Controlled Release Experiments on Methane Fate in the Vadose Zone

Transcription

1 Controlled Release Experiments on Methane Fate in the Vadose Zone Nick de Sieyes, Juan Peng, Radomir Schmidt, Mark Felice, Maya Buelow, Ioana Petcan, Nicole Spadone, Mirann Tsumura, Kate Scow and Doug Mackay University of California, Davis, CA, USA Presented at AEHS Conference, San Diego, MAR 23, 216 This version truncated so suitable for posting on RTI webpage

2 Broad research goals Vadose zone field experiments to investigate and inform modeling of shallow, slow releases of ethanol blended fuels or vapors and/or their in situ degradation products (e.g. methane) Similar to low rate releases from USTs that meet upgrade requirements (former study in CA by others) Migration within soil to/through surface 2

3 Field site at Putah Creek Riparian Reserve Plots X1 and X2 for experiments (PCRR) 1m Coarse Coarse, gas permeable media in top 1.5 m Deep water table, dropping over time GW flow X1 Putah Creek X2 Water Table X1 4/13 ~8 m bgs 6/13 ~12 m bgs 215 X2 Fine Coarse Fine Coarse Fine?????? 3

4 Field experiment 1: Controlled release of methane Methane injection at X1 1 L/d methane expected from anaerobic transformation of all ethanol in an E1 UST release at 1% of average rate in prior CA UST study (15 ml/d) X1 JUL 214 FEB 215 (~7 mo.) 4

5 Field experiment 1: Controlled releases of methane Monitor over time: Soil gas: methane, carbon dioxide, oxygen, nitrogen, tracer (1,1 difluroethane), pressure Surface flux: Soil: methane, carbon dioxide, oxygen moisture content, temperature, methane oxidizing microbes 5

6 Inject gas mixture continuously Initial experimental setup Release line (orange) runs underground to release point at 1 m bgs Soil gas sampling: (blue red green) LICOR collars on surface for surface efflux measurement with LICOR chamber Coarser? Finer m 6

7 At start of methane release: JUL 214 CH 4 injection LIGR Efflux LICOR System Efflux and System cart and cart Neutron Logging Temperature Logging Casing Casing (4 of 5 visible in this slide) Manual drive point sampler North South Drive point cluster Pressure Sensor Pressure Housing Sensor Housing Pressure sensors attached to drive points 7

8 At end of methane release: FEB 215, in continuing drought Solar panel Methane source and pump Battery housing 8

9 X1 Plot Layout (rotated for consistency with later plots of data within blue or dashed blue hexagons) Key Efflux collar Efflux collar + gas sampler cluster Moisture/temperature access tube 3 6 m 9

10 Results: Steady State Methane Efflux PRE RELEASE: 29 APR 214 BACKGROUND Plan view Moist conditions in Spring VWC 14% ( 1 m bgs).8 Y (cm) All Efflux <.4 Efflux (μmol/m 2 /s) X (cm) LOQ > +.6 <.8 1

11 Results: Steady State Methane Efflux RELEASE: 1 L/d CH 4 DRY CONDITIONS: 2 SEP 214 Plan view Dry conditions at end of summer VWC 7% ( 1 m bgs).8 Y (cm).4 Efflux (μmol/m 2 /s) All Efflux > Total efflux % of that injected X (cm) LOQ > +.6 <.8 11

12 Results: X1 Steady State Methane Efflux RELEASE: 1 L/d CH 4 MOISTER CONDITIONS: 15 JAN 215 Plan view Moister conditions in winter VWC 18% ( 1 m bgs).8 Y (cm) Efflux > = < Total efflux 2% of that injected.4 Efflux (μmol/m 2 /s) LOQ > +.6 <.8 X (cm) 12

13 Depth (cm, bgs) Microbial community composition (M. Felice: 1/28/15 coring) gene copies per g dry soil vs depth bgs 16S 16S rrna Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Methylobacter Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E ND 1 Methylosinus Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Methylococcus Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Center of network Conclusions: Methylosinus group dominates under natural conditions (atmospheric methane scavengers?) Methylobacter group dominates in region immediately above experimental release, as expected (adaptable to higher methane 13 concentrations)

14 Depth (cm, bgs) Microbial community composition (M. Felice: 1/28/15 coring) gene copies per g dry soil vs depth bgs 16S 16S rrna Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Methylobacter Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E ND 1 Methylosinus Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Methylococcus Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Center of network Conclusions: Methylosinus group dominates under natural conditions (atmospheric methane scavengers?) Methylobacter group dominates in region immediately above experimental release, as expected (adaptable to higher methane 14 concentrations)

15 Depth (cm, bgs) Microbial community composition (M. Felice: 1/28/15 coring) gene copies per g dry soil vs depth bgs 16S 16S rrna Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Methylobacter Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E ND 1 Methylosinus Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Methylococcus Group pmoa Gene Copies/g Dry Soil 1.E+ 1.E+3 1.E+6 1.E Center of network Conclusions: Methylosinus group dominates under natural conditions (atmospheric methane scavengers?) Methylobacter group dominates in region immediately above experimental release, as expected (adaptable to higher methane 15 concentrations)

16 Summary of Field experiment 1: Controlled releases of methane Symmetrical migration CH 4 oxidation rate and efflux to atmosphere was highly correlated to soil moisture content Efflux greater during drier periods Substantial shifts in CH 4 oxidizing microbial communities near the release Modeling of results in collaboration with Golder Associates Ltd. (next talk in this session) 16

17 Field experiment 2: Controlled release of E1 E1 injection at plot X1 15 ml/d 1% of average in prior study of USTs in CA APR NOV 215 (~7 mo.) 15 ml/d Nov 215 to present (~4 mo. to date) X1 17

18 T Solar panel E1 reservoir and pump Battery housing E1 T P T T P T Moisture T T 18

19 Field experiment 3: Controlled release of E85 E85 injection at plot X2 Soil similar to plot X1 Injection 15 ml/d May Nov 215 (~6 mo.) 15 ml/d Nov 215 to present (~4 mo. to date) X1 X1 X2 19

20 E85 E1 2

21 Overview of results to date Neither TPH nor benzene detected in efflux from either test, but detection limit was high to date Required manual gas sampling of LICOR chamber For gas samples, benzene DL = 1 4 μg/m 3 (1 ug/l) Soil gas remained aerobic O 2 partly consumed near the release depth aerobic biodegradation No methane attributable to e blend degradation was detected in efflux or soil gas 21

22 E1 & E85 controlled release: plans Releases to be stopped when new steady state is confirmed Characterize in 3D vapor and soil Evaluate adaptation and shifts in microbial communities LNAPL body dimensions Amount and distribution of sorbed TPH components or degradation products Monitor subsequent natural attenuation of LNAPL and vapors Initiate modeling of E1 and E85 experiments, if possible Evaluate options for other releases, e.g. deeper, covered, etc. 22

23 Acknowledgements Field and lab assistants at UC Davis Collaboration Chevron Energy Technology Company Emma Hong Luo, Natasha Sihota, Ravi Kolhatkar, and Tim Buscheck Golder Associates Parisa Jourabchi and Ian Hers Funding Chevron American Petroleum Institute Approvals and oversight UC Davis Environmental Health & Safety UC Davis Putah Creek Riparian Reserve California Regional Water Quality Control Board Central Valley Flood Protection Board Solano County Department of Resource Management 23