Civil Engineering Reference
In-Depth Information
In the spring of 2001, an outbreak of Cryptosporidiosis occurred in the town of North
Battleford, Saskatchewan, causing approximately 6,500 people to become ill.
Cryptosporidium parvum
is a gastro-intestinal parasite transported by an oocyst,
which is resistant to traditional water treatment. The oocyst leaves the parent host
with fecal material, is ingested by mouth (through poor sanitation, such as dirty hands
or contaminated water) and enters the digestive system of the new host. Symptoms
of the disease are diarrhea, abdominal cramps, vomiting, and headaches.
Failure of the city's surface water treatment plant, located downstream from
their water treatment plant, was found to be the source of the outbreak (Figure 3-2).
The Sedimentation Contact Unit (SCU), which had been re-started after the plant had
been shut down for planned maintenance, did not satisfactorily remove suspended
solids from the source water, and contaminated water was released into the
distribution system. Communication breakdown and confusion, triggered by
personnel turnover, insufficient budget and lack of effective communication with the
Saskatchewan Environment and Resource Management (SERM) resulted in an
extended exposure to the public.
Physical changes were made in the water treatment system, including new
valves and pipes added at the SCU and filter banks so that water could be run to
waste (Figure 3-3). Sampling sites were added after the filter runs to allow for
manual water collection and continuous monitoring of turbidity and particulates.
Coagulant chemicals were added at the sand separators for better mixing. Ultraviolet
(UV) disinfection units were added after both filter banks. UV light has been shown
to be more effective than chemicals for inactivating
Cryptosporidium
oocysts.
Chlorine disinfection was moved to the clearwells instead of before the SCU.
Chlorination units were also installed for the town's water supply reservoirs within
the distribution system. Chlorine disinfection was increased at the sewage plant for
the purpose of treating bypass sewage.
Finally, Standard Operating Procedures (SOPs) were added for the purposes
of quality assurance. The new SOPs called for the surface water plant to shut down
or run water to waste when the following occur:
1.
Sewage bypass events
2.
Chlorination malfunction
3.
Malfunction in the SCU
Finished water with a turbidity greater than 0.3 NTU
Some of the additional changes included:
1.
4.
Increased funding for the regulatory branch of SERM as well as more
personnel.
