Brownfield Remediation: Solutions for Urban Agriculture

Introduction

Urban agriculture is becoming more important in today's cities. It has great potential to improve the quality of life in urban areas by increasing food security, providing opportunities for community development, and improving the aesthetics of the urban landscape. Community organizations practicing urban agriculture face many obstacles, such as land availability, restricted budgets and soil contamination. Soil contamination is a major barrier to urban agriculture initiatives, because contaminants are present in most urban soils at levels higher than are accepted for agricultural use. These contaminants can be taken up by plants grown in these soils, and can be harmful to human health if the produce is consumed. The barrier of land availability could be partially overcome if brownfields could be used as sites for urban agriculture. Brownfields are unused plots of urban land that are contaminated from previous land uses. If these brownfields could be remediated by community groups, they would further the development of urban agriculture projects. Remediation involves the removal of contaminants, in this case such that the soil meets conditions for urban agriculture.

This project is concerned with the viability of brownfield remediation for urban agriculture. It explores the applicability of various remediation techniques to community groups practicing urban agriculture. It describes agricultural soil standards, resources available for determining the land use history of a plot of land and for soil testing (to determine the level of contamination in the soil), several physical and biological remediation techniques, and the pros and cons of these soil remediation techniques from the perspective of community groups.

This research was accomplished by consulting available literature, government sources, internet resources, and through interviews with academics, city officials, representatives of remediation companies, and members of community groups, who provided us with case studies of remediation for urban agriculture. Our research was limited by the relative youth of the field of soil remediation. In particular, biological remediation techniques are only recently coming into use, and some are still in the developmental stages. As for the evaluation and recommendations of the most appropriate techniques, only very general conclusions can be reached. The specifics of an urban agriculture project will ultimately determine which technique(s) should be used. Variation in contamination, soil type and characteristics, time and funds allotted for remediation will all influence which technique a group should pursue. The following eight remediation techniques were chosen for analysis:

Physical remediation techniques

Excavation refers to physically removing contaminated soil, normally for disposal at a landfill. Excavation is generally accomplished with heavy machinery. New soil is needed after the excavation.

Geotextiles are a synthetic blanket-like material. They can be used after the excavation process to provide a protective barrier, impermeable to contaminants which may otherwise migrate into the new soil after excavation. One concern with geotextiles is that the fabric can tear, allowing contaminants to pass through into the new soil.

Soil washing is a technique which involves the physical removal of the contaminated soil, followed by treatment at a plant on or off-site. After the contamination is removed through the treatment process, the soil is put back into the ground.

Soil vapour extraction involves the installation of wells and pipes in the soil, through which soil contaminants are extracted in vapour form.

Biological remediation techniques

Microbial remediation refers to the use of microbes in degrading contaminants into a less toxic form. This technique can be very effective in the treatment of hydrocarbons, PAH's, pesticides, and PCB's.

Phytoremediation is the process of using plants to degrade organic contaminants or to extract toxic metals from the soil and transport them into the above-ground shoots. In the case of extraction, the contaminated plants must later be disposed of.

Fungal remediation refers to the use of certain species of fungus to degrade contaminants, particularly hydrocarbons.

Compost remediation involves the addition of compost to the soil. It is not a true remediation technique, as the contaminants generally remain intact in the soil. The addition of compost can, however, be used to create a raised bed, in which the plant roots may not reach the contaminated soil.