Was It Worth the Price? I/I Reduction Effectiveness of a Foundation Drain Disconnection Program in Duluth, Minnesota

As the C in the emerging CMOM regulations refers to Capacity Assurance of a collection system, many communities are taking necessary steps to make decisions on how to better operate their collection system facilities. In particular, USEPA recommends the use of continuous infiltration and inflow (I/I) models, coupled with hydraulic models to perform capacity analyses of critical facilities. Implementing such tools was key to understanding the I/I reduction evaluation achieved by a foundation drain disconnection program conducted by the City of Duluth, Minnesota. The study of I/I reduction effectiveness evaluation was conducted by Brown and Caldwell through a contract with the Western Lake Superior Sanitary District (WLSSD), the regional wastewater wholesaler for the City.The intent of the disconnection program was to reduce the amount of wet weather infiltration and inflow to eliminate the overflow at the Dodge St. Pump Station. The removal project consists of redirecting residential footing drains into a new sump pump pit installed in the house. The sump pump is required to discharge to a satisfactory area to minimize the likelihood that clear water recycles back to the foundation. From concept to reality took a great deal of effort from City staff. This work included changing state law to allow public funds to be spent on private assets in order to reduce clear water in the system. The work began in 1996 and was declared complete in 2002.The effectiveness evaluation of the removal project was based on modeling before and after construction conditions. The key to the analysis was use of a calibrated continuous RDII simulation model, coupled with a dynamic hydraulic model of the collection system. In summary, the RDII removal effectiveness took place in the following steps:Model calibrationLong-term simulationStatistical ComparisonThe paper will present details of the techniques used to simulate I/I and hydraulic conditions before and after program completion. Details of the City's foundation drain disconnection program are also provided