 |
 |
|
T.H.
Agriculture & Nutrition
(THAN) Superfund Site
Montgomery, Alabama, USA
Project
Bioremediation of Pesticide Impacted
Soil/Sediment
Summary
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.
The Challenge
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.
The Solution
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 Result
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 Cost
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.
The Timeline
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).
|
|
