'EXPLANATION OF SIGNIFICANT DIFFERENCES TO THE … · 5 9 0006 TABLE OF CONTENTS SECTION PAGE 1.0...

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EXPLANATION OF SIGNIFICANT DIFFERENCESTO THE REMEDIAL ACTION

GEIGY CHEMICAL CORPORATION SITEABERDEEN, MOORE COUNTY

NORTH CAROLINA

Prepared byU.S. Environmental Protection Agency

Region IVAtlanta, Georgia

January, 1998

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TABLE OF CONTENTS

SECTION PAGE

1.0 Introduction 1

2.0 Site Location and Description 13.0 Site History 2

4.0 Record of Decision 2

5.0 Status of Remedial Design 36.0 Rationale for BSD 5

6.1 Sampling Results 56.2 Analysis of Sampling Results 56.3 Additional Work Required 8

7.0 Statutory Determinations 11

8.0 Public Notification 12

LIST OF FIGURES

Figure 1 Groundwater Plume based on 1992 informationand Current Remediation System 4

Figure 2 Upper Black Creek Groundwater Plume 6Figure 3 Lower Black Creek Groundwater Plume 7Figure 4 Modeling Results for Pump and Treat Scenario 9

Figure 5 Modeling Results for Natural Conditions Scenario 10

Geigy Chemical Corporation SiteExplanation of Significant DifferencesJanuary 1998

5 9 0 0 0 7EXPLANATION OF SIGNIFICANT DIFFERENCES

TO THE REMEDIAL ACTIONGEIGY CHEMICAL CORPORATION SITE

ABERDEEN, MOORE COUNTY, NORTH CAROLINA

1.0 INTRODUCTION

This Explanation of Significant Differences (BSD) was prepared for the GeigyChemical Corporation Superfund Site ("Site"). The purpose of this ESD is to documentthat the Environmental Protection Agency (EPA or the Agency) is adding additionalmonitoring requirements to the Record of Decision (ROD) for the Site.

EPA previously issued the Geigy ROD on August 27, 1992. The originalrequirements and goals of the August 1992 ROD are reiterated in Section 4 below.The necessity of this ESD is based on information generated during the development ofthe Site's Remedial Design (RD). The new information is summarized in Section 6below.

This ESD is issued pursuant to Section 117(c) of the ComprehensiveEnvironmental Response, Compensation and Liability Act (CERCLA), 42 U.S.C Section9617(c), and the National Oil and Hazardous Substances Pollution Contingency Plan(NCP), 40 CFR Section 300.435(c)(2)(l). A copy of this ESD will be added to the SiteAdministrative Record and to the Information Repository, both of which can be found inthe Aberdeen Town Hall or in EPA's Region 4 Records Center. The public isencouraged to review both the Administrative Record and the Information Repositoryduring normal working hours.

2.0 SITE LOCATION AND DESCRIPTION

The Geigy Site is located just east of the corporate city limits of Aberdeen, NorthCarolina on Highway 211 in southeastern Moore County. The Site is approximatelyone-acre and is located on the Aberdeen and Rockfish Railroad right-of-way. It is inthe form of an elongated triangle between Highway 211 and the railroad, with thehighway and railroad intersecting at the apex of the triangle.

The Site soils have been remediated; the surface of the Site has beenrestorated. It currently is covered with rye grass, wild flowers, and pine trees.


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3.0 SITE HISTORY

The Site was operated as a pesticide blending and formulation facility by variousoperators from approximately 1947 to 1967 and by retail distributors of agriculturalchemicals from 1968 to 1989. The pesticides DOT, toxaphene, and BHC werereceived in bulk at the Site, blended with clay and other inert materials, repackaged,and sold. Pesticides were not manufactured at the Site, but were formulated by drymixing into a product suitable for local consumer use. Spills occurred during thenormal formulation activities.

Soil removal actions were conducted in 1989 and 1991. In February 1989,visual areas of pesticide contamination were removed and the wastes placed at alandfill in Pinewood, South Carolina. A total of 462 tons of material were removed anddisposed. A second removal action was conducted in 1991. Approximately 2841 tonsof soils and debris were removed. Of this, 505 tons of soils were transported to aTexas facility for incineration. The remainder was disposed at a landfill in Louisiana.

4.0 RECORD OF DECISION

The ROD was signed on August 27, 1992, and addresses groundwater and soilcontamination at the Site. The major components of the selected remedy, as depictedin the 1992 ROD include:

• Extraction of groundwater across the Site in the upper aquifer (surficial) and thesecond uppermost aquifer (Upper Black Creek) that is contaminated aboveMaximum Contaminant Levels or the North Carolina Groundwater Standards,whichever are more protective;

• On-site treatment of extracted groundwater via carbon adsorption;

• Discharge of treated groundwater to the local POTW or an infiltration gallery.

• Continued analytical monitoring for contaminants in groundwater.

• Demolition of former warehouse foundation; disposal at a municipal or securelandfill;

• Excavation of the top foot of on-site soils contaminated above the performancestandards;

• TCLP testing of the stockpile of contaminated soil to determine final disposition;

Geigy Chemical Corporation SiteExplanation of Significant DifferencesJanuary 1998 2

5 9 0 0 0 9• Off-site incineration of contaminated soils that fail the TCLP test;

• Off-site disposal in an approved hazardous waste landfill of contaminated soilsthat pass the TCLP test;

• Backfilling, grading and revegetation of excavated area;

• Additional sampling and analyses of the second uppermost aquifer to determinethe extent of pesticide contamination, and to determine if the trichloroethene(TCE) found in two wells is site-related.

5.0 STATUS OF REMEDIAL DESIGN AND REMEDIAL ACTION

The RD was initiated on July 15,1993. The design of the remediation activitiesidentified in the ROD, including the additional sampling, has been completed. The RDwas approved by EPA in March 1996.

Remedial action (RA) activities started in September 1996. The RA included:

• Removal of the remaining concrete foundations and the disposal of 2,460 tonsof debris to a Subtitle D landfill;

• Disposal of 4,475 tons of contaminated soils to a Subtitle C landfill;

• Installation of four extraction wells in the surficial aquifer and three extractionwells in the Upper Black Creek aquifer in the vicinity of the facility property;

• Construction of a groundwater treatment facility that includes an equalizationtank and two series of activated carbon canisters;

• Construction of an infiltration gallery (the 1992 ROD gave an option fordischarge of either an infiltration gallery or the local POTW) for discharge oftreated groundwater; and

• Installation of six additional monitoring wells and three additional piezometers.

The groundwater extraction and treatment system began operating in January1997. In Figure 1, the extent of the groundwater plumes in the surficial aquifer and theUpper Black Creek aquifer as identified in the 1992 ROD, along with the sevenextraction wells are shown.


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6.0 RATIONALE FOR BSD

There are three types of post-ROD changes. Depending on the extent or scopeof the modification being considered, the post-ROD change is either (1) non-significantor minor; (2) significant; or (3) fundamental. A different documentation procedure isassociated with each type. For non-significant or minor changes, these changes aredocumented by recording the change in the post-decision document file. Thedissemination of a fact sheet to the public is optional. For significant changes to aROD or RA, these changes should be documented in an BSD, as required by CERCLAand the NCR. Fundamental changes to the remedy should be documented in a RODamendment.

EPA has determined that the changes and additions covered by this ESDconstitute a significant, not fundamental change to the original scope of the remedyselected in the ROD. Therefore, an ESD is appropriate to document these changes.

6.1 Sampling Results

The remedy as stated in the ROD has been implemented; the soils have beenremediated and the groundwater near the facility is being treated in accordance withthe ROD. However, as stated in Section 4 of this document, the ROD requiredadditional sampling in the second uppermost aquifer to determine the extent of thepesticide contamination and to determine if the TCE was site-related. This samplingwas completed and the extent of the pesticide-contaminated groundwater plume wasdetermined.

Figure 2 shows the extent of groundwater contamination identified in the UpperBlack Creek aquifer. This sampling investigation also revealed that the Lower BlackCreek aquifer was contaminated with pesticides. This plume is shown in Figure 3. Itwas also determined that the TCE was not site-related.

6.2 Analysis of Sampling Results

A Downgradient Groundwater Remedial Action Work Plan was finalized inOctober 1997. This workplan details the results of the pre-RD sampling and providesextensive analysis of the results of this sampling activity. The results of this analysisindicates that periodic monitoring of the downgradient portion of the plume along withperiodic monitoring of the surface water bodies would address this groundwatercontamination. This determination was based on the following:

• There are no receptors of untreated groundwater in the downgradient area.Currently, there is one private well user in this area. All other residences and


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businesses are connected to the city water system. The private well has beensampled and the water is contaminated with pesticides. However, the PotentiallyResponsible Parties (PRPs) have installed a carbon filter on the well, andconducts periodic monitoring to ensure the proper operation and maintenance.

• The City of Aberdeen, by letter dated April 1997. informed EPA that the Citywould not install any municipal water supply wells in this downgradient area.

• Groundwater discharge to surface waters limits the further migration of theplume. Groundwater flow directions have been identified to verify that thegroundwater pesticide contamination plume is contained by the following creeks:McFarland's Branch, Aberdeen Creek, Ray's Mill Creek, and Trough Branch.

• Pesticide concentrations in surface waters do not currently pose a risk to humanhealth or wildlife. The risk assessment for McFarland's Branch was updatedbased on the new sampling results and indicates that the risk associated withthe downgradient plume is well below EPA's acceptable risk range of 1CT4 to 10"6

• Groundwater modeling has shown that the concentrations of pesticides in thisdowngradient area will decrease in a time frame comparable to a pump-and-treatsystem. A groundwater flow model was used to simulate the performance of sixextraction wells in the downgradient plume area. The model was also used toestimate the extent and longevity of the groundwater plume under naturally-occurring conditions. The results of this modeling show that the plume would beremediated in 19 years under pump-and-treat conditions (Figure 4) and wouldbe remediated in 25 years under natural conditions (Figure 5).

6.3 Additional Work Required

This BSD documents that the groundwater plume not currently covered by theextraction and monitoring system will be monitored and this monitoring, as well as otheractivities will be incorporated as part of the overall site remedy. The additionalremedial action activities are detailed in the Downgradient Groundwater RemedialAction Workplan and will be conducted in addition to the current facility propertygroundwater extraction and treatment system. They are as follows:

1. Natural Hydraulic Containment

Periodic measurement of water-levels will be conducted to verify thatgroundwater flow patterns do not change over time. In addition, the naturalprocesses of dispersion, adsorption, and degradation will be evaluated by


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FIGURE 4Modeling Results for Puinp and Treat Scenario

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GEIGY CHEMICAL CORPORATION SITEABERDEEN. NORTH CAROLINA

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updating the groundwater model with monitoring well data as it is collected todetermine its effectiveness.

2. Groundwater Monitoring

Periodic groundwater monitoring of select existing and proposed monitoringwells and piezometers. Monitoring locations and frequencies will be reevaluatedevery year for the first five years and every five years thereafter.

3. Surface Water and Stream Sediment Monitoring

Periodic surface water sampling and stream sediment sampling will beconducted in McFarland's Branch, Aberdeen Creek, Ray's Mill Creek andTrough Branch.

4. Water Supply Protection

Municipal Water Supply Well Number 2 of the Town of Aberdeen's water supplysystem will be monitored to ensure that the well is not adversely affected by Sitecontaminants. Residential well protection will be accomplished by well permitapplication reviews, drive-through surveys of the downgradient area andinformal interviews with residents to determine if new residential wells have goneinto service. The one residential well currently in this area will continue to besupplied with a granular activated carbon filter and will be monitored to ensurethat the treated water meets Federal and State drinking water standards.

5. Periodic Remedy Reviews

Periodic remedy reviews will be conducted to evaluate the effectiveness of theremedial action. The remedy reviews will focus on evaluating the protection ofpotential receptors and the effectiveness of the remedy with respect toforecasted concentration trends in the groundwater.

7.0 STATUTORY DETERMINATIONS

EPA has considered the new information that has been developed and theaddition made to the selected remedy by this ESD and believes that the remedyselected in the ROD remains protective of human health and the environment, complieswith Federal and State requirements that are applicable or relevant and appropriate tothis remedial action, and is cost-effective. In addition, the remedy utilizes permanentsolutions and alternative treatment technologies to the maximum extent practicable atthis Site.


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8.0 PUBLIC NOTIFICATION

In accordance with Section 117(c) of CERCLA, EPA published a notice of theESD in the local newspapers, which describes the ESD and its availability for review.An ESD Fact Sheet was also prepared and mailed out to the persons on the Sitemailing list. A 30-day public comment period was also held from November 13, 1997 toDecember 13, 1997. No comments were received.

Richard D. GreenActing DirectorWaste Management Division

Date


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