There was no permit to dispose of the dredging material spilled on a key section of the westbound side of the H-1 freeway in Aiea on Saturday afternoon, causing a four-hour traffic jam, city officials said Tuesday.

City officials are investigating SER Silva Equipment Rental for the spill.

And city officials also confirmed Tuesday that the Department of Planning and Permitting is looking into complaints that illegal dumping or stockpiling is taking place on a Waianae Valley Road property owned by Sandra Silva, the principal of SER Silva Equipment Rental. It is unknown if the material spilled Saturday is connected to the Waianae property.

Thousands of motorists were stuck on the freeway and Aiea-Pearl City surface roads after the truck spilled a cement mixture over three westbound lanes near the Aiea Heights overpass about 2:50 p.m.

Six lanes in the area were merged into one lane and, as crews worked to clean up the mess, traffic backed up as far as Nimitz Highway, according to disgruntled motorists. All lanes were reopened about 7 p.m.

A city Department of Environmental Services investigation concluded that a permit had not been issued to SER Silva Equipment Rental to dispose of the waste at Waimanalo Gulch Sanitary Landfill, the city’s only landfill and the only facility where the material could legally be disposed.

Silva could not be reached for comment.

Honolulu police said the company was hauling material dredged from Koko Marina. But because the company did not obtain a permit to dispose of the material at the landfill, city officials don’t know where the waste was going, said Curtis Lum, a DPP spokesman.

Lum, in response to media inquiries, said DPP is investigating three complaints it has received about illegal dumping or stockpiling at a Waianae Valley Road property owned by Silva. An inspection on Aug. 20 uncovered earthen material that was trucked in and used as fill without a grading permit, Lum said. The department is “in the process of taking enforcement action” against Silva, he said.