Introduction

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.

Introduction

In this book, current scientific knowledge and practical experiences with bioremediation of petroleum-contaminated soils in cold regions are reviewed and compiled. We now more fully understand the inter-relationships between cold temperatures, soil and water properties, and biological processes. This aids decision making about practical remediation treatment for petroleum-contaminated sites in cold regions. Landfarming and enhanced bioremediation schemes have emerged as viable soil treatment methods that offer a number of advantages over other methods. Nevertheless, work still needs to be done to optimize these methods, and with regards to evaluating phytoremediation and rhizosphere enhancement potentials for cold soils.

Two emerging technologies have been identified that could offer significant cost savings; low-cost heating and controlled-release nutrient systems are described briefly here (see also Chapter 8). In addition, natural attenuation has received little rigorous evaluation for use in cold soils. The main limitation for natural attenuation in cold regions is the low rate of degradation, coupled with off-site migration that can be relatively rapid in soils or gravel pads that have a poor adsorption capacity. Permeable reactive barriers are one groundwater treatment technology that could buy time for slower in situ techniques such as natural attenuation to take place. An outline of emerging permeable-reactive barrier technology is presented here, although full-scale trials are not yet complete. It is possible that such in situ techniques, when coupled with aeration, sparging and biostimulation could offer methods for groundwater treatment in cold regions.