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Virginia Administrative Code
Title 12. Health
Agency 5. Department of Health
Chapter 590. Waterworks Regulations
8/15/2022

12VAC5-590-374. Residual disinfectant, disinfection byproducts, and disinfection byproduct precursors monitoring.

A. Unless otherwise noted, an owner of a waterworks that uses a chemical disinfectant shall comply with the requirements of this section as follows:

1. The owner of a community waterworks or a NTNC shall comply with this section.

2. The owner of a TNC that uses any combination of a surface water source, a GUDI source, or a groundwater source and uses chlorine dioxide as a disinfectant or oxidant shall comply with all the requirements for chlorine dioxide in this section.

B. The owner shall collect all samples during normal operating conditions.

1. Analysis under this section for DBPs (TTHM, HAA5, chlorite, and bromate) shall be conducted by laboratories that have received certification by EPA or DCLS as specified in 12VAC5-590-440, except as noted in subdivisions B 2 and B 3 of this section.

2. Measurement under this section of daily chlorite samples at the entry point to the distribution system, residual disinfectant (free chlorine, combined chlorine, total chlorine, and chlorine dioxide), alkalinity, bromide, TOC, SUVA (DOC and UV254), pH, and magnesium shall be made by a party approved by the department.

3. Residual disinfectant concentrations for free chlorine, combined chlorine, total chlorine, and chlorine dioxide shall be made using equipment deemed satisfactory by the department.

C. Monitoring plan. The owner required to monitor under this section shall develop and implement a monitoring plan. The owner shall maintain the plan and make it available for inspection by the department and the general public. The owner of a community waterworks or a NTNC that uses a surface water source, a GUDI source, or both and serves more than 3,300 people shall submit a copy of the monitoring plan to the department no later than the date of the first report required under 12VAC5-590-531 A. The department may also require the plan to be submitted by any other owner. After evaluation, the department may require changes in any of the plan elements. The plan shall include at least the following:

1. Specific locations and schedules with monitoring dates for collecting samples for any parameters included in this section.

2. How the owner will calculate compliance with PMCLs, MRDLs, and treatment techniques.

3. The sampling plan for a consecutive waterworks shall reflect the entire consecutive distribution system.

4. All new waterworks shall comply with the monitoring location requirements of 40 CFR 141 Subpart U, Initial distribution system evaluations, in the development of the waterworks monitoring plan.

D. Failure to monitor in accordance with the monitoring plan required under subsection C of this section is a monitoring violation. Failure to monitor shall be treated as a violation for the entire period covered by the annual average where compliance is based on an RAA of monthly or quarterly samples or averages, and the owner's failure to monitor makes it impossible to determine compliance with PMCLs or MRDLs.

E. The owner may use only data collected under the provisions of this section to qualify for reduced monitoring.

F. TTHM and HAA5 monitoring. The owner of a community waterworks or a NTNC shall conduct the LRAA monitoring for TTHM and HAA5 at the frequency given below, unless otherwise indicated.

1. This subdivision establishes monitoring and other requirements for achieving compliance with PMCLs based on the LRAA for TTHM and HAA5, and for achieving compliance with MRDLs for chlorine and chloramines for certain consecutive waterworks.

2. This subdivision applies to a community waterworks or a NTNC that uses a primary or secondary disinfectant other than UV light or delivers water that has been treated with a primary or secondary disinfectant other than UV light.

3. Routine monitoring.

a. If the waterworks is a NTNC serving fewer than 10,000 people, then the owner shall monitor at the location or locations and dates identified in the monitoring plan in subsection C of this section, updated as required by subdivision F 3 e of this section.

b. The owner shall monitor at no fewer than the number of locations identified in Table 374.1:

TABLE 374.1

Monitoring Frequency by Source Water Type for TTHM and HAA5

SOURCE WATER TYPE

POPULATION SIZE CATEGORY

MONITORING FREQUENCYa

DISTRIBUTION SYSTEM MONITORING LOCATION TOTAL PER MONITORING PERIODb

Surface water or GUDI Source

Less than 500

per year

2

500 - 3,300

per quarter

2

3,301 - 9,999

per quarter

2

10,000 - 49,999

per quarter

4

50,000 - 249,999

per quarter

8

250,000 - 999,999

per quarter

12

1,000,000 - 4,999,999

per quarter

16

Equal to or greater than 5,000,000

per quarter

20

Groundwater

Less than 500

per year

2

500 - 9,999

per year

2

10,000 - 99,999

per quarter

4

100,000 - 499,999

per quarter

6

Equal to or greater than 500,000

per quarter

8

aThe owner shall monitor during the month of highest DBP concentrations.

bThe owner of a waterworks on quarterly monitoring (except those using a surface water source, a GUDI source, or both and serving 500 to 3,300 people) shall collect dual sample sets every 90 days at each monitoring location. A groundwater system serving 500 to 9,999 people shall collect dual sample sets annually at each monitoring location. A waterworks serving fewer than 500 people and a waterworks using a surface water source, a GUDI source, or both and serving 500 to 3,300 people shall collect individual TTHM and HAA5 samples (instead of a dual sample set) at the locations with the highest TTHM and HAA5 concentrations, respectively. A waterworks serving fewer than 500 people shall sample annually, and a waterworks using a surface water source, a GUDI source, or both and serving 500 to 3,300 people shall sample every 90 days. For a waterworks serving fewer than 500 people, only one location with a dual sample set per monitoring period is needed if the highest TTHM and HAA5 concentrations occur at the same location (and month, if monitoring annually).

c. The owner of a waterworks not using disinfection that then begins using a disinfectant other than UV light shall consult with the department to identify compliance monitoring locations. The owner shall develop a monitoring plan under subdivision F 3 e of this section to include those monitoring locations.

d. The owner shall use an approved method listed in 12VAC5-590-440 for TTHM and HAA5 analyses. Analyses shall be conducted by laboratories that have received certification by EPA or DCLS as specified in 12VAC5-590-440.

e. The owner may revise the monitoring plan to reflect changes in treatment, distribution system operations and layout (including new service areas), or other factors that may affect TTHM or HAA5 formation, or for reasons approved by the department after consultation with the department regarding the need for changes and the appropriateness of the changes. If the owner changes monitoring locations, then the owner shall replace existing compliance monitoring locations with the lowest LRAA with new locations that reflect the current distribution system locations with expected high TTHM or HAA5 levels. The department may also require modifications in the monitoring plan. The owner of a waterworks using a surface water source, a GUDI source, or both and serving more than 3,300 people shall submit a copy of the modified monitoring plan to the department before the date the owner is required to comply with the revised monitoring plan.

4. Reduced monitoring.

a. The owner may reduce monitoring to the level specified in Table 374.2 any time the LRAA is less than or equal to 0.040 mg/L for TTHM and less than or equal to 0.030 mg/L for HAA5 at all monitoring locations. The owner may only use data collected under the provisions of this section to qualify for reduced monitoring. In addition, the source water annual average TOC level, before any treatment, shall be less than or equal to 4.0 mg/L at each water treatment plant treating a surface water source, a GUDI source, or both based on monitoring conducted under subsection J of this section.

TABLE 374.2

Reduced Monitoring for TTHM and HAA5

SOURCE WATER TYPE

POPULATION SIZE CATEGORY

MONITORING FREQUENCYa

DISTRIBUTION SYSTEM MONITORING LOCATION PER MONITORING PERIOD

Surface water or GUDI Source

Less than 500

Monitoring may not be reduced.

500 - 3,300

per year

One TTHM and one HAA5 sample: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement; one dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

3,301 - 9,999

per year

Two dual sample sets: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement.

10,000 - 49,999

per quarter

Two dual sample sets: at the locations with the highest TTHM and highest HAA5 LRAAs.

50,000 - 249,999

per quarter

Four dual sample sets: at the locations with the two highest TTHM and two highest HAA5 LRAAs.

250,000 - 999,999

per quarter

Six dual sample sets: at the locations with the three highest TTHM and three highest HAA5 LRAAs.

1,000,000 - 4,999,999

per quarter

Eight dual sample sets: at the locations with the four highest TTHM and four highest HAA5 LRAAs.

Equal to or greater than 5,000,000

per quarter

Ten dual sample sets: at the locations with the five highest TTHM and five highest HAA5 LRAAs.

Groundwater

Less than 500

every third year

One TTHM and one HAA5 sample: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement; one dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

500 - 9,999

per year

One TTHM and one HAA5 sample: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement; one dual sample set per year if the highest TTHM and HAA5 measurements occurred at the same location and quarter.

10,000 - 99,999

per year

Two dual sample sets: one at the location and during the quarter with the highest TTHM single measurement, one at the location and during the quarter with the highest HAA5 single measurement.

100,000 - 499,999

per quarter

Two dual sample sets: at the locations with the highest TTHM and highest HAA5 LRAAs.

Equal to or greater than 500,000

per quarter

Four dual sample sets: at the locations with the two highest TTHM and two highest HAA5 LRAAs.

aThe owner of a waterworks on quarterly monitoring shall collect dual sample sets every 90 days.

b. The owner may remain on reduced monitoring as long as the TTHM LRAA is less than or equal to 0.040 mg/L and the HAA5 LRAA is less than or equal to 0.030 mg/L at each monitoring location (for waterworks with quarterly reduced monitoring) or each TTHM sample is less than or equal to 0.060 mg/L and each HAA5 sample is less than or equal to 0.045 mg/L (for waterworks with annual or less frequent monitoring). In addition, the source water annual average TOC level, before any treatment, shall be less than or equal to 4.0 mg/L at each water treatment plant treating a surface water source or a GUDI source, based on monitoring conducted under subsection J of this section.

c. If the LRAA based on quarterly monitoring at any monitoring location exceeds either 0.040 mg/L for TTHM or 0.030 mg/L for HAA5 or if the annual (or less frequent) sample at any location exceeds either 0.060 mg/L for TTHM or 0.045 mg/L for HAA5, or if the source water annual average TOC level, before any treatment, is greater than 4.0 mg/L at any water treatment plant treating a surface water source, a GUDI source, or both then the owner shall resume routine monitoring under subdivision F 3 of this section or begin increased monitoring if subdivision F 5 of this section applies.

d. A waterworks may return to routine monitoring at the department's discretion.

5. Increased monitoring.

a. The owner of a waterworks required to monitor at a particular location annually or less frequently than annually under subdivision F 3 or F 4 of this section, shall increase monitoring to dual sample sets once per quarter (collected every 90 days) at all locations if a TTHM sample is greater than 0.080 mg/L or a HAA5 sample is greater than 0.060 mg/L at any location.

b. The owner may return to routine monitoring once the waterworks has conducted increased monitoring for at least four consecutive quarters and the LRAA for every monitoring location is less than or equal to 0.060 mg/L for TTHM and less than or equal to 0.045 mg/L for HAA5.

G. Chlorite. The owner of a community waterworks or a NTNC using chlorine dioxide, for disinfection or oxidation, shall conduct monitoring for chlorite.

1. Routine monitoring.

a. The owner shall collect daily samples at the entry point to the distribution system. For any daily sample that exceeds the chlorite PMCL listed in Table 340.6, the owner shall collect additional samples in the distribution system the following day at the locations required by subdivision G 1 c of this section, in addition to the sample required at the entrance to the distribution system.

b. The owner shall collect a three-sample set each month in the distribution system. The owner shall collect one sample at each of the following locations: near the first customer, at a location representative of average residence time, and at a location reflecting maximum residence time in the distribution system. Any additional routine sampling shall be conducted in the same manner (as three-sample sets, at the specified locations). The owner may use the results of additional monitoring conducted under subdivision G 1 c of this section to meet the requirement for monitoring in this subdivision G 1 b.

c. On each day following a routine sample monitoring result that exceeds the chlorite PMCL listed in Table 340.6 at the entrance to the distribution system, the owner is required to collect three chlorite distribution system samples at the following locations: as close to the first customer as possible, in a location representative of average residence time, and as close to the end of the distribution system as possible (reflecting maximum residence time in the distribution system).

2. Reduced monitoring.

a. Chlorite monitoring at the entrance to the distribution system required by subdivision G 1 a of this subsection may not be reduced.

b. Chlorite monitoring in the distribution system required by subdivision G 1 b of this section may be reduced to one three-sample set per quarter after one year of monitoring where no individual chlorite sample collected in the distribution system under subdivision G 1 b of this section has exceeded the chlorite PMCL listed in Table 340.6 and the owner has not been required to conduct monitoring under subdivision G 1 c of this section. The owner may remain on the reduced monitoring schedule until either any of the three individual chlorite samples collected quarterly in the distribution system under subdivision G 1 b of this section exceeds the chlorite PMCL or the owner is required to conduct monitoring under subdivision G 1 c of this section, at which time the owner shall revert to routine monitoring.

H. Bromate.

1. The owner of a community waterworks or a NTNC water treatment plant using ozone for disinfection or oxidation shall collect one sample per month and analyze it for bromate. The owner shall collect samples monthly at the entrance to the distribution system while the ozonation system is operating under normal conditions.

2. The owner required to analyze for bromate may reduce monitoring from monthly to quarterly if the waterworks RAA bromate concentration is less than or equal to 0.0025 mg/L based on monthly bromate measurements under subdivision H 1 of this section for the most recent four quarters. If a waterworks has qualified for reduced bromate monitoring under this subdivision, then the owner may remain on reduced monitoring as long as the RAA of quarterly bromate samples is equal to or less than 0.0025 mg/L. If the RAA bromate concentration is greater than 0.0025 mg/L, then the owner shall resume routine monitoring required by subdivision H 1 of this section.

I. Monitoring requirements for the residual disinfectant.

1. Chlorine and chloramines.

a. The owner of a waterworks that uses chlorine or chloramines shall measure the residual disinfectant level in the distribution system at the same point in the distribution system and at the same time as total coliform bacteria are sampled, as specified in 12VAC5-590-370 A and 12VAC5-590-380 D. The owner of a waterworks using a surface water source, a GUDI source, or both may use the results of the residual disinfectant concentration sampling found in 12VAC5-590-376 D instead of collecting separate samples.

b. Residual disinfectant level monitoring may not be reduced.

2. Chlorine dioxide.

a. The owner of a waterworks that uses chlorine dioxide for disinfection or oxidation shall collect daily samples at the entrance to the distribution system. For any daily sample that exceeds the MRDL listed in Table 340.7, the owner shall collect samples in the distribution system the following day at the locations required by subdivision I 2 b of this section, in addition to the sample required at the entrance to the distribution system.

b. On each day following a routine sample monitoring result that exceeds the MRDL listed in Table 340.7, the owner is required to collect three chlorine dioxide distribution system samples. If chlorine dioxide or chloramines are used to maintain a residual disinfectant in the distribution system, or if chlorine is used to maintain a residual disinfectant in the distribution system and there is no rechlorination after the entry point, then the owner shall collect three samples as close to the first customer as possible, at intervals of at least six hours. If chlorine is used to maintain a residual disinfectant in the distribution system and there are one or more rechlorination points after the entry point, then the owner shall collect one sample at each of the following locations: as close to the first customer as possible, in a location representative of average residence time, and as close to the end of the distribution system as possible (reflecting maximum residence time in the distribution system).

c. Chlorine dioxide monitoring may not be reduced.

3. Ozone. Ozone residual levels shall be monitored continuously and recorded. A portable ozone meter is recommended as a backup.

4. Additional monitoring and reporting requirements are specified in 12VAC5-590-500 to demonstrate log inactivation or removal of Giardia lamblia, virus, and Cryptosporidium.

J. Monitoring requirements for DBPPs.

1. The owner of a community waterworks or a NTNC using a surface water source, a GUDI source, or both and using conventional filtration treatment, as defined in 12VAC5-590-10, shall monitor each water treatment plant for TOC no later than the point of CFE turbidity monitoring and representative of the treated water. The owner shall also monitor for TOC in the source water before any treatment at the same time as monitoring for TOC in the treated water. These samples (source water and treated water) are referred to as paired samples. At the same time as the source water sample is collected, the owner shall monitor for alkalinity in the source water before any treatment. The owner shall collect one paired sample and one source water alkalinity sample per month per water treatment plant at a time representative of normal operating conditions and influent water quality.

2. The owner of a community waterworks or a NTNC that uses a surface water source, a GUDI source, or both with an average treated water TOC of less than 2.0 mg/L for two consecutive years, or less than 1.0 mg/L for one year, may reduce monitoring for both TOC and alkalinity to one paired sample and one source water alkalinity sample per water treatment plant per quarter. The owner shall revert to routine monitoring in the month following the quarter when the annual average treated water TOC is equal to or greater than 2.0 mg/L.

Statutory Authority

§§ 32.1-12 and 32.1-170 of the Code of Virginia.

Historical Notes

Derived from Virginia Register Volume 37, Issue 20, eff. June 23, 2021.

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