Environmental Engineering Reference
In-Depth Information
home (from the tap and most likely piping with the home). During the spring,
homes are heated; note the spring average temperature is 2.2 C on average from the
Ottawa data and it is highly likely that the home was heated at the time of sampling.
So while the external temperature (e.g. 2.2 C) is low, the internal temperature of the
home can be quite high. The opposite occurs during summer months when homes
are cooled rather than heated. This can explain the high lead levels for the
first liter
(only) in spring versus the low lead levels in summer.
11.3.3 The Simulation of Lead Samples
In this subsection, we use information from the estimated lead values obtained in
Sect.
11.3.2
to simulate samples for a 6-h stagnation protocol for the
'
rest of
Ontario
data. We use a simple linear approach as our benchmark model. First, we
use the same approach as in Sect.
11.3.2
to estimate the lead values for
'
first liter
sample for the rest of Ontario (30-min Stagnation) such that all samples have a
common pH value of 7.4.
2
After the completion of this process, we would have
Ottawa data under 6-h stagnation protocol with a pH of 7.4 and the rest of Ontario
data under the 30-min Stagnation protocol also with a pH of 7.4. To obtain
'
rest of
Ontario
'
lead values in a manner that would reflect a 6 h stagnation, we take the rate
of dissolution of lead as the average percentage change between the
'
6h
'
samples
and
samples. This percentage change (an increase) will be applied to the
lead values for the
'
30 min
'
as if taken
under the 6-h Stagnation protocol. We are not specifying the functional form for the
rate of dissolution of lead but merely assuming the percentage change in lead
between the 6 h samples and 30 min samples is a
'
30 min
'
samples in order to obtain
'
new samples
'
xed amount and does not depend
on the path of the functional form (linear or nonlinear) from time at 30 min to time
at 6 h (see Fig.
11.8
for an example).
Figures
11.9
,
11.10
and
11.11
show a summary of the results from the simu-
lation of Ontario
first liter samples under the 6-h stagnation protocol. The per-
centage change factor was obtained in three ways: (1) Using all of Ottawa data
—
Spring 2007, Summer 2007 pre water main rehab and Summer 2007 post water
main rehab, (2) Ottawa spring 2007 data only and (3) Ottawa summer data only
(pre- and post-water main rehab).
The number of samples above 10
g/L for the rest of Ontario under the 30-min
stagnation protocol was 52. Under the 6-h stagnation protocol, the number of
samples above 10
μ
g/L is 231 using all Ottawa data. If we base the percentage
increase in lead values from 30 min stagnation to 6 h stagnation using only Ottawa
summer data, the number of samples for the rest of Ontario above 10
μ
g/L is 214
compared to that of 253 when basing the percentage increase using Ottawa spring
μ
2
Although the Ontario average pH is 7.4, individual samples would be higher or lower than the
average. Hence it is bene
cial to have a common pH value for a consistent analysis.
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