Soil Vapor Extraction at the Rocky Mountain Arsenal Superfund Site, Motor Pool Area (OU 18), Commerce City, Colorado

Site Name:

Rocky Mountain Arsenal Superfund Site


Commerce City, Colorado

Period of

July 1991 to December 1991


Full-scale cleanup


Rick Beyak
Woodward-Clyde Federal Services
4582 S. Ulster St., Suite 1200
Denver, CO 80237
(303) 740-2600

Soil Vapor Extraction - 1 shallow vapor extraction well and 1 deep vapor extraction well - Shallow well screened between 13 and 28 feet below ground surface (bgs); deep well screened between 43 and 58 feet bgs - Liquid/vapor separator tank, sediment filter, and regenerative blower - Exhaust air from blower treated using two granular activated carbon systems in series

Cleanup Authority:
CERCLA - Federal Facilities Agreement - ROD Date: 2/26/90

SIC Code:
7699 (Repair Shops
and Related Services,
Not Elsewhere Classified)
Point of Contact:
James D. Smith
Program Manager
Rocky Mountain Arsenal
Commerce City, CO 80022-1749
(303) 289-0249

Chlorinated Aliphatics - Trichloroethylene (TCE) - Levels of TCE in soil vapor of up to 65 ppm

Waste Source:
Other: Motor Vehicle, Railcar, and Heavy Equipment Maintenance, Repair, and Cleaning Activities

Type/Quantity of Media Treated:
Soil - 34,000 yd3 (70 ft radius by 60 ft deep) - Unconsolidated deposits beneath Motor Pool Area consist of discontinuous sand and gravel lenses - 1-3 foot low-permeability clayey sand to clay layer 32 to 38 feet bgs - Moisture content - 4.7 to 30.9%; permeability - 167 darcys at 38 ft bgs and 2,860 darcys at 55 ft bgs

Purpose/Significance of Application:
This application demonstrated that a pilot-scale SVE system removed sufficient vapor contaminants from the vadose zone, and expansion of the system beyond a pilot-scale was not necessary.

Regulatory Requirements/Cleanup Goals:
- No specific cleanup goals were specified for Motor Pool Area OU-18

- TCE concentrations decreased to less than 1 ppm after 5 months of operation of the SVE system - Rate of TCE extraction decreased from 35 pounds per month to less than 10 pounds per month - Approximately 70 pounds of TCE removed during operation of the system

Cost Factors:
- Costs attributed to treatment activities: $75,600 (installation and operation) - Costs attributed to before-treatment activities: $88,490 (including mobilization and preparatory work, monitoring, and laboratory analytical) - Costs attributed to after-treatment activities: $19,650 (including pilot study)

Soil vapor extraction (SVE) was performed at the Rocky Mountain Arsenal (RMA) Superfund site, Motor Pool Area, in Commerce City, Colorado to remove halogenated volatile organic compounds (VOCs), primarily trichloroethylene, from the vadose zone. The Motor Pool Area at RMA, referred to as Operable Unit 18, had been used for cleaning and servicing equipment, vehicles, and railroad cars, and for storing diesel, gasoline, and oil products in aboveground and underground storage tanks. VOCs, detected in the Motor Pool Area's soil and groundwater have been attributed to releases of chlorinated solvents used during cleaning operations; these solvents were discharged through floor drains and pipes into unlined ditches at the site.

This system was initially considered to be a pilot study because it was expected to provide performance data on SVE at this site that could be used to expand the system to a full-scale operation. This application, operated from July to December 1991, demonstrated that a pilot-scale SVE system removed sufficient vapor contaminants from the vadose zone, and expansion of the system beyond pilot-scale was not necessary. The SVE system used within the Motor Pool Area consisted of one shallow vapor extraction well and one deep vapor extraction well. Four clusters of vapor monitoring wells were installed to aid in the assessment of the performance of the SVE system. TCE levels in soil vapors collected from the vapor monitoring wells were reduced to non-detect or to levels of less than 1 ppm from initial vapor monitoring well samples as high as 65 ppm. Approximately 70 pounds of TCE were recovered during this cleanup action.

The operating parameters collected during the system's 1991 operation indicated that a clay lense located beneath the site affected the SVE system's performance by limiting both the shallow and deep vapor extraction wells' vertical zones of influence. The contract award cost for procuring, installing, and operating the SVE pilot system, as well as preparing a pilot study report was $182,800. This cost was approximately 15% less than the preliminary cost estimate provided by the remediation contractor for the project. Factors contributing to the lower cost included lower construction and system operating costs.