The City of Alexandria has been conducting an ongoing program to address excessive infiltration and inflow into sanitary sewers throughout major areas in the City. Infiltration is groundwater that enters sanitary sewers through leaks in pipes. Inflow is storm water that is directed to the sanitary sewers through connections such as roof downspouts, driveway drains and groundwater sump pumps. During wet weather, infiltration and inflow can increase the flow to sanitary sewers to the point of overload. When this occurs, the excess water can cause sewers to overflow and release pollutants into our waterways and damage private property by creating backups into basements.

How do the sewers become overloaded?

The sanitary sewers are meant to carry only wastewater, which comes from fixtures such as sinks, toilets, bathtubs, showers and washers. The City's sanitary sewers convey wastewater to the Alexandria Renew treatment facility. Infiltration and inflow are terms that describe groundwater and stormwater that enter the sanitary sewers through leaks in pipes and through connections such as roof downspouts, driveway drains and sump pumps. When infiltration and inflow enter the sanitary sewer, they take up pipe capacity that is otherwise required for the wastewater. The infiltration and inflow can cause sewer backups and overflow into the environment during wet weather. They can also cause overloading at the treatment facility.

Why did a sewer survey take place?

Through 2010, City contractors have collected data in the Four Mile Run, Commonwealth, Taylor and Holmes Run sewer service areas over the past fifteen years to look for sources of infiltration and inflow. You may have noticed them sending a camera through the sewers to look for sewer defects, lifting manhole covers to check the condition of the manholes, or looking at connections on houses and in driveways. Valuable information has been obtained. In addition to televising the inside of the sewers, an alternative method called smoke testing was performed in some locations. Smoke testing sewers is a commonly used practice to identify defects that sometimes cannot be seen by camera. Property owners were notified prior to smoke testing being conducted in their area.

Results of Field Surveys

As of 2015, sanitary sewers and manholes were inspected in the Four Mile Run, Commonwealth, Taylor Run and Holmes Run sewer service areas. The survey provided City engineers useful information pertaining to the conditions of the sanitary sewers and manholes in the evaluation areas. The information obtained shows that many of the sewers and manholes in the public streets need to be rehabilitated in order to reduce inflow and infiltration. The following photos illustrate some of the defects discovered. Most of the work required to correct the defects can be accomplished by internal methods such as pipe lining so that excavation can be kept to a minimum. Overall, the studies revealed the following work needs to be done in the Four Mile Run, Commonwealth, Taylor Run and Holmes Run areas:

What steps are currently being taken to reduce infiltration and inflow from the sanitary sewers?

The sewer pipe lining work is being done using CIPP (cured-in-place pipe) technology, which allows for rehabilitation of the sewer from manhole to manhole without excavation. However, some excavation may be required to repair sewer defects that cannot be rehabilitated using CIPP technology. More information on the CIPP process is available at Insituform's web site: 

         http://www.insituform.com/Wastewater/InsituformCIPP

The sewer point repairs refer to rehabilitating specific defects along the sewer. Point repairs are required when only a portion of the sewer is in need of rehabilitation. Some of these defects can be rehabilitated using internal methods, but most of them will require excavation. The amount of excavation required to repair these defects will be kept to a minimum.

A majority of the sanitary sewer manholes are scheduled for rehabilitation. The amount of repair required to reduce infiltration and inflow varies from manhole to manhole, based upon the results of the survey. Some of the rehabilitation techniques include installing manhole inserts to keep surface runoff from entering the manhole during wet weather events, spraying the inside of the manhole with a cementitious coating, and reconstructing severely deteriorated manholes. No excavation is necessary for most of the manholes being rehabilitated.

Sewer Rehabilitation Contracts

In January 2004, the City awarded a contract to Insituform Technologies, Inc. to rehabilitate the sewers and manholes in the Four Mile Run sewer service area. The rehabilitation work started in Spring 2004 and was completed in Fall 2005 at a cost of $3.05 million.

In May 2005, the City awarded a contract to Am-Liner East Inc. to rehabilitate the sewers and manholes in the Commonwealth sewer services area. The rehabilitation work started in Summer 2005 and was completed in Fall 2007 at a cost of $4.45 million.

In January 2008, the City awarded a contract to Am-Liner East Inc for $4.59 million to rehabilitate the sewers and manholes in the Taylor Run sewer service area.  The rehabilitation work started in Fall 2008 and was completed in Spring 2010.

In January 2015, a contract was awarded to Am-Liner East, Inc for $2.46 million to rehabilitate the sewers in the Pegram and Strawberry Run sub-basins of the Holmes Run sewer service area.  The construction will be completed in the early Spring 2016.

In March 2015, a contract was awarded to Insituform Technologies, Inc for $1.60 million to rehabilitate the sewers in the Holmes Run sewer service area.  The construction work started in Fall 2015 and will be completed in Spring 2016.

In March 2015, a contract was awarded to Midas Utilities, Inc for $2.78 million to rehabilitate the manholes in the Holmes Run sewer service area.  The construction work started in Fall 2015 and was completed in 2019.

Current Sewer Work Areas

The City is planning to restart its inspection and rehabilitation program in early 2021. Inspections will start in areas of the City that experience sanitary sewer back-ups during significant wet weather events, such as the wet weather events of July 2019, July 2020 and September 2020. A total of $33 million is programmed in the FY2021-2030 Sanitary Sewer Capital Improvement Program for both inspections and rehabilitation over the next 10 years.

                                             Before (left) and after photos of sewer lining installation