New Applications of Current Methods to Assess and Monitor Natural Attenuation

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1 New Applications of Current Methods to Assess and Monitor Natural Attenuation Liz van Warmerdam Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

2 Outline What is Natural Attenuation? When and why is it important? Where did we do this work? How to identify it? And another here? How to monitor it? Uncertainties Conclusions 2 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

3 What is Natural Attenuation Natural Attenuation: Degradation processes occur without human intervention Biodegradation creates shorter chain hydrogen-based compounds (including CO 2 ) and water Dissolution of soluble PHCs into water Dilution of PHCs as they mix with groundwater Volatilization/evaporation of low molecular weight, volatile compounds Sorption of compounds onto soil particles causing immobilization Chemical reactions with minerals in the soil 3 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

4 When and Why is Natural Attenuation Important? Low levels of contamination Remote sites Onsite areas with limited access Sites where costs are a significant factor Sites where time is not a significant factor Where site disturbance is not preferable Where natural attenuation is more effective than remediation efforts 4 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

5 Where we did our Testing PHC contamination on active sites Adjacent to ecologically and culturally significant rivers Permafrost vs Discontinuous Permafrost Fine Soils vs. Coarse Soils Include map of Yukon, highlighting location of sites 5 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

6 Some Basics PHC in Soil Evidence of changes in PHC concentrations are observed in all 3 media: soil, groundwater and soil vapour Traditionally, groundwater monitoring was used to quantify the rate of biodegradation Now soil vapour can be monitored to quantify the rate of biodegradation Identifying Natural Attenuation Aerobic Degradation CO 2 Anaerobic Degradation Methane CO 2 PHC and CO 2 CO 2 is also a bi-product of biological activity in the subsurface Gas exchange takes place between soil and atmosphere O 2 CO 2 Exchange is affected by temperature and pressure 6 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

7 Natural Attenuation 7 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

8 Isotopic Analysis for Identifying Natural Attenuation Isotopic research breakthrough in 1960 s as isotopic identification techniques became more sensitive Isotopic analysis of CO 2 to indicate biodegradation processes has become more prominent since the early 1990 s Not implemented in industry as a method of monitored natural attenuation (MNA) yet 8 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

9 Performing Isotopic Analysis Theory The 13 C/ 12 C isotopic ratios and 14 C concentration in carbon dioxide can be determined geochemically to evaluate the biodegradation occurring at the site Equipment Soil vapour probe Conntective tubing Pre-evacuated bottle Gas chromotograph, iosotope ratio mass spectrometer, and accelerated mass spectrometer for analysis 9 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

10 Geochemical Analyses The concentration of CO 2 increases with depth, consistent with expectation, since biodegradation would produce large quantities of CO 2 which diffuse from the source at depth Heavy carbon depleted at depth, again indicating biodegradation Low radiocarbon fraction with depth, indicating a large portion of the CO 2 comes from an old carbon source (consistent with biodegradation of hydrocarbons) 10 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

11 Measuring CO 2 Soil Flux Theory The rate of change of CO 2 concentration inside a vented flux chamber is equated to flux Equipment Ground surface collar Vented bellows-controlled flux chamber with rubber gasket Application software, analyzer unit (infrared gas analyzer) and pump 11 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

12 Background CO 2 Contribution Grass Location Grass Location Background ranged from 0.6 to 5.3 µmol/m 2 /s (average 1.3 µmol/m 2 /s) CO 2 Concentrations Grass > Gravel Gravel Location Gravel Location Background ranged from 0.8 to 5.8 µmol/m 2 /s (average 3.2 µmol/m 2 /s) 12 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

13 Monitoring CO 2 in soil July Klondike details Sampled CO 2 concentrations three seasons in 2014 Summer (July), Fall (October), Winter (December) Groundwater parameters for typical MNA analyses October Nitrate/nitrite, sulphate/sulphite, alkalinity, ferrous iron, dissolved methane, dissolved oxygen and dissolved carbon dioxide Weather affects measurements Weather affects LICOR monitoring Cost Temperature, pressure, rain/snow/ice LICOR ~$1800 per month for unit rental GW monitoring - NA parametres only ~ $ $4500 per well December 13 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

14 Range of CO 2 Efflux at 6 Locations Ground cover Average Background CO 2 Min Corrected CO 2 Average Corrected CO 2 Max Corrected CO 2 Average LNAPL Degradation Rate Grass Grass Gravel Gravel Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

15 Groundwater and LI-COR Results LI-COR estimated LNAPL source zone rate: 120 kg/yr Pre-existing estimated LNAPL source zone rate: between 35 and 94 kg/yr 15 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

16 Managing Variability Standard installation protocol Standard weighted tamping device for re compaction of soil to natural conditions Wait at least 4 hours after a precipitation event Record weather conditions including pressure and temperature Maintain a 1.5-m distance from ground surface disturbances Regular practice of duplicate efflux systems approximately 1 m Create a detailed method for background corrections 16 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

17 Conclusions LI-COR CO 2 Efflux Analyzers Measure free phase NAPL LI-COR precision observed ~+/- 0.3mmol/m 2 /s (total efflux) Quicker sample collection Cheaper to analyze for NAIP parameters Fewer field staff required Isotopic CO 2 Analysis Concentration of CO 2 increases with depth Heavy carbon depleted at depth Low radiocarbon fraction with depth, thus a large portion of the CO 2 comes from an old carbon source All indicators of biodegradation Uncertainties Ecosystem-related (background) contributions to total CO2 efflux are generally small ~ mmol/m2/s Temperature showed most significant effects to total efflux Further work Next step assess effects of subsurface changes on efflux (i.e., seasonality) Data analysis underway 17 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

18 Thanks to Co-Authors Tom Palaia CH2M HILL, Denver Ellen Porter CH2M HILL, Calgary Fiona D Arcy University of Ottawa Ian Clark University of Ottawa Ruth Hall Environment Yukon 18 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

19 Thank You Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide