The School Parking Lot Problem
A school wants to build a new parking lot on a grassy field. The field is home to a population of ground-nesting bees and a small wetland area that drains into a nearby stream. The school board proposes covering the entire field with asphalt. A group of students investigates the potential environmental impact. They find that the field absorbs rainwater, reducing runoff, and that the bees are important pollinators for nearby gardens. The students propose an alternative: a permeable pavement parking lot that allows water to filter through, and leaving a strip of wildflowers along the edge. They present data: permeable pavement costs 20% more upfront but reduces runoff by 70% and supports bee habitat. The school board is concerned about cost.
1. Identify the trade-offs involved in choosing between the conventional asphalt parking lot and the permeable pavement with wildflower strip. Consider environmental, economic, and social factors. Which option would you recommend and why?
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Trade-offs include: Environmental: asphalt increases runoff, which can cause flooding and pollution of the stream; it destroys bee habitat. Permeable pavement reduces runoff and preserves some habitat, but may require more maintenance (clogging) and may not be suitable for heavy vehicles. Economic: asphalt is cheaper upfront (20% less), but permeable pavement may have lower long-term costs due to reduced drainage infrastructure needs and environmental benefits. Social: the wildflower strip provides aesthetic value and educational opportunities, but some may prefer more parking spaces. Recommendation: permeable pavement with wildflower strip is preferable because it mitigates environmental harm, supports pollinators, and aligns with sustainability education. The higher upfront cost can be justified by long-term savings and community benefits. However, if budget is extremely tight, a compromise could be to use conventional asphalt but incorporate rain gardens and bee hotels. The decision should involve stakeholders and consider life-cycle costs.
2. The students claim that permeable pavement reduces runoff by 70%. What evidence would they need to support this claim, and how could they design a simple experiment to test it?
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To support the claim, the students need quantitative data comparing runoff from permeable pavement versus conventional asphalt under controlled conditions. They could design an experiment using two small trays: one filled with a permeable pavement sample (or a simulated porous surface like gravel) and one with a solid impermeable surface (like a plastic sheet or asphalt sample). They would simulate rain by pouring a measured volume of water (e.g., 1 L) over each tray at a consistent rate, and collect and measure the runoff. They should repeat trials and calculate the percentage reduction. They also need to control slope, compaction, and initial moisture. To be more realistic, they could test actual permeable pavement installations and measure runoff during rain events, but that requires access. The claim of 70% would be supported if the average runoff from permeable pavement is 30% of that from asphalt. They should also consider that permeable pavement may have different runoff characteristics over time as it clogs, so they should test both new and maintained surfaces.