Stagnant aquifer

The discussion so far has dealt with through-flow systems that have active recharge and discharge. However, there are stagnant aquifers in which static groundwater is stored. This topic is discussed in section 2.12. 

Composition of Water in Adjacent Wells as a Tool for Spatial Mapping of Stagnant Aquifers... 

Pressurized stagnant aquifers with good-quality water should be preserved for times of need severe droughts, large-scale pollution accidents, or nuclear catastrophes. In times of crises, a few weeks may pass before it is clear which of the ordinary wells are contaminated. In this critical period stagnant aquifers can supply pollution-free water. Hence, selected high-quality pressurized aquifers should be drilled and equipped for emergency water extraction. 

Pressurized stagnant aquifers with slightly saline water should be preserved for similar reasons, because their water may be useful for large-scale decontamination activities, for domestic and industrial needs in times of shortage, and for future desalinization, especially in remote inland regions. 

The practice of exploiting artesian systems has produced a large number of depressurized stagnant aquifers that are at present of no use. Such aquifers, which supplied high-quality water, can be reused by reinjecting fresh water to create pollution-immune underground water reservoirs. 

Fridman, V., Mazor, E., Becker, A., Avraham, D., and Adar, E. (1995) Stagnant aquifer concept III. Stagnant mini-aquifers in the stage of formation, Makhtesh Ramon, Israel. /. of Hydrology 173, 263-282. 

Mazor, E. (1995) Stagnant aquifer concept I. Large scale artesian systems—Great Artesian Basin, Australia. J. of Hydrology 174, 219-240. 

Fig. 16.42 Atrazine degradation in sterilized aquifer material (Al, Bl, Cl) and in natural (unamended) aquifer material (A2, B2, C2) for reactors under stagnant (15°C), stagnant (25°C), and recirculating (15°C) conditions. Data points are the mean of three replications. The least significant difference between these treatments at the p < 0.05 level is 0.075. Figures are identified as (A) Topeka, (B) Ashland, and (C) Hutchinson aquifers. (Schwab et al. 2006)...

Once a substance has found its way into a ground water aquifer, it is usually not affected by the anoxic, stagnant conditions that prevail underground. 

Mazor, E. and Nativ R., (1994) Stagnant groundwaters stored in isolated aquifers implications related to hydraulic calculations and isotopic dating—a reply to a comment by T. Torgersen. J. of Hydrology, 154, 409-418. 

The fracture system is modeled as a Id aquifer with high permeability (20 mobile cells with the numbers 1-20), each one connected to immobile cells (number 22-41, number 21 is reserved for the column s discharge). The content of the immobile cells can only be transferred to the mobile cells by diffusion. The value for a is calculated from Eq. 101 assuming De = 210"10 m2/s (range from 3-10"10 to 2-10"9 for ions in water, approximately one order of magnitude less for water in clays), 9im = 0.15, a = 0.1 m (thickness of the stagnant zone accompanying the fracture), and f,, i = 0.533 (Table 17)... 

Figure 27. Measured and computed He contents of groundwaters in sedimentaiy Tertiary to Permo-Carboniferous sequence of Northern Switzerland after Tolstikhin et al. (1996). The measured He contents of rocks and waters are much lower than those expected for a closed system, pointing to loss of helium by groundwater circulation. These authors concluded that no He source external to the aquifers were required and that the He contents of sampled groundwaters could all be accounted for by mixing between circulating groundwaters and old, stagnant waters.

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