Sewer Inflow/Infiltration Reduction Project

Project overview

The City of Dover owns and operates a wastewater collection and treatment system serving more than 31,000 residents. The collection system includes approximately 115 miles of sanitary sewer (8 to 40 inches in diameter) and 23 pumping stations. All flows are conveyed to the Dover Wastewater Treatment Facility (WWTF) on Middle Road for treatment and discharge to the Piscataqua River.

In 2000, the City of Dover launched Phase I of an Infiltration and Inflow (I/I) Study to identify areas with high I/I and to develop a plan to reduce peak flows in the wastewater collection system. Since then, the City has continued to pursue projects that remove existing I/I sources and prevent new I/I from entering the system.

To help reduce peak flows during wet-weather events, the City is identifying potential direct connections to the wastewater collection system. Common sources include roof drains on flat roofs and roof gutters.

When excessive stormwater or groundwater enters the sanitary sewer system during rain events, it strains the wastewater treatment facility operations. Since 2000, the city has been working to identify and correct inflow and infiltration into the system.

The greatest flow-reductions have been by reducing illegal, direct connections into the sewer system, known as the “inflow” of the I/I acronym. These include roof drains, catch basins, and residential sump pumps. “Infiltration” is the other part of the acronym which refers to water seeping through cracked pipes, broken maintenance holes, or utility cover access hatch openings.

A comprehensive follow-up I/I flow study in 2019 identified areas of high-flow inputs in various sub-drainage sheds of the sanitary sewer system, including in and around Bellamy Road, Knox Marsh Road, and Mount Vernon Street.

The city uses multiple methods to identify and eliminate I/I, including maintenance hole inspections, closed-circuit TV inspections on the interior of piping, dye-testing, and smoke-testing.

Smoke Testing

WRIGHT-PIERCE will be conducting a smoke test of portions of your sanitary sewer system. Work crews will be in your area based on the testing schedule listed below.

A "smoke test" survey will be conducted to assist our inspection crews in locating breaks and defects in the sewer system. The smoke you may see coming from building vent stacks, building roof leaders, the ground, or manholes is fog like, non-toxic, non-staining, has a faint odor, is white to gray in color, and creates no fire hazard.

There is no need to be home during smoke testing. No one will enter your house/ building.

The smoke should not enter your home unless you have defective plumbing or dried up plumbing traps.

It is advisable for the homeowner to pour a gallon of water into floor drains/other plumbing fixtures upon receipt of this notice. If smoke enters your home or business, this is an indicator that sewer gases may also be entering your home or business. You should notify our work crews if this occurs. If you are not home and discover smoke when you return, please call the contact below.

IMPORTANT! If there is any individual in your home or business who has respiratory problems and is immobile and you have concerns, please call the contact below prior to testing.

Responsible Party for Testing: City of Dover Community Services & Wright-Pierce

Testing Schedule: Within 1 to 4 business days hours of this notice

Contact: Kristin Sullivan, 603.570.7101, 8:00am – 4:00pm M-F

Additional Info: Jillian Semprini, City of Dover Community Services, 603.516.6450

Smoke Testing

Frequently Asked Questions 

What is sewer smoke testing?

When we smoke test the sewer system, the field crew use a blower to push a non-toxic smoke (similar to that seen at concerts and theatres) through a sewer manhole into the sewer pipes. The field crew then observe and make notes of where the smoke exits the sewer system. The exiting smoke may indicate that drain manholes, catch basins, roof gutters and/or foundation drains are connected to the sewer system. The smoke may also indicate broken sewer pipes.

Why do we perform smoke testing?

There are several main reasons for smoke testing. Identifying inflow and infiltration helps show areas where groundwater or rainwater is entering the sewer system. Smoke testing detects poor connections and defects such as cracks and gaps. By addressing leaks and other issues, it may prevent sewage backflows or overflows, which also protects the public health and surrounding wildlife. Overall, smoke testing identifies issues for repair, improving the overall efficiency of the sewer system.

Is the smoke hazardous?

The smoke you see is fog like, non-toxic, non-staining, has a faint odor, is white to gray in color, non-flammable, and creates no fire hazard. The smoke does not pose any harm to people, animals, nor plants. It is similar to what is used in events such as concerts and haunted houses.  The door hangers have a QR code that will bring you to a website with the safety data sheet on the liquid smoke.

What if the smoke enters my home or business?

We recommend you pour a gallon of water down into plumbing fixtures and floor drains upon receipt of this notice. This is especially critical for drains that are seldomly used; for example, a spare bathroom sink or shower, a utility sink, or a basement drain. This leaves a small amount of water in the p-trap drain and blocks smoke from entering home.

If the smoke does enter the house, open a window, turn on a fan, and/or step outside for a few moments if you feel bothered by the smoke. It dissipates fast and leaves no lingering scents or stains.

If smoke does enter a home from the inside, property owners should be advised to contact a licensed plumber to find out if the building has defective plumbing.

How long does the process take?

This depends on the testing area. For one street in a community, it could take approximately 30 – 60 minutes.

Will I be notified of when the smoke testing work will be on my street?

The engineering firm will place a door hanger on each residence/business approximately 1 – 4 business days before the work will take place on your street. Refer to the door hanger for more information.

Will the municipality or engineering staff enter my home?

Neither the municipality staff nor the engineering field crew will enter your home. However, if smoke is found in your home, you can request they enter to determine where the smoke is entering from.

Will first responders be on standby in case of emergency?

The engineering firm has already notified the local fire and police departments of planned smoke testing so that they can be on notice and educate residents if calls related to smoke testing arrive. Smoke testing will not create an emergency situation.