Abstract

In 1995, the Northeast Ohio Regional Sewer District (NEORSD) initiated the Mill Creek Interceptor (MCI) Project, a multi-year undertaking aimed at developing a comprehensive facilities plan for the area. It is envisioned that, once implemented, the plan will alleviate sewer system surcharging and control combined sewer overflows (CS0s) within the Mill Creek drainage basin, at the same time complying with current and potential state and local permitting requirements.

In light of the fact that significant water quality impacts to Mill Creek had been identified as part of previous studies of the area, it was determined that an assessment of Mill Creek be undertaken. As part of the assessment of Mill Creek, an extensive monitoring program was completed, the results of which complemented the considerable data previously collected. The results of the monitoring program, along with the previously collected data, were used to develop a water quality model for Mill Creek. Once developed, the Mill Creek water quality model was used to assist in the formulation of an overall drainage basin plan, as well as in the analysis of a Use Attainability Analysis for the Mill Creek.

This chapter discusses the process undertaken to set up, calibrate and apply a water quality model to support the CSO facility planning process. Specifically, in the Mill Creek drainage area, there was a significant amount of effort spent in defining and quantifying sources of fecal coliform whether from CSOs, stormwater, dry weather seepage, or other sources contributing to Mill Creek that were identified in the watershed. Source identification was extremely important to the water quality model in order that the impact of source correction could be reliably predicted. Fecal coliforrn was modeled by the TRANSPORT module of XP-SWMM in the study. The calibrated water quality model was used in continuous simulations to evaluate the sensitivity of water quality in Mill Creek to vat control alternatives being considered and for the evaluation of the overall facility plan.

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