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A Secret Service spokesperson confirmed the second positive test in an email to The Post, but had no further statement.
The drug was found Sunday night in a dime-size bag inside a cubby used by staff and guests, according to a source familiar with the investigation. The discovery forced a brief evacuation of the White House.
An initial dispatch call stated that the substance was found in the library on the ground floor of the executive mansion, but officials familiar with the incident later told The Post it was located in the West Wing holding area.
The cubby is used by employees and visitors to store phones and personal items that are not taken into other parts of the West Wing, an official close to the matter told The Post on Wednesday.
In a radio call at 8:49 p.m. Sunday, a DC firefighter said: "We have a yellow bar stating cocaine hydrochloride."
President Biden was at Camp David at the time of the incident, as was his son Hunter, who has admitted to a past crack cocaine addiction. The first son was part of the family party that later returned to Washington from the presidential retreat for July 4 festivities.
Authorities were trying to determine how the substance got into the White House after a Secret Service agent found it during a routine sweep.
The agency told The Post that it "does not comment on an active investigation," with rep Anthony Guglielmi later saying that additional tests will be conducted on the substance.
"On Sunday evening, the White House complex went into a precautionary closure as officers from the Secret Service Uniformed Division investigated an unknown item found inside a work area," Guglielmi said in a statement.
"The DC Fire Department was called to evaluate and quickly determined the item to be non-hazardous," he added.
A source familiar with the probe told NBC News said the Secret Service will conduct a full review, which will include scanning surveillance videos and entrance logs to determine who had access to the location.
The source acknowledged that the task could be difficult due to the large number of people who have been at the location, adding that it was unknown how long the bag had been there.
According to White House visitor logs reviewed by The Post, more than 4,000 entries for West Wing tours were recorded in March, the most recent month for which records are available.
Comment: The New York Post also reports Hunter Biden was at the White House Friday, just days before the cocaine was discovered: