Polymer-enhanced bentonite–sand to cover calcium-rich soil

The hydraulic and chemical properties of a polymer-enhanced bentonite–sand mixture (PEBSM) used as cover over calcium (Ca)-rich soil for 4 years is evaluated based on a series of isothermal laboratory-scale experiments. A 0·5 m thick calcium-rich soil (porewater with 1500 mg/l calcium ion (Ca²⁺)) was compacted into a laboratory column and then covered by a 0·07 m thick PEBSM layer. The PEBSM either was covered by an intact geomembrane (GMB) to mimic a composite liner or was in direct contact with the overlying soil (to simulate the case of a single-liner system). The hydraulic conductivity (k) and exchangeable cations of PEBSM were measured after 9, 21 and 48 months of exposure. The test results show that when PEBSM is used as a barrier over calcium-rich soil, there is only a small difference between the k of PEBSM covered with GMB (2·7 × 10⁻¹⁰ m/s) compared to the case without GMB (7·8 × 10⁻¹⁰ m/s) after 4 years in service. For both cases, k values after 48 months are considered low.