Options to Comply with the IDSE?

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What is the IDSE? What is its purpose?

Initial Distribution System Evaluation (IDSE) is the first part of the Stage 2 Disinfectants and
Disinfection Byproducts Rule (Stage 2 DBPR).  IDSE is a one-time study conducted by water systems
to identify locations with high concentrations of trihalomethanes (TTHM) and haloacetic acids (HAA5)
in their distribution system. Water systems will use the results from the IDSE, in conjunction with their
Stage 1 DBPR compliance monitoring data, to select compliance monitoring locations for the
Stage 2 DBPR.

Do I have to comply with the IDSE?

You have to if you are a community water system that treats water with any disinfectant other
than ultraviolet light (UV), or if you are a community consecutive system that delivers water that
has been treated with a disinfectant other than UV.  

Options to Comply with the IDSE

There are four (4) options to comply with the IDSE:

• Qualify for a Very Small System (VSS) Waiver:  If you serve less than 500 people and have
  a set of TTHM/HAA5 data you will automatically qualify for a VSS waiver and are waived of
  conducting an IDSE.  EPA will inform you of this waiver.  If you do not have any TTHM/HAA5
  data, you can take a set of samples during the summer months of 2006 or 2007 and send us the
  results.  EPA will inform you of this waiver once we receive your data. 
             
• Meet the 40/30 Certification requirement: If you have 8 consecutive quarters of data to show
  TTHM/HAA5 levels that are consistently below respective 40/30 mg/L and there is no Stage 1
  DBPR violation against you, you are waived of conducting an IDSE.  You do not have to do
  anything other than send EPA a signed certification letter by the deadline of your assigned
  schedule (April/01/2007, October/01/2007, or April/01/2008). 
  
  
• Conduct a System Specific Study (SSS) for the IDSE using existing (Stage 1 DBPR and others)
  monitoring results, or a distribution system hydraulic model.
  
  
• Conduct Standard Monitoring for the IDSE.