Geoscience Reference
In-Depth Information
Fig. 12.48 Kerosene
retention capacity (KRC) as
affected by soil type and soil
moisture conditions,
expressed as volume of
kerosene per bulk volume of
air-dry soil. Reprinted from
Jarsjo et al. (
1994
). Copyright
1994 with permission of
Elsevier
KRC ¼ 0
:
13
ð
%clay
Þþ
1
:
46
ð
%OM
Þ
0
:
32
ð
%moisture
Þþ
4
:
31
;
ð
12
:
3
Þ
where OM denotes organic matter. The KRC is negatively correlated with the soil
moisture content and positively correlated with clay and organic matter contents.
An illustration of the effects of moisture content and soil type on kerosene
retention capacity is shown in Fig.
12.48
. As soil moisture increases from oven-
dried to 50 % field capacity, the KRC retention capacity decreases markedly in all
soils studied. It may be assumed that water retained in small soil pores reduces the
effective soil pore volume, thus decreasing capacity of the soil to entrap NAPLs.
At relative humidities of about 50 % field capacity (most relevant to a soil envi-
ronment in a temperate climate), a monolayer (or more) of water evidently is
presented n external surfaces of macro- and mesopores, while the micropores and
some mesopores are filled with water. These results imply that, for characteristi-
cally high soil water contents in humid zones, differences between soils on NAPL
transport are reduced. In arid and semiarid areas, these differences are significantly
greater because the small water content in some soils allows access of NAPL to a
larger pore volume.
12.5.2 Transport of Soluble NAPL Fractions in Aquifers
As discussed previously, NAPLs are transported through the partially saturated
zone to the groundwater (Feenstra et al.
1991
). Natural groundwater flow through a
NAPL source zone forms plumes of aqueous-phase contamination that can extend
over aquifer volumes much larger than the initial source zone. Simultaneously, the
