growing. To meet customer demand, the company began storing gas in large holding tanks. In 1941, the company introduced a new system to the Southwest United States: underground storage of natural gas. By 2016, the company had four separate underground storage facilities, all of them depleted oil and gas fields repurposed as gas storage. The four are, in order from largest to smallest, the Aliso Canyon field, north of Porter Ranch; Honor Rancho, near Newhall; the La Goleta Gas Field adjacent to Goleta; and the Playa del Rey storage facility, north of Playa del Rey, near the Los Angeles International Airport. As Southern California's population grew, so too, did the company, eventually becoming the nation's largest natural gas distribution utility, serving 19.5 million people through 5.5 million gas meters in more than 530 communities. Headquartered in Los Angeles, Southern California Gas Company is a subsidiary of Sempra, a Fortune 500 company based in San Diego. Its service area encompasses 23,000 sq mi (60,000 km2) of diverse terrain throughout most of Central and Southern California, from just south of Sanger to the Mexican border. In late 2012, the company began the Advanced Meter Installation (AMI) Project that consists of upgrading over 6 million gas meters with the new Advanced Meter communication device. This device is attached to an analog gas meter that automatically and securely transfers gas usage information to the company's customer service and billing centers. The California Public Utilities Commission (CPUC) has approved a budget of $1.05 billion for this project, which is expected to be completed in 2017. On March 6, 2019, SoCalGas announced a plan to replace 20 percent of its traditional natural gas supply with renewable natural gas (RNG) by 2030. SoCalGas' aims to be the cleanest natural gas utility in North America, which it plans to achieve by delivering increasingly renewable energy to its customers. As part of this effort, SoCalGas has partnered with startup Twelve to convert CO2 from raw biogas into methane. Environmental impact A gas leak from the underground Aliso Canyon gas storage started in October 2015 releasing methane uncontrollably. By December 2015, thousands of people from Porter Ranch had been temporarily relocated and the leak had added more than 150 million pounds of methane to the atmosphere. The NGO Environmental Defense Fund has called the incident "unprecedented for California" and compared the leak's continuous output of greenhouse gas emissions to that