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Re: Odor Prevention at Lift Stations

Tammy Allen writes:
> In addition to concerns for sewer personnel exposed to accumulated
> gases, sewer gases left to accumulate in air-tight environments can
> create additional toxic gases and underground potential for explosion,
> stagnation, and dead space in lines.  Aeration is a viable option to
> reduce odor.  Many odors accumulate because of oxygen-deficient
> environments.  The cost to retrofit old sewer systems (lines, stations,
> can be astronomical for a municipality.)  Judy, I am still looking
> forward to your additional information on pump rates, etc. for odor
> prevention.

>>> Rudy Moehrbach <Rudy_Moehrbach@p2pays.org> 01/29 9:04 AM >>>
> Judy Mirro, Tammy Allen opened the subject a few days ago. 
>You have
> a great deal of experience in that area and offered suggestions for
> dealing with the odor. I am interested in the problem but
> unfortunately I don't know one thing about it. I inquired why the
> odor must be allowed to get out and was told that the fumes
> presented a danger to maintenance personnel(I'm assuming that a
> lift station is not occupied). Obviously that is an important
> consideration, but that type of problem is dealt with safely in many
> other situations---OSHA addresses it in detail. My question was:
> "Let me ask some questions since I am not familiar with a waste
> water lift station. Are you pumping from one underground waste pipe
> to another under ground waste pipe at a higher elevation? Is
> venting to atmosphere necessary or is it "just there". Why is there
> a vent? Can everything just be sealed up? Can the atmospheric vent
> be changed to a closed vent, perhaps with a blower, that ends up in
> the upper pipe?" I'm looking for an opportunity to PREVENT
> POLLUTION. Prevent the fumes from polluting the air and causing a
> nuisance. Prevent the addition of chemicals to mask the odors that
> pollute the air. So, Judy, have you run into a sealed lift station?
> If not, and knowing the requirements, do you believe one can be
> designed to be sealed? Can existing ones easily be modified to be
> sealed? 

Where do I begin?  Prevent pollution by preventing the wastewater? 
Obviously, with industry we do our best to help them reduce at the 
source, but when it comes to domestic wastes in communities... 
reduction is really limited.  So you end up with wastewater and you 
have to deal with its inherent problems.  Odors being one of them.

Lift stations:  Yes, typically located at a junction, a lift/pump 
station pumps the waste stream upward into another part of the 
collection system to hopefully flow freely toward the wastewater 
treatment facility.  Normally, a pump station has two parts:  a dry 
well (where the pumps are located) connected to a wet well (where 
the sewage accumulates).  Venting is necessary and required by 
OSHA in both the wet well and the dry well.  Both are considered a 
Confined Space.. and entry into one means you follow the confined 
space entry procedures your facility has established.

Sealed stations would be impractical and dangerous.  Access   
and maintenance in the "wet" well portion of the station is 
necessary (and required by most state regulatory agency's), in 
order to clean pump control mechanisms and insure the station is 
running properly.  (I'll get back to the maintenance of a pump 
station a little later.)  Since the wastewater is accumulating in the 
wet well, you'll naturally have odors and need to vent them.  
Explosion proof electrical systems are required in a wet well 
situation because of the potential for such a hazard.

Gases can vary in a wet well.  O2 difficiency, hydrogen sulfide, 
methane, ammonia,... and again, the explosion potential can be 
high.  With proper pumping rates, some of this goes away.  In 
some situations, with the best pumping rates, the problems will 
still be there and 'other' mechanisms are brought in to help out.  
Hence the need for chemical addition or some sort of odor control 
mechanism (such as biofilters).

Most of the time the odors leaving a pump station are not 'toxic' to 
the public, but they are considered a nuisance.  I suppose you 
could tell the tax payers that they just need to live with the odors - 
but I don't think you'll get far with that. ; )  Again, in order to reduce 
what chemicals you'll use, first (reduce!) by optimizing pumping 
rates.  You really will need to get an engineer to sit down with your 
pump station design plans and a years worth of actual flows, in 
order to do this.  Unfortunately, I can't give you an easy fix for this 
problem over e-mail.  I would need to see collection pipe sizes, 
current daily pumping rates, pump capacities, wet well size, wet 
well operating depths,... and talk to the neighbors to see when the 
odors are at their worst and to the operator that maintenances the 
station.  That's why bringing in someone (engineer or not) would be 

I am not saying that *all* pump stations require chemical or other 
odor control methods.  On the contrary, odor control at a pump 
station is NOT a typical part of the operation.  If anything, it is the  
rare case.  I can count on one hand the number of odor control 
systems in place at pump stations here in VT.  

A little more on pump station maintenance:
If pumps have failed, there will be only a certain amount of time 
(depending upon the size of the wet well) before raw sewage will 
reach ground level.  Pollution prevention IS maintenancing the 
pump station on a regular basis.  A pump seal could blow and even 
though the pump appears to operate properly while you are 
standing in the dry well reading a pump hour meter, it may not 
actually be pumping..  Unless you access the wet well, you may 
not know until its to late.   

And Yes, you do have alarms built into the system for just such a 
reason, but how do you know your alarms are working unless you 
test them regularly, tripping them on and testing the audio and 
visual alarms.  Another reason to access the wet well.

Tammy mentioned the high cost of replacing wastewater collection 
system pipes.  Re-lining, instead of replacing collection system 
lines is a viable alternative for older systems.  Quite cost effective, 
at that.

I sure hope I've helped clarify some of your questions.  I could just 
keep rambling on here, but I won't.  If you need more specific 
answers, ask away.

Judy Mirro

           Judy Mirro, Compliance Assistance Engineer
           VT ANR/DEC/Environmental Assistance Division
           Small Business Compliance Assistance Program
           103 South Main St./Waterbury/VT/05671-0411
           phone   802-241-3745      fax   802-241-3273
           e-mail  judym@dec.anr.state.vt.us