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 Stage 2 Disinfectant Disinfection Byproducts Drinking Water     Central District Highlights


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Stage 2 Disinfectant/Disinfection Byproducts

What are Disinfection Byproducts? Who does this rule apply to? What is required? Assistance


What are Disinfection Byproducts?

  • Disinfection Byproducts (DBPs) are chemicals formed as a result of the reaction between chlorine added to the water (for disinfection) and naturally occurring organic material already present in the water.


  • Rule 62-550.514 and 62-550.822, Florida Administrative Code requires public water systems adding a chemical disinfectant to their water to comply with the requirements of 40 CFR 141, subparts U (Stage 2 IDSE) and V (Stage 2 D/DBP).

Who does this rule apply to?

  • Community and non-transient non-community public water systems which add chemical disinfection to their water at any point in the water treatment process


  • Community and non-transient non-community public water systems that deliver water that has been treated with chemical disinfection.


What is required?

Suppliers of water must monitor:

1. Disinfectant Residuals

a. Continue to monitor in accordance with the Stage 1 D/DBP Rule.

2. Stage 1 Disinfection Byproducts

a. The first step to meeting this requirement is to identify when your system is required to begin Stage 2 sampling. Review Table 1 and based on your water system population (or the largest water system population if you are consecutive), identify your “Schedule”.

Table 1

Schedule Population Compliance Date
Schedule 1 >100,000 April 1, 2012
Schedule 2 50,00 - 99,999 October 1, 2012
Schedule 3 10,000 - 49,999 October 1, 2013
Schedule 4 <10,000 October 1, 2013


i. Please note that the dates listed in the right hand column are “compliance dates” not necessarily Stage 2 “start dates”. Your specific Stage 2 “start date” will be identified in your annual monitoring reminder schedule.

b. Complete a  Stage 2 Disinfectant/Disinfection Byproducts Rule Monitoring Plan  and have the Plan available for review during Department sanitary survey inspections and compliance inspections.

i. If your water system completed an Initial Distribution System Evaluation (IDSE), your IDSE will specify the required number and location(s) for sampling. In general, most water systems in the Central District will be commencing Stage 2 on “routine” monitoring. Routine monitoring requirements for ground water systems are listed in Table 2.

Table 2

Populations Number of Locations Monitoring frequency
<500 2 Annual
500 - 9,999 2 Annual
10,000 -99,999 4 Quarterly
100,000 - 499,999 6 Quarterly
>500,000 8 Quarterly

*Additional monitoring tables can be viewed in Subpart V

c. Completion of a sampling plan will require the designation of location(s) based on the population of your water system. These locations are to be places in the distribution system that represent high TTHM) and high HAA5 locations.

d. During your required monitoring period (quarterly, annual, or triennial), conduct Stage 2 DBP sampling in accordance with your sampling plan. All samples should be taken under normal operating conditions and at the midpoint between flushing events.

e. Compliance with the MCLs is calculated based on Locational Running Annual Averages (LRAAs). Water systems will be required to calculate LRAAs for each monitoring location. You may not average locations together. If there is an MCL violation at one location, then the entire water system is in violation of the MCL.

f. Systems with a population of 10,000 or greater must submit a Disinfectant Byproduct Report quarterly, or annually, depending on sampling frequency.   This report will indicate current DBP averages.

3. Additional Monitoring Requirements

a. Systems which ozonate must test for Bromate monthly (point of entry sample).

b. Total Organic Carbon (TOC) and alkalinity monitoring is required monthly to demonstrate compliance with the treatment technique requirements for surface water systems that are using conventional filtration treatment.

4. Operational Evaluation Levels (OELs)

a. This is an early warning system built into the Stage 2 Rule. An OEL exceedance may indicate a potential DBP or treatment process problem. OELs are set at the same level as the MCLs for TTHMs and HAA5s (80 and 60 ug/L). They are calculated as follows:

OEL = ((2 * A) + B + C) / 4

A = TTHM or HAA5 results for the current quarter;

B = TTHM or HAA5 results for the previous quarter;

C = TTHM or HAA5 results for the quarter before the previous quarter.

b. If an OEL is exceeded you must submit an OEL Report to the Department. Unless the water system requests and the Department approves limitations of scope, the report must consist of an examination of system treatment and distribution system operational practices:

 i. Storage tank operations;

 ii. Excess storage capacity;

 iii.  Distribution system flushing,

 iv. Changes in sources or source water quality and;

 v. Treatment changes or problems that may contribute to TTHM and HAA5 formation including what steps could be considered to minimize future exceedances.

c. An OEL report will not be required if all of the following criteria are met:

i. No MCL violation has occurred; and

ii. The OEL exceedance occurs in the third calendar quarter; and

iii. The OEL for TTHM does not exceed 100 ug/L and the OEL for HAA5 does not exceed 75 ug/L 

5. Reporting Results

a. Results of all sampling shall be reported to the Department by the 10th of the month following the end of the monitoring period or by the 10th of the month following the month in which your results were received, whichever is soonest.

b. Results shall be reported on Department approved formats

i. Stage 2 Reporting Format [557 kb]

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