Spiritwood Valley Aquifer Characterization Using a New Helicopter TDEM System

As part of continued testing of its new VTEM^TM ET (early-time) time-domain electromagnetic (TDEM) system, a test survey was recently performed over the Spiritwood Valley Aquifer that compared results from both VTEM ET and our standard VTEM Plus system with Full-waveform processing.

The VTEM ET receiver uses a re-designed broadband receiver, a re-configured transmitter, and a new digital acquisition system to achieve precise, distortion free measurements of the time-domain EM decay as early as 0.005 msec after the transmitter turn-off. This allows VTEM ET to better characterize aquifers at shallow depth (<10-30m).

The Spiritwood Valley aquifer system extends from South Dakota to North Dakota, where it is 15-20km wide and up to 100-150 m deep, and into southern Manitoba. The Spiritwood aquifer system is a complex network of glacially deposited sand and gravel bodies that are interbedded with till and clay that are relatively impermeable. It is an important supply of water both in the United States and Canada, where in particular it has been successfully mapped and studied using helicopter time-domain EM.

Over the test area, the VTEM ET results appear to reveal more complexity within the aquifer than predicted based on available drilling. The results appear to define the lateral boundaries of the Spiritwood aquifer, as well as defining both an upper aquifer, at approximately 35m, and a lower aquifer at 100m depth. The lower aquifer also appears to deviate in direction relative to the upper aquifer. The 40-50 ohm-m gravel aquifers are relatively well differentiated from the 10-30 ohm-m till-clay host sediments. In addition to improved near-surface aquifer characterization, the 100-150m investigation depths achieved by the VTEM ET system are of the same order as those achieved by the VTEM Plus system.