Bioretention basins are a stormwater control method implemented in urban areas to curtail runoff and pollution; however, recent studies show inconsistent nitrate (NO3-) removal, and in many cases average nitrate concentrations in basin outflow are higher than inflow. Microbial denitrification to promote nitrate removal can be enhanced by using underdrains in basin design that provide anoxic conditions. This study examines the impact of basin design and storm characteristics (precipitation intensity and antecedent dry period length) on microbial denitrification efficacy. Three basins in the Philadelphia area were selected for storm sampling: a large (~0.6 ha) wet basin without internal water storage, a small (~0.02 ha) basin without internal water storage, and a medium-sized (~0.1 ha) basin with internal water storage and a raised underdrain. In addition, three laboratory bioretention columns with underdrain configurations at the bottom, middle, and top of an internal water storage zone were sampled under steady-state and transient flow conditions. Samples collected as time series and grab samples during storm events were analyzed for nitrate concentrations and nitrate isotopes. Because microbes preferentially consume lighter nitrate isotopes (14N and 16O), stable isotope analysis offers an indication of denitrification. Stormwater outlet nitrate concentrations were lower than the inlet in the large suburban basin, similar to the inlet in the small suburban basin, and higher than the inlet in the urban basin. Differences in storm intensity and dry periods did not appear to increase or decrease nitrate concentrations in any basin, suggesting that basin design is a more dominant factor. The values of δ15N and δ18O in basin samples showed stormwater mixing without denitrification in all three basins. Only in the basin with water internal storage were periods of denitrification in samples observed, based on heavier δ15N and δ18O ratios. In laboratory studies, a lower underdrain configuration is preferred to promote denitrification based on heavier isotopic ratios and enrichment calculations. Bioretention columns had the largest enrichment factors (up to -5.3‰ ɛ 15N and -5.0‰ ɛ 18O) during steady-state flow. Lower enrichment factors associated with the low-intensity storm (-2.6‰ ɛ 15N and -1.3‰ ɛ 18O) show that transient flow disrupted denitrification rates. Field enrichment factors were greater than those in the columns (up to -11.9‰ ɛ 15N and -7.4‰ ɛ 18O). Even though nitrate decreased consistently over three storms, isotopic ratios did not exhibit these denitrification trends until at least eight hours after the onset of the storm events. Therefore, decreases in nitrate concentration alone are an unreliable assessment of denitrification efficacy. This study suggests that isotope analysis should be considered to better understand the conditions that promote denitrification. / Geology

Developments that have been taking place on Cal Poly campus over the years have altered the natural hydrology of the area. Stormwater management practices could help reduce the impacts of these developments. Computer models can help to design effective and economical stormwater management solutions at a watershed scale. As such, the objective of this study was to develop a stormwater management model for Cal Poly campus. The model was developed based on the utility data obtained from the university and other watershed data available from open sources. Field surveys were conducted to address some anomalies in the utility data, and streamflow monitoring was performed. The model was calibrated using the streamflow data measured during this study. The calibration effort significantly improved the prediction accuracy of the model. The calibrated model was then used to analyze the hydrologic performance of implementing LID systems for two projects that Cal Poly plans to build. Permeable Pavements (PPs) and Bioretention Cells (BRCs) were the LID types examined. The LIDs were evaluated based on peak flow and runoff volume reductions they would achieve. The potential reductions were compared for current conditions and the proposed project if LIDs were implemented, and for inflows to the LIDs and outflows from the LIDs. The results indicate that implementing a PP system for the proposed student apartment at the current H-1 and R-1 parking lots and a BRC system for the proposed engineering project facilities at the current H-2 parking lots will significantly reduce peak flow and runoff volume. Overall, the developed model will help the university with the traditional stormwater management practices such as flood control and to identify effective LID practices for future developments. Limitations of the current model and recommendations on how to improve the model are also discussed.

Diclofenac (DCF) and other emerging contaminants have been found in environments worldwide. These contaminants may enter the environment due to the application of treated wastewater, biosolids and direct excrement related to veterinary application. Leakage from the soils toward the groundwater is largely controlled by sorption and microbial degradation. Most studies on the environmental fate of DCF have focused on degradation during wastewater treatment processes. However, little is known about their behavior in soil. In this study, the combined effect of adsorption and degradation of diclofenac has been investigated in four (4) 24 ft3 agricultural soil-filled beds designed to mimic natural vegetated soil environments, enhanced via controlled wetting and drying cycles. Contour bund installation on slopes of 5, 10, 15 and 20° were mimicked in the beds. Results showed that the soil environment was a strong inhibitor to the leaching of DCF through the soil. Saturating slopes via contour bund application however can lead to landslides that may impact structures and human life. A feasible contour bund installation site was investigated and found that 20° slopes under saturated conditions resulted in an unsafe factor of safety and is not encouraged as a solution for stormwater management. The effect of contour bund application on slopes under 15° at the installation site can potentially increase removal of emerging contaminants, thereby protecting groundwater resources without endangering life or property.

Stream ecosystems are increasingly at risk for thermal impairment as urbanization intensifies, resulting in more heated runoff from impervious cover that is less likely to be cooled naturally. While several best management practices, including bioretention filters, have been able to reduce thermal pollution, success has been limited. The extent of thermal mitigation required to prevent ecological damage is unknown. A calibrated runoff temperature model of a case study watershed in Blacksburg, VA was developed to determine the cumulative treatment volume of bioretention filters required to reduce thermal impacts caused by runoff from development in the watershed to biologically acceptable levels. A future build out scenario of the study watershed was also analyzed. Results from this study established that runoff thermal pollution cannot be fully reduced to goal thresholds during all storms using bioretention filter retrofits. While retrofitting significantly decreased temperatures and heat exports relative to the controls, increasing treatment volumes did not really enhance mitigation. Alternate thermal mitigation methods which actively remove runoff volume should be considered where more thermal mitigation is required. / Master of Science / Stream temperature is a significant ecological, biological, and chemical property affecting the long-term health of streams. However, as development intensifies, stream ecosystems are increasingly at risk of being damaged by thermal pollution, which causes warmer and less stable temperatures that distress aquatic organisms. While several stormwater management methods that reduce runoff-related pollution, known as best management practices (BMPs), were found to also decrease thermal pollution, their success has been limited. Furthermore, the extent of thermal mitigation required to prevent ecological damage is unclear. This study aimed to determine how much treatment by a popular BMP, the bioretention filter, was necessary across a watershed in Blacksburg, VA to adequately reduce thermal pollution to protect stream health. Mitigation impacts were tested on both existing and predicted future development conditions through model simulations. Results from this study established that thermal pollution from runoff cannot be fully reduced to goal thresholds consistently using bioretention filter retrofits. While retrofitting significantly decreased thermal pollution, increasing treatment volume did not considerably enhance mitigation. Results suggested that bioretention filters are not an effective method, and alternate thermal mitigation practices which actively remove runoff volume should instead be considered where intensive reductions in thermal pollution are necessary.

The Ministry of Environment and Climate Change establishes design criteria for the sizing of Low Impact Development (LID) practices in the province of Ontario. The current sizing standards are based on the concept of the 90th percentile storm and require LIDs to provide enough storage capacity to store catchment runoff from a 25 mm rainfall event. The notion of 90th percentile storm means that 90% of all rainfall events have event volumes below a 25 mm rainfall event. This research examines the performance and cost of infiltration trenches and bioretention cells sized for alternative sizing standards ranging from 5–50 mm. Analytical probabilistic equations are used to determine the runoff reduction rates of infiltration trenches and bioretention cells, while the Sustainable Technologies Evaluation Program (STEP)’s LID Practices Costing Tool is used to estimate the overall cost of each LID. The costs are used to create a ratio denoted the fraction of maximum cost by dividing each cost by the cost of the 50 mm sized LID to receive a unitless ratio. This ratio is compared with the runoff reduction rates of both LIDs. Four different catchment sizes and various soil types are included to broaden the scope of the analysis and make the conclusions more dependable. Results indicate that the current sizing standard of 25 mm is probably too high and not cost-effective. In fact, depending on the type of soil and LID, little increase in performance occurs while there is a large increase in cost. A new methodology is proposed for setting sizing criteria for infiltration trenches and bioretention cells which focuses on achieving a desired capture efficiency instead of a required volume of rainfall. The method proposes using the capture efficiency, fraction of maximum cost and sizing criteria to determine what value is an economically more justifiable sizing standard based on individual catchment size and soil type. Use of the analytical probabilistic approach allows for the capture efficiency to be easily calculated and provides better sizing targets on a case by case basis. Recommending a specific capture efficiency can be more uniformly applied LID design in any soil conditions or any catchment size. This can reduce government spending when building LIDs and greatly reduce the possibility of over-design. / Thesis / Master of Applied Science (MASc)

Urban areas are affected by anthropogenic activities and produce pollutants that are transported to recipients and receiving waters during precipitation. Untreated stormwater runoff is a main driver of environmental degradation, and the interest in stormwater quality treatment has increased with the awareness of stormwater pollution. Several pollutants, including metals PAHs, PCBs, phthalates, and phenols, pose a hazard to aquatic life and are listed among the 45 priority substances in The European Water Framework Directive list (Directive 2013/39/EU). Stormwater bioretention technology is employed to efficiently remove pollutants during stormwater treatment in urban areas. However, the resulting accumulation of pollutants in bioretention facilities could ultimately create a pollutant depot. Hence, it is important to understand the occurrence, availability, and mobility of pollutants in bioretention facilities, as well as the processes that control their accumulation and mobility over time. The aim of the work in this licentiate thesis was to investigate the occurrence, accumulation, distribution, and concentration of organic micropollutants and metals inbioretention facilities after long-term stormwater treatment in urban areas of Ohio, Michigan, and Kentucky in November 2019. Samples were collected from 29 bioretention facilities, 20 of which were equipped with forebays. A total of 269 samples were analysed for metals commonly found in stormwater (Cr, Cu, Ni, Pb, and Zn), and a five-step sequential extraction method was used to assess the metal mobility in the filter material. Additionally, 116 samples from 12 sites were analysed for 38 organic micropollutants (OMPs), including 16 PAHs, 7 PCBs, 13 phthalates, and 2 alkylphenols. All studied metals were found in all samples, except for Cd, which was detected in 245 samples (91%). For the OMPs, 32 of 38 analytes were detected in at least one sample. PAHs and PCBs were the most frequently detected pollutants, and were found in 12 and 10 sites, respectively. The bioretention sites showed large variations in the concentrations of pollutants. The concentration of OMPs was highest in the upper 10 cm of the filter material and decreased with increasing depth, while a similar, but less obvious trend was observed for Cr, Cu, Pb, and Zn. A trend of decreasing concentration with increasing distance from the inlet was observed for OMPs but was less clear for the metals. Thefore bays, which contain sediment but no filter material, had the highest concentrations of OMPs. A strong correlation was observed between the pollutant concentrations and the ratio between the filter area and catchment area in a Principle Component Analysis. The accumulation and pathways of particle-bound OMPs and particle-bound metals showed similarities. These results will assist with improving the methods used for stormwater management. Importantly, regular replacement of the top filter layer and regular forebay maintenance may prevent pollutant accumulation and clogging, thereby extending the filters’ treatment function.