Clean Harbors Completes Acquisition of Peak Energy Services Ltd.

Transaction Creates Cross-Selling Opportunities
in Energy Services Market

Norwell, MA – June 10, 2011 – Clean Harbors, Inc. (“Clean Harbors”) (NYSE: CLH), the leading provider of environmental, energy and industrial services throughout North America, today announced the completion of its acquisition of Peak Energy Services Ltd. (“Peak”) (TSX: PES). The transaction, which was approved by Peak shareholders on May 25, is valued at approximately CAD $202 million (including the 3.15% of Peak’s outstanding shares previously acquired by Clean Harbors), consisting of a combination of cash and assumed debt.

Peak shareholders (other than Clean Harbors) are receiving CAD $0.95 in cash for each Peak share, and holders of Peak’s in-the-money stock options received a total of CAD $1.6 million. In addition, as part of the transaction, Clean Harbors retired Peak’s net debt of approximately CAD $36 million.

“Peak complements the Industrial Services and Oil and Gas Field Services segments of our business,” said Alan S. McKim, Chairman and Chief Executive Officer of Clean Harbors. “We are excited about the cross-selling opportunities created by this acquisition, particularly the oil and gas plays in the United States. The addition of Peak significantly expands our presence in oil and natural gas drilling and production support, and enhances our one-stop shop approach for our customers. We are pleased to welcome Peak’s management and personnel to the Clean Harbors team.”

Clean Harbors expects the acquisition to be immediately accretive, excluding any one-time fees and acquisition-related expenses. Peak reported 2010 revenue of CAD $153 million and CAD $23.3 million of EBITDA. Clean Harbors anticipates updating its 2011 revenue and EBITDA guidance to reflect the inclusion of Peak as part of its second-quarter 2011 financial results, which are scheduled to be released in early August.

With its head office located in Calgary, Alberta, Canada, Peak is a diversified energy services organization. It offers over 4,000 pieces of rental equipment and related services to the oil and natural gas business in North America through a network of 13 full service facilities located in western Canada and five operating areas in the United States, including Wyoming, Colorado, North Dakota, Montana and Pennsylvania. Peak provides drilling and production services to its customers both in the conventional and unconventional oil and natural gas industries as well as the oil sands regions of western Canada. The company, which employs approximately 900 people, also provides water technology solutions to a variety of customers throughout North America.

About Clean Harbors

Clean Harbors is the leading provider of environmental, energy and industrial services throughout North America. The Company serves more than 50,000 customers, including a majority of the Fortune 500 companies, thousands of smaller private entities and numerous federal, state, provincial and local governmental agencies.

Headquartered in Norwell, Massachusetts, Clean Harbors has more than 175 locations, including over 50 waste management facilities, throughout North America in 38 U.S. states, seven Canadian provinces, Mexico and Puerto Rico. The Company also operates international locations in Bulgaria, China, Singapore, Sweden, Thailand and the United Kingdom. For more information, visit www.cleanharbors.com.

Safe Harbor Statement

Any statements contained herein that are not historical facts are forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements may include, but are not limited to, statements about the benefits of the acquisition of Peak, including future financial and operating results, the combined company’s plans, objectives, expectations and intentions and other statements that are not historical facts. Such statements are based upon the beliefs and expectations of Clean Harbors’ management as of this date only and are subject to certain risks and uncertainties that could cause actual results to differ materially, including, without limitation, those items identified as “risk factors” in the Company’s most recently filed Form 10-K and Form 10-Q. Therefore, readers are cautioned not to place undue reliance on these forward-looking statements. The Company undertakes no obligation to revise or publicly release the results of any revision to these forward-looking statements other than through its various filings with the Securities and Exchange Commission, which may be viewed at www.cleanharbors.com/investor_relations.

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