Planning authority inspectors yesterday found grit, possibly hazardous, buried under concrete at Palumbo Shipyards in Cospicua.

They were paying a surprise visit after receiving a tip-off that residue from grit-blasting operations had been dumped there illegally.

The residue is made up of aluminium shreds that have been mixed with water and sprayed onto ships to strip paint. The aluminium deposits can be toxic.

Palumbo yesterday denied any wrongdoing.

Mepa inspectors took samples from an area that had been cemented over in 2012 and are investigating photographs, passed on by Times of Malta, taken while the works were being carried out.

The photographs appear to show two industrial skips, a bulldozer filled with grit and a layer of the black substance that was later covered with concrete.

In a statement, Mepa said its officers were unearthing quantities of “possible hazardous waste which had been illegally buried under layers of concrete flooring in two sites of the shipyard”.

“The authority is collecting various samples of the unearthed waste material to send for testing to determine what procedures and safeguards it needs to take. Investigations are still ongoing,” it said.

But Palumbo managing director Joseph Calleja was not impressed. He said grit blasting had been taking place at the yard for about 70 years before it was taken over by Palumbo.

Palumbo is obliged to store the grit from its operations and dispose of it safely.

“We are collaborating with the planning authority because we have nothing to hide. We have a sub-contractor which collects the grit blasting and takes it overseas for dumping. The last shipment we had was on Saturday,” he said when contacted. He expressed surprise at the statement issued by Mepa because the samples have still to be analysed. The company has also taken its own samples for analysis.

“The area from where Mepa officers took their samples was previously used as a grit blasting and spraying section. Since it was close to the boundary wall and close to residents, we decided to close this section and covered the area in concrete to have space for boat storage,” he said.

Mr Calleja said that Mepa and Palumbo received such claims “practically on a daily basis”.

“We are doing everything by the book. In the past, the grit was dumped into the sea but we cannot do that so we have a contractor who exports it to Portugal to be dumped safely. The grit is kept in temporary storage until there is enough for it to be exported.”

Mepa officials were seen digging up an area that had been laid with concrete two years ago after the shipyard dismantled one of its sheds and removed rails carrying heavy machinery.

Mr Calleja confirmed the sample taken was six inches deep, with four-and-a-half inches consisting of concrete. The officers also inspected a gutter which runs across the property as this was possibly contaminating the inland sea.

When timesofmalta.com broke the story online yesterday morning, Natalie Boehm remembered taking photographs of the operation in July 2012 when works were under way.

When Times of Malta visited her house, which overlooks the area, she said she never thought twice about those works until she saw the story. She hopes the photos can help in the investigations.

Palumbo’s CEO Antonio Palumbo and his son Raffaele were arrested last April by the Sicilian authorities in connection with illegal dumping of chemicals.

The Palumbos have denied wrongdoing and blamed the subcontractor.