195: Hydrological Mapping: A Vital Component of Effective Water Conservation Plans

If you want science-backed earth, water, biological, and mapping data about your land, look no further than the United States Geological Survey. Geoffrey Cromwell, Geologist at USGS at the California Water Science Center shares what this nonregulatory agency can do for growers and delves into two studies on California water basins.

The USGS’s mission is to investigate Earth sciences and make all research data available to the public. Studies cover floods, climate, earthquakes, volcanos, species, and geology.  

The Adeladia Area Hydrological Study located in San Luis Obispo County California, aims to understand how water moves in this atypical basin. Researchers are using stream gauges and monitoring wells to better understand how water flow changes seasonally and if there are differences in areas included in the project.

In Northern Santa Barbara County California, the San Antonio Creek Study is developing a holistic hydrological model to support the region’s Sustainable Groundwater Management Plan (SGMA).



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Craig Macmillan  0:00 

Our guest today is Geoff Cromwell, he is geologist with the United States Geological Survey at the California Water Science Center. And today we're going to talk about you guessed it, water. Thanks for being on the podcast, Geoff.


Geoffrey Cromwell  0:12 

Absolutely happy to be here.


Craig Macmillan  0:14 

Before I met you, I thought that the US Geological Survey made maps that you buy on paper. I've had many of them. And turns out, there's a lot more going on with that group. First, what is the United States Geological Survey?


Geoffrey Cromwell  0:23 

I also had a very limited view of the USGS even when when I started working, I also have had to do some background on my own. And I've learned quite a lot, having been with the survey of what different people do and really that overlap, then at these different intersections of science. The USGS is one of the bureaus within the Department of Interior. And so this is under the executive branch. And what is unique about the USGS, among other bureaus within Department of Interior, is that the USGS has non regulatory. And so the USGS, really the mission is to investigate earth sciences, collect data, interpret the data, and then make all those data publicly available that then other agencies, the federal or state, or local or any other entity can then make decisions or action decisions. Based on the interpretive science that the USGS puts out. There's a quote that I pulled that USGS does Science in the Public Interest, the mission is to supply timely, relevant and useful information about the Earth and its processes. And so the earth and it's processing things very, you know, brought up to go. So not only do we do mapping, so topographic maps, geologic maps, there's just a whole swath of data collection and just digital map information available, but for water, floods, climate two, there's a whole breadth there, there are currently five science missionaries for the USGS. There's the mapping group, there's the biological arm focusing on Ecosystem Science. So there's a group in San Diego that studies a lot of frogs, the reptiles down there, energy and minerals. And so where are the mineral resources for the country? What are the economic and then natural environment impacts of identifying and extracting minerals? In my mind when I think of the USGS, even as I'm in the water world, is earthquakes and volcanoes. So there's the monitoring of natural hazards? And what are the effects of life and property that could occur from these natural and natural hazards? Lastly, is the Water Resources area and that's what I'm involved with. And what the California Water Science Center is a part of in this is to evaluate and monitor and interpret water resources of the nation so that we do monitor and collect data on streamflow, groundwater, water quality, water use and availability. So just how much is there? Where is it? And can you drink it? Can you irrigate?


Craig Macmillan  0:31 

It sounds like this would be the kind of thing where you mentioned working with different entities that sounds like you would be working with all kinds of different institutions and scientific groups you work with, with universities, you go up to grant funding, how is this funded? And what are some of the other scientists that are involved in this stuff?


Geoffrey Cromwell  3:21 

The USGS doesn't, you know, operate independently necessarily. So we do collaborate and coordinate with other universities, definitely other science branches of the government to find the intersection of what needs to be learned. And in a particular area, it could be a biologic, or water or geologic and so my, my training and expertise is in geology, and, you know, identifying and mapping the subsurface in three dimensions and those a direct intersection of that earthquakes and hazards. And then what I do in my job is intersect the geology with the groundwater system. So you know, the rocks, there's the water on the surface of the water in the ground, and it all kind of flows above and through the materials in the subsurface, you know, I work a lot to with my colleagues to understand the dynamics of the subsurface, and that allows for better understanding of, of the groundwater and then other surface water and how human dynamics are affected by that. Normally, local water districts, we work with universities, we work with companies, all to find the answer for what we're what we're trying to learn.


Craig Macmillan  4:27 

So how exactly do you do that? I mean, you can put flow monitors and streams and things on the surface. Obviously, groundwater is underground, we don't see it. What is your job like? What, what do you do? How do you find things?


Geoffrey Cromwell  4:40 

You picked on you know, in some ways, the first step of a study is collecting data, or even go back a step. It's still what is the problem? And so we will coordinate in the Water World Water Resources world at the USGS we have, in general a different business model than other parts of the USGS like the natural hazards folks and for earthquakes and volcanoes, a lot of other sciences have funded directly by Congress. And so they are you know, there's a there are a line item in the in the Congressional Budget. But in the water world, we are primarily funded through cooperative programs. So we work with counties, the state, other federal agencies, such as Department of Defense on military bases, we work a lot with the California Department of Water Resources as a state agency. And then for a local study here in San Luis Obispo County, and we're working with the county, and they are a cooperator in that study. So the first part is to talk to the cooperators. And in talking to them, what are their needs? What are they uncertain about? What are their concerns? Are they worried about contamination from pollutants? Are they worried about wells going dry? Are they worried about future management of water resources? So especially in California, where drought is an ongoing issue? Future sustainable management is a big question. So how can we help these other agencies think about their water resources?


Craig Macmillan  6:01 

Which reminds me something so we're talking about California, and I met you through sounds bespoke County, but I'm guessing that this this kind of work is happening all over the nation? I would think.


Geoffrey Cromwell  6:10 

yes, these types of investigations are happening all over the country. And you can think about just the geography of the nation where it's hot, and where it seems to rain a lot more than other places are going to have different water issues. And so different investigations are occurring via for water chemistry, or groundwater availability or surface water resources. And if you look just in within California, it can be a microcosm of the whole country where Northern California in general surface water resources are more plentiful versus Southern California, where the primary water concerns are groundwater based.


Craig Macmillan  6:43 

How does this work proceed? You said you get to identify a problem and you were trying to cooperators then what what kind of tools do you have to investigate a problem?


Geoffrey Cromwell  6:52 

I think we use the study in San Luis Obispo County that you and I partner on, we will for service water monitoring, we have stream gauges that are placed on selected streams. And there are instrumentation there that allows for continuous monitoring to the stage or the height of the water. And then that gets translated into a total volume or discharge of water that's moving through streams and you can track seasonal cycles, that's a value for groundwater, we can usually see the groundwater. And so we will take individual tape down measurements of groundwater wells. So groundwater well is basically a hole in the ground with a steel or PVC casing. And you can one can drop down a tape, which will be either steel tape or an electronic tape that will signal what the Depth to groundwater is at that location. At that time. If you do this over a broad enough area and over, especially continuously, you know, with regular readings, you get a sense of how groundwater levels change seasonally and whether they change seasonally, the same amount everywhere. Or if there's different dynamics within that particular study area that are affecting how groundwater flows.


Craig Macmillan  8:03 

You also use water chemistry, is that right?


Geoffrey Cromwell  8:05 

Yeah, water chemistry, both surface water and groundwater. And this can tell a lot about the aquifer system. So the water level measurements and surface water measurements we just mentioned, those are useful for basically the ups and downs of groundwater and to get a sense of the direction that, especially for groundwater, where groundwater is moving in the subsurface, the water chemistry can inform a lot about not only the direction of groundwater flow, it can inform about any contaminants, or in the cases of, you know, something to think about often that comes up as the presence of nitrates in the subsurface. So that can be related to agricultural fertilizers. That's something that can be observed, but also can tell about which types of rocks the water is flowing through. And so that helps us understand the aquifer system, the different earth materials in the subsurface go stepping way back to my geology training here is we can use this water chemistry to help us identify which geologic units are in different parts of the aquifer. And that is going to help us inform how the groundwater flows through the system.


Craig Macmillan  9:08 

Are there other tools I remember a helicopter with like some kind of antenna hanging off the bottom of it. And I never understood what that was. But I think that's part of your project, isn't it?


Geoffrey Cromwell  9:19 

Now we're getting into the geophysical work.


Craig Macmillan  9:21 

Okay, let's go for it.


Geoffrey Cromwell  9:22 

Comon joke in geophysics is, What do you want the answer to be? I love geophysicist. But geophysical tools are a way to sense the different properties of materials in the subsurface. So that helicopter that was flying had a big hoop underneath it, and this was an airborne electromagnetic system. So this helicopter flies over over the terrain, and in the signal that gets bounced back provides information on the resistivity or the electrical properties of the materials in the subsurface and so then different electrical properties can get tied to different geologic materials. So this is another way for us to map and understand this subsurface geology. It also is very sensitive to changes in salinity, saline water versus freshwater will have a different electrical conductance electrical properties, that type of system can also be used to track you know, the presence of saline water in the subsurface. And so that's another another tool there. So, in this Adelaida study, we're really getting on all these different types of data collection that then can eventually be used to interpret and holistically evaluates the hydrogeologic character of the of the aquifer here.


Craig Macmillan  10:30 

What you're referring to is the Adelaida Area Hydrological Study, which is a project with San Luis Obispo County Board of Supervisors, I believe they're funding it or funding part of it. And let's just use that as an example. Obviously, we are involved in it, but I think it's a good case study. Overall, the kinds of things that you folks do tell us about that project. How did it start? What is it and what are you doing?


Geoffrey Cromwell  10:54 

Yeah, Adelaida hydrological study is in northern San Luis Obispo County. And this was a study partnership or in cooperation with the San Luis Obispo County flood control and Water Conservation District there are a cooperator here, the Adelaida area is the west part of the city of Paso Robles. And this is a, you know, a highland upland kind of rolling hills. It's even some more sort of steeper mountain type terrain. So it is not a classical eluvial Groundwater eluvial Basin aluvium would be unconsolidated sands and gravels and some finer materials that tend to erode off the hillsides that will fill the cemetery depressions. That's often where a lot of agriculture and people live with water is extracted from these groundwater basins because water is historically more readily available. But in the Adelaida area, this is a relatively small population of local residents, there is been a presence of agriculture for some time, many, many decades.


Craig Macmillan  11:55 

More than a century.


Geoffrey Cromwell  11:56 

The county asked us to do this study to evaluate the groundwater resources and learn what we can do to concerns from from landowners about a potential overuse of water, concerns at some local wells might be going dry. And so the county wants to understand the groundwater system. And so it's a bit just typical of USGS. What are the data? What are the interpretations and make that information publicly available that then the county or any other entity can then make decisions on what actions to take.


Craig Macmillan  12:25 

But how did that proceed? We've talked a little bit about the kinds of data that you collect. But what's the actual what was the actual timeline like and what's the future timeline like?


Geoffrey Cromwell  12:33 

Projects started, we got funded just before COVID. So it was end of the very early 2020, I believe. And we spent that that first year of with the county, we said that USGS would compile all available data that we could find. And so this particular area because of the small population, you know, relative perceive low impact. There hadn't been any hydrologic or geologic studies in the area, besides some some broad geologic maps and regional geophysical investigations. So this was really an unknown, I should say, publicly unknown, because you'll local farmers and local residents who've been there for decades or centuries, they know what what is in on their land, and you have a sense of of the world there. So we were trying to compile we can from what we would use, and maybe in a report to help us just understand as we're coming in, what's the geology? What are changes in land use? What groundwater information is there that might be available to help us think about, okay, how do we then collect new data? Where do we go? What do we do? So we compiled data for a year and evaluate and learn just what we could have the area. Now we're on our second phase of the study, which is collecting groundwater level data, and surface water data and water quality data for a period of just about two years. And so we're taking groundwater measurements every three months. And we have a series of just about 60, groundwater wells that were that were taking water levels from all around the Adelaida area. And we are being able to see seasonal shifts in in groundwater, as you know, recharge generally occurs in the winter months with with rainfall. And then we also see in some places where water levels might be increasing more versus others. And so that'll be as we're collecting this data will be interesting that as we get to the interpretation phase, what does that mean?


Craig Macmillan  14:25 

One thing that I think is interesting, so like you said, there's a kind of the classical groundwater basin idea, which in my mind is kind of a big bathtub. So everybody pokes a straw into the same Slurpee, essentially, and then rain falls and it refills but these mountainous areas and the rolling topography is a little bit different in like, for instance, in in the scope of this area that you're studying is all the water below the ground. Is it all connected, or is it isolated from each other? Or could it be I know you're really in your study.


Geoffrey Cromwell  14:53 

What is likely to occur where we have these geologic structures with hills and folds is that you know, although There's groundwater is present everywhere, what will be interesting to see is how the structure of the geology affects where groundwater flows and is present. So it's possible someone coming in one valley, a person in a nearby valley may or may not see the effects of that pumpage in their groundwater wells. And so we have groundwater monitoring wells has dispersed across the areas, we were able to find the hope of identifying then whether or not different areas are connected, what the effects are between the shallow and deeper systems of the of the aquifer, based on the geologic structures. So it's really is this dynamic and complex question that we're looking to to learn more about.


Craig Macmillan  15:44 

This is an idea that I just thought of, because it comes up in the local conversation, and that is, when water starts to become scarce. The solution in some people's minds is to drill a deeper well, just very expensive in the kind of geology you're talking about. That doesn't necessarily sound like that would work. Is that accurate statement? Or? Or even in a groundwater basin? Is there a limit to kind of how long that straw can be and still be be affected?


Geoffrey Cromwell  16:13 

That's interesting question that would be on a probably a basin by basin or area by area question. In general, though, the deeper you go, the more poor the water quality can be. And that's not to say that 100 feet is great and 200 feet, it's going to be hyper saline everywhere. But groundwater basin dependent area dependence, the fresher, more usable water was going to be closer to land surface. And so that gets into the question of water quality. And so just by digging, drilling a deeper Well, there could be other impacts or concerns that one might have in drilling deeper.


Craig Macmillan  16:50 

Water is not necessarily water everywhere. Oh, this is a question that someone asked me does water have an age? Can you tell when it fell from the sky?


Geoffrey Cromwell  17:00 

Yes, that is one of the neat things to learn from either water quality samples that we get. So we test for and we'll go into water chemistry, we'll sample for major and minor ions, calcium, magnesium, sodium, we'll measure for nitrates. And those types of constituents are useful for identifying the aquifer system, what rock are we in, and that will collect the stable isotopes, hydrogen and oxygen. Those allow us to tell from what elevation or area to groundwater recharge. So you expect water to be coming in the mountains and flow down and we should be able to see that indicator in those stable isotopes. And then the two age constituents we usually measure would be for tritium. And then we'll also be for carbon 14. So carbon 14 is probably one that most people are aware of, or heard of, right, you take clean organic materials, and you can get a sense of age back to think about 50,000 years old. So we can directly measure can estimate of groundwater age, many groundwater basins in California, oftentimes, the water can be 10,000 years old or so oftentimes, much more. Than tritium is neat, because tritium allows us to tell if water has been recharged since about 1950. So tritium was naturally occurring in the atmosphere. But in the 1950s, during all the nuclear tests, tritium within is released in the atmosphere in great abundance. And so if tritium is present in groundwater, above background levels, we are very confident that that water recharge since 1950, we have these age measurements of groundwater, that you within a study area, we get a sense of where recharge is occurring, and whether it's recent recharge, or old or older recharge, and so that can help understand that aquifer dynamics,


Craig Macmillan  18:39 

That's fascinating. Just blows my mind. Future timeline. So you're well levels, stream gauges, chemistry, this radiological kind of stuff, you're in the middle of the data collection, what's going to happen after that?


Geoffrey Cromwell  18:54 

We're in the middle of our of our data collection, like you said, we have about one more year of groundwater level measurements that we will take as part of the current the current agreement with the county and then the surface water will also continue for just about another year. And then we're going to have conversations with the county to hopefully take the the next steps. And that could include additional, you know, ongoing groundwater monitoring, surface water monitoring, always value in developing these long term records. And so being able to track seasonal cycles, ideally decades, right? Because then you can really see how things are changing. So there could be value in continuing this monitoring effort. And then the next step would be to put up an interpretive product. And so basically take the data that we've compiled in look at the how the aquifer system changes, look at the age of the groundwater, look at the flow paths and maybe you know, understand if there are structural controls to groundwater flow. The next phase of our project will kick in probably early 2025. In the conversation with the county and possible we could we could start sooner the era Boerne em that we mentioned before the helicopter with a big hoop flying under that, we're using that right now to help construct a geologic framework. And so that's product that we should be able to, we anticipate being able to put out next year or so. So there will be some interim bits in there. But one thing is very important in the USGS does is that all the data we collect is publicly available. So as we go out, and we take our groundwater level measurements, that will be out again in August in the Adelaida. area, within a couple of days, that data is online, it is accessible, it is viewable by the anyone in the world can can go to our website and look at this data. And so the transparency of that is valuable, just just that real time knowledge of the Earth system is I think, hugely important, valuable.


Craig Macmillan  20:48 

These wells and the streams and whatnot, they're gonna oftentimes be on private land. So you're gonna have to find participants that will let you come in and take your measurements. How did you go about recruiting participants? And also, I would guess that you would want to have wells in particular spots of interests to help you with your mapping your data collection, how did how did that process work?


Geoffrey Cromwell  21:14 

There's a lot of initial interest in the study itself. From the get go, there were there was a pool of several dozen interested landowners who were more than willing to provide access to let us just access their property and, you know, take these groundwater measurements, and allow us to, you know, install stream gaging equipment on there, you know, we spent the first part of of our data collection, part of our agreement there, identifying additional landowners. And so some of this was was word of mouth, we've been holding at least once a year, a community meeting specific to the Adelaida study. And so we've garnered more interest and think as we've explained more what the study is and purpose and the outcomes and the projected outcomes in terms of reports, we've gotten more interest in that sense. And sometimes we're just out knocking on doors and looking for it, like you said, there are some some geographic holes, if you will, of where we either we can identify the landowner or the land owner says no, which is fine. But also, we just haven't had luck contacting or reaching out or finding anybody in those particular spots. So we're especially interested always in deeper wells, so anything you have, if you only have hundreds of feet deep, more than a few, but a well, more than 500 feet deep, we'd love to come back. That'd be definitely a value to it to the study. But we've had very good conversations with landowners across the Adelaida area, and some have granted permissions and some said no, and, you know, we say thank you, we keep moving. So it is ongoing. And I think it's we the next community meeting, hopefully will be this fall before the end of the end of the calendar year. And we'll be able to share some of our next set of studies, you know, outcomes, what we've done, and hopefully talk to folks and continue to identify geographic areas that we can use more data in.


Craig Macmillan  23:00 

Cool, that's neat. Individuals within communities recognize the value to themselves, but then they also recognize and feel like they have a responsibility to the rest of the community. And I think it's pretty cool that we're seeing folks step up to be participants. And I encourage people nationwide if they're, if you're listening, and to not be afraid, I can speak for the company that I worked for Niner wine estates were a participant. When I first heard about this, I jumped, I jumped all over it. I was like, This is so cool. But also I had questions about our own property. Our location is such that there's lots of other neighbors, both residential and agricultural, but also we have wells in different different spots. And we could just look around and see, hey, is the geology between these wells? Is it the same? Is it different? What can we learn from what you guys learn? So there was kind of a two fold piece to that. And I think that that's really important for communities to do. We got a couple of minutes left, you're also working on a project in Santa Barbara County in the San Antonio Creek area. Can you tell us just just a little bit about that? Because that's a different kind of project.


Geoffrey Cromwell  23:00 

Yes. Let me go back to the last thing you said about about participants. Yes, this is free. We it's paid for by taxpayer dollars. But these are essentially free groundwater level measurements and free water quality if we take water quality. So like you said, there's there's there's value in knowing what's under the ground in your well your spot. And if you're interested, then we might be able to accommodate, obviously, constraints and things from the study public interest.


Craig Macmillan  24:28 

That's right USGS is here for you. Well, it's true. I mean,


Geoffrey Cromwell  24:31 

Yeah, no, I was gonna say we're, we're with the government. We're here to help word. 


Craig Macmillan  24:35 

Yeah, exactly.


Geoffrey Cromwell  24:37 

We really, we really are.


Craig Macmillan  24:40 

And you folks have been great to work with, by the way. I really appreciate it. Yeah. So just a little bit, a little bit about the San Antonio Creek project.


Geoffrey Cromwell  24:48 

The San Antonio Creek project. This is San Antonio Creek is the groundwater basin in Northern Santa Barbara County. And so that's a Santa Barbara County is the county directly south of San Luis Obispo. San Antonio Creek is a coastal groundwater basin. So to the west is the Pacific Ocean. And then to the east is the other Highland and upland areas. And this is a project in cooperation with the Santa Barbara County Water Agency and Vandenberg Air Force Base, there was recent legislation. And at this point about almost 10 years ago in the state of California called SIGMA, the Sustainable Groundwater Management Act. Part of SIGMA process was identifying groundwater basins of high and medium priority, those types of basins were required to by the state to develop groundwater sustainability plans to basically manage groundwater resources into the future. And this is one such basin, San Antonio Creek. And so our work USGS work here has been to provide this holistic hydrogeologic characterization of the groundwater basin. So looking at historical groundwater trends, current groundwater trends, identify the groundwater budget, so how much water is coming out how much water is coming in naturally, and then also to develop a miracle groundwater flow model. So that's pretty typical of a lot of our California Water Science Center availability projects is we we look at the geology look, the groundwater, okay, this is what's been happening. And then we feed that we develop a computer model of that. So the computer model is then a simulation of the earth as we can best understand it and model it in, which is neat, because then you can if you've modeled the historical system, then you can project into the future. And you can see like, Okay, what happens if the climate is drier? Okay, what if we're anticipating, you know, a two fold increase in population, we need to pump more for municipal needs? Or what if we're anticipating an increase in agricultural use is a tool to project changes, and then help identify how you can manage your water resources. So we develop those two products in San Antonio Creek, and I'll share both of those published sources with you.


Craig Macmillan  26:48 

Yeah, that'd be great.


Geoffrey Cromwell  26:50 

But since a creek is an agricultural basin, Vandenburg Airforce Base and the town of Los Alamos for the two municipal users, but primarily, you know, groundwater needs in the basin, this was for agricultural purposes.


Craig Macmillan  27:01 

That is really interesting. And I liked this idea of looking ahead to the future, I think we need to be thinking ahead. And the way to do that is to get good quality data on what's happening now. And to get a sense of what may be happened in the past, if we can.


Geoffrey Cromwell  27:16 

In San Antonio Creek, in the past, there's a long term record long term partnership there. And so we're very fortunate to be able to look at these decades long trends dating back to the mid 1900s.


Craig Macmillan  27:25 

Oh, wow.


Geoffrey Cromwell  27:26 

There were some that were very long term monitoring wells. And from that, you can learn a lot about that study. So this, I think that's very neat. If you're interested in learning more, this is a nice, compact little study here of investigation. We have ongoing work, keep updated.


Craig Macmillan  27:42 

Cool. Well, we're getting short on time, is there is there one thing related to kind of this water topic in the USGS that one thing that you would tell people one thing you'd like growers to know,


Geoffrey Cromwell  27:53 

The one thing for growers to know about the USGS is that the USGS is unbiased, it is nonpartisan, and most importantly, is that the data that we collect is publicly available not only allows people to access the data that's there, but it means that everyone can access it and then make decisions and see what the interpretive products are based off of here's the data. And so everything that USGS does is intended to be reproducible. It's intended to be shared, and it's in the public interest. And this is here, any number of datasets the USGS puts out, so if growers are interested in their local geology, local soils, local water, and local climate, and I'm sure there's many others there that people interested in, the USGS probably has a data set out there, or at least has historical records, you know, going to the USGS website, there's a lot of information on there, but you can find that data, you can also reach out to a local USGS office, and those are, we're all over the state many different capacities and one of us doesn't know the answer. We probably know someone who knows someone who knows the answer.


Craig Macmillan  28:58 

And again, that would be nationwide. Nationwide, where can people find out more about you?


Geoffrey Cromwell  29:02 

About me, the easiest would probably be to look at my contact on the Adelaida website, the Adelaidaa Area Project website and I'll share that with you Craig and I'm based out of our Santa Maria field office. This is in very northern Santa Barbara County. So I'm the Central Coast local California Water Science Center. We have our main project hubs are San Diego and Sacramento. And we do we do geology, we do groundwater. We do surface water, we do biology, we do modeling climate data collection, we touch a lot.


Craig Macmillan  29:29 

USGS touches a lot of different things. I want to thank you for being on the podcast. Our guest today has been Geoff Cromwell, geologist with the United States Geological Survey, specifically the California Water Science Center. Thanks for being on podcast. This is great conversation. I really appreciate you taking the time to do it.


Geoffrey Cromwell  29:45 

Loved to be here, Craig. Thanks so much.


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