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Worksheet Grade 8 Science

Granite Fork Reservoir Water Quality: Reading a Sample Data Table

A grade 8 worksheet where students read a fictional reservoir's dissolved oxygen, pH, and bacteria data, compare it to real thresholds, and use scientific notation.

Objectives

  1. Students will interpret a water-quality data table to determine which sample sites are safe for fish and within the pH standard.
  2. Students will convert bacteria counts between scientific notation and standard form and order them by magnitude.
  3. Students will identify which combination of data points signals likely pollution at a sample site.

Vocabulary

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: scientific notation, bacteria count

Teacher overview

The fictional Granite Fork Reservoir supplies a small town, and its water quality team collects samples from four sites each month to check dissolved oxygen, pH, and bacteria levels. This worksheet has students read that team's data table, compare it against real water-quality standards, and use scientific notation to compare bacteria counts that can range across several orders of magnitude. A common misconception is that any bacteria in a water sample means the water is unsafe; in practice, technicians compare counts against a standard and consider multiple readings together, such as low oxygen alongside a high bacteria count, before flagging a site for cleanup.

Granite Fork Reservoir Water Quality: Reading a Sample Data Table — Grade 8 Science
Name: ____________________________ Date: ______________

Student Worksheet

The table below shows the fictional Granite Fork Reservoir monitoring team's results from four sample sites, collected on the same August morning. Use the table and the real water-quality facts beneath it to answer the questions.

Site Temperature (°C) Dissolved oxygen (mg/L) pH Bacteria count (CFU/100 mL)
A 22 7.5 7.4 3.0 × 10^2
B 27 3.8 7.0 6.7 × 10^3
C 15 9.6 7.2 4.5 × 10^2
D 20 6.9 9.8 8.5 × 10^2

Real water-quality facts:

  • Most fish need dissolved oxygen above 5 mg/L to survive, and cold water holds more dissolved oxygen than warm water.
  • The secondary (aesthetic) drinking-water standard for pH is 6.5 to 8.5.
  • In fresh water, 1 mg/L is approximately equal to 1 part per million (ppm).
  1. Which site recorded the coldest water temperature? Which recorded the warmest?
  2. List every site whose dissolved oxygen reading is safe for fish (above 5 mg/L), and every site whose reading is not.
  3. Site C is both the coldest site and the site with the highest dissolved oxygen reading. Explain why this fits the real pattern that cold water holds more dissolved oxygen than warm water.
  4. List every site whose pH falls within the secondary standard range of 6.5 to 8.5, and any site that falls outside it.
  5. Write Site B's bacteria count, 6.7 × 10^3 CFU/100 mL, in standard (expanded) form.
  6. Write Site D's bacteria count, 8.5 × 10^2 CFU/100 mL, in standard (expanded) form.
  7. Order all four sites' bacteria counts from least to greatest, using the exponents in the table to compare magnitudes without converting every value to standard form first.
  8. The reservoir manager wants to prioritize cleanup at the site with both low dissolved oxygen and a high bacteria count, since that combination often signals a pollution source such as a leaking sewer line. Which site should be the priority, and why?
  9. Site D's pH of 9.8 falls outside the secondary standard range. Suggest one reason a field technician might want to re-test Site D rather than assume the reading is correct.
  10. Convert Site C's dissolved oxygen reading of 9.6 mg/L to parts per million (ppm).

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: Site C is coldest, Site B is warmest.
    Site C recorded 15°C, the coldest reading; Site B recorded 27°C, the warmest.
  2. Answer: Sites A, C, D safe; Site B not safe.
    Site A (7.5 mg/L), Site C (9.6 mg/L), and Site D (6.9 mg/L) are all above the 5 mg/L threshold. Site B (3.8 mg/L) is below it.
  3. Answer: Colder water can hold more dissolved gas, including oxygen, than warmer water; Site C's low temperature of 15°C matches its highest dissolved oxygen reading of 9.6 mg/L, which is consistent with that real-world pattern.
  4. Answer: Sites A, B, C within range; Site D outside.
    Site A (7.4), Site B (7.0), and Site C (7.2) fall within 6.5 to 8.5. Site D (9.8) is above the upper limit.
  5. Answer: 6700 CFU/100 mL.
    6.7 × 10^3 = 6.7 × 1,000 = 6,700 CFU/100 mL.
  6. Answer: 850 CFU/100 mL.
    8.5 × 10^2 = 8.5 × 100 = 850 CFU/100 mL.
  7. Answer: A, C, D, then B, from least to greatest.
    Site A (3.0 × 10^2) < Site C (4.5 × 10^2) < Site D (8.5 × 10^2) < Site B (6.7 × 10^3). Comparing the exponents first (10^2 for A, C, and D versus 10^3 for B) and then the leading digits places B highest and A lowest.
  8. Answer: Site B.
    Site B combines the lowest dissolved oxygen reading (3.8 mg/L) with the highest bacteria count (6.7 × 10^3 CFU/100 mL), the exact combination the reservoir manager described as a likely pollution signal.
  9. Answer: A single unusual reading may reflect an error rather than reality.
    A pH of 9.8 falls well outside the normal 6.5 to 8.5 range, so it could result from sample contamination, equipment miscalibration, or a temporary local event; re-testing confirms whether the result is real before the utility responds.
  10. Answer: About 9.6 ppm.
    Because 1 mg/L is approximately equal to 1 ppm in fresh water such as a reservoir, 9.6 mg/L converts directly to about 9.6 ppm.

Differentiation

Support (below grade level)

Provide a simplified table showing only the site, temperature, dissolved oxygen, and pH columns for the pattern-recognition questions (items 2 through 4), and give students a printed conversion card showing "10^2 = 100" and "10^3 = 1,000" before items 5 through 7.

Extension (above grade level)

Ask students to calculate the removal efficiency a treatment step would need to reach if it cut Site B's bacteria count from 6.7 × 10^3 CFU/100 mL down to Site A's 3.0 × 10^2 CFU/100 mL, using the formula removal % = (influent − effluent) ÷ influent × 100. (6,700 − 300 = 6,400; 6,400 ÷ 6,700 × 100 ≈ 95.5 percent removal.)

ELL supports

Pre-teach "dissolved oxygen," "pH," and "bacteria count" with simple visuals (a fish icon next to the dissolved-oxygen threshold, a pH number line marked 6.5 to 8.5) before students read the table. Allow items 1, 2, and 4 to be answered by circling or highlighting values directly in the table instead of writing full sentences.

Extensions

Ask students to design their own fifth sample site with a temperature, dissolved oxygen reading, pH, and bacteria count in scientific notation that would make it the new cleanup priority, and explain why using the reasoning from item 8.