EXPLANATION OF SIGNIFICANT DIFFERENCES And CORRECTIVE ACTION COMPLETED DuPont Glasgow Business Community Facility Glasgow, Delaware RCRA ID: DED 042 263 764 I. INTRODUCTION The U.S. Environmental Protection Agency, Region III (EPA) is proposing to modify the selected corrective measure for the former DuPont Glasgow Business Community Facility (Facility). EPA proposes this modification to document that RCRA Corrective Action has been completed at this facility. EPA prepared this Explanation of Significant Differences (ESD) to explain to the public why it is proposing to modify the selected corrective measure for the facility. This ESD summarizes the information that supports the corrective measures modification and completion of corrective action at this Facility. The corrective measures goal is to protect human health and the environment, and based on the data collected over the years, EPA proposes that the corrective measures goal has been met at this Facility. EPA is proposing to remove two requirements from the Final Decision corrective measures (August 2000) for the Facility. First, EPA proposes to remove the requirement for the facility to maintain a deed notice for Solid Waste Management Unit (SWMU) 13 with New Castle County, Delaware. Other protective institutional controls will be placed on the property by the State of Delaware. Delaware's institutional controls will control groundwater use for drinking water purposes. Second, EPA proposes removing the requirement for on-going ground water monitoring at SWMU 13 because the contaminants of concern in groundwater are at or just above drinking water standards and are attenuating. Once these two proposed requirements are removed from the corrective measures listed in the Final Decision dated August 2000, DuPont will have completed all RCRA Corrective Action requirements for this Facility. This ESD and the supporting documents are part of the Administrative Record for the Facility. The Administrative Record is located at the State of Delaware Department of Natural Resources and Environmental Control office at the address shown under Section VII. Information on the Corrective Action Program can be found at http://www.epa.gov/reg3wcmd/correctiveaction.htm II. SUMMARY OF SITE HISTORY, CONTAMINATION AND THE SELECTED REMEDY The Facility is located near the intersection of State Routes 896 and 40 in Glasgow, New Castle County, Delaware (see the attached location map). The current Facility consists of a 22- acre lot with two buildings, a parking lot and some open space. The Facility was originally part -1 - ------- of a 977-acre tract purchased by E.I. du Pont de Nemours & Company, Inc. (DuPont) in 1966. DuPont constructed several buildings for medical instrument systems and products manufacturing operations, with most of the site remaining undeveloped. DuPont sold 750-acres in 1995, only retaining a small fraction of the original property. In August 1991, DuPont entered into an Administrative Order on Consent with EPA to study and remedy releases of contaminants at Solid Waste Management Units (SWMUs) and areas of concern (AOCs) at the Facility. EPA issued the Order under Section 3008(h) of the Resource Conservation and Recovery Act of 1976, as amended by the Hazardous and Solid Waste Amendments of 1984 (RCRA), 42 U.S.C. Section 6928(h). . EPA and DuPont identified 24 potentially contaminated areas in the Facility, and after further investigation, identified only six units which needed further study to determine if releases of contamination had occurred. Investigations found that releases occurred at the six units. DuPont investigated, removed contaminant sources or otherwise treated contamination at three of the six units to meet EPA's clean-up goals. The three remaining units needing further corrective action were listed in the Final Remedy decision document, which EPA issued in August 2000. The locations of the three units are shown on the attached location map. The following discussion for the three remaining units explains what corrective measures were required at the three remaining units and what was completed. 1. SWMU 12 (Well No. 4): Well No. 4 supplied drinking and process water to the Facility. Well No. 4 was sampled in 1988 and volatile organic compounds (VOCs), mostly trichloroethylene (TCE) were found. The source(s) of contamination are unknown; however, uncontrolled disposal of chemicals is suspected. In 1990, DuPont installed a groundwater treatment system that pumped contaminated groundwater through air sparging and carbon absorption units to remove the VOCs. The system treated about 50 million gallons of groundwater a year. About ten years of treatment and groundwater sampling showed that the treatment system was successful in removing VOCs from the groundwater. In 2000, DuPont completed the final confirmatory groundwater monitoring requirements to document the removal of volatile organic compounds (VOCs) from the groundwater. The groundwater was cleaned-up to drinking water standards. Therefore, EPA Corrective Action is completed, and no further action (NFA) is necessary. 2. SWMU-13 (Permasep Building and groundwater plume): In 1993, DuPont encountered VOCs in soil while excavating at the Permacep Building. Subsequent groundwater investigations showed the same VOCs in groundwater in a plume associated with the Permasep Building. The contamination resulted from cleaning paint brushes in a drum using PCE outside the northern door to the building. In June 1999, DuPont removed the soil source of contamination located along the northern side of the Permasep building. A small portion of contaminated soil was left under the building (about 1.5 yds3) due to concerns about undermining the foundation and structural integrity of the building. The Final Remedy was for monitored natural attenuation of the low level VOCs in the groundwater, and recording a deed restriction/notification of contamination associated with the building with the County. Over nine years of groundwater monitoring data has shown that natural attenuation reduced the size of the plume and the amount of VOCs in groundwater, with VOC levels (PCE and cis-l,2-DCE) at or near EPA's drinking water levels (clean-up goal). Recent soil samples collected beneath the building are below EPA's clean-up goals. Therefore, EPA is proposing: (1) eliminating the requirement for the county deed restriction because State institutional controls are adequate for -2- ------- restricting groundwater use at the facility, and (2) discontinuing groundwater monitoring. If there are no modifications to the proposal after public comment, then NFA will be required. 3. Area of Concern D: In 2002, DuPont excavated zinc and copper contaminated sediments from the drainage ditch, replaced pipe and lined the channel. This remedied the sediments and prevents any leaching of metals into the channel. Therefore, no further action is required. III. DESCRIPTION OF SIGNIFICANT DIFFERENCES AND THE BASIS FOR CURRENT CHANGES TO THE SELECTED CORRECTIVE MEASURE This ESD proposes to modify or update the selected corrective measures of the Final Remedy Decision issued by EPA in 2000, with no further corrective action required for this Facility. Delaware DNREC will designate SWMU-13 as a groundwater management zone (GMZ). The GMZ designation restricts groundwater use. If a property owner applies to the State for a groundwater permit and the area is designated as a GMZ, then Delaware can deny the request, and/or impose conditions in the permit to protect human health and the environment. Currently, State restrictions do not allow use of the aquifer beneath SWMU-13 for domestic (private) wells. EPA and the Delaware Department of Natural Resources and Environmental Control (DNREC) propose eliminating the SWMU-13 deed notice with New Castle County because the State institutional controls provide adequate protections for public health. This ESD also proposes that groundwater monitoring at SWMU-13 be discontinued, as the nine years of data show that VOC levels in groundwater have attenuated EPA drinking water levels or just above these levels. EPA expects the VOCs will continue to attenuate to below drinking water levels. IV. STATE AGENCY REVIEW DNREC is the lead agency for oversight and clean-up at this Facility. EPA consulted with DNREC regarding this modification and corrective action completion and DNREC concurs with this ESD. V. AFFIRMATION OF DECLARATION Given that contaminants are cleaned-up to EPA's risk based goals and State institutional controls are adequately protective of public health, EPA and Delaware DNREC propose that corrective action is complete and the remedies have achieved the goals of protecting human health and the environment. VI. PUBLIC PARTICIPATION The public is invited to comment on EPA's two proposed modifications to the Final Decision as discussed in this ESD. The public comment period will last thirty (30) calendar days from the date the notice is published in the Delaware News Journal. A public meeting will be held upon request. -3- ------- This ESD is available for public review at the location listed in Section VII below and at http://www.epa.gov/reg3wcmd/public_notices.htm. Comments or questions regarding the ESD may be submitted to: Ms. Barbara Smith U.S. EPA, Region III 1650 Arch Street (3LC20) Philadelphia, PA 19103 (215) 814-3226 FAX (215)814-3113 Email: smith.barbara@epa.gov EPA will respond to all comments received. On the basis of comments received or other relevant information, if EPA makes minor changes to the ESD, the ESD will become effective upon those changes being made. If EPA makes significant changes to the ESD, EPA may seek additional public comments. All comments received during the thirty (30) day comment period will become part of the Administrative Record for the Site, as will EPA responses to the significant comments. VII. ADMINISTRATIVE RECORD The Administrative Record supporting this ESD will be available for public review on Mondays through Fridays, from 8:00 a.m. to 4:00 p.m., by contacting the DNREC Project Manager, Mr. Douglas Zeiters, at: State of Delaware Department of Natural Resources and Environmental Control Solid and Hazardous Waste Management Branch 89 Kings Highway Dover, DE 19901 Phone: (302)739-9403 Date Abraham Ferdas, Director Land and Chemicals Division U.S. EPA Region III -4- ------- NEWARK ,WELL 17 SWMU 12 FACILTY OPEN LAND (FARMED & WOODED) B100 Soil Foundation Area DELMARVA POWER ELEC. SUBSTATION (PARKING) GLASGOW SITE SWMU 13 GROUNDWATER SITE BOUNDARY AT TIME OF CONSENT ORDER LEGEND • PZ-10 = APPROXIMATE WELL LOCATION = BORROW PIT AREA SCALE 1400 1400' Corporate Remediation Group An Alliance between. LhiPont and The W-C Diamond Croup Barley Mill Plaza, Building 27 Wilmington, Delaware 19880-0027 SITE LOCATION MAP DuPont Glasgow Site Glasgow, Delaware 10/29/09 3TOWB- ------- |