On October 23, 2015, a wellhead at SoCalGas's Aliso Canyon underground storage field — perched on the ridge directly north of Porter Ranch — failed. Methane leaked for 112 days before the well was sealed. It became the largest single-event methane release in U.S. history. Eleven years later, the legal, health, and disclosure consequences are still active concerns for buyers.
What the law requires
California Civil Code Section 1102 mandates that sellers of residential real estate disclose 'material facts affecting the value or desirability' of a property. Courts and DRE guidance have consistently treated the Aliso Canyon site as a material fact for properties within a 5-mile radius. Sellers typically attach a supplemental TDS addressing: (1) proximity to the storage field, (2) any class-action participation or settlement, (3) any residual remediation activity, and (4) air-quality or odor incidents during ownership.
What the 5-mile zone actually covers
The disclosure zone covers nearly all of Porter Ranch (91326), most of Granada Hills (91344), much of Northridge (91326, 91325), and small slices of Chatsworth (91311) and Sylmar (91342). Outside the 5-mile ring, disclosure is not legally required but many sellers volunteer it on the supplement to avoid post-close litigation.
Settlements and ongoing litigation
SoCalGas has paid over $1.8 billion across multiple class-action settlements, including the 2021 settlement covering 35,000+ residents. Smaller individual claims continue to be filed. Buyers should ask whether the current owners participated in any settlement — participation can affect disclosure of ongoing health complaints. New settlement classes occasionally re-open.
Buyer due diligence checklist
Before removing contingencies, buyers should: (1) obtain the seller's full TDS plus any Aliso supplement; (2) request the SoCalGas notification record for the property; (3) consider an air-quality test ($300-$800) — most testing companies in the area now offer Aliso-specific panels; (4) review insurance quotes early — some carriers price 91326 homes 15-25% higher; (5) ask the seller's listing agent directly whether any odor or health complaints occurred during ownership.
Resale impact on Porter Ranch homes
Studies by UCLA and CSU Northridge have found a 4-7% pricing discount on Porter Ranch homes within the 5-mile zone compared to demographically and structurally identical homes outside it. The discount has narrowed since 2017 but persists. Time-on-market in 91326 also runs about 12% longer than comparable Northridge or Granada Hills inventory outside the zone.
