Shallow Pressurized Dispersal Systems

More than 90% of microorganisms and 40% of plant roots -- which remove nutrients from wastewater -- occur in the top 16 inches of the soil column. Shallow Pressurized Dispersal Systems (SPDSs -- formerly known as "Shallow Gravelless Drainfields") are an excellent way to disperse high-quality treated effluent to this shallow, biologically active layer of soil. And they allow for higher hydraulic loading rates, compared with conventional drainfields, as long as most of the organic material is removed by advanced treatment prior to dispersal.

Not only do SPDSs deliver the benefits of drip irrigation in a simpler, less expensive way, but they are also a low-impact method of installing a dispersal field. Lines can be excavated with a rotary tiller and a shovel to minimize impact on ecologically sensitive areas. And they can be routed around vegetation and other landscape features to further minimize site impact.

Important SPDS Design Principles

  • Organic loading to the soil must be greatly reduced by pretreatment using an advanced treatment system that consistently and reliably produces effluent with BOD5 and Total Suspended Solids less than 10 mg/L.
  • The bottom of SPDS infiltration channels must be located in the biologically-active shallow soil mantle where oxygen can penetrate.
  • Pressurized dispersal must be used to uniformly spread the pretreated effluent throughout the soil absorption system.
  • Unsaturated, well-oxygenated (aerobic) soil conditions must be maintained by applying effluent in small, frequent doses (“controlled dosing”).

SPDS system using HP12 by Orenco Systems®, Inc.

SPDS system using chambers by Infiltrator Systems®