Multi-Phase Extraction and Air Sparging/Soil Vapor Extraction at Scotchman #94, Florence, South Carolina

Site Name:

Scotchman #94


Florence, SC

Period of

April 1998 - present (data available through March 2000)


Full scale

Multi-Phase Extraction (MPE) and Air Sparging/Soil Vapor Extraction (SVE)
- MPE system consisting of five extraction (recovery) wells
- Air sparging/SVE system includes 28 air sparging wells, arranged in seven groups of air sparging wells
- A total of 19 monitoring wells at the site, installed at depths ranging from 14 to 30 feet below ground surface (bgs); each well includes a 10-foot screened interval, with the depths of the screened intervals ranging from about 10 to 27.5 feet bgs.

Cleanup Authority:

Site Contact:
Worsley Companies, Inc.
P.O. Box 3227
Wilmington, SC 28406
Telephone: (910) 395-5300

State Contact:
Kimberly Wilson, P.G.
South Carolina Dept. of Health
and Environmental Control
2600 Bull St.
Columbia, SC 29201
Telephone: (803) 898-4350
Fax: (803) 898-4330
CBM Environmental
P.O. Box 411387
Charlotte, NC 28241
Telephone: (800) 743-1226
Fax: (803) 548-5892

MTBE, BTEX, Naphthalene
- MTBE concentrations as high as 87,000 ug/L in groundwater
- BTEX concentrations as high as 140,000 ug/L for toluene in groundwater
- Naphthalene concentrations as high as 4,600 ug/L in groundwater

Waste Source:
Leaks from an underground gasoline storage tank

Type/Quantity of Media Treated:
Soil and Groundwater
- Soil at the site consists of clayey sands and sandy-clays; hard clay layer is present at approximately 10 feet bgs
- Average hydraulic gradient is 0.004 feet/feet with a calculated seepage velocity of 4.415 feet per year
- Depth to groundwater is 5.4 to 23 feet bgs

Purpose/Significance of Application:
Use of multiphase extraction and air sparging/soil vapor extraction to treat MTBE in soil and groundwater

Regulatory Requirements/Cleanup Goals:
- Site-specific target levels (SSTLs) were established by SCDHEC for MTBE, benzene, toluene, ethylbenzene, and xylenes, and naphthalene, with seven monitoring wells (MW-1, MW-2, MW-6, MW-11, MW-15, MW-18, MW-19) and outfall OS-1 used in setting the total SSTLs
- Total SSTLs (sum of individual SSTLs for each well) - MTBE - 7,700 ug/L; benzene - 957 ug/L; toluene - 119,250 ug/l; ethylbenzene - 37,082 ug/L; xylenes - 187,511 ug/L; naphthalene - 2,808 ug/L

MTBE concentrations in the groundwater decreased through December 1999 to 17,736 ug/L, then increased to more than 192,000 ug/L in March 2000
- Similar trends were observed for BTEX constituents and naphthalene, with total mass decreasing through December 1999, then increasing in March 2000
- Decreases in the maximum concentrations (as measured in an individual well) were observed for each of the constituents. For example, maximum MTBE concentrations were reduced from 37,000 ug/L to 9,800 ug/L (about 74%), and concentrations of benzene from 14,000 ug/L to 1,300 ug/L (91%).
- As of March 2000, all constituents remained above the SSTLs; and operations will continue until all SSTLs have been met.
- According to the contractor, cleanup of the site is projected to be completed by March 2001.

Cost Factors:
The total cost for the cleanup of this site is $383,000.
- The South Carolina Petroleum Cleanup Fund awarded the contract for the cleanup at this site as a fixed-price, lump sum with no change orders; no additional information on cost breakdown was available.

Scotchman #94 is a gasoline service station located in Florence, South Carolina. In December 1991, a release was reported from the station's underground storage tanks (USTs), and soil and groundwater at the site were found to be contaminated with MTBE, BTEX, and naphthalene, and free product was present in the groundwater. Contaminants in groundwater were found to be as high as 87,000 ug/L for MTBE, 23,000 ug/L for benzene, 140,000 ug/L for toluene, 18,000 ug/L for ethylbenzene, 91,000 ug/L for xylenes, and 4,600 ug/L for naphthalene. A Corrective Action Plan (CAP) was implemented in March 1999 under Subtitle I of the RCRA program, which included free product recovery using MPE and treatment of dissolved-phase groundwater contamination using air sparging/SVE.

The MPE system consists of five extraction (recovery) wells and the air sparging/SVE system includes 28 air sparging wells, arranged in seven groups of air sparging wells. MTBE, BTEX, and napthalene levels initially decreased through December 1999, then increased. After two years of operation, all constituents remained above the SSTLs. The system will continue to be operated until the SSTLs are met (projected completion in March 2001).