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Groundwater Rule Monitoring Requirements
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Triggered Source Water Monitoring
Also called triggered source sampling, triggered source water monitoring tests the untreated source water (from a well or spring) for coliform bacteria when "triggered." The trigger is a positive (present) result from a routine coliform sample in the distribution system. Groundwater systems that disinfect are subject to the triggered monitoring requirement under the Groundwater Rule unless they are implementing the GWR compliance monitoring option. The triggered samples must be incorporated into the water system's coliform sampling plan.
  • Frequently Asked Questions (FAQs) About Triggered Source Water Monitoring
  • Updates to the Coliform Sampling Plan Template for Small Systems (PDF; Summer 2009 Pipeline newsletter, page 7)
  • Coliform Sampling Plan Template for Small Public Water Systems Serving Up to 1,000 Persons:  fillable MS Word -or- PDF
    Note: There is no template for systems with populations over 1,000 people. For those sized systems, add into the coliform sampling plan that the triggered samples at the well(s) or spring(s) are also required, in addition to the repeat distribution samples.
  • Representative Triggered Source Water Monitoring Plans: Systems with large distributions or multiple pressure zones may request to take triggered source samples only at those sources contributing to the location where the routine coliform distribution sample was positive. Prior approval of a representative triggered source water monitoring plan is required.

Source Assessment Monitoring
In the Groundwater Rule, source assessment monitoring refers to ongoing, periodic sampling of the source water that is not triggered by another test result. There are two types of source assessment monitoring:

Additional or Confirmation Monitoring
After one E. coli-positive result from the source, a system must take five additional source samples within 24 hours to confirm fecal contamination, unless the system pursues corrective action immediately (with regulator approval).

GWR Compliance Monitoring
In lieu of triggered monitoring, a groundwater system that provides 4-log (99.99%) inactivation or removal of viruses can pursue the compliance monitoring option to meet Groundwater Rule requirements (GWR compliance monitoring). This option is only available to systems that: a) Drinking Water Services hydrogeologists determine do not need source reconstruction; and b) demonstrate that they achieve 4-log virus treatment before the first user. If approved, the water system will be assigned a minimum chlorine residual that must be maintained and monitored at the entry point.