Final Rule is Here

After many delays the USEPA has published final versions of the Stage 2 Disinfectants and Disinfectants By-Products Rule (DBPR) and the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). The Rules will trigger several deadlines -- some of which are almost immediate. The first deadline requires all systems to submit two formal written reports outlining their plans for: a) the Initial Distribution System Evaluation (IDSE) and b) Cryptosporidium monitoring. Systems serving 100,000 or more people (and any wholesale purchasers from the system) must submit their plans by October 2006. Systems serving 50,000 to 99,999 have until April 2007, systems serving 10,000 to 49,999 have until October 2007, and systems <10,000 have until April 2008.

What is an IDSE?

The DBPR requires that new DBP monitoring locations be identified for the Stage 2 DBPR compliance samples. Some of these new sites are to represent the maximum THM and HAA levels in the distribution system. The highest THM sampling point and the highest HAA sampling point will not necessarily be the same points. The utility is required to locate these maximum points, as well as the other sampling points as prescribed by the DBPR. The procedure for finding the appropriate sample points and justifying their selection to the Primary Agency is called the Initial Distribution System Evaluation (IDSE). All utilities must do an IDSE except those that can certify that all of their existing compliance monitoring data (each sampling period and point not the annual average) is below 40-µg/L THM and below 30-µg/L HAA. There is one other possible exception, but only for very small systems (VSS) that have existing Stage 1 DBPR data that serve populations <500.

What does the IDSE require?

There are two ways to satisfy the requirements of the IDSE for systems not eligible for 40/30 certification or the VSS waiver. One is called the System-Specific Study (SSS) and the other is the Standard Monitoring Plan (SMP). An SSS is primarily based on having a calibrated hydraulic/water quality model that can accurately predict THM and HAA values in the distribution system. One round of sampling is required to verify the model. Due to the inherent difficulty in most utilities having such a model, it is anticipated that the SMP will be the most widely used IDSE method. For all utilities serving over 10,000 people or small purchasers of water from a wholesaler serving over 10,000 people, the SMP requires that a number of samples be collected throughout the distribution system over the course of one year. Samples must be collected and analyzed every other month (six sample events) for one year at systems using surface water sources (or a mixture of groundwater and surface water sources) and every 90 days (four sample events) for one year for systems using only groundwater sources. One of the sampling events must occur during the estimated highest month for TTHM and HAA production. That leaves the questions of how many samples to collect and where to collect them, which is outlined below for PWS serving > 10,000 people (see link below for systems < 10,000):

So a utility using a surface water source serving a population of 60,000 people would collect 16 samples x 6 sample events = 96 IDSE samples. During the one year your utility collects IDSE samples you will also be required to continue to collect your current Stage 1 DBPR compliance samples.

These sample site locations must be properly selected and it is the identification of these sites and the rationale associated with this selection that must be documented prior to submitting the IDSE plan to your Primary Agency (e.g., October 2006 for systems >100,000). There are several methods available to select the sites and justify their selection including:

• Models allowing detention time prediction
• Tracer data
• A large historical DBP database
• Laboratory SDS testing calibrated against distributed system data

Developing this plan for many distribution systems will not be trivial, and utilities should start as soon as possible, but at least several months prior to the deadline for submitting the plan.

What Can EE&T Do to Help With IDSE?

EE&T staff have been helping AWWA negotiate these rules since their inception and have completed impact analysis, including costs, and development of regulatory alternatives and supporting documentation. As such we are completely familiar with the requirements of both the DBPR and LT2ESWTR and can help your utility develop and implement compliance strategies for these regulations while also maintaining compliance with other exiting regulations. EE&T is already assisting utilities in developing their IDSE plans and have used modeling techniques, tracer studies, distribution testing, and DBP sampling to develop the IDSE plans. We have internally developed and used GIS techniques to allow selection of appropriate sample sites based on chlorine die-off, tracer data, demand and deterioration predictions, and DBP data. In addition, the EE&T Laboratory is fully equipped and certified to analyze your IDSE DBP data providing you with one firm able to fulfill all the IDSE requirements. EE&T is also available to help your utility interpret IDSE results in order to prepare the required report at the end of the IDSE necessary to validate selection of Stage 2 DBPR monitoring locations to be reviewed and approved by the State.

Therefore, EE&T can help you:

• Prepare IDSE plans for State Review
• Provide sample analysis assistance during the one year IDSE (or take over your Stage 1 DBPR sample analysis load while your laboratory analyzes IDSE samples)
• Evaluate results of IDSE in order to prepare a report to State validating selection of monitoring locations for future Stage 2 DBPR compliance monitoring
• Develop recommendations for changes in treatment or distribution system operations either before or after IDSE to help your system to reduce DBP production while also maintaining compliance with other regulatory requirements or operational goals
• Develop modifications to system infrastructure, if needed to meet Stage 2 DBPR requirements, and/or
• Provide an independent critique and review of any of the above activities that your utility is doing on your own (e.g., review your IDSE plan prior to submittal to State)

For additional information and to see how we can help you please contact Mr. Richard Brown, P.E. at 757-873-1534 Ext. 224 (rbrown@eetinc.com)

IDSE Resources

Click here for compliance schedules

Click here if your system provides finished water to fewer than 10,000 people.

Click here if your public water system (PWS) is a wholesale supplier or purchaser of finished water.

Click here for a Glossary of Terms




Last Updated: January 25, 2006