CLEAN HARBORS INC

In 2020, the Company's shareholders approved the Clean Harbors, Inc. 2020 Stock Incentive Plan (the “2020 Plan”). The 2020 Plan provides for future awards of up to 2.5 million shares of the Company’s common stock (subject to certain anti-dilution adjustments) in the form of stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. The 2020 Plan is administered by the Compensation and Human Capital Committee of the Company’s Board of Directors.

The Company grants restricted stock awards and performance stock awards. The restricted stock awards generally vest over three tofive years subject to continued employment. Performance stock awards are subject to performance criteria established by the Compensation and Human Capital Committee of the Company's Board of Directors prior to or at the date of grant. The vesting of the performance stock awards is dependent upon the satisfaction of certain performance conditions currently based on revenue, Adjusted EBITDA, Adjusted EBITDA margin, return on invested capital and a measure of workplace safety. In addition, performance stock awards include continued service conditions through the vesting date.

Total stock-based compensation cost recognized for the years ended December 31, 2025, 2024 and 2023 was $32.7 million, $28.0 million and $20.7 million, respectively. The total income tax benefit recognized in the consolidated statements of operations from stock-based compensation expense was $5.5 million, $5.1 million and $3.5 million for the years ended December 31, 2025, 2024 and 2023, respectively.

Restricted Stock Awards

The following table summarizes information about restricted stock awards for the year ended December 31, 2025:

As of December 31, 2025, there was $36.8 million of total unrecognized compensation cost arising from restricted stock awards. This cost is expected to be recognized over a weighted average period of 2.3 years. The total fair value of restricted stock vested during 2025, 2024 and 2023 was $32.3 million, $31.9 million and $26.5 million, respectively.

Performance Stock Awards

The following table summarizes information about performance stock awards for the year ended December 31, 2025:

(1) The granted activity for performance stock awards is recorded based on the target performance level of 100%. The actual number of performance share awards earned for the 2025 performance stock grants could range from 0% to 200% of target depending on the achievement of the pre-established performance goals.

As of December 31, 2025, there was $15.0 million of total unrecognized compensation cost arising from unvested performance stock awards deemed probable of vesting. This cost is expected to be recognized over a weighted average period of 2.2 years. The total fair value of performance awards vested during 2025, 2024 and 2023 was $11.9 million, $8.6 million and $17.0 million, respectively.

Employee Stock Purchase Plan

On May 22, 2024, the Company’s shareholders approved the Clean Harbors Employee Stock Purchase Plan (the “ESPP”). The ESPP provides a means for eligible employees of the Company to authorize after-tax payroll deductions on a voluntary basis to be used for the periodic purchase of the Company's common stock at a 10% discount to its fair market value. The purchase price paid by the employees will be 90% of the lower of the closing price of the Company's common stock on (i) the first trading day of the offering period or (ii) the last trading day of the offering period. The contribution periods run from January to June and July to December with share issuances under the ESPP occurring on the closest business day on or prior to June 30 and December 31. A total of 500,000 shares of common stock are reserved for issuance under the ESPP. In 2025,34,651 shares were issued under the plan. For the year ended December 31, 2025 and 2024 total stock-based compensation cost recognized for the ESPP was $1.6 million and $0.7 million, respectively.