what is the essence of environmental engineering to civil engineering?
Civil Engineering is more concerned with building structures such as roads and bridges. They deal with determining the suitability of soils and bedrock for building locations. In cities they deal with infrastructure, bridges, roads, piping, sewers, rain drainage systems and erosion control to name just a few.
Environmental Engineers get more specialized training in areas such as building sanitary landfills, design and installation of ground water remediation systems, conduct site investigations, design containment systems to prevent the spread of contaminated ground water and ways to confine or contain hazardous materials.
For instance, an engineer I worked with implemented a process of encapsulating fly ash that contained toxic metals by mixing it with concrete.
Another designed a sanitary landfill we built in Monterey Mexico. We installed a ground water remediation system that prevented the spread of ground water containing gasoline from affecting the Houston Medical Center. Still another project, they designed was a slurry wall that "dammed" up ground water containing Mercury, preventing it from moving down gradient and affecting a neighboring property. The dammed up water was then pumped out and treated by a ground water remediation system that we designed and built.
I hope that adequately explains the difference.