Disinfection by product | MCL (mg/L) |
Bromate | 0.010 |
Chlorite | 1.0 |
Haloacetic acids (HAA5) | 0.060 |
Total trihalomethanes (TTHM)* | 0.080 |
*The TTHM MCL changed from 0.10 mg/L to 0.080 mg/L effective January 1, 2002, for CWS serving at least 10,000 people and effective January 1, 2004, for all other CWS and NTNC systems which are subject to this rule.
System Size (number of people served) | Date system must comply with MCL at each sampling location* |
Systems that are not part of a combined distribution system and systems that serve the largest population in the combined distribution system | |
System serving at least 100,000 people | April 1, 2012 |
System serving 50,000-99,999 people | October 1,2012 |
System serving 10,000-49,999 people | October 1,2013 |
System serving fewer than 10,000 people | * October 1, 2013, for all groundwater systems and for SW/IGW systems that did not collectCryptosporidium source water samples |
* October 1, 2014, for SW/IGW systems that collected Cryptosporidium source water samples | |
Other systems that are part of a combined distribution system | |
Consecutive or wholesale system | At the same time as the system with the earliest compliance date in the combined distribution system |
*The department may grant up to an additional 24 months for compliance with the MCLs and operational evaluation levels if the system requires capital improvements to comply with an MCL.
* Specific locations and schedules for collecting samples for any parameters included in this rule.
* How the system will calculate compliance with MCLs, MRDLs, and treatment techniques.
* Daily chlorite monitoring at the entrance to the distribution system required by 41.6(1)"c "(3) 1" may not be reduced.
* The department may allow systems with monthly chlorite monitoring in the distribution system required by 41.6(1) "c "(3)"2" to be reduced to a requirement of 1 three-sample set per quarter after one year of monitoring where no individual chlorite sample taken in the distribution system under 41.6(1) "c "(3)"2" has exceeded the chlorite MCL and the system has not been required to conduct additional monitoring under 41.6(1)"c "(3)"3." The system may remain on the reduced monitoring schedule until either any of the three individual chlorite samples taken quarterly in the distribution system under 41.6(1)"c "(3)"2" exceeds the chlorite MCL or the system is required to conduct monitoring under 41.6(1) "c "(3)"3" of this rule, at which time the system must revert to routine monitoring.
Routine Monitoring Frequency for TTHM and HAA5
Type of System (source water type and population served) | Minimum Monitoring Frequency | Sample Location in the Distribution System |
SW/IGW3system serving [GRETAR THAN IS =] 10,000 persons | Four water samples per quarter per treatment plant | At least 25 percent of all samples collected each quarter at locations representing maximum residence time. Remaining samples taken at locations representative of at least average residence time in the distribution system and representing the entire distribution system, taking into account number of persons served, different sources of water, and different treatment methods.1 |
SW/IGW3system serving 500-9,999 persons | One water sample per quarter per treatment plant | Locations representing maximum residence time.1 |
SW/IGW3system serving <500 persons | One sample per year per treatment plant during month of warmest water temperature | Locations representing maximum residence time.1If the sample (or average of annual samples, if more than one sample is taken) exceeds MCL, system must increase monitoring to one sample per treatment plant per quarter, taken at a point reflecting the maximum residence time in the distribution system, until system meets reduced monitoring criteria in 41.6(1)"c "(4)"2," second bulleted paragraph. |
System using only non-IGW groundwater using chemical disinfectant and serving [GRETAR THAN EQUAL] 10,000 persons | One water sample per quarter per treatment plant2 | Locations representing maximum residence time.1 |
System using only non-IGW groundwater using chemical disinfectant and serving <10,000 persons | One sample per year per treatment plant during month of warmest water temperature | Locations representing maximum residence time.1If the sample (or average of annual samples, if more than one sample is taken) exceeds MCL, system must increase monitoring to one sample per treatment plant per quarter, taken at a point reflecting the maximum residence time in the distribution system, until system meets reduced monitoring criteria in 41.6(1)"c "(4)"2," second bulleted paragraph. |
1If a system chooses to sample more frequently than the minimum required, at least 25 percent of all samples collected each quarter (including those taken in excess of the required frequency) must be taken at locations that represent the maximum residence time of the water in the distribution system. The remaining samples must be taken at locations representative of at least average residence time in the distribution system.
2Multiple wells drawing water from a single aquifer may be considered one treatment plant for determining the minimum number of samples required, with department approval.
3SW/IGW indicates those systems that use either surface water (SW) or groundwater under the direct influence of surface water (IGW), in whole or in part.
Reduced Monitoring Frequency for TTHM and HAA5
If you are a | And you have monitored at least one year and your | You may reduce monitoring to this level |
SW/IGW1 system serving [GRETAR THAN EQUAL TO] 10,000 persons which has a source water annual average TOC level, before any treatment, of [LESS THAN EQUAL TO] 4 0 mg/L | TTHM annual average [LESS THAN EQUAL TO] 040 mg/L and HA A 5 annual average [LESS THAN EQUAL TO] 030 mg/L | One sample per treatment plant per quarter at distribution system location reflecting maximum residence time |
SW/IGW1 system serving 500 -9,999 persons that has a source water annual average TOC level, before any treatment, of [LESS THAN EQUAL TO] 4.0 mg/L | TTHM annual average [LESS THAN EQUAL TO]0.040 mg/L and HA A 5 annual average [LESS THAN EQUAL TO]0.030 mg/L | One sample per treatment plant per year at distribution system location reflecting maximum residence time during month of warmest water temperature |
SW/IGW1 system serving [LESS THAN EQUAL TO] 500 persons | Any SW/IGW1 system monitoring to less than serving <500 persons may not reduce its one sample per treatment plant per year | |
System using only non-IGW groundwater using chemical disinfectant and serving [GRETAR THAN EQUAL TO]10,000 persons | TTHM annual average [LESS THAN EQUAL TO]0. 040 mg/L and HA A 5 annual average [LESS THAN EQUAL TO]0. 030 mg/L | One sample per treatment plant per year at distribution system location reflecting maximum residence time during month of warmest water temperature |
System using only non-IGW groundwater using chemical disinfectant and serving [GRETAR THAN EQUAL TO]10,000 persons | TTHM annual average [LESS THAN EQUAL TO] 0.040 mg/L and HA A 5 annual average [LESS THAN EQUAL TO] 0.030 mg/L for two consecutive years, or, TTHM annual average [LESS THAN EQUAL TO] 0.020 mg/L and HA A 5 annual average [LESS THAN EQUAL TO] 0.015 mg/L for one year | One sample per treatment plant per three-year monitoring cycle at distribution system location reflecting maximum residence time during month of warmest water temperature, with the three-year cycle beginning on January 1 following quarter in which system qualifies for reduced monitoring |
1SW/IGW indicates those systems that use either surface water (SW) or groundwater under the direct influence of surface water (IGW), in whole or in part.
* Systems on a reduced monitoring schedule may remain on that reduced schedule as long as the average of all samples taken in the year (for systems which must monitor quarterly) or the result of the sample (for systems which must monitor no more frequently than annually) is less than or equal to 0.060 mg/L for TTHMs and is less than or equal to 0.045 mg/L for HAA5. Systems that do not meet these levels must resume monitoring at the frequency identified in 41.6(1)"c "(4)"1" in the quarter immediately following the quarter in which the system exceeds 0.060 mg/L for TTHMs and 0.045 mg/L for HAA5. For systems using only groundwater not under the direct influence of surface water and serving fewer than 10,000 persons, if either the TTHM annual average is >0.080 mg/L or the HAA5 annual average is >0.060 mg/L, the system must go to increased monitoring identified in 41.6(1) "c "(4)"1" in the quarter immediately following the monitoring period in which the system exceeds 0.080 mg/L for TTHMs or 0.060 mg/L for HAA5.
* The department may allow systems on increased monitoring to return to routine monitoring if, after one year of monitoring, TTHM annual average is less than or equal to 0.060 mg/L and HAA5 annual average is less than or equal to 0.045 mg/L.
* The department may return a system to routine monitoring at the department's discretion.
Approved Methods for Disinfection Byproduct Compliance Monitoring
Contaminant and Methodology | EPA Methodi | Standard Method2 | ASTM Methods |
TTHM | |||
P&T/GC/EICD & PID | 502.24 | ||
P&T/GC/MS | 524.2, 524.3, 524.4 | ||
LLE/GC/ECD | 551.1 | ||
HAA5 | |||
LLE (diazomethane)/GC/ECD | 6251 B5, 6251 B-0712 | ||
SPE (acidic methanol)/GC/ECD | 552.15 | ||
LLE (acidic methanol)/GC/ECD | 552.2, 552.3 | ||
Ion chromatography electrospray ionization tandem mass spectrometry (IC-ESI-MS/MS) | 55710 | ||
Bromate | |||
Ion chromatography | 300.1 | D 6581-00 | |
Ion chromatography & postcolumn reaction9 | 317.0Rev. 2.06, 326.06 | ||
IC/ICP-MS9 | 321.86,7 | ||
Two-dimensional ion chromatography (IC) | 302.011 | ||
Ion chromatography electrospray ionization tandem mass spectrometry (IC-ESI-MS/MS) | 55710 | ||
Chemically suppressed ion chromatography | D 6581-08 A | ||
Electrolytically suppressed ion chromatography | D 6581-08 B | ||
Chlorite** | |||
Amperometric titration | 4500-ClO2E8 | ||
Amperometric sensor | ChlordioX Plus8, 13 | ||
Spectophotometry | 327.0 Rev. 1.18 | ||
Ion chromatography | 300.0, 300.1, 317.0 Rev. 2, 326.0 | ||
Chemically suppressed ion chromatography | D 6581-08 A | ||
Electrolytically suppressed ion chromatography | D 6581-08 B |
ECD = electron capture detector
EICD = electrolytic conductivity detector
GC = gas chromatography
IC = ion chromatography
LLE = liquid/liquid extraction
MS = mass spectrometer
P&T = purge and trap
PID = photoionization detector
SPE = solid phase extractor
The procedures shall be done in accordance with the documents listed below. The incorporation by reference of the following documents was approved by the Director of the Federal Register on February 16, 1999, 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, 401 M Street, SW, Washington, DC 20460 (telephone: (202)260-3027); or at the Office of Federal Register, 800 North Capitol Street, NW, Suite 700, Washington, DC 20408.
1EPA: The following methods are available from the National Technical Information Service (NTIS), U.S. Department of Commerce, 5285 Port Royal Road, Springfield, VA 22161 (telephone: (800)553-6847):
Methods 300.0 and 321.8: Methods for the Determination of Organic and Inorganic Compounds in Drinking Water, Volume 1, USEPA, August 2000, EPA 815-R-00-014 (available through NTIS, PB2000-106981).
Method 300.1: "Determination of Inorganic Anions in Drinking Water by Ion Chromatography, Revision 1.0," EPA-600/R-98/118, 1997 (available through NTIS, PB98-169196).
Method 317.0: "Determination of Inorganic Oxyhalide Disinfection By-Products in Drinking Water Using Ion Chromatography with the Addition of a Postcolumn Reagent for Trace Bromate Analysis, Revision 2.0," USEPA, July 2001, EPA 815-B-01-001.
Method 326.0: "Determination of Inorganic Oxyhalide Disinfection By-Products in Drinking Water Using Ion Chromatography Incorporating the Addition of a Suppressor Acidified Postcolumn Reagent for Trace Bromate Analysis, Revision 1.0," USEPA, June 2002, EPA 815-R-03-007.
Method 327.0: "Determination of Chlorine Dioxide and Chlorite Ion in Drinking Water Using Lissamine Green B and Horseradish Peroxidase with Detection by Visible Spectrophotometry, Revision 1.1," USEPA, May 2005, EPA 815-R-05-008.
Methods 502.2, 524.2, 551.1, and 552.2: Methods for the Determination of Organic Compounds in Drinking Water-Supplement III, EPA-600/R-95-131, August 1995 (NTIS PB95-261616).
Method 524.3: "Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry, Version 1.0," June 2009. EPA 815-B-09-009. Available at www.nemi.gov.
Method 524.4: "Measurement of Purgeable Organic Compounds in Water by Gas Chromatography/Mass Spectrometry Using Nitrogen Purge Gas, Version 1.0," May 2013. EPA 815-R-13-002. Available at www.nepis.epa.gov.
Method 552.1: Methods for the Determination of Organic Compounds in Drinking Water-Supplement II, EPA-600/R-92-129, August 1992 (NTIS PB92-207703).
Method 552.3: "Determination of Haloacetic Acids and Dalapon in Drinking Water by Liquid-liquid Microextraction, Derivatization, and Gas Chromatography with Electron Capture Detection, Revision 1.0," USEPA, July 2003, EPA-815-B-03-002.
24500-ClO2 E and 6251B: Standard Methods for the Examination of Water and Wastewater, 19th (1995), 20th (1998), 21st (2005), and 22nd (2012) editions, American Public Health Association, which are available from the American Public Health Association, 800 I Street, NW, Washington, DC 20001-3710.
3Method D 6581-00: American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428: Annual Book of ASTM Standards, Volume 11.01, American Society for Testing and Materials, 2001 (or any year containing the cited version).
4If TTHMs are the only analytes being measured in the sample, then a PID is not required.
5The samples must be extracted within 14 days of sample collection.
6Ion chromatography and postcolumn reaction or IC/ICP-MS must be used for bromate analysis for purposes of demonstrating eligibility of reduced monitoring.
7Samples must be preserved at sample collection with 50 mg ethylenediamine (EDA)/L of sample and must be analyzed within 28 days.
8Amperometric titration or spectrophotometry may be used for routine daily monitoring of chlorite at the entrance to the distribution system, as prescribed in 41.6(1) "c "(3)"1." Ion chromatography must be used for routine monthly monitoring of chlorite and additional monitoring of chlorite in the distribution system, as prescribed in 41.6(1)"c "(3)"2" and "3."
9These are the only methods approved for reduced bromate monitoring under 41.6(1)"c "(2)"2."
10EPA Method 557, "Determination of Haloacetic Acids, Bromate, and Dalapon in Drinking Water by Ion Chromatography Electrospray Ionization Tandem Mass Spectrometry (IC-ESI-MS/MS)," August 2009. EPA 815-B-09-012. Available at www.nemi.gov.
11EPA Method 302.0, "Determination of Bromate in Drinking Water Using Two-Dimensional Ion Chromatography with Suppressed Conductivity Detection," September 2009. EPA 815-B-014. Available at www.nemi.gov.
12Standard Methods Online is available at www.standardmethods.org.The year in which each method was approved by the Standard Methods Committee is designated by the last two digits in the method number. The methods listed are the only online versions that may be used.
13ChlordioX Plus. "Chlorine Dioxide and Chlorite in Drinking Water by Amperometry Using Disposable Sensors," November 2013. Available from Palintest Ltd., Jamike Avenue (Suite 100), Erlanger, KY 41018.
Schedule | System Population | Date by which system must begin Stage 2 compliance monitoring |
1 | At least 100,000 | April 1,2012 |
2 | 50,000-99,999 | October 1,2012 |
3 | 10,000-49,999 | October 1,2013 |
4 | Fewer than 10,000 | *October 1, 2013, for all GW systems and any SW/IGW systems that did not conduct Cryptosporidium sampling under 567-paragraph 43.11 (3) "b "(2)"4" *October 1, 2014, for SW/IGW systems that conducted Cryptosporidium sampling under 567-paragraph 43.11 (3) "b" (2)"4" |
If the system does not complete the four consecutive quarters of monitoring, the system must calculate the compliance with the MCL based on the average of the available data from the most recent four quarters. If the system collects more than one sample per quarter at a monitoring location, all samples taken in the quarter at that location must be averaged to determine a quarterly average to be used for the LRAA calculation. If a system fails to monitor, it is in violation of the monitoring requirements for each quarter that a monitoring result would be used in calculating an LRAA.
Routine Monitoring
Source water type | Population size category | Monitoring frequency | Total number of distribution system monitoring location sites per monitoring period |
SW/IGW | <500 | per year | 2 |
500-3,300 | per quarter | 2 | |
3,301-9,999 | per quarter | 2 | |
10,000-49,999 | per quarter | 4 | |
50,000-249,999 | per quarter | 8 | |
250,000-999,999 | per quarter | 12 | |
Groundwater | <500 | per year | 2 |
500-9,999 | per year | 2 | |
10,000-99,999 | per quarter | 4 | |
100,000-499,999 | per quarter | 6 |
Reduced Monitoring
Source water type | Population size category | Monitoring frequency1 | Distribution system monitoring location sites per monitoring period2 |
SW/IGW | <500 | per year | Monitoring may not be reduced |
500-3,300 | per year | 1 sample per year at the same location if the highest TTHM and HAA5 measurements occurred at the same location and in the same quarter, analyzed for both TTHM and HAA5 | |
3,301-9,999 | per year | 2 samples: one at the location and during the quarter with the highest TTHM single measurement; one at the location and during the quarter with the highest HAA5 single measurement | |
10,000-49,999 | per quarter | 2 samples: one at the highest TTHM LRAA location and one at the highest HAA5 LRAA location | |
50,000-249,999 | per quarter | 4 samples: one sample each at the highest two TTHM LRAA locations and one sample each at the highest two HAA5 LRAA locations | |
250,000-999,999 | per quarter | 6 samples: one sample each at the highest three TTHM LRAA locations and one sample each at the highest three HAA5 LRAA locations | |
Groundwater | <500 | every third year | 1 sample at the same location if the highest TTHM and HAA5 measurements occurred at the same location and in the same quarter, analyzed for both TTHM and HAA5 |
500-9,999 | per year | 1 sample per year at the same location if the highest TTHM and HAA5 measurements occurred at the same location and in the same quarter, analyzed for both TTHM and HAA5 | |
10,000-99,999 | per year | 2 samples: one at the location and during the quarter with the highest TTHM single measurement; one at the location and during the quarter with the highest HAA5 single measurement | |
100,000-499,999 | per quarter | 2 samples: one at the highest TTHM LRAA location and one at the highest HAA5 LRAA location |
1Systems on a quarterly monitoring frequency must collect the sample(s) every 90 days.
2Each sample must be analyzed for all TTHM and HAA5 components.
Iowa Admin. Code r. 567-41.6