SAN FRANCISCO (AP) — California Attorney General Kamala Harris is suing ConocoPhillips and its spinoff, Phillips 66, over underground tanks used to store gasoline at more than 500 gas stations in the state.

Harris alleges the companies have tampered with or disabled leak detection devices and failed to properly inspect and maintain the tanks since November 2006.

Harris accuses the companies of violating state laws intended to protect residents from contaminated groundwater.

Her civil lawsuit was filed on Wednesday in Alameda County. She was joined by district attorneys from numerous counties in the state.

ConocoPhillips spun off its refineries and pipelines last year into Phillips 66, a separate company.

ConocoPhillips spokesman Daren Beaudo said the assets and liabilities of the gas stations referred to in the suit are owned by Phillips 66.

Phillips66 spokeswoman Janet Grothe says the company does not comment on legal matters.