Ms. Twitchell was named a director in December 2009. From 2010 to 2013, Ms. Twitchell served as the Executive Vice President and Chief Financial Officer of Landmark Aviation. From 2001 to 2009, Ms. Twitchell was a Vice President and Treasurer of LyondellBasell Industries and Lyondell Chemical Company. Prior to that, she served as a Vice President and Treasurer of Kaiser Aluminum Corporation and Southdown, Inc. Before joining Southdown, Ms. Twitchell was an investment banker with Credit Suisse First Boston in its corporate finance department. Ms. Twitchell serves on the board of directors of Trecora Resources. During the past five years, Ms. Twitchell served on the board of directors of KMG Chemicals, Inc. Ms. Twitchell holds a B.A. in economics from Wellesley College and an M.B.A. from Harvard University.