Worksheet Grade 9 Science

Dunmore Lead Tap Sampling: Reading the Action Level

A grade 9 worksheet where students analyze a fictional town's lead tap-sampling data, find the 90th-percentile value, and compare it to the action levels.

Grade: Grade 9
Subject: Science
Material: Worksheet
Time: 40 min
Prep: No prep
Materials: Calculator

Standards

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: Items 1 through 7 move students from a set of parts-per-billion readings to counts, percents, and a percentile comparison, requiring the consistent unit tracking this standard specifies.

All materials for HSN-Q.A.1 →

HSN-Q.A.3 Common Core Math

Choose a level of accuracy appropriate to limitations on measurement when reporting quantities.

How this material aligns: Item 10 asks students to judge how many decimal places a lead result can support given a test lab that reports to the nearest whole part per billion, the accuracy-matching this standard requires.

All materials for HSN-Q.A.3 →

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: Items 8 and 9 explain how water standing in a pipe dissolves lead from the metal and how a corrosion-control coating blocks that contact, with items 1 through 7 supplying the tap-sampling evidence.

All materials for HS-ESS2-5 →

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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 find the 90th-percentile value of a small lead-sampling data set.
Students will compare sample results against the current and future federal action levels.
Students will explain how corrosion control and sampling method affect lead readings.

Vocabulary

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.
First-draw sample: A water sample taken from a faucet after the water has sat still in the pipes for hours, usually first thing in the morning. It shows how much lead can build up in water that sits in a home's pipes.

Also: 90th percentile

Teacher overview

Utilities check for lead by collecting first-draw tap samples from homes that are likely to have lead pipes or lead solder. A system does not pass or fail on a single house. Instead, the rule looks at the 90th-percentile value across the samples and compares it to the action level, which is 15 parts per billion now and drops to 10 parts per billion in 2027. EPA's health-based goal for lead in drinking water is zero, so the action level is a trigger for treatment and public notice rather than a safe level. This worksheet has students work with a small sampling data set from the fictional town of Dunmore.

A common student error is to compare only the highest sample to the action level. The rule uses the 90th percentile, not the single worst house, so students should sort the data and find that value carefully.

Dunmore Lead Tap Sampling: Reading the Action Level — Grade 9 Science

Name: ____________________________ Date: ______________

Student Worksheet

The town of Dunmore (a fictional town) collected first-draw tap samples from 10 homes with older plumbing. First-draw means the water sat in the pipes overnight before the sample was taken. The 10 lead results, in parts per billion, are: 3, 4, 5, 6, 8, 9, 11, 13, 16, 22.

What is the range of the lead results (the highest value minus the lowest value)?
The current federal action level is 15 parts per billion. How many of the 10 samples are above 15 parts per billion?
What percent of the 10 samples exceed the current 15 parts-per-billion action level?
For these 10 sorted samples, the 90th-percentile value is taken as the 9th value in order from lowest to highest. What is that value?
Because the 90th-percentile value is above 15 parts per billion, Dunmore exceeds the action level. By how many parts per billion does the 90th-percentile value exceed 15?
In 2027 the action level drops to 10 parts per billion. If the same 10 samples were compared to 10 parts per billion, how many would exceed it?
What percent of the samples exceed the future 10 parts-per-billion level?
Explain why a first-draw sample, taken after water has sat in the pipe overnight, usually shows more lead than water that has run for two minutes.
Corrosion control adds a chemical that coats the inside of the pipes. Explain how this lowers lead at the tap even when lead pipes are still in the ground.
The test lab reports lead to the nearest whole part per billion. A student records one result as 16.0 parts per billion. Is that level of precision supported by the lab's reporting? Explain what the student should write instead.

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: 19 ppb. 22 − 3 = 19 parts per billion.
Answer: 2 samples. Only 16 and 22 are above 15 parts per billion.
Answer: 20 percent. 2 of 10 samples exceed the level, and 2 ÷ 10 × 100 = 20 percent.
Answer: 16 ppb. Sorted in order, the 9th of the 10 values is 16 parts per billion.
Answer: 1 ppb. 16 − 15 = 1 part per billion above the action level.
Answer: 4 samples. The values 11, 13, 16, and 22 are all above 10 parts per billion.
Answer: 40 percent. 4 of 10 samples exceed 10 parts per billion, and 4 ÷ 10 × 100 = 40 percent.
Answer: Because water sitting in a lead pipe overnight has more time in contact with the metal, so more lead dissolves into it. Water that has run for two minutes has cleared most of that standing water out of the pipe.
Answer: The corrosion-control chemical builds a thin protective coating on the inside of the pipe. That coating keeps the water from touching the lead directly, so less lead dissolves into the water even though the lead pipe is still there.
Answer: No. The lab reports to the nearest whole part per billion, so the extra decimal in 16.0 claims more precision than the measurement supports. The student should write 16 parts per billion.

Differentiation

Support

Provide the data already sorted from lowest to highest, and mark the 9th value so students can focus on the interpretation in items 4 and 5 rather than the sorting step.

Extension

Have students change one of the 10 results so that the 90th-percentile value (the 9th value in order) would fall below the 15 parts-per-billion action level, and explain why the value they chose changes the result.

ELL supports

Pre-teach "action level," "first-draw sample," and "corrosion control" with a labeled pipe diagram showing standing water and a protective coating. Allow items 8 and 9 to be answered with a labeled sketch and a short phrase.