We are very excited to welcome Tara Harvey to the blog today. Tara is a researcher with the G360 Institute for Groundwater Research. For more about Tara see the end of this post.
You might be wondering why I tend to stand in fields a lot. Am I studying agriculture? No. Am I interested in the biodiversity in a field? No. Do I study soil? No. So, what am I doing? Well, to the casual observer, not much at all, but if you knew there was a very deep hole at my feet, 2 to 6 inches in diameter and upwards of 100s of feet deep, then you might start to guess what I research. I study groundwater.
Groundwater is the water that moves within the spaces and fractures of the sediment and rock under our feet. A common misconception is that groundwater flows in large underground rivers, but this is not a typical occurrence. Instead groundwater can be found in any sediment or rock within the small spaces between the grains or crystals.
However, since groundwater is hidden beneath our feet, I never physically get to see what I am studying. To study groundwater we have to get creative in order to answer the question: “how do you study something that you can’t see or touch”? In the rest of this post I’ll take you through a quick look at all the different field work steps that need to happen to 1) give us access to the groundwater and 2) allow us to actually measure and monitor it.
Drilling holes in fields
Obviously there is a lot of behind the scenes work that has to be done before any fieldwork can happen: developing a plan of what we want to do, determining the best location to study the groundwater, gathering all the required equipment, hiring and booking the drilling company and consultants, obtaining permits to approve the work, etc.. But once all that is in place, we can start digging our holes to access the groundwater.
The only way we can access groundwater is to drill really deep holes into the earth. When we are drilling these holes we aren’t looking directly at the groundwater yet. Instead, we are gathering very important information about the geology of the location to help us understand how the groundwater might be moving through the sediment or rock. In addition, depending on the site, we might also be collecting samples of the sediment/rock for later analyses. These analyses could include sampling to determine the moisture content or grain size of the rock, but could also include sampling to see if there are any contaminants in the sediment porewater (groundwater left within the rock pores).
Installing wells in fields
Once a hole the desired depth and width (typically 4-8 inches diameter) is drilled we can do several things with it. But first things first: if we are concerned with contamination we must seal the hole. This is very important because if you leave a drilled hole open then contamination at one depth can migrate into the open hole and move anywhere it wants. This means that previously uncontaminated and possibly protected groundwater may now be contaminated because of us! This is called cross-contamination and we want to make sure this never happens. Therefore, immediately after removing the drilling rods (which were sealing the hole), we can install either a temporary liner or a permanent monitoring well.
Typically we do both. We will install a temporary liner while we design the permanent well with the geologic details we collected during drilling. As we design the well we can also use down-hole geophysical tools to give us more information about the groundwater and geology. Once we have our design we get to work building and installing our well.
Sampling groundwater in fields
Now we finally have access to the groundwater directly to take in situ measurements of its properties. With these groundwater monitoring wells we can do 2 main things.
First, we can take what are called hydraulic head measurements. Hydraulic head is very important as it can help us understand what direction the groundwater is moving and if it is moving up or down (yes groundwater can move upwards towards the surface). Although hydraulic head may be difficult to understand initially, it is actually very easy to measure in the field as all we have to do is measure the distance from the ground surface to the water. We do this by putting a waterlevel tape down the hole until it beeps, indicating that it is now touching water.
Second, we can collect physical groundwater samples by pumping the water out of the well. This water can then be tested for different parameters and contaminants to give us an understanding of what is in the groundwater and where contamination might be.
Monitoring groundwater in fields
As many of you know, in Canada we have seasonal weather changes that affect the amount of precipitation we receive. Similarly, there are seasonal changes in the groundwater and therefore it is important to do regular monitoring throughout the year. I spend at least 1 week, 4 times a year at just one of our research sites measuring groundwater and hydraulic head in about 40 wells. And although my monitoring fieldwork may only take 1 week each time, there is a lot of work done after I’m out of the field to make sure the data I collected is good and to interpret the results.
Dropping things down holes in fields
Although groundwater monitoring fieldwork may not seem that thrilling, it can actually get very exciting and chaotic, especially if you accidentally drop a piece of field equipment down the hole that you weren’t supposed to. This is obviously never a good idea because now you’ve lost something you probably didn’t want to lose. On top of that, there is the possibility it is now jamming up your well, making it unusable. But getting it back out gives you a chance to put your problem solving skills to the test – and maybe even enjoy one of your hobbies, if that hobby happens to be fishing. Luckily, last year when we dropped something down a hole we were able to get it back using a small fishing hook and line a couple days later.
Tara Harvey now works as a hydrogeology researcher with the G360 Institute for Groundwater Research after completing her Masters in Hydrogeology at the University of Guelph in 2016. Tara specializes in Quaternary geology, aka glacial geology, and spent most of her Masters studying the glacial landscape of Wisconsin and how the glacial deposits affect groundwater and contaminant movement.