Environmental Engineering Reference
In-Depth Information
responsible to a point-source or person-to-person contact. Furthermore, if it is
envisioned that a point-source is possible, it will be necessary to determine the
point of access by disease-producing agents to the finished water. For example,
an infectious agent believed responsible for a waterborne outbreak may be asso-
ciated with a cross-connection somewhere in the distribution system or regrowth
in an activated carbon filter at the treatment plant compounded by ineffective
disinfectant residual in the finished water. Knowledge of past outbreaks and epi-
demiology of the suspected infectious agent, combined with the total of current
data logs and analyses of the outbreak in question will serve to identify the
hypothesis with greatest likelihood explaining the outbreak. Publications sum-
marizing disease outbreak investigation procedures are very helpful. 134 - 137
Remedial Control Measures During hypothesis formulation, implications as
to the cause of the outbreak may emerge, justifying a simultaneous review of
options for remedial control measures. Since the hypothesis advanced has not
been proven at this point, any remedial actions called for must be directed at
immediate protection of the public. Where a danger in the drinking water supply
is envisioned, decisions are limited to disconnecting the purveyor from the users,
issuing a boil order, or supplying an auxiliary source of safe drinking water. In
the example of the Alamosa, Colorado, outbreak, residents were advised not to
use tap water for potable uses on the day bacterial contamination was discov-
ered and to bring large containers to obtain safe water from distribution centers
located within the community. Bottled water was supplied mostly to schools.
Main flushing following superchlorination took place in stages, beginning six
days from the time the outbreak was announced and residents were asked to
refrain from using tap water for drinking and cooking at that time. Water author-
ities should not be required to undertake expensive repair and retrofitting of the
treatment system before it is definitely ascertained that there is a physical prob-
lem in need of attention. The mere enactment of precautionary measures will
prescribe a liability, both in terms of monetary cost and public relations.
Hypothesis Testing This is the important “proof” step in the investigatory
program. All parties affected and the rest of the community will anxiously await
the final word on the cause of the outbreak. All evidence obtained during the
investigation is evaluated in an acceptable plan for testing a particular hypothe-
sis. The evidence presented is the sum total of microbiological, epidemiological,
and environmental findings collected during the course of the investigation. The
most definitive microbiological evidence is the unequivocal identification of the
waterborne disease agent in case specimens and samples taken at the source of
the outbreak, however, the latter may be difficult to accomplish. New method-
ologies are available to aid in rapid detection of suspected pathogenic agents in
environmental samples including water. A brief description of the procedures is
given in the following section. Epidemiological evidence arises from the results
of retrospective studies conducted on known cases and randomly selected con-
trol subjects within the affected community. Environmental evidence pertains to
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