4.3 Environmental Engineering

Scope on the Exam

Environmental Engineering contributes about 5–8 questions to FE Civil. It blends conceptual public-health knowledge with mass-balance calculations. The NCEES FE Reference Handbook Environmental Engineering chapter contains the treatment-process equations, water-quality definitions, and air-quality standards you will need.

Water Quality Parameters

BOD is the headline organic-pollution indicator; high BOD depletes DO and harms aquatic life. The first-order BOD model is BOD_t = L₀(1 − e^(−kt)), where L₀ is the ultimate BOD.

Mass Balance — The Core Tool

The general mass-balance statement around a control volume is:

Accumulation = Inflow − Outflow + Generation − Consumption

At steady state with no reaction, mass in = mass out. A common exam form is a blending/dilution problem: Q₁C₁ + Q₂C₂ = (Q₁ + Q₂)C_mix. Always carry mass-flow units (e.g., mg/L × m³/s → kg/day with the proper conversion).

Drinking-Water Treatment Train

Conventional surface-water treatment under the Safe Drinking Water Act (SDWA) follows a fixed sequence:

Treatment-Process Order

The unit processes always run in this order — a frequent exam recall item:

1. Coagulation — add alum/ferric to destabilize colloids
2. Flocculation — gentle mixing builds settleable floc
3. Sedimentation — gravity removes floc (overflow rate = Q/A_surface)
4. Filtration — removes residual particles/turbidity
5. Disinfection — chlorine, chloramine, UV, or ozone inactivates pathogens

Wastewater treatment adds preliminary screening/grit removal, primary sedimentation, secondary biological treatment (activated sludge, trickling filter — removes BOD), and optional tertiary nutrient removal before disinfection and discharge.

EPA Drinking-Water Standards

The EPA sets Maximum Contaminant Levels (MCLs) under the SDWA. Microbiological standards target effectively zero detectable total coliform / E. coli. Primary standards protect health (e.g., lead action level, nitrate, disinfection byproducts); secondary standards address aesthetics (taste, odor, color).

Air Quality Basics

Under the Clean Air Act, the EPA defines National Ambient Air Quality Standards (NAAQS) for six criteria pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO₂), ozone (O₃), sulfur dioxide (SO₂), and particulate matter (PM₁₀ and PM₂.₅). Ground-level ozone is a secondary pollutant formed from NO_x and volatile organic compounds in sunlight.

Solid and Hazardous Waste

Municipal solid waste (MSW) is managed by the hierarchy: source reduction → recycling/composting → energy recovery → landfilling. Engineered sanitary landfills use liners and leachate collection. Hazardous waste is regulated under the Resource Conservation and Recovery Act (RCRA) by the characteristics ignitability, corrosivity, reactivity, and toxicity (cradle-to-grave tracking).