Caffeine and artificial sweeteners may bring a measure of satisfaction into Lewiston residents’ morning routines, but they’re also helping researchers track nitrate pollution from septic systems in the Lindsay Creek drainage.
A new study from the Idaho Department of Environmental Quality’s Lewiston Region office found hard evidence that septic tanks in the eastern Lewiston Orchards are contributing to chronically high concentrations of nitrates in the creek. But further exploration will be needed before the agency can say just how much of the pollutant is coming from people.
Water quality analyst Jason Williams said the presence of nitrogen from septic systems has long been suspected and isn’t surprising.
“Septic systems are designed to discharge water to subsurface soils, so we would expect that to be the case,” Williams said. “But now we have a way to track where the septic effluent is by using these indicator chemicals.”
One of the indicators is the artificial sweetener acesulfame potassium, which is 200 times sweeter than sugar. It is commonly used to sweeten soft drinks, baked goods, candy, gum and tabletop sweeteners without adding calories. The other sweetener DEQ looked for was sucralose, more commonly known by the brand name Splenda.
Artificial sweeteners are unique to human waste and aren’t completely removed by septic systems, even systems that are functioning properly. That makes the sweeteners a good marker for pollutants that have a human origin.
“They don’t completely break down in the body or in septic systems or in treatment plants,” Williams said. “They’re pretty persistent.”
Caffeine, on the other hand, can be removed from effluent by septic tanks that are in good working order. Williams said that makes it an effective indicator that poorly functioning septic systems are putting nitrates into the groundwater.
That conclusion is supported by public health district records, because caffeine was detected in sampling areas downstream from areas with documented cases of septic system failures, he said.
DEQ has studied the water quality in the Lindsay Creek watershed and the connected Saddle Mountains aquifer for decades. Elevated levels of nitrates have been a persistent problem, leading many residents in the area to abandon shallow wells over the fear of adverse health effects. Nitrogen can affect the amount of oxygen in the blood, an especially acute problem for infants who can literally turn blue.
High levels of nitrogen can also lead to algal blooms in surface water, depleting it of oxygen and leading to adverse effects for fish and other wildlife. But until now, the agency hasn’t been able to definitively say that septic systems have been a contributor to those high nitrate levels.
Just how much of the nitrate pollution is human-caused will require further study. Other sources of nitrates include fertilizers, livestock, stormwater discharges and naturally occurring nitrogen in soil.
“This study says we know the septic effluent is there, we know where it is and we know it overlaps with high nitrates,” Williams said. “But we’re not able, from this data, to say if it’s 1 percent or 100 percent.”
What to do with the study will be up to landowners, residents and local governments. The city of Lewiston and its urban renewal agency have already started a major effort to reduce the number of septic tanks in the eastern Lewiston Orchards with the installation of a new wastewater trunk line last year. More than 60 residents along the project have either decommissioned their septic tanks or pledged to do so in the future.
But with nearly 800 parcels in the overall watershed relying on septic tanks for wastewater treatment, the problem isn’t likely to go away any time soon. With that in mind, DEQ officials plan to start a watershed advisory group for Lindsay Creek. Public meetings that will probably be scheduled this spring will invite advice from stakeholders about where the agency should go from here.