STOCK-BASED COMPENSATION

6 Months Ended

Jun. 30, 2024

Share-Based Payment Arrangement [Abstract]

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. Total stock-based compensation cost recognized for the three and six months ended June 30, 2023 was $4.5 million and $10.5 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. 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, 2023 was $0.6 million and $1.7 million, respectively.

Restricted Stock Awards

The following table summarizes information about restricted stock awards for the six months ended June 30, 2024:


Restricted Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2024	414,623	$	114.02
Granted	137,966	185.38
Vested	(55,992)	116.86
Forfeited	(15,780)	134.69
Balance at June 30, 2024	480,817	$	133.49

As of June 30, 2024, there was $48.2 million of total unrecognized compensation cost arising from restricted stock awards. This cost is expected to be recognized over a weighted average period of 3.1 years. 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. The total fair value of restricted stock vested during the three and six months ended June 30, 2023 was $5.9 million and $8.1 million, respectively.

Performance Stock Awards

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 Margin, Return on Invested Capital and Total Recordable Incident Rate targets set forth in the applicable award agreements. Performance stock awards include continued service conditions through vesting.

The following table summarizes information about performance stock awards for the six months ended June 30, 2024:


Performance Stock	Number of Shares	Weighted Average Grant-Date Fair Value
Balance at January 1, 2024	181,284	$	114.10
Granted	79,738	173.45
Vested	(19,589)	104.31
Forfeited	(3,680)	143.59
Balance at June 30, 2024	237,753	$	134.36

As of June 30, 2024, there was $10.1 million of total unrecognized compensation cost arising from performance stock awards achieved or deemed probable of vesting. No performance awards vested during the three months ended June 30, 2024 and June 30, 2023. The total fair value of performance awards vested during the six months ended June 30, 2024 and June 30, 2023 was $3.7 million and $7.8 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. A total of 500,000 shares of common stock are reserved for issuance under the ESPP. As of June 30, 2024, no shares have been issued under the plan.