Aquifer types

Aquifer test analyses can be conducted by one or several methods depending upon whether the solution is applied to a specific aquifer type and with certain assumptions being made on the hydrogeologic nature of the aquifer and nature of the test. The initial analytical methods employed assume that the aquifer is... 

Aquifer Type(s) Phenomenon Modeled Method of Solution for Calculations Remarks Ref. 

Hydrogeologic factors for consideration include aquifer type, hydrogeologic gradient, permeability, recharge capability, depth to groundwater, moisture content/field capacity, dissolved oxygen (DO), depth to contamination, extent of contamination, and plume stability. 

Region/country Population exposed Arsenic concentration ranges (ng L 1) Aquifer type Groundwater conditions Year(s) of discovery... 

Ayotte, J.D., Nielsen, M.G., Robinson, G.R., Jr. and Moore, R.B. (1999) Relation of Arsenic, Iron, and Manganese in Ground Water to Aquifer Type, Bedrock Lithogeochemistry, and Land Use in the New England Coastal Basins. U.S. Geological Survey Water-Resources Investigations Report 99-4162, USGS, Pembroke, NH. 

Frdhlich K., Franke T., Gellermann G., Herbert D., and Jordan H. (1987) Silicon-32 in different aquifer types and implications for groundwater dating. In Proceedings International Symposium on Isotopic Techniques in Water Resources Development. IAEA, Vienna, pp. 149-163. 

In eastern New England, analysis of arsenic occurrence by aquifer type finds that arsenic concentrations are typically lower in glacial aquifers than in bedrock aquifers (Ayotte et al, 1999). Arsenic concentrations are also generally lower in public supply wells than in domestic wells, and lower in higher-pumpage wells than in smaller systems. However, Ayotte et al. 

Location Areal extent (km > Population at risk As concentration range (jis f ) Aquifer type... 

The frequency of monitoring ranges between one and four times per year, depending on the aquifer type and behaviour, and its susceptibility to pollution pressures. Because sampling frequency is low, sampling takes place at the same time each year as far as possible to allow comparability of results between years. 

As mentioned above such investigations have already been performed for some specific aquifer types from the outcrop analogue -project, other investigations are available in the literature (e.g. Borden, Cape Cod). Additionally existing data have to be systematically collected and compiled for different aquifer types. The extent to which data from existing geological investigations can be transferred to the virtual aquifer approach is not known, since they were not performed with this special aspect in mind. 

Figure 3 shows the high pressure network (70 bar and 16 bar) under operation and the location of a big underground storage of the aquifer type, which was exploited for seasonal equalisation of gas purchase. More details of high pressure transportation are given in /3/. Let us at first have a look on the present situation and special problems caused by different qualities. 

Possible water sources for injection are sea water, fresh surface water, produced water or aquifer water (not from the producing reservoir). Once it has been established that there is enough water to meet demand (not an issue in the case of sea water), it is important to determine what type of treatment is required to make the water suitable for injection. This is investigated by performing laboratory tests on representative water samples. 

The term aquifer is used to denote an extensive region of saturated material. There are many types of aquifers. The primary distinction between types involves the boundaries that define the aquifer. An unconfined aquifer, also known as a phraetic or water table aquifer, is assumed to have an upper boundary of saturated soil at a pressure of zero gauge, or atmospheric pressure. A confined aquifer has a low permeabiUty upper boundary that maintains the interstitial water within the aquifer at pressures greater than atmospheric. For both types of aquifers, the lower boundary is frequendy a low permeabihty soil or rock formation. Further distinctions exist. An artesian aquifer is a confined aquifer for which the interstitial water pressure is sufficient to allow the aquifer water entering the monitoring well to rise above the local ground surface. Figure 1 identifies the primary types of aquifers. 

Nested wells can also be used to analyze multilayer aquifer flow. There are many situations involving interaquifer transport owing to leaky boundaries between the aquifers. The primary case of interest involves the vertical transport of fluid across a horizontal semipermeable boundary between two or more aquifers. Figure 4 sets out the details of this type of problem. Unit 1 is a phraetic aquifer, bound from below by two confined aquifers, having semipermeable formations at each interface. 

The demand for gas is highly seasonal. Thus pipeline companies economi2e by si2ing production faciUties to accommodate less than the system s maximum wintertime demand. Underground storage faciUties are used to meet seasonal and daily demand peaks. In North America, gas is stored in three main types of underground formations depleted oil or gas fields, aquifers that originally contained water, and caverns formed by salt domes or mines. 

Contaminants. The type and concentration of contaminants in an aquifer dictate what type of in situ bioremediation system, aerobic, anaerobic, or combination, ate the most effective. 

Porous Media Packed beds of granular solids are one type of the general class referred to as porous media, which include geological formations such as petroleum reservoirs and aquifers, manufactured materials such as sintered metals and porous catalysts, burning coal or char particles, and textile fabrics, to name a few. Pressure drop for incompressible flow across a porous medium has the same quahtative behavior as that given by Leva s correlation in the preceding. At low Reynolds numbers, viscous forces dominate and pressure drop is proportional to fluid viscosity and superficial velocity, and at high Reynolds numbers, pressure drop is proportional to fluid density and to the square of superficial velocity. 

Even when horticultural crops leave substantial amounts of nitrate in the soil at harvest, they are not usually a very important factor in the nitrate problem because horticulture occupies only about 6% of the cultivable land. However, there could be a problem if, because of the type of soil, a number of market gardens were concentrated above an aquifer that was an important source of potable water. 

The modeling of a groundwater chemical pollution problem may be one-, two-, or tlu-cc-dimcnsional. The proper approach is dependent on the problem context. For c.xamplc, tlie vertical migration of a chemical from a surface source to the water table is generally treated as a one-dimensional problem. Within an aquifer, this type of analysis may be valid if the chemical nipidly penetrates the aquifer so that concentrations are uniform vertically and laterally. This is likely to be the case when the vertical and latcrtil dimensions of the aquifer arc small relative to the longitudinal scale of the problem or when the source fully penetrates the aquifer and forms a strip source. 

C22-0083. Many places have underground water, called aquifers, that can be tapped using wells. Depending on the types of geological formations above these aquifers, water from the surface may or may not reach these underground reservoirs. How could radioactive tracers be used to determine if rainwater falling on a particular location makes Its way down into an aquifer beneath that location ... 

Immunological abnormalities were reported in 23 adults in Woburn, Massachusetts, who were exposed to contaminated well water and who were family members of children with leukemia (Byers et al. 1988). These immunological abnormalities, tested for 5 years after well closure, included persistent lymphocytosis, increased numbers of T-lymphocytes, and depressed helper suppressor T-cell ratio. Auto-antibodies, particularly anti-nuclear antibodies, were detected in 11 of 23 adults tested. This study is limited by the possible bias in identifying risk factors for immunological abnormalities in a small, nonpopulation-based group identified by leukemia types. Other limitations of this study are described in Section 2.2.2.8. A study of 356 residents of Tucson, Arizona, who were exposed to trichloroethylene (6-500 ppb) and other chemicals in well water drawn from the Santa Cmz aquifer found increased frequencies of 10 systemic lupus erythematosus symptoms, 5 (arthritis, Raynaud s phenomenon, malar rash, skin lesions related to sun exposure, seizure or convulsions) of which were statistically significant (Kilbum and Warshaw 1992). 

Munakata-Marr J, PL McCarty, MS Shields, M Reagin, CS Francesconi (1996) Enhancement of trichloroethylene degradation in aquifer microcosms bioaugmented with wild-type and genetically altered Burk-holderia Pseudomonas cepacia G4 and PRl. Environ Sci Technol 30 2045-2052. 

The confined type of aquifer has a hydraulic pressure (static head) that is on a higher level than the top of the aquifer. This artesian pressure can sometimes reach above the surface level resulting in self flowing wells (artesian wells). 

---