CCR Alternative Source Evaluation Process for Aquifers at an Electric Power Facility Using δD, δ~(18)O, δ~(11)B, δ~(34)S, ~(87)Sr/~(86)Sr and Chemical Composition

摘要

In response to the federal Coal Combustion Residual (CCR) rule, power utilities are evaluating intra-well differences in concentrations of groundwater constituents specified in Appendix III of the rule. Changes in constituent concentrations may be due to sources beyond site facilities, and the rule allows the demonstration of alternative sources other than the CCR facility for these concentration changes. Chemical concentration and distribution of groundwater constituents alone may not be sufficient to identify a source, primarily because the monitored constituents are commonly present in groundwater. Distinguishing the constituents by source becomes critically important if the origin is off-site, and the isotopic values of indicator elements can provide this independent information. Stable isotope analyses for δ~(11)B and δ~(34)S directly relate to monitored constituents; δD and δ~(18)O of water becomes useful if landfill materials experience evaporation, or multiple aquifer assessment is needed; and ~(87)Sr/~(86)Sr provides additional information as a co-migrating constituent. At the Sutton Energy Complex, New Hanover County, North Carolina, evaluation of δ~(11)B, ~(87)Sr/~(86)Sr, and δ~(34)S in the surficial aquifer and underlying Pee Dee Aquifer confirmed the Pee Dee values were consistent with marine water influence and are unrelated to CCR waste sources; furthermore the δD and δ~(18)O range was narrowly confined compared to the surficial aquifer, also indicating hydraulic separation of the two aquifers. The isotopic results provide independent data supporting separation of the Pee Dee Aquifer from the surficial aquifer and the CCR source leachate. This evaluation identifies a marine water influence as an alternative source for elevated Appendix III constituents, specifically B and SO4.