Built in the 1960's. The 8 inch (20 cm) natural gas pipeline runs adjacent to an 8 inch oil pipeline under Cook Inlet northwest of Nikiski.
State regulators have given Hillcorp until May 1 to fix the leak.
The leak volume is estimated to be 210,000 to 310,000 ft3 per day.
More info and maps at links below
https://www.adn.com/business-economy/energy/2017/03/19/with-one-cook-inlet-pipeline-leaking-feds-want-hilcorp-to-inspect-another/