Water Resources Research Act Program

Details for Project ID 2006ID60B

A geochemical investigation of groundwater sources in the Blackfoot River and Snake River floodplain

Institute: Idaho
Year Established: 2006 Start Date: 2006-03-01 End Date: 2007-05-15
Total Federal Funds: $29,878 Total Non-Federal Funds: $69,430

Principal Investigators: J. Mcnamara, J. Mcnamara

Project Summary: The Eastern Snake River Plain (ESRP) Aquifer is a Sole Source Aquifer (EPA, 1990) and vital to over 400,000 people as a source of irrigation and drinking water. The Snake River is equally vital for irrigators who pump from its aquifers for crops and stock water. Recent drought has caused concern for upper Snake River tributaries which are dependent on recharge from the aquifer. Land managers note that water being pumped from the ESRP for agricultural and domestic use may impact flow of the Blackfoot River at Blackfoot, Idaho. Knowledge of the hydraulic connection of groundwater to the river channel is critical to floodplain management of the Blackfoot River. While considerable work has been done to evaluate how agricultural practices impact flows in the Snake River, little is know how these practices impact tributaries. The Blackfoot River is particularly sensitive because it runs parallel and close to the Snake River for approximately 30 miles, and intensive agriculture exists in the floodplain between the two rivers. Further, the boundary for the heavily used ESRP groundwater model used by numerous agencies does not include the upper Blackfoot River watershed. Consequently, the impacts of agricultural practices on flows in the Blackfoot River are not well understood. Flow levels in the Blackfoot River are of interest to numerous agencies and stakeholders. For example, seventeen segments of the Blackfoot River are listed as impaired on the Federal Clean Water Act 303(d) list. Currently, an interagency effort is being organized to evaluate the water resources in the Blackfoot River watershed. This proposal outlines an initiative to bring Boise State University into this working group. A key first order problem from a water management perspective is simply delineating the watershed boundary through the shared floodplain between the Snake and Blackfoot rivers. Are groundwater withdrawals from specific wells coming from the Snake River watershed, the Blackfoot River watershed, or a mixture of both? We propose to evaluate the relative proportions of Blackfoot River water and Snake River water in wells across the Snake/Blackfoot floodplain using geochemical tracer techniques.