Tag Archives: rainwater

Stormwater could release contaminants to ground and surface water

While giving a sense of cleansing in any city, rainstorms usually cause substances in buildings, streets, and sidewalks to wash off into the drain. This can cause contaminants to end up in ground and surface waters, according to a new study.

Credit: Flickr

Researchers reporting in ACS’ Environmental Science & Technology have analyzed untreated urban stormwater from 50 rainstorms across the US. They found a wide variety of contaminants that could potentially harm aquatic organisms in surface waters and infiltrate groundwater.

Other studies in the past of urban stormwater runoff have revealed a mixture of industrial chemicals, pesticides, pharmaceuticals and other substances that, at certain levels, can be toxic to aquatic life. As a result, many cities and water-management agencies are trying to develop stormwater control measures to keep these contaminants out of other water bodies, such as rivers or aquifers.

However, data from a wide variety of locations across the U.S. are lacking. To help fill this research gap, Jason Masoner and colleagues wanted to catalog and quantify the contaminants in urban stormwater from 50 storm events at 21 sites across the nation.

The team of researchers measured levels of 500 chemical compounds in urban stormwater collected during rainstorms. Samples contained a median of 73 organic chemicals, with pesticides being the most frequently detected chemical group.

Eleven contaminants, including the insect repellent DEET, nicotine, caffeine, and bisphenol A, were found in more than 90% of samples. The researchers also frequently detected prescription and non-prescription pharmaceuticals, indicating that the stormwater was contaminated with human waste, possibly from sewage leaks or other urban sources.

Some of the contaminants were present at levels known to be toxic to aquatic life, but those at lower concentrations could also have effects when combined with all of the other substances in the water.

The study highlighted the need for more research about the long-term effects of these contaminants on aquatic organisms exposed to the stormwater, the researchers said, concluding their paper.

Researchers find that that water penetrates upper crust layer, goes down to 6-8 km

General depiction of the crust.

Most geologists did not believe that water could penetrate into the lower ductile crust, but a new study has shown that this does indeed happen. Researchers conducted isotopic analysis on minerals brought up by tectonic uplift showed that rainwater can reach (and perhaps even surpass) the brittle ductile transition zone, at 6-8 km.

Dr. Catriona Menzies and Professor Stephen Roberts, with their team of scientists from the University of South Hampton, the University of Otago and the Scottish Universities Environmental Research Centre, conducted the analysis in New Zealand’s Southern Alps – where tectonic movement constantly pushes deeper parts of the tectonic plate upwards. These minerals carry with them a history of the fluids which passed through them, and that history can be scanned for isotopes and reconstructed. Basically, whenever a fluid passes through a rock they leave behind a tiny deposit – and that is the key here.

Geological map of New Zealand.

By identifying hydrogen and oxygen isotopes the authors mapped the water content at different depths. In the 0-2 km traces of rainwater can be easily found, but they were quite surprised to find the same thing as they went deeper and deeper – even further than 6 km. Again, they didn’t core to those depths, they just studied minerals which were at that depth and brought up by tectonic activity.

It’s also important to note that this is meteoric water – water from meteorological cycles which precipitates as rain or snow; it is not magmatic (or juvenile) water, the water present in magma since its genesis, which can only be brought up by eruptions or magma uplift.

Rainwater can play an important role in fault activation or reactivation – weakening the rocks and acting like a lubricant, so understanding how it infiltrates and what depths it reaches can improve our understanding of seismic risk and earthquake triggering. It also has interesting implications for our understanding of valuable minerals, such as gold and quartz. Furthermore, it can also play a role in orogenesis, depending on its flowpath.

*Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2014.04.046