Long-Term Hydraulic Conductivity of a Geosynthetic Clay Liner Permeated with Inorganic Salt Solutions

TLDR

"Permeation with CaCl₂ increased hydraulic conductivity by more than an order of magnitude, with the rate of change depending on concentration; weaker solutions caused slower changes, whereas NaCl, KCl, or DI water produced no appreciable change. Let's craft. Purpose sentence: "The study evaluates how long‑term hydraulic conductivity of a geosynthetic clay liner is affected by cation concentration and valence and demonstrates the importance of termination criteria in conductivity measurements with salt solutions." Mechanism sentence: "Hydraulic‑conductivity tests were conducted on a GCL for over 2.5 years and up to 686 pore volumes of flow using single‑species salt solutions (NaCl, KCl, CaCl₂)." Findings sentence: "Permeation with CaCl₂ increased hydraulic conductivity by more than an order of magnitude, with the rate of change depending on concentration; weaker solutions caused slower changes, whereas NaCl, KCl, or DI water produced no appreciable change.

Abstract

Hydraulic conductivity tests were conducted on a geosynthetic clay liner (GCL) for more than 2.5years and as many as 686 pore volumes of flow (PVF) using single-species salt solutions (NaCl, KCl, or CaCl2) to (1) evaluate how the long-term hydraulic conductivity (KL) is affected by cation concentration and valence and (2) demonstrate the relevance and importance of termination criteria when measuring hydraulic conductivity of GCLs to salt solutions. Permeation with CaCl2 solutions resulted in an increase in the hydraulic conductivity of 1 order of magnitude or more. The rate at which these changes occurred depended on concentration, with slower changes (years and hundreds of PVF) occurring for weaker solutions. In contrast, permeation with 100mM NaCl or KCl solutions or de-ionized (DI) water resulted in no appreciable change in hydraulic conductivity, regardless of the duration of permeation or number of pore volumes of flow. Hydraulic conductivities determined in accordance with ASTM D 5084 and D 6766 (K5084 and K6766) equaled KL when the permeant solution contained NaCl, KCl, or was a strong (⩾50mM)CaCl2 solution. In contrast, when the permeant liquid was a weak (⩽20mM)CaCl2 solution, K6766 and K5084 were 2–13 times lower than KL. Closer agreement between K6766 and KL(3×) was obtained for weak CaCl2 solutions when the electrical conductivity ratio criterion was tightened to ±5%. Hydraulic conductivities obtained after comparable influent and effluent concentrations of the permeant salt (±10%) were approximately 2× lower than KL for weak CaCl2 solutions. Hydraulic conductivities equal to KL were obtained from the tests permeated with weak CaCl2 solutions only when Na was no longer eluted at detectable levels.