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. She also accuses them of improperly disposing of hazardous wastes associated with the tanks.

Harris says the companies violated state laws intended to protect residents from contaminated groundwater.

Her civil lawsuit was filed on Wednesday in Alameda County. Harris was joined by district attorneys from Alameda, El Dorado, Placer, Nevada, Merced, Stanislaus and San Bernardino counties.

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

A call to ConocoPhillips was not immediately returned.