Lesson plan Grade 9 Science

Alder Mesa's Shrinking Aquifer: Modeling Groundwater Drawdown

A grade 9 Earth science lesson using aquifer storage change to write a linear equation projecting when a fictional town's water table hits a critical level.

Grade: Grade 9
Subject: Science
Material: Lesson plan
Time: 60 min
Prep: Low prep
Materials: projector or whiteboard, printed cross-section diagram of an aquifer and a pumping well, calculator

Standards

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 guided practice and exit ticket have students explain, using Alder Mesa's recharge and withdrawal data, how groundwater availability has shaped where and how the town grew and how it is now constrained.

All materials for HS-ESS3-1 →

HSA-CED.A.1 Common Core Math

Create equations and inequalities in one variable and use them to solve problems. Include equations arising from linear and quadratic functions, and simple rational and exponential functions.

How this material aligns: Independent practice has students write and solve a one-variable linear equation modeling the aquifer's storage decline over time, the equation-creation this standard requires.

All materials for HSA-CED.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-16.

Objectives

Students will calculate an aquifer's net annual change in storage from its recharge and withdrawal rates.
Students will explain how a cone of depression forms around a pumping well.
Students will write and solve a one-variable linear equation to project when an aquifer's storage will reach a critical level.

Vocabulary

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.
Recharge: Recharge is water soaking down through the ground to refill an aquifer, the way rain refills an underground sponge. Aquifers stay healthy only if recharge keeps up with pumping.
Drawdown: Drawdown is how far the water level in a well drops when a pump pulls water out. The harder and longer you pump, the bigger the drawdown gets.
Cone of depression: A cone of depression is the dip in the water table that forms in a circle around a well while it is pumping, like a shallow bowl scooped out of the underground water surface. The harder a well pumps, the wider and deeper this dip becomes.
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: withdrawal

Teacher overview

The town of Alder Mesa (a fictional town used for this lesson) draws its entire water supply from a single unconfined aquifer beneath the surrounding farmland. For decades, the aquifer took in about as much water through rainfall recharge as the town and nearby farms pumped out, keeping the water table roughly stable. As Alder Mesa has grown, annual withdrawal has started to outpace recharge, and the water table has begun a slow, steady decline. This lesson uses Alder Mesa's numbers to teach both the physical process (how pumping draws down the water table around a well) and the algebra needed to project how long the current trend can continue.

A common misconception this lesson addresses is the idea that groundwater is an unlimited, self-refilling resource simply because it is hidden underground. Students often assume an aquifer restores itself instantly once pumping stops, when in fact recharge is a slow process governed by rainfall, soil permeability, and the aquifer's geology, and a large storage deficit can take years or decades to reverse even after withdrawal is reduced.

Procedure

Hook (5 min): Display or sketch a cross-section diagram showing a well pumping water from an aquifer, with the water table dipping into a funnel shape immediately around the well casing. Ask students to guess, based on the picture alone, what the funnel-shaped dip is called and why it forms. Take two or three guesses without confirming or correcting yet.

Direct instruction (15 min): Introduce the vocabulary: an aquifer gains water through recharge (rain and snowmelt soaking down through the soil) and loses water through withdrawal (wells pumping it out for use). Write the storage-change relationship on the board: change in storage = recharge − withdrawal. Explain that when a well pumps, the water table drops fastest right at the well and less as distance from the well increases, forming the cone-shaped dip students saw in the hook; this is the cone of depression. Define drawdown as the difference between the water table's normal (static) level and its lower level while the well is pumping (drawdown = pumping water level − static water level, with both measured as depth below the surface).

Guided practice (15 min): Work through Alder Mesa's numbers as a class. The aquifer currently recharges at a rate of about 500 acre-feet per year from rainfall soaking into the ground, while the town and surrounding farms withdraw about 650 acre-feet per year. As a class, calculate the net annual change in storage (500 − 650 = −150 acre-feet per year, a net loss). Discuss what a negative number means physically: the aquifer's total stored volume is shrinking by about 150 acre-feet every year even though it still receives some recharge.

Independent practice (15 min): Students work individually or in pairs on the handout problems below, which extend the guided-practice numbers into a one-variable equation and a drawdown calculation.

Hydrogeologists estimate Alder Mesa's aquifer currently holds about 9,000 acre-feet of stored water. If the net annual loss of 150 acre-feet per year (from guided practice) continues unchanged, write an equation for the aquifer's stored volume, S, after x years.
Using your equation from item 1, how many years until the aquifer's storage drops to 6,000 acre-feet, the level at which the state requires Alder Mesa to activate a mandatory conservation plan?
A monitoring well near the center of town shows a static (non-pumping) water level of 80 feet below the surface. While the town's main well is actively pumping, that same monitoring well reads 95 feet below the surface. Calculate the drawdown.
Based on your answer to item 2, is Alder Mesa's current path sustainable over the next 30 years without a change in either recharge or withdrawal? Explain your reasoning in one or two sentences.

Closure / exit ticket (10 min): Students answer one question individually on an index card: "If Alder Mesa cut its withdrawal to exactly match its 500 acre-foot recharge rate, what would happen to the aquifer's storage over time, and why?" Collect the cards and scan for the correct idea (storage would stabilize, since change in storage would equal zero) before dismissal; if fewer than three-quarters of students show that understanding, revisit the storage-change relationship briefly at the start of the next class.

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: S = 9,000 − 150x.
The starting storage is 9,000 acre-feet, and it decreases by 150 acre-feet for every year, x, that passes, giving the linear equation S = 9,000 − 150x.
Answer: 20 years.
Set S = 6,000 and solve: 6,000 = 9,000 − 150x. Subtracting 9,000 from both sides gives −3,000 = −150x, so x = 20 years.
Answer: 15 ft.
Drawdown = pumping water level − static water level = 95 ft − 80 ft = 15 ft. (Both levels are measured as depth below the surface, so the larger number, 95 ft, represents the lower water level while pumping.)
Answer: short explanation.
Based on the 20-year projection to reach the conservation threshold, the current path is not sustainable through 30 years without a change: the model predicts the aquifer would already trigger mandatory conservation measures at year 20, ten years before the 30-year mark, unless recharge increases or withdrawal decreases.

Exit ticket answer: Storage would stabilize (stop changing) because change in storage = recharge − withdrawal = 500 − 500 = 0 acre-feet per year, meaning the aquifer would take in the same amount it loses.

Differentiation

Support (below grade level)

Provide the storage-change equation with the numbers already substituted for item 1, so students only need to solve 6,000 = 9,000 − 150x for item 2. Pair the drawdown calculation in item 3 with a labeled diagram showing both depths as arrows measured from the surface.

Extension (above grade level)

Ask students to write and solve a second equation: if Alder Mesa reduced annual withdrawal to 550 acre-feet per year (keeping recharge at 500 acre-feet per year), how many years would it now take to reach the 6,000 acre-foot conservation threshold, and how many additional years does that buy the town compared to item 2?

ELL supports

Pre-teach "recharge," "withdrawal," and "drawdown" using the cross-section diagram from the hook, labeling each term directly on the picture in English and students' home languages where possible. Allow the exit ticket to be answered with the equation "500 − 500 = 0" plus a short phrase instead of a full sentence.