LNAPL Recovery Using Vacuum Enhanced Technology. Theresa Ferguson, R.G. June 2014

Transcription

1 LNAPL Recovery Using Vacuum Enhanced Technology Theresa Ferguson, R.G. June 2014

2 Presentation Overview v LNAPL in the Subsurface v What is Vacuum Enhanced Technology? v Technology Description and Application v Technology Advantages/Disadvantages v Case Study

3 LNAPL in the Subsurface v A Light non-aqueous phase liquid (LNAPL) is one of a group of organic substances that are relatively insoluble in water and are less dense than water. v The most common LNAPL related ground-water contamination problems (across country) result from the release of petroleum products.

4 LNAPL in the Subsurface v LNAPL can exist in the subsurface many phases. Insoluble liquid (above water table) Sorbed to soil particles Vapor in soil gas Dissolve into soil moisture and/or groundwater

5 LNAPL in the Subsurface v Vadose Zone Volatilization Sorbed to soil Residual phase (immobile) Dissolution v Saturated Zone (capillary fringe/ water table) Spreads laterally Shares pore space only with water. v Smear Zone LNAPL is retained in soil pores and leaves behind residual. LNAPL can be trapped below water table.

6 LNAPL in the Subsurface v Migrating LNAPL Spreads or expands laterally or vertically. Increased volume of LNAPL extent. v Mobile LNAPL Hydraulically connected and has the potential to be mobile. v Residual saturation Relatively immobile Not present in in the subsurface an amount sufficient to flow readily into wells or excavations. LNAPL sat > residual Migrating LNAPL LNAPL sat > residual Mobile LNAPL LNAPL sat < residual Residual LNAPL Courtesy of ITRC Evaluating LNAPL Remedial Technologies for Achieving Project Goals December 2009

7 LNAPL in the Subsurface v In Well LNAPL Thickness Poor indicator LNAPL thickness > true thickness in the aquifer Site setting (i.e soil type) v LNAPL will not accumulate in a well unless the water table drops and LNAPL trapped below the water table can flow into the well.

8 What is Vacuum Enhanced Technology? v Extraction technology that can simultaneously remove vapor, LNAPL, and groundwater.

9 EPA, 1997 Typical Schematic of a Vacuum Enhanced Extraction System - Stationary

10 Typical Schematic of Vacuum Enhanced Technology Mobile

11 Technology Description and Application v Prevent LNAPL migration, remove LNAPL, and reduce dissolved phase constituents. v Addresses saturation based LNAPL remedial objectives v Recovery is achieved by pumping and applying vacuum at or below the water table. Can be applied at multiple wells v Enhances the extraction of soil vapor and the recovery of groundwater. De-water the smear zone to expose soil column below water table v Enhances biodegradation by introducing oxygen to the vadose and saturated zones.

12 Technology Advantages v Ability to simultaneously treat all phases of contamination (vapor, residual, dissolved, non-aqueous). v Ability to address the entire impacted (unsaturated and saturated) zone. v Smearing of LNAPL is minimized.

13 Technology Advantages v Effective in low permeability soils. LNAPL thicknesses smaller; Occurrences - short lived. Drawdown exposes the LNAPL smear zone for vapor recovery, reducing groundwater recovery costs. v Effective in high permeability soils. Efficient and increased groundwater recovery. High LNAPL recovery and saturation reduction.

14 Technology Advantages v Large radius of influence capturing more of groundwater plume. v Requires fewer recovery wells. v Reduces drawdown necessary to obtain a given flow rate. v Increased groundwater and vapor removal rates - cost savings compared to conventional methods. v Reduced duration of remediation.

15 Technology Disadvantages/Limitations v Limited to reducing LNAPL saturation to residual saturation. v Permeability affects the radius of influence of the recovery well. v Fine grained/low permeability soils produce very low mobility and recoverability. v Increased equipment and instrument requirements compared to conventional pumping (i.e. vacuum pump or blower). LNAPL sat < residual Residual LNAPL

16 Technology Disadvantages/Limitations v Vacuum lift depth is limited. v May result in increased treatment requirements (i.e vapor phase and groundwater). v Initial startup and adjustment periods may be longer. Optimize flow rates Vacuum pressures Drawdown throughout the recovery network

17 Things to Remember v LNAPL CSM. v Cost savings versus effectiveness. v Vacuum enhanced LNAPL removal will in most cases leave some LNAPL behind in the subsurface (i.e. immobile residue). v Understanding the relationship between in well LNAPL thickness and its occurrence in subsurface is critical to effectively recovery LNAPL. v LNAPL saturations are substantially lower in fine grained soils as compared to coarse grained soil. Decreases in LNAPL saturations will decrease mobility and recoverability of LNAPL for a given soil type.

18 Case Study- Underground Storage Tank Site

19 Site Setting v Active retail petroleum service station since approximately v Impacted soils identified during the UST removal through v Additional investigations since v LIF completed in August v Enhanced Fluid Recovery (EFR) completed June 2012, October 2012, February v Followup groundwater monitoring and gauging.

20 Site Setting v LNAPL has been identified in multiple wells since v Investigations have indicated two separate LNAPL plumes at two possible source areas at former UST basin area and at dispenser islands. shallow soils (~15 feet bgs) deeper soils (~20-41 feet bgs) v LIF confirmed LNAPL in two source areas and residual LNAPL surrounding wells with measurable LNAPL.

21 Geologic Cross Section v Glacial till: silty clay with layers of sand and gravel. v Weathered limestone and shale bedrock 25 feet to 44 feet.

22 In Well LNAPL Thickness: August 2013-February 2014 LNAPL Thickness

23 LIF - 2D Results

24 LIF - 3D Results with High/Low Water Table

25 LIF - 2D/3D Results with EC Results and High/Low Water Table

26 EFR General Schematic and Site Setup v Truck with two rotary vein vacuum pumps. 29 inches Hg, 880 CFM (2 pumps) v Applied to 5 to 6 wells for eight hours during each event. v Stinger depth at water table to 2 feet below water.

27 EFR Results Radius of Influence: June 2012-February 2014 v ROI lateral distance 8 feet - 96 feet v ROI pressure 0.0 H 2 O H 2 O ROI in H 2 O

28 MW-02 In Well LNAPL Thickness Vs. Depth to Groundwater DTW: feet feet LNAPL: 0.0 feet-3.45 feet

29 MW-12 In Well LNAPL Thickness Vs. Depth to Groundwater DTW: feet feet LNAPL: 0.0 feet-1.83 feet

30 MW-15 In Well LNAPL Thickness Vs. Depth to Groundwater DTW: feet feet LNAPL: 0.0 feet-6.49 feet

31 MW-16 In Well LNAPL Thickness Vs. Depth to Groundwater DTW: feet feet LNAPL: 0.0 feet-1.15 feet

32 Cumulative Pounds Removed Vs. LNAPL Thickness

33 EFR Results v June 2012 MW-02, MW-12, MW-15, MW-16, MW-25, MW lbs, ~29 gallons removal rate lbs per hour v October 2012 MW-02, MW-12, MW-15, MW-16, MW-25, MW lbs, ~51 gallons removal rate lbs per hour v February 2014 MW-15, MW-16, MW-26, RW-02 (4 ), RW-04(4 ) 377 lbs, ~58 gallons removal rate lbs per hour

34 Questions