iii STAGE 2 DISINFECTANTS AND DISINFECTION BYPRODUCTS RULE United States Environmental Protection Agency Office of Water ( 4601) EPA [ No. TBD] July 2003 Draft 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 It has not had a final review for technical accuracy or adherence to EPA policy; do not quote or cite except as a public comment. SIGNIFICANT EXCURSION GUIDANCE MANUAL i 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 DBP 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 DBP 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. gov and 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. ii 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 email 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. Significant Excursion Guidance Manual July 2003 Proposal Draft iii Contents Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv Acronym List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v 1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1.1 What is a Significant DBP 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 DBP Excursions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 2.1 Fundamentals of DBP Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 2.2 Impacts of Changes in Source Water Quality on DBP Concentrations . . . . . . . 2 2 2.3 Impacts of Changes in Treatment Plant Operations on DBP Concentrations . . 2 8 2.4 Impacts of Distribution System Characteristics on DBP Concentration . . . . . 2 15 3.0 Identifying the Cause Of and Documenting Your DBP 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 Significant Excursion Guidance Manual July 2003 Proposal Draft iv Tables and Figures Tables 1. Example 1 1 TTHM and HAA5 Monitoring Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 2.1 Free Chlorine, TTHM, and HAA5 Data for Five Storage Tanks . . . . . . . . . . . . . . . 2 15 Figures 2.1 Effect of NOM Concentration on TTHM and HAA5 Concentration . . . . . . . . . . . . . 2 3 2.2 Impact of Water Temperature on DBP 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 DBP 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 HAA5 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 HAA5 Concentrations . . . . . . . . . . . 2 16 Significant Excursion Guidance Manual Proposal Draft July 2003 v Acronyms CFD Computational Fluid Dynamic CFR Code of Federal Regulations CT Disinfectant residual × contact time DBP Disinfection Byproduct DOC Dissolved Organic Carbon EPA Environmental Protection Agency FACA Federal Advisory Committees Act GAC Granular Activated Carbon HAA5 Haloacetic Acids [ total of five] HPC Heterotrophic Plate Count IDSE Initial Distribution System Evaluation IESWTR Interim Enhanced Surface Water Treatment Rule LRAA Locational Running Annual Average LT1ESWTR Long Term 1 Enhanced Surface Water Treatment Rule MCL Maximum Contaminant Level M DBP Microbial Disinfectants/ Disinfection Byproduct MG Milligrams MGD Million Gallons per Day NOM Natural Organic Matter QA/ QC Quality Assurance/ Quality Control SCADA Supervisory Control and Data Acquisition Stage 2 DBPR Stage 2 Disinfectants and Disinfection Byproducts Rule SWTR Surface Water Treatment Rule THM Trihalomethane TOC Total Organic Carbon TTHM Total Trihalomethanes Significant Excursion Guidance Manual ProposalDraft July 2003 1 1 1.0 Introduction The Stage 2 Microbial Disinfection Byproducts ( M/ DBP) Agreement in Principle acknowledges that significant excursions of DBP 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 DBP 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 DBP concentrations in the distribution system ° List additional references 1.1 What is a Significant DBP Excursion?

The Stage 2 Disinfectants and Disinfection Byproducts Rule ( DBPR), under Stage 2B, requires systems to meet a running annual average of 80 µ g/ L for total trihalomethanes ( TTHM), and 60 µ g/ L for haloacetic acids ( HAA5) 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 DBP 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 DBP 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 DBP excursion as any compliance sample that exceeds the following:

° TTHM concentration of 100 µ g/ L ° HAA5 concentration of 75 µ g/ L Another approach a State may take to defining a significant DBP excursion is to compare results from individual quarterly measurement from compliance monitoring with the LRAAs Significant Excursion Guidance Manual ProposalDraft July 2003 1 2 computed for that period. Using 40 µ g/ L for TTHM and 30 µ g/ L for HAA5 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 µ g/ L and the LRAA is $ 40 µ g/ L for TTHM a significant excursion has occurred.

° For HAA5, the difference between a quarterly location measurement and the quarterly LRAA is > 25 µ g/ L and the LRAA is $ 40 µ g/ 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 HAA5 values relative to the LRAA at one monitoring location (# 4). DBP data from the previous year and most recent sampling period ( five quarters total) are presented in the table below.

Example TTHM and HAA5 Monitoring Data Locations TTHM ( ug/ L) HAA5 ( ug/ L)

LRAA Pre June 2004 Avg. June 2004 Data LRAA June 2004 Avg. LRAA Pre June 2004 Avg. June 2004 Data LRAA June 2004 Avg.

# 1 65 63 67 40 52 40 # 2 63 72 64 33 59 38 # 3 64 81 68 43 51 46 # 4 49 79 66 40 84 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 ( HAA5 Significant Excursion):

Step 1: Is the quarterly pre June 2004 LRAA ( HAA5) > 30 µ g/ L? If yes a significant excursion is possible. Significant Excursion Guidance Manual ProposalDraft July 2003 1 3 The quarterly Pre June 2004 LRAA ( HAA5) is 33 µ g/ L ( see Table 1 1) and is greater then 25 µ g/ 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 HAA5 and quarterly pre June 2004 LRAA ( HAA5) > 25 µ g/ L? If yes a significant excursion has occurred.

Quarterly location measurement is 59 µ g/ L and the quarterly Pre June 2004 LRAA ( HAA5) is 33 µ g/ L ( see data in table).

59  33 µ g/ L = 26 µ g/ L.

The difference between quarterly location measurement and quarterly Pre June 2004 LRAA is greater than 25 µ 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 DBP 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 DBP precursor removal technologies that can be used to reduce DBP concentrations.

The Stage 2 DBPR does require you to:

1) Evaluate distribution system operational practices to identify opportunities to reduce DBP 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 DBP excursions. Significant Excursion Guidance Manual ProposalDraft July 2003 1 4 ° Chapter 2  Causes of Significant DBP Excursions: Identifies the most common causes of significant DBP excursions.

° Chapter 3  Identifying the Cause Of and Documenting Your DBP 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 DBP Concentrations: Summarizes the options available to reduce DBP significant concentrations, including operational changes and distribution system modifications.

° Chapter 5  References Appendix A discusses the fundamentals of DBP formation. Appendices B through E are examples of completed evaluation reports compiled when the significant excursion is identified using the " maximum concentration approach" (> 100 µ g/ L for TTHMs and > 75 µ g/ L for HAA5). Appendice F is an examples of completed evaluation reports compiled when the significant excursion is identified using the " difference approach." Significant Excursion Guidance Manual Proposal Draft July 2003 2 1 2.0 Causes of Significant DBP 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 DBP Formation 2.2 Impacts of Changes in Source Water Quality on DBP Concentrations 2.3 Impacts of Changes in Treatment Plant Operations on DBP Concentrations 2.4 Impacts of Distribution System Characteristics on DBP Concentrations Chapter 3 follows with a guide to identifying causes of specific DBP excursion events.

2.1 Fundamentals of DBP Formation TTHM and HAA5 are primarily formed by the reaction of chlorine or chloramines with natural organic matter ( NOM). The amount of TTHM and HAA5 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 HAA5 and how changes in these parameters may result in increases in TTHM and HAA5 concentrations. Greater detail regarding the formation of TTHM and HAA5 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 HAA5 concentrations. Typically, changes that increase TTHM and HAA5 concentrations include the following occurrences: Significant Excursion Guidance Manual Proposal Draft July 2003 2 2 ° 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 HAA5. Therefore, increases in the source water NOM concentration not addressed by adjustments in the treatment process can lead to increased formation of TTHM and HAA5 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 HAA5 concentrations. As NOM concentration increases, both TTHM and HAA5 concentrations also increase. Significant Excursion Guidance Manual Proposal Draft July 2003 2 3 Effect of Organic Content on TTHM and HAA5 Concentration 0 20 40 60 80 100 0.5 1 1.5 2 TOC ( mg/ L) TTHM or HAA5 ( ug/ L)

TTHM HAA5 Figure 2.1 Effect of NOM Concentration on TTHM and HAA5 Concentration ( chlorine dose 4.3 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 HAA5 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 HAA5 resulting in the formation of proportionally more TTHM or HAA5. 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 HAA5 than TTHM concentrations when the water temperature reaches 3 ° C. Significant Excursion Guidance Manual Proposal Draft July 2003 2 4 TTHM and HAA5 Concentrations ( T = 24 C)

0 20 40 60 80 0 5 10 15 20 25 Water Age ( days) TTHM or HAA5 ( ug/ L)

TTHM HAA5 TTHM and HAA5 Concentrations ( T = 3 C)

0 20 40 60 80 0 5 10 15 20 25 Water Age ( days) TTHM or HAA5 ( ug/ L)

TTHM HAA5 Figure 2.2 Impact of Water Temperature on DBP Speciation 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 HAA5 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. Significant Excursion Guidance Manual Proposal Draft July 2003 2 5 Variation in TTHM Speciation with Increasing Influent Bromide Concentration 0% 20% 40% 60% 80% 100%

0.035 0.077 0.09 0.17 0.22 Influent Bromide ( mg/ L) Percent of TTHM CHCl3 BDCM DBCM CHBr3 Figure 2.3 Impact of Bromide Concentration on TTHM Speciation 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 DBPs. 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 DBPs than hydrophobic NOM ( Liang and Singer, 2001). Therefore, an increase in the concentration of hydrophobic NOM may be accompanied by an increase in DBP 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. Significant Excursion Guidance Manual Proposal Draft July 2003 2 6 Effect of pH on TTHM Formation 0 10 20 30 40 50 60 0 50 100 150 Time ( hours) TTHM ( ug/ L) pH = 7.5 pH = 9 2.2.5 Changes in Other Source Water Characteristics Changes in other source water characteristics, such as pH or alkalinity, can impact TTHM and HAA5 formation. Increases in pH can affect DBP 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 HAA5 concentrations. Figures 2.4 ( for TTHM only) and 2.5 ( for TTHM and HAA5) 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 HAA5 concentrations.

Figure 2.4 Effect of pH on TTHM Formation Source: Plot obtained using the mathematical model developed by Amy et al. ( 1987). Significant Excursion Guidance Manual Proposal Draft July 2003 2 7 7.6 8.8 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 pH Effect of pH on TTHMs and HAA5 Concentrations HAA5 TTHMs Figure 2.5 Effect of pH on TTHM and HAA5 Formation ( results obtained through SDS tests, DBPs measured after a time correspondent to plant effluent, the chlorine residual after application was 2.3 mg/ L)

Source: Data from Franchi et al., 2002 Increases in source water alkalinity can also result in an increase in TTHM and HAA5 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 HAA5 concentrations. For example, a system that supplements a low NOM ground water source with surface water supply during the summer may experience increases in DBPs 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 DBP concentrations. Significant Excursion Guidance Manual Proposal Draft July 2003 2 8 2.3 Impacts of Changes in Treatment Plant Operations on DBP Concentrations Changes or deficiencies in treatment practices can increase TTHM and HAA5 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 DBP formation.

2.3.1 Pretreatment The primary causes of increased TTHM and HAA5 formation resulting from the pretreatment 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 HAA5 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 HAA5 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 DBP concentrations. Figure 2.6 illustrates that greater DBP 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 Significant Excursion Guidance Manual Proposal Draft July 2003 2 9 Effect of Pre Chlorination on In Plant DBP Formation 0 5 10 15 20 25 30 Pre chlorination Post sedimentation point of chlorine addition TTHM or HAA5 ( ug/ L)

TTHM HAA5 ( results obtained through SDS tests, DBPs measured after a time correspondent to plant effluent, the chlorine residual after application was 1.5 mg/ L)

Source: A. Franchi and C. Hill ( 2002).

An increase in the chlorine dosage can increase TTHM and HAA5 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 HAA5) to using chlorine for disinfection credit may experience increases in TTHM and HAA5 as a result. Similarly, systems that switch from chlorine to ozone will likely experience a decrease in plant TTHM and HAA5 concentrations. However, ozonation can result in increases in bromate concentrations ( also a regulated DBP) in systems with sufficient bromide present in the source water. Significant Excursion Guidance Manual Proposal Draft July 2003 2 10 Effect of Chlorine Dose on In Plant DBP Formation 20 25 30 35 40 45 50 2 2.5 3 3.5 Chlorine Dose ( mg/ L) TTHM or HAA5 ( ug/ L)

TTHM HAA5 Figure 2.7 Impact of Increasing Chlorine Dose on In Plant DBP Formation ( results obtained through SDS simulations, DBPs measured after a time correspondent to plant effluent, the chlorine added after flash mixing, residual after application was 1.5 mg/ L)

Source: A. Franchi and C. Hill ( 2002).

2.3.2 Coagulation/ Flocculation The primary causes of increased TTHM and HAA5 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 HAA5. Significant Excursion Guidance Manual Proposal Draft July 2003 2 11 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 HAA5 formation.

During coagulation, pH variations can affect NOM removal and DBP 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 HAA5 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 HAA5 ( see Figures 2.4 and 2.5).

2.3.3 Settling If a chlorine residual is carried through the settling basin, TTHM and HAA5 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 HAA5 concentrations. The effects of increasing chlorine dose on TTHM and HAA5 levels have been previously illustrated in Figure 2.7.

Process changes can still result in the occurrence of peak TTHM or HAA5 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 DBPs 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 DBP removal after chlorination, exhaustion of adsorptive capacity may result in sudden TTHM and HAA5 peak concentrations in the finished water. Significant Excursion Guidance Manual Proposal Draft July 2003 2 12 2.3.5 Disinfection The following disinfection related events can increase the formation of TTHM and HAA5:

° 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 ( LT1ESWTR) to maintain a certain level of CT ( disinfectant residual × 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 HAA5 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 HAA5 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 HAA5 concentrations is similar, but less pronounced. In other words, HAA5 formation occurs more rapidly and may not increase as significantly as TTHM over long periods of time ( particularly in chloraminated systems). Significant Excursion Guidance Manual Proposal Draft July 2003 2 13 Effect of Disinfectant Residual on TTHM Concentration 0 5 10 15 20 25 30 35 40 45 0 25 50 Distribution System Residence Time ( hours) TTHM ( ug/ L) Chlorine = 1 mg/ L Chlorine = 3 mg/ L Figure 2.8 Effect of Disinfectant Residual and Residence Time on TTHM 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 HAA5 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 HAA5 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 HAA5 formation. Systems that practice pre chlorination ( i. e., addition of chlorine to raw water) will likely form more TTHM and HAA5 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 HAA5 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 HAA5 concentrations. As shown in the figure, there is little difference in TTHM and HAA5 between pre chlorination and rapid mix. This is primarily due to the fact that no NOM has been Significant Excursion Guidance Manual Proposal Draft July 2003 2 14 Effect of Alternative Locations for Chlorine Addition Point on In Plant DBP Formation 0 5 10 15 20 25 30 Prechlorination Rapid Mix Postflocculation Postsedimentation point of chlorine addition TTHM or HAA5 ( ug/ L)

TTHM HAA5 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 HAA5 concentrations are reduced by greater than 70% and 50%, respectively.

Figure 2.9 Effect of Point of Chlorination on TTHM and HAA5 Concentrations 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 DBPs 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 HAA5 concentrations during those periods.

Many systems have converted to chloramines for secondary disinfection to reduce TTHM and HAA5 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 HAA5 concentrations.

2.3.6 Plant Shutdowns Plant shutdowns and routine start/ stop operations can lead to peak TTHM and HAA5 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 HAA5 concentrations. When the plant is placed back in service, water containing high TTHM and HAA5 levels may enter the distribution system. Similar increases in TTHM and HAA5 concentrations may be observed at Significant Excursion Guidance Manual Proposal Draft July 2003 2 15 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 HAA5 may form in the treatment plant.

2.4 Impacts of Distribution System Characteristics on DBP Concentration This section discusses distribution system conditions which may result in higher than normal formation of TTHM and HAA5. 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 HAA5 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 HAA5 Data for Five Storage Tanks Tank No. Free Cl2 @ Top of Tank Free Cl2 @ Bottom of Tank TTHM @ Top of Tank TTHM @ Bottom of Tank HAA5 @ Top of Tank HAA5 @ Bottom of Tank 1 0.3 1.3 110 72 57 61 2 0.2 1.0 130 59 12 44 3 0.0 1.0 98 99 31 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. HAA5 concentration is fairly consistent indicating HAA5 formation has stopped, or more likely the early stages of biodegradation of HAA5. Significant Excursion Guidance Manual Proposal Draft July 2003 2 16 Tank 2 Like Tank 1, TTHM concentration has increased in the top of the tank, but biodegradation of HAA5 has clearly begun.

Tank 3 Based on TTHM data, it would appear the tank is well mixed. However, the difference in free chlorine and HAA5 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 HAA5 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/ off line); 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). Significant Excursion Guidance Manual Proposal Draft July 2003 2 17 Relationship Between TTHM Concentrations and Distribution System Residence Time 40 80 120 160 200 0 10 20 30 40 50 60 Residence Time ( hours) TTHM ( ug/ L) Free Chlorine Chloramines Figure 2.10 Relationship Between TTHM and Distribution System Residence Time 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 DBP concentrations. To accomplish this, the disinfectant dose applied at the plant must be minimized to reduce DBP 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 DBP concentrations, DBPs are likely to increase after booster disinfection is applied. Table 2.2 illustrates this point, showing DBP concentrations for locations before and after booster disinfection. Prior to booster disinfection ( water age = 24 to 40 hours), the TTHM concentration remained fairly constant Significant Excursion Guidance Manual Proposal Draft July 2003 2 18 because the disinfectant residual was nearly depleted. On the other hand, as the disinfectant residual depleted ( suggesting microbiological activity), the HAA5 concentration decreased substantially. After booster chlorination, both TTHM and HAA5 concentrations increased ( HAA5 increased beyond the concentrations present before biodegradation).

Table 2.2 Effect of Booster Chlorination on TTHM and HAA5 Concentrations ( Concentrations measured at various locations in the distribution system)

Before Booster Chlorine Addition After Booster Chlorine Addition Water Age ( Hours) 2 24 40 41 50 70 TTHMs ( ppb) 66 130 150 160 170 170 HAA5 ( ppb) 41 47 7 77 95 71 Free Chlorine Residual ( mg/ L) 2.6 0.3 0.0 1.0 2.2 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 DBP levels. The use of several smaller booster stations closer to the end of the system may be more effective in reducing system average DBP 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 HAA5 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 DBP 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 1 3.0 Identifying the Cause Of and Documenting a DBP 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 DBP 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 DBP 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 DBP 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 2 Examples of peak excursion evaluation reports and completed checklists are provided in the appendices:

Appendix Cause of Significant Peak Excursion B Changes in source water quality C Changes in treatment plant operation D Changes in distribution system operation E Changes in treatment plant and distribution system operation Significant Excursion Guidance Manual Proposal Draft July 2003 3 3 Significant Excursion Report date:

Evaluation Report Report prepared by:

Page 1 System name:

1) When was the significant excursion sample( s) collected? What were the TTHM and HAA5 concentrations?

Location No. # # # #

Location description Sample collection date Sample collection time TTHM LRAA Concentration ( ug/ L)

TTHM Concentration ( ug/ L)

HAA5 LRAA Concentration ( ug/ L)

HAA5 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 4 Significant Excursion Evaluation Report Page 2 Report date:

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 HAA5 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 HAA5 data for the location( s) at which the significant excursion( s) occurred. Provide at least three years of data, if available. Significant Excursion Guidance Manual Proposal Draft July 2003 3 5 Significant Excursion Evaluation Report Page 3 Report date:

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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 6 Significant Excursion Evaluation Report Page 4 Report date:

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 melt/ runoff   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 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 7 Significant Excursion Evaluation Report Page 5 Report date:

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? S Were there any changes or malfunctions of the coagulation process in the days leading to the excursion? S Were the coagulant dose and pH properly adjusted for incoming source water conditions? S 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? S Did the pH change at the point of chlorine addition? S Were there any feed pump failures, or were feed pumps operating at improper feed rate?

° Were there changes in settling practices? S Was there excess sludge build up in the settling basin that may have carried over to the point of disinfectant addition? S Was there any disruption in the sludge blanket that may have resulted in carryover to the point of disinfection? S 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? S Have filter run times been changed to meet raw water quality changes? S Were there any spikes in individual filter effluent turbidity ( which may indicate particulate or colloidal TOC breakthrough) in the days leading to the excursion? S Did chlorinated water sit in the filter for an extended period of time? S Were all filters run in a filter to waste mode during initial filter ripening? S Were any filters operated beyond their normal filter run time? S If GAC filters are used: Is it possible the adsorptive capacity of the GAC bed was reached before reactivation occurred? S If biological filtration is used: Were there any process upsets that may have resulted in breakthrough of TOC ( particularly biodegradable TOC)? S 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 clearwell on the days prior to the excursion? S For example, a temporary plant shutdown.

° Were there any other equipment failures or process upsets?

Continued on next page Significant Excursion Guidance Manual Proposal Draft July 2003 3 8 Significant Excursion Evaluation Report Page 6 Report date:

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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 9 Significant Excursion Evaluation Report Page 7 Report date:

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? S For example, a switch from chloramines to free chlorine for burnout period. S Discontinuation of ozone. S 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 10 Significant Excursion Evaluation Report Page 8 Report date:

D. Planned Distribution System Operations or Maintenance Activities ° Was a tank drained for cleaning or other maintenance? S Was the tank drained to waste or to the distribution system? S Was the tank returned to service directly to the system after disinfection with a high residual remaining S 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? S Change in flow can cause water in stagnant areas to be drawn into another area.

° Did any pipeline replacement occur? S 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 11 Significant Excursion Evaluation Report Page 9 Report date:

E. Unplanned Distribution System Events ° Were there increases in demand that caused older water in storage tanks to be drawn into the system? S Were there any major fire events? S 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? S 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. Significant Excursion Guidance Manual Proposal Draft July 2003 3 12 Significant Excursion Evaluation Report Page 10 Report date:

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 DBP 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 July 2003 3 13 Supplemental Data Form for the Significant Excursion Evaluation Report 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)

HAA5 ( ug/ L)

Free Chlorine ( mg/ L)

Total Chlorine ( mg/ L)

pH 2) Supplemental data from each treatment facility:

Plant # 1: Plant # 2: Raw Water Temperature: Raw Water Temperature:

Plant Effluent Water Temperature: Plant Effluent Water Temperature:

Raw Water TOC: Raw Water TOC:

Other Data: Other Data:

3) Historical TTHM and HAA5 data at significant excursion sampling locations.

TTHM Data ( ug/ L) HAA5 Data ( ug/ L)

Monitoring # _____ #_____ #_____ #_____ Monitoring # _____ #_____ #_____ #_____ Location Location Date 1 Date 1 Date 2 Date 2 Date 3 Date 3 Date 4 Date 4 Date 5 Date 5 Avg. Avg.

Attach additional sheets if necessary Significant Excursion Guidance Manual Proposal Draft July 2003 4 1 4.0 Best Management Practices and Distribution System Improvements to Reduce DBP Concentrations It is common to find higher TTHM and HAA5 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 HAA5 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 HAA5 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 DBP 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 DBP formation. Further, high temperatures in tanks during the summer season can increase DBP 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 DBP 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 DBP formation. Operating procedures ( control of empty/ fill periods), inspections and maintenance activities can minimize this problem. Significant Excursion Guidance Manual Proposal Draft July 2003 4 2 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 DBP levels. The average hydraulic residence time can be estimated by the following equation:

Average hydraulic residence time = [ Vmax/( Vmax  Vmin)]/ 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.

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, 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) in 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  1)]/ 4 = 0.5 days Significant Excursion Guidance Manual Proposal Draft July 2003 4 3 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 DBP formation. Based on the evaluations of mixing characteristics, physical and operational modifications can then be recommended to improve storage tank mixing.

<IP_ADDRESS> 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 DBP 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.

<IP_ADDRESS> Increasing Inlet Momentum Inlet momentum ( defined as velocity × 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.

<IP_ADDRESS> 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 Significant Excursion Guidance Manual Proposal Draft July 2003 4 4 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 DBPs may form in the older water stagnating at the top of the tank.

<IP_ADDRESS> 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 DBP formation potential. Therefore, baffles should not be used in distribution system storage facilities under most circumstances.

<IP_ADDRESS> Avoiding 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. Significant Excursion Guidance Manual Proposal Draft July 2003 4 5 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 DBP 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 DBP 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 DBP 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 DBP 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 Significant Excursion Guidance Manual Proposal Draft July 2003 4 6 4.3.1 Minimizing Hydraulic Residence Time in Pipes <IP_ADDRESS> Looping of Dead Ends and Re routing of Valves The highest DBP concentrations in a system are often observed in dead ends with stagnant water. Water in dead ends experience long contact times for DBP 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 DBP 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 DBP 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.

<IP_ADDRESS> 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 DBP levels.

Continuous or automatic intermittent blow offs can be used on a seasonal basis when DBP 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 HAA5 concentrations. A distribution system model can be used to develop time of travel estimates that can help in choosing optimal blow off locations.

<IP_ADDRESS> 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 DBP 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 Significant Excursion Guidance Manual Proposal Draft July 2003 4 7 needed to reduce the residence time of water and the potential for the formation of DBP peak concentrations. Distribution system models can be used as a tool to determine the appropriate pipe diameters.

4.3.2 Reducing Disinfectant Demand <IP_ADDRESS> 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 DBP 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.

<IP_ADDRESS> Flushing Frequent flushing can be an effective tool to control DBP 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 DBP 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 blowoffs conventional flushing of high detention areas is an effective tool for controlling the occurrence of DBP peaks and can reduce the need for looping dead ends. When conducted on a regular basis, conventional flushing can achieve temporary reduction of DBPs 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 DBP 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). Significant Excursion Guidance Manual Proposal Draft July 2003 4 8 Directional ( or unidirectional) flushing is a more effective method for DBP 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 DBP 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 DBP 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 DBP.

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 DBP 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 DBP 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 Significant Excursion Guidance Manual Proposal Draft July 2003 4 9 be flow or dose paced to avoid overfeeding disinfectant. Where chlorine is overfeed, high DBPs 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 DBP concentrations within the distribution system. Generally, as long as chlorine residuals and reactive DBP precursors are present in drinking water, DBPs continue to form. Thus, the longer the contact time between chlorine and NOM, the greater the concentration of DBPs 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, DBP 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 DBP 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. Significant Excursion Guidance Manual Proposal Draft July 2003 4 10 Significant Excursion Guidance Manual Proposal Draft 5 1 July 2003 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. Appendix A Formation and Control of Disinfection Byproducts This page intentionally left blank. Significant Excursion Guidance Manual Proposal Draft July 2003 A 1 A. 1 Introduction The purpose of this appendix is to identify the factors that affect formation of disinfection byproducts ( DBPs) in water treatment processes and distribution systems. It is intended to serve as a tool for systems in identifying potential strategies for reducing DBP concentrations. This appendix is divided into two main sections. Section A. 2 discusses the factors that affect DBP formation. Section A. 3 discusses options for controlling DBP formation in general terms; it is not intended to provide guidance on implementation of DBP control strategies.

A. 2 Formation of DBPs Organic DBPs ( 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 DBP 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 DBPs 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 DBP Formation Organic DBPs 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 DBPs including THMs and HAAs. Further, the oxidation of organic nitrogen can lead to the formation of DBPs Significant Excursion Guidance Manual Proposal Draft July 2003 A 2 containing nitrogen, such as haloacetonitriles, halopicrins, and cyanogens halides ( Reckhow et al., 1990; Hoigné and Bader, 1988).

Non halogenated DBPs 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 DBPs ( Singer and Harrington, 1993). Many of the low molecular weight non halogenated DBPs are biodegradable.

Trussell and Umphres ( 1978) reported that the presence of bromide can affect both the rate and the yield of DBPs, as well as that as the ratio of bromide to NOM ( measured as total organic carbon) increases, the percentage of brominated DBPs 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 DBPs 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 DBP 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 DBP 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 DBP 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 DBP species ( Swanson et al., 2001). The benefits of low DBP formation with chloramines are especially important for controlling formation at the extremities of the distribution system.

When chloramination is used, it is possible that DBPs might form if chlorine is added before ammonia. If the mixing process is inefficient, it is also possible that DBPs 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 DBPs in the distribution system.

The application of chlorine dioxide does not produce significant amounts of organic halogenated DBPs 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. Significant Excursion Guidance Manual Proposal Draft July 2003 A 3 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 DBP formation has focused on chlorinated DBP 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 DBP formation in either of these two cases.

Ozone does not directly produce chlorinated DBPs. However, if chlorine is added before or after ozonation mixed bromo chloro DBPs as well as chlorinated DBPs can form. Ozone can alter the reactions characteristics of NOM and affect the concentration and speciation of halogenated DBPs when chlorine is subsequently added downstream. In waters with sufficient bromide concentrations, ozonation can lead to the formation of bromate and other brominated DBPs. Bromate, like TTHMs and HAA5, is a regulated DBP. 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 DBPs. As the concentration of disinfectant increases the production of DBPs 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 DBP 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, DBP 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, Significant Excursion Guidance Manual Proposal Draft July 2003 A 4 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 DBP 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, DBPs 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 DBPs that can be formed. High concentrations of DBPs 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 DBPs 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. Significant Excursion Guidance Manual Proposal Draft July 2003 A 5 A. 2.5 Water Temperature Significant Excursion Guidance Manual Proposal Draft July 2003 A 6 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 DBP formation. Furthermore, high temperature conditions in the distribution system promote the accelerated depletion of residual chlorine, which can mitigate DBP 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 DBP 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 DBPs 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 DBPs Alternatives to minimize the formation of DBPs 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 Significant Excursion Guidance Manual Proposal Draft July 2003 A 7 DBPs after formation. Because DBPs 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 DBP 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 DBP 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 DBP 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 Significant Excursion Guidance Manual Proposal Draft July 2003 A 8 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 DBPs 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 DBP Formation in the Distribution System For systems maintaining free chlorine residual, significant DBP 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 DBP 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 DBP formation.

In some cases, booster chlorination has also been used to control disinfectant application and minimize DBP 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 DBP 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 DBP control strategy.

A. 3.5 Assessing DBP Formation and Control with the WTP Model If a utility determines, based upon distribution system monitoring, that the DBP levels in their system need to be reduced, they may consider implementing treatment changes in their Significant Excursion Guidance Manual Proposal Draft July 2003 A 9 water treatment plant. To evaluate the potential impact of treatment changes on distribution system DBP 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 DBP 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 DBP 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 DBP formation. Significant Excursion Guidance Manual Proposal Draft July 2003 A 10 References Bichsel, Y., and Von Gunten U., 2000. Environmental Science and Technology, 34 ( 13): 2784 Harrington, G. W., Z. K. Chowdhury, and D. M. Owen. 1992. Journal of the American Water Works Association, 84( 11): 78.

Hozalski, R. M., and E. J. 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 of groundwaters with ultraviolet irradiation. AWWA Research Foundation Report and AWWA, Denver CO.

Owen et al., 1998. Removal of DBP precursors by GAC adsorption. AWWA Research Foundation Report No. 90744, Denver CO.

Krasner S. W., 1999. Chemistry of disinfection by product formation, In Formation 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, and R. L. Malcom. 1990. Chlorination of humic materials: byproduct formation and chemical interpretations. Environmental Science and Technology. 24( 11): 1655. Significant Excursion Guidance Manual Proposal Draft July 2003 A 11 Singer, P. C. and D. 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 DBP 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, W. J. Swanson, Z. K. Chowdhury, and G. Amy. 1999. Extensions and verification of the Water Treatment Plant Model for DBP 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 DBPs 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. Appendix B Changes in Source Water Quality Significant Excursions Identified Using the " Maximum Concentration Approach" This page intentionally left blank. Significant Excursion Guidance Manual Proposal Draft July 2003 B 1 The first part of this appendix includes general system information and a summary of TTHM and HAA5 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 DBP 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 µ g/ L TTHM and 75 µ g/ L HAA5 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 100 ntu 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 115 ntu Significant Excursion Guidance Manual Proposal Draft July 2003 B 2 Treatment Provided: Hardwood, conventional ( 15 MGD design, 7.5 MGD 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. 1 summarizes the Stage 2 DBPR monitoring locations used by Elm City. Sample locations are marked in the distribution system schematic presented in Figure B. 1.

Table B. 1 Stage 2 DBPR Monitoring Locations Location Description Location # 1 Hardwood Plant  average residence time Location # 2 Hardwood Plant  high TTHM Location # 3 Hardwood Plant  high HAA5 Location # 4 Hardwood/ Softwood Mix Zone  high TTHM Location # 5 Hardwood/ Softwood Mix Zone  high TTHM Location # 6 Hardwood/ Softwood Mix Zone  high TTHM Location # 7 Softwood Plant  average residence time Location # 8 Softwood Plant  high HAA5 Significant Excursion Guidance Manual Proposal Draft July 2003 B 3 Pineville MIXING ZONE Softwood River WTP Hardwood WTP Elevated Storage Tank Ground storage tank Pump station 2 Oakville 1 3 Elmville 5 Downtown Appleville Weeping Willow Poplarville Cedarville Cypressville 6 7 4 8 Peak DBP location Figure B. 1 Schematic of Elm City Distribution System and Stage 2 DBPR Monitoring Locations 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 Significant Excursion Guidance Manual Proposal Draft July 2003 B 4 (# 6, # 8). Similarly, unusually high HAA5 values were detected at one monitoring location (# 8). DBP data from the previous year and most recent sampling period ( five quarters total) are presented in Table B. 2.

Table B. 2 TTHM and HAA5 Monitoring Data Loc atio n TTHM ( ug/ L) HAA5 ( ug/ L)

Quarterly Pre Sept. 2004 Data1 LRAA Pre Sept. 2004 Avg. Sept. 2004 Data LRAA Sept. 2004 Avg. Quarterly Pre Sept. 2004 Data1 LRAA Pre Sept. 2004 Avg. Sept. 2004 Data LRAA Sept. 2004 Avg.

# 1 54, 67, 58, 75 65 63 67 52, 37, 30, 41 40 52 40 # 2 68, 68, 55, 69 63 72 64 38, 45, 28, 19 33 39 33 # 3 66, 52, 71, 72 64 81 68 41, 46, 45, 39 43 51 46 # 4 50, 55, 51, 61 55 78 62 42, 43, 38, 34 39 66 45 # 5 34, 48, 55, 50 44 79 55 32, 43, 55, 38 42 58 49 # 6 44, 62, 58, 60 49 121 66 45, 33, 41, 40 40 72 47 # 7 40, 41, 37, 46 41 77 50 31, 38, 28, 19 27 59 37 # 8 49, 39, 50, 76 52 146 76 43, 39, 41, 45 42 98 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 # 6 and # 8, and unusually high HAA5 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 HAA5 values at those locations for the years 1999 2003 ( see Significant Excursions Evaluation Report). Significant excursion were identified when DBP levels exceeded 100 µ g/ L TTHM or 75 µ g/ L HAA5. All of the monitoring locations affected by high DBP 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 DBPs. Significant Excursion Guidance Manual Proposal Draft July 2003 B 5 Significant Excursion Report date: October 16th, 2004 Evaluation Report Report prepared by: Robert Doe, P. E.

Page 1 System name: Elm City 1) When was the significant excursion sample( s) collected? What were the TTHM and HAA5 concentrations?

Location No. # 6 # 8 Location description Hardwood/ Softwood Mix Zone   High TTHM Softwood plant   High HAA5 Sample collection date Sept. 4th, 2004 Sept. 4th, 2004 Sample collection time 2 p. m. 3 p. m.

TTHM LRAA Concentration ( ug/ L) 66 76 TTHM Concentration ( ug/ L) 121 146 HAA5 LRAA Concentration ( ug/ L) 56 HAA5 Concentration ( ug/ L) 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.