Streams Of Noxiousness

Long after crews have cleaned up a chemical spill on the ground, the contaminants persist underground and eventually make their way through the soil and rock to groundwater that supplies drinking wells and sustains aquatic ecosystems. Now scientists have developed an easier way to monitor groundwater contamination in cities, which should allow for more proactive screening (Environ. Sci. Technol., DOI: 10.1021/es101492x).

In urban areas, spills from manufacturing plants and underground gasoline storage tanks "can act as long-term sources of groundwater contamination, lasting from decades to centuries," says hydrogeologist James Roy at Environment Canada, the nation's environmental regulation agency. But monitoring urban groundwater is patchy at best, because it often depends on sampling from observation wells. In cities, drilling these wells is costly, time-consuming, and sometimes unfeasible due to land ownership issues.

Roy and his colleagues wanted to develop an approach that avoided these wells. So they decided to sample from urban streams, which often run through public land and receive discharge from groundwater.

The researchers collected groundwater beneath streams in three Canadian cities: Angus, Ontario; Amherst, Nova Scotia; and Halifax, Nova Scotia. The team used a device that consisted of a steel tube attached to a drive head, which they could drill into the sediment at the stream's bottom. Holes in the drive head allowed the researchers to pump water from below the streambed into collection tubes for analysis. They collected multiple samples along several-hundred-meter stretches of the streams to perform a complete survey of the area's groundwater.

In these test streams, the researchers detected previously-identified chlorinated solvent contaminants from nearby dry-cleaning shops and an aerospace facility. But they also identified a broad range of unexpected contaminants, such as petroleum, arsenic, and chemical signatures consistent with sewage and lawn-care products. The technique is only semi-quantitative, so the scientists could not measure exact quantities of these pollutants.

Still Brewster Conant, a hydrogeologist at the University of Waterloo in Canada, says that by sampling below streambeds, this new approach offers "a good reconnaissance method for determining contamination problems in a watershed."