Sequenced Permeable Reactive Barrier for the Pretreatment of Nitrate and Remediation of Trichloroethene - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 115

varied from 0.18 to 17.9 m/day. These results indicate a highly variable and
heterogeneous sand, sandy clay aquifer at the base of the escarpment.

7.3 ZVI Bench-Scale Tests
A bench-scale treatability study was conducted by EnviroMetals Technologies
Inc. (EnviroMetals 2009) of Waterloo, Canada, to determine the feasibility of
using ZVI to remediate TCE from site groundwater.
The bench-scale testing used groundwater from a monitoring well on site
with the highest recorded concentrations of TCE. ETI indicated that the water
provided to them had TCE concentrations of 820 μg/L and nitrate concen-
trations of about 3 mg/L. ZVI from two different manufacturers, Connelly
GPM of Chicago, USA, and Quebec Metal Powders Ltd (QMP) of Sorel-Tracy,
Canada, were used in the column experiments. A summary of the properties
of the two ZVI materials is provided in Table 7.1.
The column experiments indicated that both the ZVI materials tested
completely degraded TCE present in the site groundwater samples to below
the remediation targets and laboratory limits of reporting without break-
through of any chlorinated intermediate breakdown products. From these
data, TCE half-lives at the 19.5°C site groundwater temperature were esti-
mated to be 0.75 and 2.0 h for the QMP and Connelly ZVI, respectively. The
residence time required to degrade TCE concentrations to below RBC was
calculated to be between 2 and 9 h depending on the selected ZVI and TCE
input concentrations.
An additional factor that must be considered in determining the required
ZVI thickness in a PRB is the potential effect of nitrate passivation. Nitrate
passivation rates of 0.44 and 0.53 mg NO3-N /g Fe were estimated by ETI from
observed column nitrate concentrations profiles for the Connelly and QMP
ZVI materials, respectively.
Owing to higher reactivity and lower nitrate passivation rates, QMP ZVI
was selected as the more suitable material for the construction of the ZVI PRB.
An assessment of the required thickness of ZVI to degrade TCE to concen-
trations below the RBC was made based on the half-life estimates from the

TABLE 7.1
Summary of ZVI Physical Properties

Hydraulic
Conductivity Grain Size Density

QMP 3.94 g/cm 3 13 m/d

<0.045 to 1.7 mm

Connelly 0.25 to 2.0 mm 2.73 g/cm 3 44 m/d