Environmental Engineering Reference
In-Depth Information
When the longevity of the PRB is considered, one of the key concerns is min-
eral fouling. Mineral fouling is the reduction in pore space caused by mineral
precipitation in the reactive material of the barrier (Li et al., 2006). This will
result in the reduction of the porosity and hydraulic conductivity (Johnson
et al., 2005) of the reactive media that will in turn influence groundwater flow
and pollutant transport pathways. Li et al. (2006) conducted a study using
ZVI as the reactive medium to identify and assess the most significant param-
eters impacting PRB hydraulics when influenced by a reduction in porosity.
4.2.2 Process-Based Modeling
The contaminant migration in the subsurface environment is influenced by
various physical processes such as flow and nonreactive transport mecha-
nisms, and geochemical processes. Understanding these processes holds
the key for developing the reactive transport models to simulate the con-
taminant transport in the subsurface environment. Process-based reactive
transport modeling is an important tool for building a reliable simulation
model for PRBs (Amos et al., 2004). Assessment and evaluation of a PRB
requires the integration of complex biogeochemical processes occurring in
the heterogeneous subsurface (Mayer et al., 2006). The primary goal of using
process-based models is to predict the long-term performance of PRBs. A
case study involving process-based reactive transport modeling has been
conducted at Nickel Rim site (Benner et al., 1999) using the MIN3P (Mayer
et al., 2002) numerical simulation model. This study integrated pore water
data and solid-phase data from the reactive barrier, using the reactive trans-
port model. The conceptual model included reduction rates and secondary
geochemical parameters such as alkalinity and soil-phase data. This integra-
tion process resulted in simulated sulfate reduction rates within a factor of
1.5 of the field values. The same model was successfully used by Jeen et al.
(2007) for the evolution of iron reactivity and dynamic changes in geochemi-
cal conditions and remediation. Predictions under various hydrogeochemi-
cal conditions showed that trichloroethene (TCE) could be treated effectively
for an extended period without significant loss of permeability. The model-
ing aimed to incorporate the effects of mineral precipitation on ZVI into a
reactive transport model, in order to improve the prediction of long-term
performance of ZVI PRBs. MIN3P was modified and tested against observed
data from long-term column experiments designed to assess the extent of
secondary mineral formation and its effect on the performance of the iron.
The longevity of an iron PRB under various hydrogeochemical conditions
was also estimated using the modified MIN3P.
Abiotic reductive dechlorination using ZVI is considered one of the most
important remediation techniques for remediating chlorinated hydrocar-
bon compounds (Gilliam and O'Hannesin, 1992, 1994). This technique has
been demonstrated at various contaminated sites across the world using PRB
technology.
Search WWH ::
Custom Search