Michael Blackhurst

Cost-Effectiveness of Green Roofs

Life-cycle assessment was used to evaluate the widespread installation of green roofs in a typical urban mixed-use neighborhood. Market prices of materials, construction, energy conservation, storm-water management, and greenhouse gas (GHG) emission reductions were used to evaluate private and social costs and benefits. Results suggest green roofs are currently not cost effective on a private cost basis, but multifamily and commercial building green roofs are competitive when social benefits are included. Multifamily and commercial green roofs are also competitive alternatives for reducing greenhouse gases and storm-water runoff. However, green roofs are not the most competitive energy conservation techniques. GHG impacts are dominated by the material production and use phases. Energy impacts are dominated by the use phase, with urban heat island (UHI) impacts being an order of magnitude higher than direct building impacts. The quantification of private and social costs and benefits should help guide green roof policy. Results should encourage green roof enthusiasts to set appropriate life-cycle assessment boundaries, including construction material impacts and UHI effects.

Cost-effectiveness of nitrogen mitigation by alternative household wastewater management technologies.

Household wastewater, especially from conventional septic systems, is a major contributor to nitrogen pollution. Alternative household wastewater management technologies provide similar sewerage management services but their life cycle costs and nitrogen flow implications remain uncertain. This paper addresses two key questions: (1) what are the total costs, nitrogen mitigation potential, and cost-effectiveness of a range of conventional and alternative municipal wastewater treatment technologies, and (2) what uncertainties influence these outcomes and how can we improve our understanding of these technologies? We estimate a household nitrogen mass balance for various household wastewater treatment systems and combine this mass balance with life cycle cost assessment to calculate the cost-effectiveness of nitrogen mitigation, which we define as nitrogen removed from the local watershed. We apply our methods to Falmouth, MA, where failing septic systems have caused heightened eutrophication in local receiving water bodies. We find that flushing and dry (composting) urine-diversion toilets paired with conventional septic systems for greywater management demonstrate the lowest life cycle cost and highest cost-effectiveness (dollars per kilogram of nitrogen removed from the watershed). Composting toilets are also attractive options in some cases, particularly best-case nitrogen mitigation. Innovative/advanced septic systems designed for high-level nitrogen removal are cost-competitive options for newly constructed homes, except at their most expensive. A centralized wastewater treatment plant is the most expensive and least cost-effective option in all cases. Using a greywater recycling system with any treatment technology increases the cost without adding any nitrogen removal benefits. Sensitivity analysis shows that these results are robust considering a range of cases and uncertainties.

Preparing US community greenhouse gas inventories for climate action plans

This study illustrates how alternative and supplemental community-level greenhouse gas (GHG) inventory techniques could improve climate action planning. Eighteen US community GHG inventories are reviewed for current practice. Inventory techniques could be improved by disaggregating the sectors reported, reporting inventory uncertainty and variability, and aligning inventories with local organizations that could facilitate emissions reductions. The potential advantages and challenges of supplementing inventories with comparative benchmarks are also discussed. While GHG inventorying and climate action planning are nascent fields, these techniques can improve CAP design, help communities set more meaningful emission reduction targets, and facilitate CAP implementation and progress monitoring.

Do US metropolitan core counties have lower scope 1 and 2 CO2 emissions than less urbanized counties

Recent sustainability research has focused on urban systems given their high share of environmental impacts and potential for centralized impact mitigation. Recent research emphasizes descriptive statistics from place-based case studies to argue for policy action. This limits the potential for general insights and decision support. Here, we implement generalized linear and multiple linear regression analyses to obtain more robust insights on the relationship between urbanization and greenhouse gas (GHG) emissions in the US We used consistently derived county-level scope 1 and scope 2 GHG inventories for our response variable while predictor variables included dummy-coded variables for county geographic type (central, outlying, and nonmetropolitan), median household income, population density, and climate indices (heating degree days (HDD) and cooling degree days (CDD)). We find that there is not enough statistical evidence indicating per capita scope 1 and 2 emissions differ by geographic type, ceteris paribus. These results are robust for different assumed electricity emissions factors. We do find statistically significant differences in per capita emissions by sector for different county types, with transportation and residential emissions highest in nonmetropolitan (rural) counties, transportation emissions lowest in central counties, and commercial sector emissions highest in central counties. These results indicate the importance of regional land use and transportation dynamics when planning local emissions mitigation measures.

Incentivizing Decentralized Sanitation: The Role of Discount Rates

In adoption decisions for decentralized sanitation technologies, two decision makers are involved: the public utility and the individual homeowner. Standard life cycle cost is calculated from the perspective of the utility, which uses a market-based discount rate in these calculations. However, both decision-makers must be considered, including their differing perceptions of the time trade-offs inherent in a stream of costs and benefits. This study uses the discount rate as a proxy for these perceptions and decision-maker preferences. The results in two case studies emphasize the dependence on location of such analyses. Falmouth, Massachusetts, appears to be a good candidate for incentivizing decentralized sanitation while the Allegheny County Sanitary Authority service area in Pennsylvania appears to have no need for similar incentives. This method can be applied to any two-party decision in which the parties are expected to have different discount rates.

To Sewer or Not to Sewer: Incentivizing Decentralized Wastewater Treatment

Household sewage causes several problems if not managed properly. Centralized wastewater treatment systems have long been considered the preferred form of sewage treatment, but they can be expensive. Several decentralized wastewater technologies can manage household sewage safely and effectively and may appear to be less expensive than centralized systems on a life cycle cost basis. Homeowners may be reluctant to bear the costs of these technologies, forcing municipalities to weigh the expense of monetary incentives to householders against the costs of centralized systems. Accurate life cycle cost comparisons rely on the use of discount rates representative of the appropriate investors. Centralized systems are typically financed by public municipalities, who use market interest rates or social discount rates in life cycle cost calculations, whereas homeowners have been observed to demonstrate much higher implicit discount rates. When system costs are compared using appropriate discount rates, decentralized systems might lose their cost advantage. We examine this phenomenon with two case studies. The methodology developed herein can be applied to any case in which centralized and decentralized technologies may be appropriate solutions; it also gives a basis for sound decisions about incentivizing homeowner adoption of decentralized technologies.

Estimating direct and indirect withdrawals of water for manufacturing consumer goods

Water is critical to healthy economic, social, and environmental systems. However, existing domestic water use data are limiting. Typically, only water withdrawals are available for broad end-use categories. These data do not reflect process-specific information needed to meaningfully assess life cycle water uses. Existing use patterns, such as supply chain impacts, are not clear, limiting opportunities to manage water more efficiently.