Contaminants pervasive in Cape Cod's drinking water supply

Pharmaceuticals, consumer product chemicals, and other emerging contaminants can be found in the majority of public drinking water wells tested on Cape Cod, MA, according to a newly published study by Silent Spring Institute. Septic systems are likely the main source for these chemicals.

The study, which appears online September 18 in the peer-reviewed journal Science of the Total Environment, is among the first to examine the impact of septic systems on groundwater used for drinking supplies. The findings suggest that Cape Cod communities should develop stronger protections for drinking water at the same time as they design plans to curb nutrient pollution, which causes damaging algal blooms in the area's scenic watersheds.

“In addition to protecting the health of our beautiful coastal waters, we also need to protect the Cape's drinking water supply from wastewater contaminants,” says Dr. Laurel Schaider, a research scientist at Silent Spring Institute and study lead author. “The presence of emerging contaminants in drinking water raises human health concerns.”

Although Cape Cod is particularly vulnerable to contamination due to the prevalence of septic systems and its shallow sandy aquifer, the study has national implications. A quarter of U.S. households use septic systems or small community systems to process wastewater, and about 40% of Americans rely on groundwater for drinking supplies.

The study found contaminants in 15 of 20 public wells and two distribution systems supplying drinking water on Cape Cod, from nine water districts. Most frequently detected were the antibiotic sulfamethoxazole and PFOS, which is used in stain-resistant and nonstick coatings and fire-fighting foams. Levels were among the highest reported in U.S. drinking water (excluding industrial contamination). None of the chemicals detected are federally regulated, although the Environmental Protection Agency is considering such rules.

“Silent Spring Institute has conducted critical research related to emerging contaminants in the environment. Their work on septic systems and subsequent impact to local groundwater is particularly important,” says Dr. Shane A. Snyder, a professor of chemical and environmental engineering at the University of Arizona who has helped Silent Spring with past analyses. “The vast majority of studies focus on large centralized systems. However, large numbers of Americans are served by smaller systems and private wells. Moreover, current efforts from Silent Spring are investigating new technologies to reduce loading of emerging contaminants to septic systems.”

The wells with higher levels and more frequent detections were located in more developed areas that have more septic systems. The findings bolster efforts by Cape Cod communities to protect “Zone I” and “Zone II” areas surrounding public wells by limiting development, buying up land, enforcing zoning restrictions, and replacing or upgrading septic systems.

Although more research is needed on the health impacts of these chemicals, Dr. Schaider says there is still good reason to be proactive. Antibiotics in drinking water may increase the spread of resistant bacteria. Few research studies consider complex mixtures of chemicals like those found in drinking water; such chemicals can combine in ways that magnify their health impacts. And Cape Cod has long had a history of elevated breast cancer incidence, with drinking water contaminated by hormone disruptors as a possible factor.

To evaluate options for protecting drinking water in the future, Silent Spring Institute researchers have also conducted a second study, which compiled the most comprehensive dataset of emerging contaminants discharged from septic systems.

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 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. In the meantime, residents of Cape Cod and other areas can protect water quality by pumping their septic system as recommended, properly disposing of medications and hazardous substances, and purchasing additive-free household products. 

Funding for the wells study came from Massachusetts Environmental Trust and U.S. Centers for Disease Control and Prevention.