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I just finished installing a new Grey Water Pit (4’deep, 4’wide & 32’long). 4” perforated PVC runs down the middle of pit to 8” off the bottom & tees out in both directions 16’. Then filled pit up with 15 yards of gravel to 10” from top. Then covered gravel with ( 2’x 8’x 1/8”) corrugated black plastic panels & a layer of 8 mill plastic to keep dirt from seeping down into gravel. Then covered to grade with dirt.
DID I MESS UP BY PUTTING PLASTIC ON TOP OF GRAVEL???
My neighbor says I should not have used plastic & just covered gravel with dirt so water would evaporate out the top. The pit ditch sides are pretty hard solid clay dug down to a sand layer at the very bottom of the pit, so probably not going to get water to soak into walls of pit, just the bottom at sand layer.
I live in the middle of Oklahoma panhandle & only get average of 17” of rain per year. The new G/W pit only gets the cloths washer & kitchen sink water to releave stress on my 20 year old septic tank.

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Putting plastic on top when you cover with dirt will extend the life of the drain. This can be verified by looking at how to design a French drain--if you prevent the dirt from settling in the rock the drain will last much longer. Your gray water drain is a French drain.

  • Ed Beal, thanks for your reply. I feel better now regarding your description of my Gray Water pit as a French drain. I was planning on drilling ( 12” ) holes with my tractor auger down through the top of the 10”clay layer, corregated black plastic & 8 mill poly liner, & then backfill the holes with gravel to grade level, hoping to create a wicking action to help keep pit dried up. I think neighbor had a good idea about omitting the plastic seal & letting moisture escape out the top, but I like your reasoning better, thanks Oilytex – Oily Tex Nov 29 '19 at 19:21
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I would have uesd geofabric/geotextile (a porous cloth-like plastic material) over the gravel to keep the dirt out.

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    Hi. Would you spend a few seconds to fix the spelling/grammatical errors? Thanks. – Daniel Griscom Nov 22 '19 at 13:18
  • You might justify your suggestion with some reasoning. We can infer the benefits, but they should be there, in your words. – isherwood Nov 22 '19 at 21:28
  • Jasen, yes that would of been a good idea also. The geo-fabric would of kept the dirt from washing down into the gravel & still let the moisture wick up & migrate through the soil, thank you very much for your reply, oilytex. – Oily Tex Nov 29 '19 at 19:51

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