Total stock-based compensation cost recognized for the three and six months ended June 30, 2025 was $6.1 million and $13.7 million, respectively. Total stock-based compensation cost recognized for the three and six months ended June 30, 2024 was $8.5 million and $14.9 million, respectively. The total income tax benefit recognized in the unaudited consolidated statements of operations from stock-based compensation expense for the three and six months ended June 30, 2025 was $0.9 million and $2.2

million, respectively. The total income tax benefit recognized in the unaudited consolidated statements of operations from stock-based compensation expense for the three and six months ended June 30, 2024 was $1.5 million and $2.7 million, respectively.


Restricted Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2025	387,960	$	143.69
Granted	81,600	228.39
Vested	(97,116)	135.18
Forfeited	(24,363)	143.52
Balance at June 30, 2025	348,081	$	165.93

As of June 30, 2025, there was $44.7 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 the three and six months ended June 30, 2025 was $7.1 million and $22.1 million, respectively. The total fair value of restricted stock vested during the three and six months ended June 30, 2024 was $7.2 million and $10.9 million, respectively.

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 performance stock awards are earned based on achieving certain revenue, Adjusted EBITDA, Adjusted EBITDA Margin and Return on Invested Capital targets set forth in the applicable award agreements. Performance stock awards include continued service conditions through vesting.


Performance Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2025	159,196	$	102.09
Granted (1)	74,124	232.78
Vested	(34,056)	133.64
Forfeited	(24,787)	155.34
Balance at June 30, 2025	174,477	$	177.29

(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 June 30, 2025, there was $9.9 million of total unrecognized compensation cost arising from performance stock awards achieved or deemed probable of vesting. No performance awards vested during each of the three months ended June 30, 2025 and June 30, 2024. The total fair value of performance awards vested during the six months ended June 30, 2025 and June 30, 2024 was $6.6 million and $3.7 million, respectively.

The Clean Harbors Employee Stock Purchase Plan (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. There were 16,266 shares issued under the plan during the three and six months ended June 30, 2025.