On the website of the I-94, in the FAQ, it details in what cases your departure is recorded or not, when you got an electronic I94 at the port of entry.
- If you leave the USA by air or by sea, your departure is recorded electronically. You do not need to specifically turn in the I-94 or any procedure :
If you are departing by air or sea, your departure is recorded electronically.
- If you leave by land, this is covered by the FAQ question
How do I report my departure if I enter via air and depart via land? which suggests your departure is not recorded. There are 2 cases : either you will re-enter before the end of your allowed period of stay and this entry will be recorded, or you will re-enter after, and in that case you will need evidence you left the country:
If you are not a resident of Canada or Mexico and you receive an electronic I-94 and depart via land, but do not re-enter the United States prior to the expiration date stamped on your passport, you may want to travel with evidence of your departure into Canada or Mexico. Evidence of departure can include, but is not limited to, entry stamps in a passport, transportation tickets, pay stubs and/or other receipts.