Stormwater Infiltration Systems Research Articles

Runoff microbiome quality assessment of a city center rainwater harvesting zone shows a differentiation of pathogen loads according to human mobility patterns

The hygienic quality of urban surfaces can be impaired by multiple sources of microbiological contaminants. These surfaces can trigger the development of multiple bacterial taxa and favor their spread during rain events through the circulation of runoff waters. These runoff waters are commonly directed toward sewer networks, stormwater infiltration systems or detention tanks prior a release into natural water ways. With water scarcity becoming a major worldwide issue, these runoffs are representing an alternative supply for some usage like street cleaning and plant watering. Microbiological hazards associated with these urban runoffs, and surveillance guidelines must be defined to favor these uses. Runoff microbiological quality from a recently implemented city center rainwater harvesting zone was evaluated through classical fecal indicator bacteria (FIB) assays, quantitative PCR and DNA meta-barcoding analyses. The incidence of socio-urbanistic patterns on the organization of these urban microbiomes were investigated. FIB and DNA from Human-specific Bacteroidales and pathogens such as Staphylococcus aureus were detected from most runoffs and showed broad distribution patterns. 16S rRNA DNA meta-barcoding profilings further identified core recurrent taxa of health concerns like Acinetobacter, Mycobacterium, Aeromonas and Pseudomonas, and divided these communities according to two main groups of socio-urbanistic patterns. One of these was highly impacted by heavy traffic, and showed recurrent correlation networks involving bacterial hydrocarbon degraders harboring significant virulence properties. The tpm-based meta-barcoding approach identified some of these taxa at the species level for more than 30 genera. Among these, recurrent pathogens were recorded such as P. aeruginosa, P. paraeruginosa, and Aeromonas caviae. P. aeruginosa and A. caviae tpm reads were found evenly distributed over the study site but those of P. paraeruginosa were higher among sub-catchments impacted by heavy traffic. Health risks associated with these runoff P. paraeruginosa emerging pathogens were high and associated with strong cytotoxicity on A549 lung cells. Recurrent detections of pathogens in runoff waters highlight the need of a microbiological surveillance prior allowing their use. Good microbiological quality can be obtained for certain typologies of sub-catchments with good hygienic practices but not all. A reorganization of Human mobility and behaviors would likely trigger changes in these bacterial diversity patterns and reduce the occurrences of the most hazardous groups.

Biocides in Soils of Urban Stormwater Infiltration Systems—Indications of Inputs from Point and Non-point Sources

AbstractUrban stormwater contains various micropollutants, such as biocides, which are washed off from facades during wind-driven rain events. Biocides can reach the groundwater via stormwater infiltration systems (SIS), although the soil layer acts as a reactive barrier preventing the leaching of biocides but producing transformation products (TPs). Little is known about the occurrence and concentration of biocides in SIS soils, their distribution and temporal behavior. Here, we present a first systematic screening of three commonly used biocides (diuron, octylisothiazolinone (OIT), terbutryn) and four TPs of terbutryn in 46 French and German SIS. Overall, biocide occurrence in SIS topsoils was ubiquitous but low, while point source inputs to specific SIS were high but rare. Low concentrations (< 2ng g-1) of terbutryn were detected in 78% of the SIS. Maximum concentrations occurred in recently constructed SIS, suggesting that this is due to higher biocide loads entering the SIS. The frequent detection of terbutryn supports the idea that it is a non-point source marker, as it is relatively stable in soil (t1/2 > 90 days) and widely used in renders and paints. In contrast, high concentrations of diuron (168 ng g-1) and OIT (58 ng g-1) were observed in only one sample, suggesting an urban point source contamination, possibly from a freshly repainted facade. The distinction between source types provides a basis for targeted measures to prevent biocide entry to groundwater. Altogether, this study opens the door to a more systematic consideration of micropollutant dissipation and ecotoxicological effects in SIS design and monitoring.

Aquifer recharge by stormwater infiltration basins: Hydrological and vadose zone characteristics control the impacts of basins on groundwater chemistry and microbiology

Stormwater infiltration systems (SIS) are designed to collect and infiltrate urban stormwater runoff into the ground for flood risk mitigation and artificial aquifer recharge. Many studies have demonstrated that infiltration practices can impact groundwater chemistry and microbiology. However, quantitative assessments of the hydrogeological factors responsible of these changes remain scarce. Thus, the present study aimed to quantitatively test whether changes of groundwater chemistry and microbiology induced by SIS were linked to two factors associated with vadose zone properties (vadose zone thickness, water transit time from surface to groundwater) and one factor associated with groundwater recharge rate (assessed by groundwater table elevation during rain events). To evaluate changes in chemistry (NO3−, PO43− and dissolved organic carbon concentrations), groundwater samples were collected in wells located in SIS-impacted and non-SIS-impacted zones during experimental periods of 10 days. During the same periods, clay beads were incubated in the same wells to measure changes of groundwater microbial biofilms (microbial biomass, dehydrogenase and hydrolytic activities) induced by SIS. Results showed that changes in PO43− supplied to groundwater during stormwater infiltration was negatively correlated with vadose zone thickness. A short water transit time from surface to groundwater increased dissolved organic carbon concentrations in the aquifer which, in turn, increased biofilm biomasses in groundwater. The groundwater recharge rate during rain events (assessed by groundwater table elevation) diluted NO3− concentrations in the aquifer but also influenced the changes of biofilm activities induced by SIS. Groundwater recharge rate during rain events probably increased the fluxes of water and dissolved organic carbon in groundwater, stimulating the activity of microbial biofilms. Overall, the present study is the first to quantify conjointly several factors and processes (water transfer, dilution, solute fluxes) that could explain the impact of stormwater infiltration on chemistry and/or microbiology in groundwater.

Consequences of interactions between stormwater infiltration systems, shallow groundwater and underground structures at the neighborhood scale

ABSTRACT This study investigates the interplay between stormwater infiltration devices, shallow groundwater and underground structures (sewer pipes and building foundations) at the neighborhood scale. Considering a hypothetical urban area, different scenarios are designed by varying the underground components taken into account within two soil types. For the least permeable soil, interactions with groundwater reduce the infiltration within devices (−99 to −151 mm/y) and increase the transpiration in surrounding areas (+42 to +50 mm/y). For both soils, the overall water table rise due to infiltration and mounding beneath infiltration devices increases groundwater drainage by sewer pipes and draining systems (+7 to +96 mm/y) and the water elevation differential between opposite walls of impervious structures (up to +1.5 m). In turn, underground structures strongly modify groundwater flow. For the least permeable soil, this directly affects groundwater influence on infiltration and transpiration and thus the overall effects of infiltration strategies at the neighborhood scale.

Analyzing the impact of hydrological storage and connected impervious area on the performance of distributed kerbside infiltration systems in an urban catchment

The popularity of subsurface distributed storage-based kerbside stormwater infiltration systems is increasing because they can be integrated within the strict spatial constraints of existing infrastructure. Distributed systems operate based on the concept of spreading a limited amount of storage throughout the catchment area to achieve runoff management objectives. Storage can also limit the performance of urban stormwater systems. This study investigated the role of storage capacity, especially the volumetric capacity and the emptying time, in the performance of kerbside leaky well systems in a residential catchment area with a native clay soil environment. A detailed, process-based deterministic hydrological model was used to analyze hydrologic storage via a continuous simulation approach. The model was calibrated against catchment outflows measured with stormwater infiltration devices. Individual kerbside infiltration systems were also calibrated to monitor the behavior of on-site kerbside infiltration systems. By using approach of continuous simulations during designed scenarios, this study considered the prestorm storage availability in the hydrological analysis. The results demonstrated that hydrologic storage greatly influences the performance of kerbside leaky well systems during higher-intensity storms. In addition, the results show that distributing a stormwater storage volume equal to thirty-five 1-kL rainwater tanks across the catchment area as a kerbside infiltration system could notably reduce the runoff flow rates and volumes. The results further highlight that the addition of more homes within the connected area could diminish the stormwater reduction benefits achieved through the installation of a distributed kerbside infiltration system.

Modelling the interaction between vegetation and infiltrated stormwater

A major problem associated with sealing native soils with impervious surfaces in urban areas is reduced groundwater recharge. This in turn reduces stream baseflows which has serious implications for freshwater ecosystems. To address this problem, the use of stormwater infiltration systems is becoming increasingly common worldwide. There is, however, substantial uncertainty on the fate of infiltrated stormwater and its interactions with downslope vegetation. This study aimed to investigate the role of vegetation on the amount of infiltrated stormwater reaching the stream. A model using MIKE SHE was constructed, calibrated, and validated based on a real infiltration system which features extensive vegetation between the site of stormwater infiltration and the stream. We then used the calibrated model to predict the amount of infiltrated stormwater reaching the stream in the absence of vegetation. We also predicted the impact of infiltrated stormwater on the evapotranspiration downslope of the system. The results showed that the performance of the model was satisfactory, and the model captured the overall groundwater dynamic very well. The amount of infiltrated stormwater reaching the stream increased by about 17 percent in the absence of vegetation. The model also predicted that evapotranspiration would be 13 percent lower in the warmer months if stormwater was not infiltrated upslope. The results suggest that the choice of location of infiltration systems should consider the potential of vegetation to intercept infiltrated water and impact on achievement of the design objectives, which, in this case, included restoring baseflow. Where increasing the baseflows is not a priority, the increased evapotranspiration afforded by stormwater infiltration could provide important microclimate benefits.

An analytical approach for urban groundwater transit time distributions accounting for the effect of stormwater infiltration system

The stormwater infiltration system (SIS) has been recognized as a feasible way to manage stormwater and restore streamflow. As a lumped representation of the flow and transport processes, the groundwater transit time distribution (TTD) is highly relevant to this restoration goal. However, the influence of the SIS on groundwater TTDs has rarely been studied. In this paper, we propose a novel analytical model for groundwater TTDs in regional urban aquifers accounting for the impact of the SIS. This analytical solution is developed for a homogeneous 2-D cross-section of an idealized unconfined aquifer following the Dupuit-Forchheimer assumption. The analytical solution is verified through the comparison with simulated TTDs using the Lagrangian particle tracking algorithm. The global sensitivity analysis reveals that the stormwater infiltration rate, the number of infiltration facilities, the size of the urban area, and the evapotranspiration are the most important factors for groundwater mean transit times (MTTs). Although groundwater discharge and MTT can be restored to the pre-urban one, groundwater TTDs will inevitably deviate from the pre-urban ones due to the alteration from diffuse recharge to infiltration-focused recharge, indicating that the urban groundwater flow regime cannot be fully restored to the pre-urban conditions. Overall, as a first-order approximation of the real-world urban groundwater system, the proposed analytical model provides decision-making support for urban water resources management and the design of the SIS.

Impacts of stormwater infiltration on downslope soil moisture and tree water use

Infiltration of stormwater is a widely used strategy to mitigate the flooding and environmental risks that come from urban runoff and conventional urban drainage. An understanding of the fate of this infiltrated water is required for rigorous design. Principal design objectives are typically to restore more natural hydrology in order to protect receiving waters from pollution and hydrologic change. Without such understanding there is also a risk of unforeseen impacts on nearby infrastructure and urban vegetation. We sought to understand the pathways and fate of water from a stormwater infiltration basin. To trace water, we used a combination of water table monitoring and isotopic composition analysis in the infiltration basin, as well as in rainfall, soil water, the shallow groundwater, and in vegetation upslope and downslope of the basin. We also measured tree water use directly using sap flow sensors. The infiltration basin was shown to increase the availability of water downslope, allowing trees to maintain elevated levels of water use during dry periods with high energy demand. In contrast, water limitation upslope saw substantial seasonal reductions in tree water use. The soil water isotopic composition demonstrated significant differences from upslope to downslope, with downslope water being more reflective of rainfall, while the upslope water used by the trees was more depleted. The results paint a picture of stormwater infiltration being a significant source of lateral flow, while trees are a significant sink of lateral flow emanating from the basin. This finding suggests that stormwater infiltration could be used as a strategy to support the health and growth of urban trees. Urban trees have demonstrated benefits for human health and comfort, particularly in a warming climate. It also suggests that stormwater infiltration may not always recharge groundwater and provide baseflow in receiving waters, being instead taken up by vegetation. These findings should be considered in the siting of stormwater infiltration systems, to ensure that the objectives they were designed for are actually met.

Sources and pathways of biocides and their transformation products in urban storm water infrastructure of a 2 ha urban district

Abstract. Biocides used in film protection products leaching from facades are known to be a potential threat to the environment. This study identifies individual sources and entry pathways in a small-scale urban area. We investigate emissions of commonly used biocides (terbutryn, diuron, and octylisothiazolinone – OIT) and some of their transformation products (TPs; diuron-desmethyl, terbumeton, terbuthylazine-2-hydroxy, and terbutryn-desethyl) from a 2 ha residential area 13 years after construction has ended. Sampling utilizes existing urban water infrastructure representative for decentralized storm water management in central and northern Europe and applies a two-step approach to (a) determine the occurrence of biocides above water quality limits (i.e., predicted no-effect concentration, PNEC) and (b) identify source areas and characterize entry pathways into surface and groundwater. Monitoring focuses on the analysis of selected biocides and TPs by liquid chromatography–mass spectrometry/mass spectrometry (LC-MS/MS) in water samples taken from facades, rainwater pipes, drainage, and storm water infiltration systems. In standing water in a swale, we found high concentrations of diuron (174 ng L−1) and terbutryn (40 ng L−1) above PNEC for surface water. We confirmed expected sources, i.e., facades. Sampling of rain downpipes from flat roofs identified additional sources of all biocides and two TPs of terbutryn and one TP of diuron. Diuron and terbutryn were found in three drainage pipes representing different entry pathways of biocides. In one drainage pipe collecting road runoff, only diuron-desmethyl and terbutryn-desethyl were detected. In two other drainage pipes collecting infiltrated water through soil, terbuthylazine-2-hydroxy was additionally detected. One of the pipes collecting infiltrated water through soil concentration showed the highest concentrations of terbutryn and two of its TPs (terbutryn-desethyl and terbuthylazine-2-hydroxy). This suggests a high leaching potential of terbutryn. The applied two-step approach determined sources and pathways of biocide and their TPs. This study contributes to expanding knowledge on their entry and distribution and, thus, eventually towards reducing emissions.

Urban storm water infiltration systems are not reliable sinks for biocides: evidence from column experiments

Groundwater quality in urban catchments is endangered by the input of biocides, such as those used in facade paints to suppress algae and fungal growth and washed off by heavy rainfall. Their retention in storm water infiltration systems (SIS) depends, in addition to their molecular properties, on chemical properties and structure of the integrated soil layer. These soil properties change over time and thus possibly also the relevance of preferential flow paths, e.g. due to ongoing biological activity. To investigate the mobility of biocides in SIS, we analyzed the breakthrough of differently adsorbing tracers (bromide, uranine, sulforhodamine B) and commonly used biocides (diuron, terbutryn, octhilinone) in laboratory column experiments of undisturbed soil cores of SIS, covering ages from 3 to 18 years. Despite similar soil texture and chemical soil properties, retention of tracers and biocides differed distinctly between SIS. Tracer and biocide breakthrough ranged from 54% and 5%, to 96% and 54%, respectively. We related the reduced solute retention to preferential transport in macropores as could be confirmed by brilliant blue staining. Our results suggest an increasing risk of groundwater pollution with increasing number of macropores related to biological activity and the age of SIS.

Influence of stormwater infiltration systems on the structure and the activities of groundwater biofilms: Are the effects restricted to rainy periods?

Stormwater infiltration systems (SIS) have been set up to collect and infiltrate urban stormwater runoff in order to reduce flooding and to artificially recharge aquifers. Such practices produce environmental changes in shallow groundwater ecosystems like an increase in organic matter concentrations that could drive changes in structure and functions of groundwater microbial communities. Previous works suggested that SIS influence groundwater physico-chemistry during either rainy and dry period but no study has examined the impact of SIS on groundwater microorganisms during both periods. This study aimed to fill this gap by assessing SIS impacts on groundwater quality parameters in three SIS with vadose zone thickness < 3 m during two contrasting meteorological conditions (rainy/dry periods). Physicochemical (dissolved organic carbon and nutrient concentrations) and microbial variables (biomass, dehydrogenase and hydrolytic activities, and bacterial community structure) were assessed on SIS-impacted and non-SIS-impacted zones of the aquifers for the three SIS. Using clay beads incubated in the aquifer to collect microbial biofilm, we show that SIS increased microbial activities, bacterial richness and diversity in groundwater biofilms during the rainy period but not during the dry period. In contrast, the significant differences in dissolved organic carbon and nutrient concentrations, biofilm biomass and bacterial community structures (Bray-Curtis distances, relative abundances of main bacterial orders) measured between SIS-impacted and non-SIS-impacted zones of the aquifer were comparable during the two periods. These results suggest that structural indicators of biofilm like biomass were probably controlled by long-term effects of SIS on concentrations of dissolved organic matter and nutrients whereas biofilm activities and bacterial richness were temporally stimulated by stormwater runoff infiltrations during the rainy period. This decoupling between the structural and functional responses of groundwater biofilms to stormwater infiltration practices suggests that biofilms functions were highly reactive to fluxes associated with aquifer recharge events.

Coalescence of bacterial groups originating from urban runoffs and artificial infiltration systems among aquifer microbiomes

Abstract. The invasion of aquifer microbial communities by aboveground microorganisms, a phenomenon known as community coalescence, is likely to be exacerbated in groundwaters fed by stormwater infiltration systems (SISs). Here, the incidence of this increased connectivity with upslope soils and impermeabilized surfaces was assessed through a meta-analysis of 16S rRNA gene libraries. Specifically, DNA sequences encoding 16S rRNA V5-V6 regions from free-living and attached aquifer bacteria (i.e., water and biofilm samples) were analysed upstream and downstream of a SIS and compared with those from bacterial communities from watershed runoffs and surface sediments from the SIS detention and infiltration basins. Significant bacterial transfers were inferred by the SourceTracker Bayesian approach, with 23 % to 57 % of the aquifer bacterial biofilms being composed of taxa from aboveground sediments and urban runoffs. Sediments from the detention basin were found more significant contributors of taxa involved in the buildup of these biofilms than soils from the infiltration basin. Inferred taxa among the coalesced biofilm community were predicted to be high in hydrocarbon degraders such as Sphingobium and Nocardia. The 16S rRNA-based bacterial community structure of the downstream-SIS aquifer waters showed lower coalescence with aboveground taxa (8 % to 38 %) than those of biofilms and higher numbers of taxa predicted to be involved in the N and S cycles. A DNA marker named tpm enabled the tracking of bacterial species from 24 genera including Pseudomonas, Aeromonas and Xanthomonas, among these communities. Several tpm sequence types were found to be shared between the aboveground and aquifer samples. Reads related to Pseudomonas were allocated to 50 species, of which 16 were found in the aquifer samples. Several of these aquifer species were found to be involved in denitrification but also hydrocarbon degradation (P. aeruginosa, P. putida and P. fluorescens). Some tpm sequence types allocated to P. umsongensis and P. chengduensis were found to be enriched among the tpm-harbouring bacteria, respectively, of the aquifer biofilms and waters. Reads related to Aeromonas were allocated to 11 species, but only those from A. caviae were recovered aboveground and in the aquifer samples. Some tpm sequence types of the X. axonopodis phytopathogen were recorded in higher proportions among the tpm-harbouring bacteria of the aquifer waters than in the aboveground samples. A significant coalescence of microbial communities from an urban watershed with those of an aquifer was thus observed, and recent aquifer biofilms were found to be significantly colonized by runoff-opportunistic taxa able to use urban C sources from aboveground compartments.

Sorption and transport behavior of zinc in the soil; Implications for stormwater management

Long-term leaching of accumulated heavy metals from the filter media of stormwater infiltration systems into groundwater, and its subsequent movement into receiving waters, is a concern for stormwater management in urban landscapes. This study provides a critical understanding of the fate of heavy metals, in particular zinc, in the subsurface to improve stormwater management. We studied the sorption behavior of zinc during its transport in soil using batch and column experiments. The use of sorption parameters from batch studies failed to suitably describe the zinc breakthrough curves simulated with the HYDRUS-1D model. While a sharp breakthrough curve front was expected due to the nonlinear nature of the batch sorption isotherms, we observed a more dispersed asymmetrical front in the columns. This demonstrates the existence of chemical non-equilibrium sorption during zinc transport. Conversely, no asymmetry was observed in the conservative tracer (chloride) breakthrough curve, suggesting that there is no physical non-equilibrium component. We conclude that (1) batch tests overpredict the transport behavior of zinc in the soil, (2) column tests better approximate non-equilibrium sorption behavior of zinc during its transport through the soil, and therefore should be conducted to better predict the contaminant transport behavior in the surrounding soils, and that (3) the sorption behavior of zinc transport is predominantly influenced by chemical sorption-related than physical transport-related mechanism. The outcomes of this research suggest that stormwater managers should consider the heterogeneity of surrounding soil between the infiltration systems and receiving waters and its impact on the transport of heavy metals when designing stormwater infiltration systems. Otherwise, they run the risk of not delivering the desired restoration of urban ecosystems.

Problems and promise of managed recharge in karstified aquifers: the example of Lebanon

ABSTRACTManaged aquifer recharge can store surface water as safe and reliable groundwater for later recovery. However, most options are problematic in karstic aquifers due to complex hydrodynamics reducing their effectiveness and hence general applicability. River bank filtration and urban stormwater infiltration systems are among the main managed recharge approaches to cope with this complexity. Experiences in Lebanon demonstrate the viability of these and other options in karstic domains.

Use of passive sampling and high resolution mass spectrometry using a suspect screening approach to characterise emerging pollutants in contaminated groundwater and runoff

Groundwater systems are being increasingly used to provide potable and other water supplies. Due to human activities, a range of organic pollutants is often detected in groundwater. One source of groundwater contamination is via stormwater infiltration basins, however, there is little information on the types of compounds present in these collection systems and their influence on the underlying groundwater. We developed an analytical strategy based on the use of passive sampling combined with liquid chromatography/high resolution quadrupole-time-of-flight mass spectrometry for screening for the presence of pesticide and pharmaceutical compounds in groundwater and stormwater runoff. Empore™ disk-based passive samplers (SDB-RPS and SDB-XC sorbents) were exposed, using for the first time a new specially designed deployment rig, for 10 days during a rainfall event in five different stormwater infiltration systems around Lyon, France. Stormwater runoff and groundwater (via a well, upstream and downstream of each basin) was sampled. Exposed Empore™ disks were solvent extracted (acetone and methanol) and the extracts analysed using a specific suspect compound screening workflow. High resolution mass spectrometry coupled with a suspect screening approach was found to be a useful tool as it allows a more comprehensive analysis than with targeted screening whilst being less time consuming than non-targeted screening. Using this analytical approach, 101 suspect compounds were tentatively identified, with 40 of this set being subsequently confirmed. The chemicals detected included fungicides, herbicides, insecticides, indicators of human activity, antibiotics, antiepileptics, antihypertensive and non-steroidal anti-inflammatory drugs as well as their metabolites. Polar pesticides were mainly detected in groundwater and pharmaceuticals were more frequently found in runoff. In terms of detection frequency of the pollutants, groundwater impacted by infiltration was found not to be significantly more contaminated than non-impacted groundwater.

Clay beads as artificial trapping matrices for monitoring bacterial distribution among urban stormwater infiltration systems and their connected aquifers.

Stormwater infiltration systems (SIS) have been developed to limit surface runoff and flooding in urban areas. The impacts of such practices on the ecological and biological quality of groundwater ecosystems remain poorly studied due to the lack of efficient methodologies to assess microbiological quality of aquifers. In the present study, a monitoring method based on the incubation of artificial matrices (clay beads) is presented to evaluate microbial biomass, microbial activities, and bacterial community structure. Four microbial variables (biomass, dehydrogenase and hydrolytic activities, bacterial community structures) were measured on clay beads incubated in three urban water types (stormwater surface runoffs, SIS-impacted and non-impacted groundwaters) for six SIS. Analyses based on next-generation sequencing (NGS) of partial rrs (16S rRNA) PCR products (V5-V6) were used to compare bacterial community structures of biofilms on clay beads after 10days of incubation with those of waters collected from the same sampling points at three occasions. Biofilm biomass and activities on clay beads were indicative of nutrient transfers from surface to SIS-impacted groundwaters. Biofilms allowed impacts of SIS on groundwater bacterial community structures to be determined. Although bacterial communities on clay beads did not perfectly match those of waters, clay beads captured the most abundant bacterial taxa. They also captured bacterial taxa that were not detected in waters collected at three occasions during the incubation, demonstrating the integrative character of this approach. Monitoring biofilms on clay beads also allowed the tracking of bacterial genera containing species representing health concerns.

Chemical Regeneration of Manganese Oxide-Coated Sand for Oxidation of Organic Stormwater Contaminants.

Urban stormwater, municipal wastewater effluent, and agricultural runoff contain trace amounts of organic contaminants that can compromise water quality. To provide a passive, low-cost means of oxidizing substituted phenols, aromatic amines, and other electron-rich organic compounds during infiltration of contaminated waters, we coated sand with manganese oxide using a new approach involving the room-temperature oxidation of Mn2+ with permanganate. Manganese oxide-coated sand effectively oxidized bisphenol A under typical infiltration conditions and sustained reactivity longer than previously described geomedia. Because geomedia reactivity decreased after extended operation, chlorine was evaluated for use as an in situ geomedia regenerant. Geomedia regenerated by HOCl demonstrated similar reactivity and longevity to that of virgin geomedia. Chemical analyses indicated that the average manganese oxidation state of the coatings decreased as the geomedia passivated. X-ray absorption spectroscopy and X-ray diffraction showed that the reactive virgin and regenerated geomedia coatings had nanocrystalline manganese oxide structures, whereas the failed geomedia coating exhibited greater crystallinity and resembled cryptomelane. These results suggest that it is possible to regenerate the oxidative capacity of manganese oxide-coated sands without excavating stormwater infiltration systems. These results also suggest that manganese oxide geomedia may be a cost-effective means of treating urban stormwater and other contaminated waters.

Entry of biocides and their transformation products into groundwater via urban stormwater infiltration systems

Biocides are, inter alia, applied as preservatives on facades to prevent the growth of microorganisms. Their incomplete mineralization results in new compounds, so-called transformation products (TPs). Rain causes that both applied biocides and their TPs leach from facades with stormwater into the urban aquatic environment. This study is the first to investigate the introduction of the biocides Diuron, Terbutryn, and Octylisothiazolinone (OIT) and their TPs into the groundwater via urban stormwater infiltration systems. In this study, the TPs of these biocides were created by laboratory photolysis and elucidated using LC-HRMS. The results were then used to analyze TPs by LC-MS/MS in stormwater and groundwater samples, which were taken from an urban swale-trench system and from groundwater wells upgradient and downgradient of the infiltration system. A sprinkling experiment was conducted to evaluate facades as a contamination source. Biodegradation tests were conducted to determine bio-persistence of biocides and their TPs.Fourteen TPs were identified under laboratory photolysis. TP-186, TP-210, and TP-256 of Terbutryn were hitherto unknown. Nine TPs were qualitatively detected in environmental water samples. Parent compounds, TP-219 of Diuron and TP-212, TP-214, and TP-226 of Terbutryn were detected at a maximum concentration of 140 ng L−1 during stormwater events. Concentrations in groundwater were considerably below German drinking water limits, but were higher in groundwater samples downgradient from the investigated swale-trench system than in those collected upgradient. Neither the biocides nor most of their TPs were readily biodegradable under simulated surface water conditions. The results show that entry of biocides and their TPs into groundwater is caused by infiltration of urban stormwater.

Aquifer recharge with stormwater runoff in urban areas: Influence of vadose zone thickness on nutrient and bacterial transfers from the surface of infiltration basins to groundwater

Stormwater infiltration systems (SIS) have been built in urban areas to reduce the environmental impacts of stormwater runoff. Infiltration basins allow the transfer of stormwater runoff to aquifers but their abilities to retain contaminants depend on vadose zone properties. This study assessed the influence of vadose zone thickness (VZT) on the transfer of inorganic nutrients (PO43−, NO3−, NH4+), dissolved organic carbon (total -DOC- and biodegradable -BDOC-) and bacteria. A field experiment was conducted on three SIS with a thin vadose zone (<3 m) and three SIS with a thick vadose zone (>10 m). Water samples were collected at three times during a rainy period of 10 days in each infiltration basin (stormwater runoff), in the aquifer impacted by infiltration (impacted groundwater) and in the same aquifer but upstream of the infiltration area (non-impacted groundwater). Inorganic nutrients, organic matter, and dissolved oxygen (DO) were measured on all water samples. Bacterial community structures were investigated on water samples through a next-generation sequencing (NGS) scheme of 16S rRNA gene amplicons (V5-V6). The concentrations of DO and phosphate measured in SIS-impacted groundwaters were significantly influenced by VZT due to distinct biogeochemical processes occurring in the vadose zone. DOC and BDOC were efficiently retained in the vadose zone, regardless of its thickness. Bacterial transfers to the aquifer were overall low, but data obtained on day 10 indicated a significant bacterial transfer in SIS with a thin vadose zone. Water transit time and water saturation of the vadose zone were found important parameters for bacterial transfers. Most bacterial taxa (>60%) from impacted groundwaters were not detected in stormwater runoff and in non-impacted groundwaters, indicating that groundwater bacterial communities were significantly modified by processes associated with infiltration (remobilization of bacteria from vadose zone and/or species sorting).

Clogging Characteristics of Stormwater Infiltration System According to Filter Media Conditions

Filter clogging in stormwater infiltration system affects significantly on the removal efficiency and facility lifespan. Although contaminants are removed by clogging process, excessive clogging could reduce removal efficiency and terminate function. Thus, to understand influencing factors on the optimal design, is essential to accomplish effective operation and proper lifespan. In this study, effects of a particle diameter and layering of media on contaminant removal and clogging were examined by conducting a series of 1-D column infiltration tests. Pure, mixed and layered filters built with sand with particle size and gradation of 0.85~2 mm and 2~4.75 mm were tested. It was found from the tests that a pure small particle and a mixed filters clogged faster than a pure large particle filter. The filter layered as a large particle layer with thickness of 325 mm overlying a small particle layer with thickness of 250mm clogged slowly compared the filters involving small particles, but faster than the large particle filter. As a result, it was verified that the filter involved with small particles could be designed to improve removal efficiency. The filter composed of a large and a small particle layers was also verified to be the more efficient filter for the case where a long life span was required in addition to removal efficiency. Keywords: Stormwater Management System, Clogging, Filter Media