BASIS OF PRESENTATION

9 Months Ended

Sep. 30, 2011

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 Current Report on Form 8-K filed on July 15, 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, 2011, the Company re-aligned its management reporting structure. Under the new structure, the Company’s operations are managed in four segments: Technical Services, Field Services, Industrial Services and Oil and Gas Field Services. The new segment, Oil and Gas Field Services, consists of the previous Exploration Services segment, as well as certain departments that were re-assigned from the Industrial Services segment. In addition, certain departments from the Field Services segment were re-assigned to the Industrial Services segment. Accordingly, the Company re-aligned and re-allocated departmental costs being allocated among the segments to support these management reporting changes. The Company has recast the segment information to conform to the current year presentation. See Note 14, “Segment Reporting.”

The four operating segments consist of:

• Technical Services — provides a broad range of hazardous material management services including the packaging, collection, transportation, treatment and disposal of hazardous and non-hazardous waste at Company owned incineration, landfill, wastewater, and other treatment facilities.

• Field Services — provides a wide variety of environmental cleanup services on customer sites or other locations on a scheduled or emergency response basis including tank cleaning, decontamination, remediation, and spill cleanup.

• Industrial Services — provides industrial and specialty services, such as high-pressure and chemical cleaning, catalyst handling, decoking, material processing, surface rentals and industrial lodging services to refineries, chemical plants, oil sands facilities, pulp and paper mills, and other industrial facilities.

• Oil and Gas Field Services — provides fluid handling, fluid hauling, down hole servicing, surface rentals, exploration, mapping and directional boring services to the energy sector serving oil and gas exploration, production, and power generation.

Technical Services and Field Services are included as part of Clean Harbors Environmental Services, and Industrial Services and Oil and Gas Field Services are included as part of Clean Harbors Energy and Industrial Services.