Phytoremediation Using Constructed Wetlands at the Milan Army Ammunition Plant, Milan, Tennessee

Site Name:

Milan Army Ammunition Plant


Milan, Tennessee

Period of

June 17, 1996 to July 21, 1998


Field demonstration


Technology Research Biologist:
Dr. Susan L. Sprecher
Chemical Control Technology
U.S. Army Corps of Engineers
Waterways Experiment Station, ES-p
3909 Halls Ferry Rd.
Vicksburg, MS 39180-6199
(601) 634-2435
Fax: (601) 634-2617

Constructed Wetlands
- Two types of wetlands were demonstrated - a gravel-based system and a lagoon-based system
- Both systems were designed to retain groundwater for approximately 10 days at an influent flow rate of 5 gpm per system
- The gravel system consisted of two 4 ft deep gravel-filled beds (cells) connected in series and planted with emergent plants; the first cell (0.088 acre) was maintained as anaerobic (by carbon addition) and the second cell (0.030 acre) as aerobic; emergent plants used were canary grass, wool grass, sweetflag, and parrotfeather
- The lagoon system consisted of two 2 ft deep lagoons (cells) connected in series and planted with submergent plants
- The demonstration was conducted in three phases - (I) plant screening and treatability studies; (II) design, construction, and 16 months of monitoring; and (III) longer-term monitoring and optimization

Cleanup Authority:
Not identified

AEC Project Manager:
Darlene F. Bader
U.S. Army Environmental Center
5179 Hoadley Road
APG, MD 21010-5401
(410) 436-6861
Fax: (410) 436-6836
TVA Program Manager:
Richard A. (Rick) Almond
Tennessee Valley Authority
Reservation Road CEB 4C
Muscle Shoals, AL 35661
(256) 386-3030
Fax: (256) 386-3799

- Total nitrobody (the sum of the following six explosives: TNT, RDX, HMX, TNB, 2A-DNT, and 4A- DNT) concentrations in groundwater ranged from 3,250 to 9,200 ppb
- TNT concentrations in groundwater ranged from 1,250 to 4,440 ppb
- RDX concentrations in groundwater ranged from 1,770 to 4,240 ppb
- HMX concentrations in groundwater ranged from 87 to 110 ppb

Waste Source:
Industrial wastewater discharged to ditches

Type/Quantity of Media Treated:
- Groundwater flow north-northwest

Purpose/Significance of Application:
Use of constructed wetlands for treatment of explosives-contaminated groundwater

Regulatory Requirements/Cleanup Goals:
- Reduce concentration of TNT to less than 2 ppb, and total nitrobody concentrations (see contaminants) to less than 50 ppb

- The gravel-based system performed better than the lagoon-based system
- The gravel system reduced TNT, RDX, and HMX concentrations to below the cleanup goals during all but the coldest months; in addition, a sustainable ecosystem was established
- The lagoon system met the cleanup goal for TNT of 2 ppb only during the first 50 days of the demonstration, but did not remove RDX and HMX or meet the total nitrobody goals; in addition, an adequate plant population was not maintained within the lagoon system

Cost Factors:
- Projected costs for a 10-acre, full-scale, gravel-based system designed to treat 200 gpm of contaminated groundwater at Milan AAP were $3,466,000 ($1998).
- Assuming a 95% system availability and 30-yr life, the total cost (capital plus O&M) for use of this system was estimated as $1.78 per 1,000 gals of groundwater

The Milan Army Ammunition Plant (MAAP) is a government-owned, contractor-operated military industrial installation within the U.S. Army Industrial Operations Command. The original facility was constructed during World War II. MAAP is located on 22,436 acres of land, which include approximately 548 acres for various production lines, 7,930 acres for storage areas, and 1,395 acres for administrative, shop maintenance, housing, recreation, and other functions. From World War II to 1981, MAAP's production facilities discharged explosives-contaminated wastewater directly into open ditches that drained from sumps or surface impoundments into local streams. Several of these drainage ditches became contaminated with explosive residuals which leached into the groundwater. In 1981, the production facility's wastewaters were redirected to explosives-contaminated wastewater treatment plants.

A wetlands demonstration system was constructed in Area K adjacent to Building K-100. The demonstration consisted of gravel- and lagoon-based systems, and was conducted over a two-year period. The study found that the gravel-based system had results better than the lagoon system, and met the goals during all but the coldest months. The lagoon system did not consistently meet the goals, and had several operational problems, including a severe tadpole infestation and a hailstorm. The demonstration study authors concluded that a wetland's economic and technical feasibility depends on site-specific factors such as regional temperature variations, rainfall patterns, groundwater flow characteristics, explosive type and concentration, the presence of other contaminants, and regulatory requirements. In general, they found that wetlands perform better in warmer climates with moderate levels of rainfall.