Story

Yorktown Naval Weapons Station Yorktown, Virginia, USA

Project: Full-Scale Bioremediation of Organic Explosives and Chlorinated Solvents in Soil & Sediment

Summary

Soils and sediments (~5,000 yd3) impacted with organic explosive compounds and chlorinated solvents were treated ex-situ in a covered land treatment unit containing approximately 1,200 yd3. In the first four batches, the initial mean TNT concentration was generally near 10,000 mg/kg and was reduced by greater than 99.9% following treatment. Similarly, the mean RDX and DNT concentrations for the first four batches were reduced by over 98.4%.

The Challenge

In total, an estimated 9,000 yd3 of soil is to be treated at Yorktown Naval Weapons Station. Remedial goals for TNT, RDX, and DNT are 14mg/kg, 5mg/kg, and 44 mg/kg, respectively. To reach these goals, removal efficiencies of over 99% must be achieved.

The Solution

DARAMEND®, a proprietary organic bioremediation product, was applied ex-situ on four 1,200 ton batches of soil heavily impacted with organic explosives. DARAMEND® was applied to the soil surface and incorporated to a depth of 2 feet with simple soil mixing equipment. Mixing also aerated and homogenized the soil. Water was applied to increase soil moisture content.

These steps are repeated through each treatment cycle (usually 7 – 10 days). Subsequently, a decision was made to employ an innovative treatment application method on additional, less heavily impacted soils at the site. This pre-treatment step, applied in place at the excavation site, would reduce the organic explosive concentrations prior to moving sediment to the bioremediation treatment cell. This would reduce treatment time for each batch. Pretreatment is expected to substantially reduce the volume of soil to be moved to the treatment cell, as concentrations of organic explosives in these lightly contaminated soils may be reduced to levels below the remedial standards during pre-treatment.

The Result

DARAMEND® bioremediation technology supported efficient removal of all target compounds in soil and sediment at Yorktown Naval Weapons Station to levels well below the cleanup criteria for each of the first four batches.

• TNT concentrations were reduced by 99.9% (15,359 mg/kg to below 14 mg/kg in fourth treatment batch)

• RDX concentrations were reduced by 99.9% (1,090 mg/kg to 1.6 mg/kg in third treatment batch)

• Total amino-DNT concentration was reduced by 98.7% (1,002 mg/kg to 13 mg/kg in first treatment batch)

To our knowledge, this is the only case in which soil containing organic explosives at more than 10,000 mg/kg has been successfully treated without dilution.