Septic tank/sewage ejector pumps

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will_b

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Hi,

Currently I'm starting the process of building a house. We are closing on a piece of land tomorrow. The land planning engineer we are working with tells us that we will likely need a sewage ejector pump for any basement plumbing fixtures. Other than the basement, it's all gravity drain. I would prefer not to have any sewage ejectors in the house at all. Since it's all raw land with only an approved septic field at the moment, now would probably be the best time to look into options.

1) How deep can a septic tank/drain field be? I went through Maryland's requirements for on-site sewage disposal systems and found nothing indicating the depth of the tank or drain field. The preliminary engineering sketch shows the basement floor at 455.5 ft. The beginning of the approved drainfield closest to the house would be ~460 ft. @ ~25 ft. setback from the house. The rear of the drain field is ~450 ft. The perc test documents do indicate depth of stone and various invert depths for tank inputs/outputs etc. which are currently around 5-6 ft. below the existing grade where the house will be. However, during the building process there's always regrading. I don't know whether those numbers are set in stone or are relative to the final grade or are minimums that must be met. Can I regrade to get the tank lower? I will already be regrading some areas so that part of the basement will be walk-out at 455 ft.

2) If it's just not possible or practical to regrade and/or put the septic tank deeper, how reliable are ejector pumps? Do they fail often and/or catastrophically if treated well (i.e. nothing goes in the toilet that isn't supposed to)? My worst fear is a catastrophic failure of a sewage ejector pump.

3) Do the holding tanks leak gases? I know they are supposed to be vented and sealed, but over years, can or will the seal degrade?

Thanks in advance.
 

Smooky

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In most states the depth and size of the septic field is determined by the county or state environmental health dept. I would not grade the site until they have done their evaluation. The site for the drain field should not be disturbed or graded unless you have their blessing. If elevation is an issue and a pump is needed, I would put the septic tank on the lower end and follow that with a pump tank. The depth of the septic tank is not very important if there is a pump, you just want it deep enough for everything to gravity flow into the tank. It all has to be deep enough but not too deep because you need access to both tanks. The heavy solids sink to the bottom of the septic tank and oil and grease float to the top. Septic tanks have a baffle wall and an outlet tee or an effluent filter. Only liquid/effluent flows into the pump tank. Then in the pump tank there is an effluent pump that pumps the liquid to a distribution box or manifold and then it flows to a drain field. The tanks are vented out through the roof if everything is plumbed correctly. There should be risers and some type of man hole on top for access to the septic tank to pump out the solids that build up in the tank and to have access to the outlet filter. The pump tank also has to have access to do repairs when needed to floats, the pump etc. You may want to keep a backup pump on site. The system should have a high water alarm so you know when the pump etc. has failed.

I like a 1/2 hp pump, they seem to hold up better. I would set up the alarm so when it goes off there is reserve space in the pump tank and septic till you can get some one out to fix it.
http://www.zoellerpumps.com/de-ea/category/3-sump-effluent-dewatering
 
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