Determining flow, recharge, and vadose zonedrainage in anunconfined aquifer from groundwater strontium isotope measurements, PascoBasin, WA
Strontium isotope compositions (87Sr/86Sr) measured in groundwater samples from 273 wells in the Pasco Basin unconfined aquifer below the Hanford Site show large and systematic variations that provide constraints on groundwater recharge, weathering rates of the aquifer host rocks, communication between unconfined and deeper confined aquifers, and vadose zone-groundwater interaction. The impact of millions of cubic meters of wastewater discharged to the vadose zone (103-105 times higher than ambient drainage) shows up strikingly on maps of groundwater 87Sr/86Sr. Extensive access through the many groundwater monitoring wells at the site allows for an unprecedented opportunity to evaluate the strontium geochemistry of a major aquifer, hosted primarily in unconsolidated sediments, and relate it to both long term properties and recent disturbances. Groundwater 87Sr/86Sr increases systematically from 0.707 to 0.712 from west to east across the Hanford Site, in the general direction of groundwater flow, as a result of addition of Sr from the weathering of aquifer sediments and from diffuse drainage through the vadose zone. The lower 87Sr/86Sr groundwater reflects recharge waters that have acquired Sr from Columbia River Basalts. Based on a steady-state model of Sr reactive transport and drainage, there is an average natural drainage flux of 0-1.4 mm/yr near the western margin of the Hanford Site, and ambient drainage may be up to 30 mm/yr in the center of the site assuming an average bulk rock weathering rate of 10-7.5 g/g/yr.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE. Assistant Secretary for Environmental Management.Office of Science and Technology. Environmental Management ScienceProgram, Director. Office of Science. Office of Basic Energy Sciences.Chemical Sciences Geosciences and Biosciences Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 891195
- Report Number(s):
- LBNL-55679; WRERAQ; R&D Project: G42301; BnR: KP1301020; TRN: US0605315
- Journal Information:
- Water Resources Research, Vol. 321, Issue 1-4; Related Information: Journal Publication Date: 04/30/2006; ISSN 0043-1397
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
AQUIFERS
COLUMBIA RIVER
COMMUNICATIONS
DISTURBANCES
DRAINAGE
GEOCHEMISTRY
GROUNDWATER RECHARGE
MONITORING
PASCO BASIN
SEDIMENTS
STRONTIUM
STRONTIUM ISOTOPES
TRANSPORT
WEATHERING
Reactive transport isotope model weathering drainageunsaturated zone