Research into groundwater contamination from onsite wastewater systems has primarily focused on the bacteria and viruses that make people sick. But there is another imminent problem wastewater professionals need to be aware of: micropollutants. These chemicals, present in very low concentrations, are an emerging issue for wastewater plants, and two recent studies suggest they may be the same for onsite systems.
In daily life, micropollutants are medicines, sunscreen, cleaning products and artificial sweeteners used in products such as toothpaste. Except for a few cases, scientists generally do not know the effects when people and animals are exposed for a long time to very small amounts of these substances.
Two recent studies found micropollutants flowing from onsite wastewater systems and migrating to nearby private wells. These were not advanced treatment systems, but densely clustered conventional onsite systems, and the study results hold lessons about how public health officials and onsite professionals should think about this newly discovered problem.
SANDY SOILS, OLD SYSTEMS
“Fire Island in many ways is a worst-case scenario,” says Patrick Phillips, a scientist with the U.S. Geological Survey in Troy, New York. His study, published last year in Science of the Total Environment, looked at onsite systems on the island and at a health care facility for the elderly in New England.
Fire Island stretches along the southern shore of Long Island. Clustered along its narrow length are small communities of mostly seasonal homes. Treatment consists of cesspools, typically a hole lined with cement blocks, Phillips says. This was the system of choice when the island developed after World War II. “It’s a barrier island so there’s lots of sand. There is little organic matter in the soil so transit times are very quick. And there are about four dwellings per acre.”
The 60-bed health care facility had a septic system more than 20 years old consisting of a settling tank, four septic tanks and two drainfields of about 5,400 square feet each and alternately dosed for two to three days at a time. The aquifer is sandy.
A study of Cape Cod well contamination was led by Laurel Schaider, a research scientist at the Silent Spring Institute in Newton, Massachusetts. Cape Cod homes are typically served by standard septic tanks discharging to drainfields. The aquifer is sand and gravel.
Wells downstream of the treatment areas ranged from a depth of about 3 feet on Fire Island to about 130 feet on Cape Cod.
MEDICATIONS FOUND
At the elder care facility, tests of water wells detected several chemicals, among them a sedative, a muscle relaxant, the antibiotic sulfamethoxazole, the topical anesthetic lidocaine, an anti-seizure drug and an opioid pain reliever. On Fire Island, tests found traces of the insect repellent DEET, a fragrance called galaxolide and a food additive called triethyl citrate. Tests of Cape Cod water looked for 117 chemicals, and 85 percent of the tested wells contained detectable amounts of at least one. Among others found were sulfamethoxazole, another drug called carbamazepine used to treat seizures and nerve pain, several flame retardants, and a broad class of chemicals called polyfluoroalkyls that are used in cleaners and paints, and in nonstick, waterproof and stain-resistant coatings.
For most of the chemicals detected, there are no guidelines for what a safe dose is. For chemicals that do have maximum allowable doses, the tests found concentrations well below the threshold. But the absence of a safety guideline does not mean chemicals are risk-free. This is particularly true for chemicals that can act like hormones.
“This is a new area,” Phillips says. “There have been reports of subtle effects on fish. Fish aren’t killed, but their mating behavior changes, and it’s pretty well established that some chemicals will change the ratio of males to females and their sexual characteristics.” These results have been found in fish exposed to discharge from wastewater treatment plants, he says. The effects of septic systems have not been studied, although Cape Cod ponds affected by septic systems show elevated levels of hormones.
“For a lot of these chemicals, we don’t have a basis for evaluating the effects of chronic exposure: a long period of time at very low doses,” Schaider says. The effect of exposure to combinations of the chemicals is also not known, she says. “We tend to study one chemical at a time, but a certain combination of chemicals may act to block the effects of one or enhance its effects.”
How well chemicals are broken down depends on the chemical and the wastewater treatment system. Some aren’t degraded unless there is very advanced treatment or a blast of UV light, Phillips says. Some chemical compounds readily bind to soil particles and break down in the biologically active zone of soil. Some chemicals don’t break down at all, such as acesulfame, an artificial sweetener widely used in everything from soft drinks to toothpaste.
WHAT CAN THE ONSITE INDUSTRY DO?
A key point from Schaider’s study and others is that the minimum required distance from wells to drainfields may not be enough to allow treatment for chemicals. One idea for new developments is to have a single well serving all the homes and to locate that well upstream in the groundwater flow, she says.
A wastewater professional who wants to test well water for the presence of chemicals migrating from an onsite system faces a difficult task. Testing for the chemicals detected in the studies required specialized laboratory equipment. Schaider said her group spent $1,800 per water sample to search for those 117 chemicals. An alternative is to use markers, easily found substances that tend to appear with the substances you’re looking for. One is nitrate.
When contaminants turned up in wells, so did nitrate, she says. The same was true for boron, which is used in home cleaning products. The problem with nitrate is it can also come from fertilizer, which makes it a poor indicator in areas dominated by agriculture. Another option is to test for the artificial sweetener acesulfame, Schaider says. It doesn’t break down in our bodies or in the soil, and because it is used in consumer products, its presence signals the presence of other chemicals.
