Agency
LONG TERM 2 ENHANCED SURFACE
WATER TREATMENT RULE
TOOLBOX GUIDANCE MANUAL
-------
Office of Water (4606)
EPA815-R-09-016
April 2010
www. epa.gov/safewater
-------
Purpose:
The purpose of this guidance manual 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.
Questions 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
LT2ESWTR Toolbox Guidance Manual i April 2010
-------
CONTENTS
Exhibits xi
Appendices xiii
Acronyms xiv
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 1-6
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 2-5
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 2-7
2.2.3.2.2 Watershed Sanitary Survey Report 2-7
2.2.3.3 State Review and Continuation of the WCP Credit 2-9
2.2.4 PWS and State Checklist for Preparation, Implementation,
and Maintenance of the WCP Plan and Associated Credit 2-9
LT2ESWTR Toolbox Guidance Manual ii April 2010
-------
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
2.3.2.2 Disadvantages 2-15
2.3.3 Incorporation of New Versus Existing Source Water Protection
Activities Into a Watershed Control Program 2-17
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 2-23
2.4.2.1 How Do Fate and Transport Affect the Way
Cryptosporidium Impacts My Water Supply? 2-26
2.4.2.2 What Role Should Monitoring Play in the Evaluation
of Potential and Existing Sources of Cryptosporidium^ 2-30
2.4.3 Analysis of Control Measures 2-32
2.4.3.1 Available Regulatory and Management Strategies 2-32
2.4.3.2 Partnerships in Watershed Control Plans 2-35
2.4.3.3 Addressing Point Sources 2-36
2.4.3.4 AddressingNonpoint Sources 2-38
2.4.3.5 Is Purchase/Ownership of All or Part of the Watershed
a Viable Option? 2-43
2.5 References 2-45
3. Alternative Source/Intake 3-1
3.1 Introduction 3-1
3.2 Changing Sources 3-1
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 3-2
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 3-3
3.3.2.2 Stratification and Mixing 3-4
3.3.2.3 Proximity to Inflows 3-4
3.3.3 Streams and Rivers 3-4
3.3.3.1 Depth 3-4
3.3.3.2 Flow and River Hydraulics 3-5
3.3.3.3 Upstream Sources of Contamination 3-5
3.3.3.4 Seasonal Effects 3-5
LT2ESWTR Toolbox Guidance Manual in April 2010
-------
3.4 Changing Timing of Withdrawals 3-5
3.4.1 Toolbox Selection Considerations 3-5
3.4.1.1 Advantages and Disadvantages 3-6
3.5 References 3-6
4. Bank Filtration 4-1
4.1 Introduction 4-1
4.2 LT2ESWTR Compliance Requirements 4-2
4.2.1 Credits 4-3
4.2.2 Monitoring Requirements 4-4
4.3 Toolbox Selection Considerations 4-5
4.3.1 Advantages and Disadvantages 4-5
4.3.1.1 Removal of Additional Contaminants 4-5
4.3.1.2 Clogging of Pores 4-7
4.3.1.3 Scour 4-8
4.3.1.4 Additional Treatment Steps 4-8
4.4 Site Selection and Aquifer Requirements 4-9
4.4.1 Selected Bank Filtration Sites 4-10
4.4.2 Aquifer Type 4-10
4.4.2.1 Unconsolidated, Granular Aquifers 4-10
4.4.2.2 Karst, Consolidated Clastic, and Fractured Bedrock
Aquifers 4-11
4.4.2.3 Partially Consolidated, Granular Aquifers 4-11
4.4.3 Aquifer Characterization 4-12
4.4.3.1 Coring 4-13
4.4.3.2 Sieve Analysis 4-14
4.4.4 Site Selection as it Relates to Scour 4-15
4.4.4.1 Stream Channel Erosional Processes 4-15
4.4.4.2 Unsuitable Sites 4-17
4.5 Design and Construction 4-20
4.5.1 Well Type 4-20
4.5.2 Filtrate Flow Path and Well Location 4-25
4.5.2.1 Required Separation Distance Between a Well and the Surface
Water Source 4-25
4.5.2.2 Locating Wells at Greater than Required Distances from the
Surface Water Source 4-25
4.5.2.3 Delineating the Edge of the Surface Water Source 4-29
4.5.2.4 Measuring Separation Distances for Horizontal Wells and Wells
that are Neither Horizontal Nor Vertical 4-30
4.6 Operational Considerations 4-31
4.6.1 High River Stage 4-31
4.6.2 Implications of Scour for Bank Filtration System Operations 4-31
4.6.3 Anticipating High Flow Events /Flooding 4-32
LT2ESWTR Toolbox Guidance Manual iv April 2010
-------
4.6.4 Possible Responses to Spill Events and Poor Surface Water
Quality 4-32
4.6.5 Maintaining Required Separation Distances 4-32
4.7 Demonstration of Performance 4-33
4.7.1 Identification of Collection Devices and Alternative Treatment
Technologies at the Site 4-34
4.7.2 Source Water Quality and Quantity 4-35
4.7.3 Ground Water Travel and Residence Time Calculations and Ambient
Ground Water Dilution 4-35
4.7.4 Surface and Ground Water Data Collection, Methods and Sampling
Locations 4-36
4.7.5 Monitoring Tools 4-38
4.7.6 Tracer Tests and Use of Isotopes 4-44
4.7.7 Monitoring Wells Located Along the Shortest Flow Path 4-45
4.7.8 Post-decision Routine Monitoring and Sampling 4-45
4.8 Reference 4-45
5. Presedimentation 5-1
5.1 Introduction 5-1
5.2 LT2ESWTR Compliance Requirements 5-1
5.2.1 Credits 5-1
5.2.2 Monitoring Requirements 5-2
5.2.3 Calculations 5-2
5.3 Toolbox Selection Considerations 5-3
5.3.1 Source Water Quality 5-3
5.3.2 Advantages and Disadvantages of Installing a
Presedimentation Basin 5-4
5.4 Types of Sedimentation Basins 5-4
5.4.1 Horizontal Flow 5-7
5.4.1.1 Rectangular 5-7
5.4.1.2 Circular 5-7
5.4.2 Upflow Clarifier 5-7
5.4.3 Reactor Clarifier 5-7
5.4.4 High Flow Rate Designs 5-8
5.4.5 Ballasted Flocculation 5-8
5.5 Design and Operational Issues 5-8
5.5.1 Redundancy 5-8
5.5.2 Short Circuiting 5-8
5.5.3 Sludge Removal 5-9
5.5.4 Coagulant Addition and Dose Ranges of Common Coagulants 5-9
5.6 References 5-10
LT2ESWTR Toolbox Guidance Manual v April 2010
-------
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 6-3
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
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) 7-5
7.3 Reporting Requirements 7-5
7.3.1 Combined Filter Performance 7-5
7.3.2 Individual Filter Performance 7-6
7.4 Process Control Techniques 7-6
7.4.1 Chemical Feed 7-10
1 A.I.I Type of Chemical and Dose 7-11
7.4.1.2 Mixing 7-11
7.4.1.3 Streaming Current Detectors and Zeta Potential Monitors...7-12
7.4.2 Flocculation 7-12
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 7-18
7.5.3 Adequate Chemical Storage 7-18
7.5.4 Voluntary Programs 7-18
7.5.4.1 Partnership for Safe Water 7-19
7.5.4.2 Composite Correction Program (CCP) 7-19
7.6 References 7-20
LT2ESWTR Toolbox Guidance Manual vi April 2010
-------
8. 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 8-6
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
LT2ESWTR Toolbox Guidance Manual vii April 2010
-------
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 9-4
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 1DBPR 10-6
10.4 Unfiltered System LT2ESWTR Requirements 10-7
10.5 Disinfection with Chlorine Dioxide 10-7
10.6 Toolbox Selection Considerations 10-8
10.6.1 Advantages 10-8
10.6.2 Disadvantages 10-8
10.7 Design Considerations 10-9
10.7.1 Designing to Lowest Temperature 10-9
10.7.2 Point of Addition 10-10
10.8 Operational Considerations 10-10
10.9 Safety Issues 10-11
10.9.1 Chemical Storage 10-11
10.9.2 Acute Health Risks of Chlorine Dioxide 10-11
10.10 References 10-11
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 Tio and CSTR Methods 11-7
11.3.2 Tio Method 11-7
11.3.3 CSTR Method 11-10
11.3.4 Extended Tio and Extended CSTR Methods 11-13
11.4 Monitoring Requirements 11-13
11.4.1 LT2ESWTR 11-13
11.4.2 Stage 1 DBPR and Stage 2 DBPR 11-13
11.5 Unfiltered System LT2ESWTR Requirements 11-14
11.6 Toolbox Selection 11-14
11.6.1 Advantages 11-15
11.6.2 Disadvantages 11-15
11.7 Disinfection With Ozone 11-16
11.7.1 Chemistry 11-16
LT2ESWTR Toolbox Guidance Manual viii April 2010
-------
11.7.2 Byproduct Formation 11-18
11.7.2.1 Bromate and Brominated Organic Compounds 11-18
11.7.2.2 Non-Brominated Organic Compounds 11-18
11.8 Design 11-19
11.8.1 Generators and Contactors 11-19
11.8.2 Point of Addition 11-19
11.8.3 Biologically Active Filters 11-20
11.8.3.1 Media for Biologically Active Filters 11-20
11.8.3.2 Operating Biologically Active Filters 11-20
11.9 Safety Considerations in Design 11-21
11.10 Operational Considerations 11-21
11.10.1 Ozone Demand 11-21
11.10.2 pH 11-22
11.10.3 Temperature 11-22
11.10.4 Maintaining Residual Disinfectant in the
Distribution System 11-22
11.11 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 12-9
12.4.3 Full-Scale Versus Pilot-Scale Testing 12-9
12.5 Demonstration Protocol 12-10
12.5.1 DOP Test Matrix 12-11
12.5.2 DOP Monitoring Plan 12-11
12.5.2.1 Sampling Location 12-14
12.5.2.2 Monitoring Parameters 12-14
12.5.2.3 Monitoring Frequency 12-14
12.5.2.4 Quality Assurance/Quality Control (QA/QC) 12-14
12.5.3 DOP Implementation 12-15
12.5.3.1 Sample Collection Methods 12-15
LT2ESWTR Toolbox Guidance Manual ix April 2010
-------
12.5.3.2 Analytical Methods 12-15
12.5.3.3 Microbial Dosing 12-16
12.5.3.4 Documentation of WTP Operating Conditions 12-16
12.5.4 Data Analysis and Reporting 12-17
12.5.4.1 Evaluation of Performance 12-17
12.5.4.2 Reporting for the OOP 12-17
12.5.4.3 Ongoing Reporting 12-18
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 UVDose and Validation Testing Requirements 13-1
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 14-6
LT2ESWTR Toolbox Guidance Manual x April 2010
-------
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 2-22
Exhibit 4.1 Selected Bank Filtration Systems in Europe and the United States 4-10
Exhibit 4.2 Generalized Depiction of Stream Channel Lateral Migration 4-16
Exhibit 4.3 Schematic Showing Generalized Flow and Required Separation
Distance to a Vertical Well 4-22
Exhibit 4.4 Schematic Showing Generalized Flow and Required Separation
Distance to a Horizontal Well With Three Laterals 4-23
Exhibit 4.5 Taking a Water Level Reading 4-24
Exhibit 4.6 The Streambed of a Perched Stream Is Well above the Water Table 4-26
Exhibit 4.7 Size of Pathogenic Protozoa and Surrogate Bacteria 4-40
Exhibit 4.8 Size of Some Common Fresh Water Diatoms 4-43
Exhibit 5.1 Example 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 7-4
Exhibit 7.2 Maintenance and Calibration Activities for Bench Top Turbidimeters 7-5
Exhibit 7.3 Performance Limiting Factors (Adapted from the Composite
Correction Program) 7-8
Exhibit 7.4 Effluent Turbidity Goals for the Sedimentation Process 7-14
LT2ESWTR Toolbox Guidance Manual
April 2010
-------
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 10-4
Exhibit 10.2 CT Calculation Example Schematic 10-4
Exhibit 10.3 Distribution System Monitoring Requirements at Each Plant 10-7
Exhibit 11.1 CT Values for Cryptosporidium Inactivation by
Ozone (40 CFR 141.730) 11-3
Exhibit 11.2 Recommended Methods and Terminology for Calculating the
Log-Inactivation Credit in an Ozone Contactor 11-6
Exhibit 11.3 Correlations to Predict C* Based on Ozone Residual Concentrations
in the Outlet of a Chamber 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 Example 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 12-13
Exhibit 13.1 UV Dose Requirements - millijoules per centimeter squared (mJ/cm2) 13-2
LT2ESWTR Toolbox Guidance Manual
xi i
April 2010
-------
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. Tracer Test Data Development & Analysis
Appendix F. Watershed Control Best Management Practices (BMPs) and Case Studies
Appendix G. Review Criteria for Use by States When Reviewing Watershed Control
(WSC)Program Plans
LT2ESWTR Toolbox Guidance Manual xiii April 2010
-------
ACRONYMS
AFO Animal Feeding Operation
AOC Assimilable Organic Carbon
AOP Advanced Oxidation Process
ASTM American Society for Testing and Materials
AW OP Area Wide Optimization Program
AWWA American Water Works Association
BMP Best Management Practice
CAFO Concentrated Animal Feeding Operation
CCP Composite Correction Program
CFC Chlorofluorocarbon
CFE Combined Filter Effluent
CMOM Capacity, Management, Operation, and Maintenance
CPE Comprehensive Performance Evaluation
CSO Combined Sewer Overflow
CSTR Continuously Stirred Tank Reactor
CT Contact Time
CTE Comprehensive Technical Assistance
CWA Clean Water Act
CWSRF Clean Water State Revolving Fund
DBF Disinfection Byproduct
DBPR Disinfectants and Disinfection Byproducts Rule
DEM Digital Elevation Model
DNA Deoxyribonucleic Acid
DOP Demonstration Of Performance
DWSRF Drinking Water State Revolving Fund
EDTA Ethylenediamine Tetra-acetic Acid
EM Electromagnetic
EPA United State Environmental Protection Agency
FBR Filter Backwash Rule
FEMA Federal Emergency Management Agency
GAC Granular Activated Carbon
GIS Geographic Information System
GPM Gallons Per Minute
GPR Ground Penetrating Radar
GROW Geotechnical, Rock and Water Resources Library
GWUDI Ground Water Under the Direct Influence of surface water
HAA Haloacetic Acids
HDT Hydraulic Detention Time
HEC-RAS Hydrologic Engineering Centers River Analysis System
HUC Hydrologic Unit Code
IDSE Initial Distribution System Evaluation
LT2ESWTR Toolbox Guidance Manual
xiv
April 2010
-------
IESWTR Interim Enhanced Surface Water Treatment Rule
IFE Individual Filter Effluent
IP Induced Polarization
LRAA Locational Running Annual Average
LRV Log Removal Value
LT1ESWTR Long Term 1 Enhanced Surface Water Treatment Rule
LT2ESWTR Long Term 2 Enhanced Surface Water Treatment Rule
MCF Membrane Cartridge Filter
MCL Maximum Contaminant Level
MDBP Microbial and Disinfection Byproduct
MF Microfiltration
MOD Million Gallons per Day
MPA Microscopic Particulate Analysis
MRDL Maximum Residual Disinfectant Level
MS4 Municipal Separate Storm Sewer System
MST Microbial Source Tracking
MTBE Methyltertiarybutylether
NFF National Flood Frequency
NGWA National Groundwater Association
NUDES New Hampshire Department of Environmental Services
NMP Nutrient Management Plan
NOM Natural Organic Matter
NPDES National Pollutant Discharge Elimination System
NRCS Natural Resource Conservation Service
NSF National Science Foundation
NTNCWS Nontransient Noncommunity Water Systems
NTU Nephelometric Turbidity Unit
ORP Oxidation-Reduction Potential
OSHA Occupational Safety and Health Administration
PCR Polymerase Chain Reaction
PEL Permissible Exposure Limit
POTW Publically Owned Treatment Works
PWS Public Water System
QA Quality Assurance
QC Quality Control
RAA Running Annual Average
RNA Ribonucleic Acid
RO Reverse Osmosis
SCD Streaming Current Detector
SDWA Safe Drinking Water Act
SOC Synthetic Organic Compound
SOP Standard Operating Procedure
SP Self Potential
SPDES State Pollutant Discharge Elimination System
LT2ESWTR Toolbox Guidance Manual xv April 2010
-------
SRF State Revolving Fund
SSO Sanitary Sewer Overflow
SSRC Spores of Sulfide Reducing Clostridia
SSS Specific System Study
SWAP Source Water Assessment Program
SWP Source Water Protection
SWTR Surface Water Treatment Rule
TCE Trichloroethylene
TEM Transient Electromagnetic
THM Trihalomethane
TMDL Total Maximum Daily Load
TNCWS Transient Noncommunity Water Systems
TNTC Too Numerous To Count
TOC Total Organic Carbon
TTHM Total Trihalomethanes
UF Ultrafiltration
UFRV Unit Filter Run Volume
USDA United States Department of Agriculture
USGS United States Geological Survey
UV Ultraviolet light
WCP Watershed Control Program
WSC Watershed Control
WTP Water Treatment Plant
LT2ESWTR Toolbox Guidance Manual
xvi
April 2010
-------
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. coll to determine '^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.
LT2ESWTR Toolbox Guidance Manual 1-1 April 2010
-------
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
Appendix G
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*.
Tracer Test Data Development and Analysis - describes how to conduct
and analyze the results of tracer tests to determine the contact time for CT
calculations.
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.
Review Criteria for Use By States When Reviewing Watershed Control
(WSC) Program 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
LT2ESWTR Toolbox Guidance Manual
1-2
April 2010
-------
1. Introduction
(DBPR), which was promulgated simultaneously with the LT2ESWTR to balance the risks
between DBFs and microbial pathogens.
1.3.1 Surface Water Treatment Rule
Under the 1989 Surface Water Treatment Rule (SWTR) (54 FR 27486 June 29, 1989),
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
December 16, 1998) 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.
LT2ESWTR Toolbox Guidance Manual 1-3 April 2010
-------
1. Introduction
• A disinfection benchmark to assess the level of microbial protection provided before
facilities change their disinfection practices to meet the requirements of the Stage 1
DBPR.
• Inclusion of Cryptosporidium in the definition of GWUDI and in the watershed control
requirements for unfiltered PWSs.
• All new finished water reservoirs must be covered.
1.3.3 Stage 1 Disinfectants and Disinfection Byproducts Rule
Pursuant to requirements under the Safe Drinking Water Act (SDWA), EPA developed
interrelated regulations to control microbial pathogens and disinfectants/DBPs in drinking water.
These rules, collectively known as the M-DBP rules, are intended to address complex risk
trade-offs between the two different types of contaminants. EPA promulgated the IESWTR
concurrently with the Stage 1 DBPR so that systems could coordinate their responses to the risks
posed by DBFs and microbial pathogens.
The 1998 Stage 1 DBPR (63 FR 69390 December 16, 1998) 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 (LTIESWTR) (67 FR 1811
January 14, 2002) 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 (71 FR 388 January 4, 2006) 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.
LT2ESWTR Toolbox Guidance Manual 1-4 April 2010
-------
1. Introduction
Initial Distribution System Evaluations
For many systems, compliance monitoring will be preceded by an Initial Distribution
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.
LT2ESWTR Toolbox Guidance Manual 1-5 April 2010
-------
1. Introduction
1.4 Overview of the Long Term 2 Enhanced Surface Water Treatment Rule
The LT2ESWTR (71 FR 654 January 5, 2006) 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 LT1ESWTR 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 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).
LT2ESWTR Toolbox Guidance Manual 1-6 April 2010
-------
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
treatment
2-log
treatment
2.5-log
treatment3
Direct
Filtration
No
additional
treatment
1 .5-log
treatment2
2.5-log
treatment3
3-log
treatment
Slow Sand or
Diatomaceous
Earth
Filtration
No additional
treatment
1-log
treatment
2-log
treatment
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
"'40CFR 141.710 and 40 CFR 141.711.
2Systems may use any technology or combination of technologies from the microbial toolbox.
3Systems must achieve at least 1-log of the required treatment using ozone, chlorine dioxide, UV, membranes,
bag/cartridge filters, or bank filtration.
4Total Cryptosporidium treatment must be at least 4.0-log.
5Total Cryptosporidium treatment must be at least 5.0-log.
6Total 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 4-1 og 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
LT2ESWTR Toolbox Guidance Manual
1-7
April 2010
-------
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
"'40CFR 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.
LT2ESWTR Toolbox Guidance Manual
April 2010
-------
1. Introduction
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 1 41 .71 6 (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 141.71 7(b) and Chapter 6 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 0.15 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.
LT2ESWTR Toolbox Guidance Manual
1-9
April 2010
-------
1. Introduction
Additional Filtration Toolbox Options
Bag or cartridge
filters (individual
filters)
Bag or cartridge
filters (in series)
Membrane
filtration
Second stage
filtration
Slow sand filters
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
Chapter 8 of this manual for specific criteria.
Up to 2.5-log credit based on the removal efficiency demonstrated during
challenge testing with a 0.5-log factor of safety. See 40 CFR 141.719(a) and
Chapter 8 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 1 0 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
one or more year(s). A benchmark is the lowest monthly average of microbial inactivation during
the disinfection profile period.
LT2ESWTR Toolbox Guidance Manual
1-10
April 2010
-------
1. Introduction
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.
• Changes to the disinfectant used at the treatment plant.
• Changes to the disinfection process.
• 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.
• 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, if applicable.
LT2ESWTR Toolbox Guidance Manual 1-11 April 2010
-------
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
producing surface water 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
producing surface water 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
producing surface water 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: U.S. EPA 2007. The LT2ESWTR Implementation Guidance. EPA816-R-07-006, U.S. Environmental
Protection Agency, Office of Groundwater and 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.
LT2ESWTR Toolbox Guidance Manual
1-12
April 2010
-------
1. Introduction
Exhibit 1.5 Implementation Timeline for the LT2ESWTR
2006
,
,
(c
C
2007
ypfo mor
Review
>subm ssion
i
2006
r
(c
2008
litoring
IDSE
'
2009
'
Crypto monitoring
Review
^submission
(<
]
<-
IDSE
r
(j
5)
2010
Treatm
Installs
2011
snt
ion
Cc
2012
mp
2013
2014
Possible
Extension
lian
ce
r Treatment
Installation
Crypto monitoring
Review
^subm ssion
y~
2007
-------
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 WCP 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 WCP credit can be added
to the credit awarded for any other toolbox component.
LT2ESWTR Toolbox Guidance Manual 2-1 April 2010
-------
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.
• 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 a WCP 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), the PWS must notify
its state of its 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 Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) must
have these credits in place within three years after the bin assignment deadline. Consequently, the
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 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 SWP that might result from the proposed change.
LT2ESWTR Toolbox Guidance Manual 2-2 April 2010
-------
2. Watershed Control Program
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
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)
>1 00,000
April 2009
April 201 0T
April 201 1T
April 201 2T
April 201 3T
April 201 5T
April 201 5
50,000 to 99,999
October 2009
October 20 10T
October 201 1T
October 20 12T
October 20 13T
October 20 15T
October 201 5
10,000 to 49,999
October 20 10
October 201 1T
October 201 2T
October 201 3T
October 201 4T
October 201 6T
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
A system must notify its state of its intention to implement a WCP at least two years prior
to the applicable compliance date. (40 CFR 141.716(a)(l)). For example, as shown in Exhibit 2.1,
a system serving 10,000 people has an October 2013 deadline for implementing the WCP plan.
Therefore, it must inform the state that it intends to develop a WCP plan by October 2011. The
application and plan must be submitted for approval at least one year prior to the applicable
LT2ESWTR Toolbox Guidance Manual
2-3
April 2010
-------
2. Watershed Control Program
compliance date (i.e., one year after informing the state of the intent to implement a WCP plan).
(40CFR141.716(a)(2)).
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.
LT2ESWTR Toolbox Guidance Manual 2-4 April 2010
-------
2. Watershed Control Program
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 (e.g., publicly owned treatment works (POTWs), concentrated animal feeding
operations (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 best management practices (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
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 WCP plan and either approve, reject, or
conditionally approve the plan. See Appendix G for review criteria for use by states when
LT2ESWTR Toolbox Guidance Manual 2-5 April 2010
-------
2. Watershed Control Program
reviewing WCP plans (both required and recommended elements of a WCP are presented in
Appendix G). If the plan is approved, or if the system agrees to implement 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) and
(6)).
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 WCP status report to the state (40 CFR 141.716(a)(5)(i)).
• 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 SWP 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, WCP plan, and watershed sanitary surveys that are conducted
every three years 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, WCP 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
LT2ESWTR Toolbox Guidance Manual 2-6 April 2010
-------
2. Watershed Control Program
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 WCP 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 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 SWP, 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 WCP plan. Implementation delays should be explained, and actions to
prevent further delays should be described.
The original watershed program plans must include an analysis of the effectiveness and
feasibility of control measures that could reduce Cryptosporidium loadings from sources of
contamination to the system's source water. Annual status reports should provide updates on the
control measures as they 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. The survey must meet the
following criteria (40 CFR 141.716(a)(5)(ii)(A)):
LT2ESWTR Toolbox Guidance Manual 2-7 April 2010
-------
2. Watershed Control Program
• Cover the area of the watershed that was identified in the approved WCP plan as the area
of influence.
• Assess the implementation of actions to reduce source water Cryptosporidium levels.
• 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.
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 American Water Works Association (AWWA). PWSs are required
to use state-designated persons 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 National Pollutant Discharge Elimination System (NPDES) permits
and discharge records.
• Review of pertinent databases (e.g., county geographic information system (GIS)
systems, etc.).
• Review of most recent available aerial photography.
• Interviews with Natural Resources Conservation Service (NRCS), 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.
LT2ESWTR Toolbox Guidance Manual 2-8 April 2010
-------
2. Watershed Control Program
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 SWP that is likely to result from this
change (40 CFR 141.716 (a)(5)(i)). The description should include the impact of that change on
the protection of the watershed so the state and water system will both understand whether the
assumptions made during the "verbal approval" stage are holding true.
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.
LT2ESWTR Toolbox Guidance Manual 2-9 April 2010
-------
2. Watershed Control Program
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
141.716(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
141.716(a)(2)
141.716(a)(2)(i)
141.716(a)(2)(ii)
141.716(a)(2)(iii)
141. 716(a)(2)(iv)
141. 716(a)(2)(iv)
141. 716(a)(2)(iv)
141. 716(a)(2)(iv)
141. 716(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
LT2ESWTR Toolbox Guidance Manual
2-10
April 2010
-------
2. Watershed Control Program
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.
141.716(a)(2)
141.716(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
SWP. These changes must be described in the
next annual progress report.
141. 716(a)(6)
141. 716(a)(5)
141.716(a)(5)(i)
141. 716(a)(5)(i)
141.716(a)(5)(i)
141. 716(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
LT2ESWTR Toolbox Guidance Manual
2-11
April 2010
-------
2. Watershed Control Program
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:
141. 716(a)(5)(ii)
2.2.3
2.2.3.2,
2.2.3.2.2
Encompass the area of influence defined in the
state-approved WCP plan
141. 716(a)(5)(ii)(A)
2.2.3.2.2
Assess actions implemented to reduce
Cryptosporidium levels within the area of influence
141. 716(a)(5)(ii)(A)
2.2.3.2.2
Identify any significant new sources of
Cryptosporidium in the area of influence
141. 716(a)(5)(ii)(A)
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.
141. 716(a)(5)(ii)(B)
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
LT2ESWTR Toolbox Guidance Manual
2-12
April 2010
-------
2. Watershed Control Program
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 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 WCP 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 WCP credit, SWP activities for
identification, prioritization, and control of Cryptosporidium sources are important. These
activities also provide proactive, preventive 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 WCP targeting Cryptosporidium reduction is the most advantageous when it is also
the component of a larger comprehensive SWP 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 WCP and comprehensive SWP program are already
available as a result of the source water assessments required under the 1996 Amendments to the
Safe Drinking Water Act (SDWA). 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."
LT2ESWTR Toolbox Guidance Manual 2-13 April 2010
-------
2. Watershed Control Program
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
occurrence.
2.3.2 Advantages and Disadvantages of a Watershed Control Program
Section 2.3.2.1, and 2.3.2.2 explain the advantages and disadvantages of a WCP
(respectively). Topics covered include the side impacts on public health and ecological goals, the
incorporation of a multiple barrier strategy, the availability of analytical methods to track water
quality progress, the level of commitment required of PWSs, and the potential costs and payoffs
of implementation efforts.
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. The reduction in
organic material in the source water will make treatment more efficient (and less expensive) and
reduce the incidence of disinfection byproducts (DBFs).
While WCPs may be a cost-effective Microbial Toolbox option, the PWS commitment
needed to initiate and maintain SWP efforts may be substantial. SWP 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 SWP 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 WCP 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.
LT2ESWTR Toolbox Guidance Manual 2-14 April 2010
-------
2. Watershed Control Program
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 SDWA
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 WCP 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., ultraviolet light (UV) irradiation).
Control of Cryptosporidium sources in the watershed can benefit more than a single water
treatment facility. In even small watersheds, there may be multiple water intakes that may 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.
LT2ESWTR Toolbox Guidance Manual 2-15 April 2010
-------
2. Watershed Control Program
The PWS commitment needed to initiate and maintain source water protection efforts is
substantial. SWP 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 WCP will
be viable for any individual water system. Some federal funding is available to implement some
aspects of a WCP. For example, the Clean Water Act (CWA) 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 (DWSRF) are also
available to a limited extent for SWP. Each state may set aside as much as 15 percent of its grant
each year to provide loans for SWP activities, including land or easement acquisition,
implementation of incentive-based voluntary SWP programs, and implementation of wellhead
protection programs. A review of potential funding sources is provided in Gullick et al. (2007).
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 WCP 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 WCP 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 WCP plan.
A successful WCP 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
LT2ESWTR Toolbox Guidance Manual 2-16 April 2010
-------
2. Watershed Control Program
of building strong relationships with their stakeholders may decide that a WCP is not
appropriate for them. In some watersheds, depending on size of the WCP 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
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 BMPs
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 SDWA 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
WCP plan. However in some cases the information available from the source water assessments is
quite limited or outdated, 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
(LT1ESWTR) (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
AWWA and the California Department of Health Services Division of Drinking Water and
Environmental Management also have developed guidance specifically for watershed sanitary
LT2ESWTR Toolbox Guidance Manual 2-17 April 2010
-------
2. Watershed Control Program
surveys. Coordination of SWP efforts with those of CWA programs such as Total Maximum
Daily Loads (TMDLs) is beneficial and encouraged.
Guidance for SWP 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).
• Source Water Protection: Best Management Practices and Other Measures for Protecting
Drinking Water Supplies (U.S. EPA 2002d).
• 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. 2007).
• AwwaRF (AWWA Research Foundation) 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).
LT2ESWTR Toolbox Guidance Manual 2-18 April 2010
-------
2. Watershed Control Program
• 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).
• 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;
http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm7action=Case Studies.)
• 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;
http://www.blueprintjordanriver.slco.org/docToPdf/WatershedSuccessStor.pdf
• Protecting Sources of Drinking Water: Selected Case Studies in Watershed Management
(U.S. EPA 1999a, http://www.epa.gov/safewater/sourcewater/pubs/swpcases.pdf)
• Source Water Collaborative; see www.protectdrinkingwater.org.
2.4.1 Identification of the Area of Influence
An essential element for the WCP plan is the identification of the "area of influence." The
area of influence is the area outside of which the likelihood of Cryptosporidium or fecal
contamination affecting the treatment plant is not significant. 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
LT2ESWTR Toolbox Guidance Manual 2-19 April 2010
-------
2. Watershed Control Program
are at the discretion of the PWS, as long as the state considers it sufficient to approve the area
delineated.
Delineation
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
program (SWAP). 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 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.nh.nrcs.usda.gov/technical/Publications/Topowatershed.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.
LT2ESWTR Toolbox Guidance Manual 2-20 April 2010
-------
2. Watershed Control Program
Watershed Hydrology
Once the watershed has been delineated, PWSs should examine the hydrology of their
watersheds to help determine the area of influence. The 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.
LT2ESWTR Toolbox Guidance Manual 2-21 April 2010
-------
2. Watershed Control Program
Exhibit 2.3 Ground Water/Surface Water Interaction
Precipitation
Well
Runoff
Septic
f\ System
Road with
Catch Basin
Recharge
Ground Water / Surface Water
Interaction
Ground water that is considered to be under the direct influence of surface water 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 sources under the
SWTR, IESWTR, and LT2ESWTR). GWUDI may be contaminated 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.
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
LT2ESWTR Toolbox Guidance Manual
2-22
April 2010
-------
2. Watershed Control Program
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., NPDES are 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/indexj ava.html. Local, state and federal data
sets are useful for 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 affect oocyst
levels released to surface water in the watershed.
Land Use
Many land uses in a watershed have the potential to introduce Cryptosporidium into water
supplies. These include point sources—combined sewer overflows (CSOs), wastewater treatment
plants, and CAFOs—and nonpoint sources, including livestock, wildlife, pets, stormwater runoff,
and septic systems.
LT2ESWTR Toolbox Guidance Manual 2-23 April 2010
-------
2. Watershed Control Program
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-specific—in streams in an agricultural watershed in southern Ontario, no
connection was found between Cryptosporidium concentration and sources or land use such as
wastewater treatment plants, CSOs, 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 CSOoutfalls, 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 stormwater. In one study, Cryptosporidium concentrations at
CSO outfalls on the Allegheny River in Pittsburgh during storms ranged from 0 to 3,000
oocysts/100 L, with a geometric mean of 2,013 oocysts/100 L (States et al. 1997).
Wastewater treatment plants may also contribute to oocyst loads, depending on the amount
of treatment provided. Primary treatment can remove as little as 27 percent of oocysts from
effluent (Payment et al. 2001); most plants in the United States provide secondary treatment, so
removal should be better. In the Netherlands, it is estimated that 85 percent of Cryptosporidium
oocysts occurring in surface water are discharged in wastewater treatment plant effluent
(Medema and Schijven 2001). In one study in Pittsburgh, oocysts were detected in 33 percent of
samples with a geometric mean concentration of 924 oocysts/100 L over 24 months of
sampling (States et al. 1997). In another study near Philadelphia, concentrations ranged from 33
to 2,490 oocysts per 100 L (67 percent of samples were positive); downstream from the plant,
concentrations ranged from 325 to 825 oocysts per 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.
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
LT2ESWTR Toolbox Guidance Manual 2-24 April 2010
-------
2. Watershed Control Program
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 stormwater, 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.
coll, Giardia, Cryptosporidium, and viruses, and identify whether the source is from human,
LT2ESWTR Toolbox Guidance Manual 2-25 April 2010
-------
2. Watershed Control Program
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, CSOs, or stormwater runoff.
Numerous references are available that summarize the capabilities and state-of-the-science
of MST, including the following:
• U. S. EPA Microbial Source Tracking Guide Document (U. S. EPA 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
• Microbial Source Tracking and Detection Techniques (USGS website)
http://water.usgs.gov/owq/microbial.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, 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.
LT2ESWTR Toolbox Guidance Manual 2-26 April 2010
-------
2. Watershed Control Program
Influence of Precipitation
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
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
LT2ESWTR Toolbox Guidance Manual 2-27 April 2010
-------
2. Watershed Control Program
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 AFOs
(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
studies suggests that migration of Cryptosporidium parvum 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).
LT2ESWTR Toolbox Guidance Manual 2-28 April 2010
-------
2. Watershed Control Program
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. coli) are more easily transported (Davies et al. 2005, CRC 2004).
LT2ESWTR Toolbox Guidance Manual 2-29 April 2010
-------
2. Watershed Control Program
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.
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 BMPs 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 WCP controls
New technologies for MST including deoxyribonucleic acid (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
LT2ESWTR Toolbox Guidance Manual 2-30 April 2010
-------
2. Watershed Control Program
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 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 upstream and
downstream of a suspected or known point or nonpoint source, as the Philadelphia Water
Department did (Crockett and Haas 1997). Such monitoring is appropriate where impacted
stream reaches have already been identified. The results of any monitoring should enable the
system to compare the relative contribution of various sources to the overall Cryptosporidium
occurrence in the watershed and their effect on water quality.
Monitoring 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 several wastewater
treatment plants in its upper reach and farms and parks along its lower reach. In the first phase,
the water department tested the Queen Lane intake during dry flow. It then sampled a site along
the creek downstream of the wastewater treatment plants and one downstream of the farms
during various weather conditions. In the third phase 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.
LT2ESWTR Toolbox Guidance Manual 2-31 April 2010
-------
2. Watershed Control Program
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 GIS to analyze their water quality and contaminant
source data. For systems that have Arc View software, BASINS 3.0, a software and GIS package
developed by EPA can assist systems with integrating local data and nationally available pre-
formatted spatial data (e.g., watershed HUCs, 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 WCP 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 141.716(a)(2)(iii)). 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
stormwater 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.
LT2ESWTR Toolbox Guidance Manual 2-32 April 2010
-------
2. Watershed Control Program
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 a 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
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 WCP 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
LT2ESWTR Toolbox Guidance Manual 2-33 April 2010
-------
2. Watershed Control Program
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
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 WCP plan. All existing zoning or land use regulations apply
within that area, but additional requirements apply within the overlay district. Within your
watershed, particularly within the area of influence, there are many different kinds of regulatory
controls you may wish to consider:
• Large-lot or low-density zoning.
• Limits on certain types of land use except by special permit.
• Impact fees.
• Submission and approval of a watershed protection plan or impact study as a condition for
development of a subdivision or apartment complex.
• Performance standards, which permit development but limit the impact of the
development.
More detail on each of these types of ordinances is found in Appendix E. Examples of
source water protection ordinances can be found on EPA's website at
http://www.epa.gov/owow/nps/ordinance/osm7.htm.
Land Acquisition/Conservation Easements
Acquisition of watershed land by the 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.
LT2ESWTR Toolbox Guidance Manual 2-34 April 2010
-------
2. Watershed Control Program
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.htmfor frequently asked questions about
easements and for an example of a model easement for use in the state of Michigan. The Land
Trust Alliance (http://www.lta.org), a trade organization for land trusts, has published handbooks
on designing and managing conservation easement programs.
Other government agencies, such as the U.S. Forest Service or state natural resource
departments, may be able to buy parcels in your watershed if you are unable to afford to purchase
all the land that needs to be protected.
2.4.3.2 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 WCP 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).
LT2ESWTR Toolbox Guidance Manual 2-35 April 2010
-------
2. Watershed Control Program
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 cannot
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
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)(2)(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 WCP
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 (CWSRF) can be used to fund projects associated with wastewater treatment and
watershed and estuary management. See www.epa.gov/owm/cwfmance/cwsrf/index.htm for more
information.
Concentrated 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 CAFOs (see Appendix E). EPA recently issued a rule that changed the requirements on
CAFOs that must apply for 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 BMPs primarily designed to reduce nitrate and phosphorus
LT2ESWTR Toolbox Guidance Manual 2-36 April 2010
-------
2. Watershed Control Program
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
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 (CSOs)
Combined sewers carry both sewage and stormwater 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 stormwater 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 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. Stormwater BMPs can
also reduce the impact of CSOs.
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
LT2ESWTR Toolbox Guidance Manual 2-3 7 April 2010
-------
2. Watershed Control Program
sewage backs up into basements, streets, and surface water. SSOs discharging to surface water
are prohibited under the CWA. 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
Municipal separate storm sewer systems (MS4s) in areas with populations of more
than 100,000 are also required to obtain NPDES permits. Information on storm sewer outfall
locations, volume discharged, conventional pollutant loads, and existence of illicit discharges is
submitted as part of the permit application process (U.S. EPA 1996). In addition, these MS4s
must develop management plans addressing items such as outfall monitoring, structural and
nonstructural BMPs to be implemented, and identification and elimination of illicit discharges.
Illicit discharges to MS4s include any non-stormwater discharges, such as discharges that should
be connected to sanitary sewers (e.g., water from sinks, floor drains, and occasionally toilets),
illegal dumping of sewage from recreational vehicles, sanitary sewer overflow backing up through
manhole covers into storm drains, effluent from failing septic systems, water from sump pumps,
etc.
Small MS4s (serving areas with populations of less than 100,000), with some exceptions,
are subject to NPDES permit requirements if they are located in "urbanized areas" as determined
by the Bureau of the Census. Those MS4s subject to NPDES permits must implement "control
measures" in six areas, including a plan for eliminating illicit discharges (U.S. EPA 2000b).
PWSs should work with all MS4 utilities in the area of influence to gather existing
information about stormwater 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
of Cryptosporidium; more detailed descriptions are provided in Appendix E. Your WCP 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.
LT2ESWTR Toolbox Guidance Manual 2-38 April 2010
-------
2. Watershed Control Program
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.
BMPs that can reduce pathogen loading include the following:
• Composting.
• Waste management (manure storage and land application).
• Grazing management.
• F eedl ot runoff diver si 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 adjacent streams or
lakes.
• USDA (2000) recommends that buffer and filter strips be considered secondary practices
for pathogen control and be used in conjunction with control measures.
LT2ESWTR Toolbox Guidance Manual 2-39 April 2010
-------
2. Watershed Control Program
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.
• 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.
LT2ESWTR Toolbox Guidance Manual 2-40 April 2010
-------
2. Watershed Control Program
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.htm for fact sheets on technologies and BMPs
municipalities can use to reduce contamination from wastewater and stormwater.
Buffer Zones
• For watersheds in urban areas, buffer zones help to protect development on the floodplain
from being damaged when the water is high, as well as protect the stream from the effects
of the development.
• The extent to which buffer zones reduce Cryptosporidium loading is not well understood;
therefore, they should be used to augment, rather than replace, other watershed
management practices.
Dry Detention Basins
• Dry detention basins temporarily store stormwater runoff and release the water slowly to
allow for settling of particulates and the reduction of peak flows.
Infiltration Devices
• Infiltration devices remove pathogens and particles by adsorption onto soil particles and
filtration as the water moves through the soil to the ground water. Infiltration devices
include (NALMS 2000):
- infiltration basins
infiltration trenches
dry wells
LT2ESWTR Toolbox Guidance Manual 2-41 April 2010
-------
2. Watershed Control Program
Sand Filters
• Sand filters can be used to treat stormwater 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 stormwater or other polluted water.
Runoff Diversion
• Structures can be installed in urban settings to divert clean water flow before it reaches a
contamination source. Structures that channel runoff away from contamination sources
include stormwater conveyances, such as:
swales
- gutters
channels
drains
sewers
Pet Waste Management
• Municipalities can implement pet waste management programs to encourage pet owners to
properly collect and dispose of their animals' waste.
LT2ESWTR Toolbox Guidance Manual 2-42 April 2010
-------
2. Watershed Control Program
Water Conservation
• Can help preserve the amount of water available for use, especially during times of
drought.
• Can also decrease the amount of wastewater and stormwater generated, thereby protecting
the quality of the water supply (U.S. EPA 2002d).
• The following are examples of water conservation methods:
low-flow toilets and showerheads
reducing lawn watering
Low Impact Development
• Low impact development tries to reduce the amount of impervious cover, increase natural
lands set aside for conservation, and use pervious areas for more effective stormwater
treatment of residential and commercial developments.
Septic Systems
• 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
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
LT2ESWTR Toolbox Guidance Manual 2-43 April 2010
-------
2. Watershed Control Program
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.
LT2ESWTR Toolbox Guidance Manual 2-44 April 2010
-------
2. Watershed Control Program
2.5 References
Amirtharajah, A., M.H. Young, K.D. Pennell, J.L. Steiner, D.S. Fisher, D.M. Endale, and J.P.
Campbell. 2002. Field Transport of Cryptosporidium Surrogate in a Grazed Catchment.
Denver: Awwa Research Foundation.
Arora, H., M. LeChevallier, R. Aboytes, E. Bouwer, C. O'Melia, W. Ball, W. Weis, and T.
Speth. Full-scale evaluation of riverbank filtration at three Midwest water treatment plants. In:
Proceedings of the AWWA Water Quality Technology Conference, Salt Lake City, Utah,
November, 2000. Denver: American Water Works Association.
Ashendorff, A., M. Principe, A. Seeley, J. LaDuca, L. Beckhardt, W. Faber, and J. Mantus.
1997. Watershed Protection for New York City's Supply. Jour. AWWA. 89(3):75-88.
Atherholt, T., M. LeChevallier, W. Norton, and J. Rosen. 1998. Effect of rainfall on Giardia
and Cryptosporidium. Jour. AWWA. 90:9:66-80.
Atwill, E.R., L. Hou, B.M. Karle, T. Harter, K.W. Tate, and R.A. Dahlgren. 2002. Transport
of Cryptosporidium parvum oocysts through vegetated buffer strips and estimated filtration
efficiency. Appl. Environ. Microbiol. 68(11): 5517-27.
Atwill, E.R., S.M. Camargo, R. Phillips, L.H. Alonso, K.W. Tate, W.A. Jensen, J. Bennet, S.
Little, T.P. Salmon. 2001. Quantitative shedding of two genotypes of Cryptosporidium parvum
in California ground squirrels (Spermophilus beecheyi). Appl. Environ. Microbiol. 67(6):2840-
43.
AWWA, 1999. Source Water Protection: Effective Tools and Techniques You Can Use. 1999
Participant Manual. Denver: American Water Works Association. Developed for a technical
training seminar for public water suppliers and local officials.
AwwaRF. 1991. Effective Watershed Management for Surface Water Supplies. Prepared by
R.W. Robbins, J.L. Glicker, D.M. Bloem, and B.M. Niss, Portland (OR) Water Bureau.
Denver: American Water Works Association Research Foundation.
AwwaRF. 2001. Guidance to Utilities on Building Alliances with Watershed Stakeholders.
Denver: American Waterworks Association Research Foundation. Order No. 90826.
Bitton, G. 2005. Microbial Indicators of Fecal Contamination: Application to Microbial
Source Tracking. Gainesville, Florida: University of Florida, 71 pp.
http://www.florida-stormwater.org/pdfs/FSAMicrobialSourceTrackingReport.pdf.
Blewett, DA. 1989. Disinfection and oocysts. Cryptosporidiosis Proceedings of Ma Pint
International Workshop, 1988. Ed K.W. Amur and D.A. Blewett. Edinburgh: The Animal
Disease Research Association. 107-116.
LT2ESWTR Toolbox Guidance Manual 2-45 April 2010
-------
2. Watershed Control Program
Brush, C.F., M.F. Walter, LJ. Anguish, and W.C. Ghiorse. 1998. Influence of pretreatment
and experimental conditions on electrophoretic mobility and hydrophobicity of
Cryptosporidium parvum oocysts. Appl. Env. Microbiol. 64: 4439-4445.
Brush, C.F., W.C. Ghiorse, LJ. Anguish, J.-Y. Parlange, andH.G. Grimes. 1999. Transport
of Cryptosporidium oocysts through saturated columns. Env. Qual. 28: 809-815.
Capacasa, J. 2005. Partners and Possibilities: Schuylkill Action Network. InProc. of 2005
Source Water Protection Symposium. Denver, CO: AWWA.
CCME (Canadian Council of Ministers of the Environment). 2002. From Source to Tap:
Guidance on the Multi-Barrier Approach to Safe Drinking Water. Developed by the
Federal-Provincial-Territorial Committee on Drinking Water and the CCME Water Quality
Task Group. Winnipeg, Manitoba, Canada: CCME, 242 pp.
http://www.ccme.ca/assets/pdf/mba eng.pdf.
COM (Camp Dresser & McKee, Inc.). 2002. Source Water Protection Reference Manual
(CD-ROM). Denver, CO: AWWA Research Foundation and AWWA.
Center for Watershed Protection 1999. An Introduction to Better Site Design. Watershed
Protection Techniques 3(2): 623-632.
Chauret, C.; S. Springthorpe, and S. Sattar. 1999. Fate of Cryptosporidium Oocysts,
Giardia Cysts, and Microbial Indicators During Wastewater Treatment and Anaerobic
Sludge Digestion. Can. J. Microbiol.., 45, 257.
Corsi, S.; J. Walker; R. Waschbusch, and J. Standridge. 2003. Sources and Variability of
Cryptosporidium in the Milwaukee River Watershed (Report 99-HHE-2). Alexandria, VA:
Water Environment Research Foundation.
Coyne, M.S. and R.L. Blevins. 1995. Fecal bacteria in surface runoff from poultry-manured
fields. In K.Steele (ed.), Animal Water and the Land-Water Interface, pp. 77-87. Boca
Raton: Lewis Publishers, CRC Press.
CRC (Cooperative Research Centre for Water Quality and Treatment). 2004. Pathogen
Movement and Survival in Catchments, Groundwaters and Raw Water Storages. Salisbury,
South Australia: The Cooperative Research Centre for Water Quality and Treatment. 17 pp.
http://www. wqra.com.au/crc_archive/dwfacts/techfact_pathogen_movement.PDF.
Crockett, C. 2005. Personal Communication. (December 14, 2005).
Crockett, C. L. Gaffney, D. Bane, and G. Cavallo. 2005. How to Prioritize and Implement
Projects to Protect and Improve Water Quality. In Proc. of 2005 Source Water Protection
Symposium. Denver, CO: AWWA.
Crockett, C. S. [N.d.] The Role Of Wastewater Treatment In Protecting Water Supplies
Against Emerging Pathogens. Water Environment Research. Forthcoming 2006.
LT2ESWTR Toolbox Guidance Manual 2-46 April 2010
-------
2. Watershed Control Program
Crockett, C. S., and C. Johnson. 2000. Philadelphia Investigates Cryptosporidium : Five
Years of Monitoring, Treatment and Epidemiological Studies. InProc. oftheAWWA Water
Quality Technology Conference. Denver, CO: AWWA.
Crockett, C.S., and C.N. Haas. 1997. Understanding protozoa in your watershed. J
AWWA 89(9): 62-73.
Curriero, F.C., J.A. Patz, J.B. Rose, and S. Lele. The association between extreme
precipitation and waterborne disease outbreaks in the United States, 1948-1994. Am. J.
Public Health 91(8): 1194-99.
Davies, C., C. Kaucner, N. Altavilla, N. Ashbolt, C. Ferguson, M. Krogh, W. Hijnen, G.
Medema, and D. Deere. 2005. Fate and Transport of Surface Water Pathogens in
Watersheds. Denver, CO: AWWA and AwwaRF, 261 pp.
Ernst, C. 2004. Protecting the Source: Land Conservation and the Future of America's
Drinking Water. Trust for Public Land (Washington, D.C.) and AWWA (Denver, CO), 52
pp.
Ernst, C. and K. Hart. 2005. Path to Protection: Ten Strategies for Successful Source Water
Protection. Washington, D.C.: Trust for Public Land, 23 pp.
Fact Sheet 2.0. Office of Water. EPA 833-F-00-002. www.epa.gov/npdes/pubs/fact2-0.pdf.
Website accessed March 2003.
Fairfax County. 2001. Wastewater Treatment Plant.
www.co.fairfax.va.us/gov/DPWES/utilities/wwtrmnt_0600.htm. Last modified May 16,
2001. Website accessed January 2002.
Finstein, M. 2004. Protecting Watersheds from Cryptosporidium in manure: A Literature
Review. Jour. AWWA. 96(2): 114-116.
Fleming, R., D. Hocking, H. Fraser, and D. Alves. 1999. Extent and Magnitude of
Agricultural Sources of Cryptosporidium in Surface Water. Project #40. National Soil and
Water Conservation Program. Submitted to Ontario Farm Environmental Coalition, c/o
Ontario Federation of Agriculture, on behalf of Agricultural Adaptation Council, West
Guelph, Ontario. Final Report. December 1999. Downloaded January 2002 from
http://www.ridgetownc.on.ca/research/reports/subject/waterhtrn.
Fletcher, A., S. Davis, and G. Pyke. 2004. Water Utility/Agricultural Alliances: Working
Together for Cleaner Water. AWWA Research Foundation, Denver, CO. 163 pp.
Frankenberger, J.R. et al. 1999. A GIS-based variable source area hydrology model.
Hydrologic Processes 13:805-822.
Gburek, W.J. and H.B. Pionke. 1995. Management strategies for land-based disposal of
animal wastes: Hydrologic implications, pp. 313-323. In K.Steele (ed.), Animal Water and
the Land-Water Interface, pp. 77-87. Boca Raton: Lewis Publishers, CRC Press.
LT2ESWTR Toolbox Guidance Manual 2-47 April 2010
-------
2. Watershed Control Program
Gennaccaro, A., M. McLaughlin, W. Quintero-Betancourt, D. Huffman, and J. Rose. 2003.
Infectious Cryptosporidium parvum Oocysts in Final Reclaimed Effluent. Appl. Environ.
Microbiol., 69(8), 4983-4984.
GeoLogics Corporation (Alexandria, VA). 2004. EPA Regional Priority AFO Science
Question Synthesis Document - Pharmaceuticals and Pathogens. Washington, D.C.: U.S.
EPA Office of Science Policy and U.S. EPA Office of Research and Development.
Workshop Review Draft: Supporting Documentation for the EPA Regional Science
Workshop on Animal Feeding Operations (AFOs) - Science and Technical Support Needs,
December 6-9, 2004, College Park, Maryland, 60 pp.
http://www.manure.umn.edu/regulatorv/4Pharmaceuticals%20and%20Pathogens.pdf
Gracyk, T, and J. Grace. 2003. Maryland Department of the Environment Cryptosporidium
Occurrence Study in the Potomac River. In Proc. oftheAWWA Water Quality Technology
Conference. Denver, CO: AWWA.
Graczyk, T.K., R. Payer, J.M. Trout, EJ. Lewis, C.A. Farley, I. Sulaiman, and A.A. Lai. 1998.
Giardia sp. cysts and infectious Cryptosporidium parvum oocysts in the feces of migratory
Canada geese (Branta canadensis). Appl. Env. Microbiol. 64(7): 2736-2738.
Gregory, J. 1994. Cryptosporidium in water: Treatment and monitoring methods. Filtr. Sep.
31(3): 283-289.
Gullick, R., R. Brown, and D. Cornwell. 2007. Source Water Protection for Concentrated
Animal Feeding Operations: A Guide for Drinking Water Utilities. Report #3020. Denver, CO:
AWWA and AwwaRF.
http://www.waterresearchfoundation.org/research/TopicsAndProjects/projectSnapshot.aspx7pn
=3020.
Hansen, J.S., and I.E. Ongerth. 1991. Effects of time and watershed characteristics on the
concentration of Cryptosporidium oocysts in river water. Appl. Environ. Microbiol. 57(10):
27902795.
Harter, T., S. Wagner, and E.R. Atwill. 2000. Colloid transport and filtration of
Cryptosporidium parvum in sandy soils and aquifer sediments. Env. Sci. Tech. 34(1): 62-70.
Heisz, M. 1997. In vitro survival of Cryptosporidium oocysts in natural waters. International
Symposium on Waterborne Cryptosporidium. Newport Beach, March 1997.
Hopper, K. and C. Ernst. 2005. Source Protection Handbook: Using Conservation to Protect
Drinking Water Supplies. Trust for Public Land (Washington, D.C.) and AWWA (Denver,
CO), 88 pp.
Huetink, R.E., J.W. van der Giessen, J.P. Noordhuizen, and H.W. Ploeger. Epidemiology of
Cryptosporidium spp. and Giardia duodenalis on a dairy farm. Veterinary Parasitology 102(1-
2): 53 -67.
LT2ESWTR Toolbox Guidance Manual 2-48 April 2010
-------
2. Watershed Control Program
Hurst, CJ. 1997. Modeling the fate of microorganisms in water, wastewater, and soil. Manual
of Environmental Microbiology. Ed. CJ. Hurst, G.R. Knudsen, MJ. Mclnerney, L.D.
Stetzenback, andM.V. Walter. Ch. 22. Washington, DC: American Society for Microbiology.
John, D.E. and J.B. Rose. 2005. Review of Factors Affecting Microbial Survival in
Groundwater. Env. Sci. Tech. 39(19): 7345-7356.
Kaplan, L.A., LJ. Standley, J.D. Newbold, J.H. Standridge, A.L. Mager, S.M. Kluender, L.L.
Peterson, D.B. Smith, W.C. Hession, and P. Luitweiler. 2002. Evaluation of Sources of
Pathogens and NOM in Watersheds. Denver: Awwa Research Foundation and AWWA.
Kistemann, T., T. Classen, C. Koch, F. Dangendorf, R. Fischeder, J. Gebel, V. Vacata, and M.
Exner. 2002. Microbial load of drinking water reservoir tributaries during extreme rainfall and
runoff. Appl. Environ. Microbiol. 68(5):2188-97.
Klett, Brian. 1996. Delineation of a sixty day travel buffer for the protection of the New York
City Water Supply. In: Proceedings of the AWRA Session on New York City Water Supplies at
the Symposium on Watershed Restoration Management: Physical, Chemical, and Biological
Considerations. 103-109. JJ. McDonnell, DJ. Leopold, J.B. Stribling, and L.R. Neville,
editors. American Water Resources Association, Herndon, Virginia, TPS-96-2.
LeChevallier, M., W. Norton, M. Abbaszadegan, and T. Atherholt. 1998. Variation in Giardia
and Cryptosporidium Levels in the Delaware River. Voorhees, NJ: American Water Works
Service Company, 124 pp.
Lipp, E.K., S.A. Farrah, and J.B. Rose. Assessment and impact of microbial fecal pollution and
human enteric pathogens in a coastal community. Marine Pollution Bulletin 42(4): 286-93.
Lisle, J.T., and J.B. Rose. 1995 . Cryptosporidium contamination of water in the U.S. and UK:
a mini-review. Water SRT—Aqua 44(3): 103-117.
Mawdsley, J.L., A.E. Brooks, and R.J. Merry. 1996. Movement of the protozoan pathogen
Cryptosporidiumparvum through three contrasting soil types. Biol. Fertil. Soils 21(1-2): 30-36.
McCuin, R. and J. Clancy. 2004. Cryptosporidium occurrence, removal, and inactivation
methods for wastewaters. Alexandria, VA: Water Environment Research Foundation.
Medema, G., F. Schets, P. Teunis, and A. Havelaar. 1998. Sedimentation of free and attached
Cryptosporidium oocysts and Giardia cysts in water. Appl. Environ. Microbiol. 64(1): 4460-
4466.
Medema, G.J., and J.F. Schijven. 2001. Modeling the sewage discharge and dispersion of
Cryptosporidium and Giardia in surface water. Water Res. 35(18): 4307-16.
Metcalf and Eddy. 1994. Final CSO Conceptual Plan and System Master Plan: Part IICSO
Strategies. Prepared for the Massachusetts Water Resources Authority. Wakefield,
Massachusetts.
LT2ESWTR Toolbox Guidance Manual 2-49 April 2010
-------
2. Watershed Control Program
Moore, J.A. et al. 1988. Evaluating coliform concentrations in runoff from various animal
waste management systems. Special Report 817. Agricultural Experimental Stations, Oregon
State University, Corvallis, and the U.S.D.A., Portland, OR.
MWRD. 1999. Tunnel and Reservoir Plan. Metropolitan Water Reclamation District.
www.mwrdgc.dst.il.us/plants/tarp.htm. Last modified August 6, 1999. Website accessed
January 2002.
NEIWPCC (New England Interstate Water Pollution Control Commission). 2000. Source
Protection: A National Guidance Manual for Surface Water Supplies. Lowell, MA: NEIWPCC.
Available at http://www.neiwpcc.org (click on "Publications", then click "Technical Guides"
and find the report).
North American Lake Management Society (NALMS). March 2000. Best Management
Practices to Protect Water Quality.
NRCS. 1992. Agricultural Waste Management Field Handbook .
NRCS. 1999. National Handbook of Conservation Practices. Natural Resources Conservation
Service, http://www.ftw.nrcs.usda.gov/nhcp 2.html.
Ohio State University Extension. 1992. Ohio Livestock Manure and Wastewater Management
Guide, Bulletin 604. http://ohioline.osu.edu/b604/index.html. Website accessed March 2003.
Ohio State University Extension. No date. Getting Started Grazing. Edited by Henry
Bartholomew, http://ohioline.osu.edu/gsg/index.html.
Ohio State University Extension. No date. Vegetation Filter Strips: Application, Installation,
and Maintenance. AEX-467-94. http://ohioline.osu.edu/aex-fact/0467.html. Website accessed
March 2003.
Olson, M.E., J. Goh, M. Phillips, N. Guselle, and T.A. McAllister. 1999. Giardia cyst and
Cryptosporidium oocyst survival in water, soil, and cattle feces. J. Environ. Qual. 28(6): 1991-
1996.
Payment, P., R. Plante, P. Cejka. 2001. Removal of indicator bacteria, human enteric viruses,
Giardia cysts, and Cryptosporidium oocysts at a large wastewater primary treatment facility.
Can. Microbiol. 47(3): 188-93.
Perz, J.F. and S.M. Le Blancq. 2001. Cryptosporidiumparvum infection involving novel
genotypes in wildlife from lower New York State. Appl. Environ. Microbiol. 67(3): 1154-1162.
Philadelphia Water Department. 2003. Philadelphia Projects. Website.
http://www.phillywater.org/Schuylkill/proiects%20pages/ProjectMain.htmtfGoose%20Project.
Undated. Accessed February 12, 2003.
Robertson, L.J., A.T. Campbell, andH.V. Smith.1992. Survival of Cryptosporidium parvum
oocysts under various environmental pressures. Appl. Environ. Microbiol. 58: 3494-3500.
LT2ESWTR Toolbox Guidance Manual 2-50 April 2010
-------
2. Watershed Control Program
Rose, J.B. 1997. Environmental ecology of Cryptosporidium and public health implications.
Annual Rev. Public Health 18:135-161.
Santin, M., J. Trout, L. Xiao, L. Zhou, E. Greiner, and R. Payer. 2004. Prevalence And Age
Related Variation Of Cryptosporidium Species And Genotypes In Dairy Calves. Veterinary
Parasitology. 122:103-117.
Schueler, T.R. 1999. Microbes and urban watersheds: concentrations, sources, and pathways.
Watershed Protection Techniques. 3(1): 554-565. http://www.stormwatercenter.net.
Scott, T.M., J.B. Rose, T.M. Jenkins, S.R. Farrah, and J. Lukasik. 2002. Microbial Source
Tracking: Current Methodology and Future Directions. Applied and Environmental
Microbiology, 68(12): 5796-5803. http://aem.asm.org/cgi/content/full/68/12/5796.
Sischo, W.M. E.R. Atwill, L.E. Lanyon, and J. George. 2000. Cryptosporidia on dairy farms
and the role these farms may have in contaminating surface water supplies in the northeastern
United States. Preventive Veterinary Medicine 43(4): 253-67.
Sobrinho, J.A.H., J.S. Rosen, M.W. LeChevallier, M.M. Frey, and J.L. Clancy. 2001.
Variability of Pathogens and Indicators in Source Waters. In: Proceedings of AWWA Water
Quality Technology Conference, Nov. 11-15, 2001, Nashville, Tennessee. Session M8.
States, S., K. Stadterman, L. Ammon, P. Vogel, J. Baldizar, D. Wright, L. Conley, J. Sykora.
1997. Protozoa in river water: sources, occurrence, and treatment. J. AWWA 89(9): 74-83.
Stern, D. 1996. Initial investigation of the sources and sinks of Cryptosporidium spp. and
Giardia spp. within the watersheds of the New York City water supply system. In: Proceedings
of the AWRA Session on New York City Water Supplies at the Symposium on Watershed
Restoration Management: Physical, Chemical, and Biological Considerations. 111-121. J.J.
McDonnell, D.J. Leopold, J.B. Stribling, and L.R. Neville, editors. American Water Resources
Association, Herndon, Virginia, TPS96-2.
Sturdevant Rees, P.L., S.C. Long, R. Baker, D.H. Bordeau, R. Pei, and P.K. Barten. N.d.
Development of Event-Based Pathogen Monitoring Strategies for Watersheds. Denver: Awwa
Research Foundation (forthcoming).
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.
Tetra Tech, Inc. 2003. Getting in Step: A Guide for Conducting Watershed Outreach
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
Near-Surface Transport of Cryptosporidium parvum from Vegetated and Nonvegetated
LT2ESWTR Toolbox Guidance Manual 2-51 April 2010
-------
2. Watershed Control Program
Surfaces. J. Environ. Qual. 33:984-993 (2004).
http ://j eg. scij ournals. org/cgi/content/full/3 3/3/984.
Tsuchihashi, R., F. Loge, and J. Darby. 2003. Detection of Cryptosporidiumparvum in
Secondary Effluents Using a Most Probable Number - Polymerase Chain Reaction Assay.
Water Environment Research. 75(4):292-299.
U.S. Department of Agriculture. 2000. Waterborne Pathogens in Agricultural Watersheds.
Watershed Science Institute. ftp://ftp-
fc.sc.egov.usda.gov/WSI/pdffiles/Pathogens_in_Agricultural_Watersheds.pdf. Website
accessed March 2010.
U.S. EPA 1999b. Combined Sewer Overflow Management Fact Sheet: Sewer Separation.
Office of Water. EPA 832-F-99-041. September, http://www.epa.gov/npdes/pubs/sepa.pdf
Website accessed March 2003.
U.S. EPA 2000c. Wastewater Technology Fact Sheet. Wetlands: Subsurface Flow. Office of
Water EPA 832-F-00-023. September, http://www.epa.gov/owm/mtb/wetlands-
subsurface flow.pdf Website accessed March 2003.
U.S. EPA 200 If Sanitary Sewer Overflows Frequently Asked Questions. Office of Wastewater
Management. Web page updated March 20, 2001.
http://cfpub.epa.gov/npdes/faqs.cfm?program_id=4. Website accessed January 2002.
U.S. EPA 2002c. Polluted Runoff (Nonpoint Source Pollution: Managing Nonpoint Source
Pollution from Forestry. Pointer No. 8. EPA 841-F-96-004H. Office of Wetlands, Oceans, and
Watersheds, www.epa.gov/owow/nps/facts/point8.htm. Last modified August 28, 2002.
Website accessed March 2003.
U.S. EPA 2009. Activity Update: Funding Decentralized Wastewater Systems Using the Clean
Water State Revolving Fund. Office of Water (4204M). EPA 832-F-09-005. 7 pages.
http://www.epa.gov/owm/septic/pubs/arra septic fs.pdf. Website accessed March 2010.
U.S. EPA. 1994. Combined Sewer Overflow (CSO) Policy; Notice. Federal Register
59(75): 1868818698. April 19.
U.S. EPA. 1996. Overview of the Storm Water Program. Office of Water. EPA 833-R-96-008.
June. 42 pp. http://www.epa.gov/npdes/pubs/owmO 195.pdf. Website accessed March 2003.
U.S. EPA. 1997. State Source Water Assessment and Protection Programs. Final Guidance.
Office of Water. EPA 816-R-97-009. August.
http://www.epa.gov/safewater/sourcewater/pubs/swpguidance.pdf
U.S. EPA. 1999a. Protecting Sources of Drinking Water: Selected Case Studies in Watershed
Management. Office of Water. EPA 816-R-98-019, 38 pp. April.
http://www.epa.gov/safewater/sourcewater/pubs/swpcases.pdf Accessed December 10, 2002.
LT2ESWTR Toolbox Guidance Manual 2-52 April 2010
-------
2. Watershed Control Program
U.S. EPA. 2000a. Wastewater Technology Fact Sheet: Granular Activated Carbon Adsorption
and Regeneration. Office of Water. EPA 832-F-00-017. September.
http://www.epa.gov/npdes/pubs/carbon absorption.pdfU.S. EPA 2000b. Storm Water Phase II
Final Rule: Small MS4 Storm Water Program Overview.
U.S. EPA. 2000d. Watershed Success Stories - Applying the Principles and Spirit of the Clean
Water Action Plan. Washington, DC: U.S. EPA, 68 pp.
http://www.blueprintjordanriver.slco.org/docToPdf/WatershedSuccessStor.pdf.
U.S. EPA. 2001a. Case Study of Local Source Water Protection Program—Burlington,
Vermont. Web page updated May 11, 2001.
http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm?action=Case_Studies.
U.S. EPA. 2001b. Case Study of Local Source Water Protection Program—Manchester, New
Hampshire. Web page updated November 26, 2002.
http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm?action=Case Studies. Accessed
on December 12, 2002.
U.S. EPA. 2001c. Case Study of Local Source Water Protection Program—Springfield,
Missouri. Web page updated November 26, 2002.
http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm?action=Case Studies.
U.S. EPA. 2001d. Proposed Revisions to CAFO Regulations (January 12, 2001; 66 FR 2960):
Frequently Asked Questions, http://www.epa.gov/npdes/pubs/cafo faq.pdf Downloaded
February, 2002.
U.S. EPA. 2001e. Secondary Treatment Standards.
http://cfpub.epa.gov/npdes/techbasedpermitting/sectreat.cfm. Last updated February 21, 2001.
Downloaded January 22, 2002.
U.S. EPA. 2001g. Protecting and Restoring America's Watersheds: Status, Trends, and
Initiatives in Watershed Management. EPA 840-R-00-001. Washington, D.C.: U.S. EPA Office
of Water, 56 pp. http://www.epa.gov/owow/protecting/.
U.S. EPA. 2002a. Preamble to Long Term 2 Enhanced Surface Water Treatment Rule. Draft.
November 6, 2002.
U.S. EPA. 2002b. Occurrence and Exposure Assessment for Long-Term 2 Enhanced Surface
Water Treatment Rule. Draft. Prepared by The Cadmus Group, Inc., Arlington, VA. March
2002.
U.S. EPA. 2002d. Source Water Protection: Best Management Practices and Other Measures
for Protecting Drinking Water Supplies. Washington, D.C.: U.S. EPA Office of Ground Water
and Drinking Water, 125 pp. http://www.epa.gov/watertrain/pdf/swpbmp.pdf.
U.S. EPA. 2003b. Introduction to EPA's Drinking Water Source Protection Programs.
Washington, D.C.: U.S. EPA Office of Ground Water and Drinking Water, 119 pp.
http://www.epa.gov/watertrain/pdf/swp.pdf.
LT2ESWTR Toolbox Guidance Manual 2-53 April 2010
-------
2. Watershed Control Program
U.S. EPA. 2005a. Case Studies of Local Source Water Protection. U.S. EPA Office of Ground
Water and Drinking Water, Washington, D.C.
http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm7action=Case Studies.
U.S. EPA. 2005b. Section 319 Nonpoint Success Stories Website. Washington, DC: U.S. EPA
Office of Water. EPA 841-F-05-004. www.epa.gov/owow/nps/Success319.
U.S. EPA. 2005c. Microbial Source Tracking Guide Document. Cincinnati, Ohio: U.S. EPA
Office of Research and Development. EPA/600-R-05-064, 133 pp., June 2005.
http://www.calcoast.org/news/MSTGuide.pdf
U.S. EPA. 2005d. Draft - Handbook for Developing Watershed Plans to Restore and Protect
our Waters. U.S. EPA Office of Water. EPA 841-B-05-005, 414 pp., October 2005.
http://www.epa.gov/owow/nps/watershed handbook.
U.S. EPA. 2006. Water Conservation Practices for Homeowners: Public Education and
Outreach on Storm Water Impacts.
http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail
&bmp=2&minmeasure= 1. Last updated May 24, 2006. Downloaded March 17, 2010.
U.S. EPA. 2008. National Pollutant Discharge Elimination System Permit Regulation and
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
City Strategy. Washington, DC: National Academy of Sciences.
Vendrall, P.F., K.A. Teague, and D.W. Wolf. 1997. Pathogen indicator organism die-off in soil.
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.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.
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.ncbi.nlm.nih.gov/pmc/articles/PMC93339/.
Yeghiazarian, L., P. Kalita, M. Kuhlenschmidt, S. McLaughlin, and C. Montemagno. 2004. Field
Calibration and Verification of a Pathogen Transport Model. Washington, DC: WERF.
LT2ESWTR Toolbox Guidance Manual 2-54 April 2010
-------
2. Watershed Control Program
Young, R.A., T. Huntrods, and W. Anderson. 1980. Effectiveness of vegetated buffer strips in
controlling pollution from feedlot runoff. J. Environ. Qual. 9:483-487.
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.
LT2ESWTR Toolbox Guidance Manual 2-55 April 2010
-------
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 monitoring using an alternative procedure for managing
the timing or level of withdrawal. This monitoring must be conducted in addition to and
concurrently with monitoring conducted using the existing intake or withdrawal practice. Since
the LT2ESWTR requires that alternative monitoring be conducted concurrently with source
water monitoring, this toolbox option needs to be evaluated prior to the start of source water
monitoring. After monitoring and with state approval, a system would then choose which
source, intake location, or intake procedure it will use based on bin classification results. (40
CFR141.716(b))
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.
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. It is
recommended that both drinking water programs and state water resource agencies be contacted
regarding putting new sources into service. 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.
LT2ESWTR Toolbox Guidance Manual 3-1 April 2010
-------
3. Alternative Source/Intake
3.2.1 Advantages and Disadvantages
The main advantage of changing sources 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
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.
LT2ESWTR Toolbox Guidance Manual 3-2 April 2010
-------
3. Alternative Source/Intake
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.
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.
LT2ESWTR Toolbox Guidance Manual 3-3 April 2010
-------
3. Alternative Source/Intake
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.
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.
LT2ESWTR Toolbox Guidance Manual 3-4 April 2010
-------
3. Alternative Source/Intake
3.3.3.2 Flow and River Hydraulics
Hydraulics of the river and the flow around the intake are extremely important in
determining the quality of water that enters the system. In general, portions of a stream or river
with lower velocities and less turbulence will contain less sediment and possibly less
Cryptosporidium oocysts. Care should also be taken to make sure that the design of the intake
does not cause turbulence which might stir up sediments.
3.3.3.3 Upstream Sources of Contamination
Any potential sources of contamination upstream of a new intake should be identified and
their impact considered with respect to both biological and chemical contamination.
Contaminant sources of particular concern for Cryptosporidium include animal feeding
operations and sewage outfalls. If an intake cannot be located upstream of such a source, then
locating it as far as possible downstream to allow time for particles to settle may be the next best
alternative. Analyses of the vulnerability of a stream source should be made on a regular basis.
Any changes in the vulnerability of a source to Cryptosporidium or other contaminants should be
reported to the primacy agency.
3.3.3.4 Seasonal Effects
Cryptosporidium concentrations tend to be higher during runoff events, particularly in the
spring. Although it is probably not feasible to cease withdrawals during such incidents, it may be
possible to alter flow rates and coagulant doses to offset the effect of such events.
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
141.716(b)(l)). If the system calculates its bin assignment based on this alternative timing, then
after the compliance deadline, it must continue to draw its source water in the same manner (40
CFR 141.716(b)(4)). 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
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
LT2ESWTR Toolbox Guidance Manual 3-5 April 2010
-------
3. Alternative Source/Intake
days, unless extreme conditions or situations arise that prevent sampling (40 CFR 141.702(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.
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.
LT2ESWTR Toolbox Guidance Manual 3-6 April 2010
-------
3. Alternative Source/Intake
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.
LT2ESWTR Toolbox Guidance Manual 3-7 April 2010
-------
4. Bank Filtration
4.1 Introduction
Bank filtration is a surface water pretreatment process that uses the bed or bank of a river
(or lake) and the adjacent aquifer as a natural filter. The natural filter performs most efficiently
when the surface water passes slowly through unconsolidated granular material. In such locations
and under normal ground water flow 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 (LT2ESWTR). 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 different contaminants and contaminant concentrations than bank filtrate because its
origin and flow pathways differ significantly. Ambient ground water should not be assumed to be
uncontaminated.
Aquifers suitable for bank filtration are composed of unconsolidated, granular material
(i.e., grains) and have open, interconnected pores that allow ground water to flow. Pathogen
removal is enhanced when fine-grained sediment is present along the flow path. Geologic units
consisting primarily of fine-grained (e.g., clay-sized) materials will have higher removal but will
be incapable of yielding economically significant water flow rates. In aquifers containing both
sand-sized and finer grains, the presence of fine grains increases the possibility that pathogens
will encounter a grain surface. This is because flow is slower and flow paths are longer than they
would be in aquifers without such fine grains. Microorganisms will be removed from flow as
they contact and attach to grain surfaces. Although microorganism (e.g., Cryptosporidium)
detachment can occur, it usually does so at slow rates (Harter et al. 2000). When little or no
LT2ESWTR Toolbox Guidance Manual 4-1 April 2010
-------
4. Bank Filtration
detachment occurs or when detachment is slow, microorganisms can become non-viable while
attached to grain surfaces. Thus, bank filtration provides physical removal, and in some cases,
inactivation, to remove pathogens from water supplies.
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 and monitoring requirements of
LT2ESWTR) may receive Cryptosporidium log removal credit. 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
LT2ESWTR Toolbox Guidance Manual 4-2 April 2010
-------
4. Bank Filtration
produced water from the bank filtration well. This will determine the initial bin classification for
these systems. Because their source water monitoring accounts for any bank filtration treatment,
these systems are not eligible for subsequent additional bank filtration credits (40 CFR
Systems using ground water under the direct influence of surface water (GWUDI) 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 Interim
Enhanced Surface Water Treatment Rule (IESWTR) or Long Term 1 Enhanced Surface Water
Treatment Rule (LT1ESWTR) (40 CFR 141.173(b) and 141.552(a)). 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 LT1ESWTR compliance.
Alternatively, PWSs may apply to the state for Cryptosporidium treatment credit using a
DOP (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 DOP
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
DOP 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.
LT2ESWTR Toolbox Guidance Manual 4-3 April 2010
-------
4. Bank Filtration
Systems using horizontal or vertical wells located at least 25 feet from the surface water
source are eligible for a 0.5 log removal credit and those located at least 50 feet from the
surface water source are eligible for a 1.0 log removal credit.
- Systems with vertical wells must identify the distance to surface water using the
floodway boundary or 100 year flood elevation boundary as delineated on Federal
Emergency Management Agency (FEMA) Flood Insurance Rate maps.
- 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 should 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 should 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 millimeter (mm) in diameter.
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 141.717(c)(5)):
• Turbidity measurements must be performed on representative water samples from each
wellhead every four hours that the bank filtration system is in operation or more
frequently if required by the state.
• Continuous turbidity monitoring at each wellhead may be used.
• If the monthly average of daily maximum turbidity values at any well exceeds 1
nephelometric turbidity units (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.
LT2ESWTR Toolbox Guidance Manual 4-4 April 2010
-------
4. Bank Filtration
4.3 Toolbox Selection Considerations
Bank filtration is best suited to systems that are located adjacent to rivers with consistent
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 will be 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 DOP 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.
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 shown 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 byproducts (DBFs) precursors 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
LT2ESWTR Toolbox Guidance Manual 4-5 April 2010
-------
4. Bank Filtration
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 to nitrate and nitrite, 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 percent of polar organic contaminants at a site in central
Germany (Juttner 1995). Miettinen et al (1994) found that almost 90 percent of the high
molecular weight fraction of NOM had been removed at a bank filtration site in Finland.
Bank filtration can reduce treatment costs by reducing the need for more expensive
treatment technologies. Particle and microorganism removal during bank filtration allows for
more efficient filtration, use of membranes, and disinfection during subsequent treatment steps.
For example, decreasing the concentration of dissolved organic carbon during bank filtration can
reduce the amount of dissolved organic carbon that needs to be removed in a downstream
treatment process such as activated carbon filtration. 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 of flocculants to
drinking water (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 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.
LT2ESWTR Toolbox Guidance Manual 4-6 April 2010
-------
4. Bank Filtration
2000). Residence time depends on site-specific hydrogeology as well as bank filtration system
design. Bank filtration also smoothes out fluctuations in water temperature.
The removal of NOM during bank filtration is useful because NOM occurrence can result
in the production of harmful DBFs, as discussed above. In addition, moderate to high
concentrations of NOM in drinking water can result in unpleasant taste and odor. Finally, NOM
removal via bank filtration can also aid in the removal of a large variety of additional organic and
inorganic contaminants. These contaminants are sometimes made more mobile in surface and
ground waters due to a partitioning process whereby they are attached to NOM, which is
relatively mobile, and thereby carried along a flow path. The removal of NOM and associated
contaminants prior to above-ground treatment is likely to lessen the overall cost of water
treatment at a given facility.
4.3.1.2 Clogging of Pores
Clogging of the surface water - ground water interface by physical, chemical, and
biological processes has the potential to be a problem with any riverbank filtration system. 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 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.
Lastly, 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
LT2ESWTR Toolbox Guidance Manual 4-7 April 2010
-------
4. Bank Filtration
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 percent 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. The extent of erosion depends on both flood conditions and the resistance
of the bed and bank material that has been deposited at a particular site. During flooding, the
river channel may be scoured and fine sediments at the surface water - ground water interface
mobilized.
Much of the removal of the contaminants and microbes discussed previously 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 that 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 due to the
possible depletion of oxygen from biological activity during riverbank filtration pretreatment
(Kuehn et al. 2000). This oxygen depletion may lead to extremely anaerobic conditions over a
LT2ESWTR Toolbox Guidance Manual 4-8 April 2010
-------
4. Bank Filtration
portion of the flow path, which may result in the release of iron and manganese from the bank
sediment into the flowing water. This process occurs due to a redox reaction which reduces iron
and manganese to their water-soluble forms. This condition may necessitate the removal of these
metals during subsequent treatment steps (Kuehn et al. 2000, Tufenkji et al. 2002).
On the other hand, if the flow path between the riverbank and the well is long enough,
iron and manganese may precipitate onto the sediments in the subsurface before ever reaching
the well (Tufenkji et al. 2002). The aquifer becomes reaerated with increasing distance from the
riverbed. This is one reason for locating riverbank filtration wells greater than 25 or 50 feet from
the river, as discussed in section 4.5.2.2. Even though most contaminant removal occurs during
the first few centimeters of subsurface transport, the reaeration and associated precipitation
reactions in the aquifer may significantly improve water quality before it reaches the well
(Tufenkji et al. 2002). The location of the aerated and anaerobic portions of the aquifer vary
seasonally due to variable recharge, precipitation infiltration, microbial activity and changing
pumping rates.
Lastly, 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). These 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 should 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.
LT2ESWTR Toolbox Guidance Manual 4-9 April 2010
-------
4. Bank Filtration
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 (mj/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, providing many opportunities for
removal of microorganisms by straining or by their attachment to grain surfaces.
Many alluvial aquifers contain significant amounts of well-sorted, fine-grained sediments.
Alluvial aquifers are produced by fluvial 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,
LT2ESWTR Toolbox Guidance Manual
4-10
April 2010
-------
4. Bank Filtration
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 likely 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. Because they do not meet 40 CFR 141.717(c)(2), 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 meet 40 CFR 141.717(c)(2), and therefore would not be
eligible for bank filtration credit.
4.4.2.3 Partially Consolidated, Granular Aquifers
Granular aquifers formed by marine processes earlier than Quaternary alluvial or glacial
deposition may be partially consolidated by natural cement that fills pores, connects grains, and
makes the aquifer material less friable. Partially consolidated, granular aquifers are present
within the Atlantic Coastal Plain, Gulf Coast Lowland, Texas Coastal Upland, and Mississippi
LT2ESWTR Toolbox Guidance Manual 4-11 April 2010
-------
4. Bank Filtration
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. A triaxial compression test can also 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 (40 CFR 141.717(c)(2)). 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 under the LT2ESWTR and steps
recommended by EPA to perform such a characterization, which will ultimately determine
eligibility for bank filtration treatment credits under the LT2ESWTR.
The necessary steps are:
• Systems must characterize the aquifer at the proposed production well site to
determine aquifer properties.
- The recovered core length must be at least 90 percent of the total.
- 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.
EPA also recommends:
• The aquifer characterization should 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.
• Each sampled interval should be a composite of no more than 2 feet in length.
If core recovery is insufficient, another well core should be obtained.
LT2ESWTR Toolbox Guidance Manual 4-12 April 2010
-------
4. Bank Filtration
Each 2 foot long composite sample of recovered core should be examined in a laboratory
using sieve analysis to determine grain size distribution. Core intervals are typically 2 feet
long for a conventional split-spoon sampler and 3 or 4 feet long for soil probes (e.g., a
Giddings-type soil probe).
4.4.3.1 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).
LT2ESWTR Toolbox Guidance Manual 4-13 April 2010
-------
4. Bank Filtration
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:
• A balance, accurate to 0. Ig or 0.1 percent of test load for fine aggregate, or accurate to
0.5g or 0.1 percent of test load for a mixture of fine and coarse aggregate.
• Stackable sieves.
• A mechanical sieve shaker (for sample sizes greater than 20kg).
• 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 by hand begins. Sieving should be
continued until no more than 1 percent by mass of the material retained on an individual sieve
will pass through that sieve during 1 minute of continuous hand sieving. Lastly 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/Grow-
GrowResources.php?ResourceId=139.
ASTM also provides a search engine which allows the user to search for laboratories that
perform sieve analyses (http://www.astm.org/LABS/search.html). The EnviroDirectory™
provides listings for laboratories and drillers in New England, the Mid-Atlantic, and the Great
Lakes regions (http://www.envirodirectory.com).
LT2ESWTR Toolbox Guidance Manual 4-14 April 2010
-------
4. Bank Filtration
4.4.4 Site Selection as it Relates to Scour
Stream channel scour may often be an important consideration in choosing sites that are
suitable for riverbank filtration. This section discusses stream channel erosional processes in
general, as well as reasons sites with certain characteristics may be unsuitable for riverbank
filtration. Section 4.6 discusses the implications of periodic scour for riverbank filtration system
operations. Detailed information on fluvial erosional processes can be obtained from any of a
number of texts on fluvial geomorphology, hydrology, and river hydraulics (e.g., Leopold et al.
1964, Ritter et al. 1995, Chow 1964).
4.4.4.1 Stream Channel Erosional Processes
This discussion focuses on the dominant erosional processes of alluvial rivers because,
given the LT2ESWTR's aquifer requirements, such rivers may be among the most suitable for
bank filtration credits. Although many lake banks are also suitable sites for bank filtration, lakes
will not be discussed in detail in this section. Lake bank filtration settings typically do not change
rapidly with time and climate. Their hydrologic properties are not highly variable and thus do not
require the detailed evaluation discussed here for riverbank filtration settings.
The width, depth, and gradient of an undisturbed alluvial river has typically adjusted to
prevailing discharge conditions and sediment loads such that no net erosion or deposition occurs
over long time periods (Mackin 1948, Leopold and Maddock 1953). The dominant scouring
process in alluvial rivers is lateral migration (Exhibit 4.2). 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.
LT2ESWTR Toolbox Guidance Manual 4-15 April 2010
-------
4. Bank Filtration
Exhibit 4.2 Generalized Depiction of Stream Channel Lateral Migration
Net erosion at outside
bank of meander
(a) Map of a Stream Meander; (b) Cross-
section of the Channel from A-A' with
Channel Positions at 2 Successive Times (to,
and t-i); (c) Map of Stream Meander Showing
Location After Migration.
(a)
Net deposition at
inside bank
A1
(b)
(c)
• • • Location of river at time, t0
— Location of river at time, ti
LT2ESWTR Toolbox Guidance Manual
4-16
April 2010
-------
4. Bank Filtration
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.
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
Some sites may be unsuitable 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
LT2ESWTR Toolbox Guidance Manual 4-17 April 2010
-------
4. Bank Filtration
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.
The potential for scour can be evaluated first by examining the past frequency of high
flow and flood events. Data on flood history and discharge is typically available from the U.S.
Geological Survey, the Army Corps of Engineers, the U.S. 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.
LT2ESWTR Toolbox Guidance Manual 4-18 April 2010
-------
4. Bank Filtration
Sources of high flow and flood data
United States Geological Survey (USGS)
Main Page: http://water.usgs.gov
The National Flood Frequency (NFF) Program:
http://water.usgs.gov/pubs/wri/wri024168/pdf/entirereport.pdf
A computer program developed by the USGS for estimating the magnitude and frequency of
floods for ungaged sites. Since 1993, updated equations have been developed by the USGS for
various areas of the nation. These new equations have been incorporated into an updated
version of the NFF Program.
USGS Fact Sheets (listed by state):
http ://water.usgs. gov/wid/index-state.html
Includes NFF program methods for estimating flood magnitude and frequency (in rural and
urban areas) for: AL, AZ, AR, CA, CN, HI, LA, MD, MO, NV, NM, NC, OK, SC, SD, TX UT,
VT, VA, and WA. These fact sheets describe the application of the updated NFF Program to
various waterways within the specific state. Includes maps of each of the above state's
hydrologic regions, as well as regression equations and statistics.
WaterWatch:
http://water.usgs.gov/cgi-bin/dailvMainW?state=us&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.armv.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
16.6 16.1 15.6
15.8 15.314.7
Flood
Level
16.0
16.0
Gage
Zero
449.3
446 .1
Record
Level
31.80
29.58
Record
Date
07/1 0/93
07/1 6/93
LT2ESWTR Toolbox Guidance Manual
4-19
April 2010
-------
4. Bank Filtration
U.S. 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.
The Department of Homeland Security (FEMA)
Main Page: http://www.fema.gov/
Flood Hazard Mapping: http://www.fema.gov/fhm/
The flood maps describe where the flood risks are, based on local hydrology, topology,
precipitation, flood protection measures such as levees, and other scientific data. Fee to obtain
maps.
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 U.S. EPA (1975).
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 (40
CFR141.717(c)(6)).
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
LT2ESWTR Toolbox Guidance Manual 4-20 April 2010
-------
4. Bank Filtration
bank filtration even if the material overlying an infiltration gallery is 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 through a
demonstration of performance under 40 CFR 141.718(c).
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, 2001a). 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 200la). 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
2001a) 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,
Kentucky, is shown in Exhibit 4.5. It is elevated to prevent flood waters from entering it.
LT2ESWTR Toolbox Guidance Manual 4-21 April 2010
-------
4. Bank Filtration
Exhibit 4.3 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
X\\ "'/'
Note that the exhibit shows tortuous ground water flow at the micro-scale.
A
\/
LT2ESWTR Toolbox Guidance Manual
4-22
April 2010
-------
4. Bank Filtration
Exhibit 4.4 Schematic Showing Generalized Flow and Required Separation
Distance to a Horizontal Well With Three Laterals
Horizontal
Pumping
Well
Minimum 25
Feet for Log
Removal Credits
Bedrock
LT2ESWTR Toolbox Guidance Manual
4-23
April 2010
-------
4. Bank Filtration
Exhibit 4.5 Taking a Water Level Reading
The pump house for the horizontal collector well caisson is in the background.
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 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
200 la).
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.
LT2ESWTR Toolbox Guidance Manual
4-24
April 2010
-------
4. Bank Filtration
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 should 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. A number of 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 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.
LT2ESWTR Toolbox Guidance Manual 4-25 April 2010
-------
4. Bank Filtration
The remainder of this section discusses geophysical methods which may be of used to
construct 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 in Exhibit 4.6. 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, over-pumping can decrease 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 should
be investigated to provide additional information regarding the desirability of locating wells at
greater than required distances from the surface water source.
Exhibit 4.6 The Streambed of a Perched Stream Is Well above the Water
Table
LT2ESWTR Toolbox Guidance Manual 4-26 April 2010
-------
4. Bank Filtration
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 (GPR).
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 USGS,
gravity methods have been in use for over 15 years to evaluate changes in water storage in
aquifers. These methods can detect water table elevation changes of as little as a few inches
(Callegary 2003). Thus, gravity methods may be useful at riverbank filtration sites for assessing
the depth to water table, aquifer thickness, and seasonal effects on the dilution of infiltrating river
water with ambient groundwater. Magnetic surveying or magnetic anomolies can also be used in
hydrogeologic investigations. For example, clay infilling bedrock cavities can be detected due to
slight changes in the magnetic susceptibility of clay and most bedrock (Reynolds 1997).
Seismic methods are widely used in hydrogeologic investigations. Applied seismology
involves generating a signal through an explosion or other method at a specific time. The
generated seismic waves travel through the subsurface, are reflected and refracted back to the
surface, and the return signals are detected on monitoring instruments. The amount of time that
elapses is the basis for determining the nature of subsurface layers/materials (Reynolds 1997).
Reynolds (1997) provides a detailed example of the use of seismic refraction surveying for
locating the bedrock/alluvial interface at one particular site.
Seismic methods can be used to:
• Estimate depth to bedrock (ideal for riverbank filtration applications).
• Determine the nature of bedrock (e.g., cavernous) or location of cavities. Note that karst
buried by alluvium may contain unexpected ground water flowpaths.
LT2ESWTR Toolbox Guidance Manual 4-27 April 2010
-------
4. Bank Filtration
• Determine the location of faults that may juxtapose bedrock against alluvial material.
• Determine stratigraphy (useful where sands and clays may be interlayered).
• Estimate porosity prior to coring.
• 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 (EM) 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).
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 if
there is a significant contrast between river water and ambient ground water. Pulse-transient EM
(TEM) surveys (a type of EM method) may be useful in conceptualizing flow for riverbank
filtration. 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.
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 should be used. Generated radiowaves 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.
LT2ESWTR Toolbox Guidance Manual 4-28 April 2010
-------
4. Bank Filtration
Before choosing a specific geophysical method the following should be considered:
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. 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 screen. 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 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 web site can be used
to order these maps: http://www.fema.gov/hazard/map/flood.shtm.
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/plan/prevent/fhm/en_hyala.shtm. EPA recommends using the US Army
Corps of Engineers' Hydrologic Engineering Centers River Analysis System (HEC-RAS) model
for mapping floodway limits. The HEC-RAS software is available for free downloading from
http://www.hec.usace.army.mil/software/hec-ras/hecras-download.html. The user's manual,
applications guide, and hydraulic reference manual are available at
http://www.hec.usace. army.mil/publicati ons/pub_download. 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
LT2ESWTR Toolbox Guidance Manual 4-29 April 2010
-------
4. Bank Filtration
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.
This is because it typically allows wells to be placed slightly closer to the river and is thus a
somewhat less restrictive requirement. The floodway is a regulatory concept, and is defined as
that portion of the overbanks that must be kept free from encroachment to discharge the one
percent annual chance
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.
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
LT2ESWTR Toolbox Guidance Manual 4-30 April 2010
-------
4. Bank Filtration
from surface water. For simplicity, if the well inclination is 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.
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 previously 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).
LT2ESWTR Toolbox Guidance Manual 4-31 April 2010
-------
4. Bank Filtration
When high river stages or high turbidity levels indicate that flood scour may be occurring
and compromising the effectiveness of a bank filtration system, pumping rates can be decreased.
This will lead to lower velocities and longer subsurface residence times, thereby increasing the
protectiveness of the system (Medema et al. 2000, Juhasz-Holterman 2000).
4.6.3 Anticipating High Flow Events / Flooding
Many factors can affect the probability of flood events. 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, 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
LT2ESWTR Toolbox Guidance Manual 4-32 April 2010
-------
4. Bank Filtration
reductions may be more frequent in an urbanizing basin as a consequence of more frequent
flooding and associated scouring. In extreme cases, long term degradation of the bed or banks
may reduce the threshold separation distances between the surface water source and bank
filtration well. Recall that these separation distances - 25 feet for 0.5 log removal credit and 50
feet for 1.0 log removal credit - are required to receive log removal credits under the
LT2ESWTR.
Systems may wish to assess their sites for active, progressive erosion. Lateral migration
rates can be calculated using sequential aerial photography and/or topographic maps, if available.
Systems without such data may need to obtain the needed information by conducting sequential
field surveys of the floodplain area proposed for the site. This will require a far more lengthy
investigation period. Progressive downcutting could also be measured with sequential field
surveys of the channel bed 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
PWSs using GWUDI 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 section 4.2. Alternatively,
PWSs may apply to the state for Cryptosporidium treatment credit using a 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 DOP 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 section 4.2.1.
PWSs 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 LT2ESWTR.
For a bank filtration DOP 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).
The purpose of this section is to provide additional guidance on the design and conduct of
a DOP study, as well as guidance on the interpretation of the study data and the award of
LT2ESWTR Toolbox Guidance Manual 4-33 April 2010
-------
4. Bank Filtration
Cryptosporidium removal credits if warranted. Finally, this section 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 DOP 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; or 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 section 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
DOP 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 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
LT2ESWTR Toolbox Guidance Manual 4-34 April 2010
-------
4. Bank Filtration
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 earlier in this chapter, 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 (because river water tends to
remain unmixed, river flow is idealized as flow in a composite of parallel tubes). River water
samples should be proportionately representative of the actual flow conditions based on the
historic record and should be collected during both low water and high water stages (if safety
conditions permit) 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
approximate 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, Chlorofluorocarbons (CFCs), pharmaceutical
compounds, etc.) can 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 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
LT2ESWTR Toolbox Guidance Manual 4-35 April 2010
-------
4. Bank Filtration
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 percent ambient
groundwater and 20 percent 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 percent ambient ground water and 80 percent 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 percent
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.
4.7.4 Surface and Ground Water Data Collection, Methods and Sampling Locations
As required by the LT2ESWTR, 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
LT2ESWTR Toolbox Guidance Manual 4-36 April 2010
-------
4. Bank Filtration
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. Safe sample collection procedures however,
should be observed at all times. Ongoing data collection takes place over a longer period of time,
but tends to provide an average characterization. Event based sample collection is a high
frequency of monitoring over short periods of time 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, and irrigation) 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, total dissolved solids
(TDS), hydrogen, oxygen, 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
LT2ESWTR Toolbox Guidance Manual 4-3 7 April 2010
-------
4. Bank Filtration
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
should 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 coming from the source water rather than from land-side septic tanks. Well-water counts of
E. coli for example, that includes E. coli that originates at a nearby septic tank, rather than at the
river, will yield lesser calculated removal efficiencies than the actual removal.
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) 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 transport capability or have
unknown original or final size and shape (and charge), such as turbidity, standard particle counts,
and total algae, or larger organisms such as rotifers, crustaceans or fish are less meaningful and
should not be used. Pumping wells generate turbidity in the aquifer as a result of pumping (van
Beek et al 2010). Therefore, for groundwater, turbidity data are useful primarily 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.
LT2ESWTR Toolbox Guidance Manual 4-38 April 2010
-------
4. Bank Filtration
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. coll recovery in Dusseldorf bank filtration wells only following a flood event.
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) equivalent in size
and shape to Cryptosporidium oocysts (i.e., 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 lists
the size ranges of common pathogenic protozoa and surrogate bacteria.
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., Clostridiumperfringens 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)
(U.S. EPA 1992, AWWA 1990). EPA recommends monitoring for at least three or four surrogate
LT2ESWTR Toolbox Guidance Manual 4-39 April 2010
-------
4. Bank Filtration
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 less expensive 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.
Exhibit 4.7 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 et al., 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 (12 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
LT2ESWTR Toolbox Guidance Manual
4-40
April 2010
-------
4. Bank Filtration
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
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 can 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
LT2ESWTR Toolbox Guidance Manual 4-41 April 2010
-------
4. Bank Filtration
unpublished data from Casper, WY and results reported in Locas et al. (2008), Schubert (1975)
and Rice et al (1999), the aerobic spore natural background concentration is about 10 CFU/100
ml or less. Based on these studies, 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
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," should 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 jim), 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.
LT2ESWTR Toolbox Guidance Manual 4-42 April 2010
-------
4. Bank Filtration
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
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 MPA (U.S. EPA 1992). The MPA method
only counts whole diatoms; diatom fragments are not considered. Exhibit 4.8 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 pass through sand and other porous media. Diatoms are
photosynthesizing algae that require light to maintain their green chlorophyll. After about 6
months residence time in the subsurface, the green color will fade. (Susan Boutros, EPA GWUDI
Determination Presentation, Denver CO, verbal communication on unpublished laboratory
experiments with diatoms placed in a refrigerator).
Exhibit 4.8 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 (see section 4.7.2),
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),
LT2ESWTR Toolbox Guidance Manual
4-43
April 2010
-------
4. Bank Filtration
although the detection limit is high (500 cells per liter) and 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
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 (including microspheres) 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 CFCs and SF6 were less useful at the site.
LT2ESWTR Toolbox Guidance Manual 4-44 April 2010
-------
4. Bank Filtration
4.7.7 Monitoring Wells Located Along the Shortest Flow Path
The LT2ESWTR 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 section 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 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 degradation of alternative filtration performance is
occurring and to document improvements in alternative treatment removals based on improved
wellfield operation and maintenance.
4.8 Reference
Abdel-Fattah, A., R. Langford, D. Schulze-Makuch. 2007. Application of particle-tracking
techniques to bank infiltration: a case study from El Paso, Texas, USA. Environmental Geology
(in press).
APHA (American Public Health Association). 2004. 9218 Aerobic Endospores in Standard
Methods for the Examination of Water and Wastewater, p. 9-47-9-48.
ASTM (American Society for Testing and Materials). 2003. Standard Test Method for Sieve
Analysis of Fine and Coarse Aggregates - Standard C 136-1.
AWWA (American Waterworks Association). 1990. Guidance Manual for Compliance with the
Filtration and Disinfection Requirements for Public Water Systems Using Surface Water
Sources. American Water Works Association, Denver, 573 p.
AWWA (American Waterworks Association). 1995. Problem Organisms in Water:
Identification and Treatment., AWWA Manual of Water Supply Practices M7, AWWA, Denver,
Colorado, 153 p.
Bakker, M., V.A. Kelson and K.H. Luther. 2005. Multilayer Analytical Element Modeling of
Radial Collector Wells. Ground Water 43(6):926-934.
LT2ESWTR Toolbox Guidance Manual 4-45 April 2010
-------
4. Bank Filtration
Baveye, P., Berger, P., Schijven, J., and Grischek, T. 2003. Research needs to improve
knowledge of bank filtration removal of pathogens, in Riverbank Filtration: Improving Source
Water Quality, edited by Ray, C., Melin, G. and Linsky, R., Kluwer, Dordrecht.
Baveye, P., P. Vandevivere, B. L. Hoyle, P.C. DeLeo, and D. Sanchez de Lozada. 1998.
Environmental impact and mechanisms of the biological clogging of saturated soils and aquifer
materials. Critical Review sin Environmental Science and Technology. 28(2): 123-191.
Berger, P. 2002. Removal of Cryptosporidium Using Bank Filtration in Riverbank Filtration:
Understanding Contaminant Biogeochemistry and Pathogen Removal, C. Ray (ed.). The
Netherlands: Kluwer Academic Publishers, p. 85-121.
Booth, D.B. 1990. Stream-channel incision following drainage basin urbanization. Water
Resources Bulletin. 26(3): 407-417.
Brock, T.D. and M.T. Madigan. 1991. Biology of Microorganisms. Prentice Hall, Englewood
Cliffs, New Jersey, 776 p.
Brusseau, M.L., J.K. Oleen, J. Santamaria, L. Cheng, P. Orosz-Coghlan, A.S. Chetochine, WJ.
Blandford, P. Rykwalder, and C.P. Gerba. 2005. Transport of microsporidium Encephalitozoon
intestinales spores in sandy porous media. 39:3636-3642.
Burger, H.R., D.C. Burger, and R.H. Burger, 1992. Exploration Geophysics of the Shallow
Subsurface. Upper Saddle River, NJ: Prentice Hall.
Callegary, James, United States Geological Survey, personal communication, 3/03.
Chow, V.T. 1964. Handbook of Applied Hydrology. New York: McGrawHill.
Coplen, T.B., A.L. Herczeg and C. Barnes. 1999. Isotope Engineering - Using Stable Isotopes of
the Water Molecule to Solve Practical Problems in P.G. Cook and A. L. Herczeg (eds.)
Environmental Tracers in Subsurface Hydrology, Kluwer, Boston.
Driscoll, F.G. 1986. Groundwater and Wells. 2nd Edition. St. Paul, Minnesota: Johnson Division.
Dunne, T., and Leopold, L.B. 1978. Water in Environmental Planning. New York: W.H.
Freeman and Company. 818 pp.
Eckert, P. and R. Irmscher. 2006. Over 130 years of experience with riverbank filtration in
Dusseldorf, Germany. Journal of Water Supply: Research and Technology-AQUA, 55(4):283-
291.
FEMAMap Assistance Center. 2003. Personal communication.
LT2ESWTR Toolbox Guidance Manual 4-46 April 2010
-------
4. Bank Filtration
Foppen, J.W.A and J.F. Schijven. 2006. Evaluation of data from the literature on the transport
and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated
conditions. Water Research 40:401-426.
Gaut, S., L. Robertson, B. Gjerde, A. Dagestad and B. Brattli. 2008. Occurrence of
Cryptosporidium oocysts and Giardia cysts in Norwegian groundwater wells in bedrock. Journal
of Water and Health, 9(3):383-388.
Goldenberg, L.C., I. Hutcheon, N. Wardlaw, and AJ. Melloul. 1993. Rearrangement of fine
particles in porous media causing reduction of permeability and formation of preferred pathways
of flow: experimental findings and a conceptual model. Transport in Porous Media 13: 221-237.
Goldschneider, A.A., K.A. Haralampides, K.T.B. MacQuarrie. 2007. River sediment and flow
characteristics near a bank filtration water supply: Implications for riverbed clogging. Jour.
Hydrology, 344:55-69.
Gollnitz, W.D. 1999. Induced infiltration rate variability and water quality sampling issues.
Proceedings of the International Riverbank Filtration Conference. November 4-6, 1999.
Louisville, Kentucky.
Gollnitz, W.D. and J.L. Clancy. 1994. Evaluation of the Casper Aquifer and Wellfield for
Ground Water Under the Direct Influence of Surface Water, unpublished report prepared for the
Casper Public Utilities, Casper, Wyoming, 35 p.
Gollnitz, W.D., B.L.Whitteberry and J.A. Vogt. 2004. Riverbank filtration: Induced infiltration
and groundwater quality. Journal AWWA 96(12):98-110.
Gollnitz, W.D., J.L. Clancy, J.B. McEwen and S.C. Garner. 2005. Riverbank filtration for
IESWTR Compliance. Journal AWWA 97(12):64-76.
Gollnitz, W.D., J.L. Clancy, M. Cunnane, and B. Beauchene. 2007. Riverbank filtration for
SWTR Compliance-Kennewick, Washington in Proceedings Water Quality Technology
Conference, Charlotte, North Carolina, American Water Works Association, Denver Colorado.
Harter, T., S. Wagner, and E. R. Atwill, 2000. Colloid Transport and Filtration of
Cryptosporidium parvum in Sandy Soils and Aquifer Sediments, Environmental Science and
Technology, 34(1), pp. 62-70.
Hearst, J.R., P.H. Nelson, and F.L. Paillet, 2000. Well Logging for Physical Properties: A
Handbook for Geophysicists, Geologists, and Engineers, 2nd Edition. New York: Wiley.
Hendricks, D.W., 2001. Biological Particle Surrogates for Filtration Performance Evaluation,
American Water Works Association Research Foundation Report #181, Denver, Colorado.
LT2ESWTR Toolbox Guidance Manual 4-47 April 2010
-------
4. Bank Filtration
Holt, J.G. 1986. Bergey's Manual of Systematic Bacteriology, vol. 2, Lippincott, Williams and
Wilkins, Baltimore, Maryland.
Hubbard, Susan M., Lawrence Berkeley National Laboratory, personal communication, 3/03.
Hubbs, S., J.Z. Wang, and R. Song. 2001. Use of Riverbank Filtration to Meet the Requirements
of SWTR and DBF Rules. Presentation at the American Water Works Association Water Quality
Technology Conference, November 11-15, Nashville, TN.
Hunt, R.L., T.B. Coplen, N.L. Haas, D.A. Saad, M.A. Borchardt. 2005. Investigating surface
water-well interaction using stable isotope ratios of water. Jour. Hydrology 302:154-172.
Jacobson, R.B., S.R. Femmer, and R.A. McKenney. 2001. Land-use Changes and the Physical
Habitat of Streams : a review with emphasis on studies within the U.S. Geological Survey
Federal-State cooperative program. U.S. Geological Survey Circular 1175. Reston, VA.: U.S.
Geological Survey. 63 pp.
Juhasz-Hoterman, M.H. A. 2000. Reliable drinking water by bank filtration along the river Maas
(Meuse), by knowledge of the system combined with simple resources, in Proceedings of
International Riverbank Filtration Conference, Nov. 2-4, Duesseldorf., W. Julich and J. Schubert
(eds.), International Arbeitgemeinschaft der Wasserwerke im Rheineinzugsgebiet, Amsterdam.
Juttner, F. 1995. Elimination of terpenoid odorous compounds by slow sand and river bank
filtration of the Ruhr River, Germany. Water Science & Technology. 31: 211-217.
Juttner, F. 1999. Efficacy of bank filtration for the removal of fragrance compounds and aromatic
hydrocarbons. Water Science Technology 40(6): 123-128.
Keys, W.S., 1990, Borehole geophysics applied to groundwater investigations: U.S. Geological
Survey, Techniques of Water-Resources Investigations of the U.S. Geological Survey, Book 2,
Collection of Environmental Data, Chapter E2, 150 p.
Kuehn, W. and U. Mueller. 2000. Riverbank filtration: an overview. AWWA Journal. 92(12):
60-69.
Leland, D., J. McAnulty, W. Keene, and G. Stevens. 1993. A cryptosporidiosis outbreak in a
filtered-water supply. AWWA Journal. 85(6):34-42.
Leopold, L.B. and Maddock, T. 1953. The Hydraulic Geometry of Stream Channels and Some
Physiographic Implications. U.S. Geological Survey Professional Paper 252. Washington: U.S.
Government Printing Office.
Leopold, L.B., M.G. Wolman, and J.P. Miller. 1964. Fluvial Processes in Geomorphology. San
Francisco: W H Freeman and Co.
LT2ESWTR Toolbox Guidance Manual 4-48 April 2010
-------
4. Bank Filtration
Locas, A., C. Barthe, A.B. Margolin, and P. Payment. 2008. Groundwater microbiological
quality in Canadian drinking water municipal wells. Can. J. Microbiol. 54:1-7.
Lund, B.M. and Peck, M.W. 1994. Heat resistance and recovery of spores of non-proteolytic
Clostridium botulinum in relation to refrigerated, processed foods with an extended shelf-life.
Journal of Applied Bacteriology Symposium Supplement 76:1158-1288.
Mazoua, 8. and D. Chauveheid. 2005. Aerobic spore-forming bacteria for assessing quality of
drinking water produced from surface water. Water Research 39:5186-5198.
Medema, GJ. and PJ. Stuyfzand. 2002. Removal of micro-organisms upon basin recharge, deep
well injection and river bank filtration in the Netherlands, in Management of Aquifer Recharge
for Sustainability, P. Dillon (ed.), Swets & Zeitlinger, Lisse, p. 125-131.
Medema, G.J., M.H.A. Juhasz-Hoterman, and J.A. Luitjen. 2000. Removal of micro-organisms
by bank filtration in a gravel-sand soil, in Proceedings of International Riverbank Filtration
Conference, Nov. 2-4, Duesseldorf, W. Julich and J. Schubert (eds.), International
Arbeitgemeinschaft der Wasserwerke im Rheineinzugsgebiet, Amsterdam.
Metge, D.W., R.W. Harvey, R. Anders, D. O. Rosenberry, D. Seymour and J. Jasperse. 2007.
Use of carboxylated microspheres to assess transport potential of Cryptosporidium parvum
oocysts at the Russian River water supply facility, Sonoma County, California, Geomicrobiology
Journal, 24:231-245.
Miettinen, IT., P.J. Martikainen, T. Vartiainen. 1994. Humus transformation at the bank
filtration water plant. Water Science & Technology, 30 (10): 179.
Montgomery, Carla W., 2000. Environmental Geology, updated 5th edition. Boston: McGraw
Hill.
Mota, P., C.A. Rauch and S.C. Edberg. 2000. Microsporidia and Cyclospora: Epidemiology and
assessment of risk from the environment. Critical Reviews in Microbiology 26(2):69-90.
Oberdorfer, J.A. andF.L. Peterson. 1985. Waste-water injection: geochemical and
biogeochemical clogging processes. Ground Water 23: 753-761.
Orlob, G.T. and G.N, Radhakrishna. 1958. The effects of entrapped gases on the hydraulic
characteristics of porous media. Transactions of the American Geophysical Union 39: 648-659.
Palcsak, B.B. 1995. Using the Freeze-Core Method to Collect Streambed Samples for
Determination of Particle-Size Distribution. US Geological Survey Open-File Report 95-466.
14p.
Pang, L., M. Close, and M. Noonan. 1998. Rhodamine WT and Bacillus subtilis transport
through an alluvial gravel aquifer. Ground Water 36:112-122.
LT2ESWTR Toolbox Guidance Manual 4-49 April 2010
-------
4. Bank Filtration
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
groundwater under the direct influence of surface water depends on river conditions in Abstracts,
International Riverbank Filtration Conference, November 4-6, 1999, Louisville, Kentucky,
National Water Research Institute, Fountain Valley, CA.
Purdue University. 2001. Well Water Location and Condition on the Farm. Available on the
Internet at: http://www.epa.gov/seahome/welloc.html. accessed November 27, 2002.
Ray, C. 2001a. Riverbank filtration: an analysis of parameters for optimal performance.
Proceedings of the Annual Conference of the American Waterworks Association. June 17-21,
2001. Washington, DC.
Ray, C. 2001b. Modeling riverbank filtration systems to attenuate shock loads in rivers.
Proceedings of the Annual Conference of the American Waterworks Association. June 17-21,
2001. Washington, DC.
Ray, C., T. Grischek, J. Schubert, J. Wang, and T. Speth. 2002. A perspective of riverbank
filtration, J. AWWA, 94(4): 149-160.
Reilly, T.J., C.E. Walker, A. L. Baehr, R. M. Schrock, and J.R. Reinfelder. 2005. Occurrence of
Diatoms in Lakeside Wells in Northern New Jersey as an Indicator of the Effect of Surface Water
on Ground-Water Quality. U.S. Geological Survey Scientific Investigations Report 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
for monitoring ground water quality in Proceedings, Annual Meeting of the American Water
Works Association, Chicago, Illinois, American Water Works Association, Denver Colorado.
Ritter, D.F., C.R. Kochel, and J.R. Miller. 1995. Process Geomorphology. 3rd edition. Dubuque,
Iowa: Wm. C. Brown Publishers.
Rohns, H.-P., C. Forner, P. Exkert and R. Irmscher. 2006. Efficiency of riverbank filtration
considering the removal of pathogenic microorganisms of the River Rhine in R. Gimbel, N.
LT2ESWTR Toolbox Guidance Manual 4-50 April 2010
-------
4. Bank Filtration
Graham and R. Collins (eds.), Recent Progress in Slow Sand and Alternative Biofiltration
Processes. IWA Publishers, London UK, 539-546.
Rubin Y. and S. Hubbard, 2003. Hydrogeophysics. Kluwer.
Sanchez de Lozada, D., P. Vandevivere, P. Baveye, and S. Zinder. 1994. Decrease of the
hydraulic conductivity of sand columns by Methanosarcina barkeri. World Journal of
Microbiology and Biotechnology 10: 325-333.
Schafer, D. 2000. Groundwater modeling in support of riverbank infiltration for Louisville Water
Company, in Proceedings of International Riverbank Filtration Conference, Nov. 2-4,
Duesseldorf, W. Julich and J. Schubert (eds.), International Arbeitgemeinschaft der Wasserwerke
im Rheineinzugsgebiet, Amsterdam.
Schijven, J., Berger, P., Miettenen, I. 2003. Removal of viruses, bacteria, protozoa and toxins
using bank filtration, in Riverbank Filtration: Improving Source Water Quality, edited by Ray,
C., Melin, G. and Linsky, R., Kluwer, Dordrecht.
Schubert, R.H.W. 1975. The detection of spores of the Bacillus-species within the scope of the
hygeienic control of water pollution. Zbl. Bakt. Hyg. Abt. Orig. B 160:155-162 (in German with
and English Abstract).
State Coordinating Committee on Ground Water (SCCGW). 2000. State of Ohio Technical
Guidance for Well Construction and Ground Water Protection. Available on the Internet at:
http://www.dnr.state.oh.us/portals/7/pubs/pdfs/wellconguide.pdf. accessed November 27, 2002.
Symons, J.M., L.C. Bradley, Jr., T.C. Cleveland, eds. 2000. The Drinking Water Dictionary.
American Water Works Association, Denver, CO.
Tufenkji, N. 2007. Modeling microbial transport in porous media: Traditional approaches and
recent developments. Advances in Water Resources 30:1455-1469.
Tufenkji, N., D.R. Dixon, R. Considine, C. J. Drummond. 2006. Multi-scale
Cryptosporidium/sand interactions in water treatment. Water Research 40:3315-3331.
Tufenkji, N., J.N. Ryan, and M. Elimelech. 2002. The promise of bank filtration: a simple
technology may inexpensively clean up poor-quality raw surface water. Environmental Science
and Technology. 36: 422A - 428A.
United States Enviromental Protection Agency (U.S. EPA). 1975. Manual of Water Well
Construction Practices. Office of Water Supply. EPA/ 570/9-75-001. Washington, D.C. 156 pp.
United States Environmental Protection Agency (U.S. EPA). 1992. Consensus Method for
Determining Groundwaters Under the Direct Influence of Surface Water Using Microscopic
Particulate Analysis (MPA). EPA 910/9-92-029.
LT2ESWTR Toolbox Guidance Manual 4-51 April 2010
-------
4. Bank Filtration
United States Environmental Protection Agency (U.S. EPA). 2006. Long Term 2 Enhanced
Surface Water Treatment Rule (LT2ESWTR). Federal Register. Thursday, January 5, 2006.
71(3):654-786 (US EPA 815-Z-06-001).
United States Geological Survey (USGS). 1998. The National Atlas of the United States of
America. Principal Aquifers. [Map]. Reston, VA: U.S. Department of the Interior, U.S.
Geological Survey.
Van Beek, C.G.E.M., A.H. de Zwart, M. Balemans, J.W. Kooiman, C. van Rosmalen, H. timmer,
J. Vandersluys and PJ. Stuyfzand. Concentration and size distribution of particles in abstracted
groundwater. Water Research 44:868-878.
Vandevivere, P., P. Baveye, D. Sanchez de Lozada, and P. DeLeo. 1995. Microbial clogging of
saturated soils and aquifer materials: Evaluation of mathematical models. Water Resources
Research 31(9): 2173-2180.
Vogel, J.R., S.I. Harris, T.B. Coplen, E.W. Rice and I.M. Verstraeten. 2005. Microbe
Concentrations, Laser particle counts, and Stable Hydrogen and Oxygen Isotope Ratios in
Samples from a Riverbank Filtration Study, Platte River, Nebraska, 2002 to 2004. US Geological
Survey Data Series 133, 61 p.
Walker, C.E., R.M. Schrock, TJ. Reilly and A.L. Baehr. 2005. A direct immunoassay for
detecting diatoms in groundwater as a indicator of the direct influence of surface water. Journal
of Applied Phycology 17:81-90.
Wang, J.Z., Hubbs, S.A. and Song, R. 2002. Evaluation of Riverbank Filtration as a Drinking
Water Treatment Process, American Water Works Association Research Foundation Report
90922, 145 p.
Wang, J.Z., R. Song, and S.A. Hubbs. 2000. Particle removal through riverbank filtration
process, in Proceedings of the International Riverbank Filtration Conference, Nov. 2-4,
Duesseldorf, W. Julich and J. Schubert (eds.), International Arbeitgemeinschaft der Wasserwerke
im Rheineinzugsgebiet, Amsterdam.
Wang, J.Z., S.A. Hubbs, and M. Unthank. 2001. Factors Impacting the Yield of Riverbank
Filtration Systems. Presentation at the American Water Works Association Water Quality
Technology Conference, November 11-15, Nashville, TN.
Warner, J.W., T.K. Gates, R., Namvargolian, P. Miller, and G. Comes. 1994. Sediment and
microbial fouling of experimental groundwater recharge trenches. Journal of Contaminant
Hydrology 15: 321-344.
LT2ESWTR Toolbox Guidance Manual 4-52 April 2010
-------
4. Bank Filtration
Weiss, W.J., EJ. Bouwer, R. Aboytes, M.W. LeChevallier, C.R. O'Melia, B.T. Le, KJ. Schwab.
2005. Riverbank filtration for control of microorganisms: Results from field monitoring. Water
Research 39:1990-2001.
Weiss, W.J., EJ. Bouwer, W.P. Ball, C.R. O'Melia, H. Arora, T.F. Speth. 2003. Reduction in
DBF precursors and pathogens during riverbank filtration at three midwestern drinking water
utilities, in Riverbank Filtration for Water Supply, C. Ray and R. Linsky (eds). Kluwer Academic
Publishers.
WHO. 2004. Guidelines for Drinking Water Quality, Third Edition, Volume 1,
Recommendations, World Health Organization, Geneva, 515 p.
Williams, G.P., and Wolman, M.G. 1984. Downstream Effects of Dams on Alluvial Rivers. U.S.
Geological Survey Professional Paper 1286. Washington: U.S. Government Printing Office.
Xiao, L., U.M. Morgan, R. Payer, R.C.A. Thompson, and A.A. Lai. 2000. Cryptosporidium
sytematics and implications for public health. Parsitology Today 16(7):287-292.
Youden, WJ. 1969. Ranking Laboratories by Round-Robin Tests in Precision Measurement and
Calibration, Statistical Concepts and Procedures, US Department of Commerce, National Bureau
of Standards, Special Publication 300, 1:165-169.
LT2ESWTR Toolbox Guidance Manual 4-53 April 2010
-------
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. A plant may receive credit for a presedimentation basin for any month the basin
meets the requirements as described in 40 CFR 141.717(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 Long Term 2 Enhanced Surface Water Treatment Rule (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.
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 141.717(a)):
• The presedimentation basin must be in continuous operation and must treat all of the flow
taken from a surface water or ground water under the direct influence of surface water
(GWUDI) source.
LT2ESWTR Toolbox Guidance Manual 5-1 April 2010
-------
5. Presedimentation
• A coagulant must be continuously added to the presedimentation basin while the plant is
in operation.
• The presedimentation basin must achieve a monthly mean reduction of 0.5 log (68
percent) or greater in turbidity or alternative state-approved performance criteria that
demonstrate at least 0.5 log mean removal of micron sized parti culate material through
the presedimentation process.
5.2.2 Monitoring Requirements
Systems must measure presedimentation basin influent and effluent turbidity at least once
per day or meet state-specified performance criteria (40 CFR 141.717(a)). State-specified criteria
could include aerobic spore removal (see Chapter 12, Section 12.4.2.1 of this guidance manual)
or particle count reduction. Laboratory support would be needed for spore counts and grab
sampling and dilution would be needed to assess particle count reduction.
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
Log Reduction =
Logio(Monthly Average Influent Turbidity) - Logio(Monthly Average Effluent Turbidity)
Or if calculated as a percent,
Percent Reduction =
(Monthly Average Influent Turbidity) - (Monthly Average Effluent Turbidity) x 100
(Monthly Average Influent Turbidity)
Example Calculation
Average influent turbidity = 16.3 nephelometric turbidity units (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%
LT2ESWTR Toolbox Guidance Manual 5-2 April 2010
-------
5. Presedimentation
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, and comply with state specified performance criteria. When source
water turbidity is seasonally or consistently low, most presedimentation basins will have
difficulty achieving 0.5 log reduction, and systems may need to use another tool in the toolbox to
meet state-specified criteria such as aerobic spore removal or particle count reduction. For
example, if a system has an average of 10 NTU source water turbidity for a few months of the
year, the average effluent turbidity would have to be 3.2 NTU for those months, which could be
difficult for some systems to achieve. Exhibit 5.1 lists influent and effluent turbidity values that
yield 0.5 log reduction. These are example values to help when considering using the tool.
LT2ESWTR Toolbox Guidance Manual 5-3 April 2010
-------
5. Presedimentation
Exhibit 5.1 Example Influent and Effluent Turbidity Values Resulting in 0.5 Log
Reduction
Monthly Average Turbidity (NTU)
Influent
2
10
30
50
70
80
100
Effluent
0.6
3.2
9.5
15.8
22.1
25.3
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:
Water Quality and Treatment-
(AWWA 1999).
-A Handbook of Community Water Supplies, 5th ed.
Integrated Design and Operation of Water Treatment Facilities, 2nd ed. (Kawamura
2000).
LT2ESWTR Toolbox Guidance Manual
5-4
April 2010
-------
5. Presedimentation
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.
LT2ESWTR Toolbox Guidance Manual 5-5 April 2010
-------
5. Presedimentation
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
-Poor flocculation 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).
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
LT2ESWTR Toolbox Guidance Manual
5-6
April 2010
-------
5. Presedimentation
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 commonly from a center feed well, radially outward to the
peripheral weirs. In comparison to rectangular basins, circular basins will have more land
between the basins and also require more yard piping. Circular basins have easy sludge removal,
can obtain high clarification efficiency, and are adaptable to high rate settling modules. However,
if flow distribution from the inlet is not uniform, the settling efficiency will be hindered. These
basins are not as hydraulically stable as rectangular basins.
5.4.2 Upflow Clarifier
In upflow clarifiers the influent enters at the bottom and clarified water flows upward
while the solids settle to the bottom. As with horizontal flow basins, upflow clarifiers can also be
modified with high rate settling modules. Upflow clarifiers can provide higher clarification
efficiency than horizontal flow; however, they are more sensitive to shock loads than horizontal
flow basins.
5.4.3 Reactor Clarifier
Reactor clarifiers use the seeding concept to improve settling. The water flows through
the sludge layer so particles can coalesce with already formed floes. Two common designs of
reactor clarifiers are slurry recirculation and sludge blanket clarifiers. Both operate on a center
feed system with built-in flocculation zones. The process is more complex than traditional
horizontal or upflow clarifiers. Reactor clarifiers can provide high clarification efficiency but at
the cost of flexibility—the source water quality and hydraulic loads must be constant.
LT2ESWTR Toolbox Guidance Manual 5-7 April 2010
-------
5. Presedimentation
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 141.717(a)).
Systems should consider the need for redundancy in the design of a presedimentation process.
Smaller systems or systems with a demand much lower than the design capacity may be able to
shut down the water treatment plant for presedimentation basin maintenance activities and, thus,
not require additional basins for redundancy. However, systems that operate on a continuous
basis do not have that flexibility and should have a plan for staying in compliance while a basin
is shut down.
5.5.2 Short Circuiting
A common issue that must be considered in the design and operation of presedimentation
basins is short-circuiting. If a portion of flow does not have the adequate 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
LT2ESWTR Toolbox Guidance Manual 5-8 April 2010
-------
5. Presedimentation
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 practices of presedimention processes often focus on mitigating
shock loads in the raw water supply (such as turbidity spikes due to precipitation in river source
waters). However, during periods of low influent turbidity less attention may be given to the
actual performance of the basin, resulting in less than 0.5 log turbidity reduction through the
basin. To receive the credit, the presedimentation basin may need to be operated more
stringently, including the addition of coagulant. The coagulant dose required to treat an influent
stream depends on the chemical composition of the influent, the characteristics of the colloids
and suspended matter in the influent, the addition of a 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.
LT2ESWTR Toolbox Guidance Manual 5-9 April 2010
-------
5. Presedimentation
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.
U.S. EPA, 1998. Optimizing Water Treatment Plant Performance Using the Composite
Correction Program, pp. 233-236.
LT2ESWTR Toolbox Guidance Manual 5-10 April 2010
-------
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 Long Term 2 Enhanced Surface Water Treatment Rule
(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)):
LT2ESWTR Toolbox Guidance Manual 6-1 April 2010
-------
6. Lime Softening
The plant must have a second clarification step between the primary clarifier1 and filter
which is operated continuously. For split treatment processes, only the portion of flow
going through two clarification stages can receive credit. If a portion of flow bypasses one
stage, additional treatment must be provided to the bypassed portion (see section 6.3).
Chemical addition and hardness removal must occur in two separate and sequential
stages.
Exhibit 6.1 shows a typical two stage lime softening process.
Exhibit 6.1 Typical Two-Stage Lime Softening Process
Lime
CO,
i
1
Recarbonation
Soda Asr
i
co2
i
Recarbonation
Filters
Primary Clarifier
Secondary Ciarifier
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 141.721):
• 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.
For purposes of compliance with the lime-softening toolbox option, "clarifier" is used as a general term
for processes with settling and solids removal.
LT2ESWTR Toolbox Guidance Manual
6-1
April 2010
-------
6. Lime Softening
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
through both stages, or 2) treat the bypassed portion with another toolbox option, such as
chlorine dioxide, membranes, or ozone to receive Cryptosporidium inactivation/removal credit
for that stream.
LT2ESWTR Toolbox Guidance Manual 6-3 April 2010
-------
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 (LT1ESWTR) all motivate public water systems to achieve a
certain level of finished water quality by requiring them to meet specified filtered water turbidity
limits. Under the IESWTR and LT1ESWTR, combined filter effluent (CFE) turbidity in
conventional and direct filtration plants must be less than or equal to 0.3 nephelometric turbidity
units (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 (IFE) turbidity are exceeded.
The Long Term 2 Enhanced Surface Water Treatment Rule (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
(SOPs), response plans for loss of chemical feed, adequate chemical storage, and
voluntary programs that encourage full process control from administration to
operation and maintenance.
LT2ESWTR Toolbox Guidance Manual 7-1 April 2010
-------
7. Combined and Individual Filter Performance
1.2 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 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 IFE turbidity requirements (40 CFR 141.718(b)):
1) IFE turbidity must be less than 0.15 NTU in at least 95 percent of 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 141.718). In other
words, the LT2ESWTR does not require any additional monitoring from the IESWTR and
LT1ESWTR.
7.2.2.1 Combined Filter Effluent
The monitoring frequency and compliance calculation requirements for the CFE option
are that CFE turbidity must be measured at 4-hour intervals (or more frequently) and 95 percent
of the measurements from each month must be less than or equal to 0.15 NTU (40 CFR
141.721).
LT2ESWTR Toolbox Guidance Manual 7-2 April 2010
-------
7. Combined and Individual Filter Performance
7.2.2.2 Individual Filter Effluent
The LT2ESWTR has specific reporting requirements. 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 141.721).
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 141.721). 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 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 LT1ESWTR guidance manuals are available on EPA's website at:
http://www.epa.gov/ogwdwOOO/mdbp/ltleswtr/guidance Itl turb.pdf
LT2ESWTR Toolbox Guidance Manual 7-3 April 2010
-------
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.
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.
LT2ESWTR Toolbox Guidance Manual
7-4
April 2010
-------
7. Combined and Individual Filter Performance
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
Regularly, such as monthly or quarterly
Daily1
Quarterly
Annually or according to manufacturer's
recommendations
Instrument calibration should be verified on a daily basis
(http://vwwv.epa.qov/oqwdwOOO/mdbp/pdf/turbidity/chap 03.pdf). Clean and recalibrate with primary standard if
verification indicates greater than a +/-10 percent deviation from secondary standard.
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.
• Quality assurance/quality control (QA/QC) plan for accuracy and consistency.
• SOPs
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 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).
LT2ESWTR Toolbox Guidance Manual 7-5 April 2010
-------
7. Combined and Individual Filter Performance
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).
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 (U.S. 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:
http ://www. epa. gov/OGWDW/mdbp/mdbptg.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
LT2ESWTR Toolbox Guidance Manual 7-6 April 2010
-------
7. Combined and Individual Filter Performance
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 (CCP), an EPA
program for optimizing water treatment plant performance (discussed in section 7.5.4.2).
LT2ESWTR Toolbox Guidance Manual 7-7 April 2010
-------
7. Combined and Individual Filter Performance
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?
LT2ESWTR Toolbox Guidance Manual
April 2010
-------
7. Combined and Individual Filter Performance
Unit Process Adequacy
Intake Structure
Presedimentation Basin
Raw Water Pumping
Flow Measurement
Chemical Storage and Feed
Facilities
Flash Mix
Flocculation
Sedimentation
Filtration
Disinfection
Sludge/Backwash Water
Treatment and Disposal
Does the design of the intake structure result in excessive clogging of screens, build-
up of silt, or passage of material that affects plant equipment?
Does the design of an existing presedimentation basin or the lack of a
presedimentation basin contribute to degraded plant performance?
Does the use of constant speed pumps cause undesirable hydraulic loading on
downstream unit processes?
Does the lack of flow measurement devices or their accuracy limit plant control or
impact process control adjustments?
Do inadequate chemical storage and feed facilities limit process needs in a plant?
Does an inadequate mixing result in excessive chemical use or insufficient
coagulation to the extent that it impacts plant performance?
Does a lack of flocculation time, inadequate equipment, or lack of multiple flocculation
stages result in poor floe formation and degrade plant performance?
Does the sedimentation basin configuration or equipment cause inadequate solids
removal that negatively impact filter performance?
Do filter or filter media characteristics limit the filtration process performance?
Do the disinfection facilities have limitations, such as inadequate detention time,
improper mixing, feed rates, proportional feeds, or baffling, that contribute to poor
disinfection?
Do inadequate sludge or backwash water treatment facilities negatively influence
plant performance?
Plant Operability
Process Flexibility
Process Controllability
Process Instrumentation
/Automation
Standby Units
Flow Proportioning
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?
LT2ESWTR Toolbox Guidance Manual
7-9
April 2010
-------
7. Combined and Individual Filter Performance
OPERATION
Testing
Process Control Testing
Representative Sampling
Does the absence or wrong type of process control testing cause improper
operational control decisions to be made?
Do monitoring results inaccurately represent plant performance or are samples
collected improperly?
Process Control
Time on the Job
Water Treatment
Understanding
Application of Concepts and
Testing to Process Control
Does staff's short time on the job and associated unfamiliarity with process control
and plant needs result in inadequate or improper control adjustments?
Does the operator's lack of basic water treatment understanding contribute to
improper operational decisions and poor plant performance or reliability?
Is the staff deficient in the application of their knowledge of water treatment and
interpretation of process control testing such that improper process control
adjustments are made?
Operational Resources
Training Program
Technical Guidance
Operational
Guidelines/Procedures
Does inadequate training result in improper process control decisions by plant staff?
Does inappropriate information received from a technical resource (e.g., design
engineer, equipment representative, regulator, peer) cause improper decision or
priorities to be implemented?
Does the lack of plant-specific operating guidelines and procedures result in
inconsistent operational decision that impact performance?
MAINTENANCE
Maintenance Program
Preventive
Corrective
Housekeeping
Does the absence or lack of an effective preventive maintenance program cause
unnecessary equipment failures or excessive downtime that results in plant
performance or reliability problems?
Does the lack of corrective maintenance procedures affect the completion of
emergency equipment maintenance?
Does a lack of good housekeeping procedures detract from the professional image of
the water treatment plant?
Maintenance Resources
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?
LT2ESWTR Toolbox Guidance Manual
7-10
April 2010
-------
7. Combined and Individual Filter Performance
7.4.1.1 Type of Chemical and Dose
Optimizing the coagulation and flocculation for the range of water quality and demand
experienced by the plant is a key factor in improving the overall treatment performance and
ensuring process control. One method commonly used to evaluate the type and dose of coagulant
and other chemical additives is the jar test (AWWA 2000a).
To provide the process control necessary for producing consistently low filter water
turbidity, systems should establish SOPs for changing chemical additions when raw water
quality changes significantly. The SOPs should list the appropriate chemicals to be added and
the dose according to specified raw water conditions. Jar tests or other chemical evaluations
should be conducted with raw water samples representing conditions from high water quality to
the worst-case scenario and should reasonably represent the treatment process.
7.4.1.2 Mixing
Adding coagulants at the proper location and providing the right amount of mixing is
critical to the coagulation and flocculation processes.
• Metal salts such as alum and ferric chloride should be added at the point of highest
mixing.
• Low weight polymers can be added with the metal salts or at a second stage mixing
process.
• High weight polymers should be added at a point of gentle mixing.
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.
LT2ESWTR Toolbox Guidance Manual 7-11 April 2010
-------
7. Combined and Individual Filter Performance
5) Mechanical flash mixing.
6) Diffusion by pipe grid.
The mixing speed should be adjustable and changed with flow and raw water conditions
as necessary. Cold water is more viscous and may require a higher mixing energy. Highly turbid
or colored water may also require more mixing power to properly disperse the coagulant. For
flash mixing, Kawamura (2000) recommends G x t values of 300 to 1600, where G is the mixing
energy (expressed in seconds-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. Zeta potential monitors also indicate particle
surface charge and can be used in the same manner as SCDs.
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 SCD and zeta potential monitoring
results to jar tests on a regular basis (AWWA 2000a).
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:
LT2ESWTR Toolbox Guidance Manual 7-12 April 2010
-------
7. Combined and Individual Filter Performance
• Tapered mixing is most appropriate with variable G values ranging from 70 sec"1 to 15
sec"1.
• 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 should 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 re-suspend 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 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, such as the Area-Wide Optimization Program
(AWOP). This is a multi-state effort whose goal is to help conventional surface water treatment
plants optimize their existing particle removal and disinfection capabilities. For information on
AWOP, including state contacts, please visit this site:
http://www.asdwa.org/index.cfm?fuseaction=Page.viewPage&pageId=481&parentID=473&nod
eID=l. 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
LT2ESWTR Toolbox Guidance Manual 7-13 April 2010
-------
7. Combined and Individual Filter Performance
settling process can provide valuable information for optimizing the overall sedimentation
process.
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 <
2 NTU for raw water conditions of >
10 NTU
10 NTU
Note: For information on the Partnership for Safe Water, please visit this site:
http://vwwv.avwva.orq/Resources/PartnershipMain.cfm?ltemNumber=51227&navltemNumber=51231.
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
LT2ESWTR Toolbox Guidance Manual
7-14
April 2010
-------
7. Combined and Individual Filter Performance
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.
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.
LT2ESWTR Toolbox Guidance Manual 7-15 April 2010
-------
7. Combined and Individual Filter Performance
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
should minimize turbidity spikes in the filter effluent resulting from the backwashing process—it
only takes a few high turbidity readings to cause non-compliance. The following operational
practices may provide improved filter effluent during start-up:
Ramping the backwash rate down in increments to allow better media gradation.
Resting a filter after backwash for several minutes or up to several hours before putting
the filter in service.
Adding a polymer to the backwash water.
Slowly increasing the hydraulic load on the filter as it is brought back on line.
7.4.4.4 Filter to Waste
During the beginning of a filter cycle the filter is "ripening" and the effluent turbidity is
usually higher. To avoid sending this poorer quality water to the CFE stream, the filter effluent
produced during the first few minutes of a filter cycle can be sent to waste (filter to waste) or
recycled to the head of the plant. Some systems filter to waste or recycle until the filter effluent
reaches the desired level of turbidity. Practicing filter to waste produces an overall higher quality
water and may be necessary to maintain a CFE or IFE below 0.15 NTU.
7.4.4.5 Backwash Recycle
Plants that recycle the backwash water to the head of the plant should evaluate the
impacts the backwash stream has on the coagulation, flocculation, and sedimentation processes.
For example, the operator should know how the coagulation and flocculation processes need
adjusting when there is a 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 (FBR) 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)).
LT2ESWTR Toolbox Guidance Manual 7-16 April 2010
-------
7. Combined and Individual Filter Performance
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.
LT2ESWTR Toolbox Guidance Manual 7-17 April 2010
-------
7. Combined and Individual Filter Performance
7.5.2 Prevention and Response Plan for Loss of Chemical Feed
Loss of chemical feed is a common cause of increased turbidity through the treatment
processes. Plants should have equipment and SOPs for preventing such occurrences or reacting
to them rapidly if they do occur. The following items are necessary to prevent an upset in water
quality due to a chemical feed failure.
• SOPs to verify doses with feed response time (lag time) accounted for.
• Redundant feeds.
• Routine maintenance of all chemical feed parts (e.g., pump, feed line).
• Inventory of spare parts available so repairs can be made quickly.
• Pump or feed failure alarms.
• Process monitors detecting chemical feed failure (e.g., streaming current, zeta potential,
and pH monitors).
7.5.3 Adequate Chemical Storage
Sufficient chemical storage is necessary to ensure continued operation of the plant at
proper dosages, including enough to run at higher dosages if an unexpected turbidity spike
should occur in the raw water. Care must also be taken, however, to follow manufacturer's
suggestions on the useful life of the chemical. Many coagulants will degrade over time and will
not perform properly and may even cause increased turbidity if allowed to age too long. Storage
tanks should also be designed so that there are no dead spaces where chemicals may accumulate
with much longer residence times than the hydraulic residence time of the tank.
7.5.4 Voluntary Programs
EPA, state regulatory agencies, AWWA, and other drinking water organizations have
established voluntary programs for systems to ensure the delivery of safe water to their
customers. These programs often focus on optimizing the treatment process and identifying the
limiting factors of performance. Consequently, they are excellent aids for systems considering
this toolbox option. This section discusses two programs, the Partnership for Safe Water and the
CCP. (The CCP is also promoted as part of the Partnership for Safe Water).
LT2ESWTR Toolbox Guidance Manual 7-18 April 2010
-------
7. Combined and Individual Filter Performance
7.5.4.1 Partnership for Safe Water
The Partnership for Safe Water is a voluntary cooperative effort between EPA, AWWA,
and surface water systems. The goal of the program is to "provide a new measure of safety to
millions of Americans by implementing prevention programs where legislation or regulation
does not exist. The preventive measures are based around optimizing treatment plant
performance, and thus increasing protection against microbial contamination in America's
drinking water supply." (http://www.awwa.org/partner/partnerl.htm).
For further information about the Partnership for Safe Water and how to join, see AWWA's
website:
http ://www. awwa. org/Resources/PartnershipMain. cfm?ItemNumber=51227&navItemNumber=5
1231.
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
LT2ESWTR Toolbox Guidance Manual 7-19 April 2010
-------
7. Combined and Individual Filter Performance
performance from the facility. It can be conducted by the system or by a third party over a period
of roughly 3 to 4 days. The CTA builds on the results of the CPE by addressing the combination
of factors that limit a facility's performance. If conducted by a third party, it should be
implemented by a third party who is in a position to pursue corrective actions in all areas,
including politically sensitive, administrative, or operational limitations.
EPA published a handbook, Optimizing Water Treatment Plant Performance Using the
Composite Correction Program (1998), that fully describes the goals, methods, and procedures
of the CCP. To obtain a copy, call the EPA Safe Drinking Water Hotline at 1-800-426-4791.
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.
U.S. EPA. 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.
LT2ESWTR Toolbox Guidance Manual 7-20 April 2010
-------
8. Bag and Cartridge Filters
8.1 Introduction
Under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), bag and
cartridge filters are defined as pressure driven separation devices that remove particles larger
than 1 micrometer (|im) using an engineered porous filtration media. Bag filters are typically
constructed of non-rigid, fabric filtration media housed in a pressure vessel in which the
direction of flow is from the inside of the bag to the outside. Cartridge filters are typically
constructed as rigid or semi-rigid self supporting filter elements housed in pressure vessels in
which flow is from the outside of the cartridge to the inside (40 CFR 141.2).
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 National Science Foundation (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.
LT2ESWTR Toolbox Guidance Manual 8-1 April 2010
-------
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 conducted 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 (U.S. EPA 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 LT IESWTR does not change with the installation of a bag or
cartridge filter as a secondary filtration process. That is, a system would still monitor filter
effluent turbidity after the primary filters for compliance with the IESWTR and LT1ESWTR.
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)):
LT2ESWTR Toolbox Guidance Manual 8-2 April 2010
-------
8. Bag and Cartridge Filters
• Process meets the definition of a bag or cartridge filter.
• 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 LTIESWTR. 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
Raw
-o-l
11
C
Coagulation Fbcculaton
Sedimentation
Bag or Cartridge Filter
Granular Filers
*»»
Service pimo
ff needed)
i"
Qearwel
Distrtouiicn
System
Hcfi service pmip
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).
LT2ESWTR Toolbox Guidance Manual
8-3
April 2 010
-------
8. Bag and Cartridge Filters
Exhibit 8.2 Bag/Cartridge Filters in Series
Raw
water
Distribution
System
High service pump
Primary Bag or
Cartridge Fitters)
Secondary Bag or
Cartridge Filters)
Qearwell
Another possible configuration is a bag or cartridge filter followed by an ultraviolet light
(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 (U.S. EPA 2006)
for information regarding UV systems and associated requirements with LT2ESWTR.
Exhibit 8.3 Bag/Cartridge Filter with UV System
water
/—? - »
~P\J
Bag or Cartridge
Fitters)
UVSvstem
Distribution
System
v. J High service pump
Clearw&ll
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
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.
LT2ESWTR Toolbox Guidance Manual
8-4
April 2010
-------
8. Bag and Cartridge Filters
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 (U.S. EPA 2007) for additional
recommendations.
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
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 ofCryptosporidium 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
LT2ESWTR Toolbox Guidance Manual 8-5 April 2010
-------
8. Bag and Cartridge Filters
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 (U. S. EPA 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 (LRV) 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
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 ofCryptosporidium.
8.4.1.2 Challenge Particulate
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
particulate 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. Chapters of EPA's Membrane Filtration Guidance Manual (\J.S. EPA 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.
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.
LT2ESWTR Toolbox Guidance Manual 8-6 April 2010
-------
8. Bag and Cartridge Filters
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:
Equation 8-1
Maximum Feed Concentration = 1.0 x 104 x Filtrate Detection Limit
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 8-1 - 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.
• 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.
LT2ESWTR Toolbox Guidance Manual 8-7 April 2010
-------
8. Bag and Cartridge Filters
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 nephelometric turbidity units
(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. Paniculate 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
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
LT2ESWTR Toolbox Guidance Manual 8-8 April 2010
-------
8. Bag and Cartridge Filters
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 (U.S. EPA 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 (U.S. EPA 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
(U.S. EPA 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 quality assurance/quality control (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
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.
LT2ESWTR Toolbox Guidance Manual 8-9 April 2010
-------
8. Bag and Cartridge Filters
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 (U.S. EPA 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.
Equation 8-2
LRV =Logio(Cf)-Logio(CP)
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 8-2 - 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.
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:
LT2ESWTR Toolbox Guidance Manual 8-10 April 2010
-------
8. Bag and Cartridge Filters
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.
• 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).
LT2ESWTR Toolbox Guidance Manual 8-11 April 2010
-------
8. Bag and Cartridge Filters
Exhibit 8.4 Single Filter Vessel
i
Atfustable 16" Starwtonl
Outlet
131.*" Foot Print
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.
LT2ESWTR Toolbox Guidance Manual
8-11
April 2 010
-------
8. Bag and Cartridge Filters
Exhibit 8.5 Manifold Bag Filter Design
Exhibit 8.6 Multiple Filter Vessel
56 1/2
Hydraulic lid
opening jack
12 3/4"Foot Print
Source: U.F. Strainrite
LT2ESWTR Toolbox Guidance Manual
8-13
April 2010
-------
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 particulate 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 clogs the filter media faster 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 and to allow for filter
maintenance and replacement. 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.
LT2ESWTR Toolbox Guidance Manual 8-14 April 2010
-------
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.
• 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 few 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.
LT2ESWTR Toolbox Guidance Manual 8-15 April 2010
-------
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 the outlet header should be monitored to
determine when the filter needs replacement. Also the differential pressure should be monitored
immediately after replacing a filter and placing the unit back in service to verify that the filter
was properly installed to prevent bypassing around the seals. An alarm could also be linked to
the pressure gauges to ensure the operator is alerted when a filter needs to be replaced due to
fouling or failure of the filer or associated seals.
8.6.2 Water Quality Monitoring
In addition to monitoring the pressure drop across the filter, the influent and effluent
turbidity or particle count can 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 can be checked daily. If the filter is used to meet the treatment
requirements of IESWTR/LT1ESTWR, turbidity monitoring is required and the state will set a
turbidity performance standard. During the initial start-up phase of a newly integrated bag or
LT2ESWTR Toolbox Guidance Manual 8-16 April 2010
-------
8. Bag and Cartridge Filters
cartridge filtration system, monitoring can be more frequent and then can be reduced once the
operator becomes familiar with the system. If continuous monitoring of turbidity and/or pressure
differential is employed, the output from the sensors should be sent to an alarm to warn operators
of sudden changes in operation, or if the filter element needs replacing.
EPA recognizes turbidity has limitations as an indicator of filter failure or pathogen
breakthrough. However, in the absence of a better indicator, monitoring both influent and
effluent turbidity over a full run (i.e., from start to end of the filter life) can provide a
performance baseline. The baseline can then be used to indicate process upsets. This method
may not be applicable to systems with very low raw water turbidity or where the influent has
been filtered; 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
U.S. EPA. 2005. Membrane Filtration Guidance Manual. Office of Water. EPA 815-R-06-009.
November, 2005. http://www.epa.gov/ogwdw/disinfection/lt2/compliance.html.
U.S. EPA. 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/1 t2/compliance.html.
U.S. EPA. 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.
LT2ESWTR Toolbox Guidance Manual 8-17 April 2010
-------
9. Second Stage Filtration
9.1 Introduction
The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) 40 CFR
141.719(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 may
receive 0.5 log credit for Cryptosporidium removal (40 CFR 141.719(c)) under the following
conditions.
• 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.
Under the LT2ESWTR, a system integrating a slow sand filtration process for the second
stage of filtration can receive 2.5 log credit for Cryptosporidium removal (40 CFR 141719(d))
under the following conditions.
LT2ESWTR Toolbox Guidance Manual 9-1 April 2010
-------
9. Second Stage Filtration
• 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 verify that 100 percent of the flow was filtered through both stages and that the
first stage was preceded by a coagulation step (40 CFR 141.721(f)).
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.
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.
LT2ESWTR Toolbox Guidance Manual 9-2 April 2010
-------
9. Second Stage Filtration
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.
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
LT2ESWTR Toolbox Guidance Manual 9-3 April 2010
-------
9. Second Stage Filtration
second stage is also not specified; however, typical design standards for regular or deep bed
filters should be followed.
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.
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 combined filter effluent (CFE) of the second stage. Individual filter
LT2ESWTR Toolbox Guidance Manual 9-4 April 2010
-------
9. Second Stage Filtration
effluent (IFE) monitoring of the second stage filters on a continuous or routine basis may identify
performance issues that can be addressed proactively.
LT2ESWTR Toolbox Guidance Manual 9-5 April 2010
-------
10. Chlorine Dioxide
10.1 Introduction
Chlorine dioxide (C1O2) 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 (U.S. EPA 1991) (commonly
referred to as the Surface Water Treatment Rule Guidance Manual).
- Describes how to calculate the contact time (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 (U.S. EPA 1999) provides full
descriptions of:
- Chlorine dioxide chemistry.
- On-site generation.
- Primary uses and points of applications.
- Pathogen inactivation and disinfection efficiency.
- Byproduct production.
- Analytical methods.
- Operational considerations.
The Alternative Disinfectants and Oxidants Guidance Manual is available on EPA's
website, http://www.epa.gov/safewater/mdbp/implement.html.
LT2ESWTR Toolbox Guidance Manual 10-1 April 2010
-------
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 0.25- 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 CT and is defined in the LT2ESWTR (40 CFR
141.720(a)):
LT2ESWTR Toolbox Guidance Manual 10-2 April 2010
-------
10. Chlorine Dioxide
CT = Disinfectant (mg/L) x Contact Time (minutes)
"T" is the time (in minutes) it takes the water, during peak hourly flow, to move from the point
of disinfectant application to a point where, C, residual concentration is measured 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.
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).
LT2ESWTR Toolbox Guidance Manual 10-3 April 2010
-------
10. Chlorine Dioxide
Exhibit 10.1 CT Values (mg-min/L) for Cryptosporidium Inactivation by Chlorine
Dioxide
1
Log
credit
U.^D
U.G
1.U
1.5
Z.(J
Z.3
J.U
Water Temperature, C
<-U.D
isy
3iy
bj/'
yj)t>
I^VD
iDy4
nyi^
i
1D3
3UD
(DID
yiD
1ZZ(J
1Dz!D
ia3U
2
14U
zvy
D^a
aja
m /
uyt)
ib/'D
j
i^a
z!Dt)
DTI
(&(
1UZ6
\2.it$
1DJ4
D
1(J(
z!14
4^y
t)4J
a^a
1U/ Z
i^at)
/
yu
nau
jbu
Djy
ny
ayy
lu/y
1U
by
ua
^/ 1
41D
DDJ
eyi
aju
ID
4D
ay
i /y
z!ba
JD/
44 /
DJb
Z(J
zv
Da
i id
1M
^j^
z:ay
J4/
^D
iy
ja
/D
nj
1DU
naa
ZZ£>
JU
i^
z!4
4y
(6
ya
I/:/:
14^
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)(1)
Example CT Calculation
A plant draws 1.5 million gallons per day (MGD) 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:
C initial = 1.8 mg/L
Centering tank =1.6 mg/L
Cleaving tank = 0.8 mg/L
Cleaving 2nd pipe = 0.2 mg/L
Exhibit 10.2 CT Calculation Example Schematic
Gn-1,8rng/L
Q Transmission line
Big tank
SudmacLake
2 miles
0.25 miles
Segment 1
Segment 2
Segments
LT2ESWTR Toolbox Guidance Manual
April 2010
-------
10. Chlorine Dioxide
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) = (7ir2Li/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)* jc*(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)T*(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.
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:
= (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 CTtabie in Exhibit 10.1. For 5°C and 0.5-log inactivation,
CTtabie = 214mgxmin/L
Step 3. Calculate the ratio of CTcaic/CTtabie for each segment.
! = 95.2/214 = 0.44
(CTcaic/CTtabie)2 = 120 7214 = 0.56
(CTcalc/CTtable)3 = 1.5/214 = 0.01
Step 4. Sum the CTcaic/CTtabie for each segment.
(CTcaic/CTtabie)totai = 0.44 + 0.56 + 0.01 = 1.01
LT2ESWTR Toolbox Guidance Manual 10-5 April 2010
-------
10. Chlorine Dioxide
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.
This example is intended to show a CT determination. Meeting log inactivation requirements
using a disinfectant in a raw water supply may not be appropriate for raw water conditions (e.g.,
high turbidity) that may interfere with disinfectant efficacy.
10.3 Monitoring Requirements
10.3.1 LT2ESWTR
The LT2ESWTR requires CT calculation at least once per day with both C and T
measured during peak hourly flow (40 CFR 141.720 (a)). Since systems may not know when
the peak hourly flow is, EPA recommends monitoring flow on an hourly basis. Continuous flow
monitoring and recording can also be used to determine peak flow. Systems should reevaluate
CT 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
Standard Methods for the Examination of Water and Wastewater, 20th edition, American Public
Health Association, 1998.
Note, if a system changes its disinfection process, the LT2ESWTR requires the system to
calculate a disinfection profile and benchmark (40 CFR 141.708) (see Chapter 1, section 1.4.5
for details).
10.3.2 Stage 1DBPR
The Stage 1 DBPR requires all systems using chlorine dioxide for disinfection or
oxidation to monitor daily for chlorine dioxide and chlorite at the distribution system entry point.
In addition, systems must take monthly chlorite samples at three locations in the distribution
system. Exhibit 10.3 lists the chlorine dioxide and chlorite distribution system monitoring
requirements.
LT2ESWTR Toolbox Guidance Manual 10-6 April 2010
-------
10. Chlorine Dioxide
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 At Average Residence Time
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). Depending on the results of the additional samples, the system could have an acute
violation with more serious public notification requirements than for a chlorine MRDL violation.
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 ofGiardia and 4-1 og 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
Chlorine dioxide (C1O2) is an uncharged compound of chlorine in the +IV oxidation
state. It is a relatively small, volatile, and highly energetic molecule, and a free radical even in
dilute aqueous solutions. At high concentrations, it reacts violently with reducing agents.
However, it is stable in dilute solution in a closed container in the absence of light. When an
aqueous solution is open to the atmosphere, chlorine dioxide readily comes out of solution.
Aqueous solutions of chlorine dioxide are also susceptible to photolytic decomposition,
depending on the time of exposure and intensity of ultraviolet light (UV) light.
LT2ESWTR Toolbox Guidance Manual 10-7 April 2010
-------
10. Chlorine Dioxide
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 (ClOs") 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.
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:
LT2ESWTR Toolbox Guidance Manual 10-8 April 2010
-------
10. Chlorine Dioxide
• 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 disinfection byproducts (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 granular activated carbon (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
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
LT2ESWTR Toolbox Guidance Manual 10-9 April 2010
-------
10. Chlorine Dioxide
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.
10.7.2 Point of Addition
There are two main considerations for determining locations of chlorine dioxide addition
for the purpose of Cryptosporidium inactivation—CT 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 CT 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 CT.
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).
LT2ESWTR Toolbox Guidance Manual 10-10 April 2010
-------
10. Chlorine Dioxide
Based on the research discussed above, the optimal conditions for Cryptosporidium
disinfection with chlorine dioxide are low turbidity, high pH, and high temperature.
10.9 Safety Issues
Because chlorine dioxide can be explosive and pose
acute health risks to those exposed to gaseous chlorine
dioxide, a safety plan should be developed that includes
precautions for generation, handling, storage, and emergency
response.
Airborne concentrations
greater than 10 percent
may cause explosions.
10.9.1 Chemical Storage
Most chlorine dioxide generators use sodium chlorite solutions as a raw material. If
sodium chlorite solutions are accidently acidified or exposed to a reducing agent, uncontrolled
production and release of gaseous chlorine dioxide can result. In addition to being toxic, if the
gaseous chlorine dioxide reaches concentrations greater than 10 percent, it can spontaneously
explode.
Sodium chlorite should be stored away from other chemicals, particularly any acid
solutions or chemicals that could act as reducing agents. Construction materials in sodium
chlorite storage areas, as well as chlorine dioxide generating areas, should be fire resistant such
as concrete. Sodium chlorite fires burn especially hot and produce oxygen as a byproduct, so
special fire fighting techniques are required to extinguish the fire. These firefighting techniques
should be part of the safety plan and proper equipment and supplies should be stored nearby.
Temperatures in storage and generation areas should be kept below 30 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
Aieta, E., and J.D.Berg. 1986. A Review of Chlorine Dioxide in Drinking Water Treatment. J.
AWWA. 78(6):62-72.
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.
LT2ESWTR Toolbox Guidance Manual 10-11 April 2010
-------
10. Chlorine Dioxide
APHA. 1998. Standard Methods for the Examination of Water and Wastewater, 20th edition,
American Public Health Association.
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.
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.
U.S. EPA. 1999. Alternative Disinfectants andOxidants Guidance Manual. EPA 815-R-99-014.
April, 1999. http://www.epa.gov/safewater/mdbp/mdbptg.html.
U.S. EPA. 1991. Guidance Manual for Compliance with the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water Sources. Washington, D.C.
U.S. EPA. 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.
LT2ESWTR Toolbox Guidance Manual 10-12 April 2010
-------
11. Ozone
11.1 Introduction
Ozone is commonly used in drinking water treatment for disinfection as well as taste and
odor control. Ozone is a strong oxidant that can inactivate microorganisms, including
Cryptosporidium, Giardia, and viruses, as well as oxidize and break down natural organic matter
(NOM). 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), 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 (U.S. EPA 1991) (commonly
referred to as the SWTR Guidance Manual).
- Describes how to calculate the contact time (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 ofGiardia and viruses.
• Alternative Disinfectants and Oxidants Guidance Manual (U. S. EPA 1999) provides full
descriptions of:
- Ozone chemistry
- On-site generation
- Primary uses and points of application
- Byproduct production
- Analytical methods
- Operational considerations
The SWTR Guidance Manual and Alternative Disinfectants and Oxidants
Guidance Manual are available on EPA's website:
http://www.epa.gov/safewater/mdbp/implement.html
LT2ESWTR Toolbox Guidance Manual 11-1 April 2010
-------
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 Long Term
2 Enhanced Surface Water Treatment Rule (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 as well
as 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 0.25 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
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:
LT2ESWTR Toolbox Guidance Manual 11-2 April 2010
-------
11. Ozone
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 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 inactivation 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
(40CFR141.730)
Log
credit
0.25
0.5
1.0
1.5
2.0
2.5
3.0
Water Temperature, "C1
<=0.5
6.0
12
24
36
48
60
72
1
5.8
12
23
35
46
58
69
2
5.2
10
21
31
42
52
63
3
4.8
9.5
19
29
38
48
57
5
4.0
7.9
16
24
32
40
47
7
3.3
6.5
13
20
26
33
39
10
2.5
4.9
9.9
15
20
25
30
15
1.6
3.1
6.2
9.3
12
16
19
20
1.0
2.0
3.9
5.9
7.8
9.8
12
25
0.6
1.2
2.5
3.7
4.9
6.2
7.4
>30
0.39
0.78
1.6
2.4
3.1
3.9
4.7
1CT values between the indicated temperatures may be determined by linear interpolation.
The CT values reported in Exhibit 11.1 were developed from the following equation:
Cryptosporidium Log Credit = 0.0397 x (l .0975l)Temp x CT Equation 11-1
where "Temp" is the water temperature expressed in degrees Celsius between 0.5 and 25 °C. A
water system may use the above equation in lieu of the table. Equations for Giardia and virus
shown below for ozone were derived from the kw values presented in Appendix O to the SWTR
Guidance Manual for Giardia and virus.
Giardia Log Credit = 1.0380x(l.074l)rem;' xCT
virus Log Credit = 2.1744x(1.0726)^ xCT
Equation 11-2
Equation 11-3
LT2ESWTR Toolbox Guidance Manual
11-3
April 2010
-------
11. Ozone
If a utility believes that the CT values for Cryptosporidium presented in Exhibit 11.1 or
calculated by Equation 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.
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 Giardia and virus inactivation credit for a "first chamber" (i.e. dissolution chamber; see
section O.3.3 of Appendix O of the SWTR guidance manual ) of an ozone contactor, provided
that the residual ozone concentration measured at the outlet from the first chamber met minimum
concentration levels. For Cryptosporidium, 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 TIO, EPA recommends using the
Continuous Stirred Tank Reactor (CSTR) approach (described below) or the Extended CSTR
approach (described in Appendix B). In the SWTR Guidance Manual methods were presented
for determining the ratio of TIO to the theoretical hydraulic detention time (HDT) based on
baffling characteristics (see Table C-5 of the SWTR Guidance Manual). However, these TIO/
(HDT) ratios based on baffling characteristics were based on baffling characteristics 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 and hence tracer studies are
recommended for determining Tio/HDT ratios.
This guidance manual presents four methods for calculating CT in an ozone contactor:
Method.
• CSTR Method.
• Extended TIO Method.
• Extended CSTR Method.
These methods differ in the level of effort associated with them. Selecting the appropriate
method(s) to use depends on the configuration of the ozone contactor, the availability of state-
approved tracer testing results, and the amount of process evaluation and monitoring that a
LT2ESWTR Toolbox Guidance Manual 11-4 April 201 0
-------
11. Ozone
system wishes to undertake. The TIO and CSTR methods 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 TIO and Extended CSTR methods. Exhibit 11.2
summarizes the current methods, including a description of the situations when their use is
appropriate. It should be noted that, while this Manual is focused on Cryptosporidium
inactivation, any of the four CT calculation methods discussed herein can also be applied to
calculate the CT for obtaining credits for Giardia or virus inactivation in an ozone contactor
under the requirements of the SWTR, recognizing that the first chamber credit for Giardia and
virus inactivation provided under the SWTR remain valid, while no such credit is recommended
for Cryptosporidium.
LT2ESWTR Toolbox Guidance Manual 11-5 April 2010
-------
11. Ozone
Exhibit 11.2 Recommended Methods and Terminology for Calculating the
Log-lnactivation Credit in an Ozone Contactor
Without Tracer Data
With Approved Tracer Data
Section
Description
Terminology
Method for Calculating
Log-lnactivation
Recommended Restrictions
Chambers where ozone is added
First chamber
Other chambers
First Dissolution
Chamber
Co-Current or
Counter-Current
Dissolution
Chambers
No Cryptosporidium log-
inactivation credit is
recommended
CSTR Method in each
chamber with a
measured effluent ozone
residual concentration
The SWTR criteria for 1st chamber
credit should still be used if
calculating inactivation of Giardia
and virus
No credit should 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
Reactive Zone
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
The SWTR criteria for 1st chamber
credit should still be used if
calculating inactivation of Giardia
and virus
Chambers where ozone is added
First chamber
Other chambers
First Dissolution
Chamber
Co-Current or
Counter-Current
Dissolution
Chambers
No Cryptosporidium log-
inactivation is credited to
this section
T10,orCSTR Method in
each chamber with a
measured effluent ozone
residual concentration
The SWTR criteria for 1st chamber
credit should still be used if
calculating inactivation of Giardia
and virus
No credit should 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
Reactive Zone
Reactive
Chamber(s)
Extended T10 or
Extended CSTR Method
in each chamber. The
Extended CSTR method
is not appropriate for
non-conventional
contactors.
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
LT2ESWTR Toolbox Guidance Manual
11-6
April 2 010
-------
11. Ozone
The remainder of this section describes how to calculate C for the TIO and CSTR
methods and then describes the TIO and CSTR methodologies.
11.3.1 Measuring C for TIO and CSTR Methods
The recommended 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 measurement 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 characteristic 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 that involves predicting the characteristic C based on outlet
measurements, the correlations presented in Exhibit 11.3 should be used based on C;n and Cout
measurements. 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).
Exhibit 11.3 Correlations to Predict C* Based on Ozone Residual Concentrations
in the Outlet of a Chamber
Method
TIO
CSTR
Turbine
C0ut
C0ut
Dissolution Chamber
Co-Current Flow
Cout or (Cin+Cout)/2
Cout or (Cin+Cout)/2
Dissolution
Chamber Counter-
Current Flow
Cout/2
Cout/2
Reactive Chamber
C0ut
C0ut
C* - Characteristic concentration, used for CT calculation.
Cout - Ozone residual concentration at the outlet from the chamber.
Cjn - Ozone residual concentration at the inlet to the chamber, which can be Cout of the immediate upstream
chamber.
11.3.2
Method
Using the TIO approach, the TIO is the time at which 10 percent of the water in the
contactor or segment has passed through the contactor or segment. EPA recommends that tracer
studies be used to determine the Tio/HDT ratio for ozone contactors. The SWTR Guidance
Manual and Tracer Studies in Water Treatment Facilities: A Protocol and Case Studies describe
how to conduct a tracer test.
Appendix C of the SWTR Guidance Manual provides a description of tracer studies and
tracer study methods. Appendix E of this guidance provides a description of tracer test
development and analysis. In general, tracer studies should represent the range of flow and
LT2ESWTR Toolbox Guidance Manual
11-7
April 2010
-------
11. Ozone
operational conditions expected for the ozone process and should include data quality criteria
(i.e. percent tracer recovered). Tracer chemicals should be conservative (high percent recovery)
and should be acceptable to the primacy agency for use in public water systems.
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 CTcaicby multiplying the measured C and T values. Sum CTcaic for individual
segments to obtain CTcaic for the entire ozone contactor.
2) Calculate log inactivation credit using CT tables, or Equations 11.1, 11.2 or 11.3.
3) Calculate the Inactivation Ratio as Log-Credit Achieved / Log-Credit Required.
4) If the Inactivation Ratio is at least 1.0, then the treatment process provides the level of log
inactivation desired.
Example CT Calculation and Log Credit Determination using the TwMethod
A water system employs a four 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
C40ut = °-
'
Chamber 1
Counter-Current
o o o o o
I
Chamber 2
Co-Current
O o °O O O
T
1
Chambers
Counter-Current
OQ O O O
Chamber 4
Reactive Flow
T
C, out = 1.2 mg/L = C2n
C3out = 0.9 mg/L = C4in
The water temperature is 5 degrees Celsius. Each chamber has a volume of 1,000 gallons.
The flowrate through the contactor is 100 gpm. Results from a tracer test showed the Tio/HDT
ratio for the contactor is 0.60.
LT2ESWTR Toolbox Guidance Manual
11-8
April 2010
-------
11. Ozone
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 11.3, C can be determined with the
following equations:
Chamber 2: C = (Cin + Cout) / 2 or C = C
Chambers: C = Cout/2
Chamber 4: C = Cout
Therefore for:
out
Chamber 2: C = (1.2 + 0.8) / 2 = 1.0 mg/L (this equation gives the higher C value)
Chamber 3: C = 0.9 / 2 = 0.45 mg/L
Chamber 4: C = 0.0 mg/L
2) Calculate the T for each chamber.
The TIO measured across all four chambers is divided proportionally by volume among
the four chambers. This method should not be used if the sum of the volumes of the chambers
with effluent ozone concentrations of zero (non-detectable) is 50 percent or greater than the
entire volume of the chambers. In this example, only the last chamber had a non-detectable final
concentration and that chamber is 25 percent the volume of all the chambers. Therefore the
overall TIO can be extrapolated among the chambers to estimate individual chamber TIO values.
Tin of each chamber =
T
-* i r
HDT
xHDT,
T
-* ir
HDT
Vol
chamber
Flowrate
1000
100
= 6
mm.
(In this example, the volume of each chamber is the same. Therefore, the TIO of each
chamber is also 6 minutes)
3) Calculate the CT for each chamber. CT for the total contactor is the sum of the CT for
individual chambers.
Chamber 1: not calculated
Chamber 2: CT = 1.0 mg/L x 6 min = 6.0 mg-min/L
Chamber3: 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
Total CT = 8.7 mg-min/L
4) Calculate the Cryptosporidium log credit using Equation 11-1:
Cryptosporidium Log Credit = 0.0397x(l.09757)5 x8.7 = 0.55 logs
LT2ESWTR Toolbox Guidance Manual
11-9
April 2010
-------
11. Ozone
5) Calculate Cryptosporidium inactivation Ratio as 0.55/0.5 = 1.1.
The inactivation ratio is greater than 1.0, and 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 (Tio/HDT < 0.5) or when no tracer data is available. This method uses the HDT 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, log inactivation is calculated with the following equation:
-Log (I/I0) = Log (1 + 2.303 x kio x C x HDT) Equation 11-4
where:
-Log (I/Io) = the log inactivation
kio = log base 10 inactivation coefficient (L/mg-min)1
C = Concentration from Exhibit 11-3 (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
1
0.0430
2
0.0482
3
0.0524
5
0.0629
7
0.0764
10
0.101
15
0.161
20
0.254
25
0.407
>30
0.648
To interpolate between the temperatures in the table, Equation 11-5 can be used.
kw = 0.0397 x (1.09757femp Equation 11-5
k10 is calculated from the CT table with the following equation: Log inactivation = k10 x CT
LT2ESWTR Toolbox Guidance Manual
11-10
April 2010
-------
11. Ozone
In order to apply Equation 11-4, 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 provide a larger CT credit than CSTR method alone, so the basic
CSRT method will likely not be used.
EPA recognizes that, for many situations, either the CSTR or the 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
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, Exhibit 11-4 shows the
kio value at 0.101 L/mg-min. The HDT for each chamber is 20 minutes.
Chamber 1
Counter-Current
O o °
o o
1
Chamber 2
Counter-Current
0 o °0 0 0
Chambers
Reactive Flow
T
C3out - 0.2 mg/L
icut = 0-3 mg/L = C2in
C2out = 0.3 mg/L
1) Determine the C values for each chamber for the CSTR calculation
Chamber 1: No Cryptosporidium inactivation credit recommended
Chamber 2: C = C2out/2 = 0.3 / 2 = 0.15 mg/L
Chamber 3: C = C3out = 0.2 mg/L
LT2ESWTR Toolbox Guidance Manual
11-11
April 2010
-------
11. Ozone
2) Calculate the log inactivation for each chamber using Equation 11-4
Chamber 2: Log inactivation = Log(l + 2.303x0.101x0.15x20) = 0.23
Chambers: Log inactivation = Log(l + 2.303x0.101x0.20x20) = 0.28
3) Sum the log inactivation values to determine the total log credit achieved.
The total log-inactivation across the contactor is 0.23 + 0.28 = 0.51 log inactivation,
which is greater than the target of 0.5 logs. Therefore, 0.5 log credit is achieved.
Example - CT Calculation and Log Credit Determination using the CSTR Method with the
concentration not measured for each chamber
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 = 0.101 L/mg-min. The HDT for each chamber = 20 minutes. Chambers
3 and 4 are considered a single zone, and the effluent concentration of Chamber 3 is assumed to
be equal to that of Chamber 4.
Chamber 1
Counter-current
0o°ocP0
U0 000 0°
i
r
Chamber 2
Counter-current
°0 OOo 0°
i
r
Chamber 3
Reactive Flow
T
r
Chamber 4
Reactive Flow
k.
ciou, = 0-3 mg/L = Cm C2ou1 = 0.3 mg/L
4out = 0.1 mg/L
1) Determine the C values for each chamber
Chamber 1: No Cryptosporidium inactivation credit recommended
Chamber 2: C = C2out/2 = 0.3 / 2 = 0.15 mg/L
Chamber 3: C = C/tout = 0.1 mg/L
Chamber 4: C = C/tout = 0.1 mg/L
2) Calculate the log inactivation for each chamber using Equation 11-4
LT2ESWTR Toolbox Guidance Manual
11-12
April 2010
-------
11. Ozone
Chamber 2: Log inactivation = Log(l + 2.303x0.101x0.15x20) = 0.23
Chamber3: Log inactivation = Log(l + 2.303x0.101x0.10x20) = 0.17
Chamber 4: Log inactivation = Log(l + 2.303x0.101x0.1x20) = 0.17
3) Sum the log inactivation values 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, the minimum 0.5 log credit is achieved.
11.3.4 Extended TIO and Extended CSTR Methods
The Extended TIO and Extended CSTR methods require the measurement of the ozone
concentration at a minimum of three points within the contactor. These data are used to predict
an ozone concentration profile through the contactor. The Extended methods generally result in
greater CT credit and hence lower doses of ozone needed to achieve the same calculated level of
inactivation, when compared to the direct TIO or CSTR method. Appendix B provides a complete
description of the extended methods and how they are applied to an ozone contactor.
11.4 Monitoring Requirements
11.4.1 LT2ESWTR
The LT2ESWTR (40 CFR 141.720(a)) requires daily CT monitoring conducted during
peak hourly flow. Since systems may not know when the peak hour flow will occur, EPA
recommends monitoring on an hourly basis. Systems should re-evaluate 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 is measured with the indigo methods, Standard Method 4500-
O3 B and Standard Method 4500 O3 B-97. Details on these methods can be found in Standard
Methods for the Examination of Water and Wastewater, 20th edition, American Public Health
Association, 1998. Appendix C provides information on sample collection, preparation and
stability of reagent, and calibration and maintenance of online monitors.
11.4.2 Stage 1 DBPR and Stage 2 DBPR
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. Under the Stage
2 DBPR (40 CFR 141.132 (b) (3) (ii) (B), beginning April 1, 2009, systems may reduce
monitoring from monthly to quarterly if the system demonstrates that the running annual average
LT2ESWTR Toolbox Guidance Manual 11-13 April 2010
-------
11. Ozone
raw water bromide concentration is less than 0.0025 mg/L, based on monthly measurements for
the most recent four quarters. Systems that were allowed to reduce bromate monitoring to
quarterly prior to April 1, 2009, may remain on quarterly monitoring if the running annual
average raw water bromide concentration is less than 0.0025 mg/L. The MCL for bromate is 10
|ig/L based on a running annual average.
11.5 Unfiltered System LT2ESWTR Requirements
The LT2ESWTR requires unfiltered systems to meet the following requirements (40 CFR
141.712(b), (c)and(d)):
• 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
141.712(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.
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 those for Giardia and virus, and capital requirements could be substantial for a
system seeking higher than 0.5 log 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.
LT2ESWTR Toolbox Guidance Manual 11-14 April 2010
-------
11. Ozone
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.
• Lower formation of trihalomethanes (THMs) and haloacetic acids (HAAs) upon post
chlorination due to precursor removal and generally lower chlorine doses.
• Biological stability when ozonation is followed 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 disinfection byproduct (DBF)).
• Potential enhanced formation of other unregulated DBFs either from ozonation alone
(e.g. formaldehyde) or upon secondary chlorination/chloramination (e.g. chloropicrin).
• 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).
LT2ESWTR Toolbox Guidance Manual 11-15 April 2010
-------
11. Ozone
11.7 Disinfection With Ozone
11.7.1 Chemistry
The stability of ozone upon dissolution into natural waters is governed by both the direct
reaction of ozone with various constituents in the water, as well as the so-called "auto catalytic
chain decomposition" reaction. The general behavior in the dissolved ozone concentration over
time has been described by numerous investigators (e.g. Park et al. 2001; Elovitz et al. 1999,
2000) as a two-stage process: an initial rapid consumption step (ozone consumed after a few
seconds to 30 seconds) followed by a slower ozone decay step which can often be described by
first-order kinetics. Various water quality parameters, including temperature, pH, DOC
concentration, DOC character, and alkalinity, as well as the ozone dose can affect the amount
and rate of ozone consumed in these two stages (Elovitz et al. 2000; Park et al. 2001; Buffle et al.
2006). For example, increasing ozone dose can increase the amount of ozone consumed in the
initial reaction phase; however, the rate of ozone decay in the second phase is slower. This is of
importance for considerations to ozone dose requirements in order to maintain dissolved ozone
for sufficient disinfection (i.e. CT requirements).
One of the consequences of the spontaneous decomposition of ozone during water
treatment is the generation of hydroxyl free radicals (Hoigne and Bader 1983a, 1983b; Glaze et
al. 1987). The hydroxyl free radicals are among the most reactive oxidizing agents in water, with
most reaction rates on the order of 108 - 1010 M"1 s"1. Because of their high reactivity, the half-life
of hydroxyl free radicals is on the order of microseconds. The formation of hydroxyl radicals is
affected by the same water quality parameters that affect ozone decomposition (see above), and
is also vastly different in the initial reaction phase versus the secondary reaction phase (Elovitz et
al. 1999, 2000; Buffle et al. 2006). Under typical conditions for ozonation of drinking water
source waters, the transient concentration of the hydroxyl free radicals can reach as high as 10"11
M during the first 20 milliseconds of the initial reaction phase (Buffle et al. 2006). During the
secondary phase, hydroxyl radical concentrations are typically on the order of 10"13 to 10"14 M
(Elovitz et al. 1999, 2000) and reach levels above 10"12 M under typical ozonation conditions
(Glaze and Kang 1988). Despite these low transient concentrations, the hydroxyl free radical can
be a very important reactant for the oxidation of constituents that are slow reacting with respect
to molecular ozone. Under certain conditions, an ozonation process can be operated with the
intent of creating an "Advanced Oxidation Process" (AOP) which purposefully enhances the
formation of hydroxyl free radicals from the decomposition of ozone. While the enhanced
formation of hydroxyl radicals can lead to enhanced oxidation of certain micropollutants, it will
also lower the overall ozone CT. The application of AOPs is discussed further in Chapter 7 of the
Alternative Disinfectants Guidance Manual for information on advanced oxidation processes).
LT2ESWTR Toolbox Guidance Manual 11-16 April 2010
-------
11. Ozone
Exhibit 11.5 illustrates the major pathways that develop during ozonation:
• Direct oxidation of compounds by molecular ozone in the aqueous phase.
• Oxidation of compounds by hydroxyl free radicals produced during the decomposition of
ozone.
As indicated in Exhibit 11.5, 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. In addition, the concentration of ozone is orders of
magnitude greater then the concentration of hydroxyl radicals. Hence, when assessing the role of
the two pathways, both the intrinsic reaction rate as well as the concentration of the two oxidants
must be considered.
The reaction of hydroxyl free radicals with carbonate and bicarbonate produces carbonate
and bicarbonate radicals. These free radicals may also participate in the oxidation of chemical
and microbial species. However, these reactions tend to be selective and, with some exception,
their contribution to micropollutant oxidation is negligible compared to the two main pathways.
Exhibit 11.5 Reaction Pathways of Ozone in Water
- 3(aqueous)
Direct Pathway
Slower
Selective
Oxidation of Substrate and
Microbial Inactivation
Byproducts
Indirect Pathway
OH
Fast
Non-Selective
Oxidation of Substrate and
Microbial Inactivation
Byproducts
CO,-2 and HCO3 >
co3-
* and HCO3 •
-> Byproducts
LT2ESWTR Toolbox Guidance Manual
11-17
April 2010
-------
11. Ozone
11.7.2 Byproduct Formation
Reactions between ozone and 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 jig/1. Oxidation of bromide to hypobromous acid during ozonation, and subsequent reaction of
he hypobromous acid with natural organic matter can lead to the formation of brominated
organic compounds, 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 formation
occurs through a very complex, nonlinear mechanism involving both ozone and hydroxyl free
radical pathways. Bromate formation generally increases with increasing pH, carbonate
alkalinity, ozone dose, and temperature, and perhaps most importantly, bromide concentration.
However, attempts at reducing bromate formation by lowering pH may increase the formation of
brominated organic byproducts. Other methods for minimizing bromate formation during
ozonation include ammonia addition (Hoffman et al. 2001), and more recently the so-called
Chlorine-Ammonia Process (Buffle et al. 2004). Overall, the source water bromide concentration
is a very important factor when considering adding ozone to a treatment process. Source waters
with bromide concentrations greater than 50 ppb likely need to consider the possibility of
significant bromate formation (von Gunten, 2003)
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 AOC (the fraction of TOC 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 11.8.3 describes biofilters and their operation.)
LT2ESWTR Toolbox Guidance Manual 11-18 April 2010
-------
11. Ozone
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:
• Integrating ozone into overall disinfection strategy for the treatment facility.
• Placing the ozone addition point further downstream, 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
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.
LT2ESWTR Toolbox Guidance Manual 11-19 April 2010
-------
11. Ozone
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 that has sufficient surface area for microbes to attach to can be used for
biological filtration. Slow sand, rapid sand, and granular activated carbon (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).
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
LT2ESWTR Toolbox Guidance Manual 11-20 April 2010
-------
11. Ozone
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 ppm (by volume)
averaged over an eight-hour work shift.
Ozone generators should be housed indoors for protection from the environment, and to
protect personnel from leaking ozone in the case of a malfunction. Ventilation should be
provided to prevent excess temperature rise in the generator room, and to exhaust the room in the
case of a leak. Adequate space should be provided to remove the tubes from the generator shell
and to service the generator power supplies. Off-gas destruct units can be located outside if the
climate is not too extreme. If placed inside, an ambient ozone detector should be provided in the
enclosure. All rooms should be properly ventilated, heated, and cooled to match the equipment-
operating environment.
11.10 Operational Considerations
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, the residual concentrations will decrease unless ozone dose is adjusted. 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 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.
LT2ESWTR Toolbox Guidance Manual 11-21 April 2010
-------
11. Ozone
• Bromide—Ozone will oxidize bromide forming, hypobromous acid, hypobromite ion,
bromate ion, brominated organics, and bromamines.
• Bicarbonate or carbonate ions—The hydroxyl radical reacts with bicarbonate and
carbonate ions and form carbonate radicals.
Ozone demand is particularly important to the CT calculation since it directly affects the
residual ozone used in the CT calculation. Ozone concentrations in water are generally
monitored continuously using an on-line residual monitor, and confirmed periodically with a
bench top instrument. 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, ozone
decomposition increases, and there is a concomitant increase in the formation of the hydroxyl
radical. Under the pH range typically used for drinking water treatment (e.g. pH 6 - 9), the initial
demand may be only increased by increasing pH due to changing pH speciation of compounds
that react directly with ozone (Buffle et al, 2006b). However, increasing pH has a significant
effect on the secondary reaction phase due to increased contribution of the autocatalytic chain
decomposition (Elovitz et al., 2000; Buffle et al, 2006b).
11.10.3 Temperature
Like all chemical reactions, the reaction rate between ozone and a pathogen increases
with increasing 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 and hydraulic resident time. 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 should be used, usually either chlorine or chloramine.
LT2ESWTR Toolbox Guidance Manual 11-22 April 2010
-------
11. Ozone
11.11 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.
Buffle, M.-O., Galli, S. and von Gunten, U. 2004. Enhanced Bromate Control During Ozonation:
The Chlorine-Ammonia Process. Environ. Sci. Technol., 38, 5187-5195.
Buffle, M.-O., J. Schumacher, Meylan, S., Jekel, M., von Gunten, U. 2006. Ozonation and
Advanced Oxidation of Wastewater: Effect of O3 Dose, pH, DOM and HO»-scavengers on
Ozone Decomposition and HO» Generation. Ozone Sci. Eng. 28:247-259.
Buffle, M.-O. and von Gunten, U. 2006b. Phenol and Amine Induced HO» Generation during
Initial Phase of Natural Water Ozonation. Environ. Sci. Technol. 40, 3057-3063.
Coffey, B.M., S.W. Krasner, MJ. 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.
Elovitz, M. S. and U. von Gunten. 1999. Hydroxyl Radical/Ozone Ratios during Ozonation
Processes. I. The^ Concept. Ozone Sci. Eng. 21(3): 239-260.
Elovitz, M. S., U. von Gunten, H.-P. Kaiser. 2000. Hydroxyl Radical/Ozone Ratios during
Ozonation Processes. II. The Effect Of Temperature, pH, Alkalinity and DOM Properties. Ozone
Sci. Eng. 22: 123-150.
Escobar 1C. and A.Randall. 2001. Case Study: Ozonation and Distribution System Biostability.
J.AWWA.93(W):77-89.
Glaze, W.H., et al. 1987. The Chemistry of Water Treatment Processes Involving Ozone,
Hydrogen Peroxide, and Ultraviolet Radiation. Ozone Sci. Eng. 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 and PEROXONE. Ozone Sci. Eng., 16(3): 197-212.
Hofmann, R. and R. C. Andrews. 2001. Ammoniacal Bromamines: A Review of their Influence
on Bromate Formation during Ozonation. Water Res. 35(3): 599-604.
LT2ESWTR Toolbox Guidance Manual 11-23 April 2010
-------
11. Ozone
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.
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
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, J., Choi, H, and Oh, H. 2001. Characterization of Raw Water for the
Ozone Application Measuring Ozone Consumption Rate. Water Res. (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.
Teefy, S. 1996. Tracer Studies in Water Treatment Facilities: A Protocol and Case Studies.
AWWARF.
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.
von Gunten, U. 2003. Ozonation Of Drinking Water: Part II. Disinfection and By-Product
Formation in Presence of Bromide, Iodide or Chlorine. Water Res. 37(7): 1469-1487.
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. Res., 30(5): 1195.
LT2ESWTR Toolbox Guidance Manual 11-24 April 2010
-------
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 Long Term 2
Enhanced Surface Water Treatment Rule (LT2ESWTR). Presumptive treatment credits are
applicable to any physical removal process that complies with the provisions of the Interim
Enhanced Surface Water Treatment Rule (IESWTR) and Long Term 1 Enhanced Surface Water
Treatment Rule (LT1ESWTR) (40 CFR 141.552). Exhibit 12.1 gives some examples of typical
plants that could be eligible for a DOP credit. DOP credits can be granted for any process,
including inactivation processes; however, this chapter is limited to a discussion of physical
removal processes. Membrane processes receiving DOP credit must still meet challenge testing
and direct integrity testing requirements as specified in 40 CFR 141.719.
Exhibit 12.1 Example Filtration Plant Types Eligible for DOP
Plant Type
Conventional
Slow Sand Filtration
Diatomaceous Earth
Softening/Granular Media Filtration
Direct Filtration
Minimum Elements of Process Train
Coagulation/Flocculation, Sedimentation,
High Rate Granular Media Filtration
Slow Sand Filtration
Diatomaceous Earth Filtration
Single Stage Lime Softening, High Rate
Granular Media Filtration
Coagulation/Flocculation, High Rate
Granular Media Filtration
Where a system can demonstrate that a plant, or a unit process within a plant,
consistently achieves a Cryptosporidium treatment efficiency greater than the presumptive credit
specified in the LT2ESWTR, the state may allow the system to receive a higher Cryptosporidium
treatment credit for compliance with the LT2ESWTR (40 CFR 141.718(c)). To demonstrate the
higher level of Cryptosporidium treatment, systems must conduct a site-specific study using a
protocol approved by the state. This study must account for all expected operating conditions
and, at the discretion of the state, determine ongoing monitoring and/or performance
requirements to ensure conditions under which the DOP was awarded are maintained during
routine operations.
In general, the term "treatment" in the LT2ESWTR refers to both physical removal and
inactivation of Cryptosporidium. Treatment credits discussed in this chapter pertain to physical
removal.
1 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.
LT2ESWTR Toolbox Guidance Manual
12-1
April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
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 141.718(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 141.718(c)(l)).
• Pre sedimentation
• Two-stage lime softening
• Bank filtration
• Combined or individual filter performance
• Membrane filters
• Bag and cartridge filters
• Second stage filtration
LT2ESWTR Toolbox Guidance Manual 12-2 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
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 141.718(c)).
12.2.2 Reporting Requirements
The LT2ESWTR requires results from the testing be submitted no later than the
Cryptosporidium compliance date (40 CFR 141.721):
• Schedule 1 - April 1, 2012
• Schedule 2 - October 1, 2012
• Schedule 3 - October 1,2013
• Schedule 4 - October 1, 2014
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 141.721).
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 nephelometric turbidity units (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 address the range of operating conditions (e.g., flow rates, chemical
and disinfection practices and dosages) and seasonal raw water quality variations based on a
LT2ESWTR Toolbox Guidance Manual 12-3 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
review of plant operating records and historical water quality records. If source or operating
conditions are expected to change (e.g., turbidity events, high watershed runoff, increased
system demands) these should be addressed in the DOP study. Systems should have a
contingency plan for achieving compliance with the LT2ESWTR if the DOP does not provide
the anticipated credit.
12.3.1 Overview of the Demonstration Protocol
This chapter presents one approach for conducting a DOP study. Other approaches or
modifications to this approach may be approved by the state. Major elements of the DOP
protocol include the following:
• Development of DOP evaluation criteria and test matrix.
• DOP implementation.
• Data analysis and reporting.
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
BIN CLASSIFICATION
MICROBIAL TOOLBOX
STRATEGY
1
4
DOP EVAl
CRITERIA
MAT
ADD DISINFECTION
OR
ALTERNATIVE
PHYSICAL REMOVAL
TECHNOLOGIES
OOP IMPLEMENTATION
DATA ANALYSIS
AND
REPORTING
X
\
\
\
DEMONSTAT10N
OF PERFORMANCE
{DOP)
/ CONVENTIONAL
/ FILTRATION
TECHNOLOGIES
RlrQUEST TREATMENT CREDIT
LT2ESWTR Toolbox Guidance Manual
12-4
April 2010
-------
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 ended—the DOP credit is based on the operational strategy used in the study. For
example, a system that uses enhanced coagulation throughout the study period should also use it
during routine operation for compliance with the LT2ESWTR.
Other examples of treatment techniques that can affect Cryptosporidium removal and
thus should be considered in the development stage include the following:
LT2ESWTR Toolbox Guidance Manual 12-5 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
• Prechlorination may be used to enhance floe formation (and Cryptosporidium removal) in
filtration trains. However, prechlorination may also promote trihalomethane (THM) and
haloacetic acid (HAA) formation. Therefore, prechlorination doses used during the DOP
study should be set to balance floe and disinfection byproduct formation. Operational
guidelines should be documented in the DOP plan.
• Granular media filter run times may be extended to increase unit filter run volumes
(UFRVs) and filter efficiency. However, increased UFRVs also increase the potential for
Cryptosporidium breakthrough. Maximum UFRVs should be established to minimize
Cryptosporidium breakthrough.
• Alternative coagulation strategies may be used to enhance Cryptosporidium removal in
granular media filters but may also result in post-filtration flocculation that can cause
deposition or scaling in water distribution systems. Coagulant dosing rates should be set
during the DOP study to minimize downstream floe formation.
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.
LT2ESWTR Toolbox Guidance Manual 12-6 April 2010
-------
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
summarized by Cornwell et al. 2001) are:
LT2ESWTR Toolbox Guidance Manual 12-7 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
• 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.
Microspheres may also be used as an alternative indicator for Cryptosporidium removal.
Microspheres are chemically inert, easy to handle, and relatively inexpensive. They can be
manufactured with a uniform particle size and smooth surface, making them appropriate as a
conservative indicator. They can also be manufactured without a significant surface charge to
minimize particle interaction and loss to processes such as adsorption. Microspheres are easily
obtainable in concentrations of 107 to 109 particles per mL, which should be adequate to prove
desired removal rates.
The biggest disadvantage of the use of microspheres is in detection methods. Particle
counters are effective in counting microspheres. In fact, microspheres are often used to calibrate
particle counters. However, particle counters may not be able to distinguish between
microspheres and other particles and may not be able to distinguish conglomerated particles.
Other problems with particle counters such as coincidence error and the limited dynamic range
can also skew results. A more effective method of measurement involves capturing the
microspheres by filtering the sample and then counting microspheres. Use of fluorescent
microspheres can aid in the counting process (Abbaszadegan et al. 1997, Li et al. 1997).
Microspheres also tend to have lower zeta potentials than live Cryptosporidium oocysts (Dai and
Hozalski 2003). Recent work, however, has found ways to adjust the surface charge on
microspheres to more closely mimic natural pathogens (Pang et al. 2009).
If appropriate detection methods are used and the microspheres are conservative
representatives of Cryptosporidium oocysts, microspheres can be a good surrogate for
LT2ESWTR Toolbox Guidance Manual 12-8 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
Cryptosporidium. Emelko and Huck (2004) found that 4.6 micron carboxylated fluorescent dyed
polystyrene microspheres acted as a good indicator for Cryptosporidium over a wide range of log
removals. For example; neutrally charged, 1 micron, spherical latex microspheres could provide
an acceptable conservative indicator for Cryptosporidium removal.
The state may accept alternative indicators for Cryptosporidium; however, they should
not be more easily removed than Cryptosporidium. The surrogate parameter should give a direct
view of removal and should be an element that is not created in the plant (e.g., particle counts
caused by chemical precipitation). Furthermore, the method of measurement should be sensitive
enough to detect temporal variations in the parameter. Parameters such as turbidity or particle
counts may be used in the DOP study, but are not suitable as stand-alone surrogates.
12.4.2.2 Long-Term Performance Indicators
As discussed previously, plants that implement a DOP plan should document long-term
performance of filtration facilities for turbidity and/or particle count reduction. While turbidity
and particle counts are not suitable as stand-alone indicators for full-scale Cryptosporidium
removal, such data can be used to identify changes in the filtration performance.
It is recommended that individual filter efficiency be monitored frequently to identify
differences in individual filter performance. This will allow the plant to assess temporal
variations in filter effluent quality and will provide improved process control.
12.4.3 Full-Scale Versus Pilot-Scale Testing
In general, full-scale testing is preferred over pilot-scale testing since the performance of
existing process trains is demonstrated directly. However, full-scale studies may not be feasible
for many facilities for the following reasons:
• Influent Cryptosporidium levels will not be high enough to demonstrate high log
removal. Likewise, influent aerobic spore concentrations may not be high enough to
demonstrate significant log removal.
• Full-scale spiking with aerobic spores may not be feasible due to larger flows.
• Facilities may operate well below design or permitted flow capacity for the entire study
period.
• Demonstration of worst-case operating conditions at full-scale may be difficult to plan,
especially with regard to raw water quality and flow rates.
LT2ESWTR Toolbox Guidance Manual 12-9 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
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 (U.S. EPA
1991):
• Unit filtration rate in the pilot system should be identical to that of the full-scale plant.
• Pilot filter diameter should be greater than or equal to 100 times the media diameter.
• Media diameter and depth should be identical to that of the full-scale system.
Pilot systems should also incorporate all major process elements of the full-scale process
train, including chemical addition systems and recycle streams. Such systems must be able to
simulate flow rate and water quality perturbations (i.e., temporal disturbances to steady state
conditions).
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.
LT2ESWTR Toolbox Guidance Manual 12-10 April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
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.
Exhibit 12.3 Example DOP Test Matrix
Scenario
Condition
S1
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:
LT2ESWTR Toolbox Guidance Manual
12-11
April 2010
-------
12. Demonstration of Performance (DOP): Microbial Removal
• 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
LT2ESWTR Toolbox Guidance Manual 12-12 April 2010
-------
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'11
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.
LT2ESWTR Toolbox Guidance Manual
12-13
April 2010
-------
12. Demonstration of Performance (POP)
12.5.2.1 Sampling Location
Paired samples should be collected from the plant influent (raw source sample) 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 (QA/QC)
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.
LT2ESWTR Toolbox Guidance Manual 12-14 April 2010
-------
12. Demonstration of Performance (POP)
12.5.3 DOP Implementation
The DOP should commence only after the state approves the DOP test matrix and
monitoring protocol. The DOP plan should be administered by a qualified WTP 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.
12.5.3.2 Analytical Methods
The analytical methods for monitoring Cryptosporidium under the LT2ESWTR are
prescribed at 40 CFR 141.704 and described in the Public Water System Guidance Manual for
Source Water Monitoring under the LT2ESWTR. 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.
LT2ESWTR Toolbox Guidance Manual 12-15 April 2010
-------
12. Demonstration of Performance (POP)
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. Cpiiot 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:
• System flow rate (instantaneous/flow chart, hourly and daily average).
• Operating mode (process scheme, number of trains, number of units in service).
LT2ESWTR Toolbox Guidance Manual 12-16 April 2010
-------
12. Demonstration of Performance (POP)
• Water pH, alkalinity, turbidity and temperature.
• Performance data.
• Chemical addition rates/doses.
• Mechanical equipment in operation, with flow rates (major pumps, blowers, etc.).
• Recycle and backwash flows/rates.
• Related maintenance activities occurring prior to or during sampling event.
12.5.4 Data Analysis and Reporting
12.5.4.1 Evaluation of Performance
To receive DOP treatment credits above presumptive credits in the LT2ESWTR, a plant
should demonstrate consistent attainment of a specific log reduction of Cryptosporidium (or
suitable indicators). To meet this objective, log reduction should first be computed for each
monitoring event according to:
Log Removal = - log (C;nf/Ceff) Equation 12-2
where: C;nf = 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.
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:
LT2ESWTR Toolbox Guidance Manual 12-17 April 2010
-------
12. Demonstration of Performance (POP)
• 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.
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) or similar operational evaluation to
identify causes and solutions for exceptions.
LT2ESWTR Toolbox Guidance Manual 12-18 April 2010
-------
12. Demonstration of Performance (POP)
12.6 References
Abbaszadegan, M., M.N. Hansan, C.P. Gerba, P.P. Roessler, B.R. Wilson, R. Kuennen, and E.
Van Dellen. 1997. The disinfection efficacy of a point-of-use water treatment system
against bacterial, viral, and protozoan waterborne pathogens. Water Research.
31(3):574-582.
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.
Dai, X., Hozalski, R.M. 2003. Evaluation of microspheres as Surrogates for Cryptosporidium
Parvum Oocysts in Filtration Experiments. Environmental Science and Technology. 37(5): 1037-
1042.
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., Huck, P. 2004. Microspheres as Surrogates for Cryptosporidium Filtration. Journal
AWWA.96(3):77-9l.
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.
Li, S.Y., J.A. Goodrich, J.H. Owens, GE. Willeke, F.W. Schaefer III, and R.M. Clark. 1997.
Reliability of non-hazardous surrogates for determining Cryptosporidium removal in bag
filters. Journal AWWA. 89(5):90-99.
LT2ESWTR Toolbox Guidance Manual 12-19 April 2010
-------
12. Demonstration of Performance (POP)
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.
Pang, L., Nawostawska, V., Ryan, J.N., Williamson, W. M., Walshe, G., Hunter, K.A. 2009.
Modifying the Surface Charge of Pathogen Sized Microspheres for Studying Pathogen Transport
in Groundwater. Journal of Environmental Quality 38 2210-2217.
Rice, E., Fox, K., Miltner, R., Lytle, D., Johnson, C. 1996. Evaluating plant performance with
endospores. Journal AWWA. 88(9): 122-130.
U.S. EPA. 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.
LT2ESWTR Toolbox Guidance Manual 12-20 April 2010
-------
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 Long Term 2 Enhanced Surface Water Treatment Rule
(LT2ESWTR) and provides considerations for toolbox selection. Water systems and states
should refer to the UV Disinfection Guidance Manual (U.S. EPA 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:
• UV doses for different levels of inactivation credit.
• Performance validation testing of UV reactors.
• Monitoring.
• Reporting.
• 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 meeting turbidity requirements.
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 Toolbox Guidance Manual 13-1 April 2010
-------
13. Ultraviolet Light
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.
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 141.720(d)(2)(i)].
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.S. EPA
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
LT2ESWTR.
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
LT2ESWTR Toolbox Guidance Manual
13-2
April 2010
-------
13. Ultraviolet Light
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 disinfection byproducts (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.
LT2ESWTR Toolbox Guidance Manual 13-3 April 2010
-------
13. Ultraviolet Light
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 (U.S.
EPA 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.
• LT2 Reporting Requirements - Systems are required to submit validation test results
demonstrating operating conditions that achieve required UV dose as well as with a
monthly report summarizing the percentage of water entering the distribution system that
was not treated by UV reactors operating within validated conditions for the required
dose.
LT2ESWTR Toolbox Guidance Manual 13-4 April 2010
-------
13. Ultraviolet Light
13.5 References
U.S. EPA. 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.
LT2ESWTR Toolbox Guidance Manual 13-5 April 2010
-------
14. Membrane Filtration
14.1 Introduction
The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) defines
membrane filtration as follows:
Membrane filtration is a pressure or vacuum driven separation process in which
particulate 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 of microfiltration, ultrafiltration, nanofiltration, and
reverse osmosis. [40 CFR 141.2]
Membrane processes that meet the requirements of LT2ESWTR will receive
Cryptosporidium removal credit.
The U.S. Environmental Protection Agency (EPA) recently published the Membrane
Filtration Guidance Manual for systems considering using membranes to comply with the
requirements of the LT2ESWTR (U.S. EPA 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)]:
LT2ESWTR Toolbox Guidance Manual 14-1 April 2010
-------
14. Membrane Filtration
• The removal efficiency demonstrated during challenge testing.
OR
• 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.
LT2ESWTR Toolbox Guidance Manual 14-2 April 2010
-------
14. Membrane Filtration
• 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.
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 and protozoa.
• Can lower DBFs by allowing lower disinfectant doses and removing DBF precursors.
• 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.
• UF, NF, and RO can remove viruses, however it is very difficult to perform a direct
integrity test that can detect a defect as small as a virus.
LT2ESWTR Toolbox Guidance Manual 14-3 April 2010
-------
14. Membrane Filtration
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.
• Increased loss of process water.
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
LT2ESWTR Toolbox Guidance Manual 14-4 April 2010
-------
14. Membrane Filtration
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 MF/UF systems, high levels of
turbidity and TOC can increase backwashing requirements and chemical cleaning frequencies,
causing poor performance and shortening membrane life. Additionally for NF/RO systems, high
levels of scaling ions can increase energy consumption and chemical cleaning frequency and can
result in poor performance and shortened membrane life. In many cases, pretreatment may
improve feed water quality at lower cost than 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.
LT2ESWTR Toolbox Guidance Manual 14-5 April 2010
-------
14. Membrane Filtration
14.5 References
U.S. EPA. 2005. Membrane Filtration Guidance Manual. Office of Water. EPA 815-R-06-009.
November, 2005. http://www.epa.gov/ogwdw/disinfection/lt2/compliance.htm.
LT2ESWTR Toolbox Guidance Manual 14-6 April 2010
-------
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 contact time (CT) values for that site if it believes those developed by the U.S.
Environmental Protection Agency (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 Long Term 2 Enhanced Surface Water Treatment Rule (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 141.720(c)). This appendix describes the different recommended
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 total
organic carbon (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.
LT2ESWTR Toolbox Guidance Manual A-l April 2010
-------
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 degrees C until needed.
When ready for use, the oocysts should be suspended in 0.01 M pH 7 buffer and centrifuged at a
relative centrifugal force of approximately 1,100 for at least 10 minutes. Following centrifugation, the
oocysts should be aspirated and re-suspended in the buffer, then centrifuged again at the same conditions.
This step should be repeated once more to remove as much of the antibiotic or dichromate solution as
possible. Following the last aspiration, the oocysts should be re-suspended in approximately 10 mL of the
pH 7 buffer. The oocysts should then be stored at 4°C until the experiment is initiated. The oocysts should
be vortexed thoroughly prior to initiation of the experiment. Additional details regarding this procedure
can be found in Rennecker et al. 1999.
LT2ESWTR Toolbox Guidance Manual
April 2010
-------
Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
A.2.2 Source Water Preservation
Testing should be conducted as close as possible to the date that the experimental water is
collected. If testing is to be performed at a location other than the utility where the water was
collected, the water should be sent to the laboratory via an overnight delivery service and stored
at 4 degrees Celsius until the start of testing.
A.2.3 Experimental Apparatus
A.2.3.1 Chlorine Dioxide
It is recommended that chlorine dioxide be generated using the equipment and procedures
outlined in Standard Methods for the Examination of Water and Wastewater (APHA 1998). With
this as a basis, all inactivation experiments using chlorine dioxide should be performed using a
batch-reactor configuration. An example of such a system is provided by Ruffell et al. 2000. This
system uses an enclosed recirculating water bath to maintain the desired temperature inside the
reactor vessels, which consist of 2-liter amber glass bottles. During the experiment, care should
be taken to minimize the exposure of the reactors to light. Mixing of the reactor contents is
provided with a magnetic stir bar and stir plate.
A.2.3.2 Ozone
Inactivation experiments can be performed with either a semi-batch or batch reactor
configuration. When performing experiments with a semi-batch system, it is recommended that
analytical components similar to those described by Hunt and Marinas (1997) be used. Using this
system, the reactor vessel containing the experimental water is maintained at the experimental
temperature by immersion in a water bath. Ozone can be generated from either compressed air or
oxygen and passed through a continuously-stirred glass bottle, which serves to dampen the effect
of fluctuating ozone concentration. The ozonated gas leaving the dampening bottle is then
introduced to the experimental water via a fine-bubble diffuser. The ozonated water is stirred
continuously using a magnetic stirring plate and a stir bar.
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.
LT2ESWTR Toolbox Guidance Manual A-3 April 2010
-------
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 min after
dosing. An experiment was conducted by adding approximately a pre-determined number of
oocysts to the reactor that will be sufficient for at least six data points. Note the volume of the
oocyst aliquot should be less than 1 mL. Samples are then taken periodically at the contact times
that correspond to the desired CT. The samples are immediately filtered through a Ifim 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 of oocysts inside a similar reactor containing
the experimental water minus the disinfectant at the target temperature. The oocysts are typically
exposed to this condition for the duration of the experiment and subsequently processed for
viability assessment with methods similar to those for the disinfected samples.
LT2ESWTR Toolbox Guidance Manual A-4 April 2010
-------
Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
A.2.4.2 Ozone
If a semi-batch reactor configuration is used, the protocol described by Rennecker et al.
(1999) is recommended. The protocol is described briefly as follows. Ozonated gas is applied to
the temperature-acclimated experimental water via a fine bubble diffuser. The ozone gas
concentration is adjusted to achieve steady-state at dissolved ozone concentrations representative
of what would be observed at the facility. The actual dissolved ozone concentration achieved for
each experiment is measured. Mixing of the ozonated water is performed with a magnetic stir bar
and stirring plate. An inactivation experiment is initiated by injecting a suspension containing a
sufficient number of oocysts into the reactor, and ends by simultaneously removing the bubble
diffuser and injecting a quenching agent. It should be noted that the number of oocysts necessary
for each data point is dependent on the viability assessment method selected. Oocysts are then
removed from the quenched solution by filtration through a 1 um 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.
LT2ESWTR Toolbox Guidance Manual A-5 April 2010
-------
Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
Experiments performed with batch reactor components that are not head-space free
typically follow a similar, although less complex protocol. An example of such a system and the
associated experimental protocol can be obtained from Finch et al. 1993a.
It should be noted that for all batch-reactor systems, a careful characterization of the
ozone demand and decay kinetics of the experimental water should be performed prior to any
disinfection testing. In addition, it is also recommended that ozone concentration samples be
procured alternately between inactivation samples to verify ozone concentrations observed
during the disinfection study.
A.2.5 Sample Processing
After procuring each sample point, the samples should be stored at 4°C until the end of
the experiment. At the end of each experiment, the samples should be centrifuged at a relative
centrifugal force of 1,100 for at least 10 minutes to remove quenching agents or surfactants.
Following centrifugation, the samples should be carefully aspirated and re-suspended in 0.01 M
pH 7 buffer solution. The samples should be stored at 4 degrees until the time of viability
assessment.
A.2.6 Viability Assessment
Determining the viability of oocysts for varying levels of disinfection is one of the most
critical components of the inactivation experiments. At present, there are three methods available
to assess Cryptosporidium parvum viability, each presenting unique advantages and
disadvantages. These methods include the following techniques:
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.
LT2ESWTR Toolbox Guidance Manual A-6 April 2010
-------
Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
A second method used to assess the viability of Cryptosporidiumparvum 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 Ribonucleic acid (RNA) is extracted. Infectivity is then determined by
targeting specific genetic sequences in the RNA. The primary advantage of using cell culture to
assess Cryptosporidium parvum infectivity is that it can measure very low concentrations of
oocysts. Therefore, cell culture is capable of demonstrating high levels of inactivation. In
contrast, the disadvantages associated with using cell culture include a lack of agreement over the
preferred cell lines and viability assessment technique. In addition, there has been no
extrapolation between cell culture techniques and human infectivity. Lastly, cell culture
techniques are complex and typically require specialized equipment and rigorous training, which
makes this procedure somewhat expensive.
A third method known as in vitro excystation has also been developed to assess the
viability of Cryptosporidium parvum (Rennecker et al. 1999). This method involves exposing
oocysts to a simulation of a mammalian digestive tract. Following the simulation, the oocysts are
then examined microscopically for oocyst life stages that are indicative of viability. The
advantages of this method are that it is cost-effective, offers the ability to rapidly develop data,
and requires minimal training. The main disadvantage of the method is that of the three methods
described, in vitro excystation has the least similarity to an actual infection. However, it should
be noted that in spite of this fact, two 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).
LT2ESWTR Toolbox Guidance Manual A-7 April 2010
-------
Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
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.
1) Calculating and applying a factor of safety for the average predicted CT
requirement.
One approach by Clark et al. (2002) used a one-parameter Chick-Watson model to fit
experimental data sets and develop standard CT curves, relative to inactivation level and
temperature. As described in the LT2ESWTR Preamble, EPA used the Clark et al. approach for
developing CT values but adjusted the analysis to account for different types of uncertainties and
variability inherent in the data. EPA wanted to account for variability among different water
matrices and oocyst strains, but not variability within the same group (i.e., same oocyst lot and
water), and uncertainty in the regression. While such a complex approach may not be necessary
for a site-specific study, the water system should be aware of the uncertainties and variability of
the experimental data and use a statistical method that builds in a reasonable safety factor to
ensure public health is protected.
Two types of confidence bounds that are commonly used when assessing relationships
between variables, such as disinfectant dose (CT) and log inactivation, are confidence in the
regression and confidence in the prediction. Confidence in the regression accounts for uncertainty
in the regression line (e.g., a linear relationship between temperature and the log of the ratio of
CT to log inactivation). Confidence in the prediction accounts for both uncertainty in the
regression line and variability in experimental observations it describes the likelihood of a single
future data point falling within a range. Bounds for confidence in prediction are wider (i.e., more
conservative) than those for confidence in the regression. Depending on the degree of confidence
applied, most points in a data set typically will fall within the bounds for confidence in the
prediction, while a significant fraction will fall outside the bounds for confidence in the
regression.
LT2ESWTR Toolbox Guidance Manual A-8 April 2010
-------
Appendix A - Site Specific Determination of Contact Time for Chlorine Dioxide and Ozone
A.4 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 IE, F.W.; and Belosevic, M. .(1993b). Dose
response of C. parvum in outbred neonatal CD-I mice. J.Appl. Environ. Microbiol. 59(11), 3661-
3665.
Hunt, N. K.; and Marinas, BJ. (1997) Kinetics of Escherichia coli inactivation with ozone.
Wat. Res. 31(6), 1355-1362.
Kim, J. H.; Tomiak, R. B.; Rennecker, J. L.; Marinas, B. 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.
LT2ESWTR Toolbox Guidance Manual A-9 April 2010
-------
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.
LT2ESWTR Toolbox Guidance Manual A-10 April 2010
-------
Abbreviations and Glossary
Appendix B
Ozone CT Methods
BrO3
Co-current
chamber
Counter-
current
chamber
CSTR
CT
DBF
gpm
HOT
In-situ sample
ports
*'
kw
-Log (W0)
PQL
Q
RTD
segment
Bromate ion
Chamber effluent ozone residual in mg/L times chamber TIO time in minutes
A chamber in an ozone contactor where the water is flowing upward and the
ozone gas bubbles are rising. The direction of flow of the water and the gas
is the same.
A chamber in an ozone contactor where the water is flowing downward and
the ozone gas bubbles are rising. The direction of flow of the water is in the
opposite direction of the gas flow.
Completely Stirred Tank Reactor - fully mixed volume
The product of Concentration and Time in mg/L-min
Disinfection byproduct
Gallons per minute
Hydraulic detention time calculated as the volume divided by the flow.
When volume is expressed in gallons, and flow expressed in gallons/minute,
then the calculated HDT is in minutes.
Sample ports that take a sample from the flow of the chamber, typically
through tubing that projects into the flow.
The first-order ozone decay coefficient, min"1
Log-base-10 value of the lethality coefficient for the inactivation of
Cryptosporidium, Giardia or virus with ozone. The units of kw in this
document are L/mg-min.
Log inactivation. Negative log-base-10 of the survival rate (N/N0) of the
microorganisms, where I0 is the number of viable organisms entering the
contactor, and I is the number of viable organisms leaving the contactor.
Practical Quantitation Limit: The minimum concentration of an analyte
(substance) that can be measured with a high degree of confidence that the
analyte is present at or above that concentration.
Water flow - usually expressed in gallons per minute (gpm) or million
gallons per day (MOD).
Residence Time Distribution probability distribution function describing
the residence time of a fluid element within a contactor.
A theoretical or physically real chamber within a contactor. Used
predominantly to denote a theoretical chamber for non-conventional
contactors.
LT2ESWTR Toolbox Guidance Manual
B-l
April 2010
-------
Appendix B - Ozone CTMethods
TIO The time at which 10 percent of the water in the contactor or segment has
passed through the contactor or segment. EPA recommends that tracer
studies be used to determine the Tio/HDT ratio for ozone contactors. The
SWTR Guidance Manual and Tracer Studies in Water Treatment Facilities:
A Protocol and Case Studies describe how to conduct a tracer test.
Up flow A chamber within an over-under baffled bubble-diffuser ozone contactor in
chamber which the direction of water flow is upward.
V Volume of the contacting zone in question - usually expressed in gallons or
million gallons.
LT2ESWTR Toolbox Guidance Manual B-2 April 2010
-------
Appendix B - Ozone CTMethods
B.I Introduction
B.1.1 Background
Appendix O of the Surface Water Treatment Rule (SWTR) Guidance Manual (U.S. EPA
1991) includes a description of different methods for determining inactivation credit using an
ozone contactor. These recommended 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 TIO method and extended continuous stirred
tank reactor (CSTR) method. Appendices C, 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 approach (Appendix E).
The four 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 only be used with tracer study data. Using the TIO approach, the contact
time (T) is the time at which 10 percent of the water in the contactor or segment has
passed through the contactor or segment. Even in well-baffled contactors, the TIO is most
often less than 65 percent of the average hydraulic detention time (HDT) through the
contactor, and generally underestimates the true CT achieved. (The TIO approach is
described in Chapter 11, section 11.3.)
2. CSTR—calculates log inactivation credit in a chamber by assuming it to be completely
mixed. 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 TIO—a method that utilizes three measured ozone residuals at three chamber
effluents in a reactive zone to predict the ozone residual concentrations at the effluents of
the non-monitored chambers in the zone. It then uses the standard TIO method to
calculate the CT from all chambers using both measured and predicted ozone residuals.
This method is only applied to reactive chambers and not to dissolution chambers, and
requires tracer study data.
4. Extended CSTR—a method that utilizes three measured ozone residuals at three chamber
effluents in a reactive zone to predict the ozone residual concentrations at the effluents of
the non-monitored chambers in the zone. It then uses the standard CSTR method to
calculate the CT from all chambers using both measured and predicted ozone residuals.
This method is only applied to reactive chambers and not to dissolution chambers, and
does not require tracer study data.
LT2ESWTR Toolbox Guidance Manual B-3 April 2010
-------
Appendix B - Ozone CTMethods
While this guidance manual describes four methods, other methods or modifications to
these methods may be used at the discretion of the state.
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 TIO or the Extended CSTR method.
Of the four methods described in the previous section, the two Extended methods are
more complex. The Extended methods require measurements of the ozone concentration at a
minimum of three points within this portion of the contactor. The residual measurements are then
used to develop a predicted ozone concentration profile through this portion of the contactor.
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. If no tracer test data are available, it is recommended
that the CSTR method be used. The Extended methods are applied over a minimum of three
consecutive reactive chambers. Exhibit B.I shows the recommended methods.
LT2ESWTR Toolbox Guidance Manual B-4 April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.1 Recommended Methods and Terminology for Calculating the Log
Inactivation Credit
Without Tracer Data
S
re
Q
^
3 consecutive
reactive chambers
< 3 consecutive
reactive chambers
Extended-
CSTR Zone
CSTR
Reactive
Chambers)
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 Cryptosporidium
inactivation is credited
to this section
T10 or CSTR Method in
each chamber
The SWTR criteria for 1st chamber
credit should still be used if
calculating inactivation of Giardia
and virus
No credit should 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
Chambers)
Extended T10 or
Extended CSTR
Method in each
chamber. The Extended
CSTR method is not
appropriate for non-
conventional contactors.
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
LT2ESWTR Toolbox Guidance Manual
B-5
April 2010
-------
Appendix B - Ozone CTMethods
B.3 Dissecting an Ozone Contactor
B.3.1 Ozone Contactor Configurations
Ozone contactors are designed in a wide variety of configurations. Different
configurations are adaptable to the Extended TIO or Extended CSTR methods, 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.
In contrast to the multi-chamber configuration, ozone contactors may also be comprised
of only one or two reactive zones. 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 depict a long and narrow water flow path that may
promote more plug-flow hydrodynamics within the majority of the chamber. 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.
LT2ESWTR Toolbox Guidance Manual B-6 April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.2 Schematics of Typical Conventional Configurations of Ozone
Contactors with Multiple Chambers
Side View of an Over-Under
Contactor with In-Chamber
Ozone Addition
(A)
Over-UnderJ
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)
Exhibit B.3 Example Schematics of Non-conventional Configurations of Ozone
Contactors
Pipe Ozone Contactor
(A)
Side View of an Open-Channel Ozone
Contactor with In-Line Ozone Addition
(B)
Side View of an Open-Channel
Contactor with In-Chamber
Ozone Addition
(C)
LT2ESWTR Toolbox Guidance Manual
B-7
April 2010
-------
Appendix B - Ozone CTMethods
Whether the contactor is configured with multiple chambers or predominantly a single
long and narrow chamber, a major consideration of determining inactivation credit is
characterizing the hydrodynamics within the contactor. The EPA recommends performing a
tracer study to ascertain a description of the hydrodynamics. A tracer study will afford the
necessary information for utilizing the TIO or Extended TIO methods. However, as with SWTR
guidance manual, this guidance offers possibilities to apply an assumed, theoretical
hydrodynamic condition to the contactor if a tracer study is not performed. However, since this
option involves a major assumption, the guidance recommends assuming a hydrodynamic
condition that is somewhat conservative with respect to the efficiency of disinfection kinetics. In
particular, for utilities that opt to not perform a tracer study, this guidance offers the CSTR and
Extended CSTR methods, which assumes that each chamber within a contactor has a high degree
of mixing equivalent to an ideal CSTR.
B.3.2 Classification of the Chambers and Contactor Zones
To properly apply the methods discussed in this manual, the contactor should be divided
into specific sections or zones. To ensure clarity, certain terminology is adopted for unique
sections of an ozone contactor, as presented in Exhibit B.I.
ExhibitB.4 shows example schematics of conventional and non-conventional
configurations of ozone contactors. Schematic A is that of a conventional configuration of a 10-
chamber over-under baffled ozone contactor with in-chamber ozone addition. Ozone is being
added only in Chambers 1 and 4 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 schematic A of Exhibit B.4 are reactive chambers through which ozone is
decaying. These chambers are called "Reactive Chambers." The TIO or CSTR method could be
used to calculate the log inactivation across such Reactive Chambers when ozone residual values
are available from the effluent of the chamber. The TIO and CSTR methods are described in
Chapter 11.
The fourth chamber in the contactor shown in schematic A of Exhibit B.4 includes ozone
addition. This chamber is called a Co-Current "Dissolution Chamber." It should be emphasized
that there is a distinction between a "Dissolution Chamber" and "First Dissolution Chamber." 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, thus signifying that the initial (i.e.
instantaneous) ozone demand has been met. In other words, chamber 4 in schematic A of 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 TIO or CSTR method could be 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, and is treated as, a "First
Dissolution Chamber" and as with chamber 1, no log inactivation credit is granted.
LT2ESWTR Toolbox Guidance Manual B-8 April 2010
-------
Appendix B - Ozone CTMethods
Chambers 5 through 10 in schematic A in Exhibit B.4 represent the "Extended zone"
since they meet the criterion of containing a minimum of three consecutive reactive chambers. If
tracer data are unavailable, the Extended-CSTR approach is used to calculate the log inactivation
across each chamber in this zone. If tracer data are available and can be used to calculate the
TIO/HDT ratio of the contactor, then the Extended TIO approach or the Extended CSTR approach
could be 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 zone. Either Extended method requires an accurate estimation of the ozone decay
coefficient, k , and the initial ozone residual at the entrance to the zone, Cin. Estimation of these
two parameters, which is discussed in sections B.4.3.1 and B.4.3.2, 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 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 Qn
have been met and the entire contactor can be treated as an Extended 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.
LT2ESWTR Toolbox Guidance Manual B-9 April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.4 Names of Various Sections of Different Types of Ozone Contactors
Extended Zom
°°0°° 0°
'.&
•;4
r
©
j
T T
^
©
^
a ° °/^T
'.&
"A °
-S*Q 0
~r -r
>
©
^
r
©
j
i
©
^
r
©
j
^
©
^
no)
>
TTii
(A)
.1 I I
Extended Zone
©CD©
(B)
(C)
Schematics B and C in Exhibit B.4 represent non-conventional configurations of ozone
contactors used in water treatment. While these contactors do not necessarily have clearly
defined chambers divided by baffle walls, this guidance provides for methods such that they can
be evaluated in a similar manner as conventional contactors with chambers are evaluated under
the Extended TIO method. For such contactors, the Extended zone could be divided into
segments that represent theoretical chambers; the number of theoretical chambers determined by
a tracer test. Subsequent sections of this Appendix and Appendix E include examples and
calculations that illustrate this approach.
LT2ESWTR Toolbox Guidance Manual
B-10
April 2010
-------
Appendix B - Ozone CTMethods
B.4 Extended T10 or Extended-CSTR Approaches for Ozone Contactors
B.4.1 Introduction
The methods 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 microbial inactivation than that obtained using the TIO approach. The potential benefits
of using these more sophisticated measures are lower ozone doses and consequently lower
formation of some 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 Approach. Certain aspects
of this methodology were 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. As indicated in Chapter 11, the approached described herein
can be used for calculating CT for Cryptosporidium, Giardia, or virus inactivation credit.
The Extended method relies on measured ozone residuals across the Extended zone to
model the ozone decay through the zone. The outcome is then used to project the ozone residual
at any location in the Extended zone. This approach, which is applied only to an Extended zone
as defined in the earlier section, includes the following four steps:
Step 1 - Measure the ozone residual at the effluent of at least three chambers in the Extended
zone.
Step 2 - Utilizing the measured residuals and flowrate through the contactor, calculate the
empirical ozone decay coefficient, k*, and the ozone residual in the influent of the
Extended zone, Cin.
Step 3 - Utilize the calculated k* and Cin to predict the ozone residual concentration at the
influent or effluent of any chamber in the Extended zone.
Step 4 - Utilize the calculated ozone residual values to calculate the CT and subsequent log
inactivation across each chamber in the Extended zone.
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 C should be implemented to ensure that the ozone
residual measurements are accurate. For on-line control systems that utilize continuous residual
monitoring, instantaneous disinfection calculation will not be possible because of general
fluctuations in the residual monitor's responses to small changes in system operation. Most
control systems include a function to conduct a rolling average of monitor readings at a preset
interval. If this approach is used, EPA recommends that the averaging interval not exceed the
LT2ESWTR Toolbox Guidance Manual B-l 1 April 2010
-------
Appendix B - Ozone CTMethods
HDT of the contactor at design flowrate. For example, if the contactor is designed with an HDT
of 10 minutes at its design flowrate, then the control system's averaging interval should not
exceed 10 minutes. Therefore, if the monitor collects an ozone residual reading every two (2)
minutes, then the control system would report an average of the previous five (5) consecutive
readings every two minutes. The k* and Cin values for the Extended zone are calculated using
these rolling average residual values.
B.4.2 Extended T10 Method
To utilize this method for calculating the CT across an Extended zone of an ozone
contactor, the contactor must have a representative set of tracer test results that have been used to
set the Tio/HDT ratio for the contactor. Guidance on determining the Tio/HDT ratio for the
contactor is found in SWTR Guidance Manual., Tracer Studies in Water Treatment Facilities: A
Protocol and Case Studies., and Appendix E. The Extended zone comprises three or more
individual chambers. Inactivation within each individual chamber is calculated in accordance
with the TIO method described in Section 11.3.2. The sum of CT and log inactivation values for
individual chambers gives the CT and log inactivation across the entire zone. The distinction
between a standard Reactive Chamber and a chamber that is a component of an Extended zone is
the manner in which each chamber's Cout value is obtained. In the case of a standard Reactive
Chamber, Cout is obtained from an actual measurement of the dissolved ozone residual at the exit
of the chamber. In contrast, Cout for a chamber in an Extended TIO zone is a calculated value. It
is important to note that the calculation of Cout for a chamber is performed only on as many
physical chambers (as in the case of multi-chamber contactors) or theoretical segments (as in the
case on non-conventional contactors) within the Extended zone.
In addition to enabling the calculation of Cout for all individual chambers, the Extended
the TIO method follows the guidance established in Appendix O of the SWTR Guidance Manual
in allowing the overall the Tio/HDT ratio calculated for the entire contactor to be applied to each
individual chamber - the so-called linear extrapolation of the Tio/HDT ratio. As noted in
Appendix O of the SWTR Guidance Manual and in Lev and Regli (1992), this allowance is not
theoretically correct, and except for atypical contactor designs where a more plug-flow region is
followed by a highly mixed zone of similar volume, this allowance will lead to a higher
calculation of CT credit than if the actual Tio/HDT ratio of each chamber was used. As described
in Appendix O (and also alluded to in Section 11.3.2. of this guidance), this allowance comes
with the proviso that the linear extrapolation of the overall Tio/HDT ratio is not appropriate if
more than 50% of the volume of the contactor has an ozone concentration of "zero." In the
context of the SWTR, a measurement of "zero" ozone residual is equivalent to "below the ozone
method practical quantitation limit (PQL)." Because the Extended TIO method allows ozone
concentrations to be calculated to values that may be below the PQL of the allowable ozone
methods (see Appendix C), essentially a value of "zero", the proviso in Appendix O needs to be
revised. As such, the EPA recommends that the linear extrapolation of the overall Tio/HDT ratio
is not applicable if more than 50% of the contactor volume has a measured or calculated (using
the more conservative k* value) ozone residual of less than 0.05 mg/L. If the proviso is not met,
the system may estimate its CT credit using other methods, or it may conduct a tracer test to
evaluate the Tio/HDT ratio for a shorter section of the contactor, and use that ratio in the same
manner. Because of the possibility of the 50% criteria not being met, the EPA recommends that
LT2ESWTR Toolbox Guidance Manual B-12 April 2010
-------
Appendix B - Ozone CTMethods
if a system is conducting its first or new tracer tests to characterize the contactor, that they collect
tracer data at intermediate points in the contactor in addition to the exit of the entire contactor.
The procedure for calculating Cout for a chamber in an Extended TIO zone is described in
this section. The value ofCout for a chamber in an Extended TIO zone is calculated using an
empirical ozone decay coefficient, k*, and the ozone residual concentration at the entrance to the
zone, Cin. Equation B-l shows how to calculate the ozone residual at any location X along the
Extended zone:
where: k* = Empirical ozone decay coefficient, min"1, calculated as described in section
B.4.2.1.
Cin = Calculated ozone residual concentration at the entrance to the Extended zone,
mg/L, calculated as described in section B.4.2.2.
[Volume] QX = Volume, in gallons, from the beginning of the Extended zone to a location X
along the water path in the Extended TIO zone.
Q = Water flow through the contactor, gpm
Equation B-l describes the Extended zone as a plug flow reactor for the purpose of calculating
the profile of the ozone residual, C, along the zone.
Once the values of the ozone residual concentrations at the effluent of each chamber in
the Extended TIO zone are calculated, Equation 11-4 can then be used to calculate the log
inactivation achieved across that chamber. The total log inactivation achieved across the entire
contactor is equal to the sum of the log inactivation values calculated for each chamber.
(\ / rp \
•f = *10 *CxHDTchamber x -£- Equation 11-4
10J \HD1 )
where:
-Log (I/Io) = the log inactivation
k]0 = log base-ten inactivation coefficient for the target organism (L/mg-min)
C = Ozone residual concentration from Exhibit 11.3 (mg/L)
HDTchamber = Hydraulic detention time through the chamber (minutes)
(Tio/HDT) = approved Tio/HDT ratio for the contactor
The values of kw for the inactivation of Cryptosporidium, Giardia, and virus with ozone
can be expressed by the following equations (Temp = water temperature in °C):
LT2ESWTR Toolbox Guidance Manual B-l3 April 2010
-------
Appendix B - Ozone CTMethods
Inactivation of Cryptosporidium with Ozone: k10 = 0.0397 x (\.Q975T)Temp
Inactivation of Giardia with Ozone: k,0 = 1.0380 x (l.074lfemp
Inactivation of virus with Ozone: kw = 2.1744 x (\.Q126)Temp
The values of kw for the inactivation of Giardia and virus were derived from the kw
values for Giardia and virus inactivation listed in Appendix O of the SWTR Guidance Manual.
The values of k* and Cin should be determined every time log inactivation credit is
calculated (i.e., at least daily). The following sub sections describe the procedures for estimating
the values ofk* and Cin across the Extended zone.
B. 4.2.1 Determining the Value of k*
The empirical ozone decay coefficient, k* is calculated using ozone sample
measurements, taken from in-situ sample ports, and an assumed theoretical model of the
chamber's hydrodynamics. In the application of the Extended TIQ method, the Extended zone is
modeled as a plug-flow reactor. It is important to note that the empirical ozone decay coefficient,
k*, will unlikely be the same value as the first-order decay rate constant that would be measured
in a batch or plug-flow reactor. Only when the Extended zone hydrodynamics are that of a plug-
flow system will the empirical k* be equivalent to the true first-order rate constant. Nonetheless,
the simplifying assumption of plug-flow hydrodynamics and use of the two-parameter
exponential (i.e. first-order kinetic) equation to fit two or three ozone residual measurements and
subsequently predict the ozone concentration at other points in an Extended zone has been shown
to be useful (Rakness, Najm et al. 2005).
The steps outlined below pertain to an Extended zone 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 zone with measurable ozone residual. The three ozone
residual measurements, Ci, €2, and €3, are needed to estimate the value of the ozone decay
coefficient, k*. For example, the Extended zone in the contactor shown in Exhibit B.4(A)
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 k* value:
LT2ESWTR Toolbox Guidance Manual B-14 April 2010
-------
Appendix B - Ozone CTMethods
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):
Q
(Ln
C,
(B-2)
where: k\_2
C2
[Volume] l
Q
Empirical ozone decay coefficient between sampling locations 1 & 2, min"1
Measured ozone residual at location 1, mg/L
Measured ozone residual at location 2, mg/L
Volume between sampling locations 1 and 2, gallons
Water flow through the contactor, gpm
Step 2 - Use residual measurements Ci and Cj along with Equation B-3 to calculate the k value
*
representing ozone decay between sampling locations 1 and 3, &j_3:
_
\Volume\ 3
(B-3)
where:
[Volume]^
Q
Empricial ozone decay coefficient between sampling locations 1 & 3, min"1
Measured ozone residual at location 1, mg/L
Measured ozone residual at location 3, mg/L
Volume between sampling locations 1 and 3, gallons
Water flow through the contactor, gpm
It should be emphasized that sampling location 1 should not be at the entrance to the
Extended zone, but should be at least one chamber into the zone. For example, in Exhibit B.4(A),
Ci should not be measured at the entrance to chamber 5, since that is the entrance to the
Extended zone (notice in Figure B.4(A) that ozone is added to chamber 4). Instead, the first
Extended 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
&!_2 and &!_3 as shown in Equation B-4.
k =
£2
n-3
(B-4)
LT2ESWTR Toolbox Guidance Manual
B-15
April 2010
-------
Appendix B - Ozone CTMethods
It is normal for the individual values of k\_2 and ^_3 to be somewhat different.
However, it is recommended that they be within the range of 80 percent to 120 percent of the
average k* value calculated in Step 3. That is,
abstk* -&,_.
X . ' < 20%
k
If the two k* values do not meet this criterion, the utility may 1) reject the measured residual
values and collect new samples until this quality assurance (QA) criterion is met, or 2) select the
higher of the two k* values as the more conservative estimate.
B.4.2.2 Determining the Value of Cin
While it is possible to measure the ozone residual at the entrance to the Extended 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 zone should be back-extrapolated using the three downstream
rolling average ozone residual values.
The value of Cin can be calculated once the value ofk* is estimated from the three rolling
average residual ozone values. Maintaining the assumption of a first-order decay rate, Equations
B-5 through B-7 can be used to estimate the value of Cin from the three rolling average ozone
residual concentrations:
(B-5)
(B-6)
;
( * \Volume]0_3^\
Cm,3 = Q x exp \k x ± —-J2-1 (B-7)
where: A:* = Average decay coefficient from Equation B-4, min"1
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
[Volume] Q_l = Volume, in gallons, between the entrance of the Extended zone and sampling
location 1
LT2ESWTR Toolbox Guidance Manual B-16 April 2010
-------
Appendix B - Ozone CTMethods
[Volume] Q 2 = Volume, in gallons, between the entrance of the Extended zone and sampling
location 2
[Volume] Q 3 = Volume, in gallons, between the entrance of the Extended 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)
A systematic example of the Extended TIO approach is presented in section B.4.5
B.4.3 Extended CSTR Approach
The direct CSTR approach for calculating log inactivation across a chamber in an ozone
contactor is discussed in Section 11.3.3. This section includes a discussion of the application of
the Extended CSTR method to an Extended zone as defined in Sections B.3.2 and B.4.1. The
Extended CSTR approach can be used whether or not tracer test results are available for the
ozone contactor. However, it was developed primarily to afford a method for systems that choose
not to perform a tracer study. In particular, in cases where a system chooses not to perform a
tracer study, the Extended CSTR method makes an assumption that the hydrodynamics of each
individual chamber is equivalent to an ideal CSTR. The assumption of CSTR hydrodynamics is
considered somewhat conservative in terms of the efficiency towards chemical conversion for
first-order and higher-order reactions. That is, the predicted disinfection in an ideal CSTR will be
less than for an equivalent-volume, ideal plug-flow chamber. However, the CSTR assumption is
not the most conservative assumption. Recent studies have indicated that in typical over-under
baffled contactors, the hydrodynamics of an individual chamber can be worse in terms of
reaction efficiency than a single CSTR due to recirculation patterns, dead-volumes, and short
circuiting (Kim, Kim, et al. 2010; Kim, Nemlioglu, et al. 2010; Kim, Elovitz, et al. 2010). EPA
therefore considers the CSTR assumption inherent in the Extended CSTR method as a
reasonable balance between conservatism and pragmatism.
As discussed earlier, the Extended CSTR approach applies to a zone that includes at least
three consecutive reactive chambers. Inactivation within each chamber is calculated according to
Equation 11-1, exactly as it is for the CSTR chamber, 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.
LT2ESWTR Toolbox Guidance Manual B-l 7 April 2010
-------
Appendix B - Ozone CTMethods
The value of C for an Extended CSTR is also calculated using an empirical ozone decay
coefficient, k*, and the ozone residual concentration at the entrance to the zone, Cin. Equation B-
9 shows how to calculate the ozone residual at the effluent of chamber "X" in an Extended
CSTR zone:
C
— (B-9)
\Volume]0}
l + k x
where: k* = Empricial ozone decay coefficient, min"1, calculated as described in section
B.4.3.1
Cin = Calculated ozone residual concentration at the entrance to the Extended CSTR
zone, mg/L, calculated as described in section B.4.3.2
[Volume] QX = 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"
Q = Water flow through the contactor, gpm
Equation B-9 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 11-4 can then be used to calculate the log
inactivation achieved across that chamber. The total log inactivation achieved across the entire
contactor is equal to the sum of the log inactivation values calculated for each chamber.
-Log (W0) = Log (1 + 2.303 x kw x C x HOT) Equation 11-4
where:
-Log (Wo) = the log inactivation
kio = log base ten inactivation coefficient (L/mg-min)
C = Concentration from Exhibit 11-2 (mg/L)
HDT = Hydraulic detention time (minutes)
The kio can be determined using the equations as presented in Section B.4.2 or calculated
from the CT table with the following equation: Log inactivation = kio x CT.
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.
LT2ESWTR Toolbox Guidance Manual B-18 April 2010
-------
Appendix B - Ozone CTMethods
B.4.3.1 Determining the Value of k*
The ozone decay coefficient, k* is calculated using ozone sample measurements, taken
from in-situ sample ports, and an assumed theoretical model of the chamber's hydrodynamics.
The Extended CSTR approach assumes that each individual chamber in the Extended zone is as
a CSTR, and hence the Extended zone can be modeled as a group of CSTRs in series. It is
important to note that the empirical ozone decay coefficient, k*, will unlikely be the same value
as the first-order decay rate constant that would be measured in a batch or plug-flow reactor.
Only when the each chamber of the Extended zone behaves as an ideal CSTR and, consequently,
the series of chambers acts as CSTRs-in-series, will the empirical k* be equivalent to the true
first-order rate constant. Nonetheless, the simplifying assumption of CSTR hydrodynamics and
use of the CSTR-in-series equation (e.g. Equation B.10) enables a reasonable prediction of the
ozone concentration at other points in an Extended (Rakness, Najm et al. 2005).
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, Cj, €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 Exhibit B.5 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 k value:
Step 1 - Use Equation B-10 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-10 is presented in Appendix D):
(B-10)
where: k^_2 = Empirical ozone decay coefficient between sampling locations 1 & 2, min"1
Ci = Measured ozone residual at location 1, mg/L
€2 = Measured ozone residual at location 2, mg/L
[Volume]^ 2 = Volume between sampling locations 1 and 2, gallons
N12 = Number of chambers between sampling locations 1 and 2
Q = Water flow through the contactor, gpm
Step 2 - Use residual measurements Ci and €3 along with Equation B-l 1 to calculate the k*
value representing ozone decay between sampling locations 1 and 3, ^_3:
LT2ESWTR Toolbox Guidance Manual B-l9 April 2010
-------
Appendix B - Ozone CTMethods
1-3 =
(B-H)
where: k\_^
C3
[Volume] l3
^1-3
Q
Empirical ozone decay coefficient between sampling locations 1 & 3, min"1
Measured ozone residual at location 1, mg/L
Measured ozone residual at location 3, mg/L
Volume between sampling locations 1 and 3, gallons
Number of chambers between sampling locations 1 and 3
Water flow through the contactor, gpm
It should be emphasized that sampling location 1 should not be at the entrance to the
Extended zone, but should be at least one chamber into the zone. For example, in Exhibit B.4(A),
Ci should not be measured at the entrance to chamber 5, since that is the entrance to the
Extended 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
k\_2 and ki_3 as shown in Equation B-12.
k =
* 7 *
+ k
1-2
1-3
(B-12)
It is normal for the individual values of k^_2 and A:1-3 to be somewhat different.
However, it is recommended that they be within the range of 80 percent to 120 percent of the
average k* value calculated in Step 3. That is,
abstk* - &!_. \
< 20%
If the two k* values do not meet this criterion, the utility may 1) reject the measured residual
values and collect new samples until this quality assurance (QA) criterion is met, or 2) select the
higher of the two k* values as the more conservative estimate.
B.4.3.2 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
LT2ESWTR Toolbox Guidance Manual
B-20
April 2010
-------
Appendix B - Ozone CTMethods
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 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-13 through B-15 can be used to estimate the value of Cin
from the three measured ozone residual concentrations:
ci x
C - C
*— ,•„ i — ^t
Ci .^r
= C X
\Volume] 0 j
„ \Volume]0 2
#0-2 xe
„ \Volume]0 3
#o-3xe
(B-13)
(B-14)
(B-15)
where:
-i
k = Ozone first-order decay coefficient, min"
Ci = Measured ozone residual at location 1, mg/L
C2 = Measured ozone residual at location 2, mg/L
€3 = Measured ozone residual at location 3, mg/L
NQ j = Number of chambers between the entrance to the Extended CSTR Zone and
sampling location 1
NQ 2 = Number of chambers between the entrance to the Extended- CSTR Zone and
sampling location 2
N0_3 = Number of chambers between the entrance to the Extended- CSTR Zone and
sampling location 3
[Volume] Q_l = 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-13 through B-15:
C, =
^
LT2ESWTR Toolbox Guidance Manual
B-21
April 2010
-------
Appendix B - Ozone CTMethods
A systematic example of the Extended CSTR approach is presented in section B.4.5.
B.4.4 Quality Assurance for Extended Method Calculations
The Extended method depends on ozone residual measurements and assumed contactor
hydrodynamics in order to predict ozone concentrations through the contactor. This section
includes recommended QA controls intended to verify the validity of the residual predictions.
Other considerations that have an important impact on characterizing the hydrodynamics and the
ozone profile are discussed in Appendices C and E.
The predicted ozone residual concentration, the parameter C in Equation 11-1,
encompasses both the hydrodynamic 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 Cin. In section B.4.3.1, as part of the discussion on the calculation of &*, it is
stipulated that the individual k* values (i.e., k*\.^ and k*\.^) should be within 20 percent of the
average value. This QA control is meant to ensure that ozone residual measurements used to
calculate the ozone decay profile are consistent with the calculated profile. Since the calculation
of Cin (Equations B-13 through B-15) depends on k*, as well as the measured ozone
concentrations, the QA criteria for k* is sufficient for Cin. Therefore, no additional QA criteria
are necessary for it.
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
target microorganism. 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 more than 20 percent higher than the measured value. Note that this is a
one-sided QA control. In other words, an under-prediction of the ozone residual is acceptable
since it results in a conservative CT value. However, an over-prediction by more than 20 percent
is not desirable.
The ozone concentration measurements used to calculate k* and Cin 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 at those locations.
LT2ESWTR Toolbox Guidance Manual B-22 April 2010
-------
Appendix B - Ozone CTMethods
B.4.5 Examples of Extended Method Application
This section provides examples calculating the log inactivation credits across
conventional and non-conventional contactors using the Extended TIQ method and the Extended
CSTR method. The calculations are completed for Cryptosporidium log inactivation using k10
for Cryptosporidium. Calculations for Giardia and virus log inactivation are completed similarly
by using kw for Giardia or virus in place of kw for Cryptosporidium.
Example 1 — Conventional 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 MOD 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.
LT2ESWTR Toolbox Guidance Manual B-23 April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.5 Schematic of the Ozone Contactor and the Measured Ozone Residual
Values in Example 1
SFA Reactive Zone
50 MOD
[34,720 gpm]
12 15 18 21 24 27 30 33
36
The goal is to calculate the Cryptosporidium inactivation credit across the contactor using
the Extended TIO and Extended CSTR methods.
Extended TIO Method
Chamber 1 (First Dissolution Chamber) - No Cryptosporidium inactivation credit is given to
the first dissolution chamber.
Chambers 2 through 12 (Extended TIO zone) - This zone is classified as an Extended zone.
The Extended TIO zone calculations are applied to determine the log inactivation across each of
the 11 chambers. Since the third ozone residual measurement, €3, is above 0.05 mg/L, and it is
made at point in the contactor more than 50% of the volume, it is permissible to use the overall
Tio/HDT ratio for each individual chamber. The following steps are implemented:
Step 1: Calculate k~ value - The k value is calculated as described in section B.3.2.1 using the
three ozone residual measurements, Ci, €2, and €3 that are shown in Figure B.6. The values of
* *
ki_2 and ki_3 can be calculated using Equations B-2 and B-3 as follows:
LT2ESWTR Toolbox Guidance Manual
B-24
April 2010
-------
Appendix B - Ozone CTMethods
k* -
"•1-9 ~~
C9
34,720
3x104,000
-xLn
0.71
0.41
= 0.0611 miri
-i
O
c,
34,720
6x104,000
0.71
O20
= 0.0705 min"
The A: value is then calculated as the average of k\_2 and ^_3 as follows:
0.0611 + 0.0705
= 0.0658 min
-i
A QA check shows that the values of ^_2 and ^_3 are within 7.1 percent of the average k
value of 0.0658 min"1. This value of &* is within the recommended maximum variability of 20
percent. If this criterion were not met, then the k* value could be set at 0.0705 min"1, which is the
higher (i.e., more rapid decay rate) of the two values.
Step 2: Calculate Cm value - The value of Cin is calculated using the approach described in
Section B.4.2.2. With the value of k* calculated at 0.0658 min"1, Equations B-5 to B-7 can be
used to calculate the Cin value as follows:
C , = C,
»,i i
= o.7ixexpo.0658
34,720
= 0.86 mg/L
5
C. 2 = C2xexp
»,2 2 P
2 = o.4lxexpo.0658
C. 3 =C3xexp
IB'3 3
[Fofa^-
Q
=0.20xexpo.0658
34,720
7xl04-00°
34,720
= 0.90 mg/L
5
= 0.79 mg/L
5
Therefore,
C,, =
0.86 + 0.90+0.79
= 0.85 mg/L
5; 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 equation 11-2 directly and
equals 0.2555 L/mg-min.
LT2ESWTR Toolbox Guidance Manual
B-25
April 2010
-------
Appendix B - Ozone CTMethods
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 TIO zone
can be calculated. These values are calculated using Equation B-l:
Cx=CmxExp -
. ([Volume]0_x
I A
I G
where Cx is the calculated concentration at a location "X" along the water path through the
Extended TIO zone. For example, the residual concentration at the effluent of chamber 4,
is calculated as:
-0.0658x
3x104,000
34,720
= 0.47 mg/L
Note that the Extended TIO 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.
Exhibit B.6 Application of the Extended I™ Method to the Example
Vol./Chamber = 104,000 gallons
Flowrate = 34,720 gpm
Cm = 0.85 mg/L
k*= 0.0658 min1
k10 = 0.2555 L/mg-min
T10/HDT= 0.65
(1) (2)
HDT from
Entrance of Zone
Chamber HDT, min
2 3.0
3 6.0
4 9.0
5 12
6 15
7 18
8 21
9 24
10 27
11 30
12 33
(3)
C =
Calculated
*"out
mg/L
0.70
0.57
0.47
0.39
0.32
0.26
0.21
0.18
0.14
0.12
0.10
Sum =|
(4)
*"out
Log
In activation
0.35
0.29
0.23
0.19
0.16
0.13
0.11
0.09
0.07
0.06
0.05
1.7
(5)
C
Integrated
Residual
mg/L
0.77
0.63
0.52
0.43
0.35
0.29
0.24
0.19
0.16
0.13
0.11
Sum =|
(6)
= cint
Log
Inactivation
0.38
0.32
0.26
0.21
0.17
0.14
0.12
0.10
0.08
0.07
0.05
1.9
LT2ESWTR Toolbox Guidance Manual
B-26
April 2010
-------
Appendix B - Ozone CTMethods
Step 4: Calculate Log Inactivation - To calculate the log inactivation across a chamber using the
TIO method, the values of C, T10 and k10 are required. The value of k10 for the inactivation of
Cryptosporidium with ozone at the water temperature of 20°C was determined earlier at
0.2555 L/mg-min. Using Exhibit 11.5, the value of C used in calculating CT in a reactive
chamber can be set equal to Cout or to the integrated residual, Cint. Exhibit B.6 lists the Cout and
CM values for each chamber in the Extended TIO zone, as well as the associated log inactivation
using the following equation:
Log Inactivation = klo xCxHDTchamber x
T
HDT)
For example, if C is set to Cout, the log inactivation achieved in chamber 4 is calculated as:
Log Inactivation = kw xCout4 xHDT4 x
T
HDT
\= 0.2555x0.47x3x 0.65 = 0.23 logs
On the other hand, if C is set to the CM, then CM is calculated using the following equation:
„ fc,,,-c,,
Ln
For chamber 4, Cint is calculated as:
r -(»•"-0.47) =
Ln
0.57
0.47
The log inactivation achieved in chamber 4 is then calculated as:
Log Inactivation = kw xCout4 xHDT4 x
T
HDT
= 0.2555x0.52x3x0.65 = 0.26 logs
Column (4) in Exhibit B.6 lists the log inactivation values calculated for chambers 2 through 12
after setting C equal to Cout. Column (6) in Exhibit B.6 lists the log inactivation values calculated
for chambers 2 through 12 after setting C equal to CM- The sum of the log inactivation achieved
(totals of Columns 4 and 6 in Exhibit B.6) is 1.7 logs using the Cout approach, and 1.9 logs using
the CM approach.
LT2ESWTR Toolbox Guidance Manual
B-27
April 2010
-------
Appendix B - Ozone CTMethods
Extended CSTR Method
Chamber 1 (First Dissolution Chamber) - No Cryptosporidium inactivation credit is given to
the first dissolution chamber.
Chambers 2 through 12 (Extended CSTR zone) - This zone is classified as an Extended-
CSTR zone. The Extended CSTR calculations (Section 4.3) are applied to determine the log
inactivation across each of the eleven chambers. The following steps are implemented
Step 1: Calculate k~ value - The k value is calculated as described in section B.4.3.2.1 using the
three ozone-residual measurements, Ci, €2, and €3 that are shown in Figure B.6. The values of
k\_2 and ^_3 can be calculated using Equations B-2 and B-3 as follows:
3x34,720
[3x104,000]
0.71
0.41
- 1
= 0.0670 miri
-i
\Volume] j_3
6x34,720
[6x104,000]
0.71
0.2
- 1
= 0.0785 min
-i
The k* value is then calculated as the average of kl-2 and &1-3 as follows:
k* =
~k*_2 + k*_3 ~
2
"0
0670
+
0
0785"
2
= 0.0728 min"
A QA check shows that the values of ^_2 and &j_3 are within 8 percent of the average k value
of 0.0728 min"1. This value of k* is within the recommended maximum variability of 20 percent.
If this criterion were not met, then the k* value could be set at 0.0785 min"1, which is the higher
(i.e., most rapid decay rate) of the two values.
Also note that the k* value determined by the Extended T10 method is not the same as that
determined by here by the Extended CSTR method. This is to be expected since the two methods
use different conceptual hydrodynamic models to determine the ozone profile.
Step 2: Calculate C,^ value - The value of Cin is calculated using the approach described in
Section 4.2.2. With the value of k* calculated at 0.0728 min"1, Equations B-5 to B-7 can be used
to calculate the Cin value as follows:
LT2ESWTR Toolbox Guidance Manual
B-28
April 2010
-------
Appendix B - Ozone CTMethods
= x
l+k x
= 0.71x
l + 0.0728x
[104,000]
1x34,720
= 0.86mg/L
c = c
^-in 9 ^9 '
[Volume], _2
1 + A: x-
N0_2xQ
= 0.41x
1 + 0.0728:
[4x104,000]'
4x34,720
= 0.90mg/L
C3 x
[Volume], 3
1 + A: x
= 0.20x
l + 0.0728x
[7x104,000]
7x34,720
= 0.80mg/L
Therefore,
++
,3
0.86+0.90+0.80
= 0.85mg/L
Step 3: Calculate the value ofk^n - The value of k]0 for the inactivation of Cryptosporidium
with ozone at the measured temperature of 20°C can be obtained from Equation 11-5 directly
and equals 0.2555 L/mg-min. Otherwise the value for k10 could be determined using Equation
11-4.
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:
C,
, \Polume]0 _}
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:
0.85
l + 0.0728x
[3x104,000]
3x34,720
= 0.47 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.7 lists the calculated
residual values for each chamber using the same approach, beginning with chamber 2.
LT2ESWTR Toolbox Guidance Manual
B-29
April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.7 Application of the Extended CSTR Method to the Example
VoL/Chamber =
Flowrate =
cm =
k* =
kio =
(1)
Chamber
2
3
4
5
6
7
8
9
10
11
12
104,000
34,720
0.854
0.0728
0.2555
(2)
HDT from
Entrance of Zone
HDT, min
3.0
6.0
9.0
12
15
18
21
24
27
30
33
gallons
gpm
mg/L
min"1
L/mg-min
(3)
Calculated
*"out
mg/L
0.70
0.58
0.47
0.39
0.32
0.26
0.21
0.18
0.14
0.12
0.10
Sum=|
(4)
Log
Inactivation
0.35
0.30
0.26
0.23
0.19
0.16
0.14
0.12
0.10
0.08
0.07
2.0
Step 4: Calculate Log Inactivation - Knowing the values of C, kio, and k , Equation 11-4 is used
to calculate the log inactivation achieved in each chamber in the Extended CSTR Zone:
Log - inactivation = Log
2.303 k C
Q
where Cx is the effluent residual concentration from Chamber X, Cx,out (see Exhibit 11-
3), while [Volume]x is the volume of that chamber. For example, for chamber 4, if the Cx is set
at Cx,out, then the log inactivation achieved in chamber 4 is calculated as:
Log - inactivation = Log
1 + 2.303 x 0.2555x0.47x
104,000
34,720
= 0.26 logs
Column (4) in Exhibit B.7 lists the log inactivation values calculated for chambers 2
through 12 under this approach. The sum of the log inactivation achieved (total of Column 4 in
Exhibit B.6) is 2.0 logs.
LT2ESWTR Toolbox Guidance Manual
B-30
April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.8 shows a schematic of a non-conventional ozone contactor. The contactor is
treating 12.5 MGD of water at a temperature of 8°C. The contactor is comprised of a long and
narrow channel with no baffle walls. Ozone is added into the raw water line upstream of the
contactor. Ozone analyzers are installed at three locations along the length of the contactor. The
bottom graph in Exhibit B.8 shows the values of the rolling average ozone residuals reported by
the ozone analyzers at the three monitored locations. It is noted that the contactor length:width
ratio is 90:12 (7.5:1), while the length:height ratio is 90:9 (10:1), both of which are greater than
the minimum desired value of 5:1. The goal is to calculate the Giardia inactivation credit across
the contactor using the Extended TIO and Extended CSTR methods.
Because non-conventional contactors do not possess specific zones, such as the baffle
gaps in conventional over-under contactors, where a high degree of mixing can create
homogeneity of solute concentrations, they pose additional considerations for measuring
representative ozone concentrations at specific HDTs in the contactor. That is, measuring ozone
concentrations at the baffle gaps of a conventional contactor is generally regarded as providing a
representative average ozone concentration exiting the specific chamber. In contrast, it is not as
well understood what the exact hydrodynamics are within the non-conventional contactors, and
consequently whether an ozone sample taken at one point along the length of the contactor is
representative of the average concentration across the cross-section at that theoretical HDT. The
issue of a representative ozone measurement is also true for calculated ozone residuals.
Furthermore, since the non-conventional contactor does not have clearly defined chambers, it is
necessary to subdivide the Extended zone of non-conventional contactors into an appropriate
number of conceptual segments such that characteristic ozone concentrations can be calculated
and the Extended CTi0 method applied. The term "segment" is chosen here to avoid confusion
with the term "chamber," which may connote an actual physical chamber in a baffled contactor,
as opposed to a conceptual or theoretical segment denoted here.
This guidance utilizes a calculation described in numerous chemical reactor design texts
(e.g. Levenspiel 1999; Fogler 2005) for defining the hydrodynamics measured by a tracer test in
terms of a series of ideal CSTRs. The so-called Tanks-in-Series (sometimes called CSTR-in-
series) model, as applied to non-conventional contactors, affords a method for subdividing the
single large chamber of the contactor into multiple equal-sized conceptual segments based on an
analysis of a tracer test. The calculations necessary are similar to those required for calculating
the TIO value. Appendix E provides guidance on performing this calculation for both pulse input
and step input tracer tests.
The tanks-in-series model is typically used in reaction engineering by employing CSTR-
specific reaction equations (e.g. Equations B-l 1 and B-13) to each of the theoretical tanks.
Application of the tanks-in-series calculation here is used only to calculate a theoretical number
of segments in which to subdivide the single large chamber. Once the chamber is divided into
segments with theoretical HDTs for each, the Extended TIO method can be applied accordingly.
This calculation is viewed as a pragmatic method to determine a reasonable number of segments.
Taken with the discussion regarding the linear extrapolation of the overall Tio/HDT ratio across
all segments (see section B.4.2 above), it is reasonable to establish some recommendation for
limiting the extrapolation of Tio/HDT and calculation of Cx to what could otherwise be an
infinite number of conceptual segments.
LT2ESWTR Toolbox Guidance Manual B-31 April 2010
-------
Appendix B - Ozone CTMethods
Extended TIO Method
The entire contactor shown in Exhibit B.8 is treated as an Extended zone. Tracer analysis
performed as per Appendix E determined a Ti0/HDT ratio of 0.67 Furthermore, the tanks-in-
series tracer analysis determined that the tracer output corresponded to a series of 12 equal-sized
segments. The Extended zone, which is 90 ft long, has ozone sample points at approximately
16%, 33% and 50% of the contactor volume. Since the third ozone residual measurement, Cs, is
above 0.05 mg/L, and it is measured at point in the contactor that is at least 50% of the volume, it
is permissible to use the overall Ti0/HDT ratio for each of the 12 theoretical chambers, or
segments. The Extended TIO zone calculations (Section B.4.2) are applied to determine the log
inactivation across each segment, and thus the entire contactor. The following steps are
implemented:
Step 1: Calculate k~ value - The k value is calculated as described in section B.4.2.1 using the
three ozone residual measurements, Ci, €2, and Cs that are shown in Exhibit B.8. With 12 equal
segments, each segment would have a volume of approximately 6059 gallons. Ozone sample
ports depicted in Exhibit B.8 are located at approximately the effluents of segments 2, 4, and 6.
With a flowrate of 8,680 gpm, values of k\_2 and ^_3 can be calculated using Equations B-2
and B-3 as follows:
Q
8,680
2x6,059
-xLn
0.54
0.32
= 0.375 min
-i
O
Ln
C,
8,680
4x6,059
-xLn
0.54
0.25
= 0.276 min"
, * , *
The k* value is then calculated as the average of !~2 and 1-3 as follows:
k" =
k* + k
0.375 + 0.276
= 0.325 min"
lr if
A QA check shows that the values of i~2 and 1-3 are within 15 percent of the average
k* value of 0.325 min"1. This value of k* is within the recommended maximum variability of 20
percent. If this criterion were not met, then the k* value could be set at 0.375 min"1, which is the
higher of the two values.
LT2ESWTR Toolbox Guidance Manual
B-32
April 2010
-------
Appendix B - Ozone CTMethods
Exhibit B.8 Schematic of the Ozone Contactor and the Measured
Ozone Residual Values in Example 2
Top View
12.5 MOD
Side View
12ft
\ .
— >
9ft
2 = 0.32 mg/L
C3 = 0.25 mg/L
HDT, min
Step 2: Calculate C,^ value - The value of Cin is calculated using the approach described in
Section 4.2.2. With the value of k* calculated at 0.325 min"1, Equations B-5 to B-7 can be used to
calculate the Cin value as follows:
LT2ESWTR Toolbox Guidance Manual
B-33
April 2010
-------
Appendix B - Ozone CTMethods
C , = C, xexp x = 0.54xexpo.325x 2X ' = 0.85 mg/L
"u 2 J I 8,680
C- 2 = C2 xexpr x - = Q.32xexpo.325x ' = 0.79 mg/L
M'2 2 *\ Q ) V 8,680 J
C. 3=C3xexpfrx[FofaOT4-0=0.25xexpfo.325x6x6-°59l = 0.98 mg/L
IB'3 (9 8,680
Therefore,
_r~B.i ~m.< "».," ^0.85 + 0.79+0.98
= 0.87 mg/L
.Step 5; Calculate the value ofkin - The value of kw for the inactivation ofGiardia with ozone
at the measured temperature of 8°C can be obtained using the equation presented in B.4.2, which
states:
Giardia kw = 1.0380x(l.074if8"*
Using the above equation, the k10 value for the inactivation ofGiardia with ozone at 8 °C is
calculated at 1.839 L/mg-min.
Step 4: Calculate the Ozone Residual at the Effluent of Each Segment - As with a conventional
contactor composed of multiple chambers, knowing the values of Cin and k*, the ozone
concentration at the effluent of each chamber within the Extended TIO zone can be calculated. In
the case of non-conventional contactors, the tanks-in-series tracer analysis (see Appendix E) is
employed to subdivide the single large chamber into multiple theoretical segments, and the
concentration at the effluent of each segment determined as with conventional contactors. These
values are calculated using Equation B-l:
* (\Volume]0_x\]
K V —
K X
where Cx is the calculated concentration at a location "X" along the water path through the
Extended TIO zone. For exampl*
segment, CS;OMf, is calculated as:
Extended TIO zone. For example, the residual concentration at the effluent of the 8th theoretical
^ =0.87xE»p -0.325x =0.14 mg/L
Note that the Extended TIO zone begins at the effluent of segment 1, which makes the subscript
to [Volume} in the equation above depicted as "1-8". Exhibit B.6 lists the calculated residual
LT2ESWTR Toolbox Guidance Manual B-34 April 201 0
-------
Appendix B - Ozone CTMethods
values for each segment using the same approach, beginning with segment 2. In many cases, the
ozone sampling ports will be located at HDTs that do not coincide with the HDT of a theoretical
segment. However, since values of Cx will be calculated for all the theoretical segments, it is
problematic that the actual ozone measurements are not used as the characteristic Cx value.
Exhibit B.9 Application of the Extended T-io Method to the Example
Vol./Segment =
Flowrate =
Qn =
k* =
kio =
T10/HDT =
(1)
Segment
1
2
3
4
5
6
7
8
9
10
11
12
6,059
8,680
0.87
0.325
1.839
0.67
(2)
HDT from
Entrance of Zone
HDT, min
0.7
1.4
2.1
2.8
3.5
4.2
4.9
5.6
6.3
7.0
7.7
8.4
gallons
gpm
mg/L
min"
L/mg-min
(3)
C = <
Calculated
Cout
mg/L
0.69
0.55
0.44
0.35
0.28
0.22
0.18
0.14
0.11
0.09
0.07
0.06
Sum =1
(4)
"'Ollt
Log
Inactivation
0.60
0.48
0.38
0.30
0.24
0.19
0.15
0.12
0.10
0.08
0.06
0.05
2.7
Step 4: Calculate Log Inactivation - To calculate the log inactivation across a segment using the
TIO method, the values of C and kw are required. The value of kw for the inactivation ofGiardia
with ozone at the water temperature of 8 °C was determined earlier at 1.839 L/mg-min. Using
Exhibit 11.2, the value ofCout is used in calculating CT for each segment in the Extended zone.
Exhibit B.9 lists the Cout values for each segment in the Extended TIO zone, as well as the
associated log inactivation using the following equation:
LT2ESWTR Toolbox Guidance Manual
B-35
April 2010
-------
Appendix B - Ozone CTMethods
( T
Log Inactivation = kw xCxHDTsegment x
For example, the log inactivation achieved in segment 8 is calculated as:
Log Inactivation = kwxCnuti,xHDT, x —^- = 1.839x0.14x(5.6-4.9)x 0.67 = 0.12 logs
O § 1U OUt,0 5 7~T7~\ T7 ^ '
flLtl
Column (4) in Exhibit B.9 lists the log inactivation values calculated for segments 1 through 12
The sum of the log inactivation achieved (total of Column 4 in Exhibit B.9) is 2.7 logs.
Extended CSTR Method
The Extended CSTR method is presented in this guidance primarily as a method for
systems which choose not to perform a tracer study. For conventional multi-chamber contactors,
the utility has the option of using the Extended CSTR method even when a tracer is available.
This method may afford a better inactivation credit than the Extended TIO method when the
Tio/HDT ratio is considerably low (e.g. below 0.5). However, as explained in section B.4.3, the
CSTR assumption may be somewhat conservative with regards to a multi-chamber contactor's
hydrodynamics, whose design is to promote plug-flow as opposed to highly mixed flow. In the
context of the non-conventional contactor, the guidance described immediately above and in
Appendix E uses a tracer study to closely characterize the hydrodynamics in terms of tanks-in-
series. In as much as the tanks-in-series analysis calculates the exact number of segments
corresponding to the contactor's residence time distribution, there is virtually no conservatism
with respect to the hydrodynamic model. There is minor conservatism in rounding down the
tanks-in-series calculation to the nearest integer. Additionally, the CSTR assumption inherently
leads to a lower reaction efficiency as compared to the complete segregation assumption.
Nonetheless, the EPA feels that the overall lack of conservatism related to the hydrodynamic
assumption precludes the use of the Extended CSTR method to non-conventional contactors.
LT2ESWTR Toolbox Guidance Manual B-36 April 2010
-------
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.
Fogler, H.S. (2005). Elements of Chemical Reaction Engineering. Upper Saddle River, NJ,
Prentice Hall.
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, Journal 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. U.S. EPA 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.
Kim, D.-L, M. Elovitz, P.J.W. Roberts, J.-H. Kim. 2010. Investigating and enhancing
performance of a multi-chamber ozone contactor using 3D laser induced fluorescence. Journal
AWWA, 102(10): 61-70.
Kim, D., D.-I. Kim, et al. 2010. Large eddy simulation of flow and tracer transport in
multichamber ozone contactors. Journal of Environmental Engineering 136(1): 22-31.
Kim, D., S. Nemlioglu, et al. 2010. Ozone contactor flow visualization and quantification using
3-dimensional laser induced fluorescence. Journal AWWA 102: 90-99.
Lev, O. and S. Regli 1992. Evaluation of Ozone Disinfection Systems: Characteristic
Time T. J. Envir. Engrg. 118: 268-285.
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.
LT2ESWTR Toolbox Guidance Manual B-3 7 April 2010
-------
Appendix B - Ozone CTMethods
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, DJ. Rexing, and E.G. Wert. 2002. Reported Ozone Residual Data
Might Be Undervalued. Conference Proceedings: American Water Works Association Annual
Conference; New Orleans, LA - June 2002.
Rakness, K. L., I. Najm, et al. 2005. Cryptosporidium log-inactivation with ozone using Effluent
CTio, Geometric Mean CTi0, Extended Integrated CTi0, and Extended CSTR calculations.
Ozone Science and Engineering 27(5): 335-350.
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. etal., 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.
LT2ESWTR Toolbox Guidance Manual B-38 April 2010
-------
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.
• Standardization and maintenance of on-line ozone analyzers.
C.I Sample Collection
Ozone contactors are sealed vessels that may have a single large chamber, referred to as
non-conventional contactors, or multiple chambers (typically separated by walls or baffles with
somewhat small openings separating the chambers) referred to as conventional contactors. Water
samples from the interior of the contactor are collected via sample lines that penetrate the walls
or roof structure of the contactor. Since dissolved ozone decays in water with a half-life ranging
from less than a minute to 30 minutes for typical drinking water treatment applications, the
ozone profile (the concentration of ozone along the general flow-path of a contactor) will vary
significantly depending on the water quality, the method of operation, and water flow conditions
(e.g. hydrodynamics and HDT). Consequently, the location, number, and design of sample tubes
plays an important role in operating the ozonation process and calculating CT credit. This
guidance, and additional information found in the SWTR, provides recommendations for
measuring ozone residual including sample ports considerations and analytical methods.
Placement of sample ports depends on the configuration of the contactor - conventional
versus non-conventional. For conventional contactors, considerable experience of practitioners,
as well as more recent studies (Shiono and Teixeira 2000; Kim, Kim, et al. 2010; Kim,
Nemlioglu, et al. 2010; Kim, Elovitz, et al. 2010), suggest that the water flowing through the
baffle gap (i.e. exiting one chamber and flowing into the next, see Exhibit C.I) is reasonably well
mixed. Whether the water arrives that way from the previous chamber, or slip-streams or
"parcels" of different water with greatly varying age distributions arrive simultaneously and mix
thoroughly in the constricted region of the baffle gap is not well understood. However, it appears
that for typical baffle gaps (i.e. not too wide), placement of the sample tube within the (3-
dimensional) center of the gap (1A to 1A the distance), can afford a representative sample of water
exiting the chamber.
Once again, because the rate of ozone decay varies considerably with operating
conditions, 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. Gas bubbles might be carried into the sample inlet and
LT2ESWTR Toolbox Guidance Manual C-l April 2010
-------
Appendix C - Measuring Ozone Residual
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.
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
©
Minimizing the travel time through the sample line is also 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 during travel from the inside of the contactor to end of the tube 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.
LT2ESWTR Toolbox Guidance Manual
C-l
April 2010
-------
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
Ozone Half-live
--»-- HL= 30 sec
•-D-- HL= 1 min
-A--HL= 2min
—e— HL= 5min
0 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 %-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. Section O.3.2 of Appendix O of the Guidance
Manual for Compliance with the Filtration and Disinfection Requirements for Public Water
Systems Using Surface Water Sources (U.S. EPA 1991) (commonly referred to as the SWTR
Guidance Manual) includes further information regarding direct measurement of dissolved
ozone.
This guidance also addresses the use of the Extended TIO method for non-conventional
contactors. Because these contactors are typically, by definition, dominated by a single large
chamber, there are no distinct physical structures (e.g. baffle gaps) that tend to provide a well-
mixed environment from which to collect a representative water sample with an estimable HDT.
Consequently, the question arises as to how to collect a representative sample, and whether a
basic measure of the distance along the longitudinal transect of the theoretical flow-path is a
good measure of the HDT associated with a sample port. There is not sufficient knowledge
LT2ESWTR Toolbox Guidance Manual
C-3
April 2010
-------
Appendix C - Measuring Ozone Residual
regarding the range of hydrodynamic conditions that might be present at any point within the
array of non-conventional contactor geometries. However, in this guidance, the EPA has taken a
pragmatic approach, based on considerable input from stakeholders, that for contactors with
sufficiently long chambers (relative to the height and width), the distance along the longitudinal
transect is a reasonable proxy for HDT. In addition, water samples representative of the cross-
section of the contactor at that HDT can be collected with proper placement of a sample tube.
In this consideration, it is recognized that the inlet and outlet to most non-conventional
contactors, regardless of the overall length, are not designed for optimal hydrodynamic
efficiency. As a result, the hydrodynamics in the regions of the inlet and outlet may be prone to
dead volumes, short-circuiting and large eddy effects. In contrast, if the length-scale of the
chamber is large with respect to the cross-sectional dimensions, the hydrodynamics may become
more developed, more plug-flow-like and homogeneous (across the cross-section) within the
majority of the length of the contactor. Once again, in a pragmatic approach to develop a useful
method for calculating CT credit in such contactors, the EPA proposes that representative water
(ozone) samples can be collected in the same manner as samples from conventional contactors
provided the contactor meets certain geometric criteria. In the context of assuming potentially
poor hydrodynamics at the inlet and outlet regions, but more homogenous flow elsewhere, non-
conventional contactors should have high length-to-width (L:W) and length-to-height (L:H)
ratios.
To employ the Extended TIO method, a minimum of three sample ports is needed.
Because of the potential to have considerable inlet/outlet effects, placement of the sample tubes
is important, and consideration should be given to placement in the areas believed to have more
developed, steady-state flow. The EPA suggests the installation of additional ports to allow
flexibility in monitoring and control. Moreover, the EPA suggests an assessment of the short-
term variability in the ozone measurement from any sample port to help determine if the
hydrodynamics in that region are irregular (unsteady and non-ideal) or relatively stabile (more
plug-flow-like). For example, if multiple ozone samples collected over a short time-span during
steady operating conditions demonstrate high variability (e.g. > 20%) in ozone concentration,
then this may indicate that the hydrodynamics of the contactor in that region are not conducive to
affording a representative ozone sample.
All other considerations regarding sample port design follow those of
conventional contactors.
C.2 Ozone Residual Measurement
Ozone residual should be determined using the Indigo Method (Standard Methods 4500-
Ozone - 20th 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 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
LT2ESWTR Toolbox Guidance Manual C-4 April 2010
-------
Appendix C - Measuring Ozone Residual
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. EPA does
not have information that these issues are resolved at the time of issuing the guidance manual.
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).
• 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.
LT2ESWTR Toolbox Guidance Manual C-5 April 2010
-------
Appendix C - Measuring Ozone Residual
• 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.
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 -
83.62g] * ImL/l 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.
LT2ESWTR Toolbox Guidance Manual C-6 April 2010
-------
Appendix C - Measuring Ozone Residual
[ Absorbance
x Volume of Blank = Absorbance in cm"1 (a) 100 mL (C-1)
lOOmL
0.234'
-1
lOOmL
:96.15mL = 0.225cm'
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.
(A XV.HA.XV,)
f x Vs x b
where AB = absorbance of the blank (as measured, not as corrected by equation C-l)
AS = absorbance of the sample
VB = volume of the blank plus indigo, mL
VT = total volume of the sample plus indigo, mL
Vs = volume of the sample (total weight - tare weight - 10)
f=0.42
b = path length of cell, cm
(0.234 x 96. 1 5) - (0. 1 59 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
LT2ESWTR Toolbox Guidance Manual C-7 April 2010
-------
Appendix C - Measuring Ozone Residual
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 should not deviate more than 10 percent 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 percent or 0.05 mg/L greater than the grab samples.
However, a negative deviation (negative bias), while not effecting public health, 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
percent of the grab-sample average and <0.05 mg/L.
LT2ESWTR Toolbox Guidance Manual C-8 April 2010
-------
Appendix C - Measuring Ozone Residual
C.4 References
Kim, D.-L, M. Elovitz, P.J.W. Roberts, J.-H. Kim. 2010. Investigating and enhancing
performance of a multi-chamber ozone contactor using 3D laser induced fluorescence.
JAWWA, 102(10): 61-70.
Kim, D., D.-I. Kim, et al. (2010). Large eddy simulation of flow and tracer transport in
multichamber ozone contactors. Journal of Environmental Engineering 136(1): 22-31.
Kim, D., S. Nemlioglu, et al. (2010). Ozone contactor flow visualization and quantification
using 3-dimensional laser induced fluorescence. JAWWA 102: 90-99.
Shiono, K. and E. C. Teixeira (2000). Turbulent characteristics in a baffled contact tank. J.
Hydraul. Res. 38(4): 271-416.
LT2ESWTR Toolbox Guidance Manual C-9 April 2010
-------
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 of k* between two points 1 and 2 as
shown by Equation D-l:
(D-l)
Equation D-l is a transformation from the equation of first-order decay across a series of
TV equal-size continuous stirred tank reactors (CSTRs):
Co
,* HDT]
+ k^\^^\
l#i-2J
(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 hydraulic detention time
(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:
Therefore,
i
[Volume]^
vl-2
(D-3)
1 +
\Volume\i_2
n-2
(D-4)
LT2ESWTR Toolbox Guidance Manual
D-l
April 2010
-------
Appendix D - Derivation of Extended CSTR Equations
then,
l + k
1-2
then,
\-2
and then,
(D-5)
(D-6)
kl-2 =
(D-7)
As noted, Equation D-2 is based on the fundamental assumption that the hydrodynamic
profile through the volume separating locations 1 and 2 can be approximated by a series of TV
equal-size CSTRs. If equal-size chambers separate locations 1 and 2, then each chamber is
somewhat conservatively assumed to be an ideal CSTR, with HDT = \Volume]IQ, and the value
of TV in the above derivation is set equal to the number of chambers between locations 1 and 2.
However, it was recognized that not all ozone contactors are configured with equal-size
chambers in series. It is possible to treat each chamber as its own CSTR and have a series of
unequal-size CSTRs. An expression of 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
(HDTa}\
(HDTb}\
2 (HDTc}\
(D-8)
Or in general terms,
C
(D-9)
Unfortunately, it is not possible to transform Equation D-9 to derive a simple linear
expression of &* 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
LT2ESWTR Toolbox Guidance Manual
D-2
April 2010
-------
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 &*.
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
principle, as the reaction rate increases, the number of chambers approaches two (the minimum),
and the volume differences among the chambers increases, the difference between the reaction
efficiencies of 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, the utility and the primacy agency may consider further analysis for
contactors with 2-3 chambers with a large volume difference and a large Dai.
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.
LT2ESWTR Toolbox Guidance Manual D-3 April 2010
-------
Appendix E
Tracer Test Data Development & Analysis
E.I Overview & Quality Assurance
Tracer test data are required to implement the Extended TIQ method. The tracer test is
conducted only once, and its results are applicable as long as the contactor geometry remains
unchanged. Tracer tests can be conducted in the same manner as those described in Appendix C
of the Surface Water Treatment Rule Guidance Manual (SWTR Guidance Manual) (USEPA
1991). Either a "step input" or a "pulse input" tracer test could be used. The step input tracer
test consists of applying a constant dosage of a conservative chemical (tracer) at the head of the
ozone contactor and measuring the concentration of the tracer chemical at the outlet of the
contactor at selected time intervals, while maintaining constant flowrate through the contactor.
The pulse input tracer test (also called a slug dose test) consists of a rapid injection of a specific
mass of a tracer chemical at the head of the ozone contactor over a very short period of time, and
then measuring the tracer concentration at the outlet of the contactor at selected time intervals,
again while maintaining a relatively constant flowrate through the contactor.
Appendix C of the SWTR Guidance Manual recommends that at least four tracers be
performed at a range of expected operational flowrates. This Guidance supports the earlier
recommendation and further strongly recommends that at least two tracer tests be conducted at
the lowest and highest expected operational flowrates. This recommendation is based on
possibility that hydrodynamic efficiency of the contactor could vary as a function of flowrate.
For example, in terms of dispersion, it could be expected that the overall dispersion in a
contactor could vary with the flowrate. For the ozone-Cryptosporidium reaction system,
increasing dispersion leads to an effective decrease in efficiency of the relevant reactions in the
contactor. Therefore, it is important to consider the effect of flowrate on the hydrodynamic
efficiency. Once all the tracer tests have been evaluated, it is recommended that the utility use
the tracer data that demonstrates the greatest "spread" (i.e. dispersion or variance) in the tracer.
This is a measure of conservatism applied to the Extended TIQ approach, and perhaps more
important for the newly developed approach for non-conventional contactors. The added safety
factor it provides depends strongly on the specific contactor geometry and the range of the
expected flowrates.
Systems considering tracer studies should contact their state regulatory agencies
regarding the use of tracer chemicals. Commonly used tracer chemicals are fluoride or lithium
ions. Fluoride might be added as sodium fluoride (NaF) or as fluosilicic acid (FeF^Si). Lithium
is typically added as lithium chloride (LiCl). At the time of preparation of this document, only
sodium fluoride and fluosilicic acid were NSF-certified additives for drinking water. As such, a
fluoride-based chemical has been the tracer of choice in many applications.
Lithium chloride is not yet NSF-approved, but some State regulatory agencies allow the
use of lithium for tracer testing because of the following three primary advantages it has over
fluoride:
LT2ESWTR Toolbox Guidance Manual E-l April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
1. Lithium is present at very low background concentrations (about 5 to 10 ppb) in most
natural waters compared to the fluoride background concentration, which might range
from0.2to0.5mg/L.
2. Lithium can be analyzed reliably at concentrations as low as 5 ppb, which is much lower
than the typical minimum-reporting limit for fluoride (which is about 0.1 mg/L).
3. There is no health-based limit for lithium in drinking water. The fluoride limit is 4 mg/L.
The range of lithium concentration during a tracer test is typically between 5 and 250
ppb, which is a 50-fold range. The range of fluoride concentration in the tracer test is between
about 0.5-mg/L to 3.5 mg/L, which is a 5-fold range. A broader range provides for a better
resolution in the tracer test results. The collection of reliable tracer test data is important for
accurate assessment of the variance as well as TIO values. The Quality Assurance criteria
outlined below are applicable for obtaining high-quality tracer test results. Once completed,
follow the steps concerning preparing test results for calculation of the variance of the data.
1. At least two tracer tests should be performed for each contactor. The tracer tests
should be conducted at the lowest and highest expected flowrates through the
contactor. The expected flowrate is that which the utility plans on operating the
system. If there are multiple identical parallel contactors, tracer tests can be
conducted on one contactor and applied to the other identical contactors. Of the RTDs
developed from the tracer tests, it is recommended that, for further use in the
Extended TIO method, the utility use the RTD demonstrating the greatest tracer
spread.
2. During the tracer test, the flow rate through the contactor should remain as constant
as possible, with the maximum or minimum value remaining within 90 percent to 110
percent of the average flowrate during the test. That is, the flow rates should be + 10
percent of the set flow rate.
3. The tracer test should be conducted over a minimum period of three hydraulic
detention times (HDT) of the contactor. For example, if the HDT of the contactor is
eight (8) minutes, then the minimum test duration (during which effluent samples are
being collected) is 24 minutes.
4. The number of samples collected during a tracer test should be maximized to generate
the most accurate estimate of the RTD as possible. There are practical limitations to
the number of samples that can be taken and analyzed. However, it is recommended
that a minimum of thirty samples (30) should be collected during a tracer test.
Samples can be collected at unequal time intervals. Sampling density should be
focused on the inflection and peak (for pulse-input) portions of the breakthrough
curve to minimize the numerical errors due to approximations during the RTD
calculations. This would benefit the utility by decreasing the estimated spread of the
tracer and hence the inefficiency of the contactor hydrodynamics.
LT2ESWTR Toolbox Guidance Manual E-2 April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
5. The background concentration of the tracer chemical upstream of the point of tracer
injection should be measured over the duration of the tracer test. The number of
background samples collected should be no less than 20 percent of the number of
effluent samples collected during the test.
6. For pulse input tests, the total mass of the tracer ion or chemical recovered should be
calculated and should be between 85 percent and 115 percent of the mass added. It
should be emphasized that this refers to the tracer ion being measured (i.e., Li+ or F")
and not the chemical being added (i.e., LiCl or NaF). Therefore, the mass of Li+ or F"
added is calculated and then compared to the total mass of Li+ or F" recovered from
the contactor effluent over the course of the tracer test.
7. For step-input tests, the average tracer ion or chemical concentration in the samples
collected during the last 10 percent of the sampling period should be between 85
percent and 115 percent of the tracer dose being added. It is also noted here that the
concentration referenced is that of the tracer ion being measured (such as Li+ or F"),
and not the tracer chemical being added (i.e., LiCl or NaF).
E.2 Development & Analysis of Tracer Test Data for Variance Calculation
The tracer test characterizes the hydrodynamic patterns inside a flow-through contactor.
Details concerning tracer tests are described in Appendices C and O of the SWTR Guidance
Manual, in Teefy & Singer (1990), and Teefy (1996). The two types of tracer tests - step tracer
test and pulse (or slug) tracer test - differ in how the test is conducted, but they result in nearly
the same final set of values that are required for the implementation of the extended TIO
approach. The guidance outlined here generally follows precedence set in Appendices C and O
of the SWTR Guidance Manual. In particular, Appendix C describes the technique for
spreadsheet-style numerical integration of tracer data using right rectangle rule integration step
(described on page C-21, Appendix C simply as the "rectangle rule"). Appendix O in turn
describes a technique for numerical differentiation of the tracer data using the forward
differentiation technique. These two techniques take slightly different approaches to step-wise
treatment of the data; an aspect that is apparent only for treatment of the step dose data.
The tracer data analysis presented here outlines the procedure for transforming the tracer
data to a residence time distribution (RTD), or exit age distribution E. In addition, the
procedures allow for calculation of the mean residence time (tm) (which is defined as the first-
moment of the RTD) and the variance of the RTD (also called the second moment about the
mean of the RTD). Finally, calculations are outlined for determining the cumulative distribution
function F (also called F-curve, which is useful in determining the TIO value.
E.2.1 Pulse-Input Tracer Test Data Development & Analysis
An example of a pulse input tracer study test and the RTD analysis results are shown in
Exhibit E. 1. The tracer test corresponds to the Extended TIO example shown in Appendix B,
section B.4.5, Exhibits B.8 and B.9 for the non-conventional contactor. The tracer test was
conducted at a flow rate that resulted in a theoretical hydraulic detention time (HOT) of 8.4
minutes. This HOT value was calculated as the total volume (in gallons) of the main large
chamber shown in Exhibit B.8 divided by the water flow rate during the tracer test (in gpm).
LT2ESWTR Toolbox Guidance Manual E-3 April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
In this example, a 5-gallon solution containing 10 Ibs of fluoride (F) was injected as
quickly as possible (<15 seconds) into the influent water flow to the contactor. Samples were
collected frequently from the feed water upstream of the point of tracer injection (background
samples) and from the contactor effluent. The background fluoride concentration was monitored
throughout the test duration and the average was calculated at 0.20 mg/L. The HDT of the water
volume between the tracer addition point and the effluent tracer sampling location was 8.35
minutes. The contactor effluent samples were collected every minute for 25 minutes.
The first four columns in Exhibit E. 1 represent the actual tracer test results. The
subsequent columns include calculated values based on the tracer test results. Columns 5
through 10 contain information that is required for the Extended TIQ calculation for the non-
conventional contactors. Column 11 contains additional information. A description of the
contents and calculations for each column is presented below:
Column 1: Datapoint counter.
Column 2: Time of tracer chemical sample collection from the start of the test.
Column 3: Background tracer chemical concentration measured in the influent water during the
test.
Column 4: Tracer chemical concentration measured at the effluent of the contactor during the
test.
Column 5: Average background tracer chemical concentration calculated as the average of all
the background values listed in Column 3.
Column 6: "Effective Concentration", which refers to the tracer concentration measured in the
effluent of the contactor (Column 4) minus the average background tracer
concentration (Column 5). The value of the effective concentration must be
positive. At the beginning and at the end of the step-tracer test, the value of the
effective concentration may be calculated as a negative value because the effluent
tracer concentration may be slightly lower than the background concentration due to
minor analytical errors. This is the case, for example, for the first two time points
with measured concentrations of 0.15 and 0.19 mg/L. In such cases, the value of
effective concentration must be set to zero instead of a negative value.
Column 7: The values in Column 7 are the product of the effective concentration (Column 6)
and the preceding timestep (i.e. tt - tj.j). For example, the effective concentration at
datapoint #8 (2.27 mg/L) is multiplied by the difference between the elapsed time
for datapoint #8 (7 minutes) and the elapsed time for datapoint #7 (6 minutes).
All the values Column 7 are summed at the bottom Column 7. This sum calculates
the area under the pulse response curve according the equation
area =
LT2ESWTR Toolbox Guidance Manual
E-4
April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
where At. = ti -t^ .
It has units of [mass x time/volume] and is used to calculate the total mass
recovered during the tracer test. This is examined further below.
This summation is an example of the right rectangle rule for integration established
in Appendix C of the SWTR Guidance Manual. Note, that due to the process of
using the previous timestep, the first cell in this column is blank (or "0").
Column 8: The values in Column 8 are a simple multiplication of the time (Column 2) and the
value in Column 7.
All the values Column 8 are summed at the bottom Column 8. This sum represents
the integral
where
In addition, this value is used in the calculation of the mean residence time, tm, by
dividing the sum of Column 8 (128.27) by the sum of Column 7 (14.29).
sum column 8
sum column 1
In this example, a value of 8.97 minutes is calculated. This compares well with the
theoretical HDT of 8.35 minutes. Differences may arise due to experimental error
in conducting the tracer test or numerical dispersion related to the quality and time-
resolution of the tracer data.
Column 9: The values in Column 9 represent the values for the residence time distribution
(RTD) or exit age distribution E. These values are calculated by dividing the
effective concentration (Column 6) by the sum of the values of Column 7 (i.e.
14.29, shown at the bottom of Column 7). For example, the value for E for data
point #11 is calculated by dividing the concentration (1.81; Column 6) by 14.29.
Column 10: The values in Column 10 are calculated as the product of several terms according to
the equation
where Ar. = tt -1^, and tm is taken as the value calculated at the bottom of the
Exhibit. Note, one should use the calculated value of the mean residence time
rather than the theoretical HDT.
Once the values for each term in Column 10 are calculated, the sum of all values is
made at the bottom of Column 10. \(t-tm)2Edt = ^(t, -tm)2ElAtl
LT2ESWTR Toolbox Guidance Manual
E-5
April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
The summed value at the bottom of Column 10 represents the variance of the RTD
about the mean, typically denoted by the term a2. The significance of this value is
discussed below.
Note, this summation is again an example of the right rectangle established in
Appendix C of the SWTR Guidance Manual. Due to the process of using the
previous timestep, the first cell in this column is blank (or "0").
Column 1 1 : Finally, the values in Column 1 1 represent the F-curve. They are calculated
according to the equation
The value for each datapoint is calculated by multiplying the value in Column 10 by
the preceding time step (i.e.<^ = tt - t^i) and then adding this value to the
preceding value of F (i.e. in the cell above). For example, for datapoint #12,
Fu =EnAtu+Fu =0.09(1 1-10) + 0.76 = 0.85
The F-curve is useful for determining the TIQ value as described the Appendix O of
the SWTR Guidance Manual.
LT2ESWTR Toolbox Guidance Manual E-6 April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
Exhibit E.1 Example of Pulse-Tracer Test Results & RTD Analysis
theoretical HOT = 8.35 min
Flow Rate = 12.5 MOD
Mass Added =
Mass Recovered (tm-basis) =
Mass Recovered (HDT-basis) =
(1) (2) (3) (4) (5) (6)
Tracer Test Data: Avg.
Background Background Effective
Data Time Cone. Cone. Cone. Cone.
Point min mg/L mg/L mg/L mg/L
1 0 0.200 0.150 0.20 0.00
2 1 0.190 0.20 0.00
3 2 0.230 0.200 0.20 0.00
4 3 0.203 0.20 0.00
5 4 0.210 0.293 0.20 0.09
6 5 0.793 0.20 0.59
7 6 0.220 1.700 0.20 1.50
8 7 2.469 0.20 2.27
9 8 0.180 2.530 0.20 2.33
10 9 2.475 0.20 2.27
11 10 0.190 2.0150 0.20 1.81
12 11 1.470 0.20 1.27
13 12 0.200 1.0931 0.20 0.89
14 13 0.780 0.20 0.58
15 14 0.200 0.490 0.20 0.29
16 15 0.380 0.20 0.18
17 16 0.200 0.312 0.20 0.11
18 17 0.262 0.20 0.06
19 18 0.220 0.250 0.20 0.05
20 19 0.218 0.20 0.02
21 20 0.200 0.210 0.20 0.01
22 21 0.210 0.20 0.01
23 22 0.190 0.203 0.20 0.00
24 23 0.195 0.20 0.00
25 24 0.200 0.201 0.20 0.00
26 25 0.200 0.20 0.00
note, all
values must
be>0
10
9.3
8.6
(7)
QAt
0.00
0.00
0.00
0.09
0.59
1.50
2.27
2.33
2.27
1.81
1.27
0.89
0.58
0.29
0.18
0.11
0.06
0.05
0.02
0.01
0.01
0.00
0.00
0.00
0.00
14.29
Ibs
Ibs
Ibs
(8)
tjQAt
0.00
0.00
0.00
0.36
2.95
8.98
15.86
18.62
20.45
18.12
13.94
10.68
7.50
4.02
2.65
1.74
1.00
0.84
0.29
0.13
0.15
0.00
0.00
0.00
0.00
128.27
Recovered
93%
86%
(9)
E(t)
0.00
0.00
0.00
0.00
0.01
0.04
0.10
0.16
0.16
0.16
0.13
0.09
0.06
0.04
0.02
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
tm =
-------
Appendix E- Tracer Test Data Development & Analysis
As shown in Exhibit E. 1,
t1 (8 97)2
-^-^ '
6.32
=12.7
Therefore, the tracer test determined that the contactor has a hydrodynamic character similar to a
series of 12.7 CSTRs in series. Implementation of the Extended TIO method rounds the value of
N down to the nearest integer, and uses this value for the number of segments for subdividing the
non-conventional contactor. In this example, the Extended TIO calculation would use 12
segments.
Exhibit E. 1 contains additional calculations that are not necessary for implementing the
Extended TIO method, but are needed for quality control of the tracer test, or for further general
information concerning the contactor hydrodynamics.
The mass of the tracer chemical recovered is calculated according to:
Tracer Mass, Ibs = 0.005792xQxtmx^C,At1
where: Q = water flow rate during the test, MGD
tm_= mean residence time determined by the RTD analysis, minutes
^C.A^. = total sum of the area under the tracer response curve, calculated as the sum of
the terms in Column 7.
0.005792 = conversion factor, which is 8.34 Ibs/gallon divided-by 1440 min/day
The mass of tracer chemical recovered was calculated at 8.6 Ibs using the above equation, which
is 93 percent of the tracer mass added (10 Ibs). This value is within the acceptable range of 85
percent - 1 15 percent. For comparison, the mass of tracer recovered if the calculation is based
on HDT instead of tm is 8.6 Ibs for a 86 percent recovery.
Exhibit E.I also shows the value for the dimensionless variance denoted by the term, oe2,
which is the dimensionless form of the variance, o2. The variance represents the second moment
abut the mean of the RTD. It is calculated according to
°*-T
m
which is the inverse of the equation for determining N, such that
2 1
CTn = -
6 N
r\
Aside from an alternate form of calculating N, the value of GO is useful for comparing
the results of different tracer studies. For example, a higher value of oe2 measured at a tracer
study of a different flowrate suggests that there is greater mixing in the contactor under that
flowrate. When more than one tracer test is performed, such as at various flowrates as
LT2ESWTR Toolbox Guidance Manual E-8 April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
recommended, the conservative recommendation is to use the RTD data set associated with the
greatest variance, oe2.
Finally, Column 11 shows the calculation of the F-curve which is one method for
determining the TIO value for the contactor. The TIO value for this tracer study appears to be
between 5 and 6 minutes. When interpolated properly, and divided by the mean residence time
tm, the TIO ratio is obtained.
E.2.2 Step-Input Tracer Data Development & Analysis
An example of a step-input tracer test data and the RTD analysis results are shown in
Exhibit E.2. As with the pulse test above the step tracer test was conducted in the non-
conventional contactor shown for the Extended TIO example in Appendix B (section B.4.5,
Exhibits B.8 and B.9). This tracer test was also conducted at a flow rate that resulted in a
theoretical hydraulic detention time (HDT) of 8.35 minutes. This theoretical HDT value was
calculated as the total volume (in gallons) of the main large chamber shown in Exhibit B.8
divided by the water flow rate during the tracer test (in gpm). The chemical feed solution
concentration and flowrate achieved a theoretical tracer concentration of 1.7 mg/L. This tracer
dose value is denoted as C0 in the header of Exhibit E.2.
LT2ESWTR Toolbox Guidance Manual E-9 April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
Exhibit E.2 Example of Step-Tracer Test Results and RTD Analysis
c.=
Average Final Effective Cone. =
% Steady State =
(1) (2) (3) (4) (5) (6)
Tracer Test Data: Avg.
Background Background Effective
Data Time Cone. Cone. Cone. Cone.
Point min mg/L mg/L mg/L mg/L
0 0 0.20 0.20 0.20 0.00
1 1 0.20 0.20 0.00
2 2 0.25 0.20 0.20 0.00
3 3 0.20 0.20 0.00
4 4 0.22 0.21 0.20 0.01
5 5 0.27 0.20 0.07
6 6 0.18 0.43 0.20 0.22
7 7 0.67 0.20 0.46
8 8 0.21 0.94 0.20 0.73
9 9 1.18 0.20 0.98
10 10 0.20 1.37 0.20 1.17
11 11 1.51 0.20 1.31
12 12 0.19 1.60 0.20 1.40
13 13 1.66 0.20 1.46
14 14 0.18 1.70 0.20 1.49
15 15 1.72 0.20 1.51
16 16 0.21 1.73 0.20 1.52
17 17 1.73 0.20 1.53
18 18 0.20 1.74 0.20 1.53
19 19 1.74 0.20 1.53
20 20 0.20 1.74 0.20 1.54
21 21 1.74 0.20 1.54
22 22 0.20 1.74 0.20 1.54
23 23 1.74 0.20 1.54
24 24 0.20 1.74 0.20 1.54
25 25 1.74 0.20 1.54
1.7
1.54
90%
(7)
0
(9)
t,
-------
Appendix E- Tracer Test Data Development & Analysis
Column 1: Datapoint counter.
Column 2: Time of tracer chemical sample collection from the start of the test.
Column 3: Background tracer chemical concentration measured in the influent water during the
test.
Column 4: Tracer chemical concentration measured at the effluent of the contactor during the
test.
Column 5: Average background tracer chemical concentration calculated as the average of all
the background values listed in Column 3.
Column 6: "Effective Concentration", which refers to the tracer concentration measured in the
effluent of the contactor (Column 4) minus the average background tracer
concentration (Column 5). The value of the effective concentration must be
positive. At the beginning of the step-tracer test, the value of the effective
concentration may be calculated as a negative value because the effluent tracer
concentration may be slightly lower than the background concentration due to
minor analytical errors. This is the case, for example, for the first two time points
with measured concentrations of 0.15 and 0.19 mg/L. In such cases, the value of
effective concentration must be set to zero instead of a negative value.
Column 7: The values in Column 7 are calculated as the change between the effective
concentration (Column 6) at this timestep and the value of the effective
concentration of the preceding time step (i.e.
-------
Appendix E- Tracer Test Data Development & Analysis
Column 8:
Column 9:
Column 8 determines the values for the F-curve, or the cumulative distribution
function, F, calculated as the ratio of the effective concentration (Column 6) to the
calculated tracer chemical dose (1.54 mg/L) determined at the bottom of Column 7.
It is noted that all the F values must be positive. The value of F might be returned
as negative at the beginning of the step tracer test, because the effluent tracer
concentration is slightly lower than the background concentration due to minor
analytical errors. In such cases, the value of F must be set to zero instead of the
negative value. The F-curve can be used for calculating the TIQ value. It is also
used further for calculating the E-curve (Column 10).
The values in Column 9 are the product between the time at that datapoint (Column
2) and the change in the effective concentration (Column 6) at this timestep and the
value of the effective concentration of the preceding timestep (i.e.
-------
Appendix E- Tracer Test Data Development & Analysis
As noted, this forward differentiation maintains a slight conservatism with regard to
determining the E function. Because the process is a forward process, the last value
in the column is blank (or "0").
As an example, to calculate the E value for datapoint #5,
_F6-F5 _ 0.044 - 0.004 _
5" t6-t5 ~ 5^4 "
The E function is used further in Column 11.
Column 1 1 : The values in Column 10 are calculated as the product of several terms according to
the equation
where A^. = ti - 1^ , and tm is taken as the value calculated at the bottom of the
Exhibit. Note, one should use the calculated value of the mean residence, tm, time
rather than the theoretical HDT.
Once the values for each term in Column 1 1 are calculated, the sum of all values is
made at the bottom of Column 11. J (t - tm )2 Edt = ^ (tt - tm )2 El Att
The summed value at the bottom of Column 1 1 represents the variance of the RTD
about the mean, typically denoted by the term o . The significance of this value is
discussed below.
Note, this summation is again an example of the right rectangle established in
Appendix C of the SWTR Guidance Manual. Due to the process of using the
previous timestep, the first cell in this column is blank (or "0").
In Exhibit E.2, the summations at the bottom of specific columns are the information
needed to implement the Extended TIO method for non-conventional contactors. The principal
calculation needed is the equivalent number of tanks-in-series represented by the RTD.
According to the tanks-in-series theory, the number of theoretical number of tanks, N, is
determined according to
a
As shown in the example above,
a2 7.27
Therefore, the tracer test determined that the contactor has a hydrodynamic character
similar to a series of 1 1.1 CSTRs in series. Implementation of the Extended TIO method rounds
LT2ESWTR Toolbox Guidance Manual E-13 April 201 0
-------
Appendix E- Tracer Test Data Development & Analysis
the value of N down to the nearest integer, and uses this value for the number of segments for
subdividing the non-conventional contactor. In this example, the Extended TIQ calculation
would use 11 segments.
It is interesting to note that the results of the step dose tracer test analyzed in Exhibit E.2
differed somewhat from the results of the pulse dose tracer test analyzed previously in Exhibit
E. 1. Some of this difference may be attributed to basic errors in dosing and analytical
determinations in the tracer tests. In addition, the step dose tracer test involves a numerical
differentiation (Column 10, step dose) that is typically less accurate than numerical integration
(used several times in each analysis). This could be a source for numeric dispersion which leads
to higher estimated hydrodynamic variance. This is not to imply that one procedure is better
than another. There are advantages and disadvantages to both dose methods. Details of those
issues can be found in Bellamy, Finch et al (1998) and the previous referenced sources.
Exhibit E.2 contains additional calculations that are not necessary for implementing the
Extended TIQ method, but are needed for quality control of the tracer test, or for further general
information concerning the contactor hydrodynamics.
The average effective concentration during the last 10 percent of the test duration (ca. 3
minutes) was 1.54 mg/L. That is also the maximum concentration calculated according to
Column 7. That maximum was within was 90 percent of the dose of 1.7 mg/L added to the
influent water. This value is within the acceptable range of 85 percent to 115 percent.
r\
Exhibit E.2 also shows the value for the dimensionless variance denoted by the term, oe ,
which is the dimensionless form of the variance, a2. The variance represents the second moment
abut the mean of the RTD. It is calculated according to
9 G/
'»
which is the inverse of the equation for determining N, such that
2 _ J_
°e ~ N
r\
Aside from an alternate form of calculating N, the value of oe is useful for comparing
the results of different tracer studies. For example, a higher value of oe2 measured at a tracer
study of a different flowrate suggests that there is greater mixing in the contactor under that
flowrate. When more than one tracer test is performed, such as at various flowrates as
recommended, the conservative recommendation is to use the RTD data set associated with the
greatest variance, oe2.
LT2ESWTR Toolbox Guidance Manual E-14 April 2010
-------
Appendix E- Tracer Test Data Development & Analysis
E.3 References
Bellamy, W. D., G. R. Finch, et al. (1998). Integrated Disinfection Design Framework. Denver,
CO, AWWA Research Foundation.
Fogler, H. S., Elements of Chemical Reaction Engineering. 4th ed.; Prentice Hall: Upper Saddle
River, NJ, 2005.
Levenspiel, O., Chemical Reaction Engineering. 3rd ed.; John Wiley & Sons: New York, 1999.
Teefy, S. 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.
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.
Wen, C. Y.; Fan, L. T., Models for Flow Systems and Chemical Reactors. Decker: New York,
1975.
LT2ESWTR Toolbox Guidance Manual E-15 April 2010
-------
Appendix F
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 2.4.3.2; this appendix provides further detail to the control measures described in chapter
2.
F.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.
F.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
within their watersheds even if the watershed is outside municipal boundaries. For instance, New
LT2ESWTR Toolbox Guidance Manual F-l April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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, public water systems (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, U.S. Environmental Protection Agency (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.
F.1.2 Zoning
This section describes the steps you should follow to make a zoning law that is likely to
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.
LT2ESWTR Toolbox Guidance Manual F-2 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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
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 usually 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
LT2ESWTR Toolbox Guidance Manual F-3 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
analysis will help you show how your proposed ordinance advances a legitimate government
interest and how the effect of the ordinance is proportional to the impact of land use in your
watershed.
Types of Ordinances
Watershed ordinances usually apply within an overlay district, which may be the area of
influence you determined for your watershed control plan. All existing zoning or land use
regulations apply within that area, but additional requirements apply within the overlay district.
Following are some land use ordinances you may wish to consider:
• Large-lot or low-density zoning. Unless lots are very large (such lots can use septic
systems and wells), large-lot zoning may be inefficient, as it increases costs for sewer,
water, and road development. This type of zoning also may go against affordable housing
requirements. However, it may be useful in agricultural areas for preserving rural
character and preventing subdivision of farms.
• Limits on certain types of land use except by special permit. Such ordinances should
specify criteria for granting special permits and designate an authority that may grant
permits. The authority should present findings that back up its decision to grant the
permit. Special permits are granted for a particular lot, not for the owner of that lot.
• Impact fees. The regulating authority must be sure it has authority to impose such fees.
Impact fees collected can be used to pay for mitigation of pollution caused by
development, e.g., for preventing runoff or buying land elsewhere in the watershed. Fees
should be proportional to the impact and the cost of mitigation, and the purpose of the
fees should be specified in the regulation. A disadvantage to impact fees is that they may
in some cases be considered taxes, and local government's 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
LT2ESWTR Toolbox Guidance Manual F-4 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
developer would also be required to list mitigation steps it would take if it exceeded the
pollutant loading requirements.
Most zoning ordinances have grandfather clauses that allow nonconforming land uses to
continue. Ordinances may also allow the zoning authority to grant variances if the topography or
size of a lot make it difficult to comply with a zoning requirement.
Examples of source water protection ordinances can be found at:
http ://www. epa.gov/owow/nps/ordinance/osm7. htm.
F.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 (SRF) allows a
percentage of the fund to be set aside for land acquisition associated with watershed protection.
Note that some states may not allow SRF funds to be used in this manner.
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. Ita. org), a trade organization for land trusts, has published handbooks
on designing and managing conservation easement programs.
LT2ESWTR Toolbox Guidance Manual F-5 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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.
F.2 Addressing Point Sources
F.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 or SPDES) 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.
F.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
LT2ESWTR Toolbox Guidance Manual F-6 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
provides oxygen to bacteria that take in nutrients and digest organic material) (U.S. EPA 2001b).
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.
F.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
LT2ESWTR Toolbox Guidance Manual F-7 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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. Stormwater Best Management Practices (BMPs) can also
reduce the impact of CSOs.
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.
F.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
LT2ESWTR Toolbox Guidance Manual F-8 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
developments that did not exist when the wastewater treatment plant was designed. SSOs can be
reduced by cleaning and maintaining the sewer system; reducing inflow and infiltration by
repairing leaking or broken service lines; increasing sewer, pumping, and/or wastewater
treatment plant capacity; and constructing storage for excess wastewater (U.S. EPA 2001c).
EPA 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).
F.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).
LT2ESWTR Toolbox Guidance Manual F-9 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F.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 (CWSRF) loans can be used for nonpoint sources and
watershed management purposes.
F.3.1 Agricultural BMPs
F.3.1.1 Management Programs
The U.S. Department of Agriculture (USD A) (2000) recommends a multiple-barrier
approach to controlling pathogen transport and proliferation on farms and in agricultural
watersheds. It recommends the following control points:
• Preventing initial infection by controlling pathogen import to the farm.
• Controlling the reproduction and spread of the pathogen throughout the farm.
• Managing waste.
• Controlling pathogen export from the farm.
These control points should not be treated separately. For example, waste management
affects reproduction and spread of the pathogen if feed becomes contaminated with waste. Waste
management is also related to pathogen export; composting can kill Cryptosporidium oocysts
before they leave the farm.
BMPs that can reduce pathogen loading include composting, waste management (manure
storage and land application), grazing management, feedlot runoff diversion, and buffer or filter
strips. PWSs should work with their local soil and water conservation districts and agricultural or
cooperative extensions, which can help farmers design and implement pollution management
plans and BMPs. Details about these conservation practices are provided in the USDA Natural
Resources Conservation Service's (NRCS) National Handbook of Conservation Practices (NRCS
1999) at http://www.ftw.nrcs.usda.gov/nhcp_2.html.
Management strategies designed to minimize direct livestock contamination of surface
water with Cryptosporidium should focus primarily on young animals (those less than 3 months
old) and their waste, since calves are more likely to shed Cryptosporidium. Efforts should also
focus on cow herds as a whole when calves are present.
LT2ESWTR Toolbox Guidance Manual F-l 0 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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.
F.3.1.2 Composting
Composting can effectively reduce pathogen concentrations. Temperatures greater than
55 degrees Celsius (13 IE 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 the 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).
F.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
LT2ESWTR Toolbox Guidance Manual F-l 1 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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 percent 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 percent of Cryptosporidium oocysts from agricultural runoff
when slopes were less than or equal to 20 percent and had a length of at least 3 meters (Atwill et
al. 2002).
F.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
LT2ESWTR Toolbox Guidance Manual F-12 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
fencing and use of a buffer strip) and to provide alternative water sources for livestock. Providing
water in each paddock can increase the number of cattle the pasture is able to support. Even
where rotational grazing is not used, surface water contamination can be reduced by keeping
cattle, especially calves, out of streams.
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. Exhibit
F-l represents the average reduction in concentration for the specific contaminant.
Exhibit F-1 Average Reduction of Specific Contaminant
£. co/;
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 (U.S. EPA 2002c).
F.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.
LT2ESWTR Toolbox Guidance Manual F-l3 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
Manure storage facilities should be designed to prevent discharge through leaching or
runoff. They should be lined and, if possible, covered. Facilities that are not covered should be
designed to contain precipitation and runoff from a 25-year 24-hour storm. Storage areas should
have embankments to prevent overflow and collapse of the storage facility and to divert runoff
from outside the facility from contamination. Facilities should be sited outside of flood plains.
Manure should be stored for a time period sufficient for microorganisms to die off.
F.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 dry this enables significant pathogen die-off (Vendrall et al. 1997) by
exposure to ultraviolet light (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.
LT2ESWTR Toolbox Guidance Manual F-14 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F.3.1.7 Feedlot Runoff Diversion
Clean roof and surface water can be diverted away from feedlots to a drainage system that
is independent of a farm's waste management system (Ohio State University Extension 1992).
All roofs that could contribute to feedlot runoff should have gutters, downspouts, and outlets that
discharge away from the feedlot. Berms around the feedlot can divert surface runoff. Diverting
clean water before it drains into the feedlot can significantly reduce the amount of wastewater
that needs to be managed. Runoff within the feedlot should be contained and treated in the waste
management system for the lot.
F.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).
F.3.3 Urban/Suburban BMPs
Urban/Suburban BMPs can reduce burden on sewage infrastructure and address CSOs
and non-point sources. 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.
LT2ESWTR Toolbox Guidance Manual F-15 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F.3.3.1 Buffer Zones
For watersheds in urban areas, buffer zones help to protect development on the floodplain
from being damaged when the water is high, as well as protect the stream from the effects of the
development.
The utility, municipality, or cooperating jurisdictions may acquire land bordering the
reservoir and/or its tributaries. Alternatively, buffers can be required by zoning ordinances,
conservation easements, or subdivision regulations. Buffer zones can be fixed width or
variable width. In a fixed-width zone, the buffer zone encompasses a certain distance from the
stream bank or some other hydrological reference point (e.g., the high water mark of a stream).
The widths of fixed buffer zones vary considerably among water sources, frequently ranging
from 50 feet to 250 feet of buffer from the stream edge. Another form of buffer zone, the
variable-width buffer, can vary in width depending on the hydrological sensitivity, stream size,
and character of the land adjacent to the watercourse.
Considerations for developing local buffer requirements are the size and location of the
stream, the nature of existing or potential development, and the financial and political feasibility
of establishing 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.
F.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.
LT2ESWTR Toolbox Guidance Manual F-16 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F.3.3.3 Infiltration Devices
Infiltration devices remove pathogens and particles by adsorption onto soil particles and
filtration as the water moves through the soil to the ground water. Infiltration devices include
infiltration basins, infiltration trenches, and dry wells (NALMS 2000). Properly designed devices
can reproduce hydrological conditions that existed before urban development, and provide
ground water recharge and control of peak storm water flows. In order for them to function
effectively, infiltration devices must be used only where the soil is porous and can readily absorb
storm water at an adequate rate. An advantage of infiltration devices over many other urban
BMPs is that they provide significant ground water recharge in areas with a high percentage of
impervious surface.
F.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.
F.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
LT2ESWTR Toolbox Guidance Manual F-l 7 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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.
F.3.3.6 Constructed Wetlands
Constructed subsurface flow wetlands (where wetland plants are not submerged) can
reduce Cryptosporidium and bacteria concentrations in wastewater (Thurston et al. 2001).
Subsurface flow prevents the public from coming into contact with wastewater and prevents
mosquitos problems. Wetlands may also be useful for treating storm water or other polluted
water. However, the matrix material of a constructed subsurface flow wetland (gravel is often
used) may provide an environment for bacterial growth, and animals living in the wetlands may
contribute microbes to the effluent (Thurston et al. 2001). Animals are probably less significant
than they would be in a free water surface wetland. The growth of bacteria in the wetland
medium is both positive and negative; bacteria that help break down materials in wastewater are
more plentiful, but fecal coliform also can survive in such environments. Constructed wetlands
are relatively inexpensive and are 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
percent of Cryptosporidium oocysts from the secondary sewage effluent (Thurston et al. 2001).
Two wetlands were constructed to determine if they could effectively remove
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 percent 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).
F.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
LT2ESWTR Toolbox Guidance Manual F-18 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
diversion dikes or berms can be installed to route sheet flow around areas that are being protected
from runoff.
F.3.3.8 Pet Waste Management
Municipalities can implement pet waste management programs to encourage pet owners
to properly collect and dispose of their animal's waste. Many communities have pet waste
ordinances that require pet owners to clean up after their pets on public property or anywhere
outside their own yards; however, compliance is limited, and enforcement is usually not a
priority. In addition, most ordinances do not require pet owners to clean up pet waste in their own
yards (this problem can usually be addressed, though only reactively, through nuisance or pet
neglect laws). Some communities have ordinances that govern the cleanup process by requiring
disposal of pet waste with regular trash, burial, or flushing it down the toilet. Enforcement of
these ordinances with fines for noncompliance is probably the best way to increase compliance.
To increase public awareness about pet waste, you can distribute educational materials
through emails, letters, public service announcements, and signs. Posting is the most common
outreach strategy for managing pet waste. Pet waste stations containing waste receptacles for
public use are another popular solution. Public works departments have also formed voluntary
commitment and partnership programs with pet owners and local pet stores in the community to
promote good pet waste management.
F.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.
F.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
LT2ESWTR Toolbox Guidance Manual F-19 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
set aside for conservation, and use pervious areas for more effective stormwater treatment. Low
impact development involves changing traditional practices for residential street and parking lot
design, lot development, and conservation of natural areas. Some specific steps for better site
design include the following (Center for Watershed Protection 1999):
• Design residential streets based on the minimum width needed to support travel
lanes, on-street parking, and emergency and maintenance vehicle access. For
example, a street with single family houses with driveways does not need two
lanes for parking. Construct sidewalks on only one side of the street.
• Minimize the number of cul-de-sacs. Where cul-de-sacs are built, place
landscaped islands to reduce their impervious cover.
• Advocate open space or cluster design subdivisions on smaller lots.
• Reduce imperviousness by promoting alternative driveway surfaces and shared
driveways that connect two or more homes together. Reduce driveway length by
allowing decreased front setbacks.
• Direct rooftop runoff to pervious areas such as yards, open channels, or vegetated
areas rather than the roadway and stormwater sewers. Better yet, install open
vegetated channels instead of storm sewers.
• Reduce the imperviousness and size of parking lots by minimizing stall
dimensions, incorporating efficient parking lanes, and using pervious materials in
the spillover parking areas where possible. Use lower parking ratios where
possible (e.g., where mass transit is available and codes permit).
• Provide stormwater treatment for parking lot runoff using bioretention areas, filter
strips, and/or other practices.
• Create a naturally vegetated buffer system along all perennial streams that
encompasses critical environmental features such as the 100-year floodplain, steep
slopes, and wetlands.
• Clearing and grading of forests and native vegetation at a site should be limited to
the minimum amount needed to build lots, allow access, and provide fire
protection. Specify a party legally responsible for maintaining the vegetated area.
Some aspects of low impact development may be prohibited outright under traditional
zoning and development regulations, so low impact development practices may need to be
codified. Where such practices remain voluntary or require exemptions from existing regulations,
water systems should work with local planners to encourage the switch to better site design.
LT2ESWTR Toolbox Guidance Manual F-20 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F.3.3.11 Septic Systems
Failing septic systems can be a major source of microbial contamination in a watershed.
Poor placement of leachfields can feed partially treated waste directly into a drinking water
source. Poorly constructed percolation systems may allow wastewater to escape before it has
been properly treated. Failing systems can result in clogging and overflow of waste onto land or
into surface water.
Most septic system regulations require construction permits and an inspection before the
system begins operating, but few require any follow-up. Where failing systems are a serious
problem or are close to a drinking water source, however, some municipalities have maintenance
or inspection requirements. For example, the Portland (Maine) Water District requires permits
for all septic systems within 200 feet of Sebago Lake, its primary source (U.S. EPA 1999a).
These septic systems are subject to regular inspection and may face stricter design requirements
than systems outside the boundary. Portland also has the authority to inspect systems within
1,000 feet of Sebago Lake tributaries. Similarly, the Onondaga County Water Authority in New
York visually inspects every septic system in the water system annually. Every three years each
septic system is subject to a dye tracer test. Enforcement cases are referred to the county health
department (U.S. EPA 1999a).
Although water systems rarely have enforcement authority over septic systems, they
should work closely with the local regulatory authority to ensure that septic system codes are
being properly enforced and to strengthen codes where necessary. Utilities should also encourage
residents with septic systems in the watershed to understand their systems and the proper
maintenance that their systems require. 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. CWSRF 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.
F.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).
LT2ESWTR Toolbox Guidance Manual F-21 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F. 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
each watershed is different, the appropriate watershed control program (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;
http://cfpub.epa.gov/safewater/sourcewater/sourcewater.cfm?action=Case Studies).
• 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;
http://nepis.epa. gov/EPA/html/DLwait.htm?url=/Exe/ZvNET.exe/20001P7N.PDF?Zy Act
ionP=PDF&Client=EPA&Index=2000Thru
2005&File=D%3A%5CZYFE.ES%5CINDEX%20DATA%5COOTHRU05%5CTXT%5C
00000001%5C20001P7N.txt&Query=%E2%80%A2%09Watershed%20Success%20Stor
ies%20%E2%80%93%20Applving%20the%20Principles%20and%20Spirit%20of%20th
e%20Clean%20Water%20Action%20Plan&SearchMethod=3&FuzzvDegree=0&User=A
NONYMOUS&Password=anonvmous&QField=pubnumber%5E%22800R00003%22&U
seQField=pubnumber&IntQFieldOp=l&ExtQFieldQp=l&Docs=).
• Protecting Sources of Drinking Water: Selected Case Studies in Watershed Management
(U.S. EPA 1999a; http://www.epa.gov/safewater/sourcewater/pubs/swpcases.pdf).
LT2ESWTR Toolbox Guidance Manual F-22 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
Burlington, Vermont
Medium Surface Water PWS, Watershed Located in Multiple Jurisdictions
The City of Burlington has a population of 40,000 and is located on the shore of Lake
Champlain, a 120-mile long, 12-mile wide lake that is the source of drinking water for the city
and other municipalities. In such a large watershed with multiple landowners, it is difficult to
control activities that affect water quality. Burlington addresses microbial pollution through a
combination of land use control, reduction in combined sewer overflow, watershed
restoration, and outreach.
Through Act 250, the state of Vermont regulates land use near lake shores and rivers,
accounting for new wastewater treatment plants and sewer systems, timber management,
impervious surface area, water withdrawal by ski areas for snowmaking, and other issues. To
address combined sewer overflow problems that were affecting Lake Champlain water quality,
the city increased the capacity of its main wastewater treatment plant and extended the outfall
far into the lake to dilute the effluent. The city separated the sanitary and storm sewers at its
smaller plants. Two streams feeding into the lake that suffer from poor water quality are
currently undergoing restoration, including retrofitting of existing storm water detention ponds,
channel stabilization to prevent erosion, and outreach to change pet waste management, lawn
care, and other practices (U.S. EPA 200la).
Manchester, New Hampshire
Large Surface Water System Where State Plays an Active Role
The City of Manchester 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 subject to review and permitting by this agency. Parts of Lake Massabesic
closest to the intake are closed to all activity.
LT2ESWTR Toolbox Guidance Manual F-23 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
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. DBS 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.
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.
EPA2001c).
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 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).
LT2ESWTR Toolbox Guidance Manual F-24 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
F.5 References
Atwill, E.R., L. Hou, B.M. Karle, T. Harter, K.W. Tate, and R.A. Dahlgren. 2002. Transport of
Cryptosporidium parvum oocysts through vegetated buffer strips and estimated filtration
efficiency. Appl. Environ. Microbiol. 68(11): 5517-27.
AWWARF. 1991. Effective Water shed Management for Surface Water Supplies. Prepared by
R.W. Robbins, J.L. Glicker, D.M. Bloem, and B.M. Niss, Portland (OR) Water Bureau. Denver:
American Water Works Association Research Foundation.
AWWA. 1999. Source Water Protection: Effective Tools and Techniques You Can Use. 1999
Participant Manual. Denver: American Water Works Association. Developed for a technical
training seminar for public water suppliers and local officials.
Blewett, D.A. 1989. Disinfection and oocysts. Cryptosporidiosis. Proceedings of the First
International Workshop, 1988. Ed. K.W. Angus and D.A. Blewett. Edinburgh: The Animal
Disease Research Association. 107-116.
Center for Watershed Protection. 1999. An Introduction to Better Site Design. Watershed
Protection Techniques 3(2): 623-632.
Coyne, M.S. and R.L. Blevins. 1995. Fecal bacteria in surface runoff from poultry-manured
fields. In K.Steele (ed.), Animal Water and the Land-Water Interface, pp. 77-87. Boca Raton:
Lewis Publishers, CRC Press.
Fairfax County. 2001. Wastewater Treatment Plant.
http://www.co.fairfax.va.us/gov/DPWES/utilities/wwtrmnt 0600.htm. Last modified May 16,
2001. Website accessed January 2002.
Frankenberger, J.R. et al. 1999. A GIS-based variable source area hydrology model. Hydrologic
Processes 13:805-822.
Gburek, WJ. and H.B. Pionke. 1995. Management strategies for land-based disposal of animal
wastes: Hydrologic implications, pp. 313-323. In K.Steele (ed.), Animal Water and the Land-
Water Interface, pp. 77-87. Boca Raton: Lewis Publishers, CRC Press.
Jenkins, M.B, M. J. Walker, D. D. Bowman, L. C. Anthony, and W. C. Ghiorse. Use of a
Sentinel System for Field Measurements of Cryptosporidium parvum Oocyst Inactivation in Soil
and Animal Waste. Appl. Environ. Microbiol. 1999(65): 1998-2005.
Metcalf and Eddy. 1994. Final CSO Conceptual Plan and System Master Plan: Part IICSO
Strategies. Prepared for the Massachusetts Water Resources Authority. Wakefield,
Massachusetts.
LT2ESWTR Toolbox Guidance Manual F-25 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
Moore, J.A. et al. 1988. Evaluating coliform concentrations in runoff from various animal waste
management systems. Special Report 817. Agricultural Experimental Stations, Oregon State
University, Corvallis, and the U.S.D.A., Portland, OR.
MWRD. 1999. Tunnel and Reservoir Plan. Metropolitan Water Reclamation District.
http://www.mwrd.org/irj/portal/anonymous/tarp. Last modified August 6, 1999. Website
accessed January 2002.
NALMS (North American Lake Management Society). March 2000. Best Management Practices
to Protect Water Quality.
NRCS. 1999. National Handbook of Conservation Practices. Natural Resources Conservation
Service, http://www.nrcs.usda.gov/technical/standards/nhcp.html.
NRCS. 1992. Agricultural Waste Management Field Handbook.
Ohio State University Extension. 1992. Ohio Livestock Manure and Wastewater Management
Guide, Bulletin 604. http://ohioline.osu.edu/b604/index.html. Website accessed March 2003.
Ohio State University Extension. No date. Vegetation Filter Strips: Application, Installation, and
Maintenance. AEX-467-94. http://ohioline.osu.edu/aex-fact/0467.html. Website accessed March
2003.
Ohio State University Extension. No date. Getting Started Grazing. Edited by Henry
Bartholomew, http://ohioline.osu.edu/gsg/index.html.
Philadelphia Water Department. 2003. Philadelphia Projects. Website.
http://www.phila.gov/water/index.html. Undated. Accessed February 12, 2003.
Quinez-Daz, M. de J., M.M. Karpiscak; E. D. Ellman, and C.P. Gerba. Removal of Pathogenic
and Indicator Microorganisms by a Constructed Wetland Receiving Untreated Domestic
Wastewater. 2001. Environmental Sci. health Part A Tox Hazard Subst Environ Eng. 36(7):
1311-1320.
Schueler, T.R. 1999. Microbes and urban watersheds: concentrations, sources, and pathways.
Watershed Protection Techniques. 3(1): 554-565. http ://www. stormwatercenter.net.
Thurston, J.A., C.P. Gerba, K.E. Foster, and M.M. Karpiscak. 2001. Water Res. 35(6):1547-
1551. Fate of Indicator Microorganisms, Giardia and Cryptosporidium in Subsurface Flow
Constructed Wetlands.
LT2ESWTR Toolbox Guidance Manual F-26 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
U.S. Department of Agriculture. 2000. Water borne Pathogens in Agricultural Watersheds.
Watershed Science Institute.
ftp://ftp-fc.sc.egov.usda.gov/WSI/pdffiles/Pathogens_in_Agricultural_Watersheds.pdf. Website
accessed March 2003.
U.S. EPA. 2009. The Clean Water Act: Sanitary Sewer Overflow Strategy Summary of 2008 -
2010.
http://www.epa.gov/compliance/resources/publications/data/planning/priorities/fy2008prioritycw
asso.pdf Website access May 2009.
U.S. EPA. 2008. National Pollutant Discharge Elimination System Permit Regulation and
Effluent Limitation Guidelines and Standards for Concentrated Animal Feeding Operations
(CAFOs). Federal Register 73(225): 70418-70486. November 20.
U.S. EPA 2002a. Polluted Runoff (Nonpoint Source Pollution: Managing Nonpoint Source
Pollution from Forestry. Pointer No. 8. EPA 841-F-96-004H. Office of Wetlands, Oceans, and
Watersheds, http://www.epa.gov/owow/nps/facts/point8.htm. Last modified August 28, 2002.
Website accessed March 2003.
U.S. EPA. 2002b. Public Education and Outreach on Storm Water Impacts: Water Conservation
Practices for Homeowners, http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm. Last
updated November 25, 2002. Downloaded December 10, 2002.
U.S. EPA. 2002c. Section 319 Success Stories. 3:154-155. Available online:
http://www.epa.gov/owow/nps/Section319in/.
U.S. EPA. 2001a. Proposed Revisions to CAFO Regulations (January 12, 2001; 66 FR 2960):
Frequently Asked Questions. http://www.epa.gov/npdes/pubs/cafo_faq.pdf. Downloaded
February, 2002.
U.S. EPA. 2001b. Secondary Treatment Standards.
http://cfpub.epa.gov/npdes/techbasedpermitting/sectreat.cfm. Last updated April 9, 2007.
Downloaded January 22, 2002.
U.S. EPA 200Ic. Sanitary Sewer Overflows Frequently Asked Questions. Office of Wastewater
Management. Web page updated March 20, 2001.
http://cfpub.epa.gov/npdes/faqs.cfm?program_id=4. Website accessed January 2002.
U.S. EPA. 2000a. Wastewater Technology Fact Sheet: Granular Activated Carbon Adsorption
and Regeneration. Office of Water. EPA 832-F-00-017. September.
http://www.epa.gov/owmitnet/mtb/carbon absorption.pdf
LT2ESWTR Toolbox Guidance Manual F-27 April 2010
-------
Appendix F - Watershed Control Best Management Practices (BMPs) and Case Studies
U.S. EPA 2000b. Storm Water Phase II Final Rule: Small MS4 Storm Water Program Overview.
Fact Sheet 2.0. Office of Water. EPA 833-F-00-002. http://www.epa. gov/npdes/pub s/fact2-0. pdf.
Website accessed March 2003.
U.S. EPA 2000c. Wastewater Technology Fact Sheet. Wetlands: Subsurface Flow. Office of
Water EPA 832-F-00-023. September.
http://www.epa.gov/owm/mtb/wetlands-subsurface_flow.pdf Website accessed March 2003.
U.S. EPA. 1999a. Protecting Sources of Drinking Water: Selected Case Studies in Watershed
Management. Office of Water. EPA 816-R-98-016. April.
http://www.epa.gov/enviroed/pdf/swpcases.pdf Accessed December 10, 2002.
U.S. EPA 1999b. Funding Decentralized Wastewater Systems Using the Clean Water State
Revolving Fund. Office of Water (4204). EPA 832-F-09-005. 4 pages.
http://www.epa.gov/owm/septic/pubs/arra_septic_fs.pdf Website accessed March 2003.
U.S. EPA 1999c. Combined Sewer Overflow Management Fact Sheet: Sewer Separation. Office
of Water. EPA 832-F-99-041. September, http://www.epa.gov/npdes/pubs/sepa.pdf. Website
accessed March 2003.
U.S. EPA. 1996. Overview of the Storm Water Program. Office of Water. EPA 833-R-96-008.
June. 42 pp. www.epa.gov/npdes/pubs/owmO 195.pdf Website accessed March 2003.
U.S. EPA. 1994. Combined Sewer Overflow (CSO) Policy; Notice. Federal Register
59(75): 18688-18698. April 19.
Vendrall, P.F., K.A. league, and D.W. Wolf. 1997. Pathogen indicator organism die-off in soil.
ASA Annual Meeting, Anaheim, CA.
Young, R.A. et al. 1980. Effectiveness of vegetated buffer strips in controlling pollution from
feedlot runoff. J. Environ. Qual. 9:483-487.
LT2ESWTR Toolbox Guidance Manual F-28 April 2010
-------
Appendix G
Review Criteria for Use by States When Reviewing Watershed Control (WSC)
Program Plans
LT2 WSC
Requirement
Assessment Criteria
Addressed in Sufficient Detail?
Watershed Control Program Plan
*
*
*
*
Does the plan specifically address potential and
existing Cryptosporidium sources in the watershed?
Have the proposed actions in the plan been clearly
defined and sufficiently addressed?
Does the plan explain how the actions described are
expected to contribute to specified goals?
Does the plan prioritize its proposed efforts? Does it
define short-term and long-term actions and prioritize
them?
Does the plan include, in detail, what other resources
will be required to implement the watershed control
measures? Does it identify the source(s) of those
resources?
Review of Potential Sources
*
*
*
Has the area of influence been delineated in
appropriate detail, taking into consideration available
information about Cryptosporidium fate, transport
and local hydrogeological characteristics? Have
sensitive areas been identified?
Is the scale of the delineation appropriate for the
watershed plan? Does it provide a level of detail
sufficient for effective decisions to be made?
Has the intake location been identified relative to the
water body?
Is any information available about time of travel in
the watershed?
Does it seem that all activities within the watershed
that could result in Cryptosporidium contamination of
the water supply have been identified and located?
Have contaminant sources been located and
described relative to the drinking water source intake
location?
Have the likelihood and timing of releases of
contamination been addressed?
LT2ESWTR Toolbox Guidance Manual
G-l
April 2 010
-------
Appendix G - Review Criteria for Use by States When Reviewing Watershed Control (WSC) Program Plans
LT2 WSC
Requirement
Assessment Criteria
Addressed in Sufficient Detail?
Are there permitted wastewater discharges (NPDES)
of concern? If there are wastewater treatment plants
in the area of influence, systems should include
information about their size, discharge quantity, and
whether there has been any recent significant
noncompliance with permit conditions.
Are sludge disposal areas identified and
characterized? Are there any locations in the
watershed where biosolids have been applied?
Have they been identified? When in the year are
they applied?
Have stormwater discharges been located? Are
there any discharges directly into the surface water
supply?
Have septic systems been identified and located? Is
information available about their age, condition,
design, and siting?
Has land use been characterized and mapped? Are
areas subject to zoning requirements or changes in
zoning?
If land uses in the watershed include agriculture,
have the types of farming been identified? Are
feedlots located? Are fields where manure is spread
identified?
Have Concentrated Animal Feeding Operations
(CAFOs) been identified and located?
Have natural sources of Cryptosporidium been
identified and located?
Have recreational areas (e.g., campgrounds, trailer
parks) been identified and located?
Has any on-site landfilling, land treating, or surface
impounding of waste other than landscape waste or
construction and demolition debris taken place, and
will such circumstances continue?
Does the analysis address the effectiveness of
physical barriers (e.g., geology, hydraulic conditions,
intake structure and location) at preventing the
movement of contaminants to the drinking water
source?
LT2ESWTR Toolbox Guidance Manual
G-2
April 2 010
-------
Appendix G - Review Criteria for Use by States When Reviewing Watershed Control (WSC) Program Plans
LT2 WSC
Requirement
*
*
*
Assessment Criteria
Have tributaries or areas of the reservoir with
evidence of high levels of microbial contamination
been identified? If so where are they located relative
to the intake?
If Cryptosporidium monitoring data exist for the
watershed, have results been addressed and
discussed?
Have recreational uses of the surface water supply
been identified? Has the effect of those uses on
Cryptosporidium loading been addressed?
Are there portions of the watershed with high
percentages of impervious surfaces which might lead
to increased stormwater runoff?
Is water quality monitoring and assessment
information (305(b) Report available?
Have existing best management practices or controls
been identified and located?
Is there any information available about the
effectiveness of current pollution prevention
activities?
Addressed in Sufficient Detail?
Potential Control Measures to Control Cryptosporidium
Contamination
*
*
*
*
Do the control measures proposed specifically
address the reduction of Cryptosporidium
contamination?
Would the implementation of the proposed control
measures take place in areas where there would be
an impact on Cryptosporidium loading into the water
supply?
If the proposed control measures are ongoing, has
the utility explained how they would be sustained?
Is the water utility in a position where it could
implement the control measures itself, or would other
parties be responsible?
Are there implementation agreements between the
utility and other parties responsible for
implementation?
How does the utility track control measures
implemented by other parties?
LT2ESWTR Toolbox Guidance Manual
G-3
April 2 010
-------
Appendix G - Review Criteria for Use by States When Reviewing Watershed Control (WSC) Program Plans
LT2 WSC
Requirement
Assessment Criteria
Has the water system responded adequately to
concerns expressed about the source or watershed
area in past inspections and sanitary surveys?
Addressed in Sufficient Detail?
LT2ESWTR Toolbox Guidance Manual
G-4
April 2010
------- |