° Controlling Asiatic clams and zebra mussels Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 2 ° Oxidizing iron, manganese, and sulfides ° Preventing microbial regrowth in the distribution system and maintaining biological stability ° Removing undesirable tastes and odors through chemical oxidation ° Improving coagulation and filtration efficiency ° Preventing algal growth in sedimentation basins and filters ° Oxidizing organic micropollutants such as pesticides and volatile organic compounds The effectiveness of disinfection depends on the contact time ( the amount of time a disinfectant is in contact with the water) and the residual disinfectant concentration. The efficacy of disinfection also depends on other factors, including pH, temperature, and the type and amount of disinfectant used.

2.2 Disinfection Byproducts ( DBPs)

Disinfectants react with naturally occurring organic matter ( NOM) to form DBPs. Three main types of DBPs are discussed in this document.

° Halogenated organic byproducts ° Organic oxidation byproducts ° Inorganic DBPs Halogenated organic byproducts form during reactions with free chlorine or free bromine. Although bromine is not used as a disinfectant, bromide ions can be naturally present in water and, when oxidized, form free bromine. Organic oxidation byproducts, such as acetaldehyde, form during oxidation reactions with the disinfectants. Inorganic DBPs are usually formed during reactions with chlorine dioxide and ozone.

Temperature, pH, alkalinity, total hardness, turbidity, disinfectant type, and the composition of NOM ( usually measured as total organic carbon, or TOC) affect the types and rates of DBP formation. It should be noted that many DBPs have been identified, but only a select subset ( shown in Exhibit 2.1) were monitored during the ICR and are the focus of this analysis. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 3 Exhibit 2.1 List of Disinfection Byproducts ( DBPs) Measured During the ICR Halogenated Organic Byproducts1 Trihalomethanes Chloroform ( CHCl3) Bromodichloromethane ( BDCM) Dibromochloromethane ( DBCM) Bromoform ( CHBr3)

Haloacetic Acids ( HAA) HAA5: Monochloroacetic acid ( MCAA) Dichloroacetic acid ( DCAA) Trichloroacetic acid ( TCAA) Monobromoacetic acid ( MBAA) Dibromoacetic acid ( DBAA)

HAA6: HAA5 plus Bromochloroacetic acid ( BCAA)

HAA9: HAA6 plus Bromodichloroacetic acid ( BDCAA) Chlorodibromoacetic acid ( CDBAA) Tribromoacetic acid ( TBAA)

Haloacetonitriles ( HAN4) Dichloroacetonitrile ( DCAN) Bromochloroacetonitrile ( BCAN) Dibromoacetonitrile ( DBAN) Trichloroacetonitrile ( TCAN)

Haloketones 1,1 Dichloropropanone 1,1,1 Trichloropropanone Chloropicrin ( CP)

Chloral Hydrate ( CH)

Cyanogen Chloride ( CNCl)

Total Organic Halides ( TOX) Organic Oxidation Byproducts Aldehydes Formaldehyde Acetaldehyde Propanal Butanal Pentanal Glyoxal Methyl Glyoxal Inorganic Byproducts Chlorate Ion Chlorite Ion Bromate Ion 1 Not all individual organic halides could be measured during the ICR. TOX is used to estimate the total quantity of dissolved halogenated organic material in water.

Source: Cohn et al. ( 1999). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 4 System Size ( Population Served) Ground Water ( Percent of Total) Surface Water ( Percent of Total) Total ( Percent of Total) Small (< 10,001) 37,980 ( 73.6%) 9,921 ( 19.2%) 47,901 ( 92.8%)

Medium ( 10,001  100,000) 1,365 ( 2.6%) 2,013 ( 3.9%) 3,378 ( 6.5%)

Large (> 100,000) 63 ( 0.1%) 290 ( 0.6%) 353 ( 0.7%)

Total 39,408 ( 76.3%) 12,224 ( 23.7%) 51,632 ( 100.0%) 2.3 Inventory of Disinfecting Water Systems and Population Served Both CWSs and nontransient noncommunity water systems ( NTNCWSs) that disinfect their water supplies are regulated under the Stage 2 DBPR. All surface water systems are required to disinfect, but only an estimated 68 percent of ground water CWSs and 37 percent of ground water NTNCWSs disinfect ( USEPA 2003a). Exhibit 2.2 shows the combined CWS and NTNCWS estimated system size distribution of disinfecting systems, classified by source water type ( systems using GWUDI are included in the surface water category) and by population served. Exhibit 2.2 shows that approximately 76 percent of disinfecting CWSs and NTNCWSs are ground water systems.

Exhibit 2.3 show other size distribution findings. The distribution of the population served by disinfecting systems is nearly the opposite of the distribution of systems: 63 percent of the population is served by surface water systems, and 37 percent is served by ground water. This is because most large systems serving more than 100,000 people are surface water systems.

Exhibits 2.2 and 2.3 also show the distribution of systems and population between different size categories. Approximately 93 percent of all disinfecting CWSs and NTNCWSs are small systems serving less than 10,000 people, while fewer than one percent are large systems serving more than 100,000 people. Although there are many more small systems than large in the United States, an estimated 140 million people ( 55 percent) are served by large disinfecting systems, 77 million ( 30 percent) by medium disinfecting systems, and only 38 million ( 15 percent) by small disinfecting systems.

Exhibit 2.2 Number ( and Percent) of Disinfecting CWSs and NTNCWSs Detail may not add due to independent rounding.

Notes: The " surface water" designation includes GWUDI systems.

Percent disinfecting based on 1995 CWSS, as summarized in the Drinking Water Baseline Handbook, and adjusted for potential impacts of the Ground Water Rule. See Chapter 3 of the Stage 2 DBPR Economic Analysis ( USEPA 2003a) for further details.

Source: Derived from Chapter 3, Exhibit 3.3 of the Stage 2 DBPR Economic Analysis ( USEPA 2003a). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 5 System Size ( Population Served) Ground Water ( Percent of Total) Surface Water ( Percent of Total) Total ( Percent of Total) Small (< 10,001) 29,413,975 ( 11.6%) 8,197,640 ( 3.2%) 37,611,615 ( 14.8%)

Medium ( 10,001  100,000) 37,986,723 ( 14.9%) 38,616,140 ( 15.2%) 76,602,863 ( 30.1%)

Large (> 100,000) 26,392,250 ( 10.4%) 113,871,860 ( 44.7%) 140,264,110 ( 55.1%)

Total 93,792,948 ( 36.9%) 160,685,640 ( 63.1%) 254,478,588 ( 100.0%) Exhibit 2.3 Population Total ( and Percent) Served by Disinfecting CWSs Detail may not add due to independent rounding.

Notes: The " surface water" designation includes GWUDI systems.

Percent disinfecting based on 1995 CWSS, as summarized in the Drinking Water Baseline Handbook, and adjusted for potential impacts of the Ground Water Rule. See Chapter 3 of the Stage 2 DBPR Economic Analysis ( USEPA 2003a) for further details. NTNCWSs are typically schools, restaurants, etc., and their population is already counted in the CWS population, thus only population served by CWSs is shown in this exhibit.

Source: Derived from Chapter 3, Exhibit 3.5 of the Stage 2 DBPR Economic Analysis ( USEPA 2003a).

2.4 Disinfection Types This section presents data on chemical disinfection practices among large surface and ground water plants as derived from the Information Collection Rule Auxiliary Database 1 ( ICR AUX1) ( USEPA 2000d). It also presents disinfectant dose data for chlorine, ozone, and chlorine dioxide from the Information Collection Rule Auxiliary Database 2 ( ICR AUX2) ( USEPA 2000i). See Chapter 1, section 1.4.6 for a description of these databases.

In the ICR databases, disinfectant types associated with a treatment plant are classified based on disinfectant usage within the plant and distribution system. At the plant level, five disinfectant types are defined in the ICR AUX1 and AUX2 databases as:

° CL2   Free chlorine when only Cl 2 is used as a disinfectant.

° CLM   Chloramine when Cl 2 and ammonia ( NH 3) are added simultaneously into a unit process in the plant where no earlier point of chlorination exists.

° CL2_ CLM   Free chlorine followed by chloramine ( CLM) when NH 3 is added after free chlorine has previously been applied in one or more preceding unit processes.

° CLX   Chlorine dioxide ( ClO 2) if chlorine dioxide is used anywhere in the plant.

° O3   Ozone if ozone is used anywhere in the plant.

At the distribution system level, two disinfectant types are defined ( i. e., CL2 and CLM) according to the disinfectant type applied at the last disinfectant application point before the entry point to the distribution system.

In order to characterize disinfection practices of surface water plants, the ICR AUX2 database was used to derive information for plants that reported both plant and distribution system level disinfectant use for the last 12 months of the ICR collection period. Because some plants switched disinfectants during the 12 month period, the analysis was done for each plant month individually. Exhibit 2.4 shows the findings of the analysis for surface water plants for each combination of plant and Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 6 53.7%

23.1%

6.5% 5.1%

2.7% 3.7% 3.0% 2.1% 0.1% 0% 10% 20% 30% 40% 50% 60%

CL2/ CL2 CL2_ CLM/ CLM CL2/ CLM CLM/ CLM CLX/ CLM CLX/ CL2 O3/ CLM O3/ CL2 CL2_ CLM/ CL2 Percentage of Plant Months ( N = 3,927) distribution system disinfectant for 3,927 plant months. Chapter 15, Table 15.1, in the Information Collection Rule Data Analysis document ( McGuire et al. 2002) provides additional information on the type of disinfectants used for different treatment plant types ( e. g., conventional softening, unfiltered).

For ground water plants, the ICR AUX2 database was also used to derive information. Information was extracted for ground water plants that reported both plant and distribution system level disinfectant use for the last 12 months of the ICR collection period. Exhibit 2.5 shows the results of the ground water plant analysis for chlorine only, chloramines only, and each combination of plant and distribution system disinfectant for 647 plant months. The " CL2 only" category includes plants that reported chlorine use for both the plant and distribution system category, and includes plants that reported chlorine use only in the distribution system.

Exhibit 2.4 Percentage of Surface Water Plants Applying Specific Disinfection Types for Combined Plant/ Distribution System Source: ICR AUX1 Database ( USEPA 2000d).

Query: Screened Plant Disinfectant Type. See Appendix B for details.

Excel File: Plant Distribution Disinfectant Types. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 7 84.9%

13.4%

0.0% 0.8% 0.0% 0.0% 0.0% 0.8% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

CL2 Only CLM Only CL2_ CLM/ CL2 CL2/ CLM CLX/ CL2 CLX/ CLM O3/ CL2 O3/ CLM Percent of Plant Months ( N= 647) Exhibit 2.5 Percentage of Ground Water Plants Applying Specific Disinfection Types for Individual and Combined Plant/ Distribution System Source: ICR AUX1 Database ( USEPA 2000d).

Query: Screened Plant Disinfectant Type. See Appendix B for details.

Excel File: Plant Distribution Disinfectant Types. xls Among medium surface water plants, chlorine is the most common disinfectant ( see Exhibit 3.30, which compares disinfectant use in medium and large plants). This is expected, since both medium and large plants are subject to the 1979 Total Trihalomethane ( TTHM) rule. The National Rural Water Association ( NRWA) Survey indicates that almost all small surface water systems use free chlorine ( see Exhibit 3.39).

2.5 Chlorine Chlorine is the most commonly used disinfectant in public water systems in the United States. Through filtration and chlorination, waterborne diseases, including typhoid and cholera, have been virtually eliminated in this country. For example, in only four years ( between 1911 and 1915), the number of typhoid cases in Niagara Falls, New York dropped from 185 deaths for every 100,000 people to nearly zero following the introduction of filtration and chlorination ( White 1986). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 8 Disinfection with chlorine is simple, economical, efficient, measurable, and practical. Several types of chlorine are available for use as a disinfectant.

° Chlorine gas ( Cl 2)

° Sodium hypochlorite ( liquid) ( NaOCl)

° Calcium hypochlorite ( tablet, granular, or powdered) ( Ca( OCl) 2)

2.5.1 Description of Chemistry The chemistries of these disinfectants are similar; they all react with water to form disinfecting agents. Chlorine hydrolyzes in water to form hypochlorous acid ( HOCl). HOCl is a weak acid and ionizes to yield hypochlorite ion, or OCl. Free residual chlorine is the sum of HOCl and OClconcentrations the relative quantity of each depends on pH. Both hypochlorous acid and hypochlorite inactivate or kill pathogens, but hypochlorous acid is more effective.

Upon addition to water, free chlorine chemically reacts with constituents in the water by various mechanisms. Chlorine oxidizes soluble iron, manganese, and sulfides typically found in drinking water sources. Once oxidized, the resulting products precipitate and are primarily removed by clarification and filtration processes. When chlorine reacts with natural organic matter in the water, it reacts with electron rich sites to form halogenated organic byproducts ( e. g., trihalomethanes and chlorophenols), some of which have been shown to be possible human carcinogens ( Weisel et al. 1999). Chlorine also oxidizes organic matter to form compounds that do not contain a halogen, such as aldehydes, carboxylic acids, ketones, and alcohols ( Richardson 1998). The occurrence of halogenated byproducts has been studied the most because halogenated DBPs are easily detected.

The three forms of chlorine that are typically used at water treatment plants ( chlorine gas, sodium hypochorite, and calcium hypochlorite) are described below.

Chlorine gas is often referred to as elemental chlorine. Chlorine is produced, collected, purified, compressed, cooled, packaged, and shipped as a liquefied gas under pressure. Systems then inject chlorine gas into the water stream, where hydrolysis and ionization ( as described above) produce the disinfecting agents.

Sodium hypochlorite is produced by reacting chlorine with sodium hydroxide. Sodium hypochlorite solutions are also referred to as liquid bleach or Javelle water. Generally, commercial or industrial grade solutions have hypochlorite strengths of 10 to 16 percent. Low concentrations ( i. e., 5.25 percent or less) are sold as common household bleach. The stability of a sodium hypochlorite solution depends on the hypochlorite concentration, storage temperature, time in storage, impurities, pH, and exposure to light. Decomposition of hypochlorite solution over time can affect the feed rate and dosage, as well as produce undesirable byproducts such as chlorite or chlorate ions ( Gordon et al. 1995). Because of these storage problems, many systems are investigating onsite generation of sodium hypochlorite in lieu of purchasing hypochlorite stock supplies in the granular or tablet form from a manufacturer or vendor.

Calcium hypochlorite is a crystal and can be produced by combining equivalent amounts of sodium hypochlorite and calcium chloride ( known as the Perchloron process). A slurry of lime and caustic soda is chlorinated and cooled so that crystals are formed. These crystals are centrifuged, then added to a chlorinated lime slurry; when warmed, the calcium hypochlorite precipitates. Generally, the final product contains up to 70 percent available chlorine and less than 3 percent lime ( White 1992). Storage of calcium hypochlorite is a major safety consideration. It Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 9 should never be stored where it is subject to heat or allowed to contact any easily oxidized organic material.

Based on analysis of the ICR AUX2 data, gaseous chlorine is by far the most common form of chlorine used for water system disinfection ( chlorine was used in its gaseous form 91 percent of the time). See the Information Collection Rule Data Analysis document ( McGuire et al. 2002) for more details.

2.5.2 Use and Distribution Chlorine gas feeders used to treat drinking water can be either direct feed or solution feed. Direct gas feeders deliver chlorine gas under pressure directly to the point of application. Because direct feeders are less safe than solution feed chlorinators, solution feed is typically used. In a solution feeder, chlorine gas is metered under vacuum conditions and mixed with water in an injector to produce a chlorine solution, which is injected at the appropriate application point( s). With this type of system, the flow of chlorine gas automatically shuts off if there is a loss of vacuum, stoppage of the solution discharge line, or loss of operating solution water pressure. This safety mechanism is important because chlorine gas released into the atmosphere can cause acute health problems or even death if inhaled.

Sodium hypochlorite is normally fed directly with a motor driven diaphragm and plunger type chemical metering pump( s) to the appropriate application point( s). Although unusual, feeding sodium hypochlorite using a hydraulic injector or simple gravity flow is possible.

When calcium hypochlorite is used as a treatment process for continuous disinfection, it is mixed with water to form a dilute hypochlorite solution and fed in the same manner as sodium hypochlorite. For spot disinfection in a basin or pipe, calcium hypochlorite tablets are deposited in the appropriate location, water is added, and the tablets allowed to dissolve to form a liquid hypochlorite solution.

According to the 1995 Community Water Systems Survey ( USEPA 1997b), most surface water and ground water systems that have primary disinfection use chlorine. Exhibits 2.4 and 2.5 ( displayed previously) show that 54 percent of large ICR surface water and 85 percent of large ICR ground water systems use chlorine. Additionally, these exhibits show that chlorine is also the most widely used secondary disinfectant.

2.5.3 Advantages and Disadvantages The following list presents selected advantages and disadvantages of using chlorine to disinfect drinking water ( Masschelein 1992; Process Applications, Inc. 1992).

° Advantages   Chlorine is an effective biocide.   Chlorine oxidizes soluble iron, manganese, and sulfides.   Chlorine enhances color removal.   Chlorine controls taste and odor.   The use of chlorine is the easiest and least expensive disinfection method, regardless of system size.   Chlorine is the most widely used disinfection method and, therefore, the most well known. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 10   Chlorine is available as calcium and sodium hypochlorite, which are more advantageous for smaller systems than chlorine gas because they are easier to use, safer, and need less equipment compared to chlorine gas.   Chlorine provides a residual ( for a prolonged treatment effect).

° Disadvantages   Chlorine forms both halogenated and non halogenated organic byproducts ( some of which pose health concerns).   Chlorine gas is a hazardous corrosive gas, and special leak containment and scrubber facilities could be required to ensure safety.   Sodium hypochlorite degrades over time and with exposure to light ( which diminishes its treatment effectiveness).   Sodium hypochlorite is a corrosive chemical.   Calcium hypochlorite requires proper storage. It must be stored in a cool, dry place to reduce potential reactions. Also, an antiscalant chemical may be needed since impurities may cause a precipitate to form.   Higher concentrations of hypochlorite solutions are unstable and will produce chlorate as a decomposition byproduct.   Hypochlorite can contain bromate as a contaminant, resulting in an inadvertent introduction of low concentrations of bromate to drinking water.   Chlorine is less effective in water with higher pH.   Chlorine forms biodegradable oxygenated byproducts that can lead to regrowth of biological material in the distribution system.

Because of the variety of forms and dosage of chlorine and their different usage depending on system size and water quality, not all of these advantages and disadvantages apply to all systems.

2.5.4 Dose Ranges and Points of Application Two key operational parameters that affect DBP formation are disinfectant dose and point of application. The chlorine dose range guideline used in reviewing public water systems' ( PWSs) ICR initial sampling plans was based on dosages provided in engineering design manuals and published articles ( see the Occurrence Assessment for Disinfectants/ Disinfection Byproducts in Public Drinking Water Supplies [ USEPA 1998c] for further information). This range of doses, shown in Exhibit 2.6, includes primary and secondary disinfection. Note that these ranges represent the extreme upper and lower dose values, with normal doses well within these ranges. The combination of chlorination at the treatment plant and strategic locations in the distribution system may be more effective at maintaining residuals than an equivalent single dosage at the treatment plant ( Tryby et al. 1999). Public health benefits of booster chlorination can include decreased DBP formation and better control of biological regrowth and biofilm formation in the distribution system. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 11 Exhibit 2.6 Chlorine Dose Ranges Derived from in ICR Initial Sampling Plans Chlorine Compound Range of Doses ( mg/ L)

Calcium hypochlorite 0.5  5 Sodium hypochlorite 0.2  2 Chlorine gas 1  16 Source: USEPA 1998c.

Exhibit 2.7 illustrates the difference in total chlorine dose in large surface water plants using only free chlorine versus those using chloramines ( median of 2.7 mg/ L as Cl 2 for chlorine only plants versus a median of 5.0 mg/ L as Cl 2 for chloramine plants). Chapter 15 in the Information Collection Rule Data Analysis document ( McGuire et al. 2002) provides additional information on chlorine dose for different plant types ( e. g., direct filtration, softening) and different influent TOC concentrations.

Exhibit 2.8 shows the difference in total chlorine dose in ground water plants using only free chlorine versus those using chloramines ( median of 1.6 mg/ L as Cl 2 for chlorine only plants versus a median of 5.0 for chloramine plants). Higher chlorine doses applied in plants using chloramines may be due to higher levels of organic material, higher chlorine demand, and thus higher chlorine doses are needed to achieve adequate disinfection. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 12 0% 20% 40% 60% 80% 100%

0 2 4 6 8 10 12 14 Plant Mean Total Cl2 Doses ( mg Cl2/ L) Percentile of Plants CL2 Only Plants ( N= 166)

CL2_ CLM or CLM Only Plants ( N= 85) Exhibit 2.7 Cumulative Distributions of Mean Total Chlorine Dose for Surface Water Plants Source: ICR AUX2 Database ( USEPA 2000i).

Query: Screened SW Plant Mean CL2 Doses ( w AUX2). See Appendix B for details.

Excel File: ICR Dose Data and Graphs. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 13 0% 20% 40% 60% 80% 100%

0 2 4 6 8 10 12 14 Plant Mean Total Cl2 Dose ( mg Cl2/ L) Percentile of Plants CL2 Plants ( N= 28)

CLM Plants ( N= 14) Exhibit 2.8 Cumulative Distributions of Mean TotalChlorine Dose for Ground Water Plants Source: ICR AUX2 Database ( USEPA 2000i)

Query: Screened SW Plant Mean CL2 Doses ( w AUX2). See Appendix B for details.

Excel File: ICR Dose Data and Graphs. xls Table 15.3 in the Information Collection Rule Data Analysis document ( McGuire et al. 2002) shows the number of disinfectant application points for various types of surface water plants using free chlorine only. The data indicate that most plant types used either one or two application points. Approximately 10 percent of direct filtration, in line filtration plants, and conventional plants used three Cl2 application points. Plants with multiple application points were most likely using Cl2 to address multiple treatment objectives ( e. g., disinfection, preoxidation, taste and odor control, and prevention of microbial growth within unit processes).

Figure 15.3 in the Information Collection Rule Data Analysis document ( McGuire et al. 2002) shows the proportion of plants using specific chlorine dose locations ( e. g., rapid mix). Results are shown separately for subsets of plants with one, two, or three points of application. Results for the three subsets were consistent: plants apply disinfection primarily at the clearwell, at a point just prior to filtration, or at the rapid mix stage. For plants with one application point, rapid mix is the application point 36 percent of the time, the point just prior to filtration 28 percent, and the clearwell is used 27 percent of the time. For plants with two application points, the rapid mix is used 53 percent, the point just prior to filtration 32 percent, and the clearwell is used 80 percent of the time. Given the prevalence of the rapid mix stage and Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 14 the point just prior to filtration as the application points, chlorine only systems may have some flexibility to move the point of chlorination to reduce the formation of DBPs.

2.5.5 Byproducts Although disinfection of water destroys microbes that can transmit disease, it has the drawback of producing hundreds of DBPs, some of which are considered to be harmful to humans ( Carlson and Hardy 1998; Chen and Weisel 1998). Exhibit 2.1 listed the halogenated organic byproducts that were measured during the ICR. The two most abundant groups of DBPs are trihalomethanes ( THMs) and haloacetic acides ( HAAs) ( Weisel et al. 1999; Hoyer 1998).

Halogenated organic byproducts form when NOM reacts with free chlorine or free bromine. Free chlorine is normally introduced into water directly as a primary or secondary disinfectant. Free bromine results from the oxidation of naturally occurring bromide ion by chlorine. Factors affecting the rate of formation and concentration of halogenated organic DBPs include type and concentration of NOM, form and dose of chlorine, contact time, bromide ion concentration, pH, organic nitrogen concentration, and temperature ( Chen and Weisel 1998; Clark and Sivaganesan 1998). Organic nitrogen significantly influences the formation of nitrogen containing DBPs, including the haloacetonitriles and halopicrins ( Reckhow et al. 1990; Hoigne and Bader 1988). See Chapter 1 for a full discussion of factors affecting DBP formation.

Other DBPs can result from impurities in feed chemicals. Sodium hypochlorite is formed by combining chlorine gas and sodium hydroxide. Both chemicals are manufactured by electrolysis of sodium chloride ( table salt), which can contain naturally occurring impurities, such as bromide ions, that are difficult to remove. While manufacturing sodium chloride, bromide is converted to bromate, which has been found in small amounts in sodium hypochlorite solutions ( The Chlorine Institute 2000).

2.6 Chloramines Chloramines were first considered for use in disinfection after scientists observed that disinfection still occurred when ammonia was present, even though free available chlorine had dissipated. This lingering disinfection was caused by inorganic chloramines.

Chloramines were used regularly for disinfection during the 1930s and 1940s to provide a residual disinfectant and to control taste and odor. Because of an ammonia shortage during World War II, however, the popularity of chloramination declined. In recent years, choramines were recognized as being more stable than free chlorine in the distribution system and, consequently, were found to be effective in controlling bacterial regrowth in the distribution system ( LeChevallier et al. 1996). The concern over halogenated organic byproduct ( THM and HAA) formation in water treatment and distribution systems has increased interest in chloramines because they react differently with NOM than chlorine, generally producing lower concentrations of DBPs ( Symons et al. 1998). Currently, monochloramine is used to disinfect drinking water in approximately 25 percent of U. S. municipalities ( Kool et al. 1999).

2.6.1 Description of Chemistry Chloramines are formed by the reaction of ammonia with aqueous chlorine. In aqueous solutions, hypochlorous acid from the chlorine reacts with ammonia to form inorganic chloramines in a series of Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 15 competing reactions. In these reactions, monochloramine ( NH 2 Cl), dichloramine ( NHCl 2), or nitrogen trichloride ( NCl 3), also referred to as trichloramine, is formed. These competing reactions depend primarily on pH and are controlled to a large extent by the chlorine: ammonia nitrogen ratio ( Cl 2: NH 3 N). Temperature and contact time also regulate this reaction. Monochloramine is formed primarily when the applied Cl 2: NH 3 N ratio is less than 5: 1 by weight. When certain ratios of chlorine and ammonia nitrogen are present, chloramines may not form, and ammonia and chlorine may be converted to other molecules that do not act as disinfectants and are not detected when chlorine residual is measured. For instance, as the applied Cl 2: NH 3 N ratio increases from 5: 1 to 7.6: 1, a " breakpoint" reaction occurs, reducing the residual chloramine and ammonia nitrogen level to a minimum. Breakpoint chlorination results in the formation of nitrogen gas or nitrate and hydrochloric acid. At Cl 2: NH 3 N ratios above 7.6: 1, free chlorine and nitrogen trichloride are present; being quite volatile, the latter usually dissipates. To avoid breakpoint reactions, utilities normally maintain a Cl 2: NH 3 N ratio of between 3: 1 and 5: 1 by weight. A ratio of 6: 1 is actually optimum for disinfection because dichloramine predominates ( dichloramine is a stronger disinfectant than monochloramine), but maintaining a stable operation at that point on the breakthrough curve is difficult. Therefore, as noted above, a Cl 2: NH 3 N ratio of 3: 1 to 5: 1 is typically accepted as optimal for chloramination.

2.6.2 Use and Distribution Monochloramine is used primarily as a secondary disinfectant for maintaining a residual in the distribution system. Monochloramine can be formed by adding ammonia first and then chlorine, by adding chlorine first and then ammonia, or by concurrently adding both reactants. Ammonia is added first when the formation of objectionable taste and odor compounds caused by the reaction of chlorine and organic matter are a concern. Currently, most drinking water systems add chlorine first and then ammonia, in order to meet the EPA Surface Water Treatment Rule ( SWTR) disinfection requirements. The point of ammonia addition typically is selected to " quench" the free chlorine residual after the optimal contact time has been achieved.

2.6.3 Advantages and Disadvantages The following list highlights selected advantages and disadvantages of using chloramines as a method of disinfecting drinking water ( Masschelein 1992).

° Advantages   The monochloramine residual is more stable and lasts longer than free chlorine or chlorine dioxide   thereby providing better bacterial regrowth protection in the distribution system.   Chloramines are very effective in addressing taste and odor problems.   Chloramines are inexpensive and easy to produce.   Production of chlorinated DBPs is minimized if Cl 2: NH 3 ratio is maintained at a low level.

° Disadvantages   The disinfecting properties of chloramine are not as strong as other disinfectants, such as chlorine, ozone, and chlorine dioxide.   Chloramines cannot oxidize iron, manganese, or sulfides. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 16 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 40 45 50 Cl2: N Weight Ratios ( Plant Averages [ indicated by o], Minimums, and Maximums) Percentiles of Plants ( N= 82)   When using chloramine as the secondary disinfectant, it may be necessary to periodically convert to free chlorine for biofilm control in the water distribution system ( chloramine does not effectively control biofilm).   Excess ammonia in the distribution system, in the presence of chloramine, may lead to nitrification problems.   Monochloramine is less effective in waters with high pH.   Dichloramines can pose problems for taste and odor.   Chloramines must be made on site.   As Cl 2: NH 3 ratio approaches the breakpoint, the greater the potential for DBP formation.

Because of the different forms and dosages of chloramine, and different usages depending on system size and water quality, not all of these advantages and disadvantages apply to all systems.

2.6.4 Dose Ranges and Points of Application The normal primary disinfection dose range for monochloramine is 1.0 to 4.0 mg/ L. The minimum dosage of monochloramine in the distribution system is typically 0.5 mg/ L ( Texas Natural Resource Conservation Commission 1996). Exhibit 2.7 showed the cumulative distributions of mean chloramine dose for surface water plants. Another way to characterize total chlorine dose is by Cl 2: NH 3 N weight ratios. These weight ratios determine the species of chloramines formed ( e. g., monochloramine, dichloramine, trichloramine). Exhibit 2.9 shows the distribution of Cl 2: NH 3 N weight ratios in plants using chloramines. The distributions indicate that approximately 95 percent of plants using chloramines had a plant average Cl 2: NH 3 N weight ratio above 2.5, which is the stoichiometric ratio for formation of monochloramine in chlorine demand free water ( McGuire et al. 2002).

Exhibit 2.9 Cl2: NH3 N Weight Ratios in Surface Water CL2_ CLM and CLM Plants Source: McGuire et al. 2002.

Approximately 92 percent of ICR plants using CL2_ CLM have one point of application and the remaining 8 percent have two points of application. For CLM plants, 78 percent have one point of Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 17 application and 22 percent have two points of application. Figures 15.4A and B in the Information Collection Rule Data Analysis document ( McGuire et al. 2002) show the point of application of ammonia for CL2_ CLM and CLM plants. For CL2_ CLM plants with one point of application, 53 percent applied it at the clearwell, while approximately 19 percent applied ammonia at the rapid mix stage ( the remaining plants added ammonia during flocculation, sedimentation, or prior to filtration). For plants with two points of application, most plants applied ammonia at the rapid mix and clearwell points. For CLM plants, the rapid mix point was the predominant point of application for plants with both one and two points of application. The predominance of the rapid mix point indicates that ammonia is already being added early in the treatment train to minimize DBP formation.

2.6.5 Byproducts The effectiveness of chloramines in controlling DBP production depends upon a variety of factors, notably the chlorine to ammonia ratio, the point of addition of ammonia relative to that of chlorine, the extent of mixing, and pH levels in the water.

Direct reactions between monochloramine and organic matter in water produce very few halogenated organic compounds. However, some dichloroacetic acid can be formed, and cyanogen chloride formation is greater than with free chlorine ( Jacangelo et al. 1989; Smith et al. 1993; Cowman and Singer 1994; Symons et al. 1998). If chlorine and NH 3 are added separately to water ( not preformed then some free chlorine is available to react with organic matter. Another potential source of free chlorine is monochloramine, which slowly hydrolyzes to free chlorine in an aqueous solution. Therefore, halogen substitution reactions occur even when pre formed monochloramine is used ( Rice and Gomez Taylor 1986). The closer the Cl 2: NH 3 N ratio is to the breakpoint, the greater the formation of DBPs ( Speed et al. 1987).

The application of chloramines results in the formation of total organic halide ( TOX), which includes unidentified organic byproducts. However, TOX formation occurs to a much lesser degree than it would given an equivalent dose of free chlorine. Little is known about the nature of these byproducts, except that they are more hydrophilic and larger in molecular size than the organic halides produced from free chlorine ( Jensen et al. 1985; Singer 1992; Symons et al. 1998).

2.7 Chlorine Dioxide Chlorine dioxide is a powerful oxidant originally used by industries as a bleaching agent and disinfectant. Chlorine dioxide was first used for drinking water treatment in 1944 at the Niagara Falls, New York Water Treatment Plant. Currently, the major use of chlorine dioxide is as a pre oxidant to control tastes and odors and to reduce THM formation in finished water ( DeMers and Renner 1992).

2.7.1 Description of Chemistry Chlorine dioxide ( ClO 2) is a neutral compound of chlorine in the + IV oxidation state. ClO 2 is a yellow to red colored gas at temperatures above 11   12 ° C. Because ClO 2 does not hydrolyze in water, it exists as a dissolved gas as long as the pH of the water ranges from 2 to 10. In strongly alkaline solutions ( pH greater than 9 or 10), however, formation rates of DBPs increase with increasing concentrations of chlorine dioxide. Chlorine dioxide is a volatile free radical that functions as an oxidant by way of a oneelectron transfer mechanism in which it is reduced to chlorite ( ClO 2 ! ) ( Hoehn et al. 1996; Doerr 1981). During drinking water treatment, chlorite is the predominant reaction byproduct, with 50 to 70 percent of Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 18 the reacted chlorine dioxide being converted to chlorite and 30 percent to chlorate ( ClO 3 ! ) or chloride ( Cl ! ) depending on the secondary disinfectant.

Although chlorine dioxide can be produced from sodium chlorate ( NaClO 3), for most potable water applications, chlorine dioxide is generated from sodium chlorite ( NaClO 2). The proportion of chlorine dioxide relative to impurities, including chlorite, chlorate, or free chlorine, is important when chlorine dioxide is applied to drinking water ( Aieta and Berg 1986). Although a significant amount of chlorite ion can appear in drinking water from the application and subsequent reduction of chlorine dioxide, both precursor chlorite and chlorate ions can be constituent contaminants in generated solutions. EPA recommends that systems limit the formation of chlorite and chlorate by maintaining high generator purity ( i. e., more than 95 percent efficiency) and limiting excess chlorine to no more than 5 percent of the applied dose of chlorine dioxide. Two feed chemical combinations that generate chlorine dioxide yield in excess of 95 percent are chlorine sodium chlorite and acid sodium hypochlorite sodium chlorite.

Several feed chemical combinations that are used in the water industry are described below.

Acid   Chlorite Solution. Chlorine dioxide can be generated by acidification of a sodium chlorite solution, usually with hydrochloric acid, and several stoichiometric reactions have been reported for such processes ( Gordon et al. 1972). When catalyzed by the presence of chloride ions, acid activation of sodium chlorite has a maximum possible yield of 80 percent of the quantity of chlorine dioxide that could be produced from a reaction of the same amount of sodium chlorite with chlorine ( Petochelli 1995). The reaction is relatively slow, and production rates using this method are practically limited to about 25 to 30 pounds per day, due to the exothermic nature of the reactions.

Chlorine Solution   Chlorite Solution. Chlorite ions ( from dissolved sodium chlorite) will react in aqueous solutions with chlorine or hypochlorous acid to form chlorine dioxide. Two moles of chlorite ions will theoretically react with one mole of chlorine to produce two moles of chlorine dioxide. To fully utilize the sodium chlorite solution, excess chlorine is often used, reducing the pH and driving the reaction further toward completion. The reaction is faster than the acid   chlorite solution method, but much slower than the other commercial methods described in the following discussion. Chlorine dioxide production by this method is limited to about 1,000 pounds per day.

Chlorine Gas   Chlorite Solution. Sodium chlorite solution can be " vaporized" and reacted in a vacuum with molecular gaseous chlorine. This process uses concentrated reactants and is much more rapid than chlorine solution   chlorite solution methods ( Petochelli 1995). If the chlorine and chlorite ions react stoichiometrically, the resulting pH is close to 7. Production rates are virtually unlimited, and some systems have reported producing more than 60,000 pounds per day.

Chlorine Gas   Solid Chlorite. This process reacts dilute, humidified chlorine gas with specially processed solid sodium chlorite contained in sealed reactor cartridges. The reaction is rapid and produces high purity chlorine dioxide gas inherently free of chlorine and chlorate ions because these ions do not carry into the gas phase. Using multiple cartridges in series ensures an excess of sodium chlorite; thus, all chlorine is reacted and the chlorine dioxide produced is chlorine free. Because the chlorine dioxide production rate is solely a function of the chlorine gas feed rate, generators that use chlorine gas   solid chlorite technology are capable of infinite turndown ( i. e., the chlorine dioxide production rate can be adjusted without requiring recalibration between settings) ( Petochelli 1995; Hoehn and Rosenblatt 1996). Chlorine gas   solid chlorite solution method production capacities are limited to 2,000 pounds per day. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 19 In addition to the commercial processes discussed previously, other potential methods for generating chlorine dioxide include electrolysis of a sodium chlorite solution ( with or without the use of membranes to purify the chlorine dioxide product), irradiation of dilute sodium chlorite solution with UV light, and reduction of sodium chlorate with concentrated sulphuric acid and 50 percent hydrogen peroxide.

2.7.2 Use and Distribution Chlorine dioxide is almost never used commercially as a gas because it cannot be safely compressed and shipped. For potable water treatment process, it is predominantly generated in aqueous solutions. Because of the volatile nature of the gas, chlorine dioxide works extremely well in plug flow reactors, such as pipe lines. It can be easily removed from dilute aqueous solution by aerated turbulence, such as in a rapid mix tank or aerated cascade. For post disinfection, chlorine dioxide can be added before clearwells or transfer pipelines.

An estimated 700 to 900 U. S. drinking water systems use chlorine dioxide, largely to oxidize iron and manganese, control taste and odor, and reduce THM levels ( Hoehn et al. 1992). Some systems are looking to the higher disinfection efficacy of chlorine dioxide to decrease contact time needed for Cryptosporidium control. Nineteen plants ( 3.7 percent) that participated in the ICR reported using chlorine dioxide for at least 9 of the last 12 months of the ICR collection period ( USEPA 2000i).

2.7.3 Advantages and Disadvantages The following list highlights selected advantages and disadvantages of using chlorine dioxide to disinfect drinking water ( Masschelein 1992; DeMers and Renner Inc. 1992; Gallagher et al. 1994).

° Advantages   More effective than chlorine and chloramines for inactivation of viruses ( with longer contact times), Cryptosporidium, and Giardia ( with shorter contact times).   Oxidizes iron, manganese, and sulfides.   Provides taste, odor, and color control.   Under proper generation conditions ( i. e., no excess chlorine), TTHM is not formed.   Biocidal properties are not influenced by pH.

° Disadvantages   Incomplete generation of chlorine dioxide leaves unreacted chlorite and chlorate.   Generator inefficiency and optimization difficulty can result in excess chlorine feed at the application point, leading to formation of halogenated organic DBPs.   Costs are a concern: training, sampling, and laboratory testing for chlorite and chlorate are expensive; in many cases equipment must be rented; and the cost of the sodium chlorite is high.   Measuring a chlorine dioxide residual for determining disinfection credit is difficult.   Chlorine dioxide gas is explosive, so it must be generated on site and requires careful handling.   Chlorine dioxide decomposes in sunlight.   Chlorine dioxide can lead to production of noxious odors in some systems.   It is difficult to maintain a chlorine dioxide residual in the distribution system. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 20 Because of the wide variation in system size, water quality, and resulting dosages of chlorine dioxide applied, not all of these advantages and disadvantages apply to all systems.

2.7.4 Dose Ranges Before chlorine dioxide is selected as a primary disinfectant, an oxidant demand study must be completed. Ideally, this study should consider the seasonal variations in water quality, temperature, and application points. EPA recommends that the combined concentrations of chlorine dioxide, chlorate, and chlorite not exceed 1.0 mg/ L in finished water. This means that if the desired oxidant dosage is greater than about 1.4 mg/ L, the chlorite/ chlorate byproduct concentrations would already be at the maximum level; therefore, chlorine dioxide would not be acceptable as a disinfectant. The range of doses includes both primary and secondary disinfection, although chlorine dioxide typically is used for primary disinfection. Note that these ranges represent the extremes; normal doses fall within these ranges.

Exhibit 2.10 presents chlorine dioxide doses ( average, minimum, and maximum of all plant months where data was reported for 9 of the last 12 months of the ICR collection period) for surface water plants using chlorine dioxide. A number of surface water plants using chlorine dioxide ( 58 percent) had average chlorine dioxide doses between 1.0 and 1.5 mg/ L as ClO 2. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 21 0% 20% 40% 60% 80% 100%

0 0.5 1 1.5 2 2.5 3 3.5 Chlorine Dioxide Dose ( mg ClO2/ L) Percentile ( N= 20) Exhibit 2.10 Chlorine Dioxide Doses ( Plant Minimum, Mean, and Maximum)

Note: Open circles represent plant means and lines represent minimum and maximum values.

Source: ICR AUX2 Database ( USEPA 2000i).

Query: Screened SW Plant Mean CLX Doses ( w AUX2). See Appendix B for details.

Excel File: ICR Dose Data and Graphs. xls 2.7.5 Byproducts Small amounts of chlorine are often present when chlorine dioxide is used, so halogenated organic DBPs are often detected in small quantities. However, the application of chlorine free chlorine dioxide does not form THMs and produces only a small amount of TOX ( Werdehoff and Singer 1987) and other halogenated substituted compounds at very low concentrations ( Richardson 1998). Chlorine dioxide oxidizes NOM to form organic DBPs. Primarily, however, the application of chlorine dioxide to water results in oxidation/ reduction reactions that form two inorganic DBPs: chlorite and chlorate ( Rav Acha et al. 1984; Werdehoff and Singer 1987). Chlorite and chlorate frequently are found as contaminants in chlorine dioxide feed streams, and chlorite is formed as a byproduct from disinfection with chlorine dioxide ( Griese et al. 1991). However, chlorine dioxide does not generate bromine substituted byproducts to the same extent as ozone in bromide containing waters. Chlorite in drinking water results from two parts of the chlorine dioxide disinfection process: . ° Unreacted chlorite from the chlorine dioxide generation process Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 22 ° Reduction of chlorine dioxide when it reacts with organic matter in water Incomplete reaction or non stoichiometric addition of the sodium chlorite and chlorine reactants can result in unreacted chlorite or, more likely, chlorate in the chlorine dioxide feed stream. Upon application to water, chlorine dioxide is fairly unstable and rapidly dissociates into chlorite and chlorate at pHs above 10. This occurs only to a limited extent where residuals of chlorine dioxide are greater than 1 percent. Chlorite ions are the primary product of chlorine dioxide reduction, but the percentage of chlorite and chlorate present is influenced by pH and sunlight, as well as the efficiency of the chlorine dioxide generator.

The quantity of chlorate produced during chlorine dioxide generation increases with excess chlorine addition. Similarly, low pH can increase the quantity of chlorate during chlorine dioxide generation. The predominant source of chlorate ions in finished water, however, results from the oxidation of chlorite ( from the applied chlorine dioxide) by free available chlorine used as a final distribution system disinfectant ( Gallagher et al. 1994). Consequently, chlorate concentrations are expected to increase with increasing contact time in water containing chlorite and chlorine. Once formed, chlorate is stable in finished drinking water.

2.8 Ozonation Ozone ( O 3) is used in water treatment for disinfection and oxidation. Early application of ozone was primarily for non disinfection purposes, such as color removal or taste and odor control. Since implementation of the SWTR, Stage 1 DBPR, and IESWTR, ozone usage for disinfection has increased. Ozone is a powerful oxidant capable of oxidizing many organic and inorganic compounds in water.

Ozone was first used for drinking water treatment in 1893 in the Netherlands. While used frequently in Europe to disinfect drinking water, ozonation technology was slow to transfer to the United States. In 1991, approximately 40 water treatment plants serving more than 10,000 people in the United States used ozone ( Langlais et al. 1991). This number had grown to 201 by 1997 ( Rice and Dimitrou 1997). Most of these facilities are small: 90 plants treat fewer than 1 million gallons per day ( mgd) and only 6 exceeded 100 mgd as of May 1997. ICR data show that 14 large surface water plants reported using ozone for at least 9 of the last 12 months of the ICR collection period ( USEPA 2000d). Another source cites that as of January 2000, 275 plants were using ozone, with another 16 plants expected to come on line in the next year ( Rice 2000). Many of these plants are using ozone for purposes besides disinfection. Rice also estimates that many very small systems in California, many of which may be noncommunity systems, use ozone as a disinfectant in their storage tanks.

2.8.1 Description of Chemistry A gas at room temperature, ozone is highly corrosive and toxic. The gas is colorless with a pungent odor readily detectable at concentrations as low as 0.01 to 0.05 parts per million ( ppm), which is below concentrations that would cause a health problem.

Ozone decomposes spontaneously in water by a complex reaction involving the generation of oxygen and hydroxyl free radicals. Hydroxyl radicals are among the most reactive oxidizing agents in water due to their unpaired electrons ( Hoigne and Bader 1983a; Hoigne and Bader 1983b; Glaze 1987). Ozone reacts in two modes in aqueous solutions: direct oxidation of compounds by aqueous ozone ( O 3( aq)) and oxidation of compounds by hydroxyl radicals produced during the spontaneous decomposition of ozone ( Hoigne and Bader 1977). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 23 2.8.2 Use and Distribution Ozone is used in drinking water treatment for various purposes.

° Disinfection ° Inorganic pollutant oxidation, including iron, manganese, and sulfide ° Organic micropollutant oxidation, including taste and odor compounds, phenolic pollutants, and pesticides ° Organic macropollutant oxidation, including color removal, increasing the biodegradability of organic compounds, THM and TOX precursor control, and destruction of chlorine demand ° Improvement of coagulation and filtration Ozone is unstable, so it must be generated at the point of application. It is generally formed by combining an oxygen atom with an oxygen molecule ( O 2). This reaction is endothermic and requires considerable energy. Ozone can be produced several ways, including by irradiating an oxygen containing gas with electrolytic reactions, ultraviolet light, or high energy radiation. These are all processes that produce free oxygen radicals from electron or photon energy input.

One method, corona discharge, predominates in the water industry. Corona discharge, also known as silent electrical discharge, consists of passing an oxygen containing gas through two electrodes separated by a dielectric and an air gap. A voltage is applied to the electrodes, causing an electron flow across the air gap. These electrons provide the energy to dissociate the oxygen molecules, leading to the formation of ozone directly in the water source. Therefore, no chemical inputs are needed.

For most applications, ozone is applied either to the raw water or after some type of clarification process. Turbidity and ozone demand ( the amount of ozone required to oxidize all the constituents in the water) influence the way ozone is used in the treatment process. By moving the ozonation process further downstream, the ozone demand and production of oxidation byproducts are reduced. The advantage of placing ozone ahead of filtration is that biodegradable organics produced during ozonation can be removed in the filters if they are operated with biological processes. Bacteria living in the biofilm growing on filters can break down and feed on NOM. Biological filtration is often necessary for waters that have high levels of NOM.

2.8.3 Advantages and Disadvantages The following list highlights selected advantages and disadvantages of using ozone to disinfect drinking water ( Masschelein 1992).

° Advantages   Ozone is more effective than chlorine, chloramines, and chlorine dioxide for inactivation of viruses, Cryptosporidium, and Giardia.   Ozone oxidizes iron, manganese, and sulfides.   Ozone can sometimes enhance the clarification process and turbidity removal.   Ozone improves color, taste, and odors.   Ozone requires a very short contact time. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 24   Halogenated organic DBPs are not formed by ozonation if bromide is absent.   Enhances the biodegradability of natural and synthetic organic compounds and destroys many organic compounds.   Created in the water to be treated, so does not require storage space for disinfection chemicals.

° Disadvantages   DBPs formed include bromate and bromine substituted DBPs ( when bromide is present), as well as aldehydes and ketones ( if there is incomplete oxidation of some organic compounds).   The initial cost of ozonation equipment is high.   The generation of ozone is energy intensive and must be generated on site.   Ozone is highly corrosive and toxic.   Ozone decays rapidly at high pH and warm temperatures.   Ozone provides no residual.   Ozone plants require a higher level of maintenance and operator skill.

Because of the wide variation in system size, water quality, and ozonation dosages applied, not all of these advantages and disadvantages apply to all systems.

2.8.4 Dose Ranges Engineering design manuals and published articles were used in developing an ozone dose range for the guideline used to review PWSs' ICR initial sampling plans. This range of doses is for primary disinfection only. Note that these ranges represent extremes, and normal values fall between these values. Ozone plants participating in the ICR also reported the doses of ozone they used. Exhibit 2.11 presents ozone doses ( average, minimum, and maximum of all plant months where data was reported for 9 of the last 12 months of the ICR collection period) for surface water plants using ozone. Approximately 86 percent of surface water plants using ozone had an average ozone dose below 3.0 mg/ L as O 3. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 25 0% 20% 40% 60% 80% 100%

0 2 4 6 8 10 12 14 16 18 Ozone Dose ( mg O3/ L) Percentile ( N= 14) Exhibit 2.11 Ozone Doses ( Plant Minimum, Mean, and Maximum)

Note: Open circles represent plant means and lines represent minimum and maximum values.

Source: ICR AUX2 Database ( USEPA 2000i).

Query: Screened SW Plant Mean O3 Doses ( w AUX2). See Appendix B for details.

Excel File: ICR Dose Data and Graphs. xls 2.8.5 Byproducts A variety of organic and inorganic byproducts have been observed following ozonation of water. Ozone can react with bromide naturally present in water to form bromate. If bromide is present in the source water, however, bromine substituted DBPs can also be formed. The primary factors affecting the speciation and concentrations of bromine substituted byproducts are pH and the ratios of ozone tobromide and total organic carbon to bromide ( Singer 1992). Refer to Chapter 15 of the Information Collection Rule Data Analysis document ( McGuire et al. 2002) for data on source water bromide concentrations for plants using ozone.

The principal benefit of using ozone to control THM formation is that ozone allows free chlorine to be applied at lower doses later in the treatment process, after some of the DBP precursors have been removed, thereby reducing the potential for DBP formation. However, application of a secondary disinfectant following ozonation requires special consideration for potential interaction between disinfectants. For example, chloral hydrate formation has been observed to increase when chlorine is used as a secondary disinfectant after ozone ( McKnight and Reckhow 1992; Logsdon et al. 1992). One Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 2 26 byproduct of ozonation, acetaldehyde, is a known precursor of chloral hydrate. Enhancement of chloral hydrate formation has not been observed when monochloramine is applied as the secondary disinfectant, or if biologically active filtration is used following ozonation and prior to chlorination ( Singer 1992). Chloropicrin formation from free chlorine also appears to be enhanced by pre ozonation ( Hoigne and Bader 1988).

Organic oxidation byproducts, including aldehydes, ketones, aldo acids, ketoacids, and assimilable organic carbon ( AOC) can be formed upon ozonation of water containing a high level of NOM. The primary aldehydes that have been detected are formaldehyde, acetaldehyde, glyoxal, and methyl glyoxal ( Glaze et al. 1991). The ICR data provided occurrence information on these substances along with propanal, pentanal, and butanal. Total aldehyde concentration in drinking water disinfected with ozone ranges from less than 5 to 300 : g/ L, depending on the TOC concentration and the applied ozone toorganic carbon ratio ( Van Hoof et al. 1985; Yamada and Somiya 1989; Glaze et al. 1989; Krasner et al. 1989; Glaze et al. 1991; LeLacheur et al. 1991).

Ozonation of water containing bromide can produce hypobromous acid and hypobromite, which, in turn, contribute to the formation of bromine substituted byproducts, the brominated analogues of the chlorinated DBPs. These bromine substituted byproducts include: bromoform; the bromine substituted acetic acids, acetonitriles, and aldo acids; bromopicrin; and cyanogen bromide. An ozone dose of 2 mg/ L produced 53 : g/ L of bromoform and 17 : g/ L of dibromoacetic acid in water containing 2 mg/ L of bromide ion ( McGuire et al., 1990). Ozonation of the same water spiked with 2 mg/ L bromide ion showed cyanogen bromide formation of 10 : g/ L ( McGuire et al. 1990). An ICR plant with the median ozone dose of 1.84 mg/ L had influent bromide levels of 0.133 mg/ L and finished water bromate levels of 3.1 : g/ L. Dibromoacetic acid levels of 3.5 : g/ L were also detected, but all other brominated DBPs were below their minimum reporting levels.

Ozone can react with the hypobromite ion to form bromate ( Siddiqui and Amy 1993; Krasner et al. 1993; Amy et al. 1997). Bromate formation is affected by NOM, pH, bromide ion concentrations, inorganic carbon, and ozone dose. Decreasing pH ( 8.5   6.5) generally decreases bromate formation because the equilibrium is shifted to hypobromous acid, which does not form bromate. Lower pH, however, enhances the formation of bromine substituted DBPs formed by the reaction of hypobromous acid and NOM. Higher bromide ion concentrations and high inorganic carbon concentrations have been noted with increased bromate ion formations ( Amy et al. 1997).

The amount of bromide incorporated into the detected DBPs accounts for only one third of the total source water bromide concentration. This indicates that other bromine substituted DBPs exist that are not yet identified ( McGuire et al. 1989; AWWARF 1991). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 1 3. National Occurrence Data This chapter summarizes the data collected to assess disinfectants and disinfection byproduct ( DBP) occurrence in public drinking water supplies. Because the compliance deadline for the Stage 1 Disinfectants and Disinfection Byproducts Rule ( DBPR) passed recently ( January 2002) for large and medium surface water systems, all occurrence data presented in this chapter represent pre Stage 1 conditions ( i. e., conditions before the implementation of the Stage 1 DBPR). Chapter 4 provides a prediction of post Stage 1 DBP occurrence.

The main source of DBP data is the Information Collection Rule ( ICR), which authorized EPA to collect occurrence and treatment information from water systems serving at least 100,000 people. The ICR data described in this chapter are from the AUX1 Database, CD version 5.0 ( USEPA 2000d). Information about medium ( 10,001 to 100,000 people served) and small ( 10,000 or fewer people served) systems comes from the National Rural Water Association ( NRWA) Survey ( USEPA 2001g), ICR Supplemental Surveys, the Water Utility Database ( WATER:\ STATS), and data provided by several States. Because the data available for medium and small systems are not as extensive as the ICR data, the majority of this chapter is a presentation of ICR data for individual water quality parameters and DBPs for large systems. EPA found that there are significant similarities between large systems and medium and small systems with regard to source water quality ( affecting DBP formation) and use of treatment technologies. Because of these similarities, EPA expects that small and medium systems would find DBP distribution system levels similar to those found in large systems following compliance with the Stage 1 DBPR requirements.

The organization of the remainder of this chapter is as follows:

° Section 3.1 presents large system occurrence data provided through the ICR for DBP precursors and other parameters that affect DBP formation, disinfectant residuals, and DBPs. ° Section 3.2 presents medium and small system occurrence data derived from sources other than the ICR.

° Section 3.3 evaluates co occurrence among certain ICR water quality parameters and the relationships of these interactions.

° Section 3.4 evaluates regional occurrence trends for some DBP precursors Data analyses in this chapter are supported by two appendices. Appendix A supplements section 3.1 by describing additional analyses of ICR data presented in this chapter and additional data related to DBP formation that were gathered during the ICR. Appendix B provides the Microsoft AccessTM query language that was used to extract data from the ICR AUX1 database. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 2 3.1 ICR Data Sections 3.1.1 through 3.1.3 present the ICR summary data for large systems with a description of analyte characteristics as follows:

Section 3.1.1 DBP Precursors Section 3.1.2 Disinfectant Residuals Section 3.1.3 DBPs Summary statistics in this section are generally for " plant mean" data   that is, for each plant, the mean concentration of an analyte is calculated using all reported data during the last 12 months of the ICR collection period. Summary statistics were then generated based on the distribution of all plant means. See section 1.4.8 for a detailed description of the methodology used to generate ICR data summaries in this section.

3.1.1 DBP Precursors This section summarizes plant mean data for water quality parameters that can affect the formation of DBPs. These water quality parameters are total organic carbon ( TOC), temperature, bromide, and UV 254 absorbance. Summary statistics, calculated using the last 12 months of the ICR collection period for plants that have at least 9 months of data for each parameter, are shown in Exhibit 3.1. Exhibits 3.2 through 3.5 compare the cumulative distributions of plant mean values for ground and surface water plants. Exhibit 3.6 characterizes plant level variability by showing the distribution of the maximum value minus the minimum value at each plant for each water quality parameter. Analyses of individual observations for these and other water quality parameters ( pH, alkalinity, total hardness, and turbidity) are presented in Appendix A.

All data in this section represent samples collected from the influent water sampling location. Although the ICR required samples to be collected throughout the treatment plant, the influent water sampling point was selected to illustrate parameters of the influent water quality matrix that ICR systems consider during treatment. Although the water quality characteristics that directly affect DBP formation are present at the point of disinfectant addition, this section focuses on influent characteristics with the understanding that treatment will change the parameters.

Observations regarding the data follow the exhibits. Appendix A contains additional discussion and background information on each parameter. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 3 Source Water Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Total Organic Carbon ( mg/ L as Carbon [ C])

Surface 307 3.14 2.71 5.29 < 0.7  21.4 Ground 103 1.46 0.19 3.36 < 0.7  16.1 All1 423 2.71 0.08 0.73 < 0.7  21.4 Temperature ( degrees Celsius)

Surface 334 16.0 16.1 20.7 3.7  27.7 Ground 121 19.9 20.1 26.3 9.5  30.5 All1 473 17.1 17.0 24.5 3.7  30.5 Bromide ( mg/ L) 2 Surface 320 0.055 0.027 0.115 < 0.02  1.325 Ground 118 0.103 0.066 0.190 < 0.02  1.325 All1 449 0.068 0.036 0.151 < 0.02  1.325 UV 254 Absorbance ( cm 1)

Surface 306 0.098 0.079 0.176 < 0.009  0.880 Ground 104 0.062 0.009 0.266 < 0.009  0.606 All1 424 0.091 0.069 0.180 < 0.009  0.880 Exhibit 3.1 Summary of Influent Water Quality Parameter ICR Data for All Large Plants Notes: 1" All" plants include those with surface, ground, blended, mixed, or purchased source water types, so " All" does not equal the sum of surface and ground. 2Plant 402 was removed from the analysis for bromide. Its plant mean bromide value of 2.36 mg/ L was calculated based on one month of bromide levels of 28 mg/ L. All the other values for that plant in the last 12 months of the ICR were below 0.1 mg/ L. The 28 mg/ L value is most likely a reporting error as laboratories often report bromide values in µ g/ L rather than mg/ L, and this value may not have been converted to mg/ L.

Source: ICR AUX1 database ( USEPA 2000d).

Queries: Screened TOC INF, Screened TEMP INF, Screened BROMIDE INF, and Screened UV_ 254 INF. See Appendix B for query language.

Excel File: ICR Influent WQP. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 4 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 2 4 6 8 10 12 14 16 18 20 22 24 Plant Mean TOC ( mg/ L as C) Percentile SW ICR TOC Plant Means ( N= 307)

GW ICR TOC Plant Means ( N= 103) Exhibit 3.2 Cumulative Distribution of Plant Mean TOC Concentrations of Influent Samples Based on ICR Data for Large Surface and Ground Water Plants ( mg/ L as C)

Source: ICR AUX1 database ( USEPA 2000d).

Query: Screened TOC INF. See Appendix B for query language.

Excel File: ICR Influent WQP. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 5 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 5 10 15 20 25 30 35 Plant Mean Temperature ( degrees Celsius) Percentile SW ICR Temperature Plant Means ( N= 334)

GW ICR Temperature Plant Means ( N= 121) Exhibit 3.3 Cumulative Distribution of Plant Mean Water Temperature of Influent Samples Based on ICR Data for Large Surface and Ground Water Plants ( degrees Celsius)

Source: ICR AUX1 database ( USEPA 2000d).

Query: Screened TEMP INF. See Appendix B for query language.

Excel File: ICR Influent WQP. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 6 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 0.2 0.4 0.6 0.8 1 1.2 1.4 Plant Mean Bromide ( mg/ L) Percentile SW ICR Bromide Plant Means ( N= 320)

GW ICR Bromide Plant Means ( N= 118) Exhibit 3.4 Cumulative Distribution of Plant Mean Bromide Concentrations of Influent Samples Based on ICR Data for Large Surface and Ground Water Plants ( mg/ L)

Note: Plant 402 was removed from the analysis for bromide. Its plant mean bromide value of 2.36 mg/ L was calculated based on one month of bromide levels of 28 mg/ L. All the other values for that plant in the last 12 months of the ICR were below 0.1 mg/ L. The 28 mg/ L value is most likely a reporting error as laboratories often report bromide values in µ g/ L rather than mg/ L, and this value may not have been converted to mg/ L.

Source: ICR AUX1 database ( USEPA 2000d).

Query: Screened BROMIDE INF. See Appendix B for query language.

Excel File: ICR Influent WQP. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 7 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Plant Mean UV 254 ( cm 1) Percentile SW ICR UV 254 Plant Means ( N= 306)

GW ICR UV 254 Plant Means ( N= 104) Exhibit 3.5 Cumulative Distribution of Plant Mean UV 254 Concentrations of Influent Samples Based on ICR Data for Large Surface and Ground Water Plants ( mg/ L)

Source: ICR AUX1 database ( USEPA 2000d).

Query: Screened UV_ 254 INF. See Appendix B for query language.

Excel File: ICR Influent WQP. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 8 TOC is a measure of the organic content of water. This organic matter contributes to the formation of DBPs. In unpolluted source water, humic and fulvic acids from the decay of vegetation are the major constituents of TOC; in polluted water, pesticides and other manmade chemicals may be constituents of TOC as well ( Amirtharajah and O'Melia 1990). Researchers have found that TOC can be a good indicator of the amount of THMs and other DBPs that may form as a result of chemical disinfection ( Singer and Chang 1989). Correlations between TOC and DBPs are presented in section 3.3.

Mean TOC concentrations for ICR influent samples at surface water plants are more than double the mean influent TOC concentrations in ground water plants. Approximately 42 percent of ground water plants have mean TOC concentrations less than or equal to 0.1 mg/ L as C, whereas less than 1 percent of surface water plants have mean TOC concentrations less than 0.1 mg/ L as C. However, as shown in the cumulative distribution of TOC concentrations in Exhibit 3.2, TOC concentrations in the upper 95th percentile are similar for ground water and surface water plants.

Temperature, like pH, can affect many aspects of water chemistry and treatment. Generally, as temperature increases so do chemical reaction rates which increase the amount of DBPs formed ( specifically trihalomethanes). Temperature also affects the solubility of different substances in water ( including calcium carbonate, which can change pH, alkalinity, and hardness) and rates of chemical reaction. Also, increased temperature often means increased efficiency of chlorine disinfection.

Temperature fluctuates much more in surface water than in ground water. Plant mean temperature can be lower in surface water than in ground water, since the surface water is directly exposed to the air and ground water sources are insulated by the ground. The mean of plant mean temperature level for surface water plants is 16.0 ° C, while the mean of plant mean temperature levels for ground water plants is 19.9 ° C.

Bromide can be present as a result of salt water intrusion into an aquifer, human activities such as pesticide and road salt application, and dissolution of minerals in geologic formations ( Siddiqui et al. 1995). The presence of bromide in source water can affect the type and amount of DBPs formed, shifting the distribution of DBPs generated to the more brominated species ( Krasner et al. 1989). In addition, bromide can react with strong oxidants, such as ozone or chlorine dioxide, to form bromate, another byproduct of concern.

Bromide concentrations are typically higher in ground water than in surface water sources, in part because ground water has long contact time with geologic formations that can act as sources of bromide. This is reflected by the ICR results   mean bromide concentration was 0.1 : g/ L for ground water plants compared to 0.055 : g/ L for surface water plants. Peak values, however, were identical for surface and ground water plants, calculated at 1.33 : g/ L. Bromide levels can be impacted by seasonal climate conditions. Concentrations tend to be higher during drought periods because of concentration of ions in a smaller volume of water. Bromide occurrence also varies regionally. Section 3.4 shows analysis of regional trends for influent bromide. See Chapter 14 of the Information Collection Rule Data Analysis document ( McGuire et al. 2002) for additional information regarding bromide occurrence.

The absorbance of UV radiation at a wavelength of 254 nanometers correlates with the amount of unsaturated organic compounds, particularly dissolved matter such as humic substances, in the water ( USEPA 1999a). UV 254 absorbance can be used as an alternative to measuring TOC or dissolved organic carbon ( DOC) as an indicator of DBP precursors. Exhibits 3.2 and 3.5 show that the distributions of TOC and UV 254 absorbance for ground and surface water plants follow very similar trends, with surface water plants generally showing higher plant mean values ( except in the upper 5th percentile). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 9 Source Water Number of Plants Mean 25th Percentile 50th Percentile 75th Percentile 90th Percentile 95th Percentile Total Organic Carbon ( mg/ L as Carbon [ C])

Surface 307 2.26 0.95 1.55 2.70 4.10 5.60 Ground 103 1.01 0.00 0.80 1.30 1.95 2.75 All1 423 1.93 0.80 1.30 2.30 3.75 5.35 Temperature ( degrees Celsius)

Surface 334 17.0 13.2 18.0 21.0 23.0 24.5 Ground 121 4.3 2.0 3.8 5.2 8.2 12.0 All1 473 13.5 6.9 14.3 19.8 22.0 24.0 Bromide ( mg/ L) 2 Surface 320 0.078 0.023 0.040 0.091 0.160 0.260 Ground 118 0.060 0.024 0.043 0.082 0.110 0.210 All1 449 0.073 0.024 0.041 0.090 0.150 0.260 UV 254 Absorbance ( cm 1)

Surface 306 0.121 0.034 0.070 0.134 0.302 0.448 Ground 104 0.033 0.000 0.015 0.036 0.085 0.127 All1 424 0.106 0.023 0.049 0.120 0.280 0.412 Exhibit 3.6 provides statistics for the difference between the plant highest and plant lowest monthly values ( as reported during the last 12 months of the ICR) for TOC, temperature, bromide, and UV 254. On average, the difference between the highest and lowest values is roughly three to four times greater in plants using surface waters than in plants using ground waters for TOC, temperature, and UV 254. The difference between the highest and lowest bromide value is also greater, on average, for surface water plants compared to ground water plants, but not by as much. These general trends are consistent across the range of percentiles. These findings are consistent with general observations that ground water varies less over a year than surface water.

Exhibit 3.6 Cumulative Distribution of Differences Between Highest and Lowest Monthly Parameter Values for Influent Water Sample Location Based on ICR Data for All Large Plants Notes: 1" All" plants include those with surface, ground, blended, mixed, or purchased source water types, so " All" does not equal the sum of surface and ground. 2Plant 402 was removed from the analysis for bromide. Its plant mean bromide value of 2.36 mg/ L was calculated based on one month of bromide levels of 28 mg/ L. All the other values for that plant in the last 12 months of the ICR were below 0.1 mg/ L. The 28 mg/ L value is most likely a reporting error as laboratories often report bromide values in µ g/ L rather than mg/ L, and this value may not have been converted to mg/ L.

Source: ICR AUX1 database ( USEPA 2000d).

Queries: Screened TOC INF, Screened TEMP INF, Screened BROMIDE INF, and Screened UV_ 254 INF. See Appendix B for query language.

Excel File: ICR Influent WQP. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 10 Source Data Sample Location Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Free Chlorine Residual ( mg/ L) 1 Surface Finished 183 1.23 1.14 1.98 0.00 4.37 Ground Finished 33 1.13 1.04 2.06 0.17 2.61 All3 Finished 224 1.22 1.13 1.98 0.00 4.37 Total Chlorine Residual ( mg/ L)

Surface  CL2 1 Finished 187 1.56 1.33 2.53 0.33 4.58 Ground  CL2 1 Finished 37 1.45 1.17 3.25 0.17 3.73 All3  CL2 1 Finished 232 1.55 1.33 2.58 0.17 4.58 Surface  CLM2 Finished 89 2.51 2.35 3.58 1.07 5.19 Ground  CLM2 Finished 14 3.07 3.23 4.57 1.33 4.62 All3  CLM2 Finished 105 2.58 2.46 3.66 1.07 5.19 Chlorine Dioxide Residual ( mg/ L)

Surface Finished 20 0.61 0.21 2.13 0.00 2.74 Ozone Residual ( mg/ L)

Surface After Last Contact Chamber 13 0.08 0.06 0.13 0.01 0.21 3.1.2 Disinfectant Residuals This section summarizes residual concentrations for chlorine, chloramine, and chlorine dioxide in finished water and ozone residuals after the last contact chamber ( see Chapter 2 for a discussion of disinfectant use and doses). Disinfectants were monitored monthly, although there are no ground water data for some of the disinfectant types. Summary statistics, calculated using the last 12 months of the ICR collection period for plants that have at least 9 months of data for each parameter, are shown in Exhibit 3.7. Further analyses of individual observations are presented in Appendix A. General observations regarding the data follow Exhibit 3.7.

Exhibit 3.7 Summary of Disinfectant Residual ICR Data for All Large Plants Notes: 1 For plants using chlorine only. 2 For plants using chlorine and chloramines or chloramines only. 3 " All" plants include those with surface, ground, blended, mixed, or purchased source water types.

Source: ICR AUX1 database ( USEPA 2000d).

Queries: Screened EXFCLRES FIN, Screened EXTCLRES FIN, Screened EXCLXRES FIN, and Screened EXO3RES. See Appendix B for query language.

Excel File: ICR Disinfectant Residuals. xls In water, chlorine exists as hypochlorous acid ( HOCl) and hypochlorite ( OCl). Free chlorine is defined as the sum of the concentrations of HOCl, OCl, and gaseous Cl 2 measured as Cl 2. The Surface Water Treatment Rule sets minimum requirements for residual disinfectant concentration. For instance, the residual disinfectant concentration at the point of entry to the distribution system may not drop below 0.2 mg/ L for more than four hours, although the regulations do not state that the disinfection concentration must be measured as free chlorine residual. The rule also sets CT ( the product of contact time and Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 11 disinfectant concentration) requirements for systems using free chlorine as a disinfectant ( USEPA 1989a).

The mean of all plant mean free chlorine residual concentrations were similar for surface water ( 1.23 mg/ L) and ground water plants ( 1.13 mg/ L), with the mean for all plants of approximately 1.22 mg/ L. Although surface water plants exhibit a higher upper range value ( 4.37 mg/ L), ground water plants have a slightly higher 90th percentile of plant means ( 2.06 mg/ L).

Total chlorine is defined as the sum of free chlorine and combined chlorine ( chloramine) concentrations, and is expressed in mg/ L as Cl 2. Total chlorine residuals for surface and ground water plants that use chloramines are higher than total chlorine residuals for surface and ground water plants that use only free chlorine. Higher total chlorine residual concentrations in chloramine systems may be due to organic material and DBP precursors and thus, higher chlorine demand in those systems.

Only twenty surface water plants reported using chlorine dioxide for at least 9 of the last 12 months of the ICR collection period. Although not in effect at the time of the ICR, the Stage 1 DBPR sets a daily maximum residual disinfectant level ( MRDL) of 0.8 mg/ L for chlorine dioxide based on sampling at the entry point to the distribution system ( which can be interpreted in most cases to mean finished water). Average chlorine dioxide residuals range from 0 to 2.74, with 4 plants ( or 20 percent) having mean residual concentrations greater than 0.8 mg/ L.

Ozone ( O 3) is a colorless gas that is unstable and decomposes rapidly, reacting with hydroxide ions ( OH) to form hydroxyl radicals and organic radicals. ( Radicals are unstable molecules with unpaired electrons.) As part of ICR sampling, plants measured ozone residuals of the effluent of each ozone contact chamber. For CT calculation, plants must take all contact chambers into account. For this current analysis, only the ozone residual at the last contact chamber is presented to show the small potential for DBP formation outside the contact chambers. The plant mean ozone residual concentrations in the last ozone contact chamber are very low, with an average of 0.08 mg/ L. Averages ranged from 0.01 to 0.21 mg/ L for the 13 surface water plants that submitted ICR data.

3.1.3 DBPs Halogenated organic DBPs form as a result of reactions of free chlorine, bromide, or chloramines with naturally occurring organic matter. Studies show that some of these DBPs can cause adverse reproductive and development health effects and some forms of cancer ( USEPA 2003a). Inorganic DBPs are also of concern, and are usually formed during reactions of chlorine dioxide with water and ozone with bromide.

A description of how distribution system DBP data are aggregated is provided below. Next, this section summarizes results for all halogenated DBPs measured during the ICR ( see Exhibit 1.4 for a full list of DBPs measured during the ICR). The remainder of the section focuses on regulated DBPs ( TTHM, HAA5, bromate, and chlorite). See section 1.4.8 for a detailed description of the methodology used to generate DBP results using ICR data.

Chapter 4 builds on this section by providing additional analyses of TTHM and HAA5 occurrence ( e. g. spatial and temporal variation in the distribution system ( DS)) for only those plants in compliance with the Stage 1 DBPR. Appendix A presents individual observation results for halogenated DBPs ( including individual species for each grouping), organic DBPs ( e. g., butanol and propanol) and inorganic DBPs ( e. g., chlorate). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 12 Aggregation of DBP Data As explained in section 1.4.1, each ICR plant collected samples from a single finished water location and from four distribution system sample locations ( DSE, AVG1, AVG2, DS Maximum) for the ICR. DBP data in this section, in Chapter 4, and in Appendix A are aggregated into the following data types for analyses:

° Finished Water means a sample taken from the end of the treatment plant, before water enters the distribution system. The plant mean finished water concentration is the average of the last four quarters of finished water data for that plant.

° DS Average ( or RAA) is the calculated average of four distribution system samples ( DSE, AVG 1, AVG 2, and DS Maximum). The plant mean DS Average concentration is the average of the last four quarters of calculated DS Average data for that plant. The plantmean DS Average concentration is equivalent to the running annual average ( RAA) concentration for that year.

° Single Highest is the highest concentration of the four distribution system samples collected by a plant in the last four quarters of the ICR ( 16 possible values). This value may represent any of the four distribution system locations   DSE, AVG1, AVG2, or DS Maximum.

° Locational Running Annual Average ( LRAA) is the average of four quarters of data from a single distribution system location ( DSE, AVG1, AVG2, and DS Maximum). For example, the LRAA for the DSE location would be the average of the last four quarters of data collected from that location. The highest LRAA is the maximum of the four ( DSE, AVG1, AVG2, and DS Maximum) calculated LRAAs. Since the LRAA covers one year's worth of data, it already represents a plant mean value.

° Max Min is the highest concentration of the four distribution system samples collected by a plant during the last four quarters of the ICR ( 16 possible values) minus the lowest concentration of the four distribution system samples reported during the last four quarters of the ICR. In other words, Max Min is a single value that represents the difference between the maximum and minimum concentrations from all four distribution system samples collected during the last four quarters of the ICR.

All Measured Halogenated DBPs Exhibit 3.8 summarizes DS Average results for all halogenated DBPs measured under the ICR ( results for individual species are shown Appendix A). As can be seen from the measured concentrations for all plants, TTHMs and HAA5 comprise approximately 50 percent of the measured total organic halides ( TOX), whereas the other measured organic halides ( HAN4, CH, CP, DCP, and TCP) represent approximately 7 percent of the TOX concentration. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 13 Source Parameter Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means TTHM 213 68.68 63.90 118.70 0 177 HAA5 213 24.60 20.85 45.78 0 104 HAN4 209 3.79 3.20 7.62 0 17.5 CH 208 4.82 4.36 9.91 0 18.7 CP 208 0.34 0.19 0.94 0 2.4 DCP 209 0.54 0.37 1.35 0 2.8 TCP 209 1.50 1.23 0.00 0 6.4 TOX 213 144.19 138.16 241.25 0 305 TTHM 82 15.36 6.79 36.95 0 123 HAA5 82 6.35 0.33 18.83 0 97 HAN4 80 2.22 0.75 6.01 0 14.8 CH 80 0.59 0.03 2.18 0 5.5 CP 79 0.03 0.00 0.13 0 0.6 DCP 80 0.19 0.00 0.91 0 2.0 TCP 80 0.07 0.00 0.00 0 1.2 TOX 81 54.40 7.88 160.00 0 482 TTHM 304 25.78 23.13 53.83 0 119 HAA5 304 19.40 16.20 41.45 0 104 HAN4 305 3.37 2.69 7.32 0 17.5 CH 304 3.63 2.76 8.56 0 18.7 CP 303 0.25 0.07 0.74 0 2.4 DCP 305 0.44 0.20 1.24 0 2.8 TCP 305 1.09 0.53 3.02 0 6.4 TOX 310 119.40 115.86 237.19 0 482 All Ground Surface Exhibit 3.8 Summary of Halogenated DBP Data Measured During the ICR, DS Average ( Parameter Occurrence Values in µ g/ L) for All Large Plants Source: ICR AUX1 database ( USEPA 2000d).

Queries: Plants min 3x3, RAA  Other DBPs and Plants min 3x3, RAA and Max LRAA  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR Other DBP Data, Pre Stage 1. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 14 Source Data Type 1 Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Finished Water 213 31.60 28.75 55.53 0 97 DS Average ( or RAA) 213 42.28 40.36 69.82 0 117 Single Highest 213 68.68 63.90 118.70 0 177 Highest LRAA 213 49.29 45.80 80.67 0 124 Max  Min 213 50.01 44.30 91.90 0 129 Finished Water 82 9.69 1.48 24.75 0 119 DS Average ( or RAA) 82 15.36 6.79 36.95 0 123 Single Highest 82 32.32 18.50 74.40 0 300 Highest LRAA 82 20.21 11.80 52.63 0 127 Max  Min 82 26.53 15.40 60.00 0 300 Finished Water 304 25.78 23.13 53.83 0 119 DS Average ( or RAA) 311 34.98 33.16 65.88 0 123 Single Highest 311 58.48 54.00 113.80 0 300 Highest LRAA 311 41.38 39.50 78.20 0 127 Max  Min 311 43.15 38.40 85.20 0 300 Surface Ground All2 TTHM TTHM measurements are the sum of concentrations of chloroform ( CHCl 3), bromodichloromethane ( BDCM), dibromochloromethane ( DBCM), and bromoform ( CHBr 3). Exhibit 3.9 presents summary statistics of plant mean TTHM data collected under the ICR by source water and data type. ( See Appendix A and Chapter 6 of the Information Collection Rule Data Analysis document [ McGuire et al. 2002] for occurrence data on individual TTHM constituents.) Exhibit 3.10 shows the cumulative distribution of the plant mean DS Average ( or RAA) TTHM data for ICR surface and ground water plants. Exhibits 3.11 and 3.12 show the cumulative distributions of plant mean TTHM single highest and plant mean highest TTHM LRAA, respectively. Appendix A contains additional discussion and background information on each individual THM. Discussions of the findings follow the exhibits.

Exhibit 3.9 Summary of TTHM ( : g/ L) ICR Data for All Large Plants Notes: 1 For a description of the data types, see " Aggregation of DBP Data" at the beginning of the subsection. 2 The " All" plants include those with surface, ground, blended, mixed, or purchased source water types. Finished water data were not available for blended plants.

Source: ICR AUX1 Database ( USEPA 2000d).

Queries: Plants min 3x3, average by finish location  TTHM & HAA5, Plants min 3x3, RAA & Max LRAA  TTHM & HAA5 and Plants min 3x3, Single High  TTHM & HAA5, Plants min 3x3, Max Min  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 15 0% 20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140 Plant Mean TTHM ( ug/ L) Cumulative Percentile Surface Water TTHM ( N= 213)

Ground Water TTHM ( N= 82) Exhibit 3.10 Cumulative Distribution of Plant Mean DS Average ( RAA) for ICR TTHM Occurrence Data for All Large Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, RAA & Max LRAA  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 16 0% 20% 40% 60% 80% 100%

0 50 100 150 200 250 300 350 Plant Mean TTHM ( ug/ L) Cumulative Percentile Surface Water TTHM ( N= 213)

Ground Water TTHM ( N= 82) Exhibit 3.11 Cumulative Distribution of Single Highest ICR TTHM Occurrence Data for All Large Surface and Ground Water Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, Single High  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls 1 See Chapter 4 of the Information Collection Rule Data Analysis document ( McGuire et al. 2002) for a thorough analysis of historical TTHM occurrence in large systems since the mid to late 1970' s.

Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 17 0% 20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140 Plant Mean TTHM ( ug/ L) Cumulative Percentile Surface Water TTHM ( N= 213)

Ground Water TTHM ( N= 82) Exhibit 3.12 Cumulative Distribution of Highest LRAA for ICR TTHM Occurrence Data for Large Surface and Ground Water Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, RAA & Max LRAA  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls TTHM has been regulated by EPA since the interim TTHM Rule, promulgated in 1979.1 The TTHM Rule established an MCL of 100 µ g/ L, calculated as an RAA of distribution system TTHM data measured at four locations, collected quarterly. As explained at the beginning of this section, an RAA is the average of the most recent four quarters of data; when data from a new quarter is obtained it replaces the data from the oldest quarter in the four quarter averaging. The Stage 1 DBPR sets an MCL for TTHM of 80 µ g/ L, calculated as an RAA. However, compliance with the Stage 1 DBPR was not required until 2002 for large surface water systems and 2004 for ground water and small surface water systems ( USEPA 1998a). Thus, TTHM ICR data, collected in 1997 and 1998 and presented in this section, represents pre Stage 1 DBPR conditions.

Plant mean DS Average ( or RAA) TTHM data can be used to estimate the percentage of plants that may have exceeded the Stage 1 MCLs at the time of the ICR. Although the 90th percentile RAA concentrations for ground and surface plants are less than the Stage 1 DBPR MCL of 80 : g/ L, the maximum plant mean RAA concentrations are higher than 80 : g/ L for both plant types. From the cumulative distributions of TTHM RAA data ( Exhibit 3.10), the following information can be derived: Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 18 ° For surface water plants, approximately 4 percent had TTHM RAA levels above 80 : g/ L; however, 13 percent had TTHM RAA levels above 64 : g/ L ( 20 percent less than the Stage 1 DBPR MCL). The 64 : g/ L level represents the safety margin occurrence level that utilities may try to achieve to avoid noncompliance.

° For ground water plants, approximately 2 percent had TTHM RAA levels above 80 : g/ L; however, 4 percent had TTHM RAA levels greater than 64 : g/ L.

It is important to note that ICR sampling locations may not be the locations that will be used for compliance with the Stage 1 DBPR. Also, because compliance is based on a RAA for the water system rather than the plant, it is possible for a plant to report TTHM data that is above the Stage 1 DBPR MCLs but for the system to still be in compliance with this regulation.

The Single Highest and Highest LRAA TTHM values in Exhibit 3.9 indicate that concentrations at some locations in the distribution system are much higher than DS Average concentrations. Many of these high values may not be reduced through compliance with the Stage 1 DBPR. Chapter 4 provides additional analyses of peak TTHM data as it relates to the Stage 1 DBPR and proposed Stage 2 DBPR.

HAA5 HAA5 measurements represent the sum of concentrations of monochloroacetic acid ( MCAA), dichloroacetic acid ( DCAA), trichloroacetic acid ( TCAA), monobromoacetic acid ( MBAA), and dibromoacetic acid ( DBAA). Exhibit 3.13 presents summary statistics of plant mean HAA5 data collected under the ICR by source water and data type. ( See Appendix A and Chapter 6 of the Information Collection Rule Data Analysis document [ McGuire et al. 2002] for occurrence data on individual HAA5 constituents.) Exhibit 3.14 shows the cumulative distribution of the plant mean DS Average ( or RAA) for HAA5 data for ICR surface and ground water plants. Exhibits 3.15 and 3.16 show the cumulative distributions of plant mean HAA5 single highest and plant mean highest HAA5 LRAA, respectively. Appendix A contains additional discussion and background information on each individual HAA. Observations follow the exhibits. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 19 Source Data Type 1 Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Finished Water 213 24.60 20.85 45.78 0 104 DS Average ( or RAA) 213 29.07 24.38 52.31 0 116 Single Highest 213 47.77 40.00 86.00 0 189 Highest LRAA 213 33.66 28.30 58.37 0 124 Max  Min 213 34.85 28.20 68.00 0 150 Finished Water 82 6.35 0.33 18.83 0 97 DS Average ( or RAA) 82 8.45 2.24 21.53 0 71 Single Highest 82 17.79 6.30 46.30 0 124 Highest LRAA 82 11.13 3.80 30.43 0 93 Max  Min 82 14.68 6.20 43.60 0 94 Finished Water 304 19.40 16.20 41.45 0 104 DS Average ( or RAA) 311 22.98 19.11 47.14 0 116 Single Highest 311 38.66 31.40 75.30 0 189 Highest LRAA 311 26.93 22.53 55.73 0 124 Max  Min 311 28.48 23.30 59.00 0 150 Surface Ground All2 Exhibit 3.13 Summary of HAA5 ICR Data for All Large Plants ( : g/ L)

Notes: 1 For a description of the data types, see " Aggregation of DBP Data" at the beginning of the subsection. 2 The " All" plants include those with surface, ground, blended, mixed, or purchased source water types. Finished water data were not available for blended plants.

Source: ICR AUX1 Database ( USEPA 2000d).

Queries: Plants min 3x3, average by finish location  TTHM & HAA5, Plants min 3x3, RAA & Max LRAA  TTHM & HAA5 and Plants min 3x3, Single High  TTHM & HAA5, Plants min 3x3, Max Min  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 20 0% 20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140 Plant Mean HAA5 ( ug/ L) Cumulative Percentile Surface Water HAA5 ( N= 213)

Ground Water HAA5 ( N= 82) Exhibit 3.14 Cumulative Distribution of Plant Mean DS Average ( RAA) for ICR HAA5 Occurrence Data for Large Surface and Ground Water Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, RAA & Max LRAA  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 21 0% 20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140 160 180 200 Plant Mean HAA5 ( ug/ L) Cumulative Percentile Surface Water HAA5 ( N= 213)

Ground Water HAA5 ( N= 82) Exhibit 3.15 Cumulative Distribution of Single Highest ICR HAA5 Occurrence Data for Large Surface and Ground Water Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, Single High  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 22 0% 20% 40% 60% 80% 100%

0 20 40 60 80 100 120 140 Plant Mean HAA5 ( ug/ L) Cumulative Percentile Surface Water HAA5 ( N= 213)

Ground Water HAA5 ( N= 82) Exhibit 3.16 Cumulative Distribution of Highest LRAA ICR HAA5 Occurrence Data for Large Surface and Ground Water Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, RAA & Max LRAA  TTHM & HAA5. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls The Stage 1 DBPR sets an HAA5 MCL of 60 µ g/ L, with the HAA5 regulated value calculated as the RAA of distribution system data measured at four locations, collected quarterly. As noted previously, compliance with the Stage 1 DBPR was not required until 2002 for large surface water systems and 2004 for ground water and small surface water systems. Thus, HAA5 ICR data in this section represent pre Stage 1 conditions.

Plant mean DS Average ( or RAA) HAA5 data can be used to estimate the percent of plants that may have exceeded the Stage 1 MCLs at the time of the ICR. Although the 90th percentile RAA concentrations for ground and surface water plants are less than the Stage 1 DBPR MCL of 60 : g/ L, the maximum plant mean RAA concentrations are higher than 60 : g/ L for both plant types. From the cumulative distributions of HAA5 RAA data ( Exhibit 3.14), the following information can be derived:

° For surface water plants, approximately 6 percent had HAA5 RAA levels above 60 : g/ L; however, 12 percent had HAA5 RAA levels greater than 48 : g/ L ( 20 percent less than the Stage 1 DBPR MCL). The 48 : g/ L level represents the safety margin occurrence level that utilities may try to achieve to avoid noncompliance. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 23 ° For ground water plants, approximately 2 percent had HAA5 RAA levels above 60 : g/; however, 4 percent had HAA5 RAA levels greater than 48 : g/ L.

It is important to note that ICR sampling locations may not be the locations used for compliance with the Stage 1 DBPR. Also, because compliance is based on a RAA for the water system rather than the plant, it is possible for a plant to report HAA5 data that is above the Stage 1 DBPR MCLs but still be in compliance with current regulations.

The Single Highest and Highest LRAA HAA5 values in Exhibit 3.13 indicate that concentrations at some locations in the distribution system are much higher than DS Average concentrations. Many of these high values may not be reduced by the Stage 1 DBPR. Chapter 4 provides additional analysis of peak HAA5 data as it relates to the Stage 1 DBPR and proposed Stage 2 DBPR.

Bromate ICR requirements for bromate monitoring pertained to plants that use oxygenated disinfectants   ozone or chlorine dioxide. Bromate forms when these disinfectants react with bromide, which is commonly found in many source waters ( see Exhibit 3.1 for source water bromide concentrations). Bromate also occurs as an impurity in hypochlorite solutions. Because bromide reacts immediately with ozone and bromate formation does not increase with residence time in the absence of a residual, monthly monitoring was required at the finished water sampling point but not in the distribution system. However, bromate formation does increase with contact time if there is a residual present.

Split samples for bromate were collected during the ICR: one set was analyzed by plant laboratory personnel and one was analyzed by EPA. EPA's laboratory used a different laboratory analytical method and was able to detect bromate at much lower levels than most utility laboratories. The MRL for the utility method is 5.0 µ g/ L, while the MRL for the EPA method is 0.20 µ g/ L. Plant mean bromate data are summarized in Exhibit 3.17. Ground water plant data were not included in this analysis   no ground water plants used chlorine dioxide, and only one used ozone.

For surface water plants using chlorine dioxide disinfection, approximately 47 percent of plantmean finished water results were less than the MRL based on the EPA method, and 88 percent were less than the MRL based on the utility method. Bromate concentrations for plants using ozone are much higher than for plants using chlorine dioxide. Plant mean finished water concentrations were as high as 7.2 µ g/ L based on the EPA method and 6.4 µ g/ L based on the plant laboratory method. It is difficult to compare values obtained by the EPA and plant laboratory methods. Because the MRL for the utility method is so high, most individual values were below the MRL of 5.0 µ g/ L and thus were assigned a value of zero, affecting the calculation of the medians and means. For plants treating with chlorine dioxide, the median of the EPA method data was 0.02 µ g/ L, while the median of the plant laboratory data was 0 µ g/ L. For plants using ozone, the mean, median, and 90th percentile plant mean bromate concentrations were higher based on the EPA method versus the plant laboratory method. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 24 Data Type Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Chlorine Dioxide Plants EPA Analytical Method 19 0.06 0.02 0.10 0 0.7 Plant Laboratory Analytical Method 16 0.09 0.0 0.64 0 0.8 Ozone Plants EPA Analytical Method 16 2.42 2.2 5.64 0 7.2 Plant Laboratory Analytical Method 14 1.75 0.0 5.09 0 6.4 Exhibit 3.17 Summary of Bromate in Finished Water, Plant Mean ICR Data for All Large Plants ( : g/ L)

Note: EPA laboratory analytical method has an MRL of 0.02 µ g/ L and the plant laboratory analytical method has an MRL of 5.0 µ g/ L. These different MRLs greatly affect plant mean bromate calculations.

Source: ICR AUX1 Database ( USEPA 2000d).

Queries: Screened BROMATE EPA FIN and Screened BROMATE UTIL FIN. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls Chlorite ICR requirements for chlorite monitoring pertained only to plants that use chlorine dioxide for disinfection. Monthly monitoring was required at the finished water sampling location and at three rather than four locations in the distribution system. The three required monitoring locations were: ( 1) a location near the first customer; ( 2) a location with average residence time ( AVG1), and; ( 3) the location with maximum residence time ( DS Max).

Exhibit 3.18 summarizes plant mean chlorite data. All data is for surface water systems ( there were no ICR ground water systems that used chlorine dioxide). Different plant mean data types are displayed to reflect the Stage 1 DBPR compliance calculations: ( 1) Plant mean finished water chlorite concentrations reported by a plant; ( 2) Maximum of monthly finished water chlorite concentrations reported by a plant; ( 3) Plant mean DS Average concentration ( DS Average for chlorite is the average of data from the 3 distribution system sample locations described above) for a plant; ( 4) Maximum of monthly calculated DS Average concentration for a plant, and; ( 5) Single Highest concentration reported in one year in the distribution system for a plant.

The Stage 1 DBPR requires daily monitoring for chlorite at the finished water location and monthly monitoring at three locations in the distribution system. Under that rule, if a single daily sample at the finished water location exceeds 1,000 µ g/ L, additional monitoring ( outside the monthly monitoring requirement) at the three distribution system locations is then required. The MCL for chlorite is 1.0 mg/ L ( 1,000 µ g/ L), based on the average of the three distribution system locations. The maximum of monthly finished water chorite concentrations ranged from 0 to 1,719 µ g/ L. Approximately 78 percent of maximum finished water samples are below 1,000 µ g/ L. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 25 Data Type Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Finished Water, Plant Mean 18 432 461 768 2 1,105 Finished Water, Maximum Plant Month 18 720 690 1,300 20 1,719 DS Average, Plant Mean 16 345 409 645 5 650 DS Average, Maximum Plant Month 16 572 653 871 20 1,100 Single Highest 16 645 700 886 41 1,200 Exhibit 3.18 Summary of Chlorite ICR Data ( µ g/ L) for Large Surface Water Plants Source: ICR AUX1 Database ( USEPA 2000d).

Queries: Screened Chlorite DSAVG, Screened CHLORITE FIN, and Screened Chlorite Single High. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 1. xls 3.2 Medium and Small Systems As discussed in Chapter 2, an estimated 12,224 surface water systems and 39,408 ground water systems ( 51,632 systems total) use disinfection and are subject to the Stage 1 and Stage 2 DBPRs. Although less than 1 percent of disinfecting systems fall into the large system size category ( serving more than 100,000 people), they serve 55.1 percent of the total population served by disinfecting systems ( see Exhibit 2.3). This is one reason that the ICR data collection effort focused on large plants. However, because roughly 45 percent of the population served by disinfecting systems obtains water from small and medium systems, it is also important to characterize DBP occurrence in drinking water provided by these systems.

There is no extensive, focused database similar to the ICR that provides information on DBP occurrence in small and medium systems. Consequently, it is necessary to use more limited and disparate sets of occurrence data, together with inferences drawn from the ICR data on large plants, to characterize DBP occurrence in medium and small systems.

This section presents available information on DBP occurrence, the occurrence of DBP precursors ( e. g., TOC, bromide), and operational characteristics for small and medium systems in order to compare them to large system ICR data. One important factor to note when considering the possible similarities and differences in DBP levels among small, medium, and large systems is that the 1979 interim standards for TTHMs do not apply to systems serving fewer than 10,000 people. Some States do have DBP standards in place for small systems, but it is expected that nationally, a larger percentage of small systems will have higher DBP levels than large systems, due to the absence of that regulatory " driver." Similarly, it is expected that DBP levels in medium systems ( serving 10,000 to 100,000 people) will be closer to those in large systems than the levels in small systems will, because these systems are currently regulated under the 1979 TTHM Rule.

3.2.1 Overview of Available Data for Medium and Small Systems In addition to the ICR data on large plants, which can be used to draw inferences about small and medium systems, several data sets provide information specifically useful for evaluating small and medium systems. Chapter 1, section 1.5 describes each data set in full. A summary of each is provided below. ° ICR Supplemental Survey ( ICRSS). The ICRSS, conducted by EPA from March 1999 through February 2000, was designed to provide information to supplement the ICR data Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 26 collection effort for microbiological and byproduct occurrence data. The ICRSS involved 40 randomly selected surface water systems in each of the small, medium, and large system size categories, as well as 7 very large systems. The ICRSS did not collect DBP occurrence data, but did collect information on byproduct precursors in influent source waters, notably TOC and bromide levels.

° The National Rural Water Association ( NRWA) Survey. Developed in cooperation with EPA, the NRWA Survey was designed to obtain relevant treatment, influent water quality, and byproduct occurrence information for a random sample of 117 small surface water systems ( serving fewer than 10,000 people). The survey collected water quality and byproduct data during a cold weather period ( November 1999 to March 2000) and a warm weather period ( July 2000 to November 2000).

DBP samples were collected at a finished water location, a distribution system site with average residence time, and a distribution system site with maximum residence time. For small system DBP analyses presented in Section <IP_ADDRESS>, samples at the average residence time location are given a weight three times that of data at the maximum residence location to produce a " DS Weighted Avg" result. The weighted average was used to make NRWA data comparable to ICR DS Average ( or RAA) data, which is calculated by averaging data at four locations approximating the average residence time and at the maximum residence location.

° Water Utility Database ( WATER:\ STATS). Published by the American Water Works Association ( AWWA), WATER\: STATS is derived from the AWWA Water Industry Database resulting from a 1996 survey of approximately 900 water utilities, mostly entities serving at least 10,000 people. The WATER:\ STATS data used here are aimed mainly at characterizing relevant treatment and byproduct information for medium surface water plants.

Although 900 systems participated in the 1996 survey, the relevant table in WATER:\ STATS contains data only from those systems that chose to respond to the section on water quality. WATER:\ STATS does not contain data on individual samples; it contains averages, minima, and maxima for each parameter for each plant.

° The Ground Water Supply Survey ( GWSS). This survey, conducted by EPA in 1981   82, was designed to collect treatment, influent water quality, and finished water contaminant occurrence information on 979 small, medium, and large ground water systems from across the United States. Although TTHM data from this survey are available, they are probably not representative of current TTHM levels for large and medium systems because they were collected more than 20 years ago, prior to the implementation of the 1979 TTHM standard. In addition, the TTHM data were collected only at the entry point to the distribution system, not from the distribution system itself. Due to the rolling implementation schedule of the TTHM Rule, systems may or may not have been in compliance with the rule in 1981 and 1982.

° State Data. Data from several States were used to gain insights into the occurrence of DBPs and DBP precursors in surface water and ground water. For surface water, the data were available from eight States: Alaska, California, Illinois, Minnesota, Missouri, North Carolina, Texas, and Washington. The data from these States represent 562 small surface water systems. While the systems in these data sets were not randomly selected, they include at least 50 percent of the small systems in each State. Also, all the small surface Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 27 water systems in these eight States together account for approximately one third of all small non purchased surface water systems in the United States, which is a significant sample. There were also some ground water data on DBPs available from seven States: Alaska, California, Florida, Illinois, North Carolina, Texas, and Washington.

The data available from each State are not exactly comparable; some States reported individual sample data, while others reported only plant averages. Some of the data appear to be from distribution system locations, while other samples are from the plant or from raw water. Samples in some States were collected quarterly, while in others, the time between samples at some plants was anywhere from two months to more than a year.

3.2.2 Surface Water Systems DBP precursor occurrence data for medium and small surface water systems from the sources described in Section 3.2.1 are summarized in Exhibits 3.19 and 3.20. Exhibit 3.19 shows plant mean data, while Exhibit 3.20 shows individual observations for the plants included in Exhibit 3.19. NRWA data were included only if both summer and winter data were available for a plant. ICRSS data were included only for plants that had data for at least three fourths of the total possible number of samples. Detailed discussion of medium and small system data are provided in the next two subsections. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 28 System Size & Type Source of Data Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means Source Water TOC ( mg/ L as C) NRWA 96 3.0 2.6 5.4 0.3 9.0 ICRSS 38 2.4 2.1 4.5 0.1 7.1 ICRSS 40 3.6 3.7 5.5 0.2 7.9 WATER:\ STATS 102 5.6 3.2 6.4 0.0 200 Medium Ground Water WATER:\ STATS 51 2.3 0.8 7.0 0.0 25 Source Water Bromide ( mg/ L) NRWA 95 0.063 0.021 0.108 0 1.724 ICRSS 38 0.020 < 0.02 0.044 < 0.02 0.274 Medium Surface Water ICRSS 40 0.050 0.016 0.092 < 0.02 0.534 Source Water UV 254 ( cm 1) NRWA 96 0.082 0.074 0.127 0.012 0.228 ICRSS 38 0.074 0.051 0.113 0.016 0.444 Medium Surface Water ICRSS 40 0.093 0.083 0.171 0.029 0.208 Small Surface Water Medium Surface Water Small Surface Water Small Surface Water System Size & Type Source of Data Number of Observations Mean Median 90th Percentile Range Source Water TOC ( mg/ L as C) NRWA 192 3.0 2.6 5.5 0.3 9.9 ICRSS 384 2.4 1.8 5.7 0.0 17.0 Medium Surface Water ICRSS 478 3.6 3.2 7.0 0.0 21.6 Source Water Bromide ( mg/ L) NRWA 190 0.063 0.019 0.114 0 1.862 ICRSS 384 0.020 0.000 0.056 0 0.355 Medium Surface Water ICRSS 473 0.050 0.014 0.116 0 0.865 Source Water UV 254 ( cm 1)

NRWA 192 0.082 0.070 0.150 0 0.350 ICRSS 380 0.074 0.053 0.118 0.004 0.676 Medium Surface Water ICRSS 467 0.1 0.1 0.2 0 0.805 Small Surface Water Small Surface Water Small Surface Water Exhibit 3.19 Summary of Non ICR DBP Precursor ICR Data for Large Surface and Ground Water Plants, Plant Means Notes: Small systems are those that serve fewer than 10,000 people; medium systems serve between 10,000 and 100,000 people. See text in Section 3.2.1 for a description of " Source of Data."

Sources: USEPA 2001g; USEPA 2000k; AWWA 2000.

Exhibit 3.20 Summary of Non ICR DBP Precursor ICR Data for Large Surface Water Plants, Individual Observations Notes: Small systems are those that serve fewer than 10,000 people; medium systems serve between 10,000 and 100,000 people. See text in Section 3.2.1 for a description of " Source of Data."

Sources: USEPA 2001g; USEPA 2000k. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 29 <IP_ADDRESS> Medium Surface Water Systems The main purpose of this section is to evaluate medium surface water system DBP occurrence and water quality data and determine if these parameters in medium surface water systems are similar to those in large surface water systems. The data in the WATER:\ STATS ( AWWA 2000) and ICRSS ( USEPA 2000k) data were primarily used for this purpose. All WATER:\ STATS data in this section represent plant average values.

WATER:\ STATS occurrence data shows that source water types and quality in medium and large surface water systems are similar on a national level. Exhibit 3.21 indicates that medium and large surface water systems use very similar types of water sources. Exhibits 3.22 and 3.23 compare TOC data for different system sizes using WATER:\ STATS and ICRSS data, respectively. These graphs show similar distributions of TOC occurrence in large and medium surface water systems. TOC occurrence can also be assessed by comparing medium system TOC data in Exhibit 3.19 to large system TOC data in Exhibit 3.1. WATER:\ STATS and ICRSS values are similar to ICR TOC data, with median values of 3.2 mg/ L, 3.7 mg/ L, and 2.7 mg/ L, respectively. ICRSS data on bromide and UV 254 levels, shown in Exhibit 3.19, are quite close to ICR plant levels ( see Exhibit 3.1). Exhibits 3.24 and 3.25 show that medium and large systems have similar distributions of other parameters affecting treatability and, indirectly, DBP formation, such as turbidity and alkalinity.

The type of treatment technologies used by medium surface water systems is also similar to those used by large systems. As shown in Exhibits 3.26 through 3.28, medium and large systems are similar with respect to major categories of treatment ( conventional vs. others), the use of key physical unit processes, and the use of specific disinfection methods among conventional plants. One reason that medium and large plants are similar is that both have historically been subject to the same regulatory requirements.

Exhibits 3.29 and 3.30 compare cumulative distributions of annual average TTHM levels in finished water and in distribution system water from WATER:\ STATS for medium and large surface water systems, and confirm that the distributions are similar. Also, these cumulative distributions are consistent with TTHM values reported for large ICR plants earlier in this chapter for DS Averages ( where the median plant mean TTHM value is 41 µ g/ L). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 30 0% 10% 20% 30% 40% 50% 60%

Reservoir/ Lake Flowing Stream Mix Percent of Systems Medium Large 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 5 10 15 20 25 30 Plant Mean TOC ( mg/ L as C) Cumulative Percentile Medium Surface Water Systems ( N= 102) Large Surface Water Systems ( N= 196) Exhibit 3.21 Percentages of Medium and Large Surface Water Systems Using Different Source Water Types Source: WATER:\ STATS ( AWWA 2000).

Exhibit 3.22 Comparison of Source Water TOC for Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 31 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 1 2 3 4 5 6 7 8 9 Plant Mean TOC ( mg/ L as C) Cumulative Percentile Large Systems ( N= 47)

Medium Systems ( N= 40)

Small Systems ( N= 38)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 Plant Mean Turbidity ( NTU) Cumulative Percentile Medium Surface Water Systems ( N = 243)

Large Surface Water Systems ( N = 240) Exhibit 3.23 Comparison of Source Water TOC for Small, Medium and Large Surface Water Systems Source: ICRSS ( USEPA 2000k).

Exhibit 3.24 Comparison of Source Water Turbidity For Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 32 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 Plant Mean Alkalinity ( mg CaCO3/ L) Cumulative Percentile Medium Surface Water Systems ( N= 224)

Large Surface Water Systems ( N= 234)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

Conventional Softening Direct Filtration Unfiltered Other Percent of Systems Medium Surface Water Systems ( N = 265)

Large Surface Water Systems ( N = 255) 100% Exhibit 3.25 Comparison of Source Water Alkalinity for Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000).

Exhibit 3.26 Comparison of Treatment In Place for Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 33 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Pre Sedimentation Rapid Mix Flocculation Sedimentation Filtration Percent of Systems Medium Surface Water Systems ( N = 266)

Large Surface Water Systems ( N = 249)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

PreCl2/ PostCl2 Post Cl2 Only PreCl2/ PostNH2Cl w/ O3 w/ ClO2 Other Percent of Systems Medium Surface Water Systems ( N = 266)

Large Surface Water Systems ( N = 249) Exhibit 3.27 Comparison of Physical Unit Processes for Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000).

Exhibit 3.28 Comparison of Disinfectant Type for Medium and Large Surface Water Systems Using Conventional Filtration Source: WATER:\ STATS ( AWWA 2000). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 34 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 20 40 60 80 100 120 TTHM ( ug/ L) Cumulative Percentile Medium Surface Water Systems ( N= 211)

Large Surface Water Systems ( N= 210)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 20 40 60 80 100 120 TTHM ( ug/ L) Cumulative Percentile Medium Surface Water Systems ( N= 207)

Large Surface Water Systems ( N= 131) Exhibit 3.29 Comparison of Finished Water Annual Average TTHM for Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000).

Exhibit 3.30 Comparison of Distribution System TTHM Data for Medium and Large Surface Water Systems Source: WATER:\ STATS ( AWWA 2000). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 35 <IP_ADDRESS> Small Surface Water Systems The key sources of information for small surface water systems are the ICRSS, the NRWA Survey, and some State data. DBP Precursor data from these sources are summarized in Exhibits 3.19 and 3.20.

Exhibits 3.19 and 3.23 show that the distribution of TOC levels for small surface water plants differs somewhat from that for medium and large plants. Generally, small plants appear to have lower TOC levels ( i. e., lower levels of byproduct precursors) than do the medium and large plants. However, at the upper end of the TOC distributions, above approximately the 90th percentile, small plant TOC levels are very similar to those of medium and large plants ( see Exhibit 3.23).

Exhibits 3.31 through 3.34 provide the cumulative distributions of influent TOC, bromide, alkalinity, and temperature measurements from the NRWA Survey for winter and summer monitoring periods. Seasonal variability in TOC, Bromide, and Alkalinity appear low, although temperature was markedly different between winter and summer months ( as expected). The TOC distribution in Exhibit 3.31 is similar to but slightly higher than that for small systems in the ICRSS ( see Exhibit 3.19 for summary statistics on TOC). However, the ICRSS data set is more comprehensive than the NRWA data set. The ICRSS data reflect mean values for 12 months of sampling, whereas the NRWA data reflect a single sample for each site during two sampling periods. The alkalinity levels in Exhibit 3.33 are higher than for ICRSS data ( where the median for small systems is 50 mg/ L as CaCO 3), but are similar to those observed for medium and large surface water plants in the ICR and WATER:\ STATS. The bromide levels in Exhibit 3.32 are higher than the small surface waters in the ICRSS, but similar to medium ICRSS plants, as well as the ICR plants. The temperature levels in Exhibit 3.34 are similar to those found in the ICR.

Exhibits 3.35 to 3.38 illustrate some operational characteristics of small surface water plants that may correlate with the DBP levels observed in such plants. For example, Exhibit 3.35 shows that almost 50 percent of plants in the NRWA survey are in operation 12 hours a day or less. Some small plants are designed for a peak flow that may be seasonal, and the rest of the time they may operate at reduced flow. In addition, small plants must often operate at a minimum flow rate based on the design of their package plants or based on requirements for redundant treatment units. At these rates they may meet their production needs in less than 24 hours. Because they do not operate all of the time, small water systems may have water with higher residence times within their plant. This may increase DBP formation in cases where water stays for a long period of time in a clearwell or finished water storage facility after chlorination.

Exhibit 3.36 indicates that only 15 percent of NRWA survey plants listed DBP control as a treatment objective. This is understandable due to the fact that small systems are not subject to the 1979 TTHM Rule. As shown in Exhibit 3.37, almost all NRWA plants use chlorine as a disinfectant, whereas 40 percent of ICR plants use chloramines, chlorine dioxide, and ozone, which are thought to contribute less to DBP formation than chlorine. With respect to disinfectant dose, small plants reported larger chlorine doses than the large ICR plants ( Exhibit 3.38). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 36 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 2 4 6 8 10 12 TOC ( mg/ L as C) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 500 1000 1500 2000 2500 Bromide ( ug/ L) Cumulative Percentile Winter Data ( N= 95)

Summer Data ( N= 95) Exhibit 3.31 Plant Influent TOC Data for Small Surface Water Plants Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.32 Plant Influent Bromide Data for Small Surface Water Plants Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 37 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 Alkalinity ( mg/ L as CaCO3) Cumulative Percentile Winter Data ( N= 95)

Summer Data ( N= 95)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 5 10 15 20 25 30 35 Temperature ( as degrees Celsius) Cumulative Percentile Winter Data ( N= 73)

Summer Data ( N= 73) Exhibit 3.33 Plant Influent Alkalinity for Small Surface Water Systems Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.34 Plant Influent Temperature for Small Surface Water Systems Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 38 0% 20% 40% 60% 80% 100%

0 2 4 6 8 10 12 14 16 18 20 22 24 Time Operated per Day ( Hours) Cumulative Percentile Average ( N= 113)

Maximum ( N= 108)

At Time of Sampling ( N= 104)

0% 20% 40% 60% 80% 100%