Page 1 of 4 Fact Sheet: Disinfection Profiling and Benchmarking

The process consists of the following 3 steps:

Ø Determining if a PWS must develop a disinfection profile—§141.172 (a)

Ù Developing the disinfection profile—§141.172 (b)

Ú Calculating the disinfection benchmark and consulting with the state—§141.172 (c) 

United States Office of Ground Water EPA 816-F-98-017b 

Environmental Protection and Drinking Water December 16, 1998

Agency Washington, DC 20460

Fact Sheet: 

Disinfection Profiling and

Benchmarking

The Interim Enhanced Surface Water Treatment Rule

(IESWTR) requires certain public water systems (PWSs) to

evaluate their disinfection practices and work with the state

to assure there are no unintended reductions in microbial

protection

Is your PWS affected?

Your PWS is affected if it is a surface water or GWUDI* system that—

1. Serves 10,000 or more people; and,

2. Has Total Trihalomethanes $ 0.064 mg/L or Haloacetic Acids $ 0.048 mg/L. 

* Ground water under the direct influence (of surface water)
Fact Sheet: Disinfection Profiling and Benchmarking Page 2 of 4

Ø Determining if a PWS Must Develop a Disinfection Profile

How can a PWS determine if it must develop a disinfection profile?

A PWS determines if it must establish a disinfection profile using 4 consecutive quarters of TTHM and HAA5 data. If the

PWS has an annual average level of TTHM $ 0.064 mg/L or an annual average level of HAA5 $ 0.048mg/L, it must then

develop a disinfection profile. 

Alternatively, a PWS may choose to develop a disinfection profile and not collect these data.

How should a PWS collect TTHM and HAA5 data?

‘ Most PWSs serving 100,000 or more people have collected TTHM and HAA5 data under the 1996 Information

Collection Rule (ICR). These systems must use these data (from calendar year 1998) to determine if they must profile,

unless the state determines there is a more representative data set for them to use. PWSs must submit these data to the

state no later than December 1999 (Timeline Milestone ã).

‘ A PWS that has not collected data under the ICR but has 4

consecutive quarters of TTHM compliance data and HAA5

occurrence data may use these data to determine if it must

profile. The PWS must submit these data to the state for

approval no later than April 1999 (Timeline Milestone â). 

‘ A PWS that has no data or inadequate data for TTHM and HAA5 should collect 4 consecutive quarters of data. The

PWS should submit these data to the state and determine whether or not to develop a disinfection profile no later than

March 2000 (Timeline Milestone ä).

What are the monitoring requirements for TTHM and HAA5 data?

‘ TTHM and HAA5 data must be collected during the same quarter.

‘ For TTHM, samples must be taken in accordance with current TTHM monitoring requirements under 

40 CFR 141.12 and 141.30. For HAA5, at least 4 samples must be taken per plant per quarter in accordance with 

routine monitoring requirements under 40 CFR 141.12 and 141.30.

‘ At least 25 percent of the samples for TTHM and HAA5 shall be taken at locations within the distribution system

reflecting maximum residence time of the water in the system.

‘ The remaining 75 percent of the samples for TTHM and HAA5 shall be taken at representative locations in the

distribution system, taking into account the number of people served, the different sources of water, and the

different treatment methods employed.

‘ Analytical Methods and Handling Requirements

TTHM: EPA 502.2 HAA5: EPA 552.1

EPA 524.2 EPA 552.2

EPA 551 Std. 6251 B

Which labs may conduct analyses for HAA5?

‘ Any lab that received approval under the 1996 ICR

‘ Any lab using ICR-approved methods
Page 3 of 4 Fact Sheet: Disinfection Profiling and Benchmarking

April 1999 December 1999

1 2

March 2001

3

March 2000

Timeframe for collecting 4 consecutive 

quarters of TTHM and HAA5 data

Timeframe for collecting 12 months of disinfection profiling data

Publication

December 16, 1998

Timeline

4

Ù Developing the Disinfection Profile

How does a PWS develop a disinfection profile?

‘ The disinfection profile is developed by compiling daily Giardia lamblia log inactivations computed over a period of 12

months. In addition, a disinfection profile for daily virus log inactivations must be developed for PWSs that use either

chloramines or ozone for primary disinfection. The log inactivation values are calculated using daily measurements of

operational data collected during peak-hour flows. This disinfection profiling must be completed no later than March

2001 (Timeline Milestone å).

‘ A PWS that has 3 years of existing operational data may use these data to develop a disinfection profile as long as the

state has determined that these data are substantially equivalent to data that would be collected under the IESWTR.

‘ The PWS must keep the disinfection profile on file to be reviewed during its Sanitary Survey.

Ú Calculating the Disinfection Benchmark and Consulting with the State

A PWS required to develop a disinfection profile that subsequently decides to make a significant modification to its

disinfection practice must calculate a disinfection benchmark and consult with the state prior to implementing such a change.

The state consultation process helps assure that the PWS will meet the new disinfection byproduct standards without

compromising protection from microbial contaminants.

How does a PWS calculate a disinfection benchmark?

A disinfection benchmark is an indicator of disinfection effectiveness and depends upon the inactivation of Giardia lamblia

(or viruses). The benchmark is determined by calculating the average daily inactivation value for each of 12 consecutive

months. The lowest monthly average becomes the disinfection benchmark. If the system has data from more than 1 year, it

repeats this calculation for each year. The benchmark is the average of the lowest month’s value for each of the years.

What are significant modifications to a disinfection practice?

Significant modifications to disinfection practices include:

‘ Changes to the point of disinfection ‘ Changes to the disinfectant(s) used in the treatment plant

‘ Changes to the disinfection process ‘ Any other modification identified by the state
Fact Sheet: Disinfection Profiling and Benchmarking Page 4 of 4

PLEASE LOOK INSIDE:

Your water system is expected to

be affected by the requirements of

the new IESWTR

United States

Environmental Protection Agency

(4101)

Washington, DC 20460

Official Business

Penalty for Private Use

$300 

Bulk Rate

Postage and Fees Paid

EPA

G-35

More information can be obtained from:

L Your state’s primacy agency

L The EPA Safe Drinking Water Hotline, Telephone: 1.800.426.4791