A presentation on the groundwater models (both Tetra Tech and EL Montgomery) associated with the Rosemont Copper Project Operations. This presentation was given by Engineering Analytics to the Forest Service, Bureau of Land Management, Fish and Wildlife Service, Arizona Game and Fish and their contractors during a meeting in March 2012.

1. Regional Groundwater
Flow Models
Presented to
U.S. Fish and Wildlife Service
Grady O’Brien
March 8, 2012

2. Discussion Outline
 Introduction
 Modeling Objectives, Approaches, and Model Uses
 Data / Pumping / Fractures / GW-SW interactions
 Interpreting Results – What to Consider
 Model Construction Comparison
 Model Prediction Comparison
 Conclusions
March 8, 2012 2

3. INTRODUCTION
Rosemont Site Location
3
March 8, 2012

4. Regional Site Map for the Proposed Rosemont Mine

5. ROSEMONT PROJECT
Hydrologic Highlights
 Open pit mine
 2,000+ feet deep
 ~ 1 mile in diameter
 Pit dewatering for 22 year life of mine
 Major facilities
 Heap leach pads
 Dry stack tailings
 Waste rock
March 8, 2012 5

6. MODELING OBJECTIVES
 Predict regional hydrologic impacts
 Sensitive areas
 Davidson Canyon
 Cienega Creek
 Las Cienegas National Conservation Area
 Sensitive features
 Springs
 Stream flow
 Riparian vegetation
March 8, 2012 6
 Aquatic life

7. IMPORTANT HYDROLOGIC
PROCESSES
 Groundwater and surface-water interactions
 Nature of spring flow
 Nature of stream flow
 Fractured bedrock
 Hydraulic connections
 Recharge areas
 Backbone fault
 Mountain front
 Stream channels
March 8, 2012 7

8. MODELING APPROACH
 Satisfy the objectives
 Appropriate scale
 Site versus Regional
 Fracture network versus porous media
 Simulate hydrogeologic features
 Data availability
March 8, 2012 8

9. MODELING SCALE INFLUENCES
APPROACH
 Regional impacts  regional scale
 Regional scale  regional resolution
 Data availability
 Fracture network versus porous media
March 8, 2012 9

10. DATA AVAILABILITY
 Geology (site and regional scales)
 Wells
 730+ water-level targets
 Lithology
 Water quality
 Springs and Streams
 Discharge
 Water quality
 Riparian vegetation
March 8, 2012 10
Wells used for model calibration (Tetra Tech, 2010)

11. DATA AVAILABILITY
 Montgomery & Associates
 Geology / Hydrogeologic framework
 Aquifer tests / Hydraulic properties
 Short-term and Long-term tests
 Regional data
 Evapotranspiration (ET)
 Water levels
 Spring flows
March 8, 2012 11

12. DATA AVAILABILITY
 Tetra Tech
 Site Water Management
 Infiltration analysis
 Infiltration, seepage, fate, and transport
modeling
 Storm-water runoff
March 8, 2012 12

13. DATA AVAILABILITY
 Arizona Geological Survey
 Geologic mapping
 Pima Association of Governments
 Cienega Creek
 Davidson Canyon
 U.S. Geological Survey
Stream flows
 San Pedro flow model
 Tucson basin
March 8, 2012 13
 Various recharge analyses

14. TETRA TECH ANALYSES / REVIEW
 Recharge
 Hydraulic properties
 Short-term, single well tests
 Long-term, multiple well tests
 Spring flow
 Field observations
 Water-level weighting
 3D hydrogeologic framework model
 Davidson Canyon conceptual model
March 8, 2012 14

15. DATA AVAILABILITY
 Extensive data available for model input
 Coverage across the region
 Best available data used
March 8, 2012 15

16. GROUNDWATER PUMPING
 Significant pumping in Sonoita and Elgin areas
 Declining water levels
 Outside of model domain
 Exempt wells (<35 gpm)
 Hilton Ranch
 Singing Valley
 Pumping data unavailable
 Water-level data do not show pumping impact
March 8, 2012 16

17. FRACTURE NETWORK versus
POROUS MEDIA
 Fracture networks
 Highly data intensive
 Practical for very small areas
 Not used for regional models
 Research site specific processes
 Equivalent Porous Media (MODFLOW)
 Widely used and accepted
 Well developed functionality
 Appropriate based on objectives and
hydrogeology
March 8, 2012 17

18. FRACTURED BEDROCK
 Very low matrix permeability
 Low storage
 Types of fractures
 Interconnected, blind, diffuse
 Hydraulic connections
 Scale dependent - small versus large areas
 How far do connections extend?
 At what scale does it behave as a porous
media?
March 8, 2012 18

19. FRACTURED BEDROCK
Intersecting Fractures
March 8, 2012 19

20. FRACTURE CONNECTIVITY
Influence of Persistence of Discontinuity on the Degree of
Fracturing and Interconnectivity
March 8, 2012
Anderson, M.P. and Woessner, W.W., 2002, Applied Groundwater 20
Modeling: Academic Press, San Diego, CA, 381p.

21. GROUNDWATER FLOW
THROUGH FRACTURES
Type 1: Flow and storage only in
fractures (single porosity)
March 8, 2012
Nelson, R.A.,2001, Geologic Analysis of Naturally 21
Fractured Reservoirs (2nd Edition): Elsevier.

22. HYDRAULIC CONNECTION BETWEEN
PIT AND SENSITIVE AREAS
 “What if there is a fracture between the pit
and…”
 Evidence?
 Davidson Canyon fault zone
 High water-levels in pit area
 No large, perennial springs in Davidson
Canyon
 Water quality and isotopes
 Weak connection
March 8, 2012 22

23. INTERACTION OF STREAMS
and GROUNDWATER
March 8, 2012 23
Alley, W.M., Reilly, T.E., and Franke, O.L., 2007, Sustainability of Ground-Water Resources: U.S.
Geological Survey Circular 1186, available at http://pubs.usgs.gov/circ/circ1186/index.html.

24. INTERACTION OF STREAMS
and GROUNDWATER
March 8, 2012 24

25. MODELING APPROACH AND USES
 Conditions to simulate?
 Average Annual
 Average Seasonal
 Non-Average – response to specific changes
 Input data consistent with conditions
 Recharge (precipitation)
 Evapotranspiration
 Water levels
 Stream flow
March 8, 2012 25

26. AVERAGE ANNUAL CONDITIONS
 Reference point for relating changes
 Identify important processes
 Identify sensitive areas
 Relative changes – not absolute values
 In context of natural variability
March 8, 2012 26

27. INTERPRETING RESULTS
What To Consider – How to Use
 Representation of the conceptual model –
major features
 Model boundaries
 Proximity to stresses
 Inflows and outflows
 Reasonable and conservative parameter
values
 Water budget
 Calibration targets and statistics
March 8, 2012 27

28. INTERPRETING RESULTS
What To Consider – How to Use
 Conditions being simulated – average annual
 No natural seasonal or annual variations
 Predictions – best estimate with best
parameter values
 Sensitivity analysis – vary parameter values
 Compare predicted impacts to natural
variability
March 8, 2012 28

29. INTERPRETING RESULTS
What To Consider – How to Use
 Identify most important features and conditions
 Identify where to monitor
 Identify where and how to mitigate impacts
March 8, 2012 29

30. MODEL CONSTRUCTION COMPARISON
Tetra Tech (2010) and Montgomery & Associates (2010)
 MODFLOW-SURFACT code
 Steady-state conditions (current / pre-mining)
 Calibrated to stable, observed water levels
 M&A calibration to 30-day test
 Mining phase (22 years)
 Simulates pit deepening in 2 year steps
 Pit dewatering simulated with drains
 Post-closure phase (1,000 years)
 Pit-lake formation simulated with LAK2 package
March 8, 2012 30

31. MODEL CONSTRUCTION COMPARISON
 External model boundaries
 Geology
 Recharge
 Streams
 ET
March 8, 2012 31

32. MODEL GRID
AND
EXTERNAL
BOUNDARY
CONDITIONS
Montgomery & Associates (2010)

33. MODEL LAYERS
Tetra Tech (2010)
March 8, 2012 33

34. CONCEPTUAL MODELS
 Tetra Tech (2010)
 Davidson Canyon Dike
 Backbone Fault
 Montgomery & Associates (2010)
 Davidson Canyon Fault Zone
 Backbone Fault
 Flat Fault
March 8, 2012 34

35. GEOLOGY
(Tetra Tech, 2010)

36. GEOLOGY
(Montgomery and
Assoc., 2010)

37. HYDRAULIC
CONDUCTIVITY
(Tetra Tech, 2010)

38. HYDRAULIC
CONDUCTIVITY
(Montgomery and
Assoc., 2010)

39. GEOLOGY TO FLOW MODEL

40. GEOLOGY
March 8, 2012 40

41. RECHARGE
Precipitation – runoff
approach by
surface-water basin
(Tetra Tech, 2010)

42. RECHARGE
Simulated
pre-mining steady-
state recharge
(Tetra Tech, 2010)

43. RECHARGE
Simulated recharge -
before and during
22-year mining
period
(Montgomery & Associates,
2010)

44. RECHARGE
Post-closure
recharge in project
facility area
(Tetra Tech, 2010)

45. RECHARGE
Simulated recharge
for mining facilities
for 1,000-year post-
mining period
(Montgomery & Associates,
2010)

46. Evapotranspiration
(ET)
(Montgomery & Associates,
2010)

47. MODEL PREDICTION COMPARISONS
 Pit-lake formation and inflows
 Drawdown propagation
 Stream flow changes
 ET changes
March 8, 2012 47

48. MODEL PREDICTION COMPARISON
Pit-Lake Formation and Inflows
Pit Lake Conceptual Model (Tetra Tech, 2010b)
March 8, 2012 48

49. MODEL PREDICTION COMPARISON
Pit-Lake Formation and Inflows
Simulated Pit Lake Water Balance (Tetra Tech, 2010)
March 8, 2012 49

50. MODEL PREDICTION COMPARISON
Pit-Lake Formation and Inflows
Simulated Pit Lake Water Balance (Montgomery and Associates,
2010)
March 8, 2012 50

51. DRAWDOWN
Simulated drawdown
at end of mining
(Tetra Tech, 2010)

52. DRAWDOWN
Simulated drawdown
at end of mining
(Montgomery & Associates,
2010)

53. DRAWDOWN
Simulated drawdown
20 years after
closure
(Tetra Tech, 2010)

54. DRAWDOWN
Simulated drawdown
20 years after
closure (Montgomery &
Associates, 2010)

55. DRAWDOWN
Simulated drawdown
150 years after
closure
(Tetra Tech, 2010)

56. DRAWDOWN
Simulated drawdown
150 years after
closure
(Montgomery & Associates,
2010)

57. DRAWDOWN
Simulated drawdown
1,000 years after
closure
(Tetra Tech, 2010)

58. DRAWDOWN
Simulated drawdown
1,000 years after
closure
(Montgomery & Associates,
2010)

59. STREAMS
Stream gage
locations and
simulated flows
(Tetra Tech, 2010)

60. STREAMS
Simulated Stream
Flow
(Montgomery & Associates,
2010)

61. STREAM FLOW
CHANGES
Simulated change in
stream flows at end
of operations
(Tetra Tech, 2010)

62. STREAM FLOW
CHANGES
Simulated change in
stream flows 1,000
years post closure
(Tetra Tech, 2010)

63. MODEL PREDICTION COMPARISON
Stream Flow Changes
Impact of Dewatering at Cienega Creek
(Montgomery & Associates, 2010)
March 8, 2012 63

64. MODEL PREDICTION COMPARISON
Stream Flow Changes
Impact of Dewatering at Davidson Canyon
(Montgomery & Associates, 2010)
March 8, 2012 64

65. MEASURED STREAM FLOW CHANGES
March 8, 2012 65

66. FLUCTUATION IN
GROUNDWATER LEVELS
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)
March 8, 2012 66

67. SENSITIVITY ANALYSIS
Tetra Tech
 Most sensitive parameters
 Bedrock specific yield decrease (at 150 years)
 Basin fill specific yield increase (at 150 years)
 Recharge near pit (no infiltration due to facilities)
 20-percent pit lake evaporation increase
March 8, 2012 67

68. SENSITIVITY
ANALYSIS
Tetra Tech
Bedrock specific yield
decrease
(at 150 years)

69. SENSITIVITY
ANALYSIS
Tetra Tech
Basin fill specific yield
decrease
(at 150 years)

70. SENSITIVITY
ANALYSIS
Tetra Tech
Steady State Recharge
near pit
(no infiltration due
to facilities)

71. SENSITIVITY
ANALYSIS
Tetra Tech
Steady State Recharge
near pit
(no infiltration due
to facilities)

72. SENSITIVITY
ANALYSIS
Tetra Tech
20-percent pit lake
evaporation increase

73. CONCLUSIONS
 Different conceptual models provide similar
predictions
 Rate and direction of drawdown propagation
varies
 Impacts are generally within the range of natural
fluctuations at distant locations
 Stream and riparian vegetation impacts depend
on groundwater and surface-water interactions
 Groundwater disconnected from Davidson Canyon stream
channel
March 8, 2012 73