Policy Analysis. Environmental Implications of Service Industries

Transcription

1 Downloaded via on September 21, 2018 at 18:29:44 (UTC). See for options on how to legitimately share published articles. Policy Analysis Environmental Implications of Service Industries JEFFREY ROSENBLUM, ARPAD HORVATH, AND CHRIS HENDRICKSON*, Department of Civil and Environmental Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania , and Department of Civil and Environmental Engineering, University of California at Berkeley, Berkeley, California The service sector in the U.S. economy accounts for twice the monetary output of manufacturing and is typically perceived as less damaging to the environment than manufacturing sectors. We use an Economic Input- Output Life-Cycle Assessment model (EIO-LCA) to assess both the direct and indirect (supply chain) effects of services on the economy and the environment. As expected, environmental emissions and wastes generated directly by service providers are small per dollar of output, and energy use per dollar output is lower for services than for most manufacturing industries. However, with such a large share of the Gross Domestic Product (GDP), the impacts of services have become a significant component of overall U.S. emissions, wastes, and energy consumption. For several environmental metrics (e.g., hazardous waste generation), service industries have significant indirect environmental effects on an economy-wide basis even when their direct emissions are negligible. When an average annual market basket of goods and services is purchased by an average consumer in the U.S., the amount spent on manufactured goods is about 25% greater than that spent on services, but the environmental effects associated with manufacturing are about two to three times that of services. To investigate services in more detail, four representative service industries were analyzed: trucking and courier services, retail trade, colleges and universities, and hotels. Some results are expected, such as the high direct consumption of electricity, the low direct emission of toxic chemicals, and the low direct generation of hazardous wastes. We demonstrate that the supply chain environmental effects associated with these four services are more significant and merit further consideration. A better understanding of these impacts will encourage service providers to consider more carefully the environmental implications of their supply chain. Introduction As economies of industrialized nations are increasingly becoming service-oriented, more attention to the environ- * Corresponding author phone: (412) ; fax: (412) ; cth@cmu.edu. Carnegie Mellon University. University of California at Berkeley. mental impacts of providing such services is warranted. In the United States, roughly 60% of the 1996 GDP is associated with the service sector (which excludes manufacturing, mining, agriculture, forestry and fishing, government services, electric, gas, and sanitary services, and transportation) (1). With transportation, government, electric, gas, and sanitary services added, this fraction jumps to 80%. Traditional manufacturing companies are developing a substantial presence in the service sector, such as the financing, information technology, and real estate subsidiaries of automobile companies, and new service domains are emerging, such as e-commerce. Environmental engineering and policy has tended to focus upon processes with a high concentration of pollution as measured by emissions to different media or quantity of emissions per unit of production. Service industries have tended to be ignored in the formulation of environmental policy because of their relatively low emissions at their point of generation (2). In addition, services often lack a well-defined unit of production, so it is difficult to assess their relative performance over time or between companies. The service sector can influence environmental performance in some important ways: 1. Influencing suppliers to provide more environmentally conscious products and services. 2. Reducing resource inputs in their operations such as through energy efficiency programs and cutting business travel. 3. Educating consumers about the relative merits of different products that are offered (particularly in the retail sales sectors). 4. Reducing resource use on the part of consumers by substituting more environmentally beneficial services or activities (e.g., substituting teleconferencing services for business travel). Measurement and assessment of these various activities can be difficult, especially in item 4. For example, telecommuting services might reduce travel but might lead to increased sprawl as telecommuters opt for ex-urban residences. Measuring the benefits of telecommuting is further complicated by rebound effects if reduced work-related commuting time is used for increased pleasure travel (such as more trips for shopping or vacations). In this paper, we focus upon item 1 and 2 effects and attempt to trace both the direct and the indirect supply chain environmental effects for several important service industries. In particular, we shall examine the four services described in Table 1. We selected these as representatives of major service categories: transportation, trade, education, and tourism. Approach: Economic Input-Output Analysis Life-Cycle Assessment (EIO-LCA). Life-cycle assessment (LCA) is an appropriate method for systematic assessment and analysis of the environmental implications of services generation. Because of its comprehensiveness and public availability of data, we employed an economic input-output analysisbased LCA approach in this paper (3). Leontief developed a linearized general equilibrium model to examine the economy-wide implications of a change in the output of economic industries (4). Leontief and others have suggested the incorporation of resource consumption and environmental discharges into the I-O framework (5-7) but lacked comprehensive data. Carnegie Mellon University researchers have developed the Economic Input /es CCC: $ American Chemical Society VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY Published on Web 09/28/2000

2 TABLE 1. Service Sectors Selected for Detailed Analysis sector 1992 sector output ($ million) standard industrial classification (SIC) codes a trucking and courier services (nonair) 157, , 423 retail trade, except eating and drinking 522, [excl. *546], 59 colleges, universities, and professional schools 43, hotels 52, a Descriptions available at TABLE 2. Service Sectors in the 1992 Input-Output Tables railroads and related services; funeral service and crematories; motion picture services and local and suburban transit and portrait photographic studios, and theaters; interurban highway passenger other miscellaneous personal videotape rental; transportation; services; theatrical producers (except trucking and courier services, electrical repair shops; motion picture), bands, orchestras except air; watch, clock, jewelry, and and entertainers; warehousing and storage; furniture repair; bowling centers; water transportation; beauty and barber shops; professional sports clubs and air transportation; miscellaneous repair shops; promoters; pipelines, except natural gas; services to dwellings and other racing, including track operation; freight forwarders and other buildings; physical fitness facilities and transportation services; personnel supply services; membership sports and recreation arrangement of passenger computer and data processing clubs; transportation; services; other amusement and recreation telephone, telegraph detective and protective services; services; communications, and miscellaneous equipment rental doctors and dentists; communications services, nec a ; and leasing; hospitals; cable and other pay television photofinishing labs and nursing and personal care services; commercial photography; facilities; radio and tv broadcasting; other business services; other medical and health services; sanitary services, steam supply, management and public relations veterinary services; and irrigation systems; services; other medical and health services; wholesale trade; research, development, and elementary and secondary schools; retail trade, except eating and testing services, except colleges, universities, and drinking; noncommercial; professional schools; banking; advertising; private libraries, vocational credit agencies other than banks; legal services; schools, and educational services, security and commodity brokers; engineering, architectural, and nec a ; insurance carriers; surveying services; business associations and insurance agents, brokers, and accounting, auditing and professional membership services; bookkeeping, and miscellaneous organizations; real estate agents, managers, services, nec a ; labor organizations, civic, social, operators, and lessors; eating and drinking places; and fraternal associations; owner-occupied dwellings; automotive rental and leasing, religious organizations; royalties; without drivers; other membership organizations; hotels; automotive repair shops and job training and related services; other lodging places; services; child day care services; laundry, cleaning, garment automobile parking and car residential care; services, and shoe repair; washes; social services, nec a a nec ) not elsewhere classified. Output Life Cycle Assessment (EIO-LCA) method using U.S. data (8, 9). The model utilizes the 1992 U.S. Department ofcommerce I-O technical coefficient matrix (10, 11) in which the economy is disaggregated into 485 commodity industries, representing one or more of the four-digit Standard Industrial Classification (SIC) codes. Services are comprehensively covered in the 1992 coefficient matrix. (The 1997 tables are expected in 2001.) EIO-LCA extends the I-O matrix by augmenting it with vectors of environmental discharge and resource use coefficients by each sector. The industry coefficient is the unit resource use, emission, or waste per dollar of industry output. The resource use data include electricity, fuel use, ore (e.g., iron and copper), and fertilizer consumption. Total energy consumption includes electricity and fuels (bituminous and anthracite coal, natural gas, liquefied natural gas, liquefied petroleum gas, motor gasoline, kerosene, aviation fuel, jet fuel, light fuel oil, heavy fuel oil). Environmental discharge data include some 650 toxic chemical emissions from the U.S. Environmental Protection Agency s (EPA) Toxics Release Inventory (TRI) to air, water, land, and underground wells (12), hazardous waste generation amounts from the Resource Conservation and Recovery Act (RCRA) data set (13), and some conventional pollutants (e.g., SO 2, volatile organic compounds - VOC). An index of toxicity potential called CMU-ET is also calculated. CMU-ET weights different chemical species of emissions using relative toxicity based on occupational health and safety threshold limit values (TLV) (14). The EIO-LCA model captures both the direct and indirect environmental discharge implications of a simulated change in demand for a commodity produced by an industry (e.g., VOC emissions resulting from a one million dollar change in demand for the paints and allied products industry s manufacturing). The direct component is defined as the environmental emission effect that can be attributed directly to an industry s operations (e.g., VOC emissions attributed the facilities designated as making paints and allied ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 22, 2000

3 FIGURE 1. Relative contribution of the major economic sectors to the 1992 U.S. economic output (1). products.) The indirect component results from a corresponding change in demand for all other industries in the economy associated with the supply chain for an industry (e.g., VOC emissions from the industries which supply goods and services to the paints and allied products industry, and the VOC emissions resulting from their suppliers, then the suppliers of their suppliers, etc.). In its current form, using sectoral analysis, EIO-LCA does not provide information about specific products (e.g., two different brands of paint) or producers. However, product comparisons using specific compositions are possible using the Product EIO-LCA approach (15). Impacts of Services Compared with Other Major Sectors of the Economy. Formally, the 485 commodity industries, as defined by the U.S. Department of Commerce, consist of manufacturing (352 industries), services (79), construction (15), agriculture (20), mining (10), and special industries (10). For this analysis, we grouped the 485 industries into four sectors: manufacturing, utilities, services, and other. Table 2 lists the I-O commodity industries defined as services here. We grouped electric services (utilities), natural gas transportation, natural gas distribution, and water supply and sewerage systems in a utilities category as their outputs are more of a product than a service. The construction, agriculture, mining, and special industries sectors are grouped into a category called other. Figure 1 shows each major economic sector s contribution to the 1992 U.S. FIGURE 2. Direct and indirect energy use (electricity plus fuels) by the major sectors of the U.S. economy. FIGURE 3. Direct and indirect generation of RCRA hazardous wastes by the major sectors of the U.S. economy. economic output. Services represent over half of the overall economy. Note that the total economic output for the U.S. is higher than the GDP because total output includes material, energy, etc. costs, while the GDP is an economic indicator that sums only the value added (employee compensation, indirect business taxes and property-type income) orsin another definitionsthe total final demand (largely, domestic private and government purchases, and exports). Table 3 compares the impacts of the service industries to other sectors of the economy for energy use, global warming TABLE 3. Direct and Indirect Environmental Implications of the Major Sectors of the U.S. Economy manufacturing services utilities other direct indirect direct indirect direct indirect direct indirect For Total Sector Economic Output energy (10 6 Terajoules) RCRA haz. wastes generated (10 6 metric tons) GWP (10 6 mt CO 2 equiv.) Per Million Dollars of Economic Output energy (Terajoules) RCRA haz. wastes generated (metric tons) GWP (mt CO 2 equiv) TABLE 4. Selected Environmental Emissions of Major Consumer Spending Categories for $29,850 of Average Consumer Demand in 1992 total emissions (direct plus indirect) expenditure CO NO 2 PM10 SO 2 VOC GWP category $29,851 total (lbs/yr): ,186 manufacturing 38% 59% 46% 34% 30% 63% 41% services 30% 25% 15% 21% 14% 25% 15% utility 5% 6% 31% 21% 48% 6% 37% property rent 27% 10% 8% 23% 8% 7% 7% VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

4 TABLE 5. Resource Inputs and Environmental Outputs of Four Service Sectors for One Million Dollars of Demand in Each Sector trucking/ courier retail trade colleges and universities hotels total % direct total % direct total % direct total % direct Resource Inputs electricity (million kwh) % % % % energy (Terajoules) 25 56% % % ores iron ore (metric ton) 6.6 0% 3.2 0% 6.2 0% 3.6 0% copper ore (metric ton) 18 0% 10 0% 23 0% 12 0% bauxite (metric ton) % % % % gold ore (metric ton) 4.2 0% 2.3 0% 4.9 0% 2.6 0% Environmental Outputs TRI total (metric ton) % % % % air % 69% 0% 73% 0% 69% 0% 67% 0% water % 5% 0% 6% 0% 5% 0% 9% 0% land % 12% 0% 8% 0% 9% 0% 8% 0% underground % 14% 0% 13% 0% 16% 0% 16% 0% CMU-ET total (metric ton) % % % % RCRA generated (metric ton) 43 0% 9.4 0% 13 9% 14 0% SO2 (metric ton) % 2.1 0% % % NOx (metric ton) 11 87% % % 2.0 6% CO (metric ton) 24 92% % % 1.2 1% VOC (metric ton) % % 0.3 3% 0.3 2% PM10 (metric ton) % % % % GWP mt CO 2 equiv % % % 770 7% TABLE 6. Resource Inputs and Environmental Outputs of Four Service Sectors for Total Output of Each Sector trucking/courier retail trade colleges and universities hotels total % direct total % direct total % direct total % direct total output ($ million) 157, ,000 44,000 52,000 Resource Inputs electricity (million kwh) 34,000 34% 200,000 81% 8,000 42% 34,000 86% energy (Terajoules) 3,900,000 56% 4,100,000 22% 180,000 12% 540,000 12% ores iron ore (metric ton) 1,000,000 0% 1,700,000 0% 300,000 0% 200,000 0% copper ore (metric ton) 2,800,000 0% 5,300,000 0% 1,000,000 0% 650,000 0% bauxite (metric ton) 110,000 0% 210,000 0% 33,000 0% 30,000 0% gold ore (metric ton) 660,000 0% 1,180,000 0% 210,000 0% 140,000 0% Environmental Outputs TRI total (metric ton) 14,000 0% 27,000 0% 3,600 0% 4,200 0% air % 69% 0% 73% 0% 69% 0% 67% 0% water % 5% 0% 6% 0% 5% 0% 9% 0% land % 12% 0% 8% 0% 9% 0% 8% 0% underground % 14% 0% 13% 0% 16% 0% 16% 0% CMU-ET total (metric ton) 18,000 0% 34,000 0% 5,800 0% 4,500 0% RCRA generated (metric ton) 6,80,000 0% 4,900,000 0% 570,000 9% 740,000 0% SO2 (metric ton) 330,000 45% 1,100,000 0% 74,000 46% 170,000 10% NOx (metric ton) 1,700,000 87% 1,100,000 40% 58,000 35% 100,000 6% CO (metric ton) 3,800,000 92% 1,400,000 68% 56,000 11% 65,000 1% VOC (metric ton) 740,000 88% 360,000 70% 11,000 3% 16,000 2% PM10 (metric ton) 28,000 0% 93,000 0% 25,000 3% 16,000 4% GWP 10 6 mt CO 2 equiv % % 13 11% 40 7% potential (converted to CO 2 equivalents), and RCRA hazardous wastes generated. Results are presented for total sector economic output as well as normalized by million dollars of output. The service sector contributed about half the direct energy use and global warming potential and about 50 times less RCRA generated hazardous wastes compared with the manufacturing sector on a per million dollar basis. However, because the service sector has twice the total economic output compared to manufacturing, the service industries have about the same energy use and global warming potential as the manufacturing sector on a total sector economic basis (Figure 2). (Note that the utility category has a large energy use contribution because the use of fuels to generate electricity creates significant direct emissions.) For some environmental metrics, the contribution of nonmanufacturing sectors appears significantly smaller. For example, the manufacturing sector is responsible for the direct generation of nearly all of the RCRA hazardous wastes (Figure 3). This does not present the full picture because service industries are responsible indirectly, through their supply chain, for a significant amount of RCRA wastes generated. In general, service industries have significant environmental effects on an economy-wide basis even when their direct emissions are negligible. With a large share of ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 22, 2000

5 FIGURE 4. Resource inputs and environmental outputs of four service industries for $1 million dollars of demand for each industry. the economy, the direct and indirect environmental effects of the service sector become a significant component of overall U.S. emissions, wastes, and energy use. Consumer Impacts. The above analyses focus on the overall environmental effects of the service sector. Indirect consumption effects are also interesting. The U.S. Consumer Price Index, a widely recognized economic indicator generated by the Bureau of Labor Statistics, relies on a market basket to determine the goods and services (in about 200 subcategories) purchased by an average consumer. The I-O sector numbers were mapped against each subcategory (16), and the EIO-LCA model was used to determine the annual total (direct and indirect) environmental effects of average U.S. household expenditures ($29,850 in 1992) (17). The results are presented in Table 4. Each subcategory was given one of four classifications: manufacturing, service, utilities, and property rental. Though the amount spent on manufactured goods is about 25% greater than that spent on services, the environmental effects associated with manufacturing are about 2-3 times that of services. Four Service Sectors Analyzed in Detail. To illustrate the environmental effects of particular service industries, we selected representatives of four major categories of services in the U.S. economy: trucking and courier services, retail trade, colleges and universities, and hotels. The EIO-LCA model was used to estimate the resource inputs and environmental outputs, both direct and indirect. A purchase of one million dollars of services from these four sectors was simulated. The results are presented in Table 5. To estimate the total environmental effect of these services, the total economic outputs were used. Results are shown in Table 6. Figures 4 and 5 present the findings graphically for selected environmental metrics. VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

6 FIGURE 5. Resource inputs and environmental outputs of four service industries using total economic output for each industry. Some results are expected, such as the high direct consumption of electricity, the low direct emissions of TRI toxic chemicals, and the low direct generation of RCRA hazardous wastes. Indirect impacts of services on resource use (e.g., iron ore) and environmental emissions (e.g., SO 2 emissions, TRI releases) may be substantial and in some cases comparable to direct manufacturing impacts. For example, the manufacturing industry blast furnaces and steel mills (the four SIC digit sector that produces steel) reports direct TRI emissions of 32,000 metric tons, with retail trade close by with indirect emissions of 27,000 metric tons. However, the CMU-ET results for steel production (98,000 metric tons) are almost three times higher than for retail trade (34,000 metric tons) on the account of chemicals of higher toxicity being used in the steel making process than in the supply chain of retail trade. The supply chain environmental effects associated with services appear to be significant and merit further consideration. In particular, trucking displays significant direct and indirect impacts from combustion of fuels, both on a total and per-dollar basis. Retail trade is a large sector with significant supply chain resource and energy demands. Hotels consume significant amounts of electricity directly, though most of the total energy use is consumed in the supply chain. Relative to the three other examples, the hotel industry requires large direct electricity inputs per dollar of output. Colleges and universities are a relatively small sector with small direct impacts, except for emissions presumably associated with laboratory work. The top five supply chain sectors of the four selected services for two environmental outputs, total TRI emissions (to air, water, underground wells, and land) and RCRA hazardous waste generated, are presented in Table 7. The ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 22, 2000

7 TABLE 7. Top Five Supply Chain Sectors Associated with Four Selected Service Sectors TRI% RCRA% Trucking and Courier Services (Nonair) total 100% total 100% petroleum refining 19% petroleum refining 64% industrial inorganic and organic chemicals 15% industrial inorganic and organic chemicals 14% primary nonferrous metals 14% sanitary services, steam supply, irrigation 14% synthetic rubber 8% warehousing and storage 3% carbon black 6% synthetic rubber 1% Retail Trade, Except Eating and Drinking total 100% total 100% paper and paperboard mills 17% petroleum refining 38% industrial inorganic and organic chemicals 14% industrial inorganic and organic chemicals 37% primary nonferrous metals 12% sanitary services, steam supply, irrigation 15% pulp mills 11% plastics materials and resins 2% misc. plastic products 6% other business services 1% Colleges, Universities, and Professional Schools total 100% total 100% primary nonferrous metals 17% industrial inorganic and organic chemicals 50% industrial inorganic and organic chemicals 16% petroleum refining 20% paper and paperboard mills 13% colleges, universities, and trade schools 9% pulp mills 8% sanitary services, steam supply, irrigation 7% misc. plastic products 4% pesticides and agricultural chemicals 4% Hotels total 100% total 100% nitrogenous and phosphatic fertilizers 27% industrial inorganic and organic chemicals 35% industrial inorganic and organic chemicals 13% sanitary services, steam supply, irrigation 33% primary nonferrous metals 9% petroleum refining 25% paper and paperboard mills 8% plastics materials and resins 1% pulp mills 6% other business services <1% values represent the percentage of each supply chain sector of the total (direct plus indirect) environmental effect. Paper and chemicals production and petroleum refining represent significant supply chain sectors in terms of overall environmental effects for all four services analyzed. If the four service industries were to reduce the TRI emissions and the RCRA hazardous waste generation as a consequence of their activities and supply chain purchases, paper and chemicals production and petroleum refining would be targets for reduction in a program of environmentally optimized supply chain management. Discussion The analysis conducted in this paper provides a macroscopic view of environmental impacts of resource consumption and environmental outputs of the service sector of our economy in general (focusing on a comparison with manufacturing) as well as a life-cycle environmental assessment of four representative services in particular. Our major findings include the following: (1) Services contribute about twice the economic output compared with manufacturing, making their overall economywide direct environmental impact in areas such as energy consumption much more significant than expected when compared with the effect normalized by output. Thus, the potential for reducing the environmental effects of services is significant and warrants increased attention even when compared with manufacturing. (2) When assessing and analyzing service industries, the supply chain effects must be considered along with direct environmental impacts. This is especially the case for certain environmental emissions that are not directly associated with services (e.g., TRI emissions, RCRA hazardous wastes generated) but are significant when indirect supply chain impacts are considered. (3) For the four services detailed in this paper, EIO-LCA can be used to determine where the majority of indirect supply chain impacts occur. Similar analysis of other service industries is warranted. Greening the service industries has to include the greening of their supply chains. Acknowledgments The authors wish to acknowledge the support of the National Science Foundation/Lucent Technologies Industrial Ecology Fellowship program (BES ), the NSF Structures, Geomechanics and Building Systems program (Project CMS ), and the Green Design Initiative at Carnegie Mellon University. Arpad Horvath is grateful for the support of the AT&T Industrial Ecology Faculty Fellowship. Literature Cited (1) Accessed July 15, (2) Allenby, B. R. Industrial Ecology: Policy Framework and Implementation; Prentice Hall: Upper Saddle River, NJ, ISBN , (3) Accessed December 1, (4) Leontief, W. Input-Output Economics, 2nd ed.; Oxford University Press: New York, (5) Leontief, W. Rev. Economic Statistics 1970, 52(3), (6) Duchin, F.; Lange, G. M.; Johnsen, T. Strategies for Environmentally Sound Development: Progress Report 5; Institute of Economic Analysis: New York, (7) Duchin, F. In Industrial Input/Output Analysis: Implications for Industrial Ecology. The Greening of Industrial Ecosystems; Allenby, B. R., Richards, D. R., Eds.; National Academy of Engineering: Washington, DC, 1994; pp (8) Hendrickson, C.; Horvath, A.; Joshi, S.; Lave, L. Environ. Sci. Technol. 1998, 3(4), 184A-191A. (9) Lave, L. B.; Cobas-Flores, E.; Hendrickson, C.; McMichael, F. C. Environ. Sci. Technol. 1995, 29(9), 420A-426A. (10) Input-Output Accounts of the U.S. Economy, 1992 Benchmark; Interindustry Economics Division, U.S. Department of Commerce, U.S. Government Printing Office: Washington, DC, (11) Lawson, A. M. Benchmark Input-Output Accounts for the U.S. Economy, 1992; Survey of Current Business, U.S. Department of Commerce, U.S. Government Printing Office: Washington, DC, November VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

8 (12) Toxics Release Inventory; CD-ROM, EPA 749-C ; U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics; Government Printing Office: Washington, DC, (13) 1995 National Biennial RCRA Hazardous Waste Report; U.S. Environmental Protection Agency, Solid Waste and Emergency Response, Obtained through a Freedom of Information Act request; Government Printing Office: Washington, DC, (14) Horvath, A.; Hendrickson, C.; Lave, L.; McMichael, F. C.; Wu, T. S.Environmental Science & Technology. 1995, 29(2), pp (15) Joshi, S. Product Environmental Life-Cycle Assessment Using Input-Output Techniques, J. of Industrial Ecology. 2000, 3(2-3), pp (16) Matthews, H. S. Ph.D. Dissertation, Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA, March (17) Bureau of Labor Statistics, 1992 Consumer Expenditure Survey, via ftp://ftp.bls.gov/pub/special.requests/ce/standard/1992/ age.txt, Accessed December 11, Received for review December 17, Revised manuscript received July 25, Accepted August 16, ES ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 34, NO. 22, 2000