Comparing the partitioning behavior of Giardia and Cryptosporidium with that of indicator organisms in stormwater runoff

Microbial association with particles can significantly affect the fate and transport characteristics of microbes in aquatic systems as particle-associated organisms will be less mobile in the environment than their free phase (i.e. unattached) counterparts. As such, similarities or dissimilarities in the partitioning behavior of indicator organisms and pathogens may have an impact on the suitability of a particular indicator to act as a surrogate for a pathogen. This research analyzed the partitioning behavior of two pathogens (Cryptosporidium, Giardia) and several common indicator organisms (fecal coliform, Escherichia coli, Enterococci, Clostridium perfringens spores, and coliphage) in natural waters under both dry and wet weather conditions. Samples were taken from several streams in two distinct sampling phases: (i) single grab samples; and (ii) intrastorm samples obtained throughout the duration of four storms. Partitioning behavior varied by microbial type, with 15-30% of bacterial indicators (fecal coliform, E. coli, and Enterococci) associated with settleable particles compared to 50% for C. perfringens spores. Both pathogens exhibited similar levels of particle association during dry weather (roughly 30%), with increased levels observed during wet weather events (Giardia to 60% and Cryptosporidium to 40%). The settling velocities of particle-associated microbes were also estimated, with those of the bacterial indicators (fecal coliform, E. coli, and Enterococci), as well as C. perfringens spores, being similar to that of the Giardia and Cryptosporidium, suggesting these organisms may exhibit similar transport behavior. With respect to intrastorm analysis, the highest microbial concentrations, in both particle-associated and free phase, occurred during the earlier stages of a storm. The total loadings of both indicators and pathogens were also estimated over the course of individual storms.     

Intra-storm variability in microbial partitioning and microbial loading rates

Association with particles in the water column can have a significant impact on microbial fate and transport. This study analyzed multiple stormwater samples taken throughout the duration of three separate storms (at two different sites) to evaluate the fraction of microbes partitioning to denser "settleable" particles and to examine how partitioning behavior varied over the course of a storm. Intra-storm sampling also allowed for estimates of microbial loading rates (both total and particle-associated) and cumulative storm-induced microbial load. Five different indicator organisms were examined, with the fraction of microbes associated with settleable particles assessed via a calibrated centrifugation method. Partitioning behavior varied across microorganism type, with an average of 40% of fecal coliforms, Escherichia coli, and enterococci associating with settleable particles, compared to approximately 65% of Clostridium perfringens spores and only 13% of total coliphage. Partitioning remained fairly constant for each type of organism throughout storm events. Nonetheless, higher concentrations of both settleable particles and microbes entering the water column soon after the onset of a storm led to higher loading rates of settleable microbes in the storm's earliest stages, a trend that could have important implications for the design of stormwater management structures (e.g., detention basins). Estimates of cumulative storm-induced microbial loading suggested that one day's worth of storm loading can be the equivalent of months, or even years, of dry-weather loading.     

Priority pollutants in surface waters and settleable particles within a densely urbanised area: Case study of Paris (France)

Implementation of the European Water Framework Directive 2000/60/EC (WFD) requires Member States to expand their collective knowledge of priority pollutants (PPs) within receiving waters. To achieve this objective, information on the occurrence of PPs in surface waters and, more specifically, within densely urbanised areas needs to be collected. This study has therefore been designed to provide information on both PP occurrence and concentration build-up along a heavily urbanised transect of the Seine River in the Paris region (France). A large range of PPs were observed in settleable particles and, to a lesser extent, in the waters surveyed. In surface waters, a total of 18 PPs, including 15 priority hazardous substances?, were indeed detected, yet concentrations rarely exceeded the limit of quantification. In fact, only diuron?, DEHP?, fluoranthene and para-tert-octylphenol? are observed on a frequent basis, with concentrations ranging from < 0.01 to 1.0 µg l^− 1. As regards the Environmental Quality Standards (EQS), 10 substances or groups of substances were found in surface waters to exhibit concentrations above the annual average value, while only the benzo(a)pyrene? concentration exceed the maximum allowable level. As for the Canadian Sediment Quality Guidelines, settleable particles collected in the Seine River appear to be heavily contaminated since most samples contain PP levels above the guideline values (18 PPs) and, in many cases, above the probable effect levels (15 PPs), which underscores that the levels of metals, PAHs and PCBs in settleable particles constitute a potential risk to freshwater organisms.     

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.     

Simulated rain events on an urban roadway to understand the dynamics of mercury mobilization in stormwater runoff

This research focuses on mercury (Hg) mobilization in stormwater runoff from an urban roadway. The objectives were to determine: how the transport of surface-derived Hg changes during an event hydrograph; the influence of antecedent dry days on the runoff Hg load; the relationship between total suspended sediments (TSS) and Hg transport, and; the fate of new Hg input in rain and its relative importance to the runoff Hg load. Simulated rain events were used to control variables to elucidate transport processes and a Hg stable isotope was used to trace the fate of Hg inputs in rain. The results showed that Hg concentrations were highest at the beginning of the hydrograph and were predominately particulate bound (HgP). On average, almost 50% of the total Hg load was transported during the first minutes of runoff, underscoring the importance of the initial runoff on load calculations. Hg accumulated on the road surface during dry periods resulting in the Hg runoff load increasing with antecedent dry days. The Hg concentrations in runoff were significantly correlated with TSS concentrations (mean r² = 0.94 ± 0.09). The results from the isotope experiments showed that the new Hg inputs quickly become associated with the surface particles and that the majority of Hg in runoff is derived from non-event surface-derived sources.     

Modelling the fate of organic micropollutants in stormwater ponds

Urban water managers need to estimate the potential removal of organic micropollutants (MP) in stormwater treatment systems to support MP pollution control strategies. This study documents how the potential removal of organic MP in stormwater treatment systems can be quantified by using multimedia models. The fate of four different MP in a stormwater retention pond was simulated by applying two steady-state multimedia fate models (EPI Suite and SimpleBox) commonly applied in chemical risk assessment and a dynamic multimedia fate model (Stormwater Treatment Unit Model for Micro Pollutants — STUMP). The four simulated organic stormwater MP (iodopropynyl butylcarbamate — IPBC, benzene, glyphosate and pyrene) were selected according to their different urban sources and environmental fate. This ensures that the results can be extended to other relevant stormwater pollutants. All three models use substance inherent properties to calculate MP fate but differ in their ability to represent the small physical scale and high temporal variability of stormwater treatment systems. Therefore the three models generate different results. A Global Sensitivity Analysis (GSA) highlighted that settling/resuspension of particulate matter was the most sensitive process for the dynamic model. The uncertainty of the estimated MP fluxes can be reduced by calibrating the dynamic model against total suspended solids data. This reduction in uncertainty was more significant for the substances with strong tendency to sorb, i.e. glyphosate and pyrene and less significant for substances with a smaller tendency to sorb, i.e. IPBC and benzene. The results provide support to the elaboration of MP pollution control strategies by limiting the need for extensive and complex monitoring campaigns targeting the wide range of specific organic MP found in stormwater runoff.     

Confirmation of putative stormwater impact on water quality at a Florida beach by microbial source tracking methods and structure of indicator organism populations

The effect of a stormwater conveyance system on indicator bacteria levels at a Florida beach was assessed using microbial source tracking methods, and by investigating indicator bacteria population structure in water and sediments. During a rain event, regulatory standards for both fecal coliforms and Enterococcus spp. were exceeded, contrasting with significantly lower levels under dry conditions. Indicator bacteria levels were high in sediments under all conditions. The involvement of human sewage in the contamination was investigated using polymerase chain reaction (PCR) assays for the esp gene of Enterococcus faecium and for the conserved T antigen of human polyomaviruses, all of which were negative. BOX-PCR subtyping of Escherichia coli and Enterococcus showed higher population diversity during the rain event; and higher population similarity during dry conditions, suggesting that without fresh inputs, only a subset of the population survives the selective pressure of the secondary habitat. These data indicate that high indicator bacteria levels were attributable to a stormwater system that acted as a reservoir and conduit, flushing high levels of indicator bacteria to the beach during a rain event. Such environmental reservoirs of indicator bacteria further complicate the already questionable relationship between indicator organisms and human pathogens, and call for a better understanding of the ecology, fate and persistence of indicator bacteria.     

Application of microcarriers in stormwater treatment

This paper present the results of an experimental investigation on removing colloidal particles from stormwater runoff by microcarrier process. The mechanisms of the microcarrier process involve particle capturing, suspension and sedimentation. The results indicated that this process is effective in treating stormwater runoff. The removal rate for particle count, turbidity, suspended solids and volatile solids reach 96% and higher. The total treatment include a 30‐second mixing with a 3‐minute settling, a substantial time reduction from that of the conventional approach. This rapid treatment indicates that the microcarrier process has the capacity to treat large volumes of surface runoff during a storm event.     

Contrasts in concentrations and loads of conventional and alternative indicators of fecal contamination in coastal stormwater

Fecal contamination in stormwater is often complex. Because conventional fecal indicator bacteria (FIB) cannot be used to ascertain source of fecal contamination, alternative indicators are being explored to partition these sources. As they are assessed for future use, it is critical to compare alternative indicators to conventional FIB under a range of stormwater delivery conditions. In this study, conventional FIB and fecal Bacteroides spp. were monitored throughout the duration of five storm events from coastal stormwater outfalls in Dare County, North Carolina, USA to characterize relationships among FIB concentrations, alternative fecal markers, and loading of contaminants. Water samples were collected multiple times during each storm and analyzed for Enterococcus sp. and Escherichia coli using enzymatic tests and fecal Bacteroides spp. by QPCR. Both conventional FIB and fecal Bacteroides spp. concentrations in stormwater were generally high and extremely variable over the course of the storm events. Over the very short distances between sites, we observed statistically significant spatial and temporal variability, indicating that stormwater monitoring based on single grab-samples is inappropriate. Loading of FIB and fecal Bacteroides spp. appeared to be affected differently by various hydrologic factors. Specifically, Spearman correlations between fecal Bacteroides spp. and drainage area and antecedent rainfall were lower than those between conventional FIB and these hydrologic factors. Furthermore, the patterns of fecal Bacteroides spp. concentrations generally increased over the duration of the storms, whereas E. coli and Enterococcus sp. concentrations generally followed the patterns of the hydrograph, peaking early and tailing off. Given the greater source-specificity and limited persistence of fecal Bacteroides spp. in oxygenated environments, differences in these patterns suggest multiple delivery modes of fecal contamination (i.e. landscape scouring versus groundwater discharge).     

Particle-associated microorganisms in stormwater runoff

This research investigated the effects of blending and chemical addition before analysis of the concentration of microorganisms in stormwater runoff from a single summer storm to determine whether clumped or particle-associated organisms play a significant role. The standard membrane filtration method was used to enumerate the microorganisms. All organisms, except for Escherichia coli, showed an increase in the measured concentration after blending samples at 22,000 rpm with or without the chemical mixture. Other than fecal streptococci, the organism concentrations decreased with the addition of the Camper's solution in both blended and unblended samples before analyses. There was a statistically significant interaction between the effects of Camper's solution and the effects of blending for all the organisms tested, except for total coliform. Blending did not alter the mean particle size significantly. The results show no correlation between increased total coliform, fecal coliform, and fecal streptococcus concentrations and the mean particle size.     

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.     

Nitrogen composition in urban runoff--implications for stormwater management

A study was conducted to characterise the composition of nitrogen in urban stormwater in Melbourne, Australia, during baseflows and storm events, and to compare the results with international data. Nitrogen in Melbourne stormwater was predominantly dissolved (approximately 80%), with ammonia the least-abundant form (approximately 11%). Concentrations of nitrogen species did not vary significantly between baseflow and storms, although the proportion of nitrogen in particulate form was higher during storm events (p = 0.04). Whilst the composition of nitrogen in Melbourne was broadly consistent with international data, the level of dissolved inorganic nitrogen was higher in Melbourne (mu = 48% during baseflows and 49% during storms) than in the international literature (mu = 29%). Limitations in the international dataset precluded comparison of total dissolved nitrogen. The results have implications for stormwater management. Whilst nitrogen species concentrations are variable, they are not strongly related to flow conditions, so treatment systems must be designed to cope with stochastic inflow concentrations at all times. To optimise their performance, stormwater treatments should be designed to improve dissolved nitrogen removal. Further research is needed to improve the ability of treatment systems to achieve this aim.     

Design of stormwater monitoring programs

Stormwater runoff is now the leading source of water pollution in the United States, and stormwater monitoring programs have only recently been developed. This paper evaluates several stormwater monitoring programs to identify ways of increasing the likelihood of identification of high-risk dischargers and increasing data reliability for assisting in the development of total maximum daily loads. No relationship was found between various types of industrial activity or landuse and water quality data. Stormwater data collected with grab samples has much greater pollutant concentration variability than in potable water or wastewater monitoring programs. Industrial land use is an important source of metals. For grab samples, sampling time during the storm event will affect results. Data from California, which has distinct dry periods, showed a seasonal first flush, whereas data from areas with more uniform rainfall throughout the year did not show a seasonal first flush. Selecting a subset of sites from each monitored category using a flow-weighted composite sampler is an alternative strategy, and may result in lower overall cost with improved accuracy and variability in mass emissions, but may not be less successful in identifying high-risk dischargers.     

Optimization methods applied to stormwater management problems: a review

Stormwater management essentially aims at controlling the surface runoff to reduce water pollution and restore ecosystem integrity. This paper reviews and discusses several optimization problems associated with this field. Different features of such problems were identified to provide a classified investigation of the literature in terms of control approach, performance criteria, stormwater management approach, and uncertainty consideration. Having evaluated the relevant literature based on these factors, the knowledge gaps were extracted. We have noticed that there is an upward trend towards sustainable management of stormwater systems to deal with climate change. Despite this progress, there are still many areas to further develop stormwater management models, many of which relate to uncertainty identification, system-level real-time control, and the proper formulation of multi-objective optimization models. Hence, integration of different criteria in optimization models, and also the study of design vs. operation of stormwater management systems are proposed as further studies.     

A landscape ecological model for wildlife enhancement of stormwater management practices in urban greenways

A spatial distribution model has been developed to predict the pattern of stormwater catchment facilities in developing urban areas. The model has been validated through comparison of predicted results with historical data in Guelph, Canada, using nearest neighbour analysis. The validated model has been applied to developing urban-rural fringe lands in Guelph to illustrate land use patterns likely to occur under different scenarios. Simulations of various scenarios for incorporating stormwater catchment facilities into greenways have been tested with the model and the resultant land use patterns compared with the status quo, through measures of landscape ecological integrity such as connectivity and porosity. The model was applied to an area on the edge of Guelph scheduled for development. The predicted land use patterns of various planning scenarios were generated and analysed. The results demonstrated that landscape integrity could be increased, urban wildlife habitat enhanced, and opportunities for residential non-consumptive wildlife recreation improved through integration of the evolving ‘blue-green’ open space provided by urban stormwater management facilities into existing greenways.     

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.     

Determination of a set of surrogate parameters to assess urban stormwater quality

This paper presents the outcomes of a research project, which focused on developing a set of surrogate parameters to evaluate urban stormwater quality using simulated rainfall. Use of surrogate parameters has the potential to enhance the rapid generation of urban stormwater quality data based on on-site measurements and thereby reduce resource intensive laboratory analysis. The samples collected from rainfall simulations were tested for a range of physico-chemical parameters which are key indicators of nutrients, solids and organic matter. The analysis revealed that [total dissolved solids (TDS) and dissolved organic carbon (DOC)]; [total solids (TS) and total organic carbon (TOC)]; [turbidity (TTU)]; [electrical conductivity (EC)]; [TTU and EC] as appropriate surrogate parameters for dissolved total nitrogen (DTN), total phosphorus (TP), total suspended solids (TSS), TDS and TS respectively. Relationships obtained for DTN-TDS, DTN-DOC, and TP-TS demonstrated good portability potential. The portability of the relationship developed for TP and TOC was found to be unsatisfactory. The relationship developed for TDS-EC and TS-EC also demonstrated poor portability.     

Metals and PAHs adsorbed to street particles

Particles were collected from 18 different city streets adjacent to five different landuses in the City of Santa Monica, California. Landuses were classified as industrial, roads, multifamily residential, commercial and single family residential. Particles were collected using a vacuum cleaner with a 0.1-microm filter and a rotating brush head. Particles were first sized into six fractions from 43-2200 microm using two sets of sieves. Representative samples of the four size fractions smaller than 841 microm from each landuse were separately digested to extract metals and polynuclear aromatic hydrocarbons (PAHs). Smaller particles had higher solid-phase concentrations, but not as high as the ratios of their specific surface areas, assuming spherical shape. Relative PAHs concentrations were higher on small particles than were metal concentrations. Single-family residential areas were the lowest in metals and PAHs, with only a few exceptions. The greatest mass of pollutants was associated with the particles in the 100-250 microm range.     

Application of probabilistic neural networks in modelling structural deterioration of stormwater pipes

In Australia, when stormwater systems were first introduced over 100 years ago, they were constructed independently of the sewer systems, and they are normally the responsibility of the third level of government, i.e., local government or city councils. Because of the increasing age of these stormwater systems and their worsening performance, there are serious concerns in a significant number of city councils regarding their deterioration. A study has been conducted on the structural deterioration of concrete pipes that make up the bulk of the stormwater pipe systems in these councils. In an attempt to look for a reliable deterioration model, a probabilistic neural network (PNN) model was developed using the data set supplied from participating councils. The PNN model was validated with snapshot-based sample data, which makes up the data set. The predictive performance of the PNN model was compared with a traditional parametric model using discriminant analysis on the same data set. Structural deterioration was hypothesised to be influenced by a set of explanatory factors, including pipe design and construction factors—such as pipe size, buried depth—and site factors—such as soil type, moisture index, tree root intrusion, etc. The results show that the PNN model has a better predictive power and uses significantly more input variables (i.e., explanatory factors) than the discriminant model. More importantly, the key factors for prediction in the PNN model are difficult to interpret, suggesting that besides prediction accuracy, model interpretation is an important issue for further investigation.     

Removal of pesticide mixtures in a stormwater wetland collecting runoff from a vineyard catchment

Wetlands can collect contaminated runoff from agricultural catchments and retain dissolved and particle-laden pesticides. However, knowledge about the capacity and functioning of wetland systems with respect to the removal of pesticides is very limited. Here we show that stormwater wetlands can efficiently remove pesticides in runoff from vineyard catchments during the period of pesticide application, although flow and hydrochemical conditions of the wetland largely vary over time. During the entire agricultural season, the inflowing load of nine fungicides, six herbicides, one insecticide and four degradation products was 8.039 g whereas the outflowing load was 2.181 g. Removal rates of dissolved loads by the wetland ranged from 39% (simazine) to 100% (cymoxanil, gluphosinate, kresoxim methyl and terbuthylazine). Dimethomorph, diuron, glyphosate, metalaxyl and tetraconazole were more efficiently removed in spring than in summer. More than 88% of the input mass of suspended solids was retained, underscoring the capability of the wetland to trap pesticide-laden particles via sedimentation. Only the insecticide flufenoxuron was frequently detected in the wetland sediments. Our results demonstrate that stormwater wetlands can efficiently remove pesticide mixtures in agricultural runoff during critical periods of pesticide application, although fluctuations in the runoff regime and hydrochemical characteristics can affect the removal rates of individual pesticides.