Purus PADRE® Regenerative Resin System for the Treatment of Hydrocarbon Vapors from Fuel-Contaminated Soils

Site Name:

Vandenberg Air Force Base

Location:

Lompoc, CA

Period of
Operation:

2/11/94 to 6/1/94

Cleanup
Type:

Field demonstration

Technology:
Resin Adsorption (supplement to SVE)
- Demonstration used a Purus Padre® Model 1.6 vapor treatment system to treat hydrocarbon vapors removed using soil vapor extraction (5 SVE wells; flow rates 20 49 scfm)
- System used filter beds filled with synthetic polymeric adsorbent (PurSorb_ 200); preceded by a water and dirt trap; two beds were used with 180 lbs adsorbent/bed; beds were switched between adsorption and desorption cycles
- In the desorption cycle, organic material was volatilized, condensed, and transferred to a tank; 2-stage condenser operated at 2oC and 45oC
- Treated soil gas with less than 1,000 ppm total hydrocarbons was returned to the soil using a perimeter injection trench for in situ biotreatment

Cleanup Authority:
Santa Barbara County Air Pollution Control District
California Department of Toxic Substances
Central Coast Regional Water Quality Control Board

Vendor:
Purus Inc.
2713 N. First Street
San Jose, CA 95134-2000
Sponsor:
U.S. Air Force
Center for Environmental Excellence
Technology Transfer Division
Brooks AFB, TX

Contaminants:
Petroleum hydrocarbons and BTEX
- Maximum concentrations in soil: TPH-gasoline - 22,000 mg/kg; benzene 210 mg/kg; toluene - 2,000 mg/kg; ethylbenzene 490 mg/kg; xylenes 2,900 mg/kg
- Maximum concentrations in soil gas: volatile hydrocarbons - 54,000 ppmv; benzene 400 ppmv

Waste Source:
Leaks from USTs

Type/Quantity of Media Treated:
Soil vapors
- Contamination found within a permeable silty sand, extending from 3 to 14 ft bgs
- Depth to groundwater varies from 7 to 9 ft bgs and fluctuates seasonally
- Impermeable clay bed located between 14 and 20 ft bgs
- Soil vapor depleted of oxygen due to fuel biodegradation

Purpose/Significance of Application:
Treatment of extracted vapors from an SVE system

Regulatory Requirements/Cleanup Goals:
- Objectives of the demonstration included evaluating the performance and cost of the Purus Padre® technology
- No air emission permit was required; instead operating conditions were established for ambient air, flux emissions, and site emissions

Results:
- Average soil vapor concentrations reduced by factor of 5 during first 18 days of treatment and by factor of 20 during 110th day of operation, with increase in oxygen content
- Resin system removal rates averaged > 98% for total hydrocarbons and >99% for benzene
- The system recovered approximately 570 gallons of hydrocarbons (1,600 kgs; 3,520 lbs) and 70 gallons of water during the 110 day demonstration

Cost Factors:
- Demonstration costs were $36,634, consisting of setup - $2,500; rental - $25,667; operation labor - $4,500; power - $1,212; nitrogen - $1,760; and mobilization/demobilization - $1,000
- Total treatment cost corresponded to a unit cost of $23/kg ($10.45/lb) of hydrocarbons removed
- A comparison of technologies showed that internal combustion engine technology will be less expensive that Purus Padre® at fuel spill sites

Description:
In 1985, two 10,000 gallon unleaded gasoline tanks and associated piping were removed from the Vandenburg AFB BX service station. Two additional gasoline storage tanks and a 250-gallon waste oil tank were removed in 1991. Hydrocarbon contamination was discovered in soil and groundwater beneath the tanks. A two-phased bioventing pilot test began on February 11, 1994. During phase one, high levels of hydrocarbon vapors were removed using soil vapor extraction, treated using a Purus Padre® resin adsorption unit, and returned to the soil using a perimeter injection trench for in situ biotreatment. When the average soil gas concentrations had been reduced to less than 1,000 ppmv, the Purus Padre® unit was removed and soil gas returned directly through the trench.

This demonstration used a Purus Padre® Model 1.6 vapor treatment system to treat hydrocarbon vapors removed using five soil vapor extraction wells, with a total flow rate of 20 49 scfm. The system used filter beds filled with PurSorb_ 200; 180 lbs adsorbent/bed were used. System removal rates averaged > 98% for total hydrocarbons and >99% for benzene, and recovered approximately 570 gallons of hydrocarbons (1,600 kgs). Demonstration costs were $36,634, corresponding to a unit cost of $23/kg of hydrocarbon removed. This system was found to be an effective method of controlling vapor emissions.