Electronic version of Jim Pankow’s English translation of Friedrich Schwille’s seminal book on the physico-chemical properties and behavior of non-aqueous phase liquids (NAPLs) formed by dense chlorinated solvents in porous and fractured media such as in contaminated aquifers. Schwille’s original book was published in 1988 (with W. Bertsch, R. Linke, W. Reif, and S. Zauter) as “Leichtflüchtige Chlorkohlenwasserstoffe in porösenund klüftigen Medien: Modellversuche”, Besondere Mittelungen zum Deutschen Gewasserkundlichen Jahrbuch Nr. 46, Koblenz, West Germany. Pankow’s translation (with Schwille's permission) was originally published by Lewis Publishers (Chelsea, Michigan, USA) in 1988 and reprinted in 1991. The book went out of print around 2000, and the copyright for the book was transferred to Jim Pankow by the publisher at that time. A scanned version of Pankow’s translation was made available from 2006 to 2013 from the webpage of the Center for Groundwater Research at the Oregon Graduate Institute (Beaverton, Oregon, USA). From 2013 to 2019, no electronic version of the book was available, so the previous version was reoptimized with character recognition to make the text-searchable version provided here. With Pankow’s permission, the version provided here has been designated open access.