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HomeMy WebLinkAboutDWQ-2025-004403 GROUND WATER QUALITY DISCHARGE PERMIT STATEMENT OF BASIS Kennecott Bingham Canyon Mine and Water Collection System Introduction The Division of Water Quality (“Division”), under the authority of the Utah Ground Water Quality Protection Rules (Ground Water Rules), issues ground water discharge permits to facilities which have a potential to discharge contaminants to ground water. As defined by the Ground Water Rules, such facilities include mining operations. The Ground Water Rules are based on an anti-degradation strategy for ground water protection, as opposed to non-degradation; therefore, discharge of contaminants to ground water may be allowed provided that current and future beneficial uses of the ground water are not impaired and the other requirements of Utah Administrative Code (UAC) 317-6-6.4.A are met. Following this strategy, ground water is divided into classes based on its quality; and higher-quality ground water is given greater protection due to the greater potential for beneficial uses. The Division has developed permit conditions consistent with UAC R317-6 and appropriate to the nature of the mined materials, facility operations, maintenance, best available technology (BAT), and the hydrogeologic and climatic conditions of the site, to ensure that the operation will not contaminate ground water. Basis for Permit Issuance Under UAC 317-6-6.4A, The Division may issue a ground water discharge permit if: The applicant demonstrates that the applicable class total dissolved solids (TDS) limits, ground water quality standards protection levels, and permit limits established under UAC R317-6-6.4E will be met; The monitoring plan, sampling and reporting requirements are adequate to determine compliance with applicable requirements; The applicant is using best available technology to minimize the discharge of any pollutant; and There is no impairment of present and future beneficial uses of ground water. Purpose Ground Water Discharge Permit No. UGW350010 for the Bingham Canyon Mine and Water Collection System is undergoing the renewal process which occurs every five years. The permit was last renewed in 2020. As part of the renewal process, the permit will also incorporate modifications associated with new waste rock placement within the Copper IV to Yosemite drainage areas and relocation of the toe drain in the area. The permit was originally issued in 1999 and included a number of source control measures such as the cessation of active waste rock leaching and the installation of an engineered water collection system along the toe of the valley-facing waste rock dumps. This renewal will comprise changes to the original permit and, if needed, include adoption of permit limits determined in accordance with Part II.F.3 for all wells covered by the permit. Description of Facility Bingham Canyon Mine - The Kennecott Utah Copper Bingham Canyon Mine operations are located in the Oquirrh Mountains approximately 18 miles southwest of Salt Lake City, Utah. This mine produces copper and other metals that are currently extracted using an open pit method of mining. Open pit operations have been conducted at this site for over 120 years. Increased underground mine operation in the pit started in 2023 and is expected to ramp up in the coming years. Facilities included in the mine operations include the truck maintenance shops, warehouses, and mine support activities. Waste Rock Dumps - The waste rock associated with this mining operation has been placed adjacent to the open pit on the slopes of the Oquirrh Mountains. The waste rock disposal areas consist of over 6 billion tons of waste rock located in three principal areas. These three areas are referred to as the East Side, South Side, and West Side waste rock dumps. The waste rock consists of low concentrations of sulfide mineralization and trace metals in an intrusive host rock, limestone, and quartzite. Active leaching of the waste rock dumps ended in October 2000. Previously, parts of the dumps were leached by recycling water collected at the base of the dumps and placing it back on top of the waste rock. Although active leaching, i.e., recycling the collected water, has stopped, poor-quality mine-impacted water is still collected in the water collection system at the base of the dumps. Other portions of the dumps were not actively leached but do generate acidic drainage due to the contact of meteoric precipitation with waste rock. This water is collected and used as process water or discharged, as permitted under the Utah Pollutant Discharge Elimination System (UPDES) permit (UT0000051). The current collection system for the East Side dumps was constructed between 1993 and 2017 and consists of a series of 26 cut-off walls (see Figure 1) constructed in each drainage downgradient of the waste rock dumps. To augment the effectiveness of the cut-off walls in the formerly leached area from Bluewater 1 to the Copper IV drainage, toe and French drains were installed. The collection system downgradient of the east waste rock dumps was modified starting in 2012 to accommodate the continuation of mining, which includes placing waste rock to the east of the existing East Side dumps. This project, generally referred to as the East Waste Rock Extension (EWRE), was approved by the Division in 2013. In this effort, nine cut-off walls were replaced with 12 new cut-off walls between the Copper and Midas drainages to accommodate the eastern extension of waste rock. Where modifications were made, the modified collection system employs a toe drain beginning at the Copper IV drainage and ending at the Midas drainage where it overlaps the existing toe drain collection system in the Midas drainage. The newly installed collection system runs continuously along the entire eastern toe of the new waste rock dump between the Copper IV and Midas drainages and acts as the primary means of collecting waste rock contact water (WRCW). The new cut-off walls act as a secondary collection point for WRCW and the point of compliance. The South East Waste Rock Optimization (SEWOP) project required extending a toe drain by 2,000 feet in the Copper IV drainage. The existing cut-off walls and other features of the contact water collection system in the area were not modified. The Division approved the engineering drawings as a construction permit on March 28, 2024. In addition to the EWRE, a reclamation project referred to as the South Waste Rock Reclamation (SWRR) project began in 2014, which modified portions of the water collection system associated with the South Dumps, primarily in Butterfield Canyon. The SWRR project included the placement of waste rock adjacent to the existing south dumps and eventual reclamation of the dumps associated with the drainages from Yosemite to Olsen. Three existing cut-off walls were relocated and replaced with four newly constructed cut-off walls to better accommodate a relaxed and reclaimed waste rock slope. The drainages affected by reclamation activities and cut-off wall relocations include Yosemite, Butterfield 1, and Olsen. Modifications to the south dump drainages also include enhanced storm water detention basins. Operation and Maintenance manuals for the cut-off walls and detention basins are included in Appendix H (EWRE) and Appendix I (SWRR) of the permit. The collected water is conveyed by HDPE pipelines to the South Area Water Services (SAWS) Precipitation Plant for metal extraction or to the Large Reservoir system. Following the extraction of copper, the collected water is stored in the lined Bingham Reservoirs (permit #UGW350006) and/or pumped to the tailings pipelines and then gravity-fed to the Tailings Impoundment (permit #UGW350011). Leach water was applied to the Dry Fork waste rock dump until 1999. The Dry Fork plume is located under the historic Dry Fork leaching operation and is the result of historic mining activities. Controls related to the plume and WRCW include the cut-off wall in lower Bingham Canyon and groundwater extraction wells located in Bingham Canyon and Dry Fork. These wells are designed to either intercept groundwater impacted by the historic leach water applications or to capture clean water before it comes in contact with waste rock. SXEW Operations - Kennecott has conducted a pilot-scale Solvent Extraction/Electrowinning (SXEW) project in a lined and monitored area on the Dry Fork dump. The original pilot plant was decommissioned in 1999. The pads associated with the project were being used for heap leach test work. However, the pads are currently not in operation and have been taken out of service; the associated facilities have been removed. This system will be further evaluated to decide if the type of operation should be decommissioned. Pregnant leach solution from this type of test facility is either used in pilot SXEW operations adjacent to the heap leach or can be piped to the Precipitation Plant area at the mouth of Bingham Canyon. The extent of SXEW operations depends on various future market conditions. Bluewater Repository - The Bingham Canyon Mine and Water Collection System groundwater quality discharge permit includes pertinent portions of the prior groundwater permits issued for the Bluewater Repository. Each segment of the repository includes a leachate collection system that routes flows to the leach collection pipeline. Only a portion of the footprint was occupied through 2024. The Bluewater repository expansion of 500,000 cubic yards has been designed to occupy around half of the remaining permitted area in 2024, and the construction work is expected to be completed in 2025. The design of the expansion fully meets the pre-existing BAT requirements specified in Part II Section E Item 2. It is anticipated that the repository will be expanded over the next several years within the original permitted footprint and in accordance with the permitted specifications. Site Hydrogeology Tertiary volcanic bedrock is the primary stratigraphic unit that underlies the majority of the East Side waste rock dumps. The South Side waste rock is underlain by both Tertiary volcanic and Paleozoic bedrock. There is a thin layer of unsaturated alluvial and colluvial material under parts of the waste rock dumps. Beneath the Tertiary volcanics are quartzites and limestones of Paleozoic age. The Paleozoic bedrock beneath the Dry Fork waste rock dump area is fractured and is more permeable than the bedrock beneath the other waste rock dumps. Beneath most of the dumps, water tends to perch at the waste rock/bedrock contact. To the east of the waste rock disposal areas, the Tertiary volcanics and Paleozoic bedrock are covered by Plio-Pleistocene alluvial deposits. These deposits thicken to the east to form the principal aquifer in the Southwest Salt Lake Valley. The central portion of the Salt Lake Valley is generally characterized as having a shallow unconfined and a principal confined aquifer system. Confining layers are generally not present or discontinuous near the base of the mountains and are more pronounced towards the center of the valley. Except for a thin veneer of alluvial material in the area from the Copper IV drainage northward to the Bluewater drainage, Kennecott’s East Side waste rock dumps and water collection system are located on top of Tertiary volcanic rocks that transition to the alluvial aquifer system to the east of and downgradient from the collection system. Based on mapping of recharge areas completed by the U.S. Geological Survey, Kennecott’s former East Side leaching operations are immediately adjacent to the primary recharge area for the west side of the Salt Lake Valley. Background Water Quality Water quality in the principal aquifer adjacent to the East Side and South Side waste rock dumps is somewhat variable. The effects of historic mining practices are evident in certain areas. Generally, the water quality downgradient of the non-leached waste rock dumps has a total dissolved solids (TDS) value between 500 mg/L and 3,000 mg/L, which is Class II water. There are a few areas that exhibit Class I water, with TDS values less than 500 mg/L. In areas impacted by acidic waters, a typical water quality signature includes Class III or Class IV water with elevated levels of TDS, sulfate, magnesium, copper, cadmium, and zinc. Basis for Permit Issuance Kennecott has proposed a discharge minimization approach coupled with source control for this groundwater discharge permit. Discharge minimization is achieved through the use of a cut-off wall/collection system, which Kennecott has installed to enhance the capture of WRCW. Changes to the existing permit anticipated during the new permit term include the addition of a toe drain extension from the Copper IV to Yosemite drainage. Control Technology - Cut-off walls have been placed in all principal drainages along the perimeter of the East Side and South Side waste rock dumps. The site for each wall was excavated to bedrock to allow the wall to be keyed into bedrock. Along with the concrete cut-off wall, a collection pond immediately upstream of the wall is installed. In the Bluewater 1 to the Midas drainages, the collection basins upstream of the walls are lined, and seepage collection trenches extend from each side of the wall to the top of the local drainage catchment. These trenches are excavated to bedrock, clay lined and have a perforated collector pipe lain in a filter-cloth enclosed gravel drain on top of the clay liner. The trenches augment interception of subsurface flow in the thin veneer of alluvial material and direct the water to the collection pond upgradient of the cut-off wall. In the modified collection system from Midas to the Copper IV drainages, seepage is captured along the toe of the dump using a trench system that employs dual 12” perforated pipe excavated into bedrock and lined with clay, which directs water via piping to drainage bottoms and the cut-off walls. The wall acts as a secondary collection system and employs a 6” perforated pipe along the base of the wall to capture water seepage not collected by the trench. The modified system also employs storm water detention basins, which manage surface water separately from sub-surface water. These basins will help reduce maintenance requirements associated with scale, which forms when two sources of water of varying quality commingle and generate precipitates. The storm water will be transported separately by HDPE to the Bingham Canyon Reservoir. Waters collected at a cut-off wall are directed via HDPE pipeline to the primary collection pipe. Two concrete-lined canals, with an upper canal from Congor to the Eastside Reservoir and a lower canal from Copper III to the Bingham Reservoir, function as a secondary means of conveying the collected water. The upper canal is designed primarily to convey mine-impacted water under upset conditions or pipeline cleanout, and the lower canal is principally used for storm water conveyance. The lower canal can also serve as a secondary containment structure for water piped from Bingham Tunnel and/or Lark Shaft to the Large Reservoir and/or the Wastewater Disposal Pump Station. The lower canal can also be used to capture water generated from upset conditions such as a pipeline break. The concrete ditch is not used for routine conveyance of mine-impacted water. Flows from the South Side are collected by gravity flow and commingled with flows from the East Side. Cut-off walls are excavated into bedrock. Sedimentation basins are located upstream of each cut-off wall. In some cases, additional basin capacity will be established downstream of the cut-off walls but will continue to report to the primary collection pipe under gravity flow. Flows from the Dry Fork waste rock dump and other West Side dumps that drain into the Bingham Canyon are contained and collected as follows with specific permit conditions outlined in Table 2 and discussed in detail in Appendix G; well locations can be identified in Figure 2 of the Permit: 1. Two clean water extraction wells (Mid Valley and Picnic Flats) are maintained in upper Dry Fork Canyon to capture water before it contacts the waste rock dumps and underlying contaminated groundwater. Water is collected by the Mid Valley well (COP2701) and the Picnic Flats well (COG2865, which replaced COG1172) and routed to the Copperton Concentrator for use as process water. 2. The Bingham Creek cut-off wall was constructed upstream of the Bingham Reservoir System in 1994-95 to collect surface and subsurface alluvial flow in the Bingham Creek drainage. The scale of this wall is considerably larger than other cut-off walls constructed for the East Side dumps. The depth of the excavation to bedrock exceeded 100 feet. The wall is over 300 feet across at the top, with a maximum thickness of 20 feet at its base. Alluvial flows are collected by the wall through pumping and are ultimately sent to the tailings pipeline. 3. An alluvial extraction well identified as the Copperton Channel well (ECG1185) is located in the Copperton channel, a small alluvial channel that trends eastward. The well was commissioned for alluvial extraction in 1996. The well is screened between 130 and 200 feet below ground surface to capture subsurface alluvial flows. Flows captured in this channel are ultimately sent to the tailings pipeline. 4. An alluvial extraction well in Bingham Creek, identified as ECG2787, was installed in Bingham Canyon in 2009. The well is screened in alluvium between 75 and 129 feet below ground surface and extracts mine-impacted water from the surrounding alluvium. This well is located down-gradient of the Bingham Canyon waste rock dump. Under normal operating conditions, water from this well is sent to the Precipitation Plant to recover copper. 5. An alluvial extraction well identified as Curtis Springs (K83) has operated in Bingham Canyon since the 1960s. The well is located down-gradient of ECG2787 and is screened in alluvium between the depths of 46.5 and 96.5 feet below ground surface. Flows reporting to and captured by this well are contingent upon alluvial water levels. Water levels for K83 respond to pumping conducted at the upgradient ECG2787. The Bingham Canyon Mine pit acts as a large groundwater collection basin in this portion of the Oquirrhs. On average, Kennecott removes water from the pit continuously at a rate of approximately 1,000 to 1,500 gallons per minute. Several water quality issues related to mine closure are addressed in the closure plan (Appendix D). This 2003 conceptual plan has been approved by the Director. The water management concepts in Appendix D remain the same as projected for the term of this reissued permit. Water management planning may be separated into a stand-alone version of Appendix D from reclamation requirements; this would not automatically trigger a review or substantive revision of the conceptual plan but could include minor and administrative changes. Likewise, changes to Appendix D that are not under the Division’s purview would not automatically trigger a review or revision. The majority of these issues are related to pit water accumulation and quality, as well as flows from various tunnels associated with mine operations. The increased underground mine operation, which began in 2023, does not have any new water features outside the pit basin, and is part of the dewatering operation of the Bingham Open Pit Mine. Monitoring Approach A monitoring well network of 43 wells, 36 on the east side and 7 in the Dry Fork area, is utilized for compliance monitoring of the Bingham Canyon Mine and Water Collection System. In addition, wells listed in Table 3 will be used for additional informational monitoring on the east side and within the Dry Fork/Bingham Canyon area. Before 2004, only 15 wells were used for compliance monitoring. In 2004, 28 wells were added to the existing network of compliance monitoring wells. The primary objective of compliance wells is to monitor the principal valley-fill principal aquifer system. Permit limits are based on groundwater class protection levels and monitor the effectiveness of the upgraded cut-off walls, source controls, and collection system. Where possible, East Side well locations were selected to provide completions in the saturated alluvial aquifer system to the east of the waste rock disposal areas where at least 50 to 100 feet of saturation exists adjacent and above bedrock. In the southern portion of the East Side and the South Side waste rock disposal areas, as well as in areas immediately down-gradient of the cut-off walls; compliance monitor wells are completed in bedrock because no saturated alluvial deposits exist. The seven compliance wells located in the Dry Fork/Bingham Canyon area (Table 1) are screened in bedrock and are sited to confirm that contamination is not migrating out of the Dry Fork/Bingham Canyon area via bedrock flow paths. These compliance monitoring wells are all located upgradient of the Bingham Canyon cut-off wall. Permit limits for pH, total dissolved solids, sulfate, and dissolved metals of cadmium, copper and zinc (Table 1) were established in 1999 for the original 15 compliance wells; in 2004 for the additional compliance wells; and adjusted in 2010 to account for the full history and data available for each compliance well. These parameters were selected as good indicators of mine-impacted water. The permit limits established in 1999 were based on monitoring data collected over a period of 4 to 5 years, while limits established in 2004, 2010, 2015, and 2020 are based on monitoring data collected over 10, 15, 20, and 25 years, respectively. Operational monitoring for this permit includes flow and quality sampling of mine-impacted waters from the collection system, tunnel flows, leachate from repository sumps, seeps (if present), informational wells, and extraction wells. One of the technical issues associated with the monitoring well system is the ability to distinguish contamination that is historical in nature from contamination that has a recent origin. Before the installation of the upgraded cut-off wall systems in 1994-1996 and 2016-2018, the old cut-off wall system was in operation. The old cut-off wall system was less effective, resulting in a significant loss of leach water. Additionally, the velocity of groundwater in the bedrock material is relatively low, as indicated by numerous hydraulic conductivity tests conducted by Kennecott. It is likely that the contaminated groundwater present in the vicinity of some monitoring wells is from a time frame that predates the installation of the upgraded cut-off wall system. The monitoring well data will need to distinguish between historical contamination and any recent contamination. If recent contamination is detected, it may indicate that the upgraded cut-off wall system is not performing properly. Kennecott conducted several studies to age-date and identify the source of groundwater contamination in the area to provide clarification on this issue (DWQ-2001-001082, DWQ-2002-001141 and DWQ-2002-001101). Although most of the compliance monitoring wells show stable water quality results below the established protection limits, six wells show TDS exceedance and five wells show sulfate concentrations exceeding the limit as of 2024. Basis for Specific Permit Conditions Suspension of Specific Compliance Reporting Requirements - The Division is suspending the compliance reporting and sampling requirements in compliance monitoring wells as follows: If the TDS concentration exceeds the limit in any compliance well due to regular salt concentration other than sulfate, compliance reporting requirements, including those identified in Part II.G, H, and I, are suspended unless results are greater than 15% over the current protection level. All exceedances will still be included in quarterly reports corresponding to the sampling period. This will prevent unnecessary frequent notifications of elevated TDS due to salting mine roads for winter access. Monitoring wells completed in the bedrock: The ECG1100B, ECG907, and ECG925 wells can be sampled semi-annually even though they show exceedances for TDS and sulfate concentrations. The groundwater transmissivity in the bedrock is extremely low, and more frequent sampling will not present any new data. The results should be included in the quarterly reports corresponding to the sampling period. Permit Renewal Application Items - As part of the application for permit renewal, which is submitted every five years, Kennecott will include a water quality summary of the previous data collected for operational and compliance monitoring wells. Data from the Operational Monitoring program will be included in this summary. The summary will include an analysis of trends and any changes in the data throughout the life of the permit. Updated Site Maps and Well Information – Kennecott will provide within one year of permit issuance: Updated site maps and diagrams of all monitoring wells, leach water collection sites, cutoff walls, and all other parts of the East Side Collection System, including updated plume maps, aquifer contour maps with flow rate and direction, and Coordinates of all monitoring wells and leach water collection sites associated with the East Side Collection System. BAT Inspection - Kennecott will conduct a comprehensive BAT inspection of the entire East Side Collection System within 2 years of permit issuance to ensure that all components of the collection and drainage system are functioning as designed and to identify any maintenance work that may be necessary. Kennecott will submit a BAT inspection work plan for approval by the Division within 1 year of permit issuance. Kennecott will provide the Division with the results of the BAT inspection, identifying any deficiencies found. Kennecott will provide the Division with a plan to correct any deficiencies within 90 days of completion of the BAT inspection, including milestones and completion schedules for Director approval. Kennecott will begin implementing the approved schedule and provide updates in quarterly reports submitted to the Division. Final Closure - Kennecott has an approved conceptual closure plan attached in Appendix D of this permit. One year prior to final closure, Kennecott shall submit, for approval by the Director, a final closure plan that addresses the water quality management aspects of closure.