Bioremediation of Pesticide Impacted Soil/Sediment
Soil and sediment (~4,500 tons) impacted with Toxaphene, DDT, DDD and DDE were excavated from impacted areas on the site, including a surface water drainage way. Impacted soils were placed in a prepared bed on site and a cycled, anaerobic/aerobic bioremediation treatment protocol was administered. Following the application of 3 to 12 treatment cycles, Toxaphene, DDT, DDE, and DDD concentrations were reduced by 95%, 89%, 71%, and 76%, respectively.
Toxaphene, DDT, and DDD exceeded remedial objectives in most areas of the site. Toxaphene and DDD concentrations, in particular, were highly elevated in some areas. We believe that Toxaphene and DDD concentrations in this range have never been successfully remediated using a biological treatment technology.
Application of DARAMEND®, a proprietary organic amendment, and powdered iron through repeated and sequential application generate anaerobic and aerobic conditions. Amendments are incorporated to a depth of two feet using a specialized deep rotary tiller. Water is then applied to bring soil moisture content up to 90% of the soil water holding capacity (WHC). These steps are repeated for each treatment cycle.
The remedial goals (i.e., Toxaphene ≤ 29 mg/kg, DDT ≤ 94 mg/kg, DDD ≤ 132 mg/kg, and DDE ≤ 94 mg/kg) were reached in all areas of the treatment cell following the application of 3 to 12 treatment cycles. The number of treatment cycles required to reach the remedial goal was primarily dependent on the initial concentrations. Analytical results indicate that mean Toxaphene, DDT, DDD, and DDE concentrations were reduced from 189 mg/kg, 81 mg/kg, 180 mg/kg, and 25 mg/kg to 10 mg/kg, 9 mg/kg, 52 mg/kg, and 6 mg/kg, respectively. This corresponds to removal and destruction efficiencies (RDE) of 95%, 89%, 71%, and 76%.
In some sampling zones, initial pesticide concentrations were much higher than the mean concentrations, and performance in these zones was correspondingly more effective. For example, Toxaphene, DDT, DDD, and DDE concentrations were reduced from 720 mg/kg, 227 mg/kg, 590 mg/kg, and 65 mg/kg to 10.5 mg/kg, 15 mg/kg, 87 mg/kg, and 8.6 mg/kg, respectively, in heavily impacted regions of the site. This corresponds to RDEs of 99%, 94%, 85%, and 87%.
The treatment cost per ton varied according to the initial concentration and ranged between $29/ton and $63/ton. The average unit cost for the treatment of approximately 4,500 tons of soils was approximately $55/ton.
As indicated above, variable contaminant concentrations resulted in variable treatment time requirements. Remedial goals were reached after three treatment cycles (6 weeks) in less heavily impacted regions on the site, while the most heavily impacted areas required 12 treatment cycles (24 weeks). On average, remedial goals were achieved following the application of approximately 8 treatment cycles (16 weeks).