Pump Station Before Septic Tank?

[SPSUEngineer]

Here's the deal. I'm the civil site engineer on a school addition with an existing septic system we want to use.

The architect wishes to lower the floor elevation of the new addition and that means the sanitary invert will be lower than the existing septic tank I need to tie into. I can't lower the tank elevation because it is already as low as it can be for the nitrification fields.

Can I install a pump station before the septic tank and pump effluent into it? I could design the force main to keep the velocity low (+/-2.5 ft/sec). I don't have much expertise in this area. I've searched the code and a few textbooks but can't find an answer to this. It seems to me that a grinder pump would create a "slurry" and the tank wouldn't be able to do its job of separating solids from liquids. Is this correct or am I overthinking it?

I'm trying to do this without installing an additional tank if possible. I have a situation where I can't increase the capacity of the existing system without bringing it up to code and I don't have the land area available.

This is in the State of Georgia and under the jurisdiction of the EPD (flow rate over 10,000 GPD) if anyone knows of a code issue.Thanks!!

 

[Dleg]

I don't know Georgia code, but I have never heard of anything preventing the use of a grinder pump ahead of a septic tank. I don't believe that would really affect the performance of the tank - the solids should still settle, and you're talking about an addition only, so the load of "ground" solids will be relatively small compared to the rest of the flow.

Maybe check the tank design - a two compartment tank would be something to cite as additional protection. Or, if you are feeling generous, or are worried about the reviewers, retrofit the tank with a pre-fabricated effluent filter. That would satisfy me, and would be good for the owner, too.

 

[mattsffrd]

my father designs septic systems for a living, and you can absolutely install a pump for this...he designs them with pumps all the time. they're very common, but people tend to stay away from them if possible because of the obvious addition in maintenance (pumps need to replaced after they wear out, etc.).

 

[SPSUEngineer]

Thanks for all the replies. I think I have figured out the perfect solution for this particular project. I'm going to specify a septic tank effluent pump that has a filtering system included. That will add some protection for the drain field.

 

[DVINNY]

A STEP pump is placed in the tank and pumps to the field. This is your ideal situation, but your septic tank will need to be lowered, then it can pump up to the field.

There are fields at elevations higher than the tank all the time, but must be done properly.

you're best if you can gravity to your septic tank, then pump it to the field. Just make sure it's designed so that the grey water does not drain back to your pump, you should have a high point and distribution manifolds, or a "D-Box" type of setup.

 

[humner]

A STEP pump is placed in the tank and pumps to the field. This is your ideal situation, but your septic tank will need to be lowered, then it can pump up to the field.
There are fields at elevations higher than the tank all the time, but must be done properly.

you're best if you can gravity to your septic tank, then pump it to the field. Just make sure it's designed so that the grey water does not drain back to your pump, you should have a high point and distribution manifolds, or a "D-Box" type of setup.

Remember to take the volume of the pipe into consideration when determining absorption bed volume. I have seen many engineers design their grey water delivery system with a 1/4" hole in the pipe inside of the pump chamber just above the check valve. This is done so that water left sitting in the line does not freeze, causing line failure. Yes the pump is running a little bit longer, but it is negligible compared to digging up the line and trying to find the leak source.