The Nassau district attorney's office has subpoenaed records related to the awarding of a $12 million cleanup contract to a company that gave money to the political club run by County Executive Edward Mangano's top aide on the day the deal was completed, county sources said Wednesday.

The county legislature on Tuesday received the grand jury subpoenas, which requested contract documents and meeting minutes, sources said. The district attorney's office declined to comment Wednesday.

Nassau in 2013 had solicited bids to clean the large volume of debris left in waterways by superstorm Sandy. Newsday reported in March that officials chose a company that had incorporated only a month prior over three firms with years of storm cleanup experience.

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Several principals of the winning company, VIP Splash Waterways Recovery Group, of Island Park, also had ties to a well-known nonprofit that lobbied the county on environmental issues. The nonprofit, Freeport-based Operation SPLASH, last summer announced its support of a controversial plan to privatize management of Nassau's massive sewer system, after previously opposing it.

On Aug. 18, 2014, the day the contract amendment that increased VIP Splash's payment to $12 million was signed and executed by the Mangano administration, the company contributed $2,925 to the Hicksville Republican Committee run by Rob Walker, chief deputy to Mangano, records show.

County Attorney Carnell Foskey said Wednesday that the Mangano "administration stands by the integrity of the procurement process, and welcomes any external inquiries seeking further clarification."

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Walker has said he did not solicit the donation from VIP Splash and that the company is independent of the nonprofit.

Operation SPLASH president Rob Weltner has said his change of heart on the sewer privatization had nothing to do with the contract to VIP Splash, which listed Weltner's wife as one of its principals.

The subpoenas come as acting District Attorney Madeline Singas' office is probing several other county contracts. They include two consulting agreements with retired NYPD Det. Richard "Bo" Dietl, CEO of a private investigation firm, that fell just below the $25,000 threshold for county legislative approval, and another for welfare fraud investigators that went to the county's current vendor after social services officials rewrote the bid specifications in their favor. County officials said the changes were not designed to steer the contract to the current vendor, Summit Security. County officials haven't been accused of wrongdoing in any of the matters.