Comparative performance of tire-derived aggregate as a substitute for natural aggregate in full-scale septic drainfield systems: a Manitoba, Canada field study

The beneficial reuse of tire waste materials in wastewater infrastructure supports circular resource management while reducing environmental burdens associated with tire disposal and aggregate quarrying. Despite growing interest in tire-derived aggregate (TDA) as a sustainable drainfield medium, full-scale field evidence comparing its performance to conventional natural aggregate remains limited. A pilot-scale septic system was constructed at a rural residential site in Manitoba, Canada, comprising a two-zone trench-style drainfield receiving effluent from a 1000-gallon fiberglass septic tank serving a three-bedroom household. Type A nominal TDA (2-4 inch, sourced from off-the-road tires) was benchmarked against conventional washed natural aggregate (3/8-3 inch) over an 18-month monitoring period. Vadose zone effluent quality was assessed at 0.3 m and 0.9 m below the trench base using suction lysimeters. Both systems achieved statistically equivalent reductions exceeding 90% for COD, ammonia-nitrogen, and orthophosphate (p > 0.05). Monitored metals (Ag, Al, Cu, Fe, Zn) remained below U.S. National Secondary Drinking Water Regulation thresholds. Manganese exceeded secondary guidelines at 0.3 m in both systems, attributable to site-specific redox geochemistry rather than TDA leaching. Total coliforms and E. coli were below detection limits beneath both fields. Soil metal concentrations remained within established regional background ranges after 1 year. TDA is a technically viable and environmentally acceptable alternative to natural aggregate in onsite septic drainfield applications, delivering equivalent treatment performance without adverse effects on leachate quality or soil metal loading, supporting broader adoption as a circular economy strategy.