As part of a project team, V&A provided confined space entry assessments to evaluate the condition of concrete and metal features of the Lake Tapps Lower Conveyance System facilities. Information gained from the condition assessment will be used to facilitate the development of rehabilitation methods for the facility.
OBSERVATION & Evaluation
The Lake Tapps Lower Conveyance System was evaluated in six discrete areas: the Lake Intake Structure, Outlet Tunnel, the Bear Trap Overflow, the Forebay Caisson, the Penstocks, Stand Pipes, and the Tailrace Structure. The structures were evaluated in two stages, Early Drawdown and Full Drawdown, determined by the water level in Lake Tapps. The Early Drawdown assessment, which occurred while Lake Tapps was at approximately 533 feet, provided an opportunity to evaluate the upper reaches of the Intake Structure and its appurtenances. The Full Drawdown assessment occurred when Lake Tapps was fully drained at Elevation 490 feet or lower to permit entry into most of the facilities.
V&A retained the services of a specialty contractor, Jamison Engineering, to assist in the confined space entries and to provide emergency rescue services. Condition assessment services provided by V&A included visual evaluation, concrete sounding and penetration tests, concrete pH sample collection, surface penetrating radar on reinforced concrete surfaces to determine depth and spacing of reinforcing steel, and concrete coring. For steel structures, V&A conducted visual evaluation, ultrasonic thickness testing, and broadband electromagnetic testing (BEM).