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Worksheet Grade 6 Science

Hazel Run's Aquifer: Withdrawal, Recharge, and Unit Conversion

A grade 6 worksheet where students convert a fictional town's groundwater withdrawal and recharge from acre-feet to gallons and compare the yearly gap.

Objectives

  1. Students will convert groundwater volumes between acre-feet and gallons using a given conversion rate.
  2. Students will compare a fictional town's groundwater withdrawal and recharge to explain a supply gap.

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.
Acre-foot
The amount of water it takes to cover one acre of land, about the size of a football field, one foot deep. Western states use acre-feet to measure large amounts of water.

Also: withdrawal

Teacher overview

The fictional town of Hazel Run pumps its drinking water from an aquifer, an underground layer of rock and sediment that holds water in the spaces between grains. Every well field depends on recharge, the rain and snowmelt that soak down through the soil above and refill the aquifer, and in many real places, including Hazel Run in this worksheet, people withdraw water faster than recharge can replace it. This worksheet has students convert Hazel Run's withdrawal and recharge totals from acre-feet, the unit water managers commonly use, into gallons, and then compare the two. A common misconception is that an aquifer is an underground lake that simply refills itself; the recharge numbers here show that refilling is limited, and it depends on how much rain and snowmelt reach the ground above the aquifer and how much of that water actually soaks in rather than running off.

Hazel Run's Aquifer: Withdrawal, Recharge, and Unit Conversion — Grade 6 Science
Name: ____________________________ Date: ______________

Student Worksheet

Use this conversion rate for every item: 1 acre-foot = 325,851 gallons.

Hazel Run's aquifer, in its current condition:

  • Annual withdrawal by the town's wells: 300 acre-feet.
  • Annual recharge from rain and snowmelt: 180 acre-feet.
  1. In one or two sentences, explain why aquifer recharge depends on local rainfall and how much of that rain soaks into the ground.
  2. Convert Hazel Run's annual withdrawal, 300 acre-feet, into gallons.
  3. Convert Hazel Run's annual recharge, 180 acre-feet, into gallons.
  4. How many more acre-feet does Hazel Run withdraw each year than the aquifer recharges?
  5. Convert the yearly shortfall from item 4 into gallons.
  6. At this same yearly shortfall rate, about how many years would it take for the total shortfall to reach 600 acre-feet?
  7. Engineers plan a new retention pond. It lets 60 more acre-feet soak into the ground each year. What would Hazel Run's new annual recharge total be?
  8. Using the new recharge total from item 7, what is the new yearly gap between withdrawal and recharge?
  9. Convert the new yearly gap from item 8 into gallons.
  10. Compare your answers to items 4 and 8. Did the pond cut the yearly shortfall in half, more than half, or less than half? Explain your reasoning.

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

Answer Key
  1. Answer: An aquifer's recharge depends on local rainfall and how much of it soaks through the soil above the aquifer rather than running off, so a place with less rain or more paved surface recharges more slowly than a place with more rain and open ground.
  2. Answer: 97,755,300 gal.
    300 acre-feet × 325,851 gal/acre-foot = 97,755,300 gallons.
  3. Answer: 58,653,180 gal.
    180 acre-feet × 325,851 gal/acre-foot = 58,653,180 gallons.
  4. Answer: 120 acre-feet.
    300 acre-feet − 180 acre-feet = 120 acre-feet withdrawn beyond what recharges each year.
  5. Answer: 39,102,120 gal.
    120 acre-feet × 325,851 gal/acre-foot = 39,102,120 gallons.
  6. Answer: 5 years.
    600 acre-feet ÷ 120 acre-feet per year = 5 years.
  7. Answer: 240 acre-feet.
    180 acre-feet (current recharge) + 60 acre-feet (added by the retention pond) = 240 acre-feet.
  8. Answer: 60 acre-feet.
    300 acre-feet (withdrawal) − 240 acre-feet (new recharge) = 60 acre-feet.
  9. Answer: 19,551,060 gal.
    60 acre-feet × 325,851 gal/acre-foot = 19,551,060 gallons.
  10. Answer: Exactly in half. The shortfall dropped from 120 acre-feet to 60 acre-feet, and 60 is exactly half of 120, so the retention pond project cut the yearly gap in half, though it did not close the gap completely.

Differentiation

Support

Provide a printed multiplication reference showing 325,851 already multiplied by 10, 100, and several small whole numbers, and allow students to use these partial products to build their answers for items 2, 3, 5, and 9 instead of multiplying the full number from scratch.

Extension

Ask students to determine how many additional acre-feet of recharge (beyond the 60 acre-feet in item 7) the retention pond project would need to add each year to close Hazel Run's withdrawal-recharge gap completely, and to state that answer in both acre-feet and gallons.

ELL supports

Pre-teach "aquifer," "withdrawal," "recharge," and "acre-foot" with a labeled cross-section diagram showing rain soaking into the ground above an aquifer and a well pumping water out. Provide the conversion rate (1 acre-foot = 325,851 gallons) on a card students can keep at their desks throughout the worksheet.