Grantee Research Project Results
2004 Progress Report: Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
EPA Grant Number: R828771C013Subproject: this is subproject number 013 , established and managed by the Center Director under grant R828771
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Center for the Study of Childhood Asthma in the Urban Environment
Center Director: Hansel, Nadia
Title: Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
Investigators: MacKay, Allison , Smets, Barth F. , Fairbrother, D. Howard
Institution: University of Connecticut , The Johns Hopkins University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2007
Project Period Covered by this Report: October 1, 2003 through September 30, 2004
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
Many industrial and urban sites with subsurface contamination are characterized by shallow aquifers that discharge to nearby surface water bodies. There is little understanding of the ecological risk posed by groundwater contaminant discharges to surface water ecosystems. A limited number of studies suggest that chemical and biological processes in the groundwater-surface water interface (GSI) may play an important role in attenuating groundwater contaminant discharges to surface water bodies. Preliminary observations at the Auburn Road landfill Superfund site suggest groundwater arsenic transport to the Cohas Brook is controlled by the formation of iron oxides in the sediments. In particular, iron oxidizing bacteria are present in the sediments and may play a central role in generation of iron oxyhydroxide solids because abiotic iron oxidation is extremely slow given the pore water chemistry in the GSI.
The goal of this research project is to identify the seasonal cycle of arsenic sequestration and release between sediments and pore waters in the groundwater-surface water interface. The specific objectives are to: (1) quantify the seasonal distributions of arsenic, iron and sulfur species and other key electron-donating and -accepting species relative to the GSI; (2) determine the significance of microbial and chemical iron oxidation in the GSI, including temporal and spatial trends, and (3) characterize the composition and crystallinity of iron solids, including arsenic associations and speciation in oxyhydroxide precipitates newly formed in the field or under chemically or microbially enhanced laboratory conditions.
Progress Summary:
Field Observations of Pore Water Constituents and Solid Phases at the Same Location
Spatial heterogeneity of arsenic and iron concentrations in near-shore Cohas Brook sediments were characterized using three freeze cores obtained during June 2003 sampling trip. The cores were sub-sectioned with 0.8 cm resolution and extracted sequentially to identify various ‘pools’ of arsenic and iron. Two of the three cores showed sharp decreases in arsenic and iron concentrations with depth, whereas the third core (CB-4) had approximately constant arsenic and iron concentrations with depth. Arsenic concentrations at 0.8 cm below ground surface ranged from 500 to 4,000 mg/kg, indicating that seasonal changes may be difficult to discern within this range of spatial variation. Each core that was observed, including cores collected in November 2002 and July 2004, showed a consistent arsenic-to-iron ratio of 1:100 with iron accounting for 20 to 30 percent by weight of the sediments. Also consistent across all cores was the presence of most arsenic in the ‘strongly sorbed’ pool and most iron in the ‘amorphous’ pool.
Pore water concentrations were measured with thin-film diffusion samplers. Upon retrieval, the films were orange in color, indicating the presence of iron oxides. The films were covered with a protective membrane with 0.45 μm pores. It is unknown whether oxides were formed in the films after diffusion of reduced iron and oxygen, or whether existing colloidal particles diffused across the membrane. The arsenic-to-iron ratio of 0.04 in the films was elevated over the solid phase ratios, but this difference was not statistically significant.
Enumeration and Phylogenetic Diversity of Iron-Oxidizing Bacteria
High (0.8-cm) resolution microbial enumerations of iron-oxidizing bacteria were obtained from core CB-4 collected in June 2003. From 0 to 12 cm below ground surface, iron-oxidizing bacteria varied between 6 x 105 and 7 x 106 cells/g dry weight where approximately constant iron and arsenic concentrations were observed in the same core. The abundance of iron-oxidizing bacteria dropped by almost 2 orders of magnitude at 15 cm below ground surface where the iron concentration was only 10 percent of the value observed at shallower depths. Iron-oxidizing bacteria accounted for 0.01 to 1 percent of the total bacterial populations in these sediments.
Enrichments of iron oxidizing bacteria were grown in gradient tubes and cloned to develop the 16s rRNA phylogenetic tree. Sixteen distinct rRNA sequences were obtained and distributed among three groups: β-proteobacteria (2/16), γ-proteobacteria (12/16), and gram positive bacteria (2/16). Most (72%) of the γ-proteobacteria was closely related to Pseudomonas putida that is able to grow under microaerophilic conditions. The remaining γ-proteobacteria were closely related to iron-depositing sheathed bacteria.
Chemical Characterization of Precipitated Phases Formed In Situ on Solid Support Devices or Biogenic Iron Oxidation Experiments
Solids have been collected from biogenic iron oxidation experiments, but have not been analyzed yet.
Future Activities:
Seasonal monitoring will be continued on a quarterly cycle (November 2004, and February, May, and August 2005) by collecting freeze cores, bead columns, and pore water samples and continuously monitoring water level fluctuations. The rates of iron oxidation with whole cell extracts will be measured. The rate of iron oxide reduction under biogenic control will be measured and compared to the timescales of transient fluctuations in water levels on site. An improved method will be developed to collect in situ precipitate phases for chemical characterization. Together, these activities will indicate the conditions under which arsenic sequestration in sediments limits the transport of arsenic from groundwater to surface water at this and other hydrogeologically similar sites in New England. Ultimately, the results of this research project will direct the development of predictive models of arsenic transport and lead to effective remediation approaches for abandoned landfill sites.
Journal Articles:
No journal articles submitted with this report: View all 14 publications for this subprojectSupplemental Keywords:
GSI, metal transport, arsenic, iron-oxidizing bacteria, iron-reducing bacteria, toxics, exposure, hazardous substances, assessment, cleanup, risk communication,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, POLLUTANTS/TOXICS, Environmental Chemistry, Chemicals, Hazardous Waste, Ecological Risk Assessment, Hazardous, Environmental Engineering, contaminated sediments, hazardous waste disposal, hazardous waste management, hazardous waste treatment, contaminated waste sites, fate and transport , landfills, contaminated groundwater, chemical releases, hazardous waste characterization, arsenic, heavy metals, groundwaterRelevant Websites:
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R828771 Center for the Study of Childhood Asthma in the Urban Environment Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828771C001 Co-Contaminant Effects on Risk Assessment and Remediation Activities Involving Urban Sediments and Soils: Phase II
R828771C002 The Fate and Potential Bioavailability of Airborne Urban
Contaminants
R828771C003 Geochemistry, Biochemistry, and Surface/Groundwater Interactions
for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts
R828771C004 Large Eddy Simulation of Dispersion in Urban Areas
R828771C005 Speciation of chromium in environmental media using capillary
electrophoresis with multiple wavlength UV/visible detection
R828771C006 Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas
R828771C007 The Center for Hazardous Substances in Urban Environments (CHSUE) Outreach Program
R828771C008 New Jersey Institute of Technology Outreach Program for EPA Region II
R828771C009 Urban Environmental Issues: Hartford Technology Transfer and Outreach
R828771C010 University of Maryland Outreach Component
R828771C011 Environmental Assessment and GIS System Development of Brownfield Sites in Baltimore
R828771C012 Solubilization of Particulate-Bound Ni(II) and Zn(II)
R828771C013 Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
R828771C014 Research Needs in the EPA Regions Covered by the Center for Hazardous Substances in Urban Environments
R828771C015 Transport of Hazardous Substances Between Brownfields and the Surrounding Urban Atmosphere
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
2 journal articles for this subproject
Main Center: R828771
108 publications for this center
20 journal articles for this center