CARSON, Calif.—Los Angeles County will investigate the cause of the 8.5-million-gallon sewage spill in Carson, as well as evaluate the condition of the county’s sewer systems amid residents’ calls for better leadership and infrastructure in the city. On Jan. 11, the Los Angeles County Board of Supervisors approved a motion (pdf) introduced by Supervisors Holly J. Mitchell and Janice Hahn to investigate the cause of the Dec. 30 sewer pipe collapse in Carson, where 8.5 million gallons of untreated sewage flooded residential streets and flowed through the Dominguez Channel and into the Los Angeles Harbor. The sewer pipe incident comes just months after the City of Carson declared a local state of emergency in October over a foul smell emanating from the Dominguez Channel that caused residents headaches, nausea, and vomiting for months. Mitchell, whose District 2 oversees Carson, acknowledged the city’s infrastructure issues, as well as the impact that the …