Two Drinking Water Outbreaks Caused by Wastewater Intrusion Including Sapovirus in Finland

Drinking water outbreaks occur worldwide and may be caused by several factors, including raw water contamination, treatment deficiencies, and distribution network failure. This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In addition, traditional fecal indicator bacteria and host-specific microbial source tracking (MST) markers (GenBac3 and HF183) were analyzed from water. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. The MST markers proved useful in the detection of contamination and to ensure the success of contaminant removal from the water distribution system. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study highlights the emerging role of sapoviruses as a waterborne pathogen and warrants the need for testing of multiple viruses during outbreak investigation.

Field performance of in-service cast iron water reticulation pipe buried in reactive clay

Field monitoring is an important means for understanding soil behaviour and its interaction with buried structures such as pipeline. This paper details the successful instrumentation of a section of an in-service cast iron water main buried in an area of reactive clay where frequent water pipe breakage has been observed. The instrumentation included measurement of pipe strain; pipe water pressure and temperature; soil pressure, temperature, moisture content, and matric suction; as well as the meteorological conditions on site. The data generally indicated that changes in soil temperature, suction, and moisture content were directly related to the local climatic variations. The suction and moisture content data indicated that the soil profile at the site down to around 700 mm, and probably down to 1000 mm, is affected by changes in surface weather, while soil conditions below this depth appear to be more stable. Analysis of pipe strain indicated that the pipe behaves like a cantilever beam, with the top experiencing predominantly tensile strains during summer. Subsequently, these trends reduce to compressive strains as soil swelling occurs because of the increase of moisture content with the onset of winter.

Mean values of water pipe breakage rates around the world and in geographical areas

One of the most frequently used parameters in water supply systems is the pipe breakage rate, which is often expressed by λ. Its definition can be deterministic or probabilistic, but both definitions lead to the same value under certain assumptions. This parameter can be defined per unit time only or per unit time and per unit length of the pipes (using a kilometre as the unit of measurement). The symbol λ is used in both cases and can occasionally generate confusion. In a water supply system, most failures occur because of pipe breakage, and only those cases are considered in this work. For a pipe, λ can be evaluated in terms of time (years) and length (km) and expressed by Λ. This paper aims to investigate the mechanical reliability of a water supply system with reference to pipeline breakages worldwide. A statistical approach is applied to a wide database of Λ values relative to certain variables (e.g., the diameter, material, age, pressure, and chemical characteristics of the water) for water supply systems worldwide (over 3,500 data points were collected from approximately 200 papers). The pipe length L and monitoring period T are often reported in the database. For each water supply system, it is necessary to apply a statistical weight to each value of Λ because the considered variables are notably different. The chosen weight is the product of L · T; the weight is evaluated using statistical analysis if L and/or T are unknown. Finally, a particular treatment is applied to the obtained weights to eliminate distortions in the Λ evaluation because of the different socioeconomic conditions of more or less developed countries. Four results are reported in this work: (1) the weighted average value of Λ in the world (Λm), (2) the average values of Λ in different continents (Λmc), (3) the average values of Λ in different countries (Λmn), and (4) the management correction factor (fCE).

Water distribution network simulation by optimization approaches

When a fire-flow condition occurs and a nodal demand is excessive or when a pipe breaks, a water distribution system (WDS) may temporarily become deficient and unable to satisfy all nodal demands. Thus, estimation of the influences of failure conditions on the network is needed. A method for analyzing the hydraulic condition of the network in such a situation is proposed. The method, which is constructed based on the amount of supply on each consumption node, is called node flow analysis (NFA). Given the limitations of the NFA method proposed earlier for determining optimal solutions, such as inflexibility of the approach toward more complicated problems and its time-consuming process, this paper presents the honey-bee mating optimization (HBMO) algorithm for maximizing the total supply of the Two-loop and Hanoi water distribution networks (WDNs) under a failure condition. The proposed method is much faster and simpler to use than the NFA method. Consequently, obtained results confirm the higher accuracy of the proposed method to conditions of WDNs under local pipe breakage. In addition, results make one aware of the effects of each pipe breakage on consumption nodes and in the entire network under two scenarios for maximizing total supply in the network.

Analysis of soil conditions and pipe behaviour at a field site

Water main pipes buried in expansive soils are often subjected to severe distress subsequent to installation. Excessive stresses may be induced due to either differential movement of the soils or swelling pressures from the soils along the pipes, impairing their performance or even breaking them. Field monitoring is an important means for understanding soil behaviour and its interaction with water mains. For this purpose, field instrumentation was successfully installed to monitor the performance of a section of water main placed in a well-developed area of a city neighbourhood where more frequent pipe breakage had occurred in recent years. The instrumentation included sensors to measure pipe wall strains, pipe displacement, in situ soil water content, soil pressure, and temperature. The instruments were installed in both the soil backfill and native soil around the backfill. This paper presents the analyses of monitoring data collected during the first 3 years after instrument installation. It was observed that the soil and pipe behaviour was affected significantly by soil properties and seasonal changes and correlated closely with the change pattern of the local meteorological conditions.