Sustainability and Remediation - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 918

A rule of thumb is that the system boundaries should be the smallest set of project
operations that allows options to be compared across the same system for the options
being considered (i.e. like is compared with like) and fully describes likely benefits
and impacts.
Another important system consideration is that any comparison is made over
the same scale of operation. For example, it would not be helpful to make a direct
unscaled comparison between a pilot scale bioremediation process and full scale
excavation and disposal operation. Many sustainability indicators would be com-
pletely different on the basis of the relative scale of the operations alone, for instance
considering the impacts of vehicle movements. Quantitative Life Cycle Assessment
and carbon foot-printing uses a concept called a “functional unit” (Carbon Trust
et al. 2008a ) to ensure that like is compared with like, for example: “An appro-
priate functional unit for an ex situ treatment processes might be the treatment of
a specified amount of contaminated soil (e.g. per tonne of treatment capacity per
year)”.
Life cycle assessment boundaries consider how far the option being considered
should be broken down into sub-units requiring some sort of analysis. A key part of
understanding life cycle boundaries is the concept of cradle to grave. Thecradleis
the origin of materials or substances being considered. The grave is their ultimate
fate (US Environmental Protection Agency 2006 ). Life cycle comparisons consider
effect from origin to fate, i.e. cradle to grave. There are practical limits to how far
a cradle to grave comparison is feasible for a sustainability appraisal process. For
example, at its most extreme a determination might consider amongst other things
the impacts of using/making resources in each individual pipe, joint and fan used in
a soil venting process, even each nut and bolt. Clearly this level of detail poses great
demands on an assessor's time and resources. Another problem is how to consider
equipment that might be used over several projects, for example an excavator or
other plant. The total number of projects each of these vehicles will be used for
is probably unknown. Hence, it becomes very difficult to apportion impacts to one
single project for the production of components that are used multiple times. To set
life cycle boundaries stakeholders will need to agree:

• what is a practical limit to the level of detail, for example whether staff welfare

consumables and facilities such as protective equipment and toilets should be
considered or disregarded as broadly similar for each option being compared;

•

whether “generic” assessments for particular universal components such as
hardware can be accepted;

•

what is consumed by the project and what is used non-exclusively by the project;
where an item is consumed the impacts of its production and use must be con-
sidered; where it is re-used and not consumed the impacts of its use must be
considered but in many cases the impacts of its production might be discounted;

• where facilities already exist on a site, such as monitoring wells, the environ-

mental impacts of their construction can be discounted from the sustainability
appraisal; where facilities are constructed they should be regarded as consumed
by the project.