Ow can engineers resolve conflicts between their obligation to meet client s needs and their obligation to sustainable development?

This is an essay of maximum 2000 words. It is worth 60% of the total mark for this module which is a core(major) module. I am studying Environmental Systems Engineering which brings together the basic concepts of Environmental Engineering and System Engineering. The Topic of this is: How can engineers resolve conflicts between their obligation to meet client s needs and their obligation to sustainable development? By engineers they mean Civil Engineers.
Regarding the topic, obviously Civil Engineers have to deliver the projects that they have been given to on-time and on-budget with maximum efficiency. In addition with rising concerns about the Environmental issues they have to take into account the sustainability of their work. They basically have to work all together towards reaching a sustainable development.
I have attached my lecture notes here also.
Dryzek J. S. and Schlosberg D. (eds) Debating the Earth 2nd edition, Oxford, Oxford University Press

Hay P. (2002) A Companion to Environmental Thought Edinburgh, Edinburgh University Press.

van Vliet, B., Chappells, H. and Shove, E. (2005) Infrastructures of Consumption Earthscan, London.
Baker S. (2006) The concept of sustainable development, Chapter 2 in Sustainable Development London, Routledge, pp. 17-48.

Bates, B.C., Z.W. Kundzewicz, S. Wu and J.P. Palutikof (2008) Implications for policy and sustainable development, Chapter 7 in Climate Change and Water. Technical Paper of the Intergovernmental Panel on Climate Change, IPCC Secretariat, Geneva, pp 125-131. Available on-line ~latour/articles/article/050.html last accessed 25th
Sismondo S. (2004) Actor-network theory, Chapter 6 in An Introduction to Science and Technology Studies Malden and Oxford, Blackwell Publishing, pp. 51-64.
Shove E. (2003) Consumption, Everyday Life and Sustainability, Chapter 1 in Comfort, Cleanliness and Convenience Oxford, Berg, pp. 1-21.
van Vliet B., Chappells H. and Shove, E. (2005) Linking Utilities and Users, Chapter 2 in Infrastructures of Consumption London, Earthscan, pp. 13-27.