The new and exciting face of waterunderground.org

by Tom Gleeson

I started waterunderground.org a few years ago as my personal groundwater nerd blog with the odd guest post written by others. Since I love working with others, I thought it would be more fun, and more interesting for readers, to expand the number of voices regularly posting. So here is the new face of the blog…

https://i2.wp.com/www.fragilestates.org/wp-content/uploads/2012/10/collective-action.jpg
a kind of weird image of collective action

What is the new blog all about?

Written by a global collective of hydrogeologic researchers for water resource professionals, academics and anyone interested in groundwater, research, teaching and supervision. We share the following aspirations:

  • approachable groundwater science at the interface of other earth and human systems
  • encourage sustainable use of groundwater that reduces poverty, social injustice and food security while maintaining the highest environmental standards
  • compassionate, effective supervision
  • innovative, effective teaching
  • transparency of scientific methods, assumptions and data

Check out more details and how to be part of the blog on about.

Frequent contributors include:

  • Andy Baker (University of New South Wales, Australia) – caves and karst (I actually visit the water underground!), climate and past climate
  • Kevin Befus (University of Wyoming, United States) – groundwater-surface interactions, coastal groundwater, groundwater age
  • Mark Cuthbert (University of Birmingham, United Kingdom) – groundwater recharge & discharge processes, paleo-hydrogeology, dryland hydro(geo)logy, climate-groundwater interactions
  • Matt Currell (RMIT University, Australia) – isotope hydrology; groundwater quality; transient responses in aquifer systems
  • Inge de Graaf (Colorado School of Mines, United States) – global groundwater withdrawal, flow and sustainability
  • Grant Ferguson (University of Saskatchewan, Canada) – groundwater & energy, regional groundwater flow, sustainability
  • Tom Gleeson (University of Victoria, Canada) – mega-scale groundwater systems and sustainability
  • Scott Jasechko (University of Calgary, Canada) – global isotope hydrology; groundwater, precipitation, evapotranspiration
  • Elco Luijendijk (University of Gottingen, Germany) – paleo-hydrogeology,deep groundwater flow,large scale groundwater systems
  • Sam Zipper (University of Wisconsin – Madison, United States) – ecohydrology, agriculture, urbanization, land use change

Just in case you weren’t sure…groundwater flow around a fault zone is complex!

By Erin Mundy – a plain language summary of part of her Masters thesis

Groundwater is the water that collects underground in pores and cracks in the rock. Understanding, protecting and sustaining groundwater flow is critical because over two billion people drink groundwater every day. The flow of groundwater can be impacted by geologic structures, such as fractures and faults. A fracture is a break in the rock; a fault is a break in the rock where the rocks move relative to each other (ie. one rock will move up, one rock will move down, as seen in Figure 1).

CTF1
Figure 1. Diagram of a thrust fault

Faults can act as barriers slowing down groundwater flow, they can be a conduit speeding up groundwater flow, or amazingly they can act both slow it down and speed it up!

How groundwater moves through these rock structures is difficult to directly observe because it all happens underground and rarely exposed on the surface. The Champlain thrust fault at Lone Rock Point in Burlington, Vermont, provides a unique opportunity to study groundwater flow around a fault because approximately 1 km of the fault is exposed along the edge of Lake Champlain (Figure 2). Here, an older rock

CTF2
Figure 2: Photograph of the Champlain Thrust fault at Lone Rock Point, Burlington, Vermont. Note the person at the bottom right for scale

(yellow) is thrust over a younger rock (black). No one has studied groundwater flow around this fault in detail, so we hoped to find out a basic understanding of the relationship between the fault and groundwater flow at this location.

To understand groundwater flow around this fault, we did three things: 1) we walked along the fault and made note of changes in the fault (ie. the width of the fault, the angle of the fault, the shape of the fault, etc.); (2) we looked for areas where groundwater was leaking from the rock surface (this is known as groundwater seepage – we wanted to see if there was a relationship between where groundwater was leaking out and the changes in the angle/width of the fault); and (3) we drilled three wells and then pumped water out of these wells. We pumped water out of one well and measured the water level in the other wells – this gives you an idea of how the groundwater moves. For example, if you pump water out of one well and the water level in a nearby well declines drastically, this suggests that the water is easily moving through the rock. So if you’re pumping water from the fault and that happens, then the fault is most likely channeling water along the fault. If the opposite happens, then the fault may be acting as a barrier to groundwater flow.

We found four main geologic structures at the Champlain thrust fault: (1) the main fault, (2) an area where the fault splayed into many smaller faults, (3) areas where the fault thickness increased to 3 m, and (4) areas where there are traces of older, cemented fault rock (Fig. 3).

CTF3
Figure 3. Most important structures we observed at the Champlain thrust fault. the thin dashed white line follows the main fault, thicker black dashed line follows the main structural features. Hanging wall is the older rock; footwall is the younger rock. a) main fault; b) fault splay; c) increased fault thickness; and d) older abandoned fault rock

We found 19 areas along the rock where groundwater was leaking out of the cliff (Note: This was done in the winter so the groundwater was frozen into ice). We found that most of the groundwater seepage occurred in the younger (black) rock, with a few at the fault and where the fault splays out into smaller faults (Figure 4).

CTF4
Figure 4. Seeps located a) at the intersection of a multi-stranded fault structure and b) at the fault core. Note measuring tape for scale (1 foot)

While drilling the two wells at the site, we had two unexpected problems. One, there was a large difference between the depth of the fault in the two wells. The fault depth in one well was 27.4m, while in the other well (which was 10 m away), the fault depth was 70 m. This suggests that there must be another fault in between these two wells that offsets the fault depth. The other unexpected complication was that we drilled into 1.8 m and 2.1 m caves beneath the ground. Caves are common features in limestone, but the rock at our site is a dolostone, which is usually more resistant, so caves are an interesting find! The pumping test revealed a complex system. Further testing is needed to better refine these results.

Combining the data from the surface and subsurface observations, we created a preliminary three-dimensional model of the Champlain thrust fault (Figure 5). Where the rock is exposed at the edge of Lake Champlain, the fault thickness varies, splaying out into smaller faults and showing traces of older fault rock. Groundwater is leaking out of the younger rock (footwall) and along the fault. At the well-site, the fault is offset by another fault and caves are present. The three approaches we used (geology, seepage, pumping tests) all revealed different aspects of the Champlain Thrust fault, and exposed the complexity of groundwater flow around faults.

 

CTF5
Figure 5. Three-dimensional conceptual model of the Champlain thrust fault.

 

Can we use an infrared camera to tell us how much groundwater is coming out of the side of a cliff?

By Erin Mundy – a plain language summary of part of her Masters thesis

Groundwater is an important resource, with approximately 2 billion people around the world using groundwater everyday. Although most groundwater is beneath our feet, sometimes groundwater leaks out of stream-banks, hill sides and cliff faces – this is called groundwater seepage. Current scientific methods are not able to measure the amount of groundwater that leaks out of these landscapes. Scientists have used infrared cameras (cameras that show the heat of an objects) to identify groundwater seepage on hill-slopes and stream banks (Figure 1).

seep1
Figure 1. Digital image (a) and temperature image (b) of a seep in the summer and a digital image (c) and temperature image (d) of the same seep in the winter

This is because groundwater has an distinct heat signal, having a relatively constant temperature throughout the year (~10 degrees Celsius). Building on these studies, we hoped to find out the possibilities and limitations of using infrared cameras to measure the amount of groundwater that leaks out of the side of a cliff. We wanted to test if groundwater was flowing out of a cliff face slowly in the summer would warm up as it traveled down the rock, so the heat signature of the groundwater would go from cool water (that comes out of the rock, ~10 °C) to warmer water (warmed due to the sun and air temperature). On the other hand, we wondered if groundwater was flowing fast out of the cliff-face, it would not have time to warm, because the cool groundwater would be consistently running over it. In the winter, we believed the opposite would happen, that the groundwater would be warmer, relative to the surroundings, and show a cooling trend as the water traveled down the rock.

 

We found an unused mining pit in Saint Dominique, Quebec, that had lots of groundwater seeps coming out of the exposed rock, and used this as our test location. The mining pit had 3 different levels, as shown in Figure 2.

seep2a
Figure 2: an aerial shot of the quarry with the seeps labeled.

We took infrared and optical photographs of the seeps during seven visits that spanned from January 2013 – October 2014. Three visits took place during the winter (January – February 2013), coinciding with periods of below freezing so that the effect of extreme cold on seeps could be analyzed. Four visits took place during the summer/fall (June – October 2014), coinciding with sunny and hot conditions, and cloudy and warm conditions in order to determine the effect warmer temperatures have on seepage. In addition to these visits, we also completed a 24-hour experiment, where we took infrared pictures of two seeps every half hour for 24-hours, to determine the effect of sunlight and changing air temperature on the seep temperature signature. We also created an “artificial seep” experiment, where we released water from two large tubs over the cliff at the pit for 8 hours; one tub had water released at a slow rate, while the other at a faster rate, to see if we could replicate the heat signals from the real seeps. We took pictures with the infrared camera every half hour for eight hours for that experiment. We analyzed the infrared photos from each visit using a computer software that allowed us to determine the temperature along the seep.

In the winter, groundwater flows out the rock at warmer temperatures than it’s surroundings, making it easily distinguishable. We found that there was a clear relationship between seeps with active groundwater flow and areas of ice growth on the following visit. So, in the winter, if you use an infrared camera to locate where groundwater is flowing on the side of a cliff, you can assume there is a good chance that ice will eventually form at these spots. However, the groundwater did not cool along the rock face, as we had expected it would. This suggests frozen seeps are complex and it is unlikely that temperature pictures can determine the rate of flow of groundwater seeps in the winter.

In the summer, we found that lower flowing seeps did warm up as the water traveled down the rock face, as compared to faster flowing seeps, which did not show as much warming. However, in the 24-hour experiment (where we took infrared pictures every half hour for 24 hours of two seeps), we found that the temperature signature of the seeps changed throughout the day. During the day, there was much more warming of the groundwater as it traveled down the cliff, whereas at night it did not warm as much. This is most likely due to the presence of sunlight and warmer air temperature during the day, which warms the water more as it is traveling down the rock.

In the “artificial seep” experiment, we found that the “seeps” showed more warming than the real seeps. This is probably because we only ran the experiment for 8 hours, so it did not have time to mimic the conditions of real seeps. Also, we noticed that instead of flowing down the rock face, some of the water was actually seeping into the rock, along the breaks in the rock. This may be another reason why the seeps showed more warming, as not enough water was flowing down the rock (instead it was flowing into it).

After completing these experiments, we have concluded several possibilities and limitations for infrared pictures of groundwater seeps.

Possibilities:

  • Locate groundwater seeps in all seasons
  • Locate groundwater seeps in winter and from this, areas of ice growth can be predicted
  • Distinguish between lower flowing seeps and higher flowing seeps in summer (lower flowing seeps have more warming as the water travels down the rock face, higher flowing seeps do not have as much warming)

 Limitations:

  • Need to have a large difference in temperature between the air and groundwater to notice seeps. During the third winter visit, only one seep was identified to be flowing by the infrared camera. However, visual observations showed that eight seeps had groundwater flowing. This is because the temperature of the groundwater was too similar to the temperature of the air, making it not possible to detect the groundwater flow.
  • Groundwater seeps in the winter are complex and do not show a cooling trend, therefore it is unlikely that temperature pictures can determine the rate of flow of groundwater seeps in the winter
  • Breaks in the rock affect the flow of seeps, redirecting the flow, making it hard for temperature pictures to accurately determine flow
  • Sunlight and air temperature affect the “warming” and “cooling” of the groundwater flow, with more warming present during the day and less at night. Focus needs to be on determining the optimal time to use infrared pictures to show the “warming” (or “cooling”) trend.
  • The infrared camera itself has limitations. To use some functions of the camera, you have to correct your data for certain factors (like angle of the camera, humidity, etc.). If you don’t, you won’t be showing accurate data. This limits the amount of things you can do with the infrared camera and must be taken into account in order to ensure the pictures you captured are correct.

 

Despite the large number of limitations, infrared pictures is effective at locating groundwater seeps in all seasons, and able to distinguish between lower flowing seeps and higher flowing seeps (in the summer), which makes this technique a valuable, non-invasive way to study groundwater seepage. Future work should look at determining the optimal time to capture infrared pictures of seeps to determine a relationship between groundwater flow and temperature signatures.

 


 

Baseflow, groundwater pumping, and river regulation in the Wisconsin Central Sands

By Sam Zipper, postdoctoral fellow at Madison and author of tacosmog.com

We often think of groundwater as a nonrenewable reservoir, deep underground, and with good reason – less than ~6% of groundwater globally entered the ground within the past 50 years. However, where a river or stream intersects the water table, water is able to move from the aquifer to the stream (or vice versa). This supply of shallow groundwater to streams is called ‘baseflow’, and is an important supply of water for many streams worldwide, especially during dry seasons or periods of drought. Below, we can see that baseflow makes up more than 50% of total streamflow over most of the world:

global_baseflow
Global estimates of baseflow index – the proportion of streamflow that comes from groundwater or other slowly varying sources, like upstream lakes and wetlands.

The ability of groundwater to contribute to streamflow depends on the water level of the aquifer in the area surrounding the stream. Therefore, human actions that lower groundwater levels (such as pumping for urban or agricultural use) can impair the ability of an aquifer to supply water to streams during dry periods, with potentially devastating consequences for streamflow.

One example close to my home is the Central Sands region of Wisconsin, which is a large region found (not surprisingly) in the center of the state with particularly sandy soils. The sandy soils are perfect for growing potatoes, and the Central Sands is primarily an agricultural region; however, because water drains quickly from sandy soils, irrigation has become an increasingly important part of the landscape:

centralsands

In addition to agriculture, however, the Central Sands region is home to many rivers, lakes, and streams. Recently, one river in particular has become a microcosm of the debate surrounding the impacts and trade-offs of agricultural water use: the Little Plover River. While only 6 miles long, the Little Plover is a prized brook trout fishery and important ecosystem within the region. According to American Rivers, which listed the Little Plover as one of America’s 10 most endangered rivers in 2013, streamflow in the Little Plover has been decreasing since the 1970s and flows today are roughly half of the historical normal. The situation in the Little Plover came to a head in 2005, when several stretches of the Little Plover dried up, with predictably negative consequences for the fish.

Over the past decade, the Little Plover has been mired in legal controversy. In 2009, the Wisconsin Department of Natural Resources established what they call a “Public Rights Flow”, or a required amount of streamflow that the public is entitled to flow through the river. The advocacy leading to the establishment of this Public Rights Flow was primarily by conservation groups like the River Alliance and Trout Unlimited, with the goal of protecting fish and the rest of the stream ecosystems. In order to set the threshold, the Wisconsin Department of Natural Resources first established a baseline level as the 7-day average low flow with a 10% probability of occurring in a given year, and then adjusted this value upwards based on estimates of the flow necessary for to provide fish habitat and recruit trout. Despite the positive step of establishing a Public Rights Flow, measurements during the 2012 drought were consistently below the thresholds set by the Department of Natural Resources, and the Little Plover even dropped below the thresholds in 2013 and 2014, both of which were relatively wet years for Wisconsin.

plover
The Little Plover in 1997 and the first time in ran dry in 2005 (Friends of the Little Plover)

The current debate surrounding the Little Plover hinges on whether the Department of Natural Resources is legally allowed to consider cumulative impacts when permitting new high capacity wells in the region. Previously, the Department of Natural Resources was not considering cumulative impacts, which means that for every well application, they are only allowed to think about that well in isolation – and the effects of a single well are typically small enough that the Department of Natural Resources does not have sufficient grounds to deny a permit. However, the relatively small impacts of many individual wells can add up to cause a big overall effects on local groundwater resources. This changed in 2014, when a judge ruled that the Department of Natural Resources should be considering cumulative impacts. The effects of this ruling remain to be seen, but it improves the DNR’s ability to manage groundwater and surface water resources while considering the interactions between the two.

Thus, the Little Plover River provides a powerful example of a case where a little bit of groundwater drawdown can lead to big environmental, political, and economic issues. Currently, hydrogeologists at the Wisconsin Geological Natural History Survey and USGS Wisconsin Water Science Center are working on developing a groundwater flow model of the region to help understand the impacts of groundwater withdrawals on the aquifer, and what that means for local surface water features like streams and lakes. Because the waters of the Central Sands are valued for many different uses, including farming, urban supply, and outdoor recreation, the team building this model has been working closely with different groups of users to determine the priorities and needs of the various water users the region, and make sure that their scientific tool they develop is both useful to and trusted by the decision-makers in the region. As the future of the Little Plover and other rivers unfold under increasing human pressures and climate change, it is critical that water scientists work together with the public to conduct fair and unbiased science that provides timely and useful information for the decision-making process.

Tracking the Fallout and Fate of Fukushima Iodine-129 in Rain and Groundwater

This post is written by Matt Herod, and reposted here with permission…

A recently published paper (by myself and colleagues from uOttawa and Environment Canada) investigates the environmental fate of the long lived radioisotope of iodine, 129I, which was released by the Fukushima-Daichii Nuclear Accident (FDNA). Within 6 days of the FDNA 129I concentrations in Vancouver precipitation increased 5-15 times above pre-Fukushima concentrations and then rapidly returned to background. The concentrations of 129I reached were never remotely close to being dangerous, however they were sufficient to distinguish the impact of the FDNA on the region.

Subsequent sampling of groundwater revealed slight increases in 129I concentration that were coincident with the expected recharge times. This suggests that a small fraction of the FDNA-derived 129I may have been transported into local groundwater after infiltrating through soils.

Iodine129_Precip_Sample_BC_JP

What is iodine-129 and where does it come from?

Iodine-129 is the longest lived isotope of iodine with a half-life of 15.7 million years. It is radioactive and occurs everywhere throughout the environment. It is produced in three ways. The first two are natural and the third is by the nuclear industry.

The natural production of 129I occurs in the atmosphere and in soil/rocks. The atmospheric production happens when a cosmic ray proton hits a xenon-129 nucleus and removes a neutron, replacing it and creating an iodine-129 nucleus. The production in soil and rocks happens when a uranium-238 nucleus spontaneously fissions and one of the halves it releases has a mass of 129 ala, iodine-129.

The anthropogenic production occurs because when uranium fissions in a nuclear reactor sometimes one of the parts is 129I. This anthropogenic production is by far the largest source in the environment as substantial amounts have been released by nuclear fuel reprocessing. This 129I that has been released can trace a host of environmental processes and inform us about what happens to 129I or the much more dangerous, 131I. The current levels of 129I are much too low to pose a health threat to humans or the environment, but do allow 129I to be used as an environmental tracer.

129I from Fukushima is present in Vancouver, B.C. rain

The purpose of this research was to discover the fate of 129I in the released by Fukushima, which although a small amount, was isolated in time and space. We measured the 129I deposition in rain and its subsequent movement though soils and see if it reached groundwater. The results tell us about the impact of Fukushima, how 129I moves, where it is attenuated, and how quickly contaminants in this aquifer move from the ground surface to the water table. This knowledge can then be applied to understand 129I behavior in other settings such as nuclear waste repositories and watersheds or it can be used to learn about the behavior of other types of contaminant in this aquifer and how vulnerable it is to contamination.

The results in rain show an increase in 129I concentrations of up to 220 million atoms/L*. This increase was seen ~6-10 days after the emission from Fukushima began and are 5-15 times higher than rain samples collected before Fukushima. Following this increase 129I concentrations returned to background with a few weeks. This agrees with other studies monitoring the fallout of Fukushima derived radioisotopes [Wetherbee et al., 2012]. Furthermore, atmospheric back trajectory modelling shows trajectories for air parcels arriving in Vancouver from over the Pacific ocean and Japan.

Figure2_129IPrecip

We also calculated the mass flux of 129I from Fukushima. That is the actual quantity of 129I that was deposited on the region in grams, or in this case in atoms/m2. This was calculated by simply multiplying the concentration of 129I in rain by the amount of rain that fell. We found that only about 15% of the annual 129I deposition in the Vancouver region could be directly linked to Fukushima affected rain events. The total mass deposited by Fukushima was ~0.0000000000002 (2 x 10^-13) grams. This is a negligibly small quantity with respect to radioactive risk.

Despite the fact that the deposition of 129I from Fukushima was infinitesimally small it was still measurable. Therefore, the question became where did it go and can we learn about local groundwater resources using 129I as a tracer?

129I variation in groundwater may be due to Fukushima

The results in groundwater show very small 129I concentration increases. Two different wells were sampled. The first had a recharge time, which is the time it takes for water to move from the water table to the well screen, where it is sampled, of 0.9 years and the second had a recharge time of 1.2 years [Wassenaar et al., 2006]. The exact time it takes for water and dissolved contaminants to travel through the unsaturated zone was unknown. However, the sediments of this aquifer are very coarse and are known for their ability to rapidly transport contaminants, such as nitrate [Chesnaux and Allen, 2007]. Therefore, if we were going to see 129I from Fukushima this was an ideal location.

The increases in groundwater 129I concentrations were seen in two different wells (ABB03 and PB20) located close to one another. The two wells also had slightly different recharge times. The first was 0.9 years and the second was 1.2 years. The 129I anomaly in the first well occurred at 0.9 years and in the second well at 1.2 years. These 129I anomalies, which occurred exactly when the recharge age predicted they would, suggests that some of the 129I deposited by Fukushima was reaching the wells and causing these increases.

Gwater_129Iconc

In order to verify if it was possible for 129I to travel from the ground surface to the water table in the time required to produce the variations observed we modelled its transport time and attenuation through the unsaturated zone.

The time it took for 129I to reach the water table in the model was then added to the previously dated recharge time to get an estimate for how long it might take 129I from Fukushima to reach the wells we sampled. The results show that it is indeed possible for 129I deposited in rain to infiltrate through the unsaturated zone and reach the wells in time for us to detect it. However, this rapid transport assumes that certain flow paths exist to rapidly conduct 129I due to the heterogeneous lithology of the unsaturated zone. There is evidence of such flow paths [McArthur et al., 2010].

To summarize,

 

  • Within a week of the FDNPP accident elevated 129I concentrations were observed in precipitation. This agrees very well with work on other radionuclides in air filters and rain.
  • 129I concentrations in rain returned to background within a few weeks. However, discrete pulses of elevated 129I occurred for another several months.
  • Elevated 129I concentrations were measured in two wells and corresponded with the expected recharge times indicating that 129I from Fukushima can be traced into groundwater.
  • Vadose zone modeling has shown that 129I can be rapidly transported to the water table and reach the well screen in accordance with groundwater ages.
  • We propose 129I transport is enhanced by preferential dispersion of 129I that exists due to the heterogeneous nature of the vadose zone.
  • This results in variability in groundwater 129I concentrations that preserve the variability in the input of 129I via washout with some dampening of the signal due to attenuation and dilution.

 

 

Fukushima Model

 

Thanks for reading, if you have any questions or concerns please leave a comment or send me an email to discuss further!

*Note: 100 million atoms/L of 129I is equivalent to an activity of 0.00000014 (1.4 x 10^-7) Bq/L. These quantities are extremely low level and only the most sensitive analytical methods in the world can detect them. This amount of radioactivity is several orders of magnitude lower than the natural background radiation produced by naturally occurring radionuclides in soil and the atmosphere. For more on naturally occurring radioactivity see here. Even a clean rainfall has about 1 Bq/L of tritium (radioactive hydrogen), which remains from atmospheric weapons testing in the 1960’s

Access the full paper here: http://onlinelibrary.wiley.com/doi/10.1002/2015WR017325/abstract

References

Chesnaux, R., and D. M. Allen (2007), Simulating Nitrate Leaching Profiles in a Highly Permeable Vadose Zone, Environ. Model. Assess., 13(4), 527–539, doi:10.1007/s10666-007-9116-4.

McArthur, S. A. Q., D. M. Allen, and R. D. Luzitano (2010), Resolving scales of aquifer heterogeneity using ground penetrating radar and borehole geophysical logging, Environ. Earth Sci., 63(3), 581–593, doi:10.1007/s12665-010-0726-9.

Wassenaar, L. I., M. J. Hendry, and N. Harrington (2006), Decadal geochemical and isotopic trends for nitrate in a transboundary aquifer and implications for agricultural beneficial management practices., Environ. Sci. Technol., 40(15), 4626–32.

Wetherbee, G. A., D. A. Gay, T. M. Debey, C. M. B. Lehmann, and M. A. Nilles (2012), Wet Deposition of Fission-Product Isotopes to North America from the Fukushima Dai-ichi Incident, March 2011, Environ. Sci. Technol., 46(5), 2574–2582.

Nature Geoscience digging into water underground this month!

Nature Geoscience is digging hard into water underground – the February issue is part of a special focus on groundwater. The cover this month is a gorgeous (groundwater-filled?) waterfall by Glen Jasechko, Scott’s brother.  The groundwater focus includes:

As part of the focus the journal made our paper on modern groundwater free to registered users for a month – so go download it an check out this and the other papers too!

Multidisciplinary research and active learning about groundwater

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