Training

Monitored Natural Attenuation of Inorganics USEPA Scientist - to - Scientist Meeting Las Vegas, Nevada June 14 - 15, 2000 Robert W. Puls, Ph.D. National Risk Management Research Laboratory OSWER Directive on MNA  Recognizes monitored natural attenuation of inorganics in ground water and soils Requires knowledge of specific mechanisms Most applicable when contaminant is irreversibly immobilized   Presentation Topics  Monitored Natural Attenuation of Metals   Processes controlling MNA Site Characterization Issues    Research Questions Factors Affecting MNA of Metals NRMRL/SPRD Research Natural Attenuation of Inorganics PROCESSES Adsorption-Desorption …..… Precipitation-Dissolution …… Oxidation-Reduction ………. Immobilization-Mobilization Immobilization-Mobilization Change in chemical state speciation; may affect mobility and toxicity Change in phase Volatilization ………. Colloid, Sediment Transport .. Facilitated transport, sediment loading Site Characterization Inorganics Monitored Natural Attenuation 1.1 Identity and Extent of Contamination Contaminant Flux 1.4 Temporal & Spatial Ground Water Geochemistry 1.3 Ground Water Hydrogeology Contaminant Attenuation Capacity 1.5 Mechanism and Stability of Attenuation 1.2 Aquifer Composition and Heterogeneity Geochemical Buffering Capacity Research Questions for MNA of Inorganics  What are the important processes to measure for natural attenuation for metal contaminants?   How do you make these measurements? How do you integrate these data to understand the behavior of the system? Factors Affecting MNA of Inorganics  Speciation (e.g. Cr(III), Cr(VI), As(III), As(V)  Geochemical factors       pH Eh DO Water chemistry Microbial activity Sorbents  Mineralogy Natural Attenuation Definition: Naturally occurring processes in the environment that act without human intervention to reduce the mass, toxicity, mobility, volume or concentration of contaminants. Source: Waste Research Strategy Office of Research and Devolopment Washington, DC 20460 EPA/600/R-98/154 www.epa.gov/ORD NRMRL Research on MNA of Inorganics  Laboratory studies of the role of mineralogy for MNA    Arsenic and Iron (Hydr)oxides (6400) Solid phase speciation/extractions (4279) Arsenic and Iron sulfides (7060)  Field studies of the natural attenuation of arsenic in an urban watershed (6401) MNA of As in an Urban Watershed  Aberjona watershed in Woburn, MA (industriplex site); pesticide manufacturer and tannery Cooperative effort between ORD/NRMRL and region 1   Involves ground water, surface water, soils and sediments Provide part of the science needed to develop guidance on MNA for metals  Industriplex Site, Woburn, MA Holding Area Halls Brook Plume Discharge into HBHA Halls Brook Holding Area THE POND Hall’s Brook Cross-Section Picnocline (turbidity high) Fe S As organics Project Goal “ … to understand the hydrogeochemical and biogeochemical mechanisms controlling arsenic mobilization, immobilization, and bioavailability in subsurface and surface aquatic environments, and develop practical and cost-effective ecosystem restoration measures to manage risk to human and environmental health.” Note: Results should be applicable to a variety of sites including both industrial and mining sites Objectives  Site-specific assessment of potential for natural attenuation of arsenic  Preliminary guidance for monitoring requirements to assess the potential of MNA  Develop/evaluate sampling protocols arsenic speciation in ground and surface water samples. Project Tasks  Collect soil cores from Industri-Plex site and HBHA wetlands to assess arsenic levels  Collect ground water samples in suspected samples in HBHA pond and tributaries source areas and adjacent to HBHA wetland  Collect surface water samples and sediment  Establish monitoring wells to intercept flow into HBHA pond (adjacent to pond and within pond sediments) Project Milestones and Products Agency documents: • Project Report on the Natural Attenuation of Arsenic in Soils and Sediments (12/2001) Peer-reviewed journal articles: • Preservation methods for maintaining aqueous arsenic speciation in ground water samples (12/2000) • Solid phase arsenic speciation as a function of geochemical parameters in soils and sediments (05/2001) • Assessing natural attenuation of arsenic in soils and sediments (10/2001) Agency Needs GPRA Goal 5: Improvements in Waste Management Practice ORD • Remediation & Restoration => Natural Attenuation NRMRL • Provides Region I with scientifically valid data • Remediation/watershed restoration for heavy metals SPRD • Research on chemical and physical processes of subsurface environment • Research on fluxes to other environmental media, i.e. ground water to surface water Task 6400 (Robert Ford) Attenuation/Stabilization of Arsenic by Iron (Hydr)oxides in Soils/Sediments: Laboratory Study Task 4279 (Cynthia Paul) Natural Attenuation of Inorganic Contaminants Laboratory study, solid phase extraction methods Task 7060 (Richard Wilkin) Natural Attenuation of Metals During Sulfide Formation Connection to other in-house research: Task 6403 (Richard Wilkin) Monitoring Oxidation-Reduction Processes in Ground Water, Sediments Task 1579 (Guy Sewell) Microbial Ecology of the Subsurface/Biomarker Development Natural Attenuation of Metals During Sulfide Formation Task 7060 (Richard Wilkin) Fe-O2-S-H2O (25 °C) 1.00 FeSO4+ 0.75 0.50 FeSO4 0.25 0 O2 2+ FeHSO4 -6 -4 FeOOH Oxidizing (6401) environments: sorption/co-ppt with iron oxyhyrox. Reducing (7060) environments: sorption/co-ppt with iron sulfides 12 Eh (V) 0.00 -0.25 -0.50 -0.75 -1.00 2 3 4 5 6 7 8 9 10 11 S=10 -4 C=10 -6 -4 Fe=10 and10 -3 Fe 2+ H2 FeS2 Fe7S8 pH Objectives  (Task 7060) Laboratory studies to identify mechanisms of metal uptake and evaluate rates Focus on As, Ni, Zn, Mn   Identify controls on attenuation capacity => reactive Fe, sulfate, organic C Identify controls on formation of pure Mesulfide vs. co-precipitation with Fe Develop practices for field monitoring   Monitoring Oxidation-Reduction Processes in Ground waters, Sediments, and Soils Task 6403 (Richard Wilkin)  Objectives  DO methods comparison  Winkler titrations, colorimetric, electrodes   Eh interpretation: H2S/S° equilibrium Develop methods to partition S in the solid phase  AVS, CRS, S°, S-organic, S-sulfate EPA Workshop on Monitoring OxidationReduction Processes for Ground Water Restoration April 25-27, 2000 in Dallas •About 50 experts from government, academia, and industry met to discuss redox characterization, methods, and data interpretation as they apply to the remediation of chlorinated hydrocarbons, petroleum hydrocarbons, and inorganic contaminants •Process: Plenary talks, Breakout Sessions, Summary •Product: Workshop Document planned for early 2001 Task 4279 - Natural Attenuation of Inorganic Contaminants (Lab-based)  Reliable/acceptable extractions to assess speciation on the solid phase? Reliable/acceptable methods to assess oxidation capacities for soils/seds?   Reliable/acceptable methods to assess reduction capacities for soils/seds? Cheap, fast, reliable analytical methods for solid phase speciation assessments?  Summary NRMRL/SPRD MNA Research  Mineralogy role in MNA (arsenic)  Fe and S cycling extraction methods arsenic speciation solids analyses  Solid phase analyses, site assessment   Sample collection, preservation methods    Development of MNA protocols for field application NRMRL/SPRD MNA Research & Mining  Arsenic a common contaminant of mine wastes  Fe and S cycling important processes for mine waste site assessment and treatment Solid phase analyses and extraction methods important for mine waste assessments MNA may be an important part of any mine waste remedial measure  