South Dakota USGS 104B 2012 Annual Report

Transcription

1 South Dakota USGS 14B 212 Annual Report Project Title: Life cycle assessment analysis of engineered stormwater control methods common to South Dakota Investigators: Dr. James Stone, South Dakota School of Mines & Technology Tyler Hengen, South Dakota School of Mines & Technology Maria Squillace, South Dakota School of Mines & Technology Dr. Molly Gribb, South Dakota School of Mines & Technology Dr. Jennifer Benning, South Dakota School of Mines & Technology Introduction: The following report addresses the progress to date and findings of significance related to the project titled Life cycle assessment analysis of engineered stormwater control methods common to urban South Dakota watersheds during the funding period of January 212 to December 212. Funding from this project has supported a life cycle assessment (LCA) research effort modeling urban stormwater treatment. The objective of both studies was to comparatively assess the life cycle impacts of various treatment options that are common for South Dakota municipalities (stormwater) and mining operations (AMD). LCA is an approach to quantitatively analyzing the environmental impacts associated with a process, typically using a cradle-to-grave or a cradle-to-cradle approach (that encourages material recycling), and takes into account the (reasonable) burdens from the entire supply chain for a specific item or process (Goedkoop, Heijungs et al. 29). International standards for LCA are outlined in ISO 144:26 and ISO 1444:26. We examined the changes in the environmental impacts resulting from the implementation of green best management procedures, or BMPs. Porous detention basins (PDB) and sand filtration (SF) are common urban stormwater treatment and mitigation methods, however many of the construction materials used within these treatment basins and filters have significant environmental burdens associated with them. As a result, there has been a considerable push towards the development of sustainable approaches to offset or minimize these potentially avoidable environmental burdens. This green development has resulted in the design of BMP s such as bioretention, porous pavement, and vegetated swales, among others. Their primary purpose of these upstream measures is to further reduce the volume of impervious area in a watershed, promote groundwater recharge, and reduce the water quality volume that must be treated by the primary stormwater treatment system (Conservation 21). Research Objectives: To date, stormwater BMP have been designed to meet the requirements set forth in the Clean Water Act and The EPA Phase II Final Rule. The selection of BMPs has traditionally been driven by economic costs and treatment criteria, with very little focus being put on the sustainability of the operation and implementation of the BMP s. However, LCA evaluations are becoming increasingly common within

2 government and industries as a requirement to address sustainability efforts. The objective of this study was to assess multiple different combinations of the traditional and Low-Impact Development BMPs, and to evaluate and identify potential sources of avoidable environmental burdens. All designs were sized to treat the stormwater runoff in an average Rapid City watershed, to the EPA Phase II standards of 8% TSS removal during a 2 year, 24 hour storm event. The system boundaries for the stormwater management study consisted of the processes and alternatives shown in Figure 1. Porous Detention Basin Sand Filter Detention Basin Peat Sand HDPE Pipe Liner O & M Lawn Mowing Aggregate Gravel Sand Liner O& M Filter Rep. Filter Rem. Rain Garden Vegetated Swale Compost Topsoil Sand Liner Perennial Ryegrass Topsoil O & M Lawn Mowing Porous Asphalt Bituminous Asphalt Filter Stone Choker Stone Pea Gravel PVC Figure 1: Stormwater BMP System Boundaries With the exception of porous pavement, the systems consisted of raw materials processing, transportation, construction, operations and maintenance, and finally recycling. With regards to porous pavement, the system boundaries begin with excavation of an existing paved area, recycling of that material, processing of any additional raw materials, transportation, and finally construction. Recycling of these materials was not included as the system started with prior recycling, so it was assumed that

3 the next system s boundaries would also begin at excavation of an existing site. The porous pavement was modeled differently since a developer would opt to implement porous pavement in any situation other than an already paved area. Porous pavement would not generally be implemented in the same way as vegetated swales, raingardens, etc. Within each process for all of the different BMP s, raw materials, transportation, construction energy, and operations and maintenance were specified. Methodology: The LCA was conducted using SimaPro 7.3 LCA modelling software (PRé Consultants, Netherlands) and life cycle inventory database EcoInvent, produced by the Swiss center for life cycle inventories (Frischknecht, Althaus et al. 27) following ISO 144 protocols. Results were quantified using ReCiPe hierarchist midpoint and endpoint methodologies. Principal Findings: For the purposes of this study, the following midpoint impact categories were evaluated: climate change (kg CO 2 eq.), terrestrial acidification (kg SO2 eq.), freshwater and marine eutrophication (kg N eq. and kg P eq., respectively), terrestrial ecotoxicity (kg 1,4-DB eq.). These categories were selected due to the fact that both they are the typical categories presented in LCA studies, and the results of an ecological impact assessment such as this, where land and water management are the areas of concern, are most easily presentable in terms of land and water results. While the midpoint results reflect the physical environmental contribution to a process, the endpoint categories reflect the societal implications of these environmental contributions. Generally, there is a higher degree of uncertainty with the endpoint analysis; however, the units for the endpoint analysis tend to be more understandable in the context of a discussion of environmental impacts. We assessed the total endpoint damage in categories of: Damage to Human Health, measured in DALY (Disability Adjusted Life Years, a measure of the number of years of life lost per 1 people due to illness), Damage to Ecosystems, measured in species.yr (Species per year, a measure of the number of species, both plant and animal, to go extinct per year due to a process), and Damage to Resources, measured in dollars. In general, the midpoint and endpoint impacts were primarily attributed to transportation and materials used for various scenarios., operations and maintenance, and disposal all resulted in relatively minor contributions to the LCA impacts. Climate Change The initial climate change examination between the porous detention basin and the sand filter extended detention basin showed 27% higher climate change impacts for the porous detention basin. As green offsets were included, the magnitude of climate change impacts was reduced compared to its corresponding baseline condition. The results for the climate change impacts are shown in Fig. 2. The ordinate of the Fig. 2 is the LCA impact category, in this case climate change, while the abscissa is the percent impervious area reduction The results demonstrate that all of the different green offsets have similar climate change mitigation affects for both the

4 porous detention basin and the sand filtration basin, though the porous detention basin scenarios show a slightly larger slope as green offsets are introduced. 4 Climate Change (kg CO2 eq) % Impervious Area Reduction PD VS SF VS Figure 2: Stormwater LCA climate change results Terrestrial Acidification Terrestrial acidification (Fig. 3), showed similar results to the climate change graphs. In the case of terrestrial acidification, the porous detention basin had 2% higher results with no offsets compared to the sand filter extended detention basin. Declining impacts were observed as any of the green BMPs were introduced, though the slope of the line through the rain garden scenarios was significantly steeper. Terrestrial Acidification (kg SO2 eq.) % Impervious Area Reduction PD VS SF VS Figure 3: Stormwater LCA terrestrial acidification results Freshwater Eutrophication Freshwater eutrophication (Fig. 4) showed a much sharper decrease in the porous detention scenarios compared to the sand filter extended detention scenarios. The sand filter and offsets

5 range from 185 to 217% lower freshwater eutrophication results compared to the porous detention with offsets. Figure 4: Stormwater LCA freshwater eutrophication impacts Marine Eutrophication Marine eutrophication (Fig. 5) showed similar trends to the freshwater eutrophication. As has been the case, a decreasing trend is observed with the impacts as offsets are introduced, resulting in the porous detention scenarios ranging between 172 and 197% higher marine eutrophication results compared to the respective sand filter scenarios. 4 Marine Eutrophication (kg P eq.) % Impervious Area Reduction PD VS SF VS Figure 5: Stormwater LCA marine eutrophication results Terrestrial Ecotoxicity The previously demonstrated trends hold true for the terrestrial ecotoxicity measurements (Fig. 6), where the porous detention scenarios have much higher values than the sand filter scenarios. The porous detention scenarios range from 175 to 199% higher than the comparable sand filter scenarios.

6 Terrestrial Ecotoxicity (kg 1,4-DB eq.) % Impervious Area Reduction PD VS SF VS Figure 6: Stormwater LCA terrestrial ecotoxicity results Total Damage Assessment For the sake of clarity, this study only measured the Total Damage Assessment at % offset and 2% offset for the different scenarios. For all of the scenarios, you see transportation being the primary contributor to the impact categories. Materials were the second largest contributor in the damage assessment categories. The materials and transport together made up nearly 95% of the overall contribution to each of the different damage assessment categories, while the operations and maintenance, construction energy, and disposal all combined for the remaining approximate 5% of the overall contribution. All endpoint results can be found in Figure 7.

7 .45 Damage to Human Health (DALY) Recycling O & M Materials PD VS SF RV 2.E-3 Damage to Ecosystems (species.yr) 1.8E-3 1.6E-3 1.4E-3 1.2E-3 1.E-3 8.E-4 6.E-4 4.E-4 2.E-4 Recycling O & M Materials.E+ PD VS SF RV Damage to Resources ($) Recycling O & M Materials PD VS SF RV Figure 7:Stormwater LCA endpoint results Summary To date, we have looked at the life cycle assessment of stormwater management BMP s. The results found have supported what we expected to find from the outset of these studies, with low-impact development treatment methods generally showing lower environmental impacts. Our study has been able to emphasize that not all of the low-impact systems demonstrate the same environmental benefit, and that the environmental impacts of treatment methods are highly variable and dependent on the entire cradle-to-grave process.

8 Works Cited Conservation, N. D. o. E. (21). "New York State Stormwater Management Design Manual." Frischknecht, R., et al. (27). "The environmental relevance of capital goods in life cycle assessments of products and services." International Journal of Life Cycle Assessment 12: Goedkoop, M., et al. (29). "ReCiPe 28: A life cycle impact assessment method which comprises harmonised category indicators at the midpoint and the endpoint level." report I: Characterisation.