The primary objective of this project was to evaluate the long-term stability and effectiveness of an activated carbon (AC)-based amendment as in situ treatment for sediments impacted by persistent hydrophobic organic contaminant (HOC). The demonstration focused specifically on polychlorinated biphenyls (PCB), but should be applicable to other HOC-impacted sediment sites. The demonstration also evaluated the secondary consideration of ensuring the amendment would not adversely affect benthic ecological resources. While many studies have addressed the short-term performance of AC amendments, there is a general data gap with respect to long-term performance. This data gap leaves uncertainty based on the multitude of potential long-term outcomes associated with AC performance at impacted sediment sites.

To meet the overall goals of the project, the specific project objectives included evaluation of the following:

1. Long-term effectiveness of AC amendment to reduce bioavailable concentrations of PCBs in biota and available concentrations of PCBs in porewater.
2. Long-term stability of the AC amendment with observations of the lateral and vertical extent, uniformity, and persistence in surface sediments.
3. Long-term potential for adverse impacts to the benthic community due to the remedy.
4. The potential for technology transfer through commercial availability and acceptance of the technology.

These project objectives were evaluated with respect to quantitative and qualitative performance objectives. Data collected in support of the performance objectives provided multiple lines of evidence for assessing the long-term persistence of the amendment as an in situ strategy for limiting chemical bioavailability at impacted sediment sites. This project extended current pilot-scale testing of the application of AC to decrease the bioavailability of PCBs in impacted sediment to near full-scale demonstration under realistic conditions at an active harbor site. The evaluation was conducted under field conditions at Pier 7 at the Puget Sound Naval Shipyard, Bremerton, Washington.

This study successfully continued the evaluation of the performance of an AC amendment in an active harbor area throughout a multi-year monitoring period. The results showed a sustained reduction in PCB availability 82 months post application of the AC amendment in the uppermost 10 cm of the surface sediment. As noted in previous events, reductions in PCB availability of 85 to >90% (relative to baseline) were found using the solid-phase microextraction (SPME) porewater and in situ bioaccumulation measurement approaches. These reduced PCB availability levels would meet typical risk-based screening or management criteria for surface sediments and many impacted sites. This achievement is especially significant given that traditional sediment remedies (e.g., dredging and capping) would be challenging or infeasible for this location, which includes an area adjacent to/beneath a pier and within a vessel berth with specific water-depth requirements.

Measurements of amendment placement using total organic carbon (TOC), black carbon (BC), and aggregate presence indicated results similar to previous monitoring events: the amended area is stable and AC levels in the surficial layers continue to approximate 1% AC. A novel approach (carbon petrography) was employed to evaluate the accuracy of the BC results, and data support the use of BC measurements to confirm AC presence and dosing rates. Carbon petrography may be useful to validate BC measurements at other sites, particularly those with levels of BC that may interfere with post-amendment monitoring.

Benthic invertebrate census results from the 82-month study did not indicate differences in benthic community ecological metrics among the pre-amendment and 4 post-amendment monitoring events that would indicate a negative impact of the AC amendment. The recent data confirm previous observations noted by Kirtay et al. (2018) that the AC amendment applied at the site did not affect the benthic community.

Overall, the performance of the amendment shown in the present study, now demonstrated over a 7-year period following the AC amendment placement in 2012, will ideally encourage the consideration of activated carbon amendments for similar logistically challenging settings in contaminated sediment sites and as an alternative to traditional sediment remedies. (Project Completion - 2024)

Kirtay, V., J. Conder, G. Rosen, V. Magar, M. Grover, J.  Arblaste, K. Fetters, and B. Chadwick. 2018. Performance of an In Situ Activated Carbon Treatment to Reduce PCB Availability in an Active Harbor. Environmental Toxicology and Chemistry, 37:1767-1777. doi.org/10.1002/etc.4121.

Wang, C., J. Conder, and R. Chadwick. 2022. Long-Term Monitoring of an In Situ Activated Carbon Treatment to Reduce Polychlorinated Biphenyl Availability in an Active Harbor. Environmental Toxicology and Chemistry, 41:1568-1574. doi.org/10.1002/etc.5318.