United States
Environmental Protection
Agency
Office of Water
(4607)
EPA815-R-99-015
August 1999
Microbial and Disinfection
Byproduct Rules
Simultaneous Compliance
Guidance Manual
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DISCLAIMER
This manual describes many of the potential conflicts that may arise as systems comply
with the rules currently being developed by the U.S. Environmental Protection Agency
(EPA), known collectively as the Microbial and Disinfection Byproduct (M-DBP) cluster
of rules.
This document was issued in support of EPA regulations and policy initiatives involving
development and implementation of the Information Collection Rule, Disinfectants and
Disinfection Byproduct Rule, Enhanced Surface Water Treatment Rule, and Ground
Water Rule. This document also discusses simultaneous compliance issues involving the
Lead and Copper Rule and the Total Coliform Rule.
This document is EPA guidance only. It does not establish or affect legal rights or
obligation. EPA decisions in any particular case will be made applying the laws and
regulation on the basis of specific facts when permits are issued or regulations
promulgated.
Mention of trade names or commercial products does not constitute an EPA endorsement
or recommendation for use.
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ACKNOWLEDGMENTS
The guidance manual has been reviewed in accordance with the EPA's technical and
administrative review policies and approved for publication. The EPA gratefully acknowledges
the assistance of the members of the Microbial and Disinfection Byproducts Federal Advisory
Committee and Technical Work Group for their comments and suggestions to improve this
document. EPA also wishes to thank the representatives of drinking water utilities, researchers,
and the American Water Works Association for their review and comment, as well as the
following individuals:
Mark LeChevallier, American Water Works Service Company
Sarah Clark, City of Austin
Cayce Warf, Vulcan Chemical
Dan Fraser, Cadmus Group
Roger Yeardley, EPA
Mike Schock, EPA
Tom Grubbs, EPA
Faysal Bekdash, SAIC
Jennifer Cohen, SAIC
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CONTENTS
1. INTRODUCTION 1-1
1.1 REGULATORY CONTEXT
1.1.1 DBPR
1.1.2 IESWTR
1.2 USE OF DISINFECTANTS
1.3 GOAL OF MANUAL
1.4 ORGANIZATION OF MANUAL ...
-1
-3
-5
-6
2. BACKGROUND AND SPECIFIC REGULATORY REQUIREMENTS 2-1
2.1 INACTIVATION OF PATHOGENS 2-1
2.1.1 Recent Waterborne Outbreaks 2-1
2.1.2 Pathogens of Primary Concern 2-2
2.1.3 Mechanisms of Pathogen Inactivation 2-5
2.1.4 Effect of Parameters on Inactivation 2-5
2.1.5 Comparison of Disinfectant Inactivation Values 2-6
2.1.6 Disinfectant Residual 2-8
2.2 STAGE 1 DISINFECTANT AND DISINFECTION BYPRODUCTS RULE (DBPR) 2-9
2.2.1 Disinfection Byproduct Formation 2-9
2.2.2 Factors Affecting DBF Formation 2-12
2.2.3 DBF Control Strategies 2-14
2.3 STAGE 1 DISINFECTION BYPRODUCTS RULE (DBPR) 2-16
2.3.1 DBF Maximum Contaminant Levels (MCLs) 2-16
2.3.2 Maximum Residual Disinfectant Levels (MRDLs) 2-16
2.3.3 TOC Removal Requirements 2-17
2.4 INTERIM ENHANCED SURF ACE WATER TREATMENT RULE (IESWTR) 2-18
2.4.1 Turbidity Requirements 2-18
2.4.2 Giardia and Virus Removal/Inactivation Requirements 2-19
2.4.3 Cryptosporidium Removal Requirements 2-19
2.4.4 Microbial Profiling/Benchmarking Requirements 2-20
3. SIMULTANEOUS COMPLIANCE ISSUES BETWEEN STAGE 1 DBPR AND IESWTR 3-1
3.1 INTRODUCTION 3-1
3.2 DBPR VERSUS IESWTR MICROBIAL PROFILING/BENCHMARKING 3-2
3.2.1 Moving the Point of Disinfectant Application 3-3
3.2.2 Changing the Type of Disinfectant(s) Used 3-5
3.2.3 Temperature Effects on Chlorine and DBF Formation 3-11
3.2.4 pH Effects on Chlorine 3-12
3.2.5 Case Study 3-13
3.3 DBF MCLS AND INACTIVATION REQUIREMENTS FOR NON-PROFILING WATER SYSTEMS 3-16
3.3.1 Issues 3-16
3.3.2 Recommendations 3-16
3.4 STAGE 1 DBPR ENHANCED COAGULATION AND IBSWTR TURBIDITY REQUIREMENTS 3-17
3.4.1 DBF Control 3-17
3.4.2 Pathogen Inactivation/Removal 3-19
3.4.3 Issues and Recommendations for Simultaneous Compliance 3-20
3.4.4 Case Study 3-22
3.5 SUMMARY AND RECOMMENDATIONS 3-31
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4. SIMULTANEOUS COMPLIANCE ISSUES BETWEEN THE STAGE 1 DBPR, THE IESWTR, AND
LEAD AND COPPER RULE 4-1
4.1 OVERVIEW OF THE LEAD AND COPPER RULE 4-1
4.1.1 Lead and Copper Corrosion Control Strategies 4-2
4.1.2 LCR Compliance Relationships with the Stage 1 DBPR and the IESWTR 4-5
4.2 PH IMPACTS ON THE LCR AND THE STAGE 1 DBPR AND THE IESWTR 4-5
4.2.1 Coagulation 4-7
4.2.2 DBF Formation 4-8
4.2.3 Chlorine CT Values 4-9
4.2.4 Case Study 4-10
4.3 TURBIDITY 4-11
4.3.1 Corrosion Inhibitor Addition 4-12
4.3.2 Lime Addition 4-12
4.4 MICROBIAL REGROWTH 4-13
4.4.1 Phosphate Corrosion Inhibitor Addition 4-13
4.5 ENHANCED COAGULATION 4-15
4.5.1 NOM Removal 4-16
4.5.2 Coagulant Changes 4-17
4.5.3 Case Study 4-18
4.6 DISINFECTION STRATEGY 4-21
4.6.1 Switching Disinfectants 4-21
4.6.2 Ozonation and Unfiltered Systems 4-22
4.7 SUMMARY 4-23
4.7.1 DBF Controls Required 4-24
4.7.2 IESWTR Controls Required 4-27
5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE STAGE 1 DBPR AND
IESWTR 5-1
5.1 REQUIREMENTS OF THE TCR AND COMPLIANCE ISSUES 5-1
5.1.1 TCR Requirements 5-1
5.1.2 Issues 5-2
5.2 COLIFORM GROWTH IN DISTRIBUTION SYSTEM WHEN SECONDARY DISINFECTANT is CHANGED TO
CHLORAMINE 5-3
5.2.1 Occurrences of Conform Growth 5-3
5.2.2 Nitrification 5-4
5.2.3 Recommendations 5-6
5.2.4 Case Study 5-8
5.3 COLIFORM GROWTH IN DISTRIBUTION SYSTEM WHEN PRIMARY DISINFECTANT is CHANGED TO
OZONE 5-10
5.3.1 Occurrence 5-10
5.3.2 Recommendations 5-10
5.3.3 Summary and Recommendations 5-12
5.3.4 Case Study 5-12
5.4 COLIFORM GROWTH IN THE DISTRIBUTION SYSTEM RESULTING FROM CHANGES TO PRIMARY AND
SECONDARY DISINFECTION PRACTICES 5-14
5.4.1 Change from Chlorine/Chlorine to Chlorine/Chloramine 5-15
5.4.2 Change from Chlorine/Chlorine to Ozone/Chlorine 5-15
5.4.3 Change from Chlorine/Chlorine to Ozone/Chloramine 5-18
5.4.4 Change from Chlorine/Chlorine to Chlorine Dioxide/ Chlorine Dioxide 5-19
5.4.5 Change from Chlorine/Chloramine to Ozone/Chloramine 5-19
5.4.6 Change from Chlorine/Chloramine to Chlorine Dioxide/ Chloramine 5-20
5.4.7 Change from Ozone/Chlorine to Ozone/Chloramine 5-20
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5.5 COLIFORM GROWTH IN THE DISTRIBUTION SYSTEM WHICH COULD RESULT FROM ALTERNATIVE
DISINFECTION BENCHMARKING 5-20
5.6 COLIFORM GROWTH IN THE DISTRIBUTION SYSTEM WHICH COULD RESULT FROM ENHANCED
COAGULATION OR ENHANCED SOFTENING 5-22
5.6.1 Occurrence 5-22
5.6.2 Enhanced Coagulation 5-22
5.6.3 Enhanced Softening 5-23
5.7 SUMMARY AND RECOMMENDATIONS 5-23
6. OPERATIONAL ISSUES 6-1
6.1 CONSTRUCTION MATERIALS 6-2
6.1.1 Impact of Enhanced Coagulation 6-2
6.1.2 Impact of Disinfectant Changes 6-3
6.2 TREATMENT EQUIPMENT 6-3
6.3 OPERATIONS AND MAINTENANCE STAFF TRAINING 6-4
6.4 IMPACT OF ENHANCED COAGULATION ON PROCESS RESIDUALS 6-5
6.4.1 Solids Volume 6-5
6.4.2 Residual Solids Dewatering Characteristics 6-7
6.5 TASTES AND ODORS 6-8
6.5.1 Taste and Odor Sources 6-9
6.5.2 Taste and Odor Controls 6-10
6.5.3 Recommendations 6-11
7. REFERENCES 7-1
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CONTENTS
FIGURES
FIGURE 4-1. DBF CONTROL DECISION TREE 4-26
FIGURE 4-2. IESWTR CONTROL DECISION TREE 4-27
FIGURE 5-1. EXAMPLE OF DISINFECTANT RESIDUAL/BACTERIAL RELATIONSHIP DURING A
NITRIFICATION CONTROL EPISODE 5-4
FIGURE 5-2. RELATIONSHIP BETWEEN TARGET pH AND ALKALINITY FOR ENHANCED COAGULATION 5-23
TABLES
TABLE 1-1. KEY DATES FOR M-DBP REGULATORY ACTIVITIES 1-3
TABLE 1 -2. NATIONAL PRIMARY DRINKING WATER STANDARDS FOR DISINFECTANTS 1-4
TABLE 1 -3. STANDARDS RELATED TO DISINFECTANTS AND DISINFECTION BYPRODUCTS 1-4
TABLE 1 -4. LOG REMOVAL/IN ACTIVATION THROUGH FILTRATION AND DISINFECTION REQUIRED UNDER
THE 1989 SWTR 1-5
TABLE 2-1. ATTRIBUTES OF WATERBORNE PATHOGENS OF PRIMARY CONCERN 2-3
TABLE 2-2. SUMMARY OF FACTORS THAT AFFECT DISINFECTION 2-6
TABLE 2-3. CT VALUES FOR INACTIVATION OF VIRUSES IN WATER AT 10 ° C WITH pH 6.0-9.0 2-8
TABLE 2-4. CT VALUES FOR INACTIVATION OF GIARDIA CYSTS IN WATER AT 10 ° C WITH pH 6.0-9.0 2-8
TABLE 2-5. IMPACTS OF pH ON ORGANIC HALOGEN FORMATION DURING CHLORINATION 2-13
TABLE2-6. STAGE 1 DBPR PERCENT TOC REMOVAL REQUIREMENTS 2-17
TABLE 3-1. STRATEGIES FOR PRIMARY AND SECONDARY DISINFECTANTS 3-7
TABLE 3-2. IMPACTS OF DISINFECTION PRACTICE ON DBF FORMATION 3-8
TABLE 3-3. SUMMARY OF DISINFECTANT PROPERTIES 3-11
TABLE 3-4. CONDITIONS OF FORMATION OF DBFs 3-26
TABLE 4-1. SUMMARY OF CORROSION CONTROL APPROACHES 4-3
TABLE 4-2. LCR IMPACTS ON STAGE 1 DBPR AND IESWTR REQUIREMENTS 4-6
TABLE 4-3. STAGE 1 DBPR AND IESWTR IMPACTS ON LCR REQUIREMENTS 4-6
TABLE 4-4. CHEMICALS FOR pH ADJUSTMENT OR ALKALINITY ADDITION 4-8
TABLE 5-1. TCR, STAGE 1 DBPR, AND IESWTR CONFLICTS RESULTING FROM THE SOURCE OF
MICROBIAL CONTAMINATION 5-3
TABLE 5-2. TCR CONTROL STRATEGIES FOLLOWING CHANGES IN DISINFECTION PRACTICE 5-16
TABLE 5-3. RAW AND TREATED WATER QUALITY AT A PLANT USING OZONE/CHLORINE 5-17
TABLE 5-4. DBF SPECIATION AT A PLANT USING OZONE/CHLORINE 5-18
TABLE 5-5. GENERALIZED RELATIONSHIPS BETWEEN pH AND EFFECTIVENESS OF DISINFECTANTS USED
FOR SECONDARY DISINFECTION 5-22
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CONTENTS
ACRONYMS
AIDS
AOB
AOC
AWWA
AWWARF
BAT
BDOC
C12
C1O2
CMA
CPE
CT
DBAA
DBFs
DBPR
D/DBPs
DNA
DOC
EBCT
EPA
ESWTR
FPA
GAC
GWR
HAAs
HAAS
HOC1
HPC
ICR
IESWTR
LCR
LOX
LT IESWTR
LT2ESWTR
MCC
MCLs
MCLGs
M-DBP
Acquired immune deficiency syndrome
Ammonia-oxidizing bacteria
Assimilable organic carbon
American Water Works Association
AWWA Research Foundation
Best available technology
Biodegradable dissolved organic carbon
Chlorine
Chlorine dioxide
Chlorine Manufacturers Association
Comprehensive Performance Evaluation
Residual disinfectant concentration (in mg/L) multiplied by the contact time (in
min); a measure of disinfection effectiveness
Dibromoacetic Acid
Disinfection byproducts
Disinfectants and Disinfection Byproducts Rule
Disinfectants/disinfection byproducts
Deoxyribonucleic acid
Dissolved organic carbon
Empty bed contact time
U.S. Environmental Protection Agency
Enhanced Surface Water Treatment Rule
Flavor profile analysis
Granular activated carbon
Ground Water Rule
Haloacetic acids
Five Haloacetic acids (the sum of mono-, di-, and trichloroacetic acids and mono-
and dibromoacetic acids)
Hypochlorous Acid
Heterotrophic plate count
Information Collection Rule
Interim Enhanced Surface Water Treatment Rule
Lead and Copper Rule
Liquefied oxygen
Long-Term 1 ESWTR
Long-Term 2 ESWTR
Motor control center
Maximum contaminant levels
Maximum contaminant level goals
Microbial and disinfection byproducts
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CONTENTS
mg/L
MIB
mm
mpy
MRDLs
MRDLGs
MWCO
MWD
NF
nm
NODA
NOM
NTU
PAC
POOR
POE
POU
PWS
RNA
SCCRWA
SDS
SDWA
SUVA
SWTR
TCAA
TCR
THM
THMFP
TOC
TOX
TTHMs
UF
UV
VFDs
jam
Milligrams per liter
2- methylisoborneol
millimeters
mils per year
Maximum residual disinfectant levels
Maximum residual disinfectant level goals
Molecular weight cutoff
Metropolitan Water District of Southern California
Nanofiltration
Nanometer
Notice of Data Availability
Natural organic matter
Nephelometric turbidity units
Powdered activated carbon
Point of diminishing return
Point-of-entry
Point-of-use
Public Water System
Ribonucleic acid
South Central Connecticut Regional Water Authority
Simulated distribution system
Safe Drinking Water Act
Specific ultraviolet absorbance (UV254/DOC in L/mg-m)
Surface Water Treatment Rule
Trichloroacetic Acid
Total Coliform Rule
Trihalomethane
Trihalomethane formation potential
Total organic carbon
Total organic halides
Total trihalomethanes
Ultrafiltration
Ultraviolet
Variable frequency drives
Micrometer
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1. INTRODUCTION
The Safe Drinking Water Act (SDWA) Amendments of 1996 require the U.S. Environmental
Protection Agency (EPA) to develop several new drinking water regulations. A group of these
regulations, known as the Microbial and Disinfection Byproduct (M-DBP) Rules, addresses
two key public health concerns: acute threats from microbial contamination and chronic threats
from disinfectant residuals and byproducts of disinfection.
EPA recognizes that some Public Water Systems (PWSs) may encounter technological
conflicts when trying to meet the goals of the different regulations. Because each of these rules
has equivalent stature in the law and requires simultaneous compliance, the goal of one rule
cannot be undermined in favor of the goal of another. Simultaneous compliance issues may
present a significant challenge to PWSs.
This guidance manual describes many of the potential conflicts that may arise as systems
comply with these rules, and provides possible solutions and approaches to resolve these
conflicts. The remainder of this chapter provides a brief overview of the major M-DBP Rules,
an explanation of how conflicts between some of these regulations can occur, an overview of
the use of disinfectants in water treatment, and a discussion of the goals and contents of this
manual.
1.1 Regulatory Context
The application of chemical disinfection and filtration to drinking water in the United States has
successfully controlled the transmission of disease-causing organisms (pathogens) through
drinking water supply systems. Waterborne diseases, such as typhoid and cholera, have been
virtually eliminated as a result. For example, in Niagara Falls, New York, between 1911 and
1915, the number of typhoid-related deaths dropped from 185 out of 100,000 people to nearly
zero after introduction of filtration and disinfection to the city's water supply (White, 1992).
Nevertheless, the United States is still vulnerable to waterborne disease outbreaks, as
demonstrated by the 1993 Milwaukee Cryptosporidium outbreak.
While disinfection (or the inactivation of infectious organisms) will continue to be a critical
element of drinking water treatment, recent research confirms that disinfection can create
health risks from disinfectant residuals and disinfection byproducts (DBFs). As such, pursuant
to the 1996 SDWA Amendments, EPA is developing interrelated regulations (i.e., the M-DBP
cluster of rules) to control health risks from microbial pathogens and disinfectants/disinfection
byproducts (D/DBPs). The following four sets of rules address, or will address, disinfection
practices for the control of pathogens and DBFs:
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1. INTRODUCTION
• Information Collection Rule (ICR). On May 14, 1996, EPA promulgated a final ICR that
requires PWSs to submit data to EPA on source water quality, byproduct formation, and
drinking water treatment plant design and operations (61 FR 24353). This information will be
used to support development of the remaining M-DBP Rules.
• Disinfectants and Disinfection Byproducts Rule (DBPR). This rule, being promulgated in
two phases, will limit the amount of disinfectant residual and DBFs allowed in the distribution
system. EPA promulgated the Stage 1 DBPR on December 16, 1998 (63 FR 69390). This
rule is applicable to all community water systems (CWSs) and non-transient non-community
water systems (NTNCWSs) that add a disinfectant, and transient non-community water
systems (TNCWSs) that use chlorine dioxide. EPA expects to propose the Stage 2 DBPR in
the fall of 2000, with promulgation scheduled for May 2002.
• Enhanced Surface Water Treatment Rule (ESWTR). This rule, being promulgated in two
phases, will amend the existing Surface Water Treatment Rule (SWTR) and will include new
requirements for improved particle removal in drinking water treatment plants. EPA
promulgated the Interim ESWTR (IESWTR) on December 16, 1998, which generally applies
only to systems serving at least 10,000 people (63 FR 69477). The Long-Term 1 ESWTR will
address systems serving fewer than 10,000 people. The Long-Term 2 ESWTR will
incorporate ICR data and may include site-specific treatment requirement. These rules are
scheduled to be promulgated in November 2000 and May 2002, respectively.
• Ground Water Rule (GWR). This rule, which is still in the proposal development phase, will
address microbial contamination in drinking water systems using ground water as their source.
This rule will apply to the approximately 180,000 PWSs using ground water not under the
direct influence of surface water and will specify the appropriate use of disinfection and
encourage the use of best management practices (BMPs) to assure public health protection.
EPA expects the GWR to be promulgated in November 2000.
Table 1-1 lists the dates for M-DBP regulatory activities.
Table 1-1. Key Dates for M-DBP Regulatory Activities
Date Regulatory Action
November 2000 Promulgate Ground Water Rule (GWR)
November 2000 Promulgate Long-Term 1 Enhanced Surface Water Treatment Rule (LT1 ESWTR)
May 2002 Promulgate Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR)
May 2002 Promulgate Stage 2 Disinfection Byproducts Rule (Stage 2 DBPR)
Although a PWS may be in compliance with current SDWA regulations, it may encounter
compliance issues as it begins to implement the M-DBP Rules. Simplistically, the regulations
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1. INTRODUCTION
may conflict because PWSs will have to increase/upgrade disinfection to reduce the risk of
microbial contamination in finished water, while at the same time minimize the formation of
DBFs. For example, enhanced coagulation lowers pH which increases the formation of
haloacetic acids (HAAs), while enhanced softening raises pH which promotes trihalomethane
(THM) formation. A PWS can raise the pH of water through the treatment process, which
favors DBF precursor removal through removal of organic carbon, but may also reduce the
disinfection effectiveness of free chlorine. Similarly, rules designed to ensure chemical stability
can compete with rules designed to protect against byproduct risk. For example, removal of
organic carbon under the DBPR may reduce the chemical stability of the treated water as
required by the Lead and Copper Rule (LCR).
These two examples highlight potential conflicts that could occur as PWSs attempt to comply
with all applicable regulations. A possible solution to the problems in these two examples
might involve pH adjustments to the water prior to leaving the plant. Implementation of this
solution means the PWS must recognize the competing demands in complying with the new
rules and take action to eliminate the potential for noncompliance among these and other
SDWA rules.
Since the DBPR and IESWTR are the most likely to cause conflicts, either with each other, or
with other drinking water regulations, this guidance manual focuses on these two regulatory
packages.
1.1.1 DBPR
The Stage 1 DBPR regulates the public health risks associated with DBFs and disinfectant
chemicals in drinking water. The rule lowers the only pre-existing Maximum Contaminant
Level (MCL); establishes new MCLs, Maximum Contaminant Level Goals (MCLGs),
Maximum Residual Disinfectant Levels (MRDLs), and Maximum Residual Disinfectant Level
Goals (MRDLGs); and extends MCLs to all system sizes. The rule also requires enhanced
coagulation or enhanced precipitative softening for certain systems. Table 1-2 shows the
MRDLGs and MRDLs for chlorine, chloramines, and chlorine dioxide. Table 1-3 summarizes
MCLGs and MCLs for the various primary drinking water contaminants related to disinfection.
In some cases, a treatment technique is prescribed in lieu of an MCL where it is not
economically or technically feasible to determine compliance with a numeric standard. Under
the Stage 2 DBPR, EPA will reevaluate MCLs for total trihalomethanes (TTHMs), five
haloacetic acids (HAAS), and other DBFs.
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1. INTRODUCTION
Table 1-2. National Primary Drinking Water Standards for Disinfectants
Disinfectant
Chlorine+
Chloramines++
Chlorine Dioxide
+ Measured as free chlorine.
++ Measured as total chlorine.
MRDLG
4 (as CI2)
4 (as CI2)
0.8 (as CIO2)
MRDL
(mg/L)_
4.0 (as CI2)
4.0 (as CI2)
0.8 (as CIO2)
Table 1-3. Standards Related to Disinfectants and Disinfection Byproducts
Compound
Potential Health Effects
MCLG MCL
(mg/L) (m9/L)
Total Coliform Rule (TCR) and SWTR Standards
Giardia lamblia
Legionella
Heterotrophic Plate Count
Total Coliform
Turbidity
Zero
Zero
N/A
Zero
N/A
: 5% positive"1"
Gastroenteric Disease
Legionnaire's Disease
Indicates Water Quality and
Effectiveness of Treatment
Indicates Gastroenteric Pathogens
Interferes with Disinfection
Viruses
Chloroform
Dibromochloromethane
Bromodichloromethane
Bromoform
TTHMs
Dichloroacetic Acid
Trichloroacetic Acid
HAAS
Bromate
Chlorite
Zero TT
DBPR Standards for
Zero See TTHMs
Gastroenteric Disease
DBFs
Cancer, Liver, Kidney, and
Reproductive Effects
0.06 See TTHMs Nervous System, Liver, Kidney,
Reproductive Effects
Zero See TTHMs Cancer, Liver, Kidney, and
Reproductive Effects
Zero See TTHMs Cancer, Nervous System, Liver and
Kidney Effects
N/A 0.10 (I) Cancer and Other Effects
0.080(51)
Zero See HAAS Cancer, Reproductive, Developmental
Effects
Zero See HAAS Liver, Kidney, Spleen, Developmental
Effects
N/A 0.060(51) Cancer and Other Effects
Zero 0.010(51) Cancer
0.8 1.0(51) Developmental and Reproductive
Effects
Source: AVWVA Internet, 1997.
I = 1979 Interim, only applies to public water systems serving 10,000 people or more.
S1 = Stage 1 DBPR
TT = Treatment technique requirement
+ = No more than one positive if < 40 samples/month
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1. INTRODUCTION
1.1.2 IESWTR
The SWTR of 1989 established the goals of microbial integrity and focused specifically on
reducing risks from Giardia cysts and viruses in surface water and ground water under the
direct influence of surface water. The IESWTR does not change these goals. To meet these
goals, the SWTR established treatment removal efficiencies for Giardia cysts and viruses in
filtered and unfiltered surface water systems (AWWA, 1991). Table 1-4 summarizes these log
removal/inactivation requirements. EPA also provided guidance for systems with poorer
quality source water to evaluate the need for additional treatment.
Table 1-4. Log Removal/inactivation through Filtration and Disinfection Required Under
the 1989 SWTR
Log Removal Requirements
Process Giardia Cysts Viruses
Total log removal/inactivation required 3.0 4.0
• Conventional sedimentation/filtration credit1 2.5 2.0
. Disinfection inactivation required 0.5 2.0
. Direct filtration credit1
• Disinfection inactivation required
• Slow sand filtration credit1
. Disinfection inactivation required
. Diatomaceous earth credit1
• Disinfection inactivation required
• No filtration
. Disinfection inactivation required
2.0
1.0
2.0
1.0
2.0
1.0
0.0
3.0
1.0
3.0
2.0
2.0
1.0
3.0
0.0
4.0
Source: AWWA, 1991.
1 Credits for guidance only. The State may allow a different credit.
The IESWTR adds requirements for control of Cryptosporidium and sets an MCLG of zero
for this pathogen. The IESWTR applies to public water systems that use surface water or
ground water under the direct influence of surface water (GWUDI) and serve at least 10,000
people. In addition, States are required to conduct sanitary surveys for all surface water and
GWUDI systems, including those that serve fewer than 10,000 people (63 FR 69477). Five
treatment alternatives for Cryptosporidium were proposed by EPA in its 1994 proposed
IESWTR. One alternative required a 2-log removal of Cryptosporidium oocysts by filtration
with pretreatment. In the 1997 IESWTR Notice of Data Availability (NODA), EPA
recognized the limited data available and solicited comments. Most commentors opposed
greater log removal requirements for Cryptosporidium due to a lack of understanding of dose-
response relationships, treatment effectiveness, site-specific occurrence data, and analysis
justifying higher treatment costs (USEPA, 1997b).
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1. INTRODUCTION
The IESWTR requires that all surface water systems required to filter, using conventional
filtration treatment or direct filtration, achieve a turbidity performance criterion of 0.3
Nephelometric Turbidity Units (NTUs), 95 percent of the time within any one-month period,
based on four-hour sampling intervals in the system's combined filter effluent water. In
addition, the turbidity level of a system's combined filtered effluent at each plant must at no
time exceed 1 NTU, based on samples taken every four hours. Requirements for technologies
such as diatomaceous earth filtration and slow sand filtration remain the same (i.e., as regulated
by the SWTR).
1.2 Use of Disinfectants
As noted previously, disinfection is a critical element in the elimination of pathogens from
drinking water. Disinfection inactivates disease-causing pathogens, such as bacteria, protozoa,
and viruses, that can affect humans by causing illnesses such as diarrhea and fever or, in the
most extreme cases, death. Infection and disease can occur following even one-time exposure
to a pathogen in drinking water.
Although disinfection has reduced the risk of people contracting an illness through public
drinking water systems, one of the side effects of disinfection is the formation of DBFs. DBFs
are formed when disinfectants react with organic and inorganic compounds in the water. The
adverse effects of DBFs are generally associated with chronic (i.e., long-term) exposure.
However, some DBFs pose potential acute, or short-term risks, to consumers.
Chlorine is, by far, the most commonly used disinfectant in the United States and is used as a
post-treatment disinfectant in 68 percent of all surface water treatment plants (USEPA,
1997b). Chlorine however, reacts with natural organic matter (NOM) and bromide to form
halogenated compounds such as THMs, HAAs, and haloketones.
In addition to chlorine, other disinfectants and disinfection techniques, such as chloramines,
chlorine dioxide, and ozone, are also used in the United States. These different disinfectants
have various levels of effectiveness in eliminating disease-causing pathogens. For example,
while chlorine is more effective than chlorine dioxide at inactivating viruses, the opposite is
true for the inactivation of Giardia cysts. Ozone is better than both chlorine and chlorine
dioxide at inactivating viruses and Giardia cysts, while chloramines are less effective than
chlorine and chlorine dioxide at inactivating both organisms (AWWA, 1991).
Various disinfectants react with NOM to form different DBFs. While chlorine predominantly
produces halogenated organics, ozone produces aldehydes, ketones, and inorganic byproducts.
Chlorine dioxide produces chlorate and chlorite, while ozone produces bromate when used in
the presence of bromide. The type and amount of DBFs formed during treatment not only
depends on the type and dose of disinfectant used, but also on water quality, treatment
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1. INTRODUCTION
sequences, and environmental factors such as temperature, pH, and contact time (Bellar et al.,
1974; Rook, 1974; McGuire et al., 1990).
Disinfectants and DBFs of current interest in drinking water treatment, based on limited
occurrence and health effects data, include the following:
• Halogenated organic byproducts
- THMs
- HAAs
• Inorganic byproducts
- Bromate
- Chlorite
• Disinfection residuals
- Chlorine
- Chloramines
- Chlorine dioxide
In addition to inactivating pathogens in the source water, disinfectants are also used as oxidants
in drinking water treatment to:
• Control nuisance Asiatic clams and zebra mussels
• Oxidize iron and manganese
• Maintain a residual to prevent biological regrowth in the distribution system
• Remove taste and odors
• Improve coagulation and filtration efficiency
• Prevent algal growth in sedimentation basins and filters
• Act as indicators of distribution system integrity.
These additional uses for disinfectants can compound the problem of DBF formation since
different types of DBFs are lowered or increased with different types of disinfectants/oxidants.
In addition, DBF control in the distribution system might necessitate further action at or
beyond the treatment plant limits.
Given the range of disinfectants available, each having unique inactivation efficiencies and
producing a variety of DBFs, PWSs will have to evaluate the risk-risk tradeoffs associated with
each of these alternative disinfectants. The rules will force the PWSs to figure out the
appropriate technology/engineering solutions in order to meet all of their requirements. It is
expected that alternative disinfectants will play an increasingly important role in the efforts of
utilities to meet treatment standards. PWSs will have to make complicated technological and
economic decisions to comply with the different drinking water regulations.
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1.3 Goal of Manual
The goal of this manual is to provide information that PWSs can use to address operational
problems which may result from their efforts to implement the Stage 1 DBPR and the
IESWTR. Co-implementation of these new rules can lead to conflicts, potentially resulting in
noncompliance with either of these regulations or with pre-existing regulations, such as the
LCR and the TCR. This manual identifies many of the known conflicts that may occur
between these rules and provides recommendations for resolving them. In conjunction with
promulgation of the IESWTR and Stage 1 DBPR, EPA recently published several additional
guidance manuals that may also assist PWSs in resolving these potential conflicts. These
references include the following:
• Disinfection Profiling and Benchmarking Guidance Manual (1999)
• Alternative Disinfectants and Oxidants Guidance Manual (1999)
• Uncovered Finished Water Reservoirs Guidance Manual (1999)
• Unfiltered Systems Guidance Manual (1999)
• Guidance Manual for Compliance with the Interim Enhanced Surface Water Treatment Rule:
Turbidity Provisions (1999)
• Conducting Sanitary Surveys of Public Water Systems; Surface Water Systems and Ground
Water Under the Direct Influence (GWUDI) of Surface Water Systems Guidance Manual
(1999)
• Guidance Manual for Enhanced Coagulation and Enhanced Precipitative Softening (1999).
1.4 Organization of Manual
This manual is organized to provide a tool for PWSs, States, and others to consult when
evaluating simultaneous compliance issues and alternatives. Several case studies are presented
throughout this document to better illustrate how the guidance can be put into practice. The
remaining chapters of this manual are organized as follows:
• Chapter 2 provides general background information on pathogen inactivation and the role of
disinfectants in DBF formation. This chapter also describes the Stage 1 DBPR and the
IESWTR and some of the known compliance issues.
• Chapter 3 describes the difficulties a PWS may have in simultaneously meeting regulatory
requirements of the Stage 1 DBPR and IESWTR and addresses specific simultaneous
compliance issues.
• Chapter 4 describes the difficulties a PWS may have in simultaneously meeting regulatory
requirements of the M-DBPR and LCR and addresses specific simultaneous compliance
issues.
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1. INTRODUCTION
Chapter 5 describes the difficulties a PWS may have in simultaneously meeting regulatory
requirements of the M-DBPR and TCR and addresses specific simultaneous compliance
issues.
Chapter 6 identifies operational issues associated with implementation of treatment plant
modifications and enhancements to achieve simultaneous compliance.
Chapter 7 lists the references used in the development of this report.
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REGULATORY REQUIREMENTS
Rook's discovery of trihalomethanes in drinking water in 1972 both fostered and underlined
the perception that many drinking water supplies are contaminated and that the nation's
drinking water supply is at risk for future contamination (Rook, 1974). At the time, the
identification of these potential carcinogens was one of the most important factors leading to
the enactment of the original 1974 SDWA. Since then, regulatory agencies have been charged
with developing health risk assessments as a means of guiding risk management.
This chapter discusses the inactivation of pathogens and the role of disinfectants in DBF
formation. This discussion provides a brief overview of waterborne disease-causing pathogens,
methods of inactivating these pathogens using disinfectants, DBF formation potential and
control strategies. In addition, a summary of compliance issues related to the regulatory
requirements of the Stage 1 DBPR and the IESWTR is included.
2.1 Inactivation of Pathogens
Although the epidemiological relationship between water and disease was suggested as early as
the mid-1850s, it was not accepted that water could be a carrier of disease-producing
organisms until the establishment of Pasteur's germ theory of disease in the mid-1880s.
Cholera was one of the first diseases to be recognized as capable of being waterborne. During
the mid-1880s, London experienced the "Broad Street Well" cholera epidemic and Dr. John
Snow conducted his now famous epidemiological study (Culp/Wesner/Culp, 1986). He
concluded that the source of the contamination was a soldier who had contracted the infection
while stationed in India. Solutions for eliminating the threat of waterborne disease evolved
years later with the introduction of filtration and disinfection. Since then, filtration and
disinfection have dramatically reduced the transmission of waterborne diseases in the United
States. However, while the threat of waterborne disease has been drastically reduced since the
early 1900s, it has not been entirely eliminated.
2.1.1 Recent Waterborne Outbreaks
Within the past 25 years, pathogens such as E. coli, Giardia lamblia, Cryptosporidium
parvum, and Legionellapneumophila have been involved in numerous documented waterborne
disease outbreaks. Enteropathogenic E. coli and Giardia lamblia were first identified as
etiological agents responsible for waterborne outbreaks in the 1960s. In 1975, a large
waterborne disease outbreak at Crater Lake National Park in Oregon was attributed to E. coli
bacteria (Craun, 1981). Between 1972 and 1981, 50 waterborne outbreaks of giardiasis
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occurred nationwide involving about 20,000 reported cases (Craun and Jakubowski, 1986).
The biggest documented outbreak in the United States occurred in 1993 in Milwaukee, where
an estimated 403,000 people became ill and 4,400 people were hospitalized because of
exposure from Cryptosporidium. This was also the first recorded infection in humans as a
result of exposure to Cryptosporidium in water.
White (1992) considered the two most significant causes of illnesses attributed to public
drinking water supplies to be source water contamination and deficiencies in treatment. About
46 percent of the outbreaks in public water systems have been related to these two particular
problems, with 92 percent of individual illnesses caused by these two problems. The 1993
Cryptosporidium outbreak was associated with a deterioration of raw water quality and a
simultaneous decrease in the effectiveness of the coagulation-filtration process, which led to an
increase in the turbidity of the treated water and inadequate removal of Cryptosporidium
oocysts (Kramer et al., 1996; MacKenzie et al., 1994).
Levy et al. (1998), using 1995 through 1996 Centers for Disease Control (CDC) data,
concluded that only three of the ten reported outbreaks during this time period, associated with
community water systems, were caused by problems at water treatment plants. The other
seven outbreaks resulted from problems in the water distribution systems and cross-
connection/plumbing of individual facilities such as restaurants.
Outbreaks are also possible in drinking water systems with no apparent treatment deficiencies
or breakdowns, such as that which occurred in Las Vegas, Nevada from January to May 1994
(Roefer et al., 1996). In this instance, the CDC found the "... first documented
epidemiologically confirmed waterborne outbreak from a water system with no treatment
deficiencies or breakdowns" (Roefer et al., 1996).
2.1.2 Pathogens of Primary Concern
Source waters, especially surface waters, support microbiological communities that include
pathogens. Because these microorganisms can be responsible for public health problems, the
microbiological characteristics of the water source are one of the most important parameters in
ensuring effective water treatment. In addition to public health, microbiological characteristics
can also affect the physical and chemical quality of the water and treatment plant operations.
Table 2-1 shows the attributes of three pathogen groups of primary concern in water treatment:
bacteria, viruses, and protozoa.
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Table 2-1. Attributes of Waterborne Pathogens of Primary Concern
Organism
Size
(Mm)
Mobility Point(s) Of Origin
Resistance to
Disinfection
Removal by
Sedimentation,
Coagulation, and
Filtration
Bacteria
0.1-10 Motile,
Nonmotile
Viruses
Protozoa
0.01-0.1 Nonmotile
Humans and animals,
water, and
contaminated food
Humans and animals,
polluted water, and
contaminated food
Type specific - bacterial 2- to 3-log removal
spores typically have the
highest resistance,
whereas vegetative
bacteria have the lowest
resistance
4-20 Motile, Humans and animals,
Nonmotile sewage, decaying
vegetation, and water
More resistant than
vegetative bacteria
More resistant than
viruses or vegetative
bacteria
1-to 3-log removal
2- to 3-log removal
Source: Culp/Wesner/Culp, 1986.
2.1.2.1 Bacteria
Bacteria are single-celled organisms ranging in size from 0.1 to 10 micrometers (|J,m). Their
shape, components, size, and manner of growth are used to characterize these organisms.
Most bacteria can be grouped by shape using four general categories: spheroid, rod, curved
rod or spiral, and filamentous. Cholera, a disease prevalent in Europe during the eighteenth
and nineteenth centuries is transmitted by the bacterium, Vibrio cholerae. Outbreaks of
cholera in the mid 1800's prompted Dr. John Snow to study the disease's transmission through
a common water supply. Salmonella typhosa and shigella spp. are also well known types of
bacteria known to affect PWSs. Outbreaks of these bacterial diseases are especially rampant in
parts of the world with poor sanitary practices.
2.1.2.2 Viruses
Viruses are composed of a strand of genetic material, either deoxyribonucleic acid (DNA) or
ribonucleic acid (RNA), and a protective protein coat. All viruses are obligate parasites,
unable to carry out any form of metabolism, and are completely dependent upon host cells for
replication. Viruses typically range from 0.01 to 0.1 |j,m in size, are very species-specific with
respect to infection, and typically attack only one type of host. Viruses such as Hepatitis B
virus, poliovirus, and picornavirus are transmitted through food, personal contact, exchange of
body fluids, or potable water. Some viruses, such as the retroviruses (including the human
immunodeficient virus (HIV) group) appear to be too fragile for water transmission to warrant
significant danger to public health (Riggs, 1989).
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2.1.2.3 Protozoa
Protozoa are single-celled eucaryotic microorganisms without cell walls that utilize bacteria
and other organisms for food. Most protozoa are free-living in nature and can be encountered
in water; however, several species are parasitic and live on or in host organisms. Host
organisms vary from primitive organisms, such as algae, to highly complex organisms, such as
humans. Giardia lamblia and Cryptosporidium are two protozoa that present greater
challenges to treatment because of their resistance to disinfection.
Giardia lamblia
Giardia lamblia is a flagellated protozoan that is responsible for giardiasis, a disease that can
cause symptoms such as fatigue, cramping, and intermittent diarrhea. The life cycle of Giardia
includes a cyst stage. During the cyst stage, the organism remains dormant and is extremely
resilient, allowing it to survive extreme environmental conditions. A Giardia cyst's life cycle
continues with the formation of an environmentally resistant outer shell (cyst) and the process
in which the vegetative form of the parasite emerges from the cyst, known as excystation.
Giardia is spread from person to person when a person touches the stool, or an object which
has been contaminated by the stool, of an infected person and then ingests the cyst. Infection is
often spread by not properly washing hands after bowel movements, after changing diapers, or
before preparing foods (CDC, 1998). In addition to humans, wild and domestic animals have
been implicated as hosts.
Currently, there is no simple and reliable method for assaying Giardia cysts in water samples.
Microscopic methods for detection and enumeration are tedious and require examiner skill and
patience. Although Giardia cysts are considered relatively resistant to chlorine, especially at
higher pH levels and low temperatures, there are systems that are effectively using chlorine and
chlorine dioxide for disinfection of Giardia cysts. Ozone and removal by filtration also appear
to be an effective disinfectant for inactivating Giardia. Giardia cysts are relatively large (i.e.,
between 7 and 15 ]am) and can be filtered effectively using diatomaceous earth, granular media,
or membranes.
Cryptosporidium
Cryptosporidium is a protozoan similar to Giardia. It forms oocysts (i.e., the fertilized egg
form of the Cryptosporidium) as part of its life cycle that are resistant to disinfection. The
oocysts are smaller than Giardia cysts, typically ranging from about 4 to 6 |j,m in diameter.
These oocysts can survive under adverse conditions. Once ingested by a warm-blooded
animal, they will undergo excystation and continue their life cycle. The primary symptom of
cryptospordiosis is acute diarrhea. Other symptoms include vomiting, abdominal pain, and
low-grade fever. Animals, person-to-person contact, and contaminated drinking water have
been identified as sources of infection.
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Due to the increase in outbreaks of cryptosporidiosis, a tremendous amount of research has
focused on Cryptosporidium within the last 10 years. Medical interest has increased due to its
potentially life-threatening impact on individuals with acquired immune deficiency syndrome
(ADDS), other immunocompromised populations, such as people undergoing chemotherapy for
cancer, pregnant women, and the very old or very young.
2.1.3 Mechanisms of Pathogen Inactivation
In water treatment, disinfection is one of the primary methods used to inactivate pathogens.
Three primary mechanisms are responsible for pathogenic inactivation by disinfection:
• Destruction or impairment of cellular structural organization
• Interference with energy-yielding metabolism
• Interference with biosynthesis and growth.
The first mechanism of pathogen inactivation is to adversely affect the structure of the cell.
The destruction or impairment of the structural integrity of cells is achieved by attacking major
cell constituents, such as destroying the cell wall or impairing the functions of semi-permeable
membranes. The second mechanism of inactivation is to interfere with the metabolism or
cellular activity of a pathogen. Metabolic interference can occur through oxidizing enzyme
functional groups, thus rendering the enzymes non-functional. The third mechanism is to
interfere with biosynthesis and growth. This can be achieved by preventing synthesis of normal
proteins, nucleic acids, coenzymes, or the cell wall.
Disinfectants can cause combinations of inactivation mechanisms depending on the type of
disinfectant and microorganism. Montgomery (1985) believed that the primary factors
controlling disinfection efficiency, and hence pathogen inactivation, are: (1) the ability of the
disinfectant to oxidize or rupture the cell wall, and (2) the ability of the disinfectant to diffuse
into the cell and interfere with cellular activity.
2.1.4 Effect of Parameters on Inactivation
Disinfection effectiveness depends on many factors including the type and amount of
disinfectant used, the organisms being treated, physiological condition of the organisms, time
the disinfectant is in contact with the water, and other water quality characteristics (such as the
quantity of dissolved organics in the water). The type of disinfectant used greatly affects the
efficiency of inactivation. The stronger the disinfectant, the more quickly the disinfection
process occurs. Increasing the disinfectant dose, or disinfectant residual, will increase the rate
of pathogen inactivation but may also increase the formation of harmful DBFs. The efficiency
of pathogen inactivation can also be affected by the pH of the water. At certain pH levels a
disinfectant may be transformed into a form that may be more benign to pathogens. Typically,
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increasing temperatures will increase the rate of disinfection. Turbidity interferes with
disinfection because particles in the water can surround and shield pathogenic microorganisms
from the disinfectants. Dissolved organics interfere with disinfection by reacting with the
disinfectant to produce compounds with little or no microbiocidal activity, thereby reducing the
amount of disinfectant available for pathogen inactivation.
2.1.5 Comparison of Disinfectant Inactivation Values
There is considerable variability in the effectiveness of different disinfectants. Some of the
factors affecting disinfection effectiveness are discussed in Table 2-2.
Table 2-2. Summary of Factors that Affect Disinfection
Factor Description
Disinfectant type The stronger the disinfectant, the quicker the disinfection process.
Disinfectant dose Increasing the disinfectant dose will increase the disinfection rate, but may also
increase the formation of harmful byproducts.
Type of organism and its A microorganism's susceptibility to disinfection varies according to pathogen group
physiological condition and agent. In general, protozoa are more resistant to disinfectants than are bacteria
or viruses.
Contact time In general, increasing the contact time will decrease the disinfectant dose required
for pathogen inactivation.
pH pH may affect the disinfectant form and, in turn, the efficiency of the disinfectant.
Temperature Typically, increasing the temperature will increase the rate of disinfection.
Turbidity Particles responsible for turbidity can surround and shield pathogenic
microorganisms from disinfectants and exert a disinfectant demand.
Dissolved organics and Dissolved organics can interfere with disinfection by consuming the disinfectants to
inorganics produce compounds with little or no microbiocidal activity, thereby reducing the
amount of disinfectant available for pathogen inactivation.
While there is some promising research on the Ultraviolet (UV) disinfection, there are currently
no provisions for its use for regulatory compliance.
One of the most useful ways of characterizing the germicidal efficiency of any disinfectant is
the CT factor, a version of the Chick-Watson law (Chick, 1908; Watson, 1908). CT is defined
as the product of the residual disinfectant, C, in milligrams per liter (mg/L), and the contact
time, T, in minutes.
The CT factor implies that an equivalent level of disinfection can be achieved by different
combinations of disinfectant concentrations and contact times. CT factors are typically
determined for different levels of pathogen inactivation. Inactivation is usually measured in log
base 10, while CT values are usually measured in mg-min/L. The following formula
demonstrates how to calculate the different levels of inactivation:
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X = -log 10(1-N) or N = l-lffx
where: X = level of pathogen removal/inactivation
N = fraction of pathogen removed/inactivated
The level of inactivation, X, is usually expressed as "log removal" or "log inactivation." For
example, a 2-log inactivation is equivalent to a 99 percent pathogen inactivation. Each unit
increase in the log removal of pathogens will result in a ten-fold decrease in the fraction of
viable pathogens. For example, a 3-log inactivation is equivalent to a 99.9 percent inactivation.
When discussing filtration and disinfection, removal levels from filtration can be combined with
disinfection inactivation levels to create an overall removal/inactivation level.
EPA has identified CT values for the inactivation of Giardia cysts and viruses for various
disinfectants. Table 2-3 and Table 2-4 summarize the CT values for the inactivation of viruses
and Giardia cysts, respectively, using various disinfectants at a water temperature of 10°C and
a pH range of 6.0 to 9.0. CT values for chlorine disinfection are based on a free chlorine
residual as opposed to a chloramine residual.
Some systems employ different disinfectants to meet their system's demands. These
disinfectants are used for primary and/or secondary disinfection depending on the utility's need
and the specific disinfectant. Primary disinfection provides the appropriate CT to inactivate
microbial pathogens. Disinfectants proven effective for this purpose include free chlorine,
chlorine dioxide, and ozone. Secondary disinfection ensures residual protection to control
microorganism regrowth or recontamination during water storage and distribution. Either free
chlorine, or chlorine plus the addition of ammonia to form chloramine, accomplishes this task
(AWWA, 1999).
The most effective chemical disinfectant, overall, in terms of total pathogen inactivation, is
ozone. Ozone is an extremely strong disinfectant and has excellent inactivation efficiencies for
bacteria, viruses, and Giardia. Chlorine and chlorine dioxide are both excellent disinfectants
for bacteria. Chlorine is slightly more efficient than chlorine dioxide at inactivating viruses
while chlorine dioxide is much better at inactivating Giardia cysts. Chloramine is generally not
considered a strong disinfectant for bacteria, viruses, or Giardia cysts because it requires a
high CT value and, therefore, is a poor primary disinfectant, although some systems with long
contact times use chloramines for primary disinfection (e.g., Austin, Texas). Chloramine,
however, is used because it does not form TFDVIs even after extended contact times and is
therefore, an attractive secondary disinfectant for maintaining a residual in the distribution
system.
Continuous Wave (CW) Ultraviolet (UV) light is not included in Table 2-3 since it is not
allowed under the SWTR and the IESWTR. EPA did not include UV light disinfection in
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these two rules since literature data on Cryptosporidium inactivation with UV appear
controversial because of different experimental protocols used by different investigators
(USEPA, 1997b). UV light disinfection also does not provide a residual.
Table 2-3. CT Values for Inactivation of Viruses in Water at 10°C with pH 6.0-9.0
CT values (in mg-min/L)
Disinfectant
Chlorine
Chloramine
Chlorine Dioxide
Ozone
2-log
Inactivation
(99.0%)
3
643
4.2
0.5
3-log
Inactivation
(99.9%)
4
1,067
12.8
0.8
4-log
Inactivation
(99.99%)
6
1,491
25.1
1.0
CT values were obtained from Appendix E (AVWVA, 1991).
Table 2-4. CT Values for Inactivation of Giardia Cysts in Water at 10°C
with pH 6.0-9.0
Disinfectant
Chlorine1
Chloramine
Chlorine Dioxide
Ozone
0.5-log
Inactivation
(68.0%)
17
310
4
0.23
1-log
Inactivation
(90.0%)
35
615
7.7
0.48
1.5-log
Inactivation
(96.8%)
52
930
12
0.72
2.5-log
Inactivation
(99.7%)
87
1,540
19
1.2
3-log
Inactivation
(99.9%)
104
1,850
23
1.43
CT values were obtained from Appendix E (AVWVA, 1991).
1 at pH 7.0 and chlorine residual < 0.4 mg/L.
2.1.6 Disinfectant Residual
Disinfectant residual is necessary to inactivate pathogens, maintain water quality, and protect
the distribution system against regrowth (Snead et al., 1980). The SWTR provides minimum
requirements on the amount of disinfection residual that must exist in treated water.
Specifically, the SWTR requires that filtration and disinfection must be provided to ensure that
the total treatment of the system achieves at least a 3-log (99.9 percent) removal/inactivation of
Giardia cysts and a 4-log (99.99 percent) removal/inactivation of viruses (USEPA, 1989a). In
addition, the disinfection process must demonstrate, by continuous monitoring and recording,
that the disinfectant residual concentration in water entering the distribution system is never
less than 0.2 mg/L and that a detectable residual is maintained in the distribution system.
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Although a disinfectant residual is generally necessary to maintain water quality, it is
recognized that an excessive amount of disinfectant residual may also pose a threat to health as
well as contribute to the increased formation of harmful DBFs. The Stage 1 DBPR sets
MRDLs and MRDLGs of 4.0 mg/L for chlorine and chloramines and 0.8 mg/L for chlorine
dioxide.
2.2 Stage 1 Disinfectant and Disinfection Byproducts
Rule (DBPR)
As mentioned previously, the Stage 1 DBPR finalizes the following:
. MRDLGs for chlorine, chloramines, and chlorine dioxide
. MCLGs for four THMS, two HAAs
. National Primary Drinking Water Regulations (NPDWRs) for
- Three disinfectants (chlorine, chloramines, and chlorine dioxide)
- Two groups of organic DBFs (TTHMs and HAAS)
- Two inorganic DBFs (chlorite and bromate).
Although disinfection plays a crucial role in water treatment, its application does have side
effects. In addition to inactivating pathogens, disinfectants react with organic matter to
produce DBFs. Numerous researchers have documented that NOM is the principal precursor
of DBF formation (Stevens et al., 1976; Babcock and Singer, 1979; Christman et al., 1983).
This section discusses the role of disinfectants in the formation of DBFs, highlighting those
disinfectants and DBFs that are of current regulatory interest to EPA. In addition, this section
discusses parameters that affect the formation of DBFs and concludes with a discussion of
strategies to minimize DBF formation.
2.2.1 Disinfection Byproduct Formation
Natural water contains NOM in the form of humic and nonhumic substances. The precursors
of DBF formation are generally naturally occurring organic substances, such as humic and
fulvic acids. These acids belong to a family of compounds having similar structure and
chemical properties and are formed during the decomposition of vegetation. These natural
organic DBF precursors can be subdivided into a hydrophobic (i.e., water repellent) fraction of
primarily humic material and a hydrophilic (i.e., water attractive) fraction of primarily fulvic
material.
The amount of NOM in water can be estimated by measuring surrogate parameters. Although
surrogate parameters have limitations, they are used because they may be measured more
easily, rapidly, and inexpensively than the NOM parameter of interest. Estimation of NOM
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concentration allows water treatment plant operators to monitor the operation and
performance of the water treatment plant. The following surrogate parameters can be used to
assess the type and concentration of NOM:
• Total and dissolved organic carbon
• UV light absorbency at 254 nanometer (nm) wavelength (UV-254)
• THM formation potential (THMFP) - a test measuring THM formation with a high dosage of
free chlorine and a long reaction time
• THM Simulated Distribution System (SDS) - a test that predicts the total THM concentration
at some selected point in a given distribution system, where the conditions of the chlorination
test simulate the distribution system at the point desired.
Additional details on NOM type and concentration assessment are available in the Guidance
Manual for Enhanced Coagulation and Precipitative Softening (USEPA, 1999g).
About 90 percent of total organic carbon (TOC) concentration in a water supply is typically
dissolved. The dissolved organic carbon (DOC) concentration is defined as the TOC able to
pass through a 0.45 • m filter. Measurement of UV absorbency is a good technique for
assessing the presence of DOC, such as humic substances, because these substances contain
aromatic structures that absorb light in the UV spectrum. Oxidative processes can reduce the
UV absorbance without changing the DOC concentration, however, the UV7DOC coorelation
would change after oxidation.
EPA has identified numerous compounds that are of current regulatory interest and pose the
greatest health risk based on the frequency of their occurrence and their potential health effects
(USEPA, 1992a). The categories of DBFs of interest to EPA include disinfectant residuals,
inorganic byproducts, and halogenated organic byproducts, as summarized below, but EPA
may add additional DBFs as more information becomes available:
• Disinfection residuals
- Chlorine
- Chloramines
- Chlorine dioxide
• Inorganic byproducts
- Bromate ion
- Chlorite ion
• Halogenated organic byproducts
- THMs
Chloroform
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Bromodichloromethane
Dibromochloromethane
Bromoform
- Haloacetic acids
Monochloroacetic acid
Dichloroacetic acid
Trichloroacetic acid
Monobromoacetic acid
Dibromoacetic acid
2.2.1.1 Free Chlorine
Halogenated organic byproducts (such as chloroform) are produced when free chlorine reacts
with NOM. In addition, brominated byproducts are formed when source water containing
bromide ions is chlorinated. Chlorine oxidizes bromide ions resulting in the formation of free
bromine that, in turn, reacts with NOM to produce the brominated analogs of chlorination
byproducts. Currently regulated brominated byproducts include bromoform,
bromodichloromethane, dibromochloromethane, monobromoacetic acid, and dibromoacetic
acid.
2.2.1.2 Chloramine
Application of high-grade chloramine does not generally produce detectable concentrations of
THMs. Although detectable concentrations of mono- and dichloroacetic acids can be
produced, these are generally significantly lower than corresponding concentrations produced
by free chlorine. If chlorine is added prior to ammonia to form chloramines in-situ (as often
done to insure virus inactivation through free chlorine contact), all of the byproducts associated
with the use of free chlorine can be formed (although formation is significantly retarded when
ammonia is added). No detectable trihaloacetic acids are produced from chloramination.
2.2.1.3 Chlorine Dioxide
Chlorine dioxide does not produce halogenated DBFs to any significant degree, although it
does produce chlorite ion, an inorganic byproduct. Approximately 50 to 70 percent of the
chlorine dioxide consumed reduces to chlorite ion (Rav Acha et al., 1995; Werdehoff and
Singer, 1987). Moreover, chlorine dioxide generators usually result in some excess free
chlorine (typically less than 2 percent by weight in the generator effluent) (USEPA, 1999b).
Because chlorine reacts with NOM to produce DBFs, it is important to use high purity chlorine
dioxide. The oxidation byproducts of chlorine dioxide treatment have not been studied
extensively and until the Chemical Manufacturers Association (CMA) completed a two-
generation reproductive rat study in 1996, the public health impact of chlorine dioxide
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treatment, has been largely unknown (CMA, 1997). Using sodium chlorite as the test
compound, CMA designed the study to evaluate the effects of chlorite on reproduction and
pre- and post-natal development when administrated orally via drinking water for two
successful generations. As a result of this study, an external peer review, and an EPA
reassessment, the EPA changed the MCLG for chlorite to 0.8 mg/L and the MRDLG for
chlorine dioxide to 0.8 mg/L.
2.2.1.4 Ozone
Although ozone itself does not produce halogenated DBFs, ozonation of waters containing
bromide ion can result in the production of brominated DBFs. Ozone will oxidize bromide ion
to hypobromous acid which, in turn, reacts with NOM to produce the fully brominated analogs
of chlorination byproducts (Cooper et al., 1986; Siddiqui and Amy, 1993). In addition,
hypobromite, which is in equilibrium with hypobromous acid, can be oxidized by ozone to
produce bromate as an inorganic byproduct. Bromate formation can be controlled by
performing ozonation at acidic pH values where hypobromous acid dominates over the
hypobromite ion (Siddiqui and Amy, 1993; Krasner et al., 1993), but this may present a
significant cost and operational burden for systems. Other bromate control techniques include
(USEPA, 1999b):
. Ammonia addition and ozonation to form bromamines
. Manipulating contact time and residual by applying ozone in stages to reduce the ozone
residual while maintaining the required CT
. Reducing ambient bromide concentration
. Maintaining a low ozone:DOC ratio.
2.2.2 Factors Affecting DBF Formation
DBF formation is influenced by a number of factors, including precursor concentrations and
seasonal variations. According to Singer (1992), the presence of organic precursors and the
formation of halogenated DBFs increase as temperature increases. This, in turn, leads to a
higher chlorine demand during the warmer summer months or in certain geographical locations
in order to maintain effective disinfection residuals.
The pH of the water being chlorinated has an impact on the formation of halogenated byproducts,
with the exception of dichloroacetic acid, monochloroacetic acid, and dibromoacetic acid, as
shown in Table 2-5. THM formation increases with increasing pH, while the formation of
trichloroacetic acid, dichloroacetonitrile, trichloroacetone, and overall total organic halides (TOX)
decreases with increased pH (Reckhow and Singer, 1985; Stevens et al., 1988). High pH also
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affects chloral hydrate. According to Miller and Uden (1983), chloral hydrate is hydrolyzed and
forms chloroform as the decomposition product under high pH conditions.
Table 2-5. Impacts of pH on Organic Halogen Formation During Chlorination
pH of Chlorination
Organic Halogen — — —
Total Trihalomethanes Lower formation Higher formation
Trichloracetic Acid Similar formation Similar formation Lower formation
Dichloroacetic Acid Similar formation - perhaps slightly higher at pH 7
Monochloracetic Acid Concentrations below 5 u.g/L, trends not discernible at low levels
Dribomacetic Acid Concentrations below 1 u.g/L, trends not discernible at low levels
Source: Stevens et al., 1988.
Based on Chlorination studies of humic material in model systems, high pH tends to favor
Chlorination formation over the formation of trichloracetic acid and other organic halides.
Accordingly, water treatment plants practicing precipitative softening at pH values greater than
9.5 to 10 are likely to have a higher fraction of TOX attributable to THMs than plants treating
surface waters by conventional treatment in pH ranges of 6.0 to 8.0 (Singer and Chang, 1989).
To the extent that the application of chlorine dioxide and chloramines introduces free chlorine into
water, any chlorination byproducts would be influenced by pH as discussed above. For a constant
chlorine to ammonia dose ratio, the ratio of chloramine to total chlorine increases with increasing
pH(AWWA, 1990).
Disinfection of source water containing bromide ions can lead to the formation of brominated
DBFs as discussed in Section 2.2.1.1. Increases in the ratios of bromide ion to the chlorine dose
and the ratio of the bromied ion to the DOC concentration results in a shift in THM and HAA
speciation to the more bromine-substituted species (Krasner et al., 1989; Black et al., 1996). In
Krasner's study, the chlorine dose was roughly proportional to TOC concentration. As TOC was
removed through the treatment train, the chlorine dose decreased and TTHM formation declined.
At the same time, however, the bromide ion to chlorine dose ratio increased and shifted the
TTHM concentrations towards brominated THMs. Therefore, improving the removal of NOM
prior to chlorination can shift the speciation of halogenated byproducts toward more brominated
forms. Ozone application to bromide ion-containing waters at high pH favors the formation of
bromate ion, while application at low pH favors the formation of brominated organic byproducts.
Since there is some evidence that brominated DBFs may have more significant health effects,
absolute levels of DBFs may not be comparable.
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2.2.3 DBF Control Strategies
In 1983, the EPA identified the best technologies and treatment techniques that public water
systems could use to comply with the MCL for TTHMs (USEPA, 1983). The principal
treatment modifications involved moving the point of chlorination downstream in the water
treatment plant, optimizing the coagulation process to enhance the removal of DBF precursors,
and using chloramines to supplement or replace the use of free chlorine (Singer, 1993).
Moving the point of chlorination downstream in the treatment train proves to be extremely
effective in reducing byproduct concentrations because it allows the NOM precursor
concentration of the water to be reduced prior to chlorine addition. Replacing prechlorination
by preoxidation with an alternate disinfectant that produces less DBFs is an attractive option
for reducing the formation of chlorinated byproducts.
Efforts to control the formation of DBFs should focus on:
Source water selection and control
DBF precursor removal
Disinfection strategy selection.
These efforts will affect the types and concentrations of DBFs that are formed. Each of these
efforts is briefly discussed below.
2.2.3.1 Source Water Control
Source water control strategies involve managing the source water to lower the concentrations
of NOM and bromide ion. Source water control strategies may include changing the water
source and blending water high in NOM and bromide ion concentrations with high quality
water that is low in NOM and bromide ion concentrations. Research has shown that algal
growth leads to the production of DBF precursors (Hoehn et al., 1980; Oliver and Shindler,
1980; Wachter and Andelman, 1984; Karimi and Singer, 1991). Therefore, nutrient and algal
management is one method of controlling the DBF formation potential of source waters or
presedimentation basins used by systems with highly variable turbidities. Control of bromide
ion precursors may be accomplished by preventing brine or salt water intrusion into the water
source.
2.2.3.2 DBP Precursor Removal
Raw water can include DBP precursors in dissolved and particulate forms. In conventional
treatment, dissolved precursors must be converted to particulate form for subsequent removal
during settling and filtering. The potential THM formation generally decreases by about 50
percent through conventional coagulation and settling, indicating the importance of moving the
point of chlorine application downstream of coagulation and settling (and even filtration) to
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control the formation of TOX and TTHMs (Singer and Chang, 1989). Systems can lower the
DBF formation potential of water prior to disinfection by removing precursors with bank
filtration, infiltration gallery, enhanced coagulation, granular activated carbon adsorption
following filtration, or membrane filtration.
Aluminum (alum) and iron (ferric) salts both have the ability to reduce pH which improves
NOM removal. For alum, the optimal pH for NOM removal is in the range of 5.5 to 6.0. The
addition of alum decreases pH and may allow the optimal pH range to be reached without acid
or base addition. However, waters with very low or very high alkalinities may require the
addition of a base or an acid to keep the pH in the range of optimal coagulation (Singer, 1992).
Systems will evaluate the optimal combination of coagulant, acid/base, coagulant/filter aids,
etc. to remove precursors.
Granular activated carbon (GAC) adsorption can be used following filtration to remove
additional NOM. For most applications, empty bed contact times (EBCTs) in the range of 5 to
30 minutes are required, with regeneration frequencies on the order of two- to nine- months
(Singer, 1992). Changing the pH, or addition of a disinfectant to the GAC bed, can result in
specific reactions in which previously absorbed compounds leach into the treated water.
Powdered activated carbon (PAC) can be used seasonally for TFDVI precursor, or TTFDVI,
reduction.
Membrane filtration has been shown to be effective in removing DBF precursors in some
instances. In pilot studies, ultrafiltration (UF) with a molecular weight cutoff (MWCO) of
100,000 daltons was ineffective for controlling DBF formation. However, when little or no
bromide ion was present in the source water, nanofiltration (NF) membranes with MWCOs of
400 to 800 daltons effectively controlled DBF formation (Laine et al., 1993). In waters
containing bromide ion, higher bromoform concentrations were observed after chlorination of
membrane permeate (compared with the raw water). TTHMs were lower in the chlorinated
permeate than in the chlorinated raw water. However, due to the shift in speciation of THMs
toward more brominated forms, bromoform concentration was actually greater in the
chlorinated treated water than in the chlorinated raw water. Use of spiral-wound NF
membranes (200-300 daltons) more effectively controlled the formation of brominated THMs,
but pretreatment of the water was necessary (Laine et al., 1993). Significant limitations in the
use of membranes include disposal of the waste brine generated, fouling of the membranes,
membrane replacement cost, and total system costs.
2.2.3.3 Disinfection Strategy Selection
In addition to improving the quality of the raw or predisinfected water, alternative disinfection
strategies may be used to control DBFs. These strategies include the following:
• Use of an alternative or supplemental disinfectant
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• Movement of the point of disinfection to reduce TTHM formation
• Use of multiple disinfectants at various points in the treatment plant to avoid DBF formation at
locations where precursors are still prevalent.
2.3 Stage 1 Disinfection Byproducts Rule (DBPR)
As noted previously, the Stage 1 DBPR is aimed at limiting the amount of disinfection residual
and DBFs in the distribution system. The Stage 1 DBPR is intended to limit the formation of
byproducts such as THMs and HAAS and is directed at PWSs that are CWSs and NTNCWs
that treat their drinking water with a chemical disinfectant for either primary or residual
treatment. In addition, certain provisions apply to TNCWSs that use chlorine dioxide.
The Stage I DBPR uses two approaches to limit the amount of residual disinfectants and DBFs
in distribution systems. First, EPA is requiring the removal of NOM, measured in the form of
TOC. Second, EPA is requiring PWSs to reduce the level of TTHMs, HAAs, and bromate ion
in distribution systems.
2.3.1 DBF Maximum Contaminant Levels (MCLs)
The Stage 1 DBPR reduces allowable DBFs in PWS distribution systems to the following
concentrations:
• TTHMs: 0.080 mg/L (as a running annual average)
• HAAS: 0.060 mg/L (as a running annual average)
• Bromate ion: 0.010 mg/L (as a running annual average)
• Chlorite ion: 1.0 mg/L (as a three-sample set average)
These allowable concentrations may be further reduced in the Stage 2 DBPR or the compliance
determination procedure may be changed.
2.3.2 Maximum Residual Disinfectant Levels (MRDLs)
As part of the Stage 1 DBPR, EPA has also set MRDLs and MRDLGs for chlorine,
chloramines, and chlorine dioxide. As with MCLs, MRDLs are enforceable limits, whereas
MRDLGs, similar to MCLGs, are unenforceable health goals. The MRDLs and MRDLGs, for
the three disinfectants are as follows:
MRDL MRDLG
• Chlorine: 4.0 mg/L 4.0 mg/L
• Chloramine: 4.0 mg/L 4.0 mg/L
• Chlorine dioxide: 0.8 mg/L 0.8 mg/L
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2.3.3 TOC Removal Requirements
The Stage 1 DBPR bases TOC removal requirements on the TOC concentration and alkalinity
of the raw water. The required removal is adjusted for alkalinity because the optimal pH for
TOC removal is often below 6.0. As a result, waters with high alkalinity require an extensive
amount of coagulant and/or pH adjustment to drive the pH into an optimal range. Recent
research confirms this situation and has demonstrated that waters with high alkalinity will have
a more difficult time meeting the TOC removal requirements as compared to waters with low
alkalinity (Krasner and Amy, 1995; White et al., 1997; Arora et al., 1997).
Therefore, the higher cost of chemical addition for waters with high alkalinity has prompted
EPA to lower the TOC removal requirements as compared to waters with lower alkalinity.
Furthermore, the additional chemicals that would be required to drive the pH into an optimum
range might produce byproducts (e.g., sulfuric acid to sulfate) that would become a concern
relative to corrosion and/or other public health issues (e.g., gastrointestinal distress).
Table 2-6 outlines the TOC removal requirements of the Stage 1 DBPR (USEPA, 1998a).
Table 2-6. Stage 1 DBPR Percent TOC Removal Requirements
TOC
2.0-4.0 mg/L
4.0 -8.0 mg/L
> 8.0 mg/L
0 - <60 mg/L
Alkalinity
35%
45%
50%
TOC Removal
>60-<120mg/L
Alkalinity
25%
35%
40%
>1 20 mg/L
Alkalinity
15%
25%
30%
The Stage 1 DBPR also provides for six alternative compliance criteria from the treatment
technique requirements provided certain conditions are met. These criteria are independent of
the softening requirements and are listed in Section 3.4.1. These criteria differ in the
monitoring requirements; they are either determined based on monthly monitoring calculated
quarterly as a running annual average of all measurements, on monthly monitoring for TOC
and alkalinity or quarterly monitoring for TTHMs and HAAS, calculated quarterly as a running
annual average of all measurements, or on monitoring for TTHMs and HAAS, calculated
quarterly as a running annual average of all measurements.
It was also agreed during the regulatory negotiation process that specific ultraviolet absorbency
(SUVA) should be considered when determinations of exemption status for TOC removal are
being made. SUVA is an easily measured indicator of the organic fraction of water that is not
amenable to removal through coagulation. It is also a measure of the humic/non-humic
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compositions of NOM and, therefore, by including a SUVA provision in the rule, EPA is
specifically targeting waters with a NOM fraction that is difficult to remove through enhanced
coagulation or enhanced softening. SUVA, is defined as the UV-254 (measured in m"1) divided
by the DOC concentration (measured as mg/L).
2.4 Interim Enhanced Surface Water Treatment Rule
(IESWTR)
As mentioned previously, the IESWTR focuses primarily on improving particulate removal at
drinking water treatment systems. While the "interim" rule applies to systems serving 10,000
people or more, the Long-Term 1 ESWTR (LT1ESWTR) will regulate systems serving fewer
than 10,000 people. The overall scope of the LT1ESWTR will depend on the results of the
ICR. The LT1ESWTR is expected to be promulgated in the year 2000.
The primary requirements associated with the IESWTR include meeting:
• Filtered effluent turbidity levels (both combined and individual filter effluents)
• Continued Giardia lamblia and virus removal/inactivation requirements
• Cryptosporidium removal requirements
• Microbial profiling/benchmarking requirements.
2.4.1 Turbidity Requirements
The new turbidity requirements in the IESWTR are as follows (USEPA, 1998b):
• Combined effluent performance requirements for plants using conventional filtration treatment
or direct filtration:
- Combined filtered water effluent turbidity must be less than or equal to 0.3 NTU in at least
95 percent of the measurements taken each month, with measurements taken every four
hours of operation; and
- Combined filtered water effluent turbidity must not exceed 1.0 NTU at any time with
measurements taken in four-hour intervals.
• Combined effluent performance requirements for plants using slow sand and diatomaceous
earth filtration:
- The turbidity level of representative samples of a system's filtered water must be less than
or equal to 1.0 NTU in at least 95 percent of the measurements taken each month, with
measurements taken every four hours of operation; and
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- The turbidity level of representative samples of a system's filtered water must at no time
exceed 5.0 NTU with measurements taken in four-hour intervals.
• Individual filter performance requirements:
- Individual filter effluents must be monitored continuously for turbidity
- Any individual filter with a turbidity level greater than 1.0 NTU, based on two consecutive
measurements 15 minutes apart, must be reported to the governing agency
- Any individual filter with a turbidity level greater than 0.5 NTU at the end of the first four
hours of filter operation (following backwash or when off-line filters are put on-line) based
on two consecutive measurements 15 minutes apart, must be reported to the governing
agency.
A PWS also has the option to use an alternative filtration technology. The PWS may do so if it
demonstrates to the State, using pilot plant studies or other means, that the alternative filtration
technology, in combination with disinfection treatment that meets the requirements of 40 CFR
141.72(b), consistently achieves 99.9 percent removal and/or inactivation ofGiardia lamblia
cysts and 99.99 percent removal and/or inactivation of viruses, and 99 percent removal of
Cryptosporidium oocysts, and the State approves the use of the filtration technology.
Depending on the frequency of exceptions, the system may also be required to perform a self-
assessment or have the State or a third-party perform a Comprehensive Performance
Evaluation (CPE) (USEPA, 1998c).
2.4.2 Giardia and Virus Removal/lnactivation Requirements
The IESWTR maintains the existing disinfection requirements as set forth in the 1989 SWTR
(USEPA, 1989a). These requirements will be applied to disinfection practices using chlorine,
chlorine dioxide, ozone, and chloramines. The concentration/contact time values in the 1989
SWTR continue to apply for Giardia and virus removal/inactivation. PWSs are still required
to meet a 3-log removal/inactivation ofGiardia and a 4-log removal/inactivation of viruses,
which can be accomplished via filtration followed by disinfection or through disinfection alone.
Disinfection credit for compliance with turbidity removal requirements is continued as outlined
under the 1989 SWTR.
2.4.3 Cryptosporidium Removal Requirements
In addition to Giardia and virus removal/inactivation, the IESWTR requires that all surface
water systems serving 10,000 people or more, which are required to filter, must achieve at least
a 2-log removal of Cryptosporidium. This is a new requirement updated from the 1989
SWTR. PWSs using rapid granular filtration (conventional and direct filtration) and meeting
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the turbidity requirements outlined above will be considered to be achieving at least a 2-log
removal of Cryptosporidium, as will systems using slow sand filtration or diatomaceous earth
filtration meeting SWTR turbidity requirements (USEPA, 1998b). Systems using alternative
filtration technologies must demonstrate to the State that the technology achieves 2-log
removal.
2.4.4 Microbial Profiling/Benchmarking Requirements
Another new and primary requirement associated with the IESWTR is microbial profiling and
benchmarking. Disinfection profiles must be prepared by PWSs with measured TTHM or
HAAS distribution system levels of 0.064 mg/L or 0.048 mg/L or higher, respectively, as
annual averages for the most recent 12 month compliance period. The disinfection profiles will
consist of a compilation of daily Giardia lamblia log inactivations (or virus inactivations under
conditions to be specified), computed over a period of one- to three-years.
Benchmarking is not intended to serve as a regulatory standard. USEPA intends benchmarking
to serve as a methodology by which the PWS and State can assure that there are no significant
reductions in microbial protection as a result of the system modifying its disinfection practices
to meet the Stage 1 DBF MCLs and MRDLs (USEPA, 1998b).
The guidance manual, Disinfection Profiling and Benchmarking (USEPA, 1999a) describes
the procedures necessary to comply with these requirements, including development of a
profile and calculation of a benchmark.
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BETWEEN STAGE 1 DBPRANDlESWTR
3.1 Introduction
As outlined in Chapters 1 and 2, the 1996 Amendments to the SDWA require the EPA to
develop regulations for the control and monitoring of microbial pathogens and DBFs in
drinking water. Two new rules promulgated in response to the 1996 SDWA Amendments are
the Stage 1 DBPR and the IESWTR. These two rules are part of the Microbial and
Disinfection Byproduct (M-DBP) cluster of rules discussed in Chapter 1.
The Stage 1 DBPR focuses on minimizing the formation of DBFs in the distribution system of
PWSs to reduce the long-term exposure of customers to these potentially carcinogenic
compounds through enhanced coagulation or enhanced softening. In contrast, the IESWTR
focuses primarily on achieving adequate disinfection and removal of pathogens to protect PWS
customers from acute pathogenic exposure that can cause outbreaks of waterborne disease.
Since the Stage 1 DBPR is intended to minimize the formation of DBFs and residual
disinfectants, this rule may conflict with the IESWTR which specifies levels of treatment
techniques required for Cryptosporidium.
As a result of the potential conflict inherent in these two rules, EPA sponsored an extensive
negotiation process during the development of these regulations. This regulatory negotiation
process included extensive input from a variety of stakeholders and resulted in the specific
requirements described in Chapter 2.
Both the Stage 1 DBPR and the IESWTR are based on "best available science." Early in the
regulatory negotiation process, the Negotiating Committee agreed that the large amount of
information necessary to understand how to optimize the use of disinfectants while
concurrently minimizing microbial and DBF risks were unavailable. Some of this information,
however, will become available as results from ICR are collected and analyzed. Nevertheless,
in the interim, it was agreed that EPA would propose the IESWTR and Stage 1 DBPR to
extend coverage to community and nontransient, noncommunity public water systems using
disinfectants. The Stage 1 DBPR is applicable to all community and nontransient
noncommunity systems, while the IESWTR affects only PWSs serving 10,000 or more people
that use surface water or ground water under the direct influence of surface water. EPA will
promulgate the Long-Term 1 ESWTR, which will update the IESWTR requirements and
extend the regulations to systems serving less than 10,000 persons. Using ICR data and
associated research, EPA expects to propose the Stage 2 DBPR and Long-Term 2 ESWTR in
late 2000, with promulgation scheduled for May 2002.
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IESWTR
This chapter provides technical guidance for addressing many of the issues associated with
meeting the different objectives of the Stage 1 DBPR and the IESWTR. Achieving
simultaneous compliance for both rules may have significant impacts on many systems. In a
few cases, treatment process changes to achieve compliance with one of the regulations may
impair a system's ability to meet the requirements of the other regulation unless other changes
are made. Conversely, compliance with one regulation may enhance a system's ability to meet
the requirements of the second regulation. This chapter highlights many of these potential
conflicts between the Stage 1 DBPR and the IESWTR and discusses how compliance can be
achieved concurrently.
This chapter focuses on three key regulatory components: profiling and benchmarking,
inactivation requirements for non-profiling water systems, and enhanced coagulation
considerations relating to turbidity.
3.2 DBPR versus IESWTR Microbial Profiling/
Benchmarking
The IESWTR requires Subpart H1 systems serving 10,000 or more people to develop a
disinfection profile (a compilation of daily Giardia lamblia and/or virus log inactivations over a
period of a year or more) if the average concentration of TTHMs or HAAs in the distribution
system is within 80 percent of the Stage 1 DBPR requirements in the 12 months prior to rule
promulgation. According to this standard, applicable PWSs must develop a disinfection profile
if either of the following conditions exist:
• The TTHM annual average, based on quarterly samples, is 0.064mg/Lor
• The HAAS annual average, based on quarterly samples, is 0.048 mg/L.
The threshold value of 80 percent of the new MCLs was chosen to identify systems that may
have to make significant disinfectant changes to comply with the new MCLs. This excludes
systems that experience minor variations in DBF levels due to factors such as seasonal changes
in source water quality or water demand. The goal of the IESWTR profiling requirement is to
identify a "benchmark" of the existing disinfection level being achieved by the targeted system.
The disinfection benchmark is the lowest monthly average value (for systems with one year of
profiling data) or average of lowest monthly average values (for systems with more than one
year of profiling data) of the monthly logs of Giardia lamblia inactivation in each year of
profiling data (USEPA, 1998b). The IESWTR requires States to review disinfection profiles
when conducting sanitary surveys of their PWSs. If a PWS decides to make a significant
change in its disinfection practices, the system will need to consult with the State before
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implementing the change. This is especially important if the PWS is also required to develop a
disinfection profile since it needs to ensure that the disinfection reached with the new process is
not less than the benchmark level. Significant changes to a disinfection process may include
the following:
• Moving the point of disinfection application (e.g., from raw water inlet point to post-
sedimentation point)
• Changing the type of disinfectant used (e.g., from chlorine to ozone)
• Changing the disinfection process (e.g., changing the contact basin geometry or increasing the
pH prior to disinfection by greater than one unit (chlorine only))
• Making any other change designated as significant by the State (e.g., changing the raw water
source).
Supporting materials for a State consultation include a description of the proposed change, the
disinfection profile, and an analysis of how the proposed change will affect the current
disinfection benchmark. For additional information on disinfection profiling and benchmarking,
refer to EPA's Disinfection Profiling and Benchmarking Guidance Manual (1999a).
Several issues are associated with the significant changes to a disinfection process identified
above. These issues affect a PWS's ability to achieve compliance with the Stage 1 DBPR and
the profiling requirements of the IESWTR. The following sections highlight and present
recommendations for addressing some of these issues. This discussion also includes
information on how to use water temperature measurement as a tool to reduce DBF formation.
3.2.1 Moving the Point of Disinfectant Application
3.2.1.1 Issues
Public water systems with a conventional treatment plant might consider moving the
application point for their disinfectant downstream to reduce the concentration of DBF
precursors in contact with the disinfectant. Raw water can include DBF precursors in both
dissolved and particulate forms. In conventional treatment, dissolved precursors must be
converted to particulate form during coagulation for subsequent removal during settling and
filtering. Depending on the plant, THM formation potential can be decreased by up to
50 percent, as a result of conventional coagulation and settling due to the removal of
precursors. This indicates the importance of moving the point of chlorine application after
coagulation and settling (and even filtration) in order to control DBF formation (Singer and
Chang, 1989).
1 Subpart H Systems are public water systems that use surface water or ground water under the direct influence of surface water, in
whole or in part.
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Moving the point of chlorination from pre-rapid mixing to post-rapid mixing may be beneficial
in reducing TOX. Solarik et al. (1997) claimed that moving the point of chlorination from pre-
to post-rapid mixing was beneficial in six out of 11 waters tested with varying TOX reductions
by 1 to 40 percent.
Plants that use conventional water treatment and disinfect raw water prior to filtration
generally have adequate contact time to achieve the IESWTR disinfection requirements. When
moving the point of disinfection downstream in the treatment process, a PWS must consider
the reduced contact time available and the maximum residual concentration that can be
maintained under the provisions of the Stage 1 DBPR. Disinfection compliance is measured by
CT values (i.e., the residual disinfectant concentration multiplied by the contact time).
Increasing CT (and thus inactivation) can be achieved by raising the residual disinfectant
concentration through a disinfection zone to compensate for the reduced contact time.
Moreover, higher disinfectant doses for the same water disinfectant demand will result in
higher residual concentrations, which can cause greater formation of DBFs. However, raising
the residual disinfectant concentration has to be within the limits of the MRDL and CT credit is
not allowed for chlorine residual levels above 3.0 mg/L.
In addition to evaluating residual disinfectant concentrations, the hydraulic conditions of the
downstream processes must be examined to determine if adequate contact time is available. If
the disinfectant application point is moved downstream of clarification, filtration units and
piping will generally have favorable hydraulic characteristics for contact time, but clearwells, if
not properly baffled, might exhibit hydraulic short-circuiting. Therefore, if clearwell contact is
needed to maintain disinfection compliance, the clearwells may need to be baffled to eliminate
short-circuiting and to achieve adequate contact time. Similarly, the use of storage tanks for
contact time might be complicated by fluctuating storage volumes. The amount of contact
time achieved is to be based on worst-case conditions, generally considered to be when water
in the storage tank is at its lowest level or when storage is bypassed altogether (i.e., during high
demand periods).
3.2.1.2 Recommendations
If a PWS opts to move its disinfection point as a control strategy for meeting the Stage 1
DBPR, the following strategies can be implemented to aid the system in maintaining its
benchmark for microbial protection and in meeting the requirements of the IESWTR:
• Evaluate the CT that may be achieved downstream of the new application point to ensure that
the benchmark CT can be maintained. The evaluation should include a review of temporal
changes to understand seasonal impacts on CT as a result of moving the point of disinfection
(e.g., during cold weather when higher CT values are needed or during warm weather when
the pH of the water drops as a result of runoff). Increased CT can be gained by raising the
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residual concentration through the disinfection zone. However, appropriate disinfectant
residual concentrations must be determined that will result in an acceptable level of DBF
formation and meet the MRDL requirements of the Stage 1 DBPR.
• Examine hydraulic conditions so as to maximize contact time, which will decrease the required
disinfectant residual concentration. If disinfection is moved downstream of clarification,
contact time can be achieved in filters, piping, and clearwell storage tanks. However,
clearwells may have to be modified (e.g., baffling and/or improved inlet and outlet structures
added) to improve their hydraulic performance. Constructing additional storage or dedicated
disinfection contact basins can allow the system to gain additional contact time.
• Evaluate the operational impacts on coagulation, filter fouling, algal growth, oxidation of iron
and manganese, control of tastes and odors, and other issues. Systems may not be able to
completely eliminate pre-disinfection but may be able to reduce levels or use alternative
oxidants. This is discussed in greater detail in the Alternative Disinfectants and Oxidants
Guidance Manual (USEPA, 1999b) and the Guidance Manual for Enhanced Coagulation
andPrecipitative Softening (USEPA, 1999g). It is important to note that the oxidation of iron
and manganese can be accomplished without maintaining a disinfectant residual (or even
maintaining a minimum residual), and DBFs will not always form to appreciable levels in the
absence of a disinfectant residual.
3.2.2 Changing the Type of Disinfectant(s) Used
3.2.2.1 Issues
The formation of DBFs and the reactions between the different disinfectants and the precursors
present in water are complex. A comprehensive discussion of the factors dictating the
formation of DBFs by the various disinfectants can be found in EPA's Alternative
Disinfectants and Oxidants Guidance Manual (1999b). In general, halogenated organic
byproducts are formed when NOM reacts with free chlorine or free bromine present in the
water. Free bromine results from the oxidation of bromide ion in the source water by chlorine,
chlorine dioxide, or ozone. The factors affecting the formation of both halogenated and
brominated DBFs include the:
1. Type and concentration of natural organic matter present
2. Disinfectant type and dosage
3. Contact time
4. Bromide ion concentration
5. pH
6. Temperature
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7. Mixing conditions of the water and disinfectant.
Nonhalogenated DBFs can also form when strong oxidants react with various compounds
found in the water. Ozone can oxidize organics to form aldehydes, aldo- and keto-acids,
organic acids, and brominated organics in the presence of bromide ion (Singer, 1992). Many
of these byproducts are simple organic compounds that are more available as a substrate to
microorganisms and appear as biodegradable dissolved organic carbon (BDOC) and assimilable
organic carbon (AOC) in the treated water. AOC, or the fraction that is assimilated by specific
strains of heterotrophic organisms, namely Pseudomonas fluorescens and Spirilum NOX,
contributes to the growth of biofilms in the distribution system, while BDOC is defined as the
carbon in dissolved organic compounds that are biodegradable by microorganisms (e.g.,
carboxylic acids and carbohydrates). The presence of AOC or BDOC creates a water quality
issue, as it may lead to the presence of opportunistic pathogens in drinking water. In addition,
chlorine dioxide forms the inorganic DBFs chlorite ion and chlorate ion upon oxidation of
compounds in water.
EPA and the Association of Metropolitan Water Agencies funded a two-year study of 35 water
treatment facilities to evaluate DBF production. Among four of the facilities, 11 alternative
disinfection strategies were investigated to evaluate the difference in DBF production from the
plants' previous disinfection strategies (or base disinfection conditions). Three reports
(Metropolitan and Montgomery, 1989; Jacangelo et al., 1989; USEPA, 1992a) analyzed and
documented different aspects of the study.
Table 3-1 presents the ten potential strategies that may be used for primary and secondary
disinfection. Table 3-2 lists the changes in DBF production observed in the four plants after
new disinfection strategies were implemented.
Table 3-1. Strategies for Primary and Secondary Disinfectants
Base Disinfection Condition Modified Disinfection Practice
Chlorine/Chlorine Chlorine/Chloramine
Chlorine/Chlorine Chloramine/Chloramine
Chlorine/Chlorine Chlorine Dioxide/Chloramine
Chlorine/Chlorine Ozone/Chlorine
Chlorine/Chlorine Ozone/Chloramine
Chlorine/Chlorine Chlorine Dioxide/Chlorine
Chlorine/Chloramine Ozone/Chloramine
Chlorine/Chloramine Chlorine Dioxide/Chloramine
Chloramine/Chloramine Ozone/Chloramine
Ozone/Chlorine Ozone/Chloramine
Note: Disinfectants are listed as primary disinfectant/secondary disinfectant
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As can be seen from Table 3-2, changing primary and secondary disinfectants might not lead to
reductions in DBF levels for all systems, the table does demonstrate how changes in
disinfection practices at several different Utilities resulted in a reduction (or no change) in
TTHM and HAAs formation. These results may differ depending on the water quality.
In general, the EPA study found that by carefully selecting the primary and secondary
disinfectant based on source water quality and by avoiding long contact times and high dosages
of DBF-forming disinfectants, the total DBF formation declined. However, it is important to
understand that when changes are made in the disinfectants used, each disinfectant has different
pathogen inactivation mechanisms, resulting in variations in inactivation effectiveness. As a
result, the CT requirements for the various disinfectants can be radically different. For
instance, the CT required for chloramines to achieve 1-log inactivation ofGiardia is about 18
times greater than the CT required for free chlorine. Therefore, if a PWS is considering
changing from chlorine to chloramines, CT will have to be achieved either by raising the
residual concentration in the disinfection zone or by increasing the contact time. As described
in the previous section, the MRDLs included in the Stage 1 DBPR can limit the levels to which
the disinfectant residual can be raised.
If a PWS evaluates its current disinfection strategy and decides to modify the type of
disinfectant used, the evaluation should ensure that the disinfection requirements of the SWTR
and IESWTR are also met.
Selection of the most appropriate disinfectant requires balance between the following three key
factors:
• Meeting the disinfection requirements
• Avoiding the production of excessive levels of DBFs
• Balancing the formation of DBFs from different disinfectants
• Maintaining a disinfectant residual in the distribution system without increasing DBF
formation.
If a new disinfectant is evaluated, DBF precursors, primarily in the form of TOC and bromide ion
concentration, should be examined along with the required log inactivation required to meet the
disinfection requirements. High levels of TOC and bromide ion concentrations indicate a high potential
for DBF formation.
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Table 3-2. Impacts of Disinfection Practice on DBP Formation
Change in DBP Formation
Changes in Disinfection
Practices
(Primary/Secondary)
Disinfection By-Product
Total Trihalomethanes
Haloacetic Acids
Haloacetonitriles
Haloketones
Aldehydes
Chloropicrin
Cyanogen Chloride
Changes in Disinfection
Practices
(Primary/Secondary)
Disinfection By-Product
Total Trihalomethanes
Haloacetic Acids
Haloacetonitriles
Haloketones
Aldehydes
Chloropicrin
Cyanogen Chloride
Notes: Results based on full-scale evaluation at Utilities #19 and #25 and on pilot scale evaluations at Utilities #7 and #36. Free chlorine contact time was 4 hours for Utility #7 during use
of chlorine/chloramine strategy. Systems must demonstrate efficacy of chloramines as a primary disinfectant if they are to be used as such.
Source: USEPA, 1992a; Jacangelo et al., 1989; Metropolitan and Montgomery, 1989.
Chlorine/Chlorine
To
Chlorine/Chloramines
Utility #7
Decrease
Decrease
Decrease
Decrease
Not analyzed
No change
No change
Ozone/Chlorine
To
Ozone/Chloramines
Utility #36
Decrease
: Decrease
Decrease
: Decrease
Decrease
: Increase
Increase
Chlorine/Chlorine
To
Ozone/Chlorine
Utility #19
Decrease
Decrease
Decrease
No change
Not analyzed
Increase
Not analyzed
Utility #36
No change
No change
No change
Increase
Increase
Increase
No change
Change in DBP
Chlorine/Chloramines ; Chlorine/Chlorine
to
to
Ozone/Chloramines j Chloramines/Chloramines
Utility #7
Decrease
Decrease
Decrease
Increase
Not analyzed
Decrease
No change
Formation
Chloramines/Chloramines
To
Ozone/Chloramines
Utility #25
Decrease
Decrease
No change
No change
Increase
Increase
Increase
Utility #36
No change
No change
No change
Increase
Increase
Increase
Increase
Utility #7
Decrease
Decrease
: Decrease
Decrease
: Not analyzed
Decrease
: No change
Utility #36
Decrease
Decrease
Decrease
Decrease
Decrease
No change
Increase
Chlorine/Chlorine
To
Ozone/Chloramines
Utility #36
Decrease
Decrease
Decrease
Decrease
Increase
Increase
Increase
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If ozone is selected as the primary disinfectant, the potential for biological regrowth in the
distribution system should also be evaluated closely. As stated previously, ozone can change
the nature of the TOC present in the water and increase the biodegradable portions of the TOC
(measured as BDOC and AOC). These two measurements evaluate the portion of the TOC in
the water that can be utilized readily as food by microorganisms. Elevated BDOC and AOC
levels can result in significant biological regrowth in a distribution system, and, hence,
provisions must be made to minimize biological activity in the distribution system or remove
the AOC during treatment. AOC reduction is often accomplished by the use of biologically
active filtration or carbon filtration after ozonation.
In addition, if the primary disinfectant is changed, the use of an alternative oxidant in the raw
water may be required. Raw water oxidants have uses other than disinfection. They are often
used to achieve the following:
• Control nuisance Asiatic clams and zebra mussel
• Oxidize iron and manganese
• Remove tastes and odors
• Improve coagulation and filtration efficiency
• Prevent algal growth in the treatment plant prior to disinfection.
EPA's Alternative Disinfectants and Oxidants Guidance Manual (1999b) includes a discussion
of many alternative oxidants for raw water and their effectiveness for accomplishing treatment
objectives other than disinfection.
If a new secondary disinfectant is contemplated, the major considerations for implementation
are DBF formation potential and distribution system retention time. Free chlorine continues to
form DBFs until precursors are exhausted or the chlorine residual is diminished. Distribution
systems with long retention times can cause elevated DBF levels. Long retention times with
chlorine dioxide residuals can generate elevated chlorite ion and chlorate ion levels.
Chloramines, which are weaker disinfectants, do not form appreciable DBFs and are often used
as secondary disinfectants to control DBF formation when residence time is long.
3.2.2.2 Recommendations
If a PWS is considering a change in disinfectants, it should consider the following strategies
during evaluation and implementation of the change:
• For facilities that add chlorine early in the treatment process (e.g., to the raw water) and form
excessive levels of DBFs, strong consideration should be given to eliminating or reducing this
practice and focusing on the addition of free chlorine after TOC reduction by coagulation. If a
predisinfectant or oxidant is required to meet CT requirements or accomplish other treatment
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requirements, consideration should be given to an alternative disinfectant such as chlorine
dioxide or ozone, both of which can achieve disinfection and provide chemical oxidation for
taste and odor and inorganic pollutant control.
• If a change in disinfectant strategy is desired, the new strategy should be bench-tested and
piloted. Table 3-3 presents a summary of the treatment properties of eight different
disinfectants to help assist PWSs in the selection of new primary and/or secondary
disinfectants. The information in Table 3-3 serves as a basis for selecting the most appropriate
disinfectant and addresses many of the key technical and regulatory issues that must be
assessed. The characterizations in Table 3-3 are based on typical disinfectant applications.
Thus, even though chlorine is considered to be prone to THM formation, the table does not
address the degree or amount of THMs produced. Similarity, more than 2-log inactivation
could be achievable for some disinfectants, but the high dose required may not be a reasonable.
Detailed information on the properties and use of alternative disinfectants is provided in EPA's
Alternative Disinfectants and Oxidants Guidance Manual (1999b).
• A disinfection strategy that may become more attractive to many PWSs involves the use of
chlorine dioxide as a primary disinfectant (within allowable concentrations) and chloramines as
a secondary disinfectant. Chlorine dioxide provides rapid inactivation of pathogens and some
preliminary oxidation benefits without the formation of halogenated DBFs. However, chlorine
dioxide dosage is limited by the formation of the inorganic DBFs chlorite ion and chlorate ion.
Under the Stage 1 DBPR, the use of chlorine dioxide requires additional monitoring to address
the acute risk associated with the use of chlorine dioxide. Chlorine dioxide must be measured
daily at the entrance to the distribution system. Chlorite must be monitored in the distribution
system three times per month. Chloramines serve to maintain a long-term distribution system
residual without forming high levels of DBFs (refer to EPA's Alternative Disinfectants and
Oxidants Guidance Manual, 1999b).
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Table 3-3. Summary of Disinfectant Properties
Chlorine
y
s
y
n
y
y
n
y
n
n
n
y
y
y
1
y
y
2.0 log
Meet Crypto - <2.0 log
Meet Crypto - >2.0 log
Meet Virus - <2.0 log
Meet Virus - >2.0 log
Secondary disinfectant
Operator skill (1=low; 5=high)
Applicable to large utilities
Applicable to small utilities
y = yes, n = no, s = sometimes
1 Not approved for compliance with SWTR inactivation requirements
3.2.3 Temperature Effects on Chlorine and DBF Formation
3.2.3.1 Issues
In general, as temperature increases, a greater potential for DBF formation normally results. This
occurs as a result of chlorine being more effective at higher temperatures, resulting in faster
chemical reactions. Also, at higher temperatures chlorine is a more effective disinfectant because
of the disinfection kinetics. Warm surface waters also typically support more organic growth and
thus have elevated levels of NOM. Conversely, the increase in chlorine effectiveness at higher
temperatures can be beneficial to the disinfection process since less chlorine or less contact time is
required to provide adequate log inactivations of Giardia and viruses. This characteristic allows
the reduction of chlorine dosage or contact time in warm weather without compromising
microbial protection, which can assist in limiting DBF formation.
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3.2.3.2 Recommendations
If elevated levels of DBFs are formed in a warm water source, PWSs may employ the
following strategies:
• In all cases, PWSs should closely monitor DBF formation at higher water temperatures to
ensure that the MCLs are not exceeded. If increased monitoring shows that DBF formation is
not a concern at higher temperatures, then monitoring at regular intervals should suffice.
• Since chlorine effectiveness increases at higher temperatures, PWSs should consider reducing
the disinfectant dose in warm weather to reduce the formation of DBFs. However, the
disinfectant dosage may not be lowered below the point of compliance with all other rules, such
as what is dictated by the SWTR (USEPA, 1989a).
• If DBF production cannot be controlled by the reduction of disinfectant dosage in warm water,
PWSs should consider other modifications to the disinfection scheme such as moving the point
of disinfection application or the use of an alternative disinfectant for primary or secondary
disinfection. Systems may be able to use these strategies on a seasonal basis.
3.2.4 pH Effects on Chlorine
3.2.4.1 Issues
As discussed in Chapter 2, the pathogen inactivation of free chlorine is dependent on
disinfection pH. Therefore, the pH maintained in the treatment process can impact the level of
inactivation achieved. However, pH changes also can have wide ranging impacts on treatment
chemistry and should be evaluated carefully. Typical impacts of pH changes can include
changes in coagulation chemistry, floe settling characteristics, sludge dewatering, and corrosion
potential.
Since the CT required for disinfection is lower at reduced pH levels, the required chlorine dose
is lower, thus reducing the amount of free chlorine available for DBF formation. As a result,
DBF formation may be reduced as pH is lowered (which may not be true for specific DBFs
such as HAAs). The formation of some DBFs, such as HAAs, increases at lower pH levels,
however, the low CT required at the lower pH may be partially offset by this increase.
3.2.4.2 Recommendations
pH adjustments may be made to stabilize finished water, aid inorganic constituent removal, and
enhance coagulation to achieve TOC removal. Strategies for maintaining adequate disinfection
levels include:
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• Maintaining a low pH after chlorine application and during the required disinfection contact
time. Since chlorine is more effective at lower pHs, the benchmark CT can be achieved with a
lower chlorine dosage, thus generally reducing the formation of DBFs (although some may be
increased). This strategy may result in corrosion impacts at locations with depressed pH
levels, such as in clearwells and piping, unless the system takes adequate precautions.
• Carefully evaluating pH adjustment prior to implementation. Variation of pH levels can affect
treatment chemistry and result in impacts to coagulation, settling, and sludge dewatering.
Variations in pH can also create problems with the solubility of inorganic constituents and
result in impacts such as increased iron and manganese levels in the treated water or the
reformation of insoluble calcium carbonate particles in lime softened waters. Both of these
effects are aesthetic issues and can result in increased finished water turbidity and precipitation
in piping.
3.2.5 Case Study
Case Study No. 1 presents an example of how the DBF MCLs were met after changing the
disinfectant and manipulating pH levels and contact times while also achieving the required
pathogen inactivation.
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Case Study No. 1: Simultaneous Compliance between DBPR and SWTR by
Changing the Disinfectant and Manipulating pH Levels and Contact Time
Background
The following case study describes how Plant A could simultaneously comply with the DBPR, the
IESWTR, and the SWTR. The design parameters (including treatment processes), and raw and finished
water quality of Plant A (serving 25,000) people are provided below.
Source Type:
Flow Rate:
Treatment System:
Raw Water Quality:
Surface Water
Average Daily Flow - 2 mgd
Design Flow - 4 mgd
Rapid Mix
Coagulation/Flocculation (alum, 20 mg/L; theoretical detention time - 1 hour)
Sedimentation (theoretical detention time - 3 hours)
Filtration (No. of units - 5, single media, loading rate 2 gpm/ft2)
Clearwell (theoretical detention time - 30 min)
Disinfection points of application
- raw water inlet (maximum chlorine dose - 5.0 mg/L)
- clearwell water inlet (maximum chlorine dose - 5.0 mg/L)
TOC-3.0 mg/L
pH - 7.8
Alkalinity - 100 420 mg/L as CaCO3
Turbidity - 20 to 110NTU
Finished Water Quality: TOC - 1.8 (40 percent removal)
pH-7.1
Residual Chlorine - 2 mg/L
Alkalinity - 70 to 95 mg/L as CaCO3
Turbidity-0.1NTU
Distribution System
Water Quality:
TTHM - 0.095 mg/L (Running Annual Average)*
F£AA5 - 0.050 mg/L (Running Annual Average)*
* profiling required
Simultaneous Compliance Issues
Stage 1 DBPR. The Stage 1 DBPR requires a TOC removal of 25 percent (based on influent TOC and
alkalinity conditions). The TOC removal achieved was 40 percent, which is greater than the minimum
percent removal of TOC required. TTHM level in the distribution system is required to be below the
specified MCL of 80 |o,g/L. The residual chlorine is required to be below the specified MRDL of 4.0
mg/L.
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SWTR. The SWTR requires Plant A to achieve 3-log inactivation/removal of Giardia and a 4-log
inactivation/removal of viruses. The State credits this plant with a 2.5-log removal for Giardia for
conventional filtration. Plant A must maintain a CT of 25 mg-min/L to achieve the additional 0.5-log
inactivation of Giardia with chlorine at 10°C with pH 7.1. The CT value of 25 mg-min/L corresponds
to pH 7.5 (i.e., the conservative approximation method is used to determine CT value rather than the
linear interpolation method). Disinfection profiling and benchmarking are required and any significant
change in the treatment must be preceded by consultation with the State.
Potential Conflicts. Reducing chlorine dose levels to achieve the desired DBP levels and MRDL levels
may jeopardize meeting the required CT levels. Lower free chlorine levels make it difficult to meet CT
requirements. Enhanced coagulation will require the coagulant dosage to be increased or the coagulant
changed (e.g., ferric chloride) resulting in a lower pH level than that of the raw water. Excess
coagulant and pH adjustment might affect disinfectant efficacy. Additionally, problems with biofouling
of distribution network may occur causing the TTHM MCL to be exceeded. Moreover, the system
making significant changes in disinfection practices may choose under State guidance to develop an
alternative disinfection benchmark and must consult with the State prior to making any significant
modifications.
Steps to Resolve Conflicts and Results Achieved
Plant A makes three modifications to its treatment practices so that it may simultaneously comply with
the SWTR and the Stage 1 DBPR.
In the first modification, the plant switches to chloramine as the secondary disinfectant during the
summer months when the water is the warmest and biological growth is the highest. Because
chloramines do not react with NOM to form significant amounts of TTHMs, the plant is able to comply
with the Stage 1 DBPR. The plant is also able to meet the 0.5-log Giardia inactivation CT requirement
for chlorine at the higher temperature using a dose of 3.5 mg/L. The Stage 1 DBPR MRDL for
chloramine of 4.0 mg/L is also not exceeded.
In the second modification, the plant operator reduces the pH level by adding an acid and employing
enhanced coagulation. It should be noted that the system already meets the TOC removal requirements.
The plant operators employ enhanced coagulation to further reduce DBP precursors and save money as
a result of reduced chlorine demand. Because chlorine is more effective as a disinfectant at lower pH
levels, the system achieves the required inactivation. The lower chlorine dose results in reduced DBP
levels and the system is in compliance with both the DBPR and the SWTR. However, low pH and
alkalinity (due to enhanced coagulant dosage), together with an increase in the chloride concentration (if
ferric chloride is used) could result in a potential LCR compliance problem.
In the third modification, Plant A moved the point of primary disinfectant application to the filter
discharge, and improved the baffle conditions in the clearwell to increase the disinfectant contact time
to attain the required CT. The plant is able to meet the required CT of 25 using a free chlorine residual
of 3.0 mg/L. Also, since disinfection takes place after the NOM is removed, the TTHM level is
considerably reduced to below the MCL.
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3.3 DBF MCLs and Inactivation Requirements for Non-
Profiling Water Systems
As discussed previously, PWSs with DBF levels below 0.064 mg/L for TTHM and 0.048 mg/L
for HAAS, based on annual averages, are not expected to make significant modifications to
their disinfection process to comply with the Stage 1 DBPR. Therefore, the Stage 1 DBPR
does not require disinfection profiles for these water systems. As a result, only a few potential
challenges exist in complying with the Stage 1 DBPR and maintaining microbial protection.
3.3.1 Issues
The Stage 1 DBPR establishes MRDLs for the various disinfectants. PWSs cannot exceed
these concentration levels in the water distribution system based on a running average of the
last 12 monthly averages. This running annual average is computed every 3 months. While not
experiencing significant DBF formation, some systems may have large distribution systems
with long residence times. Systems that use free chlorine as a residual disinfectant may
experience significant residual concentration decay in areas of the distribution system with long
detention times due to such factors as corrosion and regrowth. As a result, some systems may
have historically maintained disinfectant residual concentrations at very high levels in the
distribution system to achieve the required minimum residual concentration levels at all
locations in the system. It is possible that these high concentrations can exceed the MRDLs.
3.3.2 Recommendations
To reduce the amount of disinfectant needed to maintain the minimum required levels in all
areas of the distribution system, the utility should consider the following activities:
• Implementation of an aggressive flushing program in the long-detention time areas of the
system. Flushing can purge the system of "old" water as well as scour the piping to remove
biogrowth.
• Evaluating distribution system corrosion potential to ensure that the corrosion of ferrous
surfaces is not causing elevated disinfectant demand. If corrosion appears to be a problem, a
corrosion control plan may be required.
• Evaluating the use of booster disinfection at key locations in the distribution system rather than
maintaining high concentration levels in the finished water.
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3.4 Stage 1 DBPR Enhanced Coagulation and IESWTR
Turbidity Requirements
Subpart H PWSs using conventional treatment (i.e., coagulation, sedimentation, and filtration)
or precipative softening to meet the MCL and MRDL requirements of the Stage 1 DBPR must
also comply with the TOC removal requirements listed in the rule. Typically, enhanced
coagulation or enhanced softening is used to meet TOC requirements in these instances.
Enhanced coagulation includes the addition of higher levels of a coagulant to achieve TOC
removal and may include lowering of the coagulation pH. Enhanced coagulation has shown to
be an effective strategy for reduction of DBF precursors by reducing a portion of the NOM
prior to disinfectant addition for many systems (Krasner and Amy, 1995). However, the effect
of enhanced coagulation on pathogen removal/inactivation has not been widely investigated.
Recent work indicates that moving from conventional to enhanced coagulation tends to
improve particulate and microbial removal.
The remainder of this section defines the issues related to enhanced coagulation and how these
issues relate to particulate and microbial control. Following this introduction, specific impacts
and conflicts that might result from implementation of enhanced coagulation are presented.
3.4.1 DBP Control
One of the best methods to minimize DBP formation is to remove DBP precursors (e.g.,
natural organic material) prior to adding a disinfectant. As noted above, EPA has determined
that "enhanced coagulation" is an effective technique for DBP precursor removal.
Chemical coagulation with aluminum (i.e., alum) and iron (i.e., ferric) salts is most often
utilized for turbidity removal. These two coagulants can also remove certain portions of the
NOM present in water, if dosage and pH conditions are optimized. Typically, enhanced
coagulation can remove the hydrophobic portions of the NOM, which generally consist of the
humic substances found in the water. The hydrophilic portion of the NOM, which are
generally the fulvic substances, is much more difficult to remove by coagulation. Therefore,
the effectiveness of TOC removal by enhanced coagulation is dependent on the relative
portions of hydrophobic and hydrophilic materials present in the water.
For alum, the optimal pH for NOM removal ranges from 5.5 to 6.0, while the optimum pH
range for ferric salts is slightly lower. Ferric salts appear to perform better for TOC removal
for equivalent doses of the metal coagulant than alum in some situations. In addition, the ferric
salts are stronger acids and tend to lower pH more per mass dose of coagulant than alum,
thereby reducing the amount of coagulant required to achieve the optimum pH range.
However, waters with very high alkalinity may require the addition of an acid, while very low
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alkalinity waters may require the addition of a base to reach the optimal NOM coagulation pH
(Singer, 1992)
The NOM removal required under the Stage 1 DBPR is based on the surrogate parameter
TOC. The TOC removal percentages, summarized in Chapter 2, depend on the amount of
TOC and alkalinity present in the raw water. Since the removal of TOC is dependent on the
make-up of the organics present, the character of the NOM present will dictate the amount of
TOC actually removed.
As required under the Stage 1 DBPR, Subpart H systems using conventional treatment must
use enhanced coagulation or enhanced softening to remove TOC unless they meet one of the
following alternative compliance criteria:
• The system's source water or treated water TOC level, is < 2.0 mg/L.
• The system's source water TOC level, prior to any treatment, is < 4.0 mg/L; the
alkalinity is > 60 mg/L; and the TTHM annual average is 0.040 mg/L and the
HAAS annual average is 0.030 mg/L or the system has made an irrevocable
financial commitment to achieve these levels.
• The system's TTHM annual average is 0.040 mg/L and the HAAS annual average
is 0.30 mg/L and the system uses only chlorine for primary disinfection and
maintenance of a disinfectant residual.
• The system practices softening and removes at least 10 mg/L of magnesium
hardness (as CaCOs), except for systems that use ion exchange (applicable for
systems that use enhanced softening only).
• The system has a source water or treated water SUVA 2.0 mg/L-m. If a PWS
can demonstrate that the NOM present has a SUVA of less than this level (which
indicates that the NOM present is primarily hydrophilic), the system does not have
to comply with the TOC removal requirements in the rule.
• The system has lowered the treated water alkalinity to < 60 mg/L as CaCOs
(applicable for systems that use enhanced softening only).
In instances where little TOC can be removed by coagulation, the Stage 1 DBPR allows a
system to comply with the TOC removal requirements by achieving a "point of diminishing
return" (POOR). The PODR is the coagulant dose beyond which less than 0.3 mg/L of TOC is
removed for every additional 10 mg/L alum dosage (or equivalent ferric dose).
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According to some studies (Krasner and Amy, 1995; White et al., 1997; Arora et al., 1997),
many facilities will have a difficult time meeting the TOC removal criteria due to the
characteristics of the NOM present. Based on available research, the difficulty in removing
TOC appears to be particularly applicable to waters low in TOC and high in alkalinity. Jar
tests have shown that waters high in TOC and low in alkalinity had the highest probability of
meeting the TOC removal requirements, while waters low in TOC and high in alkalinity
typically reached the PODR before meeting the criteria (Krasner and Amy, 1995; White et al.,
1997; Arora et al., 1997).
To assist PWSs in achieving optimum coagulation for TOC removal, it may be beneficial to
consider the addition of an acid to reduce the pH prior to adding a coagulant. By doing so, the
optimal pH level for NOM removal can be achieved with a lower quantity of coagulant needed
to meet TOC removal requirements. Since acids are typically more economical than
coagulants, it may be cheaper to use the coagulant only for coagulation purposes and use an
acid for pH reduction. In addition, water with low alkalinity may need to have alkalinity
added, as chemical coagulation and certain acids, such as sulfuric acid and other acids that are
likely to be used to adjust pH in a water treatment design, will consume alkalinity from the
water.
3.4.2 Pathogen Inactivation/Removal
Traditionally, filtration and disinfection have been the mechanisms by which pathogens have
been removed and/or inactivated in potable water. Disinfection has been characterized by the
log inactivation achieved under specific disinfection conditions. Research has shown that
sedimentation alone following coagulation may provide only small reductions of viruses and
moderate (i.e., 20 to 35 percent) removals of bacteria and coliforms (Abbaszadegan et al.,
1997). The removal of microorganisms is primarily due to the adsorption of the microbial
contaminants onto the coagulant, the floe formed in the coagulation process, and through
physical removal during the settling of floes.
Most studies dealing with enhanced coagulation have focused on NOM and/or TOC removal
as outlined above. As a result, little is known of the effect of enhanced coagulation on
pathogen removal. One recent study indicated that the overall average of microbial log
removal under optimized coagulation conditions for viruses, parasites, and bacteria were higher
than the baseline practices with the same coagulant type (Abbaszadegan et al., 1997).
Therefore, it might be expected that enhanced coagulation practices could improve pathogen
removal. This outcome is likely the result of pathogens adsorbing onto larger metal hydroxide
floes which are subsequently removed by sedimentation and filtration.
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3.4.3 Issues and Recommendations for Simultaneous
Compliance
Employing enhanced coagulation and/or other alternative TOC removal technologies should
improve the overall water treatment process, as many DBF precursors will be removed. By
doing so, less disinfectant will be needed for pathogen inactivation as less DBF precursors will
be present to be oxidized (i.e., lower disinfectant demand). Furthermore, enhanced coagulation
should also improve the sedimentation of microbial particles, as the additional coagulant will
provide an opportunity for larger particle growth and more spatial area coverage of settling
floes. As a result, properly implemented enhanced coagulation may improve compliance with
both the Stage 1 DBPR and the IESWTR.
However, there are some specific simultaneous compliance issues with respect to the IESWTR
that result from optimizing TOC removal with enhanced coagulation for Stage 1 DBPR
compliance. Many of these issues and subsequent recommendations are presented in the
following subsections.
3.4.3.1 Enhanced Coagulation and Turbidity Requirements
Issues
As mentioned previously, the IESWTR has new, more restrictive turbidity requirements for
surface water or GWUDI systems that use conventional filtration treatment or direct filtration
and serve 10,000 or more people . The primary purpose of the turbidity requirements is the
improved removal of particulates, especially pathogens. High levels of turbidity exert an
oxidant demand and may prevent inactivation by shielding the pathogens.
The available research suggests that enhanced coagulation generally improves overall filtration
performance by reducing particle loading on the filter media. Enhanced coagulation may
improve the capture of small previously unfilterable particles due to the larger floe formation.
Care should be taken, however, since excess coagulant can form a film on the filter surface or
solubilize/precipitate upon final pH adjustment.
In addition, pH adjustment to acceptable levels (i.e., between pH 6 and 8.5) can also cause
solubility problems with several inorganic contaminants. If pH adjustment is not carefully
planned, systems may experience increased levels of turbidity from iron and manganese
precipitation. Lime softening plants can also cause calcium carbonate to precipitate after pH
adjustment, which will also affect turbidity. However, the rule does allow the acidification of
turbidity samples that will dissolve calcium carbonate which may have formed after pH
adjustment.
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Recommendations
In general, employing enhanced coagulation should assist facilities in meeting the turbidity
requirements set forth in the IESWTR. Meeting the required turbidity levels will improve
disinfection by limiting the effluent water disinfectant demand. It also appears that the turbidity
requirements associated with the IESWTR are achievable for most PWSs, especially if filter-to-
waste is employed for ripening filters (McTigue and Cornwell, 1997).
In cases where facilities do not meet the combined filter effluent turbidity requirements after
backwashing, consideration should be given to a filter-to-waste period for the first 30 to 60
minutes after backwashing individual filters. If filter-to-waste cannot be provided, post-
backwash turbidity spikes can also be controlled by reducing the start-up filtration rate or by
adding coagulant polymer or a coagulant aid to the backwash water to facilitate ripening.
To ensure that the proper coagulant dose is applied and to minimize overdosing, extensive
bench and/or pilot studies should be performed to determine the coagulant dose required for
enhanced coagulation under various operating conditions. The coagulant feed should then be
flow paced to ensure that the proper coagulant concentration is provided through all flow
regimes. Other strategies for maintaining optimal coagulant dosages include:
• Careful evaluation of pH adjustment prior to implementation. Variation of pH levels can affect
treatment chemistry and the effectiveness of chlorine and result in impacts to settling and
sludge dewatering. Variations in pH can also create problems with the solubility of inorganic
constituents and result in impacts, such as increased iron and manganese levels or the
recalcification of lime softened waters, resulting in increased turbidity.
• Maximizing turbidity removal by continually seeking to optimize the treatment process (refer
to EPA's Guidance Manual for Compliance with the Interim Enhanced Surface Water
Treatment Rule: Turbidity Provisions (1999e)).
• Using acid to lower pH into the optimum range for TOC removal in lieu of overdosing
coagulant, which can be more expensive and impact turbidity, particle removal, and sludge
handling.
• Using jar tests regularly to maintain proper coagulant dose for enhanced coagulation.
• If applicable, switching coagulants. In some cases, ferric salts have proven to be more
effective than aluminum salts in the removal of microorganisms by enhanced coagulation.
• Using filter aids/polymers during coagulation. Synthetic organic polymers can be used in
addition to or in place of alum and ferric salts based on the results of bench pilot tests.
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Strategies are discussed in greater detail in the Guidance Manual for Enhanced Coagulation and
Precipitative Softening (USEPA, 1999g). This manual also discusses operational problems that may
occur.
3.4.4 Case Study
Case Study No. 2 presents an example of how compliance issues for the TOC removal
requirements of the DBPR were met using enhanced coagulation while also achieving the
turbidity removal requirements of the IESWTR.
Case Study No. 2: Simultaneous Compliance between TOC Removal and Turbidity
Background
The following case study describes how Plant B could simultaneously comply with the TOC removal
requirements of the DBPR and the turbidity removal requirements of the IESWTR. The design
parameters (including treatment processes), and raw and finished water quality of Plant B (serving
700,000) people are provided below.
Source Type:
Flow Rate:
Treatment System:
Raw Water Quality:
Surface Water
Average Daily Flow - 50 mgd
Design Flow - 100 mgd
Rapid Mix
Coagulation/Flocculation (alum, 20 mg/L)
Sedimentation (theoretical detention time - 3 hours)
Filtration (No. of units - 50, single media, loading rate 2 gpm/ft2)
Clearwell (theoretical detention time - 30 min)
Disinfection (maximum chlorine dose - 5.0 mg/L, point of application -
raw water inlet)
TOC - 7.0 mg/L
pH - 7.3
Alkalinity - 60 to 80 mg/L as CaCO3
Turbidity - 45 to 110NTU
Finished Water Quality: TOC - 4.9 (30 percent removal)
pH - 6.5
Alkalinity - 40 to 60 mg/L as CaCO3
Turbidity - 0.2 NTU
Residual Chlorine - 2.0 mg/L
Distribution System
Water Quality:
* profiling required
TTHM - 0.090 mg/L (Running Annual Average)*
HAA5 - 0.045 mg/L (Running Annual Average)*
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Simultaneous Compliance Issues
IESWTR. The IESWTR requires the combined filtered water effluent turbidity to be less than 0.3
NTU in at least 95 percent of the measurements taken each month, with measurements being taken at
continuously at 4-hour intervals, and less than 1 NTU at all times. Disinfection profiling and
benchmarking are required and any significant change in the treatment must be preceded by
consultation with the State.
Stage 1 DBPR. The Stage 1 DBPR requires a TOC removal of 35 percent (based on influent TOC and
alkalinity conditions). The TTHM in the finished water is required to be below the specified MCL of
80 ng/L and residual chlorine is required to be below the specified MRDL of 4.0 mg/L Enhanced
coagulation, which requires the coagulant dosage to be increased, will remove DBP precursors and limit
the formation of DBFs to within the MCLs.
Potential Conflicts. Increased coagulant dosage and pH adjustment after coagulation may cause an
increase in turbidity. Excess coagulant can form a film on the filter surface, and which may solubilize
and then precipitate upon post-filtration final pH adjustment.
Steps to Resolve Conflicts and Results Achieved
To comply with Stage 1 DBPR requirements for TOC, Plant B employed enhanced coagulation. The
coagulant dosage was increased to 30 mg/L which helped achieve a 40 percent reduction in TOC from
7.0 mg/L to 4.2 mg/L but resulted in a decrease in pH to 6.5. A pH adjustment was necessary after
treatment to raise the finished water pH to its previous level at 7.3. Due to the additional removal of
DBP precursors, a lower chlorine dose of 4.0 mg/L was sufficient to meet chlorine demand and provide
a chlorine residual of 2.0 mg/L. The TTHM in the finished water was reduced to 60 |o,g/L which is
below the MCL.
To meet the turbidity requirements for the IESWTR, the operators ensured that the coagulant dosage
applied for enhanced coagulation was proper and hence, minimized overdosing. Bench and pilot studies
were performed initially to determine the appropriate dose, and the dose was checked regularly through
additional jar tests. Operators also ensured that the coagulant feed is flow paced and proper coagulant
concentration is provided at all times.
3.4.4.1 Enhanced Coagulation and Cryptosporidium Removal
Issues
As stated previously, most research on enhanced coagulation reports that particulate removal is
usually improved under enhanced coagulation conditions as compared to conventional
coagulation. However, some research has indicated that overdosing coagulant chemicals to
maximize TOC removal may reduce Cryptosporidium removal (Oilier et al, 1997). As a result,
until further research either confirms or contradicts the results of the Oilier study, PWSs should
closely monitor turbidity to ensure particle removal is maintained throughout enhanced
coagulation practices. Particle counting can also be used to monitor the size range of the
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particles passing through the filter to ensure that particles in the Cryptosporidium size range
are removed.
Recommendations
Some strategies available to maintain Cryptosporidium removal during enhanced coagulation
include the following:
• Maximize turbidity removal by continually seeking to optimize the treatment process.
• Use acid to lower pH into the optimum range for TOC removal in lieu of overdosing the
coagulant, which can impact turbidity.
• Use jar tests regularly to maintain proper coagulant dose for enhanced coagulation and turbidity
removal.
• Use particle counters to monitor the size of particles passing through the filters to ensure that
Cryptosporidium-sized particles are being removed. Note that particle counting cannot be used
as a surrogate for pathogens but it can provide information on changes in particle size
distribution and removal.
• Particle counters may also detect particle breakthrough well in advance of increased headloss
and be used to optimize the filtration process.
• Employ enhanced coagulation and, if applicable, consider switching to a ferric salt coagulant,
as this has proven to be more effective, in some cases, in the removal of microorganisms.
3.4.4.2 pH and Chlorine Effectiveness
Issues
Due to a variety of factors, the effectiveness of chlorine as a disinfectant is enhanced at lower
pH levels. Thus, the CT values required for Giardia decrease as pH levels decrease (AWWA,
1991). If chlorine is used as a disinfectant, the impact of pH changes resulting from enhanced
coagulation (both pH depression during coagulation and pH adjustment prior to distribution)
should be considered if the adjustment occurs in a chlorine disinfection zone.
The pH of the water being chlorinated has an impact on the formation of halogenated
byproducts (Reckhow and Singer, 1985; Stevens et al., 1989). Since the application of
chlorine dioxide and chloramines introduces free chlorine into water, chlorination byproducts
that may be formed would be influenced by pH. Although many DBFs do not exhibit any
changes relating to water pH, THM formation increases with increasing pH and the formation
of trichloracetic acid, dichloroacentonitrile, and trichloropropanone decreases with increasing
pH. Overall, TOX formation decreases with an increase in pH.
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High pH tends to favor chloroform formation over the formation of trichloracetic acid and
other organic halides (Singer and Chang, 1989). Ozone application to bromide ion-containing
waters at high pH favors the formation of bromate ion, while application at low pH favors the
formation of brominated organic byproducts. Table 3-4 discusses how the pH of water being
chlorinated impacts the formation of halogenated byproducts.
Recommendations
To maintain the effectiveness of chlorine as a disinfectant, the following pH control strategies
are available:
• Keep pH low after chlorine application and during the required contact time. Since chlorine is
more effective at lower pH levels, the required CT can be achieved with a lower chlorine
dosage. The rate of TTHM formation should be reduced, but HAAS levels may not be
reduced.
• Carefully evaluate pH adjustment prior to implementation. Variation of pH levels can affect
treatment chemistry and result in impacts to settling and sludge dewatering in addition to the
effects on chlorine. Variations in pH can also create problems with the solubility of inorganic
constituents and result in impacts such as increased iron and manganese levels or, in the treated
water, the recalcification of lime softened waters resulting in increased turbidity and levels of
copper and lead in the treated water.
Evaluate pH effects on the treatment plant (i.e., pipes, tanks, etc.).
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Table 3-4. Conditions of Formation of DBFs
Byproduct
Total Trihalomethanes
Trichloroacetic Acid
Dichloroacetic Acid
Monochloroacetic Acid
Dibromoacetic Acid
Chloral Hydrate
Chloropicrin
Dichloroacetonitrile
Bromochloroacetonitrile
Dibromoacetonitrile
Chlorination at pH 5.0
Lower formation
Similar formation
Similar formation -
perhaps slightly higher at
pH7.0
At concentrations <5
ng/L, trends not
discernible
At concentrations <1
|ig/L, trends not
discernible
Similar formation
At concentrations <1
|xg/L, trends not
discernible
Higher formation
At concentrations <2
|xg/L, trends not
discernible
At concentrations
<.5 u.g/L, trends not
discernible
Conditions of Formation
Chlorination at pH 7.0
Similar formation
Similar formation -
perhaps slightly higher at
pH7.0
At concentrations <5
u.g/L, trends not
discernible
At concentrations <1
|ig/L, trends not
discernible
Similar formation
Trichloroacetonitrile Not detected
1,1,1-Trichloropropanone Higher formation
Source: Stevens etal., 1989
At concentrations <1
|xg/L, trends not
discernible
Forms within 4 hours;
decays overtime to
<5 u.g/L
At concentrations <2
(xg/L, trends not
discernible
At concentrations
<.5 u.g/L, trends not
discernible
Not detected
At concentrations <2
(xg/L, trends not
discernible
Chlorination at pH 9.4
Higher formation
Lower formation
Similar formation -
perhaps slightly higher at
pH7.0
At concentrations <5
u.g/L, trends not
discernible
At concentrations <1
(xg/L, trends not
discernible
Forms within 4 hours;
decays over time to <5
At concentrations <1
(xg/L, trends not
discernible
Concentrations <2 jxg/L,
trends not discernible
At concentrations <2
(xg/L, trends not
discernible
At concentrations
<.5 u.g/L, trends not
discernible
Not detected
Not detected
Case Study
Case Study No. 3 presents an example of how the pathogen removal/inactivation requirements
were met under high pH conditions while also complying with lime softening requirements.
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Case Study No. 3: Simultaneous Compliance between Lime Softening and DBF MCLs
Background
The following case study describes how Plant C could simultaneously comply with lime softening
requirements and meet the DBPR MCLs using chlorine as the disinfectant. The design parameters
(including treatment processes), and raw and finished water quality of Plant C (serving 200,000 people)
are provided below.
Source Type:
Flow Rate:
Treatment System:
Raw Water Quality:
Surface Water
Average Daily Flow - 20 mgd
Design Flow - 40 mgd
Rapid Mix
Coagulation/Flocculation (alum, 20 mg/L, lime softening, detention time 45
min)
Sedimentation (theoretical detention time - 6 hours)
Filtration (No. of units - 20, single media, loading rate 2 gpm/ft2)
Clearwell (theoretical detention time - 30 min)
Disinfection (maximum chlorine dose - 12 mg/L, point of application -
raw water inlet)
TOC - 7.0 mg/L
pH - 7.3
Alkalinity - 50 to 60 mg/L as CaCO3
Turbidity - 45 to 110 NTU
Total Hardness - 140 mg/L as CaCO3
Finished Water Quality: TOC - 4.2 (40 percent removal)
pH-8.5
Alkalinity - 90 to 100 mg/L as CaCO3
Turbidity - 0.2 NTU
Total Hardness - 60 mg/L as CaCO3
Residual Chlorine -4.0 mg/L
Distribution System TTHM -0.090 mg/L (Running Annual Average)*
Water Quality: HAA5 -0.045 mg/L (Running Annual Average)*
* profiling required
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Simultaneous Compliance Issues
SWTR. The SWTR requires Plant C to achieve 3-log removal ofGiardia and 4-log removal of
viruses. The State credits the system with 2.5-log removal for Giardia for conventional filtration.
Plant C must maintain a CT value determined by the State at 65 mg-min/L.
Lime Softening. Lime softening is used by PWSs to reduce the total hardness of the treated water.
Because lime softening occurs at pH values above 9, the finished water from softening plants often has
an elevated pH. Disinfection may not be effective at high pH conditions.
Stage 1 DBPR. The Stage 1 DBPR reduces the MCL of TTHMs in the finished water to 80 |o,g/L; the
current TTHM concentration at Plant C is 90 |o,g/L. Also, the MRDL for chlorine is set at 4.0 mg/L.
Plant C also needs to reduce the residual chlorine level. Plant C determined high chlorine dosages are
used under high pH conditions to achieve the desired pathogen inactivation.
Potential Conflicts. High CT values are required for effective chlorine disinfection in waters with
elevated pH levels during lime softening. High chlorine doses required under these high pH conditions
may result in formation of DBFs and excess chlorine residuals. However, no CT credit is given for the
chlorine residuals greater than 3.0 mg/L.
Steps to Resolve Conflicts and Results Achieved
Plant C is currently adding chlorine for disinfection at the raw water inlet. Disinfection is not effective
at the high pH (9.5 to 11.5) required for lime softening. The plant determined that changing the point of
application to after lime softening and pH adjustment increased the disinfection effectiveness. The plant
is required to consult with the State prior modifying its disinfection practice and disinfection profiling
and benchmarking also is required. Hydrochloric acid was used to decrease the pH to 8.5 prior to
filtration. The hydraulic performance of the clearwell storage tank was improved by adding baffles to
increase the contact time. The plant reduced the chlorine dose to 5.0 mg/L while still achieving the CT
disinfection requirements. Adequate contact time was achieved in the filters, piping, and the clearwell
storage tanks. Additional storage tanks or contact basins were not necessary.
The pH adjustment reduced the finished water pH to 8.5 which allowed Plant C to reduce the chlorine
residual concentration to 2.0 mg/L. This reduced chlorine dose also helped reduce the TTHM
concentration to 62 |o,g/L, which is within the required level of 80 |o,g/L.
3.4.4.3 Prechlorination and TOC Removal
Issues
Prechlorination, which is chlorine addition prior to sedimentation and/or filtration, is often
practiced to increase the available CT, and thus, the log inactivation of Giardia and viruses.
This process often improves coagulation processes, and it often improves water quality by
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increasing taste and odor control and inorganic contaminant removal through the oxidation of
both organic and inorganic constituents. All of the effects of adding chlorine prior to enhanced
coagulation are not well documented. It is known, however, that during prechlorination, free
chlorine will react with the organic material in the raw water to form DBFs. Therefore, since
some precursors in the raw water are converted into DBFs, prechlorination may conflict with
the purpose of enhanced coagulation, which is the removal of precursors before DBFs are
formed. In addition, research suggests that prechlorination can also impact TOC removal in
lime softening processes (AWWA, 1990).
Recommendations
Where prechlorination is reducing the effectiveness of enhanced coagulation for TOC removal
and/or is increasing the distribution system DBFs to levels above Stage 1 DBPR requirements,
the following strategies are available to address the issues associated with enhanced
coagulation:
• Change the predisinfectant from chlorine to an alternate disinfectant such as chlorine dioxide,
ozone, or another oxidant. These chemicals are strong oxidants, as well as very effective
disinfectants, that can in certain instances reduce DBF formation. PWSs, however, should be
aware of other issues associated with the use of these disinfectants. For example, chlorine
dioxide forms the inorganic DBFs, chlorite and chlorate. Ozone can form a variety of DBFs
depending on water quality. In addition, ozone can increase the biodegradable portion of TOC
remaining in the water, which can lead to biological regrowth in the distribution system.
Similarly, water systems may opt to use chloramine to disinfect and maintain a residual. If the
system intends on switching to ozone or chloramine for primary disinfection, disinfection
profiling and benchmarking for virus disinfection is required. Also, systems switching to
chlorine dioxide should strongly consider profiling and benchmarking for virus disinfection.
All systems switching to an alternative disinfectant are required to consult with the State prior
to changing disinfection practices. A more detailed discussion of alternative disinfectants
available for use can be found in the Alternative Disinfectants and Oxidants Guidance Manual
(USEPA, 1999b). A more detailed descriptiong of disinfection and profiling requirements can
be found in the Disinfection Profiling and Benchmarking Guidance Manual (USEPA, 1999a).
• Consider eliminating prechlorination (during certain seasons) and relying on disinfection
downstream of clarification. This approach will require recalculation of the available CT to
ensure that adequate disinfection is maintained. If the available CT does not meet the log
inactivation requirements, the facility can consider increasing the free chlorine residual (within
the limit of the MRDLs) to meet the required CT value or maintain a lower pH in the
disinfection zone as discussed previously, or increase contact time by adding storage or
changing the baffling conditions in the clearwells. Note that if prechlorination is discontinued,
the system may need to consider an alternate raw water oxidant (e.g., potassium
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permanganate) or other treatment technology to control tastes and odors or enhance iron and
manganese removal.
• If prechlorination is not impeding a system from achieving TOC removal requirements and
maintaining distribution DBF levels, then a facility is not required to modify any of their
disinfection practices. However, in this case, a facility should closely monitor DBF levels to
ensure continued compliance with DBF requirements. The system may wish to profile to
better understand inactivation and DBF formation relationships and then be able to modify
operations.
3.4.4.4 Enhanced Coagulation and Distribution System Surfaces
Issues
As mentioned previously, enhanced coagulation typically includes lowering the coagulation pH
to levels optimal for TOC removal. An additional pH adjustment is required to stabilize the
water chemistry and bring the water to acceptable pH levels prior to distribution. However,
any changes in the pH levels historically maintained in the distribution system can disrupt any
films and scales that have accumulated on natural corrosion surfaces. These films and scales
have formed over long periods of time and serve to passivate the corrosion process from
further development. A pH change can disrupt these surfaces releasing inorganic contaminants
as well as microbes and TOC trapped in the films and scales, and increase corrosion release
rates.
Although disruption of the corrosion surfaces in the distribution system may not result in a
direct violation of either the Stage 1 DBPR or the IESWTR, the disruption could cause
aesthetic problems or the release of microbes and pathogens. However, if TOC is released
from the corrosion surfaces, the TOC could react with free chlorine to form more chlorinated
DBFs, which could cause a violation of the Stage 1 DBPR. In addition, the release of
microbes could cause a violation of the Total Coliform Rule, and further corrosion could
impact compliance with the Lead and Copper Rule. These latter impacts are addressed in
Chapters 4 and 5 of this guidance manual, respectively.
Recommendations
The primary strategies available for addressing the impacts of enhanced coagulation on
distribution svstems are as follows'
distribution systems are as follows:
Attempt to maintain the distribution system pH (and alkalinity) at historic levels after
implementing enhanced coagulation. The pH adjustment prior to distribution should be
designed to return the water chemistry to a stable, or slightly scaling, condition that is similar to
the historic finished water quality. This approach will significantly reduce the potential for
attack on corrosion surfaces from a more aggressive water that may result from a pH change.
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• If it is difficult to maintain the distribution system pH at current levels after enhanced
coagulation is employed, a program can be implemented to strategically flush the distribution
system to scour biofilms and remove dissolved encrustation materials before they are released
into the water. After flushing, the system should evaluate the corrosion potential and either
stabilize water chemistry or institute a corrosion control program to ensure that the continuation
of corrosion and the associated dissolution of corrosion surfaces is minimized.
3.5 Summary and Recommendations
In summary, compliance with the Stage 1 DBPR will, in many instances, enhance a system's
ability to comply with the IESWTR. However, in some cases, simultaneous compliance will
involve systems performing a delicate balancing act between many issues and may require
significant treatment modifications to be made. Alternative technologies for TOC removal may
be required, as well as an evaluation of current disinfection strategies. PWSs should consider
the following items when complying with both the Stage 1 DBPR and the IESWTR:
• Practice enhanced (or optimized) coagulation. Enhanced coagulation will remove DBF
precursors and help improve disinfection efficiency. Optimize the coagulation process for
maximum turbidity removal.
• Conduct rigorous monitoring of the treatment process, including jar testing, DBF monitoring,
and TOC measurement, to ensure that proper coagulation is occurring and impacts to other
treatment processes are being minimized.
• Evaluate alternative treatment technologies for TOC removal compliance and additional DBF
precursor removal.
• Consider modifying disinfection strategy. Strategies such as the use of free chlorine, chlorine
dioxide, or ozone followed by chloramination may provide the benefit of pretreatment oxidation
and pathogen inactivation with reduced formation of DBFs.
• Monitor turbidity levels and particle counts to evaluate filter performance and minimize
impacts to particle removals. Consider filter-to-waste or other backwash treatment strategies
to limit turbidity spikes during the filter ripening period after backwashing.
• Continually seek to optimize water treatment processes to balance particle removal,
disinfection of pathogens, and control of DBFs.
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BETWEEN THE STAGE 1 DBPR, THE
IESWTR, AND LEAD AND COPPER RULE
Conflicts between the Stage 1 DBPR, IESWTR, and the LCR can occur when the chemical
stability of drinking water is affected. Lead and copper are released into drinking water by
corrosion, specific chemical measures such as pH and alkalinity adjustment and the addition of
corrosion inhibitors are employed. Certain actions that may be necessary for PWSs to comply
with the Stage 1 DBPR, such as enhanced coagulation, can upset the established operating
chemistry in a system by lowering the pH. Similarly, certain actions that may be necessary for
PWSs to comply with the IESWTR, such as removing additional turbidity, can be affected by the
addition of chemicals that inhibit corrosion.
This chapter briefly discusses the LCR and presents several potential conflicts between the
Stage 1 DBPR, the IESWTR, and the LCR. It includes discussion of the following topics:
• pH impacts
• Turbidity issues
• Microbial re-growth issues
• Enhanced coagulation issues
• Disinfection strategy issues.
Under each topic area, issues are presented and possible solutions for resolving these conflicts
are provided. PWSs have recently had to determine the actions they would take to comply
with the LCR. Compliance with the Stage 1 DBPR and IESWTR will complicate corrosion
control issues. Additional research into these issues are needed. Systems intending to make
"significant changes" to the treatment process, such as disinfection or coagulation changes,
may wish to employ coupon tests in the distribution system before and after the changes are
made to better understand the impact of change on corrosion control.
4.1 Overview of the Lead and Copper Rule
The 1986 Amendments to the SDWA required EPA to promulgate drinking water standards
for contaminants that impose potential adverse health risks. Lead and copper were specifically
listed in the 1986 SDWA amendments for mandatory development of a National Primary
Drinking Water Regulation. EPA responded to this mandate by promulgating the LCR
(USEPA, 1991). The stated goal of the LCR is to "minimize lead and copper at users' taps
while ensuring that the treatment does not cause the system to violate any national primary
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drinking water regulation" (USEPA, 1991). This goal will be accomplished through the
application of corrosion control strategies (i.e., varying pH levels, alkalinity levels, and
inhibitor requirements). The corrosion control steps are necessary for a PWS to minimize lead
and copper concentrations at its customers' taps.
The LCR action levels for lead and copper are 0.015 mg/L and 1.30 mg/L, respectively, at the
90th percentile of the samples measured at customer taps. Monitoring for a variety of water
quality parameters is required. In addition to monitoring, all large PWSs (i.e., those systems
serving more than 50,000 people) are required to conduct corrosion studies to determine
optimal lead and copper corrosion control strategies. For smaller PWSs, corrosion control
studies are not required unless the action limits are exceeded.
4.1.1 Lead and Copper Corrosion Control Strategies
Under the LCR, the action level triggers steps to be taken by the PWS to remain in compliance
with the LCR. The PWS is required to explore:
1. Public education
2. Source water treatment
3. Corrosion control practices, and, if corrosion control treatment fails,
4. Lead pipe replacement.
As part of the corrosion control study, the LCR mandates PWSs to consider the following
three basic approaches for achieving corrosion control:
• pH/alkaliniry adjustment
• Corrosion inhibitor addition
• Calcium adjustment (i.e., CaCOs deposition).
When tailoring a program to meet the specific needs of a particular PWS, characterization of
corrosion controls is necessary. Corrosion control technologies can be characterized by two
very general mechanisms, each of which has a multitude of variations that carry specific
advantages and disadvantages. These mechanisms are:
• Barrier Protection - The deposition of a precipitate film on plumbing surfaces to prevent
oxidizing agents in the water from reaching the plumbing surface and/or oxidized metals on the
plumbing surface from leaching into the water.
• Passivation - The manipulation of the water chemistry so that the plumbing material and a
number of soluble water constituents react to form protective surface compounds that limit the
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release of metal into the water. The degree of passivation is a function of the electrical
properties of the surface compounds formed.
Passivation occurs at a specific anodic overpotential (i.e., a deviation from the equilibrium
corrosion potential) called the passivation potential (i.e., Epp) and is characterized by a sudden
drop/reversal in the anodic current density with a very slight increment in the anodic
overpotential. This transformation of the anodic current behavior occurs over a 5-10 mV range.
Beyond this overpotential value, there is a zone where anodic current density is virtually
becomes independent of overpotential. About 40-100mV above Epp (depending on the water
chemistry, surface film characteristics etc.), the passivated surface becomes unstable and the
anodic current density thus starts increasing with increasing overpotential, once again. The key
to this form of protection is to be able to control the applied anodic potential to about 20-40 mV
above EPP.
Table 4-1 summarizes the various chemical treatment systems available to promote barrier protection
and/or passivation. Each of these approaches must be evaluated relative to dosage range and specific
water quality concerns. Moreover, it should be realized that a particular treatment approach will not be
universally effective on all metal types and that corrosion control must be tailored to the plumbing
material of interest (i.e., lead or copper) and water characteristics.
Table 4-1. Summary of Corrosion Control Approaches
Treatment Approach
(Control Mechanism)
pH/Alkalinity
Adjustment
(Passivation)
Key Water Quality
Parameters
Potential Chemical Feed
Systems
pH, alkalinity, Total
Dissolved Solids (TDSs),
temperature
Lime (Calcium Oxide)
Soda Ash (Sodium
Carbonate)
Potassium Carbonate
Sodium hexa-
metaphosphate
Sodium Bicarbonate
Sodium Hydroxide
(Caustic Soda)
Potassium hydroxide
Carbon Dioxide
Corrosion Inhibitor
Addition
(Passivation)
pH, metals, hardness,
temperature
Orthophosphate
Polyphosphate
Phosphate blends
Silicates
Silicate/phosphate blends
Calcium Carbonate
Adjustment
(Barrier)
Calcium, pH, alkalinity,
IDS, temperature
Lime (Calcium Oxide)
Soda Ash (Sodium
Carbonate)
Sodium Bicarbonate
Sodium Hydroxide
(Caustic Soda)
Carbon Dioxide
Adjusting the pH or alkalinity of the water offers "passive" protection from corrosion.
Moderate increases in pH/alkalinity normally induce the formation of less soluble hydroxyl-
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carbonate compounds on the lead or copper piping material. If the alkalinity of the water is
increased to high levels (usually > 250 mg/L of CaCOs) corrosive conditions for copper are
recreated. This is due to the high propensity of cupric ions (Cu2+) to form carbonate and
hydroxy-carbonate complexes and the consequent shift in the equilibrium of the following
reaction to the right.
Cu o. Cu2+ + 2e
The corresponding lead complexes are less soluble and hence form a protective scale that
results in better protection from high alkalinity waters.
The addition of corrosion inhibitor chemicals also reduces the corrosion potential of the water
by forming a protective passivating film. Adding orthophosphate, blended phosphates, silicate,
or a blend of these chemicals induces the formation of a less soluble compound that reduces
corrosion or slows metal release from the targeted piping material (i.e., lead or copper).
In addition, calcium and/or carbonate additions elevate the pH level of the finished water. For
corrosion protection, enough calcium and/or carbonate must be added to achieve the
supersaturation and precipitation of calcium carbonate (CaCO3) in the water. The precipitation
collects on the piping material and acts as a barrier between the piping material from potentially
corrosive conditions. Care must be taken not to over-precipitate calcium carbonate as this can
result in pipeline plugging. Compared to lime or caustic addition, raising pH by aeration has
several inherent advantages for copper corrosion control in low-pH, high alkalinity waters.
These advantages are attributed to lower final alkalinity and a reduced likelihood of over-
precipitation of calcite. Conversely, insufficient amounts of calcium carbonate precipitate may
cause spotty surface coatings and lead to localized corrosion.
When selecting a lead and copper corrosion control strategy, it is important to understand the
chemistry of the finished water. Important water quality parameters influencing lead and
copper corrosion include the following (AWWA, 1990; AWWARF, 1985):
• pH • calcium
• alkalinity • magnesium
• dissolved inorganic carbonate • sodium
• hardness • potassium
• conductivity/ionic strength • bicarbonate
• reduction/oxidation (redox) potential • sulfate
• residual chlorine • chloride
• temperature • nitrate
• dissolved oxygen • total dissolved solids
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The relationships among these water quality parameters are such that changing one parameter
will directly or indirectly impact the effect of the other chemicals on corrosion control
(AWWA, 1990). For example, systems may increase the buffering capacity of their waters to
control copper release. Buffering is provided in most distribution systems by dissolved
inorganic carbon species (represented by Ct = [COs2"] + [H C(V] + [CO2(aq)]) and
orthophosphate. There are however a number of trade-offs that need consideration. For
example, the increase in Ct affects the aqueous phase chemical speciation of lead and copper,
which in turn influences the corrosion reaction kinetics and equilibria. Moreover, addition of
phosphoric acid or dissolved inorganic carbon (DIG) species increases the conductivity of the
water, which could increase reaction kinetics and copper release by decreasing the chances of
cuprous/cupric ion build-up at the metal-water interface. The increased conductivity results in
increased copper by-product release and reduced scale formation. The above clearly
demonstrates how various water quality parameters that influence lead/copper corrosion, are
intricately interconnected.
4.1.2 LCR Compliance Relationships with the Stage 1 DBPR and
the IESWTR
The control measures for LCR compliance consist of chemical additions to raise pH and
alkalinity, and/or the addition of corrosion inhibitors. In general, control strategies for
achieving compliance with the Stage 1 DBPR and IESWTR favor:
• Lowering pH to enhance coagulation to improve DBF precursor removal and chlorine
disinfection efficiency; and
• Employing filtration and disinfection to improve microbial inactivation and to minimize DBF
formation.
Table 4-2 summarizes the potential impact of LCR control strategies on the compliance
requirements of the Stage 1 DBPR and IESWTR. Table 4-3 summarizes the potential impacts
of control strategies for Stage 1 DBPR and IESWTR on LCR compliance requirements. These
potential impacts are discussed in detail in the following sections.
4.2 pH Impacts on the LCR and the Stage 1 DBPR and
the IESWTR
The pH adjustment presents compliance issues for the LCR and the Stage 1 DBPR and
IESWTR in the following areas of water treatment and distribution:
• Coagulation
• DBF formation
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• Chlorine CT values.
This section presents issues and recommendations in these areas relative to pH levels.
Table 4-2. LCR Impacts on Stage 1 DBPR and IESWTR Requirements
Corrosion Control
Treatment
for LCR
Impacts on IESWTR Compliance
Impacts on Stage 1 DBPR
Compliance
Increase pH
Alkalinity adjustment
Orthophosphate and/or
Polyphosphate/blended
phosphate addition
Silicate addition
Requires higher CT values for chlorine
disinfection
Use of coagulants at higher pHs may
increase residual aluminum concentrations
Coagulant chemical dosage may need to
be adjusted to achieve optimal pH
May need to reduce optimum pH for
aluminum precipitation
Turbidity increase from zinc carbonate
precipitate, if zinc orthophosphate is used
Potential to stimulate regrowth in the
distribution system. However, recent
research indicates improved management
of biological regrowth with the use of
orthophosphates1
Increased turbidity from algae blooms in
open finished water reservoirs is possible
High silica levels can form precipitates,
causing increased turbidity
Increased THM formation
Higher CT requirement may
increase disinfectant dosage
and increase DBP formation
potential
None
None
None
1 There has been a lot of speculation about the ability of orthophosphate and/or blended phosphates to stimulate regrowth in the system.
Systematic studies documenting this fact are almost non-existent. However, post 1990 research conducted, by LeChavallier et al. (1993),
shows improved disinfectant stability and less regrowth. Moreover, in most cases, carbon has been identified as the limiting nutrient and
not phosphorous (C:N:P=100:20:10 is the optimal nutrient ratio that favors the growth of micro-organisms).
Source: AWWARF, 1990c.
Table 4-3. Stage 1 DBPR and IESWTR Impacts on LCR Requirements
Stage 1 DBPR and IESWTR Control
Strategy
LCR Impact
Increase disinfectant dose to meet CT
requirements
Enhance DBP precursor removal by optimizing
coagulation
Change disinfectants
Variable—Alters water chemistry for the
treated water, which impacts the corrosion
rate and metal release for lead and copper
Source: AWWARF, 1990b.
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4.2.1 Coagulation
As stated in Chapter 3, chemical coagulation with aluminum (alum) and iron (ferric) salts can
be an effective strategy for reducing DBF precursors (in the form of NOM) prior to
disinfection. The optimal pH for NOM removal with alum is in the range of 5.5 to 6.0. Using
ferric salts, the pH range is slightly lower (Singer, 1992).
4.2.1.1 Issues
Issues arise when pH and alkalinity levels are altered to achieve optimum NOM removal.
Coagulants themselves consume alkalinity. For example, 0.5 mg alkalinity (as CaCOs) is
consumed per mg alum (Culp/Wesner/Culp, 1986). The changes in pH and alkalinity levels
due to enhanced coagulation may impact the existing corrosion control scheme for lead and
copper in the distribution system and may impact LCR compliance
Alternatively, the pH levels typically associated with lead and copper corrosion control reduce
the effectiveness of coagulation. Ineffective coagulation may impact Stage 1 DBPR
compliance (in addition to other operating problems). When coagulation or enhanced
coagulation results in low pH or is practiced at low pH, the finished water pH level needs to be
revised before being pumped to consumers. Coagulation and enhanced coagulation conducted
at low pH levels often produce water that is supersaturated with carbon dioxide. For waters
with sufficient levels of carbonate alkalinity, aeration (carbon dioxide stripping) could be an
attractive low-cost option and could provide the flexibility to raise the pH without precipitating
calcite or altering the alkalinity (Edwards et al., 1996). Also, caustic compounds, as detailed
below, can be used to shift the system from carbon dioxide to bicarbonate/
4.2.1.2 Recommendations
Potential resolutions to the conflicts between the pH levels needed to minimize lead and copper
corrosion and to enhance coagulation include:
• Adjusting pH prior to coagulation to optimize coagulation, sedimentation, and filtration.
• Readjusting pH levels in the finished water by chemical addition (see Table 4-1) following
coagulation and filtration to pH and alkalinity levels prior to optimized coagulation. Several
chemicals can be added to increase both pH and alkalinity levels in the finished water. Table 4-
4 presents the chemicals commonly used for pH/alkaliniry adjustment.
• Monitoring lead and copper corrosion rates in the distribution system and implementing an
LCR compliance strategy (see Section 4.7 of this Chapter).
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Table 4-4. Chemicals for pH Adjustment or Alkalinity Addition
pH/Alkalinity Adjustment Alkalinity Added1
Chemical (as mg CaCO3 per mg dose)
Sodium Hydroxide 1.25
(50% solution)
Lime, as Ca(OH)2 1.35
Soda Ash, Na2CO3 0.94
Sodium Bicarbonate, 0.59
1 Sodium hydroxide and lime add hydroxide alkalinity only.
Soda ash and sodium bicarbonate add carbonate or bicarbonate alkalinity, depending on pH.
Source: AVWVA, 1990.
4.2.2 DBF Formation
The pH of water has an impact on DBF formation when chlorine is used. Higher rates of
TTHM formation occur at a pH level of 9.4, while HAA formation tends to remain constant or
decrease with increasing pH level (Stevens et al., 1989). Lower pH levels decrease bromate
ion formation while increasing brominated organic compound formation (Song et al., 1997).
4.2.2.1 Issues
When pH levels are increased in the finished water as a LCR compliance strategy, TTHM levels will
increase in the distribution system if chlorine is used as the secondary disinfectant. The increase in
TTHM levels in the distribution system may exceed the TTHM MCL of the Stage 1 DBPR.
4.2.2.2 Recommendations
Potential resolutions to the conflicts between pH and DBF formation include:
• Limiting pH levels in the distribution system to less than 8.2 to limit TTHM formation (Reiber
et al., 1997). Four LCR compliance strategy case studies showed that TTHM increases were
less than 20 percent if the pH shift implemented for lead and/or copper corrosion control was
from near neutral to less than 8.2. When the pH was shifted from near neutral to greater than
8.5, TTHM production increased as much as 40 percent. At one plant, TTHM increases due to
pH adjustment ranged from 2 percent at a pH of 8.1 up to 43 percent at a pH of 8.7. HAA
production was shown to decrease (about 10 percent) for all of the pH increases implemented
(Reiber et al., 1997).
• Switching the secondary disinfectant to a chemical producing fewer DBFs such as
monochloramine, which does not produce DBFs to any significant degree.
• Implementating an alternative LCR compliance strategy using corrosion inhibitors or a
combination of pH and alkalinity adjustment instead of just pH adjustment (see Table 4-1).
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While increasing alkalinity in poorly-buffered waters helps, except for a few odd cases with
lead, alkalinity adjustment alone is not often helpful, and may be counter-productive for copper.
4.2.3 Chlorine CT Values
CT values for Giardia inactivation by chlorine disinfection are pH dependent. For a given level
of inactivation, the higher the pH, the higher the CT value required.
4.2.3.1 Issues
If pH increases for LCR compliance are implemented prior to disinfection, the chlorine CT
values required for Giardia inactivation will be increased. Increased chlorine CT values
require an increase in disinfection detention time and/or chlorine residual. For example, if the
pH is increased from 6.0 to 9.0 prior to disinfection, then the CT value (at 0.6 mg/L residual
chlorine and 10°C) will increase from 13 to 36 mg-min/L for 0.5 log Giardia inactivation
(AWWA, 1991). To meet this increased CT value, the Tio1 must be increased from 22 to 60
minutes. If additional contact volume is not available, a chlorine residual of 2.0 mg/L is
required corresponding to a CT of 44 mg-min/L, representing an increase in chlorine residual
of more than three times the original residual level. Note that the chlorine residual increase
(from 0.6 mg/L to 2.0 mg/L) is greater than the TIO increase (from 22 to 60 minutes) because
the CT value required depends on chlorine residual level. Increasing chlorine residual levels or
extending contact time may increase the rate of DBF formation and may cause DBF MCLs to
be exceeded under the Stage 1 DBPR.
4.2.3.2 Recommendations
Potential resolutions to the conflicts between pH, chlorine CT values, DBF formation, and
compliance with the LCR include:
• Relocating the application point for pH adjustment to a point after disinfection CT is achieved.
• Switching to an alternative primary disinfectant that is not pH dependent between the pH levels
of 6.0 and 9.0 (e.g., chlorine dioxide, ozone, or monochloramine). Since ozone does not
maintain an appreciable residual level, another chemical must be added for secondary
disinfection (i.e., chlorine or monochloramine).
• Implementing an alternative LCR compliance strategy using corrosion inhibitors or a
combination of pH and alkalinity adjustment (see Table 4-1).
1 TIO is based on the detention time that is equaled or exceeded by 90 percent of the water passing through the basin. TIO is developed
by measuring the peak hourly flow rate and using other plant hydraulic information.
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4.2.4 Case Study
Case Study No. 4 presents an example of how the IESWTR pathogen removal/inactivation
requirements were met while also achieving the LCR requirements.
Case Study No. 4: Simultaneous Compliance between Pathogen
Removal/inactivation and Lead and Copper Control
Background
The following case study describes how Plant D could simultaneously comply with the Giardia
removal/inactivation requirements of the IESWTR and the lead and copper concentration requirements
of the LCR. The design parameters (including treatment processes), and raw and finished water quality
of Plant D (serving 500,000 people) are provided below:
Source Type:
Flow Rate:
Treatment System:
Raw Water Quality:
Surface Water
Average Daily Flow - 40 mgd
Design Flow - 80 mgd
Rapid Mix
Coagulation/Flocculation (alum, 20 mg/L)
Sedimentation (theoretical detention time: 3 hours)
Filtration (No. of units: 40, single media, loading rate 2 gpm/ft2)
Clearwell (theoretical detention time: 30 min)
Disinfection (maximum chlorine dose: 7.0-8.0 mg/L, point of
application - raw water inlet)
TOC-3.0 mg/L
pH - 6.5
Alkalinity - 20 to 40 mg/L
Turbidity - 40 to 100 NTU
Finished Water Quality: TOC -2.1 mg/L (30 percent removal)
pH - 6.0
Alkalinity - 20 to 35 mg/L
Turbidity - 0.2 NTU
Residual Chlorine - 1.0 mg/L
Distribution System
Water Quality:
* profiling required
TTHM -0.090 mg/L*
HAA5 -0.050 mg/L*
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Simultaneous Compliance Issues
IESWTR. The IESWTR requires a 3-log removal/inactivation ofGiardia. This is a total log
removal/inactivation requirement which can be achieved by filtration and disinfection or disinfection
alone. The IESWTR also requires the combined filtered water effluent turbidity to be less than 0.3
NTU in at least 95 percent of the measurements taken each month, with measurements being taken at 4-
hour intervals, and less than 1 NTU at all times. Disinfection profiling and benchmarking are required
and any significant change in the benchmark must be preceeded by consultation with the State.
LCR. The LCR action level requirements for lead and copper are 0.015 mg/L and 1.30 mg/L,
respectively, in 10 percent or more of the samples measured at customer taps. In addition, Plant D
is required to conduct corrosion studies to determine optimal lead and copper corrosion control
strategies.
Potential Conflicts. CT values for Giardia inactivation by chlorine disinfection are pH dependent. The
CT required for disinfection is lower at reduced pH levels which reduces the chlorine dose. A lower
dose of chlorine would likely result in a reduced amount of free chlorine available for DBF formation.
However, low pH levels may result in increased lead and copper corrosion rates. Also, the additional
chemicals that would be required to raise the pH to an optimum range might produce byproducts that
would become a concern.
Steps to Resolve Conflicts and Results Achieved
To comply with IESWTR requirements for pathogen removal, Plant D employed primary disinfection
at the raw water inlet at a pH level of 6.5. Enhanced coagulation was also applied to reduce TOC
concentration by at least 35 percent, as required by the Stage 1 DBPR. The process of enhanced
coagulation, however, reduced the pH level to 5.5. As such, a pH adjustment was necessary to raise
the finished water pH to 7.5.
To comply with the LCR action level requirements for lead and copper, the operators planned on
adding lime somewhere in the treatment train to increase pH to 7.5. The operators knew that adding
lime may create a precipitate in the system that may either place additional load on the filters (possibly
causing an IESWTR turbidity violation) or become a problem in the distribution system. Rather than
creating a problem within the distribution system, plant operators decided to add lime prior to filtration
and assess feed systems, mixing conditions and flow loading rates. The operators set up a bench scale
test apparatus to demonstrate the amounts and the effectiveness of adding lime to the finished water and
how often the filters need to be backwashed. In addition, the pH levels and turbidity in the finished
4.3 Turbidity
Filtered water turbidity levels must be maintained as required under the IESWTR. The
maximum turbidity limits were developed to certify filter performance and provide high quality
water for disinfection. Addition of the following chemicals can have a negative impact on
filtered water turbidity:
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• Zinc orthophosphate and silicate-based corrosion inhibitors
• Lime.
The following subsections present the issues and recommendations in these areas.
4.3.1 Corrosion Inhibitor Addition
Zinc orthophosphate and silicate-based corrosion inhibitors may slightly increase the turbidity
of the finished water. The turbidity increase due to corrosion inhibitor addition is most likely a
function of site-specific water quality parameters and the type of corrosion inhibitor used.
Some of the products now sold as corrosion inhibitors were originally developed as
sequestering agents for iron and manganese. The sequestering nature of the corrosion inhibitor
may lead to increases in the turbidity of the water.
4.3.1.1 Issues
If zinc orthophosphate or silicate-based corrosion inhibitors are added prior to filtration,
turbidity requirements of the IESWTR may be exceeded. This exceedance may be caused by
either an inhibitor turbidity that cannot be removed by filtration or additional filter loading
leading to premature filter breakthrough. Additional research in this area is needed.
4.3.1.2 Recommendations
Potential resolutions to the turbidity impacts of corrosion inhibitor addition include:
• Relocating the application point for zinc orthophosphate and silicate-based corrosion inhibitors
downstream of filtration and disinfection contact. Moving the application beyond the point at
which disinfection is complete reduces the impact of inhibitor turbidity on disinfection.
• Implementing an alternative LCR compliance strategy using other corrosion inhibitors or
pH/alkalinity adjustment.
4.3.2 Lime Addition
Lime addition for LCR compliance or softening may slightly increase the turbidity of the water
due to calcium carbonate precipitation.
4.3.2.1 Issues
Lime addition prior to filtration may create a precipitate that will place additional load on the
filters. This additional load can lead to premature filter breakthrough and require more
frequent backwashing. The extra load on the filters may cause the turbidity requirements of the
IESWTR to be exceeded.
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Lime addition after filtration may cause a precipitate in the distribution system. If the
precipitate attaches to the walls of the pipe, barrier corrosion protection may be provided. If
the precipitate remains in solution, it can lead to consumer complaints.
4.3.2.2 Recommendations
• Potential resolutions to the turbidity impacts of lime addition include:
• Recognizing the impact of the additional load due to lime precipitates on the operation of the
filters. This recognition will require more frequent backwashing of the filters.
• Relocating the application point for lime downstream of filtration and disinfection. (This action
may move the precipitate problem to the distribution system or the consumers' tap.)
• Implementing an alternative LCR compliance strategy using corrosion inhibitors or
pH/alkaliniry adjustment with a non-calcium chemical (such as sodium hydroxide).
4.4 Microbial Regrowth
Secondary disinfectant residual levels are maintained throughout the distribution system to
prevent regrowth of microbes in the distribution system.
4.4.1 Phosphate Corrosion Inhibitor Addition
The addition of orthophosphate or polyphosphate corrosion inhibitors may stimulate regrowth
in distribution system, which may impact TCR compliance. Similarly, phosphate based
corrosion inhibitor addition to systems utilizing open finished water reservoirs can increase the
potential for algae blooms (AWWARF, 1990c). However, post 1990 research has shown that
there could be significant improvements in preventing biological regrowth by exercising good
corrosion control in the distribution system. LeChavallier et al. (1993) have examined the
relationship between iron corrosion and the disinfection of biofilm bacteria. Increased corrosion
rates were found to reduce biofilm disinfection efficiency for both chlorine and
monochloramine. For free chlorine, corrosion rates greater than 1 mpy (mils per year) reduced
disinfection efficiencies to near zero. Monochloramine was less dramatically affected by
corrosion with disinfection efficiencies dropping 10-fold for every 10-fold increase in the
corrosion rate. The South Central Connecticut Regional Water Authority (SCCRWA)
modified its corrosion program in September 1988, following several years of excessive
coliform levels in the distribution system. Coliform growth was especially prolific in the iron
tubercles within the distribution system pipelines. The utility increased the concentration of
zinc metaphosphate from 1 to 2 mg/L (Smith et al., 1989). Total phosphorous concentrations
in the distribution system increased from 0.31 to 0.43 mg PO4-P/L (phosphate as phosporous
per liter of water). Although no immediate effect was observed, weekly coliform levels
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significantly decreased from 12 percent to 5.1 percent over the following two-year period.
Turbidity levels in the distribution system also decreased from 0.10 NTU to 0.04 NTU after the
increase in the corrosion inhibitor dosage.
Several investigators (Opheim et al., 1988; Emde et al., 1992) have reported the occurrence of
coliform bacteria in corrosion tubercles on iron pipes. Lowther and Mosher (1984) reported
that levels of coliform bacteria decreased within a few weeks following the application of zinc
orthophosphate in the Seymour, Indiana distribution system. Zinc orthophosphate also has
been successfully used at other Indiana operations to control coliform occurrences
(unpublished data). The need to achieve low corrosion rates for effective inactivation of
biofilm bacteria demonstrates the importance of maintaining consistent corrosion control.
Fluctuations in the water quality variables (pH, chlorine residuals and temperature) at the
Swimming River treatment plant (American Water Works Service Co., NJ) probably made
consistent corrosion control difficult despite addition of zinc orthophosphate and
polyphosphate inhibitors (LeChavallier et al., 1987). Coliform bacteria were isolated from iron
tubercles within this distribution system. One occurrence of coliform bacteria in the Swimming
River distribution network followed the breakdown of the lime system. Although the
connection between feeding lime and coliform bacteria was not understood at that time (i.e.,
1985), subsequent research by LeChavallier et al. (1993) appear to indicate that corrosivity
resulting from lower calcium carbonate levels would provide a better environment for bacterial
growth. The elimination of distribution system coliform bacteria was due, in part, to
improvements in the consistency of the operations at the Swimming River treatment plant.
4.4.1.1 Issues
Typically, the regrowth of microorganisms in the distribution system is nutrient-limited. In
other words, the distributed water may contain limited amounts of phosphorous, nitrogen, and
trace elements (such as potassium, magnesium, etc.) required for growth (Gaudy and Gaudy,
1980). Systems that use monochloramine as a secondary disinfectant increase the nitrogen
content of the water through the addition of ammonia. Phosphorous can be added for
corrosion control in the form of orthophosphates or polyphosphates. The addition of
phosphorous increases the potential for regrowth in the distribution system, especially where
monochloramine is used for secondary disinfection.
For example, nitrification was observed during demonstration testing of LCR control strategies
at one plant. During one monitoring episode, chloramine residual levels were found to drop
from 3.2 to 0.2 mg/L across a short pipe distance. This finding was attributed to the growth of
nitrifying bacteria, which were limited until introduction of the phosphate-based corrosion
inhibitor addition (Reiber et al., 1997).
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Orthophosphate addition for the control of lead and copper corrosion in a low-DIC water at a
pH of 7.5 will have a significant impact on reducing lead solubility. However, it may not
improve copper control beyond that afforded by raising pH to 7.5 (Schock et al, 1995). For
water systems not encountering lead material problems, however, doses of Orthophosphate at
1.5 mg PO4-P/L may be effective in controlling copper levels in new plumbing, at pH values
less than 8.
4.4.1.2 Recommendations
• Potential resolutions to the regrowth impacts of phosphate-based corrosion inhibitor
addition include:
• Lowering the phosphate-based corrosion inhibitor dose to the practical minimum.
• Implementing an alternative LCR compliance strategy using silicate-based corrosion inhibitors
or pH/alkaliniry adjustment.
• Increasing secondary disinfectant residual levels in the distribution system to limit regrowth.
(Increasing the disinfectant dose may increase DBF formation.)
• Minimizing sediment build-up and tuberculation in the distribution system will help to reduce
disinfectant demand. This may require cleaning and flushing of distribution system sections and
adjusting hardness, alkalinity and pH. Sediment from a system experiencing coliform regrowth
episodes was shown to contain high levels of heterotrophic plate count (HPC bacteria (greater
than 8 x 106 CFU/gm) and coliform organisms (LeChavellier et al., 1987). The sediment in this
system was also covered by a layer of post-precipitation from improperly applied treatment
chemicals. The control of sediment accumulation in distribution system pipelines by routine
and aggressive flushing is important because even recalcitrant organic compounds can be
slowly biodegraded in the sediments and provide an endogenous supply of nutrients. In another
study by LeChavallier et al. (1996), involving seven free-chlorinating systems, the majority of
the systems that had low occurrence rates for coliforms (< 0.5 percent of the samples tested
positive for coliforms), flushed 100 percent of the distribution on an annual basis. Dead ends
and points of stagnation in the distribution system are especially prone to microbial growth and
consequent loss of disinfectant residuals.
• Where chloramines are used as a residual disinfectant, the system should practice optimization
of the chlorine to ammonia feed ratio to minimize ammonia content in the finished waters.
4.5 Enhanced Coagulation
Enhanced coagulation can have the following general effects on lead and copper corrosion:
• Decrease pH levels in the finished water (see Section 4.2.1).
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• Decrease NOM levels in the finished water. NOM levels less than 2.0 mg/L result in a
substantial increase in lead corrosion rates, especially in brass (Korshin et al., 1998).
• Change coagulant dosages and/or type of chemical used. Altering sulfate and chloride
concentrations (as the anionic portion of the coagulant) impacts lead and copper corrosion
rates.
• Reduction in residual aluminum levels may occur.
Issues and possible solutions in these areas relative to lead and copper corrosion are presented
in the following paragraphs.
4.5.1 NOM Removal
Enhancing coagulation for NOM removal is required by the Stage 1 DBPR. Of all the
parameters that impact metal corrosion in potable water, NOM is one of the least studied.
Removal of NOM during enhanced coagulation alters the lead corrosion rate for lead-
containing brass, pipe, and solder. The effects of NOM levels are dependent upon the type of
corroding material. In waters with neutral pH and low alkalinity, lead release from brass is
significantly increased with NOM concentrations between 0 and 2.0 mg/L as carbon. NOM
concentrations greater than 2.0 mg/L as carbon do not impact brass corrosion rates. The
corrosion of lead pipe and solder is initially increased due to reduced NOM concentrations.
However, once surface scales form a barrier in reduced NOM water, the lead corrosion rate
decreases and stabilizes (Korshin et al., 1998).
Several investigators have studied the interaction between Cupric ion and dissolved NOM
(Cabaniss and Shuman, 1988; Davis, 1984; Holm, 1990). The composition of NOM is
extremely diverse and greatly depends upon its source. As a result, these interactions cannot be
generalized. NOM is mainly composed of humic and fulvic substances and its interaction with
cupric ions is usually characterized empirically by statistical models that describe the binding of
metals with one or several theoretical ligands under specific experimental conditions such as
pH, ionic strength, etc. (Cabaniss and Shuman, 1988). The degree to which NOM impacts
copper corrosion has not been determined conclusively. Research indicates that NOM may
reduce pitting attack and possibly alter some scale formation characteristics of uniform copper
corrosion (Edwards et al, 1994). Rehring (1994) found that copper corrosion rates increased
with NOM concentration at pH 6, whereas at pH 7.5 and 9 it had less significant effects. The
uncoiling of NOM macromolecules at high pH values (due to repulsion between specific
charged groups on account of de-protonation), can significantly increase the number of sites
that could bind with cupric ions and result in more copper being bound in the form of Cu-NOM
complexes. This in turn would affect corrosion rates and copper release. Palit and Pehkonen
(1998) studied the correlation between copper release as well as corrosion rates (measured
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electrochemically) and the ratio of UV absorbancy to TOC. Using UV254:TOC in L/mg-min
and the BDOC:DOC ratio as surrogates for copper release, Palit and Pehkonen (1988) found
that there was a greater occurrence of corrosion with lower the BDOC levels in waters and a
higher UV254:TOC ratio.
4.5.1.1 Issues
NOM levels are reduced during enhanced coagulation for Subpart H systems using
conventional treatment as required by the Stage 1 DBPR. The increase in lead corrosion rates
associated with low NOM levels may impact LCR compliance. This impact from NOM
removal may be most evident during tap sampling from brass faucet fixtures (Korshin et al.,
1998).
4.5.1.2 Recommendations
Potential resolutions to the NOM removal impact on lead corrosion rates include:
• Increasing pH levels and/or orthophosphate levels in the finished water. Reduced NOM levels
only slightly increase lead released from brass in high pH water. Similar results have been
observed with orthophosphate addition (Korshin et al., 1998).
• Monitoring lead and copper corrosion rates in the distribution system and implementation of a
LCR compliance strategy, if required.
4.5.2 Coagulant Changes
The optimization of coagulation may alter the existing coagulant dose or even result in a
change in coagulant types. The changes in coagulant (dose and/or type) impact the overall
water quality, which impacts the rate of lead and copper corrosion (AWWARF, 1985). In
addition to the impacts on pH described in Section 4.2, changes in coagulant type may also
impact the amount of chloride and sulfate ions present in the finished water. Utilities, that are
changing the coagulant or practicing enhanced coagulation, may want to restore finished water
chemistry as much as possible to its historical levels to avoid corrosion control problems.
There is some evidence to suggest that the sulfate to chloride mass ratio is important for
predicting pitting corrosion in copper. A sulfate to chloride mass ratio greater than 1:2 may
increase the potential for copper pitting (AWWARF, 1985). Alternatively, in case studies at 22
water utilities, all 12 utilities with sulfate to chloride mass ratios of more than 1:1.7 met the
action level for lead. In contrast, 6 of the 10 utilities with sulfate to chloride ratios of less than
1:1.7 failed to meet the action limit for lead (Reiber et al., 1997). In relation to copper
corrosion, the results of these studies on copper and lead corrosion suggest that a sulfate to
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chloride mass ratio of 1:2 may increase the ability to meet the action level for lead without
increasing the potential for copper pitting corrosion.
Recent research, however, indicates that the sulfate to chloride mass ratio may be relatively
unimportant in these predictions and that the presence of sulfides may be a better indicator of
copper pitting (Jacobs et al., 1998). As a consequence of the possible role of sulfides in copper
pitting, it has been suggested by Jacobs et al. that the best predictor may be the presence of
sulfates and the conditions in the distribution system (such as low dissolved oxygen) that may
reduce sulfates to sulfides.
4.5.2.1 Issues
Enhanced coagulation requirements of the Stage 1 DBPR may alter the coagulant dose or
result in changes in coagulant chemicals. These changes may result in changes in relative
sulfate and chloride ion levels alter lead and copper corrosion rates that may, in turn, affect a
system's ability to comply with the LCR.
4.5.2.2 Recommendations
Systems, which must change coagulants or coagulant dosages to comply with enhanced
coagulation requirements, can control potential increases in lead and copper corrosion by:
. Adjusting the pH of the finished water (see Section 4.2.1);
. Adding lime or another source of calcium so that the finished water is saturated
with calcium carbonate and forms a protective coating on the pipes; or
. Adding a corrosion inhibitor (i.e., a substance that is phosphate- or silica-based) to
the finished water to form a protective coating on the pipes.
One of the earliest steps would be to consider as close a pH, hardness and DIG match to pre-
Enhanced Coagulation conditions as possible. If that is not feasible, then a new corrosion
control optimization study would be warranted to evaluate the best new treatment. Whenever
possible, the best objective would be to retain successful water chemistry and to minimize
distribution system water quality fluctuations as much as possible.
4.5.3 Case Study
Case Study No. 5 presents an example of how enhanced coagulation requirements of the Stage
1 DBPR were met while also achieving the LCR requirements.
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Case Study No. 5 (An Actual Water Utility): Simultaneous Compliance between
the Stage IDBPR and the LCR
Background
The following is a case study that describes the experience of a real Water Utility X (names of
the treatment plants and the utility withheld at the request of the Utility) in its attempt to
reduce THMs by changing the coagulant. In the process, the system exceeded the action level
for lead at customer taps; 0.015 mg/L. This case study documents the steps taken to remedy
the situation and thus enable plant operators to simultaneously comply with the DBPR and
LCR.
Prior to the establishment of the 100 ppb THM standard, the utility practiced pre-
chlorination at the intake. The finished water pH level was approximately 9.5 and THM
levels ranged from 200-250 ppb. Research by the Utility staff determined that by
eliminating pre-chlorination and reducing the finished water pH to a level between 7.5 and
8.0, compliance with the 100 ppb standard could be achieved. The THM running annual
average for Plants 1 and 2 were 60-70 ppb and 70-80 ppb, respectively. However, there
were several adverse impacts associated with removing the pre-chlorination step and
reducing the pH. These impacts included:
(a) Each plant lost 24 hours of chlorine contact time
(b) Coagulation was not considered to be as effective by the plant operators
(c) Algal blooms occurred in the treatment basins (causing more paniculate loading
on the dual media filters)
(d) The finished water became corrosive (precipitation of calcium carbonate is
precluded below a pH of 8.3).
Additional research determined that zinc-orthophosphate (ZOP) was effective in reducing
the corrosiveness of the finished water. Consequently, ZOP was added to the treatment
regimen in 1981 to protect distribution system piping and customer plumbing.
Simultaneous Compliance Issues
LCR. Utility X has completed four rounds of LCR monitoring at high-risk sites, under
worst-case conditions in the distribution system. Two rounds were completed in 1992 and
two rounds were completed in 1997. These results are shown below
Risk Areas
Round No. Period Phosphate cone. 90 percentile Lead
cone.
1 Jan.-June 1992 0.16 mg/L 15 ppb
2 July-Dec. 1992 0.18 mg/L 116 ppb
3 Jan.-June 1997 0.58 mg/L 33 ppb
4 July-Dec. 1997 1.45 mg/L 3 ppb
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City Y (a master-metered suburb receiving Utility X water) has completed four rounds of
LCR monitoring. The results from four of those are rounds are listed below.
Lead Monitoring Results Summary at City Y
Round No. Period Phosphate cone. 90tfi percentile Lead
cone.
1 July-Dec. 1992 0.18 mg/L 19 ppb
2 Jan.-June 1995 1.00 mg/L 8 ppb
3 July-Dec. 1995 0.80 mg/L 7 ppb
4 Jan.-July 1997 0.58 mg/L 46 ppb
During the 1992 and 1995 monitoring periods, the Utility used alum as the coagulant in
Plants 1 and 2. During the 1997 monitoring period, ferric chloride was used as the
coagulant. After 1992, the phosphate concentration was increased substantially which
resulted in lowering the 90th percentile lead concentration, as demonstrated in monitoring
rounds 2 and 3 at City Y. The increase in the 90th percentile lead concentration during
round 4 at both sites was very dramatic. A plausible explanation for this result is discussed
below.
Distribution system monitoring during January through June 1997, resulted in a lead
concentration of 33 ppb at the 90th percentile. This result surprised operators since
elevating the phosphate concentration after the 1992 monitoring periods had lowered the
90th percentile lead levels substantially. A literature search revealed that if the sulfate to
chloride mass ratio is greater than 0.58, then typically the lead action level would be
exceeded, regardless of the water quality. The chloride to sulfate ratio of the Water Utility
X finished water was calculated to be: (a) Alum coagulation: 0.29-0.49 (b) Ferric chloride
coagulation: 0.82-1.50. Apparently, the switch from alum to ferric chloride had shifted the
chloride to sulfate ratio into a range that nullified the effectiveness of the ZOP corrosion
inhibitor. Thus, an attempt to comply with the Stage I THM standard had created a
situation that lead to the exceedance of the LCR action level. In order to lower the lead
solubility before the July through December, 1997, LCR distribution system monitoring, the
coagulant was switched from ferric chloride back to alum, and a corrosion inhibitor with a
5:1 phosphate to zinc ratio was utilized (normally an inhibitor with a 3:1 phosphate to Zn
ratio was used), to allow an additional increase in the phosphate level without increasing
the Zn concentration. As a result, the 90th percentile lead concentration dropped to 3 ppb
during the July through December, 1997, monitoring period.
Section IV of USEPA (1997b) does not discuss the same effects on lead solubility as noted
above. Utility X has the capacity to adjust pH and alkalinity into the optimal range prior to
entry into the distribution system.
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Apparently, the reduction in lead solubility resulted from an appropriate chloride to sulfate
ratio, which enabled the corrosion inhibitor to be effective, and not from any pH or
alkalinity induced changes in the water quality. The finished water pH and alkalinity were
very similar during the use of both alum and ferric chloride.
IESWTR. In order to increase CT and flexibility at the plants, six clearwells were
constructed (at a cost of $23 million) in 1995. This additional clearwell capacity increased
the plant detention time by 16 hours. As expected, the THM RAA increased from a historic
concentration of 70-80 ppb to 90 ppb. This RAA increase expedited another cycle of
research to evaluate treatments that would reduce THM precursors more effectively.
Coagulation with ferric chloride proved to be the most efficient and plausible treatment to
lower THM RAA, obviating major capital construction/operation costs. Alum coagulation
(used historically) removed TOC sufficiently to meet the percent removal criteria of the
ESWTR, but did not remove THM precursors as effectively as ferric chloride.
Stage 1 DBPR. Compliance with the Stage I THM (80 ppb) RAA concentration was
attainable at one of the two plants, with alum coagulation. However a similar compliance
was not achieved at the other water treatment plant using alum as the coagulant. Coagulant
was changed from alum to ferric chloride at Plant 1 (August 1995) and at Plant 2
(September 1996). This resulted in a 43 percent decrease in THM RAA at Plant 1 (from 70
ppb to 40 ppb) and a 33 percent reduction in THM RAA at the plant 2 (from 90 ppb to 60
ppb). Compliance with Stage I THM concentration was assured at both treatment plants
while compliance with Stage II THM concentration (40 ppb) was feasible at one of them
alone. With ferric chloride coagulation as the only treatment change, it was not feasible at
the water treatment Plant 2.
Concluding Remarks
The Utility has resolved the lead solubility issue, but is still faced with the Stage I DBPR
issue, since the THM RAA is expected to rise again. The Utility is also concerned with
bacterial regrowth in the system due to elevated phosphate levels.
4.6 Disinfection Strategy
4.6.1 Switching Disinfectants
Compliance with the DBPR may require changing the chemical used for secondary disinfection.
Changes of the secondary disinfectant may impact the redox potential of the water as well as
overall water quality. Changes in water quality, and especially in redox potential, impact lead
and copper corrosion rates (AWWA, 1990). Moreover, the feasibility of the switch to an
alternate disinfectant may depend on how well it can be managed and the compatibility of the
scheme with consecutive systems.
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4.6.1.1 Issues
The use of chloramines as a secondary disinfectant (to provide a residual in the distribution
system) could result in a significant reduction in TTHM formation potential in the distribution
system. The chloramination process needs to be optimized in order to provide adequate
distribution system residual and at the same time minimize the possibility of nitrification.
Nitrification could be controlled by reducing the detention time, keeping water temperatures
low, increasing the chlorine to ammonia ratio, checking the ammonia concentration and
maintaining chloramine residuals > 2 mg/L. The activity of nitrifying bacteria can be detected
by monitoring HPC concentrations, chloramine residuals and nitrite and nitrate concentrations.
Nitrite is an intermediate in the nitrification process, which has a very high chlorine demand.
This accelerates the destruction of the chloramine residual. Nitrification can lower the pH of
the water in the distribution system and consequently prove detrimental for lead and copper
release control.
Changes in lead and copper corrosion rates due to changes in secondary disinfectants may
impact LCR compliance. Corrosion products and tubercles interfere with the disinfection of
coliforms and HPC bacteria. Norton and LeChevallier (1997) have conducted several studies
at the Indiana-American Water Company (Muncie, IN) to investigate the effect of
chloramination on the distribution system water quality. At Muncie, pH and alkalinity were
used for corrosion control and corrosion rates and Larson's indexes were low throughout the
project. However, the water entering the Muncie distribution system had a propensity for
pitting corrosion. After that study, phosphoric acid was fed as a corrosion inhibitor
(orthophosphate concentration between 2.0 and 2.5 mg/L was maintained). Even after 16
months of orthophosphate addition, only one of 1,246 chloraminated distribution system
samples tested positive for coliform bacteria.
4.6.1.2 Recommendations
Systems that must switch to a different secondary disinfectant may minimize increases in the
rate of lead and copper corrosion by:
. Adding lime or another source of calcium to the finished water to saturate it with
calcium carbonate and form a protective coating on the pipes
. Adding a corrosion inhibitor (i.e., a substance that is phosphate- or silica-based) to the
finished water to form a protective coating on the pipes.
4.6.2 Ozonation and Unfiltered Systems
Following ozonation, the treated water contains increased levels of dissolved oxygen.
Filtration reduces the level of dissolved oxygen to acceptable levels. Unfiltered systems (both
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surface and ground water) deliver the increased dissolved oxygen into the distribution system.
Increased dissolved oxygen levels may increase the rate of lead and copper corrosion and
encourage nitrification (AWWA, 1990).
4.6.2.1 Issues
Implementing ozone disinfection for Stage 1 DBPR compliance at unfiltered water treatment
systems can lead to changes in lead and copper corrosion rates due to increased dissolved
oxygen (DO) that may impact LCR compliance. Besides increasing the DO, another drawback
of ozonation is the formation of acidic functional groups like carboxylic caids, aldehydes, keto-
acids etc., which could reduce the pH of the water significantly. According to Palit and
Pehkonen (1998), ozonation followed by biofiltration resulted in an increase and a 30 to 40
percent decrease in the copper release rate. Ozonation followed by biofiltration ensures the
removal of the biodegradable component of the NOM (e.g., BDOC), thus minimizing the
potential for microbial regrowth in the distribution system. Furthermore, according to bench
scale studies conducted by Palit and Pehkonen (1998), a low BDOC:DOC ratio could
significantly increase the formation of the particulate copper (fraction of the copper byproduct
release that is retained by a 0.45|j,m cellulose acetate filter). The significance of converting
copper release into a particulate copper (also lead release into a lead particulate) relies on the
potential to filter these particulates out using point-of-entry (POE) or point-of-use) POU
filters.
4.6.2.2 Recommendations
Unfiltered systems that switch to ozone disinfection may manage increased corrosion because
of increased dissolved oxygen, by:
Adding lime or another source of calcium to the finished water to saturate it with
calcium carbonate and form a protective coating on the pipes
. Adding a corrosion inhibitor (i.e., a substance that is phosphate- or silica-based) to the finished
water to form a protective coating on the pipes.
4.7 Summary
The compliance relationships between the Stage 1 DBPR, IESWTR, and LCR are numerous.
Prior to promulgation of the Stage 1 DBPR and IESWTR, most water systems should have
already achieved compliance with the LCR. This compliance may include the implementation
of LCR control strategies as well as the conduct of ongoing monitoring to demonstrate that
lead and copper levels remain below their respective action limits. Implementation of the Stage
1 DBPR and IESWTR may require changes that affect current LCR compliance. Therefore,
compliance relationships between these rules and the LCR must be analyzed. The following
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two sections present decision trees for simultaneous compliance based on whether the changes
are initiated by the Stage 1 DBPR or the IESWTR.
4.7.1 DBF Controls Required
Figure 4-1 presents a decision tree showing the steps that should be taken if DBF controls are
required. As discussed in Chapter 3, DBF controls may be required for any one of the
following reasons:
1. TOC level exceeds 2.0 mg/L in the raw water
2. DBF levels in the finished water exceed the current MCL
3. Disinfectant residual levels in the finished water exceed the current MRDL
4. DBF levels in the finished water exceed 80 percent of the current MCL which initiates
disinfection profiling and may require DBF controls.
Once the changes required for DBF control are developed, a study should be performed to
determine the impact of the DBF controls on LCR compliance. If the results of the study
indicate that no impact on LCR compliance is expected, the DBF control strategy can be
implemented.
As shown in Figure 4-1, the results of the study show that there are impacts on LCR
compliance as expected (i.e., changes in finished water pH), a study should also determine if
mitigation of the DBF control is feasible and identify mitigation actions to assure LCR
compliance (i.e., pH adjustment). If the impact of DBF control on LCR compliance cannot be
mitigated, then an alternative DBF control strategy will be required.
A desktop study should determine the impact of LCR mitigation on IESWTR and TCR
compliance (i.e., CT impacts or distribution system regrowth) and if the impact of DBF control
on LCR compliance can be mitigated. If the LCR mitigation actions do not impact IESWTR
and TCR compliance, the effectiveness of the LCR mitigation actions should be demonstrated
in bench or pilot scale tests. Both the DBF control strategy and the associated LCR mitigation
actions can be implemented if the demonstrations are successful.
As shown in Figure 4-1, when the LCR mitigation actions impact either IESWTR or TCR
compliance, further studies are required to determine if other alternatives are available to avoid
the conflicts and assure simultaneous compliance. An alternative LCR mitigation or alternative
DBF control strategy may be required if the impacts cannot be avoided. When the LCR
mitigation action impact on the IESWTR and TCR can be mitigated, the DBF control strategy
and the associated LCR, IESWTR, and TCR control strategies can be implemented (following
demonstration testing of the LCR mitigation actions).
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4. SIMULTANEOUS COMPLIANCE ISSUES BETWEEN M-DBP RULES AND LEAD
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4.7.2 IESWTR Controls Required
Figure 4-2 presents a decision tree showing the steps that should be taken if IESWTR controls
are required. As discussed in Chapter 2, IESWTR controls may be required for one of the
following reasons:
• Filtered water turbidity exceeds the treatment technology level
• CT values are less than required.
Once the changes required for IESWTR control are developed, a LCR desktop study (e.g., a
study conducted based on computer simulation or modeling without laboratory testing) may be
performed to determine the impact of IESWTR controls on LCR compliance. If results of the
desktop study demonstrate no impact on LCR compliance is expected, the IESWTR control
strategy can be implemented (Chapters 3 and 5 identify conflicts with the DBPR and TCR,
respectively).
As shown in Figure 4-2, when the results of the desktop study show that impacts on LCR
compliance are expected (i.e., changes in finished water pH), the desktop study should
determine if mitigation of the IESWTR control is feasible and identify mitigation actions to
assure LCR compliance (i.e., pH adjustment). If the impact of IESWTR control on LCR
compliance cannot be mitigated, then an alternative IESWTR control strategy is required.
When the impact of IESWTR control on LCR compliance can be mitigated, the desktop study
should determine the impact of LCR mitigation on DBPR and TCR compliance (i.e.,
distribution system pH increases or distribution system regrowth). The effectiveness of the
LCR mitigation actions should be demonstrated in bench or pilot scale tests if the LCR
mitigation actions do not impact DBPR and TCR compliance. When the demonstrations are
successful, both the IESWTR control strategy and the associated LCR mitigation actions can
be implemented.
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4. SIMULTANEOUS COMPLIANCE ISSUES BETWEEN M-DBP RULES AND LEAD
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D/DBP Controls
Required?
Initiate Desktop
Corrosion Control Study
D/DBP
Controls
Impact LCR/
IESWTR/TCR
Compliance
Negatively?
Implement D/DBP
Control
Can Impact Be
Mitigated?
Identify LCR Mitigation
Actions
LCR Mitigation
Actions Impact
IESWTR/TCR?
Implement D/DBP
Control and LCR
Mitigation Actions
Develop
Alternative D/DBP
Control Strategy
Mitigation
Actions
Demonstrated1;
Alternative LCR
Mitigation
Available?
Implement D/DBP
Control and LCR,
IESWTR, and TCR
Mitigation Actions
Figure 4-1. DBP Control Decision Tree
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4. SIMULTANEOUS COMPLIANCE ISSUES BETWEEN M-DBP RULES AND LEAD
AND COPPER RULE
IESWTR
Controls Impac
LCR/ DBPR/
TCR Compliance
Negatively
Implement
IESWTR Control
Can Impacts Be
Mitigated?
Identify LCR Mitigation
Actions
Implement
IESWTR Control
and LCR
Mitigation Actions
LCR Mitigation
Actions Impact
D/DBPR/TCR?
Develop
Alternative
IESWTR Control
Strategy
Implement D/DBP
Control and LCR,
D/DBPR, and TCR
Mitigation Actions
Figure 4-2. IESWTR Control Decision Tree
August 1999
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As shown in Figure 4-2, when the LCR mitigation actions impact either DBPR or TCR
compliance, further study should determine if mitigation of the conflicts is feasible and identify
mitigation actions to assure simultaneous compliance. An alternative LCR mitigation or
alternative IESWTR control strategy may be required if the impacts cannot be mitigated.
When the LCR mitigation action impact on the DBPR and TCR can be mitigated, the IESWTR
control strategy and the associated LCR, DBPR, and TCR mitigation actions can be
implemented (following demonstration testing of the LCR mitigation actions).
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5. TOTAL COLIFORM RULE AND ISSUES ON
COMPLIANCE WITH THE STAGE 1 DBPR
AND IESWTR
In published case studies involving the modification of disinfection practices to control DBFs,
PWSs have generally been successful in maintaining bacteriological safety as DBF levels were
reduced (AWWARF, 1990b). This chapter discusses the circumstances in which PWSs may
have difficulty in simultaneously meeting the regulatory requirements of the TCR, Stage 1
DBPR and the IESWTR. For each situation discussed, approaches are described which may be
useful in achieving simultaneous compliance with the rules. These approaches involve
modifications of both disinfection and treatment practices.
5.1 Requirements of the TCR and Compliance Issues
5.1.1 TCR Requirements
The TCR became effective on December 30, 1990 (USEPA,1989b) and is intended to ensure
that drinking water remains safe from microbial contamination. Coliforms are bacteria
naturally present in the digestive tracts of warm-blooded animals. There are also coliforms that
are native to the soil and decaying vegetation (Peavy et el., 1985). While generally not harmful
to human health, coliforms are often present in water contaminated with human or animal
waste, which may contain other disease-causing organisms. Total coliforms are therefore used
as indicators of the possible presence of these disease-causing microbes. For purposes of the
TCR, EPA assumes that the treatment methods that produce coliform-free water will also
prevent the occurrence of these other microbial pathogens.
Major requirements of the TCR include the following:
• PWSs must collect a specified number of routine samples per month, dependent upon
populations served. The number of samples increases with increasing population and the
sample locations must be representative of the PWS's distribution system.
• The maximum total coliform-positive samples each month must total less than 5 percent (or no
more than one positive if the system collects fewer than 40 samples per month).
• If a sample is total coliform-positive, repeat samples must be taken at the original location, as
well as upstream and downstream of the original location within 24 hours and within five
service locations of the original location.
• If a sample is total coliform-positive, it must also be tested for the presence of fecal coliforms
or E. coli. The State must be notified if any fecal coliforms or E. coli samples in the water
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system are positive. An acute violation of the TCR occurs when a repeat sample is fecal
coliform-positive or E. co//'-positive or if a fecal coliform-positive or E. co//-positive original
sample is followed by a total coliform-positive repeat sample.
• All utilities must develop a written bacteriological sampling plan that is subject to review and
revision by the State.
Chlorine, chloramines, and chlorine dioxide are typically used to maintain a disinfectant
residual in the distribution system. In the Stage 1 DBPR, maximum residual disinfectant levels
(MRDLs) were promulgated for chlorine (4.0 mg/L), chloramine (4.0 mg/L), and chlorine
dioxide (0.8 mg/L). Therefore, the fact that the disinfectant residual concentration is limited
may (in poorly operated systems) result in failure to meet the TCR by not having sufficient
oxidizing ability. Although much smaller doses of disinfectants are needed, the residence times
in distribution systems can be large (i.e., on the order of days). However, the above should not
be a problem for most well operated systems. Maintaining microbial protection through the
use of secondary disinfection while limiting the concentrations of DBFs requires simultaneous
compliance with the TCR, Stage 1 DBPR, and the IESWTR.
5.1.2 Issues
The TCR's primary intention is to protect systems against microbial contamination from
regrowth or outside sources such as a pipeline break or cross-connection with wastewater
piping. A disinfectant residual alone will not ensure the absence of a coliform regrowth
problem; however the absence of a residual indicates a problem. The TCR, however, addresses
the occurrence of coliforms since coliforms are indicators of contamination. An acute violation
of the TCR occurs when a repeat sample is fecal coliform-positive or E. co//'-positive or if a
fecal coliform-positive or E. co//'-positive original sample is followed by a total coliform-
positive. As a result of this lack of source discrimination, the TCR can respond to coliforms
resulting from regrowth due to disinfectant resistance or reactivation of injured bacteria
(AWWARF, 1990a). There can also be events during which bacteria shed from the pipe
surface release coliforms within biofilms. Such events may be a more common source of
coliform detection than fecal source contamination (Camper et al., 1996; Camper, 1996).
Microbial contamination can result from two principal sources. The first and historically most
significant source is from cross-connections with wastewater piping or other external sources
such as pipe breaks or breakthroughs at the treatment plant (i.e., viable, but perhaps injured,
bacteria pass through the disinfection process). These external sources of microbial
contamination are due to transport phenomena rather than cell growth, which is a biochemical
reaction process. The second source of microbial contamination is growth of bacteria in the
distribution system, which may have originated outside of the system. An event of microbial
contamination, regardless of the source, is monitored under the TCR. However, the distinction
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
between the two types of sources assists in understanding the potential conflicts that can arise
between the TCR, Stage 1 DBPR, and IESWTR. Table 5-1 categorizes these conflicts in
terms of the source of microbial contamination.
Table 5-1. TCR, Stage 1 DBPR, and IESWTR Conflicts Resulting from the Source of
Microbial Contamination
Source of Microbial Contamination Potential TCR, Stage 1 DBPR, and IESWTR Conflict
Growth of bacteria in distribution system • Change in primary disinfectant to ozone
• Change in primary/secondary disinfection practices
• Enhanced coagulation/softening increased turbidity
External source of bacteria • Maximum disinfectant residual concentration
• Enhanced coagulation/softening increased turbidity
Although the TCR requires maintenance of a disinfectant residual in the distribution system, the
presence of a residual does not guarantee the prevention of bacterial occurrences. Biofilms on
the inside lining of distribution pipe can contain coliforms and other bacteria. Biofilms can be
described as the accumulation of microbial cells at the pipe surface (Characklis et al., 1988).
Occurrence of a biofilm begins when microbial cells being carried in the liquid medium become
entrapped or adsorbed at the surface of the pipe. Metabolism can occur if an energy source
(e.g., AOC and other nutrients) and other essential nutrients are available. With metabolism
comes growth and the population forming the biofilm can increase (Characklis et al., 1988).
5.2 Coliform Growth in Distribution System When
Secondary Disinfectant is Changed to Chloramine
5.2.1 Occurrences of Coliform Growth
Chloramines have been shown to be effective secondary disinfectants, which also minimize the
formation of DBFs. According to EPA (1992b) and Jacangelo et al. (1987), chloramine is
better able to penetrate the biofilm layer and inactivate attached organisms because it is more
limited, than chlorine, in the types of compounds with which it will react. Studies conducted
by LeChevallier et al. (1990) suggest that biofilm control can be achieved using chloramine
levels ranging from 2 to 4 mg/L. Another study, conducted to determine the effects of
maintaining a chloramine residual on distribution system water quality found that distribution
system water samples testing positive for coliform bacteria dropped from 56.1 percent to 18.2
percent after conversion to chloramine (MacLeod and Zimmerman, 1986). More than 70
utilities in the U.S. effectively use chloramines for disinfection of distribution water supplies
(Kreftetal., 1985).
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There are some disadvantages with the use of chloramine as a disinfectant. One of the major
disadvantages is that, with the presence of ammonia, there is a potential for biological
nitrification with chloramination. Nitrification is inversely proportional to the chloramine
residual, which can increase coliform growth and increase the growth of heterotrophic bacteria.
Also, when certain control practices are implemented, destruction of biofilms may result in
coliforms being released (Wilczak et al., 1996). As such, changing the secondary disinfectant
to chloramine to comply with the Stage 1 DBPR and IESWTR can cause potential compliance
conflicts with the TCR. Figure 5-1 shows an example of the relationships among the
chloramine residual, HPC bacterial growth, and free chlorine residual during a nitrification
episode when free chlorine was used to control nitrification (Skadsen, 1993). As nitrates
increase and chloramine is depleted, increases in coliform and HPC growth occur.
4.5
4.0
3.5
3.0
= 2.0
B
I
" 1.5
Q
1.0
0.5
0.0
1,400
1,200
1,000
800
600 b
(D
400
200
Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.
Month
Modified from Skadsen, 1993
Figure 5-1. Example of Disinfectant Residual/Bacterial Relationship During a Nitrification
Control Episode
5.2.2 Nitrification
Nitrification can have various adverse effects on water quality, including a loss of total chlorine
and ammonia residuals, consumption of dissolved oxygen, and increase in nitrate levels, and an
increase in HPC bacteria concentration, creating the potential for violation of the TCR
(Kirmeyer, et al., 1995). Nitrification in chloraminated drinking waters is usually partially due
to excess ammonia present in the distribution system (Skadsen, 1993). The excess ammonia
encourages the growth of nitrifying bacteria which convert ammonia to nitrates. An
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
intermediate step in this conversion results in a small amount of nitrite being formed. Research
has shown that a chlorine demand of 5.0 mg/L is exerted by 1.0 mg/L of nitrite (Cowman and
Singer, 1994). The nitrites rapidly reduce free chlorine, accelerate decomposition of
chloramines, and can interfere with the measurement of free chlorine (Skadsen, 1993). If
nitrification episodes are allowed to continue, very low (or zero) total chlorine residual
concentration levels may occur. Loss of chlorine residual allows an increase in HPC bacteria
and potential increases in total coliforms resulting in a positive sample (Cowman and Singer,
1994).
5.2.2.1 Biology
Nitrification occurs in two phases, with the oxidation of ammonia to nitrite followed by the
oxidation of nitrite to nitrate. Ammonia-oxidizing bacteria (AOB) facilitate the conversion to
nitrite. Nitrite causes a high free chlorine demand which accelerates the destruction of the
chloramine residual (Wolfe, 1990). Lieu et al. (1993) suggested that control of nitrification in
the distribution system could be optimized by inactivating AOB. This research demonstrated
how AOB inactivation was primarily dependent on chloramine dosage.
Several possible factors have been implicated as contributing to nitrification. These factors
include low chlorine to ammonia ratio, long detention times, and high (25°C - 30°C)
temperatures (Wolfe et al., 1988 and 1990). Though some articles note that low chloramine
dosages may lead to nitrification, other research has reported nitrification occurring at
chloramine concentrations greater than 5.0 mg/L (Kirmeyer et al., 1995). Nitrifying bacteria
are more resistant to disinfection by chloramine than by free chlorine (Wolfe et al., 1990). The
optimum conditions for nitrification consist of a water system with free-ammonia, a pH of 7.5
to 8.5, dissolved oxygen, a water temperature of 25°C to 30°C, and a dark environment.
Nitrifying bacteria, or nitrite-oxidizing bacteria (NOB), exhibit slow growth and are inhibited
by sunlight. NOB has been found in higher numbers in the sediment of distribution systems
than in the biofilm (Wolfe et al., 1988 and 1990).
5.2.2.2 Occurrence
If the water storage reservoirs in the distribution system are covered and have low disinfectant
residuals, partial nitrification may occur (White, 1992). Covering a reservoir may cause
proliferation of nitrifying bacteria that generate nitrites. Eventually, the reservoir may become
biologically unstable, and disagreeable tastes and odors may result. All surface water and
GWUDI systems serving 10,000 or more people are required to cover newly constructed
treated water reservoirs (USEPA, 1998b). EPA also recommends covering old storage
reservoirs. It is important to shock disinfect newly uncovered and newly constructed
reservoirs before use and to maintain an adequate residual disinfectant in the stored reservoir
water to inhibit nitrifying bacteria and prevent nitrification.
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
5.2.3 Recommendations
Mechanisms for controlling the occurrence of coliform growth and nitrification inlcude higher
chloramine residuals, higher chlorine:ammonia-nitrogen ratios, periodic switching to free chlorine
(particularly during warmer months), more frequent turnover in storage reservoirs, and
distribution systems flushing (AWWARF, 1993). The use of free chlorine to control nitrification
has been correlated with increased HPC bacteria without a violation of the TCR (Skadsen, 1993).
Nitrification may be controlled by taking corrective action when chloramine residuals are depleted
in the distribution system. This can be done by monitoring the monochloramine and dichloramine
residuals at strategic locations throughout the distribution system (White, 1992). Also, as stated
earlier, monitoring water, pH, and temperature is important in determining when conditions
favorable for nitrification are occurring in the distribution system, and specifically, at a pH
between 7.5 and 8.5 and a water temperature above 20°C. Therefore, to prevent coliform
occurrence, "high" levels of nitrites, loss of chloramine residual, elevated levels of HPC, and
associated taste and odor problems, good chloramines management is required. This includes, in
addition to the above-mentioned mechanisms, control of corrosion and the elimination of stagnant
areas in the distribution system (AWWARF, 1995).
The stability of the chloramine free residual is increased throughout the distribution system as a
result of microbial contaminant control and decreased bacterial concentrations in the raw water.
Recommended approaches to prevent and control nitrification in the distribution system include
(Cowman and Singer, 1994):
. Decreasing the detention time
. Increasing the chlorine to ammonia ratio
. Decreasing the excess ammonia concentration.
Kirmeyer et al. (1995) also recommends removing organic compounds at the treatment plant.
The distribution system should be evaluated to identify the low-flow or dead-end sections. The
detention times in the system should be operationally minimized (Skadsen, 1993). Additional
recommendation for monitoring parameters and locations for the control of coliform growth and
nitrification follows.
5.2.3.1 Monitoring Parameters
Nitrification is suspected in chloraminated water systems when chloramine residuals are rapidly
depleted. Primary monitoring parameters include:
Chemical balance of nitrogen species: This can be determined by measuring the free
and total ammonia, nitrate and nitrite concentrations, and calculating the differences
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
between the treatment plant finished water and a given point in the distribution
system.
. Heterotrophic Plate Counts using R2A agar: Standard plate counts may be useful,
but they are not as sensitive to changes as counts using the R2A agar. AWWA
(1995) recommends the use of R2A agar for HPC analysis for all utilities practicing
chloramination.
Secondary monitoring parameters (i.e., those which should not be used without corroboration
with a primary parameter) include the following:
. Chloramine (or total chlorine) residual: A sharp decrease in the chloramine residual
could signal the onset of nitrification. However, caution needs to be exercised since
chloramine residuals degrade over time in open reservoirs, in the presence of biofilm
and under other distribution system conditions, such as backflow incidents.
. Dissolved Oxygen (DO): Decreases in DO levels frequently correlate with
nitrification in some utilities.
. Alkalinity: Very few utilities report a strong correlation between alkalinity decreases
and nitrification (AWWA, 1995).
5.2.3.2 Monitoring Locations
Raw water: Sampling data should include baseline information on ammonia, nitrate and
nitrite concentration, and TOC concentration.
. Treatment plant finished water: AWWA recommends that utilities monitor the chlorine
to ammonia ratios as mg/L of Cl per mg/L of N. This ratio can be directly measured, or
the applied ratio can be adjusted for the chlorine demand.
Reservoirs: Measurements in reservoirs should evaluate nitrate and nitrite
concentrations, free ammonia, HPC, temperature, DO, and total disinfectant residual.
Turnover rates for the reservoir's water should also be routinely monitored.
Dead-end mains: Nitrate and nitrite concentrations, HPC, DO, temperature, and
disinfectant residual should be monitored at dead-end main locations. Accurate flushing
records should also be maintained and system detention times should be estimated on a
seasonal basis.
Designated coliform monitoring locations: These locations should be routinely sampled
for nitrate, nitrite, HPC, and chloramine residual concentrations.
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5.2.4 Case Study
Case Study No. 6 presents an example of how TCR requirements were met while also
achieving the DBF MCLs by using chloramine as a secondary disinfectant alternative.
Case Study No. 6: Simultaneous Compliance between TCR and DBF MCL
Using Chloramine as the Alternative Secondary Disinfectant
Background
The following case study describes how Plant F could simultaneously comply with the TCR
requirements and meet the DBPR MCLs using chloramine as the alternative secondary disinfectant.
The design parameters (including treatment processes), and raw and finished water quality of Plant F
(serving 400,000 people) are provided below:
Source Type:
Flow Rate:
Treatment System:
Surface Water
Average Daily Flow - 40 mgd
Design Flow - 60 mgd
Rapid Mix
Coagulation/Flocculation (alum, 20 mg/L)
Sedimentation (theoretical detention time - 3 hours)
Filtration (No. of units - 30, single media, loading rate 2 gpm/ft2)
Clearwell (theoretical detention time - 30 min)
Disinfection (maximum chlorine dose - 5.0 mg/L, point of application
raw water inlet)
TOC - 7.0 mg/L
pH - 6.8
Alkalinity - 60 to 80 mg/L
Turbidity - 45 to 110NTU
Finished Water Quality: TOC - 4.9 (30 percent removal)
pH - 6.5
Alkalinity - 40 to 60 mg/L
Turbidity - 0.2 NTU
Residual Chlorine - 2.0 mg/L
Total coliforms - No of samples collected per month - 210
No. of samples positive per month - 5
Raw Water Quality:
Distribution System
Water Quality:
* profiling required
TTHM -0.090 mg/L (Running Annual Average)*
F£AA5 -0.050 mg/L (Running Annual Average)*
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
Simultaneous Compliance Issues
Stage 1 DBPR. The Stage 1 DBPR reduces the MCL of TTHMs in the finished water to 80
which is 10 |o,g/L lower than the current TTHM concentration at Plant F. Plant F determined that
changing the secondary disinfectant from chlorine to chloramine will prevent the formation of 1 THMs
above the MCL.
TCR. For Plant F, serving 400,000 people, the TCR requires 200 routine samples to be collected per
month, out of which no more than 10 samples (5 percent) may be positive for total coliform bacteria.
None of the total coliform-positive routine samples may be positive for fecal coliform or E. coll.
Potential Conflicts. Chlorine reacts with NOM to produce a variety of DBFs, including THMs,
haloacetic acids (F£AAs), and brominated products (if bromide ion is present). Use of chloramine as an
alternative secondary disinfectant can reduce the formation of DBFs to comply with the DBPR
requirements. However, the presence of ammonia from using chloramine increases the potential for
biological nitrification in the distribution system. Nitrification can cause a loss of total chlorine and
ammonia residuals, and an increase in bacteria. The greater number of bacteria increases the potential
for TCR violation. The system must conduct disinfection profiling.
Steps to Resolve Conflicts and Results Achieved
After conducting bench- and pilot- scale studies, Plant F switched the secondary disinfectant from
chlorine to chloramine to meet the TTHM requirement. Using a chlorine concentration of 4 mg/L and
ammonia concentration of 1.0 mg/L (chlorine-to-ammonia ratio of 4:1), the plant was able to reduce the
TTHM to 70 |o,g/L and thus comply with the DBPR MCL for TTHM. The chloramine residual was
2.5 mg/L and excess ammonia was 0.2 mg/L under these conditions. The system is required to consult
with the State and disinfection profiling and benchmarking is required.
Operational mechanisms implemented by Plant F to control the coliform growth and nitrification
included maintaining a high chloramine residual (monochloramine preferred) and a high chlorine-to-
ammonia ratio. Monitoring of monochloramine and dichloroamine residuals was conducted at strategic
locations throughout the distribution system. The chorine-to-ammonia ratio was optimized to maintain
adequate chloramine residual and low excess ammonia. Increasing the ratio further to 5:1 would help
control the nitrification problem by decreasing the amount of ammonia in the distribution system, but
would increase the potential of a chlorine overdose that would reduce the chloramine residual levels that
are desired in the distribution system. Therefore, the higher dose was used only in the summer months
during the highest potential for biological growth.
Additional steps implemented by the plant were periodic switching to free chlorine, and more frequent
turnover in storage reservoirs and the distribution system. Once a year, Plant F uses chlorine past the
breakpoint to allow a free residual for 30 days. This is simply done by turning off the ammonia
addition temporarily to ensure that free chlorine is the secondary disinfectant. The increased chlorine
oxidizes any nitrite or nitrifying bacteria and eliminates the excess ammonia in the system. Using
higher chlorine dose was found to be more effective than a flushing program for the storage reservoirs
and the distribution systems that produced only temporary results. The plant is able to maintain the
number of coliform-positive samples to the MCL of less than 5 percent and thus comply with the TCR
requirements.
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5.3 Coliform Growth in Distribution System When
Primary Disinfectant is Changed to Ozone
Ozone is a powerful oxidant that is able to achieve disinfection with less contact time and
concentration than other disinfectants, such as chlorine (DeMers and Renner, 1992). Ozone,
however, can only be used as a primary disinfectant since it cannot maintain a residual in the
distribution system. Thus, ozone disinfection must be coupled with a secondary disinfectant,
such as chlorine or chloramines, for a complete disinfection system.
5.3.1 Occurrence
A principal advantage of ozone use as a primary disinfectant is THM and HAAS control. This
advantage, however, can be offset in terms of DBF formation since ozone can react with NOM
to produce unregulated organic byproducts such as ketones and aldehydes. In the presence of
bromide, ozone can react with organic matter to form bromate ion, a contaminant regulated
under the Stage 1 DBPR. In terms of the TCR, ozonation can increase organic matter which
can be biodegraded and can promote bacterial growth/regrowth in the distribution system
(Langlais et al., 1991). Bacterial growth can occur when cellular metabolism in biofilms or
suspended bacteria is increased due to the additional nutrients available from AOC. AOC is a
byproduct of ozonation in water containing sufficient NOM.
5.3.2 Recommendations
Application of ozone disinfection appears most favorable for systems with low-TOC waters or
where biological filtration is practiced at the treatment facility to reduce biodegradable organic
matter. However, the decision by a PWS to change to ozone as the primary disinfectant is
usually made to lower TTHMs or HAAS, a problem with high (not low) TOC waters.
5.3.2.1 Applicability of Ozone
Ozone can be effective in partially oxidizing organics in the water to biodegradable compounds
that can be removed by biological filtration (DeMers and Renner, 1992). This partial oxidation
gives rise to lower molecular weight compounds that are more easily biodegradable. Just as
the more easily biodegradable organics are effectively removed by biofiltration, they can
become a substrate for the microbial population in the distribution system, if not removed.
This increase in the biodegradable fraction of organic carbon occurs as a result of moderate
levels of ozonation. These ozone levels are typical of the doses commonly applied for
disinfection.
The organic acid and aldehyde byproducts of ozonation discussed above are readily
biodegradable and are a component of the AOC or BDOC. Ozonation can increase the BDOC
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
by oxidation. Therefore, if water disinfected with ozone is treated by a biologically active
process (i.e., biological active carbon), removal of these biodegradable byproducts can be
expected following the development of a biomass. The use of biologically active filters,
maintained by not applying disinfectant prior to the filters, has been shown to successfully
remove aldehydes and other compounds representing a portion of the BDOC in a water
(Bablon et al., 1988; Rittman, 1990; Reckhow et al., 1992). Oxidation of chlorinated DBF
precursors using ozone has been shown to be effective at low ozone doses (Shukairy et al.,
1992).
The wide-scale conversion from chlorination to ozonation in previously biologically stable
distribution systems in the Netherlands provides lessons for PWSs in the United States
changing to ozone as their primary disinfectant. Van der Kooij (1997) reported that the
introduction of ozonation to replace chlorination in previously biologically stable water was
followed by regrowth phenomena in a distribution system in the Netherlands. Research
showed that biodegradable low molecular weight compounds were formed when ozone
oxidized humic and fulvic acids. HPC values directly correlated with AOC concentrations
greater than 10 |j,g/L carbon (Van der Kooij, 1997). Thus, monitoring and reduction of AOC
levels could be a tool to maintain compliance with the TCR.
5.3.2.2 Biological Treatment
Incorporating biological treatment into the water treatment process when changing to ozone as
a primary disinfectant could have benefits for the distribution system beyond removing AOC
created by ozonation (Hozalski et al., 1995). Research has been shown that a very little EBCT
is required for high levels of AOC removal in biological filters. Prevost reported that as little
as 2 minutes of EBCT provided up to 90 percent AOC removal (Prevost et al., 1992). An
EBCT of 2 minutes is an atypical EBCT for a filter; to further remove the biodegradable
portions of TOC for the additional benefit of distribution system water quality required 15-20
minutes of EBCT. Thus, while AOC can be removed in an existing unit process such as the
filter beds, once it is made biologically active, a new process with more EBCT can result in a
significant reduction in the entire biodegradable fraction of TOC (Prevost et al., 1992).
It is desirable to achieve biological filtration with the same filtration system used to remove
turbidity (Krasner et al., 1990). This removal can be accomplished in unit filtration processes
which are already in place in the plant such as sand filters, sand filters with GAC, and post-
filtration GAC. Biofiltration, however, does not appear to be equivalent to chemical removal.
In parallel studies, biofiltration removed 8 to 12 percent of TOC, whereas physicochemical
processes removed 28 to 68 percent (Prevost et al., 1992).
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5.3.3 Summary and Recommendations
In summary, possible strategies for controlling bacterial growth in distribution systems when
the primary disinfectant is changed to ozone are as follows:
• Ozonation in the absence of biological or GAC treatment may result in adding biodegradable
organic carbon, which then leads to regrowth of bacteria in the distribution system. In low-
TOC waters or with biological treatment following ozone addition, biologically stable water
should be produced minimizing distribution system coliform presence.
• Establishing the lower limit of AOC concentration, which prevents bacterial regrowth, can
assist the PWS in monitoring for and effectively removing enough AOC to maintain biological
stability.
5.3.4 Case Study
Case Study No. 7 presents an example of how bacterial growth requirements under the TCR
were met while also achieving the Stage 1 DBPR requirements by using ozone as an alternative
primary disinfectant.
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Case Study No. 7: Complying with the Total Coliform Rule and
the Stage 1 DBPR Using Ozone as the Primary Disinfectant
Background
The following case study describes how Plant G could simultaneously comply with the DBPR by
switching to ozonation as a primary disinfectant and with the TCR by taking steps to prevent biological
regrowth in the distribution system. The design parameters (including treatment processes), and raw
and finished water quality of Plant G (serving 15,000 people) are provided below.
Source Type:
Flow Rate:
Treatment System:
Raw Water Quality:
Surface Water
Average Daily Flow -2.2 mgd
Design Flow - 4.0 mgd
Coagulation/Flocculation (alum, 20 mg/L)
Sedimentation (theoretical detention time - 3 hours)
Filtration (4 rapid sand filters, loading rate 2 gpm/ft2)
Primary Disinfection (maximum chlorine dose 5.0 mg/L, point of application
prior to coagulation/flocculation)
Secondary Disinfection (maximum chlorine dose -2.0 mg/L, point of
application -following filtration)
TOC - 10 mg/L
pH - 6.5
Alkalinity - 50 to 70 mg/L
Turbiditv- 10to40NTU
Finished Water Quality: TOC - 7.0 mg/L (30 percent removal)
pH - 6.5
Alkalinity - 40 to 60 mg/L
Turbidity - 0.2 NTU
Residual Chlorine - 0.2 mg/L at the furthest point in the distribution system
Total coliforms - No of samples collected per month - 20
- No. of samples positive per month - 0
Distribution System
Water Quality:
* profiling required
TTHM -0.090 mg/L (Running Annual Average)*
F£AA5 -0.050 mg/L (Running Annual Average)*
Simultaneous Compliance Issues
Stage 1 DBPR. The Stage 1 DBPR sets the TTHM MCL at 80 ng/L which requires a 10
reduction from Plant Gs existing finished water TTFEVI concentration. Plant G determined that because
of the high concentration of TOC in its raw water, it must change its primary disinfectant to ozonation
to prevent the formation of TTHMs.
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TCR. The TCR requires Plant G, serving 15,000 people, to collect 15 samples from the distribution
system per month. No more than 1 of those samples may test positive for the presence of total
coliform bacteria and none of the samples which test positive for total coliform may test positive for
fecal coliform or E. coli.
Potential Conflicts. By switching from chlorination to ozonation as the primary disinfectant, Plant G
does not eliminate its ability to provide a disinfectant residual, because it still maintains a chlorination
system following the filters. However, ozonation of the raw water would result in the partial oxidation
of the organic matter into biodegradable organic carbon (BDOC). These biodegradable organics could
provide nutrients for bacteria and promote biological regrowth in the distribution system. The
biological regrowth within the distribution system could result in an increased number of total coliform
bacteria detections. An additional problem is the potential for continued formation of TTHMs by
reaction of the organics and the chlorine disinfectant.
Steps to Resolve Conflicts and Results Achieved
Plant G determines that it must reduce the biodegradable organic carbon (BDOC) in the water prior to
applying the chlorine disinfectant. Systems switching their primary disinfectant to ozone are required to
consult with the State and profile and benchmark for virus disinfection. To accomplish this, Plant G
modifies its existing sand filters to achieve biological filtration by increasing the filter media depth
reducing the frequency of the filter backwash. The filter media depth was increased by the system from
2.5 feet to four feet, resulting in an EBCT of 15 minutes. The frequency of backwash was decreased
substantially by the operators thus resulting in filter run times which may lower filtered water rates. To
improve the filtration rate, the operators used surface water wash more frequently than before the filters
were used as biofilters. Backwashes were performed as the filters became plugged or turbidity break-
through occurred. The decreased frequency of backwash, promoted biological growth on the filters.
The biologically active filters consumed the BDOC and further reduced the TOC levels. This resulted
in the reduction of TTHM formation to levels below the TTHM MCL and in the continued control of
biological regrowth, as measured by the lack of coliform bacteria in the distribution system. There
could be problems with media carryover during backwash. Also, the biofilm formed over the media has
the tendency to slough off from time to time, resulting in sudden turbidity breakthroughs, unless the
process is properly managed.
5.4 Coliform Growth in the Distribution System Resulting
from Changes to Primary and Secondary Disinfection
Practices
This section provides a summary of potential TCR compliance issues resulting from changes in
disinfection practices, including a summary of the issues addressed in the previous two
sections. There is relatively little information available that describes distribution system
compliance issues with the TCR following changes in disinfection practice. The discussions in
the previous two sections, however, suggest that potential TCR compliance issues could arise
(e.g., nitrification). Table 5-2 outlines potential TCR control strategies for addressing
distribution system responses to disinfectant changes.
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5.4.1 Change from Chlorine/Chlorine to Chlorine/Chloramine
Section 5.2 contains a brief discussion about coliform growth in distribution systems when the
secondary disinfectant is changed from chlorine to chloramine. In summary, the use of
chloramines as a secondary disinfectant has been shown to be effective in protecting the
distribution system from microbial contamination while at the same time minimizing the
formation of DBFs. Chloramines, on the other hand, can cause methemoglobinemia and
adversely affect the health of kidney dialysis patients (USEPA, 1999b). The presence of
ammonia indicates that the potential for biological nitrification exists. For a more thorough
discussion about the chemistry, primary uses, points of application, DBF formation, and
pathogen inactivation and disinfection efficacy of chloramines please refer to the Alternative
Disinfectants and Oxidants Guidance Manual (USEPA, 1999b).
5.4.2 Change from Chlorine/Chlorine to Ozone/Chlorine
Section 5.3 discusses coliform growth in distribution systems when changing the primary
disinfectant to ozone. This section provides a discussion of recent data on byproduct
formation when changing to ozone as a primary disinfectant. For a more thorough discussion
about the chemistry, primary uses and points of application, DBF formation, and pathogen
inactivation and disinfection efficacy of ozone refer to the Alternative Disinfectants and
Oxidants Guidance Manual (USEPA, 1999b).
The ozone/chlorine strategy may result in brominated DBFs (note that brominated DBFs have
health implications). However, the main benefit derived from using ozone as the primary
disinfectant is for controlling TFDVI formation. This is because free chlorine is applied later in
the treatment process after the precursors have been removed.
The cities of Phoenix (1989) and San Diego (1990) have, however, reported that substituting
ozone for chlorine as a primary disinfectant, when not practicing pre-chlorination, resulted in
an increased TFDVI formation in the finished water (USEPA, 1999b).
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
Table 5-2. TCR Control Strategies Following Changes in Disinfection Practice
Change in Disinfection Practice
Chlorine/Chlorine to
Chlorine/Chloramine
Chlorine/Chlorine to Ozone/Chlorine
Chlorine/Chlorine to Ozone/Chloramine
Chlorine/Chlorine to Chlorine Dioxide/
Chlorine Dioxide
Chlorine/Chloramine to
Ozone/Chloramine
TCR Control Strategies
Control nitrification through:
1. Decreasing detention time
2. Increasing the chlorine to ammonia ratio
3. Decreasing the excess ammonia concentration
Control NOM after ozonation through:
1. Active biological filtration
2. Limiting ozone dosage
3. Alternative low-TOC water supply
4. Ozonation: Results in the formation of smaller and more easily
volatizing compounds (like ChsCHO, HCHO, glyoxal, etc.) and
hence, results in lowering the TOC in many cases. In some
cases, ozone may oxidize the NOM all the way to CO2 (i.e.,
mineralize), resulting in lower TOC values.
Control NOM after ozonation through:
1. Active biological filtration
2. Limiting ozone dosage
3. Alternative low-TOC water supply
4. Ozonation: Results in the formation of smaller and more easily
volatizing compounds (like Ch3CHO, HCHO, glyoxal, etc.) and
hence, results in lowering the TOC in many cases. In some
cases, ozone may oxidize the NOM all the way to CO2 (i.e.,
mineralize), resulting in lower TOC values.
Control nitrification through:
1. Decreasing detention time
2. Increasing the chlorine to ammonia ratio
3. Decreasing the excess ammonia concentration
Increase distribution system residuals:
1. Add chlorine/chloramine remotely in system
2. Eliminate free chlorine in distribution system
Control NOM after ozonation through:
1. Active biological filtration
2. Limiting ozone dosage
3. Alternative low-TOC water supply
4. Ozonation: Results in the formation of smaller and more easily
volatizing compounds (like Ch3CHO, HCHO, glyoxal, etc.) and
hence, results in lowering the TOC in many cases. In some
cases, ozone may oxidize the NOM all the way to CO2 (i.e.,
mineralize), resulting in lower TOC values.
Control nitrification through:
1. Decreasing detention time
2. Increasing the chlorine to ammonia ratio
3. Decreasing the excess ammonia concentration
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5. TOTAL COLIFORM RULE AND ISSUES ON COMPLIANCE WITH THE M-DBPR
Table 5-2. TCR Control Strategies Following Changes in Disinfection Practice
(Continued)
Change in Disinfection Practice
Chlorine/Chloramine to Chlorine Dioxide/
Chloramine
Ozone/Chlorine to Ozone/Chloramine
TCR Control Strategies
Increase distribution system residuals:
1. Add chlorine/chloramine remotely in system
2. Eliminate free chlorine in distribution system
Control nitrification through:
1. Decreasing detention time
2. Increasing the chlorine to ammonia ratio
3. Decreasing the excess ammonia concentration
Control nitrification through:
1. Decreasing detention time
2. Increasing the chlorine to ammonia ratio
3. Decreasing the excess ammonia concentration
Source: USEPA, 1994.
Research regarding the disinfection of a low-bromide water with ozone/chlorine suggests that
THMs, HAAs, and chloral hydrates (currently inregulated) are formed during disinfection
(LeBel et al., 1995). Raw and treated water characteristics from this study are shown in Table
5-3, and DBF speciation is shown in Table 5-4. The study plant uses flocculation,
sedimentation, chlorination (in summer only to improve CT and minimize biofilm growth
potential in the network), sand filtration, ozonation, and post-chlorination for processing
water.
Table 5-3. Raw and Treated Water Quality at a Plant Using Ozone/Chlorine
Parameter
PH
TOC, mg/L
TOX, u.gCI7L
Bromide ion, mg/L
TKN, mg/L
Color, TCU
Turbidity, NTU
Hardness, mg/L as CaCO3
Alkalinity, mg/L as CaCO3
Raw Water
6.8-7.6
3.4-5.8
NA
<0.002
<0.1
27.4
3.4
20
12
Treated Water
_____
1.8-3.0
13-210
<0.002
<0.1
1.7
0.3
31
12
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Table 5-4. DBF Speciation at a Plant Using Ozone/Chlorine
Mean Maximum
Parameter
Chloroform 29.6 100.1
Bromodichloromethane 1.5 3.2
Chlorodibromomethane 0.1 0.2
Bromoform <0.1 <0.1
Total THMs 31.2 103.4
HAAS 19.8 78.6
Chloral Hydrate 8.9 23.4
Seasonally, the highest concentrations occurred from July through October, and concentrations
increased with time through the water system (from raw water through the furthest sampling
point in the distribution system). Clearly, even from a relatively low TOC water, the
ozone/chlorine disinfection practice can cause MCLs to be exceeded. However, the mean
values indicate generally good results.
At plants where published data are available, there appear to be no distribution system impacts
resulting from the ozone/chlorine disinfection practice change (AWWARF, 1990b).
5.4.3 Change from Chlorine/Chlorine to Ozone/Chloramine
The primary impact of this disinfection practice change results from the effects of ozone
oxidation of organics coupled with the change from chlorine to chloramine. Distribution
system problems associated with the use of combined chlorine residual, or no residual, have
been documented in several instances (AWWARF, 1990b). In these cases, the use of
combined chlorine is characterized by an initial satisfactory phase in which chloramine residuals
are easily maintained throughout the system and bacterial counts are very low. However,
problems may develop over a period of years including increased bacterial counts, declines in
combined chlorine residual, increased taste and odor complaints, and reduced transmission
main carrying capacity. Conversion of the system to free-chlorine residual produces an initial
increase in consumer complaints of taste and odors resulting from oxidation of accumulated
organic material, and difficulty in maintaining a free-chlorine concentration at the ends of the
distribution system (AWWA, 1990).
A byproduct of ozonation, acetaldehyde, is a known precursor for chloral hydrate (neither is
currently regulated), a byproduct of chlorination. Enhancement of chloral hydrate has not been
observed when monochloramine is applied as the secondary disinfectant or if biologically active
filtration is used following ozonation and prior to chlorination (Singer, 1992). These
compounds are not currently regulated.
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5.4.4 Change from Chlorine/Chlorine to Chlorine Dioxide/
Chlorine Dioxide
A change in primary disinfectant from chlorine to chlorine dioxide and a change in secondary
disinfectant from chlorine to chlorine dioxide would likely cause a large reduction in TTHMs,
particularly where high efficiency chlorine dioxide generators are used. However, there is no
literature available where such a change has occurred and it is very unlikely that a system will
find chlorine dioxide as a feasible secondary disinfectant. A more likely scenario, for systems
seeking drastic reduction in TTHMS, is to replace a chlorine/chlorine system with a chlorine
dioxide/chloramine system.
The main concern with the use of chlorine dioxide as both the primary and secondary
disinfectant remains in the formation of the chlorite ion, an inorganic byproduct. Another
concern with the use of chlorine dioxide is meeting the chlorine dioxide MRDL and chlorite
MCL while maintaining a residual throughout the system.
According to Singer (1992), the oxidation products of chlorine dioxide have not been studied
extensively, therefore, the public health impact related to the use of chlorine dioxide is largely
unknown. The impact of the use of chlorine dioxide on the distribution system is speculative at
best. Although chlorine dioxide is expected to protect public health and the distribution system
from microbial contamination, the high reactivity of chlorine dioxide suggests that it might, like
ozone, create more biodegradable organic compounds that would enhance biofilms and
bacterial regrowth, particularly at remote sites in the distribution system and in unlooped lines.
5.4.5 Change from Chlorine/Chloramine to Ozone/Chloramine
The change to ozone as a primary disinfectant and chloramine remaining as a secondary
disinfectant will impact TCR compliance due to the action of ozone on NOM. Having already
established distribution system practices for biofilm growth in chloraminated distribution water,
PWSs making this disinfection practice modification will focus on the biological stability of the
distribution system water.
In cases where the use of ozone as the primary disinfectant increases levels of AOC, biological
stability in the distribution system could be disrupted even though chloramination has been
practiced. As previously discussed in Section 5.3, AOC provides nutrient value for cell
metabolism. In a previously chloraminated system, control of nitrification may be achieved
using one or more of the techniques listed in Table 5-2. However, the additional nutrients in
AOC may require modification to the practices. Alternatively, biological filtration can be used
to effectively reduce nutrient levels.
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5.4.6 Change from Chlorine/Chloramine to Chlorine Dioxide/
Chloramine
A change in primary disinfectant from chlorine to chlorine dioxide while continuing
chloramination as the secondary disinfectant would likely be undertaken to dramatically reduce
TTHMs. No instance could be found in the literature where this change has occurred.
Therefore, it is not known from experience what the possible conflicts or problems might be.
However, speculation on the high reactivity of chlorine dioxide would suggest that there would
be concern for creation of biodegradable organic compounds in the same way ozone creates
aldehydes and AOC. If more biodegradable organic compounds are created, additional
nutrients could be available in the distribution system that were not present when chlorination
was the primary disinfectant. A greater amount of nutrients in the distribution system could
result in enhanced biofilms and enhanced bacterial re-growth. It is possible under this
hypothetical scenario that a violation of the TCR could occur. However, a comparison of the
oxidation potentials of chlorine dioxide, ozone and free chlorine (i.e., C1O2 oxidation potential
= 0.95V, O3 = 2.07V, HOC1 = 1.36V) suggests that the formation of easily biodegradable
compounds would not be of much concern. Additional research is needed to verify the
speculation and hypotheses described above.
Mitigating this hypothetical problem is expected to utilize biologically active filters to
effectively remove the more biodegradable organics created by chorine dioxide destruction of
NOM.
5.4.7 Change from Ozone/Chlorine to Ozone/Chloramine
The primary effect of this change results from the change from chlorine as a secondary
disinfectant to chloramine. Current literature demonstrates that such a shift may create a
problem in maintaining a chlorine residual in the network (AWWA, 1990). The problems
associated with using chloramine develop over time and are manifested by increases in bacterial
counts, taste and odor problems, a decrease in residual levels, and reduced transmission
carrying capacity due to biofilm formation (AWWA, 1990). These problems can be solved
through the occasional use of free chlorine as a secondary disinfectant and a GAC filter
following ozonation.
5.5 Coliform Growth in the Distribution System Which
Could Result From Alternative Disinfection
Benchmarking
Disinfection benchmarking is a methodology and process by which PWSs and States, working
together, ensure that there will be no significant reduction in microbial protection when
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disinfection practices are modified to meet new standards for DBFs under the Stage 1 DBPR.
The Disinfection Profiling and Benchmarking Guidance Manual (USEPA, 1999a) provides a
more detailed discussion of benchmarking procedures.
The competing aims of ensuring protection against microbial pathogens while modifying
disinfection practices to comply with forthcoming rules requires a process which is based on
cooperation between States and utilities. Disinfection benchmarking attempts to establish a
historic level of disinfection effectiveness through the analysis of previous daily log inactivation
levels of Giardia or viruses. An alternative benchmark is a level of disinfection effectiveness
that the PWS and the State have determined provides microbial protection when the
disinfection practice changes substantially. One example of the need for an alternative
benchmark is when the historic log inactivations are so high that they fail to provide meaningful
representation of the risks involved. In a case like this, the PWS and the State could agree to
allow reduction in the level of log inactivations. The subsequent reduction in the amount of
disinfection could adversely affect the biological stability in the distribution system.
With daily information on the disinfectant residuals, temperature, pH, and contact times, a
PWS can determine the daily log inactivation. By recording log inactivation over a year or a
period of years, the PWS can determine the minimum log inactivation during which zero
microbial contamination events occurred. This level of log inactivation can then become the
"benchmark." Thus, since the benchmark is determined from interchangeable values, a PWS
can modify disinfectant practices and still achieve log inactivation levels above the benchmark,
as long as the CT values of the disinfectant are known. However, if a PWS has been
disinfecting at a level which produces, for example, 50 logs of Giardia or virus inactivation,
the PWS may want to apply for a lower level and work with the State to establish an
alternative benchmark.
Systems changing their disinfectants from chlorine to other alternative disinfectants (for
example, ozone or chloride dioxide) will be required to develop a virus profile and benchmark
(please refer to the Disinfection Profiling and Benchmarking Guidance Manual (USEPA,
1999a) for more details). When a new benchmark is set, coliform growth in the distribution
system is not expected to occur because the State-approved alternative benchmarks will
maintain the current level of public health protection against Giardia and viruses, which are
generally more resistant to disinfection than coliforms.
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5.6 Coliform Growth in the Distribution System Which
Could Result from Enhanced Coagulation or
Enhanced Softening
Enhanced coagulation and enhanced softening can indirectly influence coliform growth in the
distribution system by lessening disinfectant effectiveness when pH is changed.
5.6.1 Occurrence
The relationship described above is complex, since the removal of the constituents of TOC
during enhanced coagulation and enhanced softening serves to reduce disinfectant demand.
Because microbial protection will generally be maintained at the treatment plant through the
profiling and benchmarking processes, the system should focus on the secondary disinfectants
with regards to lessening disinfectant effectiveness. Table 5-5 describes the general
relationships between changes in pH and the subsequent impact(s) on secondary disinfectant
effectiveness.
Table 5-5. Generalized Relationships between pH and Effectiveness of Disinfectants
Used for Secondary Disinfection
Secondary Disinfectant Effectiveness1
Enhanced Process pH Impact Chlorine Chlorine Dioxide Chloramines
Coagulation JJ, <> H H
Softening IT it IT IT
1 Ozone not included due to its practical limits as a secondary disinfectant.
5.6.2 Enhanced Coagulation
Enhanced coagulation occurs at lower pH levels than most waters. As shown in Figure 5-2,
the target pH for enhanced coagulation decreases with decreasing alkalinity. Unfortunately,
secondary disinfectant effectiveness decreases for both chloramines and chlorine dioxide, as
well. Chloramines are destabilized at lower pH levels, resulting in a lower proportion of the
mono-species, and more of the di- and tri- species. Another indirect effect can involve an
increase in the corrosivity of chloramines, which can impact the corrosion scale containing
bacterial populations. Therefore, a PWS contemplating enhanced coagulation and using
chloramines or chlorine dioxide as secondary disinfectants should evaluate the need to adjust
pH to prevent corrosion and remain in compliance with the LCR. Also, the system may need
to evaluate the impact on biological stability in the distribution system.
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60-120 M20-240
Alkalinity (mg/L as CaCO3)
Source: USEPA, 1994
Figure 5-2. Relationship Between Target pH and Alkalinity for Enhanced Coagulation
Enhanced Softening
Enhanced softening has the opposite effect on disinfectant effectiveness. The higher pH
required for this practice will enhance the effectiveness of chloramines and reduce that of
chlorine.
5.7 Summary and Recommendations
Modifying treatment practices to comply with the Stage 1 DBPR and IESWTR may cause
violations of the TCR. These problems can arise from a number of changes to the chemistry
and biology of the distribution system. Chief among the changes are the following:
• pH changes resulting from Stage 1 DBPR compliance that can affect the disinfection
effectiveness of chlorine and chloramines
• Increases in the amount of substrate available for biological regrowth in the distribution system
when the primary disinfectant is changed to ozone and, perhaps, chlorine dioxide
• Changes in disinfectants to comply with TTHM limits, such as chloramines for secondary
disinfection. Chloramines can provide the ammonia for regrowth if the process is not
controlled.
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6. OPERATIONAL ISSUES
Promulgation of the IESWTR and the Stage 1 DBPR may have significant impacts on the
operation of existing water treatment facilities. These two rules lower the MCL for TTHMs,
set new MCLs for HAAS, bromate, and chlorite; increase the requirements for turbidity
removal; define the removal requirements for Cryptosporidium; and set requirements for the
removal of TOC. These changes may result in the use of enhanced treatment, including
increased coagulant dosages and pH depression. To comply with these new rules, treatment
facilities may also be forced to make changes in the types and dosages of oxidants and
disinfectants, the types and dosages of coagulants, and the pH of coagulation. These changes
may present several operational problems for treatment facilities including:
• Corrosion of both treatment structures and equipment due to pH changes and
oxidant/disinfectant changes
• Changes in the type of chemical feed equipment and the location of chemical dosage points
• Changes in the process equipment distribution system
• Increased need for staff training regarding operational and maintenance issues
• Impacts on the volume and characteristics of treatment residuals
• Changes in water taste and odor due to the use of new oxidants and disinfectants
• Changes in water aesthetics due to changes in the coagulant type
• Changes in process chemistry that may result in distribution system impacts such as
nitrification and biological regrowth when chloramines are used as a residual disinfectant, or
the formation of chlorite ion when chlorine dioxide is used.
This chapter discusses some of the operational issues described above which are associated
with the implementation of enhanced coagulation and the use of alternative disinfectants.
Potential problems are identified along with possible solutions to allow a facility to achieve
simultaneous compliance with the regulations. This chapter is organized into the following
sections:
• Construction Materials
• Treatment Equipment
• Operations and Maintenance Staff Training
• Impact of Enhanced Coagulation on Process Residuals
• Taste and Odors.
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6. OPERATIONAL ISSUES
6.1 Construction Materials
The construction materials in an existing treatment facility may be subject to significant
corrosion and attack as a result of several of the treatment system changes that may occur to
meet the new regulations. Changes in coagulation pH to meet the enhanced treatment
requirements, or the use of stronger oxidants, may result in aggressive attacks on concrete and
steel tankage, as well as submerged treatment equipment and piping.
6.1.1 Impact of Enhanced Coagulation
The major impact on materials of construction in treatment facilities will result from the
Stage 1 DBPR requirements for enhanced treatment to achieve TOC removal. Research has
shown that to remove additional NOM during the treatment process, coagulant dosages may
have to be increased and the pH of the water adjusted. Coagulation with metal salts has been
demonstrated to yield optimal NOM removals at pH levels of 5.0 to 6.0 (White et al., 1997).
Depending on the required TOC removal to be achieved, some treatment facilities may have to
increase coagulant dosages and reduce the pH levels in the coagulation and flocculation basins.
The slightly acidic water in these basins increases the rate at which concrete and steel corrode.
Typical dosages of metal salts result in slightly acidic water. Acidic waters can dissolve the
calcium carbonate in the concrete and corrosion (rusting) of steel materials may occur. Lime
added for softening raises the pH and can promote the development of scale. As a result,
coagulation and flocculation treatment steps have been accomplished in unlined concrete tanks,
or in coated steel structures or pipelines. Submerged treatment equipment, such as mixers,
flocculators, and pumps, have been also been coated to inhibit corrosion by preventing contact
between the process water and any ferrous (steel, iron, etc.) surfaces.
The potential process changes implemented in response to enhanced coagulation may result in
water in the coagulation flocculation tanks with a much lower pH. These waters may be
corrosive enough to attack concrete surfaces and some protective coatings that may have been
used in the past. If enhanced treatment is required, and the appropriate bench and pilot scale
process testing determine that the pH must be lowered significantly below 7.0 (e.g., pH of 5.5
to 6.5), the treatment facility should evaluate all construction materials that will come in
contact with the lower pH water. The coatings on existing equipment, pipe linings, gaskets,
and structures should all be investigated to ensure that deterioration will not occur. The
investigation should also include an evaluation of the chemical resistance of the existing
surfaces to the treatment chemicals and oxidants to be used. This evaluation may even include
long-term exposure coupon tests to analyze corrosive attack.
If the evaluation demonstrates that additional protection is required, a variety of commercially
available coatings can be used to protect both ferrous and concrete surfaces. Possible coatings
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include epoxy, polyurethane, and vinyl paints that may be applied to both ferrous surfaces and
concrete. In addition, several cementitious coatings are available for application on concrete to
provide a sacrificial and replaceable mortar coating on the concrete surface.
The areas in the treatment train where pH will be depressed will determine the locations for
additional corrosion protection. Particular attention should be given to the application point of
the acid used for lowering pH, since very low pH areas may exist in a process stream until the
acid is thoroughly mixed into the flow. Since residual streams from sedimentation (i.e., sludge)
and filtration (i.e., filter backwash washwater) may be created prior to raising the pH,
corrosion protection may be required in the residual processing and dewatering facilities of the
plant.
Depending on the particular treatment configuration, chemical addition to raise the pH after
coagulation may occur some distance downstream, even after filtration. Many existing
treatment plants are constructed with common wall construction. This configuration will make
pH adjustment after coagulation difficult without a break in the hydraulic gradient.
The Guidance Manual for Enhanced Coagulation and Precipitative Softening (USEPA,
1999g) provides additional information that can be used to assist utilities in implementing,
monitoring, and complying with the treatment technique requirements in the final Stage 1
DBPR and to provide guidance to State staff responsible for implementing the treatment
requirements.
6.1.2 Impact of Disinfectant Changes
The Stage 1 DBPR also lowers the MCLs for TTHMs and sets a MCL for HAAS. As a result,
many facilities may begin to utilize alternative disinfectants and oxidants to produce fewer
DBFs, but maintain microbial protection. Some alternative disinfectants and oxidants, such as
ozone and chlorine are very strong oxidants and can cause localized corrosion at or near their
injection point. When changes in disinfectants or oxidants are contemplated, all construction
materials and equipment that will come in contact with the process water should be evaluated.
Application of coatings as described in the previous section would be an appropriate method of
corrosion protection, should it be warranted.
More detailed information on alternative disinfectants is provided in EP'A's Alternative
Disinfectants and Oxidants Guidance Manual (1999b).
6.2 Treatment Equipment
In addition to the impacts on construction materials discussed above, many facilities may also
experience impacts to existing treatment equipment due to changes in coagulants and
disinfectants. Changes in the treatment chemicals used at a facility may require significant
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changes in chemical storage and feed equipment. Obviously, the addition of new process
treatment units to accommodate the addition of ozone as a disinfectant may require major
structural modifications, as this addition could include ozone generators, contact chambers,
off-gas control, and biologically active filtration. However, it is less obvious that seemingly
minor changes in coagulants, such as the change from ferrous sulfate to ferric sulfate, may also
require substantial modifications to existing chemical storage facilities due to ferric sulfate's
greater specific gravity and lower pH. In other instances, various chemicals may have differing
freeze characteristics or viscosity, differing unloading and storage requirements, or be
incompatible with existing construction materials used in the storage, conveyance, feed, and
chemical piping systems.
Enhanced treatment for TOC removal may also require greater coagulant dosages, making
existing chemical storage and feed facilities inadequate. If modifications to the chemical feed
systems are contemplated, a complete evaluation of the existing storage and feed systems
should be performed to determine all modifications required after the chemicals to be used,
dosages, and injection locations have been determined.
The monitoring requirements of the IESWTR for filter effluent turbidity could also require new
process instrumentation as well as data management and retrieval equipment. Facility
operators may also consider automation to provide additional process monitoring of coagulant
dosage control (e.g., zeta potential, streaming current, or raw water turbidity), pH, disinfectant
residual, and turbidity at several points in the treatment process to better monitor overall plant
performance.
6.3 Operations and Maintenance Staff Training
As with any modification to a treatment process, requirements for increased staff and staff
training must be addressed. The addition of new disinfectants/oxidants, or the integration of
enhanced treatment, will require additional staff training not only to operate the new equipment
and treatment technologies, but also to maintain the new equipment. The addition of process
monitoring instrumentation may require additional staff training to interpret the new data being
received. As with any plant modification, the overall treatment plant Operations and
Maintenance Manual must be updated to provide the information necessary for plant staff to
operate the plant effectively and safely.
Additional staff may also be needed by treatment facilities that currently utilize labor-intensive
operations, such as sludge drying beds with short rotation periods. These facilities may need
more staff to process an increased volume of residual solids caused by a change in coagulants
or the implementation of enhanced treatment.
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Likewise, facilities which have little automation, limited in-line monitoring, and manual process
control may require additional manpower to monitor and maintain new process variables (such
as chemical feed controls) included in a new treatment process. The requirements of the
IESWTR for disinfection profiling and the increased monitoring of individual filter performance
could also add significantly to an operator's administrative duties.
6.4 Impact of Enhanced Coagulation on Process
Residuals
Facilities that implement enhanced coagulation may experience significant changes in both the
volume and characteristics of process residuals. An increase in coagulant dosage could
increase the volume of residual solids created, and a change in coagulant types or coagulation
pH could alter the dewatering characteristics of existing residual streams.
6.4.1 Solids Volume
The production of residual solids is related to water production, coagulant dosage, raw water
suspended solids, and polymer dosage. If treatment facilities make changes in coagulant types
or add/modify polymer addition, significant changes may be expected in the amount of solids
produced. The following formulas can be used to estimate the amount of residual solids that
might be produced from a metal hydroxide coagulation treatment scheme (AWWA and ASCE,
1998):
For aluminum coagulant sludge: S = Q(0.44 Al + SS + P)(8.34 Ib/milgal/mg/L)
For ferric chloride sludge: S = Q(2.9 Fe + SS + P)(8.34 Ib/mil gal/mg/L)
Where: S = solids produced, pound dry solids per day
Q = water production, million gallons per day
Al= alum dosage, mg/L as solution (alum 17.1% solution)
SS = suspended solids concentration, mg/L
Fe = ferric chloride dosage, mg/L (dosage as Fe)
P = polymer dosage, mg/L
A similar equation has been developed for lime softening solids (AWWA and ASCE, 1998):
S = Q(2.0Ca + 2.6Mg)(8.34 Ib/mil gal/mg/L)
Where: Ca = calcium hardness removed as CaCOs, mg/L
Mg = magnesium hardness removed as CaCOs, mg/L
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When changes in coagulants are contemplated, the results of these equations may be compared
to actual solids production experienced with the current coagulant for verification purposes.
The equations can then be used to estimate solids production expected with a new coagulant,
or a change in coagulant dosage. If significant increases in solids volume are expected to result
from changes in coagulants, the capacity of the facility's residual management system should be
evaluated. This evaluation can be performed by developing a complete mass balance of the
solids passing through the treatment plant. The solids in the raw water should be included in
the calculation, along with solids recycled to the head of the plant and floe produced in the
treatment process.
Alum produces 0.44 mg/L of solids for each mg/L of alum added to the process. Likewise,
iron salts produce 2.9 mg/L of solids for each mg/L of coagulant added (AWWA and ASCE,
1998). It is evident that a change in coagulants from alum to iron salts as a coagulant will
produce more solids for similar dosages.
Increases in sludge wasting can also increase residual hydraulic rates which can have
substantial impacts on surface water disposal systems, or facilities that discharge solids to a
sanitary sewer. Surface water discharge may require revisions to existing discharge permits
with limits on maximum flow rates or other parameters such as total solids and pH. Sanitary
sewer discharges may exceed permitted levels, or require expansion of pretreatment measures
already in place. If permit limits are expected to be exceeded, a permit revision may be in
order. Facilities which face limits on the maximum flow rate or total volume of discharge may
need to explore ways of reducing sludge volumes by the addition of treatment steps such as
gravity thickening or floatation prior to discharge. These treatment methods, however, will not
decrease the solids levels.
Increases in solids loading rates on existing unit processes may also exceed the capacity of
existing residual treatment system, resulting in effluent sludge which may not meet the
requirements for landfilling, land application, or reuse. Residual solids are typically treated by
a variety of processes, including thickening, dewatering, or drying. All of these processes can
include chemical conditioning for optimal performance.
Thickening processes usually concentrate hydroxide residual streams to 1 to 8 percent solids by
weight, and lime sludges up to 25 percent solids (AWWA and ASCE, 1998). Thickening can
be accomplished by the use of gravity thickening basins, gravity belt thickeners, or flotation
processes. Gravity thickening basins are typically loaded directly from sedimentation basin
blowdown at 100 to 200 gpd/ft2 for hydroxide sludges, and 60 to 200 Ib solids per ft2 per day
for lime sludges (AWWA and ASCE, 1998). Typical solids loadings for gravity belt thickeners
vary by manufacturer, but are published and available with the equipment documentation.
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Flotation thickening processes usually are operated in continuous feed mode, and can
accommodate solids loadings of 10 to 30 lb/day/ft2 (AWWA and ASCE, 1998).
Dewatering processes include mechanical systems such as filter presses, belt presses,
centrifuges, vacuum-assisted drying beds, and filtration, as well as nonmechanical treatment
systems including drying beds, freeze-assisted sand beds, solar drying beds, wedgewire beds,
and lagoons. Loading rates for these processes are variable, and are affected by regional and
climatic factors, as well as depth of application and length of drying time before removal.
Typical guidelines for the various processes can be found in the references AWWA and ASCE
(1998) and ASCE/AWWA/USEPA (1997).
In all cases, chemical conditioning can be used to optimize existing dewatering processes.
Anionic polymers are typically added to influent streams to aid in the formation of very dense
and large floe, which has better settling characteristics. Lime and bentonite clay are also used
to condition and add bulk to coagulant sludges.
6.4.2 Residual Solids Dewatering Characteristics
Changes in coagulants or coagulation and flocculation conditions can have significant impacts
on the characteristics of residual solids. Hydroxide sludges produced from aluminum and iron
salts are generally gelatinous in nature, non-compactible, and difficult to dewater. In contrast,
sludges from lime softening treatment processes are generally easier to dewater. The presence
of magnesium hydroxide in softening sludges can impact dewatering, making it more difficult
achieve high percent solids sludge cake. As a result, facilities that practice enhanced softening
and change their treatment scheme to remove additional magnesium may experience difficulty
in maintaining dewatering efficiency.
Changes in pH that may be required to achieve enhanced coagulation may also change the
dewatering characteristics of some sludges. These changes may improve or degrade the ease
with which the sludges can be concentrated. pH changes can also impact facilities that have
requirements on dewatering facility effluent or discharge to surface water bodies or sanitary
sewers.
In addition, the additional NOM removed by enhanced coagulation will be present in the
residual stream and may present problems with discharge limitations, pre-treatment
requirements, or reuse requirements. The recovered solids, as well as the decanted liquids,
may have a very different quality and may lose some value for reuse, recycling, or discharge.
These solids may also require stabilization.
The expected variation in dewatering characteristics will depend largely on the character of the
raw water source and the treatment scheme utilized. Bench- and pilot- scale testing can be
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used to develop data to give general indications of the impacts on dewatering characteristics.
Thickening can be evaluated using settling tests, flotation tests, and capillary suction time tests
(Bums and Smith, 1996). Dewatering processes can be evaluated using time-to-filter tests,
filter leaf tests, capillary suction tests, and settling tests (Bums and Smith, 1996). It should be
noted that bench-scale tests may not provide direct correlation to full-scale performance.
Bench- and pilot- scale tests can, however, be useful in evaluating the magnitude of expected
changes and the effectiveness of treatment modifications.
As stated previously, chemical conditioning of residual streams can greatly improve the
performance of dewatering processes. The addition of anionic polymers has proven to aid in
the formation of large, dense floe, which is more easily separated as concentrated solids. Lime
and clay have also been used to condition hydroxide sludges and improve dewatering. The
advice and documentation available from dewatering equipment manufacturers may also
provide useful information in defining treatment modifications.
6.5 Tastes and Odors
Changes in oxidants or disinfectants used in a treatment process to control the formation of
DBFs may also result in the formation of new tastes and odors in the finished water. The
implementation of process modifications can change the intensity and character of historic
tastes and odor episodes, or change the way a facility must treat a chronic taste and odor
problem. It has been well documented that there are many causes of tastes and odors in
finished water, and the intensity and character of specific taste and odor episodes have proven
to be highly variable and often difficult to trace (AWWARF and Lyonnaise des Eaux, 1995).
Tastes and odors are common in surface water sources, and are typically caused by decaying
vegetation, algae, or industrial and municipal wastes. Finished water tastes and odors can also
be caused by biological activity in distribution systems and in-storage reservoirs.
The treatment of tastes and odors is commonly accomplished by either the application of an
oxidant to raw water prior to treatment, or by the use of an adsorbing media such as activated
carbon. The chemicals used for pre-oxidation may also be the primary disinfectant used for
microbial inactivation. Many odor causing compounds present in surface water, such as 2-
methylisoborneol (Mffi) and geosmin, are resistant to oxidation and can have competing
chemical reactions with certain oxidants that can create new tastes and odors or worsen
existing conditions. DBFs such as aldehydes, phenols, chlorophenols, and trihalomethanes can
also impart distinct tastes and odors (AWWARF and Lyonnaise des Eaux, 1995).
Most of the disinfectants and oxidants in use today are effective in reducing and controlling
specific taste and odor episodes. Stronger oxidants like ozone, potassium permanganate, and
chlorine dioxide are more effective in oxidizing odor-causing compounds, but may form
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additional tastes and odors at high residual concentrations, or form byproducts. Chloramines
have proven more effective in controlling tastes and odors when strong taste and odor
precursors are present.
6.5.1 Taste and Odor Sources
Tastes and odors are caused by many sources. Geosmin and Mffi result in earthy and musty
odors in water supplies. These compounds are naturally occurring, and are primarily formed
by the metabolism of many forms of algae (AWWARF and Lyonnaise des Eaux, 1995).
Tastes and odors can also be created in the distribution system by a variety of causes including
biological sources like fungi and bacteria from biofilms, or chemical sources like disinfectants,
construction materials, corrosion, and DBFs. System design and operation can also lead to
tastes and odors created in areas with long residence times, or by the blending of differing
sources and by the presence of cross-connections.
Chlorine has also been the source of many taste and odor complaints. The tastes and odors are
often described as bleach-like, or similar to swimming pool odors, resulting from the use of
free chlorine or chloramines (AWWARF and Lyonnaise des Eaux, 1995). Monochloramine
rarely has been found to result in significant taste and odor problems, but it is not as easy to
detect as dichloramine and trichloramine. Dichloramine has been described as a swimming
pool or bleach odor, while trichloramine has been described as chlorinous and fragrant
(AWWARF and Lyonnaise des Eaux, 1995). These two chloramines are prevalent at lower pH
levels.
In addition to the tastes and odors imparted by free chlorine and chloramines, tastes and odors
can be created from byproducts produced when these disinfectants are applied to water. The
reaction of free chlorine with amino acids or organic nitrogen present in water can form
aldehydes, which have been associated with taste and odor. Aldehydes have complex tastes
and odor characteristics, but have been described as chlorinous, earthy, stale, disinfectant,
bitter, ammonia, organic, muddy, moldy, and bleach-like (AWWARF and Lyonnaise des Eaux,
1995). Phenols present in water can also react with chlorine to produce chlorophenol, which
have medicinal tastes and odors. In addition, trihalomethanes can have strong medicinal tastes
and odors.
Chloramines can have the same reactions with amino acids, organic nitrogen, and phenols to
create taste and odor causing compounds. Since chloramines are much weaker oxidants than
free chlorine, the reaction time to form taste and odor causing compounds is much longer,
resulting in a reduced potential for taste and odor production.
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Chlorine dioxide can form detectable tastes and odors when residual concentrations reach 0.20
mg/L to 0.25 mg/L (AWWARF and Lyonnaise des Eaux, 1995). Secondary odors have also
been reported due to reactions between chlorine dioxide and household products and from the
gaseous release when taps are opened.
Ozone is effective in oxidizing organic compounds responsible for many tastes and odors, and
is highly effective when combined with hydrogen peroxide or UV light to form an advanced
oxidation process. However, ozone has been reported to impart an "oxidant" or "ozonous"
odor to waters, even when an ozone residual is not present. Aldehyde byproducts formed from
the reaction of ozone in water have also been associated with odors ranging from fruity to
sickening. Tastes and odors have not been identified with other ozone byproducts (AWWARF
and Lyonnaise des Eaux, 1995).
6.5.2 Taste and Odor Controls
Taste and odor episodes respond in various ways to different treatments. Free chlorine
application or ozonation can effectively remove some odors, such as those characterized as
fishy. Other constituents like geosmin and MTB are difficult to oxidize. In planning for the
implementation of any process modifications, incorporating flexibility in the treatment process
to allow the application of differing oxidants at various points in the treatment process for the
control of tastes and odors should be considered.
Bench-scale and pilot studies may be required to develop treatment schemes that will minimize
byproduct formation and provide taste and odor control without reducing the microbial
protection. Chemical analyses can also be performed to determine the causes of tastes and
odors. The Flavor Profile Analysis (FPA) approach can be used to define sensory responses to
tastes and odors to better understand their character and intensity. Once known, treatment and
control strategies can be developed to address specific applications. Further information
describing taste and odor identification and treatment strategies can be found in the
publications Identification and Treatment of Tastes and Odors in Drinking Water (AWWARF,
1996) and Advances in Taste and Odor Treatment and Control (AWWARF and Lyonnaise des
Eaux, 1995).
In addition to oxidation, treatment schemes utilizing activated carbon may be necessary to
control tastes and odors and minimize byproduct formation. Activated carbon is typically
applied as powered activated carbon (PAC) or as granular activated carbon (GAC). Activated
carbon is an adsorbent, and its efficiency is determined by contact time and the presence of
organic constituents in the water competing for adsorbent sites.
PAC is generally injected into raw water as a slurry prior to treatment, and is useful for
occasional control of recurring taste and odor events. The PAC is captured through
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sedimentation, regenerated, and recycled. GAC is typically used after sedimentation, and
typically in a GAC-filled basin used as a contactor. GAC contactors are normally used for
control of chronic tastes and odors. It should be noted that activated carbon has other uses in
water treatment, including the removal of natural organic matter and synthetic organic
compounds.
Activated carbon has been proven effective for the control of many tastes and odors, but the
effectiveness and economic impacts are application-specific. Bench and or pilot testing is
normally required to determine the recommended configuration, especially for the design of
GAC contactors.
Biological treatment has also been examined in Europe, but has not received wide attention in
the United States. Biological treatment utilizes slow sand filtration and attempts to control
tastes and odors by achieving biological stability of water through the removal of biological
organic matter. Biological treatment may have other benefits by controlling biological
regrowth in the distribution system, thus reducing the requirements for secondary disinfectants.
The effectiveness and application of biological treatment is not fully known at this time, but
research continues to examine its use and evaluate the benefits to be gained in the control of
tastes and odors.
6.5.3 Recommendations
Tastes and odors in the distribution system and treatment facility should be continually
monitored to ensure that high quality, stable water is being delivered. Systems should consider
the following to control taste and odor problems:
. Reviewing customer complaints to best determine the cause of tastes and odors so that
corrective action can be taken
. Considering changing the secondary disinfectant to control regrowth
. Making a pH adjustment or applying a corrosion inhibitor to address corrosion
problems
. Rehabilitating water mains to replace existing, unlined corrosion surfaces in the
distribution system
. Examining the construction materials used in the distribution system, including coatings
and linings in both piping and storage facilities
. Revising the system operations to reduce residence times in storage facilities
. Implementing a water main flushing program
. Maintaining an adequate disinfectant residual to control regrowth.
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7. REFERENCES
Abbaszadegan, M., R. Manteiga, K. Bell, K. and M. LeChevallier. 1997. "Enhanced Coagulation
for Removal of Microbial Contaminants." Conference proceedings, AWWA Water Quality
Technology Conference, Denver CO.
Aieta, E., and J.D. Berg. 1986. "A Review of Chlorine Dioxide in Drinking Water Treatment."
J.AWWA. 78(6):62-72.
Arora H., M.W. LeChevallier, and K.L. Dixon. 1997. "DBF Occurrence Survey." J. AWWA.
89(6):60.
ASCE/AWWA/USEPA (American Society of Civil Engineers/American Water Works
Association/U.S. Environmental Protection Agency). 1997. Technology Transfer Handbook:
Management of Water Treatment Plant Residuals. New York: ASCE.
AWWA. 1999. Drinking Water Chlorination White Paper; A Review of Disinfection Practices
and Issues Site: http://c3.org/library/WhitePaperCl.html#Chp 1
AWWA and ASCE (American Society of Civil Engineers). 1998. Water Treatment Plant Design.
Third edition. McGraw-Hill, New York, NY.
AWWA Internet. 1997. National Primary Drinking Water Contaminant Standards Site:
http ://www. awwa. org/govtaff/advisor/npdwcs.txt
AWWA. 1995. "Nitrification Occurrence and Control in Chloraminated Water Systems."
AWWARF.
AWWA. 1991. Guidance Manual for Compliance with the Filtration and Disinfection
Requirements for Public Works Systems Using Surface Water Sources. Denver, CO.
AWWA. 1990. Water Quality and Treatment. F.W. Pontius (editor). McGraw-Hill, New York,
NY.
AWWARF (American Water Works Association Research Foundation). 1997. "A General
Framework for Corrosion Control Based on Utility Experience."
AWWARF. 1996. "Taste and Odor in Drinking Water - Phase III " AWWA, Denver, CO.
AWWARF. 1995. "Nitrification Occurrence and Control in Chloraminated Water Systems."
AWWARF. 1993. "Optimizing Chloramine Treatment."
AWWARF. 1990a. "Assessing and Controlling Bacterial Regrowth in Distribution Systems."
January.
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AWWARF. 1990b. "Case Studies of Modified Disinfection Practices for Trihalomethane
AWWARF. I990c. Lead Control Strategies. AWWA and AWWARF. Denver, CO.
AWWARF. 1985. Internal Corrosion of Water Distribution Systems. AWWARF and DVGW-
Forschungstelle. Denver, CO.
AWWARF and Lyonnaise des Eaux. 1995. "Identification and Treatment of Tastes and Odors in
Drinking Water." AWW A, Denver, CO.
Babcock, D.S. and P.C. Singer. 1979. "Chlorination and Coagulation of Humic and Fulvic
Adds" J. AWWA. 71(3): 149.
Bablon G.P., C. Ventresque, and R.B. Aim. 1988. "Developing a Sand-GAC Filter to Achieve
High Rate Biological Filtration." J. AWWA. 80(12):47.
Bellar, T.A., JJ. Lichtenberg, and R.C. Kroner. 1974. "The Occurrence of Organohalides in
Chlorinated Drinking Water." J. AWWA. 66(12):703.
Black, B.D., G.W. Harrington, and P.C. Singer. 1996. "Reducing Cancer Risks by Improving
Organic Carbon Removal." J. AWWA. 88(6):40.
Burris, B.E., and I.E. Smith. 1996. "Management of Water Treatment Plant Residuals." USEPA
Second National Drinking Water Treatment Technology Transfer Workshop, Kansas City, MO.
Cabaniss, S.E. and Shuman, M.S. 1988. "Copper Binding by Dissolved Organic Matter: I.
Suwanee River Fulvic Acid Equilibria." Geochimica CosmochimicaActa. 52:185.
Camper, A.K. 1996. "Factors Limiting Microbial Growth in Distribution Systems: Laboratory
and Pilot-Scale Experiments." AWWARF. Denver, CO.
Camper, A.K., W.L. Jones, and J.T. Hayes. 1996. "Effect of Growth Conditions and Substrate
and Substratum Composition on the Persistence of Coliforms in Mixed-Population Biofilms."
Appl. Env. Microbiol. 62:4014-4018.
CDC (Centers for Disease Control). 1998. Fact Sheet on Giardiasis. CDC website:
http://www.cdc.gov/ncidod/dpd/giardias.htm
Characklis, W.G. 1988. BacterialRegrowth in Distribution Systems. South Central Connecticut
Regional Water Authority, American Water Works Service Company, and Stoner and Associates,
Inc. AWWA.
Chick, H. 1908. "Investigation of the Laws of Disinfection." J. Hygiene. 8:92.
Christman R.F. et al. 1983. "Identity and Yields of Major Halogenated Products of Aquatic and
Fulvic Acid Chlorination." ES&T. 17(10)625.
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CMA (Chemical Manufacturers Association). 1997. "Sodium Chlorite: Drinking Water Rat
Two-Generation Reproductive Toxicity Study." Quintiles Report Ref. CMA/17/96.
Cooper, William J., G.L Amy, and C.A. Moore. 1986. "Bromoform Formation in Ozonated
Ground water Containing Bromide and Humic Substances." Ozone Sci. & Engrg. 8(1):63.
Couri, D., M.S. Abdel-Rahman, and R.H. Bull. 1982. "lexicological Effects of Chlorine Dioxide,
Chlorite, and Chlorate." Env. Health Perspectives, 46:13.
Cowman, G.A. and P.C. Singer. 1994. "Effect of Bromide Ion on Haloacetic Acid Speciation
Resulting from Chlorination and Chloramination of Humic Extracts. " Conference proceedings,
AWWA Annual Conference, New York, NY.
Craun, GF. 1981. "Outbreaks of Waterborne Disease in the U.S.V. AWWA. 73(7):360.
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