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FAQs About Triggered Source Water Monitoring
Question 1: What is triggered monitoring?

  • Also called triggered source sampling, this requirement is to test the untreated source water (from a well or spring) for coliform when "triggered." The trigger is a positive (present) result from a routine coliform sample in the distribution system. Groundwater systems are subject to the triggered monitoring requirement under the Groundwater Rule unless they are implementing the compliance monitoring option.

Question 2: Our groundwater system does not disinfect the water (no chlorine, UV, etc.). What do the triggered monitoring requirements mean for us?

  • For systems less than 1,000 in population, there is very little change. If a routine distribution sample is positive, you will need to make sure that one of the already-required repeat samples comes directly from the groundwater source (well or spring). The repeat sample taken at the source will also serve as a triggered sample for the Groundwater Rule. (Label this double-duty sample as a "Triggered" "Source" sample.) Unlike systems that disinfect, your system does not need to take additional source sample(s) because your distribution samples have the same microbial content as the source water.
  • For systems >1,000, it is a little different. Your triggered source samples cannot serve "double duty"; they must be taken in addition to the repeat distribution samples required (that's three repeats for systems >1,000). Update the coliform sampling plan to include taking a fourth (triggered) sample at the source.

Question 3: Our groundwater system disinfects and is not conducting Compliance Monitoring. What do the Triggered Monitoring requirements mean for us?

  • If a routine coliform test comes back positive, your system needs to collect:

    1. An untreated triggered source sample within 24 hours from each groundwater source in use at the time the routine positive sample was collected. (This is a new requirement that came into effect with the Groundwater Rule.)
    2. The repeat samples from the distribution system within 24 hours that have always been required following a positive result (from the Total Coliform Rule). Be careful filling out the lab forms (PDF) so it will be clear that your system has submitted all types of follow-up samples.
    3. Extra routine samples the following month, as previously required after a positive distribution sample (from the Total Coliform Rule). For most groundwater systems, the number of routine samples required the following month will be five.
  • Your coliform sampling plan needs to include the triggered source samples, so whoever receives the positive result from a routine coliform sample will know what additional samples they need to take right away. See the revised coliform sampling plan template for systems serving up to 1,000 customers, available as a fillable MS Word or PDF document.

Question 4: We've never had a positive coliform sample in the distribution, so I doubt we'll be taking triggered samples. Are we off the hook from any new requirements?

  • Even if no source samples are triggered, the Groundwater Rule requires systems that disinfect the water in any way - either with oxidizing agents (e.g., chlorine) or ultraviolet light - to submit at least one "raw" untreated water sample from each source per year, starting in 2010.  The Groundwater Rule calls this type of source sampling (that is not tied to another test result) Assessment Monitoring.

Question 5: Can a triggered source sample count as the required annual or monthly source sample (Assessment Monitoring)?

  • Yes.

Question 6: What happens if a triggered source sample (that is, from the well or spring) comes back positive for total coliform?

  • As in the past, the operator may want to disinfect the well or spring (for example, by shock chlorination), utilizing professional judgment when applying the procedure. If there is a consistent problem with total coliform, Oregon Drinking Water Services (DWS) may ask the water system to meet the standard of 4-log inactivation of viruses.

Question 7: What happens if a triggered source sample comes back positive for fecal coliform/E. coli?

  • The water system must collect five additional or "confirmation" source samples within 24-hours. In certain circumstances, a water system may skip confirmation sampling and move directly to corrective action if the regulator approves.
  • If any one of these five source samples is fecal coliform/E. coli positive, the system must issue a Tier One (i.e., "Boil Water") Notice within 24-hours and take corrective action (PDF). In some cases, the "Boil Water" order could be lifted in a short time frame. For example: a system could increase the chlorine dosage so that it meets the CT for 4-log viral inactivation and show that the increased chlorine residual is present throughout the distribution system. This could take less than a day (or even an hour) for a system with little distribution piping (such as for a transient system). Such a system would also need to start GWR compliance monitoring from this point forward as part of corrective actions. However, if the source well (or spring) does not meet current construction standards, corrective action could require reconstructing the source, or switching to a new source. For details regarding this issue, please consult with DWS hydrogeology staff in the Springfield office at 541-726-2587 (8am-5pm PT, Mon-Fri).
  • If these additional samples confirm the presence of E. coli at the source, the water system may stop collecting triggered source samples during the period that they are implementing corrective action. At that point, the sampling has already confirmed fecal contamination in the untreated source water, so there is no need to continue checking its microbial content. The system should keep taking routine coliform samples in the distribution system, as always.
  • If any (or all) of the above five additional samples test positive only for total coliform (not E. coli), see the answer to Question 6 above. The system would continue its routine coliform sampling in the distribution system and take a source sample again if triggered by a positive distribution sample taken at another time.

Question 8: I took several coliform samples in the distribution system, and more than one came back positive. How many triggered source samples do I need to take?

  • You need to take one triggered sample from all active sources each time a routine sample tests positive. If more than one positive routine sample was taken on the same day, you still only need to collect one triggered sample per active source.
  • An illustration: In March, your routine sample tests positive for total coliform, and you quickly take the required repeat samples and triggered source sample(s). As has been the case all along, that positive routine sample from the distribution means you will need to take five additional or "temporary" routine samples the following month. In April, more than one of those temporary routine samples comes back positive for total coliform. At this point, you do not need to take any more repeats (the presence of total coliform in the distribution has already been confirmed), but you need to take another source sample because it was triggered again by the newer positive distribution samples.

Question 9: I took a source sample at the same time as a routine distribution sample that tested positive for total coliform. Can that source sample count as the triggered source sample?

  • Yes, as long as the source sample was taken no earlier than the same day as the positive sample.

Question 10: Is representative sampling allowed to meet the triggered monitoring requirements?

  • Representative sampling may be allowed for larger systems with multiple groundwater sources and distribution system pressure zones if DWS has already approved the system's sampling plan. See more information about representative monitoring under Triggered Source Water Monitoring.

Question 11: We purchase water from another water system. If our routine coliform sample(s) test positive, who takes the triggered sample at the source(s)?

  • The wholesaling water system must collect a triggered sample from each groundwater source that supplies water to the purchasing system (unless the wholesaling system is conducting Compliance Monitoring). The Groundwater Rule requires specific communications between purchasing and wholesaling systems so that these requirements are met (see related Summer 2010 Pipeline article (PDF)). These triggered sampling requirements should be spelled out in both systems' coliform sampling plans.