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BACKGROUND INFORMATION continued

GVRD EIA Summary Report (November, 1993) states, ".,.ozone in combination with
conventional or biological filtration would be appropriate for primary disinfection.
Pretreatment and maintenance practices such as filtration of the source water and pigging
and flushing of watermains would improve water quality.but could neither completely
eliminate the potential for bacterial regrowth nor control pathogens introduced into the
water system after source treatment and thus secondary disinfectant is still needed."
Minimal quantities of disinfectant may be required to meet the Canadian Water Quality
Guidelines and to compensate for the shortcomings of the current GVWD distribution
system. (GYWD treatment plant planning has allowed for the possible installation
of ozone.)

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FACEY
hee

Filtration is a long term and beneficial, first step, solution. It would reduce the number
of rechlorination stations required and decrease the overall quantity of deleterious
chemicals entering the system. It is also the first step to introducing alternative water
ft vatments,

"Biological filtration could be combined with ozone to produce a very high quality of
drinking water..." GVRD Reflections (September 1993), It would have negligible impact
on the receiving environment.

Given improved circulation of the system (looping of mains) and an active
flushing/cleaning program, a lower disinfectant residual would be required.

"There is a lack of discussion on the impact of regular water main cleaning and pigging
on bacterial regrowth. What is required is a graph showing a time series of bacterial
count in 4 particular section of pipe, plotted against the frequency of main cleaning and
pigging on the same section of pipe. We believe there may be a relation between the two,
and this should be examined to determine the impact of rigorous cleaning/flushing on
bacterial regrowth.

"It may be possible, with filtration at both Capilano and Seymour (which is required
anyway), and an active cleaning/flushing program, combined with better looping of
mains, that a lower chlorine residual could be used and still prevent bacterial regrowth
in the system.

"The concept of withdrawing colder, deeper water from tie reservoirs should be
examined. Since the bacterial regrowth is most active in the summer and fall when
temperatures increase, drawing on cooler water from deeper in the hypolimnion of each
reservoir may reduce regrowth rates." (BC Environment Comments on Stage I
Environmental Impact Assessment of Proposed Secondary Disinfection of Iorinking
Water.")