A suspicious device detonated by a state bomb squad last week in Yakima turned out to not be an explosive, but it contained enough liquid mercury that authorities ordered the surrounding area covered by fresh asphalt.

The detonation came after a series of explosions rattled a Yakima neighborhood Thursday night. Yakima police now say those explosions were triggered by devices that used a mixture of drain cleaners.

The incident began when residents and patrol officers reported hearing a series of loud explosions about 10:30 p.m. in the area of West Chestnut and South 11th avenues. The explosions set a bush on fire in the 1100 block of West Chestnut Avenue, where a resident later spotted a suspicious-looking device in a carport near the fire.

Police described it as a small plastic water bottle, tightly wrapped with tape. It appeared to have been left there for “quite some time,” Yakima police Lt. Nolan Wentz said Monday.

The Washington State Patrol bomb squad moved the device to a nearby parking lot, where it was detonated and spewed mercury, authorities said.

Over the weekend, a team of U.S. Environmental Protection Agency investigators examined the area, which tested positive for mercury, Seattle-based EPA scene coordinator Kathy Parker said Monday.

Parker estimated less than half a cup of liquid mercury was released.

“Any amount of mercury, which can spread into the air we breathe, poses a hazard,” said Parker. “There is no safe amount of mercury if people are breathing in the vapor.”

Authorities did not speculate why the device had contained mercury.

To ensure the mercury didn’t spread farther, the EPA told the city of Yakima to lay down hot asphalt over the highly contaminated area and then hired a subcontractor to place a layer of cold asphalt over areas where mercury was detected but not visibly present. Up to 8,000 square feet of the parking lot was covered in a new layer of asphalt. The city of Yakima will be reimbursed by the EPA for the cost of applying the asphalt, Parker said.

Regarding the explosions that ignited the bushes, Wentz said someone had mixed drain cleaners together. This mixture of bases and acids can have dangerous effects, he added.

“When you mix those types of household chemicals, it can start a fire,” said Wentz.

The fact that someone had mixed chemicals together does suggest questionable behavior, he said, adding that police do not have leads on an individual or group in connection with the explosions.

While some residents reported hearing more explosions elsewhere in Yakima over the weekend, Wentz said he was unaware of confirmed cases.

Worry about suspicious-looking packages was not solely isolated to Yakima. On Sunday night, Selah police got a report of a questionable backpack left in the parking lot of Save-on-Foods at 800 N. Park Court. The area was evacuated and a State Patrol bomb squad arrived to detonate the bag.

The bag turned out to be harmless, containing only tortilla chips, a soda can and some other safe items, according to police.