United States
Environmental Protection Office of Water EPA/815-F-97 OO2
4607 November 1997
Treatment Study Fact Sheet: The
v>EPA Simulated Distribution System Test
The purpose of the ICR Treatment Studies is to evaluate the ability of GAG and membranes to
remove DBF precursors. The removal of precursors to specific DBFs is assessed by chlorinating feed and
effluent samples to/from the advanced process under simulated distribution system (SDS) conditions and
measuring the concentrations of DBFs formed under these conditions. Thus, careful attention to the SDS
test is a key step towards ensuring that useful data is generated during the ICR Treatment Studies The
purpose of this fact sheet is to summarize important aspects of the procedure in order to assist utilities
labs and consultants in conducting SDS tests.
SDS Sample Collection: Both feed and effluent samples are collected for SDS testing Feed
samples are collected prior to the GAG or membrane process but after all pretreatment processes fe e
prior to entering the first stage of a pilot-scale membrane system, but after the addition of acid and
antiscalant and after cartridge filtration). Effluent samples are collected immediately after the GAG or
membrane process. Samples should be collected in clean glass containers with Teflon lined caps The
«T^°UeCted for each SDS sample must ** large Qmn& to generate samples for TOX THM4
HAA6(9), chlorine residual and pH measurement; and if a chlorine demand test will be conducted prior to
the actual SDS test, the sample volume must include the volume necessary to perform the demand study.
SDS Sample Storage Prior to Dosing: During the course of a treatment study it will likely be
necessary to store the SDS samples for a short period of time prior to dosing the sample with chlorine and
starting the actual SDS test. Storage may be necessary to allow time to conduct a chlorine demand study
or to obtain TOG results. However, there is always the potential for sample degradation during storage
due to microbial activity, light, etc. To minimize the change in sample characteristics due to degradation
the sample should be dosed as soon as possible after it is collected, and the sample should not be stored '
longer than five working days. In order to preserve sample integrity during storage, it should be placed
in a 4 C refrigerator immediately after collection and kept there until the SDS test is performed Prior to
dosing the sample, it should be adjusted to a temperature close to the SDS incubation temperature The
sample should be left at ambient pH during storage.
SDS Test Parameters: Four parameters must be selected to perform a SDS test for the ICR
Treatment Studies: incubation time, incubation temperature, sample pH prior to dosing, and the free
chlorine residual at the end of incubation. These test parameters should be selected to represent the
conditions at the average distribution system residence time at the time of the SDS test (For quarterly
studies, the SDS conditions should be based on the average conditions at me average distribution system
residence time during the quarter in which the SDS tests are being performed). Note: It is important
to chlorinate feed/effluent sample pairs under similar SDS conditions since direct comparisons will be
made between the feed/effluent DBFs. Also, for quarterly studies, it is important to keep the SDS test
conditions constant over the quarter to allow comparison among different sample sets.
The Incubation Time used in the SDS test should be equivalent to the average residence time in
distribution system during the quarter in which the SDS test is being conducted. Furthermore the
SDS aliquot should be incubated hi a headspace free container in the dark
The Incubation Temperature used in the SDS test should be equivalent to the water temperature in
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^distribution system (at a point representative of the average distribution system residence time)
during the quarter in which the SDS test is being conducted.
11716 PH Prior & Dosing used hi the SDS test should be equivalent to the pH hi the distribution
system fcf 2 point representative of the average distribution system residence tune) during the
quarter in which the SDS test is being conducted. In general, the pH prior to dosing and the pH at
the end of incubation should be comparable in a buffered system. In some cases, it may be
necessary to buffer the sample pH prior to dosing using a phosphate, borate or carbonate buffer
system.
ff free chorine is used as the residual disinfectant in the distribution system, then the Free
Chlo^n^R3d^l^t,^e En4 of SDS Incubation should be equivalent to the free chlorine residual
*? the 4istributipn system (at a point representative of the average distribution system residence
time) during the quarter hi which the SDS test is being conducted. If chloramines are used as
the residual disinfectant in the distribution system, then the Free Chlorine Residual at the End
of SDS Incubation should be set at 0.5 to 1.0 mg/L. The residual at the end of incubation should
never be less than 0.2 mg/L.
a<*ual value for each of the SDS test parameters (i.e., incubation time, pH, incubation
temperature, and free chlorine residual at the end of incubation) must be measured and reported in the
ICR Treatment Study Data Collection Spreadsheets (EPA 815-B-97-002). Do not report the target values
hi the spreadsheets.
Gpfitefor Achieving the SDS Parameters: The purpose of using distribution system conditions to
sejec| the parameters for the SDS test is to evaluate DBF formation under realistic, site-specific
conditions, thus, an effort should be made to achieve these targets during the SDS test. This section lists
tolerance goals for each of the SDS test parameters. Since these are only goals, failure to meet these
tolerances does not constitute a failure for the SDS test.
The tolerance goal for the SDS incubation time is ± 5 % (e.g. , if the SDS incubation time is 20
hours, the tolerance goal would be ± 1 hour).
• The tolerance goal for the SDS incubation temperature is ± 2°C.
• The tolerance goal for the SDS pH prior to dosing is ± 0.4 pH units.
• The tolerance goal on the free chlorine residual at the end of SDS incubation is ± 0.4 mg/L.
Determine the SDS Chlorine Dose: Unless the chlorine demand of a specific water sample is
known ahead of time, or can be estimated with accuracy, it will be necessary to conduct a chlorine
demand test prior to dosing the SDS sample. In a chlorine demand test, several aliquots of water
(typically three) are dosed at SDS pH, temperature and incubation time, but at different chlorine doses.
At the end of the incubation period, the free chlorine residual is measured hi each aliquot, and the SDS
demand can be estimated from a linear plot of dose vs. residual.
Collecting DBF Samples from the SDS Aliquot: At the end of incubation, the SDS aliquot is
imm?diately sanWlQd for THM4, TOX and HAA6(9) (THMs and TOX should be sampled prior to HAAs
smce THM4 and TQX contain volatile compounds). Samples for DBF analysis should be poured into
bottles containing the appropriate dechlorinating agents/preservatives, and care must be taken to not aerate
toe sample during this transfer. After the DBF samples are collected, the free chlorine residual and pH
arc measured. All parameters should be analyzed hi accordance with the methods and QA/QC
requirements listed in the DBP/ICR Analytical Methods Manual (EPA 814-B-96-002).
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