Air Sparging and Pump and Treat at the Del Norte County Pesticide Storage Area Superfund Site, Crescent City, California

Site Name:

Del Norte County Pesticide Storage Area Superfund Site

Location:

Crescent City, California

Period of
Operation:

April 1990 - October 1997 (Air Sparging: March 1994 - November 1996)

Cleanup
Type:

Full scale

Technology:
Air Sparging and Pump and Treat
- A pump and treat system was installed in 1990 and operated until October 1997; no details of this system were provided
- Air sparging was added in 1994 in an attempt to enhance contaminant removal
- The air sparging system included:

    - 10 air sparge points initially installed within the 1,2-dichloropropane (DCP) plume; after one year of operation, 15 additional sparge points installed
    - Points consisted of ½-inch diameter PVC tubes placed to bottom of aquifer; tubes were plumbed to air compressor to force air through tubes to bottom of aquifer
    - System was shut off in November 1996 after no discernable changes in DCP concentrations were noted

Cleanup Authority:
EPA

Contacts:
Bob Mandel
EPA Lead
EPA Region 9
Emergency Response Section
75 Hawthorne St.
San Francisco, CA 94105-3901
Telephone: (415) 972-3040
E-mail: mandel.bob@epa.gov

Patrick Lee
State Lead
California Department of Toxics Substances Control
700 Heinz Ave., Suite 200
Berkeley, CA 94710 - 2721
Telephone: (510) 540-3847
E-mail: plee1@dtsc.gov

Contaminants:
1,2-Dichloropropane (DCP), 2,4-Dichlorophenoxyacetic acid (2,4-D), chromium
DCP concentrations prior to start up of air sparging: 15 - 40 µg/L

Waste Source:
Residues and rinse water disposed of in an unlined sump

Type/Quantity of Media Treated:
Groundwater
- Groundwater depth - ranged between 3 and 10 feet bgs
- Groundwater flow direction - southeast
- Thickness of uppermost aquifer - approximately 30 feet
- Hydraulic conductivity - approximately 10-3 cm/s

Purpose/Significance of Application:
Use of air sparging, in conjunction with pump and treat, to enhance the removal of DCP in groundwater

Regulatory Requirements/Cleanup Goals:
- 1985 ROD specified 10 µg/L for DCP (health-based standard)
- 2000 ROD Amendment - included a TI Waiver and changed the groundwater remedy to plume containment through natural attenuation, groundwater monitoring, and institutional controls

Results:
- The pump and treat system operated from 1990 to 1997; the air sparging system operated from 1994 to 1996; DCP data are available for 1994 to 2003
- The areal extent of the DCP plume (greater than 5 µg/L) was reduced from approximately 12,000 ft2 to 5,000 ft2 (as of 1998)
- An estimated 3.75 gallons DCP removed from groundwater between 1990 and 1997 (95% of this amount was estimated to have been removed by the pump and treat system between 1990 and 1994)
- Operation of the air sparging system resulted in no discernable changes in groundwater DCP concentrations; the system was shut down in 1996
- Continued operation of the pump and treat system resulted in no discernable changes in groundwater DCP concentrations; the system was shut down in 1997
- As of March 2003, groundwater DCP concentrations ranged from 2.4 to 6.6 ug/L

Cost Factors:
- EPA provided actual costs for O&M for 1995 to 1997: 1995 - $166,518; 1996 - $106,928;
1997 - $84,211; no additional details were provided regarding the O&M costs; no capital cost data were provided

Description:
Del Norte County Pesticide Storage Area Superfund Site is located in Crescent City, California, and operated from 1970 to 1981 as a county-wide collection point for the interim and emergency storage of pesticide containers generated by local industry. Pesticide containers were rinsed on site, with residues and rinse water improperly disposed of in a unlined sump. This resulted in groundwater at the site becoming contaminated with pesticides, herbicides, and volatile and semi-volatile compounds. Contaminants of concern at the site included DCP, 2,4-D, and chromium. The site was listed on the NPL in 1983. The 1985 ROD specified pump and treat as the groundwater remedy for the site.

The pump and treat system was installed in 1990. In 1994, EPA determined that while DCP concentrations had decreased in monitoring wells, asymptotic levels of between 15 and 40 µg/L had been reached. In an attempt to enhance contaminant removal, an air sparging system was added, and after one year of operation, expanded to include additional sparge points. EPA noted that there were no discernable changes in DCP concentrations and the air sparging system was shut down in November 1996. Continued operation of the pump and treat system did not result in discernable changes in DCP concentrations and the system was shut down in 1997. EPA concluded that neither the pump and treat remedy nor any other technology available at the time would be able to treat DCP to below the cleanup level and a TI waiver was issued based on these findings. In August 2000, a ROD Amendment was signed amending the groundwater remedy for the site to include plume containment through natural attenuation, continued monitoring of the groundwater, and institutional controls. Final site cleanup and equipment removal was completed in December 2000, and the site was deleted from the NPL in September 2002.

During operation of these systems between 1990 and 1997, an estimated 3.75 gallons of DCP were removed from the groundwater, with 95% of this amount removed by the pump and treat system between 1990 and 1994. O&M costs available for 1995 to 1997 were: $166,518 in 1995, $106,928 in 1996, and $84,211 in 1997. Results of groundwater monitoring after system shut down showed DCP concentrations in groundwater ranging from 2.4 to 6.6 µg/L.