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Fact Sheet:
Disinfection Profiling and
Benchmarking for LT1ESWTR
7/ie Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) was finalized January 14,
2002. LT1ESWTR requires public water systems that use surface water or ground water under the
direct influence of surface water and serve fewer than 10,000 people to evaluate their disinfection
practices through disinfection profiling and benchmarking.
WHAT is A DISINFECTION PROFILE? I
A disinfection profile summarizes the effectiveness
of your system's disinfection practices. Figure 1 is
a graphical representation of a system's levej of
inactivation (i.e., pathogens killed by disinfection)
of Giardia lamblia (and viruses if your system; uses
chloramines, ozone or chlorine dioxide for primary
disinfection) each week for a period of one year.
The disinfection profile does not need to be
submitted to the State. However, it must be
available for review during a sanitary survey.:
1.400 -,
1.200 -
| 1.000 -
| 0.800 -
| 0.600
=> 0.400
-1 0.200
0.000
Log hactivalion
8 12 16 20 24 28 32 36 40 44 48 52
Week Tested
Figure 1 - Example Disinfection Profile
Systems serving 500 to 9,999 people have to begin their disinfection profile by July 1, 2003. Systems serving
fewer than 500 people must start their profile by January 1, 2004. Systems are reminded that the State
may waive the profile requirement if a system can satisfy certain TTHM and HAAS criteria.
How is A DISINFECTION PROFILE DEVELOPED?
To develop a disinfection profile, a system
should start by identifying disinfection
segments. A disinfection segment is a
section of a treatment system beginning at
one disinfectant injection or monitoring
point and ending at the next disinfectant
injection or monitoring point. The final
disinfectant monitoring point must be
located before or at the first customer.
1 Disinfection Segment 1
Chlorine
Injected
/ /Intake » * ^^ft0 '"Tp1 Sedimentation
Dis
Sc
CM
I*
Filtration
\ \ Coagulation Floccutetion ^"^
; Disinfection Segment 1
Sampling Point
Cl 2 residual
' Temperature
' PH
I
I
I
I
I
Disinfection Segment
Sampling Point
CJ, residual
Temperature
pH
M
infecti
igmen
orine
wtad
I '
t-lfc pk
2 Sy
on
2
antes
ibutkm
stem
Figure 2 - A System with Two Disinfection Segments
Page 1
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jay each week, over the course ot one year, during peaK
to determine log inactivation for the treatment plant:
lourly flow,
> The residual disinfectant concentration ("C", in mg/L);
> Contact time T" in minutes (the time the water is in contact with
the disinfectant); AND
> At each residual disinfectant concentration sampling point:
Water temperature (in degrees Celsius) and
pH (only for systems using chlorine).
The contact time T (sometimes referred to as T10) is an estimate of the
detention time within a basin, pipe or other sub-unit (such as a
clearwell).
luring peak hourly flow from ;
disinfection segments using
analytical methods specified in
40CFRPart§141.74(a).
An electronic spreadsheet to assist
systems in calculating log
inactivation values and the
disinfection profile and benchmark
is posted on the EPA website
[http://www.epa.qov/safewater/mdbp
/Itleswtr.htmll.
HINT: Before measuring or calculating T, the system should review its own permits and/or other documents,
or contact the State to see if T has already been determined (e.g., historical records or a tracer study). If T is
already known, Steps 3 through 7 in the table below (used to calculate T) can be skipped.
The following 12-step approach may be used to calculate log inactivation for the treatment plant.
12 Suggested Steps to Calculating Weekly Giardia* Log Inactivation
Step
1
2
3
4
5
6
Action/Activity/Task
Determine the peak hourly flow in gallons/minute.
Measure the residual disinfectant concentration ("C", in
mg/L), temperature (in °C), and pH (if chlorine is used)
during peak hourly flow at the same sampling point and
time.
Measure the physical dimensions of the sub-unit (e.g.,
clearwell or pipe)
Measure the inner diameter, which will be used to
determine the volume of water in the sub-unit.
Measure the minimum operating depth in the sub-
unit to obtain a conservative estimate of water
depth in the sub-unit.
Calculate the volume of the water (in ft3) in the sub-unit
based on measurements in Step 3.
See Appendix F in the LT1 ESWTR Disinfection
Profiling and Benchmarking Technical Guidance
Manual for volume equations.
Calculate the Theoretical Detention Time (TDT)
TDT=V/Q.
Where V volume and Q peak hourly flow.
Remember to work in common units
(7.48 gallons = 1 cubic foot).
Determine the baffling factor (BF) for the sub-unit [see
the LT1 ESWTR Disinfection Profiling and
Benchmarking Technical Guidance Manual (Chapter 3
and Table 3-2) for information on baffling factors or
check with your State].
Step
7
8
g
10
11
12
Action/Activity/Task
Calculate the contact time of the disinfectant in the sub-
unit (Contact Time "T" = TDT x BF).
Determine CT^,,.. Where CT^ = CxT [C is residual
disinfectant concentration, measured in Step 2 (in
mg/L), and T is contact time, calculated in Step 7 (in
minutes)].
Locate CT table for 3-log Giardia inactivation based on
water temperature, pH, and residual disinfectant
concentration. See Appendix B in the LT1 ESWTR
Disinfection Profiling and Benchmarking Technical
Guidance Manual for the CT tables.
Obtain CTgggvaluefs) from the table in Step 9.
Where applicable, repeat steps 1 through 1 1 for each
disinfection segment.
For systems with one disinfection segment calculate log
inactivation = 3 x CT^JCT^ 9. For systems with two or
more disinfection segments, calculate log inactivation =
3 X ZCTcafc/CTggg WhCTO ZCTcaK/CTggg = UlB SUrtl Of Ul6
inactivation ratios for all disinfection segments.
"Systems using chloramines, ozone, or chlorine dioxide, as the primary disinfectant must also calculate virus log inactivation. For
more information on calculating virus log inactivation see the LT1 ESWTR Disinfection Profiling and Benchmarking Technical Guidance
Manual.
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\NHAT is THE NEXT STEP?
To complete the disinfection profile, the data must be retained in a graphic
form. Figure 3 is one example of how to plot weekly log inactivation values.
Disinfection profile data are calculated over the course of one year. The log
inactivations are plotted along the vertical axis corresponding to the weeks
of the year plotted along the horizontal axis. After the points are plotted,
lines are drawn to connect the points in order by the week tested.
WHAT is A DISINFECTION BENCHMARK?
1.30
Week Tested
(Horizontal Axis)
FIGURE 3 - GRAPHIC OF WEEKLY DATA
A disinfection benchmark must be determined by your system if:
> You had to develop a disinfection profile ANp
> You are considering making a significant change to your disinfection practices.
Your system must complete the disinfection profile and benchmark and consult with the State before making a
significant change to your disinfection practices^
The disinfection benchmark is a water system's'lowest monthly average log inactivation, and is determined
using the data collected weekly for the disinfectjon^profile. To determine the benchmark, the system must first
calculate the average log inactivation for each calendar month of the disinfection profile. The monthly average
log inactivation is calculated by adding the weekly log inactivation values for a particular month and dividing
that value by the number of weekly values for that particular month. The month with the lowest monthly
average log inactivation is the benchmark.
WHAT MUST A SYSTEM Do IF CONSIDERING A SIGNIFICANT CHANGE TO DISINFECTION PRACTICES?
Significant changes include: (a) Changes to the point of disinfection; (b) Changes to the disinfectants) used in
the treatment plant; (c) Changes to the disinfection process; or (d) Any 9ther modification identified by the
State. ;
If you are considering a significant change to disinfection practices your system must consult with the State for
approval and submit the following information to the State:
> A description of the proposed change; :
> The disinfection profile and benchmark;
> An analysis of how the proposed change will affect the current levels of disinfection; and
> Any additional information requested by the State.
WHERE CAN I GET MORE INFORMATION ON DISINFECTION PROFILING AND BENCHMARKING?
LT1ESWTR Disinfection Profiling and Benchmarking Technical Guidance Manual [EPA 816-R-03-
004]- This manual will provide information on the disinfection profiling and benchmarking process.
Detailed explanations and examples will be presented to assist system operators with performing the
disinfection profiling and benchmarking analyses (anticipated publication date is June 2003).
For general information or to obtain the document listed above, contact the Safe Drinking Water Hotline at
1-800-426-4791 or visit http://www.epa.gov/safewater/mdbp/lt1eswtr.html
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PLEASE LOOK INSIDE
Your water system might be affected by the
requirements of the new Long Term 1 Enhanced
Surface Water Treatment Rule.
Office of Water (4606M)
EPA816-F-03-007
www.epa.gov/safewater
March 2003
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