HR: 0800h
AN: B31A-0954    [Abstracts]
TI: Soil Remediation of an Arsenic-Contaminated Site With Ferrous Sulfate and Type V Portland Cement
AU: * Illera, V
EM: vramon@ucmerced.edu
AF: University of California, Merced School of Natural Sciences, P.O. Box 2039, Merced, CA 95344 United States
AU: O'Day, P A
EM: poday@ucmerced.edu
AF: University of California, Merced School of Natural Sciences, P.O. Box 2039, Merced, CA 95344 United States
AU: Rivera, N
EM: nrivera@ucmerced.edu
AF: University of California, Merced School of Natural Sciences, P.O. Box 2039, Merced, CA 95344 United States
AU: Root, R
EM: rroot@ucmerced.edu
AF: University of California, Merced School of Natural Sciences, P.O. Box 2039, Merced, CA 95344 United States
AU: Rafferty, M T
EM: mrafferty@sspa.com
AF: S.S. Papadopulus and Associates, Inc, 116 New Montgomery Street, Suite 900, San Francisco, CA 94105-3629 United States
AU: Vlassopoulos, D
EM: dimitri@sspa.com
AF: S.S. Papadopulus and Associates, Inc, 815 SW Second Ave., Suite 510, Portland, OR 97204-3026 United States
AB: High levels of arsenic are present in a site adjacent to San Francisco Bay (in East Palo Alto, CA) as a consequence of the activity of a former pesticide manufacturing plant. Most of the readily accessible arsenic at the site has been removed by remedial excavation and surface capping. In-situ fixation of residual arsenic was performed close to the source about 10 years ago where arsenic values in capped soils ranged from 500 to 5000 mg kg^-1. The fixation method consisted of the addition of ferrous sulfate (3% w/w), type V Portland cement (10% w/w) and water. Both products were mixed with the contaminated soil to a treatment depth between 1.5 and 9 meters. The treated soil was then capped to prevent weathering. This long-term amended soil offers an opportunity to compare the processes that prevent microbial arsenic reduction and control the immobilization of arsenic in the treated soils versus natural soils, and to study the aging effects of arsenic sorption. Solid phase characterization of soil samples from both the field and controlled laboratory experiments were carried out to study the speciation and bioavailability of arsenic and to ascertain the mechanisms of the arsenic immobilization in the treated soil. These methods included physical description by field observations, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy, total elemental concentrations, and solid phase fractionation by sequential extraction. Both synchrotron X-ray absorption spectroscopy (XAS) and XRD measurements were used to determine oxidation state of arsenic and iron and host phases present in the soil. The remedial treatment was successful in immobilizing the arsenic in the contaminated soil, and decreasing its leachability. Measurements taken at short aging times (during the first month) showed that the treatment was effective in reducing leachable arsenic as evidenced by the TCLP wet test (< 5 mg l^-1 leached). The field amendment influenced arsenic speciation. The treated soil in both field samples and short-term laboratory experiments contained only As(V), suggesting that the microbial reduction of arsenic is prevented in the amended soils. Natural soils from cores adjacent to the amended soils contained both As(III) and As(V), and sulfides associated with the arsenic. The addition of Portland cement to soils caused alkaline conditions and pH buffering, changing the pH from 7 before the treatment to 12 afterwards. Calcium and iron sulfates are typical precipitates of iron sulfate and cement applications. Our characterizations suggest that arsenate was incorporated into new phases, either as solid solutions with sulfate or as localized arsenate phases. Arsenic incorporated into these less soluble phases is resistant to desorption and leaching, particularly under changing subsurface conditions.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0461 Metals
SC: Biogeosciences [B]
MN: Fall Meeting 2005