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Photo: Rain falling on an urban street and people standing at a bus stop.
Urban landscapes, which have a greater percentage of impervious surfaces, contribute to higher levels of enteric bacteria and nutrients in surface storm water runoff, potentially impacting the water quality in below ground aquifers. Photo courtesy of Microsoft clipart.

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Runoff Research Promotes Healthier Aquifers

By Laura McGinnis
September 24, 2008

Where rain falls can influence the quality of surface water before it enters underground reservoirs, some of which provide water that eventually comes out of our taps.

That's one conclusion from a collaborative study by the Agricultural Research Service (ARS) and the University of Arizona (UA). The ARS and UA scientists are investigating how urban landscapes influence storm runoff and water pollutants. The focus of their study is the greater Tucson metropolitan region, which has quadrupled in size since the early 1960s.

Like many Arizona cities, Tucson is looking into "enhanced stormwater recharge" to capitalize on the region's rare, but intense, downpours. Enhanced recharge is the process of improving groundwater reservoirs with strategic engineering, such as artificial wells to store water or porous pavement that allows more water to trickle into aquifers.

Understanding how housing density affects the region's aquifers can be helpful in identifying the best enhanced-recharge methods for a specific area.

Jean McLain, an ARS microbiologist at the U.S. Arid-Land Agricultural Research Center in Maricopa, Ariz., is working with a team of UA scientists, led by Kathleen Lohse of the School of Natural Resources, to examine how housing density affects the levels of nutrients, fecal bacteria, metals and organic pollutants in storm runoff.

They're also researching whether and how those substances enter aquifers. This information is essential for selecting optimal enhanced-recharge methods.

Impervious surface areas, such as paved parking lots, have higher runoff than absorbent surfaces. Preliminary studies show that this allows for less processing of pollutants, leading, in turn, to higher levels of enteric bacteria and nutrients in the water samples.

Ultimately, this collaboration will assist in developing effective best management practices for promoting aquifer water quality. For example, an effective recharge method for the kind of runoff mentioned above might allow the water to slowly filter through the soil, removing pollutants before the water enters underground reservoirs.

ARS is a scientific research agency of the U.S. Department of Agriculture.