Well Protection Program - Groundwater Modeling Presentation
4 likes1,233 views
The presentation discusses the Rosemont groundwater project, highlighting its impact on local groundwater systems due to an open pit mine projected to be over 2,000 feet deep. It presents findings from various scientific studies and groundwater models, emphasizing the limited connection between the pit area and neighboring wells, and the anticipated effects on water levels and drawdown around the mine. Monitoring wells and community involvement are suggested to track changes in groundwater levels and minimize potential impacts.
Well Protection Program - Groundwater Modeling Presentation
- 1. Rosemont Groundwater Presented to Well Protection Program Informational Meeting April 3, 2012
- 2. Presenter n Grady O’Brien, Engineering Analytics, Inc. n Professional Geologist / Hydrogeologist n U.S. Geological Survey – 14 years n Denver and Tucson n Groundwater Consulting – 9 years n Rosemont groundwater modeling project lead for Tetra Tech n University of Wyoming / Colorado School of Mines n Project focus in desert southwest – AZ, NV, UT April 3, 2012 2
- 3. Discussion Outline n Rosemont Project Groundwater Related Highlights n Supporting Scientific Studies and Data n Understanding the Groundwater Flow System n Bedrock / Fractures / Geologic Structures n How the Open Pit Effects the Groundwater System n Will my well go dry? April 3, 2012 3
- 4. ROSEMONT SITE LOCATION 4 April 3, 2012
- 5. WELL PROTECTION AREAS April 3, 2012 5
- 6. ROSEMONT PROJECT Hydrologic Highlights n Open pit mine n 2,000+ feet deep n ~ 1 mile in diameter n Pit dewatering for 22 year life of mine n Open pit is major feature that will impact groundwater levels n Terminal Pit-lake predicted after mining April 3, 2012 6
- 7. SCIENTIFIC STUDIES Supporting Groundwater Flow Modeling 3-D hydrogeologic model n Extensive data available n Many data types n Coverage across region n Best available data used April 3, 2012 7
- 8. SCIENTIFIC STUDIES Supporting Groundwater Flow Modeling n Geology Wells used for model calibration n Site and regional scales n 3-dimensional model n Wells n 730+ water-levels for model calibration n Lithology / geology n Water quality n Aquifer Tests April 3, 2012 8
- 9. SCIENTIFIC STUDIES Supporting Groundwater Flow Modeling Springs and riparian vegetation n Springs and Streams n Discharge measurements n Water-quality data n Isotope data n Riparian vegetation n Distribution n Type April 3, 2012 9
- 10. SCIENTIFIC STUDIES Montgomery & Associates n Geology / Hydrogeologic Units n Aquifer tests / Hydraulic properties n Short-term and Long-term tests n Regional data n Riparian vegetation evapotranspiration (ET) n Water levels and water quality n Spring flows and water quality n Groundwater flow models April 3, 2012 10
- 11. SCIENTIFIC STUDIES Tetra Tech n Site Water Management n Infiltration analysis n Infiltration, seepage, fate, and transport modeling n Storm-water runoff n Davidson Canyon conceptual model n 3-dimensional hydrogeologic model n Groundwater flow model April 3, 2012 11
- 12. SCIENTIFIC STUDIES Other Contributing Sources n Arizona Geological Survey n Geologic mapping n Pima Association of Governments n Cienega Creek and Davidson Canyon n Groundwater flow model n U.S. Geological Survey n Stream flows n San Pedro and Tucson basin flow models n Several recharge analyses April 3, 2012 12
- 13. GROUNDWATER FLOW MODELS n Two regional groundwater flow models n Simulate different geologic conditions to provide wider range of impacts n Davidson Canyon Fault Zone n Davidson Canyon Dike n Backbone Fault / Flat Fault n Extensive third-party peer review approved models April 3, 2012 13
- 14. GROUNDWATER FLOW SYSTEM n Fractured bedrock n Alluvium – limited layer on top of bedrock n Major geologic structures n Faults (Backbone, Flat, Davidson Canyon) n Davidson Canyon dike n High water levels near the proposed open pit n Groundwater flow paths n From pit area flow is predominately down Davidson Canyon n From upper Cienega Creek basin, flow is into lower Cienega Creek April 3, 2012 14
- 15. Current Water Levels and Flow Direction Shading illustrates large hydraulic gradient area indicating limited groundwater flow and weak fracture connections April 3, 2012 15
- 16. FRACTURED BEDROCK n Very low bedrock permeability n Low water storage in fractures n Groundwater flows in fractures n Connections between fractures n How far do fracture connections extend? n Aquifer testing and water levels indicate that pit area is not well connected to other areas April 3, 2012 16
- 17. FRACTURE CONNECTIONS Influence of Persistence of Discontinuity on the Degree of Fracturing and Interconnectivity High water levels in pit area indicate that fractures are not well connected to lower elevation areas. Water would drain rapidly from pit area if strong connection existed. April 3, 2012 Anderson, M.P. and Woessner, W.W., 2002, Applied Groundwater 17 Modeling: Academic Press, San Diego, CA, 381p.
- 18. WELLS MUST INTERSECT FRACTURES TO PRODUCE WATER This is why neighbors may have different results with nearby wells. 18 If water April 3, 2012 producing fractures were common, everyone would have high producing wells.
- 19. FRACTURE CONNECTIONS BETWEEN the PIT and YOUR WELL n “What if there is a fracture between the pit and…” n Evidence supports lack of fracture connection n High water-levels in pit area – water not flowing ‘downhill’ because fractures are limited n Varying productivity with on-site wells show limited fracture connectivity across the site n No high discharge perennial springs in area n Conclusion is weak fracture connection April 3, 2012 19
- 20. FRACTURE CONNECTIONS BETWEEN the PIT and YOUR WELL n “The pit will suck in all of the groundwater…” n In the long term, consumptive use of the pit lake is predicted to be 100 to 230 gpm n Equivalent to a few water-supply wells n This water is “captured” from across the region n Evaporation on the pit-lake surface is “consuming” groundwater, but it is limited n Not physically possible to remove all of the groundwater April 3, 2012 20
- 21. WILL MY WELL GO DRY? n Water levels will decrease dramatically in the immediate pit area n Water-level drawdown diminishes rapidly away from pit area n Which wells will go dry depends on site specific hydrogeologic conditions, well location, and well depth Geologic map illustrating complex April 3, 2012 geology that influences drawdown 21 propagation
- 22. DEWATERED PIT n Conceptual cross section through the pit (with vertical exaggeration) April 3, 2012 22
- 23. TERMINAL PIT LAKE HYDRAULIC SINK n Conceptual cross section of the pit lake after mining ends (with vertical exaggeration) April 3, 2012 23
- 24. PREDICTED WATER LEVELS n Montgomery and Associates flow model Water levels and flow directions 1,000 years after mining ends. Flow directions similar to pre-mining with exception of pit-lake capture zone With cross section location lines used on following slides April 3, 2012 24
- 25. PREDICTED WATER LEVELS Section X-X’ Drawdown decreases rapidly away from pit Water flow flows water table, not land-surface elevation April 3, 2012 25
- 26. PREDICTED WATER LEVELS Section Y-Y’ Drawdown decreases rapidly away from pit April 3, 2012 26 Water flow flows water table, not land-surface elevation
- 27. PREDICTED WATER LEVELS Section Z-Z’ Drawdown decreases rapidly away from pit April 3, 2012 27 Water flow flows water table, not land-surface elevation
- 28. WELL PROTECTION AREAS Explanation Detailed Map Area ! Well Location Extent of Ultimate Pit Davidson Canyon Dike Proposed Tailings and Waste Rock Facilities Davidson Canyon Watershed Boundary Surface Hydrogeology Qal Quaternary and Recent Alluvium QTg Late Tertiary Alluvium QTg1 QTg1 QTg2 QTg2 Tsp Tsp Tgr Late Cretaceous/Tertiary Intrusives Kv Upper Cretaceous Volcanics Ksd Lower Cretaceous Bisbee Group Pz Cambrian and Paleozoic Formations PCc PreCambrian Granodiorite and Schist 0 1 2 3 April 3, 2012 Miles 28
- 29. HILTON RANCH AREA Explanation Wells ! Groundwater Site Inventory ! 55 Wells ! Model Targets Davidson Canyon Dike Davidson Canyon Watershed Boundary Davidson Canyon Dike may limit drawdown in this area April 3, 2012 29 0 1,500 3,000 4,500 Feet
- 30. SINGING VALLEY NORTH AREA Explanation Wells ! Groundwater Site Inventory ! 55 Wells ! Model Targets Extent of Ultimate Pit Davidson Canyon Watershed Boundary Proposed Tailings and Waste Rock Facilities Surface Hydrogeology Qal Quaternary and Recent Alluvium QTg Late Tertiary Alluvium QTg1 QTg1 QTg2 QTg2 Tsp Tsp Kv Upper Cretaceous Volcanics Ksd Lower Cretaceous Bisbee Group PCc PreCambrian Granodiorite and Schist 0 1,500 3,000 4,500 April 3, 2012 30 Feet
- 31. HELVETIA AREA Explanation Wells ! Groundwater Site Inventory ! 55 Wells ! Model Targets Extent of Ultimate Pit Davidson Canyon Watershed Boundary Proposed Tailings and Waste Rock Facilities Surface Hydrogeology Qal Quaternary and Recent Alluvium QTg Late Tertiary Alluvium QTg2 QTg2 Tgr Late Cretaceous/Tertiary Intrusives Ksd Lower Cretaceous Bisbee Group Pz Cambrian and Paleozoic Formations PCc PreCambrian Granodiorite and Schist April 3, 2012 0 1,500 3,000 4,500 31 Feet
- 32. PREDICTED GROUNDWATER LEVEL DRAWDOWN Drawdown contours are composite, worst case from M&A and Tetra Tech flow models Areas within 10-foot drawdown prediction after 150 years are included in Well Protection Program April 3, 2012 32
- 33. GROUNDWATER LEVEL FLUCTUATIONS Large water-level fluctuations can occur with no mining effects Short Term Long Term Time Period 3 years 37 to 55 years (2007-2009) No. of Wells 14 52 Minimum Fluctuation (ft) 0.7 0.7 Maximum Fluctuation (ft) 33.1 69.0 Average Fluctuation (ft) 7.1 19.7 (Montgomery & Associates, 2010b) April 3, 2012 33
- 34. MONITORING WELLS n Determine long-term trends and mine-induced impacts n Early warning for mitigation n On-going monitoring network n Wells and springs n Point of Compliance wells n Required in ADEQ Aquifer Protection Permit n Davidson Canyon wells (proposed) n Sentinel Wells (planned) April 3, 2012 34
- 35. MONITORING WELLS n Proposed Davidson Canyon monitoring wells n Near Hilton Ranch area April 3, 2012 35
- 36. MONITORING WELLS n Homeowner wells n Rosemont is seeking volunteer homeowners n Document water levels so that mining impacts can be determined n Start prior to mining n Simplify potential future claim process n Minimal disturbance to homeowner April 3, 2012 36
- 37. CONCLUSIONS n Different groundwater models result in similar predictions n Provides confidence that predictions are reasonable n Rate and direction of drawdown propagation will vary n Different areas will have different impacts n Away from the immediate pit area predicted drawdown is within the range of natural fluctuations n Beneficial for homeowner’s to obtain history of water- level changes by volunteering to allow measurements in their wells April 3, 2012 37