Environmental Science and Technology
What this domain tests
Environmental Science and Technology tests the reasoning behind monitoring and cleanup: where contaminants go, how they are measured, and which treatment or control train fits the waste stream. Questions often combine fate and transport with technology selection.
Core rules
- Risk requires a source, a pathway, and a receptor. Removing any one breaks the exposure route.
- Groundwater advection moves contaminants with flow; dispersion spreads them; sorption, described by Kd or Koc, retards them; Henry's law governs volatilization; biodegradation can attenuate mass.
- Dense non-aqueous phase liquids sink; light non-aqueous phase liquids float. Dissolution from either creates long-lived plumes.
- Match technology to conditions: soil vapor extraction for volatile compounds in the vadose zone; pump-and-treat for dissolved plumes, though mass removal is often limited; in-situ chemical oxidation for amenable organics; thermal treatment for volatiles; bioremediation for biodegradable organics; stabilization for metals.
- Air control: cyclones for coarse particulate matter, baghouses and electrostatic precipitators for fine particulate matter, wet scrubbers for gases and particulate matter, selective catalytic or non-catalytic reduction for nitrogen oxides, carbon adsorption for volatile organic compounds.
- Risk assessment follows hazard identification, dose-response, exposure assessment, and risk characterization. Hazard quotient equals intake divided by the reference dose; a quotient above 1 warrants evaluation. Carcinogenic risk is commonly evaluated against a 1 in 1,000,000 to 1 in 10,000 range.
Worked example
A dissolved contaminant has an initial concentration of 100 µg/L, a first-order decay constant of 0.05 per day, and a travel time of 60 days. The concentration is 100 × e^(−0.05 × 60) = 100 × e^(−3) = 4.98 µg/L, just below a 5 µg/L standard. Reasoning: verify first-order behavior, keep units consistent, and recognize that proximity to the limit makes uncertainty in the decay constant important.
Traps
- Confusing concentration with mass; dilution reduces concentration without destroying contaminant.
- Comparing total metals results to dissolved-metal standards.
- Ignoring detection limits and non-detect handling in data analysis.