In November of 2006, the EPA Published the Ground Water Rule (GWR) to reduce the risk of illness caused by microbial contamination of public ground water systems (GWSs).  The first compliance date for the rule is December 1, 2009.  On that date, triggered source water requirements for new and existing GWSs are required when total coliform bacteria are detected in ROUTINE or INCREASED ROUTINE total coliform samples.  Repeat samples under the Total Coliform Rule do not trigger the GWR.

As of November 30, 2009, new ground water sources put in place after this date must meet triggered source water monitoring requirements or conduct compliance monitoring.  As of December 1, 2009, GWSs that do not provide at least 4-log virus inactivation (demonstrated through various treatment technologies) and have an approved 4-log application, must conduct triggered source water monitoring for positive total coliform samples within 24 hours of being notified of a total coliform positive sample. GWSs must collect at least one ground water (raw water) sample from each source in use at the time the total coliform sample was collected and submit it to a certified laboratory for analysis using one of the approved methods.  The sample(s) from the well must be unchlorinated (well pumped until no chlorine residual detected).

If the triggered monitoring is positive for fecal indicators (either E. coli, Coliphage or Enterococci), the GWS must then either take corrective action directed by the state or conduct additional source water sampling.  Additional source water sampling requires five additional samples be collected from any well that had a fecal indicator positive from the triggered source water monitoring sample within 24 hours of notification of the fecal indicator positive.

Due to the 24-hour requirement and for ease of resampling, it is advisable for systems to submit compliance total coliform samples to the laboratory Monday through Wednesday.

The EPA has approved multiple methods for monitoring of fecal indicators (e.g. E. coli, Enterococci and Coliphage) in source water. Most water systems will likely collect samples for both total coliform and E. coli by Standard Method 9223B (Colilert/Colisure).

In addition to the Total Coliform/Fecal Indicator source water monitoring requirement, systems must simultaneously collect chlorine residual samples (taken at the wellhead, not in the distribution system) in a 250 mL amber bottle, or equivalent, for any samples collected for compliance with the Ground Water Rule.