Captured streams and springs in combined sewers: a review of the evidence, consequences and opportunities.

Captured streams and springs may be flowing in combined sewers, increasing clean baseflow in pipes and wastewater treatment works (WwTWs), reducing pipe capacity and increasing treatment costs. The UK water industry is aware of this in principle, but there has been no explicit discussion of this in the published literature, nor have there been any known attempts to manage it. Instead, the current focus is on the similar intrusion of groundwater infiltration through pipe cracks and joints. We have conducted a thorough review of literature and international case studies to investigate stream and spring capture, finding several examples with convincing evidence that this occurs. We identify three modes of entry: capture by conversion, capture by interception, and direct spring capture. Methods to identify and quantify capture are limited, but the experience in Zurich suggests that it contributed 7-16% of the baseflow reaching WwTWs. There are negative impacts for the water industry in capital and operational expenditure, as well as environmental and social impacts of loss of urban streams. For a typical WwTW (Esholt, Bradford) with 16% of baseflow from captured streams and springs, we conservatively estimate annual costs of £ 2 million to £ 7 million. A detailed case study from Zurich is considered that has successfully separated captured baseflow into daylighted streams through the urban area, with multiple economic, environmental and social benefits. We conclude that there is a strong case for the UK water industry to consider captured streams and springs, quantify them, and assess the merits of managing them.

Adaption to extreme rainfall with open urban drainage system: an integrated hydrological cost-benefit analysis.

This paper presents a cross-disciplinary framework for assessment of climate change adaptation to increased precipitation extremes considering pluvial flood risk as well as additional environmental services provided by some of the adaptation options. The ability of adaptation alternatives to cope with extreme rainfalls is evaluated using a quantitative flood risk approach based on urban inundation modeling and socio-economic analysis of corresponding costs and benefits. A hedonic valuation model is applied to capture the local economic gains or losses from more water bodies in green areas. The framework was applied to the northern part of the city of Aarhus, Denmark. We investigated four adaptation strategies that encompassed laissez-faire, larger sewer pipes, local infiltration units, and open drainage system in the urban green structure. We found that when taking into account environmental amenity effects, an integration of open drainage basins in urban recreational areas is likely the best adaptation strategy, followed by pipe enlargement and local infiltration strategies. All three were improvements compared to the fourth strategy of no measures taken.

Evaluation of hydrogen sulphide concentration and control in a sewer system.

This study focused on monitoring hydrogen sulphide (dissolved and atmospheric) generation and wastewater volumetric flow in a 21.4 km sewer line of the City of San Antonio, Texas. The results were used to evaluate daily and seasonal trends of atmospheric and dissolved sulphide, and to better apply sulphide control using ferrous sulphate to prevent odour and sewer pipe deterioration. As part of this study, the evaluation of a cost-effective dosing strategy with ferrous sulphate was performed to better control the sulphide contents in wastewater. Dosing studies were performed in the laboratory to find the required ratio of ferrous sulphate for acceptable sulphide removal. The results indicate a 1.25 mole ratio requirement, to reduce sulphide by 93%. Over a typical daily diurnal cycle, necessary dosing rates to maintain sulphide concentrations below 2mg varied between 0 and 36,777 mold(-1) with a daily average rate of 14,438 mol d(-1). If, instead of dosing at the maximum required rate, dosing was matched over the diurnal cycle, chemical savings would amount to 22,339 mold(-1) while achieving sulphide control. The approximate cost of the ferrous sulphate solution dosed is $0.14 per mol and this amount of chemical savings translates into roughly $2923 per day. Actual dosing cost for the hypothetical average day will be $1889 per day. These cost savings can easily recoup the required instrumentation costs to achieve this diurnal dose matching.

Multicriteria decision-aid method to evaluate the performance of stormwater infiltration systems over the time.

Nowadays, stormwater infiltration systems are frequently used because of their ability to reduce flows and volumes in downstream sewers, decrease overflows in surface waters and make it possible to recharge groundwater. Moreover, they come in various forms with different uses. Despite these advantages the long term sustainability of these systems is questionable and their real performances have to be assessed taking into account various and sometimes conflicting aspects. To address this problem a decision support system is proposed. It is based on a multicriteria method built to help managers to evaluate the performance of an existing infiltration system at different stages of its lifespan and identify whether it performs correctly or not, according to environmental, socio-economic, technical and sanitary aspects. The paper presents successively: the performance indicators and the way they were built, the multicriteria method to identify if the system works properly and a case study.

Runoff infiltration, a desktop case study.

The use of sustainable drainage systems (SuDS) or best management practice is becoming increasingly common. However, rather than adopting the preferred 'treatment train' implementation, many developments opt for end-of-pipe control ponds. This paper discusses the use of SUDS in series to form treatment trains and compares their potential performance and effectiveness with end-of-pipe solutions. Land-use, site and catchment characteristics have been used alongside up-to-date guidance, Infoworks CS and MUSIC to determine whole-life-costs, land-take, water quality and quantity for different SuDS combinations. The results presented show that the use of a treatment train allows approaches differing from the traditional use of single SuDS, either source or 'end-of-pipe', to be proposed to treat and attenuate runoff. The outcome is a more flexible solution where the footprint allocated to SUDS, costs and water quality can be managed differently to fully meet stakeholder objectives.

Sustainable sewerage servicing options for peri-urban areas with failing septic systems.

The provision of water and wastewater services to peri-urban areas faces very different challenges to providing services to cities. Sustainable solutions for such areas are increasingly being sought, in order to solve the environmental and health risks posed by failing septic systems. These solutions should have the capability to reduce potable water demand, provide fit for purpose reuse options, and minimise impacts on the local and global environment. A methodology for the selection of sustainable sewerage servicing systems and technologies is presented in this paper. This paper describes the outcomes of applying this methodology to a case study in rural community near Melbourne, Australia, and describes the economic and environmental implications of various sewerage servicing options. Applying this methodology has found that it is possible to deliver environmental improvements at a lower community cost, by choosing servicing configurations not historically used by urban water utilities. The selected solution is currently being implemented, with the aim being to generate further transferable learnings for the water industry.

An effective multi-objective approach to prioritization of sewer pipe inspection.

The first step in the decision making process for proactive sewer rehabilitation is to assess the condition of conduits. In a risk-based decision context the set of sewers to be inspected first should be identified based on the trade-off between the risk of failures and the cost of inspections. In this paper the most effective inspection works are obtained by solving a multi-objective optimization problem where the total cost of the survey programme and the expected cost of emergency repairs subsequent to blockages and collapses are considered simultaneously. A multi-objective genetic algorithm (MOGA) is used to identify a set of Pareto-optimal inspection programmes. Regardless of the proven effectiveness of the genetic-algorithm approach, the scrutiny of MOGA-based inspection strategies shows that they can differ significantly from each other, even when having comparable costs. A post-processing of MOGA solutions is proposed herein, which allows priority to be assigned to each survey intervention. Results are of practical relevance for decision makers, as they represent the most effective sequence of inspection works to be carried out based on the available funds. The proposed approach is demonstrated on a real large sewer system in the UK.

Water privatization, water source, and pediatric diarrhea in Bolivia: epidemiologic analysis of a social experiment.

Water and sanitation services are fundamental to the prevention of pediatric diarrhea. To enhance both access to water and investment, some argue for the privatization of municipal water networks. Water networks in multiple Bolivian cities were privatized in the 1990s, but contracts ended following popular protests citing poor access. A population-based retrospective cohort study was conducted in two Bolivian cities. Data were collected on family water utilization and sanitation practices and on the prevalence of diarrhea among 596 children. Drinking from an outdoor water source (OR, 2.08; 95%CI, 1.25-3.44) and shorter in-home water boiling times (OR, 1.99; 95%CI, 1.19-3.34) were associated with prevalence of diarrhea. Increased prevalence was also observed for children from families using private versus public water services, using off-network water from cistern trucks, or not treating their water in-home. Results suggest that water source, water provider, and in-home water treatment are important predictors of pediatric diarrhea.

A cost comparison of traditional drainage and SUDS in Scotland.

The Dunfermline Eastern Expansion (DEX) is a 350 ha mixed development which commenced in 1996. Downstream water quality and flooding issues necessitated a holistic approach to drainage planning and the site has become a European showcase for the application of Sustainable Urban Drainage Systems (SUDS). However, there is minimal data available regarding the real costs of operating and maintaining SUDS to ensure they continue to perform as per their design function. This remains one of the primary barriers to the uptake and adoption of SUDS. This paper reports on what is understood to be the only study in the UK where actual costs of constructing and maintaining SUDS have been compared to an equivalent traditional drainage solution. To compare SUDS costs with traditional drainage, capital and maintenance costs of underground storage chambers of analogous storage volumes were estimated. A whole life costing methodology was then applied to data gathered. The main objective was to produce a reliable and robust cost comparison between SUDS and traditional drainage. The cost analysis is supportive of SUDS and indicates that well designed and maintained SUDS are more cost effective to construct, and cost less to maintain than traditional drainage solutions which are unable to meet the environmental requirements of current legislation.

Dynamic least-cost optimisation of wastewater system remedial works requirements.

In recent years, there has been increasing concern for wastewater system failure and identification of optimal set of remedial works requirements. So far, several methodologies have been developed and applied in asset management activities by various water companies worldwide, but often with limited success. In order to fill the gap, there are several research projects that have been undertaken in exploring various algorithms to optimise remedial works requirements, but mostly for drinking water supply systems, and very limited work has been carried out for the wastewater assets. Some of the major deficiencies of commonly used methods can be found in either one or more of the following aspects: inadequate representation of systems complexity, incorporation of a dynamic model into the decision-making loop, the choice of an appropriate optimisation technique and experience in applying that technique. This paper is oriented towards resolving these issues and discusses a new approach for the optimisation of wastewater systems remedial works requirements. It is proposed that the optimal problem search is performed by a global optimisation tool (with various random search algorithms) and the system performance is simulated by the hydrodynamic pipe network model. The work on assembling all required elements and the development of an appropriate interface protocols between the two tools, aimed to decode the potential remedial solutions into the pipe network model and to calculate the corresponding scenario costs, is currently underway.

Performance-costs evaluation for urban storm drainage.

The design process of urban stormwater systems incorporating BMPs involves more complexity unlike the design of classic drainage systems for which just the technique of pipes is likely to be used. This paper presents a simple decision aid methodology and an associated software (AvDren) concerning urban stormwater systems, devoted to the evaluation and the comparison of drainage scenarios using BMPs according to different technical, sanitary, social environmental and economical aspects. This kind of tool is particularly interesting so as to help the decision makers to select the appropriate alternative and to plan the investments especially for developing countries, with important sanitary problems and severe budget restrictions.

Performance indicators for the efficiency analysis of urban drainage systems.

Performance indicators implemented in a decision support system (DSS) for the technical, managerial and economic evaluation of urban drainage systems (UDS), called MOMA FD, are presented. Several kinds of information are collected and processed by MOMA FD to evaluate both present situation and future scenarios of development and enhancement. Particular interest is focused on the evaluation of the environmental impact, which is considered a very relevant factor in the decision making process to identify the priorities for UDS improvements.

Wastewater collection and treatment technologies for semi-urban areas of India: a case study.

Sanitation and wastewater management problems in small and medium towns in India (referred to as "semi-urban areas"--SUAs) are distinctly different from those of large cities or rural villages. There is an apparent lack of choices of appropriate sanitation options for these semi-urban areas, leading them to adopt on-site sanitation technologies. A field study of four such small towns in India was conducted to evaluate the suitability of available low-cost wastewater collection and treatment technologies, in light of their current practice. Based on the field study, this paper suggests a system comprising "combined surface sewers" and "reed-bed channel" for collection and treatment of wastewater for semi-urban areas, that can utilize all the existing infrastructure to effect better sanitation at lower costs. The suggested system involves converting the existing open wastewater collection drains on the road sides, as "decentralized" networks of covered drains with simple structural modifications to collect both wastewater and stormwater; and, converting the large open drains on the outskirts of SUAs that carry wastewater to agricultural fields, as gravel media filled beds planted with local reeds. Cost estimates for the towns studied indicate this system to be over 70% cheaper compared to conventional collection and treatment systems.

Viabilidade econômico-financeira para implantação de sistemas unitários em pequenas localidades / Viability economic financial to implantation systems unit locality small

Os sistemas de esgotamento sanitários implantados no Brasil atendem 37,7 por cento de sua população, sendo que muito desses sistemas cuidam única e exclusivamente de seu afastamento, uma vez que não são dotados de sistemas seguros de tratamento e final adequados. Além da grande carência de sistemas de esgotamento sanitário, o Brasil se ressente da falta de sistemas de drenagem pluvial que normalmente é a segunda grande obra realizada nos municípios, sendo a primeira, os sistemas de abastecimento de água. Devido a falta de recursos sistemas unitários ou combinados vêm sendo implantados, aproveitando-se redes coletoras de sistemas de drenagem existentes para o lançamento de esgotos in-natura, sem que se tenha conhecimento técnico adequado sobre as conseqüências dessa utilização, gerando como conseqüência, impactos nos corpos receptores. Surge a necessidade da criação de uma cultura voltada para a recuperação dos sistemas implantados conforme acima descrito ou quando for necessário, da elaboração de estudo de viabilidade técnica para sua implantação, segundo critérios a serem estabelecidos conforme as características locais, tendo como segundo objetivo sua viabilidade econômico-financeira. Para verificar a possibilidade de utilização de sistemas unitários em pequenas localidades, foram comparados os custos de implantação de sistemas de esgotamento sanitário e drenagem pluvial do tipo separadores absolutos, de implantação de uma sistema unitário, da recuperação de sistemas erroneamente chamados de unitários e de transformação de um sistema de drenagem pluvial do tipo separador absoluto em sistema unitário. O estudo mostrou que economicamente um sistema unitário é viável, mas se faz necessário um maior aprofundamento no que se refere a minimização dos riscos ambientais ao corpo receptor, quando da ocorrência de transbordamentos tanto em relação a quantidade quanto em relação a qualidade e suas conseqüências à biota.

Surface water drainage for low-income communities / Surface water drainage for low-income communities

For many low-income communities, lack of an adequate drainage system for surface water is a serious problem, leading to frequent flooding, land erosion, and increased transmission of a number of diseases. This publication describes how such communities can take action themselves to construct a simple, effective, low-cost drainage system or to rehabilitate an existing system that has fallen into disrepair. It gives practical guidance on the design and construction of drainage channels, and on ways of coping with specific problem areas such as steep slopes and low-lying flat terrain. Throughout the book, emphasis is placed on the importance of community participation at all stages of the project, from planning through implementation, and particularly in maintaining the system once it is built. Written in nontechnical languaje and copiously illustrated, this book will be invaluable to local authorities and community groups, as well as planners and public works official in developing countries

Desagues de superficie para comunidades de bajos ingresos / Desagues de superficie para comunidades de bajos ingresos / Surface water drainage for low-income communities

La carencia de un sistema adecuado de desague es un problema grave, que ocasiona a muchas comunidades de bajos ingresos inundaciones frecuentes, erosión del suelo y transmisión de diversas enfermedades. En esta obra se describe cómo esas comunidades pueden por sí mismas construir sistemas de desague sencillos, eficaces, baratos o habilitar instalaciones deterioradas. Ofrece orientaciones prácticas sobre el diseño y la construcción de canales y sobre el procedimiento a seguir en zonas con problemas particulares, como pendientes muy empinadas o terrenos llanos bajos. Se insiste de principio a fin en la importancia de que la comunidad participe en todas las etapas del proyecto, desde la planficación hasta la ejecución, y en especial en el posterior mantenimiento del sistema. Redactado sin tecnicismos y profusamente ilustrado, el libro será de valor inapreciable para autoridades locales y grupos comunitarios, así como para planificadores y funcionarios de obras públicas de los países en desarrollo