SILVER SPRINGS, Fla. -- Finding a marijuana grow house in Central Florida isn't that unusual, but Marion County sheriff's deputies said they found a grow house underground.

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The discovery was a first for Marion County deputies, who were lead to the grow house by an anonymous tip. They had to walk through a trap door that lead to more than 90 marijuana plants.

The trap door was concealed in a shed and led deputies to a grow house beneath a concrete slab behind a house on along NE 1st Street Road in Silver Springs (see map).

"He said he was growing a lot for personal use. There was quite a bit of marijuana," explained Cpt. Lee Sullivan, Marion County Sheriff's Office.

Deputies arrested 61-year-old Michael Klopp and members of Marion County's Multi-Agency Drug Enforcement Team said Klopp told them he did sell what he and relatives didn't use.

"He didn't involve or implicate anyone else in his operation," Sullivan said.

Unlike some of the above ground operations busted earlier this year, agents do believe the underground operation is home grown, but the value of the hydroponic plants are more than their above-ground counterparts. Deputies said they're more pure and have a street value of at least $100,000.

In a statement to agents, Klopp described the operation as "his retirement." He was charged with cultivation of marijuana and possession with intent to distribute.

In addition to the plants, the sheriff's office said they found 19 bags of marijuana around Klopp's house, as well as two bags of seeds.

The Marion County Sheriff's Office said, already this year, they have busted a total of 18 marijuana grow house operations. There were only 13 grow operations shut down all of last year.