Prepared for the New York Academy of Sciences, Harbor Project. Drew Schechtman

Transcription

1 Life Cycle Analysis: An Economic Input Output and process based LCA comparison between unsealed concrete and sealed asphalt parking lots upstream environmental impacts Prepared for the New York Academy of Sciences, Harbor Project Drew Schechtman February, 2007

2 Table of Contents I. Introduction...3 II. Scope of the Analysis... 5 A. Methodology: Economic Input Output Life Cycle Assessment... 6 B. Components of Analysis Functional Unit of comparison and Performance Characteristics Boundary Assumptions III. Results IV. Discussion V. Additional Research VI. References Appendix A

3 I. Introduction Parking lots have been identified as a source of stormwater contamination, specifically in regard to polycyclic aromatic hydrocarbons (PAHs) [1]. The sources contributing to PAHs found on parking lots can include vehicle fuel combustion, motor oil leaking and combustion, atmospheric deposition, and the more recently identified source, parking lot sealants [2]. Parking lot sealants, composed of refined coal-tar or asphalt, are used to protect the asphalt paving to which they are applied. These two materials contain PAHs (approximately % and 3-20% dry weight respectively {Barbara J. Mahler, 2005 #2}). Over time, the parking lot sealant is worn away and PAHs are released to the environment via particulate matter and volatilization. The wearing of coal-tar sealants was made apparent in a study conducted by Mahler et al. (2005) in Austin, Texas in which particles in runoff from unsealed parking lots were compared with runoff from lots sealed with coal tar and asphalt base sealant (see NYAS PAHs report for further detail). Subsequently, the City of Austin conducted a photographic wear rate study and estimated the average rate at which coal-tar sealant wear away from a set of commercial parking lots {Mateo Scoggins, 2006 #12}. Austin, Texas recently became the first city in the U.S. to ban the use of coal-tar sealants. The ban on the sale and use of this type of sealant took effect January, 2006 and restricts the use and sale of coal-tar sealants in the Austin area. As a result of the Austin ban, Home Depot and Lowe s have discontinued the sale of coal-tar sealants [3] [4]. More recently, the Lakes and Watershed Commission of Dane County, Wisconsin, has recommended a county-wide ban on the use and sale of coal tar and is awaiting final approval from the county board [5]. As communities turn to alternatives to coal-tar sealed parking lots, other parking lot materials and designs will need to be analyzed for their overall environmental impact. Two of the likely candidates for substitution of coal-tar sealed parking lots, due to their 3

4 availability and prevalence in the built environment, are asphalt sealed parking lots and concrete parking lots. However, decision makers would like to determine the overall environmental impacts of the alternatives to parking lots sealed with refined coal-tar based sealants. Therefore, we have conducted a comparison of the upstream environmental impacts of refined coal-tar sealed, asphalt sealed, and unsealed concrete parking lots. This analysis is limited to estimating the upstream environmental impacts - only those associated with the manufacturing, and installation of parking lots. An assessment of PAH releases during the use phase of these products in parking lots is provided by the NYAS PAHs (draft) report. 4

5 II. Scope of the Analysis A streamlined environmental impact assessment was performed to compare the environmental impacts of manufacturing and constructing an asphalt commercial parking lot (one lot sealed with asphalt based sealer, and one sealed with refined coal-tar based sealer) with a concrete commercial parking lot. We conducted a cradle-to-installation Life Cycle Assessment (LCA). A hybrid approach (see the methodology section of this report) is used to perform the environmental impact assessment (EIA) in which an Economic Input/Output (EIO) model and process based calculations are used to identify the impacts associated with the hypothetical parking lots. The EIO-LCA model is used to assess the impacts associated with the extraction or harvesting of materials phase, through their manufacturing as well as the production of the gasoline used in transportation, to impacts related to transportation and to the eventual placement of the materials at the site. The carbon dioxide emissions that result from transportation and placement of the materials are calculated using a process based Life Cycle Inventory. The environmental impacts of the parking lots were evaluated using Global Warming Potential 1 (the sum of Carbon Dioxide, Methane, Nitrous Oxide and Chloroflorocarbons), energy consumption, Sulfur Dioxide, Carbon Monoxide, Nitrous Oxide, Volatile Organic Compounds, Lead and Particulate Matter emissions, all of which are estimated using the EIO-LCA model. Furthermore, we estimate upstream PAH releases separately using production data and reported PAH emissions and integrated the results. 1 Global warming potentials (GWPs) are used to compare the abilities of different greenhouse gases to trap heat in the atmosphere. GWPs are based on the radiative efficiency (heat-absorbing ability) of each gas relative to that of carbon dioxide (CO 2 ), as well as the decay rate of each gas (the amount removed from the atmosphere over a given number of years) relative to that of CO 2. The GWP provides a construct for converting emissions of various gases into a common measure, which allows climate analysts to aggregate the radiative impacts of various greenhouse gases into a uniform measure denominated in carbon or carbon dioxide equivalents.[6] 5

6 A. Methodology: Economic Input Output Life Cycle Assessment The Economic Input Output-Life Cycle Assessment (EIO-LCA) is a tool that can be used to calculate relative environmental impacts of materials or services. The EIO-LCA, like all life cycle assessments, attempts to trace out the various resource requirements and environmental emissions associated with a particular product or service. Unlike other models, the EIO model also attempts to trace the often numerous economic transactions from a product or process as well as all the various manufacturing, transportation, mining and related processes necessary to produce a product or service. This is accomplished by using the methodology developed by Wassily Leontief economic input/output model, which was created over fifty years ago. The Leontief model divides the entire economy into sectors that interact to produce a supply chain that satisfies a final demand, and can be represented as a matrix or table of interactions with 500 rows and columns each representing one sector of the economy (Table 1). Table 1. Example of a concrete EIO table Inputs Transportati Aggregates Iron and ferroalloy ores mining Concrete manufacturing Transportation Aggregates Iron and ferroalloy ores mining Lime Electricity Concrete manufacturing The rows represent the inputs (in dollars) from the sectors listed in the column headings for a unit of output (in this case concrete) from this particular stage of production in the US. Data entries are expressed in dollar values because not all outputs can easily be expressed in units of mass. In order to evaluate the environmental impacts, a column is added to the EIO matrix, thus creating a hybrid of the original EIO model. This column represents the environmental impacts associated with each unit of out put for all of the sectors associated with the material or service. 6

7 The approach of combining EIO data and environmental impact data to perform life cycle assessments and determine environmental impacts have been assembled, calculated and compiled in a software program developed by researchers at Carnegie Mellon University. The analysis is calculated based on the price of material consumed. What is unique to this approach is that it can be used to estimate the total environmental impacts of all the inputs (product or processes), including all of the emissions associated with related sectors and activities, as opposed to analyzing the results from a singular process. Environmental impacts that can be calculated include energy use, air pollutants, hazardous wastes, toxics emissions and dollar estimates of external air pollution costs. Polycyclic aromatic hydrocarbons (PAHs) were not included among the environmental impacts evaluated by the EIO-LCA software. Therefore, a processbased analysis was conducted to estimate PAH emissions associated with the manufacturing of the paving materials and the sealant materials (asphalt and refined coal tar). The PAH emissions reported to the US EPA Toxic Release Inventory in 2004 and the reported production from facilities located close to the hypothetical site in New York City were used to estimate PAH releases per unit of material output. B. Components of Analysis 1. Functional Unit of comparison and Performance Characteristics The functional unit that is used in this life cycle assessment is a 50 square foot parking lot. Our analysis compares three parking lots, including two asphalt parking lots (one sealed with asphalt based sealer and the other with refined coal-tar based sealer) as well as a concrete parking lot. We assume that the functional unit has the following characteristics: 7

8 All three sites are in Manhattan, New York All materials were transported with diesel fueled trucks from manufacturers to installation site All materials were installed using diesel fueled machines 2. Boundary The boundary for the analysis performed consists of the production of the material (asphalt and concrete), the gravel sub-base for the paving, the transportation of the paving and sub-base materials from the manufacturer to the site, as well as the installation of the materials on site. The assessment of the transportation phase and the installation phase, both include the direct impacts from manufacturing the materials and the indirect impacts from producing the fuel used in installation The cost of materials for all materials was obtained using the 2007 National Construction Estimator and the Heavy Estimator for New York, both of which are cost-estimating guides. Below are the hypothetical parking lot assemblies that were compared and the associated data sources: Concrete Lot, Hypothetical 1: Assumption Area: 50 square feet Depth of gravel subbase: 5 inches 2 Subbase installation equipment: bulldozer, compactor, grader, and front-end loader Depth of concrete: 3.5 inches Installation equipment: placer/spreader, Data Source American Concrete Association, [7] Portland Cement Association, [8] American Concrete Association, [7] Portland Cement 2 It was assumed that the soil on which the parking lot would be placed is fine-grained soil in which silt and clay sized particles predominate and that to reach the desired subbase bearing capacity of 400, approximately 6 inches of gravel is needed. 8

9 concrete saw, slipform paving, texturing, and watertanker Location of cement manufacturer: Glens Falls, Warren Co., NY Annual cement production: 1,800,000 tons/year (capacity) Association, [8] Lehigh Cement Co. Lehigh Cement Co. {Brenchley, 2005 #13} Asphalt Lot with Asphalt sealer, Hypothetical lot 2: Assumption Data Source Area: 50 square feet Depth of gravel subbase: 6 inches [9] Subbase installation equipment: bulldozer, Portland Cement compactor, grader, and front-end loader Association, [8] Depth of concrete: 3.5 inches [9] Installation equipment: paver, 3-wheel roller, Portland Cement tandem roller Association, [8] Location of asphalt paving manufacturer: Chevron Perth Amboy, Middlesex, Co., NJ Annual asphalt production: 29,200,000 EIA {Association, barrels/year 2006 #14} Asphalt sealer: 1 gallon of sealer concentrate [10] per 50 square feet Asphalt Lot with Coal Tar sealer, Hypothetical lot 3: Assumption Data Source Area: 50 square feet Depth of gravel subbase: 6 inches [9] Subbase installation equipment: bulldozer, Portland Cement compactor, grader, and front-end loader Association, [8] Depth of concrete: 3.5 inches [9] Installation equipment: paver, 3-wheel roller, Portland Cement tandem roller Association, [8] Location of asphalt paving manufacturer: Chevron Perth Amboy, Middlesex, Co., NJ Annual asphalt production: 29,200,000 EIA {Association, 2006 barrels/year #14} Coal-tar sealer: 1 gallon of sealer concentrate [10] per 50 square feet 9

10 Exclusions: Since this was an impact assessment comparing the three hypothetical parking lots, exclusions were made for characteristic common to all three lots. For example, the transportation and placement of the gravel were excluded from the analysis since the relative impacts would be very similar in each case and not affect the LCA. Additionally the transport of the sealants was not included in the boundary of the project as these products are readily available at many locations which are very close to any site and therefore would have little net effects on the LCA. It was also assumed that the trucks transporting the asphalt and concrete would weigh approximately the same amount and therefore would have no net effect on the LCA. When estimating PAH emission associated with the hypothetical parking lots, only the manufacturing processes of materials were evaluated. It was assumed that the relative difference in PAH emissions associated with transportation and installation would be minimal and therefore have no net effect on the analysis. It should also be noted that when estimating the PAH emissions associated with the manufacturing of the sealants, only manufacturing of the asphalt and refined coal tar was evaluated. 3. Assumptions It was assumed that the paving materials used to construct the parking lots would be obtained from the closest available manufacturer. In this analysis, energy consumed during transportation uses an energy requirement factor of 2,500 BTU/ton-mile. 3 Other sources of data were searched to validate this factor, including one that reported that the energy

11 requirement to move the truck was 3,400 BTU/ton-mile, while another source reported 2,000 Btu/ton-mile. 4,5 These numbers are all within the same order magnitude with the chosen value. Similarly, the CO 2 emission factors were also reported by three different data sources: the Union of Concerned Scientists (22.8 lb CO 2 /gal of diesel); Diesel Today (165.7 lb/mmbtu) and the National Renewal Energy Laboratory (NREL) database (24.5 lb/ gal). Since all emission factors are within the same order of magnitude we can safely assume 22.8 lb/gal of diesel as the emission factor. III. Results When the three hypothetical parking lots are compared, the concrete lot without a sealer yields the lowest overall Global Warming Potential (GWP) (Figure 1). The concrete lot has an 8% and 12% lower GWP than the asphalt lots sealed with asphalt based sealant and the asphalt lot sealed with refined coal-tar based sealant respectively. lbs Concrete asphalt with asphalt sealer asphalt with coal tar sealant Placement of paving material (fuel combustion Transportation, Paving (fuel combustion) Placement of paving material (fuel production) Transportat ion, Paving (fuel production) M anufact uring, sealant M anufact uring, gravel M anufact uring, pavement Figure 1. Estimated Relative Global Warming Potential (GWP) for the Hypothetical Parking Lots. Of the processes that compose the manufacturing and installing of the parking lots, it is the manufacturing of the pavement that contributes the most to the GWP. In regard to the manufacturing of concrete, it is the cement manufacturing that contributes the most to the According to the U.S. Department of Agriculture, ( diesel fuel requirement is about 2,000 Btu per ton-mile for a loaded truck. 11

12 manufacturing GWP (Figure 2). In regard to the manufacturing of asphalt, it is the manufacturing of the asphalt paving mixture that contributes the most to the manufacturing GWP, followed by the power generation and supply (Figure 3). 1% 1% 11% 8% ready mix concerete cement manufacturing Truck transportation sand gravel and clay refractory 15% management of companies and enterprises whole sale trade 1% 0% stone mining and quarrying power generation and supply 0% 2% 8% 53% other basic inorganic chemical manufacturing oil and gas extraction Other Figure 2. Estimated relative contribution by the associated sectors to the GWP associated with concrete manufacturing. asphalt paving mixture 17% petroleum refineries 0% 28% oil and gas extraction mgmt of companies and enterprises wholesale trade sand gravel and clay refractory 20% truck transportation power generation and supply 13% real estate 5% Other 3% 0% 0% 14% Figure 3. Estimated relative contribution by the associated sectors to the GWP associated with asphalt paving manufacturing. 12

13 Of the compounds that compose the GWP, it is carbon dioxide that accounts for the largest fraction; approximately 83% and 84% of the total GWP of the asphalt and concrete lots respectively (Figure 4). lbs Concrete Asphalt w/ asphalt sealer Asphalt w/ coal tar sealant CO2 CH4 N2O CFC Figure 4. Estimated relative contribution of compounds to the GWP associated with the Hypothetical Parking Lots. Although he global warming potential of the concrete lot is slightly lower than that of the two other asphalt lots, other environmental impact indicators favor the asphalt lots (Figure 5). The sulfur dioxide, carbon monoxide, nitrous oxide and volatile organic compound emissions all are lower for the asphalt lots. For sealants used to cover asphalt parking lots, the coal-tar sealant has slightly fewer impacts over these indicators than the asphalt sealant lbs Concrete Asphalt w/ asphalt sealer Asphalt w/ coal tar sealant SO2 CO Nox VOC LEAD PM 13

14 Figure 5. Estimated relative environmental impacts of non GWP compounds associated with the Hypothetical Parking Lots. The estimated PAH emission associated with the manufacturing of the paving and the sealant materials (asphalt and refine coal tar) are higher for the concrete parking lot (Figure 6), followed by the refined coal-tar sealed lots. lbs 1.20E E E E E E E+00 Concrete parking lots Asphalt lot/asphalt sealant Asphalt lot/coal tar sealant Figure 6. Estimated PAH emissions related to the manufacturing of the paving (i.e., concrete or asphalt pavement) and sealants (asphalt and refined coal-tar) associated with the Hypothetical Parking Lots. IV. Discussion In assessing which lot has the lowest overall environmental impact in the upstream phase (manufacturing and installation), the result will depend on which indicator you value the most. If toxic emissions (non-gwp compounds) were of the greatest concern then the asphalt lot, specifically the asphalt lot sealed with refined coal-tar based sealant, would be the best option for the upstream phase. Alternatively, if the GWP is of greatest concern then the concrete lot would be the clear choice. However this assessment does not include potential releases during use. We have however, calculated in-use PAH emissions from sealed asphalt parking lots and this can be integrated with the upstream assessment. In this case, the data indicates that asphalt parking lots sealed with refined coal-tar based sealants release the largest quantity of PAHs followed by asphalt sealed lots (Figure 7). This is driven by the in-use estimated releases,. 14

15 1.E-02 1.E-02 8.E-03 6.E-03 Total PAHs (manufacturing, installation, & use) 4.E-03 2.E-03 0.E+00 Concrete Asphalt lot/asphalt sealant Asphalt lot/coal tar sealant Figure 7. Estimated emissions of PAHs related to paving manufacturing and parking lot pavement during use. Given that the pounds of emissions from global warming potential far outweigh the pounds of toxic emissions, it can be assessed that the concrete lot has the lowest overall environmental impact. 6 Furthermore, in terms of PAH releases, unsealed concrete parking lots appear to be the best option. V. Additional Research As with any LCA there are always was to build and improve upon the accuracy of the assessment. Below are several points which present an opportunity for further research. Examining the weight of the trucks used to transport the concrete and the asphalt and the effects on the environment. 6 The frequency of replacement for these parking lots may influence the decision on which lot is optimal. However, it is estimated that concrete parking lots do not require more frequent installation than asphalt paved lots, although the life of a parking lot will be determined by many variables, including use and maintenance. 15

16 Calculating the LCA using concrete with recycled fly ash or blast furnace slag instead of Portland cement. Calculating the LCA using recycled glass in the asphalt Researching the differences in the asphalt sealants used and using process based models to increase the accuracy of the assessment. Conduct a full EIO-LCA during the entire life cycle of the parking lots, including an assessment of PAHs releases. 16

17 VI. References 1. Jeffrey Steuer, et al., Sources of Contamination in an Urban Basin in Marquette, Michigan and an Analysis of Concentrations, Loads, and Data Quality. 1997, U.S. Geological Survey. 2. Barbara J. Mahler, et al., Parking Lot Sealcoat: An Unrecognized Source of Urban Polycyclic Aromatic Hydrocarbons. Environmental Science & Technology, (15): p Chenard, M., Public Relations, Lowe's Public Relations, Home Depot Bannerman, R., Environmental Scientist, Wisconsin State Department of Natural Resources Association, E.I. Comparison of Global Warming Potentials from the Second and Third Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) [cited; Available from: 7. American Concrete Association, Guide for Design and Construction of Concrete Parking Lots Michael A. Nisbet, et al., Environmental Life Cycle Inventory of Portland Cement Concrete and Asphalt Concrete Pavements. 2001, Portland Cement Association. 9. Boyer, B., Asphalt Consultant Crenson, G., Quality Assurance Manager, Bonsal American

18 Appendix A. Diesel fuel internal engine combustions emission factors lbs per MMBTU 138,700 BTU per gallon of diesel lb CO2 per gallon of diesel NREL- Combination truck gal to move truck 1.36E+01 Ton-mile Diesel gal to move truck 1.00E+03 Gal CO2 emmisions per unit above 2.45E+04 lb Union of concerned scientists 2,500 BTU per ton-mile 138,700 BTU per gallon of diesel 22.8 lb CO2 per gallon of diesel 18