Accessing Plant Performance using the DBP Comprehensive
Performance Evaluation

By Warren Swanson, P.E.

This year, the Stage 1 Disinfectants/Disinfection By-Product Rule (D/DBPR) became effective for small water systems.  USEPA will soon finalize the Stage 2 D/DBP Rule, which will further tighten limits on trihalomethanes (THMs) and haloacetic acids (HAAs).  Furthermore, USEPA recently released the results of a study identifying 200 more previously unaccounted-for DBPs associated with all the major disinfectants of modern water treatment practice.  These unfolding events require that utilities, especially those using surface water sources, begin to optimize their disinfection and DBP control practices.  This paper will present the approach for a DBP Comprehensive Performance Evaluation (CPE) and associated technical tools currently being developed by USEPA and a team of Colorado-based contractors, including the University of Colorado at Boulder, Process Applications Inc., and Schmueser Gordon Meyer, Inc.  The DBP-CPE methodology is a structured process for utilities and States to assess the capability of surface water systems to meet optimization goals for THMs and HAAs.  DBP-CPE implementation will be similar to, and can be performed in conjunction with, the more well-known ?microbial CPE.?  The State of Colorado has been using the microbial CPE to evaluate small surface water treatment plants struggling with filtration performance.

The project team has made significant progress in developing the methodology and tools of the DBP-CPE over the past several years.  The approach has been pilot-tested in small-to-medium-size surface water systems across the country.  The DBP-CPE identifies site-specific performance-limiting factors and potential DBP control strategies applicable to a given plant.  Similar to the microbial CPE, the DBP-CPE consists of assessments of historical data (disinfectant residuals, DBP levels, total organic carbon removals, and CT profiles), plant design, operations practices, and administrative and financial factors.  However, in the DBP-CPE, evaluation of raw water chemistry and distribution system constraints also plays a prominent role.  Furthermore, the DBP-CPE framework contains protocol for a number of special studies, such as enhanced coagulation jar testing for total organic carbon and UV-254 removal, DBP hold studies for assessing DBP formation in the distribution system, storage tank mixing and detention time analysis, and on-site DBP profiling using a field DBP method. 

These tools are designed to zero-in on the major contributors (over-chlorination, inadequate coagulation, long water residence times, etc.) to DBP formation in a specific system.  The purpose of the microbial-CPE and DBP-CPE programs is to transfer skills to operations staff and empower them to optimize their existing plant and distribution system to simultaneously meet the filtration, disinfection, and DBP goals.

The DBP-CPE development team recently identified a need to provide a quantitative screening tool.  Such a tool would be user-friendly and provide an estimate of the likelihood that a plant could meet DBP goals without major construction modifications.  This tool, a spreadsheet model called the DBP Capability Assessment Tool (DBP-CAT), is currently undergoing development and testing and will be highlighted in the paper.

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