Pump and Treat of Contaminated Groundwater at IRP Site 4, Langley Air Force Base, Virginia

Site Name:

Langley Air Force Base


Langley, Virginia

Period of

Status: Ongoing Report covers - 7/92 to 1/94


Full-scale cleanup (interim results)


Not Available

Groundwater Extraction using a Vacuum Assisted Well Point Extraction System and Aboveground Air Stripping - Extraction - 16 vacuum extraction wells connected by a header pipe to a central vacuum system; wells extend to approximately 14 ft. below ground surface - Extraction network has an average flow rate of 32 gpm (2 gpm per well); vacuum pump provides 24-25 in of Hg - Separation - initial oil/water separation occurs in a vacuum decanter followed by a high efficiency oil/water separator; oil phase is sent to a storage tank - Treatment of aqueous phase - 2 air stripping columns - Column 1 - air/water ratio of 180 and air flow of 1,440 cfm at 60 gpm; Column 2 - air/water ratio of 100 and air flow of 800 cfm at 60 gpm

Cleanup Authority:
UST Corrective Action and State: Virginia

SIC Code:
9711 (National Security)
Point of Contact:
Vern Bartels Remedial Project Manager Langley AFB

Benzene, Toluene, Ethylbenzene, Xylenes (BTEX) and Total Petroleum Hydrocarbons (TPH) - Primary constituents of JP-4 fuel are alkanes, cycloalkanes, alkylbenzenes, indans/tetralins, naphthalenes - Total Recoverable Petroleum Hydrocarbons - 25 to 4,100 ppb in groundwater; >100 ppm in soil - Free product floating on groundwater has exceeded 1 ft. in thickness

Waste Source:
Underground Storage Tanks

Type/Quantity of Media Treated:
Groundwater and Free Product - Area of free product - about 600 ft. x 300 ft.; estimated volume of free product is 12,000 to 31,000 gallons - Area of groundwater contamination - about 1,000 ft. x 2,000 ft. - Properties of aquifer include pH (6.4 - 7.2), hydraulic conductivity (0.00099 - 0.002 ft/day), transmissivity (0.99 - 2.2 ft[Sub 2]/day)

Purpose/Significance of Application:
Full-scale remediation of groundwater contaminated with fuel oil using a vacuum assisted well point extraction system and aboveground air stripping.

Regulatory Requirements/Cleanup Goals:
- Groundwater: BTEX - Benzene (1.4 ppb), Toluene (2 ppb), Ethylbenzene (1 ppb), Total Xylenes (3 ppb) - Air Stripper Criteria for discharge: BTEX - Benzene (7 ppb), Toluene (50 ppb), Ethylbenzene (4.3 ppb), Total Xylenes (13 ppb), Lead (5.6 ppb) and TPH (1,000 ppb) - Cleanup conducted under Virginia State Regulations and Federal Underground Storage Tank Regulations

As of 1/94:
- Floating product--appears to be largely unaffected at this time; no estimates of the amount of free product recovered are available at this time
- Air Stripper--average concentrations from air stripper are below discharge criteria

Cost Factors:
- Total Capital Costs - $569,739 (1992) (including demolition and excavation, system installation, startup, mobilization and site preparation) - Annual Operating Costs - $216,561 (1993), $143,047 (1994) (including labor, materials, and equipment) - An estimated total cost for completing the cleanup is not available at this time

Langley AFB has operated since 1916 as an aviation research and development facility. JP-4 fuel was stored in underground storage tanks and, in 1981, twenty-four 25,000-gallon underground fuel tanks and a fuel pipeline located at IRP Site 4 were determined to be leaking. In 1987, the tanks were abandoned by cleaning and sand-cement backfilling. Subsequent remedial investigation activities detected fuel contamination in soil and groundwater, including free product floating on the groundwater table at up to 1 foot in thickness. Primary contaminants of concern at the site are BTEX (benzene, toluene, ethylbenzene, and xylenes) and total petroleum hydrocarbons (TPH).

A groundwater pump and treat system consisting of a vacuum assisted well point extraction system, oil/water separators, and air strippers, began operating in July 1992 and was operational at the time of this report. Results to date indicate that, on average, the effluent concentration of BTEX, TRPH, and lead from the air stripper are below the discharge criteria. However, the layer of free product floating on the groundwater appears to be largely unaffected at this time. In addition, an estimate of free product recovered to date cannot be made since a sample port was not installed because of vacuum inlet conditions. It was noted that such sampling points are necessary to allow quantification of system performance.

The total capital costs for this application were about $569,700 and the annual operating costs for years 1993 and 1994 were about $216,600 and $143,000, respectively. Operational difficulties including problems with scaling, oil/water separator icing, and delays in acquiring spare parts have caused the system to be down about 51% of the time. In early 1994, adjustments to the system were made, including the use of chemical additives to prevent fouling of the system. It was noted that a roof over the treatment plant would have prevented weather-related damage and downtime (i.e., icing of oil/water separator).