The largest wastewater-to-electricity project in the world.

The world's largest wastewater-to-electricity geothermal project is up and running. Calpine Corp., San Jose, Calif., and the city of Santa Rosa celebrated the startup of the Santa Rosa Geysers Recharge Project in northern California, which provides up to 11 million gallons of recycled water to The Geysers Geothermal Field. The 40-mile-long pipeline ranks ninth among the largest wastewater reuse projects in the United States.

The Geysers pipeline project disposes of half the wastewater generated annually by Santa Rosa and its three partner cities, Rohnert Park, Cotati and Sebastopol. At the same time, the project helps breathe new life into power production at The Geysers, and extend its commercial life. Located within 30 square miles straddling the Lake and Sonoma county borders in northern California, The Geysers is the largest geothermal power operation in the world. With 21 power plants (19 owned by Calpine; two owned by the Northern California Power Agency), The Geysers produces nearly 1,000 megawatts (MW) of electricity, or enough to power a million homes. First commercially developed in the 1960s, The Geysers now satisfies much of the electrical power needs of Sonoma, Lake and Mendocino counties, as well as that of Marin and Napa counties.

The Geysers project is the world's only geothermal system to use wastewater to replenish its steam fields. Nearby Lake County pioneered the world's first wastewater-to-electricity system at The Geysers in 1997. Since constructing a 29-mile pipeline, 8 million gallons of treated effluent is injected daily from Lake County, boosting power production at The Geysers by 68 megawatts. Springing from that success, the Santa Rosa Geysers Recharge pipeline system ensures that the city and its partners can effectively dispose of its treated effluent while helping Calpine produce clean energy for California.

“By injecting recycled water into The Geysers' steam reservoir, the City of Santa Rosa has found an environmentally sound discharge solution and is helping to promote green power production in California,” explains Calpine vice president-geothermal Dennis Gilles. “There are few places on the planet where such a system could be implemented and the City of Santa Rosa is to be complimented for its vision and commitment to environmental stewardship.”

Construction of the Santa Rosa-Geysers pipeline began in April 2000. Changing goals of Calpine's city partners, new and more detailed topographic studies, lawsuits and neighborhood opposition changed not only the size of the pipeline, but almost the entire route. Though construction took almost four years instead of a planned two years, and costs rose from an expected $102 million to $200 million, the majority of stakeholders are satisfied with its solution to a vexing environmental problem.

To utilize the Santa Rosa's wastewater from the new pipeline, Calpine spent an additional $45 million to construct a network of pipes and wells to inject the treated effluent into the geothermal field's deep reservoir. Calpine project manager Steve Burden says the company's costs cover construction of 18 miles of wastewater distribution pipelines, a million-gallon storage tank, a 3,000-horsepower pump station and the conversion of eight steam wells to injection wells in The Geysers. Steam pressure derived from the injected effluent is expected to provide an additional 85 megawatts of power production. According to the Santa Rosa Press-Democrat, the wastewater pipeline will provide even more dividends, including:

  • Billions of gallons of leftover wastewater will become available each year to northern Sonoma County farmers, who currently irrigate with water pumped from the Russian River and its tributaries.

  • Help for the endangered coho salmon and steelhead trout, whose spawning habitats are depleted when water is pumped out of the river and its tributaries.

  • A nearly 60-percent annual reduction (2 billion gallons) of wastewater dumped into the Russian River.

Calpine's ownership in power generation began with the purchase of a five-percent interest in the 20-MW Aidlin facility at The Geysers in 1989. Calpine has since consolidated ownership within the geothermal resource area. As a result, the company is the world's largest private producer of electricity from geothermal resources.

The Calpine Geothermal Visitor Center in Middletown, Calif., offers free tours of one of the company's Geysers power plants. For more information, call 866-439-7377 or visit

Improving Geothermal Technology

Since the 1970s, the geothermal industry, with the assistance of government research funding, has overcome many technical drilling and power plant problems. Improvements in treatment of geothermal water have overcome early problems of corrosion and scaling of pipes. Methods have been developed to remove silica from high-silica reservoirs. In some plants, silica is being put to use making concrete, and H2S is converted to sulfur and sold. At power plants in the Imperial Valley of California, a facility is being constructed to extract zinc from the geothermal water for commercial sale.

As a result of government-assisted research and industry experience, the cost of generating geothermal power has decreased by 25 percent over the past two decades, according to the Geothermal Education Office. Research currently is underway to further improve exploration, drilling, reservoir, power plant and environmental technologies. Enhancing the recoverability of Earth's heat is an important area of ongoing research.

Geothermal energy is accessible if there is sufficient heat, permeability and water in a system, and if the system is not too deep. The available heat cannot be increased, but the permeability and water content can be enhanced. Private and government research projects in the United States, Japan and Europe are improving the accessibility of geothermal energy by developing new technologies to increase the permeability of the rocks and to supplement the water in hot, water-deficient rocks. Engineers estimate that by the year 2020, man-made geothermal reservoirs could be supplying 5 percent to 10 percent of the world's electricity.

One unique example of enhancing reservoir water is at The Geysers steam field in California, where treated wastewater from nearby communities is being piped to the steam field and injected into the reservoir to be heated. This increases the amount of steam available to produce electricity. With this enhancement, reservoir life is increased while providing nearby cities with an environmentally safe method of wastewater disposal.

Permeability can be created in hot rocks by hydraulic fracturing - injecting large volumes of water into a well at a pressure high enough to break the rocks. The artificial fracture system is mapped by seismic methods as it forms, and a second well is drilled to intersect the fracture system. Cold water can then be pumped down one well and hot water taken from the second well for use in a geothermal plant.

The outlook for geothermal energy use depends on at least three factors:

  • demand for energy in general

  • inventory of available geothermal resources

  • competitive position of geothermal among other energy sources

The demand for energy will continue to grow. Economies are expanding, populations are increasing (more than 2 billion people still do not have electricity), and energy-intensive technologies are spreading. All mean greater demand for energy. At the same time, there is growing global recognition of the environmental impacts of energy production and use from fossil fuel and nuclear resources. Public polls repeatedly show that most people prefer a policy of support for renewable energy.

The inventory of accessible geothermal energy is sizable. Using current technology geothermal energy from already-identified reservoirs can contribute as much as 10 percent of the United States' energy supply. And with more exploration, the inventory can become larger. The entire world resource base of geothermal energy has been calculated in government surveys to be larger than the resource bases of coal, oil, gas and uranium combined. The geothermal resource base becomes more available as methods and technologies for accessing it are improved through research and experience.

Production of fossil fuels (oil, natural gas and coal) is a relative bargain in the short term. Like many renewable resources, geothermal resources need relatively high initial investments to access the heat, hot water and steam. But the geothermal fuel cost is predictable and stable. Fossil fuel supplies will increase in cost as reserves are exhausted. Fossil fuel supplies can be interrupted by political disputes abroad. Renewable geothermal energy is a better long-term investment.

The monetary price we pay to our natural gas and electricity suppliers, and at the gas pump, is our direct cost for the energy we use. But the use of energy also has indirect or external costs that are imposed on society. Examples are the huge costs of global climate change; the health effects from ground level pollution of the air; future effects of pollution of water and land; military expenditures to protect petroleum sources and supply routes; and costs of safely storing radioactive waste for generations. Geothermal energy already can compete with the direct costs of conventional fuels in some locations and is a clean, indigenous, renewable resource without hidden external costs. Public polls reveal that customers are willing to pay a little more for energy from renewable resources such as geothermal energy.

Investment in the use of domestic, indigenous, renewable energy resources like geothermal energy provides jobs, expands the regional and national economies, and avoids the export of money to import fuels.

Energy demand is increasing rapidly worldwide. Some energy and environmental experts predict that the growth of electricity production and direct uses of geothermal energy will be revitalized by international commitments to reduce carbon dioxide emissions to avert global climate change and by the opening of markets to competition.

For a wealth of information on geothermal energy, visit the Geothermal Education Office's Web site at

Hard-rock Drill Bit Technology

Hot, hard, abrasive and fractured rock formations routinely are encountered when drilling geothermal wells. Consequently, rock penetration rates generally are very low, and bit life is extremely limited. Both of these problems contribute significantly to the cost of geothermal wells. If penetration rates and bit life could both be doubled from their current typical levels, well costs could be reduced by about 15 percent.

Historically, synthetic-diamond drag bits have been viewed as inadequate for geothermal drilling applications. As a result, roller-cone bits have been used preferentially. However, the inherent cutting efficiency and lack of moving parts of drag bits make them a very promising prospect for future increases in penetration rate and bit life in hard formations. In fact, geothermal drilling tests in the Imperial Valley, Calif., already have demonstrated a high (55 ft./hr.) average rate of penetration (ROP) and extended bit life (about 1,000 ft.) in a mixed drilling interval that included igneous formations. Furthermore, since drag-bit technology is not as mature as roller-bit technology, there is greater potential for making significant improvements in drag-bit performance.

A hard-rock drill bit technology project organized by Sandia National Laboratories is a national-laboratory/industry/university cooperative research and development effort aimed at producing drag cutters and bits capable of more economical drilling in geothermal formations. Sandia's mission is to coordinate this overall effort and to maintain and apply state-of-the-art expertise and capabilities for technical consulting, analysis and laboratory testing. In-house facilities include the Hard-Rock Drilling Facility, the Linear Cutter Test Facility, and the recently completed Harmonic Excitation Fixture, which simulates downhole drillstring vibration conditions.