The first incident allegedly occurred Jan. 14, 2010, at the Northwestern Mutual Mortgage Company in Newport Beach, according to the Orange County district attorney's office.
Investigators say Lallana entered the victim's office and deposited his semen into a water bottle that was on his co-worker's desk.
The defendant is accused of leaving the semen-filled water bottle on the victim's desk, which she drank when she returned to her office.
The victim was unaware of the bottle's contaminated contents. She threw it away after feeling sick, investigators say.
Three months later, the victim and six other employees, including the defendant, were transferred to the Northwestern Mutual Mortgage Company's Orange branch. That's where a second incident occurred, according to officials.
On April 9, Lallana is accused of assaulting the same victim by depositing his ejaculated semen into another water bottle that the victim left on her desk. The victim took a sip from the bottle, then felt sick again. She decided to send the specimen to a private lab to be tested.
The lab contacted her and told her that the water bottle contained semen, police said.
The victim then notified the Orange Police Department.
DNA tests confirmed the semen belonged to Lallana. He was arrested at his Fullerton home by Orange Police Department officers.
If convicted, Lallana faces a minimum of three months to a maximum of three years in jail with mandatory sex-offender registration.