2021-10511. National Oil and Hazardous Substances Pollution Contingency Plan; National Priorities List: Explanation of Significant Differences for the Del Norte County Pesticide Storage Area Superfund Site

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Notice of explanation of significant differences.

SUMMARY:

The U.S. Environmental Protection Agency (EPA) Region 9 is issuing an explanation of significant differences (ESD) for the Del Norte County Pesticide Storage Area Superfund Site (the Site), located at 2650 West Washington Boulevard in Crescent City, Del Norte County, California, and is notifying the public of this undertaking. When significant but not fundamental changes are made to the scope, performance, or cost of a remedy after a final remedy has been adopted, Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), require that the lead agency prepare an ESD. Because the Site's remaining contaminant of concern (COC) has reached drinking water standards, this ESD was issued to modify the remedy at the Site to remove the technical impracticability (TI) waiver for 1,2-dichloropropane (1,2-DCP) and reinstate the applicable or relevant and appropriate requirement (ARAR) for 1,2-DCP. In accordance with CERCLA, the EPA consulted with the support agency, the California Department of Toxic Substances Control (DTSC). DTSC provided written concurrence on the ESD. The Site was delisted from EPA's National Priorities List (NPL) in 2002, and this remedy modification does not impact EPA's determination that the Site remedy remains protective of human health and the environment, complies with federal and state requirements that were identified as applicable or relevant and appropriate to this remedial action, and is cost-effective.

DATES:

The Final ESD became effective on April 14, 2021.

FOR FURTHER INFORMATION CONTACT:

Cynthia Ruelas, Superfund Remedial Project Manager, EPA, Region 9 (SFD-7-1), 75 Hawthorne Street, San Francisco, CA 94105; telephone number: 415-972-3329; email address: [e-mail].

SUPPLEMENTARY INFORMATION:

I. Introduction

Region 9 of the EPA announces the issuance of an ESD at the Del Norte County Pesticide Storage Area Superfund Site (Site). When significant, but not fundamental, changes are made to the scope, performance, or cost of a remedy after a final remedy has been adopted, CERCLA and the NCP require that the lead agency prepare an ESD pursuant to the NCP, 40 CFR 300.435(c)(2) and 300.825(a).

Section II of this notice explains the purpose of an ESD. Section III discusses the process that the EPA has undertaken for this action. Section IV discusses the site and describes the basis for issuance of an ESD.

II. ESD Purpose

EPA adopted this ESD to document a change to the selected remedy to remove a TI waiver for 1,2-DCP, adopt the maximum contaminant level (MCL) as the cleanup level, and describe how the Site has met that ARAR standard. Changes to a Selected Remedy described in a Record of Decision (ROD) are documented using one of the following documents, depending on the nature of the change: (1) A technical memorandum in the Administrative Record for an insignificant or minor change; (2) an ESD for a significant change; or (3) a ROD Amendment for a fundamental change. A significant change is defined as a change to a component of a remedy that does not fundamentally alter the overall cleanup approach. Because this remedy change updates the status of the Site TI Waiver and ARAR requirements and does not change the remedy approach, an ESD was deemed to be the appropriate document to record the changes to the ROD. An ESD provides a description of the nature of the significant change, summarizes the information that led to making the change, and affirms that the revised remedy complies with the NCP and the statutory requirements of CERCLA. In accordance with the ROD for the Site, the overall cleanup goal of the remediation, which is to protect public health from exposure to COCs, remains in place. The ROD for the Site is being modified so that remedy implementation can be refined and improved to reflect achievement of health protective cleanup levels.

III. ESD Process

The following describes the general process that the EPA followed to prepare and issue the ESD.

(1) The ESD identifies and discusses the significant differences between the remedy as presented in the ROD and subsequent decision documents and the change now proposed. It identifies the remedial action objectives (RAOs) of the remedy, which include a reinstated objective from the ROD to clean up contaminated groundwater to meet drinking water standards and enable beneficial use of the Site. The ESD also summarizes the scope and performance of the current and previous Site decision documents (the 1985 ROD, 1989 ESD, 2000 ROD Amendment, and 2021 ESD).

(2) The ESD confirms that the Site remedy continues to meet ARARs (in compliance with the NCP, 40 CFR 300.430(f)(1)(ii)(B)(1) and (2)), satisfies Section 121 of CERCLA, 42 U.S.C. 9621, and remains protective of human health and the environment.

(3) Before issuance of the ESD, the EPA as lead agency consulted with DTSC, the support agency, in accordance with the NCP, 40 CFR 300.435(c)(2). The EPA provided DTSC the opportunity to comment on the ESD. DTSC concurred with the issuance of the ESD for the Site, and DTSC's concurrence memo is included as an attachment to the ESD.

(4) The EPA Regional Administrator's designee approved and signed the ESD.

(5) Concurrent with the publication of this notice of issuance of this ESD in the Federal Register, the EPA published a notice of availability and a brief description of the ESD in a major local newspaper of general circulation (as required by the NCP at 40 CFR 300.435(c)(2)(i)(B)). A formal public comment period is not required for issuance of an ESD.

(6) The ESD and supporting documents are available for public review in the Administrative Record file and information repository, pursuant to the NCP, 40 CFR 300.435(c)(2)(i)(A) and 300.825(a)(2).

IV. Basis for Issuance of an ESD

The following information provides the EPA's basis for issuing the ESD for the Site.

Site Background and History

The Site (CERCLIS ID #CAD000626176) is located at 2650 West Washington Boulevard in Crescent City, Del Norte County, California, and is an approximately 1-acre property consisting of 2 parcels. From 1970 to 1981, the site served as a collection facility for pesticide storage containers used in local agricultural and forestry operations in Del Norte County. The facility was operated by the County, with approval from the North Coast Regional Water Quality Control Board (NCRWQCB), and was intended to serve as a county-wide collection point for interim or emergency storage of pesticide containers generated by local agricultural and forestry-related industries. Inspections conducted by the EPA and NCRWQCB in 1981 revealed violations of the Resource Conservation and Recovery Act (RCRA), and a failure to operate under the conditions previously agreed upon with the NCRWQCB. Shortly after receiving a Cleanup and Abatement Order from NCRWQCB, the County decided to close the facility. State and County sampling efforts revealed a variety of contaminants in the soil and groundwater at the Site. Due to lack of County funding to investigate the extent of contamination and develop a cleanup plan, the EPA placed the Site on the NPL in 1984.

Basis for Taking Action

NCRWQCB conducted initial investigations at the Site and found that both the soil and groundwater were contaminated with various herbicides, pesticides, and volatile and semi-volatile organic compounds and chromium. The specific COCs identified were 1,2-DCP and 2,4-dichlorophenoxyacetic acid (2,4-D). Soil contamination was detected to a depth of 15 feet but was contained to an on-site sump of 15 feet by 20 feet. At the time, the groundwater contaminant plume was estimated to extend approximately 170 feet to the southeast of the sump, in the direction of groundwater movement. If the contaminated aquifer were to be used as a drinking water supply, it would pose a significant health risk. Ingestion of these contaminants has been linked to increased cancer risk. Investigations indicated that elevated levels of chromium were also present at the Site.

Original Remedy Selection

In 1985, the EPA selected a remedy in a ROD to address the soil and groundwater contamination at the Site. The major components of the Selected Remedy included: Excavation and off-site disposal of contaminated soils; extraction and treatment of groundwater through carbon adsorption and coagulation/filtration treatment; disposal of treated groundwater to the Crescent City Wastewater Treatment Plant; and groundwater monitoring.

Actions Taken Following ROD Issuance

The 1989 ESD explained that because the chromium at the Site was determined to be naturally-occuring, it could not be remedied under CERCLA, pursuant to 42 U.S.C. 104(a)(3)(A). The ESD also documented and justified a change in the groundwater treatment method from carbon adsorption and coagulation/filtration to air sparging.

The EPA issued a ROD Amendment in 2000 that revised the remedy, because the Site RAO of restoring the contaminated groundwater to the drinking water standard for 1,2-DCP could not be met, because no technology existed that was capable of reaching the 10 micrograms per liter (µg/L) level set out in the ROD. Notably, this applied as well to the Maximum Contaminant Level (MCL) of 5 µg/L that had since been adopted since the cleanup level had been selected for the Site. In light of the inability to reach these cleanup levels, the ROD Amendment's revised remedy instead sought to contain the groundwater contamination through natural attenuation and monitoring and prevent its use as drinking water for as long as contaminant concentrations exceeded drinking water quality standards. The ROD Amendment identified the new ARAR for 1,2-DCP (equivalent to the new MCL of 5 µg/L); adopted a TI waiver of the newly identified ARAR for groundwater within the existing contaminated area where 1,2-DCP exceeded 5 µg/L; and required semi-annual groundwater monitoring and the enactment of institutional controls (ICs) to prevent exposure to contaminated groundwater.

In 2002, the EPA, DTSC, and Del Norte County entered into a Consent Decree, and in doing so, Del Norte County agreed to carry out and finance continued remediation efforts at the Site, including monitoring groundwater and implementing ICs in accordance with Site decision documents and plans. Also, in that same year, because all response actions required under CERCLA had been completed, except for ongoing operation and maintenance and Five-Year Reviews, following a 30-day public comment period, the EPA deleted the Site from the NPL.

Basis for ESD

Nearly 20 years after issuance of the TI waiver for 1,2-DCP, groundwater data from the Site consistently demonstrate that concentrations of 1,2-DCP have significantly decreased and are now below the drinking water standard of 5 µg/L. Given the effectiveness of natural attenuation in lowering concentrations of 1,2-DCP in Site groundwater to meet the MCL, the TI waiver adopted in the 2000 ROD Amendment is no longer necessary. Through this ESD, the EPA is removing the TI waiver for 1,2-DCP and reinstating the 1,2-DCP ARAR. The ESD also reinstates the original RAO that sought to clean up contaminated groundwater to meet drinking water standards. Cleanup under CERCLA is considered complete, although groundwater monitoring is currently ongoing at the Site under state oversight, and EPA plans to continue the Five-Year Review process as required until such time that groundwater attainment is formally achieved.

Enrique Manzanilla,

Director, Superfund Division, U.S. EPA, Region 9.