EtG does not store in your system (1). It is a direct byproduct of alcohol metabolism (metabolite). Therefore it is created in proportion to the amount of alcohol consumed.
Somewhere between 3-5 hours after drinking the EtG reaches peak levels and then declines through elimination. See
page 597, Figure 4 for a graphic illustration (2) comparing both alcohol and EtG.
EtG is detectable for a longer period than alcohol. As example one standard drink (13.g pa) can be detected in urine for approx one hour while the EtG can be detected for 10-20 hours. More alcohol creates more EtG which in turn requires longer periods for elimination. Smaller amounts require lesser time and when dealing with very small amounts, a sip or two, the EtG may never rise above the cutoff level of the test.(3) This would be particularly true of the 500 cutoff.
Besides the Thierauf study (using 1 and 3 g) Musshoff also studied the small amounts of alcohol in food and drinks for EtG detection with the same conclusion, all cleared in under 20 hours (4) generally substanially less time.
Ref:
1)
Sarkola, 2003
2)
Rosano & Lin, 2008
3)
Thierauf, 2009
4)
Musshoff, 2010