Study Provides Ammo for Malibu Septic Critics
• Stanford Research Project Says Leakage Pollutes Ocean
BY ANNE SOBLE
BY ANNE SOBLE
The California Sea Grant Program of the Scripps Institution of Oceanography is drawing attention to an ongoing study by scientists at Stanford University with major implications for Malibu wastewater management.
Titled “Submarine discharge of nutrient-enriched fresh groundwater at Stinson Beach, California is enhanced during neap tides,” the research seeks to show how septic tanks affect coastal water quality.
The conclusions by the multidisciplinary team studying the Northern California community that has served as a poster child for successful use of septic tanks on the coast does not bode well for local proponents of their use.
The article first appeared in the academic journal Limnology and Oceanography in 2008 and is now beginning to attract the attention of the mainstream media.
The researchers, funded by CSG and NOAA, assert that their fieldwork demonstrates that septic tanks leak nitrogen and phosphate into coastal waters that can trigger algal blooms. They report finding elevated levels of these so-called nutrients in the surf zone during periods of high groundwater flows to the beach.
Following freshwater pulses, they observed four-day elevations in chlorophyll-a levels—a proxy for phytoplankton concentrations. Noting that it is difficult to attribute any single algal bloom to the presence of higher than normal nutrient levels, the link between nutrification and algal blooms is said to be generally acknowledged for marine and freshwater ecosystems.
In a CSG statement, Alexandria Boehm, a professor in the Department of Civil and Environmental Engineering at Stanford University said, “Our project is one of the first in California to show definitively that septic tanks can affect coastal water quality through submarine groundwater discharge.”
Most research on septic systems has focused on their effects on terrestrial ecosystems, Boehm noted, adding that “the value of this project is that it shows they can also impact marine ecosystems via polluted groundwater discharging directly to the ocean.”
In theory, the nutrient spikes detected off Stinson Beach could have come from polluted creeks or runoff but the scientists don’t think that was the case because their fieldwork was conducted in summer when, they said, groundwater is the only, or primary, source of freshwater to the coast.
The scientists also ruled our fertilizers “because of the concomitantly high levels of human fecal indicator bacteria detected in groundwater samples collected between the septic systems and the shoreline.”
The researchers said they were not surprised to find a link between septic systems and beach water quality. “It is what we expected,” Boehm said.
The team emphasizes that its findings should not be viewed as site-specific. They note that septic systems in other communities, they cite Malibu among them, share “the [same adverse] potential environmental implications for beach, ocean and river ecosystems.”
Because of the same concerns explored in the Stanford study, the California legislature has directed the State Water Resources Control Board to establish state regulations for septic systems. California and Michigan are currently the only two states in the country that do not have statewide regulations for septic systems.
Malibu critics of the proposed state regulations and the concomitant threat of local sewering often cite a lack of data showing that septic systems contribute to actual water-quality problems, which is why the CSG and related agencies are pushing for more public awareness of this research project.
The Stanford team has quantified the impact of septic systems on coastal waters at one California location, documented their effects on groundwater and ocean water quality, and determined that, in general, on-site wastewater treatment “is an important environmental concern and may require additional regulatory attention.”