Transport of stormwater pollutants through a roadside grassed swale

Investigations of the pollutant trapping capability of a grassed swale receiving runoff from a road with a traffic intensity of 8,000 vehicles/day were carried out in central Luleå, Sweden. Transport and retention of suspended solids, particles and heavy metals (copper, lead and zinc) were analysed. The sampling was carried out during seven rain events. The results show that once pollutants are trapped in a grassed swale they are not permanently bound to vegetation or soil. A roadside grassed swale may be regarded as a stormwater treatment facility that attenuates the peaks in pollutant loads, without being capable of producing consistently high removal rates.     

Long-term changes in pollutant load outflows and purification function in a paddy field watershed using a circular irrigation system

A long-term investigation on the water quality and hydrology was carried out for 8 years and 7 months (from October 1991 to April 2000) in a paddy field watershed using a circular irrigation system. The annual amount of rainfall ranged from 1270 to 2226 mm and it was found that the amount of irrigation water tended to decrease as rainfall increased. Phosphorus and chemical oxygen demand (COD) concentrations tended to decrease with the river flowing down, whereas nitrogen concentrations showed no significant difference. The annual outflow loads (sum of the net-outflow load during irrigation periods and the outflow load during non-irrigation periods) of total nitrogen (T-N), total phosphorus (T-P), and COD ranged from 13.6 to 75.3 kg ha(-1)yr(-1), -3.55 to 2.21 kg ha(-1)yr(-1), and -24.7 to 48.5 kg ha(-1)yr(-1), respectively. The negative values for T-P and COD loads indicated that the study watershed performed a purification function. The change in annual pollutant loads was primarily attributed to the amount of hydrological water volumes (the annual amount of rainfall or that of rainfall plus irrigation water) for T-N and COD loads and partially for T-P load. In addition, the purification function was related to the hydraulic retention time, and the study watershed allows sufficient retention for pollutant purification for phosphorus and COD contents and partially for nitrogen content.     

Particles and associated metals in road runoff during snowmelt and rainfall

This study analysed road runoff in northern Sweden with respect to the concentrations of and the loads of particles in different size fractions (4-6, 6-9, 9-15, 15-25, 25-40, and 40-120 mum) between a snowmelt period and a rainfall period, as well as during events within each period. There are also comparisons of the transport of different particle sizes between the two periods and during events within the periods and discussions on how different metals are associated with the varying particle sizes. The results showed, on average, eight times higher concentrations and five times higher loads of particles during the snowmelt period compared to the rain period for all particle size intervals. Using a t-test with 14 degrees of freedom, at a 90% and 95% confidence level, the mean- and the event mean concentrations of all particle size intervals were higher during the melt period compared to the rain period. Also, the particle concentrations for both periods decrease as the particle size increases. During the snowmelt and rainfall period, important factors influencing the concentrations and loads were the availability of material, the intensity of the lateral flow for the transport of the particles, and, additionally, for the rain period, the length of dry weather in between events. During the melt period, investigated particle sizes and TSS were highly correlated with total concentrations of Cd, Cu, Ni, Pb, and Zn. During the rain period, the correlations between total metal concentrations and the different particle sizes were not as significant.     

Mesocosm study of enhanced bioretention media in treating nutrient rich stormwater for mixed development area

A well-designed engineered soil for bioretention is important as it ensures that pollutant removal requirements are met. This laboratory study investigated the nutrient removal efficiency of bioretention media enhanced with 10% (by volume) additives from various waste materials (cockle shell, newspaper, printed paper, coconut husk and tyre crumb) and planted with Red Hot Chinese Hibiscus (Hibiscus rosa-sinensis), a common landscape shrub in tropical countries. The results showed that media enhanced with shredded newspaper demonstrated a significant improvement in total nitrogen (TN) removal (80.4%), compared to standard bioretention media (57.5%) without compromising total suspended solids (TSS) and total phosphorus (TP) removal, when dosed with actual runoff. The thick root system and rapid growth rate of the plant was proven to contribute to TN removal. This study concluded that shredded newspaper can be a potential addition to enhance bioretention media performance in treating stormwater, especially nutrient rich runoff from mixed development areas.     

Uncertainty in measuring the event pollutant removal performance of online detention tanks with permanent outflow

Detention tanks are frequently used in today's urban stormwater management. It is a recognized fact that these structures are efficient in order to reduce the frequency of flooding. By settling suspended solids and specific particle pollutants, detention tanks also may contribute to reduce pollutant loads discharged into the receiving waters. However, some recent studies report the measured event removal performance of tanks functioning with permanent outflow (online) to be quite low and relatively variable from one site to another. Even if the studies do not refer to it, the measured performance is probably impaired by considerable uncertainty. The aim of this paper is to ascertain to which point uncertainty could explain the weakness and the variability of the measured performance. Initially, the theoretical formulation of relative uncertainty in the pollutant removal performance of any tank is given. Then, this relationship is applied to the case study of an online tank functioning with permanent outflow: the Vénissieux tank. Some original methods are presented in order to assess uncertainty components. Final results obtained show that absolute uncertainty in the measured performance is far from negligible (between 13% and 37% whilst removal rates range between 25% and 73%). In conclusion, a coherent plan of action is proposed that can be used on other sites to reduce uncertainty to a minimum. A critical look is also taken at the general problem of uncertainty assessment.     

Land-use based stormwater pollutant load estimation and monitoring system design

Accurate quantification of the amount, quality and sources of urban stormwater runoff are a prerequisite for effective stormwater management. The goal of this study was to estimate city-scale stormwater pollutant export, examine the effect of data sources on export estimates, and develop an optimization method for stormwater monitoring. The results were presented for the city of Lahti in southern Finland, where site mean pollutant concentrations (SMCs), annual pollutant loads, and monitoring guidelines for specific land use types were determined for total suspended solids (TSS), nutrients (total nitrogen TN and total phosphorus TP), chemical oxygen demand (COD), and metals (Pb, Zn, Cu, Cr, and Ni). Depending on the data source, differences between estimated pollutant exports ranged from -89% to 215%. Lack of reference data for every urban land use type and differences in land use classification schemes were identified as key factors limiting the accuracy of pollutant load estimation.     

Hydrochemistry and mercury cycling in a High Arctic watershed

Mass budgets for total mercury, major ions and nutrients were calculated for Amituk Lake, located on Cornwallis Island, Nunavut, Canada. Total mercury in two distinct snowpacks averaged 1.25 and 4.21 ng L(-1); the discharge-weighted concentration of influent streams averaged 0.76 ng L(-1). The recent and pre-industrial Hg(T) fluxes in atmospheric deposition to the catchment were estimated to be 0.57 and 0.23 microg m(-2) but through retention within the catchment and/or re-volatilization from the melting snowpack, these decreased by 69% in the lake inflow. The spring freshet was the prime conduit for transporting Hg(T) into Amituk Lake. Because of limited mixing of surface runoff with the lake water column during snowmelt, 59% of the Hg(T) input was directly discharged through the outflow, 16% entered the lake water column where concentrations increased from 0.23 to 0.33 ng L(-1) from June to August and 25% was deposited to the bottom sediments producing a sediment Hg(T) flux of 3.1 microg m(-2).     

Spatial variability of the characteristics of combined wet weather pollutant loads in Paris

An on-site observatory of urban pollutant loads in combined sewers has been created in Paris in order to investigate wet weather pollutant loads at different spatial scales. This observatory is composed of six urban catchments, covering areas from 41 to 2581ha. For a wide range of parameters including suspended solids (SS), volatile suspended solids (VSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), metals (Cd, Cu, Pb, Zn), aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (AHs and PAHs), this article serves to evaluate the potential scale effect on wet weather flow (WWF) quality. Although the extensive data set compiled herein has emphasized the high variability in WWF quality from one rain event to the next, no scale effect could be observed for a given rain event on pollutant concentrations, distributions between dissolved and particulate phases, pollutant contents and loads. Such results are of prime importance since they suggest (i) no spatial scale influence on WWF quality for the considered catchments and (ii) similar dominant sources and transfer processes at the various spatial scales.     

The toxic effects of selected heavy metals on unadapted populations of Vorticella convallaria var similis

The presence of large amounts of heavy metals in sewages may cause severe disruption of the biological processes involved in sewage treatment, and thus a decline in the quality of the effluent produced. Unadapted populations of Vorticella convallaria var similis, a sessile peritrich protozoan found abundantly in healthy rivers, activated sludge, percolating filters and slow sand filters, were subjected to a range of concentrations of three common pollutant metals. It was found that these populations were killed by concentrations of, and above, 0.0005 mg/l. of the free metal ion of either lead or mercury. Colonies were also killed by concentrations of, and above, 0.075 mg/l. of the free metal ion of zinc. 12 hr 50% lethal doses were calculated, and for V. convallaria var similis were found to be 0.0036 mg/l. for lead, 0.005 mg/l. for mercury and 0.29 mg/l. for zinc.     

Occurrence and fate of corrosion-induced zinc in runoff water from external structures

This paper comprises data from an extensive cross-disciplinary research project aiming to elucidate the environmental fate of corrosion-induced zinc release from external structures. It includes an exposure assessment that provide long-term runoff rates, concentrations and chemical speciation of zinc, from 14 zinc-based materials exposed during 5 years in Stockholm, Sweden, and an effect assessment including bioavailability and ecotoxicity measurements, both at the immediate release situation and after soil interaction. Runoff rates of total zinc ranged from 0.07 to 2.5 g Znm-2 yr-1 with zinc primarily released as the free ion for all materials investigated. The average effect concentration, causing a 50% growth reduction after 72 h to the green algae Raphidocelis subcapitata, was at the immediate release situation 69 microg ZnL-1. Upon interaction of runoff water with soil, which simulated 18 to 34 years of exposure, the total zinc concentration was significantly reduced, from milligram per litre to microgram per litre levels. Simultaneously, the most bioavailable fraction of zinc in runoff, the hydrated zinc(II)-ion, decreased from more than 95% to about 30%. The major fraction, 98-99%, of the introduced total zinc concentration in the runoff water was retained within the soil. As long as the soil retention capacity was not reached, this resulted in zinc concentrations in the percolate water transported through the soil layer, close to background values and below growth inhibition concentrations for the green algae investigated. Zinc retained in soil was to a large extent (85-99.9%) extractable with EDTA, and available for plant uptake after 5 to 7 months of ageing.     

Heavy metals in the lagos lagoon sediments

Concentrations of cadmium, cobalt, copper, chromium, iron, manganese, nickel, lead and zinc were determined in surface sediments of the Lagos Lagoon, Nigeria. The results revealed largely anthropogenic heavy metal enrichment and implicated urban and industrial wastes and runoff water transporting metals from land‐derived wastes, as the sources of the enrichment. Higher levels (F < 0.05) of cadmium, iron, manganese, nickel and zinc occurred in sediment samples collected near industrialized‐urban areas than in those from unindustrialized‐rural areas only in the wet season. While iron constituted about 1% of dry sediment by weight, the other metals were present in trace amounts.     

Sequential extraction of sulfide-rich tailings remediated by the application of till cover,Kristineberg mine,northern Sweden

A sequential extraction has been carried out on sulfide-rich mine tailings. The purpose was to investigate how elements released by oxidation are secondarily retained in the tailings and the possible consequences of the remediation. After investigating the solid tailings, seven samples were chosen for sequential extractions. Two samples were oxidised, situated just above the oxidation front; two samples from just below the former oxidation front with increased concentrations of several elements; two unoxidised samples were from an intermediate depth, and the deepest sample was from the tailings-peat boundary at the bottom of the impoundment. Five phases were extracted: adsorbed/exchangeable/carbonate; labile organics; amorphous Fe-oxyhydroxides/Mn-oxides; crystalline Fe-oxides; and organics/sulfides. The addition from dried porewater to the extracted fractions has been calculated and considered as minor. In the oxidised tailings, the sulfide fraction still dominates for elements such as Fe, S, Cd, Co, Cu, Hg and Zn, although the concentrations are low compared to the unoxidised tailings. Generally, the second most important fraction is the adsorbed/exchangeable/carbonate fraction. Below the oxidation front, the sulfide content of the tailings sharply increases. In the secondary enrichment zone, the total element concentrations increase compared with the deeper unoxidised samples, mainly due to secondary retention. For some elements, secondary retention is greater than the total amount extracted for the deeper unoxidised samples. In the secondary enrichment zone the adsorbed/exchangeable/carbonate fraction represents approximately 20 wt.% or more for Cd, Co, Mn, Ni and Zn. The amorphous iron oxyhydroxide or the crystalline iron oxide fractions are less important at this level, although for As, Ba and Cu the amorphous iron oxyhydroxide fraction represents up to 20 wt.%. At the lower border of the enrichment zone, the total concentration for most metals is lower, but the importance of the adsorbed/exchangeable/carbonate fraction is further enhanced for Cd, Cu, Ni and Zn. These elements have 35-60 wt.% of the total amount from this fraction. For As, Cd, Cu, Ni and Pb, the secondary fractions extracted (extractions A-D) represent between 60 and 80 wt.% of the total content. At greater depth in the impoundment the relative importance of the adsorbed/exchangeable/carbonate fraction decreases, whilst the importance of amorphous iron oxyhydroxide and crystalline iron oxide fractions increases. The adsorbed/exchangeable/carbonate fraction is the most easily remobilised fraction. A raised groundwater table previously situated below the enrichment zone may result in the release of secondarily retained metals.     

Direct observations of colloid retention in granular media in the presence of energy barriers, and implications for inferred mechanisms from indirect observations

In this paper we present direct observations of retention of colloids in granular porous media over a large size range (0.21-9.0 μm) and generalize the significance of attachment in grain to grain contacts and attachment on the open surface as a function of colloid:collector ratio. We examine reversibility of attachment via these mechanisms with respect to ionic strength reduction and fluid velocity increase. We relate these direct observations to existing literature, and in some cases offer alternative interpretations of mechanisms of retention drawn from indirect observations (e.g. via column effluent and retained concentrations).     

Contribution of trace metals from atmospheric deposition to stormwater runoff in a small impervious urban catchment

The contribution of atmospheric deposition to emissions of trace metals in stormwater runoff was investigated by quantifying wet and dry deposition fluxes and stormwater discharges within a small, highly impervious urban catchment in Los Angeles. At the beginning of the dry season in spring 2003, dry deposition measurements of chromium, copper, lead, nickel, and zinc were made monthly for 1 year. Stormwater runoff and wet deposition samples also were collected, and loading estimates of total annual deposition (wet+dry) were compared with annual stormwater loads. Wet deposition contributed 1-10% of the total deposition inside the catchment, indicating the dominance of dry deposition in semi-arid regions such as Los Angeles. Based on the ratio of total deposition to stormwater, atmospheric deposition potentially accounted for as much as 57-100% of the total trace metal loads in stormwater within the study area. Despite potential bias attributable to processes that were not quantified in this study (e.g., resuspension out of the catchment or sequestration within the catchment), these results demonstrate atmospheric deposition represents an important source of trace metals in stormwater to waterbodies near urban centers.     

Seasonal first flush phenomenon of urban stormwater discharges

California's climate, typified by winter and spring precipitation and summer drought, is often called a Mediterranean climate, and creates a long period for pollutant build-up. The initial storms of the winter season usually have higher pollutant concentrations, which is called a seasonal first flush. To investigate the existence of a seasonal first flush, we analyzed four major data sets, collected over the 1999-2000 to 2002-2003 wet seasons. Trends in seasonal loads were quantified by plotting pollutant concentrations or cumulative pollutant load versus cumulative rainfall or cumulative runoff volume. Pollutant concentrations in the first part of the wet season were ranged from 1.2 to 20 times higher than concentrations near the end of the season, and mass emission rates were similarly higher at the beginning of the season. A seasonal first flush existed for most cases and was strongest for organics, minerals and heavy metals except lead. This result suggests that applying treatment Best Management Practices (BMPs) early in the season could remove several times more pollutant mass than randomly timed or uniformly applied BMPs.     

Environmental impacts of urban snow management--the alpine case study of Innsbruck

In regions with colder climate, snow at roads can accumulate significant amounts of pollutant chemicals. In northern countries various efforts have been made to face this problem, but for the alpine region little is known about the pollution of urban snow. The present case study was carried out in the city of Innsbruck (Austria). It aimed at measuring pollution of roadside snow and estimating the impact of snow management practises on environmental quality. Concentrations of copper, zinc, lead, cadmium, suspended solids and chloride were determined during a series of sampling events. Various locations with low and high traffic densities and in different distances from a highway have been investigated. The concentrations of copper were generally higher at sites with high traffic density compared to locations with low traffic impact. In contrast to this, the concentrations of zinc and lead remained almost unvaried irrespective of traffic density at the different sampling sites. For cadmium, the picture was more diverse, showing moderately elevated concentrations of this metal also at the urban reference site not polluted by traffic. This indicates that there may be also other important sources for cadmium besides traffic. Suspended solids accumulated in the roadside snow, the highest concentrations were found at the sites with high traffic density. The chloride concentrations were considerable in the snow, especially at the highway. Based on the results of the present measurement campaign, the environmental impact of snow disposal in rivers was also estimated. A negative impact on rivers from snow disposal seems likely to occur, although the discharged loads could only be calculated with substantial uncertainty, considering the high variability of the measured pollutant concentrations. For a more accurate evaluation of this management practise on rivers, further investigations would be necessary.     

Wastewater quality and pollutant loads in combined sewers during dry weather periods

An observatory of urban pollutants was created in Paris in order to assess, at the urban catchment scale, the quality of sanitary sewage and pollutant loads during dry weather periods in the Paris combined sewer. Investigations were carried out for six urban catchments (varying from 42 to 2580 ha) focusing on a wide range of parameters, including: suspended solids (SS), chemical and biochemical oxygen demand (COD and BOD₅), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), heavy metals (Cd, Cu, Pb, Zn), and aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs). Despite the marginal intra-site variability of some pollutants, which serves to reflect the impact of point sources, this work attests to the spatial homogeneity, at the physical scales considered, of wastewater quality and pollutant loads within the Paris combined sewer network. These results imply that similar production and transfer processes are occurring within sewers during dry weather periods and strongly suggest that data obtained on one specific catchment could be extrapolated to smaller or larger catchments that display quite similar land use and sewer characteristics.     

Effects of chloride,sulfate and natural organic matter (NOM) on the accumulation and release of trace-level inorganic contaminants from corroding iron

This study examined effects of varying levels of anions (chloride and sulfate) and natural organic matter (NOM) on iron release from and accumulation of inorganic contaminants in corrosion scales formed on iron coupons exposed to drinking water. Changes of concentrations of sulfate and chloride were observed to affect iron release and, in lesser extent, the retention of representative inorganic contaminants (vanadium, chromium, nickel, copper, zinc, arsenic, cadmium, lead and uranium); but, effects of NOM were more pronounced. DOC concentration of 1 mg/L caused iron release to increase, with average soluble and total iron concentrations being four and two times, respectively, higher than those in the absence of NOM. In the presence of NOM, the retention of inorganic contaminants by corrosion scales was reduced. This was especially prominent for lead, vanadium, chromium and copper whose retention by the scales decreased from >80% in the absence of NOM to <30% in its presence. Some of the contaminants, notably copper, chromium, zinc and nickel retained on the surface of iron coupons in the presence of DOC largely retained their mobility and were released readily when ambient water chemistry changed. Vanadium, arsenic, cadmium, lead and uranium retained by the scales were largely unsusceptible to changes of NOM and chloride levels. Modeling indicated that the observed effects were associated with the formation of metal–NOM complexes and effects of NOM on the sorption of the inorganic contaminants on solid phases that are typical for iron corrosion in drinking water.     

Using satellite imagery for stormwater pollution management with Bayesian networks

Urban stormwater runoff is the primary source of many pollutants to Santa Monica Bay, but its monitoring and modeling is inherently difficult and often requires land use information as an intermediate process. Many approaches have been developed to estimate stormwater pollutant loading from land use. This research investigates an alternative approach, which estimates stormwater pollutant loadings directly from satellite imagery. We proposed a Bayesian network approach to classify a Landsat ETM(+) image of the Marina del Rey area in the Santa Monica Bay watershed. Eight water quality parameters were examined, including: total suspended solids, chemical oxygen demand, nutrients, heavy metals, and oil and grease. The pollutant loads for each parameter were classified into six levels: very low, low, medium low, medium high, high, and very high. The results provided spatial estimates of each pollutant load as thematic maps from which the greatest pollutant loading areas were identified. These results may be useful in developing best management strategies for stormwater pollution at regional and global scales and in establishing total maximum daily loads in the watershed. The approach can also be used for areas without ground-survey land use data.     

Heavy metals in aerosols over the seas of the Russian Arctic

A review of the data on heavy metals in aerosols over the seas of the Russian Arctic is presented. Results of heavy metal studies in aerosols obtained during 11 research expeditions in summer/autumn period from 1991 to 2000, and at Severnaya Zemlya and Wrangel Island in spring, in 1985-1989 are discussed. Concentrations of most heavy metals in the atmosphere in the marine boundary layer in the Russian Arctic are nearly of the same order as literature data from other Arctic areas. The content of heavy metals in the aerosols over the seas of the Russian Arctic shows an annual variation with maximal concentrations during the winter/spring season. In the summer/autumn period increased concentrations of heavy metals could be explained, in most cases, by natural processes (generation of sea salt aerosols, etc.). In some cases, aerosols from Norilsk and Kola Peninsula were detected. Particular attention was paid to estimation of horizontal and vertical fluxes of atmospheric heavy metals. We estimated annual variations in long-range transport of heavy metals into the Russian Arctic in 1986-1995. In winter and spring, up to 50% of the average air pollutant concentrations in the Russian Arctic are due to the Arctic atmospheric pollution itself. Moreover, the monthly and annual averaged fluxes of six anthropogenic chemical elements (arsenic, nickel, lead, vanadium, zinc and cadmium) onto the surface in the Arctic were estimated, and the values obtained were in reasonable agreement with the literature data available.