Page 272 - Materials Chemistry, Second Edition

260 LIFE CYCLE ASSESSMENT HANDBOOK

materials from waste are shipped to foreign markets. In many cases, these sec-
ondary markets are located in the East Asia region. While it is relatively straight
forward to characterize transportation-related energy consumption and associ-
ated emissions, data characterizing the energy and emissions for manufactur-
ing operations in East Asia is not readily available. This has been recognized
as perhaps being the biggest gap in knowledge for completing LCAs for recy-
cling (Kviseth and Tobiasson, 2011). Therefore, there is an implicit assumption
those manufacturing facilities have similar energy use and emissions profiles
as North American or European manufacturing facilities where data is more
readily available.

11.4.5 Time Scale Boundaries

Typically, waste management studies focus on annual waste generation and
management (tied to municipal and regional waste management and plan-
ning) and therefore most LCAs for waste management often reflect a one-year
time boundary. However, for landfills emissions occur over a long period
of time after waste placement. For landfills, the time boundary is typically
extended to 100 years (or more, or less) to capture emissions over time and
then apply those emissions to the current year being studied so results among
waste management alternatives are comparable.
LCA can be used to project future end-of-life burdens and impacts. Waste
tonnages, composition, and other aspects (e.g., energy prices, recyclables
prices, and compost product prices) can be altered to reflect changes over time.

11.4.6 Key LCA Modeling Decision Points

As with any LCA, many decisions must be made in building an LCI/LCA for
waste management. Even in quantitative LCIs/LCAs, a combination of factual
data, engineering estimates, proxies, and assumptions are used. Estimates,
proxies and assumptions allow LCA practitioners to evaluate systems when
factual data either cannot be obtained within the context of the study or do
not exist. Figure 11.5 provides a qualitative (and general) representation of the
level of significance to LCA results and uncertainty for different data elements
by waste process.
Because decisions about the use of engineering estimates, proxy data,
and assumptions can substantially affect study results, a series of "what
if" calculations or sensitivity analyses are often performed on the results to
examine the effect of making changes in the system. A sensitivity analysis
will temporarily modify one or more parameters and affect the calcula-
tion of the results. Observing the change in the results will help determine
how important the assumptions are with respect to the results. The com-
putational spreadsheet is also used to perform these sensitivity analysis
calculations.
In addition to what type of data is both available and needed to meet the
goals of the LCA, additional, and key, decision points might include: