Hydrous Pyrolysis Oxidation/Dynamic Underground Stripping (HPO/DUS) at Visalia Superfund Site, CA

Site Name:

Visalia Superfund Site

Location:

Visalia, CA

Period of
Operation:

June 1997 to mid-1999

Cleanup
Type:

Field demonstration

Vendor:

Steam Tech Environmental Services

Technology:
Hydrous Pyrolysis Oxidation/Dynamic Underground Stripping
- DUS involved continuous injection of steam and air into permeable zones over a 5 month period to create a steam front, which swept contaminants from the injection wells toward extraction wells; when the steam front collapsed, groundwater reentered the treatment zone and the steam/vacuum extraction cycle was repeated in a process called "huff and puff"
- System used 11 injection and 8 extraction wells; steam and air were injected to 80 - 100 ft bgs in paired wells; average temperature was 60oC (maximum 140oC), with groundwater extracted at 350 - 400 gpm
- Extracted vapors initially were treated with carbon; however, because of the expense of the carbon, it was replaced with treatment in steam boilers
- Extracted groundwater was treated with filtration and discharged to a POTW
- HPO occurred after the steam and air injection stopped, when groundwater returned to the heated zone and mixed with oxygen; contaminants were rapidly oxidized in this environment
- Underground mapping was performed using 29 electrical resistance tomography (ERT) wells and thermocouples to track the steam fronts and heated areas
- It was expected that the ground would remain warm for years

Cleanup Authority:
CERCLA - ROD 6/10/94

Site Contact:
Southern California Edison

Technical Contacts:
Robin Newmark
Lawrence Livermore National Laboratory
Telephone: (925) 423-3644
E-mail: newmark1@llnl.gov

Roger Aines
Lawrence Livermore National Laboratory
Telephone: (925) 423-7184
E-mail: aines1@llnl.gov

Other Contacts:
James Wright
DOE SRS
Telephone: (803) 725-5608
E-mail: jamesb.wright@srs.gov

Kathy Kauffman
LLNL
Telephone: (925) 422-2646
Regulatory Authority:
Kathi Moore
U.S. EPA Region 9
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-2221

Contaminants:
Semivolatiles Halogenated and Nonhalogenated
- Creosote and pentachlorophenol were the primary contaminants

Waste Source:
Wood preservation operations

Type/Quantity of Media Treated:
Groundwater
- Three distinct water-bearing zones are present; shallow aquifers from 35 to 75 ft bgs, an intermediate aquifer from 75 to 105 ft bgs, and a deep aquifer below 120 ft bgs; the HPO/DUS system targeted the intermediate aquifer

Purpose/Significance of Application:
Use of HPO/DUS for treatment of large quantity of creosote in groundwater

Regulatory Requirements/Cleanup Goals:
- Evaluate the performance of DUS/HPO for removing creosote

Results:
- During 25 months of operation, a total of 1,130,000 lbs (141,000 gals) of creosote were removed or treated (10,400 lbs/wk)
- Approximately 50% of the contaminants were removed in free phase, 16% as vapors, 16% in an aqueous phase, and 17% destroyed by HPO in situ
- Monitoring the progress of the heating fronts showed that all the aquifer was treated

Cost Factors:
- A comparison of projected costs for use of HPO/DUS and pump and treat at Visalia showed that HPO/DUS would have larger capital and annual O&M costs, but would be operated for less years, than pump and treat; projected unit costs were $39/yd3 for HPO/DUS and $110/yd3 for pump and treat
- Key factors affecting the cost analysis include the groundwater extraction capacity and size of plume

Description:
Since the 1920's, the four-acre Visalia Poleyard was the site of a wood preservation treatment plant for power poles. Poles were dipped into creosote, a pentachlorophenol compound, or both. Soil and groundwater to 100 ft bgs were contaminated with creosote, pentachlorophenol, and diesel fuel. A pump and treat system was installed in 1975 and several years later a slurry wall was constructed to contain the plume at its leading edge.

A field demonstration of Hydrous Pyrolysis Oxidation/Dynamic Underground Stripping (HPO/DUS) was conducted at Visalia over a 25-month period. HPO/DUS is a combination of technologies including steam and air injection, vapor extraction, pump and treat, and electrical resistance tomography. The system used at Visalia consisted of 11 injection and 8 extraction wells; steam and air were injected to 80 100 ft bgs in paired wells. Groundwater was extracted at 350-400 gpm. During the 25 months of operation, a total of 1,130,000 lbs (141,000 gals) of creosote were removed or treated (10,400 lbs/wk). Approximately 50% of the contaminants were removed in free phase, 16% as vapors, 16% in an aqueous phase, and 17% treated by HPO in situ.