Improving groundwater management in the Pasco Basin
In July 2022, we set in motion a new process to design a permanent groundwater management framework for the Pasco Basin. By working with the U.S. Bureau of Reclamation to allocate and manage groundwater in the area, a new groundwater rule will increase the amount of water in the basin that can be lawfully allocated and resolve legal and regulatory questions over how that water can be used.
Work has steadily continued on the development of the rule. Most recently, we held a public comment period for the Pasco Basin Subarea Boundary Designation that concluded on December 10, 2024. The presentation from the formal hearing can be found here.
Many rely on groundwater in the Pasco Basin, including landowners, farmers, groundwater permit holders and those living in the area. A portion of the groundwater that exists in the Pasco Basin area is the result of return flows infiltrating from surface water irrigation as part of the Federal Columbia Basin Project.
For over a half-century, however, the groundwater has been managed by interim rules. By adopting a permanent rule, longstanding uncertainty will be resolved and new groundwater supplies may become available.
Working with the U.S. Bureau of Reclamation
In 2021, the Washington Legislature revised Ecology’s authority to enter into an agreement with the U.S. Bureau of Reclamation. This allows the two agencies to develop a groundwater co-management strategy. That legislative action was necessary, because the Pasco Basin has naturally occurring groundwater that mixes with irrigation water return flows -- referred to as “commingled groundwater.”
Differentiating between these water types is important because all naturally occurring groundwater in Washington is a state resource managed by Ecology. Return flows coming from irrigation water used in the Columbia Basin Project, however, may be managed through agreement and licensed by Reclamation to be provided to irrigators to be used on crops at a per acre fee.
A Memorandum of Understanding (MOU) between Reclamation and Ecology was signed in 2022. The MOU commits Ecology and Reclamation to develop a groundwater co-management strategy. A subsequent Memorandum of Agreement will establish the details of the co-management program and will be developed concurrently with Ecology rulemaking.
Groundwater map for Grant, Adams, Othello, Franklin and Pasco counties
Pasco Basin boundary designation
A critical first step in the development of the co-management program is defining the boundaries of the Pasco Basin, where groundwater will be managed.
The subarea is located within the southern third of Grant County, the western half of Franklin County, and the western third of Adams County. The proposed boundaries are consistent with the current boundary of the Pasco Basin subarea previously established by Chapter 508-14 WAC with subsequent modifications.
The Draft Order defining the boundaries of the Pasco Basin subarea underwent a 30-day review and public comment period in December 2024. A virtual Public Hearing on the Draft Order was also held on December 5, 2024. A subsequent 30-day appeal period will be available following issuance of the Final Order.
We remain committed to providing opportunities for input from Tribes, stakeholders, interested parties and the public. We anticipate the boundary designation will be finalized through an administrative order.
USGS Study and Groundwater Model
To better understand the water balance in the Pasco Basin, the United States Geological Survey (USGS) prepared a numerical groundwater model to estimate the amount and locations of commingled groundwater in the Pasco Basin area. The USGS report and model improved the understanding of the hydrogeology and provided estimates of increased groundwater storage in the Pasco Basin area since the development of the Columbia Basin Project.
Click to enlarge map of key hydrogeologic units
The 2016 USGS model is currently being revised to refine existing conditions and to better support modeling of different water management scenarios in the Pasco Basin. A third-party review of this revised modeling effort will be completed prior to finalizing the model and its results.
The USGS study, along with additional technical work that may be identified as needed, is intended to help inform estimated volumes and location of shallow commingled groundwater in the Pasco Basin that may be available for allocation under the groundwater co-management program.
The rulemaking process
We are currently in the announcement phase. This means we have filed a Pre-Proposal Statement of Inquiry (CR-101) form with the Washington State Code Reviser’s Office that has been published in the Washington State Register. This serves to notify the public about our intent to adopt a new rule or amend or repeal an existing rule.
There are three major phases in a typical rulemaking process:
Announcement Phase
Proposal Phase
Adoption Phase
Establishing a permanent groundwater management program is anticipated to be a multi-year process with on-going outreach and public engagement. As the project progresses additional information on the project and timeline will be provided via this website and other public outreach processes.
