At-Grade Systems

Do you have an undisturbed forested area on your property?  It may be the best place for your dispersal field.  WetlandsPacific Corp. is the first company in BC to offer At-Grade effluent polishing and dispersal systems. At-Grade is an excellent method to utilize the natural biological cleansing ability of undisturbed forest soils, which is lost if trenching occurs.  It uses timed, pressure distribution of Nayadic™ advanced secondarily treated effluent to insure even loading on a 24 hour a day basis, therefore with maintenance, your WetlandsPacific At-Grade System will last as long as your home.

Forest soils are comprised of several horizons or layers beginning with above ground plant litter.  The duff or “O” horizon is comprised of three zones that blend into each other with degrees of decomposition distinguishing layers from one another, the LFH soil layer:

  • L – The uppermost level where structures of plants are easily recognized
  • F – The middle layer of accumulated organic material that is partly decomposed
  • H – The lowest layer wherein original structures of organic material are unrecognizable

The LFH horizon is very high in organic material with the “A” horizon or top soil layer located immediately below.

The “O & A” horizons are the most biologically productive area of soils, consequently should not be lost due to trenching.  To install any other final treatment/dispersal method on undisturbed forest soils destroys the forest plant litter, the biologically very active plant litter/top soil interface, the top soil, and the forest plant vegetation roots, in short, the mechanisms of contaminant removal.

British Columbia's First

WetlandsPacific At-Grade System Installation


Undisturbed Forested Area
Salal mowed and large woody debris removed
Area leveled with organic material; two runs of Infiltrators™ in place
Finished WetlandsPacific British Columbia At-Grade System
In a year or two native vegetation will again cover area
(Green lids are inspection port covers)

Alberta At-Grade System


Photo by Ellco Consulting, 2009
Gravel-less chambers before covering with organics


Photo by Ellco Consulting, 2009
After covering with organics

Treatment Train:

Primary in a pretreatment tank, advanced secondary in a Nayadic Advanced Secondary Treatment Plant, a pump chamber with timed dosing. Once in the At-Grade mound, final treatment is by the microbial and invertebrate community residing in the LFH layer, the “A” soil horizon (top soil) which begins the rhizosphere that surrounds plant roots. The rhizosphere is recognized as a highly biologically active soil horizon.


Photo by Ellco Consulting, 2009
Top soil being applied by blower


Photo by Ellco Consulting, 2009
Grass starting to grow in top soil

The mound area will be mowed, leaving clippings in place. A layer of organics will be placed over the clippings. Then the pressure distribution pipe with gravel-less chambers over the top. A minimum of 30 cm (12”) of suitable organics will cover everything. In exposed areas subject to high winds or foot traffic, erosion matting or fine netting or top soil should be added to provide stability for the organics.

Contact WetlandsPacific to see if your dispersal area is suitable for an At-Grade system.