Bioslurping of LNAPL at Multiple Air Force Sites

Site Name:

Multiple AF Sites

Location:

Multiple locations throughout U.S.

Period of
Operation:

Periods of operation were not provided for each site

Cleanup
Type:

Field Demonstration

Technology:
Bioslurping
- Field demonstration of bioslurping applied vacuum in an extraction well to recover LNAPL and induce airflow through the unsaturated zone
- Equipment included a tube placed in a well with the tip near the water table level, and operated with a vacuum of up to 20 inches of mercury

Cleanup Authority:
Not provided

Technical Contact:
Battelle
505 King Avenue
Columbus, OH 43201
Management Contact:
Jeff Cornell
Air Force Center for Environmental Excellence
Technology Transfer Division
Brooks AFB, TX 78235
E-mail: jeff.cornell@hqafcee.brooks.af.mil

Contaminants:
Light Non-aqueous Phase Liquids (LNAPL); Petroleum Hydrocarbons
- LNAPL thickness ranged from 0.12 ft to 3.89 ft; for the 18 sites, 9 had thickness as less than 1 ft, 3 from 1 - 2 ft, and 6 with more than 2 ft
- Fuel types consisted of No. 2 fuel oil, gasoline, jet fuel, aviation gasoline, and JP-4; 10 of the 18 sites had JP-4

Waste Source:
Not provided

Type/Quantity of Media Treated:
LNAPL
- Depths to groundwater ranged from 8 to 37 ft bgs
- Pressure radius of influence ranged from 12 to 250 ft
- Hydraulic conductivity ranged from 0.23 to 23.78 ft/day

Purpose/Significance of Application:
Field demonstrations of bioslurping of LNAPL at multiple Air Force sites

Regulatory Requirements/Cleanup Goals:
- Goals of the demonstration included recovering the "maximum quantity" of LNAPL
- Bioslurping was evaluated relative to the performance of skimming and drawdown pumping for the 18 sites in the study

Results:
- The LNAPL recovery rates for bioslurping ranged from <0.1 to 64.2 gal/day, compared to skimming and drawdown pumping at 3.1 gal/day and 4.5 gal/day, respectively
- The groundwater removal rates for bioslurping ranged from <30 to 4,600 gal/day, compared to drawdown pumping at 1,640 gal/day and <29 gal/day for skimming
- The off-gas flow rate from the bioslurper systems was 65 scfm (9 wells, each producing 7.2 scfm), while the skimming and drawdown systems had negligible off-gas flows

Cost Factors:
- Projected costs for a bioslurping system was capital cost of $92,507 and monthly operating cost of $12,342; the overall cost for capital and 6 months of operation was less for the bioslurper than for either the skimming or drawdown systems identified in the study
- Projected costs for a skimming system was capital cost of $110,328 and monthly operating cost of $11,120; projected costs for a single pump drawdown system was capital cost of $131,172 and monthly operating cost of $11,268
- A calculated unit cost for bioslurping was $56/gal LNAPL recovered, which was less than the unit cost for skimming ($339/gal) or drawdown ($260-312/gal)

Description:
The Air Force Center for Environmental Excellence (AFCEE) conducted an engineering evaluation and cost analysis of vacuum enhanced free product recovery (bioslurping), including a comparison of bioslurping with other free product recovery techniques skimming and drawdown pumping. Field demonstrations of bioslurping were conducted at 18 Air Force sites throughout the country.

The sites included in the evaluation showed that bioslurping recovered LNAPL at a higher rate than either skimming or drawdown pumping. The bioslurping and drawdown systems removed comparable amounts of water, while the skimming system removed negligible water. The bioslurper had measurable off-gas flow rates, while the other two systems had negligible flow rates. An analysis of costs showed that the overall cost for capital and 6 months of operation was less for the bioslurper than for either the skimming or drawdown systems identified in the study.