Distribution System Contamination Research Articles

Drinking Water Travel Time and Emergency Department Visits for Gastrointestinal Illness

ISEE-321 Objective: Aging pipe networks used to distribute treated drinking water in the United States are playing an increasing role in infectious disease outbreaks, and the potential for endemic disease transmission by this route is substantial. Water travel time, the time it takes for water to travel from the treatment plant to the end user, can serve as an indicator of the potential for distribution system contamination. It can be estimated using hydraulic models, which incorporate pipe layout, size, and flow. This analysis examined whether the average water travel time for a zip code is related to the proportion of emergency department (ED) visits for gastrointestinal (GI) illness in that zip code. Material and Methods: ED data were collected from all hospitals within a major US city from 1996 to 2003. One of the largest water utilities in the city, serving 650,000 people, was considered. People served by the utility had 1,315,040 total visits; 72,759 (5.5%) for GI illness. The relationship between water travel time and GI illness risk was assessed using logistic regression, controlling for potential confounding factors, including age, season, year, hospital, distance from zip code to hospital, and indicators of SES. Results: The risk ratio for travel time treated as a continuous variable suggested little or no association. However, the risk ratio for residents of zip codes in the top decile of water travel times compared with residents of zip codes in the lowest decile of water travel times suggested modestly increased risk (risk ratio = 1.07, 95% confidence interval = 1.02–1.14). Effect modification by year was also suggested. Conclusions: These preliminary results suggest a possible contribution of drinking water distribution system contamination to the burden of GI illness. Future analyses will use water travel time estimates from additional utilities in the study area.

Protection strategies for drinking groundwater sources in small Quebec municipalities

Awareness of groundwater protection has increased substantially in recent decades. In the Province of Quebec, Canada, the Groundwater Catchment Regulation (GWCR) was promulgated in 2002 to protect water quality in public wells. The goal of the present study was to document groundwater protection in the context of emerging regulations and identify factors explaining the propensity of municipalities applying protection strategies. Two types of information were used in this study: data from a questionnaire-based survey conducted among 665 municipalities in the Province of Quebec and complementary information gathered from various sources. Data from the survey revealed that fewer than half of the municipalities have been able to comply with the GWCR, mainly because of financial limitations. Also, close to half of the municipalities have either identified or are expecting land use conflicts to arise between protection areas required by the GWCR and other land usage, with agriculture being the main conflicting activity. Multivariate logistic regression models served to identify factors explaining the likelihood of municipalities to take groundwater protection measures. Those factors were municipality revenue, history of water contamination in distribution systems, land use near wellheads, location of municipalities within a provincial priority watershed and the importance of groundwater use in a region. Results of the study may prove helpful for government authorities in better understanding the groundwater protection issue and in implementing strategies that improve the ability of municipalities to protect groundwater.

On–Line water quality parameters as indicators of distribution system contamination

The safety and security of drinking water distribution systems have recently generated considerable interest because of the credible concern that they could be compromised with chemical, biological, and radiological contaminants. In order to protect public health, the US Environmental Protection Agency initiated a program to investigate how changes in water quality parameters, which potentially indicate contamination, can be detected by real‐ or near real‐time sensors. The sensors investigated were off‐the‐shelf commercial products designed to monitor standard drinking water parameters such as pH, free chlorine, oxidation reduction potential (ORP), dissolved oxygen, specific conductance, turbidity, total organic carbon (TOC), chloride, ammonia, and nitrate. These sensors were mounted within a recirculating pipe loop and challenged with contaminants including secondary effluent from a wastewater treatment plant, potassium ferricyanide, a malathion insecticidal formulation, a glyphosate herbicidal formulation, nicotine, arsenic trioxide, aldicarb, and Escherichia coli K‐12 strain with growth media. Overall, the sensors that responded to most contaminants were those that monitored for free chlorine, TOC, ORP, specific conductance, and chloride. Generally, the technology used in sensor design or the particular manufacturer of the sensor did not affect the response characteristics. These results may help refine the role of water quality sensors, in conjunction with other data sources such as customer complaints and public health surveillance data, in a contamination warning system within a water distribution system.

Drinking Water Quality and Emergency Department Visits for Gastrointestinal Illness, 1993–2004

P-237 Introduction: Evidence suggests that drinking water quality contributes to endemic gastrointestinal (GI) illness in the US, but the determinants of this relationship and the proportion of illness attributable to drinking water are poorly understood. Contaminated drinking water can reach the end user through inadequate treatment and through intrusion of pathogens into the distribution system. These sources of contamination are considered in this set of analyses. Methods: We collected emergency department data from 41 of 42 hospitals serving a major US city from 1993 through 2004. A total of 7,952,826 visits are being analyzed, 446,559 (5.63%) for GI illness. Six major drinking water utilities serving three million residents are participating in this study, providing water quality and distribution system network data. To better understand the role of inadequate water treatment in contributing to GI illness we are considering temporally variable water quality measurements, including turbidity and disinfection efficiency, taken at each plant and the differences in raw water sources and treatment techniques among plants. We are evaluating the role of the distribution system by considering temporally variable water quality measurements, including chlorine levels and detection of indicator bacteria, in samples taken from the distribution system. We are also evaluating the potential for distribution system contamination, as quantified by the estimated distance from treatment plant to end user and the time the water travels, or water age. Water age is being estimated using hydraulic models. We are examining the association between these water quality factors in each zip code and emergency visits for GI illness among people residing in that zip code. Poisson generalized linear models are being fit, controlling for potential confounders. Results: An average of 102 emergency visits for GI illness occurred per day in the study area, out of an average of 1810 total emergency visits per day. The maximum turbidity of the source waters serving the treatment plants, including both lakes and rivers, ranged from 0.6 to 472 nephelometric turbidity units (NTU). The average filtered water turbidity ranged from 0.03 to 0.166 NTU. The average distance from plant to end user was estimated to be 9.50 miles (range: 0.96–23.6 miles). The described epidemiological analyses are ongoing and will be presented. Discussion: Results from this study, the most comprehensive of its kind to date, will contribute important new evidence regarding the role of drinking water quality in endemic GI illness.

Bayesian Belief Networks to Integrate Monitoring Evidence of Water Distribution System Contamination

A Bayesian belief network (BBN) methodology is proposed for combining evidence to better characterize contamination events and reduce false positive sensor detections in drinking water distribution systems. A BBN is developed that integrates sensor data with other validating evidence of contamination scenarios. This network is used to graphically express the causal relationships between events such as operational changes or a true contaminant release and consequent observable evidence in an example distribution system. In the BBN methodology proposed here, multiple computer simulations of contaminant transport are used to estimate the prior probabilities of a positive sensor detection. These simulations are run over multiple combinations of possible source locations and initial mass injections for a conservative solute. This approach provides insight into the effect of uncertainties in source mass and location on the detection probability of the sensors. In addition, the simulations identify the upstream ...

Distribution System Contamination Events: Exposure, Influence, and Sensitivity

This paper presents a two-part investigation of the response of municipal water distribution systems to contamination events. In Part I of the investigation, a contamination event was modeled as a steady 6-h injection of a soluble conservative substance into a single node. The injection was repeated node by node at all 89 nodes in the pipe network. In each case, the fraction of the population at risk of contaminant exposure was estimated at the end of a 72-h simulation period. A dimensionless exposure index (EI) was introduced as a simple global measure of network response, ranging from EI=0 (no consumers are exposed) to EI=100% (all consumers are at risk of exposure). Simulation results were used to construct a zone of influence (ZOI) map, which categorizes network injection nodes on the basis of their potential to expose downstream consumers. In Part II of the investigation, a generalized sensitivity analysis was performed to determine the sensitivity of network response to four dynamic network variables (base demand, storage capacity, injection mass, and injection duration). Latin hypercube sampling was used to set up 1,152 contamination event simulations at two injection nodes. Both nodes were selected on the basis of their exposure potential (one high, one low) as determined from the ZOI map. Based on the Kolmogorov-Smirnov d statistic, exposure levels in the example network were found to be most sensitive to variations in base demand and injection mass. Tank storage capacity was important in certain cases, while injection duration tended to be least important.

A Risk Assessment Methodology for Intentional Chemical and Biological Contamination of Distribution Systems

A Risk Assessment Methodology for Intentional Chemical and Biological Contamination of Distribution Systems

Expanded Summary: Modeling intentional distribution system Contamination and Detection

The objective of this study was to utilize commercial distribution system modeling software to understand how a drinking water system could be affected by the intentional introduction of chemical contaminants. The hydraulic model results are used to estimate the risk involved in several feed scenarios and chemical contaminants. The model results are then combined with concentration‐response sensitivity data from routine monitoring instruments to determine the ability of each chemical contaminant to be detected. Because the four chemicals studied ‐‐ parathion, VX, sodium monofluoroacetate (1080) and cyanide ‐‐ are modeled as highly persistent, their comparative effects are determined by the toxicity of the highest practical dosage. The results of the modeling scenarios show that large‐scale contamination of a drinking water system may be accomplished through backflow into major network water supply lines. Strategically located points of attack outside of the major supply lines can also produce large‐scale contamination at lesser concentrations. Points chosen at random for a covert contamination attack within the distribution system will optimally affect an area of a few neighboring streets of up to 1 square mile, depending on the pipe velocities and flow patterns within the distribution system as well as other factors.

Preparing for Emergencies with Tabletop Exercises

This article discusses conducting a tabletop exercise for a distribution system contamination incident. Topics covered include: exercise objectives; exercise format; sample scenario; tabletop exercise “menu” of different exercise combinations; and, tabletop exercise disclaimers.

Explaining the occurrence of coliforms in distribution systems

According to the Total Coliform Rule, coliform bacteria constitute the main indicator used to detect microbial contamination in distribution systems. A major goal for water utilities is to prevent and control coliform occurrences and noncompliance (with respect to regulations). However, the applied solutions are sometimes successful only to a limited extent because of the variety of factors that may give rise to these occurrences. It is therefore important to identify those factors—from the structure and operation of the distribution system to the quality of the distributed water itself—that can influence the occurrence of coliform bacteria in a distribution system. The use of the identified factors makes the modeling of coliform occurrences attractive, and a number of approaches for doing so have recently been proposed. This article provides a review that includes the mechanisms of how coliform bacteria are introduced into treated and distributed drinking waters, the major factors controlling the survival and regrowth of coliforms once introduced into the system, and the modeling efforts carried out to explain or predict their occurrence.

Waterborne disease Outbreaks Caused by Distribution System Deficiencies

Distribution system contamination has resulted in a significant number of waterborne disease outbreaks in the United States. A review of the 113 distribution‐associated outbreaks reported over the past 30 years finds 498 hospitalizations and nine deaths. Since 1996, distribution system deficiencies have caused 45% of all outbreaks reported in community water systems. Most distribution‐associated outbreaks were attributable to chemical and microbial contamination from cross‐connections and backsiphonage. Preventing contamination of the distribution system is key to reducing the risk of waterborne disease outbreaks. Important preventive steps include maintaining adequate water pressure throughout the system; identifying and replacing older, leaking water mains; maintaining a chlorine residual and routinely monitoring the residual; adopting cross‐connection control programs; inspecting storage facilities on a routine basis; adequately disinfecting after system repairs; and, increasing corrosion control efforts. An aging water system infrastructure renders the United States even more vulnerable to the risk of waterborne disease outbreaks. More regulations may be required to prevent these outbreaks unless water suppliers take action to reduce distribution system contamination and sufficient funds are allocated for system maintenance, repair, and replacement.

Detection of <i>Aeromonas hydrophila</i> in a drinking- water distribution system: a field and pilot study

A 16-month study was conducted on the presence of Aeromonas hydrophila in drinking water in Indiana, U.S.A. Enumeration was conducted in source water, in various sites within a water treatment plant, and in the distribution system in both bulk water and biofilm, as well as in a simulated (annular reactors) drinking-water distribution system. Presumptive Aeromonas spp. counts on source waters regularly approached 10(3)-10(4) CFU/100 mL, during summer months and granular activated carbon - filtered water counts ranged from <1 to 490 CFU/100 mL. In source water, presumptive Aeromonas levels were related to water temperature. Aeromonas hydrophila was never detected in the treatment plant effluent or distributed bulk water, showing disinfectant efficiency on suspended bacteria; however, isolates of A. hydrophila were identified in 7.7% of the biofilm samples, indicating a potential for regrowth and contamination of drinking-water distribution systems.

The case for maintaining a disinfectant residual

North American water suppliers should continue to maintain a disinfectant residual until limitation of bacterial regrowth and control of distribution system contamination are better understood.Maintenance of a disinfectant residual in drinking water systems has been the cornerstone of sanitary engineering for nearly a century. The author argues that eliminating the disinfectant residual in North American systems is ill advised until issues related to controlling bacterial regrowth and distribution system contamination are better understood. In the meantime, the water supply industry should direct its efforts toward making disinfection practices compatible with other water quality and aesthetic goals.

Contaminant Propagation in Distribution Systems

The Safe Drinking Water Act (SDWA) of 1974 requires that the U.S. Environmental Protection Agency (EPA) establish maximum contaminant levels (MCLs) for each contaminant which may have an adverse effect on the health of persons. The SDWA clearly specifies that these MCLs shall be met at the consumers tap. Nevertheless most regulatory concern has been focused on water as it leaves the treatment plant before entering the distribution system. There is, however, growing interest in determining the factors that cause water quality variations in drinking water distribution systems. In order to study this effect, the Drinking Water Research Division of EPA initiated a cooperative agreement with the North Penn Water Authority. This cooperative agreement has resulted in a series of field monitoring and systems modeling studies that lend insight into the movement of contaminants in distribution systems. Previous research has resulted in development of a steady-state model, a quasi-steady-state model and dynamic model that have provided useful approaches to modeling the general propagation of contaminants in distribution systems. In this paper, results from the steady-state model are utilized to examine the actual pathways of water flow and the time of passage and percentage of water that flows from a given source to a given node in a distribution system. The contaminant propagation technique developed from this extension of the steady-state model provides a useful technique for analyzing many of the factors that affect water quality in a distribution system. A major finding of this research study is the importance of adequate hydraulic modeling of the systems being studied and the importance of field studies in verifying systems performance. The approach suggested in this research will provide useful insight into the water quality variations that may impact consumers at the tap and the development of time and spatially sensitive monitoring strategies.