United States
Environmental Protection
Agency
Environmental Monitoring and
Support Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S4-86/040 Apr. 1987
&EPA Project Summary
USEPA Method Study, Method
510.1, The Determination of the
Maximum Total Trihalomethane
Potential
Harold Clements, John Winter, and Paul Britton
The Quality Assurance Branch of the
Environmental Monitoring and Support
Laboratory - Cincinnati (EMSL-Cincin-
nati) conducted a method validation
study of the Method, 510.1: "The
Determination of the Maximum Total
Trihalomethane Potential" for the Office
of Drinking Water of the U.S. Environ-
mental Protection Agency (USEPA). The
MTP determination maximizes the
formation of THMs and indicates how
high the TTHM concentration could be-
come under conditions favoring TTHM
formation. It may be used by systems
employing ground water sources to
demonstrate the appropriateness of a
reduced monitoring requirement.
This method involves the reaction of
3,5-dihydroxybenzoic acid with a chlo-
rine residual for a 7-day period. When a
chlorine residual is maintained con-
tinually, the dihydroxybenzoic acid is
converted to chloroform. If other halo-
gens are present in the make-up water,
other trihalomethanes are formed in
small amounts. Method 510.1, involves
the sample treatment phase, followed
by the determination of trihalomethanes
by either the purge and trap or liquid-
liquid extraction procedure.
The study design was based on
Youden's non-replicate plan for col-
laborative testing by laboratories famil-
iar with the method. Ten laboratories
returned results for this study. Analyses
included the standard statistical esti-
mates of precision and bias, and the
development of linear relationships
between these statistics and concen-
tration. The linear relationship for bias
involved the true known concentration
as the independent variable and mean
recovery as the dependent variable,
while the linear relationship tor precision
involved mean recovery as the inde-
pendent variable and standard deviation
as the dependent variable.
This Project Summary was developed
by EPA's Environmental Monitoring and
Support Laboratory, Cincinnati, OH, to
announce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
Waterborne diseases were a major
public health menace in the U.S. as
recently as the last 100 years. Today,
methods of water purification, particularly
chlorination, are remarkably effective in
reducing waterborne diseases. However,
in recent years, public health profes-
sionals have become increasingly con-
cerned about other contaminants in our
water supplies. These include inorganic
chemicals such as nitrate, arsenic, and
lead, as well as toxic industrial and agri-
cultural organic compounds which have
been produced in ever-growing volumes.
Some of these pollutants are harmful at
very low concentrations and can be ex-
tremely difficult to remove from a water
supply.
To deal with these problems, Congress
passed the Safe Drinking Water Act of
1974, and amended Interim Regulations
in 1977. Under the Act, USEPA estab-
lished national standards for drinking
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water from both surface and ground
water sources. These standards provide
maximum contaminant levels (MCLs) for
pollutants in drinking water. One group
of organic contaminants, the trihalome-
thanes (THMs), are a unique problem in
water treatment facilities. Rather than
being a result of industrial pollution, the
THMs are primarily the by-products of
the chlorination process used to disinfect
water. They are: chloroform, bromoform,
dichlorobromomethane and dibromochlo-
romethane. Drinking Water regulations
include an MCL of 0.10 mg/L for total
THMs.
Method 510.1 "The Determination of
the Maximum Total Trihalomethane
Potential" was developed to determine
the reasonable maximum TTHMs cur-
rently present within a system, not the
average TTHMs or individual THMs.
Method 510.1 is to be applied to the
finished drinking water for those ground-
water supplies that have failed the test
for the presence of excess disinfectant.
The sample is to be taken at a point in the
system that reflects the maximum resi-
dency time. These data should be used to
demonstrate compliance but are not
intended to show non-compliance. Sys-
tems that can demonstrate a MTP value
of less than 0.10 mg/L under experi-
mental conditions favoring TTHM forma-
tion are prime candidates for reduced
monitoring. The regulation allows moni-
toring requirements for systems using
groundwater as a source to be reduced to
one annual analysis for maximum total
THM potential.
This collaborative study was conducted
to determine the acceptability and un-
derstandability of the method before use
in the regulated community. About 70
federal, state and local drinking water
laboratories within the continental U.S.
were invited to participate in a method
validation study of USEPA Method 510.1,
"The Determination of Maximum Total
Trihalomethane Potential (MTP)".
A time schedule was established for
the study and six concentrates, each of a
different concentration, were shipped to
laboratories on March 1,1985. A quality
control (QC) sample with a known true
value was also sent. Prior to analyses of
the six unknown samples, each laboratory
was directed to analyze the QC samples
to develop laboratory skills and to famil-
iarize the analyst with the method. Each
laboratory was required to analyze the
six concentrates and a blank unspiked
water and to report the TTHM values
obtained. Data were to be returned to the
Quality Assurance Branch (QAB), EMSL-
Cincinnati, by April 1, 1985. Statistical
estimates were generated from the re-
turned data and the final report prepared.
Summary
Of the fourteen laboratories which
agreed to participate, ten returned data.
The summary statistics from the study
follow:
Study Results and Statistical
Treatment of Data
Each laboratory returning data was
assigned a confidential laboratory code.
Data were analyzed using the U.S. En-
vironmental Protection Agency's (USEPA)
Interlaboratory Method Validation Study
(IMVS) computer program (1) which is
similar to ASTM procedure D2777, "Stan-
dard Practice for Determination of Preci-
sion and Bias of Methods of Committee
D-19 on Water" (2). The IMVS stastical
program includes tests for the rejection
of outliers by laboratory ranking within
each water-type and by individual data
points within data for each sample, fol-
lowed by estimation of mean recovery,
single-analyst standard deviation and
overall standard deviation and overall
standard deviation. Finally, regressions
are produced which relate mean recovery
(bias) and both standard deviations (pre-
cision) to sample concentration.
Discussion of Results and
Related Comments
Analysts seemed to encounter a prob-
lem with high THM blank values. The
high THM values for blanks (greater than
5 M9/L) appear to be the contribution
from the water and the buffer hypochlorite
solution. In the final calculations, the
blank contribution is subtracted from the
total amount. When the blank values are
20 to 30 jug/U it is not feasible to subtract
these values from samples of 30 to 35
In examining the data in Table 1, the
average recoveries for each sample com-
pare very well with the "true values".
This would lead one to believe that with
repeated analyses, the analyst should
develop skills necessary to overcome the
problems associated with the method.
The quality control (QC) sample dis-
tributed in this study had a known value
of 116.8 Aig/L Each analyst was in-
structed to analyze this sample until data
compared favorably to this known value.
Only then was the analyst to proceed
with the six unknowns. The unknown
sample 4 was the same sample as the
QC sample, therefore, the data from each
laboratory for sample 4 should be
comparable.
The full report contains a table showing
that the percent error and percent relative
standard deviation (RSD) are small for
the higher concentration levels (80 to
250 M9/L). The lower levels (25 and 37
M9/L) (sample 1 and 2) have an RSD
quite high for this type data. This fact,
low RSD at high concentrations and
higher RSD at low concentrations of
analyte is very common m most studies.
The Federal Register of November 29,
1979 (3.4) states that the acceptable level
of analyses of THM's cannot deviate more
than 20% from the true value. In the
performance evaluation (PE) studies con-
ducted for certification of ODW labora-
Table 1. Data Generated with USEPA Method 510.1 for Maximum Trihalomethane Potential
(MTP) Total Trihalomethanes, vglL as CHCI3
Sample
Parameters
n
TV
X
S
Sr
1 2
8 9
24.9 37.3
22.11 38.70
12.31 12.47
4.887
3 4
9 9
80.8 116.8
83.31 116.6
9.42 17.19
10.48
5 6
9 8
186.4 248.6
1900 239.2
29.61 15.03
16.40
Where n = the number of data values after removal of outliers
TV - true value,
X = arithmetic mean,
S - overall standard deviation, and
Sr = single-analyst standard deviation.
For the range of TTHM's from 24.9 - 248.6 pg/liter, regression equations for bias and precision
of USEPA Method 510.1_ were calculated as follows:
X = 1.023 (TV) - 2.09
S = 0.0367 (XJ_ + 11.26
S, = 0.0692 (X) + 2.82
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lories, acceptance limits of ±20% around
the true value are applied for TTHMs. If
these limits (true value ±20%) were
applied to the study data, almost all the
data on samples 3, 4, 5 and 6 would be
acceptable, but many values for Sample
1 and 2 would not be acceptable, as
shown in Table 2 by the asterisk.
Recommendations
This method was developed to assist
ground-water supply systems to qualify
for reduced monitoring. In using any
analytical method, it should be obvious
that experience is necessary. However,
this method is particularly complex and
therefore susceptible to failure when
applied by inexperienced analysts. The
following points are considered very
important:
• It is highly recommended that the
analysts prepare their own known
QC sample, (see Method Sections
5.5 and 9.2) and analyze it many
times to assure that all parts of the
method are being performed cor-
rectly before using the method for
real world samples. Duplicate
analyses should not vary greater than
± 20% at concentrations above 50
iug/L TTHMs. If duplicate results do
vary more than 20%, clean all glass-
ware and prepare reagents again.
• When a background above 5 ng/L
TTHMs is found in the blank water-
hypochlorite solution, it is unac-
ceptable as reagent in this method.
Repeat Section 5.2 and 5.3 to reduce
THM background to less than 5 M9/L-
If background cannot be lowered to
acceptable levels, a new source of
reagents must be found.
• When the blank water-hypochlorite
solution is persistently above the 5
/ug/L TTHM concentration, prepare
the solution a week in advance.
Reflux as in Section 5.1.2 and cool.
Purge with clean nitrogen or helium.
Before using, test for chlorine con-
tent and the presence of chloroform.
If TTHMs background remains high,
purge again with clean nitrogen or
helium. The background will even-
tually be reduced to the acceptable
TTHMs level.
• Prepare blank water-hypochlorite
solution in a laboratory away from
organic standard-organic analyses.
Minimum exposure can result in
major contamination and unaccept-
able high blank values.
Although the method is cumbersome,
in the hands of a qualified analyst, it does
work.
References
1. Gutter, E. C. and McCreary, J. H.,
Interlaboratory Method Validation
Study: Program Documentation,
Battelle Columbus Laboratories, 1982.
2. ASTM 02777-77, 1980 Annual Book
of ASTM Standards, Part 31, pp. 16-
28. American Society for Testing and
Materials, Philadelphia, PA.
3. Federal Register, Thursday, November
29, 1979, Volume 44. No. 231 40
CFR, Appendix C - Part I.
4. Federal Register, Thursday, November
29, 1979, Volume 44. No. 231 40 CFR
Appendix C - Part II.
Table 2 Maximum Trihalomethane Potential, as TTHM, ng/L Ordered Data ± 20% Criteria
Sample.
1
TV
TV ± 20%
40.8"
35*
25
22.7
22.2
18*
11*
22*
24.9
19.9
to
29.9
54.8*
54*
57*
41
37.7
34.1
28*
267*
21*
37.3
29.8
to
44.8
97
93.2
91.5
86
84.5
77
76.6
74
70
80.8
64.6
to
97.0
138
138
130
129.8
107
105
104.3
104
93*
116.8
93.4
to
140.2
254*
204
202.1
195
185
180.1
177
159
154
186.4
1491
to
233.7
255.2
257
248.9
247
239
237.1
224
211
248.6
198.9
to
298.3
* beyond ± 20% limit
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The EPA authors, Harold Clements (also the EPA Project Officer, see below).
John Winter, and Paul Britton are with Environmental Monitoring and
Support Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH
45268).
The complete report, entitled "USEPA Method Study, Method 510.1: The
Determination of the Maximum Total Trihalomethane Potential," (Order No.
PB 87-170 825/AS; Cost: $13.95, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
EPA
Official Business
Penalty for Private Use $300
EPA/600/S4-86/040
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