Quick Reference Guide for the Ground Water Rule

What is the Ground Water Rule?

The U.S. Environmental Protection Agency (EPA) published the Ground Water Rule (GWR) on November 8, 2006.  One goal of the GWR is to provide increased protection against microbial pathogens, specifically bacterial and viral pathogens, in public water systems (PWSs) that use ground water.  One of the key elements to the GWR is monitoring.  There are two types of monitoring that are a part of the GWR:

  • Source Water Monitoring:  Triggered source water monitoring is required for any GWS that has a routine, positive total coliform result under the Total Coliform Rule (TCR) and does not provide and monitor for 4-log treatment of viruses.
  • Compliance Monitoring:  GWSs that provide at least 99.99 percent (4-log) treatment of viruses of all of their ground water can conduct compliance monitoring to show they are providing consistent and sufficient treatment of their ground water.  Systems that choose to do compliance monitoring are not subject to triggered source water monitoring.

Requirements of Source Water Monitoring for GWSs with Their Own Source

When a GWS has a routine, positive total coliform result under the TCR that system must collect at least one ground water source sample before treatment from each source in use when the positive total coliform result was collected.  This source sample is called a triggered source water sample.

If the triggered source water sample is positive for E. coli, the Department will require the GWS to take five follow-up triggered source water samples from that same source.  If any one of the follow-up triggered source water samples is E. coli positive, the system must take corrective action.

Requirements of Source Water Monitoring for GWSs that Purchase Their Source Water

Per the Ground Water Rule, a consecutive system with a routine, positive total coliform result under the TCR must notify its wholesale system(s) within 24 hours of being notified of the positive sample.  However, to ensure notification is being consistent, the Department is notifying the wholesaler on behalf of the consecutive system.

Requirements of Source Water Monitoring for GWSs that Sell Their Water

A wholesale system that receives notice from the Department of a routine, positive total coliform result under the TCR must collect a triggered source water sample before treatment from each source in use when the positive total coliform result was collected.  If the triggered source water sample is positive for E. coli, the wholesale system must notify, by public notice, their consumers and all consecutive systems served by that source within 24 hours of being notified.  Any consecutive systems served by that source must notify, by public notice, their consumers within 24 hours of being notified of the result.  The wholesale system must collect five follow-up triggered source water samples from that same source.  If any one of the follow-up triggered source water samples is E. coli positive, the wholesale system must take corrective action.

Requirements of Compliance Monitoring

GWSs that choose to perform compliance monitoring are not subject to triggered source water monitoring; however, those systems must report monthly chlorine disinfectant residuals to the Department.  GWSs that decide to do compliance monitoring must work with the Department to determine if that system meets 4-log removal/inactivation of viruses and to determine the minimum chlorine disinfectant level.  GWSs using chloramines for disinfection would not qualify for this monitoring.  Compliance monitoring is based on a system's population. 

  • GWSs serving ≤ 3300 must take a daily grab sample during peak flow and record that chlorine disinfectant residual.  These results are reported monthly to the Department.
  • GWSs serving > 3300 must monitor continuously and record the lowest, daily chlorine disinfectant residual.  These results are reported monthly to the Department.

If there are any questions regarding the Ground Water Rule, please contact Gary Stefanovsky at 701-328-5287.