[Code of Federal Regulations]
[Title 40, Volume 22]
[Revised as of July 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR141.74]
[Page 446-453]
TITLE 40--PROTECTION OF ENVIRONMENT
CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
PART 141_NATIONAL PRIMARY DRINKING WATER REGULATIONS--Table of Contents
Subpart H_Filtration and Disinfection
Sec. 141.74 Analytical and monitoring requirements.
(a) Analytical requirements. Only the analytical method(s) specified
in this paragraph, or otherwise approved by EPA, may be used to
demonstrate compliance with Sec. Sec. 141.71, 141.72 and 141.73.
Measurements for pH, turbidity, temperature and residual disinfectant
concentrations must be conducted by a person approved by the State.
Measurement for total coliforms, fecal coliforms and HPC must be
conducted by a laboratory certified by the State or EPA to do such
analysis. Until laboratory certification criteria are developed for the
analysis of fecal coliforms and HPC, any laboratory certified for total
coliforms analysis by the State or EPA is deemed certified for fecal
coliforms and HPC analysis. The following procedures shall be conducted
in accordance with the publications listed in the following section.
This incorporation by reference was approved by the Director of the
Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51.
Copies of the methods published in Standard Methods for the Examination
of Water and Wastewater may be obtained from the American Public Health
Association et al., 1015 Fifteenth Street, NW., Washington, DC 20005;
copies of the Minimal Medium ONPG-MUG Method as set forth in the article
``National Field Evaluation of a Defined Substrate Method for the
Simultaneous Enumeration of Total Coliforms and Esherichia coli from
Drinking Water: Comparison with the Standard
[[Page 447]]
Multiple Tube Fermentation Method'' (Edberg et al.), Applied and
Environmental Microbiology, Volume 54, pp. 1595-1601, June 1988 (as
amended under Erratum, Applied and Environmental Microbiology, Volume
54, p. 3197, December, 1988), may be obtained from the American Water
Works Association Research Foundation, 6666 West Quincy Avenue, Denver,
Colorado, 80235; and copies of the Indigo Method as set forth in the
article ``Determination of Ozone in Water by the Indigo Method'' (Bader
and Hoigne), may be obtained from Ozone Science & Engineering, Pergamon
Press Ltd., Fairview Park, Elmsford, New York 10523. Copies may be
inspected at the U.S. Environmental Protection Agency, Room EB15, 401 M
St., SW., Washington, DC 20460 or at the National Archives and Records
Administration (NARA). For information on the availability of this
material at NARA, call 202-741-6030, or go to: http://www.archives.gov/
federal--register/code--of--federal--regulations/ibr--locations.html.
(1) Public water systems must conduct analysis of pH and temperature
in accordance with one of the methods listed at Sec. 141.23(k)(1).
Public water systems must conduct analysis of total coliforms, fecal
coliforms, heterotrophic bacteria, and turbidity in accordance with one
of the following analytical methods and by using analytical test
procedures contained in Technical Notes on Drinking Water Methods, EPA-
600/R-94-173, October 1994, which is available at NTIS PB95-104766.
------------------------------------------------------------------------
Organism Methodology Citation \1\
------------------------------------------------------------------------
Total Coliform \2\............. Total Coliform 9221 A, B, C
Fermentation
Technique 3 4 5.
Total Coliform 9222 A, B, C
Membrane Filter
Technique \6\.
ONPG-MUG Test \7\. 9223
Fecal Coliforms \2\............ Fecal Coliform 9221 E
Procedure \8\.
Fecal Coliform 9222 D
Filter Procedure.
Heterotrophic bacteria \2\..... Pour Plate Method. 9215 B
SimPlate \11\.....
Turbidity...................... Nephelometric 2130 B
Method.
Nephelometric 180.1 \9\
Method.
Great Lakes Method 2 \10\
Instruments.
Hach FilterTrak... 10133 \12\
------------------------------------------------------------------------
The procedures shall be done in accordance with the documents listed
below. The incorporation by reference of the following documents
listed in footnotes 1, 6, 7 and 9-12 was approved by the Director of
the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part
51. Copies of the documents may be obtained from the sources listed
below. Information regarding obtaining these documents can be obtained
from the Safe Drinking Water Hotline at 800-426-4791. Documents may be
inspected at EPA's Drinking Water Docket, 1301 Constitution Avenue,
NW., EPA West, Room B102, Washington DC 20460 (Telephone: 202-566-
2426); or at the National Archives and Records Administration (NARA).
For information on the availability of this material at NARA, call 202-
741-6030, or go to: http://www.archives.gov/federal--register/code--
of--federal--regulations/ibr--locations.html.
\1\ Except where noted, all methods refer to Standard Methods for the
Examination of Water and Wastewater, 18th edition (1992), 19th edition
(1995), or 20th edition (1998), American Public Health Association,
1015 Fifteenth Street, NW., Washington, DC 20005. The cited methods
published in any of these three editions may be used.
\2\ The time from sample collection to initiation of analysis may not
exceed 8 hours. Systems must hold samples below 10 deg. C during
transit.
\3\ Lactose broth, as commercially available, may be used in lieu of
lauryl tryptose broth, if the system conducts at least 25 parallel
tests between this medium and lauryl tryptose broth using the water
normally tested, and this comparison demonstrates that the false-
positive rate and false-negative rate for total coliform, using
lactose broth, is less than 10 percent.
\4\ Media should cover inverted tubes at least one-half to two-thirds
after the sample is added.
\5\ No requirement exists to run the completed phase on 10 percent of
all total coliform-positive confirmed tubes.
\6\ MI agar also may be used. Preparation and use of MI agar is set
forth in the article, ``New medium for the simultaneous detection of
total coliform and Escherichia coli in water'' by Brenner, K.P., et.
al., 1993, Appl. Environ. Microbiol. 59:3534-3544. Also available from
the Office of Water Resource Center (RC-4100T), 1200 Pennsylvania
Avenue, NW., Washington DC 20460, EPA/600/J-99/225. Verification of
colonies is not required.
\7\ The ONPG-MUG Test is also known as the Autoanalysis Colilert System.
\8\ A-1 Broth may be held up to three months in a tightly closed screw
cap tube at 4 deg. C.
\9\ ``Methods for the Determination of Inorganic Substances in
Environmental Samples'', EPA/600/R-93/100, August 1993. Available at
NTIS, PB94-121811.
\10\ GLI Method 2, ``Turbidity'', November 2, 1992, Great Lakes
Instruments, Inc., 8855 North 55th Street, Milwaukee, Wisconsin 53223.
\11\ A description of the SimPlate method, ``IDEXX SimPlate TM HPC Test
Method for Heterotrophs in Water'', November 2000, can be obtained
from IDEXX Laboratories, Inc., One IDEXX Drive, Westbrook, Maine
04092, telephone (800) 321-0207.
\12\ A description of the Hach FilterTrak Method 10133, ``Determination
of Turbidity by Laser Nephelometry'', January 2000, Revision 2.0, can
be obtained from; Hach Co., P.O. Box 389, Loveland, Colorado 80539-
0389. Phone: 800-227-4224.
(2) Public water systems must measure residual disinfectant
concentrations with one of the analytical methods in the following
table. Except for the method for ozone residuals, the disinfectant
residual methods are contained in the 18th, 19th, and 20th editions of
Standard Methods for the Examination of Water and Wastewater, 1992,
1995, and 1998; the cited methods published in any of these three
editions may be used. The ozone method, 4500-O3 B, is
contained in both the 18th and
[[Page 448]]
19th editions of Standard Methods for the Examination of Water and
Wastewater, 1992, 1995; either edition may be used. If approved by the
State, residual disinfectant concentrations for free chlorine and
combined chlorine also may be measured by using DPD colorimetric test
kits. Free and total chlorine residuals may be measured continuously by
adapting a specified chlorine residual method for use with a continuous
monitoring instrument provided the chemistry, accuracy, and precision
remain same. Instruments used for continuous monitoring must be
calibrated with a grab sample measurement at least every five days, or
with a protocol approved by the State.
------------------------------------------------------------------------
Residual Methodology Methods
------------------------------------------------------------------------
Free Chlorine................. Amperometric 4500-Cl D
Titration.
DPD Ferrous 4500-Cl F
Titrimetric.
DPD Colorimetric. 4500-Cl G
Syringaldazine 4500-Cl H
(FACTS).
Total Chlorine................ Amperometric 4500-Cl D
Titration.
Amperometric 4500-Cl E
Titration (low
level
measurement).
DPD Ferrous 4500-Cl F
Titrimetric.
DPD Colorimetric. 4500-Cl G
Iodometric 4500-Cl I
Electrode.
Chlorine Dioxide.............. Amperometric 4500-ClO2 C
Titration.
DPD Method....... 4500-ClO2 D
Amperometric 4500-ClO2 E
Titration.
Ozone......................... Indigo Method.... 4500-O3 B
------------------------------------------------------------------------
(b) Monitoring requirements for systems that do not provide
filtration. A public water system that uses a surface water source and
does not provide filtration treatment must begin monitoring, as
specified in this paragraph (b), beginning December 31, 1990, unless the
State has determined that filtration is required in writing pursuant to
Sec. 1412(b)(7)(C)(iii), in which case the State may specify
alternative monitoring requirements, as appropriate, until filtration is
in place. A public water system that uses a ground water source under
the direct influence of surface water and does not provide filtration
treatment must begin monitoring as specified in this paragraph (b)
beginning December 31, 1990, or 6 months after the State determines that
the ground water source is under the direct influence of surface water,
whichever is later, unless the State has determined that filtration is
required in writing pursuant to Sec. 1412(b)(7)(C)(iii), in which case
the State may specify alternative monitoring requirements, as
appropriate, until filtration is in place.
(1) Fecal coliform or total coliform density measurements as
required by Sec. 141.71(a)(1) must be performed on representative
source water samples immediately prior to the first or only point of
disinfectant application. The system must sample for fecal or total
coliforms at the following minimum frequency each week the system serves
water to the public:
------------------------------------------------------------------------
Samples/
System size (persons served) week\1\
------------------------------------------------------------------------
<=500........................................................ 1
501 to 3,300................................................. 2
3,301 to 10,000.............................................. 3
10,001 to 25,000............................................. 4
25,000............................................ 5
------------------------------------------------------------------------
\1\ Must be taken on separate days.
Also, one fecal or total coliform density measurement must be made
every day the system serves water to the public and the turbidity of the
source water exceeds 1 NTU (these samples count towards the weekly
coliform sampling requirement) unless the State determines that the
system, for logistical reasons outside the system's control, cannot have
the sample analyzed within 30 hours of collection.
(2) Turbidity measurements as required by Sec. 141.71(a)(2) must be
performed on representative grab samples of source water immediately
prior to the first or only point of disinfectant application every four
hours (or more frequently) that the system serves water to the public. A
public water system may substitute continuous turbidity monitoring for
grab sample monitoring if it validates the continuous measurement for
accuracy on a regular basis using a protocol approved by the State.
(3) The total inactivation ratio for each day that the system is in
operation must be determined based on the CT99.9 values in
tables 1.1-1.6, 2.1, and 3.1 of this section, as appropriate. The
parameters necessary to determine the total inactivation ratio must be
monitored as follows:
[[Page 449]]
(i) The temperature of the disinfected water must be measured at
least once per day at each residual disinfectant concentration sampling
point.
(ii) If the system uses chlorine, the pH of the disinfected water
must be measured at least once per day at each chlorine residual
disinfectant concentration sampling point.
(iii) The disinfectant contact time(s) (``T'') must be determined
for each day during peak hourly flow.
(iv) The residual disinfectant concentration(s) (``C'') of the water
before or at the first customer must be measured each day during peak
hourly flow.
(v) If a system uses a disinfectant other than chlorine, the system
may demonstrate to the State, through the use of a State-approved
protocol for on-site disinfection challenge studies or other information
satisfactory to the State, that CT99.9 values other than
those specified in tables 2.1 and 3.1 in this section other operational
parameters are adequate to demonstrate that the system is achieving the
minimum inactivation rates required by Sec. 141.72(a)(1).
Table 1.1--CT Values (CT99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Free Chlorine at 0.5
[deg]C or Lower \1\
----------------------------------------------------------------------------------------------------------------
pH
Residual (mg/l) --------------------------------------------------
<=6.0 6.5 7.0 7.5 8.0 8.5 <=9.0
----------------------------------------------------------------------------------------------------------------
<=0.4........................................................ 137 163 195 237 277 329 390
0.6.......................................................... 141 168 200 239 286 342 407
0.8.......................................................... 145 172 205 246 295 354 422
1.0.......................................................... 148 176 210 253 304 365 437
1.2.......................................................... 152 180 215 259 313 376 451
1.4.......................................................... 155 184 221 266 321 387 464
1.6.......................................................... 157 189 226 273 329 397 477
1.8.......................................................... 162 193 231 279 338 407 489
2.0.......................................................... 165 197 236 286 346 417 500
2.2.......................................................... 169 201 242 297 353 426 511
2.4.......................................................... 172 205 247 298 361 435 522
2.6.......................................................... 175 209 252 304 368 444 533
2.8.......................................................... 178 213 257 310 375 452 543
3.0.......................................................... 181 217 261 316 382 460 552
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than a 99.99 percent inactivation of viruses. CT values between the
indicated pH values may be determined by linear interpolation. CT values between the indicated temperatures of
different tables may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value
at the lower temperature and at the higher pH.
Table 1.2--CT Values (CT 99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Free Chlorine at 5.0
[deg]C\1\
----------------------------------------------------------------------------------------------------------------
pH
Free residual (mg/l) --------------------------------------------------
<=6.0 6.5 7.0 7.5 8.0 8.5 <=9.0
----------------------------------------------------------------------------------------------------------------
<=0.4........................................................ 97 117 139 166 198 236 279
0.6........................................................ 100 120 143 171 204 244 291
0.8........................................................ 103 122 146 175 210 252 301
1.0........................................................ 105 125 149 179 216 260 312
1.2........................................................ 107 127 152 183 221 267 320
1.4........................................................ 109 130 155 187 227 274 329
1.6........................................................ 111 132 158 192 232 281 337
1.8........................................................ 114 135 162 196 238 287 345
2.0........................................................ 116 138 165 200 243 294 353
2.2........................................................ 118 140 169 204 248 300 361
2.4........................................................ 120 143 172 209 253 306 368
2.6........................................................ 122 146 175 213 258 312 375
2.8........................................................ 124 148 178 217 263 318 382
3.0........................................................ 126 151 182 221 268 324 389
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than a 99.99 percent inactivation of viruses. CT values between the
indicated pH values may be determined by linear interpolation. CT values between the indicated temperatures of
different tables may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value
at the lower temperature, and at the higher pH.
Table 1.3--CT Values (CT 99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Free Chlorine at 10.0
[deg]C\1\
----------------------------------------------------------------------------------------------------------------
pH
Free residual (mg/l) --------------------------------------------------
<=6.0 6.5 7.0 7.5 8.0 8.5 <=9.0
----------------------------------------------------------------------------------------------------------------
<=0.4........................................................ 73 88 104 125 149 177 209
0.6........................................................ 75 90 107 128 153 183 218
0.8........................................................ 78 92 110 131 158 189 226
1.0........................................................ 79 94 112 134 162 195 234
1.2........................................................ 80 95 114 137 166 200 240
1.4........................................................ 82 98 116 140 170 206 247
1.6........................................................ 83 99 119 144 174 211 253
1.8........................................................ 86 101 122 147 179 215 259
2.0........................................................ 87 104 124 150 182 221 265
2.2........................................................ 89 105 127 153 186 225 271
2.4........................................................ 90 107 129 157 190 230 276
2.6........................................................ 92 110 131 160 194 234 281
2.8........................................................ 93 111 134 163 197 239 287
3.0........................................................ 95 113 137 166 201 243 292
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than a 99.99 percent inactivation of viruses. CT values between the
indicated pH values may be determined by linear interpolation. CT values between the indicated temperatures of
different tables may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value
at the lower temperature, and at the higher pH.
Table 1.4--CT Values (CT 99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Free Chlorine at 15.0
[deg]C\1\
----------------------------------------------------------------------------------------------------------------
pH
Free residual (mg/l) --------------------------------------------------
<=6.0 6.5 7.0 7.5 8.0 8.5 <=9.0
----------------------------------------------------------------------------------------------------------------
<=0.4........................................................ 49 59 70 83 99 118 140
0.6........................................................ 50 60 72 86 102 122 146
0.8........................................................ 52 61 73 88 105 126 151
1.0........................................................ 53 63 75 90 108 130 156
1.2........................................................ 54 64 76 92 111 134 160
[[Page 450]]
1.4........................................................ 55 65 78 94 114 137 165
1.6........................................................ 56 66 79 96 116 141 169
1.8........................................................ 57 68 81 98 119 144 173
2.0........................................................ 58 69 83 100 122 147 177
2.2........................................................ 59 70 85 102 124 150 181
2.4........................................................ 60 72 86 105 127 153 184
2.6........................................................ 61 73 88 107 129 156 188
2.8........................................................ 62 74 89 109 132 159 191
3.0........................................................ 63 76 91 111 134 162 195
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than a 99.99 percent inactivation of viruses. CT values between the
indicated pH values may be determined by linear interpolation. CT values between the indicated temperatures of
different tables may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value
at the lower temperature, and at the higher pH.
Table 1.5--CT Values (CT99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Free Chlorine at 20
[deg]C\1\
----------------------------------------------------------------------------------------------------------------
pH
Free residual (mg/l) --------------------------------------------------
<= 6.0 6.5 7.0 7.5 8.0 8.5 <= 9.0
----------------------------------------------------------------------------------------------------------------
<= 0.4....................................................... 36 44 52 62 74 89 105
0.6.......................................................... 38 45 54 64 77 92 109
0.8.......................................................... 39 46 55 66 79 95 113
1.0.......................................................... 39 47 56 67 81 98 117
1.2.......................................................... 40 48 57 69 83 100 120
1.4.......................................................... 41 49 58 70 85 103 123
1.6.......................................................... 42 50 59 72 87 105 126
1.8.......................................................... 43 51 61 74 89 108 129
2.0.......................................................... 44 52 62 75 91 110 132
2.2.......................................................... 44 53 63 77 93 113 135
2.4.......................................................... 45 54 65 78 95 115 138
2.6.......................................................... 46 55 66 80 97 117 141
2.8.......................................................... 47 56 67 81 99 119 143
3.0.......................................................... 47 57 68 83 101 122 146
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than a 99.99 percent inactivation of viruses. CT values between the
indicated pH values may be determined by linear interpolation. CT values between the indicated temperatures of
different tables may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value
at the lower temperature, and at the higher pH.
Table 1.6--CT Values (CT99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Free Chlorine at 25
[deg]C\1\ and Higher
----------------------------------------------------------------------------------------------------------------
pH
Free residual (mg/l) --------------------------------------------------
<= 6.0 6.5 7.0 7.5 8.0 8.5 <= 9.0
----------------------------------------------------------------------------------------------------------------
<= 0.4....................................................... 24 29 35 42 50 59 70
0.6.......................................................... 25 30 36 43 51 61 73
0.8.......................................................... 26 31 37 44 53 63 75
1.0.......................................................... 26 31 37 45 54 65 78
1.2.......................................................... 27 32 38 46 55 67 80
1.4.......................................................... 27 33 39 47 57 69 82
1.6.......................................................... 28 33 40 48 58 70 84
1.8.......................................................... 29 34 41 49 60 72 86
2.0.......................................................... 29 35 41 50 61 74 88
2.2.......................................................... 30 35 42 51 62 75 90
2.4.......................................................... 30 36 43 52 63 77 92
2.6.......................................................... 31 37 44 53 65 78 94
2.8.......................................................... 31 37 45 54 66 80 96
3.0.......................................................... 32 38 46 55 67 81 97
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than a 99.99 percent inactivation of viruses. CT values between the
indicated pH values may be determined by linear interpolation. CT values between the indicated temperatures of
different tables may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value
at the lower temperature, and at the higher pH.
Table 2.1--CT Values (CT99.9) for 99.9 Percent Inactivation of Giardia Lamblia Cysts by Chlorine Dioxide and
Ozone\1\
----------------------------------------------------------------------------------------------------------------
Temperature
---------------------------------------------------------------
< 1 10 15 20 =
[deg]C 5 [deg]C [deg]C [deg]C [deg]C 25 [deg]C
----------------------------------------------------------------------------------------------------------------
Chlorine dioxide................................ 63 26 23 19 15 11
Ozone........................................... 2.9 1.9 1.4 0.95 0.72 0.48
----------------------------------------------------------------------------------------------------------------
\1\ These CT values achieve greater than 99.99 percent inactivation of viruses. CT values between the indicated
temperatures may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value at
the lower temperature for determining CT99.9 values between indicated temperatures.
[[Page 451]]
Table 3.1--CT Values (CT 99.9) for 99.9 Percent Inactivation of Giardia
Lamblia Cysts By Chloramines\1\
------------------------------------------------------------------------
Temperature
-------------------------------------------------------------------------
< 1 [deg]C 5 [deg]C 10 [deg]C 15 [deg]C 20 [deg]C 25 [deg]C
------------------------------------------------------------------------
3,800 2,200 1,850 1,500 1,100 750
------------------------------------------------------------------------
\1\ These values are for pH values of 6 to 9. These CT values may be
assumed to achieve greater than 99.99 percent inactivation of viruses
only if chlorine is added and mixed in the water prior to the addition
of ammonia. If this condition is not met, the system must demonstrate,
based on on-site studies or other information, as approved by the
State, that the system is achieving at least 99.99 percent
inactivation of viruses. CT values between the indicated temperatures
may be determined by linear interpolation. If no interpolation is
used, use the CT99.9 value at the lower temperature for determining
CT99.9 values between indicated temperatures.
(4) The total inactivation ratio must be calculated as follows:
(i) If the system uses only one point of disinfectant application,
the system may determine the total inactivation ratio based on either of
the following two methods:
(A) One inactivation ratio (CTcalc/CT99.9) is determined
before or at the first customer during peak hourly flow and if the
CTcalc/CT99.9 = 1.0, the 99.9 percent Giardia
lamblia inactivation requirement has been achieved; or
(B) Successive CTcalc/CT99.9 values, representing
sequential inactivation ratios, are determined between the point of
disinfectant application and a point before or at the first customer
during peak hourly flow. Under this alternative, the following method
must be used to calculate the total inactivation ratio:
[GRAPHIC] [TIFF OMITTED] TC15NO91.133
lamblia inactivation requirement has been achieved.
(ii) If the system uses more than one point of disinfectant
application before or at the first customer, the system must determine
the CT value of each disinfection sequence immediately prior to the next
point of disinfectant application during peak hourly flow. The CTcalc/
CT99.9 value of each sequence and
[GRAPHIC] [TIFF OMITTED] TC15NO91.134
must be calculated using the method in paragraph (b)(4)(i)(B) of this
section to determine if the system is in compliance with Sec.
141.72(a).
(iii) Although not required, the total percent inactivation for a
system with one or more points of residual disinfectant concentration
monitoring may be calculated by solving the following equation:
[GRAPHIC] [TIFF OMITTED] TC15NO91.135
(5) The residual disinfectant concentration of the water entering
the distribution system must be monitored continuously, and the lowest
value must be recorded each day, except that if there is a failure in
the continuous monitoring equipment, grab sampling every 4 hours may be
conducted in lieu of continuous monitoring, but for no more than 5
working days following the failure of the equipment, and systems serving
3,300 or fewer persons may take grab samples in lieu of providing
continuous monitoring on an ongoing
[[Page 452]]
basis at the frequencies prescribed below:
------------------------------------------------------------------------
Samples/
System size by population day\1\
------------------------------------------------------------------------
<500......................................................... 1
501 to 1,000................................................. 2
1,001 to 2,500............................................... 3
2,501 to 3,300............................................... 4
------------------------------------------------------------------------
\1\ The day's samples cannot be taken at the same time. The sampling
intervals are subject to State review and approval.
If at any time the residual disinfectant concentration falls below 0.2
mg/l in a system using grab sampling in lieu of continuous monitoring,
the system must take a grab sample every 4 hours until the residual
concentration is equal to or greater than 0.2 mg/l.
(6)(i) The residual disinfectant concentration must be measured at
least at the same points in the distribution system and at the same time
as total coliforms are sampled, as specified in Sec. 141.21, except
that the State may allow a public water system which uses both a surface
water source or a ground water source under direct influence of surface
water, and a ground water source, to take disinfectant residual samples
at points other than the total coliform sampling points if the State
determines that such points are more representative of treated
(disinfected) water quality within the distribution system.
Heterotrophic bacteria, measured as heterotrophic plate count (HPC) as
specified in paragraph (a)(3) of this section, may be measured in lieu
of residual disinfectant concentration.
(ii) If the State determines, based on site-specific considerations,
that a system has no means for having a sample transported and analyzed
for HPC by a certified laboratory under the requisite time and
temperature conditions specified by paragraph (a)(1) of this section and
that the system is providing adequate disinfection in the distribution
system, the requirements of paragraph (b)(6)(i) of this section do not
apply to that system.
(c) Monitoring requirements for systems using filtration treatment.
A public water system that uses a surface water source or a ground water
source under the influence of surface water and provides filtration
treatment must monitor in accordance with this paragraph (c) beginning
June 29, 1993, or when filtration is installed, whichever is later.
(1) Turbidity measurements as required by Sec. 141.73 must be
performed on representative samples of the system's filtered water every
four hours (or more frequently) that the system serves water to the
public. A public water system may substitute continuous turbidity
monitoring for grab sample monitoring if it validates the continuous
measurement for accuracy on a regular basis using a protocol approved by
the State. For any systems using slow sand filtration or filtration
treatment other than conventional treatment, direct filtration, or
diatomaceous earth filtration, the State may reduce the sampling
frequency to once per day if it determines that less frequent monitoring
is sufficient to indicate effective filtration performance. For systems
serving 500 or fewer persons, the State may reduce the turbidity
sampling frequency to once per day, regardless of the type of filtration
treatment used, if the State determines that less frequent monitoring is
sufficient to indicate effective filtration performance.
(2) The residual disinfectant concentration of the water entering
the distribution system must be monitored continuously, and the lowest
value must be recorded each day, except that if there is a failure in
the continuous monitoring equipment, grab sampling every 4 hours may be
conducted in lieu of continuous monitoring, but for no more than 5
working days following the failure of the equipment, and systems serving
3,300 or fewer persons may take grab samples in lieu of providing
continuous monitoring on an ongoing basis at the frequencies each day
prescribed below:
------------------------------------------------------------------------
Samples/
System size by population day \1\
------------------------------------------------------------------------
500.................................... 1
501 to 1,000................................................. 2
1,001 to 2,500............................................... 3
2,501 to 3,300............................................... 4
------------------------------------------------------------------------
\1\ The day's samples cannot be taken at the same time. The sampling
intervals are subject to State review and approval.
If at any time the residual disinfectant concentration falls below 0.2
mg/l in a system using grab sampling in lieu of continuous monitoring,
the system must take a grab sample every 4 hours
[[Page 453]]
until the residual disinfectant concentration is equal to or greater
than 0.2 mg/l.
(3)(i) The residual disinfectant concentration must be measured at
least at the same points in the distribution system and at the same time
as total coliforms are sampled, as specified in Sec. 141.21, except
that the State may allow a public water system which uses both a surface
water source or a ground water source under direct influence of surface
water, and a ground water source to take disinfectant residual samples
at points other than the total coliform sampling points if the State
determines that such points are more representative of treated
(disinfected) water quality within the distribution system.
Heterotrophic bacteria, measured as heterotrophic plate count (HPC) as
specified in paragraph (a)(1) of this section, may be measured in lieu
of residual disinfectant concentration.
(ii) If the State determines, based on site-specific considerations,
that a system has no means for having a sample transported and analyzed
for HPC by a certified laboratory under the requisite time and
temperature conditions specified by paragraph (a)(1) of this section and
that the system is providing adequate disinfection in the distribution
system, the requirements of paragraph (c)(3)(i) of this section do not
apply to that system.
[54 FR 27527, June 29, 1989, as amended at 59 FR 62470, Dec. 5, 1994; 60
FR 34086, June 29, 1995; 64 FR 67465, Dec. 1, 1999; 67 FR 65252, Oct.
23, 2002; 67 FR 65901, Oct. 29, 2002; 69 FR 38856, June 29, 2004]