Articles and the physical investigation, a
would be difficult for the site operator to
data following the tank leak has been
second tank test was arranged to
identify any trends within the data.
disregarded.
confirm the likely position of the tank
Although the loss levels are fairly
These levels of wetstock loss are not
leak.
consistent the site operator is unable to
typical for a site being supplied by Oil
- It was found that the tank was
take account of the effect of meter
Company from Supply Terminal. Taking
leaking from near the bottom of
inaccuracy, and has no control site
into
the tank, and that water was now
against which wetstock loss levels
average year to date wetstock loss for
entering
could be compared. A comparison of
sites supplied from Supply Terminal is
one period against another shows that
0.49%, with a maximum of 0.77% and a
the levels of wetstock loss were
minimum of 0.38%. These figures
consistent over the period analysed.
compare with the 0.62% reported by
For the purposes of this analysis the
Leaking Garage in the period 01/04/03
the
tank
in
small
quantities. Levels of Wetstock Loss From the documents provided it
account
meter
settings,
the
to 29/10/04. Period
Average Daily Loss Average Daily Loss Average Daily Loss For Period (Litres) For Most Recent 60 For Most Recent 30 Day Period (Litres) Day Period (Litres)
Percentage Loss For Period
Percentage Loss For Period (Taking account of meter settings)
01/04/03 to 29/10/04
33
28
19
0.54
0.66
01/04/04 to 29/10/04
34
28
19
0.50
0.62
01/06/04 to 29/10/04
24
28
19
0.35
0.47
01/08/04 to 29/10/04
35
28
19
0.49
0.62
01/09/04 to 29/10/04
27
27
19
0.37
0.49
Conclusions Tank Age
in order to check that the ullage
pumps in isolation, necessitating the
reported is accurate. One of problems
opening and closing of the shut-off
associated with the hydrostatic gauge
valves
The tanks are very old and are single
is that, prior to delivery; any imbalance
operational difficulties, and the Health
skin steel. The site operator has been
within the tank system can cause
& Safety implications of doing this
aware of the problems associated with
inaccurate ullage space to be reported.
make it impractical to do unless as part
having tanks of such an age and has
This may lead to a tank overfill.
of a wetstock loss investigation.
Sales Volumes
Additional Analysis Using SIR
on
a
regular
basis.
The
instigated a regime of annual tank testing. Prior to this incident all spirit tanks were tested and passed on August 3rd 2004. Tank Gauging Perhaps this is the most significant area
of
weakness
within
the
reconciliation process. The hydrostatic gauges
are
susceptible
to
Following the initial investigation the
reference to the mechanical totalisers
data was processed using an approved
on the dispensers. This offers the site
SIR system. The system used the data
operator an accurate reference of the
from a number of sites supplied from
usage and protects against fraud and
the same supply source to generate an
failures within the dispensing unit or
'acceptable' loss characteristic, and
pump controller.
then used statistical tools to analyse
large
variances, and, although the vapour balancing valve goes some way to
how 'Leaking Garage' differed from this Wetstock Control
norm.
It appears that the site operator had
The chart below plots the cumulative
reducing these variances, the gauges
been
are liable to reporting tank contents
reconciliation
Leaking
percentage of the cumulative sales for
with a significant degree of inaccuracy.
Garage Ltd. Although reconciliation was
the period of time for which data was
only being performed at grade level it is
supplied. As can be seen the suspect
not unusual for sites with pressure
tank is consistently below the other
It is important that the vapour
systems to do this. The alternative
tanks supplied from this same supply
balancing valve is used prior to delivery
would be to run individual tanks and
source.
Deliveries
44
Sales volumes are recorded by
keeping
adequate records
for
wetstock
wetstock
loss,
expressed
as
a
