Joseph Scalia

Long-Term Hydraulic Conductivity of a Bentonite-Polymer Composite Permeated with Aggressive Inorganic Solutions

AbstractBentonite was modified to prevent alterations in hydraulic conductivity when permeated with aggressive inorganic solutions. Acrylic acid within bentonite slurry was polymerized to create a bentonite-polymer composite (BPC). Tests indicate that BPC generally swells more and retains low hydraulic conductivity compared with natural sodium bentonite (Na-bentonite) when contacted with aggressive inorganic solutions. BPC in deionized water swelled greater than 3.8 times the swell of the Na-bentonite used to create BPC (73 versus 19 mL/2 g). In 500 mM CaCl2, however, swell of BPC was similar to swell of calcium bentonite ( 2 years). In contrast, Na-bentonite and superabsorbent polymer (similar...

Hydration and Cation Exchange during Subgrade Hydration and Effect on Hydraulic Conductivity of Geosynthetic Clay Liners

AbstractExperiments were conducted to evaluate cation exchange during hydration of geosynthetic clay liners (GCLs) used in composite hydraulic barriers and the effect on their hydraulic conductivity. GCLs arranged in a composite barrier configuration were hydrated by contact with moist compacted subgrades (two clays, one silt, and one sand) under a confining stress of 10 kPa for 30 days to 1 year. No measurable exchange occurred in GCLs hydrated for 30 days. For hydration periods longer than 30 days, the exchange increased as the duration of hydration increased. The exchange during subgrade hydration had no measurable effect on the hydraulic conductivity to deionized (DI) water. However, if the GCL was desiccated after hydration, the hydraulic conductivity increased more than 1,000-fold. Dissolution of calcite within the bentonite during permeation with DI water also induced the replacement of sodium by calcium; however, this additional exchange had no measurable effect on the hydraulic conductivity to DI...

Preferential flow in geosynthetic clay liners exhumed from final covers with composite barriers

Geosynthetic clay liners (GCLs) were exhumed from final covers with composite barriers (geomembrane over GCL) at two municipal solid waste landfills in the USA. Preferential flow and high hydraulic conductivity (>2 × 10−9 m/s) was observed in eight of the 18 GCL samples collected from both sites. At one site, manganese oxide precipitate was concomitant with bundles of needle-punched fibers that conducted preferential flow. Nearly complete replacement of Na by Ca on the bentonite surface occurred in all GCL samples. GCLs with and without preferential flow could not be differentiated by physical and chemical properties commonly used to differentiate GCLs with high and low hydraulic conductivities (exhumed water content, swell index, mole fraction monovalent cations, soluble cation concentrations). The relative abundance of soluble cations in the pore water of GCLs exhibiting preferential flow was comparable to the relative abundance in the subgrade pore water, whereas the pore water in GCLs with distributed...