High Resolution Groundwater Characterization Methods and the Triad Approach
Seth Pitkin, Vice President, Stone Environmental, Inc.
Inherent in the Triad Approach is the principle of reducing sampling uncertainty as a key element in reducing the uncertainty associated with the making key site management decisions. Sampling uncertainty is the largest source of uncertainty in a groundwater investigation and is a direct result of geological heterogeneity and the attendant spatial variability of key variables in the subsurface.
Successful remedies are dependent on understanding the spatial structure of the contaminant mass and the hydrogeologic factors that control fate and transport. These include factors such as hydraulic conductivity, capillary pressure, hydraulic gradients, organic carbon, as well as geochemical conditions which control degradation, both biotic and abiotic. While all of these factors vary over short distances in three dimensions, most groundwater investigations are not designed to assess the degree of variability that is commonly present.
Conceptual Site Models (CSMs) must be developed with clear and specific hypotheses which are then explicitly tested in the field using methods that assess the problem at the appropriate scale (typically a scale of centimeters). In addition, a systematic approach in which explorations are conducted in transects oriented at right angles to the direction of groundwater flow is essential to developing an accurate understanding of site contamination, which is required for sound decision-making.
A variety of tools and techniques are available to the investigator for use in a dynamic work strategy framework, including the Waterloo Advanced Profiling System (WaterlooAPS ™), Membrane Interface Probe (MIP), cone penetrometer (CPT)-based sensors, detailed soil and porous bedrock matrix coring and subsampling, FLUTe™ NAPL ribbon samplers and others. Using these tools in combination provides a cost effective means of developing a robust data set for hypothesis testing, CSM updating and ultimately, site management decision-making.
Hydraulic Parameter and Mass Flux Distribution Using the High-Resolution Piezocone and GMS
Dr. Mark Kram, Groundswell Technologies, Inc., (Presenter). Paper authors also include, Dr. Norm Jones (Brigham Young University), Jessica Chau (University of Connecticut), Dr. Gary Robbins (University of Connecticut), Dr. Amvrossios Bagtzoglou (University of Connecticut), Jeff Farrar (Bureau of Reclamation), Thomas D. Dalzell (AMS)
Understanding ground water flow pathways, gradients, and the distribution of contaminant mass flux is essential for proper remedial design, risk determination, and evaluation of remediation effectiveness. Conventional long-screened wells are not adequate for determining ground water and contaminant flow pathways in three dimensions. Therefore, flux distribution estimates resulting from non-discreet well measurements can be flawed. The objective of this project is to demonstrate the use of the high-resolution piezocone direct push sensor probe to determine direction and rate of ground water flow in three dimensions. Field hydraulic measurements can be used to determine seepage velocity distributions through interpolation methods recently incorporated into Groundwater Modeling System. Probe data comprised of soil type and co-located hydraulic information is particularly amenable to innovative data fusion based interpolations available through the modeling platform. Following chemical concentration data collection, these innovative data processing approaches allow for the determination of flux distributions at resolutions and spatial configurations never before available. Field scale data collection, interpolation, and modeling results will be presented and discussed.
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