Bioassessment of wet-weather pollution impacts on fine sediments in urban waters by benthic indices and the sediment quality triad.

Benthic invertebrate assessments can be used to gauge the impact of urban wet-weather flows in receiving waters. Experiences from Cemagref in France have shown that standardized benthic indices (e.g. Oligochaete Index of Sediment Bioindication - IOBS) can be used to reliably determine the ecological status of urban streams and can be incorporated into the new European Water Framework Directive. The Canadian studies on streams and stormwater ponds using chemical analyses, benthic toxicity testing and benthic invertebrate community structure (i.e. the sediment quality triad) comparisons have shown that toxicity was more likely to occur in ponds at sites with higher concentrations of heavy metals and heavier polycyclic aromatic hydrocarbons, and at greater water depths, where fine sediments from urban runoff accumulated. A more comprehensive evaluation of wet-weather flow impacts could be obtained by combining approaches from both countries.     

Assessing urban stormwater toxicity: methodology evolution from point observations to longitudinal profiling.

The quality of aquatic habitat in a stormwater management facility located in Toronto, Ontario, was assessed by examining ecotoxicological responses of benthic invertebrates exposed to sediment and water from this system. Besides residential stormwater, the facility receives highway runoff contaminated with trace metals, polycyclic aromatic hydrocarbons (PAHs), and road salt. The combined flow passes through two extended detention ponds (in series) and a vegetated outlet channel. Toxicity of surficial sediment collected from 14 longitudinally arrayed locations was assessed based on 10 acute and chronic endpoints from laboratory tests with four benthic organisms. Greatest overall toxicity was observed in sediment from sites in the upstream pond, where mortality to amphipods and mayflies reached up to 100%. Downstream pond sediment was less toxic on average than the upstream pond sediment, but not the outlet channel sediment where untreated stormwater discharges provided additional sources of contamination. Macroinvertebrate communities in sediment cores were depauperate and dominated by oligochaetes and chironomids, with minimum densities and diversity at the deeper central pond sites. While sediment toxicity was associated with high concentrations of trace metals and high-molecular weight PAHs, benthic community impoverishment appeared related to high water column salinity.     

The ecological value of constructed wetlands for treating urban runoff.

The Sweetwater Authority's urban runoff diversion system (URDS) comprises constructed wetlands on a hillside between the town of Spring Valley and the Sweetwater Reservoir, California, USA. The URDS were designed to divert dry-weather and first-flush urban runoff flows from the Sweetwater reservoir. However, these constructed wetlands have developed into ecologically valuable habitat. This paper evaluates the following ecological questions related to the URDS: (1) the natural development of the species present and their growth pattern; (2) the biodiversity and pollutant stress on the plants and invertebrates; and (3) the question of habitat provided for endangered species. The URDS wetlands are comprised primarily of rush (Scirpus spp.) and cattails (Typha spp.). This vegetative cover ranged from 39-78% of the area of the individual wetland ponds. Current analyses of plant tissues and wetland sediment indicates the importance of sediment sorption for metals and plant uptake of nutrients. Analyses of URDS water following runoff events show the URDS wetlands do reduce the amount of nutrients and metals in the water column. Invertebrate surveys of the wetland ponds revealed lower habitat quality and environmental stress compared to unpolluted natural habitat. The value of the wetlands as wildlife habitat is constrained by low plant biodiversity and pollution stress from the runoff. Since the primary Sweetwater Authority goal is to maintain good water quality for drinking, any secondary utilization of URDS habitat by species (endangered or otherwise) is deemed an added benefit.     

Characteristics of urban run-off derived sediments captured by proprietary flow-through stormwater interceptors.

Sediment entrained in urban run-off is acknowledged as being an important carrier of pollutants. The paper reports on the physical and chemical characteristics of sediments captured by six installations of a proprietary interceptor device. The sites, located in the United Kingdom and the Republic of Ireland, were selected to represent a range of urban contexts. Particle D(50) values were found to range from 7 to 112 mum, corresponding with ranges reported for stormwater ponds. Heavy metal and hydrocarbon concentrations were also found to vary, with the highest corresponding to the most established and heavily trafficked sites. Further to confirming the ability of the interceptor to remove contaminated sediments, useful insights are provided into the interrelation between sediment characteristics and site conditions.     

Retrofitting a stormwater retention pond using a deflector island

Stormwater retention ponds are one of the principal methods to treat stormwater runoff. Analysis of residence time distribution (RTD) curves can be used to evaluate the capability of these ponds for sediment removal. Deflector islands have been suggested as a means of improving the performance of retention ponds, due to their diffusing the inlet jet. In this study, the effect of an island on retention pond performance was investigated using a physical model of an existing stormwater retention pond. The physical model is a trapezoidal pond having top dimensions 4.1 x 1.5 x 0.23 m and side slopes of 2:1 (h:v). Three different arrangements were studied. The results show that placing an island to deflect the influent to a stormwater retention pond does not improve pond performance, rather it stimulates short-circuiting. This unexpected behaviour, in relation to previous studies, is considered to be a consequence of the model pond incorporating sloping walls; which is a novel aspect of this paper.     

Achieving multiple benefits from stormwater harvesting.

As the concept of integrated urban water management is incorporated into the practice of urban water servicing, new options, such as stormwater harvesting, which can have multiple benefits, are of increasing interest. The multi-functional benefits of stormwater harvesting include the potential to enhance urban stream health through improvements to the flow regime as well as providing a valuable water supply source. This paper synthesises a current research programme being undertaken to assess the viability of, and develop recommendations for, stormwater harvesting. The design of the collection, treatment, storage, flood protection, and distribution components of an integrated system are each discussed, along with the environmental flow consequences of urban stormwater harvesting. The incorporation of swales and biofilters into the collection system was not found to lead to significant exfiltration and evaporation losses in most circumstances and so can be employed as part of the treatment train. Further treatment can be provided by WSUD-type biophysical measures such as ponds, wetlands or novelly designed biofilters or physio-chemical treatment processes. Depending on the design, the stormwater storage component may or may not provide flood protection. In many circumstances, the storage capacity requirements are not considered to be a barrier to stormwater harvesting.     

Microbial challenge-testing of treatment processes for quantifying stormwater recycling risks and management.

Pathogenic microorganisms have been identified as the main human health risks associated with the reuse of treated urban stormwater (runoff from paved and unpaved urban areas). As part of the Smart Water initiative (Victorian Government, Australia), a collaborative evaluation of three existing integrated stormwater recycling systems, and the risks involved in non-potable reuse of treated urban stormwater is being undertaken. Three stormwater recycling systems were selected at urban locations to provide a range of barriers including biofiltration, storage tanks, UV disinfection, a constructed wetland, and retention ponds. Recycled water from each of the systems is used for open space irrigation. In order to adequately undertake exposure assessments, it was necessary to quantify the efficacy of key barriers in each exposure pathway. Given that none of the selected treatment systems had previously been evaluated for their treatment efficiency, experimental work was carried out comprising dry and wet weather monitoring of each system (for a period of 12 months), as well as challenging the barriers with model microbes (for viruses, bacteria and parasitic protozoa) to provide input data for use in Quantitative Microbial Risk Assessment.     

Integrated urban stormwater management: Evolution and multidisciplinary perspective

This paper proposes an introductory review of the historical evolution of urban stormwater management, as well as of current trends, challenges, and changes of paradigm. It reminds us first that most of the existing urban stormwater infrastructures in developed cities are based on the modern urban sewer systems developed in the second half of the 19^th century in Europe. They have been built and for decades managed almost solely by urban sanitation and water specialists, relatively independently of other technical services and, more generally, of other stakeholders in cities. They contributed significantly to public health and fast conveyance of stormwater outside the cities. However, at the turn of the 1970s, it became evident with increasing urbanisation that they also had drawbacks: artificialisation of soils, reduction of aquifer recharge, pollution of surface water and ecological impacts, etc. The paper indicates how new concepts and paradigms thereafter emerged to manage stormwater by means of more sustainable and integrated approaches, aiming to solve the problems engendered by the previous approaches. This integration embraces more and more disciplines and issues, far beyond the traditional field of urban water engineers and specialists. The paper attempts to explain the need for this evolution, making urban stormwater management more much complex, dealing and interacting with ecology, biodiversity, bioinspiration, architecture, landscape and water values, citizens’ well-being, history, culture, and socio-economic aspects.     

The Impacts of Natural Flood Management Approaches on In‐Channel Sediment Quality

Natural Flood Management (NFM) techniques aim to reduce downstream flooding by storing and slowing the flow of stormwater to river channels. These techniques include a range of measures, including setback stormwater outfalls and the physical restoration of channels and floodplains, to improve the natural functioning of catchments. An additional benefit of NFM measures is the potential reduction in sediment and pollutant delivery to the channel. Urban development releases a variety of heavy metal and nutrient pollutants that enter rivers through stormwater outfalls with adverse effects on the aquatic ecosystem. In this study, the influence of channel modification and quality of the river habitat on the sediment quality surrounding stormwater outfalls was assessed. Sediment samples were taken at several outfalls within the Johnson Creek catchment, Oregon, USA, and analysed for a variety of urban pollutants. The level of river habitat quality and modification at each site were assessed using a semi‐quantitative scoring methodology. Significant increases in pollutant levels were observed at outfalls, with a greater and more variable increase at direct compared to setback outfalls. Removal efficiency of certain pollutants was found to be significantly correlated to the level of habitat quality or modification (for Fe, Ba, Sn, Mg, P, K) indicating that more natural reaches had greater potential for pollutant removal. The findings highlight the multiple benefits associated with NFM and river restoration approaches in relation to sediment quality and pollutant content. © 2016 The Authors River Research and Applications Published by John Wiley & Sons, Ltd.     

Assessment of the Impact of Stormwater Characteristics on Clogging in Stormwater Filters

Hydraulic conductivity of granular filter media and its evolution over time is a key design parameter for stormwater filtration and infiltration systems that are now widely used in management of polluted urban runoff. In fact, clogging of filter media is recognised as the main limiting factor of these stormwater treatment systems. This paper focuses on the effect of stormwater characteristics on the clogging of stormwater filters. Effect of five different operational regimes has been tested in this study of sediment concentration; pollutant concentrations; stormwater sediment size; loading rate and stormwater loading/dosing regime and compared with the Base case. For each operational condition, five column replicates were tested. Results suggest that sediment concentration in stormwater is a significant parameter affecting hydraulic and treatment performance, eventually affecting longevity of these stormwater treatment systems. Further, the size of sediments (and their relation to the size of filter media grains) in stormwater was found to be an important parameter to be considered in design of coarse filters with high infiltration rates that are used for stormwater treatment. As expected, the addition of metals and nutrients had limited or no contribution to changes in hydraulic or sediment removal performance of the studied stormwater filters. Whilst loading rate was found to be an important parameter affecting the hydraulic and treatment performance of these systems, any variation in the stormwater loading regime had a limited effect on their performance. This study therefore develops an understanding of the effect of catchment characteristics on design of filters and hence their longevity and maintenance needs.     

Inadequacy of Land Use and Impervious Area Fraction for Determining Urban Stormwater Quality

Urban stormwater quality is multifaceted and the use of a limited number of factors to represent catchment characteristics may not be adequate to explain the complexity of water quality response to a rainfall event or site-to-site differences in stormwater quality modelling. This paper presents the outcomes of a research study which investigated the adequacy of using land use and impervious area fraction only, to represent catchment characteristics in urban stormwater quality modelling. The research outcomes confirmed the inadequacy of the use of these two parameters alone to represent urban catchment characteristics in stormwater quality prediction. Urban form also needs to be taken into consideration as it was found have an important impact on stormwater quality by influencing pollutant generation, build-up and wash-off. Urban form refers to characteristics related to an urban development such as road layout, spatial distribution of urban areas and urban design features.     

The Influence of Watershed and Development Characteristics on the Cumulative Impacts of Stormwater Detention Ponds

Stormwater detention ponds are a popular stormwater management practice in many communities, and city ordinances often require the uniform use of detention ponds on all new developments. Although peak flow reduction can be achieved immediately downstream from a development, this practice may not be successful for controlling peak discharges from the watershed as a whole. The purpose of this research was to correlate watershed and development characteristics with the cumulative impacts of detention ponds in a watershed. A sensitivity analysis was performed to evaluate the influence of six watershed and development characteristics in synthetic watersheds. The sensitivity analysis evaluated two watershed characteristics: shape and slope. Four development characteristics were evaluated: size, intensity, stage, and sequence. Of the six watershed and development characteristics considered in the sensitivity analysis, watershed shape, the stage of development within the watershed, and the sequence of development within the watershed had the greatest effect on the cumulative impacts of detention ponds in the watershed. These three factors determined the pattern of impacts that occurred within a watershed. Development intensity, development size, and watershed slope contributed to the magnitude of the impacts which were created, but they were not the overriding factors that determined the pattern of impacts. These system-wide factors are not typically considered in the design and management of stormwater systems.     

Definition of realistic disturbances as a crucial step during the assessment of resilience of natural wastewater treatment systems

Natural wastewater treatment systems (WWTSs) for urban areas in developing countries are subjected to large fluctuations in their inflow. This situation can result in a decreased treatment performance. The main aims of this paper are to introduce resilience as a performance indicator for natural WWTSs and to propose a methodology for the identification and generation of realistic disturbances of WWTSs. Firstly, a definition of resilience is formulated for natural WWTSs together with a short discussion of its most relevant properties. An important aspect during the evaluation process of resilience is the selection of appropriate disturbances. Disturbances of the WWTS are caused by fluctuations in water quantity and quality characteristics of the inflow. An approach to defining appropriate disturbances is presented by means of water quantity and quality data collected for the urban wastewater system of Coronel Oviedo (Paraguay). The main problem under consideration is the potential negative impact of stormwater inflow and infiltration in the sanitary sewer system on the treatment performance of anaerobic waste stabilisation ponds.     

Trace metal levels in sediments deposited in urban stormwater management facilities.

Characteristics of solids recovered from stormwater best management practice (BMP) facilities, including stormwater ponds, constructed wetlands, an infiltration basin, a biofilter, a stormwater treatment clarifier, and three-chamber oil and grit separators were described with respect to their metal chemistry. The reported trace metal concentrations in BMP sediments were assessed against the Ontario Sediment Quality Guidelines. Between 80 to 100% of all samples were marginally-to-intermediately polluted by Cd, Cr, Cu, Fe, Pb, Mn, Ni and Zn. Severe pollution of sediments was noted for Cr (122 microg/g), Cu (151 and 196 microg/g), Mn (1,259 and 1,433 microg/g), and Zn (1,116 microg/g), at several facilities studied, and even higher levels of metals were reported in the literature for certain oil and grit separators. With respect to individual BMPs, the severe pollution was found in sediments from oil and grit separators (for Cd, Cr, Cu, Pb and Zn), the stormwater clarifier sludge (Cu, Mn and Zn), a biofilter (Cu and Mn), an industrial area stormwater pond (Cu only), and a commercial/residential pond (Cr only). Finally, the chemical pollution of pond sediment triggered toxicity testing at some of the facilities studied, and sediment toxicity was confirmed at several sites.     

Monitor-based evaluation of pollutant load from urban stormwater runoff in Beijing.

As a major pollutant source to urban receiving waters, the non-point source pollution from urban runoff needs to be well studied and effectively controlled. Based on monitoring data from urban runoff pollutant sources, this article describes a systematic estimation of total pollutant loads from the urban areas of Beijing. A numerical model was developed to quantify main pollutant loads of urban runoff in Beijing. A sub-procedure is involved in this method, in which the flush process influences both the quantity and quality of stormwater runoff. A statistics-based method was applied in computing the annual pollutant load as an output of the runoff. The proportions of pollutant from point-source and non-point sources were compared. This provides a scientific basis for proper environmental input assessment of urban stormwater pollution to receiving waters, improvement of infrastructure performance, implementation of urban stormwater management, and utilization of stormwater.     

Evaluating Escherichia coli removal performance in stormwater biofilters: a laboratory-scale study

Biofilters are common, low energy technologies used for the treatment of urban stormwater. While they have shown promising results for the removal of stormwater microorganisms, certain factors affect their performance. Hence, this study investigated the effects of particle-microbial interaction, inflow concentration, antecedent microbial levels and plant species on microbial removal capacity. A biofilter column study was set up to evaluate removal performance and a sequential filtration procedure was used to estimate microbial partitioning. The columns were dosed with different concentrations of free phase Escherichia coli only and E. coli mixed with stormwater sediment. Results indicate that the microbial removal is significantly affected by inflow concentration and antecedent microbial levels. Leaching was only observed when a relatively low inflow concentration event occurred within a short period after a very high inflow concentration event. Finally, Lomandra longifolia showed better removal compared with Carex appressa.     

生态雨水设施的污染物积累效应及风险研究进展

对植被浅沟、雨水花园及雨水塘3种具有代表性的生态雨水设施应用于径流中有机质、颗粒物、重金属等污染物控制时,污染物在设施内的积累特性进行了归纳总结,分析了设施长期运行时面临的污染风险,提出了这3种生态雨水设施运行管理与维护的建议:植被浅沟运行寿命应结合我国道路雨水径流水质综合确定,超期运行的植被浅沟应对表层5cm种植土进行更换;雨水花园表层介质重金属含量较高时,可更换0~10 cm深度范围内的种植土,为减少表层磷溶出量,可在表层覆盖树皮以加强对磷的吸附;雨水塘中沉积物的清理周期应按功能区分类确定,对于沉积物中多环芳烃含量较高的干塘应酌情增加清理次数。     

Understanding the Role of Urban Road Surface Characteristics in influencing Stormwater Quality

Urban road surfaces are one of the most important stormwater pollution sources. Asphalt and concrete road surfaces are typical road types in China and have different characteristics such as roughness, textures and infiltration rates. This could lead to differences of collecting and retaining pollutants. In this context, designing stormwater treatment for different road surfaces respectively is crucial to effectively minimize the stormwater deterioration. This closely depends on an in-depth understanding of stormwater quality characteristics on urban road surfaces. This research study investigated the stormwater quality characteristics on typical asphalt and concrete surfaces. The research outcomes show that road surface characteristics could play a more important role in influencing the resulting stormwater runoff quality than rainfall characteristics. Additionally, asphalt surface due to the relatively rough nature could play a more important role in influencing the overall pollutant export characteristics from urban road surfaces. It is also noted that there are notable differences in pollutant wash-off processes on different surfaces, where the wash-off process on asphalt surfaces tends to be a transport limiting process, while the wash-off process on concrete surfaces tends to be a source limiting process. These results can contribute to stormwater treatment design enhancement for urban roads such as treatment placement, rainfall event selection and water quality estimation.     

Element patterns for particulate matter in stormwater effluent

Particulate matter in stormwater deteriorates the quality of receiving water and sediment. Characterization of stormwater particulate matter by means of its particle-associated element pattern provides an aid to determining its impact on receiving surface waters. During a 6 month measurement campaign, we determined particle-associated concentrations of major pollutants and rare earths for three combined water/stormwater outlets in the town of Stassfurt. We differentiated the particle-associated constituents on the basis of a hierarchical cluster analysis. Repeating the cluster analysis on random subsets, we gained information about the variability of the element patterns between and within the sites. In general, constituents associated with sewage and sewer sediment behave differently compared with constituents associated with runoff. The degree to which associations can be established for element patterns from site to site is limited by the variability encountered within sample sets taken from individual sites. The latter variability depends on the complexity of the catchment.