WA Dept. of Corrections McNeil Island Water System Replacement

McNeil Island, a 6.63-square-mile island located in southern Puget Sound, Washington,  is the former site of former federal and a state correctional facilities. Due to the aging and structurally compromised surface water system, the Washington State Department of Corrections sought to develop a new groundwater-based water supply system. Terraphase was part of the competitively selected project team tasked with developing a long-term groundwater solution for the island.

Scope of Services

Terraphase began with a review of available well data in the Washington State Department of Ecology (Ecology) database, finding limited groundwater potential from existing modern wells. Through extensive research, including review of unpublished U.S. Geological Survey (USGS) reports and regional sediment studies, our hydrogeologist identified the locally known “E Aquifer” at depths of approximately 700 feet below ground surface. While this aquifer had been reached by wells drilled in the 1920s, it had never been successfully developed due to construction issues, resulting in shallow well completions and seawater intrusion.

Terraphase facilitated site approvals with local and state health departments and provided water rights support with Ecology. Our hydrogeologist obtained security clearance and provided on-site oversight for drilling, construction, and testing of the well. A 741-foot-deep well was drilled using air- and fluid-rotary methods, and the final design included a stainless-steel, filter-packed well screen exposed to the formation from 700 to 735 feet below ground surface in a sand and gravel aquifer. Although water quality was generally good, treatment for iron and manganese was recommended–common for deep aquifers in the region.

Notable Accomplishments 

• Supported the Department of Corrections in transitioning from surface to groundwater supply
• Facilitated site approvals and water rights coordination with local and state agencies
• Oversaw drilling and testing of a 741-foot-deep well in a remote, secure island environment
• Successfully developed a new groundwater source under challenging logistical conditions

Port of Grays Harbor Wellhead Protection Program/Hazard Ranking

The Port of Grays Harbor in Washington state proposed using water from Ranney Collector Well No. 1 on the Chehalis River to supply potable water to the Satsop Business Park. Ranney Collector Well No. 1 was originally installed for the Washington Public Power Supply System’s Nuclear Project No. 3. Ranney wells are specifically designed to induce infiltration from a surface water source through permeable sediments, taking advantage of the vertical head drive and filtration this provides. Given this dual-source dynamic, the Washington State Department of Health (DOH) required a “hybrid approach” to protect both groundwater and surface water pathways from potential sources of contamination. DOH specifically recommended Terraphase for this work based on our prior successful hydrogeologic mapping work for the nearby City of Elma.

Scope of Services

Terraphase was selected to carry out the groundwater component of the Wellhead Protection Plan, including the wellhead protection area (WHPA) delineation and hazard inventory. After obtaining historical construction documentation for the Ranney well, our team reviewed well logs from 164 regional wells, selecting 91 to define the local potentiometric surface. Water levels were converted to elevations using Light Detection and Ranging (LiDAR) data, which also provided accurate surface elevations for the Chehalis and Satsop Rivers. An analytical model was developed to simulate drawdown from the Ranney well and create a pumped-surface map. Virtual particles released in the model were tracked to identify upgradient groundwater flowpaths for a 6-month time-of-travel; these flowpaths were extended upgradient, and hydrogeologic mapping was used to identify the1-, 5-, and 10-year time-of-travel zones. These zones were used to delineate the WHPAs.

To assess contamination risks, Terraphase mapped potential hazard sites within the WHPAs based on third-party environmental database research. Following field verification, these sites were ranked using a custom methodology developed through previous work with DOH. This ranking also considered land use patterns, transportation corridors, and waste disposal practices to ensure a comprehensive evaluation of contamination risks.

Notable Accomplishments

• Used LiDAR data to enhance groundwater elevation accuracy for potentiometric mapping
• Completed groundwater source protection for Ranney Collector Well No. 1
• Identified and ranked contamination risks within WHPAs
• Delivered a complete Wellhead Protection Plan
• Provided templates for agency and stakeholder notifications

Chelan Falls Wellfield Expansion Management Plan and Well Maintenance

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