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Difficulty: Very hardWeakening Arguments

To combat the depletion of its primary freshwater aquifer, a coastal agricultural district plans to install solar-powered desalination micro-turbines along drainage channels. These turbines will convert brackish surface runoff into water suitable for crop irrigation. District officials project that because the converted water will meet 35 percent of the district's current annual irrigation volume, agricultural pumpage from the aquifer will decrease significantly over the next five years.

Which of the following, if true, most seriously weakens the district officials' projection?

  1. Farmers in the district plan to use the converted runoff to cultivate high-yield crop varieties that require routine soil flushing with pure freshwater from the aquifer to prevent salt buildup.Answer
  2. B
    The solar-powered turbines operate at maximum output during peak summer months when crop water demand and aquifer drawdown are highest.
  3. C
    The initial capital cost of purchasing and installing the micro-turbines will not be fully recouped by farmers within the five-year projection period.
  4. D
    Desalination facilities operating in adjacent inland agricultural districts rely on electrical grid power rather than solar energy.
  5. E
    Organic sediments present in brackish surface runoff slightly decrease the operational lifespan of the micro-turbine filtration membranes.

Answer

The argument is most seriously weakened by the finding that using converted brackish runoff requires farmers to routinely flush soil with pure freshwater drawn from the aquifer. This unstated operational side effect directly undermines the expected net reduction in aquifer pumpage.
The correct answer identifies an unintended operational consequence: using desalinated brackish water increases salt accumulation in soil, which in turn requires farmers to pump pure freshwater from the aquifer to flush the crops. This extra freshwater demand counteracts the projected 35 percent savings, severely undermining the claim that total aquifer pumpage will decrease.

Step-by-Step Solution

1
Deconstruct the core argument
Premise: Micro-turbines will supply desalinated runoff equal to 35% of current irrigation volume. Conclusion: Aquifer pumpage will decrease significantly over the next five years.
Identifying the premise-to-conclusion leap reveals the author's unstated assumption that total freshwater demand from the aquifer will drop proportionately to the new water supply.
2
Identify the unstated assumption and vulnerability
The argument assumes that introducing desalinated runoff will not trigger secondary actions or requirements that increase freshwater consumption from the aquifer.
Weakening questions for plan-to-goal arguments often rely on identifying unexpected secondary consequences that negate the goal.
3
Evaluate the choices for logical impact
The finding that farmers must flush fields with aquifer freshwater to mitigate salt buildup from the converted runoff demonstrates that using the new water source directly causes additional freshwater pumpage, invalidating the net savings projection.
This provides new empirical evidence directly attacking the central assumption of net pumpage reduction.

Key Concept

Evaluating Plan Feasibility and Counterproductive Side Effects
Estimated Time:2m 0s
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Topics

Weakening Arguments

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