Ma L., Castro M.C, Hall C.M, Walter L.M.  2005.  Cross-formational flow and salinity sources inferred from a combined study of helium concentrations, isotopic ratios, and major elements in the Marshall aquifer, southern Michigan. Geochemistry Geophysics Geosystems. 6(10)

Ma L., Castro M.C, Hall C.M, Walter L.M.  2005.  Unusually high helium fluxes in the shallow Marshall aquifer in southern Michigan: implications for cross-formational flow and salinity sources. Eos Trans. AGU Fall Meeting Supplement. 86(52)