Transcript Slide 1

Rapid Closure of Lingering Off-Site
Plume Remediation Program in
Residential Neighborhood using
Horizontal Air Sparge and Soil Vapor
Extraction Wells
Narayanan Raghupathi, P.E. (AMEC Environment &
Infrastructure), Tallahassee, Florida; Sequino, Mike (Directional
Technologies, Inc.), North Haven, Connecticut; George
Losonsky, Ph.D., P.G., (Losonsky & Associates, Inc.), Baton
Rouge, Louisiana; Angela R. Finney (AMEC Environment &
Infrastructure), Tallahassee, Florida
Site Location
Site History
 Active gas station
 Located at intersection of Hwy 319 and Hwy-27 in
Tallahassee, Florida
 1986- Approximately 1,000 gallons of premium unleaded gas
leaked from an UST
 Cleanup being conducted under FDEP Preapproval Program
(Robert Brown, FDEP Site Manager)
 1995- Installed groundwater recovery and AS/SVE systems
(Delta, Inc.)
Site Map
Site Assessment
 Site Geology consists of sandy clay to clayey sand and grading
to fine silty sand at 40 ft bls.
 Depth to water – 41 feet bls
 Soil plume – 9,620 square feet (15 to 30 ft bls)
 Groundwater plume – 46,722 square feet
 COCs – VOCs, PAHs and TRPH
 Highest Total BTEX – 11,720 (MW-20R2)
 Down gradient contamination migration
Baseline Groundwater Plume
Down Gradient Horizontal AS and SVE
Layout
Up Gradient Horizontal AS and SVE
Well Layout
Current Groundwater Plume
Horizontal Well Screen Design
 Design specifies the open area of the well screen that
will allow uniform flow of fluid (e.g., air) into or out of
the formation
 Numerical model uses iterative calculation process to
generate key mechanical parameters:
 Pressure along the screen
 Flow through the slotted screen pipe
 Injection or extraction rate of in-situ treatment
fluids
Figure 1
Pressure Along the Screen (psig) in Well HAS-1
OPEN AREA 0.28 %
30.00
29.95
29.90
29.85
29.80
29.75
29.70
0
50
100
150
200
250
Distance Along the Screen (ft)
300
350
400
Figure 2
Injection Rate (SCFM / foot of screen) in Well HAS-1
OPEN AREA 0.28 %
0.8100
0.8050
0.8000
0.7950
0.7900
0
50
100
150
200
250
Distance Along the Screen (ft)
300
350
400
Horizontal Well Screen Design
 Flow of the air into the aquifer or water-bearing unit
surrounding the horizontal screen is governed by
equations related to Darcy’s Law and the Laplace
Equations for mass balance
 Air extraction follows the principles of mass
conservation for isothermal gas in porous media as
described by various forms of the Richards equation.
The relative permeability of the soil gas is related to
water saturation and head by the van Genuchten
equations. The key relationships are described by
Huyakorn and Pinder
Figure 25
Pressure Along the Screen (psig) in Well HVE-1
OPEN AREA 0.97 %
-6.20
0
50
100
150
200
250
-6.30
-6.40
-6.50
-6.60
-6.70
-6.80
Distance Along the Screen (ft)
300
350
400
Figure 26
Extraction Rate (SCFM / foot of screen) in Well HVE-1
OPEN AREA 0.97 %
1.5200
1.5150
1.5100
1.5050
1.5000
1.4950
1.4900
0
50
100
150
200
250
Distance Along the Screen (ft)
300
350
400
System Installation
 Eight horizontal wells installed in September and
October 2008 to address hydrocarbon impact in sand
and silt soils
 Four horizontal air sparge well screens were installed
at depths of 47 to 48 feet below ground surface
 One horizontal soil vapor extraction screen was
installed above each of the horizontal air sparge
screens, at depths of 35 to 37 feet below ground
surfac
 Two of the well pairs were installed in the
southwestward direction and the other two pairs were
installed in the northeastward direction
Well HAS-2 Pitch Profile
Distance in Feet from Entry Point
Vertical Depth in Feet from Ground Surface at Rig
0
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
-10
-20
-30
-40
-50
4-inch SDR-11 HDPE Screen
-60
Markers Denote
End-of-Rod Locations
900
Well HVE-1 Pitch Profile
Distance in Feet from Entry Point
Vertical Depth in Feet from Ground Surface at Rig
0
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
-10
-20
-30
-40
4-inch SDR-11 HDPE Screen
-50
Markers Denote
End-of-Rod Locations
-60
Drilling Fluids
Management
 Flowing sands produced
high volume of solid
returns
 Mud recycler separates sand/silt cuttings from fluid
returns
Air Sparge Screen
 Longitudinally slotted
 0.27% average open area
 1.0” average slot length
 0.1” slot width
Soil Vapor Extraction Screen
 Longitudinally slotted
 1.01% average open area
 3.7” average slot length
 0.1” slot width
System Performance
 Four key monitoring wells MW-16, MW-20R2, MW-22, and
MW-28 were selected for monitoring of remedial progress at
the site. The BTEX and MTBE concentrations are used to
evaluate the achievement of milestones.
 The total worst case emissions rate from the SVE and MPE
system was 2.67 pounds/day, which is below the State of
Florida regulatory limit of 13.7 lbs/day
AS/SVE and MPE System
Cleanup Progress Evaluation
Designation
Baseline BTEX (µg/l)
Nov 2008
Year 2, 1st Qtrly
BTEX (µg/l) July 2010
% Reduction from
Baseline
MW-16
Down gradient
2,114
0.99
99.99
MW-20R2
Source area
11,720
107
99.08
MW-22
Source area
11,000
0.32
99.99
MW-28
Source area
583
BDL
99.99
25,417
108.31
99.57
Designation
Baseline MTBE (µg/l)
Nov 2008
Year 2, 1st Qtrly
MTBE (µg/l) July 2010
% Reduction from
Baseline
MW-16
Down gradient
37
4.2
92.7
MW-20R2
Source area
590
87
76.27
MW-22
Source area
260
13
81.53
MW-28
Source area
140
2
98.71
1,027
106.2
89.65
Monitoring Well ID
Totals
Monitoring Well ID
Totals
System Performance
 Within the five quarters of system operation, the VOC
concentrations have declined by approximately 98 percent,
MTBE (81 percent), PAHs (98 percent), and TRPH (99 percent)
since system startup, based on data from the four primary
monitoring wells.
 After 11 years of operation of a series of vertical well systems
that failed to thwart down-gradient migration of groundwater
contamination, the horizontal well system achieved site
objectives within 2 years of operation, reducing all regulated
compounds were reduced below regulatory limits (SCTLs and
GCTLs)
2500
MW-16
2000
11/17/2008
1500
5/11/2009
7/23/2009
1000
11/2/2009
500
0
Benzene Toluene EthylBenz Xylenes
VOA
MTBE
14,000
12,000
10,000
MW-20R2
8,000
11/19/2008
6,000
2/12/2009
4,000
2,000
0
7/23/2009
11/2/2009
Clean-Up Summary
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Target Contaminant concentrations below NAM
PAHs below GCTLs
BTEX Plume Area – 6,500 sq. ft
MTBE Plume Area – 7,000 sq. ft
BTEX – 99 percent reduction
MTBE – 90 percent reduction
Project Summary
 Successfully installed horizontal AS and SVE wells
(Mike Sequino, Directional Technologies)
 Horizontal AS/SVE wells are effective in reducing
contaminant concentrations.
 Achieved even air flow through the length of the
horizontal well screens.
 MACTEC Project Manager, Angela Finney,
successfully worked with FDEP, property owners,
and merchants.
 Completed project on time and budget.
QUESTIONS