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Standard Methods 9060B: Preservation and Storage (20th Edition) recommends that nonpotable water (e.g. source water) samples be held below 10EC for a maximum of 8 hours for E. coli analyses performed for compliance purposes. This 8 hours is based on a maximum of 6 hours transport + 2 hours to begin analyses at the laboratory. Standard Methods also recommends that, when transport conditions result in delays longer than 6 hours, the use of field laboratory facilities located at the site of collection or delayed incubation procedures be considered. These holding times may not be feasible for many small drinking water utilities interested in monitoring their source waters for E. coli, as many do not have facilities to analyze E. coli samples on site and are not within driving distance of a laboratory certified to perform coliform analyses on drinking water samples. The use of delayed incubation procedures, such as Standard Methods 9222E, which could increase the allowable sample holding time, also may not be appropriate for most small drinking water utilities, as most do not have personnel that have been trained to perform the on-site filtration and sterile-transfer techniques that would be required. Because of these limitations, many small drinking water utilities interested in monitoring their source waters for E. coli would have to ship E. coli samples off-site to a qualified laboratory resulting in holding times that would exceed 8 hours. To determine whether holding time has an effect on E. coli sample results, studies were conducted in three phases: Phase 1 - US Environmental Protection Agency (EPA), the Wisconsin State Laboratory of Hygiene (WSLH), and DynCorp conducted a study to evaluate E. coli sample concentrations from four sites at 8, 24, 30, and 48 hours after sample collection for samples stored at 4EC, 10EC, 20EC, and 35EC (to assess the effect of different shipping conditions for small systems), samples were analyzed in triplicate by membrane filtration (mFC followed by transfer to NA-MUG) and Colilert (Quanti-Tray 2000); Phase 2 - EPA conducted a study to evaluate E. coli sample concentrations from seven sites at 8, 24, 30, and 48 hours after sample collection for samples stored in coolers containing wet ice or Utek ice packs (to assess real-world storage conditions). Samples were analyzed in triplicate by membrane filtration (mFC followed by transfer to NA-MUG), Colilert (Quanti-Tray 2000), and Colisure (stored in coolers with wet ice only); Phase 3 - EPA obtained E. coli holding time data from multiple regions throughout the United States through the cooperation of AWWA, and ten drinking water utilities evaluated samples from 12 source waters. Each utility used an E. coli method of their choice (Colilert, mTEC, mEndo to NA-MUG, or mFC to NA-MUG). Samples were stored in coolers with wet ice, Utek ice packs, or Blue ice.

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Edition: Vol. - No. Published: 11/01/2002 Number of Pages: 2 File Size: 1 file , 220 KB