In Situ Chemical Reduction for Remediation of Soil Containing Chlorinated Pesticides and Herbicides
Problematic: Soil sterilant are non-selective residual herbicides that render the treated soil unfit for plant growth for relatively long periods of time. Sterilant, were commonly used in Alberta from the 1960s to late 1990s for non-selective vegetation control on oil and gas wells, gas processing plants, rights-of-way, railways, saw mills, pulp mills, and electrical utility sites ([1], [2], [7]); residues may also be found at agrochemical dealer sites ([8]). Sterilant treated areas can remain devoid of vegetation for many years, depending upon the type, rate and frequency of application of soil sterilant and the climatic conditions. Soils treated with sterilant can be a source of contamination through leaching, surface runoff and wind dispersion of the sterilant to adjacent land and waterbodies. Reclamation and remediation issues arise when a treated site is no longer needed for industrial use and the site must be returned to equivalent land capability. At present, many of these sites either remain as liabilities for industry, or impacted soil is excavated and disposed at a landfill.
In Alberta, awareness of the issues associated with soil sterilant is on the rise as more legacy oil and gas sites (constructed prior to 1970; operational prior to 1990), where sterilant were typically used, are abandoned and slated for remediation and reclamation. Cotton and Sharma ([1]) estimated the number of oil and gas sites in Alberta with soil sterilant residues to be as many as 61,750 sites. Historical work has focused on upstream oil and gas sites, however there are many others in the province. It’s estimated that there are well over 3,000 additional sites associated with distribution sites, pipelines and electric metering stations and many other industrial facilities not yet identified. While a considerable amount of literature review, experimentation and operational activities have occurred over the past 20 years on this topic in Alberta, as of 2018, many of these sites are still in the queue for reclamation and remediation due to the recalcitrant nature of the contaminants that have impacted soil and groundwater and remain as liabilities for their owners..
Overview. Peroxychem manufactures a family of in situ chemical reduction (ISCR) products (i.e., soil amendments) for treatment of soil, sediment and other solid wastes contaminated with halogenated organic compounds. When the contaminants of interest are organochlorine pesticides (OCPs) or herbicides, the keys to this remedial approach are the composition of the soil amendment and application of repeated and sequential anoxic then oxic conditions to the contaminated matrix. The patented products are composed of plant fiber-based organic material and micro-scale elemental iron (US Patent No. 6,083,394) and may be supplemented with sulfate in the form of alkaline earth salts.
Approach. Treatment proceeds via reductive dechlorination of the pesticides/herbicides followed by aerobic biodegradation of the partially or fully dechlorinated breakdown products.
The soil amendment is typically applied at dosages of between 0.4% and 4% w/w) and therefore causes very little, if any, increase in soil volume following treatment. Over the last 15 years, the technology has been used successfully for in situ and ex-situ treatment of soils contaminated with a range of OCPs, including Chlordane, Lindande, DDT, Toxaphene, 2,4-D, 2,4,5-T, Atrazine, Dieldrin and Metolachlor at sites in North America and Europe.
Results. This presentation will include an overview of chemistry involved in OCP degradation using the ISCR products, along with case studies from several completed applications in the United States, Canada, and Europe, and cost analysis.