AWWA WQTC60708

Results are presented from a study examining the temporal changes in pathogen andindicator numbers during storm events in April and May of 2003 in a watershed inSouthwestern Ontario, Canada. Water samples were collected for total coliforms, fecalcoliforms, Escherichia coli, Escherichia coli O157:H7, and Campylobacter spp. Sampleswere not analyzed for Cryptosporidium spp. and Giardia spp. at that time; however,subsequent storm event samples were collected and analyzed for the two protozoa. Eventsamples were collected from within an intensely farmed subwatershed of the GrandRiver.All samples were positive for total coliforms, fecal coliforms and Escherichia coli.During precipitation events, coliform indicators increased to peak numbers very rapidlyfrom their baseline concentrations, and a tailing of their numbers was also observedfollowing an event, as expected. Peak concentrations of coliform bacteria were morethan 3 orders of magnitude greater than baseline concentrations for the events sampled.E. coli O157:H7 was not detected in any event samples. Campylobacter spp. wasobserved in water samples at the beginning of one of the events; however, the numbers ofCampylobacter spp. dropped off to undetectable levels as the event progressed. Usingthe Spearman rank correlation test, a positive correlation was observed between E. coliand turbidity (R_s=0.89). Although E. coli bacteria originate in fecal matter, they arewidespread in the environment and are therefore rarely flushed out completely followinga precipitation event.In order to predict the levels of indicator bacteria and potentially pathogenicmicroorganisms in a stream, an existing watershed-scale hydrologic model,WATFLOOD/SPL, was augmented for pathogen fate and transport from point and nonpointsources. The pathogen model considers transport as a result of overland flow,subsurface flow to tile drainage systems, as well as in-stream routing. Model results werereliable in estimating E. coli concentrations (at an order-of-magnitude level). However,for pathogenic microorganisms which are less widespread in the environment with highlylocalized sources, more research in estimating actual environmental loadings is needed.It is essential that drinking water treatment plants be capable of handling peakconcentrations of pathogens. Information on baseline levels and peak concentrations ofmajor pathogens of concern should be available to ensure robust treatment plant design.This study offers additional insight into temporal fluctuations of potential pathogenconcentrations arriving at a treatment plant intake. Includes 25 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

13

File Size:

1 file , 980 KB