REACTIVE AND INERT GASES IN GROUNDWATER CONTAMINATION AND REMEDIATION STUDIES

Transcription

1 REACTIVE AND INERT GASES IN GROUNDWATER CONTAMINATION AND REMEDIATION STUDIES K. Ulrich Mayer Dept. Earth, Ocean and Atmospheric Sciences University of British Columbia

2 Acnowledements Randi Williams, M.A.Sc., UBC, 2005, now at BGC Enineerin Ltd.) Richard Amos (Ph.D, UBC, 2006, now at Carleton Univ) Seri Molins (Ph.D., UBC, 2007, now at LBNL) Katie Jones (M.Sc., UBC, 2009, now at BGC Enineerin Ltd.) Natasha Sihota (Ph.D. UBC, 2014, now at Chevron Enery Technoloy Company ) Andrea Chon (M.Sc., UBC, in proress) Barbara Beins, USGS, Menlo Par, CA Jared Trost, USGS, Minneapolis, MN

3 Dissolved ases and soil as and the field of contaminant hydroeoloy

4 Components of tal Gas exsolution and ebullition in the saturated zone Monitored natural attenuation of hydrocarbons GW remediation with permeable reactive barriers Gas transfer durin GW remediation Reactive and non-reactive ases as tracers in the vadose zone Monitored natural attenuation of hydrocarbons Surficial as efflux measurements for source zone delineation and quantification of contaminant deradation rates

5 Reactive and non-reactive ases Saturated zone processes Modified from USGS Fact Sheet

6 Microbially mediated as eneration Gas exsolution and ebullition

7 CH 4 (m L -1 ) CH 4 (m L -1 ) B: 2002 Saturated 25 Zone: Evidence for R 2 = Gas Exsolution 5 R 2 = A: Downradient Wells Source Zone Wells Bacround Wells Ar Depletion 15 R 2 = R 2 = N 2 Depletion From Amos et al, WRR, 2005

8 Henry s Law constants and as exsolution Gas Henry s law constant [mol L -1 atm -1 ] reported as lo K H,cp O CH CO N He Ne Ar Kr -2.44

9 From Jones et al, GCA, 2014 Noble ases as as exsolution tracers Noble as ratios and concentrations can be related to as eneration (reaction proress) Stronest response for Ne/Kr ratio

10 Noble as sinature for ebullition From Jones et al, GCA, 2014 Reversal of pne/pxe and pkr/xe ratios PHREEQC modelin of as exsolution due to CH 4 and CO 2 eneration by methanoenesis For hih as production volumes noble as ratios may be useful to prove ebullition in the field

11 Gas exsolution in permeable reactive barriers Treatment of Fe and SO4 in mine drainae by oranic carbon mixture Generation of CO 2 and CH 4 N 2 and Ar indicate occurrence of as exsolution From Williams et al, Appl. Geochem., 2007

12 Current project: Enhanced ebullition due to roundwater remediation? Focus on chlorinated solvents Consider various treatments includin permananate and enhanced bioremediation

13 Reactive and non-reactive ases Vadose zone processes Modified from USGS Fact Sheet

14 Contaminant deradation in the vadose zone

15 Vadose Zone O 2, CH 4, CO 2, and N 2 From Jones et al, GCA, 2014

16 Vadose Zone Interpretation 2 O CH CO 2 H O CH O CO CH 2 ( aq ) 2 ( ) 4 ( ) Methanoenic Zone Increases as pressure Induces an upward advective as flow Deplete non-reactive ases Methanotrophic Zone Decrease in as pressure Induces an inward advective as flow Enrichment nonreactive ases Can we use depletion and enrichment of nonreactive ases to constrain the dynamics between reactions and fluxes?

17 Mass Balance Equation c ext ext a s a a a a a a a a a a N Q Q Q Q T S T S T T T S t T S t 1, 0,,,, D D q q Momentum Balance Equation T Reactive Transport Modelin of Vadose Zone Processes z p r q N i i p p 1 i i RTc p Molins and Mayer, Water Resour. Res., 2007 Molins et al., JCH, 2010

18 Bemidji Vadose Zone Simulation = 0.38 K h =10-11 m 2 K v = m 2 lens: = 0.30 K h =10-13 m 2 K v = m 2 Molins et al., JCH, 2010

19 Simulated O 2, CH 4, and N 2 Concentrations Good qualitative areement was obtained with the field observations Model also allows to visualize fluxes and rates

20 Noble ases in the vadose zone at the Bemidji site Jones et al., GCA, 2014 CH 4 production: preferential depletion of heavy noble ases CH 4 oxidation: preferential enrichment of heavy noble ases

21 MIN3P-Dusty simulation of as eneration and fate Use of noble ases as tracers for advection/pressure radients Heavy noble ases are the most sensitive tracers in the vadose zone Jones et al., GCA, 2014

22 Implications for Natural Attenuation Research Simulations and field observations suest that CH 4 eneration is focused on smear zone More than 95% of carbon will leave via CO 2 as efflux?? CH 4? Gas miration in soil is very sensitive to soil moisture and soil structure Uncertainties for C-balance remain? CO 2?? Need to measure rates (or fluxes)

23 Model results indicate that most CO 2 reports to the round surface C flux/rate [moles d -1 m -1 ] Bioderadation Calcite dissolution Total source Rechare to saturated zone Chane in storae Gas efflux to atmosphere Total sin C flux/rate (%) From Molins et al., 2010 and Sihota et al., 2011

24 How can we measure contaminant deradation rates? Measure CO 2 efflux above, upradient, and downradient of source zone Real-time infrared as analysis Need to distinuish between bacround soil respiration and contaminant deradation 24

25 Elevation (masl) Measured flux (umolco 2 /m 2 /sec) CO 2 Efflux Measurements Contaminant respiration and soil respiration A) Well locations associated with surficial carbon dioxide flux B) Carbon dioxide in the vadose zone Water table Groundwater flow % 5% 1% 50 Distance from the center of the oil body (m) Use bacround correction Flux attributable to SZNA is 2.6 μmol m -2 s -1 Corresponds to depth-interated rate of bioderadation Method effective for source zone and rate delineation and Sihota et al., ES&T,

26 How do we now that enhanced CO 2 efflux is due to contaminant deradation? 14 C in CO 2 provides direct measurement of TPH-derived CO 2 Half-life of 14 C is 5,730 years TPH will have 14 C sinature of 0 percent modern carbon (pmc) Analyze 14 C contents of CO 2 in soil as Calculate rates based on 14 C contents Compare results to rate measured usin CO 2 efflux method 26

27 Radiocarbon and stable carbon isotopes Radiocarbon allows to distinuish between soil respiration and contaminant deradation Model hihly constrained Sihota and Mayer, VZJ, 2012

28 Conclusions and Outloo Reactive ases provide important information on contaminant fate in the vadose and GW zones Inert ases can serve as powerful indicators for transport and reaction processes, but are often underutilized in GW contamination studies Gas efflux measurements show promise for delineatin contaminant deradation rates

29 Than You Questions? Amos, R. T., K. U. Mayer, B. A. Beins, G. N. Delin, and R. L. Williams Use of dissolved and vapor phase ases to investiate methanoenic deradation of petroleum hydrocarbon contamination in the subsurface, Water Resour. Res., 41, W02001, doi: /2004wr Williams, R. L., K. U. Mayer, R. T. Amos, D.W. Blowes, C. J. Ptace, and J. Bain, Usin dissolved as analysis to investiate the performance of an oranic carbon permeable reactive barrier for the treatment of mine drainae, Appl. Geochem., 22: Amos, R. T., and K. U. Mayer, Investiatin the role of as bubble formation and entrapment in contaminated aquifers: Reactive transport modelin, J. Contam. Hydrol., 87: Molins, S., K. U. Mayer, R. T. Amos, and B. A. Beins, Vadose zone attenuation of oranic compounds at a crude oil spill site - Interactions between bioeochemical reactions and multicomponent as transport, J. Contam. Hydrol, 112:15-29 Sihota, N.J., O. Sinurindy, and K. U. Mayer, CO 2 efflux measurements for evaluatin source zone natural attenuation rates in a petroleum hydrocarbon contaminated aquifer, Environ. Sci. Technol., 45: Sihota, N.J., and K.U. Mayer, Characterizin vadose zone hydrocarbon bioderadation usin CO 2 -effluxes, isotopes, and reactive transport modelin, Vadose Zone J., 11, doi: /vzj Jones, K.L., M.B.J. Lindsay, R. Kipfer, and K.U. Mayer, Atmospheric noble ases as tracers of bioenic as dynamics in a shallow unconfined aquifer, Geochimica Cosmochimica Acta, 128: