Phytoremediation at Naval Air Station - Joint Reserve Base Fort Worth, Fort Worth, Texas

Site Name:

Naval Air Station - Joint Reserve Base Fort Worth

Location:

Fort Worth, Texas

Period of
Operation:

April 1996 - Ongoing (expected demonstration project completion in 2006) (data available through 2001)

Cleanup
Type:

Field demonstration

Technology:
Phytoremediation
- In April 1996, 660 eastern cottonwood trees were planted at two plantations in a 4,000-square meter area.
- Two types of trees were planted (whips and calipers).
- Demonstration area is located approximately 1.5 kilometers downgradient from the origin of contaminated groundwater plume.

Cleanup Authority:
Field demonstration

Contacts:
Greg Harvey
U.S. Air Force, ASC/EMR
1801 10th Street - Area B
Wright Patterson AFB, OH 45433
Tel: 937-255-3276
Fax: 937-255-4155
E-mail: Gregory.Harvey@wpafb.af.mil

Contaminants:
Chlorinated solvents (TCE - maximum concentration 1,000 ug/L)

Waste Source:
Manufacture and assembly of military aircraft

Type/Quantity of Media Treated:
Groundwater
- Shallow (under 12 ft) aerobic aquifer

Purpose/Significance of Application:
Long-term field demonstration of phytoremediation for treatment of chlorinated solvents in groundwater

Regulatory Requirements/Cleanup Goals:
- Primary performance objectives include reducing mass of TCE in the aquifer transported across the downgradient end of the site (1) by 30% during the second growing season and (2) by 50% during the third growing season, as compared to baseline TCE mass flux calculations. To assess the primary objective, groundwater levels were measured to evaluate hydraulic control and samples were collected and analyzed for TCE.
- Secondary objectives, such as analyzing contaminant uptake into plants and evaluating tree transpiration rates, were also addressed.

Results:
- TCE Mass Flux and Hydraulic Control - During the first 3 years of the demonstration, the maximum observed reduction in the mass flux of TCE across the downgradient end of the demonstration site was 11 percent, which occurred at the peak of the third growing season.
- TCE Concentrations in Tree Samples - In October 1998 (third growing season), all five whip and five caliper trees sampled contained detectable levels of TCE in the stems with an average concentration of 32.8 ug/kg for whips and 24.6 ug/kg for caliper trees.
- TCE Transformation Kinetics - Seven types of trees located near the demonstration study area were sampled to determine the kinetics of TCE transformation. Each species appeared to have properties effective for degrading TCE.
- TCE Concentrations in Groundwater - Within three years of planting, there was evidence that the aquifer was supporting anaerobic microbial populations capable of biodegrading TCE. Average TCE concentrations were reduced site-wide from 532 ug/L in July 1997 to 182 ug/L in July 2001.
- Transpiration Rates - In 1997 (second growing season), the total average daily transpiration rate was estimated at 1,872 liters per day for the caliper-tree plantation and 1,750 liters per day for the whip plantation. After five years, caliper trees transpired nearly four times the water (79 liters per tree per day) as the whip trees (19 liters per tree per day).
- Groundwater Chemistry Parameters - Preliminary field data collected during the fifth dormant season (January 2001) indicate that the trees were beginning to have a widespread effect on groundwater geochemistry, reducing dissolved oxygen content beneath the plantations to less than 1 mg/L in some wells.
- Tree Parameters - Root biomass and extent were examined in September 1997 (the second growing season). At that time, the roots of both the whips and caliper trees had reached the water table and the depth distribution of the roots was similar. Overall, trees in both
plantations grew well and significantly increased in all physical parameters measured.

Cost Factors:
Total capital cost for this demonstration was $193,200, which included $22,000 for preparatory work and $171,200 for site work. Annual costs totaled $252,000, which included $2,000 for O&M; and $250,000 for research level monitoring of groundwater, soil, vegetation, transpiration, climate, soil moisture, and water levels. Based on the costs incurred during this demonstration study, full-scale costs for a 18,600 square meter phytoremediation research model were estimated at $466,000.

Description:
Groundwater at the U.S. Air Force Plant 4 and adjacent Naval Air Station - Joint Reserve Base (NAS-JRB) Fort Worth became contaminated with chlorinated solvents from operations associated with the manufacture and assembly of military aircraft. The contamination was first noted in September 1982. A demonstration of phytoremediation to clean up shallow groundwater is being performed at the site by the U.S. Air Force as part of the Department of Defense's Environmental Security Technology Certification Program (ESTCP) and U.S. Environmental Protection Agency’s Superfund Innovative Technology Evaluation (SITE) Program. In April 1996, 660 eastern cottonwood trees were planted at two plantations in the demonstration area. Within three years of planting, there was evidence that the aquifer was supporting anaerobic microbial populations capable of biodegrading TCE. After three growing seasons at NAS-JRB Fort Worth, the trees reduced the mass of contaminants moving through the site. The maximum observed reduction in the mass flux of TCE across the downgradient end of the site during the demonstration period was 11 percent. In October 1998 (third growing season), all five whip and five caliper trees sampled contained detectable levels of TCE in the stems with an average concentration of 32.8 ug/kg for whips and 24.6 ug/kg for caliper trees.

Preliminary field data collected during the fifth dormant season (January 2001) indicated that the trees were beginning to have a widespread effect on groundwater geochemistry, reducing dissolved oxygen content beneath the plantations to less than 1 mg/L in some wells. From July 1997 to July 2001, average TCE concentrations were reduced site-wide from 532 ug/L to 182 ug/L. Overall, trees in both plantations grew well and significantly increased in all physical parameters measured. The total cost for the demonstration included $22,000 for site preparation; $171,200 for site work; and $2,000 for annual O&M. Additional costs included approximately $250,000 annually for research level monitoring. The demonstration study is expected to be completed in 2006.