As required by the Michigan Department of Environmental Quality (MDEQ), the City of Fenton obtained the services of HRC to conduct an Inflow/Infiltration (I/I) Flow Metering Study and Sanitary Sewer Evaluation Study (SSES) on the City's sanitary sewer system to determine if there were excess flows in the sanitary sewer system. These excess flows could be storm (rain) water entering the sanitary sewers through cracks in sanitary pipes or through sanitary/storm sewer cross connections. The studies are required for the City to effectively identify the sewer system improvement needs for a planning period of 20 years. This effort was required as part of the project planning process to be eligible for a State Revolving Fund (SRF) low interest loan.
Infiltration/Inflow (I/I) Flow Metering Study
HRC conducted an Infiltration/Inflow (I/I) Study in 2007 that examined the City's sewer system to determine where excessive amounts of groundwater or surface runoff (storm water) may be entering the sanitary sewers and whether further studies and sewer rehabilitation were required. Sewage flows from the system were metered during the I/I Flow Metering Study at 7 locations to isolate areas of potentially excessive I/I. It was determined that 4 of the 7 meter districts contribute excessive flows to the sanitary sewer system. Based on this metering information and historical data about the system's construction and operating problems, a detailed Sewer System Evaluation Survey was conducted on these aforementioned meter districts.
Sanitary Sewer Evaluation Survey (SSES)
The City of Fenton SSES was conducted by HRC during the fall/winter of 2007. It focused on identifying sources of inflow in the meter districts that had previously been determined as having excess flows (from the I/I Flow Metering Study). It also confirmed the location of stormwater connections at two locations the City identified. The SSES consisted of a visual inspection of approximately 1,000 manholes and smoke testing of approximately 220,000 linear feet of sewers. The inspection and smoke testing data was analyzed to isolate I/I problems, gauge their severity and determine an appropriate and cost-effective course of action.
The result of this study work was the identification of I/I sources contributing approximately 1,530 gpm of I/I or 13.8 million gallons (MG) per year. The I/I sources included perforated or grated manhole covers; cracked or broken brickwork below manhole castings; shifted manhole castings; and storm drainage structures connected to the sanitary sewer system.
A cost-effectiveness analysis determined that the present worth of the repairs required to remove the I/I would be approximately $444,000. This is less than the present worth of continuing to treat the I/I, which was determined to be approximately $807,000.
