Geoscience Reference
In-Depth Information
Liquid Mixture Transformation Changes in the composition and concentra-
tion of volatile fractions of a volatile organic liquid mixture (VOLM) contami-
nating a subsurface water occur when the (immiscible with water) liquid is
volatilized into the gaseous phase of the porous medium and subsequently trans-
ported into the atmosphere. Fine and Yaron (
1993
) showed that the volatilization
of each hydrocarbon from kerosene (containing more than 100 hydrocarbons),
added to a subsurface, occurred at different rates. The mass transfer of spilled
VOLM from natural water bodies into the subsurface and near surface atmosphere
and the effect of this process on their distribution between the gaseous, liquid and
solid phases have been the subject of a series of studies (e.g., Mackay and Yeun
1983
; Burris and Macintyre
1986
; Nye et al.
1994
; Yaron et al.
1998
; Dror
2005
).
The rate of volatilization is controlled by the vapor pressure of the components and
environmental conditions. The less-volatile components of a VOLM are trans-
ported as liquid into the porous medium. During their transport, differential dis-
solution of the component mixture into the subsurface water or adsorption on the
subsurface solid phase occurs simultaneously with the transport of the volatile
fraction in the gaseous phase. Adsorption leads to retardation of volatilization but
not to cessation of the process. A change in the VOLM composition occurs as
result of this process.
Adapting the approach of Nye et al. (
1994
) to subsurface conditions, the fol-
lowing stages in contaminant transformations of VOLMs can be identified:
1. A volatilization-induced VOLM depletion stage of the components, charac-
terized by a high vapor pressure.
2. A VOLM depletion stage caused by dissolution in the liquid and adsorption on
solid phases of the components, characterized by aqueous solubility.
3. A VOLM enrichment stage caused by desorption of the previously adsorbed
fraction on the solid phase.
4. A liquid depletion stage of the gas molecules sorbed on solids or dissolved in
water phases.
In stages 2 and 3, the components accumulate or deplete according to their
aqueous solubility, volatility, diffusivity, and cosolvent presence. The transfor-
mation rate of VOLMs occurs accordingly. In this system, two distinct liquid
phases can be recognized: the first is a VOLM, insoluble in water and having
chemical properties different from the original VOLM; the second is a mixed
aqueous solution of partially miscible organic compounds dissolved in water from
the original VOLM.
The chemodynamic properties of a multiphase liquid are transformed with
respect to the initial state of their components. In the case of VOLMs, both
chemical and physical properties of the initial liquid are changed. A second type of
liquid transformation is that of water with a given quality, when it mixes with
water of different chemical composition. For example, consider the case of a
mixture of two aqueous solutions having a similar total salt content and different
electrolyte composition, with one having a high Na content and low Ca concen-
tration
(SAR = 2.5)
and
the
other
having
a
low
Na
and
high
Ca
content
