Coliform Resources

The information on this page is designed for and intended for use by Drinking Water Services County and Department of Agriculture partners who have specialized training and are registered as environmental health specialists. If you have questions regarding this material please contact Drinking Water Services at (971) 673-0405 or email info.drinkingwater@dhsoha.state.or.us.

On this page:

Coliform Monitoring Resources
Groundwater Rule procedures following a positive routine coliform sample
Resources to address confirmed E. coli-positive sources under Groundwater Rule
Representative and combined source monitoring

The Groundwater Rule (GWR), which took effect December 1st, 2009, applies to all public water systems that use groundwater sources or purchase groundwater. The primary purpose of the rule is to protect the public from fecal-related bacterial and viral pathogens in public groundwater systems. E. coli is used as the indicator of fecal contamination. If a groundwater source (well or spring) is found to be fecally contaminated, or a significant deficiency or rule violation is identified during a water system survey, the public water system must take corrective action to assure that their consumers are adequately protected. See the following resources for more information on implementing the rule.

Coliform Monitoring Resources

The following coliform monitoring resources are available to assist regulators when responding to coliform positive alerts, required follow-up sampling, and actions needed to investigate and correct coliform issues. Based on monitoring results or violations incurred, non-community water systems may require changes to coliform monitoring frequencies. Removal of disinfection at groundwater systems requires action to demonstrate source water quality standards are met.

Coliform Response Chart - For groundwater systems serving up to 1,000 persons
Coliform Alert Response Procedure - For responding to routine sample coliform alerts for all groundwater systems.
Coliform Investigation Procedure - Investigations must be completed within 30 days.
Level 1 Coliform Investigation Form (Fillable) - Conducted by water system operators after exceeding total coliform trigger
Level 2 Coliform Investigation Form (Fillable) - Required after exceeding E. coli MCL or second level 1 coliform investigation in a 12-month period.
Coliform – Increase to monthly and steps to return to quarterly monitoring
Removing Chlorination or UV Light Procedure - Applies to groundwater systems
Total Coliform Invalidation Procedure

Resources for Shock Chlorination for Storage Tank, Well and Distribution System.

Groundwater Rule procedures following a positive routine coliform sample
Under the Groundwater Rule, triggered source water monitoring is required after (or "triggered by") a total coliform positive routine sample.

The main Groundwater Rule Monitoring Requirements page has definitions for the different types of GWR monitoring and answers Frequently Asked Questions about triggered sampling.

Resources to address confirmed E. coli-positive sources under Groundwater Rule

Confirmed E. coli Positive Source Procedure: Guidance for the groundwater source evaluation process. Ensures that the proper corrective action is implemented after E. coli has been confirmed in the source.

Appendix I: Monitoring Following Removal of Temporary Sources of Fecal Contamination (not yet available)
Appendix II: Ongoing Verification that PWS is Meeting Compliance Monitoring Requirements

Response Flow Chart for E. coli Contaminated Groundwater Source - This flow chart helps show what protocols shall be taken following E. coli confirmed in a groundwater source
Source Evaluation Request Form: Use this fillable document to request an evaluation of the well by the DWS Regional Hydrogeologist.
Disinfection Verification Form for Groundwater Systems: This form may be used to determine whether the groundwater system provides the required level of 4-log inactivation viruses through chlorination with contact time.
Cover Letter Template for Requiring GWR Compliance Monitoring (Chlorine Residual Monitoring at the Entry Point): If the approved corrective action consists of the water system providing continuous 4-log treatment of viruses and conducting compliance monitoring, use the attached template. Note that the source construction must be approved by the DWS Regional Hydrogeologist.
Monthly Groundwater Disinfection Reporting Form: fillable -or- PDF
The monthly reporting form will need to be attached to the cover letter for compliance monitoring.
Determining 4-hr interruption of 4-log disinfection – revised 01/29/2020
Template Follow Up Letter When Corrective Action is Not Completed on Schedule: Use this template letter when the groundwater system fails to take corrective action or be on an approved schedule within the required 120 day timeframe. The timeline starts when the confirmed E. coli groundwater source is reported.
Hydrogeologist responsibilities for confirmed E. coli & ground water under direct influence of surface water evaluation procedure.

Representative and Combined Source Monitoring

Systems with large distribution or multiple pressure zones may request to take triggered source samples only at those sources contributing to or representative of the location where the routine coliform distribution sample was positive. Systems with difficulty sampling at each individual source may request to take triggered or assessment source samples at the combined source location prior to any treatment. Prior approval of a representative or combined source monitoring plan is required. Contact your DWS Technical Services staff for further information.