Disinfection Particulate/ Turbidity Removal Corrosion Control Taste/ Odor Control Fluoridation Algae Control Mn Removal Organics Removal Iron Removal DBP Control Softening Arsenic Removal Percent of Systems ( N= 112) Exhibit 3.35 Distribution of Time Operated per Day Among Small Surface Water Plants Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.36 Treatment Objectives Among Small Surface Water Plants Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 39 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Cl2 only Cl2 & NH3 ClO2 O3 Percentage of Plants ICR SW Plants ( N= 292, based on month 8)

Small Plants in NRWA Survey ( N= 107)

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

0 5 10 15 20 25 30 35 40 Total Chlorine Dose ( mg CL2/ L) Cumulative Percentile ICR SW Plants ( N= 166, ave. of months 7 9)

Small Plants in NWRA Survey ( N= 94) Exhibit 3.37 Comparison of Disinfectants Used by Small and Large Surface Water Plants Sources: ICR AUX1 ( USEPA 2000d); NRWA Survey ( USEPA 2001g).

Exhibit 3.38 Comparison of Total Chlorine Doses in Large and Small Surface Water Plants Using Only Chlorination ( Cl2/ Cl2)

Sources: ICR AUX1 ( USEPA 2000d); NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 40 Data Type Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means TTHM Finished 96 62.78 46.20 137.00 0 326.05 Avg Res Time 96 80.22 56.75 181.35 0 328.85 DS Weighted Average 96 82.80 62.06 179.05 0 328.09 Single High 96 118.40 97.20 224.80 0 451.40 Max Res Time 96 90.54 67.15 188.30 0 325.80 HAA5 Finished 96 42.19 31.75 82.50 0 326.90 Avg Res Time 96 46.17 35.30 85.00 0 327.50 DS Weighted Average 96 45.32 33.99 83.89 0 261.56 Single High 96 65.34 52.90 113.40 0 474.90 Max Res Time 96 42.78 35.20 88.95 0 182.20 Data Type Number of Observations Mean Median 90th Percentile Range TTHM Finished 192 62.78 45.10 132.90 0 471.50 Avg Res Time 192 80.22 58.00 153.50 0 443.90 Max Res Time 192 90.54 73.30 174.50 0 451.40 HAA5 Finished 192 42.19 28.80 87.30 0 481.10 Avg Res Time 192 46.17 34.10 90.10 0 474.90 Max Res Time 192 42.78 34.60 87.90 0 225.00 Although the NRWA survey, a key source of DBP data for small surface water systems, paralleled the ICR effort, the data collection was not as extensive. In the distribution system, NRWA samples were collected only at the location with the maximum residence time and one location with an average residence time. Exhibits 3.39 and 3.40 summarize the combined winter and summer NRWA results for TTHM and HAA5 occurrence data. Exhibits 3.41 through 3.43 provide the summer and winter cumulative distributions of the NRWA TTHM analyses for finished water, average residence time, and maximum residence time locations, respectively. Similar data are provided for HAA5 in Exhibits 3.44 through 3.46 Despite the fact that small systems general have lower DBP precursor concentrations than medium and large systems, NRWA results for small surface water systems show higher byproduct levels than in medium and large systems. This is understandable, given that small systems have not been subject to the requirements of the 1979 TTHM standards, which resulted in some medium and large systems making treatment changes to limit byproduct formation.

Exhibit 3.39 Summary of NRWA DBP Occurrence Data by Plant Note: DS Weighted Average is calculated by giving the average residence time result a weight three times that of data at the maximum residence location. Refer to section 3.2.1 for a full description of NRWA data types.

Source: USEPA 2001g.

Exhibit 3.40 Summary of NRWA DBP Individual Observations Note: Refer to section 3.2.1 for a description of NRWA data types.

Source: USEPA 2001g. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 41 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 400 450 500 TTHM ( ug/ L) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 400 450 500 TTHM ( ug/ L) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96) Exhibit 3.41 Distribution of TTHM Occurrence in Plant Finished Water Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.42 Distribution of TTHM Occurrence at the Point of Average Residence Time in the Distribution System Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 42 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 400 450 500 TTHM ( ug/ L) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96)

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

0 100 200 300 400 500 600 HAA5 ( ug/ L) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96) Exhibit 3.43 Distribution of TTHM Occurrence at the Point of Maximum Residence Time in the Distribution System Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.44 Distribution of HAA5 Occurrence in Plant Finished Water Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 43 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 400 450 500 HAA5 ( ug/ L) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96)

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

0 50 100 150 200 250 HAA5 ( ug/ L) Cumulative Percentile Winter Data ( N= 96)

Summer Data ( N= 96) Exhibit 3.45 Distribution of HAA5 Occurrence at the Point of Average Residence Time in the Distribution System Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.46 Distribution of HAA5 Occurrence at the Point of Maximum Residence Time in the Distribution System Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 44 Exhibit 3.47 compares cumulative distributions of ICR, NRWA, and State plant mean TTHM occurrence in distribution systems for small and large surface water plants. For the ICR, the running annual average of the last four quarters of distribution system data, based on plants with at least three sampling locations each quarter and at least three quarters of data, is plotted. The NRWA plant means are weighted averages of the winter and summer average and maximum residence time samples, where average residence time samples are given weights three times those of maximum residence samples. ( As noted previously, the NRWA data were weighted to make them comparable to ICR data, for which the DS Average is calculated for each quarter by averaging results of three samples from locations approximating average residence time and one sample at the maximum residence location.) The State data on small surface water systems were collected from over 500 small surface water systems. However, not all points on the graph represent the same type of data   the points are plant " averages", but some plants took only one sample, while others took multiple samples. The plants with single samples may explain some of the very high TTHM plant means at the upper end of the distribution.

The median TTHM plant mean value was 66 µ g/ L and 62 µ g/ L for State and NRWA data, respectively, while the median RAA value for the ICR was 41 µ g/ L. The upper end of the NRWA distributions for TTHM is much higher than that of the ICR distributions. For example, NRWA 90th percentile TTHM concentrations are more than double their corresponding ICR concentrations. Only 5 ICR plants ( 2 percent) have TTHM levels exceeding 100 µ g/ L ( the MCL under the 1979 rule), while 23 ( 24 percent) NRWA plants and 192 ( 34 percent) of plants in the State data set do. These patterns are to be expected, since small systems do not have to comply with the 1979 TTHM standards.

The distribution of the State data shows TTHM levels at the upper end of the distribution are higher than those observed in the NRWA data. For example, the 90th percentile concentration in the State data set is 215 µ g/ L, while the NRWA value is 168 µ g/ L. This probably is due to the fact that some of the data points in the State data set were not averaged since some plants reported only one observation.

Exhibit 3.48 shows the co occurrence of HAA5 and TTHM at NRWA plants. The TTHM and HAA5 values are plant means weighted as discussed above. Roughly 22 percent of NRWA ( small) plants had both TTHM and HAA5 plant means exceeding Stage 1 DBPR limits, as compared to 1.4 percent of ICR SW plants ( see section 3.3.3 for ICR large plant DBP data analyses).

Although results in this section show that TTHM levels from the State data set are higher than the levels from the NRWA data set, the NRWA data may also be biased slightly high in terms of national DBP concentrations. This is because some States with high TOC ( as compared to the national average and based on ICR data) are overrepresented in the survey, while other States with low TOC may be underrepresented. For example, plants in Louisiana, a high TOC State, represent 4 percent of plants in the NRWA survey, but only 1 percent of small non purchased surface water plants in the country, according to the Baseline Handbook ( USEPA 2001e). The sampling results from plants in over or underrepresented States may be skewing the distribution of TOC and DBP data. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 45 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 50 100 150 200 250 300 350 400 450 500 TTHM ( ug/ L) Cumulative Percentile Data from 8 States ( Small plants, 1998 1999, N= 562)

Data from ICR ( Large Plant RAA of last 4 quarter values, N= 213)

NRWA Data ( Weighted Small Plant Means, N= 96)

80 ug/ L, Stage 1 MCL Exhibit 3.47 Cumulative Distribution of Mean TTHM Occurrence in Distribution Systems for Small and Large Surface Water Plants Sources: USEPA 2000l; USEPA 2000d; USEPA 2001g. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 46 0 50 100 150 200 250 300 0 50 100 150 200 250 300 350 400 TTHM RAA ( ug/ L) HAA5 RAA ( ug/ L) 2.1% 21.9%

12.5% 63.5% Exhibit 3.48 RAA TTHM vs. RAA HAA5 for Small Surface Water Plants Source: NRWA Survey ( USEPA 2001g).

Exhibit 3.49 shows the percent of plants that reported the maximum TTHM LRAA's at the finished water, average residence time, and maximum residence time locations. NRWA plants have the highest TTHM LRAA concentration occurring at sites other than the maximum residence time monitoring site 33 percent of the time. The highest HAA5 LRAA occurred at the maximum residence time monitoring site in only 48 percent of the plants.

If TTHM and HAA5 occur at the same location rather than different locations, fewer monitoring sites would be needed to represent TTHM and HAA5 occurrence. However, this is not the case. The NRWA data set indicates that 56 percent of their plants experienced their highest LRAA TTHM and HAA5 concentrations at different locations in the distribution system. For plants that had their highest TTHM and HAA5 LRAA concentrations at the same location, it was not necessarily at the maximum residence time location. Exhibit 3.50 illustrates that for NRWA plants with the highest TTHM and HAA5 levels occurring at the same location, the highest TTHM and HAA5 LRAA simultaneously occurred at a location other than the maximum residence time monitoring location 36 percent of the time. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 47 0% 10% 20% 30% 40% 50% 60% 70% 80%

Finished Water Point Average Residence Time Maximum Residence Time Percentage of Systems ( N= 96) TTHM HAA5 Highest LRAA TTHM/ HAA5 ( N= 96) Among Plant with Highest LRAA TTHM/ HAA5 at Same Location ( N= 42)

31% @ AVG 4.8% @ FINISH Maximum occurred at same locations for 43.8% of plants Maximum occurred at different locations for 56.3% of plants 64.3% @ MAX Exhibit 3.49 Percentage of DS Maximum Observations for TTHM and HAA5 by Sampling Location Source: NRWA Survey ( USEPA 2001g)

Exhibit 3.50 Frequency at Which Highest TTHM or HAA5 LRAAs Occurred at the Same Location for All NRWA Plants Source: NRWA Survey ( USEPA 2001g). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 48 3.2.3 Ground Water Systems <IP_ADDRESS> Medium Ground Water Systems Only limited data are available on precursor and byproduct occurrence for medium disinfecting ground water systems. The most relevant information for assessing byproduct occurrence in ground water is that provided in the WATER:\ STATS database. Exhibits 3.51 to 3.53 provide comparisons of influent average TOC levels, treatment used, and average TTHM levels for medium and large ground water systems in the WATER:\ STATS data set.

The TOC data and the treatment process information show considerable similarity between medium and large systems. It should also be noted that the TOC distributions derived from WATER:\ STATS for large and medium systems are similar to those observed for the large ground water plants in the ICR ( see Exhibit 3.2). Average TTHM levels in medium and large ground water systems are also similar, as shown in Exhibit 3.53, based on WATER:\ STATS data. The median average distribution system concentration for large ground water systems was 12 µ g/ L and for medium systems was 10 µ g/ L. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 49 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 5 10 15 20 25 30 Plant Mean TOC ( mg/ L C) Cumulative Percent Medium Ground Water Systems ( N= 51)

Large Ground Water Systems ( N= 38)

0% 5% 10% 15% 20% 25% 30% 35% 40% 45%

No trmt.

Pre storage/ Sed Aeration/ Air stripping Rapid Mix Floc/ Coag Sed Filt Percentage of Systems Medium systems 10 100K ( N= 364)

Large systems > 100K ( N= 110) Exhibit 3.51 Annual Average TOC in Influent Water TOC for Ground Water Systems Source: WATER:\ STATS ( AWWA 2000).

Exhibit 3.52 Treatment Summary for Ground Water Systems ( Chlorinating and Non Chlorinating)

Source: WATER:\ STATS ( AWWA 2000). Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 50 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 20 40 60 80 100 120 TTHM ( ug/ L) Cumulative Percentile Medium Ground Water Systems ( N= 169)

Large Ground Water Systems ( N= 68) Exhibit 3.53 Annual Average Finished Water TTHM for Ground Water Systems Source: WATER:\ STATS ( AWWA 2000)

<IP_ADDRESS> Small Ground Water Systems As with the small surface water systems, there is very limited information available on DBP precursor levels in small ground water systems that disinfect and insufficient data for determining national occurrence levels of DBPs ( GWSS DBP data were not used because only distribution system entry point data were available).

Data are not available on influent TOC levels for small ground water systems that disinfect. However, there are some data available on effluent ( finished water) TOC in small, medium, and large disinfecting ground water systems that can provide some insight into how small system DBP precursor levels compare with those at larger systems.

Exhibit 3.54 provides the effluent TOC data obtained in the 1982 GWSS. Though this information is somewhat dated, it is reasonable to assume the following with respect to these data: ( 1) the fraction of TOC removed in ground water systems is probably not substantial ( based on comparisons of influent and effluent ICR TOC levels), so these effluent TOC levels are reasonable indicators of influent TOC; ( 2) the levels of TOC in influent ground waters probably have not changed much since these data were collected ( support for this is provided by comparing the effluent data for the large systems in the GWSS data set to the observed influent TOC levels for large systems in the ICR); and ( 3) the comparison across system sizes indicates that, on a national scale, TOC levels in small disinfecting ground water systems are similar to those of medium and large systems.

For TTHMs themselves, there are some data available for small ground water systems. These data were collected by seven States during 1998 and/ or 1999, as described in the beginning of the chapter. Exhibit 3.55 shows annual average TTHM levels for more than 2,300 observations and compares them Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 51 with ground water ICR running annual averages from the last four quarters of data collection. As with the surface water data, the State data are inconsistent. A few systems took only one sample per year; the average of such a value cannot easily be compared to that of a system taking 20 samples a year. This may explain some of the very high ground water values ( e. g., the maximum value is 655 µ g/ L). Overall, however, the State ground water data compare favorably with WATER:\ STATS TTHM data for medium and large plants, with a median value of 3 µ g/ L, much less than the median distribution system values for the other size categories ( see Exhibit 3.21). The mean concentration, 17 µ g/ L, is slightly below the mean of 19 µ g/ L for medium WATER:\ STATS plants. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 52 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

0 2 4 6 8 10 12 14 16 Effluent TOC ( mg/ L) Cumulative Percentile of Systems Small Systems (< 10K)

Medium Systems ( 10  100 K)

Large Systems (> 100K)

Source: GWSS ( 1981 82)

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

0 20 40 60 80 100 120 140 160 180 200 TTHM ( ug/ L) Cumulative Percentile of Systems Data from 7 States ( 1998 1999, N= 2336)

Data from ICR ( RAA, N= 82)

80 ug/ L, Stage1 MCL Exhibit 3.54 Comparison of Effluent TOC for Chlorinating Small, Medium, and Large Ground Water Systems Exhibit 3.55 Cumulative Distribution of TTHM Occurrence as Distribution System Average for Small and Large Ground Water Plants Sources: USEPA 2000l; USEPA 2000d. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 53 3.3 Analysis of Co Occurrence Due to the extensive data collection effort of the ICR, many analyses of source water quality parameters, treatment characteristics, and the resulting finished water quality are possible. This section presents the results of select analyses of the relationships between several source water quality parameters, disinfectants, and DBPs.

3.3.1 Total Organic Carbon Concentration and Alkalinity Organic DBP formation occurs when disinfectants react with organic matter in water. The Stage 1 DBPR requires water systems to remove a certain percentage of TOC based on the TOC and alkalinity levels of the influent water. Exhibit 3.56 shows the percentage removals required by the Stage 1 DBPR in the 3 × 3 matrix for conventional plants. The last column of the matrix also applies to enhanced softening plants. There are various exceptions and alternative compliance criteria, which are explained in detail in the Stage 1 DBPR ( USEPA 1998a).

Exhibit 3.56 Percent TOC Removal Requirements for Systems Employing Enhanced Coagulation Source Water TOC ( mg/ L) Source Water Alkalinity ( mg/ L as CaCO3)

0   60 > 60   120 > 120 > 2.0   4.0 35 % 25 % 15 %

> 4.0   8.0 45 % 35 % 25 %

> 8.0 50 % 40 % 30%

Source: The Stage 1 Disinfectants/ Disinfection Byproducts Rule ( USEPA 1998a)

Exhibit 3.57 shows the number of monthly samples in each TOC removal category over the last 12 months ( January to December 1998) of the ICR monitoring period. Due to seasonal variation and other factors affecting source water, the percentage removal requirements for each plant may change from month to month as the influent TOC and alkalinity vary. Of the three alkalinity groups, the 60 120 mg/ L category had the fewest samples. The number of samples with TOC concentrations greater than 4.0 mg/ L decreased substantially from the two lower TOC concentration groups over all three alkalinity ranges. In the 4.0 8.0 mg/ L TOC range there is virtually no difference in the number of samples across the alkalinity groups. Many times, samples are close to the limits for a percentage removal group, indicating that the treatment requirements of a plant can easily change.

Note that almost 40 percent of the sample points have TOC observations below 2.0 mg/ L, and the few very high alkalinity observations ( 400 mg/ L  500 mg/ L) are also in the below 2.0 mg/ L TOC category. Also note that observations below the TOC MRL are graphed as zeroes. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 54 0 100 200 300 400 500 0 5 10 15 20 25 Influent TOC ( mg/ L) Influent Alkalinity ( mg/ L) Percentage < 60 60  120 > 120 Total < 2.0 14% 10% 16% 39% 2.0  4.0 14% 14% 13% 41% 4.0  8.0 5% 5% 6% 16% > 8.0 1% 0% 2% 4% Total 34% 29% 37% 100% Source Water TOC Range ( mg/ L) Alkalinity ( mg/ L) Exhibit 3.57 Distribution of Monthly TOC ( mg/ L) and Monthly Alkalinity ( mg/ L) Samples Based on ICR Data for All Large Plants Source: ICR AUX1 database ( USEPA 2000d).

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

Excel File: INF TOC versus ALK. xls 3.3.2 TOC, Bromide, and TTHM TOC and bromide in raw water influence the formation of DBPs. Although the concentration of DBPs in the finished water is affected by the treatment applied, higher concentrations of TOC in the source water are expected to cause a greater occurrence of DBPs if not well controlled. Increases in the concentration of influent bromide are expected to shift the types of DBPs formed more to brominated species and raise the concentration by weight of DBPs, because bromide is heavier than chlorine. DBP formation and speciation, however, depend on many factors other than TOC and bromide, and include the type of disinfectant, pH, temperature, inorganic demand, and disinfectant residual. This section examines the relationship between influent TOC and bromide; this relationship is an indicator of the treatability of the water. A comparison of TOC and bromide source water occurrence is presented. Additional analyses were performed relating TOC and bromide occurrence in source water to TTHM and HAA5 levels in finished water. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 55 Exhibits 3.58 and 3.59 contain three dimensional graphs comparing influent bromide, influent TOC, and finished water TTHM concentrations for surface and ground water plants. Exhibits 3.60 and 3.61 contain the same graphs for finished water HAA5 concentrations. The graphs were prepared by first categorizing each ICR plant by its mean influent water TOC and bromide concentration based on the last 12 months of the ICR collection period ( TOC and bromide plant means were based on monthly data for only those months that had corresponding TTHM or HAA5 data). This resulted in a 5 by 5 matrix according to the following bromide and TOC concentrations:

° TOC ( mg/ L): < MRL  1; 1  2; 2  3; 3 4; and > 4 ° Bromide ( : g/ L): < MRL; MRL  30; 30  50; 50  100; > 100 For each of the 25 TOC/ bromide categories, the mean and 90th percentile of all plant mean TTHM and HAA5 concentrations were calculated using data from all of the plants in that category. Like influent TOC and bromide, TTHM and HAA5 plant mean data is based on the last 12 months of the ICR collection period. The highest level of TTHM, approximately 50 : g/ L, is indicated by a light colored bar that identifies corresponding values of TOC of > 4 mg/ L and of bromide of 30 50 : g/ L.

These comparisons have some uncertainty because TOC and bromide levels are from raw water, and TTHM and HAA5 are from finished water. It is therefore not known how treatment ( other than disinfection) might have affected the TOC and bromide concentrations. If not controlled, higher influent TOC and bromide levels result in higher concentrations of DBPs. However, the pattern is not clear in this data set because the different treatment processes of most plants reduce DBP formation by removing TOC at varying levels. Also, bromide forms many other brominated acids that are not included in the measurements of TTHM or HAA5, making a direct correlation between TTHM, TOC and bromide unlikely.

The general trend from all graphs is that TTHM formation increases as TOC increases, but there seems to be no simple correlation with bromide. These analyses do not account for the effect of alternative disinfectants, which may have been used in plants that had difficulty treating water with high TOC and particularly high bromide concentrations. In addition, because all TOC, bromide, and DBP concentrations are calculated as averages or 90th percentiles for each plant, the exhibits may not capture relationships between individual observations in one quarter.

The formation of HAA5 related to TOC and bromide in finished water is shown in Exhibit 3.60 and 3.61. The mean and 90th percentile graphs of all sampling points show that HAA5 formation increases as TOC increases and bromide decreases. Increasing bromide concentrations are expected to shift the speciation of HAAs to the more bromine substituted species, which are not included in HAA5. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 56 < MRL MRL 30 30 50 50 100 > 100 < MRL 1 1 2 2 3 3 4 > 4 0 10 20 30 40 50 60 70 80 90 100 TTHM ( ug/ L)

Bromide ( ug/ L) TOC ( mg/ L) Exhibit 3.58 Finished Water TTHM Concentrations ( Mean of Plant Means) by Influent TOC and Bromide Concentrations Based on ICR Data for All Large Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, FW TTHM & HAA5 by Inf Bromide & TOC. See Appendix B for query language.

Excel File: TTHM and HAA5 by Bromide and TOC. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 57 < MRL MRL 30 30 50 50 100 > 100 < MRL 1 1 2 2 3 3 4 > 4 0 10 20 30 40 50 60 70 80 90 100 TTHM ( ug/ L)

Bromide ( ug/ L) TOC ( mg/ L) Exhibit 3.59 Finished Water TTHM Concentrations ( 90th Percentile of Plant Means) by Influent TOC and Bromide Concentrations Based on ICR Data for All Large Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, FW TTHM & HAA5 by Inf Bromide & TOC. See Appendix B for query language.

Excel File: TTHM and HAA5 by Bromide and TOC. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 58 < MRL MRL 30 30 50 50 100 > 100 < MRL 1 1 2 2 3 3 4 > 4 0 10 20 30 40 50 60 70 80 90 HAA5 ( ug/ L)

Bromide ( ug/ L) TOC ( mg/ L) Exhibit 3.60 Finished Water HAA5 Concentrations ( Mean of Plant Means) by Influent TOC and Bromide Concentrations Based on ICR Data for All Large Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, FW TTHM & HAA5 by Inf Bromide & TOC. See Appendix B for query language.

Excel File: TTHM and HAA5 by Bromide and TOC. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 59 < MRL MRL 30 30 50 50 100 > 100 < MRL 1 1 2 2 3 3 4 > 4 0 10 20 30 40 50 60 70 80 90 HAA5 ( ug/ L)

Bromide ( ug/ L) TOC ( mg/ L) Exhibit 3.61 Finished Water HAA5 Concentrations ( 90th Percentile of Plant Means) by Influent TOC and Bromide Concentrations Based on ICR Data for All Large Plants Source: ICR AUX1 Database ( USEPA 2000d).

Query: Plants min 3x3, FW TTHM & HAA5 by Inf Bromide & TOC. See Appendix B for query language.

Excel File: TTHM and HAA5 by Bromide and TOC. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 60 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 RAA TTHM ( ug/ L) RAA HAA5 ( ug/ L) 4.2%

2.3% 92.0% 1.4% 3.3.3 TTHM and HAA5 Exhibit 3.62 through 3.67 compare DS Averages and Single Highest observations for TTHM and HAA5 samples drawn at the same location and time. Exhibits 3.62 and 3.63 show RAAs for surface water and ground water, respectively. Exhibits 3.64 and 3.65 compare each plant's highest TTHM and HAA5 LRAA values during the last four quarters of the ICR, and Exhibits 3.66 and 3.67 show individual Single Highest values. Each exhibit divides TTHM and HAA5 occurrence into quadrants, based on whether TTHM and/ or HAA5 levels from a given sampling period exceed the Stage 1 DBPR MCLs of 80 µ g/ L for TTHM and 60 µ g/ L for HAA5. Each exhibit shows the percentage of plants ( or observations) falling into each quadrant. For example, in Exhibit 3.62, 1.4 percent of plants have TTHM and HAA5 RAAs that exceed the contaminants respective MCLs. The graphs demonstrate a slight relation between TTHM and HAA5, with one increasing as the other increases. Most observations fall below the Stage 1 DBPR MCLs, especially for ground water data. The exhibits also show that more plants would exceed both the 80 and 60 µ g/ L TTHM and HAA5 levels if compliance were calculated differently than under the Stage 1 DBPR, which uses RAAs to determine compliance.

Note that HAA5 does not represent all the HAAs, particularly the more bromine substituted HAAs. Hence, for high bromide waters, HAA5 may not be as representative of brominated DBP formation as TTHM.

Exhibit 3.62 RAA of TTHM Occurrence versus RAA of HAA5 Occurrence for Large Surface Water Plants Based on ICR Data ( N = 213)

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 61 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 RAA TTHM ( ug/ L) RAA HAA5 ( ug/ L) 1.2%

1.2% 96.3% 1.2% Exhibit 3.63 RAA of TTHM Occurrence versus RAA of HAA5 Occurrence for Large Ground Water Plants Based on ICR Data ( N = 82)

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 62 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 LRAA TTHM ( ug/ L) LRAA HAA5 ( ug/ L) 4.7%

6.6% 84.5% 4.2% Exhibit 3.64 Highest LRAA TTHM versus Highest LRAA HAA5 for Large Surface Water Plants Based on ICR Data ( N = 213)

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 63 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 LRAA TTHM ( ug/ L) LRAA HAA5 ( ug/ L) 4.7%

6.6% 84.5% 4.2% Exhibit 3.65 Highest LRAA TTHM versus Highest LRAA HAA5 for Large Ground Water Plants Based on ICR Data ( N = 82)

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 64 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Single High TTHM ( ug/ L) Single High HAA5 ( ug/ L) 9.4%

17.4% 58.2% 15.0% Exhibit 3.66 Single Highest TTHM versus Single Highest HAA5 for Large Surface Water Plants Based on ICR Data ( N = 213)

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 65 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Single High TTHM ( ug/ L) Single High HAA5 ( ug/ L) 6.1%

6.1% 86.6% 1.2% Exhibit 3.67 Single Highest TTHM versus Single Highest HAA5 Based on ICR Data for Large Ground Water Plants ( N = 82)

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 66 TOC >= 2 to 3 mg/ L TOC >= 3 to 4 mg/ L No Data TOC < 1 to mg/ L TOC >= 1 to 2 mg/ L TOC >= 4 mg/ L 3.4 Analysis of Regional Trends 3.4.1 Occurrence of TOC EPA evaluated ICR surface and ground water system data to determine if there were differences in influent water quality among regions. Exhibits 3.68a and 3.68b show average TOC concentrations by State for surface and ground water systems, respectively, using ICR data. Exhibit 3.68c shows average TOC concentrations by State for ground water systems using Ground Water Supply Survey ( GWSS) data. Surface water systems did not exhibit any notable regional trends; however, ICR and GWSS data show that Florida has very high TOC concentrations compared to other States. Florida also has the largest proportion of large ground water systems of all the States.

Exhibit 3.68a Influent Water TOC Occurrence Distribution for Large ICR Surface Water Systems Source: ICR AUX1 Database ( USEPA 2000d); mean of all plant means for each State. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 67 TOC >= 2 to 3 mg/ L TOC >= 3 to 4 mg/ L No Data TOC < 1 to mg/ L TOC >= 1 to 2 mg/ L TOC >= 4 mg/ L TOC >= 2 to 3 mg/ L TOC >= 3 to 4 mg/ L No Data TOC < 1 to mg/ L TOC >= 1 to 2 mg/ L TOC >= 4 mg/ L Exhibit 3.68b Influent Water TOC Occurrence Distribution for Large ICR Ground Water Systems Source: ICR AUX1 Database ( USEPA 2000d); mean of all plant means for each State.

Exhibit 3.68c Influent Water TOC Occurrence Distribution for Ground Water Systems, Derived from the Ground Water Supply Survey ( GWSS)

Source: GWSS ( USEPA 1983), mean of all finished water TOC samples in the State. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 3 68 No data > 100 ³ 50 100 < MRL ( 20)

³ MRL  30 ³ 30  50 Mean Bromide ( m g/ L) 3.4.2 Occurrence of Bromide Regional trends in occurrence of bromide in source water were evaluated in the Information Collection Rule Data Analysis document ( McGuire et al. 2002). Exhibit 3.69 shows the State by State average bromide levels in surface water systems for each State. Texas and Florida exhibit the highest influent bromide concentrations, both over 100 µ g/ L. The Midwest region of the country exhibits high influent bromide concentrations overall whereas the Northeast water contains very little influent bromide.

Exhibit 3.69 Mean Influent Bromide Concentrations, Large ICR Surface Water Plants Source: Chapter 14 Information Collection Rule Data Analysis document ( McGuire et al. 2002). 1Note that the Surface Water Analytical Tool ( SWAT) was used to predict changes in average DBP occurrence between both post Stage 2 and post Stage 2 conditions. SWAT is discussed in detail in the Economic Analysis for the Stage 2 DBPR ( USEPA 2003a).

Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 1 4. Predicted Post Stage 1 DBP Occurrence Analyses of disinfectants and disinfection byproducts ( DBP) occurrence data to support the development of the Stage 2 Disinfectants and Disinfection Byproducts Rule ( DBPR) is complicated by the fact that existing national occurrence data do not reflect changes resulting from the implementation of the Stage 1 DBPR. This is because many utilities have only recently changed their treatment to comply with the Stage 1 DBPR ( e. g., surface water systems serving 10,000 or more people were required to comply by January 2002) or are about to make changes to comply ( e. g., surface water systems serving fewer than 10,000 people and all ground water systems are required to comply by January 2004). DBP occurrence data collected under the Information Collection Rule ( ICR) represent conditions during late 1997 and 1998, well before systems had to comply with the Stage 1 DBPR. Other occurrence data for medium and small systems represent similar time frames.

The purpose of this section is to support the development of the Stage 2 DBPR by evaluating DBP occurrence likely to exist after the Stage 1 DBPR is implemented. In this regard, the analysis presented in section 4.3 of this chapter focuses on the spatial and temporal variability in distribution system total trihalomethanes ( TTHM) and haloacetic acids ( HAA5) occurrence following the implementation of the Stage 1 DBPR. Preceding sections describe the methodology for predicting post Stage 1 DBP occurrence ( section 4.1) and summarize the results ( section 4.2).

4.1 Methodology for Predicting Post Stage 1 DBP Occurrence The ICR was the primary data source used to characterize post Stage 1 ( or Pre Stage 2) DBPR occurrence for TTHM and HAA5 in this document1. To assess Post Stage 1 DBP occurrence, the analysis in this section uses the subset of ICR plants that are already in compliance with Stage 1 to characterize Post Stage 1 DBP occurrence. This assumes the cumulative distribution of TTHM and HAA5 concentrations for the subset of plants in compliance with the Stage 1 DBPR is unchanged when non compliant plants make changes to meet Stage 1. This may not be the case   systems that make changes may be concentrated near the upper end of the cumulative distribution since these plants will have poor water quality with respect to DBPs. EPA believes, however, that given the small number of plants that make changes compared to those that don't, the impact on the Post Stage 1 DBPR occurrence distribution is small.

To determine if an ICR plant is in compliance with the Stage 1 DBPR, EPA calcuated the TTHM and HAA5 running annual averages ( RAAs) using the last four quarters of ICR data ( January to December 1998) at the four distribution system locations ( DSE, AVG1, AVG2, and DS Maximum). The analysis is done only for plants that meet the screening criteria discussed in section 1.4.8 ( plants must have at least 3 of 4 quarters with at least 3 of 4 locations having data for both TTHM and HAA5).

Once TTHM and HAA5 RAAs were calculated for the screened plants, compliance was determined using two approaches:

° Compare TTHM RAA to the Stage 1 DBPR MCL of 80 : g/ L, and HAA5 RAA to the Stage 1 DBPR MCL of 60 : g/ L Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 2 ° Same as above, except consider the Stage 1 DBPR MCLs with a 20 percent safety factor ( 64 : g/ L for TTHM and 48 : g/ L for HAA5)

Based on recommendations from the Microbial/ Disinfection Byproducts Technical Work Group ( M DBP TWG), EPA uses a 20 percent operational safety factor for DBP MCLs ( TTHM, HAA5, bromate, and chlorite) when evaluating all regulatory alternatives. This safety factor is consistent with practices in prior DBP regulatory development efforts and is intended to represent the level at which systems would be compelled to take some action to ensure compliance with a new drinking water standard. In addition to reflecting industry practices, the safety factor also is intended to account for year to year fluctuations in DBP data ( ICR data is limited to one year and may not reflect the highest DBP concentrations that occur in a system).

Although EPA believes that the use of a safety factor generally reflects industry practices, there is variability in the concentration below the MCL value at which systems are confident operating ( e. g., the safety factor may be more or less in some cases) and, therefore, uncertainty in the average safety factor. In addition to this uncertainty, EPA believes that the post Stage 1 DBPR distribution of TTHM and HAA5 may be slightly higher than the results using subsets of Stage 1 compliant plants from the ICR. To essentially " bound" these uncertainties, analyses of predicted Post Stage 1 TTHM and HAA5 occurrence are done both with and without a 20 percent safety factor. All analyses of spatial and temporal variability, however, ( presented in Section 4.3), are done based on compliance evaluation without the safety factor ( i. e., 80/ 60 RAA).

4.2 Summary of Post Stage 1 Occurrence, Plant Mean Data Exhibits 4.1 and 4.2 summarize post Stage 1 DBPR TTHM and HAA5 data, respectively. The data are presented separately for different source water types ( surface, ground, and all) and data types ( plant mean finished water, running annual average ( RAA), locational running annual average ( LRAA), and single high). See section 3.1.3 for a description of the different data types. Plant compliance was determined by using the Stage 1 DBPR MCLs with and without a 20 percent safety factor. Note that applying a 20 percent safety factor to the Stage 1 DBPR MCLs resulted in reduced Post Stage 1 TTHM and HAA5 values compared to results without the safety factor.

For surface water systems results show that the highest LRAA for some Stage 1 compliant plants is significantly above the Stage 2 DBPR MCL of 80 : g/ L for TTHM and 60 : g/ L for HAA5. Single highest values are also still very high after Stage 1 compliance ( maximum of 134 and 132 : g/ L for TTHM and HAA5, respectively, based on compliance without a safety factor). Ground water peaks are less, but LRAA values are still above the Stage 2 DBPR MCLs for some plants. Section 4.3.1 provides more detailed analyses of the occurrence of individual TTHM and HAA5 peak measurements. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 3 Source Data Type 1 Stage 1 MCLs With or Without 20% Safety Factor Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means w/ o S. F. 196 29.29 27.37 52.13 0 75 w/ 20% S. F. 172 26.70 25.68 46.20 0 75 w/ o S. F. 196 39.32 37.97 63.42 0 80 w/ 20% S. F. 172 35.83 35.65 55.86 0 64 w/ o S. F. 196 46.18 43.97 75.23 0 98 w/ 20% S. F. 172 42.49 41.17 68.43 0 98 w/ o S. F. 196 64.26 60.10 106.70 0 142 w/ 20% S. F. 172 58.60 56.60 94.50 0 124 w/ o S. F. 79 7.59 1.40 24.57 0 58 w/ 20% S. F. 77 6.93 1.23 23.48 0 58 w/ o S. F. 79 13.07 6.51 35.76 0 69 w/ 20% S. F. 77 12.23 6.42 35.39 0 55 w/ o S. F. 79 17.91 11.65 49.83 0 99 w/ 20% S. F. 77 17.05 11.40 49.30 0 99 w/ o S. F. 79 29.48 17.10 65.50 0 300 w/ 20% S. F. 77 28.31 16.00 63.70 0 300 w/ o S. F. 284 23.42 21.48 49.90 0 87 w/ 20% S. F. 256 20.85 19.33 45.48 0 87 w/ o S. F. 290 31.93 31.68 60.46 0 80 w/ 20% S. F. 262 28.57 29.39 52.89 0 64 w/ o S. F. 290 38.17 37.05 69.95 0 99 w/ 20% S. F. 262 34.62 33.27 63.30 0 99 w/ o S. F. 290 54.18 52.40 100.00 0 300 w/ 20% S. F. 262 49.10 49.30 89.10 0 300 Finished, Plant Mean DS Average ( or RAA)

Highest LRAA Single Highest Finished, Plant Mean DS Average ( or RAA)

Highest LRAA Single Highest Finished, Plant Mean DS Average ( or RAA)

Highest LRAA Single Highest Surface Ground All 2 Exhibit 4.1 Summary of Post Stage 1 TTHM Occurrence for ICR Plants in Compliance with Stage 1 MCLs with or without a Safety Factor Notes: 1 For a description of the data types. See " Aggregation of DBP Data" in section 3.1.3. 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. MCLs without safety factor: TTHM/ HAA5= 80/ 60 : g/ L; MCLs with safety fact: TTHM/ HAA5= 64/ 48 : g/ L 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. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 4 Source Data Type 1 Stage 1 MCLs With or Without 20% Safety Factor Number of Plants Mean of Plant Means Median of Plant Means 90th Percentile of Plant Means Range of Plant Means w/ o S. F. 196 21.79 20.00 40.85 0 61 w/ 20% S. F. 172 20.04 18.13 38.33 0 53 w/ o S. F. 196 25.58 22.99 45.85 0 59 w/ 20% S. F. 172 23.27 22.50 40.74 0 48 w/ o S. F. 196 29.81 26.87 53.10 0 110 w/ 20% S. F. 172 26.98 25.33 46.28 0 60 w/ o S. F. 196 41.94 37.80 74.20 0 134 w/ 20% S. F. 172 37.88 34.30 63.50 0 115 w/ o S. F. 79 4.39 0.33 17.53 0 34 w/ 20% S. F. 77 4.06 0.33 15.20 0 34 w/ o S. F. 79 6.82 2.20 18.48 0 49 w/ 20% S. F. 77 6.18 2.16 17.69 0 46 w/ o S. F. 79 9.24 3.33 26.97 0 74 w/ 20% S. F. 77 8.32 3.17 25.55 0 58 w/ o S. F. 79 15.18 6.20 45.80 0 103 w/ 20% S. F. 77 13.97 6.20 45.00 0 84 w/ o S. F. 284 16.74 15.07 37.33 0 61 w/ 20% S. F. 256 15.11 14.08 34.18 0 53 w/ o S. F. 290 20.00 17.96 41.96 0 59 w/ 20% S. F. 262 17.89 17.24 36.45 0 48 w/ o S. F. 290 23.62 21.17 48.60 0 110 w/ 20% S. F. 262 21.05 19.95 42.00 0 60 w/ o S. F. 290 33.76 29.00 67.60 0 134 w/ 20% S. F. 262 30.19 27.20 59.80 0 115 Highest LRAA Single Highest All 2 Finished, Plant Mean DS Average ( or RAA)

Highest LRAA Single Highest Surface Finished, Plant Mean DS Average ( or RAA)

Highest LRAA Single Highest Ground Finished, Plant Mean DS Average ( or RAA) Exhibit 4.2 Summary of Post Stage 1 HAA5 Occurrence for ICR Plants in Compliance with Stage 1 MCLs with or without a Safety Factor Notes: 1 For a description of the data types. See " Aggregation of DBP Data" in section 3.1.3. 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. MCLs without safety factor: TTHM/ HAA5= 80/ 60 : g/ L; MCLs with safety fact: TTHM/ HAA5= 64/ 48 : g/ L 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. See Appendix B for query language.

Excel File: ICR DBP Data, Pre Stage 2. xls 4.3 Spatial and Temporal Variability of TTHM and HAA5 Occurrence, Post Stage 1 Conditions This section supports the development of the Stage 2 DBPR by evaluating spatial and temporal variability of TTHM and HAA5 occurrence for Post Stage 1 conditions. For the purposes of these analyses, EPA uses the subsets of plants in compliance with Stage 1 DBPR MCLs of 80/ 60 : g/ L for TTHM/ HAA5, respectively ( no safety factor). Additional analyses for the subsets of plants in compliance with MCLs of 64/ 48 : g/ L for TTHM/ HAA5, respectively, were not done because they are expected to show almost identical results.

Section 4.3.1 evaluates the occurrence of individual TTHM and HAA5 peaks for post Stage 2 conditions. Sections 4.3.2 and 4.3.3 characterize the occurrence of yearly average TTHM and HAA5 data at different locations. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 5 4.3.1 Occurrence of Individual DBP Observations Above the MCL Exhibit 4.3 compares the TTHM running annual average ( RAA) results with the single highest TTHM concentration in the distribution system for all plants in compliance with the Stage 1 DBPR MCLs of 80/ 60 RAA ( 4.3a) and the Stage 1 MCLs with a 20 percent safety factor ( 64/ 48 RAA) ( 4.3b). As derived from data in Exhibit 4.3a, twenty one percent ( 61 of 290) of all plants meeting the Stage 1 DBPR MCL of 80/ 60 RAA had single TTHM concentrations higher than the 0.080 mg/ L MCL. From Exhibit 4.3b, about fifteen percent ( 38 of 262) of all plants meeting the Stage 1 DBPR MCL of 64/ 48 RAA had single TTHM concentrations higher than the 0.080 mg/ L MCL. Exhibit 4.4 makes the same comparisons for HAA5.

Data in Exhibit 4.4a show that fourteen percent ( 42 of 290) of all ICR plants meeting the Stage 1 DBPR MCL of 80/ 60 RAA had single HAA5 concentrations higher than the 0.060 mg/ L MCL. From Exhibit 4.4b, about ten percent ( 25 of 262) of all ICR plants meeting the Stage 1 DBPR MCL of 64/ 48 RAA had single HAA5 concentrations higher than the 0.060 mg/ L MCL. In systems with a low RAA for TTHM and HAA5, the highest single TTHM and HAA5 values are generally not much higher than the respective Stage 1 DBPR MCLs. However, as the RAAs increase, there is a greater likelihood of having peak levels above the MCLs. As the RAAs approach the Stage 1 DBPR MCLs, some of the distribution system single highest concentrations approach levels that are double the Stage 1 DBPR MCLs. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 6 0 50 100 150 200 250 300 350 0 10 20 30 40 50 60 70 80 90 TTHM RAA, ug/ L ( N= 290) TTHM Single Highest, ug/ L ( N= 290) Exhibit 4.3a Single Highest vs. RAA for TTHM, All Plants in Compliance with Stage 1 MCLs of 80/ 60 RAA Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 7 0 50 100 150 200 250 300 350 0 10 20 30 40 50 60 70 80 90 TTHM RAA, ug/ L ( N= 262) TTHM Single Highest, ug/ L ( N= 262) Exhibit 4.3b Single Highest vs. RAA for TTHM, All Plants in Compliance with Stage 1 MCLs with Safety Factor ( 64/ 48 RAA)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 8 0 25 50 75 100 125 150 175 200 0 10 20 30 40 50 60 70 HAA5 RAA, ug/ L ( N= 290) HAA5 Single Highest, ug/ L ( N= 290) Exhibit 4.4a Single Highest vs. RAA for HAA5, All Plants in Compliance with Stage 1 MCLs of 80/ 60 RAA Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 9 0 25 50 75 100 125 150 175 200 0 10 20 30 40 50 60 70 HAA5 RAA, ug/ L ( N= 262) HAA5 Single Highest, ug/ L ( N= 262) Exhibit 4.4b Single Highest vs. RAA for HAA5, All Plants in Compliance with Stage 1 MCLS with Safety Factor ( 64/ 48 RAA)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 10 4.3.2 Occurrence of Yearly Averages Above the MCL at Specific Locations Cumulative distributions of LRAA values for each distribution system location ( AVG1, AVG2, MAX, and DSE) for all plants are shown in Exhibit 4.5. Exhibit 4.5a shows results for plants in compliance with Stage 1 DBPR MCLs of 80/ 60 RAA, while Exhibit 4.5b shows results for plants in compliance with Stage 1 MCLs with a 20 percent safety factor ( 64/ 48 RAA). Results show that there are still locations that regularly receive water over the MCLs following the implementation of the Stage 1 DBPR. From data in Exhibit 4.5a, approximately five percent of plants ( 15 out of 290) in compliance with Stage 1 MCLs of 80/ 60 RAA had one or more locations that, on average, exceeded 0.080 mg/ L as a TTHM LRAA, and one of these 15 did so at two locations. From Exhibit 4.5b, approximately two percent of plants ( six out of 262) in compliance with Stage 1 MCLs of 64/ 48 RAA had one or more locations that, on average, exceeded 0.080 mg/ L as a TTHM LRAA for that same year. Customers served at these locations regularly received water with TTHM concentrations higher than the MCL.

Exhibit 4.6 shows similar results for HAA5. From Exhibit 4.6a, three percent of plants ( eight of 290) in compliance with Stage 1 MCLs of 80/ 60 RAA exceeded 0.060 mg/ L as an LRAA, and three of these eight plants did so at two or three locations. Exhibit 4.6b shows that no plants in compliance with Stage 1 MCLS of 64/ 48 RAA exceeded 0.060 mg/ L as an LRAA.

Evaluating TTHM and HAA5 results together, 23 plants have a maximum TTHM LRAA of 0.080 mg/ l or greater, or a maximum HAA5 LRAA of 0.060 mg/ l or greater ( four plants exceeded both MCLs) among the 290 plants in the ICR database meeting the Stage 1 MCLs of 80/ 60 RAA, Among the 262 plants in the ICR database meeting the Stage 1 MCLs of 64/ 48 RAA, six plants have a maximum TTHM LRAA of 0.080 mg/ L or greater, or a maximum HAA5 LRAA of 0.060 mg/ L or greater. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 11 60% 65% 70% 75% 80% 85% 90% 95% 100%

50 60 70 80 90 100 110 TTHM LRAA, ug/ L Cumulative Percentage of Plants TTHM LRAA @ DSE ( N= 284)

TTHM LRAA @ AVG1 ( N= 283)

TTHM LRAA @ AVG2 ( N= 284)

TTHM LRAA @ MAX ( N= 290) Exhibit 4.5a Cumulative Percentage of TTHM LRAAs, All Plants in Compliance with 80/ 60 RAA ( Stage 1 MCL)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 12 60% 65% 70% 75% 80% 85% 90% 95% 100%

50 60 70 80 90 100 110 TTHM LRAA, ug/ L Cumulative Percentage of Plants TTHM LRAA @ DSE ( N= 256)

TTHM LRAA @ AVG1 ( N= 255)

TTHM LRAA @ AVG2 ( N= 256)

TTHM LRAA @ MAX ( N= 262) Exhibit 4.5b Cumulative Percentage of TTHM LRAAs, All Plants in Compliance with 64/ 48 RAA ( Stage 1 MCL with SF)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 13 70% 75% 80% 85% 90% 95% 100%

30 40 50 60 70 80 90 100 110 120 HAA5 LRAA, ug/ L Cumulative Percentage of Plants HAA5 LRAA @ DSE ( N= 284)

HAA5 LRAA @ AVG1 ( N= 283)

HAA5 LRAA @ AVG2 ( N= 284)

HAA5 LRAA @ MAX ( N= 290) Exhibit 4.6a Cumulative Percentage of HAA5 LRAAs, All Plants in Compliance with 80/ 60 RAA ( Stage 1 MCL)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 14 70% 75% 80% 85% 90% 95% 100%

30 40 50 60 70 80 90 100 110 120 HAA5 LRAA, ug/ L Cumulative Percentage of Plants HAA5 LRAA @ DSE ( N= 256)

HAA5 LRAA @ AVG1 ( N= 255)

HAA5 LRAA @ AVG2 ( N= 256)

HAA5 LRAA @ MAX ( N= 262) Exhibit 4.6b Cumulative Percentage of HAA5 LRAAs, All Plants in Compliance with 64/ 48 RAA ( Stage 1 MCL with SF)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 15 4.3.3 Occurrence of Peak DBPs at Locations Other Than the DS Maximum The 1979 TTHM rule and Stage 1 DBPR monitoring locations must include a site reflecting maximum residence time in the distribution system with the intent of capturing the highest DBP levels in the distribution system. As described in Section 1.4.8, this location is referred to as the " DS Maximum" for the ICR data set. Analysis of the ICR data in this section show two important results: 1) the monitoring locations identified as the maximum residence time locations often did not represent those locations with the highest DBP levels and 2) the highest TTHM and HAA5 level often occurred at different points in the distribution system.

Exhibit 4.7 illustrates that the highest TTHM and HAA5 concentrations could be at any of the four ICR distribution system sample locations or, in some cases, at the finished water location. Exhibit 4.7 shows the frequency at which the maximum TTHM or HAA5 LRAA occurred at each distribution sampling location for all plants that are in compliance with the Stage 1 DBPR MCLs of 80/ 60 RAA. Results show that 52 percent of ICR plants have the highest TTHM LRAA concentration occurring at sites other than the maximum residence time monitoring site. The highest HAA5 LRAA occurred at the maximum residence time monitoring site in only 36 percent of the plants. For small surface water plants, the frequency at which the highest LRAA occurred at different locations can be analyzed using National Rural Water Association ( NRWA) data. Because the post Stage 1 data set was determined to be too small to produce meaningful results with respect to spatial and temporal variability of DBPs, the analysis was done for pre stage 1 conditions and presented in Chapter 3 ( Section 3.2). Results are similar to Exhibit 4.7   Exhibit 3.55 shows that 33 percent of NRWA plants have the highest TTHM LRAA concentration occurring at sites other than the maximum residence time monitoring site. The highest HAA5 LRAA occurred at the maximum residence time monitoring site in only 49 percent of the plants.

The occurrence patterns shown in Exhibit 4.7 may be due to several factors, such as HAA5 degrading over time in the distribution system, maximum residence time monitoring sites not actually representing the maximum residence time, or that using a simple estimation of maximum residence time cannot characterize a complex distribution system.

EPA also analyzed whether the highest LRAA for TTHM and HAA5 occurred at the same location. If TTHM and HAA5 occur at the same location rather than different locations, fewer monitoring sites would be needed to represent TTHM and HAA5 occurrence. However, this is not the case. The ICR and NRWA data sets, respectively indicate, that 49 percent and 38 percent of their plants in compliance with Stage 1 DBPR MCLs of 80/ 60 RAA experienced their highest LRAA TTHM and HAA5 concentrations at different locations in the distribution system. For plants that did have their highest LRAA TTHM and HAA5 concentrations at the same location, it was not necessarily the maximum residence time monitoring location. Exhibit 4.8 illustrates that for Stage 1 compliant ICR plants with the highest TTHM and HAA5 levels occurring at the same location, the highest TTHM and HAA5 LRAA simultaneously occurred at the maximum residence time monitoring location in 50 percent of the cases. Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 16 0% 10% 20% 30% 40% 50% 60%

FIN DSE AVG1 AVG2 MAX ICR Sampling Locations Percentage of Plants TTHM ( N= 290)

HAA5 ( N= 290) Exhibit 4.7 Frequency at Which Highest TTHM or HAA5 LRAAs Occurred at Each Sample Location for All ICR Plants in Compliance with 80/ 60 RAA ( Stage 1 MCL)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 4 17 Highest LRAA TTHM/ HAA5 Among Plants with Highest LRAA TTHM/ HAA5 at Same Location Maximum occurred at same location 51.4% of plants Maximum occurred at different locations for 48.6% of plants 8.7% @ FINISH 50.3% @ MAX 16.8% @ AVG1 15.4% @ AVG2 8.7% @ DSE Exhibit 4.8 Frequency at Which Highest TTHM or HAA5 LRAAs Occurred at the Same Location for All ICR Plants in Compliance with 80/ 60 RAA ( Stage 1 MCL)

Source: ICR AUX1 Database ( USEPA 2000d).

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

Excel File: ICR DBP Data, Pre Stage 2. xls Occurrence Assessment for the Stage 2 DBPR Proposal July 2003 5 1 5. References Aieta, E. M.; Berg, J. D. 1986. A review of chlorine dioxide in drinking water treatment. Journal of American Water Works Association 78( 6): 64 72. [ Stage 1 Occurrence]

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