Triggered Source Water Monitoring Requirements

Waterworks must collect a raw water sample from each groundwater source in use at the time a Total Coliform Rule (TCR) sample from the distribution system indicates the presence of coliform bacteria.

If the triggered source water sample is E. coli positive, then the waterworks must collect five additional source water samples and have them analyzed for the presence of E. coli. If any of these additional samples are E. coli positive then the Office of Drinking Water (ODW) will require Corrective Action.

An ODW-approved triggered source water monitoring plan will be required for all waterworks.

The triggered source water monitoring plan may be a separate document, or may be incorporated into the waterworks’ overall distribution system TCR Bacteriological Sample Site Report. A triggered source water monitoring plan should include:

• Map or schematic of the system, noting all sources, treatment, entry points, main distribution lines, storage tanks, pump stations, and pressure zones.
• Identification of each source, with an indication of type (well, spring or surface water) and use (permanent, emergency, seasonal).
• Well construction information, including depth to screen levels, water quality characteristics and well drillers logs.
• Each TCR monitoring location must have a source associated with it. If needed, provide the basis for this determination (system hydraulics, operation, water quality data, etc.) Representative source water sampling may be allowed for waterworks with multiple groundwater sources to meet the triggered source water monitoring requirements. Two scenarios will be considered for representative source water sampling:
• Hydraulically isolated portions of a distribution system receive water only from specific well(s)
• Wells are in the same hydrogeological setting.

Some waterworks may need to develop multiple scenarios to reflect the variety of ways their system is operated over the year. The waterworks should submit appropriate supporting studies and a narrative explanation. Locating sources, entry points, pressure zones, and TCR sites on the distribution system map may be sufficient for a simple distribution system plan. Systems that are hydraulically complex will require a more advanced hydraulic analysis.

More detailed information can be found at:

• Ground Water Rule Triggered and Representative Monitoring: A Quick Reference Guide