Engineering a Model of the Earth As a Water Filter by Jonathon Kilpatrick, Nanette Marcum-Dietrich, John Wallace, and Carolyn Staudt

Engineering a Model of the Earth as a Water Filter By Jonathon Kilpatrick, Nanette Marcum-Dietrich, John Wallace, and Carolyn Staudt

eaching students about the wa- from groundwater. Most is supplied smaller pieces lower down,” offered ter cycle is a staple of elemen- through public drinking water sys- one student. Another replied, “A lot of Ttary science instruction. When tems. But over 15 million families rely sand is mixing with the water though, asked to describe the water cycle, most on private, household wells and use and now it looks really dirty. Maybe students can quickly recite the contin- groundwater as their source of fresh sand should go first.” These conversa- ual cyclical process of condensation, water” (EPA 2016). Noting the im- tions continued throughout the design precipitation, and evaporation. But portance of infiltration in the water process. this simple definition misses the es- cycle and in the supply of essential By the end of the session, the stu- sential process of infiltration. Ground- groundwater led us to develop an engi- dents had constructed three filters. water and the process of infiltration, neering activity in which students are Two of them were stackable filters which cleans that water, are vital to our challenged to build a stackable filter with the water passing in turn through survival, but they are also hidden from using the Earth process of infiltration different layers and materials. The view and too often absent from our sci- as a model. third was a single cup with all of the ence curriculum. materials mixed together. When the Infiltration is the process by which filters were tested, all of them filtered WATER FILTRATION water is naturally filtered by the Earth. the water remarkably well. There was a Rain falls on the Earth’s surface and ACTIVITY noticeable difference in the before and seeps into the ground. The type of soil On a sunny summer afternoon, our after samples of water. particles and vegetation covering the team of teacher researchers met with soil influences infiltration rate. Soil a small group of students and a pile FIGURE 1 pores exist between particle types and of materials (Figure 1). During one of are occupied by water and air. Some of the activities, students were presented Materials (per group). this water soaks deeper into the ground with a large pitcher of “gross” (as they through layers of humus (organic de- described it) water full of dirt and • 6 clear plastic cups bris such as twigs and leaves), surface debris found outside. Make sure stu- soil, subsoil, gravel, sand, and other dents properly wash hands after work- • Pushpins (30 or so) particles, creating a macropore filtra- ing with soil. • Coffee filters tion system and joining the ground- Students were asked, “Can you fil- • Rubber bands (5-10) water storage areas called aquifers that ter water?” Students were instructed are important resources for drinking how to build a stackable filter with • Cheesecloth (1 sq ft., water. cups and pushpins. They were then minimum) An amazing thing happens as left to their own creativity. Using the • Sandwich bag of aquarium this water travels through the layers cups and pushpins plus sand, charcoal, sand of the Earth. During its travels, it is cheesecloth, gravel, and rubber bands, • Sandwich bag of aquarium cleaned. In fact, it is this macropore they experimented until they found charcoal filtration that aids the cleansing pro- what they considered to be the best cess by trapping “dirty” particles in possible way to filter the water. “What • Sandwich bag of aquarium gravel the pores between different soil types. if we pour the water through the gravel According to the Environmental Pro- first to catch the big stuff, then the • “Dirty” water (water mixed tection Agency (EPA), “About half charcoal, then the sand? That would with dirt and debris) of our nation’s drinking water comes work the best because it would catch

www.nsta.org/elementaryschool • 73 74 • • • sponses werethoughtfulandvaried: were inspiredbynature. Their re- students tothinkofinventions that the question,however,weasked water?” Before asking “Can you filter sented themwiththesamechallenge, activity,afternoon filtering wepre- When the students convened for the THE EARTHAS AMODEL modeledafter Earthprocesses. a filter ing devices,wewantedthemtocreate - merely constructinginterestingfilter systems thatexists:Earth.Insteadof filtration one ofthemostefficientwater in by seekinginspirationfortheirfilters think asscientistsandproblemsolvers create theirstackablefilter. tration andthematerialstheyusedto - waterthroughinfil the Earthfilters making theconnectionbetweenhow in sciencecontent.Studentswerenot tion toaparticularproblem,itlacked ity given its focus on designing a solu- activity wasastrongengineeringactiv- and orderdidnotmatter? While the did thestudentsassumethatlayers seemed tocleanthewaterequallywell, in thesummer.Sinceallthreefilters the studentslearnedfromactivity session, wewonderedtogetherwhat “Water Science” club. In planning the few youngersiblingsinanafterschool group of15fifth-gradestudentsanda activity with a select of the filtering we setouttocompletethedevelopment Our solution was to help students Our solutionwastohelpstudents In thespringoffollowingyear, clothes inthewoods?” little burrthingsthatstickto your “Didn’t Velcro comefromthose blend intotheirsurroundings.” come fromseeingfishandanimals “Camouflage clothingmighthave described bystudents. proboscis asthe“straw-thing” The teacherintroducedtheword straws camefrombutterflies.” a straw-thing onhisface,somaybe “A butterflysucksnectarthrough •

PHOTOS COURTESY OF THE AUTHORS plicity ofthediagramwasintentional, mented rock,andbedrock. The sim- layers ofhumus, topsoil, subsoil,frag- diagram ontheboardthatillustrated university assistantthendrew asimple came fromawell. The undergraduate students responded that their water your housecomefrom?”Manyofthe “Where does the drinking water in rural area,soweaskedthestudents, various layers.” We liveinarelatively downthroughits ing watertoinfiltrate waterbyallow- own wayoffiltering told thestudents,“The Earthhasits uate student assisting with the activity did offer was the Earth. An undergrad- clean thewater. The answerstudents student thoughtcloudsmighthelpto somehow cleanwaterandanother One student wondered if waterfalls Studentshadfewideas. fective filter?” to inorderhelpyoubuildamoreef- thatyoucouldlook natural waterfilter new questionwasposed.“Istherea • water filters. dents test different materials for their As partofthedesignprocess, stu - • As theideasstartedtodwindle,a sponges.” “Kitchen spongesarelikeocean OCTOBER 2018 looks so“dirty”cancleanwater. by thequestionofhowsomething that Studentswere intrigued water filters. topsoil orsubsoilintheirEarth-model ed thatitwouldtaketheplace ofeither son—was usedforcleaninganddecid- cluded thatcharcoal—forsomerea- have toresearchthe“why,” theycon- charcoal init. fered thathermotherusessoapwith job of cleaning water.” Another of- So maybecharcoaldoesareallygood ters tocleanthewaterinmy fishtank. - right, but I think we use charcoal fil student replied,“Idon’tknowifthisis black charcoalasanexample.Another dirty,” can clean water. He held up the the variousmaterials,whichall“look layer!” humus, sothisisdefinitelyourhumus all spongy, justlikethedescriptionof “When the cheesecloth gets wet it’s • • • • were livelyandcreative: of eachmaterial. The conversations compared their notes to the attributes they sorted through their supplies and Earth. Insmallgroupsofthreeorfour, their materialswiththelayersof the box of materialsand asked toalign the students,theywereprovidedwith the drawing asamodel. as weintendedforthestudentstouse Although the students would later At onepoint,astudentaskedhow Later, onestudentcommented, Once thelayersweredescribedto we couldusethisasourhumus.” all tangledlikerootsandgrass,so and folditoverover,looks “When wetakethecheesecloth and it’s stickylikesubsoil.” the sandisharderwhenitgetswet because itlooksliketopsoiland “I thinkcharcoalshouldbefirst like thetopsoilinterrarium?” charcoal togethersothatitlooks “Can wemixthesandand fragmented rock!” “The gravel hastobethe ous water testing activities that they conducted earlier in the week using a simple chemical water testing kit. A student explained, “There are lots of things in the water we can’t see, like chlorine, nitrogen, phosphate, and there can even be bacteria in water.” Another student added, “You can’t see bacteria but, if you drink it, it can make you really sick!” They concluded that clear was not necessarily clean, depending on the definition used. “As scientists,” one student expressed, “we have to think of all of the possible definitions.” By the end of the session, four groups had created four stackable filters, each unique in the order and amount of materials used. Every group was able to explain how their filter re- created the Earth model. Though this was not a graded activity, the expecta- Students eagerly test their completed water filters. tion (and the standard against which the filters were assessed) was that the They wanted to know more about shared ideas and tested various pre- students could explain not only the how charcoal filters in a fish tank work. dictions regarding how much or how way their filter worked but also how it The students learned that there are little of each material to use as well as was an accurate model of the Earth’s pores between the carbon particles the order of layers to filter the water. filtration system. of the charcoal in the filter. As water One of the greatest benefits of using percolates through a carbon filtration the stackable filters is that each layer CONCLUSION system in an aquarium, it is cleaned. is easily moved and modified. Ad- Because the materials for this activity The “dirt” is actually organic and inor- ditionally, using clear cups (a modi- are non-hazardous and inexpensive, it ganic materials dissolved in the water. fication we made after our first trials) was easy for us to provide students in This “dirt” gets trapped in the filter. allowed students to watch the water the water science club with extra ma- This process works the same way in as it moved through the layers. This terials for the days following the wa- the ground. When water infiltrates the not only allowed for some immediate ter filtration activity. We had learned soil, particles and vegetation act like the gratification but also kept the students from our previous experiences that fish tank’s charcoal filter trapping the engaged as they could watch the water students often come in with “I just “dirt.” Indeed, the vegetation and vari- in transit rather than simply wait for thought of something” and “What ous soil types (which may look “dirty” the water to fill the bottom cup. if…?” comments and ideas after their to some), in fact, are part of Earth’s nat- A conversation presented itself initial design. Allowing students time ural and elaborate macropore filtration during the end stages of the filtration and access to materials to test and re- system in which the organic and inor- activity. The question presented to test their ideas reinforces the notion ganic materials absorb into the pores. the students was, “So, the water was that science is not a series of discrete obviously dirty when you started, and lessons, but an ongoing cycle of ideas, MORE MODELING it is clear now. Does clear water mean investigations, and experimentation, Students used the information they that it is clean water?” The students and that designing engineering solu- learned from their examination of the answered that there were different tions involves multiple iterations of materials and their research to create a “kinds of clean.” Although they all testing and revising. It also allowed us detailed sketch of their water filter de- agreed that clear water was “cleaner” to get the most use out of our materials sign in their science notebook. As the than the dirty water they started with, rather than treating them as “one and students built their water filters, they some students referred back to previ- done” activity supplements.

www.nsta.org/elementaryschool • 75 One of the most valuable classroom a filter without a humus layer (cheese- REFERENCES discussions took place after a video cloth and coffee filters) and used an United States Environmental conference with a school in Fresno, old filter cup of hardened sand as their Protection Agency (EPA). 2016. California, that completed the same topsoil layer. When water was poured About Private Water Wells. filtration activity. The students dis- into this filter, the students remarked Retrieved from: www.epa.gov/ cussed the drought conditions facing “nothing’s happening.” With further privatewells/about-private-water- the school in California and asked probing, they came to the conclusion wells whether or not they would have a hu- that infiltration in drought-affected NGSS Lead States. 2013. Next mus layer at the California school. areas is difficult, which means that Generation Science Standards: “Humus is the layer of plants and runoff is prevalent. The modeling ac- For states, by states. Washington, roots, and not much is growing there, tivity (and modeling in general), at this DC: National Academies so I don’t think they have much of point, took on a new meaning for the Press. one.” The teacher asked if the students students, as they realized that it could Soil Society of America. 2017. What thought they could build a filter for an be adapted in order to explore different is Soil? Retrieved August 30, 2018, area in a drought. The students built questions about their watershed. ● from www.soils4kids.org/about.

Jonathon Kilpatrick is an elementary teacher at Greenwood Elementary School in Kennett Square, Pennsylvania. Nanette Marcum-Dietrich ([email protected]) is a professor of science education, and John Wallace is a professor of biology, both at Millersville University of Pennsylvania in Millersville, Pennsylvania. Carolyn Staudt is a Senior Scientist at The Concord Consortium in Concord, Massachusetts.

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76 • • OCTOBER 2018 Connecting to the Next Generation Science Standards (NGSS Lead States 2013)

• The chart below makes one set of connections between the instruction outlined in this article and the NGSS. Other valid connections are likely; however, space restrictions prevent us from listing all possibilities. • The materials, lessons, and activities outlined in the article are just one step toward reaching the performance expectations listed below.

Standard 3-5-ETS1 Engineering Design www.nextgenscience.org/pe/3-5-ets1-2-engineering-design

Performance Expectation 3-5-ETS1-2. Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.

DIMENSIONS CLASSROOM CONNECTIONS

Science and Engineering Practice

Constructing Explanations and Designing Solutions Students built a filter to clean water modeled after Earth processes. Students compared their filter apparatus with a redesign.

Disciplinary Core Idea

ETS1.B: Developing Possible Solutions Students predicted how each Earth material would interact with Research on a problem should be carried out before beginning to design a the sample water. solution. Testing a solution involves investigating how well it performs under a Students tested predictions by observing how Earth materials range of likely conditions. remove different contaminants from the sample water. At whatever stage, communicating with peers about proposed solutions is an important part of the design process, and shared ideas can lead to improved designs. ESS2.C: The Roles of Water in Earth’s Surface Processes Students evaluated results to share how effective certain Earth Nearly all of Earth’s available water is in the ocean. Most fresh water is in materials are as filters. glaciers or underground; only a tiny fraction is in streams, lakes, wetlands, and the atmosphere.

Science, Technology, Society and the Environment

Influence of Engineering, Technology, and Science on Society Students understand that all human activity draws on natural and the Natural World resources and has both short- and long-term consequences, positive as well as negative, for the health of people and the natural environment. Acknowledgment This material is based upon work supported by the National Science Foundation under Grant No. DRL 1433761, 1417527. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.