Grantee Research Project Results

Final Report: Measures of Distribution System Water Quality and Their Relation to Health Outcomes in Atlanta

EPA Grant Number: R834250
Title: Measures of Distribution System Water Quality and Their Relation to Health Outcomes in Atlanta
Investigators: Moe, Christine L. , Sarnat, Stefanie Ebelt , Kirby, Amy , Levy, Karen , Klein, Mitchel , Tolbert, Paige
Institution: Rollins School of Public Health, Emory University
EPA Project Officer: Page, Angela
Project Period: July 1, 2009 through June 30, 2012 (Extended to June 30, 2014)
Project Amount: $599,756
RFA: Innovative and Integrative Approaches for Advancing Public Health Protection Through Water Infrastructure Sustainability (2008) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , Water , Sustainable and Healthy Communities

Objective:

The investigators proposed research to link health outcomes, quantified through emergency department (ED) visits for gastrointestinal (GI) illness, to distribution system water quality and infrastructure characteristics. In addition, the investigators proposed an integrative approach for characterizing health risks associated with microbial contamination of drinking water distribution systems through the development of vulnerability assessments and the implementation of an innovative automated continuous water quality monitor for use in distribution systems.

This study had four aims:

Aim A (spatially refined analysis): Refine the previously-conducted analyses assessing the association between rates of ED visits for GI illness and estimated residence times of drinking water serving the study area of two utilities, using geocoded patient address data to identify the closest node in the distribution system.

Aim B (1993-2004, 2005-2009, 1993-2009 analysis): Extend the previously-conducted analyses assessing the association between rates of ED visits for GI illness and estimated residence times of drinking water serving the service area of two utilities by considering data from these utilities covering 2005 through 2009.

Aim C (vulnerability assessment): Assess the association between rates of ED visits for GI illness and exposure metrics derived from the results of the vulnerability assessment. Compare these associations to those observed when only chlorine residual or water age metrics are considered as the exposure. One distribution system will be studied.

Aim D (AMS evaluation of vulnerability assessment results): Use an automated monitoring system (AMS) to examine the results of the vulnerability assessment by comparing continuously monitored water quality in areas of the distribution system predicted to be “high risk” for microbial contamination to areas predicted to be “low risk."

Summary/Accomplishments (Outputs/Outcomes):

We examined the relationship between modeled water residence time (WRT), a proxy for probability of microorganism intrusion into the distribution system, and emergency department visits for gastrointestinal (GI) illness for two water utilities in Metro Atlanta, USA during 1993–2004. We also examined the association between proximity to the nearest distribution system node, based on patients’ residential address, and GI illness using logistic regression models. Comparing long (>90th percentile) with intermediate WRTs (11th to 89th percentile), we observed a modestly increased risk for GI illness for Utility 1 (OR=1.07, 95% CI: 1.02–1.13), which had substantially higher average WRT than Utility 2, for which we found no increased risk (OR=0.98, 95% CI: 0.94–1.02). Examining finer, 12-hour increments of WRT, we found that exposures >48 h were associated with increased risk of GI illness, and exposures of >96 h had the strongest associations, although none of these associations was statistically significant. Our results suggest that utilities might consider reducing WRTs to <2–3 days or adding booster disinfection in areas with longer WRT, to minimize risk of GI illness from water consumption.

A distribution vulnerability assessment was conducted based on spatial analyses of historic data on estimated water residence time, main breaks (data provided by utility for 2010-2011), pressure fluctuations (based on data from 29 in-line pressure monitors in 2011). The water residence time nodes with estimated residence times ≥100 hours and the main break records from 2010-2011 were analyzed for statistically significant geographic clusters. For both analyses, the geocoded datasets were analyzed using SaTScan v. 9.1.1 software (SaTScan, Boston, MA) and a Ripley’s K function. This analysis identifies spatial clusters and ranks them by statistical likelihood. Multiple, statistically significant geographic clusters of long residence time, main breaks were identified in the distribution system.

The results of the vulnerability assessment were used to guide decisions about locating an Automated Monitoring and Sampling (AMS) Device. The device was installed to continuously monitor seven physical-chemical water quality parameters at three sites:

Site 1: Entry point to the distribution system (Jan-Sept 2012)

Site 2: Distribution system site (Fire Station A) with no known physical vulnerabilities (Sept 2012-March 2013)

Site 3: Distribution system site (Fire Station B) within a statistically significant geographic cluster of main breaks occurring between January 2010 and December 2011. (April-June 2013)

The AMS device continuously monitored redox potential, conductivity, pH, chlorine residual, turbidity, pressure, and temperature. Analyses of the data distributions indicated clear differences between the water at the entry point to the distribution system (Site 1) and the water at the two distribution system sites (Sites 2 and 3) for pH, chlorine residual, and water pressure. Site 1 generally had higher pressure and chlorine residual (as expected) than Site 2. Water at Sites 2 and 3 had notably higher pH (>8) compared to Site 1 (pH between 7-8). Water at Site 2 had consistently lower redox measurements than Sites 1 and 3. Water at Site 2 also had higher conductivity than Sites 1 and 3. Site 3 had higher turbidity than Sites 1 and 2.

Conclusions:

This study demonstrates the challenges of characterizing distribution system water quality. There are considerable temporal and spatial variations in physical and chemical water characteristics that are not readily explained by geographic location, water residence time or historic main breaks. A companion study supported by another funding source included large volume water sampling and microbiological analyses at these three sites where the AMS was located and three other distribution system sites located in clusters with long water residence time, or more frequent main breaks, or more frequent pressure loss. The characteristics of the six sites, analyses of the physical-chemical data from the AMS, and the results of the microbiological water quality analyses at these sites will be reported in a future publication.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Publications Views
Other project views:	All 14 publications	1 publications in selected types	All 1 journal articles

Publications
Type	Citation	Project	Document Sources
Journal Article	Levy K, Klein M, Sarnat SE, Panwhar S, Huttinger A, Tolbert P, Moe C. Refined assessment of associations between drinking water residence time and emergency department visits for gastrointestinal illness in Metro Atlanta, Georgia. Journal of Water and Health 2016;14(4):672-681.	R834250 (Final)	Abstract from PubMed Abstract: IWA Publishing-Abstract Exit

Supplemental Keywords:

Drinking water distribution systems, drinking water quality, gastrointestinal illness, drinking water residence time, time series study, emergency department visits

Relevant Websites:

Center for Global Safe WASH Exit

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.