Date of Report: March 31, 2003 EPA agreement number: R829515C003 Center Name and Institution of Ctr. Director: Rocky Mountain Regional Hazardous Substance Research Center, Colorado State University, Fort Collins, Colorado Identifier used by Center for Project: Project 2 Title of Project: Fate and Transport of Metals and Sediment in Surface Water Investigator(s) and Institution(s): Pierre Julien, Chester Watson, and Brian Bledsoe at Colorado State University Type of Research: Applied Project Period: November 1, 2002 September 31, 2003 Goal of Research This effort focuses on surface water and sediment transport, with an emphasis on the fate and transport of metals in rivers from mining wastes. The main objectives of this project are to: (1) improve and develop computer modeling tools for the simulation of erosion and sedimentation of sediment and metals in surface waters; and (2) develop methodology for evaluating impacts from sediment and metals on watersheds. Statement of Work The CASC2D-SED numerical model is used as a basic framework to simulate metals transport and fate. CASC2D-SED was developed at Colorado State University and has a substantial development history (Julien and Saghafian 1991; Julien et al. 1995; Johnson et al. 2000; Julien and Rojas 2002). It is an event-based model and provides mechanisms to simulate overland flow, surface erosion, and sediment transport through stream channels. CASC2D-SED is well suited for development as a tool to evaluate the transport and fate of metals from mine waste because it can be directly coupled with GISbased site characterization data and remote sensing sources. Physical characterization of waste rock piles such as degree of erosion, slope stability, distance from surface water, proximity to a drainage channel, presence of vegetation on mine waste and presence of a kill zone can be taken into account in the model. Objective 1 tasks: Recognizing that the transport of particles from any one source is typically independent of transport from other sources, existing transport algorithms in CASC2D-SED have been modified to allow the simulation of an unlimited number of particle types. In this manner, soil and metallic particles from different source areas (e.g. waste piles and uncontaminated areas) are simulated as unique particle types and the total delivery of solids is computed as the sum of all particle types simulated. The simulation of heavy metals transport during a rainfall event is visualized as an animated sequence of raster grids. At the end of the simulation, spatial variability of deposited or scoured volumes is shown for each metal as a raster grid. Objective 2 tasks: The CASC2D-SED model is applied to the EPA California Gulch Superfund site. The California Gulch basin is located in Lake County, Colorado, in the Upper Arkansas River watershed and comprises an extension of 30.6 km 2. The basin includes the town of Leadville and various parts of the Leadville Historic Mining District. Raster data sets
collected on the site consist of a Digital Elevation Model (DEM) at 30-m resolution, land use / land cover map at 30-m resolution (see Figure 1), soil type map at 30-m resolution, digital orthophoto quadrangles at 2-m resolution (see Figure 2), and AVIRIS mineral map at 17-m resolution (see Figure 2). The USBR and USGS analyzed the AVIRIS images to map the distribution of minerals associated with the sources of acid rock drainage and heavy metal contamination. Suspended metal concentrations of Zn, Cd and Cu are used as predictors for contaminants lethal effects on wildlife. These metals transport are explored assuming that all metals are present in particle-associated (100% particulate) forms. Based on soil analyses at some waste rock piles at California Gulch (Julien and Rojas field trip on June 2002), the average content of Zn, Cd and Cu was obtained for the California Gulch basin. These waste rock piles are located using the AVIRIS data. A simple case scenario is to consider as contaminated soil all the areas of the watershed where a non-zero value of the AVIRIS data is found. The rest is considered as contaminated soil (see Figure 2). CASC2D-SED simulates erosion, transport and deposition of Zn, Cd and Cu during the 100-yr, 2-hr storm event in California Gulch. This event is estimated to have a depth of 1.73 in. Figure 1. California Gulch basin land use / land cover grid (30-m resolution)
Figure 2. California Gulch basin and channel and AVIRIS data overlaid over digital orthophotos Output raster maps from the simulated event include the distribution of: rainfall rate, accumulated infiltration depth, surface flow depth, total sediment volume, suspended sediment volume, and sediment flux and concentration by size fraction, and transport rates for each of the metals taken into account. At the end of the simulation, eroded sediment and metal particles are deposited in the watershed, creating a kill zone downstream from the waste rock piles. The simulated Zn deposited in the basin following the event is shown in Figure 3. Deposition of metals in Figure 3 shows where re-vegetation should be considered as a remediation alternative. Figure 3. Deposited Zinc [gr/m 2 ] after the 100-yr, 2-hr event at California Gulch.
Relevance of Research The main expected benefit of this research includes an improved understanding and representation of metals transport and fate in mine waste impacted hillslopes and streams. The results of this study provide remediation managers with a tool to examine the contribution of individual contaminated areas to the total impairment of a site in terms of heavy metals transport. Progress Objective 1: improve and develop computer modeling tools for the simulation of erosion and sedimentation of sediment and metals in surface waters Progress to date: Accomplished Percentage completed: 100% Problems encountered and/or unexpected results: None Future activities: None Planned Objective 2: develop methodology for evaluating impacts from sediment and metals on watersheds Progress to date: Accomplished Percentage completed: 80% Problems encountered and/or unexpected results: None Future activities: Model will be further tested to simulate the fate and transport of metals from different sources. Summary of Relevant Data GIS data: (a) Raster data: Digital elevation model (DEM) and land use grids at 30-m resolution; soils information from the NRCS STATSGO database is at scale 1:250,000 (b) Line and polygon coverages: California gulch basin boundary and channel network hydrography at scale 1:100,000; roads and streets at scale 1:24000; elevation contour lines at 5-ft spacing. Aerial photographs: USGS Orthophotos were downloaded at 1-m resolution from the Terraserver web site. Remote sensing data: the AVIRIS data was collected from a visit to the USGS (Denver Federal Center) from Sam Vance and Greg Swayze. More data to be collected from Sam Vance at the EPA in Denver; Archived data: Various reports of the remediation projects carried out at the California Gulch operable units 4 and 6 obtained from a visit to the EPA Region 8 in Denver. Stanley Christensen at EPA and Karmen King at CMC provided the runoff data for the 2002 rainfall events. Field trips: A set of soil samples and site pictures were taken at contaminated sites on June 11, 2002: soil samples. Another site visit was made on September 19, 2002 accompanied by Stanley Christensen and Michael Holmes, both at the EPA Region 8. Schedule and Scope Our model development and testing is going on as planned. We will deliver nice results and computer model simulations at California Gulch before the end of the fiscal year. Our next step will be in the development of algorithms for the different phases of metal transport. This will enhance modeling capabilities with applications to remediation strategies.
Appendix Publications/Presentations: Julien, P.Y., B.P. Bledsoe and CC. Watson, Fate and Transport of Metals and Sediment in Surface Waters, Presentation on January 17, and Proceedings of the Ninth International Conference on Tailings and Mine Waste, Fort Collins Colorado, USA, January 27-30, 2002, Balkema, pp. 17-20. Seminar presentation entitled Fate and Transport of Metals and Sediment in Surface Waters at the Colorado School of Mines Golden, Colorado, January 17, 2002. Poster and oral presentation entitled Fate and Transport of Metals and Sediment in Surface Waters at Colorado State University, Fort Collins Colorado, July 31, 2002. Presentation entitled Sediment transport with CASC2D-SED at the EPA Regional Center in Denver, September 2, 2002. Related Presentations/Publications: Johnson, B. E., Julien, P. Y., Molnar, D. K., and others (2000). The two-dimensionalupland erosion model CASC2D-SED J. of the AWRA, v. 36, no. 1, p. 31-42. Julien, P. Y., and Rojas, R. (2002). Upland erosion modeling with CASC2D-SED International Journal of Sediment Research, v. 17, no. 4, p. 265-274. Julien, P. Y. and Rojas, R. (2002). "Watershed erosion modeling with CASC2D-SED." National Meeting of the Korean Water Resources Association, Inchon University, 27-40. Julien, P. Y., and Saghafian, B. (1991). CASC2D users manual - A two dimensional watershed rainfall-runoff model Fort Collins, CO., Colorado State University, Fort Collins, 66 pp. Julien, P. Y., Saghafian, B., and Ogden, F. L. (1995). Raster-Based hydrologic modeling of spatially-varied surface runoff Water Resources Bulletin, v. 31, no. 3, p. 523-536. Rojas, R. (2002). "GIS-based upland erosion modeling, geovisualization and grid size effects on erosion simulations with CASC2D-SED." PhD thesis, Civil Engr., Colorado State University, 273 p. Rojas, R. and Julien, P. Y. "Grid Resolution Effects on Upland Erosion Predictions." Procs. 2nd Federal Interagency Hydrologic Modeling Conference. CD-ROM. Rojas, R. and Julien, P. Y. (2002). "Modeling sediment transport with CASC2D-SED." Procs. 22th AGU Hydrology Days, Colorado State University, 233-244. Relevant Web Sites: http://www.engr.colostate.edu/hsrc