In early 2002, the City of Howell began a proactive effort to identify inflow and infiltration sources in the City's sanitary sewer system.  Although the Wastewater Treatment Plant (WWTP) has not violated any permit conditions or discharge limits, wet weather causes the average 1 to 2 million gallons per day (mgd) flow to spike up to 8 mgd.  The City's goal is to tighten up their system, reduce long-term treatment costs and lengthen the life of the WWTP before an expansion is required.

HRC conducted flow metering and analysis of meter data to identify those sanitary districts that were contributing the highest percentage of I/I.  Following two 3 to 4 month metering periods, enough data had been recorded to develop a smoke and dye testing program designed to identify specific I/I sources within the suspect areas.

Smoke and dye testing identified approximately 40 inflow sources accounting for 50% to 60% of the total I/I of the study area.  By removing the identified inflow sources a net savings of approximately $520,000 in treatment costs can be seen over the next twenty years.

Notable features include:

• Study included system-wide metering of dry and wet weather sanitary flows
• GIS data incorporated into I/I Study and mapping
• Smoke and dye testing to identify specific sources of I/I throughout the system
• Cost-effective analysis of I/I removal