Minimizing Sanitary Collection System Overflows
Here are methods suggested to prevent overflows from sanitary collection systems. Some may not work, some are intended for humor only.
- Regular cleaning of sewer lines.
- Preventive maintenance cleaning of troublesome sewer mains.
- Pumps, barriers to keep overflowing liquid out of waterways.
- First you need to determine when overflows are occurring.
Do they occur during rains? If so you may have a serious infiltration
or inflow problem that needs to be corrected. If the overflows
occur near creeks, perhaps there is a break in the line that needs
to be repaired or one or more manhole covers off.
- If overflows occur during dry periods, then you may have an
overloaded sewer and a relief line may be the answer.
- Preventative maintenance of the lines to maximize the capacity
is always best. Perhaps installing water tight lids would help,
provided such action would not cause the backup into a basement.
- Conduct an I&I survey to see where your flow is coming
from and then perhaps perform a pipe lining or other suitable
technique for elimination of this.
- Use manhole covers to buffer the inflow into the manholes.
- Install some type of holding tank/pump station as a temporary
solution. But eventually population growth would overcome this.
- Using pipe bursting equipment or other means, install larger
interceptor and/or lateral lines.
- Proper design sizing and slope of pipes.
- Selection of good quality manholes, lids. etc. and good quality,
factory tested pipes with good quality joining systems (while
problems with pipe breakage or collapse, infiltration and/or exfiltration
from pipes or joints, are obvious, problems can also be caused
by later root intrusion, etc. in poor quality pipe or joints as
- Well designed and effective pipe/structure/manhole and service
- Effective installation, inspection, and acceptance testing
of the pipeline, etc. with available resources in the construction
- Go leak hunting in the wet season and patch leaks.
- Go house to house and get rid of all the sump pump connections.
- Smoke test in the summer.
- Feed long chain polymers about 20 minutes upstream of the
overflow. If you get the dosage right, you can increase pipe capacity
by about 30%. [untested in field conditions]
- Bolt the manhole covers shut and store the water in people's
- look for areas where "kids take the covers off".
My experience is that kids don't often do this.....surcharged
flow does! I have seen sewage flowing out of the top of a manhole
such that the lid was suspended 8 inches [20 cm.] above the fountain of
sewage and spinning slowly around.
- Pull lids in wet raining weather...amazing what the sewers
will show you....be prepared to get very wet and work evening
hours...it is well worth it.
- I agree with the water tight lids. I have seen many sanitary
sewers acting as surface effect storm sewers.
- Do some flow monitoring....branch approach...to help define
areas that may be suspect. In every sewer system I have worked
on, we have found "Big Boys"...those locations where
a little $$ saves a lot of flow.
- How about dissuading people from putting in stuff that is
likely to cause a blockage or reduction in capacity. Like building
materials, grease, large solids etc.
- Better management and control of pumping stations may be important,
depending on your system.
These ideas originally were posted on the SEWER-LIST mailing list.
Contributors: Randy Connor, Eric Greenberg, Alan VanDeBoe, Jerry
Haimowitz, Doug Uhren, Martin Osborne, Miles Abernathy.
Return to the SwopNet Engineering Databank