When fighting inflow and infiltration (I/I) in your sanitary and storm sewer systems, most municipal and large facility managers’ minds go first to an illegal/illicit tie-in, damaged cleanout covers, or pipe breaks. While all of those certainly play a large role in the efficiency and safety of sanitary and storm sewer lines, there is one cause that is often overlooked: manholes.
It has been estimated that there are more than 20 million manholes in the U.S., and according to sewer scope equipment manufacturer, Envirosight, “The sheer volume of deficit-ridden manholes that exist in our sewer infrastructure, which are failing at a rate much faster than sewer pipeline, is proof enough that manhole inspections are critical now more than ever.”
However, most municipalities skip manhole inspections altogether, or think that popping off the cover every now and then and inspecting the area from the surface with a flashlight is sufficient to confirm a node’s condition. It is not.
More than 50% of all manholes in the U.S. were installed before 1960 and have been proven to be responsible for as much as 90% of the inflow and infiltration in a sewer system, making them a far higher risk factor than piping.
The American Society for Civil Engineers (ASCE) states that “Effective manhole inspection and rehabilitation are necessary to remove excessive manhole infiltration and inflow, improve manhole structural integrity, address public safety issues, and implement general system maintenance requirements.”
And NASSCO (National Association of Sewer Service Companies) developed the Manhole Assessment and Certification Program (MACP) to help municipalities, wastewater managers, and companies, complete thorough manhole inspections to locate, document their condition, and note defects for planning, repair, and maintenance.
Why Manhole Defects Matter
There are three main types of manhole defects: blockages, structural failures, and leaks
Blockages can be caused by a number of factors including waste from illicit tie-ins, sediment, and tree roots. When either the manhole itself is blocked, or a pipe that feeds directly into it is, sewage and debris can overflow, creating an immediate health and welfare risk. The EPA (Environmental Protection Agency) may then impose fines for improper wastewater management.
Structural Failure is often caused by rust/corrosion and simple erosion, which, if left unaddressed, can cause the manhole itself to fail – or collapse – creating a sinkhole. Sinkholes can cause more than contamination. They can damage property, roadways, and endanger the community, leading to expensive repairs, and in the worst cases, usually a new story splashed across the news and social media about the “sinkhole.”
Leaks do not necessarily mean the manhole is leaking due to a defect. While manhole deterioration, as mentioned earlier, can be a major source of I/I, a leaking manhole could be due to excessive flow from an overwhelmed system, indicating the need to update the sanitary or storm sewer infrastructure.
Determining the Condition of Your Manhole Infrastructure
NASSCO’s MACP is designed to help municipalities and large facilities assess the condition of their manholes and can provide detailed digital information on each node’s location, its tie-ins, overall condition, and any defects discovered. It can even rank the defects by type and severity to aid in long-range O&M planning.
There are two levels to the MACP. Level 1 is considered more cost-effective initially, but is labor intensive, and has a sizeable margin of error because it relies on individual personal inspection of each manhole. Level 2 has a higher up-front cost, but provides detailed digital and video data capture, is quicker, and has a lower error rate.
Level 1: The MACP Level 1 inspection is essentially a physical inspection. A sewer inspection professional near you will open the manhole, shine a flashlight down it for an initial assessment, and may climb down into the manhole to visually inspect its condition. There are usually no photos taken and a basic report created to map each node and its condition, unless a major defect is found.
“Level one is very basic,” says GPRS Director of Pipe Inspection Services, Kyle Humphreys. “It’s a written report just really giving you the basics like manhole material structure, depth information, and things like that. Just very basic according to NASSCO level one standards.”
Level 2: The MACP Level 2 inspection is significantly more in-depth because the inspector utilizes digital technology and video to capture manhole condition data and create a NASSCO-certified report in software like WinCan that the municipal or wastewater manager can access online to view still shots from the CCTV cameras deployed into the manhole, and often, the video itself.
The level 2 MACP report, according to Humphreys, “is actually very in-depth NASSCO reporting, similar to what we do with mainline video pipe inspections. And with manhole inspections, you actually get a full 360º video of the structure. So, you get video with a written report – the MACP report – as well.”
For either inspection level, it is highly recommended that your inspectors be NASSCO-certified so that you receive the most accurate reporting available.
In the case of GPRS’ process for Level 2 manhole inspections, our NASSCO-certified VPI (Video Pipe Inspection) Project Managers utilize either the CleverScan or the Quickview 360 to gather data for the MACP report.
CleverScan is advertised as “rapid, automated mobile inspection” and behaves like a vertical push camera that drops directly into the manhole on a line. It’s equipped with five HD cameras and four lasers to capture video, flat scans, and point cloud data that can be uploaded to WinCan for use in CAD design and viewing.
The Quickview 360 is mounted on a telescoping pole and is deployed by the Project Manager lowering it into the manhole manually. Its two HD cameras and LED lamps can capture a manhole’s dimensions and condition in under five minutes, according to information from Envirosight, and it uses an AI component to speed up reporting via its app.
The CleverScan provides more data due to its laser scanning capabilities, which could be an advantage for large infrastructure operations that have little or no existing conditions documentation on file. However, it is a more expensive piece of equipment and does require additional training to properly deploy and capture data. The Quickview 360 on the other hand is a more cost-effective investigation tool. Either one, in the hands of a SIM and NASSCO-certified GPRS Project Manager, can provide a clear picture of the state of your manholes.
For municipal or large facility systems that have outdated and/or incomplete infrastructure data, it is highly recommended that a full wastewater system VPI survey be conducted to accurately locate, map, and capture every mainline, lateral, manhole, and cleanout – detailing every pipe defect, its severity and the overall condition of the system, so that repair and replacement decisions can be made with all the data available. We can also conduct valuable inclination reporting and find illicit tie-ins and other inflow and infiltration issues via smoke testing and dye tracing to provide the most comprehensive maps, photographs, video, and digital as-builts of the entire system, as well as a full NASSCO-certified Video Pipe Inspection Report.
GPRS takes manhole inspections further by geolocating and mapping each system node inspected via GPS and/or RTK positioning technology, and delivers all manhole inspection reports, photos, and video via SiteMap® (patent pending), our proprietary existing conditions and data management software application. SiteMap® allows you to take your data with you, to securely access it 24/7 from anywhere, and to share it with those you choose via the SiteMap® mobile app.
How Much Does It Cost to Repair or Replace a Damaged Manhole?
The total cost to repair or replace a failing manhole will be somewhere between $250,000 - $500,000 according to manufacturers.
The costs will vary, depending on the level of repair needed. The higher end of the budget item ($500,000) factors in the cost of a new manhole chamber, the manhole cover, excavation and removal of the existing manhole, tying the sewer system back into the manhole, backfilling the area, and testing to make sure the tie-ins are properly installed.
While there is no way to completely avoid the costs associated with maintaining, repairing, and replacing manholes in any sewer system, regular inspections can greatly reduce the up-front costs by cataloguing each node’s condition, ranking the severity of any defects discovered, and planning for long-term operations and maintenance costs.
How Much Does It Cost to Inspect Manholes?
According to Humphreys, a municipal sewer system can have as many as 3,400 manholes, each one a potential I/I source. The cost to properly inspect manholes is calculated on a “per manhole” basis, so the more manholes that are investigated, the lower the cost per unit. That’s why, Humphreys says, “A lot of large projects come across my desk with RFPs (request for price/quote) for hundreds of manholes at a time.”
At GPRS, our mission is to Intelligently Visualize The Built World®, above and below-ground, to provide accurate existing conditions documentation, reduce subsurface damages, and provide secure, accessible digital data management for our customers.
What can we help you visualize?
GPRS sponsors Water & Sewer Damage Awareness Week (WSDAW), an annual municipal water safety event held in October. If you would like to schedule a WSDAW educational event for your community or facility, click below to register.
