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Historically, wastes are assessed for waste classification on the basis of total and leachate pollutant concentrations. The approved methods for leaching are TCLP USEPA 1311 and SPLP USEPA 1312.

Although these two methods provide a simple value which can be compared against a target limit, they are arguably inaccurate at providing a prediction of pollutant fate as these methods offer limitations on the mechanisms which mirror the level of pollutants which solubilise from solid form into a liquid phase. The main reasons for this are:

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TCLP USEPA 1311 and SPLP USEPA 1312

• Single leaching pH

• Single set of oxidation/reduction conditions (ORP not measured)

• Single form of waste (granular)

• Single time of exposure (18 hours)

• Single Liquid/Solid Ratio (20:1)

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over predict the release of pollutants in the environment

 

The above set of conditions tend to produce results which do not accurately reflect possible solubility of pollutants found in the solid waste. Rather it has a tendency to over predict the release of pollutants in the environment.

In the world of waste treatment, this over prediction inadvertently means treatment of wastes is conducted by overdosing of reagents which in turns represents:

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• Greater mass of waste produced and disposed in landfills

• Greater carbon footprint from treatment components (reagents, energy consumption, fuel requirements and transportation of waste from site to facility to landfill)

• Greater cost to treat

 

costs were 20% higher when using USEPA 1311

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In one recent study conducted on PAH impacted soil, the additional reagents, transport and disposal costs were 20% higher when using USEPA 1311 and EPA concentration criteria vs an argument founded on the LEAF methodology findings. The findings showed a much greater insight into the solubility of pollutants under potential conditions which in turn resulted in a significant reduction in reagent mass requirement.

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So as scientists and organisations are working together to achieve lower emissions, reduce waste and lower environmental impact, the above leaching methods seem in many ways outdated and over simplistic. 

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The “new” generation of leaching procedures introduced by USEPA is called LEAF (Leaching Environmental Assessment Framework). They are designed at providing multiple set of leaching conditions which can be used to assess possible transport of pollutants found in solid waste into a liquid phase.

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These leaching methods include USEPA 1313, 1314, 1315 and 1316. They provide many variables for assessing classification, disposal, and treatment effectiveness and provides a much more in depth data set which will help consultants, scientists and regulators make more informed decisions about waste characteristics.

 

LEAF methods provide greater context in which decisions can be based upon

 

 

The below table highlights the differences between each leaching method:

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USEPA Leaching Procedure Comparison

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The LEAF methods provide greater context in which decisions can be based upon. They include varying pH values, varying Liquid/Solid ratios, long extraction contact times, percolation effects, repeated extractions via the replacement of extraction fluid, and very importantly definition on particle size and its effect on leaching.

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The resultant data can be used to produce graphs which can accurately identify conditions which will cause a compound to leach above a set limit and when used along with other LEAF methods data can serve as solid technical argument for using this methodology as an assessment tool.

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Many micro-encapsulation stabilisation process include the use of cement as a reagent to ensure pollutants are trapped in the waste matrix. These processes use UCS (Unconfined Compressive Strength AS1012.9-2014) as a measure of monolith strength, however very few processes actually dispose material to landfill in monolith form. USEPA 1315 however, serves as an accurate test where a monolithic cylinder is tested over 63 days with frequent renewal of the leaching fluid, this is a much closer representation of landfill disposal conditions.

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With over two decades conducting leaching procedures for environmental laboratories and the waste industry alike we have a pragmatic view on how testing techniques impact treatment processes and ultimately the environment.

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If your organisation requires assistance in understanding or producing a founded technical argument for using the LEAF methods, we are here to assist.

 

Written by:

Pablo Casenave – Director & Analytical Chemist – AquaChem Solutions

pablo.casenave@aquachemsolutions.com.au