<P> In the United States, the practice of environmental assessment was formally initiated on January 1, 1970, the effective date of the National Environmental Policy Act (NEPA). Since that time, more than 100 developing and developed nations either have planned specific analogous laws or have adopted procedure used elsewhere . NEPA is applicable to all federal agencies in the United States . </P> <P> They evaluate the water balance within a watershed and determine the available water supply, the water needed for various needs in that watershed, the seasonal cycles of water movement through the watershed and they develop systems to store, treat, and convey water for various uses . Water is treated to achieve water quality objectives for the end uses . In the case of a potable water supply, water is treated to minimize the risk of infectious disease transmission, the risk of non-infectious illness, and to create a palatable water flavor . Water distribution systems are designed and built to provide adequate water pressure and flow rates to meet various end - user needs such as domestic use, fire suppression, and irrigation . </P> <P> There are numerous wastewater treatment technologies . A wastewater treatment train can consist of a primary clarifier system to remove solid and floating materials, a secondary treatment system consisting of an aeration basin followed by flocculation and sedimentation or an activated sludge system and a secondary clarifier, a tertiary biological nitrogen removal system, and a final disinfection process . The aeration basin / activated sludge system removes organic material by growing bacteria (activated sludge). The secondary clarifier removes the activated sludge from the water . The tertiary system, although not always included due to costs, is becoming more prevalent to remove nitrogen and phosphorus and to disinfect the water before discharge to a surface water stream or ocean outfall . </P> <P> Scientists have developed air pollution dispersion models to evaluate the concentration of a pollutant at a receptor or the impact on overall air quality from vehicle exhausts and industrial flue gas stack emissions . To some extent, this field overlaps the desire to decrease carbon dioxide and other greenhouse gas emissions from combustion processes . </P>

What is the role of engineer in environmental protection