COVINA, Calif. – Two female California teachers face criminal charges after authorities allege they engaged in sex on the beach with multiple students, multiple times.

Covina-Valley Unified School District teachers Melody Lippert, 38, and Michelle Ghirelli, 30, allegedly met with several students from South Hills High School in November at San Clemente State Beach, where they plied them with alcohol and engaged in sex acts, according to KTLA5.

Police contend Lippert supplied students with alcohol and engaged in a sexual relationship with one of them during one trip. She then organized an overnight camping trip a few weeks later with Ghirelli and several students from the first trip, and both teachers allegedly engaged in sex with students during the second outing, according to the news site.

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Neither excursion was sponsored or authorized by the school district.

Some of the students on the trip were over 18 years old, while others were not, according to a police press release cited by KTLA.

Lippert was arrested Saturday on charges of conspiracy and contributing to the delinquency of a minor, while Ghirelli was arrested the same day for oral copulation and unlawful sex with a minor, according to the police statement.

“Based on the charges the teachers were booked to, you can make that assumption as to which teacher was with students that were of age,” Lt. Jeff Hallock told the news site.

“But, of course, regardless of somebody’s of age or not it is very serious. We take these very serious when you’re talking about a student-teacher relationship.”

Student Keanu Estrada told NBC he was surprised to hear Lippert was arrested.

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“I’ve known her since I was like 4. She’s a really nice persona and I would never think that she would do something like this,” he said.

Both teachers live in Covina. They were booked and released from jail soon after their arrest, according to media reports.

School officials told the media teachers heard rumors about the illicit outings and reported it to administrators.

“As soon as we became aware of these allegations, we immediately contacted the West Covina Police Department and have been working closely with their detectives,” Covina-Valley spokeswoman Michelle Van Der Linden told KTLA.

West Covina Police worked the case with the Orange County Sheriff’s Department.

The teachers were put on paid administrative leave on Sunday, Van Der Linden said, but declined to discuss the allegations further, NBC reports.

“I think it’s best to leave that up to the investigation,” she said. “Obviously, we have to respect their right to privacy.”

The teacher-student sex allegations come about a week after police announced the arrest of South Hills High School part-time girls’ wrestling coach Anthony Vidales for allegedly engaging in inappropriate contact with a 17-year-old student at the school, NBC reports.

The cases have parents like Roza Hajialiakbar quite concerned.

“I’m honestly shocked, I’m really shocked,” she told NBC. “This can’t go on. Who does this?”