WTO Source Water Characteristics 3 — Questions and Answers
Question 1: What term describes the phenomenon where warm and cold water layers fail to mix in a lake or reservoir?
- Upwelling
- Thermal stratification (Correct answer)
- Hydraulic dispersion
- Advection
Correct answer: Thermal stratification
Thermal stratification occurs when temperature-driven density differences prevent mixing between the warm epilimnion and cold hypolimnion layers.
Question 2: Which characteristic of source water most directly affects the required coagulant dose in a conventional treatment plant?
- Water temperature only
- Turbidity and NOM concentration (Correct answer)
- Dissolved oxygen level
- Calcium hardness
Correct answer: Turbidity and NOM concentration
Turbidity (suspended particles) and natural organic matter (NOM) are the primary factors that determine how much coagulant is needed to form settleable floc.
Question 3: A source water with very low alkalinity (less than 30 mg/L as CaCO3) presents what challenge during coagulation?
- Excessive sludge production
- Insufficient buffering to maintain optimal coagulation pH (Correct answer)
- Increased disinfection byproduct formation
- Elevated corrosion of distribution pipes
Correct answer: Insufficient buffering to maintain optimal coagulation pH
Low alkalinity water lacks the buffering capacity needed to maintain the optimal pH range for coagulation, often requiring alkali addition.
Question 4: What does the term 'specific conductance' measure in source water?
- The rate of heat transfer through the water
- The ability of water to conduct electrical current, indicating dissolved ion content (Correct answer)
- The concentration of suspended solids
- The rate at which turbidity settles
Correct answer: The ability of water to conduct electrical current, indicating dissolved ion content
Specific conductance measures the capacity of water to conduct electricity, which correlates directly with the total concentration of dissolved ions.
Question 5: Which naturally occurring compound in source water is most commonly responsible for a rotten egg odor?
- Ammonia
- Hydrogen sulfide (Correct answer)
- Methane
- Carbon dioxide
Correct answer: Hydrogen sulfide
Hydrogen sulfide gas, produced by sulfate-reducing bacteria in anaerobic conditions, is responsible for the characteristic rotten egg odor in some source waters.
Question 6: What is the primary significance of measuring a source water's 'true color' versus 'apparent color'?
- True color measures pH; apparent color measures turbidity
- True color is measured after filtering to remove turbidity interference, reflecting only dissolved organics (Correct answer)
- Apparent color is always higher than true color due to disinfection
- True color only applies to groundwater sources
Correct answer: True color is measured after filtering to remove turbidity interference, reflecting only dissolved organics
True color is measured after removing suspended particles by filtration, isolating the color contribution from dissolved substances like humic and fulvic acids.
Question 7: A lake experiencing eutrophication will typically show which source water quality trend?
- Decreasing turbidity and increasing dissolved oxygen
- Increasing algae growth, decreasing dissolved oxygen, and rising nutrient levels (Correct answer)
- Stable pH with declining coliform counts
- Reduced TOC with increased alkalinity
Correct answer: Increasing algae growth, decreasing dissolved oxygen, and rising nutrient levels
Eutrophication involves excessive nutrient enrichment leading to algal overgrowth, which consumes oxygen during decomposition and degrades overall water quality.
WTO Source Water Characteristics 3
What term describes the phenomenon where warm and cold water layers fail to mix in a lake or reservoir?