The effective source area of 90Sr for a stream near Chernobyl, Ukraine

Title: The effective source area of ⁹⁰Sr for a stream near Chernobyl, Ukraine

Author: Rina Freed, Leslie Smith, Dmitri Bugai

Reference: Journal of Contaminant Hydrology, Volume 71, Issues 1–4, July 2004, Pages 1-26

DOI: http://dx.doi.org/10.1016/j.jconhyd.2003.07.002

Keywords: Chernobyl; Hydrologic contaminant transport; Non-point source; Soil contamination; Strontium-90

Abstract: Remediation of streams impacted by non-point source contaminants requires an understanding of both the areas within a watershed that are contributing contamination to streams and the pathways of contaminant migration to streams. From 1998 to 2002, we studied the migration of ⁹⁰Sr in the Borschi watershed, a small (8.5 km²) catchment three km south of the Chernobyl Nuclear Power Plant, Ukraine. Fuel particles, distributed in a heterogeneous pattern across the watershed, are weathering and releasing ⁹⁰Sr from the fuel matrix. Depletion of ⁹⁰Sr, evaluated in comparison to the immobile fission product europium-154, is occurring in the channel and wetland sediment. Channel sediments are uniformly depleted in ⁹⁰Sr with depth. In wetland sediments, there is a zone of depletion in the top10 cm and a zone of accumulation at depths from 10 to 25 cm. Estimates of ⁹⁰Sr depletion are used to map the effective source area that has contributed ⁹⁰Sr loading to the main channel. The effective source area includes channel bottom sediments, a wetland in the central region of the watershed, and periodically flooded soils surrounding the wetland. The total depletion from the effective source area is estimated to be 36±7×10¹⁰ Bq. Based on observations of stream flow rate and water quality in 1999–2001, the annual ⁹⁰Sr removal rate from the watershed is estimated to be 1.4±0.2×10¹⁰ or 1.5% of the inventory per year. When extrapolated over a 15-year period following the Chernobyl accident, the last value is in reasonable agreement with the estimated depletion of the source area based on ⁹⁰Sr/¹⁵⁴Eu ratios. The ⁹⁰Sr yearly leaching rate considering the whole watershed is 0.2% while the ⁹⁰Sr leaching rate considering the effective source area is an order of magnitude higher. Most of the ⁹⁰Sr release in the watershed has originated from an effective source area of 0.62 km², or 7% of the watershed area.

URL: http://www.sciencedirect.com/science/article/pii/S0169772203002225

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