Urban Areas See More Chemicals in Ground Water

Areas with more development and higher human populations tend to have well water contaminated with greater levels of man-made chemicals, according to a new study by the U.S. Geological Survey (USGS).

In a survey of 30 randomly chosen wells that provide public water supplies in the north Tampa Bay area, USGS researchers found urban areas showed low, pre-treatment levels of home-and-garden pesticides and other chemicals. While the concentrations were far too low -- less than one microgram per liter -- to meet any health concerns under U.S. Environmental Protection Agency (EPA) standards, the findings indicate that human activity can have a measurable impact on the water quality of aquifers deep underground.

Researchers chose the Tampa area because much of the region relies on the Upper Floridian aquifer for drinking water supplies.

"We are seeing the effect of human activity and land-use practices on our ground-water supplies," said Patricia Metz, a hydrologist with the USGS and lead author of the study. "Although concentrations are very low, their presence indicates the relatively rapid mobility of these contaminants to the ground-water system and the vulnerability of ground-water supplies to contamination from human activities."

Researchers found few or no man-made chemicals in wells in low-population areas with little development. They also found that ground-water contamination was twice as high in areas where the Upper Floridian aquifer was unconfined, meaning it can more easily absorb water and other compounds from the surface, than in places where the aquifer is more protected from above-ground seepage.

"Both the unconfined nature of the aquifer and the higher population are determining factors in the number of anthropogenic compounds detected," Metz said.

She added that studies such as these can provide important guidance to resource managers and decision-makers in the future.

"For the past several decades we've seen land-use changes that may affect the future of our potable ground-water supplies," Metz said.

The man-made chemicals found most frequently in ground water included atrazine (an herbicide used in many lawn-care products) and its breakdown components, deethyatrazine, 2-hydroatrazine and deisopropylatrazine; chloroform, a volatile organic compound (VOC) linked to lawn irrigation, pools and spas; and DEET, an insect repellant.

While the USGS study focused on well water prior to treatment by water utilities, it also found that water after treatment actually had higher concentrations of man-made chemicals. Researchers attributed this to the way in which water disinfection treatment works.

An earlier study by the USGS reported finding residues of pesticides, flame-retardant chemicals and personal-care products in several tributaries of the Potomac River. Among those chemicals were several that act as endocrine disruptors, compounds that interfere with normal hormonal activity. Researchers in that study concluded the presence of such endocrine disruptors might account for the high numbers of male smallmouth bass they found showing female sexual characteristics.

U.S. Geological Survey, "Land-Use, Human Activity Impact Aquifers and Drinking Water Supplies." URL: (http://www.usgs.gov/newsroom/article.asp?ID=1771)