BASIS OF PRESENTATION

3 Months Ended

Mar. 31, 2012

Organization, Consolidation and Presentation of Financial Statements [Abstract]

BASIS OF PRESENTATION

BASIS OF PRESENTATION

The accompanying consolidated interim financial statements include the accounts of Clean Harbors, Inc. and its subsidiaries (collectively, “Clean Harbors” or the “Company”) and have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) and, in the opinion of management, include all adjustments which are of a normal recurring nature, necessary for a fair presentation of the financial position, results of operations, and cash flows for the periods presented. The results for interim periods are not necessarily indicative of results for the entire year or any other interim periods. The financial statements presented herein should be read in connection with the financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2011.

On June 8, 2011, the Company’s Board of Directors authorized a two-for-one stock split of the Company’s common stock in the form of a stock dividend of one share for each outstanding share. The stock dividend was paid on July 26, 2011 to holders of record at the close of business on July 6, 2011. The stock split followed the approval, at the Company’s 2011 annual meeting of stockholders, of a proposal to increase the Company’s authorized shares of common stock from 40 million to 80 million. The stock split did not change the proportionate interest that a stockholder maintained in the Company. All share and per share information, including options, restricted and performance stock awards, stock option exercises, employee stock purchase plan purchases, common stock and additional paid-in capital accounts on the consolidated balance sheets and consolidated statements of income and stockholders’ equity, have been retroactively adjusted to reflect the two-for-one stock split. In addition, awards granted and weighted average fair value of awards granted in Note 12, “Stock-Based Compensation,” have also been retroactively adjusted.

During the quarter ended March 31, 2012, the Company re-assigned certain departments among its segments to support management reporting changes. Accordingly, the Company re-allocated shared departmental costs among its segments. The Company has recast the prior year segment information to conform to the current year presentation. See Note 14, “Segment Reporting.”

In preparing the accompanying unaudited consolidated financial statements, the Company has reviewed, as determined necessary by the Company’s management, events that have occurred after March 31, 2012, until the issuance of the financial statements.