Environmental engineering addresses the protection of water, land, and air through the design of treatment systems, pollution control measures, and impact assessment. The strength of municipal and industrial wastewater is characterized by oxygen demand. Biochemical Oxygen Demand measures the dissolved oxygen consumed by microorganisms as they decompose biodegradable organic matter over a standard period, typically five days at 20 °C. Chemical Oxygen Demand, in contrast, oxidizes both organic and inorganic matter chemically, so COD is always equal to or greater than BOD. The ratio between the two helps identify whether pollutants are readily biodegradable or contain refractory compounds that need more advanced treatment.
Wastewater treatment proceeds in stages. Primary treatment removes settleable solids and floating material through screening, grit chambers, and sedimentation, typically reducing BOD by 25 to 40 percent. Secondary, or biological, treatment employs microorganisms to degrade dissolved and colloidal organics, commonly through activated sludge or trickling filters, achieving 85 to 95 percent BOD removal. In the activated sludge process, wastewater is mixed with a floc of aerobic microorganisms in an aeration tank and then separated in a secondary clarifier, with return sludge recycled to maintain biomass. Disinfection, usually by chlorination, inactivates remaining pathogens; a residual chlorine concentration is held in the distribution system to prevent microbial regrowth. Throughout, Total Dissolved Solids quantify the sum of dissolved inorganic and organic substances in the water, indicating salinity, mineralization, and potential taste or health concerns. Sanitary sewer systems, separate from stormwater drainage, collect domestic and industrial wastewater and convey it to treatment, while Environmental Impact Assessments systematically evaluate potential environmental effects of proposed projects and inform mitigation before construction proceeds. Solid waste is managed in landfills protected by liner systems, typically compacted clay, geomembranes such as HDPE, or composite liners, that prevent leachate from migrating into groundwater and surrounding soil.
Construction management translates design into completed facilities through planning, scheduling, cost control, and quality assurance. The Critical Path Method sequences project activities into a network, identifies the longest path of dependent tasks that determines the minimum project duration, and flags activities whose delay would extend the overall schedule. Activities on the critical path carry zero float, while non-critical activities have positive float, expressed as total float (delay that does not postpone project completion) or free float (delay that does not postpone any successor's earliest start).
Project performance is tracked using the Earned Value Method, which compares planned value, earned value, and actual cost to produce cost and schedule indices. A Cost Performance Index less than 1.0 signals cost overrun, in which each dollar spent earns less than a dollar of value; a Schedule Performance Index less than 1.0 signals schedule slip. Visual scheduling is provided by Gantt charts, timelines that show start dates, durations, and dependencies for each activity and make progress and conflicts easy to track. The Work Breakdown Structure hierarchically decomposes total scope into manageable work packages, providing the foundation for estimating, scheduling, and resource allocation.
Field execution is governed by documents and roles that translate plans into compliant work. A punch list records incomplete or deficient items identified during a final walkthrough that the contractor must correct before substantial completion. A change order formally authorizes modifications to contract scope, cost, or schedule after agreement among owner, contractor, and engineer. The clerk of the works is the owner's on-site representative, inspecting daily construction for conformance with contract documents, specifications, and approved shop drawings. Building codes set the minimum requirements that all of these processes must satisfy: the International Building Code is widely adopted across the United States and provides minimum standards for structural, fire safety, and egress systems. Occupancy classification assigns buildings to categories such as Assembly, Business, Educational, or Residential, so that appropriate fire protection and egress provisions apply. Fire-resistance ratings express in hours how long a building element can withstand a standard fire while maintaining integrity and limiting fire spread. ADA compliance mandates accessible routes, entrances, restrooms, and facilities for persons with disabilities.
Loads are prescribed by ASCE 7, which establishes the basic wind speed used to compute wind pressures for a specified return period and lists the load combinations used in LRFD design, such as 1.2D + 1.6L for dead and live loads or 1.2D + 1.0W + L for combinations including wind, where D is dead load, L is live load, and W is wind load. Seismic design uses the response modification factor R, which reduces the elastic seismic force to reflect a structure's ductility, energy dissipation capacity, and overstrength. Higher R values are assigned to more ductile systems, permitting lower design forces for equivalent performance. Through these interlocking frameworks, environmental safeguards, scheduling and cost discipline, building code requirements, and load design ensure that projects are delivered safely, economically, and sustainably.