vvEPA
United States
Environmental
Protection Agency
Office of Water
(4601)
EPA815-D-03-004
July 2003
Draft
STAGE 2 DISINFECTANTS AND DISINFECTION
BYPRODUCTS RULE
SIGNIFICANT EXCURSION GUIDANCE MANUAL
This text is a draft provided for public comment. It has not had a final review for
technical accuracy or adherence to EPA policy; do not quote or cite except as a
public comment.
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Note on the Stage 2 Disinfectants and Disinfection Byproducts
Significant Excursion Guidance Manual, July 2003 Draft
Purpose:
The purpose of this guidance manual, when finalized, is solely to provide technical
information for water systems and States to use for identifying and reducing significant
excursions of DBF levels. The Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2
DBPR) contains a provision for significant excursions. EPA is developing the Stage 2 DBPR to
reduce DBF occurrence peaks in the distribution system based on changes to compliance
monitoring provisions.
This guidance is not a substitute for applicable legal requirements, nor is it a regulation
itself. Thus, it does not impose legally-binding requirements on any party, including EPA,
states, or the regulated community. Interested parties are free to raise questions and objections to
the guidance and the appropriateness of using it in a particular situation. Although this manual
describes many methods for complying with significant excursion requirements, the guidance
presented here may not be appropriate for all situations, and alternative approaches may provide
satisfactory performance. The mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
Authorship:
This manual was developed under the direction of EPA's Office of Water, and was
prepared by The Cadmus Group, Inc. and Malcolm Pirnie, Inc. Questions concerning this
document should be addressed to:
Thomas Grubbs and Mike Finn
U.S. Environmental Protection Agency
Mail Code 4607M
1200 Pennsylvania Avenue NW
Washington, DC 20460-0001
Tel: (202) 564-5262 (Thomas Grubbs)
(202) 564-5261 (Mike Finn)
Fax: (202) 564-3767
Email: Grubbs.Thomas@epamail.epa.govand Finn.Michael@epamail.epa.gov
Request for comments:
EPA is releasing this manual in draft form in order to solicit public review and comment.
The Agency would appreciate comments on the content and organization of technical
information presented in this manual. Please submit any comments no later than 90 days after
publication of the Stage 2 Disinfectants and Disinfection Byproducts Rule proposal in the
Federal Register. Detailed procedures for submitting comments are stated below.
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Procedures for submitting comments:
Comments on this draft guidance manual should be submitted to EPA's Water Docket.
You may submit comments electronically, by mail, or through hand delivery/courier.
• To submit comments using EPA's electronic public docket, go directly to EPA Dockets at
http://www.epa.gov/edocket, and follow the online instructions for submitting comments.
Once in the system, select "search," and then key in Docket ID No. OW-2002-0039.
• To submit comments by e-mail, send comments to OW_Docket@epa.gov, Attention Docket
ID No. OW-2002-0043. If you send an e-mail comment directly to the Docket without going
through EPA's electronic public docket, EPA's e-mail system automatically captures your e-
mail address, which is included as part of the comment that is placed in the official public
docket.
To submit comments on a disk or CD ROM, mail it to the address identified below. These
electronic submissions will be accepted in WordPerfect or ASCII file format. Avoid the use
of special characters and any form of encryption.
To submit comments by mail, send three copies of your comments and any enclosures to:
Water Docket, Environmental Protection Agency, Mail Code 4101T, 1200 Pennsylvania
Ave., NW, Washington, DC, 20460, Attention Docket ID No. OW-2002-0043.
• To submit comments by hand delivery or courier, deliver your comments to: Water Docket,
EPA Docket Center, Environmental Protection Agency, Room B102, 1301 Constitution
Ave., NW, Washington, DC, Attention Docket ID No. OW-2002-0043.
Please identify the appropriate docket identification number in the subject line on the first page
of your comment. If you submit an electronic comment, please include your name, mailing
address, and an e-mail address or other contact information in the body of your comment. Also
include this contact information on the outside of any disk or CD ROM you submit, and in any
cover letter accompanying the disk or CD ROM.
For public commenting, please note that EPA's policy is that public comments, whether
submitted electronically or in paper, will be made available for public viewing in EPA's
electronic public docket as EPA receives them and without change, unless the comment contains
copyrighted material, confidential business information, or other information whose disclosure is
restricted by statute.
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Contents
Tables and Figures iv
Acronym List v
1.0 Introduction 1-1
1.1 What is a Significant DBF Excursion? 1-1
1.2 What Should Systems do to Address Significant Excursions? 1-3
1.3 Organization of this Guidance Manual 1-3
2.0 Causes of Significant DBF Excursions 2-1
2.1 Fundamentals of DBF Formation 2-1
2.2 Impacts of Changes in Source Water Quality on DBF Concentrations 2-2
2.3 Impacts of Changes in Treatment Plant Operations on DBF Concentrations .. 2-8
2.4 Impacts of Distribution System Characteristics on DBF Concentration 2-15
3.0 Identifying the Cause Of and Documenting Your
DBF Significant Peak Excursion 3-1
4.0 Best Management Practices and Distribution System
Improvements to Reduce DBP Concentrations 4-1
4.1 Modifications to Improve Water Quality in Storage Tanks 4-1
4.1.1 Minimizing Hydraulic Residence Time of Storage Tanks 4-2
4.1.2 Improving Mixing Characteristics of Storage Tanks 4-2
4.2 Decommissioning Storage Tanks 4-5
4.3 Modifications to Improve Water Quality in Pipes 4-5
4.3.1 Minimizing Hydraulic Residence Time in Pipes 4-6
4.3.2 Reducing Disinfectant Demand 4-7
4.4 Booster Disinfection 4-8
4.5 Overall Strategy to Manage Water Age 4-9
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Tables and Figures
Tables
1. Example 1-1 TTHM and HAAS Monitoring Data 1-2
2.1 Free Chlorine, TTHM, and HAAS Data for Five Storage Tanks 2-15
Figures
2.1 Effect of NOM Concentration on TTHM and HAAS Concentration 2-3
2.2 Impact of Water Temperature on DBF Speciation 2-4
2.3 Impact of Bromide on TTHM Speciation 2-5
2.4 Effect of pH on TTHM Formation 2-6
2.5 Impact of Pre-chlorination Dose on In-Plant DBF Formation 2-7
2.6 Effect of Disinfectant Residual and Residence Time on TTHM 2-9
2.7 Effect of Point of Chlorination on TTHM and HAAS Concentrations 2-10
2.8 Effect of Disinfectant Residual and Residence Time on TTHM 2-15
2.9 Effect of Point of Chlorination on TTHM and HAAS Concentrations 2-16
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Acronyms
CFD
CFR
CT
DBF
DOC
EPA
FACA
GAC
HAAS
HPC
IDSE
IESWTR
LRAA
LT1ESWTR
MCL
M-DBP
MG
MOD
NOM
QA/QC
SCADA
Stage 2 DBPR
SWTR
THM
TOC
TTHM
Computational Fluid Dynamic
Code of Federal Regulations
Disinfectant residual x contact time
Disinfection Byproduct
Dissolved Organic Carbon
Environmental Protection Agency
Federal Advisory Committees Act
Granular Activated Carbon
Haloacetic Acids [total of five]
Heterotrophic Plate Count
Initial Distribution System Evaluation
Interim Enhanced Surface Water Treatment Rule
Locational Running Annual Average
Long Term 1 Enhanced Surface Water Treatment Rule
Maximum Contaminant Level
Microbial-Disinfectants/Disinfection Byproduct
Milligrams
Million Gallons per Day
Natural Organic Matter
Quality Assurance/Quality Control
Supervisory Control and Data Acquisition
Stage 2 Disinfectants and Disinfection Byproducts Rule
Surface Water Treatment Rule
Trihalomethane
Total Organic Carbon
Total Trihalomethanes
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1.0 Introduction
The Stage 2 Microbial-Disinfection Byproducts (M/DBP) Agreement in Principle
acknowledges that significant excursions of DBF levels will sometimes occur, even when
systems are in full compliance with the enforceable Maximum Contaminant Level (MCL). EPA
has developed this manual to give guidance to States and public water systems on identifying
significant excursions and how to conduct peak excursion evaluations and reduce such peaks.
The specific objectives of this manual are to:
• Define significant DBF excursions
• Summarize requirements for addressing significant excursions
• Provide a methodology for identifying the cause of significant excursions
• Provide guidance for documenting significant excursions
• Present the options available to reduce DBF concentrations in the distribution system
• List additional references
1.1 What is a Significant DBF Excursion?
The Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR), under Stage 2B,
requires systems to meet a running annual average of 80 |ig/L for total trihalomethanes (TTHM),
and 60 |ig/L for haloacetic acids (HAAS) at each monitoring location in the distribution system
(40 CFR 141, Subpart Q, Appendix A). Because the individual samples are averaged over one
year to determine compliance with the Stage 2 DBPR, the DBF levels at a given location can
fluctuate throughout the year. This is normal and generally the result of seasonal changes in
water temperature and/or organic content.
States must define the criteria for determining that a significant DBF excursion has
occurred as a special primacy condition of the Stage 2 DBPR (40 CFR 142.16). One approach a
State might use in identifying a significant excursion is to define a maximum concentration that,
if exceeded, would require an evaluation. For example, a State may define a significant DBF
excursion as any compliance sample that exceeds the following:
• TTFDVI concentration of 100 |ig/L
• HAAS concentration of 75 |ig/L
Another approach a State may take to defining a significant DBF excursion is to compare
results from individual quarterly measurement from compliance monitoring with the LRAAs
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computed for that period. Using 40 ug/L for TTHM and 30 ug/L for HAAS as a benchmark, a
significant excursion occurrs under the following conditions:
• For TTHM, the difference between a quarterly location measurement and the quarterly
LRAA is > 30 ug/L and the LRAA is • *40 ug/L for TTHM a significant excursion has
occurred.
For HAAS, the difference between a quarterly location measurement and the quarterly
LRAA is > 25 ug/L and the LRAA is • 40 ug/L for TTHM
EPA developed this approach based on analyses of data collected under the Information
Collection Rule (ICR). The following example illustrates how a significant excursion is
identified with the "difference approach."
Example - Significant Excursion Occurrence Identified by the Difference
Approach
Your system is required to monitor at 4 SMP locations. During the last sampling period which
took place in June 2004, your city experienced higher HAAS values relative to the LRAA at one
monitoring location (#4). DBF data from the previous year and most recent sampling period
(five quarters total) are presented in the table below.
Example TTHM and HAAS Monitoring Data
Locations
#1
#2
#3
#4
TTHM (ug/L)
LRAA
Pre-June
2004
Avg.
65
63
64
49
June
2004
Data
63
72
81
79
LRAA
June
2004
Avg.
67
64
68
66
HAAS (ug/L)
LRAA
Pre-June
2004
Avg.
40
33
43
40
June
2004
Data
52
59
51
84
LRAA
June
2004
Avg.
40
38
46
50
1Data for sampling conducted on June 2004, September 2004, March 2004, and December 2003. Data
relevant to peak excursions are bold and underlined.
Data for June 2004 at location #2 meet the criteria of significant excursion. Specifically, the
significant excursion was identified using the following two-step procedure:
Monitoring location #2 (HAAS Significant Excursion):
Step 1: Is the quarterly pre-June 2004 LRAA (HAAS) >30 |ig/L?
If yes a significant excursion is possible.
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The quarterly Pre-June 2004 LRAA (HAAS) is 33 ng/L (see Table 1-1) and is greater then 25
Hg/L, thus a significant excursion is possible (see definition of significant excursion in section
1.1).
Step 2: Is the difference between the quarterly location measurement for HAAS and
quarterly pre-June 2004 LRAA (HAAS) > 25 ug/L?
If yes a significant excursion has occurred.
Quarterly location measurement is 59 |j,g/L and the quarterly Pre-June 2004 LRAA (HAAS) is
33 |J,g/L (see data in table).
59 - 33 ng/L = 26 ng/L.
The difference between quarterly location measurement and quarterly Pre-June 2004 LRAA is
greater than 25 |J,g/L, thus a significant excursion has occurred (see definition of significant
excursion in section 1.1).
1.2 What Should Systems do to Address Significant Excursions?
A significant excursion, as defined above, is not a violation of the Stage 2 DBPR and
does not require any public notification or reporting as significant excursions or violations in
your Consumer Confidence Reports. Reducing DBF concentrations is a primary objective of the
Stage 2 DBPR and is an important goal in providing quality drinking water. Chapter 4 of this
guidance manual suggests operational improvements, alternative disinfection strategies, and
DBF precursor removal technologies that can be used to reduce DBF concentrations.
The Stage 2 DBPR does require you to:
1) Evaluate distribution system operational practices to identify opportunities to reduce
DBF levels (such as tank management and to reduce residence time and flushing
programs to reduce disinfectant demand).
2) Review the evaluation with your State no later than the next sanitary survey.
Because it may be a few years between the significant excursion and your next sanitary survey,
EPA strongly encourages systems to take immediate steps to identify and document the cause of
the excursion.
1.3 Organization of this Guidance Manual
This guidance manual is organized as follows:
• Chapter 1 - Introduction: Presents the Stage 2 DBPR requirements for addressing
significant DBF excursions.
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Chapter 2 - Causes of Significant DBF Excursions: Identifies the most common causes
of significant DBF excursions.
• Chapter 3 - Identifying the Cause Of and Documenting Your DBF Significant Peak
Excursion: Provides a template for documenting a significant excursion in addition to
guidance for identifying the cause.
Chapter 4 - Best Management Practices and Distribution System Improvements to
Reduce DBF Concentrations: Summarizes the options available to reduce DBF
significant concentrations, including operational changes and distribution system
modifications.
• Chapter 5 - References
Appendix A discusses the fundamentals of DBF formation. Appendices B through E are
examples of completed evaluation reports compiled when the significant excursion is identified
using the "maximum concentration approach" (> 100 |ig/L for TTHMs and > 75 |ig/L for
HAAS). Appendice F is an examples of completed evaluation reports compiled when the
significant excursion is identified using the "difference approach."
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2.0 Causes of Significant DBF Excursions
Significant excursions typically occur as a result of changes in source water quality,
changes in treatment plant operations or as a result of distribution system characteristics or
changes that impact DPB levels. This chapter discusses each of these causes, and is organized as
follows:
2.1 Fundamentals of DBF Formation
2.2 Impacts of Changes in Source Water Quality on DBF Concentrations
2.3 Impacts of Changes in Treatment Plant Operations on DBF Concentrations
2.4 Impacts of Distribution System Characteristics on DBF Concentrations
Chapter 3 follows with a guide to identifying causes of specific DBF excursion events.
2.1 Fundamentals of DBP Formation
TTHM and HAAS are primarily formed by the reaction of chlorine or chloramines with
natural organic matter (NOM). The amount of TTHM and HAAS formed is impacted by a
number of occurrences including the following factors:
• NOM concentration
• NOM characteristics
• Chlorine or chloramine concentration
• Concentration of other DBP precursors (e.g., bromide)
• pH
Temperature
• Reaction time (contact time)
The following sections discuss how each of these factors affects the formation of TTHM
and HAAS and how changes in these parameters may result in increases in TTHM and HAAS
concentrations. Greater detail regarding the formation of TTHM and HAAS is provided in
Appendix A.
2.2 Impacts of Changes in Source Water Quality on DBP Concentrations
Changes in source water quality that affect the reaction between NOM and chlorine or
chloramines can increase TTHM and HAAS concentrations. Typically, changes that increase
TTHM and HAAS concentrations include the following occurrences:
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• Increase in source water NOM
• Increase in source water temperature
• Increase in source water bromide concentration
• Changes in NOM characteristics
Changes in other source water characteristics (e.g., pH or alkalinity)
Change in source of water supply
2.2.1 Increase in Source Water NOM
NOM is a precursor to the formation of TTHM and HAAS. Therefore, increases in the
source water NOM concentration not addressed by adjustments in the treatment process can
lead to increased formation of TTHM and HAAS both in the plant and in the distribution system.
Surface water sources may have increases in organic matter following periods of heavy
rainfall which causes greater surface water runoff. These events do not need to occur locally to
result in an increase in NOM. A rainfall event miles upstream from a raw water intake can result
in increased NOM concentrations. Other causes of increased NOM concentrations include lake
or reservoir turnover, river scour, and point source pollution (e.g., wastewater treatment plant
discharges, filter backwash or other discharges from upstream water treatment plants, and
industrial discharges). Some plant operation changes can cause increases in source water NOM
(e.g., inadequate sludge removal in pre-sedimentation or sedimentation basins).
Figure 2.1 shows the effect of NOM concentration (measured as total organic carbon
[TOC]) and time on TTHM and HAAS concentrations. As NOM concentration increases, both
TTHM and HAAS concentrations also increase.
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Figure 2.1 Effect of NOM Concentration on TTHM and HAAS Concentration
(chlorine dose 4.3 mg/L)
Effect of Organic Content on
TTHM and HAAS Concentration
100
0.5
1 1.5
TOC (mg/L)
Source: A. Franchi and C. Hill (2002).
2.2.1 Increase in Source Water Temperature
The rate of reaction between chlorine (and chloramines) and NOM increases as the water
temperature increases. As a result, TTHM and HAAS concentrations can be higher during
periods of warmer source water temperatures. Most 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 is dependent on a
number of -specific factors, including source water type (ground or surface water), climate, and
hydrology.
Surface water temperatures are normally impacted by ambient temperatures and other
environmental factors, such as rainfall and snow melt, while ground water temperatures
generally exhibit less seasonal variability. Raw water storage can also effect the source water
temperature. Specifically, long holding times in raw water storage basins in summer months can
significantly increase temperatures.
Water temperature can also affect the relative concentrations of TTHM and HAAS
resulting in the formation of proportionally more TTHM or HAAS. Figure 2.2 illustrates this
effect. In the example, TTHM is the predominant species formed at a water temperature of 24°
C. However, the situation is reversed with greater HAAS than TTHM concentrations when the
water temperature reaches 3° C.
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Figure 2.2 Impact of Water Temperature on DBF Speciation
TTHM and HAAS Concentrations (T = 24 C)
10 15
Water Age (days)
TTHM and HAAS Concentrations (T = 3 C)
10 15
Water Age (days)
Source: A. Franchi and C. Hill (2002).
2.2.3 Increase in Source Water Bromide Concentration
Some source waters may experience periodic changes in bromide concentration. For
example, as an aquifer's water level decreases, the bromide concentration of ground water from
that aquifer may increase, resulting in higher than normal bromide levels during drought
conditions. As the aquifer is recharged, bromide concentrations are diluted to normal levels.
Brackish water or seawater intrusion into ground water and surface water sources due to
withdrawals or drought conditions are other potential causes of increased bromide
concentrations.
An increase in the source water bromide concentration can increase the formation of
brominated THM and HAA species. This may be accompanied by corresponding decreases in
chlorinated THM and HAA species. However, it can result in an overall increase in TTHM and
HAAS concentrations.
Figure 2.3 demonstrates the impact of bromide concentration on THM speciation. The
figure shows individual THM species as a percent of TTHM. For this particular source water, at
low bromide concentrations the TTHM concentration consists almost entirely of chloroform. As
the bromide concentration increases, the concentration of the brominated THM species
increases, and is accompanied by a decrease in the chlorinated THM species (both as a percent
and as a measured concentration). Although not shown, similar trends can occur for HAA
species.
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Figure 2.3 Impact of Bromide Concentration on TTHM Speciation
Variation in TTHM Speciation with Increasing
Influent Bromide Concentration
100%
80%
60%
40%
20%
0%
n
IE
0.035 0.077 0.09 0.17
Influent Bromide (mg/L)
0.22
Source: C. Hill (2002). [To be published.]
2.2.4 Change in NOM Characteristics
The characteristics of NOM in a system can have significant impacts on the formation of
DBFs. NOM can be derived from many sources in a watershed, such as decomposition of
vegetation and dead organisms. Water and wastewater treatment plant discharges, agricultural
and urban area runoff, and septic system leachate discharge are other potential sources of NOM.
NOM is typically classified as either hydrophilic (more soluble) or hydrophobic (less
soluble and containing a greater aromatic fraction). Hydrophilic NOM is more difficult to
remove than hydrophobic NOM, but also forms fewer DBFs than hydrophobic NOM (Liang and
Singer, 2001). Therefore, an increase in the concentration of hydrophobic NOM may be
accompanied by an increase in DBF concentrations. Potential causes which may change the
balance between hydrophilic and hydrophobic fractions of NOM include the following events:
• Rain events that can wash organic matter of terrestrial origin (normally more
hydrophilic) into a receiving water body.
• Algal blooms that result in the production of aquagenic organic matter (more
hydrophobic).
Surface water intrusion into ground water supplies which can affect the composition
of NOM in the blended water.
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2.2.5 Changes in Other Source Water Characteristics
Changes in other source water characteristics, such as pH or alkalinity, can impact
TTHM and HAAS formation. 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), resulting in less NOM
removal and leaving more NOM available for reaction with chlorine or other disinfectants
downstream in the treatment process.
Increasing pH conditions typically lead to increasing TTHM and decreasing HAAS
concentrations. Figures 2.4 (for TTHM only) and 2.5 (for TTHM and HAAS) illustrates this
effect. It is worth mentioning that many plants adjust pH to above 7 for corrosion control and,
thus affect the balance between TTHM and HAAS concentrations.
Figure 2.4 Effect of pH on TTHM Formation
Effect of pH on TTHM Formation
50 100
Time (hours)
150
Source: Plot obtained using the mathematical model developed by Amy et al. (1987).
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Figure 2.5 Effect of pH on TTHM and HAAS Formation
(results obtained through SDS tests, DBFs measured after a time correspondent to
plant effluent, the chlorine residual after application was 2.3 mg/L)
Effect of pH on TTHMs and HAAS Concentrations
140.0
120.0
100.0
80.0
60.0
40.0
20.0
Source: Data from Franchi et al., 2002
Increases in source water alkalinity can also result in an increase in TTHM and HAAS
concentrations. Alkalinity serves as a buffer and minimizes the reduction in pH which typically
results from the addition of a coagulant during the treatment process. High alkalinity can reduce
NOM removal during treatment as a result of the higher process pH.
2.2.6 Change in Raw Water Supply
Seasonal changes in source water supplies or the use of a temporary water supply may
also result in an increase in TTHM and HAAS concentrations. For example, a system that
supplements a low-NOM ground water source with surface water supply during the summer may
experience increases in DBFs as a result of increased source water NOM, or increases in source
water temperature (surface water supplies are typically warmer than ground water supplies
during summer months). On the other hand, a system that supplements its surface water supply
with high-bromide ground water may also experience an increase in DBF concentrations.
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2.3 Impacts of Changes in Treatment Plant Operations on DBF Concentrations
Changes or deficiencies in treatment practices can increase TTHM and HAAS
concentrations. This section describes the potential impact of common changes in treatment
processes, including the following common treatment units:
• Pretreatment
Coagulation/flocculation
• Settling
• Filtration
• Disinfection
Lastly, this section discusses the impact of treatment plant shutdowns on DBF formation.
2.3.1 Pretreatment
The primary causes of increased TTHM and HAAS formation resulting from the pre-
treatment process include:
• Increases in raw water storage holding time
• Poorly controlled or excessive pre-chlorine dose
Change in oxidant
As previously discussed, the rate of TTHM and HAAS formation increases as
temperature increases. Long detention times in raw water storage basins may cause source water
temperature to increase and consequently, increase the amount of TTHM and HAAS formed.
Pre-oxidation of raw water with chlorine is a common practice used for several reasons,
including color removal, taste and odor control, iron and manganese removal, hydrogen sulfide
control and removal, and coagulation enhancement. However, because of the large
concentration of NOM and the long residence time available for the reaction with chlorine
adding chlorine to the raw water can result in high DBF concentrations. Figure 2.6 illustrates
that greater DBF concentrations are produced when chlorine is added to the raw water than when
added to the settling basin effluent.
Figure 2.6 Effect of Pre-Chlorination on In-Plant DBP Formation
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(results obtained through SDS tests, DBFs measured after a time correspondent to
plant effluent, the chlorine residual after application was 1.5 mg/L)
Effect of Pre-Chlorination on In-Plant DBP Formation
30
| 25
w 20
I 15
| 10
t 5
0
Pre-chlorination Post-sedimentation
point of chlorine addition
Source: A.
Franchi and C. Hill (2002).
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 which involve the use of pre-oxidation with chlorine (i.e., for arsenic
treatment) may also increase DBP formation. Figure 2.7 demonstrates the impact of the chlorine
dose on in-plant DBP formation.
A change in the pre-oxidant type may result in an increase in DBP concentrations.
Systems that change from using potassium permanganate as a pre-oxidant (which does not form
TTHM and HAAS) to using chlorine for disinfection credit may experience increases in TTHM
and HAAS as a result. Similarly, 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 DBP) in systems with sufficient bromide
present in the source water.
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Figure 2.7 Impact of Increasing Chlorine Dose on In-Plant DBF Formation
(results obtained through SDS simulations, DBFs measured after a time correspondent
to plant effluent, the chlorine added after flash-mixing, residual after application was 1.5
mg/L)
^0 -,
5" 45
0) 4t>
3
"~" 4D
U) ^u
< 35
i_
° ^0
^
E 25
h- £3
Of)
f
Effect of Chlorine Dose on
In-Plant DBP Formation
*TTHM
• HM5
•
I 2.5 3 3
Chlorine Dose (mg/L)
5
Source: A. Franchi and C. Hill (2002).
2.3.2 Coagulation/Flocculation
The primary causes of increased TTHM and HAAS formation during the coagulation/
flocculation process include the following events:
• Changes in the raw water matrix that are not adequately addressed with process
control.
• Spikes in the influent NOM concentration (e.g., when backwash water is returned to
the plant influent) that are not addressed by treatment process adjustments (e.g.,
coagulant dose).
• Poor regulation of coagulant feed rate or coagulant equipment failure.
• Poor regulation of chemicals (including lime, caustic, or acid) used to control pH
and/or chemical feed equipment failure.
The coagulant type (e.g., alum or ferric chloride) and dose are critical to the effective
removal of NOM. An inadequate coagulant dose or poorly selected coagulant may result in a
larger fraction of NOM passing through the coagulation/flocculation and settling processes. This
increased NOM concentration can lead to increased formation of TTHM and HAAS.
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Filter backwash may contain elevated concentrations of NOM. 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 NOM. Similarly, if an increase in source
water NOM is not accompanied by a corresponding increase in the coagulant dose, additional
NOM will likely be present at the point of chlorination and will likely increase TTHM and
HAAS formation.
During coagulation, pH variations can affect NOM removal and DBF formation.
Generally, NOM removal decreases as pH increases. If less NOM is removed during the
coagulation process, then more NOM is available for TTHM and HAAS formation in the
downstream treatment process (see Figure 2.1). Since higher pHs favor THM formation
reactions, increasing pH tends to increase TTHM levels in relation to HAAS (see Figures 2.4 and
2.5).
2.3.3 Settling
If a chlorine residual is carried through the settling basin, TTHM and HAAS levels can
increase as a result of:
• Poor regulation of chlorine dose due to improper feed rate control or equipment
failure
• Increased holding time for settling due to reductions in plant flow
Both of these circumstances, independently or in combination, can cause increases in
TTHM and HAAS concentrations. The effects of increasing chlorine dose on TTHM and
HAAS levels have been previously illustrated in Figure 2.7.
Process changes can still result in the occurrence of peak TTHM or HAAS even if the
chlorine residual is not carried through the settling basin(s). For example, 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 soluble or particulate NOM. This "additional" NOM load is available for
reaction with chlorine in the basin, or may be carried through the settling process to the point of
disinfection addition.
2.3.4 Filtration
Increases in organic loading during a filter cycle, or the breakthrough of particles at the
end of the filter cycle run, result in an increase of DBFs entering the distribution system. When
biologically active filters and granular activated carbon (GAC) filters are used for organic
precursors removal, breakthroughs 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 sudden TTHM and HAAS peak concentrations in
the finished water.
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2.3.5 Disinfection
The following disinfection related events can increase the formation of TTHM and
HAAS:
• Increased chlorine dose and/or residual (intentional or unintentional)
• Increased holding time of water in the clearwell
• Changing point of chlorine addition
• Changes in primary disinfectant type
• Free chlorine "burnout" periods in chloraminated systems
Systems are required by the Surface Water Treatment Rule (SWTR), Interim Enhanced
Surface Water Treatment Rule (IESWTR) and Long Term 1 Enhanced Surface Water Treatment
Rule (LTIESWTR) to maintain a certain level of CT (disinfectant residual x contact time) for
disinfection. As the disinfectant dose decreases, the required contact time increases to maintain
a required level of CT, and vice versa. 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). Figure 2.8
shows the impact of residence time on TTHM concentrations at two disinfectant residual
concentrations. The effect of residence time on HAAS concentrations is similar, but less
pronounced. In other words, HAAS formation occurs more rapidly and may not increase as
significantly as TTHM over long periods of time (particularly in chloraminated systems).
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Figure 2.8 Effect of Disinfectant Residual and Residence Time on TTHM
Effect of Disinfectant Residual on TTHM
Concentration
45
40
35
• Chlorine = 1 mg/L
• Chlorine = 3 mg/L
0
0 25 50
Distribution System Residence Time (hours)
Source: Plot obtained using the mathematical model developed by Amy et al. (1987).
Poor mixing in the clearwell 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. Section 2.4 discusses this issue in
greater detail. 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.
In addition to changes in detention time and dose in the clearwell, changing the point of
chlorine (or other disinfectant) addition can have a significant impact on TTHM and HAAS
formation. Systems that practice pre-chlorination (i.e., addition of chlorine to raw water) will
likely form more TTHM and HAAS as a result of the higher NOM content of the water prior to
coagulation and clarification, as well as the increased contact time through the treatment plant.
Similar effects are likely for systems that add chlorine to the rapid mix basin, as NOM typically
has not yet been removed from the raw water at this point in the treatment plant. Systems that
add chlorine following clarification, or post-filtration, will likely experience lower TTHM and
HAAS concentrations because of the removal of NOM prior to chlorine addition.
Figure 2.9 shows 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
between pre-chlorination and rapid mix. This is primarily due to the fact that no NOM has been
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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% and 50%, respectively.
Figure 2.9 Effect of Point of Chlorination on TTHM and HAAS Concentrations
Effect of Alternative Locations for Chlorine Addition
Point on In-Plant DBP Formation
Pre-
chlorination
Rapid Mix Post-
flocculation
point of chlorine addition
Post-
sedimentation
Source: A. Franchi and C. Hill (2002).
Systems that change the point of chlorine addition seasonally to adjust for changes in raw
water quality may experience fluctuations in DBFs as a result of those changes. For example
systems where pre-chlorination is used seasonally to control taste and odor may see increases in
TTHM and HAAS concentrations during those periods.
Many systems have converted to chloramines for secondary disinfection to reduce TTHM
and HAAS formation. Use of chloramines can lead to nitrification in the distribution system,
causing microbiological and taste and odor problems. Some chloraminated systems periodically
switch to free chlorine for a "burnout" period to inactivate the nitrifying bacteria. During these
burnout periods, systems may experience temporary increases in TTHM and HAAS
concentrations.
2.3.6 Plant Shutdowns
Plant shutdowns and routine start/stop operations can lead to peak TTHM and HAAS
concentrations. During shutdowns, the holding time of chlorinated water within the plant can be
long and result in the formation of higher than normal TTHM and HAAS concentrations. When
the plant is placed back in service, water containing high TTHM and HAAS levels may enter the
distribution system. Similar increases in TTHM and HAAS concentrations may be observed at
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the beginning of each working cycle at plants that operate less than 24 hours per day. Effect of
filter spikes coagulation not optimized in start/stop operations. Even small start spikes can
increase NOM. In these plants, the residence time can be extremely long. If a plant practices
pre-chlorination, significant concentrations of TTHM and HAAS may form in the treatment
plant.
2.4 Impacts of Distribution System Characteristics on DBF Concentration
This section discusses distribution system conditions which may result in higher than
normal formation of TTHM and HAAS. Specifically, this section discusses:
• Poor mixing and inadequate volume turnover in storage tanks
• Dead ends and stagnant zones in the distribution system
• Use of booster disinfection
System maintenance activities
2.4.1 Poor Mixing and Inadequate Volume Turnover in Storage Tanks
To illustrate water quality problems associated with storage tanks, Table 2.1 presents free
chlorine, TTHM, and HAAS concentrations at the top and bottom of three tanks. Each tank has
a common inlet/outlet located at the bottom of the tank. Each tank is also poorly mixed, as
evidenced by the difference in free chlorine concentrations at the top and bottom of the tank, but
each has a different associated water quality problem.
Table 2.1 Free Chlorine, TTHM, and HAAS Data for Five Storage Tanks
Tank No.
1
2
3
Free CI2 @
Top of
Tank
0.3
0.2
0.0
Free CI2 @
Bottom of
Tank
1.3
1.0
1.0
TTHM@
Top of
Tank
110
130
98
TTHM@
Bottom of
Tank
72
59
99
HAA5@
Top of
Tank
57
12
31
HAA5@
Bottom of
Tank
61
44
61
Source: Mahmood (2002). [To be published.]
Tank 1 Free chlorine concentration is relatively low at the top of the tank. TTHM
concentration is higher in the top of the tank. HAAS concentration is fairly consistent
indicating HAAS formation has stopped, or more likely the early stages of
biodegradation of HAAS.
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Tank 2 Like Tank 1, TTHM concentration has increased in the top of the tank, but
biodegradation of HAAS has clearly begun.
Tank 3 Based on TTHM data, it would appear the tank is well mixed. However, the difference
in free chlorine and HAAS concentrations indicate otherwise. This demonstrates the
importance of looking at multiple parameters when evaluating mixing in storage tanks.
Under normal daily operation, older water or unmixed portions of the stored water at the
top of these tanks may not be utilized. However, events such as a main break or fire flow can
draw water from the portions of the tank with high water age (and high TTHM and/or HAAS
concentrations) into the distribution system.
2.4.2 Dead Ends and Stagnant Zones in the Distribution System
Dead ends in a distribution system can lead to excessive water age. A dead end may be
the result of distribution 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).
The water age in a stagnant zone can also be very high. 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 flow to a stagnant zone from other areas. When there is an unusual shift in water
demand pattern in the vicinity of a stagnant zone, high age water from the stagnant areas can
flow to other parts of the distribution system and become available for consumption. The shift in
water demand pattern can be due to several factors including: unusually high water demand (e.g.
large customers on/offline); increased seasonal demand; changes in the water pressure, or flow
patterns and flow rates (e.g., when a seasonal groundwater source is directly fed into the
distribution system).
Figure 2.10 shows the effect of distribution system residence time on TTHM
concentrations for both free chlorine and chloraminated systems. Note that the effect of water
age is more dramatic for chlorine systems than for chloramine systems (see Appendix A for a
discussion of formation kinetics).
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Figure 2.10 Relationship Between TTHM and Distribution System
Residence Time
Relationship Between TTHM Concentrations and
Distribution System Residence Time
200
160
O)
~ 120
80
40
-Free Chlorine
-Chloramines
10 20 30 40
Residence Time (hours)
50
60
Source: A. Franchi and C. Hill (2002).
2.4.3 Booster Disinfection
Booster disinfection is often used to maintain a disinfectant residual in sections of a
distribution system that might not otherwise maintain a residual. In some cases, booster
disinfection is used on an intermittent basis based on water quality conditions. For example, the
loss of chlorine residual in certain sections of a distribution system may be due to a seasonal
change in the source water, changes in the water demand, or may occur during the summer when
higher temperatures promote microbial growth and increase chlorine demand, warranting use of
booster chlorination.
When properly controlled and coordinated with the treatment plant disinfection process,
booster disinfection can be used to reduce average distribution system DBF concentrations. To
accomplish this, the disinfectant dose applied at the plant must be minimized to reduce DBF
formation while maintaing 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.
While booster disinfection can reduce system average DBF concentrations, DBFs are
likely to increase after booster disinfection is applied. Table 2.2 illustrates this point, showing
DBF concentrations for locations before and after booster disinfection. Prior to booster
disinfection (water age = 24 to 40 hours), the TTHM concentration remained fairly constant
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because the disinfectant residual was nearly depleted. On the other hand, as the disinfectant
residual depleted (suggesting microbiological activity), the HAAS concentration decreased
substantially. After booster chlorination, both TTHM and HAAS concentrations increased
(HAAS increased beyond the concentrations present before biodegradation).
Table 2.2 Effect of Booster Chlorination on TTHM and HAAS Concentrations
(Concentrations measured at various locations in the distribution system)
Water Age
(Hours)
TTHMs
(ppb)
HAAS (ppb)
Free
Chlorine
Residual
(mg/L)
Before Booster Chlorine Addition
2
66
41
2.6
24
130
47
0.3
40
150
7
0.0
After Booster Chlorine Addition
41
160
77
1.0
50
170
95
2.2
70
170
71
0.5
Source: A. Franchi and C. Hill (2002)
The location of the booster station can also impact the effectiveness of booster
disinfection at reducing system average DBF levels. The use of several smaller booster stations
closer to the end of the system may be more effective in reducing system average DBF levels
compared to a single large station that treats a much larger percentage of the system water, some
of which may not need additional disinfection. Several smaller booster stations can also allow
the total amount of added disinfectant to be reduced compared to a single large booster station.
2.4.4 System Maintenance Activities
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.
AWWA Standard C651-99, Disinfecting Water Mains., provides more detailed information
regarding the disinfection of new and repaired distribution system piping.
Frequently, pipe repair work is accompanied by the closure of valves to isolate sections
of pipes. 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.
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3.0 Identifying the Cause Of and Documenting a
DBF Significant Peak Excursion
Under the Stage 2 DBPR, if a significant excursion occurs, systems are required to
evaluate distribution system operations to identify opportunities to reduce DBF levels and
discuss the evaluation with the State no later than the next sanitary survey (40 CFR 141.626).
This chapter provides guidelines to help identify the cause of an excursion event and presents a
template for documenting the evaluation of it (referred to as a "Significant Excursion Evaluation
Report"). Distribution system best management practices that can be implemented to reduce
peak DBF concentrations are discussed in Chapter 4.
The Significant Excursion Evaluation Report form begins on page 3-3. A supplemental
form for recording water quality data is presented on page 3-13. While the use of these forms is
not required, a significant excursion evaluation report should be detailed enough to provide
information regarding the location and cause of the excursion, as well as any proposed changes
or actions intended to prevent the reoccurrence. At a minimum, the documentation should
include:
1. Location, date, and time that the excursion sample(s) was collected. (Were multiple
excursions recorded during this sampling period? If so, and it is believed the
excursions are related, only one report is needed.)
2. Schematic or map showing the location of each excursion relative to the distribution
system and treatment plant(s).
3. Summary of monitoring results from this sampling period.
4. Historical summary of DBF concentrations at the excursion sample location(s). (Has
this sample location had a significant excursion before? If yes, when did the previous
excursion(s) occur?)
5. Perceived cause of the significant excursion. The template in this chapter includes a
checklist to help identify the cause(s) of the peak.
6. Steps taken or planned to reduce future peaks.
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Examples of peak excursion evaluation reports and completed checklists are provided in the
appendices:
Appendix
B
C
D
E
Cause of Significant Peak Excursion
Changes in source water quality
Changes in treatment plant operation
Changes in distribution system operation
Changes in treatment plant and distribution system operation
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Significant Excursion
Evaluation Report
Page 1
Report date:
Report prepared by:
System name:
1) When was the significant excursion sample(s) collected? What were the TTHM and HAAS
concentrations?
Location No.
Location
description
Sample collection
date
Sample collection
time
TTHM LRAA
Concentration
(ug/L)
TTHM
Concentration
(ug/L)
HAAS LRAA
Concentration
(ug/L)
HAAS
Concentration
(ug/L)
Note: Attach additional sheets if you observed more than four significant excursions during this
round of sampling.
2) Where did the excursion(s) occur? Attach a schematic of your system, sketch your system in
the space below, or have a schematic of your system available to review with your state at the
time of your next sanitary survey. Indicate the location(s) of the significant excursion(s) on your
schematic.
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3) Attach (or provide in the Supplemental Data Form) all available water quality data for the round
of sampling in which the significant excursion occurred. At a minimum, include all TTHM and
HAAS results from the sampling period. You should also consider including pH, temperature,
alkalinity, TOC, disinfectant residual, and any other data that you think would be useful.
a) Were there any unusual circumstances associated with this round of sampling?
Yes No
If yes, please explain.
b) Were all analytical QA/QC measures met?
Sample preservation Yes No
Sample holding time Yes No
Other
If no, please explain.
4) Attach (or provide in the Supplemental Data Form) historical TTHM and HAAS data for the
locations) at which the significant excursions) occurred. Provide at least three years of data, if
available.
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5) What caused your excursion(s) to occur?
Sections A through F starting on page 4 can help you determine the possible cause(s) of your
excursion. Please note there may be more than one factor which resulted in your excursion.
Section A: Source water quality change
Section B: Process upset at treatment plant
Section C: Planned change or maintenance activities at plant
Section D: Planned distribution system operations or maintenance activities
Section E: Unplanned events in distribution system
If you already suspect a cause, go directly to that section. If you read Sections A through E and
are unable to determine a cause of your excursion, then complete Section F.
Consecutive systems should also contact their wholesaler to identify the cause(s) of the
significant excursion(s).
6) List steps taken or planned to reduce DBP peak levels.
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A. Source Water Quality Changes
Did any of the events listed below take place before the DBP excursion to cause TOC levels to
increase?
Heavy rain fall
Flooding
Spring snow-me It/run off
Significant decrease in rainfall or source flow
Algae bloom
Reservoir turnover
Did any of the events listed below take place before the DBP excursion to cause bromide levels
to increase?
Significant decrease in rainfall or source flow
Brackish or seawater intrusion
Did pH and/or alkalinity significantly change?
If two or more supplies are used, was a greater portion of water drawn from the one with higher
TOC?
Was raw water stored for an unusually long period of time resulting in a significant increase in
water temperature?
Conclusions:
Did source water quality changes cause or contribute to your significant excursions)?
Yes No
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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B. Process Upset at Treatment Plant
Was raw water stored for an unusually long time, providing additional contact time for DBP
formation after prechlorination?
Were there changes in coagulation practices?
Were there any changes or malfunctions of the coagulation process in the days
leading to the excursion?
Were the coagulant dose and pH properly adjusted for incoming source water
conditions?
Were there any feed pump failures, or were feed pumps operating at improper feed
rate?
Were there changes in chlorination practices?
Were there any changes in chlorine dose at any location in the plant?
Were there changes in plant flow that may have resulted in longer than normal
residence time at any location in the plant?
Did the pH change at the point of chlorine addition?
Were there any feed pump failures, or were feed pumps operating at improper feed
rate?
Were there changes in settling practices?
Was there excess sludge build-up in the settling basin that may have carried over to
the point of disinfectant addition?
Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
Were there large changes in plant flow rate that may have resulted in a decrease in
settling time or carry over of process solids?
Were there changes in filtration practices?
Have filter run times been changed to meet raw water quality changes?
Were there any spikes in individual filter effluent turbidity (which may indicate
particulate or colloidal TOC breakthrough) in the days leading to the excursion?
Did chlorinated water sit in the filter for an extended period of time?
Were all filters run in a filter-to-waste mode during initial filter ripening?
Were any filters operated beyond their normal filter run time?
If GAG filters are used: Is it possible the adsorptive capacity of the GAG bed was
reached before reactivation occurred?
If biological filtration is used: Were there any process upsets that may have resulted
in breakthrough of TOC (particularly biodegradable TOC)?
Were there significant increases in filter loading rates?
Were there changes in plant flow (i.e a temporary plant shutdown) that may have resulted in an
unusually high residence time in the clean/veil on the days prior to the excursion?
For example, a temporary plant shutdown.
Were there any other equipment failures or process upsets?
Continued on next page
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B. Process Upset at Treatment Plant (Continued)
Conclusions:
Did a process upset in the treatment plant cause or contribute to your significant excursion(s)?
Yes No
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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C. Planned Change or Maintenance Activities for the Treatment Plant
Was there a recent change (or addition) of pre-oxidant?
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?
Did you change the type or manufacturer of the coagulant?
Were there any changes in disinfection practices in the days prior to the excursion?
For example, a switch from chloramines to free chlorine for burnout period.
Discontinuation of ozone.
Prechlorination affecting biological filtration
Was a filter(s) taken off-line for an extended period of time that caused the other filters to operate
near maximum design capacity and creating the conditions for possible breakthrough?
Were any pumps shut down for maintenance, leading to changes in flow patterns or hydraulic
surges?
Conclusions:
Did a planned maintenance or operational activity in the treatment plant cause or contribute to your
significant excursion(s)?
Yes No
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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D. Planned Distribution System Operations or Maintenance Activities
Was a tank drained for cleaning or other maintenance?
Was the tank drained to waste or to the distribution system?
Was the tank returned to service directly to the system after disinfection with a high
residual remaining
Was a larger volume than normal drained to the distribution system?
If booster disinfection is used, was the booster disinfectant dose higher than the normal booster
disinfectant dose for that season?
Were there any system maintenance activities in the days prior to DBP excursion? Including:
Repairing mains or installing new mains
Closure of valves to isolate sections of pipes
Were the pipes flushed properly or were the appropriate valves re-opened after work was
completed?
Did any pump or pipeline maintenance occur that would have changed the flow pattern in the
area the sample was drawn from?
Change in flow can cause water in stagnant areas to be drawn into another area.
Did any pipeline replacement occur?
Disinfecting piping could result in a high concentration of chlorine entering the
distribution system and thus increase DBPs.
Conclusions:
Did a planned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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E. Unplanned Distribution System Events
Were there increases in demand that caused older water in storage tanks to be drawn into the
system?
Were there any major fire events?
Did one or more storage tank have greater than average drawdown preceding the
time of DBP peak excursion?
Were there decreases in demand that resulted in longer than normal system residence times?
Were there any large customers off-line?
Did any main breaks occur causing changes in flow patterns in the influence area of the sample
location?
If you collect water temperature inside storage tanks, was the temperature inside the tank higher
than normal for the season?
Were any storage tanks hydraulically or mechanically isolated from the system for an extended
period and then used preceding the time of DBP peak excursion?
Did changes in overall water demand cause a change in water demand patterns in the vicinity of
dead ends and/or stagnant zones in the system?
Were there large variations in localized system pressures that were different from the normal
pressure range that could have caused a change in water demand patterns in the vicinity of dead
ends and/or stagnant zones in the system?
Conclusions:
Did an unplanned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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F. If you were unable to identify the cause of your significant excursion(s) after reviewing
Sections A through E, are you able to identify another potential cause of your increase in
DBF concentrations? Explain.
Note: If you are unable to determine the cause of your excursion you may wish to consider:
More frequent raw water temperature monitoring.
More frequent raw water TOC monitoring.
Increased disinfectant residual monitoring in the distribution system.
Tracer studies to characterize distribution system water age.
Development of a hydraulic model to characterize the distribution system.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Supplemental Data Form
for the Significant Excursion
Evaluation
Report date:
Report prepared by:
System name:
1) Water quality data from significant excursion sampling period.
Location No.
#1
#2
#3
#4
#5
#6
#7
#8
Location Name
TTHM (ug/L)
HAAS (ug/L)
Free Chlorine (mg/L)
Total Chlorine (mg/L)
PH
2) Supplemental data from each treatment facility:
Plant #1:
Raw Water Temperature:
Plant #2:
Raw Water Temperature:
Plant Effluent Water Temperature:
Raw Water TOC:
Other Data:
Plant Effluent Water Temperature:
Raw Water TOC:
Other Data:
3) Historical TTHM and HAAS data at significant excursion sampling locations.
TTHM Data (ug/L) HAAS Data (ug/L)
Monitorina # # # # Monitorina # # #
Location
Date 1
Location
Datel
Date 2
Date 2
DateS
DateS
Date 4
Date 4
Date 5
DateS
Ava.
Avq.
Attach additional sheets if necessary
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4.0 Best Management Practices and Distribution System
Improvements to Reduce DBF Concentrations
It is common to find higher TTHM and HAAS concentrations in the distribution system
compared to concentrations leaving the treatment plant. In systems using free chlorine for
secondary disinfection, significant increases in TTHM and HAAS may occur in the distribution
system. Water age, type and concentration of NOM, the disinfectant type, and residual
concentration in the finished water are all factors that can affect TTHM and HAAS
concentrations. The previous chapter provided guidelines for identifying and documenting the
cause of significant excursions. This chapter describes several options that can be used to reduce
peak DBF concentrations in the distribution system, and is divided into the following sections:
4.1 Modifications to Improve Water Quality in Storage Tanks
4.1.1 Minimizing Hydraulic Residence Time of Storage Tanks
4.1.2 Improving Mixing Characteristics of Storage Tanks
4.2 Decommissioning Storage Tanks
4.3 Modifications to Improve Water Quality in Pipes
4.3.1 Minimizing Hydraulic Residence Time in Pipes
4.3.2 Reducing Disinfectant Demand
4.4 Booster Disinfection
4.5 Overall Strategy to Manage Water Age
4.1 Modifications to Improve Water Quality in Storage Tanks
As discussed in Section 2.4, storage tanks that are underutilized and have poor mixing
characteristics can have water with a high residence time in certain portions of the tank, causing
high DBF formation. Further, high temperatures in tanks during the summer season can increase
DBF formation. Storage tanks should be designed and operated so the overall hydraulic
residence time is minimized and the water is well mixed. Generally, water mixing in the
finished water storage tanks is not achieved through mechanical mixers, but through the kinetic
energy of the tank inflow. Low average hydraulic residence time and adequate mixing are
critical factors for minimizing DBF formation in storage tanks.
Quiescent conditions in storage tanks may lead to sediment accumulation. This
accumulation may result in loss of disinfectant residual and increased DBF formation. Operating
procedures (control of empty/fill periods), inspections and maintenance activities can minimize
this problem.
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4.1.1 Minimizing Hydraulic Residence Time of Storage Tanks
Excessive hydraulic residence time in a storage tank can result in older water with high
DBF levels. The average hydraulic residence time can be estimated by the following equation:
Average hydraulic residence time = [Vmax/(Vmax - V^n^/N
where, Vmin = average minimum daily volume
Vmax = maximum daily volume
N = number of drain/fill cycles per day
Example 4.1 shows how this formula can be used to calculate residence time in a real
tank. The formula assumes that a tank is ideally mixed. In tanks with poor mixing
characteristics, the residence time of portions of the water can be much higher than the average.
The average hydraulic residence time in a storage tank can be reduced when the volume turnover
is increased by extending drain cycles and/or increasing the number of drain/fill cycles per day.
Pumps may need to be added to a storage tank to pump out water from the tank into the
distribution system and thus increase the volume turnover of the tank. Changes in pumping
cycles may be needed to increase volume turnover.
Example 4.1 Calculating the Average Hydraulic Residence Time
Assume Your City has a 3-MG storage tank located in the distribution system. The maximum
volume (Vmax) in the tank is 2 MG at any given time during a day. The minimum volume
(Vmin) m the tank is 1 MG at any given time during the day. There are four drain/fill cycles
(N) per day. Calculate the average hydraulic residence time of the tank.
Average hydraulic residence time = [2/(2 - l)]/4
= 0.5 days
4.1.2 Improving Mixing Characteristics of Storage Tanks
The following factors effect the mixing characteristics of storage tanks:
• Fill time
• Inlet momentum
• Inlet/outlet pipe location, orientation, and tank dimensions
Desktop theoretical evaluations of hydraulic residence time, fill time, and inlet
momentum can be used to predict water mixing characteristics of a storage tank. In addition,
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temperature measurements inside a storage tank can be an effective tool in predicting the water
mixing characteristics of the tank. A temperature profile can be developed by continually
measuring the water temperature at various depths in the tank over the course of several days.
The temperature profile can then be compared against tank water level data to determine the
effectiveness of mixing and the existence of thermal stratification in the tank.
While the desktop theoretical evaluations and temperature measurements can describe
mixing characteristics quantitatively, computational fluid dynamic (CFD) modeling can describe
mixing characteristics qualitatively by providing visual images of water mixing inside a tank.
The impact of design changes on mixing characteristics can be effectively visualized using CFD
modeling, making this modeling a very useful tool to supplement desktop theoretical evaluations
and temperature measurements.
The mixing predictions can be used to identify a storage tank with inadequate mixing
characteristics and, therefore, a potential for high DBF formation. Based on the evaluations of
mixing characteristics, physical and operational modifications can then be recommended to
improve storage tank mixing.
4.1.2.1 Increasing Fill Time
For a tank operating in a fill and drain mode, 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. Experimentation has shown
that the time required for good mixing is dependent upon the volume of water in the tank, the
inlet diameter, and the filling flow rate. For some types of tanks, researchers have developed
empirical relationships for the mixing time theoretically required to completely mix the water in
the tank (Grayman et al., 2000). It is generally desirable for the actual filling time to exceed this
theoretical mixing time. Therefore, one way of increasing fill time is to allow the tank to drain
to a lower level before refilling.
4.1.2.2 Increasing Inlet Momentum
Inlet momentum (defined as velocity x flow rate) is a key factor for mixing of water in
storage tanks. The higher the inlet momentum, the better the mixing characteristics in the
storage tanks. Increasing the flow rate could be a simple way to increase momentum, but may
not be practical due to limitations of system hydraulics. For example, a pump may not be
available at the tank location and the distribution system pressure may not be high enough to get
desirable increases in flow rates. In some cases, even if a pump were available, it may not be
possible to increase the pumping rate into the tanks. In such cases, it may be more feasible to
increase the inlet momentum by increasing the velocity with a reduced inlet diameter.
4.1.2.3 Optimizing Inlet Location and Orientation
Mixing a fluid requires a source of energy input. In distribution system storage tanks,
this energy is normally introduced during tank filling. As water enters a tank, a jet is formed and
the water present in the tank is drawn into the jet. Circulation patterns are formed that result in
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mixing. The path of the jet must be long enough to allow the mixing process to develop for
efficient mixing to occur. Therefore, the inlet jet should not be pointed directly towards nearby
impediments such as a wall, the bottom of the tank, or deflectors. The degree and speed of
mixing depends primarily upon the size of the tank and the momentum of the incoming jet.
The location and orientation of the inlet pipe relative to the tank walls can have a
significant impact on mixing characteristics. For example, when the height of a tank is much
larger than the diameter or width, the location of the inlet pipe at the bottom of the tank in the
horizontal direction is likely to cause the water jet to hit the vertical wall of the tank resulting in
loss of inlet momentum and incomplete water mixing. Besides geometrical characteristics of
tanks, the mixing of water is also depend on the initial water depth in the tank. When water level
is high and the inlet pipe is oriented horizontally, the inlet momentum may not be sufficient to
completely mix water during the fill cycle. Under both situations, high concentrations of DBFs
may form in the older water stagnating at the top of the tank.
4.1.2.4 Avoiding Baffles
Water can be forced to flow through a storage tank either in a completely mixed state or a
plug flow manner. In treatment plant contact chambers where there is generally simultaneous
inflow and outflow, internal baffles are sometimes placed in tanks to encourage plug flow and
avoid short-circuiting and dead zones. However, in distribution system tanks and reservoirs that
are generally "fill and draw" operations, and where a mixed condition is preferable to plug flow,
baffles can inhibit mixing and produce zones of poor mixing. These zones have higher water age
and therefore higher DBF formation potential. Therefore, baffles should not be used in
distribution system storage facilities under most circumstances.
4.1.2.5 A voiding Tank Stratification
The temperature difference through the depth of a storage tank is referred to as thermal
stratification. Thermal stratification can be either the result or the cause of poor mixing.
Depending on the location of the inlet pipe and tank geometry, the water entering the 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 tanks with poor mixing characteristics (i.e.,
insufficient volume turnover or inlet momentum), colder, denser water may hover in the lower
depths of the tank, whereas the warmer, less dense water will have a tendency to rise to the top
of the tank. Temperature differences of less than 1°C can affect mixing characteristics.
Generally, tall tanks and tanks with large diameter inlets located near the bottom of the
tank have a greater potential for thermal stratification. If significant temperature differences are
experienced, then the orientation and diameter of the inlet pipes may need to be modified to
reduce the potential for stratification.
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4.2 Decommissioning Storage Tanks
A tank may be oversized for the water system needs and, thus, it may not be possible to
get adequate flow and water turnover in the tank. A storage tank may also be hydraulically
locked out of the distribution system due to high system pressures and low system demand,
resulting in excessive water age and high DBF formation potential. When events such as main
breaks or fire flow cause the water from these tanks to be drawn into the distribution system, the
areas receiving water from the tank may have higher than normal DBF levels. For a tank that is
hydraulically locked out under normal system operating conditions, physical modifications are
ineffective to significantly improve mixing characteristics. In such cases, operational changes
(such as reducing normal operating tank water level or increasing draw cycle time duration) or
permanent decommissioning can be considered to prevent water with high DBF levels from
entering the distribution system.
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 for equalization storage, fire flow, or emergency conditions such as main breaks or
treatment plant shutdowns.
4.3 Modifications to Improve Water Quality in Pipes
System piping improvements to reduce DBF levels include reducing the hydraulic
residence time of water in the pipes and reducing the overall disinfectant demand so that the
average chlorine dose for the finished water is lowered.
The hydraulic residence time of the water in the pipes can be lowered by:
• Looping of dead-ends and re-routing of valves
• Using blow-offs
• Replacing oversized pipes with smaller diameter pipes
The overall disinfectant demand can be lowered by:
• Replacing or cleaning and lining of unlined cast iron pipes
• Flushing
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4.3.1 Minimizing Hydraulic Residence Time in Pipes
4.3.1.1 Looping of Dead-Ends and Re-routing of Valves
The highest DBF concentrations in a system are often observed in dead ends with
stagnant water. Water in dead ends experience long contact times for DBF formation.
Construction of new pipes to loop dead ends, thereby eliminating them, can eliminate the
stagnation of water and reduce residence time, decreasing the opportunity for the formation of
high DBF levels. However, looping can also result in the creation of an even larger section of
very slow moving water. The specific hydraulic response of a system to looping must be
assessed to determine if looping will improve water flow and reduce hydraulic residence time.
Closed valves can create artificial dead-ends and lead to the development of high DBF
levels. The closed valves may remain undetected until serious water quality or fire emergency
problems develop. Attention should be paid to identify valves set in the wrong position and
correct their setting to lower detention time in the system. A complete database of all valves in
the system is essential for identifying broken or lost valves that may affect water flow.
Distribution system models and/or system maps can be useful tools to identify the occurrence of
dead ends and determine what type of piping or valve modifications may be needed.
4.3.1.2 Using Blow-Offs
Blow-offs can be used in areas of high water age and as an alternative to looping. A
continuous or automatic intermittent blow-off can remove old water from a distribution system
and pull fresh water into areas that otherwise would become stagnant. Fresh water entering an
area affected by a blow-off will have had a shorter contact time between precursors and chlorine
and, generally, lower DBF levels.
Continuous or automatic intermittent blow-offs can be used on a seasonal basis when
DBF peaks are more likely to occur (e.g., during high water temperature periods) and can vary
based on geographical regions. The need for and appropriate locations of blow-offs can be
determined by analyzing distribution system historical records for low disinfectant residuals,
presence of total coliforms or nusiance bacteria (fecal coliforms are not a result of water age or
regrowth, they are an indicator of contamination), high heterotrophic plate counts (HPCs), and
high TTHM and HAAS concentrations. A distribution system model can be used to develop
time-of-travel estimates that can help in choosing optimal blow-off locations.
4.3.1.3 Replacing Oversized Pipes
Pipe size affects water velocity and, in turn, detention time. In portions of the
distribution system where pipes are oversized, the hydraulic residence times are longer than
needed and can lead to formation of high DBF concentrations. The pipes in abandoned areas
may still be part of the overall distribution system, but may not be required or may be too large,
causing excessive hydraulic residence time. When planning replacement projects, the pipe sizes
should be reassessed based on current needs, redevelopment plans, and fire protection. Where
appropriate, the pipe sizes can be reduced or sections of pipes valved off if they are no longer
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needed to reduce the residence time of water and the potential for the formation of DBF peak
concentrations. Distribution system models can be used as a tool to determine the appropriate
pipe diameters.
4.3.2 Reducing Disinfectant Demand
4.3.2.1 Replacing, Cleaning, and Lining of Cast Iron Pipes
Corrosion and biofilms in unlined cast iron pipes or sediment deposits can exert a
disinfectant demand that lowers chlorine residual. Utilities are often forced to increase chlorine
dosages at the treatment plant or use booster chlorination to supply enough chlorine to maintain
sufficient residual in the portions of their distribution system with unlined cast-iron pipe. This
results in an excess of chlorine in other areas of the distribution system which can lead to DBF
peaks.
Systems can reduce localized chlorine decay (and thus, reduce the overall concentration
needed to maintain a residual in all parts of the system) through pipeline replacement programs.
Alternatively, pipeline cleaning-and-lining can be used to reduce chlorine residual. Pipeline
cleaning methods include high pressure sand blasting, various rodding methods, and chemical
cleaning. Among the more common lining materials are cement-mortar, asphalt (bituminous),
epoxy resins, rubber, and calcite. Cement is most commonly used, 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). For example, soft waters can progressively
hydrolize calcium silicates constituents of concrete into silica gels producing soft surfaces, and
leach calcium hydroxide from the cement lining (AWWA, 2002). Both of these occurrences can,
in the long run, compromise the integrity of the lining.
4.3.2.2 Flushing
Frequent flushing can be an effective tool to control DBF peaks by cleaning pipes that
exert chlorine demand and by lowering water age. When the chlorine demand is lowered, the
chlorine dose at the treatment plant or booster disinfection facilities may be lowered, leading to
lower DBF formation. There are alternative flushing methods: emergency flushing, conventional
flushing of dead-ends and problem areas, and directional (also known as unidirectional) flushing.
Conventional flushing is conducted by opening hydrants (it does not include directing the
flow with valves) and is considered routine distribution system maintenance. Similar to blow-
offs, conventional flushing of high detention areas is an effective tool for controlling the
occurrence of DBF peaks and can reduce the need for looping dead-ends. When conducted on a
regular basis, conventional flushing can achieve temporary reduction of DBFs primarily by
discarding old water and allowing fresher water to enter the affected area. However, with this
method it is difficult to control the quality of water entering the main being flushed and it is
possible that the quality of this water may not be superior to that leaving the system. In addition,
conventional flushing is less than optimal in controlling other factors that can contribute to high
DBF levels, since, in most pipes, the velocity of 5 to 6 ft/s required to remove sand, sediments,
corrosion byproducts, and other debris is not achieved (Joseph and Pimblett, 2000).
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Directional (or unidirectional) flushing is a more effective method for DBF reduction. It
is conducted in a systematic manner directing the flow to enhance the flushing of the desired
main. A properly designed and implemented directional flushing program can achieve water
velocities to more than 5 ft/s that can scour the pipe (Joseph and Pimblett, 2000). In addition to
increasing water flow in the selected main, directional flushing can reduce the impact of other
factors contributing to the formation of high DBF concentrations including biofilms, the
accumulation of sediments, and the build-up of corrosion For a successful directional flushing
program, the order in which pipes are flushed, the hydrants that must be opened, and the valves
that must be closed or opened must be carefully planned. Directional flushing should be
configured to maximize water velocity when an hydrant is opened while minimizing the chance
of dirty water reaching customers. Water that enters the main being flushed flows from other
sections that have already been cleaned. Usually, this requires that flushing start at a source of
supply and worked outward in the distribution system. Accurate maps of the system, hydraulic
models, and a complete database of valves and hydrants facilitate planning and execution of
directional flushing programs.
Emergency flushing (or spot flushing) is performed in response to customer complaints
for color, taste, or odor problems, and in response to other water quality problems, such as
insufficient disinfectant residual, evidence of nitrification, or positive coliform results. This type
of flushing, is not effective for DBF control because of the small volumes of water moved and
low velocities acheived.
Regardless of the flushing method implemented, systems should identify problem periods
and areas using historical records. The appropriate timing of flushing can be a key factor for
reducing DBF.
4.4 Booster Disinfection
Practical considerations may not allow appropriate piping or operational modifications
for reducing hydraulic residence time or disinfectant demand in remote parts of the distribution
system. In such cases, the use of booster disinfection can be considered to maintain a more
consistent disinfectant residual throughout large distribution systems. Booster disinfection
provides the opportunity to increase chlorine residual in only the areas that require it, allowing
the average chlorine residual and resulting average DBF formation to be kept as low as possible.
If the majority of a distribution system is confined to an area near the plant but a small
part of the system is far away from the plant, a large dose of disinfectant needs to be added at the
plant to maintain the minimum required disinfectant residual in the remote part of the system. In
such cases, the residual concentration in the majority of a system near the plant would be higher
than what is required. The use of a booster disinfection in the remote part of the system to
maintain the minimum required disinfectant residual can reduce the disinfectant dose at the plant
and limit DBF formation throughout the majority the system.
It is important that the disinfectant dose added at booster stations is carefully calibrated
to changes in water quality conditions and disinfection needs. Booster disinfection doses should
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be flow or dose paced to avoid overfeeding disinfectant. Where chlorine is overfeed, high DBFs
levels can be found in water downstream of the boosting station.
4.5 Overall Strategy to Manage Water Age
Water age can contribute to the formation of high DBF concentrations within the
distribution system. Generally, as long as chlorine residuals and reactive DBF precursors are
present in drinking water, DBFs continue to form. Thus, the longer the contact-time between
chlorine and NOM, the greater the concentration of DBFs that can be found in water as a result
of the continuous formation and accumulation. This accumulation is a consequence of the
formation of THMs and HAAs, and their associated chemical stabilities, which are generally
quite high in disinfected drinking water as long as a significant disinfectant residual is still
present (Singer and Reckhow, 1999).
In the distribution system, when the contact time between NOM and chlorine may be long,
DBF levels greater than those in the finished water leaving the plant are often found. High
TTHM values usually occur where the water age is the oldest. Unlike THMs, 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.
In addition to high DBF concentrations, high water age may also result in other water quality
problems including increased microbial activity, and taste and odor problems. Water age is
controlled through system design and operational strategies including tank management (sections
4.1.1 and 4.1.2), flushing (section 4.3.2), looping of dead-ends (section 4.3.1) and re-routing of
valves (section 4.3.1), and using blow-offs (section 4.3.1). All of these strategies have been
presented in detail in relevant sections of this report. Figure 4.1 schematically illustrates a overall
strategy for water age management and achievement of water quality goals.
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5.0 References
Amy G. L., Chadick P. A., Chowdhury Z. K., "Developing Models for Predicting Trihalomethane
Formation Potential and Kinetics," Journal, American Water Works Association, Vol. 79, No. 7, July
1987.
Franchi A., Singer P.C., Chowdhury Z., Carter J., Grace N. O., 2002, Evaluation of "low-cost" strategies
for the control of trihalomethanes and haloacetic acids, paper presented at the AWWA Water Quality
Technology annual conference, Seattle, WA.
Franchi A. and Hill C., 2002, Factors Affecting DBP Formation in the Distribution System, Paper
Presented at the Water Quality from Source to Tap, AWWA Chesapeake Section Seminar.
Grayman W., Rossman L., Arnold C., Deininger R., Smith C., Smith J., Schnipke R. , 2000, Water
Quality Modeling of Distribution System Storage Facilities, AWWARF.
Hill C., 2003. Managing Distribution System Water Quality. Ohio Section AWWA Southeast/Southwest
Joint Meeting, April 15, 2003.
Liang L., and Singer P.C., Factors Influencing the Formation and Relative Distribution of Haloacetic Acids
and Trihalomethanes under Controlled Chlorination Conditions, 2001 AWWA Water Quality and Technology
Conference.
Singer P.C. and. Reckhow D.A. 1999. "Chemical Oxidation." Water Quality and Treatment, 5th edition.
Letterman R.D. technical editor, American Water Works Association, McGraw-Hill, New York, NY.
Stephane J. and Pimblett J., 2000, Unidirectional Flushing Program Is Clean Sweep, Opflow, v. 26, No. 1.
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Appendix A
Formation and Control of Disinfection Byproducts
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A.1 Introduction
The purpose of this appendix is to identify the factors that affect formation of disinfection
byproducts (DBFs) in water treatment processes and distribution systems. It is intended to serve
as a tool for systems in identifying potential strategies for reducing DBF concentrations. This
appendix is divided into two main sections. Section A.2 discusses the factors that affect DBF
formation. Section A.3 discusses options for controlling DBF formation in general terms; it is
not intended to provide guidance on implementation of DBF control strategies.
A.2 Formation of DBFs
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. 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 NOM levels. The two terms are used interchangeably in much of the
discussion presented here. The following major factor affecting the type and amount of DBFs
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
•• Water chemistry (including pH, bromide ion concentration, organic nitrogen
concentration, and presence of other reducing agents such as iron and manganese)
A summary of these factors follows.
A.2.1 Impact of Disinfection Method on Organic DBF Formation
Organic DBFs can be subdivided into halogenated and non-halogenated byproducts.
Halogenated organic disinfection byproducts are formed when organic and inorganic compounds
found in water react with free chlorine, free bromine, or free iodine. The formation reactions
may take place in the treatment plant and the distribution system. 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. Reactions between NOM, bromide and
iodide ions and chlorine lead to the formation of a variety of halogenated DBFs including THMs
and HAAs. Further, the oxidation of organic nitrogen can lead to the formation of DBFs
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containing nitrogen, such as haloacetonitriles, halopicrins, and cyanogens halides (Reckhow et
al., 1990; Hoigne and Bader, 1988).
Non-halogenated DBFs may form when precursors react with strong oxidants. For
example, the reaction of organics with ozone and hydrogen peroxide results in the formation of
aldehydes, aldo- and keto-acids, and organic acids (Singer, 1999). Chlorine can also trigger the
formation of some non-halogenated DBFs (Singer and Harrington, 1993). Many of the low
molecular weight non-halogenated DBFs are biodegradable.
Trussell and Umphres (1978) reported that the presence of bromide can affect both the
rate and the yield of DBFs, as well as that as the ratio of bromide to NOM (measured as total
organic carbon) increases, the percentage of brominated DBFs also increases. Free chlorine and
ozone oxidize bromide ion to hypobromite ion/hypobromous acid. Hypobromous acid is a more
effective substituting agent than hypochlorous acid (a better oxidant) and can in turn react with
NOM, forming brominated DBFs such as bromoform, and mixed bromo-chloro species (Krasner,
1999). Similarly, the presence of iodide may result in the formation of mixed
chlorobromoiodomethanes byproducts (Bichsel and Von Gunten, 2000).
Studies have documented that chloramines produce significantly lower halogenated DBF
levels than free chlorine, and there is no clear evidence that the reaction of NOM and chloramine
leads to the formation of THMs (Singer and Reckhow, 1999; USEPA, 1999). Predictions of an
empirical DBF formation model calibrated using ICR data indicated that under chloraminated
conditions THMs and HAAs are formed in full-scale plants and distribution systems at a fraction
of the amount that would be expected based on observations of DBF formation under free
chlorine conditions. The amount of formation with chloramines varied from 5% to 35% of that
calculated for free chlorine, depending on the individual DBF species (Swanson et al., 2001).
The benefits of low DBF formation with chloramines are especially important for controlling
formation at the extremities of the distribution system.
When chloramination is used, it is possible that DBFs might form if chlorine is added
before ammonia. If the mixing process is inefficient, it is also possible that DBFs might form
during the mixing of chlorine and ammonia. In this case, free chlorine might react with NOM
before the complete formation of chloramines. In addition, monochloramine slowly hydrolyzes
to release free chlorine in water. This free chlorine may contribute to the formation of small
amounts of additional DBFs in the distribution system.
The application of chlorine dioxide does not produce significant amounts of organic
halogenated DBFs unless chlorine is formed as an impurity in the generation process. Only small
amounts of total organic halides (TOXs, a surrogate measure for halogenated organic
compounds including THMs and HAAs) are formed. However, THMs and HAAs will form if
excess chlorine is added to water to ensure complete reaction with sodium chlorite during the
production of chlorine dioxide.
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To date, there is no evidence to suggest that ultraviolet irradiation (UV) results in the
formation of any disinfection byproducts; however, little research has been performed in this
area. Most of the research regarding application of UV and DBF formation has focused on
chlorinated DBF formation as a result of UV application prior to the addition of chlorine or
chloramines (Malley et al., 1995). Malley, et al. conducted studies comparing the effects of UV
light followed by chlorination versus chloramination. Evidence suggests UV does not affect DBF
formation in either of these two cases.
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 reactions characteristics of NOM and affect the concentration and speciation of
halogenated DBFs when chlorine is subsequently added downstream. In waters with sufficient
bromide concentrations, ozonation can lead to the formation of bromate and other brominated
DBFs. Bromate, like TTHMs and HAAS, is a regulated DBF. Ozonation of natural waters also
produces aldehydes, haloketones, ketoacids, carboxylic acids, and other types of biodegradable
organic material. The biodegradable fraction of organic material can serve as a nutrient source
for microorganisms, and should be removed to prevent microbial regrowth in the distribution
system.
To date, many of the byproducts that result from chlorination or from alternative
disinfectants are still unknown and unregulated. One explanation for this shortcoming is that
these compounds are too polar or too high in molecular weight to be detected using conventional
gas chromotography techniques (James, 1999). As more refined analytical techniques become
available additional classes of disinfection byproducts may be scrutinized.
A.2.2 Disinfectant Dose
The concentration of disinfectant can affect the formation of DBFs. As the concentration
of disinfectant increases the production of DBFs also increases and formation reactions continue
as long as precursors (NOM) and disinfectant are present. In general, the impact of disinfectant
concentration is greater during primary disinfection than during secondary disinfection. The
amount of disinfectant added during primary disinfection is usually less than the long-term
demand, therefore, the concentration of disinfectant is often the limiting factor while unreacted
precursors are available. On the contrary, during secondary disinfection DBF formation
reactions are often precursor limited since an excess of disinfectant is added to the water to
maintain a residual concentration (Singer and Reckhow, 1999). In distribution systems, DBF
formation reactions can become disinfectant-limited 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.
In many systems booster disinfection is applied 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,
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booster chlorination can maintain high HAA concentrations because the increased disinfection
residuals can prevent the biodegradation of HAAs. However, as discussed further in Section
A.3.4 booster chlorination can also be useful in decreasing DBF levels by reducing levels of
secondary disinfectant needed in the finished water leaving the plant.
A.2.3 Time Dependency of DBP Formation
In general, DBFs continue to form in drinking water as long as disinfectant residuals and
reactive DBP precursors are present, and the longer is the contact time between
disinfectant/oxidant and NOM present, the greater is the amount of DBFs that can be formed.
High concentrations of DBFs can accumulate in water. This is a consequence of the chemical
stabilities of THMs and HAAs, which are generally quite high in the disinfected drinking water
as long as a significant disinfectant residual is still present (Singer and Reckhow, 1999).
High THM levels usually occur where the water age is the oldest. Unlike THMs, 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 HAAs concentrations in
areas of the distribution system where disinfectant residuals are depleted.
In contrast to chlorination byproducts, ozonation byproducts form more rapidly, but their
period of formation is much shorter than that of chlorination byproducts. This is due to the
quicker dissipation of the ozone residual compared to chlorine (Singer and Reckhow, 1999).
A.2.4 Concentration and Characteristics of Precursors
The formation of halogenated DBFs is related to the concentration of NOM at the point
of chlorination. In general greater DBP levels are formed in waters with higher concentrations
of precursors. Studies conducted with different fractions of NOM have indicated the reaction
between chlorine and NOM with high aromatic content tends to form higher DBP levels than
NOM with low aromatic content. For this reason, UV absorption at 254 nm [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 THMs and HAAs (Owen et al., 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 ration 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.
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A.2.5 Water Temperature
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The rate of formation of THMs 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 which helps to control DBF formation. Furthermore, high
temperature conditions in the distribution system promote the accelerated depletion of residual
chlorine, which can mitigate DBF formation and promote 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 which are warm, but not necessarily the warmest.
Seasonal trends affect differently where high THM and HAA concentrations might be
found. For example, when water is colder, microbial activity is typically lower and DBF
formation kinetics are slower. Under these conditions, the highest THM and HAA
concentrations might appear coincident with the oldest water in the system. In warmer water,
the highest HAA concentrations might appear in fresher water, which is likely to contain higher
disinfectant residuals that can prevent the biodegradation of HAAs.
A.2.6 Water pH
In the presence of NOM and chlorine, THM formation increases with increasing pH,
whereas the formation of HAAs and other DBFs decrease with increasing pH. The increased
THM 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).
The major byproducts of ozonation are not affected by base hydrolysis. However, pH
can play a role by affecting the rate of decomposition of ozone to hydroxyl radical. The
decomposition of ozone accelerates as pH increases. This occurrence is thought to be
responsible for the decrease of some byproducts (e.g., aldeydes) and the increase of others (e.g.,
carbonyl byproduct and total organic halides; Singer and Reckhow, 1999). Water pH affects the
balance of hypobromite and hypobromous acid formation during the ozonation of waters
containing significant concentrations of bromides. At low pH, the equilibrium shifts to the less
reactive hypobromous acid. Consequently, the overall formation of bromate decrease as pH
decrease (Singer and Reckhow, 1999). On the other hand, Song et al. (1997) suggested that
lower pHs favor the formation of TOX (most likely TOBr) during ozonation. Singer and
Reckhow (1999) attributed this occurrence to the concurrent suppressed decomposition of ozone,
changes in the speciation of the oxidized bromine and the hydrolysis of brominated byproducts.
A.3 Control of DBFs
Alternatives to minimize the formation of DBFs focus on the removal of precursors
during treatment, modifications of the oxidation and disinfection processes, control of oxidants
dose and residual, reduction of the residence time in the distribution system, and removal of
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DBFs after formation. Because DBFs are difficult to remove after they have formed, control
strategies typically focus on the first four methods.
A.3.1 Improving Precursors Removal
The removal of organic precursors can be improved by optimizing coagulation practices
or by employing advanced precursor removal processes such as granular activated carbon (GAC)
adsorption, membrane filtration, or biofiltration.
The process of improving the removal of NOM during the coagulation process is defined
as enhanced coagulation. Greater NOM removal can be obtained with adjustments in treatment
practice, specifically pH reduction and increased coagulant dosage. The coagulation of NOM
appears to be most efficient in the 5 to 6 pH range.
A number of sources have documented that granular activated carbon (GAC) and
nanofiltration (NF) can be more effective DBF precursor removal processes than conventional
coagulation treatment (McGuire et al., 1989; Owen et al., 1998; Snoeyink et al., 1999; Jacangelo,
1999; Taylor and Wiesner, 1999; and references therein). Reverse osmosis (RO) can also be
very effective for removing precursors. However, when precursor removal (as opposed to
demineralization) is the primary treatment objective, NF is usually preferred to RO because of
its lower operating pressure and associated costs. Both NF and RO can remove bromide
(Jacangelo, 1999) while GAC does not appear to remove bromide to any significant extent
(Snoeyink et al., 1999)
Biofiltration can be used to remove a portion of the NOM from water by converting it
into inorganic carbon (CO2) and it is considered a viable treatment alternative for precursors
removal (Hozalski and Bouwer, 1999). In general, the ideal location for a biofilter is in a rapid
media filter and its performance can vary from one plant to another depending on factors such as
NOM source and characteristics, use of ozone for preoxidation, residence time in the biofilter,
media type, and water temperature (Hozalski and Bouwer, 1999).
Watershed management practices as well as timing and location of withdrawals can also
achieve reductions of DBF precursors in the raw water. The extent of the benefit of
implementing this strategy is site specific.
A.3.2 Disinfection and Oxidation Methods and Disinfectant Dose
Chlorination generally produces the highest THM and HAA levels. Other oxidation
alternatives to chlorine (e.g., use of ozone, chloramines, chlorine dioxide, potassium
permanganate, and UV radiation) can be used to minimize the formation of TTHM and HAAs.
Generally, decreasing the disinfectant dose and residual reduces DBF levels (see Section A.2).
However, when considering disinfectant changes it is important to consider disinfection needs
and maintain the appropriate CT for disinfection. Some alternative disinfectants cannot be used
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for secondary disinfection. A detailed discussion of alternative disinfectants can be found in the
Alternative Disinfectants and Oxidants Guidance Manual (USEPA, 1999, 815-R-99-014).
A.3.3 Shifting the Point of Disinfectant Application
Shifting the point of disinfectant application from upstream to downstream of the
coagulation/settling process can significantly reduce the formation of DBFs for two main
reasons: the amount of precursors is reduced prior to disinfectant addition, and (particularly for
chlorination) the contact time between disinfectant and NOM is reduced. The implementation of
this strategy must, however, take into account disinfection needs. Adequate contact time must
be always provided after the application of disinfectant to achieve the desired inactivation of
microorganisms.
A.3.4 Control of DBF Formation in the Distribution System
For systems maintaining free chlorine residual, significant DBF formation can occur in
the distribution system. A long detention time in the distribution system, the presence of NOM
in the finished water and the presence of free chlorine residual can promote this occurrence. It is
not uncommon that water leaving a treatment plant with low THM and HAA concentrations is
found to have high levels of these compounds in the distribution system. Generally, application
of secondary disinfectant (particularly chlorine) to form and maintain a residual in the
distribution system results in DBF formation. Implementation of distribution system water
quality monitoring, minimization of "dead ends," optimization of storage tank utilization,
execution of effective planned system flushing and management of water age can minimize
DBF formation.
In some cases, booster chlorination has also been used to control disinfectant application
and minimize DBF formation. For example, where the majority of the distribution system is in a
confined area near the plant, but a small part is far away from the plant a large dose of
disinfectant would be required to maintain a residual in the extreme part of the system. A much
higher residual concentration than is needed would be present in the majority of the system.
Thus, booster disinfection in the extreme part of the system could dramatically reduce the
disinfectant dose at the plant and reduce DBF formation through the system. However, it must
also be noted that in areas following booster disinfection facilities, the residence time is often
long. If conditions favor formation (i.e. water age, temperature, NOM concentration) the
additional disinfectant added might lead to the formation of high TTHM and HAA levels.
Increased disinfectant residual can also prevent biodegradation of HAA, further increasing
distribution system levels. The use or addition of booster disinfection requires careful
consideration in any DBF control strategy.
A.3.5 Assessing DBF Formation and Control with the WTP Model
If a utility determines, based upon distribution system monitoring, that the DBF levels in
their system need to be reduced, they may consider implementing treatment changes in their
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water treatment plant. To evaluate the potential impact of treatment changes on distribution
system DBF levels prior to the implementation of these changes, a system may consider using
the Water Treatment Plant Simulation Model (WTP Model) as a preliminary tool. This model
was initially developed to support the DBF rule making process and was later revised to improve
the predictive accuracy using data collected under the Information Collection Rule (ICR). The
WTP Model consists of empirical models developed from bench-, pilot-, and full-scale
treatability data. The majority of the predictive algorithms have been verified with independent
data sets (Solarik et al., 1999), and many key algorithms have been calibrated using ICR data
from full-scale surface water treatment plants (Swanson et al., 2001). A description of the
original model was presented by Harrington, et al. (1992) and is available from the USEPA's
Technical Support Center in Cincinnati. The WTP Model was developed as a central tendency
model, and was not specifically designed to yield site specific predictions. However, a
significantly improved form of the WTP Model (Version 2.0) currently under review by the
agency will facilitate site specific calibration of the model. Extensive experiments to determine
water quality characteristics are required to validate site specific model use.
In addition to simulating the effects of traditional surface water treatment processes, such
as coagulation (or lime softening), flocculation, sedimentation, and filtration, the WTP Model
supports many advanced disinfection and DBF control processes, such as:
•• Enhanced coagulation
•• GAC adsorption
• • Microfiltration/ultrafiltration
•• Nanofiltration/reverse osmosis
•• Ozonation
•• Biological filtration
•• Chlorine dioxide addition
The WTP Model generates predictions of bromate formation during ozonation, chlorite
formation during chlorine dioxide addition, and THM, HAA, and TOX formation due to free
chlorine and chloramine addition. These predictions are generated at the effluent of each unit
treatment process and within the distribution system (detention times are required as inputs).
The WTP Model also calculates CT values achieved for the various disinfectants used during
treatment and log inactivation values for virus, Giardia, and Cryptosporidium. Thus, the
program can be used to evaluate the relative effects of treatment modifications on disinfection
and DBF formation.
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References
Bichsel, Y., and Von Gunten U., 2000. Environmental Science and Technology, 34 (13): 2784
Harrington, G.W., Z.K. Chowdhury, andD.M. Owen. 1992. Journal of the American Water
Works Association, 84( 11):78.
Hozalski, R. M., and EJ. Bouwer, 1999. Biofiltration for removal of natural organic matter. In
Formation and control of disinfection by-products in drinking water. Singer, P.C. (editor)
American Water Works Association, Denver, CO.
Hoigne J., and H. Bader. 1988. The formation of trichloronitromethane (chloropicrin) and
chloroform in a combined ozonation/chlorination treatment of drinking water. Water Resources.
22(3):313.
Jacangelo, J.G.. 1999. Control of disinfection by-products by pressure-driven membrane
processes. In Formation and control of disinfection by-products in drinking water. Singer, P.C.
(editor) American Water Works Association, Denver, CO.
James, M. S. 1999. "Disinfection by-products: an historical perspective." In Formation and
control of disinfection by-products in drinking water. Singer, P.C. (editor) American Water
Works Association, Denver, CO.
Letterman, R.D., A. Amirtharajah, and C.R. O'Melia. 1999. Coagulation and flocculation. In
Water quality and treatment. 5th edition. Letterman R.D. technical editor, American Water
Works Association, McGraw-Hill, New York, NY.
Malley, J.P., J.P. Shaw, and J.D. Ropp. 1995. Evaluation of by-products produced by treatment
ofgroundwaters with ultraviolet irradiation. AWWA Research Foundation Report and AWWA,
Denver CO.
Owen et al., 1998. Removal of DBF precursors by GAC adsorption. AWWA Research
Foundation Report No. 90744, Denver CO.
Krasner S. W., 1999. Chemistry of disinfection by-product formation, InFormation and control
of disinfection by-products in drinking water. Singer, P.C. (editor) American Water Works
Association, Denver, CO.
Reckhow, D.A., P.C. Singer, andR.L. Malcom. 1990. Chlorination of humic materials:
byproduct formation and chemical interpretations. Environmental Science and Technology.
24(11): 1655.
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Singer, P.C. andD.A. Reckhow. 1999. Chemical oxidation. In Water quality and treatment. 5th
edition. Letterman R.D. technical editor, American Water Works Association, McGraw-Hill,
New York, NY.
Singer, P.C. (editor) 1999. Formation and control of disinfection by-products in drinking water.
American Water Works Association, Denver, CO.
Singer, P.C., and G.W. Harrington. 1993. Coagulation of DBF precursors: theoretical and
practical considerations. Conference proceedings, AWWA Water Quality Technology
Conference, Miami, FL.
Snoeyink, V.L., Kirisits, M.J., C. Pelekani, 1999. "Adsorption of disinfection by-product
precursors." In Formation and control of disinfection by-products in drinking water. Singer, P.C.
(editor) American Water Works Association, Denver, CO.
Solarik, G., R.S. Summers, J. Sohn, WJ. Swanson, Z.K.Chowdhury, and G. Amy. 1999.
Extensions and verification of the Water Treatment Plant Model for DBF formation. Conference
proceedings, 1999 American Chemical Society Conference, Anaheim, CA.
Song, R.P., P. Westerhoff, R. Minear, and G.L. Amy. 1997. Journal of the American Water
Works Association., 89(6): 69.
Swanson, W.J., Z. Chowdhury, R. Summers, and G. Solarik. 2001. Predicting DBFs at full-scale:
calibration and validation of the Water Treatment Plant Model using ICR data. Conference
proceedings, 2001 AWWA Annual Conference, Washington, DC.
Taylor J.S., Wiesner M., 1999. Membranes. In Water quality and treatment. 5th edition.
Letterman R.D. technical editor, American Water Works Association, McGraw-Hill, New York,
NY.
USEPA, 1999. Alternative disinfectants and oxidants guidance manual. EPA 815-R-99-014.
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Appendix B
Changes in Source Water Quality
Significant Excursions Identified Using the "Maximum Concentration Approach"
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The first part of this appendix includes general system information and a summary of
TTHM and HAAS data that resulted in Elm City having to perform a significant excursion
evaluation. This information is not required as part of the documentation of a significant
excursion. Only the Significant Excursion Report is required to be completed by systems that
experience a significant excursion.
This appendix is provided as an example of a system in which changes in source water
quality led to a DBF Significant Excursion. Possible strategies to reduce excursions are
presented in Chapter 4, but they are not to be included in the identification and documentation
process. Appendices C through E provide similar examples for systems in which changes in
treatment plant operations, changes in distribution system, and multiple causes resulted in a
significant excursion.
This example assumes the state has chosen to use 100 /ug/L TTHM and 75 /ug/L HAAS as
the trigger levels for determining that a significant excursion has occurred and that a significant
excursion evaluation is required.
Background Information for this Example
System Description:
General system characteristics:
Service area: Elm City plus surrounding suburban areas
Production: Annual average daily demand 15 MOD
Source Water Information:
Hardwood Lake (surface water)
pH: from 6.9 to 7.5
Alkalinity: from 82 to 98 mg/L as CaCO3
TOC: from 2.1 to 4.0 mg/L as C
Bromide: from 0.04 to 0.1 mg/L
Turbidity: 1 to lOOntu
Softwood River (surface water)
pH: from 6.8 to 7.9
Alkalinity: from 77 to 94 mg/L as CaCO3
TOC: from 1.6 to 9.4 mg/L as C
Bromide: from 0.03 to 0.1 mg/L
Turbidity: 2 to 115ntu
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Treatment Provided:
Hardwood, conventional (15 MOD design, 7.5 MOD average)
Softwood River, conventional with GAC (20 MGD design, 7.5 MGD average)
Primary and residual disinfection: Chlorine/chlorine at both plants
Summary of Stage 2 DBPR Monitoring Locations:
Table B.I summarizes the Stage 2 DBPR monitoring locations used by Elm City.
Sample locations are marked in the distribution system schematic presented in Figure
B.I.
Table B.1 Stage 2 DBPR Monitoring Locations
Location
Location #1
Location #2
Location #3
Location #4
Location #5
Location #6
Location #7
Location #8
Description
Hardwood Plant - average residence time
Hardwood Plant - high TTHM
Hardwood Plant - high HAAS
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Softwood Plant - average residence time
Softwood Plant - high HAAS
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Figure B.1 Schematic of Elm City Distribution System
and Stage 2 DBPR Monitoring Locations
Softwood River WTP
Elevated Storage Tank
Ground storage tank
Pump station
Peak DBP location
Hardwood WTP
DBP Excursion Investigation:
During the last sampling period which took place in September 2004, Elm City
experienced unusually high TTHM values (relative to the LRAA) at two monitoring locations
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(#6, #8). Similarly, unusually high HAAS values were detected at one monitoring location (#8).
DBF data from the previous year and most recent sampling period (five quarters total) are
presented in Table B.2.
Table B.2 TTHM and HAAS Monitoring Data
Loc
atio
n
#1
#2
#3
#4
#5
#6
#7
#8
TTHM (ug/L)
Quarterly
Pre-Sept.
2004
Data1
54, 67, 58, 75
68, 68, 55, 69
66,52,71,72
50,55,51,61
34, 48, 55, 50
44, 62, 58, 60
40,41,37,46
49, 39, 50, 76
LRAA
Pre-Sept.
2004
Avg.
65
63
64
55
44
49
41
52
Sept.
2004
Data
63
72
81
78
79
121
77
146
LRAA
Sept.
2004
Avg.
67
64
68
62
55
66
50
76
HAAS (ug/L)
Quarterly
Pre-Sept.
2004
Data1
52, 37, 30,
41
38, 45, 28,
19
41,46,45,
39
42, 43, 38,
34
32, 43, 55,
38
45,33,41,
40
31,38,28,
19
43,39,41,
45
LRAA
Pre-Sept.
2004
Avg.
40
33
43
39
42
40
27
42
Sept.
2004
Data
52
39
51
66
58
72
59
98
LRAA
Sept.
2004
Avg.
40
33
46
45
49
47
37
56
1Data for sampling conducted on September 2003,
peak excursions are bold and underlined.
December 2003, March 2004 and June 2004. Data relevant to
Unusually high TTHM samples were collected at locations #6 and #8, and unusually
high HAAS samples were collected at location #8. The results are significantly higher than both
the LRAA at those locations for the previous 12-month period and the historic TTHM and
HAAS values at those locations for the years 1999-2003 (see Significant Excursions Evaluation
Report). Significant excursion were identified when DBF levels exceeded 100 |J,g/L TTHM or
75 |J,g/L HAAS. All of the monitoring locations affected by high DBF are located in the area
served by the Softwood plant or in the mixing zone. The city staff has reason to believe that a
water quality change that has occurred in Softwood River caused the increase in DBFs.
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Significant Excursion
Evaluation Report
Page 1
Report date: October 16th. 2004
Report prepared by: Robert Doe. P.E.
System name: Elm City
1) When was the significant excursion sample(s) collected? What were the TTHM and HAAS
concentrations?
Location No.
Location description
Sample collection date
Sample collection time
TTHM LRAA
Concentration (ug/L)
TTHM Concentration
(ug/L)
HAAS LRAA
Concentration (ug/L)
HAAS Concentration
(ug/L)
# 6
Hardwood/Soft-
wood Mix Zone -
High TTHM
Sept. 4th, 2004
2p.m.
66
121
# 8
Softwood plant -
High HAAS
Sept. 4th, 2004
3 p.m.
76
146
56
98
Note: Attach additional sheets if you observed more than four significant excursions during this
round of sampling.
2) Where did the excursion(s) occur? Attach a schematic of your system, sketch your system in
the space below, or have a schematic of your system available to review with your state at the
time of your next sanitary survey. Indicate the location(s) of the significant excursion(s) on your
schematic.
Location #6 - This sample location is a faucet at a connection located in Weeping Willow - a zone of the
distribution system that has been recently developed. This connection is located downstream from a chlorine
booster station. Water in this area is generally a mix of water from the Hardwood and Softwood River Plants.
Location #8 - This sampling location is in an area that receives water from the Softwood Plant. Samples are
collected at a hose bib near the first house on the cul-de-sac (which has 12 homes total). For this example, the
location of these sample locations is illustrated in Figure B. 1
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3) Attach (or provide in the Supplemental Data Form) all available water quality data for the round
of sampling in which the significant excursion occurred. At a minimum, include all TTHM and
HAAS results from the sampling period. You should also consider including pH, temperature,
alkalinity, TOC, disinfectant residual, and any other data that you think would be useful.
a) Were there any unusual circumstances associated with this round of sampling?
Yes No X
If yes, please explain.
b) Were all analytical QA/QC measures met?
Sample preservation Yes X No
Sample holding time Yes X No
Other
If no, please explain.
4) Attach (or provide in the Supplemental Data Form) historical TTHM and HAAS data for the
locations) at which the significant excursions) occurred. Provide at least three years of data, if
available.
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PageS
5) What caused your excursion(s) to occur?
Sections A through F starting on page 4 can help you determine the possible cause(s) of your
excursion. Please note there may be more than one factor which resulted in your excursion.
Section A: Source water quality change
Section B: Process upset at treatment plant
Section C: Planned change or maintenance activities at plant
Section D: Planned distribution system operations or maintenance activities
Section E: Unplanned events in distribution system
If you already suspect a cause, go directly to that section. If you read Sections A through E and
are unable to determine a cause of your excursion, then complete Section F.
Consecutive systems should also contact their wholesaler to identify the cause(s) of the
significant excursion(s).
6) List steps taken or planned to reduce DBP peak levels.
We are considering adjustments of the coagulation processes to improve TOC removal including: increasing
the coagulant dose, evaluation of alternative coagulants, evaluation of coagulant aids, lowering the pH of
coagulation, use of a pre-oxidant (permanganate or chlorine dioxide), and use of PAC.
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Page 4
A. Source Water Quality Changes
Did any of the events listed below take place before the DBP excursion to cause TOC levels to
increase?
Heavy rain fall
Flooding
Spring snow-me It/run off
Significant decrease in rainfall or source flow
Algae bloom
Did any of the events listed below take place before the DBP excursion to cause bromide levels
to increase?
Significant decrease in rainfall or source flow
Brackish or seawater intrusion
Did pH and/or alkalinity significantly change?
If two or more supplies are used, was a greater portion of water drawn from the one with higher
TOC?
Was raw water stored for an unusually long period of time resulting in a significant increase in
water temperature?
Conclusions:
Did source water quality changes cause or contribute to your significant excursions)?
Yes X No
If yes, please explain:
The most probable cause of the DBP excursion noted during the September 2004 sampling even was a rapid
increase of the organic matter concentration in the Softwood River. Following two days of heavy rainfall the
TOC measured in the plant influent increased from 2.7 mg/L to 8.4 mg/L. At the same time, turbidity of the
source water also increased from 5 ntu to a maximum of 98 ntu. The coagulant (ferric chloride) dose was
increased from 20 mg/L to 75 mg/L to match water quality changes. For the duration of this high turbidity/
high NOM event, the pH of coagulation was maintained between 61. and 6.3. The higher coagulant dose
prevented any significant increases of turbidity in the settled water, but the concentration of TOC in the plant
effluent increased from 1.8 mg/L to 3.8 mg/L. 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.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft B-8 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 5
B. Process Upset at Treatment Plant
Was raw water stored for an unusually long time, providing additional contact time for DBP
formation after prechlorination?
Were there changes in coagulation practices?
Were there any changes or malfunctions of the coagulation process in the days
leading to the excursion?
Were the coagulant dose and pH properly adjusted for incoming source water
conditions?
Were there changes in chlorination practices?
Were there any changes in chlorine dose at any location in the plant?
Were there changes in plant flow that may have resulted in longer than normal
residence time at any location in the plant?
Did the pH change at the point of chlorine addition?
Were there changes in settling practices?
Was there excess sludge build-up in the settling basin that may have carried over to
the point of disinfectant addition?
Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
Were there changes in filtration practices?
Have filter run times been changed to meet raw water quality changes?
Were there any spikes in individual filter effluent turbidity (which may indicate
particulate or colloidal TOC breakthrough) in the days leading to the excursion?
Did chlorinated water sit in the filter for an extended period of time?
Were all filters run in a filter-to-waste mode during initial filter ripening?
Were any filters operated beyond their normal filter run time?
If GAG filters are used: Is it possible the adsorptive capacity of the GAG bed was
reached before reactivation occurred?
If biological filtration is used: Were there any process upsets that may have resulted
in breakthrough of TOC (particularly biodegradable TOC)?
Were there changes in plant flow that may have resulted in an unusually high residence time in
the clean/veil on the days prior to the excursion?
For example, a temporary plant shutdown.
Continued on next page
Significant Excursion Guidance Manual
Proposal Draft B-9 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 6
B. Process Upset at Treatment Plant (Continued)
Conclusions:
Did a process upset in the treatment plant cause or contribute to your significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft B-10 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 7
C. Planned Change or Maintenance Activities for the Treatment Plant
Was there a recent change (or addition) of pre-oxidant?
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?
Did you change the type or manufacturer of the coagulant?
Were there any changes in disinfection practices in the days prior to the excursion?
For example, a switch from chloramines to free chlorine for burnout period.
Discontinuation of ozone which forms very little TTHM.
Was a filter(s) taken off-line for an extended period of time that caused the other filters to operate
near maximum design capacity and creating the conditions for possible breakthrough?
Were any pumps shut down for maintenance, leading to changes in flow patterns or hydraulic
surges?
Conclusions:
Did a planned maintenance or operational activity in the treatment plant cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft B-11 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
PageS
D. Planned Distribution System Operations or Maintenance Activities
Was a tank drained for cleaning or other maintenance?
Was the tank drained to waste or to the distribution system?
Was a larger volume than normal drained to the distribution system?
If booster disinfection is used, was the booster disinfectant dose higher than the normal booster
disinfectant dose for that season?
Were there any system maintenance activities in the days prior to DBP excursion? Including:
Repairing mains or installing new mains
Closure of valves to isolate sections of pipes
Were the pipes flushed properly or were the appropriate valves re-opened after work was
completed?
Did any pump or pipeline maintenance occur that would have changed the flow pattern in the
area the sample was drawn from?
Change in flow can cause water in stagnant areas to be drawn into another area.
Did any pipeline replacement occur?
Disinfecting piping in contact with drinking water could result in a high concentration
of chlorine entering the distribution system and thus increase DBPs.
Conclusions:
Did a planned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft B-12 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 9
E. Unplanned Distribution System Events
Were there increases in demand that caused older water in storage tanks to be drawn into the
system?
Were there any major fire events?
Did one or more storage tank have greater than average drawdown preceding the
time of DBP peak excursion?
Were there decreases in demand that resulted in longer than normal system residence times?
Were there any large customers off-line?
Did any main breaks occur causing changes in flow patterns in the influence area of the sample
location?
If you collect water temperature inside storage tanks, was the temperature inside the tank higher
than normal for the season?
Were any storage tanks hydraulically locked out of the system for an extended period and then
used preceding the time of DBP peak excursion?
Did changes in overall water demand cause a change in water demand patterns in the vicinity of
dead ends and/or stagnant zones in the system?
Were there large variations in localized system pressures that were different from the normal
pressure range that could have caused a change in water demand patterns in the vicinity of dead
ends and/or stagnant zones in the system?
Conclusions:
Did an unplanned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft B-13 July 2003
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Significant Excursion Evaluation Report Rebate: october 16-.2004
Page 10
F. If you were unable to identify the cause of your significant excursion(s) after reviewing
Sections A through E, are you able to identify another potential cause of your increase in
DBF concentrations? Explain.
Note: If you are unable to determine the cause of your excursion you may wish to consider:
More frequent raw water temperature monitoring.
More frequent raw water TOC monitoring.
Increased disinfectant residual monitoring in the distribution system.
Tracer studies to characterize distribution system water age.
Development of a hydraulic model to characterize the distribution system.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft B-14 July 2003
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Supplemental Data F<
for the Significant Exci
Evaluation Report
MTW Report d
irsion Report p
System r
ate: October 16th, 2004
re pa red by: Robert
ame: Elm City
Doe, P.E.
1) Water quality data from significant excursion sampling period.
Location No. #1 #2
Location Name
TTHM (ug/L) 63 72
HAAS (ug/L) 52 39
Free Chlorine (mg/L) 1.8 1.3
Total Chlorine (mg/L) 2.1 1.8
pH 7.9 8.0
#3 #4
81 78
51 66
NA NA
NA NA
8.3 8.1
#5 #6
55 121
58 72
NA 1.1
NA 1.8
7.8 8.3
#7 #8
77 146
59 98
NA 0.8
NA 1.2
7.5 8.2
2) Supplemental data from each treatment facility:
Plant #1 : Hardwood Plant Plant #2: Softwood Plant
Raw Water Temperature: NA
Plant Effluent Water Temperature: 20
Raw Water Temperature:
°C Plant E
Raw Water TOC: 2.2 ms/L (Avs. <2.0ms/L) Raw \A
Other Data:
ffluent Water Temp
teterTOC: 3.8ms/I
NA
erature: 20 °C
^ (Avs.<2.0ms/L)
Other Data: Inf. turb. 98 ntu (Avs. <20 ntu)
3) Historical TTHM and HAAS data at
TTHM Data (ug/L)
Monitorina # 5 # 6 # 7 #
Location
Date - 1999 43 58 45
Date -2000 51 49 56
Date -2001 46 69 41
Date -2002 48 61 73
Date -2003 34 44 53
Avd. 99-03 44 56 54
significant excursion sampling locations.
HAAS Data (ug/L)
8 Monitorina # 8 # # #
Location
49 Date - 1999
64 Date -2000
69 Date - 2001
66 Date -2002
79 Date -2003
65 Avq. 99-03
56
47
33
34
43
43
Attach additional sheets if necessary
Significant Excursion Guidance Manual
Proposal Draft
B-15
July 2003
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Appendix C
Changes in Treatment Plant Operation
Significant Excursions Identified Using the "Maximum Concentration Approach"
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This page intentionally left blank.
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The first part of this appendix includes general system information and a summary of
TTHM and HAAS data that resulted in Elm City having to perform a significant excursion
evaluation. This information as part of the documentation of a significant excursion. Only the
Significant Excursion Report is required to be completed by systems that experience a significant
excursion.
This appendix is provided as an example of a system in which changes in treatment plant
operations led to a DBF Significant Excursion. Possible strategies to reduce excursions are
presented in Chapter 4, but they are not to be included in the identification and documentation
process. Appendices B, D, and E provide similar examples for systems in which changes in
source water quality, changes in distribution system, and multiple causes resulted in a
significant excursion.
This example assumes the state has chosen to use 100 fjg/L TTHM and 75 fjg/L HAAS as
the trigger levels for determining that a significant excursion has occurred and that a significant
excursion evaluation is required.
Background Information for this Example
System Description:
General system characteristics:
Service area: Elm City plus surrounding suburban areas
Production: Annual average daily demand 15 MGD
Source Water Information:
Hardwood Lake (surface water)
pH: from 6.9 to 7.5
Alkalinity: from 82 to 98 mg/L as CaCO3
TOC: from 2.1 to 4.0 mg/L as C
Bromide: from 0.04 to 0.1 mg/L
Turbidity: 1 to lOOntu
Softwood River (surface water)
pH: from 6.8 to 7.9
Alkalinity: from 77 to 94 mg/L as CaCO3
TOC: from 1.6 to 9.4 mg/L as C
Bromide: from 0.03 to 0.1 mg/L
Turbidity: 2 to 115ntu
Significant Excursion Guidance Manual
Proposal Draft C-l July 2003
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Treatment Provided:
Hardwood, conventional (15 MOD design, 7.5 MOD average)
Softwood River, conventional with GAC (20 MGD design, 7.5 MGD average)
Primary and residual disinfection: Chlorine/chlorine at both plants
Summary of Stage 2 DBPR Monitoring Locations:
Table C.I summarizes the Stage 2 DBPR monitoring locations used by Elm City.
Sample locations are marked in the distribution system schematic presented in Figure
C.I.
Table C.1 Stage 2 DBPR Monitoring Locations
Location
Location #1
Location #2
Location #3
Location #4
Location #5
Location #6
Location #7
Location #8
Description
Hardwood Plant - average residence time
Hardwood Plant - high TTHM
Hardwood Plant - high HAAS
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Softwood Plant - average residence time
Softwood Plant - high HAAS
Significant Excursion Guidance Manual
Proposal Draft
C-2
July 2003
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Figure C.1 Schematic of Elm City Distribution System
and Stage 2 DBPR Monitoring Locations
Softwood River WTP
Elevated Storage Tank
Ground storage tank
Pump station
Peak DBP location
Hardwood WTP
Significant Excursion Guidance Manual
Proposal Draft
C-3
July 2003
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DBF Excursion Investigation:
During the last sampling period which took place in September 2004, Elm City
experienced unusually high TTHM values (relative to the LRAA) at five monitoring locations
(#4, #5, #6, #7, #8). Similarly, unusually high HAAS values were detected at two monitoring
locations (#7 and #8). DBF data from the previous year and most recent sampling period (five
quarters total) are presented in Table C.2.
Table C.2. TTHM and HAAS Monitoring Data
Loc
atio
n
#1
#2
#3
#4
#5
#6
#7
#8
TTHM (ug/L)
Quarterly
Pre-Sept.
2004
Data1
54, 67, 58, 75
68, 68, 55, 69
66,52,71,72
50,55,51,61
34, 48, 55, 50
44, 62, 58, 60
40,41,37,46
49, 39, 50, 76
LRAA
Pre-Sept.
2004
Avg.
65
63
64
55
44
49
41
52
Sept.
2004
Data
118
145
122
82
68
70
58
78
LRAA
Sept.
2004
Avg.
74
77
74
60
48
53
46
56
HAAS (ug/L)
Quarterly
Pre-Sept.
2004
Data1
52, 37, 30,
41
38, 45, 28,
19
41,46,45,
39
42, 43, 38,
34
32, 43, 55,
38
45,33,41,
40
21,38,28,
19
43,39,41,
45
LRAA
Pre-Sept.
2004
Avg.
40
33
43
39
42
40
27
42
Sept.
2004
Data
84
7J>
58
54
37
53
29
49
LRAA
Sept.
2004
Avg.
48
42
47
42
43
42
29
44
1Data for sampling conducted on September 2003, December 2003, March 2004 and June 2004.
relevant to peak excursions are bold and underlined.
Data
Unusually high TTHM samples were collected at locations #1, #2, and #3, and unusually
high HAAS samples were collected at locations #1 and #2. The results are significantly higher
than both the LRAA at those locations for the previous 12-month period and the historic TTHM
and HAAS values at those locations for the years 1999-2003 (see Significant Excursions
Evaluation Report). Significant excursion were identified when DBF levels exceeded 100 ug/L
TTHM or 75 [ig/L HAAS. All of the monitoring locations affected by high DBF are located in
the area served by the Hardwood plant. The city staff has reason to believe that a process change
occurred during treatment operations at the Hardwood plant caused this increase in DBF levels.
Significant Excursion Guidance Manual
Proposal Draft
C-4
July 2003
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Significant Excursion
Evaluation Report
Page 1
Report date: October 16th. 2004
Report prepared by: Ronald Doe. P.E.
System name: Elm City
1) When was the significant excursion sample(s) collected? What were the TTHM and HAAS
concentrations?
Location No.
Location description
Sample collection date
Sample collection time
TTHM LRAA
Concentration (ug/L)
TTHM Concentration
(ug/L)
HAAS LRAA
Concentration (ug/L)
HAAS Concentration
(ug/L)
# 1
Hardwood Plant -
average residence
time
Sept. 4th, 2004
1 p.m.
74
118
48
84
# 2
Hardwood Plant -
high TTHM
Sept. 4*, 2004
3 p.m.
77
145
42
75
# 3
Hardwood Plant -
high HAA5
Sept. 4*, 2004
1 1 a.m.
74
122
#
Note: Attach additional sheets if you observed more than four significant excursions during this
round of sampling.
2) Where did the excursion(s) occur? Attach a schematic of your system, sketch your system in
the space below, or have a schematic of your system available to review with your state at the
time of your next sanitary survey. Indicate the location(s) of the significant excursion(s) on your
schematic.
Location #1 - Represents average residence time of water leaving the Hardwood Plant. It is located in the
Oakville neighborhood. There are no storage facilities between the treatment plant and this location.
Location #2 - Sample tap is a hose bib at a building located in Pineville in a zone of the distribution system
with water age greater than average. Water in this area is from the Hardwood Plant.
Location #3 - This location is located in the Downtown area. Water is primarily from the Hardwood Plant. A
ground storage tank is near this location.
The location of these sample locations is illustrated in Figure C. 1.
Significant Excursion Guidance Manual
Proposal Draft
C-5
July 2003
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Significant Excursion Evaluation Report Rebate: october 16-.2004
Page 2
3) Attach (or provide in the Supplemental Data Form) all available water quality data for the round
of sampling in which the significant excursion occurred. At a minimum, include all TTHM and
HAAS results from the sampling period. You should also consider including pH, temperature,
alkalinity, TOC, disinfectant residual, and any other data that you think would be useful.
a) Were there any unusual circumstances associated with this round of sampling?
Yes No X
If yes, please explain.
b) Were all analytical QA/QC measures met?
Sample preservation Yes X No
Sample holding time Yes X No
Other
If no, please explain.
4) Attach (or provide in the Supplemental Data Form) historical TTHM and HAAS data for the
locations) at which the significant excursions) occurred. Provide at least three years of data, if
available.
Significant Excursion Guidance Manual
Proposal Draft C-6 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
PageS
5) What caused your excursion(s) to occur?
Sections A through F starting on page 4 can help you determine the possible cause(s) of your
excursion. Please note there may be more than one factor which resulted in your excursion.
Section A: Source water quality change
Section B: Process upset at treatment plant
Section C: Planned change or maintenance activities at plant
Section D: Planned distribution system operations or maintenance activities
Section E: Unplanned events in distribution system
6) List steps taken or planned to reduce DBP peak levels.
Plan to calibrate standby pumps for future maintenance of coagulant process feed pumps. Considering
improvements to coagulant process monitoring (daily verification with pump catch, streaming current
monitoring).
Significant Excursion Guidance Manual
Proposal Draft C-7 July 2003
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Significant Excursion Evaluation Report Rebate: october 16-.2004
Page 4
A. Source Water Quality Changes
Did any of the events listed below take place before the DBF excursion to cause TOC levels to increase?
Heavy rain fall
Flooding
Spring snow-melt/runoff
Significant decrease in rainfall or source flow
Algae bloom
Did any of the events listed below take place before the DBF excursion to cause bromide levels to
increase?
Significant decrease in rainfall or source flow
Brackish or seawater intrusion
Did pH and/or alkalinity significantly change?
If two or more supplies are used, was a greater portion of water drawn from the one with higher TOC?
Was raw water stored for an unusually long period of time resulting in a significant increase in water
temperature?
Conclusions:
Did source water quality changes cause or contribute to your significant excursions)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft C-8 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 5
B. Process Upset at Treatment Plant
Was raw water stored for an unusually long time, providing additional contact time for DBF formation
after prechlorination?
Were there changes in coagulation practices?
- Were there any changes or malfunctions of the coagulation process in the days leading to the
excursion?
- Were the coagulant dose and pH properly adjusted for incoming source water conditions?
Were there changes in chlorination practices?
Were there any changes in chlorine dose at any location in the plant?
Were there changes in plant flow that may have resulted in longer than normal residence
time at any location in the plant?
- Did the pH change at the point of chlorine addition?
Were there changes in settling practices?
- Was there excess sludge build-up in the settling basin that may have carried over to the point
of disinfectant addition?
- Was there any disruption in the sludge blanket that may have resulted in carryover to the
point of disinfection?
Were there changes in filtration practices?
- Have filter run times been changed to meet raw water quality changes?
- Were there any spikes in individual filter effluent turbidity (which may indicate paniculate
or colloidal TOC breakthrough) in the days leading to the excursion?
- Did chlorinated water sit in the filter for an extended period of time?
- Were all filters run in a filter-to-waste mode during initial filter ripening?
- Were any filters operated beyond their normal filter run time?
- If GAC filters are used: Is it possible the adsorptive capacity of the GAC bed was reached
before reactivation occurred?
- If biological filtration is used: Were there any process upsets that may have resulted in
breakthrough of TOC (particularly biodegradable TOC)?
Were there changes in plant flow that may have resulted in an unusually high residence time in the
clearwell on the days prior to the excursion?
- For example, a temporary plant shutdown.
Continued on next page
Significant Excursion Guidance Manual
Proposal Draft C-9 July 2003
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Significant Excursion Evaluation Report Rebate: october 16*2004
Page 6
B. Process Upset at Treatment Plant (Continued)
Conclusions:
Did a process upset in the treatment plant cause or contribute to your significant excursion(s)?
Yes _JC No
If yes, please explain:
The combination of two process changes at the Hardwood Plant is the most probable cause of the DBF
excursion noted during the September 2004 sampling event. Specifically the two events were:
• Pre-oxidation of raw water with chlorine for taste and odor control following an algae bloom in Hardwood
Lake. Chlorine addition to the raw water is not a routine practice.
• Ferric chloride was underfed for two days around the September 2004 sampling resulting in a
decrease in TOC removal at the Hardwood Plant. The increased TOC concentration passing through
the treatment process has probably lead to increased formation of TTHM and HAAS. The low ferric
dose was the result of poor calibration of the standby pumps that were placed in service during the
maintenance of the feed pumps that are normally used. It was noticed that pH of coagulation increased
from the usual 5.5 to 6.2 range to 7.1 to 7.3.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft C-10 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 7
C. Planned Change or Maintenance Activities for the Treatment Plant
Was there a recent change (or addition) of pre-oxidant?
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?
Did you change the type or manufacturer of the coagulant?
Were there any changes in disinfection practices in the days prior to the excursion?
- For example, a switch from chloramines to free chlorine for burnout period.
- Discontinuation of ozone which forms very little TTHM.
Was a filter(s) taken off-line for an extended period of time that caused the other filters to operate near
maximum design capacity and creating the conditions for possible breakthrough?
Were any pumps shut down for maintenance, leading to changes in flow patterns or hydraulic surges?
Conclusions:
Did a planned maintenance or operational activity in the treatment plant cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Evaluation Report Reportdate: October 16fl.2004
PageS
Significant Excursion Guidance Manual
Proposal Draft C-11 July 2003
-------
D. Planned Distribution System Operations or Maintenance Activities
Was a tank drained for cleaning or other maintenance?
- Was the tank drained to waste or to the distribution system?
- Was a larger volume than normal drained to the distribution system?
If booster disinfection is used, was the booster disinfectant dose higher than the normal booster
disinfectant dose for that season?
Were there any system maintenance activities in the days prior to DBF excursion? Including:
Repairing mains or installing new mains
Closure of valves to isolate sections of pipes
Were the pipes flushed properly or were the appropriate valves re-opened after work was completed?
Did any pump or pipeline maintenance occur that would have changed the flow pattern in the area the
sample was drawn from?
- Change in flow can cause water in stagnant areas to be drawn into another area.
Did any pipeline replacement occur?
- Disinfecting piping in contact with drinking water could result in a high concentration of
chlorine entering the distribution system and thus increase DBFs.
Conclusions:
Did a planned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Evaluation Report RePOrtdate: October
Page 9
Significant Excursion Guidance Manual
Proposal Draft C-12 July 2003
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E. Unplanned Distribution System Events
Were there increases in demand that caused older water in storage tanks to be drawn into the system?
- Were there any major fire events?
- Did one or more storage tank have greater than average drawdown preceding the time of
DBF peak excursion?
Were there decreases in demand that resulted in longer than normal system residence times?
- Were there any large customers off-line?
Did any main breaks occur causing changes in flow patterns in the influence area of the sample location?
If you collect water temperature inside storage tanks, was the temperature inside the tank higher than
normal for the season?
Were any storage tanks hydraulically locked out of the system for an extended period and then used
preceding the time of DBF peak excursion?
Did changes in overall water demand cause a change in water demand patterns in the vicinity of dead ends
and/or stagnant zones in the system?
Were there large variations in localized system pressures that were different from the normal pressure
range that could have caused a change in water demand patterns in the vicinity of dead ends and/or
stagnant zones in the system?
Conclusions:
Did an unplanned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft C-13 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 10
F. If you were unable to identify the cause of your significant excursion(s) after reviewing
Sections A through E, are you able to identify another potential cause of your increase in DBF
concentrations? Explain.
Note: If you are unable to determine the cause of your excursion you may wish to consider:
More frequent raw water temperature monitoring.
More frequent raw water TOC monitoring.
Increased disinfectant residual monitoring in the distribution system.
Tracer studies to characterize distribution system water age.
Development of a hydraulic model to characterize the distribution system.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft C-14 July 2003
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Supplemental Data Form
for the Significant Excursion
Evaluation Report
Report da
Report pr
System m
te: October 16*. 2004
spared bv: Ronald Doe, P.E.
ime: Elm City
1) Water quality data from significant excursion sampling period.
Location No.
Location Name
TTHM (ug/L)
HAAS (ug/L)
Free Chlorine (mg/L)
Total Chlorine (mg/L)
pH
2) Supplemental data fr
Plant #1: Hardwood Plan
Raw Water Temperature:
Plant Effluent Water Ten
Raw Water TOC: 2.2 n
Other Data:
#1
118
84
0.6
0.8
8.2
#2
145
75
0.8
1.2
8.5
#3
122
65
0.2
0.4
7.9
om each treatment facility:
t Plant
NA Raw
iperature:
is/L (Avs. '
20 °C
' £ .Oms/L)
Planl
#4
82
58
NA
NA
8.1
#2: Softwo
Water Tern
Effluent V
RawW
#5 #6
68 70
47 53
NA 1.1
NA 1.8
7.8 8.3
od Plant
oerature: NA
Vater Temperature:
aterTOC: 1.8ms/L
Other Data: Inf. turb. 25 ntu (Avs. *
#7 #8
58 78
30 50
NA 0.8
NA 1.2
7.5 8.2
20 °C
(Avs. * -2.0ms/L)
•20 ntu)
3) Historical TTHM and HAAS data at significant excursion sampling locations.
TTHM Data (ug/L) HAAS Data (ug/L)
Monitoring #1 #2 #3 # Monitoring # 1 # 2 # #
Location
Date -1999 61
Date - 2000 55
Date -2001 70
Date -2002 64
Date -2003 66
78 45
59 56
69 41
81 73
54 53
Location
Date - 1999 32
Date -2000 29
56
47
Date - 2001 48 23
Avq. 99-03 63 68 54
Date -2002 36
Date -2003 41
34
45
Avq. 99-03 37 45
Attach additional sheets if necessary
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Appendix D
Changes in Distribution System Operation
Significant Excursions Identified Using the "Maximum Concentration Approach"
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The first part of this appendix includes general system information and a summary of
TTHM and HAAS data that resulted in Elm City having to perform a significant excursion
evaluation. This information is not required e as part of the documentation of a significant
excursion. Only the Significant Excursion Report is required to be completed by systems that
experience a significant excursion.
This appendix is provided as an example of a system in which changes in distribution
system operations led to a DBF Significant Excursion. Possible strategies to reduce excursions
are presented in Chapter 4, but they are not to be included in the identification and
documentation process. Appendices B, C, and E provide similar examples for systems in which
changes in source water quality, changes in treatment plant operations, and multiple causes
resulted in a significant excursion.
This example assumes the state has chosen to use 100 fjg/L TTHM and 75 fjg/L HAAS as
the trigger levels for determining that a significant excursion has occurred and that a significant
excursion evaluation is required.
Background Information for this Example
System Description:
General system characteristics:
Service area: Elm City plus surrounding suburban areas
Production: Annual average daily demand 15 MOD
Source Water Information:
Hardwood Lake (surface water)
pH: from 6.9 to 7.5
Alkalinity: from 82 to 98 mg/L as CaCO3
TOC: from 2.1 to 4.0 mg/L as C
Bromide: from 0.04 to 0.1 mg/L
Turbidity: 1 to lOOntu
Softwood River (surface water)
pH: from 6.8 to 7.9
Alkalinity: from 77 to 94 mg/L as CaCO3
TOC: from 1.6 to 9.4 mg/L as C
Bromide: from 0.03 to 0.1 mg/L
Turbidity: 2 to 115ntu
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Treatment Provided:
Hardwood, conventional (15 MOD design, 7.5 MOD average)
Softwood River, conventional with GAC (20 MGD design, 7.5 MGD average)
Primary and residual disinfection: Chlorine/chlorine at both plants
Summary of Stage 2 DBPR Monitoring Locations:
Table D.I summarizes the Stage 2 DBPR monitoring locations used by Elm City.
Sample locations are marked in the distribution system schematic presented in Figure
D.I.
Table D.1 Stage 2 DBPR Monitoring Locations
Location
Location #1
Location #2
Location #3
Location #4
Location #5
Location #6
Location #7
Location #8
Description
Hardwood Plant - average residence time
Hardwood Plant - high TTHM
Hardwood Plant - high HAAS
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Softwood Plant - average residence time
Softwood Plant - high HAAS
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Figure D.1 Schematic of Elm City Distribution System
and Stage 2 DBPR Monitoring Locations
Softwood River WTP
Elevated Storage Tank
Ground storage tank
Booster disinfection
Peak DBP site
Hardwood WTP
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DBF Excursion Investigation:
During the last sampling period which took place in September 2004, Elm City
experienced unusually high TTHM values (relative to the LRAA) at monitoring location #2.
DBF data from the previous year and most recent sampling period (five quarters total) are
presented in Table D.2.
Table D.2 TTHM and HAAS Monitoring Data
Loc
atio
n
#1
#2
#2
#3
#4
#5
#6
#7
#8
TTHM (ug/L)
Quarterly
Pre-Sept
2004
Data1
54, 67, 58, 75
49, 39, 50, 76
68, 68, 55, 69
66,52,71,72
50,55,51,61
34, 48, 55, 50
44, 62, 58, 60
40,41,37,46
68, 68, 55, 69
LRAA
Pre-Sept
2004
65
52
63
64
55
44
49
41
63
Sept
2004
Data
72
122
69
76
82
68
70
58
69
LRAA
incl.
Sept
2004
68
72
65
68
60
48
63
46
65
HAAS (ug/L)
Quarterly
Pre-Sept
2004
Data1
52, 37, 30,
41
43,39,41,
45
38, 45, 28,
19
41,46,45,
39
42, 43, 38,
34
32, 43, 55,
38
45,33,41,
40
21,38,28,
19
38, 45, 28,
19
LRAA
Pre-Sept
2004
40
42
33
43
39
42
40
27
33
Sept
2004
Data
53
49
40
58
54
37
53
29
40
LRAA
incl.
Sept
2004
40
44
33
47
42
43
42
29
33
1Data for sampling conducted on September 2003, December 2003, March 2004 and June 2004. Data relevant to
peak excursions are bold and underlined.
Unusually high TTHM concentrations were observed at location #2. The results are
significantly higher than both the LRAA at those locations for the previous 12-month period and
the historic TTHM and HAAS values at those locations for the years 1999-2003 (see Significant
Excursions Evaluation Report). Data for September 2004 meets the criteria of peak excursion.
The city staff does not believe that treatment plant or source water quality changes caused the
increase in the DBF level because such changes would likely impact all locations supplied by the
treatment plant or source water, but only one location was affected by high DBF level. The city
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staff believes that distribution system operations in the vicinity of the location caused the
increase in the DBF level.
Significant Excursion
Evaluation Report
Page 1
Report date: October 16th. 2004
Report prepared by: Ronald Doe. P.E.
System name: Elm City
1) When was the significant excursion sample(s) collected? What were the TTHM and HAAS
concentrations?
Location No.
Location description
Hardwood Plant
high TTHM
Sample collection date
Sept. 4, 2004
Sample collection time
2p.m.
TTHM LRAA
Concentration (ug/L)
72
TTHM Concentration
(ug/L)
122
HAAS LRAA
Concentration (ug/L)
HAAS Concentration
(ug/L)
Note: Attach additional sheets if you observed more than four significant excursions during this
round of sampling.
2) Where did the excursion(s) occur? Attach a schematic of your system, sketch your system in
the space below, or have a schematic of your system available to review with your state at the
time of your next sanitary survey. Indicate the location(s) of the significant excursion(s) on your
schematic.
Location #2 - Represents high residence time of water leaving the Hardwood Plant. It is located in the Pineville
neighborhood. An elevated storage tank also supplies water to this subdivision.
The location of these sample locations is illustrated in Figure D.I.
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Page 2
3) Attach (or provide in the Supplemental Data Form) all available water quality data for the round
of sampling in which the significant excursion occurred. At a minimum, include all TTHM and
HAAS results from the sampling period. You should also consider including pH, temperature,
alkalinity, TOC, disinfectant residual, and any other data that you think would be useful.
a) Were there any unusual circumstances associated with this round of sampling?
Yes No X
If yes, please explain.
b) Were all analytical QA/QC measures met?
Sample preservation Yes X No
Sample holding time Yes X No
Other
If no, please explain.
4) Attach (or provide in the Supplemental Data Form) historical TTHM and HAAS data for the
locations) at which the significant excursions) occurred. Provide at least three years of data, if
available.
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PageS
5) What caused your excursion(s) to occur?
Sections A through F starting on page 4 can help you determine the possible cause(s) of your
excursion. Please note there may be more than one factor which resulted in your excursion.
Section A: Source water quality change
Section B: Process upset at treatment plant
Section C: Planned change or maintenance activities at plant
Section D: Planned distribution system operations or maintenance activities
Section E: Unplanned events in distribution system
If you already suspect a cause, go directly to that section. If you read Sections A through E and
are unable to determine a cause of your excursion, then complete Section F.
Consecutive systems should also contact their wholesaler to identify the cause(s) of the
significant excursion(s).
6) List steps taken or planned to reduce DBP peak levels.
Considering modifications to configuration of inflow piping at the Pineville tank to improve mixing.
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Page 4
A. Source Water Quality Changes
Did any of the events listed below take place before the DBP excursion to cause TOC levels to
increase?
Heavy rain fall
Flooding
Spring snow-me It/run off
Significant decrease in rainfall or source flow
Algae bloom
Did any of the events listed below take place before the DBP excursion to cause bromide levels
to increase?
Significant decrease in rainfall or source flow
Brackish or seawater intrusion
Did pH and/or alkalinity significantly change?
If two or more supplies are used, was a greater portion of water drawn from the one with higher
TOC?
Was raw water stored for an unusually long period of time resulting in a significant increase in
water temperature?
Conclusions:
Did source water quality changes cause or contribute to your significant excursions)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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B. Process Upset at Treatment Plant
Was raw water stored for an unusually long time, providing additional contact time for DBP
formation after prechlorination?
Were there changes in coagulation practices?
Were there any changes or malfunctions of the coagulation process in the days
leading to the excursion?
Were the coagulant dose and pH properly adjusted for incoming source water
conditions?
Were there changes in chlorination practices?
Were there any changes in chlorine dose at any location in the plant?
Were there changes in plant flow that may have resulted in longer than normal
residence time at any location in the plant?
Did the pH change at the point of chlorine addition?
Were there changes in settling practices?
Was there excess sludge build-up in the settling basin that may have carried over to
the point of disinfectant addition?
Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
Were there changes in filtration practices?
Have filter run times been changed to meet raw water quality changes?
Were there any spikes in individual filter effluent turbidity (which may indicate
particulate or colloidal TOC breakthrough) in the days leading to the excursion?
Did chlorinated water sit in the filter for an extended period of time?
Were all filters run in a filter-to-waste mode during initial filter ripening?
Were any filters operated beyond their normal filter run time?
If GAG filters are used: Is it possible the adsorptive capacity of the GAG bed was
reached before reactivation occurred?
If biological filtration is used: Were there any process upsets that may have resulted
in breakthrough of TOC (particularly biodegradable TOC)?
Were there changes in plant flow that may have resulted in an unusually high residence time in
the clean/veil on the days prior to the excursion?
For example, a temporary plant shutdown.
Continued on next page
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Page 6
B. Process Upset at Treatment Plant (Continued)
Conclusions:
Did a process upset in the treatment plant cause or contribute to your significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Page?
C. Planned Change or Maintenance Activities for the Treatment Plant
Was there a recent change (or addition) of pre-oxidant?
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?
Did you change the type or manufacturer of the coagulant?
Were there any changes in disinfection practices in the days prior to the excursion?
For example, a switch from chloramines to free chlorine for burnout period.
Discontinuation of ozone which forms very little TTHM.
Was a filter(s) taken off-line for an extended period of time that caused the other filters to operate
near maximum design capacity and creating the conditions for possible breakthrough?
Were any pumps shut down for maintenance, leading to changes in flow patterns or hydraulic
surges?
Conclusions:
Did a planned maintenance or operational activity in the treatment plant cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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PageS
D. Planned Distribution System Operations or Maintenance Activities
Was a tank drained for cleaning or other maintenance?
Was the tank drained to waste or to the distribution system?
Was a larger volume than normal drained to the distribution system?
If booster disinfection is used, was the booster disinfectant dose higher than the normal booster
disinfectant dose for that season?
Were there any system maintenance activities in the days prior to DBP excursion? Including:
Repairing mains or installing new mains
Closure of valves to isolate sections of pipes
Were the pipes flushed properly or were the appropriate valves re-opened after work was
completed?
Did any pump or pipeline maintenance occur that would have changed the flow pattern in the
area the sample was drawn from?
Change in flow can cause water in stagnant areas to be drawn into another area.
Did any pipeline replacement occur?
Disinfecting piping in contact with drinking water could result in a high concentration
of chlorine entering the distribution system and thus increase DBPs.
Conclusions:
Did a planned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes X No
If yes, please explain:
Refer to the explanation following Section E.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Page 9
E. Unplanned Distribution System Events
Were there increases in demand that caused older water in storage tanks to be drawn into the
system?
Were there any major fire events?
Did one or more storage tank have greater than average drawdown preceding the
time of DBP peak excursion?
Were there decreases in demand that resulted in longer than normal system residence times?
Were there any large customers off-line?
Did any main breaks occur causing changes in flow patterns in the influence area of the sample
location?
If you collect water temperature inside storage tanks, was the temperature inside the tank higher
than normal for the season?
Were any storage tanks hydraulically locked out of the system for an extended period and then
used preceding the time of DBP peak excursion?
Did changes in overall water demand cause a change in water demand patterns in the vicinity of
dead ends and/or stagnant zones in the system?
Were there large variations in localized system pressures that were different from the normal
pressure range that could have caused a change in water demand patterns in the vicinity of dead
ends and/or stagnant zones in the system?
Conclusions:
Did an unplanned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes X No
If yes, please explain:
The city staff believes distribution system operations caused the peak THM excursion. Therefore, the
likelihood that distribution issues contributed to the peak THM excursion has been explored first. To
determine the cause of the THM peak excursion, the city staff reviewed the following information for a period
of two weeks prior to the occurrence of peak THM excursion:
System maintenance activities
Main breaks
System pressure fluctuations
Overall system demand
Water level in storage tanks
Boost disinfection operation
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Proposal Draft D-13 July 2003
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System maintenance activities:
Installation of a new 12-inch main for a new development in Elmville subdivision was completed. The city
staff reviewed the main disinfection logbook which indicated that the new main was flushed properly, and
chlorine residual in the pipe was 1 mg/L before it was connected to the rest of the water system. Three valves
were closed to isolate sections of pipes from the rest of the water system, during installation of the new main.
These valves were checked to make sure that they were all opened after installation of the new main was
completed. One valve was found to be inadvertently left in the closed position. However, the closure of this
valve did not affect the water quality in Pineville subdivision where the peak THM concentration occurred.
The city's hydraulic model indicated that water does not flow from Elmville to Pineville and closing the valve
in the pipe in Elmville does not alter the water flow patters in Pineville.
Main breaks:
A road repair worker in Pineville subdivision damaged a 12-inch water main that runs along that road. The
broken section of the water main was isolated and shut off within two hours. However, it is anticipated that
there was significant loss of water during those two hours. Hydraulic analyses using the city's hydraulic
model have indicated that the piping network in Pineville does not have any stagnant zones with high
residence time. Also, using the city's hydraulic model to simulate the main break by creating artificial
demand at the location of the main break indicated that the influence of the main break did not draw water
from any stagnant zones towards the sample location where peak THM excursion occurred.
System pressure fluctuations:
The distribution system pressure in the Pineville subdivision was generally within the normal range expected
for the month of September, approximately 52-65 psi. However, the pressure was about 10 psi lower at the
location of the main break for about two hours. As soon as the damaged section of the main was isolated, the
pressure at that location returned to the normal pressure range generally expected for the month of September.
The piping network in Pineville does not have any stagnant zones. There may be stagnant zones outside the
Pineville subdivision, but the lower pressure in the vicinity of the peak THM occurrence did not impact water
flow patterns outside the Pineville subdivision, as verified by the city's hydraulic model.
Overall system demand:
The total hourly distribution system demand was checked using treatment plant production figures and tank
level data. The hourly total system demand during September 2004 ranged between 14-17 mgd, which was
also the general range for the system demand during the month of September for 1999-2003. An unusual
increase or decrease in the total system demand was not observed two weeks prior to the peak THM
occurrence. The loss of water due to the main break did not cause a significant change in the overall system
demand. Therefore, there was not any unusual shift in the water demand patterns and water flow patterns in
the vicinity of stagnant zones and thus did not contribute to the peak THM occurrence.
Water level in storage tanks:
The hourly water level for all the tank in Elm City was plotted using the SCADA system data. The water
levels fluctuated within the normal range for all the tanks except for the elevated tank located in Pineville.
The water level in the Pineville tank generally fluctuates approximately 20 feet to 35 feet above the bottom of
the tank. The water level in this tank dropped to about 12 feet above the bottom of the tank at the time of the
main break and then rose to normal levels once the broken section of the main was isolated. The increased
water demand and pressure drop at the location of the main break was responsible for the unusual drop in the
water level of the Pineville tank. The proximity of Sample Location 2 to the main break also decreased the
pressure at the sampling location, this allowing the water from the top portion of the tank to reach that location
during the main break. The SCADA data indicated that the average inflow rate into the tank is 1000 gpm and
the inlet diameter is 36 inches. This inflow rate and inlet diameter may not provide adequate momentum to
mix the water near the top portion of the tank where the water came from during the main break. Therefore,
the water age in the top portion of the tank was higher and may have caused the peak DBF level at Sample Site
2.
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Booster disinfection operation:
There is a booster disinfection station located in the Polarville subdivision. The disinfectant residual leaving
this booster station was within the normal range of 1-2 mg/L. Pineville subdivision receives all the water
either from the treatment plant directly or from the Pineville tank. It does not receive any portion of its water
from the booster station. Thus, the disinfectant residuals at the booster station did not contribute to peak THM
occurrence at Location 2.
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Significant Excursion Evaluation Report RePOrtdate: October
Page 10
F. If you were unable to identify the cause of your significant excursion(s) after reviewing
Sections A through E, are you able to identify another potential cause of your increase in
DBF concentrations? Explain.
Note: If you are unable to determine the cause of your excursion you may wish to consider:
More frequent raw water temperature monitoring.
More frequent raw water TOC monitoring.
Increased disinfectant residual monitoring in the distribution system.
Tracer studies to characterize distribution system water age.
Development of a hydraulic model to characterize the distribution system.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Proposal Draft D-16 July 2003
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Supplemental Data Form
for the Significant Excursion
Evaluation Report
Report d
Report p
System r
ate: October 16*. 2004
repared by: Ronald Doe, P.E.
ame: Elm City
1) Water quality data from significant excursion sampling period.
Location No.
Location Name
TTHM (ug/L)
HAAS (ug/L)
Free Chlorine (mg/L)
Total Chlorine (mg/L)
PH
#1
72
53
1.5
1.7
7.9
#2
122
38
0.1
0.2
8.0
#3
82
58
NA
NA
8.3
#4
68
54
0.5
0.7
8.1
#5 #6
68 70
37 53
0.8 1.1
1.1 1.5
7.8 8.3
#7 #8
58 69
29 40
NA 0.9
NA 1.2
7.5 8.2
2) Supplemental data from each treatment facility:
Plant #1 : Hardwood Plant Plant #2: Softwood Plant
Raw Water Temperatu
Plant Effluent Water Te
Raw Water TOC: 2.2 r
Other Data:
re: NA
mperature
ns/L (Avs.
: 20 °C
• £ .Oms/L)
Raw\A
Plant E
Raw\A
Other [
teter Temperature:
ffluent Water Temp
teterTOC: 1.8 mg/L
NA
erature: 20 °C
(Avs. • i.Omg/L)
Data: Inf. turb. : 25 ntu (Avs • iO ntu)
3) Historical TTHM and HAAS data at significant excursion sampling locations.
TTHM Data (ug/L) HAAS Data (ug/L)
Monitorinq Location # 2 # # # Monitorinq Location # 2 # #
#
Date - 1998 61
Date - 1999 55
Date -2000 70
Date -2001 64
Date - 2002 49
Avs. 98-02 60
Date - 1998
Date - 1999
Date -2000
Date -2001
Date - 2002
Avq. 98-02
32
29
48
36
43
49
Attach additional sheets if necessary
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July 2003
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Appendix E
Changes in Treatment Plant and Distribution System Operation
Significant Excursions Identified Using the "Maximum Concentration Approach"
-------
This page intentionally left blank.
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The first part of this appendix includes general system information and a summary of
TTHM and HAAS data that resulted in Elm City having to perform a significant excursion
evaluation. This information is not required when documenting a significant excursion. Only
the Significant Excursion Report is required to be completed by systems that experience a
significant excursion.
This appendix is provided as an example of a system in which changes in both treatment
plant and distribution system operations led to a DBF Significant Excursion. Possible strategies
to reduce excursions are presented in Chapter 4, but they are not to be included in the
identification and documentation process. Appendices B through D provide similar examples
for systems in which one primary change either in source water quality, treatment plant
operations, or distribution system operations resulted in a significant excursion.
This example assumes the state has chosen to use 100 fjg/L TTHM and 75 fjg/L HAAS as
the trigger levels for determining that a significant excursion has occurred and that a significant
excursion evaluation is required.
Background Information for this Example
System Description:
General system characteristics:
Service area: Elm City plus surrounding suburban areas
Production: Annual average daily demand 15 MOD
Source Water Information:
Hardwood Lake (surface water)
pH: from 6.9 to 7.5
Alkalinity: from 82 to 98 mg/L as CaCO3
TOC: from 2.1 to 4.0 mg/L as C
Bromide: from 0.04 to 0.1 mg/L
Turbidity: 1 to lOOntu
Softwood River (surface water)
pH: from 6.8 to 7.9
Alkalinity: from 77 to 94 mg/L as CaCO3
TOC: from 1.6 to 9.4 mg/L as C
Bromide: from 0.03 to 0.1 mg/L
Turbidity: 2 to 115ntu
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Treatment Provided:
Hardwood, conventional (15 MOD design, 7.5 MOD average)
Softwood River, conventional with GAC (20 MGD design, 7.5 MGD average)
Primary and residual disinfection: Chlorine/chlorine at both plants
Summary of Stage 2 DBPR Monitoring Locations:
Table E. 1 summarizes the Stage 2 DBPR monitoring locations used by Elm City. Sample
locations are marked in the distribution system schematic presented in Figure E.I.
Table E.1 Stage 2 DBPR Monitoring Locations
Location
Location #1
Location #2
Location #3
Location #4
Location #5
Location #6
Location #7
Location #8
Description
Hardwood Plant - average residence time
Hardwood Plant - high TTHM
Hardwood Plant - high HAAS
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Softwood Plant - average residence time
Softwood Plant - high HAAS
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Figure E.1 Schematic of Elm City Distribution System
and Stage 2 DBPR Monitoring Locations
Softwood River WTP
Elevated Storage Tank
Ground storage tank
Pump station
Peak DBP location
Hardwood WTP
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DBF Excursion Investigation:
During the last sampling period which took place in September 2004, Elm City
experienced unusually high TTHM values (relative to the LRAA) at three monitoring locations
(#1, #2, #3). Similarly, unusually high HAAS values were detected at two monitoring locations
(#1 and #2). DBF data from the previous year and most recent sampling period (five quarters
total) are presented in Table E.2.
Table E.2 TTHM and HAAS Monitoring Data
Loc
atio
n
#1
#2
#3
#4
#5
#6
#7
#8
TTHM (ug/L)
Quarterly
Pre-Sept.
2004
Data1
54, 67, 58, 75
68, 68, 55, 69
66,52,71,72
50,55,51,61
34, 48, 55, 50
44, 62, 58, 60
40,41,37,46
49, 39, 50, 76
LRAA
Pre-Sept.
2004
Avg.
65
63
64
55
44
49
41
52
Sept.
2004
Data
118
145
122
82
68
70
58
78
LRAA
Sept.
2004
Avg.
74
77
74
60
48
53
46
56
HAAS (ug/L)
Quarterly
Pre-Sept.
2004
Data1
52, 37, 30,
41
38, 45, 28,
19
41,46,45,
39
42, 43, 38,
34
32, 43, 55,
38
45,33,41,
40
21,38,28,
19
43,39,41,
45
LRAA
Pre-Sept.
2004
Avg.
40
33
43
39
42
40
27
42
Sept.
2004
Data
84
75
58
54
37
53
29
49
LRAA
Sept.
2004
Avg.
48
42
47
42
43
42
29
44
1Data for sampling conducted on September 2003,
peak excursions are bold and underlined.
December 2003, March 2004 and June 2004. Data relevant to
Unusually high TTHM samples were collected at locations #1, #2, and #3, and unusually
high HAAS samples were collected at locations #1 and #2. The results are significantly higher
than both the LRAA at those locations for the previous 12-month period and the historic TTHM
and HAAS values at those locations for the years 1998-2002 (see Significant Excursions
Evaluation Report). Significant excursions were identified when DBF levels exceeded 100 [ig/L
TTHM or 75 [ig/L HAAS. All of the monitoring locations affected by high DBF are located in
the area served by the Hardwood plant. The city staff has reason to believe that a process change
that occurred during treatment operations at the Hardwood plant caused this increase in DBF
levels.
Significant Excursion Guidance Manual
Proposal Draft
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Significant Excursion
Evaluation Report
Page 1
Report date: October 16. 2004
Report prepared by: Ronald Doe. P.E.
System name: Elm City
1) When was the significant excursion sample(s) collected? What were the TTHM and HAAS
concentrations?
Location No.
Location description
Sample collection date
Sample collection time
TTHM LRAA
Concentration (ug/L)
TTHM Concentration
(ug/L)
HAAS LRAA
Concentration (ug/L)
HAAS Concentration
(ug/L)
#1
Hardwood Plant -
average residence
time
Sept. 4, 2004
3 p.m.
74
118
48
84
# 2
Hardwood Plant -
high TTHM
Sept. 4, 2004
2p.m.
77
145
42
75
# 3
Hardwood Plant -
high HAAS
Sept. 4, 2004
12 noon
74
122
#
Note: Attach additional sheets if you observed more than four significant excursions during this
round of sampling.
2) Where did the excursion(s) occur? Attach a schematic of your system, sketch your system in
the space below, or have a schematic of your system available to review with your state at the
time of your next sanitary survey. Indicate the location(s) of the significant excursion(s) on your
schematic.
Location #1 - Represents the average residence time of water leaving the Hardwood Plant. It is located in the
Oakville neighborhood. There are no storage facilities between the treatment plant and this location
Location #2 - Sample tap is a hose bib at a building located in Pineville in a zone of the distribution system
with water age greater than average. Water in this area is from the Hardwood Plant.
Location #3- This location is located in the downtown area. Water is primarily from Hardwood Plant. A ground
storage tank is near this location.
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Significant Excursion Evaluation Report Reportdate:
Page 2
3) Attach (or provide in the Supplemental Data Form) all available water quality data for the round
of sampling in which the significant excursion occurred. At a minimum, include all TTHM and
HAAS results from the sampling period. You should also consider including pH, temperature,
alkalinity, TOC, disinfectant residual, and any other data that you think would be useful.
a) Were there any unusual circumstances associated with this round of sampling?
Yes No X
If yes, please explain.
b) Were all analytical QA/QC measures met?
Sample preservation Yes X No
Sample holding time Yes X No
Other
If no, please explain.
4) Attach (or provide in the Supplemental Data Form) historical TTHM and HAAS data for the
locations) at which the significant excursions) occurred. Provide at least three years of data, if
available.
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Significant Excursion Evaluation Report RePOrtdate: October i6.2004
PageS
5) What caused your excursion(s) to occur?
Sections A through F starting on page 4 can help you determine the possible cause(s) of your
excursion. Please note there may be more than one factor which resulted in your excursion.
Section A: Source water quality change
Section B: Process upset at treatment plant
Section C: Planned change or maintenance activities at plant
Section D: Planned distribution system operations or maintenance activities
Section E: Unplanned events in distribution system
If you already suspect a cause, go directly to that section. If you read Sections A through E and
are unable to determine a cause of your excursion, then complete Section F.
Consecutive systems should also contact their wholesaler to identify the cause(s) of the
significant excursion(s).
6) List steps taken or planned to reduce DBP peak levels.
Considering modifications to configuration of inflow piping at the Pineville tank to improve mixing.
Considering improvements to coagulant process monitoring (daily verification of coagulant dose delivered
with pump catch, streaming current monitoring) to minimize possible process upsets.
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Page 4
A. Source Water Quality Changes
Did any of the events listed below take place before the DBP excursion to cause TOC levels to
increase?
Heavy rain fall
Flooding
Spring snow-me It/run off
Significant decrease in rainfall or source flow
Algae bloom
Did any of the events listed below take place before the DBP excursion to cause bromide levels
to increase?
Significant decrease in rainfall or source flow
Brackish or seawater intrusion
Did pH and/or alkalinity significantly change?
If two or more supplies are used, was a greater portion of water drawn from the one with higher
TOC?
Was raw water stored for an unusually long period of time resulting in a significant increase in
water temperature?
Conclusions:
Did source water quality changes cause or contribute to your significant excursions)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Significant Excursion Evaluation Report RePOrtdate: October i6.2004
Page 5
B. Process Upset at Treatment Plant
Was raw water stored for an unusually long time, providing additional contact time for DBP
formation after prechlorination?
Were there changes in coagulation practices?
Were there any changes or malfunctions of the coagulation process in the days
leading to the excursion?
Were the coagulant dose and pH properly adjusted for incoming source water
conditions?
Were there changes in chlorination practices?
Were there any changes in chlorine dose at any location in the plant?
Were there changes in plant flow that may have resulted in longer than normal
residence time at any location in the plant?
Did the pH change at the point of chlorine addition?
Were there changes in settling practices?
Was there excess sludge build-up in the settling basin that may have carried over to
the point of disinfectant addition?
Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
Were there changes in filtration practices?
Have filter run times been changed to meet raw water quality changes?
Were there any spikes in individual filter effluent turbidity (which may indicate
particulate or colloidal TOC breakthrough) in the days leading to the excursion?
Did chlorinated water sit in the filter for an extended period of time?
Were all filters run in a filter-to-waste mode during initial filter ripening?
Were any filters operated beyond their normal filter run time?
If GAG filters are used: Is it possible the adsorptive capacity of the GAG bed was
reached before reactivation occurred?
If biological filtration is used: Were there any process upsets that may have resulted
in breakthrough of TOC (particularly biodegradable TOC)?
Were there changes in plant flow that may have resulted in an unusually high residence time in
the clean/veil on the days prior to the excursion?
For example, a temporary plant shutdown.
Continued on next page
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Significant Excursion Evaluation Report RePOrtdate: October i6.2004
Page 6
B. Process Upset at Treatment Plant (Continued)
Conclusions:
Did a process upset in the treatment plant cause or contribute to your significant excursion(s)?
Yes X No
If yes, please explain:
Ferric chloride was underfed for two days prior to the September 2004 sampling event resulting in lower TOC
removal at the Hardwood plant. The increased TOC concentration passing through the treatment process
contributed to increased formation of TTHM and HAA5 at Locations 1, 2, and 3 as these locations are supplied
by the Hardwood treatment plant. The low ferric dose was the result of poor calibration of the standby feed
pumps that were placed in service during the maintenance of the duty feed pumps. The pH of coagulation
increased from the usual 5.5 to 6.2 range to 7.1 to 7.3 during the low coagulant dose.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft E-10 July 2003
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Significant Excursion Evaluation Report RePOrtdate: October i6.2004
Page 7
C. Planned Change or Maintenance Activities for the Treatment Plant
Was there a recent change (or addition) of pre-oxidant?
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?
Did you change the type or manufacturer of the coagulant?
Were there any changes in disinfection practices in the days prior to the excursion?
For example, a switch from chloramines to free chlorine for burnout period.
Discontinuation of ozone which forms very little TTHM.
Was a filter(s) taken off-line for an extended period of time that caused the other filters to operate
near maximum design capacity and creating the conditions for possible breakthrough?
Were any pumps shut down for maintenance, leading to changes in flow patterns or hydraulic
surges?
Conclusions:
Did a planned maintenance or operational activity in the treatment plant cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft E-11 July 2003
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Significant Excursion Evaluation Report Reportdate:
PageS
D. Planned Distribution System Operations or Maintenance Activities
Was a tank drained for cleaning or other maintenance?
Was the tank drained to waste or to the distribution system?
Was a larger volume than normal drained to the distribution system?
If booster disinfection is used, was the booster disinfectant dose higher than the normal booster
disinfectant dose for that season?
Were there any system maintenance activities in the days prior to DBP excursion? Including:
Repairing mains or installing new mains
Closure of valves to isolate sections of pipes
Were the pipes flushed properly or were the appropriate valves re-opened after work was
completed?
Did any pump or pipeline maintenance occur that would have changed the flow pattern in the
area the sample was drawn from?
Change in flow can cause water in stagnant areas to be drawn into another area.
Did any pipeline replacement occur?
Disinfecting piping in contact with drinking water could result in a high concentration
of chlorine entering the distribution system and thus increase DBPs.
Conclusions:
Did a planned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes X No
If yes, please explain:
One area of the Pineville subdivision was flushed in response to customer complaints about water quality.
The flushing activity created additional water demand in that area and reduced the pressure in the vicinity of
the fire hydrants that were flushed. The low pressure altered water flow patterns and caused more than
normal drawdown from one of the storage tanks. Simulation of the flushing activities using the city's
hydraulic model indicated that a change in water flow pattern caused water from one of the stagnant zones in
Oakwood subdivison to flow to the flushed areas. As the water flowed towards the flushed areas, it flowed
through the vicinity of Location 3 bringing old water to this location.
An overview of the tank level data from SCAD A indicated that the water level in Pineville tank generally
drops to about 10 feet below the maximum tank water level of 35 feet. However, at the time of the flushing
activities, the water level in this tank dropped 25 feet below the maximum tank water level. This unusual
drop in water level caused the relatively unmixed water with high age to be drawn into the distribution system
and reach Location 2 which is located close to the tank.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
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Proposal Draft E-12 July 2003
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Significant Excursion Evaluation Report RePOrtdate: October i6.2004
Page 9
E. Unplanned Distribution System Events
Were there increases in demand that caused older water in storage tanks to be drawn into the
system?
Were there any major fire events?
Did one or more storage tank have greater than average drawdown preceding the
time of DBP peak excursion?
Were there decreases in demand that resulted in longer than normal system residence times?
Were there any large customers off-line?
Did any main breaks occur causing changes in flow patterns in the influence area of the sample
location?
If you collect water temperature inside storage tanks, was the temperature inside the tank higher
than normal for the season?
Were any storage tanks hydraulically locked out of the system for an extended period and then
used preceding the time of DBP peak excursion?
Did changes in overall water demand cause a change in water demand patterns in the vicinity of
dead ends and/or stagnant zones in the system?
Were there large variations in localized system pressures that were different from the normal
pressure range that could have caused a change in water demand patterns in the vicinity of dead
ends and/or stagnant zones in the system?
Conclusions:
Did an unplanned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft E-13 July 2003
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Significant Excursion Evaluation Report RePOrtdate: 0^^16.2004
Page 10
F. If you were unable to identify the cause of your significant excursion(s) after reviewing
Sections A through E, are you able to identify another potential cause of your increase in
DBF concentrations? Explain.
Note: If you are unable to determine the cause of your excursion you may wish to consider:
More frequent raw water temperature monitoring.
More frequent raw water TOC monitoring.
Increased disinfectant residual monitoring in the distribution system.
Tracer studies to characterize distribution system water age.
Development of a hydraulic model to characterize the distribution system.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft E-14 July 2003
-------
Supplemental Data Form
for the Significant Excursion
Evaluation Report
Report d
Report p
System r
ate: October 16, 2004
re pa red b>v
ame: El
: Ronald Doe, P.E.
mCitv
1) Water quality data from significant excursion sampling period.
Location No.
Location Name
TTHM (ug/L)
HAAS (ug/L)
Free Chlorine (mg/L)
Total Chlorine (mg/L)
PH
2) Supplemental data
Plant #1 : Hardwood plai
Raw Water Temperatu
Plant Effluent Water Te
Raw Water TOC: 3.2
Other Data:
#1
118
84
1.5
1.7
7.9
#2
145
75
0.1
0.2
8.0
#3
122
58
NA
NA
8.3
from each treatment facility
it
re: NA
mperature
ms/L Cave
: 20 °C
= 2.0)
#4
82
54
0.5
0.7
8.1
Plant*
RawW
Plant E
RawW
Other [
#5
68
37
0.8
1.1
7.8
2: Softwoo
ater Temp
ffluent Ws
teter TOC
Data: Plar
#6 #
70 5
53 2
1.1 N
1.5 N
8.3 7
d plant
erature: NA
ter Temperati
1.8 mg/L d
7 #8
8 78
9 49
A 0.9
A 1.2
5 8.2
re: 20 °C
ive = 2.0)
it influent turbidity = 25 ntu
Average = 20 ntu
3) Historical TTHM and HAAS data at significant excursion sampling locations.
TTHM Data (ug/L) HAAS Data (ug/L)
Monitorina #1 #2 # 3 # Monitorina #1 # 2 #
Location
Date 1998 61
Date 1999 55
Date 2000 70
Date 2001 64
Date 2002 66
Avq. 63
78 45
59 56
69 41
81 73
54 53
68 54
Location
Date 1998
Date 1999
Date 2000
Date 2001
Date 2002
Avq.
32
29
48
36
43
38
56
47
23
34
45
45
#
Attach additional sheets if necessary
Significant Excursion Guidance Manual
Proposal Draft
E-15
July 2003
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Appendix F
Changes in Source Water Quality
Significant Excursions Identified Using the "Difference Approach"
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This page intentionally left blank.
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The first part of this appendix includes general system information and a summary of
TTHM and HAAS data that resulted in Elm City having to perform a significant excursion
evaluation. This information is not required as part of the documentation of a significant
excursion. Only the Significant Excursion Report is required to be completed by systems that
experience a significant excursion.
This appendix is provided as an example of a system in which changes in source water
quality led to a DBF Significant Excursion. Possible strategies to reduce excursions are
presented in Chapter 4, but they are not to be included in the identification and documentation
process. Appendices C through E provide similar examples for systems in which changes in
treatment plant operations, changes in distribution system, and multiple causes resulted in a
significant excursion.
This example assumes the state has chosen to use the "difference approach " (see
Chapter 1.1) for determining that a significant excursion has occurred and that a significant
excursion evaluation is required.
Background Information for this Example
System Description:
General system characteristics:
Service area: Elm City plus surrounding suburban areas
Production: Annual average daily demand 15 MOD
Source Water Information:
Hardwood Lake (surface water)
pH: from 6.9 to 7.5
Alkalinity: from 82 to 98 mg/L as CaCO3
TOC: from 2.1 to 4.0 mg/L as C
Bromide: from 0.04 to 0.1 mg/L
Turbidity: 1 to lOOntu
Softwood River (surface water)
pH: from 6.8 to 7.9
Alkalinity: from 77 to 94 mg/L as CaCO3
TOC: from 1.6 to 9.4 mg/L as C
Bromide: from 0.03 to 0.1 mg/L
Turbidity: 2 to 115ntu
Significant Excursion Guidance Manual
Proposal Draft F-l July 2003
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Treatment Provided:
Hardwood, conventional (15 MOD design, 7.5 MOD average)
Softwood River, conventional with GAC (20 MGD design, 7.5 MGD average)
Primary and residual disinfection: Chlorine/chlorine at both plants
Summary of Stage 2 DBPR Monitoring Locations:
Table F. 1 summarizes the Stage 2 DBPR monitoring locations used by Elm City. Sample
locations are marked in the distribution system schematic presented in Figure F.I.
Table F.1 Stage 2 DBPR Monitoring Locations
Location
Location #1
Location #2
Location #3
Location #4
Location #5
Location #6
Location #7
Location #8
Description
Hardwood Plant - average residence time
Hardwood Plant - high TTHM
Hardwood Plant - high HAAS
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Hardwood/Softwood Mix Zone - high TTHM
Softwood Plant - average residence time
Softwood Plant - high HAAS
Significant Excursion Guidance Manual
Proposal Draft
F-2
July 2003
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Figure F.1 Schematic of Elm City Distribution System
and Stage 2 DBPR Monitoring Locations
Softwood River WTP
Elevated Storage Tank
Ground storage tank
Pump station
Peak DBP location
Hardwood WTP
Significant Excursion Guidance Manual
Proposal Draft
F-3
July 2003
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DBF Excursion Investigation:
During the last sampling period which took place in September 2004, Elm City
experienced unusually high TTHM and HAAS levels (relative to the LRAA). DBF data from the
previous year and most recent sampling period (five quarters total) are presented in Table F.2.
Table F.2 TTHM and HAAS Monitoring Data
Loc
atio
n
#1
#2
#3
#4
#5
#6
#7
#8
TTHM (ug/L)
Quarterly
Pre-Sept.
2004
Data1
54, 67, 58, 75
68, 68, 55, 69
66,52,71,72
50,55,51,61
34, 48, 55, 50
44, 62, 58, 60
40,41,37,46
49, 39, 50, 76
LRAA
Pre-Sept.
2004
Avg.
65
63
64
55
44
49
41
52
Sept.
2004
Data
63
72
81
78
79
121
77
146
LRAA
Sept.
2004
Avg.
67
64
68
62
55
66
50
76
HAAS (ug/L)
Quarterly
Pre-Sept.
2004
Data1
52, 37, 30,
41
38, 45, 28,
19
41,46,45,
39
42, 43, 38,
34
32, 43, 55,
38
45,33,41,
40
31,38,28,
19
43,39,41,
45
LRAA
Pre-Sept.
2004
Avg.
40
33
43
39
42
40
27
42
Sept.
2004
Data
52
39
51
66
58
72
59
98
LRAA
Sept.
2004
Avg.
40
33
46
45
49
47
37
56
1Data for sampling conducted on September 2003, December 2003, March 2004 and June 2004. Data relevant to
peak excursions are bold and underlined.
Unusually high TTHM samples were collected at locations #5, #6, #7 and #8, and
unusually high HAAS samples were collected at locations #6, #7 and #8. The results are
significantly higher than both the LRAA at those locations for the previous 12-month period and
the historic TTHM and HAAS values at those locations for the years 1999-2003 (see Significant
Excursions Evaluation Report). Significant excursions (see Chapter 1.1) were identified if:
and/or
the difference between quarterly location measurement and quarterly LRAA is >
30 ug/L and the LRAA is • «40 ug/L for TTHM.
the difference between quarterly location measurement and quarterly LRAA is >
25 ug/L and LRAA is • »30 ug/L for HAAS.
Significant Excursion Guidance Manual
Proposal Draft
F-4
July 2003
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All of the monitoring locations affected by high DBF are located in the area served by the
Softwood plant or in the mixing zone. The city staff has reason to believe that a water quality
change that has occurred in Softwood River caused the increase in DBFs.
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Proposal Draft F-5 July 2003
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Significant Excursion
Evaluation Report
Page 1
Report date: October 16th. 2004
Report prepared by: Robert Doe. P.E.
System name: Elm City
1) When was the significant excursion sample(s) collected? What were the TTHM and HAAS
concentrations?
Location No.
Location description
Sample collection date
Sample collection time
TTHM LRAA
Concentration (ug/L)
TTHM Concentration
(ug/L)
HAAS LRAA
Concentration (ug/L)
HAAS Concentration
(ug/L)
# 5
Hardwood/Soft-
wood Mix Zone -
High TTHM
Sept. 4th, 2004
10 a.m.
55
79
# 6
Hardwood/Soft-
wood Mix Zone -
High TTHM
Sept. 4th, 2004
2p.m.
66
121
47
72
# 7
Softwood plant -
average residence
time
Sept. 4th, 2004
1 1 a.m.
50
77
27
59
# 8
Softwood plant -
High HAA5
Sept. 4th, 2004
3 p.m.
76
146
56
98
Note: Attach additional sheets if you observed more than four significant excursions during this
round of sampling.
2) Where did the excursion(s) occur? Attach a schematic of your system, sketch your system in
the space below, or have a schematic of your system available to review with your state at the
time of your next sanitary survey. Indicate the location(s) of the significant excursion(s) on your
schematic.
Location #5 - This site is in the downtown area and is located in the Hardwood/Softwood plants mixing zone.
Location #6 - This sample location is a faucet at a connection located in Weeping Willow - a zone of the
distribution system that has been recently developed. This connection is located downstream from a chlorine
booster station. Water in this area is generally a mix of water from the Hardwood and Softwood River Plants.
Location #7 - Represents average residence time of water leaving the Softwood Plant.
Location #8 - This sampling location is in an area that receives water from the Softwood Plant. Samples are
collected at a hose bib near the first house on the cul-de-sac (which has 12 homes total).
For this example, these sample locations are illustrated in Figure F. 1
Significant Excursion Guidance Manual
Proposal Draft
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July 2003
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Significant Excursion Evaluation Report Rebate: october 16-.2004
Page 2
3) Attach (or provide in the Supplemental Data Form) all available water quality data for the round
of sampling in which the significant excursion occurred. At a minimum, include all TTHM and
HAAS results from the sampling period. You should also consider including pH, temperature,
alkalinity, TOC, disinfectant residual, and any other data that you think would be useful.
a) Were there any unusual circumstances associated with this round of sampling?
Yes No X
If yes, please explain.
b) Were all analytical QA/QC measures met?
Sample preservation Yes X No
Sample holding time Yes X No
Other
If no, please explain.
4) Attach (or provide in the Supplemental Data Form) historical TTHM and HAAS data for the
locations) at which the significant excursions) occurred. Provide at least three years of data, if
available.
Significant Excursion Guidance Manual
Proposal Draft F-7 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
PageS
5) What caused your excursion(s) to occur?
Sections A through F starting on page 4 can help you determine the possible cause(s) of your
excursion. Please note there may be more than one factor which resulted in your excursion.
Section A: Source water quality change
Section B: Process upset at treatment plant
Section C: Planned change or maintenance activities at plant
Section D: Planned distribution system operations or maintenance activities
Section E: Unplanned events in distribution system
If you already suspect a cause, go directly to that section. If you read Sections A through E and
are unable to determine a cause of your excursion, then complete Section F.
Consecutive systems should also contact their wholesaler to identify the cause(s) of the
significant excursion(s).
6) List steps taken or planned to reduce DBP peak levels.
We are considering adjustments of the coagulation processes to improve TOC removal including: increasing
the coagulant dose, evaluation of alternative coagulants, evaluation of coagulant aids, lowering the pH of
coagulation, use of a pre-oxidant (permanganate or chlorine dioxide), and use of PAC.
Significant Excursion Guidance Manual
Proposal Draft F-8 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 4
A. Source Water Quality Changes
Did any of the events listed below take place before the DBP excursion to cause TOC levels to
increase?
Heavy rain fall
Flooding
Spring snow-me It/run off
Significant decrease in rainfall or source flow
Algae bloom
Did any of the events listed below take place before the DBP excursion to cause bromide levels
to increase?
Significant decrease in rainfall or source flow
Brackish or seawater intrusion
Did pH and/or alkalinity significantly change?
If two or more supplies are used, was a greater portion of water drawn from the one with higher
TOC?
Was raw water stored for an unusually long period of time resulting in a significant increase in
water temperature?
Conclusions:
Did source water quality changes cause or contribute to your significant excursions)?
Yes X No
If yes, please explain:
The most probable cause of the DBP excursion noted during the September 2004 sampling even was a rapid
increase of the organic matter concentration in the Softwood River. Following two days of heavy rainfall the
TOC measured in the plant influent increased from 2.7 mg/L to 8.4 mg/L. At the same time, turbidity of the
source water also increased from 5 ntu to a maximum of 98 ntu. The coagulant (ferric chloride) dose was
increased from 20 mg/L to 75 mg/L to match water quality changes. For the duration of this high turbidity/
high NOM event, the pH of coagulation was maintained between 61. and 6.3. The higher coagulant dose
prevented any significant increases of turbidity in the settled water, but the concentration of TOC in the plant
effluent increased from 1.8 mg/L to 3.8 mg/L. 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.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Evaluation Report Reportdate: October 16fl.2004
PageS
Significant Excursion Guidance Manual
Proposal Draft F-9 July 2003
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B. Process Upset at Treatment Plant
Was raw water stored for an unusually long time, providing additional contact time for DBP
formation after prechlorination?
Were there changes in coagulation practices?
Were there any changes or malfunctions of the coagulation process in the days
leading to the excursion?
Were the coagulant dose and pH properly adjusted for incoming source water
conditions?
Were there changes in chlorination practices?
Were there any changes in chlorine dose at any location in the plant?
Were there changes in plant flow that may have resulted in longer than normal
residence time at any location in the plant?
Did the pH change at the point of chlorine addition?
Were there changes in settling practices?
Was there excess sludge build-up in the settling basin that may have carried over to
the point of disinfectant addition?
Was there any disruption in the sludge blanket that may have resulted in carryover
to the point of disinfection?
Were there changes in filtration practices?
Have filter run times been changed to meet raw water quality changes?
Were there any spikes in individual filter effluent turbidity (which may indicate
particulate or colloidal TOC breakthrough) in the days leading to the excursion?
Did chlorinated water sit in the filter for an extended period of time?
Were all filters run in a filter-to-waste mode during initial filter ripening?
Were any filters operated beyond their normal filter run time?
If GAG filters are used: Is it possible the adsorptive capacity of the GAG bed was
reached before reactivation occurred?
If biological filtration is used: Were there any process upsets that may have resulted
in breakthrough of TOC (particularly biodegradable TOC)?
Were there changes in plant flow that may have resulted in an unusually high residence time in
the clean/veil on the days prior to the excursion?
For example, a temporary plant shutdown.
Continued on next page
Significant Excursion Guidance Manual
Proposal Draft F-10 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 6
B. Process Upset at Treatment Plant (Continued)
Conclusions:
Did a process upset in the treatment plant cause or contribute to your significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft F-11 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 7
C. Planned Change or Maintenance Activities for the Treatment Plant
Was there a recent change (or addition) of pre-oxidant?
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?
Did you change the type or manufacturer of the coagulant?
Were there any changes in disinfection practices in the days prior to the excursion?
For example, a switch from chloramines to free chlorine for burnout period.
Discontinuation of ozone which forms very little TTHM.
Was a filter(s) taken off-line for an extended period of time that caused the other filters to operate
near maximum design capacity and creating the conditions for possible breakthrough?
Were any pumps shut down for maintenance, leading to changes in flow patterns or hydraulic
surges?
Conclusions:
Did a planned maintenance or operational activity in the treatment plant cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft F-12 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
PageS
D. Planned Distribution System Operations or Maintenance Activities
Was a tank drained for cleaning or other maintenance?
Was the tank drained to waste or to the distribution system?
Was a larger volume than normal drained to the distribution system?
If booster disinfection is used, was the booster disinfectant dose higher than the normal booster
disinfectant dose for that season?
Were there any system maintenance activities in the days prior to DBP excursion? Including:
Repairing mains or installing new mains
Closure of valves to isolate sections of pipes
Were the pipes flushed properly or were the appropriate valves re-opened after work was
completed?
Did any pump or pipeline maintenance occur that would have changed the flow pattern in the
area the sample was drawn from?
Change in flow can cause water in stagnant areas to be drawn into another area.
Did any pipeline replacement occur?
Disinfecting piping in contact with drinking water could result in a high concentration
of chlorine entering the distribution system and thus increase DBPs.
Conclusions:
Did a planned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft F-13 July 2003
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Significant Excursion Evaluation Report Reportdate: October 16fl.2004
Page 9
E. Unplanned Distribution System Events
Were there increases in demand that caused older water in storage tanks to be drawn into the
system?
Were there any major fire events?
Did one or more storage tank have greater than average drawdown preceding the
time of DBP peak excursion?
Were there decreases in demand that resulted in longer than normal system residence times?
Were there any large customers off-line?
Did any main breaks occur causing changes in flow patterns in the influence area of the sample
location?
If you collect water temperature inside storage tanks, was the temperature inside the tank higher
than normal for the season?
Were any storage tanks hydraulically locked out of the system for an extended period and then
used preceding the time of DBP peak excursion?
Did changes in overall water demand cause a change in water demand patterns in the vicinity of
dead ends and/or stagnant zones in the system?
Were there large variations in localized system pressures that were different from the normal
pressure range that could have caused a change in water demand patterns in the vicinity of dead
ends and/or stagnant zones in the system?
Conclusions:
Did an unplanned distribution system maintenance or operational activity cause or contribute to your
significant excursion(s)?
Yes No X
If yes, please explain:
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft F-14 July 2003
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Significant Excursion Evaluation Report Rebate: october 16-.2004
Page 10
F. If you were unable to identify the cause of your significant excursion(s) after reviewing
Sections A through E, are you able to identify another potential cause of your increase in
DBF concentrations? Explain.
Note: If you are unable to determine the cause of your excursion you may wish to consider:
More frequent raw water temperature monitoring.
More frequent raw water TOC monitoring.
Increased disinfectant residual monitoring in the distribution system.
Tracer studies to characterize distribution system water age.
Development of a hydraulic model to characterize the distribution system.
Attach all supporting operational or other data which led you to conclude this was the cause of your
excursion(s) or make sure this data is available during your sanitary survey.
Significant Excursion Guidance Manual
Proposal Draft F-15 July 2003
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Supplemental Data Form
for the Significant Excursion
Evaluation Report
1) Water quality data
Location No.
Location Name
TTHM (ug/L)
HAAS (ug/L)
Free Chlorine (mg/L)
Total Chlorine (mg/L)
PH
Report d
Report p
System r
ate: October 16th, 2004
re pa red by: Robert
ame: Elm City
Doe, P.E.
from significant excursion sampling period.
#1
63
52
1.8
2.1
7.9
#2
72
39
1.3
1.8
8.0
#3
81
51
NA
NA
8.3
#4
78
66
NA
NA
8.1
#5 #6
79 121
58 72
NA 1.1
NA 1.8
7.8 8.3
#7 #8
77 146
59 98
NA 0.8
NA 1.2
7.5 8.2
Data relevant to peak excursions are bold and underlined.
2) Supplemental data from each treatment facility:
Plant #1 : Hardwood Plant Plant #2: Softwood Plant
Raw Water Temperatu
Plant Effluent Water Te
Raw Water TOC: 2.2 r
Other Data:
re: NA
mperature
ng/L (Avg
Raw Water Temperature:
: 20 °C
'. <2.0mg/L)
Plant Effluent Water Temp
Raw Water TOC: 3.8 mg/I
NA
erature: 20 °C
^ (Avg.<2.0mg/L)
Other Data: Inf. turb. 98 ntu (Avg. <20 ntu)
3) Historical TTHM and HAAS data at significant excursion sampling locations.
TTHM Data (ug/L) HAAS Data (ug/L)
Monitoring #5#6#7#8 Monitoring # 6 # 7 # 8 #
Location
Date - 1999 43
Date -2000 51
Date -2001 46
Date -2002 48
Date -2003 34
Avg. 99-03 44
58
49
69
61
44
56
45 49
Location
Date - 1999
56 64 Date -2000
41 69 Date -2001
73 66 Date -2002
53 79 Date -2003
54 65
Avg. 99-03
57 52
48 39
45 48
51 56
45 31
56
47
33
34
43
49 45 43
Attach additional sheets if necessary
Significant Excursion Guidance Manual
Proposal Draft
F-16
July 2003
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