EPA is responding to soils contaminated with the pesticide toxaphene, resulting from the disposal activities of a pesticide aerial applicator who ceased operations over 20 years ago. The Site is on lands of the Gila River Indian Community (GRIC). Extensive planning with the Tribe over the past year has resulted in this removal action. Toxaphene concentrations over portions of this 17 acre site pose human health and environmental threats.
Bench-scale and pilot-scale studies over the past yearr have confirmed the effectiveness of anaerobic bioremediation in treating his contamination to levels below concern.
Contaminated soil containing greater than 17 milligrams/kilogram (mg/kg) was excavated based on 6 inch, below ground surface (bgs), interval sampling results from EPA’s removal assessment (October 2002). Elevated concentrations of toxaphene were excavated as deep as 4 feet bgs in some areas. A statistical approach (concentration isopleth or “contour” map) was used to expand the contaminated soil excavation beyond the sampling points used in the removal assessment.
Personnel and equipment have completed excavation and stockpiling of contaminated soil. EPA’s Emergency Response and Removal Support (ERRS) contractor has begun backfilling the excavated areas of the Site with fill from clean portions of the Site. An estimated 7,500 cubic yards of soil was excavated and stockpiled. ERRS achieved sufficient dust suppression using water trucks to spray the construction operations area.
The Superfund Technical Assessment and Response Team (START) identified excavation cut lines, collected global positioning system (GPS), documented field activities, and conducted dust monitoring.
A small portion of the Site, owned by the Salt River Project, has been excavated and backfilled.
ERRS completed excavation of two treatment cells. One cell was lined with a 20 millimeter (thick) plastic liner and was prepared for loading.
A pug mill and soil screen were delivered to the Site as well as ½ of the necessary treatment amendments (i.e., blood meal, mono- and di-sodium phosphate, and starch).
EPA and the GRIC Department of Environmental Quality presented information regarding the removal action to the GRIC Tribal Council in their meeting on April 21, 2004.
ERRS will continue treatment cell construction, building as many as 9 cells or "burritos." Contaminated soil will be screened and mixed with amendments in the on-Site pug mill. The soil and amendments will be heavily watered and loaded into the cells. The burritos will be covered with the liner and vents will be installed for off-gasing and sampling.
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