Each of the 260 orphaned wells will cost an average of $80,000 to clean up.
Former Anadarko Petroleum cited in the suit say the company had only "a skeleton crew" left for safety and repairs.
The biggest change came in February when regulators changed how flowlines are created, tested and eventually abandoned.
The company shut down hundreds of wells after an April 2017 explosion killed two people in Firestone.
CPR News found a common practice designed to let oil and gas companies maintain ownership of old holdings.
CPR’s Grace Hood and Ben Markus have been reporting this story all year, and tell Colorado Matters about what’s changed in Firestone.
Mark Martinez and his brother-in-law Joe Irwin, both 42 years old, were killed in the Firestone blast. Martinez’ wife Erin was seriously injured.
The regulations set requirements for installing, testing and shutting down flowlines, which carry oil and gas from wells to nearby equipment.
Few, if any states, map flowlines. Big energy developing states like neighboring Wyoming or Texas do not have any mapping requirement.
Colorado regulators will discuss what, if any, revisions are needed to the rules. They could approve them as soon as today.