Quiz & test questions Grade 9 Science
Verdon Water Quality Unit Test: Treatment and Standards
A grade 9 unit test on drinking-water treatment and quality standards, mixing multiple-choice, short-answer, and computation items at a fictional town's plant.
Objectives
- Students will recall key drinking-water quality standards and treatment steps.
- Students will calculate removal efficiency, chlorine feed, and filter loading.
- Students will explain how treatment protects public health and river life.
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.
- Chlorine residual
- Chlorine residual is the small amount of chlorine still left in the water after it leaves the treatment plant. It keeps protecting the water from germs all the way to your faucet.
- 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.
Also: removal efficiency, filter loading rate
Teacher overview
This 40-minute unit test (30 points total) checks whether students can recall drinking-water quality standards and apply treatment math. It is set at the fictional town of Verdon's surface water plant and mixes three multiple-choice items, three short-answer items, and four computation items. The computation items use operator formulas for removal efficiency, chlorine feed, filter loading, and detention time.
Assessment
The town of Verdon (a fictional town) runs a surface water treatment plant. Use these formulas where needed: removal efficiency (%) = (influent − effluent) ÷ influent × 100, pounds per day = dose (mg/L) × flow (MGD) × 8.34, filter loading rate = filter flow ÷ filter area, and detention time = volume ÷ flow.
- (2 points) Finished drinking water must stay at or below which turbidity value in 95 percent of monthly samples?
- A) 3.0 NTU
- B) 1.0 NTU
- C) 0.3 NTU
- D) 15 NTU
- (2 points) A safe chlorine residual to maintain in the distribution system is usually in which range?
- A) 0.2 to 2.0 mg/L
- B) 10 to 20 mg/L
- C) 0.001 mg/L
- D) above 4.0 mg/L everywhere
- (3 points) Name the four main steps of conventional surface water treatment, in the order they happen.
- (4 points) Verdon's raw water enters at 15 NTU of turbidity and leaves treatment at 0.3 NTU. Calculate the turbidity removal efficiency as a percent.
- (4 points) Verdon adds chlorine to 2 MGD of water at a dose of 2.5 mg/L. Find the chlorine feed in pounds per day, using pounds per day = dose × flow × 8.34.
- (3 points) Verdon's wastewater treatment plant releases treated water into the river below town, and the river needs dissolved oxygen above 5 mg/L for fish. Explain one way the wastewater plant helps protect the health of that river.
- (2 points) The secondary, aesthetic standard for drinking-water pH is which range?
- A) 0 to 3
- B) 6.5 to 8.5
- C) 10 to 12
- D) exactly 7
- (4 points) One of Verdon's filters has a surface area of 150 square feet and passes 600 gpm. Find the filter loading rate in gallons per minute per square foot, and state whether it falls within the usual 2 to 6 range.
- (2 points) Explain why a plant keeps a small chlorine residual in the pipes all the way to homes, rather than removing all chlorine at the plant.
- (4 points) Verdon's clearwell holds 300,000 gallons and the plant flow is 1,000 gpm. Find the detention time in the clearwell in minutes.
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: C) 0.3 NTU. The surface water rules require finished water at or below 0.3 NTU in 95 percent of monthly samples.
- Answer: A) 0.2 to 2.0 mg/L. Systems keep a small residual in this range; the 4.0 mg/L figure is the maximum allowed, not the target everywhere.
- Answer: Coagulation, sedimentation, filtration, disinfection. These are the four main steps of conventional treatment, in order.
- Answer: 98 percent. (15 − 0.3) ÷ 15 × 100 = 14.7 ÷ 15 × 100 = 98 percent.
- Answer: 41.7 pounds per day. 2.5 mg/L × 2 MGD × 8.34 = 5 × 8.34 = 41.7 pounds per day.
- Answer: Accept any correct idea, such as removing organic matter and solids so the released water uses less oxygen, which helps keep the river's dissolved oxygen above the 5 mg/L that fish need.
- Answer: B) 6.5 to 8.5. This is the secondary, aesthetic pH range for drinking water.
- Answer: 4 gpm per square foot, within the range. 600 gpm ÷ 150 square feet = 4, which falls within the usual 2 to 6 gpm per square foot range.
- Answer: The residual keeps disinfecting the water as it travels, so germs that enter through a leak or that regrow in the pipes are controlled before the water reaches homes.
- Answer: 300 minutes. 300,000 gallons ÷ 1,000 gpm = 300 minutes of detention in the clearwell.
Differentiation
Support
Provide the four formulas on a reference card and give the subtraction step for item 4 already set up (15 − 0.3), so students can focus on completing the division and multiplication.
Extension
Have students find what plant flow, in gallons per minute, would cut the clearwell detention time in item 10 to exactly 200 minutes, working backward from the detention-time formula.
ELL supports
Pre-teach "turbidity," "chlorine residual," "removal efficiency," and "detention time" with labeled diagrams. Allow short-answer items 3, 6, and 9 to be answered with a labeled sketch and a short phrase, and provide a word bank of the four treatment steps for item 3.