AWRA National Conference –Tyson Corner, Virginia, November 5, 2014 Water Quality Modeling for Evaluation of Potential Surface Water and Groundwater Impacts: Aurora Gold Projects, Guyana Felix Kristanovich, PhD, PE, ENVIRON - Seattle Farid Achour, PhD, ENVIRON - Irvine
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AWRA National Conference –Tyson Corner, Virginia, November 5, 2014 Water Quality Modeling for Evaluation of Potential Surface Water and Groundwater Impacts: Aurora Gold Projects, Guyana Felix Kristanovich, PhD, PE, ENVIRON - Seattle Farid Achour, PhD, ENVIRON - Irvine
Site Location – Guyana, South America
Cuyuni River
Project Site
Outline
• Proposed Mining Operation • Contaminants of Concern and International
Finance Corporation (IFC) Effluent Guidelines • Overall Modeling Approach • Surface Water Modeling and Conclusions • Groundwater Modeling and Conclusions
Mining Operation
Source: TT, 2013
Mine – Overall Site Plan
Source: TT, 2013
Selected Potential Contaminants of Concern
Mine Water Pond (MWP): • Petroleum hydrocarbons (benzene) – leakage
from mining operations, accidental spills • Leachate metals (As, Cr, Cu, Ni) - leaching from
mine pit and mining rocks
Tailing Management Area (TMA): • Fe and residual CN (post gold leaching and
cyanide detoxification processes)
Project Regulatory Obligations
• This project is part of an updated ESIA study. • These studies are developed to meet current IFC
environmental/social performance standards and mine effluent guidelines, International Cyanide Management Code (ICMC), and other BMPs.
• IFC mine effluent guidelines are invoked by the environmental permit, and provide regulatory basis for tailings/water management facility design.
• All discharges, releases, and/or spills from the project are subject to IFC/ICMC discharge guidelines.
Modeling Approach
Surface Water Impacts: • EFDC and WMS models through TMA Diversion
Ponds 1 and 2 to receiving stream, and from FWP through MWP and to receiving stream
Groundwater Impacts: • WHI Unsat Suite (HELP & VS2DT)(unsaturated
zone) and Visual MODFLOW (saturated zone) (conversion from Mine-DW model) (unsaturated zone and aquifer under TMA)
Conclusions – Surface Water Simulation Results –TMA-D2 Pond System
• Concentrations of Free CN are predicted to be below IFC guidelines.
• Concentrations of Total CN are also below IFC guidelines. • Concentrations of TSS may slightly exceed IFC guidelines
during wet seasons.
Simulation Results –MWP Pond System • Concentrations of leachate metals are far below IFC guidelines. • Discharge concentration of petroleum hydrocarbons (i.e.
benzene) is far below IFC guidelines (quick biodegradation). • Concentration of TSS consistently exceeds the IFC guideline of
50 mg/L during most operational periods, except for dry seasons; indicates additional treatment or polishing for TSS may be required in development of mine design
GROUNDWATER IMPACTS
Assumptions for data input • Volatilization rate for CN was assumed conservatively
low • Nominal leaching concentration for runoff input into
MWP • Nominal performance for CNWAD from CN detoxification
plant, and estimate of CNF and CNT based on decant test results
• Spill concentrations were based on the maximum spill from a typical truck (in a mining pit), that is then pumped during 12-hour period into MWP
• Solute transport of metals and CN was simulated by including retardation parameter for each solute (representing its adsorption onto particles in subsurface)
Modeling procedure Under TMA:
• Input concentrations of Fe (20 mg/L) and CNT (2 mg/L) in dissolved state (daily basis)
• Unsaturated flow through 30 m layer (27 m sand, 3 m clay) – VS2SDT model
• MODFLOW used to simulate flow into groundwater
Under MWP: • Input concentrations of As (0.27 mg/L), Cr (0.035
mg/L), Cu (0.19 mg/L), Ni (0.023 mg/L) • Unsaturated flow through 3 m layer (2 m sand, 1
m clay) – VS2SDT model • MODFLOW used to simulate flow into groundwater
Selected Modeling Parameters - Groundwater
Facility Contaminants
Primary Attenuation Mechanisms and Model Parameter Values