Urban Stormwater and Groundwater Quality: Pathways, Risks, and Green Infrastructure Solutions

Abstract

The development of urban areas and the proliferation of impervious surfaces have significantly altered natural hydrological cycles, resulting in an increase in stormwater runoff and substantial risks to groundwater quality. This review synthesizes current research on the transport mechanisms of stormwater contaminants, including toxic elements, nutrients, pathogens, and emerging pollutants such as microplastics and pharmaceuticals, into aquifers. This study analyzes the physicochemical and biological processes that affect pollutant mobility and retention in urban soils, emphasizing the vulnerability of groundwater systems, particularly in areas with permeable soils and shallow water tables. The article evaluates a range of green infrastructure (GI) and low-impact development (LID) strategies—including rain gardens, bioswales, infiltration basins, constructed wetlands, and urban forestry—to assess how effectively they can mitigate stormwater pollution and improve groundwater protection. Case studies from North America illustrate the practical implementation and performance of GI systems, emphasizing the importance of site-specific design, monitoring, and adaptive management. The review also discusses global policy frameworks and community engagement strategies that support sustainable stormwater management. Ultimately, it advocates for an integrated, multidisciplinary approach that combines engineering, ecological science, and public policy to safeguard groundwater resources in the face of climate variability and urban expansion.

1. Introduction

As the source of freshwater for terrestrial, riparian, and aquatic ecosystems, groundwater plays a crucial role in human communities as well as diverse ecosystems [1]. It provides essential ecosystem services such as habitat provision, water purification, and nutrient cycling. In cities and urban areas, groundwater is increasingly managed as the receiving reservoir for stormwater in infiltration basins, permeable pavements, and distributed green-infrastructure cells to detain peak flows, reduce flood risk, and intentionally recharge aquifers to support baseflow and drought resilience [2]. Urban development has significantly altered the natural hydrological cycle by increasing impervious surfaces such as rooftops, roads, and parking lots, which seal the ground and prevent water infiltration and increase stormwater runoff [3]. Many models predict that climate change will intensify short-duration rainfall events across most of the world’s major cities [4]. As rainfall intensity increases, surface runoff generation increases, both in terms of total quantity and peak flow, particularly in urban catchments with reduced soil storage capacity [5]. In addition, increased impervious surfaces contribute to urban heat islands, potentially increasing rainfall and flooding [6]. Increased imperviousness leads to reduced groundwater replenishment, decreased soil moisture, and decreased evapotranspiration, disrupting the entire hydrological cycle [6].

The runoff of stormwater in urban areas contributes significantly to the pollution of both groundwater and surface waters [7]. These contaminants include toxic elements, nutrients, pharmaceuticals, and emerging substances of concern such as perfluoroalkyl substances [8]. The movement and potential effects of chemicals in soil are influenced by their physical properties, including solubility, volatility, and their interaction with soil properties. Pollutants, such as heavy metals, can accumulate in upper soil layers, but others, such as nitrates, can easily permeate groundwater due to their high solubility [9]. As these contaminants pose toxicity, genotoxicity, and carcinogenic risk to aquatic and terrestrial organisms, they are evidently having significant impacts on water quality and ecosystems. Additionally, the high transport rate of contaminants from stormwater runoff to freshwater bodies could limit opportunities for biogeochemical cycling and contaminant degradation [10]. In order to protect water resources and develop effective stormwater management strategies, it is crucial to understand how these pollutants are transported, behave, and how they can be remedied.

Green infrastructure (GI) can be used to manage stormwater in urban areas, providing multiple ecosystem services and environmental benefits [11]. Different GI techniques, such as rain gardens, bioswales, green roofs, and permeable pavements, have demonstrated their ability to reduce runoff volume, peak flows, and pollutant loads. Through mechanisms such as adsorption, sedimentation, and plant uptake, these systems can effectively remove sediments, toxic elements, nutrients, and pathogens. While GI performance can vary depending on factors such as climate and scale, it generally performs better than traditional stormwater management methods [11]. Furthermore, GI can improve urban aesthetics, recharge groundwater, and provide habitat for wildlife [12].

This review article will focus on sources and composition of stormwater runoff, groundwater contamination mechanisms, and mitigation strategies, particularly those that have been developed recently.

2. Sources and Composition of Stormwater Runoff

Stormwater runoff contributes significantly to water pollution, affecting both surface and groundwater. Among the most important pollutants are toxic elements, pesticides, and pharmaceuticals [13,14]. A majority of urban runoff pollution, including heavy metals like copper, lead, and zinc, comes from vehicular emissions, industrial emissions, and atmospheric deposition that can negatively impact water quality [15,16]. These metals can accumulate up to 100 times higher in urban environments than background levels, posing a significant threat to aquatic ecosystems [17]. Additionally, heavy metals are highly toxic and mobile, leading to adverse health effects, including neurological problems, organ dysfunction, and digestive problems [18,19]. As toxic elements can be adsorbed onto soil particles, there is a strong correlation between heavy metal concentrations in runoff and particle size, with concentrations increasing as particle size decreases [20]. When considering toxic elements in stormwater, it is crucial to consider the quality of urban storm runoff in arid and semi-arid regions that can fluctuate with extended periods of dry weather and intense rainfall. A study conducted by Conrad et al. [21] found that heavy metal concentrations were higher in the first flush of rain after a long dry period.

Stormwater runoff from urban areas is a major source of nitrogen (N) pollution in water bodies. Residential runoff is dominated by dissolved organic nitrogen (DON), followed by particulate organic nitrogen (PON), nitrate (NO₃), and ammonium (NH₄) [22]. Air pollution and atmospheric deposition, chemical fertilizers, and soil organic matter are the primary sources of NO₃-N in street runoff. In residential stormwater, atmospheric deposition contributes up to 70% of NO₃-N [23]. Several factors influence nitrogen transport, including rainfall intensity, antecedent dry periods, and catchment characteristics [22]. Based on a recent study by Wang et al. [24], roof runoff is the major source of nitrate during light and moderate rainfall, while road runoff contributes the most during heavy rainfall. In addition, their findings indicated that road runoff was the primary source of PON during light and moderate rainfall, while drainage sediment was the main source of PON during heavy rainfall. The evaluation of rainfall characteristics on nitrogen species in urban runoff found that only rainfall intensity and depth are significantly correlated with nitrate concentrations in road and roof runoff [24]. The results showed that the composition of road runoff largely consists of NH₃-N, while erosion of pervious surfaces and leaching of litter can result in elevated DON/TDN values. To develop effective strategies for reducing nitrogen export and improving water quality in urban areas, it is crucial to understand the sources and transport mechanisms of nitrogen.

Stormwater runoff contains a variety of microbial contaminants, including pathogens and fecal indicators, which pose health risks [25]. A variety of factors, including land use, seasons, and precipitation, influence microbial populations in the stormwater runoff [26]. A higher concentration of fecal indicator bacteria was observed in watersheds with more development and during storm events compared to conditions in which it was dry [27]. A recent study, representing one of the largest-scale databases of enteric pathogens in U.S. roof runoff collections, showed an association between the physicochemical parameters (such as COD, TDS, TSS, and VSS) of roof runoff and the concentrations of enterococci [28]. Additionally, this study found that Salmonella spp. detection was influenced by geographical location and the number of antecedent dry days prior to a rain event. Furthermore, the presence of Giardia duodenalis in roof runoff was positively correlated with rainfall depth. If these contaminants are present in stormwater, they can contaminate groundwater, particularly in areas with geologically sensitive conditions [29]. There is, however, some evidence that fine-grained sediments (silty till and fine alluvium) are protective by reducing the concentrations of microbial contaminants [29]. In another study, plant-based biofilters remove more indicator virus MS2 when measured by RT-qPCR than non-vegetated biofilters [30]. It is important for water authorities to investigate treatment options and implement water-sensitive urban design practices in order to mitigate health risks.

3. Mechanisms of Groundwater Contamination

As a result of stormwater infiltration practices, groundwater may be contaminated with a variety of contaminants, including toxic elements, nutrients, pathogens, and emerging contaminants [9]. Environmental factors such as pollutant concentration in runoff, soil properties, and geological setting influence the contamination potential [31]. The majority of toxic elements in soil are retained in the upper layers through adsorption; however, nitrates and some pathogens, particularly viruses, can reach the groundwater more readily [29]. In the long run, the finite sorption capacity of soil particles may lead to breakthrough and groundwater contamination. The amount of precipitation and the ratio of chloride to bromide in groundwater have been linked to microbial populations in the groundwater [29]. There is a variation in retention of nutrients such as nitrogen and phosphorus, with phosphorus being removed mainly by precipitation and adsorption, while nitrate is poorly retained due to its high solubility [32].

It has been studied that fine-grained sediments, such as fine alluvium including particles ranging from silt to clay, can significantly reduce the transport of contamination to aquifers [33]. While bioretention and fine media filtration can effectively reduce metal concentrations, they may also leach nutrients [34]. The potential for groundwater contamination caused by stormwater infiltration is more important, particularly in areas with sandy soils and shallow water tables [35]. In practice, soils in urban parks also retain metals and nutrients, with accumulation patterns influenced by the type of vegetation and the age of the park [36]. Some strategies to mitigate groundwater contamination risks associated with bioretention systems include periodically replacing upper soil layers in infiltration systems and properly treating stormwater before it infiltrates the ground, which can prevent hydraulic failure and excessive metal accumulation [9,31,34]. Despite potential risks associated with infiltration practices, they can be effectively managed when site selection and design considerations are taken into account.

As a result of increasing anthropogenic activities, the abundance of emerging pollutants such as microplastics in the environment is increasingly significant, which can be accumulated and contaminate the subsoils [37]. In addition to their own toxic additives, microplastics tend to absorb and transport a wide range of hazardous substances, including antibiotics, pesticides, and heavy metals [38,39]. High concentrations of microplastics have been found in surface runoff, and it is considered one of the significant sources of microplastic contamination in groundwater [40].

4. Management of Stormwater Pollution Using Green Infrastructure

In urban areas, pollutants transported from impervious surfaces into aquifers pose a significant threat to groundwater quality. To minimize groundwater contamination and promote a clean natural environment, stormwater management can use structural and non-structural green infrastructure (GI). The use of green infrastructure and low-impact development (LID) as an innovative approach to mimic natural hydrological processes can help manage stormwater in a more environmentally friendly manner than traditional stormwater management techniques. It has been studied that LID practices reduce runoff volume, improve water quality, and promote groundwater recharge [41,42,43]. Additionally, GIs can be used to enhance resilience to extreme weather events, protect transportation infrastructure, and improve ecosystem services [43]. In this section, we look at several green infrastructures and low-impact development alternatives, their mechanisms, and their effectiveness in protecting groundwater.

4.1. Rain Garden

A rain garden (also known as bioretention basin) is a shallow, vegetated depression engineered to capture and treat runoff as it passes through a layered profile that mimics the natural soil–plant filtering process. From top to bottom, typical anatomy includes a surface ponding zone with native or adapted vegetation, a mulch/organic layer, an engineered filter medium, and a drainage/storage layer that may house a perforated underdrain. Many modern systems incorporate an internal water storage (IWS) or saturated zone—created by raising the underdrain outlet—to promote denitrification while the upper media and vegetation support filtration, sorption, and evapotranspiration processes [44].

Rain gardens employ a suite of integrated physical, chemical and biological mechanisms that allow them to remove various contaminants. Sediments can be removed via settling and filtration, while toxic elements are removed via sorption, precipitation, cation-exchange, and redox transformations. In addition, rain gardens can remove pathogens via filtration, attachment to media/biofilms and microbial inactivation, while nutrients can be removed via plant uptake, nitrification in aerobic zones, denitrification in saturated zones for nitrogen, and sorption and precipitation for phosphorus [45,46,47,48]. Nitrogen species in stormwater, including ammonium, nitrite, and nitrate, can be partially removed in rain gardens through microbial processes. These processes include the mineralization of organic nitrogen into ammonium, the oxidation of ammonium to nitrate, the denitrification of nitrate into nitrogen gas, the assimilation of dissolved nitrogen by biomass, and the immobilization of nitrogen into plant and microbial biomass. Although typical rain gardens are less effective in removing nitrates, as nitrates do not bind to most soil types, adding carbon amendments [10] and artificial electron donors such as wood chips, mulch, and limestone [11], achieving optimum pH (pH 6.4), and maintaining wet conditions in deep soil can promote significant reductions in nitrate levels. Phosphorus is removed from stormwater mainly by the adsorption mechanism. During sorption/immobilization/fixation processes, orthophosphate is fixed to solid-phase particles, such as organic matter, iron oxides, and aluminum oxides [5]. A study conducted by Wadzuk et al. [5] has found that phosphorus removal capacity is higher in sandy soils that contain minerals such as calcium, iron, and aluminum.

In rain gardens, soil amendments delay saturation, increase sorption capacity, limit pollutant mobility, and increase metal/organic compound bioaccumulation/biotransformation. Chen et al. [49] reported nutrient removal increases of 34–99% and heavy metal removal of 25–100% when biochar-amended media were employed. Likewise, amendments of mineral-rich residuals such as water treatment residuals (WTRs) or iron/aluminum oxide-rich sands have been shown to significantly enhance dissolved phosphorus capture when incorporated into the media; in mixed-flow bioretention columns with 10% (v/v) WTRs, total P removal improved from ~83% to ~97% [50]. As part of the rain garden design process, soil/media type, vegetation, depth of media, and footprint/area relative to drainage must be taken into consideration [51]. A well-engineered planting media—typically a sand or loamy sand matrix with limited clay and organic content—ensures rapid infiltration while supporting vegetation and pollutant removal processes [52]. Additionally, plants play a critical role in rain gardens to remove contaminants before they reach groundwater. Ideally, the plants for rain gardens are native plants capable of tolerating both periodic ponding and drying [53]. In addition, invertebrates in soil can retain and remove pathogens, toxic elements, nutrients, and other contaminants, while also influencing plant growth and water infiltration [54].

4.2. Infiltration Basin

An infiltration basin is a shallow, bermed, or excavated impoundment that temporarily stores stormwater and allows it to percolate into underlying soils. Functionally, it reduces surface runoff and peak flow, promotes groundwater recharge, and treats water primarily by settling in the basin, followed by filtration, sorption, and biodegradation as water moves through the vadose zone [55]. Because the practice relies on native soil permeability, infiltration basins are prone to clogging due to a low percolation rate. Bardin et al. [56] found that pre-treatment facilities, such as sedimentation basins, could enhance the removal of pollutants and reduce the risk of clogging. It has been suggested that using a combination of silty soil and sand layers is more effective in preventing clogging than using sand and gravel alone [57]. Despite infiltration systems’ tendency to retain toxic elements in upper soil layers, groundwater contamination can occur, particularly with nitrates, because they are highly soluble [9]. Therefore, using infiltration basins requires careful site screening for adequate vertical separation from groundwater, setbacks from wells, and avoidance of “hot-spot” land uses, as well as robust pretreatment such as forebays, swales, or hydrodynamic devices to control sediment loading and clogging.

Contaminant removal effectiveness in infiltration basins depends on soil characteristics, pretreatment, contributing land use, and maintenance. Particulate pollutants such as TSS and particle-bound phosphorus/metals are effectively removed by physical retention, while dissolved species, including nitrate, chloride, and trace organics, depend more on soil redox conditions and contact time. A recent study conducted by Tedoldi et al. [58] shows that sediments accumulating on basin floors can concentrate metals and organic micropollutants—supporting the need for sediment monitoring and maintenance—while Edward et al. [59] study of infiltration wells/dry wells highlights the potential risks to groundwater quality if pretreatment is inadequate or if infiltration shortcuts the biologically active soil zone. For optimal performance and minimized contamination risks, frequent maintenance, including periodic soil replacement, is recommended [9].

4.3. Bioswale

A bioswale is one of the best management practices (BMPs) commonly used to capture and treat runoff from impervious surfaces, like roads and parking lots, and improve water quality. A bioswale is a linear, vegetated open channel engineered to convey, slow, and treat stormwater through a combination of shallow ponding, sedimentation, filtration through vegetation and soil, and limited infiltration where soils allow. Variants include dry swales with engineered underdrained media for filtration and wet swales that intersect groundwater or maintain wetland-like conditions. When an underdrain system is included in the design of bioswales, they are referred to as filtration BMPs, and there is less concern regarding groundwater contamination from stormwater. However, bioswales without an underdrain function as infiltration BMPs, which slow down the stormwater flow, trap sediment, and remove pollutants, but eventually infiltrate the groundwater.

By spreading and slowing flow, bioswales enhance sedimentation of particulates and particle-bound phosphorus and metals, while filtration, sorption, plant uptake, and microbial processes address finer particles and some dissolved pollutants. Ekka et al. [60] indicate that well-maintained dry swales with retention dams perform better in reducing runoff volume and removing sediment and heavy metals, while wet swales tend to be more effective for nitrogen removal via longer contact times and anoxic microzones. Although bioswales temporarily mitigate stormwater pollution and delay the release of pollutants into surface waters, the long-term sustainability of this BMP in preventing groundwater contamination is questionable. Several studies have shown that due to the limited storage capacity of the soil, bioswales can only store a small percentage of dissolved ions and metals [61,62]. To enhance bioswale performance, particularly where dissolved nutrients and trace organics are a concern, engineered media amendments can be added to the sand. A study by Buates et al. [63] indicates that biochar (1–4% by weight) with compost (2% by weight) has improved multi-pollutant removal in pilot-scale bioswale–bioretention trains. Furthermore, recent studies have shown promising results for zeolite [64] and expanded shale media [65], which can aid in suspended solids and ammonium retention.

Table 1. A summary of soil amendment types, their removal mechanisms and efficiency.

Soil Amendment Type	Dose (% v/v or % w/w) *	Hydraulic Impacts	Primary Contaminants	Removal Efficiency	Removal Mechanisms	References
Iron-enhanced sand (elemental Fe mixed in sand)	Specified by weight: 5–8% iron (w/w) of iron–sand mix	Keep Fe ≤ 8% (w/w) to avoid cementation/clogging; design for ≤48 h drawdown; pretreatment required	Dissolved & total phosphorus	>90% net retention of total P (TP)	Ligand exchange/adsorption of phosphate onto Fe(III) oxyhydroxides; co-precipitation as Fe-P minerals; filtration of particulate P	[66]
Zeolite blended into soil mixture	10–20% v/v replacing a portion of sand	Saturated Ksat similar to or higher than standard BSM in columns	Ammonium, Nitrate	87% ammonium reduction, increased nitrate due to leaching	Cation exchange in zeolite	[67]
Al-based drinking water treatment residuals (WTR)	5–10% v/v mixed into sand	Mixed layer: no adverse flow; solid layer: restricted flow & bypass.	Phosphorus species (TP, PP, DP)	97% total phosphorus (TP) mass removal, 98.2% particulate phosphorus (PP) removal	Ligand exchange/inner-sphere complexation on Al/Fe (hydr)oxides; filtration of particulate P	[50]
Biochar (red pine woodchip) blended with sand	Research range 2–10% v/v	Often increases porosity and storage; Ksat impact varies by feedstock/size	Zinc (Zn), total inorganic nitrogen (TIN), TP, E. coli	Improved Zn and TIN retention, >90% TP achieved, no clear E. coli improvement.	Surface adsorption (oxygenated functional groups) for metals; ammonium sorption and nitrification suppression; particulate filtration	[66]
Granular Activated Carbon (GAC) and biochar	N/A	Headloss rises with loading; maintenance on breakthrough; pretreatment critical	PAHs & PCBs	99.8% PAHs reduction, 97.7% PCBs reduction	Hydrophobic adsorption on high surface area carbon	[68]

* % v/v means the percentage ratio of soil amendment volume to native soil volume. % w/w means the percentage ratio of soil amendment weight to native soil weight.

below summarizes several recent studies that implement soil improvement alternatives in bioswales.

4.4. Urban Wetland

Urban (constructed) stormwater wetlands are engineered, shallow basins with open-water and vegetated zones that slow, spread, and store runoff, thereby removing contaminants and lowering risks to contaminating groundwater, particularly in shallow aquifers. A variety of physical, biological, and chemical processes are employed to remove pollutants, including sediment, nutrients, toxic elements, and pathogens [69,70]. In addition to decreasing water velocity, wetland vegetation facilitates sedimentation, absorbs nutrients, and fixes metals [69]. The wetlands’ microbial community plays a crucial role in the removal and transformation of nutrients, particularly nitrogen [70]. In general, constructed wetlands outperform detention ponds in terms of pollutant removal efficiency; however, their performance varies depending on factors such as pollutant loading rates, hydraulic retention time, and system design [71]. To maximize pollutant removal efficiency, design considerations such as pretreatment, water depth, and plant species selection must be carefully considered. In addition to storing water, wetlands serve multiple purposes, including peak-flow attenuation, recreation, and providing habitat for wildlife [70].

Organic matter, phosphorus, bacteria, and suspended solids can be effectively removed through filtration in urban constructed wetlands. In addition, gravitational settling of particle-bound pollutants, sorption of metals and hydrophobic organics to organic/mineral substrates and biofilms, plant uptake of nitrogen and phosphorus, and redox-driven microbial transformations are among the pathways in wetlands that reduce contaminants before they reach the groundwater. Several recent studies have shown that urban constructed wetlands have high removal efficiencies in removing major pollutants such as total suspended solids (TSS), total phosphorus (TP), total nitrogen (TN), and fecal coliform [72,73,74]. In addition, constructed wetlands have shown a potential to improve water quality and reduce oxygen-consuming pollutants such as biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD) up to 80% and 74%, respectively [72]. Since plant uptake plays a vital role in TP and TN removal, a reduction in ambient temperature has been shown to decrease the removal of total N, total P, and particulate P in autumn and winter [74].

In addition to conventional pollutants that urban wetlands are capable of removing, recent studies investigated the effectiveness of constructed wetlands to remove hydrophobic organic pollutants, such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and emerging contaminants such as pharmaceuticals and personal care products (PPCPs). A review study on the removal of PAHs using urban wetlands indicates that PAHs in stormwater can be substantially attenuated in urban wetlands via a combination of particle capture, sorption, and aerobic/anaerobic biodegradation [75]. Another study conducted by Al-Benna et al. [76] highlights the removal of many PAH species in stormwater treatment systems and suggests adding organic carbon to strengthen the treatment efficiency. Furthermore, wetlands provide the anaerobic–aerobic interfaces needed for reductive (anaerobic) dechlorination of PCBs followed by aerobic oxidation of less-chlorinated congeners [77,78]. Similarly, pharmaceutical and personal care products (PPCPs) can be removed in urban wetlands by settling of particle-associated fractions and by sorption, plant uptake, and microbially mediated biodegradation across aerobic–anaerobic zones. A review article by Zheng et al. [79] studies organic micropollutant (OMP) removal in stormwater and lists constructed wetlands as among the more effective nature-based options for PPCP/OMP control in stormwater treatment trains.

4.5. Urban Forestry and Vegetative Buffer

Urban forestry and vegetative buffer zones serve as nature-based stormwater management systems, intercepting, slowing, and treating runoff before it reaches conveyance systems or receiving waters. In an urban forest, the tree canopy intercepts rainfall and reduces the instantaneous runoff volume, while the roots and soil structure enhance infiltration and delay the flow paths. The vegetated buffer—typically a strip of trees, shrubs, and grasses located along watercourses or between impervious surfaces—further filters pollutants by trapping sediments, adsorbing soluble contaminants, and stabilizing soils to reduce erosion. A recent review study by Dowtin et al. [80] suggests that increasing urban tree cover has a significant influence on stormwater runoff response, achieved through a combination of interception, infiltration, and evapotranspiration.

The effectiveness of urban forests and vegetative buffers in removing pollutants depends on factors such as canopy structure, soil permeability, root zone volume, vegetation type, leaf characteristics, and branching structure [80]. Studies show that trees and buffer vegetation can reduce nutrient loads, sediments, and heavy metals by enabling infiltration through conditioned soils and providing residence time for microbial and physicochemical processes [81]. Another study by Selbig et al. [82] found that urban tree systems reduced runoff volume by approximately 5–15% over a range of storm conditions, with greater benefits in catchments with higher canopy cover and fewer impervious areas. Furthermore, the rainfall intensity and duration can affect the effectiveness of urban forests, as shown in a study by Kuehler et al. [83]. They found that trees are most effective during short, low-intensity storms, and their impacts decrease with increasing rainfall volume and intensity. It has been demonstrated that trees are effective in managing stormwater on watershed scales when integrated with other green infrastructure strategies [84].

To synthesize the role of nature-based stormwater control measures in protecting both surface and groundwater quality and provide a comparative understanding of how different stormwater control measures contribute to water quality improvement and groundwater protection,

Table 2. Summary of common Best Management Practices (BMPs) used for stormwater pollution control and groundwater protection.

BMP Type	Primary Function	Target Pollutants	Typical Removal Efficiency (%)	Potential for Groundwater Contamination	Pretreatment Requirements	Lining or Separation Measures	Recommended Siting Constraints	Suitability for Sensitive Aquifers	References
Rain garden (bioretention basin)	Filtration + infiltration; volume reduction; evapotranspiration	TSS, nutrients (TN, TP), dissolved metals (Cu, Zn), hydrocarbons, microplastics	TSS 70–95; TP 40–70; TN 30–60; metals 40–80; microplastics 84–96	Low–Moderate (higher for dissolved N/metals if unlined and shallow water tables)	Forebay, filter strip, grass channel, gravel diaphragm for larger drainage areas	Optional liner or underdrain; ≥0.9–1.0 m separation to groundwater recommended	Small drainage areas (<2 ha); slopes ≤ 5%; avoid industrial ‘hot spots’ unless lined	Conditionally suitable (lined/underdrained preferred in vulnerable aquifers)	[84,85,86,87]
Infiltration basin	Infiltration; groundwater recharge; peak flow reduction	TSS, particulate nutrients & metals; some dissolved species	TSS > 60–90; nutrients/metals variable; Zn reduction ~65%	Moderate–High (depends on pretreatment and soil attenuation)	Sediment forebay, vegetated strip, hydrodynamic separator	Maintain vertical separation from groundwater; liners where vulnerability is high	Permeable soils; avoid contaminated source areas; maintain setbacks from wells	Conditionally suitable (requires pretreatment, separation, and soil capacity)	[55,88]
Bioswale (vegetated/grassed swale)	Conveyance, filtration, and infiltration; velocity control	TSS, TP, TN, metals, hydrocarbons	Dry swales: TP 65, TN 50, metals 80–90, TSS 80–90; Wet swales: TP 20, TN 40, metals 40–70	Low–Moderate (higher in permeable soils with shallow groundwater)	Upstream sediment forebay or filter strip; check dams to increase residence time	Underdrain or soil amendment for low-permeability sites; liners where infiltration discouraged	Long, shallow slopes (1–2%); avoid sustained baseflow unless designed as wet swale	Often suitable with pretreatment; conditionally suitable in vulnerable aquifers	[89,90]
Urban wetland (constructed/stormwater wetland)	Settling, filtration, plant uptake, denitrification; flow regulation	TSS, TP, TN, metals, hydrocarbons, organics, CECs	TSS 60–90; TP 40–70; TN 30–60; metals > 50	Low–Moderate (lined or low seepage; risk if unlined over permeable soils)	Forebay/sedimentation cell; inlet energy dissipation	Liners or low-permeability subgrade common; seepage control recommended	Adequate area; avoid high seepage foundations; provide bypass for extreme storms	Generally suitable (lined or low-seepage design preferred)	[91,92]
Urban forestry & vegetative buffer	Interception, evapotranspiration, shallow infiltration, shading, filtration	Runoff volume, TSS, TP, TN, temperature, metals, hydrocarbons	Vegetated filter strips: TN 56, TP 66, TSS 86; runoff reduction ~51%	Low (primarily surface and canopy processes)	Stable vegetated strip; level spreaders to diffuse concentrated flow	Not typically lined; maintain buffer width and channel separation	Gentle to moderate slopes; avoid concentrated inflow without dispersion	Suitable (recommended for aquifer protection and receiving waters)	[82,93,94]

summarizes commonly implemented Best Management Practices (BMPs) and Low-Impact Development (LID) systems reported in the recent literature. Various practices have different hydrologic functions, pollutant removal efficiencies, and implications for groundwater contamination risks. This table highlights how infiltration-based systems such as bioretention cells, infiltration trenches, and permeable pavements are highly effective at reducing surface runoff and pollutants, but require careful design to prevent contaminants from migrating downward. Alternatively, filtration- and detention-based systems, such as constructed wetlands and vegetated swales, often improve water quality in shallow or vulnerable aquifer areas.

5. Case Studies and Monitoring Efforts

Stormwater runoff poses a significant risk to groundwater quality, especially in urban areas with impervious surfaces that prevent natural infiltration. A number of case studies and monitoring efforts have demonstrated that stormwater management practices have a complex interaction with groundwater systems. The mounding of groundwater beneath stormwater infiltration basins is a significant problem in urban water management. The formation of mounds reduces soil infiltration and soil filtration capacity [95]. A number of factors influence mound height, including sedimentation layer thickness, soil hydraulic conductivity, and aquifer characteristics. There are also individual factors that influence infiltration rates in basins, such as the depth of the groundwater table [96] and the presence of clogging layers [97]. Models such as SWMM, HYDRUS-2D, and MODFLOW have been used to simulate runoff volume and flow rate, mounding, and contamination transport [98]. These models can be used to determine mound height and extent, which is crucial to assessing the impact on nearby structures. Understanding these dynamics is essential in designing and managing infiltration basins to maximize hydraulic load while minimizing negative effects. Figure 1 illustrates a schematic illustration of these models in simulating stormwater flow rate, mounding, and contaminant transport.

In urban areas, the implementation of green stormwater infrastructure (GSI) is becoming increasingly common to manage runoff and enhance water quality. A study in Detroit and other mid-Atlantic cities has shown that GSI can reduce hydrologic flashiness, with watersheds featuring higher GSI exhibiting a 44% decrease in peak runoff and a 26% reduction in runoff events [99]. RecoveryPark in Detroit, Michigan, is a good example of urban green infrastructure for stormwater management. An analysis of pre-construction conditions revealed complex urban hydrologic fluxes, including unusual exchanges between sewers and groundwater [100]. GSIs, such as bioswales, are beneficial for mitigating flooding and the urban heat island effect by storing stormwater and allowing it to evaporate [100]. The effectiveness of GSI depends on several factors, including its location within the watershed and the extent to which it is implemented [101]. The long-term effectiveness of GSI for stormwater management may be influenced by changing precipitation patterns, which may require adaptive designs [100].

In outdated infrastructures that utilize combined sewer systems, urban stormwater management and combined sewer overflows (CSOs) can be enhanced with green infrastructure practices, including porous pavements, rain gardens, and rain barrels. In Buffalo, New York, Roseboro et al. [102] studied the impact of climate change and GI on CSO and found that without GI, CSO volumes in 2070–2099 could increase by 11–73% compared to historic 1970–1999 rainfall periods. They demonstrated that implementing porous pavements as GI can reduce future CSO volumes by 23% to 31% [102]. In this project, a multi-objective tool combining SWMM (Stormwater Management Model) and OSTRICH (Optimization Software Toolkit for Research Involving Computational Heuristics) was developed to optimize the placement of porous pavements [103]. In another case study from the Province of Quebec in Canada, an integrated modelling and optimization study showed that combining GI, grey infrastructure, and real-time control (RTC) could achieve CSO volume reduction of up to 98% for the study sub-catchment, whereas GI alone or grey alone achieved lower reductions. Additionally, their cost analysis indicates that combining GI, grey infrastructure, and RTC scenarios provided a ~95% reduction at a reduced cost [104].

These case studies underscore the importance of monitoring and evaluating stormwater management practices, highlighting the need for site-specific assessments that consider factors such as soil composition, groundwater depth, and infiltration system design. It is essential to conduct research and monitor stormwater management strategies in order to ensure their effectiveness in protecting groundwater resources.

6. Other Mitigation Strategies

6.1. Policy and Regulatory Measures

In order to effectively manage stormwater, robust policies and regulations such as the EPA’s National Menu of Best Management Practices for Stormwater are needed. In addition, local governments may adopt ordinances requiring green infrastructure in new developments and retrofits [105]. Furthermore, property owners can benefit from grant and tax credit incentives for adopting stormwater mitigation practices [106]. In addition to regulatory instruments, incentives, and outreach policies, citizen stormwater management can be promoted, fostering citizen participation in green infrastructure initiatives [106]. According to a game theory analysis, municipal regulation has the greatest effect on reducing pollution; however, the optimal policy approach will be determined by a variety of factors, including politics and financial concerns [107]. It should be noted that stormwater policy impacts are strongly influenced by spatial location [107], raising issues of social equity and environmental justice.

To understand the diversity of policy frameworks that shape stormwater management and groundwater protection worldwide,

Table 3. Global stormwater & groundwater policy comparison.

Region/Country	Policy Goals	Groundwater Protection Emphasis	Pollutant Control Priorities	Stormwater Quality Standards	References
United States	Reduce pollutant loads to receiving waters; control MS4, construction & industrial stormwater; encourage GI/LID; support TMDLs & climate resilience	Moderate (protect via siting/design of infiltration BMPs; prevent hot-spot infiltration; Underground Injection Control programs where applicable)	TSS/sediment, nutrients (N, P), metals (Cu, Zn), hydrocarbons, bacteria; growing focus on PFAS & microplastics	Primarily narrative standards in permits (BMP-based) with state-specific numeric criteria/TMDLs; monitoring & adaptive management for MS4s	[108,109]
European Union	Achieve good ecological & chemical status; prevent/limit groundwater pollution; implement river-basin planning; update watch lists for emerging pollutants	High (threshold values, trend reversal, prevention/limitation of hazardous substances)	Priority substances (e.g., PAHs, metals), nutrients, pesticides, pharmaceuticals/PFAS via watch lists (i.e., regulatory tools used to identify and monitor emerging pollutants)	Environmental Quality Standards (EQS) for surface waters; Groundwater Directive (GWD) threshold values; member states set additional standards & source controls for urban runoff	[110,111]
China	Urban flood mitigation; stormwater retention/infiltration; water quality improvement; multi-benefit GI/LID uptake	Moderate (infiltration with attention to soil/aquifer sensitivity; integration with urban water quality goals	TSS, nutrients, heavy metals, hydrocarbons; urban diffuse sources	Sponge City technical guides set performance targets (e.g., rainfall capture/retention) and water quality design criteria; city-specific standards	[112,113]
Australia	Integrate WSUD; reduce pollutant loads; increase infiltration/reuse; climate resilience & liveability co-benefits	Moderate (guidelines address infiltration siting/soil constraints; protection near groundwater-dependent ecosystems)	Nutrients, sediments, gross pollutants; metals & hydrocarbons where relevant	State/municipal performance objectives for stormwater quality (e.g., percent load reductions) and Water Sensitive Urban Design (WSUD) guidelines; monitoring & maintenance requirements	[114,115]
India	Protect groundwater quality; manage urban stormwater; promote recharge; strengthen legal/institutional frameworks	High (policy emphasis on recharge & pollution control; ongoing reforms)	Nitrates, fluoride, arsenic; urban diffuse pollution (nutrients, metals, pathogens); emerging contaminants	National/state rules for water quality; city-level stormwater bylaws; expanding use of recharge structures with quality pretreatment	[116,117]
Japan	Control groundwater extraction & pollution; manage urban flooding; integrate water cycle in planning	High (extraction/pollution control; quality protection via national acts and local ordinances)	Nitrates, VOCs/solvents, metals; coastal salinization	National standards through Water Pollution Prevention Act; local ordinances guide stormwater quality & infiltration siting	[118,119]
Canada	Flood risk reduction; water quality protection; asset management; GI adoption; climate resilience	Moderate (province/municipal policies integrate source control & infiltration with groundwater safeguards)	Sediment, nutrients, metals; road runoff contaminants; emphasis on cold-climate performance	Province/municipal objectives (BMP-based) with monitoring; asset management and integrated watershed plans	[120]

compares the major regulatory approaches and quality standards adopted since 2020. This table synthesizes information from recent review studies and policy analyses to illustrate how different jurisdictions have balanced water-quality objectives, groundwater vulnerability, and stormwater design performance. Although most regions share the goal of reducing pollutant loads and improving infiltration through green infrastructure, they differ in their regulatory focus, implementation mechanisms, and numeric performance targets. For example, the United States commonly requires storing 1 inch of rain on-site, but China’s Sponge City program sets annual runoff control rates of 70–85 percent, and Australian states specify pollutant load reductions of 85 percent. These quantitative benchmarks illustrate an emerging shift from purely narrative standards toward performance-based regulation, integrating climate resilience, groundwater recharge, and water-quality protection within a unified stormwater policy framework.

6.2. Public Education and Community Engagement

Stormwater management and groundwater protection require public awareness and education campaigns. It has been shown that targeted education programs can raise public awareness and engagement with water conservation practices [121]. In order to reduce watershed pollution, several strategies have been identified, including grassroots efforts, mass media campaigns, and community engagement [122]. Education programs should focus on practical solutions to stormwater management problems, such as proper disposal of household chemicals and the benefits of rain gardens [121,123]. Research has demonstrated the effectiveness of integrating extension, teaching, and research components into educational programs to reach professionals, municipal officials, and homeowners [124]. Several studies have demonstrated that community partnerships and targeted messages can overcome cognitive barriers and promote water conservation among diverse communities [121,123].

7. Future Directions and Sustainability

As cities recognize the importance of sustainable urban development, green infrastructure holds promise for the future. Stormwater management strategies will increasingly incorporate GIs into comprehensive strategies in the future. Due to climate change, cities will be subject to more frequent and severe storm events, adding to the need for effective stormwater management solutions. As green infrastructures absorb and filter stormwater runoff, they will likely become even more essential elements of urban resilience strategies, decreasing flood risks and relieving sewer pressure.

It is also important to recognize that green infrastructure encompasses multi-functional urban spaces as well. In addition to managing stormwater, GIs can provide additional benefits, such as urban cooling, biodiversity conservation, and improved recreational opportunities. Green infrastructure can be designed innovatively to maximize ecological and social value, incorporating features such as native plants, habitat structures, seating areas, and community gardens. As a result of this transformation, green infrastructures could be transformed into vibrant, green corridors that improve urban residents’ quality of life while contributing to overall sustainability.

The design and performance of green infrastructure may also be improved by future advancements in technology and materials. For instance, innovations in permeable pavement materials could make green infrastructure surfaces more durable and effective, making them more resilient to traffic and extreme weather. Furthermore, integrating smart sensors and monitoring systems into green infrastructure can facilitate real-time analysis of stormwater runoff, vegetation health, and air quality, which would facilitate informed management decisions.

Community engagement and social equity will continue to play an important role in the development of green infrastructures in the future. It is important for cities to make sure that green infrastructure projects are inclusive, responsive to local needs, and accessible to all residents, especially those living in historically underserved areas. Community participation in the planning, design, and maintenance of green infrastructure projects can promote a sense of ownership and stewardship, resulting in more sustainable and resilient neighborhoods.

8. Conclusions

The proliferation of impervious surfaces and the accumulation of diverse pollutants in urban stormwater runoff pose a significant and multifaceted threat to groundwater quality. This review article highlights how stormwater infiltration, while beneficial for groundwater recharge, can inadvertently facilitate the transport of contaminants into aquifers, especially in areas with permeable soils and shallow water tables. In order to mitigate these risks, green infrastructure (GI) could be a promising solution.

Green infrastructure (GI) presents a promising solution to mitigate these risks. Infiltration basins, urban wetlands, rain gardens, bioswales, and vegetative buffers demonstrate varying degrees of effectiveness for removing pollutants through mechanisms including adsorption, sedimentation, microbial transformation, and plants’ uptake of pollutants. GI systems are further enhanced by adding soil amendments such as iron-enhanced sand, zeolite, biochar, and granular activated carbon. For long-term success, site-specific design, continuous monitoring, and adaptive management are essential, as illustrated by case studies in this article. Furthermore, policy frameworks, public education, and community engagement are crucial to facilitating GI adoption and implementation. Looking forward, the evolution of green infrastructure into multifunctional urban spaces, coupled with technological innovations and inclusive planning, will be critical in building resilient and sustainable cities.