December 9, 2013
MIRAMAR NORTHERN MINING LTD.
Hydrogeological Study Con Mine Closure
Submitted to: Miramar Northern Mining Ltd. P.O. Box 2000 Yellowknife, NT X1A 2M1
Report Number: 1314350004-001-R-Rev0 Distribution: 8 Copies - Miramar Northern Mining Ltd. REPORT 2 Copies - Golder Associates Ltd.
HYDROGEOLOGICAL STUDY - CON MINE CLOSURE
Study Limitations
This report has been prepared for the exclusive use of the Miramar Northern Mining Ltd. or its agents. The factual information, descriptions, interpretations, comments, conclusions and recommendations contained herein are specific to the project described in this report and do not apply to any other project or site. Under no circumstances may this information be used for any other purposes than those specified in the scope of work unless explicitly stipulated in the text of this report or formally authorized by Golder. This report must be read in its entirety as some sections could be falsely interpreted when taken individually or out-of-context. As well, the final version of this report and its content supersedes any other text, opinion or preliminary version produced by Golder. Plans, specifications, calculations, notes, electronic files and similar material used to construct the groundwater model and complete the simulations herein are instruments of service, not products. Golder shall not be held responsible for damages resulting from unpredictable or unknown underground conditions, from erroneous information provided by and/or obtained from sources other than Golder, and from ulterior changes in the site conditions unless Golder has been notified of any occurrence, activity, information or discovery, past or future, susceptible of modifying the underground conditions described herein, and have had the opportunity of revising its interpretations, comments and recommendations. Furthermore, Golder shall not be held responsible for damages resulting from any use of this report and its content by a third party, and/or for its use for other purposes than those intended. Hydrogeological investigations and groundwater modelling are dynamic and inexact sciences. They are dynamic in the sense that the state of any hydrological system is changing with time, and in the sense that the science is continually developing new techniques to evaluate these systems. They are inexact in the sense that subsurface conditions are not known between the specific investigation locations, and there is invariably a lack of complete information both spatially and temporally about the geological and hydrogeological conditions. A groundwater model uses the laws of science and mathematics to draw together the available data into a mathematical or computer-based representation of the essential features of an existing hydrogeological system. While the model itself obviously lacks the detailed reality of the existing hydrogeological system, the behaviour of a valid groundwater model reasonably approximates that of the real system. The validity and accuracy of the model depends on the amount of data available relative to the degree of complexity of the geologic formations, the site hydrogeology, and on the quality and degree of accuracy of the data entered. Therefore, every groundwater model is a simplification and the models described in this report are not an exception. The professional groundwater modelling services performed as described in this report were conducted in a manner consistent with the level of care and skill normally exercised by other members of the engineering and science professions currently practising under similar conditions, subject to the quantity and quality of available data, the time limits and financial and physical constraints applicable to the services. Unless otherwise specified, the results of previous or simultaneous work provided by sources other than Golder and quoted and/or used herein are considered as having been obtained according to recognised and accepted professional rules and practices, and therefore deemed valid. This model provides a predictive scientific tool to evaluate the impacts on a real groundwater system of specified hydrological stresses and/or to compare various scenarios in a decision-making process. However, and despite the professional care taken during the construction of the model and in conducting the simulations, its accuracy is bound to the normal uncertainty associated to groundwater modelling and no warranty, expressed or implied, is made.
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Table of Contents
1.0 INTRODUCTION AND BACKGROUND ...... 1
2.0 DATA REVIEW ...... 3
2.1 Geology and Hydrogeology ...... 3
2.2 Permafrost ...... 4
2.3 Groundwater Monitoring ...... 4
2.4 Mine Inflows and Flooding ...... 5
2.5 Mine Inflow Water Quality ...... 7
3.0 HYDROGEOLOGICAL MODEL UPDATE ...... 9
3.1 Conceptual Model ...... 9
3.2 Numerical Model ...... 10
3.2.1 Model Modifications ...... 11
3.2.2 Calibration to Observed Mine Inflows...... 12
3.3 Prediction of Future Groundwater Conditions – Base Case ...... 14
3.4 Sensitivity Analysis and Model Uncertainty ...... 15
3.4.1 Parameter Sensitivity ...... 15
3.4.2 Calibration Sensitivity ...... 16
4.0 MITIGATION MEASURES ...... 18
5.0 SUMMARY AND RECOMMENDATIONS ...... 19
6.0 CLOSURE ...... 22
7.0 REFERENCES ...... 23
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TABLES Table 1: Shaft Observed Water Levels and Quality ...... 8 Table 2: Initial Model Parameter Values ...... 11 Table 3: Calibrated Model Parameter Values ...... 13
FIGURES Figure 1: Con Mine Key Plan
Figure 2: Site Plan
Figure 3: Longitudinal Section of the Con Mine Subsurface Workings
Figure 4: Bedrock Geology
Figure 5: Monitoring Well Locations
Figure 6: Total Arsenic Concentrations in Monitoring Wells in 2012
Figure 7: Robertson Shaft Water Level and Quality
Figure 8: Conceptual Hydrogeological Model – Pre-Development and End-of-Mining
Figure 9: Conceptual Hydrogeological Model – Mine Flooding and Closure
Figure 10: MODFLOW Numerical Hydrogeological Model
Figure 11: Model Hydrostratigraphy and Boundary Conditions
Figure 12: Comparison of Measured and Predicted Water Level in Robertson Shaft and Mine Inflow
Figure 13: Predicted Hydrogeological Conditions – Mine Dewatering System Active
Figure 14: Predicted Hydrogeological Conditions – 2013
Figure 15: Predicted Hydrogeological Conditions - 2015
Figure 16: Results of Parameter Uncertainty Analysis
No table of figures entries found.
APPENDICES APPENDIX A MNML 2012 Spreadsheet Model
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1.0 INTRODUCTION AND BACKGROUND This report documents the hydrogeological study that was conducted for the Miramar Northern Mining Ltd. (MNML) Con Mine in Yellowknife, NWT (Figure 1 and 2). As outlined in MNML’s request for proposal dated April 24, 2013, the main objective of this study is to “delineate potential discharge points and actions to be taken to control seepage from the underground workings when water flooding the mine reaches the 50 m level from the ground surface at the Robertson shaft.” Delineation of these potential discharge points is required under the terms and conditions of the approved Final Closure and Reclamation (C&R) Plan for the mine.
Underground operations at the Con Mine commenced in 1938 and continued until 2003, with the mill shutting down in 2007 following processing of remaining sluges and calcines. In total 5.5 million ounces of gold have been produced using primarily cut and fill, shrinkage, and longhole stoping methods. As shown on Figure 3, the underground workings extend to the 6100 mine level (1,900 m below ground) at the Robertson Shaft, which was one of the two main access and hoisting shafts. At the second shaft, C-1, the underground development reaches the 2500 mine level (750 m below ground). The surface locations of these two shafts, together with the secondary Negus and Rycon Shafts, are presented on Figure 2. During mining, most of the waste rock was left underground as structural backfill and at some locations mine tailings were utilized for backfilling. Mine tailings were also deposited on the surface in five Tailing Containment Areas (TCA), including Upper, Middle, and Lower Pud TCAs, Neil Lake TCA, and Crank Lake TCA (Figure 2). During mining, the mine dewatering system was comprised of a number of pumping stations located adjacent to the C1, B3 Winze, and Robertson Shafts. In 2003, once underground mining was finished, the mine’s dewatering system was turned off and the mine workings have been passively flooding since that time. As discussed in greater detail in Section 2.4, in late 2012 the water level in the Robertson Shaft was approximately at the 2150 mine level (655 m below ground), and by late 2013 the water level in the Robertson Shaft has risen to the 1380 mine level (420 m below ground).
The Final C&R plan identified the 204Q stope opening to the surface near Rat Lake as the lowest known surface opening from the mine. Other known surface openings include the Robertson Shaft, the C-1 Shaft, a number of raises and stopes in the area of the Negus Shaft, the Negus Shaft, the Con 454 Raise, the C-1 Vent Raise, the Rycon Shaft, the Mine Air Heaters, and the Rycon R-1 Shaft (Figure 2). It should be noted that all openings to surface have been capped with concrete and that the caps have been approved by the WSCC Chief Inspector of Mines.
The Final C&R plan requires installation of water quality monitoring and pump openings in the concrete caps on the Robertson Shaft, the C-1 Shaft, the Negus Shaft, and the 204 Stope. The C&R Plan provides for contingent pumping and treatment of the mine water if it does not meet the Water License discharge standards. However, if the mine water meets Water License discharge standards, it may be directed into Rat Lake from a spill point constructed in the 204Q stope cap. In October 2013, the water level in the mine had risen to a level sufficient to obtain initial water level measurements in the Negus and C-1 Shafts, and an initial sample of water quality in the C-1 Shaft. Water levels recorded at that time indicated that the mine water levels in these two shafts were consistent with those measured in the Robertson Shaft at approximately 420 m below ground. MNML (2012) indicated that, in accordance with the Final C&R Plan, when the mine water level approaches 300 m below the ground surface (1000 ft. mine level), the monitoring frequency will increase to quarterly and sampling at the Robertson Shaft, the C-1 Shaft and the Negus Shaft will be added to the quarterly monitoring plan. Therefore, based on the result of monitoring in 2013, quarterly monitoring in the Robertson, C-1, and Negus shafts is planned to commence in 2014.
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Information collected during this monitoring will be used by MNML to refine the existing Mine Flooding Management Plan. As per Part D, Item 15 of the Water License, this detailed plan will be developed and submitted to the MacKenzie Valley Land and Water Board (MVLWB) for approval before the water level in the mine is within fifty (50) metres of the ground surface (MNML 2012).
This report is divided into five sections consisting of introduction and background in Section 1 and Section 2 consisting of the review of the available data, including geology and hydrogeology, mine flooding history, and groundwater monitoring. Section 3 describes the update of the site conceptual and numerical hydrogeological model for the mine, and provides predictions of future hydrogeological conditions during flooding of the mine workings above the 1380 mine level and at closure. Mitigation methods that could reduce potential impacts of mine water on the surrounding environment are discussed in Section 4. A summary of the study findings and recommendations are provided in Section 5.
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2.0 DATA REVIEW Hydrogeological data has been collected at the Con Mine throughout the mine life. Key recent studies that were considered in the data review include: INTERA (1997) – this report provides information on historical mine inflows, results of underground permeability and water quality testing, and the conceptual understanding of groundwater conditions developed based on that information; Douglas et al. (2000) and Greene et al. (2008) – these publications discuss the chemical origin of mine inflow waters based on water quality sampling from the south end of the underground development; SRK (2002) and SRK (2005) – these reports discuss hydrogeological conditions of the Giant Mine, which is located in a similar hydrogeological setting at a distance of less than 10 km north of the Con Mine; Golder (2003) – this technical memorandum documents hydrogeological modelling that was conducted to provide a preliminary assessment of groundwater conditions after closure; URS (2005) – this document provides an evaluation of the risks associated with the flooding of the underground workings; MNML (2007) – this document outlines the final closure and reclamation plan for the mine; Hauser et al. (2007) – this publication discusses geological setting of the Con Mine area; MNML (2012) – this document provides the mine flooding plan for the mine, including a spreadsheet model that provides the most recent predictions of mine flooding rates, and summarizes the results of 2012 monitoring of mine water; and Golder (2012) – this document provides a summary of the most recent results of shallow groundwater monitoring at the site.
In addition to data obtained from the studies referenced above, the results of the most recent monitoring of mine water level and quality, undertaken in October 2013, were provided to Golder by MNML, and these results were compiled along with the historical data referenced above.
2.1 Geology and Hydrogeology A summary of geological setting of the Con Mine has been provided by Douglas et al. (2000) and Hauser et al. (2007). The mine is located in the volcanic rocks of the Yellowknife Greenstone Belt, which is part of the Slave Province of the Canadian Shield. Mining was focused on the Campbell and the Con mineralized shears which were formed during the intrusion of granodiorite batholith of the Western Plutonic Complex. Structurally, the area is dominated by near-vertical faults in three main orientations. As shown on Figure 4, the oldest faults are oriented in the NE-SW direction (e.g., Negus Fault), the intermediate-age faults extend in the NNW-SSE direction (e.g., Pud Fault, West Bay Fault) and the youngest faults intersect the area in the E-W direction (e.g., Angel Fault). Surficial geology consists of thin and discontinuous glaciolacustrine sediments, glacial till, silts and clays that are present between bedrock outcrops. Locally, surface depressions are filled with water, and these small water bodies are underlain by residual lake sediments or contain bogs that have overgrown historic lake and stream courses.
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Hydrogeological conditions near the mine are largely influenced by water levels in nearby lakes, as presented on Figure 2. These lakes include Great Slave Lake a bay of which (Yellowknife Bay) is located east of the mine, Kam Lake which is located west of the mine, Frame and Niven Lakes located north of the mine, and Meg Lake to the south. Yellowknife Bay is located east of the underground mine and is the lowest elevation lake in the area at 5493 ft. mine datum (156 masl) followed by Kam Lake located to the southwest at 5543 ft. (167 masl). Rat Lake (5567 ft / 178 masl) is a minor water body located within the northern extent of the site in the vicinity of the 204Q Stope. Average annual recharge to groundwater from precipitation has not been previously estimated for the site; however, at the nearby mines, recharge within the footprint of the underground development was estimated to be 55 mm/year to 72 mm/year with 7.5 mm/year to 37 mm/year outside of this footprint (SRK, 2002 and 2005). INTERA (1997) found that groundwater flow near the mine occurs primarily within the fault network that intersects the underground development. Based on the back analysis of inflows recorded in the exploration and development drillholes, the transmissivity of the Angel, Negus, Pud, and West Bay Faults was estimated to range between 1x10-7 m2/s to 2x10-7 m2/s. Frequency of inflows encountered in these drillholes also suggested that overall Angel and Negus Faults could be more permeable than the Pud and West Bay Faults. Single-well and interference testing conducted by Intera in 1997 supported these observations of the relative permeability of individual faults, and indicated that locally the transmissivity of the Angel Fault could be up to 2x10-2 m2/s. Hydraulic conductivity of bedrock outside of the fault network was not estimated by INTERA; however, at the nearby Giant Mine, SRK (2002) used mine inflow data to calculate a bulk hydraulic conductivity of shallow and deep bedrock of about 1x10-8 m/s and 1x10-9 m/s, respectively.
2.2 Permafrost Con Mine is located within the Canadian zone of discontinuous permafrost (Natural Resources Canada, 1993). Permafrost occurrence is highly variable with islands or pockets of permafrost generally occurring in areas occupied by peat bogs, and absent in areas of exposed bedrock outcrop (Geological Survey of Canada, 1998). Where present, the depth of permafrost is relatively shallow extending only to depths of 50 to 85 m (Geological Survey of Canada, 1998). In areas of permafrost where temperatures are in the range of 0 to -1 ˚C, water in the voids spaces within the rock may consist of a mix of ice and water. The existence of permafrost in the shallow bedrock may result in a reduction of the hydraulic conductivity of the upper 50 to 100 m of bedrock compared to areas without permafrost (McCauley et al. 2002, Burt and Williams, 1976).
2.3 Groundwater Monitoring A groundwater monitoring program was initiated at the Con Mine in 2004. This program is ongoing and the most recent report on the results of this sampling is the 2012 Annual report (Golder 2012). In 2012, 20 wells (Figure 5) were monitored to characterize shallow groundwater flow patterns and groundwater quality in the vicinity of historic tailings containment areas. These wells are installed in tailings, surficial sediments, and shallow bedrock with the deepest wells installed at elevations up to 17 m below the elevation of Great Slave Lake (5493 ft. mine datum or 156 masl). The deepest of these wells (SNP0025-16) extends to 37 m depth in contrast with the total depth of the mine of approximately 1.9 km (6100 mine level); therefore, these wells are considered to be representative only of shallow, near surface groundwater flow conditions.
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Shallow groundwater flow conditions have been discussed in Golder (2012) based on the data from the wells that were monitored in 2012. The shallow groundwater system appears to be discontinuous with some monitoring wells becoming periodically dry, and with a groundwater high located near the Crank Lake TCA. Although the potential for lateral flow from this area exists, the presence of relatively strong vertical gradients measured beneath the Crank Lake TCA suggests that the downward flow towards the underground workings currently dominates. Water quality data support the conclusion that the shallow groundwater flow system is discontinuous with total arsenic concentrations (0.005 mg/L to 0.188 mg/L) measured in groundwater samples from wells outside of the Crank Lake TCA relatively low compared to arsenic concentrations (240 mg/L to 400 mg/L) measured within the Crank Lake TCA, the latter of which are reflective of tailings pore water (Figure 6). Based on average annual water table elevations in the shallow monitoring wells, hydraulic heads in the shallow groundwater flow system have not been increasing in response to rising water levels within the flooding underground mine over the nine year period of monitoring (Golder, 2012). The hydraulic head data collected since 2004 in the shallow flow system suggests that the shallow groundwater flow system is perched above the underlying bedrock flow system with much of the bedrock depressurized by the underground mine. This perched shallow flow system is consistent with observations made at the nearby Giant Mine (SRK, 2005) where deep multi-level WestBay monitoring wells indicated a downward gradient between the shallow flow system and deep bedrock during mine re-flooding. No deep groundwater monitoring wells are currently present at the site, but water levels and water quality data measured in the Robertson Shaft (discussed below) suggest that a downward gradient between the shallow flow system and underground mine is present.
2.4 Mine Inflows and Flooding INTERA (1997) provides a summary of mine dewatering records available for the period between 1983 and 1996. During this period the average annual inflow of groundwater to the underground development ranged between approximately 800 m3/day and 1,600 m3/day, with inflow rates higher annually between July and October when compared with the remainder of each year. For example, in 1996 over the July to October period the groundwater inflow was approximately 20% higher than the winter and spring months, suggesting that recharge originating from direct precipitation and snowmelt within the mine footprint was contributing to higher groundwater inflow. Chemical and isotope analyses discussed by Douglas et al. (2000) and Greene et al. (2008) support these observations and demonstrate relatively rapid migration of modern meteoritic water to a depth of 1300 m within 17 to 23 years. On November 29, 2003 the mine dewatering system was turned off and the flooding of the underground workings commenced. As presented in Table 1, since that time the water level in the Robertson Shaft has been measured eight times and water samples have been collected to provide information on mine water quality. Figure 7 provides a plot of the measured water level in the Robertson shaft, which by October 2, 2013 had reached the 1,380 mine level (420 m below ground). Measurements of water levels in the C-1 and Negus shafts collected for the first time on October 4, 2013, and October 21, 2013, respectively, indicated that at that time the water levels in the three shafts were essentially equal, suggesting that there was a reasonably good hydraulic connection between the three shafts.
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Historical measurements of water levels in the Robertson Shaft were used by MNML to make predictions of the time needed for complete flooding of the mine. This was accomplished using the MNML spreadsheet model developed by Con Mine which utilizes estimates of mine volumes to estimate past flooding rates. These flooding rates were then used to estimate future water levels in the mine. As discussed in MNML (2012), on October 11, 2012 the water level in the Robertson shaft was at the 2150 level (655 m below the ground), and the estimated average flooding rate based on water levels measured since mine flooding began in 2003 was approximately 283 m3/day (8609 m3/month). By October 2, 2013 the water level in the Robertson Shaft had reached the 1380 mine level (420 m below ground) suggesting that between October 2012 and October 2013 the water level in the Robertson Shaft increased more quickly than predicted with the estimated average flooding rate revised to approximately 301 m3/day (9170 m3/month). The corresponding estimated time remaining to complete flooding of the workings is approximately 3.5 years with complete flooding predicted to occur in March, 2017. Previously, it had been noted that the estimated flooding rates over each monitoring period have generally been gradually decreasing for each successive measurement (MNML, 2012). Table 1 also presents flooding rates calculated for each period when the shaft water elevation was measured and using corresponding volumes of mine workings as incorporated into the MNML spreadsheet model. These calculations show that the apparent period flooding rate has generally been gradually decreasing from approximately 370 m3/day (11,300 m3/month) in September, 2006 to about 196 m3/day (6000 m3/month) in October, 2012. However, based on the volumes provided in the MNML spreadsheet model for mine levels between the 2150 level (655 m below ground) and the 1380 level (420 m below ground), the apparent period flooding rate increased to approximately 422 m3/day. This result suggests that either the rate of groundwater inflow to the mine has indeed increased or the mine volumes assumed for the upper levels of the mine may have been overestimated. The MNML spreadsheet model (MNML, 2012) is based on actual surveys of the mine workings during mining operations, the tons of ore and waste hoisted to the surface, and the amount of material left or placed underground as backfill. Consideration was also given to the void space in the backfill (MNML, 2012). However, as noted by URS (2005), in the near surface stopes on the Con Shear backfilling was not used extensively and fill is unlikely to support the existing pillars in this area of the mine. In addition, near surface stopes and raises in the C1 Shaft area and Con Mill Complex have been described as potentially unstable. A history of instability at the 204Q stope has also been noted (URS, 2005). In these near surface stopes, the mine volumes incorporated in the MNML spreadsheet model (MNML, 2012) may provide an upper bound estimate of the actual void space if the stopes and raises in the upper levels of the mine have been subjected to collapse. It is also possible that some areas of the mine may have been hydraulically isolated from the Robertson Shaft prior to October 2012. In this case some of the mine voids in the upper levels of the mine may have become partially filled with water while the water level in the Robertson Shaft remained at lower levels. In this case, the effect on the apparent period flooding rate would be similar to collapse in that there would be a reduction in the void space available for filling. Considering the uncertainties in the void space available for filling due to the possibility of collapse, and/or hydraulic isolation in the upper levels of the mine, and the observed decrease in flooding rate in all previous events, the actual mine volumes filled between October 2012 and October 2013 could potentially be one third to one half of that estimated from the mine volumes provided in the MNML spreadsheet model. Assuming that the mine volume filled between October 2012 and October 2013 was approximately one third to one half of those given in MNML (2012), the apparent period flooding rate would be between 141 m3/day and 211 m3/day. These apparent flooding rates are consistent with the period flooding rates calculated using mine water level data collected prior to October 2012, as shown on Figure 7.
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Assuming that all mine levels above the 2150 level, have been reduced to one half to one third of those estimated (MNML 2012), and using the corresponding apparent period flooding rate of 422 m3/day, the predicted time to flooding would be reduced to approximately 2.5 years with complete flooding of the mine workings predicted to occur in April of 2016. This estimate provides a lower bound estimate of the time to flooding. If the reduction in void space is limited to the mine workings only between the 2150 level and 1380 level (650 to 420 m below ground), and the volumes assumed in the MNML spreadsheet model for mining level above 1380 level (420 m below ground) are correct, then assuming a future flooding rate of 211 m3/day, the estimated time to flooding would be approximately 5 years with the complete flooding of the workings estimated to occur in October of 2018. Assuming a future flooding rate of 141 m3/day, the estimated time to flooding would be 7.5 years with complete flooding of the mine workings predicted to occur in April 2021.
The results of quarterly monitoring of water levels in Robertson, C-1 and Negus shafts in 2014 will determine which of the three flooding scenarios most appropriately describes future flooding of the mine workings, but at present, the predicted time to flood of 3.5 years (by March 2017) which is based on the MNML spreadsheet model and using the average flooding rate of 301 m3/day is a reasonable best estimate. However, due to uncertainty in the volume of the mine voids above the 2150 level, the predicted time to flooding based on this model could be as low as 2.5 years (flooding occurring in April 2016) or as long as 7.5 years (flooding occurring in April 2021).
2.5 Mine Inflow Water Quality Table 1 and Figure 7 present chloride, total zinc, and total arsenic concentrations in water samples collected from the Robertson Shaft between 2004 and 2013, and in the C-1 shaft in 2013. Chloride and total zinc concentrations have generally decreased in the Robertson Shaft during mine flooding with chloride decreasing from 25,500 mg/L in June 2004 to 335 mg/L in October 2013, and zinc decreasing from 5.44 mg/l in June 2004 to 0.387 mg/l in October 2013. In contrast, over the same time period, the arsenic concentration of Robertson Shaft water samples increased from 0.154 mg/L to 11.7 mg/L. The increasing arsenic concentrations as the mine floods suggest that vertical seepage of high arsenic water from the Crank Lake TCA is providing an increasing component of the groundwater discharge to the mine as the water level in the mine rises. This supposition is supported by the quality of water sampled in the C-1 shaft in October 2013 with a much higher concentration of arsenic of 26.8 mg/l, and a concentration of zinc of 0.729 mg/l sampled in this shaft which is located in much closer proximity to the Crank Lake TCA. Arsenic concentrations of up to 400 mg/l were measured in groundwater samples collected in shallow monitoring wells within the Crank Lake TCA in 2012 (discussed in Section 2.3 above). Arsenic in mine water could also originate from the backfill used within the underground mine as both waste rock and tailing were used in some locations as structural backfill. In contrast, zinc concentrations were below the applicable guidelines in all shallow monitoring wells in 2012, and have been diminishing in groundwater samples collected in the Robertson Shaft as the mine floods.
These results are consistent with those documented by Douglas et al. (2000). For comparison chloride concentrations in water samples collected when the mine was in operation between the 2300 and the 3500 mine level (700 m to 1070 m below ground) ranged between 142 mg/L and 25,700 mg/L, whereas samples from the 4900 to the 5300 mine levels (1500 m to 1620 m below ground) ranged between 78,000 mg/L to 186,000 mg/L. Douglas et al. (2000) results and associated analyses suggest that shallow meteoritic water was a substantive
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component of groundwater inflows to shallow mine openings. Conversely, the quality of inflows at lower mine levels reflected the presence of the deep seated saline brines commonly encountered in bedrock of the Canadian Shield (Gascoyne and Kamineni, 1994). At Con Mine, these brines likely originated by infiltration of residual hypersaline fluids following evaporation of shallow inland seas present during the Paleozoic era (roughly 500 to 250 million years ago) with estimated ages of some 400 million years (Green at al., 2008). Table 1: Shaft Observed Water Levels and Quality Period Mine Level Total As Total Zinc Shaft Date Depth (m) Flooding Rate Cl (mg/l) (ft) (mg/l) (mg/l) (m3/d)1 June 18, 2004 5,681 1,730 25,500 0.154 5.44 September 8, 2006 4,700 1,430 370 13,700 0.56 4.23 September 10, 2007 4,330 1,320 314 4,600 2.33 4.53 December 17, 2008 3,630 1,110 269 4,800 0.117 1.02 Robertson October 9, 2009 3,258 990 291 1,650 2.5 0.285 November 8, 2011 2,547 780 231 2,300 2.97 0.781 October 11, 2012 2,150 660 196 308 7.49 0.434 October 2, 2013 1,380 420 4222 335 11.7 0.387 C-13. October 4, 2013 1,388 420 869 26.8 0.729 Negus October 21, 2013 1366 420 Notes: 1. Period flooding rate was calculated using the water level rise between each water level measurement and its preceding measurement, and the mine volumes per mine level provided by MNML (2012). 2. If mine volumes between the 2150 level and the 1380 level were 50% to 70% lower than those provided in MNML (2012) due to collapse or hydraulic isolation of some areas of the mine workings between these two levels then the apparent flooding rate for this period would be revised to between 141 m3/day to 211 m3/day. 3. The collar elevation of the C-1 Shaft is approximately 18 ft higher than the Robertson and Negus Shafts; therefore this depth is equivalent to 1370 mine level from the Robertson Shaft.
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3.0 HYDROGEOLOGICAL MODEL UPDATE The available hydrogeological data, in particular mine flooding records collected after 2003, was used to update the hydrogeological model that was previously developed for the Con Mine (Golder, 2003). This included revision of the conceptual understanding of groundwater flow conditions near the mine and the subsequent update of the numerical groundwater model. Following calibration of this model to the measured mine inflow rates and water level in the Robertson Shaft, the model was used to provide predictions of future groundwater conditions and verify predictions of time to flooding of the mine workings derived from the MNML spreadsheet model (MNML, 2012). As described in Section 4, the model was also used to provide estimates of pumping rates of mine water required to maintain downward gradients between the shallow and deep groundwater flow systems which may be necessary to limit groundwater with high arsenic levels from discharging to nearby surface water bodies.
3.1 Conceptual Model The conceptual model of groundwater flow conditions near the Con Mine is presented on four schematic cross sections that show hydrogeological conditions inferred to exist prior to mining (Figure 8a), conditions at the end of mining (Figure 8b), conditions during mine flooding (Figure 9a) and conditions that are likely to develop at closure (Figure 9b) should the mine water level be allowed to equilibrate. This model is a simplified and pictorial representation of hydrogeological conditions near the mine, yet it retains sufficient complexity so that it adequately reproduces the actual groundwater behavior and provides a basis for a numerical groundwater model that can be used to produce reasonably accurate predictions of mine flooding. As presented on Figure 8a, prior to mining, groundwater flow on the local-scale occurred in response to recharge from direct precipitation in the area between Kam Lake and Yellowknife Bay. It is likely that some of this shallow flow, which was restricted primarily to the overburden and weathered bedrock, was directed west towards Kam Lake and the remainder of this flow was directed east ultimately discharging to Yellowknife Bay. Groundwater flow in the deeper bedrock was focused mainly in the fault network which provided pathways for flow in the otherwise low-permeability bedrock. Considering that the surface water elevation of lakes located immediately west of the mine is higher than the water elevation in Yellowknife Bay, it is also possible that, prior to mining, the regional groundwater flow direction was from west to east, with groundwater discharge to Yellowknife Bay. At greater depth (greater than approximately 1500 m below ground) high TDS (total dissolved solids) brackish water dominated the groundwater flow system, with groundwater flow rates relatively low and primarily driven by density gradients. Mine dewatering resulted in a significant disturbance to the pre-existing hydrogeological regime. As the depth of the mine workings gradually increased throughout the 65 years of operation, the underground workings acted as a progressively stronger sink for groundwater flow and a cone of depression gradually formed in their vicinity (Figure 8b). Groundwater flow in both the shallow and the deep flow system was directed away from the nearby lakes and towards the mine, except in localized areas where perched conditions likely developed in low permeability overburden. The fault network, in particular east-west striking structures (e.g., Angel Fault), were major pathways for groundwater inflow. This, in combination with an overall increase in bulk bedrock permeability within the mine footprint due to mine development and exploration drilling, resulted in relatively rapid transmission of shallow groundwater, originating from precipitation and lakes, to the deeper portion of the mine. Mine dewatering has also resulted in up-coning of high TDS brackish water from beneath the mine thereby affecting mine water quality in the lower stopes and drifts.
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Figure 9a presents groundwater conditions when the water level in the Robertson Shaft was at about 1380 mine level (420 m below ground) at the end of 2013. During mine flooding, the underground workings continue to act as a groundwater sink, albeit of progressively diminishing strength as the head differential between the nearby lakes and the flooded mine decreases. Mine inflow rates have decreased from 800 m3/day to 1600 m3/day range reported during mine operation, to less than 422 m3/day by October 2013 (Table 1 and Figure 7). As the significance of the groundwater inflow originating from the lakes decreases, groundwater recharge from direct precipitation within the mine footprint increases in importance. The gradual decrease in total dissolved chloride concentration in shaft water samples indicates that fresh groundwater recharges the upper portion of the mine workings, and that the inflow of more saline groundwater is limited to the lower mine levels. The gradual increases in the total arsenic concentration in mine water (Section 2.4) suggest that the arsenic sources are in the upper levels of the mine and/or in the surficial sources (TCAs). The contribution of these shallow sources to the mine water quality is expected to increase during the late stages of mine flooding as recharge from direct precipitation becomes the main source of groundwater inflow to the mine.
Figure 9b shows groundwater conditions that could develop at closure, once the water level in the underground workings stabilizes, and in the absence of any mitigative measures (e.g., pumping) that would prevent the mine water level increasing above the elevation of Yellowknife Bay and Kam Lake. In the absence of mitigation, the water table in the area of the underground development would mound and the groundwater flow pattern would resemble the pre-mining conditions. That is, the shallow groundwater flow from the mine area would be directed laterally east towards Yellowknife Bay and west towards Kam Lake, and the downward flow in bedrock would diminish. The main source of this shallow flow system would be recharge from precipitation within the area between these two lakes. The deep groundwater flow would be controlled primarily by hydraulic heads in the flooded underground workings which would provide the main pathways for flow, and would generally be directed from west to east.
3.2 Numerical Model The conceptual model of hydrogeological conditions near the Con Mine was used to update the numerical groundwater model that Golder developed for the area in 2003. This model, which was previously constructed using MODFLOW, was used to provide preliminary predictions of groundwater conditions that could develop at closure, once the mine water level reaches steady-state conditions. Details of model construction and calibration to inflows that were measured during mine operation were provided in Golder (2003). In summary, the model included three hydrostratigraphic units that represented shallow bedrock, deep bedrock, and major faults; and incorporated the details of underground development from the ground surface to the 6100 mine level. Due to the absence of calibration data, all model predictions made in 2003 were conducted in steady-state and the time to reach steady-state was not predicted. Figure 10 presents the lateral and vertical extents of the model domain. Figure 11 presents the model hydrostratigraphy and boundary conditions.
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3.2.1 Model Modifications The following modifications were made to the original model configuration so it could adequately represent the conceptual model discussed in Section 3.1 and could provide reasonably accurate predictions of mine flooding over time (transient mode): Vertical mesh discretization was refined; the number of numerical layers was increased from 6 to 10, with the original upper 2 layers that represented the mine above the 2000 mine level (610 m below ground) now divided into 6 layers each 300 feet (91 m) thick. Specified head boundaries that represent major lakes in model layer 1 were adjusted to the most recent topography data available from cityExplorer database maintained by City of Yellowknife. These elevations, expressed in the mine coordinate system, were as follows: Yellowknife Bay – 5493 feet, Niven Lake - 5588 feet, Frame Lake – 5590 feet, Kam Lake – 5531 feet, and Meg Lake – 5568 feet. Specified Head boundaries constrained to inflow only were used to represent minor surface water bodies in model layer 1. Middle Pud TCA and Rat Lake were represented with elevations of 5566 ft. Other areas of identified surface water discharge were assigned elevations corresponding to topography. All hydrostratigraphic units were assigned initial values of groundwater storage parameters (i.e., specific storage and specific yield), as presented in Table 2. For the Pud, West Bay, Negus, and Angel Faults these values were based on the geometric mean of hydraulic testing results presented in INTERA (1997). Model cells containing these features were assigned an enhanced equivalent hydraulic conductivity calculated from the estimated transmissivity of the fault and hydraulic conductivity of the bedrock. For all other hydrostratigraphic units, due to absence of site specific data, these initial values were based on typical values reported in the literature for similar hydrogeological settings (Maidment, 1992, and Stober and Bucher, 2007). Specified flux boundaries were assigned to the top of model layer 1 to represent recharge from precipitation. Recharge was set to a greater value within the mine envelope (72.5 mm/yr) than outside the mine envelope (35 mm/yr) according to the preliminary estimates that were made for the nearby mines. Gridblocks representing the underground development in each model layer were assigned equivalent values of specific yield that accounted for the volume of mine working within the corresponding mine level, as summarized in the MNML Model (Appendix A). These gridblocks were initially assigned an equivalent hydraulic conductivity of 1 x10-6 m/s. Table 2: Initial Model Parameter Values Horizontal Specific Hydraulic Specific Hydrostratigraphic Unit Elevation (ft) Mine Level Storage Conductivity Yield (-) (1/m) (m/s) 5200 to 5600 400 to 0 1 x 10-7 1 x 10-6 0.0005 Bedrock 4600 to 5200 1000 to 400 1 x 10-8 1 x 10-6 0.0005 -1400 to 4600 6100 to 1000 1 x 10-9 1 x 10-7 0.0005 Pud and West Bay Faults -1400 to 5600 6100 to 0 1 x 10-7 1 x 10-7 0.001 Negus and Angel Faults -1400 to 5600 6100 to 0 1 x 10-7 1 x 10-7 0.001
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3.2.2 Calibration to Observed Mine Inflows During model calibration, the groundwater model was run repeatedly with various combinations of model input parameters. After each simulation, the model predictions were evaluated against multiple calibration targets and individual model parameters were adjusted in subsequent simulations until an acceptable match between model predictions and model calibration targets was achieved. Targets used in calibration of the model included: The average annual inflow of groundwater to the underground development during mining (between approximately 800 m3/day and 1,600 m3/day); Water levels measured in the Robertson Shaft on eight separate occasions between June 18, 2004 and October 2, 2013; and Inflow to the underground mine estimated from the volumes of void space per mining level (MNML, 2012), and the water levels measured in the Robertson Shaft between June 18, 2004 and October 2, 2013.
When the model was run with the initial model input parameters presented in Table 2, the model was found to predict greater inflows and water levels in the Robertson Shaft than have been observed during re-flooding of the underground mine. In addition, the model could not match the relatively rapid decrease in groundwater flow to the mine observed during the initial stages of re-flooding. As a result, the following adjustments were made to model input parameters: The hydraulic conductivity of competent rock at all depth intervals was reduced by up to an order of magnitude. The calibrated hydraulic conductivity of bedrock in the model is within the range, but at the low end, of representative hydraulic conductivities for similar hydrostratigraphic units presented in the literature (Maidment, 1992, Stober and Bucher, 2007); The hydraulic conductivities of Negus and Angel Faults were increased by a factor of 3 to a hydraulic conductivity of 3 x 10-7 m/s. Assuming a width of 1 m, this transmissivity is within the range provided by INTERA (1997); The specific storage of shallow and intermediate rock was decreased by a factor of 10 to provide a better match to the most recent estimates of groundwater inflow to the mine. This value is within the range, but at the low end, of representative values of specific storage in bedrock presented in Maidment (1992); The specific yield of all hydrostratigraphic units was increased by a factor of 10 from the initial values to 0.001 (0.1%) to provide a better match to the water level measured in the Robertson Shaft. This value is within the range of representative values of effective porosity (a parameter closely correlated with specific yield) provided in Maidment (1992) and Stober and Bucher (2007); Recharge within the mine envelope was decreased from the initial value of 72.5 mm/yr, to 55 mm/yr. Outside of this area, an intermediate recharge zone (45 mm/yr) was added to the model that is outside of the mine envelope, but where depressurization of the bedrock results in strong downward gradients. Away from the mine footprint, to the north and west, recharge was decreased to 10 mm/yr. to prevent groundwater mounding in areas where the downward gradients induced by mining are much less;
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The equivalent hydraulic conductivity of the mine workings below 1940 ft elevation (3660 mine level) was decreased by approximately a factor of 2 to 4 x 10-7 m/s to provide an improved match to the observed water level in the Robertson Shaft. Conversely, the hydraulic conductivity of the mine workings above this elevation was increased to 8 x 10-6 m/s. This result suggests that the shallow mine workings which are largely expected not to have been backfilled could have better hydraulic connectivity than the deeper levels of the mine which were backfilled (URS, 2005); A dilation zone with specific yield 5 times greater than the surrounding rock was assigned from -400 to 1940 ft elevation (6100 level to 3660 mine level) in a relatively small area around the mine workings to improve the match to observed water levels in the Robertson Shaft. This assumed dilation zone is considered reasonable as stress relief and relaxation in the rock mass may have occurred due to mining, thus increasing its storage properties; and The volume of the mine above 2150 mine level was reduced to one third of the initial value. This reduction in volume is conservative from the perspective of predicting future flooding, and provides a better match to the most recent mine water level measurements collected in October 2013. Table 3: Calibrated Model Parameter Values Hydrostratigraphic Horizontal Hydraulic Specific Storage Specific Elevation (ft.) Mine Level Unit Conductivity (m/s) (1/m) Yield (-) 5200 to 5600 400 to 0 7 x 10-8 1 x 10-7 0.001 4600 to 5200 1000 to 400 5 x 10-10 1 x 10-7 0.001 Bedrock 2920 to 4600 2700 to 1000 3 x 10-10 1 x 10-7 0.001 -1400 to 2920 6100 to 2700 3 x 10-10 1 x 10-7 0.001 Bedrock Dilation 6100 to 3700 -400 to 1940 3 x 10-10 1 x 10-7 0.005 Zone Pud and West Bay -1400 to 5600 6100 to 0 1 x 10-7 1 x 10-7 0.001 Faults Negus and Angel -1400 to 5600 6100 to 0 3 x 10-7 1 x 10-7 0.001 Faults
The calibration between model predicted water levels in the Robertson Shaft and inflow to the underground mine is presented in Figure 12. Overall the match is reasonably good. The model somewhat over-predicted the water level in the Robertson Shaft; this result is intentional to provide conservatively high, but still reasonable predictions of the future water level in the mine, and therefore, a conservatively short prediction of the time until flooding of the mine will be complete. A sensitivity analysis of the effect of model assumptions on the estimated time to complete flooding of the mine is also included in Section 3.4. The hydraulic heads predicted by the calibrated model in the deep groundwater flow system for November 2003 just before the dewatering system was de-activated are presented in Figure 13. The model predicted that dewatering of the mine at its ultimate depth resulted in depressurization of the surrounding bedrock, and during mining groundwater flow was directed from the surrounding lakes towards the underground mine. Groundwater flow to the mine was supplied by a combination of recharge, flow from the surrounding lakes, and porewater released from storage in the bedrock. Downward vertical gradients were predicted over the entire model domain.
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The hydraulic heads predicted by the calibrated model in the deep groundwater flow system for 2013, approximately 10 years after the dewatering system was de-activated, are presented in Figure 14. The model predicted that although the water levels in the bedrock surrounding the mine have increased by over 4000 ft (1290 m), the bedrock surrounding the mine was still largely depressurized, and downward vertical gradients remained between the shallow and deep bedrock underlying the surface footprint of the mine, including the Crank Lake TCA in 2012.
3.3 Prediction of Future Groundwater Conditions – Base Case The calibrated numerical hydrogeological model, referred to as the base case model, was used to predict future groundwater conditions that are expected to develop until the mine flooding is complete. Uncertainty in these predictions resulting from the uncertainty in the site hydrogeological conditions is discussed in Section 3.4 where a reasonable upper bound case and reasonable lower bound case are defined and discussed.
As per Part D, Item 15 of the Water License, the detailed Mine Flooding Management Plan will be further developed and submitted to the MVLWB for approval before the water level in the mine is within fifty (50) metres from the ground surface (MNML 2012). The groundwater model predicts that the flooding rate of the mine would continue to gradually decrease with the flooding rate in March 2018 predicted to be approximately half the current assumed apparent period flooding rate of 141 m3/day (assuming that the actual mine volume between 2150 and 1380 mine level is approximately one third of that provided in MNML 2012). The groundwater model also predicts that, due to the predicted gradual decrease in flooding rate, the water level in the Robertson Shaft, without mitigation, would not reach within 50 m of the ground surface until the year 2020.
The Final C&R Plan provides for contingent pumping and treatment of the mine water if it does not meet the Water License discharge standards. However, if the mine water meets Water License discharge standards, it may be directed into Rat Lake from a spill point constructed in the 204Q Stope cap. The model predicts if the mine is allowed to passively flood approximately 190 m3/day of groundwater discharge would occur to surface openings located at the mine site with up to 120 m3/day at the 204Q Stope. This discharge would most likely be dominated by shallow groundwater recharge that may include runoff from TCAs that could infiltrate into the mine envelope and discharge at these surface openings.
As per Part B, Item 17 of the Surveillance Network Program appended to the Water License, the frequency of mine water monitoring and the number of monitoring points will increase as the water approaches surface. MNML (2012) has indicated that when the mine water level approaches the 300 m (1000 ft) level, the monitoring frequency will increase to quarterly, and sampling at the Robertson Shaft, the C-1 Shaft and the Negus Shaft will be added to the quarterly monitoring plan. Figure 15 presents hydraulic heads predicted for 2015 when the water level within the Robertson Shaft is predicted to rise within 300 m of the ground surface. These results indicate that at that time groundwater flow would continue to be directed towards the mine.
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3.4 Sensitivity Analysis and Model Uncertainty The base case predictions discussed in the preceding section are the most likely hydrogeological conditions that could be encountered during mining. Due to inherent uncertainty in the subsurface conditions and parameters controlling groundwater flow, uncertainty exists in the model predictions such that the time to flood could be somewhat higher or lower than the base case values. This uncertainty was evaluated using sensitivity analysis that was performed in two stages: Parameter Sensitivity: In this stage of the analysis, model parameters were systematically varied from their calibrated values and the results were used to identify the parameters to which predicted time to flood was most sensitive. Calibration Sensitivity: Two model scenarios were prepared to provide the lower and upper range of potential time to flood and groundwater inflows, while maintaining a reasonable model calibration to pre-development conditions. These scenarios are referred to hereafter as reasonable lower bound and reasonable upper bound.
3.4.1 Parameter Sensitivity An analysis was conducted to evaluate the sensitivity of model predictions resulting from the uncertainty in model input parameters, and to identify which model input parameters are the most sensitive (i.e., results in the largest change in predictions). Parameters were varied within ranges that are considered to be reasonable based on those presented in the literature (Maidment, 1992, Stober and Bucher, 2007), and the available site data. In all cases, varying of model parameters resulted in a poorer calibration between the measured and model predicted inflows to the mine and mine water level. However, the results of this analysis demonstrate which parameter uncertainties have the greatest impact on model predictions.
Results of sensitivity analysis are presented in Figure 16. These results indicate that increasing the hydraulic conductivity of bedrock, increasing the hydraulic conductivity of faults, increasing recharge and decreasing the specific yield of all units resulted in a shorter predicted time to mine flooding (defined as the time when the water level within the Robertson Shaft reaches within 50 m of the ground surface). In contrast, decreasing the hydraulic conductivity of bedrock, decreasing the hydraulic conductivity of faults, decreasing recharge, and increasing specific yield resulted in longer predicted time to mine flooding.
All of the changes to model parameters made during sensitivity analysis resulted in unacceptable changes to the model calibration with the exception of one model run. When the hydraulic conductivity of all faults was decreased by a factor of three, very little impact on model calibration, or predicted time to flooding was observed indicating that model predictions are not sensitive to this parameter. Therefore, the uncertainty in all parameters examined during sensitivity analysis is not carried forward to the upper and low bound estimates discussed in the next section. Instead, reasonable upper bound and reasonable lower bound estimates are based on the uncertainty in parameters that could not be constrained by the available calibration data. This analysis is discussed in further detail in the following section.
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3.4.2 Calibration Sensitivity Parameters were selected for the reasonable upper bound scenario such that the time to complete mine flooding would be higher than predicted by the base case calibrated model while still maintaining a reasonable calibration to the observed data. Parameters were selected for the reasonable lower bound scenario such that the predicted time to complete mine flooding would be lower than predicted by the base case (again while maintaining a reasonable calibration to the observed data). Thus, the time to flooding predicted for these two scenarios could be considered to bracket the range of probable future conditions.
The future predicted rate of flooding in the underground mine is dependent both on the specific yield of shallow bedrock, and the future rate of recharge within the mine envelope; however, these two parameters could not be assessed accurately through the model calibration, as these parameters have little or no influence on current observed data. As the water levels rise, however, these parameters will have a progressively greater influence on future conditions. Although it is expected that the specific yield of the shallow bedrock will be greater than that of the deep bedrock, in the base case model, the specific yield of shallow bedrock is assumed to be equal to the specific yield of the deeper bedrock resulting in a conservatively short predicted time of flooding. Likewise, in the base case model, the future rate of recharge from the shallow system within the mine envelope is not assumed to decrease as the hydraulic gradient between the shallow groundwater flow regime and deep bedrock decreases, also resulting in a conservatively short predicted time to flooding. Therefore, the base case model predictions are expected to provide a somewhat conservatively short time for complete flooding.
To investigate the impact that uncertainty in the specific yield of shallow bedrock and future decreases in recharge rates could have on the estimated time to flooding, a reasonable upper bound simulation was conducted in which the specific yield of layer 1 and 2 of the model which extend to 4900 feet elevation (approximately 200 m depth or the 700 mine level) was increased by 5 times, and recharge was assumed to decrease by 50% after January 1, 2014. Results of this simulation can be considered to give a plausible upper bound estimate of the time to flooding. These results showed that the water level in the Robertson Shaft may not reach within 50 m of the ground surface until the year 2025 (approximately 5 years later than the base case). Due to the lower assumed future recharge in this scenario, the predicted discharge to surface openings if the mine is assumed to passively flood, in this scenario is approximately 70 m3/day which is about 40% of discharge predicted in the base case (190 m3/day). However, the predicted water level in the Robertson Shaft was predicted to rise to within 300 m of the ground surface by 2015 which is essentially the same as the base case.
Although the base case model is considered to provide a conservatively short period of flooding, the results of sensitivity analysis were used to develop a reasonable lower bound simulation that still resulted in a reasonable model calibration. In this scenario, the specific yield of bedrock above 5200 feet elevation (approximately 120 m depth or 400 mine level) was reduced by half, and the horizontal hydraulic conductivity of the uppermost zone of bedrock (5200 ft elevation or 120 m depth or 400 mine level) was increased by 50% to 1 x 10-7 m/s. The reduction specific yield accounts for the possibility of a reduction in pore space available for filling due to ice partially filling the pore space in the shallow bedrock where ground temperatures are below or near zero for much of the year. The adjustment made to the horizontal hydraulic conductivity of the uppermost bedrock accounts for the possibility of horizontal exfoliation fractures in the shallow bedrock due to relaxation of the rock that could occur due to isostatic rebound. Results of this simulation can be considered to give a plausible lower bound estimate of the time to flooding. Results of the lower bound simulation predicted that the water level in the Robertson Shaft would reach within 50 m of the ground surface in the year 2017 or 3 years
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earlier than predicted in the base case. Predicted discharge to surface openings when the mine was assumed to be allowed to passively flood as slightly less than the base case at approximately 170 m3/day with the majority of this flow discharging to the 204Q Stope (120 m3/day). Furthermore, the water level in the Robertson Shaft is predicted to rise to within 300 m of the ground surface by the year 2014 (approximately one year earlier than the base case).
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4.0 MITIGATION MEASURES Currently downward gradients between the shallow groundwater flow system immediately underlying the tailing containment areas and the deeper bedrock, play a role in restricting lateral movement of groundwater in the Crank Lake TCA preventing high arsenic concentrations beneath the tailings from discharging to neighbouring surface water bodies. Similarly, because the mine water level is at present at a significant depth below the levels of the surrounding lakes it is unlikely that deep mine water discharges to these water bodies. The Final C&R plan allows for contingent pumping from the Robertson Shaft, the C-1 Shaft, the Negus Shaft, and the 204Q Stope if the mine water does not meet discharge standards at the time when the water level in the mine reaches 40 m below ground surface as per Part D Item 11 and Item 12 of the Water license. Mine water pumping from one, two or all of these shafts to lower the water levels in the mine below the ground surface could be used to maintain the downward gradients between the shallow and deep groundwater flow systems thereby preventing discharge of water with high arsenic levels from discharging to nearby surface water bodies.
The largest uncertainty in the effectiveness of mine water pumping on maintaining the mine water level below the ground surface everywhere within the mine footprint is the hydraulic connection between various mine components. At present, information on the mine water level in the three shafts is only available for one sampling event (October 2013); therefore, the presence or lack of the hydraulic connection throughout the mine cannot be conclusively determined. Consequently, the existing groundwater model was used to simulate dewatering of the mine assuming that the water level in the mine is preserved at 5435 feet elevation, a water level approximately 40 m to 50 m below the elevation of the ground surface at the Robertson Shaft (5600 ft). This water level was assumed to be maintained at the Robertson Shaft, the C-1 Shaft, and the Negus Shaft by an active dewatering system. Results of this scenario predicted that if the water level in the mine was assumed to be maintained at this level, discharge of mine water to surface openings would not occur. To maintain these levels, the model predicted that approximately 290 m3/day of water would need to be removed from the mine by the dewatering system. It should be noted that this value is likely greater than the present flooding rate of the mine. This result is reasonable as presently groundwater flowing towards the mine is not only filling the mine voids but also filling the fractures/pores in the dewatered bedrock surrounding the mine. In the future, when the groundwater flow system approaches steady state conditions, the fractures/pores in the bedrock will already be filled.
In practice, dewatering of the entire mine to 40 to 50 m below the ground surface at the Robertson Shaft (5435 ft. elevation) may be achieved by pumping of mine water only in the Robertson Shaft or the C1 Shaft, if there is good hydraulic connection throughout the mine or may require pumping in the Robertson Shaft, the C-1 Shaft, and the Negus Shaft, if the connection is poor. The degree of hydraulic connectivity in the mine is dependent on the degree of collapse of the mine workings, and the presence and hydraulic properties of the backfill materials. As discussed above, initial measurements of water levels in the C-1, and Negus shafts suggest that the hydraulic connectivity between these three shafts is good. However, as discussed in the following section, it is anticipated that the degree of hydraulic connection throughout the mine can be assessed in 2014 by further monitoring of mine water level in the C-1 Shaft and the Negus Shaft, together with on-going monitoring in the Robertson Shaft.
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5.0 SUMMARY AND RECOMMENDATIONS A review of the most recently available shallow groundwater monitoring data (Golder 2012) and mine flooding data (MNML 2012) has been used to update the hydrogeological conceptual model of the Con Mine site. This information was reviewed in addition to the Final C&R Plan for the site to assess current conditions and the impact that mine water presently has on the near surface hydrogeological regime; to complete a review and verification of the updated MNML spreadsheet mine flooding model; and to predict future groundwater flow rates, anticipated seepage locations and volumes. In addition, an assessment of mitigative measures that could be used to control mine seepage was performed.
The groundwater monitoring program was initiated at the Con Mine in 2004 with the most recent results of this program reported in Golder (2012). The shallow groundwater system appears to be discontinuous with some monitoring wells becoming periodically dry and with a groundwater high located near the Crank Lake TCA. Although the potential for lateral flow from the Crank Lake TCA exists, the presence of relatively strong vertical gradients measured beneath it suggests that the downward flow to the underground workings currently dominates. Water quality monitoring results support the conclusion that the shallow groundwater flow system is perched when relatively low total arsenic concentrations (0.005 mg/L to 0.188 mg/L) measured in groundwater samples from wells outside of the Crank Lake TCA are compared to much greater arsenic concentrations (240 mg/L to 400 mg/L) measured within the Crank Lake TCA. Based on average annual water table elevations in the shallow monitoring wells, hydraulic heads in the shallow groundwater flow system have not been increasing in response to rising water levels within the underground mine over the nine year period of monitoring (Golder 2012).
Past measurements of water levels in the Robertson Shaft together with estimates of mine volumes per mining level have been used by MNML to make predictions of the time for complete flooding of the mine and to make projections of future water levels in the mine using a spreadsheet model. As discussed in MNML (2012), on October 11, 2012 the water level in the Robertson Shaft was at the 2150 level (655 m below the ground), and the estimated average flooding rate based on water levels measured since mine flooding began in 2003 was approximately 283 m3/day (8609 m3/month). By October 2, 2013 the water level in the Robertson Shaft had reached the 1380 mine level (420 m below ground) suggesting that between October 2012 and October 2013 the water level in the Robertson Shaft increased more quickly than predicted with the estimated average flooding rate revised to approximately 301 m3/day (9170 m3/month). Assuming that the current average flooding rate of 301 m3/day is maintained for the duration of mine flooding, the water level in the mine has been predicted to reach the ground surface in 3.5 years in March 2017.
Estimated flooding rates have generally been gradually decreasing for each successive measurement as the water level in the mine rises; and the apparent increase in flooding rate in 2013 appears anomalous. This result may be due to a lower unsaturated mine volume than assumed by the MNML spreadsheet model between the 2150 level (at 655 m below ground surface) reached in October 2012 and the 1380 level (at 420 m below ground surface) reached in October 2013. Possible explanations for a reduction in volume could include partial flooding of portions of the shallow mine workings prior to the water level in the Robertson Shaft reaching these elevations or partial collapse of portions of the shallow workings. If the mine volume between the 2150 level and the 1380 level is assumed to be one third to one half of that assumed in the MNML spreadsheet model, the corresponding apparent period flooding rate would be between 141 m3/day to 211 m3/day, which is consistent with period flooding rates estimated previously. Assuming that this reduction in volume is also encountered in
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levels above the 1380 level, the estimated time to mine flooding based on the MNML spreadsheet model could be as low as 2.5 years with the water level in the mine has been predicted to reach the ground surface in April of 2016. Assuming that the reduction in mine volume is restricted to between the 2150 level and the 1380 level, and that the volumes given by the MNML spreadsheet model are accurate for all levels above, the estimated time to mine flooding would between approximately 5 and 7.5 years with the water level in the mine predicted to reach the ground surface in between 2018 and 2021.
The results of quarterly monitoring of water levels in Robertson, C-1 and Negus shafts in 2014 will determine which of the three flooding rates most appropriately describes future flooding of the mine workings, but at present, the predicted time to flood derived from the mine flooding of 3.5 years with complete flooding of the workings occurring in March of 2017 is a reasonable best estimate based on the MNML spreadsheet model. However, due to uncertainty in the volume of the mine voids above the 2150 level, the predicted time to flooding could be as low as 2.5 years (flooding complete in April 2016) or as long as 7.5 years (flooding complete in 2021).
The numerical hydrogeological model developed for the Con Mine site has been updated based on the refinements to the conceptual model described in Section 3.1. The numerical model has been calibrated to the observed pre-mining groundwater inflows to the mine, water levels measured in the Robertson Shaft from 2004 to 2013, water levels in the C-1 and Negus Shafts in 2013, and the inferred mine flooding rate between each water level measurement. The calibrated model was then used to estimate the future water levels in the mine, and the anticipated surface seepage points and volumes. Results of this modelling indicated that the water level within the mine would likely rise more slowly than predicted by the MNML mine flooding spreadsheet model due to a predicted decrease in the future mine flooding rate as the mine water level approaches the levels of surrounding lakes. For the base case scenario, the water level within the mine was predicted to reach within 50 m of the ground surface at the Robertson Shaft in the year 2020. The model predicts that approximately 190 m3/day of groundwater that could include water that has been in contact with the mine would discharge to surface openings located at the mine site including up to 120 m3/day to the 204Q Stope if the mine is allowed to passively flood. Considering the uncertainty in the hydrogeological conditions near the currently dewatered mine openings as represented in the reasonable upper and reasonable lower bound scenarios, the mine water level could reach to within 50 m of the ground surface at the Robertson Shaft between the year 2017 and 2025 and the total mine water discharge could range between 70 m3/day and 190 m3/day. Mine water could reach within 300 m of the ground surface between 2014 and 2015.
Results of model simulations performed to evaluate the effectiveness of mitigative pumping of mine water to control mine water discharge to surface showed that approximately 290 m3/day of water would need to be removed by a dewatering system in the mine to maintain the water level everywhere in the mine at 5435 feet elevation (40 to 50 m below the elevation of the ground at the location of the Robertson Shaft). In practice, depending on the degree of hydraulic connection throughout the mine, dewatering of the entire mine to 40 m to 50 m below the ground surface at the Robertson Shaft (5435 feet elevation) may be achieved by pumping of the Robertson Shaft only or it may require pumping in the Robertson Shaft, the C-1 Shaft, the 204Q Stope, and the Negus Shaft. The degree of hydraulic connectivity in the mine is dependent on the degree of collapse of the mine workings, and the presence and hydraulic properties of the mine backfill.
December 9, 2013 Report No. 1314350004-001-R-Rev0 20
HYDROGEOLOGICAL STUDY - CON MINE CLOSURE
Measurements of mine water levels obtained in October 2013, suggest that these three shafts are connected hydraulically. Further quarterly monitoring in 2014 will verify the inferred hydraulic connectivity. In accordance with the Final C&R Plan, monitoring of the water level and mine water quality in the Robertson Shaft would continue on an annual basis until the mine water level reaches 300 m below the ground surface (approximately 1000 mine level). Therefore, based on the result of monitoring in 2013, quarterly monitoring in the Robertson, C-1, and Negus shafts will commence in 2014.
Recommendations for future data collection and further analysis that will allow MNML to further develop the detailed Mine Flooding Plan for the site are detailed below. Groundwater monitoring in shallow monitoring wells completed in the overburden and shallow bedrock should continue on a monthly basis when unfrozen conditions are present as per Part B Item 16 of the Water License; Information gathered from the three mine shafts and shallow monitoring wells should be reviewed at the end of 2014. At this time sufficient information should be available to assess the level of hydraulic connection between different areas of the underground development and the flooding level(s) throughout the entire mine. This information should be compared to the findings presented in this report and, if significant discrepancy is found in the forecasted flooding rates and times, the hydrogeological model should be updated and its predictions revised; and Consideration should be given to the installation of designated automated data loggers in the Robertson Shaft, the C-1 Shaft, and the Negus Shaft. These devices would allow for continuous monitoring of mine water level, water temperature, and water electrical conductivity which can be correlated to total dissolved solids (TDS) to estimate mine water quality. Installation of these devices would allow for more accurate monitoring in the final stages of mine flooding, and would aid in the assessment of the effectiveness of mine water pumping once the mine water level reaches 40 m to 50 m depth below ground. Continuous monitoring in the shafts would also allow for evaluation of the seasonality of mine water conditions, which will need to be factored into the mine water pumping plan.
December 9, 2013 Report No. 1314350004-001-R-Rev0 21
HYDROGEOLOGICAL STUDY - CON MINE CLOSURE
6.0 CLOSURE We trust that this report meets your current requirements. If you have any questions, please do not hesitate to contact the undersigned.
GOLDER ASSOCIATES LTD.
Christine Bieber, M.Sc., P.Geo. Willy Zawadzki, M.Sc., P.Geo. Senior Hydrogeologist Principal, Senior Hydrogeologist
John Hull, M.Sc., P.Eng. Don Chorley, M.Sc., P.Geo. Principal Principal, Senior Hydrogeologist
CB/WZ/JH/DWC/asd
Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation.
o:\final\2013\1435\13-1435-0004\1314350004-001-rev0-5000\1314350004-001-r-rev0-5000-con mine hydrogeo study-09dec_13.docx
December 9, 2013 Report No. 1314350004-001-R-Rev0 22
HYDROGEOLOGICAL STUDY - CON MINE CLOSURE
7.0 REFERENCES Burt, T.P, and P.J. Williams. 1976. Hydraulic conductivity in frozen soils. Earth Surface Processes, Vol. 1, pp 349– 360. Douglas, M., Clark, I.D., Raven, K., and Bottemley, D. 2000. Groundwater mixing dynamics at a Canadian Shield mine. Journal of Hydrology. 235 (2000), 88-103 Gascoyne, M., Kamineni, D.C., 1994. The hydrogeochemistry of fractured plutonic rocks in the Canadian shield. Applied Hydrogeology 2, 43–49 Geological Survey of Canada. 1998. Living with Frozen Ground: A field guide to permafrost in Yellowknife, Northwest Territories. Miscellaneous Report 64 Golder Associates Ltd., 2003. Predicted Hydrogeologic Conditions after Closure – Con Mine. Submitted to Miramar Con Mine. Project Number 03-1412-062/3000. Golder Associates Ltd., 2012. Report on Miramar Northern Mining Ltd. Con Mine Groundwater Monitoring Program 2012 Annual Report. submitted to MNML in March 2012. Greene, Shane, Battye, Nick, Clark, Ian, Kotzer, Tom, and Bottemley, Dennis. 2008. Canadian Shield brine from the Con Mine, Yellowknife, NT, Canada: Noble gas evidence for an evaporated Paleozoic seawater origin mixed with glacial meltwater and Holocene recharge. Geochimica et Cosmochimica Acta 72 (2008) 4008-4019 Hauser, R.L., McDonald D.W. and Siddorn J.P. 2007. Geology of the Miramar Con Mine. in Gold in the Yellowknife Greenstone Belt, Northwest Territories: Results of the EXTECF III Multidiscipline Research Project, Geologic Association of Canada, Mineral Deposits Division, Special Publication No. 3. INTERA Consultants Ltd., Clark, I.D., Douglas, M.C., 1997. Hydrogeological and Hydrogeochemical Study of the Miramar Con Mine – Yellowknife, NWT Maidment, David R. 1992. Handbook of Hydrology. McGraw-Hill, New York. McCauley, C.A., D.M. White, M.R. Lilly, and D.M. Nyman. 2002. A comparison of hydraulic conductivities, permeabilities and infiltration rates in frozen and unfrozen soils. Cold Regions Science and Technology, v. 34. Pp 117-125. Miramar Con Mine Ltd., 2007. Final Closure and Reclamation Plan. Submitted to the Mackenzie Valley Land and Water Board. Miramar Northern Mining Ltd. - Con Mine, 2012. 2012 Update – Mine Flooding Plan for Con Mine. Submitted to the Mackenzie Valley Land and Water Board. Natural Resources Canada. 1993. Canada-Permafrost [map]. Fifth Edition, National Atlas of Canada SRK Consulting Ltd. 2005. Groundwater Modelling Model Design and Simulation Results. Giant Mine Arsenic Trioxide Project. Prepared for Department of Indian and Northern Affairs. Steffen Robertson and Kirsten (Canada) Inc. 2002. Supporting Document 2 Giant Mine Hydrogeology. Prepared for the Department of Indian Affairs and Northern Development Stober, I., and K. Bucher. 2007. Hydraulic properties of the crystalline basement. Hydrogeology Journal. 15:213-224. URS. 2005. Miramar Con Mine Engineering Risk Assessment and Risk Management Plan for the Flooding of the Underground Workings. Prepared for Miramar Con Mine Ltd.
December 9, 2013 Report No. 1314350004-001-R-Rev0 23
632,000 633,000 634,000 635,000 636,000 637,000 638,000 639,000 640,000 641,000
Rat Lake 0 0 0 0 0 0 , , 1 1 3 3 9 9 , , 6 6 ³ Project Area Yellowknife 0 0 0 0 0 0 , , 0 0 3 3 9 9 , , 6 6 0 0 0 0 0 0 , , 9 9
2 Yellowknife 2 9 9 , ,
6 Bay 6 Main Gate
Niven Lake
0 Crank Lake 0
0 5 0 5 0 0 0 , ,
8 TCA 8 2 2 9 9 , SCALE1:200,000 KILOMETRES , 6 6
Frame Lake 0 0 0 0 0 0 , , 7 7 2 2 9 9 , , 6 6 0 0 0 0 0 0 , Yellowknife , 6 6 2 2 9 9 , , 6 6 0 0 0 0 0 0 , , 5 5 2 2 9 9 , , 6 6 0 0 0 0 0 0 , , 4 4 d 2 2 x 9 9 , , m 6 6 . p Kam a Lake M y e K _
1 Meg Lake g i 0 0 F 0 0 \ 0 0 1 , Yellowknife , 3 3 g i 2 2 F 9 9 \
, Bay , 6 6 S I G \ 4 0 0 0 - 5 3 4 0 1 - 0 3 0 , 1 2 \ 2 5 9 , 3 6
4 632,000 633,000 634,000 635,000 636,000 637,000 638,000 639,000 640,000 641,000 1 \ 3
1 LEGEND 1,000 0 1,000 0 2
\ Watercourse s t c Lease 940 Boundary e j o Paved Road r SCALE 1:50,000 KILOMETRES P \ Un-Paved Road s c i Residential Area PROJECT h p
a Wetland MIRAMAR NORTHERN MINING LTD. r G
- Waterbody HYDROGEOLOGICAL STUDY r u Site B CON MINE CLOSURE \ S
I TITLE G - D A C \ CON MINE KEY MAP y b a n r u b \ l PROJECT 13-1435-0004 FILE No. a g REFERENCE \ DESIGN CB 24 SEPT 2013 SCALE AS SHOWN REV. 0 s
d Base Data: 1:50000 Canvec. g GIS AD 24 SEPT. 2013 . r Con Mine Data: Provided to Newmont Con Mine from Ollerhead Surveying. e
d CHECK C B 25 Nov . 2013
l DATUM: NAD83 PROJECTION: UTM ZONE 11
o FIGURE: 1 g REVIEW \ Yellowknife, Northwest Territories WZ 25 Nov . 2013 \ 634,500 635,000 635,500 636,000 636,500 637,000 0 0 0 0 5 5 , ,
6 R 6 2 2 9 9
, y ,
6 DE 6 454 Raise Rat c Lake o n - N
e g ³ Mosher u Island Rycon R1 ShaftDE s 204Q Stope S DE h
e
a
0 204 Raise 0 r 0 DE 0 0 0 , , 6 6 2 2 9 9 , , 6 6
C1 Shaft Rycon Shaft Ga DE rde C1 Vent Raise DE DE n DE Dra C103J Stope w Main Gate Crank Lake Negus 220 Raise Negus 114 Raise TCA DE DE DE Upper Negus 115 Stope Negus 116 Stope Con DE 0 0
0 DE 0 5 Pond 5 , Pud Negus Shaft , 5 5
2 r 2 9 9 , TCA a , 6 e DE 6 h Negus 120 Stope S n o Negus C Negus Pond Drainage Channel DE Negus 351 Raise
DE Robertson Mine Air Heaters 0 DE 0 0 0
0 Middle Pud 0 , , 5 5 2 2 9 9 , TCA , 6 6
Warehouse
Kam Neil Lake Water Treatment TCA East Perimeter Lake Plant Drainage Channel d x m . y g 0 0 o l 0 0 o 5 5 , , e 4 4 2 2 G
9 Lower Pud 9 , , _ l 6 6 l e TCA W _ n o C _ 2 g i F _ l a n i F \ P 1
0 u 1
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\ t 4 l Yellowknife 4
2 u 2 S S u I 9 a 9 , l , G 6 F t 6 \ n s Bay 4 o u 0 g 0 C e 0
- N 5 3 4 1 - 3 1 \ 5 3
4 634,500 635,000 635,500 636,000 636,500 637,000 1 \ 3
1 LEGEND 0 300 0 300 2 \ s SURFACE OPENING WATERCOURSE t
c DE (APPROX. LOCATION) e j INTERMITTENT WATERCOURSE o r FAULT SCALE 1:15,000 METRES P
\ LEASE 940 BOUNDARY s c SHEAR i PROJECT
h TAILING CONTAINMENT AREA p DRAINAGE CHANNEL MIRAMAR NORTHERN MINING LTD. a r BUILDING G
- DRAINAGE PROPOSED HYDROGEOLOGICAL STUDY r RESIDENTIAL AREA u
B CON MINE CLOSURE
\ PAVED ROAD PARK S
I TITLE
G UN-PAVED ROAD
- WETLAND D LEASE BOUNDARY FROM THE CITY A WATERBODY C \
y CONTOUR LINE SITE PLAN b a n r u b \ l PROJECT 13-1435-0004 FILE No. a g REFERENCE \ DESIGN CB 24 Sept. 2013 SCALE AS SHOWN REV. 0 s
d BASE DATA: 1:50000 CANVEC. g GIS AD 24 Sept. 2013 . r CON MINE DATA: PROVIDED TO NEWMONT CON MINE FROM OLLERHEAD SURVEYING. e d CHECK C B 25 Nov . 2013 l DATUM: NAD83 PROJECTION: UTM ZONE 11
o FIGURE: 2 g REVIEW W Z 25 Nov. 2013 \ Yellowknife, Northwest Territories \ 12/05/2013
TYKlassen | Plotted: 12/05/2013 9:58 AM
TYKlassen | Modified: 4 LONGITUDINAL SECTION OF THE CON MINE SUBSURFACE WORKINGS | Layout:
LEGEND REFERENCE PROJECT 1. BASE PLAN PROVIDED BY "MIRAMAR CON MINE LTD." REFRACTORY RESERVES MIRAMAR NORTHERN MINING LTD. TITLED: LONGITUDINAL SECTION OF THE CONE MINE SUBSURFACE WORKINGS', HYDROGEOLOGICAL STUDY DATED: 16DEC02, FREEMILLING RESERVES CON MINE CLOSURE FIGURE 1.7. RESOURCE TITLE
MINED OUT LONGITUDINAL SECTION OF THE CON MINE SUBSURFACE WORKINGS DIABASE DYKES
CON SHEAR MINING FILE No. 13-1435-0004-03 DESIGN CB 24 Sept. 2013 SCALE AS SHOWN REV. 0 CADD RH 24 Sept. 2013 CHECK CB 25 Nov. 2013 FIGURE: 3 REVIEW WZ 25 Nov. 2013 N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\PRODUCTION\13-1435-0004-03.dwg N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\PRODUCTION\13-1435-0004-04.dwg | Layout: Fig 1.9 11x17 | Modified: TYKlassen 12/05/2013 9:58 AM | Plotted: TYKlassen 12/05/2013
LEGEND SHEER ZONES
GRANITE
DIBASE DYKES
JACKSON LAKES SEDIMENTS
INTERMEDIATE VOLCANICS
GABBRO DYKES (#8)
GABBRO SILLS (#7)
TOWNSITE FORMATION DACITE
VARIOLITIC PILLOW BASALT
MASSIVE AND PILLOW BASALT
MIRAMAR NORTHERN MINING LTD. HYDROGEOLOGICAL STUDY CON MINE CLOSURE
REFERENCE BEDROCK GEOLOGY
1. MIRAMAR CON MINE LTD., 2007. FINAL CLOSURE AND RECLAMATION PLAN. 13-1435-0004 13-1435-0004-04 SUBMITTED TO THE MACKENZIE VALLEY LAND AND WATER BOARD. FIGURE 1.9 CB 24 Sept. 2013 AS SHOWN RH 24 Sept. 2013 CB 25 Nov. 2013 FIGURE: 4 WZ 25 Nov. 2013 635,000 635,600 636,200 0 0 0 0
4 Rat 4 , , 6 6
2 Lake 2 9 9 , , 6 6
SNP0025-20 A! SNP0025-21 A! ³ A SNP0025-30 ! SNP0025-26 ! SNP0025-35 AA! A SNP0025-26A SNP0025-18 AA!! SNP0025-27 0 0 0 0 8 8 , ,
5 SNP0025-34 5 2 2
9 Main Gate 9 , SNP0025-22 , 6 SNP0025-29 6 !! ! SNP0025-28 AA! A A! SNP0025-17 Crank Lake TCA Upper AA!! SNP0025-23 SNP0025-25 SNP0025-33 A! Pud Con TCA Pond A! SNP0025-24
Negus Pond Negus
d Drainage Channel 0 0 x 0 0 m 2 2 . , , 5 5 s 2 2 n 9 9 o , , i 6 6 t a c o
L Robertson _ l
l Shaft e SNP0025-32 W SNP0025-16A Middle Pud _ n o TCA ! C !! SNP0025-16 A _ A
5 A g i
F ! _ l A a East Perimeter n i SNP0025-19 Warehouse
F Drainage Channel \ 1 0 1 v \ s Water Treatment Neil Lake n o i t Plant TCA a c o L _ l l e W _
0 SNP0025-31 0 n 0 0 o 6 6 , , C 4 4
2 ! 2 _ 9 9
6 A , , 6 6 _ 5 g i F e \ k S I a
G Lower Pud \ L 4
0 TCA 0 0 m - 5 a 3 4 K 1 - 3 1 \ 5 3
4 635,000 635,600 636,200 1 \ 3
1 LEGEND 500 0 500 0 2 \ DRAINAGE CHANNEL s t
c CRANK LAKE TCA WELL; IN TAILINGS ! DRAINAGE PROPOSED e j A o r LEASE BOUNDARY FROM THE CITY SCALE 1:11,000 KILOMETRES P \ CRANK LAKE TCA WELL; OUTSIDE OF TAILINGS PAVED ROAD s ! c i A PROJECT
h UN-PAVED ROAD p MIRAMAR NORTHERN MINING LTD. a CONTOUR LINE r ! NEGUS TCA WELL
G A - WATERCOURSE HYDROGEOLOGICAL STUDY r u INTERMITTENT WATERCOURSE B CON MINE CLOSURE \ ! PUD TCA WELL S BUILDING I A TITLE G
- LEASE 940 BOUNDARY D ! RAT LAKE AREA WELL A A TAILING CONTAINMENT AREA C
\ MONITORING WELL LOCATIONS RESIDENTIAL AREA y b BLOCKED / DECOMMISSIONED WELL a ! PARK n
r A WETLAND u b \ l WATERBODY PROJECT 13-1435-0004 FILE No. a g REFERENCE \ DESIGN CB 24 Sept 2013 SCALE AS SHOWN REV. 0 s
d Base Data: 1:50000 Canvec. g GIS AD 25 Sept. 2013 . r Con Mine Data: Provided to Newmont Con Mine from Ollerhead Surveying. e
d CHECK C B 25 Nov . 2013
l DATUM: NAD83 PROJECTION: UTM ZONE 11
o FIGURE: 5 g REVIEW W Z 25 Nov. 2013 \ Yellowknife, Northwest Territories \ 635,000 635,600 636,200 0 0 0 0
4 Rat 4 , , 6 6
2 Lake 2 9 9 , , 6 6
SNP0025-20 A! SNP0025-21 A! ³ SNP0025-30 A SNP0025-26 (0.07 mg/l) SNP0025-35 !! ! AA SNP0025-18 A SNP0025-26A (0.01 mg/l) !! SNP0025-27AA (0.06 mg/l)
0 SNP0025-34* 0 0 0 8 8 , ,
5 (321.33 mg/l) 5 2 2
9 Main Gate 9 , SNP0025-22 , 6 SNP0025-29 6 !! ! SNP0025-28 AA! A A! SNP0025-17 Crank Lake TCA SNP0025-23 Upper AA!! (0.027 mg/l) SNP0025-25 SNP0025-33 A! Pud Con TCA Pond A! SNP0025-24
Negus
d Pond
x Negus m
. Drainage Channel 0 0 s 0 0 n 2 2 , , o i 5 5 t 2 2 a 9 9 r , , t 6 6 n e c n Robertson o SNP0025-32 C SNP0025-16A Shaft _ c i (0.06 mg/l) Middle Pud (0.76 mg/l) n e s SNP0025-16 r TCA ! A !! A _ A (0.06 mg/l)
6 A g i
F ! _ l ASNP0025-19 a East Perimeter n i (0.12 mg/l) Warehouse
F Drainage Channel \ 1 0 1 v \ s Water Treatment Neil Lake n o i t Plant TCA a c o L _ l l e W _
0 SNP0025-31 0 n 0 0 o 6 6 , , C 4 4
2 ! 2 _ 9 9
6 A , , 6 6 _ 5 g i F \ S e I k
G Lower Pud a \ L 4
0 TCA m 0 a 0 - K 5
3 NOTES 4 1
- * TOTAL ARSENIC CONCENTRATION EXCEEDS THE WATER LICENSE GUIDELINE. 3 1 \ 5 3
4 635,000 635,600 636,200 1 \ 3
1 LEGEND 0 220 0 220 2 \ DRAINAGE CHANNEL s t
c PUD TCA WELL ! DRAINAGE PROPOSED e j A o r LEASE BOUNDARY FROM THE CITY SCALE 1:11,000 METRES P \ CRANK LAKE TCA WELL; IN TAILINGS PAVED ROAD s ! c i A PROJECT
h UN-PAVED ROAD p MIRAMAR NORTHERN MINING LTD. a CONTOUR LINE r ! CRANK LAKE TCA WELL; OUTSIDE OF TAILINGS
G A - WATERCOURSE HYDROGEOLOGICAL STUDY r u INTERMITTENT WATERCOURSE B CON MINE CLOSURE \ ! NEGUS TCA WELL S BUILDING I A TITLE G
- LEASE 940 BOUNDARY D ! RAT LAKE AREA WELL A A TAILING CONTAINMENT AREA TOTAL ARSENIC CONCENTRATIONS IN C \ RESIDENTIAL AREA y b WELL NOT SAMPLED IN 2012 a ! PARK MONITORING WELLS IN 2012 n
r A WETLAND u b \ l WATERBODY PROJECT 13-1435-0004 FILE No. a g REFERENCE \ DESIGN CB 24 Sept 2013 SCALE AS SHOWN REV. 0 s d BASE DATA: 1:50000 CANVEC. g GIS AD 1 Oct. 2013 . r CON MINE DATA: PROVIDED TO NEWMONT CON MINE FROM OLLERHEAD SURVEYING. e d CHECK C B 25 Nov . 2013 l TOTAL ARSENIC DATA BASED ON GOLDER (2012) MONITORING REPORT o FIGURE: 6 g DATUM: NAD83 PROJECTION: UTM ZONE 11 REVIEW \ Yellowknife, Northwest Territories WZ 25 Nov . 2013 \ REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt Flooding Average Rate
TITLE PROJECT
WATERLEVEL ANDQUALITY MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL ROBERTSON SHAFTROBERTSON CON MINE CLOSURE CON MINE DESIGN PROJECT No. REVIEW CHECK CADD
CB CB CB WZ
13
- 1435 25NOV13 25NOV13 25NOV13 01OCT13
- 0004
FILE No.
SCALE FIGURE 7 FIGURE
NTS ----
REV.
REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt LEGEND Flow Direction Flow Inferred Groundwater Fault Surface BodyWater Table Water (Offset (Offset Approx. 2200 ft) Con Shear Mining Underground Mine MineShaft
SW 5543 ft el. 5543 ft el. Kam Lake Kam Kam Lake Kam
B. A. Groundwater FlowSystem
Hydrogeologicalconditions at the end of mining Hydrogeologicalconditions before development mine Density Driven Deep DensityDriven
Robertson Shaft (Offset Approx.(Offset
C1 Shaft Shaft C1 2800 ft) 2800
TITLE PROJECT
(Offset Approx. 500 ft) 500Approx.(Offset
CONCEPTUALHYDROGEOLOGICAL
Negus Negus Shaft MODELPRE
MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL ANDMININGEND OF
CON MINE CLOSURE CON MINE
DESIGN PROJECT No. REVIEW CHECK CADD -
DEVELOPMENT DEVELOPMENT
YellowknifeBay YellowknifeBay
CB CB CB WZ 5493 ft el. 5493 ft el.
13
- 1435 NE 25NOV13 01OCT13 01OCT13 01OCT13
- 0004
(Mine Level 6100) approx. Mine Bottom FILE No.
SCALE FIGURE 8 FIGURE
NTS ----
-
700 700 ft el.
REV.
REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt LEGEND Flow Direction Flow Inferred Groundwater Fault Surface BodyWater Table Water (Offset (Offset Approx. 2200 ft) Con Shear Mining Underground Mine MineShaft
SW 5543 ft el. 5543 ft el. Kam Lake Kam Kam Lake Kam
B. A.
Potentialhydrogeological conditions at withoutmitigation closure Hydrogeologicalconditions at the end of 2013
Robertson Robertson Shaft Shaft (Offset Approx.(Offset (Offset Approx.(Offset
C1 Shaft Shaft C1
C1 Shaft Shaft C1 2800 ft) 2800 2800 ft) 2800
TITLE PROJECT CONCEPTUALHYDROGEOLOGICALMODEL
(Offset Approx. 500 ft) 500Approx.(Offset
(Offset Approx. 500 ft) 500Approx.(Offset
Negus Negus Shaft Negus Negus Shaft MINE FLOODING MINE ANDCLOSURE
MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL
CON MINE CLOSURE CON MINE
DESIGN PROJECT No. REVIEW CHECK CADD
YellowknifeBay YellowknifeBay
CB CB CB WZ 5493 ft el. 5493 ft el.
13
- 1435 NE 25NOV13 25NOV13 25NOV13 01OCT13
- 0004
(Mine Level 6100) approx. Mine Bottom (Mine Level 6100) approx. Mine Bottom FILE No.
SCALE FIGURE 9 FIGURE
NTS ----
- -
700 700 ft el. 700 700 ft el.
REV.
REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt Y Mine Coordinates (ft) B. Model domain Model domain and grid A. Model domain Model domain Kam Lake –
3D 3D view Frame Frame Lake –
X Mine Coordinates XMine Coordinates (ft) plan view plan
Opening Surface Surface
Yellowknife Yellowknife Bay TITLE PROJECT . Frame Frame
Lake
HYDROGEOLOGICALMODEL MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR Kam Kam Lake MODFLOW HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL Opening Surface Surface Extent Model Model CON MINE CLOSURE CON MINE
DESIGN PROJECT No. REVIEW CHECK CADD
NUMERICAL CB CB CB WZ
13
- 1435 25NOV13 01OCT13 01OCT13 01OCT13
- 0004
FILE No.
SCALE FIGURE 10 FIGURE
NTS ----
REV.
REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt A. B. Boundary Boundary Conditions Hydrostratigraphy Underground Underground Mine Frame Frame Lake
Kam Kam Lake Opening Surface Surface
Intermediate Shallow and Bedrock
Deep Deep Bedrock
Frame Frame TITLE PROJECT Lake
MODEL
Boundary Head Specified
Mine Underground MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR Outflow Only) (Constrained to Boundary Head Specified Kam Kam Lake BOUNDARYCONDITIONS
HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL
HYDROSTRATIGRAPHY
CON MINE CLOSURE CON MINE
precipitation. 1 to represent recharge from wasassigned to the top of layer Note
DESIGN PROJECT No.
REVIEW CHECK CADD
: A specified flux boundary
CB CB CB WZ
13
- 1435 25NOV13 01OCT13 01OCT13 01OCT13
- 0004
FILE No.
SCALE FIGURE 11FIGURE
NTS ---- AND
REV.
REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt measured in the Robertson Shaft (1380 ft). respectively, thanis less which 14 ft from that in October, 2013 were1366 ft, and 1388 ft, levelstheWater in andNegus C Note:
- 1 Shafts measured 1 Shafts measured
TITLE PROJECT
ROBERTSON SHAFTROBERTSON ANDINFLOW MINE
COMPARISONMEASUREDOF AND PREDICTED PREDICTED WATERLEVEL THE IN MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL CON MINE CLOSURE CON MINE DESIGN PROJECT No. REVIEW CHECK CADD
CB CB CB WZ
13
- 1435 25NOV13 25NOV13 25NOV13 01OCT13
- 0004
FILE No.
SCALE FIGURE 12 FIGURE
NTS ----
REV.
REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt © 2012 ©GeoEye 2012 State of Michigan Service Layer Credits: ©DigitalGlobe 2012 All distances are given are in model coordinates (ft). Note LEGEND :
Surface Surface Opening Contour Hydraulic of Head (ft) Inactive Area
Elevation (ft mine datum) Distance (ft)
Section Section Plan Plan
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Layer 7 7 Layer – Kam Lake
Row 55 Row
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2300 2300 mine ft level
RobertsonShaft Robertson TITLE PROJECT Shaft
Frame Frame Lake
Shaft C
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1 Negus Shaft
CONDITIONS
204Q Stope
PREDICTED PREDICTED HYDROGEOLOGICAL
NegusShaft
MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR
HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL CON MINE CLOSURE CON MINE SYSTEM ACTIVE
DESIGN PROJECT No. REVIEW CHECK CADD – Yellowknife Yellowknife
MINE DEWATERINGMINE
Bay
CB CB CB WZ
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REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt © 2012 ©GeoEye 2012 State of Michigan Service Layer Credits: ©DigitalGlobe 2012 All distances are given are in model coordinates (ft). Note LEGEND :
Surface Surface Opening Contour Hydraulic of Head (ft) Inactive Area
Elevation (ft mine datum) Distance (ft)
Section Section Plan Plan
–
Layer 7 7 Layer – Kam Kam Lake
Row 55 Row
–
2300 2300 mine ft level
RobertsonShaft Robertson TITLE PROJECT Shaft
Frame Frame Lake
Shaft C
-
1 Negus Shaft
PREDICTED PREDICTED HYDROGEOLOGICAL
204Q Stope
NegusShaft
MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR
HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL CONDITIONS CON MINE CLOSURE CON MINE
DESIGN PROJECT No. REVIEW CHECK CADD Yellowknife
Bay CB CB CB WZ
13
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2013 0004
FILE No.
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REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt © 2012 ©GeoEye 2012 State of Michigan Service Layer Credits: ©DigitalGlobe 2012 All distances are given are in model coordinates (ft). Note LEGEND :
Surface Surface Opening Contour Hydraulic of Head (ft) Inactive Area
Elevation (ft mine datum) Distance (ft)
Section Section Plan Plan
–
Layer 7 7 Layer – Kam Lake
Row 55 Row
–
2300 2300 mine ft level
RobertsonShaft Robertson TITLE PROJECT Shaft
Frame Frame Lake
Shaft C
-
1 Negus Shaft
PREDICTED PREDICTED HYDROGEOLOGICAL
204Q Stope
NegusShaft
MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR
HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL CONDITIONS CON MINE CLOSURE CON MINE
DESIGN PROJECT No. REVIEW CHECK CADD Yellowknife Yellowknife
Bay CB CB CB WZ
13
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1435 – Row 55 Row 25NOV13 25NOV13 25NOV13 01OCT13
- 2015 0004
FILE No.
SCALE FIGURE 15 FIGURE
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REVISION DATE: 2013-11- BY: CBieber FILE: N:\Bur-Graphics\Projects\2013\1435\13-1435-0004\5000\PRODUCTION\Powerpoint\Figure 7_to_16.ppt predicted to 50 torise withinof them ground surface at the Robertson Shaft. Note : Year of floodingdefined was as the whenyearthe mine waterwaslevel TITLE PROJECT
MIRAMAR NORTHERN MINING LTD. MINING NORTHERN MIRAMAR RESULTSPARAMETER OF UNCERTAINTY ANALYSIS HYDROGEOLOGICAL STUDY STUDY HYDROGEOLOGICAL CON MINE CLOSURE CON MINE DESIGN PROJECT No. REVIEW CHECK CADD
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HYDROGEOLOGICAL STUDY - CON MINE CLOSURE
APPENDIX A MNML 2012 Spreadsheet Model
December 9, 2013 Report No. 1314350004-001-R-Rev0
MINE FLOODING MODEL October 11, 2012 I CON MINE UNDERGROUND VOLUME CALCULATIONS- CUBIC METERS- Page 1 Time to flood (months)@ 8608.6 m3/month From Level I To Level I Cubic Meters By Level I Total Months 100 Surface 26,997 3.14 170.42 200 100 30,789 3.58 167.29 300 200 31,095 3.61 163.71 400 300 37,925 4.41 160.10 500 400 24,265 2.82 155.69 600 500 28,903 3.36 152.88 700 600 24,938 2.90 149.52 800 700 27,078 3.15 146.62 900 800 33,888 3.94 143.48 1000 900 25,386 2.95 139.54 1100 1000 30,840 3.58 136.59 1200 1100 27,323 3.17 133.01 1300 1200 31,655 3.68 129.83 1400 1300 28,923 3.36 126.16 1500 1400 28,374 3.30 122.80 1600 1500 25,153 2.92 119.50 1700 1600 26,286 3.05 116.58 1800 1700 27,490 3.19 113.53 1900 1800 6,446 0.75 110.33 2000 1900 7,669 0.89 109.58 2100 2000 6,854 0.80 108.69 2300 2100 65,312 7.59 107.90 2600 2300 21,112 2.45 100.31 2700 2600 29,475 3.42 97.86 2900 2700 42,064 4.89 94.43 3100 2900 74,575 8.66 89.55 3300 3100 32,514 3.78 80.88 3500 3300 52,860 6.14 77.11 3700 3500 40,612 4.72 70.97 3900 3700 38,499 4.47 66.25 4100 3900 28,457 3.31 61.78 4300 4100 43,736 5.08 58.47
Page 1 of 2 CON MINE UNDERGROUND VOLUME CALCULATIONS- CUBIC METERS- Page 2 Time to flood (months) @ 8906.8 m3/month From Level I To Level I Cubic Meters I By Level I Cummulative 4500 4300 53,508 6.22 53.39 4700 4500 61,910 7.19 47.18 4900 4700 93,528 10.86 39.98 5100 4900 76,314 8.86 29.12 5300 5100 75,267 8.74 20.25 5500 5300 32,768 3.81 11.51 5700 5500 25,295 2.94 7.70 5900 5700 30,815 3.58 4.77 6000 5900 5,861 0.68 1.19 6100 6000 4,357 0.51 0.51 Total Volume 1,467,116 170.42 170.42 Flooded Volume to Oct. 11/12 912,511 @ Water Level 2150 Feet
Notes: 1. The levels indicated with a light blue background were flooded as of Oct. 11, 2012. Flooded-Oct. 11/12 Cubic Meters 912,511 106 months @ 8,608.6 The flooding rate is now estimated at 8,608.6 cubic meters per month. As predicted, the flooding rate continues to be lower each year as the hydraulic head is reduced by the rising water.
2. The levels indicated with a light green background are not flooded as of Oct. 11, 2012. Remaining Volume Cubic Meters 554,605 Months to flood-> 64.42
3. On October 11, 2012 the depth of minewater in the shaft was measured at 2,150 feet. Based on this measurement, 75.0% of the volume of the void space between the 2100' level and the 2300' level was added to the volume at the 2300' level to lend further accuracy to the flooding model.
4. 2012 Water Temperature- 9.0 degrees Celsius. pH- 7.97
5. IN SUMMARY: Based on the updated and recalibrated Flooding Model, the minewater is now expected to reach surface in March 2018. Estimated Total Time to Flood: 170.42 months or 14.2 years Estimated Remaining Time to Flood: 64.42 months or 5.4 years
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