Hi everyone,
We’re building a house and need to have a pumped system. The only approved drainfield is uphill of the house site. It was designed by an engineer, and we’re confused on whether the septic tanks are gravity fed, then pumped uphill, or whether the grinder pump we have to install in the basement for that bathroom will be pumping up to the septic tanks. Is there a standard, or does it all depend on the site? Doesn’t appear as if the lines from the house need to be below the frost line–anyone know why they don’t have to be?
Just don’t want to sound like a moron when talking to the engineer and the septic installer.
Thanks,
Jo
Replies
Usually I just browse this site, but since I've been doing septic design/regulation for awhile, I'll respond.
The "typical" set-up for a pump system is gravity flow from the house to a septic tank, then an effluent pump to the drainfield. Some systems use a pump system that sits in the septic tank: most use a second tank as a pump vault (so the sewage gravity flows from the house to the septic tank then from the septic tank to the pump vault). Usually the second tank (or pump vault) is sized to provide reserve storage capacity so that you can still use your plumbing for day or so if the pump dies.
Hope this helps.
What's to keep groundwater from entering through the leech field and flowing back into the pump tank in a case where the field is above the pump tank in elevation?
If youhave that kind of groundwater system in the field, you have an improperly designed system. A field cannot be built in hydric soils. it must be designed to mound above them.
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As piffen said, the water table should not be above the bottom depth of the leach field and pump station/septic tank. = bad design!!!
If you have ground water from rain, spring melt coming down the hill to the leach field and then possibly soaking down into the field since it is designed for drainage, the solution is an interceptor drain above the field, consisting of crushed stone and drain tile to catch this groundwater and divert it around the field, tank, etc.
the mound system is refered to as a "wisconsin mound". 2+3=7
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never heard that one! Some guys call it a GD ugly mound though;)
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http://www.cet.nau.edu/Projects/WDP/resources/treatmentsyst/Mound.htm. 2+3=7
The responses by the other posters (Piffen, et al) are correct. The leach field itself works by gravity, even when the effluent is pumped to it or distributed through the leachfield by pressure. So, in order to work at all, the hydraulic gradient has to be away from the leach lines--typically that is designed in to the system by maintaining some depth of unsaturated soil below the bottom of the leach field (depth depends on local regulations).
For a "typical" system, the effluent is pumped to a distribution box or drop box, and then flows by gravity through the leach field (for simplicity, I'll skip the pressure distribution systems) and into the soil. If ground water or surface water (or even too much sewage from the building) saturate the leachfield, what typically happens is that the effluent in the drainfield breaks out onto the surface, alerting the owner to a problem with design or maintenance of the system.
In the case of poor design/poor location of septic tank and drainfield, it sometimes happens that effluent and ground water from the leach field will back up into the tank, but I've only seen that on gravity flow systems with little elevation change from the tank to leach field.
I hope all that explanation helps, because there is also a one sentence answer to your question. A check valve installed in the pipe downstream from the pump prevents effluent from flowing from "force main" back into the pump tank. That's to save the pump from having to fill the force main each time it kicks on. And that isn't meant to be a smart-@$$ response, just wanted to be somewhat complete, without being too long-winded.
There's some really good info available at the Small Flows Clearinghouse. I don't recall the web address, but you should be able to find it at the National Environmental Services Center website http://www.nesc.wvu.edu
Thanks, that gives me a much better understanding of the system.
Great!
It could be either way. Jim's description is the most common and probably better from several aspects, but doing it the other way wouldn't be unreasonable, especially when siting the septic tank is a problem. Depends on the situation.
Septic lines do not have to be below frost line because of the heat from off gassing keeps it from freezing. However beware of septic systems installed in late fall when there has not been enough gas build up to prevent freezing. Often you can horse manure to your tank to speed up the heat up.
Cheers
Grinder pump in the basement is typical and is usually used for the basement only in most cases. This is pumped into the existing sanitary line and rest of house is gravity fed to tank. In your described situation it appears that the whole house will dump to grinder pump and then pump to sanitary line to tank. There will be a check valve installed that will stop the sewage from running back to house after pump shuts off, if you are pumping uphill the whole distance, keep in mind that the sanitary line to tank will always have effulent in it.
It is also possible that you will have a grinder pump in basement and a second pump in pump chamber to pump to field. Where as the house would gravity flow to tanks with exception of basement. Most of these systems will also have a alarm incorporated into them to warn you of pump failure. I nsuspect this will be the type of system that you will have.