| 1. |
- Rosen, Lars, 1962, et al.
(författare)
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Comparing risk-reduction measures to reach water safety targets using an integrated fault tree model
- 2010
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Ingår i: Water Science and Technology: Water Supply. - : IWA Publishing. - 1606-9749. ; 10:3, s. 428-436
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Tidskriftsartikel (refereegranskat)abstract
- In the third edition of the Guidelines for Drinking-water Quality, the World Health Organization concludes that an integrated management of risks in source waters, treatment systems and distribution networks is the most effective way to guarantee safe drinking water to consumers. The integrated approach is fundamental to avoid sub-optimisation of risk-reduction measures. This paper presents an application of an integrated and quantitative risk model for comparing risk-reduction measures to support decisions for reaching specified water safety targets. A fault tree approach is used for structuring the risk analysis and for estimating the risk, expressed as Customer Minutes Lost (CML). Input information is a combination of hard data and expert judgements. Uncertainties in input information are considerable and modelled by a Bayesianstatistical approach. A drinking water system in Sweden is used to exemplify model application. Quantitative safety targets have been confirmed at the political level as a basis for long-term planning of investments and reinvestments. One target defines an acceptable risk level of 144 annual CML for the average consumer. For the current system structure an estimated risk of 612CML was obtained. Four risk-reduction alternatives were compared and they reduce the risk to between 50 and 81 CML, i.e. below the acceptable level. The paper describes how a structuredand thorough analysis of risk-reduction measures can facilitate transparency and long-term planning of drinking water systems.
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| 2. |
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| 3. |
- Vinas, Victor, 1988, et al.
(författare)
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Cross-connections in drinking water distribution networks: Quantitative microbial risk assessment in combination with fault tree analysis and hydraulic modelling
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 831
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Tidskriftsartikel (refereegranskat)abstract
- Deficiencies in drinking water distribution networks, such as cross-connections, may lead to contamination of the drinking water and pose a serious health risk to consumers. Cross-connections and backflows are considered among the most severe public health risks in distribution networks. The aim of this paper was to provide a framework for estimating the risk of infection from cross-connection and backflow events. Campylobacter, norovirus, and Cryptosporidium were chosen as reference pathogens for this study. The theoretical framework was constructed based on the fault tree analysis methodology. National aggregated cross-connection incident data was used to calculate the probability of a contamination event occurring in Swedish networks. Three risk cases were evaluated: endemic, elevated, and extreme. Quantitative microbial risk assessment (QMRA) was used to assess daily risk of infection for average national estimates. The framework was also evaluated using local data from the Gothenburg network. The daily risk of infection from cross-connection and backflow events in Swedish networks was generally above an acceptable target level of 10−6 for all reference pathogens and modelled cases; the exception was for the Gothenburg system where the risk was lower than 10−7. An outbreak case study was used to validate the framework results. For the outbreak case study, contaminant transport in the network was simulated using hydraulic modelling (EPANET), and risk estimates were calculated using QMRA. The outbreak simulation predicted between 97 and 148 symptomatic infections, while the epidemiological survey conducted during the outbreak reported 179 cases of illness. The fault tree analysis framework was successfully validated using an outbreak case study, though it was shown on the example of Gothenburg that local data is still needed for well-performing systems. The framework can help inform microbial risk assessments for drinking water suppliers, especially ones with limited resources and expertise in this area.
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| 4. |
- Bondelind, Mia, 1980, et al.
(författare)
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Benchmarkingmodell för dricksvattenförsörjning i Sverige
- 2012
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Ingår i: Proceedings för Åttonde Nordiska Dricksvattenkonferensen, Stockholm Sverige 2012. ; , s. 36-39
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish Water & Wastewater Association has initiated a benchmarking project to assess the quality and quantity, safety and efficiency of drinking water systems in Sweden. An important part of the project is to develop a benchmarking model which provides a useful tool for the municipalities to evaluate the status of their drinking water systems in respect to a safe drinking water quality and quantity. The increased focus on a safe drinking water, in terms of microbiological contaminants, originates from recent outbreaks of waterborne diseases in Östersund and Skellefteå in Sweden. The derived benchmarking model presented in this paper evaluates the safety of the water by a few carefully selected parameters. The model will apply to both small and large drinking water systems and will provide a useful tool for comparison of drinking water systems within Sweden to encourage for a continued improvement of the systems. In addition, the model provides a straightforward and transparent tool for the municipalities to communicate the status of the drinking water systems to the public.
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| 5. |
- Heinicke, Gerald, 1973, et al.
(författare)
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Application of a QMRA model for surface water treatment to investigate a waterborne outbreak of calicivirus
- 2009
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Ingår i: American Water Works Association, Global Conference on Microbial Contaminants in Drinking Water 2009, 5-8 October, Singapore. ; , s. 7-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The QMRA modelling tool developed by the Swedish Water & Wastewater Association was applied to investigate a probably waterborne outbreak of calicivirus that occurred in the municipality of Lilla Edet, Sweden, after a period with heavy rain. Of the inhabitants that receive water from the municipal water works, 32% reported gastroenteritis in the period investigated. For the QMRA study, the pathogen load in the raw water source was estimated by describing specific discharge events of wastewater upstream the intake of the municipal water works, including dilution and transport time in the river. Estimates of the concentration of norovirus in wastewater, the efficiency of treatment processes in the waterworks, exposure volumes and dose-response relationships were based on literature data that are included in the modelling tool. In a scenario analysis, the probability of infection related to the three discharge events was quantified. The QMRA model estimated probabilities of infection comparable to the proportion of people reported estimated to have fallen ill in the epidemiological study. Sources of uncertainty and potential for improvement were identified for the in-data and for the modelling tool.
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| 6. |
- Lindhe, Andreas, 1981, et al.
(författare)
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Integrated risk analysis from source to tap: Case study Göteborg
- 2008
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Ingår i: The 6th Nordic Drinking Water Conference, Oslo, Norway, 9-11 June, 2008. - 9788241402937 ; , s. 231-241
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To achieve an efficient risk management of a drinking-water system the entire system has to be considered, from source to tap. An important part of risk management is to identify hazards and estimate risks, i.e. to conduct risk analyses. In order to provide a relevant basis for evaluating risks and efficiently prioritising risk reduction options, a risk analysis needs to properly consider interaction between different parts and components of the system. This is especially important in complex systems. Logic tree models have the capability of properly reflect system functionality as well as facilitating quantification of risk levels. A fault-tree model was therefore constructed for an integrated and probabilistic risk analysis of the drinking-water system in Göteborg, Sweden. The main (top) event studied in the analysis was supply failure, which included quantity and quality failures. Quantity failure occurs when no water is delivered to the consumer and quality failure when water is delivered, but unfit for human consumption according to existing water-quality standards. Hard data and expert judgements were used for estimating probabilities of events, consequences and uncertainties of estimates. Monte Carlo simulations were used for the calculations in order to facilitate uncertainty analysis of risk levels. The risk analysis provided information on the probability of failure, rate of failure and mean down time of the system. The number of people affected was also included in the fault tree and risk levels were expressed as Costumer Minutes Lost. The primary aims of this paper were to apply a fault-tree method, for integrated and probabilistic risk analysis of drinking-water systems, on the system in Göteborg and show how the results can be used. The results showed, for example, that the raw water part contributes most to the total risk level and that the distribution part includes frequent failures that most often have a short duration and affect a small number of people. The method was found to facilitate a quantitative and integrated risk analysis of the drinking-water system and the results provide information not only on risk levels, but also on the dynamic behaviour of the system. In addition, the method is capable of relevant handling interaction of system components. Furthermore, it provides transparency and facilitates for formal updating when new information becomes available. Hence, it is concluded that the method provides useful information for discussing and evaluating risks as well as possible risk reduction options.
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| 7. |
- Lindhe, Andreas, 1981, et al.
(författare)
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Quantitative risk assessment of water supply systems from source to tap
- 2009
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Ingår i: TECHNEAU: Safe Drinking Water from Source to Tap. - 1843392755
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the 3rd edition of the Guidelines for Drinking-water Quality, the World Health Organisation concludes that an integrated management of risks in source waters, treatment systems and distribution networks is the most efficient way to guarantee safe drinking water to consumers. The integrated approach is fundamental to avoid sub-optimisation of risk-reduction efforts. This paper presents an application of an integrated and quantitative risk model for comparing risk-reduction alternatives to support decisions for reaching specified water safety targets. A fault tree approach is used for structuring the risk analysis and for estimating the risk, expressed as Costumer Minutes Lost (CML). Input information is a combination of hard data and expert judgements. Uncertainties in input information are considerable and modelled by a Bayesian statistical approach. The Göteborg drinking water system is used to exemplify model application. Quantitative safety targets have been confirmed at the political level as a basis for long-term planning of investments and reinvestments. Four different risk-reduction alternatives concerning additional raw water supplies and increased treatment capacity were compared. A combination of increased treatment capacity and additional raw water sources was shown to provide the greatest risk reduction. The paper describes how a structured and thorough analysis of risk-reduction options can facilitate transparency and long-term planning of drinking water systems.
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| 8. |
- Malm, Annika, 1970, et al.
(författare)
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Förnyelseplanering av vatten- och avloppsförsörjningsnät i 18 svenska kommuner
- 2009
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Ingår i: The 11th Nordic Wastewater Conference, 10-12 November 2009, Odense, Denmark.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The water and wastewater pipe net management is of considerable interest. The management influences risk for distribution interruption, health disruptions and environmental safe sewer discharge. There are also huge values involved. The renewal of the pipe networks is the major question, each municipality has to handle. There is a lot of knowledge among the water administrations in the municipalities; however the knowledge is often in the mind of the employees. Water engineers in 18 Swedish municipalities of various categories have been interviewed. Most municipalities are in short of a systematic renewal planning, such as risk analysis or cost calculated goals. The interviewed municipalities felt that there renewal rate should be higher, but they have no structural instrument to show the reasons. Priorities were done as “worst first”, and the selection of “worst” were built on experience. There is a need of structure in order to assist the municipalities to rely on their work, and to express to politicians and others the future rehabilitation needs.
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| 9. |
- Malm, Annika, 1970, et al.
(författare)
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The association of drinking water treatment and distribution network disturbances with Health Call Centre contacts for gastrointestinal illness symptoms
- 2013
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 47:13, s. 4474-4484
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Tidskriftsartikel (refereegranskat)abstract
- There are relatively few studies on the association between disturbances in drinking waterservices and symptoms of gastrointestinal (GI) illness. Health Call Centres data concerningGI illness may be a useful source of information. This study investigates if there is anincreased frequency of contacts with the Health Call Centre (HCC) concerning gastrointestinal symptoms at times when there is a risk of impaired water quality due to disturbances at water works or the distribution network. The study was conducted inGothenburg, a Swedish city with 0.5 million inhabitants with a surface water source ofdrinking water and two water works. All HCC contacts due to GI symptoms (diarrhoea,vomiting or abdominal pain) were recorded for a three-year period, including also sex, age,and geocoded location of residence. The number of contacts with the HCC in the affectedgeographical areas were recorded during eight periods of disturbances in the water works(e.g. short stops of chlorine dosing), six periods of large disturbances in the distributionnetwork (e.g. pumping station failure or pipe breaks with major consequences), and 818pipe break and leak repairs over a three-year period. For each period of disturbance theobserved number of calls was compared with the number of calls during a control periodwithout disturbances in the same geographical area. In total about 55, 000 calls to the HCCdue to GI symptoms were recorded over the three-year period, 35 per 1000 inhabitants andyear, but much higher (>200) for children
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