By Wendell A. Duffield
Flagstaff Resident

The August 5, 2001, edition of the Daily Sun carried a story by my NAU colleague, Paul Morgan, and me. Our message was intended to make people think about how to extend the life of Flagstaff’s finite groundwater resources. Our bottom-line recommendation was to put used water back into the deep aquifer from whence it came, rather than using this treated sewage to grow lush green grass in our semi-arid climate, and causing Rio de Flag to flow when Nature doesn’t want it to. Such recycling would reduce the rate at which our region’s water table is being drawn down. We should not fool ourselves. We are mining our groundwater resources.

If the amount of feedback from readers is an accurate measure of how effective our message was delivered, we failed miserably. Rather than give up, though, let me describe another possible use for treated sewage, one that just might someday be appropriate to Flagstaff. I wish not to offend readers of the Tea Party by dwelling on such an unsavory topic. But hey, sewage by any other name is still … well, you know what.

Have you ever thought that when you flush the toilet, once you’ve finished with your business, you could be helping to generate electricity? If you’re a normal and reasonably fastidious person, the answer probably is a resounding no. Most of us just want that messy stuff to disappear, or we have other thoughts, if any, on our minds while accomplishing this mundane yet essential care-taking of the human body.

Well, what that simple flush can accomplish today holds energetic possibilities unthought of, if not unthinkable, just a few years ago. In California, the technique of flashing liquid sewage to high-pressure turbine-driving steam, graphically referred to as flush-to-flash, conjures up an entertaining double entendre for the words brownout and blackout. The story behind this catchy phrase is contained in the history of exploiting geothermal energy at a place called The Geysers, about fifty miles north of San Francisco. It’s also a tale of two seemingly unrelated nagging problems that unexpectedly find a common solution that is simultaneously good for business and the environment. If this sounds too good to be true, read on.

Geothermal energy is simply the earth’s natural heat, vast amounts of which continuously make their way to the surface and dissipate into space. There’s still plenty of this internal heat for humans to harness, in spite of the fact that cooling has been underway since creation of our planet, about 4.6 billion years ago.

During 1904 at a place called Larderello in Tuscany, Prince Piero Ginori Conti was the first person to generate electricity by harnessing geothermal steam. The rest of the world was a bit slow to follow this creative Italian’s lead, but by the late 1950s and early 1960s, geothermally powered electrical plants were in operation at several places around the globe. One of these places was The Geysers, an area with hot springs and fumaroles in the California Coast Ranges.

As any entrepreneur would agree, free fuel for driving a turbine generator is good for the company’s bottom line. And geothermal steam is virtually free, once production wells and a network of steam-transporting piping are in place. With dirt-cheap fuel and other incentives as driving forces, during the 1980s The Geysers grew to be the largest geothermal electrical development in the world. At its peak in the late 1980s, about 2,100 megawatts of generating capacity had been installed over a land-surface area of nearly forty-five square miles. This large development was capable of generating enough electrical juice to satisfy the sometimes voracious thirst of a “typical” USA city with 2,000,000 people.

For comparison, 2,100 megawatts is roughly the electrical-generation equivalent of the turbines of two Glen Canyon dams spinning at full bore. But at The Geysers, electrical power has come without drowning a preciously beautiful canyon in the process. Deer and cattle grazed the hilly pastures at The Geysers before geothermal development, and they can still do so today.

The future of the geothermal-energy industry at The Geysers looked rosy in those halcyon 1980s. Steam was streaming. Turbines were turning. And profits were piling. Then, the inevitable(?) consequence of over-zealous exploitation, lack of foresight and planning, and perhaps other unrecognized factors turned rose petals brown.

The rate at which steam was being removed was noticeably depleting this source of free fuel. There were several companies producing steam, and together they simply had too many straws in the milkshake. Roughly four hundred production wells, ranging from about 5,000 to 9,000 feet deep, were removing steam at a rate much faster than Nature could replace it. The subsurface geothermal resource, a network of interconnected steam-filled cracks and fractures within a large volume of very hot rock, was literally going dry. Steam pressure began dropping drastically. By 1992, steam production could drive only about 1,000 megawatts of the 2,100 installed capacity.

What to do? It was apparent that sources of “make up” water were needed … water that could be pumped underground in attempts to keep the fractured hot rock saturated with high-pressure steam. However, locally available sources of stream and shallow ground water, augmented by some steam condensate at the bottom end of the electricity-generation cycle, were woefully inadequate for the geothermal needs. Steam production continued to drop. The future seemed pretty bleak.

Meanwhile, just over the crest of the first Coast Range ridge to the northeast, communities along and near Clear Lake were in need of new ways to properly dispose of their treated sewage. At this point, the interplay between supply and demand led to a deal advantageous to all stakeholders… and pretty friendly to Mother Earth, too.

Geothermal developers recognized that treated sewage could be used to artificially replenish the subsurface supply of steam at The Geysers. In terms of thermal energy, there was, and still is today, an immense resource in the ground. The only real problem was that dwindling supply of steam, the stuff needed to carry calories to the surface where they can be put to work.

Negotiations led to a partnership among the Lake County Sanitation District, the Northern California Power Agency, and three private companies heavily invested at The Geysers. In the end, construction of roughly thirty miles of pipeline got underway in 1995. This pipe began to carry the wastewater of treated sewage to the southern part of The Geysers by late 1997, and continues to do so today.

Rate of delivery is about 8 million gallons a day. At the delivery end of the pipeline, wastewater is injected underground through about a dozen wells, which are located to try to optimize the subsurface flow to production wells. The relatively cool injected fluid becomes heated through contact with hot rock, and it then appears as high-pressure steam at nearby production wells.

It’s too early in the process to know what the long-term outcome will eventually be. But short-term results are very encouraging.

For example, during 1996 and 1997, before injection of wastewater began, the five power plants located in what was to be the injection area lost 13% of their output due to steadily diminishing steam pressure in production wells. Shortly after injection got underway, this downward trend was reversed. It has subsequently reappeared, though pressure now drops at a much lower rate than that experienced before the substantial amount of wastewater injection began.

Projecting three years of operating experience to distant out years can be dicey, but most geothermal experts believe that continuous injection at the present rate will sustain, for the next two decades or longer, considerable otherwise-lost power production within this southern part of the Geysers geothermal field. According to Bill Smith, a geologist with the Northern California Power Agency, with injection, “We are now able to generate an additional 75 megawatts, enough for 75,000 customers.” The project is considered so successful, that the pipeline system from Clear Lake is being expanded.

Another measure of real short-term success and anticipated long-term benefits is apparent in the fact that construction of a 40-mile pipeline to import treated sewage from Santa Rosa was begun in 2000. This project is designed to deliver 11 million gallons daily, to the central part of the geothermal field.

Together, these two sources of “make up” fluid are anticipated to sustain total electrical output from The Geysers at about 1,000 megawatts for at least two more decades, and possibly much longer.

Who knows? Once the results of a few more years of injection are available, perhaps injection of wastewater at even higher rates will be desirable. We humans seem to have a knack for producing prodigious quantities of liquid sewage. And there’s certainly still plenty of thermal energy in the rocks, waiting to be lifted to the surface as turbine-driving steam.

Will geothermal energy ever be used to generate electricity in the Flagstaff area? For several decades, geologists have had sound scientific reasons to believe that the answer might be yes. But until someone drills several thousand feet into the possibly-very-hot roots of our local volcanoes, the question will remain unanswered.

Whatever that answer may be, next time you rise up from your throne and flush your efforts down the drain, feel uplifted and heartened by the fact that someone doing the same thing in northern California is helping to keep the USA’s electrical grid charged with dancing electrons.

You should also feel a warm glow knowing that electricity generated by geothermal steam, be it natural or the product of injected wastewater, releases virtually no greenhouse gases to the atmosphere, in stark contrast to those dirty coal- and hydrocarbon-fueled plants.

Flush to flash. Effluent to affluent. One person’s waste can be another person’s treasure.