Worksheet Grade 10 Science

Calumet Heights Lead Service Lines: Reading the New Rule

A grade 10 worksheet on the fictional Calumet Heights system: students find a 90th-percentile lead reading, compare it to a tightening action level, and plan replacement.

Grade: Grade 10
Subject: Science
Material: Worksheet
Time: 40 min
Prep: No prep
Materials: None

Standards

HSS-ID.A.3 Common Core Math

Interpret differences in shape, center, and spread in the context of the data sets, accounting for possible effects of outliers.

How this material aligns: Students rank the ten lead readings, identify the 90th-percentile value in item 3, and reason about how the single high outlier affects the spread of the sample.

All materials for HSS-ID.A.3 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Students carry parts-per-billion, percent, and lines-per-year units through the multistep replacement-planning calculations in items 6, 7, and 8, interpreting each figure in context.

All materials for HSN-Q.A.1 →

HS-ETS1-1 NGSS

Analyze a major global challenge to specify qualitative and quantitative criteria and constraints for solutions that account for societal needs and wants.

How this material aligns: Items 4, 5, and 10 treat the current and 2027 lead action levels as quantitative criteria the system must meet, while items 6 and 8 turn the ten-year replacement mandate into a lines-per-year constraint on the utility's plan.

All materials for HS-ETS1-1 →

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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 identify the 90th-percentile value from a set of lead sample readings.
Students will compare a system's lead reading to the current and future action levels.
Students will calculate a lead service line replacement rate and percent complete.

Vocabulary

Lead service line: A lead service line is an old water pipe made of lead metal that connects a house to the water main. Lead can get into the drinking water, so these pipes are being dug up and replaced across the country.
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.
Corrosion control: Treatment that keeps water from slowly eating away at the inside of pipes. It helps stop metals like lead from getting into drinking water.

Also: 90th percentile, parts per billion

Teacher overview

Lead can dissolve into tap water from the short pipe, called a service line, that connects a water main to a house. Federal rules do not use a single sample to judge a system; they use the 90th-percentile value from many homes, and the action level is tightening from 15 ppb today to 10 ppb in 2027. This worksheet uses the fictional Calumet Heights system to practice finding a 90th-percentile reading and planning line replacement, a task that carries real weight because EPA estimates that about 4 million lead service lines still remain in water systems across the country. Watch for the error of averaging the readings instead of ranking them to find the percentile.

Calumet Heights Lead Service Lines: Reading the New Rule — Grade 10 Science

Name: ____________________________ Date: ______________

Student Worksheet

Calumet Heights is a fictional water system with 500 service lines, 120 of which are known to be lead. To find the 90th-percentile lead level, rank the sample readings from lowest to highest; with 10 samples, the 90th percentile is the 9th reading. The system's 10 home readings, in parts per billion (ppb), are: 2, 3, 4, 5, 6, 8, 9, 11, 14, and 22 ppb. The lead action level is 15 ppb now and drops to 10 ppb in 2027.

In one sentence, explain what a lead service line is and why it can raise the lead level at a home's tap.
The action level is not a limit on any single home. Explain, in your own words, what the 90th-percentile value represents for the whole system.
Rank the 10 readings and identify the system's 90th-percentile lead level in ppb.
Is the 90th-percentile value from item 3 below the current action level of 15 ppb, and by how many ppb does it clear or exceed it?
In 2027 the action level drops to 10 ppb. Compare the same 90th-percentile value to the new level, and state by how many ppb it would then clear or exceed it.
Calumet Heights must replace nearly all 120 of its lead lines within 10 years. What is the minimum average number of lines it must replace each year?
So far the system has replaced 84 of the 120 lead lines. What percent of the lead lines has it replaced?
At the rate of 12 lines per year, how many more years will it take to replace the remaining lead lines?
While lines are still being replaced, the plant keeps adding corrosion-control treatment. Explain what corrosion control does and why it still matters during the replacement years.
Explain why the lead rule, with its change from 15 ppb to 10 ppb, can be called a rule "in motion," and what it means for a system that reads 14 ppb today.

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: A lead service line is the pipe that connects the water main to a house; lead can dissolve from its walls into the water sitting in it, raising the lead level at the tap.
Answer: The 90th-percentile value is the reading at or below which 90 percent of the sampled homes fall. It describes the system as a whole, so one high home does not by itself decide compliance, but a widespread problem does.
Answer: 14 ppb. Ranked lowest to highest, the 9th of the 10 readings is 14 ppb; the 22 ppb reading is the single highest value and sits above it as an outlier.
Answer: Yes, below by 1 ppb. The 90th-percentile value of 14 ppb is under the current 15 ppb action level by 15 − 14 = 1 ppb.
Answer: Exceeds by 4 ppb. Against the 2027 action level of 10 ppb, the same 14 ppb reading is 14 − 10 = 4 ppb over the new action level.
Answer: 12 lines per year. 120 lead lines divided by 10 years = 12 lines each year at minimum.
Answer: 70%. 84 replaced divided by 120 total = 0.70, or 70 percent complete.
Answer: 3 years. The remaining lines are 120 − 84 = 36, and 36 divided by 12 lines per year = 3 years.
Answer: Corrosion control adds a treatment that coats the inside of pipes with a protective layer, keeping lead from dissolving into the water. It matters during replacement because many lead lines are still in the ground and need that protection until they are removed.
Answer: The rule is tightening over time rather than staying fixed, so a system can pass today and fail later. A system reading 14 ppb clears the 15 ppb level now but would exceed the 10 ppb level in 2027, so it must keep lowering lead before then.

Differentiation

Support

Provide the 10 readings already ranked in order, and mark the 9th value so students can focus on interpreting the 90th percentile rather than sorting. Work item 6 together as a model before students attempt items 7 and 8.

Extension

Ask students to propose a faster replacement schedule that finishes the remaining lines in 2 years instead of 3, calculate the new lines-per-year rate, and explain one cost or staffing trade-off that a faster pace would create for a small system.

ELL supports

Pre-teach "service line," "action level," "percentile," and "corrosion control" with a labeled picture of a house, its service line, and the water main. Provide a sentence frame for item 2: "The 90th-percentile value tells the system that ___."