Protecting Public Health and the Environment.

Long Term 2 Enhanced Surface Water Treatment Rule – Source Water Monitoring for Public Water Systems Serving <10,000

The purpose of the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is to reduce illness linked with the contaminant Cryptosporidium and other microbial pathogens in drinking water. The LT2ESWTR supplements existing regulations for surface water systems, including ground water under the direct influence of surface water (GWUDI) systems, by targeting additional Cryptosporidium treatment requirements for systems with higher risk sources found during LT2ESWTR monitoring. It is important to note that the LT2ESWTR does not require additional Cryptosporidium treatment for all public water systems (PWS). The LT2ESWTR also contains provisions to reduce risks resulting from uncovered finished water reservoirs and to ensure that systems maintain microbial protection as they take steps to decrease the formation of disinfection byproducts that result from chemical water treatment.

Key Provisions

  • The LT2ESWTR applies to all PWS supplied by a surface water or GWUDI source.
  • All surface water and GWUDI systems must conduct an initial round of source water monitoring and a second round 6 years later for each plant that treats a surface water or GWUDI source. This monitoring includes  E. coli enumeration (and turbidity if required) to determine what level, if any, of additional treatment must be provided.
  • Filtered systems must determine their Cryptosporidium treatment bin classification and provide additional treatment for Cryptosporidium, if required.
  • All unfiltered systems must provide treatment for Cryptosporidium.

General Source Water Monitoring Information

  • Any new surface water or GWUDI sources must conduct an initial and a second round of source water monitoring.
  • Filtered systems serving fewer than 10,000 people must sample their source water (prior to any treatment) for E. coli enumeration (not presence/absence) at least once every two weeks for 12 months.
    • A filtered system serving fewer than 10,000 people may avoid E. coli monitoring by monitoring for Cryptosporidium and notifying DEQ of this no later than 3 months prior to the date the system is otherwise required to start E. coli monitoring.
    • Filtered systems serving fewer than 10,000 people must sample their source water (prior to any treatment) for Cryptosporidium at least twice per month for 12 months or at least monthly for 24 months based on the annual mean E. coli concentration of their source water type (lake/reservoir vs. flowing stream).
  • Systems using GWUDI must also sample their source water (prior to any treatment) for E. coli at least once every two weeks for 12 months based on the E. coli level that applies to the nearest surface water body. If no surface water body is nearby, the system must comply based on the requirements that apply to systems using lake/reservoir sources.

Source Water Monitoring Starting Dates for Filtered Systems Serving <10,000

Filtered systems serving fewer than 10,000 Second round of source water monitoring
no later than the month beginning ... 
Monitoring for E. coli October 1, 2017
Monitoring for Cryptosporidium (if required based on E.coli sampling results) April 1, 2019

Sample Schedule Plans

Prior to sampling, owners and operators must submit to DEQ a sampling plan that includes the following:

  • Specific dates for sampling events that must occur at least once every 2 weeks  for 12 months for systems serving less than 10,000 people and monitoring for E. coli, beginning October 1, 2017.
    • Samples must be collected within 2 days before or 2 days after the specified date (Wednesdays are recommended), and the results must submitted to DEQ by the 10th day of the following month.
  • Description or diagram of sample location(s) in relation to sources, treatment processes, (including pretreatment) and any filter backwash recycling.

System Specific Sampling Requirements

Systems with more than one surface water supply source, one of the following is required for collecting samples:

  • Collect samples from a tap where all sources are combined and before any treatment.
  • Collect composite samples that represent all sources. In a composite sample, the volume of sample from each source must be weighted according to the proportion of each source in the total plant flow at the time of the sample. You should contact DEQ and your laboratory for assistance.
  • Collect and analyze a sample from each source separately and calculate a weighted average of all the results for the sampling date. You should contact DEQ and your laboratory for assistance.

Seasonal Sources

  • Owners and operators of systems with seasonal sources need to sample in the months of operation, which is when the plant is running, not only when water is being served.
    • If the system operates fewer than 6 months a year, two sampling periods, with six evenly spaced samples in each period, must take place over the course of 2 seasons. For example if a system operates May through September, they would sample May through September 2017 and again in May – September 2018).
  • If the system operates ≥ 6 months but less than a full year, two sampling periods during months of operation must take place and samples must be taken at least once every 2 weeks.

Systems Using Bank Filtration

  • Systems using bank filtration followed by a filtration plant must collect samples from the well and after bank filtration.
  • Systems receiving Cryptosporidium treatment credit for bank filtration must collect source water samples in the surface water before bank filtration.

If conditions pose a danger to someone collecting samples or are unforeseen and could not be avoided that prevent a sample from being collected, the operator must collect a sample as close to the scheduled date as possible and submit an explanation for the new sampling date along with the laboratory results.

Sample Collection and Submission

For sample collection information see:

**NOTE – Samples must be maintained at 0–10 oC (32–50 oF), but not frozen, during shipment to the laboratory for E.coli enumeration analysis. Samples received outside this temperature range will be rejected.

Bin Calculations for Filtered Systems

Following completion of the second round of source water monitoring, DEQ will recalculate each PWS’s Cryptosporidium bin concentration using the results reported.

  • Step #1 - The results of all the samples for 12 months (one sample at least every two weeks) are added together.
  • Step #2 - The sum of all the samples from Step #1 is divided by the total number of samples to determine the annual mean.

Under LT2ESWTR, DEQ may approve an alternative to the small water system E. coli trigger levels (currently 10 E. coli/100ml for lake/reservoir or less than 50 E.coli/100ml for flowing stream sources. 

According to EPA “analysis indicates 100 E. coli/100ml for lake/reservoir AND flowing streams provide more accurate identification of systems requiring Crypto monitoring and compliance with LT2 treatment technique requirements.” Idaho has adopted this approach of using 100 E. coli/100 ml.