Flow path
"The subsurface course a water molecule or solute would follow in a given groundwater velocity field (ASTM, 1980)"
Sources
American Society for Testing and Materials, 1980, Standard definitions of terms and symbols relating to soil and rock mechanics, in (D653-80) 1981 Annual Book of ASTM Standards, Part 19: Philadelphia, Pennsylvania, American Society for Testing Materials, p. 1402-1419.