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Water/Wastewater Engineering Report (Storm Sewer/Infiltration Sanitary Sewage Separation-M1 Model)
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In some cities, the municipal sewer system collects both storm water and sanitary sewage in the same pipes. During dry weather these sewers carry all the sanitary sewage to the wastewater treatment plant for treatment. However, when rainstorms or snow melt increase the amount of runoff, the combined flow of sanitary sewage and storm water can exceed the capacity of the sewer system, which can cause serious problems like the storm water and sewage mix are discharged untreated into the river or the sewage backs up into streets and basement. Storm water treated in the sewage treatment plant also causes unnecessary energy use. Sewer systems can also have unintended ground water entering the network, which occurs because of hydraulic pressure on the buried sewer lines infiltration. Therefore, separating the storm water/infiltration and sanitary sewage reduces the possibility of sewage discharge during heavy rain periods, and saves energy.
DescriptionIn this document, a statistical methodology for calculating the savings from the storm water/infiltration sanitary sewage separation (i.e., the “M1 model”) is presented. This method uses ASHRAE’s Inverse Model Toolkit (IMT) for the weather-normalization analysis. This document provides a review of the ASHRAE IMT, a description of the M1 model, and provides an example to illustrate the methodology.
- Technical Reports 
Liu, Z.; Brumbelow, K.; Haberl, J. S. (2006). Water/Wastewater Engineering Report (Storm Sewer/Infiltration Sanitary Sewage Separation-M1 Model). Available electronically from