chapter 4: temperature inside the landfill

and/or should consist of more than thirty values. The formulation for the t-test can be expressed
as follows:
_
T
t−15
If,
Then,
_
p
_ _
t+ 15 < T t−15
T
_ _
= t
t − test(
T t+ 15,
T −15)
(4-1)
(4-2)
Where T t+
15 is the mean of the temperature readings over fifteen days after the time t,
is the mean of over fifteen days before the time t and p (or probability value) of the t-test is
the probability of obtaining a sample statistic with a value as extreme or more extreme than the
one determined from the sample data.
The approach was first applied to injection wells and did not seem to work as it gave too
many events when compared with actual injection events. The statistical approach was then
applied with a 99% confidence interval. Again the mean was calculated over fifteen-days of data.
The result was still a large number of unrealistic events. This step established that the use of
statistics to identify the temperature drop events is not effective presumably due to high data
variability.
Identification of relevant temperature drop events at the injection events as well as
monitoring locations was accomplished using a difference in mean approach after statistics failed
to give realistic results. Mathematically the approach can be described as,
If
T t+ Y < T t−Y
_
_
45
(4-3)