Ten decaying oil and gas wells, long abandoned by their owners, will be sealed shut and cleaned up in Allegheny County beginning early next year.

The orphan well-plugging project is one of the first in Pennsylvania to be funded by a 2021 federal infrastructure law that promises to spend an unprecedented amount to clean up hazardous, polluting wells that litter the commonwealth.

The project to cement shut just 10 wells in Allegheny County — out of 27,000 abandoned wells documented by Pennsylvania regulators and roughly 200,000 that are yet to be found — demonstrates the challenge of cleaning up the scattershot remnants of past drilling booms.

Legacy oil and gas fields left behind over a century are now neighborhoods, public parks, golf courses, farms and forests. Old wells have been broken down by rust and overtaken by dirt, brush and shifting property uses.