Field-scale observations of a transient geobattery resulting from natural attenuation of a crude oil spill - Heenan, Jeffrey; Ntarlagiannis, Dimitris; Slater, Lee; Beaver, Carol; Rossbach, S.; Revil, A.; Atekwana, E.A.; Bekins, Barbara (Journal of Geophysical Research G: Biogeosciences, 2017)