Natural Protection of Spring and Well Drinking Water Against Surface
Microbial Contamination:
II. Indicators and Monitoring Parameters for Parasites
THE ISSUE
Groundwater, which is not under the direct influence of surface
water, should
be free of Cryptosporidium and free of other parasites. However,
to claim this
sequestration it is critical to develop a defendable testing protocol.
This proto-
col should be more intensive than that currently required for potable
water.
RESEARCH STRATEGY
Practicing microbiologists in the United States and Europe (Dr.
Stephen
Edberg, Yale University and Dr. Henri Leclerc, University of
Lille) and a prac-
ticing hydrogeologist (Mr. John Robertson, Hydro Geologic)
collaborated to
analyze all possible indicators and monitoring parameters.
MAJOR FINDINGS AND SIGNIFICANCE
Recent outbreaks of cryptosporidiosis and reports of other
newly described
parasitic diseases associated with drinking water transmission
prompted a re-
evaluation of source water monitoring criteria for public
health protection. The
field of microbial indicators was reviewed and each candidate
sentinel evalu-
ated. The distinction was made between source water monitoring
and moni-
toring in the distribution system. Of all potential candidate
microbial sentinels,
Escherichia coli is deemed the most efficacious for public
health protection.
Based on a conservative estimate of its half-life in groundwater
of eight days,
it is recommended that at least two samples be obtained
during this half-life.
In addition to E. coli, two water quality indicator sentinels,
which are not nec-
essarily direct public health threats, should also be monitored
at the same fre-
quency. These are the total coliform group and the enterococci.
If
E. coli is present in any source water sample, the borehole
and any directly
connected borehole should be embargoed. If either total
coliforms or entero-
cocci are detected, only that individual borehole should
be taken off line and
not used until the situation is remediated and the cause
of the fecal contami-
nation eliminated. Clostridium perfringens spores serve
as a useful long-lived
indicator. However, its perseverance in a sample should
not be considered a
direct public health threat since spores may far outlive
pathogens. As a parasite
indicator, C. perfringens should have the same importance as a positive
col-
iform or enterococcus analysis. Coliphages do not yet fulfill
enough of the cri-
teria to be routinely employed. Biological monitoring should
be coupled with
physical-chemical monitoring to establish a long-term history
of the source.
Because all natural waters vary in the amounts of heterotrophic
plate count
bacteria, test methods should be employed which are refractory
to them.
Combination of rigorous source protection plus extraordinary
source monitor-
ing serve as sufficient multiple barriers for parasite
protection.
Edberg, S.C., LeClerc, H., and Robertson, J. B., Natural
Protection of Spring and Well Drinking
Water Against Surface Microbial Contamination: II. Indicators
and Monitoring Parameters For
Parasites, Critical Reviews in Microbiology, 23(2):179-206
(1997).
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