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<br />Cl16~~J <br /> <br />Horizontal hydraulic conductivity of most of the inner valley alluvium was assumed to be <br />40 feet per day by Kernodle and others (1995, p. 25,110; table 1). They assumed a value of 0.5 foot <br />per day for the silty-clay layer in the vicinity of the Albuquerque South Valley (table 1). The ratio <br />of vertical to horizontal hydraulic conductivity was assumed to be 1:200 throughout the inner <br />valley alluvium. <br /> <br />As noted in the previous section on the Santa Fe Group, calculated values of horizontal and <br />vertical hydraulic conductivity are essential for providing a basis for extrapolating or estimating <br />hydraulic conductivity on the basis of lithology. This is particularly important for the inner <br />valley alluvium because it is the hydraulic connection between the Rio Grande surface-water <br />system and the remainder of the Santa Fe Group aquifer system, <br /> <br />Areas where coarse sediments of the inner valley alluvium are adjacent to coarse terrace <br />Santa Fe Group deposits provide preferential pathways for water to move laterally through the <br />alluvium to the main part of the Santa Fe Group aquifer system. Whitworth and Hawley (in <br />press) have identified some of these areas. <br /> <br />Hydraulic Heads <br /> <br />The distribution of hydraulic head in an aquifer system represents the effects of all stresses <br />on the aquifer. Hydraulic head varies vertically as well as horizontally throughout an aquifer <br />system, most significantly in areas of recharge or discharge. The difference between the <br />hydraulic head in the aquifer at the interface between the ground-water and surface-water <br />systems and the head or stage of the surface-water body is the driving force of the hydraulic <br />interaction or movement of water between the two systems. Aquifer stresses must be <br />propagated through the aquifer to a ground-water/surface-water interface to influence the <br />movement of water between the two systems. This results in changes in hydraulic head. <br />Although other characteristics must be estimated using analysis of changes or variations in <br />hydraulic head, hydraulic head is one of the few characteristics of an aquifer system that can be <br />directly measured. Therefore, measuring hydraulic heads in the aquifer system is essential. <br /> <br />Hydraulic heads are measured in some wells in the Albuquerque area (fig. 4), but few of <br />these are dedicated observation wells where. measurements represent the vertical head <br />distribution in the aquifer. The majority of these dedicated observation wells that do represent <br />the vertical head distribution are in the Rio Grande inner valley. Many observation wells are <br />converted production wells, which are generally open to a large vertical interval of the aquifer. <br />Heads measured in these wells cannot easily be related to a specific vertical location within the <br />aquifer because they are vertically averaged over a large interval. . <br /> <br />The largest volume of ground-water withdrawal in the Albuquerque area is east of the <br />inner valley. Few observation wells are in this area and none are screened in the production <br />intervals. As a result, water levels measured in high-capacity City production wells are the only <br />source of information on hydraulic head. Not only are these wells open to a large vertical section <br />of the aquifer, but also the water levels in them are largely influenced by recent pumping of the <br />wells. Vertically averaged measurements of head over large screened intervals can indicate long- <br />term trends, but are of little use for observing and analyzing the propagation of the effects of <br />ground-water withdrawals through the aquifer system. Because these wells are in the major <br />production zone of the aquifer, the vertically averaged hydraulic heads measured in them will be <br />lower than the elevation of the water table. <br /> <br />Additional observation wells are essential in the Albuquerque area to fill in gaps where <br />meaningful hydraulic-head measurements are not available. Knowledge of the vertical <br />distribution of hydraulic heads is essential for measuring aquifer response to stresses, such as <br />ground-water withdrawal, and for estimating vertical hydraulic conductivity. In turn, <br /> <br />19 <br />