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Septic tank risers or access covers for deep septic tanks:
This article defines septic tank riser and explains how these components are installed to provide adequate cleaning & inspection access openings to pump & maintain a septic tank, cesspool, drywell, soakpit or similar wastewater disposal system.
Septic Tank Risers: What if the septic tank is buried deep below ground surface?
Reader question: I was told my septic system needs a riser. What's that?
(May 14, 2011) Charles said:
I was told that my septic system needs a riser. What is that and what does it look like?
[Click to enlarge any image]
Reply: definition & description of septic tank riser
A septic tank riser is simply a large diameter round pipe, typically a couple of feet across, that is placed over the septic tank cleanout opening to extend that opening up to close to the ground surface so that the septic pumping company does not have to dig deep into the soil in order to reach the septic tank cleanout cover for pumping and cleaning the tank.
Watch out: just as a septic tank must have a save and secure and childproof cover, so must a septic tank riser, cesspool, drywell, etc. Boys will be boys, as my grandsons demonstrate, standing atop a septic tank riser cover in Seal Isle City, New Jersey. The Gilligan boys provide ample testing of the security and curiosity-proofing necessary at site hazards including septic tanks.
Shown below: an easy-to-access septic tank riser at a property we inspected in Norway. [Click to enlarge any image]
Indeed we've seen septic tanks partially above ground, and others buried more than six feet deep. It's not necessarily a mistake, and deep septic components may be required by site conditions, but here are some considerations when the septic tank is more than a foot below ground surface:
Deep septic tanks should have a service riser installed. Septic risers are large-diameter "wells" that are placed over a septic tank inlet baffle access port (and possibly outlet) to permit easy access for septic tank pumping, inspection, and baffle repair.
If the septic tank happens to be buried more than just a few inches below ground surface, good practice includes installing a septic riser, a large diameter pipe that gives good access to the septic tank for inspection and cleaning.
A large diameter riser is 24" or more in diameter. Small septic pumping risers that are just 4" or 6" in diameter are easy to install and cheap, but they do not permit inspection of the tank baffles, and their small diameter makes it difficult for the septic pumper to actually clean out the floating scum layer and sludge layer when the tank is pumped.
Steps in Adding a Septic Tank Riser
To add a septic tank riser we
dig down to expose the septic tank cleanout cover - this may be at the inlet and outlet ends of the tank or more often over the center of the septic tank.
remove the septic tank cleanout cover
place the large diameter round septic "riser" over the septic tank cleanout opening. The diameter of the riser will have to be big enough that it is outside the perimeter of the septic tank opening (else it would fall in) and it will have to be tall enough to reach ground level or a few inches below ground level if you don't want it sticking up in view.
seal the bottom edge of the septic tank riser to the surface of the septic tank. This means that the tank surface including mud and debris needs to be cleaned off and dry; installers use epoxy or other suitable sealants. This step is probably less critical if the septic tank is located in dry soils at an elevation not subject to surface runoff or groundwater intrusion.
place a secure and safe cover over the top of the septic tank riser
backfill soil around the riser so that things look nice again.
Watch out: Deep drainfields mean poor septic effluent processing. If a deep septic tank means that the absorption area (leach field or drainfield are synonyms) is deep, such that the top of the soil trenches are more than a foot below ground surface, then the reduction in aerobic bacteria in the soil will limit the effectiveness of the drainfield in reducing pathogens and other environmental contaminants.
Additional septic effluent treatment methods can correct these conditions, but it's useful to keep in mind that there is a difference between successful septic effluent disposal and successful septic effluent treatment. A deep septic tank does not necessarily mean that the absorption area is also deep, since site conditions and use of septic effluent pumps may change the required depth of a drainfield.
Safety warning:Be sure that the septic tank riser and all septic tank covers are sound and secure since falling into a septic tank can be fatal. See SEPTIC & CESSPOOL SAFETY .
The two septic tank access risers shown below are dangerous and could easily involve a fatality. At below left is a collapsing home made septic tank made of concrete blocks over which someone placed a concrete cover and slabs of slate to try to cover this dangerous hazard - an inadequate response.
At below right was a two-concrete-block high septic tank riser provided at a mobile home park in New York. The site manager had simply left the septic tank cover off.
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