Superfund Research Program
In-situ Sediment Remediation Using Benthic Waterjet Amendment
Project Leader: Joel G. Burken
Grant Number: R01ES016158
Funding Period: 2008-2011
Year: 2010 2009
In situ remediation of contaminated sediments is a desired approach, as the dredging of sediments can lead to episodes of increased bioavailability and contamination for the overlying water column as well as downstream areas. Such instances of resuspension have lead to temporary curtailing dredging activities on the Upper Hudson River and the decision to continue dredging operations for the long-term are under evaluation. Once dredged, the sediments require considerable infrastructure and energy intensive processing before subsequent disposal. Nationally, multiple efforts are looking at stabilizing and remediating sediments in-situ to avoid these issues.
Recent research involves using a traditionally high pressure waterjet in a new and innovative manner to inject remediation amendments at varying depths in contaminated sediments. Previously published works identify Powdered Activated Carbon (PAC) as effective remedial amendment to decrease contaminant bioavailability. This investigation focuses on delivering remedial amendments such as PAC to depths by varying pressure, stand-off distance, nozzle geometry, and amendment delivery methods. Laboratory testing has thus far focused on means of injecting maximum solid amendment concentrations to targeted concentrations and concurrently minimizing resuspension and impacton benthic communities.
Both single injection and continuous injection tests have been conducted to determine timing and the effective delivery methods. Waterjetting of amendments was tested on sediments and also treating “capped” contaminated sediments. A means to rapidly dewater these tests was also needed identified as a limiting factor to timely completion. The researchers developed a unique and innovative use of electro-osmosis to dry samples from saturation to a degree of “dryness” acceptable for analytical analysis of amendment distribution in surrogate sediments, in as little as four hours.
Results to date include the ability to jet amendments to depths of 70 cm in dense, cohesive sediments, but minimal distribution was observed horizontally. Other methods can apply amendments uniformly into the surface sediments using slurries of PAC of up to 35% by weight, thereby adding minimal water to the contaminated sediment. The impacts to benthic communities have also been assessed, showing viable populations can survive and benthic impacts at the sediment surface are minimized, as measured as %percentage disturbed. The surface disturbance was also beneficial in jetting through capped amendments. Testing on aged, PAH-contaminated sediments also reveal a drop of over 95% in the bioavailable porewater concentration as measured using SPME methods, continuing to depths of over 30 cm. Further testing is ongoing to optimize the distribution at a desired depth and to develop pilot scale units.