Recent study findings where tire shreds were used for lightweight fill in road base construction in a wetland suggest that wrapping the tire shreds with a geotextile fabric could trap heavy metals and organic chemicals within the fabric wrap.  The mechanisms for the retention are not known and this proposed study will not attempt to identify them.  The observed trapping could be unique to the groundwater chemistry or geology of the current study site where installed.  This proposed study will determine if the chemical trapping phenomenon is specific to this single site or can be utilized in other wetland locations with similar groundwater chemistry.  The results of the current tire shreds study indicate that long term testing of groundwater is required to evaluate the long-term environmental effects of a waste material.  For this reason, the proposed study will be conducted over five years.

This proposed study will construct field diffusion chambers at the Minnesota Department of Transportation MnRoad research facility.  Three chambers will be constructed with an impermeable membrane/sheet to retain leachate from waste materials used in road base construction.  The chambers will be in-soil trenches with tire rubber (belts removed), fly ash in flowable fill, and a tire rubber/flowable fill with fly ash mixture as treatment chambers and covered with excavated soils.  Each treatment chamber waste material will be wrapped in geotextile fabric of the same slit width.  Control chambers without geotextile fabric but with the same waste material will be constructed for statistical testing of chemical concentrations.  Depth to groundwater in the MnRoad facility prevents the installation of waste materials into the groundwater table, however groundwater will be conveyed by hose or a well will be installed to supply well water to the diffusion chambers.

Once constructed with waste materials and flooded with well water, the chambers will equilibrate with leachate diffusing to the surrounding soils and water.  Initial well water and chamber water will be analyzed for heavy metals and semi-volatile organic chemicals to establish baseline concentrations.  In-chamber water levels will be maintained for long-term leaching of the waste materials by natural precipitation and groundwater additions at the site.  Beginning the second year of the study, chemical analysis of the chamber water will be conducted three times per year and continue for the study duration.  During the third and fifth years of the study, chamber water will be withdrawn for ecotoxicity testing of three species of aquatic or terrestrial organisms for survival and reproductive chronic effects.