S-EPA
United States
Environmental Protection
Agency
STAGE 2 DISINFECTANTS AND DISINFECTION
BYPRODUCTS RULE
OPERATIONAL EVALUATION GUIDANCE MANUAL
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Office of Water EPA 815-R-08-018 www. epa. gov/safewater December 2008
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Purpose:
The purpose of this guidance manual is solely to provide technical information on
completing an operational evaluation as required by the Stage 2 Disinfectants and Disinfection
Byproducts Rule (DBPR). This guidance is not a substitute for applicable legal requirements,
nor is it a regulation itself. Thus, it does not impose legally-binding requirements on any party,
including EPA, States, or the regulated community. Interested parties are free to raise questions
and objections to the guidance and the appropriateness of using it in a particular situation. The
mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
Authorship:
This manual was developed under the direction of EPA's Office of Water, and was
prepared by The Cadmus Group, Inc., and Malcolm Pirnie, Inc. Questions concerning this
document should be addressed to:
Michael Finn
U.S. Environmental Protection Agency
Mail Code 4606M
1200 Pennsylvania Avenue, NW
Washington, DC 20460-0001
Tel: (202) 564-5261
Email: fmn.michael@epa.gov
Acknowledgements:
Harish Arora - Narasimhan Consulting Services
Brian Ramaley - City of Newport News Waterworks
Anthony Bennett - Texas Commission on Environmental Quality
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Contents
Appendices iv
Exhibits v
Examples v
Forms v
Checklists v
Acronyms vi
Glossary vii
1. Introduction 1-1
1.1 Purpose and Scope 1-2
1.2 Who Must Comply with the Operational Evaluation Requirements of the
Stage2DBPR? 1-2
1.3 What Is an Operational Evaluation Level Exceedance? 1-3
1.4 What Are the Requirements If the Operational Evaluation Level is
Exceeded? 1-5
1.5 When Do the Operational Evaluation Requirements Take Effect? 1-7
1.6 Organization of this Guidance Manual 1-7
1.7 Additional Resources 1-8
2. Recommended Approach for Conducting an Operational Evaluation 2-1
2.1 Step 1: Confirm that Data Collection and Analysis Protocols Were
Followed 2-6
2.2 Step 2: Review DBF Data at Other Sites 2-10
2.3 Step 3: If the Cause of the OEL Exceedance Is Known, Request State
Approval to Limit Scope of Operational Evaluation 2-13
2.4 Step 4: Conduct Operational Evaluation 2-13
2.5 Step 5: Identify Steps to Minimize Future OEL Exceedances 2-14
2.6 Step 6: Prepare and Submit Report 2-14
2.7 Uses of Operational Evaluation Reports 2-15
3. Distribution System Evaluation 3-1
3.1 System Maintenance 3-6
3.2 Changes in System Demand 3-7
3.3 Storage Facility Operations 3-8
3.4 Booster Disinfection Practices 3-10
3.5 References 3-11
3.6 Additional Resources 3-11
4. Treatment Process Evaluation 4-1
4.1 Predisinfection 4-8
4.2 Presedimentation 4-10
4.3 Coagulation/Flocculation 4-11
4.4 Sedimentation/Clarification 4-13
4.5 Filtration 4-14
4.6 Primary Disinfection 4-16
4.7 Recycle Practices 4-18
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4.8 Secondary Disinfection 4-19
4.9 References 4-20
4.10 Additional Resources 4-21
5. Source Water Evaluation 5-1
5.1 Water Temperature 5-5
5.2 Organic Matter 5-6
5.3 Bromide 5-9
5.4 Turbidity and Particle Count Data 5-10
5.5 pH and Alkalinity 5-12
5.6 References 5-13
5.7 Additional Resources 5-14
6. Minimizing Future Operational Evaluation Level Exceedances 6-1
6.1 Distribution System Improvements 6-2
6.1.1 Managing Water Age 6-3
6.1.1.1 Reducing Water Age and Improving Water Quality in
Storage Tanks 6-3
6.1.1.2 Minimizing Hydraulic Residence Time in Pipes 6-8
6.1.2 Reducing Disinfectant Demand 6-10
6.1.2.1 Replacing or Cleaning and Lining Unlined Cast Iron Pipes 6-10
6.1.2.2 Conducting Periodic Flushing 6-11
6.1.3 Implementing Booster Disinfection 6-12
6.1.4 Additional Resources 6-13
6.2 Plant Operational Improvement 6-14
6.2.1 General Strategies for Enhanced Precursor Removal 6-14
6.2.1.1 Enhanced Removal of Organic DBF Precursors by
Coagulation 6-14
6.2.1.2 Enhanced Removal of Organic DBF Precursors by
Softening 6-17
6.2.1.3 Optimizing Settling 6-17
6.2.1.4 Optimizing Conventional and GAC Filtration 6-18
6.2.1.5 Adjust pH to Balance TTHM vs HAAS Production 6-19
6.2.2 Seasonal Strategies for Enhanced Precursor Removal 6-20
6.2.3 Review of Disinfect!on Practices 6-21
6.2.4 Additional Resources 6-22
6.3 Source Water Management 6-23
6.3.1 Watershed Management 6-24
6.3.2 Source Water Monitoring 6-24
6.3.3 Seasonal Source Water Management Strategies 6-26
6.3.4 Blending of Alternative Sources 6-26
6.3.5 Optimizing Intake Operations 6-27
6.3.6 Additional Resources 6-28
6.4 References 6-29
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Appendices
Appendix A Fundamentals of TTHM and HAAS Formation
Appendix B Example Operational Evaluation Report for OEL Exceedances Due to Changes in
Source Water Quality with Limited Operational Evaluation Scope Approved by
the State
Appendix C Example Operational Evaluation Report for OEL Exceedance Due to Changes in
Distribution System Operation
Appendix D Example Operational Evaluation Report for OEL Exceedance Due to Changes in
Source Water Quality and Booster Disinfection
Appendix E Example Operational Evaluation Report for OEL Exceedances Due to
Maintenance Activities in the Wholesale System
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Exhibits
Exhibit 1.1 Operational Evaluation Flow Chart (40 CFR 141.626) 1-6
Exhibit 1.2 Effective Dates for Stage 2 DBPR Compliance Monitoring 1-7
Exhibit 2.1 Suggested Steps for Performing an Operational Evaluation 2-5
Exhibit 2.2 Sampling Requirements of TTHM and HAAS Analyses 2-7
Exhibit 3.1 Distribution System Monitoring Data 3-2
Exhibit 4.1 Treatment Plant Monitoring Data 4-2
Exhibit 4.2 Effects of Chlorine Addition at Different Treatment Process Locations 4-9
Exhibit 4.3 Typical Conventional Filtration Plant 4-12
Exhibit 5.1 System Source Water Monitoring Data 5-2
Exhibit 6.1 Examples of Operational Strategies to Reduce DBFs 6-2
Examples
Example 1.1 Determining If There Is an OEL Exceedance 1-4
Example 2.1 System-wide DBF Increases 2-11
Example 2.2 Localized DBF Increase 2-12
Example 6.1 Calculating the Theoretical Average Hydraulic Residence Time 6-4
Forms
Operational Evaluation Reporting Form 2-2
Checklists
TTHM and HAAS Sample Collection and Handling Checklist 2-8
Distribution System Evaluation Checklist 3-4
Treatment Process Evaluation Checklist 4-4
Source Water Evaluation Checklist 5-3
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Acronyms
AWWA
AwwaRF
CCR
CFD
CFR
CT
DBF
DBPR
DOC
EPA
ft/sec
IESWTR
GAC
GIS
GWUDI
HAA
HAAS
HPC
IDSE
LCR
LRAA
LT1ESWTR
LT2ESWTR
MCL
M/DBP
MG
mg/L
nm
NOM
OEL
ppm
SUVA
SWTR
THM
TOC
TTHM
USGS
UV
UV254
voc
WTP
American Water Works Association
American Water Works Association Research Foundation
Consumer Confidence Report
Computational Fluid Dynamics
Code of Federal Regulations
Disinfectant Residual Concentration x Contact Time
Disinfection Byproduct
Disinfectants and Disinfection Byproducts Rule
Dissolved Organic Carbon
Environmental Protection Agency
feet per second
Interim Enhanced Surface Water Treatment Rule
Granular Activated Carbon
Geographic Information System
Ground Water Under the Direct Influence of Surface Water
Haloacetic Acid
The Sum of Five HAA Species
Heterotrophic Plate Count
Initial Distribution System Evaluation
Lead and Copper Rule
Locational Running Annual Average
Long Term 1 Enhanced Surface Water Treatment Rule
Long Term 2 Enhanced Surface Water Treatment Rule
Maximum Contaminant Level
Microbial/Disinfection Byproducts
million gallons
milligrams per liter
nanometer
Natural Organic Matter
Operational Evaluation Level
parts per million
Specific Ultraviolet Absorbance
Surface Water Treatment Rule
Trihalomethane
Total Organic Carbon
Total Trihalomethanes
United States Geological Survey
Ultraviolet Light
UV absorption at 254 nm
Volatile Organic Compound
Water Treatment Plant
micrograms per liter
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Glossary
Booster disinfection: the practice of adding disinfectant in the distribution system to maintain
disinfectant residual concentration throughout the distribution system.
Combined distribution system: the interconnected distribution system consisting of the
distribution systems of wholesale systems and of the consecutive systems that receive some or all
of their finished water from those wholesale system(s).
Consecutive system: a public water system that buys or otherwise receives some or all of its
finished water from one or more wholesale systems. Delivery may be through a direct
connection or through the distribution system of one or more consecutive systems.
Disinfectant: any oxidant, including but not limited to chlorine, chlorine dioxide, chloramines,
and ozone added to water in any part of the treatment or distribution process, that is intended to
kill or inactivate pathogenic microorganisms.
Disinfectant residual concentration: the concentration of disinfectant that is maintained in a
distribution system. Disinfectant could be free chlorine (the sum of the concentrations of
hypochlorous acid (HOC1) and hypochlorite acid (OC1")) or combined chlorine (chloramines). It
is used in the Surface Water Treatment Rule as a measure for determining CT.
Disinfection: a process which inactivates pathogenic organisms in water by chemical oxidants or
equivalent agents.
Disinfection byproduct (DBF): compound formed from the reaction of a disinfectant with
organic and inorganic compounds in the source or finished water during the disinfection process.
Dual sample set: a set of two samples collected at the same time and same location, with one
sample analyzed for TTHM and the other sample analyzed for HAAS. Dual sample sets are
collected for the purposes of conducting an Initial Distribution System Evaluation and
determining compliance with the TTHM and HAAS Maximum Contaminant Levels.
Finished water: water that is introduced into the distribution system of a public water system and
is intended for distribution and consumption without further treatment, except that treatment
necessary to maintain water quality in the distribution system (e.g., booster disinfection, addition
of corrosion control chemicals).
GAC10: granular activated carbon filter beds with an empty-bed contact time of 10 minutes
based on average daily flow and a carbon reactivation frequency of every 180 days.
GAC20: granular activated carbon filter beds with an empty-bed contact time of 20 minutes
based on average daily flow and a carbon reactivation frequency of every 240 days.
Ground water under the direct influence of surface water (GWUDI): any water beneath the
surface of the ground with (1) significant occurrence of insects or other macroorganisms, algae,
or large-diameter pathogens such as Giardia lamblia, or (2) significant and relatively rapid shifts
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in water characteristics such as turbidity, temperature, conductivity, or pH that closely correlate
to climatological or surface water conditions. Direct influence should be determined for
individual sources in accordance with criteria established by the State. The State determination
of direct influence may be based on site-specific measurements of water quality and/or
documentation of well construction characteristics and geology with field evaluation.
Haloacetic acid (HAA): one of the family of organic compounds named as a derivative of acetic
acid, wherein one to three hydrogen atoms in the methyl group in acetic acid are each substituted
by a halogen atom (namely, chlorine and bromine) in the molecular structure.
Haloacetic acids (five) (HAAS): the sum of the concentrations in milligrams per liter of the
haloacetic acid compounds (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid,
monobromoacetic acid, and dibromoacetic acid), rounded to two significant figures after
addition.
Locational running annual average (LRAA): the average of sample analytical results for samples
taken at a particular monitoring location during the previous four calendar quarters.
Maximum contaminant level (MCL): the maximum permissible level of a contaminant in water
which is delivered to any user of a public water system.
Mixing zone: an area in the distribution system where water flowing from two or more different
sources blend.
Monitoring site: the location where samples are collected.
Public water system (PWS): a system for the provision to the public of piped water for human
consumption, if such system has at least 15 service connections or regularly serves an average of
at least twenty-five individuals daily at least 60 days of the year. Such term includes (1) any
collection, treatment, storage, and distribution facilities under control of the operator of such
system and used primarily in connection with such system, and (2) any collection or pretreatment
storage facilities not under such control which are used primarily in connection with such
system.
Residence time: the time period lasting from when the water is treated to a particular point in the
distribution system. Also referred to as water age.
Residual disinfection: also referred to as "secondary disinfection". The process whereby a
disinfectant (typically chlorine or chloramine) is added to finished water in order to maintain a
disinfection residual in the distribution system.
Secondary disinfection: see definition for "residual disinfection".
State: the agency of the State or Tribal government which has jurisdiction over public water
systems. During any period when a State or Tribal government does not have primary
enforcement responsibility pursuant to section 1413 of the Act, the term "State" means the
Regional Administrator, U.S. Environmental Protection Agency.
Surface water: all water which is open to the atmosphere and subject to surface runoff.
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Total trihalomethanes (TTHM): the sum of the concentration in milligrams per liter of the
trihalomethane compounds (trichloromethane [chloroform], dibromochloromethane,
bromodichloromethane, and tribromomethane [bromoform]), rounded to two significant figures.
Note that some publications may use the term "THM4" instead of "TTHM."
Trihalomethane (THM): one of the family of organic compounds named as derivatives of
methane, wherein three of the four hydrogen atoms in methane are each substituted by a halogen
atom in the molecular structure.
Water age: see definition for "residence time."
Wholesale system: a public water system that treats source water as necessary to produce finished
water and then sells or otherwise delivers finished water to another public water system.
Delivery may be through a direct connection or through the distribution system of one or more
consecutive systems.
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1. Introduction
This chapter covers:
1.1 Purpose and Scope
1.2 Who Must Comply with the Operational Evaluation Requirements
oftheStage2DBPR?
1.3 What Is an Operational Evaluation Level Exceedance?
1.4 What Are the Requirements If the Operational Evaluation Level Is
Exceeded?
1.5 When Do the Operational Evaluation Requirements Take Effect?
1.6 Organization of this Guidance Manual
1.7 Additional Resources
The Environmental Protection Agency (EPA) promulgated the Stage 2 Disinfectants and
Disinfection Byproducts Rule (DBPR) in January 2006. The Stage 2 DBPR provides for
increased protection against the potential risks for cancer and reproductive and developmental
health effects associated with disinfection byproducts (DBF). The Stage 2 DBPR establishes
maximum contaminant level goals for chloroform, monochloroacetic acid and trichloroacetic
acid; maximum contaminant levels (MCLs), based on a locational running annual average
(LRAA)1, for total trihalomethanes (TTHM) and haloacetic acids (HAAS); monitoring,
reporting, and public notification requirements based on the TTHM and HAAS MCLs; and
revisions to the reduced monitoring requirements for bromate. The complete Stage 2 DBPR can
be found at http://www.epa.gov/safewater/disinfection/stage2/regulations.html.
The Stage 2 DBPR also establishes operational evaluation requirements that are initiated
by the TTHM and HAAS levels found during Stage 2 DBPR compliance monitoring.
Compliance with Stage 2 DBPR MCLs is based on the average of four individual quarterly DBF
measurements collected at a given location (i.e., LRAA). However, a system that is in
compliance with the Stage 2 DBPR MCLs, based on the LRAA, at a location may still have
individual (i.e., not averaged) DPB measurements at that location that exceed the Stage 2 DBPR
MCLs. EPA and the Stage 2 Microbial/Disinfection Byproducts (M/DBP) Advisory Committee
were concerned about these higher levels of DBFs. The Stage 2 DBBR operational evaluation
requirements were established to address these concerns.
The Stage DBPR requires systems to conduct operational evaluations, initiated by the
operational evaluation levels (OEL) found in Stage 2 DBPR compliance monitoring, and to
submit an operational evaluation report to the State. The OELs are determined with an algorithm,
described later in this section, based on Stage 2 monitoring results. The OELs initiate a
comprehensive review of system operations and act as an early warning for a possible Stage 2
DBPR violation in the following quarter. This early warning allows systems to act to prevent the
violation. The Stage DBPR process for initiating an operational evaluation is not based on health
effects information. The operational evaluation requirements of the Stage 2 DBPR are
1 The Stage 2 DBPR requires systems to meet an LRAA of 0.080 mg/L for TTHM and 0.060 mg/L for HAAS at
each compliance monitoring location (40 CFR 141.620 (d)).
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intended as an indicator of operational performance and to allow systems to take proactive
steps to remain in compliance with the Stage 2 DBPR MCLs
1.1 Purpose and Scope
EPA has developed this manual to provide guidance to water systems on identifying
TTHM and HAAS peaks and conducting operational evaluations to determine the cause(s) of and
reduce such peaks, and to assist States in implementing the Stage 2 operational evaluation
requirements and in reviewing operational evaluation reports. The specific objectives of this
manual are to:
Describe an OEL exceedance.
Summarize regulatory requirements for addressing an OEL exceedance.
Provide guidance for documenting and reporting an OEL exceedance.
Provide a methodology for identifying the cause of an OEL exceedance.
Present options available to reduce TTHM and HAAS concentrations in the
distribution system to minimize a future OEL exceedance.
The options presented to reduce TTHM and HAAS concentrations in the distribution
system to minimize future OEL exceedances are intended to assist systems in meeting their
operational evaluation requirements and to assist States in reviewing operational evaluation
reports. An OEL exceedance requires an operational evaluation meeting specific criteria
and reporting of the evaluation to the State, but does not require systems to take corrective
actions. The operational evaluation and report will provide valuable information to both
the system and the State. This guidance manual focuses on common surface and ground water
and treatment processes that affect formation of TTHM and HAAS. References are provided
throughout the document to help you optimize other treatment processes. You should also
consider contacting your State to discuss your particular system needs and concerns.
1.2 Who Must Comply with the Operational Evaluation Requirements of the
Stage 2 DBPR?
All community water and non-transient non-community water systems that use a primary
or residual disinfectant other than ultraviolet light (UV), or that deliver water that has been
treated with a primary or residual disinfectant other than UV, must comply with the Stage 2
DBPR MCLs for TTHM and HAAS and the Stage 2 DBPR operational evaluation requirements.
This includes consecutive systems delivering water that has been treated with a primary or
residual disinfectant other than UV. If you are one of these systems, you must comply with the
operational evaluation requirements of the Stage 2 DBPR if you meet both of the following
criteria:
1) You are required to conduct compliance monitoring for the Stage 2 DBPR; and
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2) You collect Stage 2 DBPR compliance samples quarterly. If you are on annual
monitoring, you are not subject to the operational evaluation requirements of the
Stage 2 DBPR. If you are required to increase Stage 2 monitoring to quarterly
(§141.625), you are also required to meet the operational evaluation requirements.
1.3 What Is an Operational Evaluation Level Exceedance?
The Stage 2 DBPR states that a system exceeds the OEL if one of the following occurs at
any compliance monitoring location (40 CFR 141.626(a)):
TTHM compliance monitoring results for the two previous quarters plus two times
the TTHM result for the current quarter, divided by 4, exceeds 0.080 milligrams per
liter (mg/L); or
HAAS compliance monitoring results for the two previous quarters plus two times the
HAAS result for the current quarter, divided by 4, exceeds 0.060 mg/L.
You can use the formula below to determine if you have an OEL exceedance. Example
1.1 shows how this formula can be used with distribution system TTHM and HAAS data.
Formula for Determining if You Have an OEL Exceedance
For both TTHM and HAAS and for each compliance monitoring location, calculate the
following:
(A + B + (2*C))/4 = D
Where:
A = TTHM or HAAS result for the quarter before the previous quarter (mg/L)
B = TTHM or HAAS result for the previous quarter (mg/L)
C = TTHM or HAAS result for the current quarter (mg/L)
D = your Operational Evaluation Value (mg/L)
If D for TTHM is > 0.080 mg/L, you have an OEL Exceedance
If D for HAAS is > 0.060 mg/L, you have an OEL Exceedance
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Example 1.1 Determining If There Is an OEL Exceedance
A system is conducting Stage 2 compliance monitoring at four locations. TTHM and HAAS
data from the previous two quarters (February and May) and the current quarter (August) are
presented below.
TTHM Data
Stage 2
DBPR
Location
#1
#2
#3
#4
February
A
0.065 mg/L
0.064 mg/L
0.068 mg/L
0.066 mg/L
May
B
0.074 mg/L
0.072 mg/L
0.075 mg/L
0.070 mg/L
August
C
0.087 mg/L
0.084 mg/L
0.093 mg/L
0.082 mg/L
Operational
Evaluation
Value:
D =
(A+B+(2*C))/4
0.078 mg/L
0.076 mg/L
0.082 mg/L
0.075 mg/L
HAAS Data
Stage 2
DBPR
Location
#1
#2
#3
#4
February
A
0.033 mg/L
0.042 mg/L
0.037 mg/L
0.043 mg/L
May
B
0.041 mg/L
0.048 mg/L
0.043 mg/L
0.045 mg/L
August
C
0.050 mg/L
0.055 mg/L
0.046 mg/L
0.052 mg/L
Operational
Evaluation
Value:
D =
(A+B+(2*C))/4
0.044 mg/L
0.050 mg/L
0.043 mg/L
0.048 mg/L
In August, the system exceeds the OEL at location #3 because the TTHM value in column D
exceeds the OEL (0.080 mg/L).
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1.4 What Are the Requirements If the Operational Evaluation Level is
Exceeded?
If the OEL is exceeded, you must take the following actions (40 CFR 141.626(b)):
1) Conduct an operational evaluation to determine the cause of the exceedance(s).
2) Submit a written report of the evaluation to the State no later than 90 days after being
notified of the analytical result that caused the exceedance(s).
3) Keep a copy of the operational evaluation report and make it available to the public
upon request.
An OEL exceedance is not a violation of the Stage 2 DBPR. However, failure to submit
an evaluation report to the State in the required time frame is a violation and requires Tier 3
public notice (as required by the Public Notification Rule). All Stage 2 DBPR compliance
monitoring results must be included in the system's Consumer Confidence Report (CCR). There
are no additional CCR requirements related to an OEL exceedance unless the system is in
violation due to failure to complete and submit an evaluation report.
The operational evaluation must include an examination of system treatment and
distribution operational practices that may contribute to TTHM and HAAS
formation including:
Storage tank operations,
Excess storage capacity,
Distribution system flushing,
Sources of supply and source water quality, and
Treatment processes and finished water quality.
The operational evaluation must also include what steps could be considered to
minimize future exceedances (40 CFR 141.626(b)(2)).
The system may request and the State may allow a limited scope of the operational
evaluation if the system is able to identify the cause of the OEL exceedance to the State's
satisfaction. The State must then approve the limited scope of the evaluation in writing and the
system must keep the written approval with the completed report. Note that submitting this
request will not extend the 90 day deadline for submitting the operational evaluation report.
Exhibit 1.1 presents a flow chart with the operational evaluation rule requirements.
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Exhibit 1.1 Operational Evaluation Flow Chart (40 CFR 141.626)
For each location, add the
TTHM results from the prior
quarter and from two quarters
ago plus twice the current
quarter's TTHM result and
divide the total by 4.
For each location, add the
HAAS results from the prior
quarter and from two quarters
ago plus twice the current
quarter's HAAS result and
divide the total by 4.
Do any
of the calculated
values exceed the
OEL of 0.080 mg/L for TTHM
or
0.060 mg/L
for HAAS?
You have no further \
requirements under 40 j
CFR 141.626. J
Do you know the
cause of the
exceedance(s)?
You may request that the State
allow you to limit the scope of
your operational evaluation.1
You must conduct an
operational evaluation.
You must submit a report of your evaluation to
the State no later than 90 days after being
notified of the result that exceeded the OEL.
(1) The State must approve the limited scope of
the evaluation in writing and you must keep that
approval with the complete report.
(2) The operational evaluation must include an
examination of system treatment and distribution
operational practices including storage tank
operations, excess storage capacity, distribution
system flushing, changes in source water quality,
and treatment changes or problems that may
contribute to TTHM and HAAS formation. You
must also evaluate what steps could be
considered to minimize future exceedances
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1.5 When Do the Operational Evaluation Requirements Take Effect?
The operational evaluation provision of the Stage 2 DBPR applies to compliance
monitoring results. The first determination of OELs would be after the completion of your first
three quarterly monitoring periods. Thereafter, the determination of OELs would be completed
each quarter when new monitoring results are available. The schedule for Stage 2 compliance
monitoring is summarized in Exhibit 1.2.
Exhibit 1.2 Effective Dates for Stage 2 DBPR Compliance Monitoring
If you are a system serving:
At least 1 00,000 people or part of a combined
distribution system serving at least 100,000
people (Schedule 1)
50,000 - 99,999 people or part of a combined
distribution system serving 50,000 - 99,999
people (Schedule 2)
1 0,000 - 49,999 people or part of a combined
distribution system serving 10,000 - 49,999
people (Schedule 3)
Less than 1 0,000 people or part of a combined
distribution system serving Less than 10,000
people (Schedule 4)
Begin Compliance Monitoring by:
April 1,201 2
October 1,201 2
October 1,201 3
October 1 , 201 3 for systems not conducting
Cryptosporidium monitoring under 40 CFR
141 .701 (a)(4). October 1 , 201 4 for systems
conducting Cryptosporidium monitoring.
1.6 Organization of this Guidance Manual
This guidance manual is organized as follows:
Chapter 1 - Introduction: Presents the Stage 2 DBPR requirements for systems that
exceed the OEL.
Chapter 2 - Recommended Approach for Conducting an Operational Evaluation:
Describes the required components of the operational evaluation and presents EPA's
recommended approach.
Chapter 3 - Distribution System Evaluation: Provides guidance for evaluating
distribution system monitoring data and other operational data to determine if
distribution system operations were the cause of the OEL exceedance.
Chapter 4 - Treatment Process Evaluation: Provides guidance for evaluating treatment
plant processes, monitoring data, and other treatment plant operational data to
determine if a change in treatment was the cause of the OEL exceedance.
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Chapter 5 - Source Water Evaluation: Provides guidance for evaluating source water
monitoring and other operational data to determine if a change in source water
conditions was the cause of the OEL exceedance.
Chapter 6 - Minimizing Future Operational Evaluation Level Exceedances:
Summarizes options available to reduce OEL exceedances, including operational
changes and distribution system modifications.
Appendix A discusses the fundamentals of DBF formation. Appendices B through E are
examples of completed operational evaluation reports.
1.7 Additional Resources
USEPA. 2006. Initial Distribution System Evaluation Guidance Manual for the Final Stage 2
Disinfectants and Disinfection Byproducts Rule. EPA 815-B-06-002. Available online at:
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
USEPA. 2007a. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. EPA 815-R-07-017. Available online at:
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
USEPA. 2007b. Complying with the Stage 2 Disinfectant and Disinfection Byproducts Rule:
Small Entity Compliance Guide. EPA 815-R-07-014. Available online at:
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
USEPA. 2007c. The Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR)
Implementation Guidance. EPA 816-R-07-007. Available online at:
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
USEPA. TBD. Consecutive Systems Guidance Manual (Draft) for the Stage 2 Disinfectants and
Disinfection Byproducts Rule. EPA TBD. Available online at:
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
Operational Evaluation Guidance Manual 1-8 December 2008
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2. Recommended Approach for Conducting an Operational Evaluation
This chapter covers:
2.1 Step 1: Confirm that Data Collection and Analysis Protocols Were
Followed
2.2 Step 2: Review DBF Data at Other Sites
2.3 Step 3: Limit the Scope of the Evaluation If the Cause of the OEL
Exceedance Is Known
2.4 Step 4: Conduct a Detailed Operational Evaluation
2.5 Step 5: Identify Steps to Minimize Future OEL Exceedances
2.6 Step 6: Prepare and Submit a Report
2.7 Uses of Operational Evaluation Reports
If your system exceeds an operational evaluation level (OEL), an operational evaluation
must be conducted to determine the cause of the exceedance. A written report summarizing the
operational evaluation must be submitted to the State no later than 90 days after being notified of
the analytical result that exceeded the OEL.
Systems that expect, based on Stage 1 monitoring and Initial Distribution System
Evaluation (IDSE) data, that they may have to prepare an operational evaluation report should
begin data collection efforts for data that would be needed. Data will be valuable in proactive
efforts to avoid OEL exceedances. Systems may also want to review how historical data are
collected and saved and how historical data represent current system configuration and operating
conditions.
This chapter provides a general approach for systems to follow if they experience an OEL
exceedance. The Operational Evaluation Reporting Form on pages 2-2 and 2-3 can be used as a
template for the operational evaluation report. While the use of this form is not required by the
Stage 2 DBPR, it serves as a guideline for collecting pertinent information needed for the
operational evaluation report. Detailed information is needed in the operational evaluation report
regarding the location and cause of the OEL exceedance, and what steps could be considered to
minimize future exceedances. The questions posed in the report form are designed to help the
evaluator identify the causes of the exceedance. There may be additional causes of OEL
exceedances that are not listed in this form. If the exceedance continues to occur in the next
monitoring period, the evaluator may want to review any "no" and "possibly" answers in this
form and conduct a more detailed evaluation.
Examples of completed operational evaluation reports are included in Appendices B
through E for a variety of system conditions. Site-specific conditions may warrant a more
detailed report than shown in these examples.
Operational Evaluation Guidance Manual 2-1 December 2008
-------
Operational Evaluation Reporting Form
Page 1 of 2
I. GENERAL INFORMATION
A. Facility Information
Facility Name:
Facility Address:
City:
PVVSID:
State:
Zip:
B. Report Prepared by:
(Print):
(Signature):
Date prepared:
Contact Telephone Number:
I. MONITORING RESULTS
A. Provide the Compliance Monitoring Site(s) where the OEL was Exceeded.
A/ofe: The site name or number should correspond to a site in your Stage 2 DB~'R compliance monitoring plan.
B. Monitoring Results for the Site(s) Identified in II.A (include duplicate pages if there was more than
one exceedance)
1. Check TTHM or HAA5 to indicate which result caused the OEL -
exceedance.
2. Enter your results for TTHM or HAAS (whichever you checked above).
I TTHM
IHAA5
Date sample was
collected
TTHM (mg/L)
HAAS (mg/L)
Quarter
Results from
Two Quarters
Ago
A
Prior Quarters
Results
B
Current
Quarter
C
Operational
Evaluation Value
D = {A+B+(2*C)}/4
Note: The operational evaluation value is calculated by summing the two previous quarters of TTHM or HAAS
values plus twice the current quarter value, divided by four, ifthe value exceeds O.G80 mg/L for TTHM or 0.060
mg/L for HAAS, an OEL exceedance has occurred.
C. Has an OEL exceedance occurred at this location in the past?
If NO, proceed to item D. If YES, when did
exceedance occur?
DYes
DNO
Was the cause determined for the previous exceedance(s)?
Are the previous evaluations/determinations applicable to the current OEL
exceedance?
DYes
QYes
DNO
DNO
Operational Evaluation Guidance Manual
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December 2008
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Operational Evaluation Reporting Form Page 2 of 2
III. OPERATIONAL EVALUATION FINDINGS
A.
B.
C.
D.
E.
F.
G.
H.
Did the State allow you to limit the scope of the operational evaluation? Q Yes D
If NO, proceed to item B. If YES, attach written correspondence from the State.
DYes D
Did the distribution system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item C. If YES or POSSIBLY, explain (attach additional pages if
necessary):
Did the treatment system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item D. If YES or POSSIBLY, explain (attach additional pages if
necessary):
QYes D
Did source water quality cause or contribute to your OEL exceedance(s)?
Q Possibly
If NO, proceed to item E. If YES or POSSIBLY, explain (attach additional pages if
necessary):
Attach all supporting operational or other data that support the determination of the cause(s)
of your OEL exceedance(s).
If you are unable to determine the cause(s) of the OEL exceedance(s), list the steps that you
can use to better identify the cause(s) in the future (attach additional pages if necessary):
List steps that could be considered to minimize future OEL exceedances (attach additional
pages if necessary)
Total Number of Pages Submitted, Including Attachments and Checklists:
No
No
No
No
Operational Evaluation Guidance Manual 2-3 December 2008
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Overview of Recommended Approach
To fulfill the operational evaluation requirements, EPA recommends that you perform the
following steps:
Step 1 Confirm that samples were properly collected, preserved, and analyzed.
Step 2 Review TTHM and HAAS data at other sites within your distribution system
to determine if the exceedance is localized or system-wide.
Step 3 If the cause of the OEL exceedance is known, request approval from the State
to limit the scope of the operational evaluation.
Step 4 Conduct a detailed or limited operational evaluation depending on State
response in Step 3.
Step 5 Identify steps to minimize exceedances.
Step 6 Prepare the operational evaluation report and submit it to the State.
Exhibit 2.1 presents these steps in a flow chart. Each step is described in detail starting in
Section 2.1. Additional guidance for Step 4, conducting the detailed operational evaluation, is
provided in Chapters 3 through 5. Guidance for Step 5, minimizing future exceedences, is
provided in Chapter 6.
Special Considerations for Consecutive Systems
If you are a consecutive system and purchase all of your water, the operational evaluation
should focus on the distribution system. Consecutive systems should consider collecting TTHM
and HAAS data at the wholesale connection point (e.g., master meter, intertie, turnout, etc.).
This operational data will assist consecutive systems in understanding where DBF formation is
occurring. Knowledge of the concentration of these DBFs at the entry point to the system will
help assess how they change (i.e., increase or decrease) within the system. This knowledge will
assist consecutive systems in identifying the cause(s) of OEL exceedances, in identifying steps
that could be considered to minimize future exceedances, and in any needed interaction with the
wholesale supplier(s). TTHM and HAAS can change day-to-day, so taking TTHM and HAAS
samples at the entry point to your distribution system is encouraged at the same time as Stage 2
compliance distribution samples are taken to allow valid comparison of results.
Once you have reviewed your system and identified the cause of the OEL exceedance
and the potential for the exceedance to reoccur, you should consider initiating a discussion with
the wholesaler about treatment and other alternatives. Refer to the Stage 2 Consecutive System
Guidance Manual (to be published) for more information on how to communicate with your
wholesaler on this issue.
Operational Evaluation Guidance Manual 2-4 December 2008
-------
Exhibit 2.1 Suggested Steps for Performing an Operational Evaluation
Step 1:
Were samples
properly collected,
preserved, and
analyzed?
Do not use these
samples for
compliance
purposes.
Step 2:
Review TTHM and
HAAS data at other
sites within your
distribution system.
Was the
OEL exceedance
localized?
/ Collect and
W analyze new
V samples.
This probably
indicates a source
and/or treatment
issue.
Yes
This probably
indicates a localized
distribution system
issue.
Step 3:
Is the cause of the
OEL exceedance
known?
Yes-
Request that the State
allow you to limit the
scope of your
evaluation.
Step 4:
Conduct an operational
evaluation to determine
the cause of the
exceedance.1
Step 5:
Identify steps to minimize
future OEL exceedances.2
Step 6:
Prepare your operational
Devaluation report and submit y
it to the State.
(1) See Chapters 3, 4, and 5 for more
information on evaluating your
distribution system, treatment, and
source, respectively.
(2) See Chapter 6 for more information
on how to minimize future
exceedances.
Operational Evaluation Guidance Manual
2-5
December 2008
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2.1 Step 1: Confirm that Data Collection and Analysis Protocols Were Followed
Before conducting an operational evaluation, you should ensure that all compliance
sample results are accurate. Accurate sample results depend on proper execution of all
procedures for sample collection and analysis.
Exhibit 2.2 shows the methods, sample containers, preservatives, dechlorinating agents,
storage guidelines, and sample collection guidelines that should be followed when collecting and
analyzing TTHM and HAAS samples. The checklist at the end of this section can be used to
ensure that all of the sample collection and storage guidelines were met. You may need to
contact your laboratory to ensure that the proper analytical method was used for analysis and that
all analytical protocols were followed. Remember, all TTHM and HAAS samples collected for
Stage 2 DBPR compliance must be analyzed by a certified laboratory. Several States control the
sampling process. In some States, samples are analyzed by State laboratories. If either of these
situations occurs in your State, you should contact the State drinking water program before
contacting the laboratory or before filling in the TTHM and HAAS Sample Collection and
Handling Checklist.
If the laboratory has invalidated samples based on holding times being exceeded or other
factors, you should not use these sample results for compliance purposes. New samples should
be collected and analyzed. In these circumstances, the system should contact the State regarding
invalidation and a new sample schedule/date for that quarter.
Before you conduct an operational
evaluation you should ensure that all
sample collection, holding, and
laboratory procedures were followed
correctly.
Operational Evaluation Guidance Manual
2-6
December 2008
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Exhibit 2.2 Sampling Requirements of TTHM and HAAS Analyses
Analyte
Group
TTHM
HAAS
Analytical
Method1
EPA 502.2
EPA 524.2
EPA 551.1
EPA 552.1
EPA 552.2
EPA 552. 34
SM 6251 B
Sample Container
Material2
40 ml -120 ml
screw cap glass
vials with PTFE-
faced silicone
septum
40 ml -120 ml
screw cap glass
vials with Teflon-
faced silicone
septum
60 ml screw cap
glass vials with
PTFE-faced
silicone septum
250 ml (approx.)
amber glass bottles
fitted with Teflon-
lined screw caps
50 ml (approx.)
amber glass bottles
fitted with Teflon-
lined screw caps
50 ml (approx.)
amber glass bottles
fitted with Teflon-
lined screw caps
40 ml or 60 ml
screw cap glass
Preservative/Dechlorinating Agent
(Recommended amount)
Options:
(1) 3 mg Na2S2O3/40 ml sample or
(2) 3 mg Na2S2O3/40 ml sample and
immediate acidification using HCI to pH < 2 or
(3) 25 mg ascorbic acid/40 ml sample and
immediate acidification using HCI to pH < 2.
Option 1 may be used if THMs are the only
compounds being determined in the sample.
Options 2 & 3 require the sample to be
dechlorinated prior to the addition of acid.
1 g phosphate buffer & NH4CI or Na2SO3
mixture per 60 ml sample (mixture consists of
1 part Na2HPO4, 99 parts KH2PO4, and 0.6
parts NH4CI or Na2SO3. 1 g per 60 ml results
in a pH of 4.5-5.5 and 0.1 mg NH4CI or
Na2SO3 per ml of sample.)
0.1 mg NH4CI per ml of sample
65 mg NH4CI
Storage
Guidelines
Keep at 4°C.
14 days
maximum
hold time3.
Sample Collection
Guidelines
Fill bottle to just overflowing
but do not flush out
preservatives.
No air bubbles.
Do not overfill.
Seal sample vials with no head
space.
If ascorbic acid is used to
dechlorinate TTHM samples,
then the samples should be
acidified. Acidification of
TTHM samples containing
Na2S2O3 is required if the
samples will also be analyzed
for VOCs. In both cases, the
pH should be adjusted at the
time of sample collection, not
later at the laboratory.
^(40CFR 141.131 (b))
2 Selection of container should be coordinated with the laboratory.
3 The holding time has been changed to 14 days for all HAAS samples as a part of the methods update rule.
' EPA Method 552.3 has been added as an approved HAAS method as part of the Stage 2 DBPR.
Operational Evaluation Guidance Manual
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December 2008
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TTHM and HAAS Sample Collection and Handling Page 1 of 2
Checklist
Facility Name:
Checklist Completed by: Date:
Yes No
n n Did you obtain appropriate sample collection vials provided from the laboratory?
n n Did the sample vials contain the proper preservative and dechlorinating agents?
n n Was each vial labeled using waterproof labels and indelible ink?
n n Did each vial contain the following information on the label?
n n Unique sample ID
D D System name
n n Sample location
n n Sample date and time
n n Analysis required, if not already on label
n n Did you remove the aerator from the tap if there was one present?
Q Q Did you open the water tap and allow the system to flush until the water temperature had
stabilized (usually about 3-5 minutes)?
Q Q Did you adjust the flow so that no air bubbles were visually detected in the flowing
stream?
n O Did you slowly fill the sample vial almost to the top without overflowing?
n n Were you careful not to rinse out any of the preservative/dechlorinating agent during this
process?
Q Q After the bottle was filled, did you invert it three or four times to mix the sample with the
preservative and dechlorinating agents?
D D If you collected a TTHM sample that requires acidification, did you:
n n Let the sample set for about 1 minute, allowing the dechlorinating chemical to
take effect?
n D Carefully open the vial and adjust the pH of the TTHM sample to < 2 by adding
approximately 4 drops of hydrochloric acid for every 40 ml_ of sample (amount of
acid needed will depend on buffering capacity of sample)?
n n Recap the vial, and invertthree orfour times?
Operational Evaluation Guidance Manual 2-8 December 2008
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TTHM and HAAS Sample Collection and Handling Page 2 of 2
Checklist
Yes No
D D Did you invert the vial and tap it to check for air bubbles?
D D If bubbles were detected, did you carefully open the vial and add more sample water
using the cap to achieve a headspace-free sample? Note that air bubbles would more
likely lead to a lower level of THMs or HAAs.
n D Did you immediately cool the samples to 4°C by placing them in a cooler with frozen
refrigerant packs or ice, or in a refrigerator? Samples should be maintained at this
temperature during shipping to the laboratory.
n n Did you complete the Sample Chain of Custody provided by the laboratory and include it
with the sample shipment?
D D Was the sample holding time of 14 days exceeded?
n D Was the extract holding time exceeded?
EPA Method 551.1: 14 days at a temperature less than -10°C
EPA Method 552.1: 48 hours at 4 °C or less
EPA Method 552.2: 7 days at4°Cor14 days at a temperature less than -10°C
EPA Method 552.3: 21 days for MTBE extraction solvent at-10°C or less
OR 28 days for TAME extraction solvent at-10°Cor less
Standard Method 6251 B: 21 days at -11 °C
D D Did the laboratory invalidate the sample?
Notes/Comments
Operational Evaluation Guidance Manual 2-9 December 2008
-------
2.2 Step 2: Review DBF Data at Other Sites
You should review TTHM and HAAS data at other sites within the distribution system to
assess whether the OEL exceedance is:
System-wide. If TTHM and HAAS are increasing proportionally throughout the
distribution system, it probably indicates a source and/or treatment issue.
OR
Localized. This probably indicates a localized distribution issue.
You may be allowed to limit the focus of the evaluation if the cause is known (refer to
Section 2.3).
Following are two simple examples that illustrate, respectively, a system-wide and
localized OEL exceedance. For more complex systems with multiple water treatment plants,
pressure zones, and finished water storage facilities, a hydraulic or water quality model may be
needed to determine if the OEL exceedance is a system-wide or localized problem. For example,
the case study in Appendix C describes how the system's hydraulic model was used to trace an
OEL exceedance to a finished water storage facility.
Operational Evaluation Guidance Manual 2-10 December 2008
-------
Example 2.1 System-wide DBP Increases
TTHM and HAAS monitoring results for three quarters are shown below for a system
serving 35,000 people with one surface water treatment plant. In August, the system
exceeded the OELs for TTHM and HAAS at location #1 and for TTHM at location #4.
Notice that the TTHM values and most of the HAAS values are much higher at all
monitoring locations in August than in February or May. The system conducted an
operational evaluation and determined that high summer temperatures were the cause of
the OEL exceedance and distribution system-wide high TTHM and HAAS values.
TTHM Data
Stage 2
DBPR
Location
#1
#2
#3
#4
February
A
0.032 mg/L
0.026 mg/L
0.030 mg/L
0.035 mg/L
May
B
0.050 mg/L
0.045 mg/L
0.044 mg/L
0.052 mg/L
August
C
0.121 mg/L
0.1 05 mg/L
0.1 15 mg/L
0.1 25 mg/L
Operational
Evaluation Level
D = (A+B+(2*C))/4
0.081 mg/L
0.070 mg/L
0.076 mg/L
0.084 mg/L
HAAS Data
Stage 2
DBPR
Location
#1
#2
#3
#4
February
A
0.020 mg/L
0.025 mg/L
0.022 mg/L
0.029 mg/L
May
B
0.034 mg/L
0.032 mg/L
0.038 mg/L
0.034 mg/L
August
C
0.095 mg/L
0.068 mg/L
0.074 mg/L
0.079 mg/L
Operational
Evaluation Level
D = (A+B+(2*C))/4
0.061 mg/L
0.048 mg/L
0.052 mg/L
0.055 mg/L
DBPR - Disinfection Byproducts Rule
HAAS - sum of five haloacetic acids
mg/L - milligrams per liter
TTHM - total trihalomethane
Operational Evaluation Guidance Manual
2-11
December 2008
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Example 2.2 Localized DBF Increase
TTHM and HAAS monitoring results for three quarters are shown below for a system
serving 48,000 people with two surface water treatment plants. In August, the system
exceeded the OEL for TTHM at monitoring location #3. Notice that there was not a
significant increase in TTHM or HAAS at any other location. The system conducted an
operational evaluation and determined that a tank serving monitoring location 3 was not
operated properly during this period and discharged water with unusually high water age.
TTHM Data
Stage 2
DBPR
Location
#1
#2
#3
#4
February
A
0.033 mg/L
0.035 mg/L
0.032 mg/L
0.029 mg/L
May
B
0.035 mg/L
0.037 mg/L
0.035 mg/L
0.033 mg/L
August
C
0.039 mg/L
0.038 mg/L
0.131 mg/L
0.036 mg/L
Operational
Evaluation Level
D = (A+B+(2*C))/4
0.037 mg/L
0.037 mg/L
0.082 mg/L
0.034 mg/L
HAAS Data
Stage 2
DBPR
Location
#1
#2
#3
#4
February
A
0.020 mg/L
0.024 mg/L
0.01 8 mg/L
0.026 mg/L
May
B
0.025 mg/L
0.028 mg/L
0.022 mg/L
0.023 mg/L
August
C
0.022 mg/L
0.029 mg/L
0.010 mg/L
0.028 mg/L
Operational
Evaluation Level
D = (A+B+(2*C))/4
0.022 mg/L
0.028 mg/L
0.015 mg/L
0.026 mg/L
DBPR - Disinfection Byproducts Rule
HAAS - sum of five haloacetic acids
mg/L - milligrams per liter
TTHM - total trihalomethane
Operational Evaluation Guidance Manual
2-12
December 2008
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2.3 Step 3: If the Cause of the OEL Exceedance Is Known, Request State
Approval to Limit Scope of Operational Evaluation
The system may request that the State allow a limited scope of the operational evaluation
if the cause of the exceedance can be identified to the State's satisfaction. The State must then
approve the use of a limited scope in writing. The system should confirm recordkeeping
requirements with the State for the written approval and the completed report. Note that
submitting this request will not extend the 90-day deadline for submitting the operational
evaluation report.
Examples where the OEL exceedance may be known include the following:
Total organic carbon (TOC) source water and finished water data indicate poor TOC
removal across the plant.
Source water and finished water data indicate a sudden increase in temperature.
Plant flows were reduced due to lower demand, resulting in a much longer contact
time between the chlorine and DBF precursors.
Predisinfection chlorine feed rates were unusually high.
OEL exceedance occurs at same location as previous monitoring period for which a
cause has been identified but the solution has not yet been implemented.
2.4 Step 4: Conduct Operational Evaluation
The detailed operational evaluation must include an examination of distribution,
treatment, and source operational conditions representing the time of the OEL exceedance within
the distribution system. If the State approves a limited operational evaluation (see section 2.3
above), it may not be necessary to review all operational conditions. For example, the system
may show that the source water quality did not cause the OEL exceedance.
It is important to review data representing all three monitoring periods used to calculate
the OEL. It cannot be assumed that the monitoring period with the highest TTHM or HAAS
level "caused" the exceedance. If
multiple sources and treatment
facilities provide finished water to the
distribution system, the operational
evaluation can focus on the source(s)
and treatment facilities that feed the
location where the OEL exceedances
occurred. Detailed guidance is
provided in subsequent chapters of this
report.
For guidance on identifying the cause of
the OEL exceedance, refer to
Chapter 3: Distribution System Evaluation
Chapter 4: Treatment Process Evaluation
Chapter 5: Source Water Evaluation
Operational Evaluation Guidance Manual
2-13
December 2008
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Each Chapter contains comprehensive checklists that may be useful when evaluating
potential causes of the OEL exceedance. Appendix A contains additional information on DBF
formation.
For consecutive systems, additional source water and treatment data may be needed from
the wholesaler to help identify the cause of the OEL exceedance.
In cases where it is not possible to identify the cause of an OEL exceedance, systems
should consider seeking assistance from the State, American Water Works Association
(AWWA) and American Water Works Association Research Foundation (AwwaRF)
publications, an engineering consultant, or other systems with similar issues.
2.5 Step 5: Identify Steps to Minimize Future OEL Exceedances
As part of the operational evaluation, the system must identify steps to minimize future
exceedances. Steps may include both treatment and distribution system changes such as
improved DBF precursor removal flushing, modified disinfection practices, reduced distribution
system residence time, and/or expanded water quality monitoring programs. Chapter 6 contains
more information on steps to consider for minimizing future OEL exceedances.
There may be instances where the
current system configuration poses
limitations in controlling the formation of
TTHM and HAAS, particularly for
consecutive systems. Consecutive systems
should work with their wholesaler on
developing an approach for minimizing
DBF formation.
For guidance on minimizing future OEL
exceedances, refer to
Chapter 6: Minimizing Future
Exceedances
2.6 Step 6: Prepare and Submit Report
You must submit a written report to the State within 90 days after being notified of the
analytical result that caused the OEL exceedance. The written report must be made available to
the public upon request. The report must include the results of examining your distribution,
treatment, and source water operational practices that may have contributed to the OEL
exceedance. The report must also include steps that could be considered to minimize future
OEL exceedances.
The form contained at the beginning of this chapter and checklists in Chapters 3, 4, and 5
can be used when preparing your report. You should check with the State regulatory agency to
see if any of these or other forms are required as part of the operational evaluation report.
Appendices B through E contain example reports using the form and checklists.
Operational Evaluation Guidance Manual 2-14 December 2008
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2.7 Uses of Operational Evaluation Reports
The operational evaluation provides information that allows systems to act to prevent a
violation of the Stage 2 DBPR MCLs. The operational evaluation provides systems with valuable
information to evaluate current operational practices (e.g., water age management, flushing,
source blending) or in planning system modifications or improvements (e.g., disinfection
practices, storage tank modifications, distribution system looping). The operational evaluation
will also provide valuable information for use in:
System capital improvement and planning;
Preventative maintenance and asset management plans;
Treatment and distribution operations plans and standard operating procedures; and
Treatment and distribution system optimization efforts.
State review of operational evaluations will also be valuable for both States and systems
in their interactions, particularly when systems may be in discussions with, or requesting
approval from, the State for system improvements or modifications. Review of operational
evaluations will be valuable for States in reviewing other compliance submittals. The operational
evaluation report will also provide valuable information for use in:
Sanitary surveys and inspections;
Review of distribution, treatment, or source modifications;
Review or approval of operations plans or operating permits;
State optimization efforts; and
Technical and compliance assistance.
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Operational Evaluation Guidance Manual 2-16 December 2008
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3. Distribution System Evaluation
This chapter covers:
3.1 System Maintenance
3.2 Changes in System Demand
3.3 Storage Facility Operations
3.4 Booster Disinfection Practices
3.5 References
3.6 Additional Resources
Although a significant portion of TTHM and HAAS can form during primary
disinfection, they can continue to form within the distribution system as a result of continual
exposure to disinfectant residuals and extended contact time. TTHM and HAAS can increase
further if precursors contained in pipeline or storage tank sediment come into contact with
disinfectant residuals.
This chapter provides guidance on how distribution data and records can be evaluated to
determine the cause of the operational evaluation level (OEL) exceedance. The checklist on
pages 3-4 and 3-5 can be used to collect information and document the distribution system
evaluation. The Stage 2 DBPR does not require the use of this checklist, but you should check
with the State regulatory agency to ask if any of these or other forms are required as part of the
evaluation report. Items on the checklist are discussed in detail in the applicable sections of this
chapter. There may be additional causes of an OEL exceedance that are not included in the
checklist.
Before you begin:
Gather distribution system monitoring and operations data that reflect conditions just
prior to and during the time of the OEL exceedance. Types of information that could
be useful include:
Temperature data;
- Disinfectant residual data;
- Pump station and storage facility operating data (e.g., tank level data);
System flow and pressure data;
Maintenance records (planned and emergency); and
- Customer complaint records.
Different systems will have different types of data available to them. Exhibit 3.1
shows the water quality parameters that may be collected by systems using ground
water, filtered surface water, unfiltered surface water, and groundwater under the
direct influence of surface water (GWUDI). Many systems have water quality
monitoring programs above and beyond regulatory requirements to help optimize
distribution system operations and finished water quality.
Operational Evaluation Guidance Manual 3-1 December 2008
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Exhibit 3.1 Distribution System Monitoring Data
Parameter
Temperature
Disinfectant
residual
Pump records,
meter records,
and other flow
information
Tank operations
Maintenance and
operations records
(flushing, repairs,
replacement, and
other)
Customer
complaint records
System Type
Ground water
Optional
Required1
Optional
Optional
Optional
Optional
Filtered surface
water/GWUDI
Optional
Required
Optional
Optional
Optional
Optional
Unfiltered surface
water/GWUDI
Optional
Required
Optional
Optional
Optional
Optional
Required = Required data a system should have based on Federal regulatory requirements. Additional monitoring
parameters may be required by the State.
Optional = Optional data a system may have for optimization, process control purposes or State requirements.
1 Ground water systems that disinfect are required to monitor disinfectant residual.
You may wish to obtain historical water quality monitoring data for comparison to
data collected at the time of the OEL exceedance to determine if deviations from
normal patterns occurred. In particular, evaluate historical temperature and
disinfectant residual data for the monitoring site where the OEL exceedances
occurred. If water temperature is unusually high or disinfectant residual is unusually
low at the location compared to previous years, the site may have experienced longer
than normal water residence time. If disinfectant residual is unusually high for that
time of year, an increase in finished water residual concentration may be the cause
(see Chapter 4 for guidance on treatment process evaluations for OEL exceedances).
Hydraulic models, water quality models or other similar tools may be helpful in
conducting this data evaluation. For example, Besner et al. (2001) developed a data
integration approach to help identify the causes of water quality variations in the
distribution system. Besner emphasizes the need to evaluate system hydraulics data
and be aware of operations and maintenance events in the distribution system that can
affect water quality. Besner's data integration approach uses Excel spreadsheets, a
hydraulic model, and a geographic information system (GIS) program, all tools that
are commercially available and familiar to many water system personnel.
Operational Evaluation Guidance Manual
3-2
December 2008
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Customer complaint records can be very helpful in identifying a problem with the
distribution system that could have contributed to the OEL exceedance. Check
records for the following types of customer complaints:
- Low pressure. Reports of low pressure can indicate that a main break or
firefighting event occurred. These events can allow old water from tanks, dead
ends, or stagnant zones to be drawn into other areas of the distribution system.
This water may contain high levels of TTHM and HAAS.
- Color. A sudden change in color may also indicate that sediment or pipe scales
have been released into the distribution system. However, systems should be
careful when examining color data because source water contaminants such as
algae, metals, iron, and sulfur bacteria can also cause color in water.
Odor. Customer complaints of a strong chlorine odor can indicate that
disinfectant concentrations are higher than normal, which may indicate that
TTHM and HAAS levels are also high. Odor complaints may also occur if pipe
scales or sediment are disturbed and released into the bulk water.
- General Taste and Odor. Musty, dirty, or stagnant taste and odor could indicate
low water use areas or areas where the chlorine residual is low or depleted. The
water in these areas of the distribution system may have longer residence times
and higher DBFs.
As recommended in Chapter 2, you should compare TTHM and HAAS data from
different points in the distribution system from the time of the exceedance (See Step 2
in Section 2.2). If OELs were exceeded at only a few locations, you may be able to
narrow your focus to monitoring data from those parts of the distribution system.
Remember, you must obtain State approval to limit the focus of your evaluation.
Operational Evaluation Guidance Manual 3-3 December 2008
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Distribution System Evaluation Checklist Page 1 of 2
System Name:
Checklist Completed by: Date:
Do you have disinfectant residual or temperature data for the monitoring 1-1Y n No
location where you experienced the OEL exceedance?
If NO, proceed to item B. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
L^ L^ Was the water temperature higher than normal for that time of the year at that
location?
L^ Q Was the disinfectant residual lower than normal for that time of the year at that
location?
Q Q Was the disinfectant residual higher than normal for that time of the year at that
location?
B. Do you have maintenance records available for the time period just prior to the I-IY |~l No
OEL exceedance?
If NO, proceed to item C. If YES, answer the following questions:
Yes No
D D Did any line breaks or replacements occur in the vicinity of the exceedance?
D n Were any storage tanks or reservoirs taken off-line and cleaned?
Q [] Did flushing or other hydraulic disturbances (e.g., fires) occur in the vicinity of
the exceedance?
D D Were any valves operated in the vicinity of the OEL exceedances?
C. If your system is metered, do you have access to historical records showing 1-1 y |~| No
water use at individual service connections?
If NO, proceed to item D. If YES, was overall water use in your system 1-1 y n No
unusually low, indicating higher than normal water age? LJ es |_|
D. Do you have high-volume customers in your system (e.g., an industrial IY |~| Mn
processing plant)? LJ es |_|
If NO, proceed to item E. If YES, was there a change in water use by a 1-1 y |~l No
high-volume customer? LJ es |_J
E. Is there a finished water storage facility hydraulically upstream from the 1-1 y 1-1 N
monitoring location where you experienced the OEL exceedance? LJ es |_|
If NO, proceed to item F. If YES, review storage facility operations and water quality
data to answer the following questions for the period in which the OEL exceedance
occurred:
Yes No
n n Was a disinfectant residual detected in the stored water or at the tank outlet?
D D Do you know of any mixing problems with the tank or reservoir?
D D Does the facility operate in "last in-first out" mode?
L^ LI Was the tank or reservoir drawn down more than usual prior to OEL
exceedance, indicating a possible discharge of stagnant water?
Q Q^ Was there a change in water level fluctuations that would have resulted in
increased water age within the tank or reservoir?
Operational Evaluation Guidance Manual 3-4 December 2008
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Distribution System Evaluation Checklist Page 2 of 2
F. Does your system practice booster chlorination? DYes Q No
If NO, proceed to item G. If YES, was there an increase in booster 1-1 y n No
chlorination feed rates?
G. Did you have customer complaints in the vicinity of the OEL exceedance? D Yes D No
If NO, proceed to item H. If YES, explain.
Did concern about complying with a rule other than Stage 2 DBPR, such as the 1-1 y _
Lead and Copper rule, the TCP, or any other rule constrain your options to LJ °
reduce the DBP levels at this site? For example, are you limited by the need to
maintain a detectable disinfectant residual in your ability to control DBP levels
in the distribution system?
If NO, proceed to item I. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
I. Conclusion
D Yes D No
Did the distribution system cause or contribute to the OEL exceedance(s)?
n Possibly
If NO, proceed to evaluations of treatment systems and source water. If YES or
POSSIBLY, explain below.
Operational Evaluation Guidance Manual 3-5 December 2008
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3.1 System Maintenance
Maintenance records are useful supplements to distribution system monitoring data.
Although monitoring data can show fluctuations in temperature, disinfectant residual, and other
factors that contribute to TTHM and HAAS formation, maintenance records can reveal short
term, physical distribution system changes that can influence TTHM and HAAS formation but
may not be identified through monitoring.
Data Analysis
Systems should examine maintenance records for any activities that may have affected
disinfection practices or flow in the areas where OEL exceedances occurred. Systems should
examine records of both planned maintenance, such as tank cleaning and flushing, and
unplanned maintenance, such as repairing a broken pipe.
Causes
The primary causes of increased TTHM and HAAS formation resulting from system
maintenance activities include:
Line breaks. Line breaks can cause a pressure drop and change the pattern of flow
through the distribution system. As a result, older water from stagnant zones may be
drawn into other areas of the distribution system where water use is higher. What to
check: Review maintenance records and determine if a main break occurred in the
vicinity of the OEL exceedance.
System isolation for repairs. Frequently, system maintenance work is accompanied
by the closure of valves to isolate sections of the distribution system. This changes
the flow patterns in surrounding areas of the distribution system, which can
potentially cause stagnant water with high DBF levels to flow into areas of the
distribution system serving customers. Also, after repair work is completed, the
repair crew may fail to open all the valves that were closed due to construction work,
which can create artificial dead ends. What to check: Review maintenance records
and determine if an event, such as a main repair, occurred that resulted in a valve
being closed. Also, check valves in the vicinity of the OEL exceedance to assess if a
valve is closed that should typically be open. Review customer complaint records to
see if anyone reported discolored water in the vicinity of the OEL exceedance.
Disinfection of pipe after repair/replacement. Disinfection of new or repaired
distribution system piping is typically accomplished using a highly concentrated (>
25 ppm) chlorine solution. Failure to properly flush a section of new or repaired pipe
before placing it into service can introduce excessive amounts of chlorine to the
distribution system and result in short-term spikes in TTHM and HAAS
concentrations. What to check: Check maintenance records to determine if a section
of pipe was replaced or repaired in the area near where an OEL exceedance occurred.
Storage tank cleaning and disinfection. Storage tanks are cleaned periodically.
During this cleaning process, sediment can be disturbed and released into the
Operational Evaluation Guidance Manual 3-6 December 2008
-------
distribution system. This sediment can react with residual disinfectants to form
TTHM and HAAS. Storage tanks should be disinfected after any maintenance
activities. If disinfection is not conducted properly, water containing high
concentrations of chlorine can be released into the distribution system. What to
check: Review maintenance records and determine if a storage facility was cleaned in
the vicinity of the OEL exceedance. Check customer complaint records for reports of
a chlorinous odor.
Flushing. Flushing can cause the
release of pipe scales and sediment
into the water column. Organic
matter can be present in these scales
and sediment that can react to form
TTHM and HAAS. Flushing can
also result in a reversal of flow in
the vicinity of the OEL exceedance,
potentially causing older water to be
delivered to an area for a limited
time. What to check: Review
maintenance and other operational
data and determine if a flushing or
other event occurred in the vicinity
of the OEL exceedance. Check
customer complaint records for reports of discolored water.
Breakpoint chlorination to address nitrification. Some systems that chloraminate
periodically use breakpoint chlorination to control nitrification or biofilm growth in
the distribution system. DBF formation can increase during these periods. What to
Check: If your system practices breakpoint chlorination, review operating records to
determine if breakpoint chlorination was used prior to or during the OEL exceedance.
Flushing the distribution system.
3.2 Changes in System Demand
It is important to understand how the hydraulic design of the system and system operation
affect TTHM and HAAS formation. High water residence time in the distribution system can
lead to higher TTHM and HAAS concentrations. High residence times can be the result of low
system demand overall, or can occur locally, particularly in dead ends or stagnant zones. System
operators should understand ".. .the amount of water being used, where it is being used, and how
this usage varies with time." (National Research Council 2006) With this knowledge, system
operators can estimate water ages for various parts of the system and can modify operations to
minimize water age.
A dead end may be the result of distribution system piping configuration (e.g., the actual
end of a long pipe with few connections) or valving configuration (e.g., a closed valve that
prevents flow from one area to another). Stagnant zones are created when water flow from
opposing directions meets at a location where there is little or no water demand. There is no net
water movement in any direction in that particular location and, therefore, fresh water cannot
Operational Evaluation Guidance Manual
3-7
December 2008
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flow to a stagnant zone from other areas. A hydraulic model may allow you to estimate
residence times and identify stagnant zones.
Data Analysis
Systems should review pump and meter data to determine if demands were lower than
normal, resulting in high distribution system residence times. It may also be helpful to review
hydraulic model results or other data to identify dead ends or stagnant zones near the vicinity of
the OEL exceedance. Water quality data should be reviewed from sites in the vicinity of the
OEL exceedance. Decreased disinfectant residual and high temperatures may be water quality
indicators of high water residence time.
Systems should use caution when using disinfectant residual data to assess water
residence times. Disinfectant residual decay is highly dependent on local distribution system
conditions including piping materials, corrosion and conditions inside the pipe, microbiological
activity, water temperature, level of disinfectant demand, and accumulation of sediment.
Causes
The primary causes of excessive residence times that can lead to increased TTHM and
HAAS formation include:
Low system demands. An overall reduction in system demand can increase
residence time throughout the distribution system. Also, reduced water demand from
a high-volume industrial water user can have a large impact on water residence time
in a specific area. In the summer, demand may be lower during rainy periods due to
lower outdoor water use. What to check: Review pump and meter data to determine
if water demand was low. Check demands for high-volume industrial customers.
Check disinfectant residual data throughout the system compared to finished water
levels to determine if there was a larger than normal decrease in residual levels.
Dead ends and stagnant zones. If your Stage 2 monitoring site is near a dead end,
residence time may be unusually high in this area. If two sources of water supply the
area in which the OEL exceedance occurred, a stagnant zone could be occurring at or
near the monitoring site. What to check: Review system operating data, perhaps
with the use of a hydraulic model, to identify dead ends or stagnant zones within the
vicinity of the OEL exceedance. Check disinfectant residual data to determine if
levels at the site were unusually low at the time of the exceedance compared to
previous years, indicating longer than normal residence times in that area.
3.3 Storage Facility Operations
Configuration and operation of storage facilities has a significant impact on water age in
the areas "downstream" of the storage tank. In general, storage facilities can impact TTHM and
HAAS formation by increasing residence time for the water as a whole, discharging water with
very high residence times from stagnant zones in the tank. If bottom sediments are stirred up as
Operational Evaluation Guidance Manual 3-8 December 2008
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the water is discharged from the storage facility, the water may have elevated levels of DBF
precursors.
Storage tank configuration and operation
can significantly affect DBF levels.
If the storage facility is operated such
that water level fluctuations are small and
turnover of the water is infrequent, the stored
water age can be high. Storage facilities are
sometimes oversized to provide water under
emergency circumstances. One disadvantage
of this design approach is that a much smaller
volume of water is needed under normal
operations. The longer the water is in contact
with a disinfectant, the more likely TTHM
and HAAS will form.
The mixing characteristics of storage
tanks are impacted by the inlet/outlet piping
configuration, inlet momentum, temperature, and duration of drain/fill cycles. For example,
common inlet/outlet piping and oversized inlet piping that results in low inlet velocity are
potential causes of poor mixing in storage facilities.
A common problem occurs when tanks operate in "last in-first out" mode, meaning that
the freshest water in the tank is the first to be discharged during a drain cycle. During periods of
higher than normal demand when drain periods are extended, these tanks may discharge water
from the upper regions of the tank where water age is substantially (e.g., several days or weeks)
higher than water in the lower regions of the tank. If a system has one or more poorly mixed
storage tanks, areas receiving the stored water from those tanks may occasionally have high DBF
concentrations.
The presence of sediment in the tank may result in higher TTHM and HAAS levels.
Organic matter in the sediment can react with disinfectants in the water, resulting in increased
concentrations of TTHM and HAAS.
Data Analysis
If the OEL exceedance occurred in the area downstream of a storage tank, you should
evaluate tank circulation, turnover, and drawdown levels. Examine pump on/off cycles and
associated tank levels. A methodology for evaluating storage tank mixing characteristics is
presented in Water Quality Modeling of Distribution System Storage Facilities (Grayman et al.,
2000). Also check maintenance records for the last tank cleaning and inspection. Infrequent
draining and cleaning can result in the presence of sediment in storage facilities.
Causes
The primary causes of increased TTHM and HAAS formation resulting from storage tank
operations include:
Discharge of stagnant water. During periods of higher than normal demand when
the storage facility is drained to a lower level than usual, water that had previously
Operational Evaluation Guidance Manual 3-9 December 2008
-------
stagnated in poorly mixed hydraulic zones in the tank may be discharged into the
distribution system. What to check: Review tank configuration and operations to
identify potential stagnant zones. You may also want to evaluate disinfectant
residuals and temperatures at different levels and locations to help determine if there
are stagnant zones within a tank. Review tank level records to determine if a tank
was drawn down to unusually low levels, allowing water from stagnant zones to enter
the distribution system.
Increased residence time. Increased residence times can result if water in the
storage facility is turned over infrequently. What to check: Check tank operating
levels and system demands to determine if excessive residence time occurred prior to
the OEL exceedance. Check temperature and disinfectant residual data for water
discharged from the storage facility. Loss of a disinfectant residual and/or increased
temperature may be water quality indicators of high water residence time.
Sediment in tank. The presence of sediment may contribute to higher TTHM and
HAAS formation. What to check: Check system maintenance records to determine
the last time the tank was drained and cleaned. You may also wish to inspect the tank
and determine if sediment is present.
Breakpoint chlorination to address nitrification. Some systems that chloraminate
periodically use breakpoint chlorination to control nitrification or biofilm growth in
tanks. DBF formation can increase during these periods. What to Check: If your
system practices breakpoint chlorination, review operating records determine if
breakpoint chlorination was used prior to or during the OEL exceedance.
3.4 Booster Disinfection Practices
Booster disinfection is used by some systems to maintain a disinfectant residual in
sections of a distribution system that might not otherwise maintain a residual. When properly
controlled and coordinated with the treatment plant disinfection process, booster disinfection can
be used to reduce average distribution system TTHM and HAAS concentrations. To accomplish
this, the disinfectant dose applied at the plant should be minimized to reduce TTHM and HAAS
formation while maintaining the necessary residual in the distribution system prior to the
boosting station. The booster disinfectant dose is then added to maintain a residual to the end of
the system. The booster disinfection feed system needs to be maintained in working, calibrated
order in order to prevent an overfeed that introduces too much chlorine into the distribution
system and increases DBF levels.
Data Analysis
Review the distribution system disinfectant residual data during the time period that
would have most impacted TTHM and HAAS levels at the time and location of the OEL
exceedance. It may be helpful to review historical distribution system disinfectant residual data
and compare it to residual data collected during the period leading up to the OEL exceedance. It
is also helpful to evaluate disinfection feed practices at booster disinfection facilities.
Operational Evaluation Guidance Manual 3-10 December 2008
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Causes
The primary causes of increased TTHM and HAAS formation resulting from a problem
with booster disinfection include:
Sudden increase in booster chlorination feed rates. A malfunction or poor
calibration of a booster chlorination feed pump could cause overdosing of chlorine.
What to check: Review booster chlorination feed rates during the time period that
would have most impacted TTHM and HAAS levels at the time and location of the
OEL exceedance. Verify that chemical feed pumps are delivering chemicals at set
rate (i.e., perform a "pump catch").
3.5 References
Besner, M.C., V. Gauthier, B. Barbeau, R. Millette, R. Chapleau, and M. Prevost. 2001.
Understanding Distribution System Water Quality. JournalAWWA. 93(7): 101.
Grayman, W. M., L. A. Rossman, C. Arnold, R. A. Deininger, C. Smith, J. F. Smith, and R.
Schnipke. 2000. Water Quality Modeling of Distribution System Storage Facilities. Denver:
AwwaRF and AWWA.
National Research Council. 2006. Drinking Water Distribution Systems: Assessing and Reducing
Risks. Washington D.C.: The National Academies Press.
3.6 Additional Resources
Baribeau, H., P.C. Singer, R.W. Gullick, S.L. Williams, R.L. Williams, S.A. Andrews, L.
Boulos, H. Haileselassie, C. Nichols, S.A. Schlesinger, L. Fountleroy, E. Moffat, and G.F.
Crozes. 2006. Formation and Decay of Disinfection By-Products in the Distribution System.
Denver: AwwaRF.
Clement, J., J. Powell, M. Brandt, R. Casey, D. Holt, W. Grayman, and M. LeChevallier. 2004.
Predictive Models for Water Quality in Distribution Systems. Denver: AwwaRF.
Emmert. G.L., G. Cao, G. Geme, N. Joshi, and M. Rahman. 2004. Methods for Real-Time
Measurement ofTHMs andHAAs in Distribution Systems. Denver: AwwaRF.
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Operational Evaluation Guidance Manual 3-12 December 2008
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4. Treatment Process Evaluation
This chapter covers:
4.1 Predisinfection
4.2 Presedimentation
4.3 Coagulation/Flocculation
4.4 Sedimentation/Clarification
4.5 Filtration
4.6 Primary Disinfection
4.7 Recycle Practices
4.8 Secondary Disinfection
4.9 References
4.10 Additional Resources
This chapter provides guidance on how treatment processes can be evaluated to
determine the cause of an operational evaluation level (OEL) exceedance. Different systems will
have different types of data available to them - Exhibit 4.1 shows the water quality parameters
and operational data that ground water systems, filtered surface water systems, and unfiltered
surface water systems may be collecting on a regular basis for regulatory purposes and/or for
treatment process control. Systems are encouraged to expand water quality monitoring programs
above and beyond regulatory requirements to help optimize treatment processes. Consecutive
systems that purchase all water may want to obtain this data from the wholesaler to help identify
the cause of the OEL exceedance.
The checklist on pages 4-4 through 4-7 can be used to collect information and document
treatment process evaluations. The Stage 2 DBPR does not require the use of the checklist, but
you should check with your State regulatory agency to see if any of these or other forms are
required as part of the evaluation report. Items on the checklist are discussed in detail in
applicable sections of this Chapter. There may be additional causes of OEL exceedances that are
not identified in the checklist. Note that treatment plant processes (including recycle practices)
are organized according to the order in which they are typically configured in a conventional
plant.
Operational Evaluation Guidance Manual
December 2008
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Exhibit 4.1 Treatment Plant Monitoring Data
Parameter
Raw water TOC
Predisinfectant and other
pretreatment feed rates
Coagulant/polymer
feed rates
Other chemical feed rates for pH or
alkalinity adjustment to improve
coagulation
Settled water turbidity
Combined and individual filter
effluent turbidity
Particle counts
Primary disinfectant concentration
Temperature3
PH3
Flow3
Finished water TOC
Finished water TTHM, HAAS, pH,
temperature, DOC, SUVA, color
Disinfectant concentration at entry
to the distribution system
System Type1
Ground water
Optional
Optional
Optional
Optional
Optional
Optional
Optional
Required (if using
chlorine dioxide)
Filtered surface
water/GWUDI
Required4, Optional
Optional
Optional
Optional
Optional
Required2
Optional
Required
Required
Required
Required
Required4, Optional
Optional
Required
Unfiltered surface
water/GWUDI
Optional
Optional
Required
Required
Required
Required
Optional
Optional
Required
Required = Required data a system should have based on Federal regulatory requirements. Additional monitoring
parameters may be required by the State.
Optional = Optional data a system may have for optimization, process control purposes or State requirements.
1 Consecutive systems may wish to obtain some of the information in the table from their wholesaler.
2 Only conventional and direct filtration systems are required by the Surface Water Treatment Rule (SVVTR) to
monitor individual filter effluent turbidity.
3 Temperature, pH, and flow must be measured to determine microbial inactivation credit (CT).
4 Only conventional filtration systems are required by the Stage 1 DBPR to monitor alkalinity and TOC in the source
water.
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December 2008
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Before you begin:
You should have a good understanding of the time of travel from the treatment plant
to the distribution system monitoring locations to determine the relevant period of
treatment process data.
Review finished water data collected prior to the OEL exceedance to help focus the
evaluation. Key parameters to review may include:
DBF precursors levels (TOC), specific ultraviolet absorbance (SUVA), dissolved
organic carbon (DOC), bromide);
- TOC characteristics (hydrophobic and hydrophilic fractions);
- pH;
Temperature;
- Turbidity;
- Disinfectant concentration; and
- TTHM and HAAS.
Compare the current finished water data to historical data taken during the same time
frame in past years. Increases in one or more of these parameters may provide
important clues for the evaluation. For example, if TOC is higher than normal, you
may have had a problem with the coagulation process. If the chlorine concentration
is higher than normal, you may have overfed chlorine for primary disinfection. An
increase in finished water TTHM and/or HAAS concentrations could be a result of
poor DBF precursor removal, overdose of disinfectant, longer than normal residence
times, or other factors.
If there are no obvious changes in these finished water parameters, the cause of the
OEL exceedance may be in the distribution system. Remember, an operational
evaluation of source, treatment, and distribution system practices must be completed
unless the State allows an evaluation with a limited scope. The evaluation may not
require a detailed review of all available data in order to identify possible causes of
the OEL exceedance. You should determine the level of review necessary based on
system-specific circumstances.
Operational Evaluation Guidance Manual 4-3 December 2008
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Treatment Process Evaluation Checklist Page 1 of 4
I NO DATA AVAILABLE
Facility Name:
Checklist Completed by: Date:
A. Review finished water data for the time period prior to the OEL exceedance(s) and compare to
historical finished water data using the following questions:
Were DBP precursors (TOC, DOC, SUVA, bromide, etc.) higherthan normal? DYes Q No
Was finished water pH higher or lower than normal? QYes Q No
Was the finished water temperature higher than normal? QYes Q No
Was finished water turbidity higher than normal? QYes Q No
Was the disinfectant concentration leaving the plant(s) higher than normal? D Yes Q No
Were finished water TTHM/HAA5 levels higher than normal? QYes Q No
Were operational and water quality data available to the system operator for L^Yes n No
effective decision making?
B. Does the treatment process include predisinfection? D Yes D No
If NO, proceed to item C. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D n Was disinfected raw water stored for an unusually long time?
fj D Were treatment plant flows lower than normal?
fj n Were treatment pi ant flows equally distributed among different trains?
fj n Were water temperatures high or warmer than usual?
fj n Were chlorine feed rates outside the normal range?
fj n Was a disinfectant residual present in the treatment train following predisinfection?
rj n Were online instruments utilized for process control?
D n Did you switch to free chlorine as the oxidant?
rj n Was there a recent change (or addition) of pre-oxidant?
D n Did you change the location of the predisinfection application?
C. Does your treatment process include presedimentation? DYes D No
If NO, proceed to item D. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D n Were flows low?
D n Were flows high?
D n Were online instruments utilized for process control?
D n Was sludge removed from the presedimentation basin?
D n Was sludge allowed to accumulate for an excessively long time?
D n Do you add a coagulant to your presedimentation basin?
D n Was there a problem with the coagulant feed?
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Treatment Process Evaluation Checklist Page 2 of 4
D. Does your treatment process include coagulation and/or flocculation? QYes fj No
If NO, proceed to item E. If YES, answer the following questions forthe period in which
an OEL exceedance occurred:
Yes No
r-i r-i Were there any feed pump failures or were feed pumps operating at improper feed
rates?
D n Were chemical feed systems controlled by flow pacing?
D n Were there changes in coagulation practices or the feed point?
D n Did you change the type or manufacturer of the coagulant?
fj Q Do you suspect that the coagulant in use at the time of the OEL exceedance did
not meet industry standards?
D n Did the pH or alkalinity change at the point of coagulant addition?
fj n Were there broken or plugged mixers?
fj D Were flow rates above the design rate or was there short-circuiting?
E. Does your treatment process include sedimentation or clarification? QYes fj No
If NO, proceed to item F. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rn n Were there changes in plant flow rate that may have resulted in a decrease in
settling time or carry-over of process solids?
fj D Were settled water turbidities higher than normal?
r-i r-i Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
fj n Was there any maintenance in the basin that may have stirred sludge from the
bottom of the basin and caused it to carry over to the point of disinfectant
addition?
rj n Was sludge allowed to accumulate for an excessively long time or was there a
malfunction in the sludge removal equipment?
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Treatment Process Evaluation Checklist Page 3 of 4
F. Does your treatment process include filtration? QYes fj No
If NO, proceed to item G. If YES, answerthe following questions forthe period in which
an OEL exceedance occurred:
Yes No
Q Q Was there an increase in individual or combined filter effluent turbidity or particle
counts?
D n Was there an increase in turbidity or particle loading onto the filters?
r-i r-i Was there an increase in flow onto the filters or malfunction of the rate of flow
controllers?
Q Q Were any filters taken off-line for an extended period of time that caused the other
filters to operate near maximum design capacity and created the conditions for
possible breakthrough?
D n Were any filters operated beyond their normal filter run time?
r-i r-i Were there any unusual spikes in individual filter effluent turbidity (which may
indicate particulate or colloidal TOC breakthrough) in the days leading to the
excursion?
D n Were all filters run in a filter-to-waste mode during initial filter ripen ing?
n n If GAC filters are used, is it possible the adsorptive capacity of the GAC bed was
reached before reactivation occurred (leave blank if not applicable)?
fj n If biological filtration is used, were there any process upsets that may have
resulted in the breakthrough of TOC (leave blank if not applicable)?
G. Does your treatment process include primary disinfection by injecting chlorine n No
prior to a clearwell? es
If NO, proceed to item H. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rj n Was there a sudden increase in the amount of chlorine fed or an increase in the
chlorine residual?
fj Q Was there an increase in clearwell holding time?
D n Was the plant shut down or were plant flows low?
D n Was there an increase in clearwell water temperature?
rj n Did you switch to free chlorine recently as the primary disinfectant?
D n Was the inactivation of Giardia and/or viruses exceptionally high?
i-i |-i Was there a change in the mixing strategy (i.e., mixers not used, adjustment of
tank level)?
H. Does your plant recycle spent filter backwash or other streams? QYes fj No
If NO, proceed to item I. If YES, answerthe following questions forthe period in which
an OEL exceedance occurred:
Yes No
r-i r-i Did a change in the recycle stream quality contribute to increased DBP precursor
loading that was not addressed by treatment plant processes?
D D Did a recycle event result in flows in excess of typical or design flows?
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Treatment Process Evaluation Checklist Page 4 of 4
I. Do you inject a disinfectant after your clearwell to maintain a distribution - N
system residual?
If NO, proceed to item J. If YES, answer the following questions forthe period in which
an OEL exceedance occurred:
Yes No
D n Was there a sudden increase in the amount of chlorine fed?
fj D Was there a switch from chloramines to free chlorine for a burnout period?
D n If using chloramines, was the chlorine to ammonia ratio in the proper range?
D n Was there a problem with either chlorine or ammonia mixing?
J. Did concern about complying with a rule other than Stage 2 DBPR, such as the
Lead and Copper rule, the LT2ESWTR, or any other rule constrain your options LJ No
to reduce the DBP levels at this site? For example, are you limited by other
treatment targets/requirements in your ability to control precursors in
coagulation/flocculation?
If NO, proceed to item K. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
K. Conclusion
I Yes
Did treatment factors and/or variations in the plant performance contribute to the
OEL exceedance(s)? rj Possib|y
If YES or POSSIBLY, explain below.
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4.1 Predisinfection
Predisinfection is the addition of a disinfectant to the treatment train prior to filtration.
Generally, the purposes of predisinfection are to obtain an additional inactivation credit, to
control microbiological growth in subsequent treatment processes, to improve coagulation, to
oxidize contaminants such as arsenic or manganese, and to reduce tastes and odors. The most
commonly used predisinfectants are chlorine, chlorine dioxide, and ozone. This section focuses
on systems using chlorine as their predisinfectant.
Predisinfection with chlorine can result in significant TTHM and HAAS formation due to
the high concentration of DBF precursors available (prior to removal by coagulation,
flocculation, sedimentation, and/or filtration) to react with the disinfectant, as well as the
increased contact time through the treatment plant. DBFs will continue to form in subsequent
treatment processes, not only during predisinfection, as long as there is a disinfectant residual
present.
Systems that add chlorine following clarification, or post-filtration, will likely experience lower
TTHM and HAAS concentrations because of the removal of DBF precursors prior to chlorine
addition.
Exhibit 4.2 shows one example of the effect of the point of chlorination on treatment
plant TTHM and HAAS concentrations. As shown in the figure, there is little difference in
TTHM and HAAS concentrations between prechlorination and rapid mix. This is primarily due
to the fact that DBF precursors have not been removed from the water at this point in the
treatment process. However, when the point of chlorine addition is moved to post-
sedimentation, in-plant TTHM and HAAS concentrations are reduced by greater than 70 percent
and 50 percent, respectively.
Systems that change the point of chlorine addition seasonally to adjust for changes in raw
water quality may experience fluctuations in DBFs. For example, systems that use
prechlorination seasonally to control taste and odor may see increases in TTHM and HAAS
concentrations during those periods.
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Exhibit 4.2 Effects of Chlorine Addition at Different Treatment Process Locations
Effect of Alternative Locations for Chlorine Addition
Point on In-Plant DBP Formation
Pre- Rapid Mix Post- Post-
chlorination flocculation sedimentation
Point of chlorine addition
Source: A. Franchi and C. Hill (2002).
Data Analysis
You should review predisinfectant feed rates and operational data during the time period
that would have most impacted distribution system TTHM and HAAS levels. You may also
want to examine historical predisinfectant feed rates to determine if the chemical feed rates that
were in effect at the time of the exceedance were unusual in comparison. Other data, such as
flow, may also provide useful information on what factors may have contributed to increased
DBP levels.
Causes
The primary causes of increased TTHM and HAAS formation resulting from problems
with predisinfection include:
Poorly controlled or excessive pre-chlorine dose. An increase in the chlorine
dosage can increase TTHM and HAAS concentrations. High chlorine dosages may
be intentionally applied during periods of algal bloom for the control of color, taste,
and odor. There can also be unintentional results of poor chemical feed regulation
amplified by a decrease in water volume processed by the plant or equipment failure.
Changes in the plant process that involve the use of pre-oxidation with chlorine (i.e.,
for arsenic treatment) may also increase DBP formation. What to check: Chlorine
doses during the time period that would have most impacted distribution system
TTHM and HAAS levels.
Change in oxidant. A change in the preoxidant type may result in a change in DBP
concentrations. Systems that switch from potassium permanganate (which does not
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form TTHM and HAAS) to chlorine may experience increases in TTHM and HAAS.
Systems that switch from chlorine to ozone will likely experience a decrease in plant
TTHM and HAAS concentrations. However, ozonation can result in increases in
bromate concentrations (also a regulated DBF) in systems with sufficient bromide
present in the source water. Some systems use chlorine dioxide because it produces
relatively few THMs and HAAs. What to check: Plant operating records during the
time period that would have most impacted distribution TTHM and HAAS levels to
see if oxidation with chlorine was implemented.
4.2 Presedimentation
Presedimentation is used to allow suspended material (inorganic and organic) to settle out
to reduce the loading on the remaining treatment processes. In some plants, a coagulant and/or
polymer is added to enhance settling, and mechanical flocculators can be used. Upsets to the
presedimentation process can inhibit DBF precursor removal, resulting in higher concentrations
of DBF precursors traveling through plant processes to react with disinfectants injected later in
the treatment process.
Data Analysis
Review operating practices for the
presedimentation basin and weather conditions to
determine if there were any activities that might have
inhibited settling in the basin (e.g., sludge removal).
You should also review plant flow records to see if there
was a change in flow through the basin. If you add
coagulant and/or polymer to the presedimentation basin,
you should review chemical feed records during the time
period that would most impact distribution system
TTHM and HAAS levels.
Causes
The primary causes of increased TTHM and
HAAS formation resulting from problems with
presedimentation include:
Presedimentation basin with
flocculator in foreground.
Increased flow rate through the basin. A sudden increase in flow through the
presedimentation basin could upset settled sludge or pass DBF precursors into the
treatment plant at levels that are difficult to remove by major plant processes. What
to check: Review flow rates into and out of the presedimentation basin and
determine if flows were unusually high.
Decreased flow rate through the basin. If the residence time in the
presedimentation basin is unusually long, the temperature of the water could increase,
which could result in increased formation of TTHM and HAAS. What to check:
Review flow records into and out of the presedimentation basin to determine if longer
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than usual holding times occurred. You may also want to check temperature data (see
Section 5.1 for additional discussion of temperature effects on DBF formation) and
turbidity data if available.
Maintenance activities in presedimentation basins. Sludge removal in
presedimentation basins can stir up sediment and organic matter that has settled to the
bottom of the basin. What to check: Review operational records to determine if
sludge was removed from the presedimentation basin during the time period that
would have most impacted distribution TTHM and HAAS levels.
Poor basin maintenance practices. Failure to remove sediment or sludge can result
in re-suspension of particles, increased turbidity, and increased DBF precursors that
could lead to higher TTHM and HAAS formation in the plant. What to check:
Review operational records to determine if or when sludge removal was last
conducted.
Changes in coagulant and/or polymer feed rates. A failure in the coagulant feed
system or failure of the feed system to account for changes in flow could result in
poor DBF precursor removal. What to check: Examine coagulant/polymer feed
records and compare to flow data. Verify that chemical feed pumps are delivering
chemicals at set rate (i.e., perform a "pump catch"). Also examine zeta meter or
streaming current data, if available.
Extreme weather changes. In large presedimentation basins, wind can cause bank
erosion, creating deteriorated raw water quality. Ice formation and other weather
conditions can also affect performance of the presedimentation basin. What to
check: Review the weather logs (if available) or operator visual reports.
4.3 Coagulation/Flocculation
Coagulation is a process used for increasing the tendency of small particles in suspension
to attach to one another and to attach to surfaces, such as the grains in the filter bed (AWWA,
1999). Coagulation is accomplished by feeding a coagulant, polymer, or combined
coagulant/polymer. Flocculation is the "snowballing" of small particles into larger particles
(called floe) that can be more easily removed from the water during sedimentation and filtration.
Detention time and mixing of the coagulated water is necessary in order for the floe to form.
Exhibit 4.3 illustrates where coagulation and flocculation are found in a typical conventional
filtration plant.
The coagulant or polymer type and dose are critical for the effective removal of DBF
precursors. Alum and ferric chloride (two commonly used coagulants) performance depends on
the flow, turbidity, organic content, temperature, alkalinity, and pH of the water. The absence of
alkalinity or a pH that is too low or too high will result in poor coagulation and flocculation for
DBF precursor removal. Temperature can also affect the performance of certain coagulants,
such as alum. Alum is less effective at colder temperatures. Feeding the wrong type or amount
of polymer can also result in poor precursor removal. The more DBF precursors that remain in
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the water and come into contact with a disinfectant, the more potential for TTHM and HAAS
formation, particularly if chlorine is used.
Exhibit 4.3 Typical Conventional Filtration Plant
Coagulant
or Polymer
Injected
Sedimentation
Coagulation Flocculation
Note : pH adjustment may also occur prior to coagulant feed
Filtration
Clean/veil
i
r
Distribution
System
Data Analysis
Review coagulant, polymer, and other chemical feed records during the time period that
would have most impacted distribution TTHM and HAAS levels in comparison with historical
chemical feed rates. Also, it is helpful to compare available raw water to finished water
parameters (TOC, turbidity, pH, flow, and other available data). Determine if a change in raw
water conditions was not adequately addressed through coagulant/polymer feed rates.
Causes
The primary causes of increased TTHM and HAAS formation resulting from problems
with coagulation and flocculation include:
Poor regulation or failure of coagulant/polymer feed rate. A system's inability to
modify the coagulant/polymer feed rate in response to raw water quality changes or
flow can result in poor DBF precursor removal. A failure of the feed system can also
result in poor DBF removal. What to check: Examine coagulant/polymer feed
records and compare to available raw water data to determine if a change in raw
water conditions was not adequately addressed through coagulant/polymer feed rates.
Also examine zeta meter or streaming current data, if available.
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Poor regulation or failure of chemical feed system used to control pH and
alkalinity. The coagulant's performance depends on (in part) the alkalinity and pH
of the water. A system's inability to maintain the proper alkalinity or pH (e.g.,
though the addition of lime, caustic soda, or acid) can result in poor DBF precursor
removal. What to check: Check chemical feed records and compare to raw water
data to determine if a change in raw water conditions was not adequately addressed
through chemical feed rates. Verify that chemical feed pumps are delivering
chemicals at set rate.
Poor mixing. Broken or plugged mixers can result in poor mixing between
chemicals and the water, resulting in poor floe formation. What to check: Check
that mixers are properly functioning.
Lack of adequate detention time in the flocculation basin due to flows above the
design capacity or short circuiting. Flocculation basins are sized based on a
specific design flow and flows in excess of the design flow may result in DBF
precursors being passed through to subsequent treatment processes. What to check:
Check plant flow rates and plant operational records to determine if the increase in
flow was due to poor control at the plant inlet or a recycle event. Also examine
chemical injection point and mixing mechanism to identify any potential short
circuiting.
4.4 Sedimentation/Clarification
Sedimentation basins are designed
for specific flows to maintain a certain
overflow rate that allows floe and other
particles to settle prior to filtration. Flows
in excess of these design flows will result in
particles, including DBF precursors,
loading onto the filters. Short circuiting can
also result in poor floe formation and
carryover onto the filters. Poor or
inadequate removal of sludge from the
sedimentation basin, as well as maintenance
in the basin that stirs or moves the sludge,
can release soluble or particulate organic
matter. As a result, organic matter may be
carried through to subsequent treatment
process and react with the disinfectants used at the plant. Exhibit 4.3 illustrates the
sedimentation process in a typical conventional filtration plant.
Data Analysis
You should review settled water turbidity values during the time period that would have
most impacted distribution TTFDVI and HAAS levels. You may want to also examine historical
settled water turbidity values to determine if these values that resulted in the exceedance were
Sedimentation basin.
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unusual in comparison to historic values. You should also review plant operational records and
other data such as flow and temperature.
Causes
The primary causes of increased TTHM and HAAS formation resulting from problems
with sedimentation and clarification include:
Short circuiting or flows in excess of design. When water passes too quickly
through a sedimentation or clarification basin, particles will not have sufficient time
to settle and will pass through the treatment process. This will result in increased
DBF precursors. What to check: Review flow rates into and out of the
sedimentation basin to determine if flows were above allowed design flow values.
Review settled water turbidity values. Also examine settling basin hydraulics to
identify any potential short circuiting.
Basin cleaning or maintenance. DBF precursors can be re-suspended during basin
cleaning, resulting in increased formation of TTHM and HAAS. What to check:
Review plant operational records and determine if sludge was removed from the
sedimentation basin during the time period that would have most impacted
distribution TTHM and HAAS levels.
Poor basin maintenance practices. Failure to remove sediment or sludge at regular
intervals can result in re-suspension of particles and DBF precursors that can
subsequently come into contact with chlorine. What to check: Review operational
records to determine if or when sludge removal was last conducted. Review settled
water turbidity data to determine if it has been increasing over time.
Weather conditions. Periods of extended sunlight or uneven sunlight on multiple
basins can cause density gradients in the basins and contribute to excessive floe
carryover on to the filters. Ice formation and other weather conditions can also affect
performance of the sedimentation basin. What to check: Review settled water
turbidity levels in the sedimentation basin to determine if turbidity values were higher
than normal during the OEL exceedance. Review the weather logs (if available) or
operator visual reports.
4.5 Filtration
Breakthrough in filters occurs when the
level of particles or contaminants in the
effluent increase beyond acceptable levels.
This may occur as a result of overloading of
the filter or excessive filter run times.
Filtration is typically the last
treatment process that physically removes
particles and contaminants from the water
(filtration is highlighted in Exhibit 4.3).
Filter performance can be affected by
inadequate coagulation, particle loading,
hydraulic loading, filter run time, and method
for placing a filter back into service. When a filter becomes overloaded or is left in service for
too long, particles can begin to pass through the filter, and accumulated particles may be shed
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from the filter. These particles may contain DBF precursors that are available to react with the
disinfectant in the clearwell, resulting in a higher potential for TTHM and HAAS formation. The
more DBF precursors that come into contact with the chlorine, the more likely that TTHM and
HAAS will form.
When biologically active filters and granular activated carbon (GAC) filters are used for
organic precursor removal, breakthroughs may be a concern because soluble organic compounds
or solids, which may be organic precursors, can be released. Likewise, when GAC columns are
used for DBF removal after chlorination, exhaustion of adsorptive capacity may result in sudden
TTHM and HAAS peak concentrations in the finished water.
Membrane filtration technologies including microfiltration and ultrafiltration can remove
high levels of bacteria. If systems employing these technologies are allowed to use a lower
dosage rate for primary disinfection, lower DBF levels may be achieved. Nanofiltration
membranes can remove virtually all particulate matter as well as dissolved organic matter that
serve as DBF precursors.
Data Analysis
Review individual and combined filter effluent turbidity data collected during the time
period that would have most impacted distribution TTHM and HAAS levels. These values
should be compared to historical individual and combined filter effluent turbidities to determine
if the turbidity values are unusual. If particle count data are available on individual or combined
filter effluent, these data can also be trended and provide valuable information similar to
turbidity. If possible, you should also examine turbidity values from the settled water going onto
the filters during the time period that would have most impacted distribution TTHM and HAAS
levels. If settled water turbidity values were higher than usual, you will want to evaluate
upstream processes (sedimentation, coagulation, and flocculation) to determine which process
may have contributed to the event. Filter operational data may also provide valuable information
and is discussed in more detail in the following section.
Causes
The primary causes of filter
breakthrough that can result in increased
TTHM and HAAS formation include:
Particle loading onto filters. If
upstream processes fail to
remove sufficient particles, the
increased burden may overload
the filters and cause them to shed
particles into the water. What to
check: Examine settled water
turbidity data to determine if a
sudden increase of particle
loading onto the filter occurred.
Also review individual and
combined filter effluent turbidity
Filter during draining operation.
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and particle count data to see if these values increased in conjunction with settled
water turbidity data.
Hydraulic loading rates onto the filters. A sudden increase in hydraulic loading
rates to the filter can cause particles to be shed. The increased loading rate can be
caused by other filters being off-line or an overall increase in plant flows. What to
check: Check individual and combined filter effluent turbidities and particle count
data. Also, check plant operational records to determine if other filters were off-line
but plant flow was not adjusted to account for the other filters being off-line. In
addition, examine plant flow records and determine if the plant flow suddenly
increased due to a recycle event or other event.
Filter run time. If a filter is allowed to stay on-line beyond its design or typical filter
run time, breakthrough of particles can occur. What to check: Review individual
and combined filter effluent turbidity values and see if turbidity values (and particle
count data if available) increased steadily toward the end of the filter run. Also
review plant operating records and determine if a particular filter or filters were left
on-line to the point of breakthrough.
Filter not ripening after being placed back into service. Filters can experience
turbidity spikes after being placed on-line. These spikes can result in particles that
contain DBF precursors being passed to the clearwell. Spikes can be attributed to
inadequate coagulation, poor backwash practices, improper or inability to filter-to-
waste, or placement of a dirty filter back into service without backwashing or proper
filter-to-waste period. What to check: When reviewing individual and combined
filter effluent turbidity (and particle count data if available), determine if the filter
routinely experiences spikes after being placed back into service. If so, the system
should evaluate coagulation and backwash practices. A floe retention analysis can
also be performed (refer to the suggested manuals for this procedure) that may
provide more information on how well filters are cleaned during the backwash. The
system should also review when and how the filter was placed on-line and if water
was sent to the clearwell without an adequate filter-to-waste period.
4.6 Primary Disinfection
The purpose of primary disinfection is to inactivate Giardia, Cryptosporidium, and
viruses. Commonly used primary disinfectants are chlorine, chlorine dioxide, chloramines,
ozone, and UV. This section will focus on systems using chlorine since chlorine is the most
commonly used primary disinfectant.
Systems are required by the Surface Water Treatment Rule (SWTR) and Long Term 2
Enhanced Surface Water Treatment Rule (LT2ESWTR) to achieve a certain level of microbial
inactivation. For chemical disinfectants, this level of inactivation is determined by multiplying
the disinfectant residual concentration (C) measured in a contact basin (vessel, pipeline or plant
process) during peak hourly flow and the amount of time (T) the disinfectant is in contact with
the water at peak hour flow. The contact time is a function of the contact basin hydraulics,
configuration, baffling, and flow rate through the contact basin. Systems, in consultation with
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the State, will typically identify the minimum CT value
needed in order to maintain the required amount of
microbial inactivation under all operating conditions for
compliance purposes. As the disinfectant dose
decreases, the required contact time should be increased
to maintain a required level of CT, and vice versa.
Data Analysis
Review primary disinfectant feed rates and
operational data during the time period that would have
most impacted distribution TTHM and HAAS levels.
You may want to also examine historical primary
disinfectant feed rates to determine if the disinfectant
feed rates just prior to the exceedance were unusual in
comparison to historic primary disinfectant feed rates.
You should also check other operational parameters,
such as flow, pH, and temperature. This data should be
readily available since systems need to measure these
parameters to calculate inactivation values.
Chlorine is commonly used as
a primary disinfectant.
Causes
The following disinfection related events can increase the formation of TTHM and
HAAS:
Increased chlorine dose and/or residual (intentional or unintentional). An
increase in the disinfectant dose (particularly chlorine) can increase TTHM and
HAAS concentrations. The change in disinfectant dose may be intentional or
unintentional. For example, systems that control the disinfectant dose manually and
not based on plant flow may experience increases in TTHM and HAAS if the plant
flow rate suddenly decreases or the dose is not adjusted frequently to account for
reductions in plant flow. In such instances, those systems would likely be overdosing
chlorine. On the other hand, a system may intentionally increase the dose to account
for a decrease in water temperature and maintain the required CT (CT requirements
increase as water temperature decreases when using chlorine). What to check:
Review disinfectant feed rates for the primary disinfectant during the time period that
would have most impacted distribution TTHM and HAAS levels. Systems may want
to also examine historical disinfectant feed rates to determine if the chemical feed
rates just prior to the exceedance were unusual in comparison to historic disinfectant
feed rates.
Seasonal changes in water's disinfectant demand. Systems may use alternate
sources of supply to supplement the primary supplies during high demand periods or
to temporarily replace a source of supply that has poorer water quality during certain
times of the year (e.g., algal blooms in warmer months). When source water quality
changes, the water's disinfectant demand may change, requiring a change in the
primary disinfection dosage rate in order to maintain similar microbial inactivation
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levels. What to check: Review operational records to determine which sources of
supply were in use just prior to the OEL exceedance.
Increased free chlorine contact time. Poor mixing in the clearwell or other chlorine
contact facilities (i.e., pipes or other storage tank) can result in dead zones where the
hydraulic residence time is significantly higher than the residence time of the bulk of
the water passing through the clearwell. As a result of the increased contact (i.e.,
reaction) time, TTHM and HAAS concentrations may be significantly higher in the
dead zones. A reduction in system demand (particularly in a system with little or no
storage beyond the clearwell) may also result in longer hydraulic residence times in
the clearwell and increased TTHM and/or HAAS concentrations. Longer residence
time within the clearwell can also result in increased temperatures, further increasing
TTHM and HAAS formation. What to check: Review flow records into and out of
the clearwell or other chlorine contact facilities during the time period that would
have most impacted distribution TTHM and HAAS levels. This effort may involve
the review of flow meter data or pump record data to obtain flows. Also check plant
operation records to assess if the plant was shut down or off-line during this time
period that resulted in excessive chlorine contact times. You may also want to check
temperature values to determine if an increase in finished water temperature occurred.
Changes in primary disinfectant type. Switching from ozone or chlorine dioxide to
chlorine for primary disinfection could result in increased TTHM and HAAS
formation. What to check: Check plant operation records during the time period that
would have most impacted distribution TTHM and HAAS levels to determine if a
switch to chlorine for primary disinfection occurred.
Changes in water temperature and pH. CT requirements increase as water
temperature decreases when using chlorine. During times that the water temperature
increases, the plant may see a reduction of the CT required. If operating practices are
not changed, the chlorine residual may be higher than required, increasing DBF
formation. The same is true of pH if the raw water quality changes. What to check:
Review water temperature, pH and chlorine dosage records. Compare required to
actual chlorine dosage rate.
Control of ammonia and chlorine feed. DBF formation can be minimized by using
appropriate chlorine to ammonia ratios. In systems where ammonia and chlorine are
injected concurrently, rapid and complete initial mixing could reduce the DBF
formation rate. What to check: Chemical feed equipment for proper maintenance,
calibration, and alarm settings. Mixing equipment for proper operation and
maintenance. Monitor chlorine to ammonia ratio at point of mixing and downstream.
4.7 Recycle Practices
Some systems recycle residual streams back to the front of the treatment plant, a practice
governed by the Filter Backwash Recycling Rule. Commonly recycled streams include filter-to-
waste, spent filter backwash, thickener supernatant, and liquids from dewatering processes.
These recycle streams may contain elevated concentrations of DBF precursors, in addition to
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other contaminants. For instance, spent filter backwash has been shown to contain significantly
higher levels of TOC and DOC when compared to the raw water concentrations for these same
parameters (Cornwell and Lee, 1993; Cornwell et al., 2001). If no additional treatment (e.g.,
coagulation/settling) of these recycle streams is provided, adjustment of the coagulant dose to
account for the resulting change in water quality will likely be necessary. The return of these
recycle streams may also cause a sudden increase in plant flow rates that result in treatment
processes operating above design flow rates.
The primary causes of increased TTHM and HAAS formation as a result of recycle
practices include:
Spikes in the influent DBF precursor concentration and other contaminants.
When backwash water or other recycle streams are returned to the plant influent it
increases the load of particles and DBF precursors or other contaminants in
subsequent treatment processes. If appropriate treatment adjustments (such as
changing the coagulant dose) are not made, the increased particle and contaminant
concentrations may overload the subsequent treatment processes and allow the
contaminants to pass through the treatment plant. What to check: Examine plant
operational records to determine if a recycle event occurred during the time period
that would have most impacted distribution TTHM and HAAS levels. Also review
coagulant/polymer and chemical feed rates, as suggested in Section 4.3.
Increase in the plant flow rate. When recycle streams are returned to the head of
the plant they can increase the overall plant flow rate and can overload subsequent
treatment processes. What to check: Examine plant operational records to
determine if a recycle event occurred during the time period that would have most
impacted distribution TTHM and HAAS levels. Check plant flow rates during that
time period to determine if flow rates were above design plant flow.
4.8 Secondary Disinfection
The secondary disinfectant is used to maintain a disinfectant residual in the distribution
system. Chlorine and chloramine are the most commonly used. Chlorine dioxide is used by
systems that are able to maintain a residual without violating the chlorite MCL or chlorine
dioxide MRDL. In some plants, the primary disinfectant is used (instead of adding another
disinfectant after the clearwells) to maintain the distribution system residual.
If chlorine is applied as the secondary disinfectant, the concentration in finished water
can have a significant impact on TTHM and HAAS formation within the distribution system. If
chloramines are used, chemical feed practices are more important than the concentration with
respect to TTHM and HAAS formation (chloramines do not react as quickly with DBF
precursors to form DBFs). Some systems that chloraminate may periodically switch to free
chlorine disinfection for a few weeks or month to reduce the population of nitrifying bacteria in
the distribution system.
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Data Analysis
You should review plant operating records to determine the amount of chlorine fed as the
secondary disinfectant, whether temporarily or permanently fed, during the time period that
would have most impacted distribution TTHM and HAAS levels. These values should be
compared to historical feed rates to determine if they are unusually high.
Causes
The primary causes of increased TTHM and HAAS formation resulting from secondary
disinfection practices include:
Sudden increase in chlorine feed rates. A sudden increase in the amount of
chlorine being fed into the distribution system directly affects the amount of TTHM
and HAAS concentrations. What to check: Chlorine doses during the time period
that would have most impacted distribution TTHM and HAAS levels.
Switch to chlorine. A temporary or permanent switch to chlorine may result in
increased TTHM and HAAS formation because chlorine forms THMs and HAAs
more readily than other common disinfectants. What to check: Review operational
records and determine if the system switched to chlorine as the secondary disinfectant
during the time period that would have most impacted distribution TTHM and HAAS
levels.
Control of ammonia and chlorine feed. DBF formation can be minimized by using
appropriate chlorine to ammonia ratios. In systems where ammonia and chlorine are
injected concurrently, rapid and complete initial mixing could reduce the DBF
formation rate. What to check: Chemical feed equipment for proper maintenance,
calibration, and alarm settings. Mixing equipment for proper operation and
maintenance. Monitor chlorine to ammonia ratio at point of mixing and downstream.
4.9 References
AWWA. 1999. Water Quality & Treatment -A Handbook of Community Water Supplies. Fifth
Edition. New York, NY: McGraw-Hill.
Cornwell, D., andR. Lee. 1993. Recycle Stream Effects on Water Treatment. Denver:
AwwaRF.
Cornwell, D., M. MacPhee, N. McTigue, H. Arora, G. DiGiovanni, M. LeChevallier, and J.
Taylor. 2001. Treatment Options for Giardia, Cryptosporidium, and Other Contaminants in
Recycled Backwash Water. Denver: AwwaRF.
Franchi, A. and C. Hill. 2002. Factors Affecting DBF Formation in the Distribution System.
Paper Presented at the Water Quality from Source To Tap, AWWA Chesapeake Section
Seminar.
Operational Evaluation Guidance Manual 4-20 December 2008
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Vikesland, P.J., N.G. Love, K. Chandran, E.M. Fiss, R. Rebodos, A.E. Zaklikowski, F.A.
DiGiano, and B. Ferguson. 2006. Seasonal Chloranimation Practices and Impacts to
Chloranimating Utilities. Denver, Colo.: AwwaRF.
4.10 Additional Resources
AWWA. 2000. Operational Control of Coagulation and Filtration Processes. AWWA Manual
M37. Denver: AWWA.
Bell et al. 2001. Enhanced and Optimized Coagulation for Particulate andMicrobial Removal.
Project #155. Denver: AwwaRF.
Kirmeyer, G.J., M. LeChevallier, H. Barbeau, K. Martel, G. Thompson, L. Radder, W. Klement,
and A. Flores. 2004. Optimizing Chloramine Treatment. Second Edition. Denver, Colo.:
AwwaRF.
Logsdon et al. 2002. Filter Maintenance and Operations Guidance Manual. Project #2511.
Denver: AwwaRF and AWWA.
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. Office of Water. EPA 815-R-07-017.
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
USEPA. 2006. Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced
Surface Water Treatment Rule. EPA 815-R-06-007. Available online at:
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
USEPA. 2005. Membrane Filtration Guidance Manual. November, 2005. EPA 815-R-06-009.
Available online at: http://www.epa.gov/safewater/disinfection/lt2/compliance.html
USEPA. 2004. Comprehensive Surface Water Treatment Rules Quick Reference Guide: Systems
Using Conventional or Direct Filtration. August, 2004. Available online at:
http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 2002. Filter Backwash Recycling Rule Technical Guidance Manual. December, 2002.
EPA 816-R-02-014. Available online at: http://www.epa.gov/safewater/filterbackwash.html
USEPA. 1999a. Enhanced Coagulation and Enhanced Precipitative Softening Guidance
Manual. Document #815-R-99-012. Available online at:
http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 1999b. Alternative Disinfectants and Oxidants Guidance Manual. EPA 815-R-99-014.
Available online at: http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 1998. Optimizing Water Treatment Plant Performance Using the Composite Correction
Program, 1998 Edition. August, 1998. EPA 625/6-91/027. Available online at:
http://www.epa.gov/ORD/NRMRL/pubs9879.html
Operational Evaluation Guidance Manual 4-21 December 2008
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Partnership for Safe Water Information Center at
http://www.awwa.org/Resources/partnershipforsafewater. cfm?ItemNumber=3787&navItemNum
ber=33969. The Partnership for Safe Water is a voluntary program designed to help water
systems optimize water treatment plant performance without major capital improvements.
For consecutive systems, EPA will be publishing a consecutive systems guidance manual for the
Stage 2 DBPR (refer to http://www.epa.gov/safewater/disinfection/stage2/compliance.html for
updates. Also refer to the on-going AwwaRF project #3026, Evaluation of Disinfection
Practices for DBF and Precursor Occurrence in Consecutive Systems.
Operational Evaluation Guidance Manual 4-22 December 2008
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5. Source Water Evaluation
This chapter covers:
5.1 Water Temperature
5.2 Organic Matter
5.3 Bromide
5.4 Turbidity and Particle Count Data
5.5 pH and Alkalinity
5.6 References
5.7 Additional Resources
This chapter provides guidance on how watershed and source water monitoring data can
be evaluated to determine the cause of your operational evaluation level (OEL) exceedance.
Different systems will have different types of data available to them - Exhibit 5.1 shows the
water quality parameters that ground water systems, filtered surface water systems, and
unfiltered surface water systems may be collecting on a regular basis for regulatory purposes
and/or for process control. Consecutive systems that purchase all water may want to obtain these
data from the wholesaler to help identify the cause of the OEL exceedance.
Expanded water quality data
collection and review can assist
systems in meeting OEL requirements
(identifying causes and actions that
could be considered to minimize
future exceedances) and in optimizing
treatment processes and distribution
system operations.
The checklist on pages 5-3 and 5-4 can be
used to collect information and document the
source water evaluation. The Stage 2 DBPR does
not require the use of the checklist, but you should
check with the State regulatory agency to see if any
checklists or other forms are required as part of
your evaluation report. Items on the checklist are
discussed in detail in the applicable sections of this
Chapter. There may be additional causes of OEL
exceedances that are not identified in the checklist.
Before you begin:
You should have a good understanding of the time of travel from the source water to
distribution system monitoring locations to determine the relevant time period for
watershed and source water data.
If you utilize multiple water sources, determine which sources were in use at and just
prior to the OEL exceedances, and which source(s) likely influenced the location
where the exceedance occurred. This will help narrow the evaluation to only those
sources that could have contributed to the OEL exceedance.
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December 2008
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Exhibit 5.1 System Source Water Monitoring Data
Source Water
Monitoring Parameter
Total organic carbon
(TOG)
Dissolved organic
carbon (DOC)
Specific ultraviolet
absorbance (SUVA)
Color
Bromide
Turbidity
Particle counts
Temperature
Flow
PH
Alkalinity
System Type1
Ground Water
Optional
Optional
Optional
Optional
Filtered Surface
Water/GWUDI
Required2
Optional
Optional
Optional
Optional
Required
Optional
Required
Required
Required
Required2
Unfiltered Surface
Water/GWUDI
Optional
Optional
Optional
Optional
Optional
Required
Optional
Required
Required
Required
Required = Required data a system should have based on Federal regulatory requirements. Additional monitoring
parameters may be required by the State.
Optional = Optional data a system may have for optimization, process control purposes or State requirements.
1 Consecutive systems may wish to obtain source water information from their wholesaler.
2 Only conventional filtration systems are required under Stage 1 DBPR to monitor alkalinity and TOC in the source
water.
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December 2008
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Source Water Evaluation Checklist Page 1 of 2
D NO DATA AVAILABLE
System Name:
Checklist Completed by: Date:
A. Do you have source water temperature data? QYes D No
If NO, proceed to item B. If YES, was the source water temperature _ M
high? UYes U
If NO, proceed to item B. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was the raw water storage time longer than usual?
D D Did you place another water source on-line?
Q rj Were river/reservoir flow rates lower than usual? If yes, indicate the location of
lower flow rates and the anticipated impact on the OEL exceedance.
n fj Did point or non-point sources in the watershed contribute to the OEL
exceedance?
B. Do you have data that characterizes organic matter in your source water (e.g., 1-1 N
TOC, DOC, SUVA, color, THM formation potential)?
If NO, proceed to item C. If YES, were these values higher than _ N
normal? LJ es |_J
If NO, proceed to item C. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n D Did heavy rainfall or snowmelt occur in the watershed?
n D Did you place another water source on-line?
n D Did lake or reservoir turnover occur?
r-1 r~| Did point or non-point sources in the watershed contribute to the OEL
exceedance?
D D Did an algal bloom occur in the source water?
r-1 r~i If algal blooms were present, were appropriate algae control measures
employed (e.g., addition of copper sulfate)?
n n Did a taste and odor incident occur?
C. Do you have source water bromide data? D Yes D No
If NO, proceed to item D. If YES, were the bromide levels higher or _ n No
lower than normal? LJ es |_J
If NO, proceed to item D. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Has saltwater intrusion occurred?
n D Are you experiencing a long-term drought?
D D Did heavy rainfall or snowmelt occur in the watershed?
D D Did you place another water source on-line?
D D Are you aware of any industrial spills in the watershed?
Operational Evaluation Guidance Manual 5-3 December 2008
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Source Water Evaluation Checklist Page 2 of 2
D. Do you have source water turbidity or particle count data? D Yes D No
If NO, proceed to item E. If YES, were the turbidity values or particle _ N
counts higherthan normal?
If NO, proceed to item E. If YES, answerthe following questions for the time period
prior to the OEL exceedance.
Yes No
n D Did lake or reservoir turnover occur?
n D Did heavy rainfall or snowmelt occur in the watershed?
n D Did logging, fires, or landslides occur in the watershed?
n D Were river/reservoir flow rates higher than normal?
E. Do you have source water pH or alkalinity data? QYes Q No
If NO, proceed to item F. If YES, was the pH or alkalinity different from - N
normal values?
If NO, proceed to item F. If YES, answerthe following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was there an algal bloom in the source water?
G D If algal blooms were present, were algae control measures employed?
D fj Did heavy rainfall or snowmelt occur in the watershed?
n D Has the PWS experienced diurnal pH changes in source water?
F. Conclusion
rjYes
Did source water quality factors contribute to your OEL exceedance?
fj Possibly
If YES or POSSIBLY, explain below.
Operational Evaluation Guidance Manual 5-4 December 2008
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5.1 Water Temperature
The rate of reaction between chlorine
(and chloramines) and DBF precursors
increases as the water temperature increases.
As a result, TTHM and HAAS concentrations
increase with increasing water temperature.
Many water supplies experience seasonal
temperature changes with higher temperatures
in the summer and early fall and lower
temperatures in the winter and early spring. The magnitude of the increase depends on a number
of site-specific factors, including source water type (ground or surface water), climate, and
hydrology.
Data Analysis
Systems should compare historical water temperature data to water temperature data
collected during the period leading up to the OEL exceedance to determine if a significant
increase in source water temperature occurred. Systems should also examine recent weather
data. Sustained high air temperatures, particularly during droughts when water levels are low,
will increase the temperature of surface water bodies, causing increased reaction rates and
increased TTHM and HAAS formation. However, increased demand during warmer weather
(e.g., outdoor uses such as watering, car washing, and filling pools) that reduces the residence
time may mitigate DBF formation associated with increased temperature. Other operational data
may be helpful, as specified below.
Causes
Some potential causes of increased water temperature include:
Source water residence time and flows. Long holding times in raw water storage
basins and reservoirs in summer months can increase water temperatures. Low flows
in streams and low lake levels can also result in increased water temperatures. What
to check: Review flow data to determine if a decrease in flow occurred that resulted
in longer source water residence times.
Air temperatures and sunlight. An increase in air temperatures and sunlight can
lead to an increase in source water temperatures. What to check: Review
climatological records to determine if air temperatures were warmer than usual.
Change in raw water supply. Ground water sources are typically cooler than
surface water sources during the summer months and exhibit less seasonal variability
in temperature than surface water sources. Therefore, seasonal use of sources can
have a major impact on the temperature of the water entering a plant. For example, a
system that supplements a ground water source with a surface water source in the
summer may experience a significant increase in temperature. What to check:
Review operational records to determine if another source was placed on-line that
may have impacted temperature.
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5.2 Organic Matter
Organic matter in source water generally results from decay of plant and animal
materials. Sources of organic matter include water and wastewater treatment plant discharges,
some industrial discharges, agricultural and urban area runoff, septic system leachate discharge
and natural sources. Surface water tends to have higher levels of organic matter than ground
water.
Organic matter is a DBF precursor that reacts with chlorine to form TTHM and HAAS.
Organic matter can be classified as hydrophilic (more soluble) or hydrophobic (less soluble).
Hydrophilic compounds are more difficult to remove from water than hydrophobic compounds,
but also form fewer DBFs (Liang and Singer, 2001). If an increase in source water organic
matter is not adequately addressed by adjustments to the treatment process, TTHM and HAAS
levels can increase.
Total organic carbon (TOC) is a direct measurement of the dissolved and paniculate
organic carbon in water. TOC is often used as a surrogate measurement for DBF precursors,
although only a small fraction of the organic carbon will react to form DBFs (Symons et al.,
2000). Conventional filtration plants are required to measure source water TOC and alkalinity
and compare them to finished water TOC under Stage 1 DBPR.
There are several other measurements of organic carbon that can be useful in
characterizing DBF precursors:
Dissolved organic carbon (DOC). DOC is the soluble portion of TOC that can pass
through a membrane with a 0.45 micrometer pore size. Most of the organic carbon in
drinking water supplies is typically dissolved.
Specific ultraviolet absorbance (SUVA). A SUVA analysis can indicate whether
the organic matter in water is predominantly hydrophobic or hydrophilic.
Hydrophilic compounds have lower SUVA than hydrophobic compounds (Croue et
al., 1999). SUVA is determined by dividing the measured UV absorption of the
water at 254 nanometer (in m"1) by the measured DOC concentration of the water (in
mg/L).
Color. Organic material contributes to the color of a source water. Therefore,
monitoring the color of the source water can serve as an indicator of the amount of
TOC in the source water. A study by Alvarez et al. (1997) showed good correlation
between TOC and color in water from a surficial aquifer. Color is measured using a
spectrophotometer and is quantified in color units.
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Trihalomethane (THM) Formation Potential. The measurement of THM formation
potential for source water indicates the maximum level of THMs that would occur if
no treatment is provided. The test is conducted by adding chlorine to identical water
samples at various dosage rates and measuring THMs. The water samples are subject
to the same conditions (pH adjustment, holding time, temperature, etc.). These tests
can also be conducted on finished water to provide information that may be more
useful for the operational evaluation.
Data Analysis
If you routinely collect source water TOC, DOC, SUVA, color, or THM formation
potential data, you should review these data during the time period that would have most
impacted distribution system TTHM and HAAS levels. You may also want to examine historical
concentrations of these parameters to determine if a sudden increase in these concentrations
results in an exceedance. If such an increase is identified, you should examine other watershed
information (i.e., watershed protection plan, maps, property records, related newspaper articles
etc.) to determine the possible cause(s) of the increase in DBF precursors. You should also
examine the concentrations of these parameters in the finished water to determine if treatment
was adequate in removing DBF precursors prior to disinfectant application (refer to Chapter 4 for
more information on treatment plant evaluation).
With respect to SUVA, a change in the balance of hydrophobic and hydrophilic
compounds in source waters can affect the formation of DBFs in the finished water. A sudden
decrease in SUVA values compared to historical data indicates that the amount of hydrophilic
compounds is increasing relative to the amount of hydrophobic compounds. As a result, TOC
removal may be more difficult to achieve through coagulation. Alternatively, an increase in
SUVA indicates that the organic compounds are more easily removed, but readily form DBFs.
This can result in increased TTHM and HAAS formation if sufficient TOC removal is not
achieved prior to disinfection.
Systems that use color data as an indicator of TOC should exercise caution when
examining this data because algae, metals, iron, manganese, sulfur bacteria, and industrial wastes
can also cause color in water.
Causes
There are many possible causes of
sudden increases in source water TOC
including:
Heavy rainfall or snowmelt.
Heavy rainfall and snowmelt
cause heavy runoff that washes
organic matter from soils into
surface water sources. These
events do not need to occur locally
to result in an increase in TOC. A
runoff event miles upstream from
Surface water source with snow in
watershed.
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December 2008
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a raw water intake can result in increased TOC concentrations. The effects of runoff
on TOC levels are most pronounced after a period of drought, when organics are able
to accumulate in soils (Aiken and Cotsaris, 1995). What to check: Review
streamflow records, rainfall data, or other available climatological data during the
period that would have most impacted distribution system TTHM and HAAS levels.
Historical and recent streamflow data can be obtained from the National Weather
Service, United States Geological Survey (USGS), or other local agencies. Systems
can examine recent streamflow and precipitation data to determine when and where
runoff events have occurred to wash DBF precursors into surface water supplies.
Change in raw water supply. Ground water sources typically contain less TOC than
surface water supplies. Different surface water supplies can also have very different
levels of TOC depending on climate and watershed characteristics. Therefore,
seasonal use of sources can have a major impact on TOC. In addition, systems that
regularly draw water from two sources with different TOC concentrations will have
increased TOC if the portion of water withdrawn from the higher TOC source is
increased. What to check: Review operational records to determine if a different
source was placed on-line that may have been high in TOC.
Lake or reservoir turnover. When turnover occurs, sediment and organic matter at
the bottom of the lake or reservoir are stirred up and become resuspended. The
resuspended organic matter can increase the organic load entering the plant.
Reservoir turnover is typically triggered by water temperature differences in the
different vertical layers within the water body. Wind can also help to trigger a
reservoir turnover. What to check: Review operational records to determine if
turnover was noted on any particular day. Turnover may also be accompanied by a
sudden change in turbidity and water temperature. A review of source water turbidity
(see Section 5.4) and temperature (see Section 5.1) data may be useful.
Point and non-point source pollution. Discharge from wastewater treatment plants,
upstream water treatment plants, and industrial plants may contain high amounts of
organic carbon. Although lakes and rivers dilute the discharge from these plants,
these point sources can still cause a significant increase in downstream organic
carbon loads. Seasonal or intermittent operation of these facilities can cause
fluctuations in organic carbon loads downstream. Other activities within the
watershed, such as logging, landslides, or fire, may contribute a significant amount of
sediment and organic loading to the source water. What to check: Previous
watershed surveys, permitted discharges, watershed partnerships, State and Federal
natural resource and regulatory agencies may also provide key information on
watershed activities and point source dischargers respectively. A watershed survey
could also be conducted to try to identify any unusual activities.
Algal blooms. Algae convert inorganic carbon in the water into organic carbon
compounds (Knappe et al.; 2004, Nguyen et al., 2000). Although research is not
conclusive, studies suggest that in some cases, this process can lead to detectable
increases in TOC and DOC in the surface water body during algal blooms (Knappe et
al., 2004; Nguyen et al., 2000). Algal blooms also result in the production of organic
matter that is generally more hydrophobic than hydrophilic. What to check: Review
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operational records to determine if algal blooms were noted within the raw water and
document what control strategies were being used at the time of the OEL exceedance
(i.e. copper sulfate addition). If chlorine was added to the source water for algae
control, it is a likely contributor to THM formation.
5.3 Bromide
Bromide is an ion that occurs in salts in seas, oceans, mineral springs, and natural salt
deposits. It can be found in both surface and ground waters. Bromide is an inorganic DBF
precursor that reacts with chlorine and organic DBF precursors to form TTHM and HAAS.
Bromide is oxidized by chlorine (hypochlorous acid) to form hypobromous acid. Both
hypochlorous acid and hypobromous acid react with organic DBF precursors to form TTHM and
HAAS by substituting chloride or bromide for one or more hydrogen ions on organic molecules.
Hypobromous acid is a stronger substituting agent than hypochlorous acid. Therefore, waters
with bromide typically form more TTHM and HAAS than waters without bromide (AWWA
1999; Krasner 1999; Baribeau et al. 2006). Increases in bromide levels in bromide-containing
waters can also change the balance of TTHM and HAAS species formed. For example, a recent
AwwaRF research report (Baribeau et al. 2006) shows that waters with increasing influent
bromide levels had lower levels of dichloroacetic acid and trichloroacetic acid, and higher levels
of monobromoacetic acid and dibromoacetic acid.
Some water systems have reported that source waters with lower influent bromide
resulting in higher finished water HAAS levels and higher bromide resulting in lower finished
water HAAS levels, which may indicate that higher bromide concentrations shift the formation
of HAAs to brominated species that are not part of HAAS (McGuire, McLain and Obolensky
2003). However, these data trends only represent site-specific conditions and cannot be applied
universally.
The operational exceedance provisions do not apply to bromate.
Data Analysis
Compare historical bromide data to bromide levels measured in the period leading up to
the OEL exceedance. If it is determined that a significant change in bromide levels occurred,
examine other watershed and/or source water monitoring data to determine the cause.
Causes
Some possible causes of increased bromide levels include:
Saltwater intrusion. Because bromide is an ion that occurs in salts, it is naturally
present in saltwater. When ground water withdrawals are too high or aquifer levels
are depleted during drought, saltwater can displace fresh water. If ground water wells
are located within an affected zone, bromide levels in the wells will increase. Some
surface water intakes in rivers may draw salt water under low flow conditions if the
intakes are located near the mouth of the river and the river discharges into an ocean
or bay. In this case, a salt "wedge" extends upriver far enough to influence the
Operational Evaluation Guidance Manual 5-9 December 2008
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bromide concentration in the intake's water. What to check: If available, review
nearby stream gage and well depth data to determine if there have been tidal
influences or other ground water level fluctuations. State and Federal natural
resource agencies may also have useful hydrogeologic information. Surface water
systems that may be influenced by a salt "wedge" can review tide charts and be
informed when high tides may impact their water quality. They should also try to
document river flow conditions that allow for the salt wedge to reach their intake.
USGS has flow data available for most rivers across the country.
Droughts. Bromide levels can increase when water levels in the aquifer are depleted
by withdrawals and recharge is low. As the aquifer's water level decreases, the
bromide in the aquifer becomes more concentrated, resulting in higher than normal
bromide levels. If rainfall increases and the drought eases, the aquifer is recharged
and bromide concentrations are diluted to normal levels. Industrial wastewater
discharges that contain bromide or brominated byproducts (e.g., paper mills) may
have more of an influence on water quality under low flow conditions during a
drought. What to check: Review available precipitation data or contact your local
National Weather Service to obtain drought status information. State and Federal
natural resource agencies may also have useful information on drought conditions.
Heavy rainfall or snowmelt. Runoff events can increase bromide levels in surface
water sources if bromide-containing industrial or agricultural chemicals are used in
the watershed. What to check: Review available streamflow records, rainfall data,
or other available climatological data during the time period that would have most
impacted distribution TTHM and HAAS levels. Historical and recent streamflow
data can be obtained from the National Weather Service, USGS, or other local
agencies. Check with local public works and highway management departments to
see whether road salts used under icy or snowy conditions contain bromide.
Change in raw water supply. Systems with multiple sources may find that the
sources have significantly different bromide concentrations. If a system uses a
seasonal source that has high bromide levels, an increase in DBF formation may
occur when the seasonal source is in use. What to check: Review operational
records to determine if another source was placed on-line that may have been high in
bromide.
5.4 Turbidity and Particle Count Data
Turbidity and particle counts are measures of the amount of suspended particles in water.
While turbidimeters measure the amount of light reflected by particles in the water, particle
counters measure the number of particles in specific size ranges that are present in the water.
Many of the factors that contribute to DBF precursors in source waters also affect turbidity and
particle counts. Therefore, increased turbidity levels can serve as an indicator of an event that
may have resulted in increased DBF precursors in the source water. High turbidity levels and
particle counts can also overload treatment processes, resulting in decreased removal and/or
breakthrough of DBF precursors (see Chapter 4).
Operational Evaluation Guidance Manual 5-10 December 2008
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Data Analysis
Historical source water turbidity (or particle count) data should be compared to data
collected in the period leading up to the exceedance of OELs to determine if a significant
increase in turbidity (or particle counts) occurred. Climatological and operational data should
also be examined to identify the event that caused the increase in turbidity or particle counts in
the source water. In addition, turbidity and particle count data for finished water should be
reviewed to determine if treatment was adequate in removing DBF precursors prior to
disinfectant application (refer to Chapter 4 for more information on treatment plant evaluation).
Other data, such as streamflow data, may provide useful information on what may have
contributed to increased source water turbidity and particle counts.
Causes
Some potential causes of increased source water turbidity include:
Lake or reservoir turnover. When turnover occurs, sediment and organic matter at
the bottom of the lake or reservoir are stirred up and become resuspended. Reservoir
turnover is typically triggered by water temperature differences in the different
vertical layers within the water body. Wind can also help to trigger a reservoir
turnover. What to check: Review operational records to determine if turnover was
noted on any particular day. Turnover is usually accompanied by a sudden change in
water temperature and a review of source water temperature data may be useful (see
Section 5.1).
Heavy rainfall or snowmelt. Heavy rainfall and snowmelt can create runoff events
that wash sediment and soils into surface water sources. These events do not need to
occur locally to result in an increase in turbidity. A runoff event miles upstream from
a raw water intake can result in increased turbidity at the intake. What to check:
Review streamflow records, rainfall data, or other available climatological data
during the time period that would have most impacted distribution TTHM and HAAS
levels. Historical and recent streamflow data can be obtained from the National
Weather Service, USGS, or other local agencies. Systems can examine recent
streamflow and precipitation data to determine when and where runoff events
occurred to wash DBF precursors into surface water supplies. This effect can be most
pronounced after a long dry spell when DBF precursors are able to accumulate in
soils.
Watershed activities. Activities such as logging, fires, and landslides loosen soils in
the watershed, allowing them to be more easily washed into surface water bodies
during runoff events. In addition, landslides or logging near a surface water body can
directly introduce large amounts of sediment into the water. What to check: Review
available watershed information to determine if any unusual activities occurred. A
watershed survey could also be conducted to try to identify any unusual activities.
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5.5 pH and Alkalinity
Increases in pH can affect DBF formation in several ways. Most coagulation processes
using metal salts, such as alum and ferric chloride, are optimized at pH less than 7. Therefore,
increases in source water pH may be detrimental to the coagulation process (assuming no pH
control is available at the treatment plant). Poor coagulation can result in less DBF precursor
removal, leaving them available to react with chlorine or other disinfectants downstream in the
treatment process. An increase in pH also decreases the efficacy of chlorine as a disinfectant. At
higher pH values, systems may need to add more chlorine to maintain a certain level of
inactivation. This in turn will increase DBF formation. A change in pH can affect the balance of
HAAS and TTHM formation. At higher pH, TTHM formation increases and HAAS formation
decreases. At lower pH, the reverse occurs.
Alkalinity is a measure of the capacity of water to neutralize acids. Carbonate,
bicarbonate, and hydroxides that are present in the water contribute to alkalinity. Alkalinity is
expressed in mg/L as calcium carbonate
Alkalinity serves as a buffer, making pH changes more difficult to achieve. When metal
coagulants are used, the highest removal of DBF precursors occurs at low pH. As alkalinity
increases, systems will have more difficulty decreasing the pH of the water for optimum
coagulation. This in turn can lead to decreased precursor removal and increased TTHM and
HAAS formation. In addition, some coagulants consume alkalinity in the water. If the alkalinity
in the source water decreases significantly, systems may need to add alkalinity to avoid
decreased coagulation efficiency and decreased DBF precursor removal.
Data Analysis
You should compare historical pH and alkalinity data to recent data to determine if an
increase in source water pH or alkalinity occurred at the time of the OEL exceedance. You
should also examine other watershed and source water monitoring data to determine the cause of
the pH or alkalinity change.
Causes
Some potential causes of a pH or alkalinity change include:
Algae. During photosynthesis, algae consume carbon dioxide from the water. The
series of chemical reactions that convert bicarbonate and carbonate into carbon
dioxide result in the production of hydroxide ions, which can significantly increase
the pH of the water (Knappe et al., 2004). Algae can result in fluctuations of pH over
the course of a day, with pH values generally higher during the day and lower at
night. The amount of direct sunlight directly impacts the algae lifecycle and impacts
source water pH. What to check: Review operational records to determine if an
algal bloom was noted in the raw water and document what control strategies were
being used at the time of the OEL exceedance (i.e., copper sulfate addition). You
may also want to determine if pH fluctuates between daytime and nighttime readings.
Operational Evaluation Guidance Manual 5-12 December 2008
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Seasonal use of surface water
sources can significantly affect DBF
levels.
Change in raw water supply. Systems
with multiple sources may find that the
sources have significantly different pH
or alkalinity values. If two or more
sources with different pH or alkalinity
are being utilized at the same time,
source water blending in the distribution
system may be occurring, and may
affect distribution system levels of pH
and alkalinity. If a system uses a
seasonal source that has a higher pH, an
increase in DBF formation may occur
when the seasonal source is in use.
Intakes at different depths in a thermally
stratified reservoir will likely have
different pH values, with higher pH
values generally being near the surface and lower values being closer to the reservoir
or lake bottom. If a system switches its intake depth, it should be aware that the
source water may have a different pH. What to check: Review operational records
to determine if another source was placed on-line or intake depths were changed that
may have affected pH or alkalinity.
Heavy rainfall or snowmelt. Soils have different pH and alkalinity values
depending on the types and amounts of ions and organic matter in the soil. When a
runoff event occurs, the ions and organic matter can be washed into surface water
bodies, changing the pH or alkalinity of the water. What to check: Review
streamflow records, rainfall data, or other available climatological data during the
time period that would have most impacted distribution TTHM and HAAS levels.
Historical and recent streamflow data can be obtained from the National Weather
Service, USGS, or other local agencies.
Drought. Like heavy rainfall, a drought changes the ratio of surface water to ground
water supplied to a reservoir or river. If the ground water has a higher alkalinity than
the surface water, the alkalinity of the supply water will increase if more ground
water is supplied during a drought. Surface waters receiving permitted discharges
may see a change in pH or alkalinity when flows are low due to drought and the
discharges have a greater influence on water quality. What to check: Review
streamflow records, rainfall data, or other available climatological data during the
time period that would have most impacted distribution TTHM and HAAS levels to
determine if a drought occurred. Historical and recent streamflow data can be
obtained from the National Weather Service, USGS, or other local agencies.
5.6 References
Aiken, G. and E. Cotsaris. 1995. Soil and Hydrology: Their Effect on NOM. Journal AWWA.
87(l):36-45.
Operational Evaluation Guidance Manual
5-13
December 2008
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Alvarez, M. B., J. R. Voorhees, G. C. Hartman, and G. L. Basham. 1997. Using Color as an
Indicator to Comply with the Proposed D/DBP Rule. In Proc. OftheAWWA Water Quality
Technology Conference. Denver: AWWA.
AWWA. 1999. Water Quality & Treatment - A Handbook of Community Water Supplies. Fifth
Edition. McGraw-Hill. New York, NY.
Baribeau, H., P.C. Singer, R.W. Gullick, S.L. Williams, R.L. Williams, S.A. Andrews, L.
Boulos, H. Haileselassie, C. Nichols, S.A. Schlesinger, L. Fountleroy, E. Moffat, and G.F.
Crozes. 2006. Formation and Decay of Disinfection By-Products in the Distribution System.
Denver: AwwaRF.
Croue, J. P., J. F. Debroux, G. L. Amy, G. R. Aiken, J. A. Leenheer. 1999. Natural Organic
Matter: Structural Characteristics and Reactive Properties. In Formation and Control of
Disinfection By-Products in Drinking Water. AWWA. Denver, CO.
Knappe, D. R. U., R. C. Belk, D. S. Briley, S. R. Gandy, N. Rastogi, A. H. Rike, H. Glasgow, E.
Hannon, W. D. Frazier, P. Kohl, and S. Pugsley. 2004. Algae Detection and Removal Strategies
for Drinking Water Treatment Plants. Awwa Research Foundation. Denver, CO.
Krasner, S. W. 1999. Chemistry of Disinfect!on By-Product Formation. In Formation and
Control of Disinfection By-Products in Drinking Water. Denver: AWWA.
Liang, L. and P. C. Singer. 2001. Factors Influencing the Formation and Relative Distribution
of Haloacetic Acids and Trihalomethanes under Controlled Chlorination Conditions. In Proc. Of
the AWWA Water Quality and Technology Conference. Denver: AWWA.
McGuire, M.J., J.L. McLain, and A. Obolensky. 2003. Information Collection Rule Data
Analysis. Denver: AwwaRF.
Nguyen, M., P. K. Westerhoff, L. A. Baker, M. R. Sommerfield. 2000. Production of
DOC/DBP Precursors from Algal Growth in Arid Region Surface Water Supply. In Proc. Of the
AWWA Water Quality Technology Conference. Denver: AWWA.
Symons, J., L. Bradley, Jr., and T. Cleveland, editors. 2000. The Drinking Water Dictionary.
Denver: AWWA.
5.7 Additional Resources
AWWA Standard G300-07 Source Water Protection. Denver: AWWA.
Cooke, G. D. and R. E. Carlson. 1989. Reservoir Management for Water Quality and THM
Precursor Control. Denver: AwwaRF.
Cooke, G.D. and R.H. Kennedy. 2001. Managing drinking water supplies. Lake and Reservoir
Management. 17(3): 157-174.
Operational Evaluation Guidance Manual 5-14 December 2008
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Effler, S.W., D.A. Matthews, M.T. Auer, M. Xiao, B.E. Forrer, and E.M. Owens. 2005. Origins,
Behavior, and Modeling of THM Precursors in Lakes and Reservoirs. AwwaRF Report 91057F.
Project #557. Denver: AwwaRF.
Kornegay, B.H. 2000. Natural Organic Matter in Drinking Water: Recommendations to Water
Utilities. Denver: AwwaRF.
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6. Minimizing Future Operational Evaluation Level Exceedances
This chapter covers:
6.1 Distribution System Improvements
6.2 Plant Operational Improvement
6.3 Source Water Management
6.4 References
As part of the operational evaluation, steps must be identified that could minimize future
operational evaluation level (OEL) exceedances. This chapter discusses some common problems
that can lead to an OEL exceedance and suggests alternatives for remedying these problems.
Steps may include:
Increasing monitoring,
Modifying distribution system infrastructure or operations,
Improving DBF precursor removal through treatment modifications, or
Improving source water management.
There may be instances when your current system configuration poses limitations in
controlling TTHM and HAAS formation, particularly if you are a consecutive system.
Consecutive systems should work with their wholesalers on developing an approach for
minimizing DBF formation.
You may find additional information in theMicrobial and Disinfection Byproduct Rules
Simultaneous Compliance Guidance Manual, (USEPA, 2007) which may be useful as you
consider options for minimizing TTHM and HAAS levels in your distribution system.
Exhibit 6.1 provides examples of operational strategies that can be used to reduce DBFs.
Note that Exhibit 6.1 does not provide a comprehensive list of strategies - other operational or
low-cost capital modifications provided in this chapter may work better for your system.
Operational Evaluation Guidance Manual 6-1 December 2008
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Exhibit 6.1 Examples of Operational Strategies to Reduce DBFs
Turn over water in finished water tanks and reservoirs more frequently to reduce
waterage. (6.1.1.1)
Use blowoffs or flush dead ends in the distribution system to reduce water age.
(6.1.1.2)
Conduct periodic flushing. (6.1.2.2)
Increase TOC removal by optimizing coagulation. (6.2.1.1)
Clean settling basins before your peak DBF period. (6.2.1.3)
Optimize filtration. (6.2.1.4)
Review disinfection practices. Note that you MUST contact your State first before
making any changes to disinfection practices. (6.2.3)
Monitor source water and manage intake operations to draw raw water with the
lowest possible TOC. (6.3)
6.1 Distribution System Improvements
Higher concentrations of TTHM and HAAS are often found in the distribution system
compared to the concentrations leaving the treatment plant, particularly for systems using free
chlorine for secondary disinfection. Factors that can affect TTHM and HAAS concentrations in
the distribution system include water age, type and concentration of DBF precursors, disinfectant
type and dose, disinfectant residual concentration in the finished water, and in the case of HAAS,
biological activity.
Although there are many good operational practices that will improve overall water
quality in distribution systems, this section focuses on the following specific practices that can be
used to reduce TTHM and HAAS levels and minimize future OEL exceedances:
Managing water age (Section 6.1.1);
Reducing disinfectant demand (Section 6.1.2); and
Implementing booster disinfection (Section 6.1.3).
Each water system should prioritize the implementation of these management practices
based on their system conditions and needs.
Operational Evaluation Guidance Manual 6-2 December 2008
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6.1.1 Managing Water Age
As water travels through the distribution system, chlorine continues to react with NOM to
form DBFs. The longer the travel time or water age, the more likely it is that water quality will
degrade and exhibit higher TTHM and HAAS concentrations, reduced levels of residual chlorine,
reduced effectiveness of chlorine residual through formation of organochlorine compounds,
increased microbial activity, nitrification, and/or taste and odor problems. Chapter 3, Section 3.2
discusses how to evaluate system data and operational records to identify areas of the system
with high water age.
An overall strategy to manage water age in the distribution system can help systems
reduce future OEL exceedances. Establishing a water age goal is system-specific depending on
system design and operation, water demands, and water quality (e.g., DBF formation potential).
The next two sections provide guidance on controlling water age through management of
finished water storage facilities and minimizing hydraulic residence time in distribution system
piping.
Storage tanks with high hydraulic
residence time and/or poor mixing can
lead to DBP formation.
6.1.1.1 Reducing Water Age and Improving
Water Quality in Storage Tanks
A storage tank that has a high hydraulic
residence time and/or poor mixing characteristics
can lead to increased water age, causing high
TTHM and possibly high HAAS formation in the
tank. Sometimes, high water age in a tank can
also lead to other types of water quality problems
such as depletion of the disinfectant residual for
chlorinated or chloraminated systems, and
nitrification for chloraminated systems. High
temperatures during the summer in conjunction
with poor water mixing characteristics of a tank
may lead to thermal stratification in the tank,
causing high DBP formation in a stagnant,
stratified layer. Lack of a proper maintenance program in conjunction with poor water mixing
characteristics of a tank may lead to sediment accumulation at the bottom of the tank. This
accumulation may result in loss of disinfectant residual and increased DBP formation. Chapter
3, Section 3.3 describes how to evaluate storage tank operations to determine if water age is
excessive.
A storage tank should be designed and operated so the overall hydraulic residence time is
minimized and the water is well-mixed. Generally, water mixing in a distribution system water
storage tank is not achieved through mechanical mixers, but through operational procedures such
as maintaining adequate volume turnover, inflow rate, and inflow velocity, and through proper
design of the inlet/outlet piping. Inspections and maintenance activities such as sediment
removal and repairing or replacing coatings are also important to minimize water quality
problems.
Operational Evaluation Guidance Manual
6-3
December 2008
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This section discusses several practices to reduce water age and improve water quality in
storage tanks including minimizing the hydraulic residence time, improvements to mixing within
the tank and decommissioning storage facilities that are oversized or no longer useful.
Minimizing Hydraulic Residence Time
The average hydraulic residence time in a tank can be estimated by the following
equation:
Theoretical average hydraulic residence time = [Vmax / (Vmax - Vm;n)] / N
where, Vm;n = average minimum daily volume
Vmax = average maximum daily volume
N = number of drain/fill cycles per day
Example 6.1 shows how this formula can be used to calculate the average hydraulic
residence time in a tank. It is important to recognize that the above equation provides
information about the average amount of time spent by water inside a tank, and it is possible for
water in some portions of the tank to spend less time or more time in portions of a tank,
especially if the tank is not well-mixed. In a tank with poor mixing characteristics, the residence
time of portions of water in the tank can be much higher than the average. The Vmax and Vmin
values are numbers that are averaged over data from several days or weeks to represent the
typical operational characteristics of the tank. If the tank operation is changed from one season
to another, then the Vmax and Vm;n values would be different for different seasons.
Example 6.1 Calculating the Theoretical Average Hydraulic Residence Time
Your City has a 4 million gallon (MG) storage tank located in the distribution system. During
the summer, the average maximum volume (Vmax) in the tank is 3 MG and the average
minimum volume (Vmin) in the tank is 2 MG (obtained by averaging data from several weeks).
There are two drain/fill cycles per day (N) during the summer season. Calculate the average
hydraulic residence time of the tank.
Theoretical average hydraulic residence time = [3 MG / (3 MG - 2 MG)] / 2 cycles per day
= 1.5 days
The volume turnover can be increased by increasing the volume of water that flows in
and out of a tank during a given fill/drain cycle. Kirmeyer et al. (2000) recommend a complete
water turnover every three to five days but suggest that water system's establish their own
turnover goal based on system-specific needs and goals. Turnover can be accomplished by
increasing the water level fluctuation or drawdown between fill and draw cycles. The water
level should be lowered in one continuous operation not small incremental drops throughout the
day. Converting tanks to hydraulic plug-flow conditions and eliminating common inlet/outlet
configurations can also reduce average hydraulic residence time.
Operational Evaluation Guidance Manual 6-4 December 2008
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Improving Mixing Characteristics of Storage Tanks
Improving the mixing characteristics of a storage tank can help eliminate stagnant zones
where DBF formation can be the highest. Old water in stagnant zones can have high TTHM and
HAAS concentrations and no or low disinfectant residual. This water can be released into the
system during periods of high demand.
Several tools can be used to predict water mixing characteristics of a tank. A brief
description of each is provided below.
Desktop calculations of hydraulic residence time, fill time, and inlet momentum.
A method for estimating hydraulic residence time in a tank is presented in Section
6.1.1.1. Fill time and inlet momentum can be estimated from operational records and
SCADA data.
Computational fluid dynamic (CFD) modeling. CFD modeling provides a
qualitative description of water mixing characteristics by providing visual images of
water mixing inside a tank. It can be used to determine the effect of fill time and inlet
momentum on the mixing characteristics of a specific tank configuration.
Temperature measurements. Depending on the location of the inlet pipe and tank
geometry, the water entering a tank from buried pipes may be cooler than the bulk
water in the tank during the summer or warmer than the bulk water in the tank during
the winter. In a tank with poor mixing characteristics, colder, denser water remains in
the lower portion of the tank, whereas the warmer, less dense water has a tendency to
rise to the top of the tank. Water temperature profiles can be used to determine the
existence of thermal stratification inside a tank. The temperature profiles can be
obtained from continuous water temperature measurements collected at various
locations in the tank over the course of several days. Temperature differences as low
as 2 degrees Fahrenheit between the top and bottom of a tank may indicate that the
tank is thermally stratified and has poor mixing.
Disinfectant residual measurements. Disinfectant residual measurements collected
at various locations in a tank can also be used to determine mixing conditions and
stratification. Grab samples or continuous online monitoring can be used for this
purpose. However, acceptable differences in disinfectant residuals among various
locations in a tank are situation specific and depends on a system's water quality.
After the water mixing characteristics of a storage tank have been evaluated, appropriate
operational and/or physical modifications can be selected to improve water mixing in the tank.
These modifications, which are discussed in more detail below, include:
Increasing fill time and inlet momentum,
Optimizing inlet pipe location and orientation, and
Prudent use of baffles.
Operational Evaluation Guidance Manual 6-5 December 2008
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Increasing Fill Time and Inlet Momentum
Mixing a fluid requires a source of energy input. In a distribution system storage tank,
this energy is normally introduced during tank filling, and therefore mixing occurs primarily
during the fill cycle. As a result, if a tank is relatively well-mixed at the end of each fill cycle,
then significant variations in water age and DBF levels within the tank are unlikely. Fill time
can be increased by allowing a tank to drain to a lower level before refilling. This strategy also
has the desirable effect of decreasing overall hydraulic residence time and increasing volume
turnover.
Inlet momentum (defined as velocity * flow , , ,, ,, , , .
, x. , f . f . . .1 Inlet momentum (denned as velocity
rate) is a key factor tor mixing water in a storage tank. _ . . , f r . .
rpU u- u ., , . . ., , .. ., x flow rate) is a key factor for mixing
The higher the inlet momentum, the better the mixing J / j j j &
u * ^- f^u 4. 4. i TU i 4. water ma storage tank
characteristics of the storage tank. The inlet *
momentum can be increased by increasing the flow
rate (which also has the desirable effect of increasing
the velocity). One way to accomplish this is to install pumps near the tank. However, increasing
the flow rate may not be practical due to the limitations of system hydraulics. For example,
distribution system pressure may not be high enough to get desirable increases in flow rates or a
pump may not be available at the tank location to increase the pumping rate into the tanks. In
such cases, the inlet momentum can be increased by reducing the inlet diameter to increase the
inlet velocity.
Optimizing Inlet Pipe Location and Orientation
The location and orientation of the inlet pipe relative to the tank walls can have a
significant impact on mixing characteristics. As water enters a tank through an inlet pipe, a jet is
formed and the water present in the tank is drawn into the jet. Circulation patterns are formed
that result in mixing. The path of the jet should be long enough to allow the mixing process to
develop, and therefore should not be pointed directly towards nearby impediments such as a wall
or deflector. For example, for a tall tank with relatively small width or diameter, a horizontal
inlet pipe at the bottom of the tank is likely to cause the water jet to hit the vertical wall of the
tank resulting in loss of inlet momentum and poor mixing near the top portion of the tank. In
general, outlet pipes are located near the bottom of the tank and relocating the inlet pipe near the
top of the tank may improve mixing characteristics. However, the system hydraulics need to be
evaluated to ensure there would be adequate pressure to allow the tank to fill to the desired level.
Inlet pipes located near the bottom of a tank can be angled upwards, or multiple inlet pipes can
be used to improve mixing conditions in a tank. The optimum inlet pipe location and orientation
for a tank to achieve good mixing depends on a number of factors including:
Tank geometry,
Inflow rate, and
Temperature differences between the inflow and the bulk water in the tank.
CFD modeling can be a useful tool to determine the optimum pipe location and
orientation for a tank.
Operational Evaluation Guidance Manual 6-6 December 2008
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Prudent Use of Baffles
In treatment plant tanks, where chlorine contact time is
. . The use of baffles should
required and there is generally simultaneous inflow and outflow, A / , , ,
. ,, ~ & . J ,,..,, , ' oe carefully evaluated.
internal baffles are sometimes placed inside the tanks to
encourage plug flow conditions. However, in distribution system
tanks and reservoirs, chlorine contact time is not an issue and there is generally a "fill and draw"
operation. The use of baffles in distribution system storage tanks encourages plug flow
conditions. Plug flow conditions in a storage tank will result in a greater retention time of water
in the tank when compared to complete mixing conditions. Because the rate of disinfectant loss
is dependent on both concentration and time, plug flow conditions will likely result in a greater
disinfectant loss than complete mixing conditions. For distribution system tanks that operate in a
fill and draw mode, the use of baffles should be generally avoided to encourage mixed flow
condition, and baffles can also produce poor mixing zones (dead zones). These zones can have
higher water age and therefore higher DBF formation. There may be special situations such as
separate inlet and outlet pipes in close proximity to each other where a baffle wall between the
inlet and outlet may be desirable to circulate water throughout the tank. However, because of the
wide variations in tank geometry and inlet/outlet piping configurations for distribution system
storage tanks, the use of baffles should be carefully evaluated for each specific situation to
determine if baffles have any beneficial impact. Tracer testing, CFD modeling, and disinfectant
residual monitoring are useful tools to determine the effect of baffles.
Decommissioning of Storage Tanks
Decommissioning storage facilities may also be an appropriate strategy to reduce water
age if existing facilities are oversized and not needed for emergency conditions or for
maintaining system pressure. Historically, distribution system storage tanks have been built to
provide adequate pressures, fire flows, and peak demand capabilities. Often, tanks are also
designed to accommodate future growth and long-term water system needs. Therefore, some
distribution system storage tanks may be oversized. Storage tanks may also be hydraulically
locked out of the distribution system due to high system pressures, low system demands, or
inadequate tank height. Oversized tanks and/or tanks that are hydraulically locked out (due to
system pressure being comparable to the maximum water level in the tank most of the time) do
not have adequate flow through the tanks and turnover, resulting in high water age and high DBF
formation. When events such as main breaks, fire flows, or other unexpected peak demand
conditions occur in a system, water from these tanks are drawn into the distribution system.
Thus, the areas receiving water from the tanks may have higher than normal TTHM and HAAS
levels.
Specific steps you can take to identify tanks that could be decommissioned include:
Solicit the assistance of a professional engineer to review system needs, system
design, and operation to determine if the existing storage capacity is appropriate.
For a tank that is hydraulically locked out of the system, determine if the operational
hydraulic grade in the vicinity of that tank can be lowered so that volume turnover
can be achieved. One way to accomplish this is to valve off pipe sections during
Operational Evaluation Guidance Manual 6-7 December 2008
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certain hours so that water demand in the vicinity of the tank is supplied primarily by
the tank, rather than directly from the plant through distribution system pipes. If
these operational changes cannot be accomplished, permanent decommissioning can
be considered.
For an oversized tank, determine if more water can be forced in and out of the tank on
a daily basis by installing pumps, adjusting pumping schedules (if pumps already
exist), or adjusting the control settings for altitude valves. If such modifications are
not feasible, permanent decommissioning of the tank can be considered.
Before a tank is decommissioned, the effects of taking the tank out of service should
be determined. A distribution system analysis should be performed to make sure that
the tank is not needed and there is adequate hydraulic connectivity for equalization
storage, fire flow, or emergency conditions such as main breaks or treatment plant
shutdowns.
6.1.1.2 Minimizing Hydraulic Residence Time in Pipes
The finished water leaving a treatment plant can spend considerable amount of time
(more than a week) in the distribution system pipes before reaching a customer's tap. High
hydraulic residence time in the distribution pipe network can lead to high DBF formation.
Water distribution system models offer an r-n^Arr^ i ^ r ^ i s
. , .,,,,. ., . EPANET, a hydraulic model for
effective way to determine the hydraulic residence time ,. , ., ,. , /
_, J .. J . . . . distribution systems, can be
in pipes. To predict water age accurately, the model , , , , ,.
i i j i ji .LI *. r-ii .LI downloaded from
should include the ma onty or the pipes in the , ,, ,, /Ann /A *m
.. ... , , Vr -1- / 1 http://www.epa.sov/ORD/NRMRL
distribution system and all physical facilities (such as ~~ ~T, ,,, w-r, ',T~
, 11^ 1 /wswrd/epanet. html#Downloads
storage tanks, pumps, and valves), provide an accurate
simulation of water consumption, and be well-calibrated.
Such a model can be used to quickly and accurately
simulate complex water systems under various operating conditions. The hydraulic models can
be used to determine the need for and the effect of various methods to reduce hydraulic residence
time such as looping dead-ends, blow-offs, closing/opening valves, and replacing large diameter
pipes with smaller ones. There are some hydraulic models available that have these capabilities.
One such model that is available in the public domain is called the EPANET. This hydraulic
model is available for free and can be downloaded from
http://www.epa.gov/ORD/NRMRL/wswrd/epanet.htmltfDownloads. It can be used to perform
extended period simulation of hydraulic and water quality behavior of distribution system
networks. There are also some hydraulic models available that can be integrated with GIS to
take advantage of the database capabilities of GIS. One such model that is available for free
through EPA is called PipelineNet. In addition to the hydraulic, water quality, and GIS
capabilities, the model contains maps and a U.S. Census population database. It can also be
connected to the Internet via a model or cellular accessible network.
Minimizing the hydraulic residence time in pipes can help reduce the time available for
DBF formation, although it is possible for an increase in HAAS to occur because of less
biological degradation. Reducing hydraulic residence time can also minimize disinfectant
Operational Evaluation Guidance Manual 6-8 December 2008
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residual loss and allow systems to use a lower overall residual concentration, thereby reducing
DBFs. Systems can reduce hydraulic residence time and disinfectant loss through physical
system improvements such as:
Looping dead ends,
Managing valves,
Installing blow-offs, and
Replacing oversized pipes.
These system improvements are discussed further below. It is important to note that most
of these options require new construction and may be cost-prohibitive for some systems.
Looping Dead-Ends
The highest DBF concentrations in a distribution system are often observed at dead ends.
Water at dead ends is stagnant and therefore provides long contact times for DBF formation.
Excessive hydraulic residence time at dead ends can be reduced with pipe looping, which
generally involves constructing new pipe sections to make appropriate hydraulic connections
among existing pipes. However, in some cases, pipe looping can also create zones with very
slow moving water elsewhere in the system. For example, looping a dead end may cause water
with opposite flow directions and similar flow rates to meet and cause very slow moving water at
that location. Therefore, the specific hydraulic response of a system to looping should be
assessed to make sure that looping does not negatively impact the residence time of other parts of
the system.
Managing Valves
Isolation valves in the distribution system are sometimes in the wrong position (either
open or closed), which can change the hydraulic path of water in the distribution system. For
example, a closed valve may create a dead end with stagnant water and high TTHM and HAAS
levels. There are many reasons why a valve could be left in the wrong position including human
error, lack of training, mechanical failure, poor record keeping and failure to locate valves
because the valve boxes are buried or paved-over. A comprehensive valve inventory and
maintenance program is necessary to identify the location and status of valves in a system. A
valve exercise program is also necessary to determine improperly positioned and broken valves.
As these valves are discovered, their positions can be corrected or they can be replaced to
minimize stagnant water zones and associated high water age in distribution system pipes.
Using Blow-Offs
Blow-offs can be used to purge old water from dead-end or stagnant zones and pull
fresher water into these locations from other areas. Blow-offs may operate in a continuous flow
mode or an automatic intermittent flow mode. The velocities for blow-offs are generally
insufficient (< 2.5 feet/sec) to remove sediments or biofilms. Continuous or automatic
intermittent blow-offs can be used on a seasonal basis when TTHM and HAAS peaks are more
Operational Evaluation Guidance Manual 6-9 December 2008
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likely to occur (e.g., during high water temperature periods). Blowoffs can be located using
hydraulic models, historical water quality data (targeting areas with low disinfectant residuals
and high bacteria counts), and customer complaints.
Replacing Oversized Pipes
In portions of a distribution system where pipes are oversized, the water velocity is lower
and therefore hydraulic residence times are longer than necessary causing high DBF levels.
Areas of a distribution system that have been abandoned or have experienced negative demand
growth over many years may contain oversized pipes, causing excessive hydraulic residence
time. Where appropriate, the pipe sizes in these areas can be reduced or sections of pipes can be
valved off if they are no longer needed to reduce the residence time of water. However, the
effect of replacing or valving oversized pipes on downstream areas should be evaluated to make
sure that such modifications will not cause hydraulic constrictions for the downstream areas.
6.1.2 Reducing Disinfectant Demand
Aging pipes such as unlined cast iron pipes exert high
disinfectant demand because of the presence of corrosion
byproducts, biofilms, and sediment deposits. To maintain a
sufficient disinfectant residual in the distribution system,
increased chlorine dose at the treatment plant may be needed,
and for systems that use chlorine for secondary disinfection,
booster chlorination may also be needed. High chlorine dose
at the plant increases TTHM and HAAS formation, and
booster chlorination leads to excess chlorine residual in some
areas of the distribution system, resulting in high TTHM and
HAAS formation in these areas. Systems can reduce
localized chlorine decay and thus reduce the overall
disinfectant demand through:
Replacing or cleaning and lining pipes, and
Conducting periodic flushing.
The selection of any specific method depends on
water quality data, hydraulic condition, pipe condition, and
economic factors.
Aging pipes can exert
high disinfectant
demand.
6.1.2.1 Replacing or Cleaning and Lining Unlined Cast Iron Pipes
For a water distribution system, disinfectant demand due to pipe corrosion, biofilm, and
sediment deposition is most prevalent with unlined cast iron pipes. This problem can be reduced
by replacing or cleaning and lining aging unlined cast iron pipes. Pipe replacement may be the
preferred option for reducing disinfectant demand if a pipeline has structural problems or if there
is a need to increase hydraulic capacity with a larger diameter pipe. If a pipeline is structurally
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sound, then pipe cleaning is a less expensive option. For unlined cast iron pipes, pipe lining may
also be necessary to achieve a permanent improvement and prevent a recurrence of the
disinfectant demand problem.
Pipe cleaning methods include high pressure sand blasting, mechanical scrapers, pigging,
swabbing, flow-jetting, and chemical cleaning. Among the more common lining materials are
cement-mortar, asphalt (bituminous), epoxy resins, rubber, and calcite. Cement is the most
commonly used pipe lining material, although several types of degradation of cement material
can occur in the presence of acidic waters or waters that are aggressive to calcium carbonate
(e.g., soft waters). The AWWA Standard, Rehabilitation of Water Mains (M28), 2nd Ed.
(AWWA 2001), provides additional information and guidance on cleaning and lining
technologies.
6.1.2.2 Conducting Periodic Flushing
Periodic flushing can be an effective tool to control TTHM and HAAS peaks by purging
stagnant water to reduce water age and by cleaning pipes that exert chlorine demand. There are
several approaches to conducting distribution system flushing depending on system
configuration and water quality goals. The AwwaRF report, Guidance Manual for Maintaining
Distribution System Water Quality (Kirmeyer et al. 2000) categorizes flushing as conventional,
unidirectional, or continuous
Conventional flushing typically involves opening hydrants in an area of the distribution
system (without closing valves beforehand to direct the water) until certain water quality goals
are met. Conventional flushing can be effectively used to restore disinfectant residual
concentration and to remove poor quality water from a specific area of the distribution system.
Unidirectional flushing involves
flushing of water in one direction through a
pipeline through a carefully planned sequence
of closing valves and opening hydrants.
Unidirectional flushing can achieve higher
velocities through the pipe (> 6 feet per second
(ft /sec)) as compared to conventional flushing.
Higher velocity flushing operations can not only
remove poor quality water from an area, but
also can scour the inside of the pipeline to
remove biofilm, corrosion products, and other
debris attached to the pipe wall. Accurate maps
of the system, hydraulic models, and a complete
database of valves and hydrants facilitate
planning and execution of directional flushing
programs. Additional guidance on unidirectional flushing is provided by AWWA in DVD
format (AWWA 2002).
Continuous flushing at blowoffs is used by water systems that have numerous dead ends
and severe water circulation problems. Typically, velocities at continuous blowoffs are much
Unidirectional flushing at high
velocities can scour water mains,
removing corrosion products, biofilm,
and sediment.
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lower than seen during unidirectional or even conventional flushing (< 1 ft/sec, Kirmeyer et al.
2000).
Minimum elements of a flushing program are outlined in the AWWA G200 Standard and
include: (1) a preventive approach including spot flushing to address local problems or customer
concerns and routine flushing to avoid water quality problems; (2) use of an appropriate flushing
velocity to address water quality concerns; and (3) written procedures for all elements of the
flushing program including water quality monitoring, regulatory requirements and specific
flushing procedures. Kirmeyer et al. (2000) presents a 4-step approach to assist utilities with
developing, implementing, and evaluating the effectiveness of individual flushing programs.
Care should be taken regarding disposal of disinfected water. The AwwaRF report
Guidelines for the Disposal of Chlorinated Water (Tikkanen et al. 2001) provides strategies for
removing chlorine and chloramine from water during flushing.
6.1.3 Implementing Booster Disinfection
Systems can use booster disinfection to improve disinfectant residual maintenance and to
minimize formation of DBFs. It allows the system to use a lower chlorine dosage rate at the
water treatment plant and feed chlorine at select locations in the distribution system as needed to
maintain a residual.
The advantages of using booster disinfection facilities include:
Increasing disinfectant residual only in the areas that require it without increasing the
disinfectant residual in other parts of the system beyond acceptable levels. This
prevents potentially high TTHM and HAAS levels in some parts of the system.
Reducing residual disinfectant concentration leaving the treatment plant.
The disadvantages of using booster disinfection facilities include:
Difficulty in controlling the required disinfectant dose due to the dynamic nature of
chlorine demand in the system.
Potential to produce unpredictable disinfectant levels in the system due to over- or
under-feeding.
Regulatory concerns with degradation byproducts if hypochlorite is used or safety
issues if chlorine gas is used.
Concerns with strength and stability of the disinfectants when storage time is long.
The location of booster disinfection facilities in the distribution system is important to
obtain desired results. The results from hydraulic models, disinfectant residual data, disinfectant
decay data, and other water quality data are needed to determine appropriate booster disinfection
locations. For chlorinated systems, the primary controlling factor is the difference between the
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measured and desired free chlorine residual. For chloraminated systems there are other
controlling factors, such as excess free ammonia in the system due to chloramine decay.
6.1.4 Additional Resources
The following references may be useful in evaluating options for minimizing TTHM and
HAAS in the distribution system:
AWWA. Water Supply Operations: Flushing and Cleaning. Edition 2006 - DVD
AWWA. Unidirectional Flushing. Edition 2002 - DVD
AwwaRF. 2003. Investigation of Pipe Cleaning Methods. Denver: AwwaRF.
Brandt, M., J. Clement, J. Powell, R. Casey, D. Holt, N. Harris, C.T. Ta. 2004. Managing
Distribution System Retention Time to Improve Water Quality - Phase I. Denver: AwwaRF.
Clark, R.M. and Grayman, W.M. 1998. Modeling Water Quality in Drinking Water
Distribution Systems. Denver: AWWA.
Grayman, W. M., L. A. Rossman, C. Arnold, R. A. Deininger, C. Smith, J. F. Smith, and R.
Schnipke. 2000. Water Quality Modeling of Distribution System Storage Facilities. Denver:
AwwaRF and AWWA.
Grayman, W. M., L. A. Rossman, R. A. Deininger, C. D. Smith, C. N. Arnold, and J. F. Smith.
2004. Mixing and Aging of Water in Distribution System Storage Facilities. Journal AWWA.,
96:9:70-80.
Kirmeyer, G., M. Friedman, K. Martel, G. Thompson, A. Sandvig, J. Clement, and M. Frey.
2002. Guidance Manual for Monitoring Distribution System Water Quality. Denver: AwwaRF
and AWWA.
Roberts, P.J.W., X. Tian, F. Sotiropoulos, M. Duer. 2006. Physical Modeling of Mixing in Water
Storage Tanks. Denver: AwwaRF.
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. Office of Water. EPA 815-R-07-017.
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
USEPA. 2006. Initial Distribution System Evaluation Guidance Manual for the Final Stage 2
DBPR. Office of Water. EPA 815-B-06-002.
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
Walski, T., D.V. Chase, D. Savic, W.M. Grayman, S. Beckwith, andE. Koelle. 2003. Advanced
Water Distribution Modeling and Management. Bentley Institute Press.
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6.2 Plant Operational Improvement
It may be possible to modify water treatment operations to reduce DBF formation.
However, any operational changes should be evaluated to assure that they do not compromise
treatment effectiveness for inactivating or removing microorganisms.
This section describes the potential impact of operational changes in common treatment
units for decreasing TTHM and HAAS concentrations in the finished water. Operational
changes that will be discussed in further detail include:
General strategies for enhanced precursor removal,
Seasonal strategies for enhanced precursor removal, and
Review of disinfection practices.
6.2.1 General Strategies for Enhanced Precursor Removal
Strategies that can be implemented to lower DBF levels include:
Optimize coagulation process to improve removal of organic DBF precursors,
Optimize settling process,
Optimize conventional and GAC filtration processes, and
Adjust pH to balance TTHM vs. HAAS production.
6.2.1.1 Enhanced Removal of Organic DBF Precursors by Coagulation
Failure to optimize the coagulation process may result in a larger fraction of natural
organic matter (NOM) passing through the
coagulation/flocculation and settling processes.
This increased NOM concentration can lead to
increased formation of TTHM and HAAS.
Chapter 4 Section 4.3 discusses how to
determine if the current coagulation practices
are optimized through review of historical
water quality data and chemical feed records,
and inspection of chemical feed pumps and
mixing equipment.
If the coagulation process needs further
optimization, there are several operational
changes that can be implemented independently
or in combination to enhance the removal of
Optimizing coagulation and flocculation
can be an effective tool in minimizing
DBFs.
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organic DBF precursors by coagulation (Randtke, 1999). These strategies, which are discussed
in greater detail below, include the following:
Optimize the coagulation pH;
Optimize the coagulant dosage for paniculate removal and/or enhance it for DBF
removal;
Change the type of coagulant;
Add a polymer; and
Use a preoxidant.
In general, optimizing the coagulation process should be the goal. The above strategies
may be effective alone or in combination with another strategy(s). The first strategy (optimizing
the coagulation pH) can be very effective. Switching to an alternative coagulant can also be
effective given the wide variety of coagulant products available today.
Optimizing the Coagulation pH
The maximum removal of precursors
by metal-salt coagulants and cationic
polymers typically occurs at a pH between
5.5 and 6 (USEPA 1999). However, the
appropriate optimal pH should be selected by
balancing the benefits of improving precursor
removal with possible negative impacts on
turbidity removal and corrosion of concrete
and mechanical equipment at lower pH. The
pH should be restored to above neutral (greater than 7.0) after treatment. Under most water
quality conditions, the addition of alum or ferric salts decreases pH and the optimal pH for
precursor removal can be reached by progressively increasing the coagulant dosage. In waters
with sufficient alkalinity, the optimum pH can be reached either by increasing the coagulant
dosage, by adding an acid, or a combination of both. The major advantage of adding an acid is
the reduced production of coagulation residuals. In waters with very low alkalinity or high color,
it is often necessary to add a base to maintain the pH in the optimal range. Jar tests are an
effective tool to determine the optimal pH of coagulation and to identify precursor removal
trends during coagulation. Another tool is the simulated distribution system test, which can give
an indication of DBF levels that can be expected at different time intervals in the distribution
system.
Increasing the Coagulant Dosage at Constant pH
Increasing the coagulant dosage beyond the amount required for satisfactory turbidity
removal can result in improved precursor removal. However, systems should watch for possible
problems caused by overfeeding coagulant such as:
Operational Evaluation Guidance Manual 6-15 December 2008
More information on conducting simulated
distribution system tests can be found in
EPA's Simultaneous Compliance Guidance
Manual for the Long Term 2 and Stage 2
DBF Rules
(http://www.epa.gov/safewater/disinfection/lt
2/compliance.html)
-------
Increased sludge production,
Poor settling,
Shortened filter runs,
Reduced pH and alkalinity, and
Filter breakthrough.
Jar testing can be used to identify the optimum coagulant dosage that can be use to
achieve turbidity and organic DBF precursor removal goals.
Changing the Type of Coagulant
Systems may find that one coagulant can be more effective than another in promoting
removal of DBF precursors. Many polymer blends have been developed specifically for removal
of TOC/DBP precursors, and cold water applications. However, the differences in performance
should be carefully analyzed in terms of equivalent weight and costs. It has been reported that a
greater maximum removal of precursors can be achieved with iron salts than with alum (Randtke
et al., 1994; Edwards, 1997). However, these differences are only evident when the dosages
exceed those used in most practical applications. At lower dosages alum can be more effective
than ferric (Edwards, 1997), but these differences are difficult to determine because of the
different acidity of alum and iron salts. Before making changes to full-scale treatment processes,
systems should conduct jar tests to identify the best coagulant for organic DBF precursor
removal with system-specific water quality and operating conditions.
Adding a Polymer
Polymers can improve settleability of floe and thereby result in better removal of DBF
precursors through the coagulation/flocculation/sedimentation process. Many types of polymers
have been found to be effective, including cationic, anionic, and non-ionic polymers. Because
overdosing polymers can adversely affect filter media, water systems should carefully evaluate
polymers before adding them to full-scale operations (USEPA 1999).
Using a Preoxidant
In some cases, preoxidation has been found to improve organic DBF precursor removal.
For example, in plants that use ozone for disinfection, preoxidation with a small dosage of ozone
can promote precursor removal by increasing the number of functional groups on the organic
matter available for complexation with metal hydrolysis products and enhancing the
biodegradation of organic molecules in biologically active filters. On the other hand, a high
dosage of ozone can have negative effects on organic DBF precursor removal (i.e., produce
smaller and more soluble organic molecules that are more difficult to remove). Preoxidation
with chlorine is not recommended because the addition of chlorine to raw water will increase the
contact time between chlorine and high concentrations of DBF precursors. Systems that use
prechlorination to control algal growth or to aid coagulation should consider switching to another
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preoxidant such as potassium permanganate. Potassium permanganate does not cause TTHM or
HAAS formation but presents other operational challenges.
6.2.1.2 Enhanced Removal of Organic DBF Precursors by Softening
Precursor removal by precipitative softening with coagulation follows the same basic
mechanisms, but process chemistry and the type of solids formed are very different. In
precipitative softening, precursor removal can be enhanced by one or more of the following
operational changes (Randtke, 1999):
Increasing the lime dosage. Precursor removal improves with increasing lime dose as
follows:
- If sufficient carbonate alkalinity is available, more calcium carbonate precipitates,
providing an increased opportunity for precursors to co-precipitate.
- If insufficient carbonate alkalinity is available, excess calcium provided by lime
addition promotes precipitation and co-precipitation of precursors and adsorption of
precursors on settling solids.
- The pH increase resulting from the higher lime dose promotes stronger interactions
between calcium ions and precursors.
- If magnesium is present in the raw water and the pH of the water is increased to
between 10.5 and 10.8, substantial co-precipitation of magnesium hydroxide and
calcium carbonate occurs. Precursor removal is enhanced because precursors have
a strong tendency to adsorb onto magnesium hydroxide (Liao and Randtke, 1985).
Adding a coagulant in combination with lime addition. The addition of a coagulant
during lime softening can increase precursor removal. This increase is normally
achieved with low coagulant dosages and there is no significant increase when the
coagulant dosage is further increased.
Eliminating or reducing solids recycling. There is limited evidence that eliminating
or reducing solids recycling or delaying the application of soda ash to a subsequent
stage of treatment can increase precursor removal (Liao and Randtke, 1985).
However, these operational changes should be carefully tested to determine their site-
specific effectiveness and careful consideration should be given to potential negative
impacts on the overall treatment performance.
6.2.1.3 Optimizing Settling
Poor settling can result in floe carryover through the sedimentation basin and to the
filters. Because floe contains significant amounts of coagulated precursor material, poor settling
may negatively affect DBF levels, especially in those systems that add chlorine upstream of their
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filters. Chapter 4 Section 4.4 describes how to
evaluate existing sedimentation processes using
historical water quality and operations data,
weather data, and operations records.
In many cases, settling can be improved
by optimizing the coagulant dosage and/or
adding a polymeric aid. Jar tests can be used to
determine the optimal amounts of these
chemicals. Settling can also be improved by
reducing the hydraulic loading rate through the
settling basin or balancing the hydraulics
amongst multiple settling basins. Systems that
operate more than one plant may want to
explore the opportunity of shifting some of the
hydraulic load from a plant with poor settling to one with better performance during peak DBF
season.
Poor or inadequate removal of sludge from the settling basin, as well as maintenance in
the basin that stirs or moves the sludge, can release DBF precursors. This "additional" precursor
load is available for reaction with free chlorine in the chlorine contact facilities, or may be
carried through the settling process to the point of disinfectant addition. To minimize this type
of problem a system should improve sludge removal operations. One way to do so is by
scheduling basin cleaning before peak DBF periods or on a continuous basis.
Regularly clean out sludge from
settling basins.
6.2.1.4 Optimizing Conventional and GAC Filtration
Increases in organic loading during a filter cycle, or the breakthrough of particles at the
end of the filter run cycle, can allow significant concentrations of precursors to come into contact
with free chlorine in the clearwell or other chlorine contact facilities. This will lead to an
increase in DBF levels in these facilities and
ultimately, in the distribution system.
Chapter 4 Section 4.5 describes how to
evaluate potential causes of filter
breakthrough using historical data and
operations records.
To minimize the potential of such
breakthrough, the following should be
evaluated:
The coagulation process;
The filter run length;
Filter loading rates; and
Operational practices to optimize filtration
operation include:
Limiting the amount of backwashing
time,
Distributing hydraulic load across
filters,
Maintaining consistent precursor
removal levels, and
Adjusting the coagulant dose to
account for the resulting increase in
DBF precursors in recycled water.
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The benefits of applying a filter aid polymer.
This evaluation should include measuring:
TOC,
Turbidity,
Particle counts on individual filters (if available), and
Alternative filter practices tested at pilot-scale.
Particle breakthrough can also take place during the initial phase of the filtration cycle
(ripening). Therefore, systems should check that filters are not backwashed for an excessive
length of time. Backwash should be conducted for a duration of time that restores the target
headloss but does not completely remove all the filtered solids in the backwash water
supernatant. The presence of some solids remaining on the filter media will allow quicker
ripening and better filter performance when the unit is placed back into service after backwash.
Some systems allow the filter to rest or filter-to-waste after backwash to improve water quality
when the filter is brought back into service.
Hydraulic surges can disrupt filter operations and lead to particle breakthrough.
Hydraulic surges may occur when filters are taken offline for backwash or maintenance, or if a
sudden increase in plant flow occurs. The hydraulic load should be distributed among as many
filters as possible, especially in small plants with few filters. When the hydraulic load is
distributed across many filters, the relative increase in loading onto each individual filter is lower
and is less likely to disrupt the filter.
When biologically active filters and GAC filters are used for organic precursor removal,
breakthrough may be a concern because soluble organic compounds can be released. Likewise,
when GAC columns are used for DBF removal after chlorination, exhaustion of adsorptive
capacity may result in a sudden release of high concentrations of TTHM and HAAS into the
finished water. The performance of these types of filters should be checked to ensure that
consistent precursor removal levels are maintained.
Filter backwash may contain elevated concentrations of DBF precursors. If no additional
treatment (e.g., coagulation/settling) of recycled backwash water is provided, it is important to
adjust the coagulant dose to account for the resulting increase in DBF precursors when recycled
water is returned to the head of the plant.
6.2.1.5 Adjust pH to Balance TTHM vs HAAS Production
The pH of water has been characterized as one of the most important chemical variables
affecting the formation and speciation of chlorinated DBFs (Stevens, Moore, and Miltner, 1989).
Studies and field observations have shown that TTHM formation typically increases at high pH
and decreases at low pH, while HAAS formation follows an opposite trend. In some cases, this
knowledge can be used to adjust the treatment pH after coagulation to improve regulatory
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compliance. For example, a plant producing
water with moderate TTHM levels and high
HAAS could benefit from increasing the pH
The pH of water has been characterized as
one of the most important chemical variables
affecting the formation and speciation of
of filtration, provided that opportunities for
pH adjustment during treatment are available. chlorinated DBFs.
Systems that are considering altering the pH
to balance TTHM and HAAS production
should carefully consider the impacts of this strategy on virus and Giardia log inactivation
because chlorine is less effective at higher pH values. When the pH is increased prior to chlorine
contact basins, a higher chlorine dose or longer contact time may be needed to achieve the
necessary levels of log inactivation. Systems should also carefully consider the effects of pH
changes on corrosion of plant materials and Lead and Copper Rule (LCR) compliance
implications.
6.2.2 Seasonal Strategies for Enhanced Precursor Removal
Variations in temperature, chlorine dosages, and NOM characteristics in water affect
DBF formation. Precursor removal targets could be adjusted to follow these water quality
changes. This knowledge could be used to adjust treatment objectives and DBF control strategy
on a seasonal basis. Chapter 4 Section 4.3 describes how to evaluate existing coagulation
practices and seasonal changes in water quality and demand that may reduce treatment
effectiveness. Appropriate precursor removal targets can be identified by:
Conducting a desktop analysis using computer tools, such as EPA's Water Treatment
Plant (WTP) simulation program (available through the National Technical
Information Service at http://www.ntis.gov), to define the interrelationship between
historical finished water TOC, temperature, and DBF levels.
Monitoring raw and finished water or conducting jar tests and simulated distribution
system tests. Suggested monitoring parameters include:
-TOC,
- UV254 (UV absorption at 254 nanometers (nm)),
-pH,
- Temperature,
- Chemical dosage rate, and
- Alkalinity.
Some examples of possible seasonal strategies include:
Improve the performance of the coagulation process by lowering pH, increasing
coagulant dosage, adding a polymer, and/or changing coagulation in response to
seasonal increases in precursor levels or their increased predisposition to removal.
Discontinue chlorine addition upstream of gravity filters with a GAC layer and use
the filter for biological precursor removal.
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Systems that experience periodic high HAAS levels while TTHM remain moderate
may consider temporarily increasing the pH during settling and filtration to limit
HAAS formation.
Modify filter operations for different water temperatures.
6.2.3 Review of Disinfection Practices
Systems are required to maintain a certain microbial inactivation level (measured as CT =
disinfectant residual (C, in mg/L) x contact time (t, in min)) for disinfection. As the disinfectant
dose decreases, the required contact time increases to maintain a required level of CT, and vice
versa. TTHM and HAAS levels increase with the chlorine concentration when precursors are
present. The following are examples of intentional or unintentional events that can lead to
increased chlorine dosages within a plant:
Systems that control the disinfectant dose manually and not based on plant flow may
experience increases in TTHM and HAAS if the plant flow rate suddenly decreases or
the dose is not adjusted frequently to account for reductions in plant flow. In such
instances, those systems would likely be overdosing chlorine.
Systems may intentionally increase the dose to account for a decrease in water
temperature and maintain the required CT (CT requirements increase as water
temperature decreases).
Preoxidation with chlorine is particularly problematic because of the larger
concentration of precursors in the untreated water and the long residence time
available for the reaction with chlorine.
Systems may intentionally make changes in the plant process that involve the use of
pre-oxidation with chlorine (i.e., for arsenic treatment).
High chlorine dosages may be intentionally applied during periods of algal bloom for
the control of color, taste and odor, and iron and manganese.
Increasing the holding time of water in the chlorine contact facilities or any unit
process results in a longer reaction time between free chlorine and precursors. This
can lead to increased TTHM levels. The increased residence time can also lead to
increased HAAS concentrations, but this effect is less pronounced because HAAS
formation occurs more rapidly and may not increase as significantly as TTHM over
long periods of time. The issue of residence time within the plant is particularly
important for systems that use chloramines for secondary disinfection. In many
chloraminated systems, most DBFs are formed within the plant and a much smaller
fraction is formed in the distribution system.
In all of the above cases, systems experiencing high TTHM and HAAS levels should
review their disinfection practices to determine if the chlorine dosage can be reduced without
compromising disinfection goals. Proper inactivation levels should be maintained at all times.
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Chapter 4 describes how to evaluate existing practices for predisinfection (Section 4.1), primary
disinfection (Section 4.6) and secondary disinfection (Section 4.8) using historical data and
operations records. If a system was required to produce a disinfection profile and benchmark
under the Interim Enhanced Surface Water Treatment Rule (IESWTR), the Long Term 1
Enhanced Surface Water Treatment Rule (LT1ESWTR), or LT2ESWTR it should use this
information to assess the potential impact of changes to the disinfection practices and the State
must be contacted prior to any changes. The following operational changes to disinfection may
be undertaken to limit the production of DBFs within the plant:
Systems that control the disinfectant dose manually should adjust the chlorine dosage
frequently to account for changes in plant flow.
Systems should frequently check that their chlorine dosage is appropriate to meet the
required CT at the current water temperature and pH.
When possible, preoxidation with chlorine should be discontinued, especially during
periods of high DBF formation, and (if available on site) replaced with an alternative
preoxidant. For example, potassium permanganate can, in many instances, replace
chlorine for the oxidation of iron and manganese (if adequate contact time is
available) or taste and odor control.
Algae control through source management, in many systems, can be implemented
instead of prechlorination.
Excessive retention time within the treatment plant and chlorine contact facilities that
occur when the plant is not operating can be mitigated in some cases by adjusting the
plant flow rate to more closely match system water demands.
6.2.4 Additional Resources
The following references provide additional information on plant processes that may be
useful as you consider options for minimizing TTHM and HAAS in your distribution system:
AWWA. 2000. Operational Control of Coagulation and Filtration Processes. 2nd Edition.
AWWA Manual M37. Denver: AWWA.
Logsdon, G.S., A.F. Hess, MJ. Chipps, and AJ. Rachwal. 2002. Filter Maintenance and
Operations Guidance Manual. Project #2511. Denver: AwwaRF and AWWA.
Parsons, S.A., B. Jefferson, P. Jarvis, E. Sharp, D. Dixon, B. Bolto, and P. Scales. 2007.
Treatment of Water with Elevated Organic Content. Denver: AwwaRF.
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. Office of Water. EPA 815-R-07-017.
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
Operational Evaluation Guidance Manual 6-22 December 2008
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USEPA. 2005. Membrane Filtration Guidance Manual. Office of Water. EPA 815-R-06-009.
November, 2005. http://www.epa.gov/safewater/disinfection/lt2/compliance.html
USEPA. 2003. LT1ESWTR Disinfection Profiling andBenchmarking: Technical Guidance
Manual Office of Water. EPA 816-R-03-004. May, 2003.
http://www.epa.gov/safewater/mdbp/ltleswtr.html
USEPA. 2002. Long Term 1 Enhanced Surface Water Treatment Rule: A Quick Reference
Guide. Office of Water. EPA 816-F-02-001. January, 2002.
http://www.epa.gov/safewater/mdbp/ltleswtr.html
USEPA. 2002. Filter Backwash Recycling Rule Technical Guidance Manual. Office of Water.
EPA 816-R-02-014. December, 2002. http://www.epa.gov/safewater/filterbackwash.html
USEPA. 1999. Alternative Disinfectants and Oxidants Guidance Manual. Office of Water. EPA
815-R-99-014. April, 1999. http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 1999. Enhanced Coagulation and Enhanced Precipitative Softening Guidance Manual.
EPA 815-R-99-012. http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 1998. Handbook: Optimizing Water Treatment Plant Performance Using the Composite
Correction Program. EPA 625/6-91/027. Available online at:
http ://www. epa. gov/safewater/mdbp/implement.html
6.3 Source Water Management
Source water precursor concentrations and temperature can have significant effects on
DBF formation. For some systems, it may be possible to implement a source water management
plan designed to minimize the occurrence of DBFs. The following sections introduce some
source water management alternatives and identify source water quality parameters that systems
should consider monitoring to aid in process control and in identifying the causes of future OEL
exceedances. These alternatives include:
Watershed management,
Source water monitoring,
Seasonal source water management strategies,
Blending of alternative sources, and
Optimizing intake operation.
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6.3.1 Watershed Management
Watershed management can provide long-term benefits to the water system by helping to
reduce the loading of DBF precursors and nutrients into source waters. Systems should be aware,
however, that the introduction of watershed management practices frequently does not have an
immediate effect on TTHM or HAAS concentrations.
As a starting point, a water system should identify nonpoint and point sources of organic
matter in the watershed. Ideally, the system has delineated the watershed boundary and mapped
out land uses, locations of permitted discharges, storm drains, other significant polluters as well
as natural sources of organic matter. Locations of potential sources of organic matter and other
DBF precursors (or sources of DBFs that have already been formed) should be identified relative
to the locations of tributaries to the reservoir. This exercise will help watershed managers
prioritize efforts to control inputs that are more likely to contribute to TTHM and HAAS
formation. Controlling organic contamination that is likely to immediately impact the intake
should be given the highest priority.
Many successful watershed management programs rely on a committee of stakeholders
working together to improve a lake or reservoir's water quality. Water system representatives
should consider coordinating with stakeholders such as:
Local soil and water conservation districts,
Nonprofit conservation groups,
Farming organizations,
Fish and game commissions, and
Officials from towns located in the watersheds,
as well as other groups that may have an interest in land and water management in the watershed.
By forming a watershed committee that meets regularly, committee members can identify the
various issues and interests that need to be addressed in order to more effectively control nutrient
and organic loading that contributes to TTHM and HAAS formation.
EPA provides technical tools for watershed management at
http://www.epa.gov/owow/watershed/tool s/.
6.3.2 Source Water Monitoring
Source water monitoring is a key first step for systems considering using source water
management for TTHM and HAAS control. Water system personnel that collect and otherwise
handle water quality samples should have adequate training in sample handling techniques.
Operational Evaluation Guidance Manual 6-24 December 2008
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Source water monitoring enables systems
to appropriately manage their water
supplies.
Systems Using either Surface or Ground
Water
To determine changes in water
quality conditions that may impact DBF
levels and precursor removal, systems using
either surface or ground water sources
should consider monitoring the following
parameters:
TOC,
SUVA,
Temperature,
Bromide,
Alkalinity, and
pH.
Systems should also consider monitoring hardness to ensure consistent corrosion control
practices. Chapter 5 provides details on how each monitoring parameter can help evaluate
potential OEL exceedances.
Systems Using Surface Water
Systems using surface water sources may also find it useful to measure additional
parameters such as:
Turbidity,
Secchi disk depth, and
Color
to help identify conditions that adversely affect water treatment, such as storm events,
stratification, and turnover. To detect the early stages of algal blooms, surface water systems
should also consider measuring:
Algae counts,
Chlorophyll a, and
Nutrients (particularly phosphorus).
Operational Evaluation Guidance Manual
6-25
December 2008
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Data will be valuable in proactive efforts to avoid OEL exceedances. Systems may want
to develop a database of historical data that can be analyzed for trends, unusual events, etc.
Historical data can be compared to current data to help identify any potential problems with DBF
precursors or DBF levels.
6.3.3 Seasonal Source Water Management Strategies
Using an alternate ground water source to
supplement surface water supply during the
summer can be an effective strategy to reduce
DBF levels.
Systems can consider using an
alternative water source to reduce high DBF
levels that may occur seasonally. For
example, for systems that use surface water,
high temperatures during the summer may
lead to high DBF formation at the treatment
plant. The system may be able to draw water from an intake located at a lower depth during
summer in order to utilize colder water. Water systems with significant concentrations of
bromide in their raw water supply should consider using an alternative supply (if available) or
blending during high DBF formation periods. Using an available ground water source or high
quality surface water source to supplement a poorer quality surface water supply during high
DBF periods can be a valuable strategy to reduce DBF levels. Ground water tends to have lower
TOC levels and lower temperatures during the summer than surface water and therefore has a
lower DBF formation potential than many surface water sources.
Algal blooms can result in a variety of water quality problems including tastes and odors,
shortened filter runs, increased chlorine demand, increased turbidity, pH fluctuations, and, in
some cases, increased organic DBF precursors. There are several techniques including aeration,
destratification, dredging, and aquatic weed harvesting that have been used with some success
for managing eutrophication. Systems may also have the option of utilizing other sources of
supply that do not have algal blooms. However, it is uncertain whether any of these techniques
significantly reduce organic DBF precursors. Many water systems that use lakes or reservoirs
for their surface water supply have been practicing algae control through the use of chemicals,
such as copper sulfate. It is generally
possible for water systems to detect the early
The effects of algal blooms can be minimized
with an aggressive source water quality
monitoring program.
stages of an algal bloom through an
aggressive source water quality monitoring
program and at that time, use copper sulfate
to control algal growth. Systems that are
considering using copper sulfate should first
consult with the State to determine if it will be allowed. In many States, copper sulfate
application requires a pesticide permit application or certified pesticide applicator. Directly
applying chlorine to a supply from a reservoir undergoing an algal bloom will very likely result
in an increase in TTHM or HAAS concentrations.
6.3.4 Blending of Alternative Sources
Blending water sources is another possible strategy for controlling DBF levels. When
two or more sources are mixed, the characteristics of the blended water depend on the
Operational Evaluation Guidance Manual 6-26 December 2008
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characteristics of the individual sources and the blending ratio. For DBF control, the primary
water quality characteristics of concern for determining blending ratios are:
The types and concentrations of DBF precursors; and
Temperature in each water source.
Other water quality characteristics of the resulting blended water should also be
considered:
Corrosion potential,
Taste,
Loss of disinfectant residual, and
Hardness.
In general, it is more advantageous to blend alternative sources prior to entering the
distribution system. For example, two surface waters should be blended before entering the
plant. When an alternative source of ground water is blended with a surface water source that
requires treatment or with a ground water source that only requires disinfection, the blending
location should be carefully selected. Ideal blending locations include the plant clearwell or a
well-mixed finished water tank where the two waters can mix before entering the system.
Blending may incur infrastructure and operating costs as well as operational changes.
6.3.5 Optimizing Intake Operations
Poor water quality in a reservoir can result from a number of factors including flooding,
thermal stratification, and eutrophication. In some cases, systems can avoid withdrawing poor
quality water with high DBF formation potential by optimizing the management of raw water
intake operations.
One method for avoiding withdrawing water with poor quality is to have raw water
intakes located at several levels. Systems that are able to draw water from multiple depths
should consider regularly measuring TOC, color, temperature, turbidity, bromide, or other
parameters (see Chapter 5) to determine which depth is providing the highest water quality.
During flood events, systems may hold water longer in reservoirs to allow turbidity associated
with agricultural or urban runoff to settle to lower levels. These systems can then draw water
from an alternate intake level where the water quality is better. If thermal stratification occurs,
systems can opt for their intake level with the lowest potential for DBF formation. Some
systems aerate their raw water reservoirs to minimize or prevent thermal stratification, but this
option can lead to other water quality problems such as algal blooms and increased dissolved
oxygen concentrations. Increased dissolved oxygen concentrations can result in microbially-
influenced corrosion in the treatment plant, or more likely, the distribution system. Dissolved
Operational Evaluation Guidance Manual 6-27 December 2008
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oxygen can be consumed by aerobic bacteria causing localized
pH gradients or the production of corrosive metabolites, such
as hydrogen sulfide or iron phosphide, which may result in
increased corrosion (Lee et al., 1980; Tuovinen et al. 1980).
Dissolved oxygen itself is also corrosive, and if not removed
through treatment, it can directly cause lead and copper
corrosion in the distribution system.
Summer and early fall algal blooms tend to occur in
the warmest layer of water, or epilimnion, nearer the surface
of a thermally stratified reservoir. Systems that routinely
monitor their water temperature profile and perform algae
counts or measure chlorophyll a can withdraw water from the
intake level with the lowest algae counts or chlorophyll a
concentration to avoid algae-related problems such as tastes
and odors, shortened filter runs, and DBF precursors. Systems
should be careful, however, to avoid anoxic waters with
elevated concentrations of iron, manganese, and sulfide that
may be found in the bottom layer, or hypolimnion, of their
reservoirs.
Another intake management method involves the
adjustment of the spill structure of a reservoir so that water
from the poor water quality zones or layers can be spilled.
If there are more than one interconnected reservoirs, partitioning the reservoirs and
withdrawing water from the reservoir that has the lowest potential for DBF formation should be
considered. Finally, bypassing basins that contain algae blooms (such as presedimentation
basins) may be appropriate if other efforts are unsuccessful.
Poor water quality in a
reservoir can result from a
number of factors
including flooding, thermal
stratification, and
eutrophication.
6.3.6 Additional Resources
The following references provide additional information on source water management
practices that may help minimize formation of TTHM and HAAS:
AWWA Standard G300-07 Source Water Protection. 2007. Denver: AWWA.
Cooke, G. D. and R. E. Carlson. 1989. Reservoir Management for Water Quality and THM
Precursor Control. Denver: AwwaRF.
Cooke, G.D. and R.H. Kennedy. 2001. Managing drinking water supplies. Lake and Reservoir
Management. 17(3): 157-174.
Kornegay, B.H. 2000. Natural Organic Matter in Drinking Water: Recommendations to Water
Utilities. Denver: AwwaRF.
MacLaughlin, K. and P. Chernin. 2002. Source Water Protection Reference Manual. Denver:
AwwaRF.
Operational Evaluation Guidance Manual
6-28
December 2008
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USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. Office of Water. EPA 815-R-07-017.
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
6.4 References
->nd
AWWA. 2001. Rehabilitation of Water Mains. 2na Edition. AWWA Manual M28. Denver:
AWWA.
Edwards, M. 1997. Predicting DOC Removal During Enhanced Coagulation. Journal AWWA.
89(5):78.
Kirmeyer, G.J., M. Friedman, J. Clement, A. Sandvig, P.P. Noran, K.D. Martel, D. Smith, M.
LeChevallier, C. Volk, E. Antoun, D. Hiltebrand, J. Dykesen, and R. Gushing. 2000. Guidance
Manual for Maintaining Distribution System Water Quality. AwwaRF Report 90798. Project
#357. Denver: AwwaRF.
Lee, S.H., O'Conner, J.T. and Banerji, S.K. (1980). Biologically mediated corrosion and its
effects on water quality in the distribution system. J. AWWA., 72:11:636.
Liao, M.Y. and SJ. Randtke. 1985. Removing Fulvic Acid by Lime Softening. Journal AWWA.
77(8):78.
Randtke S.J., et al. 1994. A Comprehensive Assessment of DBF Precursors Removal by
Enhanced Coagulation and Softening. InProc. Of the 1994 AWWA Annual Conference. Denver:
AWWA.
Randtke S. J. 1999. In Formation and Control of Disinfection By-Products in Drinking Water.
Singer P.C. editor. Denver: AWWA.
Stevens, A.A., L.A. Moore, and RJ. Miltner. 1989. Formation and Control of Non-
Trihalomethane Disinfection By-products. Journal AWWA. 81(8):54-60.
Tikkanen, M., J.H. Schroeter, L.Y.C. Leong, and R. Ganesh. 2001. Guidance Manual for
Disposal of Chlorinated Water. AwwaRF Report 90863. Project #2513. Denver: AwwaRF.
Tuovinen, O.K. et al. (1980). Bacterial, chemical, and mineralogical characteristics of tubercles
in distribution pipelines. J. AWWA, 72:11:626.
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. Office of Water. EPA 815-R-07-017.
http://www.epa.gov/safewater/disinfection/lt2/compliance.html
USEPA. 1999. Enhanced Coagulation and Enhanced Precipitative Softening Guidance Manual.
EPA 815-R-99-012. http://www.epa.gov/safewater/mdbp/implement.html
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Operational Evaluation Guidance Manual 6-30 December 2008
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Appendix A
Fundamentals of TTHM and HAAS Formation
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A.I Introduction
The formation of total trihalomethanes (TTHM) and haloacetic acids (five) (HAAS) is a
function of many factors, including:
Precursor concentration,
Chlorine dose,
Chlorination pH,
Temperature,
Contact time, and
Bromide ion concentration.
The purpose of this appendix is to provide a brief summary of the factors that affect the
formation of these disinfection byproducts (DBFs) in water treatment processes and distribution
systems. More detailed information on this subject can be found in the existing literature,
including the additional resources in section A.4:
A.2 Formation of TTHM and HAAS
All organic DBFs (and oxidation byproducts) are formed by the reaction between organic
substances, inorganic compounds such as bromide, and oxidizing agents that are added to water
during treatment (e.g., chlorine). The following are the major factors affecting the type and
amount of TTHM and HAAS formed.
Type of disinfectant, dose, and residual concentration;
Contact time and mixing conditions between disinfectant (oxidant) and precursors;
Concentration and characteristics of precursors;
Water temperature; and
Water chemistry (including pH and bromide ion concentration).
Sections A.2.1 through A.2.5 provide a discussion of each major factor.
A.2.1 Type of Disinfectant
All other factors being equal, TTHM and HAAS formation are highest for waters that are
chlorinated either for primary disinfection, residual disinfection, or both. All chemical
Operational Evaluation Guidance Manual A-l December 2008
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disinfectants, however, are known to form various types of DBFs. The following is a discussion
of DBF formation by alternative disinfectants including chloramines, chlorine dioxide,
ultraviolet (UV), and ozone.
Chloramines
Many water systems have experienced significant decreases in TTHM and HAAS levels
when switching from free chlorine to chloramines in the distribution system. The AwwaRF
manual, Optimizing Chloramine Treatment (Kirmeyer et al. 2004), reports typical reductions in
TTHM concentrations of 40 to 80 percent after chloramine conversion, although reductions as
high as 95 percent were observed at some water systems. TTHM formation is known to still
occur under chloraminated conditions, but at a very slow rate. Formation of TTHM is possibly
attributable to hydrolysis of monochloramine to hypochlorous acid, which reacts with DBF
precursors to form TTHM; the presence of free chlorine that has not reacted with ammonia to
form chloramines; or the transfer of a chlorine atom from dichloramine to an organic compound
(Kirmeyer et al. 2004 and references therein). Several studies have reported minimal production
of haloacetic acids (HAAs) such as dichloracetic acid and trichloracetic acid by chloramines.
Other studies, however, show formation of brominated HAAs by chloramines.
The design and location of chlorine and ammonia feed systems to form chloramines can
have significant implications on TTHM and HAAS formation. Any contact time with free
chlorine prior to the addition of ammonia will increase TTHM and HAAS concentrations.
Additionally, insufficient mixing of chlorine and ammonia could lead to additional TTHM and
HAAS production.
Chlorine Dioxide
Under typical water treatment conditions, chlorine dioxide oxidizes rather than
chlorinates organic matter and thus, does not form chlorination byproducts such as TTHM and
HAAS. Chlorine produced as an impurity in the chlorine dioxide generation process, however,
can lead to formation of TTHM and HAAS. Chlorine dioxide can react with organic matter to
form chlorite, which is a regulated DBF, and chlorate.
Ultraviolet Light
Multiple research studies have found that UV light at doses commonly used at water
treatment plants does not effect the formation of THMs or HAAs in subsequent chlorination
(USEPA 2006 and references therein).
Ozone
Ozone does not directly produce chlorinated DBFs. However, if chlorine is added before
or after ozonation, mixed bromo-chloro DBFs as well as chlorinated DBFs can form. Ozone can
alter the characteristics of precursors and affect the concentration and speciation of halogenated
DBFs when chlorine is subsequently added downstream. In waters with sufficiently high
bromide concentrations, ozonation can lead to the formation of bromate and other brominated
DBFs. Bromate, like TTHM and HAAS, is a regulated DBF. Ozonation of natural waters also
Operational Evaluation Guidance Manual A-2 December 2008
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produces aldehydes, haloketones, ketoacids, carboxylic acids, and other types of biodegradable
organic material.
A.2.2 Chlorine Dose
Free chlorine can be introduced to water directly as a primary or secondary disinfectant,
or as a byproduct of the manufacturing of chlorine dioxide and chloramines. As the
concentration of chlorine increases, the production of DBFs increases. The formation reactions
may take place in the treatment plant and the distribution system. Formation reactions continue
as long as precursors and disinfectant are present (Krasner, 1999 and references therein).
In general, the impact of chlorine concentration is greater during primary disinfection
than during secondary disinfection. The amount of chlorine added during primary disinfection is
usually less than the long-term demand; therefore, the concentration of chlorine is often the
limiting factor while un-reacted precursors are available. Conversely, reactions in the
distribution system are often precursor limited since an excess of chlorine is added to the water
to maintain a residual concentration (Singer and Reckhow, 1999). DBF formation reactions can
become disinfectant-limited, however, when the free chlorine residual drops to low levels. As a
rule of thumb, Singer and Reckhow (1999) suggested this event takes place when the chlorine
concentration drops below approximately 0.3 mg/L.
Booster disinfection is applied in some systems to raise disinfectant residual
concentration, especially in remote areas of the distribution system or near storage tanks where
water age may be high and disinfectant residuals can be low. The additional chlorine dose
applied to the water at these booster facilities may increase THM and HAA levels. Further,
booster chlorination can maintain high HAA concentrations because the increased disinfection
residuals can prevent the biodegradation of HAAs. However booster chlorination can also be
useful in decreasing TTHM and HAAS levels by reducing the concentration of secondary
disinfectant needed in the finished water leaving the plant.
A.2.3 Contact Time
The longer the contact time between disinfectant/oxidant and precursors, the greater the
amount of DBFs that can form. Generally, DBFs continue to form in drinking water as long as
chlorine residual and precursors are present. In chlorinated systems, the highest TTHM levels
usually occur where water is the oldest. Conversely, HAAs cannot be consistently related to
water age because HAAs are known to biodegrade over time when the disinfectant residual is
low. This might result in relatively low HAA concentrations in areas of the distribution system
where disinfectant residuals are depleted.
A.2.4 Concentration and Characteristics of Precursors
The formation of TTHM and HAAS is related to the concentration of precursors at the
point of chlorination. In general, greater DBF levels are formed in waters with higher
concentrations of precursors.
Operational Evaluation Guidance Manual A-3 December 2008
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In most water sources, natural organic matter (NOM) is the major constituent of organic
substances and DBF precursors. Total organic carbon (TOC) is typically used as a surrogate
measure for precursor levels and is used in Stage 1 DBPR to determine precursor removal
compliance. Dissolved organic carbon (DOC) and UV absorption at 254 nm [UV254] are also often
used as surrogate parameters for monitoring precursor levels.
Studies conducted with different fractions of NOM have indicated the reaction between
chlorine and NOM with high aromatic content tends to form higher DBF levels than NOM with
low aromatic content. For this reason, UV254, which is generally linked to the aromatic and
unsaturated components of NOM, is considered a good predictor of the tendency of a source
water to form TTHM and HAAS (Owen 1998; Singer and Reckhow, 1999).
Specific ultraviolet light absorbance (SUVA) is also often used to characterize
aromaticity and molecular weight distribution of NOM. This parameter is defined as the ratio
between UV254 and the dissolved organic carbon (DOC) concentration of water (Letterman et al.,
1999). It should be noted, that the more highly aromatic precursors, characterized by high
UV254, in source waters are more easily removed by coagulation. Thus, it is the UV254
measurement immediately upstream of the point(s) of chlorination within a treatment plant that
is more directly related to THM and HAA formation potential.
A.2.5 Water Temperature
The rate of formation of TTHM and HAAS increases with increasing temperature.
Consequently, the highest THM and HAA levels may occur in the warm summer months.
However, water demands are often higher during these months, resulting in lower water age
within the distribution system. Furthermore, high temperature conditions in the distribution
system promote the accelerated depletion of residual chlorine, which can reduce DBF formation
and allow biodegradation of HAAs unless chlorine dosages are increased to maintain high
residuals (Singer and Reckhow, 1999). For these reasons, depending on the specific system, the
highest THM and HAA levels may be observed during months that are warm, but not necessarily
the warmest.
A.2.6 Water Chemistry
In the presence of precursors and chlorine, TTHM formation generally increases with
increasing pH, whereas the formation of some HAAS species decreases with increasing pH. The
increased THMs production at high pH is likely promoted by base hydrolysis (favored at high
pH). HAAs are not sensitive to base hydrolysis but their precursors are. Consequently, pH can
alter their formation pathways leading to decreased production with increasing pH (Singer and
Reckhow, 1999).
Studies have shown that the rate of TTHM formation is higher in waters with increased
bromide concentrations (Krasner, 1999 and references therein). If the ratio of bromide to
precursors (measured as TOC) increases, the percentage of brominated DBFs also increases.
Operational Evaluation Guidance Manual A-4 December 2008
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A.3 References
Kirmeyer, G.J., M. LeChevallier, H. Barbeau, K. Martel, G. Thompson, L. Radder, W. Klement,
and A. Flores. 2004. Optimizing Chloramine Treatment, 2nd edition. AwwaRF Report 90993.
Project #2760. Denver: AwwaRF and AWWA.
Krasner S. W., 1999. Chemistry of disinfection by-product formation, InFormation and control
of disinfection by-products in drinking water. Singer, P.C. (editor). Denver, CO: AWWA.
Letterman, R.D., A. Amirtharajah, and C.R. O'Melia. 1999. Coagulation and flocculation. In
Water quality and treatment. 5th edition. New York, NY: McGraw-Hill.
Owen, D.M., 1998. Removal of DBF precursors by GAC adsorption. Denver CO: AwwaRF.
th
Singer, P.C. andD.A. Reckhow. 1999. Chemical oxidation. In Water Quality and Treatment. 5
edition. New York, NY: McGraw-Hill.
USEPA. 2006. Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced
Surface Water Treatment Rule. EPA 815-R-06-007. Available online at:
http://www.epa.gov/safewater/disinfection/lt2/compliance.html.
A.4 Additional Resources
Baribeau, H., L. Boulos, H. Haileselassi, G. Crozes, P. Singer, C. Nichols, S. Schlesinger, R.
Gullick, S. Wiliams, R. Williams, L. Fountleroy, S. Andrews, and E. Moffat. 2006. Formation
and Decay of Disinfection By-Products in the Distribution System. Denver, CO. AwwaRF.
Bichsel, Y., and Von Gunten U., 2000. Environmental Science and Technology, 34 (13): 2784.
USEPA. 1999a. Enhanced Coagulation and Enhanced Precipitative Softening Guidance
Manual. Document #815-R-99-012. Available online at:
http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 1999b. Alternative Disinfectants and Oxidants Guidance Manual. EPA 815-R-99-014.
Available online at: http://www.epa.gov/safewater/mdbp/implement.html
USEPA. 2001. Controlling Disinfection By-Products andMicrobial Contaminants in Drinking
Water. Document #600-R-01-110. Available online at:
http ://www. epa.gov/nrmrl/pubsO 199. html
USEPA. 2007. Simultaneous Compliance Guidance Manual for the Long Term 2 and Stage 2
DBF Rules. EPA 815-R-07-017. Available online at:
http://www.epa.gov/safewater/disinfection/stage2/compliance.html
Operational Evaluation Guidance Manual A-5 December 2008
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White, G.C. 1992. Handbook ofChlorination andAlternative Disinfectants. 3rd Edition.
New York: Van Nostrand Reinhold Co.
Operational Evaluation Guidance Manual A-6 December 2008
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Appendix B
Example Operational Evaluation Report
for
OEL Exceedances Due to Changes in Source Water Quality with
Limited Operational Evaluation Scope Approved by the State
-------
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Operational Evaluation Reporting Form
Page I of 2
I. GENERAL INFORMATION
A. Facility Information
Facility Name: Elm City Water Department
Facility Address: 3456 East Street
City:
PVVSID: US4598765
Elm City
State: US Zip: 12345
B. Report Prepared by:
(Print): Ronald Doe
Date prepared:
July 31, 2018
(Signature):
Contact Telephone Number: 123-465-7890
II. MONITORING RESULTS
A. Provide the Compliance Monitoring Site(s) where the DEL was Exceeded.
Stage 2 DBPR compliance site #7: Located in CedarvMIe neighborhood
.'Vote: The site name or number should correspond to a site ir, your Stage 2 DBPR compliance monitoring
plan.
B. Monitoring Results for the Sitefs) Identified in II.A (include duplicate pages if there was more than
one exceedance}
1. Check TTHM or HAAS to indicate which result caused the OEL
exceedance.
2. Enter your results for TTHM or HAAS (whichever you checked above).
I TTHM
I HAAS
Date sample was
collected
TTHM (mg/L)
HAAS (mg/L)
Quarter
Results from
Two Quarters
Ago
A
12/02/2017
0.063
Prior Quarter's
Results
B
03/05/2018
0.067
Current
Quarter
C
06/03/201 8
0.098
Operational
Evaluation Value
D = (A+B+{2*C)}/4
0.082
Note: ,' he operational evaluation value is calculated by summing the two previous quarters of TTHM or HAAS
values pius twice the current quarter value, divided by four, if the value exceeds O.G80 mg/L for TTHM or 0.060
mg/L for HAAS, an OEL exceedance has occurred.
C. Has an OEL exceedance occurred at this location in the past?
If NO, proceed to item D. If YES, when did
exceedance occur?
0Yes
DNO
2nd quarter 2014. See attachment II.C for
additional details.
Was the cause determined for the previous exceedance(s)?
Are the previous evaluations/determinations applicable to the current OEL
exceedance?
QYes
DYes
El No
0No
Operational Evaluation Guidance Manual
B-l
December 2008
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Operational Evaluation Reporting Form Page 2 of 2
I. OPERATIONAL EVALUATION FINDINGS
A. Did the State allow you to limit the scope of the operational evaluation? El Yes D No
If NO, proceed to item B. If YES, attach written correspondence from the State.
D Yes El No
B. Did the distribution system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item C. If YES or POSSIBLY, explain (attach additional pages if
necessary):
D Yes El No
C. Did the treatment system cause or contribute to your OEL exceedance(s)?
| Possibly
If NO, proceed to item D. If YES or POSSIBLY, explain (attach additional pages if
necessary):
El Yes D No
D. Did source water quality cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item E. If YES or POSSIBLY, explain (attach additional pages if
necessary):
See attachment III.B
E. Attach all supporting operational or other data that support the determination of the cause(s)
of your OEL exceedance(s).
F. If you are unable to determine the cause(s) of the OEL exceedance(s), list the steps that you
can use to better identify the cause(s) in the future (attach additional pages if necessary):
G. List steps that could be considered to minimize future OEL exceedances (attach additional
pages if necessary)
See attachment III.G
H. Total Number of Pages Submitted, Including Attachments and Checklists: 12
Operational Evaluation Guidance Manual B-2 December 2008
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July 1,2018
Mr. Ronald Doe
Elm City Water Department
3456 East Street
Elm City, US 12345
RE: Request for limiting scope of operational evaluation level exceedence occurring for the 2rd
quarter 2018
Dear Mr. Doe:
Thank you for sending the raw and finished water TOC data from the Elm City Water Treatment
Plant for May 25 through June 5. Based on our review of this data and based on our telephone
conversation on June 15, 2018, we have approved your request to limit the scope of your
operational evaluation to your source water and treatment only. Please keep this letter for your
records and submit it along with your operational evaluation report.
Sincerely,
William H. Smith
State Regulator, Drinking Water Program
Operational Evaluation Guidance Manual B-3 December 2008
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Attachments
II.C. Past Exceedances
Historic DBP data are presented below for Stage 2 DBPR monitoring site # 7. During 2nd quarter of 2014,
the TTHM level for Stage 2 DBPR monitoring site # 7 was 95 ug/L. Using the current definition of OEL,
the computed THM value for the 2nd quarter of 2014 is 82 ug/L, and therefore an OEL exceedance
occurred.
TTHM Data (ug/L) HAAS Data (ug/L)
Quarter 1234 Quarter 1234
2012 53 58 82 58 2012 43 58 45 49
2013 51 65 79 75 2013 51 49 56 41
2014 62 95 72 69 2014 46 64 41 52
2015 58 61 81 66 2015 48 61 52 56
2016 52 53 75 79 2016 34 44 53 51
III.B. Changes in Source Water
The most probable cause of the DBP excursion noted during the June 2018 sampling event was a rapid
increase of the organic matter concentration in the Softwood River. A heavy rainfall event in May 31 -
June 1, 2018 was identified as the primary cause of TOC and turbidity increase. A significant portion of
the land upstream of the treatment plant is agricultural land, and excessive runoff from these areas
causes high concentration of organic matter (TOC) and soil particles (turbidity). Following two days of
heavy rainfall on May 31 - June 1, 2018, the TOC measured in the plant raw water increased from 2.7
mg/L on June 1, 2018, to 8.4 mg/L on June 3, 2018. At the same time, turbidity of the source water also
increased from 5 NTU on June 1, 2018, to a maximum of 98 NTU on June 3, 2018.
The coagulant (ferric chloride) dose was steadily increased from 20 mg/L to 75 mg/L during June 1-3,
2018, to match water quality changes. For the duration of this high turbidity/ high TOC event, the pH of
coagulation was maintained between 6.1 and 6.3. The concentration of TOC in the plant effluent
increased from 1.8 mg/L on Junel, 2018, to 3.8 mg/L on June 2, 2018. Jar testing conducted at the time
of the event indicated that a further increase of the coagulant dose (dosages up to 120 mg/L were tested)
would have not significantly improved TOC removal under the pH conditions presently used to conduct
the coagulation process. The chlorine residual for the finished water leaving the treatment plant is
maintained at 2 mg/L.
Monitoring sites # 7 and 8 are both supplied by Softwood River water. The hydraulic residence time
between the Softwood plant and these monitoring sites is approximately three days. Laboratory tests
indicated that for an initial chlorine residual of 2 mg/L, the THM levels will exceed 80 mg/L within three
days when the TOC of the finished water increases above 3 mg/L.
The following data are attached to support the conclusion stated above:
1. TOC and turbidity data for raw and finished water from May 25 2018, to June 4, 2018 (not included as
part of this example).
2. Jar test results conducted with Softwood river water for TOC ranging from 1.0 to 3.0 mg/L (not included
as part of this example).
Operational Evaluation Guidance Manual B-4 December 2008
-------
III.G. Minimizing Future Exceedances
Because some of the runoff comes from agricultural areas, the turbidity causing suspended soil particles
are also a source of TOC because of the adsorbed organic matter to the soil particles. The raw water
intake needs to be skillfully managed during rainfall events. The raw water intake has two levels. During
a storm event, the suspended particles from agricultural runoff are likely to remain in suspension as a
result of turbulence, and therefore the top level intake can be closed. Water can be withdrawn from the
lower intake during the storm. As the storm subsides and turbulence decreases, particles will tend to
settle down, and the lower level intake can be closed allowing water to be withdrawn from the upper level
intake only. After the turbidity returns to normal, the bottom intake level can be opened also. We will
conduct additional testing to determine the optimum operation of the intake system during storm events.
In addition to evaluating intake operations, we will investigate the use of a coagulant aid to address short
term turbidity and TOC spikes. We will identify various options and perform jar testing. We will also
investigate whether or not lower sedimentation flow rates would have helped reduce TOC concentrations
in the plant effluent.
Operational Evaluation Guidance Manual B-5 December 2008
-------
Treatment Process Evaluation Checklist Page 1 of 4
I NO DATA AVAILABLE
Facility Name: Elm City Water
Checklist Completed by: Ronald Doe Date: July 31, 2018
A. Review finished water data for the time period prior to the OEL exceedance(s) and compare to
historical finished water data using the following questions:
Were DBP precursors (TOG, DOC, SUVA, bromide, etc.) higher than normal? 0 Yes Q No
Was finished water pH higher or lower than normal? fJ Yes 0 No
Was the finished water temperature higher than normal? D Yes El No
Was finished water turbidity higher than normal? D Yes 0 No
Was the disinfectant concentration leaving the plant(s) higher than normal? D Yes 0 No
Were finished water TTHM/H AA5 levels higher than normal? 0 Yes D No
Were operational and water quality data available to the system operator for 0 Yes r~| NO
effective decision making?
B. Does the treatment process include predisinfection? 0 Yes D No
If NO, proceed to item C. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D 0 Was disinfected raw water stored for an unusually long time?
D 0 Were treatment plant flows lower than normal?
0 n Were treatment plant flows equally distributed among different trains?
D 0 Were water temperatures high or warmer than usual?
D 0 Were chlorine feed rates outside the normal range?
0 n Was a disinfectant residual present in the treatment train following predisinfection?
D 0 Were online instruments utilized for process control?
D 0 Did you switch to free chlorine as the oxidant?
n 0 Was there a recent change (or addition) of pre-oxidant?
D 0 Did you change the location of the predisinfection application?
C. Does your treatment process include presedimentation? D Yes 0 No
If NO, proceed to item D. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D n Were flows low?
D n Were flows high?
D D Were online instruments utilized for process control?
D n Was sludge removed from the presedimentation basin?
D D Was sludge allowed to accumulate for an excessively long time?
D D Do you add a coagulant to your presedimentation basin?
D n Was there a problem with the coagulant feed?
Operational Evaluation Guidance Manual B-6 December 2008
-------
Treatment Process Evaluation Checklist Page 2 of 4
D. Does your treatment process include coagulation and/or flocculation? El Yes Q No
If NO, proceed to item E. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
r-i o Were there any feed pump failures or were feed pumps operating at improper feed
rates?
El D Were chemical feed systems controlled by flow pacing?
El D Were there changes in coagulation practices or the feed point?
D El Did you change the type or manufacturer of the coagulant?
Q 0 Do you suspect that the coagulant in use at the time of the OEL exceedance did
not meet industry standards?
D El Did the pH or alkalinity change at the point of coagulant addition?
D El Were there broken or plugged mixers?
D El Were flow rates above the design rate or was there short-circuiting?
Does your treatment process include sedimentation or clarification? El Yes D No
If NO, proceed to item F. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
m ra Were there changes in plant flow rate that may have resulted in a decrease in
settling time or carry-over of process solids?
El D Were settled water turbidities higher than normal?
rn ra Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
Q El Was there any maintenance in the basin that may have stirred sludge from the
bottom of the basin and caused it to carry over to the point of disinfectant
addition?
r-i pi Was sludge allowed to accumulate for an excessively long time or was there a
malfunction in the sludge removal equipment?
Operational Evaluation Guidance Manual B-7 December 2008
-------
Treatment Process Evaluation Checklist Page 3 of 4
F. Does your treatment process include filtration? 0Yes Q No
If NO, proceed to item G. If YES, answerthe following questions forthe period in which
an OEL excee dance occurred:
Yes No
ra n Was there an increase in individual or combined filter effluent turbidity or particle
counts?
0 D Was there an increase in turbidity or particle loading onto the filters?
r-1 pj Was there an increase in flow onto the filters or malfunction of the rate of flow
controllers?
rn pj Were any filters taken off-line for an extended period of time that caused the other
filters to operate near maximum design capacity and created the conditions for
possible breakthrough?
n 0 Were any filters operated beyond their normal filter run time?
r-1 pj Were there any unusual spikes in individual filter effluent turbidity (which may
indicate particulate or colloidal TOC breakthrough) in the days leading to the
excursion?
0 D Were all filters run in a filter-to-waste mode during initial filter ripen ing?
n fj If GAC filters are used, is it possible the adsorptive capacity of the GACbedwas
reached before reactivation occurred (leave blank if not applicable)?
Q fj If biological filtration is used, were there any process upsets that may have
resulted in the breakthrough of TOC (leave blank if not applicable)?
G. Does your treatment process include primary disinfection by injecting chlorine N
prior to a clearwell?
If NO, proceed to item H. If YES, answer the following questions for the period in which
an OEL excee dance occurred:
Yes No
Q |2j Was there a sudden increase in the amount of chlorine fed or an increase in the
chlorine residual?
n 0 Was there an increase in clearwell holding time?
n 0 Was the plant shut down or were plant flows low?
D 0 Was there an increase in clearwell water temperature?
n 0 Did you switch to free chlorine recently as the primary disinfectant?
D 0 Was the inactivation of Giardia and/or viruses exceptionally high?
r-1 ra Was there a change in the mixing strategy (i.e., mixers not used, adjustment of
tank level)?
H. Does your plant recycle spent filter backwash or other streams? fjYes 0 No
If NO, proceed to item I. If YES, answer the following questions forthe period in which
an OEL excee dance occurred:
Yes No
rn rn Did a change in the recycle stream quality contribute to increased DBP precursor
loading that was not addressed by treatment plant processes?
D D Did a recycle event result in flows in excess of typical or design flows?
Operational Evaluation Guidance Manual B-8 December 2008
-------
Treatment Process Evaluation Checklist Page 4 of 4
I. Do you inject a disinfectant after your clearwelI to maintain a distribution I-IY pi MO
system residual?
If NO, proceed to item J. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D D Was there a sudden increase in the amount of chlorine fed?
D D Was there a switch from chloramines to free chlorine for a burnout period?
D D If using chloramines, was the chlorine to ammonia ratio in the proper range?
D D Was there a problem with either chlorine or ammonia mixing?
Did concern about complying with a rule other than Stage 2 DBPR, such as the 1-1Y p, M
Lead and Copper rule, the LT2ESWTR, or any other rule constrain your options Ld NO
to reduce the DBP levels at this site? For example, are you limited by other
treatment targets/requirements in your ability to control precursors in
coagulation/flocculation?
If NO, proceed to item K. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
K. Conclusion
I Yes El No
Did treatment factors and/or variations in the plant performance contribute to the
OEL exceedance(s)? Q Possibly
If YES or POSSIBLY, explain below.
Operational Evaluation Guidance Manual B-9 December 2008
-------
Source Water Evaluation Checklist Page 1 of 2
I NO DATA AVAILABLE
System Name: Elm City Water Department
Checklist Completed by: Ronald Doe Date: July 31, 2018
A. Do you have source water temperature data? El Yes D No
If NO, proceed to item B. If YES, was the source water temperature ., 131 MO
high?
If NO, proceed to item B. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was the raw water storage time longer than usual?
n D Did you place another water source on-line?
Q fj Were river/reservoir flow rates lower than usual? If yes, indicate the location of
lower flow rates and the anticipated impact on the OEL exceedance.
Q fj Did point or non-point sources in the watershed contribute to the OEL
exceedance?
B. Do you have data that characterizes organic matter in your source water (e.g., Y
TOC, DOC, SUVA, color, THM formation potential)? LJYes
If NO, proceed to item C. If YES, were these values higher than
._ 0 Yes D No
normal?
If NO, proceed to item C. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
El D Did heavy rainfall or snowmelt occur in the watershed?
n 0 Did you place another water source on-line?
n 0 Did lake or reservoir turnover occur?
n i-i Did point or non-point sources in the watershed contribute to the OEL
exceedance?
n 0 Did an algal bloom occur in the source water?
n n If algal blooms were present, were appropriate algae control measures
employed (e.g., addition of copper sulfate)?
n 0 Did a taste and odor incident occur?
C. Do you have source water bromide data? D Yes 0 No
If NO, proceed to item D. If YES, were the bromide levels higher or y ii N
lower than normal? es
If NO, proceed to item D. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n n Has saltwater intrusion occurred?
n D Are you experiencing a long-term drought?
n fj Did heavy rainfall or snowmelt occur in the watershed?
n fj Did you place another water source on-line?
n D Are you aware of any industrial spills in the watershed?
Operational Evaluation Guidance Manual B-10 December 2008
-------
Source Water Evaluation Checklist Page 2 of 2
D. Do you have source water turbidity or particle count data? 0 Yes Q No
If NO, proceed to item E. If YES, were the turbidity values or particle n No
counts higherthan normal? LJ es |_J
If NO, proceed to item E. If YES, answerthe following questions for the time period
prior to the OEL exceedance.
Yes No
n 0 Did lake or reservoir turnover occur?
El D Did heavy rainfall or snowmelt occur in the watershed?
n 0 Did logging, fires, or landslides occur in the watershed?
n 0 Were river/reservoir flow rates higher than normal?
E. Do you have source water pH or alkalinity data? 0Yes D No
If NO, proceed to item F. If YES, was the pH or alkalinity different from _ N
normal values?
If NO, proceed to item F. If YES, answerthe following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was there an algal bloom in the source water?
D fJ If algal blooms were present, were algae control measures employed?
n D Did heavy rainfall or snowmelt occur in the watershed?
D fj Has the PWS experienced diurnal pH changes in source water?
F. Conclusion
0Yes D No
Did source water quality factors contribute to your OEL exceedance?
fj Possibly
If YES or POSSIBLY, explain below.
We had heavy rainfall on May 31 -June 1, 2018, with runoff from agricultural land that brought
increased turbidity and organic DBP precursors in our source water.
Operational Evaluation Guidance Manual B-ll December 2008
-------
-------
Appendix C
Example Operational Evaluation Report
for
OEL Exceedance Due to Changes in Distribution System Operation
-------
-------
Operational Evaluation Reporting Form
Page i of 2
I. GENERAL INFORMATION
A. Facility Information
Facility Name: Elm City Water Dept.
PWSID: US4598762
Facility Address: 34561 East Street
City:
Elm City
State: US Zip: 12345
B. Report Prepared by:
(Print): Ronald Doe
(Signature):
Date prepared:
June 22.2012
Contact Telephone Number: 123-555-9876
II. MONITORING RESULTS
A. Provide the Compliance Monitoring Site(s) where the DEL was Exceeded.
Stage 2 DBPR compliance monitoring location #2: Located in Pineville neighborhood
Note: The site .name or number should correspond to a site in your Stage 2 DBPR compiiarice monitoring
plan.
B. Monitoring Results for the Site(s) Identified in II.A (include duplicate pages if there was more than
one exceedance}
I. Check TTHM or HAA5 to indicate which result caused the DEL
exceedance.
p] TTHM
2. Enter your results for TTHM or HAA5 (whichever you checked above).
Date sample was
col lected
TTHM (mg/L)
HAAS (mg/L)
Quarter
Results from
Two Quarters
Ago
A
12/03/2011
0.065
Prior Quarter's
Results
B
03/03/2012
0.072
Current
Quarter
C
06/03/2012
0.098
Operational
Evaluation Value
D = {A+B+(2*C))/4
0.083
Note: The operational evaluation value is calculated by summing the two previous quarters of 1THM or HAAS
values pins twice the current quarter value, divided by four, if the vaiue exceeds 0.080 mg/L for TTHM or 0.060
mg/L forHAAS, an DEL exceedance has occurred.
C. Has an OEL exceedance occurred at this location in the past?
If NO, proceed to item D, If YES. when did
exceedance occur?
DYes
El No
Was the cause determined for the previous exceedance(s)?
Are the previous evaluations/determinations applicable to the current OEL
exceedance?
QYes
ClYes
DNO
DNO
Operational Evaluation Guidance Manual
C-l
December 2008
-------
Operational Evaluation Reporting Form Page 2 of 2
I. OPERATIONAL EVALUATION FINDINGS
A. Did the State allow you to limit the scope of the operational evaluation? D Yes El No
If NO, proceed to item B. If YES, attach written correspondence from the State.
El Yes D No
B. Did the distribution system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item C. If YES or POSSIBLY, explain (attach additional pages if
necessary):
See attachment III.D
D Yes El No
C. Did the treatment system cause or contribute to your OEL exceedance(s)?
[] Possibly
If NO, proceed to item D. If YES or POSSIBLY, explain (attach additional pages if
necessary):
D Yes El No
D. Did source water quality cause or contribute to your OEL exceedance(s)?
LJ Possibly
If NO, proceed to item E. If YES or POSSIBLY, explain (attach additional pages if
necessary):
E. Attach all supporting operational or other data that support the determination of the cause(s)
of your OEL exceedance(s).
F. If you are unable to determine the cause(s) of the OEL exceedance(s), list the steps that you
can use to better identify the cause(s) in the future (attach additional pages if necessary):
G. List steps that could be considered to minimize future OEL exceedances (attach additional
pages if necessary)
See attachment III.G
H. Total Number of Pages Submitted, Including Attachments and Checklists: 12
Operational Evaluation Guidance Manual C-2 December 2008
-------
Attachments
III.D. Changes in the Distribution System
A main break in the Pineville neighborhood occurred on June 2, 2012, early in the morning. The system
pressure in the vicinity of the main break dropped to 30 psi, which is significantly below the normal
pressure range for that area (50-60 psi). SCADA data indicated that rapid drawdown from the Pineville
tank began on June 3, 2012, at 5 am. The water level in the tank dropped to a hydraulic grade of 80 feet
at 7 am. The normal minimum hydraulic grade for the tank is 115 feet as determined from historic
SCADA data for the tank. It is anticipated that the rapid and excessive drawdown was due to the main
break and subsequent pressure drop in the region. The tank did not refill prior to the morning peak
demand period (7 am to 9 am), and the water level dropped to 70 feet during this period, as evident from
the SCADA data.
The DBP sampling at monitoring site #2 was conducted on June 3 at 10 am. The city's hydraulic model
was used to predict whether a significant portion of the water at that site originated from the Pineville
tank. A main break was simulated and the pressures in the surrounding areas were within 5 psi of what
was observed on June 3, 2012, in the early morning. The results from the model indicated that a
significant portion of the water at monitoring site # 2 originated from the Pineville tank during the morning
hours of June 3.
The Pineville elevated tank has a large diameter inlet (36-inch) at the base of the tank. When the tank
supplies water during normal conditions, water comes from the bottom portion of the tank where the
turnover is expected to be good and water age is expected to be relatively low. However, during the main
break that resulted in pressure loss in the vicinity of monitoring site # 2, water was introduced into the
area from the top portion of that tank. It is anticipated that the top portion of the tank remains relatively
unmixed and therefore has high water age and DBP levels.
The following data are attached to support the conclusion stated above:
1. Schematic of distribution system map
2. SCADA data for Pineville tank level from May 3, 2012, to June 4, 2012 (not included as part of this
example)
3. Results from hydraulic model indicating contribution of Pineville tank water to monitoring site # 2 (not
included as part of this example)
III.G. Minimizing Future Exceedances
The water turnover in the top portion of Pineville tank needs to be improved to minimize water age and
DBP formation in that part of the tank so that high DBP levels are not introduced into the distribution
system. We plan to reduce the inlet diameter to increase the inlet velocity. The water jet will then reach
the top portion of the tank and mix the stored water in that portion of the tank. Computational fluid
dynamic modeling for the tank indicated that under current inflow rate conditions, the inlet pipe diameter
needs to be 12-inches to produce a water jet sufficient enough to reach the top portion of the tank.
Operational Evaluation Guidance Manual C-3 December 2008
-------
Distribution System Evaluation Checklist Page 1 of 2
System Name: Elm City Water Dept.
Checklist Completed by: Ronald Doe Date: June 22, 2012
A. Do you have disinfectant residual or temperature data for the monitoring ...
location where you experienced the OEL exceedance? LJ es |_J
If NO, proceed to item B. If YES, answer the following questions forthe period in which
an OEL exceedance occurred:
Yes No
Q 0 Was the water temperature higher than normal for that time of the year at that
location?
n 0 Was the disinfectant residual lower than normal for that time of the year at that
location?
Q 0 Was the disinfectant residual higher than normal for that time of the year at that
location?
B. Do you have maintenance records available forthe time period just prior to the pjY |~| No
OEL exceedance?
If NO, proceed to item C. If YES, answer the following questions:
Yes No
El D Did any line breaks or replacements occur in the vicinity of the exceedance?
D 0 Were any storage tanks or reservoirs taken off-line and cleaned?
Q 0 Did flushing or other hydraulic disturbances (e.g., fires) occur in the vicinity of
the exceedance?
n 0 Were any valves operated in the vicinity of the OEL exceedances?
C. If your system is metered, do you have access to historical records showing ii N
water use at individual service connections?
If NO, proceed to item D. If YES, was overall water use in your system Y N
unusually low, indicating higher than normal waterage? LJ es LJ
D. Do you have high-volume customers in your system (e.g., an industrial ii N
processing plant)?
If NO, proceed to item E. If YES, was there a change in water use by a iIY rn M
high-volume customer?
E. Is there a finished water storage facility hydraulically upstream from the Y |~| No
monitoring location where you experienced the OEL exceedance?
If NO, proceed to item F. If YES, review storage facility operations and water quality
data to answer the following questions forthe period in which the OEL exceedance
occu rred:
Yes No
n 0 Was a disinfectant residual detected in the stored water or at the tank outlet?
0 D Do you know of any mixing problems with the tank or reservoir?
0 D Does the facility operate in "last in-first out" mode?
|7| Q Was the tank or reservoir drawn down more than usual prior to OEL
exceedance, indicating a possible discharge of stagnant water?
Q 0 Was there a change in water level fluctuations that would have resulted in
increased water age within the tank or reservoir?
Operational Evaluation Guidance Manual C-4 December 2008
-------
Distribution System Evaluation Checklist Page 2 of 2
Does your system practice booster chlorination? QYes 0 No
If NO, proceed to item G. If YES, was there an increase in booster Y N
chlorination feed rates?
G. Did you have customer complaints in the vicinity of the OEL exceedance? 0Yes D No
If NO, proceed to item H. If YES, explain.
There were complaints of low water pressure in the vicinity.
Did concern about complying with a rule other than Stage 2 DBPR, such as the -
Lead and Copper rule, the TCR, or any other rule constrain your options to Ld No
reduce the DBP levels at this site? For example, are you limited by the need to
maintain a detectable disinfectant residual in your ability to control DBP levels
in the distribution system?
If NO, proceed to item I. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
I. Conclusion
0Yes n No
Did the distribution system cause or contribute to the OEL exceedance(s)?
n Possibly
If NO, proceed to evaluations of treatment systems and source water. If YES or
POSSIBLY, explain below.
A main break caused a sudden decrease in Pineville tank water levels. Model results indicate the
main break and associates pressure loss caused high age water from the tank to flow into the
distribution system.
Operational Evaluation Guidance Manual C-5 December 2008
-------
Treatment Process Evaluation Checklist Page 1 of 4
I NO DATA AVAILABLE
Facility Name: Elm City Water Treatment Plant
Checklist Completed by: Ronald Doe, PE Date: June 22, 2012
A. Review finished water data for the time period prior to the OEL exceedance(s) and compare to
historical finished water data using the following questions:
Were DBP precursors (TOG, DOC, SUVA, bromide, etc.) higher than normal? D Yes 0 No
Was finished water pH higher or lower than normal? D Yes 0 No
Was the finished water temperature higher than normal? DYes 0 No
Was finished water turbidity higher than normal? D Yes 0 No
Was the disinfectant concentration leaving the plant(s) higher than normal? D Yes 0 No
Were finished water TTHM/HAA5 levels higher than normal? D Yes 0 No
Were operational and water quality data available to the system operator for 0 Yes n NO
effective decision making?
B. Does the treatment process include predisinfection? D Yes 0 No
If NO, proceed to item C. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D D Was disinfected raw water stored for an unusually long time?
D D Were treatment plant flows lower than normal?
n n Were treatment plant flows equally distributed among different trains?
D D Were water temperatures high or warmer than usual?
D n Were chlorine feed rates outside the normal range?
D D Was a disinfectant residual present in the treatment train following predisinfection?
D D Were online instruments utilized for process control?
D D Did you switch to free chlorine as the oxidant?
D D Was there a recent change (or addition) of pre-oxidant?
n n Did you change the location of the predisinfection application?
C. Does your treatment process include presedimentation? D Yes 0 No
If NO, proceed to item D. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D D Were flows low?
n n Were flows high?
D D Were online instruments utilized for process control?
D n Was sludge removed from the presedimentation basin?
D D Was sludge allowed to accumulate for an excessively long time?
D D Do you add a coagulant to your presedimentation basin?
Q n Was there a problem with the coagulant feed?
Operational Evaluation Guidance Manual C-6 December 2008
-------
Treatment Process Evaluation Checklist Page 2 of 4
D. Does your treatment process include coagulation and/or flocculation? El Yes D No
If NO, proceed to item E. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n El Were there any feed pump failures or were feed pumps operating at improper feed
rates?
El Q Were chemical feed systems controlled by flow pacing?
D El Were there changes in coagulation practices or the feed point?
D El Did you change the type or manufacturer of the coagulant?
Q pj Do you suspect that the coagulant in use at the time of the OEL exceedance did
not meet industry standards?
D El Did the pH or alkalinity change at the point of coagulant addition?
D El Were there broken or plugged mixers?
D El Were flow rates above the design rate or was there short-circuiting?
E. Does your treatment process include sedimentation or clarification? El Yes D No
If NO, proceed to item F. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n El Were there changes in plant flow rate that may have resulted in a decrease in
settling time or carry-over of process solids?
D El Were settled water turbidities higher than normal?
r-i pi Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
n El Was there any maintenance in the basin that may have stirred sludge from the
bottom of the basin and caused it to carry over to the point of disinfectant
addition?
pn pi Was sludge allowed to accumulate for an excessively long time or was there a
malfunction in the sludge removal equipment?
Operational Evaluation Guidance Manual C-7 December 2008
-------
Treatment Process Evaluation Checklist Page 3 of 4
F. Does your treatment process include filtration? 0Yes D No
If NO, proceed to item G. If YES, answerthe following questions forthe period in which
an OEL exceedance occurred:
Yes No
Q |2| Was there an increase in individual or combined filter effluent turbidity or particle
counts?
n 0 Was there an increase in turbidity or particle loading onto the filters?
r-1 ra Was there an increase in flow onto the filters or malfunction of the rate of flow
controllers?
Q |2| Were any filters taken off-line for an extended period of time that caused the other
filters to operate near maximum design capacity and created the conditions for
possible breakthrough?
n 0 Were any filters operated beyond their normal filter run time?
r-1 ra Were there any unusual spikes in individual filter effluent turbidity (which may
indicate particulate or colloidal TOC breakthrough) in the days leading to the
excursion?
El D Were all filters run in a filter-to-waste mode during initial filter ripen ing?
n fj If GAC filters are used, is it possible the adsorptive capacity of the GACbedwas
reached before reactivation occurred (leave blank if not applicable)?
Q fj If biological filtration is used, were there any process upsets that may have
resulted in the breakthrough of TOC (leave blank if not applicable)?
G. Does your treatment process include primary disinfection by injecting chlorine r~| No
prior to a clearwell? LJ es |_J
If NO, proceed to item H. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rn pj Was there a sudden increase in the amount of chlorine fed or an increase in the
chlorine residual?
n 0 Was there an increase in clearwell holding time?
n 0 Was the plant shut down or were plant flows low?
n 0 Was there an increase in clearwell water temperature?
n 0 Did you switch to free chlorine recently as the primary disinfectant?
n 0 Was the inactivation of Giardia and/or viruses exceptionally high?
r-1 ra Was there a change in the mixing strategy (i.e., mixers not used, adjustment of
tank level)?
H. Does your plant recycle spent filter backwash or other streams? QYes 0 No
If NO, proceed to item I. If YES, answer the following questions forthe period in which
an OEL exceedance occurred:
Yes No
r-1 r~| Did a change in the recycle stream quality contribute to increased DBP precursor
loading that was not addressed by treatment plant processes?
n D Did a recycle event result in flows in excess of typical or design flows?
Operational Evaluation Guidance Manual C-8 December 2008
-------
Treatment Process Evaluation Checklist Page 4 of 4
Do you inject a disinfectant after your clearwell to maintain a distribution Y r~l No
system residual?
If NO, proceed to item J. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D El Was there a sudden increase in the amount of chlorine fed?
D El Was there a switch from chloramines to free chlorine for a burnout period?
D D If using chloramines, was the chlorine to ammonia ratio in the proper range?
D El Was there a problem with either chlorine or ammonia mixing?
J. Did concern about complying with a rule other than Stage 2 DBPR, such as the i-i y _
Lead and Copper rule, the LT2ESWTR, or any other rule constrain your options fcd No
to reduce the DBP levels at this site? For example, are you limited by other
treatment targets/requirements in your ability to control precursors in
coagulation/flocculation?
If NO, proceed to item K. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
K. Conclusion
I Yes 0 No
Did treatment factors and/or variations in the plant performance contribute to the
OEL exceedance(s)? Q Possibly
If YES or POSSIBLY, explain below.
Operational Evaluation Guidance Manual C-9 December 2008
-------
Source Water Evaluation Checklist Page 1 of 2
D NO DATA AVAILABLE
System Name: Elm City Water Dept.
Checklist Completed by: Ronald Doe, PE Date: June 22, 2012
A. Do you have source water temperature data? 0Yes D No
If NO, proceed to item B. If YES, was the source water temperature _ 171 No
If NO, proceed to item B. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was the raw water storage time longer than usual?
D D Did you place another water source on-line?
Q rj Were river/reservoir flow rates lower than usual? If yes, indicate the location of
lower flow rates and the anticipated impact on the OEL exceedance.
n fj Did point or non-point sources in the watershed contribute to the OEL
exceedance?
B. Do you have data that characterizes organic matter in your source water (e.g., N
TOC, DOC, SUVA, color, THM formation potential)?
If NO, proceed to item C. If YES, were these values higher than _ M
normal? UYes m
If NO, proceed to item C. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n D Did heavy rainfall or snowmelt occur in the watershed?
n D Did you place another water source on-line?
n D Did lake or reservoir turnover occur?
r-1 r~| Did point or non-point sources in the watershed contribute to the OEL
exceedance?
D D Did an algal bloom occur in the source water?
r-1 r~i If algal blooms were present, were appropriate algae control measures
employed (e.g., addition of copper sulfate)?
n n Did a taste and odor incident occur?
C. Do you have source water bromide data? D Yes 0 No
If NO, proceed to item D. If YES, were the bromide levels higher or _ n No
lower than normal? LJ es |_J
If NO, proceed to item D. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Has saltwater intrusion occurred?
n D Are you experiencing a long-term drought?
D D Did heavy rainfall or snowmelt occur in the watershed?
D D Did you place another water source on-line?
D D Are you aware of any industrial spills in the watershed?
Operational Evaluation Guidance Manual C-10 December 2008
-------
Source Water Evaluation Checklist Page 2 of 2
D. Do you have source water turbidity or particle count data? 0 Yes Q No
If NO, proceed to item E. If YES, were the turbidity values or particle - 171 No
counts higherthan normal? LJ es |_J
If NO, proceed to item E. If YES, answerthe following questions for the time period
prior to the OEL exceedance.
Yes No
n D Did lake or reservoir turnover occur?
n D Did heavy rainfall or snowmelt occur in the watershed?
n D Did logging, fires, or landslides occur in the watershed?
n D Were river/reservoir flow rates higher than normal?
E. Do you have source water pH or alkalinity data? 0Yes D No
If NO, proceed to item F. If YES, was the pH or alkalinity different from _ N
normal values?
If NO, proceed to item F. If YES, answerthe following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was there an algal bloom in the source water?
D D If algal blooms were present, were algae control measures employed?
n D Did heavy rainfall or snowmelt occur in the watershed?
D fj Has the PWS experienced diurnal pH changes in source water?
F. Conclusion
rjYes El No
Did source water quality factors contribute to your OEL exceedance?
fj Possibly
If YES or POSSIBLY, explain below.
Operational Evaluation Guidance Manual C-ll December 2008
-------
System Schematic
Softwood River WTP
Elevated Storage Tank
Ground storage tank
Boosterdisinfection
Peak DBP site
Hardwood WTP
Operational Evaluation Guidance Manual
C-12
December 2008
-------
Appendix D
Example Operational Evaluation Report
for
OEL Exceedance Due to Changes in Source Water Quality and
Booster Disinfection
-------
-------
Operational Evaluation Reporting Form
Page 1 of 2
I. GENERAL INFORMATION
A. Facility Information
Facility Name: Oak City
PWSID: US1234570
Facility Address: 101 Main St.
City:
Oak City
State: US Zip: 98768
B. Report Prepared by:
(Print): Jim Green
Date prepared: September 3, 2010
(Signature):
Contact Telephone Number: 124-666-9876
I. MONITORING RESULTS
A. Provide the Compliance Monitoring Site(s) where the DEL was Exceeded.
Stage 2 DBPR compliance monitoring location #1; See enclosed system schematics
Note: The site name or number should correspond to a site in your Stage 2 DBPR compliance monitoring
plan.
B. Monitoring Results for the Site(s) Identified in M.A (include duplicate pages if there was more than
one exceedance}
1. Check TTHM or HAA5 to indicate which result caused the OEL -
exceedance.
2. Enter your results for TTHM or HAA5 (whichever you checked above).
\ TTHM
HAA5
Date sample was
collected
TTHM (mg/L)
HAAS (mg/L)
Quarter
Results from
Two Quarters
Ago
A
02/03/2018
0.065
Prior Quarter's
Results
B
05/03/2018
0.062
Current
Quarter
C
08/03/2018
0.108
Operational
Evaluation Value
D = (A+B+(2*C))/4
0.086
Note: The operational evaluation value is calculated by summing the two previous quarters of Tl HM or HAAS
vaiues pins twice the current quarter value, divided by four, if the value exceeds 0.080 mg/L for TTHM or 0.060
mg/L forHAA5, an OEL exceedance has occurred.
C. Has an OEL exceedance occurred at this location in the past?
If NO, proceed to item D, If YES, when did
exceedance occur?
EJ Yes
DNO
Third quarter of 201 3: 2015, 2016
Was the cause determined for the previous exceedance(s)?
Are the previous evaluations/determinations applicable to the current OEL
exceedance?
EYes
El Yes
DNO
DNO
Operational Evaluation Guidance Manual
D-l
December 2008
-------
Operational Evaluation Reporting Form Page 2 of 2
III. OPERATIONAL EVALUATION FINDINGS
A.
B.
C.
D.
E.
F.
G.
H.
Did the State allow you to limit the scope of the operational evaluation? D Yes E
If NO, proceed to item B. If YES, attach written correspondence from the State.
Did the distribution system cause or contribute to your OEL exceedance(s)?
0 Possibly
If NO, proceed to item C. If YES or POSSIBLY, explain (attach additional pages if
necessary):
Increased chlorine dosage at booster station and increased temperature in the distribution
system.
See attachment III.D.
Did the treatment system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item D. If YES or POSSIBLY, explain (attach additional pages if
necessary):
Did source water quality cause or contribute to your OEL exceedance(s)?
0 Possibly
If NO, proceed to item E. If YES or POSSIBLY, explain (attach additional pages if
necessary):
Algae bloom, increased wastewater baseflow, and high temperature in river water.
See attachment III.B.
Attach all supporting operational or other data that support the determination of the cause(s)
of your OEL exceedance(s).
If you are unable to determine the cause(s) of the OEL exceedance(s), list the steps that you
can use to better identify the cause(s) in the future (attach additional pages if necessary):
List steps that could be considered to minimize future OEL exceedances (attach additional
pages if necessary)
See attachment III.G
Total Number of Pages Submitted, Including Attachments and Checklists: 12
No
No
No
No
Operational Evaluation Guidance Manual D-2 December 2008
-------
Attachments
II.C. Past Exceedances
Oak City is a consecutive system purchasing all of its finished water from Maple City. Historically, TTHM
levels in the water supplied during the summer months are higher than during the rest of the year. The
OEL exceedance observed in this quarter is consistent with those observed in previous years. We have
discussed this problem with the wholesaler (Maple City) and it is apparent that the high TTHM levels are a
result of increased DBP precursor levels and water temperature in the Maple City's source water and
distribution system. Increased chlorine dosage delivered at our booster chlorine station located at the
entry point to our system also contributed to the exceedance.
III.B. Changes in the Source Water Quality
According to Maple City's treatment plant staff, the increased precursor concentration in the source water
was a result of two factors:
Algal blooms that normally take place in the Long River from which the water is withdrawn.
Increased contribution (up to 15 percent) of wastewater effluent to the river flow during the
month of August when the river is normally at its lowest level.
During the summer months, Maple City has taken measures to lower DBP precursors at the water
treatment plant by increasing the coagulant dosage (ferric sulfate) and lowering the pH of coagulation
from the usual 7.1 to 7.3 range to the 5.5 to 6.2 range. However, precursor levels in the finished water
are still higher than during the rest of the year. Algae management in the river has been attempted in
past years with modest results.
Data in support of the above assessment is available upon request from Maple City.
III.D. Changes in the Distribution System
Two factors related to the distribution system may have contributed to increased TTHM levels:
Due to a lower than normal chlorine residual at the Oak City system entry point, the chlorine
dosage rate at the booster chlorine station was increased. This increase is needed to ensure
a minimum residual of at least 0.3 mg/L throughout the distribution system.
Temperature across the distribution system is at the highest level of the year during the
month of August.
Data on chlorine dosage rates fed at the booster station feed point, chlorine residuals before and after
booster chlorination, and distribution system water temperature are available upon request. Water
delivered by Maple City is typically less than two days old.
III.G. Minimizing Future Exceedances
Since the latest OEL exceedance occurred after the booster chlorination rate was increased, we will
research whether this rate can be reduced slightly and still maintain chlorine residuals throughout the
distribution system. It is possible that we can improve residual maintenance at dead ends and low usage
areas by implementing periodic flushing with blow off valves. We will also use our hydraulic model to
become more familiar with flow paths from the entry point to the extremes of the system. This exercise
will help us to identify areas of the system that may have higher water age. Next we will review summer
operating procedures to see if water age can be further reduced in these areas by changing pumping
schedules, tank operating levels or otherwise increase tank water turnover rates.
Operational Evaluation Guidance Manual D-3 December 2008
-------
Distribution System Evaluation Checklist Page 1 of 2
System Name: Oak City
Checklist Completed by: Jim Green Date: Septembers, 2018
A. Do you have disinfectant residual or temperature data for the monitoring Y n No
location where you experienced the OEL exceedance?
If NO, proceed to item B. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n pj Was the water temperature higher than normal for that time of the year at that
location?
n pj Was the disinfectant residual lower than normal for that time of the year at that
location?
n pj Was the disinfectant residual higher than normal for that time of the year at that
location?
B. Do you have maintenance records available for the time period just prior to the pi y r~| MO
OEL exceedance?
If NO, proceed to item C. If YES, answer the following questions:
Yes No
D El Did any line breaks or replacements occur in the vicinity of the exceedance?
D El Were any storage tanks or reservoirs taken off-line and cleaned?
[] pj Did flushing or other hydraulic disturbances (e.g., fires) occur in the vicinity of
the exceedance?
D El Were any valves operated in the vicinity of the OEL exceedances?
C. If your system is metered, do you have access to historical records showing Y |~l No
water use at individual service connections?
If NO, proceed to item D. If YES, was overall water use in your system 1-1 y pi No
unusually low, indicating higher than normal water age?
D. Do you have high-volume customers in your system (e.g., an industrial pjY n No
processing plant)? LJ es |_J
If NO, proceed to item E. If YES, was there a change in water use by a 1-1 y pi MO
high-volume customer? LJ es |_J
E. Is there a finished water storage facility hydraulically upstream from the |-iy pi MO
monitoring location where you experienced the OEL exceedance? LJ es LJ
If NO, proceed to item F. If YES, review storage facility operations and water quality
data to answer the following questions for the period in which the OEL exceedance
occurred:
Yes No
D D Was a disinfectant residual detected in the stored water or at the tank outlet?
D D Do you know of any mixing problems with the tank or reservoir?
D D Does the facility operate in "last in-first out" mode?
L^ Q Was the tank or reservoir drawn down more than usual prior to OEL
exceedance, indicating a possible discharge of stagnant water?
n Q^ Was there a change in water level fluctuations that would have resulted in
increased water age within the tank or reservoir?
Operational Evaluation Guidance Manual D-4 December 2008
-------
Distribution System Evaluation Checklist Page 2 of 2
F. Does your system practice booster chlorination? El Yes Q No
If NO, proceed to item G. If YES, was there an increase in booster n Y |~| No
chlorination feed rates?
G. Did you have customer complaints in the vicinity of the OEL exceedance? D Yes El No
If NO, proceed to item H. If YES, explain.
Did concern about complying with a rule other than Stage 2 DBPR, such as the [- _
Lead and Copper rule, the TCP, or any other rule constrain your options to LJ es |>/j o
reduce the DBP levels at this site? For example, are you limited by the need to
maintain a detectable disinfectant residual in your ability to control DBP levels
in the distribution system?
If NO, proceed to item I. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
I. Conclusion
D Yes D No
Did the distribution system cause or contribute to the OEL exceedance(s)?
El Possibly
If NO, proceed to evaluations of treatment systems and source water. If YES or
POSSIBLY, explain below.
Booster chlorination levels were increased to maintain sufficient residuals at the system ends.
The distribution system temperature was also high, but this is normal for August.
Operational Evaluation Guidance Manual D-5 December 2008
-------
Treatment Process Evaluation Checklist Page 1 of 4
I NO DATA AVAILABLE
Facility Name: Oak City
Checklist Completed by: Jim Green, assisted by Maple City TP personnel Date: 09/03/2018
A. Review finished water data for the time period prior to the OEL exceedance(s) and compare to
historical finished water data using the following questions:
Were DBP precursors (TOG, DOC, SUVA, bromide, etc.) higher than normal? El Yes Q No
Was finished water pH higher or lower than normal? fJ Yes 0 No
Was the finished water temperature higher than normal? D Yes El No
Was finished water turbidity higher than normal? QYes El No
Was the disinfectant concentration leaving the plant(s) higher than normal? D Yes El No
Were finished water TTHM/HAA5 levels higher than normal? D Yes El No
Were operational and water quality data available to the system operator for FJ Yes D] NO
effective decision making?
B. Does the treatment process include predisinfection? D Yes El No
If NO, proceed to item C. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D n Was disinfected raw water stored for an unusually long time?
D D Were treatment plant flows lower than normal?
D D Were treatment plant flows equally distributed among different trains?
D n Were water temperatures high or warmer than usual?
D D Were chlorine feed rates outside the normal range?
D D Was a disinfectant residual present in the treatment train following predisinfection?
D D Were online instruments utilized for process control?
D El Did you switch to free chlorine as the oxidant?
n n Was there a recent change (or addition) of pre-oxidant?
n n Did you change the location of the predisinfection application?
C. Does your treatment process include presedimentation? D Yes El No
If NO, proceed to item D. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n n Were flows low?
D D Were flows high?
D D Were online instruments utilized for process control?
D D Was sludge removed from the presedimentation basin?
D D Was sludge allowed to accumulate for an excessively long time?
n n Do you add a coagulant to your presedimentation basin?
n n Was there a problem with the coagulant feed?
Operational Evaluation Guidance Manual D-6 December 2008
-------
Treatment Process Evaluation Checklist Page 2 of 4
D. Does your treatment process include coagulation and/or flocculation? El Yes D No
If NO, proceed to item E. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
r-i ra Were there any feed pump failures or were feed pumps operating at improper feed
rates?
El D Were chemical feed systems controlled by flow pacing?
El D Were there changes in coagulation practices or the feed point?
D El Did you change the type or manufacturer of the coagulant?
Q [3 Do you suspect that the coagulant in use at the time of the OEL exceedance did
not meet industry standards?
El CD Did the pH or alkalinity change at the point of coagulant addition?
D El Were there broken or plugged mixers?
D El Were flow rates above the design rate or was there short-circuiting?
E. Does your treatment process include sedimentation or clarification? El Yes D No
If NO, proceed to item F. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rn ra Were there changes in plant flow rate that may have resulted in a decrease in
settling time or carry-over of process solids?
D El Were settled water turbidities higher than normal?
rn [7] Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
n El Was there any maintenance in the basin that may have stirred sludge from the
bottom of the basin and caused it to carry over to the point of disinfectant
addition?
rn ra Was sludge allowed to accumulate for an excessively long time or was there a
malfunction in the sludge removal equipment?
Operational Evaluation Guidance Manual D-7 December 2008
-------
Treatment Process Evaluation Checklist Page 3 of 4
F. Does your treatment process include filtration? 0Yes D No
If NO, proceed to item G. If YES, answerthe following questions forthe period in which
an OEL exceedance occurred:
Yes No
Q |2| Was there an increase in individual or combined filter effluent turbidity or particle
counts?
n 0 Was there an increase in turbidity or particle loading onto the filters?
r-1 ra Was there an increase in flow onto the filters or malfunction of the rate of flow
controllers?
Q |2| Were any filters taken off-line for an extended period of time that caused the other
filters to operate near maximum design capacity and created the conditions for
possible breakthrough?
n 0 Were any filters operated beyond their normal filter run time?
r-1 ra Were there any unusual spikes in individual filter effluent turbidity (which may
indicate particulate or colloidal TOC breakthrough) in the days leading to the
excursion?
El D Were all filters run in a filter-to-waste mode during initial filter ripen ing?
n fj If GAC filters are used, is it possible the adsorptive capacity of the GACbedwas
reached before reactivation occurred (leave blank if not applicable)?
Q fj If biological filtration is used, were there any process upsets that may have
resulted in the breakthrough of TOC (leave blank if not applicable)?
G. Does your treatment process include primary disinfection by injecting chlorine r~| No
prior to a clearwell? LJ es |_J
If NO, proceed to item H. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rn pj Was there a sudden increase in the amount of chlorine fed or an increase in the
chlorine residual?
n 0 Was there an increase in clearwell holding time?
n 0 Was the plant shut down or were plant flows low?
n 0 Was there an increase in clearwell water temperature?
n 0 Did you switch to free chlorine recently as the primary disinfectant?
n 0 Was the inactivation of Giardia and/or viruses exceptionally high?
r-1 ra Was there a change in the mixing strategy (i.e., mixers not used, adjustment of
tank level)?
H. Does your plant recycle spent filter backwash or other streams? 0Yes Q No
If NO, proceed to item I. If YES, answer the following questions forthe period in which
an OEL exceedance occurred:
Yes No
r-1 ra Did a change in the recycle stream quality contribute to increased DBP precursor
loading that was not addressed by treatment plant processes?
n 0 Did a recycle event result in flows in excess of typical or design flows?
Operational Evaluation Guidance Manual D-8 December 2008
-------
Treatment Process Evaluation Checklist Page 4 of 4
I. Do you inject a disinfectant after your clearwell to maintain a distribution iv r/i Mn
, I irt ^^J I GS tf^J INU
system residual?
If NO, proceed to item J. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D D Was there a sudden increase in the amount of chlorine fed?
D D Was there a switch from chloramines to free chlorine for a burnout period?
D D If using chloramines, was the chlorine to ammonia ratio in the proper range?
D D Was there a problem with either chlorine or ammonia mixing?
J. Did concern about complying with a rule other than Stage 2 DBPR, such as the r-i Y
Lead and Copper rule, the LT2ESWTR, or any other rule constrain your options
to reduce the DBF levels at this site? For example, are you limited by other
treatment targets/requirements in your ability to control precursors in
coagulation/flocculation?
If NO, proceed to item K. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
K. Conclusion
| Yes 0 No
Did treatment factors and/or variations in the plant performance contribute to the
OELexceedance(s)? Q Possibly
If YES or POSSIBLY, explain below.
Operational Evaluation Guidance Manual D-9 December 2008
-------
Source Water Evaluation Checklist Page 1 of 2
D NO DATA AVAILABLE
System Name: Oak City
Checklist Completed by: Jim Green, assisted by Maple CityTP personnel Date: 09/03/2018
A. Do you have source water temperature data? 0Yes D No
If NO, proceed to item B. If YES, was the source water temperature n No
If NO, proceed to item B. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n 0 Was the raw water storage time longer than usual?
D 0 Did you place another water source on-line?
Q 0 Were river/reservoir flow rates lower than usual? If yes, indicate the location of
lower flow rates and the anticipated impact on the OEL exceedance.
0 fj Did point or non-point sources in the watershed contribute to the OEL
exceedance?
B. Do you have data that characterizes organic matter in your source water (e.g., N
TOC, DOC, SUVA, color, THM formation potential)?
If NO, proceed to item C. If YES, were these values higher than M
normal? LJYes U
If NO, proceed to item C. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n 0 Did heavy rainfall or snowmelt occur in the watershed?
n 0 Did you place another water source on-line?
n 0 Did lake or reservoir turnover occur?
ra rn Did point or non-point sources in the watershed contribute to the OEL
exceedance?
0 D Did an algal bloom occur in the source water?
ra rn If algal blooms were present, were appropriate algae control measures
employed (e.g., addition of copper sulfate)?
n 0 Did a taste and odor incident occur?
C. Do you have source water bromide data? 0 Yes D No
If NO, proceed to item D. If YES, were the bromide levels higher or _ 171 No
lower than normal? LJ es |_J
If NO, proceed to item D. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Has saltwater intrusion occurred?
n D Are you experiencing a long-term drought?
D D Did heavy rainfall or snowmelt occur in the watershed?
D D Did you place another water source on-line?
D D Are you aware of any industrial spills in the watershed?
Operational Evaluation Guidance Manual D-10 December 2008
-------
Source Water Evaluation Checklist Page 2 of 2
D. Do you have source water turbidity or particle count data? EJ Yes Q No
If NO, proceed to item E. If YES, were the turbidity values or particle r-i y pi MO
counts higher than normal?
If NO, proceed to item E. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Did lake or reservoir turnover occur?
n rj Did heavy rainfall or snowmelt occur in the watershed?
D rj Did logging, fires, or landslides occur in the watershed?
D rj Were river/reservoir flow rates higher than normal?
E. Do you have source water pH or alkalinity data? El Yes D No
If NO, proceed to item F. If YES, was the pH or alkalinity different from Y r~l MO
normal values? LJ es |_J
If NO, proceed to item F. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
0 EH Was there an algal bloom in the source water?
D El If algal blooms were present, were algae control measures employed?
D EJ Did heavy rainfall or snowmelt occur in the watershed?
D EJ Has the PWS experienced diurnal pH changes in source water?
F. Conclusion
D Yes D No
Did source water quality factors contribute to your OEL exceedance?
EJ Possibly
If YES or POSSIBLY, explain below.
Algae bloom is typical for the Maple City source water during the month of August.
See report form for explanation.
Operational Evaluation Guidance Manual D-ll December 2008
-------
Oak City Distribution System Schematic
System Entry Point
Elevated Storage Tank
Ground storage tank
Pump and chlorine boosting
station
Peak DBP site
Operational Evaluation Guidance Manual
D-12
December 2008
-------
Appendix E
Example Operational Evaluation Report
for
OEL Exceedances Due to Maintenance Activities in the Wholesale
System
-------
-------
Operational Evaluation Reporting Form
Page 1 of 2
I. GENERAL INFORMATION
A. Facility Information
Facility Name: Pine City
PWSID: US1234575
Facility Address: 101 Broadway St.
City:
Pine City
State: US
Zip: 88768
B. Report Prepared by:
(Print): John Brown
(Signature): ^"/'w
Date prepared:
June 15. 2014
Contact Telephone Number: 456-666-7777
I. MONITORING RESULTS
A. Provide the Compliance Monitoring Site(s) where the DEL was Exceeded.
Stage 2 DBPR compliance monitoring location #2; Located in downtown area -fed by
water from Poplar City
Note: The site name or rtun-iber should correspond to a s:te in your Stage 2 DBPR compliance monitoring
pian.
B. Monitoring Results for the Site(s) Identified in II.A (include duplicate pages if there was more than
one exceedance}
1. Check TTHM or HAAS to indicate which result caused the OEL -
exceedance.
2. Enter your results for TTHM or HAA5 (whichever you checked above).
TTHM
HAA5
Date sample was
collected
TTHM (mg/L)
HAA5 (mg/L)
Quarter
Results from
Two Quarters
Ago
A
11/30/2013
0.054
Prior Quarter's
Results
B
02/26/2014
0.050
Current
Quarter
C
05/31/2014
0.081
Operational
Evaluation Value
D = (A+B+(2*C})/4
0.062
Note: ,' he operational evaluation value is calculated by summing the two previous quarters of I I H,W or HAA5
values pins twice the current quarter value, divided by four. If the value exceeds 0.080 mg/L for TTHM or 0. Q60
ma/L for HAAS, an OEL exceedance has occurred.
C. Has an OEL exceedance occurred at this location in the past?
If NO, proceed to item D. If YES, when did
exceedance occur?
Lives
0No
Was the cause determined for the previous exceedance(s)?
Are the previous evaluations/determinations applicable to the current OEL
exceedance?
DYes
Dves
DNO
DNO
Operational Evaluation Guidance Manual
E-l
December 2008
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Operational Evaluation Reporting Form Page 2 of 2
I. OPERATIONAL EVALUATION FINDINGS
A. Did the State allow you to limit the scope of the operational evaluation? D Yes El No
If NO, proceed to item B. If YES, attach written correspondence from the State.
El Yes D No
B. Did the distribution system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item C. If YES or POSSIBLY, explain (attach additional pages if
necessary):
See attachment III.D
D Yes El No
C. Did the treatment system cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item D. If YES or POSSIBLY, explain (attach additional pages if
necessary):
D Yes El No
D. Did source water quality cause or contribute to your OEL exceedance(s)?
n Possibly
If NO, proceed to item E. If YES or POSSIBLY, explain (attach additional pages if
necessary):
E. Attach all supporting operational or other data that support the determination of the cause(s)
of your OEL exceedance(s).
F. If you are unable to determine the cause(s) of the OEL exceedance(s), list the steps that you
can use to better identify the cause(s) in the future (attach additional pages if necessary):
G. List steps that could be considered to minimize future OEL exceedances (attach additional
pages if necessary)
See attachment III.G
H. Total Number of Pages Submitted, Including Attachments and Checklists: 11
Operational Evaluation Guidance Manual E-2 December 2008
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Attachments
III.D. Changes in the Distribution System
The OEL exceedance occurred in an area served by water we purchase from Poplar City. We contacted
Poplar City's Department of Public Works for an explanation. We were told that as a consequence of
maintenance work on a main near Pine City's entry point, water in an elevated tank remained practically
unused for two weeks. High HAAS levels in the Pine City downtown area are most likely the result of "old"
water being released by the tank.
SCADA data for Poplar City's tank levels from May 10, 2014, to May 31, 2014, and Poplar City's
maintenance records are available upon request.
III.G. Minimizing Future Exceedances
We have asked Poplar City to review their maintenance and tank management practices to minimize
future exceedances. We have also asked Poplar City to contact us by telephone (John Brown at 456-
666-7777) 24 hours in advance of maintenance work in the area of the distribution system that feeds our
system so that we can be aware of potential problems.
Operational Evaluation Guidance Manual E-3 December 2008
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Distribution System Evaluation Checklist Page 1 of 2
System Name: Pine City
Checklist Completed by: John Brown Date: June 15, 2014
A. Do you have disinfectant residual or temperature data for the monitoring ^ly n No
location where you experienced the DEL exceedance?
If NO, proceed to item B. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n 0 Was the water temperature higher than normal for that time of the year at that
location?
Q 0 Was the disinfectant residual lower than normal for that time of the year at that
location?
n 0 Was the disinfectant residual higher than normal for that time of the year at that
location?
B. Do you have maintenance records available for the time period just prior to the n v 1-1 M
/"-V I I I /**! Ij^l I 6S ^^J I »*J
OEL exceedance?
If NO, proceed to item C. If YES, answer the following questions:
Yes No
n El Did any line breaks or replacements occur in the vicinity of the exceedance?
D El Were any storage tanks or reservoirs taken off-line and cleaned?
Q [7j Did flushing or other hydraulic disturbances (e.g., fires) occur in the vicinity of
the exceedance?
n El Were any valves operated in the vicinity of the OEL exceedances?
C. If your system is metered, do you have access to historical records showing pi Y |~| No
water use at individual service connections?
If NO, proceed to item D. If YES, was overall water use in your system Y 171 Mn
unusually low, indicating higher than normal water age?
D. Do you have high-volume customers in your system (e.g., an industrial ^ y |~| No
processing plant)?
If NO, proceed to item E. If YES, was there a change in water use by a 1-1 y ni MO
high-volume customer?
E. Is there a finished water storage facility hydraulically upstream from the r^,y n No
monitoring location where you experienced the OEL exceedance? LJ es |_|
If NO, proceed to item F. If YES, review storage facility operations and water quality
data to answer the following questions for the period in which the OEL exceedance
occurred:
Yes No
El D Was a disinfectant residual detected in the stored water or at the tank outlet?
D El Do you know of any mixing problems with the tank or reservoir?
n El Does the facility operate in "last in-first out" mode?
n [3 Was the tank or reservoir drawn down more than usual prior to OEL
exceedance, indicating a possible discharge of stagnant water?
0 Q Was there a change in water level fluctuations that would have resulted in
increased water age within the tank or reservoir?
Operational Evaluation Guidance Manual E-4 December 2008
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Distribution System Evaluation Checklist Page 2 of 2
F. Does your system practice booster chlorination? D Yes 0 No
If NO, proceed to item G. If YES, was there an increase in booster r-,,, n No
chlorination feed rates?
G. Did you have customer complaints in the vicinity of the OEL exceedance? D Yes El No
If NO, proceed to item H. If YES, explain.
Did concern about complying with a rule other than Stage 2 DBPR, such as the i y _
Lead and Copper rule, the TCP, or any other rule constrain your options to Ld o
reduce the DBP levels at this site? For example, are you limited by the need to
maintain a detectable disinfectant residual in your ability to control DBP levels
in the distribution system?
If NO, proceed to item I. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
I. Conclusion
El Yes D No
Did the distribution system cause or contribute to the OEL exceedance(s)?
n Possibly
If NO, proceed to evaluations of treatment systems and source water. If YES or
POSSIBLY, explain below.
Due to maintenance in the vicinity of a Poplar City tank, the tank was hardly used during a two
week period in May. This allowed water age to significantly increase, which contributed to our
exceedance when the water was released into our system.
Operational Evaluation Guidance Manual E-5 December 2008
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Treatment Process Evaluation Checklist Page 1 of 4
I NO DATA AVAILABLE
Facility Name: Pine City
Checklist Completed by: John Brown, assisted by Poplar City DPW Date: June 15, 2014
A. Review finished water data for the time period prior to the OEL exceedance(s) and compare to
historical finished water data using the following questions:
Were DBP precursors (TOG, DOC, SUVA, bromide, etc.) higher than normal? D Yes 0 No
Was finished water pH higher or lower than normal? D Yes 0 No
Was the finished water temperature higher than normal? D Yes El No
Was finished water turbidity higher than normal? D Yes 0 No
Was the disinfectant concentration leaving the plant(s) higher than normal? D Yes 0 No
Were finished water TTHM/HAA5 levels higher than normal? D Yes 0 No
Were operational and water quality data available to the system operator for 0 Yes n NO
effective decision making?
B. Does the treatment process include predisinfection? D Yes 0 No
If NO, proceed to item C. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D D Was disinfected raw water stored for an unusually long time?
D D Were treatment plant flows lower than normal?
D D Were treatment plant flows equally distributed among different trains?
D D Were water temperatures high or warmer than usual?
D D Were chlorine feed rates outside the normal range?
D D Was a disinfectant residual present in the treatment train following predisinfection?
D D Were online instruments utilized for process control?
D D Did you switch to free chlorine as the oxidant?
n n Was there a recent change (or addition) of pre-oxidant?
Q n Did you change the location of the predisinfection application?
C. Does your treatment process include presedimentation? QYes 0 No
If NO, proceed to item D. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n 0! Were flows low?
Q n Were flows high?
D D Were online instruments utilized for process control?
D D Was sludge removed from the presedimentation basin?
D n Was sludge allowed to accumulate for an excessively long time?
D n Do you add a coagulant to your presedimentation basin?
D D Was there a problem with the coagulant feed?
Operational Evaluation Guidance Manual E-6 December 2008
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Treatment Process Evaluation Checklist Page 2 of 4
D. Does your treatment process include coagulation and/or flocculation? El Yes Q No
If NO, proceed to item E. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
n 0 Were there any feed pump failures or were feed pumps operating at improper feed
rates?
El Q Were chemical feed systems controlled by flow pacing?
D El Were there changes in coagulation practices or the feed point?
D El Did you change the type or manufacturer of the coagulant?
fj 0 Do you suspect that the coagulant in use at the time of the OEL exceedance did
not meet industry standards?
D El Did the pH or alkalinity change at the point of coagulant addition?
D El Were there broken or plugged mixers?
n El Were flow rates above the design rate or was there short-circuiting?
E. Does your treatment process include sedimentation or clarification? DYes El No
If NO, proceed to item F. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rn n Were there changes in plant flow rate that may have resulted in a decrease in
settling time or carry-over of process solids?
D D Were settled water turbidities higher than normal?
rn n Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
fj Q Was there any maintenance in the basin that may have stirred sludge from the
bottom of the basin and caused it to carry over to the point of disinfectant
addition?
rn n Was sludge allowed to accumulate for an excessively long time or was there a
malfunction in the sludge removal equipment?
Operational Evaluation Guidance Manual E-7 December 2008
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Treatment Process Evaluation Checklist Page 3 of 4
F. Does your treatment process include filtration? 0Yes D No
If NO, proceed to item G. If YES, answerthe following questions forthe period in which
an OEL exceedance occurred:
Yes No
Q |2| Was there an increase in individual or combined filter effluent turbidity or particle
counts?
n 0 Was there an increase in turbidity or particle loading onto the filters?
r-1 ra Was there an increase in flow onto the filters or malfunction of the rate of flow
controllers?
Q |2| Were any filters taken off-line for an extended period of time that caused the other
filters to operate near maximum design capacity and created the conditions for
possible breakthrough?
n 0 Were any filters operated beyond their normal filter run time?
r-1 ra Were there any unusual spikes in individual filter effluent turbidity (which may
indicate particulate or colloidal TOC breakthrough) in the days leading to the
excursion?
El D Were all filters run in a filter-to-waste mode during initial filter ripen ing?
n fj If GAC filters are used, is it possible the adsorptive capacity of the GACbedwas
reached before reactivation occurred (leave blank if not applicable)?
Q fj If biological filtration is used, were there any process upsets that may have
resulted in the breakthrough of TOC (leave blank if not applicable)?
G. Does your treatment process include primary disinfection by injecting chlorine r~| No
prior to a clearwell? LJ es |_J
If NO, proceed to item H. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
rn pj Was there a sudden increase in the amount of chlorine fed or an increase in the
chlorine residual?
n 0 Was there an increase in clearwell holding time?
n 0 Was the plant shut down or were plant flows low?
n 0 Was there an increase in clearwell water temperature?
n 0 Did you switch to free chlorine recently as the primary disinfectant?
n 0 Was the inactivation of Giardia and/or viruses exceptionally high?
r-1 ra Was there a change in the mixing strategy (i.e., mixers not used, adjustment of
tank level)?
H. Does your plant recycle spent filter backwash or other streams? QYes 0 No
If NO, proceed to item I. If YES, answer the following questions forthe period in which
an OEL exceedance occurred:
Yes No
r-1 r~| Did a change in the recycle stream quality contribute to increased DBP precursor
loading that was not addressed by treatment plant processes?
n D Did a recycle event result in flows in excess of typical or design flows?
Operational Evaluation Guidance Manual E-8 December 2008
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Treatment Process Evaluation Checklist Page 4 of 4
Do you inject a disinfectant after your clearwell to maintain a distribution ra v 1-1 w
i - i i /-i Ij^J Y GS ^^J I ' vJ
system residual?
If NO, proceed to item J. If YES, answer the following questions for the period in which
an OEL exceedance occurred:
Yes No
D El Was there a sudden increase in the amount of chlorine fed?
D El Was there a switch from chloramines to free chlorine for a burnout period?
D El If using chloramines, was the chlorine to ammonia ratio in the proper range?
D El Was there a problem with either chlorine or ammonia mixing?
Did concern about complying with a rule other than Stage 2 DBPR, such as the 1-1Y n w
Lead and Copper rule, the LT2ESWTR, or any other rule constrain your options La No
to reduce the DBP levels at this site? For example, are you limited by other
treatment targets/requirements in your ability to control precursors in
coagulation/flocculation?
If NO, proceed to item K. If YES, explain below and consult EPA's Simultaneous
Compliance Guidance Manual for alternative compliance approaches.
K. Conclusion
I Yes El No
Did treatment factors and/or variations in the plant performance contribute to the
OEL exceedance(s)? Q Possibly
If YES or POSSIBLY, explain below.
Operational Evaluation Guidance Manual E-9 December 2008
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Source Water Evaluation Checklist Page 1 of 2
D NO DATA AVAILABLE
System Name: Pine City
Checklist Completed by: John Brown, assisted by Poplar City DPW Date: June 15,2014
A. Do you have source water temperature data? 0Yes D No
If NO, proceed to item B. If YES, was the source water temperature _ 171 No
If NO, proceed to item B. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n n Was the raw water storage time longer than usual?
D D Did you place another water source on-line?
Q rj Were river/reservoir flow rates lower than usual? If yes, indicate the location of
lower flow rates and the anticipated impact on the OEL exceedance.
n fj Did point or non-point sources in the watershed contribute to the OEL
exceedance?
B. Do you have data that characterizes organic matter in your source water (e.g., N
TOC, DOC, SUVA, color, THM formation potential)?
If NO, proceed to item C. If YES, were these values higher than _ M
normal? UYes m
If NO, proceed to item C. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
n D Did heavy rainfall or snowmelt occur in the watershed?
n D Did you place another water source on-line?
n D Did lake or reservoir turnover occur?
r-1 r~| Did point or non-point sources in the watershed contribute to the OEL
exceedance?
D D Did an algal bloom occur in the source water?
r-1 r~i If algal blooms were present, were appropriate algae control measures
employed (e.g., addition of copper sulfate)?
n n Did a taste and odor incident occur?
C. Do you have source water bromide data? D Yes 0 No
If NO, proceed to item D. If YES, were the bromide levels higher or _ n No
lower than normal? LJ es |_J
If NO, proceed to item D. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Has saltwater intrusion occurred?
n D Are you experiencing a long-term drought?
D D Did heavy rainfall or snowmelt occur in the watershed?
D D Did you place another water source on-line?
D D Are you aware of any industrial spills in the watershed?
Operational Evaluation Guidance Manual E-10 December 2008
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Source Water Evaluation Checklist Page 2
D.
E.
F.
Do you have source water turbidity or particle count data? El Yes C
If NO, proceed to item E. If YES, were the turbidity values or particle flYes 17
counts higher than normal?
If NO, proceed to item E. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Did lake or reservoir turnover occur?
D D Did heavy rainfall or snowmelt occur in the watershed?
n Q Did logging, fires, or landslides occur in the watershed?
n Q Were river/reservoir flow rates higher than normal?
Do you have source water pH or alkalinity data? 13 Yes C
If NO, proceed to item F. If YES, was the pH or alkalinity different from 1-1 Y rr
normal values?
If NO, proceed to item F. If YES, answer the following questions for the time period
prior to the OEL exceedance.
Yes No
D D Was there an algal bloom in the source water?
Q Q If algal blooms were present, were algae control measures employed?
D D Did heavy rainfall or snowmelt occur in the watershed?
D D Has the PWS experienced diurnal pH changes in source water?
Conclusion
Did source water quality factors contribute to your OEL exceedance?
d Possibly
If YES or POSSIBLY, explain below.
of 2
|No
|No
|No
|No
No
Operational Evaluation Guidance Manual E-ll December 2008
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