Infiltration and Inflow
The City of Springfield's Infiltration and Inflow (I/I) Program works to maintain and improve the efficiency of the City's sanitary sewer collection system and treatment plants and to prevent sewer overflow and backups. Currently, 3 regular full-time and 5 temporary/contract personnel perform infiltration and inflow reduction efforts.
What is Infiltration/Inflow (I/I)?
Infiltration occurs when groundwater enters the sewer system through cracks, holes, faulty connections, or other openings. Inflow occurs when surface water such as storm water enters the sewer system through roof downspout connections, holes in manhole covers, illegal plumbing connections, or other defects. The sanitary sewer collection system and treatment plants have a maximum flow capacity of wastewater that can be handled. I/I, which is essentially clean water, takes up this capacity and can result in sewer overflows into streets and waterways, sewer backups in homes, and unnecessary costs for treatment of this water. It can even lead to unnecessary expansion of the treatment plants to handle the extra capacity. These costs get passed on to the consumer.
Flow monitoring and flow modeling provide measurements and data used to determine estimates of I/I. Flow meters are placed at varying locations throughout the sewer collection system to take measurements and identify general I/I source areas. Measurements taken before and after a precipitation event indicate the extent that I/I is increasing total flow. Both infiltration and inflow increase with precipitation. Infiltration increases when groundwater rises from precipitation, and inflow is mainly stormwater and rainwater. The city monitors rainfall with an automated rain gauge system. These rain gauges are placed throughout the city so that data about variations in rainfall can be monitored and correlated.
Identifying Sources of I/I
The City of Springfield completed a Sewer System Evaluation Survey (SSES) in 2001. The SSES involved inspection of the sewer system using several methods to identify sources of I/I:
- Visual inspection - Accessible pipes, gutter and plumbing connections, and manholes are visually inspected for faults.
- Smoke testing - Smoke is pumped into sewer pipes. Its reappearance aboveground indicates points of I/I. These points can be on public property such as along street cracks or around manholes, or on private property such as along house foundations or in yards where sewer pipes lay underground.
- TV inspection - Camera equipment is used to do internal pipe inspections. The City has one 2-3 person crew that performs TV inspection on over 34 miles of sewer pipe per year.
- Building Inspection - Two-person crews go door-to-door, gathering information from residents and businesses about any history of sewer backup and stormwater flooding in their buildings. Basements are inspected for possible illegal plumbing connections, including foundation drains and sump pumps connected to the sanitary sewer.
- Dye testing - Dye is used at suspected I/I sources. The source is confirmed if the dye appears in the sewer system.
Sources of I/I are also sometimes identified when sewer backups or overflows bring attention to that part of the system. The purpose of the SSES is to proactively reduce these incidences by seeking out the sources before they cause a problem.
Repairing I/I Sources
Repair techniques include manhole wall spraying, Insituform pipe relining, manhole frame and lid replacement, and disconnecting illegal plumbing, drains, and roof downspouts. Since 1995 the City of Springfield has engaged in an active rehabilitation effort to reduce the entry of I/I into the collection system. As a result of these efforts 33.6% of active I/I has been removed from the collection system as of 2008. This has been achieved through a combination of contracted and in-house rehabilitation.
Sanitary Sewer Infiltration and Inflow (I/I) Program
A primary objective of the City's Sanitary Sewer Infiltration and Inflow (I/I) Program is to reduce the occurrence of wet-weather sanitary sewer overflows (SSOs). The SSES, which was completed in 2001, identified possible sources of I/I. Rehabilitation and repair of identified sources is performed using manhole wall spraying, in-place pipe relining, and manhole frame and lid replacement. Initial rehabilitation of the City's 155 sanitary sewer basins was completed in 2006. Evaluation and rehabilitation of the sanitary sewer system is ongoing. During 2007-2008 18,733 lineal feet of sanitary sewer lines and 277 manholes were rehabilitated. Since 1996 117,780 lineal feet and 12,488 manholes have been rehabilitated, resulting in a 33.8% reduction of I/I into the City's sanitary sewer system. As a result, wet-weather SSOs have significantly decreased in both frequency and duration.
The results of the SSES indicated that approximately 50% of the I/I into the City's sanitary sewer system is from private sewer laterals. In 2005-2006 a workgroup was formed to study this issue, resulting in a Sanitary Sewer Laterals Plan based on a phased approach. The first phase will address uncapped cleanouts and connections of roof downspouts to the sanitary sewer system. These two types of lateral defects account for 58% of the total I/I from all identified private property sources. The City's Environmental Advisory Board recommended the implementation of this plan, which was approved by City Council in November 2006. Implementation of Phase I of the Sanitary Sewer Laterals Plan began in May 2007. At 2007-2008 year-end a total of 4,068 cleanouts had been repaired by our Sewer Capacity Assurance Team (SCAT) or the property owner. The cleanout part of Phase I of the Sanitary Sewer Laterals Plan is now complete. The City plans to implement the downspout part of Phase I in 2008-2009.