LEACHATE COLLECTION PLATFORMS

Collecting compost leachate is easy - simply place the compost containment on top of an impervious (to liquid) surface at sufficient slope to permit collection to a container.

Since there are numerous 'details' to consider in building a raised pallet platform, it is highly recommended that the reader study the appropriate description at least twice - then make a 'cheat sheet' listing of each major step in the process, to consult as construction proceeds... OR - highlight all of this text - copy and paste into a Word.doc or as OpenDocument text (if you use LibreOffice4.3).

Flexible impervious surfaces on which to compost

There are MANY flexible, impervious surfaces that are strong enough to use as a compost "platform" - with STRONG being the 3rd-most important attribute.
Many flexible, impervious surfaces are NOT strong enough for this purpose, such as:

  • Tar paper (or any other roofing underlay sheeting)
  • Shower curtains (can tear just from foot traffic)
  • Plastic sheeting less than 20-mil thickness

Recommended:

  • 20-40 mil PVC Shower/Tub under-lay material
  • Tarpoline, heavy-duty (tarp)
  • Canvas, treated for outdoor use (sections of tents, awnings, etc.)
  • Advertising Banners (joined with tape or sewn-together)

The lighter-weight materials also make good pile COVERS

While the rest of this article focuses on construction of WOOD platforms for leachate collection, there are many other building materials that qualify as a strong, above-grade impervious platform, including: 1) grouted tile mastic-laid on treated-sealed plywood, 2) grouted 12"x 12" x 2" pavers or bricks set on compacted fine sand - and The SoilGuy's favorite for folks that can do masonry work - 3) 3.5" thick 3,500psi wiremesh-reinforced concrete pad with 4" x 8" x 16" laid-in and cement-filled cinderblock back & sidewalls, with formed trough to inset Sched.40 PVC split-pipe to the collection container. Until I have time to get such instructions posted, if a reader desires instruction about how to construct such masonry or concrete pads - send email to: robert@thesoilguy.com

At-Grade Plywood Platform-To-Tub' leachate collection method

A common leachate collection method is to scarp the ground so that one 4' x 8' x 1/2" thick pressure-treated plywood sheet lays sideways on a down-slope with fall of at least 1/2" in 4' (2" fall in 4' is better, since the sheet may 'warp' a bit over time).
(yes, the word 'scarp' is spelled correctly - meaning: slope to a steep trench)

Each 4'x 8' piece of plywood provides adequate space to support two wire bins.

After determining and marking the up-slope corners (with a stake at each direction) AND the two front corners points - the plywood is removed so the final position area can receive a 1" layer of coarse [river] sand (or a mix of coarse sand and pea-gravel).
The sand bedding should be leveled to fully-support the plywood sheet and compacted (with a tamper and/or a light spray of water) which allows water and air to move below the plywood - allowing it to dry - to reduce decay.

If one desires to considerably extend by several years the useful life of an at-grade plywood sheet, a 1"x 4"x 9-10' length of pressure-treated lumber is centered and trenched-in %. The above-ground portion of the 1x4" lumber then becomes the up-slope edge of the sheet instead of the 2 up-slope stakes - which acts as a ground-water flow-barrier). The 1.5" above-ground portion of the 1x4" lumber should be screwed to the 2x2" lumber to which the platform backboard is to be attached (remember to QUAD-caulk that seam too).
Also, the underside of the plywood sheet should be oil-base painted, and with two coats on all exposed edges.

However, most folks don't expend such effort/time/cost - because when the first sheet does begin to deteriorate, it's easier and faster to just remove the backboard, sideboards and surface 1x2" leachate-guide boards (sometimes called 'cornice' boards) from the old sheet - then attach another painted sheet on top of the first one then re-apply the lumber removed from the old sheet - and re-caulk).

All at-grade platforms should also have a backboard and end sideboards, made by attaching 2x2" lumber at the sheet rear and side perimeters, then attaching 1x8" lumber or 8" wide strips of plywood to the inside edge of the 2x2".

To drain leachate off of a 1/2" thick at-grade 8' long plywood sheet - to a front-center tub, one of two methods can be utilized:

  • Build-up the compacted sand bed, from 1" thick at middle, to at least 2" on each end (3" is better), to give the sheet an up-curve from middle to edges (until a pile or two is built on the sheet, sufficient weight may not exist for the plywood to conform to such curve) or:
  • Screw lengths of 1x2" (end angles mitered to fit) firring strips to the top of the plywood sheet (to guide leachate toward the center tub - like extending your arms in front of you, elbows bent and palms facing the opposite elbow, with fingertips almost touching) starting from the sideboards to a 6" wide opening at the tub. remember to Quad-caulk all seams.

The collection tub should be

At-Grade Platform-To-Trough leachate collection method

If composting with 3+ wire bins, install two or more on-ground 4'x 8' plywood sheets placed end-to-end on side-slope, with caulked 1x3" lumber strip secured to cover seams. Leachate flows across the full face of the plywood slope, to the front 'drip edge', then into a 3" PVC split-pipe, (usually Schedule 40 thickness in such case).

Once the plywood sheets are positioned, the front corners should be also be marked with driven stakes, then the plywood moved out of the way - so the trench for the 3" PVC lengthwise split-pipe is then excavated and leveled - and the

excajust below & under the water drainage edge, and thence to an in-ground collection container that has a 3" hole-saw cutout to connect the in-ground trough via a separate split-pipe "tray" assembly. (which is why most in-ground troughs do not have a rainwater overflow - but some do).
Not having a rainwater overflow is no problem for a plant-propagator, IF they are willing to 'use whatever dilution they get' - or remove collected leachate prior to rain. On the other hand, the best way to handle 'at-grade' compost leachate collection, is to keep every pile fully covered (except when irrigated by the composter).
If the composter installed a PVC top-pile watering 'grid', the cover does not need to be removed, except for inspection of material (unless the cover had velcro-held inspection access ports sewn in - which eliminates removal until turning).
And, if the pile was made with reduced-particle/homogenized/inoculated-soaked feedstocks, and aeration and irrigation grids are used, then the material becomes an Aerated Static Pile (ASP) - making cover removal only necessary ONCE, at final harvest. (How much to irrigate? Depends on how & with what, the pile is made, and whether feedstocks were soaked in inoculated water - but the 'generic' answer is: "How much natural liquid plant food do you need")?

COMPOST CONTAINMENTS
Click Here to see: Compost Containments
COMPOST PILES
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