Grantee Research Project Results
2005 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, 2004 through September 30, 2005
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 groundwater/surface water interface.
The goal of this research project is to identify the seasonal cycle of arsenic sequestration and release between sediments and pore waters in the GSI. The specific objectives of this work were: (1) quantify the seasonal distributions of arsenic, iron and sulfur species and other key electron donating/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:
Task 1: Field Observations of Pore Water Constituents and Solid Phases at the Same Location
Seasonal changes in sediment phase concentrations f arsenic andiron have been monitored at three locations of increasing distance from the Cohas Brook shoreline. Monitoring approaches consisted of: (1) freeze core solids collection with sequential extraction to quantify the fraction of total arsenic and iron in various pools; and (2) artificial bead columns that were used to quantify arsenic and iron accumulation rates (mg/kg/d) in the solid phase over known time durations.
The freeze core extractions indicated that the only differences between cores were lower inventories of total arsenic and iron in the cores located closest to the brook shoreline. The average arsenic and iron concentrations in the three near-shore cores were 720 ± 30 mg/kg and 55700 ± 21200 mg/kg, respectively; the other six cores had average arsenic concentrations of 1500 ± 500 and iron concentrations of 13100 ± 21000 mg/kg. No significant differences in distributions of arsenic and iron concentrations as a function of depth were observed (0.8 cm vertical resolution). More than 90 percent of the total arsenic and iron masses were in the top 6-cm below ground surface. Similarly, no significant differences in associations of arsenic and iron were observed between cores. In general, arsenic was strongly sorbed to the surfaces of amorphous iron oxides in the sediments.
The bead columns indicated that arsenic and iron accumulation rates in the sediment phase at the groundwater seep were significantly lower when the sediments were fully submerged under water. During a 3-month period of sustained flooding in spring 2005, arsenic and iron deposition rates on the bead columns were 0.03 mg/kg/d and 7 mg/kg/d, respectively; whereas, bead columns deployed for 3- to 9-month intervals with short (about 1 week) durations of sediment flooding had arsenic accumulation rates of 0.1 to 0.9 mg/kg/d and iron accumulation rates of 17 to 70 mg/kg/d. The average column accumulation rates of 1–2 µg/d of arsenic and 240–640 µg/d of iron from June 2003, a period with no flooding, compared favorably with the fluxes of arsenic (0.8 µg/d) and iron (265 µg/d) from the upgradient groundwater zone. This comparison suggests that, under dry conditions, all of the arsenic and iron in groundwater that seeps through this zone is sequestered in the sediments. The total inventory of arsenic and iron in freeze cores corresponds to between 2 and 20 years of accumulation.
Laboratory sediment incubations suggested that biological iron reduction was not a significant source of re-mobilized arsenic and iron to Cohas Brook from the sediments. Release of arsenic and iron from sediment microcosms with and without carbon amendments was not different from poisoned controls over 30 days. Viable iron-reducing organisms were isolated from the sediments, enriched and shown to reduce synthesized ferrihydrite with the release of ferrous iron and sorbed arsenic to the aqueous phase. Apparently, in situ activity of organisms is not great enough to decrease inventories of iron and arsenic in sediments. Thus, flooded freeze core locations with low total arsenic and iron may be zones with little net iron and arsenic deposition, as suggested by the bead columns.
Some net accumulation of arsenic in the sediments may occur even at locations of flooded sediments as the arsenic-to-iron ratios in the freeze cores (0.01–0.02) were always greater than for the upgradient groundwater (0.003).
Task 2: Enumeration and Phylogenetic Diversity of Iron-Oxidizing Bacteria
A quantitative method to measure the cellular activity of iron oxidizing bacteria (IOB) in sediments has been developed. The ratio of rRNA/rDNA will be used to assess the metabolic status of IOB in sediment samples and artificial substrates with known deployment times at the same locations as arsenic and iron chemical analyses have been obtained. Group-specific rRNA primers have been developed from 16S rRNA clone libraries from three depths of sediments in the freshly-obtained July 2004 freeze core. Confirmation of the clone libraries were obtained from in-situ hybridization of IOB enrichments from the July 2004 freeze core.
The phylogenetic diversity of the IOB 16S rRNA genes were assessed to identify relationships among clones from Cohas Brook sediments and between bacteria with known ironoxidizing activity. The IOB clones from sediments of depth 1-2 cm grouped within the α-proteobacteria (52%) and β-proteobacteria (48%) classes. At depths of 5- and 9-cm below ground surface α-proteobacteria had less diversity (14-25%) and β-proteobacteria accounted for 70-84 percent of all clones. Less than 2 percent of the clones were from the γ-proteobacteria class, the bacterial group within which most previously known IOB cluster.
Task3: Chemical Characterization of Precipitated Phases Formed In Situ on Solid Support Devices or Biogenic Iron Oxidation Experiments
Chemical characterization of solids from the top 10-cm of a core obtained from a location 2-m from the water line supported the conclusions obtained from chemical and biological characterization of core solids. Microprobe analysis always showed arsenic to be concentrated in regions of high iron, and not found in regions depleted of iron. X-ray diffraction analysis showed the dominant crystalline form of iron oxide solids to be ferrihydrite that would have been quantified as amorphous iron oxides by the chemical extraction techniques. Transmission electron microscopy indicated large amounts of teardrop-shaped iron nanoparticles that can be characteristic of biological iron oxide formation. In addition, chemical analyses showed insignificant quantities of sulfur in the sediments, thus supporting the conclusions from the chemical extraction studies that links between arsenic and sulfur cycling at this site were minor.
Future Activities:
The seasonal monitoring will be complemented by laboratory studies. First, arsenic sorption kinetics and capacities of Cohas Brook sediments will be measured. Second, the rates of iron oxidation with whole cell extracts will be measured. The biological enumeration techniques will be applied to freeze core sediments and artificial substrates to quantify IOB activity for comparison with arsenic and iron deposition patterns. Additional sediment samples will be analyzed by chemical characterization, including sorbed arsenic associations, to verify findings of the chemical and biological analyses at more locations. 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 results will direct the future 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,, 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