A number of wastes from various locations across Canada were subjected to a set of leaching tests. Each set consisted of six batch extractions using three leaching media (distilled water, an acidic solution buffered at pH 4.5, and a synthetic municipal landfill leachate) at two liquid-to-solid ratios (4:1 and 20:1). The preliminary data from 19 wastes were examined to gain a better understanding of the effects that different leaching media and liquid-to-solid ratios have on contaminant release.

When distilled water was used as the leaching medium, the final pH of the leachate was controlled by the alkalinity of the waste. Changing the liquid-to-solid ratio had little effect on leaching pH. The difference in the concentrations observed at the two liquid-to-solid ratios was the result of dilution in many cases.

When an acidic solution or synthetic leachate was used as the leaching medium, final leachate pH appeared to be a function of the interaction between the waste pH and the amount of acid available in the leaching medium to react with the waste. Increasing the liquid-to-solid ratio increased the amount of acid contacting the waste and shifted the leachate pH towards the pH of the leaching medium.

Use of a synthetic leachate appeared to complex some contaminants and increase their release above that to be expected from pH-solubility considerations alone.

Linear relationships were observed between the leachate pH and the logarithm of the release for some wastes and contaminants. Knowledge of this relationship would make it possible to interpolate or extrapolate results of leaching tests performed on the same waste under different test conditions.

Contaminant release from the same waste can vary over several orders of magnitude within a short pH range. Therefore, final leachate pH should be included when reporting the results of a batch leaching test.