Keynote lecture sound recording from IAH Brussels congress in 2021. Our thanks go to David Kreamer and the Department of Geoscience, University of Nevada Las Vegas for allowing us permission to use this presentation.
Keynote lecture sound recording from IAH Brussels congress in 2021. Our thanks go to David Kreamer and the Department of Geoscience, University of Nevada Las Vegas for allowing us permission to use this presentation.
David Kreamer, IAH Belgium congress 2021
Transcript is below. To view this alongside his presentation slides in PDF, go to:
https://bit.ly/3LhdWRe
Groundwater in the Field: Challenges, Opportunities and Possible Solutions
Professor David Kreamer, Dept. of Geogsciences University of Nevada and IAH President
Marijka: Good afternoon, everybody. Welcome back. Our next keynote speaker does not require a long introduction because you all know who he is. Professor David Kreamer, the President of the International Association of Hydrogeologists. As I know, he has a lot of science that he would like to share with us today. I will keep the introduction really short. What you didn't know is that he really likes kayaking. What you also maybe didn't know is that he was really hoping to get some rain in Belgium because he lives in the desert.
He was very happy to get some rain here in Brussels. We are very, very happy that we have been able to give him what he wanted. Give a warm applause for our president, Professor David Kreamer.
[applause]
Professor David Kreamer: Thank you. Are you guys awake after lunch? It's good to be here. When our morning preliminary speakers said that British Columbia only went 40 days without rain, last year, where I live in the Southwest of the US, we went 240 days without measurable rain. For the whole year, we got less than 30 millimeters of rain for the whole year. We've been going through a 20-year drought. When I was asked to do this, I talked to a couple of my colleagues, and I said, "What should I talk about?" I gave them three, or four, or five topics.
Each colleague said, "No, you should talk about this one." The other one said, "No, you should talk about that one." I'm doing something that I haven't done before. I'm going to cover a couple of topics from different parts of the world. The disadvantage is I won't be able to go into huge depth in either one, any of them, but I will be able to give you a tour of the world, and maybe hopefully, it'll be entertaining and informative as well. What I want to talk about is examples of groundwater and fieldwork, and maybe solutions, both in practicality and in policy, from around the world.
First, I'll talk about some research in the Grand Canyon on spring sustainability, and uranium mining, then high hydraulic conductivity on a small Pacific atoll. I know that there are a couple of papers here on island hydrogeology. Hydrogeologic framework modeling in Niger, Africa, and then finally, “hydrophilanthropy”-- it's hard to read that. [Let me darken that a little bit. There we go]. Hydrophilanthropy gone wrong. How some people who go out and try and do good things in the world can actually make the situation worse. Those are the topics I'll cover.
The first one is the Grand Canyon and spring sustainability. Why are springs important in the Southwest, and are they vulnerable from things like mining activities? The reason they're important, it's to ensure recreational uses as an indicator of long term ecological benefit, and finally, for a Native American in the Southwest of the US where I'm from, the Native Indigenous people, they have religious and historical-cultural associations with springs, that are really important. Where is the Grand Canyon? Okay. It's in the United States, it's in the Southwest.
There's Arizona. It's in Northern Arizona, and it is over-- I think it should be 1,500 meters deep. It's one of the national heritage sites. It's visited by millions of people each year. There's a North Rim and a South Rim of the Grand Canyon. Let's see if I can get this pointer to work. Over in this area here, we have Havasu Canyon. Some of the Native Americans live there, and it's actually a very, very beautiful canyon. On this part over here, we have the Little Colorado River coming in. Sometimes of the year the carbonate makes it very blue, and other times, when you have heavy rainfall, you have a lot of sediment in the water.
Very, very impressive. Down at the bottom here is a town about maybe 15 kilometers away from the rim with deep wells. That's why we started our research, to see if they would impact the springs. That's the situation as to where this is. I want to say a word too, about the fun and difficulties of fieldwork before I start. The Grand Canyon is a good example. I'm sure that a lot of you out there have had a lot of experiences in fieldwork with snow, and rain, and all sorts of interesting conditions. I wanted to say a little bit about fieldwork in the Grand Canyon and the fun.
I don't know if you can see it, but there's a little trail down below there. In the Grand Canyon, sometimes you're climbing and going up and down thousands of meters each day. Some of the springs are several days away. You're off-trail a lot of times, so, you're what we call bushwhacking. You're more of a bushwhackee than a bushwhacker in many of these cases. In the summer, the temperatures can get up to 45 degrees. We hike before the sun comes up, hide in the shade, and then hike after the sun goes down. The most I've ever carried is about maybe 40 kilograms of sample bottled waters, which I could not drink.
I don't think I could do that today. In the winter, the snow can blow sideways. You have to sleep with your water bottles in your sleeping bag so they don't freeze. One of the problems is with surveys and GPS. Because of the canyon walls, you don't always get satellite reception in different places. I'm surveying there, but there are some limitations. You can get flash floods. They can be very, very beautiful, but very, very dangerous. This is the Colorado River in the Grand Canyon. Then, if you take river trips, the Grand Canyon has some of the most interesting rapids in the world.
I have gone down the Grand Canyon in these rapids about 40 times. I've never been a passenger. I've either paddled, or kayak, or rowed like this fellow is doing. They can be really impressive.
[video begins]
Female Speaker: Here comes Dave with Mel and co, ready to high side.
Professor Kreamer: I'm rowing this boat. This is the summer trip.
Female Speaker: Yes, the entrance is crucial on this rapid.
Female Speaker 2: [unintelligible 00:06:54]
Female Speaker 3: Oh, really?
Female Speaker: It looks like you've got it, right?
Female Speaker 2: Oh yes, that's [crosstalk] definitely, yes.
Female Speaker: Dave is pushing. There they go. Wow. Wooh.
Male Speaker: Oh God, [unintelligible 00:07:20]
[video ends]
Professor Kreamer: I didn't know the narration was going to come in with it, the person taking pictures on the shore. Let's talk about the Grand Canyon and uranium mining in particular. This is the stratigraphy of the Grand Canyon, again, about 1,500 meters. The two main aquifers are a bunch of limestones; the Redwall, Temple Butte, and Muav limestone underlain by a Bright Angel Shale. We call that the R Aquifer. Then upper, we have the Coconino Sandstone with the Hermit Shale underneath. We call that the C Aquifer.
If you were to look at the contact between the Coconino and the Hermit, you could see, if you look closely, Travertine coming out, where there's, historically, water coming out of the contact there.
Where they want to mine in these areas is in breccia pipes. For those of you who don't know what a breccia pipe is, it's a collapsed feature. I know a lot of you already do, but just an explanation, if in geologic history there's a cave that collapses and the roof collapses down, the broken-up rock called breccia makes a chimney. It continues to fall down and propagates all the way to the surface of the rim. It causes a depression on the top of the rim, and a lot of these depressions, sometimes the surface water connects the dots and follows those.
The result is that you have vertical water that moves up and down these breccia pipes. If that water has just a little bit of uranium dissolved in it, when it hits a reducing zone or a low-oxygen zone, it precipitates the solid uranium out, and that's where the mines want to go. In this case, here are some examples. Here's a student on the right looking at fracture flow. It's not only uranium but copper materials. You can see that there's fracture flow. This is a mine that's defunct inside the Grand Canyon, a place called Horseshoe Mesa. On the left, there's one of the students just before he committed suicide because he couldn't work with me anymore.
I'm joking. [chuckles] Here's a photo of a breccia pipe on the left and a schematic on the right. You can see that the ore in the bright red there, is mostly in the Hermit Shale or the Upper Supai Group called the Esplanade Formation. The problem with that, there's lots of problems with it. It's not only water quality but water quantity. You put a mineshaft down from the surface into that perched water system, and you can actually drain the perched water system in the springs that are supported by that. You can move the water around, and that's a real problem.
Also, if you think about it when you put a mineshaft with a lot of oxygen into a system, remember that uranium precipitates in low oxygen, but it dissolves into the aqueous phase and high oxygen just as a general rule. And so you can mobilize ore, you can mobilize uranium, which could then affect the springs. My research group was the first to find really high uranium below the site of a defunct uranium mine, which was right on the rim of the Grand Canyon. It was-- Let me just go back a second. This uranium mine operated from about '48 to '70. In 1970, it stopped operating, and many years later, we found uranium straight below it.
The Park Service had it as a visitor attraction. People would go to the sole mine site, but after we found the uranium in the groundwater down below, about 800 meters down below, they tested the soil, and it was hot. It was radioactive, and so they closed the site, dug up the-- It's a Superfund Site now, in the Grand Canyon. We did a lot of different things, and I'm not going to talk a lot about this, but my research group, about 30 years ago, started doing trace element analysis with ICP-MS, inductively coupled plasma mass spectrometry, before a lot of people were doing it.
We were looking at things in the parts per trillion range. This, by the way, poses a challenge in the field because in the parts per trillion range, you breathe on a sample funny and you change its concentration. You have to hike in the Grand Canyon with ultra-pure nitric acid in your backpack, and you have to have the plastic things with the gloves to filter the water first. It's a challenge. This is rare earth elements, and on the X-axis and on the Y-axis, what you can see is you can see concentrations versus shale. What essentially this says is the groundwater in wells in the R Aquifer are similar to what issues the springs that come out of the R Aquifer, the limestones.
The one that's a little different there is actually sewage outfall from the Grand Canyon, so it has a different rare earth element configuration. Sorry. We also did stable isotopes. You can read about that if you like. The North Rim of the Grand Canyon is higher than the South Rim, so that's precipitation in the North Rim. These are the South Rim springs. You can see it's a little heavier isotopically, with the stable isotopes of oxygen and hydrogen. The North Rim springs are coming into sight now, and you can see that they're a little bit lighter. There's one spring that had a funny mixture.
If you want to read about it, you can read this paper. It had an interesting-- A pipeline, that water supply broke and it put some North Rim waters mixing with South Rim water. This is where the spring is, a beautiful spring called Indian Garden Spring on the Bright Angel Trail. Has anybody here hiked in the Grand Canyon? Ah, a couple of you, good. Okay, some dye tracer tests. Ben Tobin was with the Park Service in the Grand Canyon. He is now one of the leaders of the Karst Commission here at IAH. He dumped some dye into the North Rim sinkholes, and weird stuff happened.
If you ever doubt that karst is weird, there is some dye that's been put in right here. Here's the closest place to the canyon, no dye went this way. It went 15 kilometers this way, and 20 kilometers to 25 kilometers this way, to come out at springs. Then we went further away here, and it did go straight down and then also over in this direction. In other words, dye tracer tests can show you just how confused a karst system can be. We also did some aerial stuff. I'm not going to talk about this a lot, but we flew over a mine site here, Iodide detectors, looking for gamma radiation.
This is potassium. We also did thorium and uranium. Here are some measurements right outside the mine itself. I'm not going to talk about that a lot. The question is, is the uranium that we find in the springs, natural background, or is it human-caused? There are other elements as well. I'm using an example, arsenic here, from the Grand Canyon. What we did is we looked at all the data from every water quality sampling of any spring in the Grand Canyon we could find. We had about 4,500 sampling events. Of those-- Oh, I'm sorry, excuse me.
Of those, 87% of the time, nobody even analyzed for arsenic. This is characteristic of a lot of elements. When it was analyzed, it was non-detect about 12% of the time. 88% of the time, there was some detected. Here's the interesting thing. When it was detected, over half the time it was above drinking water standards. The MCLs stand for maximum contaminant levels, which is the drinking water standard of 0.01 milligrams per liter or 10 micrograms per liter. 78 Springs had concentrations above that. A lot of this is natural background.
The question is, is the high uranium we found really a natural phenomenon near the breccia pipes, or is it human-caused? The whole reason I want to show you this whole area of study is embodied in the next slide here. Here we have a tritium ratio on the X-axis. On this axis, we have what's called the activity ratio or the uranium 234U/238U ratio. The uranium 238U in the world has a half-life of 4.5 billion years old, the age of the Earth. That means half of the 238U has gone to 234U. That one-to-one ratio is called secular equilibrium, and it's indicated by this one right here.
That's secular equilibrium for these things. You might notice that just about all these values are greater than one. They're enhanced. The older the groundwater is, generally, the higher the ratio is. Tritium, usually younger down in this range over here, older as you get to the lower amounts of tritium. Below this uranium mine that was defunct, guess which one of these springs was the one that was directly below? It was that one right there, close to secular equilibrium. What they found in different parts of the world is the uranium 234U/238U ratio.
When it's close to one, very often it's associated with mining activities with uranium. That's one piece of evidence that perhaps it's affected there. This is the longest one I wanted to do in uranium. I want to talk about some other things here. Let's take you out to the middle of the Pacific Ocean now. This is a small island. Actually, that's my grad student's finger, but it's a small island under his finger on the map called Johnston Atoll, and it's a very small island. It's a very beautiful island, but no beaches or anything like that. It's about 3 kilometers long and about 1 kilometer wide.
You're looking actually under the ocean there. It's very, very clear water, extremely good scuba diving. You'll see eels, seals, sharks. At night, the tiger sharks come through, and you got to be a little careful. You can see where they dug up the channels so boats could go in more easily to one side of the island. It is a coral atoll, and it's the oldest coral atoll in the world. It's got about 1,000 meters of coral, and coral has notoriously high permeability. This is a wildlife area now. One species of bird, the sooty tern, alone had 55,000 pairs of mating adults visit this island every year.
There are large frigatebirds and other things like that. The fish are amazing, but it also has some problems. There were some pollution problems, and that's why I got involved. You're looking from the upwind side on the East to the downwind side on the West, and on this side of the island is the burn pit where they burn trash. It also had heavy metals in it, and so that was a problem. Next to that, they stored Agent Orange during the Vietnam War. Herbicide that has dioxin in it, other Agent Blue, and a couple of others. The good thing about a pesticide is it's not really too mobile in water, especially these.
These are not too mobile in water. However, in a nonaqueous phase liquid like a fuel, it can move. It can get legs and travel a bit, but the fortunate thing is that it doesn't dissolve too well in water. It's fairly persistent. There is the Agent Orange leaks there, and then right next to it is where they dumped fuel. [laughs] I just said it's mobilized in fuel. They dumped it there for fire training. These are not environmental people. They would simulate plane crashes and things like that for their fire training. They would dump fuel on the ground right there with the potential to mobilize the dioxin and the Agent Orange into the lagoon past the Barrier Reef.
This part of the island right here is interesting. They had nuclear weapons there. There were some explosions. They weren't nuclear explosions, they were conventional explosions. On that side of the island, we had a little plutonium and a little uranium, and constant monitoring going on over there. In different parts of the island, there are fuel leaks and solvent leaks. I'm not measuring the water table there, I'm measuring the diesel table right there. These are different places with different types of fuel leaks. Diesel, jet fuel, Jet-A, and JP-4.
These are all fuel leaks that occurred around the area, and we were brought in to look at some of these contamination problems. I haven't gotten over to this side of the island yet over here. This is a chemical weapons disposal unit that burned mustard gas and nerve gas. With an agreement with the former Soviet Union, the US got rid of chemical weapons there. An interesting site, actually, if you're into contaminant hydrogeology. Whenever you were on the downwind side of the island, you always had to be within arm reach of your gas mask.
You fellows, you couldn't have a beard because the gas masks didn't fit too well if you had a beard. That's Johnston Atoll. Just a couple of the activities really quickly we did there. We did soil gas sampling. There's my graduate student goofing around, doing soil gas sampling on the upper left-hand picture there. Actually, the nose is very, very sensitive and very, very accurate. If you've been around fuels, you can tell the difference between an old diesel fuel, modern jet fuel, motor gasoline, that are actually, have distinctive smells. Château de 53 diesel fuel, you can really tell the difference.
There wasn't access in all places, so, the middle-upper picture, we're driving in a soil gas sampling piezometer. In the upper right, we have a syringe, and we directly inject into a gas chromatograph. In the lower-left, what you can see is solar-powered skimmer pumps. We didn't always have electricity. This is a fuel leak under here. On the water table, you have gasoline floating on top of the water table.
In this particular case, the solar power, then we would skim off the oil with time so it wouldn't go out into the lagoon. You can also see a floating barrier out there. The middle picture in the bottom, microbiology that we were doing. On the lower right, that what's called bioslurping. I'm not going to spend any time explaining that. Why I brought this whole discussion up was to talk a little bit about the high hydraulic conductivity that you get in corals. There's a couple of great papers on islands. Unfortunately, the fellow from Japan who had some things on Japanese islands and talked about hydraulic conductivity had to leave, and his poster is no longer here.
I believe. I didn't see it up there. What do you do if you want to measure hydraulic conductivity? You can't do a pumping test because the water doesn't move much. It replaces itself so quickly. Rate of rise test or what we call a slug test, is where you remove water from a system and watch its recovery. Even those tests occur so quickly, it's hard to really get good values. One method that a lot of people don't know about is the method that you see here. We put a transducer down the well. What we do is we pump air down, not so much to--
We stop before we inject air into the aquifer, but we pump the air down, and then you turn the valve on the top. Suddenly, the pressure is released, and the water can come up quickly, and you can measure that. You can do a slug test in very, very high hydraulic conductivity regions. There's ways to adjust in the field to your conditions. This is just one technical way to do that. What I also wanted to talk about a little bit here was, the freshwater lenses in some of these islands is going away. For millennia, in some of these small islands, people would just take water from the freshwater lens under the island.
As you pump more, those of you who know the [unintelligible 00:25:37] principle is if you pump down a cone of depression, 1 meter, the saltwater interface that underlies this freshwater lens up cones 40 meters to 50 meters for every meter that it's pumped down. Now that these people want more and more freshwater, and they want to expand their economies, they're getting saltwater intrusion. One possible solution is mobile desalination plants. I wrote about this. This is an artist's conception. I actually think it's bogus. It looks a little top-heavy to me like it might capsize.
The idea of a mobile desalination plant has several advantages. The first advantage of mobile desalination is that when you desalinate, you create a brine in addition to freshwater. Where do you get rid of that brine? If it's a coastal environment, you dump the brine in the coast, it could have bad environmental impacts. If you're out at sea, you can diffuse it slowly, and more or less release that briny water at not too high concentrations. Another thing is they're mobile, so there, you can react to natural disaster infrastructure failure. They could also react to tourist activity and serve a humanitarian mission as they go around the world.
A lot of ships are mothballed. They just go and they rot. There are ship graveyards in the United States. The ships have stayed there so long you could take a hammer and smash them through the hole of the ship. They're leaking fuel and fluids. If you knew how much it was to decommission a nuclear boat, say an aircraft carrier, it's really expensive, but to convert it is just about the same. It's still very expensive to do, but the idea of having instead of warships, having peace ships, I think is an interesting thing to do. Let's go over Niger, Africa.
I'm in the middle of a very large several-year project in Niger Africa, where we got satellite imagery. We tried to locate water. Let me tell you a little bit about Niger. I think, in the opening ceremony, I told you a little bit about it. Niger is West Africa. It's surrounded by seven countries and landlocked. It's about 75% in the Sahara and Tenere desert. It's called the Frying Pan of Africa. Half of the population is younger than 15 years old, so they expect to triple in population by 2050. 44% of the people don't have ready access to water, drinking water.
The children, I think the latest statistics are 43% of them have to work and can't go to school. They have jobs. It's a country that needs water, and it's going to need more water in the future. Our goals were to develop what's called a hydrogeologic framework model. It's absolutely amazed me how all the Europeans here, or not all the Europeans, but a lot of you haven't heard of a hydrogeologic framework model. You modelers out there, what you do is you develop a conceptual model about what a site looks like. Then what you do is you then model.
Based on that conceptual model, you do a predictive model, but there's an intermediate step. The intermediate step is quantifying that conceptual model. In the United States, the US Geological Survey has a separate step for that because so many people do it poorly, and so many people skip it. The idea of a hydrogeologic framework model is to quantify the size of the aquifers, the storage of the aquifers, the boundary flows in and out, more or less a water balance. The amount of recharge, the evaporation, precipitation, and to get all those figures down.
Even if you have some error bars, a high number, and a low number to get an idea. We have three steps, a conceptual model, a hydrogeologic framework model, which is a detailed, detailed model of the water balance. Then before we do that, we then go on to a predictive model. A lot of people go very easy in that middle step in quantifying their conceptual model. A hydrogeologic framework model is used to describe the physical geometry and orientation of different aquifers in a particular region or area.
It's an integrative computing platform. It can be used to access groundwater inputs, outflows, and storage in different strata. It uses the appropriate stratigraphic principles. A 3D model is developed, and it has the structural relationships of the different stratigraphic layers if you have multiple aquifers, particularly as you do in Niger. What you do is you digitize the pertinent data in a three-dimensional volumetric model with the hydrogeology. You estimate the groundwater volume within each aquifer in your domain. You make a water budget, then you look at spatial references, you georeference the maps.
Hydrogeologic assessment then is usually put in GIS format, so it's easily accessible in a tabulated form as well. Then the extent of aquifers in hydrogeologic units are made at the location of the wells are mapped, and the elements of the conceptual model then, now this conceptual model is a quantitative conceptual model. It describes the current understanding of the groundwater system. In Niger, we looked at Southern Niger because the North is the desert. Most people live in the South, and that's what we were supposed to do.
There's something called the Aluminum Basin. It's the major basin in the South of Niger. The geologic units in the aluminum basin are grouped by geologic time, stratigraphic relationships, and the capacity to store and transmit groundwater. We calculate the volumes of water and storage. The aquifer storage and yields then are estimated, usually with a high, and low, and a medium number because of the uncertainty. Then the geometry of the units, we can estimate the inputs and outputs that recharge, or we get a lot of meteorological data.
Then the boundary conditions of the domain, how much water flows in and out of each aquifer. These are the wells, an example of wells, the 8,500 wells that we looked at. Borehole logs, we did satellite imagery, we got meteorological data. We estimated recharge based on soil studies and lots of other things. There's a huge amount of data that goes into a hydrogeologic framework model. It's a steady-state model of water balance. This is the eventual technical and socio-economic benefits of this particular project is expanding the access to portable water, identifying water resources for future economic development, which is very important in this country.
Improving drilling success for new boreholes, minimizing droughts, providing a better basis and more information in managing water resources, and enhancing economic growth to improve the livelihood of the communities. The last thing that I want to talk about, and I know that Marijka has been very patient is hydrophilanthropy. I know a lot of you have worked overseas in many different areas, and there's a lot of people in need. The definition of hydrophilanthropy- we know what philanthropy is, it's doing good deeds- hydrophilanthropy is humanitarian actions which increase and sustain clean water in areas of need.
I've written on this a lot, there's a lot of mistakes you can make. I've told a couple of people, "You can put a perfectly good well in an area that really needs it, you can make sure that the surface is sealed so no animal feces go down into the well. You can make sure the community can sustain it and fix it if it's broken, and all things like that. But if you put it in the backyard of someone that everybody hates, you've created a water war that can last for years." There's ways to do it right, but one little mistake can really blow it for you. These are the things that I've found.
I know that you've found some too in your work. Pre-evaluation, and preparation, bringing adequate resources, imagining the long-term consequences, observing the local customs attire and practices, providing good oversight and leadership, planning ahead for sustainability and follow up. I want to just talk about that last one there, appropriate technology. Sometimes low technology is the best technology. Here's digging a well in Kenya. What you can see is this is the sort of thing that's very inexpensive and can be used in several different places.
Here's my student in Northern Ghana, very high arsenic in this particular well. The person pumping in the back there is where the well is. By using some local materials, it could actually [unintelligible 00:35:13] out some of the materials. A lot of people put in motorized pumps that break down and are scavenged. They estimate that about 1/3 of the pumps in Africa are non-operative. Toilets are the same way. These do-gooders came in and put in toilets in a community, didn't tell people how to use them. They had never seen them before.
There are no toilet paper factories in the area. These became a hazardous waste site a week after they put them in, and we created more hazards. There's, sometimes low tech is the best tech. Things that can be fixed by the community and maintained by the community. One last thing. There's something called play pumps. Very, very popular. They got tons of money because imagine kids going around in a circle playing on this and pumping water for people to use. That's what a play pump is. Sounds great. It's not. First of all, it's child labor to have kids going around.
Maybe at an elementary school, but they can never keep up with the demand. They're hard to handle as opposed to a hand pump or a treadle pump with your foot. They cost four times more to build, and they're much harder to maintain. Play pumps, don't give money for play pumps is my idea. In summary, what I'd like to say is Grand Canyon, we use a lot of different tracers. There's multiple approaches, and we establish many lines of evidence to try and show where groundwater flows. On island atolls, again, there are multiple contaminants and specialized methodologies.
Niger, satellite imagery, and many data sources are used to support a robust hydrogeologic framework model. Hydrophilanthropy, lots of ways to get it wrong. That's all I wanted to say. You've been very gracious with your time, Marijka, in not cutting me off. Thank you very much, everybody. Just some last acknowledgments here, of my graduate students and other people involved in the projects here. Some associations, undergrad students, and other people who have been involved in some of this work. Thank you very much.
[applause]
Marijka: Thank you, Dave. That was quite a spectacular presentation, many lessons learned. I think the main lesson we learned is that if you ever invite us on a trip to a nice island, we should think twice because it's probably not the paradise we imagine. As you thought, there is no time for questions anymore.
Professor Kreamer: No.
Marijka: But Dave will be around today, tomorrow at a gala dinner, so I'm sure he will be available to answer your questions. Then I have one minute only for you to give some-- Yes, one for some practical information.
Professor Kreamer: The other thing we've learned is, never go over your time like I just did.
Male Speaker 2: Sorry. Thank you, David. I'll try to be quick then.
[00:38:25] [END OF AUDIO]