Quantifying the impact of runoff events on microbiological contaminant concentrations entering surface drinking source waters

Short-term peaks in pathogen concentrations may increase the risks for waterborne diseases considerably. In this study the occurrence of indicator organisms and pathogens in the river Gö ta ä lv at the raw water intake to Gö teborg was evaluated and related to risk for drinking water consumption. About half of the 24 pathogen samples, taken during event and non-event conditions, were positive for at least one of the following: Cryptosporidium, Giardia, norovirus, enterovirus, Campylobacter and E. coli O157. Positive pathogen detects were often associated with heavy rainfalls and viruses with a sewage emergency discharge. The annualised probability of infection from this type of event was calculated from pathogen concentrations in a QMRA model. Given that the water intake is not closed, the risk given present water treatment seems to be acceptable for Giardia; however, it is at a borderline for Cryptosporidium and insufficient for noro-and enteroviruses. Present results emphasise the need for an appropriate intake regulation with respect to high pathogen loads, as the risk increases with time of exposure to pathogen contaminants. Rather than a threshold level on E. coli, reports on upstream microbial discharges are valuable for quick pathogen indications.

Section: Qmra Resultssupporting

confidence: 89%

Evaluation of the microbial risk reduction due to selective closure of the raw water intake before drinking water treatment

Åström

Petterson

Bergstedt

et al. 2007

“…It is important to quantify baseline and peak contamination. Outbreaks of disease through drinking water have indeed occurred as a result of hazardous events, such as heavy rainfall, which lead to peak pathogen loads in source water (Stelzer & Jacob 1991;Atherholt et al 1998;O'Connor 2002;Signor et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Assessment of source water pathogen contamination

Dechesne

Soyeux

2007

During the last decade, the source to tap risk-based approach to pathogens in drinking water has been largely promoted. This paper addresses the issue of source water pathogen contamination, which is the first step of quantitative microbial risk assessment. It is focused on a selection of pathogens considered to be a major risk to human health. Source water quality is highly variable and understanding the reasons for this variability is important as it will influence the requirements for treatment, treatment efficiency and the resulting health risk associated with the finished water.A framework for source water microbial quality assessment based on catchment surveys and monitoring programmes was set and tested on ten water sources. The monitoring programmes included faecal indicators and pathogens, during both baseline and hazardous event conditions. Concentrations varied greatly within and between systems. Faecal indicators were shown to be poor surrogates for pathogen presence and concentrations. There was no recurring evidence that the pathogens correlated together and links between microbial parameters appeared to be very site specific. Such variability between systems shows the importance of running local monitoring programs for use in risk assessment. Finally, pathogen detection methods are not yet optimal due to their sensitivity and to the lack of knowledge on viability and infectivity of pathogens. A great effort needs to be made in the future to ensure better quality data as this may have large implications in the statistical risk assessment calculations.

“…Increased microbial impact have been observed during rain periods with substantial runoff, typically resulting in elevated microbial concentrations in surface waters (Tyrrel & Quinton 2003;Signor et al 2005). Point sources for pathogens may include municipal wastewater discharges and heavily polluted tributaries within a river system.…”

Section: Introductionmentioning

confidence: 99%

Identification and management of microbial contaminations in a surface drinking water source

Åström

Pettersson

Stenström

2007

Microbial contamination of surface waters constitutes a health risk for drinking water consumers which may be lowered by closing the raw water intake. We have evaluated microbial discharge events reported in the river Gö ta ä lv, which is used for raw water supply to the city of Gö teborg.Elevated levels of faecal indicator bacteria were observed during periods of closed raw water intake. High bacteria levels were, however, also occasionally detected during periods of open intake, probably as a result of microbial discharge far upstream in the river which may be difficult to predict and manage by closing the intake. Accumulated upstream precipitations, resulting in surface runoff and wastewater contaminations in the catchment, correlated positively with the levels of total coliforms, E. coli, intestinal enterococci and sulfite-reducing clostridia. Levels of faecal indicator organisms were negatively correlated to the water temperature due to enhanced survival at lower temperatures. Wastewater discharges from a municipality located just upstream of the water intake resulted in elevated E. coli concentrations downstream at the raw water intake for Gö teborg. To improve the prediction of microbial contaminations within the river Gö ta ä lv, monitoring data on turbidity and upstream precipitation are of particular importance.