PITTSBURG (CBS SF) — Police busted perhaps the largest hash or “honey” oil lab found in Contra Costa County at a house in Pittsburg on Wednesday, arrested five people, and seized $30,000 in cash, police said Thursday.

Hash oil or “honey” oil, as it is commonly called, is a marijuana product that uses butane gas to extract THC, which increases the product’s potency, according to the Drug Enforcement Administration.

Following a lengthy investigation, police said officers executed a search warrant at a residence in the 900 block of Promenade Drive. Police arrested Adam Schiebrel, Michelle Alekseyev, Jeffrey Bellesiles, Kevin Muish and Nicholas Lawton, who are all between the ages of 24 and 30, police said.

The officers uncovered an extensive operation that occupied almost every room in the house for hash oil production, including rooms to grow marijuana, rooms to extract the THC from the plant and storage and packing rooms, police said.

Officers seized 30 pounds of finished product with a street value that police estimated to be around $750,000, along with $30,000 in cash.

One of the suspects had a hidden compartment in his car, which police said is often a tactic used to hide illegal items.

Police said detectives are trying to determine how long the operation has been active and said the case would be presented to the district attorney’s office for review.

Hash oil has recently come under scrutiny from public officials looking to crack down on its production in residential communities across California.

Senator Tony Mendoza, D-Artesia, announced Thursday that the state Senate gave final approval to a bill that would make manufacturing hash oil within close proximity to occupied houses or structures an aggravated felony. The bill will now be sent to Gov. Jerry Brown for his signature.

Using butane, a highly flammable gas, in a contained area without proper ventilation is extremely dangerous and can result in explosions and fires, according to the DEA.

Two men were left in critical condition after a similar operation led to an explosion and resulting fire at an apartment complex in Walnut Creek in October 2014, according to Walnut Creek police.

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