COMPASS MINERALS INTERNATIONAL INC

SUMMARY OVERVIEW OF MINING OPERATIONS

Information concerning our mining properties in this Form 10-K has been prepared in accordance with the requirements of subpart 1300 of Regulation S-K. Subpart 1300 of Regulation S-K requires us to disclose our mineral resources, in addition to our mineral reserves, as of the end of our most recently completed fiscal year both in the aggregate and for each of our individually material mining properties. When evaluating materiality for purposes of the disclosure, the Company considered several quantitative metrics including production, sales and capital expenditure data, as well as synergistic and other qualitative information that the Company believes investors would find important to their investing decisions.

As used in this Form 10-K, the terms “mineral resource,” “measured mineral resource,” “indicated mineral resource,” “inferred mineral resource,” “mineral reserve,” “proven mineral reserve” and “probable mineral reserve” are defined and used in accordance with subpart 1300 of Regulation S-K. Under subpart 1300 of Regulation S-K, mineral resources may not be classified as “mineral reserves” unless the determination has been made by a qualified person (“QP”) that the mineral resources can be the basis of an economically viable project. You are specifically cautioned not to assume that any part or all of the mineral deposits (including any mineral resources) in these categories will ever be converted into mineral reserves, as defined by the SEC. See Item 1A, “Risk Factors.”

You are cautioned that, except for that portion of mineral resources classified as mineral reserves, mineral resources do not have demonstrated economic value. Inferred mineral resources are estimates based on limited geological evidence and sampling and have a too high of a degree of uncertainty as to their existence to apply relevant technical and economic factors likely to influence the prospects of economic extraction in a manner useful for evaluation of economic viability. Estimates of inferred mineral resources may not be converted to a mineral reserve. It cannot be assumed that all or any part of an inferred mineral resource will ever be upgraded to a higher category. A significant amount of exploration must be completed in order to

determine whether an inferred mineral resource may be upgraded to a higher category. Therefore, you are cautioned not to assume that all or any part of an inferred mineral resource exists, that it can be the basis of an economically viable project, or that it will ever be upgraded to a higher category. Likewise, you are cautioned not to assume that all or any part of measured or indicated mineral resources will ever be converted to mineral reserves. See Item 1A, “Risk Factors.”

The Company has determined that the following properties are individually material mining properties for purposes of subpart 1300 of Regulation S-K: the Ogden facility, the Cote Blanche mine and the Goderich mine. The Company has terminated its lithium project and is no longer disclosing mineral resources of lithium or lithium carbonate equivalent, so it is not filing a technical report summary for lithium in connection with this Form 10-K. There have been no material changes in the mineral reserves or mineral resources from the last technical report summaries filed for each of the other properties, so the Company is not filing a new technical report summary for any of these properties in connection with this Form 10-K.

The following map shows the locations of our mining properties, as of September 30, 2024:

As of September 30, 2024, we had ten mining properties, as summarized in the table below:

We are the sole operator of each of our mining properties and we own all of the ownership interests in our mining operations. With respect to most of our mineral properties, we own the land and surface rights and have entered into lease agreements with respect to the mineral rights. Our mineral leases have varying terms. Some will expire after a set term of years, while others continue indefinitely. Many of these leases provide for a royalty payment to the lessor based on a specific amount per ton of minerals extracted or as a percentage of revenue. In addition, we own a number of properties and are party to non-mining leases that permit us to perform activities that are ancillary to our mining operations, such as surface use leases for storage at depots and warehouse leases. We believe that all of our leases were entered into at market terms.

We hold numerous environmental and mineral extraction permits, water rights and other permits, licenses and approvals from governmental authorities authorizing operations at each of our facilities. With respect to each facility at which we produce salt, brine or SOP, permits, licenses and approvals are obtained as needed in the normal course of business based on our mine plans and federal, state, provincial and local regulatory provisions regarding mine permitting and licensing. Based on our historical permitting experience, we expect to be able to continue to obtain necessary mining permits and approvals to support historical rates of production.

The three processing methods we use to produce salt and SOP at our production-stage properties are as follows:

•Underground Rock Salt Mining - We produce most of the salt we sell through underground mining. In North America, we use a combination of continuous mining and drill and blast techniques. At our Winsford, Cheshire, U.K., mine, we utilize continuous mining techniques. Mining machinery moves salt from the salt face to conveyor belts, which transport the salt to the mill center where it is crushed and screened. It is then hoisted to the surface where the processed salt is loaded onto shipping vessels, railcars or trucks. The primary power sources for each of our rock salt mines are electricity and diesel fuel. Rock salt is sold in our highway deicing product lines and for numerous applications in our consumer and industrial product lines.

•Mechanical Evaporation - Mechanical evaporation involves creating salt-saturated brine from brine wells in underground salt deposits and subjecting this salt-saturated brine to vacuum pressure and heat to precipitate and crystallize salt. The primary power sources used for this process are natural gas and electricity. The resulting product has a high purity and uniform physical shape. Mechanically-evaporated salt is primarily sold through our consumer and industrial salt product lines.

•Solar Evaporation - For a description of the solar evaporation process, see “—Ogden Facility” below.

Our current estimated production capacity is approximately 16.2 million tons of salt and 360,000 tons of SOP per year. The following table shows the estimated annual production capacity and type of salt or other mineral produced at each of our owned or leased processing locations as of September 30, 2024:

(1)Annual production capacity is our estimate of the tons that could be produced based on design capacity, assuming optimization of our operations, including our facilities, equipment and workforce. Incremental equipment, labor or other costs may be required to achieve these production capacity estimates. As we continue our efforts to optimize and refine our production methods, we will update our estimates if necessary.

(2)Solar salts deposited annually substantially exceed the amount converted into finished products. The amount presented here represents an approximate average amount produced based on recent market demand.

(3)The magnesium chloride amount includes both brine and flake.

(4)The annual SOP production capacity at our Ogden facility during normal weather and pond chemistry conditions, which includes amounts produced from both solar-pond based feedstock and supplemental KCl feedstock when economically feasible.

Actual annual salt, magnesium chloride and SOP production volume levels may vary from the annual production capacity shown in the table above due to a number of factors, including variations in the winter weather conditions which impact demand for highway and consumer deicing products, the quality of the reserves and the nature of the geologic formation that we are mining at a particular time, unplanned downtime due to safety concerns, incidents and mechanical failures, and other operating conditions.

The following table shows production by product at our owned and leased production locations, in tons:

(1)Excludes solar salt harvested at our Ogden facility that is not converted into finished product and salt processed at our packaging facilities.

(2)Fiscal year 2023 and 2022 production tons are less than our reserve reduction due to process timing of extracting tons to producing finished product. See Ogden Facility below for additional information regarding our sodium, sodium chloride, magnesium and magnesium chloride reserve estimates at the Ogden facility.

Our production facilities have access to vast mineral deposits. At all of our production locations, we estimate the recoverable reserves to last at least several more decades at current production rates and capacities, although additional capital resources and developmental spending may be required. Our rights to extract those minerals may be contractually limited by geographic boundaries or time. We believe that we will be able to continue extending these agreements, as we have in the past, at commercially reasonable terms without incurring substantial costs or material modifications to the existing lease terms and conditions, thereby allowing us to fully utilize our existing mineral rights.

Our underground mines in Canada (Goderich, Ontario), the U.S. (Cote Blanche, Louisiana) and the U.K. (Winsford, Cheshire) make up 85% of our salt production capacity as of September 30, 2024. Each of these mines is operated with modern mining equipment and utilizes subsurface improvements, such as vertical shaft lift systems, milling and crushing facilities, maintenance and repair shops and extensive raw materials handling systems.

In 2012, we acquired mining rights to approximately 100 million tons of salt resources in the Chilean Atacama Desert. This resource estimate is based upon an initial assessment. A feasibility study would be completed before we decide whether to proceed with the development of this project to ensure the salt resources can be converted into reserves. The development of this project would require significant infrastructure to establish extraction and logistics capabilities. As of September 30, 2024 our investment in these rights totaled $8.5 million.

Summary of Mineral Resources and Reserves

Summaries of our mineral resources and reserves at the end of fiscal 2024 are set forth in Tables 1 and 2.

Table 1. Summary Mineral Resources at September 30, 2024

(1)Mineral resources are reported in situ. Mineral resources are not mineral reserves and do not have demonstrated economic viability. There is no certainty that all or any part of the mineral resources will be converted into mineral reserves upon application of modifying factors.

(2)Based on an average sodium chloride grade of 97,350 milligrams per liter (“mg/L”) in the north arm of the Great Salt Lake and 46,300 mg/L in the south arm of the Great Salt Lake. Reported concentrations for the Great Salt Lake assume an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm. Grades of in-situ sodium chloride range from 75% at our Lyons facility to 98% at the Goderich mine. Although the actual sodium chloride grade at our underground mines is less than 100%, it is not considered in the resource, as the final saleable product is the in situ product, as-present (i.e., the saleable product includes any impurities present in the in situ rock).

(3)There are multiple saleable products based on salt quality from the underground mining operations (rock salt for road deicing and chemical grade salt). For simplicity, all sales are assumed at the lower value (and higher tonnage) product, rock salt, and are based on pricing data based on a five-year average (2020 through 2024) of historical sales data for rock salt for road deicing of $64.40 per ton to $94.98 per ton. Sales prices are projected to increase to approximately $319.63 per ton to $1,204.66 per ton for rock salt for road deicing through the current expected end of mine life.

(4)The Company does not have exclusive access to mineral resources in the lake and other existing operations, including those run by US Magnesium, Morton Salt and Cargill, also extract dissolved mineral from the lake (all in the south arm).

(5)With respect to the Ogden facility, based on an average potassium grade of 7,320 mg/L in the north arm of the Great Salt Lake and 3,060 mg/L in the south arm of the Great Salt Lake. Reported concentrations for the Great Salt Lake assume an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

(6)With respect to the Ogden facility, based on pricing data based on a five-year average (2020 through 2024) of historical sales data for SOP of $659.96 per ton. Sales prices are projected to increase to approximately $8,529 per ton through the current expected end of mine life.

(7)The Company does not have exclusive access to mineral resources in the lake and other existing operations, including those run by US Magnesium and Cargill, also extract dissolved mineral from the lake (all in the south arm).

(8)No resources or reserves have been estimated for the Wynyard facility since the production process relies on the import of KCl as a source of potassium from external sources, with supplemental potassium from a relatively dilute concentration of potassium (approximately 0.05%) from Big Quill Lake.

(9)Based on an average magnesium chloride grade of 11,150 mg/L in the north arm of the Great Salt Lake and 4,790 mg/L in the south arm of the Great Salt Lake. Reported concentrations for the Great Salt Lake assume an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

(10)Based on pricing data based on a five-year average (2020 through 2024) of historical sales data for magnesium chloride of $74.46 per ton. Sales prices are projected to increase to approximately $1,100.39 per ton through the current expected end of mine life.

(11)The Company does not have exclusive access to mineral resources in the lake and other existing operations, including those run by US Magnesium, also extract dissolved mineral from the lake (in the south arm).

Table 2. Summary Mineral Reserves at September 30, 2024

(2)Based on an average sodium chloride grade of 97,350 mg/L in the north arm of the Great Salt Lake and 46,300 mg/L in the south arm of the Great Salt Lake. Reported concentrations for the Great Salt Lake assume an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm. Grades of in-situ sodium chloride range from 75% at our Lyons facility to 98% at the Goderich mine. Although the actual sodium chloride grade at our underground mines is less than 100%, it is not considered in the reserve, as the final saleable product is the in situ product, as-present (i.e., the saleable product includes any impurities present in the in situ rock).

(3)There are multiple saleable products based on salt quality from the underground mining operations (rock salt for road deicing and chemical grade salt). For simplicity, all sales are assumed at the lower value (and higher tonnage) product, rock salt, and are based on pricing data based on a five-year average (2020 through 2024) of historical sales data for rock salt for road deicing of $64.40 per ton to $94.98 per ton. Sales prices are projected to increase to approximately $319.63 per ton to $1,204.66 per ton for rock salt for road deicing through the current expected end of mine life.

(4)With respect to the Ogden facility, based on an average potassium grade of 7,320 mg/L in the north arm of the Great Salt Lake and 3,060 mg/L in the south arm of the Great Salt Lake. Reported concentrations for the Great Salt Lake assume an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

(5)With respect to the Ogden facility, based on pricing data based on a five-year average (2020 through 2024) of historical sales data for SOP of $659.96 per ton. Sales prices are projected to increase to approximately $8,529 per ton through the current expected end of mine life.

(6)No resources or reserves have been estimated for the Wynyard facility since the production process relies on the import of KCl as a source of potassium from external sources, with supplemental potassium from a relatively dilute concentration of potassium (approximately 0.05%) from Big Quill Lake.

(7)Based on an average magnesium chloride grade of 11,150 mg/L in the north arm of the Great Salt Lake and 4,790 mg/L in the south arm of the Great Salt Lake. Reported concentrations for the Great Salt Lake assume an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

(8)Based on pricing data based on a five-year average (2020 through 2024) of historical sales data for magnesium chloride of $74.46 per ton. Sales prices are projected to increase to approximately $1,100.39 per ton through the current expected end of mine life.

Our mineral resource and reserve estimates were prepared by a QP and have a basis in periodic, historical reserve studies completed by third-party geological engineering firms. Our mineral resource and reserve estimates and the third-party reserve studies are based on many factors, including the area and volume covered by our mining rights, assumptions regarding our extraction rates based upon an expectation of operating the mines on a long-term basis and the quality of in-place reserves. Established criteria for inferred, indicated and measured resources and proven and probable reserves are primarily applicable to mining deposits of discontinuous metal, where both the presence of ore and its variable grade need to be precisely identified. However, the massive continuous nature of evaporative deposits, such as salt deposits, requires proportionately less data for the same degree of confidence in mineral resources and reserves, both in terms of quantity and quality.

OGDEN FACILITY

The Ogden facility is a production stage property that separates and processes potassium, sodium and magnesium salts from brine sourced from the Great Salt Lake in Utah. The primary product currently produced at the Ogden facility is SOP (which is a potassium-rich salt used as plant fertilizer), with coproduct production of sodium chloride (which is used for highway deicing and chemical applications) and magnesium chloride (which is used in deicing, dust control and unpaved road surface stabilization applications and is an ingredient in our fire retardant products). The Company has also identified a lithium resource at the Ogden facility, but has recently indefinitely suspended its plans to add lithium salt as a coproduct to SOP production. The Ogden facility relies upon solar evaporation to concentrate brine extracted from the north arm of the Great Salt Lake and precipitate the salts into a series of large evaporation ponds located on the east and west sides of the lake, referred to as the east ponds and the west ponds, respectively, prior to harvesting and processing at its related plant (the “Ogden plant”). Maps of the Ogden facility are shown in Figures 1 and 2.

Figure 1. Ogden Facility Property Location Map

Figure 2. Locations of East and West Ponds Relative to the Ogden Plant and the Great Salt Lake

The Great Salt Lake is the largest saltwater lake in the western hemisphere, and the fourth largest terminal lake in the world, covering approximately 1,700 square miles. It is also one of the most saline lakes in the world, with a chemical composition very similar to the world’s oceans. Salinity throughout the Great Salt Lake is governed by lake level, freshwater inflows, precipitation and re-solution of salt, mineral extraction, and circulation and constriction between bays of the lake.

The infrastructure associated with the Ogden facility, including the Ogden plant, is located on the shores of the Great Salt Lake in Box Elder and Weber Counties in the State of Utah. The Ogden plant is located at the approximate coordinates of 41˚16’51” North and 112˚13’53” West on the east side of the lake approximately 15 miles (by road) to the west of Ogden, Utah, and 50 miles (by road) to the northwest of Salt Lake City, Utah. The east ponds are located adjacent (to the north and west) to the Ogden plant in Bear River Bay. The west ponds are located on the opposite side of the Great Salt Lake (due west) in Clyman and Gunnison Bays. Access to the Ogden facility is via Ogden, Utah, and its vicinity on paved two-lane roads. From Salt Lake City, Utah, located 40 miles to the south, Ogden is accessible via Interstate Highway 15. Commercial air travel is accessible from Salt Lake City. The area population provides a more than adequate base for staffing the Ogden facility, with a pool of talent for both trades and technical management. The Ogden facility is connected to the local municipal water distribution system, Weber Basin Water Conservation District. The Ogden facility is also connected to the local electrical and natural gas distribution systems provided by Rocky Mountain Power and Dominion Energy, respectively, and houses an existing substation that services the operations at the east ponds. Rail access is provided by Union Pacific Railroad on an existing siding at the Ogden plant.

The Ogden facility is located on approximately 108,749 acres of land, of which approximately 7,434.16 acres are owned by the Company. The Great Salt Lake and minerals associated with it are owned by the State of Utah. The Company is able to extract and produce salts from the lake by rights derived from a combination of: (i) lakebed lease agreements (the “Lakebed Leases”) with the Utah Department of Natural Resources, Division of Forestry, Fire and State Lands (the “Utah FFSL”); (ii) one lease for upland evaporation ponds (the “Upland Pond Lease”) with the State of Utah School and Institutional Trust Lands Administration (the “Utah SITLA”); (iii) seven non-solar leases and easements; (iv) water rights for consumption of brines and freshwater (the “Water Rights”) through the Utah Department of Natural Resources, Division of Water Rights; (v) a large mine operation mineral extraction permit (GSL Mine M/057/0002) (the “Mineral Extraction Permit”) through the Utah Department of Natural Resources, Division of Oil, Gas and Mining (the “Utah DOGM”); and (vi) a royalty agreement for extraction of all mineral salts, dated September 1, 1962 (as amended from time to time, the “Royalty Agreement”), with the Utah State Land Board.

Leasable areas for mineral extraction on the Great Salt Lake lakebed are identified in the Great Salt Lake Comprehensive Management Plan (the “GSL Plan”), which is managed by the Utah FFSL. The GSL Plan is updated approximately every ten years, or when there are major changes to the Great Salt Lake environment and setting. A party interested in leasing lakebed for mineral extraction may nominate an area within the area designated by the GSL Plan as leasable, at which time, the Utah FFSL will issue public notice of lease nomination, conduct an environmental assessment on the nominated lease area, and ultimately consider approval of the lease nomination. This process was followed historically in the acquisition of existing Lakebed Leases held by the Company for the Ogden facility.

The Lakebed Leases and Upland Pond Lease provides the Company the right to develop mineral extraction and processing facilities on the shore of the Great Salt Lake. The Lakebed Leases and Upland Pond Lease were issued between 1965 and 2022 and amended and restated in 2024, covering a total lease area of approximately 100,068 acres among seven active leases, though not all are currently utilized.

Each of the Lakebed Leases, have an initial term (Initial term) of 20 years beginning in October 2024 and shall be extended for successive twenty years terms (Extended Terms) provided that Compass Minerals has fully performed all of its obligations under each renewing lease. FFSL may cancel the renewal of any Lease by providing written notice to Compass Minerals at least ninety (90) days prior to the expiration of the Initial Term or any Extended Term (“FFSL Notice Date”), provided however, that FFSL’s right to cancel a Lease renewal term shall be limited to the existence, at the time of the FFSL Notice Date, of a material default or breach of the terms of the applicable Lease. Most of the Lakebed Leases provide the State of Utah with the opportunity to periodically adjust the lease’s terms, except for the royalties to be paid. These readjustment opportunities occur at intervals ranging from five to 20 years. In the past, these periodic readjustments have not materially hindered the business.

Pursuant to each of the Lakebed Leases, the Company is obligated to pay rent at rates ranging from $0.50 to $2.00 per acre per year, and some leases have a minimum rent of $10,000 per year. The rent paid pursuant to each lease is credited against the Company’s royalty obligations pursuant to the Royalty Agreement (as described further below).

The Upland Pond Lease consists of a single Special Use Lease Agreement (“SULA”) 1971, consisting of 37,181 acres, which was acquired on July 14, 2022. The rent for SULA 1971 is $427,584 per year. SULA 1971 is a 50-year lease expiring on June 30, 2072. SULA 1971 consists of former SULA 1186, which was acquired in May 1999, and SULA 1267, which was acquired from Solar Resources International in 2013, as well as an additional 13,833 acres. The Upland Pond Lease allows for the construction and operation of evaporation ponds on the subject properties. The Upland Pond Lease does not impose any material conditions on the Company’s retention of the property except for payment of rent.

The Company also holds seven non-solar leases and easements granted by Utah FFSL or Utah SITLA covering approximately 1,258 acres. Two of these are material to the operation of the Ogden facility, Behrens Trench Easement 400-00313 and PS-113 Easement SOV002-0400. The Company paid a one-time fee of $42,514 for Behrens Trench Easement 400-00313, which expires in June 2051. The Company paid a one-time fee of $27,273 for PS-113 Easement SOV002-0400, which does not expire. The Company also has a lease indenture for a brine canal with the Union Pacific Railroad, dated April 13, 1967, on Promontory Point. The indenture automatically renews with payment, which is $595.72 annually.

The Water Rights are procured by application to the Utah Department of Natural Resources, Division of Water Rights, which reviews the application and evaluates the proposed nature of use, place of use, and point of diversion in light of availability of water pursuant to hydrology and/or prior claims relative to the available water, and whether the proposed use would impair existing water right holders. The application is posted for public review and comment, and the State Engineer evaluates the merits of the application and either approves or denies the application, sometimes with modifications or conditions on future use. The Water Rights control the actual extraction of minerals from the Great Salt Lake and dictate the amount of brine that can be pumped from the lake on an annual basis. The Company has 156,000 acre-feet extraction rights from the north arm of the Great Salt Lake under five Water Rights, on which it relies for its current production. As a limit on the volume of brine that can be pumped from the lake in a year, the Water Rights effectively cap the aggregate production of salt that is possible in any year. The Company has certificated the Water Rights that contribute to the 156,000 acre feet of extraction rights, meaning that demonstration of actual use in order to retain the right in perpetuity has been approved and authorized. The Company may be impacted by the Voluntary Agreement with the Utah Division of FFSL, which outlines brine withdrawal caps based on annual lake elevation, discussed further in Item 1. “Business—Environmental, Health and Safety Matters and Other Regulatory Matters”.

The Mineral Extraction Permit (GSL Mine M/057/0002) was granted by the Utah DOGM. The Mineral Extraction Permit enables extraction of brine from the Great Salt Lake and ultimate mineral extraction from the brine. The Mineral Extraction Permit also enables all lake extraction, pond operations, and plant and processing operations conducted by the Company at the Ogden facility. The Mineral Extraction Permit is supported by a reclamation plan that documents all aspects of current operations and mandates certain closure and reclamation requirements in accordance with Utah Rule R647-4-104. Financial assurance for the ultimate reclamation of facilities is documented in the reclamation plan, and security for costs that will be incurred to execute site closure is provided by a third-party insurer to the State of Utah in the form of a surety bond. The total future reclamation obligation is estimated to be $4.36 million.

Pursuant to the Royalty Agreement, the Company has rights to all salts from the Great Salt Lake, and in exchange, the Company pays a royalty to the State of Utah based on net revenues (gross revenue net of sales taxes and shipping and handling

costs) per pound of salts produced. Under the Royalty Agreement, the current royalty rate for SOP is 4.8% of gross revenues, the current royalty rate for magnesium chloride is 5% of gross revenues, and the current royalty rate for sodium chloride is $0.50/ton times the Producer Price Index.

The Ogden facility is the largest SOP production site in the western hemisphere, and one of only four large-scale solar brine evaporation operations for SOP in the world. We believe the Ogden facility has the capability to produce 320,000 tons of SOP, including amounts produced with both solar-pond based feedstock and supplemental KCl feedstock when economically feasible, approximately 750,000 tons of magnesium chloride and 1.5 million tons of sodium chloride annually during normal weather and pond chemistry conditions. These recoverable minerals exist in vast quantities in the Great Salt Lake.

Solar evaporation is used in areas of the world where high-salinity brine is available and weather conditions provide for a high natural evaporation rate. Mineral-rich lake water, or brine, from the Great Salt Lake is drawn into the solar evaporation ponds. The brine moves through a series of solar evaporation ponds over a two- to three-year production cycle. As the water evaporates and the mineral concentration increases, some of those minerals naturally precipitate out of the brine and are deposited on the pond floors. These deposits provide the minerals necessary for processing into SOP, solar salt and magnesium chloride. The evaporation process is dependent upon sufficient lake brine levels and hot, arid summer weather conditions. The potassium-bearing salts are mechanically harvested out of the solar evaporation ponds and refined to high-purity SOP through flotation, crystallization and compaction at the Ogden plant. After sodium chloride and potassium-rich salts precipitate from brine, a concentrated magnesium chloride brine solution remains, which becomes the raw material used to produce several magnesium chloride products.

Operations have been ongoing at the Ogden facility since the late 1960s, with commercial production starting in 1970. Lithium Corporation of America (“Lithcoa”), separately, and then in a partnership with a wholly owned subsidiary of Salzdetfurth, A.G., carried out initial exploration and development activities between 1963 and 1966. In 1967, Gulf Resources and Minerals Co., or Gulf Resources, acquired Lithcoa, and in 1973, acquired Salzdetfurth, A.G.’s (then known as Kaliund Salz A.G.) partnership interest. Gulf Resources made significant capital expenditures in the early 1980s to protect the evaporation pond system at the Ogden facility from the rising levels of the Great Salt Lake. On May 5, 1984, a northern dike of the system breached, resulting in severe flooding and damage to about 85% of the pond complex. The breach resulted in physical damage to dikes, pond floors, bridges, pump stations, and other structures. In addition, brine inventories were diluted, making them unusable for producing SOP. During the next five years, Gulf Resources pumped the water from its solar ponds, reconstructed peripheral and interior dikes and roads, replaced pump stations, and laid down new salt floors in order to restart its operation at the Ogden facility. In 1993, D.G. Harris & Associates acquired the Ogden facility, and in 1994, constructed the west ponds, which are connected to the east ponds by a 21-mile, open, underwater canal called the Behrens Trench, which was dredged in the lakebed from the west ponds’ outlet to a pump station near the east ponds. Ownership of the Ogden facility was transferred in 1997 to IMC Global (“IMC”), following its acquisition of Harris Chemical Group (part of D.G. Harris & Associates). IMC sold a majority of its salt operations, including the Ogden facility, to Apollo Management V, L.P. through an entity called Compass Minerals Group in 2001. Following a leveraged recapitalization, the company now known as Compass Minerals International, Inc. completed an initial public offering in 2003.

The Company has operated the Ogden facility since its initial public offering in 2003. In that time, the Company has invested funds and acquired necessary permits to increase the efficiency and expand the capacity of the Ogden facility through upgrades to the Ogden plant and solar evaporation ponds. The Company believes that the Ogden facility and its operating equipment are maintained in good working condition. The net book value of property, plant and equipment associated with the Ogden facility as of September 30, 2024 was $220,700,000, exclusive of mineral rights and the value of assets leased under operating leases.

The Ogden facility has procured and is operating in compliance with all required operating licenses, including permits pertaining to mineral extraction, effluent discharge and air permitting. The Ogden facility operates under a Title V air permit (# 5700001003), which is administered by the Utah Department of Environmental Quality. The permit covers emissions from the pond and plant operations and expires in December 2026. Surface water discharges from the Ogden facility are regulated under Utah Pollutant Discharge Elimination System permit UT0000647. The permit requires discharge monitoring for effluent flows from the nine outfalls that discharge into the saline waters of the Great Salt Lake and regulates inputs in pond and plant processes that may be discharged in project effluent.

Summaries of the Ogden facility’s potassium and SOP mineral resources and mineral reserves as of September 30, 2024 and 2023 are shown in Tables 3 and 4, respectively. Summaries of the Ogden facility’s magnesium and magnesium chloride mineral resources and mineral reserves as of September 30, 2024 and 2023 are shown in Tables 5 and 6, respectively. Summaries of the Ogden facility’s sodium and sodium chloride mineral resources and mineral reserves as of September 30, 2024 and 2023 are shown in Tables 7 and 8, respectively. Joseph Havasi, who is employed full-time as the Vice President, Natural Resources, of the Company, served as the QP and prepared the estimates of potassium and SOP, magnesium and magnesium chloride, and sodium and sodium chloride mineral resources and mineral reserves at the Ogden facility. The material assumptions and information pertaining to the Company’s disclosure of mineral resources and mineral reserves at the Ogden facility are based on the Technical Report Summary with respect to Potassium and SOP, Magnesium and Magnesium Chloride and Salt for the Ogden facility, dated November 29, 2021, as amended on December 14, 2022, with an effective date of September 30, 2021

(the “Ogden Potassium/Magnesium/Sodium TRS”). This Form 10-K also reflects more recent information obtained from the QP as of September 30, 2024, which supplements and updates information from such TRS.

Table 3. Ogden Facility – Summary of Potassium and SOP Mineral Resources at September 30, 2024 and 2023

(1)Mineral resources are not mineral reserves and do not have demonstrated economic viability. There is no certainty that all or any part of the mineral resources will be converted into mineral reserves upon application of modifying factors.

(2)Mineral resources are reported in situ for the both the north arm and the south arm of the Great Salt Lake.

(3)Conversion of potassium to SOP uses a factor of 2.2258 tons of SOP per ton of potassium.

(4)Included process recovery is approximately 7.8% based on historical production results. Mining or metallurgical recovery is not applicable for this operation.

(5)Based on pricing data described in Section 18.1 of the Ogden Potassium/Magnesium/Sodium TRS. The pricing data is based on a five-year average (2020 through 2024) of historical sales data for SOP of $659.96 per ton. Sales prices are projected to increase to approximately $8,529 per ton for SOP through year 2161 (the current expected end of mine life).

(6)Estimated cut-off grade of approximately 4,000 milligrams of potassium per liter of brine extracted from the north arm of the Great Salt Lake, and a cut-off grade of 1,660 milligrams of potassium per liter of brine in the south arm of the Great Salt Lake, which ultimately flows into the north arm of the Great Salt Lake. The QP assumes that when the north arm of the Great Salt Lake (where the Ogden facility sources its brine) reaches this concentration level, the Ogden facility will halt production of potassium and SOP.

(7)Reported potassium concentration for the Great Salt Lake assumes an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

Table 4. Ogden Facility – Summary of Potassium and SOP Mineral Reserves at September 30, 2024 and 2023

(1)Mineral reserves are as recovered, saleable product.

(2)Annual production rates for SOP are assumed to be 320,000 tons per year, relating to a depletion of 145,833 tons of potassium per year. Based on the QP’s reserve model, the life of mine is estimated to be 138 years.

(3)Conversion of potassium to SOP uses a factor of 2.2258 tons of SOP per ton of potassium.

(4)Included process recovery is approximately 7.8% based on historical production results. Mining or metallurgical recovery is not applicable for this operation.

(5)Based on pricing data described in Section 18.1 of the Ogden Potassium/Magnesium/Sodium TRS. The pricing data is based on a five-year average (2020 through 2024) of historical sales data for SOP of $659.96 per ton. Sales prices are projected to increase to approximately $8,529 per ton for SOP through year 2161 (the current expected end of mine life).

(6)Estimated cut-off grade of approximately 4,000 milligrams of potassium per liter of brine extracted from the north arm of Great Salt Lake, and a cut-off grade of 1,660 milligrams of potassium per liter of brine in the south arm of the Great Salt Lake, which ultimately flows into the north arm of the Great Salt Lake. The QP assumes that when the north arm of the Great Salt Lake (where the Ogden facility sources its brine) reaches this concentration level, the Ogden facility will halt production of potassium and SOP.

(7)Reported potassium concentration for the Great Salt Lake assumes an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

Table 5. Ogden Facility – Summary of Magnesium and Magnesium Chloride Mineral Resources at September 30, 2024 and 2023

(1) Mineral resources are not mineral reserves and do not have demonstrated economic viability. There is no certainty that all or any part of the mineral resource will be converted into mineral reserve upon application of modifying factors.

(2) Mineral resources are reported in situ for the both the north arm and the south arm of the Great Salt Lake.

(3) Conversion of magnesium to magnesium chloride uses a factor of 3.913 tons of magnesium chloride per ton of magnesium.

(5) The pricing data is based on a five-year average of historical gross sales data for MgCl of $74.46 per ton. Gross sales prices are projected to increase to approximately and $1,100.39 per ton for MgCl through year 2161 (the current expected end of mine life).

(6) Estimated cut-off grade of approximately 8,638 milligrams of magnesium per liter of brine extracted from the north arm of the Great Salt Lake, and a cut-off grade of 3,039 milligrams of magnesium per liter of brine in the south arm of the Great Salt Lake which ultimately flows into the north arm of the Great Salt Lake. The QP assumes that when the north arm of the Great Salt Lake (where the Ogden facility sources its brine) reaches this concentration level, the Ogden facility will halt production of magnesium and magnesium chloride.

(7) Reported magnesium concentration for the Great Salt Lake assumes an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

Table 6. Ogden Facility – Summary of Magnesium and Magnesium Chloride Mineral Reserves at September 30, 2024 and 2023

(1) Mineral reserves are as recovered, saleable product.

(2) Production rates for magnesium chloride are 620,000 tons per year. This relates to a depletion of 158,271 tons of magnesium per year. Based on the QP’s reserve model, the life of mine is estimated to be 139 years, based on potash operational longevity.

(3) Conversion of magnesium to magnesium chloride uses a factor of 3.913 tons of magnesium chloride per ton of magnesium.

(5) The pricing data is based on a five-year average of historical gross sales data for MgCl of $74.46 per ton. Gross sales prices are projected to increase to approximately and $1,100.39 per ton for MgCl through year 2161 (the current expected end of mine life).

(6) Estimated cut-off grade of approximately 8,638 milligrams of magnesium per liter of brine extracted from the north arm of Great Salt Lake, and a cut-off grade of 3,039 milligrams of magnesium per liter of brine in the south arm of the Great Salt Lake which ultimately flows into the north arm of the Great Salt Lake. The QP assumes that when the north arm of the Great Salt Lake (where the Ogden facility sources its brine) reaches this concentration level, the Ogden facility will halt production of magnesium and magnesium chloride.

(7) Reported magnesium concentration for the Great Salt Lake assumes an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

Table 7. Ogden Facility – Summary of Sodium and Sodium Chloride Mineral Resources at September 30, 2024 and 2023

(1) Mineral resources are not mineral reserves and do not have demonstrated economic viability. There is no certainty that all or any part of the mineral resource will be converted to a mineral reserve upon application of modifying factors.

(2) Mineral resources are reported in-situ for both the north arm and south arm of the Great Salt Lake.

(3) Conversion of sodium to sodium chloride uses a factor of 2.542 tons of sodium chloride per ton of sodium.

(5) The pricing data is based on a five-year average (2020 through 2024) of historical gross sales data for sodium chloride of $94.98 per ton. Gross sales prices are projected to increase to approximately $1,204.66 per ton for sodium chloride through year 2161 (the current expected end of mine life).

(6) Estimated cut-off grade of approximately 75,757 milligrams of sodium per liter of brine extracted from the north arm of Great Salt Lake, and a cut-off grade of 40,365 milligrams of sodium per liter of brine in the south arm of the Great Salt Lake which ultimately flows into the north arm of the Great Salt Lake. The QP assumes that when the north arm of the Great Salt Lake (where the Ogden facility sources its brine) reaches this concentration level, the Ogden facility will halt production of sodium and sodium chloride.

(7) Reported sodium concentration for the Great Salt Lake assumes an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

Table 8. Ogden Facility – Summary of Sodium and Sodium Chloride Mineral Reserves at September 30, 2024 and 2023

(1) Mineral reserves are as recovered, saleable product.

(2) Production rates for the sodium chloride are 1,045,000 tons per year. This relates to a depletion of 411,074 tons of sodium per year. Based on the QP’s reserve model, the life of mine is estimated to be 139 years, based on potash operational longevity.

(3) Conversion of sodium to sodium chloride uses a factor of 2.542 tons of NaCl per ton of sodium.

(5) The pricing data is based on a five-year average (2020 through 2024) of historical gross sales data for sodium chloride of $94.98 per ton. Gross sales prices are projected to increase to approximately $1,204.66 per ton for sodium chloride through year 2161 (the current expected end of mine life).

(6) Based on the economic analysis described in Section 19 of the Ogden Potassium/Magnesium/Sodium TRS, the QP estimated a cut-off grade of approximately 75,757 milligrams of sodium per liter of brine extracted from the north arm of Great Salt Lake, and a cut-off grade of 40,365 milligrams of sodium per liter of brine in the south arm of the Great Salt Lake which ultimately flows into the north arm of the Great Salt Lake. The QP assumes that when the north arm of the Great Salt Lake (where the Ogden facility sources its brine) reaches this concentration level, the Ogden facility will halt production of sodium and sodium chloride.

(7) Reported sodium concentration for the Great Salt Lake assumes an indicative lake level of 4,194.4 feet in the south arm and 4,193.5 feet in the north arm.

From September 30, 2023 to September 30, 2024, for both potassium and SOP, combined measured and indicated resources decreased by approximately 0.27% and total reserves decreased by approximately 0.50%. The decreases in the combined measured and indicated resources were attributable to depletion of potassium from the Great Salt Lake in connection with extraction operations of the Company and another salt producer, while the decrease in reserves was attributable to the Company’s production of SOP during that period.

COTE BLANCHE MINE

The Cote Blanche mine is a production stage, underground mine that produces rock salt primarily for highway deicing customers through a series of depots located along the Mississippi and Ohio rivers (and their major tributaries) and chemical and agricultural customers in the Southern and Midwestern United States. The Cote Blanche mine is located in south-central Louisiana in the Parish of St. Mary (T15S, R7E), at the northern edge of Cote Blanche Hummoch, commonly called “Cote Blanche Island.” Maps of the Cote Blanche mine property are shown in Figures 3 and 4.

Figure 3. Cote Blanche Mine Property Location Map

Figure 4. Aerial View of Cote Blanche Island

Cote Blanche Island is situated between the Intra-Coastal Waterway and Cote Blanche Bay in the Gulf of Mexico. The Cote Blanche mine is approximately 124 miles west of New Orleans, Louisiana, and approximately 26 miles southeast of New Iberia, Louisiana, on the Gulf Coast. The approximate coordinates of the site facilities are 29˚45’4” North and 91˚43’24” West. The site is accessed by surface roads to the Cote Blanche Landing, and then by ferry boat from the Cote Blanche Landing to Cote Blanche Island. The Company accesses Cote Blanche Island via two rights-of-way with a separate private landowner group: one for the landing for the ferry boat that the Company operates and maintains; and the other for the barge canal, which is utilized for barge access to the mine. The barges are managed by contract tug boat services.

The Cote Blanche mine has a barge loading dock, administrative offices and other services-related structures. Power is supplied to the site by CLECO Power from nearby power lines that are fed directly from the main power grid and there are telephone and cellular connections. Water is provided to the Cote Blanche mine by privately owned and operated wells that are on the mine site. The Cote Blanche mine is well established and has been in the community for over 50 years. The communities of New Iberia, Broussard and Lafayette, Louisiana, have the required infrastructure (shopping, emergency services, schools, etc.) to support the workforce. New Iberia is served by a small regional airport and a transcontinental railroad.

The Company leases the entirety of Cote Blanche Island from a private ownership group, except for 115 acres of the southeastern sector of the island (the “115 Acre Tract”), for a total mineral lease of 1,520 acres. The lease grants salt rights to the Company for all salt from the ground surface downward 3,000 feet, except for salt located within the 115 Acre Tract. The lease also grants surface rights in the western and southwestern sectors of Cote Blanche Island, with access rights to the mine road that extends north-south from the surface lease area to the Cote Blanche Crossing.

The lease has an effective end date of June 30, 2060, unless earlier terminated. In the event that no actual mining is being completed during any five consecutive years, the lessor has the option to cancel the lease. As lessee, the Company may exercise two options to extend the term of the lease, each for a 25-year period upon the same terms and conditions contained in the lease. The Company has a minimum royalty based on 1,500,000 tons of salt hoisted annually. Under the terms of the lease, the royalty for each calendar year is equal to the Net F.O.B. Mine Sales Revenue Per Ton (as defined below), multiplied by the Applicable Royalty Rate (as defined below), multiplied by the number of tons of salt hoisted from the Cote Blanche mine in that calendar year. The “Net F.O.B. Mine Sales Revenue Per Ton” for each calendar year is the quotient of the total bulk sales revenue (excluding any taxes) of the Company and its affiliates for salt sold from the Cote Blanche mine in bulk (in units of 1 short ton or more) (“Total Bulk Sales Revenue”) reduced for all freight in, freight out, fuel surcharge, additives, depot/warehouse storage, handling and operating costs, promotions/discounts and other costs as are properly deducted under generally accepted accounting principles in that calendar year, divided by the total number of tons sold. The number of tons of salt sold is the same number of tons used to generate the Total Bulk Sales Revenue. The “Applicable Royalty Rate” is 5.5%.

The lease further provides that if, on or before January 1 of 2034, 2059 or 2084 (each, a “Review Year”), the lessor or the Company determines that, in operation, the royalty provisions of the lease result in the lessor receiving more or less than 5.5% of the fair value of salt at the minehead free of all costs at that point (the “Royalty Standard”), such party shall deliver to the other party on or before January 1 of the Review Year a written statement of its reasons why the Royalty Standard is not being met, a computation of the amount that will satisfy the Royalty Standard and a proposed revision to the royalty provisions of the lease that will cause the royalty provisions to comply with the Royalty Standard. On or before January 30 of the Review Year, the other party is required to deliver to the first party a written statement of its opinion as to whether the royalty provisions as proposed comply with the Royalty Standard and a response to the first party’s statement delivered under the preceding sentence. If the parties are not in agreement, the parties are required to commence arbitration.

The lease provides that the lessor has full right to grant future oil, gas and other mineral leases, except salt, provided that each such future oil, gas and mineral lease shall expressly obligate the lessee to cooperate with the Company in the conduct of its operations in order that the purposes of both leases may be best effectuated. The lease obligates the Company to cooperate with the oil, gas and mineral lessee so as to permit drilling of oil and/or gas wells.

The Cote Blanche mine operates with a production schedule targeting approximately 2.2 million tons of salt per year. That target can vary significantly depending on the severity of winter weather conditions and the resulting market demand for road salt.

Domtar Industries, Inc. constructed the Cote Blanche mine over four years beginning in 1961 with 8-foot and 14-foot shafts and the barge loadout facility. Salt production commenced in 1966. The DG Harris Company purchased the Cote Blanche mine in 1990, which operated as Carey Salt Co. thereafter. The salt assets of The DG Harris Company were sold to IMC in 1997. IMC sold a majority of its salt operations, including the Cote Blanche mine, to Apollo Management V, L.P. through an entity called Compass Minerals Group in 2001. Following a leveraged recapitalization, the company now known as Compass Minerals International, Inc. completed an initial public offering in 2003.

Mining at the Cote Blanche mine occurs in 75-foot mining horizons at specific depths below the surface. To date, the salt dome has been mined at three levels, including the 1,300-foot level, which was mined from 1965 to 1986; the 1,100-foot level, which was mined from 1986 to 2002; and the current 1,500-foot level, which began in 1998 to and is expected to remain in operation through 2026. The Company is in the process of developing a ramp to an extension of the 1,300-foot level, for which mining is projected to start in 2022. Active mining on both the 1,300-foot level and the 1,500-foot level is anticipated to take place from 2022 to 2026. The Company’s current mine plan focuses on completion of the 1,500-foot level with future expansion to the 1,700-foot level and finally advancing to the 1,900-foot level. At this time, mining is not anticipated below the 1900-foot level.

There has been extensive historical oil and gas exploration on and adjacent to Cote Blanche Island, but the Company only has access to mapping and reports that are publicly available from external subsurface exploration. While the historical data provide a strong depiction of the salt ore body, the Company has undertaken in-seam seismic and mud-rotary drilling to verify and validate salt diapir position, morphology and margin at the Cote Blanche mine. The nature of salt diapirs lends itself to a strong understanding of the homogeneity of the morphology and mineralogy of the ore body. Thus, the primary concerns within the salt diapir are understanding the margin of the diapir to support the mine plan by ensuring geotechnical stability, and mapping the localized presence of sandstone partings and seams that are encountered from time to time as well as sheer planes along margins of salt stock formations. The combination of historic data collected through externally funded and directed seismic and drilling programs for oil and gas exploration in strata surrounding the diapir, combined with Compass Minerals’ salt diapir morphology validation drilling has created a reasonably strong characterization of the definition of the salt diapir.

As the mining continues and progresses to the next deeper mining level at 1,700 feet and eventually to the 1,900-foot level, definition of the upper surface of the salt diapir is no longer necessary as mining will be below the current mining level. Therefore, mud-rotary drilling to validate the salt dome surface will no longer be necessary and instead the mining operation will continue its in-seam seismic data collection to assess the potential for anomalies as mining progresses to the outer margins of the mine plan, and verify that the lateral margins of the diapir are not within the Company’s self-determined, 400-foot setback of mineral extraction.

The Cote Blanche mine utilizes the room and pillar method of extraction. In this method, excavations (rooms) are recovered by mining and are alternated with areas of undisturbed salt (pillars) that form the necessary support for maintaining stability of the mine roof. The layout of the rooms and pillars and their respective sizes are optimized to maximize the ratio of salt extracted, relative to in situ salt, while still meeting safety and surface subsidence requirements. All levels in the current mine plan, 1,300-foot through the 1,900-foot levels, are currently mining or are planned to be operated in the same manner, with the same mining parameters and with the same set of unit operations, altered only by the footprint of the mining of the room and pillar method as modified to reflect the constraints of the planned level and the lateral constraints of the salt dome contours of each level.

The current room and pillar layout has an extraction ratio of approximately 56% within the mined room area, but the overall extraction ratio of the property, taking into account barrier pillars and unmined zones and interruptions from oil wells among other anomalies is about 51%. Rooms are mined in a progression of two phases creating a total room height of 75 feet when completed. The rooms have a nominal width of 50 feet and are bounded by 100-foot square pillars. Variations in room and

pillar dimensions are observed due to production blasting and scaling, so values are approximate. To achieve 75 feet of height, rooms are initially developed using a 30 foot top-cut (horizontal drill and blast), which is then vertically drilled and blasted (benched) an additional 45 feet, with 5 feet of sub-drilling. Loading and hauling is completed with diesel powered loading equipment and haul trucks. Development mining typically leads ahead of benching or room advance by approximately one and a half years.

The process for salt production at the Cote Blanche mine focuses on particle size reduction of the salt product. Rock salt is processed and sized by underground crushers and the mill before it is hoisted to the surface. The mill has two distinct halves: the mine run circuit and the whole mill. Only chemical quality and non-chemical quality salt can be processed through the whole mill. Ice control quality salt is processed through the mine run circuit. Once the salt has been sized accordingly, it is either stockpiled or placed directly onto a barge for transport to market. The main stockpile area allows separate piles for chemical, non-chemical, and ice control grade salt.

The Cote Blanche mine is operated with modern mining equipment and utilizes subsurface improvements, such as vertical shaft lift systems, milling and crushing facilities, maintenance and repair shops and extensive raw materials handling systems. The milling and crushing facilities were constructed when the Cote Blanche mine developed the 1,500 foot level in 2001. As of September 30, 2024, the net book value for the plant, property and equipment at the Cote Blanche mine is $83,200,000, exclusive of mineral rights and the value of assets leased under operating leases.

The Cote Blanche mine has procured and is operating in compliance with required operating licenses, including permits pertaining to mineral extraction, effluent discharge and air permitting. The Company will be required to renew the current air permit at the Cote Blanche mine, which is administered by the Louisiana Department of Environmental Quality, when it expires in December 2026. Surface water discharges from the site are regulated under Louisiana Pollutant Discharge Elimination System (LPDES) permit LA0103233. The permit requires discharge monitoring for effluent flows from the three outfalls that discharge into the saline waters of the Intracoastal Waterway and Cote Blanche Bay. The State of Louisiana does not require an operating permit for the Cote Blanche mine. Air and NPDES permits are maintained by the site. The site is located in a Coastal Protection Zone and therefore any new site disturbance requires permitting by the U.S. Army Corps of Engineers and the Louisiana Office of Coastal Management. Initial operations at the site predate the Coastal Resources rules so no formal reporting is required under this process.

There are no mine closure plans for the Cote Blanche mine. Once the lease agreement terminates, the Company has six months to vacate the mine of any personal property it wishes to recover before the landownership group assumes control of the mine and either continues mining or initiates other commercial or industrial uses of the surface mine site and underground void space.

Summaries of the Cote Blanche mine’s salt mineral resources and mineral reserves as of September 30, 2024 and 2023 are shown in Tables 10 and 11, respectively. Joseph Havasi, who is employed full-time as the Vice President, Natural Resources, of the Company, served as the QP and prepared the estimates of salt mineral resources and mineral reserves at the Cote Blanche mine. The material assumptions and information pertaining to the Company’s disclosure of mineral resources and mineral reserves at the Cote Blanche mine are based on the Technical Report Summary dated November 16, 2021, as amended on December 14, 2022, with an effective date of September 30, 2021 (the “Cote Blanche TRS”). This Form 10-K also reflects more recent information obtained from the QP as of September 30, 2023, which supplements and updates information from such TRS. The Company periodically reviews its mining plans, including which levels of the mine to develop. Changes in the mining plan in the future may result in increases in expected capital costs or changes that may adversely impact our reported reserves. If mineral reserves were materially impacted, the QP would update the TRS accordingly.

Table 10. Cote Blanche Mine – Summary of Salt Mineral Resources at September 30, 2024 and 2023

(1)Mineral resources are reported in situ. Mineral resources are not mineral reserves and do not have demonstrated economic viability.

(2)Underground mineral resources are reported based on assumed 75-foot mining horizons, discounted for areas not accessible due to proximity to oil wells.

(3)Tonnage was calculated based on a tonnage factor of 0.0675 tons per cubic foot.

(4)Included process recovery is 94% based on production experience. Included mining recovery is approximately 56% based on the room and pillar layout.

(5)Although the actual sodium chloride grade is less than 100%, it is not considered in the resource, as the final saleable product is the in situ product, as-present after processing (i.e., the saleable product includes any impurities present in the in situ rock).

(6)A cut-off grade was not utilized for the calculation as the in situ product quality is relatively constant and saleable after processing.

(7)There are multiple saleable products based on salt quality from the operation (rock salt for road deicing and chemical grade salt). For simplicity, all sales are assumed at the lower value (and higher tonnage) product, rock salt, and are based on pricing data described in Section 16 of the Cote Blanche TRS. The pricing data is based on a five-year average (2020 through 2024) of historical sales data for rock salt for road deicing of $71.59 per ton. Sales prices are projected to increase to approximately $763.94 per ton for rock salt for road deicing through year 2138 (the current expected end of mine life).

(8)Based on approximate areas of: 5,399,000 square feet (“ft 2”) for the 1,300-foot level; 2,991,000 ft 2 for the 1,500-foot level; 45,721,000 ft 2 for the 1,700-foot level; 50,293,000 ft 2 for the 1,900-foot level; and 104,404,000 ft 2 in the aggregate.

(9)The 1,700-foot and 1,900-foot levels have been approximated using the 1,300-foot and 1,500-foot level contours, respectively, in alignment to the 400-foot contact distance restriction and site and safety constraints.

Table 11. Cote Blanche Mine – Summary of Salt Mineral Reserves at September 30, 2024 and 2023

(2)Underground mineral reserves are reported based on assumed 75-foot mining horizons, discounted for areas not accessible due to proximity to oil wells.

(3)Tonnage was calculated based on a tonnage factor of 0.0675 tons per cubic foot.

(4)Included process recovery is 94% based on production experience. Included mining recovery is approximately 56% based on the room and pillar layout.

(5)Although the actual sodium chloride grade is less than 100%, it is not considered in the reserve, as the final saleable product is the in situ product, as-present (i.e., the saleable product includes any impurities present in the in situ rock).

(6)A cut-off grade was not utilized for the calculation as the in situ product quality is relatively constant and saleable after processing.

(7)There are multiple saleable products based on salt quality from the operation (rock salt for road deicing and chemical grade salt). For simplicity, all sales are assumed at the lower value (and higher tonnage) product, rock salt, and are based on pricing data described in Section 16 of the Cote Blanche TRS. The pricing data is based on a five-year average (2020 through 2024) of historical sales data for rock salt for road deicing of $71.59 per ton. Sales prices are projected to increase to approximately $763.94 per ton for rock salt for road deicing through year 2138 (the current expected end of mine life).

(8)Based on approximate areas of: 5,399,000 ft 2 for the 1,300-foot level; 2,991,000 ft 2 for the 1,500-foot level; 45,721,000 ft 2 for the 1,700-foot level; 50,293,000 ft 2 for the 1,900-foot level; and 104,404,000 ft 2 in the aggregate.

(9)The 1,700-foot and 1,900-foot levels have been approximated using the 1,300-foot and 1,500-foot level contours, respectively, in alignment to the 400-foot contact distance restriction and site and safety constraints.

From September 30, 2023 to September 30, 2024, combined measured and indicated resources at the Cote Blanche mine decreased by approximately 0.53% and total reserves decreased by approximately 0.72%. The decreases in salt resources and reserves were attributable to depletion of salt in connection with extraction operations of the Company.

GODERICH MINE

The Goderich mine is a production stage, underground mine that produces rock salt primarily for highway use and as feed product for other uses. The Goderich mine is located in southwestern Ontario, Canada, on the eastern shore of Lake Huron. The Goderich mine is located west of the town of Goderich, Ontario, on an isthmus in the mouth of the Maitland River, as it enters Lake Huron. Maps of the Goderich mine property are shown in Figures 5 and 6.

Figure 5. Goderich Mine Property Location Map

Figure 6. Lease and Mine Map: Goderich Mine

The Goderich mine is approximately 60 miles northwest of London, Ontario, and 120 miles west of Toronto, Ontario. Its approximate coordinates are 43˚ 44’ 50” North and 81˚ 43’ 30” West. Access to the Goderich mine is considered excellent. The town of Goderich has established infrastructure for both mining and exporting salt and can be accessed via regional highways from Toronto from the east (2.5 hours). The triangular-shaped mine site is surrounded by the lake on three sides and the Maitland River on the north side. Goderich Harbor and the Goderich mine site are accessed via North Harbor Road, a municipally owned and maintained road that connects the harbor area to Highway 21. The Goderich mine is connected to local power, water, natural gas and sewage infrastructure. Primary logistics for transporting mined product include the rail siding at the mine site and direct loading into ships or barges in Goderich Harbor. The town of Goderich provides all necessary resources for the Goderich mine, with a ready labor supply, housing, hotels, food and all other typical facilities. The close proximity to rail, port and roads provides easy access for all logistical needs. Commercial air travel is available from London, Ontario, Toronto, Ontario, and Detroit, Michigan, all of which are in relative proximity to the site.

The Goderich mine site is located on 16.3 acres of Company-owned land (PIN 41369-0004) on a man-made peninsula consisting of several large buildings and silos associated with mining and material handling, a ship loading facility and three shafts. The Company actively mines salt west of its owned land under Salt Mining Lease No. 110134, dated February 5, 2024, with the Ontario Ministry of Energy, Northern Development and Mines (“MNDM”), comprising approximately 13,195 acres. The lease has a 21-year term that expires on May 31, 2043. The current royalty rate paid is $0.729 per tonne.

The Goderich mine is the largest underground rock salt mine in the world. Based on the proposed mine layout and using a 6.5 million tons per annum average production run rate assumption, the Goderich mine has a current mine life of approximately 69 years, assuming the Company is able to successfully renew the lease following the expiration of the 21-year renewal term in 2043, which the Company currently expects.

Salt production began in Goderich, Ontario, in 1867 by Sifto Canada (“Sifto”) after an unsuccessful search for oil uncovered a vast bed of rock salt. Sifto used basic solution mining and evaporation, now known as mechanical evaporation, to begin the nearby Goderich plant.

In 1956, Sifto received approval to operate an underground salt mine while under the ownership of Dominion Tar and Chemical Company Ltd. Initial drilling at the Goderich mine started in 1955 with the sinking of the first shaft beginning in

1957. The Goderich mine started production upon the completion of the first shaft in 1959. Additional increases in production were enabled after a second mine shaft and a third mine shaft were completed in 1962 and 1982, respectively. In 1990, Domtar Chemicals Limited (previously known as Dominion Tar and Chemical Company Ltd.) sold Sifto to the North American Salt Company, a subsidiary of D.G. Harris & Associates. In 1993, D.G. Harris & Associates founded Harris Chemical Group as a holding company for salt operations, which was acquired by IMC in 1997. IMC sold a majority of its salt operations, including the Goderich mine, to Apollo Management V, L.P. through an entity called Compass Minerals Group in 2001. Following a leveraged recapitalization, the company now known as Compass Minerals International, Inc. completed an initial public offering in 2003.

The Goderich mine’s underground infrastructure is situated in the A-2 salt bed approximately 1,750 feet to 1,760 feet below the surface at the mine shafts’ location. The A-2 salt bed in the shaft area is approximately 79 feet thick. The regional stratigraphic sequence is well understood from many wells drilled across the basin and locally in the Goderich, Ontario, area. The salt strata are highly continuous over the basin, and most of the major salt units can be traced for hundreds of miles. On a local scale, the continuity of the salt beds can be impacted by the presence of pinnacle reefs, displacement by faults, or the local leaching of salt. The Company can use various tools to characterize geological conditions in nearby areas to assess the possibility of encountering these local ground conditions at the mine. Accordingly, the Company has engaged third parties to conduct in-seam seismic surveys and, more recently, has begun use of ground penetrating radar to identify disturbances in salt continuity and the thickness of the A-2 salt bed in development.

The Goderich mine progresses development of main entries in advance of bench mining. The subsequent benches achieve the remainder of the 60-foot room height for room production. Development and bench mining progress at an approximate 40:60 ratio in terms of area of advance in the mine plan and are part of the production process. As needed, underground rooms for facility support functions have been and will be developed in excavated areas of the mine. This includes development of shaft areas on each level for hoist equipment, design, planning and development of ramp structures from one level to the subsequent, lower level as required, installation of underground work facilities such as maintenance shops and storage rooms. As mining progresses, development also encompasses the design, placement, repair and maintenance of support infrastructure such as crushers, screens and other plant in support of mining. All portions of mine development within the A-2 salt are planned to be operated in the same manner and mining method, with the same mining parameters with the same set of unit operations.

The general method of mining employed at the Goderich mine is known as room and pillar mining. Beginning in 2012 and 2013, the Company advanced the Goderich mine to mechanized room and pillar mining as continuous mining machines (each a “CMM”) replaced the previous under-cutter/over-cutter equipment and drilling and blasting sequence in the development areas of the mine. By 2017, the Company was engaged in continuous mining of the entire 60-foot face of the mined rooms in multiple lifts with a goal of improving efficiency and safety, reducing costs and reducing the amount of diesel equipment utilized underground, thus largely eliminating the use of drilling and blasting at the Goderich mine. The Company continues to upgrade its CMM fleet at the Goderich mine.

Certain mining units at the Goderich mine are equipped with both a CMM and a flexible conveyor train (“FCT”), a dynamic move-up unit and a belt storage unit. On these mining units, the CMM cuts the salt directly from the face and discharges it into a hopper on the end of the FCT. From the FCT, the rock salt is offloaded to the main underground belt conveyance system where it is then transported to the underground crushers and the mill. Other mining units are also equipped with a CMM, but are supported with rubber-tired haulage equipment to transfer salt. Salt mined from these CMMs is transferred from the face by rubber-tired haulage to a centralized dump point with a crusher and then follows the same process as the other units once the salt is put onto the underground conveyance system. Rock salt is processed and sized at the underground crushers and the mill before being hoisted to the surface. Salt is stockpiled at the surface in domes. The salt is then distributed to depots, packaging facilities and customers via ship (approximately 80%), and rail car and truck (approximately 20%). The net book value for the plant, property and equipment at the Goderich mine is $206,300,000 as of September 30, 2024, exclusive of mineral rights and the value of assets leased under operating leases.

The Goderich mine has procured and is operating in compliance with all required operating licenses, including permits pertaining to mineral extraction, effluent discharge and air permitting. The Ontario Ministry of Energy, Northern Development and Mines regulates closure for the Goderich mine. The most recent closure plan was approved by the ministry in 2021. Long-term cleanup of the site will essentially include demolishing surface facilities, removal of surface infrastructure and restoring a natural alvar ecological community on the surface, flooding of the workings, and decommissioning (plugging). The Goderich mine operates under two air permits issued by the Ontario Ministry of Environment, Conservation and Parks, one for the lab (8-1131-96-007), and the other for the garage for welding exhaust (5522-78NUN2). Site drainage into Snug Harbour and the Maitland River is permitted pursuant to Certificate of Approval 2342-7ULQEU and Environmental Compliance Approval 1236-8YGK8A, respectively, issued by the Ontario Ministry of Environment, Conservation and Parks.

Summaries of the Goderich mine’s salt mineral resources and mineral reserves as of September 30, 2024 and 2023 are shown in Tables 12 and 13, respectively. Joseph Havasi, who is employed full-time as the Vice President, Natural Resources, of the Company, served as the QP and prepared the estimates of salt mineral resources and mineral reserves at the Goderich mine. The material assumptions and information pertaining to the Company’s disclosure of mineral resources and mineral reserves at the Goderich mine are based on the Technical Report Summary dated November 16, 2021, as amended on December 14, 2022,

with an effective date of September 30, 2021 (the “Goderich TRS”). This Form 10-K also reflects more recent information, including revised capital expenditure forecasts, obtained from the QP as of September 30, 2024, which supplements and updates information from such TRS. These changes to the capital expenditures forecasts would affect the NPV and IRR figures stated in Section 19 of the Goderich TRS, but salt resources or reserves would not be affected.

Table 12. Goderich Mine – Summary of Salt Mineral Resources at September 30, 2024 and 2023

(1)Mineral resources are reported in situ. Mineral resources are not mineral reserves and do not have demonstrated economic viability. There is no certainty that all or any part of the mineral resources will be converted into mineral reserves upon application of modifying factors.

(2)All figures have been rounded to reflect the relative accuracy of the estimates.

(3)Underground mineral resources are reported based on an expected representative A-2 salt bed thickness of 82 feet.

(4)Tonnage was calculated based on a tonnage factor of 0.0675 tons per cubic foot.

(5)Included process recovery is 97.5% based on production experience. Included mining recovery is approximately 38.7% based on the room and pillar mine plan.

(6)Although the actual sodium chloride grade is less than 100%, it is not considered in the resource, as the final saleable product is the in situ product, as-present after processing (i.e., the saleable product includes any impurities present in the in situ rock).

(7)A cut-off grade was not utilized for the calculation as the in situ product quality is relatively constant and saleable after processing.

(8)There are multiple saleable products based on salt quality from the operation (rock salt for road deicing and chemical grade salt). For simplicity, all sales are assumed at the lower value (and higher tonnage) product, rock salt and are based on pricing data described in Section 16 of the Goderich TRS. The pricing data is based on a five-year average (2020 through 2024) of historical sales data for rock salt for road deicing of $64.38 per ton. Sales prices are projected to increase to approximately $319.63 per ton for rock salt for road deicing through year 2094 (the current expected end of mine life).

(9)Based on an area of approximately 575,257,000 square feet for the A-2 salt bed within the lease area.

Table 13. Goderich Mine – Summary of Salt Mineral Reserves at September 30, 2024 and 2023

(2)All figures have been rounded to reflect the relative accuracy of the estimates.

(3)Reserve volume assumes a mining thickness of 18 meters (approximately 60 feet) production, 8.5 meters (approximately 28 feet) mains.

(4)Tonnage was calculated based on a tonnage factor of 0.0675 tons per cubic foot.

(5)Included process recovery is 97.5% based on production experience. Included mining recovery is approximately 38.7% based on the room and pillar mine plan.

(6)Although the actual sodium chloride grade is less than 100%, it is not considered in the reserve, as the final saleable product is the in situ product, as-present after processing (i.e., the saleable product includes any impurities present in the in situ rock).

(7)A cut-off grade was not utilized for the calculation as the in situ product quality is relatively constant and saleable after processing.

(8)There are multiple saleable products based on salt quality from the operation (rock salt for road deicing and chemical grade salt). For simplicity, all sales are assumed at the lower value (and higher tonnage) product, rock salt and are based on pricing data described in Section 16 of the Goderich TRS. The pricing data is based on a five-year average (2020 through 2024) of historical sales data for rock salt for road deicing of $64.38 per ton. Sales prices are projected to increase to approximately $319.63 per ton for rock salt for road deicing through year 2094 (the current expected end of mine life).

(9)Based on an area of approximately 575,257,000 square feet for the A-2 salt bed within the lease area.

From September 30, 2023 to September 30, 2024, combined measured and indicated resources at the Goderich mine decreased by approximately 0.8% and total reserves decreased by approximately 1.0%. The decreases in salt resources and reserves were attributable to depletion of salt in connection with extraction operations of the Company.

INTERNAL CONTROLS DISCLOSURE

The modeling and analysis of the Company’s resources and reserves has been developed by Company mine personnel and reviewed by several levels of internal management, including the QP. The development of such resources and reserves

estimates, including related assumptions, was a collaborative effort between the QP and Company staff. This section summarizes the internal control considerations for the Company’s development of estimations, including assumptions, used in resource and reserve analysis and modeling.

When determining resources and reserves, as well as the differences between resources and reserves, management developed specific criteria, each of which must be met to qualify as a resource or reserve, respectively. These criteria, such as demonstration of economic viability, points of reference and grade, are specific and attainable. The QP and Company management agree on the reasonableness of the criteria for the purposes of estimating resources and reserves. Calculations using these criteria are reviewed and validated by the QP.

Estimations and assumptions were developed independently for each significant mineral location. All estimates require a combination of historical data and key assumptions and parameters. When possible, resources and data from generally accepted industry sources, such as governmental resource agencies, were used to develop these estimations.

The Company’s salt-producing locations do not utilize exploration in the development of their assumptions around mineral resources or reserves. The mineral deposits are restricted in access by bodies of water, and industry techniques used for geological exploration for other types of mineral deposits, specifically drilling, are degradational to the salt ore being assessed. Given the nature of the salt mineral, this limitation impedes the validation of mineral resources and reserves using drilling. Accordingly, geophysical techniques are utilized at both Goderich and Cote Blanche to assist in mine planning, and to verify that there are no obstructions ahead of advancement of the mine in the form of geological anomalies or structural features, such as faults that could affect future mining. In conducting these geophysical campaigns, including in-seam seismic and ground penetrating radar technologies, the Company is able to identify the continuity of ore-body ahead of mining.

Geographical modeling and mine planning efforts serve as a base assumption for resource estimates at each significant salt-producing location. These outputs have been prepared by both Company personnel and third-party consultants, and the methodology is compared to industry best practices. Mine planning decisions, such as mining height, execution of mining and ground control, are determined and agreed upon by Company management. Management adjusts forward-looking models by reference to historic mining results, including by reviewing performance versus predicted levels of production from the mineral deposit, and if necessary, re-evaluating mining methodologies if production outcomes were not realized as predicted. Ongoing mining and interrogation of the mineral deposit, coupled with product quality validation pursuant to industry best practices and customer expectations, provides further empirical evidence as to the homogeneity, continuity and characteristics of the mineral resource. Ongoing quality validation of production also provides a means to monitor for any potential changes in ore-body quality. Also, ongoing monitoring of ground conditions within the mine, surveying for evidence of subsidence and other visible signs of deterioration that may signal the need to re-evaluate rock mechanics and structure of the mine ultimately inform extraction ratios and mine design, which underpin mineral reserve estimates.

For the mass load estimations in the Great Salt Lake brine, the Utah Geological Survey (“UGS”) as of September 2020 (water samples across five locations) and United States Geological Survey bathymetry data from 2000 (sonar sampling) were used as the basis for the modeling of sodium, magnesium, and potassium mass loads, the critical ions of interest. Key data from the common sampling points were compared to confirm data correlated. Because these reports are independently produced, undergo inter-agency review, and their key data points correlate, no further evaluation of sampling methods or quality control were reviewed by Company management or the QP. The Company also collected potassium and other ion data during this campaign in order to relate ion relationships and ratios in its modelling as well. These data were derived from samples collected by the QP in hermetically sealed samples containers, sent to an external laboratory under chain of custody, analyzed by an accredited laboratory for metals analysis, and the data were reviewed and validated by SRK Consulting. Review of the data derived from the Company’s sampling campaign revealed that the data were of sufficient quality to integrate in to the historic UGS data set for further mass load modelling.

The QP is satisfied that the hydrological/chemical model for the Great Salt Lake reflects the current hydrological and chemical information and knowledge. The mineral resource model is informed by brine sampling data spanning approximately 55 years and recent bathymetry data. Continuity of the resource is not a concern, as the lake is a visible, continuous body. The Company’s experience in extracting potassium and other salts from the Great Salt Lake for over 50 years under dynamic conditions, such as changing lake elevations and ion concentrations, lends confidence regarding the ability to operate under varying conditions, utilizing ion concentrations as a tool to monitor reserve estimates and make operational decisions.

Management also assesses risks inherent in mineral resource and reserve estimates, such as the accuracy of geophysical data that is used to support mine planning, identify hazards and inform operations of the presence of mineable deposits. Also, management is aware of risks associated with potential gaps in assessing the completeness of mineral extraction licenses, entitlements or rights, or changes in laws or regulations that could directly impact the ability to assess mineral resources and reserves or impact production levels. Risks inherent in overestimated reserves can impact financial performance when revealed, such as changes in amortizations that are based on life of mine estimates.

OTHER PROPERTIES

The Company packages its Salt segment products at three additional Company-owned and operated facilities located in Illinois, Minnesota and New York. The Company estimates that its annual combined packaging capacity at these three facilities is 275,000 tons. This packaging capacity is based on the Company’s estimate of the tons that can be packaged at these facilities assuming a normal amount of scheduled down-time and operation of its facilities under normal working conditions, including staffing levels. The Company has the capability to significantly increase its annual packaging capacity by increasing its staffing levels in response to demand, which would require incremental labor and other costs.