Michael LawsonEPA Hydraulic Fracturing Study TechnicalWorkshop on Chemical and Analytical Methods24 – 25thFebruary 2011 Arlington, VirginiaIsotopic Tracers of GroundwaterContamination: Techniques, applicationsand considerations2Talk structure• Background related to hydraulic fracturing and the relationship togroundwater resources• Why should isotopic tracers be employed for determining the origin,and controls on, groundwater composition?• Use of O, H and Sr isotopes to trace natural water bodies• Introduction of3H-3He and4He techniques to monitor evolution ingroundwater age•13C systematics to constrain the origin of methane in groundwaters• Limitations and recommendations3Background• A requirement exists for the implementation of techniques that verify and insure thatgroundwater is not contaminated as a result of hydraulic fracturing.• Groundwater contamination can derive from numerous sources which may carry adistinct “fingerprint” that allows for identification of the source of contamination or theprocess which gave rise to the contamination. With respect to hydraulic fracturing,direct and indirect pathways could be investigated anytime contamination is alleged:• Direct contamination –unconventional gas or fracturing fluids migrating into groundwater anddegrading water quality. While EPA's 2004 study and others have found no directcontamination from the hydraulic fracturing process itself, the breakdown of operationalsafeguards, e.g. lack of well bore integrity, surface spills, etc. may present pathways.• Indirect contamination – e.g. migrating fluids drive (bio)geochemical processes that result inthe release of contaminants to the groundwater or naturally occurring species present ingroundwater at concentrations that exceed threshold values.• Isotopic techniques can identify the source of contamination and yield information onprocess such as redox or chemical evolution, mixing and migration.• The chemical composition of relevant end members (groundwaters, produced waters,and fracturing fluids) are needed to make best diagnostic use of isotope or othergeochemical techniques.4Why use isotopic tracers?• Major-ion chemistry of natural and injected fluids may not differsufficiently enough for identification of the source(s) of materialspresent in groundwaters.Isotopic tracers allow for:• Identification of naturally occurring surface-water contributions.• Identification of mixing of different groundwater bodies.• Identification of contributions and identification of the source ofnatural gas to shallow groundwaters.• Is this a result of the migration from shales as a direct result of hydraulicfracturing or is this naturally present e.g. through the biologicalproduction of methane in shallow groundwater?5Natural water compositionsNatural water compositions-80-60-40-20020-12 -10 -8 -6 -4 -2 0 2 4δ18OδD G M W L P a l a e o w a t e rEvaporation ofsurface watersSeawatergroundwaterExchangewith H2S LM W L-80-60-40-20020-12 -10 -8 -6 -4 -2 0 2 4δ18OδD

G M W L P a l a e o w a t e rEvaporation ofsurface watersSeawatergroundwaterExchangewith H2S LM W LAfter Geyh (2000)6Elucidating mixing processesElucidating mixing processes-80-60-40-20020-12 -10 -8 -6 -4 -2 0 2 4δ18OδD G M W LPalaeowaterEvaporation ofsurface watersSeawaterGroundwater B m i x i n g m i x i n gGroundwater A-80-60-40-20020-12 -10 -8 -6 -4 -2 0 2 4δ18OδD G M W LPalaeowaterEvaporation ofsurface watersSeawaterGroundwater B m i x i n g m i x i n gGroundwater AAfter Geyh (2000)71101001000100001000001000000-26 -24 -22 -20 -18 -16 -14 -12 -10δ18O ‰ VSMOW Cl

- (mg/l)ModernrechargeShieldBrineGlacialmeltwaterAfter Douglas et al., 2000Groundwater Mixing8Resolving small contributions• Formation waters typically havehigher Sr concentrations comparedto surface waters and shallowgroundwater.• When Sr isotopic compositionsvary between different waterbodies, Sr isotopes (87Sr/86Sr)provide a sensitive indicator of thepresence of low concentrations ofdifferently sourced fluids.PWEnd Member 1End Member 2After Peterman et al., USGS9Tritium-3He•Directly incorporated into waterDirectly incorporated into watermolecule.molecule.•Decays toDecays to3He, t1/2= 12.43 yrs.= 12.43 yrs.•GW < 60 years.GW < 60 years.4He•Radiogenic He produced by U andRadiogenic He produced by U andThdecay from crustal mineralsdecay from crustal mineralsand atmosphere.and atmosphere.•Used to identify older GW (100Used to identify older GW (100’s–100,000100,000’s years).s years).Groundwater ageGroundwater age10Examples of Biogenic vs. ThermogenicGas Interpretation Schemes1.E+011.E+021.E+031.E+041.E+05-100 -90 -80 -70 -60 -50 -40δ13C methane(‰)

C 1 (C 2 + C 3 )Mixed-30BacterialThermogenic-20-80.0 Methane δ 13 C (‰)-70.0-60.0-50.0-40.0-30.0-20.0-400 -350 -300 -250 -200 -150 -100ThermogenicTransitionBiogenic(CO2Reduction)Biogenic(Fermentation) 

# M a t

u

r a ti

o

nMethaneδD (‰)After Bernard, 1978After Rice, 199311Technical Summary• There is a need to establish natural baseline conditions to assessdeviations from the natural system.• Major-ion chemistry alone may not yield definitive results as to thesource(s) of any identified deviations.• The application of multiple isotopesystems allows for a more robustand comprehensive assessment of potential sources ofcontamination and allows for quantitative estimates of thecontribution of these sources to be made.• Sampling of potential end member fluids (surface waters,groundwaters and introduced fluids used during the fracturingprocess) may provide important compositional information that couldprove useful when attempting to identify the existence and/or sourceof any perceived contamination.