April 12, 2018
The Eleventh International Conference on Remediation of Chlorinated and Recalcitrant Compounds
Pilot Testing of Multi-Phase
Extraction Technology for
Full-Scale Remediation of
High-Concentration MTBE Source
Area
Matthew Poltorak, EIT, Stantec Consulting Services Inc. ([email protected])
David Collins, PE, Stantec Consulting Services Inc. ([email protected])
Agenda
1. Project Background
2. MPE Pilot Testing
Summary
3. Pilot Testing Results
4. Lessons Learned
5. Conclusions
6. Implications for
Full-Scale Treatment
Historical Release of MTBE Impacted Groundwater and Soil
• Release from a buried suction line • Unknown duration of release
• MTBE groundwater plume 500 ft long by 600 ft wide • MTBE ranging up to 9,500,000 µg/L
• Potential bedrock fracture network
• Technologies were evaluated for source area treatment • MPE selected
Multi-Phase Extraction (MPE) Technology Selected
for Phase 1 Pilot Testing
Phase I Objectives
1. Evaluate if air permeability at the site is conducive to vapor extraction.
2. Characterize soil gas and evaluate if MTBE is present at concentrations amenable to SVE/MPE. 3. Evaluate liquid and vapor recovery rates as a
function of vacuum.
4. Estimate the area of influence (vacuum response and groundwater capture)
5. Estimate liquid and vapor MTBE mass recovery rates.
Diagram from USACE Multi-Phase Extraction Engineering and Design Manual, 1999
Pilot Testing
• 2 wells tested
• Thermal oxidizer for vapor treatment
• Existing extraction system for groundwater treatment
Results & Conclusions of Phase I Pilot Testing
• Air permeability ranged from 10-9 to 10-10cm2
• Testing showed SVE is an effective technology for application at the site
• Extracted elevated MTBE and hydrocarbon vapors
• Vacuum influence up to 80 feet
• Could not fully evaluate MPE or liquid extraction rate due to undersized thermal oxidizer
• Need for further testing
• Install/test new MPE well targeting source zone Extraction Well 1 Vapor Extraction Flowrate ~21 SCFM Liquid Extraction Flowrate N/A GPM Liquid MTBE Concentration N/A µg/L Vapor MTBE Concentration ~900,000 µg/m 3 Extraction Well 2 Vapor Extraction Flowrate ~21 SCFM Liquid Extraction Flowrate 2.4 GPM Liquid MTBE Concentration 500,000 µg/L Vapor MTBE Concentration 40,000,000 µg/m 3
Drop tube and well head adapter
Extraction Well Monitoring Well Soil Gas Probe Buried Former Fill Line
LEGEND Extraction Hose to Treatment Unit Suspected Source Area 3
MPE for Phase II Pilot Testing
Objectives
1. Utilize higher capacity thermal oxidizer to
successfully evaluate MPE technology at the site. 2. Estimate mass removal rates and extraction
influence.
3. Evaluate thermal oxidizer heat loading and support equipment selection for a full-scale system.
4. Evaluate the subsurface vacuum response and directional dependence associated with bedrock. 5. Install a new well specifically designed for MPE and
compare MPE performance in the new well to existing Project wells.
New Well Installed Existing Well Added to Testing MPE Vacuum Blower Thermal Oxidizer 0 Feet 100 Scale 4
MPE Pilot Testing Overview
• MPE conducted at 4 different well locations near suspected source area
• 3 existing
• 1 newly installed
• Vacuum enhanced groundwater and vapor extraction
• 2-5 days of extraction
• 8 MMBtu/hr thermal oxidizer for vapor treatment
Off-gas treatment
High vacuum liquid ring pump and air/water separator tank
Pea Gravel New Well Screen Vacuum Extraction Hosing 5
Extraction System Data Collected and Monitoring
Performed
• Monitoring of influent
concentrations
• Vapors • Groundwater• Vapor and groundwater
extraction flow rates
• Monitoring of vacuum
and drawdown
Well 4 Well 3 Well 2 Well 1 0 Feet 100 Scale Extraction Well Monitoring Well Soil Gas Probe Buried Former Fill LineLEGEND Differential Pressure Gauge Flow Totalizer Well Head Vacuum Gauge Vacuum Monitoring Point
Flame Ionization Detector Photo Ionization
Detector
Wells had Unique Response with Respect to Extracted
Liquid Flow and MTBE Concentrations
Well 1 Vapor Extraction Flowrate 20 SCFM Liquid Extraction Flowrate 1.0 – 1.5 GPM Steady-state Liquid MTBE Concentration 60,000 µg/L Steady-state Vapor MTBE Concentration 3,400,000 µg/m3 Well 2 Vapor Extraction Flowrate 20 SCFM Liquid Extraction Flowrate 1.5 – 3.0 GPM Steady-state Liquid MTBE Concentration 160,000 µg/L Steady-state Vapor MTBE Concentration 14,000,000 µg/m3 Well 4 Vapor Extraction Flowrate 20 SCFM Liquid Extraction Flowrate 0.5 GPM Steady-state Liquid MTBE Concentration 40,000 µg/L Steady-state Vapor MTBE Concentration 425,000 µg/m3 Well 3 Vapor Extraction Flowrate 20 SCFM Liquid Extraction Flowrate 6.5 – 12.0 GPM Steady-state Liquid MTBE Concentration 2,000,000 µg/L Steady-state Vapor MTBE Concentration 30,500,000 µg/m3 Extraction Well Monitoring Well Soil Gas Probe Buried Former Fill Line
LEGEND
0 Feet 100
High Flows and MTBE Concentration Observed from
Screened Sandstone/Siltstone Layer
Well 2 Well 1 Well 4 Well 3 Elev. (FT MSL) 100 0 100 0 Above Ground Storage
Tank
1.25 gpm 2.25 gpm
0.5 gpm 9.25 gpm
MTBE Concentration in Extracted Liquid
Older Alluvium/Natural Soil Horizon: Clay, Sandy Clay, Sandy Silt
Weathered Bedrock: Interbedded claystone, siltstone and sandstone, severely weathered
Siltstone/sandstone bedrock
Approx. geologic contact Fresh – Slightly weathered bedrock Moderately weathered bedrock Highly weathered bedrock
Fill Legend Well 1 60,000 µg/L Well 2 160,000 µg/L Well 3 2,000,000 µg/L Well 4 40,000 µg/L
MTBE Concentration in Well 3 Groundwater Before MPE 470,000 µg/L After MPE 5,700,000 µg/L 10x higher 8
Well 3
Inconsistent Vacuum Response Observed with Respect to
Location and Direction
Well 1 Well 2
Well 4
MPE Well
Consistent Vacuum Response Periodic Vacuum Response No Vacuum Response
Vacuum Response defined as > 0.1 in-H2O
Vacuum as a function of distance from extraction well:
9
Vacuum Response and Groundwater Drawdown used to
Estimate ROI
40 Feet
20 Feet
Estimated ROI Vapor Extraction ROI 20 – 40 Feet
Liquid Extraction ROI < 30 Feet
Total MPE ROI 20 Feet Conservative to 40 Feet Maximum
Maximum ROI
Conservative ROI
Groundwater drawdown as a function of distance:
Lessons Learned: Vapor Extraction Pilot Test Data Affected
by Seasonal Weather
Monitoring Well Groundwater Elevation Increase from Dry to
Wet Conditions (Feet) A 7.5 B 6.0 Well 2 9.5 C 7.75 D 10.5 Well 4 10.5
Well 2 Testing During (Phase I) Dry Condition
Well 2 Testing During (Phase II) Wet Condition
MPE Well
Consistent Vacuum Response Periodic Vacuum Response No Vacuum Response Vacuum Response defined as
> 0.1 in-H2O 0 Feet 100 Scale A B C D Well 4 Well 2 11
Lessons Learned: Estimate BTU Loading for Vapor
Treatment Unit Sizing
Phase I Pilot Test -<1 mmBTU/hr
Phase II Pilot Test -8 mmBTU/hr
Extraction Well BTU Loading During Dry Conditions (mmBTU/hr)
BTU Loading During Wet Conditions (mmBTU/hr)
Well 1 0.14 0.007
Well 2 0.13 0.017
Well 3 N/A 0.066
Conclusions from Phase II MPE Pilot Testing
• MPE was more effective than SVE alone
• Mass transfer from liquid to vapor phase likely occurring
