Craig H. Benson

Hydraulic Conductivity of Geosynthetic Clay Liners Exhumed from Landfill Final Covers with Composite Barriers

Geosynthetic clay liners GCLs were exhumed from composite barriers, i.e., geomembrane over GCL in final covers at four sites after 4.7 to 6.7 years to evaluate the in-service condition. Monovalent bound cations were replaced by divalent cations in all GCLs, with near complete exchange at two-thirds of the sampling locations. Hydraulic conductivity was measured using two dilute solutions commonly used as permeant water: standard water SW, 0.01M CaCl2 solution and type II deionized water DW. Hydraulic conduc- tivities to SW varied over four orders of magnitude, whereas identical specimens i.e., from same sample had hydraulic conductivities to DW consistently 310 x7f10 m /s. Higher hydraulic conductivities and sensitivity to permeant water did not correspond directly to the amount of cation exchange. Exhumed GCLs with higher gravimetric higher water contents 50% exhibited a gel structure indicative of osmotic hydration and had lower hydraulic conductivities to both SW and DW, regardless of the amount of sodium Na replaced by divalent cations. These GCLs with higher water contents were placed on subgrade having water content in excess of optimum water content standard Proctor. Conditions that promote rapid hydration and osmotic swell in a GCL are recommended to ensure that a GCL in a composite barrier maintains low hydraulic conductivity 510 x7f11 m /s, even if the native Na is ultimately replaced by divalent cations. Subgrade with water contentoptimum water content is recommended. DOI: 10.1061/ASCEGT.1943-5606.0000407 CE Database subject headings: Geosynthetics; Clay liners; Landfills; Hydraulic conductivity; Barriers; Composite materials; Water content. Author keywords: Geosynthetic clay liner; Landfill; Final cover; Hydraulic conductivity; Cation exchange; Hydration; Osmotic swell; Crystalline swell; Preferential flow.

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 19u2009mL/2u2009g). In 500 mM CaCl2, however, swell of BPC was similar to swell of calcium bentonite ( 2u2009years). In contrast, Na-bentonite and superabsorbent polymer (similar...

Hydraulic Conductivity of Geosynthetic Clay Liners to Low-Level Radioactive Waste Leachate

AbstractHydraulic conductivity was evaluated for eight commercially available geosynthetic clay liners (GCLs) permeated with leachate characteristic of low-level radioactive waste (LLW) disposal facilities operated by the U.S. Department of Energy (DOE). Two of the GCLs (CS and GS) contained conventional sodium bentonite (Na-B). The others contained a bentonite–polymer mixture (CPL, CPH, GPL1, GPL2, and GPH) or bentonite–polymer composite (BPC). All GCLs (except GPL2 and GPH) were permeated directly with two synthetic LLW leachates that are essentially identical, except one has no radionuclides (nonradioactive synthetic leachate, or NSL) and the other has radionuclides (radioactive synthetic leachate, or RSL). Hydraulic conductivities to RSL and NSL were identical. For the CS and GS GCLs, the hydraulic conductivity gradually increased by a factor of 5–25 because divalent cations in the leachate replaced native sodium cations bound to the bentonite. The CPL, GPL1, and GPL2 GCLs with low polymer loading (1....

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 (>2u2009×u200910−9 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...

Characteristics of Gas and Leachate at an Elevated Temperature Landfill

Data from a municipal solid waste (MSW) landfill with elevated temperatures are evaluated to assess how characteristics of landfill gas and leachate evolved as the landfill temperature increased from ranges typically associated with methanogenic decomposition (40 – 50C) to more than 100C. The MSW landfill was deep (~ 100 m), unlined, and most of the waste was saturated and below the water table. Temporal trends in landfill gas temperature measured at the wellhead indicate that the gas temperatures increased abruptly and systematically following a shutdown to address a concern about the potential for subsurface combustion. Temperature profiles collected subsequently indicated that the highest temperatures were substantially below the leachate level, making combustion an unlikely mechanism for the elevated temperatures. Temporal trend analysis indicated that the primary gas ratio (CH4:CO2) decreased systematically and substantially when the gas temperature increased abruptly. Leachate chemistry also changed significantly after the gas temperature increased abruptly, with BOD, COD, and the BOD:COD ratio increasing rapidly, pH dropping more than one unit, and total suspended solids increasing more than two orders of magnitude.

Chemical Characteristics of Leachate in Low-Level Radioactive Waste Disposal Facilities

AbstractLeachate data from four low-level radioactive waste and mixed waste disposal facilities operated by the U.S. DOE for environmental restoration programs are presented and analyzed. Constitue...

Antioxidant Depletion and Service Life Prediction for HDPE Geomembranes Exposed to Low-Level Radioactive Waste Leachate

AbstractAntioxidant depletion was evaluated in high-density polyethylene (HDPE) geomembrane (GM) coupons immersed in radioactive synthetic leachate (RSL) representative of leachate in low-level rad...