Region 8 – Metals Fate and Transport Modeling for Contaminated Sites and Mercury TMDLs |
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This seminar will provide an overview of the Water Quality Simulation Program (WASP) model and its application to Superfund sites in Colorado and Montana. We will discuss some recent additions to the WASP model including a chemical speciation subroutine (META 4) and ongoing research to improve the model’s capability to predict mercury fate and transport in streams to assist in TMDL development Featured Speakers include: Dr. Brian Caruso from EPA Region 8, Dr. Allen Medine from Water Science and Engineering, and Robert B. Ambrose, Jr. from EPA‘s Ecosystem Research Division of the National Exposure Research Laboratory (ORD). Power Point slides can be downloaded by clicking the links to the presentations below – please email Elsie Sunderland (sunderland.elsie@epa.gov) if you have any problems downloading and/or viewing the presentations.
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Agenda |
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100-110 |
Welcome to Regional Seminar Series & Introductions Elsie Sunderland, Council for Regulatory Environmental Modeling |
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110-120 |
Regional Modeling OverviewJim Luey, Ecosystems Protection & Remediation, Region 8/Bruce Zander, Region 8 TMDL Coordinator |
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120-145 |
Modeling Metals Fate and Transport in the Upper Tenmile Creek Watershed Mining Area, Montana Brian Caruso, Hazardous Substances Technical Liaison, Region 8/ORD |
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145-150 |
Questions and Discussion |
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150-215 |
Development of the Speciation-Based Metal Exposure and Transformation Assessment Model (META4) Allen Medine, Principal Engineer and Director, Water Science and Engineering |
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215-220 |
Questions and Discussion |
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220-245 |
Modeling Mercury Transport in Watersheds and Streams Robert B. Ambrose, Jr. Ecosystem Research Division, Office of Research and Development |
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245-300 |
Questions and Open Discussion |
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Presentations |
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Modeling Metals Fate and Transport in the Upper Tenmile Creek Watershed Mining Area, MontanaThe EPA Water Quality Analysis Simulation Program (WASP5) was used to model the fate and transport of metals under low-flow, steady-state conditions in the Upper Tenmile Creek Watershed Mining Area, Montana. This mountain stream is a drinking water supply for the City of Helena, and the entire watershed is a Superfund site impacted by hundreds of abandoned hardrock mines, waste rock and tailings. The model was calibrated for baseflow using synoptic survey data collected by EPA and validated using data from USGS for higher flows. It was used to assess metals loadings and losses, concentrations and exceedances of State of Montana water quality standards, uncertainty in fate and transport processes and model parameters, and the potential utility of the model for other watersheds. The effectiveness of eight alternatives was modeled to assist in restoration planning and design. These alternatives ranged from removal of adit and point source discharges to modification of the water supply scheme to provide higher in-stream flows. The model was also used to evaluate metals interactions between stream water and bed sediment, and the effects of leaving contaminated sediment in place on stream water quality. Lastly, the model was used to help develop and evaluate preliminary metals TMDLs for the watershed. Results showed that during baseflow, adits and point sources contribute significant metals loadings to the stream, but that shallow groundwater and bed sediment also contribute metals in some key locations. Losses from the water column occur in some areas, primarily due to adsorption and precipitation onto bed sediments. Some uncertainty exists in the metal partition coefficients associated with sediment, significance of precipitation reactions, and in specific locations of unidentified sources and losses of metals. Although standards exceedances are common throughout the watershed, modeling results indicated that removal of point sources, mine waste near watercourses, and streambed sediment can help improve water quality considerably. Results also indicate, however, that alteration of the water supply scheme and increasing baseflow will probably be required to meet all water quality standards. The model showed that metals loadings, TMDLs, and the reductions needed to achieve TMDLs and standards can vary considerably over space along the mainstem based on the calculation method and due to the considerable spatial variability in flow, concentrations, hardness, and hardness-based standards.
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Development of the Speciation-Based Metal Exposure and Transformation Assessment Model (META4) (PDF 48 pp., 1 MB, info about PDF)This presentation describes the coupling of a chemical equilibrium simulation model, based upon MINTEQA2, with the generalized Water Analysis Simulation Program (WASP), which includes algorithms for predicting the dynamic impacts of transport and kinetics. The Metal Exposure and Transformation Assessment (META4) Simulation Program is a generalized metals transport, speciation, and kinetics model developed for application to a variety of receiving waters experiencing metals contamination, including ponds, streams, rivers, lakes and estuaries. The META4 model uses the basic transport scheme of WASP, allowing its application to a variety of waterbodies in one, two or three-dimensional mode, as well as the simulation of both water column and benthic layers. Algorithms for the simulation of crucial metal transformation processes, such as aqueous speciation, sorption/desorption, chemical precipitation/dissolution and kinetics were added to this basic structure, resulting in the META4 model. Model development and an application will be discussed. The model has been developed, tested and applied over a seven year period as part of studies for the Clear Creek / Central City Superfund Site (Colorado) in the North Clear Creek watershed to describe the transport and transformations of copper, cadmium, lead, iron, manganese, aluminum, zinc and major ions. Copper, cadmium and zinc have been identified as the primary contributors to aquatic resource impairment in this mining-impacted watershed. As an example of the use of the model to evaluate watershed management and load reductions, modeling in North Clear Creek has been used to evaluate a series of potential remedial activities. The dominant point loads affecting the water and sediment quality in North Clear Creek include Chase Gulch, Gregory Incline, Gregory Gulch and the National Tunnel. Non-point sources include seepage from waste piles, storm runoff, and dissolution of metals from soils and sediments, bank exchange, sediment release/resuspension, and alluvial system exchange. Chemical sinks within the North Clear Creek environment include coprecipitation/sorption losses to the bed region, alluvial system transfers, and sedimentation of particulate metals. Each of these source types have been addressed in the subsequent modeling. Modeling studies were directed at point and non-point load reductions needed to meet existing or projected goals for water quality management in the basin. Following successful calibration and verification, the model was utilized to evaluate the significance of point loads, sediment-water interactions and non-point source inputs of dissolved metals (i.e., groundwater intrusion into North Clear Creek). The modeling was also used to evaluate the impacts of several remediation scenarios on improving water quality of North Clear Creek including point source control, groundwater management and sediment remediation. The approach for evaluating the remediation scenarios involved a step-wise reduction of loading in order to better understand metal dynamics in the basin. The modeling results indicated that the point source control in the upper basin would only result in a significant improvement in water quality for a limited distance downstream. Due to the remaining non-point loads and the contaminated sediments in the downstream segments, water quality was not improved at the mouth of North Clear Creek sufficiently to meet water quality targets. Greatest improvement in water quality was realized when major point sources were treated along with some groundwater treatment and remediation of contaminated sediments. The results indicated that there would be a 75-90% improvement in water quality for cadmium, copper, manganese and zinc due to the potential source controls in various stream segments in the basin. Results of the simulations underscore the importance of an integrated approach to managing load reductions in this watershed, particularly those related to contaminated sediments in the lower segments of North Clear Creek. While control of the four major point sources should result in significant improvement in water quality, the full benefit of the loading reduction would not be realized until contaminated sediment influx is controlled. Modeling results indicated the benefit of a complex management tool, such as META4, in addressing complex issues for resource restoration which cannot be evaluated with more simplified methods. Click here for additional information. (PDF 26 pp., 705 KB, info about PDF)
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Modeling Mercury Transport in Watersheds and StreamsMercury is a complex, multimedia pollutant that is global in reach. Worldwide emissions to the atmosphere include anthropogenic, natural, and re-emitted sources in roughly equal proportions. In the natural environment, mercury is found mainly in two redox states – elemental mercury, Hg0, and divalent mercury, HgII. Atmospheric HgII partitions among three phases – aqueous, gaseous, and particulate – which are deposited to the underlying landscape through wet deposition, gaseous dry deposition, and particulate dry deposition, respectively. In soils, HgII accumulates through atmospheric deposition, and a fraction is returned to the atmosphere by reduction to Hg0 followed by evasion. Some particulate and aqueous HgII in the watershed soil is transferred to nearby water bodies through runoff and erosion, where a fraction is methylated and accumulates in fish. The competing mercury reactions in water bodies have been intensively studied in the past 15 years, but rate constants vary in time and space, and cannot be predicted precisely. Various models have been used to simulate portions of the mercury cycle in order to support management actions. These models are based on mass balance considerations within specific media, and generally include a selection of equilibrium and kinetic reactions. In watersheds, the Watershed Characterization System, Mercury Loading Model (WCS-MLM) has been used to estimate mercury loadings in several southern watersheds. A more detailed version, the new Grid-Based Mercury Model (GBMM), will be available for more detailed analyses in the near future. In stream systems, the WASP mercury module has been used to calculate mercury TMDLs. The WASP7 mercury module MERC7 utilizes a subset of the WASP7 general toxic chemical module TOXI7 to simulate mercury cycling and transport through a water body. MERC7 simulates three mercury species, Hg0, Hg(II), and MeHg, as well as inorganic silt, sand, and particulate organic matter. Simulations are driven by the speciated mercury loadings delivered from the atmosphere, from watershed tributaries, and from point sources. WCS-MLM and WASP7 were used together to simulate mercury dynamics in Brier Creek, Georgia, a tributary of the Savannah River. The WCS-MLM was run for 100 years with the current total deposition flux of 27 ug/m2-yr, allowing the buildup of mercury in soils to reach steady-state concentrations at about 60 ng/g. Calculated annual average runoff and erosion loadings within 11 subwatersheds ranged from 1.5 to 3 ug/m2-yr. The model predicts 90% response times to reductions in atmospheric loads of 35 to 100 years. The WASP7 mercury model was applied in three sequential stages. In stage 1, WASP was run for 100 years using annual average flows and predicted watershed loadings. Calculated total mercury concentrations built up to 7 – 8 ng/L in the water column and 20 – 35 ng/g in the upper sediment. In stage 2, WASP was run for 7 months using observed daily flows, and predicted tributary loadings. Calculated HgT concentrations of 6.3 – 7.8 ng/L compared well with measured downstream and upstream concentrations of 6.0 and 8.3 ng/L. Calculated MeHg concentrations of 0.8 ng/L were within the observed range of 0.7 – 1.4 ng/L. In stage 3, WASP was run for another 100 years with reduced watershed loadings to explore response times. WASP predicts 90% response times to reductions in atmospheric loadings of 75 and 90 years for upstream and downstream locations, respectively, controlled significantly by the watershed response time. There is a large uncertainty range about these estimates. Mass balance modeling technology is available for analyzing mercury dynamics in streams. Present modeling, however, requires site-specific mercury data along with ancillary chemical and environmental data for calibration. Further advances in scientific knowledge are needed to better parameterize key processes and predict response to proposed management scenarios.
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Featured Speakers |
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Robert B. Ambrose, Jr., P.E.Environmental EngineerU.S. EPA, National Exposure Research Laboratory Ecosystems Research Division 960 College Station Rd. Athens, GA 30605706-355-8334; fax: 706-355-8104 Bob joined EPA in 1974 and has over 30 years of experience modeling the fate of organic and inorganic chemicals, including mercury, PCBs, and nitrogen, in watersheds and water bodies. He has developed and applied numerous water quality models for TMDL assessments and is one of the lead developers of the WASP model. His current interests include the development and application of chemical transport and fate models in human and ecological risk assessment modeling. He has authored numerous scientific papers, technical manuscripts and reports in this area and continues to be actively involved in the development of mercury models to support TMDL development at the Agency. Professional awards include the USEPA Science Achievement Award in Water Quality (2001), the Scientific and Technological Achievement Award, in 1998, a Silver Medal for Superior Service, U.S. EPA, 1998 and EPA's Engineer of the Year and one of 10 finalists in the National Society of Professional Engineers' 1989 Federal Engineer of the Year competition, 1990.
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Allen J. Medine, Ph.D., P.E.Principal Engineer and DirectorWater Science and Engineering 900 Valley Lane Boulder, CO 80302 303-449-2409 Dr. Medine has over 30 years of professional experience in environmental engineering and environmental chemistry, including seven years of teaching and research in Civil and Environmental Engineering. He has been involved in technical assessments and remediation at over 24 Superfund sites, detailed assessments at a majority of the major mining sites in the Western U.S., environmental sampling and analysis, analytical data validation, reduction interpretation, and numerical contaminant transport modeling in over 30 river basins, and has provided enforcement and litigation support as well as expert testimony on 16 Superfund sites (6 mining sites).
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