Electrical and electromagnetic methods are well suited for coastal aquifer
studies because of the large contrast in resistivity between fresh water-be
aring and salt water-bearing formations. Interpretation models for these aq
uifers typically contain four layers: a highly resistive unsaturated zone;
a surficial fresh water aquifer of intermediate resistivity; an underlying
conductive, salt water saturated aquifer; and resistive substratum. Additio
nal layers may be added to allow for variations in lithology within the fre
sh water and salt water layers. Two methods are evaluated: direct current r
esistivity and time domain electromagnetic soundings. Use of each method al
one produces nonunique solutions for resistivities and/or thicknesses of th
e different layers. We show that joint inversion of vertical electric and t
ime domain electromagnetic soundings produces a more tightly constrained in
terpretation model at three test Sites than is produced by inversion method
s applied to each data set independently.