City of Alexandria, VA
Infiltration & Inflow Program
ALEXANDRIA IS WORKING TO IMPROVE YOUR COMMUNITY'S
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 Sanitation Authority 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 September 2008, City contractors have collected data in the Four Mile Run, Commonwealth and Taylor sewer service areas over the past eight 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.
Sewer Service Areas Survey Map
Results of Field Surveys
As of Summer 2007, sanitary sewers and manholes were inspected in the Four Mile Run, Commonwealth and Taylor 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 and Taylor 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 Technologies’ website:
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 will continue through Spring 2010.
Current Sewer Work Areas
Sewer pipe lining work is currently ongoing in the Taylor Run Area. The pictures below show a liner being installed in the sewer and before and after views of the rehabilitated sewer. Please note that other types of sewer rehabilitation, such as manhole repair and some sewer point repairs, will be completed at a later date.
The repair work and inspections being planned will take place in public streets with traffic control provided. Due to the nature of the repair work, temporary outages in service (inability to use water) may be required for some customers. The time needed for these outages will be kept to a minimum with service generally restored within 8 hours. When repair work is scheduled, affected homeowners will be notified at least one week in advance of any service interruption by door hanger.
Homeowners will also receive a second door hanger notifying them of the pipe lining work the day before it is scheduled. Homeowners are encouraged to call the contact number provided on the door hanger (also shown below) with any questions or concerns about the pipe lining work. In addition, a contractor representative will be available to answer any questions while the work is being completed. For further information you may contact the Department of Transportation and Environmental Services at (703) 519-3400 extension 235.
SEWER LINING INSTALLATION