Fresno Dam and Reservoir

The Problem

Fresno Dam required deep excavation into the existing embankment to construct a new vertical sand filter trench, gravel drain, and downstream buttress fill as part of a Bureau of Reclamation dam safety modification. The work area sat well below the existing groundwater table in variable, water-bearing glacial soils — creating a high risk of excavation slope instability, slope failure, and significant construction delays if groundwater was not effectively controlled.

JDC's Solution

The Bureau of Reclamation designed a deep well dewatering system — specifying well layout, depths, screen sizes, and filter pack gradations — and Jensen Drilling Company furnished all materials, drilled, installed, developed, and continuously operated the complete system. This included the full primary deep well network with submersible pumps, temporary observation wells, and all supplementary deep wells and observation wells as directed. The system was required to achieve the target drawdown and sustain a 30-day run time before excavation below the critical elevation could begin.

Customer Benefit

Jensen Drilling Company delivered reliable, uninterrupted groundwater control throughout multiple construction seasons, allowing the general contractor to safely excavate the dam embankment and construct the new filter and drain system on schedule. Continuous 24/7 operations with standby power and winterization ensured there was no construction downtime attributable to dewatering failure — protecting the Government's investment in a critical dam safety project.