From pollution problem to scientific breakthrough

How a poisoned groundwater plume led to a key finding by a Chico State prof

Todd Greene is an assistant professor of geology and environmental sciences at Chico State University. His campus office is filled with images of rock formations in the Sacramento Valley—along with preschool drawings by his daughter. These days he’s unusually excited. A breakthrough in Chico’s geological history is being made, he says enthusiastically.

Greene is now in possession of a set of intact core rock samples from the three geologic formations that underlie this part of the Sacramento Valley—the first samples of such high quality ever to be extracted. They promise to contribute greatly to better understanding of the exact boundaries of those formations—the Red Bluff, the Modesto and the Tuscan.

What makes the story especially interesting is the way the samples were obtained. The breakthrough is linked to a plume of toxic groundwater in south Chico known as the Skyway subdivision plume, after the small neighborhood along two streets off Hegan Lane whose drinking-water wells were contaminated by it.

After the plume was discovered in 2003, scientists from the state Department of Toxic Substances Control traced it back to the Smuckers juice plant on Southgate Avenue. That company also had been using water from the plume, but had been filtering out the toxins.

Further research showed that the site had been owned in the 1970s by C-E Building Products, which manufactured aluminum shower enclosures and windows. Former C-E employees admitted the company had used solvents to degrease machine parts and disposed of them in an unlined disposal pit in the ground.

C-E Building Products was part of a larger company called Combustion Engineering, which in 1977 sold the property. In 1990 a huge multinational Zurich-based automation-technology firm, ABB, purchased Combustion Engineering. Although ABB had no role in polluting the groundwater, DTSC determined that legally it was the “successor of interest” responsible for cleaning it up.

To its credit, the company did not flinch from the prospect. Not only did it reimburse the state the nearly $1 million already spent on cleanup, it spent an additional $2 million to put in water lines that supplied residents with clean water provided by the California Water Service Co.

ABB hired a geological-technical-services company called MACTEC Consulting to assist with that work. The company used ultra-modern sonic drilling technology as part of an investigation to determine the extent of the Skyway plume.

During the drilling process, MACTEC extracted continuous core rock samples from several bore holes, each nearly 250 deep. ABB decided to offer the rock cores to Chico State, the DTSC, the California Department of Water Resources and the California Regional Water Quality Control Board.

Those samples have the potential to reveal important geological data about Chico’s aquifers and the 3.3-million-year-old Tuscan Formation that holds the Sacramento Valley’s groundwater.

Greene has been studying the Tuscan Formation mostly in Big Chico Creek Canyon and the Big Chico Creek Ecological Reserve area, but says this is the first time rock data for the Chico area has been made available in such good condition. This discovery will have tremendous benefits in the scientific community, and can also help the public to better understand where our water comes from.

“Chico’s water supply is pumped out of the aquifer known as the Tuscan Formation,” Greene explained. “It’s very uncommon to find actual rock material to represent our water.”

Ziploc bags marked with drilling locations and the depths at which the samples where extracted crowd a large table in Room 112 in the Physical Sciences Building at Chico State. Ranging from crumbling red-orange sandstone at 80 feet to compact grey volcanic rock at 200 feet, these colorful data samples can give geologists like Greene an idea of how long each of the three aquifer layers was exposed to the elements before the next sedimentary layer took over.

“Looking at the sandstones and clays, we can really narrow in on what defines the boundaries, which is important when looking to define Chico’s three aquifer zones—shallow, intermediate and deep.”

Chico State geology students will also get to partake in educating the city about the Tuscan Formation aquifer, its flow paths and the changes in volume of groundwater. Always trying to bring local impacts into his classes, Greene may possibly use the core sample in his Sedimentary Base and Analysis class in the fall semester. He is still looking for the right students to do the laborious work of cleaning and analyzing the data, he said.