Density-Driven Groundwater Sparging at Amcor Precast Ogden, Utah

Site Name:

Amcor Precast


Ogden, Utah

Period of

March 1992 to September 1993


Full-scale cleanup


Todd Schrauf
Wasatch Env., Inc.
2251B West California Ave.
Salt Lake City, UT 84104
(801) 972-8400

In situ Density-Driven Groundwater Sparging and Soil Vapor Extraction - System consists of three main components - groundwater sparging system; groundwater recirculation system; and soil vapor extraction system - Groundwater sparging was principal method of remediation; SVE was used locally Sparging System - Density-driven groundwater sparging - removed petroleum hydrocarbons using (1) aerobic degradation and (2) in situ air stripping; water inside the wellbore was aerated directly by injecting air at the base of the wellbore - 12 groundwater sparging wells installed to a depth of 18 feet Groundwater Recirculation - 3 downgradient extraction (pumping) wells installed to a depth of 20 feet and 1 upgradient injection galley (former tank excavation backfilled with pea gravel) SVE - 3 vertical extraction wells located adjacent to the pumping wells - Vapor discharged to atmosphere

Cleanup Authority:
State: Utah Department of Environmental Quality, Division of Response and Remediation (DERR)

SIC Code:
Not available
Point of Contact:
Shelly Quick Utah DERR

Benzene, Toluene, Ethylbenzene, Total Xylenes (BTEX), Naphthalene, and Total Petroleum Hydrocarbons (TPH)

Groundwater - Average groundwater concentrations (mg/L) in plume area/site maximum - TPH (51/190), benzene (1.3/4.7), toluene (2.4/9.4), ethylbenzene (0.78/2.7), total xylenes (2.5/8.0), naphthalene (0.18/0.63) Soil - Average soil concentrations (mg/kg) in plume area/site maximum - TPH (555/1,600), benzene (2.0/7.8), toluene (1.4/2.5), ethylbenzene (5.7/19), total xylenes (37/110

Waste Source:
Underground Storage Tanks

Type/Quantity of Media Treated:
Groundwater and Soil - Site stratigraphy - interbedded silty sand and poorly graded fine gravel underlain by a silty clay aquitard at a depth of approximately 18 feet below ground surface - Depth to groundwater - 5 to 11 feet; aquifer thickness (7-13 feet) - Porosity (20-35%), hydraulic conductivity (190 ft/day) - Aerial extent of the plume - approximately 30,000 ft[Sup 2]; vertical extent of contamination - contaminants concentrated in vertical zone from approximately 5 to 11 feet below ground surface - Estimated volume of contaminated soil - 7,000 yd[Sup 3]

Purpose/Significance of Application:
Full-scale remediation of groundwater contaminated with diesel and gasoline fuels using in situ density-driven groundwater sparging and soil vapor extraction.

Regulatory Requirements/Cleanup Goals:
- Soil - DEQ Recommended Cleanup Levels (RCLs) - TPH - 30 mg/kg; Benzene - 0.2 mg/kg; Toluene - 100 mg/kg; Ethylbenzene - 70 mg/kg; Xylenes - 1,000 mg/kg; Naphthalene - 2.0 mg/kg - Groundwater - BTEX and naphthalene to below MCLs; no cleanup goal for TPH in groundwater - Air - no air discharge permit was required because air emissions were below de minimis standards of the Utah Division of Air Quality.

- The cleanup goals were achieved for all contaminants of concern in both soil and groundwater

Cost Factors:
- Total Capital Cost: $156,950 (including drill/install wells and sparging system, start-up, project management) - Total Annual Operating Cost: $62,750 (including electricity, maintenance, monitoring)

Amcor Precast in Ogden, Utah, stored gasoline and diesel fuel in three underground storage tanks. A release was discovered in 1990. An investigation in 1991 indicated that the areal extent of groundwater contamination was approximately 30,000 ft[Sup 2] and that an estimated 6,700-7,000 yd[Sup 3] of soil had been contaminated. The primary contaminants of concern were benzene, toluene, ethylbenzene, and xylenes (BTEX), naphthalene, and total petroleum hydrocarbons (TPH). A density- driven groundwater sparging system and soil vapor extraction (SVE) system were installed in January/February 1992 and operated from March 1992 to September 1993. The sparging system was used as the primary remediation technology. SVE was used locally to treat volatilized hydrocarbons, created by the air stripping process, and prevent contaminants from migrating to nearby office buildings.

With the density-driven groundwater sparging system at Amcor, water inside the wellbore was aerated by injecting air into the base of the wellbore (rather than injected under pressure) with the resulting injection air bubbles stripping contaminants from the water while increasing the dissolved oxygen content. In addition, the aeration process acted to create groundwater circulation and transport. Therefore, with this system, petroleum hydrocarbons were removed from the subsurface by (1) aerobic biodegradation resulting from the supply of oxygen to the saturated zone; and (2) in situ air stripping. The air stripped vapors are transferred to the vadose zone and are biodegraded in place. The application of density- driven groundwater sparging and SVE achieved the specified cleanup goals for both soil and groundwater. The cleanup goals for soil and for all contaminants except naphthalene in groundwater were achieved within 11 months of system operation. The cleanup goal for naphthalene in groundwater was achieved within 18 months.

The total capital cost for this application was about $157,000 and total annual operating costs were $62,750. Air sparging is limited to contaminants that can be degraded by indigenous bacteria under aerobic conditions. Maximum sparging well air flow and groundwater wellbore circulation rates are dependent on well diameter, depth to groundwater, and the hydraulic conductivity of the formation. Therefore, longer remediation times or a greater number of sparging wells may be required in lower permeability formations.