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Classroom activity Grade 6 Science

Northgate Water Lab Relay: Matching Contaminants to Limits

A grade 6 science relay game where teams match four real drinking water contaminants to their federal limits and to the treatment that removes each one.

Objectives

  1. Students will match four real drinking water contaminants to their federal limits and to a treatment that removes each.
  2. Students will explain why two limits that share the number 4.0 are not the same strictness.

Vocabulary

Contaminant
A contaminant is anything in water that should not be there, whether it is a germ, a chemical, or too much of a natural mineral, that could make the water unsafe or unpleasant to use. Treatment plants are built specifically to find and remove contaminants before water reaches the 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.
PFAS
A large family of human-made chemicals used in things like nonstick pans, waterproof fabric, and firefighting foam. They are called forever chemicals because they take a very long time to break down.
Turbidity
Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.

Also: limit

Teacher overview

This is a whole-class relay game for four teams. The class is set up as a make-believe testing lab called Northgate Water Lab, but every limit on the cards is a real federal drinking water rule. Each contaminant matches exactly one limit and one treatment, so building a correct set of three shows how a utility spots a problem and fixes it. Because two of the limits share the number 4.0 but use very different units, the game forces students to read carefully rather than grab the first card that looks right.

Activity Directions

  1. Before class, print and cut the card decks in the Student Handout. Give each team its own set of the four contaminant cards. Spread the shared limit cards and treatment cards face up on a table across the room. Tell students the goal directly: match each contaminant to its correct limit and to the treatment that removes or controls it.

  2. Split the class into four teams and have each team stand behind a build spot (a desk where they will lay out their matched sets).

  3. Explain the relay rule: one runner at a time may jog to the far table, pick up a single card, and bring it back. The team decides where that card belongs, then the next runner may go. Only one card per trip.

  4. Teams build four complete sets, each with one contaminant card, one limit card, and one treatment card. If a team realizes it grabbed a wrong card, a later runner may carry it back and swap it.

  5. End the round when the first team has all four sets laid out and the teacher confirms every match is correct, or when the timer reaches 10 minutes, whichever comes first. If the timer ends first, the team with the most correct sets wins.

  6. Debrief together. Rebuild the four correct sets on the board so every team sees them, then ask the debrief questions below and discuss the answers as a class.

Northgate Water Lab Relay: Matching Contaminants to Limits — Grade 6 Science
Name: ____________________________ Date: ______________

Student Handout

Print and cut these cards. Each team needs the four contaminant cards. Make four copies of the limit cards and the treatment cards, one per team, for the far table.

Contaminant cards: Lead; PFAS (PFOA and PFOS); Turbidity (cloudiness); Chlorine (leftover disinfectant).

Limit cards:

  • Action level of 15 ppb today, dropping to 10 ppb in 2027.
  • 4.0 parts per trillion (ppt) each, to be met by April 2029, with a 2026 proposal that would let some systems apply for two more years.
  • At or below 0.3 NTU in 95 percent of monthly samples.
  • A maximum residual level of 4.0 mg/L, usually kept at 0.2 to 2.0 mg/L in the pipes.

Treatment cards:

  • Corrosion control coating on pipes, plus replacing old service lines.
  • Granular activated carbon or reverse osmosis membranes.
  • Coagulation, then settling, then filtration.
  • Adjusting the disinfectant dose so enough stays in the water without going too high.

Debrief questions:

  1. Which two limits both use the number 4.0, and what makes them very different?
  2. Which contaminant's limit is getting stricter soon, and how does it change?
  3. Chlorine is added to water on purpose but also has an upper limit. Why both?

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: Lead set. Lead matches the "action level of 15 ppb today, dropping to 10 ppb in 2027" limit and the "corrosion control coating on pipes, plus replacing old service lines" treatment.
  2. Answer: PFAS set. PFAS matches the "4.0 parts per trillion each" limit and the "granular activated carbon or reverse osmosis membranes" treatment.
  3. Answer: Turbidity set. Turbidity matches the "at or below 0.3 NTU in 95 percent of monthly samples" limit and the "coagulation, then settling, then filtration" treatment.
  4. Answer: Chlorine set. Chlorine matches the "maximum residual level of 4.0 mg/L" limit and the "adjusting the disinfectant dose" treatment.
  5. Debrief question 1: The PFAS limit of 4.0 ppt and the chlorine limit of 4.0 mg/L share the number 4.0, but a part per trillion is far smaller than a milligram per liter, so the PFAS limit is a much tinier allowed amount.
  6. Debrief question 2: Lead's limit is getting stricter. The action level drops from 15 ppb to 10 ppb in 2027, which means a system must take action at a lower lead level than before.
  7. Debrief question 3: Chlorine is added to kill germs, so some is needed, but too much is unhealthy and tastes bad, so it also has an upper limit; operators aim for enough to protect the water without going over.

Differentiation

Support

Color-code the backs of the three decks (one color for contaminants, one for limits, one for treatments) so students can see that each set needs one card of each color. Let a support team build one set together with the teacher as a model before the relay begins.

Extension

Ask students to write a fifth card set for a contaminant not used in the game, using only teacher-provided facts, and to explain why they paired their limit and treatment as they did.

ELL supports

Provide the contaminant and treatment cards with a small labeled picture on each, such as a pipe for lead or a filter for turbidity. Pre-teach "contaminant," "limit," and "treatment," and allow students to explain their matches by pointing to cards and using short phrases.