United States               Office of Ground Water          EPA 816-F-98-017b
                      Environmental Protection         and Drinking Water            December 16, 1998
                      Agency                  Washington, DC 20460

    vvEPA      Fact Sheet:

                     Disinfection Profiling and


                      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

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.
       The process consists of the following 3 steps:

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

         • Developing the disinfection profile—§ 141.172 (b)

         • Calculating the disinfection benchmark and consulting with the state—§141.172 (c)
* Ground water under the direct influence (of surface water)
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•   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 HAAS data. If the
PWS has an annual average level of TTHM • 0.064 mg/L or an annual average level of HAAS •  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 HAAS data?

•   Most PWSs serving 100,000 or more people have collected TTHM and HAAS 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 • ).
    A PWS that has not collected data under the ICR but has 4
    consecutive quarters of TTHM compliance data and HAAS
    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 •  ).
                                         Which labs may conduct analyses for HAAS?

                                         •   Any lab that received approval under the 1996 ICR

                                         •   Any lab using ICR-approved methods
    A PWS that has no data or inadequate data for TTHM and HAAS 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 • ).
     What are the monitoring requirements for TTHM and HAAS data?

     •   TTHM and HAAS 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 HAAS, 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 HAAS 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 HAAS 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
EPA  502.2
EPA  524.2
EPA  551
EPA  552.1
EPA  552.2
Std.   625 IB
Fact Sheet: Disinfection Profiling and Benchmarking
                                                                              Page 2 of 4

                             Timeframe for collecting 4 consecutive
                               quarters ofTTHMandHAAS data
    December 16, 1998
                         April 1999                 December 1999    March 2000                          March 2001|

                                       Timeframe for collecting 12 months of disinfection profiling data
    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 • ).

    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.

•   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
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Your water system is expected to
be affected by the requirements of
the new IESWTR
       More information can be obtained from:

          Your state's primacy agency
          The EPA Safe Drinking Water Hotline, Telephone: 1.800.426.4791
 United States
 Environmental Protection Agency
 Washington, DC 20460
 Official Business
 Penalty for Private Use
Bulk Rate
Postage and Fees Paid
Fact Sheet: Disinfection Profiling and Benchmarking
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