Future Treatment Options at Point Loma (FAQ 2)
What are the basic regulations of the Clean Water Act?
A standard permit requires wastewater treatment plants discharging into any body of water treat to a Secondary level, which removes a minimum 85% of the Total Suspended Solids (TSS) and 85% of all Biological Oxygen Demand (BOD) material. This reduces TSS and BOD from as much as 250 Parts per Million (ppm) coming into the plant to 30 ppm in the treated wastewater. San Diego operates under a modified permit for the PLWTP which requires an 80 percent removal of TSS and a 58 percent removal rate for BOD. Current Point Loma discharge to the ocean is about 45 ppm TSS and 105 ppm BOD.
What is BOD?
Biochemical Oxygen Demand (BOD) is a measure of the concentration of biodegradable organic matter present in water. Consider it as 'food' for small marine organisms. If too much 'food' is put in a given environment, the organisms that grow to consume this 'food' use oxygen from the water as part of the process. If too many marine organisms grow, the local oxygen level can be reduced affecting the entire marine environment. The BOD test specifically measures the demand for oxygen that wastewater effluent imposes on the water body to which it is discharged, checking that discharged waste does not exceed the capacity of the receiving water. This prevents conditions where the entire marine environment can become oxygen- starved.
The National Research Council (1993) reported "Biochemical Oxygen Demand (BOD) is of concern in bays, estuaries, and semi-enclosed water bodies but is generally not important in the open ocean."
How does the City of San Diego comply with the Clean Water Act?
The City of San Diego is in compliance with the Clean Water Act, operating under a modified permit. The five-year modified permit, also known as a 'waiver,' is a provision of the Clean Water Act that allows the PLWTP to treat wastewater at the Advanced Primary level before discharging into the ocean, only as long as it continues to show that there is no harm to the environment. The modified permit requires the City to perform additional monitoring to ensure compliance. The permit must be renewed every five years by the EPA and the Regional Water Quality Control Board.