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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

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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.

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