The Chelan Falls Wellfield in Washington state, was developed in the 1960s and designed to supply groundwater to the nearby Chelan Falls Hatchery to augment relatively warm spring water from the North Beebe Spring. Originally producing between 500 and 2,000 gallons per minute, the wells gradually experienced efficiency declines. Additionally, the hatchery needed to fully utilize its water rights and sought methods to moderately increase groundwater temperatures to improve fish health.

To support these goals, Terraphase was engaged by Chelan County Public Utility District (Chelan PUD) to evaluate, rehabilitate, and optimize the wellfield system through multiple phases of work, including initial investigations, long-term planning, and ongoing performance improvements.

Scope of Services

In the initial phase, Terraphase evaluated the adjacent property with both microgravity and resistivity surveys, and drilled, designed, and tested wells which identified the presence of a deep, cold-water, confined aquifer beneath the Columbia River. Four of the 10 original wells were rehabilitated, and a comprehensive Wellfield Management Plan (WMP) was developed to guide future wellfield operation and maintenance, including the potential production capacity of the wellfield, which includes likely sources of well inefficiency and the temperature implications of wellfield production; a series of data collection protocols to facilitate wellfield management; operational protocols and a general production scenario to help maximize well efficiency; and contingency plans to address acute and chronic problems. Specific plan recommendations highlighted strategies to maximize groundwater production and minimize the temperature of water produced by the wellfield.

In 2019, Terraphase was re-selected as part of the team to provide a condition assessment of the Chelan Falls Wellfield, make recommendations to improve the wellfield and the surface water intake system, and update the WMP. Following comprehensive wellfield testing which revealed substantial efficiency losses, we supervised the redevelopment of eight wells, achieving efficiency improvements of between 149 and 334 percent. Terraphase worked with Chelan PUD and its engineer to evaluate additional options for maintaining wellfield efficiency, including the use of novel well modifications like a suction flow control device. An updated WMP, reflecting new infrastructure and operational insights, is being completed in 2025.

Notable Accomplishments

• Geophysical surveys and a test drilling program to identify and develop a previously unknown confined aquifer below the Columbia River providing a cool water source for hatchery operations
• Temperature monitoring of wells to evaluate both the vertical temperature profiles within wells and the lag time between production and the arrival of Columbia River water at the wells
• The redevelopment of eight wells resulted in well efficiency improvements between 149 and 334 percent, in some cases with post-development efficiency in at least one well now higher than at construction
• A wellfield management plan for operators to guide the operation of the wells while minimizing water temperature, maximizing well efficiencies, and providing best management practices