Environmental Engineering Reference
In-Depth Information
in Chapters 2 and 3. The implementation stages of PRB technology include
the initial feasibility assessment, laboratory treatability studies (including
column studies), estimation of PRB design parameters, and development of a
long-term monitoring network for the performance evaluation of the barrier.
This chapter provides a general overview of mathematical models used for
implementing the PRB technologies.
4.2 Design of PRBs
The most important parameter in designing the PRB is the thickness of bar-
rier, which is a function of both hydrogeological and contaminant param-
eters. The contaminant concentration entering the barrier and its spatial
distribution is the key for the design purposes. Since the contaminant trans-
port depends on various hydrogeological and chemical properties it is criti-
cal to estimate the hydraulic conductivity (K), dispersion coefficient (D) of
the subsurface environment and the first-order decay coefficient of the con-
taminant. Estimates of various parameters for designing the PRB are pro-
vided in the following sections.
A simple mathematical model (Rabideau et al., 2005) governing the trans-
port process through the reactive barrier is represented by a one-dimensional
advective-dispersive-reactive equation (ADRE). The governing equation for
the single decay ADRE assuming a homogenous subsurface medium is as
follows:
2
=−
c
t
c
x
c
v
+
D
k
ʹ
2
x
where
c = aqueous phase contaminant concentration (M/L3)
t = time (T)
x = distance from the entrance of the PRB (L)
v = interstitial fluid velocity (L/T)
D = dispersion coefficient (L2/T)
k = first-order decay constant (l/T)
Application of the above equation to a PRB setting is commonly accom-
plished by neglecting the dispersion term and treating the PRB as an ideal
plug flow reactor, which leads to the following simple design equation (e.g.,
Gavaskar et al., 1998; USEPA, 1998):
cx
(
=
L
)
L
v
=
exp
k
ʹ
c
0
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