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1. •r.+'..i.• ....� ♦ - - sticuents into less-or non-harmFul chemi- I Even if sediment removal is the required I being developed almost daily. However, cols. Immobilization reduces risk by alternative,the ulumate costs of[he project cost remains a problem,particularly when reducing the potential exposure, prevent- can still be limited. Carefully evaluating combined with the initial expense of in,its escape from the sediment. such sire-specific Factors as the sediment's dredging, permitting oFany related dis- Bioremediation may be the most cost- physical characteristics, type and extent of charges,and ultimate disposal of any effective remedial actsan,particular[ if contamination,hydrodvnamlc and meteo- remaining residuals. Costs can reach sever- creatabiliry tests show it is possible to rological conditions.and the preferred dis- a] thousand dollars per cubic yard. In the case of the PCB hot spot in New$edFord enhance or speed the action of the natural poral and/or remedial options can lead to the selection of more cosr,effecciye dredg- Harbor, for example, the proposed remedi- Microbes present in the sediment. acion requires ciredain dewatering incin- Immobilization technoiooies can be divid- Ing operations. V q o g' Z' eration,stabilization,and landfilling at a ed Inco solidification,which works by Disposal options can help control costs. cost of nearly S 1500 per cubic yard. eliminating the free water in the sediment. Being able to dispose of dredged materials Unavoidable delays are sure to drive the and stabilization,which alters the phvsi - without having to treat them is preferable. cast even higher. callchemical properties of the sediment to Environmental experts can help select dis sscutralize the contaminants. posal sites and conditions that juscih'less cost['disposal options. For instance.an I Tiered Approach Gives Answers Removal and Disposal: unacceptable level of conraminaaon in an Determining which action to take The Last Resort estuarine situation does not necessarily pre- depends on a variety of Factors. Evaluating sent the same risk when removed to an o#-F- a site in a tiered approach enables a compa- Removing the ronraminatzd sediment shore open-water site where exposure is ny to shape the ultimate extent and cost of should only be considered as a last resort. greadv diminished. Two of the newest dis the Final remedial action. By assuming a Large-scale dredging is not only expensive, poral options are shoreline-confined dis proactive posture with regulators and It also has the highest potential for spread- poral facilities(CDFs)and confined aquar- %yorking sequentially through the available j Ing contaminants over a much larger area. is disposal (CAD). Both offer cost savings responses,companies with responsibility �lthouoh environmental enotneers can by linliun�sediment transport. ��`hile for dealing."with contaminated sediments design silt curtains or other barriers to pre- CDFs are more widely used,CAD may can achieve their environmental objectives vent contaminant release during dredging, ulcimarely prove m be the best comoro while conuolling their costs. such measures add to project costs. mise berween colt and efficiency. About the Author Identified Contaminated New Treatment Solutions Richard iVleGrath,a Senior program Sediment Site [New high-tech solutions for creating Manager in ENSR's Accon office,has 22 contaminated sediments are years of experience in water quality man- Evaluate Site-specific Risks Action Necessar agemenr and NPDES permittinhas helped many companies manage g. He vs. Cost and Risk of Remedial Action P contaminated sediments projects and ocher marine-related zt Isciaticn ineilective Evaluate Risk of Isolation Technologies or Not Feasible hazardous waste vs. Cost and Risk of Remediation cleanups. No Action " " In Situ Treatment Evaluate Feasibility of In situ Not Feasible Treatment Technologies Isolate in Place _ isolation oetermine it Material Can Be Not Feasible Isolated By Using COF or CAO In Situ Treatment High Risk Materials in Unusual Situations sa ate:1 •,� _ .� �., ,a er -:.t�`a ^'-``x;iii., t ��. r:'' -�i,_.�•L'?�d� 'h�.�'. Remove and Treat 3_ ENSR INSIGHT-VO[--No.2- 1993