Competition for shrinking window of low salinity groundwater
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| Number of Parts | 29 | |
| Author | 0000-0001-8519-1771 (ORCID) | |
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| Identifiers | 10.5446/39380 (DOI) | |
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Transcript: English(auto-generated)
00:03
I'm Grant Ferguson. I'm an associate professor with the College of Engineering in the Geological Engineering program at the University of Saskatchewan. So my co-authors on this are Jennifer McIntosh, who's a hydrogeologist, hydrogeochemist from the University of Arizona and their Department of Hydrology and Atmospheric Sciences.
00:21
I'm also working with Scott Jacheco from the Bren School of Environment from UCSB and Deb Perrone who's also at UCSB with their Environmental Studies program. So what we've done is we've looked at the distribution of salinity in groundwater over a range of sedimentary basins in the United States.
00:41
So our premise was is that a lot of areas we are seeing groundwater stress and typically that's been studied kind of from the top down. So we've looked at dropping water tables, research that has been done by either monitoring groundwater levels or through other techniques like the GRACE satellites. But what's been missing from this picture is just how deep those groundwater resources extend and it's a little bit trickier to get at that question.
01:04
So we went through a bit of a data mining exercise to try and sort out the water chemistry constraints on that. So we went through some data from the United States Geological Survey primarily. So they have a database of brackish groundwaters that's been put together over the past few years and they maintain a
01:22
database of produced waters from the oil and gas industry that they've been slowly adding to over the past number of years. So we meshed those two together and tried to come up with some composite profiles of what groundwater salinity would look like going deeper into the earth. Well there have been some assumptions about how deep fresh groundwater extends.
01:42
So historically these have mostly been from assumptions but we've seen anywhere from a kilometer to two kilometers that potentially you should be able to find fresh groundwater if you were to continue drilling. But when we looked at the data that was out there that doesn't seem to be supported. That there are a number of cases where potentially you could go a kilometer or so deep.
02:01
But there's other areas of the United States where it's maybe a maximum of 200 or 300 meters and you'd run into saline groundwater and essentially you'd be done in terms of water resources. Well our conclusion is there's not as much groundwater as we thought. So some of these previous estimates aren't quite right that we don't have as much groundwater as we thought we did.
02:22
And then there's some other issues around other activities that are going on specifically oil and gas. So if we look at where we've had say hydraulic fracturing for oil and gas development, coal bed methane development or disposal wells for produced water from the oil and gas industry. Some of these are actually quite close to fresh groundwater resources or maybe even overlap with brackish groundwater resources in some places.
02:44
And brackish groundwater as of right now it's maybe not a viable drinking water resource in a widespread way. But there are a few hundred of these systems where municipalities in the United States are using brackish groundwater through technologies like reverse osmosis for drinking water supplies.
03:01
So that overlap is perhaps damaging some of these strategic resources. In one of the figures we show a map of these groundwater systems in the United States. And one of the things that is quite stark is that there is kind of an east-west trend in the data. And that's interesting because we have places like California where we have had droughts in say the Central Valley.
03:23
And as it turns out it is a viable strategy at least for now to drill deeper and deeper wells in places like California or Arizona that are arid and water short. But if we ever had that problem in say Michigan or Ohio it looks like saline groundwater is perhaps only a few hundred meters deep. So those types of deep water wells that we're drilling in the U.S. southwest it just wouldn't be an option in other parts of the United States.