Although it is not a conclusive indicator, total coliform (TC) bacteria have been used for
decades as indicators of fecal contamination and/or distribution system breaches.
Despite new data indicating TC are not useful as indicators of fecal contamination, TC
sampling is still seen by water quality managers as a useful indicator of the integrity of
their distribution system. A number of researchers have identified the difficulty in
estimating the underlying spatial and temporal distributions of TC in distribution systems
based on the presence/absence of sampling. For TC to be a useful indicator there must be an
underlying assumption that monitoring will result in observing TC when present.
However, the sampling plans currently employed by water utilities are not based on
optimizing sampling to identify TC when present but rather they are optimized by
accessibility and logistics. TC sampling of even large numbers of samples (e480/month)
tests an infinitesimal portion of the water flowing through the system in a month; since
TC are highly heterogeneous, mostly zeros and perhaps a few positives, result. In order
to optimize a sampling plan to detect TC when present, the plan, including locations,
periodicity and sample volumes, should be based on the underlying distribution. This
distribution cannot be measured directly, but the distributions of the sampling results can
be evaluated. A recent study on sample volume determined that when taking 100mL
and 2L samples side by side and comparing the results, the 100mL samples significantly
underestimated the occurrence of TC. While these results suggest that the current
sampling and analytical strategies may not be optimal, they do not resolve the issue of
how many samples of what size are needed to meet the objectives listed above. It may
be that different objectives require different sampling and analytical plans. To explore
high volume sampling, we have developed a method using capsule filtration and enzyme
substrate technology that can accommodate samples up to 20L. We evaluated the
ability of the process to filter, recover and identify total coliform and E. coli at different
concentrations and sample volumes ranging from 100 mL to 20L. Includes 2 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 240 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 9 |
| Published : | 11/01/2007 |
