Journal of Sustainable Water in the Built Environment

Adoption of green stormwater infrastructure (GSI) as a sustainable stormwater measure to manage urban flooding has gained momentum globally. Modeling and analysis tools are available to guide its design and planning. However, the impact of uncertainty in design precipitation estimates, and change in land use on the optimal configuration of GSI has not yet been assessed. The uncertainty in design precipitation estimates influences the amount and cost of GSI; and urban forms, space availability and existing drainage infrastructure influence the placement and ideal types of GSI. Further, climate change and conversion of pervious to impervious surfaces create varied impacts across cities. In this paper we investigate how such catchment scale optimal configurations of GSI, defined as ideal selection of type, amount and spatial distribution of GSI, vary (1) across uncertainty within design precipitation estimates from NOAA Atlas 14; and (2) with increasing urban imperviousness. We analyze this across two different cases of urban forms: (1) a catchment with mixed use buildings where bioretention (i.e., ground based) and green roofs (i.e., over ground based) are feasible, and (2) a catchment with only residential buildings where only bioretention is feasible. For this aim we utilize the USEPA’s stormwater management model (SWMM) to construct one-dimensional hydrologic-hydraulic models using stormwater networks of two separate locations in Phoenix, Arizona. We couple the SWMM model with nondominated sorting genetic algorithm (NSGA-II) to develop a multiobjective optimal GSI planning framework to determine amount, type and location for GSI implementation. We found that varying the design precipitation from the lower to upper bound of the confidence interval for NOAA Atlas 14, resulted in a larger difference in the amount of GSI required than the effect of land use change from 2001 to 2019. This highlights the important of accurate design storm estimates and the value of modular GSI in adapting stormwater systems under uncertainty.

Abstract

There has been a push to adopt onsite nonpotable water reuse systems (ONWS) as a supplement for conventional centralized water infrastructure. While a majority of work has centered on developing the technology, we instead focus on the implications for equity when attempting wide-scale adoption. Using existing definitions and resources for water equity in the sector, we investigate ONWS in San Francisco and New York City, using semi-structured interviews conducted with stakeholders. A qualitative approach with thematic coding and sentiment analysis is used to explore how stakeholders perceive equity in relation to their work and the resulting social, economic, and environmental implications for ONWS. Results confirm a general sentiment—equity is necessary, yet it is unclear how to incorporate this concept into practice. In some instances, equity is viewed as secondary to utility planning, operation, and management; we propose that it should be incorporated intentionally as an approach to enhance service provision. This study has implications for literature and practice as it demonstrates how decision-makers in ONWS programs engage with the concept of equity. We demonstrate how stakeholders’ roles can impact their implementation of equity, and discuss how practitioners may use this work as foundational understanding in assessing internal operations and practices, improving infrastructure in the pathway to sustainable development.

Practical Applications

This study deconstructs the concept of equity into three constitutive pillars to enable more informed implementation strategies for the adoptions of onsite nonpotable water reuse systems. Data showed that stakeholders showed an interest in equity, however they stated that they did not know how to incorporate it into their work. By deconstructing equity into an economic, environmental, and social pillar, equity impacts can be assessed, measured, and achieved more readily. This study found that stakeholders look both within their organization’s impacts on equity, and externally at what others can do to help them achieve equity. The tradeoffs at the intersection of economic, environmental, and social equity are discussed. While the perfect balance was not discovered in this study, it emphasizes the need for future work to investigate the optimal scale and system configuration that can leverage who has access (social equity), who can afford these systems (economic equity), and the environmental benefits for such adoption (environmental equity).

Bioretention is a popular stormwater control measure (SCM) with limited information regarding the impact of compost addition to the media. Although compost combined with bioretention soil media (BSM) has the potential for increased pollutant removal and water storage, it also may leach harmful nutrients. This project analyzes the effects of incorporating two forms of compost, biosolids-derived and green waste–derived, at two compost-BSM ratios, on bioretention nutrients performance; addition of aluminum-based water treatment residual (WTR) was also evaluated. Bioretention mesocosm column studies compared leaching/removal effects of a standard BSM (sand, topsoil, and hardwood mulch) and BSM mixed with 15% and 30% compost (biosolids and green waste) as well as 30% tap water–washed biosolids compost and 15% green-waste compost + WTR. Synthetic stormwater was applied to the columns and the effluent was analyzed for total nitrogen (TN), total phosphorus (TP), and their speciation. All compost-amended columns leached greater TN (2.1-fold to 67-fold) and TP (2.8-fold to 19-fold) concentrations than BSM-only, with biosolids compost leaching the most nutrients. This was largely due to greater nutrients exported within the initial flush, but also due to the continued mineralization of compost organic matter, resulting in constant leaching and 2-fold to 21-fold greater TN and 1.3-fold to 28-fold greater TP than BSM. Initial washout of compost fines contributed to nutrients in the bioretention discharge. Based on results from this study, addition of compost to BSM is not recommended. Unamended BSM produced the most nutrient removal from input stormwater.

Abstract

This work demonstrates how a water and energy sustainable building’s heating, ventilation, and air conditioning (HVAC) system may be operated to maximize condensate production while upholding user thermal comfort and energy consumption requirements. A physics-based HVAC condensate model was presented and validated against operating data from the Kendeda Building for Innovative Sustainable Design (KBISD), a $\mathrm{3,437.4}\text{-}{\mathrm{m}}^2$ ($\mathrm{37,000}\text{-}{\mathrm{ft}}^2$) academic building on the Georgia Institute of Technology’s Atlanta campus. A sensitivity study of the HVAC condensate production and power consumption was performed. Metamodels were developed to concisely yet accurately represent the physics-based model, and these were used as the basis of an optimization exercise to identify competitive operating conditions for maximizing condensate production. The case studies included here found optimized HVAC system operation strategies to produce up to 708% more condensate. The demonstrated approach may be reproduced by system operators or building automation systems to increase condensate production without sacrificing building system-level energy and thermal comfort requirements.

Practical Applications

This work demonstrates how a building’s heating, ventilation, and air conditioning (HVAC) system may be operated to increase the amount of water, or condensate, which may be pulled out of the air and collected. A simple engineering model is presented and verified against real-world data. This is used as the basis for an optimization approach that allows operators to make strategic, mathematically substantiated decisions to impact the amount of condensate collected and the power required to do so. In addition, the use of so-called metamodels for reducing complex engineering models or systems into simple mathematical representations is exemplified for increasing the speed of the analyses performed in this work. These metamodels may be used to represent HVAC or other building systems and allow for optimization efforts similar to those presented herein or potentially model predictive control. The case studies discussed in this work bring the optimization approach and metamodels together to demonstrate how a building may theoretically be operated to increase its condensate production by 708% within reasonable power requirements and without sacrificing the comfort of the building’s occupants.

Results are presented from a large-scale Monte Carlo–style simulation of the use of low-impact development (LID) technologies to reduce runoff from severe storms. Simulations were run to model the hydrologic behavior of a municipal-scale storm sewer network that included porous pavements and green-blue roof systems as part of a distributed stormwater management system. Simulations were run for a variety of land-use types (residential, commercial, and mixed use), design approaches (traditional, LID, and traditional designs with a single LID technology), and pipe networks. The land-use and design approaches for a given location in the municipal network were allocated randomly and run for a broad range of design rainfall depths resulting in over 200,000 individual hydrologic simulations. The results indicate that green-blue roof systems can significantly reduce the peak discharge compared with impervious roof systems, and porous pavements can significantly reduce the total discharge over the municipality compared with impervious pavement systems. This study can inform municipalities about how to achieve current discharge performance with a significantly larger storm volume. Results show that the same peak discharge can be achieved for a 10% deeper storm with the adoption of LID technologies over 30% of the municipality drainage area. This in turn will ensure that the storm system is able to manage the increased storm depths that will result from climate change over the coming decades.

Stream temperatures across the world are increasing due to changes in land use and climate, especially in urban areas. This leads to hydrologic urban heat islands, where higher water body temperatures can have negative consequences on ecological and human health. Green infrastructure is a potential solution to mitigate the temperature of urban runoff; however, it is unclear how green infrastructure systems, especially those connected in series, can be best utilized to reduce the impact of urban runoff on downstream temperatures. This study seeks to fill this gap by monitoring a green infrastructure system in Milwaukee, WI—a bioswale and permeable paver that both discharge into a second bioswale—to evaluate its temperature mitigation potential. Results indicate that for the bioswale and permeable pavers connected in parallel, the bioswale outperformed the permeable pavers in reducing event mean temperatures (2.8°C cooler). In addition, the bioswale that performed secondary treatment further reduced the average event mean temperature across all storms by 4.2°C from the permeable pavers and 2.4°C from the bioswale. This study demonstrates the effectiveness of a green infrastructure connected in series in reducing runoff temperatures, which is important for addressing a critical threat to environmental and human health.

One of the tools used to assess water availability is a water budget, which is useful for tracking quantity, but does not provide information regarding the quality of the water. This paper introduces a seven-step method for creating a water budget, in the form of a modified mass flow diagram that depicts the quality of each quantity of water. The method involves delineating the system boundary for the water balance; selecting the water budget time period to be used for analysis; collecting water quantity data applicable to the selected system boundary and time period; drawing a modified mass flow diagram; selecting and assigning a color code to the selected water quality scale; applying the color code representing water quality to the modified mass flow diagram; and ordering diagram slices by level of water quality. Adding water quality to water budgets may not only show areas where there is room for improvement, but also depict areas where there are resources and opportunities that might not have been visually obvious from a table of numbers.