OUR OVERALL SERVICE
Like our former corporation --Geoscience Services Associates, Inc. -- we continue to support electrical, electromagnetic, magnetic seismic and ground penetrating radar and seismic survey services on an advisory basis. However, as mentioned earlier, we do specialize in the electrical survey service areas of Electrical Resistivity and Induced Polarization which is our object of technical service focus presently. These techniques are a highlight among the many methods we employ in subsurface imaging. With advances made in the acquisition of data under computer control and with 2 and 3 dimensional data inversion to render a true picture of resistivity and chargeability distribution below survey lines they have developed as a tool which surpasses most other methods where resolving power is demanded in understanding difficult sites. These complementary techniques are particularly useful in locating such chemicals as LNAPL, DNAPL, MTBE, chlorinated hydrocarbons and perchlorates if they contaminate ground water resource in either sands and gravels or fractured rock. Survey costs are fraction of those incurred by traditional boring and water sampling routines.
Resistivity is a measure of a material's ability to pass electrical current; chargeability is a measure of a material's ability to sustain an electrical charge. Geophysicists measure resistivity by observing the potential (voltage) between stations along a traverse line subjected to a known current of certain amperage. Chargeability is determined by first charging sections along a traverse with a certain voltage and observing the time the voltage decays to a certain level after the charging voltage has been removed. The unit of measure for resistivity is ohm-meters or ohm-feet and for chargeability it is in units of time (milliseconds). The two techniques compliment one another and greatly facilitate subsurface characterization.
There follows some exemplary vertical sections which illustrate characterization of contaminated sites and the discovery of potable water resources. Please see Resistivity Imaging and Resistivity -IP - Imaging pages.