Bottomless Sand Filter
The wood frame holds up the plastic liner which separates the sand from the native soil.
After the frame was built, Cameron, Brandon and Damian placed and fastened the 6×6 treated timber around the top of the box, nailed on scrap OSB sheets to protect the plastic liner from sharp rocks in the backfill material and then fastened on the plastic liner. 
A row of roofing nails spaced about 8 in. along the top and bottom edges ensure the liner won’t sag or lift up when it’s backfilled.
The excavator hauled in specially graded and double-washed sand to fill the filter box. He filled the box partially with sand 
then backfilled part way up the box on the outside so the fill and backfill balanced each other. Then he topped off the sand and backfill up to within a few inches of the 6×6.
When he returns, we’ll install the PVC piping over the sand and cover it with peastone.
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View Comments
What exactly is this sand filter pit for? Is this a septic drain field? Or a storm water drain pit? Or what??
My thoughts exactly, what is the filter for?
It's the septic leech field https://www.finehomebuilding.com/2017/01/10/31-ft-x-10-ft-sandbox