Story

Iowa Army Ammunition Plant US Army Corps of Engineers (USACE) Burlington, Iowa, USA

Project: Full-Scale Bioremediation of Organic Explosive Impacted Soil

Summary

RDX, an organic explosive (Hexahydro-1,3,5-trinitro-1,3,5-triazine), was the primary contaminant of concern at IAAP, due to its high initial concentration relative to its remedial goal of 53 mg/kg. Initial RDX concentrations ranged from 819 mg/kg to 2,270 mg/kg with a mean concentration of 1,530 mg/kg. Secondary contaminants included HMX and TNT. The initial HMX mean concentration was 1,112 mg/kg, and the initial TNT mean concentration was 95.8mg/kg.

The Challenge

Remediation of 6,000 cubic yards of organic explosive impacted soil with remedial goals of 53 mg/kg for TNT, RDX and HMX was the challenge. To reach these goals, removal efficiencies of greater than 97% had to be achieved for the more heavily impacted soil.

The Solution

DARAMEND®, a proprietary organic bioremediation product, was applied ex-situ on two batched samples of soil impacted with nitroaromatic explosive compounds. DARAMEND® was selected due its lack of soil bulking, its effectiveness in the presence of elevated heavy metal concentrations, and its significant cost savings over available alternatives. At the IAAP, the technology was applied ex-situ in two soil treatment units known as Trench 6 and Trench 7. DARAMEND® was applied to the soil and mixed to a depth of 2 feet using a tractor-driven deep rotary tiller. The tilling process also served to aerate and homogenize the soil. Water was then applied to increase the soil moisture content to approximately 85% of the soil water holding capacity.

These steps were repeated for each treatment cycle (every 7-10 days).

The Result

DARAMEND® bioremediation technology supported efficient removal of all target compounds in soil at the IAAP. Following the application of five treatment cycles to Trench 6 and six treatment cycles to Trench 7 over a period of approximately 8 weeks, the concentrations of RDX were reduced significantly.

The concentrations of all regulated compounds, including key degradation intermediates, were reduced to less than their respective remedial criteria in all sampling zones.

• RDX concentrations were found to range from 3 mg/kg to 32 mg/kg following treatment. The mean RDX concentration was reduced by almost 99% to 16.2 mg/kg (Figure 1).

• The mean concentration of HMX was reduced by 92.4% from 1,112 mg/kg to 84.5 mg/kg, and the mean TNT concentration was reduced by 93.7% from 95.8 mg/kg to 6.1 mg/kg.

The Cost

The USACE estimates that the overall unit cost for soil treatment at IAAP was $167/yd3 (approx. $150/ton). The Timeline From start to finish, remedial goals were met in approximately eight weeks, beginning in late August and continuing through to mid October 2001.