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Set Impact
Limits

Learn to define criteria and constraints that guide real-world solutions for reducing environmental impact.

Earth & Space Science

What Is Environmental Impact?

An environmental impact is any change to the natural world caused by human activities. These changes can affect air, water, soil, wildlife, and climate systems.

Pollution
Chemicals, plastics, and waste released into air, water, or soil
Resource Use
Extracting fossil fuels, minerals, water, and timber beyond sustainable rates
Habitat Loss
Clearing forests, draining wetlands, and converting land for agriculture

Why Do We Set Limits?

Nature can absorb a certain amount of human activity without permanent damage. Setting impact limits means drawing a line that keeps our actions within that safe zone. Without limits, small impacts accumulate into large-scale problems.

Time Impact Level Limit Safe Zone Danger Zone Uncontrolled Managed

Key Terms: Criteria & Constraints

Criteria
The goals your solution must achieve. They describe what success looks like: for example, reduce water pollution by \( 50\% \).
Constraints
The limits your solution must work within: budget, time, materials, laws, and technology. They describe what you cannot exceed.

The Core Principle

This principle ensures solutions are measurable, achievable, and comparable. Without criteria you cannot tell if your solution works; without constraints you cannot tell if it is realistic.

Environmental Problem Proposed Solution Criteria
"Must reduce CO\( _2 \) by \( 30\% \)"
 Constraints "Budget: $10,000" "Timeline: 1 year"

Types of Criteria

Quantitative
Measurable targets with numbers: "Reduce waste by \( 40\% \)" or "Keep emissions below \( 500 \) tonnes per year"
Qualitative
Descriptive goals: "Improve local water quality to support native fish populations"
Comparative
Relative benchmarks: "Perform better than the current system" or "Match industry best practices"

Criteria vs. Constraints

Criteria Constraints
Definition Goals the solution must achieve Limits the solution must respect
Question it answers "What does success look like?" "What boundaries exist?"
Example Reduce runoff by \( 60\% \) Budget under $5,000
Can you have many? Yes: multiple criteria prioritized Yes: budget, time, material, legal
What happens if ignored? Solution fails to solve the problem Solution is impossible to build

Types of Constraints

Budget
How much money is available to design and build the solution?
Time
Deadlines, seasonal windows, or urgency of the environmental problem
Materials
Available tools, technology, and raw materials in the region
Legal / Social
Laws, regulations, community approval, and ethical standards

How to Define Criteria & Constraints

1
Identify the problem. Name the specific environmental impact you want to reduce (e.g., plastic in the school's waterway).
2
Set measurable criteria. Define what success looks like with numbers when possible: "Reduce plastic waste by \( 50\% \) in 6 months."
3
List all constraints. Budget, time, materials, laws, safety rules, and community needs.
4
Prioritize. Rank criteria from most to least important. Rank constraints from hardest to softest limits.
5
Test and revise. Check if your proposed solution meets every criterion within every constraint. If not, adjust the design.

Example 1: School Rain Garden

Problem: Stormwater runoff from the school parking lot carries oil and trash into a nearby stream.

Criteria
Reduce runoff volume by at least \( 40\% \) during a typical rainstorm. Filter out \( 80\% \) of oil and sediment.
Constraints
Budget: $2,000. Space: 200 sq ft of available land. Must be safe for students.

Rain Garden: Impact Flow

Parking Lot Oil + Trash Runoff Rain Garden Filters + Absorbs Clean Water to Stream Criteria Check
✓ Runoff reduced by \( 45\% \)
✓ Oil filtered by \( 82\% \)
 Constraint Check ✓ Cost: $1,800 < $2,000 ✓ Area: 180 sq ft < 200 ✓ Solution Approved

Example 2: Factory Emissions

Problem: A local factory releases \( 1{,}200 \) tonnes of CO₂ per year, twice the regional target.

Criteria
Reduce CO₂ emissions to at most \( 600 \) tonnes per year (a \( 50\% \) reduction).
Constraints
Budget: $50,000. Cannot shut down the factory. Must comply with air quality laws.

Example 3: School Cafeteria Waste

Problem: The cafeteria throws away \( 120 \) kg of food per week. Most ends up in a landfill producing methane.

1
Criterion 1: Reduce food waste to landfill by at least \( 60\% \) (from \( 120 \) kg to \( \leq 48 \) kg per week).
2
Criterion 2: Divert waste to composting or donation programs.
3
Constraint: Budget of $\( 500 \) for bins and signage. Must not change the lunch schedule.
4
Constraint: Must follow school health and safety rules for food handling.

Navigating Tradeoffs

Rarely does one solution satisfy every criterion perfectly. Engineers make tradeoffs: sacrificing a little on one criterion to gain on another, while staying within constraints.

Cost: Low ($\( 500 \) solution) Effectiveness
(\( 35\% \) reduction)
 vs. Cost: $5,000
\( 70\% \) reduction

Common Mistakes

✕ Vague Criteria
Saying "make it better" instead of "reduce pollution by \( 40\% \)." Without a number, you cannot measure success.
✕ Ignoring Constraints
Designing a $\( 100{,}000 \) solution when the budget is $\( 5{,}000 \). A brilliant plan that cannot be built is not a solution.
✕ Swapping the Two
Confusing criteria with constraints. "Under $\( 5{,}000 \)" is a constraint (limit), not a criterion (goal). Keep them separate.

Summary: Putting It All Together

Step Action Output
1 Identify the environmental problem Clear problem statement
2 Define criteria (goals) Measurable targets
3 Identify constraints (limits) Budget, time, material list
4 Propose a solution Design or plan
5 Evaluate against criteria + constraints Pass / fail / revise

Question 1 of 5

A town wants to reduce river pollution. Which of the following is a criterion?

Question 2 of 5

A school's eco-club has a $\( 300 \) budget to reduce cafeteria waste. The $\( 300 \) budget is best described as a:

Question 3 of 5

Which criterion is most measurable for a project to reduce air pollution from a power plant?

Question 4 of 5

A team designs a wetland filter to clean farm runoff. It removes \( 70\% \) of fertilizer but costs $\( 80{,}000 \) when the budget is $\( 50{,}000 \). What should they do next?

Question 5 of 5

Why is it important to define both criteria and constraints before designing a solution to an environmental problem?