Energy companies are reporting they have nearly 129,000 underground oil and gas pipelines within 1,000 feet (300 meters) of occupied buildings in Colorado.
Friday is the deadline for companies to test those lines for leaks, and about 9,500 results were available at mid-day, with the vast majority indicating the pipelines passed the test.
The state ordered the inspections after investigators blamed a severed gas line for an April house explosion that killed two people in Firestone, about 30 miles (50 kilometers) north of Denver.
Investigators said the severed pipeline was thought to be abandoned but was still connected to a well.
The pipelines are known as flow lines and connect wells to tanks or other collection points. A well can have as many as four flow lines of varying lengths.