Bioremediation of Petroleum Hydrocarbons in Cold
RegionsPublisher: Cambridge University Press
Print Publication Year: 2008
Online Publication Date:August 2009
Online ISBN:9780511535956
Hardback ISBN:9780521869706
Paperback ISBN:9781107410503Chapter DOI:
http://dx.doi.org/10.1017/CBO9780511535956.003
1 - Contamination, regulation, and remediation: an introduction
to bioremediation of petroleum hydrocarbons in cold regions pp.
1-37Oil and fuel spills are among the most extensive and
environmentally damaging pollution problems in cold regions and are
recognized as potential threats to human and ecosystem health. It
is generally thought that spills are more damaging in cold regions,
and that ecosystem recovery is slower than in warmer climates (AMAP
1998; Det Norske Veritas 2003). Slow natural attenuation rates mean
that petroleum concentrations remain high for many years, and site
managers are therefore often forced to select among a range of more
active remediation options, each of which involves a trade-off
between cost and treatment time (Figure 11). The acceptable
treatment timeline is usually dictated by financial circumstance,
perceived risks, regulatory pressure, or transfer of land
ownership.
In situations where remediation and site closure are not urgent,
natural attenuation is often considered an option. However, for
many cold region sites, contaminants rapidly migrate off-site (Gore
et al. 1999; Snape et al. 2006a). In seasonally frozen ground,
especially in wetlands, a pulse of contamination is often released
with each summer thaw (AMAP 1998; Snape et al. 2002). In these
circumstances natural attenuation is likely not a satisfactory
option. Simply excavating contaminants and removing them for
off-site treatment may not be viable either, because the costs are
often prohibitive and the environmental consequences of bulk
extraction can equal or exceed the damage caused by the initial
spill (Filler et al. 2006; Riser-Roberts 1998).2 - Freezing and
frozen soils pp. 38-54Introduction
Frozen soil is defined as a soil where the soil moisture has
turned totally or partially into ice. On the other hand, permafrost
is defined solely on the basis of soil temperature. If the soil
temperature remains below 0 C for at least two years, the soil is
considered permafrost. The upper layer of the permafrost undergoes
a cyclic temperature change during the year from frozen in the
winter to thawed in the summer. This layer is called the active
layer or seasonally thawed layer. The active layer in a permafrost
region can extend from as little as 20 cm to about 2 m (Shur et al.
2005) depending on climate, soil texture, and organic content above
mineral soil. In areas without permafrost the layer of soil which
is frozen in the winter is called the seasonally frozen layer. Most
permafrost on earth is thousands of years old, but some can be
quite new. In permafrost regions, contaminant impacts generally
initiate at or near the soil surface and affect the active layer,
suprapermafrost water, and uppermost permafrost (Chapter 3). It is
this realm that most concerns environmental scientists and
engineers tasked with environmental cleanup. A thorough
understanding of properties of the active layer and the upper
permafrost is necessary for planning and implementing effective
remediation of cold media.
Review and recent advances
Thermal and physical properties of frozen ground
Thermal conductivity of soils
The thermal conductivity of soil is the measure of its ability
to conduct heat. Soil thermal conductivity is a function of the
thermal state of the ground (frozen or unfrozen), water content,
dry density, gradation, and mineralogy.3 - Movement of petroleum
through freezing and frozen soils pp. 55-68Introduction
Movement of petroleum through non-freezing soils has been
studied extensively over the last several decades. Little work has
been done on understanding how petroleum moves through seasonal
freezing soils (active layer) and frozen soil (permafrost).
Petroleum migration through active layer and permafrost soils is
influenced by the formation and presence of ice at all scales. At
the millimeter scale, ice in pore spaces will either interrupt
downward migration causing petroleum to spread laterally, or impede
petroleum movement altogether due to the lack of open pore space.
Segregated ice at centimeter-to-meter scales will most likely cause
the contamination to spread laterally in frozen soils. Segregated
ice formation in the active layer can also generate fissures that
will enhance petroleum movement when the soil is thawed. At larger
scales, discontinuous and continuous permafrost will slow,
redirect, or impede contaminant migration.
Understanding the impact freezing and frozen soil conditions
have on petroleum movement through soils is necessary to
regulation, assessment, and cleanup of contaminated soil and
groundwater. A good example of this impact is provided when
considering natural attenuation. Seasonal ice and post-cryogenic
structure present in active layer soil will influence the movement
of petroleum and dissolved compounds, thereby impacting the design
of monitoring systems to track natural attenuation. Moreover, cold
soil temperatures will slow the physical weathering of compounds in
the subsurface. Cleanup levels established for cold regions
contaminated soil (Chapter 1) and any remediation plan developed
for these sites must account for these impacts.