Remediation of Tributary

Remediation of PCB Contaminated Tributary SedimentRoss MacNames Edward Jackson Samantha Quiroga IntroductionElevated levels of Polychlorinated Biphenyls (PCBs) found in sediment of the Little Brazos River5-100 ppmOverview:The ContaminantThe SiteRemediation StrategyMonitoring/ClosingExpected ResultsPCBsBelong to a large family of man made organic chemicals known as chlorinated hydrocarbonsWidely used throughout much of the early 20th centuryBanned in 1979Common Sources:Transformers and capacitorsOil used in motors and hydraulic systemsFluorescent light ballasts Oil-based paintPlastics

Human Health RiskEPAs First Assessment (1987)Data was limited, results were inconclusiveEPA Reassessment(1996)Peer-reviewed by 15 PCB expertsConcluded PCB was a probable human carcinogen

Can also cause other serious health conditionsImmune system Reproductive system Nervous system

Ecological Health RiskProven to cause cancer in animals Very persistent in the environmentHighly unreactiveResistant to breakdown by acids, bases, and heat

Is known to bio-accumulate, magnifying concentrations in higher levels of the food chain

SiteApproximately 1,000 ft. of affected riverbedTributary leads to the Brazos RiverApproximately 5 miles upstream of confluence with the Brazos RiverSection of tributary targeted is fairly shallowLess than 10 ft. deepFairly straight/contiguous section of river

DetailedOverview Contaminated MediaTributary sediment is contaminated media60-70% coarse material (sand and gravel)Sediment characteristics fluctuate geographically

IncreasesDecreasesDepthMore clayMore sand/gravelFlowMore sand/gravelMore clay

Source and Exposure PathwaysSource is unknownVariety of industrial facilities in the areaEnergy ProductionAutomotiveManufacturing

Previous site investigation has concluded no ongoing releases exist

Exposure PathwaysDirect ExposurePhysical contact with sedimenti.e. swimming, wading, etc.

Indirect ExposureIngestion of contaminated organismsi.e. fish, shellfish, etc.

Remediation Locating ContaminationBefore Remediation may begin, areas of highest sediment contamination must be located

Sediment samples to be taken every 40 ft.Sampling should begin at the most downstream location

A more precisely targeted sampling regime is not feasibleLack of a known contaminant source

Remediation - Dredging Dredging will be used to bring contaminated sediment to the surfaceSmall scale dredgersSilt curtains will implemented Will reduce contaminant transportation offsite

Remediation Soil WashingSoil washing is a technology that uses liquids and a mechanical process to scrub soils. Separates soils by particle sizeConcentrates contaminants into a smaller volume

PCBs preferentially bind to silt and clay soil fractions

Soil Washing Cont.ProductFateClean Sand/GravelReturned to siteContaminated Clay FinesHazardous Waste FacilityWashwaterOn Site Treatment and Re-useFugitive Air EmissionsCollection and Filtration

Why Soil Washing?Technology CharacteristicsRelatively low costTransportable technology/On-siteProvides a closed system

Site CharacteristicsPCBs as primary contaminantLarge coarse particle fraction

Site Closure/MonitoringShould occur once cleanup has resulted in PCB levels meeting TCEQ standardsSediment 7.1 ppmSurface water - .00064 ug/L

Monitoring to be performed using sediment samples at key tributary locations

Monitoring Phase 1 (during dredging)Sample dailyEnsure PCB contamination is not re-suspended and carried offsiteAs in Hudson River Dredging ProjectModerate increases in concentration, adjacent to dredging will be acceptable

Monitoring Phase 2 (post-closure)Sample monthlyEnsure PCB concentrations remain at acceptable levels

Expected ResultsPCB concentrations below applicable TCEQ standards

Little to no PCB transport offsite

Goals expected to be reached within one year of commencement of dredging

Remediation will be completed in a cost-effective manner

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