Methods of detecting, characterizing, and mapping an environmental subsurface PFAS-stabilized viscoelastic non-Newtonian light non-aqueous phase liquid (LNAPL), including collecting an environmental sample that is a fluid sample, or is collected as a solid that is subsequently extracted with water to generate a fluid sample; and where the environmental sample is associated with a location where it was collected; analyzing the fluid sample using one or more rheological methods; and correlating the rheological characteristics with a presence or an absence of the non-Newtonian LNAPL at the location where the environmental sample was collected.