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.