Ecological risk assessment of zinc from stormwater runoff to an aquatic ecosystem

Zinc (Zn) risks from stormwater runoff to an aquatic ecosystem were studied. Monitoring data on waterborne, porewater, and sediment Zn concentrations collected at 20 stations throughout a stormwater collection/detention facility consisting of forested wetlands, a retention pond and first order stream were used to conduct the assessment. Bioavailability in the water column was estimated using biotic ligand models for invertebrates and fish while bioavailability in the sediment was assessed using acid volatile sulfide-simultaneously extracted metal (AVS-SEM). The screening level assessment indicated no significant risks were posed to benthic organisms from Zn concentrations in sediments and pore water. As would be expected for stormwater, Zn concentrations were temporally quite variable within a storm event, varying by factors of 2 to 4. Overall, probabilistic assessment indicated low (5-10% of species affected) to negligible risks in the system, especially at the discharge to the first order stream. Moderate to high risks (10-50% of species affected) were identified at sampling locations most upgradient in the collection system. The largest uncertainty with the assessment is associated with how best to estimate chronic exposure/risks from time-varying exposure concentrations. Further research on pulse exposure metal toxicity is clearly needed to assess stormwater impacts on the environment.     

Modelling sedimentation processes in a constructed stormwater wetland

The design and operation of constructed wetlands for the treatment of stormwater relies heavily on promoting sedimentation, and being able to predict accurately the expected effectiveness of the pond in removing material from the inflows. A study of sediment behaviour has been carried out in a stormwater wetland in Adelaide, Australia where computer predictions, based on solving the hydrodynamic equations and the transport equation, have been compared to deposition patterns observed in the field. The long-term residence time distribution has been shown to be useful in predicting overall sediment removal rates. Comparisons between the model and field observations indicate generally good agreement. Sources of potential error identified include the variable nature of the runoff concentrations entering the pond and the sediment size distribution. The importance of the transient nature of the flow events was highlighted by the spread of sediment throughout the whole pond.     

A computer-aided tunneling system (CATS) aids in planning and building an urban underground reservoir project

The Hirano River underground stormwater detention reservoir was planned as a first phase of an ambitious municipal plan to prevent flooding in the southeastern district of Osaka, Japan. The reservoir has been under construction since 1981. The concept involved in the design of the reservoir is stormwater detention through temporary storage of rainwater during heavy rainfalls in order to prevent flooding in the vicinity. The underground reservoir is a 1880-m-long tunnel with a storage capacity of 140,000 m³ and a finished diameter of 10 m. The tunnel is being bored by the world's largest slurry shield (11.22-m boring diameter). This paper is primarily concerned with Phase I tunnel construction, in which the latest computer monitoring and data processing technology CATS (Computer-Aided Tunneling System) was applied to provide complete environmental protection. Some aspects of project planning are also discussed. The Phase I tunnel reservoir construction was completed on schedule, in time to prevent possible flooding of the area by intercepting 29,000 m³ (approx. 29 million l) of stormwater in 40 min when a heavy rainfall poured down on July 21, 1986.     

Spatial and seasonal toxicity in a stormwater management facility: Evidence obtained by adapting an integrated sediment quality assessment approach

Stormwater ponds have been widely used to control increased surface runoff resulting from urbanization, and to enhance runoff quality. As receiving waters, they are impacted by intermittent stormwater pollution while also serving as newly created aquatic habitats, which partly offset changes of aquatic ecosystems and their biodiversity by urbanization. Thus, determining ecological risks in stormwater ponds is important for the preservation and rehabilitation of biodiversity in urban areas. Limitations of the conventional toxicity assessment techniques in stormwater ponds have led us to use the sediment quality triad approach with the specific analyses of oligochaetes. The latter analyses build on the earlier work by the Cemagref (Lyon, France) and use the oligochaetes as bioindicators of the sediment quality. This integrative approach was tested at eight sites in the Terraview–Willowfield stormwater facility in Toronto, Ontario, in all four seasons (summer 2008–spring 2009). The facility receives direct runoff from the MacDonald-Cartier freeway with a traffic intensity of 340,000 vehicles/d. Sediment chemistry results indicate that several heavy metals and PAH compounds exceeded the Ontario sediment quality guidelines in the facility. Regardless of the season, laboratory bioassays revealed a strong spatial variation in sediment toxicity along the flow path from the inlet to the outlet, agreeing with decreasing concentrations of contaminants in sediment, especially of heavy metals. However, in situ assessments of the benthic macroinvertebrate community structure and in particular of the oligochaete community revealed an overriding influence of seasonally varying toxicity. This seasonal pattern was described as high toxicity in spring and recovery in fall and corresponded to the influx and flushing-out of road salts and of several heavy metals within the facility.     

Metal sorption to natural filter substrates for storm water treatment--column studies

Storm water generated from road runoff contains pollutants such as metals that are either dissolved in storm water or bound to particulates. Using detention ponds for the treatment of storm water from road runoff, where particles can settle, can reduce the level of particulate-bound metals in the water, while small particles and dissolved matter pass through the detention pond. Some of these metals can be removed by filtrating water through specially constructed filter systems. This investigation is a laboratory study where different filter substrates were tested in order to evaluate their efficiency in reducing heavy metals from water. Metal solutions were filtered through columns filled with various substrates consisting of combinations of calcium silicate rock (opoka), zeolite and peat. The metal-removal efficiency was correlated to hydraulic load, and for the metal species the reduction efficiency decreased with increased hydraulic load. Mixtures of opoka and zeolite were found to be superior to the other filter-substrate combinations tested with regard to both hydraulic aspects and removal efficiency. Peat mixed with the calcium silicate rock was not successful due to clogging which stopped the experiment. A manufactured product made from the calcium silicate rock (burned opoka) was found to be less useful because of its calcium oxide (CaO) content. Among the tested filter substrates, mixtures of opoka and zeolite seemed to be the most useful compositions with respect to reduction-efficiency and clogging aspects. The removal capacity of metals varied from 0.6 to 1.8 kg m(-3) depending on the metal and the filter substrate.     

Bioaccumulation of heavy metals in two wet retention ponds

Metal accumulation in stormwater ponds may contaminate the inhabiting fauna, thus jeopardizing their ecosystem servicing function. We evaluated bioaccumulation of metals in natural fauna and caged mussel indicator organisms in two wet retention ponds. Mussel cages were distributed throughout the ponds to detect bioaccumulation gradients and obtain a time-integrated measure of metal bioavailability. We further investigated if sediment metal concentrations correlate with those in the fauna and mussels. Metal concentrations in the fauna tended to be higher in the ponds than in a reference lake, but statistical significance was only shown for Cu. Positive correlations were found for some metals in fauna and sediment. Sediment metal concentrations in one pond decreased from inlet to outlet while no gradients were observed in the mussels in either pond. These findings indicate that metal accumulation in the examined ponds currently does not pose a threat to their habitat function.     

A novel tracer technique for the assessment of fine sediment dynamics in urban water management systems

Urban storm water run off can reduce the quality of receiving waters due to high sediment load and associated sediment-bound contaminants. Consequently, urban water management systems, such as detention ponds, that both modify water quantity through storage and improve water quality through sediment retention are frequently-used best management practices. To manage such systems effectively and to improve their efficiency, there is a need to understand the dynamics (transport and settling) of sediment, and in particular the fine sediment fraction (<63 μm) and its associated contaminants within urban storm water management systems. This can be difficult to achieve, as modelling the transport behaviour of fine-grained and cohesive sediment is problematic and field-based measurements can be costly, time-consuming and unrepresentative.The aim of this study was to test the application of a novel cohesive sediment tracer and to determine fine sediment transport dynamics within a storm water detention pond. The cohesive sediment tracer used was a holmium labelled montmorillonite clay which flocculated and had similar size and settling velocity to the natural pond sediment it was intended to mimic. The tracer demonstrated that fine sediment was deposited across the entire pond, with the presence of reed beds and water depth being important factors for maximising sediment retention. The results of the sediment tracer experiment were in good agreement with those of a mathematical sediment transport model. Here, the deposited sediment tracer was sampled by collecting and analysing surface pond sediments for holmium. However, analysis and sampling of the three dimensional suspended tracer ‘cloud’ may provide more accurate information regarding internal pond sediment dynamics.     

Prediction of sand mass and organic matter distribution via in situ measured wet sediment bulk density profile

The objective of the study is to develop a spatial prediction model of sand mass and organic matter distribution in an urban stormwater holding pond using in situ measured wet sediment bulk density profile data to spatially distinguish the most likely contaminated sediment deposit areas. The wet bulk density profiles of deposited sediment at 25 locations in the Berembang (Malaysia) stormwater holding pond were measured using a single-probe nuclear density gauge. The sand and organic matter compositions of the surface sediment sample, 5 cm thickness from the bed surface, were determined. Discriminant analysis (DA) was conducted to generate two Fisher’s linear discriminant functions for the prediction of sand mass and organic matter composition areas, respectively. The linear discriminant functions generated better area classifications of surface organic matter composition compared to the sand mass distribution using wet sediment bulk density data measured at more than 15 cm depth levels.     

Modelling of flocculation and transport of cohesive sediment from an on-stream stormwater detention pond

A new model to predict the transport characteristics of suspended sediment from an on-stream stormwater management pond is presented. It is based on Krishnappan's model of flocculated settling in still water, which was extended to dynamic conditions and verified by experiments with stormwater pond sediment in a laboratory rotating flume. The model was derived from first principles, but some input parameters, such as floc properties, had to be obtained by calibration, and input parameters describing flow field properties were obtained from a kappa-epsilon turbulence model. Simulated suspended concentrations vs. time and the size distribution of the flocculated sediment, produced with the calibrated model, agreed well with flume measurements.     

Influence of a stormwater sediment deposit on microbial and biogeochemical processes in infiltration porous media

The purpose of this study was to test the relative influence of organic matter quantity and quality and the pollutant content of a stormwater sediment deposit on mineralization processes, microbial characteristics, and the release of solutes in infiltration sediment systems. In microcosm experiments, two other natural sediment deposits (one low and one rich particulate organic matter deposits) were studied to compare their effects with those of the stormwater deposit. The results showed that the biogeochemical processes (aerobic respiration, denitrification, fermentative processes), the microbial metabolism (enzymatic activities), and the releases of several solutes (NH(4)(+) and DOC) were stimulated in presence of the stormwater deposit and the natural particulate organic matter (POM)-rich deposit because of the quantity of the POM in these deposits. In the stormwater deposit, the high availability of the POM (indicated by its low C/N ratio and its high P content) produced a higher stimulation of the microbial metabolism than in presence of the POM-rich deposit (with a high C/N ratio). Pollutant (hydrocarbon and heavy metal) contents of the stormwater deposit did not have a significant effect on microbial processes. Thus, main effects of the stormwater sedimentary deposit on infiltration system were due to its organic matter characteristics (quantity and quality). Such organic matter characteristics need to be considered in future studies to determine the contamination potential of stormwater management practices.     

A preliminary model for predicting heavy metal contaminant loading from an urban catchment

The toxicity of heavy metals to biota in urban catchments has been regarded as a very important non-point source pollution issue. Numerous studies on heavy metal pollution in urban receiving waters have found that metal transport by surface runoff is closely correlated to the partitioning of the metal forms between dissolved and particulate phases, where sediment plays an important role in the transport process. Sediment cycling on urban streets, metal binding form, and rainfall character in the catchment area are considered to be the key factors for metal transport. A preliminary model is developed based on these considerations. Starting from classical build-up and wash-off processes for the suspended sediment (SS) on the urban impervious surface, the model links the transport of suspended sediment to the transport of metal species. Monitoring data from a small highway catchment were used in the model development. A total of 47 rain events over 1 year were monitored intensively at short time intervals (5-10 min) for hydrological data, rainfall intensity, and stormwater quality. In developing the model, lead was used for the metal load prediction, as it has been a common fuel additive for urban transportation. Agreement between model results and monitoring data indicates that the model can be used in predicting metal load from impervious urban areas, such as streets and roadways, on a long-term basis.     

Influence of intermittent wetting and drying conditions on heavy metal removal by stormwater biofilters

Biofiltration is a technology to treat urban stormwater runoff, which conveys pollutants, including heavy metals. However, the variability of metals removal performance in biofiltration systems is as yet unknown. A laboratory study has been conducted with vegetated biofilter mesocosms, partly fitted with a submerged zone at the bottom of the filter combined with a carbon source. The biofilters were dosed with stormwater according to three different dry/wet schemes, to investigate the effect of intermittent wetting and drying conditions on metal removal.Provided that the biofilters received regular stormwater input, metal removal exceeded 95%. The highest metal accumulation occurs in the top layer of the filter media. However, after antecedent drying before a storm event exceeding 3–4 weeks the filters performed significantly worse, although metal removal still remained relatively high. Introducing a submerged zone into the filter improved the performance significantly after extended dry periods. In particular, copper removal in filters equipped with a submerged zone was increased by around 12% (α = 0.05) both during wet and dry periods and for lead the negative effect of drying could completely be eliminated, with consistently low outflow concentrations even after long drying periods.     

Size fractionation of metals in runoff from residential and highway storm sewers

Stormwater sampling for particulate, colloidal, and dissolved metals was conducted for several storms at six outfalls in Monmouth County, NJ. Samples were initially sequentially filtered through 5 microm, 0.45 microm, and 10 kDa filters. Of the heavy metals, Cu and Zn were mostly either dissolved (<10 kDa) (20-100%) or in the particulate size fractions >5 microm (0->70%). Pb and Cr were associated exclusively with particles >5 microm in size. Fe, Al, and Si were found mostly in larger size fractions (>70%), with smaller amounts 0.45-5 microm in size. Preliminary data from a small set of samples passed through coarser filters suggested that metals may actually be largely associated with particles larger than 20 microm. Variable and sometimes large dissolved fractions of Cu and Zn can contribute to erratic metals removal by structural best management practices (e.g., wet ponds, detention basins). The size fractionation of stormwater constituents has implications for the design and performance of stormwater control structures and the aquatic toxicity risks posed by the metals. The results demonstrate the importance of obtaining particle size data when planning stormwater treatment.     

Measurement and three-dimensional simulation of flow in a rectangular detention tank

There are two main ways to obtain better knowledge of the hydraulics of ponds, namely measurements and simulations. In this study, the applicability of using three-dimensional simulations as an engineering tool in stormwater pond design was investigated. To do this, three-dimensional simulations were compared with measurements of flow pattern and residence time in a large physical model of a detention tank (13 × 9 × 1 m). The agreement between measurements and simulations concerning both flow pattern and residence time distribution curves was found to be good for high flow rates.     

Toxicity characterization of urban stormwater with bioanalytical tools

Stormwater harvesting has become an attractive alternative strategy to address the rising demand for urban water supply due to limited water sources and population growth. Nevertheless, urban stormwater is also a major source of surface water pollution. Runoff from different urban catchments with source contributions from anthropogenic activities and various land uses causes variable contaminant profiles, thus posing a challenging task for environmental monitoring and risk assessment. A thorough understanding of raw stormwater quality is essential to develop appropriate treatment facilities for potential indirect potable reuse of stormwater. While some of the key chemical components have previously been characterized, only scarce data are available on stormwater toxicity. We benchmarked stormwater samples from urban, residential and industrial sites across various Australian capital cities against samples from the entire water cycle, from sewage to drinking water. Six biological endpoints, targeting groups of chemicals with modes of toxic action of particular relevance for human and environmental health, were investigated: non-specific toxicity (Microtox and combined algae test), the specific modes of action of phytotoxicity (combined algae test), dioxin-like activity (AhR-CAFLUX), and estrogenicity (E-SCREEN), as well as reactive toxicity encompassing genotoxicity (umuC) and oxidative stress (AREc32). Non-specific toxicity was highly variable across sites. The baseline toxicity equivalent concentrations of the most polluted samples were similar to secondary treated effluent from wastewater treatment plants. Phytotoxicity results correlated well with the measured herbicide concentrations at all sites. High estrogenicity was found in two sampling events and could be related to sewage overflow. Genotoxicity, dioxin-like activity, and oxidative stress response were evident in only three of the samples where the stormwater drain was beside a heavy traffic road, confirming that road runoff is the potential source of contaminants, while the bioanalytical equivalent concentrations (BEQ) of these samples were similar to those of raw sewage. This study demonstrates the benefit of bioanalytical tools for screening-level stormwater quality assessment, forming the basis for the evaluation of future stormwater treatment and reuse schemes.     

The impact of detention basin design on residential property value: Case studies using GIS in the hedonic price modeling

This study examined the impact of two different detention basin designs on residential property value. The hedonic price model was applied to analyze two College Station, TX, subdivisions. One subdivision had only uniuse flood control detention basins (UDBs) and the other included a multi-use detention basin (MDB) integrating a detention pond with a recreational neighborhood park. Geographic information system (GIS) was used for analysis. Spatial autocorrelation and spatial regression were analyzed. The results indicate that the network distance from the UDBs did not have a significant effect on residential property value. Yet, the properties with a view of the UDBs were significantly lowered in property value. In contrast, the network distance from the MDB where a neighborhood park was merged had a significant impact on residential property value within the 274-m (900-ft) impact area, consistent with expectations. The study also found that environmental amenities such as recreational facilities improved the hedonic price model for the impact area of the MDB, whereas the effect of spatial and locational features was not significant due to its spatial location. The findings of this study imply that thoughtful integration between recreation facilities and detention basins could significantly alter public’s perception of detention basins from stormwater collection eyesores to neighborhood parks. The challenge is whether municipal governments are willing to adopt a policy that encourages developments with MDBs as these municipalities will typically become responsible for maintaining them after construction.     

Stormwater quality associated with a silt trap (empty and full) discharging into an urban watercourse in Scotland

The aim was to assess the influence of a full silt trap at the end of a stormwater drainage pipe on the water quality of stormwater discharged into a semi‐natural urban watercourse. For approximately eleven weeks, the water qualities of the preliminarily treated stormwater and of the receiving watercourse (Braid Burn) were studied. The mean outflow concentrations of suspended solids were 2.0 mg/l and 34.1 mg/l during dry and wet weather conditions, respectively. Suspended solids concentrations of up to 141.6 mg/l were recorded during storm events. Suspended solids values for treated stormwater were often too high compared to international secondary wastewater treatment standards of around 30 mg/l. Pollutants including heavy metals (e.g., zinc, copper and nickel) accumulated in the silt trap. However, high outflow velocities during heavy rainfall events did not result in clearly defined sediment layers due to sediment re‐suspension. Metals did not accumulate in the receiving watercourse.     

The character of the suspended and dissolved phases in the water cover of the flooded mine tailings at Stekenjokk, northern Sweden

Studies of the suspended and dissolved phases of the pond water, material collected from sediment traps, and surficial sediments/tailings from the flooded tailings pond at Stekenjokk have been performed. The aim was to characterise the material, to study the seasonal variations and to quantify possible resuspension of the tailings in the pond. The element concentrations in the pond at Stekenjokk seem to be largely controlled by processes controlling the precipitation and dissolution of Mn- and Fe-oxyhydroxides in both the water column and in the surficial tailings. Physiochemical processes such as weathering of silicates on the surrounding mountain slopes or dykes contributes both dissolved elements and detrital particles. The suspended phase consists of detrital silicate material as well as Fe- and Mn-oxyhydroxides. The average heavy metal concentrations are high, e.g. 0.42% Cu, 0.15% Pb and 3.1% Zn, which is probably due to sorption onto Fe- and Mn-oxyhydroxides. The suspended phase is richer in Fe, and particularly Mn, during the winter. The suspended phase resembles the material collected in sediment traps and the material in the surficial sediments. The pond water is well mixed during the ice-free season. The dissolved heavy metal concentrations are generally rather low with, e.g. maximum concentrations of 2.03 micrograms/l Cu, 0.23 microgram/l Pb and 268 micrograms/l Zn during the winter. Higher dissolved concentrations are found below the ice-cover above the sediment surface during the winter, caused by diffusion of elements from the sediment-water interface up into the pond water. Most of the metals occurring in the pond are dissolved and resuspension of tailings is negligible.     

Clogging of stormwater gravel infiltration systems and filters: insights from a laboratory study

Stormwater infiltration systems are widely used in the control of polluted urban runoff. They are very effective in reducing the volume of stormwater runoff and improving its quality, but they are known to be prone to clogging. Whilst it is evident that clogging determines the design lifespan of infiltration systems, quantitative understanding of the clogging process is currently very limited. A laboratory study was therefore undertaken to better understand physical clogging processes, with the ultimate aim of developing a clogging model for stormwater infiltration systems. This paper presents findings from one-dimensional (1-D) experiments conducted on a gravel filter column. Physical clogging was studied under both constant and variable water levels, and for different sediment inflow concentrations. It was found that a clogging layer forms at the interface between the filter and underlying soil, irrespective of the inflow regime of both water and sediment. It was also found that clogging is much slower if the water level is kept at a constant level than if it varies within the column, due to formation of a sediment plug that 'shelters' the filter/soil interface. Most importantly it was shown that physical clogging is mainly caused by migration of sediment particles less than 6 microm in diameter. A simple regression model was proposed and tested for the prediction of clogging due to stormwater sediment.     

Prediction of heavy metal concentrations in urban stormwater

Heavy metals in urban stormwater runoff can adversely impact aquatic ecosystems. Successful management of such systems requires the accurate prediction of contaminant concentrations. This has created the need for simplistic statistical models. In this study, models were constructed to predict three of the most prevalent heavy metal constituents in urban stormwater: copper (Cu), lead (Pb) and zinc (Zn). Data from the United States, obtained during the Nationwide Urban Runoff Program (NURP), were used to calibrate and verify the models. A comparison of the models revealed that regression models were more accurate than the landuse‐based or metropolitan area averages of event mean concentration (EMC). The regression models also provided insight into important stormwater processes. It was found that pollutant accumulation on the catchment surface was essentially supply limited, and that significant portions of heavy metals originate from highly impervious areas.