Aggressive I/I Program Saves City Money

August 2012, Vol. 67 No. 8

The city of Manassas, VA, is helping to save on sewer treatment costs, so much so that in the past five years, they’ve decreased sewer flow by more than 123,000 gallons per year, saving the city of Manassas $775,000, as part of an aggressive inflow and infiltration (I/I) program.

“Manassas Utilities is in an ongoing process to review our sanitary sewer processes, making sure we’re reducing overflows, maintaining proper capacity and rehabilitating any pipes,” said Mike Moon, director of public works and utilities for the city of Manassas. “By proactively monitoring our sewer systems, we’re able to significantly save on sewer treatment costs and pass on some additional savings to our customers.”

Customers are billed on two basic rates: distribution and a “pass through” rate for treatment costs through the Upper Occoquan Service Authority (UOSA) treatment plant. Although Manassas’ sewer distribution rate has increased a few percentage points in the past few years, the I/I program has helped reduce the pass-through UOSA costs paid by customers. In other words, customers’ overall rate would have increased more if the I/I program had not been implemented.

Inflow and infiltration are terms used to describe the ways that groundwater and storm water enter a sanitary sewer system, which is a pipe located in the street that is designed to transport wastewater from sanitary fixtures, like sinks, showers, bathtubs, etc. This is not to be confused with a storm sewer, which is a pipe designed to carry rainwater away. Inflow is the water that is dumped into the sewer system through improper connections, such as downspouts and groundwater sump pumps. Infiltration is groundwater that enters the sewer system through leaks in the pipe.

Manassas has conducted a sanitary sewer evaluation of its system and identified areas where excessive I/I exist, as well as operates routine inspections and testing methods, which include smoke testing, TV inspections, manhole inspections, flow monitoring, dye testing, sump pump removal and pipe replacement.