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Revised Coliform Monitoring Requirements

EPA Revised Total Coliform Rule

On April 1, 2016, Oregon Health Authority Drinking Water Services (DWS) began implementing provisions of the Environmental Protection Agency (EPA) Revised Total Coliform Rule. These regulations apply to all public water systems with the intent of minimizing potential pathways for fecal contamination to enter distribution systems and to better protect the public from waterborne illness. The coliform monitoring revisions under this rule do not alter the source water monitoring required for groundwater systems. Changes to the revised rules are summarized below with links to additional resources for reference.

These requirements took effect on April 1, 2016

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Revised Maximum Contaminant level (MCL)

Under the revised rule, total coliform occurrence will continue to be investigated although it is no longer associated with an MCL. Instead, emphasis is placed on the MCL for E. coli because it is a reliable indicator of fecal contamination.

The E. coli MCL is exceeded if:

  • The presence of E. coli is confirmed,
  • Repeat samples are not collected, or
  • When a total coliform-positive sample is not analyzed for E. coli.
Combinations resulting in E. coli MCL
Routine Repeat
EC+ Any missing sample
TC+ TC+ (with no E. coli analysis)

Coliform Monitoring Changes

To learn how the revised rule applies to your water system, please review the article PDf iconColiform Monitoring Changes published in the DWS October 2015 Pipeline Newsletter. The article describes routine and repeat sampling required in the distribution system and what may trigger an increase in sampling frequency.

Some coliform monitoring changes include:

  • The number of repeat samples to collect after a routine coliform positive is reduced from 4 to 3 for all water systems. (Note: The requirement for groundwater systems to collect triggered source water samples remains unchanged.)
  • Additional routine samples the month following a total coliform detection are:
    • No longer required for water suppliers sampling monthly, and
    • Reduced from 5 to 3 samples for water suppliers monitoring quarterly.
  • Systems affected by increased sampling include:
    • Seasonally operated water systems will sample monthly rather than quarterly.
    • Non-Community water systems will sample monthly rather than quarterly:
      • After exceeding the E. coli MCL,
      • After multiple coliform investigations have been triggered, or
      • After the water system has incurred certain violations

Investigations Following Coliform-Positive Samples

A formal investigation is required when total coliform or E. coli is confirmed in the water system, or when repeat samples are not collected. The purpose of the investigation is to identify and correct sanitary defects that could provide a pathway for microbial contamination to enter the distribution system.

There are two levels of investigations:

  • The first is conducted by water system operators.
  • The second, a more detailed investigation, is conducted by your water system's drinking water regulator when the E. coli MCL is exceeded or if total coliform is confirmed multiple times within a year.

To learn more about the investigation process, please review the PDf iconLevel 1 and Level 2 Coliform Investigations article published in the October 2015 DWS Pipeline Newsletter. The investigation forms are available at the following links:

  • Level 1 Coliform Investigation Form (Investigation completed by water supplier): Fillable MS Word or PDf iconPDF
  • Level 2 Coliform Investigation Form (Investigation completed by regulator): Fillable MS Word or PDf iconPDF


Revised Coliform Sampling Plan

Coliform sampling plans are required for all public water systems to ensure sampling represents water being served in the distribution system. An article in the October 2015 DWS Pipeline Newsletter PDf iconIs your water system's coliform sampling plan up-to-date summarizes the required elements for a coliform sampling plan and describes changes water suppliers may consider for routine and repeat sampling sites under the revised rules. A revised coliform sampling plan template and response chart are available for small water systems:


New Requirements for Seasonal Systems

Seasonal water systems are non-community systems that are not operated as a public water system on a year-round basis and that start up and shut down at the beginning and end of an operating season. To learn more about coliform monitoring and reporting changes for seasonal water systems, please review the DWS October 2015 Pipeline article PDf iconNew Requirements for Seasonal Water Systems.

Some changes include:

  • Seasonally operated water systems will increase coliform sampling from quarterly to monthly while operating.
  • Seasonal systems that depressurize all or part of the distribution system during the off season must complete an authorized start-up procedure before opening each year. (Note: Systems consisting solely of a hand pump are not required to complete seasonal start-up procedures.)

PDf iconNew Seasonal Water System Start-Up Checklist - Form to certify seasonal start-up procedures were completed prior to serving the public in the current calendar year.

Public Notice Templates

Several new and revised public notice templates may be found on our Public Notice Resources & Templates page under "Notices for Microbiological Contaminants".

Additional Resources