Ross ISR Groundwater ModelGroundwater Model Overview

October 26, 2010

Ross ISR Groundwater Model Overview• Groundwater Vistas Software

• Uses USGS public domain(MODFLOW)• Widely used and accepted.

• Model is regional • Detailed to simulate local well effects

Groundwater Model Goals1. Identify potential influences to the surficial aquifer and

surface impoundments. 2. Identify potential impacts (if any) to adjacent water

rights.3. Estimate long term impacts from ISR recovery.4. Estimate adequate perimeter well offset/setback

distances within project area.5. Demonstrate the ability to identify and remedy a lateral

excursion (i.e. lixiviants moving out of ore zone).6. Restoration time/efficiency analysis.7. Wellfield optimization.8. Optimize wellfield bleed rate

Groundwater Model Building Blocks1. Geology2. Understanding of groundwater flow

system3. Initial potentiometric surfaces4. Stresses to the aquifer system5. Hydraulic parameters

Bedrock Geology in Project Area

Conceptual Geologic Cross Section

Lance Uranium Project Geologic Modeling

Utilizing GEMCOM software to produce a 3D subsurface Geologic model• Central database incorporates historic and current drilling data• Collaborative geologic and resource data guides development program• 3 Dimensional control of key geologic surfaces validated against known drill hole data points

Created solid surfaces – shown with 3x vertical exaggeration

Resulting surface is much more well defined than 

previous “hand”

estimated surfaces from other 

available methods.

Resulting Defined Surfaces

Regional Fox Hills Groundwater Surface

• Data Sources• Water Supply

Wells

• Project drilling

• Natural springs

Fox Hills Groundwater Discharge Zone

USGS MappedFox Hills Outcrop

GW Discharge Location

Existing Stresses to the System1. Pre-1980 No significant stresses2. 1980-Present Oil field water supply wells

Hydraulic Parameters1. Hydraulic Conductivity

1. Strata monitor wells (pump tests)2. Nubeth monitor wells (pump tests)3. Core holes4. Literature values

2. Specific Storage1. Pump tests2. Literature values

Model External Boundary Conditions

Layer 6 (OZ)Pre-1980 Potentiometric surface

Recharge

Recharge spatial distribution based on NRCS soils mappingRecharge rates adjusted during model calibrationDrain discharge rates and surficial aquifer elevations used as calibration targets.

Model Development1. Three Step Process

1. Steady State Pre-1980 Model.1. Calibration step.

2. Transient 1980-2010 model1. Simulates Oil Field Water Supply Well

Production for 30 years2. Verified to 2010 surface

3. ISR Recovery Simulation.

Model Calibration1. Steady state (pre-1980) calibration

1. GHB’s2. Recharge rates.

2. Transient (1980-2010) calibration1. Specific Storage (not particularly sensitive)2. Hydraulic Conductivity (heterogeneity added in

layers 4 (SM) and 6 (OZ)

Hydraulic conductivity

Actual measured K values input where available.Automatic parameter estimation technique (PEST) used to add heterogeneityGoal was to match measured heads in monitor wells.

Model Calibration Summary1. Calibration to monitor wells in OZ very

good.1. Total estimated drawdown in OZ = 200ft2. Largest residual at monitor well 4.9 ft3. Percent error less than 2.5 percent of drawdown

2. Calibration to other layers acceptable1. Less data available2. Pre-1980 water Potentiometric surfaces not available

ISR Recovery Simulation Regional Impacts

1.Impacts to surficial system minor1. Losses from streams occur from infiltration across OZ

outcrop 950’ and 800’ of channel in Little Missouri River and Good Lad Creek, respectively.

2. Modeled impacts less than 2 gpm.

2.Minor drawdown recorded in stock and water wells completed within OZ and SM aquifers.3.“Merit” water supply wells will see significant drawdown. 4.Aquifer recovery occurs 5-20 years depending on scenario

Pre-ISR Simulation Flow Vectors

Normal ISR simulation Flow Vectors

Excursion Flow Vectors

Excursion Recovery Flow Vectors

Head Response at Various Monitor Points

ISR Sim-Model Applications1. Regional impacts can be evaluated.2. Wellfield balance can be obtained by

adjusting inj/rec flows.3. Wellfield progression can be optimized4. Excursions and excursion recovery can be

simulated5. Bleed rate can be optimized6. Perimeter wells can be evaluated7. Wellfield restoration can be evaluated

Questions

July 2010 Aquifer Pump Tests

Bedrock Geology in Project Area