Inflow and Infiltration Study/Rehabilitation
and Interceptor Monitoring Project (Phase II)
for Sewer District No.3 - Southwest 
CP 8181
Suffolk County
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On behalf of Suffolk County Department of Public Works  



Project Purpose

The purpose of the Suffolk County Sewer District No. 3 – Southwest Inflow and Infiltration (I/I) study is to minimize inputs of stormwater and groundwater into sewage infrastructure in order to avoid overburdening the system and limiting its capacity, ensure the continued protection of public health and the environment, and reduce operational and capital improvements costs. To do this, Suffolk County has hired consultants to conduct an evaluation of sewer system infrastructure and develop I/I reduction plans for a significant portion of the collection system area as shown on the map provided below under "Project Area". (Project Area Map)  

In conjunction with the infrastructure improvement projects, it is vital to educate homeowners, business owners and other relevant stakeholders about wastewater and stormwater infrastructure; the causes and potential impacts of I/I; and the ways property owners can reduce inflow from sump pumps, roof gutters and downspouts, foundation drains, and other private sources.  

As part of this public education effort, the website provides the following information:

  • project scope and background;
  • a Project Area Map;
  • answers to frequently asked questions (FAQs); 
  • description of techniques for identifying I/I problems and how they can be resolved;
  • Suffolk County’s rules and regulations governing sewer connections (Chapter 740); and
  • project contact information, including an online form for submitting questions and comments.  (Contact)

The website will be updated periodically to provide additional educational materials and updates regarding the progress of the project.

Project Scope

The scope of work for the project includes:

  • an evaluation of existing sewer system infrastructure;
  • identification of system deficiencies as they relate to I/I;
  • development of strategies to resolve identified I/I issues;
  • analysis of the cost-effectiveness of strategies designed to address I/I;
  • formulation of plans to implement preferred strategies; and
  • implementation of a public education campaign to inform the public of the importance of I/I control and what can be done to assist in preventing or alleviating I/I issues in the district. 

Project Area

The Southwest Sewer District (Suffolk County Sewer District No. 3), located in the southwestern quadrant of Suffolk County, NY, includes portions of the Towns of Islip, Babylon and a small part of southern Huntington. 

The study area, within the scope of this study, is segmented into three specific areas as indicated in the map below. The study areas include the following municipalities:  Town of Islip, Town of Babylon, Village of Babylon, Village of Amityville, Village of Lindenhurst, and Village of Brightwaters.

Project Schedule (Key Tasks)


Project Area 1

Project Area 2

Project Area 3

Flow Monitoring

May  – Sept. 2012

May  – Sept. 2012

May  – August 2012

Smoke and Dye Testing 

May 2013

May 2013

May 2013

Manhole Inspections

Oct. 2012 – April 2013

March - April 2013

June – August 2012

Closed Circuit Television (CCTV) Inspections

Oct. 2012 – Feb. 2013

Nov. - Dec. 2012

Oct. 2012 - Feb. 2013

Finalize Plans for I/I Abatement

December 2014

December 2014

December 2014

Bid and Award Project

Jan.  - June 2015

Jan.  - June 2015

Jan.  - June 2015


July 2015 - June 2016

July 2015 - June 2016

July 2015 - June 2016

Note: The scope of construction related tasks will be determined based on the results of the study tasks, therefore the schedule for the last two tasks is preliminary and subject to change.

Public Meetings

Meeting information will be posted when available.

Specific comments, concerns, or requests for additional information should be made via the online form, located here (CONTACT)

What is I/I?

I/I is an acronym that stands for “inflow and infiltration”. Inflow and infiltration are processes that introduce groundwater and stormwater that are not intended to be treated by sewage treatment facilities into the sewer infrastructure. 

Inflow is caused by stormwater entering sewer infrastructure through improperly connected roof downspouts, foundation drains, stormwater cross connections, manhole covers, and sump pump connections. Infiltration is caused by groundwater seeping into cracked or leaky sewer pipes and manholes, thereby decreasing the pipes’ wastewater conveyance capacity.  

Sources of Inflow and Infiltration

Identifying Sources of I/I

Sources of I/I can be identified in a variety of ways including:

  • infrastructure inspections by conducting direct visual assessments or using a closed circuit television that can be injected into sewer piping;
  • smoke tests that involve the injection of a harmless odorless smoke into sewer piping and identifying the locations where the smoke escapes (e.g., through stormwater cross connections, roof downspouts, uncapped cleanout pipes, driveway drains, stairwell drains, yard or area drains, foundation perimeter drains, and defective service pipes);  
  • dye testing which involves the injection of dyes into downspouts, drains, and other stormwater conveyances to see whether the dye is detected in downstream sections of the sewer system; and
  • flow meter analysis which involves an extended data collection period where groundwater, stormwater, and wastewater data is collected. Comparing the flows during and after precipitation events to the average daily flows, it is possible to isolate portions of the flow that are attributed to sources of I/I.

                       CCTV Inspection of Pipes                              Manhole and Pipe Inspections                                                                                                        Using Zoom Technology

                       Smoke Testing                               Image from CCTV Inspection of Pipe

Fixing I/I

Once the sources of I/I are identified some of the potential fixes can include:

  • Redirection of illegal connections such as sump pumps, foundation drains, and downspouts;
  • Replacement or repair of damaged or defective piping and other infrastructure; and
  • Public education.
Traditional Excavation for Sewer Pipe Replacement        Installation of Manhole Insert 

Trenchless Installation of Sewer Pipe

List of Primary Consultants





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