Extended detention basins are not used for stormwater quality management in many areas of the US because they generally do not achieve the 80% removal of total suspended solids required by many regulatory agencies. The objective of this research was modification of the outlet controls of an existing basin to provide batch treatment of the urban stormwater runoff through efficient control of the hydraulic residence time. A solar powered automated valve and controller were developed and placed on the outlet of an extended detention basin in Austin, Texas to increase the detention time beyond the times achievable using an orifice. This system retained the diverted runoff in the basin for a variable preset period of time. The quality of the influent and effluent of the basin was monitored for concentrations of suspended solids, nutrients, chemical oxygen demand. and total and dissolved metals. The suspended solids concentrations in the basin were controlled by adjusting the residence time of the runoff in the basin to meet the required pollutant reduction. The automated valve can also be used to regulate flow into the receiving waters to control peak flow.

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abstract: The rate of urbanization has been impacted by global economic growth. A strong economy results in more people moving to already crowded urban centers to take advantage of increased employment opportunities often resulting in sprawling of the urban area. More natural land resources are being exploited to accommodate these anthropogenic activities. Subsequently, numerous natural land resources such as green areas or porous soil, which are less flood-prone and more permeable are being converted into buildings, parking lots, roads and underground utilities that are less permeable to stormwater runoff from rain events. With the diminishing of the natural landscape that can drain stormwater during a rainfall event, urban underground drainage systems are being designed and built to tackle the excess runoff resulting from urbanization. However, the construction of a drainage system is expensive and usually involves massive land excavations and tremendous environmental disturbances. The option for constructing an underground drainage system is even more difficult in dense urban environments due to the complicated underground environments, creating a need for low footprint solutions. This need has led to emerging opportunities for low impact development (LID) methods or green infrastructures, which are viewed as an environmentally friendly alternative for dealing with stormwater runoff. LID mimics the pre-development environment to retain the stormwater runoff through infiltration, retention, detention and evaporation. Despite a significant amount of prior research having been conducted to analyze the performance of runoff volume reduction and peak flow decrement of various green infrastructures, little is known about the economic benefits of using LID practices. This dissertation fills the gap in the knowledge regarding the life-cycle-cost effectiveness of green infrastructure in current urban developments. This study’s two research objectives are: (1) Develop a life cycle cost calculation template to analyze the cost benefits of using LID compared to the traditional drainage system (2) Quantify the cost benefits based on the real-world construction projects A thorough literature review led to the data collection of the hydrological benefits of using LIDs in conjunction with overviewing three real-world construction projects to quantify the cost benefits of LIDs. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019

The studies in this dissertation address the issue of variability in runoff generation and pollutant concentration in urban areas, and specifically in the catchments of stormwater control measures. There is an imperfect correlation between runoff volumes and the capture area and land uses of urban catchments. Variable capture areas and uncertainty in urban runoff sources complicate stormwater control measure design and urban stream assessment. Four stormwater control measures in upstream suburban Philadelphia, ranging in capture area from 0.11 ha to 32 ha, were monitored, sampled, and modeled. Sampling was conducted in the watersheds of Wissahickon Creek, Tookany Creek, and Pennypack Creek. The approaches discussed below have the goal of better understanding runoff and the movement of associated contaminants into stormwater retention basins and streams. Rather than viewing runoff generation and contaminant transport as a static process, this work proposes that the amount of runoff contributed from different areas of a catchment changes during and between storm events, and that the origin and concentration of contaminants change as a result. Linking source areas to runoff volumes through natural and modeled tracers could improve predictions of water quality and quantity in stormwater control measures in urban streams. Nitrate (NO3–) isotope ratios were used as tracer of flow from different urban land uses. Time series samples of stormwater runoff entering two stormwater control measures (a constructed wetland and a small bioretention basin) were collected and analyzed to distinguish sources of NO3– by samples’ δ15N and δ18O ratios. A Bayesian mixing model was used to determine that NO3– sources were a mix of soil nitrogen (N) and atmospheric deposition across six storm events. Furthermore, atmospheric versus soil N sources varied throughout the storms. The large catchment of the constructed wetland had more NO3– source variability between samples compared to the small catchment of the bioretention basin. Thus, the NO3– isotopes suggest more distinct flow paths in the large catchment and more mixing of flow across land uses in the small catchment. Quantifying flow path variability from storm to storm and between different catchments can improve design and placement of urban stormwater control measures. A distributed hydrologic model, GSSHA, was used to simulate overland runoff from impervious and semi-pervious land covers in the catchment of a stormwater control measure. The positions of low vegetation and impervious land uses over the catchment were rearranged to create hypothetical catchments during four storm events. Fluctuating source proportions over time suggested that grab samples might not be adequate for capturing average overland runoff chemistry. It was also found that the portion of total runoff volume from impervious areas varied from 50 to 75% while the relative proportion of impervious cover remained constant at 54%. Land use percentages averaged over capture areas are frequently used to estimate runoff amounts and pollutant concentrations, but this model disrupts the assumption that urban hydrologic responses can be predicted from imperviousness alone. Overland runoff was measured and modeled before and after the installation of two stormwater control measures, a berm and a bioswale. Discharge in the stream was modeled for 9 storms ranging in size from 14 to 54 mm. We found that during 4 of the modeled storms there was no decrease in stream discharge and decreases in discharge were generally only observed for low intensity storms. Furthermore, only 5% of the stream catchment was captured by SCMs. Modeled tracers, used to track runoff contributions from areas upslope of the SCMs found that the size of upslope contributing areas did not predict the proportion of runoff generated in each area. Field data to support the models included water level loggers and samples of overland runoff collected in subsurface stormwater casing. After the SCMs were installed, less water was captured in downslope sampling bottles, but new flow paths developed. Furthermore, significant variation was observed in upslope concentrations of dissolved nutrients and total suspended solids, casting doubt on whether point samples of urban overland runoff geochemistry can be representative given variable runoff generation and heterogeneous land uses. This study points out the challenges in evaluating stormwater control measures and reveals that source areas’ contribution to stream flow varies independently of their size. Therefore, modeling before stormwater control measure installation is recommended to determine the factors that influence a capture area’s contribution to urban streamflow. / Geoscience

L’objectif de ce travail est d’évaluer le transfert des métaux lourds au sein d’une installation de traitement des eaux de ruissellement routier et de développer un procédé épuratoire qui permettrait de parfaire le traitement de ces eaux. La démarche scientifique déployée a d’abord consisté en la caractérisation des flux métalliques acheminés dans un bassin de rétention recevant des eaux de ruissellement provenant d’une autoroute et en l’évaluation du transfert de cette pollution métallique vers la végétation environnante. Les résultats de cette première étude ont permis de mettre en évidence : (1) un transfert des métaux lourds (Cd, Ni, Zn) des compartiments eau – sol vers les macrophytes aquatiques présent sur le site, (2) la capacité de ces macrophytes à accumuler des polluants métalliques au sein de leurs tissus et (3) le caractère bioindicateur de ces macrophytes pour assurer une surveillance de la pollution métallique présente dans les eaux de ruissellement. Compte tenu de la capacité des plantes à accumuler des métaux, en particulier au niveau de leurs racines, un procédé de phytoremediation appelé marais flottant a été proposé pour affiner le traitement des eaux de ruissellement. Les performances épuratoires de ces systèmes ont été évaluées en microcosmes et la faisabilité technique de pouvoir implanter de tels systèmes directement à la surface d’ouvrages existants a également été appréhendée. Les résultats ont démontré que les marais flottants peuvent tout à fait être mis en œuvre à la surface de bassins de rétention sous réserve que les matériaux choisis pour la construction de ces systèmes soient adaptés aux conditions environnementales. Les résultats ont également mis en évidence la capacité des marais flottants à éliminer les métaux présents en phase aqueuse ainsi que l’importance du réseau racinaire qui se développe dans la colonne d’eau sur la rétention des polluants et la filtration des particules fines en suspension. Enfin, cette étude a démontré que les marais flottants peuvent être considérés comme des systèmes de traitement pérennes et nécessitant très peu de maintenance. / The objective of this work is to evaluate the heavy metal transfer into an urban stormwater treatment device and to develop a treatment process which would allow improving the treatment of these waters. The scientific approach consisted first to characterize the metal loads forwarded into a retention pond receiving stormwater runoff coming from a highway and to evaluate the transfer of this metal pollution to the surrounding vegetation. The results of this preliminary study demonstrated: (1) a heavy metal transfer (Cd, Ni and Zn) from the water and soil compartments to the aquatic macrophytes present on the studied site, (2) the capacity of these macrophytes to accumulate metal pollutants into their tissues and (3) the bioindicator value of these macrophytes for biomonitoring of stormwater metal pollution. Regarding the capacity of plants to accumulate metals, especially in their roots, a phytoremediation process called floating treatment wetlands was proposed to improve urban stormwater quality. The treatment performances of these systems were evaluated through a microcosm experiment and the technical feasibility for implanting such floating systems directly on the surface of existing ponds was also evaluated. The results showed that floating treatment wetlands can be operated on the surface of retention pond provided that the material chosen for the construction of these systems are well adapted to environmental conditions. The results also brought to light the efficiency of floating treatment wetlands for metal uptake from water as well as the importance of the root system on pollutant retention and the filtration of fine suspended particles. Finally, this study showed that floating treatment wetlands can be considered as sustainable treatment systems that need low maintenance.

Nonpoint source pollution captured by urban stormwater runoff is the greatest challenge for surface water quality improvements. Computer-based design tools have been developed to help mediate this issue by guiding end users through the implementation of decentralized stormwater management. The majority of these tools focus on treatment via biofiltration, yet concern regarding this treatment regime is rising. Case studies from research past clearly indicate the susceptibility of groundwater to contamination from extensive anthropogenic activity at the surface. Contaminants, such as nitrates and pathogens, are not completely removed before runoff enters the underground watercourse. Additionally, national and state legislation, which explicitly lists where neglect for groundwater quality is permissible—exacerbate concerns. This research analyzes the efficiency the BMP Siting Tool developed by the US Environmental Protection Agency and the Grey-to-Green Decision Support Tool developed by the University of South Florida. The tools were used to obtain cartographic data illustrating suitable sites for bioswales and infiltration basins throughout northern portion of Hillsborough County, Florida. This data was then integrated with the Karst Aquifer Vulnerability Index (KAVI) groundwater vulnerability model. The area of bioswales and infiltration basins that intersected areas of the KAVI model listed as ‘highly vulnerable’ or ‘moderate-to-highly vulnerable’ was calculated. This permitted an assessment of which BMP facility had the greatest sitings atop vulnerable areas, respective of the tool. The BMP Siting Tool sited 2.80% of all bioswales and 27.89% of all infiltration basins above vulnerable areas. Likewise, the Grey-to-Green Decision Support Tool sited 21.66% of all bioswales and 9.62% of all infiltration basins above vulnerable areas. These results prompted the development of a supplemental groundwater vulnerability framework to be incorporated into both tools’ analytical process.