Stormwater Management Approaches Research Articles

Storage Scale Assessment of a Low-Impact Development System in a Sponge City

A sponge city is an established urban stormwater management approach that effectively reduces urban runoff and pollutant discharges. In order to plan and design, estimate costs, and evaluate the performance of urban sponge city systems, it is essential to calculate the storage scale. In this context, a sponge city storage scale and calculation method based on a multifactor spatial overlay was designed, utilising the starting area of the Dafeng Hi-tech Development Zone in Yancheng City, China, as an illustrative example. The indicators for assessing the impact of sponge city systems on river plain networks are constructed based on four aspects: land planning, building density, water surface rate and green space rate. The relative importance of each indicator was determined based on the necessity of controlling runoff from land parcels and the appropriateness of facility construction. The annual runoff control rate of the 39 low-impact development control units in the study area was calculated using ArcGIS through multifactor spatial overlay mapping and weighting. The results showed that (1) the Geographic Information System (GIS)overlay technology can effectively assist in the decomposition of LID scales; (2) data can be derived, including the design storage volume and other basic control scale indicators for each unit. The study results are expected to serve as a reference for the preparation of special low-impact development plans in the river plain network area of China and the promotion of the construction of a sustainable blue–green system in the city.

Mechanisms and Applications of Nature-Based Solutions for Stormwater Control in the Context of Climate Change: A Review

Nature-based solutions (NbSs) are considered to form an innovative stormwater management approach that has living resolutions grounded in natural processes and structures. NbSs offer many other environmental benefits over traditional grey infrastructure, including reduced air pollution and climate change mitigation. This review predominantly centers on the hydrological aspect of NbSs and furnishes a condensed summary of the collective understanding about NbSs as an alternatives for stormwater management. In this study, which employed the CIMO (Context, Intervention, Mechanism, Outcome) framework, a corpus of 187 NbS-related publications (2000–2023) extracted from the Web of Science database were used, and we expounded upon the origins, objectives, and significance of NbSs in urban runoff and climate change, and the operational mechanisms of NbSs (including green roofs, permeable pavements, bioretention systems, and constructed wetlands), which are widely used in urban stormwater management, were also discussed. Additionally, the efficacy of NbSs in improving stormwater quality and quantity is discussed in depth in this study. In particular, the critical role of NbSs in reducing nutrients such as TSS, TN, TP, and COD and heavy metal pollutants such as Fe, Cu, Pb, and Zn is emphasized. Finally, the main barriers encountered in the promotion and application of NbSs in different countries and regions, including financial, technological and physical, regulatory, and public awareness, are listed, and future directions for improving and strategizing NbS implementation are proposed. This review gathered knowledge from diverse sources to provide an overview of NbSs, enhancing the comprehension of their mechanisms and applications. It underscores specific areas requiring future research attention.

What contributes to local-level institutional adaptation under climate change? A configurational approach based on evidence from China's Sponge City Program

Unrestrained human industrial and agricultural production activities exacerbate climate change and environmental pollution. Climate change leads to an increase in flood risks and the spread of water and soil pollution, resulting in challenges in urban stormwater management. Institutional adaptation to climate change is vital for realizing effective local urban stormwater management. However, the accumulated knowledge on climate adaptation over the past decade has been concentrated at the technical and economic levels, with limited research on institutional adaptation. The Sponge City Program in China selects 30 pilot cities to promote a novel stormwater management approach that combines the reliability of traditional gray infrastructures made of concrete materials with the adaptability and sustainability of green-blue infrastructures based on natural-based solutions, but the extent of institutional adaptation in this process varies considerably across pilot cities. To explain what drives institutional adaptation, a configurational analysis of pilot cities is conducted using the fuzzy-set qualitative comparative analysis method. Based on data from 628 official reports and 36 interviews, we demonstrate local governments are significant institutional entrepreneurs, and high institutional adaptation occurs with the combined effects of institutional capacity, financial resources, and reputational incentives. There are three types of paths driving institutional adaptation: “strong institutional capacity-strong financial resource-low reputational reserve,” “strong institutional capacity-strong financial resource-high reputational competition,” and “strong institutional capacity-weak financial resource-low reputational reserve.” These three paths account for 72% of the instances of high institutional adaptation outcomes, and 90% of cases share a given configuration of conditions associated with an outcome. Our conclusion advances a theoretical understanding of the drivers of institutional adaptation and provides guidelines for future climate adaptation practices.

Overarching barriers to mainstream green stormwater infrastructure in Ghana: Towards good green governance

Environmental challenges associated with stormwater management, including flooding, droughts and depleting water quality, are exacerbated in urban areas. Despite growing expertise and policy advocacy for alternatives to conventional stormwater management approaches, Ghanaian cities, like many cities in developing countries, have not adopted governance principles to mainstream green stormwater infrastructure (GSI). There is very limited research which examines the governance barriers to mainstreaming GSI and their nuances within the Ghanaian context. Based on document analysis and interviews, this article explores the governance factors influencing GSI implementation and their associated barriers in Ghana’s most populated water catchment. It analyses the governance dimensions comprising actors, rules of the game, discourse, and resources and power that could influence stormwater management. The article highlights that governance dimensions are currently not framed to facilitate GSI implementation. This shortfall reflects 11 specific barriers, including poverty, unresponsive culture, lack of knowledge, and lack of collaboration. The barriers transcend multiple governance components, particularly the actors. Yet, several governance components, including the specific actors and existing policies, are not currently integrated into stormwater management despite having strong potential to overcome the barriers and facilitate GSI implementation. The article proposes a good green governance framework, which accounts for the holistic nature of the identified barriers and envisages active inclusion and collaboration between diverse actors, including a basin authority as an intermediary, communities, local governments and national-level agencies.

Influences of zinc loads in urban catchment runoff: Roof type, land use type, climate and management strategies

The contribution of ecotoxic dissolved metals from metallic roofs into urban waterways is a global issue. Identifying the specific origin of dissolved metals is critical to enabling appropriate stormwater management approaches that can provide the intended outcome of cleaner urban waterways. An event load pollutant model, Modelled Estimates of Discharges for Urban Stormwater Assessments (MEDUSA2.0), was used to predict the zinc load contributed from individual roof surfaces, under a wide range of rainfall conditions. Zinc was chosen as the pollutant of most concern given the extensive area of zinc-based roof surfaces, and the prevalence and mobility of zinc within urban waterways. The model categorized each roof by surface material and condition, and was run for individual rain events across multiple years to illustrate the influences on zinc loads from both surface type and rainfall conditions. Scenarios of future management were also assessed through the model to compare their benefits in terms of load reductions against the current baseline loadings. To understand how the load prediction and scenario modelling can provide valuable guidance for stormwater management decision-makers, the model was applied to a large urban catchment in Christchurch, New Zealand. Seven representative subcatchments of the varying proportions of industrial, commercial and residential land use type were also modelled to compare zinc loads generated. Results showed that an individual catchment's composition of roof types was the main driver of zinc load generation rather than the catchment's land use type. The modelled management scenarios demonstrated that reductions of 30% zinc could be achieved by changing only 4–13% of a subcatchment's unpainted zinc-based roof surfaces.

Co‐benefits and conflicts in alternative stormwater planning: Blue versus green infrastructure?

AbstractBlue–green infrastructure (BGI) is often promoted for its co‐benefits and multifunctionality. However, this infrastructure is repeatedly planned, implemented and researched almost entirely based on the goals of stormwater management. Thus, more knowledge is required about how co‐benefits are perceived and actioned by planning actors. By investigating co‐benefits from a value perspective, this paper will contribute to the ongoing debate on how stormwater planning actors address the potential co‐benefits and conflicts in the planning and implementation of BGI. The data are derived from policy document analyses and interviews with municipal and private planning actors in Bergen and Tromsø, Norway. The paper argues that municipal water actors are motivated to implement BGI beyond stormwater management goals and approach co‐benefits and holistic stormwater management as an ideal in stormwater planning. However, the tensions and conflicts between the co‐benefits become more evident in the actual implementation of BGI. The paper finds that when holistic BGI implementation is initiated by the municipal water actors, the stormwater management aspects dominate the BGI implementation. Finally, the paper concludes that even though blue and green values and interests are often conflicted in the implementation of BGI, urban stormwater planning is in the process of developing a blue–green value set based on the potential synergies of co‐benefits. The paper therefore empirically illustrates how collective values and interests can develop and unfold across sectors and professional disciplines in BGI planning.

Multi-criteria Decision-making Approach for Characterizing the Best Low Impact Development (LID) Techniques for Stormwater Management

Low impact development (LID) techniques are known as a novel stormwater management approach designed to mitigate the adverse effects of stormwater runoff and nonpoint source pollution. This study proposes a methodology for selecting the best LIDs based on multi-criteria decision analysis (MCDA) while incorporating different stakeholder priorities. The proposed methodology comprises analysis of alternatives, stakeholder analysis, and application of the MCDA methods. The results show that most LID techniques received ratings of more than three from the Weighted Average Method (WAM; performing well) other than green roofs and constructed filters, and no techniques averaged lower than 2.29 out of five. There is a general consensus on how vegetated filter strips and infiltration practices would perform, while there is little consensus on bioretention, level spreaders, and porous pavements. The ratings show that the majority of stakeholders thought most LIDs would perform well (a rating of more than three). The findings of this study provide an initial insight into how to support effective and widespread LID implementation for all decision-makers such as planners, designers, engineers, and stormwater managers.

Evaluation of Active, Beautiful, Clean Waters Design Features in Tropical Urban Cities: A Case Study in Singapore

In Singapore, active, beautiful, clean waters design features (ABCWDFs), such as rain gardens and vegetated swales, are used as a sustainable approach for stormwater management. Field monitoring studies characterising the performance of these design features in the tropical region are currently limited, hampering the widespread implementation of these systems. This study characterised the performance of individual ABCWDFs in the tropical climate context by monitoring a rain garden (FB7) and a vegetated swale (VS1) that were implemented in a 4-ha urban residential precinct for a period of 15 months. Results showed that total suspended solids (TSS), total phosphorus (TP) and total nitrogen (TN) concentrations were low in the new residential precinct runoff, leading to poor removal efficiency despite the effluent concentrations of individual ABCWDFs that were within the local stormwater treatment objectives. Average TSS, TP and TN EMCs of four sub-catchment outlets were lower (23.2 mg/L, 0.11 mg/L and 1.00 mg/L, respectively) when compared to the runoff quality of the major catchments in Singapore, potentially demonstrating that the ABCWDFs are effective in improving the catchment runoff quality. Findings from this study can help to better understand the performance of ABCWDFs receiving low influent concentrations and implications for further investigations to improve stormwater runoff management in the tropics.

Revising green roof design methods with downscaling model of rainfall time series.

Historically, green infrastructure for stormwater management has been event-based designed. This study aims to realign the green infrastructure design strategies with principles for robust decision making, through the example of green roofs design with the variational method and exemplified using the Norwegian context of the 3-step approach (3SA) for stormwater management. The 3SA consists of planning solutions to handle day-to-day rain at site scale through infiltration (step 1) and detention (step 2), and extreme events with safe floodways (step 3). An innovative framework based on downscaling of rainfall timeseries is suggested as follows: (i) long duration continuous simulation for retention variation and day-to-day discharge, corresponding to step 1 in the 3SA; (ii) intensive sampling of local extreme events to estimate reliability and robustness of solutions, corresponding to steps 2 and 3 in the 3SA. Comparing the traditional variational method to Highly-Informed-Design-Evaluation-Strategy (HIDES), it was found that the variational method possibly leads to incorrect decisions while the suggested novel approach was found to give more informed and reliable results by suggesting a design based on both operating mode and failure mode. It allows to embed solutions within the urban water system by facilitating the link between the steps of the 3SA. Such a framework was found to be data-wise applicable in the Norwegian context.

Flood Control and Aquifer Recharge Effects of Sponge City: A Case Study in North China

Sponge City is an integrated urban stormwater management approach and practice to tackle waterlogging, flooding, water scarcity, and their related problems. Despite many positive effects of Sponge City on flood control that have been investigated and revealed, the effect on aquifer recharge is still less known. Considering maximizing the function of natural elements such as surface water bodies and subsurface storage space, to minimize the use of a gray drainage system, a Sponge City design was proposed to substitute the planning development scheme in the study area. The stormwater management model of SWMM (storm water management model) and the groundwater flow model of MODFlow (Modular Three-dimensional Finite-difference Groundwater Flow Model) were adopted to evaluate the flood-control effect and aquifer-recharge effect, respectively. Compared with the traditional planning scenario, the peak runoff is approximately 92% less than that under the traditional planning scenario under the condition of a 5-year return period. Due to the increase in impervious areas of urban construction, the total aquifer recharge from precipitation and surface water bodies was decreased both in the present planning scenario and the Sponge City design scenario. However, the Sponge City design has a positive impact on maintaining groundwater level stabilization and even raises the groundwater level in some specific areas where stormwater seepage infrastructure is located.

Hybrid Approach for Excess Stormwater Management: Combining Decentralized and Centralized Strategies for the Enhancement of Urban Flooding Resilience

Urban sprawl and soil sealing has gradually led to an impervious surface increase with consequences on the enhancement of flooding risk. During the last decades, a hybrid approach involving both traditional storm water detention tanks (SWDTs) and low-impact development (LID) has resulted in the best solution to manage urban flooding and to improve city resilience. This research aimed at a modeling comparison between drainage scenarios involving the mentioned hybrid approach (H-SM), with (de)centralized LID supporting SWDTs, and a scenario representative of the centralized approach only involving SWDTs (C-SM). Results highlighted that the implementation of H-SM approaches could be a great opportunity to reduce SWDTs volumes. However, the performances varied according to the typology of implemented LID, their parameterization with specific reference to the draining time, and the rainfall severity. Overall, with the increase of rainfall severity and the decrease of draining time, a decrease of retention performances can be observed with SWDTs volume reductions moving from 100% to 28%. In addition, without expecting to implement multicriteria techniques, a preliminary cost analysis pointed out that the larger investment effort of the (de)centralized LID could be, in specific cases, overtaken by the cost advantages resulting from the reduction of the SWDTs volumes.

A Monitoring and Control System for Stormwater Management of Urban Green Infrastructure

Urban green infrastructure (UGI) can be used as a sustainable stormwater management approach. UGI can bring numerous ecological benefits to cities, including increased urban resilience, increased availability of water resources, and optimization of habitats. This paper used empirical research methods to describe an Internet of things (IoT)-based UGI monitoring and control system for stormwater management (MCSSWM). Using a Xuzhou-based practical project in China as a case study, we introduce the construction process, method, and monitoring results of the system. The results showed that the MCSSWM could be beneficial for UGI ecological performance evaluation and management.

Addressing the adaptive challenges of alternative stormwater planning

ABSTRACT Municipal water sectors shift from building traditional grey stormwater infrastructure to ambitious plans for holistic blue–green infrastructure due to climate vulnerability. The shift requires new ways of thinking, working, and collaborating, and we need to understand and address the new planning challenges the shift creates. While existing stormwater literature explores a range of technical, institutional, and financial barriers to alternative stormwater implementation, we hold the shift requires a deeper understanding of holistic and flexible stormwater management approaches. In this context, we investigate adaptive challenges like norms, practices, uncertainty, and new ways of collaborating across sectors in alternative stormwater planning in Norway. The studied planning processes exemplify how the need for making stormwater measures legally binding in municipal planning changes work practices in municipal water sectors. A novelty of the paper is that it shows how water departments take leadership of formal planning processes and adopt the planning department's language and working methods. We find that the studied municipalities promote cross-sectoral collaborative approaches that create space for professional negotiation and mediation and invite a deeper understanding of other's interests and views. We hold that such approaches could contribute to more holistic and flexible planning approaches, securing long-term sustainable stormwater management.

Social Barriers and the Hiatus from Successful Green Stormwater Infrastructure Implementation across the US

Green stormwater infrastructure (GSI), a nature-inspired, engineered stormwater management approach, has been increasingly implemented and studied especially over the last two decades. Though recent studies have elucidated the social benefits of GSI implementation in addition to its environmental and economic benefits, the social factors that influence its implementation remain under-explored thus, there remains a need to understand social barriers on decisions for GSI. This review draws interdisciplinary research attention to the connections between such social barriers and the potentially underlying cognitive biases that can influence rational decision making. Subsequently, this study reviewed the agent-based modeling (ABM) approach in decision support for promoting innovative strategies in water management for long-term resilience at an individual level. It is suggested that a collaborative and simultaneous effort in governance transitioning, public engagement, and adequate considerations of demographic constraints are crucial to successful GSI acceptance and implementation in the US.

Analysis of Alternatives for Sustainable Stormwater Management in Small Developments of Polish Urban Catchments

Sustainable stormwater management approaches in accordance with the EU Water Framework Directive (WFD) allow a source control to handle the quality and quantity of the runoff at local level or near the source. The most popular technologies applied in Europe are green roofs, porous pavements, retention basins and bioswales/raingardens. In this article, two of these solutions (retention tank with reuse, and rain garden, respectively), applied to single dwelling case studies in a suburban area in the Silesia Region (Poland), are illustrated and analyzed. The selected cases consider technical and economic aspects as the most important factors for decision on the selection of onsite stormwater management approach. Both systems have been operational for approximately two years. The retention tank proved a good solution, reducing stormwater overflows and allowing local water reuse for lawn irrigation; however, investment and maintenance costs in this case are relatively higher. The raingarden proved to work efficiently in this small scale implementation and implied much lower initial investment and costs. The economic sustainability of these interventions at single dwelling scale was analyzed, showing interesting returns, with outcome depending on the degree of possible water reuse (lower water bills) and availability of fiscal or fee incentives. Introduction of financial incentive schemes will encourage homeowners and developers to implement stormwater control solutions, allowing rapid amortization of investment costs with additional benefits to the community, such as reduced environmental impact of stormwater overflows and possible economies in the construction and management of stormwater systems.

Urban Streamflow Impact Assessment (USIA): a novel approach for protecting urbanising waterways and providing the justification for integrated water management

ABSTRACT As urban populations expand globally, the associated increase in urban land cover directly impacts the social and environmental amenity of natural assets, including waterways. The primary driver of urban waterway degradation changes in land uses which results in altered hydrology – from stormwater runoff, and where present, wastewater treatment plant discharge. Whilst the impacts of pollutants are relatively well regulated via public policy, a gap remains for the management of flow regime modification. The Urban Streamflow Impact Assessment (USIA) was developed to fill this management and planning knowledge gap. The approach begins with the identification of waterway values (social, ecological and geomorphic) then explicitly links these values to streamflow characteristics using hydraulic and hydrologic metrics. USIA was applied to a case study in Western Sydney and demonstrated the loss of values associated with ‘business-as-usual’ approaches to stormwater and wastewater management. Conventional stormwater management approaches do not remove enough excess flow to meet reasonable outcomes for the waterway. This excess runoff is increasingly seen as a resource and opportunity for improving water security and liveability. USIA is consistent with regulatory frameworks and can be applied across developing and established urban catchments to provide explicit input to planning controls. The approach is appropriate at multiple scales, informing urban planning from a broad strategic level through to detailed design. By linking social and ecological values with geomorphic and flow requirements, the approach enables an understanding of which management approaches could allow desirable waterway outcomes to be met.

Adapting urban best management practices for resilience to long-term environmental changes.

Stormwater best management practices (BMPs) help mitigate the adverse effects of urban development on stream hydrology and water quality, and are widely specified in development requirements and watershed management plans. However, design of stormwater BMPs largely relies on experience with historic climate, which may not be a reliable guide to the future. To inform BMP design that is robust to future conditions, it is important to examine how potential changes in precipitation, temperature, and potential evapotranspiration will affect the performance of BMPs. We use continuous simulation modeling to examine BMP performance under current and potential future climatic conditions and determine the changes needed in site configuration to address future impacts. We perform modeling for five development types in five different regions of the United States and explore both conventional ("gray") and green infrastructure (GI) stormwater management approaches. If stormwater designs are adapted to address potential future climate conditions, this study suggests that the most cost-effective approaches may use both gray and green BMPs. If the magnitude of extreme weather events increases dramatically, then gray practices that provide detention storage may have better cost-effectiveness. Incorporating risk of future climate impacts into stormwater design may help communities become more resilient. PRACTITIONER POINTS: There is a risk that projected changes in meteorological forcing will negatively affect stormwater BMP performance. Under projected future climate conditions, this study suggests the most cost-effective approaches may use both gray and green BMPs. If the magnitude of extreme weather events increases dramatically, gray practices that provide detention storage may have better cost-effectiveness. Flexibility is beneficial in adaptation and resilience planning due to uncertainty in projected precipitation volume and intensity changes.

Green Infrastructure Practice and a Sustainability Key Performance Indicators Framework for Neighbourhood-Level Construction of Sponge City Programme

In recent years, the Sponge City program (SCP) of China, as a sustainable stormwater management approach, has been strengthened as a national strategic level program. The Green Infrastructure (GI), due to its multi-objective and multi-benefits, has been adopted as an important measure of this new nationwide initiative. However, there is a lack of a comprehensive quantitative evaluation system for neighbourhood scale SCP. Hence, in the process of GI plan optimization, selection of implementation methods to balance its multi-benefits has become one of the key obstacles in the practice of SCP. To support robust decision making on multi-objective GI planning and comprehensive assessment, the analytic hierarchy process (AHP) has been used as a structural and systematic technique. In addition, a set of sustainability key performance indicators (KPIs) including requisite dimensions is the foundation for neighbourhood scale sustainability. Hence, AHP-based evaluation system including selection, weighting and ranking of the KPIs, is defined as a key performance indicator framework (KPIF), which is still in need for further development. Taking the GI planning for the Liangnong, Siming Lake sponge node restoration as an example, this paper develops KPIF with a comprehensive evaluation system for high-quality “Sponge Node” transitional construction. This KPIF consists of three basic criteria: “Environmental Performance”, “Economic and Adaptability Performance”, and “Social-cultural Performance and Wellbeing Performance”. In addition, 15 weighted KPIs are concluded and amongst them, the followings were relatively high: weight of the ATRCR, the promotion of biodiversity, the construction cost saving, the maintenance cost saving, and the level of recreational and wellbeing improvements for all people. In addition, the developed KPIF provides a reference for similar program’s decision-making, not only for the Jiangnan area of China, but also for quantitatively comprehensive evaluations of SCP in other regions.

Sustainable stormwater management: A qualitative case study of the Sponge Cities initiative in China

The Sponge Cities initiative in China is frequently described as a shift from using conventional grey infrastructure to a sustainable stormwater management (SSM) approach. However, it has been noted that Sponge City implementation includes conventional grey infrastructure too. Using the Sponge Cities initiative in China as a case, we examined how a prominent national policy is interpreted and implemented locally. We analysed national policy documents and conducted interviews with local government officials within three case cities. We found that in national policy documents, the Sponge City concept is related to the concept of low impact development, but that in implementation locally, conventional grey infrastructure still plays a significant role. Lack of space and lack of documented efficiency of green infrastructure were the most frequently mentioned reasons for this. Other challenges hindering its implementation were prioritization of quantifiable objectives within a short time-frame and lack of knowledge on SSM. Without sufficient resources (primarily space, knowledge and time), full implementation of the national Sponge City policy would be limited. In future efforts, finding the optimal combination of conventional and SSM solutions, viewing SSM and its management from a long-term perspective and promoting the understanding of SSM could help increase its implementation.

State of a sustainable drainage system at end-of-life: assessment of potential water pollution by leached metals from recycled pervious pavement materials when used as secondary aggregate.

Sustainable drainage systems (SuDS) have emerged as an effective and attractive approach for stormwater management, prevention of water pollution and flood control due to its sustainable, environmentally friendly and cost-effective approaches. One of the SuDS devices widely used to infiltrate, store and treat surface runoff which allows it to recharge groundwater is the pervious paving systems (PPS). Previous studies have demonstrated relatively high pollution removal efficiencies typically ranging from 98.7% for total hydrocarbons to 89% of COD. Although a small number of the studies have assessed the performance characteristics of the PPS system in long-established installations in terms of retention of pollutants, hydrological features, biodegradation of pollutants etc., none has assessed the risk of potential groundwater and soil pollution by pollutants such as metals retained in the PPS materials either as a disposed waste material (in the case of used geotextiles) or during re-use as secondary aggregates. Thus, this study evaluated potential risks associated with the decommissioning and beneficial use of wastes produced during the disassembly of a PPS. The authors believe that this was the first PPS to be addressed in this way. The method involved the determination of leachable concentrations of 14 metals in the PPS samples made up of extracts from the model profile which included the geotextile fibre (G), dust alone (D), aggregates and dust (AD), aggregates alone (AA) and pavement blocks (P) which were analysed and compared with two different groups of regulatory threshold limits. The results showed that the measured concentrations of all the metals were below the appropriate threshold values for irrigation purposes as specified by FAO and USEPA. Furthermore, results all indicated that the dismantled materials were all below EU LFD WAC limits for inert waste, indicating relative ease of disposal and suitability for use as recycled aggregate. This, admittedly limited data, indicates that recycling of aggregates from demolition wastes arising from end of life PPS would not be limited by the potential leaching of heavy metals, including re-use within another PPS. This would minimise dependence on virgin aggregates and hence reduce rate of exploitation of natural resources and improve sustainability score card of SuDS.