Abstracts: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.

Abstracts: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.

Abstracts: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.

Abstracts: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 hone 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.