Aliquots of collected water samples were prepared for isotopic analysis at the USGS laboratories in Menlo Park, CA by precipitating dissolved sulfate as barium sulfate, using the methods of Carmody and others (1997). Sulfur isotopes were analyzed at the USGS laboratories in Reston, Virginia. For sulfur isotope ratio measurements, dissolved sulfate is converted to BaSO4, which is analyzed by conversion to sulfur dioxide with an elemental analyzer and subsequent analysis with a continuous flow isotope ratio mass spectrometer (Brenna, 1997). Samples are analyzed simultaneously with BaSO4 isotopic reference materials. No correction for oxygen isotopic composition is made to the reported sulfur isotope data. For oxygen isotope ratio measurements, BaSO4 is converted into CO with a Thermo-Finnigan Thermo-Chemical Elemental Analyzer at 1325 deg C. The CO is analyzed for oxygen isotopic composition using a continuous flow isotope ratio mass spectrometer analyzing (Böhlke and others, 2003; Brand and others, 2009). The 2-sigma uncertainty of both sulfur and oxygen isotope ratio determinations is 0.4 per mil, and reported relative to VCDT and VSMOW respectively. References Böhlke, J.K., Mroczkowski, S. J., and Coplen, T. B., 2003, Oxygen isotopes in nitrate: New reference materials for 18O:17O:16O measurements and observations on nitrate-water equilibration: Rapid Communications in Mass Spectrometry, v. 17, p. 1835-1846. Brenna, J. T., Corso, T. N., Tobias, H. J., and Caimi, R. J., 1997, High-precision continuous-flow isotope ratio mass spectrometry: Mass Spectrometry Reviews, v. 16, p. 227-258. Carmody, R. W., Plummer, L. N., Busenberg, E., and Coplen, T. B., 1997. Methods for collection of dissolved sulfate and sulfide and analysis of their sulfur isotopic composition, U.S. Geological Survey Open-File Report 97-234, 91 pp.