The city is suggesting that we have too much water flowing through our sewer lines. They haven’t proved this, but they think it’s happening.
We have those beehive shaped manholes in the park with covers. A sewer company said some infiltration can be happening in our manholes and offered to line them for around $1,400 a piece. Has anyone dealt with lining manholes? If so, what is best practice?
Any other thoughts for how to mitigate water infiltration into sewer lines? I’ve had the pipes camera’d and pipes seem to be in good shape. Will
$1400 each seems like a lot depending on the condition. The lids are usually the culprit, although you can also get seepage in the joint between the riser sections. Some of the old style lids actually have holes in the top (for grabbing and pulling), so you need to make sure those are plugged and sealed. Also, seal around the lids with the rope style sealant or caulk (check USA Bluebook). If it is a lid you don’t pull very often put lots of caulk around it. (Silicone)
Other sources of infiltration - the risers on each lot. If you have empty lots, make sure the sewer risers are all located and sealed. Sometimes they are broken under the ground so you make have to do some digging to check for breaks and cracks, etc. It is an elusive problem - good luck.
If the city still gives you grief after replacing the manhole covers with sealed ones you can consider having a wastewater flowmeter put in on a rainy day. This can demonstrate that infiltration is limited and here is the data to prove it (e.g. flow is consistent with our blended daily water usage or closely matches master water meter readings in a 24 hour period).
I have heard of devices like the “flowshark” that can do this, but it’s expensive equipment and probably good to call either an environmental or one of the city’s larger plumbing contractors to see what they would charge to perform the service.
As far as a flow meter you can either do a doppler that you attach to the outside of the pipe this would be good on a liftstation pipe. $2500 ish Or a open channel with a flume in a manhole. $6000 ish by the time you get a flume. The challenge is a manhole is a osha permit require confined space i.e. autompsheric monitoring, blower, and rescue tripod with safety harness all required to install flume and flow meter… there are lots of cowboys out there who will climb down in the manhole with none of the above but then every year someone dies in a manhole…
As a side note I would not install an avf (area velocity flow meter) in a sewer manhole or any sewer collection system. The technology is great it measures velocity (flow speed) and depth of liquid then does the math to give you flow the catch is the sensor must be submerged in liquid. In a waste water set up there is way too much “stuff” that can get hung up on the sensor. My install was in a stream with no debris (once all the leaves quit falling it worked great). For open channel you really need a parshal flume
Most cities really have a challenge knowing exactly where their I&I is coming from. They know that when it rains the flow doubles at the treatment plant but unless they have done extensive video work, installed flow monitoring equipment at different manholes it is quite hard to pin point. High flow through the treatment plant can overwhelm the plant and virtually make treatment nonexistent it is a serious problem. Additionally many cities have grown to the point where the treatment plant is at or near capacity and when it rains the plant is overwhelmed. The problem is endemic throughout the country and is going to be a massive capital expense for most cities over the near future. They can go around and pop some manholes in the winter during a storm and see the flow looks high but it is hard to quantify unless it is obvious. However once they think your the source you have the burden to prove otherwise. The logic goes something like this; we know ABC mobile park has clay sewer lines (or even worse orangeberg, or old cast iron), clay pipe is notorious for leaking at every joint and having lots of breaks, therefore the cities Infiltration might be coming from ABC park. Pushing non city sources to solve their infiltration is the cheapest way to reduce the problem. The reality is it doesn’t take very much bad pipe to really put alot of extra water in the system.
Ask them to tell you what their policy is? What is their mandatory action point. 130%, 150%, 200% of dry weather flow? Do they have have an action plan to solve the I&I city wide?
One of our parks had the same situation. We were able to convince the city to do a smoke test in our park. It showed us a few decent leaks that were easy to fix.