Novel Sediment Pore-water Sampling and Analysis Techniques for Microbiology, Geochemistry, and Contaminants

Duane Graves, Ph.D. (Geosyntec Consultants, Inc), Greg Davis (Microbial Insights, Inc)

Sediment pore-water is an important medium through which contaminated sediments transmit their contaminants to the water column, benthic organisms, and macroinvertebrates.  Thorough understanding of pore-water chemistry, geochemistry, and microbiology is of critical importance for assessing exposure risks, natural recovery, and contaminant attenuation. Sampling techniques for pore-water can be cumbersome, prone to sampling error, and restrictive with regard to sample volume. Therefore, the collection of sediment pore-water samples with acceptable data quality to meet usability criteria represents a substantial challenge that can affect the accuracy of sediment assessments and subsequent management decisions.  Three primary methods are typically used to collect pore-water samples or constituents.  These include (1) various permutations of diffusion sampling, such as vapor, semipermeable, and porous samplers designed for single or multilevel (peepers) sampling and sorbent based devices, (2) direct pore-water collection using miniature piezometers, syringes, porous screens, and various grab samplers; and (3) direct-read instruments such as the Trident probe that collects in situ temperature and conductivity data as well as a pore-water grab sample. Common problems encountered in adapting these methods for sediment pore-water sampling include mixing with the water column, disturbance of the sediment by the sampling equipment, limited sample volume, selective sampling by diffusion samplers, correlation of the sample concentration with equilibrium conditions in pore-water, and a limited suite of analytes for in situ measurements.  This presentation describes a novel multicomponent passive sampling system that gathers equilibrated pore-water constituents using a combination of diffusion samplers for the collection of metals, organics, and inorganics (e. g., nitrate, phosphate, and sulfate).  The sampling system also contains a microbial sampler that can sample the indigenous microbial population; attract specific bacteria capable of catalyzing beneficial reactions when appropriately “baited”; assess enhanced natural biodegradation processes when appropriately amended; and introduce specific degradation or biogeochemical reactions through bioaugmentation. Biodegradation of organic contaminants can be evaluated indirectly by measuring differences among biologically enhanced and ambient samples. The biodegradation of specific chemicals can also be directly confirmed using a method known as stable isotope probing (SIP) where the sampling system is baited with a carbon-13 (13C) labeled target compound. The biomass collected in the microbial sampler accumulates 13C if the target compound is biodegraded. These capabilities support remediation technology evaluations under in situ conditions and can be used to evaluate remediation performance and natural recovery through bioattenuation.  Data from in situ sediment applications will be presented as case studies for the technology. The results suggest that the system economically provides data to support environmental management decisions and remediation design for contaminated sediment sites where active capping and other forms of remediation may have advantages over dredging.

Abstract F-11, in: G.S. Durell and E.A. Foote (Conference Chairs), Remediation of Contaminated Sediments—2009. Fifth International Conference on Remediation of Contaminated Sediments (Jacksonville, Florida; February 2–5, 2009).  ISBN 978-0-9819730-0-5, publisher: Battelle Memorial Institute, Columbus, OH. www.battelle.org/sedimentscon