CLEAN HARBORS INC (CLH) Business

ITEM 1.    BUSINESS

General

Clean Harbors, Inc., together with its subsidiaries, is a leading provider of environmental and industrial services throughout North America. Everywhere industry meets the environment, we strive to provide sustainable services and products that minimize environmental impact, maximize environmental benefit through reuse and recycling and support our customers’ business needs. We are also the largest provider of parts cleaning and related environmental services to general manufacturing, automotive and commercial customers in North America and the largest re-refiner and recycler of used oil in North America. One of our primary goals is supporting our customers in providing innovative and environmentally responsible solutions to further their sustainability goals and solve complex environmental challenges.

We have two operating segments through which we conduct our operations: (i) the Environmental Services segment and (ii) the Safety-Kleen Sustainability Solutions segment.

•Environmental Services - Our Environmental Services businesses offer an array of services to customers. We safely collect, transport, treat, recycle when suitable and dispose of hazardous and non-hazardous waste through our network of over 100 waste disposal facilities including incinerators; landfills; treatment, storage and disposal facilities, or TSDFs, wastewater treatment facilities; and solvent recycling centers. Our emergency response services leverage specialized equipment, expertise and responsiveness to support our customers. Our teams are also equipped to address our customer requirements related to per- and poly-fluorinated alkyl substances, or PFAS, offering a comprehensive range of services that include testing, water filtration, site remediation and disposal through our Total PFAS Solutions service offering. We leverage our assets to perform a wide range of industrial maintenance and specialty industrial services, both planned and unplanned. We collect containerized waste and provide parts washer and vacuum services to small quantity generators of hazardous waste. All of these services are designed to protect the environment and address environmental related challenges through the use of innovation and the latest technologies. We provide customers with sustainable solutions and include recycling options whenever possible.

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•Safety-Kleen Sustainability Solutions - Our Safety-Kleen Sustainability Solutions, or SKSS, business offerings span the life-cycle of sustainable lubricant products. SKSS provides collections services for used oil, used oil filters and other automotive related fluids, allowing customers to manage these wastes in a responsible and compliant way while also converting these waste streams into high quality products for re-use. The used oil collected by our team serves as feedstock for our oil re-refineries. At these facilities, we manufacture base oil and vacuum gas oil, or VGO, and also formulate and package high quality lubricants which are returned to the marketplace to provide our customers with sustainable solutions to meet their oil and lubricant demands.

Clean Harbors, Inc. was incorporated in Massachusetts in 1980, and our principal executive offices are located in Norwell, Massachusetts. We maintain a website at: http://www.cleanharbors.com. Through a link on this website, we provide free access to our Annual Reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act as soon as reasonably practicable after electronic filing with the SEC. Our guidelines on corporate governance, the charters for our board committees, and our code of ethics for members of our Board of Directors, or the Board, our Co-Chief Executive Officers and our other senior executive officers are available through our website at https://ir.cleanharbors.com/corporate-governance/highlights. Should it be necessary, any waivers for such policies will also be posted on our website. In September 2025, we published our 2025 Sustainability Supplement which updates some of our key sustainability metrics and is intended as a companion to our 2024 Sustainability Report, which is available on our website’s Sustainability page. Our website, and the information contained in or accessible through our website, are not incorporated by reference in, or considered to be a part of, this Annual Report on Form 10-K or any other document unless expressly incorporated by reference.

Commitment to Safety

Safety is a core value and shared belief throughout our organization. Our Safety Starts with Me: Live It 3-6-5 mindset, is the foundation to our overall safety approach. This mindset is organized around three Safety Philosophies, six Golden Rules of Safety and each employee’s five Personal Reasons why they choose to be safe at work and at home. This overall approach, along with other targeted safety and education programs, have enabled us to continue to be an industry leader in safety.

For the year ended December 31, 2025, our safety metrics of Total Recordable Incident Rate, or TRIR, and Days Away, Restricted Activity and Transfer Rate, or DART, were 0.49 and 0.23, respectively, an improvement of 25% and 15% year-over-year respectively. TRIR is a measure of total recordable injuries relative to hours worked while DART is a measure of recordable injury severity for the hours worked. For the fourth year in a row, our TRIR has remained well under 1.0, an industry leading statistic, and 2025 marks the lowest TRIR and DART rate in the Company’s history and indicates a continued decline in the frequency and severity of injuries.

As always, we remain focused on the safety of our teams, our customers and the communities in which we work, live and drive. We will remain relentless in our pursuit to improve how we work through effective partnering and collaboration, as well as innovation and technological solutions intended to deliver on our safety promise to ourselves, our customers and our neighbors. It starts with us, and we live it 3-6-5.

Compliance

We regard compliance with applicable regulations as a critical component of our overall operations. We maintain a compliance organization that is independent of the operations of the business to monitor and provide oversight throughout Clean Harbors. We strive to maintain strict professional standards in our compliance activities. Our compliance staff is responsible for the facilities’ permitting and regulatory compliance, compliance training, transportation compliance and related record keeping. To ensure the effectiveness of our regulatory compliance program, our facilities operations are monitored by our compliance staff and a compliance audit team who routinely conduct audits of our programs.

Our facilities are also frequently inspected and audited by regulatory agencies, as well as by customers. Although our facilities have been cited on occasion for regulatory violations, we believe that each of our facilities is currently in substantial compliance with applicable permit requirements.

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Competitive Strengths

As noted above, safety and compliance are our underlying core principles, and we believe our long-standing commitment to these principles is an important competitive strength and differentiator for Clean Harbors. We have attained leading positions across our business lines despite facing robust competition from local, regional, national and international companies. We believe the following are our core competitive strengths developed over 45 years of operations, which have and will continue to facilitate our prominent position in the marketplace:

•Leading Provider of Environmental and Industrial Services - We are a leading provider of environmental and industrial services which deliver sustainable solutions that help our customers protect the environment. We operate ten commercial hazardous waste incinerators, including our newest incinerator in Kimball, Nebraska, which commenced operations in late 2024 and is expected to be running at full capacity by the end of 2026. We are the largest operator of these high demand facilities in North America. In addition, we operate seven landfills, six of which are able to handle hazardous waste. We are also one of the few emergency response and industrial services companies with footprints across both the United States and Canada. Our highly trained workforce safely responds to customer needs across a variety of service lines, including hazardous waste collection, recycling services, site remediation, emergency response services and plant turnarounds. We provide multi-faceted, high-quality services to a broad mix of customers, and our vast capabilities, valuable and unique assets, skilled workforce, safety profile and breadth of services, as well as our overall size, scale and geographic footprint, help us attract customers and provide them with environmentally responsible solutions.

•Integrated Network of Assets - We believe that we operate, in the aggregate, the largest number of commercial hazardous waste incinerators, landfills, treatment facilities and TSDFs in North America. We have a footprint of service locations spanning the United States and Canada and we manage a sizable fleet of more than 20,000 vehicles. Our extensive service network enables us to effectively handle hazardous waste streams from origin to safe disposal and recycling in one of our various waste outlets, internalizing and efficiently planning the transportation to reduce costs. Our disposal facilities are very difficult to replicate because, in addition to the substantial required capital investments to build these facilities, there are significant permitting, regulatory approvals and ongoing compliance regulations necessary to become and remain operational. In addition, expertise gained through years of experience is paramount to safely operating such facilities. We believe that these longstanding capabilities create a competitive advantage and provide substantial value for our network.

•Comprehensive Service Capabilities Complementing our Customers’ Sustainability Goals - Our comprehensive service offerings and product catalog allow us to act as a full service provider for our customers’ needs. Customers can rely on us not only as a sustainability partner, but also to minimize the number of outside vendors, making us their “one-stop-shop” service provider. Our breadth of service offerings creates incremental revenue growth with no single competitor offering the portfolio of services that we can provide to our customers. Our workforce is trained to fulfill a multitude of customer needs and our complementary lines of business help drive our resiliency in times of market uncertainty. In addition, our proprietary and integrated technology platforms utilized to deliver our services provide a competitive advantage for us and continuous investments provide incremental value to our customers' experience.

•Used Motor Oil Collection and Re-refining Capabilities - As the largest re-refiner and recycler of used oil in North America, in 2025 we collected 243 million gallons of used oil. These gallons were then processed, along with additives and some purchased used oil, into new re-refined base oil, lubricants and byproducts, which were returned back into the marketplace. Our circular capability to serve as an outlet for used lubricants, which we then re-refine and convert into high-quality, environmentally responsible recycled products, distinguishes us from many competitors. This process provides a sustainable substitute for traditional used-oil management and disposal routes. In 2025, by collecting and then re-refining this used oil, we estimate that we helped to avoid the emission of approximately 2.2 million metric tons of greenhouse gases, or GHG. This magnitude of estimated GHG emission avoidance is equivalent to the GHG emissions from 5.7 billion passenger-vehicle miles driven or the carbon sequestered by growing 37 million trees for 10 years.

•Effective Cost Management - We have adopted effective cost management programs with the goal of maintaining or improving our overall margins in spite of inflation, tariffs, increased compliance and regulatory requirements and other drivers of higher costs. Our significant scale allows us to lower costs through standardized compliance procedures and purchasing synergies. By harnessing our technological investments, optimizing logistics and transportation and using our internal resources, we aim to efficiently channel waste streams to our facilities. Our support functions are highly leverageable, contributing to improved operating margins. Our SKSS segment results are significantly impacted by market pricing of oil products. To reduce this commodity exposure, we actively manage the pricing on our used oil collection services as a strategy to manage the re-refinery spreads inherent in our SKSS business.

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•Large and Diversified Customer Base - Our customer portfolio ranges from small companies to Fortune 500 companies and includes public, private and government entities that span multiple industries and business types. This diversification opens opportunities for cross-selling our large portfolio of services and limits our credit exposure to any single customer and potential cyclicality in any one industry. As a percentage of our 2025 revenues, the top ten industries we serviced totaled approximately 80% of revenues and included general manufacturing (14%), chemical (14%), refineries (12%), automotive (10%), utilities (7%), transportation (6%), government (5%), base and blended oils (4%), oil and gas (4%) and retail (4%).

•Stable and Recurring Revenue Base - We have long-standing relationships with our customers, some spanning decades. A significant portion of our revenues are derived from previously served customers with recurring needs for our services. Our operations are often embedded in customer facilities, integrating our personnel and technology into our customers’ day-to-day operations. We also sign stand-ready agreements with customers for around-the-clock emergency response services so we can be their first call for emergency response work. Additionally, we offer proprietary technology solutions that provide meaningful real time insights to our customers. Due to customers’ desire to audit disposal facilities before approving the sites and to limit the number of facilities to which their hazardous waste is shipped in order to reduce potential liability under United States and Canadian environmental laws and regulations, there can be a financial burden that accompanies switching hazardous waste disposal providers. We have been selected as an approved vendor by large and small generators of waste because, in addition to our strong safety performance, we possess comprehensive collection, recycling, treatment, transportation, disposal and hazardous waste tracking capabilities and have the expertise necessary to comply with applicable environmental laws and regulations. Those customers that have selected us as an approved vendor typically continue to use our services on a recurring basis. In our SKSS segment, despite fluctuations and volatility in oil pricing, we consistently collect the gallons needed to both service our customer’s waste oil collection needs and produce our oil products.

•Regulatory Compliance - We continue to make capital investments in our facilities to ensure that they are in compliance with current federal, state, provincial and local regulations. We have a compliance group outfitted to monitor our adherence to these compliance standards and an audit function to review for consistent compliance. Companies relying on in-house or captive disposal methods may find the current regulatory requirements to be too capital intensive or complex and may choose to outsource many of their hazardous waste disposal needs.

•Proven and Experienced Management Team - Our executive management team provides extensive knowledge and continuity, with years of experience and expertise in the environmental and industrial services industries. Together, our Co-Chief Executive Officers, Michael L. Battles and Eric W. Gerstenberg, collectively have close to 50 years of industry experience. Our experienced management team possesses the industry and operational knowledge to be able to quickly pivot in times of change and identify and respond to new market risks, opportunities and demands.

Strategy

Our strategy involves leveraging our core competitive strengths to develop and maintain ongoing relationships with a diversified group of customers while continuing to grow our service lines, ensuring that we can meet our customers’ changing environmental and sustainability needs. Targeted marketing opportunities allow us to expand market awareness of the breadth of our service offerings to current and future customers. We strive to be recognized as the premier supplier of a broad range of value-added environmental services based upon the breadth of those services, quality, responsiveness, customer service, information technologies, safety and cost effectiveness. Everywhere industry meets the environment, we aim to be a primary resource for our customers.

The principal elements of our business strategy are:

•Cross Sell Our Solutions - The breadth of our offerings allows us the opportunity to provide various services and products to meet our customers’ environmental and sustainability objectives. Our significant North American footprint allows us to quickly respond to customer needs, including in emergency response situations. We can assist with remediation needs for small- and large-scale efforts, either planned or unplanned, by providing remediation contractors and project managers together with support services, including, among others, on-site or offsite treatment of soils and groundwater and roll-off container management. We look for opportunities to be a one-stop-shop service provider, expanding the range of services we traditionally provide to a customer and offering total waste management solutions. Our team is committed to identifying opportunities to cross sell among and across our segments which we expect will continue to drive additional revenue for us.

•Expand Our Network and Suite of Offerings - We operate an extensive network of hazardous waste management facilities and oil re-refineries, providing us with significant operating leverage as volumes increase. To meet market demand for additional hazardous waste incineration capacity, we have expanded incineration capacity, notably through

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the construction of a second incinerator at our Kimball, Nebraska facility, as well as expanded our landfill capacity, and enhanced throughput at our existing incinerators and TSDF facilities. We continuously monitor market needs and look to anticipate future waste disposal requirements. For example, in response to industry and governmental focus on PFAS treatment and disposal, we launched our Total PFAS Solutions service, leveraging our unique combination of permitted laboratory, transportation, filtration and disposal assets to provide our customers with a single source provider of PFAS handling from sampling to remediation and disposal. We also seek opportunities to expand waste handling capacity including certain non-hazardous waste streams or oil processing at our facilities by modifying existing permits, improving technology or significantly expanding our facilities. Selected permit modifications within our network of facilities allow us to broaden our treatment and recycling services without the significant capital investment necessary to acquire or build new waste management facilities. Additionally, we aim to grow through opening new locations in strategic areas, expanding to new waste streams and being responsive to shifting product and service needs in the marketplace.

•Pursue Acquisitions and Divestitures - We have a history of strategic acquisitions ranging from small “tuck-ins” to large-scale operations, and we continue to actively pursue selective acquisitions that we believe can enhance and expand our business. Throughout our history, we have successfully executed over 80 acquisitions. We execute strategic acquisitions with the goal of expanding existing services, generating incremental revenues from existing and new customers, obtaining greater market presence, broadening the markets in which we operate, acquiring the assembled workforce of market participants along with their relevant expertise and expanding our total waste disposal capabilities or oil re-refining capacity. In order to maximize synergies, we aim to rapidly integrate our acquisitions into our existing processes. To complement our acquisition strategy, we also regularly review and evaluate our operations to determine whether we should divest certain non-core businesses and reallocate our resources to businesses that we believe better align with our long-term strategic direction.

•Execute Cost, Pricing and Productivity Initiatives - We continually seek to increase efficiency and reduce costs through enhanced technology, process improvements and strategic expense management. We seek to identify areas in our business where strategic investments in automation, process improvements and employees can serve to increase productivity, efficiency and safety compliance. We continuously focus on the operating leverage of our support functions, including expanding globally to achieve profitability and productivity benefits. We aim to price our services and products competitively, understanding the demands of our customers, the inherent value of our network of assets and operations and our ability to quickly respond to market and macroeconomic changes. We also understand the value our customers place on our products and services in a global market continuously focusing on sustainability, environmental compliance and safety.

•Foster Innovation through Technology - Technology has always been fundamental to our operations, influencing our strategy by increasing throughput and automation at our facilities, and deploying artificial intelligence and robotic process automation to increase productivity. We aim to utilize advanced technologies in our operations while also integrating technology-based solutions for our customers to use in the management of their generated waste streams, which promote the safety, efficiency and profitability of these operations. Our artificial intelligence initiatives are aimed at both internal efficiencies (e.g. billing and transportation routing efficiencies) and customer-facing enhancements such as waste profiling. With technology, we are able to centrally manage our transportation network by deploying, monitoring and adjusting our transportation fleet as needs change. Technology is enhancing our customer interactions through the use of our Customer Solutions Portal, our e-commerce initiatives and our proprietary tools providing customers with real-time data on the services we are providing. We anticipate that as new waste streams arise or grow in prominence, we will develop new technology and/or improve the capabilities of existing technology to respond to these waste disposal and recycling needs. We believe that making technological investments that increase the value of our services delivered to customers pays off in a variety of ways including growth, retention, profitability and overall customer experience.

•Capture Emergency Response Opportunities - With our extensive national presence of over 150 response locations, we have the manpower, equipment and technical expertise to manage large and small environmental emergencies for our customers. We can rapidly deploy experienced teams to address unplanned releases or spills of chemicals, oil, fuels, solvents or many other hazardous materials, including emerging pollutants such as PFAS or bio-contaminants. We also address damage caused by natural disasters including hurricanes, wildfires, earthquakes and storms. These opportunities can vary in size, complexity and duration, however, in any case we aim to be the first call customers make in these situations. Our Standby Emergency Response Agreement, or SERA, offering is designed to guarantee our customers a rapid response to any emergency waste management need. We can also provide turnkey offsite transportation and disposal services throughout our disposal network for soil and other contaminated materials generated from remediation activities.

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Business Overview

We operate our business in two segments: Environmental Services and SKSS. Each segment utilizes our network of specialized facilities and equipment, along with our skilled workforce, to meet the needs of our customers. Further, each has individual key performance indicators that our management uses to assess results as well as certain macroeconomic trends and influences that impact the results.

Environmental Services

Our Environmental Services business offers an array of services to customers. We safely collect, transport, treat and dispose of hazardous and non-hazardous waste, including resource recovery, physical treatment, incineration, landfill disposal, wastewater treatment, lab chemical disposal, explosives management and CleanPack® services. Our CleanPack® services include the collection, identification, categorization, specialized packaging, transportation and disposal of laboratory chemicals and household hazardous waste. Our Total PFAS Solutions service provides our customers with a single source provider of PFAS handling from sampling to remediation and disposal as well as water filtration services. We also perform a wide range of industrial maintenance and specialty industrial services and utilize specialty equipment and resources to perform services at any chosen location on a planned or emergency response basis. Additionally, we collect containerized waste and provide parts washer and vacuum services to small quantity generators of hazardous waste. All of these services are designed to address environmental challenges through innovation and the latest technologies. We offer sustainable solutions that aim to recycle waste materials whenever possible.

The results of our Environmental Services segment are driven by customer demand for our wide variety of services, the volume, pricing and mix of waste managed and project work requiring responsible waste handling and disposal. Environmental Services results are also impacted by the demand for planned and unplanned industrial related cleaning, maintenance and specialty services at customer sites as well as environmental cleanup services on a scheduled or emergency basis, including response to large-scale events such as major chemical spills, natural disasters, or other instances where immediate and specialized services are required. The Environmental Services segment results include the Safety-Kleen branches’ core environmental service offerings of containerized waste disposal, parts washer and vacuum services. These results are driven by the volumes of waste collected from these customers, the overall number of parts washers placed at customer sites and the demand for and frequency of other offered services.

In managing the business and evaluating performance, management tracks the volumes and overall mix of waste handled and disposed of or recycled, generally through our incinerators, TSDFs, wastewater treatment facilities and landfills; the utilization rates of our incinerators; equipment and workforce, including billable hours; the number of parts washer services performed; and pricing realized by our business and peer companies as well as other key metrics. Levels of activity and ultimate performance associated with this segment can be impacted by several factors including overall North American GDP; U.S. industrial production; economic conditions in the general manufacturing, chemical, refinery and automotive markets, including efforts and economic incentives to increase domestic operations; available capacity at waste disposal outlets; demand for industrial cleaning and related industrial services; weather conditions; efficiency of our operations; technology; changing regulations; competition; market pricing of our services; costs incurred to deliver our services; and the management of our related operating costs.

Technical Services

We provide technical services through a network of service centers from which a fleet of vehicles are dispatched to pick up customers’ waste either on a predetermined schedule or on demand, and to deliver the waste to permitted facilities, which are usually owned by us. Our service centers can also dispatch chemists to a customer location for collection of chemical and laboratory waste for disposal. Our InSite Service® offering is a branded on-site/in-plant service delivery program through which we offer a full range of environmental, industrial and waste management services. This signature program is built on safety, quality, efficiency and integrity, and has been offered by Clean Harbors for more than 30 years. By leveraging Clean Harbors’ expertise and capabilities, our on-site crews are dedicated to developing the safest, most cost-effective and sustainable solutions to service our customers’ needs.

As an integral part of our services, we collect industrial waste from customers and transport such waste to and between our facilities for treatment or bulking for shipment to final disposal locations. Waste is typically accumulated in containers, such as 55-gallon drums, totes, bulk storage tanks or 20-cubic-yard roll-off containers. In providing this service, we utilize a variety of specially designed and constructed tank trucks and semi-trailers as well as third-party transporters and rail.

We recycle, treat and dispose of hazardous and non-hazardous waste. Certain waste handled includes substances which are classified as “hazardous” because of their corrosive, ignitable, infectious, reactive or toxic properties and other substances subject to federal, state and provincial environmental regulation. We provide final treatment and disposal services designed to

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manage waste which cannot be otherwise safely and/or economically recycled or reused. The waste that we handle comes in solid, sludge, liquid and gas form.

We provide large scale waste removal and disposal projects for water, soil and air remediation projects, including PFAS remediation. These end-to-end service offerings include carbon filtration remediation technologies, large-scale soil excavation and remediation, environmental construction including treatment system design and fabrication, equipment rentals, waste disposal and transportation.

Incineration is the preferred method for the treatment of organic hazardous waste because it effectively destroys the contaminants at high temperatures. High temperature incineration safely and efficiently eliminates organic waste such as herbicides, halogenated solvents, pesticides and pharmaceutical and refinery waste, regardless of form as gas, liquid, sludge or solid. Federal and state incineration regulations require a destruction and removal efficiency of at least 99.9999% for most organic waste and our incinerators meet or exceed these requirements.

As of December 31, 2025, we operated ten active incinerators at five facilities with a total annual practical capacity of 631,721 tons and offered a wide range of technological capabilities to customers. Our incinerator facilities in the United States are designed to process waste through the use of high-tech, high temperature incineration. Our technologies include rotary kiln incineration, which provides greater flexibility in destruction of hazardous waste, and fluidized bed incineration which helps promote a more complete organic combustion than other incineration technologies. Our incinerator facility in Lambton, Ontario, is a liquid injection incinerator designed primarily for the destruction of liquid organic waste. Typical waste streams at this location include wastewater with low levels of organics and other higher concentration organic liquid waste not amenable to conventional physical or chemical waste treatment.

Landfills are primarily used for disposal of inorganic waste. In the United States and Canada, we operate seven commercial landfills, six of which are designed and permitted for disposal of hazardous waste and one which is operated for non-hazardous industrial waste disposal. In addition to our seven commercial landfills, we also own and operate one non-commercial landfill that only accepts waste from our Kimball incinerators.

As of December 31, 2025, the useful economic lives of our six commercial hazardous waste landfills included approximately 33.0 million cubic yards of remaining capacity. We estimate the useful economic lives of landfills to include permitted airspace and unpermitted airspace that our management believes to be probable of being permitted based on our analysis of various factors. In addition to the capacity included in the useful economic life of these landfills, there are approximately 77.8 million cubic yards of additional unpermitted airspace capacity included in the footprints of these landfills that may ultimately be permitted, although there can be no assurance that this additional capacity will be permitted. As of December 31, 2025, the useful economic life of our non-hazardous industrial landfill included 3.1 million cubic yards of remaining permitted capacity. This facility is located in the United States and has been issued operating permits under Subtitle D of the Resource Conservation and Recovery Act, or RCRA. Our non-hazardous landfill facility is permitted to accept commercial industrial waste, including waste from demolition and construction.

Another waste disposal outlet in our network of facilities are our TSDFs that collect, temporarily store, process and/or consolidate compatible waste streams for more efficient processing and transportation to final recycling, treatment or disposal destinations. These facilities hold special, hard-to-come-by permits, such as Part B permits under the RCRA, which allow them to process, transfer and dispose of waste through various technologies including recycling, incineration, landfill and wastewater treatment depending on each location's permitted and constructed capabilities.

We operate recycling systems for the reclamation and reuse of certain waste, particularly solvent-based waste generated by industrial cleaning operations, metal finishing and other manufacturing processes. Resource recovery involves the treatment of waste using various methods, which effectively remove contaminants from the original material to restore its fitness for its intended purpose and to reduce the volume of waste requiring disposal. We also operate a recycling facility that recycles refinery waste and spent catalyst. The recycled oil and catalysts, depending on market conditions, are sold to third parties.

Our wastewater treatment facilities process hazardous and non-hazardous waste through use of physical and chemical treatment methods. Our twelve wastewater treatment facilities offer or employ a range of wastewater treatment technologies. These facilities treat a broad range of liquid and semi-liquid waste containing heavy metals, organics and suspended solids. We are also able to employ mobile waste water treatment systems or manage more long-term regenerative carbon filtration and resin units at our customer sites via stand-ready agreements or on an ad hoc basis.

We also provide total project management services in areas such as chemical packing, on-site waste management, remediation, compliance training and emergency spill response, while leveraging Clean Harbors’ network of service centers and environmental capabilities. Our household hazardous waste collection services provide municipalities with a partner for the

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collection and disposal of household paints, solvents, batteries, fluorescent lamps, pesticides, cleaners and other hazardous materials.

Industrial Services

We perform industrial cleaning, maintenance and support services and specialty industrial services at refineries, chemical plants, upgraders, power generation and other utilities facilities, manufacturing facilities and other industrial customers throughout North America.

Our industrial services crews support ongoing in-plant cleaning and maintenance services on our customers' mission critical equipment and infrastructure. These services include liquid and dry vacuum services, hydro-blasting, dewatering and materials processing, leak detection and repair, tank cleaning, specialty mechanical services, vapor control, water and chemical hauling, foam cleaning, steam cleaning, ultrasonic cleaning technology and temporary housing services. We provide a variety of specialized industrial services, including plant outage and turnaround services; specialty cleaning services, including chemical cleaning and high and ultra-high pressure water cleaning; production services; and upstream energy services.

Field and Emergency Response Services

Our crews and equipment are dispatched on a planned or emergency basis and perform services such as large remediation projects, spill cleanup on land and water, demolition, site disinfecting, decontamination and disposal, confined space entry for tank cleaning, railcar cleaning, manhole/vault clean outs, product recovery and transfer, scarifying and media blasting, vacuum services, filtration, water treatment services and wetland restoration. We are also a leader in providing response services for environmental emergencies of any scale from man-made disasters such as oil spills and natural disasters such as hurricanes. We provide these field and emergency response services to a variety of customers across industries including utilities, manufacturing, transportation services and more.

Safety-Kleen Environmental

Our Safety-Kleen Environmental branches’ core service offerings focus on the small quantity waste generators predominately within the general manufacturing, automotive and transportation services industries. We provide containerized waste, parts-washer and vacuum services to a diverse range of customers including metal fabricators, machine manufacturers, fleet maintenance shops, automobile repair shops and car and truck dealers. General manufacturing customers account for more than thirty percent of the revenues for our Safety-Kleen Environmental revenues, with automotive customers making up less than twenty-five percent. We collect and transport hazardous and non-hazardous containerized waste for recycling or disposal, primarily through our network of recycling, treatment and disposal facilities. As the largest provider of parts cleaning services in North America, we offer a complete line of specially designed parts washers to customer locations and then deliver recurring service that includes machine cleaning, maintenance, disposal and replenishment of clean solvent or aqueous fluids. Our vacuum services remove solids, residual oily water and sludge and other fluids from customers' oil/water separators, sumps and collection tanks. We also remove and collect waste fluids found at large and small industrial locations, including metal fabricators, auto maintenance providers and general manufacturers.

Safety-Kleen Sustainability Solutions

Our Safety-Kleen Sustainability Solutions business offerings span the life-cycle of lubricants and other sustainable automotive products, including the collection of used waste oil and other fluids as well as production of re-refined and recycled oil and related materials. These operations include our re-refineries located in East Chicago, Indiana; Breslau, Ontario; Fallon, Nevada; Kingsland, Georgia; Tacoma, Washington; Wichita, Kansas; and Sanford, North Carolina. Our Newark, California and Rollinsford, New Hampshire, re-refineries were taken offline in early 2025.

Using our nationwide fleet of trucks, tankers, rail-cars and barges, our teams collect used waste oil from thousands of customers. These used waste oils then serve as feedstock for our oil re-refineries in order to produce sustainable recycled lubricants. In 2025, we collected 243 million gallons of used oil. Our state-of-the-art processes allow us to realize oil’s potential to be recycled and reused. We process the used oil into a variety of products, mostly base oils, including Group III base oils, and blended lubricating oils. Our Performance Plus® family of automotive and industrial lubricants are sold to on- and off-road corporate fleets, government entities, automotive service shops and industrial plants for hydraulic components, motors, pumps and valves. Our anti-wear hydraulic oils and lubricants provide extended operating life, protection from corrosion and abrasion and improved cleanliness. We also sell unbranded blended oils to distributors that resell them under their private label brands. These high-quality lubricants provide our customers with a sustainable solution to their oil demands.

Used oil can also be processed into recycled fuel oil, or RFO, which is then sold to customers such as asphalt plants, industrial plants, pulp and paper companies or into vacuum gas oil, or VGO which can be further re-refined into lubricant base oils or sold directly into the marine diesel fuel market. Our re-refineries processed 243 million gallons of used oil collected

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from customers in 2025 with some additives and additional used oil purchases, to return new re-refined oil, lubricants and byproducts back into the marketplace to help our customers meet the growing demand for the use of circular and sustainable products in their operations.

In 2025, we began construction of a state-of-the-art Solvent De-Asphalting, or SDA, unit adjacent to our East Chicago, Indiana, re-refinery. The facility will utilize industry-proven solvent de-asphalting processes, in combination with our existing hydrotreating capabilities, to reprocess certain by-products produced today into 600N base oil. 600N base oil is a high purity base oil that is typically used in heavy duty industrial applications due to its durability and high performance characteristics and historically captures a higher sales price than the base oil we currently produce. We launched this multi‑year project after recognizing a potential future shift in the market for the outlets of our existing byproducts. It is expected that this facility will be operational in 2028.

Our SKSS operations also collect and either recycle or dispose of related automotive products including antifreeze and oil filters. We sell automotive and industrial products, including antifreeze recycled through our collections, windshield washer fluid, degreasers, glass and floor cleaners, hand cleaners, absorbents, mats and spill kits.

Our SKSS segment results are impacted by our customers’ demand for high-quality, environmentally responsible recycled oil products and their demand for our related service and product offerings. Segment results are impacted by market pricing, overall demand, partnerships and the mix of our oil products sales. Segment results are also predicated on the demand for other SKSS product and service offerings, including collection services for used oil, used oil filters and other automotive fluids. These fluid collections are used as feedstock in our oil re-refining to produce our base and blended oil products and our recycled automotive related fluid products or are integrated into our recycling and disposal network.

In operating the business and evaluating performance, management tracks the volumes and relative percentages of base and blended oil sales along with various pricing metrics associated with the commodity driven margin between product pricing and the overall costs associated with the collection of used oil. Levels of activity and ultimate performance associated with this segment can be impacted by economic conditions in the manufacturing and automotive services markets, efficiency of our operations, technology, weather conditions, changing regulations, competition and the management of our related operating costs. Overall product pricing as well as revenues generated and/or costs incurred in connection with the collection of used oil and other raw materials associated with the segment’s oil related products can also be volatile and can be impacted by global events and their relative impact on commodity products and pricing. The overall market price of oil and regulations, which change the possible usage of used oil or burning of used oil as a fuel, impact the premium the segment can charge for used oil collections.

Geographical Information

For the year ended December 31, 2025, we generated $5,490.9 million or 91.0% of our third-party revenues in the United States and $540.0 million or 9.0% of our third-party revenues in Canada. For the year ended December 31, 2024, we generated $5,352.4 million or 90.9% of our third-party revenues in the United States and $537.5 million or 9.1% of our third-party revenues in Canada. For additional information about the geographical areas from which our revenues are derived and in which our assets are located, see Note 3, “Revenues,” and Note 19, “Segment Reporting,” respectively, to our consolidated financial statements included in Item 8 of this Annual Report on Form 10-K.

Acquisitions and Divestitures

We execute acquisitions as an element of our business strategy, aiming to strengthen our overall capabilities and create opportunities for continued profitable growth. We also monitor our operations for opportunities to reallocate resources through the divestiture of non-core businesses. While no acquisitions were finalized in 2025, we assessed multiple acquisition targets during the year and expect to continue evaluating potential acquisition targets going forward. Acquisitions remain an important component of our capital allocation and growth strategy, which is guided by our proven disciplined and balanced approach.

In 2024, we acquired HEPACO for an all-cash purchase price of $392.2 million, net of cash acquired. The operations of HEPACO expanded our Environmental Services segment’s field services business. Also in 2024, we acquired Noble Oil Services, Inc. and its subsidiaries, collectively Noble, for an all-cash purchase price of $68.7 million, net of cash acquired. The acquisition of Noble expanded our SKSS segment’s oil collection operations in the southeastern region of the United States while also adding incremental production from the re-refinery owned and operated by Noble.

For additional information relating to our acquisition and divestiture activities, see Note 4, “Business Combinations,” to our consolidated financial statements included in Item 8 of this report.

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Environmental Stewardship and Sustainability

Environmental Commitment

We are committed to a standard of excellence as an environmental steward and leader. We affirm to our employees, customers, stakeholders and the public that we will conduct our business activities in a manner that is protective of human health, safety and the environment. Our mission is to create a cleaner and safer environment, and our responsibility for the environment extends across the whole of our company and operations. Balancing environmental, economic and social considerations is foundational to our framework for sustained success and is expected by our employees, customers and other stakeholders. Our environmental sustainability efforts are twofold: we are focused on mitigating our own resource consumption and footprint as well as on providing industry, government and public stakeholders with a wide range of innovative solutions to minimize environmental impact and achieve sustainability goals.

Transparency

We are committed to transparency about the impacts and benefits of our business activities and actively evaluate how we as a company are addressing today’s most important issues with the intention of continuous improvement as an organization. Our sustainability program, across all lines of business, is designed to address the material environmental, societal and economic aspects of our organization. We communicate our sustainability programs, progress and performance across various channels. In September 2025, we published our 2025 Sustainability Supplement, which updates some of our key sustainability metrics and is intended as a companion to our 2024 Sustainability Report. A copy of this report can be found in the “About Us” section of our website. None of our website, our 2024 Sustainability Report, or our 2025 Sustainability Supplement are incorporated by reference in, or considered to be a part of, this Annual Report on Form 10-K or any other document, unless expressly incorporated by reference. We continue to align with materiality mapping and guidance developed by the Sustainability Account Standards Board, or SASB, which is part of the International Financial Reporting Standards, or IFRS. We also disclose according to Global Reporting Initiative, or GRI, Standards as well as report on select voluntary disclosures we believe are material but may not be formally expressed in other frameworks.

We have requirements for periodic reporting to regulatory agencies that are available to the public and we continue to monitor for legislation that may influence requirements for sustainability-related disclosures. We routinely provide environmental data to our customers to better understand and analyze their environmental footprint, including but not limited to supporting in-scope emissions reporting for waste generated in operations. We voluntarily disclose to select for-profit and non-profit external sustainability reporting and assessment organizations, many of which in-turn communicate to subscribers and the public their evaluation of corporate sustainability performance based on a combination of public and private information. These entities include EcoVadis, Carbon Disclosure Project, or CDP; Institutional Shareholder Services, or ISS, -Corporate; S&P Global Ratings; MSCI, Sustainalytics; Moody’s Analytics; The Sustainability Project, or TSP, and others.

Solving Complex Environmental Challenges

As a leading provider of environmental services, we help to both prevent the release of chemicals and hazardous waste streams into the environment as well as recover and decontaminate pollutants that have been released. This includes the safe and compliant management, destruction or disposal of hazardous materials to ensure these materials are no longer a danger to the environment. With a focus on delivering sustainable solutions to address emerging contaminants and pollutants, we launched our Total PFAS Solutions service, providing our customers with a single source provider of PFAS handling from sampling to remediation and disposal as well as filtration. We offer the most comprehensive and proven PFAS Solution in North America. We conducted a PFAS incineration study in conjunction with the Environmental Protection Agency, or EPA, and Department of War, or DOW, in November 2024. Results, which were reviewed by third-party experts, were issued in September 2025 and concluded that our RCRA-permitted, high-temperature incineration achieved a safe and permanent thermal destruction of PFAS in its various forms, demonstrating cost-effective destruction at commercial scale as well as 99.9999% effectiveness in thermal destruction.

Recycling and Product Circularity

Material recycling and reclamation is a critical element of today’s sustainability-focused industrial landscape. When providing environmental services, we are committed to the recycling, reuse and reclamation of material streams whenever practical using a wide-range of advanced methods and technologies. Many of our sustainable services and products provide critical recycling solutions to the marketplace. Wherever possible, solvents, chemicals and used oil are continuously recycled to industry standards and reprocessed into useful and sustainable products. Our tolling programs provide closed-loop systems in which the customer’s spent solvents are recycled to precise specifications and returned directly to the customer. As the largest re-refiner and recycler of used oil in North America, we collect millions of gallons of used oil and process these used oil gallons, along with additives and some purchased used oil, into millions of gallons of new re-refined base oil, lubricants and

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byproducts that are returned back into the marketplace. Our circular capability to serve as an outlet for used lubricants in the marketplace, which we then re-refine and convert into high-quality, environmentally responsible recycled products, distinguishes us from many competitors. This process also provides an alternative to other disposal options of the used lubricants.

We are committed to improving the efficiency of our environmental operations to scale with the growth of our company. Our operational assets present significant opportunities to implement sustainable and circular business practices. Our Fleet Asset Refurbishment Program is a comprehensive effort to rebuild fleet vehicles and assets to “like new” quality while reusing or recycling as much of the original materials as possible. Annually, we replace hundreds of vehicle assets, such as vacuum trucks, industrial air movers and waste oil trucks, with state-of-the-art refurbished or internally manufactured equivalents using repurposed parts whenever possible. Our parts washers services’ field repair and refurbishment program enables us to repair thousands of parts washers in the field, saving on transportation and fuel, and at dedicated reconditioning facilities conserving materials and resources for required maintenance. We also look across our operational facilities to identify recycling initiatives to improve efficiencies. Our flagship El Dorado, Arkansas, facility has the capability to recycle and reconstitute plastic containers and produce hundreds of thousands of recycled containers each year. We expect to expand these recycling capabilities across other facilities in the future. Circularity in our business extends to water conservation and stewardship as well. We treat millions of customer wastewater gallons annually both at our dedicated wastewater treatment facilities and through the advanced treatment and remediation of impacted waters at our customers’ locations.

Community Engagement and Resilience

We are dedicated to being a good neighbor in the communities in which we live and work and understand that the success of our enterprise is connected to the prosperity of the communities in which we operate. We believe that staying engaged with our communities, customers and stakeholders can contribute to the long-term health of the environment, society and local economies. Our endeavors have spanned collaborative partnerships with local organizations, active involvement in community events and the mobilization of our employees for regional volunteer efforts. We facilitate thousands of Household Hazardous Waste, or HHW, collection programs in our communities throughout North America through the collection of paints, solvents, batteries, fluorescent lamps, pesticides, cleaners and other hazardous materials that otherwise might be improperly disposed of or become dangerous. When our communities need us, we are there. We understand that adaptability and resilience are central to the sustainability of our local and global communities. With our extensive national presence of over 150 emergency response locations, we have the manpower, equipment and technical expertise to manage large and small environmental emergencies. We can rapidly deploy experienced teams to address unplanned releases of chemicals, oil, fuels, solvents or many other hazardous material spills including emerging pollutants such as PFAS or bio-contaminants. We also address damage caused by climatic events and natural disasters such as hurricanes, wildfires, earthquakes and storms. As a company, responding to emergencies is simply part of who we are and what we do.

Competitive Markets

Due to the variety of services and products offered, we face competition from companies in various industries across all lines of business. Our breadth of service offerings however has resulted in no one competitor directly competing with our full suite of offerings. Sources of competition vary by locality and by type of service rendered, with competition coming from national and regional industrial and automotive waste services companies and hundreds of privately-owned firms. Veolia North America, Enviri Corporation, Republic Services, Waste Management, GFL Environmental and Crystal Clean were the principal national firms with which we competed in 2025. Each of these competitors is able to provide one or more of the products and services we offer.

Under federal and state environmental laws in the United States, generators of hazardous waste remain liable and responsible for the proper disposal of such waste. Although generators may hire various companies that have the proper permits and licenses, because of the generators' potential liability, they tend to be very interested in the reputation and financial strength of the companies they use for the management of their hazardous waste. We believe that our technical proficiency, safety record, customer service-oriented culture and overall reputation are important considerations to our customers in selecting and continuing to utilize our services. We also believe that the depth of our recycling, treatment and disposal capabilities, and our ability to collect and transport waste materials efficiently are additional significant differentiating factors that create an advantage for us in the market for treatment and disposal services.

Competition within our Environmental Services segment varies by locality and type of service rendered. For our landfill and waste services, competitors include several major national and regional environmental services firms, as well as numerous smaller local firms. For our commercial incineration services, our competitors include Veolia North America, EQT Infrastructure and Ross Incineration. We believe the availability of skilled, technical and professional personnel, quality of performance, diversity of services, safety record, quality and scale of assets and use of current technologies, as well as price, are the key competitive factors in this service industry. With regard to commercial hazardous waste incineration services, we

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operate the largest network of such facilities in North America. For our industrial, field, emergency response and Safety-Kleen branches’ core services, competitors vary by locality and by type of service rendered, with competition coming from national and regional service providers and hundreds of privately-owned firms that offer similar services. Crystal Clean in the United States and CEDA, GFL Environmental Inc. and Secure Waste Infrastructure Corp in Canada are the principal national firms with which we compete for this work. There are also several regional and local firms with which we compete.

For our SKSS segment, competitors vary by locality and by type of services rendered, with competition coming from Crystal Clean, along with many regional and local firms. We believe that geographic coverage, pricing and breadth of services and products, including our ability to produce high quality sustainable lubricants from the used motor oil we collect, are key competitive factors in this industry. With our Safety-Kleen Oil Plus® closed loop offering, we are competing in certain markets with other North American lubricant distributors. With our KLEEN+ base oil produced at our re-refineries, we compete against base oil produced at traditional oil refineries such as Motiva Enterprises LLC and Chevron Corporation.

We believe that we offer a more comprehensive range of services and products than our competitors in major portions of the United States and Canada.

Human Capital

As of December 31, 2025, we employed 22,155 active full-time employees, of which 1,616 in the United States and 642 in Canada were represented by labor unions. In response to the needs of our business, we also employ temporary and part-time employees. As of December 31, 2025, the total of all active employees, inclusive of the temporary and part-time workforce, was 22,591.

Our human capital objectives prioritize the health and safety of our employees, employee development and training, fair and competitive compensation and benefits, and Equal Opportunity Employer hiring practices. Key metrics that management uses to measure these objectives include TRIR, voluntary turnover rates and certain training and employee engagement metrics, all of which are monitored at all levels of the organization. Our focus on these human capital objectives resulted in a 150 basis point reduction in our voluntary turnover rate in 2025, the lowest level in the last five years.

We believe that our relationship with our employees is positive, and we engage with our employees through periodic employee engagement surveys and other mechanisms to continue the development of these relationships. As part of our commitment to employee safety and quality customer service, we have an extensive compliance program and trained environmental, health and safety staff. We continually strive to invest in our employees through training programs, including training specifically aimed at workplace safety and cybersecurity. We provide the training and licensing necessary to maintain a skilled and experienced workforce. Our company-wide Green Hat program identifies newly hired teammates by their green hats, signaling to more senior teammates to provide extra help, oversight or explanation, and also highlights everyone’s ownership of a safe work environment. We also provide competitive compensation and benefit programs, including matching employee contributions towards certain retirement savings plans and health savings accounts and our Employee Stock Purchase Program.

We are committed to fundamental human rights principles and we have a comprehensive Human Rights Policy to formalize the standards to which we hold ourselves accountable. Respect is essential to our interactions with employees, customers, shareholders and the public at large. In recognition of our Human Rights Policy, we promote equal opportunity and respect in our workplaces. Our seven employee resource groups were developed to encourage belonging, inclusion and collaboration among our employees at Clean Harbors.

Resources

We have invested significantly in the development of proprietary technologies and also to establish and maintain an extensive knowledge of leading technologies, including the incorporation of artificial intelligence platforms and robotic process automation. We incorporate these technologies into the services we offer and provide to our customers to enhance the service quality and value received by our customers, which reduces the time to perform and increases the safety of such services. For example, our internally developed proprietary software system, Waste Information Network, not only allows us and our customers to track waste throughout our network, but technology also aids in safer packaging of materials and waste and incorporates artificial intelligence to optimize route efficiency and handle waste efficiently and safely.

As of December 31, 2025, we held a total of 31 U.S. and 6 foreign issued or granted patents (which will expire between 2026 and 2042), three U.S. and five foreign pending patent applications, 92 U.S. and 68 foreign trademark registrations, and five U.S. pending trademark registrations and two foreign trademark registrations. We also license software and other intellectual property from various third parties. We enter into confidentiality agreements with certain of our employees, consultants and corporate partners, and control access to software documentation and other proprietary information.

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We believe that we hold adequate rights to all intellectual property used in our business and that we do not infringe upon any intellectual property rights held by other parties.

We must obtain and maintain permits and licenses for transportation and industrial needs throughout our business. We are required to obtain federal, state, provincial and local permits or approvals for each of our hazardous waste facilities. Such permits are difficult to obtain and, in many instances, extensive studies, tests and public hearings are required before the approvals can be issued. Our compliance programs are paramount in maintaining these permits and licenses.

Management of Risks

We adhere to a program of risk management policies and practices designed to reduce potential liability, as well as to manage customers' ongoing environmental exposures. This program includes installation of risk management systems at our facilities, such as fire suppression, employee training, environmental consciousness, auditing and policy decisions restricting the types of waste handled. We evaluate all revenue opportunities and decline those that we believe involve unacceptable levels of risk.

We dispose of waste at our incinerator, wastewater treatment, landfill and other facilities, or at approved facilities owned and operated by other companies. We apply established technologies to treatment, storage and recovery of hazardous waste. We believe our operations are conducted in a safe and prudent manner and in substantial compliance with applicable laws and regulations.

Insurance and Financial Assurance

Our insurance programs cover the potential risks associated with our multifaceted operations from two primary exposures: direct physical damage and third-party liability. We maintain a casualty insurance program that provides coverage for vehicles, employer's liability and commercial general liability in the aggregate amount of $110.0 million, $102.0 million and $102.0 million, respectively, per year, subject to retentions of $2.0 million for employers' liability in the United States, $5.0 million per occurrence for auto, $2.0 million per occurrence for commercial general liability in the United States and $2.0 million (CAD) per occurrence for employer's liability, auto and commercial general liability in Canada. We have workers' compensation insurance with limits established by state statutes. We also maintain cybersecurity liability insurance that has limits of $5.0 million per occurrence.

We have pollution liability insurance policies covering potential risks in three areas: as a contractor performing services at customer sites, as a transporter of waste and as a processor of waste at our facilities. The contractor's pollution liability insurance has limits of $30.0 million per occurrence and $30.0 million in the aggregate, covering offsite remedial activities and associated liabilities.

For sudden and accidental in-transit pollution liability, our auto liability policy provides the primary $10.0 million per occurrence of transportation pollution insurance. Our pollution liability policies provide an additional $85.0 million per occurrence and $85.0 million in the aggregate for a total of $95.0 million per occurrence and $95.0 million in the aggregate, respectively. A $5.0 million deductible per occurrence applies to this coverage in the United States and Canada.

Federal and state regulations require liability insurance coverage for all facilities that treat, store or dispose of hazardous waste. RCRA, the Toxic Substances Control Act and comparable state hazardous waste regulations typically require hazardous waste handling facilities to maintain pollution liability insurance in the amount of $1.0 million per occurrence and $2.0 million in the aggregate for sudden occurrences and $3.0 million per occurrence and $6.0 million in the aggregate for non-sudden occurrences. Our liability insurance coverage meets or exceeds all federal and state regulations.

We maintain property insurance for our physical locations valued in excess of $10.0 million covering direct physical damage. We consolidated the insurance on these locations and this policy has a $10.0 million aggregate deductible. We are self-insured for locations not specifically listed on this policy.

Our international operations are insured under locally placed insurance policies that are compulsory in a specific country. In addition, we have a global foreign liability policy that will provide excess and difference in condition coverage in international countries.

It is our practice to retain a portion of certain expected losses related primarily to workers' compensation, commercial general and vehicle liability and certain employee benefits. Provisions for losses expected under these programs are recorded based upon our estimates of the actuarially determined value of the aggregate liability for claims.

Operators of hazardous waste handling and certain other permitted facilities are required by federal, state, provincial and local regulations to provide financial assurance for closure and post-closure care of those facilities should the facilities cease operation. Closure care would include the cost of removing the waste stored at a facility that ceased operating and sending

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the material to another facility for disposal and the cost of performing certain procedures for decontamination of the facility. Once a site has been certified as closed by the applicable agency, post-closure care would include maintenance and monitoring costs over a required period of time, typically 30 years. We have obtained all of the required financial assurance for our facilities through a combination of surety bonds and insurance from qualified insurance companies.

Government Regulations

Our business is subject to extensive and evolving federal, state, provincial and local environmental, health, safety and transportation laws and regulations. While our business has historically benefited from increased government regulation of hazardous waste transportation, storage and disposal, the environmental services industry itself is the subject of extensive and evolving regulation by federal, state, provincial and local authorities. Increasing regulations may have a negative impact on our operating costs; however, extensive environmental regulation applicable to our industry and operations is a barrier to rapid entry of competitors that benefits us. Additionally, the impacts of regulations on our customers further enhance the value of the disposal and environmental services we can provide.

We are required to obtain federal, state, provincial and local permits or approvals for each of our hazardous waste facilities. We have acquired all material operating permits and approvals required for the current operation of our business and have applied for, or are in the process of applying for, all permits and approvals needed in connection with planned expansion or modifications of our operations. We continue to monitor and comply with the requirements of our permits and these regulations.

We are constantly monitoring the regulatory environment, which is often influenced by leadership at the federal, state, provincial and local levels. We make a continuing effort to anticipate regulatory, political and legal developments that might affect operations, but are not always able to do so. We cannot predict the extent to which any legislation or regulation that may be enacted or enforced in the future may affect our operations.

United States Hazardous Waste Regulation

Federal Regulations.    The most significant federal environmental laws affecting us are RCRA; the Comprehensive Environmental Response, Compensation and Liability Act, also known as the Superfund Act; the Clean Air Act; the Clean Water Act; and the Toxic Substances Control Act, or TSCA.

RCRA.    RCRA is the principal federal statute governing hazardous waste generation, treatment, transportation, storage and disposal. Pursuant to RCRA, the EPA has established a comprehensive “cradle-to-grave” system for the management of a wide range of materials identified as hazardous waste. States that have adopted hazardous waste management programs with standards at least as stringent as those promulgated by the EPA have been delegated authority by the EPA to administer their facility permitting programs in lieu of the EPA's program.

Every facility that treats, stores or disposes of hazardous waste must obtain a RCRA permit from the EPA or an authorized state agency unless a specific exemption exists and must comply with certain operating requirements, also known as the Part B permitting process. RCRA also requires that Part B permits contain provisions for required on-site study and cleanup activities, known as “corrective action,” including detailed compliance schedules and provisions for assurance of financial responsibility. See Note 9, “Closure and Post-Closure Liabilities,” and Note 10, “Remedial Liabilities,” to our consolidated financial statements included in Item 8 of this Annual Report on Form 10-K for a discussion of our environmental liabilities. See “Insurance and Financial Assurance” above for a discussion of our financial assurance requirements.

The Superfund Act.    The Superfund Act is the primary federal statute regulating the cleanup of inactive hazardous substance sites and imposing liability for cleanup on the responsible parties. It provides for immediate EPA-coordinated response and removal actions for hazardous substances released into the environment. It also authorizes the government to respond to the release or threatened release of hazardous substances or to order responsible persons to perform any necessary cleanup. The statute provides for strict and, in certain cases, joint and several liability to the parties involved in the generation, transportation and disposal of hazardous substances for the cost of these responses and for the cost of damages to natural resources. Under the statute, we may be deemed liable as a generator or transporter of a hazardous substance that is released into the environment, or as the owner or operator of a facility from which there is a release of a hazardous substance into the environment. See Note 17, “Commitments and Contingencies,” to our consolidated financial statements included in Item 8 of this Annual Report on Form 10-K for a description of the principal such proceedings in which we are now involved.

The Clean Air Act.    The Clean Air Act was passed by Congress to control the emissions of pollutants into the air and requires permits to be obtained for certain sources of hazardous air pollutants. In 1990, Congress amended the Clean Air Act to require further reductions of air pollutants with specific targets for non-attainment areas in order to meet certain ambient air quality standards. These amendments also require the EPA to promulgate regulations that (i) control emissions of 188

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hazardous air pollutants; (ii) create uniform operating permits for major industrial facilities similar to RCRA operating permits; (iii) mandate the phase-out of ozone-depleting chemicals; and (iv) provide for enhanced enforcement.

The Clean Water Act.    This legislation prohibits discharge of pollutants into the waters of the United States without government authorization and regulates the discharge of pollutants into surface waters and sewers from a variety of sources, including disposal sites and treatment facilities. The EPA has promulgated “pretreatment” regulations under the Clean Water Act, which establish pretreatment standards for introduction of pollutants into publicly-owned treatment works. In the course of the treatment process, our wastewater treatment facilities generate wastewater, which we discharge to publicly-owned treatment works pursuant to permits issued by the appropriate government authorities. We are required to obtain discharge permits and conduct sampling and monitoring programs.

TSCA.    We operate a network of collection, treatment and field services (remediation) facilities throughout North America whose activities are regulated under provisions of TSCA. TSCA established a national program for the management of substances classified as PCBs, which include waste PCBs as well as RCRA waste contaminated with PCBs. The rules set minimum design and operating requirements for storage, treatment and disposal of PCB waste. Since their initial publication, the rules have been modified to enhance the management standards for TSCA-regulated operations, including the decommissioning of PCB transformers and articles, detoxification of transformer oils, incineration of PCB liquids and solids, landfill disposal of PCB solids, and remediation of PCB contamination at customer sites.

Other Regulation Impacting U.S. Operations

Federal Regulations.    In addition to regulations specifically directed at our transportation, storage and disposal facilities, there are a number of regulations that may “pass-through” to the facilities based on the acceptance of regulated waste from affected customer facilities. Each facility that accepts affected waste must comply with the regulations for that waste, facility or industry. Examples of this type of regulation are National Emission Standards for Benzene Waste Operations and National Emissions Standards for Pharmaceuticals Production. Each of our facilities addresses these regulations on a case-by-case basis determined by its requirement to comply with the pass-through regulations.

In our transportation operations, we are regulated by the U.S. Department of Transportation, the Federal Railroad Administration, the Federal Aviation Administration and the U.S. Coast Guard, as well as by the regulatory agencies of each state in which we operate or through which our vehicles pass.

Health and safety standards under the Occupational Safety and Health Act, or OSHA, are also applicable to all of our operations.

State and Local Regulations. Pursuant to the EPA's authorization of RCRA equivalent state-run programs, a number of U.S. states have regulatory programs governing the operations and permitting of hazardous waste facilities. Accordingly, the hazardous waste treatment, storage and disposal activities of a number of our facilities are regulated by the relevant state agencies in addition to federal EPA regulation.

Some states classify certain wastes as hazardous that are not regulated under RCRA. For example, certain states, including Massachusetts and California, consider used oil as “hazardous waste” while RCRA does not. Others require specific handling of used oil. Accordingly, we must comply with state and local requirements for handling state-regulated waste, and when necessary, obtain state licenses for treating, storing and disposing of such waste at our facilities.

Some states regulate other aspects of our operations as well. For example, certain states, including Delaware and New York, have set strict regulations regarding the level of volatile organic compounds in parts washer solvents. We endeavor to be and remain in compliance with all applicable state regulations.

Our facilities are also regulated pursuant to state statutes, including those addressing clean water and clean air. Local sewer discharge and flammable storage requirements are applicable to certain of our facilities. Our California RCRA permitted facilities are subject to the Violations Scoring Procedure, or VSP, a state-level facility compliance program. Our facilities are also subject to local siting, zoning and land use restrictions. We believe that each of our facilities is in substantial compliance with the applicable requirements of federal and state licenses, which we have obtained. Once issued, such licenses have maximum fixed terms of a given number of years, which differ from state to state, ranging from three to ten years. The issuing state agency may review or modify a license at any time during its term. We anticipate that once a license is issued with respect to a facility, the license will be renewed at the end of its term if the facility’s operations are in compliance with applicable requirements. However, there can be no assurance that regulations governing future licensing will remain static, or that we will be able to comply with such requirements.

Regulations by the International Maritime Organization or IMO, primarily impact shipping businesses and require that ships that traverse the oceans use marine fuels with a sulphur content of no more than 0.50% sulphur, versus the previous cap of

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3.50%, in an effort to reduce the amount of sulphur oxide and decrease pollution and greenhouse gas emissions from the global shipping fleet. The shipping industry is the last major transportation sector to utilize fuel with high levels of sulfur, which is the reason the IMO pushed the industry to more closely align with other transport sectors for pollution reduction. This regulation indirectly impacts our SKSS segment as it has reduced the end market of used oil.

Canadian Hazardous Waste Regulation

In Canada, the provinces retain control over environmental issues within their boundaries and thus have the primary responsibility for regulating management of hazardous waste. The federal government regulates issues of national scope or where activities cross provincial boundaries.

Provincial Regulations.    Most of Canada's industrial development and the major part of its population are located in four provinces: Ontario, Quebec, Alberta and British Columbia, each of which have detailed environmental regulations. We operate major waste management facilities in each of these provinces, as well as waste transfer facilities in Nova Scotia and Manitoba and a re-refinery in Ontario.

The main provincial acts dealing with hazardous waste management are:

•Ontario—Environmental Protection Act;

•Quebec—Environmental Quality Act;

•Alberta—Environmental Protection and Enhancement Act; and

•British Columbia—Waste Management Act.

These legislative acts were developed by the provinces independently and, among other things, generally control the generation, characterization, transport, treatment and disposal of hazardous waste. Regulations developed by the provinces under the relevant legislation are also developed independently, but are often quite similar in effect and sometimes in application. For example, there is some uniformity in manifest document design and utilization.

Provincial legislation also provides for the establishment of waste management facilities. In this case, the facilities are also controlled by provincial statutes and regulations governing emissions to air, groundwater and surface water and prescribing design criteria and operational guidelines.

Waste transporters require a permit to operate under provincial waste management regulations and are subject to the requirements of the Federal Transportation of Dangerous Goods Act, as discussed below. They are required to report the quantities and disposition of materials shipped.

Canadian Federal Regulations.    The Canadian federal government has authority for those matters that are national in scope and in impact and for Canada's relations with other nations. The main federal laws governing hazardous waste management are the:

•Canadian Environmental Protection Act (1999), or CEPA 99, and

•Transportation of Dangerous Goods Act.

Environment Canada is the federal agency with responsibility for environmental matters and the main legislative instrument is the CEPA 99. This act charges Environment Canada and Health Canada, the federal agency responsible for the health of individuals, with protection of human health and the environment and seeks to control the production, importation and use of substances in Canada and to control their impact on the environment.

The Export and Import of Hazardous Waste and Hazardous Recyclable Material Regulations under CEPA 99 control the export and import of hazardous waste and hazardous recyclable materials. By reference, these regulations incorporate the Transportation of Dangerous Goods Act and Regulations, which address identification, packaging, marking and documentation of hazardous materials during transport. CEPA 99 requires that anyone proposing to export or import hazardous waste or hazardous recyclable materials or to transport them through Canada must notify the Minister of the Environment and obtain a permit to do so. Section 9 of CEPA 99 allows the federal government to enter into administrative agreements with the provinces and territories for the development and improvement of environmental standards. These agreements represent cooperation towards a common goal rather than a delegation of authority under CEPA 99. To facilitate the development of provincial and territorial agreements, the federal, provincial and territorial governments participate in the Canadian Council of Ministers of the Environment, or the CCME. The CCME comprises the 14 environment ministers from the federal, provincial and territorial governments, who normally meet at least once a year to discuss national environmental priorities and to determine work to be carried out under the auspices of the CCME.

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Canadian Local and Municipal Regulations.    Local and municipal regulations seldom reference direct control of hazardous waste management activities. Municipal regulations and by-laws, however, control such issues as land use designation, access to municipal services and use of emergency services, all of which can have a significant impact on facility operation.

Compliance with Environmental Regulations

The environmental regulations discussed above guide certain operations of the Company and require that we remediate contaminated sites, operate our facilities in accordance with enacted regulations, obtain required financial assurance for closure and post-closure care of our facilities should such facilities cease operations and make capital investments in order to keep our facilities in compliance with environmental regulations.

As further discussed in Note 9, “Closure and Post-Closure Liabilities,” and Note 10, “Remedial Liabilities,” to our consolidated financial statements included in Item 8 of this Annual Report on Form 10-K, as of December 31, 2025, we had recognized closure, post-closure and environmental liabilities of $230.7 million. For the years ended December 31, 2025, 2024 and 2023, we spent $16.1 million, $27.5 million and $29.0 million, respectively, to address environmental liabilities.

As discussed more fully above under the heading “Insurance and Financial Assurance,” we are required to provide financial assurance with respect to certain statutorily required closure, post-closure and corrective action obligations at our facilities. We have placed the required financial assurance primarily through qualified insurance companies.

As described in Note 17, “Commitments and Contingencies,” to our consolidated financial statements included in Item 8 of this Annual Report on Form 10-K, from time to time we are involved in legal proceedings arising under environmental laws and regulations. Alleged failure to comply with laws and regulations may lead to the imposition of fines or the denial, revocation or delay of the renewal of permits and licenses by government entities. In addition, such government entities, as well as surrounding landowners, may claim that we are liable for environmental damages. Citizens groups have become increasingly active in challenging the grant or renewal of permits and licenses for hazardous waste facilities, and responding to such challenges has further increased the costs associated with establishing new facilities or expanding current facilities. A significant judgment against us, the loss of a significant permit or license or the imposition of a significant fine could have a material effect on our business and future prospects.