Groundwater flow pattern

Extraction wells are usually necessary to maintain hydraulic control of the plume and to ensure that the plume does not migrate into clean areas or accelerate migration toward sensitive receptors. Placement of extraction wells is especially important with systems that use nutrient injection wells or infiltration galleries. These sources of fluids can alter natural groundwater flow patterns, which may cause contaminant migration in an unintended direction or rate. If the natural groundwater system has a sufficient concentration of electron acceptors and nutrients, to achieve remediation at an acceptable rate, it may not be necessary to add any additional materials. 

Unfortunately, it is not always possible to precisely identify the cause(s) of arsenic contamination in groundwater (Chapter 6). Determining the cause(s) requires detailed field and laboratory studies of the geological, chemical, biological, and physical properties of the subsurface materials, which would include identifying groundwater flow patterns and changes in the distribution of arsenic over the study area. 

Results of several radiochemical studies at the experimental study area we installed at Maxey Flats have already been described in detail elsewhere (8-10). The areal distribution of radionuclides in the surface soil throughout the site has been mapped. Groundwater flow patterns near the experimental study area have also been mapped using tritium as a groundwater tracer. 

Back W. (1966) Hydrochemical facies and groundwater flow patterns in northern part of Atlantic Coastal Plain. US Geol. Surv. Prof. Pap. 498-A, 42pp. 

Figure 2.15 Lateral groundwater flow patterns for different geometries of simple compacting basins (classification of basin geometry types according to Pratsch, 1982).

T6th describes the gravity-induced groundwater flow pattern in terms of interdependent flow systems as existing in drainage basins. A drainage basin is a depression of the ground surface, partly or entirely surrounded by... 

Figure 2.20 Cross-section showing the theoretical distribution of hydraulic head and gravity-induced groundwater flow pattern in a homogeneous and isotropic drainage basin with complex ground surface geometry (modified after T6th, 1970. Reprinted by permission of the National Research Council of Canada).

Figure 2.21 Lateral groundwater flow patterns for isotropic drainage basins with simple ground surface geometry (ground surface geometry types patterned after basin geometry types given by Pratsch, 1982).

Figure 2.24 Cross-sections showing the theoretical effect of a partial aquifer of relatively good permeability on the distribution of hydraulic head and gravity-induced groundwater flow pattern in two drainage basins (after Freeze and Witherspoon, 1967, Water Resources Research, Vol. 3, no. 2, Fig. 4, p. 629. Copyright by the American Geophysical Union).

Under unsteady-state conditions, the regional groundwater flow pattern in all or part of a sedimentary basin is not entirely the result of the present-day relief of the water table. Different relict groundwater flow patterns reflecting former water table configurations may exist at different depths (e.g. T6th and Corbet, 1987). 

Figure 7.2 Comparison of maps showing patterns of theoretical hydrocarbon migration with maps showing groundwater flow patterns in intermediate subsystems of burial-induced flow for three hypothetical hydrodynamically and geometrically simple basins.

The migration pattern for hydrocarbons in aqueous solution and very fine suspension can be derived directly from the previously identified groundwater flow patterns. 

There are two schools of thought about the time of the initial As mobilization either (i) it is recent and has been induced by man s activities [there are proponents of this who support both the pyrite oxidation hypothesis and the iron oxide reduction hypothesis (Acharyya et al., 2000)], or (ii) it occurred much earlier and is therefore dominantly a natural process. While we believe that an early release date, (ii) above, is the more likely, this is not to imply that man s recent activities have not had, or will not have, any impact on the extent of the groundwater arsenic problem. For example, recent changes in land use such as irrigation will not only alter the groundwater flow patterns but could also affect the boundary conditions for oxygen diffusion into the aquifer and so could also affect its redox status (Bhattacharya et al., 1997). 

The act of pumping liquid into a formation creates a zone of high pressure potential. Because of this, the entering fluid flows away from this zone in all directions, locally changing the normal groundwater flow pattern. At low pumping pressure, the excess pressure potential dissipates at short distances from the injection point, and it may be possible to establish new equilibrium conditions with steady-state inflow. 

However, our understanding of the groundwater flow patterns is often an iterative process. Chemicals and isotopes can be excellent indicators of the directions and rates of groundwater flow. One goal of geochemical modeling can be to help determine the directions and rates of groundwater flow. 

Migration Pathways Groundwater flow patterns, buried utilities, drainage improvements, exposed affected surface soils. Identify based on site characterization andfate-and-transport data (see below). 

Holzbecher, E. (2005). Groundwater flow pattern in the vicinity of a salt lake. Hydrobiologia, 552, 233. 

---