STORMWATER QUALITY ASSOCIATED WITH A FULL SILT TRAP DISCHARGING INTO AN URBAN WATERCOURSE

The aim of this project was to assess the influence of a full silt trap on the quality of stormwater which was discharged into an urban watercourse. The average SS concentrations of the outflow were 2.0 and 34.1 mg/l during dry-weather and wet-weather conditions, respectively, and SS concentrations of up to 141.6 mg/l were recorded during storms. Treated stormwater SS concentrations were often high, compared with secondary sewage-treatment standards of ≤30 mg/l. Pollutants accumulated in the silt trap.     

Treatment of stormwater using a detention pond and constructed filters

A stormwater treatment plant, consisting of a detention pond, a constructed filter system and a constructed wetland, has been investigated according to stormwater quality improvement, sediment and heavy metals accumulation and potential toxicity of the stormwater and sediment. The reduction of metal content in the detention pond was on average 26?–?84%. No acute toxicity in the stormwater was detected although heavy metal levels often exceeded guideline values during storm events. Pore water samples of the collected sediments were not toxic but the whole sediment was toxic when assessed with the Microtox^® Solid-phase test. The constructed filter system became clogged due to cementation of the filter substrate.     

Uncertainties of stormwater characteristics and removal rates of stormwater treatment facilities: Implications for stormwater handling

Stormwater runoff is a major contributor to the pollution of receiving waters. This study focuses at characterising stormwater in order to be able to determine the impact of stormwater on receiving waters and to be able to select the most appropriate stormwater handling strategy. The stormwater characterisation is based on determining site mean concentrations (SMCs) and their uncertainties as well as the treatability of stormwater by monitoring specific pollutants concentration levels (TSS, COD, BOD, TKN, TP, Pb, Cu, Zn, E.coli) at three full scale stormwater treatment facilities in Arnhem, the Netherlands. This has resulted in 106 storm events being monitored at the lamella settler, 59 at the high rate sand filter and 132 at the soil filter during the 2 year monitoring period.The stormwater characteristics in Arnhem in terms of SMCs for main pollutants TSS and COD and settling velocities differ from international data. This implies that decisions for stormwater handling made on international literature data will very likely be wrong due to assuming too high concentrations of pollutants and misjudgement of the treatability of stormwater. The removal rates monitored at the full scale treatment facilities are within the expected range, with the soil filter and the sand filter having higher removal rates than the lamella settler. The full scale pilots revealed the importance of incorporating gross solids removal in the design of stormwater treatment facilities, as the gross solids determine operation and maintenance requirements.     

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.     

Real-time control of stormwater detention basins as an adaptation measure in mid-size cities

ABSTRACT

The performance of predictive real-time control (RTC) of outflow from a detention basin, integrating rainfall forecasts in the definition of the control rules, was assessed in terms of peak flow reduction in the receiving water body, improvement of the level of service of the stormwater network downstream and qualitative treatment of runoff. Evaluations were performed using the PCWMM software with rainfall data for a continuous 6-month period and four individual events, in a future climate. As compared to the situation with static control, peak flows at the outfall were reduced by an average of 46% with predictive RTC, and the downstream collector was used up to 22% less during rainfalls. Also, the detention time reached the desired period of 36 h for water quality control, for most of the simulated rainfall events. This demonstrates the usefulness of RTC as an adaption measure to climate change in existing urban areas.     

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.     

Suspended solids in Missouri reservoirs in relation to catchment features and internal processes

Mean total suspended solids (TSS), in 135 Missouri reservoirs range from 1.2 to 47 mg/l. The volatile (VSS) and non-volatile (NVSS) fractions range from 0.6 to 9.6 mg/l and 0.5 to 37 mg/l, respectively. %NVSS is the larger fraction and declines through summer as %VSS increases. Suspended solids (particularly VSS) correlate with metrics of lake trophic state and are positively related with the proportion of cropland (%C, r = 0.69-0.74) in their catchments, negatively related with forest cover (r = -0.54 to -0.56), and weakly related with grassland (r < 0.31). Regressions including %C with dam height (representing morphometry) and flushing rate (representing hydrology), explain approximately 70% of cross-system variation in TSS and 67% in VSS. Dam height and %C explain 57% of variation in NVSS. Residual analysis shows statewide models under-predict suspended solids in urban reservoirs. Effects of catchment features on summer TSS largely reflect internal plankton growth mediated by influent nutrients (affecting VSS) over direct sediment input (affecting NVSS).     

Temporal variability of combined sewer overflow contaminants: Evaluation of wastewater micropollutants as tracers of fecal contamination

A monitoring program was initiated for two sewage outfalls (OA and OB) with different land uses (mainly residential versus institutional) over the course of a year. Eleven CSO events resulting from fall and summer precipitations and a mixture of snowmelt and precipitation in late winter and early spring were monitored. Median concentrations measured in CSOs were 1.5 × 10⁶ Escherichia coli/100 mL, 136.0 mg/L of Total Suspended Solids (TSS), 4599.0 ng/L of caffeine (CAF), 158.9 ng/L of carbamazepine (CBZ), in outfall OA and 5.1 × 10⁴ E. coli/100 mL, 167.0 mg TSS/L, 300.8 ng CAF/L, 4.1 ng CBZ/L, in outfall OB. Concentration dynamics in CSOs were mostly related to the dilution by stormwater and the time of day of the onset of overflows. Snowmelt was identified as a critical period with regards to the protection of drinking water sources given the high contaminant concentrations and long duration of events in addition to a lack of restrictions on overflows during this period. Correlations among measured parameters reflected the origins and transport pathways of the contaminants, with E. coli being correlated with CBZ. TSS were not correlated with E. coli because E. coli was found to be mostly associated with raw sewage whereas TSS were additionally from the resuspension of in-sewer deposits and surface runoff. In receiving waters, E. coli remained the best indicator of fecal contamination in strongly diluted water samples as compared to WWMPs because WWMPs can be diluted to below their detection limits.     

Hydrodynamic behaviour of a new permeable pavement material under high rainfall conditions

Permeable pavements are among the most effective alternative solutions for sustainable stormwater management. They decrease impervious surfaces in urban areas, reduce the risk of flooding under high rainfall conditions and protect the natural environment against stormwater pollution. In a view to ensuring sustainable stormwater management, a new eco-material has been designed for producing permeable pavements. This material is a mixture of construction wastes (crushed concrete) and organic matter (compost). The crushed concrete is the structural support and the compost is used for retention and the biological treatment of stormwater pollution. The purpose of the research work presented in this paper was to evaluate the hydrodynamic behaviour of a new permeable pavement material under high rainfall conditions. The experimental approach adopted for this research study is a temporal moment analysis. Therefore, for the experimental study, we simulated high rainfall with a return period of 10 years (Torreilles in 2001, France). The rainfall data were provided by Meteo France. The rainfall was maintained at an intensity of 126 mm/h, corresponding to a flow rate of 16 l/h at laboratory apparatus scale. Then, the flow rate was increased three times, to 25 l/h, 50 l/h and finally 100 l/h to subject the material to extreme conditions.     

Nachweis von Natural Attenuation mittels Isotopenuntersuchungen an einem ehemaligen Kokereistandort

Natural attenuation of mono- (BTEX) and polycyclic aromatic hydrocarbons (PAHs) was studied in groundwater at a former gas plant site over a distance of about 500 m. The contamination source was located within a 4–6 m thick succession of interbedded silt and sand (K _f =1,4?10^?7 m/s) at a depth of about 5–6 m below the surface. Groundwater flow times between source and the receiving surface waters were determined on the order of a few hundred years. The main contaminants were found to be benzene and naphthalene with concentrations up to 200,000 and 8,500 μg/l, respectively. Over the past 9 years, concentrations within the contaminant plume have decreased and degradation of benzene was proven by compound specific carbon isotope analyses. In addition, sulphur isotope studies revealed that sulphate reduction has played a significant role. This was supported by ambient sulphate concentrations of 300–1,800 μg/l at the site that are sufficient to sustain a long-term perspective for this process. In agreement with these physico-chemical conditions, no transfer of BTEX or PAHs from the plume into the nearby river has been observed.     

Rainwater harvesting to control stormwater runoff in suburban areas. An experimental case-study

On a 23 ha urban watershed, 10 km East of Paris, rainwater tanks have been installed on 1/3 of the private parcels to prevent stormwater sewer overflows. This paper investigates the macroscopic effect of rainwater harvesting on runoff, and thus the potential of this technique for stormwater source control. The analysis is performed using the SWMM 5 model, calibrated on rainfall- runoff measures from two measurement campaigns, before and after the equipment. The availability of two data-sets allows the authors to point out changes in the catchment's behaviour. The main findings are that: (1) catchment's evolution, mainly caused by individual land-cover modifications, produces non-stationarity of the hydrologic behaviour; (2) the rainwater tanks installed, although they affect the catchment hydrology for usual rain events, are too small and too few to prevent sewer overflows in the case of heavy rain events.     

Sources and storm loading variations of metal species in a gullypot catchment

The temporal variations of metal species in the outflow from a single gullypot catchment are discussed for two storms with differing hydrological characteristics, and the major contributing sources within the system are identified from an analysis of six discrete storm events. Under low flow conditions the dissolved metals are complexed by organics present in the gullypot liquor and interstitial sediment waters, and the strongly bound fraction predominates in the gullypot outflow. As the flow increases the Chelex removable fraction becomes important due to acid washing initially of road-surface sediments and subsequently of the mobilized gullypot sediments. The particulate-associated metals exhibit distinct temporal similarities to the storm hydrograph and chemograph for suspended solids with the exchangeable fraction being dominant. Hydrodynamic sorting mechanisms on the road surface produce the earlier contributions for this fraction, with later inputs, particularly for Cd and Pb, from chemical exchange processes within overturned gullypot sediment. This basal sediment also provides important inputs of the carbonate and hydrous oxide fraction for Cu and Zn as the gullypot contents become oxygenated later in the storm. The consequences of these findings are discussed in terms of gullypot maintenance and the water quality of stormwater outfalls.     

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.     

Methylmercury in rivers draining cultivated watersheds

Total mercury (THg) concentrations in streams draining cultivated watersheds in Minnesota, USA are strongly correlated with total suspended sediment (TSS) concentrations, varying widely in response to precipitation-driven inputs of soil-derived suspended sediments. Methylmercury (MeHg) concentrations in these waterways have not been studied, and little is known about mercury uptake mechanisms in resident fish populations. To begin to identify factors influencing MeHg concentrations and loadings in these streams, we measured THg and MeHg concentrations in unfiltered whole water samples from the Minnesota River and two of its major tributaries, the Blue Earth and Le Sueur Rivers. Land use in the watersheds of these rivers is over 90% row-crop agriculture, and extensive artificial drainage systems deliver runoff and associated solids quickly to local streams and rivers. THg concentrations were elevated (>10 ng/l) during much of Spring 2000 and part of the summer when runoff from precipitation events increased stream discharge and carried soil materials into the streams. Reduced precipitation resulted in low flow conditions from August through October, and THg concentrations decreased to <4.0 ng/l in all three rivers. MeHg concentrations in the Le Sueur River ranged from 0.07 to 0.42 ng/l between June and December. Higher MeHg concentrations (>0.2 ng/l) were measured during summer months when THg and TSS concentrations were high after precipitation events. Elevated MeHg concentrations were also observed in late October after leaf litter inputs. Conditions on the Blue Earth River were different, with elevated MeHg concentrations (>0.5 ng/l) observed during low flow in August and September. These higher concentrations coincided with a period of enhanced microbial growth stimulated by high late-summer temperatures. A late-October increase in MeHg concentration attributed to leaf litter inputs was also observed in this river. MeHg concentration trends in the Minnesota River were similar to those in the Blue Earth River. Indicators of biological productivity (chlorophyll a, volatile suspended solids, and total Kjeldahl nitrogen) were higher in the Blue Earth and Minnesota Rivers compared to the Le Sueur River, which may signal a connection between higher biological activity and increased MeHg concentrations.     

Biomonitoring of maritime pollution by heavy metals (Pb and Zn) in the coast of Jijel (Algeria)

This paper reports a study of pollution in the coastal waters of Jijel, Algeria, using algae Ulva lactuca and Corallina officinalis as bioindicators. Samples of seawater and algae were collected at four different stations from the coast of Jijel, during the period of April–June 2014. The heavy metal content (Pb and Zn) was determined in seawater and in the algae tissue by the technique of atomic absorption spectrophotometry. In seawater, the contents of heavy metals vary from 0.017 to 0.03 mg/l (Pb) and 0.235 to 0.873 mg/l. In the algae tissues, metals concentrations vary between 1.88 to 6.25 μg g^?1 dry weight (Pb), and from 92 to 178.9 μg g^?1 dry weight (Zn). These levels differ by site and species. The calculation of the bioconcentration factor (BCF) leads us to conclude that algae bioaccumulate significant levels of Pb and Zn metals in their tissues. Our results shows that the species of C. officinalis bioaccumulate the metals Pb and Zn more than U. lactuca, where, high biosorption of Zn was observed with BCF values between 203.21 and 238.40. Zn content in seawater and algae tissues appear higher than standards set by USEPA and guides values of Certified Reference Materials, but Pb levels appear lower than this standard.     

Partition of pollution between dissolved and particulate phases: what about emerging substances in urban stormwater catchments?

This paper presents results about the occurrence, the concentrations of urban priority substances on both the dissolved and the particulate phases in stormwater. Samples were collected at the outlet of a dense urban catchment in Paris suburb (2.30 km²). 13 chemical groups were investigated including 88 individual substances. Results showed that stormwater discharges contained 45 substances among them some metals, organotins, PAHs, PCBs, alkylphenols, pesticides, phthalates, cholorophenols and one volatile organic compound, i.e. methylene chloride. With respect to the European Water Framework Directive, these substances included 47% of the priority hazardous substances (n = 8), 38% of the priority substances (n = 10). The remaining substances (n = 27) belong to a list of others specific urban substances not included in the Water Framework Directive but monitored during this work. Finally, stormwater quality was evaluated by comparing the substance concentrations to environmental quality standards (EQS) and the particulate content to Canadian sediment quality guidelines. This showed that stormwater was highly contaminated and should be treated before being discharged to receiving waters in order to avoid any adverse impact on the river quality.     

Predicting Dissolved-Oxygen Variations Downstream From An Intermittent Discharge

Intermittent discharges from unsatisfactory overflows and storm-sewage tanks to a watercourse can lead to depleted dissolved-oxygen concentrations downstream from the discharge point.
This paper assesses the accuracy and applicability of a simplified dynamic river-impact model which predicts BOD and dissolved-oxygen concentrations downstream from an intermittent discharge. The proposed model (a) requires relatively little input data, (b) is internally simple, and (c) uses well-known and established predictive equations. Concentrations of dissolved oxygen are predicted to within a mean error of 0.1 mg/l during post-storm conditions and 0.5 mg/l during actual storm conditions.     

The effect of irrigation on tile sediment transport in a headwater stream

A field-scale no-till corn plot (120 m x 90 m) located on a tile drained silt loam soil near Kintore, Ontario was irrigated with 2.5 cm of water over a 3 h period to examine the effects of irrigation on tile sediment transport in a headwater stream. Flow characteristics and the composition, concentration and size distribution of suspended solids were measured at the tile outlet, an upstream reference site and three sites located downstream of the tile drain. Results show that tile sediments at the study site are fine-grained (D50 approximately 5.0 microm) and consist primarily of quartz, anorthite/albite, dolomite and calcite. Sediment concentrations in tile effluent increased from 8 to 57 mg L(-1) after 1.5 h of irrigation and reached a maximum of 72 mg L(-1). The sediment yield from the tile drain for the irrigation event was 4.6 kg ha(-1). An unsteady, mobile boundary flow model (MOBED) was used to predict flow characteristics in the stream. According to the MOBED model, bed shear stress in the stream was approximately 6 N m(-2). This value is significantly greater than the critical shear stress for complete suspension of 1 N m(-2) for tile sediments as determined from laboratory experiments using a rotating circular flume. Grain size distributions of suspended solids in the stream were close to the dispersed size distribution because of the high shear stress in the receiving stream.     

Suspended particle characteristics in storm runoff from urban impervious surfaces in Toowoomba,Australia

Total suspended solids as a measure of suspended particles in urban stormwater has limitations and the alternative suspended sediment concentration method was adapted to determine non-coarse particle (NCP) concentration, defined as particles smaller than 500 μm. NCP was partitioned into the following classes: very fine particles (<8 μm, VFP), fine particles (8–63 μm, FP) and medium particles (63–500 μm, MP). A site mean concentration approach was adopted to differentiate the suspended particle characteristics between three impervious surfaces (roof, road and car park) using runoff data collected for 35 storms. Runoff particle size distribution (PSD) of all surfaces was dominated by particles less than 63 μm. A weak trend of relatively constant VFP concentration was present in the road runoff data. Roof runoff PSD became finer as NCP concentration increased and, overall, the PSD of car park runoff was coarser compared to road and roof runoff. These findings have runoff treatment implications as settling processes are influenced by particle size.     

Bioaccumulation of arsenic in aquatic plants and animals near a municipal landfill

This study was conducted to assess the water quality and arsenic (As) concentrations in water, sediment, aquatic plants and animals near a municipal landfill. The As concentration in the samples was analysed using inductively coupled plasma optical emission spectrometry. Thirty-six aquatic plants of four species were collected. The highest As concentration was found in Limnocharis flava (0.78 ± 0.31 mg/kg). The aquatic animals included 31 fish of four species and 27 freshwater snails of three species. The highest As concentrations in the fish and freshwater snails were found in Oreochromis niloticus (0.16 ± 0.16 mg/kg) and Filopaludina sumatrensis (0.18 ± 0.06 mg/kg), respectively. The highest bioaccumulation factor of As in the aquatic plants, fish and freshwater snails were found in L. flava (131.30 ± 15.35), O. niloticus (228.21 ± 26.99) and F. sumatrensis (33.04 ± 10.58), respectively. Since the accumulation of As was higher in the sediment than in the water, aquatic plants and animals took up As directly from the environment, resulting in As accumulation in the aquatic food web.