Lab / experiment Grade 11 Science

Pentland Aquifer Materials: Porosity and Specific Yield Lab

A grade 11 lab measuring the porosity and specific yield of gravel, sand, and fine soil to compare how well each fictional aquifer material stores and releases water.

Grade: Grade 11
Subject: Science
Material: Lab / experiment
Time: 55 min
Prep: Moderate prep
Materials: Three clear plastic cups with several small holes in the bottom (1 set per group), Three matching clear catch cups (1 set per group), Coarse gravel or aquarium gravel, about 1 cup per group, Coarse sand, about 1 cup per group, Fine potting soil or clay-rich soil, about 1 cup per group, Graduated cylinder or measuring cup marked in milliliters, Water, about 500 mL per group, Fine screen or coffee filter to line the holed cups, Duct tape or other waterproof tape to seal the holes while filling, Marker and 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: Students plan and carry out an investigation measuring how water fills and drains through gravel, sand, and fine soil, the water-and-Earth-materials investigation this standard requires.

All materials for HS-ESS2-5 →

HS-ESS3-1 NGSS

Construct an explanation based on evidence for how the availability of natural resources, occurrence of natural hazards, and changes in climate have influenced human activity.

How this material aligns: The analysis connects each material's specific yield to whether it makes a usable groundwater resource, the availability-of-fresh-water reasoning this standard highlights for human activity.

All materials for HS-ESS3-1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will measure the porosity and specific yield of three earth materials from their own data.
Students will explain why porosity and specific yield differ and which material best stores and releases groundwater.

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.
Aquifer: An aquifer is an underground layer of rock, sand, or gravel that holds water in the tiny spaces between its grains. Wells reach down into aquifers to bring water up to the surface.

Also: specific yield, specific retention, saturation

Teacher overview

An aquifer must do two things: hold water in the spaces between its grains, and give that water up to a well. The first is measured by porosity, the fraction of the material that is open pore space, and the second by specific yield, the fraction of water that actually drains out under gravity. This lab has students measure both for gravel, sand, and fine soil, standing in for the layers beneath the fictional Pentland well field, and see why a material can be very porous yet still make a poor aquifer. The investigation is a simplified classroom analog, not a field measurement.

Pentland Aquifer Materials: Porosity and Specific Yield Lab — Grade 11 Science

Name: ____________________________ Date: ______________

Procedure

Step 1. Safety: this lab uses only water and clean earth materials, so the main hazards are spills and slips. Wipe up spilled water at once, and wash your hands after handling soil. Do not taste any material or water.

Step 2. Line each of the three holed cups with a fine screen or coffee filter so grains cannot wash out through the holes. Label the cups Gravel, Sand, and Fine soil.

Step 3. Fill the Gravel cup to the same marked level with dry gravel and record that bulk volume in milliliters. Repeat for the Sand and Fine soil cups, using the same bulk volume for all three so the comparison is fair.

Step 4. Cover the holes in the bottom of the Gravel cup with a strip of waterproof tape, then rest it over a dry catch cup. Using the graduated cylinder, slowly add water to the gravel until the water just reaches the top of the material and the surface glistens. The water you added, minus any that leaked into the catch cup, is the pore volume; record it.

Step 5. Hold the saturated Gravel cup over a clean, dry catch cup, peel off the tape, and let it drain freely until dripping stops. Measure and record the volume of water that drained out. This drained volume is the water the material releases under gravity.

Step 6. Repeat Steps 4 and 5 for the Sand cup and then the Fine soil cup, recording the pore volume and the drained volume for each. Pour slowly, because adding water too fast makes the pore volume hard to read accurately.

Data & Analysis

Material	Bulk volume (mL)	Water added to saturate: pore volume (mL)	Water drained out (mL)
Gravel
Sand
Fine soil

Calculate the porosity of each material as a percent, using porosity = pore volume divided by bulk volume, times 100.
Calculate the specific yield of each material, using specific yield = drained volume divided by bulk volume, times 100.
Calculate the specific retention of each material, which is the porosity minus the specific yield.
Which material had the highest porosity, and which had the highest specific yield? Are they the same material? Explain what you found.
A good aquifer both holds water and releases it to a well. Based on your data, which of the three materials would make the best aquifer, and why?
Fine soil often has high porosity but low specific yield. Using the idea that water clings to the surfaces of small grains, explain why porosity and specific yield can be so different.
Describe one source of measurement error in your procedure and explain how it would raise or lower your porosity result.
Groundwater can stay underground for a very long time. Using your results, explain why water drains quickly from gravel but very slowly from fine soil.

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: porosity for each material as a percent.
Accept any values that equal each material's own pore volume divided by its bulk volume, times 100. Gravel and sand commonly land in a moderate-to-high range, and fine soil is often high; the exact numbers depend on the student's materials and packing.
Answer: specific yield for each material as a percent.
Accept any values equal to each material's drained volume divided by its bulk volume, times 100. Gravel and coarse sand should give a specific yield close to their porosity, while fine soil should give a much lower specific yield.
Answer: specific retention for each material.
Specific retention = porosity minus specific yield for each material. Accept values consistent with the student's own items 1 and 2; fine soil should show the largest specific retention.
Answer: the highest-porosity material is usually not the highest specific-yield material.
Most groups find fine soil among the highest in porosity but the gravel or sand highest in specific yield. Accept any answer that correctly reads the student's own table and notes whether the two winners match.
Answer: gravel or coarse sand.
Accept gravel or coarse sand, justified by a high specific yield: it both holds water and releases most of it to drain, which is what a well needs. Full credit requires citing the student's own specific-yield values.
Answer: water clings to small grains.
Fine soil has enormous surface area on its tiny grains, and a thin film of water is held tightly to those surfaces by attraction. That held water counts as pore space (high porosity) but does not drain out under gravity (low specific yield), so the two measures differ.
Answer: a reasonable error source and its effect.
Accept any genuine source, such as pouring water too fast so air is trapped in the pores (lowering measured pore volume and porosity), water leaking past the tape and not being subtracted (raising it), uneven packing, or water clinging to the cup walls. The explanation must correctly state whether the error raises or lowers porosity.
Answer: large pores drain fast, tiny pores drain slowly.
Gravel has large, well-connected pores, so gravity moves water through it quickly, while fine soil has tiny pores that hold water tightly and let it seep only slowly. This is why water can linger underground for a long time in fine-grained layers.

Differentiation

Support

Pre-build one saturated demonstration cup so students see what "just saturated" looks like before they judge their own. Provide the porosity and specific-yield formulas already written with labeled blanks for pore volume, drained volume, and bulk volume.

Extension

Have students mix sand and fine soil in a fourth cup, predict whether its porosity and specific yield will fall between the two pure materials, then test the prediction and explain any surprise in the result.

ELL supports

Pair the terms porosity, specific yield, and specific retention with a labeled picture of grains, pore spaces, and clinging water films. Allow students to record all volumes as numbers in the table and to answer items 4 through 8 with short phrases using sentence frames.