Aquifers groundwater flow

Groundwater models and other analytic techniques are available to assist in proper pump siting, choosing pump capacities, and calculating the movement of the contaminant plume. The characteristics of the aquifer, the flow of groundwater, and the size of the plume should be known. 

The wastes are injected into the lower part of the carbonate Floridan aquifer, which is extremely permeable and cavernous. The natural direction of groundwater flow is to the southeast. The confining layer is 45 m (150 ft) of dense carbonate rocks. The chloride concentration in the upper part of the injection zone is 1650 mg/L, increasing to 15,800 mg/L near the bottom of the formation.172 The sources used for this case study did not provide any data on the current injection zone. The native fluid was basically a sodium-chloride solution but also included significant quantities of sulfate (1500 mg/L), magnesium (625 mg/L), and calcium (477 mg/L). 

Sanchez JA, Coloma P, Perez A (1999) Sedimentary processes related to the groundwater flows from the Mesozoic Carbonate Aquifer of the Iberian Chain in the Tertiary Ebro Basin, northeast Spain. Sediment Geol 129 201-213... 

GWQMN (mm H20) Threshold depth of water in the shallow aquifer required for return flow to occur. Groundwater flow to the reach is allowed only if the depth of water in the shallow aquifer is equal to or greater than GWQMN. 

We take as an example the fate of benzene ((/Ur,) as it migrates with groundwater flowing through an aquifer. Benzene is a common contaminant because it makes up much of the volatile fraction of gasoline and other petroleum products. It is a suspected carcinogen with an MCL (maximum contamination level) set by the US Environmental Protection Agency of 5 qg kg-1. 

Figure 21.2 shows how in the calculation results benzene is transported through the aquifer. The pulse of benzene migrates at the rate of groundwater flow, traversing the aquifer in ten years. As a result of biodegradation by the natural microbial consortium, however, the benzene concentration decreases markedly with time, compared to the non-reacting case. 

Groundwater remediation is the often expensive process of restoring an aquifer after it has been contaminated, or at least limiting the ability of contaminants there to spread. In this chapter, we consider the widespread problem of the contamination of groundwater flows with heavy metals. We use reactive transport modeling to look at the reactions that occur as contaminated water enters a pristine aquifer, and those accompanying remediation efforts. 

Fig. 32.1. Simulation of the contamination at 25 °C of an aquifer with inorganic lead. The 100-m long section of aquifer contains a small amount of Fe(OH)3, to which Pb++ sorbs. Aquifer is initially uncontaminated, but at t = 0 water containing 1 mmolal Pb++ and 1 mmolal Br , which serves as a non-reactive tracer, passes into the left side. Pb++ is taken to sorb according to surface complexation theory, and the amount of Fe(OH)3 is chosen so that migration of the metal is retarded by a factor of two relative to the groundwater flow. After half the groundwater has been displaced by the contaminated water (V2 p.v.), clean water is flushed through the aquifer.

Fig. 32.4. Chromatographic separation of metal contaminants in a groundwater flow at 25 °C, due to differential sorption. According to the surface complexation model used, Hg++ in the simulation sorbs more strongly to the ferric surface in the aquifer than Pb++, which sorbs more strongly than Zn++. Plot at top shows concentrations of the metal ions in groundwater, and bottom plot shows sorbed metal concentrations.

In many cases, microbial life in nature develops into zones within which communities are dominated by one or a few functional groups, such as aerobes, sulfate reducers, or methanogens. Distinct zoning is characteristic, for example, of microbial mats (Konhauser, 2007), hot springs (Fouke et al., 2003), marine sediments and freshwater muds (Berner, 1980), contaminated aquifers (Bekins et al., 1999), and pristine groundwater flows (Chapelle and Lovley, 1992). Communities develop as well in laboratory experiments, when microbes are cultivated in pure or mixed culture. 

As groundwater flows along the aquifer, its sulfate content is gradually depleted by the sulfate reducers. The acetate added to the aquifer is not consumed completely by the microbes, so acetate concentration gradually rises, as required by Equation 33.15. About 100 km along the flow, acetate concentration rises to the... 

Arsenic concentrations vary from below detection to above 500 parts per billion (ppb) (Fig. 1). The highest dissolved arsenic concentrations in the aquifer occur below the in-filled abandoned channel. Groundwater flow data provides strong evidence for near surface arsenic release. 

Surface and groundwater flow within the Canada Creek watershed is SE from the high level of the mill and ARS to the low lying NATA then north through the wetlands (Fig 3). This path is based on local topography, core log data, and hydraulic head values for the confined aquifer. Hydraulic heads show groundwater in the Canada Creek... 

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