Fecal Indicator Bacteria Variability in Samples Pumped from Monitoring Wells

Abstract

The detection of microbiological contamination in drinking water from groundwater wells is often made with a limited number of samples that are collected using traditional geochemical sampling protocols. The objective of this study is to examine the variability of fecal indicator bacteria, as observed using discrete samples, due to pumping. Two wells were instrumented as multilevel piezometers in a bedrock aquifer, and bacterial enumeration was conducted on a total of 166 samples (for total coliform, fecal coliform, Escherichia coli, and fecal streptococci) using standard membrane filtration methods. Five tests were conducted using pumping rates ranging from 0.3 to 17 L/min in a variety of purging scenarios, which included constant and variable (incremental increase and decrease) flow. The results clearly show a rapid and reproducible, 1 to 2 log-unit decrease in fecal indicator bacteria at the onset of pumping to stabilized, low-level concentrations prior to the removal of three to five well volumes. The pumping rate was not found to be correlated with the magnitude of observed bacterial counts. Based on the results, we suggest sampling protocols for fecal indicator bacteria that include multiple collections during the course of pumping, including early-time samples, and consider other techniques such as microscopic enumeration when assessing the source of bacteria from the well-aquifer system.

Hand-pumps as reservoirs for microbial contamination of well water

“…Other studies have shown variability in indicator bacteria concentrations with pumped volume in hand-pumped wells in Bangladesh (Knappett et al 2011) and in Canada in wells with submersible pumps (Kozuskanich et al 2011), but this is the first study that we are aware of that confirms that the hand-pump can play a major role in this variability. The retention and release of total coliforms and E. coli from the internal pump surface is not surprising considering the ability of microorganisms to attach to surfaces and/or incorporate with existing biofilms (LeChevalier et al 1987; O’Toole et al 2000; Banning et al 2003).…”

Unsealed tubewells lead to increased fecal contamination of drinking water

“…Fecal bacteria and viruses have been detected in groundwater wells emplaced in aquifers of diverse geologic material (Rudolph et al 1996; Abbaszadegan et al 2003; Embrey & Runkle 2006; Borchardt et al 2011; Johnson et al 2011; Kozuskanich et al 2011). In developed countries like the United States wells are typically sealed with an expanding clay which fills the annulus between the well casing and the surrounding aquifer sediments from ground surface to approximately 1 m above the screened interval to prevent “short circuiting” by downward flow of contaminated surface water or shallow groundwater.…”

Water quality associated public health risk in Bo, Sierra Leone

“…The main concern of biological contamination is waterborne pathogens, such as bacteria, viruses, protozoa, and helminthic parasites, which pose widespread risks to health when drinking water that is untreated or insufficiently treated (Savichtcheva and Okabe 2006). Tests for the presence of Escherichia coli and fecal coliform are used as indicators of bacteriological contamination (Edge and Hill 2007;Cabral 2010;Foppen and Schijven 2005;Howard et al 2003;Muniesa et al 2006;Personne et al 1998;Powell et al 2003;Schets et al 2005;van Lieverloo et al 2007;Kozuskanich et al 2011;Savichtcheva and Okabe 2006). In addition to microbiological contamination, chemical substances in water, such as fluoride, nitrates, arsenic, and lead and other heavy metals, can also have adverse health effects (Prüss-Üstün et al 2008;Reimann and Banks 2004;Islam et al 2000).…”