Postconstruction Changes in the Hydraulic Properties of Water Balance Cover Soils

Hydraulic properties of soils used for water balance covers measured at the time of construction and one to four years after construction are compared to assess how the hydraulic properties of cover soils change over time as a result of exposure to field conditions. Data are evaluated from ten field sites in the United States that represent a broad range of environmental conditions. The comparison shows that the saturated hydraulic conductivity (Ks) can increase by a factor of 10,000, saturated volumetric water content ((theta)s) by a factor of 2.0, van Genuchtenʹs (alpha) parameter by a factor of 100, and van Genuchtenʹs n parameter can decrease by a factor of 1.4. Larger changes occur for denser or more plastic fine-textured soils that have lower as-built Ks, (alpha), and (theta)s and higher as-built n, resulting in a reduction in the variation in hydraulic properties that can be attributed to compaction. After two to four years, many water balance cover soils can be assumed to have Ks between 10^-5 and 10^-3 cm/s, (theta)s between 0.36 and 0.40, between 0.002 and 0.2 kPa^-1, and n between 1.2 and 1.5. The data may be used to estimate changes in hydraulic properties for applications such as waste containment, where long-term maintenance of hydraulic properties in shallow engineered soil layers is important.