An environmental firm found no imminent threats to the public or Charleston Harbor on the Yorktown after conducting an extensive study of the former warship moored on the edge of Mount Pleasant.

Shaw Environmental Inc. told Patriots Point Development Authority today that the World War II-era aircraft carrier will have to be cleaned extensively before structural repairs can take place. The estimated cost is $4.4 million and would require about six months to complete.

Patriots Point said it would seek federal funding to pay for the cleanup.

The Atlanta-based firm found 129 tanks with about 160,000 gallons of petroleum residue and 1.6 million gallons of onboard contaminated water. Just two of 21 refrigeration units are charged, and all fire-fighting systems were found to be drained or air gapped.

Most hydraulic systems were found to be empty, and all radiological devices are low-level and pose no risk to anyone, Shaw said in its report.

Of the 71 samples taken for cancer-causing polychlorinated biphenyls, or PCBs, 23 tested greater than 50 parts per million and 17 showed less than 50 parts per million.

To remove fluids, Shaw recommended pumping and separating petroleum products and affected waters. The water can be treated on site, while the oil-based residues can be used to blend fuels or make asphalt, said Ron Kenyon, a senior project manager with the firm.

The toxic PCBs will have to be pumped into small containers. Those exceeding 50 parts per million will have to incinerated while the rest can be treated and sent to a landfill.

If PCBs cannot be removed from the ship because of its layout, Shaw recommends encapsulating them.

Any radiological devices could be put in containers and disposed of in a low-level facility.

State-owned Patriots Point is staring at an estimated $81 million price tag to upgrade the aging vessel that has served as the centerpiece attraction for tourists since it was decommissioned and brought to Charleston Harbor in 1975.

The environmental elements of the ship comes before a structural analysis is conducted to determine the 70-year-old ship’s overall condition.

It could take decades to refurbish the ship, since Patriots Point’s annual income is about $9.5 million.

Read more in Thursday’s edition of The Post and Courier.

Reach Warren L. Wise at 937-5524 or twitter.com/warrenlancewise.