Snohomish County Public Utility District No. 1

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PUD Explores Geothermal Energy in Cascades

State’s First Test Wells in 30 Years

PUD Explores Geothermal Energy in Cascades

For several years, the PUD has researched geothermal energy in the Cascade Mountain foothills to help assess the viability of this energy source. In late 2010, the utility began drilling temperature gradient boreholes to determine if and where conditions are ideal for geothermal energy development.

“Our region offers significant opportunities for geothermal energy due to geological conditions that support volcanoes, hot springs and other thermal features,” says Craig Collar, PUD Senior Manager of Energy Resource Development. “Geothermal energy provides a consistent, baseload energy supply and it can be sited in Western Washington close to where it’s needed. Geothermal plants have a small overall footprint, produce minimal emissions and create limited environmental impact and safety issues.”

The boreholes, completed in fall 2010, measured six inches in diameter and reached a depth of 700 feet. Tubing was installed in each hole and filled with water. Over the course of several months, researchers monitored temperatures at different depths to assess conditions. Positive temperature measurements have merited additional research at deeper levels.

In fall 2011, the PUD began to drill to a depth of about 5,000 feet in search of underground regions with temperatures of at least 250°F with wet, permeable rock. The information gathered was valuable for researchers and provided additional experience in geothermal development. However, the temperatures and permeability conditions at this site do not warrant additional exploration.

The PUD will be broadening its assessment of geothermal potential beyond Snohomish County. Numerous sites in and around the Cascade Mountains and in Oregon could be considered for additional research.

The PUD is supplementing its research with existing data, including fracture and fault maps, seismic data and geochemistry information analyzed from existing wells and springs. Data from current testing also will help state geologists gain a better understanding of conditions in the Cascade foothills.


Adam Lewis
(M-F, 8am to 5pm)