Groundwater in the Great Lakes Basin

SPECIFIC EPISODES
Walkerton
In 2000 in Walkerton, Ontario, the largest ever
Canadian multi-bacterial waterborne outbreak associated
with a contaminated municipal water supply
occurred (Public Health Agency of Canada, 2000;
Krewski et al., 2002). Of more than 2,000 cases, 1,346
patients had gastroenteritis after drinking groundwater
from a municipal well. Stool samples confirmed that
167 patients had E. coli O157:H7 and 116 people had
Campylobacter spp. Sixty-five patients were admitted
to the hospital and, of these, 27 developed HUS. Six
people died as a result of the outbreak. A series of
circumstances led to an outbreak of this magnitude
including heavy spring rains accompanied by flooding,
presence of E. coli O157:H7 and Campylobacter spp. in the
environment due to application of cattle manure near
the poorly maintained municipal well and inadequately
disinfected well water.
Put-in-Bay
precipitation was 200% above the 50-year average for
May (Figure 3). This deluge likely raised the water
table, saturated the subsurface and, along with very
strong Lake Erie currents, forced a surge in water levels
and rapid surface water-groundwater interchange
throughout the island. Landsat images showed a
massive influx of organics and turbidity surrounding
the island. Shortly after these events the peak of the
illnesses was reported. This combination of factors and
information can be used to examine vulnerabilities in
other coastal groundwater systems.
Sixteen groundwater wells that provided potable water
on the island were tested for fecal indicator bacteria,
viruses and parasites (Fong et al., 2007). All wells
were positive for both total coliform and E. coli. Seven
wells tested positive for enterococci and Acrobacter, an
emerging bacterial pathogen; F+-specific coliphage was
present in four of the wells (Figure 4). Three wells were
positive for all three bacterial indicators, coliphages and
Arcobacter; adenovirus DNA was also recovered from
two of these wells. A cluster of the most contaminated
wells was noted on the southeast side of the island.
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At Put-in-Bay, South Bass Island, Ohio, in the summer
of 2004, a large groundwater-associated outbreak,
caused by contamination from sewage, infected ~1,450
individuals, both residents and visitors. Extensive
groundwater contamination on the island was likely
caused by transport of microbiological contaminants
from sewage discharges to the lake and to the subsurface
from wastewater treatment facilities and septic
tanks, after extreme precipitation events in May,
June and July 2004 (Fong et al., 2007). The level of
Figure 3.
LA CROSSE MUNICIPAL WELLS –
A LINK TO VIRUSES IN GROUNDWATER
Illnesses associated with Lake Erie rainfall and a wind-driven lake event
A 2004 study conducted by the Marshfield Clinic
Research Foundation in La Crosse, Wisconsin, located
near the Wisconsin River, focused on municipal well
susceptibility to enteric virus contamination from
surface water. The objective was to relate the amount
of surface water contributions to the frequency of virus
detection in La Crosse wells. The researchers sampled
for human enteric viruses
monthly for one year
(March 2001 - February
2002). Samples were
taken at five sites prior to
chlorination. Hydrogen
and oxygen isotopes were
used for estimating the
amount of surface water
in wells. The results indicated
incidence of enteric
viruses at every sample
site despite testing
negative for indicators
of sanitary quality (i.e.,
male-specific and somatic
colipahges, total coliform
bacteria, Escherichia coli
and fecal enterococci)
(Figure 5). Extrapolating
these results, approximately
one-third of
groundwater pumped