix is established, the DOP monitoring plan should be formulated to define the
following protocol details:
• Monitoring locations
• Test parameters (field and laboratory)
• Monitoring frequency
• Quality assurance/quality control (QA/QC) procedure for/during sampling
A sample DOP monitoring plan is presented in Table 12.3.
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Table 12.3 Example OOP Monitoring Plan
Monitor
Event
Number
1
2
3
52
Date
Weekl
Week 2
WeekS
Week 52
Test Scenario
ID
(see
Table 12.2)
S1
S3
S2
S4
Effluent Sample LocationsA
Filter 1
X
X
X
X
Filter 2
X
X
X
Filters
X
X
X
X
Filter 4
X
X
X
Number of Samples per Location
Crypto/
Aerobic
Spores
2B
1
1
2B
Particle
Count
1
1
1
1
PH
1
1
1
1
Temp.
1
1
1
1
A- Influent sample location identical for all test scenarios
B- duplicate samples
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12.5.2.1 Sampling Location
Paired samples should be collected from the plant influent (raw source) and the combined filter
effluent for a DOP study of an entire plant. The plant influent location should be before the pre-
sedimentation basins and off-stream storage facilities and follow any process recycles added prior to
the first major unit process element of the treatment train. For pilot studies involving microbial dosing,
the influent monitoring point should follow complete mixing of the source water and injection stream.
The plant effluent sample should be comprised of composite samples from the effluent of all operating
filters. It is recommended that at least five sample pairs (influent/effluent) be collected during each test
run to capture temporal changes in filter and effluent quality.
12.5.2.2 Monitoring Parameters
Samples should be analyzed for all parameters required to assess Cryptosporidium removal in
the treatment trains, as discussed in section 12.2. Parameters such as pH, alkalinity, temperature, and
turbidity should be measured and recorded in the field.
12.5.2.3 Monitoring Frequency
A monitoring event is defined as a paired (concurrent) sampling of plant influent and filter
effluent samples. At a minimum, monitoring should be performed once per week for 52 consecutive
weeks. More frequent monitoring may be required to capture all critical operating scenarios defined by
the DOP Test Matrix. The DOP database should be sufficiently large to allow for statistical analysis.
If a DOP credit is issued by the State, the credit will be conditional on continuing
demonstration of a higher level of performance. The DOP Monitoring Plan can be modified to
document continuing performance at a reduced sampling frequency. However, sampling events should
still capture critical operating scenarios.
12.5.2.4 Quality Assurance/Quality Control
Quality assurance/quality control (QA/QC) sampling should be performed to allow assessment
of data variability and quantification errors due to sample collection procedures and analytical methods.
At a minimum, duplicate samples should be collected during one monitoring event per month.
12.5.3 DOP Implementation
The DOP should commence only after the State approves the DOP test matrix and monitoring
protocol. The DOP plan should be administered by a qualified water treatment plant operator or water
process engineer. Data review and QA/QC practices should be conducted routinely to ensure that the
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objectives of the DOP program are met. Particular attention should be given to verification of the plant
operating conditions (influent loadings, unit process loadings, etc.) to confirm that all critical operating
scenarios identified in the DOP test matrix are evaluated during the demonstration period.
Personnel responsible for implementing the DOP monitoring plan should be properly trained in
sample collection techniques, QA/QC procedures and operational data acquisition. Specific
procedures should be used to collect and analyze samples as described in the following sections:
Sample collection and preservation methods
• Analytical methods
• Microbial dosing methods (for pilot tests)
• Documentation procedures
12.5.3.1 Sample Collection Methods
Influent and effluent samples should be collected in a manner that is representative of the entire
cross sectional flow at each monitoring point. If possible, monitoring points should be located in
straight sections of pipe or channel well downstream of bends. For open channel flows, samples should
be collected from mid-depth and mid-width of the channel. For pipe flow, samples should be collected
from the tap directly into the sample containers. In each case, the sampling method should not reduce
or prevent transfer of suspended solids from the process stream to the sample container. Parameters
such as pH, turbidity, alkalinity and temperature should be directly measured in the field.
All samples should be grab samples. The individual effluent grab samples should not be
combined to make up composite samples.
12.5.3.2 Analytical Methods
The analytical methods for monitoring Cryptosporidium under the LT2ESWTR are prescribed
in the Public Water System Guidance Manual for Source Water Monitoring under the Long-Term
2 Enhanced Surface Water Treatment Rule. Analytical methods for all other water quality
parameters should be performed in accordance with Standard Methods for the Examination of
Water and Wastewater, 20th edition, or the most recent edition.
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12.5.3.3 Microbial Dosing
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For pilot testing that involves spiking of Cryptosporidium, aerobic spores or other indicators,
microbial dosing procedures should be clearly established. Guidelines for microbial stock preparation
and dosing are presented in this section.
A concentrated mixture of microorganisms should be prepared and fed to the raw source
stream at a known feed rate, based on the microbial density in the concentrated stock, the flow rate of
the pilot system, and the desired microorganism concentration in the pilot system. An equation that
describes this relationship is:
C
_ I pilot ->
feed - | - ~ - Cpilot Equation 12.1
where:
Cpiiot = the microbial concentration in the pilot system
Cfeed = the microbial concentration in the concentrated stock solution
Qpiiot = the flow rate of the pilot system (includes all process recycles present at the
influent feed point, if applicable)
Qfeed = the flow rate of the concentrated stock solution
For each trial, the test microorganisms should be completely mixed in a volume of raw water
sufficient to supply the pilot plant for the duration of the experiment. The tank containing the suspension
of test microorganisms should be continuously mixed for the duration of each experiment to promote
homogeneity of the mixture. The concentrated stock should be delivered by a positive displacement
pump (e.g., peristaltic) to the main process flow at a flow rate dictated by Equation 12. 1 . Cpilot and
Cfeed should be selected to provide a high enough influent microbial concentration to demonstrate at
least 4 log removal in the pilot system. Based on this approach, Cpilot should be set at least 104 higher
than the method detection limit for the test microorganism. The microbial density in the stock solution
should be sampled at least twice, and preferably three times, during a feeding interval to verify
consistent densities.
12.5.3.4 Documentation of WTP Operating Conditions
It is important to document WTP operating conditions during monitoring events to evaluate the
effect of varying operating scenarios on Cryptosporidium removal. Standardized reporting forms
should be developed to provide, at a minimum, the following information:
System flow rate (instantaneous/flow chart, hourly and daily average)
• Operating mode (process scheme, number of trains, number of units in service)
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• Water pH, alkalinity, turbidity and temperature
• Performance data
Chemical addition rates/doses
• Mechanical equipment in operation, with flow rates (major pumps, blowers, etc.)
• Recycle and backwash flows/rates
• Related maintenance activities occurring prior to or during sampling event.
12.5.4 Data Analysis and Reporting
12.5.4.1 Evaluation of Performance
To receive DOP treatment credits above presumptive credits in the LT2ESWTR, a plant
should demonstrate consistent attainment of a specific log reduction of Cryptosporidium (or suitable
indicators). To meet this objective, log reduction should first be computed for each monitoring event
according to:
Log Removal = - log (C{JC^ Equation 12.2
where: Cinf= influent Cryptosporidium or indicator concentration
Cgff = effluent Cryptosporidium or indicator concentration
For effluent samples in which no Cryptosporidium, spores, or other indicators are detected, the
concentration should be set to the method detection limit.
The State will determine the level of DOP credit a facility receives based on review of the log
removal data.
For the case of pilot testing and the use of multiple indicators for Cryptosporidium removal
calculations will be site specific.
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12.5.4.2 Reporting for the DOP
At the conclusion of the DOP test period, a detailed report summarizing the major findings of
the DOP program must be submitted to the governing regulatory agency. At a minimum, the DOP
report should include the following information:
• Detailed description of full-scale WTP, including process flow schematics
Summary of treatment objectives and WTP design criteria
• DOP test matrix and monitoring plan
• DOP data summary
• Detailed pilot plant design data (if applicable)
• Data analysis for estimate of Cryptosporidium log reduction
• Appendices for raw full-scale/pilot-scale analytical and operational data
• Monitoring plan to verify that on-going performance is equivalent to treatment credit.
Source water indicators used in the study should be monitored to ensure performance is
met.
• Plan for addressing operating conditions (e.g., influent water turbidity) out of the range
tested in the study. The DOP test matrix generally sets the range of operating conditions
under which the LT2ESWTR treatment credit is applicable. Therefore, it is advisable to
develop a plan for addressing potential out-of compliance conditions. For example, if the
influent source water quality conditions ranged from 5 NTU to 25 NTU during the study,
the system may plan to make operational adjustments for influent water with turbidity
greater than 25 NTU and increase filter effluent monitoring. Any such deviations would be
reported to the State.
12.5.4.3 Ongoing Reporting
As discussed previously, if a DOP credit is issued by the State, the credit will be conditional on
continuing demonstration of a high level of performance. The DOP Monitoring Plan should be modified
to document continuing performance at a reduced sampling frequency, while still capturing critical
operating conditions. States may require systems receiving a DOP credit to report operational and
progress monitoring data on a routine basis. Operational data should verify that continuous process
control and optimization procedures are in place.
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The DOP credit is applicable to minimum and maximum raw source water and finished water
quality limits defined in the DOP Test Matrix. Routine reporting should be performed to verify that
plants operate within these limits. If an exception occurs, it should be reported to the State in a timely
manner. Frequent exceptions may prompt the State to require the plant to conduct a comprehensive
performance evaluation (CPE) to identify causes and solutions for exceptions.
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References
American Public Health Association, American Water Works Association, and Water Environment
Federation. 1998. Standard Methods for the Examination of Water and Wastewater.
Washington D.C.
Cornwell, D.A., MacPhee, M., Brown, R. 2001. Cryptosporidium Removal Credit Assignable in the
LT2ESWTR Toolbox, Report to AWWA Government Affairs Office, Washington, D.C.
Dugan, N., Fox, K, Mltner, R., Lytle, D., Williams, C., Parrett, C., Feld, Owens, J. 1999. Control of
Cryptosporidium oocysts by steady-state conventional treatment. Proc. of 1999 AWWA
Annual Conference and Exposition. Denver, CO: AWWA.
Dugan, N., Fox, K., Owens, J., Mltner, R. 2001. Controlling Cryptosporidium oocysts through
conventional treatment. Journal AWWA., 93(12):64-76.
Emelko, M., Huck, P., Slawson, R. 1999. Design and operational strategies for optimizing
Cryptosporidium removal by filters. Proceedings of the 1999 AWWA Water Quality
Technology Conference. Denver, CO: AWWA.
Emelko, M. 2001. Removal of Cryptosporidium parvum by Granular Media Filtration. Ph.D.
Dissertation. University of Waterloo, Waterloo, Ontario, Canada.
Jakubowski, W., Boutros, S., Faber, W., Payer, R., Ghiorse, W., LeChevallier, M., Rose, J., Schaub,
S., Singh, A., Stewart, M. 1996. Environmental methods for Cryptosporidium. Journal
AWWA. 88(9):107-121.
Mazounie, P., Bernazeau, F., Alia, P. 2000. Removal of Cryptosporidium by high rate contact
filtration: The Performance of the Prospect Water Filtration Plant During the Sydney Water
Crisis. Water Science and Technology. 41(7):93-101.
Nieminski, E., Bellamy, W. 2000. Application of Surrogate Measures to Improve Treatment Plant
Performance. Denver, CO: AwwaRF and AWWA.
Rice, E., Fox, K., Miltner, R., Lytle, D., Johnson, C. 1996. Evaluating plant performance with
endospores. Journal AWWA. 88(9): 122-130.
USEPA, 1991. Guidance Manual for Compliance with the Filtration and Disinfection Requirements for
Public Water Systems Using Surface Water Sources. Washington, D.C.
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Chapter 12 - Demonstration of Performance (DOP): Microbial Removal
Yates, R., Scott, K., Green, L, Bruno, J.,De Leon, R. 1998. Using aerobic spores to evaluate
treatment plant performance. Proceedings of the 1998 A WWA Annual Conference and
Exposition. Denver, CO: AWWA.
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13.0 Ultraviolet Light
13.1 Introduction
The use of ultraviolet (UV) light for disinfection of drinking water is a relatively new application
in the United States, although used for many years in the wastewater industry. UV disinfection is the
process of irradiating water with UV light. The UV light is absorbed by the genetic material of
microorganisms, damaging it and preventing the microorganisms from reproducing. UV has been found
to be particularly effective against protozoa and bacteria.
In addition to this guidance manual, EPA developed the UV Disinfection Guidance Manual
that contains detailed information of the design and operation of UV systems and the validation testing
that must be conducted for compliance with the LT2ESWTR. This chapter summarizes the
requirements for water systems using UV disinfection to achieve compliance with the LT2ESWTR.
13.2 Log Inactivation Requirements
To receive credit for disinfection with UV light, the LT2ESWTR (40 CFR 141, Subpart W,
Appendix D) requires utilities to demonstrate through validation testing that the UV reactor can deliver
the required UV dose. The testing must determine a range of operating conditions that can be
monitored by the system and under which the reactor delivers the required UV dose. EPA developed
UV dose requirements for Cryptosporidium, Giardia, and virus that are used during the validation
process (see UV Disinfection Guidance Manual for dose requirements and application during
validation).
Validation testing is not intended to be site-specific, rather product-specific. As a result,
validation testing will likely be conducted by the manufacturer or third party and tested over a range of
water quality and flow conditions. As long as the water system operates within those conditions tested,
they are achieving the log inactivation credit demonstrated during the validation testing.
13.2.1 Monitoring Requirements
In addition to reactor validation, the LT2ESWTR (40 CFR 141.729(d)) requires utilities to
monitor for parameters necessary to demonstrate compliance with the operating conditions that were
validated for the required UV dose. At a minimum, utilities must monitor each reactor for flow rate,
lamp outage, UV intensity as measured by a UV sensor, and any other parameters required by the
State.
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Chapter 13 - Ultraviolet Light
13.2.2 Reporting Requirements
The LT2ESWTR requires utilities to report the following (40 CFR 141.730):
• Initial reporting - Validation test results demonstrating operating conditions that achieve the
UV dose required for the inactivation credit desired for compliance with the LT2ESWTR.
• Routine reporting - Volume of water entering the distribution system that was not treated by
the UV reactors operating under validated conditions on a monthly basis.
13.3 Toolbox Selection Considerations—Advantages and Disadvantages
There are several advantages to using UV disinfection over other technologies for the
inactivation of Cryptosporidium. UV is a relatively simple to use and highly effective technology for
inactivating Cryptosporidium. Its main advantages include:
• Ability to achieve up to 3 log Cryptosporidium inactivation credit at relatively low
operating costs
• Low cost technology for inactivation of Cryptosporidium., relative to other toolbox options
for disinfection
• Produces no halogenated disinfection byproducts
• Easy to install and requires minimal operator attention or experience
The disadvantages of UV disinfection include:
• A higher dose is required to inactivate virus. If a water system is seeking to obtain 4 log
virus inactivation with UV disinfection, operating costs will be higher, possibly offsetting the
lower capital costs.
• Does not provide a residual disinfectant to guard against regrowth or contamination in the
distribution system.
• Lamp start-up time after a power outage can be long, at which time the UV system is not
operating within validated conditions and thus, not achieving the given log inactivation
credit.
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13.4 Design and Operational Considerations
A UV disinfection system consists of the UV reactor and a control panel. The reactor consists
of UV lamps, quartz sleeves, UV intensity sensors, quartz sleeve wipers, and temperature sensors. The
quartz sleeves serve to insulate and protect the lamps. Some reactors come with automatic cleaning
mechanisms for the quartz sleeves. Reactors are equipped with UV intensity monitors, flow meters,
and occasionally UV transmittance meters to measure the dose being delivered. There are two primary
types of lamps available, low-pressure and medium-pressure. Low-pressure lamps emit light at one
wavelength (i.e., monochromatic) and operate with the mercury under a vacuum. Medium-pressure
lamps are polychromatic and operate at higher temperatures with the mercury at pressures of 100 to
10,000 Torr.
When considering UV disinfection as a treatment option the following design and operational
issues should be addressed:
• Source water quality - Fouling of the lamp sleeves and other reactor equipment will affect
the frequency of cleaning required and type of cleaning system. Fouling is dependent on
hardness, alkalinity, lamp temperature, pH, and certain inorganic constituents (e.g., iron and
calcium).
• Power quality - The lamps operate continuously and as long as there is power to the lamps.
The quality of power supply should be considered with UV systems. When the lamp loses
power, even on the order of seconds, it requires several minutes to recharge, at which time
no disinfection is occurring. An uninterruptible power supply (UPS) is often recommended
for UV systems to supply backup power during short power interruptions.
• Hydraulic needs and limitations - Headloss through a UV system is dependent on the
specific reactor, piping configuration, and flow rate. Typical headloss ranges from 0.5 to
3.0 feet.
• Maintenance - Although maintenance requirements are low relative to other treatment
processes, the UV system will need to be taken off-line periodically to inspect and clean
lamps and sleeves.
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14.0 Membrane Filtration
14.1 Introduction
Microfiltration and ultrafiltration (MF/UF) are membrane processes which remove
microorganisms and other contaminants by filtration. Contaminants larger than the pore size of the
membrane are retained on the membrane and removed from the water. MF/UF processes that meet
the requirements for membrane filtration under the LT2ESWTR will receive Cryptosporidium removal
credit.
EPA recently published the Membrane Filtration Guidance Manual for systems applying
MF/UF for removal of pathogens from public water supplies. The manual provides detailed guidance
on applying membrane filtration to comply with the requirements of the LT2ESWTR. Readers
interested in detailed information on membrane filtration should consult the Membrane Filtration
Guidance Manual. This chapter will focus on the comparison of membrane filtration with other
technologies for inactivation of Cryptosporidium.
14.2 Log Inactivation Requirements
Most commercially available MF/UF membranes designed for drinking water treatment, have
been demonstrated to remove Cryptosporidium to detection limits, provided the membrane is intact.
Systems that demonstrate membrane integrity through a challenge test before installation and through
daily membrane integrity testing during operation will be eligible for 2.5 log additional credit for
Cryptosporidium removal under the LT2ESWTR.
14.3 Toolbox Selection Considerations
MF/UF is a highly efficient technology for removing pathogens and other particulates from
drinking water. Its main advantages are listed below:
Essentially complete removal of all particles larger than the exclusion characteristic of the
membrane
• Minimal installation effort when supplied as skid-mounted package plants
• Minimal operator attention and training needed when supplied with fully automated controls
Forms no disinfection byproducts because it is a physical removal process
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MF/UF is an advanced technology and can be more expensive than conventional technologies.
Its major disadvantages are:
Total cost may exceed that of conventional technologies
• Membrane fouling may limit application in some cases
• Does not provide a disinfectant residual in the distribution system
14.4 Design Considerations
Membrane systems are usually supplied in skid-mounted packages. The package typically
contains the membrane units, a pre-filter for removal of large particles, low pressure feed pumps, high
pressure backwash pumps, a chemical cleaning system, a chlorination system, and a backwash
residuals handling and disposal system.
A major design variable for membrane systems is the permeate flux. MF/UF membranes are
designed to operate within a specific range of pressures and fluxes, and a membrane system must be
designed to operate within these specifications. Pilot studies are often performed to find the optimal
combination of flux, pressure, pretreatment, and cleaning interval for a particular application. Flux
through a membrane is highly temperature dependent, so the average, minimum, and maximum
temperature of the water to be treated must be considered when designing the system. The flux and the
desired flow rate are used to determine the size and number of membrane units required. Water with
high turbidity or high TOC levels can foul membranes, causing poor performance and shortening
membrane life. If MF/UF is installed after conventional treatment in the treatment train, high turbidity
levels should not be a problem. TOC, however, may still be a problem, even after conventional
filtration. If there are high TOC levels, pretreatment should be considered. If the membrane process is
being relied upon to remove viruses as well as bacteria and protozoa, UF membranes will be needed.
Considerations should also be made for treatment and/or disposal of backwash residuals.
14.5 Operational Considerations
In operating a membrane system, there are several factors that must be balanced. Operating at
higher pressures will allow greater flow rates. It will also result in greater operating costs and increased
cleaning and backwash frequency. Operating at lower pressures may result in reduced cleaning and
backwash frequency but increased area requirements. To ensure the unit is working properly, regular
integrity testing of the membrane should be conducted. While indicators such as turbidity can be useful,
the integrity of the membrane should be directly tested at least daily. Even with pretreatment,
membranes will eventually foul. Periodic cleaning of the membranes will improve membrane
performance and life. The appropriate length of time between cleanings can be determined by
monitoring the long term decrease in productivity and backwash efficiency.
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Appendix A
Site Specific Determination of
Contact Time for Chlorine Dioxide and Ozone
A water system may perform a site specific study to generate a set of chlorine dioxide or ozone
CT values for that site if it believes those developed by EPA do not reflect the true inactivation
achieved. Such a study would involve measuring actual Cryptosporidium inactivation under site
conditions, with a full range of temperature and contact times. If accepted by the State, the CT values
may be used instead of those developed by EPA.
The LT2ESWTR does not specify any requirements for the chlorine dioxide or ozone site-
specific study, only that it be approved by the State (40 CFR 141.729(b)(3) and (c)(3)). This
appendix describes the different elements of a study and discusses some of the issues involved in the
statistical analysis of the results.
A.1 Experimental Design
Experiments should be conducted with water that is representative of the water to be treated
with respect to all conditions that can affect Cryptosporidium inactivation. Inactivation experiments
should be performed with water exerting the highest oxidant demand (i.e. spring run-off or summer
conditions) at high temperature to obtain the worst-case scenario in terms of chlorine dioxide or ozone
demand/decay rate. In addition, experiments should also be conducted with water obtained during the
winter months at the lowest temperatures observed at the treatment plant. These experiments would
allow for the determination of the highest CTs that would be necessary to achieve the required level of
inactivation. Additional experiments may be necessary to characterize the effects of other water quality
parameters.
In order to obtain the most challenging water to assess the chlorine dioxide or ozone process, a
predetermined testing schedule should be established based on source water TOC and UV254 levels.
Testing can occur when source water values for these parameters fall within defined worst-case ranges.
Experiments should then be performed in the laboratory at worst-case temperatures for a given month.
In order to obtain a complete data set, testing should occur at least every other month over the
course of an entire year. Each sample date should be determined by the first time the TOC or UV254
levels are within 75 percent of the maximum historical value for that month. At the time of sampling,
sufficient water should be acquired to allow for three sets of experiments to be conducted, with each
experiment having six data points (CT values) and a control. Two independent sets of experiments
should be conducted with the water. Should significant discrepancies develop between the data sets, a
third set of experiments would need to be conducted. An example experimental matrix is provided in
Table A. 1.
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Table A.1 Example Experimental Test Matrix
Date
February
April
June
August
October
December
Temperature to be
Tested
(Historical Record)
Lowest Annual
Highest in April
Highest in June
Highest Annual
Highest in October
Lowest in December
Water Quality
Criteria
TOCorUV254>
75% of max
historical value
Same
Same
Same
Same
Same
Schedule of Experiments
Testl
X
X
X
X
X
X
Test 2
X
X
X
X
X
X
Test3
If Required
If Required
If Required
If Required
If Required
If Required
A.2 Experimental Procedure
A.2.1 Preparation of oocysts
High oocyst quality is imperative to the success of the study because sub-standard oocysts
could dramatically affect the data in a way that would underestimate the CT required to achieve a
desired level of inactivation. Traditionally, Cryptosporidium parvum oocysts are derived from two
host sources, bovine and rodent. The most common strain of Cryptosporidium parvum used to date
is the Iowa strain, developed by Dr. Harley Moon. It is recommended that the utility perform all
experiments using fresh (< 1 month old) Iowa-strain oocysts obtained from a reputable supplier. The
utility should ensure that after purification the supplier stores the oocysts at 4° C in a solution of
dichromate or 0.01 M phosphate buffer saline solution (pH 7.4) containing two antibiotics (1,000 U/mL
penicillin, and 1,000 mg/mL streptomycin), and an antimycotic (2.5 mg/mL amphotericin B). The
oocysts should be shipped in a cooler on ice to the utility via next-day service. Upon arrival, the
oocysts should be placed in a refrigerator and stored at 4° C until needed.
When ready for use, the oocysts should be suspended in 0.01 M pH 7 buffer and centrifuged at
a relative centrifugal force of approximately 1,100 for at least 10 minutes. Following centrifugation, the
oocysts should be aspirated and re-suspended in the buffer, then centrifuged again at the same
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conditions. This step should be repeated once more to remove as much of the antibiotic or dichromate
solution as possible. Following the last aspiration, the oocysts should be re-suspended in approximately
10 mL of the pH 7 buffer. The oocysts should then be stored at 4° C until the experiment is initiated.
The oocysts should be vortexed thoroughly prior to initiation of the experiment. Additional details
regarding this procedure can be found in Rennecker et al. 1999.
A.2.2 Source Water Preservation
Testing should be conducted as close as possible to the date that the experimental water is
collected. If testing is to be performed at a location other than the utility where the water was collected,
the water should be sent to the laboratory via an overnight delivery service and stored at 4 degrees
Celsius until the start of testing.
A.2.3 Experimental Apparatus
A.2.3.1 Chlorine Dioxide
It is recommended that chlorine dioxide be generated using the equipment and procedures
outlined in Standard Methods for the Examination of Water and Wastewater, APHA 1998. With this
as a basis, all inactivation experiments using chlorine dioxide should be performed using a batch-reactor
configuration. An example of such a system is provided by Ruffell et al. 2000. This system uses an
enclosed recirculating water bath to maintain the desired temperature inside the reactor vessels, which
consist of 2-liter amber glass bottles. During the experiment, care should be taken to minimize the
exposure of the reactors to light. Mixing of the reactor contents is provided with a magnetic stir bar
and stir plate.
A.2.3.2 Ozone
Inactivation experiments can be performed with either a semi-batch or batch reactor
configuration. When performing experiments with a semi-batch system, it is recommended that
analytical components similar to those described by Hunt and Marinas (1997) be used. Using this
system, the reactor vessel containing the experimental water is maintained at the experimental
temperature by immersion in a water bath. Ozone can be generated from either compressed air or
oxygen and passed through a continuously-stirred glass bottle, which serves to dampen the effect of
fluctuating ozone concentration. The ozonated gas leaving the dampening bottle is then introduced to
the experimental water via a fine-bubble diffuser. The ozonated water is stirred continuously using a
magnetic stirring plate and a stir bar.
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It is recommended that inactivation experiments performed using a batch reactor configuration
use analytical components similar to those described by Kim (2002). This reactor used a 100-mL gas-
tight syringe to prevent ozone in solution from volatilizing into the atmosphere. The temperature inside
the reactor is held constant by immersion in a recirculating water bath, and mixing is provided by a stir
bar in the syringe controlled by a magnetic stir plate. Ozone can be produced from either compressed
air or oxygen. A concentrated ozone stock solution should be prepared using distilled de-ionized or
reverse osmosis-filtered water.
Other, less complex, batch reactor systems are also available which simply use an open vessel
such as an Erlenmeyer flask or beaker (Finch et al. 1993a). With these systems, the reactor containing
the experimental water is typically maintained at the desired temperature using a water bath. An
ozonated solution, prepared with distilled de-ionized or reverse osmosis water, is added to the
experimental water, and the ozone dose is measured from the diluted experimental water. When using
this type of batch-reactor configuration that is open to the atmosphere, the user should take into
account that ozone is lost to volatilization. This loss of ozone should be considered and minimized when
performing any inactivation or demand/decay experiment.
A.2.4 Inactivation experiments
The CT values obtained from each of the site-specific inactivation experiments are expected to
be similar to those provided in the standard LT2ESWTR tables. Therefore, utilities wishing to
determine site-specific inactivation data are advised to use the standard tables as a baseline. Each
experiment should be designed such that six data points span the range of the "standard" inactivation
curve for a given temperature. One "control" point with no disinfectant should also be taken.
A. 2.4.1 Chlorine Dioxide
An experimental protocol developed from Ruffell et al. 2000 is provided here as an example.
The reactor bottle should be filled with experimental water to a total volume corresponding to the
desired sample volume times the number of samples expected per bottle (6 is recommended). The
bottle is then placed in the water bath and allowed to equilibrate to the target experimental temperature.
At this point, chlorine dioxide stock solution is added to the reactor bottle at the target dose. The
reactor bottle is then capped to minimize chlorine dioxide volatilization. The chlorine dioxide
concentration is measured approximately 10 min after dosing. An experiment was started by adding
approximately a pre-determined number of oocysts to the reactor that will be sufficient for at least six
data points. Note the volume of the oocyst aliquot should be less than 1 mL. Samples are then taken
periodically at the contact times that correspond to the desired CT. The samples are immediately
filtered through al |j,m filter. The filter is then placed in a clean 50 mL beaker and rinsed with
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approximately 15 mL of the dilute surfactant. The resulting oocyst suspension is transferred into a
sterile 15 mL centrifuge tube.
These steps are repeated at various contact times corresponding to target CT parameters.
After the last sample is taken, the chlorine dioxide dose is measured again. "Control" samples are also
taken for each experiment by placing a sample of oocysts inside a similar reactor containing the
experimental water minus the disinfectant at the target temperature. The oocysts are typically exposed
to this condition for the duration of the experiment and subsequently processed for viability assessment
with methods similar to those for the disinfected samples.
A.2.4.2 Ozone
If a semi-batch reactor configuration is used, the protocol described by Rennecker et al. (1999)
is recommended. The protocol is described briefly as follows. Ozonated gas is applied to the
temperature-acclimated experimental water via a fine bubble diffuser. The ozone gas concentration is
adjusted to achieve steady-state at dissolved ozone concentrations representative of what would be
observed at the facility. The actual dissolved ozone concentration achieved for each experiment is
measured. Mixing of the ozonated water is performed with a magnetic stir bar and stirring plate. An
inactivation experiment is initiated by injecting a suspension containing a sufficient number of oocysts
into the reactor, and ends by simultaneously removing the bubble diffuser and injecting a quenching
agent. It should be noted that the number of oocysts necessary for each data point is dependent on the
viability assessment method selected. Oocysts are then removed from the quenched solution by
filtration through a 1 |im filter. The reactor is then rinsed with approximately 50 mL of a dilute
surfactant, and then again with approximately 100 mL of the experimental water to remove any residual
surfactant. Both eluents are passed through the filter that is then placed in a clean 50 mL beaker and
rinsed with approximately 15 mL of the dilute surfactant. The resulting oocyst suspension is transferred
into a sterile 15 mL centrifuge tube. These steps are repeated at various contact times corresponding
to target CT parameters (i.e., the product of dissolved ozone concentration and contact time).
Control samples are prepared with each daily experimental set by shutting off the ozone
generator, but allowing the oxygen gas to flow through the system. Oxygen gas is allowed to by-pass
the semi-batch reactor after shutting off the generator to purge residual ozone gas from the system. All
other conditions used for the control are consistent with the experimental conditions previously
described. The "contact" time for control samples is 1 minute. After completion of the experiment, the
samples are generally centrifuged at 1,1 OOg for 10 minutes and stored in a phosphate buffer solution for
a period of time not to exceed 48 hours prior to viability assessment procedures.
Experiments performed with a head-space free reactor can follow the following protocol
(described previously in Kim 2002). The experimental temperature is maintained by immersing the
100-mL syringe, which serves as the reactor in a water bath. Mixing inside the reactor is provided
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using a stir bar and magnetic stir plate. The syringe is filled with the experimental water containing
enough oocysts for all six data points. At this point, an aliquot of temperature-adjusted ozone stock
solution of known concentration is added. Samples are then taken at time intervals corresponding to
the pre-determined estimated CT using a syringe containing a quenching reagent. The samples are then
processed using filtration and centrifugation, similar to those described above. A "control" should be
performed for each experiment by placing the sample number of oocysts in the experimental water at
the desired temperature. The oocysts should remain there for a period of time equal to the duration of
the inactivation experiment. After this time, the oocysts should be processed in a manner consistent
with the disinfected samples.
Experiments performed with batch reactor components that are not head-space free typically
follow a similar, although less complex protocol. An example of such a system and the associated
experimental protocol can be obtained from Finch et al. 1993a.
It should be noted that for all batch-reactor systems, a careful characterization of the ozone
demand and decay kinetics of the experimental water should be performed prior to any disinfection
testing. In addition, it is also recommended that ozone concentration samples be procured alternately
between inactivation samples to verify ozone concentrations observed during the disinfection study.
A.2.5 Sample Processing
After procuring each sample point, the samples should be stored at 4° C until the end of the
experiment. At the end of each experiment, the samples should be centrifuged at a relative centrifugal
force of 1,100 for at least 10 minutes to remove quenching agents or surfactants. Following
centrifugation, the samples should be carefully aspirated and re-suspended in 0.01 M pH 7 buffer
solution. The samples should be stored at 4 degrees until the time of viability assessment.
A.2.6 Viability Assessment
Determining the viability of oocysts for varying levels of disinfection is one of the most critical
components of the inactivation experiments. At present, there are three methods available to assess
Cryptosporidium parvum viability, each presenting unique advantages and disadvantages. These
methods include the following techniques:
• Animal infectivity
• Cell culture (in vitro infectivity)
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• In vitro excystation
The most established of these methods is animal infectivity. This viability assessment method
typically involves inoculating immuno-suppressed neonatal mice with varying numbers of oocysts
exposed to a particular CT. After a certain "incubation" period, the mice are then sacrificed and their
intestinal tracts are examined for signs of Cryptosporidium-induced infection (cryptosporidiosis). The
primary benefit of this method is that it demonstrates that the treated oocysts are capable of
reproduction inside a mammalian host and therefore are able to induce an infection. One criticism of
this method is that although an infection is capable of being observed, mouse infectivity has not been
correlated to human infectivity. In addition, the protocol associated with this method is difficult and
expensive. It requires specialized laboratory training, facilities, and equipment. An example of this
protocol can be found in Finch et al. 1993b.
A second method used to assess the viability of Cryptosporidium parvum is known as in
vitro infectivity or cell culture. At present, cell culture methodologies used for this purpose are based
on either microscopic evaluation (Slifko et al. 1997) or polymerase chain reaction (PCR) (Rochelle et
al. 1997). The first step in using cell culture to assess oocyst viability involves applying the treated
oocysts to a lawn of cells (typically derived from human or canine cell lines). After an incubation
period, using microscopic evaluation-based culture methods, the cells are stained with fluorescent
chemicals and then examined microscopically for various cryptosporidium life stages. The presence of
these life stages suggests that the oocysts were capable of reproduction and thus were viable and likely
able to cause an infection in humans.
When using a PCR-based technique, after incubation the cells are processed and the
Cryptosporidium parvum RNA is extracted. Infectivity is then determined by targeting specific
genetic sequences in the RNA. The primary advantage of using cell culture to assess Cryptosporidium
parvum infectivity is that it can measure very low concentrations of oocysts. Therefore, cell culture is
capable of demonstrating high levels of inactivation. In contrast, the disadvantages associated with
using cell culture include a lack of agreement over the preferred cell lines and viability assessment
technique. In addition, there has been no extrapolation between cell culture techniques and human
infectivity. Lastly, cell culture techniques are complex and typically require specialized equipment and
rigorous training, which makes this procedure somewhat expensive.
A third method known as in vitro excystation has also been developed to assess the viability of
Cryptosporidium parvum (Rennecker et al. 1999). This method involves exposing oocysts to a
simulation of a mammalian digestive tract. Following the simulation, the oocysts are then examined
microscopically for oocyst life stages that are indicative of viability. The advantages of this method are
that it is cost-effective, offers the ability to rapidly develop data, and requires minimal training. The
main disadvantage of the method is that of the three methods described, in vitro excystation has the
least similarity to an actual infection. However, it should be noted that in spite of this fact, two
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
published studies have shown that inactivation data obtained with in vitro excystation closely matches
animal infectivity and/or cell culture data (Rennecker et al. 2000, Owens et al. 1999).
A.3 Statistical Analysis
A general approach for calculating a set of CT values involves the following steps:
1) Fitting an inactivation model(s) to the experimental inactivation data (for the entire year).
2) Calculating the predicted average CT requirements from the best fit model.
3) Calculating and applying a factor of safety for the average predicted CT requirement.
One approach by Clark et al. (2002) used a one-parameter Chick-Watson model to fit
experimental data sets and develop standard CT curves, relative to inactivation level and temperature.
As described in the LT2ESWTR Preamble, EPA used the Clark et al. approach for developing CT
values but adjusted the analysis to account for different types of uncertainties and variability inherent in
the data. EPA wanted to account for variability among different water matrices and oocyst strains, but
not variability within the same group (i.e., same oocyst lot and water), and uncertainty in the regression.
While such a complex approach may not be necessary for a site-specific study, the water system
should be aware of the uncertainties and variability of the experimental data and use a statistical method
that builds in a reasonable safety factor to ensure public health is protected.
Two types of confidence bounds that are commonly used when assessing relationships between
variables, such as disinfectant dose (CT) and log inactivation, are confidence in the regression and
confidence in the prediction. Confidence in the regression accounts for uncertainty in the regression line
(e.g., a linear relationship between temperature and the log of the ratio of CT to log inactivation).
Confidence in the prediction accounts for both uncertainty in the regression line and variability in
experimental observations—it describes the likelihood of a single future data point falling within a range.
Bounds for confidence in prediction are wider (i.e., more conservative) than those for confidence in the
regression. Depending on the degree of confidence applied, most points in a data set typically will fall
within the bounds for confidence in the prediction, while a significant fraction will fall outside the bounds
for confidence in the regression.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
References
American Public Health Association, American Water Works Association, and Water Environment
Federation. 1998. Standard Methods for the Examination of Water and Wastewater.
Washington D.C.
Clark, R.M.; Sivagenesan, M., Rice; E.W.; and Chen, J. (2002). Development of a Ct equation for the
inactivation of Cryptosporidium oocysts with ozone. Wat. Res. 36, 3141-3149.
Finch, G. R.; Black E. K.; Gyurek, L.; and Belosevic, M. (1993a). Ozone inactivation of C. parvum in
demand-free phosphate buffer determined by in vitro excystation and animal infectivity. J.Appl.
Environ. Microbiol. 59(12),4203-4210.
Finch, G.R.; Daniels, C.W.; Black, E.K.; Schaefer III, F.W.; and Belosevic, M. .(1993b). Dose
response of C. parvum in outbred neonatal CD-I mice. J.Appl. Environ. Microbiol. 59(11),
3661-3665.
Hunt, N. K.; and Marinas, BJ. (1997) Kinetics of Escherichia coli inactivation with ozone. Wat. Res.
31(6), 1355-1362.
Kim, J. H; Tomiak, R. B.; Rennecker, J. L.; Marinas, B. I; Miltner, R.J.; and Owens, J. H. (2002).
"Inactivation of Cryptosporidium in a Pilot-Scale Ozone Bubble-Diffuser Contactor. Part 11:
Model Verification and Application." ASCE Journal of Environmental Engineering., 128(6),
522-532.
Li, H.; Finch, G.R.; Smith, D.W.; and Belosevic, M. (2000). Chemical inactivation of
Cryptosporidium in water treatment. AWWA Research Foundation, Denver, CO.
Owens, J.H.; Miltner, R.J.; Slifko, T.R.; and Rose J.B. (1999). In vitro excystation and infectivity in
mice and cell culture to assess chlorine dioxide inactivation of Cryptosporidium oocysts.
Proceedings of the AWWA WQTC Conference., Tampa.
Rennecker, J. L.; Marinas B. J.; Owens J. H.; and Rice E. W. (1999) Inactivation of C. parvum
oocysts with Ozone. Water Res. 33 (11), 2481 - 2488.
Rochelle, P.A.; Ferguson, D.M.; Handojo, T.J.; De Leon, R; Stewart, M.H.; and Wolfe, R.L. (1997).
An assay combing cell culture with reverse transcriptase PCR to detect and determine the
infectivity of waterborne C. parvum. J.Appl. Environ. Microbiol. 63(5) 2029 - 2037.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
Ruffell, K.M; Rennecker, J.L.; and Marinas, B. J.(2000). Inactivation of C. Parvum oocysts with
chlorine dioxide. Wat. Res. 34 (3), 868 - 876.
Slifko, T.R.; Friedman, D.; Rose, J.B.; and Jakubowski, W. (1997). An in vitro method for detecting
infectious Cryptosporidium oocysts with cell culture. J.Appl. Environ. Microbiol. 63(9) 3669
-3675.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
A. 1 Experimental Design A-1
A.2 Experimental Procedure A-2
A.2.1 Preparation ofoocysts A-2
A.2.2 Source Water Preservation A-3
A.2.3 Experimental Apparatus A-3
A.2.3.1 Chlorine Dioxide A-3
A.2.3.2 Ozone A-3
A.2.4 Inactivation experiments A-4
A.2.4.1 Chlorine Dioxide A-4
A.2.4.2 Ozone A-5
A.2.5 Sample Processing A-6
A.2.6 Viability Assessment A-6
A.3 Statistical Analysis A-8
Table A.I Example Experimental Test Matrix A-2
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Appendix B
Ozone CT Methods
B.I INTRODUCTION 3
B.l.l BACKGROUND 3
B.2 SELECTION OF METHODS FOR CALCULATING INACTIVATION CREDIT. 4
B.3 OZONE CONTACTOR CONFIGURATIONS 6
B.4 EXTENDED-CSTR APPROACH FOR OZONE CONTACTORS 9
B.4.1 INTRODUCTION 9
B.4.2 OVERVIEW OF SYSTEM EVALUATION AND MONITORING 9
B.4.3 EXTENDED-CSTR APPROACH - OZONE CONTACTORS WITHOUT A TRACER TEST 9
B.4.3.1 CLASSIFICATION OF THE CHAMBERS AND CONTACTOR ZONES 10
B.4.3.2 CALCULATING LOG INACTIVATION ACROSS AN EXTENDED-CSTR ZONE 12
B.4.3.2.1 Determining the Value ofk* 13
B.4.3.2.2 Determining the Value ofCin 15
B.4.3.2.3 Quality Assurance for Extended-CSTR Calculations 16
B.4.4 EXAMPLE OF EXTENDED-CSTR APPLICATION 17
Example - Extended-CSTR Approach for a Multi-chamber Contactor With In-situ Sample
Ports and One Dissolution Chamber 17
REFERENCES 22
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Appendix B - Ozone CT Methods
S
BrCV
Co- current
chamber
Counter-
current
chamber
CSTR
CT
DBF
Half- life or HL
HOT
In-situ sample
ports
k*
-Log(I/Io)
Q
Up flow
chamber
V
Abbreviations
Molar absorbance expressed as M1 cm"1.
Bromate ion
Chamber effluent ozone residual in mg/L times chamber TIO time in minutes
A chamber in an ozone contactor where the water is flowing upward and the
ozone gas bubbles are rising. The direction of flow of the water and the gas
is the same.
A chamber in an ozone contactor where the water is flowing downward and
the ozone gas bubbles are rising. The direction of flow of the water is in the
opposite direction of the gas flow.
Completely Stirred Tank Reactor - fully mixed volume
The product of Concentration and Time in mg/L-min
Disinfection byproduct
The time that it takes for the ozone residual to decrease by 50%. It is
calculated as: HL = —\' , where k* = first-order ozone decay coefficient
k
Hydraulic detention time calculated as the volume divided by the flow.
When volume is expressed in gallons, and flow expressed in gallons/minute,
then the calculated HDT is in minutes
Sample ports that take a sample from the flow of the chamber, typically
through tubing that projects into the flow
The first-order ozone decay coefficient, min"1.
Log-base-10 value of the lethality coefficient for the inactivation of
Cryptosporidium, Giardia or virus with ozone. The units of kw in this
document are L/mg-min.
Log inactivation. Negative log-base-10 of the survival rate (N/N0) of the
microorganisms, where IQ is the number of viable organisms entering the
contactor, and I is the number of viable organisms leaving the contactor.
Water flow - usually expressed in gallons per minute (gpm) or million
gallons per day (MOD)
A chamber within an over-under baffled bubble-diffuser ozone contactor in
which the direction of water flow is upward.
Volume of the contacting zone in question - usually expressed in gallons or
million gallons.
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Appendix B - Ozone CT Methods
B.1 Introduction
B.1.1 Background
Appendix O of the Surface Water Treatment Rule (SWTR) Guidance Manual (USEPA
1991) includes a description of different methods for determining inactivation credit using an
ozone contactor. These methods differ in the level of effort associated with them and, in general,
the ozone dose needed to achieve a given level of inactivation. This appendix provides guidance
to help water systems select the more appropriate methods for their ozone process. More
importantly, it builds on the information presented in the SWTR Guidance Manual with detailed
descriptions of the extended continuous stirred tank reactor (CSTR) method. Appendices D and
E compliment this appendix with descriptions of ozone residual sampling and laboratory analysis
(Appendix D) and derivations of equations used in the extended CSTR and SFA approaches
(Appendix E).
The three methods for calculating LT2ESWTR ozone inactivation credit, presented in
Chapter 11 and this appendix, are described below.
1. TIO --calculates CT through a contactor assuming hydraulic conditions similar to plug
flow and can be used with or without tracer study data. TIO is the time it takes for 90
percent of the water to pass the contactor. Even in well-baffled contactors, the TIO is
most often less than 65 percent of the average hydraulic detention time (HDT) through
the contactor, and generally underestimates the true CT achieved. (The TIO approach is
described in Chapter 11, section 11.3.)
2. CSTR—calculates log inactivation credit using hydraulic detention time. It is applicable
to contactors that experience significant back mixing or when no tracer study data are
available. EPA recommends using this method (or the Extended CSTR) when no tracer
study data are available. (The CSTR approach is described in Chapter 11, section 11.3.)
3. Extended CSTR—a combination of the CSTR and SFA approaches. It utilizes the
hydraulic detention time for the contact time and incorporates the ozone decay rate to
calculate concentration. It is not applied to chambers into which ozone is introduced.
While this guidance manual describes three methods, other methods or modifications to
these methods may be used at the discretion of the State. A fourth method, the Segmented
Flow Analysis approach, is under consideration by EPA, but the details of the approach are
not final. EPA is requesting comment on the approach and any appropriate safety factors to
ensure the inactivation credit calculated using the method is actually achieved.
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Appendix B - Ozone CT Methods
B.2 Selection of Methods for Calculating Inactivation Credit
Selecting the appropriate methods to use depends on the configuration of the ozone
contactor and amount of process evaluation and monitoring that a water system is willing to
undertake. It is also possible that combinations methods can be used. For contactors with
multiple segments it is likely that the CT of one or two segments would be calculated using
either the TIQ or CSTR methods, while the CT for the remaining segments would be calculated
with the Extended-CSTR.
Of the three methods described in the previous section, the Extended CSTR is the most
complex method. The Extended-CSTR approach requires measurements of the ozone
concentration at a minimum of three points within the contactor to develop a predicted ozone
concentration profile through the contactor. The contact time is based on the hydraulic detention
time of the contactor and an assumption of completely mixed flow. While many mathematical
principles are discussed in these methods, their implementation is fairly straightforward. In fact,
the methods presented in this appendix can be programmed into a conventional spreadsheet or a
plant computer control system.
The following tables define the types of chambers potentially present in an ozone
contactor and show the recommended methods for calculating the inactivation credit achieved.
Only the TIQ or CSTR methods can be applied to dissolution chambers. However, they can be
applied to the reactive chambers as well. In general the TIO method should be used unless
significant back mixing occurs in the chamber. If no tracer test data are available, it is
recommended that the CSTR method be used. The Extended-CSTR method is applied over a
minimum of three consecutive reactive chambers. Table B.I shows the recommended methods.
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Appendix B - Ozone CT Methods
Table B.1 Applicable Methods and Terminology for Calculating the
Log Inactivation Credit
3
ra
Q
^
0)
u
2
o
z
2
ra
Q
^
0)
u
5
f
.*;
Section
Description
Terminology
Method for
Calculating Log
Inactivation
Restrictions
Chambers where ozone is added
First chamber
Other chambers
First
Dissolution
Chamber
Co-Current
or Counter-
Current
Dissolution
Chambers
No log inactivation
credit is
recommended
CSTR Method in
each chamber with a
measured effluent
ozone residual
concentration
None
No credit is given to a dissolution
chamber unless a detectable ozone
residual has been measured
upstream of this chamber
Reactive Chambers
>. 3 consecutive
reactive
chambers
< 3 consecutive
reactive
chambers
Extend ed-
CSTR Zone
CSTR
Reactive
Chamber(s)
Extended-CSTR
Method in each
chamber
CSTR Method in
each chamber with a
measured effluent
ozone residual
concentration
Detectable ozone residual should
be present in at least 3 chambers in
this zone, measured via in-situ
sample ports. Otherwise, the CSTR
method should be applied
individually to each chamber having
a measured ozone residual
None
Chambers where ozone is added
First chamber
Other chambers
First
Dissolution
Chamber
Co-Current
or Counter-
Current
Dissolution
Chambers
No log inactivation is
credited to this
section
T10 or CSTR Method
in each chamber
Not applicable
No credit will be given to a
dissolution chamber unless a
detectable ozone residual has been
measured upstream of this chamber
Reactive Chambers
>_ 3 consecutive
chambers with in-
situ sample ports
< 3 consecutive
chambers
Extend ed-
CSTR Zone
T-io or CSTR
Reactive
Chamber(s)
Extended-CSTR
Method in each
chamber
T10 or CSTR Method
in each chamber
Detectable ozone residual should
be present in at least 3 chambers in
this zone, measured via in-situ
sample ports. Otherwise, the T10 or
CSTR method should be applied to
each chamber having a measured
ozone residual
None
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Appendix B - Ozone CT Methods
B.3 Ozone Contactor Configurations
Ozone contactors are designed in a wide variety of configurations. Different
configurations are adaptable to the Extended-CSTR approach, but implementation details vary
with contactor configuration. It is important for a water system to identify the type of
configuration and become familiar with the terminology used in this guidance manual.
Figure B.I shows configurations with multiple, consecutive well-defined reactive
chambers. The water flow pattern in such contactors can be an "over-under" pattern, a
"serpentine" pattern, or a combination of both. Gaseous ozone is added to the water by one of
two procedures. Gaseous ozone can be injected into the influent water before the water enters
the contactor, a process often called "in-line" ozone addition (see schematic B & D in Figure
B.I). Alternatively ozone enriched gas can be bubbled into one or more chambers, a process
called "in-chamber" ozone addition (see schematic A & C in Figure B. 1). In-chamber ozone
addition takes place in chambers that have an over-under flow pattern and not in chambers that
have a serpentine flow pattern (Figure B.l-C) in order to ensure full and complete ozone
dissolution into all the water flow. These so-called bubble columns can be counter-current or co-
current, describing the directional flow of the water with respect to the upward flowing bubbles.
Note, Figure B.I only shows example configurations; size and geometry of the chambers will
vary.
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Appendix B - Ozone CT Methods
Figure B.1 Schematics of Typical Configurations of Ozone Contactors with
Multiple Chambers
Over-Under J
Chambers |
Side View of an Over-Under
Contactor with In-Chamber
Ozone Addition
(A)
*.»
Top View of a Combined Over-
Under & Serpentine Contactor
with In-Chamber Ozone Addition
(C)
Side View of an Over-Under
Contactor with In-Line Ozone
Addition
(B)
Top View of a Serpentine
Contactor with In-Line Ozone
Addition
(D)
In contrast to the multi-chamber configuration, ozone contactors may also be comprised
on only one or two reactive chambers. Examples of such contactors are shown in Figure B.2,
which include a closed-pipe contactor (see schematic A) and two open-channel contactors (see
schematics B & C). All three contactors include a long and narrow water flow path that
promotes plug-flow hydraulic characteristics. As with multi-chamber contactors, ozone can be
added in-line, or in-chamber. Contactors A and B illustrate in-line ozone addition. Contactor C
illustrates in-chamber ozone addition.
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Appendix B - Ozone CT Methods
Figure B.2 - Schematics of Example Single- or Dual-Chamber Ozone Contactors
Pipe Ozone Contactor
(A)
Side View of an Open-Channel Ozone
Contactor with In-Line Ozone Addition
(B)
Side View of an Open-Channel
Contactor with In-Chamber
Ozone Addition
(C)
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Appendix B - Ozone CT Methods
B.4 Extended-CSTR Approach for Ozone Contactors
B.4.1 Introduction
The method described in this chapter represent a more sophisticated approach to
calculating inactivation credit in an ozone contactor as compared to the TIO and CSTR
approaches. This approach could potentially provide a higher and more accurate estimate of the
level of Cryptosporidium inactivation than that obtained using the TIO approach. The potential
benefits of using these more sophisticated measures are lower ozone doses and lower ozonation
disinfection byproducts, (e.g. bromate). However, as a consequence of this added sophistication,
a higher degree of system evaluation and monitoring is needed for a given inactivation credit.
Whether use of these more sophisticated approaches actually benefit the utility depends on many
factors including the sought-after level of inactivation, the reactor configuration, and the water
quality.
The approach described in this chapter is called the Extended-CSTR Approach. Certain
aspects of this methodology was introduced in Appendix O of the SWTR Guidance Manual.
However, the material presented here greatly expands upon the SWTR Guidance Manual, and
may provide beneficial new tools for the utility.
B.4.2 Overview of System Evaluation and Monitoring
The Extended-CSTR approach relies on modeling ozone decay reactions through ozone
contactors. In principal, the kinetics of ozone decay in the contactor is modeled in concert with
the hydrodynamics of the ozone contactor, which is assumed to be that of an ideal CSTR. This
approach is applied only to "reactive chambers" within a contactor.
B.4.3 Extended-CSTR Approach - Ozone Contactors without a Tracer Test
In the event that an approved set of tracer test results is unavailable for an ozone contactor,
the utility may choose one of the following two options:
1. Use the CSTR method to calculate the log inactivation across each individual chamber.
2. Use the Extended-CSTR approach to calculate the log inactivation across each individual
chamber.
The choice of using the CSTR approach, the Extended-CSTR approach, or a combination
of the two greatly depends on the reactor configuration and the manner in which the
measurement of ozone residuals is attained. Briefly, for CSTR approach, concentrations are
measured for each chamber where log inactivation is calculated. In contrast, for the chambers in
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Appendix B - Ozone CT Methods
the Extended-CSTR approach, ozone concentrations of each chamber are calculated through
modeling of the ozone decay. This section describes the appropriate application of the CSTR
approach and Extended-CSTR approach to calculate the log inactivation credit across the
contactor.
B.4.3.1 Classification of the Chambers and Contactor Zones
The contactor should be divided into specific sections, or zones, to properly calculate the
inactivation credit across a conventional contactor. To ensure clarity, certain terminology is
adopted for unique sections of an ozone contactor, as presented in Table B.I.
Figure B.3 shows an example schematic of a 10-chamber over-under baffled, multi-
chamber ozone contactor with in-chamber ozone addition. Ozone is being added in Chambers 1
and 4 only in this example.
Chamber 1 is classified as a "First Dissolution Chamber" and it is recommended that no
disinfection credit be granted for this chamber. Rapid, initial ozone reactions and the transitional
development of the ozone residual occur in the first dissolution chamber. As such, a
representative dissolved ozone profile is difficult to estimate without multiple sample ports along
the bubble column.
The second and third chambers in the contactor shown in Figure B.3 are reactive
chambers through which ozone is decaying. These chambers are called "CSTR Reactive
Chambers". The CSTR method is used to calculate log inactivation across CSTR Reactive
Chambers when ozone residual values are available from the effluent of the chamber. The CSTR
method is described in Chapter 11.
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Appendix B - Ozone CT Methods
o
11
B 3
tg I H 1 V 1 Extended CSTR Zone
.iH 4= 00 4= O -in
fe O O O O Q [minimum of 3 consecutive reactive chambers]
Ji .A A ._«^^^.
/ I/" v ix s
v '. •"
" =" 0°
'.(5
•• «°
o°° Q"
. D *
B B D
r
©
>
T
^
0
V.
T
,° °*/^~
0 • o
:®
o« „•
V . •
" •> .
_ * 0
• « 0
V*
>
0
V.
r
©
^
^
©
v.
r
©
j
^
0
v.
(S)
J
Ozone
Figure B.3 - Names of the Various Sections of a Multi-Chamber Over-Under Ozone
Contactor
The fourth chamber in the contactor shown in Figure B.3 includes ozone addition. This
chamber is called a "Co-Current Dissolution Chamber". It should be emphasized that a chamber
is given the "Dissolution Chamber" notation only when ozone residual has been detected at any
point upstream of the influent to that chamber. In other words, chamber 4 in Figure B.3 can be
classified as a Dissolution Chamber only if ozone residual has been detected at the effluent of
either chamber 1, 2, or 3. The CSTR method is used to calculate the log inactivation credit
across a Dissolution Chamber. If no ozone residual was detected upstream of this chamber
location, then chamber 4 takes on the classification of a "First Dissolution Chamber" and as with
chamber 1, no log inactivation credit is granted.
Chambers 5 through 10 in the contactor pictured in Figure B.3 represent the "Extended-
CSTR zone" since they meet the criterion of containing a minimum of three consecutive reactive
chambers. Since tracer data are unavailable, the Extended-CSTR approach is used to calculate
the log inactivation across each chamber in this zone. Modeling is used to calculate the ozone
residual concentration at the effluent of each chamber within the Extended-CSTR zone. This
modeling requires an accurate estimation of the ozone decay coefficient, k , and the initial ozone
residual at the entrance to the zone, Cin. Estimation of these two parameters, which is discussed
in sections B.4.3.2.1 and B.4.3.2.2, requires the measurement of three ozone residual values
across the minimum span of three chambers.
In the case of a contactor with in-line ozone addition, the entire contactor potentially
becomes an Extended-CSTR zone. If the contactor has at least three chambers equipped with in-
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Appendix B - Ozone CT Methods
situ sample ports and a measurable ozone residual then the requirements for calculating k* and
Cm have been met and the entire contactor can be treated as an Extended-CSTR zone. Care
should be taken in locating the first ozone sample port such that enough reaction time is allowed
for the immediate ozone demand to be fully met before the sample port.
B.4.3.2 Calculating Log Inactivation across an Extended-CSTR Zone
Calculation of log inactivation across an Extended-CSTR zone is handled in much the
same manner as it is for a CSTR Reactive Chamber as discussed in Chapter 11. The Extended-
CSTR zone comprises three or more individual chambers. Inactivation within each chamber is
calculated according to Equation 11-1, exactly as it is for the CSTR chamber above, and the sum
of the log inactivation values for individual chambers gives the inactivation across the whole
zone. The distinction between a CSTR Reactive Chamber and a chamber that is a component of
an Extended-CSTR zone is the manner in which the value for C is obtained. In the case of the
CSTR Reactive Chamber, C is obtained from an actual measurement of the dissolved ozone
residual at the exit of the chamber (i.e., Cout). In contrast, C for a chamber in an Extended-CSTR
zone is a calculated value. The procedure for calculating C for an Extended-CSTR zone is
described in this section.
The value of C for an Extended-CSTR is calculated using the first-order ozone decay
coefficient, &*, and the ozone residual concentration at the entrance to the zone, Cin. Equation B-
1 shows how to calculate the ozone residual at the effluent of chamber "X" in an Extended-
CSTR zone:
Cx = ~ r..C'" , ^.. (B-l)
where: k* = First-order ozone decay coefficient, min"1, calculated as described in section
B.4.3.2.1
Cin = Calculated ozone residual concentration at the entrance to the Extended-CSTR
zone, mg/L, calculated as described in section B.4.3.2.2
[Volume]^_x = Volume, in gallons, from the beginning of the Extended-CSTR zone to the
effluent of chamber "X"
NO_X = Number of chambers from the beginning of the Extended-CSTR zone to the
effluent of chamber "X"
Q = Water flow through the contactor, gpm
Equation B-l describes the Extended-CSTR zone between the first chamber (subscript 0) and
chamber X as a series of equal-volume CSTR reactors. This is a simplifying assumption that is
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Appendix B - Ozone CT Methods
based on a balance between ease of implementation and consistency with other provisions within
this guidance manual.
Once the values of the ozone residual concentrations at the effluent of each chamber in
the Extended-CSTR zone are calculated, Equation 11-1 can then be used to calculate the log
inactivation achieved across that chamber. The total log inactivation achieved across the entire
contactor is equal to the sum of the log inactivation values calculated for each chamber.
-Log (I/Io) = Log (1 + 2.303kio x C x HDT) Equation 11-1
where:
-Log (IAo) = the log inactivation
kio = log base ten inactivation coefficient (L/mg-min)1
C = Concentration from Table 11-2 (mg/L)
HDT = Hydraulic detention time (minutes)
Because the ozone demand in the water is constantly changing, the values of k* and Cin
should be determined every time log inactivation credit is calculated (i.e. at least daily). These
parameters are calculated using three measured ozone residuals from three locations within the
Extended-CSTR zone.
B.4.3.2.1 Determining the Value of
The ozone decay coefficient, k* is calculated using ozone sample measurements, taken
from in-situ sample ports, and a model of the chamber's hydrodynamics. The following
approach assumes that the individual chambers can be modeled as a CSTR (or equal-volume
CSTR-in-series if there are more than one chamber between sample ports).
Calculating k*
The steps outlined below pertain to a contactor with a minimum of three consecutive
chambers with measurable ozone residuals. That is, there should be at least three in-situ sample
ports from the Extended-CSTR zone with measurable ozone residual. The three ozone residual
measurements, Ci, €2, and Cj, are needed to estimate the value of the ozone decay coefficient,
k*. For example, the Extended-CSTR zone in the contactor shown in Figure B.3 includes
chambers 5 through 10. The ozone residual values at any three chambers in that span can be
used to represent Ci, €2, and Cj in this analysis. The following steps should be followed to
calculate the k value:
^10 is calculated from the CT table with the following equation: Log inactivation = ki0 x CT
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Appendix B - Ozone CT Methods
Step 1 - Use Equation B-2 and residual measurements Ci and €2 to calculate the k value
representing the ozone decay between locations 1 and 2, ^_2 . (A derivation and
explanation of Equation B-2 is presented in Appendix E):
*l-2 =
#
1-2
\Volume\i_2
(B-2)
where: A:j_2 = First-order ozone decay coefficient between sampling locations 1 & 2, min"1
Cj = Measured ozone residual at location 1, mg/L
€2 = Measured ozone residual at location 2, mg/L
[Volume^ 2 = Volume between sampling locations 1 and 2, gallons
N12= Number of chambers between sampling locations 1 and 2
Q = Water flow through the contactor, gpm
Step 2 - Use residual measurements Ci and Cj along with Equation B-3 to calculate the k value
representing ozone decay between sampling locations 1 and 3, k\_
3-
(B-3)
where:
"1-3
Cj
[Volume^
^-3
G
First-order ozone decay coefficient between sampling locations 1 & 3, min"1
Measured ozone residual at location 1, mg/L
Measured ozone residual at location 3, mg/L
Volume between sampling locations 1 and 3, gallons
Number of chambers between sampling locations 1 and 3
Water flow through the contactor, gpm
It should be emphasized that sampling location 1 should not be at the entrance to the
Extended-CSTR zone, but should be at least one chamber into the zone. For example, in Figure
B.3, Ci should not be measured at the entrance to chamber 5, since that is the entrance to the
Extended-CSTR zone. Instead, the first Extended-CSTR zone sampling location should be
located at the effluent of chamber 5, or downstream of that location. Section O.3.2 of Appendix
O of the SWTR Guidance Manual provides guidance on the use of in-situ sample ports for direct
ozone measurements.
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Appendix B - Ozone CT Methods
Step 3 - The value of k* that is to be used in Equation B-l will be calculated as the average of
ki_2 and ^_3 as shown in Equation B-4.
k =
(B-4)
It is normal for the individual values of k\_2 and k\_3 to be somewhat different.
However, it is recommended that they be within the range of 80% to 120% of the average k*
value calculated in Step 3. That is,
abslk* - k, }
J -J- < 20%
k
If they are outside this range, the measured residual values should be rejected and new samples
should be collected until this quality assurance (QA) criterion is met.
Ozone residual measurement at the three locations might be conducted manually using
the Indigo Trisulfonate method, or continuously using on-line ozone analyzers. The Quality
Assurance protocols discussed in Appendix D should be implemented to ensure that the ozone
residual measurements are accurate.
B.4.3.2.2 Determining the Value of Cjn
While it is possible to measure the ozone residual at the entrance to the Extended-CSTR
zone (e.g., an in-situ sample port), it is not recommended that the measured value be used
because it is usually higher than the residual predicted by the first-order decay profile (Amy et
al., 1997; Carlson et al., 1997; Hoigne and Bader, 1994; Rakness and Hunter, 2000; Rouston et
al., 1998). This phenomenon is commonly attributed to the more rapid initial ozone decay,
which is followed by a somewhat slower first-order decay profile. For this reason, the Cin
representing the ozone decay in the Extended-CSTR Zone should be extrapolated using the
downstream measured ozone residual values.
The value of Cin can be calculated once the value of A:* is estimated from the three
residual ozone measurements. Maintaining the assumption of a first-order decay rate, and again
using the CSTR (or equal-volume CSTR-in-series if there are more than one chamber between
sample ports) assumption, Equations B-5 through B-7 can be used to estimate the value of Cin
from the three measured ozone residual concentrations:
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Appendix B - Ozone CT Methods
[Volume], _,
1 + & x
[Volume]02
l+k x
7V0_2 x 0
. [Volume], 3
l+£
where: A: = Ozone first-order decay coefficient, min"1
Cy = Measured ozone residual at location 1, mg/L
C2 = Measured ozone residual at location 2, mg/L
Cj = Measured ozone residual at location 3, mg/L
jVQ j = Number of chambers between the entrance to the Extended-CSTR Zone and
sampling location 1
NQ_2 = Number of chambers between the entrance to the Extended-CSTR Zone and
sampling location 2
NQ_3 = Number of chambers between the entrance to the Extended-CSTR Zone and
sampling location 3
[Volume]^_j = Volume, in gallons, between the entrance of the Extended-CSTR Zone and
sampling location 1
[Volume] Q 2 = Volume, in gallons, between the entrance of the Extended-CSTR Zone and
sampling location 2
[Volume] Q 3 = Volume, in gallons, between the entrance of the Extended-CSTR Zone and
sampling location 3
Q = Water flow through the contactor, gpm
The Cm value is then calculated as the average of the three values determined by
Equations B-5 through B-7:
-in,3
(B-8)
These calculations outline the methodology of the Extended-CSTR approach. A
systematic example of the Extended-CSTR approach is presented in section B.4.5
B.4.3.2.3 Quality Assurance for Extended-CSTR Calculations
The Extended-CSTR method depends on ozone residual measurements and an
assumption that the contactor hydrodynamics can be modeled as a CSTR in order to predict
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Appendix B - Ozone CT Methods
ozone concentrations through the contactor. To ensure that the predicted concentrations are
accurate, both the measurements and assumptions should be verified. Therefore, QA controls are
recommended as described below.
The predicted ozone residual concentration, the parameter C in Equation 11-1,
encompasses both the CSTR assumption and ozone measurements. The principal QA issues
focus on the prediction of the value of C. As seen in equation B-1, C depends on the parameters
k* and C;n. In section B.4.3.2.1, as part of the discussion on the calculation of k*, it is stipulated
that the individual k* values (i.e., k*\.2 and k*\.^) should be within 20% of the average value.
This QA control is meant to ensure that ozone residual measurements used to calculate the ozone
decay profile are consistent with the calculated profile. Since the calculation of Cjn (Equations
B-5 through B-8) depends on k*, as well as the measured ozone concentrations, the QA criteria
for k* is sufficient for C;n. Therefore, no additional QA criteria are necessary for it.
The accuracy of the CSTR assumption cannot be completely verified without conducting
a tracer study through the contactor. However, it is recommended that ozone residual
measurements be taken at different flows and ozone doses, and k* and C;n be calculated at the
different conditions, in order to determine the impact of changing conditions on the predicted
ozone decay rate.
Finally, one of the most important aspects of any application of a model towards
predicting reactor performance is the confirmation of the model's prediction. This is in essence
"model validation." Appendix O of the SWTR Guidance Manual makes several points to this
effect. Ideally, model validation would take the form of measuring the actual disinfection of the
Cryptosporidium. A more practical alternative is to compare the predicted ozone concentrations
to measured values. The general recommendation is that the predicted ozone residual should not
be greater than 20% of a measured value. Note that this is a one-sided QA control.
The ozone concentration measurements used to calculate k* and C;n cannot be compared
to the predicted ozone residuals, since they are interdependent. It is recommended that ozone
samples be taken from other sampling locations in the contactor, and those values compared to
the calculated C.
B.4.4 Example of Extended-CSTR Application
This section provides an example calculating the log inactivation credits using the
Extended-CSTR approach.
Example - Extended-CSTR Approach fora Multi-chamber Contactor With In-situ
Sample Ports and One Dissolution Chamber
Figure B.6 shows a schematic of a 12-chamber ozone contactor. The contactor is
treating 50 MOD of water at a temperature of 20°C. The volumes of the individual chambers are
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Appendix B - Ozone CT Methods
noted on the schematic. Ozone is added to the first chamber only. The bottom graph in Figure
B.6 shows the values of the ozone residual measured at the effluents of chambers 2, 5, and 8.
Figure B.6 - Schematic of the Ozone Contactor and the Measured Ozone Residual
Values in Example 1
SFA Reactive Zone
fin
3m]
It
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A ,
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. C, = 0.71 mg/L
3 6 9 12 15 18 21 24 27 30 33 36
HDT, min
The Cryptosporidium inactivation credit across the contactor is calculated as follows:
Chamber l(First Dissolution Chamber) - No inactivation credit is given to the first dissolution
chamber.
Chambers 2 through 12 (Extended-CSTR zone)- This zone is classified as an Extended-
CSTR zone. The Extended-CSTR calculations (Section 4.3) are applied to determine the log
inactivation across each chamber. The following steps are implemented
Step 1: Calculate k value - The k value is calculated as described in section B.4.3.3.1 using the
three ozone-residual measurements, Ci, €2, and Cj that are shown in Figure B.6. The values of
k\_2 and k\_3 can be calculated using Equations B-2 and B-3 as follows:
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Appendix B - Ozone CT Methods
#1-2 x G
\Volwme\i_2
1-3 x Q
\Volume\ j_3
-1
3x34,720
[3x104,000]
6x34,720
'0.71
O41
- 1
= 0.0670mm1
[6x104,000]
'0.71V
0.2
= 0.0785 mm1
The k value is then calculated as the average of k\_2 and k\_3 as follows:
7 * 7 *
*1_2 + *l-3
2
"0.0670+ 0.0785"
2
= 0.0728 miri
-i
A QA check shows that the values of ^_2 and ki_3 are within 8% of the average k* value of
0.0728 min"1. This value of k* is within the recommended maximum variability of 20%.
Step 2: Calculate Cm value - The value of Cin is calculated using the approach described in
Section 4.3.3.2. With the value of k* calculated at 0.0728 min"1, Equations B-5 to B-7 can be
used to calculate the Cin value as follows:
initial ,1 ~ Q x
* [Volume]^
l+K X
0-1
= 0.71;
1+0.0728;
[104,000]
1x34,720
= 0.865 mg/L
initial,2
c —
^•initial,3 ~
Therefore,
n =
^•initial
1+*'
\Volume] 0_3
= 0.41;
= 0.20x
1 + 0.0728:
[4x104,000]'
4x34,720
1 +0.0728 x
[7x104,000]
7x34,720
= 0.902 mg/L
= 0.796 mg/L
^initial, 1 ' ^initial,2 ' ^initial,3
0.865 + 0.902+ 0.796
= 0.854 mg/L
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Appendix B - Ozone CT Methods
Step 3: Calculate the value ofk^p - The value of kjo for the inactivation of Cryptosporidium with
ozone at the measured temperature of 20°C can be obtained from Table 11-3 directly and equals
0.2537 L/mg-min. Otherwise the value for kjo could be determined using equation 11-2.
Step 4: Calculate the Ozone Residual at the Effluent of Each Chamber - Knowing the values of
Cm and k , the ozone concentration at the effluent of each chamber within the Extended-CSTR
zone can be calculated. These values are calculated using Equation B-1:
/~< _ ^initial
* [Volume]0_x
\ + k x
where Cx is the calculated concentration at the effluent of chamber "X". For example, the
residual concentration at the effluent of chamber 4 is calculated as:
CA =
0.854
1 + 0.0728;
[3 x 104,000]
3x34,720
= 0.473 mg/L
Note that the Extended-CSTR zone begins at the effluent of Chamber 1, which makes the
subscript to [Volume] in the equation above depicted as "1-4". Table B.10 lists the calculated
residual values for each chamber using the same approach, beginning with chamber 2.
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Appendix B - Ozone CT Methods
Table B.10-Application of the Extended-CSTR Method to the Example
Vol./Chamber =
Flowrate =
r =
^ initial
k* =
^10 =
(1)
Chamber
2
3
4
5
6
7
8
9
10
12
104,000
34,720
0.854
0.0728
0.2537
(2)
HDT from
Entrance of Zone
HDT, min
3.0
6.0
9.0
12
15
18
21
24
27
33
gallons
gpm
mg/L
min"1
L/mg-min
(3)
Calculated
Residual
mg/L
0.701
0.576
0.473
0.388
0.318
0.261
0.215
0.176
0.145
0.099
Sum=|
(4)
Log Inactivation
0.35
0.30
0.26
0.23
0.19
0.16
0.14
0.12
0.10
0.07
1.9
Step 4: Calculate Los Inactivation - Knowing the values of C, kjo, and k , Equation 11-1 is used
to calculate the log inactivation achieved in each chamber in the Extended-CSTR Zone:
Log - inactivation = Log
1 + 2.303 kw Cx
\Volume\x
O
where Cx is the effluent residual concentration at Chamber X and [Volume]x is the volume of
that chamber. For example, the log inactivation achieved in chamber 4 is calculated as:
Log - inactivation = Log
1 + 2.303x0.246x0.473)
104,000
34,720
= 0.26 logs
Column (4) in Table B.10 lists the log inactivation values calculated for chambers 2 through 12.
The sum of the log inactivation achieved (total of Column 4 in Table B.9) is 1.9 logs.
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Appendix B - Ozone CT Methods
References
Amy, G.L., P. Westerhoff, R.A. Minear, and R. Song. 1997. Formation and Control of
Brominated Ozone By-Products. AWWA Research Foundation, Denver, CO.
Carlson, K., K. Rakness, and S. MacMillan. 1997. Batch Testing Protocol for Optimizing
Ozone System Design. Presented at AWWA Annual Conference in Atlanta, GA -
June 15-19, 1997.
Froment, G.F. and K.B. Bischoff 2nd ed. 1990, Chemical Reactor Analysis and Design., New
York: John Wiley & Sons.
Gordon, G, RD. Gauw, Y. Miyahara, B. Walters, and B. Bubnis. 2000A. "Using Indigo
Absorbance to Calculate the Indigo Sensitivity Coefficient," J. AWWA, 92(12): 96-100.
Gordon, G., B. Walters, and B. Bubnis. 2000B. "The Effect of Indigo Purity on Measuring the
Concentration of Aqueous Ozone," Conference Proceedings: Advances in Ozone
Technology, Orlando, FL. International Ozone Association, Pan American Group.
Guidance Manual for Compliance With the Filtration and Disinfection Requirements for Public
Water Systems Using Surface Water Sources. March 1991 Edition. USEPA Office of
Drinking Water, Cincinnati, OH.
Hoigne, J. and H. Bader. 1994. Characterization of Water Quality Criteria for Ozonation
Processes. Part II: Lifetime of Added Ozone. Ozone: Science & Engineering. Vol.16,
No. 2: pp. 121-134.
Levenspiel, O., 3rd ed. 1999. Chemical Reaction Engineering. New York: John Wiley & Sons.
Rakness, K.L. G. Gordon, B. Bubnis, D.J. Rexing, E.C. Wert, and M. Tremel. 2001.
"Underestimating Dissolved Ozone Residual Using Outdated or Impure Indigo,"
Conference Proceedings: International Ozone Association 15th World Congress;
London, England; International Ozone Association - September 2001).
Rakness, K.L. and G.F. Hunter. 2000. "Advancing Ozone Optimization During Pre-Design,
Design and Operation." AWWA Research Foundation, Denver, CO, and Electric Power
Research Institute-Community Environmental Center, St. Louis, MO.
Rakness, K.L., and G.F. Hunter. 2001. "Monitoring and Control of Ozone Disinfection for
Crypto, Giardia, and Virus Inactivation." Conference Proceedings of International
Ozone Association World Congress; London, England - September 2001.
Rakness, K.L., G. Gordon, D.J. Rexing, and E.C. Wert. 2002. "Reported Ozone Residual Data
Might Be Undervalued." Conference Proceedings: American Water Works Association
Annual Conference; New Orleans, LA - June 2002).
Roustan, M., H. Debellfontaine, Z. Do-Quang, and J. Duguet. 1998. Development of a Method
for the Determination of Ozone Demand of Water. Ozone: Science & Engineering.
Vol. 20, No. 6: pp. 513-520.
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Appendix B - Ozone CT Methods
Standard Methods for the Examination of Water and Wastewater, 20th Edition. 1998.
(American Public Health Association, American Water Works Association, and Water
Environment Federation), pp. 4-137 and 4-138.
Teefy, S. and P. Singer. 1990. Performance and Analysis of Tracer Tests to Determine
Compliance of a Disinfection Scheme with the SWTR. Journal AWWA, 82(12):88-89.
Teefy, S. et al., 1996. Tracer Studies in Water Treatment Facilities: A Protocol and Case
Studies. Final Report. American Water Works Association Research Foundation.
American Water Works Association, Denver, CO.
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Appendix C
Measuring Ozone Residual
Accurate ozone residual data will allow the calculation of correct log-inactivation values
and maintain optimized performance. Ozone residual measurements might be inaccurate if
sampled or measured incorrectly. Residual measurement Quality Assurance (QA) issues
include:
1. Configuration of the ozone sample collection lines within the contactor,
2. Stability of the indigo trisulfonate reagent when analyzing grab samples, and
3. Standardization and maintenance of on-line ozone analyzers.
C.1 Sample Collection
The ozone residual in water decays rapidly. The half-life ranges from less than 1 minute
to more than 20 minutes. Ozone contactors are sealed vessels with sample lines that penetrate
the walls or roof structure of the contactor. The detention times in the sample lines should be as
short as possible in order to minimize ozone residual decay (loss) in the sample lines.
The ozone residual profile in a contactor will vary significantly depending on the method
of operation, water quality and water flow conditions (e.g., HDT). A separate sample port
located at the outlet of each chamber within the contactor allows maximum flexibility for
sampling ozone residual over variable operating conditions. Sample ports located at the outlets
of diffusion chambers should be placed to ensure the diffusers do not interfere with the collected
sample.
The inlet to the sample pipe inside the ozone contactor should be located directly in the
main flow stream, such as shown in Figure C.I. The inlet should extend into the contactor
sufficiently in order to obtain a representative sample (i.e. about 1A to 1A of the contactor width).
Gas bubbles might be carried into the sample inlet and cause errors in the residual measurement.
A sample inlet tube that is flared and that is turned either upward or opposite the flow of the
water (depending on the location) reduces the potential for entrapment of gas bubbles. However
in highly turbid waters, a vertical inlet and flared configuration might result in clogging due to
solids deposition inside the line. In these cases a compromise is to position the sample line such
that the inlet is horizontal rather than vertical.
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Appendix C — Measuring Ozone Residual
Figure C.1 Example Sample Locations in an Over/Under Baffled Bubble Diffuser
Contactor
Sample location in flow stream (typical).
Inlet is located at a distance of 1A to 1A of
the contactor width. Inlet might be upward
and flared, or might be horizontal.
Ozone
Minimizing the travel time through the sample line is important, especially when the
ozone decay rate is high (i.e., ozone half-life is short). It is desirable to minimize the travel time
so that the ozone decay is <10 percent. Figure C.2 shows the relationship between simulated
sample line travel time and ozone residual loss for various ozone half-life values. For example,
the travel time in the sample line should be less than 10 seconds if the ozone half-life is one
minute, in order to maintain the ozone residual loss at or below 10 percent.
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Appendix C — Measuring Ozone Residual
Figure C.2 Relationship Between Ozone Residual Loss and Detention Time
through the Ozone Sample Line for Various Ozone Half-Life Values
Ozone Half-live
-»--HL=30sec
-n-- HL= 1 min
30 40 50 60 70 80
Detention Time in Sample Line (sec)
90 100 110 120
The sample line diameter should be large enough (minimum 3/8th inch inside diameter
and preferably Va-in to 3/4-inch) to minimize clogging of the line with suspended solids. Sample
pipe diameter and flow rate should be selected in order to:
1. Maintain consistent flow without plugging
2. Minimize detention time in the sample line
3. Meet flow rate requirements of an on-line analyzer installed at that location
Gravity flow is all that is necessary to meet sample flow requirements in most locations.
In other cases, pumping is necessary. Sample lines might contain some gas bubbles as well as
liquid. It is important to ensure that lines are vented in high spots where gas binding might occur.
Gaseous ozone in high concentrations is hazardous to breathe. Sample line vents and drains
should be directed away from occupied areas.
Some of these points are touched upon in Section O.3.2 of Appendix O of the SWTR
Guidance Manual (1991).
C.2 Ozone Residual Measurement
Ozone residual is determined using the Indigo Method (Standard Methods 4500-Ozone -
20th Edition, 1998) when analyzing grab samples. The method assumes that high-purity reagents
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Appendix C — Measuring Ozone Residual
are used. Since the publication of the 20th Edition, several reports (Gordon et al., 2000a and
2000b; Rakness et al., 2001; Rakness and Hunter, 2001; and Rakness et al., 2002) have been
published discussing a potential biasing in the Indigo Method. The potential biasing involves the
value of the so-called "sensitivity factor",/, as defined in the Standard Method. In short, these
reports suggest that the actual sensitivity factor might be lower than the Standard Method's
value, and hence the calculated ozone concentration will be undervalued.
The Standard method's proportionality constant,/, (0.42 L mg^cm"1) that is used to
calculate the ozone residual is based on an indigo trisulfonate molar absorbance, e, of 20,000 M"1
cm"1. These recent reports suggest that/may not be constant and may depend on:
1. The source and age of the neat indigo trisulfonate solid
2. The age and handling of the indigo stock solution that is prepared as part of the
method
Briefly, these reports indicate that, due to either of the above aspects,/can be
substantially lower than 0.42 L mg^cm"1. In other words, the molar absorbance can be much
lower than20,000 M^cm"1. Gordon et al. (2000a and 2000b), Rakness et al. (2001), Rakness and
Hunter (2001), and Rakness et al. (2002) reported that the apparent molar absorbance of some
indigo stock solutions might be as low as 11,000 M^cm"1, and in an extreme case 6,000 M^cm"1.
The authors suggest that the ramifications of applying an/value of 0.42 L mg^cm"1 when the
solution has a lower true/value are the underestimation of the ozone concentration.
These issues are not completely resolved at the time of the writing of this guidance
manual. However, the evidence is suggestive enough to warrant a new recommended QA
control concerning the quality of the indigo stock solution. Should changes in the Standard
Method be approved prior to issuing the final version of this guidance, those changes will be
discussed.
The gravimetric indigo trisulfonate method is fairly easy to apply in the field and is
accurate. It should be noted that the method described herein is somewhat different than the 20th
Edition of Standard Methods in that the volume of both the blank and the samples are determined
gravimetrically. The procedural steps include:
1. Prepare indigo stock solution as described in Standard Methods
2. Prepare Reagent II solution (for ozone residuals greater than 0.05 mg/L), as described in
Standard Methods.
3. Prepare flasks for sampling.
3.1. Clean, dry and label several 125 mL Erlenmeyer flasks (enough for each sample
plus one blank).
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Appendix C — Measuring Ozone Residual
3.2. Obtain the tare weight of each flask.
4. Add 10.0 mL of Reagent II solution to each flask.
5. Add approximately 90 mL of distilled water to one or two flasks and use these flasks as
the blank (i.e., use value from one blank or average of values from two blanks).
6. Collect ozone sample.
6.1. Thoroughly flush sample line to be used.
6.2. Do not run sample down the side of the flask, as this will cause ozone off-gassing.
6.3. Fill flask with sample, gently swirling flask until a light blue color remains. Do
not bleach completely or the residual value will be incorrect.
7. Wipe-dry the outside of sample and blank flasks.
8. Weigh sample and blank flasks.
8.1. Total weight for sample is tare weight of flask plus 10 mL indigo plus added
sample.
8.2. Total weight for blank is tare weight of flask plus 10 mL indigo plus added
distilled water.
9. Prepare the spectrophotometer for measuring absorbance.
9.1. Identify the cell path length (e.g., 1-cm, 5-cm, etc.).
9.2. Set the wavelength to 600 nanometers.
10. Measure absorbance of blank and samples within four hours.
10.1. Follow instructions for spectrophotometer concerning zeroing the instrument.
10.2. Record absorbance of each sample and each blank.
11. Complete calculations - see example below.
Example:
A 10 mL aliquot of Reagent II solution was added to a 125 mL Erlenmeyer flask that was
used for the blank. The flask had a tare weight of 83.62 g. The final weight of the flask, plus the
10 mL aliquot of reagent, plus the added distilled water was 179.77 g. The total volume of the
10 mL Reagent II aliquot plus added distilled water was determined by subtracting the bottle's
tare weight from the total weight, assuming that 1 mL of liquid weighs 1 g (96.15-mL =
[179.77-g- 83.62-g] * 1-mL / 1 g).
The spectrophotometer had a path length of 1 cm. The absorbance reading of the
gravimetric blank was measured as 0.234 cm"1 at wavelength of 600 nm. This reading must be
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Appendix C — Measuring Ozone Residual
corrected for the difference in the volume of the blank used in order to check the quality of the
reagent. The calculated absorbance of a 1:100 blank dilution can be determined using Equation
C-l. In this case, the l:100-absorbance value was 0.225-cm"1, which is greater than or equal to
0.225-cm"1. This means that the indigo trisulfonate solution was considered acceptable.
| Absorbance |
I Path Length ) (r 1^
x Volume of Blank = Absorbance in cm " (2) 100 mL l^"1^
100 mL
( 0.234 ^
1
V ; x 96.15 mL = 0.225 cm4
100 mL
The 125-mL flask that was used for the ozone sample had a tare weight of 94.10 g.
Sample water was directed into the 10-mL of Reagent II solution until a light blue color
remained. The final weight of the flask, plus the 10-mL aliquot plus the sample, was 167.39 g.
The absorbance reading at a path length of 1 cm was 0.159. The volume of the water sample
was63.29-mL(63.29-mL = [167.39-g- 94.10-g- 10-g] * 1-mL/l-g). The ozone residual was
calculated using Equation C-2, which resulted in a value of 0.41 mg/L.
xVT)
-^ (C-2)
f x Vs x b
where AB = absorbance of the blank (as measured, not as corrected by equation C-l)
AS = absorbance of the sample
VB = volume of the blank plus indigo, mL
VT = total volume of the sample plus indigo, mL
Vs = volume of the sample (total weight - tare weight - 10)
f=0.42
b = path length of cell, cm
(0.234x96.15)-(0.159x73.29) n A1 n
± '—± '- = 0.41 mg/L
0.42 x 63.29 x 1
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Appendix C — Measuring Ozone Residual
C.3 On-line Ozone Residual Analyzer Calibration
On-line ozone residual analyzers are available that can continuously monitor ozone
residual in the water. This makes it possible to automate the disinfection credit calculation using
the plant's computer-control system. However, the analyzers must be maintained properly and
their calibration must be checked periodically so that readings match grab-sample results that are
based on the indigo trisulfonate procedure. Generally, probe-type monitor readings tend to drift
downward over time due to weakening of the electrolyte solution. Calibration checks should be
conducted regularly, such as at least once per week. This section describes a calibration check
protocol which involves collecting grab-samples and analyzer readings simultaneously and
comparing the values.
The calibration check should consist of collecting at least three, and preferably five, ozone
residual grab samples and corresponding analyzer readings. The following calibration protocol
has been used successfully at operating ozone facilities.
1. Collect three to five grab-sample ozone residuals. Obtain an analyzer reading while the
grab sample is being collected. Wait 15 seconds to 30 seconds between each pair of grab
sample and analyzer reading.
2. Measure the ozone residual concentration in the grab samples using the indigo
trisulfonate method.
3. Calculate the average grab-sample ozone residual value and the average analyzer ozone
residual value.
4. Compare the average of the on-line analyzer to that of the indigo grab-samples. The
average of the on-line analyzer cannot deviate more than 10% or 0.05 mg/L (which ever
is largest) from the grab-sample average. If the average of the on-line analyzer deviates
more than this, then adjust the meter reading per the manufacturer's instructions. Note
that this QA control is two-sided. It is especially important that the on-line analyzer not
record more than 10% or 0.05 mg/L greater than the grab samples. However, a negative
deviation (negative bias), while not effecting public safety, may also be useful as an
indication of a malfunctioning unit.
5. Allow the analyzer to stabilize for a period of 30 minutes after adjusting the meter
reading and repeat steps 1 through 4 until the difference calculated in step 4 is <10% of
the grab-sample average and <0.05 mg/L.
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Appendix D
Derivation of Extended CSTR Equations
The discussion presented in the document used some key equations and relied on specific
assumptions. In this appendix, one key equation is derived, and one key assumption is discussed
and justified.
D.1 Derivation of the Equation Used to Calculate k*
In Appendix B, Equation B-2 expressed the value of k* between two points 1 and 2 as
shown by Equation D-1:
,_2 xQ
\Volume\i_2
(D-l)
Equation D-l is a transformation from the equation of first-order decay across a series of
TV equal-size CSTRs:
i /* HDT}
l+*l-2hn—
(D-2)
The derivation of this equation can be found in many reference texts on modeling
chemical reactors (e.g., Froment et al., 1990; Levenspiel, 1999). Since HDT is equal to the
volume between locations 1 and 2, \Volume\\-2, divided by the flowrate, Q, then Equation D-2 is
transformed to Equation D-3:
1
1 +
vl-2
(D-3)
Therefore,
l + k
\Volume\i_2
1-2
M 9
(D-4)
then,
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Appendix D — Derivation of Extended CSTR Equations
l + k
1-2
OxN,
1-2
then,
(\Volume\i_2
"1-2
and then,
1 2
[Volume]^
c.
(D-5)
(D-6)
(D-7)
As noted, Equation D-2 is based on the fundamental assumption that the hydrodynamic
profile through the volume separating locations 1 and 2 can be approximated by a series of TV
equal-size CSTRs. If equal-size chambers separate locations 1 and 2, then each chamber is
somewhat conservatively assumed to be an ideal CSTR, with HDT = [Volume\IQ, and the value
of TV in the above derivation is set equal to the number of chambers between locations 1 and 2.
However, it was recognized that not all ozone contactors are configured with equal-size
chambers in series. It is possible to treat each chamber as its own CSTR and have a series of
unequal-size CSTRs. An expression of CilCi similar to that shown in Equation D-2 is still
possible. For example, if locations 1 and 2 were separated by three CSTRs with HDT values of
HDTa, HDTb, and HDTC, the ratio of C^Ci for a first-order decay reaction can still be expressed
as:
C9
1
1
1
IcJ- [i + C(M)rj] [i
Or in general terms,
^^^^_^^^^^^^^^^^^^_ ^^^^^^^^^^^^^^^^^^^^^^^^^^^
l2 (HDT, )] [l + kl, (HDTc}\
(D-8)
(D-9)
Unfortunately, it is not possible transform Equation D-9 to derive a simple linear
expression of A:* as a function of the other measured parameters when the number of chambers is
greater than three. To maintain a singular methodology for any number of chambers, and to
allow the calculation to be performed in conventional spreadsheets and plant computer control
systems, a compromise was to assume equal-volume CSTRs. With this assumption, Equation
D-l is used to calculate the value of k* between two sampling locations regardless of the number
and sizes of chambers between the two locations.
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Appendix D — Derivation of Extended CSTR Equations
The simplifying assumption of equal-size CSTRs for calculating k* is non-conservative
relative to a &* value calculated by allowing for unequal sized chambers. That is, for first-order
ozone decay reaction, unequal sized CSTR reactors in series would be the least efficient (ideal)
reactor configuration for promoting ozone decay. Hence, calculating k* based on equation D-9
gives the largest, or most conservative, value of k*. The model of equal sized CSTR reactors in
series is a more efficient configuration for promoting ozone decay. Hence, calculating k* from
Equation D-l (based on equation D-2) gives a less conservative estimate of k*. To take the
comparison to the opposite extreme, calculating k* based on a plug-flow assumption (e.g.,
Equation 4-7) gives the smallest, or a non-conservative, estimate of &*.
The impact of the simplifying equal-sized CSTR assumption on the estimate of k* and
Cm involves several considerations. The first issue is the quantitative difference between the
most conservative estimate, based on Equation D-9, and the recommended approach based on
Equation D-2. This is essentially an issue of what chemical and hydrodynamic conditions affect
the efficiency of the ozone decay reaction. This is a somewhat complex issue dependent on the
reaction rate (represented by the Damkohler I Number, Dai [Dai= &*xHDT]), the number of
chambers considered, and the disparity in volumes among the unequal-sized chambers. In
principal, as the reaction rate increases, the number of chambers approaches two (the minimum),
and the volume differences among the chambers increases, the difference in reaction efficiency
between the two reactor configurations increases. Some situations could result in approximately
30% differences between k* values. Other situations could results in negligible differences.
Because of the many factors involved it is difficult to establish qualitative rules for all possible
cases. However, for contactors with 2-3 chambers with a large volume difference and a large
Dai, then the utility and the primacy agency may consider further analysis.
The second, and perhaps overriding, issue concerning the impact of the simplifying
assumption is whether or not it still provides a certain element of conservatism over the true
contactor performance. That is, an actual contactor with unequal sized chambers might have
reasonably good hydrodynamics such that even the equal-size CSTR assumption is conservative.
This too, however, is very system specific, and is a difficult issue to resolve due to the numerous
factors involved.
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Appendix E
Watershed Control Best Management Practices (BMPs)
This appendix provides a list of programmatic resources and guidance available to assist
systems in building partnerships and implementing watershed protection activities. Examples of
partnerships and possible control measures for different sources are summarized in chapter 2, section
2.4.2; this appendix provides further detail to the control measures described in chapter 2.
E.1 Regulatory and Other Management Strategies
For systems in watersheds where most of the land is privately owned, land use regulations may
be the best way to control pollution, especially in heavily developed or growing areas. Examples of
possible regulations include septic system requirements, zoning ordinances specifying minimum lot sizes
or low-impact development, limits on discharge from wastewater treatment plants and other facilities,
pet waste cleanup ordinances, and requirements for permits for certain land uses. Your ability to
regulate land use will depend on the authority granted to your municipality by the state, the ownership of
your system (public or private), and the support of your local government and the public. Regulatory
authority, steps for designing a regulation that can withstand lawsuits, and types of land use regulations
are described in the paragraphs below.
E.1.1 Determining Authority to Regulate
Where a water system is privately owned, it may be necessary to ask the cooperation of the
local government to get source water regulations passed. For a municipal water system whose
watershed is located entirely within the municipality, issuing zoning or land use ordinances should be less
of a hurdle. The ability of a municipality to pass a land use ordinance or other law to help reduce
contamination may depend on the authority the state grants to the local government in the state
constitution or through legislation, although states normally do not interfere with the actual land use and
zoning rules (AWWARF 1991). States generally permit zoning for the purposes of protecting public
health or general welfare. However, some states may prevent local governments from passing laws that
are more stringent than state law or that conflict with state laws. State laws in other states may prevent
municipal governments from passing certain local laws that are not expressly permitted elsewhere in
state law.
If the watershed or the area of influence on water quality extends throughout several
municipalities, it can be difficult to standardize watershed control practices throughout the watershed.
The legal framework used will depend on who has jurisdiction over land use in the watershed and on
the authority of the water system (AWWARF 1991). New York State law, for instance, authorizes
municipalities to draft watershed regulations, which are then approved and adopted by the state. This
gives the municipalities the authority to enforce the watershed rules within their watersheds even if the
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Appendix E - Watershed Control Best Management Practices
watershed is outside municipal boundaries. For instance, New York City sets water quality standards,
land use restrictions, and approves wastewater treatment plant designs in its watersheds in upstate New
York. The City of Syracuse conducts watershed inspections on Skaneateles Lake, its source of
supply, several miles outside of Syracuse. Both of these systems are filtration avoidance systems, so it
is especially important that they have some control over areas outside their jurisdictions.
The Metropolitan District Commission, although not a PWS, was created by the State of
Massachusetts and is authorized to promulgate and enforce watershed protection regulations in
watersheds used by the Massachusetts Water Resources Authority to provide water to the Boston
metropolitan area. Some watersheds which extend across state boundaries have governing bodies
authorized by Congress. The formation of the Tahoe Regional Planning Agency was the result of a
compact between the States of California and Nevada and was approved by Congress. The agency is
authorized to pass ordinances, including source water protection rules, that regulate land use in the area
around Lake Tahoe.
County governments in some states may have some zoning authority and may be able to assist
with enforcement of some regulations affecting source water (e.g., septic systems). In most cases
where watersheds cross jurisdictions, however, PWSs will not have regulatory or enforcement
authority. PWSs in this situation should work with other local governments' PWSs and agencies in their
watersheds to sign memoranda of agreement or understanding, in which each entity agrees to meet
certain standards or implement certain practices.
The City of New York signed a memorandum of agreement in 1997 with the State of New
York, EPA, and 79 municipalities within its watersheds. The agreement calls for the creation of local
and regional watershed protection programs and, for New York City, funding for water quality and
infrastructure improvement projects in upstate New York. Other cities, such as Salem and The Dalles,
both in Oregon, have signed memoranda of understanding with the U.S. Forest Service, which owns
most of the land in the cities' watersheds. These memoranda define the management responsibilities of
each PWS and the Forest Service.
E.1.2 Zoning
This section describes the steps you should follow to make sure a zoning law can withstand a
legal challenge. Basically, it is important to make sure the appropriate procedures are followed and that
the law has sufficient scientific basis (AWWA 1999). First, be sure you have the authority to regulate,
especially if you are proposing something besides a simple zoning law. Make sure the rule is specific
enough; if a map of an overlay district is not drawn to a small enough scale, it may be difficult to tell
which properties are affected. Comply with all administrative procedure requirements, such as notifying
the public of the proposed changes and holding a public hearing; failure to do so is the most common
reason for rules being revoked. Follow substantive due process, which means that the regulation
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Appendix E - Watershed Control Best Management Practices
should promote the municipality's public health goals. In practice, this means the ordinance should
conform to the objectives of the watershed control program plan. The plan should contain enough data
to illustrate how the ordinance will affect water quality.
Ordinances should also be designed to withstand a takings lawsuit (AWWA 1999). The fifth
amendment to the U.S. Constitution states that private property may not be taken for public use without
just compensation. Any physical invasion without consent is always considered a taking, even if the
landowner retains ownership of the land. Installation of a monitoring well or stream gauge without
consent is an example of a taking.
In addition, ordinances that "fail to advance a legitimate government interest" or "deny a
landowner economically viable use of his land" can be viewed as takings, even if the landowner retains
full ownership (AWWA 1999). The first criterion means that there should be a need for the ordinance;
for example, if a planned development's storm sewers and wastewater treatment plant will discharge
into an area outside a municipality's wellhead protection area, the municipality cannot cite impacts on
the drinking water as a factor in the decision to restrict development without compensating landowners.
Under the second criterion, if property values decrease but still retain some value (e.g., due to a
decrease in permitted building density), the ordinance does not result in a taking. A regulation that
restricts all development would probably be considered a taking. In keeping with these two criteria, the
effect of an ordinance should be proportional to the predicted impact of development. Thus, if a
municipality determines that half-acre zoning is sufficient to protect a drinking water source, it may not
zone for five acres.
To prevent takings claims, the municipality should show the need for the regulation and a
connection between the ordinance and the expected result (AWWA 1999). This proof should be
based on a scientific analysis beginning with an accurate delineation of the watershed or wellhead
protection area/recharge area. A zoning district based on an arbitrary fixed radius around a well or
lake would probably be considered insufficient in court unless it is characterized as an interim boundary.
A court challenge could claim that such a district protects an area that does not contribute to the
watershed or that land that is part of the watershed is not being protected (failing to advance the
government's interests).
Following the delineation, determine the impact the regulation will have by mapping current and
projected residential, commercial, and industrial development under current zoning requirements. Then
map current and projected development for existing regulations and for the proposed ordinance, and
determine the potential pollutant load under each scenario (AWWA 1999). You may not be able to
determine Cryptosporidium loading if you have not monitored, but there may be data available on
fecal coliform bacteria from different sources in your watershed (e.g., agriculture, septic system failure,
pets and wildlife). If your PWS has not collected such data, other local agencies, such as sewer
authorities, non-profit groups, universities, or planning commissions, as well as the U.S. Geological
Survey, may have water quality data. Water quality models can help you determine pollutant loading.
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This "buildout analysis" will help you show how your proposed ordinance advances a legitimate
government interest and how the effect of the ordinance is proportional to the impact of land use in your
watershed.
Types of Ordinances
Watershed ordinances usually apply within an "overlay district," which may be the area of
influence you determined for your watershed control plan. All existing zoning or land use regulations
apply within that area, but additional requirements apply within the overlay district. Following are some
land use ordinances you may wish to consider:
• Large-lot or low-density zoning. Unless lots are very large (such lots can use septic
systems and wells), large-lot zoning may be inefficient, as it increases costs for sewer,
water, and road development. This type of zoning also may go against affordable housing
requirements. However, it may be useful in agricultural areas for preserving rural character
and preventing subdivision of farms.
• Limits on certain types of land use except by special permit. Such ordinances should
specify criteria for granting special permits and designate an authority that may grant
permits. The authority should present findings that back up its decision to grant the permit.
Special permits are granted for a particular lot, not for the owner of that lot.
• Impact fees. The regulating authority must be sure it has authority to impose such fees.
Impact fees collected can be used to pay for mitigation of pollution caused by development,
e.g., for preventing runoff or buying land elsewhere in the watershed. Fees should be
proportional to the impact and the cost of mitigation, and the purpose of the fees should be
specified in the regulation. A disadvantage to impact fees is that they may in some cases be
considered taxes, and local governments' authority to impose taxes may be limited. Fees
are more likely to withstand challenge if they are framed as optional services provided to
the developer (i.e., the developer can choose not to develop) and if the fees are set aside
for the PWS or stormwater utility rather than put into general funds.
• Submission and approval of a watershed protection plan or impact study as a condition for
development of a subdivision or apartment complex. This type of ordinance requires that
watershed protection plan or stormwater control be implemented before a building
certificate of compliance is issued. Plans should be required to designate the party
responsible for maintaining stormwater facilities after construction is complete.
• Performance standards. A performance standard permits development but limits impact of
the development. For example, the regulation could specify that permits require that the
pollutant loading rate of the development is no more than a certain percentage of the pre-
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development loading rate of the area. This would require enforcement or monitoring to
make sure the development continues to comply. In its permit application, the developer
would also be required to list mitigation steps it would take if it exceeded the pollutant
loading requirements.
Most zoning ordinances have grandfather clauses that allow nonconforming land uses to
continue. Ordinances may also allow the zoning authority to grant variances if the topography or size of
a lot make it difficult to comply with a zoning requirement.
Examples of source water protection ordinances can be found at
htto://www.epa.gov/owow/nps/ordinance/osm7.htm.
E.1.3 Land Acquisition and Conservation Easements
Acquisition of watershed land by the utility or its affiliated jurisdiction is often the most effective
approach to protecting the water source. Landowners usually consider acquisition as fair, since it
compensates them for their property while protecting the watercourses nearby. Land conservation has
also been found to provide multiple benefits aside from controlling pathogen contamination, such as
flood control, limited recreational use, and the protection of historic and environmental resources.
EPA's Drinking Water State Revolving Fund allows a percentage of the fund to be set aside for land
acquisition associated with watershed protection.
Several organizations exist that can help systems purchase watershed land to protect drinking
water quality, especially when government agencies are unable to move quickly enough to buy land
when it becomes available. The Trust for Public Land (http ://www.tpl. org^ and small local land trusts
and conservancies can facilitate the land acquisition process. Trusts can buy and hold land from
multiple landowners on behalf of a water system until the system can assemble funding to purchase it
from the trust. Trusts may also maintain land ownership themselves. The Trust for Public Land also
can assist with development of financing strategies for land purchases.
Trusts also can work with landowners to buy or have landowners donate conservation
easements. An easement is a legal document that permanently limits the development of a piece of
land, even after the land is sold or otherwise changes ownership. The landowner selling or donating the
easement specifies the development restrictions to apply to the land. The law varies from state to state,
but the owner of the easement (the government agency or land trust) has the authority to determine if
the requirements of the easement are being followed. If not, the owner of the easement make take legal
action. Easements donated to government agencies or to land trusts may be eligible for tax deductions.
See http://www.landtmst.org/ProtectingTand/EasementInfo.htm for frequently asked questions about
easements and for an example of a model easement for use in the State of Michigan. The Land Trust
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Alliance (http://www.lta.orgl a trade organization for land trusts, has published handbooks on designing
and managing conservation easement programs.
Other government agencies, such as the U.S. Forest Service or state natural resource
departments, may be able to buy parcels in your watershed if you are unable to afford to purchase all
the land that needs to be protected.
E.2 Addressing Point Sources
E.2.1 Concentrated Animal Feeding Operations
Some animal feeding operations (AFOs) may be considered concentrated animal feeding
operations (CAFOs) if they have more than a specified number of animals and/or if they discharge
pollutants into navigable waters through a manmade ditch or other device or if they discharge directly
into waters of the United States. Possible sources of pollutants at CAFOs include runoff that flows
through feedlots; failure of pumps, pipes, or retaining walls of manure storage lagoons; runoff from
areas where manure is applied to the soil; and direct contact of animals with surface water. CAFOs
are located primarily in the South and Midwest, but the number of such facilities is increasing as farms
consolidate their operations.
EPA recently issued a rule that changed the requirements on CAFOs that must apply for
National (or State) Pollutant Discharge Elimination System (NPDES) permits (U.S. EPA 2003). All
CAFOs are regulated as point sources in the NPDES program. Previously, CAFOs could be exempt
from permitting if they could show that they did not discharge during 25-year 24-hour storms. The new
rules eliminate this exemption, unless a facility can show that it does not discharge at all. NPDES
permits for CAFOs generally allow zero discharge of pollutants and may also require the use of certain
technologies. CAFOs are required to report to the state within 24 hours of exceeding effluent limits
(U.S. EPA2001a).
Many CAFOs do not currently have permits due to limited state resources for compliance
(medium and small AFOs may be designated as CAFOs only by state or regional staff after onsite
inspection). For CAFOs (and other NPDES permittees) that do have individual permits, you may want
to attend the public hearing required as part of the permit renewal process, especially if you have any
concerns about the adequacy of the existing permit requirements to prevent Cryptosporidium or other
drinking water contamination. If a CAFO in your area of influence does not have a permit, consider
encouraging its managers to apply for one or working with them to implement a nutrient management
plan or other BMPs.
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E.2.2 Wastewater Treatment Plants
All wastewater treatment plants in the United States are required to provide secondary
treatment (primary treatment consists of sedimentation, while in secondary treatment, aeration provides
oxygen to bacteria that take in nutrients and digest organic material) (U.S. EPA 200Ib). Most plants
are also required to disinfect their effluent before discharging. However, conventional chlorine
disinfection may be ineffective against Cryptosporidium.
Some wastewater treatment facilities are beginning to implement treatment similar to that used
for drinking water treatment. The Robbins Plant of the Upper Occoquan Sewerage Authority in
Centreville, Virginia, discharges into a stream that feeds into a reservoir in northern Virginia. Following
secondary treatment using activated sludge, the facility provides other treatment, including clarification,
multimedia filtration, and disinfection (U.S. EPA 2000a). The Cole Pollution Control Plant in Fairfax
County, Virginia, which discharges into a creek flowing into the Potomac River, also uses advanced
treatment, including chlorine disinfection, filtration, and dechlorination (Fairfax County 2001).
PWSs should identify all wastewater treatment plants in their watersheds and determine what
their permit effluent limits are and whether the limits are being met. Some of this information may
already be available through the source water assessment program. PWSs may wish to work with the
wastewater utilities and appropriate government agencies to get them to voluntarily upgrade the
treatment provided. PWSs with the appropriate legal authority may wish to require wastewater plants
to use certain technologies. An example might be switching from chlorine to ozone or ultraviolet
radiation disinfection before discharging.
E.2.3 Combined Sewer Overflows
Combined sewer overflows (CSOs) are most common in older cities in the northeastern and
midwestern United States and can be a significant contributor of Cryptosporidium to urban
watersheds.
There are three major structural solutions to the problem of CSOs. The first is to separate
combined sewers into sanitary and storm sewers, where sanitary sewers flow to the wastewater
treatment plant and storm sewers release to surface water. This separation may cause the unwanted
side effect of increasing overall contamination due to the fact that storm water is no longer being
treated. For example, separating sewers resulted in only an estimated 45-percent reduction in fecal
coliform removal in a bay in Boston (Metcalf and Eddy 1994, cited in U.S. EPA 1999c). Separating
sewers is also very expensive and often impractical. The second option is to increase the capacity of the
wastewater treatment plant so that it is able to treat combined sewage from most storms. The third,
very expensive solution is to build aboveground open or covered retention basins or to construct
underground storage facilities for combined sewage to hold the sewage until the storm has passed and
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can be treated without overloading the plant. The Metropolitan Water Reclamation District in Cook
County, Illinois, chose the third option, building 109 miles of tunnel up to 35 feet wide and several
underground reservoirs underneath Chicago and its suburbs, with most funding from EPA (MWRD
1999). In addition to reducing CSOs, the tunnels eliminated flooding that had previously affected the
area due to its flat topography. The project also eliminated the need for individual municipalities to
implement their own CSO programs.
CSOs are not regulated directly under their own program, but EPA has a CSO control policy
(U.S. EPA 1994) which encourages minor improvements to optimize CSO operation, and CSO
management may be written into NPDES or SPDES permits. The CSO policy also encourages
development of long term control plans for each CSO system; such plans would require significant
construction, and few utilities have drafted or implemented them yet. Planned construction projects can
be included as control measures in watershed control plans. PWSs should determine the extent of the
CSO programs in place in municipalities within their watersheds. They may be able to work with other
utilities to address overflow sites of particular concern. Many municipalities with CSOs made major
structural changes to their systems in the 1980s and 1990s; current improvements are more likely to
involve streamlining operation and management.
Many large cities have already addressed a significant portion of their CSOs, but there are
additional smaller steps they can take to reduce the amount of sewage released during a wet weather
event. These include maximizing in-line storage (storage available in the sewer pipes themselves)
through regular inspection and removal of obstructions and sediment, installation and maintenance of
flow regulators, upgrading pumping capacity (assuming the treatment plant can handle the increased
volume); raising weirs at CSO outfalls; and installing computerized sensors to control flow during
storms.
Additionally, reducing inflow (entry of storm water into the combined sewers) and infiltration
(entry of storm water through cracks and manholes) is important. Inflow can be reduced by
disconnecting roof drains and sump pumps from sewers, restricting flow into storm drains, and
constructing storm water detention ponds and infiltration devices. If overflow events can be reduced, it
may be possible to eliminate some outfalls. Some sewer systems also have installed some treatment of
CSOs including disinfection and screening; this treatment may be required as part of a NPDES permit.
E.2.4 Sanitary Sewer Overflows
Sanitary sewer systems normally feed into wastewater treatment plants but can still cause water
quality problems. Sanitary sewer overflows (SSOs) occur when untreated and mostly undiluted
sewage backs up into basements, streets, and surface water. SSOs discharging to surface water are
prohibited under the Clean Water Act. Insufficient maintenance and capacity and illegal connections
are some of the primary causes of SSOs. Many sanitary sewers are subject to inflow and infiltration,
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just as combined sewers are, caused by cracks in pipes or bad connections to service lines. They may
receive water they were not designed to receive, such as storm water from roof drains that should be
connected to storm sewers, or wastewater from new developments that did not exist when the
wastewater treatment plant was designed. SSOs can be reduced by cleaning and maintaining the sewer
system; reducing inflow and infiltration by repairing leaking or broken service lines; increasing sewer,
pumping, and/or wastewater treatment plant capacity; and constructing storage for excess wastewater
(U.S. EPA 2001c). EPA is proposing a rule that will require sewer systems to implement capacity
assurance, management, operation, and maintenance programs and will require public notification of
overflow events. This information will assist PWSs in addressing SSO point sources.
E.2.5 Municipal Separate Storm Sewer Systems
Municipal separate storm sewer systems (MS4s) in areas with populations of more than
100,000 are also required to obtain NPDES permits. Information on storm sewer outfall locations,
volume discharged, conventional pollutant loads, and existence of illicit discharges is submitted as part
of the permit application process (U.S. EPA 1996). In addition, these MS4s must develop
management plans addressing items such as outfall monitoring, structural and nonstructural BMPs to be
implemented, and identification and elimination of illicit discharges. Illicit discharges to MS4s include
any non-stormwater discharges, such as discharges that should be connected to sanitary sewers (e.g.,
water from sinks, floor drains, and occasionally toilets), illegal dumping of sewage from recreational
vehicles, sanitary sewer overflow backing up through manhole covers into storm drains, effluent from
failing septic systems, water from sump pumps, etc.
Small MS4s (serving areas with populations of less than 100,000) are subject to NPDES
permit requirements if they are located in "urbanized areas" as determined by the Bureau of the Census.
Some small MS4s in urbanized areas may be eligible for waivers from the NPDES requirement. Those
MS4s subject to NPDES permits must implement "control measures" in six areas, including a plan for
eliminating illicit discharges (U.S. EPA 2000b).
PWSs should work with all MS4 utilities in the area of influence to gather existing information
about storm water contamination. MS4 utilities may need to install or retrofit structural BMPs, such as
retention ponds, to reduce contamination. Most studies of structural stormwater BMPs focus on
nutrient or sediment removal, so almost no information is available on Cryptosporidium removal, and
limited information is available on bacterial removal. However, a few studies of bacteria in structural
BMPs show that bacteria survive for weeks to months in retention pond sediments and natural lake
environments. In addition, other studies showed higher bacteria levels in retention pond effluent than in
influent. This suggests that stormwater pond sediments resuspended during storms can be a source of
pathogens (Schueler 1999).
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E.3 What BMPs Can Help Alleviate Nonpoint Sources?
The following sections describe BMPs for agricultural, forestry, and urban sources of
Cryptosporidium. Your watershed control program plan must discuss how these or any other BMPs
you choose will be implemented in the area of influence. EPA Section 319 grants and Clean Water
State Revolving Fund loans can be used for nonpoint sources and watershed management purposes.
E.3.1 Agricultural BMPs
E.3.1.1 Management Programs
The U.S. Department of Agriculture (USD A) (2000) recommends a multiple-barrier approach
to controlling pathogen transport and proliferation on farms and in agricultural watersheds. It
recommends the following "control points:"
• Preventing initial infection by controlling pathogen import to the farm
Controlling the reproduction and spread of the pathogen throughout the farm
• Managing waste
• Controlling pathogen export from the farm
These control points should not be treated separately. For example, waste management affects
reproduction and spread of the pathogen if feed becomes contaminated with waste. Waste
management is also related to pathogen export; composting can kill Cryptosporidium oocysts before
they leave the farm.
BMPs that can reduce pathogen loading include composting, waste management (manure
storage and land application), grazing management, feedlot runoff diversion, and buffer or filter strips.
PWSs should work with their local soil and water conservation districts and agricultural or cooperative
extensions, which can help farmers design and implement pollution management plans and BMPs.
Details about these conservation practices are provided in the USDA Natural Resources Conservation
Service's (NRCS) National Handbook of Conservation Practices (NRCS 1999) at
http://www.ftw.nrcs.usda.gov/nhcp_2.html.
Management strategies designed to minimize direct livestock contamination of surface water
with Cryptosporidium should focus primarily on young animals (those less than 3 months old) and their
waste, since calves are more likely to shed Cryptosporidium. Efforts should also focus on cow herds
as a whole when calves are present.
Several NRCS programs provide technical assistance to farmers and subsidize the cost of
implementing BMPs. These include Agricultural Management Assistance, the Environmental Quality
Incentives Program, the Conservation Reserve Program, and the Conservation Reserve Enhancement
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Program (see www.nrcs.usda.gov/programsY The last two programs also pay farmers rent on erodible
cropland taken out of production. More information is available at
http://www.fsa.usda.gov/dafp/cepd/crpinfo.htm. The 2002 Farm Bill increased funding for these
programs and created new ones as well. For example, the new Conservation Security Program will
recognize and reward farmers who are leaders in environmental management.
E.3.1.2 Composting
Composting can effectively reduce pathogen concentrations. Temperatures greater than 55
degrees Celsius (131° F) can be easily attained and maintained long enough to inactivate most oocysts
(Blewett 1989). To reliably achieve Cryptosporidium inactivation, however, the entire waste mass
should be uniformly treated and there should be no cold spots. Intense management may be needed to
completely mix the composted material.
E.3.1.3 Buffer Strips
Buffer strips, or filter strips, provide a buffer between the area of manure application or grazing
and adjacent streams or lakes. Filter strips have been studied primarily with regard to their
effectiveness at sediment and nutrient removal. Nutrient removal has been shown to be extremely
variable, while agricultural grass filter strips consistently remove 65 percent or more of sediment (Ohio
State University Extension undated). How sediment removal relates to Cryptosporidium removal is
not known. Cryptosporidium often adsorbs to suspended material the size of clay and silt particles,
which is the type of sediment that is likely to pass through the filter strip, especially at high flow
velocities.
Few studies have evaluated the ability of buffer strips to remove Cryptosporidium. However,
one study found that grass filter strips with slopes of 20 percent or less and widths of at least 3 meters
resulted in removal of 1 to 3 log (90 to 99.9 percent) during mild to moderate precipitation (Atwill et al.
2002). More data are available on removal of bacteria. Moore et al. (1988) reviewed the work of
several investigators and concluded that vegetative filters are most reliable at removing bacteria at high
concentrations from waste effluent. Bacterial populations in runoff from buffer areas seem to equilibrate
at approximately 104 to 105 organisms per 100 milliliters, regardless of experimental conditions. For
this reason, USDA (2000) recommends that buffers and filter strips be considered secondary practices
for pathogen control and be used in conjunction with other source, proliferation, and waste treatment
and control measures to form an integrated, comprehensive pathogen management system.
The NRCS encourages the use of riparian forest buffers of at least 35 to 100 feet (depending
on floodplain width) for stream restoration purposes but recommends additional width in high sediment
and animal waste application areas. Grass filter strips may be added upgradient of the forest buffers or
may be used alone. The NRCS (1999) recommends grass filter strip widths of at least 20 feet, but
width should be determined based on the slopes of the strip and the field being drained, the area being
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drained, the erosion rate, sediment grain size distribution, runoff volume, and the vegetation in the strip.
Filter strips should follow contours as much as possible to promote sheet flow. The area being drained
should have a slope of less than 10 percent. Grazing should not generally be permitted within the filter
strip. Maintenance activities should include mowing to prevent woody growth, inspection after storm
events, repair of any gullies, reseeding of disturbed areas, and any other steps needed to maintain
overland sheet flow.
E.3.1.4 Grazing Management
Managed grazing can be cheaper and less environmentally damaging than confined feeding and
unmanaged grazing. It decreases feed, herbicide, equipment, and fertilizer costs, while reducing erosion
and increasing runoff infiltration and manure decomposition rates (Ohio State University Extension,
undated). In managed, or rotational, grazing, a sustainable number of cattle or other livestock graze for
a limited time (usually 2-3 days) on each pasture before being rotated to the next pasture. This allows
vegetation regrowth and prevents overgrazing, which can contribute to erosion and runoff, and helps
distribute manure evenly over the grazed area. It also prevents soil compaction, thereby increasing
infiltration. One of the best ways to prevent surface water contamination during rotational grazing is to
prevent grazing along streams (through fencing and use of a buffer strip) and to provide alternative
water sources for livestock. Providing water in each paddock can increase the number of cattle the
pasture is able to support. Even where rotational grazing is not used, surface water contamination can
be reduced by keeping cattle, especially calves, out of streams.
E.3.1.5 Manure Storage
Manure storage facilities allow farmers to wait until field conditions are more suitable for land
application. Without manure storage facilities, farmers must distribute manure on adjacent fields daily.
However, weather conditions are not always appropriate for manure application. During the winter, for
example, frozen soil conditions allow Cryptosporidium oocysts to be washed into watercourses, and
oocysts survive longer at cold temperatures.
Manure storage facilities should be designed to prevent discharge through leaching or runoff.
They should be lined and, if possible, covered. Facilities that are not covered should be designed to
contain precipitation and runoff from a 25-year 24-hour storm. Storage areas should have
embankments to prevent overflow and collapse of the storage facility and to divert runoff from outside
the facility from contamination. Facilities should be sited outside of flood plains. Manure should be
stored for a time period sufficient for microorganisms to die off.
E.3.1.6 Land Application of Manure
Several precautions taken in manure application can prevent runoff from entering surface water,
reducing the likelihood of Cryptosporidium contamination. Buffer strips should be situated between
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the water body and area of manure application. Manure should not be applied to frozen ground or
before predicted rainfall. Manure should not be applied near tile drains or dry wells or to land subject
to flooding. If soil is dry and cracked, fields should be tilled before application. Soil and manure
should be tested for nutrient levels, and the application rate should be tailored to the soil and specific
crop needs. To minimize runoff, waste should be injected (injection creates holes 6-14 inches deep
and does not turn soil over) or applied to the surface and then plowed under. Applying manure to land
with crop residue or new crops rather than bare soil also minimizes erosion. Surface application
without plowing under may be acceptable if conditions are warm and dry—this enables significant
pathogen die-off (Vendrall et al. 1997) by exposure to UV light and desiccation. The Agricultural
Waste Management Field Handbook (NRCS 1992), Chapter 5, Table 5-3 contains a detailed review
of restricting features that should be considered during manure spreading.
For pastures to be used for grazing, waste should be stored for at least 60 days and then
applied at least 30 days before the scheduled grazing period, to avoid infection of the animals. Use of
these areas for grazing should be limited to mature animals. Manure spreading on pastures used for
grazing or on hayfields should take place when minimal amounts of vegetation are present, just after
harvesting or grazing. This allows sunlight and desiccation to destroy the most pathogens and reduces
the chance of pathogen adherence to the forage.
Critical source areas are defined as saturated areas that can expand and contract rapidly, based
on soil, hydrological, and slope characteristics (Gburek and Poinke 1995). These areas are dominated
by saturated overland flow and rapidly respond to subsurface flow. Therefore, watershed managers
should identify the boundaries of potential saturated areas and ensure that waste is only applied outside
of those boundaries to minimize Cryptosporidium oocyst runoff. Some tools have been developed to
delineate critical source areas (e.g., Cornell Soil Moisture Routing Model; Frankenberger 1999). Less
detailed delineations can also be made using information such as soil drainage class, flooding frequency,
wetland mapping, areas of concentrated flow, and aerial photo interpretations.
E.3.1.7 Feedlot Runoff Diversion
Clean roof and surface water can be diverted away from feedlots to a drainage system that is
independent of a farm's waste management system (Ohio State University Extension 1992). All roofs
that could contribute to feedlot runoff should have gutters, downspouts, and outlets that discharge away
from the feedlot. Berms around the feedlot can divert surface runoff. Diverting clean water before it
drains into the feedlot can significantly reduce the amount of wastewater that needs to be managed.
Runoff within the feedlot should be contained and treated in the waste management system for the lot.
E.3.2 Forestry BMPs
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Forestry practices are not likely to significantly contribute to Cryptosporidium sources, since
wildlife levels decrease or, at most, remain constant after logging. However, logging can cause
increased erosion, leading to increased runoff and making it more likely that Cryptosporidium present
in wildlife will reach the source water. In addition, logging can cause elevated sediment levels, resulting
in high turbidity, which affects water treatment efficiency.
Filter strips, where ground cover is maintained around lakes, permanent and intermittent
streams, and wetlands, help trap sediment. Filter strip width should increase with slope of the area
being logged. Streamside or riparian management zones are intended to stabilize stream banks and
maintain shade over streams to minimize water temperature fluctuations. Streamside management zones
and filter strips often overlap, but limited logging is often permitted within Streamside management zones
(NRCS 1999).
Logging roads should be constructed to minimize runoff through proper grading and drainage.
Road runoff should be diverted away from streams and prevented from channelizing. Loggers should
minimize soil disturbance and compaction on skid trails, the trails used to drag logs to trucks for loading
(U.S. EPA2002a).
E.3.3 Urban/Suburban BMPs
See http://www.epa.gov/owm/mtb/mtbfact.htm for fact sheets on technologies and BMPs
municipalities can use to reduce contamination from wastewater and stormwater.
E.3.3.1 Buffer Zones
For watersheds in urban areas, buffer zones help to protect development on the floodplain from
being damaged when the water is high, as well as protect the stream from the effects of the
development.
The utility, municipality, or cooperating jurisdictions may acquire land bordering the reservoir
and/or its tributaries. Alternatively, buffers can be required by zoning ordinances, conservation
easements, or subdivision regulations. Buffer zones can be fixed width or variable width. In a
fixed-width zone, the buffer zone encompasses a certain distance from the stream bank or some other
hydrological reference point (e.g., the high water mark of a stream). The widths of fixed buffer zones
vary considerably among water sources, frequently ranging from 50 feet to 250 feet of buffer from the
stream edge. Another form of buffer zone, the variable-width buffer, can vary in width depending on
the hydrological sensitivity, stream size, and character of the land adjacent to the watercourse.
Considerations for developing local buffer requirements are the size and location of the stream,
the nature of existing or potential development, and the financial and political feasibility of establishing
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protected zones around the streams and reservoir of the watershed. Although buffer zones have been
found to trap fecal waste (Coyne and Blevins 1995; Young et al. 1980), the extent to which they
reduce Cryptosporidium loading is not well understood. For this reason, buffer zones should be used
to augment, rather than replace, other watershed management practices to help protect overall source
water quality.
Buffer zones should be routinely inspected to ensure that sources of contamination have not
been introduced to the area and that the buffer is being maintained (e.g., that buffers are kept
unmowed). Watershed managers should also be aware of storm sewers and culverts that may be
draining into the waterways and bypassing the buffer zones altogether.
E.3.3.2 Dry Detention Basins
Dry detention basins temporarily store stormwater runoff and release the water slowly to allow
for settling of particulates and the reduction of peak flows. These structures hold a certain amount of
water from a storm and release the water through a controlled outlet over a specified time period based
on design criteria. Most basins dry out completely between storm events. The major failure of these
basins is that some are not designed or maintained properly, resulting in too slow a release of water to
empty the basin before the next storm. If the basin remains partially full, only a portion of the design
runoff volume from the next storm will be retained. With inadequate detention, pollutants are not
removed from the runoff. Dry detention basins also risk the possibility of resuspension of pathogens
from the basin sediments if hydraulic retention times are compromised by poor design or failure to keep
the outlets open.
E.3.3.3 Infiltration Devices
Infiltration devices remove pathogens and particles by adsorption onto soil particles and
filtration as the water moves through the soil to the ground water. Infiltration devices include infiltration
basins, infiltration trenches, and dry wells (NALMS 2000). Properly designed devices can reproduce
hydrological conditions that existed before urban development, and provide ground water recharge and
control of peak storm water flows. In order for them to function effectively, infiltration devices must be
used only where the soil is porous and can readily absorb storm water at an adequate rate. An
advantage of infiltration devices over many other urban BMPs is that they provide significant ground
water recharge in areas with a high percentage of impervious surface.
E.3.3.4 Sand Filters
Sand filters can be used to treat storm water runoff from large buildings and parking lots. As
the name implies, storm water is filtered through beds of sand, which may be located above ground in
self-contained beds, or can be installed underground in trenches or concrete boxes. Underground sand
filters can be installed in urban settings where space is restricted and the filters are not visible.
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Pathogens and particles are removed by filtering storm water through approximately 18 inches of sand.
Above-ground filters may be preceded by grassed filter strips or swales to pre-treat the incoming storm
water and prevent the sand filters from clogging.
Sand filters are often more expensive to construct than infiltration trenches (NALMS 2000).
They do not provide a significant amount of storm water detention, and their ability to remove
pathogens is limited. They require little maintenance; the sand surface should be raked and a few inches
of dirty sand on the filter surface should be removed and replaced periodically, so that the filters do not
clog.
E.3.3.5 Wet Retention Ponds
Wet retention ponds maintain a permanent pool of water that is augmented by storm water
runoff. The ponds fill with storm water, which they slowly release over several days until the pond
returns to its normal depth. Ponds can effectively reduce suspended particles and, presumably, some
pathogens, by settling and biological decomposition. There is concern, however, that ponds attract
wildlife that may contribute additional fecal pollution to the water, rather than reducing contamination.
Bacteria may also survive in pond sediment.
Many people find wet ponds aesthetically pleasing, and welcome their use for storm water
control. Some maintenance of the ponds is required in order for them to continue to function effectively
and to avoid nuisance odors and insect problems. Wetland plants should be periodically harvested,
and the pond inlets and outlets should be kept clear so that flow is not impeded. Wet ponds can be an
appealing play area for children, so safety measures should also be taken to restrict access..
E.3.3.6 Constructed Wetlands
Constructed subsurface flow wetlands (where wetland plants are not submerged) can reduce
Cryptosporidium and bacteria concentrations in wastewater (Thurston et al. 2001). Subsurface flow
prevents the public from coming into contact with wastewater and prevents mosquitos problems.
Wetlands may also be useful for treating storm water or other polluted water. However, the matrix
material of a constructed subsurface flow wetland (gravel is often used) may provide an environment for
bacterial growth, and animals living in the wetlands may contribute microbes to the effluent (Thurston et
al. 2001). Animals are probably less significant than they would be in a free water surface wetland. The
growth of bacteria in the wetland medium is both positive and negative—bacteria that help break down
materials in wastewater are more plentiful, but fecal coliform also can survive in such environments.
Constructed wetlands are relatively inexpensive often used on small scales to treat water at small
facilities such as schools, apartment complexes, and parks (U.S. EPA 2000c).
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E.3.3.7 Runoff Diversion
As with feedlot runoff diversion, structures can be installed in more urban settings to divert
clean water flow before it reaches a contamination source. Structures that channel runoff away from
contamination sources include stormwater conveyances such as swales, gutters, channels, drains, and
sewers. Graded surfaces can also be used to re-direct sheet flow, and diversion dikes or berms can be
installed to route sheet flow around areas that are being protected from runoff.
E.3.3.8 Pet Waste Management
Municipalities can implement pet waste management programs to encourage pet owners to
properly collect and dispose of their animals' waste. Many communities have pet waste ordinances
that require pet owners to clean up after their pets on public property or anywhere outside their own
yards; however, compliance is limited, and enforcement is usually not a priority. In addition, most
ordinances do not require pet owners to clean up pet waste in their own yards (this problem can usually
be addressed, though only reactively, through nuisance or pet neglect laws). Some communities have
ordinances that govern the cleanup process by requiring disposal of pet waste with regular trash, burial,
or flushing it down the toilet. Enforcement of these ordinances with fines for noncompliance is probably
the best way to increase compliance.
To increase public awareness about pet waste, you can distribute educational materials through
emails, letters, public service announcements, and signs. Posting is the most common outreach strategy
for managing pet waste. Pet waste stations containing waste receptacles for public use are another
popular solution. Public works departments have also formed voluntary commitment and partnership
programs with pet owners and local pet stores in the community to promote good pet waste
management.
E.3.3.9 Water Conservation
Water conservation is usually presented as a practice that can help preserve the amount of
water available for use, especially in times of drought. However, water conservation can also decrease
the amount of wastewater and stormwater generated, thereby protecting the quality of the water
supply (U.S. EPA 2002b). Use of low-flow toilets and showerheads, for example, can allow
wastewater treatment plants to treat wastewater from more customers without having to increase
capacity, reducing the occurrence of combined or sanitary sewer overflows. The reduced load on
wastewater treatment plants can also decrease the need for rate increases. Reducing lawn watering
decreases the amount of runoff entering storm sewers, combined sewers, and surface water.
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E.3.3.10 Low Impact Development
Low impact development, or better site design, is a watershed practice that reduces pollutant
loads, conserves natural areas, saves money, and increases property values (Center for Watershed
Protection 1999). A fundamentally different approach to residential and commercial development, site
design tries to reduce the amount of impervious cover, increase natural lands set aside for conservation,
and use pervious areas for more effective stormwater treatment. Low impact development involves
changing traditional practices for residential street and parking lot design, lot development, and
conservation of natural areas. Some specific steps for better site design include the following (Center
for Watershed Protection 1999):
• Design residential streets based on the minimum width needed to support travel lanes, on-
street parking, and emergency and maintenance vehicle access. For example, a street with
single family houses with driveways does not need two lanes for parking. Construct
sidewalks on only one side of the street.
• Minimize the number of cul-de-sacs. Where cul-de-sacs are built, place landscaped islands
to reduce their impervious cover.
• Advocate open space or cluster design subdivisions on smaller lots.
• Reduce imperviousness by promoting alternative driveway surfaces and shared driveways
that connect two or more homes together. Reduce driveway length by allowing decreased
front setbacks.
• Direct rooftop runoff to pervious areas such as yards, open channels, or vegetated areas
rather than the roadway and stormwater sewers. Better yet, install open vegetated
channels instead of storm sewers.
• Reduce the imperviousness and size of parking lots by minimizing stall dimensions,
incorporating efficient parking lanes, and using pervious materials in the spillover parking
areas where possible. Use lower parking ratios where possible (e.g., where mass transit is
available and codes permit).
• Provide stormwater treatment for parking lot runoff using bioretention areas, filter strips,
and/or other practices.
Create a naturally vegetated buffer system along all perennial streams that encompasses
critical environmental features such as the 100-year floodplain, steep slopes, and wetlands.
• Clearing and grading of forests and native vegetation at a site should be limited to the
minimum amount needed to build lots, allow access, and provide fire protection. Specify a
party legally responsible for maintaining the vegetated area.
Some aspects of low impact development may be prohibited outright under traditional zoning
and development regulations, so low impact development practices may need to be codified. Where
such practices remain voluntary or require exemptions from existing regulations, water systems should
work with local planners to encourage the switch to better site design.
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E.3.3.11 Septic Systems
Failing septic systems can be a major source of microbial contamination in a watershed. Poor
placement of leachfields can feed partially treated waste directly into a drinking water source. Poorly
constructed percolation systems may allow wastewater to escape before it has been properly treated.
Failing systems can result in clogging and overflow of waste onto land or into surface water.
Most septic system regulations require construction permits and an inspection before the system
begins operating, but few require any follow-up. Where failing systems are a serious problem or are
close to a drinking water source, however, some municipalities have maintenance or inspection
requirements. For example, the Portland (Maine) Water District requires permits for all septic systems
within 200 feet of Sebago Lake, its primary source (U.S. EPA 1999a). These septic systems are
subject to regular inspection and may face stricter design requirements than systems outside the
boundary. Portland also has the authority to inspect systems within 1,000 feet of Sebago Lake
tributaries. Similarly, the Onondaga County Water Authority in New York visually inspects every
septic system in the water system annually. Every three years each septic system is subject to a dye
tracer test. Enforcement cases are referred to the county health department (U.S. EPA 1999a).
Although water systems rarely have enforcement authority over septic systems, they should
work closely with the local regulatory authority to ensure that septic system codes are being properly
enforced and to strengthen codes where necessary. Utilities should also encourage residents with
septic systems in the watershed to understand their systems and the proper maintenance that their
systems require. Home*A*Syst programs run by many state cooperative extensions provide
educational material and checklists for septic system owners about proper siting and maintenance.
Utilities may also want to encourage residents to hook up to a sanitary sewer system where feasible.
Clean Water State Revolving Fund loans, USDA Rural Utilities Service funds, and Department of
Housing and Urban Development Community Development Block Grants are available for septic
system rehabilitation or replacement. Individual homeowners may be eligible for some of these loans
(U.S. EPA 1999b). Some of these funds may also be used to build centralized wastewater treatment.
E.3.3.12 Wildlife BMPs
Steps taken to prevent wildlife from contaminating source water vary with the source and type
of wildlife. Some reservoirs and lakes employ boats with noisemakers to scare seagulls and geese
away. Many systems with control of the land around their reservoirs place fences on the water's edge
to keep out larger land animals and humans. To keep geese from feeding along the river bank just
upstream from one of its intakes, the Philadelphia Water Department planted a riparian buffer and
wildflower meadow and conducted a public education program to prevent people from feeding the
geese (Philadelphia Water Department 2003).
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References
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Cryptosporidium parvum oocysts through vegetated buffer strips and estimated filtration efficiency.
Appl Environ. Microbiol. 68(11): 5517-27.
AWWARF. 1991. Effective Watershed Management for Surface Water Supplies. Prepared by
R.W. Robbins, J.L. Glicker, D.M. Bloem, and B.M. Niss, Portland (OR) Water Bureau. Denver:
American Water Works Association Research Foundation.
AWWA. 1999. Source Water Protection: Effective Tools and Techniques You Can Use. 1999
Participant Manual. Denver: American Water Works Association. Developed for a technical training
seminar for public water suppliers and local officials.
Blnrett. D.A. 1989. Didnfeotiou and a&uyctr CryptosporidiosK. Proceeding^ of the First
International Workshop, 1988. Ed K.W. Anguc and D.A. Bleweft Edinburgh: The Animal Disease
Research Association. 107-116.
Center for Watershed Protection. 1999. An Introduction to Better Site Design. Watershed Protection
Techniques 3(2): 623-632.
Coyne, M.S. and R.L. Blevins. 1995. Fecal bacteria in surface runoff from poultry-manured fields. In
K.Steele (ed.), Animal Water and the Land-Water Interface, pp. 77-87. Boca Raton: Lewis
Publishers, CRC Press.
Fairfax County. 2001. Wastewater Treatment Plant.
www.co.fairfax.va.us/gov/DPWES/utilities/wwtrmnt_0600.htm. Last modified May 16, 2001. Website
accessed January 2002.
Frankenberger, J.R. et al. 1999. A GIS-based variable source area hydrology model. Hydrologic
Processes 13:805-822.
Gburek, WJ. and H.B. Pionke. 1995. Management strategies for land-based disposal of animal
wastes: Hydrologic implications, pp. 313-323. In K.Steele (ed.), Animal Water and the Land-Water
Interface, pp. 77-87. Boca Raton: Lewis Publishers, CRC Press.
Metcalf and Eddy. 1994. Final CSO Conceptual Plan and System Master Plan: Part IICSO
Strategies. Prepared for the Massachusetts Water Resources Authority. Wakefield, Massachusetts.
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Moore, J.A. et al. 1988. Evaluating coliform concentrations in runoff from various animal waste
management systems. Special Report 817. Agricultural Experimental Stations, Oregon State
University, Corvallis, and the U.S.D.A., Portland, OR.
MWRD. 1999. Tunnel and Reservoir Plan. Metropolitan Water Reclamation District.
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NALMS (North American Lake Management Society). March 2000. Best Management Practices
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Ohio State University Extension. No date. Getting Started Grazing. Edited by Henry Bartholomew.
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Philadelphia Water Department. 2003. Philadelphia Projects. Website.
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Schueler, T.R. 1999. Microbes and urban watersheds: concentrations, sources, and pathways.
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Thurston, J.A., C.P. Gerba, K.E. Foster, M. M. Karpiscak. Fate of indicator microorganisms,
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U.S. Department of Agriculture. 2000. Waterborne Pathogens in Agricultural Watersheds.
Watershed Science Institute.
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accessed March 2003.
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U.S. EPA 2003. National Pollutant Discharge Elimination System Permit Regulation and Effluent
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U.S. EPA 1999b. Funding Decentralized Wastewater Systems Using the Clean Water State Revolving
Fund. Office of Water (4204). EPA 832-F-99-001. 4 pages.
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U.S. EPA 1999c. Combined Sewer Overflow Management Fact Sheet: Sewer Separation. Office of
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18698. April 19.
Vendrall, P.F., K.A. league, and D.W. Wolf. 1997. Pathogen indicator organism die-off in soil.
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runoff. J. Environ. Qual 9:483-487.
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Appendix E - Watershed Control Best Management Practices
E. 1 Regulatory and
E.I.I
E.I. 2
E.I. 3
Other Management Strategies
Determining Authority to Regulate
Zoning
Land Acquisition and Conservation Easements
E.2 Addressing Point Sources
E.2.1
E.2.2
E.2.3
E.2.4
E.2.5
Concentrated Animal Feeding Operations
Wastewater Treatment Plants
Combined Sewer Overflows
Sanitary Sewer Overflows
Municipal Separate Storm Sewer Systems
E.3 What BMPs Can Help Alleviate Nonpoint Sources?
E.3.1
E.3. 1.1
E.3. 1.2
E.3. 1.3
E.3. 1.4
E.3. 1.5
E.3. 1.6
E.3. 1.7
E.3.2
E.3.3
E.3.3.1
E.3.3.2
E.3.3.3
E.3.3.4
E.3.3. 5
E.3.3.6
E.3.3.7
E.3.3. 8
E.3.3.9
E.3.3. 10
E.3.3. 11
E.3.3. 12
Agricultural BMPs
Management Programs
Composting
Buffer Strips
Grazing Management
Manure Storage
Land Application of Manure
Feedlot Runoff Diversion
Forestry BMPs
Urban/Suburban BMPs
Buffer Zones
Dry Detention Basins
Infiltration Devices
Sand Filters
Wet Retention Ponds
Constructed Wetlands
Runoff Diversion
Pet Waste Management
Water Conservation
Low Impact Development
Septic Systems
Wildlife BMPs
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