In-Situ Contaminant Stabilization and Brownfield Redevelopment

When commercial properties in prime locations are left vacant dueto environmental impacts to the soil and groundwater caused bypast industrial practices, there is significant incentive to return

these Brownfield sites to usefulness. One such site is located in Port Newark,N.J., which is one of the largest shipping ports in the New York/New Jerseyarea. The site was previously operated as a wood treating facility from 1940until operations ceased in 1991, and remained vacant until remediationcommenced under the jurisdiction of the New Jersey Department ofEnvironmental Protection (NJDEP).

Cement-based solidification/stabilization was used to address arsenic-and creosote-impacted soils at the site. Prior investigations at the site foundfree phase creosote in deep soils (0-12 feet), and arsenic-impacted surfacesoils (0-2 feet). Remediation of the site involved the in-situsolidification/stabilization of “deep” creosote-impacted soils, ex-situ solidi-fication/stabilization of arsenic-impacted soils, and use of the treated soils assub-grade materials for construction of an asphalt surface cover systemdesigned for use as a container storage facility.

Approximately 25,000 cubic yards of material was treated in-situ using anexcavator-mounted mixing tool, and approximately 27,000 cubic yards ofmaterial was excavated, treated through a pug mill, and re-used at the site assoil-cement base for the asphaltic concrete pavement.

The use of soil-cement as an asphalt base course material reduced con-struction costs by obviating the need to import additional fill. As a result ofthe treatment, creosote and arsenic in the soil were successfully immobilizedand contained at the site and the Port Authority of New York and New Jerseyreturned the property to productive use.

BackgroundThe site consists of approximately eight acres of property, located betweenthe Elizabeth and Port Newark shipping channels, in Port Newark. The siteis owned by the City of Newark and is leased to the Port Authority of N.Y.and New Jersey (Port Authority). The site was formerly operated as a wood-treating facility (under various lessors) from 1940 until operations wereceased in May 1991. Since razing of the former wood treating facilities in1991, the property remained vacant.

The wood treating process utilized preservatives including creosote andchromated copper arsenate (CCA). The creosote and CCA were stored on-site in above-ground storage tanks, and pumped via underground pipelinesto above-ground treatment cylinders. Wood poles were moved into thetreatment cylinders via rail cars, and subsequently treated under pressurewith preservative chemicals. Following treatment, the cylinders were de-pressurized and opened (at which point excess preservative was drainedfrom the cylinder and collected in sumps located beneath the door of thecylinder), and the rail cars were wheeled out of the cylinder to an unpaveddrip track area, where excess preservative dripped from the poles to thetrack. The treated poles were removed from the rail cars and transferred tooutdoor lumber storage areas. As a result of these historical wood-treatingoperations, soil and groundwater at the site was impacted with constituents

CementingDNAPLs

By David S. Bausmith

CementingDNAPLs

related to the wood-treating chemicals.Numerous on-site environmental

investigations were performed between1984 and 1998, which identified contami-nants related to the former wood-treatingoperations in both surface and subsurfacesoils on-site. Arsenic was generally presentin the top two feet of soil across the entiresite. Creosote, in the form of Dense Non-Aqueous Phase Liquid (DNAPL), waspresent over approximately two acres ofthe site at depths up to approximately 12feet beneath ground surface. The arsenicand DNAPL represented a potentialsource material for on-going groundwaterimpacts. The NJDEP required these“sources” be removed, if practicable, ortreated. A total of approximately 50,000cubic yards (cy) of arsenic and/orDNAPL-impacted material existed inshallow and deep soil at the site.

Remedial action/redevelopmentrequirementsA Remedial Action Work Plan (RAWP)for the site was approved by the NJDEPin July, 1999, which outlined theRemedial Action Objectives (RAOs) forthe site and methods for achieving thoseobjectives. The RAO included: 1) reduc-ing the potential for direct contact expo-sure to constituents in surface soils; 2)restricting future on-site groundwateruse, and mitigating potential migrationof constituents to potential off-sitereceptors and deeper groundwater; and,3) reducing the potential mobility ofDNAPLs and minimizing future dissolu-tion of DNAPL constituents and arsenicto the groundwater. During developmentof the RAWP, numerous remedial alter-natives were considered which would sat-isfy these RAOs (i.e., potential sourcematerial removal, slurry wall contain-ment, pumping and treatment ofgroundwater, etc.). However, many alter-natives were either not practicable orextremely costly. Additionally, becausethe Port Authority ultimately desired toreturn the site to productive use as amarine cargo storage facility, the remedi-al actions selected for the site had to beconsistent with the proposed end use.

Improvements to the site’s infrastruc-ture were also required to render the

property functional as a marine cargostorage facility. Specifically, the siterequired construction of new stormwater drainage, electrical supply, andpotable water supply systems, as well asan asphaltic concrete pavement cover.Although required for redevelopment,the asphaltic concrete pavement wouldalso satisfy the remedial requirement toprevent direct contact exposure to con-stituents in the surface soil. In order forthe storm water drainage system to func-tion properly, the entire surface of thesite had to be raised by approximatelytwo feet above existing grades. The finalsite surface also had to be constructed inaccordance with strict grade tolerancesand strength requirements stipulated bythe Port Authority. For example, the finalsurface could not exhibit grade transi-tions exceeding 0.5 percent over a dis-tance of 20 feet to minimize the potentialfor stacked cargo containers to tip. Thefinal surface also had to withstand 100repetitious H-20 rated loadings per day,which represented the anticipated trafficconditions for the site.

Cement-basedsolidification/stabilizationIn order to achieve the RAOs for the siteand simultaneously provide a site that metthe Port Authority’s requirements for stor-age of marine cargo, cement-based solidi-fication/stabilization (S/S) was selected asthe primary remedial action. The NJDEPapproved this approach, based on theresults of treatability studies which showedthat contaminants in the soil would beeffectively immobilized after being blend-ed with eight percent Type I Portlandcement by wet weight of soil. As part of theremedial design phase, minimum strengthrequirements were established for the shal-low and deep stabilized soils. Deep stabi-lized soils were required to provide a min-imum 28-day unconfined compressivestrength (UCS) of 25 pounds per squareinch (psi), and shallow stabilized soils wererequired to provide a minimum seven-dayUCS of 250 psi.

Cement-based S/S of target site soilswas accomplished using a combination ofin-situ and ex-situ technologies.Treatment of deeper soils impacted with

DNAPL was completed in-situ to elimi-nate need to remove, handle and treatmaterials above-grade. In addition, in-situtreatment minimized the release ofvolatile constituents during treatmentthat could otherwise require costlyvapor/odor control equipment if DNAPL-impacted soils were removed and treatedabove-grade.

Shallow soils were treated ex-situ in apug mill. Soils treated in the pug mill notonly provided a material that could begraded to achieve final design topographyfor the site, but also provided a high-strength base for the asphaltic concretepavement which would withstand theanticipated traffic loads for the site.

In-situ S/S of the deeper soils wasaccomplished using proprietary equip-ment provided by the Lang ToolCompany, consisting of a hydraulically-powered mixing head mounted on anexcavator. A mobile on-site slurry plantwas used to prepare cement-water slurry,which was pumped directly to the in-situmixer via flexible hoses. Flow meteringequipment was used to control the quan-tity of cement blended with the soil, andto ensure that a minimum of eight percentcement by wet weight of soil was added.

Approximately 25,000 cy of deep soilwere treated in-situ for the project, at anaverage rate of 450 cy per day. The averagevolumetric increase of the deep soils fol-lowing treatment and curing was 23 per-cent. This bulking effect reduced thequantity of imported fill required toachieve final design grades by approxi-mately 5,800 cy. Laboratory testing ofsamples of the treated deep soil indicatedthat the cured material consistentlyachieved the minimum 28-day uncon-fined compressive strength requirement of25 psi. Adequate strength was generallyachieved within seven-days, with theseven-day UCS averaging 95 psi.Confirmatory test pits completed in thetreated deep soils verified that S/S activi-ties homogeneously mixed the soil andcement, and effectively immobilizedDNAPL in the deeper soils.

Ex-situ S/S of shallow soils was accom-plished by systematically stripping the toptwo feet of soil from the site, screening thesoil to remove debris larger than three

inches in diameter, crushing the oversized material down to a maximumdimension of 1.5 inches, mixing the screened soil and re-sized material witheight percent cement by wet weight of soil and placing and compacting thestabilized material on-site. The pug mill was equipped with spray bars to addwater (as needed) to the soil and cement during mixing to maintain themoisture content of the soil-cement at, or slightly above, the material’s opti-mum moisture content for compaction. The treated shallow soils were spreadin lifts between six and eight inches in thickness, and compacted to a mini-mum of 95 percent of Modified Proctor maximum dry density.

A total of approximately 27,000 cy of shallow soil were treated during theproject, and treatment rates ranged from 200 to 700 cy per day. The seven-day UCS of the soil-cement samples tested during construction consistentlyexceeded the minimum requirement of 250 psi, and averaged a value of 600psi. Because the soil-cement served as the base course for the asphaltic con-crete pavement system, the unexpectedly high UCS of the soil-cement sug-gests that the loading capacity and/or service-life of the pavement will begreater than anticipated as part of the design.

Cement-based S/S activities at the site were completed betweenDecember, 2000 and April, 2001. The storm water drainage, water supplyand electrical lighting systems were constructed concurrently with the S/Sactivities. Construction of the asphaltic concrete pavement cover was com-

pleted in November, 2001, and the Port Authority returned the site to activeuse in March, 2002.

SummaryCement-based S/S was effectively implemented for the remediation andredevelopment of a former wood-treating site in Port Newark, N.J.Approximately 52,000 cy of soil impacted with wood treating chemicalswere treated via in-situ and ex-situ S/S technologies with eight percent TypeI Portland cement by wet weight of soil. The S/S treatment effectively immo-bilized the soil and the related contaminants on-site, precluding the need toremove and dispose of soils off-site. The volumetric increase of site soilsresulting from the S/S activities also reduced construction costs by offsettingimported fill requirements. Further cost savings related to potential import-ed fill requirements were realized through the effective use of soil-cement assub base material for the asphalt pavement. Treatment of the soils viacement-based S/S also resulted in dramatic improvements in the bearingstrength of the site, which has rendered the property suitable for use as amarine cargo storage facility.

The post-remediation monitoring requirements include quarterlygroundwater flow monitoring and sampling/analysis. This will continue fora minimum of eight quarters (started the first quarter of 2002). In its earlystages, the post remediation groundwater monitoring indicates site-relatedcontaminants are being contained. More significantly, test pits and visualinspections performed after implementing the stabilization remedy con-firmed that the source material was immobilized. PE

For more information contact, David S. Bausmith, P.E., Key EnvironmentalInc., 456 Route 22 West, Suite D, Whitehouse Station, N.J., 08889.

Approximately 25,000 cy of deep soil were

treated in-situ for the project, at an average

rate of 450 cy per day.

Reprinted from Pollution Engineering, Copyright November 2002.