Technology:
Thermal Desportion
- Low temperature thermal desorption (LTTD) system; included six main units - feed system, rotary dryer, baghouse, thermal oxidizer, wet quench, and acid gas scrubber
- Stainless steel, direct-heated rotary kiln dryer approximately 40 ft long and 8.5 ft in diameter; 49 million BTU/hr propane-fired burner, and discharge screw
- Residence Time - 15 to 20 minutes; system throughput - 30 tons of soil/hr; soil exit temperature - 725°F to 750°F; thermal oxidizer exit gas temperature - > 1,810°F
- Contaminated soil screened with a PowerScreen Model Mark IV to remove debris >2 in. long
- Treated soil was moisturized and backfilled on site
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Cleanup Authority:
CERCLA
Contacts:
EPA Contact
Lynda Priddy
U.S. EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
Telephone: (206) 553-1987
Fax: (206) 553-0149
E-mail: priddy.lynda@epa.gov |
Contaminants:
- p,p’-DDD (DDD), p,p’-DDT (DDT), p,p’-DDE (DDE), hexachlorobenzene, toxaphene, bis(2-ethylhexyl)phthalate, lead, and zinc |
Waste Source:
Pesticide formulation operations and management of liquid wastes in lagoons |
Type/Quantity of Media Treated:
Soil/26,000 tons |
Purpose/Significance of Application:
Use of low temperature thermal desorption to treat soil contaminated with a wide range of organochlorine pesticides, including DDT |
Regulatory Requirements/Cleanup Goals:
- Cleanup goals were established for 15 organochlorine pesticides as well as arsenic, lead, and mercury in soil
- Goals for pesticides ranged from 0.0588 mg/kg for Aldrin to 400 mg/kg for Methoxychlor. The goal for DDT, one of the most prevalent contaminants at the site, was 2.94 mg/kg
- State’s maximum acceptable source impact levels (ASILs) were identified for ground level air and stack emissions |
Results:
- Treated soil met the cleanup goals for the 15 organochlorine pesticides and the three metals
- DDT concentrations were reduced to an average of 0.18 mg/kg
- Initially the system did not meet the performance objectives for particulate air emissions, with the average particulate concentration of 0.04 gr/dscf greater than the required 0.03 gr/dscf (corrected to 7% O2); the system was modified and subsequently met all performance objectives |
Cost Factors:
- The total cost for the LTTD application was $3,260,517, including $429,561 in capital cost and $2,830,956 in O&M costs
- The unit cost was $125 per ton, based on 26,000 tons of soil treated |
Description:
Site B (actual site name and location confidential) in the western United States was used for formulation of pesticides from 1938 to 1985. Wastes from the formulation process and an on-site laboratory were discharged to a french drain/sump area and to lagoons. Site characterization activities performed in 1986 showed elevated levels of pesticides in the soil, including p,p’-DDD (DDD), p,p’-DDT (DDT), p,p’-DDE (DDE), hexachlorobenzene, toxaphene, bis(2-ethylhexyl)phthalate, lead, and zinc. As part of a removal action conducted by EPA in1993, soils were excavated and thermal desorption was used to treat contaminated soil.
Thermal treatment system was performed from April to August 1995 using a low temperature thermal desorption (LTTD) system owned by Williams Environmental Services, Inc. The LTTD system included included a feed system, rotary dryer, baghouse, thermal oxidizer, wet quench, and acid gas scrubber. The rotary dryer was a stainless steel direct-heated rotary kiln (40 ft long and 8.5 ft in diameter) fired by a 49 million BTU/hr propane-fired burner. Prior to treatment, contaminated soil was screened to remove oversize material (> 2in.). A total of 26,000 tons of soil was treated with the treated soil meeting the cleanup goals for the 15 pesticides and three metals of concern. Treated soil was moisturized and use as backfill on site. The cost for this application was $3,260,517, including $429,561 in capital cost and $2,830,956 in O&M costs for a unit cost of $125 per ton of soil treated.
Initially the system did not meet the objective set for particulate emissions, attributed to operational problems with the demisters and scrubber. System modifications to address this problem included replacing the fabric mesh demisters in the scrubber with stainless steel chevron demisters, increasing the critical velocity capacity of the demisters, and increasing the blowdown rate from the scrubber to reduce the amount of salts being recycled in the scrubber water. The system met then met its performance objective. |
