Along with millions of gallons of water, a Seattle-based energy company plans to pour tracer chemicals down two 10,000-foot wells east of La Pine this summer during an effort to increase their geothermal power potential.

A retired Bend doctor is questioning the safety of the chemicals AltaRock Energy may use in its enhanced geothermal systems (EGS) experiment, in which the company plans to use cold water to crack hot rock and produce a new geothermal reservoir underground.

“My primary concern is health,” said Stuart Garrett, who helped lead the creation of Newberry National Volcanic Monument in the early 1990s. “Some of that could get into groundwater.”

The monument was established to keep geothermal power development out of Newberry Crater, home to Paulina and East lakes.

In previous interviews Susan Petty, AltaRock’s president and founder, said the company would be pouring pressurized water down the wells but no chemicals. Last week she said the company would be using tracers, or chemicals used to trace how much underground rock the water was contacting.

“We put them in such minute quantities I didn’t even think of them,” she said.

AltaRock plans to use about four gallons of chemicals in the 24 million gallons of water sent down the wells on the Deschutes National Forest outside the Newberry National Volcanic Monument, Petty said. She said the chemicals are also regularly used in groundwater exploration.

The company also may use biodegradable plastics, minerals and glass — the exact makeups of which were held as proprietary in Bureau of Land Management environmental documents — to plug fractures in the rock as more are created deeper down, Petty said. The $42 million EGS experiment, which is half funded by the U.S. Department of Energy, will be done in three stages starting this summer.

While similar to fracking, the controversial injection of water into the ground by companies in pursuit of oil and petroleum reserves, Petty says it is different. The difference, she said, is that fracking uses water mixed with chemicals that break rock and sand to widen the fractures. AltaRock is not trying to open large fractures that are created in fracking. Instead it is trying to build a web of small fractures for water to pass through hot rock and absorb heat before returning to the surface.

AltaRock plans to use seismometers to measure the spread of the fractures, which will produce tiny earthquakes as they are created. The BLM environmental documents said the earthquake hazard of the EGS experiment is no different than the natural earthquake hazard at the volcano, with magnitude 4.0 earthquakes possible. The documents listed the likelihood that the experiment would trigger an earthquake between magnitude 3.0 and magnitude 4.0 at less than 1 percent.

Trace of light

AltaRock will also use chemicals to measure the growth of the fractures.

The chemicals that may go down the wells near La Pine are all fluorescents, glowing in shades of green and yellow as well as pink and red, Petty said. The company is working on a tool that uses LED lights and spectrometers to measure how much of the chemicals are in the water.

The plan is to put two chemicals down the well at a time, one that sticks to rocks and one that doesn’t. The one that sticks will fade as the water contacts more rock. That will tell scientists that the water is flowing through more rock.

The company listed 19 potential chemicals it may use as tracers in the wells in Bureau of Land Management environmental documents.

Components of those chemicals include naphthalene and rhodamine, which Garrett said may be toxic. Petty said other components of the chemicals they plan to use counteract this possibly negative health effect.

The design of the wells should also keep the chemicals from entering any drinking water, Petty said. The well is lined with concrete and steel where it passes through the aquifer between about 600 and 1,200 feet below the surface.

If the cracking of the rock triggered by the EGS starts to spread upward and not outward as planned, the flow of water will be stopped said Doug Perry, president of Connecticut-based Davenport Newberry, AltaRock’s partner on the experiment.

Like Petty, he said the chemical-laden water won’t mingle with groundwater.

“The aquifer is much, much shallower — by thousands of feet — than the area we are working in,” he said.

Permitting process

Davenport Newberry originally drilled the wells set for the EGS experiment as part of its ongoing search for traditional geothermal power sources — underground hot water — but only found hot rock. AltaRock is leading the EGS experiment and, in doing so, is modifying state and federal permits to allow for the mass injection of water into the ground.

The BLM, which manages underground exploration even on land overseen by the U.S. Forest Service, closed a public comment period for the environmental documents on the project last week.

Garrett, the Bend doctor, raised his concerns about the chemicals in comments filed with the BLM. He said AltaRock didn’t provide details of how the chemicals it plans to use could affect people if they made it into groundwater.

“I just think they owe us a better explanation,” Garrett said.