Four Cross Ranch Hydrogeological Study

(Grant County, WA)  Landau Associates is assisting Four Cross Ranch to obtain Article 28 and Phase I Water Service contracts with the Quincy-Columbia Basin Irrigation District (QCBID) to develop over 1,500 acres of center pivots in the High Hills area of Irrigation Block 91 in the north portion of the Quincy Basin. Water Service contract issuance is contingent on drainage approval from the Bureau of Reclamation. The High Hills is a 14-square mile area between lower Grand Coulee and Dry Coulee and directly above Soap Lake. The lake is unique in that it has no surface water inlet or outlet and no groundwater outlet (all inflow is from groundwater; all discharge is from evaporation). Initial development of the Columbia Basin Project in the late 1940s and early 1950s led to flooding of Soap Lake and a decrease in salinity. The Bureau had deferred irrigation of the High Hills because of the unknown impact of irrigation return flows from spray irrigation on recharge to Soap Lake. Stratigraphy beneath the High Hills includes the Priest Rapids, Roza, and Frenchman Springs members of the Wanapum Basalt Formation and various N2 flow members of the Grande Ronde Basalt Formation.

Landau Associates was hired to provide the technical basis for drainage approval. This included developing a hydrogeologic conceptual model of the region, estimating irrigation return flows, and developing a monitoring and mitigation plan. Project scope included review of all existing information in the Bureau’s Ephrata, Washington field office library, field mapping of geologic outcrops, identifying and characterizing existing irrigation wells in the coulees and the High Hills, as well as video scans, rehabilitation, and pumping tests of select wells. Landau Associates made technical presentations to the QCBID and the Bureau and received approval for development of the east half of Block 91 and later portions of the west half of Block 91. We are currently implementing a 5-year groundwater monitoring plan that includes continuous water level measurements in 4 monitoring wells in the High Hills area, springflow measurements from a spring partway up the Grand Coulee wall, and water level and pumping data from 32 monitoring wells and 7 production wells associated with the Soap Lake Protective Works operated by QCBID. Monitoring plan results will be used to implement mitigation pumping as necessary to ensure the project has a zero effect on Soap Lake water levels.