DWQ-2024-003579

STATEMENT OF BASISGround Water Discharge Permit UGW350001Kennecott Barneys Canyon Mining Company
January 2024
Introduction
The Division of Water Quality (“DWQ”), under the authority of Utah Code §19-5 101 et. seq. and the Utah Ground Water Quality Protection Rules1 promulgated thereunder (“Ground Water Rules”),
issues ground water discharge permits to facilities which have a potential to discharge contaminants to ground water.2 As defined by the Ground Water Rules, such facilities include
mining operations.3 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 Admin. Code R317-6-6.4(A) are
met. Following this strategy, ground water is divided into classes based on its quality4; and higher-quality ground water is given greater protection5 due to the greater potential for
beneficial uses.
DWQ has developed permit conditions consistent with Utah Admin. Code R317-6 and appropriate to the nature of the mined materials, facility operations, maintenance, best available technology6(“BAT”)
and the hydrogeologic and climatic conditions of the site, to ensure that the operation would not contaminate ground water. Basis for Permit RenewalThis Permit is being renewed in accordance
with Utah Admin. Code R317-6-6.8 which states that a permit may be terminated or a renewal denied if any one of the four items below applies:Noncompliance by the permittee with any condition
of the Permit where the permittee has failed to take appropriate action in a timely manner to remedy the Permit violation;The permittee’s failure in the application or during the Permit
approval process to disclose fully all significant relevant facts at any time;A determination that the permitted facility endangers human health or the environment and can only be regulated
to acceptable levels by plan modification or termination; orThe permittee requests termination of the Permit.Basis for Modification and Permit Issuance
Under Utah Admin. Code R317-6-6.4(A), DWQ may issue a ground water discharge permit if:
The applicant demonstrates that the applicable class TDS limits, ground water quality standards protection levels and permit limits established under Utah Admin. Code R317-6-6.4(E) will
be met;
The monitoring plan, sampling and reporting requirements are adequate to determine compliance with applicable requirements;
The applicant is using BAT to minimize the discharge of any pollutant; and
There is no impairment of present and future beneficial uses of ground water.
Under Utah Admin. Code R317-6-6.7, a permit renewal may contain significant changes to the original permit so long as they are performed under the direction, and bear the seal, of a
professional engineer or professional geologist. Changes and modifications to the renewed permit are further described below.Facility Description
Kennecott Barneys Canyon Mining Company, a Delaware Corporation, (“Permittee”)is in final closureof its gold recovery facility, referred to herein as “the Facility,” west of Salt Lake
City,approximately two miles north of Copperton, Utah, on the east flank of the Oquirrh Mountains. Mining operations at the Facilityceased in 2001 and reclamation of the oxide waste
rock dumps and the sulfide waste rock repositories were completed by the end of 2002.Active cyanide leaching ceased in 2007, and ore on the heap leach pads wasrinsed with process water
for gold recovery until 2013.The former process ponds have been taken out of service.Closure of the heap leach pads, including recontouring the slopes and placing approximately three
feet of cover soil, were completed in 2020 under construction permits from DWQ. Part of the final closure included the relocation of a stockpile of sulfide ore consisting of approximately
125,000 tons of material. This stockpile was incorporated into the heap leach pads as part of final closure activities.In addition, soil adjacent to the heap leach pads containing materials
from ore handling has been incorporated into the leach pads beneath the final cover.
The leach pads, processing ponds, processing plant, pits, reclaimed waste rock dumps, and ancillary facilities were operated with no intentional direct discharge to waters of the State
of Utah. All drainage pad watergenerated from the heap leach pads is gravity drained to the Tailings Pipelines through a dual-contained piping conveyance system. Although sodium cyanide
(NaCN) was the lixiviant used in the original gold-leaching process, its addition was discontinued in 2007 when rinsing of the pads started and continued through 2013. Since 2013, no
rinse water has been added to the pads and drainage consists of meteoric water that falls on the pad footprint.
A series of construction permits were obtained from DWQ for the implementation of the final site closure design. Upon completion of the permitted construction, a completion report was
submitted to DWQ for approval on June 16, 2021. The Completion Report includes a summary of construction activities, as-built drawings of the executed construction and a draft operation
and maintenance plan.Historical Leach and Rinse Water
Historically, the leach solution generally contained less than 50 ppm NaCNuntil its addition was discontinued in 2007.NaCN leaching was followed by the addition of rinsewater that was
pumped in pipes to the top of the leach pads where it was distributed at the rate of 2,000 to 2,500 gallons per minute.Sodium hydroxide (NaOH)was used as necessary to manage the pH and
the base metal loading within the circulating rinse water. The rinsewater was a re-circulated combination of process water from the Kennecott process water line (when make-up water
was needed) and meteoric and barren pond waterwhich containedresidual cyanide. The solutions chemical composition varied as it moved through different stages of the gold extraction process.
At all stages of the process, the solution had high sulfate content, generally greater than 2,000 milligrams per liter (mg/l), reflecting the closed circulating system, which had been
operating continuously since 1989. Metals listed in Table 1 of the permit, Ground Water Protection Levels, are present at relatively low to moderate concentrations, generally below
20 mg/L.Currently, the pads generate a flow of 15 to 40 gallons per minute, of meteoric drainage water which is conveyed via a gravity piping system to the Tailings Pipelines. The fluctuation
in flow directly correlates with the site precipitation amounts.
Water Type Definitions
Several types of water and drainage are discussed in the fact sheet and permit and are clarified as follows. Leach water is the solution of water and cyanide used to perform active leaching
and metal recovery during the operational period of the Facility. Following closure of the Facility, leach water is no longer stored or used at the site. Rinse water is process water,
former leach water, and meteoric or contact water mixed and used to rinse the leach pads during closure activities. Process water is water the Permittee uses to make operational the
entire facility from mining, to concentration, slurry of metals to refining and smelting, and disposal of tailings. Process water is generally higher quality at its source and is kept
in the process loop to be reused as much as possible. Drainage pad water consists of residual rinse water and meteoric contact water that continues to drain from the heap leach pads.
Meteoric water is water that falls from meteorological sources like rain and snow. Contact water is water which has come in contact with site materials that contain metals or other
contaminants and is no longer representative of natural water quality.
Best Available Technology
Leach Pads
Each leach pad consisted of several cells. The vertical configuration of each leach pad is as follows, from top to bottom:1.Three (3) to 5-foot thick process solution collection system
of fine-grained ore.2.60-mil high-density polyethylene (“HDPE”) primary liner.3.12-inch minimum thickness clay secondary liner with amaximum hydraulic conductivity of 1.0 x 10-7centimeters
per second (cm/sec).4.Below the claysecondary liner is a 6-inch thick inactiveleak detection layerwith a hydraulic conductivity of 1.0 x 10-3 cm/sec or greater. 5.6-inch minimum thicknesssoiltertiary
liner with a maximum hydraulic conductivity of 1.0 x 10-6 cm/sec.Each leach pad has positive drainage from west to east. At the east end of each leach pad, a series of drains convey
drainage water to the water piping system which consistsof dual-contained pipelines, distribution and desilting boxes, and finally, a common dual-contained pipeline that discharges to

a final distribution box prior to entering the Kennecott Tailings Pipeline.Prior to the final closure covering, the leach pads were maintained in a manner that allowed sufficient freeboard
in the event of a 100-year,24-hour storm event. The leach pads were maintained and operated within these parameters until the final closure design and coverwere completed and commissioned
at the end of 2020. Hydrogeology
The former leach site is located on the east flank of the Oquirrh Mountains on the surface of an old east dipping alluvial fan. The fan deposit ranges from 100 to 200 feet thick and
consists of sand, gravel and clay. Volcanic rocks underlie the alluvial material. These rocks consist of agglomerates, mudflow deposits and lava flows, and are probably less permeable
than the overlying alluvium. The water table slopes downward to the east and according to data from the monitoring wells ranges from 82 to 380 feet in depth. A production well (BC280)
for the site pumps about 50 gallons per minute when needed for closure activities.Ground Water Quality and Protection Levels
Based on monitoring completed for the permit to date, ground water in the mine area is classified as Class II Drinking Water Quality Ground Water4. On the basis of sampling completed
since the permit was originally issued, background ground water quality, ground water protection levels, and out-of-compliance levels have been revised. The protection levels for total
dissolved solids are 1.25 times the background value. When a contaminant is present in a detectable amount in the background concentration, the concentration of the pollutant may not
exceed 1.25 times the background concentration, or exceed 0.25 times the ground water quality standard, whichever is greater. When a contaminant is not present in a detectable amount,
the concentration of the pollutant may not exceed 0.25 times the ground water quality standard, or exceed the limit of detection, whichever is greater. Permit Conditions
BAT is to be used to maintain compliance with ground water protection levels. This requires no discharge of drainage pad water from the Facility to ground water. Compliance ground
water quality monitoring is required to demonstrate that compliance with ground water protection levels is being maintained. Maintenance of BAT will be demonstrated by the absence of
drainage pad wateroff the pads and maintaining final cover of the leach pads in an erosion-free condition to prevent generation of contact water.Ground Water Quality Monitoring
All monitoring wells are to be sampled semi-annually. Ground water quality protection levels described in the permit are used to determine compliance with the Permit. Under the renewed
permit, the Permittee shall collect water quality data and report it to the DWQ Director on asemi-annual basis. In the event thatthe permit’sground water protection levelsare exceeded,
the DWQ Director will determine corrective and remedial action, if any.
Under the renewed permit, monitoring will includeparameters indicative of a release of pad drainage water. These parameters include major ions, which are present in different proportions
in the ground water compared to the pad drainage water; cyanide, a synthetic chemical present in the process solutions but not naturally present in the ground water; and nitrate, a degradation
product of cyanide. Analysis for major ions also includes sulfate, which is present in pad drainage water.Most of these parameters are highly mobile in ground water and should result
in early detection of a release of pad drainage water. If monitoring for these parameters reveals leakage from the pad drainage facilities, Permittee must monitor for other contaminants
which may have been released as part of a Contaminant Investigation as required under Utah Admin. Code R317-6-6.15.
Under therenewed permit, DWQ is eliminating monitoring obligations related to threeformer compliance wells consisting of BCG281, BCG285, andBCG849, based on the previous seven years
of data supporting the conclusion that analyte trends have been stable or reflect changes to background concentrations in the ground water. These wells, which are up-gradient and located
in the areas of the former leach pads, are being kept by Permittee as information wells available for sampling and not wells used to monitor for compliance in closure. These wells will
be sampled at the request of the DWQ Director.
Upgradient monitoring well BCG280 was removed as a point of complianceduring the 2018 permit renewal. This well was constructed as a water supply well and has a long screen interval
that may lead to dilution of samples assessing potential ground water contamination as a result of mining activities, making the well ineffective. Additionally, a portion of the screen
has collapsed, preventing reliable purging and sampling activities. Given that active mining activities are no longer occurring, this upgradient monitoring point is no longer necessary
and was abandoned in 2022.
The remaining wells are down-gradient of the former site operations and closed leach pads, and represent a compliance point capable of capturing any impacts from the site, if any are
observed. The monitoring wells remaining in the permit consist of BCG282, BCG496, BCG283, BCG848, BCG851A, BCG851B, BCG850, BCG852, BCG284, W31, and BCG2846.
Duringthe 2018 permit renewal, former compliance parameters for cadmium, copper, lead, and silver were removed from the analyte/compliance list. None of these constituents have been
detected in the compliance wells at the Facility or in the drainage padwater generated at the Facility. As such, DWQ considers these parameters unnecessary for continuedmonitoring.
Arsenic has been added as a ground water monitoring compliance parameter because it is known to exist in elevated concentrations at natural background levels, and is present in the contact
water generated from drainage through the heap leach pads.Mine Pit Water
Water from mine pits at this site, after primary sediment treatment, may beconveyed for use at the Copperton Concentratorand during final closure operating and maintenance activities.
Other use or disposal require approval from the DWQ Director.
Compliance Schedule
The following reports are included in the compliance schedule of the permit. These reports will help to assess the effectiveness of the closure activities which have been completed and
is material to the Divisions evaluation of continued risk to waters of the state from the mining activities and the remaining infrastructure and waste. This information is necessary
to evaluate the long-term need for the groundwater permit post-closure.
Leach Pad Discharge Volume Analysis and Quality Report – Within 2 years of the issuance of the permit, the permittee shall submit to the Division a report containing the following information:
A comparison of the projected reduction of flow from the former heap leach pads to the measured flow from the pad drains since capping was complete, through the most recent flow measurements
prior to the report being submitted;
Projections for continued reduction of flows from the former heap leach pads, if applicable;
An analysis comparing the water quality of the heap leach pad drainage water before and after closure;
Projections for how water quality will improve as the pads drain and contaminants are oxidized, rinsed, or otherwise reduced in the pad drainage.