Monitored Natural Attenuation at the Louisiana Army Ammunition Plant, Area P, Minden, Louisiana (2001)

Site Name:

Louisiana Army Ammunition Plant

Location:

Minden, Louisiana

Period of
Operation:

Two years (dates not provided)

Cleanup
Type:

Field demonstration

Technology:
Monitored Natural Attenuation (MNA)
- Monitoring was conducted using monitoring wells (11 wells in which most analytes were consistently detected) and cone penetrometry (51 penetrations to 40 meters)
- Monitoring well samples were collected using a micropurge sampling technique

Cleanup Authority:
N/A

Principal Investigator:
Dr. Judith C. Pennington
U.S. Army Engr.
Waterways Expt. Station
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
(601) 634-2802
penninj@ex1.wes.army.mil
Site Contact:
Doyle Williams
Environmental Officer
LAAP
Hwy 80
Minden, LA 71055
(318) 459-5108

EPA Contact:
Caroline Ziegler
U.S. EPA Region 6
1445 Ross Ave, Suite 1200
Dallas, TX 75202
(214) 665-2178

Contaminants:
Explosives
- TNT and RDX (as high as 24,000 ug/L)

Waste Source:
Loading, assembling, and packing of munitions

Type/Quantity of Media Treated:
Groundwater
- Geology is a complex stratigraphy of Pleistocene, terraced fluvial deposits unconformably overlying Eocene, nonmarine, massive sands, silty sands, silty clays, and occasional lignitic beds
- Site has clay lenses and silts, low porosity, and low organic carbon

Purpose/Significance of Application:
Field demonstration of MNA for remediation of explosives

Regulatory Requirements/Cleanup Goals:
- The objectives of the demonstration were to: (1) demonstrate that attenuation of explosives can be determined through appropriate site monitoring, (2) develop guidance for selection of MNA as a remedial alternative, (3) develop guidance for establishing a site monitoring plan and points of compliance, and (4) gain regulatory acceptance for use of MNA as an alternative for remediation of explosives
- Performance criteria included comparing actual concentrations of TNT and RDX to the concentrations predicted based on site geology and hydrology; and observing transformation/degradation products of TNT and RDX

Results:
- Significant declines in contaminant concentrations were observed in 9 of the 11 monitoring wells over a two year period
- Contaminant mass was reduced from 52 to 50 metric tons for TNT, and from 78 to 68 metric tons for RDX

Cost Factors:
- Overall cost of the demonstration was approximately $4,000,000, including costs for site characterization ($2,500,000), site monitoring, modeling, and development of biomarker techniques
- Costs for use of MNA in a full-scale application were projected to be 25% less than the costs for in situ bioremediation, and 50% less than the cost for pump and treat using activated carbon adsorption

Description:
The Louisiana Army Ammunition Plant, Area P (LAAP), in northwest Louisiana, was used for loading, assembling, and packing of munitions. Wastes from this site had been disposed of in 16 unlined lagoons. In the late 1980s, the lagoons had been pumped out and the sediment excavated and incinerated, and the area was capped with clay and topsoil. Site investigations revealed the presence of TNT and RDX in the groundwater at the site.

This site was selected for a field demonstration of MNA because the source of contamination had been removed, a large amount of groundwater monitoring data was available, and there were 50 monitoring wells in place. Two years of site monitoring showed that natural attenuation is occurring at LAAP, with decreases in contaminant concentrations and mass. Site capacity and biomarker techniques also contributed to the weight of evidence by estimating process rates. Numerical models predict significant continuing reductions in contaminant masses of TNT and RDX over a 20-year period. The overall cost of the demonstration was approximately $4,000,000, including costs for site characterization, site monitoring, modeling, and development of biomarker techniques.