Environmental Engineering Reference
In-Depth Information
As seen before, the physical properties that control the mechanisms of soil
pollution by hydrocarbons include density and solubility. These data are presented
in Table 14.1 together with Henry's constants (the constant governing the gas
solubility in water) and the biodegradability (in relation to biological
decontamination techniques). These parameters allow a better estimation of the
impact of accidental hydrocarbon pollution in the vadose zone and water table.
Table 14.2 [BRG 05] gives a more detailed synthetic presentation of certain
properties of various hydrocarbon pollutants.
When hydrocarbon pollution may potentially have a negative impact, the nature
and extent of the contamination has to be identified so as to proceed to site
remediation. The former is considered in Chapter 12 and the latter in Chapter 15.
14.3. Numerical modeling
Two different scenarios may be considered when numerically modeling soil
pollution by hydrocarbons: either the hydrocarbons behave as expected as fluid
phases or they are transported by water or air in the pores of the soil.
In the first case the model used is that for the simulation of a hydrocarbon
reservoir. This will be dealt with first because it allows us to introduce several
useful aspects for the remainder of this chapter. A typical case is that of pollution
due to oil leakage from a buried pipeline. In this case the fluids involved are oil,
water and sometimes gas or air. Another example is soil pollution by halogenated
hydrocarbons, which are heavier than water and displace it in the soil.
The second case mentioned above is the transport of polluting hydrocarbon
components by an aquifer. These hydrocarbons may also come back to the soil
surface and be dispersed in the ambient air because of diffusion in the vadose zone.
In this case diffusion-advection equations are used on top of the usual continuity
equations of the fluids transporting the pollutants.
Three fluid phases are generally considered in the numerical modeling of
hydrocarbon reservoirs: oil, water and gas. In this case distinction is rarely made
between the different liquid components of oil mentioned above because their
proportions change from one reservoir to another. Another important aspect is the
deformability of the reservoir formation: in petroleum engineering the formation is
often considered to be rigid, but for the purpose of compaction and subsidence
analysis the inclusion of rock deformation is compulsory.
