Handbook of Solvents - George Wypych - ChemTech - Ventech!

1606 Hanadi S. Rifai, Charles J. Newell, Todd H. Wiedemeier
R dC
TCE
dt
R dC
DCE
dt
R dC
VC
dt
R dC
ETH
dt
v dC
D
dx
dC
D
dx
dC
D
dy
d
2
2
2
TCE
TCE C
= − + x + y +
2
2 z
dz
TCE TCE
v dC
D
dx
dC
D
dx
dC
D
dy
d
2
2
2
DCE
DCE C
= − + x + y +
2
2 z
dz
DCE DCE
v dC
D
dx
dC
D
dx
dC
D
dy
dC
2
2
2
VC
VC
= − + x + y +
2
2 z
dz
VC VC
v dC
D
dx
dC
D
dx
dC
D
dy
d
2
2
2
ETH
ETH C
= − + x + y +
2
2 z
dz
ETH ETH
+ kC − k C [23.1.22]
TCE
2 1 PCE 2 TCE
+ kC − kC [23.1.23]
DCE
2 2 TCE 3 DCE
VC
+ kC 2 3 DCE −kC
4 VC [23.1.24]
ETH
2
+ kC [23.1.25]
where:
RPCE, RTCE, RDCE, RVC, RETH retardation factors
V seepage velocity
Dx,Dy,Dz dispersivities in the x, y, and z directions.
BIOCHLOR uses a novel analytical solution to solve these coupled transport and reaction
equations in an Excel spreadsheet. To uncouple these equations, BIOCHLOR employs
transformation equations developed by Sun and Clement. 110 The uncoupled equations were
solved using the Domenico model, and inverse transformations were used to generate concentration
profiles. Details of the transformation are presented elsewhere. 110 Typically,
source zone concentrations of cis-1,2-dichloroethythene (DCE) are high because
biodegradation of PCE and TCE has been occurring since the solvent release.
BIOCHLOR also simulates different first-order decay rates in two different zones at a
chlorinated solvent site. For example, BIOCHLOR is able to simulate a site with high
dechlorination rates in a high-carbon area near the source that becomes a zone with low
dechlorination rates downgradient when fermentation substrates have been depleted.
In addition to the model, a database of chlorinated solvent sites is currently being analyzed
to develop empirical rules for predicting first-order coefficients that can be used in
BIOCHLOR. For example, at sites with evidence of considerable halorespiration, the use of
higher first order decay coefficients will be recommended. Indicators of high rates of
halorespiration may include: i) high concentrations of fermentation substrates such as
BTEX at the site, ii) high methane concentrations, which indicate high rates of fermentation,
and iii) large ratios of progeny products to parent compounds, and iv) high concentrations
of source zone chloride compared to background chloride concentrations.
The BIOCHLOR model was used to reproduce the movement of the Cape Canaveral
plume from 1965 to 1998. The Cape Canaveral site (Figure 23.1.9) is located in Florida and
exhibits a TCE plume which is approximately 1,200 ft long and 450 ft wide. TCE concentrations
as high as 15.8 mg/L have been measured recently at the site. The site characteristics
used in the BIOCHLOR model are listed in Table 23.1.12. The hydraulic conductivity
assumed in the model was 1.8x10 -2 cm/sec and the hydraulic gradient was 0.0012. A porosity
of 0.2 was assumed as well as the Xu and Eckstein model for longitudinal dispersivity. 8
The lateral dispersivity was assumed to be 10% of the longitudinal dispersivity and vertical
dispersion was neglected.
4
ETH