Skagit County, Wash.

Lower Baker Dam Seepage Reduction

Client: Puget Sound Energy
Our Role: Geotechnical Design

A wide view of Lower Baker Dam spilling water into a steep, rocky canyon surrounded by dense forest.

Faced with water seepage through the foundation of its century-old Lower Baker Dam, Puget Sound Energy launched a proactive effort to safeguard one of Washington’s historic hydropower assets.

Recent investigations revealed that seepage had increased over time, with a geologic interpretation of multiple discrete seepage pathways within the fractured carbonate rock formation beneath the dam. Several potential failure modes were identified with an initiation of the removal of joint infill material and erosion of rock fragments, raising concerns about the long-term stability of the rock foundation.

The solution required modern grouting methods tailored to complex geologic and hydraulic conditions, while navigating the operational challenges of steep canyon terrain.

As a subcontractor, GFT provided specialized geotechnical services to support the technical complexity and community-critical outcomes of the seepage reduction project. We were directly involved with managing day and night drilling and grouting operations across 250 boreholes, providing technical guidance and oversight for a multi-line grout curtain installation designed to treat seepage paths and reduce downstream discharge. The carbonate rock formation’s fractured nature required adaptive, layered techniques using high- and medium-mobility cementitious grouts and specialized bituminous melt injections.

IntelliSystem, a real-time monitoring and data collection tool owned by Advanced Construction Techniques, was routinely used by our team to analyze subsurface responses during water pressure testing and grouting operations. This enabled dynamic adjustments to grouting pressures, sequencing of operations, and material selection, thereby improving results and reducing waste. IntelliSystem integrated pressure testing results, geologic data collected from past and current investigations, borehole deviation data, and real-time instrumentation responses to create a detailed subsurface model that guided engineering decisions and identified areas of potential incomplete treatment.

The steep canyon terrain added complexity, requiring thoughtful work platform design by the contractor and careful safety coordination to enable drilling and grouting operations. These physical constraints further emphasized the need for precision planning, agile engineering, and continuous data-driven collaboration with the owner and engineer of record.

View looking down the Lower Baker Dam spillway into a steep rocky canyon with clear pools of water, exposed rock formations, and dense evergreen forest lining both sides.

View from the top of the Lower Baker Dam spillway overlooking a narrow river canyon, with water flowing along the spillway into the rocky channel below and forested slopes on either side.

Key Features

Provided technical oversight and guidance of real-time grouting operations across 250 boreholes using IntelliSystem for adaptive decision-making.
Provided grout program leads, lead geologists, quality control engineers, and offsite technical support.
Applied specialized grouting in complex geology, including cementitious and bituminous injections targeting the fractured carbonate rock formation.
Delivered geotechnical oversight, core logging, and daily planning to navigate challenging canyon terrain safely and efficiently.
Managed the collection and interpretation of published and historic subsurface information, rock core samples, and high-resolution borehole televiewer information.

Outcomes

Reduced seepage under and around the dam, supporting long-term infrastructure reliability.
Enhanced the safety and resilience of PSE’s largest hydroelectric asset, providing benefits to PSE’s customers.
Enabled responsive, data-informed engineering in steep terrain with dynamic groundwater conditions, ensuring project goals were met.