PHYTOREMEDIATION RESEARCH CASE STUDY:
Project Name: Iowa Army Ammunitions Plant Constructed Wetlands (Kiker et al 2001, Thompson, Moses and Howe 2003)
Location: Middletown, Iowa
Scientists: Dr. Steve Larson, Research Chemist with U.S. Army Corps of Engineers ERDC, Randy Sellers Biologist with the U.S. Army Corps of Engineers – Omaha, Jackson Kiker, Chemist formerly with the U.S. Army Corps of Engineers – Omaha, Don Moses, Civil Engineer, U.S. Army Corps of Engineers
Date installed: 1997
Planting Description: Constructed wetlands were created and new depressions were lined with soil collected from local lakes. This provided a seed bank for future growth of wetland vegetation.
Dominant vegetation at the constructed wetlands is:
Rice Cutgrass (Lersia oryzoides), Smartweed (Polygonum punctatum), Reed canarygrass (Phalaris arundinacea), reshwater algae (Spirogyra spp), Barnyard Grass (Echinochloa crusgalli Michx.)Pondweed (Potemogeton sp.), Water Plantain (Alisma subcordatum), Arrowhead (Sagittaria sp.), Coontail (Ceratophylum demersum), Stonewart (Chara)
Amendments: Local lake sediments used as a seedbank
Contaminants: TNT 2,4,6 – Trinitrotoluene in soils and RDX Hexahydro – 1,3,5 – triazine within surface and groundwater
Target Media & Depth: Surface and groundwater. RDX levels reduced from 778 micrograms/liter to below 2 micrograms/liter from January to July of 1998 and reductions have continued through 2013 to meet regulatory discharge limits. TNT in soils has not been remediated.
The Iowa Army Ammunitions plant is a 19,000 acre facility in South Eastern Iowa that has produced ordnance and warheads for the Department of Defense since 1940. Isolated areas within the site were extensively contaminated with explosives related to the disposal of munitions, creating large volumes of wastewater containing TNT and RDX . Contaminated surface waters on the site were often referred to as “Pinkwater” due to the color change caused by explosives contamination. In 1990, the plant was listed by the US EPA as a Superfund site.
In 1997, two of the most contaminated areas of the Iowa Army Ammunitions plant – the Line 1 Impoundment and Line 800 Lagoon – were excavated to remove most of the contaminated soil. Instead of being backfilled, the areas were reclaimed as engineered wetlands that would treat contaminated surface and groundwater. This was the first full scale known phytotechnology system designed to treat explosives contaminated water. The goal was to reduce contamination levels to below the 2 ppb EPA health advisory lifetime level. Phytotechnology as a remediation option was chosen due to low cost. The excavated areas were lined with sediment from a nearby lake that acted as a seed source to spur the growth of wetland vegetation of over 50 different species. Line 1 is now a 3.6 acre constructed wetland, while Line 800 is a 5-acre wetland. Both are dominated by grasses and emergent vegetation. The wetlands have been successful in explosives reduction to meet regulatory discharge limits, except in winter when the planting vegetation is dormant. At these times of the year, the water must be held and discharged when the growing season again is underway.