CSO Facility Performance

While the 11 demonstration CSO facilities were in the design stages, the TRTSTORM model was developed to provide some early predictions as to how these basins would perform. The model was used to address the following questions:

• How will the proposed CSO facilities, which were designed to several different sizing criteria, perform relative to presumptive criteria in the USEPA CSO Policy (USEPA, 1994)?
• What annual pollutant load reductions are to be expected from the proposed facilities?

The TRTSTORM model is a simple hydrologic mass balance model which tracks CSO facility filling, treatment, overflow, dewatering and decanting based on long-term hourly precipitation records. It is a modified version of the U.S. Army Corps of Engineers Storage, Treatment, Overflow, Runoff Model (Hydrologic Engineering Center, 1976). The model generates annual performance statistics for flows to the treatment plant (via interceptor), treated overflows and untreated overflows.

The model was used to show that all CSO facilities designed to the demonstration sizing criteria should meet the 85 percent capture and four overflow per year presumptive criteria in the USEPA CSO policy. The model results were also used with assumed treatment efficiencies to show that for either of the two sizing criterion evaluated, annual load reduction is strongly governed by capture and is fairly insensitive to basin treatment efficiencies. For additional details see the paper Percent Treated Analysis of Demonstration CSO Control Facilities and the full report on the analysis: Percent Treated Analysis of Demonstration Combined Sewer Overflow Control Facilities.

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The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -08 and C-264000-01.