Excavation is expected to begin Monday at Roberto Clemente Park in Brentwood of some of the estimated 50,000 tons of contaminated debris illegally dumped there.

Preparations began June 1 with heavy machinery brought to the park as well as safety materials, including equipment that would keep piles of dirt damp to prevent toxins from becoming airborne, town officials said.

In April, the Islip Town Board approved a $2,992,240 contract to Gramercy Group Inc. of Wantagh, which submitted the lowest bid among five other qualified bidders. The contract is for a 120-day work period, Islip Town Supervisor Angie Carpenter said, with the work expected to be completed in that time.

DataContaminants found in parksee alsoDocuments: Illegal dumpingMore coverageToxic dumping probe

The Islip Town Board last year authorized up to $6 million in bonds to pay for the cleanup and rehabilitation of the park -- which has been closed since April 2014 -- including for a renovation of its pool, which has been shuttered since the end of summer 2012. A timeline for completing the upgrades has not been set, but the town board has vowed to let residents participate in the planning process for rebuilding.

Gramercy Group owner Vincent Parziale has said the main issue he foresees with the project is dust control. The town has received some of the dust screens that were ordered, but is still awaiting the last shipment from a California-based company to begin the project.

Enviroscience Consultants Inc. of Ronkonkoma was first hired by the town last May to aid in preparing the remediation plan and was most recently awarded a contract not to exceed $400,000 for inspection services and to monitor the air quality during the removal of the fill.

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In April 2014, Suffolk County District Attorney Thomas Spota launched an investigation into illegal dumping at the park, which spread to three other sites -- including a 1-acre private lot on Islip Avenue in Central Islip, a six-home Islandia subdivision built for veterans returning from wars in Iraq and Afghanistan, and a sensitive wetlands area in Deer Park.

In December, six men -- including two former Islip Town parks department officials -- and four companies were indicted on charges stemming from Spota's probe for their respective alleged roles in the dumping. All have pleaded not guilty.

An excavator is expected to begin digging up the fill Monday and stockpiling it for future transfer to regulated facilities, town officials said.

The plan includes about 20 to 30 trucks a day filled with debris leaving the park, with 38,000 tons of materials headed to the town-owned landfill on Blydenburgh Road in Hauppauge and 12,000 tons sent to a landfill off Long Island.

The off-Island site has not yet been designated, town officials said.