Sources delivering filtered or naturally filtered water to consumers can include which of the following?
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AInfiltration galleries connected to a sump well near a riverbank
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BInfiltration wells constructed in riverbank alluvium
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CRanney (radial collector) wells sunk to intersect riverbank gravel
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DAll of the above.
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ENone of these.
Answer
Correct Answer: All of the above.
Explanation
Introduction / Context:Riverbank filtration and riverbed infiltration are natural pre-treatment methods. Properly designed galleries and radial collector wells can provide relatively low-turbidity water with moderated temperature and reduced pathogen loads before additional treatment.
Given Data / Assumptions:
- Alluvial river setting with permeable sand/gravel deposits.
- Hydraulic connectivity between river and adjacent aquifer materials.
- Proper setback to avoid direct surface intrusion during floods.
Concept / Approach:Infiltration galleries (horizontal drains) and infiltration wells tap bank-side groundwater induced by river stage gradients, providing natural filtration through alluvium. Ranney wells extend multiple lateral collectors into the aquifer, greatly increasing intake area and capacity.
Step-by-Step Solution:
Recognize common design variants: galleries, vertical infiltration wells, and radial collectors.All rely on bank/bed filtration processes that improve raw-water quality.Therefore, each listed option is a valid consumer supply source (with appropriate treatment).Verification / Alternative check:Performance data show reductions in turbidity and microbes downstream of bank filtration; subsequent disinfection is still required for safety.
Why Other Options Are Wrong:“None of these” contradicts established practice; “All of the above” correctly aggregates the viable methods.
Common Pitfalls:Underestimating pathogen breakthrough during floods; neglecting clogging (schmutzdecke) management at the riverbed interface; ignoring wellhead protection.
Final Answer:All of the above.