B-7. Predictive Assessment Model of Quaternary Alluvium Hydrogeology. J:\scopes\04w018\10000\FVD reports\final EIA\r-EIA app.doc

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1 B-7 Model of Quaternary Alluvium Hydrogeology J:\scopes\04w018\10000\FVD reports\final EIA\r-EIA app.doc

2 PREDICTIVE ASSESSMENT MODELING OF THE QUATERNARY ALLUVIUM HYDROGEOLOGY EAGLE PROJECT MARQUETTE COUNTY, MICHIGAN February 2006 P REPARED FOR Kennecott Eagle Minerals Company, Inc., North Jackson Company, and Foth & Van Dyke and Associates, Inc. P REPARED BY

3 CONTENTS INTRODUCTION...1 OBJECTIVES FOR PREDICTIVE ASSESSMENT MODELING...1 CONCEPTUAL BASIS...2 REPRESENTATION OF MINE INFLOW AND TREATED WATER INFILTRATION5 Representation of Mine Inflow... 5 Representation of Treated Water Infiltration... 8 PARTICLE TRACKING...8 MODIFIED BASELINE CONDITIONS...9 RESULTS BASE CASE...9 Effects of Mine Inflow on Alluvium Groundwater Levels... 9 Effects of Mine Inflow on Streamflow Hydraulic Components (Sources) of Mine Inflow Effects of Treated Water Infiltration RESULTS UPPER BOUND CASE...12 Effects of Mine Inflow on Alluvium Groundwater Levels Effects of Mine Inflow on Streamflow Hydraulic Components (Sources) of Mine Inflow Effects of Treated Water Infiltration TWO-DIMENSIONAL FOCUSED ANALYSIS...15 Model Conditions Results REFERENCES...20 Marquette County, MI i

4 FIGURES 1. Stream Reaches and Associated Water Budget Zones A Zone 2. Location of Flux Boundaries 3. Location of Bedrock Calibration Points and Recharge Boundary Cells for Treated Water Infiltration System 4. Modeled Equipotentials in Model Layer 2 at Ten Years Base Case 5. Simulated Head versus Time in QAL023B Base Case 6. Hydraulic Components of Mine Inflow Base Case 7. Modeled Groundwater Mound in Alluvium Near Treated Water Infiltration System at Ten Years Base Case 8. Particle Tracks (Pathlines) from Treated Water Infiltration after Ten Years Base Case 9. Modeled Equipotentials in Model Layer 2 at Ten Years Upper Bound Case 10. Drawdown after Ten Years in Model Layer 2 Upper Bound Case 11. Simulated Head versus Time in QAL023B Upper Bound Case 12. Simulated Streamflow Changes Upper Bound Case 13. Hydraulic Components of Mine Inflow Upper Bound Case 14. Modeled Groundwater Mound in Alluvium Near Treated Water Infiltration System at Ten Years Upper Bound Case 15. Particle Tracks (Pathlines) from Treated Water Infiltration after Ten Years Upper Bound Case Marquette County, MI TABLES 1. Flow Rates Assigned to Flux Boundaries Base Case 2. Flow Rates Assigned to Flux Boundaries Upper Bound Case 3. Simulated Flow Reductions in Modeled Stream Reaches Base Case 4. Simulated Flow Reductions in Modeled Stream Reaches Upper Bound Case ii

5 INTRODUCTION This report summarizes additional modeling completed for the being undertaken by Kennecott Eagle Minerals Company (KEMC). The general purpose of this predictive assessment is to evaluate the degree that mining activities may affect the hydrogeology of the Quaternary alluvium beneath the Yellow dog Plains. In 2005, a baseline groundwater flow model was created using Visual MODFLOW (version 4.0). The primary inputs for that baseline model are described in the report Baseline Groundwater Flow Model (Fletcher Driscoll & Associates, 2005). The baseline model has been updated based on recent field data and enhanced to support predictive assessment modeling. Additionally, a two-dimensional slice analysis is presented that evaluates the potential hydraulic effects of lowered groundwater heads deeper in the alluvium. The predictive assessments and the slice analysis were completed using Visual MODFLOW (version 4.1), which implements the MODFLOW-2000 finite-difference code commonly used for hydrogeologic modeling. The following reports were used to support this second phase of modeling: Environmental Baseline Study Stage 1, Environmental Baseline Study Stage 2, Comprehensive Summary of Hydrological Reports, and Supplemental Wetland Hydrology Baseline Study all prepared by North Jackson Company, Bedrock Hydrogeologic to Assess Inflow to the Proposed by Golder Associates, Inc., and - Analytical Calculations for Treated Water Infiltration System by Foth and Van Dyke & Associates. Marquette County, MI OBJECTIVES FOR PREDICTIVE ASSESSMENT MODELING This phase of groundwater modeling focuses on the hydraulic response in the alluvial groundwater system that may occur as the result of proposed mining operations for the KEMC. The results of this analysis provide the basis for understanding how groundwater and surface water resources may be affected by mining. Project operations may affect hydraulic conditions in the project area in three primary ways: First, as the mine is developed and during subsequent operations, groundwater may seep into the mine from surrounding bedrock and any water-conductive features in the bedrock. Such seepage (inflow) draining from the bedrock would likely reduce water levels in the bedrock, and possibly, in the alluvium overlying the bedrock. Second, if groundwater levels in the alluvium are affected, these reduced levels may cause minor flow reductions in nearby streams. Third, as treated water from operations is introduced into the groundwater system by the engineered infiltration system, groundwater levels will rise 1

6 beneath and downgradient of the infiltration area. Determining the magnitude of these effects is the overall goal of this modeling effort. Specifically, objectives for this report are as follows: Define the groundwater flow field beneath the Yellow Dog Plains during operation of the mine and identify the extent of any groundwater level reduction (drawdown) that may occur over time in the uppermost saturated alluvium as the result of groundwater seeping into the mine (mine inflow) during operation. Determine any changes in streamflow that may occur over time as a result of mine inflow. Delineate the sources that contribute to water entering the mine during operations. Determine any rise in groundwater levels over time resulting from treated water discharge via the groundwater distribution system. Determine the route taken by water released at the groundwater infiltration area once it reaches the water table and establish the distance traveled for ten years following the end of mine operations. Marquette County, MI CONCEPTUAL BASIS The baseline groundwater flow model for the provides the foundation for the predictive assessment model. Model characteristics, including the structure and hydraulic parameters and boundary conditions used, were described in the Baseline Groundwater Flow Model report (Fletcher Driscoll & Associates, 2005). Most characteristics of the baseline model are retained for the predictive assessment model. The objectives for the assessment model and the availability of additional data, however, call for some modification of the baseline model. For example, the baseline model was run as a steady state simulation, whereas transient simulations are required to achieve the objectives for the predictive assessment model. Changes made to the baseline flow model are presented briefly below; new conditions relevant to analyzing mine inflow and treated water infiltration are discussed more fully in the following section, Six flux centers are added to the predictive assessment model. These discrete locations represent the accumulated mine inflow from the surrounding bedrock and 2

7 are represented using MODFLOW flux boundaries. 1 Transient inflow rates for these flux centers have been determined by separate bedrock modeling done by Golder Associates using the finite-element modeling code FEFLOW (Golder, 2006a). This bedrock modeling incorporates the progression of mine development and is described in greater detail in the next section. Marquette County, MI The previously constructed baseline model was run to steady state. Because the predictive assessment model must accommodate variations in the mine inflow rate over time, it is run as a transient model covering the ten-year mining period and the ten-year post-mining period. Each change in mine inflow rate is represented by a stress period and each stress period is divided into ten time steps. Other than inflow rate, the model inputs represent average conditions and remain constant throughout the modeled period. Stage 1 and 2 field data indicate that some seasonal variations in groundwater levels and streamflow occurs, groundwater potentiometric maps of the area showing baseline conditions indicate that fairly consistent hydraulic gradients and flow regimes exist across a watershed-scale area (North Jackson, 2004, North Jackson, 2005a and North Jackson, 2005b). Thus, constant values for parameters such as recharge and stream stage should provide a good representation of the general interactions of area hydraulic features, mapping groundwater basins, and estimating the effects of mining on average groundwater and stream levels. Model layers 12 and 13 (lowest two layers) were inactive in the baseline model. These layers represent deeper bedrock with occasional water conductive features and are activated for the predictive assessment model to extend the domain to the depth of the mine workings. Initial hydraulic parameters for these layers were determined from the Golder bedrock model, but have been subsequently adjusted so that bedrock heads and the drawdown pattern corresponded between the Visual MODFLOW and FEFLOW models. More information about this adjustment is given in the next section. Upper model layers east of the ore body were adjusted based on the boring logs of several new monitoring wells (QAL024 to QAL044) (North Jackson, 2006a). As a 1 A flux boundary condition is established in a MODFLOW and Visual MODFLOW by adding a pumping well to the model. This is a module in the MODFLOW Well Package. The term flux boundary, however, is often used and preferred because it more accurately represents the behavior of this boundary condition in the MODFLOW code. 3

8 result, the method for representing the high bedrock outcrop east of the ore body was adjusted to avoid horizontally disconnected model cells. Model cells also were shifted downward and hydraulic parameters representing the upper bedrock were assigned to layers defined elsewhere in the model as alluvial units. Marquette County, MI Hydraulic conductivity values from some alluvial units were adjusted to represent more accurately conditions in the vicinity of the new monitoring wells. Five active water budget zones were established in the baseline model using the MODFLOW Zone Budget package. These zones were established to represent subregional water budgets within the four watersheds and subwatersheds in the model domain. Five new zones have been added to the predictive assessment model to enhance the water budget definition for the upper reaches of the Main Branch of the Salmon Trout River and the Yellow Dog River. The ten active water budget zones now represent the model water balance in the groundwater system volume contributing to the following stream reaches (Figure 1): Main Branch of the Salmon Trout River from stream gauging location STRM001 to the QAL023B area (overlying the ore body) Main Branch of the Salmon Trout River from the QAL023B area to stream gauging location STRM002 Main Branch of the Salmon Trout River from STRM002 to the terrace escarpment Main Branch of the Salmon Trout River from the terrace escarpment to stream gauging location STRM004 East Branch of the Salmon Trout River West Branch of the Salmon Trout River Yellow Dog River upstream of YDRM003 Yellow Dog River from YDRM003 to YDRM001 Yellow Dog River from YDRM001 to YDRM002 Yellow Dog River downstream of YDRM002 Of these locations, the Yellow Dog River downstream of YDRM002 is not considered further in the analyses to follow because no flow data were available for calibration of the original baseline flow model in that area. Locations of all ten zone boundaries are based on particle tracking and analysis of groundwater velocity vectors in the model. Evaluation of changes in the model water balance for each of the nine primary zones will reveal if streamflow is affected by mining activities. The 4

9 added water budget zones provide better delineation in areas where any effects are most likely to occur. Recharge assignments originally made in the baseline model are increased by 5 to 10 percent in some areas north of the ore body (from Marquette County, MI the terrace escarpment north). These adjustments were necessary to establish calibration of the predictive assessment model to the same level of statistical rigor as the baseline model because of the addition of the two deep bedrock layers as well as other layer and hydraulic conductivity adjustments made in the vicinity of the terrace escarpment. Nevertheless, these modified rates are still lower than those assigned to the Yellow Dog Plains. This difference is supported by the different landscape conditions in the two areas: a generally dense woodland cover and highangle slopes inhibit precipitation recharge on and north of the terrace escarpment, whereas the open and flat terrain of Yellow Dog Plains allows precipitation to reach the ground surface readily and percolate into the subsurface. Six model cells are selected in the uppermost model layer (layer 1) to coincide with the area proposed for the treated water infiltration system. Supplemental recharge is assigned to these cells based on infiltration rates proposed for the system. Details on these recharge assignments are provided in the next section. These modifications support a more rigorous analysis of groundwater hydraulics under the transient conditions of mine development and operation. They also provide a better representation of the current understanding of actual field conditions. REPRESENTATION OF MINE INFLOW AND TREATED WATER INFILTRATION REPRESENTATION OF MINE INFLOW The predicted rate at which groundwater will flow into the proposed mine from surrounding bedrock was simulated in the predictive assessment model using six flux boundaries. These flux boundaries are located in six separate model cells as shown in Figure 2. The predicted rate at which groundwater will flow into the proposed mine from surrounding bedrock was estimated using the finite element modeling code FEFLOW and consolidated into these six flux centers (Golder, 2006a). FEFLOW was used because the infrequent occurrence of water-conductive features in the deep bedrock encountered by 5

10 the mine can be represented more accurately, thus, providing a more accurate assessment of mine inflow. 2 The intake portions of the flux boundaries used in the MODFLOW model are placed in the following depths, based on the characterization of the mine workings as represented in the FEFLOW model (from east to west): Marquette County, MI Flux Boundary 1 (located in the decline and portal ramp to the surface) intake at 353 to 383 meters (1158 to 1257 feet) above mean sea level (amsl) Flux Boundary 2 (located in the decline and portal ramp to the surface) intake at 323 to 353 meters (1060 to 1158 feet) amsl Flux Boundary 3 (located in the located in the decline and portal ramp to the surface) intake at 293 to 323 meters (961 to 1060 feet) amsl Flux Boundary 4 (located in the decline and portal ramp to the surface50) intake at 263 to 293 meters (863 to 961 feet) amsl Flux Boundary 5 (located in the development workings) intake at 143 to 383 meters (469 to 1257 feet) amsl Flux Boundary 6 (located in the development workings) intake at 143 to 383 meters (469 to 1257 feet) amsl Transient flow rates were determined for two scenarios in FEFLOW: a base case and an upper bound. The base case scenario uses hydraulic parameters based on calibration of the finite element model to results from an extended, multi-well bedrock pumping test conducted in late summer 2005 (Golder, 2006b). The base case uses very low values of hydraulic conductivity and storage for the upper and lower bedrock. The upper bound scenario assumes somewhat increased values for lower bedrock; however, these values can still be characterized as low. The values include increases both for the rock matrix properties and the water-conductive features. The water-conductive features are also represented as more frequent, extensive and highly connected in the upper bound case. The differences in the two scenarios result in greater mine inflow rates for the upper bound case than for the base case (Golder, 2006a). These same two scenarios are also evaluated in the predictive assessment modeling. Flow rates from multiple stress periods used for FEFLOW bedrock modeling were combined to 2 Water-conductive features that occur at closer intervals can often be represented as equivalent porous media. 6

11 reduce the number of stress periods in the MODFLOW model. Rate changes of less than 1 percent were combined into single time steps in this process. Flow rates used for each flux boundary both base and upper bound cases are shown in Tables 1 and 2. Marquette County, MI Hydraulic parameters used in FEFLOW serve as the starting basis for average values assigned to bedrock in MODFLOW. However, because of the different simplifying assumptions used in the FEFLOW model and because MODFLOW does not represent discrete water-conductive features as accurately, hydraulic conductivity and storage parameters required adjustment in the MODFLOW simulations to produce a better fit with the FEFLOW results. Ten calibration points were placed among and perpendicular to the flux boundaries to aid the calibration (Figure 3). Bedrock calibration points (CalObs 1 through CalObs 9) each have five observation points distributed vertically in model layers 9, 10, 11, 12 and 13. CalObs 10 has observation points placed only in layers 11, 12, and 13 because of elevation differences between the two models at that location. Thus, a total of 48 observation points were used in the calibration. Drawdown values were calculated from FELOW head data and were contoured for use as additional guidance in the calibration. The model is calibrated considering the conditions both for the base-case and upperbound simulations. Thus, the calibration process for the predictive assessment model is iterative to assure that hydraulic parameters for the upper bedrock are consistent for both scenarios. The conductivity and storage parameters for lower bedrock are integrated values that represent the combined hydraulic effects of the bedrock matrix and waterconductive features. Overall, the calibration goals were to 1) minimize the root mean squared error for all observation points (generally less than 15 percent of the total drawdown in the bedrock at the observation points), 2) minimize the mean error in the model layers representing upper bedrock, 3) obtain a reasonable visual match between drawdown contours from both models, and 4) use, as much as possible, the bedrock hydraulic parameters assigned to the FEFLOW model. Differences in model construction (for example, cell/element dimensions, layer thicknesses, boundary conditions at the top of the bedrock and especially the representation of water-conductive features) require some parameter adjustment and also prevent precise calibration at all bedrock locations. Nevertheless, by assuring that drawdowns from the FEFLOW model were generally well represented at critical locations in the MODFLOW model and that the hydraulic parameters were close to those used in FEFLOW as established by a reliable, long-term bedrock pumping test, 7

12 the objective of determining the effects of mine inflow on the uppermost alluvium should be achieved. REPRESENTATION OF TREATED WATER INFILTRATION Marquette County, MI The proposed system for infiltrating treated water from operations is designed to accommodate discharge of 400 gallons per minute (gpm) over an area of 154,000 square feet based on an infiltration rate of 0.5 feet per day (Foth & Van Dyke and Associates Inc., 2006). Based on results from the bedrock modeling, however, anticipated application rates are 80 gpm for the base case and 255 gpm for the upper bound case, which includes the range of stormwater runoff from the surface facilities to the treatment system (Foth & Van Dyke and Associates Inc., 2006). Given these application rates, the calculated infiltration rate is 0.1 feet per day (0.5 X 80 / 400) for the base case and 0.32 feet per day (0.5 X 255 / 400) for the upper bound case. A recharge boundary is used to represent the proposed infiltration area in the predictive assessment model (Figure 3). Supplemental recharge is applied to six model cells at the location of the planned infiltration system. Each model cell is 164 feet by 164 feet (50 by 50 meters); thus, the infiltration area as represented in the model is 161,474 square feet. Because the designed and modeled discharge areas are different sizes, the design recharge rate must be adjusted proportionately (normalized). The normalized infiltration rates used in the model are determined by multiplying each design infiltration rate by the ratio of the design infiltration area to the model infiltration area and converting to inches per year. This produces supplemental recharge rates for the base and upper bound cases of 418 and 1332 inches per year, respectively. Adding the supplemental recharge rates to the natural recharge rate previously assigned to the six recharge-boundary cells (9.7 inches per year) results in total assigned recharge rates of and inches per year for the base and upper bound cases, respectively. PARTICLE TRACKING The predicted flow direction and travel distance of water introduced through the treated water infiltration system is simulated in the predictive assessment model by tracking hypothetical particles. For this purpose, particles were added at the center of model layer two (corresponding to the lower section of the A zone) along the boundary of the infiltration area. A total of 20 particles were added to the upgradient and downgradient borders of the infiltration area. MODPATH is used to generate pathlines for these particles based on hydraulic heads generated by the MODFLOW model. The pathlines provide an estimation of the flow paths followed by water after it reaches the 8

13 groundwater system. 3 The calculated travel times of particles along these pathlines are also determined in using MODPATH. MODIFIED BASELINE CONDITIONS Marquette County, MI A steady state model that incorporated all modifications to the original baseline model was run to establish baseline streamflow and head conditions. The head data from this baseline run was used to establish initial heads for the transient simulations for the base and upper bound cases. These initial heads are used by Visual MODFLOW to calculate drawdown values. RESULTS BASE CASE EFFECTS OF MINE INFLOW ON ALLUVIUM GROUNDWATER LEVELS Equipotentials produced by the transient model are shown for the uppermost saturated layer in the vicinity of the at the end of mine operation (ten years) in Figure 4. These equipotentials represent heads in the uppermost saturated unit present in each model location. Generally, this represents heads in the A zone, however, where that unit and possibly any underlying units are absent or represented as unsaturated in the model, heads are shown for the uppermost saturated layer present. For example, where the alluvium is unsaturated near the bedrock outcrop east of the ore body, the uppermost saturated model layer represents the upper portion of the bedrock. indicates that the maximum potential drawdown in the uppermost saturated alluvium is less than 0.5 feet beneath the Yellow Dog Plains. 4 One particular area of interest in the uppermost alluvium is near monitoring well QAL023B in the area directly over the ore body. The maximum potential drawdown at this monitoring point is only 0.12 feet during the ten-year mining period as calculated for the base case simulation (Figure 5). The screen center point in this well is about 30 feet below the water table in the lower part of the B zone and is represented that way in the model (North Jackson, 2005a). As a result of the anisotropic character of the sediments present at this location, the potential drawdown in the uppermost saturated unit will be less. Consequently, the 3 Travel through the unsaturated zone is not addressed in this analysis and must be considered separately to determine the total travel time from the ground surface to the particle destination. 4 Calculated drawdown data presented are based on reasonable numeric precision as represented by model calculations. Numeric precision, however, cannot be equated with field measurements that must be collected in an environment subject to natural variations that occur seasonally, annually and in response to longer-term climate cycles. 9

14 simulated head response in the uppermost saturated alluvium beneath the Yellow Dog Plains is within the range considered undetectable by field measurements that are typically influenced by natural variations. EFFECTS OF MINE INFLOW ON STREAMFLOW Marquette County, MI Zone budget water balances for river boundaries (simulated streamflows) in the predictive assessment model (transient) were compared to the water balances for the same boundaries in the modified baseline model (steady state). The ten years covering the mining period was examined to determine if measurable reductions in streamflow rate occurred in the base case simulation. The maximum flow-rate reductions are shown for each stream reach in Table 3. The maximum absolute declines are shown as well as the flow reduction as a percentage of total modeled flow in each reach. This comparison is made to modeled streamflow and not to flow from field measurements. As evident from Table 3, the simulated flow reductions for the base case are small. All are less than 0.2 percent of local flow and all but one are less than or equal to 0.1 percent. Seasonal, annual or cyclical environmental changes would almost certainly conceal variations on the order of those suggested by the base case simulation. The real constraints of field measurement error would make such changes difficult to measure. HYDRAULIC COMPONENTS (SOURCES) OF MINE INFLOW Mass balance data from simulations both of static (no mine inflow) and average mine inflow conditions using the predictive assessment model were analyzed to estimate the relative contribution that each component of the hydrologic system makes (either directly or indirectly) to water seeping into the mine. Average mine inflow values for each flux boundary in this analysis are based on mine inflows calculated from FEFLOW results (Table 1). The sum of all average flux boundary rates indicates that the total mine inflow rate is 74.3 gpm (0.165 cubic feet per second [cfs]) for the base case. The mass balance analysis indicates that in the base case simulation all mine inflow comes from groundwater storage (Figure 6). This is a result partly from the low inflow rate and the large volume of bedrock influenced by mine inflow (large cone of depression) determined in the FEFLOW analysis. Additionally, as the simulation progresses, some model cells representing bedrock at the flux boundaries go dry. Subsequently, no water is removed by the dry cell at a flux boundary and the overall flux 10

15 out of the model declines. This is the result of the extremely low hydraulic conductivity and storage characteristics established for the calibrated base case simulation. These hydraulic characteristics, based on the limited extent and poor hydraulic capability of the water conductive features and surrounding bedrock matrix, suggest that such a condition of drying and mine inflow reduction may occur over time during actual mine development. Thus, this simulated condition is considered to represent anticipated field conditions. Marquette County, MI EFFECTS OF TREATED WATER INFILTRATION Infiltration of treated water during the ten-year mining period produces a groundwater mound that can be represented by contours showing the groundwater rise (Figure 7). The contours show the rise above the baseline water table across several zones in the Quaternary alluvium as they are represented by several model layers. The mound appears different than those represented by standard analytical calculations both because of the influence of mine inflow at depth near the eastern bedrock outcrop and because the water table in this area falls rapidly over short distances approaching the terrace escarpment. Groundwater flow downgradient of the infiltration area has a large vertical component and, therefore, is constrained by the anisotropic character of the sediments. 5 This horizontal flow restriction causes the mound to spread more broadly. The maximum rise in the water table (groundwater mound height) beneath the infiltration area is about 8 feet at the end of ten years. Because the depth to the water table in the area beneath and downgradient of the infiltration area is up to 80 feet, it is clear from this analysis that the mound will be well below the land surface. The mound height falls off downgradient of the infiltration area until it reaches less than 2 feet of water level rise less than 1,400 feet downgradient of the infiltration area. Results of particle tracking are shown in Figure 8. The total path length indicates the distance groundwater moves during a ten-year period. Time markers are spaced at oneyear intervals to show groundwater movement year by year. The simulation indicates that all particles but one originating beneath the infiltration area are captured by a nearby tributary of the Salmon Trout East Branch before ten years. Nearly all particles travel over five years before capture. 5 Anisotropy is expressed as the ratio of vertical to horizontal hydraulic conductivity. 11

16 The predicted height and extent of the groundwater mound, as well as the distance of particle travel over time in this analysis, are based on the assumption that infiltrating water immediately reaches the groundwater system. This condition, however, will not occur in practice. Infiltrating water must first move through the unsaturated zone before reaching the water table. Travel time through the unsaturated zone could be substantial because of the great thickness of predominantly sandy sediments (up to 80 feet) above the water table beneath the infiltration area. As a result, infiltrating water may be distributed more broadly before reaching the water table, thus, reducing the effective mound height. Furthermore, the horizontal distance that water will travel from the infiltration area will be substantially shorter than that predicted by this simulation because of the long travel time through the vadose zone. Marquette County, MI RESULTS UPPER BOUND CASE EFFECTS OF MINE INFLOW ON ALLUVIUM GROUNDWATER LEVELS Equipotentials produced by the transient simulation of the upper bound case are shown for model layer 2 (generally the uppermost saturated layer) in the vicinity of the Eagle Project at the end of mine operation (ten years) in Figure 9. These equipotentials represent heads in the uppermost saturated unit present at each model location. Drawdown between 0.5 and 0.75 feet is limited to an area less than 30 acres above the ore body near the eastern bank of the Salmon Trout Main Branch (Figure 10). The peak head reduction in this area at the end of ten years of mine inflow is 0.75 feet. Drawdown calculated by the model over time in QAL023B is presented in Figure 11. This monitoring well is the observation point nearest the maximum drawdown above the ore body. The maximum potential drawdown calculated by the model at this monitoring point is 0.95 feet. As described for the base case, the screen center point in this well is about 30 feet below the water table in the lower part of the B zone and is represented that way in the model (North Jackson, 2005a). As a result of the anisotropic character of the sediments present at this location, the potential drawdown in the uppermost saturated unit will be less. The relationship between drawdown in the B zone and the uppermost alluvium is evaluated in the section describing the two-dimensional model at the end of this report. EFFECTS OF MINE INFLOW ON STREAMFLOW Zone budget water balances for river boundaries (simulated streamflows) in the predictive assessment model (transient) were compared to the water balances for the same boundaries in the modified baseline model (steady state). The twenty years 12

17 covering the mining and post-mining periods were examined to determine if measurable reductions in streamflow rate occurred. The maximum flow-rate reductions are shown for each stream reach in Table 3. The largest absolute declines are shown as well as the reduction as a percentage of modeled flow in the reach. This comparison is made to modeled streamflow and not flow from field measurements. Marquette County, MI Simulated streamflow rates are shown for the ten-year mining period for reaches in which the flow change (either increase or reduction) exceeded 1 percent of total flow in the reach (Figure 12). As evident from Table 4 and these figures, simulated flow reductions are small (maximum of 3.29 percent), sometimes of short duration, and may fall within the range of field measurement error or would likely be obscured by natural environmental variations. Overall, streamflow increases in the East Branch of the Salmon Trout River as the result of the groundwater rise caused by treated water infiltration. A small increase in streamflow also occurs in the Yellow Dog River between YDRM001 and YDRM This change is also attributed to the alteration of groundwater heads by treated water infiltration. HYDRAULIC COMPONENTS (SOURCES) OF MINE INFLOW Mass balance data from simulations of both static (no mine inflow) and average mine inflow conditions using the predictive assessment model were analyzed to estimate the relative contribution that each component of the hydrologic system makes (either directly or indirectly) to water seeping into the mine. Average mine inflow values for each flux boundary in this analysis are based on mine inflows calculated from FEFLOW results (Table 2). The sum of all average flux boundary rates indicates that the total mine inflow rate is gpm (0.493 cfs) for the upper bound case. The relative contribution of each component is shown in Figure 13. For the upper bound case, the primary sources of water from hydraulic components of the model are as follows: Groundwater from storage both in bedrock (including water-conductive features) and in overlying alluvium contributes about 15 percent of the water seeping into the mine. Early in the simulation this component provides all mine inflow, with contribution gradually diminishing over time. 6 The model results also show a slight increase in streamflow in the reach of the Yellow Dog River downgradient of YDRM002, although this zone is not otherwise evaluated in this predictive assessment. 13

18 Water diverted from streams to replenish groundwater storage provides about 67 percent. This percentage does not represent the reduction in streamflow, which is potentially only 3.29 percent or less as described above in this report. Marquette County, MI Additional groundwater entering the system through constant head boundaries in the model, primarily representing contribution from groundwater storage outside the model domain, provides about 17 percent. Most, if not all, of the water contributing indirectly to mine inflow through this component enters the model as diffuse flow from surrounding matrix storage. A minor share of the groundwater entering the mine is diverted from seeps discharging along the terrace escarpment. This component contributes 1 percent of mine inflow (not 1 percent of the discharge at the seeps). Surface runoff from precipitation and meltwater may also be diverted to replenish groundwater storage by enhanced infiltration recharge through wetlands and likely would reduce the contribution from streams. EFFECTS OF TREATED WATER INFILTRATION Continuous infiltration of treated water produces a groundwater mound represented by contours showing the water table rise in the Quaternary alluvium (Figure 14). This figure shows the generalized mound as represented across several model layers. The mound appearance is different than that represented by standard analytical calculations both because of the influence of mine inflow at depth near the eastern bedrock outcrop and because the water table in this area falls rapidly over short distances approaching the terrace escarpment. Groundwater flow downgradient of the infiltration area has a large vertical component and, therefore, is constrained by the anisotropic character of the sediments. 7 Because of this horizontal flow restriction, the mound spreads more broadly. The maximum mound height reached beneath the infiltration area is about 21 feet. Because the depth to the water table in the area beneath and downgradient of the infiltration area is up to 80 feet, the apex of the mound will be well below the land surface. The mound height falls off downgradient of the infiltration area. The maximum 7 Anisotropy is expressed as the ratio of vertical to horizontal hydraulic conductivity. 14

19 extent of the mound to the 2-foot contour is about 2,400 feet east-northeast of the infiltration area. Results of the particle tracking analysis are shown in Figure 15. The total Marquette County, MI path length indicates the distance groundwater moves during a ten-year period. Time markers are spaced at one-year intervals to show groundwater movement year by year. The simulation indicates that all particles are captured by tributaries of the Salmon Trout East Branch before the end of ten years. Some particles from the east side of the infiltration area as well as some from the west side are captured in less than five years. As described for the base case, the predicted height and extent of the groundwater mound created, as well as the travel distance of particle of particles from beneath the infiltration area, are based on the assumption that infiltrating water immediately reaches the water table. But, because water must first move through the unsaturated zone, this condition will not occur in practice. The substantial thickness of the predominantly sandy, sediments above the water table (up to 80 feet unsaturated) beneath the infiltration area will effectively reduce the groundwater mound height and shorten the travel distance of particles from the infiltration area. TWO-DIMENSIONAL FOCUSED ANALYSIS A cross-section (slice) model was constructed using Visual MODFLOW to simulate conditions in the uppermost saturated alluvium over the ore body and to evaluate the effects of mine inflow on water levels in wetlands identified in this area. The objective for this focused analysis is to assess potential effects on near-surface groundwater in response to the lowered heads in the deeper B zone as simulated by the predictive assessment model described above. This focused model offers greater detail at the local level than the predictive model, which takes a broader perspective. MODEL CONDITIONS The focused model was constructed as a northeast-southwest vertical slice of the groundwater system with dimensions of 100 feet by 1000 feet (using 20-foot by 20-foot model cells). Head data from 4 wells (QAL023, QAL043, QAL44, and WLD025) were used to calibrate the model. The model consists of three layers that represent the following units: a thin layer of A-zone sediments, a less permeable upper B zone, and a more permeable lower B zone. The A zone generally represents conditions in the wetlands present in this area. 15

20 Simulations from the predictive assessment model indicate that potential drawdown locally in the lower portion of the B zone during mine operation could be about 1 foot (upper bound case). Therefore, this slice model focuses on estimating head losses in the A zone when heads in the lower B zone are lowered about 1 foot. Thus, the model is useful in estimating the potential response to mine operations in the wetlands. Marquette County, MI A-zone and upper B-zone conductivities are separated into two different areas in the model to help simulate the relatively high horizontal gradients in the A zone and relatively low horizontal gradients in the B zone. In addition, a high conductivity zone is placed adjacent to the river cells in layer 2 used to represent the Salmon Trout Main Branch. This zone represents conditions that may occur adjacent to the Salmon Trout Main Branch where erosion may have removed the low-conductivity B zone and locally deposited more conductive sediments on the lower B zone. Two rows of river cells are used to represent the stream; each cell is assigned a conductance of 30 feet 2 per day, a river bed elevation of 1410 feet above mean sea level (amsl) and stage of 1412 feet amsl. Different recharge rates, ranging between 0.5 and 4.75 inches per year, are used in the model to aid in calibration. These varying recharge rates may simulate the different recharge rates associated with different portions of the wetland. Conductivities and layer elevations are summarized below: Zone Location Layer Elevation (amsl) K x and K y (ft/day) K z (ft/day) A North A South Upper B North Upper B South Near River South Lower B South The model is first solved for baseline static conditions (no drawdown) to establish calibration to measured heads. Reasonable calibration is achieved, with a normalized root mean squared error of 7.6 percent and an absolute mean residual of feet. Most of the error appears to occur because calibration wells in the lower B zone are projected onto the section from adjacent areas and have only small head differences among them (all values are between and feet amsl). Calculated and observed head data from the two well pairs with head data from both the A zone and the lower B zone are summarized below: 16

21 Well A-Zone (ft amsl) Lower B-Zone (ft amsl) Head Difference (feet) Observed Model Observed Model Observed Model QAL QAL Marquette County, MI Modeled Heads after Calibration No Imposed Drawdown After calibration, drawdown of about 1 foot in the lower B zone was simulated by placing specified head cells in the lower B zone. The specified heads are calculated by subtracting the predicted drawdown expected at a cell (based on modeled head data) from the simulated head at the cell. The target drawdown of 1 foot was selected to represent the maximum head decline in well QAL023B in the upper bound simulation using the predictive assessment model. 17

22 RESULTS Modeled drawdowns in the A zone ranged from 0.41 feet to 0.66 feet, compared to lower B zone drawdowns of 0.87 to 0.98 feet. Marquette County, MI Well Zone Normal Head (ft amsl) Head in drawdown scenario (ft amsl) Change in Head (feet) QAL023 B QAL043 A QAL043 B QAL044 A QAL044 B WLD025 A The simulations show that as B-zone heads fall, A-zone heads show a more subdued response. For example, in QAL044 the head change in the A zone is 0.41 feet in response to the modeled drawdown of 0.87 feet in the lower B zone. Thus, in this case the A-zone drawdown may be less than 50 percent of the B-zone drawdown. Closer to the modeled stream, the response at QAL043 is about 71 percent of the B-zone drawdown (0.66 versus 0.93 feet). Modeled Heads Imposed Drawdown of 1 foot Much of the A-zone head reduction in the model occurs because of the good hydraulic connection provided by the higher conductivity material assumed to occur next to the Salmon Trout Main Branch. This material allows water from the stream to support the 18

23 higher heads near the stream. These higher conductivity values are necessary to achieve model calibration and represent the steep horizontal gradient in the A zone. If the actual conductivity values are lower near the stream, then A-zone drawdowns will be much less than those in the B-zone. Marquette County, MI 19

24 REFERENCES Fletcher Driscoll & Associates, LLC, 2005, Baseline Groundwater Flow Model, July Foth and Van Dyke & Associates, Inc., 2006, - Analytical Calculations for Treated Water Infiltration System, January Marquette County, MI Golder Associates, Inc., 2006a, Bedrock Hydrogeologic to Assess Inflow to the Proposed, February Golder Associates, Inc., 2006b, Phase II Bedrock Investigation, February North Jackson Company, 2004, Environmental Baseline Study Stage 1 Hydrology Report, October North Jackson Company, 2005, Environmental Baseline Study Stage 2 Hydrology Report, February 2005a. North Jackson Company, 2005, Environmental Baseline Study Hydrology Report, September 2005b. North Jackson Company, 2006b, Supplemental Wetland Hydrology Baseline Study, February

25 FIGURES Marquette County, MI

26 6 = Salmon Trout Main STRM001 to QAL023B 7 = Yellow Dog R. Upstream of YDRM003 8 = Yellow Dog R. from YDRM003 to YDRM001 9 = Yellow Dog R. from YDRM001 to YDRM = Yellow Dog R. Downstream of YDRM002 1 = Salmon Trout West Branch 2 = Salmon Trout Main Escarpment to STRM004 3 = Salmon Trout East Branch 4 = Salmon Trout Main from STRM002 to Escarpment 5 = Salmon Trout Main from QAL023B Area to STRM North Axes scale in meters. Figure 1. Stream Reaches and Associated Water Budget Zones -- A Zone of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

27 North Axes scale in meters. Figure 2. Location of Flux Boundaries of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

28 Infiltration Area North Axes scale in meters Figure 3. Location of Bedrock Calibration Points and Recharge Boundary Cells for Treated Water Infiltration System of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

29 North Contours in meters. Axes scale in meters Figure 4. Modeled Equipotentials in Model Layer 2 at Ten Years -- Base Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

30 Figure 5. Simulated Head versus Time in QAL023B -- Base Case Simulated Head (feet) Maximum Drawdown = 0.12 feet at 60 days Elapsed Time (years)

31 Figure 6. Hydraulic Components of Average Mine Inflow -- Base Case Streamflow, 0% Constant Head, 0% Seeps, 0% Groundwater Storage 100%

32 North Contours in meters. Axes scale in meters Figure 7. Modeled Groundwater Mound in Alluvium Near Treated Water Infiltration System at Ten Years -- Base Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

33 Infiltration Area Axes scale in meters Figure 8. Particle Tracks (Pathlines) from Treated Water Infiltration after Ten Years -- Base Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

34 Contours in meters. Axes scale in meters Figure 9. Modeled Equipotentials in Model Layer 2 (A Zone) at Ten Years -- Upper Bound Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

35 North Contours in meters. Axes scale in meters Figure 10. Drawdown after Ten Years in Model Layer 2 -- Upper Bound Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

36 Figure 11. Simulated Head versus Time in QAL023B -- Upper Bound Case Simulated Head (feet) Maximum Drawdown = 0.95 feet at 4 years Elapsed Time (years)

37 Figure 12. Simulated Streamflow Changes -- Upper Bound Case Simulated Streamflow Rate (cfs) Salmon Trout Main Branch -- STRM001 to QAL023 Area Salmon Trout Main Branch -- STRM QAL023B to STRM002 Salmon Trout Main Branch -- STRM002 to Terrace Escarpment Yellow Dog River -- YDRM001 toydrm002 Salmon Trout River East Branch Elapsed Time (years)

38 Figure 13. Hydraulic Components of Average Mine Inflow -- Upper Bound Case Groundwater Storage, cfs 15% Constant Head, cfs 17% Streamflow, cfs 67% Seeps, cfs 1%

39 North Contours in meters. Axes scale in meters Figure 14. Modeled Groundwater Mound in Alluvium Near Treated Water Infiltration System at Ten Years -- Upper Bound Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

40 North Contours in meters. Axes scale in meters Figure 15. Particle Tracks (Pathlines) from Treated Water Infiltration after Ten Years -- Upper Bound Case of the Quaternay Alluvium Hydrogeology, Kennecott, Marquette County, MI

41 TABLES Marquette County, MI

42 Table 1. Flow Rates Assigned to Flux Boundaries -- Base Case Start Time Flux Boundary 1 Flux Boundary 2 Flux Boundary 3 Flux Boundary 4 Flux Boundary 5 Flux Boundary 6 End Time (day) (day) (US gpm) (US gpm) (US gpm) (US gpm) (US gpm) (US gpm) Average Flow Rate, US gpm See Note 1 Note: 1. Rate for Flux Boundary 6 used for Mine Inflow analysis is 21 gpm, based on the last 3 years of mine operation, is used instead of the 15.6 value for calibration to the FEFLOW heads. This provides a reasonable representation of conditions at the end ofthe mining period.