Rosemont Project Hydrogeology & Water Supply

ROSEMONT PROJECT
HYDROGEOLOGY & WATER SUPPLY

ERROL L. MONTGOMERY & ASSOCIATES, INC.

PRESENTATION OUTLINE
q EAST SIDE - MINE AREA
Ø HYDROGEOLOGY
§  Drilling & Testing Program
§  Groundwater & Spring/Seep Monitoring
Ø GROUNDWATER FLOW MODELING

q WEST SIDE – SAHUARITA AREA
Ø WATER SUPPLY PLAN
Ø HYDROGEOLOGY
Ø GROUNDWATER FLOW MODELING


MINE AREA
LAND CONTROL & OWNERSHIP


PREVIOUS GROUNDWATER
INVESTIGATIONS

Ø Hargis and Harshbarger (UA Study,
1975 to 1977)
Ø Hargis and Montgomery (Monitoring,
1980 to 1982)
Ø Montgomery & Associates (2007)


MINE AREA HYDROGEOLOGIC
UNITS
q  CONTINENTAL GRANODIORITE
Ø  Intrusive Mountain Core
Ø  Dense, consolidated
Ø  Limited fracturing
Ø  Very Low Permeability and Groundwater Storage

q  PALEOZOIC CARBONATE ROCKS
Ø  Tilted to east, steeply-dipping
Ø  Broken-up, discontinuous blocks
Ø  Dense, but fractured and faulted
Ø  Groundwater flow and storage are fracture & fault controlled
Ø  Low permeability with locally moderate permeability along
fractures and faults


MINE AREA
HYDROGEOLOGIC UNITS
q MESOZOIC (Cretaceous) ROCKS
Ø  Tilted to east, moderately-dipping
Ø  Dense, but fractured and faulted
Ø  Groundwater flow and storage are fracture & fault controlled
Ø  Low permeability with locally moderate permeability along
fractures and faults

q CENOZOIC (Tertiary & Quaternary) BASIN-FILL
DEPOSITS
Ø  Gently-dipping to flat-lying
Ø  Strongly cemented, esp. near mountains and mine
Ø  Strongly to moderately cemented elsewhere
Ø  Groundwater flow and storage are limited and not fracture-
controlled
Ø  Low permeability with locally moderate permeability away
from mountains

HYDROGEOLOGIC UNITS


WELL,
PIEZOMETER
&
SPRING
(SEEP)
LOCATIONS


PHASE 1 DRILLING & TESTING
Ø Four wells constructed in pit area
§  (PC-1 through PC-4) during 2007
Ø Depths ranged from 1,020 to 1,503 feet
Ø Targeted chiefly Willow Canyon Formation
and cemented basin-fill deposits which will
make up majority of east pit wall
Ø Low permeabilities, with locally moderate
permeabilities along faults and/or dense
fracturing
Ø Well yields ranged from 2 to 50 gpm


q  Thirty wells and piezometers constructed in 2008
Ø  18 on Rosemont lands
Ø  12 on USFS lands
q  Four wells constructed in pit area (PC-5 through PC-8, and
three grouted multi-level piezometers (PZ-5, PZ-7, and
PZ-8) adjacent to PC wells
Ø  Depths ranged from 2,000 to 2,200 feet
q  PC wells completed with multiple screened intervals,
separated by blank zones with annular seals, to isolate
discreet aquifer zones for vertical characterization
q  PZ piezometers installed by grouting in pressure
transducers at borehole intervals corresponding to
perforated intervals of adjacent PC wells


q PC wells allowed for zonal pumping tests
using inflatable packer to isolate zones
q PZ piezometers allowed for monitoring of
aquifer response to PC well pumping
q Low permeabilities, with locally moderate
permeabilities along faults and/or strong
fracturing
q Well yields ranged from 20 to 45 gpm


(cont.)
Ø Eleven HC wells constructed in groups
outside but near pit area
Ø Depths ranged from 50 to 1,000 feet
Ø Generally within ½ to 1 mile of pit
Ø Provided vertical characterization of
aquifer properties using 2 or more wells
at each site, completed at different
depths
Ø Low permeabilities
Ø Well yields ranged from <1 to 36 gpm;
average 13 gpm


(cont.)
Ø Twelve RP wells constructed at distance
from pit area
Ø Depths ranged from 30 to 600 feet
Ø Provided vertical characterization of
aquifer properties using 2 or more wells at
sites <3 miles from pit, and single wells >3
miles from pit
Ø Low permeabilities
Ø Well yields ranged from <1 to 33 gpm;
average ~10 gpm


TYPICAL
DIAGRAM OF
PC & PZ
WELLS
Wells PC-7
& PZ-7


TYPICAL DIAGRAM OF
PC & PZ WELLS


TYPICAL
DIAGRAM OF
HC WELLS
Well HC-4A


TYPICAL
DIAGRAM OF
RP WELLS
Well RP-4A


PUMPING TESTS
Ø 24- and 12-hour zonal pumping tests at PC
wells, with PZ multi-level piezometers and
nearby wells as observation points
Ø 12-hour pumping tests at each HC and RP
well, with adjacent and nearby wells as
observation points
Ø Long-term (up to 30-day) pumping test
planned using 5 wells in mine area;
scheduled to begin in November


AQUIFER PARAMETERS FROM
SHORT-TERM TESTS
Ø Computed transmissivities ranged from <1 to
3,600 ft2/day
Ø Highly variable
Ø Fracture/fault controlled
Ø Preliminary computed storage coefficients
generally in range of 10-4 to 10-5
Ø The long-term, multi-well pumping test
should refine ranges and provide data to
determine aquifer response to dewatering


GROUNDWATER MONITORING
PROGRAM
q From July 2006-March 2008, water
levels measured periodically in existing
wells
q Since March 2008
Ø Water levels in wells measured and spring
flow monitored monthly
Ø Many wells equipped with continuous
water level recording devices
Ø Water quality sampling at wells and
springs

MINE
AREA
WATER
LEVELS


GROUNDWATER LEVEL TRENDS


GROUNDWATER QUALITY
Ø Groundwater and spring samples analyzed
for common and trace inorganic constituents,
radiochemical constituents & parameters,
organic compounds, and stable isotopes
Ø Groundwater quality good to excellent, with
very few AWQS or MCL constituents
exceeded
Ø TDS ranged from 190 - 1,480 mg/L
Ø Average TDS = 430 mg/L
Ø pH ranged from 6.9 to 7.9
Ø Average pH = 7.5


GROUND-
WATER
QUALITY


SPRINGS & SEEPS
Ø Seeps and springs nearest mine
monitored periodically since November
2006
Ø Larger number of seeps and springs
monitored monthly since January 2008
Ø 20 springs presently being monitored
Ø Monitoring conditions and flow monthly
Ø Obtaining samples quarterly where
practical


SPRINGS & SEEPS
q Of 20 springs/seeps being monitored:
Ø Most are dry or moist spots on ground,
with observable flow only during or
shortly after storms
Ø Four springs have sustained flow
§ Rosemont Spring (~0.1 to 0.5 gpm)
§ MC-2 (McCleary Canyon) (~0.1 gpm)
§ Deering Spring (~0.1 gpm)
§ Questa Spring (~0.1 gpm)


MODEL STUDY AREA


GROUNDWATER FLOW MODEL
q  Data Compilation and Evaluation
Ø Geologic framework
Ø Regional geologic framework – Previous investigations
Ø Hydrogeologic data from drilling/testing programs
Ø Water level and water quality data from monitoring
program
Ø Meteorological data from Rosemont and other weather
stations
Ø Data from existing wells
§  Historic water levels
§  Drillers logs
§  Water quality data
§  Well performance data



Ø Conceptual Model Discussion
§  Groundwater Recharge and Discharge
§  Hydrogeologic Flow System
§  Preliminary Assumptions


q Numerical Model Development
(Ongoing)
Ø Model Software
Ø Model Construction
§  Grid
§  Extent
§  Aquifer Parameters
§  Groundwater Recharge


q Numerical Model Development
Ø Model Calibration
Ø Model Projections
§  Quantification of Pit Dewatering Requirements
§  Impacts to Local Groundwater Levels
§  Impacts to Regional Groundwater Levels
§  Evaluation of Pit Lake Presence and Fate
Ø Model Sensitivity Analyses


WEST SIDE – SAHUARITA AREA


WATER SUPPLY PLAN


WATER SUPPLY PLAN
q Groundwater Withdrawal Permit obtained
from ADWR under A.R.S. 45-514
Ø Mineral Extraction & Metallurgical
Processing
q Recharge of CAP


WATER SUPPLY PLAN
q Water Delivery System
Ø Water supply wells
Ø 17 mile pipeline (24 ) to mine
site
Ø Boosters
Ø Design Capacity
Ø Right of Ways / Easements


SAHUARITA HEIGHTS WELLS
Ø Approximately 300 domestic wells in
Sahuarita Heights area
Ø Domestic wells in Sahuarita Heights
generally produce a few to 35 gpm
Ø Local Well Owner Protection Program
Ø Discussions with United Sahuarita Well Owners
Ø Established 11 sites for Groundwater Level and
Quality Monitoring
Ø Well database


WEST SIDE MONITORING PROGRAM


WEST SIDE HYDROGEOLOGY

Sahuarita
Heights


q  Groundwater occurs in basin-fill deposits
q  Hydrogeologic Units
Ø Ft. Lowell Formation (dry in Sahuarita Heights)
Ø Tinaja beds (principal aquifer)
q  Silty sand with minor gravelly zones
q  Depth to water 200 to 250 feet
Ø Substantially deeper during irrigation season
q  Groundwater flow toward northwest
q  Water level trends over time
Ø Wells in study area produce from a few to
more than 2,000 gpm


ROSEMONT TEST WELLS

Ø Two wells constructed to depths of 1,211
(RC-2) and 1,300 feet (E-1)
Ø Characterized basin-fill sediments and
groundwater quality
Ø Transmissivity ranged from 1,340 (RC-2) to
2,680 (E-1) ft2/day
Ø Anticipated well production 500 to 1,500
gpm
Ø Excellent groundwater quality –
TDS range 210 (RC-2) – 340 (E-1) mg/L


WEST SIDE

q Began with ADWR Tucson AMA
Groundwater Model
Ø Numerical Basin-Wide Model
Ø MODFLOW Software
Ø Updates Provided by ADWR
q Model Challenges


WEST SIDE
q Refinement of Model Following Data
Evaluation
Ø Aquifer Parameters from Drilling &
Testing
Ø Update Groundwater Pumpage
Ø Evaluate & Modify Groundwater
Recharge
Ø Santa Cruz Recharge


WEST SIDE

q Results of Model Calibration
Ø Overall match in study area
Ø Match in Sahuarita Heights area


LOCATIONS OF
CALIBRATION HYDROGRAPHS


WEST SIDE
q Rosemont Water Supply Simulations
Ø Rosemont Pumping 5,000 AF/year for 20
years
Ø Pumpage by Other Groundwater Users
Ø Recharge at USFs and WWTPs
Ø Model Results (Pending)
§  Impacts to Regional Groundwater Levels
§  Impacts to Local Domestic Wells
Ø Local-Scale Model Evaluation

Rosemont Project Hydrogeology & Water Supply

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