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The evaluation of alternate aggregate in septic system leachfields: A comparison of tire derived aggregate and crushed stone
Historically, the end of life disposition of scrap tires was placement in landfills or stockpiles. Landfills lost valuable space from the physical configuration of tires and stockpiles were unsightly and posed several environmental hazards including the spread of disease from breeding insects and rodents, spontaneous combustion, and chemical leaching from tire degradation. The desire to reduce the environmental impact of scrap tires is driving the current research to find beneficial end of life uses of both previously and newly discarded tires.
One beneficial end of life use is tire derived aggregate, or TDA. TDA is used as an alternate to conventional stone aggregate in many engineered systems including septic system leachfields. The Center for Integrated Waste Management (CIWM) at the University at Buffalo has performed several studies utilizing TDA in septic system leachfields. Some of these studies were conducted at the full scale aboveground leachfield at the Modern Landfill Corporation Tire Recycling Facility (Modern) in Lewiston, NY. The Modern leachfield consists of both TDA and stone aggregates which allows side by side comparisons of the media.
The goal of this project is to strengthen and extend previous research results obtained by the CIWM while contributing to the existing peer-reviewed literature with more than 10 years of pilot and full scale leachfield work using TDA. This was accomplished using statistical testing and model fitting techniques of historical and current data and producing a series of three research papers. Results from this project include old and new TDA has at least equal hydraulic conductivity and treatment performance as #2 crushed stone. In high permeability leachfields, 1" TDA, 2" TDA, and #2 crushed stone do not increase heavy metal concentrations above background levels. In low permeability leachfields, only iron concentrations differ between 1" TDA, 2" TDA, and #2 crushed stone. Also, 1" TDA promotes equal or better soil absorption capacity when compared to 2" TDA and #2 crushed stone in high permeability and low permeability leachfields.