Why there will be a helicopter flying low at 70 mph over Cedar Rapids and Linn County this week

CEDAR RAPIDS - A helicopter will be flying low above Cedar Rapids and Linn County this week towing a large cylindrical sensor to gather information about the city's water supply.

Called an airborne geophysical survey, the testing method uses electromagnetic pulses to detect the consistency of subsurface material, such as rock, sand or soil. The information is to be paired with ground level data from borings to model how and where water flows most abundantly in the Cedar River aquifer, which supplies water for Cedar Rapids.

'This will establish a tool we can use for planning,” Bruce Jacobs, the Cedar Rapids utilities engineering manager, said on Monday. 'This will tell us how does the aquifer work in a level of detail we haven't had before, and give us prospects of where to locate future wells.”

A drought in 2012 stressed the recharge of the Cedar River aquifer in a way that wasn't anticipated and city officials created a drought crisis response plan as a result.

The plan never was implemented as a wet spring followed, but the episode spurred a four-year effort to create a new model to better understand the aquifer, especially with looming growth of population and development, Jacobs said.

The aquifer pools groundwater and Cedar River water filtered through the alluvial sand riverbank. Wells tap into the water, which is then treated and flows out of faucets around the city.

The models should help with long-term management of the city's water supply, and will help identify ideal locations to drill wells that will tap a consistent, reliable water source, officials said.

Cedar Rapids has been working on the modeling with the U.S. Geological Survey since 2015. CGG Canada Services, of Mississauga, Ontario, is conducting the airborne survey, which should have results in one year.

Jacobs said the overall study costs $906,000, which includes $120,000 for the airborne testing. The city is absorbing 65 percent of the cost while U.S. Geological Survey is covering 35 percent, Jacobs said.

Eddie Haj, a hydrologist and groundwater specialist for the U.S. Geological Survey, said Cedar Rapids is ahead of the curve in studying its water supply in such a detailed way. Increasing demand on other deeper aquifers, such as the Jordan, is prompting cities to look for other sources of water, Haj said.

Cities could turn to Cedar Rapids in the future, so it is important information to prepare for city growth but other demands, he said. Because Cedar Rapids' alluvial aquifer is shallower, increased nitrate levels in the river are leading to increased nitrate levels in the aquifer, which is another factor to contend with going forward, he said.

'Cedar Rapids is what I'd call extremely progressive in applying state-of-science methods to understand the groundwater issue,” Haj said. 'Water demand is only going up, and you can't pump more out of the wells. It's all about how to pull as much out of the aquifer without endangering the aquifer.

The study aims to help answer three questions, he said. First, the nature of connectivity of the alluvial aquifer and the river itself; second, the preferred pathways of water that recharge the aquifer, and the connectivity between wetlands and the aquifer, he said.

The helicopter will be out two to three times a day for 2.5 hours at a time over the next week, weather pending. The helicopter will be flying low at about 200 feet above ground going 70 mph with the 20 foot-long, 800-pound sensor suspended horizontally below.

The probe has six coils each with a different frequency at the front with six corresponding coils at the back end, which send and receive the pulses, said Brett Robinson, project manager for CGG.

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