Geosynthetics October/November 2021 - 26

Hybrid GCLs for attenuation of PFAS in landfill leachates
concentration throughout the duration of
permeation (Figures 7 and 8).
As previously determined in other
FIGURE 6 Hydraulic conductivity data for the PMB GCL and hGCL when hydrated and permeated
with Leachate E
hGCL performance with
Australian landfill leachate
The research and development facility
undertaking this study frequently analyzes
leachates, liquors and soil elutions
for their chemical compatibility with a
range of GCLs. Current leachates were
screened for PFAS content, leading to
a more rigorous analysis of the interaction
between an hGCL with Leachate
E, which contained a total PFAS level of
~83 ppb (~83 µg/L) (Figure 6). Leachate
E was permeated through a PMB GCL
with ~0.82 pounds per square foot (~4
kg/m2) bentonite and an hGCL with the
same ~0.82 pounds per square foot (~4
kg/m2) bentonite blended with an additional
0.20 pounds per square foot (1
kg/m2) of a select grade of powdered
AC. The PMB GCL had a stable hydraulic
conductivity throughout its 290 days
of permeation, with a final termination
value of 1.77 × 10-11 m/s. After 330 days
of permeation, the hGCL had a termination
hydraulic conductivity value of 7.31
× 10-11 m/s. The effluent liquid from both
permeability cells was analyzed for PFAS
26
Geosynthetics | October November 2021
leachates, PFAS compounds passing
through the PMB GCL generally
remained at the initial concentrations,
excluding perfluoropentanoic acid
(PFPeA), which reduced from 37.6 to
0.94 ppb (37.6 to 0.94 µg/L), and perfluorobutanoic
acid (PFBA), which demonstrated
sporadic behavior, initially rising
throughout the test period, then falling
toward the final stages of analysis. These
behaviors could be attributed to degradation
reactions or analytes concentrating
within the material, resulting in
breakthrough when sorptive capacity is
attained (Gates et al. 2020).
The hGCL effluent data for Leachate E
show that the PFAS compounds were well
attenuated, and for the regulated PFOS,
PFOA and PFHxS compounds, attenuated
values were below the NEMP 2.0
guidance requirements. Once more, PFBA
gave the most observable breakthrough,
as with some of the other shorter chain
compounds in other trials conducted.
Ongoing hGCL development
The current hGCL has demonstrated a
good degree of resistance to migration of
the three currently regulated long-chain
PFAS compounds, but the regulations are
evolving, and the next revisions are likely
to encompass a wider range of PFAS compounds,
at potentially lower maximum
concentrations. The next iterations of
the hGCL-which include the addition
of other supplementary minerals, compounds
and resins in various formulations
and dosages-are under development.
The current studies have been specifically
focused on the attenuation of PFAS
compounds, but it is entirely possible that
other emerging contaminants may also be
captured by a new generation of hGCLs
currently in development. With GCLs

Geosynthetics October/November 2021

Table of Contents for the Digital Edition of Geosynthetics October/November 2021

Geosynthetics October/November 2021 - Cover1
Geosynthetics October/November 2021 - Cover2
Geosynthetics October/November 2021 - 1
Geosynthetics October/November 2021 - 2
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