Florida Remediation Conference

Site Remediation Using Horizontal Air Sparge (AS)/ Soil Vapor Extraction (SVE), and Multiphase Extraction (MPE) Wells

Narayanan Raghupathi, P.E. (MACTEC)Angela Finney (MACTEC)

Country Corner ShellTallahassee, FloridaThis paper has been

forwarded to you by:

Site Location

Site Map

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 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)• Downgradient contamination migration

Baseline Groundwater Plume

Baseline Soil Plume

Remedial Design Challenges• Remediating contamination beneath Hwy 319

and Hwy 27 and large downgradient groundwater plume (residential area)

• Conduct construction activities without closing the store

• Deep groundwater plume (41 feet bls)• Community relations• Cleanup goals – SCTLs and GCTLs per 62-

777, F.A.C

Remedial Design

• Downgradient - Install two horizontal AS and SVE wells, 800 feet long w/ 450 feet of screen

• Upgradient - Install two horizontal AS and SVE wells, 400 feet long w/200 feet of screen

• Horizontal AS Wells – 48 feet bls• Horizontal SVE Wells – 35 feet bls• Source – Install vertical AS (15) and MPE (9)

wells, and use 15 previously installed MPE wells

Engineering Design Challenges

• Determining horizontal well layout, screen depths, entry and exit locations

• Design of horizontal AS and SVE well screens to have even distribution of air flow through the length of the screen

• Remediate large BTEX and MTBE plume• Develop a complete zone of influence• Optimal equipment sizing• Develop system O&M program

Down gradient Horizontal AS and SVE Well Layout

Upgradient Horizontal AS and SVE Well Layout

Vertical AS and MPE Well Locations

29.70

29.75

29.80

29.85

29.90

29.95

30.00

0 50 100 150 200 250 300 350 400

Distance Along the Screen (ft)

Pressure Along the Screen (psig) in Well HAS-1

OPEN AREA 0.28 %

Pressure Drop in Air Sparge Screen

Head loss along screen is less than 1%

0.7900

0.7950

0.8000

0.8050

0.8100

0 50 100 150 200 250 300 350 400

Distance Along the Screen (ft)

Injection Rate (SCFM / foot of screen) in Well HAS-1

OPEN AREA 0.28 %

Injection Rate in Air Sparge Screen

Slot distribution designed to distribute flow

-6.80

-6.70

-6.60

-6.50

-6.40

-6.30

- 6.20

0 50 100 150 200 250 300 350 400

Distance Along the Screen (ft)

Pressure Along the Screen (psig) in Well HVE-1-

OPEN AREA 0.97 %

Loss of Vacuum in SVE Screen

Head loss along screen is less than 5%

Extraction Rate in SVE Screen

1.4900

1.4950

1.5000

1.5050

1.5100

1.5150

1.5200

0 50 100 150 200 250 300 350 400

Distance Along the Screen (ft)

Extraction Rate (SCFM / foot of screen) in Well HVE-1

OPEN AREA 0.97 %

Screen designed to minimize drop in flow rate

Drilling FluidsManagement

• Mud recycler separates sand/silt cuttings from fluid returns

• Flowing sands produced high volume of solid returns

Horizontal Drilling

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

-60

-50

-40

-30

-20

-10

00 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900

Ver

tica

l D

epth

in

Fe

et f

rom

Gro

un

d S

urf

ace

at R

ig Distance in Feet from Entry Point

Well HAS-1 Pitch Profile

Markers DenoteEnd-of-RodLocations

4-inchSDR-11 HDPE Screen

Horizontal Air Sparge Well Profile

-60

-50

-40

-30

-20

-10

00 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850

Ver

tica

l D

epth

in

Fe

et f

rom

Gro

un

d S

urf

ace

at R

ig

Distance in Feet from Entry Point

Well HVE-1 Pitch Profile

Markers DenoteEnd-of-RodLocations

4-inchSDR-11 HDPE Screen

Horizontal SVE Well Profile

AS/SVE and MPE System

• AS Compressor – 717 scfm @ 30 psi• SVE Blower - 2624 acfm @ 14 In. Hg• MPE LRP- 2531 acfm @ 16 In. Hg.• Air Treatment – Two, 1,600 pound carbon

vessels• GW Stripper – Air Stripper

AS/SVE and MPE System

System Operation Cycle

• Vertical AS – 8:00 AM to 8:00 PM• HAS1 – 8:00 AM to 2:00 PM• HAS-2 – 2:00 PM to 8:00 PM• HAS-3 – 8:00 PM to 2:00 AM• HAS-4 – 2:00 AM to 8:00 AM• MPE wells – 24 hours• SVE wells – 24 hours

Cleanup Progress EvaluationMonitoring Well ID Designation Baseline BTEX (µg/l)

Nov 2008Year 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

Totals 25,417 108.31 99.57

Monitoring Well ID 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

Totals 1,027 106.2 89.65

Current Groundwater Plume

Cleanup Summary

• 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