Union County authorities say a tip call led to the discovery of one of the largest marijuana grow operations in county history.

Investigators said someone called Union County Crimestoppers a few days ago to report suspicious activity at a home on Oak Drive, in a remote neighborhood near Lake Monroe.

"Of this magnitude, it's very seldom you get a tip that pans out this well," said Sheriff Eddie Cathey.

Authorities said the homeowner, Elisandra Carvalho, allowed investigators inside the home Tuesday, where they said they discovered the entire second floor had been converted into an indoor grow room for 81 plants, plus about 35 pounds of marijuana worth approximately $235,000 in street value.

"You go upstairs and it's like going in a garden with all the plants and the equipment," Cathey said.

Cathey described the operation as extremely sophisticated, with equipment hard-wired into the home's electrical system from the attic down. He also said Carvalho had been keeping painstaking documentation of what types of plants she was growing, products she was using and how much her operation was yielding.

"It's a pretty skilled operation ... it was obvious that it had been well-planned and well-documented," Cathey said.

Carvalho was arrested on felony drug-trafficking charges Wednesday but had posted a $30,000 bond and left the Union County Jail by Wednesday afternoon.

Authorities said they believe she was running the operation alone, and said they are working to determine where the drugs were headed and who Carvalho was allegedly selling to.

Neighbors in the quiet area were shocked to see the scene unfolding Wednesday, telling Eyewitness News that Carvalho is a perfect neighbor.

"Very quiet...our whole neighborhood is quiet, laid-back, keeping to themselves a lot," said neighbor Nora Boyle.