(Lancaster) -- A Lancaster County company is crediting the natural gas drilling boom across the state for its rapid expansion. Rettew is an engineering, planning and environmental consulting firm in Lancaster that's added 200 workers in the last year to double its workforce. Chairman and CEO George Rettew says the increase is largely due to a connection to the energy market as well as companies tied to drilling in the Marcellus Shale formation. "We'd design pad sites for them. Treat the frack water that's used," he says. "We have a process to treat that water, so that they can recycle it and conserve...the amount of water that's being used." A year ago, the company created a a second company to deal exclusively with natural gas drilling contracts. As part of its expansion efforts, Rettew recently opened a 21,000-square-foot addition at its Lancaster office complex and plans to increase the number of its offices to 10. To learn more about natural gas drilling in the commonwealth, visit StateImpact Pennsylvania, a collaboration among witf, NPR and WHYY in Philadelphia.