Sanitary Sewer Collection System/Inflow and Infiltration

Inflow and Infiltration (I/I) are terms used to describe excess water that enters the sanitary sewer collection system.

• Inflow is stormwater that enters the system directly through connections from leaders, gutters, sump pumps, and cross connections with storm drains.  Inflow can occur during wet weather events or can be caused by snow melt, where large quantities of water can enter the sewer pipes and cause sewer overflows and/or basement backups.
• Infiltration is groundwater that enters the sewer pipes/manholes through holes, breaks, joint failures or other faulty openings. Infiltration quantities can vary in response to changing groundwater levels, storm events, and prolonged periods of precipitation.

Issues of Inflow & Infiltration in the sanitary sewer collection system can lead to releases of sanitary sewage to the environment (also known as sanitary sewer overflows or SSOs).

By law the Town is required to report all sanitary sewer overflows, of any size or type, to regulatory authorities.  A release of sanitary sewage to the environment is a violation of the Town’s SPDES discharge permit and can result in a significant fine from New York State. 

During the period of 2010-2016, the Town reported approximately 25 sanitary sewer overflows and was cited by the New York State Department of Environmental Conservation (NYSDEC) for the number of reported SSOs and for SSOs re-occurring in the same locations as in prior releases. 

In May 2019 the Town of Yorktown signed a Consent Order with the New York State Department of Environmental Conservation (NYSDEC) that obligates the Town to perform various tasks to address sanitary sewer overflows that occurred within the Peekskill Sewer District. The order detailed requirements that were intended to better improve maintenance and operation of the collection system. These guidelines are summarized within the Schedule of Compliance and the link can be found within the supporting documents section below.

The objective of the I/I Reduction Program is to remove extraneous water sources from the collection system, which should reduce the likelihood of sanitary sewer overflows and better protect the environment. As part of Consent Order compliance, the Town and its engineering consultant completed an Inflow and Infiltration Flow Study of the Peekskill Sewer District in August 2020 to identify areas within the collection system that have elevated levels of I/I. The summary report describes the work performed, results obtained and areas for further field evaluation. A link to the report can be found within the supporting documents section below.