Polluted groundwater can find its way to the sea, indicating a direct link between septic systems and coastal contamination, a new study suggests.
In the first study of its kind, Stanford University researchers have tracked a plume of polluted groundwater from a septic system to one of Northern California’s top recreational beaches, Xinhua reported Thursday.
The researchers say their findings could be an important step toward improving groundwater management in coastal communities throughout the US.
Since 2008, the researchers have been studying the flow of groundwater from a large septic system at Stinson Beach, a favourite destination for swimmers and surfers about 36 km north of San Francisco.
To track groundwater pollution at Stinson Beach, the researchers installed a network of 120 monitoring wells near a large septic system close to a beach parking lot that collects groundwater from nearby homes and public toilets.
Test results revealed low concentrations of fecal indicator bacteria -- microbes that are used by health officials to evaluate water quality for beach closures.
Although few microbes made it out of the beach field alive, the scientists discovered a plume of nitrogen-enriched groundwater flowing through the sand toward the ocean.
Studies have shown that excess nitrogen can cause harmful blooms of phytoplankton and other algae that choke off oxygen in coastal waters.
Prior to this study, scientists had never observed in detail a plume of contaminated groundwater flowing from a septic system to the sea.
“The flow of groundwater directly to the ocean is very hard to measure,” said Alexandria Boehm, associate professor of civil and environmental engineering at Stanford.
“We hope that this work will raise awareness of the importance of groundwater as a source of pollution, and that coastal communities will look at this source when considering conservation efforts,” Boehm said in a university news release made public Thursday.
