Adventus Group

Pesticide Terminator

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Courtesy of Adventus Group

Impacted Soil Bioremediation - Environmental Protection magazine (May 2007)

As urban centers grow in size, substantial areas of agricultural and industrial land are being converted to residential use. One of the issues frequently encountered when such a change in land use is implemented is the presence of elevated concentrations of chlorinated pesticides and herbicides historically used in agricultural crop production.

Understanding the Problem
Where possible, pesticide-contaminated soil is often excavated and transported to an off-site landfill for disposal (“dig and dump”). Given the large amount of soil generally involved (commonly between 1,000 and 2,000 tons per acre), however, the cost of removing it is substantial, and in some cases, prohibitive. For example, the total cost for excavation, transportation, disposal, and backfilling is generally between $125 and $250 per ton of soil. This equates to a cost of $125,000 to $500,000 per acre. Even if such a cost were borne by the developer, other problems with the dig and dump approach must be considered.

For example, assuming a 25-acre housing development, a total of over 3,000 truckloads of soil would likely need to behauled out — often through residential areas. Furthermore, an additional 3,000 loads of clean soil would need to be hauled back into the site for backfill. This amount of truck traffic can do a lot to irritate residents of neighboring communities. Finally, the potential for industrial and other types of accidents must be considered a significant downside to this approach.

When stepping back from the financial and technical aspects of such a task, one may also question whether the digand-dump approach is responsible in this world of limited resources, increased focus on sustainable development, and concern about greenhouse gas emissions. After all, once the contaminated soil has been dug, hauled, and dumped, it is still contaminated and the potential risk it poses to the environment and human health has just been relocated, not eliminated.

One main reason that lower-cost treatment approaches, such as in situ soil bioremediation, have not been more commonly applied to these settings relates to the general recalcitrance of most chlorinated pesticides and herbicides. These types of contaminants can be very challenging to remediate. Common examples include DDT, toxaphene, dieldrin, lindane, and 2,4,5-T. These agricultural chemicals were quite effective as insecticides and herbicides, however, they are persistent under typical surficial environmental conditions. The half-lives for most chlorinated pesticides in agricultural soils are in the range of many months to many years1. Hence, natural processes can require several generations to reduce the pesticide’s concentration to levels acceptable for residential land use. Use of simple soil remediation methods, such as nutrient supplementation, composting, or microbial inoculation, have not been widely effective in removing these residuals from soil. In fact, many in the site remediation industry remain under the impression that soil contaminated with chlorinated pesticides can only be physically removed (e.g. dig and dump) or effectively treated using very expensive thermal technologies. As a result, some form of effective in situ active remediation is needed to allow sites to be developed in a timely manner.

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