LCA Background

Life-cycle assessment (LCA) is a methodology developed to systematically quantify the material and energy inputs and outputs from a product, process, or system throughout all its stages of life. It uses a cradle-to-grave (or, in some cases, cradle-to-cradle) perspective, evaluating the design process, the entire supply chain associated with manufacturing, transportation, the use phase, and waste management. The following figure illustrates the framework of LCA [SETAC 1991].

Two proven LCA methodologies are combined to analyze water and wastewater systems in WESTWeb. The older methodology is the process-based LCA. Process-based LCA is outlined in the ISO 14040 standards. Generally, the steps of an LCA include - goal and scope definition: defining study scope, boundaries, time frame, and functional unit; - inventory analysis: collecting and analyzing data; - impact assessment: translating results into meaningful, real world terms; and - improvement analysis: determining how environmental impacts can be minimized, involving iterations of the previous three steps. The steps can be iterative with the results of one phase affecting the prior steps. The figure below illustrates these steps.

Process-based LCA requires the practitioner to collect all needed data on energy and resource inputs and environmental outputs for each stage of the life-cycle and its supply chain from available sources (e.g., system operators, product manufacturers, industry experts, and available literature). As a result, it can be data-, time-, and cost-intensive. Below is a sample process diagram for concrete which might be used to guide an LCA of that product [AIA 1997]. It illustrates the complexity and diversity of products and processes that must be evaluated in an LCA for one component of a water or wastewater system. Note that there are separate process diagram figures for the Portland cement and iron oxide pigment components of the concrete.

EIO-LCA was created by the Green Design Institute at Carnegie Mellon University and can be accessed online. It utilizes the U.S. economy's input-output matrix to comprehensively map the interactions between economic sectors and define product and service supply chains. These economic data are combined with publicly-available environmental data (e.g., resource consumption and environmental emission and waste data). When the user inputs an expenditure in a particular economic sector, the model evaluates how much is spent directly in that sector and its supply chain and calculates the corresponding energy use, environmental emissions, and wastes associated with the specified expenditures. EIO-LCA allows for more cost-effective and timely LCAs at the expense of the specificity and flexibility of a process-based LCA.

WESTWeb incorporates elements from both process-based LCA and EIO-LCA because both approaches have advantages (and disadvantages). Neither provides a complete set of data for WESTWeb, and used in combination, they yield the most comprehensive results. Generally, EIO-LCA is used to determine the effects of material production, except for some chemical production. Process-based LCA is used to evaluate material production of most chemicals, energy production, direct emissions from wastewater, waste management.

More information on LCA can be found on EPA's website.