Continued operational excellence across our facilities delivered strong financial results in the second quarter and year to date 2014. We also completed our planned acquisition of EQ - The Environmental Quality Company ("EQ") in June 2014, creating a true leader in the North American environmental and industrial services industry. The addition of EQ aligns perfectly with our strategy of leveraging high quality treatment, disposal and recycling assets and complementary field and industrial service businesses to drive growth. It also significantly broadens our geographic footprint.
With the addition of EQ for 13 days, revenue grew 35% to $119.4 million in the first half of 2014. Strong project-based Event Business and continued growth in our recurring Base Business drove waste volumes up by 23% in our legacy operations. The strength across our operations, combined with a favorable service mix, enhanced the operating leverage inherent to our disposal business, pushing treatment and disposal margin up to 49% in our legacy operations in the first half of 2014. Operating income increased 20% to $26.5 million, including $5.3 million of EQ related costs. Adjusted EBITDA for the first six months of 2014 was $37.4 million, up 21%, and we saw adjusted earnings per diluted share grow 24% to $0.94.
Based on our strong first half performance, the addition of EQ, and our current outlook for the combined business for the balance of 2014, we raised our guidance for the second time in 2014. We are now projecting annual adjusted earnings per share to range from $1.70 to $1.80 per share and adjusted EBITDA to range from $100 million to $110 million. These increased estimates exclude foreign currency translation gains or losses and business development and integration expenses.
This is an exciting time for US Ecology as we work to integrate two industry leaders. With the addition of EQ, we now offer a full suite of environmental and industrial solutions across a national customer base, greatly enhancing our competitive position in the marketplace. Our management team is actively engaged in integrating these assets, identifying and generating cross-selling opportunities and other operational cost efficiencies to drive synergies. Our vision is to be the premier North American provider of environmental and industrial services, where the best people come to work delivering sustainable solutions for our customers and long-term value for our stockholders and the communities in which we live and operate. We look forward to making this vision a reality in the months and years to come.
President and Chief Executive Officer