The New York State Department of Transportation constructed a pilot project using tire shreds as embankment fill. The prototype section, measuring 200 m in length, used approximately 2500 metric tons of tire shreds as the core of the embankment section. The tire-shred zone had a maximum thickness of 3 m, and the tire shreds were covered with 1.5 and 1.0 m of embankment fill on the top and sides, respectively. The entire section was then surcharged with an additional 1.25 to 2.50 m of fill. After 4 months, the surcharge was removed to subgrade elevation, the granular base was placed, and the section was paved. The project was designed in accordance with the guidelines to limit internal heating of tire-shred fills distributed by the Federal Highway Administration. The tire shreds were produced by a hook and shear shredder, placed in the fill with a front-end loader, and compacted with a smooth-drum roller. Instrumentation of the prototype section was monitored both during and after construction. In all, 10 settlement platforms, 15 temperature sensors, 2 groundwater collection systems, and a groundwater observation well were installed and monitored. Settlements were as expected based on previous projects, and temperature measurements showed that there was no internal heating of the tire shreds. A unique incentive program developed jointly by the state’s Department of Transportation, Department of Economic Development’s Empire State Development Corporation, and Department of Environmental Conservation resulted in 267,000 tires being removed from abandoned stockpiles.
A field trial was constructed beneath a secondary state highway in North Yarmouth, Maine, to investigate the water-quality effects of tire shred fills placed above the groundwater table. Samples were collected in three 3-m2 geomembrane-lined basins located beneath the shoulder of the road. Two of the basins are overlaid by 0.61 m of tire shreds with a 75-mm maximum size topped by 0.72 to 1.37 m of granular soil. The third basin serves as a control and is overlaid by only 0.72 m of granular soil. Quarterly samples for inorganic constituents were taken from January 1994 through June 1999. In addition, samples were taken for volatile and semivolatile organic compounds on three dates. Filtered and unfiltered samples were analyzed for the following substances, which have a primary drinking water standard: barium, cadmium, chromium, lead, and selenium. There was no evidence that the presence of tire shreds altered the concentrations of these substances from their naturally occurring background levels. In addition, there was no evidence that tire shreds increased the levels of aluminum, zinc, chloride, and sulfate, which have secondary (aesthetic) drinking water standards. In a few samples, iron levels exceed their secondary standard. Manganese levels consistently exceeded their secondary standard; however, this is an aesthetic-based standard. Three sets of samples were tested for organics. Negligible levels of organics were found.
The risk to adjacent aquatic systems posed by leachates from scrap tires used in engineering applications has not been characterized adequately. Toxicity testing, toxicity identification evaluation (TIE), and groundwater modeling were used to determine the circumstances under which tire shreds could be used as roadbed fill with negligible risk to aquatic organisms in adjacent water bodies. Elevated levels of iron, manganese, and several other chemicals were found in tire shred leachates. However, chronic toxicity tests with Ceriodaphnia dubia and fathead minnows (Pimephales promelas) showed no adverse effects caused by leachates collected from tire shreds installed above the water table. Exposure to leachates collected from tire shreds installed below the water table resulted in significant reductions to both survival and reproduction in C. dubia. The TIE results indicated that exposure to soluble metals (likely ferrous iron primarily) and the formation of iron hydroxide precipitates on this invertebrate species likely were the causes of the observed effects. The available chemistry data show that iron concentrations in the affected groundwater decreased substantially within a short distance (0.61 m) downgradient of tire shred fill. Based on geochemical modeling, the use of tire shreds in applications below the water table is appropriate in settings where dissolved oxygen is greater than 2.0 mg/L, pH is greater than 5.8, and a downgradient buffer of approximately 3.0 m exists between the fill and the surface water. For settings with lower dissolved oxygen concentrations or lower pH, results of groundwater modeling indicate that a greater buffer distance (approximately 11 m) is needed to dilute the leachate to nontoxic levels under various soil and groundwater conditions solely through advection and dispersion processes.
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