Classroom activity Grade 9 Science

Kestrelford Wellfield: A Sand-Tank Groundwater Model

A 50-minute grade 9 activity where student teams build a sand-tank aquifer, trace dye toward a stream, then pump a well and watch the flow direction reverse.

Grade: Grade 9
Subject: Science
Material: Classroom activity
Time: 50 min
Prep: Moderate prep
Materials: Clear plastic bin or small aquarium per team, Clean coarse sand, Pea gravel, Food coloring, Clear plastic straws or tubing, Large syringe or turkey baster, Small pitcher of water, Cup to hold pumped water, Paper towels

Standards

HS-ESS2-5 NGSS

Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

How this material aligns: Teams conduct a sand-tank investigation of how water moves through sand and gravel and how pumping changes that movement, an investigation of water's effects on Earth materials of the kind this standard describes.

All materials for HS-ESS2-5 →

RST.9-10.3 Common Core ELA

Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.

How this material aligns: Teams follow a multistep build-and-test procedure precisely, attending to the stated exceptions about saturating sand slowly and adding dye without disturbing the surface.

All materials for RST.9-10.3 →

Download Word file

This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-04.

Objectives

Students will build a physical model of an aquifer with a water table and a discharge point.
Students will trace the direction groundwater moves before and during pumping.
Students will explain how a pumping well changes which contaminants reach a water supply.

Vocabulary

Porosity: Porosity measures how much empty space a rock or soil has between its grains, which tells you how much water it can hold. A sponge has high porosity, while a piece of glass has almost none.
Water table: The water table is the underground level below which the ground is completely soaked with water. Dig a hole deeper than the water table and it will start filling with water.

Also: hydraulic gradient, capture zone, discharge, plume

Teacher overview

Groundwater is invisible in the field, which makes it easy for students to picture underground rivers rather than water creeping through the spaces between sand grains. This activity has teams of three or four build a small sand-tank aquifer in a clear bin, watch dye travel toward a model stream, and then pump a straw well and watch the same dye turn and travel the other way. The model shows the concept directly, because the direction the dye moves is the direction the water is moving, and the change that appears when the pump starts is the well's capture zone. The scenario is the fictional Kestrelford wellfield, where a spill has been found between the town's wells and the river.

Activity Directions

1. Setup (8 min). Form teams of three or four and give each team a clear bin, sand, gravel, two straws, a syringe, food coloring, and a pitcher. Assign roles: one builder, one water keeper, one recorder, and, in teams of four, one timekeeper. Tell teams the scenario. In the fictional town of Kestrelford, two wells sit between an old fuel storage yard and the Kestrelford River, and the town wants to know whether pumping the wells will pull the spill toward them.

2. Build the aquifer (10 min). Teams pour sand into the bin to a depth of about four inches, sloping it slightly from one end to the other. At the low end they dig a narrow trench across the full width and line it with pea gravel; this trench is the river. They push two straws vertically into the sand near the middle of the bin, twisting rather than jamming so the sand stays packed around them. These are the wells. Then the water keeper adds water slowly at the high end of the bin, where the fuel yard will be, until the water surface in the trench sits about half an inch deep. Adding water slowly matters, because pouring quickly channels the sand and ruins the model.

3. Station A, natural flow (8 min). Each team places three drops of food coloring on the sand surface at the high end of the bin, at a spot they label the fuel yard, without stirring or pressing the surface. From now until the end of Station C, the water keeper keeps trickling water slowly into the high end from the pitcher, at the end wall just behind the fuel yard, so the water table stays sloped toward the trench. Recorders sketch the tank and mark where the color is after two minutes and again after five. Teams answer items 1 and 2 on the handout.

4. Station B, pumping (10 min). With the dye still in place, the builder uses the syringe to draw water steadily out of the straw nearest the fuel yard, emptying the syringe into a cup and repeating for four minutes. Recorders sketch the dye position again and mark the direction it moved. Teams answer items 3 and 4.

5. Station C, a second well (7 min). Teams stop pumping the first straw and pump the second straw instead, the one farther from the fuel yard, for three minutes. Recorders note whether the dye reaches this well and how the path differs. Teams answer item 5.

6. Debrief (7 min). The activity ends when every team has sketched all three stages and answered item 6. Ask two questions of the whole class. First: before any pumping, where was the water in the model going, and how did the dye show it? Second: what did the town of Kestrelford change about the underground system when it turned on a well, and what does that mean for where a spill can travel? Point out that the wells did not move and the spill did not move; only the direction of flow changed.

Kestrelford Wellfield: A Sand-Tank Groundwater Model — Grade 9 Science

Name: ____________________________ Date: ______________

Student Handout

Sketch your tank at each stage. Label the sand, the water table, the river trench, the fuel yard, and both wells. Then answer these questions in complete sentences.

Before any pumping, which way did the dye move across the tank, and what does that tell you about the direction the groundwater was moving?
Describe how the dye traveled through the sand. Did it move as a single line, or did it spread out as it went?
While your team pumped the well nearest the fuel yard, what happened to the direction the dye was moving?
Explain why pumping changed the direction of flow, using the words water table and slope.
When your team pumped the second, farther well instead, did the dye reach it? Explain what your result suggests about how far a well can pull water toward itself.
The fictional town of Kestrelford wants to keep pumping both wells and also keep the spill out of its drinking water. Using your model results, describe one change the town could make and state what your model would predict about it.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: The dye moved from the high end of the tank toward the river trench. Groundwater flows from where the water table is higher toward where it is lower, so the dye traced water moving downslope toward the discharge point.
Answer: The dye spread as it traveled rather than staying a thin line. Water follows many separate paths between sand grains, so a plume widens and its color fades as it mixes with clean water along the way.
Answer: The dye turned and moved toward the pumping well instead of continuing toward the river. In most teams' tanks the leading edge reached the straw within the four minutes of pumping.
Answer: Pumping lowered the water table right around the straw, creating a cone-shaped dip. Water always moves down the slope of the water table, so once the lowest point was at the well rather than at the river, the slope near the fuel yard pointed toward the well.
Answer: Results vary by team. Many teams found that the dye moved toward the farther well more slowly or did not reach it in three minutes. A well pulls water from a limited area around it, called its capture zone, and a spill outside that area is not drawn in.
Answer: Answers vary. Reasonable proposals include pumping the farther well harder and the near well less, so the capture zone shifts away from the spill; adding a separate pumping well between the spill and the supply wells to intercept the contaminated water; or reducing the total pumping rate so the water table slope still favors the river. Each proposal should be paired with a prediction the model actually supports, such as the dye returning to its original path toward the trench.

Differentiation

Support

Prebuild one tank with the sand already sloped and saturated so these students begin at the dye step. Give them a printed outline of the tank to mark rather than a blank sketch, and reduce the written work to items 1, 3, and 5. Pair each student with a partner who narrates what is happening while they record.

Extension

Ask these teams to run one more trial in which they build a layer of pea gravel through the middle of the sand before saturating, then compare how fast the dye travels in the gravel layer against the sand. They should write a short prediction before the trial and a one-paragraph result afterward that names permeability (how easily water moves through connected pore spaces) and path length.

ELL supports

Pre-teach "water table," "slope," "pump," "plume," and "capture zone" by pointing to each feature in a demonstration tank before teams build their own. Provide a labeled diagram at each station and sentence frames for the handout: "Before pumping, the dye moved toward ___, which shows that ___." and "While we pumped, the dye ___."

Extensions

Have teams photograph their three sketches and write a two-paragraph memo to the fictional Kestrelford water board explaining what the model shows and what it does not. The second paragraph should name at least two ways the model differs from the real aquifer, such as its uniform sand, its short travel distances, and its lack of clay layers, and explain why each difference matters when the board decides how much to trust the result.