Soil Restoration Following Oil Spills - A Review
Authors: McGill W.B. 
Published: March 2010

An average of 1–2 oil spills occur in Alberta per day. Most of these are on land. Although many studies have been conducted into the effects of oil on plants and water only a limited number have dealt with soil. This paper summarizes our information on soil restoration following oil spills.

The development of our understanding of oil spill effects on soil is reviewed together with the early literature examining site restoration. Recent restoration research is dealt with in detail and the advantages of various techniques are discussed. Non-biological mechanisms of oil removal from soil, such as volatilization, burning and photodecomposition, are examined first, followed by biological restoration procedures.

The effectiveness of various techniques depends on the type of oil, amount of oil and soil environment. Up to 40% of the residual oil left at a site after initial cleanup can be removed through non-biological mechanisms, primarily volatilization. Biological restoration is required to deal with much of the remainder. Biological restoration generally requires nutrient additions, aeration, maintenance of a neutral pH, tillage or mixing to break surface crusts and some form of drainage in very wet spots. Proper implementation of these techniques can increase the rate of restoration by several fold and sometimes an order of magnitude.

Introduction

ABOUT 400 million barrels of oil are produced in Alberta annually. Inevitably some of this is spilled. Oil spill sites often can be restored without intervention by man, but in some cases, where nothing is done or the wrong restoration procedures used, sites remain barren for twenty years or more. Although many studies have been conducted on the effect of oil on plants and aquatic systems, fewer have addressed the problem of spills on land, and the problem of soil restoration following an oil spill has been largely ignored in the published literature.

The fact that oil does not permanently sterilize soil has been established for some time(1.2.3.4). These early studies dealt with the effect of oil on plant growth, nitrates and numbers of microbes in soil. The first report suggesting reclamation techniques was that of Plice(4). Carr(1), Baldwin(2) and Murphy(3) generally agreed that small quantities of oil in soil had no effect on plants, that direct toxicity was not a major problem and that oil depressed nitrate levels and increased numbers of microbes. The quantities of oiladded in the experiments reported were generally low and only rarely were attempts made to saturate the soil. Plice(4) used high oil rates in some of his work, but did not try to restore the sites by any means other than? cultivation. He concluded that early cultivation was undesirable in Texas because it caused soil drifting problems. However, he also reported that cultivated treatments supported some vegetation at least three years earlier than the uncultivated treatments. At the time his paper was published, the uncultivated portions of the very heavily oiled plots (initial rates of oil addition were not given) had been barren 'for 5 years.