While wastewater treatment plants are known havens for contaminants of emerging concern (CECs), some 70 million gallons of untreated sewage a day are discharged into the environment via the tens of thousands of cesspools and septic tanks scattered throughout the state.
Several studies have found chemical indicators of cesspools in the shallow coastal zone, and “since CECs are undoubtedly a component of cesspool effluent, they also are being discharged,” says Robert Whittier of the state Department of Health’s Safe Drinking Water Branch.
So which releases more CECs into the environment, WWTPs or on-site disposal systems (OSDS) such as cesspools and septic tanks? According to Whittier, it may not be the amount that matters as much as the effect.
WWTPs release more than twice the amount of wastewater than do OSDS. “However, this is an apples and oranges comparison,” he says, noting that most treated wastewater is discharged through deep ocean outfalls, while the rest is injected into the ground or used for irrigation.
“The impact footprint of wastewater injection is likely more intense, but distributed over a smaller area than that of recycled water application and OSDS discharge,” he continues. “Recycled water is distributed over a larger area and benefits from a high level of treatment and natural remediation processes in the shallow subsurface after it is applied. OSDS effluent like recycled water is distributed over a wide area due to the distance between residences using this type of wastewater disposal. However, OSDS effluent receives no treatment (cesspools) or much less treatment (septic systems) than wastewater that is either injected or recycled. The comparison between WWTP wastewater impacts and that of OSDS would have to be done on a case-by-case basis.”
— Teresa Dawson
Volume 26, Number 12 June 2016