title: Geophysical monitoring and evaluation of coastal plain aquifers.
abstract: We use time domain electromagnetic (TDEM) soundings to monitor ground water conditions beneath the coastal plain in eastern North Carolina. The TDEM method measures the earth's response to an induced electromagnetic field. The resulting signal is converted, through a complex inversion process, to apparent resistivity values, which can be directly correlated to borehole resistivity logs. TDEM soundings are used to map the interface between fresh and salt water within coastal aquifers, and estimate depth to basement when siting new monitoring wells. Focused TDEM surveys have identified areas of salt water encroachment caused by high volumes of discharge from local supply wells. Electromagnetic sounding, when used in tandem with the state's network of monitoring wells, is an accurate and inexpensive tool for evaluating fresh water/salt water relationships on both local and regional scales within coastal plain aquifers.
authors.affiliation: New Mexico Bureau of Geology & Mineral Resources, Carlsbad, NM 88220, USA. lland@gis.nmt.edu
authors.forename: Lewis A
authors.initials: LA
authors.lastname: Land
authors.forename: Jeff C
authors.initials: JC
authors.lastname: Lautier
authors.forename: Nathaniel C
authors.initials: NC
authors.lastname: Wilson
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Chianese
authors.forename: Steven
authors.initials: S
authors.lastname: Webb
mesh_terms: D055590:Electromagnetic Phenomena; D004784:Environmental Monitoring / Q000379:methods*; D009657:North Carolina; D012680:Sensitivity and Specificity; D012987:Soil; D014872:Water Movements; D014881:Water Supply
chemical_list: D012987:Soil