Full Description

The ratio of boron isotopes 10B and 11B relative to the NBS-951 standard have been applied as intrinsic or already present tracers in groundwater studies. The usefulness and success of boron isotopes as intrinsic tracers led to the assertion of boron isotopes as a valid tool if used as artificial tracers. The validity of boric acid (H3BO3) enriched in the 10B isotope as an artificial groundwater tracer was investigated during a study to determine transport times from a wastewater recharge basin to nearby monitor wells and to estimate the degree of sample dilution. Three and one half kilograms of boric acid enriched in the 10B isotope was added to 166 acre-ft of municipal wastewater at the Rio Hondo Spreading Grounds in Whittier, California. The addition of enriched boric acid fingerprinted municipal wastewater with an average Kronecker delta B of -60 per thousand. The intrinsic Kronecker delta B value of this wastewater was 3 per thousand prior to tracer addition. The boron isotopic signature was successfully monitored in downgradient wells and used to estimate travel times and sample dilution. Arrival of the tracer at nearby monitor wells is associated with a very complex flow system resulting in a large variation in groundwater velocities and mixing due to local heterogeneities. However, boron isotope tracer arrival resulted in a relatively sharp breakthrough supporting the assumption of conservative behavior in groundwater. Shallow monitor well samples 500 feet down gradient contained a significant but diluted amount of tracer beginning approximately seven days after tracer addition due to a rapid transport pathway. Boron dilution calculations indicate a maximum impact of 31% tracer water from Basin 10E in the monitor well samples where the bulk of the sample is comprised of recharge from upgradient basins 7E, 8E, and 9E and groundwater inflow from the Whittier Narrows. Boron tracer was not found in deeper nearby monitor wells. Includes 15 references, tables, figures.

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Edition: Vol. - No. Published: 01/01/2002 Number of Pages: 13File Size: 1 file , 270 KB