2007 REMEDIAL PROGRESS KENNECOTT NORTH ZONE North Zone TRC March 5, 2008 Kelly Payne, P.G. Principal Advisor, Closure & Remediation
This Afternoon’s Discussion • Demolition Activities • Bingham Magna Ditch • Groundwater Monitoring and Management • Smelter Selenium Plume In Situ Treatment Pilot Testing • Refinery Selenium Plume Remedy Modification • Consent Decree between KUCC and US F&WS • Wetlands Monitoring
3 Presentation title 29 June 2005
4 Presentation title 29 June 2005
Demolition
Groundwater Monitoring and Management
Refinery Selenium Plume Source Area 25000 NER2546A NER2546B 20000 Se-D (µg/l) 15000 10000 5000 0 97 98 99 00 01 02 03 04 05 06 07 08
Refinery Selenium Plume Garfield Townsite 6000 NER2554A 5500 5000 Se-D (µg/l) 4500 4000 3500 3000 2500 97 98 99 00 01 02 03 04 05 06 07 08
Refinery Selenium Plume Kessler Springs 2600 WTS2577 2400 2200 2000 Se-D (µg/l) 1800 1600 1400 1200 1000 800 600 97 98 99 00 01 02 03 04 05 06 07 08
Refinery Selenium Plume Garfield Well #5 700 NEG485 600 500 Se-D (µg/l) 400 300 200 100 0 97 98 99 00 01 02 03 04 05 06 07 08
Smelter Selenium Plume In Situ Pilot Testing
Engineered Metal Sequestration • Approach: use microbes to transform selenium to a chemically stable form as it is found in ore bodies, and then additionally deposit minerals that will maintain these conditions in situ to stabilize the selenium precipitates over geological timescales. Additionally, precipitation of accessory minerals create conditions which further sorb new selenium in flux by creating sorptive barriers. • US Patents: – 5,554,290 In situ reactive zones – 5,632,715 Immobilization of heavy metals in waste stacks and affected zones – 5,710,361 Immobilization of heavy metals in earth materials (CIP of `715) – 5,833,855 In situ bioremediation of contaminated groundwater
Selenium Treatment: Diagrammed Eh-pH Conditions In Plume Eh-pH Conditions After ARCADIS Treatment
Engineered Selenium Precipitation Reductive Precipitation/In Situ Permeable Reactive Barrier • Introduction of organic carbon to aquifer via upgradient injection to create anaerobic/reducing conditions to electrochemically convert selenium from the soluble oxidized form (selenate/selenite) to the insoluble reduced form (elemental selenium). • During creation of reducing conditions, existing and potentially added iron and sulfate in the aquifer are converted to iron sulfide minerals which continue to “protect” the reduced selenium from oxidation by consuming oxygen after carbon injections stop. • As iron sulfide minerals are oxidized to ferric iron minerals, a highly sorptive permeable reactive barrier is formed in the aquifer which has an affinity for selenium, thus sequestering it in situ. As the iron oxidizes, it passivates the surface of the grains acting as a physical barrier to oxygen.
In Situ Pilot Testing • May 21-June 9, 2007 – Injection and Monitor Well Installation • August 11, 2007 – First Nutrient and Tracer Injection (Molasses, Fluorescein dye) • October 18, 2007 – 2nd Nutrient and Tracer Injection (Molasses, FeSO4, Fluorescein dye) • November 29, 2007 – 3rd Nutrient and Tracer Injection (Molasses, FeSO4, Fluorescein dye) • January 9, 2008 – 4th Nutrient and Tracer Injection (Molasses, FeSO4, Fluorescein dye) • February 27, 2008 – 5th Nutrient and Tracer Injection (Molasses, FeSO4, Fluorescein dye)
Monitor Well 1 (15 feet downgradient of injection line)
Monitor Well 2A (45 feet downgradient of injection line)
Monitor Well 3 (72 feet downgradient of injection line)
What about Arsenic? • Under oxidizing conditions, arsenic (As) is insoluble and bound to iron (oxy)hydroxide minerals. • Under iron-reducing conditions, ferric iron (Fe 3+ ) is reduced to ferrous iron (Fe 2+ ) which dissolves the iron minerals and releases the bound arsenic into solution. • If sulfate-reducing conditions are achieved, sulfate 2+ ) is reduced to sulfide (HS - ) which is very reactive (SO 4 with ferrous iron (Fe 2+ ) and quickly precipitates out as FeS (iron sulfide). FeS sequesters soluble arsenic into the structure.
Reduction/Oxidation Reactions O 2 Aerobic Metabolism Oxidizing H 2 O Nitrate Reduction - NO 3 N 2 Manganese Reduction MnO 2 Selenium Reduction Mn 2+ Iron Reduction Fe(OH) 3 (Arsenic liberation from iron matrix) Fe 2+ 2- SO 4 Sulfate Reduction (Arsenic sequestration into iron sulfides) HS - CO 2 Methanogenesis CH 4 H 2 O H 2 Reducing Organic carbon added to the system stimulates biologic growth, which drives the geochemistry to reducing conditions and depletes electron acceptors in a stepwise fashion. Aqueous arsenic concentrations typically increase when iron-reducing conditions are reached and decrease once sulfate- reducing conditions are reached. Once sulfate-reducing conditions are reached, the reduced iron (Fe 2+ ) and reduced sulfate (sulfide, HS - ) react and form insoluble iron sulfide minerals which encapsulate arsenic and sequester it.
Arsenic Control • Arsenic is only soluble between iron-reducing and sulfate-reducing conditions. • Continuing to provide carbon to maintain sulfate-reducing conditions along with a stoichiometric excess of ferrous iron stabilizes the arsenic in the iron sulfide (FeS) matrix. • Excess iron sulfide also stabilizes elemental selenium (Se) by acting as a redox buffer over time.
Arsenic Beyond the IRZ Iron-reducing conditions are reached prior to sulfate-reducing conditions so arsenic can be released and transported through the reactive zone. However, the distal end of the IRZ is oxidizing and dissolved iron and arsenic are re-oxidized in this zone. Degradable carbon (electron donor) injection O 2 -reducing NO 3 -reducing O 2 -reducing CO 2 -reducing SO 4 -reducing Mn-reducing Fe-reducing Redox Recovery Zone 200 0 100 Days Travel in Groundwater
Refinery Selenium Plume Remedy Modification • ROD-selected remedy includes in situ treatment for selenium • KUCC believes that in situ treatment is impracticable in bedrock aquifer based on dye tracer test in 2003 • KUCC also perceives risks due to aquifer plugging and arsenic mobilization • Request submitted to EPA and DEQ in February 2008 to modify remedy • Modified remedy would rely on continued capture with ex situ treatment and monitored natural attenuation
Consent Decree Between KUCC and US F&WS • Settlement of natural resources damage claims by US F&WS for alleged injury to migratory birds and habitat in North Zone Wetlands • Settlement includes – Transfer of 617 acres and water rights to The Nature Conservancy – Property Improvements – Endowment Fund – Government’s assessment costs • CD lodged with US District Court 2/15/08 – Comments accepted 2/22/08 to 3/24/08 • Draft Restoration Plan released by US F&WS – Comments accepted 3/3/08 to 4/2/08
Wetlands
2007 Monitoring Summary • All ponds sampled for water, sediment, and macroinvertebrates, except – Pond 6D2, filled in 2007 – Pond 6E, 12A, and 12C, dry – Pond 9c, no macroinvertebrates • Water and sediment analyzed by KEL • Macroinvertebrate tissue in sediment analyzed by LET, Columbia, MO, a FWS approved lab • For sediment sampling, separate samples collected from organic flocculent and underlying mineral soil
2007 2006 2005 2004 2003 60 50 40 30 20 10 0 Tissue Se (mg/kg)
Recommendations Meets Clean-up Improving Moderately Elevated, Moderately Elevated Elevated Criterion (<10 ppm) Possibly Increasing and Consistent (>15 ppm) (<5 ppm) (10-15 ppm) No Further Action Monitor Monitor Monitor and Drain or Fill Re-evaluate Risk 4C2 6A2 6A1 5 2 9C 6B 6A3 7A 4A 12A 6D1 6C 8 4B 12B 6E 10 4C1 12C 9A 11 4C3 12D 9D
Pond 4C2 6 5 Water Se (µg/l) 4 3 2 1 0 2003 2004 2005 2006 2007 2008 30 Bulk Sediment 25 Flocculent Sediment Se (mg/kg) Mineral Soil 20 15 10 5 0 2003 2004 2005 2006 2007 2008 10 8 Tissue Se (mg/kg) 6 4 2 0 2003 2004 2005 2006 2007 2008
Pond 9C 10 8 Water Se (µg/l) 6 4 2 0 2003 2004 2005 2006 2007 2008 10 Bulk Sediment Flocculent 8 Sediment Se (mg/kg) Mineral Soil 6 4 2 0 2003 2004 2005 2006 2007 2008 10 8 Tissue Se (mg/kg) 6 4 2 0 2003 2004 2005 2006 2007 2008
Pond 12A 10 8 Water Se (µg/l) 6 4 2 0 2003 2004 2005 2006 2007 2008 10 Bulk Sediment Flocculent 8 Sediment Se (mg/kg) Mineral Soil 6 4 2 0 2003 2004 2005 2006 2007 2008 10 8 Tissue Se (mg/kg) 6 4 2 0 2003 2004 2005 2006 2007 2008
Pond 12B 12 50000 10 40000 Selenium Water TDS (mg/l) Year vs TDS Water Se (µg/l) 8 30000 6 20000 4 10000 2 0 0 2003 2004 2005 2006 2007 2008 10 Bulk Sediment Flocculent 8 Sediment Se (mg/kg) Mineral Soil 6 4 2 0 2003 2004 2005 2006 2007 2008 10 8 Tissue Se (mg/kg) 6 4 2 0 2003 2004 2005 2006 2007 2008
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