Energy Technologies: How They Work and Their Induced Seismicity Potential - Induced Seismicity Potential in Energy Technologies - page 40

FIGURE 3.2 Ridgeline Unit 7 and 8 Power Plant (rated at 69 MW) in the left foreground at The Geysers
in California. The turbine building, housing the two turbine-generator sets, the operator's control room, and
various plant auxiliaries are on the left. The evaporative cooling tower with steam emanating from the top
is on the right of the main complex. The beige pipelines along the roads (with square expansion loops) are
the steam pipelines that gather the steam from the production pads and bring it to the plant. A high-voltage
transmission line (denoted by lattice towers) is in the middle foreground of the picture. SOURCE: Calpine.
the production of steam had started to decline; this decline was marked by a significant
decrease in reservoir pressure from an original pressure of about 500 pounds per square inch
(psi) 2 to levels as low as 175 psi (Barker et al., 1992). For years the annual injection volumes
returned to the geothermal reservoir were less than a third of the amount of steam being
produced, so the reservoir was drying up. New sources of water were established by con-
structing two pipelines that currently deliver about 25 million gallons of treated wastewater
a day for injection, increasing the current annual mass replacement to 86 percent compared
to 26 percent back in 1988 (CDOGGR, 2011).
Early reports of induced seismicity at The Geysers, begun by USGS researchers
(Hamilton and Muffler, 1972), described microseismicity that was observed close to where
2 A car tire for a standard, midsized automobile is usually inflated to a pressure of about 30-35 psi for comparison.