Sustainable power generation at The Geysers is possible today because of two large-scale wastewater injection projects from Lake County and the City of Santa Rosa. Together, these projects provide approximately 20 million gallons of reclaimed water per day for injection into The Geysers reservoir. The vast amount of heat in reservoir rocks efficiently converts the water into steam and supplements the production of original reservoir steam to Geysers power plants.

Throughout the 1970s and 1980s, vastly more steam was produced from The Geysers reservoir than was replaced by the injection of power plant steam condensate. By 1989, accelerated development had caused severe steam pressure decreases in the reservoir, resulting in lower steam production rates. This decline threatened the future sustainability of Geysers power generation.

To sustain reservoir pressure and steam production, The Geysers needed a large, reliable supply of water that could be used to augment injection. In 1990 a collaborative effort between Geysers operators, Lake County and the California Energy Commission identified Lake County wastewater from the southeast regional collection system as the preferred source of water.

This project, known as the Southeast Geysers Effluent Pipeline (SEGEP), was supported by the Geysers operators (Calpine, Northern California Power Agency and Unocal) and a host of federal, state and county agencies. SEGEP construction began in 1995, and delivery of wastewater to The Geysers commenced in October 1997. The original 29-mile pipeline, now lengthened to 40 miles to include effluent from additional communities in the Clear Lake area, delivers approximately 9 million gallons per day of secondary treated wastewater for injection into The Geysers Reservoir.

The success of SEGEP injection in maintaining reservoir pressure provided momentum for a similar project to bring tertiary treated effluent from the Santa Rosa area to The Geysers. In 2003, the City of Santa Rosa and Calpine Corporation partnered on constructing a 42-mile pipeline that became known at the Santa Rosa Geysers Recharge Project (SRGRP). Since 2003, SRGRP has delivered approximately 11 million gallons per day of tertiary treated wastewater to replenish The Geysers’ geothermal reservoir.