Abstract
Scientists and engineers often rely on results from the synthetic precipitation leaching procedure (SPLP) to assess the risk of groundwater contamination posed by the land application of granular solid wastes. The concentrations of pollutants in SPLP leachate can be measured and compared to groundwater quality criteria to determine if groundwater contamination is likely. These results are applied, however, inconsistently among regulatory agencies because of uncertainty over whether the SPLP leachate concentrations represent the actual pore water concentrations expected in the waste, or whether they represent diluted concentrations as might be expected in an underlying aquifer. Depending on the waste in question, the SPLP results can represent either condition. Research was conducted to examine the use of the SPLP for assessing risk to groundwater from a granular waste that is land applied in a manner consistent with use as fill material. Theoretical considerations were first explored. The complexities associated with the application of SPLP results were then illustrated by testing five granular wastes. In addition to measuring the total concentration and performing the SPLP, the wastes were leached at a series of liquid-to-solid ratios to estimate likely pore-water concentrations. The use of generic leaching risk screening levels (mg/kg) derived for soils was found inappropriate. The application of a dilution factor to the SPLP concentrations was found to underestimate possible risk in most cases. Comparing the SPLP directly to water quality limits was found to be conservative in most situations; several observations were made, however, where the SPLP underestimated pore water concentrations. The use of a total pollutant concentration (mg/kg) in conjunction with a SPLP concentrations (mg/L) to estimate a pore water concentration was found unreliable; this method underestimated the measured pore water concentrations.
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