Den urbana utvecklingen har resulterat i alltmer hårdgjorda ytor och förekomst av konstruerat material i städer, och som följd finns det en stor variation av material som kan bidra till föroreningar till kringliggande miljöer. Dagvatten, såsom regn och smältvatten, har visat sig vara en bidragande faktor till att föroreningar sprids inom urbana områden. Kemikalierna per- och polyfluorerade alkylsubstanser (PFAS) har under det senaste årtiondet hamnat mer i fokus då det framkommit att de är toxiska och svårnedbrytbara i miljön. Trots att dagvatten kan vara en faktor som påverkar spridning av PFAS i urbana områden är det ett forskningsområde med få studier. Denna rapport syftar därför till att öka kunskapen om förekomst av PFAS i dagvattensystem i urbana områden, utifrån ett svenskt perspektiv. 47 prover tagna i dagvattensystem från fyra urbana områden i Östersund under år 2012–2013, analyserades med avseende på 55 olika PFAS-ämnen inklusive beräkningar för summaparametrarna ∑PFAS55 ∑PFAS4, och ∑PFAS24. Proverna bestod av dagvatten från regn och smältvatten samt vissa basflöden tagna i dagvattenledningar. Resultaten visar att i 45 av de 47 proverna förekom minst en av de analyserade PFAS-ämnena. Främst förekommande var PFOS, PFOA, PFNA, 6:2FTS samt PFHpA. Det mest heterogena urbana området, innefattande stora delar av centrala staden och campusområde, hade högst halter av ∑PFAS55 med en median på 144 ng/l i jämförelse med de andra områdena med mediankoncentrationer på 12,6–20,6 ng/l i dagvatten och 4,4–15,1 i basflöden. Resultaten indikerar att PFAS förekommer i urbana dagvattensystem samt att det finns många faktorer i urbana miljöer som bidrar till källor samt spridning av PFAS. 

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.

Dagvattenkvaliteten varierar mycket bland platser och över tiden. Vattenkvalitetssensorer kan hjälpa till att ha långtidsdata på hög tidsupplösning och flera platser, samt att utvärdera prestandan av dagvattenanläggningar eller förbättra deras funktion genom användning av kvalitetsdriven realtidskontroll. De flesta kommersiella vattenkvalitetssensorer har dock inte utvecklats för användning i de svåra analytiska förhållanden som är förknippade med dagvatten och studier behövs för att verifiera deras tillförlitlighet i fältsammanhang. I den här studien, utvärderas prestandan hos kommersiella vattenkvalitetssensorer (pH, konduktivitet och turbiditet) för in-situ kontinuerlig övervakning av dagvatten med hög upplösning i ett kallt klimat och överväga potentialen av att använda kontinuerligt uppmätta parametrar som proxy för föroreningar i dagvatten. Sensorerna testades i ett vägupptagningsområde i Luleå. Fältmätningar jämfördes med prover uppmätta i labbet, med både identiska fältsensorer och laboratoriesensorer. Endast fältmätningar av pH fungerade enligt tillverkarnas specifikationer. På grund av applicering av vägsalt varierade konduktiviteten i ett så stort område att en enda kalibrering ledde till hög osäkerhet under sommaren, då konduktiviteten var låg. Det fanns stora fel mellan grumlighet uppmätt i fält och lab, överallt på vintern, sannolikt på grund av  (1) närvaron av en stor andel artiklar som är för små för att påverka turbiditeten i fältet och agglomeration av artiklar i prover omedelbart efter provtagning (<48 timmar). Konduktivitet visar potential som en indikator på vägsalt, eftersom det korrelerar starkt med natrium och klorid. Turbiditet kunde används för att ge en uppskattning av suspenderade material, total koncentrationer av metall och total koncentration av organiskt kol under sommaren, men fungerar inte bra under säsongen när vinterdäck används.

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.

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.

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.

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.