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Worksheet Grade 7 Science

Calder Bluff's Service Line Inventory: Which Pipes Come Out First

Students sort a fictional town's 6,000 service lines by material, find percents, and build a ten-year lead pipe replacement schedule with costs.

Objectives

  1. Students will calculate what percent of a service line inventory is made of each pipe material.
  2. Students will build a replacement schedule from a total, a deadline, and a crew rate.
  3. Students will explain why a water sample must come from the homes actually at risk.

Vocabulary

Service line
A service line is the small pipe that connects the water main under the street to the plumbing inside one home or building. It is the last leg of the trip water makes to your tap.
Action level
A trigger number in lead and copper testing. If too many homes test above this level, the utility must take steps like improving treatment and telling the public.

Also: inventory, corrosion, parts per billion

Teacher overview

A service line is the short pipe that carries water from the main under the street into one building, and its material decides whether lead can dissolve into the water sitting inside it. EPA estimates, from the inventories utilities reported in 2025, that about 4 million lead service lines remain in US water systems, and federal rules now require utilities to inventory every line and replace nearly all the lead ones within 10 years. This worksheet uses a fictional inventory from the town of Calder Bluff so students can turn that requirement into percents, an annual replacement pace, and a cost. Teaching note: many students assume lead in tap water comes from the reservoir or the treatment plant, so they look for a pollution source upstream. Point out that the lead in this scenario comes from the pipe itself, which is why the fix is replacing pipe rather than adding another treatment step.

Calder Bluff's Service Line Inventory: Which Pipes Come Out First — Grade 7 Science
Name: ____________________________ Date: ______________

Student Worksheet

The town of Calder Bluff finished its service line inventory this spring. Crews checked property records, dug test holes, and sorted all 6,000 lines into four groups.

Service line material Number of lines
Copper 3,300
Lead 1,200
Galvanized steel that must be replaced 600
Unknown material 900
Total 6,000
  1. What percent of the 6,000 service lines in the town of Calder Bluff are lead?
  2. What percent of the 6,000 lines are still listed as unknown material?
  3. The rule makes the town replace both the lead lines and the galvanized lines in the table. How many lines is that in all?
  4. Federal rules give water systems 10 years to replace nearly all lead service lines. If Calder Bluff replaces the lines from item 3 at a steady pace, how many lines is that each year?
  5. One crew replaces 15 lines per week. How many weeks of crew time does a year of 180 lines take?
  6. In the first year, crews dig up all 900 unknown lines. One third of them turn out to be lead. How many lines does that add to the replacement list?
  7. Those extra lines raise the replacement list from 1,800 lines to 2,100 lines. What is the percent increase? Round to the nearest tenth of a percent.
  8. Crews finished 180 lines during that first year. How many of the 2,100 lines are still in the ground?
  9. Nine years are left on the deadline. How many lines per year must the crews replace to finish the 1,920 that remain? Round up to the next whole line.
  10. Replacing one line costs the town $5,600 in our scenario. What does a year of 180 replacements cost?
  11. The utility plans to test tap water at 30 homes, all in a neighborhood built in 2015 where every line is copper. Explain why those results would tell the town very little about homes that still have lead lines.
  12. A home on a lead line tests at 12 ppb. Is that above or below the 10 ppb action level that takes effect in 2027?
  13. Calder Bluff tells families on lead lines to use a certified filter until their line is replaced. Explain why the town does that instead of waiting for the replacement crew.

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: 20 percent.
    1,200 lead lines divided by 6,000 total lines equals 0.20, and 0.20 times 100 gives 20 percent.
  2. Answer: 15 percent.
    900 unknown lines divided by 6,000 total lines equals 0.15, which is 15 percent.
  3. Answer: 1,800 lines.
    1,200 lead lines plus 600 galvanized lines equals 1,800 lines.
  4. Answer: 180 lines per year.
    1,800 lines divided by 10 years equals 180 lines each year.
  5. Answer: 12 weeks.
    180 lines divided by 15 lines per week equals 12 weeks.
  6. Answer: 300 lines.
    One third of 900 is 900 divided by 3, which equals 300 lines.
  7. Answer: 16.7 percent.
    The increase is 2,100 minus 1,800, or 300 lines. Then 300 divided by 1,800 equals about 0.1667, which rounds to 16.7 percent.
  8. Answer: 1,920 lines.
    2,100 lines minus the 180 already replaced equals 1,920 lines.
  9. Answer: 214 lines per year.
    1,920 divided by 9 equals 213.3, and rounding up to a whole line gives 214 lines per year. Accept 213.3 with the rounding shown.
  10. Answer: $1,008,000.
    180 lines times $5,600 per line equals $1,008,000.
  11. Answer: The sample is not representative.
    Those 30 homes were chosen from a group with no lead pipe at all, so their results describe copper-line homes only. To learn about homes at risk, the utility has to sample taps served by lead or galvanized lines.
  12. Answer: Above the 2027 action level.
    A result of 12 ppb is greater than 10 ppb, so it would exceed the action level that applies starting in 2027.
  13. Answer: A filter protects the family during the wait.
    Replacement takes years, and lead keeps dissolving from the pipe wall into water that sits in the line. A certified filter removes lead at the tap while the pipe is still in the ground.

Differentiation

Support

Give students a partly filled version of the inventory table for the town of Calder Bluff with the lead row already converted to a percent, then have them repeat the same two steps for the unknown row. Provide a number line marked from 0 to 6,000 so students can see that 1,200 is one fifth of the total before they divide.

Extension

Have students recalculate items 4 and 9 for a version of Calder Bluff in which the state shortens the deadline from 10 years to 7 years, then write two sentences on what that change would mean for crew hiring and cost.

ELL supports

Provide a labeled cross-section drawing of a street, a water main, a service line, and a house, with the words main, service line, and tap placed on the drawing. Allow students to answer items 11 and 13 in two short sentences or with a labeled sketch of the Calder Bluff scenario.

Extensions

Students can compare the town of Calder Bluff with their own community by looking up whether their water system has published a service line inventory, then writing three questions they would ask the utility about the replacement schedule.