xvEPA
United States
Environmental Protection
Agency
LONG TERM 2 ENHANCED SURFACE WATER
TREATMENT RULE
TOOLBOX GUIDANCE MANUAL
REVIEW DRAFT
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Office of Water (4606)
EPA815-D-09-001
June 2009
www. epa. gov/safewater
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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 Long Term 2 Enhanced Surface Water Treatment Rule
(LT2ESWTR). 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.
Comments should be addressed to:
Michael Finn
U.S. Environmental Protection Agency
Mail Code 4606M
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.
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Contents
1. Introduction 1-1
1.1 Guidance Manual Objectives 1-1
1.2 Guidance Manual Organization 1-2
1.3 Regulatory History 1-2
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 1-4
1.3.5 Stage 2 Disinfectant and Disinfection Byproduct Rule 1-4
1.4 Overview of the Long Term 2 Enhanced Surface Water Treatment Rule 1-5
1.4.1 Monitoring and Treatment Requirements for Filtered Systems 1-6
1.4.2 Monitoring and Treatment Requirements for Unfiltered Systems .... 1 -7
1.4.3 Summary of Microbial Toolbox Options 1-8
1.4.4 Requirements for PWSs with Uncovered
Finished Water Reservoirs 1-10
1.4.5 Disinfection Profiling and Benchmarking Requirements 1-10
1.5 LT2ESWTR Implementation Schedule 1-11
2. Watershed Control Program 2-1
2.1 Introduction 2-1
2.1.1 Credits Available 2-1
2.2 Application Process for the WCP Credit (PWS and State Responsibilities) .2-2
2.2.1 Notifying the State of Intention to Participate 2-3
2.2.2 Preparation of Watershed Control Program Plan 2-4
2.2.2.1 Delineation of Area of Influence 2-4
2.2.2.2 Identification of Cryptosporidium Sources 2-4
2.2.2.3 Analysis of Control Measures 2-5
2.2.2.4 Partnerships for Source Water Protection 2-5
2.2.3 Approval and Continuation of the WCP Credit 2-5
2.2.3.1 Initial Approval of the WCP Plan 2-5
2.2.3.2 Maintenance of the WCP Credit 2-6
2.2.3.2.1 Annual Status Report 2-6
2.2.3.2.2 Watershed Sanitary Survey Report 2-7
2.2.3.3 State Review and Continuation of the WCP Credit 2-8
2.2.4 PWS and State Checklist for Preparation, Implementation,
and Maintenance of the WCP Plan and Associated Credit 2-9
2.3 Benefits and Other Characteristics of the WCP Credit and
Related Activities 2-13
2.3.1 Benefits to the PWS and Watershed from a Successful WCP 2-13
2.3.2 Advantages and Disadvantages of a Watershed Control Program ....2-14
2.3.2.1 Advantages 2-14
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2.3.2.2 Disadvantages 2-15
2.3.3 Incorporation of New Versus Existing Source Water
Protection Activities Into a Watershed Control Program 2-16
2.4 Tools to Help PWSs Develop the Watershed Control Program Plan 2-17
2.4.1 Identification of the Area of Influence 2-19
2.4.2 Potential and Existing Sources of Cryptosporidium 2-22
2.4.2.1 How Do Fate and Transport Affect the Way
Cryptosporidium Impacts My Water Supply? 2-25
2.4.2.2 What Role Should Monitoring Play in the Evaluation
of Potential and Existing Sources of Cryptosporidium^ 2-29
2.4.3 Analysis of Control Measures 2-31
2.4.3.1 Available Regulatory and Management Strategies 2-31
2.4.3.2 Partnerships in Watershed Control Plans 2-34
2.4.3.3 Addressing Point Sources 2-35
2.4.3.4 Addressing Nonpoint Sources 2-37
2.4.3.5 Is Purchase/Ownership of All or Part of the
Watershed a Viable Option? 2-42
2.5 References 2-43
3. Alternative Source/Intake 3-1
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
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 3-6
3.4 Changing Timing of Withdrawals 3-6
3.4.1 Toolbox Selection Considerations 3-6
3.4.1.1 Advantages and Disadvantages 3-7
3.5 References 3-7
4. Bank Filtration 4-1
4.1 Introduction 4-1
4.2 LT2ESWTR Compliance Requirements 4-2
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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 4-6
4.3.1.1 Removal of Additional Contaminants 4-6
4.3.1.2 Clogging of Pores 4-7
4.3.1.3 Scour 4-9
4.3.1.4 Additional Treatment Steps 4-9
4.4 Site Selection and Aquifer Requirements 4-10
4.4.1 Selected Bank Filtration Sites 4-11
4.4.2 Aquifer Type 4-11
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 4-26
4.5.2.1 Required Separation Distance Between a Well
and the Surface Water Source 4-26
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 4-30
4.5.2.4 Measuring Separation Distances for Horizontal
Wells and Wells that are Neither Horizontal Nor Vertical ....4-32
4.6 Operational Considerations 4-33
4.6.1 High River Stage 4-33
4.6.2 Implications of Scour for Bank Filtration System Operations 4-33
4.6.3 Anticipating High Flow Events /Flooding 4-34
4.6.4 Possible Responses to Spill Events and Poor Surface
Water Quality 4-34
4.6.5 Maintaining Required Separation Distances 4-34
4.7 Demonstration of Performance 4-35
4.7.1 Identification of Collection Devices and Alternative
Treatment Technologies at the Site 4-36
4.7.2 Source Water Quality and Quantity 4-37
4.7.3 Ground Water Travel and Residence Time Calculations and
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Ambient Ground Water Dilution 4-37
4.7.4 Surface and Ground Water Data Collection,
Methods and Sampling Locations 4-39
4.7.5 Monitoring Tools 4-40
4.7.6 Tracer Tests and Use of Isotopes 4-47
4.7.7 Monitoring Wells Located Along the Shortest Flow Path 4-47
4.7.8 Post-decision Routine Monitoring and Sampling 4-48
4.8 Demonstration of Performance 4-49
5. Presedimentation 5-1
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 5-8
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 5-9
5.5.3 Sludge Removal 5-9
5.5.4 Coagulant Addition and Dose Ranges of Common Coagulants 5-9
5.6 References 5-11
6. Lime Softening 6-1
6.1 Introduction 6-1
6.2 LT2ESWTR Compliance Requirements 6-1
6.2.1 Credit for Cryptosporidium Removal 6-1
6.2.2 Reporting Requirements 6-2
6.3 Split-Flow Processes 6-2
7. Combined and Individual Filter Performance 7-1
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
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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 7-10
1 A.I.I Type of Chemical and Dose 7-10
7.4.1.2 Mixing 7-11
7.4.1.3 Streaming Current Detectors and Zeta Potential Monitors....7-12
7.4.2 Flocculation 7-12
7.4.3 Sedimentation 7-13
7.4.4 Filtration 7-14
7.4.4.1 Flow Split 7-14
7.4.4.2 Filter Beds 7-14
7.4.4.3 Backwashing 7-15
7.4.4.4 Filter to Waste 7-16
7.4.4.5 Backwash Recycle 7-16
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 7-17
7.5.3 Adequate Chemical Storage 7-18
7.5.4 Voluntary Programs 7-18
7.5.4.1 Partnership for Safe Water 7-18
7.5.4.2 Composite Correction Program (CCP) 7-19
7.6 References 7-21
Bag and Cartridge Filters 8-1
8.1 Introduction 8-1
8.2 LT2ESWTR Compliance Requirements 8-2
8.2.1 Credits 8-2
8.2.2 Reporting Requirements 8-2
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 8-5
8.4 Challenge Testing 8-5
8.4.1 Testing Conditions (141.719(a)(2)-(a)(8)) 8-6
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8.4.1.1 Full Scale Filter Testing 8-6
8.4.1.2 Challenge Particulate 8-6
8.4.1.3 Test Solution Concentration 8-7
8.4.1.4 Challenge Test Duration 8-7
8.4.1.5 Water Quality of Test Solution 8-8
8.4.1.6 Maximum Design Flow Rate 8-8
8.4.1.7 Challenge Particulate Seeding Method 8-8
8.4.1.8 Challenge Test Solution Volume 8-9
8.4.1.9 Sampling 8-9
8.4.2 Calculating Log Removal (141.719(a)(7)-(9)) 8-10
8.4.3 Modifications to Filtration Unit after Challenge Testing
(141.719(a)(10)) 8-11
8.5 Design Considerations 8-11
8.5.1 Water Quality 8-14
8.5.2 Size of Filter System and Redundancy 8-14
8.5.3 Design Layout 8-15
8.5.4 Filter Cycling 8-15
8.5.5 Pressure Monitoring, Valves, and Appurtenances 8-15
8.5.6 Air Entrapment 8-16
8.5.7 NSF Certification 8-16
8.6 Operational Issues 8-16
8.6.1 Pressure Drop (Inlet/Outlet Pressures) 8-16
8.6.2 Water Quality Monitoring 8-16
8.7 References 8-17
9. Second Stage Filtration 9-1
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 9-3
9.4.1 Hydraulic Requirements 9-4
9.4.2 Backwashing 9-4
9.4.3 Turbidity Monitoring 9-5
10. Chlorine Dioxide 10-1
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 10-8
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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 10-10
10.7 Design Considerations 10-11
10.7.1 Designing to Lowest Temperature 10-11
10.7.2 Point of Addition 10-12
10.8 Operational Considerations 10-12
10.9 Safety Issues 10-12
10.9.1 Chemical Storage 10-14
10.9.2 Acute Health Risks of Chlorine Dioxide 10-14
10.10 References 10-14
11. Ozone 11-1
11.1 Introduction 11-1
11.2 Credits 11-2
11.3 CT Determination 11-4
11.3.1 Measuring C for T10 and CSTR Methods 11-6
11.3.2 T10 Method 11-7
11.3.3 CSTR Method 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 11-15
11.7 Disinfection With Ozone 11-15
11.7.1 Chemistry 11-15
11.7.2 Byproduct Formation 11-17
11.7.2.1 Bromate and Brominated Organic Compounds 11-17
11.7.2.2Non-Brominated Organic Compounds 11-18
11.8 Design 11-18
11.8.1 Generators and Contactors 11-18
11.8.2 Point of Addition 11-18
11.8.3 Biologically Active Filters 11-19
11.8.3.1 Media for Biologically Active Filters 11-19
11.8.3.2 Operating Biologically Active Filters 11-20
11.9 Safety Considerations in Design 11-20
11.10 Operational Issues 11-21
11.10.1 Ozone Demand 11-21
11.10.2 pH 11-21
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11.10.3 Temperature 11-22
11.10.4 Maintaining Residual Disinfectant in the
Distribution System 11-22
11.11 Request for Comment on Segregated Flow Analysis 11-22
11.12 References 11-23
12. Demonstration of Performance (DOP) 12-1
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 12-5
12.4.1.1 Treatment Objectives 12-5
12.4.1.2 Influent Water Quality Characteristics 12-6
12.4.1.3 System Flow Rate 12-6
12.4.1.4 Plant Operating Conditions 12-7
12.4.2 Selection of Performance Indicators 12-7
12.4.2.1 Surrogate Parameters for Cryptosporidium 12-7
12.4.2.2 Long-Term Performance Indicators 12-8
12.4.3 Full-Scale Versus Pilot-Scale Testing 12-9
12.5 Demonstration Protocol 12-10
12.5.1 DOP Test Matrix 12-10
12.5.2 DOP Monitoring Plan 12-11
12.5.2.1 Sampling Location 12-13
12.5.2.2 Monitoring Parameters 12-13
12.5.2.3 Monitoring Frequency 12-13
12.5.2.4 Quality Assurance/Quality Control 12-13
12.5.3 DOP Implementation 12-13
12.5.3.1 Sample Collection Methods 12-14
12.5.3.2 Analytical Methods 12-14
12.5.3.3 Microbial Dosing 12-15
12.5.3.4 Documentation of WTP Operating Conditions 12-15
12.5.4 Data Analysis and Reporting 12-16
12.5.4.1 Evaluation of Performance 12-16
12.5.4.2 Reporting for the DOP 12-17
12.5.4.3 Ongoing Reporting 12-17
12.6 References 12-19
13. Ultraviolet Light 13-1
13.1 Introduction 13-1
13.2 UV Disinfection Requirements for Filtered and Unfiltered PWSs 13-1
13.2.1 UV Dose and Validation Testing Requirements 13-1
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13.2.2 UV Disinfection Monitoring Requirements 13-2
13.2.3 UV Disinfection Reporting Requirements 13-3
13.3.4 Off-specification Operational Requirement for Filtered
and Unfiltered Systems 13-3
13.3 Toolbox Selection Considerations 13-3
13.4 Design and Operational Considerations 13-4
13.5 References 13-5
14. Membrane Filtration 14-1
14.1 Introduction 14-1
14.2 Membrane Filtration Requirements under the LT2ESWTR 14-1
14.2.1 Challenge Testing 14-2
14.2.2 Direct Integrity Testing 14-2
14.2.3 Continuous Indirect Integrity Monitoring 14-3
14.3 Toolbox Selection Considerations - Advantages and Disadvantages 14-3
14.4 Design and Operational Considerations 14-4
14.5 References 14-5
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Exhibits
Exhibit 1.1 Bin Classification and Additional Treatment Requirements for
Filtered Systems 1-7
Exhibit 1.2 LT2ESWTR Treatment Requirements for Unfiltered Systems 1-8
Exhibit 1.3 Microbial Toolbox Options with Available Log Credits 1-9
Exhibit 1.4 Compliance Schedules 1-12
Exhibit 1.5 Implementation Timeline for the LT2ESWTR 1-13
Exhibit 2.1 Checklist of PWS and State activities during preparation,
implementation, and maintenance of WCP plan and associated
0.5-1 ogLT2ESWTR treatment credit 2-3
Exhibit 2.2 Checklist of PWS and State activities during preparation,
implementation, and maintenance of WCP plan and associated
0.5-1 ogLT2ESWTR treatment credit 2-10
Exhibit 2.3 Ground Water/Surface Water Interaction 2-21
Exhibit 4.1 Selected Bank Filtration Systems in Europe and the United States 4-11
Exhibit 4.2 Generalized Depiction of Stream Channel Lateral Migration 4-21
Exhibit 4.3 Taking a Water Level Reading 4-22
Exhibit 4.4 Schematic Showing Generalized Flow and Required Separation
Distance to a Vertical Well 4-24
Exhibit 4.5 Schematic Showing Generalized Flow and Required Separation
Distance to a Horizontal Well With Three Laterals 4-25
Exhibit 4.6 The Streambed of a Perched Stream Is Well above the Water Table 4-28
Exhibit 4.7.1 Estimated Costs for a Cryptosporidium Surrogate Assay 4-42
Exhibit 4.7.2 Size of Pathogenic Protozoa and Surrogate Bacteria 4-43
Exhibit 4.7.3 Size of Some Common Fresh Water Diatoms 4-46
Exhibit 5.1 Influent and Effluent Turbidity Values Resulting in 0.5 Log Reduction 5-4
Exhibit 5.2 Comparison of Sedimentation and Clarifier Types 5-6
Exhibit 6.1 Typical Two-Stage Lime Softening Process 6-2
Exhibit 7.1 Maintenance and Calibration Activities for On-line Turbidimeters 7-5
Exhibit 7.2 Maintenance and Calibration Activities for Bench Top Turbidimeters 7-5
Exhibit 7.3 Performance Limiting Factors 7-8
Exhibit 7.4 Effluent Turbidity Goals for the Sedimentation Process 7-14
Exhibit 8.1 Schematic of Treatment Process with Bag/Cartridge Filters 8-3
Exhibit 8.2 Bag/Cartridge Filters in Series 8-4
Exhibit 8.3 Bag/Cartridge Filter with UV System 8-4
Exhibit 8.4 Single Filter Vessel 8-12
Exhibit 8.5 Manifold Bag Filter Design 8-13
Exhibit 8.6 Multiple Filter Vessel 8-13
Exhibit 10.1 CT Values (mg-min/L) for Cryptosporidium Inactivation by
Chlorine Dioxide 1 10-4
Exhibit 10.2 CT Calculation Example Schematic 10-5
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Exhibit 10.3 Distribution System Monitoring Requirements at Each Plant 10-8
Exhibit 11.1 CT Values for Cryptosporidium Inactivation by Ozone (40 CFR 141.73 0) . 11 -3
Exhibit 11.2 Applicable Methods and Terminology for Calculating
the Log-Inactivation Credit 11-5
Exhibit 11.3 Correlations to Predict C* Based on Outlet Concentration 11-7
Exhibit 11.4 Inactivation Coefficients for Cryptosporidium,
Log base 10 (L/mg-min) 11-10
Exhibit 11.5 Reaction Pathways of Ozone in Water 11-17
Exhibit 12.1 Filtration Plant Types Eligible for OOP 12-1
Exhibit 12.2 Flowchart for OOP Protocol 12-4
Exhibit 12.3 Example OOP Test Matrix 12-11
Exhibit 12.4 Example OOP Monitoring Plan 12-12
Exhibit 13.1 UV Dose Requirements - millijoules per centimeter squared (mJ/cm2) 13-2
Exhibit B.I Applicable Methods and Terminology for Calculating the
Log Inactivation Credit B-4
ExhibitB.2 Schematics of Typical Configurations of Ozone Contactors
with Multiple Chambers B-6
Exhibit B.3 Schematics of Example Single- or Dual-Chamber Ozone Contactors B-7
Exhibit B.4 Names of the Various Sections of a Multi-Chamber
Over-Under Ozone Contactor B-10
Exhibits. 5 Schematic of the Ozone Contactor and the Measured Ozone
Residual Values in Example 1 B-17
Exhibits.6 Application of the Extended-CSTR Method to the Example B-20
Exhibit C.I Example Sample Locations in an Over/Under Baffled Bubble
Diffuser Contactor C-2
Exhibit C.2 Relationship Between Ozone Residual Loss and Detention
Time through the Ozone Sample Line for Various Ozone
Half-Life Values C-3
Exhibit E.I Average reduction of specific contaminant E-13
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Appendices
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) and Case Studies
Appendix F. Assessment Criteria for Use By States When Reviewing Watershed Control
Program Plans
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1. 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 microbial
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 serving 10,000 people or more initially conduct source water
monitoring to determine average Cryptosporidium concentrations (small filtered systems serving
less than 10,000 people can first monitor for E. coli to determine if Cryptosporidium monitoring
is required unless the State notifies them otherwise). 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 Guidance Manual Objectives
The primary objectives of this manual are to provide guidance to PWSs for selecting
appropriate microbial 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.
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1. Introduction
1.2 Guidance Manual Organization
This manual consists of fourteen chapters and five appendices:
Chapter 1
Chapters 2-14
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Introduction - The remainder of this chapter provides a regulatory history
and then summarizes key provisions of the LT2ESWTR including
minimum requirements for each toolbox option.
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.
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.
Ozone CT Methods - describes the Segmented Flow Analysis and
Extended-CSTR methods to calculate the CT inactivation credits with
ozone.
Measuring Ozone Residual - discusses ozone residual sample collection,
measurement, and online ozone residual analyzer calibration.
Derivation of Extended CSTR Equations - provides the derivation of the
equation used to calculate k*.
Watershed Control Best Management Practices (BMPs)
and Case Studies - provides a list of programmatic resources and guidance
available to assist systems in building partnerships and implementing
watershed protection activities.
Assessment Criteria for Watershed Control Program (WCP) Plans -
provides a list of assessment criteria for use by States when reviewing
WCP plans.
1.3 Regulatory History
The following sections describe the predecessors to the LT2ESWTR. Section 1.3.5
summarizes key requirements of the Stage 2 Disinfectants and Disinfection Byproducts Rule
(DBPR), which was promulgated simultaneously with the LT2ESWTR to balance the risks
between disinfection byproducts and microbial pathogens.
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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.
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.
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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) were required to 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
(RAAs).
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.
1.3.5 Stage 2 Disinfectant and Disinfection Byproduct Rule
The requirements of the Stage 2 DBPR apply to all CWSs and NTNCWSs that add a
disinfectant other than ultraviolet light (UV), or that deliver water that has been treated with a
disinfectant other than UV. The Stage 2 DBPR builds on the 1998 Stage 1 DBPR by requiring
reduced levels of DBFs in distribution systems. Major components of the rule are described
below.
Initial Distribution System Evaluations
For many systems, compliance monitoring will be preceded by an Initial Distribution
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1. Introduction
System Evaluation (IDSE) to identify Stage 2 DBPR compliance monitoring locations that
represent distribution system sites with high TTHM and HAAS levels. The IDSE consists of
either standard monitoring 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 with Stage 2 DBPRMCLs
The numerical MCLs for the Stage 2 DBPR are the same as for the Stage 1 DBPR MCLs:
0.080 milligrams per liter (mg/L) for TTHM, and 0.060 mg/L for HAAS. The Stage 2 DBPR is
designed to reduce high TTHM and HAAS in the distribution system by changing compliance
monitoring and calculation requirements. Compliance 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 RAA used under the Stage 1 DBPR.
Routine Monitoring Requirements
EPA has adopted a population-based monitoring approach for the Stage 2 DBPR, where
compliance and IDSE monitoring requirements are based only on source water type and retail
population served. This is a change from the plant-based approach used in the 1979 TTHM rule
and the Stage 1 DBPR.
Operational Evaluations
Because Stage 2 DBPR MCL compliance for some systems is based on individual DBF
measurements at a location averaged over a four-quarter period, a system could find higher
TTHM or HAAS levels than the MCL values, while at the same time maintaining compliance
with the Stage 2 DBPR. This is because the high concentration could be averaged with lower
concentrations at a given location. For this reason, the Stage 2 DBPR includes a provision for
"operational evaluations" as follows:
A system has exceeded an operational evaluation level at any monitoring location when
the sum of the two previous quarters' compliance monitoring results plus twice the current
quarters result, divided by 4, exceeds 0.080 mg/L for TTHM or 0.060 mg/L for HAAS.
If an operational evaluation level is exceeded, the system must conduct an "operational
evaluation" and submit a written report of the evaluation to the State.
1.4 Overview of the Long Term 2 Enhanced Surface Water Treatment Rule
The LT2ESWTR applies to all PWSs that use surface water or GWUDI (referred to
collectively as "surface water systems" in this manual). It builds on the SWTR, IESWTR, and
the LTIESWTR by improving control of microbial pathogens, specifically Cryptosporidium. It
requires filtered systems to monitor their source water for Cryptosporidium, and based on the
results, to meet one of four levels of treatment for Cryptosporidium (with the first level requiring
no additional treatment). Treatment requirements will be reassessed in the future based on a
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1. Introduction
second round of source water monitoring under the current rule. For those systems that do not
already provide filtration, the LT2ESWTR has specific requirements to inactivate two or three
logs of Cryptosporidium, depending on source water monitoring results. It also requires systems
with uncovered finished water reservoirs either to cover the reservoirs or to provide additional
treatment to the reservoir effluent.
The next several sections provide a summary of PWS requirements for the LT2ESWTR,
including a summary of microbial toolbox options in Section 1.4.3. Section 1.5 provides the
implementation timeline for the rule.
1.4.1 Monitoring and Treatment Requirements for Filtered Systems
The LT2ESWTR requires most filtered PWSs to conduct source water monitoring to
determine average Cryptosporidium concentrations. Based on the monitoring results, filtered
PWSs must calculate an initial Cryptosporidium bin concentration for each plant for which
monitoring was required [40 CFR 141.710]. Detailed requirements and guidance on how to
determine source water Cryptosporidium bin concentrations are provided in the Source Water
Monitoring Guidance Manual for Public Water Systems for the Final Long Term 2 Enhanced
Surface Water Treatment Rule., finalized in 2006 and available online at
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
Exhibit 1.1 presents the bin classifications and their corresponding additional treatment
requirements for all filtered systems. The treatment requirements are based on a determination
that conventional, slow sand, and diatomaceous earth filtration plants in compliance with the
IESWTR or LT1ESWTR achieve an average of 3-log removal of Cryptosporidium. EPA has
determined that direct filtration plants achieve an average 2.5-log removal of
Cryptosporidium (their removal is less than in conventional filtration because they lack a
sedimentation process).
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1. Introduction
Exhibit 1.1 Bin Classification and Additional Treatment Requirements for Filtered
Systems1
If your
Cryptosporidium
concentration
(oocysts/L) is...
< 0.075
> 0.075 and < 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
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
3-log
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 141.710 and 40 CFR 141.711
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.
The LT2ESWTR requires systems to comply with additional treatment requirements by
using one or more management or treatment techniques from the microbial toolbox of options.
A description of the microbial toolbox options and basic requirements for achieving inactivation
credit for each are provided in Section 1.4.3.
1.4.2 Monitoring and Treatment Requirements for Unfiltered Systems
All existing requirements for unfiltered PWSs remain in effect, including disinfection to
achieve at least 3-log inactivation ofGiardia and 4-log inactivation of viruses and to maintain a
disinfectant residual in the distribution system. The LT2ESWTR requires 2- or 3- log
inactivation of Cryptosporidium, depending on the source water concentrations of
Cryptosporidium as shown in Exhibit 1.2. Detailed requirements and guidance on how to
determine source water Cryptosporidium concentrations are provided in the Source Water
Monitoring Guidance Manual for Public Water Systems for the Final Long Term 2 Enhanced
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1. Introduction
Surface Water Treatment Rule, finalized in 2006 and available online at
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
Exhibit 1.2 LT2ESWTR Treatment Requirements for Unfiltered Systems1
Average Cryptosporidium Concentration
(oocysts/liter)
<0.01
>0.01
Additional Cryptosporidium Inactivation
Requirements
2-log2
3-log2
n40CFR 141.712
2Overall disinfection requirements must be met with a minimum of two disinfectants.
Unfiltered systems must use chlorine dioxide, ozone, or UV to meet the Cryptosporidium
inactivation requirements in Exhibit 1.2 and must meet overall disinfection requirements (i.e.,
Cryptosporidium, Giardia, and virus inactivation) with a minimum of two disinfectants [40 CFR
141.712 (d)]. Each of the two disinfectants must achieve by itself the total inactivation required
for one of the three pathogen types.
1.4.3 Summary of Microbial Toolbox Options
Systems receive LT2ESWTR treatment credits by meeting conditions for the microbial
toolbox options presented in Exhibit 1.3 [40 CFR 141.715]. Systems may use a combination of
toolbox options to achieve the required log treatment. The intent of the toolbox is to provide
systems with flexibility in selecting cost-effective LT2ESWTR compliance strategies. Unfiltered
as well as filtered systems are eligible for treatment credits for the microbial toolbox options
unless otherwise indicated in the table. Unfiltered systems must use one of the
inactivation/disinfection tools in the toolbox.
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Exhibit 1.3 Microbial Toolbox Options with Available Log Credits1
Toolbox Option
Cryptosporidium Treatment Credit with Design and Implementation Criteria
Source Toolbox Components
Watershed
control program
Alternative
source/ intake
management
0.5-log credit for State approved program comprising required elements, annual
program status report to the State, and regular watershed survey. Unfiltered
systems are not eligible for credit. See 40 CFR 141.716 (a) and Chapter 2 of this
manual for specific criteria.
No presumptive credit. Systems may conduct simultaneous monitoring for
treatment bin classification at alternative intake locations or under alternative
intake management strategies. See 40 CFR 141 716(b) and Chapter 3 of this
manual for specific criteria.
Pre-Filtration Toolbox Components
Presedimentation
basin with
coagulation
Two-stage lime
softening
Bank filtration
0.5-log credit during any month that presedimentation basins achieve a monthly
mean reduction of 0.5-log or greater in turbidity or alternative State-approved
performance criteria. To be eligible, basins must be operated continuously with
coagulant addition and all plant flow must pass through the basin. See 40 CFR
141.71 7(a) and Chapter 5 of this manual for specific criteria.
0.5-log credit for two-stage softening where chemical additional and hardness
precipitation occur in both stages. All plant flow must pass through both stages.
Single-stage softening is credited as equivalent to conventional treatment. See
40 CFR 141.717(b) and Chapters of this manual for specific criteria.
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 percent fines; average turbidity in
wells must be less than 1 NTU. Systems using wells followed by filtration when
conducting source water monitoring must sample the well to determine bin
classification and are not eligible for additional credit. See 40 CFR 141 .717(c)
and Chapter 4 of this manual for specific criteria
Treatment Performance Toolbox Components
Combined filter
performance
Individual filter
performance
Demonstration of
performance
0.5-log credit for combined filter effluent turbidity less than or equal to 0.15 NTU
in at least 95 percent of measurements each month. See 40 CFR 141.718 (a)
and Chapter 7 of this manual for specific criteria.
0.5-log credit (in addition to 0.5-log combined filter performance credit) if
individual filter effluent turbidity is less than or equal to 0.1 5 NTU in at least 95
percent of samples each month in each filter and is never greater than 0.3 NTU
in two consecutive measurements in any filter. See 141 .718 (b) and Chapter 7 of
this manual for specific criteria.
Credit awarded to unit process or treatment train based on a demonstration to
the State with a State-approved protocol. See 40 CFR 141 .718 (c) and Chapter
1 2 of this manual for specific criteria.
Additional Filtration Toolbox Options
Bag or cartridge
filters (individual
Up to 2-log credit based on the removal efficiency demonstrated during
challenge testing with a 1 .0-log factor of safety. See 40 CFR 141.71 9(a) and
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1. Introduction
Toolbox Option
filters)
Bag or cartridge
filters (in series)
Membrane
filtration
Second stage
filtration
Slow sand filters
Cryptosporidium Treatment Credit with Design and Implementation Criteria
Chapters of this manual for specific criteria.
Up to 2.5-log credit based on the removal efficiency demonstrated during
challenge testing with an 0.5-log factor of safety. See 40 CFR 141.71 9(a) and
Chapters of this manual for specific criteria.
Log credit equivalent to removal efficiency demonstrated in challenge test for
device if supported by direct integrity testing. See 40 CFR 141.719(b) and
Chapter 14 of this manual for specific criteria.
0.5-log credit for second separate granular media filtration stage if treatment train
includes coagulation prior to first filter. See 40 CFR 1 41 .71 9 (c) and Chapter 9 of
this manual for specific criteria.
2.5-log credit as a secondary filtration step; 3.0-log credit as a primary filtration
process. No prior chlorination for either option. See 40 CFR 141.719(d) and
Chapter 9 of this manual for specific criteria.
Inactivation Toolbox Components
Chlorine dioxide
Ozone
UV
Log credit based on measured CT in relation to CT table. See 40 CFR 141 .720
(b) and Chapter 10 of this manual for specific criteria.
Log credit based on measured CT in relation to CT table. See 40 CFR 141 .720
(b) and Chapter 1 1 of this manual for specific criteria.
Log credit based on measured CT in relation to CT table. See 40 CFR 141 .720
(d) and Chapter 13 of this manual for specific criteria.
40 CFR 141.715
1.4.4 Requirements for PWSs with Uncovered Finished Water Reservoirs
The LT2ESWTR requires PWSs with uncovered finished water storage facilities to either
cover the storage facility or treat the discharge of the storage facility that is distributed to
consumers to achieve inactivation and/or removal of 4-log virus, 3-log Giardia, and 2-log
Cryptosporidium [40 CFR 141.714].
1.4.5 Disinfection Profiling and Benchmarking Requirements
The LT2ESWTR includes a disinfection profile and benchmark requirement to ensure
that any significant change in disinfection, 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. A disinfection profile is a graphical
representation of a system's level of Giardia 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.
The profiling and benchmarking requirements under the LT2ESWTR are similar to those
promulgated under the IESWTR and LT1ESWTR and are applicable to systems making a
significant change to their disinfection practice. The LT2ESWTR defines significant change as
follows:
Changes to the point of disinfection,
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1. Introduction
Changes to the disinfectant used at the treatment plant,
Changes to the disinfection process, or
Any other modification identified by the State as a significant change to the disinfection
practice. [40 CFR 141.708(b)]
Prior to changing the disinfection practice, the systems must notify the State and include
the following information:
A completed disinfection profile and disinfection benchmark for Giardia lamblia and
viruses as described in 40 CFR 141.709,
A description of the proposed change in disinfection practice, and
An analysis of how the proposed change will affect the current level of disinfection. [40
CFR141.708(a)]
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 LT1ESWTR Disinfection Profiling and Benchmarking
Technical Guidance Manual for systems serving less than 10,000 people. Both manuals are
available on-line at http://www.epa.gov/safewater/mdbp/implement.html and
http://www.epa.gov/safewater/mdbp/ltleswtr.html, respectively.
1.5 LT2ESWTR Implementation Schedule
The LT2 Rule defines four compliance schedules, which are based on the population
served by systems as summarized in Exhibit 1.4. Wholesale PWSs must comply with Stage 2
DBPR and LT2ESWTR requirements based on the population of the largest PWS in the
combined distribution system. This approach will ensure that PWSs have the same compliance
schedule under both the LT2ESWTR and Stage 2 DBPR. Although consecutive systems without
their own source are not required to conduct source water monitoring, they do need to cover any
uncovered reservoirs or treat the discharge, and meet disinfection profiling and benchmarking
requirements.
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1. Introduction
Exhibit 1.4 Compliance Schedules
If you have a Subpart H source and are this kind of system:
System serving 100,000 or more people OR a wholesale system in
a combined distribution system that contains a system serving
100,000 or more people
System serving 50,000 to 99,999 people OR a wholesale system
in a combined distribution system with the largest system serving
50,000 to 99,999
System serving 10,000 to 49,999 people OR a wholesale system
in a combined distribution system with the largest system serving
10,000 to 49,999
System serving fewer than 10,000 people.
You are on schedule number
1
2
3
4
Source: USEPA2007. The LT2ESWTR Implementation Guidance. EPA 816-R-07-006, U.S. Environmental
Protection Agency, Office of Groundwaterand Drinking Water, Washington DC
Exhibit 1.5 presents monitoring and treatment deadlines for the LT2ESWTR for systems
on each of the four schedules defined in Exhibit 1.4. The compliance dates are designed to allow
systems to comply simultaneously with the Stage 2 DBPR and the LT2ESWTR in order to
balance risks associated with DBFs with risks associated with microbial pathogens. Compliance
deadlines for individual microbial toolbox options are presented in Chapters 2 through 14 of this
manual.
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1. Introduction
Exhibit 1.5 Implementation Timeline for the LT2ESWTR
Schedule Number
J_
2=1
=0
3
2006
<
r
1
Crypto monitoring
Review
-. iil-iii in h->
J-1^
<
i
[
/DSE
r
20 1 0
Treatm
Installal
2011
unt
ion
&
2012
mp
in
2013
2014
Possible
Extension
6
Y Treatment
^ | Installation
Crypto monitoring
' '
ks umlssbi
J1^
2007
«
t
V
IDSE
£ co//
RfVt*
2008
i
SDSE
2009
^
Co
nip
Possible
Extension
Lm
ice
r Treatment
Installation
C
mp
2015
Possible
Extension
mi-
6
Conplm
itf. u Ma
Qryof o rr] oh" itd Pi ng] W
©
Treatment
2010
2011
nstallation
2012
ice
BMHif 1
2016
Possible
Extension
CuBifilimrs
2013
2014
2015
2016
i% LT2 Plan or bin classification due
© Stage 2 IDSE Plan or report due
* Includes associated consecutive systems
Source: USEPA2007. The LT2ESWTR Implementation Guidance. EPA 816-R-07-006, U.S. Environmental
Protection Agency, Office of Groundwaterand Drinking Water, Washington DC
Notes:
For systems on Schedules 1 through 4 (see Exhibit 1.4)
Unfiltered systems must monitor for Cryptosporidium, regardless of size.
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2. Watershed Control Program
2.1 Introduction
The watershed control program (WCP) credit provides the opportunity for public water
systems (PWSs) with surface water sources employing filtration to obtain a 0.5-log credit from the
Microbial Toolbox by developing and implementing a State-approved WCP plan. The elements of
a State-approved WCP plan include identification of potential Cryptosporidium sources,
prioritization of the identified sources, development of control measures to address the prioritized
sources, and continuation of these efforts in the future. Systems with existing source water
protection (SWP) efforts that meet these requirements can incorporate them into their State-
approved WCP plan, while systems without existing programs can receive the same credit if they
develop and implement similar SWP efforts as part of a WCP.
PWSs in the same watershed typically need to evaluate and control the same
Cryptosporidium sources. Consequently, in order to pool resources and reduce duplication of
efforts, in many cases the State and the PWSs in the watershed should work together to develop a
single joint WCP plan that will allow the State to approve a 0.5-log credit for each PWS that
participates in the implementation of the plan. This may not be practical or achievable in all cases,
and in other cases a PWS may have a simpler and smaller watershed that does not include upstream
PWSs. These systems are still encouraged to work with any downstream PWSs to develop joint
WCP plans, but PWSs that develop and implement an individual WCP plan approved by the State
are eligible for the WCP credit.
The remainder of this chapter discusses the following in more detail:
required elements for the WCP plan, and the process associated with obtaining and
maintaining the WCP credit (Section 2.2)
benefits and advantages of the WCP (Section 2.3),
guidance and tools to help develop the WCP (Section 2.4)
2.1.1 Credits Available
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 LT2ESWTR (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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Chapter 2 - Watershed Control Program
2.2 Application Process for the WCP Credit (PWS and State Responsibilities)
The following discussion describes PWS efforts necessary to apply for, implement, and
maintain the WCP credit. Associated with the PWS efforts are complementary efforts by the State
or other primacy agency to review and approve the initial award of the credit, and subsequent
efforts to continue the credit as long as the PWS meets all of their commitments. There are six
steps associated with obtaining and continuing the WCP credit, some to be performed by the PWS
to gain the credit and some by the State to approve the credit, including the following (also see
checklist described in Section 2.2.4):
PWS notification to the State indicating that the PWS will be submitting a WCP plan,
development and submittal of a WCP plan by the PWS for review by the State,
State review and approval of the WCP plan submitted by the PWS,
implementation of the State-approved WCP plan by the PWS,
continued maintenance of the activities outlined in the WCP plan by the PWS, and
periodic review of progress by the State (annual report prepared by PWS, watershed
sanitary survey every three years using State guidelines and State-approved personnel).
A PWS intending to utilize the WCP credit must have this watershed control plan approved
and in place within three years after the Cryptosporidium sampling and bin assignment are
complete. Exhibit 2.1 outlines the deadlines for key compliance events associated with
implementing and maintaining the WCP credit. Depending on size, different PWSs will have
different deadlines for when bin assignment is completed. One year after this deadline (or earlier),
PWS must notify their State of their intent to apply for the watershed credit. One year after this
deadline, a plan for WCP implementation must be prepared by the PWS and submitted to the State.
All PWSs requiring credits under the LT2ESWTR must have these credits in place within three
years after the bin assignment deadline. Consequently, State must either approve, conditionally
approve, or reject the PWS WCP plan by this date. If the State does not respond by this time, the
credit will be assumed approved as long as all other requirements are met (i.e., WCP
implementation and maintenance). In either case, if the State determines that the PWS is not
implementing or maintaining the activities outlined in the approved WCP plan, the State may later
withdraw the credit.
As discussed below in the section on the annual WCP status report, if a PWS determines
that a significant change is needed for a State-approved WCP the PWS must notify the State, either
separately or in the body of the annual status report, prior to making any of these changes. The
notification must list actions the PWS will take in order to mitigate any "likely" (40 CFR 141.716
(a)(5)(i)) reduction in source water protection that might result from the proposed change.
When a PWS develops a WCP plan for their own system they may choose to consult with
other water systems to see if they are interested in cooperating with the water system and others to
develop joint activities or even a common WCP plan. Such collaborative efforts can help increase
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Chapter 2 - Watershed Control Program
the effectiveness of plan activities both in terms of effectively managing fiscal and technical
resources but also with respect to the size of the watershed area brought into the plan. Describing a
multi-PWS watershed control strategy to the State includes the same components as describing a
single PWS effort. However, it is important to be particularly clear when describing implementing
mechanisms, lines of authority, responsibilities, and other components that bear on inter-agency
coordination. Credit may be available for all participants in a joint State-approved WCP plan,
contingent on all participants following through on their designated roles during implementation
and maintenance of the approved WCP plan.
Exhibit 2.1 Checklist of PWS and State activities during preparation,
implementation, and maintenance of WCP plan and associated 0.5-log LT2ESWTR
treatment credit
Compliance Event
Bin assignment deadline
Notification to State of PWS intent to prepare
a WCP plan
PWS submit WCP plan
PWS implement State approved WCP plan*
First progress report (annually thereafter)
First sanitary survey report (every three years
thereafter)
Second round of Cryptosporidium sampling
Compliance Date for Systems of Different Sizes
(by population served)
>100,000
April 2009
April 20 10T
April 20 11T
April 20 12T
April 201 3 T
April 201 5 T
April 20 15
50,000 to 99,999
October 2009
October 20 10T
October 20 11T
October 20 12T
October 20 13T
October 20 15T
October 20 15
10,000 to 49,999
October 20 10
October 20 11T
October 20 12T
October 20 13T
October 20 14T
October 20 16T
October 20 15
f can be completed earlier, pending completion of prerequisite events
t If a PWS submits a WCP plan with all required elements by the required due date, and then State does not
respond by the date in this table, the credit is considered approved and the credit will continue indefinitely into the
future as long as PWS properly implements the plan and submits required annual progress reports and watershed
sanitary surveys required every three years.
2.2.1 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 141.716(a)(l)). The application and plan must be submitted for approval
within two years after initial bin assignment (40 CFR 141.716(a)(2)).
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2.2.2 Preparation of Watershed Control Program Plan
After notifying the State that the PWS intends to prepare a WCP plan, this plan and
supporting documentation must be submitted to the State for review and approval no later than
the date indicated in Exhibit 2.1, two years after the bin assignment date. The WCP plan must
include delineation of the "area of influence", identification of potential and actual
Cryptosporidium sources with this delineated area, an analysis of the proposed control measures,
and identification of an action plan to attempt to reduce Cryptosporidium source water levels
(40 CFR 141.716(a)(2)). Requirements for systems incorporating new SWP efforts into their
WCP plan are identical to requirements for systems incorporating existing SWP efforts (40
CFR 141.716(a)(3)). The WCP plan must: a) explain how actions are expected to contribute to
specified goals; b) identify watershed partners and their roles, c) identify resource requirements
and commitments; and d) outline a schedule, with deadlines, for plan implementation and
maintenance (40 CFR 141.716(a)(2)(iv)). Each of the activities in the WCP should have a
timetable for implementation, a budget, and details about how the activity will be implemented
More information on development of the WCP plan is described later in Section 2.4 and,
characteristics of some key elements in the plan are briefly outlined below.
2.2.2A Delineation of Area of Influence
An essential element for the WCP plan is the identification of the "area of influence",
outside of which there is not a significant likelihood of Cryptosporidium or fecal contamination
that affects the treatment plant intake. Identification of Cryptosporidium sources, associated
control measures, and future watershed surveys (see Section 2.4.1) will be targeted within this
area.
Methods to be used to establish the boundaries of the area of influence are at the discretion
of the PWS, as long as the State considers it sufficient to approve the area delineated. Some
methods that could be used include: a) characterization of watershed hydrology, b) modeling of
Cryptosporidium travel time, or c) when sufficient data exists it can be useful to include factors
such as fate and/or die-off/inactivation times in natural waters. A PWS could use one or more of
these methods, or it could use methods that do not include any of the above as long as the State
considers the results sufficient to adequately establish the boundaries of the area of influence.
More information on delineation of the area of influence is described later in Section 2.4.1.
2.2.2.2 Identification of Cryptosporidium Sources
Potential as well as actual sources of Cryptosporidium contamination within the delineated
area of influence must be identified and the relative impact on source water quality assessed (40
CFR 141.716(a)(2)(ii)). More information on watershed Cryptosporidium sources is included later
in Section 2.4.2. Examples of "potential" sources include various land uses or facilities (i.e.,
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POTWs, CAFOs, etc.) for which the PWS lacks specific data on Cryptosporidium occurrence in
effluent or runoff, but there is a high likelihood of oocysts being present based on published
research
2.2.2.3 Analysis of Control Measures
Cryptosporidium control measures included in watershed protection plans may include
such diverse activities as structural BMPs, land use control regulations, and public education. The
application must present an analysis of control measures that address the sources of
Cryptosporidium contamination identified for the water treatment plant source water. The analysis
of control measures must discuss the effectiveness and feasibility of each measure in reducing
Cryptosporidium loading in the source water (40 CFR 141.716(a)(2)(iii)).
More information on Cryptosporidium control measures is described later in Section 2.4.3.
2.2.2.4 Partnerships for Source Water Protection
PWSs in the same watershed typically need to evaluate and control the same
Cryptosporidium sources. Consequently, in order to pool resources and reduce duplication of
efforts, in many cases the State and the PWSs in the watershed should work together to develop a
single joint WCP plan that will allow the State to approve a 0.5-log credit for each PWS that
participates in the implementation of the plan. This may not be practical or achievable in all cases,
and in other cases a PWS may have a simpler and smaller watershed that does not include upstream
PWSs. These systems are still encouraged to work with any downstream PWSs to develop joint
WCP plans, but PWSs that develop and implement an individual WCP plan approved by the State
will get the identical credit as PWSs involved in a State-approved joint WCP plan.
2.2.3 Approval and Continuation of the WCP Credit
2.2.3.1 Initial Approval of the WCP Plan
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 the LT2ESWTR treatment requirements. The
PWS will need a decision from the State within three years after bin assignment as outlined in
Exhibit 2.1 and Figure 2-1 in order to fulfill the treatment requirements of the LT2ESWTR. If the
State does not respond to a WCP plan by the required date, the WCP plan shall be considered
"State-approved" and the 0.5-log WCP credit shall be awarded to the water system as long as
the submitted WCP plan includes all required elements (40 CFR 141.716(a)(4)). Under any
circumstances, the State can later withdraw an approved WCP credit if the State determines
that the PWS has not implemented and maintained the activities outlined in the approved WCP
plan (40 CFR 141.716(a)(5) & (6)).
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The initial approval will be valid as long as the PWS continues to implement and maintain
the approved WCP plan, as described in more detail below.
2.2.3.2 Maintenance of the WCP Credit
Systems that have obtained State approval of their watershed control programs are eligible
for the 0.5-log WCP credit as long as they continue to implement and maintain the efforts outlined
in their State-approved WCP plan, as well as satisfactorily completing the following:
Submit an annual watershed control program status report to the State (40 CFR
Conduct a watershed sanitary survey every three years for community water systems (five
years for non-community systems) using State guidelines and personnel approved by the
State for this work and submit the survey report to the State (40 CFR 141.716(a)(5)(ii)).
After approval of the WCP plan, if the PWS determines that a change in the plan is needed,
the PWS must notify the State prior to making the change and must outline any measures proposed
to mitigate any reduction in source water protection that is likely to result from this change (40
CFR 141.716 (a)(5)(i)). The description of this change must also be included in the next annual
status report.
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 as requested by the PWS based on security considerations (40 CFR
141.716(a)(5)(iii)). To assist the State in this regard, the PWS should clearly indicate the specific
information that should be held confidential. The system can identify those items for the State, or
provide parallel "vetted documents" for dissemination to the public.
Once awarded the 0.5-log WCP credit, water systems will continue to receive the credit as
long as they continue to implement and maintain the activities outlined in their State-approved
WCP plan, including preparation and submittal of annual progress reports and sanitary survey
reports every three years, as required. States may withdraw the credit if they determine that the
PWS is not carrying out the activities outlined in the State-approved WCP (40 CFR
More details on preparation and review of the required reports by the PWS (or collection
of PWSs in a joint WCP) and the State are briefly outlined below.
2.2.3.2.1 Annual Status Report
The annual watershed control program status report must be submitted by the date
established by the State. The report must describe the PWS'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
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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 141.716(a)(5)(i)).
The annual status report must describe progress being made implementing individual
control measures (40 CFR 141.716(a)(5)(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 described.
The original watershed control program plan should include specific measures by which
the PWS 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 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 the annual status
reports must be made available to the public on request, reports must be written in plain language
format (40 CFR 141.716(a)(5)(iii)), though portions of the report can be withheld for PWS
security considerations. To assist the State in this regard, the PWS should clearly indicate
information in the status report that should be held confidential. The PWS can identify those items
for the State, or provide a parallel "vetted report" for dissemination to the public.
2.2.3.2.2 Watershed Sanitary Survey Report
A State-approved watershed survey must be conducted once every three years
for community water systems (five years for non-community water systems), with the
first report due three years after the WCP approval date (see Exhibit 2.1). The survey
must be conducted according to State guidelines by persons approved by the State to
conduct watershed surveys. A report on the results of the survey must be submitted to the State
once every three years. The survey must meet the following criteria (40 CFR
cover the area of the watershed that was identified in the approved watershed control
program plan as the area of influence
assess the implementation of actions to reduce source water Cryptosporidium levels, and
identify new sources of Cryptosporidium
If the State determines that significant changes may have occurred in the watershed since
the previous watershed sanitary survey, systems must undergo another watershed sanitary survey
by a date required by the State, which may be earlier than the regularly scheduled survey (40 CFR
141.716(a)(5)(ii)(B)). In such an instance, the next survey and subsequent surveys will be required
three years from this new date.
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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). PWSs are required to use persons approved by the state for the sanitary survey.
Conducting a useful watershed survey relies in large part on the competence of the individuals
responsible for its execution. It is expected that the State will designate appropriately trained
individuals, including civil or environmental engineers, or sanitarians with experience in the
operation of water systems and a sound understanding of public health principles and waterborne
diseases. Although other people may be performing the work for these individuals, the people
designated by the State will supervise and direct the activities conducted for the survey. Efforts
performed during the survey could include activities such as the following:
review of relevant NPDES permits and discharge records
review of pertinent databases (i.e., county GIS systems, etc.)
review of most recent available aerial photography where available
interviews with USD A, soil conservation service, local county planning agencies, regional
planning organizations, and other organizations as applicable
A final survey report must be submitted to the State for approval (40 CFR
141.716(a)(5)(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 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 141.716(a)(5)(iii)). To assist the State in this
regard, the PWS should clearly indicate the specific information in the report that should be held
confidential. The system can identify those items for the State, or provide parallel "vetted
documents" for dissemination to the public.
2.2.3.3 State Review and Continuation of the WCP Credit
Once water systems are awarded the 0.5-log WCP credit, they will continue to receive the
credit as long as they implement and maintain the efforts outlined in their State-approved WCP
plan. After the WCP plan is approved, ongoing reviews are the annual status report and the report
from the sanitary surveys conducted and submitted once every three years.
The initial approval will be valid as long as the PWS continues to implement and maintain
the approved WCP plan. After approval of the WCP plan, if the PWS determines that a change in
the plan is needed, the PWS must notify the State prior to making the change and must outline any
measures proposed to mitigate any reduction in source water protection that is likely to result from
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this change (40 CFR 141.716 (a)(5)(i)). The description of this change must also be included in the
next annual status report.
2.2.4 PWS and State Checklist for Preparation, Implementation, and Maintenance of the
WCP Plan and Associated Credit
Exhibit 2.2 includes a summary of all activities associated with preparing the WCP plan by
the PWS, review and approval of the plan by the State, implementation and maintenance of the
plan by the PWS, and assessment of PWS activities by the State in order to allow continuation of
the credit.
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Exhibit 2.2 Checklist of PWS and State activities during preparation,
implementation, and maintenance of WCP plan and associated 0.5-log LT2ESWTR
treatment credit
Description of Task
Code of Federal
Regulations Citation
(40 CFR)
Section(s) of interest in
this Guidance Manual
Notification Period
(due no later than one year following bin determination, see Exhibit 2.1)
The PWS must notify the State one year after bin
assignment if they intend to later submit a WCP
plan
141.176(a)(1)
2.2.1
WCP Plan Preparation Period
(due no later than two years following bin assignment date, see Exhibit 2.1)
The PWS must submit a report containing the WCP
plan including the following required elements:
Identification of area of influence
Identification of potential and actual sources of
Cryptosporidium contamination in area of influence
and assessment of relative impact of these sources
on source water quality
Analysis of the effectiveness and feasibility of
control measures that could reduce
Cryptosporidium loading from sources identified
within area of influence
Statement of goals and actions to undertake as
part of the WCP plan implementation and
maintenance efforts to reduce source water
Cryptosporidium levels, including an explanation of
how these actions are expected to contribute to
achievement of stated goals.
Identification of watershed partners and their roles
Identification of resource requirements and
commitments
Development of an implementation schedule,
including deadlines for completing specific actions
identified in the WCP plan
Systems can use existing watershed control
programs to meet requirements of the rule, as long
as the entire WCP plan includes all the same
elements required for all systems
141.176(a)(2)
141.176(a)(2)(i)
141.176(a)(2)(ii)
141.176(a)(2)(iii)
141.176(a)(2)(iv)
141.176(a)(2)(iv)
141.176(a)(2)(iv)
141.176(a)(2)(iv)
141.176(a)(3)
2.2,
2.2.2
2.2.2.1
2.4.1
2.2.2.2
2.4.2
2.4.2.1
2.4.2.2
2.2.2.3
2.4.3
2.4.3.1 through 5
2.2.2
2.2.2.4
2.2.2
2.2.2
2.2.2
2.3.3
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Exhibit 2.2 (continued)
Description of Task
Code of Federal
Regulations Citation
(40 CFR)
Section(s) of interest in
this Guidance Manual
State Review of the WCP Plan
(due no later than three years after bin assignment date, the same time as other treatment credits, see
Exhibit 2.1)
The State is expected to approve, reject, or
conditionally approve the WCP plan if it is
submitted before the due date (see Exhibit 2.1)
If a WCP plan containing all required elements (see
"WCP Plan Preparation Period" items listed above)
is submitted by the required date, but is not
formally acted upon by the State prior to the
required deadline (see Exhibit 2.1), then the WCP
plan is considered approved by the State and the
0.5-log WCP credit is allowed. See discussion
below regarding withdrawal of this or any other
approval of the credit.
141.176(a)(2)
141.176(a)(4)
2.2
2.2.3.1
2.2.3.3
2.2
2.2.3.1
2.2.3.3
Implementation and Maintenance of the 0.5-log WCP Credit
(occurs after credit is approved by State)
If the PWS or PWSs awarded a 0.5-log WCP credit
do not carry out the actions outlined in their State-
approved WCP, the State may withdraw the credit
In order to maintain the 0.5-log WCP credit the
PWS or PWSs associated with a State-approved
WCP plan must carry out the actions outlined in the
plan, assessed by evaluating the annual status
report and report from the sanitary survey
conducted every three years
The annual status report must describe the PWS's
implementation of an approved WCP plan and
must assess the adequacy of the plan to continue
to meet its goals
The annual status report must explain how the
PWS or PWSs associated with the WCP plan are
addressing any shortcomings in the implementation
of the plan, including those previously identified by
the State after the three-year sanitary surveys.
The annual status report must describe any
significant changes that have occurred in the
watershed since the last sanitary survey.
The PWS must notify and receive verbal approval
from the State before implementing any changes to
a State-approved WCP plan. The PWSs must
propose actions they will undertake to mitigate any
changes that appear likely to reduce the level of
source water protection. These changes must be
described in the next annual progress report.
141.176(a)(6)
141.176(a)(5)
141.176(a)(5)(i)
141.176(a)(5)(i)
141.176(a)(5)(i)
141.176(a)(5)(i)
2.2.3
2.2.3.2
2.2.3
2.2.3.2
2.2.3
2.2.3.2
2.2.3.2.1
2.2.3.2.1
2.2.3.2.1
2.2.3
2.2.3.2,
2.2.3.2.1
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Exhibit 2.2 (continued)
Description of Task
Code of Federal
Regulations Citation
(40 CFR)
Section(s) of interest in
this Guidance Manual
A State-approved watershed survey must be
conducted once every three years for community
water systems (five years for non-community water
systems), with first report due three years after the
WCP plan is approved by the State. The survey
must be conducted according to State guidelines
by persons approved by the State to conduct
watershed surveys. A report on the results of the
survey must be submitted to the State once every
three years. The survey must meet the criteria
listed below:
2.2.3
2.2.3.2,
2.2.3.2.2
Encompass the area of influence defined in the
State-approved WCP plan
2.2.3.2.2
Assess actions implemented to reduce
Cryptosporidium levels within the area of influence
2.2.3.2.2
Identify any significant new sources of
Cryptosporidium in the area of influence
2.2.3.2.2
If the State determines that significant changes
may have occurred in the watershed since the
previous watershed sanitary survey, systems must
undergo another watershed sanitary survey by a
date required by the State, which may be earlier
than the regularly scheduled survey. In such an
instance, the next survey and subsequent surveys
will be required three years from this new date.
2.2.3.2.2
The WCP plan, annual status reports, and
watershed sanitary survey reports must be written
in plain language format. All of these documents
must be made available by the State to public,
upon request. The State can withhold portions of
these documents identified by the PWS due to
security considerations. To assist the State in this
regard, the PWS should clearly indicate the
information in the status report that should be held
confidential.
2.2.2
2.3.3
2.3.3.2,
2.2.3.2.1
2.2.3.2.2
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2.3 Benefits and Other Characteristics of the WCP Credit and Related Activities
2.3.1 Benefits to the PWS and Watershed from a Successful WCP
A well-designed watershed control program (WCP) 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.
PWSs with existing SWP programs, watershed information, partnerships, etc. are encouraged to
incorporate these into their WCP plans. Whether as a continuation of existing efforts or as a
result of new efforts specifically initiated for the WCP credit, SWP activities for identification,
prioritization, and control of Cryptosporidium sources are important, proactive, preventative
steps for reduction of Cryptosporidium risks for drinking water consumers. Efforts to identify,
prioritize, and control Cryptosporidium sources in the watershed offer opportunities for
cooperation and collaboration between PWSs who will benefit from joint efforts to reduce
Cryptosporidium sources in their common watershed(s). Consequently, a WCP for one or more
PWS can create the potential opportunity to extend watershed protection activities until they
become watershed-wide, basin-wide, regional, State-wide, or even multi-State-wide if enough
water systems can cooperate together to make it happen.
A watershed control program targeting Cryptosporidium reduction is the most
advantageous when it is also the component of a larger comprehensive source water protection
program that addresses other chemical and/or microbial contaminant threats. For PWSs in many
states, much of the background information and preparation needed to develop a watershed
control program and comprehensive source water protection program are already available 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 for systems where watershed sanitary surveys have been
performed. These surveys are required as part of the Interim Enhanced Surface Water Treatment
Rule (IESWTR), and some States have required them for years. The completeness of the
information contained in these existing resources may need to be supplemented by collecting
additional background information, particularly information bearing on Cryptosporidium
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occurrence.
2.3.2 Advantages and Disadvantages of a Watershed Control Program
2.3.2.1 Advantages
Measures to control prioritized Cryptosporidium sources in the watershed, as required for
the WCP credit, will in most instances control other contaminants of concern to PWSs. The
reduction and prevention of source water contamination by microbial pathogens and other
contaminants 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.
While WCPs may be a cost-effective Microbial Toolbox option, the PWS commitment
needed to initiate and maintain source water protection efforts may be substantial. Source water
protection efforts often require many years to start seeing measurable results. Furthermore, these
efforts must continue to be maintained in order for initial improvement to persist. However, the
potential payoff of these efforts are significant both for the water system and the community they
serve. For example, one PWS estimates that its current source water protection effort has helped
the PWS avoid $100 million in capital costs and $10 million/yr in operating costs. This savings
was accomplished with approximately $5 million expended to date on SWP efforts, of which $3
million was recovered through funding from grants (Crockett 2005).
Although the costs associated with implementing a particular Microbial Toolbox option
are system-specific, a watershed control program can cost less than other Microbial Toolbox
options that require installation of additional technology. This is especially the case if other
stakeholders contribute time and resources to the watershed control program. Stakeholders
could include other utilities and municipalities, other agencies in the same municipality, county
or State agencies, and concerned citizens. Though watershed control programs involving land
acquisition or purchase of conservation easements may be initially more expensive than
installing treatment, the long-term benefits (improved quality and stability of source water,
reduction in treatment costs, etc.) are potentially significant, though prediction of these
improvements beforehand and measurement afterwards may at times be problematic.
Much of the information required to implement a watershed program, such as a
contaminant source inventory and delineation of the watershed, may already be available in some
states as a result of the source water assessment conducted under the 1996 Safe Drinking
Water Act Amendments. Although source water assessment programs vary from State to State,
they should provide much of the basic information required to prepare a plan for a watershed
control program, allowing systems to incorporate existing information into their watershed
control plans at minimal cost.
Control of Cryptosporidium sources in the watershed can contribute significantly to
integrated multiple-barrier treatment strategies. For example, reducing influent Cryptosporidium
loadings will facilitate pre-treatment (e.g., riverbank filtration), conventional treatment (e.g.,
clarification followed by filtration), or post-treatment (e.g., UV irradiation). Control of
Cryptosporidium sources in the watershed can benefit more than a single water treatment facility.
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In even small watersheds, there may be multiple water intakes that may even serve other PWSs.
Consequently, watershed-based coordination can assist PWSs to develop background information
and to implement Cryptosporidium control measures. For example, since much of the
background information needed for the WCP application submitted to the State can be very
similar for multiple PWSs in the same watershed, working together PWSs can be more efficient
developing background information and identifying priority actions to manage Cryptosporidium
sources.
The use of stakeholder partnerships during development and implementation of a WCP
can be substantial. In addition to being able to share resources and work together to find funding
sources, collaboration with other stakeholders can bring important information and resources to
the PWS. For example, increased contact with upstream or downstream utilities can result in
sharing of information about source water quality issues, the means that other utilities have used
to respond to contaminants and water quality changes, and increases the likelihood that other
utilities will share information about sudden water quality changes that may also affect the other
utilities using that particular source water.
2.3.2.2 Disadvantages
Most water systems who have developed and implemented SWP efforts like those needed
for the State-approved WCP credit have found that these efforts are able to substantially improve
source water quality (Ashendorff et al. 1997, Vaux 2000). However, seldom will watershed
activities result in immediate realization of benefits. Many land use policies, wildlife
management, and public education programs require significant implementation timeframes. This
challenge is further complicated by the target organism in this rulemaking, Cryptosporidium.
Cryptosporidium occurs in low concentrations and is difficult to detect using existing analytical
methods, consequently, it can be hard to discern reductions in Cryptosporidium concentrations
resulting from watershed control programs even if substantial changes are realized in the
watershed.
The PWS commitment needed to initiate and maintain source water protection efforts is
substantial. Source water protection efforts often require many years to start seeing measurable
results. Furthermore, these efforts must continue to be maintained in order for initial
improvements to persist. Furthermore, it may not be possible to discern the improvements in
source water quality using these monitoring approaches due to natural environmental variability,
the characteristics of the source water improvements, and the limitations of the current analytical
methods for Cryptosporidium or other fecal indicators. However the potential payoff of these
efforts are significant both for the water system and the community they serve, as noted in the
"advantages" section.
As with other treatment options, cost is a significant factor in determining if a watershed
control program will be viable of any individual water system. Some federal funding is available
to implement some 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
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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. A
review of potential funding sources is provided in Gullick et al. [N.d.].
Like other components of the multiple barrier strategy, the barrier provided by watershed
protection must be maintained into the future. Consequently, while some SWP efforts can produce
visible evidence of action in fairly short periods of time (Capacasa 2005, Crockett et al. 2005), the
ongoing maintenance of land use systems and key changes in private actions in the watershed will
be more difficult to demonstrate. This lack of visibility can lead to challenges for long-term fiscal
stability and stakeholder engagement, which is compounded when there are other competing
demands for resources.
A watershed control program may not be as successful in some circumstances as in others.
Potential pitfalls are important to consider in deciding whether to undertake a watershed
control program. 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 three-year watershed survey will assist in evaluating progress, systems that
implement watershed control programs may need to be creative in finding ways to gauge the
success of their programs.
Urban growth and land development can affect the success of a watershed control program.
The success or failure of a watershed control program that is based on land use controls will rest
in large part on how committed the effected communities are to supporting the land use
constraints identified in the watershed control plan.
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 and staff
commitments may be prohibitive for some systems.
2.3.3 Incorporation of New Versus Existing Source Water Protection Activities Into a
Watershed Control Program
PWSs that already have SWP activities in place that are suitable for incorporation into a
WCP are encouraged to consider the WCP credit as one of their Microbial Toolbox options since
continuation of these existing efforts offer the best chance of producing improvements in the
watershed the most quickly. These systems are also encouraged to cooperate with other utilities in
their watershed so that information these utilities have in common can be shared, allowing all
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utilities involved to focus on prioritized control measures rather than duplicating these efforts.
PWSs with existing SWP programs must incorporate into their WCP implementation plans all
required elements described earlier in Section 2.2. Some PWSs may already have existing SWP
programs encompassing all of these elements, while others will need to develop and implement a
combination of existing and newly designed efforts to meet all of the requirements. PWSs without
existing SWP programs suitable for the WCP credit are encouraged to develop and implement
appropriate SWP programs via the WCP credit mechanism.
2.4 Tools to Help PWSs Develop the Watershed Control Program Plan
The following subsections discuss the factors PWSs should consider in developing a WCP
plan to improve Cryptosporidium reductions in source water, along with descriptions of best
management practices and other control measures.. However, each watershed is different and
therefore, each WCP plan needs to be tailored for the specific circumstances.
Systems may be able to use the results of the source water assessments conducted under the
Safe Drinking Water Act Amendments of 1996 to support this effort to develop a WCP plan. These
assessments establish a foundation for the WCP because 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. The assessments covered all
priority 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. However in some cases the information available from the source water
assessments is quite limited, and utilities will need to look for or develop other sources for this
information.
Other source water 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
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
Drinking Water and Environmental Management also have developed guidance specifically for
watershed sanitary surveys. Coordination of SWP efforts with those of Clean Water Act programs
such as Total Maximum Daily Loads (TMDLs) is beneficial and encouraged.
Guidance for source water protection activities is available from a wide variety of sources,
including the following:
U.S. EPA Source Water Protection webpage (www.epa.gov/safewater/protect.html)
contains links to a variety of guidance materials
U. S. EPA draft Handbook for Developing Watershed Plans to Restore and Protect our
Waters (U.S. EPA, 2005d)
Introduction to EPA's Drinking Water Source Protection Programs (U.S. EPA, 2003b)
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Source Water Protection: Best Management Practices and Other Measures for Protecting
Drinking Water Supplies (U.S. EPA, 2002e)
State Source Water Assessment and Protection Programs Guidance: Final Guidance (U.S.
EPA, 1997)
Protecting and Restoring America's Watersheds: Status, Trends, and Initiatives in
Watershed Management (U.S. EPA, 200Ig)
Getting in Step: A Guide for Conducting Watershed Outreach Campaigns (Tetra Tech,
Inc., 2003)
U.S. EPA Watershed Academy On-Line Training Modules (available at
www.epa.gov/watertrain/, e.g., www.epa.gov/watertrain/pdf/ swp.pdf (January 2003) and
www. epa. gov/watertrain/pdf/swpbmp. pdf (August 2002)).
U.S. EPA National Agriculture Compliance Assistance Center website - information on
animal production practices and BMPs (http://www.epa.gov/agriculture)
U.S. EPA Animal Feeding Operations (AFO) Virtual Information Center website
(http ://cfpub .epa. gov/npdes/afo/virtualcenter. cfm)
Source Water Protection for Concentrated Animal Feeding Operations: A Guide for
Drinking Water Utilities (Gullick et al., N.d.)
AwwaRF Source Water Protection Reference Manual (COM, 2002)
Source Water Protection: Effective Tools and Techniques You Can Use (1999 Participant
Manual) (AWWA, 1999)
Effective Watershed Management for Surface Water Supplies (AwwaRF, 1991)
Guidance to Utilities on Building Alliances with Watershed Stakeholders (AwwaRF,
2001)
Protecting the Source: Land Conservation and the Future of America's Drinking Water
(Ernst, 2004)
Path to Protection: Ten Strategies for Successful Source Water Protection (Ernst and Hart,
2005)
Source Protection Handbook: Using Conservation to Protect Drinking Water Supplies
(Hopper and Ernst, 2005)
Source Protection: A National Guidance Manual for Surface Water Supplies (NEIWPCC,
2000)
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The Center for Watershed Protection provides basic templates to help with design of
watershed protection programs; see www. stormwatercenter.net.
From Source to Tap: Guidance on the Multi-Barrier Approach to Safe Drinking Water
(CCME, 2002)
In addition, compilations of successful SWP program case studies are available from the
following sources:
Case Studies of Source Water Protection (U.S. EPA, 2005a;
www. epa.safewater/protect/casestv/casestudy. html)
Section 319 Nonpoint Success Stories (U.S. EPA, 2005b;
www.epa.gov/owow/nps/Success319)
Watershed Success Stories - Applying the Principles and Spirit of the Clean Water Action
Plan (U.S. EPA, 2000d; water.usgs.gov/owq/cleanwater/success/index.html)
Protecting Sources of Drinking Water: Selected Case Studies in Watershed Management
(U.S. EPA, 1999a, www.epa.gov/safewater/swp/swpcases.pdf)
2.4.1 Identification of the Area of Influence
An essential element for the WCP plan is the identification of the "area of influence".
Cryptosporidium and fecal contamination sources within the boundaries delineated for the area of
influence are considered likely to significantly impact the PWS treatment plant intake.
Identification of Cryptosporidium sources, associated control measures, and future watershed
surveys (see Section 2.2.2.1) will be targeted within this area.
Methods to be used to establish the boundaries of the area of influence are at the discretion
of the PWS, as long as the State considers it sufficient to approve the area delineated. Some
methods that could be used include: a) characterization of watershed hydrology, b) modeling of
Cryptosporidium travel time, or c) when sufficient data exists it can be useful to include factors
such as fate and/or die-off/inactivation times in natural waters. A PWS could use one or more of
these methods, or it could use methods that do not include any of the above as long as the State
considers the results sufficient to adequately establish the boundaries of the area of influence.
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, rather than investing in an extensive analysis and data collection effort on
transport issues, the plan can be developed based on consideration of all potential sources of
Cryptosporidium contamination based on the characteristics of the source and the likelihood of
Cryptosporidium release to a water body.
Delineation
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Systems may develop their own watershed delineation. The starting point for such a
delineation may be the delineation developed by the State as part of the source water assessment.
In referencing the delineation prepared in the SWAP process, systems should be careful to
understand how the initial delineation was prepared. Different states employed different
delineation approaches. To delineate watersheds, some States started with watersheds as
catalogued by the U.S. Geological Survey (USGS). 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).
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 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 http://www.terrene.org/fl 6.pdf for 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.
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 2.3. 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) associated with the soil can be transported as
individual organisms, aggregates of organisms, or within an aggregate of soil particles and
organisms.
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Exhibit 2.3 Ground Water/Surface Water Interaction
Preciptt
Well
Runoff
Rec
Ground Water / Surface Water
Interaction
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 vulnerable to contamination by microbial contaminants like
Cryptosporidium (consequently, GWUDI sources are treated like surface water source under the
SWTR, IESWTR, and LT2ESWTR). GWUDI may be contaminated by through direct
contamination (e.g., an inadequately protected spring), direct infiltration of oocysts from the
surface as a result of rain, and as a result of the action of pumping wells (see Exhibit 2.3). 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 pumping wells. If the surface water is contaminated with
microbial contaminants, 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.
2.4.2 Potential and Existing Sources of Cryptosporidium
All potential and actual Cryptosporidium sources in the area of influence must be identified
and reported in the WCP plan (40 CFR 141.716(a)(2)(ii)) and should be evaluated for suitable
control measures in the plan. Systems may be able to use source inventory data collected as part of
the source water assessment program. Many states asked systems to assist with identifying
significant potential contaminant sources, 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, it is possible to determine
whether these areas coincide with land uses that are likely to contribute microbiological
contamination to the water supply. Reviewing land use and zoning maps can be used to identify
areas for investigation or for prediction of potential future sources and loadings. Where existing
mapping does not reflect available databases, investigation of local data sources, such as health
department data on septic systems and recent sanitary survey results can provide additional
detailed information. Data on point sources such as wastewater treatment plants that require EPA
or State permits, e.g., National Pollutant Discharge Elimination System (NPDES) is also readily
available through State and federal data systems. NPDES information (also called water discharge
permit or PCS data) is available on EPA's Envirofacts website at
http://www.epa.gov/enviro/indexjava.html. Local, State and federal data sets are useful
identifying potential sources of contaminants, but these data systems can be out of date; actual field
surveys may be necessary to confirm the status of existing 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. When
possible developing site-specific relationships can facilitate how to more effectively effect oocyst
level released to surface water in the watershed.
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Land Use
Many land uses in a watershed have the potential to introduce Cryptosporidium into water
supplies. These include point sourcescombined sewer overflows, wastewater treatment plants,
and concentrated animal feeding operationsand nonpoint sources, including livestock, wildlife,
pets, storm water runoff, and septic systems.
Kaplan et al. (2002) generated a database on pathogen occurrence in watersheds ranging
from forested to highly urbanized. Corsi et al. (2003) studied the source(s) and magnitude of
Cryptosporidium by broad characterization of rural, suburban, and urban land uses. In this case the
primary sources were attributed to urban stormwater and wastewater treatment plant outflows
during baseflow and stormwater events.
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-specificin 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). Davies et al. (2005) quantifies information on prevalence and
viability of E. coli and Cryptosporidium in livestock. Crockett ([N.d.]) compares prevalence of
Cryptosporidium in wastewater versus wildlife and livestock, including adult versus neonatal
calves. Santin et al. (2004) studied genotype and speciation of Cryptosporidium in feces from
1,000 cattle on 15 farms in 7 states. Results indicate that Cryptosporidium parvum, which are
potentially infectious to humans, were detected in feces from pre-weaned calves but nearly all
Cryptosporidium in older cattle were other non-infectious species or genotypes.
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 etal. 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
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L (67 percent of samples were positive); downstream from the plant, concentrations ranged from
325 to 825 oocysts per 100 L (Crockett and Haas 1997). Results from more recent research
summarized by Crockett ([N.d.]) indicate that effluent wastewater Cryptosporidium concentrations
ranges from 0.1 to 1,000 oocysts/L.
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 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 over
applied. Gullick et al (N.d.) provide a reference guide for drinking water utilities to implement
source water protection activities related to CAFOs. Finstein (2004) describes impact of ammonia
and temperature on Cryptosporidium oocyst survival during storage of livestock manure, including
capital and management intensive treatment processes like anaerobic digestion and less capital
intensive processes such as aerobic composting.
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 barns (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
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storm water, suggesting that Cryptosporidium may also be present in urban watersheds and
stormwater runoff.
Low levels of Cryptosporidium may also enter surface water through septic systems and
subsequent subsurface transport (Lipp et al. 2001).
"Microbial source tracking" (MST) is a rapidly expanding science designed to identify
human or animal sources of fecal pollution in the environment. These methods can evaluate E.
coli, Giardia, Cryptosporidium, and viruses, and identify whether the source is from human, cattle,
swine, bird, or other origin. Fecal source tracking using DNA "fingerprinting" can be used by
water utilities to identify whether or not particular a potential fecal source in their watershed, such
as an AFO or CAFO, is an actual contributor to wastes identified in the source water.
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.
Numerous references are available that summarize the capabilities and state-of-the-science
of microbial source tracking, including the following:
USEPA Microbial Source Tracking Guide Document (USEPA, 2005c)
http://www.ces.purdue.edu/waterquality/resources/MSTGuide.pdf
Microbial Source Tracking: Current Methodology and Future Directions (Scott et al.,
2002) http://aem.asm.org/cgi/content/full/68/12/5796
Microbial Indicators of Fecal Contamination: Application to Microbial Source
Tracking (Bitton, 2005)
http://www.florida-stormwater.org/pdfs/FSAMicrobialSourceTrackingReport.pdf
Selected Bibliography for Topics Related to Microbial Source Tracking (USGS
website) http://water.usgs.gov/owq/MST bibliography.html
2.4.2.1 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. A critical review of available research on
transport of pathogens in watersheds was conducted by Ferguson et al. (2003) and Davies et al.
(2005). Pyke et al. (2003) summarized the occurrence, sources, and fate of Cryptosporidium in
agricultural environments. Approaches for reducing overall pathogen loading within an agricultural
watershed are discussed by Rosen et al. (2001). A summary of the fate of Cryptosporidium and the
effectiveness for Cryptosporidium inactivation via different agricultural BMPs (e.g., composting,
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anaerobic digestion, manure slurry storage) was provided by Finstein (2004). Yeghiazarian et al.
(2004) developed a pathogen transport model. Crockett (N.d.) discusses the role of wastewater
treatment in protecting water supplies against emerging pathogens such as Cryptosporidium.
The fate and transport of oocysts in the environment is briefly described below.
Influence of Precipitation
PWSs may find it prudent to determine the extent to which Cryptosporidium occurrence in
their watershed coincides with extreme rainfall. Sixty-eight 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.
Crockett and Johnson (2000) noted that Cryptosporidium concentration increased by about
a factor of 10 during storm events and frequency of detection doubled during these same storm
events. Research at one New Jersey utility indicated that during storm events, large turbidity
increases accompanied increases in Cryptosporidium occurrence in the raw source water
(LeChevallier et al. 1998, Atherholt et al. 1998). Consequently, the utility monitors raw water
turbidity and can shut down the intake for up to 24 hours when raw water turbidity exceeds a
certain threshold (typically -15 ntu) during storm events.
One study showed 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).
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.
One recently completed research project (Sturdevant Rees et al., N.d.) investigated the
variability of pathogen occurrence and transport through watersheds. Even small rainfall events
(less than 0.25 inches) were capable of washing Giardia cysts and Cryptosporidium oocysts into
streams, and saturated or near-saturated ground conditions, and events characterized by rain falling
on snow, resulted in higher rates of detection. In addition, little correlation was found between
rainfall event accumulation and Cryptosporidium or Giardia detection. Rather, antecedent rainfall
and/or remotely sensed soil moisture data indicating saturated or near saturated conditions may be
important for identifying rainfall events where sampling for Cryptosporidium and Giardia is
warranted (Sturdevant Rees et al., N.d.).
Transport in Surface Water
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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 rate (2 mm per hour or less) as noted by 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).
Transport in Runoff
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). Overland flow transport
models for pathogens were reviewed as part of a U.S. EPA workshop on animal feeding operations
(GeoLogics Corp., 2004). The effects of land slopes, vegetation, and rainfall intensities on overland
and near-surface transport of Cryptosporidiumparvum oocysts were examined by Trask et al.
(2004). Zhang and coworkers (2001) describe the development and implementation of a model for
simulating removal of Cryptosporidium parvum oocysts from overland flow, including modeling
transport of oocysts through vegetative filter strips.
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. Fractures and dissolution conduits in an aquifer can allow ground
water and oocysts to effectively bypass the protective action of most of the aquifer matrix. John
and Rose (2005) provide a review of the factors affecting microbial survival in groundwater.
It is known that Cryptosporidium can be transported through soil and ground water
(Mawdsley et al. 1996; Hurst 1997). 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 (Brush
etal. 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).
Amirtharajah et al. (2002) investigated the transport of a Cryptosporidium surrogate
(polystyrene microspheres) through unsaturated soils at an undisturbed field site used for cattle
production. Results showed that the vertical migration of polystyrene microspheres in column
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studies suggests that migration of Cryptosporidiumparvum oocysts through fine-textured soils is
likely to be minimal, and that a small number of these surrogate particles travel through
preferential flow paths at field sites, especially after rainfall events (Amirtharajah et al., 2002).
Survival in the Environment
Several factors influence oocyst survival, including temperature and desiccation. Davies et
al. (2005) presented results of a series of research experiments designed to identify the key factors
controlling pathogen transport. Among the many findings summarized is that temperature is a very
influential factor on the survival of Cryptosporidium oocysts. Both high heat and freezing
temperatures can result in Cryptosporidium inactivation, while at more moderate temperatures
(e.g., 4 to 25°C) inactivation rates are relatively slow (Davies et al., 2005; Finstein, 2004). Freeze-
thaw cycling is more effective than freezing, perhaps because of increased mechanical damage to
the oocyst wall during the temperature fluctuations (Walker et al., 2001).
Before oocysts enter a water source, they may be vulnerable to desiccation. 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.
Soil texture also can significantly affect inactivation of Cryptosporidium oocysts and
viruses (CRC, 2004). Vegetative filter strips can be effective at removing Cryptosporidium
oocysts from surface runoff, however, viruses (e.g., PRD1 bacteriophage) and to a lesser extent
bacteria (E. coif) are more easily transported (Davies et al., 2005; CRC, 2004).
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).
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2.4.2.2 What Role Should Monitoring Play in the Evaluation of Potential and Existing
Sources of Cryptosporidium'!
Monitoring of Cryptosporidium is not required to develop the WCP plan or to implement it
once approved by the State. It may take years to realize measurable improvements in water quality
after initiating source water protection efforts. Furthermore, discerning improvements in source
water quality using monitoring can be difficult due to natural environmental variability, the nature
of the source water improvements, and the limitations of the current analytical methods for
Cryptosporidium as well as other fecal indicators. However, PWSs that choose to employ this
option, either separately or in combination with other approaches, may gain some benefit using this
approach. For example, while the State and/or PWS may already have some knowledge of
potential Cryptosporidium sources through land use information or discharge permit data,
monitoring can help determine the extent to which these sources are impacting a source and can
help target portions of the watershed for extra protection or BMP implementation. Although not
required for WCP plan development, implementation, or maintenance, monitoring throughout the
watershed for Cryptosporidium (or indicators of fecal contamination) can be a useful tool in
evaluating the success of watershed control program controls
New technologies for microbial source tracking including DNA fingerprinting, genotyping,
and multiple antibiotic resistance may be helpful and more effective at overall pathogen source
identification (see Section 2.4.2 for references). Presumptive approaches using modeling and
literature reported in data can also be used to simulate loadings and prioritize areas for monitoring
or detailed study.
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 been 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. Use of a surrogate
such as turbidity should be supported by evidence of a correlation for that source water.
Precipitation (rainfall amount and intensity) are important in the release and detachment of
pathogens from fecal matter, and consequent mobilization in downgradient surface water or
groundwater. This precipitation also can mobilize and release turbidity.
A New Jersey utility has shown that for their source water increases in raw water turbidity
are accompanied by increases in source water Cryptosporidium during storm events (LeChevallier
et al. 1998, Atherholt et al. 1998). As a result of this research for their source water, this utility has
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established a standard operating procedure that when raw water turbidity exceeds a threshold of
about 15 ntu, intake can be shutdown for up to 24 hours without interrupting service in order to let
storm related source water flow bypass the treatment plant.
Monitoring, when implemented, 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 water quality and helps isolate the stream reaches contributing to
contamination. Second, site-specific monitoring involves monitoring just up stream 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 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
upstream of the Queen Lane plant (Crockett and Haas 1997). This creek has severalwastewater
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 andGiardia in livestock and
wildlife along the creek.
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
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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.
2.4.3 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 feasibility of each measure (40 CFR 141.725(a)(3)(ii)). This analysis can be based
on either site-specific experience or information from the peer-reviewed literature. Numerous
references are available that describe control measures and other BMPs, as listed previously in this
Section 2.4 of this guidance, and presented below for select topic areas.
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.
2.4.3.1 Available Regulatory and 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.
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 PWS does not own or otherwise have authority over the Cryptosporidium sources in the
watershed, the analysis will need to reflect developing and maintaining partnerships to assure
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adequate control is in place. This could include coordination with other municipal governments,
farmers, wastewater treatment plant operators, regional planning agencies, and others.
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 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
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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 A cquisition/Conservation Easements
Acquisition of watershed land by the PWS 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.
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.htrnfor frequently asked questions about
easements and for an example of a model easement for use in the State of Michigan. The Land
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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.
2.4.3.2 Partnerships in Watershed Control Plans
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, partnerships with local government and landowners is often
central to effectively implementing a watershed control program. The WCP can reflect a variety of
different types of partnerships:
Memoranda of agreement or other formalized arrangements with government
agencies
Education through technical assistance providers such as cooperative extension
agents or association representatives
Data collection through local university programs
Agreements to hold conservation easements with State agencies or non-
governmental organizations
Private agreements with individual property owners
Stakeholder participation can be a useful tool in watershed control planning. Dialogue with
stakeholders can be used to identify win-win solutions for both the water supplier and its partners.
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. In addition, developing alliances between water
utilities and agricultural interests is discussed by Fletcher et al. (2004).
An important potential partnership opportunity that many water systems should consider
when pursuing the WCP credit is to develop a cooperative relationship with other PWSs in the
same watershed. These PWSs in the same watershed will normally have overlapping areas of
influence and consequently will have some of the same priority Cryptosporidium sources.
Consequently, each of these PWSs will have an interest in developing control measures for these
shared Cryptosporidium sources. By cooperating together the PWSs can reduce duplication of
efforts and thereby collectively focus their energies on prioritized activities. PWSs that can not
cooperate together should not pursue joint efforts, because this will create difficulties during
implementation and maintenance of the WCP plan. However, if they can develop a plan to work
together to prepare the WCP plan, and can provide the staff and resources to complete their
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designated tasks during implementation and maintenance of the State-approved WCP plan, the
resulting joint effort can potentially produce a greater benefit (reduction in source water
Cryptosporidium ) at lower cost than the if each PWS worked separately.
Watershed control plans must identify watershed partners and their roles (40 CFR
141.716(a)(5)(iv)). 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, and 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.
2.4.3.3 Addressing Point Sources
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 141.716(a)(2)(iii)). 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/cwfmance/cwsrfmdex.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 2008).
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, instituting buffer zones where manure is applied, ensuring adequate manure
and wastewater storage, and others. Gullick et al. (2007 provide a reference guide for drinking
water utilities to implement source water protection activities related to CAFOs.
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
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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., filtration, advanced treatment such
as UV disinfection). 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 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).
Municipal Separate Storm Sewer Systems
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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-storm water 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.
2.4.3.4 Addressing Nonpoint Sources
The following sections briefly describe BMPs for agricultural, forestry, and urban sources
ofCryptosporidium; more 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
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.
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BMPs that can reduce pathogen loading include the following:
Composting
Waste management (manure storage and land application)
Grazing management
F eedl ot runoff di versi on
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 adj acent 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).
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.
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Manure should not be applied to frozen or saturated 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, and
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
^ loggers should minimize soil disturbance and compaction on skid trails
Urban/Suburban BMPs
See http://www.epa.gov/owm/mtb/mtbfact.htin 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.
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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
Sand 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.
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
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> 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 storm water 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
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.
PWSs 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
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2.4.3.5 Is Purchase/Ownership of All or Part of the Watershed a Viable Option?
PWSs will have the maximum opportunity to realize their watershed protection goals if
they have complete ownership of the watershed. Where feasible, PWSs 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. Since complete ownership of the watershed or area of influence is
not practical in almost every instance, the system should explain any efforts the PWS will make to
gain ownership of some critical elements, such as reservoir or stream shoreline and access areas.
Where ownership of land is not possible, PWSs 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 PWS to control land uses which could have an adverse
effect on the water quality. PWSs should include with these descriptions an explanation of how
they will ensure that landowners will comply with the agreements.
Utilities can also facilitate the prioritization and purchase of parcels by third parties in
upstream communities that are already looking to preserve, own, and maintain land. This can be
done by partnering on grants or other efforts.
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Campaigns. Washington, D.C.: U.S. EPA. EPA 841-B-03-002, 100+ pp.
Thurston, J.A., C.P. Gerba, K.E. Foster, M. M. Karpiscak. Fate of indicator microorganisms,
Giardia, and Cryptosporidium in subsurface flow constructed wetlands. Water Research 35(6):
1547-1551.
Trask, J.R., P.K. Kalita, M.S. Kuhlenschmidt, R.D. Smith, and T.L. Funk. 2004. Overland and
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U.S. EPA 1999b. Funding Decentralized Wastewater Systems Using the Clean Water State
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and Regeneration. Office of Water. EPA 832-F-00-017. September.
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Water EPA 832-F-00-023. September, http://www.epa.gov/owm/mtb/wetlands-
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http://www.calcoast.org/news/MSTGuide.pdf.
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Waters. U.S. EPA Office of Water. EPA 841-B-05-005, 414 pp., October 2005.
http://www.epa.gov/owow/nps/watershed handbook.
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Effluent Limitation Guidelines and Standards for Concentrated Animal Feeding Operations
(CAFOs). Federal Register 73(225): 70418-70486. November 20.
Vaux, H., ed. 2000. Water shed Management for Potable Water Supply: Assessing the New York
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ASA Annual Meeting, Anaheim, CA.
Wade, S.E., H.O. Mohammed, and S.L. Schaaf. Prevalence ofGiardiasp., 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, K. Leddy, and E. Hagar. 2001. Effects of Combined Water Potential and Temperature
Stresses on Cryptosporidium parvum Oocysts. Applied and Environmental Microbiology.67(12):
5526-5529. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=93339#B6
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.
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Yeghiazarian, L., P. Kalita, M. Kuhlenschmidt, S. McLaughlin, and C. Montemagno. 2004. Field
Calibration and Verification of a Pathogen Transport Model. Washington, DC: WERF.
Zhang, Q., K.R. Mankin, and L.E. Erickson. 2001. Modeling Transport Of Cryptosporidium
Parvum Oocysts In Overland Flow. Proceedings of the 2001 Conference on Environmental
Research. http://www.engg.ksu.edu/HSRC/01Proceed/docs/32.pdf
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3. Alternative Source/Intake
3.1 Introduction
Changing the water source or intake location can improve source water quality and
reduce 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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Chapter 3 -Alternative Source/Intake
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 treatment process, jar tests should be conducted to
determine the coagulation and settling properties of the new water and to aid in calculating the
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Chapter 3 -Alternative Source/Intake
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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Chapter 3 -Alternative Source/Intake
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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Chapter 3 -Alternative Source/Intake
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.
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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.
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 approaches that are
recommended and others that are not recommended.
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.
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Chapter 3 -Alternative Source/Intake
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.
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.
3.5 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. 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. Sites with artificial recharge and aquifer storage and recovery
operations may also receive bank filtration Cryptosporidium removal credit after a suitable site-
specific study but are not eligible for automatic credit. Slow sand filtration also relies on
engineered materials as the filter medium and so is not bank filtration.
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 differing 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
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attached to grain surfaces. Thus, bank filtration provides physical removal, and in some cases,
inactivation, to remove pathogens from water supplies.
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; 4) to provide suggestions for optimal operation of
bank filtration systems and 5) to discuss necessary and sufficient elements of a field and
laboratory investigation as part of a demonstration of performance (DOP) at a bank filtration site
(with or without engineered systems) to qualify for additional Cryptosporidium removal credits.
This chapter is organized as follows:
4.2 LT2ESWTR Compliance Requirements - describes requirements for receiving
automatic 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.
4.7 Demonstration of Performance - describes the recommendations for receiving
additional Cryptosporidium removal credits after a site-specific field and
laboratory investigation.
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 141.717(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
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Chapter 4 - Bank Filtration
bank filtration treatment, these systems are not eligible for subsequent additional bank filtration
credits (40 CFR 141.703(d)(l)).
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 determine bin classification (40 CFR 141.703(d)). 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 LTIESWTR compliance.
Alternatively, PWSs may apply to the State for Cryptosporidium treatment credit using a
demonstration of performance (see Chapter 4.7). States may award greater than 1.0-log
Cryptosporidium treatment credit for bank filtration based on a site-specific demonstration.
States may also award demonstration of performance Cryptosporidium treatment credit based on
a site-specific study to systems that are unable to qualify for the 0.5 or 1.0-log removal credit as
described in Chapter 4.2.1. For a bank filtration demonstration of performance study, the
following criteria must be met:
The study must follow a State-approved protocol and must involve the collection of data
on the removal of Cryptosporidium or a surrogate for Cryptosporidium and related
hydrogeologic and water quality parameters during the full range of operating conditions.
The study must include sampling both from the production well(s) and from monitoring
wells that are screened and located along the shortest flow path between the surface water
source(s) and the production well(s).
4.2.1 Credits
The LT2ESWTR specifies the following design requirements for systems to receive log
removal credit for bank filtration (40 CFR 141.717(c)):
Wells must draw from granular aquifers that are comprised of clay, silt, sand, or
pebbles or larger particles. Minor cement may be present.
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.
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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
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)(6)):
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.
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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.
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), Medema and Stuyfzand, 2002,
and Wang et al (2000, 2002) documented high removal of Cryptosporidium surrogate 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 for oxidized ground water. Ironhydroxides (at a pH below
7.0) may enhance the attachment of microorganisms to riverbed sediments (Medema et al., 2000;
Medema and Stuyfzand, 2002). In Louisville, Kentucky, an alluvial aquifer was chosen for the
bank filtration site. Wang et al (2000, 2002) found that removal of biological 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 from site to site, but also at a single site over time. A
site-specific demonstration of performance study requires not only a good understanding of past
ground water flow and Cryptosporidium surrogate removal efficiency but also ongoing
monitoring to identify and to take preventive action during poor removal periods.
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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; Medema and
Stuyfzand, 2002; Wang et al., 2000; Wang et al., 2002; Berger, 2002) have reported that bank
filtration is effective at removing Cryptosporidium. 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,
including trace organic contaminants, bank filtration reduces the need for adding large quantities
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Chapter 4 - Bank Filtration
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 smoothes out fluctuations in water temperature. Bank filtration is continuously
active, and the decreased amplitude of the contaminant 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. No waste stream is
produced that requires management. 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; Goldschneider et al., 2007), 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
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Chapter 4 - Bank Filtration
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 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
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Chapter 4 - Bank Filtration
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.
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).
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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 recharge, precipitation infiltration, 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 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
Exhibit 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
Ht
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 (m3/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 J AWWA 94(4) (April 2002) by permission. Copyright © 2002. American Water Works Association.
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 (Exhibit 4.3), providing many
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Chapter 4 - Bank Filtration
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 deposit!onal 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.
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 (e.g., Gaut et al., 2008). Wells
located in these aquifers would not be eligible for bank filtration credit.
4.4.2.3 Partially Consolidated, Granular Aquifers
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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.
12) 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.
13) 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.
14) 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).
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15) 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.
16) 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. The freeze-core method (Balcsak, 1995) can be used to obtain in-situ cores from
streambeds.
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).
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).
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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:
17) 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
18) Stackable sieves
19) A mechanical sieve shaker (for sample sizes greater than 20kg)
20) 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.shtml).
ASTM also provides a search engine which allows the user to search for laboratories that
perform sieve analyses (http://astm.365media.com/astm/1 abs/). The EnviroDirectory provides
listings for laboratories and drillers in New England, the Mid-Atlantic, and the Great Lakes
regions (www.envirodirectory.com).
4.4.4 Site Selection as it Relates to Scour
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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 dominant scouring
process in alluvial rivers is lateral migration (Exhibit 4.1). 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 .
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 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.
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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. For example, a stream reach adjacent to a wellfield
might be dredged for gravel mining. 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.
Lower log removals are expected to occur during and shortly after floods because
protective layers may be removed by flood scour. 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. 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.
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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/dailyMainW?state=us&map_type=flood&web_type=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 (A)
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.army.mil/dresriv.html).
Mississippi River:
River Mile
309.0
301.2
Gage
Station
Hannibal
Dam 22 tw
6am
Levels
16.9
15.9
24-hr
Change
-0.2
-0.3
National Weather Service
River Forecast
Next 3
Days
Crest Date
16.616.1 15.6
15.815.314.7
Flood
Level
16.0
16.0
Gage
Zero
449.3
446.1
Record
Level
31.80
29.58
Record
Date
07/10/93
07/16/93
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. fe ma. q ov/
Flood Hazard Mapping: http://vwwv.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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Exhibit 4.2 Generalized Depiction of Stream Channel Lateral Migration
Net erosion at outside
bank of meander
(a)
Net deposition at
inside bank
A1
to t,
y.v
(c)
- Location of river at time, t0
Location of river at time, \.\
(a) Map of a Stream Meander; (b) Cross-section of the Channel from A-A' with Channel Positions at 2 Successive
Times (t0, and t|); (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).
Exhibit 4.3 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. At least one infiltration gallery is
associated with an outbreak of cryptosporidiosis in the United States (also British Columbia,
Canada and Japan). The Medford and Talent, Oregon outbreak resulted from treated (filtered)
water taken from an infiltration gallery intake buried under Bear Creek, Talent, Oregon (Leland
et al., 1993). 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 (Exhibit 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, 200la). 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 Exhibit 4.2. It is elevated to prevent flood waters
from entering it.
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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 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, 200la). In such cases, horizontal
collector wells may be preferred.
Exhibit 4.4 Schematic Showing Generalized Flow and Required Separation
Distance to a Vertical Well
Minimum 25 Feet
for Log Removal Credits
Mapped Floodway or 100-Year Floodplain
Vertical
Pumping
Well
Bedrock
A
(Inset shows tortuous ground water flow at the micro-scale.)
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Exhibit 4.5 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
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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 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 13 m) 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 141.717(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. As discussed in Section 4.3.1.4, longer flow paths may result in
changes in the water oxygen content that may be advantageous for iron and manganese removal.
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.
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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 Exhibit 4.5. Formation of such a
variably saturated 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.
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Exhibit 4.6 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).
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
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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 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
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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 (Exhibit 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 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/. 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.
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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/software_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
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 calculation is 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.
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
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that portion of the overbanks that must be kept free from encroachment to discharge the one
percent annual chance
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 (Exhibit 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.
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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 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, 2001b; Rohns et al., 2006). 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).
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).
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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 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. In general, systems that receive water from
multiple, pumping wells should manage their well field so as to maximize the water residence
time in the subsurface, to the extent possible, while meeting changing water quantity demand.
Methods to evaluate subsurface residence time are discussed in Section 4.7, Demonstration of
Performance.
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
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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 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.
4.7 Demonstration of Performance
Public Water Supply systems using GWUDI of surface water as their source water may
receive 0.5 or 1.0-log Cryptosporidium removal credit based on well siting and aquifer critera as
described in Chapter 4.2. Alternatively, PWSs may apply to the State for Cryptosporidium
treatment credit using a demonstration of performance (DOP). States may award greater than
1.0-log Cryptosporidium treatment credit for bank filtration based on a site-specific
demonstration. States may also award demonstration of performance Cryptosporidium treatment
credit based on a site-specific study to systems that are unable to qualify for the 0.5 or 1.0-log
removal credit as described in Chapter 4.2.1.
Public Water Supply systems using existing bank filtration as pretreatment to a filtration
plant are not eligible to receive additional treatment credit for bank filtration. In these cases, the
performance of the bank filtration process in reducing Cryptosporidium levels will be reflected
in the monitoring results and bin classification under the Long Term 2 Enhanced Surface Water
Treatment Rule.
For a bank filtration demonstration of performance study, the following criteria must be
met:
The study must follow a State-approved protocol and must involve the
collection of data on the removal of Cryptosporidium or a surrogate for
Cryptosporidium and related hydrogeologic and water quality parameters
during the full range of operating conditions.
The study must include sampling both from the production well(s) and
from monitoring wells that are screened and located along the shortest
flow path between the surface water source(s) and the production well(s).
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The purpose of this chapter is provide additional guidance on the design
and conduct of a demonstration of performance study as well as guidance
on the interpretation of the study data and the award of Cryptosporidium
removal credits, if warranted. Finally, this chapter describes the necessity
for long term performance evaluation monitoring to determine if the log
removal credit continues to be appropriate.
4.7.1 Identification of Collection Devices and Alternative Treatment Technologies at the Site
Prior to initiating a demonstration of performance study, it is necessary to 1) identify all
of the treatment technologies and collection devices in use and 2) design a study tailored for each
treatment technology and collection device as a separate unit process. Evaluating each unit
process and device separately will enhance knowledge about Cryptosporidium removal at the
site.
A PWS may operate one or more vertical wells, horizontal collector wells (caisson
wells), infiltration galleries or spring boxes. Wellfield management operations may include
surface water diversion into recharge basins or injection of treated or untreated surface water
into the subsurface. Bank filtration relies upon the nature of the undisturbed (by humans)
subsurface materials to provide natural filtration, and is relatively unmodified by application of
engineered structures, flow control or engineering operations such as surface water basin
recharge. When other technologies, such as artificial recharge, or differing collection devices,
such as infiltration galleries are used, the treatment processes may vary spatially or temporally.
The physico-chemical removal processes utilized by the various well field management
technologies and collection devices will differ. Depending upon the site characteristics and
recharge operations, an artificial recharge technology may be influenced by intermittent
recharge, pre-treatment, unsaturated flow and transport, biofiltration, chemical precipitation by
oxidation and reduction, or other phenomena. The removal processes may operate with
significantly different removal rates among the differing technologies or collection devices. For
example, 1) oocyst attachment to the gas-water interface may be a significant removal process in
an intermittent artificial recharge technology, but will be absent or insignificant in a bank
filtration system where unsaturated conditions never occur; 2) a shallow infiltration gallery
might operate under aerobic conditions only, as compared with a deeper vertical well that might
operate at times under anaerobic conditions. As discussed in Chapter 4.3.1.4, oxidation and
reduction reactions may govern Cryptosporidum or especially surrogate transport through the
subsurface. Thus, each treatment unit process and collection device should be evaluated
separately in the demonstration of performance study.
Wells, both horizontal and vertical, that are significantly influenced by surface water
spreading operations may be considered to be artificial recharge alternative technology if a large
component of their yield results from artificial recharge rather than from bank filtration. As part
of the study design, a putative assignment of alternative treatment technology type should
be made for each collection device. Some wells may have high uncertainty about which
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alternative treatment technology (bank filtration or artificial recharge) is appropriate. For these
wells, the study design should include elements suitable to both technologies. For example,
spiking studies may be appropriate for artificial recharge but not for bank filtration studies. Such
spiking studies should be planned for those wells for which there is high uncertainty about the
appropriate alternative treatment technology.
4.7.2 Source Water Quality and Quantity
Water quality, flow and flood data should be compiled to characterize possible worst case
scenarios. Flooding can, for example, dilute pathogenic contamination in unsewered areas with
minimal agricultural activity or can increase contamination where combined sewer overflows are
present. As discussed in Chapter 4.6.2, flood scour can have a deleterious effect by removing the
protective fine-grained material in the riverbed.
The DOP study should identify and investigate the temporal variability of upstream point
and non-point source dischargers and pathogen concentrations. The study should compile
historical data and collect new data to determine the quality of the in-stream flow adjacent to the
well field and elsewhere upstream, focusing primarily on cyst and oocyst concentrations and
their most appropriate indicators in surface waters under a variety of surface water flow
conditions.
Surface water samples should be composite samples representative of the water quality in
differing stream tubes, both laterally and vertically within the river. River water samples should
proportionately be representative of the actual flow conditions based on the historic record and
should be collected during both low water and high water stages as well as under normal
conditions.
4.7.3 Ground Water Travel and Residence Time Calculations and Ambient Ground Water
Dilution
The study should determine the time lag due to travel between the surface water source
and the wells or other collection devices. To accurately calculate pathogen removal, the
appropriate lag times are necessary because variable pathogen concentration in surface water
will affect the removal calculations. Approximate lag times can be determined by collecting
suitable site-specific parameter data such as surface water and ground water temperature,
chloride and/or bromide concentrations, and then refined using the most appropriate site-specific
parameters.
Environmental tracer data (isotopes, CFCs, pharmaceutical compounds, etc.) should be
collected to verify lag times calculated using temperature, chloride and other parameters.
Samples from collection devices will typically be mixtures of induced stream water and ambient
ground water. The ambient ground water may have subsurface residence times of months, years
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or decades and therefore, may have very low concentrations of pathogens and indicators. The
collection device sample concentrations should be corrected for ambient ground water dilution
before determining removal by artificial recharge or bank filtration. Ground water flow models,
water quality data and environmental tracers can be used to determine the amount of ambient
ground water dilution for each well or cluster of wells. Because ambient ground water dilution
varies depending on the well pumping rate and/or schedule, the dilution should be
calculated using several well pumping scenarios.
The DOP should recognize that it is important to document the ground water flow paths
contributing to a collection device to improve confidence in the assigned pathogen removal
credit for each device. For example, a well providing water which is typically 80% ambient
groundwater and 20% naturally-filtered surface water may appear to have adequate pathogen
removal when, in fact, dilution by uncontaminated groundwater is the major factor resulting in
low pathogen concentrations in the produced water. If ambient ground water dilution changes
significantly (e.g. 20% ambient ground water and 80% naturally-filtered surface water), this well
could demonstrate markedly different pathogen removal efficiencies. For public health
protection, it is essential to ensure that the well will provide 99% Cryptosporidium removal from
the surface water through the alternative filtration technologies, without dilution by ambient
ground water.
Ground water flow models with particle tracking capability can be used to calculate
travel times, ground water residence times, lag periods and ambient ground water dilution (e.g.
Abdel-Fattah et al., 2007). Ground water flow model calculations can be improved if site-
specific data are collected on the hydraulic conductivity of the streambed using seepage meters
or other technologies and by analysis of well core or cutting samples from the aquifer. Most
recently, new models have been developed that can explicitly simulate ground water flow to a
horizontal collector well (e.g., Bakker et al., 2005). If ground water flow models are used, then
the study design should include the elements appropriate to standard ground water model quality
assurance, including calibration, history matching, verification and sensitivity analysis. Although
the dimensionality of the modeling is a site-specific decision, the groundwater flow models
should have the capability to simulate mutually-interfering pumping wells with non-uniform
surface recharge over the domain.
The concept of long and short flow paths to a well is illustrated by Gollnitz et al. (2005)
for a site in Casper, WY and was determined using a particle tracking ground water flow model.
However, at the Casper site, the shortest flow path to a collection device is from the surface to
the infiltration gallery, which is located at a depth of 15-20 feet below the bottom of the recharge
basins (Gollnitz and Clancy, 1994). Comparison of biological particle data among two 30 foot
deep vertical wells, a 30 foot deep horizontal collector well and the infiltration gallery shows
poorest removal in all samples collected from the infiltration gallery (Gollnitz et al., 2005, Table
2), suggesting that there is a correlation between flow path-length and removal efficiency.
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4.7'.4 Surface and Ground Water Data Collection, Methods and Sampling Locations
As required by the Long Term 2 Enhanced Surface Water Treatment Rule, the DOP
study must include the collection of hydrogeologic and water quality parameter data during the
full range of operating conditions. Thus, the paired surface water and ground water samples
should be collected, at a minimum, monthly for eighteen months to capture both high flow and
low flow events over a long time period. Sampling for eighteen months insures that at least one
wet season or one dry season is sampled twice. Unusual conditions associated with a wet or dry
season are less likely to re-occur during the second sampling period.
EPA recognizes that not all wells in a well field are equally at risk from
Cryptosporidium. Higher risk wells are those that receive surface water that has the shortest
ground water residence time (or flow path-length). Sampling should be more intensive at higher
risk wells (e.g. Gollnitz et al., 2005).
Data can be collected on an ongoing basis or it can be event based, with the intention of
capturing the worst case possibilities due to floods. The former will take place over a longer
period of time, but tends to provide an average characterization. The latter is a high frequency of
monitoring over short periods of time which tends to characterize the worst case scenario. The
monitoring strategy should try to maximize the possibility of capturing infrequent events without
sacrificing long-term characterization of average conditions. An appropriate data collection
strategy could include periodic data that is collected on an ongoing basis as well as data
collected during and after flood events (with consideration of appropriate lag time for ground
water samples), with the intention of capturing the worst case possibilities due to floods. Thus,
all data should be collected periodically during normal flows but at a higher monitoring
frequency over short-term, high water periods to characterize the potentially worst case scenario.
Late summer or drought low flow conditions should also be more intensively sampled if the low
water levels represent a possible worst case scenario.
The study design should ensure that the number and location of river water samples
collected are representative of high and low consumptive use (e.g. pumping for drinking water
supply, irrigation, etc.) periods. River water samples should be representative of the entire river
volume, rather than consisting only of samples collected at the surface water intake for the
treatment plant. If point sources discharge upstream and the stream is not well mixed, then the
river samples should be proportionate in number and location to the volume of the highly
concentrated plumes emanating from the point sources.
As discussed above, the study should be designed to determine proportions of each of the
unit processes operating at the site (ambient ground water, artificial recharge water and bank
filtrate water) and contributing to a collection device. Typically, identification of ground water
sources is accomplished by compilation of historical ground water geochemical data and
measurement of major and trace elements, isotopes and other environmental tracers, interpreted
with the assistance of geochemical and ground water flow models. Suitable parameters measured
could include, but are not limited to, organic carbon, chloride, bromide, TDS, hydrogen, oxygen,
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uranium and other isotopes, and CFCs.
Data collection activities should be designed to ensure that the collected samples are
representative and random. Data analyses should include quantitative assessment of the
uncertainty associated with each conclusion. Study design should include sufficient sample
numbers so as to determine statistical significance for each conclusion to a pre-determined
confidence level.
The study design should also include a quality assurance project plan, identifying 1)
reference to the analytical method and laboratory, 2) a reasonable number and percent of blank,
replicate and spiked samples, 3) detection limits, and 4) sample holding times.
The presence of multiple data collection wells can serve to increase confidence in the
conclusions. Monitoring well data (preferably from multiple wells) collected along the flow path
must show a decrease in indicator concentration with distance from surface water to improve
overall confidence that the measured log removal results are meaningful.
The DOP should determine the capture zone of each collection device and/or conduct dye
trace studies from local sources such as septic tank leach fields to ensure that indicator
organisms
are not coming from sites other than the source river water. The presence of alternative sources
will invalidate any monitoring data obtained from the collection devices.
4.7.5 Monitoring Tools
The DOP study should consist of monitoring for Cryptosporidium or a suite of
Cryptosporidium surrogate organisms at each collection device (or device type cluster) and the
source river water. Pathogen monitoring could also include Giardia and perhaps members of the
Microsporidia family (Brusseau et al., 2005). In the absence of Cryptosporidum oocyst removal
data (calculated using measurable oocyst concentrations in the river and in the collection
device), the DOP should use Cryptosporidium surrogate microorganisms and should demonstrate
that removal of the recovered surrogate organism(s) data would be similar to the removal of
Cryptosporidium oocysts (to the extent possible using the scientific literature, laboratory and/or
field studies).
Bank filtration efficiency can be meaningfully demonstrated and is permitted in a DOP
only in porous media (similar in concept to slow sand filtration but without use of engineered
materials, flow and flux control and active schmutzdecke management). Log removal
calculations require counts per volume of the same organism in both surface water and nearby
collection devices (wells). Comparison of the two values provides information on attenuation
during subsurface passage. However it is important to calculate log removal only for
microorganisms that are similar to Cryptosporidium oocysts. Log removal calculations for
particles or organisms that significantly differ from oocysts in size, shape and porous media
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transport capability or have unknown size and shape (and charge), such as turbidity, standard
particle counts, and total algae, or larger organisms such as rotifers, crustaceans or fish are not
meaningful and must not be used. Pumping wells generate turbidity in the aquifer as a result of
pumping so, for ground water, turbidity data are useful only for determining disinfectant
treatment efficiency. It is not meaningful to count particles not known to originate in the surface
water, as is the case for turbidity or standard particle counters.
Cryptosporidium and Cryptosporidium surrogate organism transport in porous media has
been well studied in both laboratory and field experiments (e.g. Schijven et al., 2003) and will
not be detailed here. In general, microorganism and porous media grain size and shape are
important parameters that govern removal efficiency together with grain coatings and water
chemistry. Predictions without field measurements are highly uncertain. Thus, paired samples
from surface water and ground water are necessary.
When subsurface materials are coarse grained (e.g. gravel), ground water flow is
relatively fast and bank filtration efficiency is significantly reduced. For example, in one study in
a gravel aquifer (not a bank filtration site), aerobic spores traveled 90 m in about one day (Pang
et al., 1998; Pang et al., 2005). For coarse grained aquifers, EPA recommends significant
additional study (increased monitoring frequency of multiple microorganisms from multiple
monitoring wells) to improve removal efficiency measurement at high ground water velocity.
Surrogate microorganisms are more likely to be recovered from collection devices when
the concentration in the surface water is high, such as during a diatomaceous algal bloom (e.g.
Kearney, Nebraska, Berger et al., 2002) or during high water stage. Eckert and Irmschser (2006)
report E. coli recovery in Dusseldorf bank filtration wells only following a flood event.
No single Cryptosporidium surrogate organism is best. Each organism has strengths and
weaknesses. Multiple surrogates should be analyzed initially to ascertain which surrogate suite is
best suited to the DOP at that site. Examples of surrogates include total aerobic bacterial spores
(e.g. Bacillus subtilus), anaerobic bacterial spores (e.g, Clostridium perfringens and/or
Clostridium bifermentans), total coliform, E. coli, enterococci bacteria, bacteriophage (e.g.
Bacteroides phage), coliphage (male-specific and somatic), diatoms (Reilly et al., 2005) at the
genus or species level, turbidity, particle counting and microscopic particulate analysis (MPA)
(US EPA, 1992; AWWA, 1990). EPA recommends monitoring for at least three or four
surrogate organisms using paired surface water and ground water samples to calculate log
removal efficiency.
As with any monitoring program, there is a trade-off between monitoring frequency and
information cost. The cost for each Cryptosporidium surrogate assay varies between $50 and
$250. EPA recommends that the cheaper assays, such as total aerobic spores, total coliform, and
enterococci be performed more frequently and the more expensive assays, such as MPA, be
performed at a lesser frequency. The assay cost for each surrogate is listed in Exhibit 4.7.1.
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Exhibit 4.7.1 Estimated Costs for a Cryptosporidium Surrogate Assay
Cryptosporidium surrogate
Total Conforms (TC) 1
Escherichia co/;1
Enterococci/Fecal Streptococci1
Total Aerobic Spore
Somatic Coliphage
Male-Specific Coliphage
Clostridium perfringens spore1
Microscopic Particulate Analysis
(MPA)
Method Cost
$0.71 -$5.95
$0.00 - $5.95
$1.02 -$4.93
$59 - $65
Lab fee ($) per sample test
$55
$55
$40 (2005 data)
$120(2001 data)
$80 -$100 (2001 data)
$50 (2005 data)
$350-$450
11ncludes costs for method(s) only. Doesn't include costs for sample collection or other laboratory operational costs
(estimated cost between $10.72 - $17.62) or equipment (e.g. autoclaves, pH meters, etc) or disposable supplies
(e.g., pipettes, Petri dishes, etc).
The choice of the appropriate suite of Cryptosporidium surrogate organisms is the most
important element of a DOP study. Favorable surrogate organisms should be 1) equal in size and
shape to Cryptosporidium oocysts (4-6 jim and slightly oblate), 2) sufficiently numerous in both
ground water and surface water so as to be suitable for log removal calculations (log removal
calculations require counts per volume of the same organism in both surface water and nearby
collection devices/wells); and 3) sufficiently long-lived in the subsurface (at least as long-lived
as oocysts) so that inactivation during subsurface passage does not significantly affect the
calculation.
The identification of Cryptosporidum oocyst surrogate organisms is based primarily on
similarity in size and shape. Other factors such as total net charge or charge distribution on the
outer surface of the microorganism are important elements governing Cryptosporidium transport
in the subsurface. However, choice of surrogate organisms based on charge or factors other than
microorganism size and shape is an important research topic (Tufenkji, 2007; Tufenkji et al.,
2006) but the available information is insufficient for inclusion in this guidance. Exhibit 4.7.2
lists the size ranges of common pathogenic protozoa and surrogate bacteria.
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Exhibit 4.7.2 Size of Pathogenic Protozoa and Surrogate Bacteria
Protozoa
Cryptosporidium parvum
oocyst
(Xiao etal., 2000)
Giardia lamblia cyst
(WHO, 2004)
Cyclospora sp.
(Mota etal., 2000)
Microsporidia
(Brusseau etal., 2005)
Size (|jm)
4.2-5.6
8-12
8-10
1-5
Surrogate Bacteria
Total Coliform
(Holt, 1986)
Escherichia coli
(vegetative cell formj
(Foppen and Schijven, 2006)
Clostridium perfringens
(vegetative cell form)
(Holt, 1986)
Clostridium perfingens spore
(Lund and Peck, 1994)
Clostridium bifermentans
(vegetative cell form)
(Holt, 1986)
Clostridium bifermentans spore
(Brock and Madigan, 1991)
Bacillus subtilus
(vegetative cell form)
(Holt, 1986)
Bacillus subtilus spore
(Rice et al., 1996 and P. Payment,
personal communication
Size (um)
-0.5-6.0
1.1-6.0
2-19
0.3-0.4
1-11
1.2
2-5
0.5-0.8
Cryptosporidium oocysts are slightly oblate with a length to width ratio that ranged, in
one study, from 1.04 to 1.33 (Xiao, 2000). Aerobic spores are typically slightly oblate as well
but smaller than oocysts, ranging from 0.5-0.8 microns in diameter as compared with 4-6
microns for oocysts. Bacterial vegetative cells of E. coli are slightly larger than aerobic spores
but significantly differ in length to width ratios (2.0-6.0 jim x 1.1-1.5 jim, Foppen and Schijven,
2006). Futhermore, vegetative cells produce extracellular polymers, particularly if these cells
form biofilms, and these polymers may significantly alter passage characteristics in the
subsurface. The bacterial spore form is significantly longer lived in the environment (and
especially the subsurface) than the vegetative cell form.
EPA recently completed a laboratory study (twelve laboratories) of the total aerobic
spore method. The study used natural ground water from a deep confined aquifer in Montana and
Ohio River surface water. The ground water was analyzed to insure that it was devoid of (but not
sterile) aerobic spore forming bacteria. Aerobic spores (from BioBall) with well-defined counts
but subject to variability were spiked in the ground water samples. Split surface water samples of
unknown variability were also prepared. One ground water and one surface water sample was
sent to each laboratory for multiple assay.
Laboratory performance was evaluated by comparing mean assay values separately for
ground water and surface water. Spiked ground water sample variability among the twelve
laboratories using Youden's Laboratory Ranking Test (Youden, 1969) did not identify any
outlying laboratories. Surface water mean values showed two outlying laboratories (one high
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Chapter 4 - Bank Filtration
outlying value) but the range of mean values was about a factor of five different between the
high (23,962 CFU/100 ml) and (low 4,370 CFU/100 ml) values. Spore removal in this guidance
is typically an assessment of whether surface water spore counts are diminished by a factor of
one hundred when measured at a well. A factor of five difference is acceptable variability,
assuming other information does not contradict that assessment.
The laboratory study shows that the aerobic spore laboratory method can be reproducibly
performed by different laboratories and also provides acceptable recoveries of spores from
spiked water samples. Because aerobic spores are: 1) relatively cheap and easy to measure, 2)
identifiable without unacceptable laboratory error, 3) long-lived in the environment, 4) similar in
shape to oocysts (albeit slightly smaller) and 5) do not produce extracellular polymers, EPA
recommends aerobic spores, if present in large numbers in the surface water at the DOP site, as
the most useful Cryptosporidium surrogate organism. Aerobic spores have long been recognized
as a useful measure of surface water influence on and hygienic quality of ground water (e.g.
Schubert, 1975). Aerobic spores are also commonly used to assess the performance of
engineered filtration systems (e.g. Mazoua and Chauveheid, 2005).
The MPA method counts spores but these are fungal spores and not bacterial spores.
Bacterial spore assay requires, at present, a culture step that is not currently part of the MPA
method. MPA simply concentrates particulates and counts them. An aerobic spore assay standard
method is available (APHA, 2004). EPA recommends that unused aerobic spore sample be
refrigerated (4 degrees C.). These refrigerated samples may then be re-assayed up to 24 hours
post-receipt of the sample at the laboratory so that additional and differing dilutions be
conducted to reanalyze samples that are reported as "Too Numerous to Count" (TNTC).
Aerobic spore data have been collected from several recent studies at potential bank
filtration sites (e.g. Weiss et al., 2005, Vogel et al., 2005, Gollnitz et al., 2004, Gollnitz et al.
2005, Partinoudi and Collins, 2007, Gollnitz et al., 2007). It is important to differentiate sites that
may be described as riverbank filtration sites but are not recognized as GWUDI by the State. For
example, both Lincoln NE (Vogel et al., 2005) and Cincinnati OH (Gollnitz et al., 2004) field
sites were studied in great detail using very sophisticated methods despite not being regulated as
GWUDI. Thus, high aerobic spore log removal at these sites is expected because they are
regulated as ground water rather than as surface water. Finally, at least one laboratory counted
aerobic spore colonies in ground water without use of a dissecting microscope (in contrast to
APHA, 2004) (Partinoudi and Collins, 2007). Partinoudi and Collins (2007) did not use a
microscope so they report a high aerobic spore detection limit (<30 CFU/100 ml). Based on
unpublished data from Casper WY and results reported in Locas et al. (2008), Schubert (1975)
and Rice et al (1999), EPA suggests that the aerobic spore natural background concentration is
about 10 CFU/100 ml or less. Values higher than 10 CFU/100 ml may be considered to have
some surface water influence. Thus, a high detection limit makes it difficult to differentiate
native and surface water-influenced ground water.
The ability to produce environmentally-resistant aerobic spores is fairly limited in the
bacterial world. Current methodology recovers almost exclusively those aerobic spores from the
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genus Bacillus. There are many species of Bacillus and all produce aerobic spores. Members of
this genus are found naturally in all environments, including surface waters and especially in
soil. It is assumed that, when found in surface water, aerobic spores found naturally in soil are
washed into surface water by natural processes. As soil bacteria, aerobic spore populations in
surface water are expected to comprise a diverse bacterial population, representing all aerobic
spore taxa within the surface water watershed. The aerobic spore population in a ground water
sample may be 1) similarly as taxonomically diverse as the surface water population, 2)
taxonomically less diverse than the surface water population because some spore taxa have
favorable properties (e.g. charge) for subsurface passage while other taxa are more likely to
attach to aquifer solids, or 3) taxonomically diverse or not but representative only of the spore
population in the soil in the immediate vicinity of the wellhead.
Gollnitz et al., (2005) suggest that ground water aerobic spore samples exhibit
"endospore monocultures" and also suggest that these "monocultures" explain the instances
when collection devices exhibit negative (low) removal efficiency. (Given the high uncertainty
in log removal calculations, the difference between negative and low removal efficiency is not
significant.} "Monocultures" implies that all of the cells recovered on the growth medium are of
the same strain and possible clonal, being genetically identical. This would ordinarily imply that
the organisms were growing either in the groundwater itself or in the sample once it was
collected. Some type of genetic profiling analysis would need to be run in order to document all
of the cells recovered as clonal. To date no such data has been reported. A more likely
explanation for a sample yielding Bacillus colonies that are morphologically similar is laboratory
contamination. Thus, any suggestion that, in the absence of genetic profile or speciation data,
colonies are "monocultures," must be recognized as premature and possibly incorrect. Finally, as
discussed above, low taxa diversity in a ground water sample (when recognized by speciation
data) provides no information on log removal by subsurface passage.
Anaerobic spores are also recommended as surrogate microorganisms because these
microorganisms, like aerobic spores, are small (0.3-1.2 |im), spherical, and long-lived.
Riverbank filtration studies in the Netherlands (e.g. Shijven et al., 2003; Medema and Stuyfzand,
2002) used spores of sulfide-reducing Clostridia (SSRC) and Clostridium bifermentans spores as
Cryptosporidium surrogates in studies of the Rhine and Meuse Rivers. However, anaerobic
spores probably do not have a significant presence in surface water unless there are significant
upstream sewage discharges to surface water, as there are in the Rhine and Meuse. Thus, the
utility of anaerobic spores at a DOP site, where surface water quality is typically very good, is
limited.
Total coliform bacteria are vegetative cells that, like Bacillus sp., originate largely as soil
bacteria, and are found at high density in surface water. Total coliform density in wells has been
used for GWUDI determination in bank filtration settings. Price et al., 1999 show that higher
total coliform density occurs in horizontal collector well #5 from January to April, during
highest flow conditions in the river. Thus, well #5 is used primarily during summer months when
water use demand is high and river flow is low. However, using measurement of aerobic spores
(or carboxylated microspheres, Metge et al. 2007) in addition to measurement of total coliform
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vegetative cells might provide a differing assessment because aerobic spores should more
efficiently passage through the subsurface and may be present in significant density before
January or after April.
Diatoms are a specialized group of marine and freshwater algae that all produce a rigid
cell wall (frustule) composed of silica. There are 58 freshwater diatom genera (AWWA, 1995).
Diatoms are counted separately from other algae in a Microscopic Particulate Analysis (USEPA,
1992). The MPA method only counts whole diatoms; diatom fragments are not considered.
Exhibit 4.7.4 shows the size and shape of some common freshwater diatoms. Diatoms vary in
size (e.g., from 4-10 microns to 60 or 70 microns). Smaller diatoms may be transported through
sand and other porous media at rates similar to oocysts. Larger diatoms may, if they have large
length to width ratios, orient themselves in the ground water flow field so that the long axis is
parallel to the flow direction, which also may allow them to passage through sand and other
porous media. Diatoms are photosynthesizing algae that require light to maintain their green
chlorophyll. After several months residence time in the subsurface, it is likely that the green
color will fade.
Exhibit 4.7.3 Size of Some Common Fresh Water Diatoms
Diatom
Stephanodiscus hantzchii
Synedra acus
Cyclotella meneghiniana
Cyclotella pseudostelligera
Fragilaria crotonensis
Aulacoseira granulata
Asterionella formosa
Nitzschiia palea
Size (length x width) (|jm)
10x5-8
60-70 x 3-4
5x3
4-10
40-170x2-4
4-30
40-80 x 1 .3-6
15-70x2.5-5
Shape
Cylindrical (Hendricks et al., 2000)
Needle (Hendricks et al., 2000)
Cylindrical (Hendricks et al., 2000)
Centric (Reilly et al., 2005)
Pennate (Reilly et al., 2005)
Centric (Reilly et al., 2005)
Pennate (Reilly et al., 2005)
Pennate (Reilly et al., 2005)
Because most diatoms are larger than Cryptosporidium oocysts, diatom occurrence in a
well signals that oocysts, like diatoms, could also be present in inadequately filtered drinking
water from a well. Diatoms occurrence is subject to less uncertainty because the rigid frustule is
not likely to be sufficiently deformable to pass through smaller pores, unlike most biological
particles. Thus, one or more whole diatom tests, identified in well water, and counted using the
MPA or another method, are particularly meaningful data. Some diatom species are also
identifiable using immunoassay methods (Walker et al., 2005), although the detection limit is
high (500 cells per liter) and not thus not well suited for porous media groundwater sites where
the diatom count is expected to be significantly lower.
EPA recommends weekly or biweekly aerobic spore samples plotted on a graph together
with monthly diatom data from MPA and river stage values to evaluate bank filtration efficiency.
The spore data are a measure of bank filtration efficiency which should decrease with increasing
river stage (i.e. high spore occurrence in a well at high river stage). For a regulated river (e.g.,
upstream dams and reservoirs) the correlation between aerobic spore recovery in wells and river
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stage might be muted or non-existent. Diatom data are used to validate the aerobic spore data;
weeks or months with high spore recovery in wells should also have accompanying diatom
occurrence in well water.
4.7.6 Tracer Tests and Use of Isotopes
It may be useful for the study design to include a pilot test at one or more collection
devices taken off-line. The pilot test could consist of adding a known quantity of inactivated
cysts or indicator organism and conservative tracer ("spiking") to the source and collecting and
analyzing samples from the collection device. This type of pilot test may assist in the assessment
of actual removal through the alternative filtration system. If a correlation between cysts and
indicator organism(s) can be established, this correlation could be used to focus and expedite
monitoring. Spiking studies are best suited for artificial recharge studies but can also be used in
bank filtration studies if an injection well is drilled to insert the spiked samples. If an injection
well is used, it would be preferable to drill it as a slant well under the riverbed that bottoms just
below the riverbed.
As a supplement to special spiking studies, the DOP could conduct pilot laboratory
column or tank studies of relatively undisturbed natural or engineered materials to evaluate their
performance when challenged with a cyst, oocyst, indicator(s) and conservative tracer spike.
These studies are especially important for demonstrating that the porous media transport of the
indicator(s) identified in field studies is similar to the transport of cysts and oocysts.
At least three studies (Coplen et al., 1999; Vogel et al., 2005; Hunt et al., 2005) have
used stable isotopes in a North American bank filtration study, although isotopes are commonly
used in less specialized ground water and surface water interaction studies in the United States
and elsewhere. Coplen et al. showed that, for Portland, OR municipal field well #1, increasing
Columbia River contribution to well yield with pumping, with about half of the yield from
surface water at day 7 and culminating at 82 percent surface water on day 23 of the pump test.
Hunt et al. showed that the travel time of surface flood water to the municipal wells in La
Crosse, WI was approximately 2 months as compared to inter-flood periods with about 9 month
travel times. Age dating using 3H-3He and tracers such as chlorofluorocarbons and SF6 were less
useful at the site.
4.7.7 Monitoring Wells Located Along the Shortest Flow Path
The Long Term 2 Enhanced Surface Water Treatment Rule allows DOP credit for a site-
specific study ONLY if one or more monitoring wells are screened and located along the shortest
flow path between the surface water source(s) and the production device(s) (well). As discussed
in Chapter 4.7.3, particle-tracking ground water flow models are best suited for identifying the
shortest flow path and the appropriate depth of the screened interval. However, optimally
located, existing monitoring wells may also be used if they are directly located between the river
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Chapter 4 - Bank Filtration
and the well and are screened at a depth intermediate between the river channel bottom and the
production well screen.
4.7.8 Post-decision Routine Monitoring and Sampling
Any DOP study should include a component to develop a routine sampling and
monitoring program that would validate the continuation of any removal credit granted. EPA
recommends continued post-decision bi-weekly or monthly aerobic spore monitoring to insure
that any approved Cryptosporidium log removal credit is maintained over time. Post-decision
routine monitoring is similar to filtration plant performance testing and will allow comparison to
previously-collected data to determine if it appears that any degradation of alternative filtration
performance is occurring and to document improvements in alternative treatment removals,
based on improved wellfield operation and maintenance.
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4.8 References
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through an alluvial gravel aquifer. Ground Water 36:112-122.
Pang, L., M. Close, M. Goltz, M. Noonan, and L. Sinton. 2005. Filtration of Bacillus subtilus
spores and the F-RNA phage MS2 in a coarse alluvial gravel aquifer: Implications in the
estimation of setback distances. Journal of Contaminant Hydrology 77:165-194.
Partinoudi, V. and M.R. Colins. 2007. Assessing RBF reduction/removal mechanisms for
microbial and organic DBF precursors. Journal AWWA 99(12):61-71.
Price, M.L., J. Flugum, P. Jeane and L. Tribbett-Peelen. 1999. Sonoma County finds
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Diatoms in Lakeside Wells in Northern New Jersey as an Indicator of the Effect of Surface
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20005-5263, 13 p.
Reynolds, J.M., 1997. An Introduction to Applied and Environmental Geophysics. New York:
Wiley.
Rice, E.W., C.H. Johnson, M.C. Meckes, K.C. Kelty and R. Moore. 1999. Microbial indicators
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Ritter, D.F., C.R. Kochel, and J.R. Miller. 1995. Process Geomorphology. 3rd edition.
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Rohns, H.-P., C. Forner, P. Exkert and R. Irmscher. 2006. Efficiency of riverbank filtration
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5. 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
CFR141.726(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 =
Logio(Monthly Average Influent Turbidity) - Logio(Monthly Average Effluent Turbidity)
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Chapter 5 - Presedimentation
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 = Logio(16.3) - Logio(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
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
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Chapter 5 - Presedimentation
be 3.2 NTU for those months, which could be difficult for some systems to achieve. Exhibit 5.1
lists influent and effluent turbidity values that yield 0.5 log reduction.
Exhibit 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.
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
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:
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Water Quality and TreatmentA Handbook of Community Water Supplies, 5th
ed. (AWWA 1999)
Integrated Design and Operation of Water Treatment Facilities, 2nd ed.
(Kawamura 2000)
Exhibit 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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Exhibit 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 blanket zone 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.
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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 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 flexibilitythe 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.
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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 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
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Chapter 5 - Presedimentation
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 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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5.6 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. 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.
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 141.717(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
For purposes of compliance with the lime-softening toolbox option, "clarifier" is used as a general term
for processes with settling and solids removal.
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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).
Chemical addition and hardness removal must occur in two separate and sequential
stages.
Exhibit 6.1 shows a typical two stage lime softening process. Lime or lime and soda ash
are added at the first stage.
Exhibit 6.1 Typical Two-Stage Lime Softening Process
Lime
Primary Clarifier
CO,
I
Flocculation and
Sedimentation Basin
1
Recarteonation
Soda Ast
i
Flocculation and
Sedimentation Basin
(JU,
1
Recarbonation
Filters
Secondary Clarifier
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):
Chemical addition and hardness precipitation occurred in two separate and sequential
softening stages prior to filtration
Both clarifiers treat 100 percent of the plant flow
A schematic of the treatment processes, clearly identifying the two stages of clarification,
will assist the State in evaluating the process for the purposes of LT2ESWTR removal credit.
Monitoring of chemical doses in the secondary clarifier over the expected range of seasonal raw
water quality and recording of minimum and average chemical concentration will assist the State
in evaluating the process and the system in determining operating criteria.
6.3 Split-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
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Chapter 6 - Lime Softening
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 (LTIESWTR) 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 LT IESWTR, 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.
The 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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Chapter 7 - Combined and Individual Filter Performance
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 141.718(a)).
The LT2ESWTR also allows systems using conventional or direct filtration treatment to
claim an additional 0.5 log Cryptosporidium removal credit for any month at each plant that
meet both of the following individual filter effluent (IFE) turbidity requirements (40 CFR
1) IFE turbidity must be less than 0. 15 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 claim credit for combined filter performance AND individual filter
performance in the same month (40 CFR 141.718(b)) for 1.0 log total.
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
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Chapter 7 - Combined and Individual Filter Performance
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 0.15 NTU (40 CFR 141.718(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 141.718(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. 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. For a full copy of this document see:
The LTIESWTR guidance manuals are available on EPA's website at:
http://www.epa.gov/ogwdwOOO/mdbp/ltleswtr.html
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Chapter 7 - Combined and Individual Filter Performance
7.2.3.1 Methods
Currently, EPA has approved four methods for the measure of turbidity (described in 40
CFR141.74).
EPA Method 180.1
Standard Method 213 OB
Great Lakes Instrument Method 2
Hach Filter Trak
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. Exhibits 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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Chapter 7 - Combined and Individual Filter Performance
Exhibit 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-top
Clean and calibrate with primary standard
Replace lamp
Recommended Frequency
Weekly
Weekly
Weekly on CFE turbidimeter and monthly on all
turbidimeters1
IFE
Quarterly
Annually
1Clean and recalibrate with primary standard if verification indicates greater than a +/-10 percent deviation from
secondary standard.
Exhibit 7.2 Maintenance and Calibration Activities for Bench Top Turbidimeters
Activity
Inspect for cleanliness of bulbs and lenses
Verify calibration with secondary standard
Clean and calibrate with primary standard
Replace lamp
Recommended Frequency
Daily
Daily1
Quarterly
Annually
Clean and recalibrate with primary standard 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 141.721).
7.3.2 Individual Filter Performance
For the 0.5 log IFE removal credit under the LT2ESWTR, a water system must report
monthly verification of IFE turbidity levels less than or equal to 0.15 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 141.721).
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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 measurements only if they have exceeded one of the IFE turbidity triggers.
Systems that would apply successfully for the 0. 5 log Cryptosporidium IFE 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 0.5 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. Exhibit 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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Exhibit 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 or the 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?
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
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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
Alarm Systems
Alternate Power Source
Laboratory Space and
Equipment
Sample Taps
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?
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
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Time on the Job
Water Treatment
Understanding
Application of Concepts and
Testing to Process Control
Does staffs 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
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).
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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.
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 jets
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
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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-1) 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).
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-1.
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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.
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. Exhibit 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.
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Exhibit 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 < 1 0 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.
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.
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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.
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.
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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 processit
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 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)).
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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.
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
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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).
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
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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/partner 1 .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 III.
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 III: 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 II with finished water turbidity levels less than 0.1 NTU (based on 95th percentiles). At
the beginning of Phase III, approximately 51 percent of plants reported 95th percentile turbidity
less than 0.1 NTU, and after completing Phase III 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 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.
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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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7.6 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. Bag and Cartridge Filters
8.1 Introduction
Under the LT2ESWTR, bag and cartridge filters are defined as pressure driven separation
devices that remove particles larger than 1 micrometer (jim) using an engineered porous
filtration media. Bag filters are typically constructed of non-rigid, fabric filtration media housed
in a pressure vessel in which 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 (40
CFR141.2).
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 is replaced.
Typically, bag and cartridge filters are used by small systems 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.
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.
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.
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8. Bag and Cartridge Filters
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 141.719(a)):
Up to 2.0-log removal for individual bag or cartridge filters showing a minimum of 3.0-
log removal in challenge testing.
Up to 2.5-log removal for bag or cartridge filters in series showing a minimum of 3.0-log
removal in challenge testing.
Challenge testing must be concluded according to the LT2ESWTR requirements outlined
in section 8.4 of this chapter. A 1-log factor of safety for a single filter and 0.5-log factor of
safety for multiple filters in series 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 (USEPA 2005) for direct integrity testing and other membrane filtration requirements.
8.2.2 Reporting Requirements
All reporting requirements for the Surface Water Treatment Rule (SWTR), Interim
Enhanced Surface Water Treatment Rule (IESWTR), and Long Term 1 Enhanced Surface Water
Treatment Rule (LTIESWTR) 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 LT1ESWTR 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.
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8. Bag and Cartridge Filters
When bag and/or cartridge filters are used to comply with treatment requirements, the
LT2ESWTR requires systems to submit an initial report that demonstrates the following (40
CFR141.721(f)):
Process meets the definition of a bag or cartridge filter; and
Removal efficiency from challenge testing (described in section 8.4). The removal
demonstrated must be 1.0-log greater than the credit awarded for a single and 0.5-log
greater than the credit awarded for multiple filters in series.
This initial report must be submitted by April 1, 2012 for systems serving more than
100,000, October 1, 2012 for systems serving between 50,000 and 99,999, October 1, 2013 for
systems serving between 10,000 and 49,999 and October 1, 2014 for small systems serving
fewer than 10,000 people.
For routine compliance reporting, systems must verify each month that 100 percent of
plant flow was treated by the bag or cartridge filter (40 CFR 141.721 (f)). 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 LT1ESWTR, 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 LT1ESWTR. 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 Exhibits 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.
Exhibit 8.1 Schematic of Treatment Process with Bag/Cartridge Filters
Pan
water
-o-l
11
Coagulation Fbcculation
Bag or Cartridge Filter
Sedimentata
Granular Fiters
*.»'
SavJogpurp
(if needed)
V.
System
^ ) Htcfi sendee pimp
CJearwel
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8. Bag and Cartridge Filters
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 Exhibit 8.2).
Exhibit 8.2 Bag/Cartridge Filters in Series
Raw
water
Distribution
System
High service pump
Primary Bag or Secondary Bag or
Cartridge Fiter{s) Cartridge Filters)
Clearwell
Another possible configuration is a bag or cartridge filter followed by a UV system (see
Exhibit 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 (USEPA 2006) for information regarding UV systems
and associated requirements with LT2ESWTR.
Exhibit 8.3 Bag/Cartridge Filter with UV System
Raw
water
/-I - »
PVjy
Bag or Cartrictje
Firter(s)
System
Distribution
System
j High service pump
QearweJI
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 considered
in the planning process. Because a significant headloss is associated with an additional filtration
process, systems should consider their hydraulic profile when integrating new filters into an
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8. Bag and Cartridge Filters
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
installations chlorinate prior to the bag filtration process to minimize biofilm growth on the bags.
However, if systems are considering using a bag or cartridge filter as the primary filter as in
Exhibit 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 training, 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.
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. Bag and cartridge filters can also be subject to clogging, by biofilm growth or excess
coagulants. Maintaining a residual through the filter is one possible way to prevent biofilm
growth. See the Simultaneous Compliance Guidance Manual (USEPA 2007) for additional
recommendati ons.
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 ofCryptosporidium. 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
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8. Bag and Cartridge Filters
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 to determine
removal credit.
Challenge testing is 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. 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 2.0- or 2.5-log Cryptosporidium removal rating. Bag or cartridge filters must
be challenge tested, however, in the same configuration that the system will use, either as
individual filters or as a series of filters.
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; States may develop additional testing requirements. The EPA Membrane
Filtration Guidance Manual (USEPA 2005) 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 P articulate
Contaminants (NSF International 2005) with a chapter for testing bag and cartridge filters
(Chapter 4). Although the protocol was developed for compliance with the SWTR, some testing
principles still apply1.
Section 8.4.1 describes the test conditions required by the LT2ESWTR (40 CFR
141.719(a)(2)-(8)). Section 8.4.2 shows how to calculate the log removal value for challenge
testing 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 (141.719(a)(2)-(a)(8))
8.4.1.1 Full Scale Filter Testing
Challenge testing must be conducted on full-scale bag or cartridge filters and the
associated filter housing or pressure vessel that are identical in material and construction to the
filters and housing the system will use for removal of Cryptosporidium.
8.4.1.2 Challenge Particulate
1 Specific sections of the EPA/NSF ETV Protocol that provide guidance for developing and conducting a challenge
test for LT2ESWTR include: section 7.0, Characterization of Feed Water; section 11.0, Operating Conditions;
section 12.3, Work Plan; section 13.0, Data Management; and section 14.0, QA/QC.
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Challenge testing must be conducted using Cryptosporidium or a surrogate which is
removed no more efficiently than Cryptosporidium. The microorganism or surrogate used
during challenge testing is referred to as the "challenge particulate." The concentration of the
challenge paniculate must be determined using a method capable of discreetly quantifying the
specific organism or surrogate used in the test; gross measurements such as turbidity may not be
used (40 CFR 141.719(a)(3)). Key physical characteristics to be considered for identifying an
acceptable surrogate include size, shape, and surface charge. Other factors include ease of
measurement and cost. Chapter 3 of EPA's Membrane Filtration Guidance Manual (USEPA
2005) describes the characteristics of acceptable surrogates and lists potential and inert
surrogates for Cryptosporidium. Examples of possible microbial surrogates are/1, dimunita and
S. marcessans.
8.4.1.3 Test Solution Concentration
In order to demonstrate a removal efficiency of at least 3-log for bag or cartridge
filters, 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:
Maximum Feed Concentration = 1.0 X 104 'Filtrate Detection Limit Equation 8-1
These concentrations allow the demonstration of up to 4.0-log removal for bag filters and
cartridge filters during challenge testing, if the challenge particulate is removed to the detection
limit.
Example 1 - Determining maximum allowable feed concentration
If the detection limit of the surrogate test is 2 units/L then the maximum feed
concentration is 1 x 104 x (2) = 2 x 104
8.4.1.4 Challenge Test Duration
Each filter must be tested for a duration sufficient to reach "terminal pressure drop" (40
CFR 141.719(a)(6)). Terminal pressure drop is a parameter specified by the manufacturer that
establishes the end of the useful life of the filter. Continuous challenge particulate 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:
Within 2 hours of start-up of a new filter.
When the pressure drop is between 45 and 55 percent of the terminal pressure drop.
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8. Bag and Cartridge Filters
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.
8.4.1.5 Water Quality of 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. For the application of
the LT2ESWTR, they typically 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 should 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.
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.
Test water should be characterized with respect to basic water quality parameters, such as
pH, turbidity, temperature, and total dissolved solids.
8.4.1.6 Maximum Design Flow Rate
The challenge test must be conducted at the maximum design flow rate for the filter as
specified by the manufacturer (40 CFR 141.719(a)(5)).
8.4.1.7 Challenge Particulate Seeding Method
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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 a uniform concentration. 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.
In-line injection is the most common seeding approach used in challenge testing,
allowing challenge particulates to be introduced into the feed on either a continuous or
intermittent basis. While either could be used, intermittent seeding may be preferable to
continuous seeding for conducting the challenge test at the required intervals (i.e., a minimum of
beginning, middle, and end-of-run). If intermittent injection is used, equilibrium should be
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. Guidelines and examples for determining challenge test feed
concentration and stock solution delivery rates are provided in Chapter 3 of the Membrane
Filtration Guidance Manual (USEPA, 2005).
In-line injection requires additional equipment, such as chemical feed pumps, injection
ports, and in-line mixers. These components should be designed to ensure a consistent challenge
particulate concentration in the feed. A chemical metering pump that delivers a steady flow is
recommended (pumps that create a pulsing action should be avoided). The injection port should
introduce the challenge material directly into the bulk feed stream to aid in dispersion. An in-
line static mixer should be placed downstream of the injection port, and a feed sample tap should
be located approximately ten pipe diameters downstream of the mixer (USEPA, 2005).
8.4.1.8 Challenge Test Solution Volume
The volume of the test solution depends on filtrate flow rate, test duration, and hold-up
volume of the test system. For intermittent, in-line injection, the seeded test solution volume can
be considerably less than that required for batch seeding. Formulas for calculating test solution
volume and examples are provided in Chapter 3 of the Membrane Filtration Guidance Manual
(USEPA, 2005).
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.
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. Grab sampling is commonly used to
determine the concentration of challenge particulates in the feed solution, while grab or
composite sampling is used to analyze the filtrate stream. Good sampling practices include
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8. Bag and Cartridge Filters
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.
In many cases, it may be advantageous to collect more filtrate samples than feed samples,
since the concentration of the challenge microorganism in the filtrate samples is expected to be
very low and error of just a few particles could have significant impact on the demonstrated
removal efficiency.
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, 2005) contains
additional information on developing sampling plans and provides schematics of typical
sampling apparatuses.
8.4.2 Calculating Log Removal (141.719(a)(7)-(9))
Removal efficiency of a filter must be determined from the results of challenge testing
and calculated using Equation 8-2.
LRV = Logio(Cf) - Logio(Cp) Equation 8-2
Where:
LRV = log removal value demonstrated during challenge testing
Cf = feed concentration measured during the challenge test
Cp = filtrate concentration measured during the challenge test
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 (Cp) must be set equal to the detection limit.
Example 2 - Calculating the LRV
Feed Concentration (Cf) 20,000 units/L
Filtrate Concentration (Cp) 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. A conservative approach would be to use the lowest feed concentration and highest
filtrate concentration from each filter run.
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8. Bag and Cartridge Filters
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, the overall removal
efficiency for the filter product line must be set equal to the lowest LRV observed among
the filters.
If 20 or more filters were tested during challenge testing, the overall removal efficiency
for the product line must be set equal to the 10th percentile of the LRVs observed during
the challenge study. (The percentile is defined by [i/(n+l)J 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 Testing (141.719(a)(10))
If a previously tested filter is modified in a manner that could change the removal
efficiency of the filter product line, challenge testing to demonstrate the removal efficiency of
the modified filter must be conducted and submitted to the State. Significant modifications may
include, 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; and
Modifications to the sealing system.
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. Exhibit 8.4 shows
a typical single filter vessel (housing).
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8. Bag and Cartridge Filters
Exhibit 8.4 Single Filter Vessel
i
18 3/4"
Adjustable 16" Standard
L
Footprint
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. Exhibits 8.5 and 8.6 show the manifold design and multiple filter vessel design,
respectively.
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8. Bag and Cartridge Filters
Exhibit 8.5 Manifold Bag Filter Design
Exhibit 8.6 Multiple Filter Vessel
56 1/2"
Went
22" Dia.
Diffuser
Inlet
Utlet
Hydraulic lid
opening jack
12 3,'4"Foot Print
Source: U.F. Strainrite
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8. Bag and Cartridge Filters
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 should 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.
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 throughout 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.
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8. Bag and Cartridge Filters
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; and
Sufficient available head to meet the terminal pressure drop and system demand.
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.
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8. Bag and Cartridge 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.
8.5.7 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
This section discusses two key issues associated with operating bag or cartridge filters,
pressure changes and water quality monitoring.
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 Water Quality 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
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8. Bag and Cartridge Filters
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; 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).
8.7 References
McMeen. 2001. Alternate Filtration: Placing New Technology in an Old Regulatory Box.
American Water Works Association, Membrane Conference Proceedings.
NSF International. 2005. Protocol for Equipment Verification Testing for Physical Removal of
Microbiological andParticulate Contaminants. 40 CFR 35.6450.
http://www.epa.gov/etv/pubs/059205epadwctr.pdf
USEPA. 2005. Membrane Filtration Guidance Manual. Office of Water. EPA 815-R-06-009.
November, 2005. http://www.epa.gov/ogwdw/disinfection/lt2/compliance.html
USEPA. 2006. Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced
Surface Water Treatment Rule. Office of Water. EPA 815-R-06-007. November, 2006.
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. EPA 815-R-07-017. March, 2007.
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
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9. 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
The State must approve the treatment credit based on an assessment of the design
characteristics of the filtration process.
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Chapter 9 - Second Stage Filtration
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 CFR 141.728(d)).
No disinfectant residual is present in the influent to the slow sand filtration process
Both filtration stages treat 100 percent of plant flow
The State must approve the treatment credit based on an assessment of the design
characteristics of the filtration process.
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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Chapter 9 - Second Stage Filtration
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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Chapter 9 - Second Stage Filtration
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 LTIESWTR 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 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.
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Chapter 9 - Second Stage Filtration
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
Depending on the removal performance of the first stage filtration process, it may be
difficult to see differences in second stage removal performance if monitoring of the second
stage process is limited to the CFE of the second stage. IFE monitoring of the second stage filters
on a continuous or routine basis may identify performance issues that can be addressed
proactively.
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10. 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), 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 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, and
operational considerations.
The Alternative Disinfectants and Oxidants Guidance Manual is available on EPA's
website, http://www.epa.gov/safewater/mdbp/implement.html
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Chapter 10- Chlorine Dioxide
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 - discusses 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 141.720(b)).
This methodology provides a conservative characterization of the dose of chlorine dioxide
necessary to achieve a specified inactivation level of Cryptosporidium. CT is the product of the
disinfectant concentration and disinfectant contact time and is defined in the LT2ESWTR (40
CFR141.720(a)):
CT = Disinfectant (mg/L) x Contact Time (minutes)
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Chapter 10- Chlorine Dioxide
"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 at or 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 ofCryptosporidium.
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 141.720(c)). 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 CTcaic by multiplying the measured C and T values.
2. From the CT table (see Exhibit 10.1 for the CT table for Cryptosporidium), find the
CT value for the log-inactivation desired, this is CTtabie.
3. Calculate the ratio of CTcaic/CTtabie for each segment.
4. If a system has multiple segments, sum the CTcaic/CTtabie ratios for a total inactivation
ratio.
5. If the ratio of CTcaic/CTtabie is at least 1, then the treatment process provides the log-
inactivation that the CTtabie represents (log-inactivation desired from step #2).
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Chapter 10- Chlorine Dioxide
Exhibit 10.1 CT Values (mg-min/L) for Cryptosporidium Inactivation by Chlorine Dioxide 1
Log
credit
0.25
0.5
1.0
1.5
2.0
2.5
3.0
Water Temperature, C
<=0.5
159
319
637
956
1275
1594
1912
1
153
305
610
915
1220
1525
1830
140
279
558
838
1117
1396
1675
3
128
256
511
767
1023
1278
1534
5
107
214
429
643
858
1072
1286
7
90
180
360
539
719
899
1079
10
69
138
277
415
553
691
830
15
45
89
179
268
357
447
536
20
29
58
116
174
232
289
347
25
19
38
75
113
150
188
226
30
12
24
49
73
98
122
147
1 Systems may use this equation to determine log credit between the indicated values:
Log credit=(0.001506x(1.09116)Temp)x CT
Source: 141.720 (b)(l)
Example CT Calculation
A plant draws 1.5 MOD of 5 degrees Celsius water from a stream, adding 1.8 mg/L 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. Exhibit 10.2 provides a schematic of an
intake, piping, and tank. The concentration of chlorine dioxide at each point is measured as
follows:
Cinitial= 1.8 mg/L
Centering tank =1.6 mg/L
Cleaving tank = 0.8 mg/L
Cleaving 2nd pipe = 0.2 mg/L
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Chapter 10- Chlorine Dioxide
Exhibit 10.2 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:
Ti = (Ai*Li/Qi) = (;ir2Li/Qi)*(7.48 gal/1 ft3)*(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; and
r is the radius of the pipe in feet.
Therefore the times for the two sections of the pipe are as follows:
Ti = 2 mi*(5,280 ft/mi)* ji*(0.5 ft)2*(0.0108 MG*sec/ft3*day)/( 1.5 MGD) = 59.7 min
T3 = 0.25 mi*(5,280 ft/mi)*TI*(0.5 ft)2*(0.0108 MG*sec/ft3*day)/( 1.5 MGD) = 7.4 min
The TIO, or time for 90 percent of a tracer to pass through the section for the tank is as
follows:
T2 = 150 minutes
CT Calculation:
Step 1. Calculate CT for each segment.
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Chapter 10- Chlorine Dioxide
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:
CTi = (1.6 mg/L) x (59.5 min) = 95.2 mgxmin/1
CT2 = (0.8 mg/L) x (150 min) = 120 mgxmin/1
CT3 = (0.2 mg/L) x (7.4 min) = 1.5 mgxmin/1
Step 2. Look up CTtabiein Exhibit 10.1. For 5°C and 0.5-log inactivation,
abie = 214 mgxmin/L
Step 3. Calculate the ratio of CTcaic/CTtabie for each segment.
(CTcalc/CTtabie)i = 95.2/214 = 0.44
(CTcaic/CTtabie)2 = 120 7214 = 0.56
(CTcalc/CTtabie)3 = 1.5/214 = 0.01
Step 4. Sum the CTcaic/CTtabie for each segment.
(CTcalc/CTtabie)totai = 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 CTtabie 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 CTcaic/CTtabie 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
The LT2ESWTR requires daily CT monitoring (40 CFR 141.720 (a)), 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 I or II,
(Standard Method 4500-C1O2 C or E, respectively). Details on these methods can be found in
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Chapter 10- Chlorine Dioxide
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 141.709) (see Chapter 1, section 1.4.5 for details).
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Chapter 10- Chlorine Dioxide
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. Exhibit 10.3 lists the chlorine dioxide and chlorite distribution system monitoring
requirements.
Exhibit 10.3 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
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 for a 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 141.712(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
141.712(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 141.712(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
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Chapter 10- Chlorine Dioxide
Chlorine dioxide (CIC^) 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).
In drinking water, chlorite (CICV) is the predominant reaction end product, with
approximately 50 to 70 percent of the chlorine dioxide converted to chlorite and 30 percent to
chlorate (CICV) 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/L 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 ofGiardia 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.
Chlorine dioxide can be used in the control of zebra mussels.
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Chapter 10- Chlorine Dioxide
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.
Ability to disinfect is reduced under colder temperatures.
It can form brominated DBFs in the presence of bromide.
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).
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.
If used together with GAC it can react to form chlorate.
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/L 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/L, chlorine dioxide
might still be able to be used for post disinfection since the oxidant demand will be less after the
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Chapter 10- Chlorine Dioxide
filters. The Simultaneous Compliance Guidance Manual can be consulted on the how to offset
the disadvantages of chlorine dioxide use.
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 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.
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Chapter 10- Chlorine Dioxide
10.7.2 Point of Addition
There are two main considerations for determining locations of chlorine dioxide addition
for the purpose of Cryptosporidium inactivationcontact 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
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. 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).
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
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Chapter 10- Chlorine Dioxide
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.
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Chapter 10- Chlorine Dioxide
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 Safety 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 respirators should also be accessible outside the building. Operators should be
trained to use the respirators.
10.10 References
Andrews, R.C., Z. Alam, R. Hofmann, L. Lachuta, R. Cantwell, S. Andrews, E. Moffet, G.A.
Gagnon, J. Rand, and C. Chauret, 2005. Impact of Chlorine Dioxide on Transmission,
Treatment, and Distribution System Performance. AWWARF. Denver, CO.
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 AJ. Rubin. 1984. "Inactivation ofNaegleria 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.
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Chapter 10- Chlorine Dioxide
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. EPA 815-R-99-014.
April, 1999. http://www.epa.gov/safewater/mdbp/mdbptg.html
USEPA, 1991. Guidance Manual for Compliance with the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water Sources. Washington, D.C.
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. EPA 815-R-07-017. March, 2007.
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
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.
Zhou, P., and J. Neemann, 2004. Use of Chlorine Dioxide and Ozone for Control of Disinfectant
By-Products. AWWARF Denver, CO.
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11. 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 (IESWTR) 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 of application operational considerations
The Surface Water Treatment Rule Guidance Manual and Alternative
Disinfectants and Oxidants Guidance Manual are available on EPA's website:
http://www.epa.gov/safewater/mdbp/implement.html.
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Chapter 11- Ozone
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
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
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Chapter 11- Ozone
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 (Exhibit
11.1).
Exhibit 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
CT values between the indicated temperatures may be determined by interpolation
If a utility believes that the CT values presented in Exhibit 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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Chapter 11- Ozone
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 Tio/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:
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 TIO or CSTR methods, while the CT for the remaining
segment is calculated using the Extended-CSTR approach. The TIO 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 method is actually achieved (see
section 11.11 for comment requests). Exhibit 11.2 summarizes the current methods, including
describing the situations when their use is appropriate.
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Chapter 11- Ozone
Exhibit 11.2 Applicable Methods and Terminology for Calculating the Log-
Inactivation Credit
CO
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i_
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-i*
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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 chamber with 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
> 3 consecutive
chambers
< 3 consecutive
chambers
Extended-CSTR
Zone
T10 or CSTR
Reactive
Chambers)
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
The remainder of this section describes how to calculate C for the TIO and CSTR methods
and then describes the TIO and CSTR methodologies.
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Chapter 11- Ozone
11.3.1 Measuring C for T10 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 Exhibit 11.3 are to be used for estimating C based on C;n 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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Exhibit 11.3 Correlations to Predict C* Based on Outlet Concentration
Turbine
Cout
Co-Current Flow
Cout or (Cin+Cout)/2
Counter-Current Flow
Cout/2
Reactive Flow
C0ut
' 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 Tio Method
The TIO method is appropriate for contactors with hydraulic conditions resembling plug
flow. Using the TIO 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 TIO 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 CTcak: by multiplying the measured C and T values.
2) From the CT table (Exhibit 11.1), find the CT value for the log inactivation credit
desired, this is CTtabie.
3) Calculate the ratio of CTcaic/CTtabie for each segment.
4) If a system has multiple segments, sum the CTcaic/CTtabie ratios for a total inactivation
ratio.
5) If the ratio of CTcaic/CTtabie is at least 1, then the treatment process provides the level of
log inactivation that CTtabie represents (log inactivation credit desired from step #2).
Example CT Calculation and Log Credit Determination using the TW 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.
C2out = 0.8 mg/L
C10ut=1.2mg/L = C2i
C4out = 0.0 mg/L
Chamber 1
Counter-Current
O o °O O O
Chamber 2
Co -Current
OQ O O O
T
A
Chambers
Counter-Current
O o °O O O
m m
Chamber 4
Reactive Flow
T
C3out = 0.9 mg/L = C4in
The water temperature is 5 degrees Celsius. Each chamber has a volume of 1,000
gallons. Results from a tracer test showed the TIO 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 Exhibit 11.2, C can be
determined with the following equations:
Chamber 2
Chamber 3
Chamber 4
Therefore for:
C = (Cjn + Cout) / 2
C = Cout/2
^ '-'OUt
or C = C
out
Chamber 2: C = (1.2 + 0.8) / 2 = 1.0 mg/L (this equation gives the higher C value)
Chambers: C = 0.9 / 2 = 0.45 mg/L
Chamber 4: C = 0.0mg/l
2) Calculate the T for each chamber.
The TIO 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 final concentration and that chamber is 25 percent the volume of
all the chambers. Therefore the TIO can be extrapolated among the chambers to estimate
individual TIO values.
TIO of each chamber = TIO (Vi.4/VT) = 24(1,000 gallons/4,000 gallons) = 6 min.
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(In this example, the volume of each chamber is same therefore the TIO of each chamber
is simply one-fourth of the total TIO.)
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 CTtabie for the log inactivation credit desired for each chamber. Calculate
the ratio of CTcaic to CTtabie, and sum the ratios to get a total log inactivation ratio.
Chamber 2
Chambers
Chamber 4
CTCaic
6.0
2.7
0
CTtabie for 0.5-log
7.9
7.9
7.9
Total Log Inactivation Ratio
Ratio of CTca|C / CTtabie
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:
-Log (Wo) = Log (1 + 2.303klO x C x HOT)
Equation 11-1
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where:
-Log (I/Io) = the log inactivation
kio = log base ten inactivation coefficient (L/mg-min)1
C = Concentration from Exhibit 11-2 (mg/L)
HDT = Hydraulic detention time (minutes)
Exhibit 11.4 presents the kio values for Cryptosporidium (kio values are calculated from the CT
table).
Exhibit 11.4 Inactivation Coefficients for Cryptosporidium, Log base 10 (L/mg-
min)
kio
Water Temperature, °C
<=0.5
0.0417
12357
0.0430 0.0482 0.0524 0.0629 0.0
10 15 20 25
764 0.101 0.161 0.254 0.407
To interpolate between the temperatures in the table, the following equation can be used:
= 0.0397 x (1.09757)
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 TIO 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
io 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 C;n = 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, ki0 = 0.1005 L/mg-
min. The HDT for each chamber = 20 minutes.
Chamber 1
Counter-Current
o o °o o o
I
|
Chamber 2
Counter-Current
OQ O O O
I
Chamber 3
Reactive Flow
r
C3out - °'2 m^
C1out = 0.3 mg/L = C2in
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 + 2.303x0.1005x0.20x20) = 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 C;n = 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, kio = 0.1005 L/mg-min. The HOT 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.
Chamber 1
Counter-current
o o
o o 00° 0
o o°o o
1
F
Chamber 2
Counter-current
o o
o ° c i c° 0
0 D°0 0
1
r
Chamber 3
Reactive Flow
1
r
Chamber 4
Reactive Flow
C10ut=0.3ng/L =
C2out = 0.3 mg/L
C4out = 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
Chambers 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 jig/1 based on a running annual average.
11.5 Unfiltered System LT2ESWTR Requirements
The LT2ESWTR requires unfiltered systems to meet the following requirements (40 CFR
141.721(b)and(c)):
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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 ofGiardia 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
Taste, odor, and color control
Trihalomethane (THM) and haloacetic acid (HAA) reduction with reduction in chlorine
use
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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 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 Exhibit
11.1):
Direct oxidation of compounds by molecular ozone in the aqueous phase.
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Oxidation of compounds by hydroxyl free radicals produced during the decomposition of
ozone.
As indicated in Exhibit 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.
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Exhibit 11.5 Reaction Pathways of Ozone in Water
O
Direct Pathway
Sower
Selective
Oxidation of Subitrate and
Microbial Inactivation
Byproducts
Indrect Pathway
OH
Fast
Hon-Selectve
Oxidation of Substrate and
Mitrubial
Byproducts
Fast
C03 -
andHC03
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 |ig/l. 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 increases with increasing pH, carbonate alkalinity, bromide concentration, ozone
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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.
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
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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.
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11.10 Operational Issues
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.
BromideOzone will oxidize bromide forming, hypobromous acid, hypobromite ion,
bromate ion, brominated organics, and bromamines.
Bicarbonate or carbonate ionsThe 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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Chapter 11- Ozone
11.12 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. InProc. 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. AWWA. 93(10):77-89.
Glaze, W.H., et al. 1987. "The Chemistry of Water Treatment Processes Involving Ozone,
Hydrogen Peroxide, and Ultraviolet Radiation." Ozone Sci. Engrg. 9(4):335.
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 andPEROXONE. Ozone Sci. Eng., 16(3): 197-212.
Hoigne J., and H. Bader. 1983a. "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 - II. Dissociating Organic Compounds." Water Res. 17:185-194.
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. AWWA. 84(4): 136-146.
McGuire, M.J. et al. 1991. Pilot-scale Evaluation of Ozone and PEROXONE (90951).
AWWARF. Denver, CO.
Miltner, R.J., R.S. Summers, N.R. Dugan, M. Koechling, and D.M. Moll. 1996. A Comparative
LT2ESWTR Toolbox Guidance Manual 11-23 June 2009
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Chapter 11- Ozone
Evaluation of Biological Filters. InProc. AWWA WQTC. Denver, CO: AWWA.
Miltner, 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, 1, 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.D.J. 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.
Demonstration of Performance (DOP)
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
Exhibit 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.
Exhibit 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
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 theState, 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 Exhibit 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
1 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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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)).
Presedimentation
Two-stage lime softening
Bank filtration
Combined or individual filter performance
Membrane filters
Bag and cartridge filters
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
Second stage filtration
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.
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.
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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
Exhibit 12.2 presents a flowchart relating these elements to the overall microbial toolbox
framework. Each of these topics is discussed in detail in this chapter.
Exhibit 12.2 Flowchart for DOP Protocol
DIN CLASSIFICATION
MICROBIAL TOOLBOX
STRATEGY
ADD DISINFECTION
OR
ALTERNATIVE
PHYSICAL REMOVAL
TECHNOLOGIES
DOP EVALUATION
CRITERIA AND TEST
MATRIX
I
OOP IMPLEMENTATION
DATA ANALYSIS
AND
REPORTING
REQUEST TREATMENT CREDIT
\
\
\
DEMGNSTAT1QN
OF PERFORMANCE
{DOP)
/ CONVENTIONAL
FILTRATION
TECHNOLOGIES
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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 parameter(s) should be used to demonstrate
removal efficiency of Cryptosporidium^
Should the DOP be conducted at full-scale or pilot-scale?
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 endedthe 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,
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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.
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.
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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?
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
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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
etal. 1996).
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.
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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.
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.
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
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).
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 Exhibit 12.3.
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
Exhibit 12.3 Example DOP Test Matrix
Scenario
Condition
SI
S2
S3
S4
S5
(Normal or
Worst-Case)
Influent
Concentration
Range Flow
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
Service
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 Exhibit 12.4.
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Chapter 12 -Demonstration of Performance (DOP): Microbial Removal
Exhibit 12.4 Example DOP Monitoring Plan
Monitor
Event
Number
1
2
3
52
Date
Weekl
Week 2
WeekS
Week 52
Test
Scenario
ID (See
Exhibit
12.2)
S1
S3
S2
S4
Effluent Sample Locations*
Filter 1
X
X
X
X
Filter 2
X
X
X
X
Filter 3
X
X
X
X
Filter 4
X
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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Chapter 12- Demonstration of Performance (POP)
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
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Chapter 12- Demonstration of Performance (POP)
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 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
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:
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. Cpii0t 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, Cpii0t 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:
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Chapter 12- Demonstration of Performance (POP)
System flow rate (instantaneous/flow chart, hourly and daily average)
Operating mode (process scheme, number of trains, number of units in service)
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 (Cinf/Ceg) Equation 12.2
where: Qnf = influent Cryptosporidium or indicator concentration
Ceff = 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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12.6 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, Miltner, 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., Miltner, 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.
Yates, R., Scott, K., Green, J., Bruno, J.,De Leon, R. 1998. Using aerobic spores to evaluate
treatment plant performance. Proceedings of the 1998 AWWA Annual Conference and
Exposition. Denver, CO: AWWA.
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13. 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 decades 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 disinfection has been found to be particularly effective against protozoa and
bacteria.
This chapter summarizes the requirements for water systems using UV disinfection to
achieve compliance with the LT2ESWTR and provides considerations for toolbox selection.
Water systems and States should refer to the UV Disinfection Guidance Manual (USEPA 2006)
for detailed guidance on design and operation of UV systems and the validation testing that must
be conducted for compliance with the LT2ESWTR.
13.2 UV Disinfection Requirements for Filtered and Unfiltered PWSs
The LT2ESWTR has several requirements related to the use of UV disinfection. They
address the UV doses for different levels of inactivation credit, performance validation testing of
UV reactors, monitoring, reporting, and off-specification operation.
13.2.1 UV Dose and Validation Testing Requirements
EPA developed UV dose requirements for PWSs to receive credit for inactivation of
Cryptosporidium, Giardia, and viruses (Exhibit 13.1). The UV dose values in Exhibit 13.1 are
applicable only to post-filter applications of UV disinfection in filtered systems and to unfiltered
systems.
Unlike chemical disinfectants, UV light does not leave a chemical residual that can be
monitored to determine UV dose and inactivation credit. The UV dose depends on the UV
intensity (measured by UV sensors), the flow rate, and the UV absorbance. To determine the
operating conditions under which the reactor delivers the required dose for treatment credit, the
LT2ESWTR requires PWSs to use UV reactors that have undergone validation testing [40 CFR
141.720(d)(2)]. These operating conditions must include flow rate, UV intensity as measured by
a UV sensor, and UV lamp status.
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Chapter 13 - Ultraviolet Light
Exhibit 13.1 UV Dose Requirements - millijoules per centimeter squared
(mJ/cm2)1
Target
Pathogens
Cryptosporidium
Giardia
Virus
Log Inactivation
0.5
1.6
1.5
39
1.0
2.5
2.1
58
1.5
3.9
3.0
79
2.0
5.8
5.2
100
2.5
8.5
7.7
121
3.0
12
11
143
3.5
15
15
163
4.0
22
22
186
40CFR141.720(d)(1)
Validation testing must meet the following requirements:
Validated operating conditions must account for UV absorbance of the water, lamp
fouling and aging, measurement uncertainty of online sensors, UV dose distributions arising
from the velocity profiles through the reactor, failure of UV lamps or other critical system
components, and inlet and outlet piping or channel configurations of the UV reactor [40 CFR
Validation testing must involve full-scale testing of a reactor that conforms uniformly to
the UV reactors used by the PWS, and it also must demonstrate inactivation of a test
microorganism whose dose-response characteristics have been quantified with a low-pressure
mercury vapor lamp [40 CFR 141.720(d)(2)(ii)].
Using the above requirements as a basis, EPA developed a recommended validation
protocol, presented in Chapter 5 of the UV Disinfection Guidance Manual (U SEP A 2006). Water
systems are not required to follow this protocol but may follow alternatives that achieve
compliance with the regulatory requirements as long as they are acceptable to the State. Also,
States may have additional requirements than are provided in the Federal rule.
13.2.2 UV Disinfection Monitoring Requirements
The LT2ESWTR requires PWSs to monitor their UV reactors to demonstrate that they
are operating within the range of conditions that were validated for the required UV dose. At a
minimum, PWSs must monitor each reactor for flow rate, lamp status, UV intensity as measured
by a UV sensor, and any other parameters required by the State. UV absorbance should also be
measured when it is used in a dose-monitoring strategy. PWSs must verify the calibration of UV
sensors and recalibrate sensors in accordance with a protocol the State approves [40 CFR
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13.2.3 UV Disinfection Reporting Requirements
The LT2ESWTR requires PWSs to report the following items [40 CFR 141.721(f)(15]:
Initial reporting - Validation test results demonstrating operating conditions that achieve
the UV dose required for compliance with the LT2ESWTR.
Routine reporting - Percentage of water entering the distribution system that was not
treated by the UV reactors operating within validated conditions on a monthly basis.
13.3.4 Off-specification Operational Requirement for Filtered and Unfiltered Systems
To receive disinfection credit for UV disinfection, both filtered and unfiltered PWSs must
treat at least 95 percent of the water delivered to the public during each month by UV reactors
operating within validated conditions for the required UV dose [40 CFR 141.720(d)(3)(ii)].
13.3 Toolbox Selection Considerations
UV disinfection is a relatively simple to use and highly effective technology for
inactivating Cryptosporidium. Its main advantages include:
It can inactivate chlorine-resistant pathogens such as Cryptosporidium oocysts and
Giardia cysts at relatively low doses. It is often the lowest cost treatment option for
inactivating Cryptosporidium.
It does not produce regulated DBFs.
Its effectiveness is not pH or temperature dependent.
The disadvantages of UV disinfection include:
UV disinfection effectiveness cannot be measured in "real-time" like chemical
disinfectants.
UV disinfection provides no distribution system residual.
Much higher UV doses are required for virus inactivation.
Power quality problems can disrupt disinfection in some cases.
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13.4 Design and Operational Considerations
UV reactors for drinking water treatment typically consist of a closed-vessel containing
UV lamps, UV sensors, and temperature sensors. UV lamps are usually housed within lamp
sleeves to protect and insulate them. Some reactors include automatic cleaning mechanisms to
keep the lamp sleeves free of deposits. UV sensors, flow meters, and in some cases, analyzers
for UV absorbance (or a related parameter, UV transmittance) are used to determine the dose
delivered by the reactor. UV lamps can be low pressure, low pressure-high output, or medium
pressure mercury vapor lamps. Low pressure lamps emit light at one wavelength (i.e.,
monochromatic) and operate with the mercury under low vapor pressures. Low pressure high-
output lamps are similar to low pressure lamps but operate at higher temperatures and have a
higher UV light output. Medium-pressure lamps are polychromatic and operate at higher
temperatures and mercury vapor pressures.
Below is an example of some key design and operational issues that should be considered
when evaluating UV treatment options. Refer to the UV Disinfection Guidance Manual (USEPA
2006) for more detailed guidance on UV facility design and operation.
Water quality - The UV absorbance of the water to be treated is very important in the
design of UV facilities. This is because UV absorbance influences UV dose delivery and
therefore affects the UV reactor selection, validation requirements, and the UV facility
size and cost. Compounds in the water can also foul lamp sleeves and other UV reactor
components. Fouling is dependent on calcium, hardness, alkalinity, lamp temperature,
pH, oxidation-reduction potential (ORP) and certain inorganic constituents (e.g., iron and
manganese). UV facilities are typically equipped with cleaning systems to prevent
fouling.
Power quality - UV lamps can turn off if a voltage fluctuation, power quality anomaly, or
power interruption occurs. Power quality tolerances depend on the UV equipment design
and vary significantly among UV manufacturers. If power quality may be a problem at
the intended installation location, a power quality assessment may be needed to quantify
and understand the potential for off-specification operations.
Hydraulic needs and limitations - Headloss through a UV reactor depends on the specific
reactor, piping configuration, and flow rate. Typical headloss ranges from 0.5 to 3.0 feet
for a reactor.
Maintenance - UV reactors will need to be periodically shut down for regular
maintenance. Typical maintenance tasks include checking UV sensor calibration,
checking lamp cleaning efficiency, and replacing lamps and sleeves.
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13.5 References
USEPA. 2006. Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced
Surface Water Treatment Rule. Office of Water. EPA 815-R-06-007. November, 2006.
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
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14. Membrane Filtration
14.1 Introduction
The LT2ESWTR defines membrane filtration as follows:
Membrane filtration is a pressure or vacuum driven separation process in which
paniculate matter larger than 1 micrometer is rejected by an engineered barrier,
primarily through a size-exclusion mechanism, and which has a measurable
removal efficiency of a target organism that can be verified through the
application of a direct integrity test. This definition includes the common
membrane technologies ofmicrofiltration, ultrafiltration, nanofiltration, and
reverse osmosis. [40 CFR 141.2]
Membrane processes that meet the requirements of LT2ESWTR will receive
Cryptosporidium removal credit.
EPA recently published the Membrane Filtration Guidance Manual for systems
considering using membranes to comply with the requirements of the LT2ESWTR (USEPA
2005). Readers interested in detailed information on membrane filtration should consult the
Membrane Filtration Guidance Manual. This chapter summarizes rule requirements and lists
advantages and disadvantages of membrane filtration compared with other toolbox technologies.
14.2 Membrane Filtration Requirements under the LT2ESWTR
In order to receive removal credit for Cryptosporidium under the LT2ESWTR, a
membrane filtration system must meet the following three criteria:
1. The process must comply with the definition of membrane filtration as stipulated by the
rule.
2. The removal efficiency of a membrane filtration process must be established through a
product-specific challenge test and ongoing, site-specific direct integrity testing during
system operation.
3. The membrane filtration system must undergo periodic direct integrity testing and
continuous indirect integrity monitoring during operation.
The rule does not prescribe a specific removal credit for membrane filtration processes.
Instead, removal credit is based on system performance as determined by challenge testing and
verified by direct integrity testing. Thus, the maximum removal credit that a membrane filtration
process may receive is the lower value of either [40 CFR 141.719(b)(l)]:
The removal efficiency demonstrated during challenge testing; OR
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Chapter 14 -Membrane Filtration
The maximum log removal value that can be verified by the direct integrity test used to
monitor the membrane filtration process.
Based on this framework, a membrane filtration process could potentially meet the Bin 4
Cryptosporidium treatment requirements, as shown in Exhibit 1.1 of this guidance manual.
These primary elements of the regulatory requirements for membrane filtration under the
LT2ESWTR, including challenge testing, direct integrity testing, and continuous indirect
integrity monitoring, are summarized in the following sections.
14.2.1 Challenge Testing
Since there are no uniform design criteria that can be used to ensure the removal
efficiency of a membrane process, challenge testing is required to demonstrate the ability of a
membrane process to remove a specific target organism. The removal efficiency demonstrated
during challenge testing establishes the maximum removal credit that a membrane process would
be eligible to receive, provided that this value is less than or equal to the maximum log removal
value that can be verified by the direct integrity test [40 CFR 141.719(b)(l)], as described in the
next section. The LT2ESWTR only requires product-specific challenge testing; once the
removal efficiency has been demonstrated, additional testing is not required unless the product is
significantly modified.
14.2.2 Direct Integrity Testing
While challenge testing can demonstrate the ability of an integral membrane process to
remove the target organism, integrity breaches can develop in the membrane during routine
operation that could allow the passage of microorganisms. In order to verify the removal
efficiency of a membrane process during operation, direct integrity testing is required for all
membrane filtration processes used to comply with the LT2ESWTR [40 CFR 141.719(b)(3)]. A
direct integrity test is defined as a physical test applied to a membrane unit in order to identify
and isolate integrity breaches. The rule does not mandate the use of a specific type of direct
integrity test, but rather performance criteria that any direct integrity test must meet. These
criteria include requirements for resolution, sensitivity, and frequency [40 CFR 141.719(b)(3)]:
Resolution: The direct integrity test must be applied in a manner such that a 3
micrometer breach contributes to the response from the test.
Sensitivity: The direct integrity test must be capable of verifying the ability of a
membrane filtration system to achieve the log removal value awarded to the
process by the State.
Frequency: The direct integrity test must be applied at a frequency of at least
once per day, although less frequent testing may be permitted by the State at its
discretion if appropriate safety factors are incorporated.
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A control limit must also be established for a direct integrity test, representing a threshold
response which, if exceeded, indicates a potential integrity problem and triggers subsequent
corrective action. For the purposes of LT2ESWTR compliance, this threshold response must be
indicative of an integral membrane unit capable of achieving the Cryptosporidium removal credit
awarded by the State.
14.2.3 Continuous Indirect Integrity Monitoring
Systems must conduct continuous indirect integrity monitoring on each membrane unit
[40 CFR 141.719(b)(4)]. For the purposes of the LT2ESWTR, indirect integrity monitoring is
defined as monitoring some filtrate water parameter that is indicative of the removal of
particulate matter, and "continuous" is defined as monitoring at a frequency of no less than once
every 15 minutes [40 CFR 141.719(b)(4)(ii)]. Although turbidity monitoring is specified as the
default method of continuous indirect integrity monitoring under the rule, other methods, such as
particle counting or particle monitoring, may be used in lieu of turbidity monitoring at the
discretion of the State [40 CFR 141.719(b)(4)(i)]. For any indirect method used, a control limit
must be established that is indicative of acceptable performance. Monitoring results exceeding
the control limit for a period of more than 15 minutes must trigger immediate direct integrity
testing [40 CFR 141.719(b)(4)(iv)].
14.3 Toolbox Selection Considerations - Advantages and Disadvantages
Membrane filtration is a highly efficient technology for removing pathogens and other
particulates from drinking water. Its main advantages are:
Removes bacteria, protozoa, and viruses (nanofiltration (NF));
Can lower DBFs by allowing lower disinfectant doses; and
Can remove arsenic. Microfiltration (MF) and ultrafiltration (UF) can remove particulate
arsenic (dissolved arsenic can be converted to particulate arsenic by coagulation prior to
the MF/UF system). NF and reverse osmosis (RO) can remove dissolved arsenic.
Membrane filtration is an advanced technology and can be more expensive than
conventional technologies. Its major disadvantages are:
Total cost may exceed that of conventional technologies;
Can be fouled by organics and minerals; and
Increased loss of process water.
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14.4 Design and Operational Considerations
There are a number of different types of membrane materials and module system designs
for different classes of membranes. In general, MF and UF use hollow-fiber membranes, while
NF and RO use spiral-wound membranes. Hollow-fiber membrane systems may be either
pressure-driven (i.e., positive pressure as a driving force for filtration) or vacuum-driven (i.e.,
utilizes negative pressure as a driving force for filtration). In pressure-driven systems, upstream
pumps are employed to push water across the membrane barrier. Vacuum-driven systems
employ downstream pumps to induce suction on the inside the membrane fibers, pulling water
across the barrier. Membrane systems using spiral-wound modules are pressure-driven, with six
to eight modules usually arranged in series inside a containment vessel.
Membrane systems are typically designed and constructed in one or more discrete water
production units, also called racks, trains, or skids. Production unit design varies widely by
manufacturer and type of system (i.e., hollow-fiber vs. spiral-wound) but typically contains the
membrane treatment system, associated piping, appurtenances, and other features. A typical
membrane treatment system is composed of a number of identical units that combine to produce
the total filtrate flow.
A major design variable for membrane systems is the flux, or the flow per unit of
membrane area. Membranes are most often designed to operate at constant flux (or within a
specific range fluxes, with the applied pressure (i.e., positive or negative) varying with the
degree of resistance to flow. This resistance may be caused by fouling or changes in
temperature, which affect water viscosity. Because the flux can vary significantly with
temperature, the average, minimum, and maximum temperature of the water to be treated should
be considered when designing the system. Pilot studies are often performed to optimize the flux,
pretreatment, and cleaning regime (chemicals, doses, and intervals) for a particular application.
Core membrane process operations include backwashing, chemical cleaning, and
integrity testing. The frequency of these processes is usually determined during pilot testing, but
in the case of integrity testing may also be dictated by regulatory requirements. Backwashing is
similar in principle to that for conventional media filters and is intended to remove contaminants
accumulated on the membrane surface. Note that backwashing is only applicable to the
microporous MF/UF membranes, but does not apply to the semi-permeable NF/RO membranes,
which cannot be backwashed. Chemical cleaning is periodically conducted to remove any
accumulated foulants; for MF/UF systems, this constitutes any fouling that is not removed on a
routine basis via backwashing. Integrity testing is conducted to ensure that the membrane is free
of any breaches, leaks, or defects that might allow unfiltered water to bypass the membrane
barrier. This testing is required by many States and at the Federal level for applications in which
membrane filtration is used to comply with the Cryptosporidium removal requirements of the
LT2ESWTR.
Feed water quality is also a primary design consideration for membrane systems, as this
can affect both the flux and rate of membrane fouling. For example, high levels of turbidity,
TOC, and/or scaling ions (for NF/RO systems) can increase backwashing requirements (for
MF/UF systems) and chemical cleaning frequencies, causing poor performance and shortening
membrane life. In many cases, pretreatment may improve feed water quality at lower cost than
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incorporating additional membrane area. Other important issues to consider in the design of
membrane filtration systems include cross connection control, system reliability, chemical
cleaning and residuals management.
14.5 References
USEPA. 2005. Membrane Filtration Guidance Manual. Office of Water. EPA 815-R-06-009.
November, 2005. http://www.epa.gov/ogwdw/disinfection/lt2/compliance.htm
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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.I 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 Exhibit A. 1.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
Exhibit 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
TOC or UV254 >
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
Tests
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 0.01M 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
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
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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 Ruffe II 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.
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.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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 mm after dosing. An experiment was started by adding approximately a pre-
determined number ofoocysts 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 'm filter. The
filter 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.
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 ofoocysts 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
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and 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 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.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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:
1) Animal infectivity
2) Cell culture (in vitro infectivity)
3) 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
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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 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 observationsit 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
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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 coll inactivation with ozone.
Wat. Res. 31(6), 1355-1362.
Kim, J. H.; Tomiak, R. B.; Rennecker, J. L.; Marinas, B. J.; 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.
Ruffell, K.M; Rennecker, J.L.; and Marinas, BJ.(2000). Inactivation of C. Parvum oocysts with
chlorine dioxide. Wat. Res. 34 (3), 868 - 876.
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Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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 B
Ozone CT Methods
Abbreviations
8
Br03-
CeffT-io
Co-current
chamber
Counter-current
chamber
CSTR
CT
DBP
Half-life or HL
HOT
In-situ sample
ports
k
-Log (I/I0)
Q
Up flow chamber
V
Molar absorbance expressed as M1 cm"1.
Bromate ion
Chamber effluent ozone residual in mg/L times chamber T10 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:
Ln(0.5)
HL = ^-, where k = first-order ozone decay coefficient
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 HOT 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 k10 in this document are L/mg-min.
Log inactivation. Negative log-base-10 of the survival rate (N/N0) of the
microorganisms, where I0 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 (MGD)
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 CTMethods
B.I 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. CSTRcalculates 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 CTMethods
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 TIO 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 exhibits define the types of chambers potentially present in an ozone
contactor and show the recommended methods for calculating the inactivation credit achieved.
Only the TIO 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. Exhibit B.I shows the recommended
methods.
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Appendix B - Ozone CTMethods
Exhibit B.1 Applicable Methods and Terminology for Calculating the Log
Inactivation Credit
re
X
Q
^
0)
o
£
o
z
2
re
Q
^
0)
o
5
*J
i
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
Extended-
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
Extended-
CSTR Zone
T10 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 CTMethods
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.
Exhibit B.2 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 Exhibit
B.2). Alternatively ozone enriched gas can be bubbled into one or more chambers, a process
called "in-chamber" ozone addition (see schematic A & C in Exhibit B.2). 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 (Exhibit B.2-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, Exhibit B.2 only shows example configurations; size and geometry of the chambers will
vary.
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Appendix B - Ozone CTMethods
Exhibit B.2 Schematics of Typical Configurations of Ozone Contactors with
Multiple Chambers
Side View of an Over-Under
Contactor with In-Chamber
Ozone Addition
(A)
Over-Under J
Chambers
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 Exhibit B.3,
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 CTMethods
Exhibit B.3 Schematics of Example Single- or Dual-Chamber Ozone Contactors
Ozone
-Lrl
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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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
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.
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Appendix B - Ozone CTMethods
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 Exhibit B.I.
Exhibits.4 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 Exhibit B.4 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 CTMethods
Exhibit B.4 Names of the Various Sections of a Multi-Chamber Over-Under Ozone
Contactor
.22
3
^
T
r
4
J
T
">
5
V.
r
6
J
1
7
V_
r
8
J
">
9
V.
10
J
Ozone
The fourth chamber in the contactor shown in Exhibit B.4 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 Exhibit B.4 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 Exhibit B.4 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, Ctn. 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-
situ sample ports and a measurable ozone residual then the requirements for calculating k* and
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Appendix B - Ozone CTMethods
C;n 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, Ctn. Equation B-
1 shows how to calculate the ozone residual at the effluent of chamber "X" in an Extended-
CSTR zone:
(B-l)
\Volume\n
* L J U
^o-x
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]^ = Volume, in gallons, from the beginning of the Extended-CSTR zone to the
effluent of chamber "X"
NQ_x = Number of chambers from the beginning of the Extended-CSTR zone to the
effluent of chamber "X"
<2 = 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
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
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Appendix B - Ozone CTMethods
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/I0) = Log (1 + 2.303kio x C x HOT) Equation 11-1
where:
-Log (I/Io) = the log inactivation
kio = log base ten inactivation coefficient (L/mg-min)1
C = Concentration from Exhibit 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 k*
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 Cs, 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 3 in this analysis. The following steps should be followed to
calculate the & value:
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, k±_2 . (A derivation and
explanation of Equation B-2 is presented in Appendix E):
kio is calculated from the CT table with the following equation: Log inactivation = kio X CT
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Appendix B - Ozone CTMethods
/r l"^ «i
12 r i
V .( i } 1
(q p-2 J
UJ
(B-2)
where: ^_2 = First-order ozone decay coefficient between sampling locations 1 & 2, min"1
Ci = Measured ozone residual at location 1, mg/L
C2 = Measured ozone residual at location 2, mg/L
[Volume]l2 = Volume between sampling locations 1 and 2, gallons
N^2 = Number of chambers between sampling locations 1 and 2
Q = Water flow through the contactor, gpm
Step 2 - Use residual measurements Ci and Cs along with Equation B-3 to calculate the k value
*
representing ozone decay between sampling locations 1 and 3, k^_^:
#1
1-3
\Volume]\_3
(B-3)
where: ^_3
C7
C3
[Volume]^
<2 =
First-order ozone decay coefficient between sampling locations 1 & 3, min
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
-i
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.
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.
*' =
kl-2
M-3
(B-4)
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Appendix B - Ozone CTMethods
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,
< 20%
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 Cm
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 k* 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:
Cr /"r
= C X
l + k
, [Volume] 0 _,
#0-1X0
r = r
^ ^
N0_3xQ
\Volume]0 2
\ + k x
[Volume] 03
l + k x-
(B-5)
(B-6)
(B-7)
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Appendix B - Ozone CTMethods
where: k = Ozone first-order decay coefficient, min"
Ci = Measured ozone residual at location 1, mg/L
2 = Measured ozone residual at location 2, mg/L
Cs = Measured ozone residual at location 3, mg/L
NQ l = Number of chambers between the entrance to the Extended-CSTR Zone and
sampling location 1
A/"0_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]Q _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 Cin value is then calculated as the average of the three values determined by Equations B-5
through B-7:
(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
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-l, 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 &*, it is stipulated
that the individual k* values (i.e., k*i.2 and k*i.3) should be within 20% of the average value.
This QA control is meant to ensure that ozone residual measurements used to calculate the ozone
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Appendix B - Ozone CTMethods
decay profile are consistent with the calculated profile. Since the calculation of C;n (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.
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Appendix B - Ozone CTMethods
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 for a Multi-chamber Contactor With In-situ Sample Ports and
One Dissolution Chamber
Exhibit B.5 shows a schematic of a 12-chamber ozone contactor. The contactor is
treating 50 MGD of water at a temperature of 20°C. The volumes of the individual chambers are
noted on the schematic. Ozone is added to the first chamber only. The bottom graph in Exhibit
B.5 shows the values of the ozone residual measured at the effluents of chambers 2, 5, and 8.
Exhibit B.5 Schematic of the Ozone Contactor and the Measured Ozone Residual
Values in Example 1
SFA Reactive Zone
50 MGD
[34,720
0.8
5 0.6
I °'4
1
o
8
3
^
T
(
IS
oo
g
o
s
>
T
1 1
c,»»j
i ^v
%
3
§
O
O
r
4
oo
g
o
§
\j^
T
1
~>
5
oo
g
o
s
r
6
IS
oo
g
o
s
\/
^
7
IS
oo
g
o
s
r
8
§
O
o
\J^
^
9
oo
g
o
§
(
X
10
^
§
O
o
^-
)
\J^
"*s
(
X
11
'
IS
oo
g
o
s
)
12
IS
oo
g
o
s
X>
»
^^O^O.Tlmg/L
V
\
\
^
^.^
2=
--,
0.41,
*-^
.
L
-~~.
**»,
'c
3=0.20mg/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.
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Appendix B - Ozone CTMethods
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 Cs that are shown in Figure B.6. The values of
&!_2 and &!_3 can be calculated using Equations B-2 and B-3 as follows:
N,_2xQ
3x34,720
[3x104,000]
0.71
0.41
- 1
= 0.0670 min"
6x34,720
[6x104,000]
0.71
0.2
- 1
= 0.0785 min
-i
The k value is then calculated as the average of k\_2 and k\_3 as follows:
** =
7 * 7 *
ki_2 + £1-3
2
"0.0670 + 0.0785"
2
= 0.0728mm'1
A QA check shows that the values of kl-2 and kl-3 are within 8% of the average k* value of
-i
0.0728 min" . This value of & 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 ofk* calculated at 0.0728 min"1, Equations B-5 to B-7 can be
used to calculate the Cin value as follows:
initial,I
[Volume]^
l + k x
= 0.71x
l + 0.0728x
[104,000]
1x34,720
= 0.865 mg/L
initial,2
+ k x
\Volume]0_2
N0_2xQ
= 0.41x
l + 0.0728x
[4x104,000]
4x34,720
= 0.902 mg/L
initial,3
[Volume]0_3
[ + k x
vO-3
= 0.20x
+ 0.0728x
[7x104,000]'
7x34,720
= 0.796 mg/L
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Appendix B - Ozone CTMethods
Therefore,
initial
^initial,!
0.865 + 0.902+ 0.796
= 0.854 mg/L
Step 3: Calculate the value ofkw - The value of kw for the inactivation of Cryptosporidium with
ozone at the measured temperature of 20°C can be obtained from Exhibit 11-3 directly and
equals 0.2537 L/mg-min. Otherwise the value for kw could be determined using equation 11-2.
Step 4: Calculate the Ozone Residual at the Effluent of Each Chamber - Knowing the values of
Cin 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-l:
Cy =
r
^-^iviifi,
initial
l + k
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:
0.854
1 + 0.0728;
[3x104,000]'
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". Exhibit B.6 lists the calculated
residual values for each chamber using the same approach, beginning with chamber 2.
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Appendix B - Ozone CTMethods
Exhibit B.6 Application of the Extended-CSTR Method to the Example
Vol./Chamber =
Flowrate =
p
Mnitial
k* =
kio =
(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"
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 Log Inactivation - Knowing the values of C, kio, 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 k C
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 + 2.303 xO.246xO.473x
104,000
34,720
= 0.26 logs
Column (4) in Exhibit B.6 lists the log inactivation values calculated for chambers 2 through 12.
The sum of the log inactivation achieved (total of Column 4 in Exhibit B.6) is 1.9 logs.
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Appendix B - Ozone CTMethods
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., R.D. 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.
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Appendix B - Ozone CTMethods
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.
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:
Configuration of the ozone sample collection lines within the contactor,
Stability of the indigo trisulfonate reagent when analyzing grab samples, and
Standardization and maintenance of on-line ozone analyzers.
C.I 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 Exhibit C. 1. 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
Exhibit 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 V* to 1A of
the contactor width. Inlet might be upward
and flared, or might be horizontal.
Ozone
T T'T T
J-
10
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. Exhibit 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
Exhibit C.2 Relationship Between Ozone Residual Loss and Detention
Time through the Ozone Sample Line for Various Ozone Half-Life Values
100
90
80
70
60
50
40
30
20
10
10 20 30 40 50 60 70 80 90 100 110 120
Detention Time in Sample Line (sec)
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:
Maintain consistent flow without plugging
Minimize detention time in the sample line
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
->th
Ozone residual is determined using the Indigo Method (Standard Methods 4500-Ozone -
20 Edition, 1998) when analyzing grab samples. The method assumes that high-purity reagents
are used. Since the publication of the 20th Edition, several reports (Gordon et al., 2000a and
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Appendix C - Measuring Ozone Residual
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, s, of 20,000 M"1
cm"1. These recent reports suggest that/may not be constant and may depend on:
The source and age of the neat indigo trisulfonate solid
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 than 20,000 M'W1. 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:
Prepare indigo stock solution as described in Standard Methods
Prepare Reagent II solution (for ozone residuals greater than 0.05 mg/L), as
described in Standard Methods.
Prepare flasks for sampling.
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
Obtain the tare weight of each flask.
Add 10.0 mL of Reagent II solution to each flask.
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).
Collect ozone sample.
Thoroughly flush sample line to be used.
Do not run sample down the side of the flask, as this will cause ozone off-gassing.
Fill flask with sample, gently swirling flask until a light blue color remains. Do
not bleach completely or the residual value will be incorrect.
Wipe-dry the outside of sample and blank flasks.
Weigh sample and blank flasks.
Total weight for sample is tare weight of flask plus 10 mL indigo plus added
sample.
Total weight for blank is tare weight of flask plus 10 mL indigo plus added
distilled water.
Prepare the spectrophotometer for measuring absorbance.
Identify the cell path length (e.g., 1-cm, 5-cm, etc.).
Set the wavelength to 600 nanometers.
Measure absorbance of blank and samples within four hours.
Follow instructions for spectrophotometer concerning zeroing the instrument.
Record absorbance of each sample and each blank.
Complete calculations - see example below.
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Appendix C - Measuring Ozone Residual
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
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 1:100-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 I ff~* -\\
- x Volume of Blank = Absorbance in cm" @100mL w~-U
lOOmL
0.234
100 mL
96.15 mL = 0.225cm4
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
was 63.29-mL (63.29-mL = [167.39-g - 94.10-g - 10-g] * 1-mL / 1-g). The ozone residual was
calculated using Equation C-2, which resulted in a value of 0.41 mg/L.
, (ARxVR)-(AsxVT)
mg/L=V B B; V s T; (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
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Appendix C - Measuring Ozone Residual
b = path length of cell, cm
(0.234 x 96.15)-(0.159 x 73.29)
-^ '^ '- = 0.41 mg/L
0.42 x 63.29 x 1
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.
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.
Measure the ozone residual concentration in the grab samples using the indigo trisulfonate
method.
Calculate the average grab-sample ozone residual value and the average analyzer ozone
residual value.
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.
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.I Derivation of the Equation Used to Calculate k*
In Appendix B, Equation B-2 expressed the value ofk between two points 1 and 2 as
shown by Equation D-l:
\Volume1i_~
, _L
(D-l)
Equation D-l is a transformation from the equation of first-order decay across a series of
N equal-size CSTRs:
i
HDT
N-
1-2
vl-2
(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\\.^ divided by the flowrate, Q, then Equation D-2 is
transformed to Equation D-3:
Co
l + k
1-2
(D-3)
Therefore,
tyolume\i_~
OxN,
1-2
1-2
(D-4)
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Appendix D - Derivation of Extended CSTR Equations
then,
[Fo/wmejj^
then,
and then,
*i-2 =
(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]/Q, 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 CJCi 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 CJCi for a first-order decay reaction can still be expressed
as:
1
1
1
(D-8)
Or in general terms,
(D-9)
Unfortunately, it is not possible transform Equation D-9 to derive a simple linear
expression ofk* 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
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Appendix D - Derivation of Extended CSTR Equations
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.
The simplifying assumption of equal-size CSTRs for calculating k* is non-conservative
relative to a k* 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 &*. 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 &*. 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 k*.
The impact of the simplifying equal-sized CSTR assumption on the estimate of k* and
Cin 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) and Case Studies
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.I 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.I.I 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
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Appendix E - Watershed Control Best Management Practices
within their watersheds even if the 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 should promote the
municipality's public health goals. In practice, this means the ordinance should conform to the
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Appendix E - Watershed Control Best Management Practices
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. 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.
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Appendix E - Watershed Control Best Management Practices
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-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.
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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
http://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.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.
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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 2008).
CAFOs that discharge or propose to discharge must apply for NPDES permits and submit
Nutrient Management Plans (NMPs) at the time that they submit a permit application.
Permitting authorities are required to review the NMPs and provide the public with an
opportunity for meaningful public review and comment. The permitting authorities are required
to incorporate the terms of NMPs as NPDES permit conditions. If an unpermitted CAFO can
certify to the permitting authority that they do not discharge or propose to discharge, then they
are not required to apply to an NPDES permit. In the final rule, EPA provided clarification on
how operators should evaluate whether they discharge or propose to discharge. The CAFO
owner or operator must determine on a case-by-case basis whether the CAFO will discharge
based on the CAFO design, construction, operation, and maintenance.
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.
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
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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 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
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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, 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
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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 and the States will continue to address these problems using various aspects of the
capacity, management, operation and maintenance (CMOM) concept. The CMOM concept
encourages the use of self-assessments and pro-active correction of system deficiencies to avoid
further deterioration of the sanitary sewer infrastructure and resultant SSOs. In some cases, EPA
and the States will use a combination of administrative and civil judicial enforcement action to
achieve these goals (U.S. EPA 2009).
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-storm water 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 (USDA) (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.
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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 Program (see www.nrcs.usda.gov/programs). 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 (13 ! »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.
A study was conducted to determine how effectiveness of compost piles in inactivating
Cryptosporidium oocysts. Four compost piles were used. Two compost piles consisted of
manure while the other two compost piles consisted of surface soil. Each compost pile was
injected with two million oocysts in an aqueous suspension. Every two to four weeks,
Cryptosporidium oocysts were extracted and tested from both sets compost piles. Both
experiments show that inactivation of Cryptosporidium oocysts occurred after 40 days of
composting. However, the compost pile with manure fared slightly better after 150 days
(Jenkins et al. 1999).
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
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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 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.
Vegetated buffer strips were tested to see if they were effective at removing
Cryptosporidium during rainfall rates of 15 or 40 mm/h for four hours. Buffers were set on a
slope of 5 to 20% and soil textures consisted of silty clay, loam, or sandy loam.
It was found that vegetated buffer strips consisting of sandy loam or higher soil bulk
densities had a 1 to 2 log reduction/m. Buffers consisting of silty clay, loam, or lower bulk
densities had a 2 to 3 log reduction/m. Also, it was found that vegetated buffer strip made of
similar soils removed at least 99.9% of Cryptosporidium oocysts from agricultural runoff when
slopes were less than or equal to 20% and had a length of at least 3 meters (Atwill et al. 2002).
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
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to support. Even where rotational grazing is not used, surface water contamination can be
reduced by keeping cattle, especially calves, out of streams.
Vermont wanted to reduce the concentration of E. coli, fecal streptococcus, and fecal
coliform bacteria as well as total phosphorus found in the Lake Champlain Basin Watershed. It
was assumed that a significant concentration of bacteria originated from nonpoint sources
located in agricultural lands. To reduce the bacterial concentration entering the watershed,
Vermont decided to improve animal waste management with dairy cows. In nearby areas,
pastures containing dairy cows near streams and streambanks were found. It was believed that
these pastures were one of the major sources of contamination due to bacterial excretion and
streambank erosion caused by dairy cows. Minimizing erosion along streambanks allows for
healthy vegetation, which will help filter nutrients. To prevent dairy cows from getting near or
in streams and streambanks, bridges were constructed across streams. Fences along streambanks
were also constructed to keep dairy cows from eroding streambanks.
When construction was complete, the watershed was monitored for three years. The data
below represents the average reduction in concentration for the specific contaminant.
Exhibit E-1 Average reduction of specific contaminant.
E. coli
Fecal streptococcus
Fecal coliform bacteria
Total phosphorus
29%
40%
38%
15%
These numbers show that the construction of bridges and fences had a significant impact
on the reduction of bacterial and total phosphorous concentrations. Only minimal fence
maintenance was required. Therefore, keeping dairy cows away from streams and streambanks
may significantly reduce bacterial and phosphorus concentration in the watershed with minimal
hassles (EPA 2002c).
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
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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 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 drythis 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
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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
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. EPA 2002a).
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,
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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 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
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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. 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
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than they would be in a free water surface wetland. The growth of bacteria in the wetland
medium is both positive and negativebacteria 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).
A wetland was constructed in Tucson, Arizona to help remove Cryptosporidium from the
secondary sewage effluent. The wetland had a maximum depth of 1.4 meter, length of 61
meters, and width of 8.2 meters. The wetland was designed to have a retention time of
approximately four days with an average flow rate of 58 liters/minute. The wetland was planted
with cattail, bulrush, black willow, and cottonwood. It was found that the wetland effectively
removed 64.2% of Cryptosporidium oocysts from the secondary sewage effluent (Thurston et al.
2001).
Two wetlands were constructed to determine if they could remove effectively
Cryptosporidium from untreated domestic wastewater. One wetland was planted with bulrush
and the other wetland was made of bare sand. The influent domestic water flowed directly into
two setting tanks in series. Then the flow split into the two wetlands in parallel. The wetlands'
detention time was 1 to 2 days. The results of this study showed that both planted and unplanted
wetlands removed about 90% Cryptosporidium oocysts. Slightly more oocysts were removed in
the planted wetland. The test shows that planted and unplanted wetlands are effective in
removing Cryptosporidium oocysts (Quinez-Daz et al. 2001).
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.
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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.
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.
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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.
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
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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).
E. 4 Case Studies of Existing 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.
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. However, since
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each watershed is different, the appropriate WCP plan for each watershed will also be
different. Some PWSs may need to develop efforts or measures completely different than those
outlined in these examples. Furthermore, some of the approaches outlined in the referenced
examples may not be suitable for other watersheds due to different site-specific conditions,
and hence may not be used by PWSs developing a successful State-approved WCP for these
watersheds.
For more case studies, see the following sources:
Case Studies of Source Water Protection (U.S. EPA, 2005a;
www.epa.safewater/protect/casesty/casestudy.html)
Section 319 Nonpoint Success Stories (U.S. EPA, 2005b;
www.epa.gov/owow/nps/Success319)
Watershed Success Stories - Applying the Principles and Spirit of the Clean Water
Action Plan (U.S. EPA, 2000d; water.usgs.gov/owq/cleanwater/success/index.html)
Protecting Sources of Drinking Water: Selected Case Studies in Watershed Management
(U.S. EPA, 1999a, www.epa.gov/safewater/swp/swpcases.pdf)
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 2001a).
Manchester, New Hampshire
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Large Surface Water System Where State Plays an Active Role
The City of Manchester receives 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, 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
subj ect 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. EPA2001b).
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 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.
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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 200Ic).
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 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).
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