A critical review of state-of-the-art and emerging approaches to identify fracking-derived gases and associated contaminants in aquifers by McIntosh, J, Hendry, M, Ballentine, C, Haszeldine, R, Mayer, B, Etiope, G, Elsner, M, Darrah, T, Prinzhofer, A, Osborn, S, Stalker, L, Kuloyo, O, Lu, Z, Martini, A, Lollar, B