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Water Service - Municipal Infrastructure

Mariemont Highly Active Sanitary Sewer Overflow, Elimination Flow Modeling Support

Client:	Metropolitan Sewer District of Greater Cincinnati
Location:	Cincinnati, OH
Budget:	$150,000
Biggest Hurdle:	Meeting the timelines set as part of the Consent Decree

As a result of a U.S. EPA Consent Decree, Cincinnati Municipal Sewer District (MSD) is required to eliminate 17 highly active sanitary sewer overflows (HASSOs) within a relatively short time frame. Three of the 17 HASSOs are located within the Mariemont sewershed, which is a sensitive area with several local issues including being located within a natural park area and in a vicinity of known archeological significance. The Mariemont sewershed is plagued by significant infiltration and inflow (I/I) which created the original need for the SSOs, and which still cause significant basement flooding. XCG Consultants Inc. was retained to provide flow modeling support to the Project Design Team.

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MIKE-SWMM and PC-SWMM graphical interfaces for EPA-SWMM were utilized to undertake the hydrologic and hydraulic modeling activities. The I/I routine within the SWMM RUNOFF block was utilized to simulate the I/I processes through which rainfall enters the sanitary system. The I/I routine is particularly suited for modeling separate sanitary systems such as the Mariemont system.

The tight time frame for the overall project created by restrictions of the Consent Decree and potentially difficult local issues in Mariemont resulted in high importance being placed on quickly creating a hydrologic and hydraulic model of the study area to allow route evaluation and selection to be conducted as soon as possible. In response, a “Rough-Cut” model was developed for preliminary alternative evaluation based upon available data. Cincinnati MSD maintains an ARC-VIEW GIS database of the Cincinnati area including collection system information. The required physical model parameters were imported directly from the GIS database into the SWMM interface. Missing physical information was initially estimated from available information and identified for subsequent field investigation. Virtually no flow information was available for model calibration, and thus, initial I/I calibration parameters were estimated from calibrated models developed for other similar areas within the Cincinnati MSD system. The resulting “Rough-Cut” model was used to estimate potential flows within the Mariemont sewershed to allow the process of route evaluation and selection to begin in a timely fashion.

Calibration of the SWMM model was performed as flow and rainfall data became available. The missing physical information was determined through a field survey. MSD installed and operated four flow meters in the vicinity. Initial calibration efforts utilized rainfall data from MSD gauges in the general area and were subsequently verified with calibrated rainfall radar information. The calibrated model is currently being utilized to hydraulically evaluate several design alternatives as part of this on-going project.