Public Water Systems Using Chlorine Dioxide or Ozone

Chlorine Dioxide and Chlorite

Chlorine dioxide can be used in the treatment of drinking water to improve taste, odor, and color, remove iron and manganese, and inactivate chlorine resistant microorganisms. Systems may choose to use chlorine dioxide because it's less likely to form DBPs in comparison to free chlorine. All systems that use chlorine dioxide must monitor for chlorine dioxide and chlorite. TCEQ regulatory guidance,  Monitoring, Analyzing, and Reporting Chlorine Dioxide and Chlorite (RG-503)  contains detailed information for systems related to requirements and procedures for the monitoring, analysis, reporting, and compliance with chlorine dioxide rules and regulations.

Ozone and Bromate

Bromate is a DBP that can form when ozone is used to treat water containing bromide. All community and non-transient, non-community public water systems that use ozone must monitor for bromate. TCEQ regulatory guidance, Monitoring, Analyzing, and Reporting Bromate for Public Water Systems Using Ozone (RG-544) contains detailed information for systems related to requirements and procedures for the monitoring, analysis, reporting, and compliance with bromate rules and regulations.

Monitoring Frequency of Analytes by Water System Location

Treatment	Sampling Location	Monitor For	Frequency
Chlorine Dioxide	Entry Point	Chlorine Dioxide	Daily
Chlorine Dioxide	Entry Point	Chlorite	Daily
Ozone	Entry Point	Bromate	Monthly
Chlorine Dioxide	Distribution	Chlorine Dioxide	In the event of a daily exceedance
Chlorine Dioxide	Distribution	Chlorite	Monthly and in the event of a daily exceedance

Systems Using Chlorine Dioxide

Monthly monitoring

Monthly chlorite monitoring in the distribution system requires a three-sample set for every entry point providing chlorine dioxide treated water. Collect samples from:

1. a location near the first customer;
2. a location representative of the average residence time; and
3. a location representative of the maximum residence time.

Each set must be collected when chlorine dioxide is in use and on the same day.

Daily Monitoring

All systems that use chlorine dioxide must monitor daily for chlorine dioxide and chlorite at the entry point. For any daily chlorine dioxide level that exceeds 0.8 mg/L, systems must collect three chlorine dioxide samples in the distribution system.

Sample Locations and Timing

If you have a chlorination facility in the distribution system, sample:

1. the service connection nearest the treatment plant two hours after the exceedance,
2. the first service connection after the point where water is re-chlorinated 6 hours after the exceedance, and
3. near the end of the distribution system 8 hours after the exceedance.

If you don't have a chlorination facility in the distribution system:

Additional samples must be taken at the service connection nearest the treatment plant at two-, six-, and eight-hour intervals.   

Daily chlorite and chlorine dioxide samples must be analyzed at an approved facility. Contact the Drinking Water Quality Team at 512-239-4691 to check your status as an approved facility. You can find the approval form at Public Water System Monitoring Plans.  

Monthly chlorite samples, the three sample set(s), must be analyzed at an accredited facility. Check Drinking Water Watch to ensure TCEQ has the correct chlorite distribution locations.  

Violations

Chlorine Dioxide MRDL 

If your system exceeds 0.8 mg/L on a daily chlorine dioxide sample, and:

• if follow-up chlorine dioxide samples are not collected = Acute maximum residual disinfectant level (MRDL),
• if chlorine dioxide samples are collected and any sample is over 0.8 mg/L = Acute MRDL,
• chlorine dioxide samples are collected and none exceed 0.8 mg/L = Non-acute MRDL

Chlorite MCL

The average of the three sample set exceeds 1.0 mg/L = a chlorite maximum contaminant level violation.

Bromate MCL 

If, at the end of any quarter, the running annual average of monthly averages, computed quarterly, exceeds 0.010 mg/L bromate = bromate MCL violation.

Monitoring and Reporting Violation

• Failure to monitor for bromate, chlorine dioxide, or chlorite,
• Failure to mail the chlorine dioxide monthly operating report (CLO2 MOR) and distribution chlorite results to TCEQ by the tenth day of the month following the end of the monitoring period, or
• Failure to mail bromate results to TCEQ by the tenth day of the quarter following the end of the monitoring period.

Reporting Requirements

Mail the CLO2 MOR and distribution chlorite results to TCEQ by the 10th day of the following month. Systems that did not use chlorine dioxide for one month are still required to mail a CLO2 MOR. Complete the required Chlorine Dioxide Monthly Operating Report (CLO2MOR), TCEQ Form 00690 to record the ClO₂ test results  using these CLO2MOR instructions.

Bromate results must be submitted by the 10th day of the month following the monitoring period.

Send to:

Regular mail:

TCEQ
MC-155, Attn: Chlorine Dioxide or Bromate
PO BOX 13087
Austin, TX 78711-3087 

Certified mail:

TCEQ
MC-155, Attn: Chlorine Dioxide or Bromate
12100 Park 35 Circle
Austin, TX 78753

Public Notice

All public notices for chlorine dioxide violations can be found at Public Notice Language for Drinking Water Compliance.

To see chlorite and bromate results visit Drinking Water Watch.

For help navigating the website please contact the Drinking Water Quality Team at (512) 239-4691 or PWSChem@tceq.texas.gov.