After 30 years in the wastewater collection industry I have seen some things. I spent the majority of my time dealing with SSO’s and basement floodings; specifically, how to reduce or eliminate them. During my 30 years I have worked on the owner side, contractor side, manufacturing side and now as a consulting engineer. All 4 aspects of manhole rehabilitation have enabled me to pinpoint some specific things that everyone involved with manhole rehab needs to know. Read my tips to learn more.
Manhole Rehabilitation: 30 Tips from 30 Years Experience
After 30 years in the wastewater collection industry I have seen some things. I spent the majority of my time dealing with SSO’s and basement floodings; specifically, how to reduce or eliminate them. A major part in the elimination or reduction, involved the rehabilitation of sewer mains and manholes. Faulty manholes can be a major contributor of Inflow & Infiltration into the sewer system. During my 30 years I have worked on the owner side, contractor side, manufacturing side and now as a consulting engineer. All 4 aspects of manhole rehabilitation have enabled me to pinpoint some specific things that everyone involved with manhole rehab needs to know. So here are 30 things in 30 years.
30 Manhole Rehabilitation Tips
- The best time to inspect manholes is when it is raining. That’s right it may not be the most desirable but certainly can give you the best indication of where the leaks occur and the severity of the leaks.
- Use MACP to code the defects. A standardized system to document defects puts everyone on the same page.
- Inspect them all. Have a plan to inspect ALL of your manholes at least every 10 years.
- Make sure the covers fit the frame. Sometimes covers are switched out but the frames aren’t. This can be a potential problem down the road.
- Inspect the drop connections. This may take an extra step but drop connections can contribute to I&I.
- Inspect the channels. Again, this may take an extra step to plug the incoming sewer but you can find problems much easier.
- Make sure the benches are sloped toward the flow. Flat benches allow debris to collect which can cause odors and potential obstructions.
- Take the PH of the manhole wall to determine if there are acidic conditions.
- Microbially Induced Corrosion exists in manholes where high sulfides are consumed by Thiobascillas bacteria that metabolizes sulfuric acid.
- Majority of the time manholes are structurally okay. Typically soil pressure is not pressing on the structure.
- Brick manholes tend to be the hardest to rehab. There are many joints in a brick manhole and joints are your weakest and most susceptible area to leak.
- The more information you give a contractor about the existing condition of the manhole the better the project seems to go.
- It’s best practice to enter manholes for inspection. There are very good cameras and video equipment but nothing replaces person entry inspection.
- Assemble a good set of specifications based on lessons learned and experienced.
- Include lots of bid items such as mobilization, bypass, set up, off-road access, grouting, ect. to obtain the best possible per foot cost of the rehab product.
- Include the channel in the rehabilitation unless bypass pumping costs are high.
- Select a family of products that best meet your goals, have a local installation contractor, readily available and has met your performance criteria.
- Require a Performance Work statement from the contractor which will include their plan to get the project done.
- Only allow experienced pre-approved contractors to bid on the project. A certain amount of manholes or vertical feet require the manufacture to be on-site.
- Make sure contractors and the individual workers are trained and certified by the manufacturer.
- Require and verify contractor references of similar projects. You will be surprised at what you find out.
- Require an ITCP – Manhole Rehab certified inspector to be onsite. An educated inspector is imperative to a successful project.
- Preparation is key to project success. Preparation includes cleaning, obtaining correct surface profile, cutting steps, filling voids, stopping leaks, and grinding or sandblasting the frame.
- Most products require a concrete surface profile (CSP) to be a 3 or a 4. If it’s too smooth it will need an extra step to roughen the surface.
- Manhole products must bond in order to stop water and prevent I&I. An annular space allows water to travel behind the installed coating or liner and enter back into the sewer system.
- Polymer products have a tendency to pinhole. Proper steps need to be followed to reduce or eliminate pinholes. Pinholes lead to concentrated deterioration of the host substrate.
- Spark testing is a viable test to locate even the smallest of pinholes. All pinholes must be repaired and retested.
- Adhesion testing should be performed on a limited amount of manholes to establish proper preparation and installation methods are used. It’s best to perform at the beginning of the project.
- Vacuum testing can be a tool to verify water tightness. Typically the flow has to be plugged and possibly bypassed, therefore an additional buy item should be included.
- Once the contractor has completed the installation it is best practice to enter the manhole for a final inspection. Blemishes, delaminating, leaks, discoloration, larger pinholes, voids and other defects that don’t meet the specifications can be located.
There you have it: 30 items that I have learned after 30 years in the industry. While there are many more items that you should be aware of, these items are some of the more important ones. By taking these into consideration it should help you with your Manhole Rehabilitation projects.
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