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OuH~~ 23. " aVailable from surface sources. Other factors, such as the physical boundaries of the aquifer, the permeability and thickness of the aquifer, and the allowable drawdown of water levels in pumping wells, gen- erally are much more important. The artesian aquifer, therefore, is substantially different from the major aquifers in unconsolidated materials where storage and replenishment rates are of considerable impo rtance. ., . From the foregoing discussion, it appears likely that the ground-water resources of most artesian aquifers in Colorado can be managed separately from the surface-water resources. Regulations pertaining to the control of artesian pressures probably are the chief ones needed for planned management. The pressures could be con- trolled either by regulating spacing of wells and discharge rates, or by regulating pumping levels. Other regulations pertaining to the conservation of the supply might include one preventing the uncontrolled discharge from flowing wells, one preventing the intermingling of water from other aquifers, and others commonly considered for all aquifers. Artesian aquifers have been extensively developed in only two major areas in the State - -the Denver metropolitan area and the Grand Junction area. WellS tapping the Dakota in the Arkansas valley are closely spaced in some areas, such as those near Rocky Ford, Colo. The problems in these areas, however, probably are not as serious as those in the Denver and Grand Junction area. In other areas, the development is scattered and artesian pre ssures have not declined substantially. The most highly developed artesian aquifers in the Denver area are the Denver and Arapahoe formations, the Dawson arkose, the Upper division Laramie, and the Fox Hills. The pressure in some of them was originally sufficient to make wells flow throughout a large area. The heavy withdrawals for industrial and domestic use are so great that, near the center of Denver, the pressure has declined as much as 700 feet in the Fox Hills sandstone, and the water level is now about 450 feet below the land surface in one well, Declines approaching this magnitude have been reported from wells tapping the Arapahoe. I "' " Development of ground water in the Grand Junction area is much less extensive and the quantity of water being withdrawn is much less than in the Denver area. The area of substantial water level declines is less than 5 square miles. The artesian wells tapping - 7 -