Filed Pursuant to Rule 424(b)(5)
Registration No. 333-224788

The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to these securities has been declared effective by the Securities and Exchange Commission. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities, and we are not soliciting offers to buy these securities, in any jurisdiction where the offer or sale is not permitted.

Subject to completion, dated January 22, 2019

Preliminary Prospectus Supplement

(To Prospectus dated May 9, 2018)

3,100,000 Shares

Class A Common Stock

We are offering 3,100,000 shares of Class A common stock, $0.01 par value per share, in this offering.

Our Class A common stock is listed on the Nasdaq Global Select Market under the symbol “CWST”. On January 18, 2019, the last reported sale price of our Class A common stock on the Nasdaq Global Select Market was $31.73 per share.

We have two classes of authorized common stock, Class A common stock and Class B common stock. The rights of the holders of Class A common stock and Class B common stock are identical, except with respect to voting and conversion rights. Each share of Class A common stock is entitled to one vote per share. Each share of Class B common stock is entitled to ten votes per share and is convertible into one share of Class A common stock.

Investing in our Class A common stock involves risks. See “Risk Factors” beginning on page S-13 of this prospectus supplement and the risk factors described in the other documents incorporated by reference herein.

If all of the shares of Class A common stock are not sold at the public offering price, the underwriters may change the offering price and may offer shares of Class A common stock from time to time for sale in negotiated transactions or otherwise, at market prices prevailing at the time of sale, at prices related to such prevailing market prices or otherwise.

We have granted the underwriters an option for a period of up to 30 days from the date of this prospectus supplement to purchase up to 465,000 additional shares of Class A common stock at the public offering price less the underwriting discounts and commissions. If the underwriters exercise this right in full, the total public offering price will be $            , the total underwriting discounts and commissions payable by us will be $            , and the total proceeds to us, before expenses, will be $            .

Neither the Securities and Exchange Commission nor any state securities regulator has approved or disapproved of these securities or determined that this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares of Class A common stock to purchasers on or about January        , 2019, subject to the satisfaction of certain conditions.

Book-Running Manager

RAYMOND JAMES

The date of this prospectus supplement is January        , 2019

TABLE OF CONTENTS

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ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this Class A common stock offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference herein or therein. The second part, the accompanying prospectus, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement and the information contained in the accompanying prospectus or any document incorporated by reference herein or therein filed prior to the date of this prospectus supplement, you should rely on the information in this prospectus supplement; provided that if any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein or in the accompanying prospectus were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreement, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

You should rely only on the information contained in this prospectus supplement or the accompanying prospectus, or incorporated by reference herein or therein. We have not authorized, and the underwriters have not authorized, anyone to provide you with any information other than that contained or incorporated by reference in this prospectus supplement, in the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us or to which we have referred you. We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. The information contained in this prospectus supplement or the accompanying prospectus, or incorporated by reference herein or therein, is accurate only as of the respective dates hereof or thereof, regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or of any sale of our Class A common stock. It is important for you to read and consider all information contained in this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, in making your investment decision. You should also read and consider the information in the documents to which we have referred you in the sections entitled “Where You Can Find More Information” and “Incorporation of Certain Information by Reference” in this prospectus supplement.

We are offering to sell, and seeking offers to buy, shares of our Class A common stock only in jurisdictions where offers and sales are permitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of the Class A common stock in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the offering of the Class A common stock and the distribution of this prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

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Unless otherwise stated, all references in this prospectus supplement and the accompanying prospectus to “we,” “us,” “our,” “Casella,” the “Company” and similar designations refer to Casella Waste Systems, Inc. and all of its subsidiaries. The Casella logo and all other Casella product names are trademarks of Casella or its subsidiaries in the United States and in other select countries. Solely for convenience, trademarks and trade names referred to in this prospectus supplement, the accompanying base prospectus and the documents incorporated by reference herein and therein may appear without the ^® and ^TM symbols, but those references are not intended to indicate, in any way, that we will not assert, to the fullest extent under applicable law, our rights or that the applicable owner will not assert its rights to these trademarks and trade names.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein contain forward-looking statements that involve substantial risks and uncertainties. All statements contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, other than statements of historical fact, are forward-looking statements. The words “anticipate,” “around,” “believe,” “estimate,” “expect,” “intend,” “may,” “plan,” “predict,” “project,” “target,” “potential,” “will,” “would,” “could,” “should,” “continue,” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. The forward-looking statements in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein include, among other things, statements about:

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements.

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These forward-looking statements are based on current expectations, estimates, forecasts and projections about the industry and markets in which we operate, as well as management’s beliefs and assumptions. These forward-looking statements are not guarantees of future performance, circumstances or events. The occurrence of the events described and the achievement of the expected results depends on many events, some or all of which are not predictable or within our control. Actual results may differ materially from those set forth in our forward-looking statements.

We have included important factors in the cautionary statements included in this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein, particularly in the “Risk Factors” section of this prospectus supplement that could cause actual results or events to differ materially from the forward-looking statements that we make. We do not assume any obligation to update any forward-looking statements, except as required by applicable law.

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RISK FACTORS

An investment in our Class A common stock involves significant risks. Before deciding whether to invest in our Class A common stock, you should consider carefully the risks described below and discussed under the heading “Risk Factors” in our Annual Report on Form 10-K for the fiscal year ended December 31, 2017, together with all of the other information contained in this prospectus supplement, the accompanying prospectus and in our filings with the Securities and Exchange Commission (“SEC”), that we have incorporated by reference in this prospectus supplement and the accompanying prospectus. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. If any of these risks actually occurs, our business, financial condition, results of operations and cash flow could be seriously harmed. This could cause the trading price of our Class A common stock to decline, resulting in a loss of all or part of your investment.

Risks Related to Our Business

We face substantial competition in the solid waste services industry, and if we cannot successfully compete in the marketplace, our business, financial condition and results of operations may be materially adversely affected.

The solid waste services industry is highly competitive, has undergone a period of consolidation and requires substantial labor and capital resources. The markets in which we compete are served by, or are adjacent to markets served by, one or more of the large national or super regional solid waste companies, as well as numerous regional and local solid waste companies. Intense competition exists not only to provide services to customers, but also to acquire other businesses within each market. Some of our competitors have significantly greater financial and other resources than we do. From time to time, competitors may reduce the price of their services in an effort to expand market share or to win a competitively bid contract. These practices may require us to reduce the pricing of our services and may result in a loss of business.

As is generally the case in our industry, municipal contracts are typically subject to periodic competitive bidding. We may not be the successful bidder to obtain or retain these contracts. If we are unable to compete with larger and better capitalized companies or replace municipal contracts lost through the competitive bidding process with comparable contracts or other revenue sources within a reasonable time period, our revenues would decrease and our operating results could be materially adversely affected.

In our solid waste disposal markets, we also compete with operators of alternative disposal and recycling facilities and with counties, municipalities and solid waste districts that maintain their own solid waste collection, recycling and disposal operations. We are also increasingly competing with companies which seek to use parts of the waste stream as feedstock for renewable energy supplies. Public entities may have financial advantages because of their ability to charge user fees or similar charges, impose taxes and apply resulting revenues, access tax-exempt financing and, in some cases, utilize government subsidies.

In addition, we may be impacted by the development and commercialization of disruptive technologies that may materially change how waste management services are provided. If we are unable to gain access to these technologies or to compete effectively against them, our financial results may suffer.

We also experience competition in our hiring of drivers and mechanics necessary to service our customers. This competition may come from other waste management companies, but it also

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comes from other employers who hire drivers and maintain fleets, such as companies that provide courier delivery services, including United Parcel Service, Inc. and FedEx Corporation, as well as from a tightening labor market. If we are unable to hire and retain sufficient numbers of drivers to service our collection and disposal routes and mechanics to maintain our trucks, our financial condition and operating results could be materially impacted.

Our growth strategy focuses on complementing or expanding our business through the acquisition of companies or assets, or the development of new operations. However, we may be unable to complete these transactions and, if executed, these transactions may not improve our business or may pose significant risks and could have a negative effect on our operations.

Our growth strategy includes engaging in acquisitions or developing operations or assets with the goal of complementing or expanding our business. These acquisitions may include “tuck-in” acquisitions within our existing markets, acquisitions of assets that are adjacent to or outside of our existing markets, or larger, more strategic acquisitions. In addition, from time to time we may acquire businesses that are complementary to our core business strategy. We may not be able to identify suitable acquisition candidates, and if we identify suitable acquisition candidates, we may be unable to successfully negotiate the acquisition at a price or on terms and conditions acceptable to us. Furthermore, we may be unable to obtain the necessary regulatory approval to complete potential acquisitions.

Our ability to achieve the benefits from any potential future acquisitions, including cost savings and operating efficiencies, depends in part on our ability to successfully integrate the operations of such acquired businesses with our operations. The integration of acquired businesses and other assets may require significant management time and resources that would otherwise be available for the ongoing management of our existing operations. Any operations, properties or facilities that we acquire may be subject to unknown liabilities, such as undisclosed environmental contamination, or other environmental liability, including off-site disposal liability for which we would have no recourse, or only limited recourse, to the former owners of such operations or properties. As a result, if a liability were asserted against us based upon ownership of an acquired property, we might be required to pay significant sums to settle it, which could adversely affect our financial results and cash flow.

The waste management industry is undergoing fundamental change as traditional waste streams are increasingly viewed as renewable resources, which may adversely affect volumes and tipping fees at our landfills.

As we continue to develop our landfill capacity, the waste management industry is recognizing the value of the waste stream as a renewable resource, and accordingly, alternatives to landfilling are being developed that seek to maximize the renewable energy and other resource benefits of solid waste. These alternatives affect the demand for landfill airspace, and could affect our ability to operate our landfills at full capacity, as well as the tipping fees and prices that waste management companies generally, and that we, in particular, can charge for landfill airspace. Reduced tipping fees can affect our willingness to incur the expenditures necessary to increase the permitted capacity of the landfills. As a result, our revenues and operating margins could be materially adversely affected due to these disposal alternatives.

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The waste industry is subject to extensive government regulations, including environmental laws and regulations, and we incur substantial costs to comply with such laws and regulations. Failure to comply with environmental or other laws and regulations, as well as enforcement actions and litigation arising from an actual or perceived breach of such laws and regulations, could subject us to fines, penalties, and judgments, and impose limits on our ability to operate and expand.

We are subject to potential liability and restrictions under environmental laws and regulations, including potential liability and restrictions arising from or relating to the transportation, handling, recycling, generation, treatment, storage and disposal of wastes, the presence, release, discharge or emission of pollutants, and the investigation, remediation and monitoring of impacts to soil, surface water, groundwater and other environmental media including natural resources, as a result of the actual or alleged presence, release, discharge or emission of hazardous substances, pollutants or contaminants on, at, under or migrating from our properties, or in connection with our operations. The waste management industry has been and will continue to be subject to regulation, including permitting and related financial assurance requirements, as well as attempts to further regulate the industry, including efforts to regulate and limit the emission of greenhouse gases. Our solid waste operations are subject to a wide range of federal, state and, in some cases, local environmental, odor and noise and land use restrictions. If we are not able to comply with the requirements that apply to a particular facility or if we operate in violation of the terms and conditions of, or without the necessary approvals or permits, we could be subject to administrative or civil, and possibly criminal, fines and penalties, and we may be required to spend substantial capital to bring an operation into compliance, to temporarily or permanently discontinue activities, and/or take corrective actions, possibly including removal of landfilled materials. Those costs or actions could be significant to us and affect our results of operations, cash flows, and available capital. Environmental and land use laws and regulations also affect our ability to expand and, in the case of our solid waste operations, may dictate those geographic areas from which we must, or, from which we may not, accept solid waste. Those laws and regulations may limit the overall size and daily solid waste volume that may be accepted by a solid waste operation. If we are not able to expand or otherwise operate one or more of our facilities because of limits imposed under such laws, we may be required to increase our utilization of disposal facilities owned by third-parties, which could reduce our revenues and/or operating margins.

In addition to complying with environmental laws and regulations, we are required to obtain government permits to operate our facilities, including all of our landfills. There is no guarantee that we will be able to obtain the requisite permits and, even if we could, that any permit (and any existing permits we currently hold) will be renewed or modified as needed to fit our business needs. Localities where we operate generally seek to regulate some or all landfill and transfer station operations, including siting and expansion of operations. The laws and regulations adopted by municipalities in which our landfills and transfer stations are located may limit or prohibit the expansion of a landfill or transfer station, as well as the amount of solid waste that we can accept at the landfill or transfer station on a daily, quarterly or annual basis, and any effort to acquire or expand landfills and transfer stations, which typically involves a significant amount of time and expense. We may not be successful in obtaining new landfill or transfer station sites or expanding the permitted capacity of any of our current landfills and transfer stations. If we are unable to develop additional disposal and transfer station capacity, our ability to achieve economies from the internalization of our waste stream will be limited. If we fail to receive new landfill permits or renew existing permits, we may incur landfill asset impairment and other charges associated with accelerated closure.

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We have historically grown through acquisitions, may make additional acquisitions in the future, and we have tried and will continue to try to evaluate and limit environmental risks and liabilities presented by businesses to be acquired prior to the acquisition. It is possible that some liabilities may prove to be more difficult or costly to address than we anticipate. It is also possible that government officials responsible for enforcing environmental laws and regulations may believe an issue is more serious than we expect, or that we will fail to identify or fully appreciate an existing liability before we become responsible for addressing it. Some of the legal sanctions to which we could become subject could cause the suspension or revocation of a permit, prevent us from, or delay us in, obtaining or renewing permits to operate or expand acquired facilities, or harm our reputation. As of September 30, 2018, we had recorded $5.7 million in environmental remediation liabilities for the estimated cost of our share of work associated with a consent order issued by the State of New York to remediate a scrap yard and solid waste transfer station owned by one of our acquired subsidiaries, including the recognition of accretion expense. There can be no assurance that the cost of such cleanup or that our share of that cost will not exceed our estimates.

In addition to the costs of complying with environmental laws and regulations, we incur costs in connection with environmental proceedings and litigation brought against us by government agencies and private parties. We are, and may be in the future, a defendant in lawsuits brought by parties alleging environmental damage, including natural resource damage, personal injury, and/or property damage or impairment, or seeking to impose civil penalties, injunctive relief or overturn or prevent the issuance of an operating permit or authorization, all of which may result in us incurring significant liabilities. On November 8, 2018, we and the Town reached a settlement to resolve claims that were the subject of litigation filed in Worcester Superior Court. For more information about the material outstanding claims against us and our subsidiaries, see Part II, Item 1. “Legal Proceedings” in our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018.

We may not have sufficient insurance coverage for our environmental liabilities, such coverage may not cover all of the potential liabilities we may be subject to and/or we may not be able to obtain insurance coverage in the future at reasonable expense, or at all.

The conduct of our businesses is also subject to various other laws and regulations administered by federal, state and local governmental agencies, including tax laws, employment laws and competition laws, among others. New laws, regulations or governmental policy and their related interpretations, or changes in any of the foregoing, including taxes or other limitations on our services, may alter the environment in which we do business and, therefore, may impact our results or increase our costs or liabilities.

In certain jurisdictions, we are subject to compliance with specific obligations under competition laws due to our competitive position in those jurisdictions. For example, in May 2002, we entered into an assurance of discontinuance with the Vermont Attorney General’s Office concerning, among other matters, the conduct of our business in Vermont relating to certain contract terms applicable to our small commercial container customers. In August 2011, a revised final judgment of consent and order was entered by the Vermont Superior Court Washington Unit, Civil Division, as a result of some of our small commercial container customers having been mistakenly issued contracts that did not strictly comply with the terms of the assurance of discontinuance. Pursuant to the order, we paid a civil penalty in an aggregate amount of $1.0 million. In July 2014, we entered into an assurance of discontinuance with the office of the New York Attorney General in connection with certain of our commercial practices in certain specified counties in New York, pursuant to which we paid the State of New York a sum of $0.1 million. The assurances of discontinuance and order provide for certain restrictions on our

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customer contract terms, certain conditions on our business acquisitions, sales and market share and require us to maintain an internal compliance program. Failure to comply with these requirements or other laws or regulations could subject us to enforcement actions or financial penalties which could have a material adverse effect on our business.

Our results of operations are affected by fluctuating commodity prices and market requirements for recyclable materials.

Our results of operations have been and will continue to be affected by changing purchase or resale prices or market requirements for recyclable materials. Our recycling business involves the purchase and sale of recyclable materials, some of which are priced on a commodity basis. The commodity markets continue to see ongoing negative pressure on pricing associated with the decline of the fiber market due to less use of paper products such as newspaper and office paper as a result of increased on-line reading. As a result of these market changes, domestic demand for various recycled fibers from mill buyers has steadily declined over the past decade, and as such we have exported more of these materials overseas to China. In 2017, China launched a campaign called “National Sword” which has imposed significant restrictions on the importation into China of recyclable materials, including a complete ban on the import into China of mixed paper and new quality standards for contaminants in recyclable materials commencing January 1, 2018. Furthermore, China has not issued import licenses for its mills to import recyclable commodities for 2018, resulting in a stoppage of essentially all imports of recyclable commodities into China. These factors have had a significant impact on our business and have required us to seek alternative export markets for recyclable commodities.

We seek to limit our exposure to fluctuating commodity prices through: our revenue sharing contracts that share commodity prices above a threshold level or charge a tipping fee below the threshold; our net commodity rate formula that allows us to pass back higher costs to sell commodities, including higher labor costs or equipment costs to meet new quality standards; our floating Sustainability Recycling Adjustment fee that passes back the cost of recycling to our collection customers; and as applicable, the use of hedging agreements, floor price contracts and long-term supply contracts with customers. Although we have introduced these risk mitigation programs to help offset volatility in commodity prices and to offset higher labor or capital costs to meet more stringent contamination standards, we cannot provide assurance that we can use these programs with our customers in all circumstances or that they will mitigate these risks in an evolving recycling environment.

Our business requires a high level of capital expenditures.

Our business is capital intensive. Our capital expenditure requirements include fixed asset purchases and capital expenditures for landfill development and cell construction, as well as site and cell closure. We use a substantial portion of our cash flows from operating activities toward capital expenditures, which reduces our flexibility to use such cash flows for other purposes, such as reducing our indebtedness. Our capital expenditures could increase if we make acquisitions or further expand our operations, or as a result of factors beyond our control, such as changes in federal, state or local governmental requirements. The amount that we spend on capital expenditures may exceed current expectations, which may require us to obtain additional funding for our operations or impair our ability to grow our business.

We are upgrading our technology infrastructure and there can be no assurance that our efforts will be completed on the projected timetable or that our investment will result in the expected gains.

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We are upgrading our technology infrastructure, including an enterprise resource planning package and other systems that we believe will improve our internal processes and the productivity of our employees. These upgrades are complex and there can be no assurance that they will result in expected productivity gains and operating cost reductions on our anticipated timeline, if at all. In addition, if we are not able to maintain the security of our data, confidential information about us or our customers or suppliers could be inadvertently disclosed, subjecting us to possible expenses and other liabilities as well as adversely impacting customer and other third party relationships. If we are unable to benefit from new technologies, we may be at a competitive disadvantage to other companies in the waste management industry, in which case our operating results could suffer.

A cybersecurity incident could negatively impact our business and our relationships with customers, adversely affecting our financial results and exposing us to litigation risk.

We use computer technology in substantially all aspects of our business operations. We also use mobile devices, social networking and other online activities to connect with our customers and our employees to be able to process transactions and provide information that we feel is necessary to manage our business. Such uses give rise to cybersecurity risks, including security breach, espionage, system disruption, theft and inadvertent release of information. Our business involves the storage and transmission of numerous classes of sensitive and/or confidential information and intellectual property, including customers’ personal information, private information about employees, and financial and strategic information about us and our business partners. We also rely on a Payment Card Industry compliant third party to protect our customers’ credit card information. Further, as we pursue our strategy to grow through acquisitions and to pursue new initiatives that improve our operations and cost structure, we are also expanding and improving our information technologies, resulting in a larger technological presence and corresponding exposure to cybersecurity risk. If we fail to assess and identify cyber security risks associated with acquisitions and new initiatives, we may become increasingly vulnerable to such risks. Additionally, while we have implemented measures to prevent security breaches and cyber incidents, our preventive measures and incident response efforts may not be entirely effective, especially as cyber security attacks continue to evolve. If our established network of security controls, policy enforcement mechanisms, educational awareness programs and monitoring systems that we use to address these threats to technology fail, the theft, destruction, loss, misappropriation, or release of sensitive and/or confidential information or intellectual property, or interference with our information technology systems or the technology systems of third parties on which we rely, could result in business disruption, negative publicity, brand damage, violation of privacy laws, loss of customers, potential litigation and liability and competitive disadvantage. While we have purchased insurance coverage for cybersecurity risks, there can be no assurance that any such coverage would be adequate to cover potential liability.

Our business is geographically concentrated and is therefore subject to regional economic downturns.

Our operations and customers are concentrated principally in New England and New York. Therefore, our business, financial condition and results of operations are susceptible to regional economic downturns and other regional factors, including state regulations and budget constraints and severe weather conditions. In addition, as we seek to expand in our existing markets, opportunities for growth within this region will become more limited and the geographic concentration of our business will increase.

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Our results of operations and financial condition may be negatively affected if we inadequately accrue for final capping, closure and post-closure costs or by the timing of these costs for our waste disposal facilities.

We have material financial obligations relating to final capping, closure and post-closure costs of our existing owned or operated landfills and will have material financial obligations with respect to any disposal facilities that we may own or operate in the future. Once the permitted capacity of a particular landfill is reached and additional capacity is not authorized, or a determination is made to cease operations at a landfill due to other considerations, the landfill must be closed and capped, and we must begin post-closure maintenance. We establish accruals for the estimated costs associated with such final capping, closure and post-closure obligations over the anticipated useful life of each landfill on a per ton basis. We have provided and expect that we will in the future provide accruals for financial obligations relating to final capping, closure and post-closure costs of our owned or operated landfills, generally for a term of 30 years after closure of a landfill. Our financial obligations for final capping, closure or post-closure costs could exceed the amounts accrued or amounts otherwise receivable pursuant to trust funds established for this purpose. Such a circumstance could result in significant unanticipated charges that would have an adverse effect on our business.

In addition, the timing of any such final capping, closure or post-closure costs, which exceed established accruals, may further negatively affect our business. Since we will be unable to control the timing and amounts of such costs, we may be forced to delay investments or planned improvements in other parts of our business or we may be unable to meet applicable financial assurance requirements. Any of the foregoing would negatively affect our business and results of operations.

Fluctuations in fuel costs could affect our operating expenses and results.

The price and supply of fuel is unpredictable and fluctuates based on events beyond our control, including among others, geopolitical developments, supply and demand for oil and gas, actions by the Organization of the Petroleum Exporting Countries and other oil and gas producers, war and unrest in oil producing countries and regional production patterns. Because fuel is needed to run our fleet of trucks, price escalations for fuel increase our operating expenses. In fiscal year 2018, we used approximately 5.3 million gallons of diesel fuel in our solid waste operations. Although we have a “fuel surcharge” program, based on a fuel index, to help offset increases in the cost of fuel, oil and lubricants arising from price volatility, contractual restrictions and competitive conditions may impact our opportunity to pass this fee on to our customers in all circumstances.

We could be precluded from entering into contracts or obtaining or maintaining permits or certain contracts if we are unable to obtain third-party financial assurance to secure our contractual obligations.

Public solid waste collection, recycling and disposal contracts, and obligations associated with landfill closure and post-closure typically require performance or surety bonds, letters of credit or other means of financial assurance to secure our contractual performance. We currently obtain performance and surety bonds from Evergreen National Indemnity Company, in which we hold a 19.9% equity interest. If we are unable to obtain the necessary financial assurance in sufficient amounts or at acceptable rates, we could be precluded from entering into additional municipal contracts or from obtaining or retaining landfill management contracts or operating permits. Any future difficulty in obtaining insurance could also impair our ability to secure future contracts conditioned upon having adequate insurance coverage.

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We may be required to write-off or impair capitalized costs or intangible assets in the future or we may incur restructuring costs or other charges, each of which could harm our earnings.

In accordance with generally accepted accounting principles in the United States, we capitalize certain expenditures and advances relating to our acquisitions, pending acquisitions, landfills, cost method investments and development projects. In addition, we have considerable unamortized assets. From time to time in future periods, we may be required to incur a charge against earnings in an amount equal to any unamortized capitalized expenditures and advances, net of any portion thereof that we estimate will be recoverable, through sale or otherwise, relating to: (1) any operation or other asset that is being sold, permanently shut down or impaired or has not generated or is not expected to generate sufficient cash flow; (2) any pending acquisition that is not consummated; (3) any landfill or development project that is not expected to be successfully completed; and (4) any goodwill or other intangible assets that are determined to be impaired.

In response to such charges and costs and other market factors, we may be required to implement restructuring plans in an effort to reduce the size and cost of our operations and to better match our resources with our market opportunities. As a result of such actions, we would expect to incur restructuring expenses and accounting charges which may be material. Several factors could cause a restructuring to adversely affect our business, financial condition and results of operations. These include potential disruption of our operations, the development of our landfill capacity and recycling technologies and other aspects of our business. Employee morale and productivity could also suffer and result in unintended employee attrition. Any restructuring would require substantial management time and attention and may divert management from other important work. Moreover, we could encounter delays in executing any restructuring plans, which could cause further disruption and additional unanticipated expense.

Our revenues and our operating income experience seasonal fluctuations.

Our transfer and disposal revenues historically have been higher in the late spring, summer and early fall months. This seasonality reflects the lower volume of solid waste during the late fall, winter and early spring months primarily because:

Since certain of our operating and fixed costs remain constant throughout the fiscal year, operating income is impacted by a similar seasonality. In addition, particularly harsh weather conditions typically result in increased operating costs.

Adverse weather conditions may limit our operations and increase the costs of collection and disposal.

Our collection and landfill operations could be adversely impacted by extended periods of inclement weather, or by increased severity of weather. Adverse weather could increase our operating costs associated with the collection and disposal of waste, delay the collection and disposal of waste, reduce the volume of waste delivered to our disposal sites, increase the volume of waste collected under our existing contracts (without corresponding compensation), decrease the throughput and operating efficiency of our materials recycling facilities, or delay construction

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or expansion of our landfill sites and other facilities. In addition, adverse weather conditions may result in the temporary suspension of our operations, which can significantly affect our operating results in the affected regions during those periods.

Efforts by labor unions to organize our employees could divert management attention and increase our operating expenses.

Certain groups of our employees have chosen to be represented by unions, and we have negotiated collective bargaining agreements with these groups. The negotiation of collective bargaining agreements could divert management attention and result in increased operating expenses and lower net income (or increased net loss). If we are unable to negotiate acceptable collective bargaining agreements, we may be subject to union-initiated work stoppages, including strikes. Depending on the type and duration of any labor disruptions, our revenues could decrease and our operating expenses could increase, which could adversely affect our financial condition, results of operations and cash flows. As of December 31, 2018, approximately 5% of our employees were represented by unions.

Our enterprise risk management process may not be effective in mitigating the risks to which we are subject, or in reducing the potential for losses in connection with such risks.

Our enterprise risk management framework is designed to minimize or mitigate the risks to which we are subject, as well as any losses stemming from such risks. Although we seek to identify, measure, monitor, report, and control our exposure to such risks, and employ a broad and diversified set of risk monitoring and mitigation techniques in the process, those techniques are inherently limited in their ability to anticipate the existence or development of risks that are currently unknown and unanticipated. The ineffectiveness of our enterprise risk management framework in mitigating the impact of known risks or the emergence of previously unknown or unanticipated risks may result in our incurring losses in the future that could adversely impact our financial condition and results of operations.

Risks Related to Our Indebtedness

We have substantial debt and have the ability to incur additional debt. The principal and interest payment obligations of such debt may restrict our future operations.

As of September 30, 2018, we had approximately $528.2 million of outstanding principal indebtedness (excluding approximately $22.5 million of outstanding letters of credit issued under our term loan A facility (“Term Loan Facility”) and revolving line of credit facility (“Revolving Credit Facility” and, together with the Term Loan Facility, the “Credit Facility”). The Credit Facility consists of the Term Loan Facility with term loans in the outstanding principal amount of $350.0 million and the Revolving Credit Facility with loans thereunder being available up to an aggregate principal amount of $200.0 million, of which $132.7 million of unused commitments remain under the Revolving Credit Facility, subject to customary borrowing conditions. In addition, the terms of our existing indebtedness permit us to incur additional debt. Our substantial debt, among other things:

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Our ability to satisfy our obligations and to reduce our total debt depends on our future operating performance and on economic, financial, competitive and other factors, many of which are beyond our control. Our business may not generate sufficient cash flow, and future financings may not be available to provide sufficient net proceeds, to meet these obligations or to successfully execute our business strategy.

The Credit Facility requires us to meet a number of financial ratios and covenants.

The Credit Facility contains certain affirmative and negative covenants which, among other things and subject, in certain cases, to certain basket amounts and other exceptions, limit the existence of additional indebtedness, the existence of liens or pledges, certain investments, acquisitions and sales or other transfers of assets, the payment of dividends and distributions and repurchases of equity, prepayments of certain junior indebtedness, and certain other transactions. Our ability to comply with these covenants may be affected by events beyond our control, including prevailing economic, financial and industry conditions. These covenants could have an adverse effect on our business by limiting our ability to take advantage of financing, merger and acquisition or other corporate opportunities. Additionally, the Credit Facility requires, solely for the benefit of the lenders under the Revolving Credit Facility, that we meet financial tests, including, without limitation:

An event of default under any of our debt agreements could permit some of our lenders, including the lenders under the Credit Facility, to declare all amounts borrowed from them to be immediately due and payable, together with accrued and unpaid interest, or, in the case of the Credit Facility, terminate the commitment to make further credit extensions thereunder, which could, in turn, trigger cross-defaults under other debt obligations. If we were unable to repay debt to our lenders, or were otherwise in default under any provision governing our outstanding debt obligations, our secured lenders could proceed against us and against the collateral securing that debt.

Risks Related to This Offering

We have broad discretion in how we use the net proceeds of this offering, and we may not use these proceeds effectively or in ways with which you agree.

Our management will have broad discretion as to the application of the net proceeds of this offering and could use them for purposes other than those contemplated at the time of this offering. Our stockholders may not agree with the manner in which our management chooses to allocate and spend the net proceeds. Moreover, our management may use the net proceeds for corporate purposes that may not increase the market price of our Class A common stock.

The market price of our Class A common stock can be volatile, and the value of your investment could decline significantly.

The trading price for our Class A common stock has been, and we expect it to continue to be, volatile. The price at which our Class A common stock trades depends upon a number of factors,

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including our historical and anticipated operating results, our financial condition, our ability or inability to raise the additional capital we may need and the terms on which we raise it, and general market and economic conditions, some of which are beyond our control. These broad market fluctuations may lower the market price of our Class A common stock and affect the volume of trading in our stock.

Future sales of our Class A common stock in the public market could cause our stock price to fall.

Sales of a substantial number of shares of our Class A common stock in the public market, or the perception that these sales might occur, could depress the market price of our Class A common stock and could impair our ability to raise capital through the sale of additional equity securities. As of December 31, 2018, we had 41,944,475 shares of Class A common stock outstanding. Of these shares, 1,993,863 shares are subject to lock-up agreements entered into in connection with this offering but may be sold beginning on the day that is 30 days after the date of this prospectus supplement. Raymond James, in its sole discretion, may release the Class A common stock and other securities subject to these lock-up agreements in whole or in part at any time with or without notice. See “Underwriting” for more information on these lock-up agreements. Any of our remaining shares are eligible for sale in the public market, subject in some cases to compliance with the requirements of Rule 144 of the Securities Act, including the volume limitations and manner of sale requirements. In addition, all of the shares offered under this prospectus supplement and the accompanying prospectus will be freely tradable without restriction or further registration upon issuance.

We have never declared or paid dividends on our capital stock, and we do not anticipate paying dividends in the foreseeable future.

Our business requires significant funding, and we currently intend to retain earnings, if any, to support our business strategy. Therefore, we do not anticipate paying any cash dividends on our Class A common stock in the foreseeable future. In addition, our credit facility and indentures restrict the payment of dividends on our Class A common stock. As a result, capital appreciation, if any, of our Class A common stock will be your sole source of potential gain for the foreseeable future.

Holders of our Class A common stock, which is the stock we are selling in this offering, are entitled to one vote per share, and holders of our Class B common stock are entitled to ten votes per share. The lower voting power of the Class A common stock may negatively affect the attractiveness of our Class A common stock to investors and, as a result, its market value.

We have two classes of common stock: Class A common stock, which is the stock we are selling in this offering and which is entitled to one vote per share, and Class B common stock, all of which are beneficially owned by John W. Casella, our Chairman and Chief Executive Officer, and his brother, Douglas R. Casella, a member of our Board of Directors, and which is entitled to ten votes per share. Except in certain limited circumstances required by applicable law, holders of Class A common stock and Class B common stock vote together as a single class on all matters to be voted on by our stockholders. As of December 31, 2018, an aggregate of 988,200 shares of our Class B common stock, representing 9,882,000 votes, were outstanding. Based on the number of shares of common stock outstanding as of December 31, 2018, the shares of our Class A common stock and Class B common stock beneficially owned by John W. Casella and Douglas R. Casella represented approximately 21.1% of the aggregate voting power of our stockholders. After the completion of this offering (assuming no exercise by the underwriters of their option to purchase

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additional shares) and based on the number of shares of common stock outstanding as of December 31, 2018, approximately 19.9% of the total voting power of our outstanding shares will be held by the Class B common stockholders (including voting power under the shares of Class A common stock held by such Class B common stockholders). Consequently, John W. Casella and Douglas R. Casella are able to substantially influence all matters for stockholder consideration and constitute, and are expected to continue to constitute, a significant portion of the shares entitled to vote on all matters requiring approval by our stockholders. The difference in the voting power of our Class A common stock and Class B common stock could diminish the market value of our Class A common stock if investors attribute value to the superior voting rights of our Class B common stock and the power those rights confer.

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USE OF PROCEEDS

We estimate that the net proceeds we will receive from this offering will be approximately $            million, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us. If the underwriters exercise their option to purchase additional shares in full, we estimate that the net proceeds to us will be approximately $            million, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.

We intend to use the net proceeds from this offering for general corporate purposes. Although we have not yet identified specific uses for these proceeds, we currently anticipate using the proceeds for some or all of the following purposes:

We have not determined the amounts we plan to spend on any of the areas listed above or the timing of these expenditures. As a result, our management will have broad discretion to allocate the net proceeds from this offering. Pending application of the net proceeds as described above, we intend to pay down some or all of the outstanding balance of our Revolving Credit Facility on a temporary basis and to invest the balance of the net proceeds of the offering in deposit accounts, money-market funds, U.S. government-sponsored enterprise obligations and corporate obligations. The Revolving Credit Facility currently bears interest at LIBOR plus 2% per annum and matures in May 2023.

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CAPITALIZATION

The following table sets forth our capitalization as of September 30, 2018:

You should read this table in conjunction with “Summary—Summary Consolidated Financial Data” and “Use of Proceeds” appearing elsewhere in this prospectus supplement and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our consolidated financial statements, including the accompanying notes, appearing in our Annual Report on Form 10-K for the fiscal year ended December 31, 2017 and our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018, which are incorporated by reference in this prospectus supplement.

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The above table does not reflect: