Grantee Research Project Results

2003 Progress Report: Geochemistry, Biochemistry, and Surface/Groundwater Interactions for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts

EPA Grant Number: R828771C003
Subproject: this is subproject number 003 , 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: HSRC (2001) - Center for Hazardous Substances in Urban Environments
Center Director: Bouwer, Edward J.
Title: Geochemistry, Biochemistry, and Surface/Groundwater Interactions for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts
Investigators: Smets, Barth F. , MacKay, Allison
Institution: University of Connecticut
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2002
Project Period Covered by this Report: October 1, 2002 through September 30, 2003
Project Amount: Refer to main center abstract for funding details.
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 (USEPA, 2000, #484). 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.

The overall goal of this research project is to identify and assess the relative importance of the complex, and potentially antagonistic, microbial and chemical processes that govern the retardation and migration of metals, specifically As, Cr, Ni, Zn, and Cd, from a reduced aquifer zone through the GSI into an adjacent surface water body. The specific objectives of this research project are to: (1) determine the significance of dissimilatory sulfate and iron reduction in the immobilization of typical cations and oxyanions; (2) determine the relative significance of microbial and chemical iron oxidation in the GSI; and (3) characterize solid-phase and dissolved heavy metal species in groundwater as a function of location with respect to the reduced or GSI zones. A field-based approach was undertaken to meet these objectives so that the obtained results would have direct relevance to actual environmental settings such as the site of investigation and other regional sites with similar hydrogeology.

Progress Summary:

The proposed experimental approach consists of field observations and controlled laboratory experiments.

Field Observations

Field activities commenced with evaluation of U.S. EPA Region 1 sites that would be feasible for sample collection and experimental observations of contaminant transport across the GSI. After reviewing four potentially suitable sites, the former Auburn Road Landfill in Londonderry, NH, was identified as most suitable because the site was characterized by accessible shoreline, a wadeable surface water body, and strong evidence linking the sequestration of arsenic in the GSI to iron oxide formation in Cohas Brook sediments.

Evidence for historic arsenic accumulation in the near shore brook sediments was obtained from Cohas Brook core samples. Solid-phase arsenic concentrations were strongly correlated with the total iron oxide content of the solids. Selective chemical extractions indicated that the mineral association of the arsenic varied with depth. Strongly and weakly sorbed arsenic pools accounted for 25-35 percent of the total arsenic in the shallowest sediments, but were below detection at depths greater than 20 cm below the ground surface. In addition, a greater fraction of arsenic was incorporated into more crystalline iron oxide structures in sediments of increasing depth. These trends indicate that the pools of arsenic that would most easily be released back to the pore waters for discharge to the brook are located in the shallowest sediments. These observations also may indicate that the shallow sediments were the most recent locations for active accumulation of arsenic in the solid phase.

The arsenic cycle in the GSI at Cohas Brook is closely tied to the biogeochemistry of iron. The formation of iron oxides is dependent on the concentration of ferrous iron in the pore water and the availability of oxygen to initiate oxidation of iron to the ferric state. With dissolved oxygen concentrations ranging from 0.05-0.8 mg/L and pH between 4.2 and 5.5 in Cohas Brook pore water, chemical oxidation of iron would be extremely slow (t1/2 ~300 days). Thus, the rate of arsenic accumulation by chemically precipitated oxides also is expected to be slow. However, iron oxide formation under these same pore water conditions can be accelerated if iron-oxidizing bacteria are present.

Laboratory Studies

A portion of the iron oxides in Cohas Brook sediments originated from biogenic sources. When cell extracts isolated from core solids were introduced into special microcosms with low, diffusion-limited concentrations of oxygen and ferrous iron, iron oxidation was observed. Control samples that were prepared by the same methods, but received an aliquot of distilled water in place of cells, did not develop oxide precipitates over the same incubation time. Microscopic observation provided further confirmation of biogenic origin of oxides in the inoculated microcosms. The estimated numbers of iron-oxidizing bacteria per gram of soil decreased with depth in Cohas Brook sediments, and were more abundant in sediments with high iron oxide contents. Iron-oxidizing bacteria densities were similar to heterotrophic plate counts, but were substantially lower than the total direct count as inferred from microscopic observations.

Future Activities:

The key chemical or biological processes that control the fate of arsenic transport across the GSI will be deduced from the high-resolution patterns of pore water chemistry and solid precipitates observed at Cohas Brook. These observations 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.

Supplemental Keywords:

groundwater-surface water interface, GSI, metal transport, arsenic, iron-oxidizing bacteria, iron-reducing bacteria, chromium, zinc, chromate, anaerobic microbial activity, aquatic ecosystems, arsenic release, bacterial degradation, biodegradation, cadmium, contaminated aquifers, contaminated groundwater, contaminated waterfront, decisionmaking, environmental rehabilitation, fate and transport, groundwater, groundwater contamination, groundwater pollution, hazardous waste treatment, heavy metals, metal wastes, metals, microbial breakdown, microbial degradation, spectroscopic studies, transport models, treatment, urban environment., RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Waste, Water, Hazardous, Restoration, Ecological Risk Assessment, Aquatic Ecosystem Restoration, Environmental Chemistry, Groundwater remediation, Hazardous Waste, Geochemistry, Bioremediation, Ecology and Ecosystems, microbial breakdown, arsenic release, heavy metals, water quality, microbial degradation, urban environment, treatment, Chromium, contaminated aquifers, contaminated waterfronts, groundwater contamination, cadmium, hazardous waste treatment, contaminated groundwater, urban environmental, transport models, arsenic, groundwater, biodegradation, fate and transport, contaminated waterfront, Zinc, aquatic ecosystems, groundwater pollution, metals, spectroscopic studies, metal wastes, anaerobic microbial activity, decision making, environmental rehabilitation

Relevant Websites:

http://www.jhu.edu/hsrc/ Exit

Progress and Final Reports:

Original Abstract

Final

Main Center Abstract and Reports:

R828771    HSRC (2001) - Center for Hazardous Substances in Urban Environments

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