Core Sample a Boon to Geologist

This summer, Todd Greene was offered some valuable core rock samples he hopes will lead to a breakthrough in mapping the rock formations under Chico.

Greene, Geological and Environ- mental Sciences, was offered 600 feet of rocks from three cores by MACTEC Consulting from locations off Hegan Lane, near the University Farm. This kind of sample would cost the University hundreds of thousands of dollars to get on its own, said Greene.

The samples were taken by MACTEC for ABB, the firm that owns the former Smuckers juice plant off Hegan. They used sonic drilling technology to take continuous rock samples every 10 feet, providing “a continuous record of the bore hole,” said Greene. MACTEC was testing the samples to discover the boundaries of the Skyway subdivision plume of toxic groundwater that originated on the site.

The company that owned the property in the 1970s, C-E Building Products, had dumped degreasers into open pits in the ground. These organic compounds seeped into the groundwater and contaminated drinking-water wells in nearby neighborhoods. In 2003, the toxic plume was discovered, and residents were given bottled water by the state Department of Toxic Substances Control.

ABB, which had owned the property since 1990, took the initiative to clean up the damage, said Greene. They connected the affected residents to municipal water and began an effort to find the boundaries of the plume. “It’s a multimillion dollar effort to fix something they had no responsibility for causing,” he said, “a great story of corporate citizenship.”

Now that MACTEC is done with the samples, Greene will be able to use them to discover, to the foot resolution, the location of the various rock formations underneath Chico.

He is particularly interested in where the Tuscan Formation begins. The Tuscan Formation is made up of 1.2 million years of flows from an old volcano in the Lake Almanor region. You can see exposed Tuscan Formation along walls of Butte Creek Canyon and in Upper Bidwell Park, but most of the formation is underground, covered by the Red Bluff formation and modern river sediments. It’s crucial to Butte County, said Greene, because we get our municipal water from the groundwater in the Tuscan Formation.

Greene said there hasn’t been a definitive way to tell when a well tapped into the larger Tuscan aquifer, and not the Red Bluff. “That’s a really fuzzy boundary right now.”

He and senior geology majors in his Sedimentary Basin Analysis class will look at the composition of each sample, sieving them and trying to tell the difference between layers by looking at the sand, clay, and pebbles that make up each. When the Tuscan Formation can be more accurately identified by composition, Greene will be able to use triangulation of data from wells all over the area to develop refined maps of the layers of rock resting under Butte County. He hopes that his maps will predict how far underground the Tuscan Formation is at any given location.

“Once we know how to tell when we hit Tuscan Formation, we can apply that to other wells,” said Greene. “In addition, if we are analyzing the amount of water that comes into our area, we need to know if we are looking in the bigger Tuscan aquifer system or in some local shallower system. It’s critical to know if we’re tapping the big system.”

With Greene’s research, defining those boundaries will be that much easier.

—Anna Harris, Public Affairs and Publications