Derek W. Tomlinson P.E., P.Eng., BCEE, is a senior practitioner in environmental engineering and contaminant hydrogeology, and Principal with GEI Consultants based in the Philadelphia, Pennsylvania area. He has more than 20 years of experience, specializing in development of strategies for managing non-aqueous phase liquids (NAPLs; both light, LNAPL, and dense, DNAPL). His graduate training at University of Waterloo used high-resolution characterization methods to understand multi-phase fluid transport within the subsurface during remediation. His technical expertise includes development of innovative site characterization methods for refinement of robust conceptual site models, which he has used in proper design, implementation, and operation of a range of in situ remediation technologies within porous media and fractured bedrock. He has worked at various types of sites under USEPA CERCLA and RCRA programs, nationally in several state and regional led and voluntary programs, and internationally. He has provided expert witness and testimony in matters related to NAPL releases and related contamination. Derek is actively involved in development of various standards, guidance documents, best-practices, internet-based and classroom workshops, and providing of training with respect to NAPLs. This work has been done with consensus based organizations of Interstate Technology & Regulatory Council (ITRC) and ASTM International, as well as industry organizations of American Petroleum Institute (API), Contaminated Land: Applications in Real Environments (CL:AIRE), and Electric Power Research Institute (EPRI). Derek earned a Bachelor degree in Civil Engineering in 1994 and a Master degree in 1999, both from the University of Waterloo in Waterloo, Ontario, Canada. He is a professional engineer in Pennsylvania and Canada and a Board Certified Environmental Engineer (BCEE) in Hazardous Waste Management and Site Remediation..