Satellite Remote Sensing Detection of Wastewater Plumes in Southern California

Wastewater discharged through ocean outfalls can surface near coastlines and beaches, posing a threat to the marine environment and human health. Coastal waters of the Southern California Bight (SCB) are an ecologically important marine habitat and a valuable resource in terms of commercial fishing and recreation. Two of the largest wastewater treatment plants along the U.S. West Coast discharge into the SCB, including the Hyperion Wastewater Treatment Plant (HWTP) and the Orange County Sanitation District (OCSD). In 2006, HWTP conducted an internal inspection of its primary 8 km outfall pipe (60 m depth), diverting treated effluent to a shorter 1.2 km pipe (18 m depth) from Nov. 28 to Nov. 30. From Sep. 11 - Oct. 4, 2012, OCSD conducted a similar diversion, diverting effluent from their 7 km outfall pipe to a shallower 2.2 km pipe, both with similar depths to HWTP. Prevailing oceanographic conditions in the SCB, such as temporally reduced stratification and surface circulation patterns, increased the risk of effluent being discharged from these shorter and shallower pipes surfacing and moving onshore. The aim of this study was to evaluate the capabilities of satellite remote sensing data (i.e., sea surface roughness from SAR, sea surface temperature from MODIS-Aqua and ASTER-Terra, chlorophyll-a and water leaving radiance from MODIS-Aqua) in the identification and tracking of wastewater plumes during the 2006 HWTP and 2012 OCSD diversion events. Satellite observations were combined with in situ, wind, and current data taken during the diversion events, to validate remote sensing techniques and gain surface to subsurface context of the nearshore diversion events. Overall, it was found that satellite remote sensing data were able to detect surfaced wastewater plumes along the coast, providing key spatial information that could inform in situ field sampling during future diversion events, such as the planned 2015 HWTP diversion, and thereby constrain costs.