• Competitive Groundwater Usage from the Navajo Sandstone

      Doye, F. H.; Roefs, T. G.; University of Arizona, Department of Hydrology and Water Resources (Arizona-Nevada Academy of Science, 1973-05-05)
      Groundwater modeling is used to theoretically relate mining pumpage of the Navajo Sandstone to declines in the potentiometric surface at Navajo and Hopi Indian community, domestic, and stock usage locations. The shallow wells on top of Black Mesa are shown to be part of a perched water table condition which is dependent upon the hydraulic conductivity of an aquatard known as the Mancos Shale. The isolation of the aquatard allows the shallow wells to be treated as a problem separate from that of the artesian and recharge areas. Computer modeling of the groundwater system is concerned only with those Indian wells which directly tap the Navajo Sandstone in either artesian or free water table areas. The computer simulation developed is a modified version of the basic artesian aquifer routine used by the Illinois State Water Survey. Computer results correspond with the low percentage of storage withdrawal calculated for the artesian area under Black Mesa.
    • Salinity Problems of the Safford Valley: An Interdisciplinary Analysis

      Muller, Anthony B.; Department of Hydrology and Water Resources, University of Arizona, Tucson (Arizona-Nevada Academy of Science, 1973-05-05)
      A change in groundwater quality, averaging approximately +0.13 millimhos electrical conductivity and +35 ppm chloride per year, has been documented between 1940 and 1972 with data from ten long -term sample wells. The decrement in the water quality of the surficial aquifer seems to be attributable to four major mechanisms. An increase in salinity may be expected from leakage of saline water from the artesian aquifer. Such leakage would be stimulated by pumping- caused reduction of confining pressure, and by the puncture of the cap beds by deep wells. Water reaching the aquifer from natural recharge may contribute salts to the system. Such recharging water, if passed through soluble beds, could contribute to the salt. Lateral movement of water through similar deposits may be a contribution, and the concentration and infiltration of agricultural water could also add to aquifer salinity. The economic analysis of the Safford Valley, based on the modeling of a "Representative Farm" analog, indicates that cotton will remain economical to produce on the basis of the projected salinity trends, for a significant time beyond limits of prediction. The analysis indicates that the optimum salt-resistant crops for the area are being cultivated, and, of these, alfalfa will cease to be productive in large areas of the valley by 1990. The entire valley will not produce alfalfa for profit by 2040. The methodologies shown in the paper indicate how pumping influences salinity change and outline salinity control recommendations for the area.