Del Norte Pesticide Storage

Description and History

The Del Norte County Pesticide Storage Area site operated from 1970 until 1981, accepting containers from local agricultural and forestry related industries. The site was intended to be an interim or emergency storage area for pesticide containers, which previously had been triple-rinsed and punctured. Wastes and rinse water were improperly disposed of in an unlined sump. Approximately 1,600 drums that had held the wastes and rinse water were recovered and recycled by the County Agricultural Department. This site is bordered by the Pacific Ocean, State-owned land, residences, and farmland. Private wells supply the domestic water to the area, and four wells are located within 2,500 feet of the site. In 2007, approximately 1500 people reside within a one-mile radius of the site.

The site is currently being monitored and the next Five Year Review (third) is planned for September, 2010.

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Contaminants and Risks

Groundwater and soil were found to be contaminated with various pesticides/herbicides and volatile organic compounds (VOCs). Coming into direct contact with or accidentally ingesting contaminated soil or groundwater may pose a potential threat to human health.

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Who is Involved

This site is being addressed through Federal actions.

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Investigation and Cleanup Activities

Immediate Actions: In 1987, the EPA removed 300 cubic yards of contaminated soils that were considered to be the source of groundwater contamination. An air stripping groundwater treatment system was built in 1989 and has been successfully stripping the pesticide DCP from the groundwater prior to discharge to the municipal waste treatment system. The groundwater system has been operating dependably with daily oversight conducted by county representatives since 1990. In 1991, operations temporarily were halted as workers repaired a discharge pipe that had been damaged from freezing conditions.

In 1985, the EPA selected a cleanup remedy for the entire site that included: excavation and off-site disposal of the remaining contaminated soils from the sump and trench areas; extraction of contaminated groundwater; treatment of contaminated groundwater by (carbon adsorption) coagulation and sand filtration technologies; piping of treated groundwater to the county sewer main; and groundwater monitoring. Since the concentration of pesticides fell after the removal of the source of contamination, high rainfall rates, volatilization, and biodegradation, the EPA decided to stop treating the contaminated groundwater with (carbon adsorption) coagulation and filtration. Instead, groundwater treatment continues through air stripping techniques initiated in 1990.

Although initial cleanup actions were thought to be completed in the spring of 1992, the lack of contaminant reduction in the groundwater during the treatment in 1992 and 1993 led the EPA to install a pumping well and an air injection system in 1994. As of May 1996, approximately 23 million gallons of contaminated groundwater had been treated and discharged.

An Amendment to the Record of Decision was signed on August 29, 2000. The remedy was changed to halt P&T, which was no longer effective at reducing the level of DCP in the groundwater. A Technical Impracticability Waiver was granted for the site, and monitoring will continue until the level of DCP reaches below the new Maximum Contamination Level of 5ppb.

The Del Norte Site was deleted from the National Priorities List on September 18, 2002. California EPA is currently the lead at the site. Del Norte County will continue to monitor contaminant levels at the site until we are confident that the groundwater has attained the MCL of 5ppb. Sampling conducted at the site through October 2008 indicate that contaminant levels are continuing to decline naturally. Monitoring Well (MW) 104 has levels of 1,2-DCP of 2.4 ppb, and MW 105 has levels of 1,2-DCP of 6.2 ppb on October 29, 2008. There are no other wells on the site with contaminated groundwater.

Table 3 in the 2005 Five Year Review and the semi-annual sampling results through 2008 show a general trend of slow decline in the levels of 1,2-DCP in the shallow groundwater. Variation in annual rainfall causes distinct changes in the depth of the water table from year to year, and the contaminant concentrations show some variation as well. Monitoring will need to continue for several years after the 5 ppb goal is first reached to ensure that the cleanup is permanent.

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Cleanup Results to Date

The removal of contaminated soils and the installation and operation of the groundwater treatment system at the Del Norte Pesticide Storage site have reduced the potential for exposure to contaminated materials. All construction at the site is complete. Concentrations of the targeted groundwater contaminant, DCP, continue to decrease with each quarterly sampling event. This year DCP concentrations are consistently under 30 ppb. The site has been delisted, and monitoring will continue until levels of 1,2-DCP are below the cleanup objective of 5 ppb

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Potentially Responsible Parties

Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.

Online information about the PRPs for the site is not yet available.

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Documents and Reports

Administrative Records
		Area A & Area B Groundwater OU
Fact Sheets
	02/01/00	EPA Proposes Plan to Select Alternate Cleanup Remedy
	05/01/05	U.S. EPA Reviews Cleanup at Site
Technical Documents
	09/01/05	Second Five-Year Review Report

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Community Involvement

Public Meetings:

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Public Information Repositories

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Additional Links

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Contacts

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