While many studies have evaluated the hydrologic effects of bioretention at the site level, few have investigated the role bioretention plays when distributed throughout a watershed. This study aims to assess bioretention's effects on an urbanized watershed using two modeled scenarios: one where runoff from many land uses was routed through the practice, and another in which only runoff from large impervious areas was routed. Peak flows, volumes, and lag times from these models were compared to the watershed's current and predeveloped conditions. Both scenarios provided reductions in peak flows with respect to existing conditions for modeled storm events, sometimes to levels below the predeveloped condition. Neither case was able to reduce volumes to predevelopment levels; the option to treat impervious areas had a negligible effect on runoff volume. Both cases were able to extend lag times from the existing development condition. Based on these results, bioretention appears to have the capability to improve watershed hydrologic characteristics. Furthermore, only treating impervious areas could be a viable alternative when funds or space are limiting factors. / Master of Science

Protection of downstream channels and reduction in flooding can potentially be improved by evaluating alternative site stormwater management (SWM) strategies at a watershed scale and selecting the optimal strategy for a subject watershed. Tailoring a management strategy for a specific watershed may be worthwhile to minimize development costs and maximize downstream benefit. A hydrologic/hydraulic model for a watershed in Blacksburg, Virginia, is used to evaluate downstream results based on implementation of several alternative SWM strategies currently practiced within the United States. Results show none of the strategies meet the goal of maintaining the baseline goal at the watershed POI for the full range of design storms. Modification to the strategy that performs best at the watershed scale did meet the watershed goal for all design storms except the 1-year. For smaller storm events, it appears that increasing the volume of an initial capture and the drawdown time to release that volume does not increase performance downstream. This is potentially significant as extra dollars spent on site would not provide extra benefit downstream. When post-development peak runoff rates are detained to the predevelopment rate for larger storm events, whether based on a site or watershed focused strategy, the watershed goal can be met. A volume reduction strategy performs well, but implementation is hindered by soils with poor infiltration and the presence of karst. Other insight to watershed based management strategies, the role of regional facilities and predevelopment condition assumptions at the site scale to maintain a baseline condition downstream are discussed. / Master of Science

Microplastics (MPs) are small pieces of plastic material including tyre wear particles (TWPs) smaller than 5000 µm. One of the primary pathways through which MPs including TWPs enter aquatic and marine environments is stormwater runoff from urban areas. The aim of this thesis is to advance the knowledge of MPs found in sediments from gully pots and stormwater ponds, as well as increase the understanding of and assess one of the sources of secondary MPs, i.e. UV-degradation of four commonly found plastic litters. To advance the knowledge, an experimental approach was used where results from a laboratory study and two field studies where synthesized.  UV-degradation of macroplastic litter (a bag, wrapper, cup lid, and bottle) into MP was studied in a laboratory experiment, highlighting one of the sources of MPs in urban environments. MPs generated using accelerated UV-degradation with three exposure times (corresponding to ¼, 1 and 2 years outdoors in Sweden) were quantified with micro-Fourier Transform Infrared Spectroscopy (µFTIR). In the field studies sediment samples were collected form 29 gully pots and six stormwater ponds in urban areas in Sweden, in order to investigate MP composition and concentrations. All sediment samples were analysed with regards to MPs (non-carbon black) using µ-FTIR, enabling the assessment of MP concentrations by number, mass as well as particle size. Using the same method (µFTIR) enabled comparison of the results between the laboratory and field studies. As a complement carbon-black MPs were analysed in gully pot sediments and TWPs in pond sediments using Attenuated Total Reflection (ATR)-FTIR and Pyrolysis-GC-MS respectively.   MPs were detected in all sediment samples, indicating that both gully pots and ponds temporarily trap MPs through sedimentation, thus they were not transported further downstream. Polypropylene (PP), EPDM (gully pots) and TWPs (ponds) were among the most commonly detected polymer type in sediment samples. The laboratory study showed that common plastic litters degrade due to UV- exposure (with the PP- wrapper being most prone to degradation), highlighting PP as a possible source of MPs in stormwater. The majority of (non-black) MPs, by number, were in the size range 126 - 250 µm in gully pot sediments, in contrast to pond sediments the majority were smaller than 100 µm. These results indicates that larger MP particles tend to settle early in the urban drainage system for example in gully pots, while smaller particles may be transported further downstream via stormwater, for example reaching ponds and mainly settle in pond sediment  Evaluating MP concentrations and composition with regards to polymer type and particle size in gully pot and stormwater pond sediments and common sources one of the source of MPs in the urban environment has advanced the understanding for example a commonly detected type (PP) and what MP sizes that tend to settle in the different studied storm water management facilities i.e., gully pots and ponds.

No description available.

No description available.

Contaminated stormwater discharge is a major concern in the United States due to a steady increase of harmful pollutants entering fresh water sources. The many congressional mandates that require local governments to reduce the impact of storm water discharge on the natural ecology have greatly increased the need for economically and environmentally viable solutions to pollution reduction. One such solution is that of constructed wetlands. Previous research conducted at the Sustainable Bio-products Department at Mississippi State University demonstrated the feasibility of kenaf fiber and wood shavings to remove toxins and crude oil from the bio-oil process water. This study proposes to amend contaminated storm water runoff from a biomass to bio-oil conversion facility through a simulated constructed wetland. The constructed wetlands were contaminated with varying dilution levels of bio-oil process water in a series of six phases. It was hypothesized that the contaminated rainwater can be remediated by constructed wetlands and safely released back into the native waterways. This study concluded that there was a significant decrease in biological oxygen demand (BOD) and micro-toxicity over a ten day cycle within the constructed wetlands for the lower levels of contaminated stormwater. A comparative screen of the bacterial community within the wetlands during the contamination process showed a similar trend in species richness and composition for the first three Phases of contamination. There was a shift in richness and diversity for the final three Phases of contamination after ten days within the constructed wetlands. The constructed wetlands were successful at lowering BOD and toxicity levels and achieving permissible pH levels when the concentration of contaminated stormwater was less than or equal to 400x dilution. Much of the BOD reduction was due to volatilization of the contaminated wastewater. When the concentration of contaminated water exceeded 300x dilution, the constructed wetland were only successful at achieving permissible pH discharge levels. Better results may be achievable with longer residence time in the wetlands.

<p> This work focuses on the advanced physical analysis of stormwater sediments using laser diffraction particle size analyzer and scanning electron microscope and chemical characterization using neutron activation analysis. Since previous studies of sediments from stormwater ponds in the Greater Toronto Area indicated a marginal-to-significant level of pollution by most of the regulated heavy metals, the characteristics of the storm water sediment samples obtained in this study were compared to the sediment quality guidelines of the Ontario Ministry of the Environment. The images from optical microscope showed that the particles in the dried sediment were irregular, and the sizes of each particle vary greatly. Using scanning electron microscope, it was shown that two different structures of particles were present in the storm water sediment. It was also observed that the main compositions (above 1000ppm) of the dried sediment included, in descending order of concentration, Ca >AI> Fe> K > Mg > Na >Ti > Mn. The trace compositions (below 1000ppm) included, also in descending order of concentration, Cl > Zn > Ba > Sr > Cr > V > La > Nd > As > Br > Co > Sc > Th > Sb > Sm > Eu. The concentrations of regulated elements such as Cr, Fe Zn, As and Mn were above the lowest effect level, suggesting that treatment of stormwater sediment may be necessary. A preliminary stormwater sediment treatment experiment using thermal plasma technology was therefore conducted. After the thermal plasma treatment, the percentage of total organic carbon decreased and eight gas compounds including CO, COz, NO, NOz, NOx, SOz, H2S and CxHy emitted during the process. Enrichments of Mg, Cl and Na were observed in the treated sludge while the concentrations of K and Ca decreased. The potential of thermal plasma technology for the treatment of contaminated stormwater sediment was demonstrated. </p> / Thesis / Master of Applied Science (MASc)

A 0.2-hectare wetland was constructed in the floodplain of Opequon Creek in Northern Virginia as a best management practice (BMP) for stormwater management. The research goals were to 1) determine if wetland hydrology existed and quantify the role of groundwater exchange in the constructed wetland (CW) water budget, 2) estimate wetland hydraulic characteristics during overbank flows, and 3) quantify the event-scale nutrient assimilative capacity of the constructed wetland. CW water table elevations and hydraulic gradients were measured through an array of nested piezometers. During controlled flooding events, stream water was pumped from the creek and amended with nutrients and a conservative tracer in two seasons to determine hydraulic characteristics and nutrient reduction. Samples were collected at the inlet, outlet structure, and at three locations along three transects along the wetland flowpath. Water table elevation monitoring demonstrated that wetland hydrology existed on the site. The mean residence time of the wetland was found to be 100 min for flow-rates of 4.25-5.1 m3/min. Residence time distributions of the high and low marsh features identified a considerable degree of flow dispersion. Manning's n varied between macrotopographic features and was significantly higher in the spring event as compared to the fall event, likely due to the presence of rigid-stem vegetation. Average wetland n was 0.62. Total suspended solid concentrations decreased with increasing residence time during both experiments. Mass reduction of pollutants were 73% total suspended solids (TSS), 54% ammonia-nitrogen (NH3-N), 16% nitrate-N (NO3-N), 16% total nitrogen (TN), 23% orthophosphate-phosphorus (PO4-P), and 37% total P (TP) in the fall, and 69% TSS, 58% NH3-N, 7% NO3-N, 22% TN, 8% PO4-P, and 25% TP in the spring. Linear regression of mass flux over the event hydrograph was used to determine pollutant removal rates between the wetland inlet and outlet. Pollutant removal rates were determined through linear regression of mass flux and were higher in the spring event than in the fall. Dissolved nitrogen species were more rapidly removed than dissolved phosphorus. TSS, TP, and TN removal were greater and faster than dissolved nutrient species, suggesting that physical settling was the dominant removal mechanism for stormwater pollutants. / Ph. D.

This dissertation develops a new distributed split-flow stormwater management strategy and compares its site design feasibility and construction cost to existing stormwater management methods. The purpose of the split-flow strategy is to manage stormwater by preserving predevelopment flows in terms of rate, quality, frequency, duration and volume. This strategy emulates the predevelopment hydrology: it retains and infiltrates additional runoff volume created by development by using bioretention and paired weirs as proportional flow splitters connected to small infiltration facilities distributed throughout a site. Results show that 1) the distributed split-flow stormwater management strategy can provide a higher level of environmental protection at comparable construction cost to existing detention-based methods, 2) split-flow systems are less expensive to construct than current truncated hydrograph-based bioretention and infiltration systems and 3) non-point source water pollution-reduction objectives, currently achieved with either detention with first flush or comparable bioretention and infiltration systems, could be achieved in a more cost-effective manner using distributed split-flow stormwater management strategy. / Ph. D.

Trout are an important game species that provide a substantial economic impact in Virginia. Along with other cold-water fish species, trout are extremely susceptible to changes in stream temperatures. Urban development and the increase in impervious surfaces alter the hydrologic cycle in urban watersheds, limiting infiltration and increasing surface runoff. Impervious surfaces absorb and store solar radiation, resulting in higher surfaces temperatures, and then transfer this thermal energy to runoff during a rainfall event, resulting in higher runoff temperatures. Bioretention cells are a common stormwater control practice identified as a possible thermal mitigation practice in urban watersheds harboring cold-water fish species. However, design specifications vary by locality and few studies have explored how design characteristics impact the temperature reduction potential. The goal of this study was to investigate changes in stormwater thermal load due to bioretention cells. In this study two bioretention cells with differing design approaches were monitored to quantify the thermal reduction impact that the bioretention cells have on stormwater from impervious surfaces. Both cells significantly reduced stormwater outflow volume, event mean temperatures and heat loads; however, outflow temperatures repeatedly exceeded the 21°C temperature threshold for cold-water fish species. This finding indicates this practice alone may not be sufficient to reduce runoff temperatures below biological stress thresholds. In addition, previous literature suggested that deeper cells may provide more cooling benefits as deeper soil layers are cooler and have more stable temperatures. In this study, the deeper cell was not as effective in reducing runoff temperatures, likely due to surface overflow and a shorter residence time in the bioretention cell. This finding indicates there is a limit to the effectiveness of cell depth in runoff thermal reduction and that other cell characteristics, such as subsurface drainage system length, may play an important role in runoff temperature reduction. / Master of Science / Cold-water fish species such as trout are a game species of large economic value that are very susceptible to changes in water temperature. Due to warmer runoff temperatures from urban watersheds stream temperatures are increasing, posing a potential impact on the cold-water fish found in these watersheds. Bioretention cells are a common method for treating and reducing pollutants from stormwater in urban areas. Recently, research has focused on the potential of bioretention cells to reduce runoff temperatures in urban watersheds. However, research is limited and does not fully address the bioretention design characteristics that may be beneficial for reducing runoff temperatures. In this study two bioretention with differing design approaches were monitored during summer months to quantify and assess the potential for runoff temperature reduction. Both cells reduced runoff volume, temperature, and overall heat energy leaving the cell. However, outflow temperatures were typically above the stress temperature threshold for many cold-water fish species, indicating that this practice may reduce runoff temperatures to a level that will not stress these fish species. Previous research has suggested that deeper cells may provide more cooling benefits as deeper soil layers are experience cooler and more stable temperatures. In this study, the deeper cell was not as effective in reducing runoff temperatures as the shallow cell with a greater overall volume. This finding suggests that there is a limit to the effectiveness of deeper cells and that other cell characteristics, such as cell volume, play an important role in runoff temperature reduction.