This chapter focuses on petroleum hydrocarbon environmental forensics, because it happens that today's society is hydrocarbon based, relying on the carbon deposits laid down eons ago and now being recovered and put to a variety of uses. Almost all of the common definitions of the word forensics involve entry into some type of formalized debate that leads ultimately to some type of legal setting. Historical knowledge of site operations is critical to forensic evaluation, because it provides a timeline of the on-site handling, use, and storage of contaminants of concern. Groundwater dynamics refers to the process in which the groundwater hydrologic characteristics change in response to local and regional hydrogeological settings. Mass flux and discharge studies are commonly conducted in sites under investigation to understand the strength of a source or solute plume to facilitate the evaluation of natural attenuation and the assessment of risks posed by contamination to downgradient receptors. Statistics is the science of data.