As part of their daily operations, the City of Los Angeles Hyperion Wastewater Treatment Plant (Hyperion Plant) and the Orange County Sanitation District (OCSD) release treated sewage into the coastal waters of Southern California in the Santa Monica Bay and San Pedro Bay, respectively. Sewage is released at depths of approximately 60 m through outfall pipes that are about 5 miles (8 km) long. Periodically, regular repair and maintenance services on the outfall pipes require the plants to temporarily divert treated sewage to shorter pipes that drain into shallow coastal zones. In these zones, buoyant, freshwater plumes of effluent may reach the surface and be transported through the action of wind and waves to nearby beach areas. Two such events have taken place: one at Hyperion Plant in November 2006; and the other at OCSD from mid-September to the beginning of October, 2012.
In both cases, the treated wastewater was diverted to 1-mile (1.6 km) pipes that discharge at a depth of about 20 m. Diversion events such as these can potentially impact coastal ecosystems and public health; thus comprehensive monitoring and tracking of these plumes is a high priority to Hyperion Plant and OCSD, the project's partners. This study focused on the 2006 and 2012 events and produces an assessment of the plumes' thermal signature, impact on coastal biogeochemistry, and surface movement based on analysis of remote sensing data from multiple NASA satellite sensors. The results are compared with in-situ data for validation. These results not only allow a better understanding of the diverted outfall plume, but they also assist the development of a strategy for improved satellite detection during future diversion events.