Aquifer surface, effective

At the time injection began, a shallow monitoring well was placed 23 m (75 ft) south of the injection well in the upper part of the Floridan aquifer above the confining layer. A downgradient, deep monitoring well was placed in the injection zone 300 m (1000 ft) southeast of the injection well. Another shallow well, located 3.2 km (2 miles) southeast of the injection site at the University of Florida s Everglades Experiment Station, has also been monitored for near-surface effects. 

In some applications, it is necessary to inject nutrients or other chemicals into the aquifer to effect a more efficient restoration. Most of the time, additives are injected into separate wells. These additives may include surfactants, nutrients, pH adjustment chemicals, or additional carbon sources. Some success has been achieved with injected heated air to improve volatility of the chemicals. Where a small quantity of methane (as a primary substrate) is required, it can be added with the injection air. The lower explosive limit (LEL) of methane in air is 5% thus, extreme care must be used to control the mixture and the methane content of the vapor that reaches the surface. 

In principle, the chemical composition of water recharging a lithologically homogeneous aquifer will depend upon the mineral phase present in the aquifer, the amount of dissolved carbon dioxide (H2CO3), the amount of aquifer surface area (S) in contact with the hydraulically effective pore volume (V), the temperature at which reaction occurs (T), the contact time (t), and the reaction rate (k). Laboratory experiments may be carried out using specific lithologic media to determine the rates of reaction of these media with water containing dissolved carbon dioxide. If the interrelationships of the above variables can be sufficiently defined, a determination of one of the above aquifer properties can be made, if the others are known, and if a representative water sample from the aquifer is available. 

Thordarson (1) and Benson (LBL, Berkeley, written commun., 1978) both describe the Paintbrush Tuff as partially saturated. Core samples obtained from the lower part of the Paintbrush in the tunnel complex were reported by Diment and others (2 ) to have saturation levels of 55-91 percent, with an average of 77 percent. Benson (LBL, Berkeley, written commun., 1978) reported an average value for water saturation in the Paintbrush of 90 percent. It would therefore be expected that the total aquifer-pore surface would not be involved in transport of water. As a matter of fact, assuming that all of the saturated-pore space is effective in transmitting water, one might predict that, on the average, somewhere between 77 and 90 percent of the aquifer surface is in contact with percolating water. 

A technique for determination of effective aquifer surface area in contact with percolating ground water has been presented. The method utilizes laboratory-determined chemical kinetic dissolution data with geologic, hydrologic, and ground-water-quality data to yield an estimate of effective aquifer surface area, a parameter not obtained by other techniques. 

CuAAsstiN, H. C. 1981. Estimation of calcium sulfate solution rate and effective aquifer surface area in a groundwater system near Carlsbad, New Mexico. Ground Water 19 287-97. 

Fortunately, if enough samples are available from a given aquifer, the variations of 2H and 180 can be compared with Craig s empirical relationship, which for normal surface waters is 62H = 8 6180 + 10°/oo. Large departures from Craig s correlation line could indicate the effects of evapotranspiration or of hydrothermal reactions. 

K( results predict that flushing only a few pore volumes of clean water through the aquifer can displace the contamination, suggesting pump-and-treat remediation will be quick and effective. Models constructed with the surface complexation model, in contrast, depict pump-and-treat as a considerably slower and less effective remedy. 

Unconfined or water table aquifers maintain a saturated surface that is exposed directly to the atmosphere. These are often similar to a bathtub full of sand or gravel to which water has been added. A well drilled through the water table would fill with water to the common water elevation in the tub. Thus, the potentiometric head in the aquifer is at the elevation of the water table. Unconfined aquifers are also characterized by a fluctuating water table, which responds seasonally. With unconfined aquifers, the water table is at atmospheric pressure, and only the lower portion of the aquifer is saturated. Recharge to a water table aquifer comes from rainfall that seeps downward to the water table. The water table level in this type of aquifer rises in direct proportion to the effective porosity. If the equivalent of 2 in. of rainfall seeps into the water table (actually reaches the water table) in an aquifer with an effective porosity of 0.3, the water table would rise 6.7 in. Alternatively, if the same water is pumped and removed from a well, the water table aquifer is then derived from the storage in the formation in the immediate vicinity of the well. Natural... 

The effectiveness of zerovalent iron in removing arsenic from water also greatly depends on the properties of the iron. As(III) removal is especially effective with high surface area 1-120 nm spheres of zerovalent iron (Kanel et al., 2005). Provided that interfering anions (such as, carbonate, silicate, and phosphate) are insignificant, colloidal spheres of zerovalent iron could be injected into arsenic-contaminated soils, sediments, and aquifers for possible in situ remediation (Kanel et al., 2005, 1291). 

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