Gasoline service stations and maintenance garages pose a potential environmental problem usually associated with leaking underground storage tanks (USTs), faulty piping systems or accidental spills at the surface. Releases such as these can lead to impacted soil, ground water and light non-aqueous phase liquid (LNAPL) contamination with contaminants of concern (COCs) such as benzene, toluene, ethylbenzene, xylenes (BTEX), naphthalene, methyl-tert butyl ether (MTBE), tert butyl alcohol (TBA), and total petroleum hydrocarbon-gasoline/diesel range organics (TPH-GRO & DRO).

Former Maintenance and Repair Garage (Isotec Case Study 11)

• Site Location: West Chester, NY
• Contamination: BTEX (4,869 ppb) and MTBE (451 ppb).
• Geology: Very fine to coarse sand and gravel underlain by fractured bedrock. Water table is approximately 3-10 ft bgs.
• Area Treated: - Two separate areas: 2,400 sq ft BTEX plume and a downgradient 17,600 sq ft MTBE plume targeting the 11 - 20 ft bgs interval.
• Effectiveness: 66% reduction of total BTEX and 62% of MTBE in hot spots, and below NYSDEC cleanup criteria in downgradient area. NYSDEC issued No Further Action letter.

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• Site Location: Northwestern Florida
• Contamination: Benzene (29,942 ppb); Toluene (25,009 ppb); and Ethylbenzene (2,942 ppb).
• Geology: Compact fine to medium grained silty clayey sands from land surface to 6 ft bgs followed by a clay lens; water table is approximately 6-7 ft bgs in source area.
• Area Treated: 14,130 Sq. ft area at 3-17 ft bgs vertical depth interval.
• Effectiveness: Benzene was reduced by >90%; Ethylbenzene and Toluene were treated to below FDEP criteria in the treated area.

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• Site Location: Western Florida
• Contamination: Benzene (3,736 m g/l); Ethylbenzene (5,769 m g/l); Toluene (10,700 m g/l ); Xylenes (9,984 m g/l ); Methyl-t-butyl ether MTBE (107 m g/l); and Naphthalene (1,372 m g/l ).
• Geology: General shallow subsurface conditions at the site consist of fine sands and silty sands ; water table at approximately 5-7 ft bgs.
• Area Treated: 12,000 Sq. ft area at 4-15 ft bgs vertical depth interval.
• Effectiveness: Greater than 99% reduction of total VOCs and SVOCs site-wide following ISOTEC pilot and full-scale treatment programs. All concentrations reduced to below the most stringent FDEP groundwater quality standards.

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• Site Location: Florida
• Contamination: Benzene (3 ppb); Toluene (127 ppb); Ethylbenzene (266 ppb); and Total Xylenes (3,028 ppb).
• Geology: Fine-to coarse-grained sand interbedded with layers of clayey to silty sand from ground surface to a depth of ~68 ft bgs underlain by weathered limestone. Depth to groundwater is ~25 ft bgs; GW flow is moderate and to the south-southwest.
• Area Treated: ~3,600 Sq. ft total area. Target treatment zone ranged from ~26-35 ft bgs.
• Effectiveness: GW VOC reduction rates exceeded 99% in all three locations. Treatment area VOC concentrations were reduced from 3,424 ppb to 17 ppb.

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• Site Location: Tampa Florida
• Contamination: Naphthalene, MTBE, Benzene, Toluene, Ethylbenzene, Total Xylenes (BTEX).  Total GW VOC Concentrations:  Naphthalene (194 ug/l); MTBE (100 ug/l); Benzene (942 mg/l); Toluene (2,750 mg/l); Ethylbenzene (784 ug/l); and Total Xylenes (2,040 ug/l).
• Geology: Site is composed of clayey fine sands, silts and clays. White to brown fine grained sand to mottled brown clayey sand from land surface to 12 ft bgs. Tan to grey sandy clay to 18 ft bgs. Clay from 18 to 30 ft bgs.
• Area Treated: Approximately 660 square feet (sf) area - 10-20 ft bgs treatment interval.
• Effectiveness: Substantial GW VOC reduction of higher than 99% was achieved after only one treatment application. Treatment area total VOC concentration was reduced from 6,810 µg/l to 6.2 µg/l . The entire project was completed for under $40,000 and the client has recommended that the site enters a natural attenuation monitoring program .

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• Site Location: Frenchglen, Oregon
• Contamination: Total Petroleum Hydrocarbons in Gasoline (TPH-G), 1,2,4-methylbenzene and Benzene.
• Geology: The subsurface is compromised of sands and silty sands with very dense silty sand layers. GW is encountered at approximately 6-7 feet bgs.
• Area Treated: Target treatment area covered an injection well network utilizing 28 injection points targeting two depth intervals at each location.
• Effectiveness: TPH-G mass was reduced by approximately 71% and benzene mass was reduced by 90%.

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• Site Location: Homer, Louisiana
• Contamination: Total Petroleum Hydrocarbons in Gasoline (TPH-G) and Benzene (350 mg/kg in soil; 1,435 µg/L in GW).
• Geology: The subsurface is compromised of sandy clays. GW is encountered at approximately 12 feet bgs.
• Area Treated: Target treatment area was approximately 2,000 sq. feet covering the 15-18 and 18-21 depth intervals.
• Effectiveness: Benzene concentrations were reduced by 85% and 90% in MW-3 and MW-5, respectively. Full-Scale ISCO remediation program reduced the TPH-G mass by approximately 2,500 lbs. (from 2,800 lbs. to 300 lbs.). Based on contaminant concentration reductions at the site, a No Further Action (NFA) determination was made by the Louisiana Department of Environmental Quality (LDEQ).

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• Site Location: Paramount, California
• Contamination: Tert-butyl-alcohol (TBA).
• Geology: The subsurface is compromised of sandy silt and silty clay to a depth of approximately 25 feet bgs underlain by silty, fine-sand to the total depth explored of 40 feet bgs.
• Area Treated: Target treatment area was approximately 11,000 sq. feet covering the 26-37 feet bgs depth interval.
• Effectiveness: Average TBA concentration in GW reduced by 96%.

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