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Urban stormwater is contaminated by a wide range of substances whose concentrations vary greatly between locations, as well as between and during rain events. This literature review evaluates advantages and limitations of current methods for using continuous water quality monitoring for stormwater characterization and control. High-temporal-resolution measurements have been used to improve the understanding of stormwater quality dynamics and pollutant pathways, facilitate the performance evaluation of stormwater control measures and improve operation of the urban drainage system with real-time control. However, most sensors used to study stormwater were developed for either centralized water treatment or natural water contexts and adaptation is necessary. At present, the primary application of interest in stormwater – characterization of pollutant concentrations – can only be achieved through the use of indirect measurements with site-specific relationships of pollutants to basic physical-chemical parameters. In addition, various problems arise in the field context, associated with intermittent or variable flow rates, the accumulation of debris and sediment, adverse conditions for electrical equipment and human factors. Obtaining reliable continuous stormwater quality data requires the adoption of best practices, including the calibration and regular maintenance of sensors, verification of data and accounting for the considerable uncertainties in data; however, the literature review showed that improvement is needed among the scientific community in implementing and documenting these practices., Validerad;2024;Nivå 2;2024-03-27 (hanlid);Full text license: CC BY 4.0

The study assessed the quality of highway runoff and a stormwater treatment system, focusing on intra-event variations (IEVs: variations within a runoff/effluent event) of the concentration of organic micropollutants (OMPs) including bisphenol-A, alkylphenols, polycyclic aromatic hydrocarbons (PAHs), and petroleum hydrocarbons (PHCs). IEVs of OMPs varied considerably with no particular recurring pattern in highway runoff and presedimentation effluent, displaying sporadic strong first flushes. IEVs are significantly associated with rainfall intensity variations, especially for particle-bound substances such as PAHs and PHCs. However, phenolic substances showed distinct IEV patterns compared to total suspended solids, PAHs, and PHCs, likely due to their higher solubility and mobility. Downstream sand filter (SF) and vegetated biofilter (BFC) mitigated IEVs, leading to more uniform discharge during outflow events. Although BFC’s IEVs were indiscernible due to low effluent concentrations, SF’s IEVs often peaked at the beginning of events (within the first 100 of ⁓600 m3), exceeding the lowest predicted non-effect concentrations for five PAHs, bisphenol-A, and octylphenol. This study highlights the advantage of IEV analysis over conventional event mean concentration analysis for identifying critical effluent stages, crucial for developing control strategies to protect sensitive water recipients or for reuse applications., Validerad;2024;Nivå 2;2024-07-25 (signyg);Fulltext license: CC BY

Reduction of runoff flow peaks and volumes is one of the performance objectives of grass swales in the context of Green Stormwater Infrastructure (GSI). Towards this end, a study of the feasibility of using a retrofitted swale outlet control weir (SOCW) to reduce runoff volume and peak flow, by enhancing swale runoff storage and infiltration into swale soils, was conducted in Luleå, Northern Sweden. Experimental field work consisted of 43 irrigation-driven runoff experiments, mimicking rainfall events with return periods between 1- to 50-years, with a constant intensity and duration of 30 min, in a 30-m long grass swale section. Experimental results confirmed that, under the tested conditions, swales with the retrofitted outflow control, reduced runoff volumes and peak flows. Such reductions ranged from 32 percentage points (for 2-year) to 1 and 4 percentage points (for 50-year return period) for runoff volumes and peak flows, respectively. Outcomes of scenarios with outflow controls clearly indicated a decreasing performance with increasing flow rates (and irrigation event return periods). Furthermore, the retrofitted swale controlled the outflow release during less frequent 20 to 50-year events, which would contribute to reducing flood risks in downstream urban areas., Validerad;2024;Nivå 2;2024-07-22 (signyg);Fulltext licence: CC BY

Urban stormwater typically enters sewer networks through gully pots, which allow a primary sedimentation of solids upstream of the piped network. The regular removal and disposal of retained sediment are necessary, costly and can involve environmental risks due to the contamination of sediments with substances from the urban environment such as metals. The concentrations and speciation of Cd, Cr, Cu, Ni, Pb and Zn were analysed in sediments from 26 gully pots located in different land use areas in Stockholm, Sweden. In addition, accumulation rates of both sediment and metal masses were evaluated, providing a basis for optimising maintenance practices and better understanding of impacts of characteristic urban land use types. Metal concentrations varied by at most a factor of eight between samples and were always below Swedish polluted site guidelines for less sensitive land use, with only eight samples exceeding the guideline values for Cu and Zn for sensitive land use. Sequential extraction showed Pb and Zn to be the most mobile metals. Sediment accumulation rates varied from 0.003 to 0.197 kg/m2 impermeable surface/year. Metal accumulation rates were much more variable than metal concentrations, with a factor of up to 172 between the highest and lowest rates and the highest metal accumulation rates corresponding to the lower range of mass loads in road runoff. Differences in metal concentrations, sediment or metal mass accumulations could not be solely attributed to either traffic or catchment land use. In contrast, traction grit used for winter road maintenance, which has low (but detectable) metal concentrations, is identified as a major component of gully pot sediments, with a combined effect of both moderating metal concentrations and contributing to total mass., Validerad;2023;Nivå 2;2023-11-14 (marisr);Full text license: CC BY

In the context of increasing urbanization and global warming, there is a growing interest in the implementation of green infrastructure (GI) across different climates and regions. Identifying an appropriate GI design criteria is essential to ensure that the design is tailored to satisfy local environmental requirements. This article aims to compare the hydrological performance of GI facilities in eleven Swedish cities by isolating the effect of climatic conditions using an identical GI design configuration. Long-term simulations based on 23-years of meteorological time-series were used as inputs for the Storm Water Management Model (SWMM) with Low Impact Development (LID) controls representing two types of facilities: a biofilter cell (BC) and a green roof. (GR). Large differences in potential annual and seasonal runoff retention were found between locations, driven mainly by the extent of winter/spring season, and the distribution of precipitation patterns (for BCs) and the sequence of rainy days-dry periods and evapotranspiration rates (for GRs). Winter/spring and summer demonstrated the highest/lowest differences between the seasons, results that suggest that implications for design might be aligned to the spatio-temporal distribution of precipitation patterns, and runoff regimes generated by snowmelt and rain-on-snow events, in locations where snowmelt represent high portion of runoff generation., Validerad;2022;Nivå 2;2022-11-28 (hanlid), Drizzle – Centre for Stormwater Management

This study details the occurrence and concentrations of organic micropollutants (OMPs) in stormwater collected from a highway bridge catchment in Sweden. The prioritized OMPs were bisphenol-A (BPA), eight alkylphenols, sixteen polycyclic aromatic hydrocarbons (PAHs), and four fractions of petroleum hydrocarbons (PHCs), along with other global parameters, namely, total organic carbon (TOC), total suspended solids (TSS), turbidity, and conductivity (EC). A Monte Carlo (MC) simulation was applied to estimate the event mean concentrations (EMC) of OMPs based on intra-event subsamples during eight rain events, and analyze the associated uncertainties. Assessing the occurrence of all OMPs in the catchment and comparing the EMC values with corresponding environmental quality standards (EQSs) revealed that BPA, octylphenol (OP), nonylphenol (NP), five carcinogenic and four non-carcinogenic PAHs, and C16-C40 fractions of PHCs can be problematic for freshwater. On the other hand, alkylphenol ethoxylates (OPnEO and NPnEO), six low molecule weight PAHs, and lighter fractions of PHCs (C10-C16) do not occur at levels that are expected to pose an environmental risk. Our data analysis revealed that turbidity has a strong correlation with PAHs, PHCs, and TSS; and TOC and EC highly associated with BPA concentrations. Furthermore, the EMC error analysis showed that high uncertainty in OMP data can influence the final interpretation of EMC values. As such, some of the challenges that were experienced in the presented research yielded suggestions for future monitoring programs to obtain more reliable data acquisition and analysis., Validerad;2023;Nivå 2;2023-06-29 (sofila)

Stormwater runoff is a key pathway for diffuse pollutants to enter receiving waters. Mitigating measures include pollutant substitution, restricting their release into the urban technosphere and limiting the (re-)mobilisation of substances to minimise their negative impacts on receiving waters. Gully pots (GPs) are one of the most ubiquitous urban drainage infrastructure components, providing both a drainage function and limiting the onward transport of pollutants through in-pot sedimentation processes. In this study, sediments accumulated over a one-year period were collected from 26 GPs in catchments of four land-use types in Stockholm, Sweden. Sediments were analysed for 101 organic substances from eight substance groups (hydrocarbons, polycyclic aromatic hydrocarbons, alkylphenols, polychlorinated biphenyls, phthalates, organotins, per- and polyfluoroalkyl substances and brominated fire retardants) to inform an assessment of their occurrence and net accumulation rates over a typical unit operation period. A total of 63 substances were quantified in at least one GP, with aliphatic hydrocarbons, phthalates and organotins quantified in all GP sediments, highlighting their ubiquitous use. The identification of 14 and 21 organic substances in two pedestrian/bike path GPs emphasise the contribution of non-vehicular sources to diffuse pollutant loads. Significantly higher mass accumulation rates of 4-tert-octylphenol, 4-nonylphenols, formaldehyde, dioctyltin and dibutyltin are identified in commercial catchment GPs suggesting the need to enhance source-tracing and runoff quality-control measures within catchments of this land-use type. Sediments in 25 GPs were identified with at least one substance exceeding toxicology-based threshold values, highlighting the runoff quality-control function of GPs in reducing the potential ecotoxic impacts on recipients., Validerad;2023;Nivå 2;2023-06-28 (hanlid)

This field study assessed the occurrence, event mean concentrations (EMCs), and removal of selected organic micro-pollutants (OMPs), namely, polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons (PHCs), nonylphenol (NP), 4-t-octylphenol (OP), and bisphenol A (BPA), in a gross pollutant trap (GPT)-biofilter/sand filter stormwater treatment train in Sundsvall, Sweden. The effects of design features of each treatment unit, including pre-sedimentation (GPT), sand filter medium, vegetation, and chalk amendment, were investigated by comparing the units' removal performances. Overall, the treatment train removed most OMPs from highway runoff effectively. The results showed that although the sand filter provided moderate (<50 % for phenolic substances) to high (50–80 % for PAHs and PHCs) removal of OMPs, adding a vegetated soil layer on top of the sand filter considerably improved the removal performance (by at least 30 %), especially for BPA, OP, and suspended solids. Moreover, GTP did not contribute to the treatment significantly. Uncertainties in the removal efficiencies of PAHs and PHCs by the filter cells increased substantially when the ratio of the influent concentration to the limit of quantification decreased. Thus, accounting for such uncertainties due to the low OMP concentrations should be considered when evaluating the removal performance of biofilters., Validerad;2023;Nivå 2;2023-08-14 (joosat);Licens fulltext: CC BY LicenseThis article has previously appeared as a manuscript in a thesis.

Due to large spatial and temporal variations of soil properties that govern swale infiltration capacities, traditional methods for estimating saturated hydraulic conductivity (ksat) values could potentially lead to erroneous estimation of the total system infiltration capacity. To increase the knowledge of grassed swale infiltration performance and the relationship between hydraulic properties related to the spatial variation within the swale, two methods were applied to estimate ksat values: 1) point measurements using the Modified Philip Dunne (MPD) Infiltrometer, and 2) a full-scale infiltration test (FSIT). A large variation in calculated ksat values was found, ranging from 22 to 1382 mm/hr, with lower/higher values at the swale bottom, and right swale slope respectively. Infiltration point measurements, with a geometric mean of 81 mm/hr, showed higher infiltration rates than those obtained from FSIT, which yielded 34 and 22 mm/hr (for test 1 and 2 respectively). Moreover, FSIT results showed an agreement with ksat values obtained from MPD infiltrometer at the swale bottom. In addition, infiltration rates are significantly reduced as the groundwater mound gets closer to the bottom of the grassed swale., En raison des grandes variations spatiales et temporelles des propriétés du sol qui régissent les capacités d'infiltration des noues, les méthodes traditionnelles d'estimation des valeurs de conductivité hydraulique saturée (ksat) pourraient potentiellement conduire à une estimation erronée de la capacité d'infiltration totale du système. Afin d'accroître la connaissance des capacités d'infiltration des noues enherbées et de la relation entre les propriétés hydrauliques liées aux classes de texture du sol, deux méthodes ont été appliquées pour estimer les valeurs de ksat : 1) des mesures ponctuelles à l'aide de l'infiltromètre Philip Dunne modifié (MPD), et 2) un test d’infiltration à pleine échelle (FSIT). Une grande variation dans les valeurs calculées de ksat a été trouvée, allant de 22 à 1382 mm/h, avec des valeurs inférieures/élevées au fond de la noue et à droite de la pente de la noue respectivement. Les mesures des points d'infiltration, avec une moyenne géométrique de 81 mm/h, ont montré des taux d'infiltration plus élevés que ceux obtenus à partir du FSIT, avec 34 et 22 mm/h (pour les tests 1 et 2 respectivement). De plus, les résultats du FSIT ont montré un accord avec les valeurs de ksat obtenues au fond de la noue. De plus, les taux d'infiltration diminuent considérablement à mesure que le niveau de la nappe phréatique se rapproche du fond de la noue enherbée.

Stormwater ponds are widely used for controlling runoff quality through the sedimentation of particles and associated pollutants. Their maintenance requires regular removal and disposal of accumulated material. This necessitates an assessment of material hazardousness, including potential hazard due to its contamination by metals. Here we analyze 32 stormwater pond sediment samples from 17 facilities using several chemical analysis methods (total extraction, sequential extraction, diffusive gradients in thin-films DGT, and pore water extraction) in order to consider the complementarity and comparability of the different approaches. No clear relationship was found between analyses that have the potential to measure similar metal fractions (DGT and either fraction 1 of the sequential extraction (adsorbed and exchangeable metals and carbonates) or pore water concentrations). Loss on ignition (LOI) had a significant positive correlation with an indicator of the environmental risk developed in this paper (∑ranks) that incorporates different metals, speciations, and environmental endpoints. Large variations in metal levels were observed between ponds. As clustering was limited between the different analyses, a comprehensive analysis of different parameters is still needed to fully understand metal speciation and bioavailability., Validerad;2022;Nivå 2;2022-11-16 (hanlid);Full text license: CC BYFor correction, see: Gavrić, S., Flanagan, K., Österlund, H., et al. Facilitating maintenance of stormwater ponds: comparison of analytical methods for determination of metal pollution. Environmental Science and Pollution Research (2022). https://doi.org/10.1007/s11356-022-21428-y

Validerad;2022;Nivå 2;2022-02-16 (sofila);Funder: Agence de l’Eau Seine Normandie; Office Français de la Biodiversité

A paired-catchment study of two adjacent commercial areas in northern Sweden, one with Green Infrastructure (GI) storm drainage and the other with a conventional storm sewer system, served to evaluate the hydrological performance of both drainage systems and demonstrate advantages of GI. The GI catchment avoided directly-connected impervious areas by diverting runoff from a parking lot to a cascade of three infiltration features, a fractured rock strip draining onto a sloping infiltration area, followed by a collector swale. Both catchments were monitored over 4 years by measuring rainfall, runoff and, in the vicinity of the swale, soil water content and groundwater levels. For frequent storms, the median GI efficiencies in reducing runoff volumes and peak flows, and extending peak flow lags, were 96, 99 and 60%, respectively, compared to conventional drainage The storm rainfall depth, initial soil water content, increases in intra-event soil water storage and groundwater levels, had statistically significant effects on either runoff volume or peak flow reductions. No effects were found for storm rainfall intensity and duration, antecedent dry days, and initial groundwater levels. The study demonstrated that GI drainage can be successfully applied even in the challenging environment of a subarctic climate., Validerad;2023;Nivå 2;2023-02-10 (joosat);Licens fulltext: CC BY License

Stormwater management in urban areas requires continuous water quality data of high-temporal resolution to better understand and control pollutant loads and dynamics. However, the difficult analytical context of stormwater may lead to significant uncertainties and/or biases in data produced by online water quality sensors. In order to provide insights into the alignment of continuous data with discreet data collected through conventional sampling and analysis, 25 grab samples were collected and analysed for pH, conductivity and turbidity in parallel with the continuous monitoring using sensors installed in a gully receiving road runoff. Analysis has shown that while differences in laboratory and field-measured pH could be explained by instrumental uncertainty alone, there were significant differences in conductivity and turbidity, meaning the presence of additional errors. This study highlights the need for further investigation of data-quality-related matters in the stormwater field.

Dimensioning green infrastructure (GI) to achieve different stormwater targets (e.g., runoff volume reductions) is essential at city scale under conditions of limited resources and space. Traditional GI sizing criteria are based on the hydrology of moderate climates. However, cold climate conditions represent an additional challenge for GI design. This paper presents an assessment of the bioretention cell (BC) area required to achieve a given runoff volume reduction (RVR), accounting for seasonal variations in infiltration rates in the Swedish cities of Gothenburg, Orebro, and Kiruna. Clear seasonal differences were found in Kiruna for the areas required to achieve 80% of RVR under winter and summer conditions. However, non-significant seasonal differences were found in Orebro and Gothenburg. For an efficient BC adoption, sizing needs to be completed in the context of the precipitation for the entire year, including the effect of snowmelt, rain-on-snow, and frozen soils.