LNAPL Remediation via Horizontal Biosparging Wells Facilitates Property Redevelopment

Transcription

1 LNAPL Remediation via Horizontal Biosparging Wells Facilitates Property Redevelopment Derek W. Tomlinson M.A.Sc. P.Eng. Environmental Resources Management RemTech 2008 Banff Alberta Canada

2 Outline Site History and Background Information Horizontal well design and installation Air delivery system design and installation Performance monitoring results Summary RemTech2008, D. Tomlinson, 2

3 Background Former 55 acre manufacturing facility Facility demolished and property redeveloped into commercial warehouses Groundwater impacted by LNAPL and dissolvedphase VOCs (toluene and derivatives) exceeding groundwater standards Residual LNAPL in smear zone soil serving as source of dissolved-phase VOCs in groundwater RemTech2008, D. Tomlinson, 3

4 Pre-Redevelopment RemTech2008, D. Tomlinson, 4

5 Redeveloped Property RemTech2008, D. Tomlinson, 5

6 Geologic Cross-Section High Permeability: Gravel, Sand & Gravel, Silty Sand, Silt & Sand Low Permeability: Clay & Silt, Silty Clay, Clay Intermediate Permeability: Sandy Silt, Silt, Clayey Silt RemTech2008, D. Tomlinson, 6

7 Remediation Issues Soil and groundwater impact delineated prior to sale Two Areas of Concern (AOCs) with residual and free LNAPL Toluene and other aromatics Source of dissolved-phase volatile organic compounds (VOCs) in groundwater Minimal impact on redevelopment RemTech2008, D. Tomlinson, 7

8 Why Horizontal Well Biosparging? VOCs are aerobically biodegradable Sandy soil conducive to air sparging 35 to 40-foot depth to water table provides sufficient soil column for VOC vapors to diffuse and biodegrade before reaching ground surface Construction and operation of horizontal wells would have low impact on property redevelopment compared to vertical wells Larger area of influence compare to vertical wells RemTech2008, D. Tomlinson, 8

9 Approved Remediation Program Horizontal Biosparging to remediate the two LNAPL AOCs Redevelopment of the site to prevent direct contact RemTech2008, D. Tomlinson, 9

10 Horizontal Well Design Complex well screen design Well screen slot sizing Injection pressure for uniform airflow distribution Well screen resistance to aid in uniform airflow distribution Specifications Two parallel horizontal wells at ~50 feet bgs ~1,200 linear feet total length ~520 linear feet of custom slotted well screen scfm air flow (260 capacity) at 9.7 psi 6 inch well casing and screen diameter Material of construction is SDR-11 HDPE RemTech2008, D. Tomlinson, 10

11 Horizontal Well Design Well Screen Slot Size: Two sections of custom slotted well screen 2 rows of lateral slots for each section First section: 26 slots/foot, 0.02-in wide by in long (measured on inside of pipe) Second section: 22 slots/foot, 0.02-in wide by 0.75-in long (measured on inside of pipe) Injection Pressure: cfm RemTech2008, D. Tomlinson, 11

12 100 WELL SCALE IN FEET 100 AOC 1 AOC 2 WELL Mean Sea Level Elevations End Well Screen at Measured Depth MSL Elevation -2.4 Well Screen Length 520 Begin Well Screen at Measured Depth MSL Elevation -3.7 LEGEND Horizontal Biosparge Well (screened interval is dashed, non-screened is solid) Estimated Boundary of Residual Phase LNAPL RemTech2008, D. Tomlinson, 12

13 Geologic Cross-Section High Permeability: Gravel, Sand & Gravel, Silty Sand, Silt & Sand Low Permeability: Clay & Silt, Silty Clay, Clay Intermediate Permeability: Sandy Silt, Silt, Clayey Silt RemTech2008, D. Tomlinson, 13

14 Geologic Cross-Section AOC 1 AOC 2 RemTech2008, D. Tomlinson, 14

15 Geologic Cross-Section AOC 1 AOC 2 Horizontal Well RemTech2008, D. Tomlinson, 15

16 Permitting/Regulatory Approvals Well Installation Permit Default well installation regulations are based on vertical wells; therefore needed State approval Proposed alternate grouting procedure to protect the well screen while satisfying intent of regulations - intent = not creating preferred pathway for surface discharge to impact groundwater - Note: >>$$ to reinstall well screen if grout impacted Air Permit State indicated that no permit is required since no air emissions expected (no SVE) RemTech2008, D. Tomlinson, 16

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19 TruTracker Navigation D.C. Power Source TruTracker Coil Wire RemTech2008, D. Tomlinson, 19

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25 Air Delivery System Design Separate air delivery system for each well Each system consisted of the following: 30-HP positive-displacement blower Air-to-air heat exchanger (outside of shed) Flow control valve and meter Air bleed line with flow control valve Pressure and temperature instrumentation PLC and autodialer Blower capable of delivering 260 cfm at a pressure of 9.7 psi (9.1 psi injection pressure plus 0.6 psi of head losses in system before entering the well) RemTech2008, D. Tomlinson, 25

26 Process Flow Diagram RemTech2008, D. Tomlinson, 26

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28 Performance Monitoring Zone of influence measurements Soil gas sampling Groundwater sampling Soil sampling RemTech2008, D. Tomlinson, 28

29 Zone of Influence Pressure transducers were used to monitor the influence of the system on ground water levels during both startup and again during shutdown The influence of the injection of air on the aquifer was evident along the length of both horizontal wells Air release within wells also used to confirm zone of influence (i.e., radius of influence) RemTech2008, D. Tomlinson, 29

30 Water Level Response Water Level (feet) well at screen entry well at screen end RemTech2008, D. Tomlinson, 30 Start Well-1 Flow Increase Flow Increase Flow Increase Shutdown Well-1 Elapsed Time (hours)

31 Soil Gas Sampling Collected weekly from 7 locations Tedlar bags from 3 feet bgs from 1 inch probes Off-site analysis during operating period Prior to start-up- weekly for 1 month Weekly for 1st month Monthly until October 2005 On-site screening daily for 1st week of operation RemTech2008, D. Tomlinson, 31

32 180 Soil Gas Concentrations Biosparge System Period of Operation /21/2002 1/11/2003 5/3/2003 8/23/ /13/2003 4/3/2004 7/24/2004 Concentration (ug/m³) x 1,000 11/13/2004 3/5/2005 6/25/ /15/2005 2/4/2006 Date RemTech2008, D. Tomlinson, 32 SG-01 SG-02 SG-03 SG-04 SG-05 SG-06 SG-07

33 Ground Water Sampling Monitored quarterly from 7 locations Monitored before, during, and after operation Low flow sampling method RemTech2008, D. Tomlinson, 33

34 Groundwater Concentrations Log Concentration (ug/l) GW Standard Sep-02 Dec-02 Mar-03 Jun-03 Oct-03 Jan-04 Apr-04 Aug-04 Nov-04 Feb-05 May-05 RemTech2008, D. Tomlinson, 34 January Testing May Startup Shutdown GW Std. MW-1 MW-2 MW-3 MW-4 MW-5 MW-6 MW-7 NJGWQC

35 Soil Sampling Results Continuous sampling within vadose zone and across water table Visual observations indicated a decrease in free and residual LNAPL One boring with indications of residual LNAPL RemTech2008, D. Tomlinson, 35

36 Summary Zone of influence of ~50 to 100 feet laterally (the targeted treatment area) with a constant pressure maintained. Toluene levels within groundwater (a direct measure of LNAPL presence) decreased and maintained after shutdown below the applicable State groundwater standards. Free phase LNAPL not observed within monitoring wells after four months of system operation. Additionally, no free phase LNAPL has been observed within onsite monitoring wells since shutdown. RemTech2008, D. Tomlinson, 36

37 Summary No free phase LNAPL and only slight indication of residual LNAPL was observed within the soil borings completed after the system was shutdown. Soil gas concentrations indicated that the system was able to contact the contaminants of concern within the formation and that some volatilization occurred, but stabilized once biomass built up. RemTech2008, D. Tomlinson, 37

38 Acknowledgements My coworkers and coauthors William Butler, P.E., BCEE Richard Wroblewski, P.G. John Hogue Michelle Mirigliano Ronald Fender Thank You RemTech2008, D. Tomlinson, 38

39 Questions? Derek W. Tomlinson Environmental Resources Management RemTech2008, D. Tomlinson, 39