40 CFR 141.720 - Inactivation toolbox components.

Status message

There is 1 rule appearing in the Federal Register for 40 CFR 141. View below or at eCFR (GPOAccess)
prev | next
§ 141.720 Inactivation toolbox components.
(a) Calculation of CT values.
(1) CT is the product of the disinfectant contact time (T, in minutes) and disinfectant concentration (C, in milligrams per liter). Systems with treatment credit for chlorine dioxide or ozone under paragraph (b) or (c) of this section must calculate CT at least once each day, with both C and T measured during peak hourly flow as specified in §§ 141.74(a) through (b).
(2) Systems with several disinfection segments in sequence may calculate CT for each segment, where a disinfection segment is defined as a treatment unit process with a measurable disinfectant residual level and a liquid volume. Under this approach, systems must add the Cryptosporidium CT values in each segment to determine the total CT for the treatment plant.
(b) CT values for chlorine dioxide and ozone.
(1) Systems receive the Cryptosporidium treatment credit listed in this table by meeting the corresponding chlorine dioxide CT value for the applicable water temperature, as described in paragraph (a) of this section.
CT Values (mg·min/L) for Cryptosporidium Inactivation by Chlorine Dioxide 1
Log credit Water Temperature, °C
<=0.5 1 2 3 5 7 10 15 20 25 30
1 Systems may use this equation to determine log credit between the indicated values: Log credit = (0.001506 × (1.09116)Temp) × CT.
(i) 0.25 159 153 140 128 107 90 69 45 29 19 12
(ii) 0.5 319 305 279 256 214 180 138 89 58 38 24
(iii) 1.0 637 610 558 511 429 360 277 179 116 75 49
(iv) 1.5 956 915 838 767 643 539 415 268 174 113 73
(v) 2.0 1275 1220 1117 1023 858 719 553 357 232 150 98
(vi) 2.5 1594 1525 1396 1278 1072 899 691 447 289 188 122
(vii) 3.0 1912 1830 1675 1534 1286 1079 830 536 347 226 147
(2) Systems receive the Cryptosporidium treatment credit listed in this table by meeting the corresponding ozone CT values for the applicable water temperature, as described in paragraph (a) of this section.
CT Values (mg·min/L) for Cryptosporidium Inactivation by Ozone 1
Log credit Water Temperature, °C
<=0.5 1 2 3 5 7 10 15 20 25 30
1 Systems may use this equation to determine log credit between the indicated values: Log credit = (0.0397 × (1.09757)Temp) × CT.
(i) 0.25 6.0 5.8 5.2 4.8 4.0 3.3 2.5 1.6 1.0 0.6 0.39
(ii) 0.5 12 12 10 9.5 7.9 6.5 4.9 3.1 2.0 1.2 0.78
(iii) 1.0 24 23 21 19 16 13 9.9 6.2 3.9 2.5 1.6
(iv) 1.5 36 35 31 29 24 20 15 9.3 5.9 3.7 2.4
(v) 2.0 48 46 42 38 32 26 20 12 7.8 4.9 3.1
(vi) 2.5 60 58 52 48 40 33 25 16 9.8 6.2 3.9
(vii) 3.0 72 69 63 57 47 39 30 19 12 7.4 4.7
(c) Site-specific study. The State may approve alternative chlorine dioxide or ozone CT values to those listed in paragraph (b) of this section on a site-specific basis. The State must base this approval on a site-specific study a system conducts that follows a State-approved protocol.
(d) Ultraviolet light. Systems receive Cryptosporidium, Giardia lamblia, and virus treatment credits for ultraviolet (UV) light reactors by achieving the corresponding UV dose values shown in paragraph (d)(1) of this section. Systems must validate and monitor UV reactors as described in paragraphs (d)(2) and (3) of this section to demonstrate that they are achieving a particular UV dose value for treatment credit.
(1) UV dose table. The treatment credits listed in this table are for UV light at a wavelength of 254 nm as produced by a low pressure mercury vapor lamp. To receive treatment credit for other lamp types, systems must demonstrate an equivalent germicidal dose through reactor validation testing, as described in paragraph (d)(2) of this section. The UV dose values in this table are applicable only to post-filter applications of UV in filtered systems and to unfiltered systems.
UV Dose Table for Cryptosporidium, Giardia lamblia, and Virus Inactivation Credit
Log credit Cryptosporidium UV dose (mJ/cm2) Giardia lamblia UV dose (mJ/cm2) VirusUV dose (mJ/cm2)
(i) 0.5 1.6 1.5 39
(ii) 1.0 2.5 2.1 58
(iii) 1.5 3.9 3.0 79
(iv) 2.0 5.8 5.2 100
(v) 2.5 8.5 7.7 121
(vi) 3.0 12 11 143
(vii) 3.5 15 15 163
(viii) 4.0 22 22 186
(2) Reactor validation testing. Systems must use UV reactors that have undergone validation testing to determine the operating conditions under which the reactor delivers the UV dose required in paragraph (d)(1) of this section (i.e., validated operating conditions). These operating conditions must include flow rate, UV intensity as measured by a UV sensor, and UV lamp status.
(i) When determining validated operating conditions, systems must account for the following factors: UV absorbance of the water; lamp fouling and aging; measurement uncertainty of on-line sensors; UV dose distributions arising from the velocity profiles through the reactor; failure of UV lamps or other critical system components; and inlet and outlet piping or channel configurations of the UV reactor.
(ii) Validation testing must include the following: Full scale testing of a reactor that conforms uniformly to the UV reactors used by the system and inactivation of a test microorganism whose dose response characteristics have been quantified with a low pressure mercury vapor lamp.
(iii) The State may approve an alternative approach to validation testing.
(3) Reactor monitoring.
(i) Systems must monitor their UV reactors to determine if the reactors are operating within validated conditions, as determined under paragraph (d)(2) of this section. This monitoring must include UV intensity as measured by a UV sensor, flow rate, lamp status, and other parameters the State designates based on UV reactor operation. Systems must verify the calibration of UV sensors and must recalibrate sensors in accordance with a protocol the State approves.
(ii) To receive treatment credit for UV light, systems must treat at least 95 percent of the water delivered to the public during each month by UV reactors operating within validated conditions for the required UV dose, as described in paragraphs (d)(1) and (2) of this section. Systems must demonstrate compliance with this condition by the monitoring required under paragraph (d)(3)(i) of this section.

Title 40 published on 2013-07-01

The following are only the Rules published in the Federal Register after the published date of Title 40.

For a complete list of all Rules, Proposed Rules, and Notices view the Rulemaking tab.

  • 2014-02-26; vol. 79 # 38 - Wednesday, February 26, 2014
    1. 79 FR 10665 - National Primary Drinking Water Regulations: Minor Corrections to the Revisions to the Total Coliform Rule
      GPO FDSys XML | Text
      ENVIRONMENTAL PROTECTION AGENCY
      Direct final rule.
      This rule is effective on April 28, 2014 without further notice, unless EPA receives adverse comment by March 28, 2014. If EPA receives adverse comment, we will publish a timely withdrawal in the Federal Register informing the public that the rule will not take effect. The incorporation by reference of certain material listed in the rule was approved by the Director of the Federal Register as of April 15, 2013.
      40 CFR Parts 141 and 142

This is a list of United States Code sections, Statutes at Large, Public Laws, and Presidential Documents, which provide rulemaking authority for this CFR Part.

This list is taken from the Parallel Table of Authorities and Rules provided by GPO [Government Printing Office].

It is not guaranteed to be accurate or up-to-date, though we do refresh the database weekly. More limitations on accuracy are described at the GPO site.


United States Code

Title 40 published on 2013-07-01

The following are ALL rules, proposed rules, and notices (chronologically) published in the Federal Register relating to 40 CFR 141 after this date.

  • 2014-02-26; vol. 79 # 38 - Wednesday, February 26, 2014
    1. 79 FR 10665 - National Primary Drinking Water Regulations: Minor Corrections to the Revisions to the Total Coliform Rule
      GPO FDSys XML | Text
      ENVIRONMENTAL PROTECTION AGENCY
      Direct final rule.
      This rule is effective on April 28, 2014 without further notice, unless EPA receives adverse comment by March 28, 2014. If EPA receives adverse comment, we will publish a timely withdrawal in the Federal Register informing the public that the rule will not take effect. The incorporation by reference of certain material listed in the rule was approved by the Director of the Federal Register as of April 15, 2013.
      40 CFR Parts 141 and 142