Mayfield and Mossyrock dams were engineered and built with a commitment to strength and safety. Assuring dam safety is one of the highest priorities of Tacoma Power and the Federal Energy Regulatory Commission’s (FERC). The Cowlitz River Project dams continuously demonstrate high performance in meeting FERC's stringent requirements.

Tacoma Power's dam safety program consists of many facets. Special equipment installed in and near the dams monitor for any changes or movement. Each dam is inspected every working day by trained on-site hydroelectric personnel. More detailed mechanical, electrical and facility inspections occur weekly and monthly. During weekends and holidays, security personnel also inspect the dams and embankments daily for any signs of distress or leakage.

Survey crews and site personnel take readings of control points, drainage weirs and other instrumentation devices on schedules that vary from a couple weeks to semi-annually. Plots of these readings are prepared for review by Tacoma Power's dam safety engineers.

FERC conducts annual inspections with Tacoma Power engineers and reviews dam safety records. In addition, independent engineering specialists conduct a thorough examination of the dams every five years. During this review, which takes approximately one year to complete, a thorough examination of all previous structural, hydraulic and geotechnical studies is made to ensure compliance with current standards.