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PT21 Environmental Assessment, Environmental Toxicology
(PT306) Aquatic Toxicity Testing: Assessing the Safe Use of Scrap Tires as Roadbed Fill.
Sheehan, P1, Warmerdam, J1, Humphrey, D2, 1 Exponent, Oakland, CA, US2 University of Maine, Orone, ME, US
ABSTRACT- Historically, it has been difficult to quantitatively evaluate the environmental effects of engineering applications of scrap materials, particularly materials known to leach chemicals when in contact with water. In this study, toxicity testing, toxicity identification evaluations (TIEs), and geochemical and groundwater modeling were used to assess and predict the effects on aquatic organisms of the use of scrap tire shreds as fill below the water table in roadbeds that are upgradient from aquatic systems. Toxicity tests with the fill leachate from a demonstration site showed no effects on juvenile fatfead minnow but significant effects on both the survival and reproduction of daphnids. The TIEs identified metals as forming percipitates, likely iron hydroxides, that attach to the organisms contributing to the observed effects. Using the "no effects" level from the toxicity tests as a threshold, modeling was used to evaluate the dilution in leachate and reduction in iron levels (and toxicity)in groundwater under various soil and flow conditions. Under all but low pH sandy soil conditions, leachate concentrations in groundwater were estimated to be reduced to levels below the toxicity threshold within approximately 30 feet downgradient of the fill material. In silty soils, the leachate levels were reduced to levels below the threshold within as little as 5 feet. This approach combining leachate toxicity tests and modeling provides promise as a quantitative assessment tool for evaluating the condition under which scrap materials such as tires can be used in engineering applications with minimal risk to adjacent aquatic ecosystems.
Key words: toxicity tests, scrap tires, TIEs, groundwater modeling
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