Hydraulic connections between aquifers is usually studied through
hydrochemical analysis or by pumping tests. However, hydrochemical analyses
are usually conducted in areas of variable lithology. In addition, the
hydrogeological data obtained by drilling and pumping tests are typically
insufficient to get 3D distributions of hydraulic head. In this paper, the
time-lapse transient electromagnetic method (TEM) is used to image
groundwater migration between aquifers in Inner Mongolia, China. First, 1D
geophysical models of aquifers are generalized according to the
hydrogeological conditions of the region, and the feasibility of detecting
the multiple aquifers by TEM is analyzed and discussed. Then, the 2D models
of aquifers pre- and post- pumping test are established based on the
distribution of groundwater in the aquifers, and the variation law of
induced electromotive force measured on the surface is analyzed. The
simulation results show that significant time-lapse electromagnetic
anomalies can be observed between pre- and post- pumping test and the
variation in the induced electromotive force reaches a distinguishable level
between 0.7 ms and 100 ms due to the vertical change in the aquifer
properties. Furthermore, the electromagnetic variation generated by
hydraulic connection between aquifers is greater than 30% within the range
of 3/4 of the transmitting loop. Finally, a successful case history to map
hydraulic connections between aquifers is conducted using a time-lapse TEM
pre- and post- a pumping experiment. This simulation and field experiment
shows that time-lapse TEM could characterize and monitor the groundwater
migration more effectively than pump tests or hydrogeochemical methods
alone.
