Especially if you carry a car battery into the field, pound metal stakes into the ground and connect them to the battery posts with cables. Why would you do such a thing? In order to “see” below the surface of the earth. Around here we have lots of sand, gravel, and rocks, deposited in layers by rivers, then glaciers, then rivers, then glaciers again. Below all that we have layers of clay and shale. The sand and gravel hold water, but the clay and shale act as a barrier. If we can map these layers, we will have a better understanding of the boundaries of our aquifers which are the source for all the wells in the area.
Well driller reports are one of the tools we can use to “see” below the surface. Drillers record the different geological layers encountered as they dig and the depths at which they occur. But to draw a useful aquifer map we need more data points. It turns out that running a current through the ground and then measuring the voltage at various points can give information that helps fill in some of the missing data. The technical term for this technique is Apparent Resistivity Sounding or ARS.
We wondered if this technique might be useful on the eastern slopes of the Beaufort Range, so we spent a week taking ARS measurements in various locations from Qualicum Bay to Union Bay. You may have seen us in the field at the Fanny Bay Hall on our first day as we laid out cables and set up the equipment under a shade-providing tent. Or perhaps you drove by the next day when we were on Ships Point Road stringing cables along the ditch bottom. You may have heard the tap-tap-tapping of hammer on steel on the rail bed behind Yake Rd or maybe you heard us yelling back and forth in the bush behind McCartney drive: “fifty is ready”, followed by, “okay, measuring”, and then, “move to eighty”.
What we were doing was the culmination of a lot of hard work by Mark Lake, a BWS member and retired geophysicist. Last year, he approached the University of Victoria with the idea of a pilot project to determine the viability of this technique for filling in the gaps in our dataset. Mike Wei, Adjunct Professor at the University of Victoria’s School of Earth and Ocean Sciences, liked the idea and now comes the third and final phase of the project. Ms. Pereversoff, under the direction of Dr. Leonard, will analyze and interpret the data, write a detailed report, and finally, make a Zoom presentation of her findings to the BWS board of trustees. Our hope is that the project will confirm the technique is useful for further aquifer mapping. It was a great experience working with the UVic team and, hopefully, we have begun adding to our knowledge of the local aquifers. As unprecedented weather patterns continue, this knowledge could be invaluable for the management of our water resources. And as a bonus, we all learned more about the electrifying field of geophysics! enlisted the help of Dr. Lucinda Leonard, Assistant Professor in Geophysics, also at the School of Earth and Ocean Sciences. They selected Victoria Pereversoff, a fourth-year student majoring in Geophysics, to participate in the project as part of a Directed Studies program. Mark and Victoria spent countless hours of prep work: Zoom meetings with the UVic team, pouring over well drillers’ reports, analyzing known lithology. Mark made scouting trips to many potential sites as they gradually narrowed the list to the best candidates from a geological perspective. Mark also managed the myriad small logistical details of hosting three people for a week.
Several BWS members helped during the actual measurement process, hauling the gear, laying out the cables and pounding in the stakes, followed by the tedious extraction of the stakes and coiling up of the cables, then hauling the gear back to the vehicles. Over the course of five days this process was repeated again and again as we gathered data at nine different locations and took twelve sets of measurements. We often worked ten-hour days.
Now comes the third and final phase of the project. Ms. Pereversoff, under the direction of Dr. Leonard, will analyze and interpret the data, write a detailed report, and finally, make a Zoom presentation of her findings to the BWS board of trustees. Our hope is that the project will confirm the technique is useful for further aquifer mapping.
It was a great experience working with the UVic team and, hopefully, we have begun adding to our knowledge of the local aquifers. As unprecedented weather patterns continue, this knowledge could be invaluable for the management of our water resources.
And as a bonus, we all learned more about the electrifying field of geophysics!