What is the preferred material for a septic tank – polyethelene, fiberglass, concrete, or steel. I am leaning toward polyethelene but could be pursuaded otherwise. A guy I work with occasionally makes steel tanks and claims they last as long as plastic or concrete and are cheaper. I am a bit sceptical of steel, however, as my place currently has a thoroughly rusted out steel septic tank that has caved in – of course it is probably well over 50 years old.
What are the guidelines for covering a tank, such as depth of cover?
Replies
polyethelene ie plastic is the weapon of choice these days.
See a concrete one now & then.
Steel needs a cathode or will rot really quick----- steel prices are outrages right now.
Depth code is a local health dept thing.
Mine has about 30" over it then asphault ( it's in my drive way)
Neighbors is right at grade level since he had the top raised to increase capacity & run to a new drain field.
I've done a couple in Alaska that were actually above ground.
Do you look to the government for an entitlement, or to GOD for empowerment. BDW
Thanks, I had thought polyethelene was probably the best choice. Did you put yours on a bed of sand or ?
>>>What are the guidelines for covering a tank, such as depth of cover?
For mine, a 1200 gal poly, I raked all obvious rocks out of the pit, threw in a skiff of fine gravel, and carefully backfilled to avoid any large objects near the tank.
The one bit of advice I would pass on is to be careful and patient with backfilling around the outlet pipe which holds (in my jurisdiction) an effluent filter. In my case the dirt around the outlet pipe settled substantially, enough to skew the angle of the pipe, which was enough to cause the effluent filter to bind. When I tried to remove the filter for its annual cleaning (now full of raw sewage), the handle broke. It made for an ugly, smelly extraction job.
In hindsight I would recommend partially backfilling around the outlet pipe; tamp the dirt; throw some fiberglass insulation down (depending on your freeze threat) and tarp it. Wait for a year or two for the ground to settle and monitor the skew on your outlet pipe. If necessary dig it up to relieve skewing forces and backfill by hand as needed. Once things are stabilized, fill 'er in and tamp.
Scott.
Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”
Edited 6/5/2006 12:54 am by Scott
Bed of compacted sand is ideal for plastic tanks.
I like pea gravel for fill around tank but not for the bed --- has a tendacy to move too much.
You can use select fill, but just like plastic pipe you want to keep the big & pointy rocks away from it.Do you look to the government for an entitlement, or to GOD for empowerment. BDW
around here its concrete, you would have to drive a hundred miles to find a plastic one and then it would just be one. Now plastic would be easiler to install, people just dont do it here.
As others have pointed out, steel can be a problem. Sewage is corrosive, the soils in your area may be acidic. In this area, we mostly see concrete, but I think that's mostly just due to tradition. Poly or fiberglass should serve well. Proper bedding is critical. That goes for both the tank and for the inlet and outlet pipes. You don't want any part of the system to shift or settle after installation.
The elevation of the tank is usually determined by the elevation of the absorption field. It sounds like you're replacing the tank, but not the absorption field, so the inlet and outlet of the new tank probably are going to need to be close to those of the existing tank, in order to maintain flow through the system.
Unless you're somewhere with really deep frost level, depth of cover is mostly a compromise between having enough soil over the tank to support grass and shallow enough to allow easy access to the inlet and outlet ports for easy servicing (i.e., you don't want to have to dig down four feet to pump the tank). If the tank is more than a couple of feet below the ground surface, you can install risers over the inlet/outlet access ports to make access more shallow.