By Warren Swanson, P.E. and Chad Paulson, P.E.
The U.S. Environmental Protection Agency plans to promulgate the Stage 2 Disinfectants/Disinfection By-Products Rule (Stage 2 Rule) in late 2005 or early 2006. The proposed Stage 2 Rule focuses on reducing peak disinfection byproduct (DBP) levels within the distribution system and will affect nearly all community water systems, both large and small. The proposed rule also requires that systems revise their compliance sampling locations to better represent areas where peak DBP levels are likely occurring. To this end, the rule requires that systems perform an initial distribution system evaluation (IDSE) to identify the new sampling locations. Large systems (greater than 10,000 customers) must submit IDSE reports to their state primacy agencies for approval within two years of the date of promulgation of the final rule.
Schmueser Gordon Meyer, Inc. (SGM) is currently completing an IDSE for Eagle River Water and Sanitation District (ERWSD). ERWSD operates two large water systems and serves several smaller outlying systems all within the Vail-Avon-Edwards corridor along Interstate 70 in central Colorado. The ERWSD system includes eight distinct sources (three surface water treatment plants and five well fields), a booster chlorination facility, 49 water storage tanks and 44 booster pump stations spread across numerous pressure zones spanning an area 20 miles in length. Given ERWSD?s head start on this project and the complexity of its distribution system and source water portfolio, the experiences of SGM and ERWSD in completing this IDSE undoubtedly will be of interest to other utilities about to embark upon similar efforts.
The IDSE for ERWSD is following a system-specific study (SSS) format, using a combination of historical DBP and chlorine residual data analysis and extended period simulation (EPS) hydraulic modeling (for water age estimation within the distribution system under critical seasonal DBP formation conditions). A single round of distribution system sampling will also be included toward the end of the project to finalize proposed sampling locations. The following aspects of the project will be highlighted in the presentation:
· The use of historical chlorine residual data and EPS hydraulic modeling to identify sites likely having high trihalomethane an/or haloacetic acid concentrations.
· The effects of source water contribution and booster chlorination on sample site selection.
· The importance of early discussions with state agencies on a proposed IDSE approach.
· The benefits and suitability of an SSS approach (as compared to the standard monitoring program (SMP) approach).
· The compilation of an IDSE report.
· Other lessons learned. Note that this project is currently in its initial phases, but will be approximately 80 percent complete by the time of the 2005 RMSAWWA/RMWEA Conference.
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