AWWA WQTC56960

In order to comply with the Stage 2 Disinfectant/Disinfection Byproduct (D/DBP) Rule, an evaluation or study of disinfection byproduct (DBP) formation in the distribution system is required. This paper discusses two options, the first being an evaluation of DBP formation in the distribution system, called an Initial Distribution System Evaluation (IDSE), that requires that one year of paired total trihalomethane (TTHM) and the five haloacetic acid species (HAA5) samples be collected every other month at eight locations within the distribution system. Compliance sample sites are then selected based on the DBP results. The other option is to complete a System-Specific-Study (SSS). An SSS uses historical data, distribution system models or other methods to assess the distribution system and select representative sample locations. The IDSE or SSS is due two years after rule promulgation. IDSE requirements apply to all public water systems serving a population of >10,000 and using surface water or groundwater under the influence (GWUI) of surface water that are subject to the requirements of the Surface Water Treatment Rule. The IDSE requirements also apply to groundwater systems that use a primary disinfectant other than ultraviolet (UV) or add a residual disinfectant to their water, or systems that deliver such water. The US Environmental Protection Agency (USEPA) has made the Draft Stage 2 Disinfectants and Disinfection Byproducts Rule Initial Distribution System Evaluation Guidance Manual (USEPA 2001) available to the public for review. While still in draft form, the manual covers IDSE requirements for all system types and sizes. Details of the IDSE requirements summary that follows in this report can be found in the draft guidance manual. Specific requirements have been developed to meet the requirements for a SSS using a hydraulic distribution system model. These guidelines address only hydraulic modeling and do not address distribution system water quality models. An integrated hydraulic and water quality distribution system model may provide even better information about DBP formation in distribution system environments. As with all SSSs, an integrated hydraulic and water quality distribution system model must provide equivalent or superior information for site selection than a system monitoring plan (SMP). To meet the requirements of the SSS, both the hydraulic and water quality components of the integrated distribution system must be detailed, comprehensive, and well calibrated. It is important to understand how each of these components function individually to meet the goal of understanding DBP formation in a distribution system environment. Hydraulic models simulate water movement in a distribution system to understand water age, demand patterns, and pressure. Water quality models estimate changes in source and treated water quality based on plant treatment processes or distribution system conditions. Specifically related to the IDSE, water quality models can characterize disinfection residual and disinfection byproduct concentrations. The main objective of a SSS is to allow utilities to gain a better understanding of the hydraulics and water quality in their distribution system. It is a tool that can be used to identify trouble spots within the distribution system. In addition, the resulting model is a powerful planning tool that can be used to predict DBP formation in the distribution system for proposed modifications. Finally, the model allows the utility to refine its operations and thoroughly evaluated alternatives on a site-by-site basis potentially avoiding costly system-wide capital changes such as the implementation of chloramination in order to decrease the formation of DBPs in the distribution system. For these reasons, the City of Golden elected to pursue the SSS compliance approach. This paper focuses on the steps taken to perform a full-scale SSS, specifically

Product Details

Edition:

Vol. - No.

Published:

11/01/2002

Number of Pages:

12

File Size:

1 file , 600 KB