That is why I continually ask what the results were from analysis of the 'retention' samples from the airport tankage. Practices vary; in the old days deliveries often had a representative sample from the bowser taken and it was sealed in something resembling a kilner jar with wire seals and a lead crimp.
Nowadays with hot hydrant systems the procedures aren't much changed: Ideally (i.e. CAP 748) there should still be a sample taken:
a) immediately before receipt into the fuel installation;
b) after receipt of fuel into the fuel installation (after settling time);
c) each day before the first delivery from the fuel installation;
d) after prolonged heavy rainfall or snow;
e) after de-fuelling;
f) after vehicle washing;
g) immediately prior to fuelling an aircraft.
Soooo.. again, I ask, where are the samples, were they subject to a proper Chain of Custody arrangement, and what are the analysis results?
It would be nice to see some records of the last delivery into tankage and the total rainfall increments between the delivery and the fuelling.
Pinkman