Environmental Engineering Reference
In-Depth Information
give a better (and an overall best) r-squared of 0.63 which was erroneously stated in
the EU Report (see p. 38) as 0.58. The average of the RDT and FF sample also has
a slope of 0.92 (for linear correlation with measured lead (COMP) sample);
although the average of the RDT and FF underestimates the COMP sample, it still
provides the best estimate (slope closest to 1.0 in relation to COMP) of all the
protocols. The average of RDT and FF provides the most representative sample
when compared with other protocols, which is not very surprising since RDT takes
into consideration many inter-use stagnation times (although the stagnation times
themselves are not known) in much the same way the COMP sample does. FF
samples consider another dimension of consumer behavior; drinking water for
dietetic purposes after running water for several minutes, e.g. drinking water or
using water to cook after washing dishes. Although FF samples are not likely to be
representative of consumer behavior, they still capture some element of it. Toge-
ther, RDT and FF samples capture more elements of consumer behavior than a
single sampling protocol alone would (i.e. RDT and FF together would capture
more elements of consumer behavior than just the 30MS alone). The EU Report
'
s
overall evaluation of the RDT sampling protocol was that it was
unexpectedly
good
which according to the Report can be explained by the fact that in general
RDT overestimates the average weekly intake of lead in drinking water (EU Report,
p. 65). The EU Report also further explained that the RDT sample was capturing
some elements of the water consumption behavior of the consumer which was close
to or greater than the average interuse stagnation time. The overestimation of the
RDT compared to the COMP can be due to other factors as well. We believe that
there is a possibility that the RDT overestimates the COMP sample because of the
time of day in which the RDT samples were taken. The RDT samples were taken
ce hours, avoiding the periods of frequent water use (breakfast, lunch,
and dinner) and the period of overnight stagnation
during of
(EU Report, p. 20). In other
words, the RDT sample was taken when there is a strong likelihood that members
of a household were not present as a result of attending school or going to work. For
instance, a
five-person household which consists of two adults and three children
would most likely have members of the household not present during the
business
day
); hence, there is a strong
possibility of having higher average inter-use stagnation times during which the
RDT sample is taken. After the regular
(hours constituting the sampler
'
s
of
ce hours
members of the family would
return home, thus reducing the mean inter-use stagnation time and the lead values
(since lead leaching depends on stagnation time) per liter of drinking water; this
would be picked up by the measured lead (COMP) sampler but not the RDT
sampler. However, the RDT sampler does pick up several inter-use stagnation
times, which is very useful. Without the restriction of sampling during of
of
ce hours,
ce hours
only, the RDT method could be closer to the COMP sample.
Another way in which
was assessed was by comparing the
ratio of lead values from a given sampling protocol and the COMP sample; this
value should ideally be equal to one or constant over a wide concentration range to
be
representativeness
(EU Report, p. 39). A prediction range for the ratio was also
calculated and test areas were divided into 11 regions (lettered A to K in the
representative
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