systems. Protect the system excavation from stormwater runoff by construct- ing berms, swales, or other erosion control structures as necessary to divert surface water away from the excavation. 6. Drainfield product selection: It is important to note that regardless of the drainfield product specified, it does not infiltrate nor treat the effluent, the soil does both of those functions. Although, the choice of product can have a significant impact upon the soils. Aggregate has many disadvantages includ- ing soil compaction, the presence of fines, and embedment of the stone; all of which are detrimental to system performance. The specification of a gravel- less product will avoid these pitfalls and allow for a much quicker installation timeframe. The faster the system can be installed, the less time the soils are exposed to the elements. The gravelless products are also absent of fines and are lightweight thus avoiding compaction and embedment. 7. Utilizing tracked equipment: Only tracked equipment should be used to excavate the wastewater treatment system. For trench systems, it is recommended to excavate individual trenches with tracked equipment with a bucket width that matches the specified trench width. Bed system excava- tion may require additional planning; large bed widths should be excavated without machinery in the base of the excavation. The bed or trench should be level and the bottom and sidewalls should be scarified. Construction foot traffic within the disposal system should be minimized Sites with Sensitive Soils and Sloping Terrain Very sensitive soils and/or sloping terrain on a site require even fur- ther precaution and preparation. Each manufacturer typically provides installation instructions for specialized conditions. Project contractors and design engineers can contact the system manufacturer to review the best method of installation when in doubt. Conclusion Due to the natural treatment capacity of the soil, decentralized systems have been and will continue to be the mainstays of wastewater treat- ment. Available to the public and developers where there are no other options, and in some cases as an alternative to cost prohibitive sanitary sewers, decentralized systems effectively protect community health. Better science, better understanding of processes, higher standards for installers, updated codes, operation and maintenance programs, and more thorough site evaluations will help to continue to raise the bar in this ever-growing field. But whatever else may change, the soil will still be working on our behalf. DENNIS F. HALLAHAN, PE has more than 30 years of experience with onsite waste- water treatment systems’ design and construction. Currently Technical Director at Infiltrator Water Technologies, he is responsible for technology transfer between Infiltrator and the regulatory and design communities and consults on product research and testing for universities and private consultants. Hallahan received his MS in civil engineering from the University of Connecticut and his BS in civil engineering from the University of Vermont. He is a registered professional engineer in Connecticut and holds several patents for on-site wastewater products. He can be reached at dhallahan@infiltratorwater.com.
Wheeled vehicles and construction laydown areas should not be allowed over the disposal fields.
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csengineermag.com
november 2020
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