Stormwater Pollution Research Articles

Identification of Stormwater Pollution Hotspots in Charleston Peninsula

Flooding is of great concern in fast-growing coastal communities, especially in the southeastern US, due to multiplying threats such as extreme precipitation, coastal storms, and rising sea levels. Contamination associated with stormwater runoff is often given less attention during stormwater planning and management decisions. The US EPA has long recognized that stormwater runoff is the biggest contributor to the impairment of water bodies in the US. In this study, we studied stormwater runoff contamination in a densely developed section of downtown Charleston, South Carolina, to better understand the extent of the problem and identify potential hotspots that could aid in future stormwater management decisions.

Greening the gray infrastructure: Green adsorbent media for catch basin inserts to remove stormwater pollutants

Stormwater pollution is a major cause of water quality impairment. Much of the existing gray stormwater infrastructures provide little or no treatment, especially for dissolved pollutants. Due to the capital cost of installing new infrastructure, retrofitting the existing gray infrastructures is a promising alternative to reduce stormwater pollution. In this study, aluminum-based drinking water treatment residuals (WTR), a byproduct from drinking water treatment, was combined with other common materials (sand and carbon material) to formulate an adsorbent media for use in catch basin inserts to remove total petroleum hydrocarbons (TPH), and dissolved Cu, Pb, and Zn from stormwater runoff. Hydraulic and treatment performance of the adsorbent media were optimized in laboratory column experiments. A dual-layer media, WTR-amended sand with a mass percentage of 5% WTR relative to sand over carbon material with the depth ratio of 1:3, was selected as optimal. The breakthrough curves correlated well with the Yan model. During the field study, influent and effluent samples were collected from two catch basins from eight storm events and analyzed for turbidity, pH, TPH, and dissolved Cu, Pb, and Zn. The median removal efficiencies of dissolved Cu, dissolved Pb, dissolved Zn, and TPH during the field study were 27.4%, 36.3%, 69.3%, and 45.6%, respectively. The removal of particulate-bound pollutants was indicated by the reduction of turbidity with the median removal efficiencies of 81.2%. A slight increase in pH was observed. There was no water ponding during the study. Our results show that this low-tech, low-cost adsorbent media is effective in reducing metal and organic pollutants in stormwater.

A coupled hydrodynamic and particle-tracking model for full-process simulation of nonpoint source pollutants

Nonpoint source (NPS) particulate pollutants are a major source of urban surface pollution. It is essential to better understand and model the dynamic process of NPS pollutants to inform the design of effective strategies for urban stormwater management and pollution control. This work presents a novel coupled hydrodynamic and particle-based model to simulate the full-process dynamics of NPS particulate pollutants from detachment, transport to deposition in urban areas. A particle-based approach is proposed to represent the physical processes of pollutant detachment and deposition. The transport of pollutant particles is simulated using a random-walk particle-tracking model, which can directly trace out the trajectories of individual particles and hence identify the pathways of pollutants. The new coupled hydrodynamic and particle-based stormwater quality model is successfully validated against several analytical and experimental test cases to demonstrate its capability in accurately simulating the full-process dynamics of NPS particulate pollutants in urban areas.

Modelling of Storm-water Drainage Systems in Residential Areas

All the processes that take place in an urban water system are parts of the hydrological cycle of water. Any urban development will have a negative impact on the environment, but through an optimal approach and management of rainwater, storm water drainage and pollution leakage, we prevent the degradation of these natural resources. This paper presents aspects regarding the management of the storm-water on the surfaces related to the developed residential areas within the localities, which do not have a centralized system of meteoric sewage. In most of the localities, the storm water is not collected centrally. It is being evacuated through the slopes of the lands to the gutter, where it exists and to the areas with the lowest levels of the localities. In recent years, the climate change and poor management of the storm-water in these localities led to a major risk of flooding. The paper analyses the potential flood risks of the drainage system designed for the residential area in the analysed river basin.

Evaluating the relationships between specific drainage area characteristics and soil metal concentrations in long-established bioswales receiving suburban stormwater runoff

Bioswales are used to attenuate stormwater pollution, but their long-term sustainability regarding sequestered metals is relatively unknown, and a clear rationale for prioritizing soil management is lacking. Impervious areas draining into four 14-year-old suburban bioswales were delineated, for which surface soils (top 10 cm; 72 samples) were sampled; soils from 4 adjacent reference sites were also sampled. Total and water soluble metals (Cd, Cu, Pb, Zn) were quantified, and the relationships between metal concentrations and drainage area characteristics evaluated. Annual metal loads were estimated using regional runoff data to simulate current and future metal concentrations; risks to soil biota were assessed by comparing metal concentrations to ecological screening levels. The drainage areas' percent imperviousness (37–71%) and ratios of impervious drainage area to bioswale area (2.0–5.7) varied, owing to differing proportions of rooftops, paved surfaces, lawns, and natural soils. Total Cu and Zn ranged from 10.0 to 43.2 mg/kg dry soil, and 15.6 to 129.5 mg/kg dry soil, respectively. Across all bioswales, total Zn was positively correlated to percent impervious area (r = 0.32, p = 0.0073), the ratio of connected impervious drainage area to infiltration area (r = 0.32, p = 0.0073), and percent drainage area as paved surfaces (r = 0.46, p = 5.6 E-05), but negatively correlated to percent drainage area as lawns (r = −0.48; p = 2.4 E-05). Water soluble metal concentrations were orders of magnitude lower than total metals. Given annual metal loads (0.2–0.4 mg Cu/kg dry soil; 1.5–3.1 mg Zn/kg dry soil), replacing bioswale soils to constrain metal concentrations would be unnecessary for decades. Taken together, this study proposes a transferable approach of estimating, then verifying via sampling and analysis, bioswale soil metal concentrations, such that soil management decisions can be benchmarked to ecological screening levels.

Mixed versus layered multi-media filter for simultaneous removal of nutrients and heavy metals from urban stormwater runoff.

Beach closings are a growing concern in coastal regions because of serious public health and economic ramifications due to the presence of pollutants in stormwater runoff. An underground permeable filter system is proposed to treat such stormwater pollution. Selection of filter media that can treat multiple contaminants in stormwater runoff has been a challenging task. This paper investigates the effectiveness of mixed or layered filter media for the removal of mixed contaminants (nutrient and heavy metal) from synthetic stormwater. Sorption experiments were used to assess the ability of the combination of various materials (calcite, zeolite, sand, and iron filings) to remove nutrients and heavy metals. Based on the results of individual removal efficiency, four sets of combinations of media mixtures were prepared: three mixed media conditions and one layered media condition. Mixed media-1, containing higher ratio of calcite, zeolite, and iron filings, was found to achieve the highest removal efficiency of nitrate (96%), Cr (~ 99%), and Cu (~ 99%). Mixed media-2 removed Zn significantly with a removal efficiency higher than 99% due to the sorption capacity of iron filings and both mixed media-2 and 3 showed efficient removal of Ni (~ 94%) in effluent. Layered media was found to be most efficient in Cd removal (~ 99%). All mixture of materials showed more than 99% removal of total phosphorus and Pb. The sorption efficiency of the different mixtures showed that a combination of traditional (sand) and alternative materials (calcite, zeolite, and iron filings) can be used as an effective medium for the treatment of nutrient and heavy metal contaminants commonly found in stormwater.

Robustness analysis of storm water quality modelling with LID infrastructures from natural event-based field monitoring

Sponge city construction (SCC) in China, as a new concept and a practical application of low-impact development (LID), is gaining wide popularity. Modelling tools are widely used to evaluate the ecological benefits of SCC in stormwater pollution mitigation. However, the understanding of the robustness of water quality modelling with different LID design options is still limited due to the paucity of water quality data as well as the high cost of water quality data collection and model calibration. This study develops a new concept of ‘robustness’ measured by model calibration performances. It combines an automatic calibration technique with intensive field monitoring data to perform the robustness analysis of storm water quality modelling using the SWMM (Storm Water Management Model). One of the national pilot areas of SCC, Fenghuang Cheng, in Shenzhen, China, is selected as the study area. Five water quality variables (COD, NH3-N, TN, TP, and SS) and 13 types of LID/non-LID infrastructures are simulated using 37 rainfall events. The results show that the model performance is satisfactory for different water quality variables and LID types. Water quality modelling of greenbelts and rain gardens has the best performance, while the models of barrels and green roofs are not as robust as those of the other LID types. In urban runoff, three water quality parameters, namely, SS, TN and COD, are better captured by the SWMM models than NH3-N and TP. The modelling performance tends to be better under heavy rain and significant pollutant concentrations, denoting a potentially more stable and reliable design of infrastructures. This study helps to improve the current understanding of the feasibility and robustness of using the SWMM model in sponge city design.

Integrated Smart Water Management of the sanitation system of the Greater Paris region

ABSTRACT This case study details the development of a real-time control system (MAGES) in the Paris region designed to better control stormwater pollution caused by combined sewer overflows and to optimize the need for additional storage or treatment facilities. It is structured to outline the challenges facing the Greater Paris region water and sanitation networks, and the solutions provided by SIAAP, the public utility in charge of the treatment and transport of wastewater, over the past 20 years.

Comprehensive evaluation of stormwater pollutants characteristics, purification process and environmental impact after low impact development practices

Understanding the stormwater characteristics and purification process of different underlying surfaces in an intensive Low Impact Development (LID) catchment is critical for summarizing problems of built LID practices and providing references for future LID construction. This research program investigated stormwater pollutants from several sites in Yuelai, Chongqing, a pilot area of Chinese Sponge Cities. The results showed that different LID areas had different stormwater pollutant characteristics and purification processes due to different LID layouts and facilities. For highway runoff, pollutants event mean concentrations (EMCs) were mainly affected by rainfall characteristics rather than road slopes. Ammonia was the primary nitrogen pollutant, and it always has a heavier first flush effect (FFE). For the green parks, runoff volume and FFE reduction were effective because of the high density of soil-based LID facilities and natural green space. However, nitrate and organic matter leaching also existed. The commercial areas often have more engineering facilities which could remove solids pollutant and phosphorus effectively. However, nitrogen removal performance was poor. The residential areas compromised between green parks and commercial areas. Overall, LID construction significantly reduced pollutants EMCs, volume and FFE, ameliorated water quality of the receiving water bodies. Nevertheless, some problems, such as inadequate nitrogen removal and runoff scouring effect, still need to be resolved in the future.

Impacts of key factors on heavy metal accumulation in urban road-deposited sediments (RDS): Implications for RDS management

Understanding of the impacts of key influential factors on RDS related heavy metal (HM) contamination is crucial for developing effective RDS management strategies to support the stormwater pollution mitigation. In this paper, three factors (i.e. traffic condition, slope of road and antecedent dry period) were considered to investigate their influences on the accumulation of RDS and adsorbed HMs. Positive correlations between truck and Zn/Ni content in RDS, car and Cu/Pb content in fine RDS, as well as bus and Cu content in coarse RDS were observed. Relative to sloping stretches, RDS from level stretches generally presented finer size distributions and aggravated HM contamination in fine fractions. Moreover, the fine RDS and adsorbed HMs increased significantly with the accumulation of RDS. Based on these findings, optimized RDS management strategies were proposed to enhance the removal of washable RDS in pollution hotspots. For example, tandem sweeping technologies, performing high efficiency in capturing fine particles, are suggested to be employed during the steady period of RDS accumulation, in order to reduce fine RDS effectively. The outcomes of this study provide useful reference for the source control of stormwater runoff pollution.

Spatial Compatibility of Implementing Nature-Based Solutions for Reducing Urban Heat Islands and Stormwater Pollution

Cities worldwide are facing several challenges connected to urbanization and climate change. Several cities have identified the implementation of nature-based solutions (NBS) as an option to mitigate several challenges at once. However, can two different aims be reached with NBS in the same location? This question has not yet been addressed. This paper discusses the spatial compatibility of NBS implementation strategies to tackle (1) urban heat island (UHI) effects and (2) water pollution at the same location. The evaluation is based on a spatial analysis of Berlin. We found a positive correlation of high UHI and median high stormwater pollution loads for zinc, total suspended solids, Polycyclic Aromatic Hydrocarbons and Terbutryn. Out of more than 14,000 building/street sections analyzed, 2270 showed spatial matching of high UHI and high stormwater pollution loads. In the majority of building/street sections, stormwater pollution was high for three out of the four parameters. We conclude that the compatibility of NBS implementation for both challenges depends both on the implementation strategies for NBS and on the specific NBS measures. Our spatial analysis can be used for further planning processes for NBS implementation.

Fate of road-dust associated microplastics and per- and polyfluorinated substances in stormwater

Emerging contaminants such as microplastics (MPs) and per- and polyfluorinated substances (PFAS) in the water environment have been documented as the major environmental threat due to their negative impact on the ecosystem. Road dust has been recognised as a potential source of these emerging pollutants in stormwater which are eventually released into open water bodies. The aim of this study was to identify the existence of MPs and PFAS in Australian road dust and stormwater samples. We found that different MP types such as polyethylene, nylon, polyester and cotton were identified in the stormwater samples. The main type of MPs in stormwater was microfibres which accounted for more than 50 %. It was also found that PFAS was detected in Australian road dust from industrial and heavily trafficked areas. Although there was no PFAS in stormwater in the selected industrial and heavy traffic study area, they can be found in airport and defence sites. This study indicated that road dust acts as the potential origin of MPs and PFAS in urban stormwater runoff.

Particulate matter exchange between atmosphere and roads surfaces in urban areas

The deposition and the re-suspension of particulate matter (PM) in urban areas are the key processes that contribute not only to stormwater pollution, but also to air pollution. However, investigation of the deposition and the re-suspension of PM is challenging because of the difficulties in distinguishing between the resuspended and the deposited PM. This study created two Bayesian Networks (BN) models to explore the deposition and the re-suspension of PM as well as the important influential factors. The outcomes of BN modelling revealed that deposition and re-suspension of PM10 occurred under both, high-traffic and low-traffic conditions, and the re-suspension of PM2.5 occurred under low-traffic conditions. The deposition of PM10 under low-volume traffic condition is 1.6 times higher than under high-volume traffic condition, which is attributed to the decrease in PM10 caused by relatively higher turbulence under high-volume traffic conditions. PM10 is more easily resuspended from road surfaces compared to PM2.5 as the particles which larger than the thickness of the laminar airflow over the road surface are more easily removed from road surfaces. The increase in wind speed contributes to the increase in PM build-up by transporting particulates from roadside areas to the road surfaces and the airborne PM2.5 and PM10 increases with the increase in relative humidity. The study outcomes provide a step improvement in the understanding of the transfer processes of PM2.5 and PM10 between atmosphere and urban road surfaces, which in turn will contribute to the effective design of mitigation measures for urban stormwater and air pollution.

Size distributions and heavy metal pollution of urban road-deposited sediments (RDS) related to traffic types.

Little is known about the particles attached on the surfaces of coarse (> 150μm) road-deposited sediments (RDS), which are potential contributors of stormwater pollution. Therefore, the size distributions and heavy metal (including Cu, Pb, Zn, Cr, and Ni) pollution of RDS were evaluated taking these attached particles into consideration. Moreover, the relationships of RDS contamination with traffic types were further discussed. The results showed that < 22, 22-38.5, 38.5-150, > 150μm RDS and attached particles accounted for 2.1 ± 1.8%, 8.5 ± 5.7%, 50.7 ± 6.8%, 38.6 ± 8.3%, and 2.0 ± 1.2% of total RDS mass, respectively. The size distributions of attached particles were comparable to that of representative stormwater particles, suggesting their great potential to contribute stormwater particles by desorption. The Zn pollution of attached particles was remarkable, which was significantly higher than that of both fine (< 150μm) and coarse (> 150μm) RDS. The Cu and Pb pollution were comparable to that of fine RDS, which were significantly higher than that of coarse RDS. Conversely, the Cr and Ni pollution were comparable to that of coarse RDS, which were significantly lower than that of fine RDS. Traffic types were found to be closely related with RDS contamination, and thus are indicative of specific RDS pollution. For example, electrombile in old residential area is indicative of abnormal Pb pollution due to past emissions of leaded gasoline; lorry is indicative of remarkable Zn pollution of > 22μm RDS due to abrasion of tires and metallic substances. Accordingly, traffic type is accessible to identify the typical pollutants in RDS to promote effective RDS management.

Stormwater runoff and pollution retention performances of permeable pavements and the effects of structural factors.

Permeable pavements, as additive structures that have a good capability for runoff and pollutant reduction, are extensively used for sustainable urban drainage techniques. However, the exact mechanisms of runoff retention and pollutant reduction of a permeable pavement system remain unclear and so, it has become an ongoing issue and motivation for hydrologists and design and structural engineers. In this research paper, a suite of four scale-based runoff plots representing permeable pavements were designed with different permeable surface types and gravel layer thickness treatments, and coupled with simulated rainfall experiments to analyze the impacts of structural factors of permeable pavements on runoff retentions and pollution reduction. The present results showed that the average time to runoff for permeable pavements under low-intensity rainfall scenarios was approximately 78.5min, while this was shortened to only 51.5min under high-intensity rainfall scenarios. In terms of the average runoff retention of permeable pavements tested under low- and high-intensity rainfall cases, the results recorded approximately 52.5% and 42.5%, respectively, but runoff retention performances were relatively greater for the case of smaller storms within the scale experiments. Importantly, there was no statistical significance for the time to runoff and runoff retention between the permeable bricks and porous concretes for the analyzed rainfall events. The thicker gravel layers significantly delayed runoff generation and increased runoff retention percentages. Runoff pollutant load reduction rates of total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) were varied between permeable bricks and porous concretes. Runoff pollutants load reduction rates of TSS, TN, and TP were highly enhanced while the gravel layer thickness increased from 10 to 20cm. Higher TSS, TN, and TP pollutant load removals were found from the lower intensity rainfalls. These findings could promote understanding of the hydrologic properties of permeable pavements and help design engineers in optimizing their design of permeable pavements for better runoff retention and pollution removal.

Compaction conditions affect the capacity of biochar-amended sand filters to treat road runoff

Amending roadside soil with adsorbents such as biochar can help remove pollutants from road runoff. To maintain soil stability, the roadside soil requires compaction. However, it is unknown how compaction conditions affect the capacity of biochar-augmented roadside biofilters to infiltrate stormwater and remove pollutants. This work examines the effect of compaction conditions on the release of biochar particles disintegrated during compaction, and the change in their capacity to infiltrate stormwater and remove E. coli. The net loss of biochar particles by mobilization with stormwater was insignificant compared to the biochar remained in the filters. The initial release of biochar particles in wet-compacted biochar columns was greater than that in dry-compacted biochar. The results revealed that compaction can affect the release of biochar particles in a series of three-step processes: generation of particles by disintegration of large biochar under compaction, diffusion of particles deposited near grain walls to bulk pore water, and transport and retention of particles in constricted pore paths based on pore water connectivity. Under similar conditions, compost columns released more particles than biochar columns, suggesting biochar is more stable than compost under compaction. E. coli removal in wet-compacted columns was greater than removal in dry-compacted columns, owing to greater pore path connectivity in wet-compacted columns. These results indicate that addition of moisture during compaction can increase contaminant removal, initial particle release, and infiltration capacity of biochar-augmented sand filters for road runoff treatment. The results would help develop design guidelines for roadside stormwater treatment systems that require compaction of filter media.

Removal of metals and hydrocarbons from stormwater using coagulation and flocculation

As the understanding of how stormwater pollutants are fractioned and need for mitigation has increased, so has the investigation into more advanced treatment techniques. The present study investigated the treatment efficiency of coagulation/flocculation and sedimentation in semi-synthetic stormwater. Five coagulants were evaluated in terms of reducing particle content, organic carbon, total and dissolved metals, hydrocarbon oil index, and polycyclic aromatic hydrocarbons (PAHs). Changes in the resulting particle size distribution as a consequence of the coagulation treatment were also investigated. The pollutants in the semi-synthetic stormwater were predominantly in the particulate phase. The medium and longer chained hydrocarbons dominated the hydrocarbon oil index, while medium to high molecular weight PAHs were most abundant. Iron chloride was the only coagulant that affected particle size distribution post-treatment, shifting the distribution toward larger particles. In terms of total metal removal, the performance of the coagulants was similar, with over 90% removal on average. Concentration of zdissolved copper, one of the metals found in the dissolved phase, was reduced by 40% via coagulation treatment. The iron chloride coagulant increased dissolved Zn, a change attributed to a considerable drop in pH resulting in higher ion mobility. Similarly, the reduction in organic content (total organic carbon, oil, and PAHs) was over 90% for most coagulants.

Nitrogen removal buffer capacity of the Lubigi wetland in Uganda

Lubigi wetland in Uganda receives sewage from Lubigi sewage treatment plant and polluted storm water from parts of Kampala city, which contain organic pollutants including nitrogen. This research was formulated to investigate and model the mechanisms and processes governing the transformation and removal of nitrogen in the Lubigi wetland. Wetland characteristics, flora and the transformation and removal of nitrogen were investigated in the Lubigi wetland in Uganda. Pertinent field investigations, surveys, data collection and laboratory tests and analyses were carried out. Nitrogen transformation and removal was modelled using STELLA II version 9.0®2006 software. The results revealed that the wetland main study area basin widths varied from 250 m to 450 m and deepest section of the wetland was 2.5 m. The study area basin total surface area and volume are 1,093,740 m2 and 1,073,060 m3, respectively. There are 9 dominant plants species, and the mean plants density, biomass and nitrogen content are 10.19 ± 4.69 plants/m2, 1.25 kgDWm−2 and 67.54 ± 37.9gNm−2, respectively. The mean influent and effluent discharges were 222,378 m3/d and 221,357 m3/d, respectively. The wetland main study area hydraulic residence times, vary between 6 h and 10 days depending on the season of the year. The major nitrogen transformation and removal mechanisms and processes are plants uptake (10.328 gNm−2day−1), sedimentation (2.467 gNm−2day−1) and denitrification (0.027 gNm−2day−1). It was concluded that wetland plants and sedimentation of organic nitrogen play a key role for nitrogen removal as they are responsible for removal of 67.54 ± 37.9 gNm−2 and 157.5 g gNm−2, respectively.

Alternative sorption filter materials effectively remove non-particulate organic pollutants from stormwater

Urban runoff contains a mixture of both particulate and non-particulate organic pollutants (OPs). Hydrophobic OPs such as higher petroleum hydrocarbons, phthalates, and polycyclic organic hydrocarbons (PAHs) are not exclusively bound to particles, but also present in runoff in colloidal and truly dissolved forms. These hydrophobic compounds can also form nano- and microsized emulsions that may carry pollutants in stormwater. Hence, it is of great importance to develop treatment technologies such as sorption filters that can remove non-particulate OPs from contaminated stormwater. A pilot plant using column bed-filters of sand as a pre-filter, in combination with granulated activated carbon, Sphagnum peat or Pinus sylvestris bark, was used to investigate the removal of non-particulate OPs from urban stormwater. Samples from the filter effluents were collected weekly; during or after rain events; and during stress tests when incoming water was spiked with contaminated sediment and petrol or diesel. All sorption filters showed efficient reduction of aliphatic diesel hydrocarbons C16–C35, benzene, and the PAHs phenanthrene, fluoranthene, and pyrene during most of the operation time, which was 18 months. During the stress test events, all sorption filters showed 100% reduction of PAH-16, petrol and diesel aliphatics C5–C35. All sorption filters released DOC and nanoparticles, which may explain some of the transportation of OPs through the filter beds. The recommendation is to use a combination of sand pre-filtration and all the studied sorption materials in stormwater filters in series, to achieve effective removal of different types of OPs. It is also important to improve the hydraulic conditions to obtain sufficient water flows through the filters.

Impact of global warming on urban stormwater quality: From the perspective of an alternative water resource

Stormwater is a largely under-utilised resource available to alleviate water shortages in urban areas. However, stormwater needs treatment before use. Further, projected changes to rainfall patterns due to global warming will alter stormwater quality characteristics. This study projects potential changes to the primary source of stormwater degradation, namely, particulates that transport the largest fraction of toxic pollutants in stormwater. The results show that 1.5 °C and 2 °C warming can influence the increase in toxic pollutant loads (heavy metals) by more than 90% on urban surfaces and by nearly 50% in stormwater runoff. Stormwater quality will be further degraded under the upper limit of the projected changes to dry periods and precipitation in the context of Representative Concentration Pathway (RCP) 8.5. Compared to the present day, results indicate that cities in the future will face more challenging tasks in designing effective measures to address increasingly complex stormwater quality responses to different combinations of dry and wet weather conditions. Therefore, this study urges the need for achieving a paradigm shift in the accuracy of stormwater quality predictions by incorporating the effects of changing weather patterns into the current practice of stormwater quality modelling, and thereby to optimise urban stormwater management.