By : Wayne B. Trusty Project Manager of the Sustainable Construction Materials Project, Fax: 613 269-3796

The Sustainable Construction Materials Project has made preliminary efforts to assess and take into account a variety of environmental impacts normally either ignored or discussed in only qualitative terms in life cycle assessments (LCA).

The objective of the Project is to develop a systems model, called Athena, which will allow building designers, researchers and policy analysts to readily assess the relative life-cycle environmental impacts of using various building materials in low-rise applications. Since 1992, the project has been undertaken by a research alliance of private, public and university researchers, organized by Forintek Canada and supported by Natural Resources Canada.

Based on detailed life cycle analysis - a method increasingly favoured as the best way to answer complex environmental impact questions and to resolve issues - the model allows comparisons of building designs in a holistic, cradle-to-grave framework. The current focus is on vertical and horizontal structural assemblies using wood, steel and concrete products in light industrial and low-rise commercial, institutional and residential buildings. The model encompasses about 35 traditional and new structural building products and more than 50 assemblies. The assemblies are recognizable units of a building structure, clearly defined in terms of size and composition, which model users can readily visualize and manipulate when developing a structural design. The perspective is Canadian and the scope national, with regional sub-divisions.

The model takes account of environmental impacts from the resource extraction and product manufacturing stages, through on-site construction, operations and maintenance to ultimate demolition and disposal of a structure, including transportation within and between activity stages. A full range of environmental impacts is incorporated, including: natural resource, energy and water use; a variety of atmospheric emissions and liquid effluents; and solid wastes. In fact, the model covers so many individual waste substances and compounds that we are now developing indices to simplify the output and provide measures that will be more meaningful to typical model users. For example, users are provided with a greenhouse gas index which shows the total effect of a design in terms of its contribution to the greenhouse gas problem.

While our basic life-cycle analyses for wood, steel and concrete building products include energy and associated emissions and other wastes for resource extraction, they do not include the many other environmental effects associated with timber harvesting, mining and quarrying: effects on biodiversity, water quality, wildlife habitat, etc.

Most studies either ignore such effects entirely, or limit themselves to a few qualitative observations and advise users to remember that this broader group of effects could be significant and might perhaps outweigh the more readily quantified impacts. Yet such effects are often the primary focus of environmental concern on the resource extraction side, particularly for wood products. Also, producers of other products feel they have a definite advantage over wood in terms of resource extraction impacts and would not consider comparisons fair if we did not take these effects into account.

We, therefore, were convinced we had to find a way of prioritizing, or combining these effects into a useful measure. In LCA terms, we had to advance from inventory analysis to impact assessment in this critical area. Deciding how to make that advance was a challenge from the beginning of the project.

We began with the premise that resource extraction activities have to be undertaken with a view to the ecological carrying capacity of the relevant ecosystems. We define ecological carrying capacity as the ability of an ecosystem to absorb the varied effects of resource extraction. The term obviously encompasses a broad and diverse range of potential effects of the type already mentioned. We implicitly consider ecological carrying capacity to be a natural resource with limits like any other. The limits define the point after which irreversible or serious damage would occur.

Background on the ATHENA Project A research alliance organized by Forintek Canada, including private, public and university researchers, first carried out a major study of the relative environmental impacts of concrete, steel and wood in structural applications. That work resulted in a series of six research volumes of environmental impacts applicable to structural systems in low-rise buildings. The Alliance has since completed a series of new studies, with funding support from Natural Resources Canada. The series includes: a study on the environmental effects of producing steel building products in mini-mills; additional work on demolition and disposal issues; the development of indices to combine atmospheric emission and liquid effluent data in terms of greenhouse gas toxicity and similar criteria; a comparative analysis of initial (non-structural as well as structural) and recurring (maintenance and retrofit) embodied energy and operational energy for a three storey generic office building. Structural embodied energy estimates for the latter study were developed by hand using data from the relevant unit factor reports, and the results are being used to test the systems model. This article focuses on the study of the relative ecological carrying capacity effects of extracting resources to manufacture building products. The ultimate product of the whole project is a computer model called Athena. The model compiles resource, water and energy use, atmospheric emissions, liquid effluents and solid wastes from the extraction of basic resources through product manufacturing and building construction.

While we consider the fact that ecological carrying capacity effects are as important as other more readily quantified resource inputs and waste outputs, these effects are much harder to incorporate because:
there are many different types of effects;
many effects are not measured or are not consistently measurable;
we are unable to compare measures across impact types;
we have to make value judgments or accept trade-offs because an environmental loss from one perspective may be a gain from another (e.g. site improvements v. wildlife habitat);
there is conflicting scientific evidence or lack of scientific concensus; and
variations in impact levels and implications depend on location, resource extraction methods, remedial actions and other very specific conditions.

The last point about location and other factors that determine impact levels is particularly critical for a model like ours. Even with full scientific agreement and ample data, it might be impossible to incorporate many of the effects in specific terms because our model deals with large geographic areas and average or typical extraction techniques. We therefore had to find some other means of quantifying the combined ecological carrying capacity effects.

We started with an overview study of ecological carrying capacity effects, carried out by by Dr. Robert Paehlke. Dr. Paehlke's task was to identify, assess and compare the critical ecological carrying capacity impacts on a qualitative basis. He was also asked to assess the potential for quantification and to recommend an approach.

Dr. Paehlke concluded it would not be possible to develop measures for ecological carrying capacity effects that would be comparable to those for other, more precisely defined, impact categories. He recommended an expert survey and scoring approach as an alternative.

Dr. Paehlke specifically suggested that we should:
distinguish several dimensions of resource extraction;
ask an expert panel to score different resource extraction activities by dimension;
combine the ranks or scores in an index; and
apply the index to the quantities of resources used for each construction product.

We accepted his recommendations and established a panel of 30 experts with background information and then sent a pre-tested questionnaire with an accompanying guide. Twenty-three of the 30 experts eventually completed and returned the questionnaires.

We asked the panelists to consider the ecological carrying capacity impacts of six resource extraction activities - timber harvesting in coastal British Columbia, timber harvesting in the boreal forest and British Columbia interior, iron ore and coal mining, limestone quarrying and aggregates extraction - in terms of four impact dimensions: intensity, extent, duration and significance.

Intensity refers to the degree of overall environmental disruption. How much of the ecology of an area is disrupted either temporarily or permanently by extraction activities?

Extent is self-explanatory and is the one dimension that can be measured fairly easily. We asked panelists to consider the extent of areas typically affected directly or indirectly per unit of resource extraction.

Duration refers to the average length of time before affected areas return to ecological productivity and balance, even though this seldom represents a return to the exact pre-extraction conditions. Panelists were asked to take account of typical regeneration or restoration practices.

Significance refers to such considerations as the uniqueness of areas typically affected, their ecological richness and aesthetic value.

Respondents were asked to consider the various extraction impacts relative only to each other and not to any other activities or environmental concerns.

The small sample size limited our choice of descriptive statistics and our ability to apply statistical significance tests. We are also cautious about how we interpret and use the results because of the very subjective nature of the responses. After trying various types of weighting approaches, we reduced the survey scores to a simple index. The index numbers are then used in Athena as weights applied to the actual resource requirements to make the products of interest. The resulting estimates can be thought of as ecologically weighted resource requirements.

This ecological capacity survey represents the first effort at a different approach to dealing with a quite complex and critical aspect of environmental impacts. Overall, we think the study is a step in the right direction. We can not wait for scientific certainty or hard ecological carrying capacity impact data before we include resource extraction impacts in life cycle assessments.

The technique described here allows us to combine estimates of the effects of extracting resources with the mass or volumes of resources required to make products. In some cases, a relatively low extraction impact per unit of resource will be overshadowed by the mass or volume of resource required. In others, the reverse may be true. Both sides of the coin need to be taken into account to get a balanced picture of environmental impacts.

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