I. HYDROGEOLOGY OF ARID REGIONS
25
Initial water pressures encountered by wells were truly spectacular and
stimulated a rapid development of groundwater. Unfortunately, despite
high initial well yields, the sandstone has only a limited permeability, so
that pressures have declined quite rapidly as water has been extracted.
Today, most of the wells need pumps in order to produce significant quantities of water. Recent development of economic methods to deionize
brackish water may place a greater demand on the artesian basin. As water
levels decline, the cost of drilling new wells and the cost of lifting water
to the surface will place economic restrictions on further development.
Oil discoveries in the southern and eastern margins of the basin during
the late 1960's will undoubtedly stimulate the drilling of additional deep
exploration holes in the remainder of the basin. The exploration activity,
in turn, should contribute new hydrologie information to our knowledge
of this vast region.
C. CARBONATE AQUIFERS OF EASTERN NEVADA
Paleozoic rocks of eastern and southern Nevada form one of the most
interesting hydrologie systems to be found in arid and semiarid regions
(Fig. 13). This system is in the northcentral part of the Basin and Range
physiographic province which is characterized by rugged north-south trending mountain ranges with arid and semiarid valleys. Most of the valleys
lack exterior surface drainage. It is commonly assumed that the basins
which are closed topographically are also closed groundwater basins. Work
in southern Nevada (Winograd, 1962) which was later extended to eastern
Nevada (Eakin, 1966) suggests very strongly that Paleozoic carbonate
rocks form an integrated subsurface drainage system for large parts of the
entire region.
The best documented interbasin groundwater flow is from Nye County
and adjacent parts of Lincoln and Clark Counties. Investigations in this
area were stimulated by requirements for water for the Nevada Test Site
of the U.S. Atomic Energy Commission. Hydrogeologists were surprised
by the fact that water was not found directly under the playa surface. In
fact, initial drilling in Frenchman Flat did not find water until almost 200
meters of valley fill had been penetrated. Later in Yucca Flat, water was
found to be more than 300 meters below the surface. If Frenchman and
Yucca Flats contained closed groundwater systems, they should eventually
fill with water to near the surface. Also, the playas contained mainly dried
mud flats and not extensive salt crusts, indicating that the playas were not
the sump area for water evaporating from a local groundwater system.
Further hydrogeological studies which included deep drilling and extensive aquifer tests showed that fractured carbonate rock of Paleozoic age
25
Initial water pressures encountered by wells were truly spectacular and
stimulated a rapid development of groundwater. Unfortunately, despite
high initial well yields, the sandstone has only a limited permeability, so
that pressures have declined quite rapidly as water has been extracted.
Today, most of the wells need pumps in order to produce significant quantities of water. Recent development of economic methods to deionize
brackish water may place a greater demand on the artesian basin. As water
levels decline, the cost of drilling new wells and the cost of lifting water
to the surface will place economic restrictions on further development.
Oil discoveries in the southern and eastern margins of the basin during
the late 1960's will undoubtedly stimulate the drilling of additional deep
exploration holes in the remainder of the basin. The exploration activity,
in turn, should contribute new hydrologie information to our knowledge
of this vast region.
C. CARBONATE AQUIFERS OF EASTERN NEVADA
Paleozoic rocks of eastern and southern Nevada form one of the most
interesting hydrologie systems to be found in arid and semiarid regions
(Fig. 13). This system is in the northcentral part of the Basin and Range
physiographic province which is characterized by rugged north-south trending mountain ranges with arid and semiarid valleys. Most of the valleys
lack exterior surface drainage. It is commonly assumed that the basins
which are closed topographically are also closed groundwater basins. Work
in southern Nevada (Winograd, 1962) which was later extended to eastern
Nevada (Eakin, 1966) suggests very strongly that Paleozoic carbonate
rocks form an integrated subsurface drainage system for large parts of the
entire region.
The best documented interbasin groundwater flow is from Nye County
and adjacent parts of Lincoln and Clark Counties. Investigations in this
area were stimulated by requirements for water for the Nevada Test Site
of the U.S. Atomic Energy Commission. Hydrogeologists were surprised
by the fact that water was not found directly under the playa surface. In
fact, initial drilling in Frenchman Flat did not find water until almost 200
meters of valley fill had been penetrated. Later in Yucca Flat, water was
found to be more than 300 meters below the surface. If Frenchman and
Yucca Flats contained closed groundwater systems, they should eventually
fill with water to near the surface. Also, the playas contained mainly dried
mud flats and not extensive salt crusts, indicating that the playas were not
the sump area for water evaporating from a local groundwater system.
Further hydrogeological studies which included deep drilling and extensive aquifer tests showed that fractured carbonate rock of Paleozoic age