The Groundwater Rule (GWR) provides increased protection against microbial pathogens in public water systems that use groundwater sources. The Environmental Protection Agency (EPA) is particularly concerned about groundwater systems susceptible to fecal contamination since they may contain disease-causing pathogens.

The rule is triggered when a Routine Total Coliform sample has a positive Total Coliform result. The GWR applies to public water systems that serve groundwater as well as any system that mixes surface and groundwater if the groundwater is added directly to the distribution system and provided to consumers without treatment.

What to Do If There's an Exceedance

Positive for Fecal Coliforms (i.e., E. coli, enterococci, coliphage)

If a system gets a notification that their Groundwater Rule sample was positive for fecal coliforms, the system has triggered a Boil Water Advisory, and the system:

• Must contact ADEQ, by the end of the business day, or within 24 hours (if the business day has already ended)
• Has the opportunity to take five confirmation samples at the well (within 24 hours of laboratory notification of positive result) to indicate whether one of the four Ground Water Rule corrective actions must be taken

​If any of the confirmation samples have a fecal coliform positive result, the system must do one or more of the following corrective actions:

• Correct all significant deficiencies
• Provide a permanent alternative source of water
• Eliminate the source of contamination
• Provide Treatment that reliably achieves 99.99 percent (4-log) inactivation and /or removal of viruses

The system has 30 days from the trigger date to consult with the state to determine corrective actions, and 120 days from the trigger date to complete the corrective actions, or be in compliance with a state-approved corrective action plan and schedule.