John Bryan Ellis

Towards a better understanding of sewer exfiltration

This paper gives a full review of the importance of sewer leakage, which has received increased attention throughout the last decades. Despite the intensive interdisciplinary research that has been invested, its magnitude is still unclear and a comprehensive solution for the assessment of sewer exfiltration does not seem to be at hand. However, given that mechanisms of exfiltration and the factors influencing its extent are similar all over the world, it seems possible to develop a generic leakage approach. Several methods for modelling sewer leakage are reviewed and the available measuring techniques are critically evaluated. Based on this evaluation, we suggest a unifying framework to facilitate focused model building. Specifically, we identify open research questions and propose to (i) standardise measurement results to enable better understanding, (ii) perform more long-term experiments under realistic field conditions, and (iii) assess the uncertainty of measurement and model results so that findings are not over-interpreted.

Sustainable surface water management and green infrastructure in UK urban catchment planning

Based on the analysis of impervious surface cover and water balance studies, it is argued that conventional, separately-sewered first-generation and alternative second-generation sustainable drainage systems (SUDS) cannot provide a fully sustainable surface water management approach for urban catchment planning. An extended approach based on the introduction of micro-and meso-vegetative SUDS systems into a wider green infrastructure (GI) framework is advocated to effectively address on-site and catchment urban surface water issues. The approach is based on the integrated planning implementation of street ‘greening’, with optimisation of existing biofiltration SUDS solutions, together with green roofs, downspout disconnection and sub-catchment riparian corridors to achieve a minimum 25–30% canopy cover level. A ‘leaf-out’ inventory procedure using GIS and satellite imagery can be employed to assess potential vegetative SUDS locations and types, and their likely impact upon the urban water cycle and receiving water health. However, there is a need to ensure that GI elements are incorporated into planning approaches and protocols for urban drainage infrastructure provision.

The performance of vegetated biofilters for highway runoff control

Abstract The design of highway drainage in the UK traditionally has provided for the rapid removal of surface runoff from the carriageway. The most commonly used methods are through direct and positive discharges to the nearest water-course (perhaps routed through a detention pond) or into a soakaway system. Such systems pay little attention to the potential loads generated from rainfall-runoff events or their possible impacts upon receiving waters. This paper reviews the potential use of vegetative systems as appropriate control measures for highway discharge pollution and discusses design options. The uptake of total petroleum hydrocarbons (TPH), lead and zinc by five species of emergent macrophyte is discussed for a constructed experimental wetland receiving runoff from a large transit base and car parking area in Washington State, USA. The data suggest that Typha latifolia and Sparganium are the most suitable species for TPH, Pb and Zn uptake, storage and metabolism.

Assessing exfiltration and infiltration on the performance of urban sewer systems

Sewer systems constitute a very significant heritage in European cities. Their structural quality and functional efficiency are key parameters to guarantee the transfer of domestic and industrial wastewater to treatment plants without infiltration nor exfiltration. Infiltration of groundwater is particularly detrimental to treatment plant efficiency, while exfiltration of wastewater can lead to groundwater contamination. The European research project APUSS (Assessing infiltration and exfiltration on the Performance of Urban Sewer Systems) was devoted to sewer infiltration and exfiltration questions. It was structured in three main Work Areas dealing respectively with i) the development of new measurement methods based on tracer experiments and accounting for detailed uncertainty analyses, ii) the implementation of models and software tools to integrate structural and experimental data and to facilitate data display, operational management and decision-making processes and iii) the integration of economic and operational questions by means of cost estimation, economic evaluation, performance indicators and multi-criteria methods applied to investment/rehabilitation strategies. This final report describes the objectives, methods and main results for each Work Area. References to detailed methods, protocols, reports and tools are given in this final report which will be an invaluable source of information for all those concerned with the performance of urban sewer systems.

Antiviral pandemic risk assessment for urban receiving waters.

An 80% metabolic conversion of the Tamiflu pro-drug (oseltamivir phosphate, OP) to its metabolite oseltamivir carboxylate (OC) and a high excretion rate combined with poor removal at sewage treatment works (STWs) means that potentially high STW OC emissions may occur in receiving waters. A risk assessment approach undertaken within the River Lee catchment in North East London indicates that predicted environmental concentrations for surface waters (PEC(sw)) are likely to be in the general range of 40-80 microg L(-1) during a pandemic sitaution within urban catchments having low dilution capacities. This implies low risk exposure levels which confirms previous studies, but there are considerable uncertainties associated with the methodology as well as risks that might result from persistent, long term chronic exposure to low-level water and sediment concentrations which might be mobilised under subsequent extreme flow conditions.

The management of urban surface water flood risks: SUDS performance in flood reduction from extreme events

The need to improve the urban drainage network to meet recent urban growth and the redevelopment of old industrial and commercial areas provides an opportunity for managing urban surface water infrastructure in a more sustainable way. The use of sustainable urban drainage systems (SUDS) can reduce urban surface water flooding as well as the pollution impact of urban discharges on receiving waters. However, these techniques are not yet well known by many stakeholders involved in the decision-making process, or at least the evidence of their performance effectiveness may be doubted compared with more traditional engineering solutions often promoted by existing 1D/2D drainage models. The use of geographic information systems (GIS) in facilitating the inter-related risk analysis of sewer surface water overflows and urban flooding as well as in better communication with stakeholders is demonstrated in this paper. An innovative coupled 1D/2D urban sewer/overland flow model has been developed and tested in conjunction with a SUDS selection and location tool (SUDSLOC) to enable a robust management approach to surface water flood risks and to improve the resilience of the urban drainage infrastructure. The paper demonstrates the numerical and modelling basis of the integrated 1D/2D and SUDSLOC approach and the working assumptions and flexibility of the application together with some limitations and uncertainties. The role of the SUDSLOC modelling component in quantifying flow, and surcharge reduction benefits arising from the strategic selection and location of differing SUDS controls are also demonstrated for an extreme storm event scenario.

Defining urban diffuse pollution loadings and receiving water hazard.

The use of unit area loading approaches to address the requirements of the US Clean Water Act (CWA) and the EU Water Framework Directive (WFD) to identify and manage diffuse urban pollution sources is outlined. Issues relating to traditional volume-concentration probabilistic modelling are highlighted and the robustness of total maximum daily load (TMDL) approaches is discussed. A hazard assessment methodology for catchment scale identification of source area pollutant loadings and receiving water ecological impacts is developed based on urban land use activities.

Urban and Highway Runoff Treatment by Constructed Wetlands

Publisher Summary The current focus on the development of sustainable urban drainage systems (SUDS) in many countries has raised awareness of the advantages of integrating constructed wetlands into urban and highway runoff treatment systems. However, it is essential that the criteria for the selection and design of constructed wetlands are rigorously applied to maximize their pollution treatment performance, and maintain and enhance their status as a valuable treatment option. A successful design of constructed wetlands for urban surface runoff management requires the adoption of an integrated multidisciplinary approach as performance criteria are difficult to set, given the inherent random fluctuations in discharge and pollution loadings that characterize storm water runoff. This temporal and spatial variability makes it difficult to define retention time and hydraulic loading, and thus general design rules for urban storm water wetlands have been developed from empirical performance data, using “single-number” techniques, such as drainage area ratio.

Sewer exfiltration and the colmation layer.

Sewer rig studies demonstrate a rapid exponential decline in exfiltration rates from gaps and joints to establish an ultimate steady-state equilibrium varying between 10(-3)-10(-6) l s(-1), with minimum average daily rates per standardised leak area and sewer length varying between 0.02-9.0 l d(-1)cm(-2) and 0.0002-2.0 l s(-1) km(-1) respectively. These loss rates are much larger than those derived from indirect monitoring/modelling studies which suggest losses between 1.4 x 10(-5)-0.179 l s(-1) km(-1). The confusion regarding conflicting definitions of the colmation, transition, bridging and biofilm layers is addressed, and the significance of these clogging layers in terms of both hydraulic and matrix potential on the exfiltration loss is evaluated. The influence of variability and instability of flow and bed turbulence on determining critical leakage conditions following the onset of equilibrium steady-state is assessed. This challenges the generally held assumption that elevated head pressure condition alone is a necessary precursor for rupture of the clogging layers.

Bacterial sources, pathways and management strategies for urban runoff

The microbiological quality of diffuse impermeable surface runoff is described in terms of bacterial densities and pathogens observed within urban catchments in North London and Milton Keynes and the use of somatic bacteriophages as faecal indicators are evaluated. The studies show the occurrence of faecal indicator organisms (FIOs) and pathogens to be ubiquitous in stormwater runoff from all types of urban land use surfaces, with the possible exception of major highways. Urban catchments in North London show a progressive downstream increase in FIOs and pathogens consonant with increasing urbanization and incidence of stormwater outfalls and combined sewer overflows (CSOs). Surface water FIOs and pathogens appear to be predominantly of non‐human origin being primarily derived from animal and bird sources, although the effect is over‐ridden in the presence of misconnections and CSO discharges. A combination of infrastructure improvement, end‐of‐pipe detention, source control and more robust local authority regulation is recommended for effective management and remediation of bacteriological urban water quality.