Here ˚ (=2ϕ/q) is the dimensionless matrix flux potential, q
[L2 T−1] is the strength of the line source (/sink), K0 is the zero-order
modified Bessel function of the second kind, and X and Z± = (Z
±
Z*)
are the dimensionless horizontal and vertical space coordinates
defined as X/x = Z/z = Z*/z* = ˛/2, where z* is the sink depth.