Butte County may soon have a better idea of what lies beneath its surface, thanks in part to the Kingdom of Denmark.
From late November, a helicopter took off from Orland Airport for several days to overfly an area between Chico and Orland, then southeast in the Butte Valley.
A hoop loaded with devices creating a weak magnetic field and instruments measuring the interaction with the layers beneath the ground was suspended below the helicopter.
Christina Buck, of the Butte County Water and Resource Conservation Department, explained that there are in the basement layers of sands and gravels holding water, divided in layers of clay and silt that block the passage of water to different degrees.
The different materials send different signals, although the picture is more blurred around 1200 feet, she said.
There is a problem that, although the signal received identifies the location of the layers, does not identify whether they are aquifers or aquitards blocking the waters. The flights had to pass close to the monitoring wells, where the county officials already know which layers are where. This gives a caption for interpreting helicopter survey data, and knowledge of what exists near wells could be extended to a much larger area.
This is important because a recent law has required local water agencies to develop groundwater management plans that prevent adverse effects on water supply and water quality. Knowing where the groundwater is and how it moves beneath the surface will yield better plans.
For example, there is a major aquifer in Butte County and in other counties in the Sacramento Valley, called Lower Tuscany. In some places it seems to be isolated from other aquifers by impenetrable layers of clay. In other places, it seems "fleeing", according to the county Web page on the project. The helicopter data could indicate differences in the layers of clay that might explain this.
It is also question of how water enters Lower Tuscany in the process called recharge. The areas around Butte Valley are thought to play a role. An examination of what is hidden underground could help determine if this is the case and how it might work.
The investigation process is known as the Airborne Electromagnetic (AEM). The helicopter traveled about 500 miles in total, 50 to 100 feet above the ground. The survey lines were about 500 meters apart from each other in critical areas, "resembling mowing a very large lawn," according to the county's web page.
"The AEM survey essentially takes a soil MRI to help us better understand the structure of underground sand and clay materials and the water system to implement the Sustainable Groundwater Management Act." said Paul Gosselin, director of the Department of Water Conservation and Resources in Africa. A press release.
AEM has generally been used to locate potential mineral deposits. But Denmark, which relies entirely on groundwater, according to Buck, has adapted the technology to map its aquifers and plan to manage them. "They were where we are now, about 20 years ago," she said.
Local information should be available this spring.