Micro Pollutants from Septic Systems
Elizabeth Ward
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Traces of pharmaceuticals, hormones and personal care products associated with everyday life in the United States are finding their way into groundwater through septic systems and these micro pollutants can find their way into drinking water supplies.
This is exactly what is happening in New York and New England, according a recently published study by the U.S. Geological Survey (USGS).
The paper, “Concentrations of hormones, pharmaceuticals and other micropollutants in groundwater affected by septic systems in New England and New York” by Patrick J. Phillips, Irene J. Fisher, et. al. details the findings at two different locations that were studied, one in New England and the other on Fire Island in New York.
This study was the first to be published that used a new highly sensitive analytical method developed by the USGS National Water Quality Laboratory that identifies more than 100 pharmaceuticals, pharmaceutical degradates and related contaminants in trace concentrations.
This method has detection limits for many compounds in the low nanogram/liter (that is about one thousandth of a part per billion) range, and significantly advances the abilities of the USGS to assess the presence and concentrations of pharmaceuticals in the environment.
The two sites were chosen because high nitrate concentrations in groundwater samples down gradient of these septic systems begged the question of what other chemicals might also be present.
Though nitrate can contaminate groundwater from fertilizer use; leaking from septic tanks, sewage and erosion of natural deposits, increased nitrate concentration is usually a sign of improperly operated or failing septic systems and is an indication that septic system waste is contaminating groundwater.
The MCL (Maximum Contaminant Level) for nitrate is 10 mg/L and easily tested for. The NO3 dissolves and moves easily through soil.
Due to plant uptake, there is a seasonal variation, and testing in the spring will usually produce the highest levels of nitrate. Elevated nitrate usually indicates contamination from septic tanks as it did here.
What is important about this study is that the USGS scientists also found traces of other chemicals in the groundwater and demonstrated that these pharmaceuticals and related contaminants do not just disappear, but are spreading through groundwater into the environment.
The USGS scientists looking for micropollutants in groundwater collected samples down gradient of septic systems. The scientists tested for items such as pharmaceuticals, personal careproducts, and plasticizer compounds used in plastics.
In New England a series of existing down gradient groundwater wells and wells installed to monitor the leach field were used to collect samples to measure the effect of a single large septic system that serves a nursing home with 65 patient beds and staff.
Samples were collected from below the septic system leach field in addition to samples from wells down gradient of the septic system.
The USGS scientists found numerous prescription drugs in the groundwater samples, such as anesthetics; a muscle relaxant; an antifungal; an antiepileptic; an antibiotic; a sleep aid; and also a floor cleaner.
Total concentrations for these compounds generally ranged from 1 to over 20μg/L in the groundwater samples.
High tris(2-butoxyethyl phosphate) plasticizer concentrations in wells beneath and down gradient of the leach beds (>20μg/L) were thought to reflect the presence of this compound in cleaning agents used at the nursing home.
On Fire Island in New York, groundwater samples were collected from an area of dense summer populations (5 dwellings/acre).
The Fire Island septic systems have minimal treatment of wastewater (they are essentially tank only systems) before mixing with shallow groundwater that moves towards a large, estuary where a decline in fisheries and shellfish along with a higher ratio of female-to-male fish had been reported.
Shallow groundwater samples collected along the beach of this estuary down gradient of the septic systems were found to have hormones; detergent degradation products; galaxolide, a fragrance found in various products; insect repellent; sunscreen additives; floor cleaner; and two pharmaceuticals (lidocaine, a local anesthetic; and carbamazepine, an anti-convulsant and mood stabilizing drug).
The highest micropollutant concentrations for the Fire Island study found in one of the shoreline wells that had personal care/domestic use, pharmaceutical, and plasticizer concentrations ranging from 0.4 to 5.7μg/L.
Most micropollutant concentrations increased with increasing total nitrogen concentrations for the shoreline well samples.
The USGS scientists draw narrow conclusions stating that “these findings suggest that septic systems serving institutional settings and densely populated areas in coastal settings may be locally important sources of micropollutants to adjacent aquifer and marine systems.”
The potential for measurable groundwater contamination and environmental impact from septic systems clearly places these systems within the expanded EPA definition of “navigable waters of the United States” and makes regulatory action possible if not likely.
Septic systems are common in rural areas and those lacking connection to larger scale sewage treatment plants.
Septic systems consist of holding tank where raw sewage collects and separates into a sludge (solid) and liquid effluent. The liquid effluent either leaches directly into the surrounding soil or goes into a leach field for final treatment by the soil.
The liquid effluent from septic systems ultimately moves into the groundwater.
There are also alternative septic systems that have a secondary treatment system (be it a secondary aerobic tank or other treatment media) to remove pollutants.
Though more than 30% of households are served by onsite septic systems, significant numbers are quite old and many are not properly operated or maintained.
Proper maintenance of septic systems (both traditional and alternative) is essential for protection of public health and local water resources.
With new more sensitive testing methods it is possible to measure the impact of these systems on groundwater supplies and the environment.
However, a simple annual nitrate measurement would indicate a problem and can be used as a proxy for the more expensive tests.
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Elizabeth Ward was awarded an MBA from the University of Pittsburgh and an MS ChE from Polytechnic Institute of NYU, worked as a chemical engineer for both the US EPA in DC, and at DuPont before working in finance and then becoming consultant with Washington Advisors and is the author of "The Lenders Guide to Developing an Environmental Risk Management Program." Elizabeth retired from Washington Advisors and began her volunteer career and is currently the Treasurer of the Prince William Soil and Water Conservation District.
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