A new coupled consolidation and contaminant transport device to test a reactive core mat for remediation of contaminated, subaqueous sediments

This thesis describes a laboratory testing program to assess the efficacy of a reactive core mat (RCM) for the remediation of contaminated, subaqueous sediments.;The RCM is a 1.25 cm (0.5 in) thick sheet that consists of a reactive layer confined within geotextile filtering layers. The reactive layer is composed of needle-punched fabric impregnated with one or more reactive and/or adsorbing materials (e.g., organoclay, activated carbon, etc.) depending on the contaminant and aqueous environment type.;To test the efficiency of the RCM, a new bench scale testing device was designed and fabricated, the Integrated Contaminated Sediment Testing Column Apparatus (ICSTAC),that physically models the bio-geo-chemical behavior of the contaminated sediment, RCM overlay and the so-called biogeneration zone where new biota could be expected to develop. The device consists of an acrylic column (20.3 cm diameter, 40.6 cm height), which serves as both the vertical process column for the testing and as a guide and sealing cylinder for the loading piston to travel through. Two independent pressurized water cylinders, actuated by deadweight hangers, provide flow and pressure through the column. Sampling ports enable the monitoring of dissolved contaminants within the testing column throughout the experiment. In the ICSTAC tests, the biogeneration zone above the RCM is clean sand mixed with 3% organic material. Sediment placed in the testing column is backpressured and then vertically loaded incrementally. Vertical deformations are monitored and sediment pore fluid samples are collected during loading. At the completion of the consolidation test, overlying sand is collected and exposure tests on tracer worms (Nereis virens) in the sand are performed for 28 days. A comprehensive experimental study was carried out, including 7 conventional consolidometer tests and 16 ICSTAC tests. Sediment used in this research was sampled from the Neponset River, Milton, Massachusetts, and used either in its natural state or after spiking with 250 ppm of naphthalene.;In addition, the CS2 large strain consolidation model (Fox and Berles, 1997) was adapted to predict the experimental consolidation behavior.;Results indicate success in design and implementation of the device. Regarding the consolidation test results on the sediment, the ICSTAC tests with non-spiked sediment shows stiffer behavior compared to ICSTAC tests with spiked sediment. Further, although the ICSTAC test results show decreasing incremental strains with increasing stress increment, conventional tests showed more or less the same incremental strain for all of the stress increments. Comparisons to the CS2 large strain consolidation model indicate that such a model will be useful for predicting field performance and linking consolidation to contaminant transport. Finally, contaminant transport data indicates that the RCM prevented the breakthrough of contaminants to overlying layers, which supports the hypothesis that the RCM can be used as thin isolation barrier even in high advective flow conditions.