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Case Study: City of Bellingham, WA — EPA Stage 2, IDSE Driven Water Model
IDModeling, Inc., as the designated hydraulic modeling engineer for the City of Bellingham, WA, has recently completed the creation, development, and calibration of the City’s water distribution system model.

PROJECT GOALS

• Meet EPA & State of Washington Criteria for an IDSE Model
• Water Comprehensive Planning (Master Planning)
• Ongoing Operational “What-ifs”

PROJECT ACHIEVEMENTS

“This is the most accurate and day-to-day useful model we’ve ever worked with. The ability to leverage our GIS investments to our water system model has paid off in confidence, decision-making, and overall communication between previously unconnected departments. Engineering has quickly become the hub for solutions which is much more conducive to Bellingham and how we choose to do business for our customers”.
— City of Bellingham, WA

What is an IDSE?
The U.S. Environmental Protection Agency (EPA) is finalizing publication of the final Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) and the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). The DBPR requires that new DBP monitoring locations be identified for the Stage 2 compliance samples. These new sites are to represent the maximum THM and HAA levels in the distribution system.

The utility is required to locate these representative points, as well as the other sampling points as prescribed by the DBPR. The procedure for identifying the appropriate sample points and justifying their selection to the Primary Agency is called the Initial Distribution System Evaluation (IDSE).

What are the requirements of an IDSE?
There are two ways to satisfy the requirements of the IDSE. One is called the System-Specific Study (SSS) and the other is the Standard Monitoring Plan (SMP). SMP requires a plan to collect a number of samples throughout the distribution system over the course of a year. Samples must be collected and analyzed every other month (6 sample events) for one year. An SSS is primarily based on having a calibrated hydraulic/water quality model that can predict locations of representatively high THM and HAA values in the distribution system.

At the AWWA Water Quality Technology Conference, the EPA distributed a flyer entitled “Five Recommended Steps to Prepare for the IDSE” where in step four discusses guidelines for ‘Gathering Useful Data’…

Why developing a hydraulic model makes sense for an IDSE?

• Hydraulic Modeling is a cost-effective way of fulfilling the requirements of an IDSE
• Developing an SMP is not a trivial task. It is costly and does not have the long-term benefits as would a hydraulic model.
• A hydraulic model allows one to do many what-if simulations on their system and take account tank levels, pump controls, etc.
• Hydraulic models tie in GIS, asset management, CAD, and billing data into a digital format where one can make educated decisions from.
• Hydraulic models can be used for future EPA requirements.
• Hydraulic Models can document operator experience and become a central water system knowledge-base between engineering and operations.
• Developing a calibrated model is getting easier with more tools available for bringing in data from paper maps, CAD drawings, GIS, etc.
• Hydraulic models quickly point out deficiencies in a system.
• The long-term benefits of a calibrated hydraulic model could be (but not limited to) the following:
• Master Planning
• Fire Flow Analysis
• Design Studies
• Pump Scheduling
• Operations
• Maintenance
• Water Security
• Unidirectional Flushing
• Water Quality

Other Links…
http://www.amwa.net/mdbp/5stepsStage2.pdf
http://www.eetinc.com/idse.asp
http://www.hdrinc.com/15/42/default.aspx?listingID=1061
http://www.epa.gov/safewater/stage2/index.html