Passive Sampling in Support of Remediation of Contaminated Sediments by Dr. Philip Gschwend
The primary objective of this work is to demonstrate that polyethylene (PE) passive sampling is well suited for determining the distribution of contaminants like PCBs in sediments, thereby facilitating remedial designs and long-term monitoring. These passive samplers are simply sheets of low-density polyethylene held in an aluminum frame. Performance reference compounds are impregnated into the polyethylene before use to allow evaluation of each deployment. The polyethylene strips are inserted into the sediment and retrieved at a later date. They are extracted with organic solvent and the extracts are analyzed by GC/MS. Using appropriate polyethylene-water partition coefficients, the porewater or bottom water concentrations of target contaminants are deduced. These data are used to show bed-water column gradients driving continuing contamination of overlying ecosystems, as well as bioavailable contaminant levels in the sediment. Compared to traditional sediment site characterization, the PE technology provides cost reductions in manpower, days in the field, equipment, and shipping. This technology is also safer than traditional sediment sampling and handling. For sites already being remediated, long-term monitoring using PE samplers can be readily implemented in place of alternatives like mussel deployments. In addition, site management certainty is improved though more accurate exposure assessment and improved understanding of the bioavailability of contaminants.
An In-Situ Friction-Sound Probe for Mapping Particle Size at Contaminated Sediment Sites by Dr. Bart Chadwick
A prototype commercial friction sound probe (SED-FSP) for in-situ measurement of sediment grain size has been developed by SPAWAR Systems Center Pacific and Zebra-Tech Ltd. of New Zealand. The technology provides several advantages over traditional methods of grain size analysis including rapid characterization of bottom sediments, cost effective grain size mapping and vertical profiling capabilities. SED-FSP operation is based on sound generated by contact friction between the SED-FSP sensor surface and sediment particles. The SED-FSP records and processes the acoustic signal using a sound intensity grain size relationship to generate mean sediment grain size. Laboratory testing of a prototype commercial SED-FSP with prepared materials and field samples confirmed that the amplitude of the sound intensity is correlated to mean grain size and that the SED-FSP can clearly delineate between sediments in the clay, silt and sand size ranges. Laboratory tests also confirmed the utility of the SED-FSP for acquiring vertical profiles of grain size. Performance testing of the technology was performed at a contaminated sediment site, a groundwater-surface water interaction site, and a thin layer capping site. Performance results are presented for the technology based on these field demonstrations as well as recent results from an application at the Quantico Embayment EMNR site.
Dr. Philip Gschwend is a Professor in the Department of Civil and Environmental Engineering and Director of the Ralph M. Parsons Laboratory for Environmental Science and Engineering at MIT in Cambridge, MA. Phil is an environmental organic chemist and geochemist who investigates the fates of organic compounds in the environment. His current projects involve diverse legacy pollutants such as PAHs, PCBs and DDTs, with a focus on contaminant mobility and bioavailability using passive samplers. His research efforts also seek to anticipate future problems from synthetic compounds like estrogens discharged into coastal seawater and environmentally benign production of new organic materials like carbon nanotubes. Phil is co-author of the textbook, Environmental Organic Chemistry (Wiley, 2003) and author of more than 90 peer-reviewed papers involving topics such as colloids in groundwater, black carbons in sediments, and field studies assessing fluxes and mass balances of pollutants in diverse systems including Superfund sites. He received his B.S. in Biology from Caltech, his Ph.D. in Chemical Oceanography from the Woods Hole Oceanographic Institution. Prior to joining the faculty at MIT in 1981, Phil gained postdoctoral experience at both MIT in Chemical Engineering and at Indiana University in the School of Public and Environmental Affairs.
Dr. Bart Chadwick earned his B.S. in Engineering from the University of California, Berkeley, and his Ph.D. in Oceanography from Scripps Institution of Oceanography, University of California, San Diego. He currently directs research and business development for the U.S Navy’s Energy and Environmental Sciences Group, SPAWAR Systems Center Pacific. He has extensive experience in oceanography, engineering, technology development, measurement and modeling of the marine environment. His research spans areas of environmental assessment, climate change vulnerability, and energy harvesting. Dr. Chadwick manages a portfolio of emerging energy and environmental projects, and has served as a principal investigator on a number of high visibility research projects support by SERDP and ESTCP. The focus of these projects includes the fate and transport of heavy metals in harbors, processes that control the fate and transport of contaminants in sediments, groundwater surface water interaction assessment tools, climate change and sea level rise vulnerability, and sediment microbial fuel cells.