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Designing a Defensible Sampling Program
Published in Mark Edward Byrnes, Field Sampling Methods for Remedial Investigations, 2023
The primary objective during site discovery and characterization is to evaluate existing site data and knowledge, develop a conceptual understanding of the site, and, if possible, obtain additional data to further that knowledge (EPA 1988). This constitutes the Remedial Investigation (RI) phase of the CERCLA RI/Feasibility Study (FS) process. The principal roles of modeling at this stage are to facilitate an initial evaluation of the nature and extent of contamination and support screening-level assessments of the threat posed by contamination to potential receptors. Depending on the available data and information, and following the preparation of an initial CSM, modeling may be used to construct potentiometric surface maps to establish approximate groundwater flow directions and rates. These estimates can then be used to estimate plausible migration rates and extents for contaminants; to estimate peak concentrations at site boundaries, potential receptors, or other locations; and to strategically place monitoring wells or other characterization methods to corroborate or update these initial estimates.
Geologic Frameworks for Contaminant Hydrogeologic Investigations
Published in Christopher M. Palmer, Principles of Contaminant Hydrogeology, 2019
Groundwater flow can be mapped by using equipotential lines, which are lines connecting points of equal head, that shows the Potentiometric surface for that aquifer. The lines of equal pressure are commonly called groundwater contour lines, plotted at a known elevation for the date they were measured. This represents a plane of equal pressure relative to atmospheric in the aquifer as it flows from areas of recharge to areas of discharge. In an unconfined aquifer, the Potentiometric surface corresponds to the groundwater occurrence in that formation. A confined aquifer is confined by an overlying stratum and the Potentiometric surface is an imaginary plane measured in wells that penetrate the confining bed. The water levels rise in the wells above the confining bed to some elevation where the pressure becomes equal to atmospheric (see Figure 9).
Groundwater Hydrology, Soil and Groundwater Contamination Assessment and Monitoring
Published in Rong Yue, Fundamentals of Environmental Site Assessment and Remediation, 2018
There are two types of aquifer: unconfined and confined. An aquifer that has a water table is called an unconfined aquifer (sometimes called a water table aquifer). The elevation of the water table may rise and fall with recharge or discharge to the aquifer. An aquifer overlain by a confining, impermeable layer is called a confined or artesian aquifer. Water in a confined aquifer is generally under pressure that is greater than atmospheric pressure. The water level in a well stands at some height above the top of the aquifer (often called piezometric head). If the water level is above the land surface, the well is a flowing artesian well. The level to which water will rise in tightly cased wells in an artesian aquifer is called the potentiometric surface.
Multitechnique approach for characterizing the hydrogeology of aquifer systems: application to the Mauricie region of Québec, Canada
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2023
Yan Lévesque, Julien Walter, Lamine Boumaiza, Mélanie Lambert, Anouck Ferroud, Romain Chesnaux
The third phase also saw the production of maps that presented an initial version of regional piezometry, the preferential zones of recharge, and the vulnerability of the regional aquifers. Some of these maps provided a first glimpse of groundwater use and quality. A conceptual model was also created to improve the environmental context of the eastern Mauricie region (Figure 3). The insight provided by this conceptual model regarding the geological and environmental context made it easier to produce a series of results, such as stratigraphic sections and fence diagrams, and validate the relevance of several thematic maps. Regional piezometry was estimated from elevations recorded in the hydrographic network. The elevation measurements were extracted from a digital elevation model (DEM) from the Québec topographic database (BDTQ) and were converted to point data using ArcMap (ArcGIS). Moreover, new piezometric data was acquired through groundwater pumping tests carried out during field work in existing wells. Regional piezometry was derived by interpolating the elevation of hydraulic head values, also known as the potentiometric surface, using the "topo to raster" method in ArcMap (ArcGIS). By using the surface topography and piezometry values, the relative depth of the water table was determined by subtracting the land surface elevation from the piezometry. In the following section, we highlight the key findings of the PACES and some singular aspects of the hydrogeological features in eastern Mauricie.