Formatted Title:

Treatability Study for Activated Carbon Amendment Treatment of Polychlorinated Biphenyl-Impacted Sediments at OU-3 of the Facilities Department Salvage Yard Site, Hawaii

Background/Objectives:

The Facilities Department Salvage Yard Site 8 (Salvage Yard site) is located along the shores of Kaneohe Bay, Oahu, Hawaii. A remedial investigation (RI) conducted at the site indicated that sediment and biota tissue within the adjacent offshore area, designated as Operable Unit 3 (OU-3), was impacted with PCBs. The RI data indicate a correlation in elevated concentrations of PCBs in sediment and bottom fish tissue, suggesting bioaccumulation in fish from exposure to impacted sediment. A pilot-scale treatability study (TS) was conducted within the Marina Inlet of OU-3 to evaluate feasibility and implementability of activated carbon (AC) amendment as a remedy for impacted sediment. The TS evaluated the effectiveness of two different types of AC amendment materials in reducing sediment porewater concentrations and bioavailability of PCBs in sediment for uptake by marine organisms. The results from the TS will provide the data and information needed to evaluate in situ treatment with AC amendment as a remedial option under site-specific conditions for the Feasibility Study to be conducted for the site.

Approach/Activities:

The TS study area is the Marina Inlet section of OU-3 where the highest concentrations of PCBs in sediment are located. The 85,000 square feet study area was divided into two test plots (220 by 200 feet each) to evaluate two different types of AC amendment material (AquaGate+PAC and Sedimite), and an untreated control plot (225 by 50 feet). A 0.63-inch layer of Sedimite and 1.76-inch layer of AquaGate+PAC were delivered into a 50-foot by 50-foot treatment cells using an oscillating conveyer with an attached bucket distributer for gradual and uniform delivery. PCB-degrading microorganisms were added to Sedimite applied to the study area to evaluate their potential impact on accelerating the rate of PCBs degradation in sediment. Monitoring programs developed for the TS included a baseline survey to document existing site conditions, post-placement survey to verify placement, and performance monitoring events at 9-month and 18-month post AC placement to evaluate stability and effectiveness of AC amendment materials. Data collected during baseline and post placement monitoring events include sediment profile imaging, sediment core sampling for physical observations and analytical chemistry, porewater sampling via passive samplers for analytical chemistry, bioaccumulation study, and benthic infauna assessment.

Results/Lessons Learned:

Both AC materials evaluated were implementable and effective at reducing bioavailability of PCBs in sediment. Post-placement verification survey indicate that both AC amendment materials were delivered at or above the design thickness. The 9-month and 18-month monitoring events indicate that both AC amendments were mixed into the sediment and remained stable, with Sedimite exhibiting greater mixing. Total PCBs in porewater concentrations were reduced by over 90 percent during the monitoring period for both AC amendment materials. The bioaccumulation study indicates greater than 85 percent reduction of PCBs in clam tissue test organisms between baseline and the 18-month event. A slight reduction in bulk sediment PCBs was observed within the Sedimite treatment plot; however, it is unclear whether the decrease is attributed to the addition of PCB-degrading microorganisms. Reduction in post placement benthic population was observed, however, data from the control plot were not available to confirm whether the reduction can be attributed to the AC amendment or from changing sitewide conditions. Monitoring event data indicate deposition of new sediment from a significant rainfall event that occurred post AC placement. An additional monitoring event is anticipated to evaluate the potential impact to the benthic population and the effectiveness of AC amendment to continue treatment of newly deposited and potentially impacted sediment.

Ed Sloan

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(Group 2, Poster Board #66) Treatability Study for Activated Carbon Amendment Treatment of Polychlorinated Biphenyl-Impacted Sediments at OU-3 of the Facilities Department Salvage Yard Site, Hawaii