Manhole Rehabilitation
Arlington’s sanitary sewer system, which carries wastewater from homes and businesses to the Water Pollution Control Plant, is more than 80 years old, with approximately 60 percent built before 1950.
During rain events, rainwater can enter the sanitary sewer system through cracks in the pipe, and this leakage is referred to as infiltration and inflow. Infiltration and inflow typically increases as the sanitary sewer system gets older. Infiltration and inflow is a problem because it dilutes the sewage, which can decrease the efficiency of the wastewater treatment. It also increases the volume of sewage, which may exceed the treatment capacity at the wastewater treatment plant.
To maintain the operation of the sanitary sewer system, we’ve implemented a rehabilitation program for the sanitary sewer system, which includes the Manhole Rehabilitation Program.
Manhole Rehabilitation Process
- In 2011, we hired an engineering company to assess the conditions of the County’s sanitary sewer manholes located in the 100 year flood zone. The manholes in the flood zone have a higher priority for rehabilitation, as they have an increased risk of floodwaters entering the manhole. We determine which manholes need to be rehabilitated from the assessment.
- Next, we inspect the manhole to determine what type of rehabilitation is needed.
- The final step is the actual manhole rehabilitation. On the day the work is scheduled to be performed, the contractor will bring the necessary equipment and materials to perform the recommended work. You will not be notified when the work is scheduled unless the manhole is located on your property.
Inspections take one day to perform and the actual rehabilitation usually takes one day. However, depending on the condition of the manhole and the type of repairs required, it may take several days to completely rehabilitate the manhole.
Rehabilitation Methods
There are several different methods of rehabilitating manholes, and the rehabilitation method selected depends on the condition of the manhole. The most common rehabilitation methods are:
- Replacing frame and cover — the metal circular lid for the manhole that is supported by a metal frame — and the steps which are used to go up and down the manhole.
- Spraying cementitious mortar to the inside of the manhole. The mortar is applied all around the inside of the manhole and then brushed to provide a smoother surface.
- Spraying an epoxy liner to the inside of the manhole.
Additional methods include sealing and grouting the manhole, adjusting the height of the manhole, and repairing the interior bottom of the manhole.
How Will I Be Affected?
Residents may see short term activities related to the manhole rehabilitation for a few weeks. You may experience parking restrictions depending on the location of the manhole. If a manhole is located on your property, a County representative will contact you.
Resource Protection Area (RPA)/Wetlands
We must be able to access and rehabilitate all manholes, even those located in the RPA/wetland areas. The contractor will implement the following measures to protect and limit disturbance to the RPA/wetlands:
- Most of the work in the RPA will be performed by hand wherever possible. The contractor will carry most of their equipment and materials to the embankments by hand to reduce their impact. Any time the work is anticipated to disturb the wetlands, such as the use of heavy equipment or removal of vegetation near the manhole, the contractor is required to fill out Arlington County’s Water Quality Assessment Impact Data Sheet prior to start of work.
- The contractor is also required to have the U.S. Army Corp of Engineer’s Nationwide 3 (Maintenance) General Permit to work in the RPA. The contractor will adhere to all the requirements and procedures as stated in the permit.
- The contractor will remove all trash from the work location and will clean their equipment offsite. This will eliminate any construction debris from getting into the streams and storm water system.