A simple field method to qualify the state of saturation in capillary barriers

Abstract: A simple and straightforward field method to rapidly qualify the state of saturation of moisture retaining layers (MRL) is proposed and the details of its calibration and operation, described. The technique is based on the simple fact that if gas samples cannot be taken from a stainless tube that is inserted to the desired depth within the MRL, the air filled voids at that depth are not interconnected and the material can be qualified, for all practical purposes, as saturated. In this case, the threshold degree of saturation beyond which gas flux substantially decreases (approximately 85 %), has been attained. In several sites covered with deinking by-products (DBP), an industrial residue that can be used as alternative construction material for landfills and acid-producing mine sites covers, it has been often impossible to collect gas samples below approximately 20 cm from the surface of the DBP layer. The question was thus to know if this is a reliable indicator that the threshold degree of saturation has or not been attained and that the layer is performing its role of gas barrier. In order to answer this question, a calibration was performed in the laboratory and in the field. The calibration consisted mainly on attempting to extract gas from samples compacted at different degrees of saturation. The results show that the threshold degree of saturation for DBP is attained at approximately 83 %