Black & Veatch Corporation

Standard Chlorine of Delaware Remediation


Courtesy of Black & Veatch Corporation

By designing a 70-foot deep barrier wall, Black & Veatch was able to cut off contaminant source areas from a creek near New Castle, Delaware. The groundwater treatment system that Black & Veatch designed prevents site contamination from reaching the underlying drinking water aquifer.

The Standard Chlorine of Delaware Site is a 65 acre area including an abandoned chlorobenzene manufacturing facility and surrounding woodlands, drainage areas, and wetlands. Site contamination consists primarily of benzene and various chlorobenzene compounds in soils, sediments, surface water, and groundwater. Other site contaminants include PCBs, dioxins, and furans that were the result of impurities in the facility’s manufacturing processes.

The majority of the site contamination resulted from four sources. A 1981 railcar loading accident spilled 5,000 gallons of chlorobenzene onto the railroad tracks and into an adjacent drainage ditch. A 1986 tank collapse released approximately 570,000 gallons of mixed chlorobenzenes into various drainage pathways that discharged into the adjoining wetlands. Additionally, a leak that was discovered in a catch basin that was part of the facility’s wastewater treatment system had discharged unknown quantities of various site-related contaminants into the subsurface soils and groundwater underlying the site. Finally, the potentially responsible party (PRP) left behind in excess of 1.3 million gallons of product and off-product chemicals when they abandoned the site in May 2002.

As part of Remedial Investigation (RI) activities at the facility and surrounding areas, Black & Veatch employed the TRIAD approach to minimize investigation costs while maximizing value of data collected during subsurface soil exploration. Using historical knowledge of site activities and topography, risk assessment sampling locations were aligned with the areas most likely to have the highest levels of contamination. An initial grid of soil borings was also laid out to assess the nature and extent of soil contamination. Passive soil gas samplers were then deployed across the site in the projected areas of investigation. Using the results of these samplers boring locations were adjusted to cover areas showing the highest levels of contamination as well as those anticipated to assist in the delineation of the contamination extents. To maximize the value of the drilling activities, certain nature and extent boring locations were adjusted to allow for collection of geotechnical samples that were used to determine soil characteristics along projected alignment of a proposed soil bentonite slurry groundwater containment barrier. A field laboratory and field portable GC/MS were used to provide fast turnaround on VOC and SVOC samples and allow the results to be taken into account in the placement of subsequent sample locations borings. Ecological and human health risk assessments were performed to determine appropriate cleanup levels for those areas not covered under PRP RI

During the Remedial Design Investigation, Black & Veatch incorporated data from multiple historic data sources to develop a sampling scheme that filled data gaps while minimizing additional sampling requirements. Black & Veatch also employed a membrane interface probe with and electrical conductivity probe to develop a three dimensional picture of subsurface contamination and identify potential areas of DNAPL concentration. Using this information, an interpretation of the site’s geology, and known properties of the contaminants, Black & Veatch performed a DNAPL investigation to identify recoverable concentrations of DNAPLs located in the subsurface.

Based on the results of the RD investigation and a cost analysis of the ROD specified cut-off wall approach, Black & Veatch proposed (and EPA approved) changing the containment barrier to one that surrounds the bulk of the site. Black & Veatch designed a 5,290 foot long soil bentonite slurry wall averaging approximately 70 feet deep that surrounds the source areas and the bulk of the groundwater contamination resulting from the site. As part of this design, Black & Veatch performed cone penetrometer testing, collected and analyzed geotechnical samples, and mapped out the site’s existing low permeability layer to identify the optimal alignment and key-in depth of the barrier. Black & Veatch also performed permeability and chemical compatibility tests (using various bentonites, imported fines, and the site soil and groundwater) to determine whether high chloride and chlorinated solvent concentrations might pose chemical attack problems for the wall. Black & Veatch also developed a three-dimensional model of the site’s groundwater to confirm that the proposed design would minimize/eliminate the discharge of site contaminants into a neighboring creek.

To ensure that contamination from the site is not driven down into an underlying drinking water aquifer, Black & Veatch designed a groundwater extraction and treatment system that will lower the water level in the contaminated upper aquifer and reverse the current downward vertical gradient between the upper and lower aquifers. This system employs air stripping with granular activated carbon polishing and green sand metals removal to ensure that the treated water meets all water quality criteria and incorporates off-gas treatment to ensure that the system does not negatively impact the surrounding environment. Construction of the wall and treatment systems are currently nearing completion.

Separately, Black & Veatch analyzed historic soil and sediment data and determined that a gap in sampling data had led the former site owner to vastly underestimate the volume of contaminated soil and sediment that would require remediation. This in turn had led to their underestimation of the projected cleanup costs associated with their selected remedy. Using revised contaminated soil volumes determined from the RD investigation, Black & Veatch developed updated cost estimates for the ROD specified remedy for the site’s soil and sediments. Black & Veatch also researched potential lower cost remedial alternatives for the soils and sediments and identified in-situ chemical oxidation as a potential best fit for the site. Black & Veatch then developed a bench-scale treatability work plan and performed the treatability studies to identify the most appropriate oxidant and the necessary application rates and concentrations. Based on successful bench-scale studies, EPA authorized a pilot-scale in-situ chemical oxidation study employing sodium persulfate applied with soil mixing equipment.

To address liquid chemicals that were left at the facility by the PRP when the site was abandoned, the EPA tasked Black & Veatch with a remedial design work assignment to prepare bid documents for a transportation and disposal subcontractor. Black & Veatch coordinated with the EPA On Scene Coordinator (OSC) and the OSC’s contractors to refine information on the waste stream materials. Black & Veatch developed an expedited RD and conducted the bidding process to remove liquid chemical wastes stored in tanks, drums, and 300-gallon totes. Because of the quantities and types wastes involved, only two disposal facilities were identified as being permitted for treatment and disposal of the liquid chemical waste streams. To date over 2,000 totes and approximately 1,900 drums of chemical wastes have been sent off-site for treatment and disposal. Black & Veatch also completed sampling and analyses of the facility’s wastewater treatment plant sludge and disposed of the sludge through a qualified disposal subcontractor.

With this multi-faceted approach Black & Veatch is providing the EPA with innovative, cost-effective solutions to deal with a very complex Site.

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