WC138 SeptOct 2024 - Flipbook - Page 26
DRINKING WATER
the soil porosity through which the contaminated
water flows; the carbon then coats the soil matrix,
ensuring sustainable immobilization of contaminants because of its specially modified adsorbent
structure. The duration of the adsorbent zone in
the aquifer can be extended over several decades,
depending on contaminant type, groundwater
flow velocity, and contaminant mass flux.
In the first application example, at a former
NATO airport in North Rhine-Westphalia, Germany, the decades-long use of fire-fighting foams
containing PFAS ended up in groundwater, which
led to the formation of a plume of PFAS.
The aim of introducing in situ CAC was to treat
the pollutant plume in the upper and lower aquifer
zone located down to 22 metres below ground
surface (mbgs). The PFAS concentration (total of
27 compounds) in the plume was determined to be
1,100 ng/l in the upper zone and 110 ng/l in the
lower zone. An in-situ adsorption barrier was then
set up in the aquifer by direct push of an injectable
CAC, called Intraplex® B, in the upper and lower
zone. The monitoring results show that the activated carbon material retained completely the pollutant load in the adsorption
zone within a few weeks, and the PFAS concentrations downstream have fallen below target values of 100 ng/l.
The second application example touches on a drinking water issue in the city of La Baie, Quebec’s, distribution network
that is contaminated with PFAS above the upcoming 30 ng/l
guideline. We have evaluated the potential of an in-situ treatment by creating a permeable sorption barrier (PRZ) based on
the modified CAC Intraplex B and compared this approach
technically and economically versus a standard above ground
filtration system using ion exchange resin (IX -See the Table 1,
page 25).
The barrier’s lifetime was carried out using a quantity of
8,000 kilograms of Intraplex® B per well and is estimated
at 20 years. On this basis, the associated treatment costs are
approximately $266,000 per well that include the total product costs and the estimated amount for their installation and
monitoring in time. This amount is significantly lower than
the typical above ground surface intervention to remove these
contaminants, as adsorption barriers are a sustainable, passive
method using natural flow gradients to remove targeted PFAS
contaminants.
To complement contaminant removal processes, the scientific
community is working on coupling in situ sorption barriers with
oxidative-catalytic or biological destruction to develop a sustainable solution for in situ treatment of PFAS. In the meantime,
sorption mechanisms will be able to protect our drinking water
sources and sensitive downgradient receptors.
wsp.com
26
WATER C AN ADA • SEP TEMBER/OCTOBER 2024
WAT E R C A N A D A . N E T
Getty Images
“Remediation of PFAS-contaminated solid and aqueous
media is extremely challenging due to their high chemical
and thermal stability in the environment.”
