The effect of a massive wastewater discharge on nearshore ocean chemistry
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An opportunity to study the effect of a massive wastewater discharge on a nearshore ocean environment arose in 2015 over a 42-day period when the City of Los Angeles diverted 9.4 billion gal of treated wastewater effluent from an outfall located 5 mi in the Pacific Ocean to a 1-mi backup in the Santa Monica Bay (SMB). SMB is a heavily used waterbody and is home to many marine organisms. To understand the impact of this diversion on human health and on SMB ecosystem, samples of the wastewater effluent, the receiving seawater, and sediments from around the backup outfall were analyzed, among others, for metals, semivolatile organic compounds (SVOC), nutrients, and total organic carbon (TOC) during the diversion project. Results show that these parameters were present at levels below local water quality guidelines (i.e., not enough to cause health or environmental concerns). In the effluent, metal levels were < 10 μg/L except Zn (23 ± 9.9 μg/L); phosphate, ammonia-nitrogen, organic-nitrogen, and TOC levels were 3.48 ± 0.37, 42.7 ± 5.3, 4.7 ± 1.4, and 19.0 ± 4.9 mg/L, respectively. In seawater and sediments around the backup outfall, metal levels were < 1.5 μg/L and < 25 mg/kg, respectively. Apart from 4,4’-DDE, SVOCs were not detected in sediments. To assess whether changes to native levels of pollutants in SMB occurred due to the diversion project, pre-diversion and post-diversion datasets were compared statistically. No significant differences were found between the two datasets (p > .05, paired t test), meaning the diversion did not change the SMB chemistry.
KeywordsHyperion 1-mi diversion Metals Semivolatile organic pollutants Nutrients Santa Monica Bay
The authors acknowledge their colleagues at the Environmental Monitoring Division for their support and the City of Los Angeles for the funding and environmental stewardship.
Role of the funding source
The funding source is named in the acknowledgement. The funding source only contributed to the study design, but not to the data analysis or the writing of this report, and makes no endorsement of the report’s finding and conclusion.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by the authors.
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