Wastewater from Septic Systems


Clean water is fundamental to life. Yet many septic systems do not rid sewage of pollutants that may be harmful to human health before discharging the sewage to groundwater—and in some cases before it contaminates drinking water wells.

In 2013, Silent Spring Institute researchers conducted an analysis to evaluate options for protecting drinking water in the future. The study compiled data from multiple studies on pharmaceuticals, consumer product chemicals, and other emerging contaminants discharged from septic systems. The meta-analysis was later expanded to include a total of 20 studies in which researchers identified 45 contaminants in total, making it the most comprehensive assessment of septic systems as important sources of emerging contaminants. The findings were reported in 2017 in the journal Environmental Science & Technology.

The Institute found that treated water from both septic systems and sewage treatment plants contain similar levels of contaminants. The systems effectively remove some chemicals, such as caffeine and acetaminophen (Tylenol); others pass through largely unchanged, including sulfamethoxazole, an antibiotic, and TCEP, a chlorinated flame retardant. The findings reinforce the case for diverting treated water from septic systems and centralized plants away from drinking water supplies.

These findings show that wastewater management decisions can impact drinking water quality by changing the levels and distribution of emerging contaminant discharges into groundwater, and that these impacts should be considered when comparing approaches to manage nutrient loading into Cape groundwater.

Silent Spring Institute scientists have been at the forefront of investigating how contaminants from septic systems can make their way into groundwater.  In 2006 they monitored—for the first time ever—hormone-disrupting chemicals such as natural estrogen and alkylphenols, as well as certain pharmaceuticals, in water that passed from a septic system into the ground. The study, published in Environmental Science & Technology, looked at a typical septic system on Cape Cod, where septic systems serve more than 85 percent of residential and commercial properties.

Two other chemicals the researchers detected indicated the presence of sewage: optical brighteners, which are found in laundry detergents, and caffeine.

The presence of hormone-disrupting chemicals in the environment has been associated with the feminization of male fish and reduced fertility in other wildlife. The scientists note that additional research is needed to determine whether the concentrations typically observed in the environment produce similar adverse effects on the human hormone system. Exposures during critical prenatal and childhood stages of reproductive development may be most critical.

Effects on hormonally responsive cancers are an additional concern. Chemicals that mimic natural estrogen, for example, may contribute to a woman’s cumulative lifetime exposure to estrogen, a factor that has been linked to an increased risk of developing breast cancer.

Silent Spring Institute research on septic systems is important beyond Cape Cod. One in every four Americans relies on septic systems for wastewater treatment. A sizeable portion of the residents in a number of states—including Delaware, Florida, Maryland, Massachusetts, New Jersey, and New York—also rely on private, shallow groundwater wells for their drinking water. With housing density increasing and lot size shrinking to accommodate population growth, the likelihood is growing that wastewater from a household’s or neighboring household’s septic system will contaminate a drinking water well. Our work will help inform best practices for wastewater management plans and steps that individuals can take to reduce contaminant levels in their wastewater.