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EMERGING CONTAMINANTS OF CONCERN

While much is known about the transport of the dominant constituents in municipal solid waste (MSW) leachate, there is a paucity of data concerning the transport of several toxic materials of emerging concern–including nanoparticles, leached plastic stabilizers and brominated flame retardants– through barrier systems, even though they have been detected or may reasonably be anticipated to be present in MSW. Likewise, while the early stages controlling GM service life have been quantified for MSW, there is a need to establish the full GM service life when used to contain MSW leachate, industrial and hazardous waste leachate, or the liquids used in heap-leach mineral recovery.

Current barrier systems for MSW landfills were developed to deal with the contaminants of known concern in the 1990s–like heavy metals and hydrocarbons [e.g., Ont. Reg. 232/98]. However, there are several new classes of contaminants where there is recent and growing concern about their potential release into the environment. These ECCs are either relatively new or recently identified in the waste stream; further they may be highly toxic. Virtually nothing has been documented regarding the effectiveness of current barrier systems for controlling the ECCs to be examined in this Strategic Project. This urgently needs to be established and, if needed, barrier system design improved to ensure environmental protection. Ignorance regarding ECC mobility and fate through barrier systems and the subsurface may result in repeating the errors of our industrial past (e.g., PCBs, global warming CFCs).

Nanotechnology wastes: Nanotechnology is an exciting, emerging industry that involves materials having at least one dimension less than 100 nm (10-7 m). Many technological breakthroughs have been achieved due to the ability to engineer particles at the nano-scale; however, there is concern related to the health and ecosystem effects of these newly developed materials. It is anticipated that nanoparticles will become prevalent in municipal waste and, if not adequately contained, are likely to reach subsurface aquifers–as have virtually all manufactured compounds. Nanoparticle mobility may be expected to be influenced by the physical and chemical properties of the nanoparticles, the geosynthetics, the porous medium and the permeant fluid. Limited studies suggest that nanoparticle mobility may vary widely in porous media systems; but these were conducted under idealized conditions (e.g., using glass beads or purified quartz sand instead of natural soils; having flow velocities orders of magnitude larger than those found in natural systems), thereby limiting their relevance to engineered barrier systems. New research is required to quantify the transport of engineered nanoparticles as well at the effects, if any, they may have on the barrier system itself (GM and GCL).

This study is examining carbon nanoparticles (CNP) because: (a) CNPs are already being produced in significant quantities (e.g., 2007-08 carbon nanotube production exceeded 300 tonnes/yr) for commercial products that will likely end up in a landfill and the quantities are likely to increase substantially as the cost of CNPs decrease and they become widespread in consumer products, (b) CNP toxicity is currently under investigation but largely unknown and may not be fully known for decades, and (c) landfills barriers are typically designed and constructed many years before the completion of waste placement and hence to avoid potential future problems it is essential to assess the mobility of CNPs through typical barrier systems, and adjust designs as needed, as soon as possible.  Other nanoparticles of interest include TiO2 and nano Ag.

Leached chemical additives: Bisphenol-A (BPA) is a contaminant of current concern to both the public and regulators.  BPA is a stabilizer added to many plastics that can subsequently be leached out. It is believed to be an endocrine disruptor, with the concern that it may mimic human estrogen at low concentrations. Likewise, polybrominated diphenyl ether (PBDE) is an additive flame retardant in plastics, foams and fabrics that may leach out of waste. PBDE may cause liver, thyroid, and neurodevelopmental toxicity [US EPA]. Both BPA and PBDE have been recently found in significant concentrations in MSW leachate; yet, there are no studies that quantify how these contaminants may migrate through geosynthetic liners.


INDUSTRIAL ECCs. Heap-leach mining is an economical method of extracting minerals from low grade ores where liquids are percolated through very large piles of crushed rock. In some cases, acid solutions with a pH as low as 1.5 may be used while for the recovery of other metals high pH may be used. Geosynthetic barrier systems are commonly used at the base of these pads to prevent these solutions from escaping to surrounding surface and ground waters. Geosynthetics may also be relied on to provide containment in stabilized hazardous solid waste landfills and low level nuclear waste landfills where they may be exposed to pH 10-12 leachates. While most research on geosynthetic barrier performance has focussed on MSW landfills, the more extreme chemical exposure in the applications to be examined in this project necessitates an evaluation of GM service life and potential for containing fluids which could have a negative environmental impact if they were to escape at anything but a negligible level.

 


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