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This is my first question here. I am in the process of designing a leach field. There is only a depth of 45cm (20") of soil (good perc test) after that another 20cm (8") of large stones in the bed rock and then it's all the way rock for a further app.100m (300')before reaching any underground water table. This is Malta in Europe and our island is pretty dry.

I was thinking of creating deeper trenches in the rock and filling with fresh soil a depth of depth of 1.2m (4') to act as the absorption layer. In a thread in 2018 : Can a septic system leach field be installed over clean fill? someone mentioned a compaction that needed to be performed on freshly filled soil. A user mentioned a code that must be followed in this case. I'd like to know which code he was mentioning please. Or what level of compaction should be achieved on the new soil before laying the leach gravel and pipes. Thanks in advance and I hope I made myself clear.

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    Check with your local authority that will approve it when finished. Here we have a building department.
    – Gil
    Commented Aug 4, 2021 at 17:54
  • I would not use soil it will compact under the field and you would end up with trenches if you want deeper why not use rock as your fill just a comment as I have not used dirt as a fill or seen it used.
    – Ed Beal
    Commented Aug 5, 2021 at 19:11
  • I don't know how it's done in Malta, but here the design (including what fill is used, if any) is done by someone licensed to perform that function, not homeowners. For what it's worth, my system required a sand-fill layer (not soil) because it actually flowed too fast in the native gravel. Soil (rather than sand) would be highly unusual, in my limited experience, as a fill material below septic leach pipes.
    – Ecnerwal
    Commented Aug 6, 2021 at 15:05
  • Unfortunately this system is new to Malta and we do not have the knowledge/ expertise. The subsoil under the infiltration (gravel) fill layer is needed for the aerobic breakdown of the effluent through microbes and bacteria. Using rock or sand will still enable that breakdown to occur? I also am thinking of adding layers of gravel every 6 inches so that the soil doesn't compact too much.
    – Maria Ellul
    Commented Aug 7, 2021 at 3:27

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