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Episode 9: Guarding Our Groundwater

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In this Episode

When we turn on the tap, many of us are tapping into the groundwater system. Whether your water comes from an aquifer or well, groundwater is flowing into your home. A range of issues, from too much pumping to changes in climate, can threaten the delicate balance of this natural resource. The summer months can be especially taxing on the underground water supply. Our guest in this episode has made it his life’s work to stay ahead of the threats and come up with solutions to keep the system in check. He tells us what it takes to guard our groundwater and how each of us can help protect it.

Listen now as we plunge into our underground waterways.


Below is a transcript of the episode, modified for clarity.

Lisa Peña (LP): What do you know about H2O? Where does our water come from? What does it take to keep it safe and clean, and how can we help? Our guest today is a groundwater hydrologist and an expert on managing our groundwater resources.

From tracking water quality to developing new groundwater technology, he's a leading voice for our waterways. Coming up, the groundwater discussion is flowing on this episode of Technology Today.


We live with technology, science, engineering, and the results of innovative research every day. Now, let's understand it better. You're listening to the Technology Today Podcast presented by Southwest Research Institute. Hello, and welcome to Technology Today. I'm your host Lisa Peña. 

Managing our groundwater resources is a major task. Stormwater runoff, leaking septic tanks, and municipal waste degrade groundwater sources like aquifers. And those are just some of the many issues that can disrupt our groundwater.

Our guest today is Southwest Research Institute scientist and groundwater hydrologist Dr. Ronald Green. He's always looking at new ways to keep our groundwater system running smoothly. Thanks for joining us, Ron.

Dr. Ronald Green (RG): You're welcome. Thank you.

LP: So let's start the conversation by classifying groundwater. What is it? What is the depth for it to be called groundwater?

RG: There are different interpretations or definitions of groundwater, but it's mostly water that's underground. You have an unsaturated zone and a saturated zone. So some define groundwater as that part of the saturated zone below the water table.

But you have to recognize that the ground above the saturated zone also has water. It's just that it's not fully saturated. We call that the unsaturated zone. So groundwater would be that water that's underground.

LP: All right. Any water beneath the surface.

RG: Yes, that would be a broad definition of groundwater.

LP: OK. So when we think about groundwater, we can also think about surface water, and that would be water we can see like lakes, streams, creeks, rivers. But these two types of water do interact. So how do surface and groundwater interact?
Lisa Peña and Ron Green against a solid blue background

Left to right: Lisa Peña and Ron Green

RG: Well, that's a very interesting question and it needs to be recognized a little bit more. Because to think of surface water being separate from groundwater is a little misleading. They are very closely related.

Groundwater serves as a source of surface water. If you look at creeks and you go upstream, you'll see that the creek is oftentimes dry. And as you go downstream, you'll see that water is seeping into the base of the creek from springs, little rivulets that are issuing out of the groundwater. That is groundwater that is providing for surface water.

Now that's not quite that simple everywhere because there are places where surface water goes back into the groundwater. So where the streams are gaining water, we refer to that as a gaining stream, obviously. And those reaches of the river or the spring or the streams where you're losing water, that would be a losing reach of the river. So they are very closely related.

Now in surface water, you also have the opportunity for surface flow to contribute to the water in the stream. And that's where water lands on the surface during precipitation and then flows into the stream without first going into groundwater.

So it's those two components from precipitation that provide for water in streams and rivers. That's the part that goes directly into the river from surface flow and then the part that goes underground and then into the river.

LP: So there is a strong connection between the surface water systems and the groundwater systems. And when we talk about keeping our streams and creeks and lakes clean, then we're also in a sense talking about keeping our groundwater clean.

RG: Exactly. So if you degrade the groundwater, you're going to impact the surface water in the same way. Whether it's by decreasing the amount of groundwater–that could dry up streams, or decreasing the quality of the groundwater–that could impact the streams also.

LP: How does pumping a groundwater system affect the surface water systems?

RG: Well, it depends upon the area. In San Antonio, the aquifer is what we define as confined. So it's at depth and it's separated from the surface water. That's in the confined portion of the aquifer.

Upstream, the aquifer is defined as the recharge zone. And then in that area, the aquifer is not confined and it may or may not be in a hydraulic contact with the surface water.

So if you're pumping groundwater in the confined zone, you're not going to impact the surface water of streams that are at the surface. If you're in the recharge zone or the contributing zone that provides water to recharge, in those circumstances, if you're pumping groundwater, you may be impacting the quantity and quality of the surface water in those areas.

LP: Are we talking about pumping wells or does it go beyond that?

RG: It's mostly pumping wells. And there are certainly places when you go out to the arid and semi-arid parts of West Texas and the United States where you can pump the groundwater to such a degree that you cause harm or you dewater the surface water.

It just depends upon how much you're pumping, where you're pumping it relative to the rivers. But it's important to recognize that they are hydraulically related and they interact, and so one can impact the other.

LP: Let's jump for a minute into exactly what you do, because you are constantly looking out for our groundwater system and looking at scenarios that can hurt it and help it. And of course, you are trying to help it. So if you can explain your field a little bit, what is groundwater management?

RG: That is the area that we're very directly involved. And to put it very simply, we look at the water budget of the aquifer. And that entails how much water is coming in from recharge, how much is going out naturally or by pumping, and how much is in storage.

So you can think of it as a bank account. So that's going to have a certain amount of money in the account. And if you're taking out more money than is going in, you're going to have a problem at some point in the future.

So our role is to determine what that water budget is. And for that, the most difficult part, typically, is to understand how recharge occurs and at what rates. And it's highly variable because it depends upon precipitation, and precipitation, as we know, can vary greatly over time.

So the other parts of the water budget that we are concerned with, how much water is being pumped out and where, and then how much water is being discharged naturally. And that usually occurs at springs. And around Texas, there are some rather iconic springs, some of which have dried up over time because the water budget has not been managed as it could be.

LP: Do you get a sense that people understand this? That there is a water budget? That it's not this endless supply for us to use?

RG: Yes, I think people understand that. And those that are near some of these large springs witness it firsthand. What may not be understood as well is how much groundwater pumping can be sustainable. And that is a more difficult question. And it goes back to understanding recharge and how much recharge there is.

You have to remember, this is Texas. And people hold their private property rights very closely. And part of that is their groundwater. So they feel that if there is water under their property that you know they have whatever right to use that water in whatever way they want.

So it can be a bit of a complex issue when you're trying to use the water to the best advantage for you while at the same time maintaining sustainability. So it's a challenge.

LP: How can those of us in the city using tap water out of the Edwards Aquifer or any aquifer, how can we help the groundwater supply?

RG: Well, one way is to be responsible for how much water you're using. And one of the biggest usages is lawn watering. And if you can keep that to some reasonable level, you're going to help the community sustain their resource.

LP: There is a term that we've said a couple of times in this conversation but it's important to the groundwater conversation, which is recharge. For our audience, can you define what recharge is?

RG: Well, recharge is the water that comes from precipitation. And it's usually rain in southern Texas. It could be snow in other areas. But that is the source of recharge to the aquifer. And it varies spatially and over time.

So in Texas, we talk about average rainfall, but that doesn't make a lot of sense. Because when you go to West Texas, for example, you may have six weeks or six days of very good precipitation, that's when most recharge occurs, followed by two or three years of drought.

So when you're talking about average numbers, it doesn't make a lot of sense because that recharge occurred during that six day period and the rest of that year, two years, three years, may be very limited precipitation, very limited recharge.

LP: So how do you measure or track recharge?

RG: Well, we calculate that several different ways. And as I mentioned, that is the greatest uncertainty in determining the water budget of an aquifer. So we can look at how much water is coming out and that will tell us how much water is going in. And that's oftentimes how we have to do that.

You can do field studies to determine how deep the groundwater is, how much water is going through that unsaturated zone. That's a bit of a challenge because that varies considerably from point to point. That's going to be very different in the base of a stream channel compared to up on a hilltop.

So there are different ways of doing that. You can use satellite data, remote sensing, to help with that. That's something we use. You can use chemical signature where you look at the chemistry of the water, and that can give you insight on how much water is being recharged. So what we have to do is put all those tools together to reduce the uncertainty to the degree possible when we're calculating the water budget.

LP: So how does climate impact recharge?

RG: Well, climate impacts recharge in terms of when the precipitation occurs. So climate is going to change over time. We know that. And if your precipitation during the summer, for example, increases, that may not improve your recharge very much because so much of that precipitation is evaporated.

Conversely, if you have increased precipitation during the winter when evaporation is down, much more of that water will get into the subsurface. So you have to look at the prevailing weather and how that changes, and how it changes over time, seasonally and in just the amount of water that's being rained or the amount of precipitation. That is going to give you better insight on how climate is going to impact recharge.

LP: So during the summer months, as we are in right now, this is a particularly challenging time for our groundwater resources then, because we're looking at increased human...

RG: Well, it's evaporation.

LP: ...evaporation.

RG: Yes, increased evaporation and increased usage by people. That's when they pump more for irrigation or for lawn watering. So it puts a greater stress on the aquifer.

And it depends upon these weather systems. You know, south Texas can have a tropical storm come and park on a localized area for several days, and some of the largest rainfalls in the world occur along the Balcones Fault Zone, which is in South Texas.

And you can get to 10 to 20 inches of rain in one or two days. And you can have considerable recharge from those events that will replenish the aquifer to some high levels that will sustain pumping for several years.

LP: So we're talking a lot about recharge and our responsibility to conserve water when we can. But there are other risks with our groundwater system. Some of those things are stormwater runoff as we mentioned at the top. Leaking septic tanks, municipal waste.

And I want to talk about the DNA trackers. You were on that team. You helped develop those. Explain to us what those DNA trackers, what they are and what their purpose is.

RG: Well just to back up a little bit, we're trying to understand what impact development is going to have on the water that's been recharged, both in quantity and in quality, mostly quality. And so if you have high development on your recharge zone, you're going to likely degrade the water that's being recharged into the aquifer.

That can be from lawn pesticides and fertilizers. It can be from runoff from driveways and streets. And it can be from septic systems, whether they are household septic systems or if they are small package plants or small wastewater facilities.

There is a bit of a debate going whether you should allow higher-density development and then put all your waste into a wastewater facility and then discharge it into surface water. That partially-treated water is less harmful than if you had probably less development, meaning larger lots, but the households have individual septic systems.

So the question is, which is worse for the environment? Having a wastewater facility or these individual septic systems? So we are looking at that question, and part of that is to understand where the water is being recharged locally. Is that occurring in the creek bed? Is it occurring in the side slope of the hills, on top of the hills?

And that's important when you try to understand where these contaminants are coming from in terms of individual septic systems. So we are working with the University of Texas in San Antonio to develop a new class of tracers where, we call them DNA tracers, where each tracer has an individual signature or fingerprint so we can put out dozens, if not hundreds of these, in different locations and then sample them in the creek bed downstream.

And as we sample them over time, we'll see when the individual tracers arrive, so we can then have much better understanding of where the water is coming from, how long it takes to get there. And so this new class of tracers is providing this opportunity to do that.

LP: Where does the DNA come from?

RG: Well it sounds a little ominous but the fact is that they can just imprint a unique DNA on these little strands of particles so that they each have an individual signature that can be recognized when they sample them.

LP: So it's obvious you are passionate about this field, and it's important work. But how did you become involved with researching groundwater?

RG: Well when I first went to school, I was an industrial engineer. But my first job out of school was in the Peace Corps where I worked in West Africa at a rural water supply.

And I came to the realization during those two years that I did not understand that system well at all. So when I returned to the [United] States, I went back to school in geology, geophysics, and hydrology and made that my career. So it was a career change in my younger years. And I've been working in groundwater hydrology now for the past 40 years or so.

LP: Yeah. So we should mention you do have a doctorate in hydrology which is, you are dedicated 100% to this field of studying our water. So what do you enjoy about studying our groundwater?

RG: Well, it's extremely rewarding. There is a lot of societal importance to the groundwater. It has to be sustainable. It has to be protected, both in terms of quality and quantity.

And the more we understand about it, the better we can conceptualize and define the resource. What kind of management decisions are going to impact it in a positive way or a negative way. That's going to empower policymakers how to make the best decision with regard to that resource.

It is not our role to be policymakers. It is our role to provide the best information possible so that when policymakers do make their decisions they make it based upon the best information available. So they will learn or they will know the consequences of their decisions as they make them.

If they make a decision to allow for additional groundwater to be extracted by pumping, we can inform them what impact that will have both on the aquifer and on the surface water. Then they can make their decision.

Sometimes those are hard decisions. You're balancing the needs of society for economic growth, for example, with the aquifer. So it's not an easy decision. Sometimes if you're pumping too much groundwater, you're going to dewater a spring. That may be the best possible outcome for a difficult decision or it may be a decision that they have to go back and say, we're not going to allow this much groundwater to be pumped.

That is the role of the policymakers. When I say policymakers, I'm talking about those folks that are working for groundwater conservation districts. It's talking about legislators. It's talking about state agencies such as the Texas Water Development Board or the Texas Commission on Environmental Quality.

So those are the folks that have to make these decisions. Our role is simply to give them the best information possible so that they make the best informed decision with regard to the resource.

LP: Yeah. That's great that you're available to inform and educate them. So today we've talked a lot about San Antonio and Texas and this area, but this is really a national conversation. This is a responsibility across the U.S., really.

RG: Well, it goes beyond that. A lot of our work focuses on arid and semi-arid areas, and so that's a good part of the Western half of the United States. We've also been involved to some degree elsewhere in the world. We're looking at some projects in Kenya.

This is an interesting situation. There is a large preserve for some of the iconic endangered species, such as the black rhino, that rely heavily on wetlands that are sustained by precipitation on Mount Kenya.

So it's the land practices on the slopes of Mount Kenya uphill from the preserve and climate change that are going to be the two biggest threats to their wetlands. If those wetlands go away, those preserves are not going to be sustainable.

So they rely heavily on understanding what impact land use, namely, irrigation pumping of the groundwater, and what impact changes in climate are going to have. They are very sensitive to the rain shadow of Mount Kenya. So if the rain pattern changes so it comes out from a different direction, or if, as we talked earlier, if the precipitation goes from the summer to the winter, you may get more recharge.

Those issues are extremely important for that area. So back to your question on is this type of work important only for Texas? No. It's important for Western United States and elsewhere in the world.

LP: Really a global issue.

RG: It is, yes.

LP: So knowing that this is an issue across the world and something we all need to be informed and educated on, how can we, all of us, help protect the groundwater system?

RG: Well, I think it's important to recognize that it has to be sustainable. This is not like oil and gas where it's a finite resource. You get it out of the ground and that's the end of it.

You have to look at the water cycle. The precipitation that lands on the surface, how much of that gets into the groundwater. Protecting the recharge areas. Limiting your use of water. The way you wash your car and the way you water your lawns, all those parts of it come together into this final solution.

LP: So be mindful of our daily water use and our water activities is what it comes down to.

RG: And land planning. So locally, we see this challenge in northern Bexar County where development pressures are very high. North of [Texas State Highway Loop]1604, those are areas that people like to live in.

But if you have high density development of very small lots, you're going to have a real impact on recharge. And currently in San Antonio, we are blessed with a very clean groundwater supply that doesn't need treatment to any degree. And if we get to the point where we're degrading that recharge, then we're going to have to go back and institute a water treatment that would cost literally billions of dollars.

LP: A lot to think about. And it really is all of our responsibility. So before we go, we want to mention the eighth annual Texas Groundwater Summit hosted by the Texas Alliance of Groundwater Districts. So there are a lot of people that come together to discuss groundwater. So tell us about this summit. What is it and who is invited to attend?

RG: The summit is a trade organization, as you mentioned, Texas Alliance for Groundwater Districts. Texas has approximately 100 groundwater conservation districts. This is an opportunity for these folks to get together to share ideas, to listen to talks on some of the advances of technology that's important to them.

We are going to be presenting on two issues. One is going to be the impact of climate change on recharge and the other is going to be risk assessment of saltwater disposal wells that are part of the oil and gas industry and the risk that they pose to groundwater systems.

So Texas is obviously a major oil and gas producer. Part of that process requires disposal of large quantities of water. That's produced water and flowback from the fracking and the drilling process.

And the way they dispose that is through injection wells. And so those wells can be operated safely, but you have to understand the risk involved. And so we will be discussing how to evaluate the risk and what to be mindful of to ensure that you're protecting your groundwater.

LP: OK. Again, the Texas Groundwater Summit, that will be next month August 20th through 22nd here in San Antonio, Texas, at the Hyatt Regency Hill Country Resort. And we'll have a link to the event page on the web page for this episode.

So again, so much goes into managing our natural resources, our groundwater. So thank you for making us more aware of everything impacting our underground waterways, Ron.

RG: Thank you. It's been a pleasure.

LP: I feel so much smarter, and I feel like there's things that I can do now to help the groundwater system. Well, that wraps up this episode of Technology Today.

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Management of groundwater is vital to promoting long-term sustainability. SwRI geoscientists develop noninvasive numerical models to characterize subsurface and groundwater geological environments for total water resource management strategies.