Worksheet Grade 10 Math
Thistledown Creek Water Quality Monitoring Worksheet
A grade 10 worksheet where students compute turbidity removal efficiency, compare dissolved oxygen to a fish benchmark, and check pH for a fictional creek.
Objectives
- Students will calculate removal efficiency as a percent from influent and effluent readings.
- Students will compare dissolved oxygen and pH readings against published water quality benchmarks.
Vocabulary
- 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.
- Dissolved oxygen
- Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.
- pH
- pH is a number that tells whether water is acidic, like lemon juice, or basic, like baking soda mixed in water. Pure water sits in the middle of the scale at a pH of 7.
Also: removal efficiency
Teacher overview
A water quality technician at the fictional town of Gullhaven collects readings from Thistledown Creek and from the treatment plant that draws on it. This worksheet gives students that sampling data and asks them to compute removal efficiency, compare dissolved oxygen against the benchmark fish need, and check pH against the drinking-water standard. The work mirrors the routine math a technician does to decide whether a sample passes or fails.
Student Worksheet
The readings below come from Thistledown Creek and the Gullhaven treatment plant (a fictional creek and plant used for this worksheet). Use these facts where needed: removal efficiency (%) = (influent − effluent) / influent × 100; in fresh water, 1 mg/L is approximately equal to 1 ppm; fish generally need dissolved oxygen above 5 mg/L; the EPA turbidity limit for finished water from conventional filtration is 0.3 NTU; the secondary standard for pH is 6.5 to 8.5.
Turbidity readings through the plant: raw creek water 8.0 NTU, water after sedimentation 1.2 NTU, finished water 0.2 NTU.
Find the turbidity removal efficiency across the whole plant, from the raw 8.0 NTU to the finished 0.2 NTU. Round to the nearest tenth of a percent.
The EPA limit requires finished-water turbidity at or below 0.3 NTU in at least 95 percent of monthly samples. Does the finished water at 0.2 NTU meet the 0.3 NTU limit? Answer yes or no and explain in one sentence.
Dissolved oxygen at creek Site A reads 6.4 mg/L. Fish generally need more than 5 mg/L. Does Site A meet the benchmark, and by how many mg/L? Show the subtraction.
Dissolved oxygen at creek Site B reads 4.2 mg/L. Compared with the 5 mg/L benchmark, by how many mg/L does Site B fall short? Show the subtraction.
Using the fact that 1 mg/L is approximately equal to 1 ppm in fresh water, write Site A's dissolved oxygen of 6.4 mg/L in ppm.
The finished water has a pH of 7.3. The secondary standard for pH is 6.5 to 8.5. Is 7.3 within that range? Answer yes or no.
Find the turbidity removal efficiency of the sedimentation step alone, from the raw 8.0 NTU to the 1.2 NTU after sedimentation. Round to the nearest whole percent.
A student records the finished-water turbidity as "0.2000 NTU," but the test kit only reads to the nearest 0.1 NTU. Explain in one or two sentences why writing four decimal places is false precision.
Compare your two removal efficiencies. By how many percentage points does the whole-plant removal (item 1) exceed the sedimentation-step removal (item 7)?
Explain in two or three sentences why measuring dissolved oxygen at two creek sites, one upstream and one downstream of a discharge, tells the technician more than a single reading would.
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: 97.5 percent. (8.0 − 0.2) / 8.0 × 100 = 7.8 / 8.0 × 100 = 97.5%.
Answer: Yes. The finished value 0.2 NTU is below the 0.3 NTU limit, so this sample meets the turbidity target.
Answer: 1.4 mg/L above the benchmark. 6.4 − 5 = 1.4 mg/L, so Site A meets the fish benchmark with 1.4 mg/L to spare.
Answer: 0.8 mg/L short. 5 − 4.2 = 0.8 mg/L, so Site B falls below the 5 mg/L benchmark by 0.8 mg/L.
Answer: 6.4 ppm. Since 1 mg/L is approximately equal to 1 ppm in fresh water such as this creek, 6.4 mg/L is about 6.4 ppm.
Answer: Yes. The pH of 7.3 lies between 6.5 and 8.5, so it is inside the secondary standard range.
Answer: 85 percent. (8.0 − 1.2) / 8.0 × 100 = 6.8 / 8.0 × 100 = 85%.
Answer: A reading of "0.2000 NTU" claims accuracy to four decimal places, but the kit only measures to the nearest 0.1 NTU. Reporting extra digits suggests the instrument is more precise than it is, so the value should be written as 0.2 NTU.
Answer: 12.5 percentage points. 97.5% − 85% = 12.5 percentage points more removal across the whole plant than in sedimentation alone.
Answer: Two readings, upstream and downstream, show whether the water changes as it passes the discharge point. If the downstream dissolved oxygen is lower, that difference points to the discharge as a likely cause, which a single reading could not reveal.
Differentiation
Support
Provide the removal-efficiency formula already set up with the item 1 numbers filled in, so students complete only the arithmetic. Give a number line marked at 5 mg/L and at the 6.5 to 8.5 pH range so items 3, 4, and 6 become a matter of placing each reading on the line.
Extension
Ask students to propose a reading at a new site for dissolved oxygen that would fall exactly halfway between Site A and Site B, state its value, and show the calculation. Then have them explain what a steady drop in dissolved oxygen from an upstream site to a downstream site might indicate about a pollution source.
ELL supports
Provide a small labeled picture glossary for "turbidity," "dissolved oxygen," and "pH," each with a simple icon. Allow students to answer the yes or no items with the word plus a labeled mark on a number line rather than a full sentence.
Extensions
On a teacher-supervised visit, have students carry a simple turbidity tube and a dissolved-oxygen test kit to a nearby stream, take their own upstream and downstream readings, and repeat the removal-efficiency and benchmark comparisons with real numbers. Students sample from the bank or from shallow, slow water, wear gloves and goggles when handling the kit's reagents, never drink the stream water, and wash their hands afterward. A short written summary can note whether each reading would pass or fail the benchmarks used in this worksheet.