Record of Decision System (RODS)
DELAWARE SAND & GRAVEL LANDFILL
|Site Name:||DELAWARE SAND & GRAVEL LANDFILL|
|Address:||229 GRANTHAM LANE|
|City & State:||NEW CASTLE DE 19720|
|NPL Status:||Currently on the Final NPL|
|Contaminant:||VOCs, Other Organics|
|Abstract:||The 27-acre Delaware Sand & Gravel (Amendment) site is an inactive industrial waste landfill located in New Castle County, Delaware. It borders Army Creek and the Army Creek Landfill NPL site to the west, Army Creek and wetlands to the north, residential and business facilities to the east, and an abandoned sand and gravel quarry to the south. Residences are located approximately 30 feet from the landfill and a residential development is located approximately 0.5 miles to the south and southwest of the site. The landfill overlies the Potomac Aquifer, which isaccessed about 1.25 miles south of the site and used as a public water source. The site consists of four disposal Areas, referred to as the Drum Disposal Area (DDA), Inert Area, Ridge Area, and Grantham South Area. Between 1968 and 1976, the site accepted approximately 550,000 yd of household and construction waste, including approximately 7,000 drums containing liquids and sludge from perfume, plastics, paint, and petroleum refining processes. In 1971, investigations revealed ground water contamination emanating from the Army Creek and Delaware Sand & Gravel (DS&G) landfills. In 1976, the State issued an enforcement action requiring DS&G to discontinue disposal activities. A ground water recovery system was installed to prevent contaminated water from reaching the nearby public water supply. The system continues to operate. Investigations were conducted to characterize the source and extent of contamination from both sites, and in 1984, EPA initiated an emergency removal action at the site to remove approximately 600 drums from the DDA. Wastes identified in the DDA include subsurface soil and debris contaminated with PCBs, organic liquids, and inorganic solids. The DDA is believed to be the major source of organic ground water contamination. The Ridge Area consists of contaminated surficial soil with drums, storage tanks, and debris scattered on the surface. The Inert Area contains construction debris and scattered chemical waste and has cars, trucks, and storage tanks scattered on the surface. In addition, the Grantham South Area contains chemical waste. A 1988 ROD addressed source and ground water contamination through excavation and onsite incineration with on- or offsite disposal of residuals and revegetation of excavated areas within the DDA and Ridge Area; removal and offsite disposal of surface debris from the Inert Area, followed by capping; construction of a RCRA cap over the Grantham South Area; ground water pump and treatment withonsite discharge; and ground water monitoring. However, a pre-design investigation conducted from 1991 to 1993, concluded that the nature and extent of contamination at the DDA were significantly more complex than anticipated in the 1988 ROD for two reasons. First, a considerable number of intact or semi-intact drums containing hazardous substances remained in the uppermost 15 feet of the soil, which makes it more difficult to incinerate successfully. Second, source constituents had moved downward from the buried drums to an underlying clay layer and created a 5-10 foot thick layer of contaminated soil within the saturated zone, which contains levels of pollutants high enough to be considered a secondary source of ground water contamination. As a result, EPA and the State determined that the selected remedy had to be amended. This ROD Amendment revises the selected remedy for the DDA and the Ridge Area as described in the 1988 ROD by employing a combination of engineering controls in conjunction with conventional and innovative treatment technologies. It also provides notice of upgrade to the design of the landfill cap at the Inert Area; it does not pertain to the Grantham South Area, which remains the same as in the 1988 ROD. The primary contaminants of concern affecting the soil and debris are VOCs, including benzene, PCE, TCE, toluene, and xylenes; and other organics, including PAHs, PCBs, and phenols. SELECTED REMEDIAL ACTION: The amended remedial action for this site includes constructing a slurry wall around the DDA to isolate the soil containing the majority of hazardous constituents in the unsaturated and saturated portion of the aquifer from the surrounding subsurface environment; dewatering the area contained by the slurry wall, and treating and discharging it onsite or treating and discharging it offsite; excavating to a depth of 15 feet and treating and/or disposing offsite buried drums and their contents from the DDA; excavating approximately 500 yd of contaminated soil from the Ridge Areaand constructing a soil cover by backfilling the excavated area with clean soil; consolidating and temporarily storing onsite the excavated soil from the DDA and the Ridge Area; installing the Soil Vapor Extraction/Bioventing System (SVE/BVS) in the DDA; backfilling and treating the consolidated soil within the DDA utilizing the SVE/BVS; constructing a multi-layer composite barrier cap over the DDA; constructing a multi-layer composite barrier cap instead of a native soil cover over the Inert Area; conducting environmental monitoring of the ground water, air, and adjacent wetlands for the entire site; and implementing institutional controls in the form of deed restrictions. The estimated present worth cost for this amended remedial action is $33,540,100, which includes an annual O&M cost of $380,500 for 6 years. PERFORMANCE STANDARDS OR GOALS: Chemical-specific soil cleanup goals are based on State and Federal standards and include acetone 5,000 ug/kg;benzene 831 ug/kg; bis (2-chloroethyl) ether 5 ug/kg; bis (2- chloroisopropyl) ether 576 ug/kg; chlorobenzene 5,000 ug/kg; 1,2-DCA 250ug/kg; ethylbenzene 45,660 ug/kg; methylene chloride 1,000 ug/kg; 2- methylphenol 485 ug/kg; 4methylphenol 1,213 ug/kg; naphthalene 560 ug/kg; PCB-1248 10,930 ug/kg; PCB-1254 52,170 ug/kg; PCE 1,000 ug/kg; phenols 5,000 ug/kg; styrene 1,000 ug/kg; TCE 1,000 ug/kg; toluene 5,000 ug/kg; and xylenes 5,000 ug/kg. Excavation goals were not provided, but all drums will be excavated. INSTITUTIONAL CONTROLS: Deed restrictions will be implemented to ensure that the containment components are not compromised by future use of the property and fences will be erected around the DDA and Inert Area to prevent unauthorized access.|
This ROD amendment revises the remedy previously selected to address the buried materials and contaminated soils in the Drum Disposal, Ridge and Inert Areas of the Site. This ROD amendment will be the final Record of Decision for the Site. The principal threats associated with these portions of the Site are buried drums and contaminated soils containing hazardous substances in the Drum Disposal Area and contaminated soils containing hazardous substances in the Ridge Area.
The selected remedy includes the following major components:
. Constructing a slurry wall around the Drum Disposal Area
. De-watering the area contained by the slurry wall
. Excavating buried drums in the Drum Disposal Area
. Treating and/or disposing excavated drums and their contents offsite
. Excavating contaminated soils within the Ridge Area and consolidating those soils in the Drum Disposal Area
. Treating contaminated soils within the Drum Disposal Area utilizing both soil vapor extraction and bioremediation
. Constructing a multi-layered landfill cap over the Drum Disposal Area
. Constructing a soil cap over the Ridge Area
. Removing surface debris and constructing a multi-layer landfill cap over the Inert Area
. Conducting maintenance and environmental monitoring to ensure the effectiveness of the remedial action.
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