New Water Rights and Associated Mitigation Plan
(Thurston County, WA) Landau Associates assisted Miller Land and Timber Company (Miller) in procuring new water right permits for two planned subdivisions in the Woodland Creek watershed in north Thurston County. Woodland Creek is closed to future appropriation by rule; however, new water rights were identified as the best water source strategy because the project sites were outside the City of Lacey service area, and development in the north-county area meant municipal water rights were generally not available for transfer.
The strategy for developing a groundwater source was to develop a workable hydrogeologic conceptual model, quantify pumping impacts, and develop a mitigation plan to offset these impacts. Landau Associates ran simulations using a county-wide numerical groundwater flow model developed by USGS to quantify hydraulic continuity with Woodland Creek. The approach and model results were approved by the Washington State Department of Ecology (Ecology) and incorporated into Reports of Examination (ROEs) for both sites.
The ROEs were appealed by a local tribe, which developed a separate numerical groundwater flow model. Landau Associates supported Miller as an expert witness in testimony on the appeal at the Pollution Control Hearings Board (PCHB); Ecology was a co-defendant. The PCHB issued a complex decision (No. 05-137) in November 2006 that reaffirmed Ecology’s authority to issue water right permits with mitigation but remanded the ROEs. The decision also specifically allowed Ecology to issue a preliminary permit to further assess the affect of groundwater withdrawals on the creek. Under a preliminary permit, Landau Associates drilled three deep (300 to 550 ft deep) wells and performed two pumping tests that included monitoring a local exempt well.
To develop an updated hydrogeologic conceptual model, Landau Associates conducted a review of well logs throughout the basin, including a number of wells recently drilled by the City of Lacey. The result was significantly different from the original USGS interpretation. A separate task included evaluating a Woodland Creek tributary to establish baseflow data. This conceptual model included the presence of a Pre-Vashon age glacial trough, over 500 ft deep in places, largely filled by lacustrine (clay) sediments.
The revised conceptual model and revised numerical model was peer reviewed by independent experts. This additional technical analysis along with an appropriate mitigation plan led Ecology to subsequently reissue the ROEs approving water rights for both parcels.