Click on a circle in the chart to view Sham immigration records. You can find out when most of the Sham families immigrated to the United States. You can focus your search to immigration records dating from that era. Immigration records can tell you an ancestor's name, ship name, port of departure, port of arrival and destination.
Probably, however...: As my colleague dr. Pappas mentions, marijuana is almost always tested in urine rather than blood, so someone would almost certainly pass a blood test but is more likely to face a urine test.
On the average, THC can be detected in the urine of a casual user during 2-5 days, 1-2 weeks for usual users and up to one month for heavy users. In the blood marijuana usually stays only 1-2 days, about 24 hours in saliva, up to 4 weeks in sweat, and in hair it can be detected for up to 90 days.