1.1 ,Paper industry sludges are industrial by-products derived from wastewater treatment operations at plants associated with the manufacturing of paper. These sludges typically consist of clay and organic matter. They may also contain low levels of inorganic and organic contaminants and can be rich in microbes. Traditionally, paper industry sludges have been disposed in municipal solid waste landfills or solid waste monofills. However, in the interest of sustainability, applications are being developed where sludges can be used beneficially. One application is using sludge to construct hydraulic barriers (for example, for use in a landfill cap). Such applications generally require that the hydraulic conductivity of the sludge be measured.