Comparing Sustainable Natural Source Zone Depletion and Active Remediation Technologies

Transcription

1 Comparing Sustainable Natural Source Zone Depletion and Active Remediation Technologies Liz van Warmerdam Tom Palaia Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide 2015 CH2M HILL

2 Drivers and Objective Measuring natural source zone depletion (NSZD) rates of petroleum hydrocarbon LNAPL is an emerging science Review 51 diverse sites/systems to improve understanding of remediation rates for various petroleum remediation approaches How does NSZD stack up against other more active (higher energy) methods? 2 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

3 Agenda Conceptualization of LNAPL in Subsurface Overview of NSZD Rates of NSZD as Measured by CO 2 Efflux Comparable Rates of Active Remediation Conclusions 3 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

4 LNAPL Setting LNAPL exists within a 4-phase variably saturated pore fluid profile often at <30% pore volume 4 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

5 Example LNAPL Smear Zone Profile 5 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

6 LNAPL Quantification Specific volume quantifies the volume of LNAPL in a unit volume of soil (m 3 /m 2 or L/m 2 ), or (ft 3 /ft 2 or gal/ft 2 for our American friends) LNAPL Distribution Recovery Model output for a well-graded fine to coarse sand with gravel 6 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

7 LNAPL Quantification (continued) A plot and geospatial integration of specific volume allows an estimate of the volume of LNAPL in the subsurface 30 cm mobile LNAPL smear zone profile with specific volume (Dn) of m 3 /m 2 (0.05 ft 3 /ft 2 ; Tn ~0.1ft 2 /d) roughly equates to 150,000 L of LNAPL/ha (16,000 gal/ac) Removing 19,000L (5,000 gal), reduces the in situ LNAPL volume by 30% Reduces in situ LNAPL pore fluid saturations in smear zone profile to a maximum equal to the residual LNAPL saturation Non-recoverable, immobile fraction will remain in situ 7 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

8 Natural Source Zone Depletion - Petroleum 8 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

9 Carbon Dioxide (CO 2 ) Efflux Measurements Estimated NSZD rates using stoichiometric conversion of sitewide CO 2 efflux measurements 8 sites, various conditions: Operating gas plant and compressor station Remote maintenance camp Natural gas well site Pipeline Terminal Railyard Predominantly pervious, but variable ground cover Consolidated and unconsolidated subsurface soil 9 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

10 Carbon Dioxide (CO 2 ) Efflux Measurements 2 measuring techniques E-Flux CO 2 Traps 3 sites LI-COR 8100A soil flux system 6 sites E-Flux CO 2 Trap LI-COR 8100A Soil Flux System Total of 86 CO 2 trap and 290 LI-COR event-locations 10 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

11 Example Results from a NSZD Evaluation Collected CO2 efflux measurements Corrected for background Performed stoichiometric conversion Plotted NSZD rates Integrated the results to estimate a sitewide NSZD rate Sites with multiple rounds of measurements were seasonally adjusted to estimate an annual rate 11 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

12 Summary of NSZD Rates 100,000 NSZD Median = 7,000 L/ha/yr NSZD Rate (L/ha/yr) 10,000 1, Site Number Note: Recall a site with LNAPL specific volume of m 3 /m 2 contains 150,000 L/ha. 12 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

13 Summary of NSZD Rates Recall: 30-cm mobile LNAPL smear zone profile with specific volume of m 3 /m 2 roughly equates to 150,000 L/ha of LNAPL (16,000 gal/ acre) Volume per acre (Litre/Hectare) Volume per acre (gallon/acre) Smear Zone Thickness (cm) (ft) Removing 7,000 liters per hectare = <1.5 centimeters removal with the same assumptions 13 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

14 Assessment of Comparable Rates of Remediation Surveyed projects to compile real site monitoring data 43 systems LNAPL Skimming 6 Groundwater drawdown- enhanced Skimming 5 Bioventing/Biosparging 4 Soil Vapor Extraction 5 Air Sparging/Soil Vapor Extraction 10 Multiphase Extraction 13 Total Number of Active Systems in Survey = 43 Sites in survey include a broad range of: petroleum products source zone dimensions remedial design bases operation and maintenance routines (i.e., zones, pulsing, etc.) 14 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

15 Remedial System Summary Required detailed mass removal tracking Median Range Treatment Area (ha) 0.8 (1.7 ac) ( ) Volume Removed (L) 17,000 (3,125 gal) 68-22,700,000 (18-6,000,000) Mass Removal Rate (kg/yr) 3,300 (7,137 lbs/yr) 1.8 2,270,000 (4-5,000,000) Years of Operation (yrs) Remediation Rates (L/ha/yr) 9,900 (936 gal/ac/yr) ,000 (0.1-11,790) Note: Survey included only petroleum LNAPL remediation sites. 15 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

16 Active Remediation Rate Survey Results 100,000 10,000 Rate of Remediation (L/ha/yr) 1, Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

17 Comparison of Median Rates of Remediation N=5 N=10 N=4 N=5 N=13 N=6 NSZD Median = 7,000 L/ha/yr Survey indicates that NSZD rates fall within the spectrum of other remedial approaches 17 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

18 Evaluation of Early and Late Stage Rates 100,000 NSZD Median = 7,000 L/ha/yr 10,000 Remedia@on Rate (L/ha/yr) 1, Early Stage Median Median Late Stage Median Midway into remediation, NSZD may become stronger than some remedies Note: 10 of the 13 MPE systems had no difference in early and late remediation rates, thus were excluded from this early/late data sets 18 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

19 Conclusions Within this survey, the NSZD rates measured using CO 2 efflux methods are reasonable i.e. They fall within the spectrum of the surveyed remedial systems roughly from ,000 L/ha/yr Are consistent with plausible rates of remediation for sites with >100,000 L/ ha present in the subsurface NSZD rates are substantial (i.e. competitive with remediation rates of active systems) Of interest is an inflection point during remediation when the efficacy of active remediation may fall below that of NSZD The NSZD rate is a useful metric for optimization of active remediation 19 Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide

20 Thank You Tom Palaia (303) Liz van Warmerdam (604) Innovation that Provides Sustainable Solutions to Complex Local Challenges, Worldwide 2015 CH2M HILL