Hummed46
Active Member
Hey all quick question here. I'm in Pennsylvania and I'm installing my own septic system. The system is a long at-grade system...1.5" pressure line runs from the pump tank up hill to a T in the field, one lateral goes left 90 feet and the other goes right 90 feet. They call it an at-grade system because all you do is chisel-plow the top few inches of topsoil and lay 6" of 3/4 clean stone right on grade...Then the laterals, 2" of stone to cover the distribution laterals, filter fabric, and topsoil to cover. From starting grade to surface, the whole system's only about 18" tall. It's just really long...
On the downhill side, the plans call for a 3' wide berm around the sides and downhill face of the stone. Goal here is to hold back any effluent trickling through the 6" of stone until it can percolate into the topsoil beneath. For the berm, the plans call for mineral soil less permeable than the aggregate (which is easy - the aggregate's 3/4 clean), with less than 20% of rock, of which none can be bigger than four inches. So from the side profile view, you have a 4' wide lateral, then on the downhill face there's 3' of lightly compacted dirt (the mineral soil), then the whole thing gets capped with 8" of topsoil.
Here's my question. Do you think it matters what dirt I use for the downhill berm? I have a topsoil pile that's been there for four months that's clean with no grass rocks or sticks. My thinking is if the effluent in the aggregate ever begins to rise above original grade and high enough for the downhill berm to have to hold anything back, it's probably because the system has failed and won't accept any more effluent anyway. I think the designer doesn't want water to percolate through the berm and find a way out on the downhill side, but unlike a sandmound where the sand is the filter media and sits above grade, the filter media here is actually the topsoil under the aggregate.
What am I missing? What am I not thinking about? What's the difference really between mineral soil and topsoil if there's only 4% organic matter in my topsoil anyway? Will the world stop turning if I use topsoil for the 3' berm around my septic field?
Also, will a 5 ton machine like a kx040 do the job or should I rent a 9 ton machine?
Posting to the excavator thread bc that's what I'm doing the install with, but mods feel free to move.
On the downhill side, the plans call for a 3' wide berm around the sides and downhill face of the stone. Goal here is to hold back any effluent trickling through the 6" of stone until it can percolate into the topsoil beneath. For the berm, the plans call for mineral soil less permeable than the aggregate (which is easy - the aggregate's 3/4 clean), with less than 20% of rock, of which none can be bigger than four inches. So from the side profile view, you have a 4' wide lateral, then on the downhill face there's 3' of lightly compacted dirt (the mineral soil), then the whole thing gets capped with 8" of topsoil.
Here's my question. Do you think it matters what dirt I use for the downhill berm? I have a topsoil pile that's been there for four months that's clean with no grass rocks or sticks. My thinking is if the effluent in the aggregate ever begins to rise above original grade and high enough for the downhill berm to have to hold anything back, it's probably because the system has failed and won't accept any more effluent anyway. I think the designer doesn't want water to percolate through the berm and find a way out on the downhill side, but unlike a sandmound where the sand is the filter media and sits above grade, the filter media here is actually the topsoil under the aggregate.
What am I missing? What am I not thinking about? What's the difference really between mineral soil and topsoil if there's only 4% organic matter in my topsoil anyway? Will the world stop turning if I use topsoil for the 3' berm around my septic field?
Also, will a 5 ton machine like a kx040 do the job or should I rent a 9 ton machine?
Posting to the excavator thread bc that's what I'm doing the install with, but mods feel free to move.