Determining flow, recharge, and vadose zone drainage in an unconfined aquifer from groundwater strontium isotope measurements, Pasco Basin, WA

摘要: Author(s): Singleton, Michael J.; Maher, Katharine; DePaolo, Donald Conrad, Mark E.; Dresel, P. Evan | Abstract: Strontium isotope compositions (87Sr/86Sr) measured in groundwater samples from 273 wells the Pasco Basin unconfined aquifer below Hanford Site show large and systematic variations that provide constraints on recharge, weathering rates of host rocks, communication between deeper confined aquifers, vadose zone-groundwater interaction. The impact millions cubic meters wastewater discharged to zone (103-105 times higher than ambient drainage) shows up strikingly maps 87Sr/86Sr. Extensive access through many monitoring at site allows for an unprecedented opportunity evaluate strontium geochemistry a major aquifer, hosted primarily unconsolidated sediments, relate it both long term properties recent disturbances. Groundwater 87Sr/86Sr increases systematically 0.707 0.712 west east across Site, general direction flow, as result addition Sr sediments diffuse drainage zone. lower reflects recharge waters have acquired Columbia River Basalts. Based steady-state model reactive transport drainage, there is average natural flux 0-1.4 mm/yr near western margin may be 30 center assuming bulk rock rate 10-7.5 g/g/yr.